CA2632995A1 - Method and apparatus for detecting occlusions in an ambulatory infusion pump - Google Patents

Abstract

An improved pump, reservoir and reservoir piston are provided for controlled delivery of fluids. A motor is operably coupled to a drive member, such as a drive screw, which is adapted to advance a plunger slide in response to operation of the motor.
The plunger slide is removably coupled to the piston. A method, system, and an article of manufacture for automatically detecting an occlusion in a medication infusion pump is provided. The electrical current to an infusion pump is measured. Based on measurements of one or more variables; the infusion pump detects whether there-is an occlusion in the system. The methods of detecting occlusions may be dynamic.

Description

METHOD AND APPARATUS FOR DETECTING
OCCLUSIONS IN AN AMBULATORY INFUSION PUMP

RELATED APPLICATIONS

[0001] This is a continuation-in-part application, which claims priority from U.S.
patent application no. 10/691,187, filed on October 22, 2003, which is a continuation-in-part claiming priority from U.S. patent application no. 09/698,783, filed on October 27, 2000, which claims priority from U.S. patent application no. 09/429,352, filed October 28, 1999, which claims priority from provisional patent application no.
60/106,237, filed October 29, 1998, and all of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION
Field of the Invention

[0002] This invention relates generally, to improvements in infusion pumps such as those used for, cantrolled delivery of medication to a patient. More specifically, this invention relates to improved methods and apparatuses for detecting errors in detecting fluid pressure and occlusions in fluid delivery paths of infusion pump systems.
Description of Related Art [00031 Infusion pump devices and systems are relatively well-known in the medical arts, for use in delivering or dispensing a prescribed medication such as insulin to a patient. In one form, such devices comprise a relatively compact pump housing adapted to receive a syringe or reservoir carrying a prescribed medication for administration to the patient through infusion tubing and an associated catheter or infusion set.
[0004] The infusion pump includes a small drive motor connected via a lead screw assembly for motor-driven advancement of a reservoir piston to administer the medication to the user. Programmable controls can operate the drive motor continuously or at periodic intervals to obtain a closely controlled and accurate delivery of the medication over an extended period of time. Such infusion pumps are used to administer insulin and other medications, with exemplary pump constructions being shown and described in U.S.
Patent Nos. 4,562,751; 4,678,408; 4,685,903; 5,080,653 and 5,097,122, which are incorporated by reference herein.

[0005] Infusion pumps of the general type described above have provided significant advantages and benefits with respect to accurate delivery of medication or other fluids over an extended period of time. The infusion pump can be designed to be extremely compact as well as water resistant, and may thus be adapted to be carried by the user, for example, by means of a belt clip or the like. As a result, important medication can be delivered to the user with precision and in an automated manner, without significant restriction on the user's mobility or life-style, including in some cases the ability to participate in water sports.
[0006] These pumps often incorporate drive systems which uses a lead screw coupled to motors. The motors can be of the DC. stepper or solenoid varieties.
These drive systems provide an axial displacement of the syringe or reservoir piston thereby dispensing the medication to the user. Powered drive systems are advantageous since they can be electronically controlled to deliver a predetermined amount of inedication by means well-known in the 'art.
[0007] In the operation of these'pump systems, the reservoir piston avill be fully advanced:when virtually.all of the fluid in the reservoir has been dispensed..
Corres.pondingly, the axial displacement of the motor lead screw is also typically fu11y displaced. In order to insert a new reservoir, which is full of fluid, it-is necessary ta restore the lead screw to its original position. Thus the lead screw will have to be rewound or reset.
[0008] DC motors and stepper motors are advantageous over solenoid motors in that the former are typically easier to operate at speeds that allow rewinding the drive system electronically. Solenoid based drive systems, on the other hand, often must be reset manually, which in turn makes water resistant construction of the pump housing more difficult.
[0009] Lead screw drive systems commonly use several gears which are external to the motor. FIG. I shows such a lead screw arrangement which is known in the art. A
motor 101 drives a lead screw 102 which has threads which are engaged with a drive nut 103. Thus the rotational force of the lead screw 102 is transferred to the drive nut 103 which causes it to move in an axial direction d. Because the drive nut 103 is fixably attached to a reservoir piston 104 by a latch arm 110, it likewise will be forced in an axial direction d', parallel to direction d, thus dispensing the fluid from a reservoir 105 into an infusion set 106. The lead screw 102 is mounted on a bearing which provides lateral

3 support. The lead screw 102 extends through the bearing and comes in contact with the occlusion detector. One known detector uses an "on/offl' pressure limit switch.
[0010] Should an occlusion arise in the infusion set 106 tubing, a back pressure will build up in the reservoir 105 as the piston 104 attempts to advance. The force of the piston 104 pushing against the incireased back pressure will result in an axial force of the lead screw 102 driving against the detector. If the detector is a pressure limit switch, then an axial force that exceeds the set point of the pressure limit switch will cause the switch to close thus providing an electrical signal through electrical leads and to the system's electronics. This, in turn, can provide a system alarm. The entire assembly can be contained in a water.resistant housing 107.
[0011] FIG. 2 shows a different drive system and lead screw arrangement which also is known in the art. -Iri this arrangement; a motor 201 (or a motor with an attached gear box) has a drive. shaft 201a which drives a set of gears 202. The torque'isthen transferred from -the gears 202 to a lead screw 203. The threads of the.lead.screw.203 are engaged with threads [not shown] in a plunger slide.204. Thus the torque.of the lead screw 203 is=transferred to the~ slide 204 which-causes it to move in an axial=direction:d',-paralTel to the drive shaft 201 a of the motor .201. The slide 204 is in=
contact with a reservoir piston 205 which likewise will be forced to travel in the axial direction d' thus dispensing fluid -from a reservoir 206 into an infusion set 207. The lead screw 203 is mounted on a bearing 209 which provides lateral support. The lead screw 203 can extend through the bearing to come in contact with an occlusion detector. As before, if the detector is a pressure limit switch, then an axial force that exceeds the set point of the pressure limit switch will cause the switch to close thus providing an electrical signal through electrical leads and to the system's electronics. This, in turn, can provide a system alarm. The assembly can be contained in a water resistant housing 208.
[0012] As previously noted, these lead screw drive systems use gears which are external to the motor. The gears are in combination with a lead screw with external threads which are used to drive the reservoir's piston. This external arrangement occupies a substantial volume which can increase the overall size of the pump.
Moreover, as the number of drive components, such as gears and lead screw, increases, the torque required to overcome inherent mechanical inefficiencies can also increase. As a result, a motor having sufficient torque also often has a consequent demand for increased electrical power.

4 [0013] Yet another known drive is depicted in FIGs. 3a and 3b. A reservoir 301 fits into the unit's housing 302. Also shown are the piston member 303 which is comprised of an elongated member with a substantially circular piston head 304 for displacing the fluid in the reservoir 301 when driven by the rotating drive screw 305 on the shaft (not visible) of the drive inotor 306.
[0014] As is more clearly shown in FIG. 3b, the reservoir 301, piston head 304 and piston member 303 comprise an integrated unit which is placed into the housing 302 (FIG.
3a)_ The circular piston head 304 displaces fluid in the reservoir upon axial motion of the piston member 303. The rearward portion of the piston member 303 is shaped like a longitudinal segment of a cylinder3as shown in FIG. 3b and is internally threaded so.that it.
may be inserted into a position of engagement with the drive screw 305. The drive screw 305 is a threaded screw gear of a.diameter to mesh with the internal threads-of the piston member 303. Thus=the motor 306 rotates the drive screw 305 which engages the threads of the pistori membex 303 to displace the piston head 304 in axi axial directioly d, :[0015] While the in-line drive-system~.of=FIG.. 3a=achieves a more.coinpact~physical pumpsize,.there- are.-probleins associatedwith the design. - The reservoir;=piston head and threaded piston member constitute an integrated-unit. Thus when the medication is depleted, the unit must be replaced. This results in a relatively expensive-disposable item due to the niumber of components which go into its construction.
[0016] Moreover the drive screw 305 and piston head 304 of FIG. 3a are not water resistant. Because the reservoir, piston head and threaded piston member are removable, the drive screw 305 is exposed to the atmosphere. Any water which might come in contact with the drive screw 305 may result in corrosion ar contamination which would affect performance or result in drive failure.
[0017] The design of FIG. 3a fu.rther gives rise to problems associated with position detection of the piston head 304. The piston member 303 can be decoupled from the drive screw 305. However, when another reservoir assembly is inserted, it is not known by the system whether the piston head 304 is in the fully retracted position or in some intermediate position. Complications therefore are presented with respect to providing an ability to electronically detect the position of the piston head 304 in order to determine the extent to which the medication in reservoir 301 has been depleted.
[0018] The construction of pumps to be water resistant can give rise to operational problems. As the user travels from various elevations, such as might occur when traveling in an air plane, or as the user engages in other activities which expose the pump to changing atmospheric pressures, differential pressures can arise between the interior of the air tight/water-resistant pump housing and the atmosphere. Should the pressure in the housing exceed external atmospheric pressure, the resulting forces could cause the reservoir piston to be driven inward thus delivering unwanted medication.
[0019] Thus it is desirable to have an improved, compact, water resistant drive system which permits safe user activity among various atmospheric pressures and other operating conditions. Moreover it is desirable to have improved medication reservoir pistons for use with such drive systems.

SUMMARY OFr THE.PREFERRED EMBODIMENTS
[0020]- An improved apparatus for dispensing a medication -fluid ig-provided.
This ~
:comprises a reservoir adapted ta? contain*tlie fltiid and-a, movable pistori'adapted-:to=vary.the size; of the. reservoir and.to di'scharge the liquid.from.the.reservoir through;anr,outlet. - In,a 'certain=aspect of the present= inventions; cthe reservoir and piston are adapted for.ause with =a , -pump drive system having a linear actuation member wherein the pi'ston can be releasably=
coupled to the linear actuation member.
[0021] The piston comprises a first member adapted to be slidably mounted within the reservoir and to form at least part of a fluid-tight barrier therein. The first member has an external proximate side and an external distal side. The external proximate side is adapted to contact the fluid and is made of a material having a first stiffness. A second member has a first side and a second side. At least a portion of the second member is disposed within the first member. The first side of the second member is adjacent to the external proximate side of the first member and is made of a material having a stiffness which is greater than the first stiffness.
[0022] In alternative embodiments, the second member first side is in a generally parallel, spaced-apart relationship with the first member external proximate side.
[0023] In yet further embodiments, the first member external proximate side is made of an elastomeric material and the second member first side is made of stainless steel or plastic.
[0024] In yet further embodiments, the second member is substantially contained within the first member.

[0025] In yet further embodiments, the second member extends past the external proximate side of the first member and is adapted for contact with the fluid to complete the fluid-tight barrier within the reservoir.
[0026] In yet further embodiments, a method of coupling an actuator to a reservoir piston is provided. Electrical* power is provided to a pump motor which is operably coupled to a plunger slide. The power is provided when the plunger slide is in a position other than fully inserted in a reservoir piston cavity. A first value corresponding to the axial force on the plunger slide is measured_ A determination is made whether the first value exceeds a second value corresponding to the axial force on the plunger slide when the plunger slide is fully inserted in the piston cavity. Electrical power to .the;pump. motor is terminated after determining that the first value exceeds the second value.
[0027] In yet furtliei'embodiments of the present invention, a meth d;'.
system'and article of manufacture to detect a malfunction=with=a force sensor in=the infixsion=puxn.p-is' described..:.-In preferred embodirrients; cizrrent measurernents to the motor.are,takeri..
Ba"sed.on.the current measurements;; the dnfusioii, pump= detects- when the pl'unger: slide: is, seated -in. the reservoir; and detects. a:.;problem with.the force sensor when-the:foroe-sensor independently fails to register a;value indicating that the plunger -slide is -seafed,.in the-reservoir. In particular embodiments, the infusion pump detects when the plunger slide is seated in the reservoir by calculating an average current based on the current measurements, comparing the average current to a threshold current; and detecting when the plunger slide is seated in the reservoir when the average current exceeds the threshold current.
[0028] In fiuther embodiments, an encoder measures movement of the plunger slide as encoder counts and the infusion pump signals an error with the force sensor when the force sensor independently fails to recognize that the plunger slide is seated in the reservoir after a preset encoder count threshold is exceeded. In yet further embodiments, the time since the plunger slide was seated in the reservoir as indicated by the current measurements is also measured and an error with the force sensor is signaled when the force sensor independently fails to recognize that the plunger slide is seated in the reservoir after a preset time threshold is exceeded.
[0029] In further embodiments, occlusions are detected using at least two values of the pump system. For example, these variables can include force, drive current, drive voltage, motor drive time, motor coast time, delivery pulse energy, motor drive count, motor coast count, and delta encoder count. In yet further embodiments, algorithms to detect occlusions based on one or more values are dynamic, and the values are calculated periodically, and may be calculated continuously, throughout delivery of each pulse.

BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. I is a side plan view of a conventional lead-screw drive mechanism.
[0031] FIG. 2 is a side plan view of another conventional lead-screw drive mechanism.
[0032] FIG. 3a is a perspective view of another conventional lead-screui drive mechanism.
100331 FIG. 3b shows the details of a disposable reservoir with the piston and drive member withdrawn of the lead-screw drive mechanism of FIG. 3a.
[0034] FIG. 4 is a side plan, cut-away view of a drive mechanism in a retracted position in accordance with an embodiment of the.present invention.
[0035] =FIG. 5 is a perspective view of the in-line drive mechanism of_FIG. 4 outside of the housing.
[0036] FIG. 6 is =a cut-away perspective view of-the drive meclian'isiri'df FIG. 4 iri a retracted position..
=[0037] f IG. 7a=.is' a,side~ plan;: cut=away.. view of the drive mechanisxri-of FIG. 4 in an. extended position.
[0038] FIG: 7b= is a cut-away perspective view of the drive mechanisin,"of FIG. 4 in an extended position.
[0039] FIG. 8 is a cut-away perspective view of an anti-rotation device for use with the drive mechanism shown in FIG. 4.
[0040] FIG. 9 is a cross-sectional view of a segmented (or telescoping) lead screw in accordance with an embodiment of the present invention.
[0041] FIGs 10a, l Ob and lOc are cross-sectional views of various embodiments of venting ports for use with the drive mechanism of FIG. 4.
[0042] FIG. 11 is a partial, cross-sectional view of a reservoir and plunger slide assembly.
[0043] FIG. 12 is a partial, cross sectional view of a reservoir and a reservoir connector.
[0044] FIGs. 13a and 13b are plunger slide force profile diagrams.
[0045] FIG. 14 is an exploded view of a reservoir, a piston, and an insert.
[0046] FIG. 15a is a perspective view of a reservoir piston.
[0047] FIG. 15b is an elevation view of the reservoir piston of FIG. 15a.

[00481 FIG. 15c is a cross-sectional view of the piston along lines 15c - 15c of FIG. 15b.
[0049] FIG. 16a is a perspective view of a piston insert.
[0050] FIG. 16b is a top plan view of the piston insert of FIG. 16a.
[0051] FIG. 16c is a cross-sectional view of the insert along lines ] 6c - 16c of FIG.
16b.
[0052] FIG. 17 is a cross-sectional view of a reservoir, reservoir piston; and insert.
[0053] FIG. 18 is a cross-sectional view of a piston and piston insert according to an alternative embodiment of the present invention.
[0054]. FIG. 19 illustrates logic for detecting occlusions in accordance:~With. an.
,mbodiment of the present invention.
[0055] FIG. 20 is a graph showing measured voltage across a force -seiisitive.' resistor as~azfunctiori of applied force:
[0056] FIG.,21.is an exploded,bottom/front perspective view;of ari4nfii5ion pump~
3five.systeirri;.sensing.system;and fl.uid,containin9 ' assernbly, incorporatingi-a:force: einsor in.accordance.with-,an embodiment;ofthe present invention:' [0057] FIG. 22 is an illustration view of an"infusion pump drive sy'sterii ;with a sensor showing -certain torque forces according to an embodiment of the present invention.
[0058] FIG. 23(a) is a perspective view of a sensor in a portion of a drive system according to another embodiment of the present invention.
[0059] FIG. 23(b) is a rear view of the sensor and pump drive system of FIG.
23(a).
[0060] FIGs. 24 and 25 illustrate an algorithm for detecting a malfunction in a force sensor in accordance with an embodiment of the present invention.
[0061] FIG. 26 is a graph showing measured force, drive count divided by 50 and multi-variable value of an embodiment of the invention shown as a function of delivery pulse.
[0062] FIG. 27 illustrates an algorithm for detecting an occlusion in accordance with an embodiment of the present invention.
[0063] FIG. 28 is a graph showing measured force across time for a single delivery pulse in an embodiment of the present invention.
[0064] FIG. 29 illustrates an algorithm for detecting an occlusion in accordance with an embodiment of the present invention.

[0065] FIG. 30 is a graph showing force and slope versus delivery in an embodiment of the present invention.
[00661 FIG. 31 is a.graph showing force versus time in an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
100671 In the following description, reference is made to the accompanying :drawings which'forma.part hereof and.which,.illustrate.several embodiments, of-the present -inventions. It.is.understood that other embodiments may be utilized and structural and ~operational changes may.be rnade without departing from= the scope of the present inventions =[0068] As=shown.-in:tlie..drawings for :purposes= of illustration,~
soin6..a's&cts of.the present:inventions are directed.to 4dr.ive mechanism;for.an infusion.pump>for.rn'edication ,or-otherfluids:.,ln preferred.enibodiments;-a releasable coupler.couples.antixi4ine drive--to a-plunger:or piston of =a reservoir to dispense fluids; such as medications;.drugs;-;yitamins, vaccines; honnones, water or the like. However, it will be recognized- that further embodiments of the invention may be used in other devices that require compact and accurate drive mechanisms. Details of the inventions are further provided in co-pending U.S. patent application serial no. 09/429,352, filed October 29, 1999, now issued U.S.
Patent No. 6,248,093 and U.S. provisional patent application serial no.
60/106,237, filed October 29, 1998, both of which are incorporated herein by reference in their entireties.
[0069] In addition, the reservoir piston includes features which provide greater stiffness against fluid back pressure thus reducing system compliance. The piston further includes a threaded attachment feature which permits a releasable yet secure coupling between the reservoir piston and the in-line drive.
[0070] FIG. 4 shows a side plan, cut-away view of an infusion pump drive mechanism according to one embodiment of the inventions, in which a housing 401, containing a lower section 402 for a power supply 420 and electronic control circuitry 422, accommodates a driving device, such as a motor 403 (e.g., a solenoid, stepper or d.c.
motor), a first drive member, such as an externally threaded drive gear or screw 404, a second drive member, such as an internally threaded plunger gear or slide 405, and a removable vial or reservoir 406. The reservoir 406 includes a plunger or piston assembly 407 with 0-rings or integral raised ridges for forming a water and air tight seal. The reservoir 406 is secured into the housing 401 with a connector 431 which also serves as the interface between the reservoir 406 and the infusion set tubing (not shown). In one embodiment, the reservoir piston assembly 407 is coupled to a linear actuation niember, such as the plunger slide 405, by a releasable coupler. In the illustrated embodiment, the coupler includes a female portion 424 which receives a male portion 426 carried by the plunger slide 405. The female portion 424 is positioned at the end face 428 of the piston assembly 407 and includes a threaded cavity which engages the threads of a-male screw .extending'from-the end_430:of: the,plunger.>slide-.405 :[Ø071] While certain embodiments=of=the present inventions are dir'ected.to :disposable, pre-filled reservoirs-,= alterriative';embodiments-may use refillableipartridges, syringes or the like. The cartridge can be pre-filled with insulin (or other -drug or fluid)-?and;inserted-into,=the p.ump :~Alternativel=y;-rthe:cart'ridge: could be=,ft.ll'ed,liy>the.user_using,==
:an-adapter handle.on?.the;.syringe=piston::=After.being-filled;
the:handle:.is:rernoved;(such;as-=
=b.y:unscrewing-tlie=.handle)=so'.that, the cartridge;can:be placed=intothe purrip [0072] Referring again;fo FIG. 4, as=;the drive shaft 431of'the motor'40.3 .rotates in the gear box 501, the drive=scirew 404 drives the plunger slide 405 directly.to obtain the axial =displacement against the reservoir piston assembly 407 to deliver the predetermined amount of medication or liquid. When using a DC or stepper motor, the motor can be rapidly rewound when the reservoir is emptied or as programmed by the user=. A
sealing device, such as an 0-ring seal 409 is in contact with the plunger slide 405 thus allowing it to move axially while maintaining a water resistant barrier between the cavity holding the reservoir 406 and the motor 403. This prevents fluids and other contaminants from entering the drive system.
[0073] An anti-rotation key 410 is affixed to the plunger slide 405 and is sized to fit within a groove (not shown) axially disposed in the housing 401. This arrangement serves to prevent motor and plunger slide rotation which might otherwise result from the torque generated by the motor 403 in the event that the friction of the 0-ring sea1409 is not sufficient alone to prevent rotation.
[0074] The motor 403 is a conventional motor, such as a DC or stepper motor, and is journal mounted in the housing 401 by a system compliance mounting 412. A
system compliance mount can be useful in aiding motor startup. Certain types of motors, such as stepper motors, may require a great deal of torque to initiate rotor motion when the rotor's initial at-rest position is in certain orientations with respect to the motor's housing. A
motor which is rigidly mounted may not have enough power to develop the necessary starting torque. Including system compliance mounting permits the motor housing to turn slightly in response to high motor torque. This alters the orientation between'tlie rotor and the housing such that less torque is required to initiate rotor motion. A
compliance mount can include a rubberized mounting bracket. Alternatively, the mounting could be accomplished using a shaft bearing and leaf spring or other known compliance mountings.
[0075) FIG. 5 shows a perspective view of the in-line drive mechanisiii'of FIG. 4 outside:of the housing. The plunger:slide::405~(internai threads not.
shown),isccylindr.ically.
shaped and has the screw-shaped.male:portion= 426 of the coupler attached.to,one end thereof. The.anti-rotation-key. 410.is affixedao! the opposite.end'of.the,slide-.405'. The:
drive screw. 404' issof such a diameter as-to =fit: within and engage-the,internal ~threads.of the plunger:-Mide=405~a& 3hown:in,F.I,G.;=4::-;A:conventional:gear:bok -501:
couple's:-ithe:driwe screw:,404 to. thei'driveshaft:432,.of the,rnotor 403 [0076] ,FIGs.- 4:and;6~show;:the,sinfusion.:pump-assembly with<the..pTunge'r slide 405 :i'ri.the retracted position. The Yeseivoir<406 whieh: rriay be. full of medication,~or other fluid is. inserted in a reservoir cavity 601.which is sized to receive a reservoir or vial. In the retracted position, the plunger slide 405 encloses the gear box 501 (not visible in Fig. 6) while the drive screw 404 (not visible in FIG. 6) remains enclosed within the plunger slide 405 but is situated close to the coupler.
[0077] The motor 403 may optionally include an encoder (not shown) which in conjunction with the system electronics can monitor the number of motor rotations. This in turn can be used to accurately determine the position of the plunger slide 405 thus providing information relating to the amount of fluid dispensed from the reservoir 406.
[0078] FIGs. 7a and 7b show the infusion pump assembly with the plunger slide 405 in the fully extended position. In this position, the plunger slide 405 has withdrawn from over the gear box 501 and advanced into the reservoir 406 behind the reservoir piston assembly 407. Accordingly, the plunger slide 405 is sized to fit within the housing of the reservoir 406, such that when the reservoir piston assembly 407 and the plunger slide 405 are in the fully extended position as shown, the reservoir piston assembly 407 has forced most, if not all, of the liquid out of the reservoir 406. As explained in greater detail below, once the reservoir piston assembly 407 has reached the end of its travel path indicating that the reservoir has been depleted, the reservoir 406 may be removed by twisting such.
that the threaded reservoir piston assembly 407 (not shown in Fig. 7b) disengages from the male portion 426 of the coupler.
[0079] In one embodiment, the motor drive shaft 432, gear box 501, drive screw 404, and plunger slide 405 are all coa.Xially centered within the'axis of trave1440 (FIG. 4) of the reservoir piston assembly 407. In certain of the alternative embodiments, one or more of these components may be offset from the center of the axis of travel 440 and yet remain aligned with the axis of travel which has a length which extends the length of the reservoir 406.
'[008Q],. FIG. 8. is a- cut:away.,pe rspective, view of an. anti-rotation'.devid&,~.;,The anti-rotation key 410 consists of,a ring:or::collar:442 with two.rectangular tabs-436 which are spaced 180 apart.. Only~one :tab :is visible:~in:FIG: 8. The ririg-~)ortion 442 =of.the key 410, surrounds-and=is attached- to the end bf the=plunger slide 405-which is-closest~to:the notor Disposed in-the{=housing.4Uh.ate=;tworariti_rotation. slots=.434;:only.orie of whieh, is visible in%
FIG. 8-. -..The-:dnti-rotation=~sldts~t4=34:=are:,siz6dao- accept the rectangular:-tabs ,of>tlie key410-.
As the plunger slide.405",moves.c:axi'ally.;in:response. to tlie motor torque=. as previously described;-the=slots 434 will perinit:the;key41=0 to.likewise-move- axial'ly.
.:However'the slots 434 and the.tabs 436 of the key 410 will prevent any twisting of the plunger slide 405 which might otherwise result from the torque generated by the motor.
[0081] FIG. 9 illustrates a split lead-screw (or plunger slide) design for use with a pump drive mechanism. The use of a split lead-screw or telescoping lead screw allows the use of an even smaller housing for the drive mechanism. A telescoping lead-screw formed from multiple segments allows the pump to minimize the dimensions of the drive mechanism, in either in-line or gear driven drive mechanisms.
[0082] An interior shaft 901 is rotated by a gear 906 which is coupled to a drive motor (not shown). This in turn extends a middle drive segment 902 by engaging with the threads of an internal segment 904. The middle segment 902 carries an outer segment 903 forward with it in direction d as it is extended to deliver fluid. When the middle segment 902 is fully extended, the internal segment 904 engages with a stop 905 on the middle segment 902 and locks it down from pressure with the threads between the middle and internal segments. The locked middle segment 902 then rotates relative to the outer segment 903 and the threads between the middle segment 902 and the outer segment 903 engage to extend the outer segment 903 in direction d to its full length.

100831 The use of multiple segments is not limited to two or three segments;
more may be used. The use of three segments reduces the length of the retracted lead-screw portion of the drive mechanism by half. In alternative embodiments, the outer segment may be connected to the motor and the inner segment may be the floating segment.. In preferred embodiments, 0-rings 907 are used to seal each segment relative'to the other and to form a seal with the housing to maintain water sealing and integrity.
(0084] As previously noted, the construction of these pumps to be water resistant can give rise to operational problems. As the user engages in activities which expose the pump to varying atmospheric pressures, differential pressures can arise between the interiou of:the air .tight/.water-resistant chousing< and..the=iatmosphere:
Should : the.pres=sure -=in.
the housing exceed external: atmospheric.pressure, the. resulting forces could=.cause the r"eser.voir:piston:to be drive&-inward .thus-delive'ring unwanted- medication:
;:Ori the=other haind; =should the= external atmosplieric- pressure -exceed the ,pressure in=
the= housing;'then the:pump:motor willvhave fo;::work:harderato>ad~ance the reservoirpisfon.
~10085Jv. To address}this~probiein;:a.venting p.orttis provided:which resists;=.th&
intiusion of rr;oistur:e:: :Referr:irig;.to FI.G: :=7b; venting= is, accomplished= thirough:the: housing:
401- into the. reservoir davity=6.01.via..a-vent port 605. The=vent+portcan be eiiclosed-by a.=
relief valve. (not shown) or covered with hydrophobic material: Hydrophobic -inaterial permits- air to pass through the material while resisting the passage of water or other liquids from doing so, thus permitting water resistant venting. One embodiment uses a hydrophobic material such as Gore-Tex , PTFE, HDPE, and UHMW polymers from sources such as W.I. Gore & Associates, Flagstaff, AZ, Porex Technologies, Fairburn, GA, or DeWAI. Industries, Saunderstown, RI. It is appreciated that other hydrophobic materials may be used as well.
[0086] These materials are available in sheet form or molded (press and sintered) in a geometry of choice. Referring to FIGs l0a - 10c, preferred methods to attach this material to the housing 401 include molding the hydrophobic material into a sphere 1001(FIG. l Oa) or a cylinder 1002 (FIG. l Ob) and pressing it into a cavity in the pre-molded plastic housing. Alternatively, a label 1003 (FIG. l Oc) of this material could be made with either a transfer adhesive or heat bond material 1004 so that the label could be applied over the vent port 605. Alternatively, the label could be sonically welded to the housing. In either method, air will be able to pass freely, but water will not.

[0087] In an alternative embodiment (not shown), the vent port could be placed in the connector 431 which secures the reservoir 406 to the housing 401 and which also serves to secure and connect the reservoir 406 to the infusion set tubing (not shown). As described in greater detail in copending application Serial No. 09/428,818, filed on October 28, 1999, which application is incorpbrated by reference in its entirety, the connector and infusion set refers to the tubing and apparatus which connects the outlet of the reservoir to the user of a medication infusion pump.
[0088) An advantage of placing the vent port and hydrophobic material in this location, as opposed to the housing 401, is that the znfusion set is disposable and is .repl"aced frequentl.y.::with.each;new.reservoir.~or: vial ;of =medication:a :Thus new thydrophobic:
=material is frequently-placed:into:service.= This provides.enhanced ventilation-as compared =with- the placernent_of=hydr..ophobi:c inaterial in:the:housing 401. Material in-tfhis4ocati6r.
-wi11 hot be replaced as=often and'-thus is-subjecttoidirt or oil build-up-whichrnay'retard, :ventilation:::Iri yet-another.--alternativ,e~.eximb=odiinent::.however,.vent:ports,withrhydrophobic ::
material could'be:placed,in:both:the purrip housirig and=in the connectonpoftionl-of the;' infusion-.set.
[0089] Regardless of=the= location of the vent port,.there remains-tlie pos'sibility that .
the vent port can become clogged by the accumulation. of dirt, oil, etc.
over.the hydrophobic material_ In another feature of certain embodiments of the present'invention, the releasable coupler can act to prevent unintentional medication delivery in those instances when the internal pump housing pressure exceeds atmospheric.pressure.
Referring to FIG. 11, the coupler includes threads formed in a cavity within the external face of the reservoir piston assembly 407. The threaded cavity 424 engages the threads of the male portion 426 which in turn is attached to the end 430 of the plunger slide 405.
[00901 This thread engagement reduces or prevents the effect of atmospheric pressure differentials acting on the water resistant, air-tight housing 401 (not shown in FIG. 11) from causing inadvertent fluid delivery. The threads of the male portion 426 act to inhibit or prevent separation of the reservoir piston assembly 407 from the plunger slide 405 which, in turn, is secured to the drive screw 404 (not shown in FIG_ 11) by engagement of the external threads of the drive screw 404 with the internal threads of the plunger slide 405. As a result, the coupler resists movement of the reservoir piston assembly 407 caused by atmospheric pressure differentials.

[0091] When the reservoir 406 is to be removed, it is twisted off of the coupler male portion 426. The system electronics then preferably cause the drive motor 403 to rapidly rewind so that the plunger slide 405 is driven into a fully retracted position (FIGs.
4 and 6). A new reservoir 406, however, may not be full of fluid. Thus the reservoir piston assembly 407 may not be l'ocated"in the furthest p6ssible position from the reservoir outlet. Should the reservoir piston assembly 407 be in such an intermediate position, then it may not be possible to engage the threads of the male portion 426 of the coupler (which is in a fully retracted position) with those in the female portion 424 of the coupler in the reservoir piston assembly 407 upon initialplacement of the reservoir.
,[0092]: In-accordance with.another;featur.e_of certain einbodiments,:the:illustrated;
embodiment provides for-advancement_of the:plunger slide 405 upon the insertion of a=
rese'r=voir=into =the puiripai6.tisirig.',The plungerhslide 405:advances=until it comes:.into-contact-with-the; reservoirpi'ston assembly-407,and the threads of'the couplerrna=le portion=
426..of.,the=co.upler=.engage--ther.thr.eads:=in tlie:fernale,portion~424;i.n.the:reser.voi.r;pi'ston assembly:407 ~t=When_the~threads>engage:tiri=:this fashi'on in:the;ill=ustrated=ernbodiment;
they.-do so riot.by:twisting. Rather;:they ratchet over one another.
-[0093] In the preferred embodiment, the.:threads of the coupler rriale'portion 426=~.
have a 5 start, 40 threads per inch ("TPI") pitch or profile while the threads of the coupler female portion 424 have a 2 start, 40 TPI pitch or profile as illustrated in FIG: 11. Thus these differing thread profiles do not allow for normal tooth-to-tooth thread engagement.
Rather, there is a cross threaded engagement.
[0094] The purpose of this intentional cross threading is to reduce the force necessary to engage the threads as the plunger slide 405 seats into the reservoir piston assembly 407. In addition, the 2 start, 40 TPI threads of the coupler female portion 424 are preferably made from a rubber material to provide a degree of compliance to the threads. On the other hand, the 5 start, 40 TPI threads of the male coupler portion 426 are preferably made of a relatively hard plastic. Other threading arrangements and profiles could be employed resulting in a similar effect.
[0095] If on the other hand, the threads had a common thread pitch with an equal number of starts given the same degree of thread interference (i.e., the OD of the male feature being larger than the OD of the female feature), then the force needed to insert the male feature would be pulsatile. Referring to FIG. 13a, as each thread tooth engages the next tooth, the insertion force would be high as compared to the point where the thread tooth passes into the valley of the next tooth. But with the cross threaded arrangement of the preferred embodiment, not all of the threads ride over one another at the same time.
Rather, they ratchet over one another individually due to the cross-threaded profile. This arrangement results in less force required to engage the threads when the plunger slide moves axially, but still allows the reservoir to easily be removed by a manual twisting action.
[0096] While the advantage of utilizing a common thread pitch would be to provide a-maximum ability to resist axial separation of the reservoir piston assembly 407 from the plunger slide 405, there are disadvantages. In engaging the threads, the peak ;force;is high and=-could result:inexcessiv.e; delivery:of-fluids as:the,plunger slide..4.05.;
moves forward to seat in the cavity of the reservoir piston= assembly 407. As described in ~gfeater =detail imcop:ending U.S. patent~=application serial No.= 09/428,41-1z.f Ied'on SOctobeI
=2,8; 1999; now issued=U.S. Patent N6: i6;362;59'1; ivhich==application is incorpoiated by .r.eference=in its. entirety;=:theapuinpi rriay,have-an:occlusion detection system.,which uses !aXial.force.as: an= indicator, o.f .pressur.e; within~the.~reservoir.~.-.If:so,athen a fal'se =alarm-rnay:be.:
.generated during, these. high.force_ conditions., 400971 It==is desirable:therefore to have:an insertion force profile"which is preferably more flat than that shown in FIG: -13a. To accomplish this, the cross threading design of the preferred embodiment causes the relatively soft rubber'teeth of the female portion 424 at the end of the reservoir piston assembly 407 to ratchet or swipe around the relatively hard plastic teeth of the coupler resulting in a significantly lower insertion force for the same degree of thread interference. (See FIG. 13b) This is due to the fact that not all of the thread teeth ride over one another simultaneously. Moreover, the cross-sectional shape of the threads are ramped. This makes it easier for the threads to ride over one another as the plunger slide is being inserted into the reservoir piston.
However, the flat opposite edge of the thread profile makes it much more difficult for the plunger slide to be separated from the reservoir piston.
[0098] When the plunger slide is fully inserted into the reservoir piston, the slide bottoms out in the cavity of the piston. At this point the presence of the hydraulic load of the fluid in the reservoir as well as the static and kinetic friction of the piston will act on the plunger slide. FIG. 13b shows the bottoming out of the plunger slide against a piston in a reservoir having fluid and the resulting increase in the axial force acting on the piston and the plunger slide. This hydraulic load in combination with the static and kinetic friction is so much higher than the force required to engage the piston threads that such a disparity can be used to advantage.
[0099] The fluid pressure and occlusion detection systems described in U.S.
provisional patent application serial no. 60/243,392 (attorney docket no. 0059-PROV) filed*October 26, 2000, later filed as a regular U.S. application serial no.
09/819,208 filed on March 27, 2001, now issued as U.S. Patent No. 6,485,465 or in U.S.
patent application serial no. 09/428,411, filed October 28, 1999, now issued U.S. Patent No. 6,362,591 (all of which are incorporated herein by reference in their entireties) or known pressure switch detectors, such as those shown and described with reference to FIGs,~ l:and-2, can-be. usedtto:.detect.the;=fluid,back..pressur.e associated with..thei.bottoming:
out of the plunger.slide against=the- piston. Certain sections of the incorporated=.references wwi.ll -be=disc.ussed;below with, regairds to.the error detection of the fl.uid. force.-sensor =ancl oceiusion detection systems'below =in reference==to-FIGs: 19-23(a &=b), tivhichris =related' to .,-thez-fluid=back;pressiure, associated:Awitli.:the'bottoming-,out of the=plunger.si.ide:'agairist=xhe'= ;
piston.
[001001, A=high pressure.:trigger.point of such a pressure switch or.
6cclizsion.
detection system can be set at a- point:above the relatively41 at cross =threadforce =as shown ~
in FIG. 13b. Alternatively, the ramping or the profiles,of such -back pressure forces can' be monitored. When an appropriate limit is reached, the pump= system electronics can send a signal to stop the pump motor. Thus the pump drive system is able to automatically detect when the plunger slide has bottomed out and stop the pump motor from advancing the plunger slide.
[00101) Referring to FIGs. 11 and 12, the 5 start, 40 TPI (0.125" lead) thread profile of the coupler male portion 426 was chosen in consideration of the thread lead on the preferred embodiment of the connector 431. The connector 431 is secured into the pump housing with threads 433 (FIG. 7b) having a 2 start, 8 TPI (0.250" lead) profile. Therefore the 0.250" lead on the connector is twice that of the reservoir piston assembly 407 which is 0.125". This was chosen to prevent inadvertent fluid delivery during removal of the reservoir from the pump housing, or alternatively, to prevent separation of the reservoir piston assembly 407 from the reservoir 406 during removal from the pump housing.
When the connector 431 is disengaged from the pump, the connector 431 as well as the-reservoir 406 will both travel with the 0.250" lead. Since the threaded coupler lead is 0.125", the plunger slide 405 will disengage somewhere between the 0.125" lead of the threaded coupler and the 0.250" lead of the infusion set 1103. Therefore, the rate that the reservoir piston assembly 407 is removed from the pump is the same down to half that of the reservoir 406/connector 431. Thus any medication, which may be present in the reservoir 406 will not be delivered to the user. Additionally, the length of the reservoir piston assembly 407 is sufficient such that it will always remain attached to the i'eservoir 406 during removal from the pump. Although the preferred embodiment describes the plunger slide 405 having a coupler male portion 426 with an external thread lead that is different from the connector 431, this is not necessary. The thread leads could be the same or of an increment other than what has been described.
[00102] .The..2:.start-thr,ead;profile.iof.the.coupler female portion.4.24..on:.the=reservoir, piston assembly 407=of4lie:preferred embodiment provides another advantage:'-.Some ver=sions:of these reser.voir.s:may..be-designedto be filled by the:=user.
.In=such,,ari=instance a lineart actuation member='comprising =a= handle-(not-shown) will need to be 'screwe=d=into the threaded-portion=ofahe,reser.voir1piston.assembly.~4.07=in.order for the.iiserto~r.etracttthe reservoir piston assembly:..40.7, and:fill.the reservoir. =The number_of-rotations=necessary:to fiilly insert the: handle>deperidsi upcin.:the distance.the handle thread #6fi1e:tr.ave1sAo1 fiilly engage=the reservoir piston assembly 407 as well-as the thread lead.
[001031. For example; a-single start, 40 TPI (0.025" lead) thread requires 4'complete rotations to travel a 0.10" =thread engagement. However, a 2 start, 40 TPI
(0.050" lead) thread only requires 2 complete rotations to travel the 0.10" thread engagement.
Therefore, an additional advantage of a 2 start thread as compared to a single start thread (given the same pitch) is that half as many rotations are needed in order to fully seat the handle.
[00104] In alternative embodiments which are not shown, the end of the plunger slide 405 may include a detente or ridge to engage with a corresponding formation in the reservoir piston assembly 407 to resist unintended separation of the plunger slide 405 from the reservoir piston assembly 407. In other embodiments, the plunger slide 405 is inserted and removed by overcoming a friction fit. Preferably, the friction fit is secure enough to resist movement of the reservoir piston assembly 407 relative to the plunger slide 405 due to changes in air pressure, but low enough to permit easy removal of the reservoir 406 and its reservoir piston assembly 407 from the plunger slide 405 once the fluid has been expended. In other embodiments, the detente or ridge may be spring loaded or activated to grasp the reservoir piston assembly 407 once the drive mechanism has been moved forward (or extended), but is retracted by a switch or cam when the drive mechanism is in the rearmost (or retracted) position. The spring action could be similar to those used on collets. In other embodiments of the inventions, the threaded coupler may be engaged with the threaded cavity of the reservoir piston by twisting or rotating the reservoir as it is being manually placed into the h6using.
[00105] As previously mentioned, some pump systems may have an occlusion detection system which uses the axial force on the drive train as an indicator of pressure within a reservoir. One problem faced by such occlusion detection systems, however, is the system compliance associated with reservoir fluid back pressures. As previously -mentioned, the::for.ce.,on a=.piston.asserrmbl.y.resulting from. increased back pr.essures, can =, deform a piston.which is constructed of:relatively flexible material such.as=rubber. Should :an.occlusion arise.in=the.fluid=systerim, this deformation:can reduce the rate~at, kvhich=fluid 'baek pressures increase: This =in,turrn can increase ,the- amount of time require d= for the ;system to. detect~ari -occhision:=;a:.situatiomswluch~'niay be undesirablc .[00106] To.'addr.ess+this, problem~,:an i:nseft =1201- which,is-made of hard=plastic;
.stainless, steeL or=.other,preferablyrelatively.stiff mater.ial:is disposed=in the~upper 'portion:.=
of the reservoir piston -assembly 407. -(FIG' 1:2) rThe ,insert 1201,of the illustrated embodiment provides-stiffness to the rubber.reservoir piston assembly 407:
This can reduce undesirable compliance which is associated with the reservoir.
[00107] FIG. 14 shows an industry standard reservoir 406 and the piston assembly 407 comprising a piston member 1404 and an insert 1201. One end of the reservoir 406 has a generally conical-shaped end portion 1401 which tapers to a neck 1402. A
swage 1403 is secured to the neck thereby forming a fluid-tight seal. The insert 1201 is placed in the cavity 424 of the piston member 1404 which in tum is placed in the opposite end of the reservoir 406.
[00108] FIGs. 15a and 15b show the piston member 1404 which is adapted to receive the insert 1201 (FIG. 14). The piston member 1404 is further adapted to be slidably mounted within the reservoir 1401 and to form a fluid-tight barrier therein. The exterior of the piston member 1404 includes a generally cylindrical side wall 1502 and an external proximate side 1501 having a generally conical convex shape which is adapted to conform to the conical-shaped end portion 1401 of the reservoir 406 (FIG. 14).
This geometry reduces the residual volume of fluid remaining in the reservoir 406 after the piston assembly 407 is fully advanced. The piston member's side wall 1502 has a plurality of ridges 1503 which form a friction fit with the interior of the reservoir side wall thereby forming a fluid-resistant seal.
[00109] Referring to FIG. 15c, the piston member 1404 has an external distal side 1505 which is opposite to the external proximate side 1501 which in turn is adapted to contact any fluid' which might be present in the reservoir. The external distal side 1505 has an opening 1506 leading into the threaded cavity 424. The cavity 424 comprises a first chamber 1508 extending from the external distal side 1505 into the cavity 424 and a second chamber 1509 extending from the first chamber 1508 to an internal proximate wall 1 S 10 which is disposed adjacent to the external proximate side 1501 of the piston member .1404.
[00110] :The first chamber :1-508 is defined by a generally cylindrically-shaped firsti wall 1511 exteriding-axially from.the-external: distal: side 1505 into.the.
cavity 424. -The first wall- 1,51*includesthreads- 1504--f6rmed on the-wall which are -adapted-to couple with -anylinear actuator.member; such:as:for;example; theahreads of the nnalepor.tion:.4.26-of the!plunger4ide=405;asipreevi6,-usly_described:(FIG.:1.1):.=The=second clia.mber. 1509:is, defined'.liy. a.generally..-c.y.lindricall=y=shap'ed~-second wall=15:12.extending=:axially~fr.om the generally cylindricall.y-shaged first wall.15,11- into the cavity 424 and.by the internal proximate wall 1510. : The generally cylindrically-shaped second wall 1512 has a radius which is greater thari that of the generally cylindrically-shaped first wall 1511. A ledge 1513 extends from the generally cylindrically-shaped first wall 1511 to the generally cylindrically-shaped second wall 1512. The internal proximate wall 1510 forms the end of the second chamber 1509 and is generally concave conical in shape. Thus the thickness of that portion of the first member which is between the internal proximate wall 1510 and the external proximate side 1501 is generally uniform.
[00111] Referring to FIGs. 16a - 16c, the insert 1201 is a solid member which has a planar back wall 1602, a generally cylindrical side wall 1603, and a conical face portion 1601 which terminates in a spherically-shaped end portion 1604. In one embodiment, the planar back wall 1602 is 0.33 inches in diameter, the cylindrical side wall 1603 is approximately 0.054 inches in length, the conical face portion 1601 is approximately 0.128 inches in length, and the spherically-shaped end portion 1604 has a radius of curvature of approximately .095 inches.
[00112] The face portion 1601 and the end portion 1604 are adapted to mate with the internal proximate wall 1510 and the back wall 1602 is adapted to seat against the ledge 1513 of the piston member 1404 (FIG. 15c). When inserted, the insert face portion 1601 and the external proximate side 1501 are in a generally parallel spaced-apart relationship. The insert 1201 is a relatively incompressible member which can be made of stainless steel or relatively stiff plastic or any other material which preferably has stiffness properties wliich are greater than that of the external proximate side 1501 of the piston member 1404. If a hard plastic material is selected, however, it preferably should be a grade of plastic which can withstand the high temperatures associated with an autoclave.
[00113] FIG. 17 shows the reservoir 406 with the piston member 1404 and the insert 1201 as assembled. As previously mentioned, the ledge 1513 supports the planar back.1602 of the insert 42Ø1.:and:secures it.into.place...Because the piston: mer.nber.1404 :is constructdd of rubber or other relatively flexible material, it can deflect sufficiently=during assembly, to permit the insert= 1201= to be inserted.in the openin;g:~1506 and through:tlie first -chamber' 1-508 and then=positioned~in-the second,chamber 15'09: The conical face;-portion -16.01;of.the>insert-.120.1:,rnates.with:tlie=internal.-pr.oxirimate wa11=:15=10-of the [iistori=-niember 1404;cthus=permitting-.a.reduced-thickness:of rubber=which is in,direct coritact-mith:.fluid.
-1704: This:.reduced'thickness::of rubber or=-:other:.flexible.material minimizes,the compliance which.might otlierwise bd caused =by the back pressure of the:fluid 1701 -actingi on the external proximate side.1501 of the piston member 1404.
[00114] It should be appreciated'that although the insert member 1201 depicted in FIGs. 14 - 17 is removable from the piston member 1404, alternative embodiments of the present invention include a piston assembly in which there are no openings or open cavities and in which an insert member is encased in such a manner so as to be not removable.
[00115] The insert member of the above-described embodiments is not adapted to contact the fluid in a reservoir. However, FIG. 18 shows yet another alternative embodiment where a portion of an insert member is adapted to contact reservoir fluid. A
piston assembly 1801 comprises a piston member 1802 and an insert 1803. The piston member 1802 is adapted to be slidably mounted within a reservoir (not shown in FIG. 18) and is further adapted to form part of a fluid-tight barrier within the reservoir. The piston member 1802 has an extemal proximate side 1804 and an external distal side 1805. The external proximate side 1804 is adapted to contact the reservoir fluid and is made of an elastomeric material, such as rubber.

[00116] The insert 1803 is substantially contained within the piston member and has a face 1806 which is made of a material, such as stainless steel or hard plastic, having a stiffness which is greater than that of the piston member 1802. The insert face 1806 has an exposed portion 1807 and an enclosed portion 1808. The exposed portion 1807 is adapted to contact the fluid within the reservoir whereas the enclosed portion 1808 is enclosed or covered by the external proximate side 1804 of the piston member 1802.
Therefore, the insert 1803 extends past the external proximate side of the piston member 1802 and is adapted for contact with the fluid to complete the fluid-tight barrier within the reservoir. Thus the arrangement of the insert 1803 in this fashion provides the necessary stiffness=to the piston assembl.y:1.801.to=reduce sy.stem;compliance:
[001-17] It should be appreciated that while the piston members and iriserts described.above include conical geom,etries;: other geometries~ can be used: ~
F6r: example in arr.alternative embodiment~showwin==FIG. 1= 1; an-insert+102 has a disc shape~
with r=.elatively.~flat faces:. ~This ,alsotcan provide. the riecessar'y. stiffness to the. pistovas'serribly ,4Ø7: to! feduce :system~cornpli.ance.
[001:18]: -In yet further:embodiments.(.inof'shown), an..insertmeniber'is ai~iritegrai -part of-a male portion of a:pluriger:siide assembly which--is adapted to fit within~a,'piston assembl.y cavity. The-male portion of the slide assembly (i.e., the insert member) is-further adapted to abut an internal proximate wall within the cavity thus providing increased stiffness to that portion of the piston assembly which is in contact with reservoir fluid.
[00119] It can be appreciated that the design of FIGs. 4-18 results in an arrangement where the plunger slide 405 is reliably but releasably coupled to the drive screw 404.
When it is time to replace the reservoir 406, it can be detached from the male end of the coupler without affecting the plunger/drive screw engagement. Moreover in one embodiment, the plunger slide 405 is shaped as a hollow cylinder with internal threads.
Thus it completely encircles and engages drive screw 404. When the plunger slide 405 is in a relatively retracted position, it encloses any gears which couple the motor 403 with the drive screw 404 thus achieving an extremely compact design. A vent port covered with hydrophobic material as well as a threaded coupler provide redundant means for permitting exposure of the pump to changing atmospheric pressures without the unintended delivery of medication. A reservoir piston assembly 407 includes an insert member 1201 which increases the stiffness of the piston assembly 407 thus reducing fluid system compliance.
[00120] In another aspect of the present invention, the above discussed drive system allows for improved occlusion detection and other error detection systems.
Relevant text froin U:S. patent applicatiori serial no. 09/428,414, filed October 28, 1999, now issued U.S. Patent No. 6,362,591, which was incorporated by reference, describes the occlusion detection scheme as follows:
[00121] The occlusion detector measures increased reservoir pressure indirectly by monitoring one or more motor parameters, such as voltage, current, running time, or rotational or- linear displacemeint. It.is:known. in .the:.art, that torque developed:by. a.brushed.
DC motor is directly proportional to the current supplied to it at steady state. Therefore, in:
a,screw type drive system; as the.>axial load increases=.due to increased fluid, pressure .
within=the~reservoir=;=mere=rnotor= torque is-required-to'dr-ive the system:~Should- therebe'an, occlusion,ahe pr.es'sure>iriside,the~r.e'servoir=wi114exceed.a-predeterminedrthreshol-d:==: Thus.
thd durrent.=necessary.to. drive that load-;will exceed -a predetermined currerit: threshold .and, the electronics will:-be4laggedsto:cease:--further delivering: - In addition;
an-'audible;Aactile-and/or display alarm typicallyS-is triggered:
[00122] However, care must be employed when clearing this alarm if the occlusion, still exists and there is still a high pressure state in the reservoir. Since the motor must operate to obtain an indication of pressure within the reservoir, more and more pressure can potentially be developed within the system. If the motor is not in operation, there is no current flowing and negligible torque on the motor body. Therefore, when an occlusion exits distal from the reservoir due to pinched tubing for example, then the measured property will indicate this only during each motor delivery increment.
[00123] If the user clears the alarm and attempts to deliver medication again when the occlusion in fact was not removed, additional pressure will be generated within the fluid system. Assuming that the system is programmed to continue to alarm when the pressure (or motor current) is above the set point, then continued alarming will occur.
Thus the user may on several occasions attempt to clear the alarm before locating and correcting the source of the occlusion.
[00124] When the occlusion is finally cleared, there could be excess pressure developed in the system which could result in the delivery of a bolus of medication larger than that which should be delivered. The improved occlusion detection system disclosed herein protects against this by causing the pump to rewind by some predetermined amount following each occlusion alarm. By rewinding the pump by, say, one delivery pulse, the occlusion alarm will trigger if the occlusion still exists. However, it will do so at the same maximum pressure as programmed and not at above this value.
[00125] On a drive system that is bi-directional, the current rneasureinerrt can also be used as an indicator of system wear. Over the life of the product, it is expected that the torque required to drive the system will change over time due to wear of the dynamic components and their interfaces. Since the torque required to rewind a bi-directional system is due to the drive system's frictional factors, the current to rewind can- be recorded and. is.,proportional: to this.torque.
[00126] As the system wears, the torque and therefore the ourrent to rewind will change. By-.storing the rewind,cuxrent, this>.can.:be= used to calibrate:the system. Ain, averaged,baseline rewind-current= can lbe determiried and used-to =adjust the.
driving-force baseliine.whichpis;the::torque.(or- current) 'requireddo.advance the-=drive -s,ystem-when-no .other.external- forces;:such.~as..a:,syringe with fluid;.=are=present. An-alternative method=
would, lie-to -'rewind=the :system,:an"'d_then=,iininediately'. thereafter, obtain: the; for'ward -oV
driving baseline :cur=rent=byM1drivirig the, system forward for some distance-and recording' it;
after which, the system is rewound again. The advantage of using either =method is that ~the calibration can be automatic and transparent to the user.
[00127] FIG. 19 illustrates the logic in one embodiment of the detector wherein motor current is measured for detecting a system occlusion. Control begins at block 501' where the system determines whether it is necessary to fully rewind the pump drive system. Conditions requiring such a rewind of the drive system will be discussed below.
If the system is not to be rewound, then a determination is made whether it is time for an increment of medication is to be delivered (block 502). This determination is a function of the programming which is unique to the medical condition of each user, the type of medication being provided, or the like. If it is not time to deliver medication, then the program loops to the start for additional time to elapse or for the receipt of other control commands.
[00128] However, if it is time for delivery of an increment of medication, control transfers to block 503 where power is applied to the pump motor thus causing medication to be dispensed from the reservoir. Next, the amount of medication delivered from the reservoir is measured (block 504). This can be accomplished directly or indirectly in several ways, including measuring (1) encoder counts, (2) pump operation time, (3) reservoir plunger position location, velocity or acceleration, (4) the location of any moveable component on the pump drive train, or (5) the mass or volumetric flow of the liquid.
[00129] A determination is then made as to whether the amount of medication delivered is sufficient (block 505). If it is sufficient, control is transferred to block 506 where the pump is stopped and the program loops to the beginning. If on the other hand, the pump is continuing to run, but the programmed dosage has not yet been delivered, then the pump motor current is measured (block 507). If there is an occlusion in the system, an increase in reservoir fluid pressure.will~likely:result. This, in turn, can cause:greater= motor:
torque and current as the motor attempts= to advance the.reservoir plunger against this fluid pressure. Thus, if.the rrieasured.rriotor=:current.is some amount greater than a.known, =average+aseline,motorcur=rent,-which may be established-when there was-no,occlizsion eondition;~themit.is determinedthats~anocclusion condition=:has;likel.y.occurred .[0013.0) Not only, eainzthis current nieasurement indicate-an=oe.clusioritcoridition,.this motor.:current can provide feedback5as. to,drive system :characteristics;.perforinance, -and functionality, especially with the addition,ofan encoder. If for example, there was'a.
failure of the gearbox causing the motor to be unable to rotate, the measured curreint.would be high (above predetermined threshold settings) and the encoder would not increment.
This would be an indication of a drive system fault. For the inline drive system, a failure of the gearbox, screw, or slide interface would be indicated by this condition.
[001311 Referring to FIG. 19, at block 508 the value of the average baseline current is retrieved from a storage location in memory represented by block 520. This value is compared with the current measured at the present time and a determination is made whether the present current exceeds the average baseline by a certain amount.
If it does not, then the pump continues to run and control loops to block 504 where the amount of medication delivery is again measured. On the other hand, if the present current exceeds the average baseline by a selected amount, then the pump motor is stopped and an alarm indication, audible, tactile and/or visible, is given (blocks 509 and 510).
[00132] Control transfers to block 511 where the system is monitored for clearing of the alarm. If the alarm has not been cleared, then control loops to block 510 where the alarm will continue to display. If the alarm has been cleared by the user, then control transfers to block 512 where the drive system is rewound by an incremental amount. This rewinding serves to decrease the reservoir fluid back pressure which in turn inhibits or prevents the delivery of an excessive bolus of medication should the user experience a series of occlusion alarms before successfully clearing the occlusion.
[00133] Control then transfers to block 513 where an alarm flag is stored. A
determination is made whether there have been an excessive number of recent alarms (block 514). If there have not, then control loops to the beginning (block 501) where the above described process is repeated. On the other hand, if there have been an excessive number of recent alarms, control transfers to block 515 where an error or reset message is displayed to the user. This message typically would .be used to advise the user to contact .the manufacturer or some iauthorized. repair.facility to=determine=the,cause..of the. excessive.
.number of alarms. This error.message will continue to be displayed until the error is .
-cleared (block:5:16) at which- point:controL loops to the beginning (block 501) where the -process-is repeated.
-[00134]. Returning,to:bloek;-501'==;%there. are time's;whewa: full rewind~of;the::drive s.ystem-may be~required:~-,One=instarice .would=be:when:the medication=reseivoir._in the , pump:liousing-is empty and:asnew>reservoir.must be inserted~--:Tfius,.when-:it.has been~r deter"mined that-rewinding -of the: drive system is desired (either -by user-commandior_ ,otherwise), control transfers to block 517 where power is applied to the pump motor. As' the motor is running in a rewind direction, the pump motor current is measured (block 518). An alternative method would be to obtain the forward or driving baseline current by driving the system forward (possibly immediately following rewind) for some distance and recording it, after which the system may need to be rewound again. Because the motor is running in the opposite direction (or forward following rewind), typically there is little or no fluid pressure against which the pump motor is driving. Thus the current measured during this phase can be used as a baseline for comparison in detecting occlusions.
[00135] Control transfers to block 519 where the previous average baseline current value is retrieved from a storage location in memory (block 520) and an updated average baseline current is calculated. This updated value is then placed in the storage location, (block 520), where it will be available for the next current measurement and comparison at block 508.
[00136] The value of repeatedly updating the average baseline current is to provide a calibration against changing drive train friction forces. The lead screw mechanism of many pump designs includes seals, a drive nut, a lead screw/motor coupling, and a bearing. All of these components have frictional properties. These properties are known to change over time and thus the motor torque and current required to advance a reservoir plunger are likely to change. This therefore provides a more accurate baseline against which current can be measured for the detection of an occlusion.
[00137] Although the foregoing description involved the measurement of motor current, other motor parameters which vary with differing fluid back pressures can be measured with like effect. Such parameters may include motor voltage, linear displacement, rotary displacement, torque, rotor speed, and the like.
[00138).. For,example,.=one alternative-.ernbodiment of therocclusion..detector involves the use of a motor_position encoder which can detect the motor's linear -or rotational.displacement.- If.:for::example, the encoder-has a resolution of 360 counts per;
~,motor revolution of a rotary%motor, then wi-th- each-motor revolution;=the -sensor'wil=1-:p'rovide 360. encoder si:ghal'pulges:~::If thepuinp:system_were designed,w.require.:orie' :,complete-motor revolution.to :deliver ;the -desired-:increment -of medication;. then;the motor ean be-controlled, to% stop:when:360-encoder counts are~received.
=Linear:displacements~of :liriear. motors may be=similarly detected=by suitable -linear encoders or sensors.-[00139] Because motors have inertia, the powensupplied to them rriust be removed prior to the actual stopping position in order for the motor to slow and stop.
- The slowing or deceleration can be accomplished in several ways including: (1) coasting which simply lets the applied and frictional torque slow the motor; or (2) dynamic braking which can be accomplished for example by shorting the motor leads or applying a potential in the opposite direction.
[00140] The applied torque affects the total rotational count. Thus as the applied torque varies, so will the error from the desired 360 counts. To account for a deviation from the target encoder count, a feedback loop is provided whereby the input power parameters to the motor, such as motor voltage or current or the time during which power is applied to the motor, may be adjusted.
[00141] In one embodiment, the motor is controlled based on the results of the previous encoder count for each cycle. Thus, for example, if360 encoder counts were desired, but only 350 were measured, then subsequent input motor parameters can be adjusted such that the running encoder average is maintained at 360 counts. If a motor system was used with a DC motor driven with a constant current source or fixed source voltage, then the motor input parameter to be adjusted for rriaintaining the desired encoder count for the next pump cycle would be power on time.
[00142] For example, a motor may be driven such that half of the rotational displacement (or 180 out of 360 counts) is due to power on time and the other half is due to the coasting down of the motor unde=r a specified nominal load (torque).
Should the load increase, then the coasting would decrease thereby reducing the total encoder count measured for a constant power input. For example, the system may measure 350 counts rather than the target value of 360 counts. To maintain medication delivery accuracy therefore, the subsequent motor increment during the next pump cycle may be increased above the_ 180..encoder count:for.the power:.on time=so thatahe rimning average is, maintained at 360 for- the entire pump cycle.
.[00143] - Yet another>embod'zmenvof.=the occlusion detector uses an eneodet count to ,determine, torque: In this ernbodiment;=torque is a function of encoder count=and one or 'more motor..inpi.it po.wer~pararneterscp Mot6r_l6ad:torque'ean =be:
deterniined~by: evaluating;
Jhe stored encoder=count'for.a kno.wndeliver.ed=amount of energy: : The:
detector. =sy.sten:.
pr.ovide"s, a.known acnount of energy.:(i..e.; power.time's= motor on.time)';t anderecoidsthe=.t.
rriotor displacement via the-numb:er of encoder:counts obtained. Using a look=up table:or .calculated value, the system determines a corresponding torque that would result from the -recorded number of encoder pulses for the amount of energy supplied.
[00144] For example, if the motor were running for a certain amount of time, this might result in an encoder count of 360. Later, the motor might run for the same arnount of time under the same voltage and current conditions, but an encoder count of 350 may result. Thus the system would have encountered increased torque as reflected by the reduced encoder count. A lookup table or calculated value of torque vs.
encoder count and input power parameters can thereby be developed and used to measure motor torque.
[00145] In summary, preferred embodiments disclose a method and apparatus for automatically detecting an occlusion or drive system failure in a medication infusion pump system. The electrical current to an infusion pump is measured and compared against a baseline average current. If the current exceeds a threshold amount, an alarm is triggered.
Alternatively, pump motor encoder pulses are measured during a pump cycle. If the number of pulses does not correspond to a normal range, an alarrn is triggered.
Alternatively, a system torque value is determined from the measurement of pump motor encoder pulses during a pump cycle. If the system torque value exceeds a maximum threshold value, an alarm is triggered. In preferred embodiments, after any alarm is triggered, the pump motor is driven in reverse for an incremental distance in order to relieve the fluid pressure in the system. Alternatively, the pump motor is not reversed.
1001461 In another aspect of the present invention, the above discussed drive system allows for improved pressure sensing, occl'usion detection, and other error detection systems. Relevant text from U.S. application serial no. 09/819,208 filed on March 27, 2001, now issued as U.S. Patent No. 6,485,465, which was incorporated by reference, describes the pressure sensing system and.occlusion detection system as follows:
[00147] In preferred embodiments, a programmable controller regulates power from -a.power_supply.toa motor. -The motor,actuates a=drive,train to:displacea slide coupled:
with a stopper inside. a fluid filled reservoir. The slide forces the fluid from the reservoir,.
,albng a fluid path, (including tubing=ancl, an infusion set), and into the user's;body. =:In.
-preferred embodiments, the pressure,sensing system is~used to-detect occlusions iri-the.
f luid+patly.-that slow; ~prevent,:.or= 6therfwiserdegrade'fluid=delivery;from the:reser.,vo.irAo the'.
user.'s-body.= In alternative ernbodiments; the.:pressure sensing systerri is.,used to detect when: the:reservoir is:empty,.tli-e,slide::is<.properly iseated with:
the.stopper;~a fhiid dose.has.;
beeri delivered,,the,infusionipump is subje.cted to shock or vibration, theinfusion device requires maintenance, or the.like. In further- alternative embodimernts, the reservoir may be a syringe, a vial, a cartridge, a bag, or the like_ [00148] In general, when an occlusion develops within the fluid path, the fluid pressure increases due to force applied on the fluid by the motor and drive train. As power is provided to urge the slide further into the reservoir, the fluid pressure in the reservoir grows. In fact, the load on the entire drive train increases as force is transferred from the motor to the slide, and the slide is constrained from movement by the stopper pressing against the fluid. An appropriately positioned sensor can measure variations in the force applied to one or more of the components within the drive train. The sensor provides at least three output levels so measurements can be used to detect an occlusion and warn the user.
[00149] In preferred embodiments, a sensor is a force sensitive resistor, whose resistance changes as the force applied to the sensor changes. In alternative embodiments, the sensor is a capacitive sensor, piezoresistive sensor, piezoelectric sensor, magnetic sensor, optical sensor, potentiometer, micro-machined sensor, linear transducer, encoder, strain gauge, and the like, which are capable of measuring compression, shear, tension, displacement, distance, rotation, torque, force, pressure, or the like. In preferred embodiments, the sensor is capable of providing an output signal in response to a physical parameter to be measured. And the range and resolution of the sensor output signal provides for at least three levels of output (three different states, values, quantities, signals, magnitudes, frequencies, steps, or the like) across the range of measurement.
For example, the sensor might generate a low or zero value when the measured parameter is at a minimum level, a high or maximum value when the measured parameter is at a relatively high level, and a medium value between the low value and the high value when the measured parameter is between the minimum and relatively high levels. In preferred embodiments, the sensor pr.ovides.~more:tham=three..output levels, and.
providesa!signal_=that corresponds to each change. in resistance in a sampled, continuous, or near continuous -. .
manner. -=:The- serisor is distinguished-from a switch, which has only, tvvo output ualues; and therefore=can:only indicate two -levelg -of output=such as,--'on' and-'off,' -or 'high'-~and-,'~low:
a[00:150] Preferredembodinierit's;aff:the present,invention=employ!a.force:sensitive resistor as the ~sensor, which changes,resistance =as :the}=force= applied- to --the'sensor changesv'.
Tlie;electronics =system-:maintairis~a, coristarit supply voltage- across=the ~sensor:=_ The output:~ =
signal->from the. sensor,is a signal= cur.rent that'passes through a resistive material;of the 'l sensor. Since the sensor resistance varies with force,=.and the supply voltage across the sensor is constant, the signal current varies with force. The signal current is converted to a signal voltage by the electronics system. The signal voltage is used as a measurement of force applied to a drive train component or fluid pressure in the reservoir.
In alternative embodiments, a constant supply current is used and the signal voltage across the sensor varies with force (fluid pressure). In further alternative embodiments, other electronics systems and/or other sensors are used to convert fluid pressure or forces into a measurement used by the electronics system to detect occlusions in the fluid path.
[00151] In preferred embodiments, the design and method for mounting the sensor must: sufficiently limit unintended movement of the slide with respect to the reservoir;
minimize space between components; be rigid enough for the sensor to immediately detect small changes in force; avoid preloading the sensor to the point that the sensor range is insufficient for occlusion, seating, and priming detection; provide sufficient resolution for early occlusion detection; compensate for sensor system and drive train component dimensional tolerance stack-up; allow sufficient movement in components of the drive system to compensate for misalignments, eccentricities, dimensional inconsistencies, or the like; avoid adding unnecessary friction that might increase the power required to run the drive system; and protect the sensor from shock and vibration damage.
[00152] Generally, once the infusion set is primed and inserted into the user's body, the slide must not be permitted to move in or out of the reservoir unless driven by the motor. If the motor and/or drive tiain components are assembled in a loose configuration' that allows the slide to move within the reservoir without motor actuation, then if the infusion pump is jolted or bumped, fluid could be inadvertently. delivered.
Consequently, the sensor and/or components associated with mounting the sensor are generally positioned snugly against the drive train component from which force is being sensed, thus ._pzeventing thedrive_train~component from:moving:when the infusion.purnp:.is.subjected to..
shock or vibration.
[001531 In preferred==.embodiments,Ahe -sensor is -positioned so that ast"soon'. as;the.
=pump motor is,loaded-duri=ng-,operation;.=a-drive trai.n component applies=a.Ioad=-to=the=
sensbr::= =Minimizirig space;between,:the; sensor :aind: the ~load-applying.
dr=ive..train: coriiponent=
-improves the sensor's~sensitivity~to:Ioad.fluctuations:, Small .ehangesin load mayb.&.used to:..detect trends;.and.ther.efore=provide an-early,war=ning-that:a;blockage=is'developinÃ
before the,fluid delivery,is stopped entirely:
[00154] In preferred erribodiments, the= senso'r and associated electronics are intended to measure forces between 0.5 pounds (0.23 kg) and 5.0 (2.3 kg) pounds with the desired resolution of less than or equal to 0.05 pounds. Yet, the infusion pump including the sensor should survive shock levels that result in much higher forces being applied to the sensor than the intended sensor measurement range. In alternative embodiments, the sensor range is from zero to 10 pounds (4.5 kg). In other alternative embodiments, the sensor range and/or resolution may be greater or smaller depending upon the concentration of the fluid being delivered, the diameter of the reservoir, the diameter of the fluid path, the force required to operate the drive train, the level of sensor noise, the algorithms applied to detect trends from sensor measurements, or the like.
[001551 In preferred embodiments, the sensor and associated electronics provide a relatively linear voltage output in response to forces applied to the sensor by one or more drive train components. An example of measured voltages from the sensor, (and its associated electronics) in response to forces ranging from 0.5 pounds to 4.0 pounds, are shown as data points 201-208 in Fig. 20.

[00156] In preferred embodiments, each sensor is calibrated by collecting calibration points throughout a specified range of known forces, such as shown in Fig. 20.
A measured voltage output for each known force is stored in a calibration lookup table.
Then, during pump operation, the voltage output is compared to the calibration points, and linear interpolation is used convert the voltage output to a measured force."
Preferably, eight calibration points are used to create the calibration lookup table.
Alternatively, more or fewer calibration points are used depending on, the sensor linearity, noise, drift rate, resolution, the required sensor accuracy, or the like. In other alternative embodiments, other calibration methods are used such as; curve fitting, a look up table without .=interpolation,..extrapolation,.si-ngle:.or,.,two, point:calibration, or the..like....:In-further=
=alternative embodiments, the voltage output in response to applied forces is.substantially rnon-linear. In furthevalternative =embodiments, no calibrations are used:
-[00157] Inpreferred- embodiments;,sensor'measurements are taken jusrprior to ;commanding=the;drive>system-.to.deliver;fluid; ,arid soon=,after.the-driveYsystem=has stopped .delivering fluid::..In; alternative. embodimerits;:serisor: data is collected==on-a'continuous .basis:at a particular_sampling,"rate,forcexample-~l0 Hz;;3=,Hz,_once::every 1.0~seconds; once=a minute, once every five~min.utes, or the like.;:=In-further alternative embodinients; the:
sensor data is only collected just prior to commanding the drive system to deliver fluid; In still further alternative embodiments, sensor data is collected during fluid delivery.
[00158) In preferred embodiments, two methods are employed to declare occlusions in the fluid path, a maximum measurement threshold method, and a slope threshold method. Either method may independently declare an occlusion. If an occlusion is declared, commands for fluid delivery are stopped and the infusion pump provides a warning to the user. Warnings may include, but are not limited to, sounds, one or more synthesized voices, vibrations, displayed symbols or messages, video, lights, transmitted signals, Braille output, or the like. In response to the warnings, the user may choose to replace one or more component in the fluid path including for example the infusion set, tubing, tubing connector, reservoir, stopper, or the like. Other responses that the user might have to an occlusion warning include: running a self test of the infusion pump, recalibrating the sensor, disregarding the warning, replacing the infusion pump, sending the infusion pump in for repair, or the like. In alternative embodiments, when an occlusion is detected, attempts for fluid delivery are continued, and a warning is provided to the user or other individuals.

[00159) When using the maximum measurement threshold method, an occlusion is declared when the measured force exceeds a threshold. In preferred embodiments, a threshold of 2.00 pounds (0.91 kg) is compared to force values measured by the sensor before delivery of fluid. If a measured force is greater than or equal to 2.00 pounds (0.91 kg), one or more confirmation measurements are taken before fluid delivery is -allovved. If four consecutive force measurements exceed 2.00 pounds (0.91 kg), an occlusion is declared. In alternative embodiments, a higher or lower threshold may be used and more or less confirmation readings may be collected before declaring an occlusion depending upon the sensor signal to noise level, the electronics signal to noise level, measurement drift,: sensitivity.to.temperatur=e:-and/.or.humidity., _the= force required to .deliver fluid, the=
maximum -allowable bolus, the sensor's susceptibility to shock and/or vibration, and the Jike. In fur.ther:alternative embodiments, the maximum measurement'threshold methvd=is-,not-used. Iw still further alternative-ernbodiments;=fluid delivery is-allowedfor one or=
more.measi.trements-that exceed aytlire=shold;but fluid.delivery is n t-allowed=and;an, occl.usion is~declared,=,after aspredetermined :number of consecutive=measurementsiexceed.
the. threshold:.
=[0016.0] -As mentioned previdusly, the use of sensors, which provide a spectrum of output levels, rather than a switch; which is dapable of providing only two discrete outpul levels, allows the use of algorithms to detect trends in the output, and thus, declare an occlusion before the maximum measurement threshold is reached. In preferred embodiments, the slope threshold method is used to evaluate trends to provide early occlusion detection. When using the slope threshold method, an occlusion is declared if a series of data points indicate that the force required for fluid delivery is increasing. A
slope is calculated for. a line passing through a series of consecutive data points. If the slope of the line exceeds a slope threshold, then pressure is increasing in the fluid path, and therefore, an occlusion may have developed. When nothing is blocking the fluid path, the force measured by the sensor before each delivery remains relatively constant, and the average slope is generally flat.
[00161] In particular embodiments as seen in FIG. 21, a sensor 706 is used to detect when a slide 711 is properly seated with a stopper 714. The reservoir 715 containing the stopper 714 is filled with fluid before it is placed into an infusion pump 701. The stopper 714 has pliable internal threads 713 designed to grip external threads 712 on the slide 711.
The stopper 714 and slide 711 do not need to rotate with respect to each other to engage the internal threads 713 with the external threads 712. In fact, in particular embodiments, the internal threads 713, and the external threads 712, have different thread pitches so that some threads cross over others when the slide 711 and stopper 714 are forced together.
Once the reservoir 715 is placed into the infusion pump 701, a motor 705 is activated to move the slide '711 into the reservoir 715 to engage the stopper 714. As the threads 712 of the slide 711 first contact the threads 713 of the stopper, a sensor 706 detects an increase in force. The force continues to increase as more threads contact each other.
When the slide 711 is properly seated with the stopper 714, the force measured by the sensor 706 increases to a level higher than the force needed to engage the internal threads .713 with .the. external.threads.7.12:; During the- seating..operation;:if the.force sensed-~by:the: sensor 706 exceeds seating threshold, the motor 705 is stopped until further commands are.
issued. ;-T.ki~e =seating threshold is- generally about =1.5 pounds (0:68:
kg). In alterriative ernbodiments higher or= lower seating=threshol'cis may be used= depending onrtheforce req:uired= to: mate:the ,slide, witli~-;tlie .stopper, the_ force -required-to: force fluid_frorn=tlie~:
.reser=voir=;:.the:speed of:the.motor;4the'sensor:-accuracy.,and.resolution, or=the-=like: ::Inaomet, embodiments;-no.force-is needed_to:matel the slide:with.the=stopper;-because.the'slide only pushes on the:stopper and is not,gripped by the-stopper: =
[00162] In still other particular= einbodiments, other force thresholds are used for other purposes. During priming for example, a threshold of about 4 pounds (2 kg) is used.
In alternative embodiments, forces greater than about 4 pounds are used to detect shock loads that may be damaging to an infusion pump.
[00163] Although the use of force sensitive resistors and capacitive sensors have been described above, it should be appreciated that the embodiments disclosed herein include any type of sensor that can provide least three different levels of output signal across the range of intended use. Sensors may be positioned within various embodiments of drive trains to measure either a force applied to a drive train component, a change in position of a drive train component, a torque applied to a drive train component, or the like.
[001641 For example, in alternative embodiments a piezoelectric sensor is used to produce varying voltages as a function of varying forces applied to a drive train component. In particular alternative embodiments, the piezoelectric sensor is made from polarized ceramic or Polyvinylidene Fluoride (PVDF) materials such as Kynar , which are available from Amp Incorporated, Valley Forge, Pennsylvania.

[00165] The previously described embodiments generally measure fluid pressure or forces exerted in an axial direction down the drive train. Alternative embodiments of the present invention however, measure a torque applied to a drive system component as an indication of the fluid pressure within a reservoir.
[00166] In other particular embodiments as seen in FIG. 22, a moto'r 2301 (or a motor with an attached gear box) has a drive shaft 2302 engaged to drive a set of gears 2303. The motor 2301 generates a torque powering the drive shaft 2302 in direction d.
The drive shaft 2302 rotates the gears 2303 to transfer the torque to a lead screw 2304, rotating the lead screw 2304 in the direction d'. The lead screw 2304 is mounted on a :.bearing.2305. for support: . The threads of the lead.;screw.23 04 are engaged:with:.threads (noVsho,wn) in a slide 2306. The=slide 2306 is engaged with a slot (not shown):in the housing (not shown) to-.prevent the.slide 2306 from=rotating; but allowingit=td:translate along=the length of=the-lead~screw,2304:rThus; the torque'd'-ofthe- lead screw 2304-is aransferred to the. slide:2306.causing the slide 23.06 to-move in.an axial direction, generally ;parallel to:=the: driv.e :shaft-,2302~.of-the,motor,2301. -The, slide 2306 --is, iri %contac't -With;a:
:.sto.pper.2307, =inside a-reservoir 2308;::=As-the=slide~2306.advances, the=stopper,23.07:iC
forced to,travel in an =axial direetion inside :the reservoir 2308; forcing fluid from=the , reservoir 2308, through tubing'2309, and into an infusion set 2310.
[00167] Should an occlusion arise, the stopper 2307 is forced to advance, and pressure in the reservoir 2308 increases. The force of the stopper 2307 pushing against the fluid results in a reaction torque d" acting on the motor 2301. In particular embodiments, sensors are used to measure the torque d" applied to the motor 2301, and the sensor measurement is used to estimate the pressure in the reservoir 2308.
[00168] In other particular embodiments as shown in Figs. 23(a and b), a motor 2401 has a motor case 2402, a proximate bearing 2403, a distal bearing 2404, a motor shaft 2408, and a gear 2405. The motor 2401 is secured to a housing (not shown) or other fixed point by a beam 2406. One end of the beam 2406 is secured to the motor case 2402 at an anchor point 2410, and the other end of the beam 2406 is secured to the housing (not shown) at a housing anchor point 2409. A strain gauge sensor 2407 is mounted on the beam 2406.
[00169] Each end of the motor shaft 2408 is mounted on the bearings 2403 and 2404 that provide axial support but allow the motor shaft 2408 and motor 2401 to rotate.
The beam 2406 supplies a counter moment in the direction d' that is equal in magnitude and opposite in direction to the motor driving torque d. As the torque produced by the motor 2401 increases, the reaction moment d" in the beam 2406 increases, thereby increasing the strain within the beam 2406 and causing the beam 2406 to deflect. The strain gauge sensor 2407 mounted on the beam 2406 is used to measure deflection of the 'beam 2406. The electronics system (not shown) coriverts the strain 'gauge sensor measurements to estimates of fluid pressure in a reservoir (not shown) or force acting on the drive train (not shown).
[00170] This method of ineasurement-provides information about the pressure within the reservoir (and frictional stack-up), as well as information about the drive train.
.If: for. example,.:there- were: a. failure. withindthe. drive.train such as, in: the: gearing, bearings,.
.or lead screw interface, the torque measured.at the=strain gauge sensor 2407 would detect the failure. In further embodiments; the strain gai.ige:2407 is used.to'confirm motor activation and fluid~deliver-y:- Duririg normal-fluid-delivery, the measured moment-increases shoiitl.ywhileathe.motor,:.is3ac#i=vated,~and:.theri)-decrease's as fluid~exitsrthe~
r.eservoir relieving:-pressur.e.:and-therefore::the iiiomerit..iThe-electronics-systemtzis.-_.
,programmed to confirm:that the.measured:'moment.increases.during motor-activation-and that.the moment decreases;back to aresting state after the motor is no longer'powered.
=[00171] The above excerpts from the-iincorporated references (i.e.
U:S.:patent application serial no. 09/428,411, filed October 28, 1999, now issued U.S.
Patent No.
6,362,591 and U.S. application serial no. 09/819,208 filed on March 27, 2001, now issued as U.S. Patent No. 6,485,465) described occlusion detection and fluid pressure sensing systems in ambulatory pumps using a sensor that is able to detect changes in the force required to deliver fluid from the reservoir of the infusion pump. The described circuitry detects changes in the force on the sensor, which can be used to indicate when the slide is properly seated in the reservoir or to detect when occlusions occur during the delivery of fluid from the infusion pump. The same circuitry is also described to be able to measure the current used by the drive system to deliver fluid to the user. In addition, a motor position encoder was described which can be used to detect the motor's linear or rotational displacement to assist in the occlusion detection and to measure motor torque.
[00172] According to further embodiments of the present invention, the same circuitry described above can be used to detect a failure in the force sensor by using current measurements to detect when the force sensor is malfunctioning. The force sensor a broad term that includes one or more of the sensor itself, the circuitry to interpret the data from the sensor and the physical structure to support the sensor. Any problem in the force sensor system that causes inaccurate readings from the sensor will be identified as a problem with the force sensor. Slight modifications of the circuitry in terms of increasing the gain amplifier and using a lower frequency filter to reduce high frequency noise was found effective to sample current values delivered to the moto'r to detect a force sensor malfunction. The force sensing system can malfunction for a variety of reasons including, but not limited to, water damage or a crack in the infusion pump casing. A
critical time for detecting a force sensing system failure is during the seating of the slide with the stopper inside the reservoir (i.e., when the 'motor is activated for the first time after loading .the,reservoir within the-.infusion:pump): As-.described previousl.y.;..the electronics:circuitry:
processes the sensor output levels to detect an. increase in the force as the slide-engages the stopper, to determine that-the>:slide -is properly,~seated in the stopper:1-:
However, if the -force sensor= =system,(or~"-force: seinsor"=,generally)-.is-broken, then the electronics~system' wilh*not~~~"
cdetect ;wlien=.tli&,;sli'de,;is seated;i.nctherstoppe'r and:the.slide=can'pbfentiallyicontinue =to' ;advance~until~=it..reaches en&of travel..and,the:stopper has=forced :virtually all fluid frorri.the ,reservoir: Thiscan have;.catastr.ophic-r.e'sults,if-the-user.is connected.to,.thetpump arid=.the ,:pump dispenses;all the fluid:(e.g: insulin) from~theireservoi'r into the pat"ient: The =overdose may be*enough to fatally harm or severely injure the user.-[00173] According=to a preferred embodiment of the present invention, a software algorithm described in FIGs. 24 and 25 is used to detect a malfunction in the force sensor using the current measurements to drive the motor and the motor position encoder as a check for the force sensor. The software algorithms described in FIGs. 24 and 25 are run by the infusion pump controller each time the plunger slide is moved forward to seat with the stopper in the reservoir. Any time the force sensor detects an increase in force greater than a set value (i.e. detects the seating of the plunger slide in the stopper), the software algorithms of FIGs. 24 and 25 are stopped during the running of the software logic. In other words, the logic of FIGs. 24 and 25 only applies before the force sensor detects a force greater than a set threshold (i.e. never detects a seating with the stopper).
[00174) Starting at block 3000 of FIG. 24, the current used to drive the motor, the force exerted on the force sensor, and the motor position encoder counts to determine the movement of the plunger slide are measured during the seating process of the plunger slide (i.e. when the plunger slide is inserted into the stopper). At block 3010, the software calculates the average current delivered to the motor to return the value of Average Current. In preferred embodiments, a Hi-Lo Average Current (HLAC) is used. The HLAC is calculated by discarding the highest and lowest current values from the five latest values and then averaging the remaining three current values. An example of the HLAC calculation is shown in FIG. 25. However, in alternative embodiments, other methods of calculating the average cuireint can be used including using more or less than the five latest current values and/or discarding fewer or more current values.
[00175] As seen in FIG. 25, an example of the Hi-Lo Average Current calculation starts at block 3200, when it receives a command from block 3010 of FIG. 24 to calculate the HLAC. According to preferred embodiments, the current to the drive motor is :sampled until~the motor is turnedeoff=.:aA.t.y.pical sarnpling-:rate.is=once.ever:yr70, milliseconds. The total current that.was used to run the motor is stored as a current value -in a=circular buffer.-The-current can =be:samprled-less=or more.fr.equently.
The latest five ,currenttvalues (i.e. Current-[0]; Current,[lj ;.=Current [2], -Current [3], and =Current' [4]), in the; current~buffer=.arerusdd toJetermine<the!Average.Current:->At:block.
3210;'=the~initialr.
,:parameters.msed for the tcalculatioris are all set to~zero :except: for.
the.High; and L- ow-valuesl which are set-to,the present-.Ctirrent~value-;(i:e:.High== C.urrent-[present];
L-ow!T'Current =[present]; Courit== 0, Average Curr.ent.=-0; and Sum = 0).
[00176] At block 3220, the logic. makes sure that five current values are available for use in the calculation (i.e. Count > 4?). As stated earlier, the number of currents can be modified in alternative embodiments to be greater or Jess than five.
Initially, there are fewer than five current values available in the circular buffer (i.e. Count <
4), so the logic proceeds to block 3230 since the Count is not greater than four. At block 3230, all of the current values are added together to create a Sum of the current values, with the current at the current count is added to the Sum each time the logic reaches block 3230.
In the first run of the logic, the first current value (i.e. current [0]) is automatically added to the sum.
The logic proceeds to block 3240 where the software identifies the highest of the latest five current values. Similarly, the logic of block 3260 identifies the lowest of the latest five current values. In the first run of the logic, the parameters Count, High, and Low were set to zero at block 3210. Thus, at block 3240, Current [0] (i.e. Current [Count]) is not greater than Current [0] (i.e. Current [High]), so the logic proceeds to block 3260.' Similarly, at block 3260, Current [0] (i.e. Current [Count]) is not less than Current [0] (i.e.
Current [Low]), so the logic proceeds to block 3280. At block 3280, the Count is then increased by one.

[00177] With the Count set at 1 at block 3220, the logic again proceeds to block 3230. At block 3230, the value of the Current [1] is added to the Sum at block 3230 and the logic proceeds to block 3240. At block 3240, the logic determines if Current [Count]
is greater than the existing Current [High]. If Current [Count] is greater than the existing Current [High], then at block 3250, the parameter High is set equal to Count, marking that the Current [Count] is the highest current. The logic then increases the Count by 1 at block 3280 and proceeds back to block 3220. Thus, for example, if Current [1] is higher than Current [0], then the parameter High would be set to 1, marking Current [1]
has the highest current received. On the other hand, if Current [Count] is lower than Current ;w[High], then the.logia.proceedsAo:block 3260.. .At.!bl'oek 3260, the logic.deterrnine's i.f.
Current [Count] is less than=the existing Current [Low]: Thus if Current [Count] is less .than the existing- Current= [Low];,.then.at. block .3270, the-parameter Low is:set equal to the,-~=~Count;*marking=that the CurrentfCouri:t] -is the lowest,current. The logic thdri -increases-the, ...Count:b:y:~1 'at block:3280,and:proceeds~back. to;block. 3220:: ~,Thus, .for. exaniple;:'sf Curreiit :
i[,1]~is=low:er: than.Current~[0];;.then the:parameter~L-=ow:would.be=set to.1, mar.king:Current;+= ' [.1'.] , as:the i lawest. current r=.eceived. n Fiuture iterations of the-logic..of blocks =32..40; ?3250 3260 and,3270 will identify.the high-and low:currents out-of the five current's=usedto.
calculate the Average Current.
[00178] - Once five currents are measured and compared to determine the high and the low currents, the logic of 3220 will then calculate the Average Current at block 3290.
At block 3290, the Sum, which has added all of the five current values together, will subtract the Current [High] and Current [Low] and divide the remaining sum by 3. At block 3300, the Average Current Calculation will be returned to block 3010 of FIG. 24 and used'as the Average Current in the logic of FIG. 24.
[00179] Referring back to FIG. 24, the Average Current is compared with the Current Threshold at block 3020. A value of the Average Current greater than the Current Threshold triggers the broken force sensor software algorithm. The Current Threshold is a unique value initially can be assigned to each insulin pump based on pre-testing of the pump before the insulin pump is issued to a user. It is also possible that there is a threshold set for all devices that does not require any testing of the individual device to determine. The Current Threshold is used to indicate the current used when the plunger slide seats within the reservoir. Each insulin pump will have slightly different values because the raw material used within the insulin pump will have slightly different physical characteristics resulting in differing Current Threshold values. In preferred embodiments, the following test is performed to derive the Current Threshold to ensure the software algorithm will function properly. The test applies a constant 3 lb force to the pump slide as the pump performs a seating, where both force and current are measured. The current values will be processed using a Hi-Lo Average Current algorithm like the one discussed earlier and will have the first and last 20 measurements thrown out. In altemative embodiments, a larger or smaller number of first and last measurements may be thrown out. These samples are thrown out to account for the system not coming to steady state for the first samples and slowing down for the last samples, making the current and force valiues notconstant..I.>T.he.cur=r.ent=values will.be:=sampled at the.same.rate:as it;isin the.
application code (e.g.- every. 70-90 milliseconds): =These values will then be averaged and .stored.for~.application- code::4he:force measurerizents will also be measured and averaged, ,but-without==removing data or usiing the Hi-Lo-averaging. ~ The AverageTForce'-AA4ll' be cotnpared:to 3.1b&"and ifit-.is~not;within_2:f4..and 3.61lbs.arrerror-4wil1!be:flagged}and-the.
pump.will,state that,the;force-calibration,was:not:-accurate:.
Alternatively;:=the:Average>
.Force can:;be= compared-,to aaazger or:smaller.~for.ce-:than .3:=lbs, and tlie *foleidnces:can: be r=ariged from greater, or4ess ~than,0:61bs froin the =force -to which the Average'force is compared. If this occurs, the Current Threshold value=is considered ~ invalid and is not stored and the pump is rejected. If there is no error with the force value, both the Current Threshold and the Average Force is stored in the pump. In still further embodiments, the values of the Current Threshold and the Average Force can also be displayed after the test is complete using the user's actuation keys. Moreover in still further embodiments, the user using the same test programrned within the insulin pump can periodically recalibrate the Current Threshold.
[001801 Returning to block 3020 of FIG. 24, if the Average Current is not greater than the Current Threshold, the logic identifies that the slide has not been seated in the reservoir yet and proceeds to block 3030. At block 3030, the Encoder Count (EC) is reset.
The Encoder Count is the count recorded by the motor position encoder to measure the movement of the slide. In preferred embodiments the encoder can record the rotations of the motor and the lead screw. For example, in preferred embodiments, there are counts per revolution of a DC motor and approximately 221 revolutions of the motor per lead screw revolution. In the algorithm of FIG. 24, the Encoder Count is based on the number of revolutions of the DC motor times the number of revolutions of the lead screw.

However, in other embodiments, the encoder can count only the revolutions of the motor, and the number of counts per revolution can vary based on the infusion pump mechanism or method of counting. In further embodiments, the use of an Encoder Count may be omitted from the software calculations.
1001811 Once the Encoder Count is reset, the logic proceeds to block 3040. At block 3040, the parameters, Encoder Count Difference and Time Difference, are set to zero. The Encoder Count Difference and Time Difference are set to zero to indicate that the plunger slide has not yet engaged the reservoir during seating, and the logic is set to repeat back to block 3010. Specifically,.when the logic proceeds to block 3070, the . Encoder Count.Differ.ence:is.compared,to.:see..if it. is greater:than tlie,Encod'er...Count Threshold. In the preferred embodiment tlie-Encoder Count Threshold is set at 60,000:
- 60,O0Q_is the approacimate value of the count -if = 10. units of RU-100 insulin is ;expelled -from theRreservoir once the~plunger=slide is=seated- in the reservoir:
In=alternative embodiments, the Encoder Count-.Thresliold levehcawbe-set=at,differenf levels;=especially with,the:.use. of ;different:types of insulin;.-m'edications;afl.uids;.ordrug.: However;-=inithis.case;_where:,the 'Eneoder Count:Differerice:is:set= to. zero, the -1ogic proceeds to-block:3080 :since 'the Encoder Count Di-fference is= less -than the Encoder Count Thre'shold: At block 3080, the Tiine Difference is compared to the-Time Threshold. In the preferred embodiments, the 'Time Threshold is set at 3 seconds. The Time Threshold is a backup to the Encoder Count Threshold to estimate the amount of advancement of the plunger slide based on the time the motor was actuated. In this case, the Time Difference is set to zero, and thus, the logic proceeds to block 3100 to indicate that no errors with the force sensor were detected.
From block 3100, the logic loops back to block 3010 to determine the latest Average Current.
[00182] Once the Average Current exceeds the Current Threshold at block 3020, the logic recognizes that the seating of the plunger slide in the reservoir has occurred. The logic proceeds to block 3050 to determine if the Average Current was above the Current Threshold last check. The logic of block 3050 uses the current to determine whether the seating of the plunger slide has just occurred or whether the plunger slide has already been seated. If the plunger slide has just been seated (i.e. this was the first time the Average Current was above the Current Threshold at block 3050), the logic proceeds to block 3040 where the parameters EC difference and Time Difference are set to zero. The logic then loops back to block 3010 as discussed above without indicating any errors with the force sensor. On the other hand, if the logic of block 3050 determines that the seating has already occurred previously, the logic proceeds to block 3060.
[001831 At block 3060, the parameters Encoder Count Difference and Time Difference are calculated. The Encoder Count Difference determines the number of additional encoder counts since the pump first detected seating of the plunge'r slide (i.e. the number of encoder counts since the Average Current has risen above the Current Threshold and stays above the Current Threshold). In addition, the Time Difference determines the amount of time that has passed since the pump first detected seating of the plunger slide (i.e. the time since the Average Current has risen above the Current T.hreshold,and;sta.y.s,.above the.:Current;Threshold): :The.calculated parameters.are.then:
compared to the Encoder Count Thre'shold in block 3070 -and the Time Difference Threshold in =block?3080. If either the-Encoder Count Threshold in block 3070 ,or= the Time Difference'Threshold =in-block 3080 is'exceeded,-wfailure=with- the'force sensor is' :detected==aricireported -'at block~3090:'Oftcour'se;,.as rimentioned above, if the,,foree sens'or, 7detects. an-increase in.rforce.-any time::during-the:algorithm- of FIG:.24 that signals the"
proper -seating of the:plunger, slide in the::r.eserivoir,-rio error=,will:be-'detected for=tlie farce sensor.
[00184] Therefore, the software algorithm of FIG. 24-is designed to determine an error with the force sensor when it does not report an increase in-force (i.e.
a force greater than the Low Force Value preset in each infusion pump to indicate seating of the plunger slide) even though the current use would indicate that a higher force should be detected.
Therefore the following two scenarios will occur with the existing algorithm.
The first is the case of a good sensor when during seating the force rises above 1.41bs on the force sensor while the Average Current remained below the Current Threshold before the seating occurred, or the current is above the Average Current but not for the required number of encoder counts before the force of 1.41bs is reached. In this first case, the pump seats the plunger slide in the reservoir and flags no errors. In the second case, during seating of the plunger slide, the Average Current reaches the Current Threshold and remains above the Current Threshold while the force is never greater than Low Force Value before the specified number of Encoder Counts is reached. In this case, the force sensor is detected as having failed once the pump reaches the specified number of Encoder Counts.

[001851 In alternative embodiments, the algorithm of FIG. 24 can be modified to detect when the sensor performance is starting to fail (i.e. a marginal sensor) such that the force reading increases above the Low Force Value, but does not increase above a Force Threshold (i.e. a value preset with the infusion pump to indicate a seating of the plunger slide in the reservoir) to clearly indicate that the seating has occurred.
Another alternative embodiment may modify the algorithm to account for cases where during seating the Average Current reaches its threshold but then drops back down below the threshold.
Each-time the Average Current drops below the threshold the Encoder Count threshold is restarted. However if this happens three or more times, on the third occurrence, the Enco.der Count.threshold.should;not-.be.re=set and.the pump should.continue=..to.seat.onl.y for the specified Encoder Count: threshold. These software algorithms may also take into account the=users ability to start.and- stop seating of the plunger slide at -will so-.thatteven::ifx -they stop andthen restartthe-seating process as,long as there-is no rewind;=the~pump~will-:recogriizedf-the.threshold has- beeri:reached.three times::;
;j0.0186] - In further~emb.odiments;'the, infusion pump'~also.performs a data storage functionYto record-data-surr.ounding:the;var.ious step=by-sfep;functions -of the:infusion.
pump. - Thus, upon each instance of seating, the data storage function records the values of =
force and current detected and stores that information into the -long-term trace buffer. In addition, if the Current Average ever reaches the Current Threshold, each subsequent measurement of force and current should also be stored in the long-term trace buffer until the pump seats or flags an error. Moreover, every time the current threshold is passed and the alarm is flagged, end of vial reached, force threshold passed, or the pump seats the plunger slide in the reservoir, these data points are recorded and a trace can be produced from the collected data points to analyze the data.
[00187) In further embodiments, multiple variables are used to detect an occlusion or obstruction. By using two or more variables, the system avoids any problems that may occur from using one variable alone. For example, if force alone is used to detect occlusions, a broken force sensor could cause false occlusions to be detected or actual occlusions to be missed. This could result in missed doses or excessively large amounts of medication to be delivered to a patient. The same potential problems can occur by using any one parameter as the basis of occlusion detection of the system.
[00188) Using two or more variables to determine an occlusion can shorten the time to recognize an occlusion andlor increase the accuracy of occlusion detection.
It is preferable to have a system that minimizes the number of false alarms but also decreases the time to indicate an occlusion. By decreasing the time to indicate an occlusion, it is possible to reduce the number of missed doses.
[00189] There are many variables that can be used in a multi-variable occlusion detection approach. Exarnples of siich variables are properties and/or parameters of the system, pump and/or motor, such as force, drive current, drive voltage, drive time of the motor, coast time of the motor, energy of the delivery pulse, and variables from the closed loop delivery algorithm, such as drive count, coast count, and delta encoder count. All of these variables are possible to be measured from the circuitry described above, however it is,!also.possible to: add:cir.cuitry,to measure,any-.of=these or:additional var-iables.if.;desired.
[00190] Force is generally measured from a force sensor, which is described in embodiments above. . Also:described in embodiments above is the drive current?of~tlie motor;~which is-the amourit'of currentappliedkto>the motor'andcan- be measured=from'the force sensitive resistor:-: Drivevoltage is:the,measiure of,voltage-applied toahemotor=sand can.also"be:measured.from.the.force:sensitive resi"stor;:which for example r=rieasures the &oltage across the, motor: windings~ c_Drive tirn.e'of.tlie motonis time; for exarnple in seconds or milliseconds, for which- the motor is powered. on (i.e., power~is=
supplied.to~the motor).' Coast time of the motor is the time, for. example in seconds or milliseconds, that the motor continues to coast or move after the motor was powered off until the end of the delivery pulse. The energy of the delivery pulse is a product of drive voltage and drive current, which may be calculated by a computing device.
[00191] Drive count and coast count are each encoder counts, which are discussed above. Drive count increases as the time that the motor is powered on increases, and coast count increases as the time that the motor is coasting after the motor is powered off increases. Drive count and coast count together are equal to the delta encoder count, or change in the encoder count from a delivery pulse.
[00192] Two or more of the variables described above can be combined in many different ways. For example, they may be multiplied together or added together. If more than two variables are used, some of the variables may be added in conjunction with multiplication of other variables. For example, one or more variables may be multiplied by a weighting coefficient before summing them. The rate of change of one or more variables may be increased by putting the magnitude of the variable to a power. For example, if F = measured force, it would be possible to increase the magnitude of measured force by Fx, where X = a desired power. Putting magnitudes of variables to powers may be used in conjunction with multiplying and/or adding variables together.
[00193] When combining the variables, it may also be useful to filter the data by using averaged values or by using averaged values taken after excluding high and low readings_ For example, if one data point is far outside the range of average data poirits taken nearby, it may be useful to discard that data point. Additional examples of filtering data that may be used are clipping data at a maximum or minimum value, limiting rate of change between values, and calculating trend and, if the trend is consistent, using fewer values.
.[00.194] . Normalization factors,can..also.:be.used'to. set.the .magnitude:
of different variables to similar=levels, -so that they can. be used in conjunction with each. other. For example, in one embodiment, the non-occluded runningforce is about 0:5:pounds, the occluded force is- about 2.0 pounds; the-non=occluded drive count is approximately 47; =and-=the-occluded drive=count~is=~approximately::100: =~These values can-be deterrnined:,for.=an, .individual purnp~basedon:pre=testing oftheipump.before issuance to a=user;.'or.tiaverage values:for certain- pump:.conf gurations-can.be:determined: = Further, it-is pos'si.ble<to vary the dependency of the occlusion detection omeach variable. For example,,it=may be desirable to have occlusion-detection depend equally on force and on current.
However, it may be desirable to have occlusion detection depend more on force in those instances where force is a better indicator of occlusion.
[00195] In one embodiment of a multi-variable occlusion detection approach, the variables drive count and force are both used to detect occlusions. While the pressure increases from an occlusion, the force required to move the slide forward increases. The increased pressure results in an increased force reading by the force sensor.
The increased force also results in an increased drive count necessary to reach the target encoder count for each delivery pulse. Multiplying drive count and force or adding these variables increases the magnitude of occlusion indication.
[00196] FIG_ 26 shows a graph illustrating the difference in magnitude between a single variable versus multi-variable occlusion detection approach. An occlusion 2601 begins between 40 and 60 delivery pulses. The graph shows data for two different approaches based on a single variable. The first series of data 2602 is based on the single variable-force, which is measured by the force sensor. For this single variable approach based on force, the occlusion was identified using a maximum threshold method at two variable magnitudes 2603. The second series of data 2604 is also based on a single variable-the drive count divided by a normalization factor of fifty. The third series of data 2605 is based on both of these variables-force and normalized drive count, which are multiplied together and then an offset is added to the product of the two variables. The equation used to create this particular series 6f data points, if F = measured force and DC
= drive count, was Multi-Variable Value = (F*(DC/50)) + 0.25. In this equation, the normalization factor was 50 and the offset was 0.25. The normalization factor or offset may be any preferred values identified as useful for. detecting -occlusions with good accuracy..
[00197] .The.graph.shows.that=before the=occlusion 2604;Ahe magnitude.=of the.
multi-variable value series 2605 is. similar to that of the single-variable.force reading 2602..
This is a result.of the normalization and 6ffset 6f.the equation. As the pump-continues to .
deliver insul.in=after the= occlusion-begins-.2601, the multi-variable=value' series 2605 reaches.magnitudes: of -almos't4wiceithat-.of the single:,variable f6rce:reading=2602:(*~Thtis:
an occlusion could.be,identified= much%sooner.in the:multi-variable-approach:n.With::tli~e multi.-var.iable.appr.oach;rthe=-threshold.for.decla'r.ing.an occlusion: could also'beraised without increasing the- amount of time=elapsed =before an occlusion-is detected, which could provide higher confidence that -an occlusion had -in fact occurred.
[00198] The multi-variable approach can be incorporated into algorithms used for single variable occlusion detection. Also, new algorithms can be created specifically for use with the multi-variable occlusion detection. Some algorithms that can be used, by way =
of example, are slope threshold and maximum threshold methods. Alternatively, variance in variables may be monitored by looking for values that are outside the general range of values for the system. If a value is more than a certain variance from the usual range of values, it may indicate an occlusion or other problem has occurred in the system.
[00199] FIG. 27 illustrates a flow chart of the logic of embodiments using the multi-variable approach. The logic starts at 2701. The system measures a first pump value at 2702 and a second pump value at 2703. These blocks may occur in series or in parallel. If they occur in series, the values may be measured at the same time or at different times, but it is preferred that they are measured during the same delivery pulse. The system then detects occlusions based on the measured pump values 2704. Occlusions may be detected as described above and by using the dynamic system described below. If there are no occlusions, the system continues with infusion 2706 as normal. If there is an occlusion detected, the system indicates an occlusion 2705. The system may set off an alarm to indicate the occlusion to the user.
[00200] Slope of one or multiple variables can be used to accelerate the detection of an occlusion as well. This is the rate of change of either one or multiple variables. During normal delivery the slope should be constant without a regular rate of change.
After anocclusion has occurred, for example the force or drive count, would increase as the pressure increases. There can be lots of small changes to these variables during normal delivery, but after an occlusion the rate of change would remain fairly steady and positive.
In a preferred embodiment the rate of change of the force would be positive for 10 .
deliveries..consecutively=then=. an.o.cclusion .would, be.identified:.:It can also= be:set with, a:
thresliold'to verify the system is running high. The rate of charige would need -to be positive -for=.IA consecutive..deliveries-'and =the force must be =greater.-:than 1' lbs. ' A- g'raph =of for=ce==measurements 4002--taken'during delivery is-=shown-in-FIG:=.30. The line formed-from-points':400.3- :shows the;slop.e:of'tlie:force:,=In the:exarnple-'shown in Figurd:30;aan' bcclusionoceurs at:4005:: After40::consecutivepositive slope_values, the'systern is=
prograxnsned,to detect the occlusioi-i 4007-.and..an..alariu:is=triggered.
:[00201] Another approach,>to determining an occlusion.is looking for a point of inflection or the rate of change of the. slope. This can be the change from constant force or other variable to a new rate of change. For example, FIG. 31 shows force measurements 4021 taken over time. The constant force shown by line 4023 changes to a new rate of change shown by line 4025. An alarm 4027 is triggered by this change.
[00202] In further embodiments of the invention, occlusion detection, either through use of one variable or multiple variables, is performed dynamically. There are many variables in the systems described above that cause variance in the variables mentioned for a delivery pulse. Some of these are a result of misalignment between the reservoir and the drive train, misalignment between the plunger or stopper and the drive train, compliance of the o-rings, and noise associated with the sensor. Due to these variables, the occlusion detection thresholds are set to compensate for these to assure a false detection of occlusions does not occur. As a result, these systems generally allow more delivery pulses before an occlusion is detected. For example, a maximum threshold detection method using force readings may allow sixty additional delivery pulses to be attempted after an occlusion occurs before the system alarm is activated. If a dynamic occlusion detection method is used, the number of excess delivery pulses can be reduced to a very small number, as low as three additional pulses.
[00203] In the occlusion detection methods described earlier in this description, only one measurement is generally taken per delivery pulse. This measurement may occur before, duiing; or after delivery. A dynamic method for occlusion detecti6n takes multiple measurements collected during each delivery pulse. The measurements may be taken periodically at a predetermined frequency, as often or as infrequently as desired, or measurements may be taken at particular times with respect to the delivery pulse. For example, measurements could be taken every few seconds or even once every second or partial: second:.::It-.is.also possible:-to_take.continuous rneasurements.throughout,..the.:
delivery pulse.
-[00204] Using_measurementaof force.as-an.example; generally the force3increases a ,lar-ge -amount right after~,a=deliwery pulse: After the-delivery-pulse; the force tlecreases' uritil-a,steady-state;force_is.aclii-eved.s>If there:-is ancocclusion; -the steady.<stateAforce will be higher than, if. there is no: occlusion;,or= when=there is an occlusion, the.:
stead.y, statei-Torce wild :be ,a l'arger percentage: af -the peak force tlian :when tthere .is no occlusion,- or if there is an occlusion the force at-'sometime after the peak-force -is a-larger percentage compared to the peak force than ifthere is no<occlusion. An illustration of this is shown in FIG.=28.
The graph in FIG. 28 shows force as a function of time during a delivery pulse. The bold line 2801 shows force in a non-occluded system. The dashed line 2802 shows force in an occluded system. Because the system is occluded, force decreases at a less rapid rate.
Using the multiple measurements taken during delivery, it is possible to determine a peak value 2804 of the measurement. As will be further discussed below, the graph also shows an occluded system post peak value 2806 and a non-occluded system post peak value 2805. A pre-peak value 2803 is also shown.
[00205] It is possible to detect occlusions dynamically using the above principles in a number of ways using many types of variables or parameters. Although the following -analysis describes using force measurement, it should be understood that the dynamic detection of occlusions may be similarly detected using any of the variables described above, including multiple-variables.
[00206] A simple algorithm can use two measurements or data points. For example, force may be measured at the peak value 2804 and at some time after the peak value 2805 or 2806. In this algorithm, the difference between the peak 2804 and post-peak values 2805 or 2806 is calculated and then compared to a difference threshold. The difference threshold may be predetermined for all pumps, determined for an individual pump based on pre-testing of the pump before issuance to a user, determined for a pump each time a new reservoir is loaded into the pump and the pump is primed (for example, the system may calculate the average difference of the first three delivery pulses after priming the pump, and use a percentage of that average difference as the difference threshold), or continually determined (for example, the system may take the average difference of a certain number of consecutive delivery pulses calculated from several pulses ago, for example, the average difference of three consecutive delivery pulses may be calculated.for six-.pulses~prior..to. the: current.idelivery:.pulse,.and -use.,that<average: i difference as the difference threshold). If the difference meets or exceeds that threshold, =
an.alarm is activated: -Thus; W.,ariability in -the non4occluded force wilE
not trigger.an acclusion. alarm: -For~example=some=variables-that may cause the unoccluded'-force to-vary irielude: rnisaligrunentEbetweenahe=.pluriger.-and'the: resexvoir, incorisisteneies ~iwthe4, reservoir.inter-ior profi.le;.var,yi.ng-friction-between,the+stopper and -th:e .reservoir;:faster or:
slower-delivery.rates; )laiger,,or.'~ismaller'delivery;q.uantities; etc...
[00207J Alternatively; ifthe difference meets or exceeds a certain percentage of the threshold, for example, 90% of the threshold value, an alarm could be activated. It is also possible to keep a record of all differences or a certain number of past differences. The system may wait until a certain number of consecutive pulses, for example three, create differences that are equal or higher to the threshold value (or a percentage of the threshold value) and then activate an alarm. Additionally, to account for variables in the system, the average difference over a certain number of consecutive pulses, for example three, may be taken and compared to the difference threshold. If the average difference is equal to or higher than the difference threshold (or a percentage of the threshold), then an alarm is activated.
[00208] Further, to account for changes in the peak over each pulse, it is possible to calculate the total force as the difference between the peak value 2804 and a predetermined steady state value, and then to calculate the difference between the peak 2804 and post-peak 2805 values as a percentage value of the total force. If this percentage is below a predetermined threshold, then an alarm is activated. However, the drawback of this method is that it assumes the force returns to the similar or identical steady state value after each pulse.

[00209] Accordingly, to account for the fact that the force never returns to zero and may not return to the identical or similar steady state value, also shown in FIG. 28 is a third value 2803, which is taken before the peak value. The third value 2803 may be used in addition to the peak 2804 and post-peak 2805 values. This pre-peak value 2803 can be used to normalize the peak value 2804. The difference between the peak value 2804 and pre-peak value 2803 can be calculated as a total force value. Then, the difference between the peak value 2804 and post-peak value 2805 or 2806 would be measured as a percentage of the total force value just determined. If this percentage is below a predetermined threshold, then an alarm is activated.
.[.00210] Also, itr.is .possible-to.calculate the rate of.decay.,.of.the .variable (e-.g.,. force)*' when decay begins- after the peak value 2804. Because the rate=.of decay is the same immediately after the peak..2904 and near..the.:erid of decay, it is-preferable-to take measurementsi'starting,at=some predeterrriined,time period after~the peak 2804:and=ending -some.predetermined.time=pe'riod-before:the-:eind~ofthe:decay: Theslope3may then be :cal.c.ulated:'for~aaine: passing through,the =seriesiof measurements and.:compared'.toa=a slope:
threshold=: -:Similar~to the.diffeirenee:threshold-described above, the siope:threshold may be predetermined:for all -puinps; d.etermined ;for, an -individual pump.based on pre-testing =of the pump before issuance to a user, determined for a pump each time- a new reservoir is loaded into the pump and the pump is primed, or continually determined. If the slope of the line is equal to or greater than the slope threshold, then an alarm is activated.
Alternatively, if the slope meets or exceeds a certain percentage of the slope threshold, for example 90% of the threshold, then an alarm can be activated. It is also possible to calculate average slope values and to compare the calculated average slope to the slope threshold (or a certain percentage of the threshold), as discussed above with respect to the other dynamic occlusion detection systems. If the average slope value is greater than or equal to the slope threshold, or some other predetermined percentage (e.g., 90%), of the slope threshold, the force can be considered to not be decaying normally.
Therefore, an occlusion can be declared.
[00211] In further embodiments, multiple measurements of a variable (e.g., force) may be taken during each delivery pulse as described above, and a curve may be fit into the measurements or data points. Then an integral can be taken of the area beneath the curve. If the integral is above a certain threshold, an occlusion can be declared. In still further alternative embodiments, other algorithms may be employed to determine whether an occlusion has occurred by using the above variables, such as using differential values rather than actual measured values, calculating the derivative of measured values, using a subset of points across the range of points to calculate the slope, using curve fitting equations, employing smoothing, clipping or other filtering techniques, or the like.
[00212] Because there is a higher likelihood of failu're, such as missed detection of an occlusion, at high flow rates (e.g., a high number of delivery pulses in a short period of time, such as for a bolus delivery), it may be preferable to use other occlusion detection methods at these high flow rates. This failure may occur, because at high flow rates there may not be enough time between pulses for the system to return to a steady state. The :dynamic,occlusion method.,ma.y.tbe:used=in.conjunction~with the other.
occlusion:detection methods described above (e.g., maximum measurement threshold, slope threshold, or the like) to allow for improved-occlusioii;detection at all tirness.
J002131- FIG: 29 illustrates a=flow~chart of the logic'ofembodiments using;a ,dynamic-occlusion detecti6n=.appr6ach:--The logic==starts~at290-1:;%The:system:measures a:.
series of pump .values -at;~L902; preferabl:y.~periodically:over.one~delivery pulse:a The,:
sy'stem determines tlie-peak value of..theseries.of pump.values:at.2903..
The,systennsalso-.
determines.-a second vali.ue laterthan=the, peak value at 2904: ~The second value- may'be.at- a predetermined time after the peak or a predetermined number of ineasurements4aken after the peak value. Alternatively, it may also be a predetermined time or number of measurements taken before the next delivery pulse or taken after the delivery pulse starts.
The system then detects occlusions 2905. Occlusions may be detected by using the algorithms described above. If there are no occlusions, the system continues with infusion 2907 as normal. If there is an occlusion detected, the system indicates an occlusion 2906.
The system may set off an alarm to indicate the occlusion to the user.
[00214] While the description above refers to particular embodiments of the present inventions, it will be understood that many modifications may be made without departing from the spirit thereof. The accompanying claims are intended to cover such modifications as would fall within the true scope and spirit of the present inventions.
When used in the claims, the phrase "selected from the group consisting ofl' followed by a list, such as "X, Y and Z," is not intended to mean that all members of the list must be present or that at least one of each of the members of the list must be present. It is intended to cover cases where one, some or all of the members of the list are present. For example, where the list is "X, Y, and Z," the claim would cover an embodiment containing just X, just Y, just Z, X and Y, X and Z, Y and Z, and X, Y, and Z. The presently disclosed embodiments are to be considered in all respects as illustrative and not .restrictive, the scope of the inventions being indicated by the appended claims rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
[00215] Multiple methods have been described to enable the pump to monitor one or more parameters inherent to the system design that can be used individually or in combination to detect reduction in insulin delivery. One of these methods or multiple of these methods could be implemented into the pump software for redundancy providing multiple methods to.monitonthe -system for.. potential occlusions. -Additionall.y,: one,or.
multiple of these methods:could be enabled by the user via software selection through the programmable.pump user inter.face ;[002161- 3ach- defined==o'cclusion measurement-method mayhave'different' ~effect'iveness iri..monitoring:~tlie;systems.far.Ãtrue obelusions resulting:in=.reduced:f:insulin-delivery. without-generating;false,alarms. In, this case;=more aggressive =rneasurement techniques:that-may prodi.ice=moreIalse=alar.ms, due.
to:higher'sensitivity.to_variables: could=
be.disabled by the user through the software programmable interface. This-would.allow-,the user to adjust the system sensitivity to occlusions by=the method selected: As an example, two methods may be implemented into the pump software as user selectable.
The first could be the slope method with defined parameters such that it would detect occlusions with less missed insulin delivery than the second method, which would be a simple force threshold with a force value resulting in more missed delivery than the first method prior to indication of an occlusion alarm. The methods could be listed by different descriptions such as "high sensitivity" and "low sensitivity." The user could select "high sensitivity" and enable both methods or "low sensitivity" and enable only one method, for example the simple threshold method. Further, the system could implement two or more differing methods providing the user more than two selections. Further, the same measurement method could be implemented with two or more parameters that affect sensitivity to detect occlusion, whereby the selected parameter with the higher sensitivity is more likely to generate a false alarm but with the advantage of being able to detect true occlusion more rapidly. For example, the system could have a simple force threshold method for detecting occlusions, such as described in U.S. Patent No.
6,362,591, which is herein incorporated by reference. The pump could have pre-programmed threshold trigger force values of, for example, 1.0 lbf, 2.0 lbf, and 3.0 lbf, and the user could select any of these force values. The lower the selected force value, the more sensitive the pump would be to increasing pressures due to occlusions thereby generating an occlusion alarm in less time at a given delivery rate. This higher sensitivity setting could result in a higher rate of false alarms. Alternatively, if the user were to select 3.0 lbf, the pump would be les's likely to generate a false alarm at the cost of an increased time to generate an occlusion alarm for a true occlusion at a given delivery rate. Alternatively, instead of the user being given a selection of 1.0 lbf, 2.01bf, and 3.01bf, the user could be given the choice of "Low,"
"Med," and "High" sensitivities. Although three different selectable force values were liscussed in this..example; the system=could~be programmed:with. any.ni.imber o~ selectable.
force values, for example, two, four or five: =Additionally, this example described the simple force threshold+rriethod. Any of the'discussed occlusion sensing methods described-, in this application. could=be-implemented=in ~a similar manner.
[0021.7] While. the:descr=iption.above; refers::.to~ particular embodiinents' of~-the present ~
invention,.it .will beunderstood that, man~6 modifications may be made.without departing, Froiir:th& spirit-thefeo~'The=accompanying,claims ace:iritended to covei such-modificatioris.:
as would fall within the true =scope -and spirit- of the :present invention;
[00218] - The presently disclosed embodiments are therefore to be coinsidered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims (50)

WHAT IS CLAIMED IS:

1. A method of detecting an occlusion in an infusion pump having a drive mechanism that includes a motor and one or more drive train components coupled to a reservoir for infusing fluid from the reservoir into a body of a user, the method comprising:
measuring a first parameter associated with the motor or one of the drive train components;

measuring a different second parameter associated with the motor or one of the drive train components;

combining the first parameter with the second parameter to create a first combined value; and determining whether an occlusion has occurred by using the first combined value.

2. The method of claim 1, wherein the first and the second parameters associated with the motor or one of the drive train components are each independently selected from the group consisting of force, drive current, drive voltage, motor drive time, motor coast time, delivery pulse energy, motor drive count, motor coast count, and delta encoder count.

3. The method of claim 1, wherein the first parameter is force and the second parameter is motor drive count.

4. The method of claim 1, wherein the combining the first parameter with the second parameter includes performing a mathematical function selected from the group consisting of adding the first parameter to the second parameter, multiplying the first parameter and the second parameter, exponentially increasing at least one of the first parameter and the second parameter, and combinations thereof.

5. The method of claim 1, further comprising:
multiplying one or more of the first parameter and the second parameter by a normalization factor; and adding an offset value.

6. The method of claim 1, wherein the determining whether an occlusion has occurred includes declaring an.occlusion has occurred if the first combined value exceeds a threshold value.

7. The method of claim 1, further comprising:
retrieving a previous first parameter and a previous second parameter associated with the motor or one of the drive train, components; and combining the previous first parameter with the previous second parameter to create a second combined value, wherein the determining whether an occlusion has occurred by using the first combined value includes:

calculating a slope of a line using the first combined value and the second combined value; and declaring an occlusion has occurred if the slope exceeds a threshold slope value.

8. The method of claim 1, further comprising:
retrieving one or more previous first parameters and one or more previous second parameters;

combining the one or more previous first parameters with the one or more previous second parameters to create one or more previous combined values;
calculating an average previous combined value from the one or more previous combined value; and determining whether the first combined value is more than a predetermined amount different than the average previous combined value.

9. An infusion pump for infusing fluid from a reservoir into a body of a user, the.infusion pump comprising:
a housing;

a drive mechanism including a motor and one or more drive components contained within the housing and operatively coupled to the reservoir to deliver fluid from the reservoir through a fluid path into the body of the user;

one or more electronic components adapted to measure at least two different parameters associated with the motor or one of the drive train components; and a processor contained within the housing and adapted to combine the at least two parameters associated with the motor or one of the drive train components and to determine whether an occlusion has occurred in the fluid path of the infusion pump using the combined parameters.

10. The infusion pump of claim 9, wherein the at least two parameters are each independently selected from the group consisting of force, drive current, drive voltage, motor drive time, motor coast time, delivery pulse energy, motor drive count, motor coast count, and delta encoder count.

11. The infusion pump of claim 9, wherein the electronic components include a sensor adapted to measure force and an encoder adapted to measure motor drive count.

12. The infusion pump of claim 9, wherein the processor combines the at least two parameters by performing a mathematical function selected from the group consisting of adding the at least two parameters, multiplying the at least two parameters, exponentially increasing at least one of the at least two parameters, and combinations thereof.

11. The infusion pump of.claim 9, wherein the processor. is further adapted to determine whether an occlusion has occurred by using an occlusion detection method selected from the group consisting of a maximum measurement threshold method, a slope threshold method, a variance monitoring method, and combinations thereof.

14. The infusion pump of claim 9, wherein the processor is further adapted to multiply one or more of the first parameter and the second parameter by a normalization value and then add an offset value.

15. An occlusion detection system for detecting an occlusion in an infusion pump having a drive mechanism that includes a motor and one or more drive train components, the occlusion detection system comprising:
means for measuring a first parameter associated with the motor or one of the drive train components;

means for measuring a second parameter associated with the motor or one of the drive train components;

means for combining the first parameter with the second parameter to create a first combined value; and means for determining whether an occlusion has occurred in the infusion pump by using the first combined value.

16. The occlusion detection system of claim 15, wherein the first and the second parameters associated with the motor or one of the drive train components are each independently selected from the group consisting of force, drive current drive voltage, motor drive time, motor coast time, delivery pulse energy, motor drive count, motor coast count, and delta encoder count.

17. A method of detecting an occlusion -in an infusion pump having a drive mechanism that includes a motor and one or more drive train components for infusing fluid into a body of a user, the method comprising:
measuring a parameter associated with the motor or one of the drive train components periodically during delivery of a current pulse of infusion fluid to obtain a series of measurements;

determining a peak value of the series of measurements;

selecting a second value within the series of measurements later than the peak value; and determining whether an occlusion has occurred based upon the peak value, the second value, and a threshold value.

18. The method of claim 17, wherein the measuring a parameter associated with the motor or one of the drive train components is continuous during the delivery of the pulse of infusion fluid.

19. The method of claim 17, wherein the parameter associated with the motor or one of the drive train components is force.

20. The method of claim 17, wherein the determining whether an occlusion has occurred includes:
calculating a difference between the peak value and the second value; and declaring an occlusion has occurred if the difference exceeds the threshold value.

21. The method of claim 17, further comprising:
calculating a difference-between the peak value and the second value;
incrementing a counter when the difference exceeds the threshold value;
and restarting the counter when the difference is below the threshold value, wherein the determining whether an occlusion has occurred includes declaring an occlusion has occurred when the counter exceeds an occlusion detection count.

22. The method of claim 17, further comprising:
calculating a current difference between the peak value and the second value;

retrieving a previous difference between a previous peak value and a previous second value later than the previous peak value calculated based on measurements of the parameter during delivery of a previous pulse of infusion fluid; and calculating an average difference using the previous difference and the current difference;

wherein the determining whether an occlusion has occurred includes declaring an occlusion has occurred if the average difference exceeds the threshold value.

23. The method of claim 22, wherein the calculating an average difference further includes using a second previous difference calculated based on measurements of the parameter during delivery of a second previous pulse of infusion fluid.

24. The method of claim 23, wherein the average difference is calculated based on measurements of the parameter during delivery of three consecutive pulses of infusion fluid.

25. The method of claim 17, further comprising measuring the parameter associated with the motor or one of the drive train components before the delivery of the pulse of infusion fluid to obtain a third value.

26. The method of claim 25, further comprising:
calculating a first difference between the peak value and the second value;
and calculating a second difference between the third value and the peak value, wherein the determining whether an occlusion has occurred includes comparing the second difference between the third value and the peak value to the first difference between the peak value and the second value.

27. The method of claim 26, wherein the comparing the second difference between the third value and the peak value to the first difference between the peak value and the second value includes:
calculating the first difference between the peak value and the second value as a percentage of the second difference between the third value and the peak value;
and declaring an occlusion has occurred if the percentage is below the threshold value.

28. The method of claim 17, wherein the determining whether an occlusion has occurred includes:
selecting a third value from the series of measurements later than the peak value;

calculating a slope of a line using the second and third values; and declaring an occlusion has occurred if the slope exceeds the threshold value.

29. The method of claim 17, wherein the determining whether an occlusion has occurred is based upon a predetermined percentage of the threshold value.

30. The method of claim 17, wherein the threshold value is predetermined for the infusion pump.

31. The method of claim 17, wherein the threshold value is dynamically updated based on measurements of the parameter associated with the motor or one of the drive train components during delivery of at least one previous pulse of infusion fluid before the delivery of the current pulse of infusion fluid.

32. The method of claim 31, further comprising:
retrieving a first previous difference between a first previous peak value and a first previous second value later than the first previous peak value calculated based on measurements of the parameter during delivery of a first previous pulse of infusion fluid;

retrieving a second previous difference between a second previous peak value and a second previous second value later than the second previous peak value calculated based on measurements of the parameter during delivery of a second previous pulse of infusion fluid; and calculating an average difference using the first previous difference and the second previous difference, wherein the threshold value is the average difference.

33. The method of claim 32, wherein the calculating an average difference further includes using a third previous difference calculated based on measurements of the parameter during delivery of a third previous pulse of infusion fluid.

34. The method of claim 33, wherein the average difference is calculated based on measurements of the parameter during delivery of three consecutive pulses of infusion fluid.

35. The method of claim 34, wherein the average difference is calculated based on measurements of the parameter during delivery of three consecutive pulses of infusion fluid that are at least three pulses prior to the delivery of the current pulse of infusion fluid.

36. The method of claim 1, wherein the determining whether an occlusion has occurred by using the first combined value comprises:
performing a first calculation of whether an occlusion has occurred using the first combined value;
performing a second calculation, different from the first calculation, of whether an occlusion has occurred using a second combined value, wherein the second combined value may be the same as or different than the first combined value;
determining that the occlusion has occurred when either or both of the first calculation and second calculation indicate that the occlusion has occurred.

37. An infusion pump for infusing fluid from a reservoir into a body of a user, the infusion pump comprising:
a housing;

a motor contained within the housing;

one or more drive train components coupled to the motor within the housing and adapted to move in response to the motor to deliver fluid from the reservoir through a-fluid path into the body of the user;

a sensor adapted to periodically measure a parameter associated with the motor or one of the drive train components during delivery of a current pulse of infusion fluid to obtain a.series of measurements; and a processor contained within the housing and adapted to determine a peak value of the series of measurements, select a second value later than the peak value from the series of measurements, and determine whether an occlusion has occurred in the fluid path of the infusion pump using the peak value, the second value, and a threshold value.

38. The infusion pump of claim 37, wherein the parameter associated with the motor or one of the drive train components is force.

39. The infusion pump of claim 37, wherein the sensor is adapted to measure the parameter continuously during the delivery of the pulse of infusion fluid.

40. The infusion pump of claim 37, wherein the processor is adapted to determine whether an occlusion has occurred by:
calculating a difference between the peak value and the second value; and declaring an occlusion has occurred if the difference exceeds the threshold value.

41. The infusion pump of claim 37, wherein the sensor is further adapted to measure the parameter associated with the motor or one of the drive train components before the delivery of the current pulse of infusion fluid to obtain a third value.

42. The infusion pump of claim 41, wherein the processor is adapted to determine whether an occlusion has occurred by:
calculating.a first difference between the peak value and the second value;
calculating a second difference between.the peak value and the third value;
calculating the first difference -between the peak value and the'second value as a percentage of the second difference between the peak value and the third value; and declaring an occlusion has occurred if the percentage is below the threshold value.

43. The infusion pump of claim 37, wherein the processor is further adapted to dynamically update the threshold value based on measurements of the parameter associated with the motor or one of the drive train components during delivery of at least one previous pulse of infusion fluid before the delivery of the current pulse of infusion fluid.

44. An occlusion detection system for detecting an occlusion in an infusion pump having a drive mechanism that includes a motor and one or more drive train components, the occlusion detection system comprising:

means for measuring a parameter associated with the motor or one of the drive train components periodically during delivery of a current pulse of infusion fluid to obtain a series of measurements;

means for determining a peak value of the series of measurements;

means for selecting a second value within the series of measurements after the peak value; and means for determining whether an occlusion has occurred using the peak value, the second value,. and a threshold value.

45. The occlusion detection system of 44, wherein the parameter associated with the motor or one of the drive train components is force.

46. The occlusion detection system of 44, wherein the means for measuring a parameter associated with the motor or one of the drive train components measures the parameter continuously during the delivery of the current pulse of infusion fluid.

47. The occlusion detection system of 44, wherein the means for determining whether an occlusion has occurred is adapted to:
calculate a difference between the peak value and the second value; and declare an occlusion if the difference exceeds the threshold value.

48. The occlusion detection system of 44, wherein the means for measuring a parameter associated with the motor or one of the drive train components is further adapted to measure the parameter before the delivery of the current pulse of infusion fluid to obtain a third value.

49. The occlusion detection system of claim 48, wherein the means for determining whether an occlusion has occurred is adapted to:

calculate a first difference between the peak value and the second value;
and calculating a second difference between the third value and the peak value;
calculate the first difference between the peak value and the second value as a percentage of the second difference between the third value and the peak value; and declare an occlusion has occurred if the percentage is below the threshold value.

50. The occlusion detection system of 49, further comprising means for dynamically updating the threshold value based on measurements of the parameter associated with the motor or one of.the drive train components during delivery of at least one previous pulse of infusion fluid before the delivery of the current.pulse of infusion fluid.