WO1999053201A1

WO1999053201A1 - Flow rate stabilizers for peristaltic pumps

Info

Publication number: WO1999053201A1
Application number: PCT/IL1999/000204
Authority: WO
Inventors: Dan Bron
Original assignee: Dan Bron
Priority date: 1998-04-16
Filing date: 1999-04-15
Publication date: 1999-10-21
Also published as: AU3343299A

Abstract

The invention provides a flow rate stabilizer for a peristaltic pump having at least one pressure-applying member (8), including pressure-applying means for applying pressure to a tubing portion (6) in addition to the pumping pressure applied thereto by the pump, the additional pressure to the tubing portion (6) being substantially perpendicular to the direction of the action of the pumping pressure, causing the tubing portion (6) to retain its original cross section or to return thereto, the pressure applied by the member (8) and the pressure applied by the pressure-applying means being applied sequentially so that at least some of the tubing portion upon which the pressure-applying member (8) operates, is alternately subjected to both pressures during the pumping period, whereby the flow rate in the tubing is stabilized, ensuring the filling of the entire original volume of the tubing (6) with fluid and preventing a decrease in the volume of the tubing portion (6) during the operation of the pump.

Description

1

FLOW RATE STABILIZERS FOR PERISTALTIC PUMPS Field of the Invention

The present invention relates to flow rate stabilizers for peristaltic pumps. Background of the Invention

Peristaltic pumps are widely used in different fields, when a liquid is to be flowed under relatively low pressure within flexible tubing without coming into contact with the pump. An unique use thereof, of wide scope, is developing in the medical field, wherein blood and infusion liquids must be flowed under sterile conditions and without being exposed to the environment.

A peristaltic pump operates by means of pressure and "squeezing" the flexible tubing along a limited section thereof in a cyclic manner, by means of a system of diverse pressure means. At the time when pressure is applied to a specific section of the tubing, it is emptied of its contents, which then flow downstream toward the consumer. After the pressure is released, that section of the tubing refills with the fluid which is supplied from upstream. Such refilling depends upon the elasticity of the tubing and its ability to return to its original shape, as well as to the dimensions of its cross-section, based on its own elastic force. Such tubing must be able to endure a great many hours and cycles of pressure until the medical use of the tubing is completed after 24-48 hours.

It turns out that the tubings used in infusion sets, made of flexible PVC, do not possess the required elasticity, nor do they have the strength to preserve their original round flow cross-section. The tubings gradually become flattened, reducing their volume and thus causing a decrease of the flow during the entire infusion time.

In order to preserve the required flow rate, it is customary to change a limited portion of the PVC tubing with an SI tube, upon which the pumping action is performed. SI tubing has good elastic qualities, but it is expensive to use and it has weak mechanical properties which introduce an element of danger to its use. In addition, it is inconvenient to reserve a particular infusion set for a particular use, while the majority of infusion sets in use do not include SI tubing. 2

Summary of the Invention

The present invention is intended to provide a solution to the above-mentioned problems through the pump itself, which will eliminate the collapse of the standard PVC tubing and ensure its return to its precise cross-section during the entire life expectancy of the tubing. Thus, the problem of decrease in the flow rate will be completely solved without adding expense to the daily use of the pump and without lessening its safety.

The present invention achieves the above objective by providing a flow rate stabilizer for a peristaltic pump having at least one pressure-applying member, comprising pressure-applying means for applying pressure to a tubing portion in addition to the pumping pressure applied thereto by the pump, said additional pressure to the tubing portion being substantially perpendicular to the direction of the action of the pumping pressure, causing said tubing portion to retain its original cross-section or to return thereto, the pressure applied by said member and the pressure applied by said pressure-applying means being applied sequentially so that at least some of the tubing portion upon which the pressure-applying member operates, is alternately subjected to both pressures during the pumping period; whereby the flow rate in said tubing is stabilized, ensuring the filling of the entire original volume of said tubing with fluid and preventing a decrease in the volume of said tubing portion during the operation of said pump. Brief Description of the Drawings

The invention will now be described in connection with certain preferred embodiments with reference to the following illustrative figures so that it may be more fully understood.

With specific reference now to the figures in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is 3

necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.

In the drawings: Fig. 1 is a vertical cross-sectional view of a peristaltic line pump without a flow rate stabilizer; Fig. 2 is a horizontal cross-sectional view through the pressure member of a peristaltic pump having a flow rate stabilizer in the body of the pump; Fig. 3 is a horizontal cross-sectional view through the pressure member of a peristaltic pump having a flow rate stabilizer in the front cover of the pump; Fig. 4 is a top view of a circular peristaltic pump having flow rate stabilizers; Fig. 5 is a cross-sectional view of a further embodiment of a peristaltic line pump according to the present invention; Fig. 6 is a cross-sectional view of a still further embodiment of a peristaltic line pump according to the present invention, and Fig. 7 is a schematic illustration of a single pressure-applying member in accordance with the present invention. Detailed Description of Preferred Embodiments

Referring to Fig. 1, there is shown a peristaltic line pump 2 having a front cover 4 and, in the space between them, an infusion tube 6. Tube 6, resting on cover 4, is squeezed from its right by a row of pressure-applying members 8 which move horizontally towards the left. The squeezing action is cyclic, a cycle beginning at the uppermost member and progressing downwards until reaching the lowest member.

The vertical infusion tube arrives at the pump full of infusion fluid, which is gravitationally supplied from a raised container. Cross-sections A-D of tubing 6, as taken at different locations during the pressure cycle, exemplify the manner of operation and the type of problem to be solved by the present invention. Assuming that the drawing illustrates the first pressure cycle applied to the tubing as it reaches the center members, cross-section A shows the original round cross-section of the tubing as it was manufactured, before any pressure and deformation is applied. 4

Cross-section B shows the tubing during the squeezing stage, in which the liquid therein is pushed downward toward the consumer. Cross-section C shows the maximum deformation of the tubing at the moment of maximal pressure and the subsequent closing of the entire flow path. Cross-section D shows the tubing after it has undergone pressure and relaxation. Because of the plastic qualities of the tubing, a slight residual deformity and the beginning of an elliptical cross-section are observed, which become worse over time; simultaneously, a decrease of the pump's general infusion rate will develop.

Fig. 2 illustrates an example of a solution to the above-described problem provided by the present invention by introducing pressure means in addition to the members 8, which additional pressure means are built in the form of rigid tongs 10 operating in coordination and tied-in with members 8 of the peristaltic line pump 2. In the stage illustrated, member 8 is in a non-operative position and does not touch the tubing 6. The jaws 12 of the tongs 10 grasp both sides of the section of the tubing 6 opposite pressure member 8, and apply pressure perpendicular to the direction of pressure applied by member 8. The amount of pressure applied is determined and limited by the movement of arms 14 on shoulders 16,, such that the jaws 12 of the tongs, having a curved surface 18 of a radius matching that of the outer surface of an undeformed tubing, apply pressure for the purpose of precisely reestablishing the original round cross-section of the tubing before any pressure was applied. Thus, the jaws 12 ensure and define the filling and infusion capacity of the section of PVC tubing and do not allow changes therein during the entire time of its use.

For proper operation and timing, tongs 10 are coupled in pairs to the members 8, ensuring synchronization and complete coordination between the two operations, which should not be performed simultaneously. At the moment that member 8 will move towards the left for the purpose of applying pressure to tubing 6, the arms 14 will slide down from shoulders 16, jaws 12 will move about hinges 18 and thus the tubing 6 will be freed. During continued movement leftwards, the corners 20 of members 8 will open the jaws 12 by pushing against the slanting surfaces 22 of the jaws 12, thus enabling the tubing to be squeezed freely. When 5 member 8 moves towards the right, arms 14 will slide up the slanting shoulders 16 and the jaws will exert pressure on opposite sides of the tubing, forcing it to return to its original configuration. Tubing 6 thus will be maintained during an entire pressure cycle.

In spite of the simplicity and ease of operation of the tongs 10 by means of the members 8, it is also possible to time and operate the tongs directly by means of the control and operating system (not shown) of the members.

Fig. 3 illustrates a horizontal cross-sectional view through the pressure member 8 of a peristaltic pump 2 and a flow rate stabilizer attached thereto. Here, the set of tongs 24 is affixed onto the front cover 4. In the depicted state, jaws 26 squeeze tubing 6 by force of spring 28 applied to arms 30, to a dimension determined by abutments 32. The principle of operation of this embodiment is similar to that of the embodiment of Fig. 2: the corners 22 of member 8, when moving leftwards, slide on the angled slanting planes 34 of jaws 26 and cause the opening of the jaws by compression of spring 28; afterwards, pressure is applied to the portion of tubing 6 abutting against tongs portion 36 which then assumes and rests in a straightened disposition. With the withdrawal of the member rightwards at the end of the application of pressure, spring 28 causes the return of jaws 26 of tongs 24 to their original position, applying pressure to both sides of the tubing and returning it to its original configuration.

In Fig. 4 there is seen an example of a circular peristaltic pump. Here, tubing 6 is placed within a circular channel 38 provided in the space between the static body of pump 40 and revolving rotor 42. At the edges of the rotor 42 are positioned several pressure means, represented here as two rollers 44. The sides of the rollers 44 project into the space within channel 38, and therefore rollers 44 must apply pressure to the tubing 6 at every point that they pass during rotation of the rotor 42. In order to reduce friction, rollers 44 are mounted on axes 46 perpendicularly disposed to the rotor 42.

In pumps without a flow rate stabilizer, rotor 42 will rotate in relation to body 40 and rollers 44 will apply full pressure to tubing 6, which abuts against the side 6

wall of channel 38, until the flow channel in the tubing is blocked. Thus, fluid is propelled within the portion of the tubing between the two rollers 44, from input section 46 to output section 48, and a continuous flow is formed in accordance with the rate of rotation of rotor 44. Here, as in the line pump, pressure is applied to tubing 6 in the radial direction as seen in the plane of the drawing, making it difficult for the tubing to return to its original configuration. This situation is corrected by adding a stabilizer in the form of small rollers 50, which apply pressure onto the tubing in a direction perpendicular to the pressure applied by the rollers 44. Small rollers 50 are coupled to the rotor by horizontal axes 52 and rotate therewith, following rollers 44. After a roller 44 passes a section of the tubing 6 and squeezes it horizontally, that section of the tubing immediately enters into the field of influence of the small rollers 50, which squeeze it one after the other in the perpendicular direction towards the floor of channel 38, which has a circular cross-section matching that of tubing 6. This pressure immediately restores the tubing to its original cross-section, and thus the decrease of the flow rate caused by accumulated deformation of the tubing is eliminated. Only a number of small rollers 50 are shown in Fig. 4, but in an actual pump according to the present invention, the rollers 50 should cover the entire open area between the rollers 44; the more small rollers 50 there are, the more the correction and restoration of the tubing will be improved.

In the center of the rotor is a lock 54, which is used for opening the rotor and raising it, for the purpose of entering and removing the tubing 6 into and from the pump.

Seen in Fig. 5 is an embodiment in which a stationary stabilizer forms part of member 8. When the pressure-applying member 8 is moved towards the tubing 6, the pressure-applying face 56 presses against the portion of tubing 6 abutting against the portion 58 of cover 4. The tips 60 of jaws 62 are free to pass through openings 64, allowing the periodic squeezing of tubing 6. While the structure of this embodiment is relatively simple, its disadvantage resides in the friction which is applied to tubing 6, eventually causing it to wear out. Also, each jaw 62 can support only a relatively short section of tubing, since the tubing must be supported by a surface 66 in order to facilitate its disengagement from the jaws without bending.

In Fig. 6 there is illustrated a still further embodiment of a stabilizer, similar to the embodiment of Fig. 3 except for the manner of abutting the tubing 6. According to this embodiment, tubing 6 is abutted by portion 68 of cover 4. In addition, the tong arms 70 are hinged on the same axis 72. The pressure applied by jaws 74 on tubing 6 is limited by the surfaces 76 of openings 64.

While in the embodiments described above the peristaltic pump uses several pressure members along the pumping section, in Fig. 7 there is illustrated an embodiment showing the utilization of a single pressure-applying member 78, flanked by two controllable valve gates, an input valve gate 80 and an output valve gate 82. Also seen in Fig. 7 is a portion of the jaw 84, constituting a part of the single stabilizer operable in accordance with any one of the above-described embodiments. As can be understood, the valve gates 80, 82 alternatingly press against the tubing 6. Initially, gate 82 is in its pressed or closed state; and gate 80 is open. Upon the entry of fluid into the tubing, gate 82 opens and gate 80 closes; simultaneously, member 78 presses against tubing 6, forcing the fluid accumulated therein to be propelled toward the consumer. Since single pressure-applying member 78 extends along and presses against a much longer portion of the tubing than that of the combined length of gates 80, 82, the error, i.e., lack of stabilization, introduced by the unstabilized gates, can be ignored, Of course, the gates can also be furnished with stabilizer jaws in accordance with the other above-described embodiments.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrated embodiments and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by 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

8CLAIMS

1. A flow rate stabilizer for a peristaltic pump having at least one pressure-applying member, comprising: pressure-applying means for applying pressure to a tubing portion in addition to the pumping pressure applied thereto by the pump, said additional pressure to the tubing portion being substantially perpendicular to the direction of the action of the pumping pressure, causing said tubing portion to retain its original cross-section or to return thereto, the pressure applied by said member and the pressure applied by said pressure-applying means being applied sequentially so that at least some of the tubing portion upon which the pressure-applying member operates, is alternately subjected to both pressures during the pumping period; whereby the flow rate in said tubing is stabilized, ensuring the filling of the entire original volume of said tubing with fluid and preventing a decrease in the volume of said tubing portion during the operation of said pump.

2. A flow rate stabilizer as claimed in claim 1, wherein said pressure-applying means comprises a plurality of rigid tongs, each having at least two jaws which hold and apply pressure to two sides of a tubing portion.

3. A flow rate stabilizer as claimed in claim 2, wherein said jaws are built into the body of a pump and are operated by means of hinged arms moving on sliding surfaces of the members of said pump, which time and operate the jaws in accordance with the operation of said members.

4. A flow rate stabilizer as claimed in claim 2, wherein said jaws are located within a cover of said pump and include a pressure-applying spring which permanently closes the jaws about said tubing portion, and wherein the movement of said members for applying pressure upon said tubing portion opens said jaws against the pressure of said spring.

5. A flow rate stabilizer as claimed in claim 2, wherein said jaws are rounded, having a radius of curvature substantially equal to that of said tubing portion prior to its being subjected to pressure. 9

6. A flow rate stabilizer as claimed in claim 1 for a circular pump, wherein said tubing portion is located in a circular channel and is subjected to radial pressure of rollers revolving with a rotor, said stabilizer comprising small rollers rotating on axes, extending around the edges of said rotor and rotating therewith; said small rotors pressing on the surface of the tubing portion against the bottom of said channel in a direction substantially perpendicular to the direction of the pressure applied by said rollers.

7. The flow rate stabilizer as claimed in claim 2, wherein said jaws are stationary and constitute extensions of said members.

8. The flow rate stabilizer as claimed in claim 1, wherein said pressure-applying means applies pressure on said tubing portion against an abutting element.

9. The flow rate stabilizer as claimed in claim 8, wherein said abutting element is constituted by a portion of the pump cover.

10. The flow rate stabilizer as claimed in claim 8, wherein said abutting element is constituted by a portion of said tongs.

11. The flow rate stabilizer as claimed in claim 1, wherein there is provided a single pressure-applying member fitted with a single pressure-applying means flanked by two valve gates, said valve gates alternatingly opening and closing the tubing portion passageway in accordance with the operation of said member.