CA1155525A - Impact wrench - Google Patents
Impact wrenchInfo
- Publication number
- CA1155525A CA1155525A CA000349144A CA349144A CA1155525A CA 1155525 A CA1155525 A CA 1155525A CA 000349144 A CA000349144 A CA 000349144A CA 349144 A CA349144 A CA 349144A CA 1155525 A CA1155525 A CA 1155525A
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- CA
- Canada
- Prior art keywords
- signal
- accordance
- tightening
- tightened
- curve
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/12—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means
- G01D5/244—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing characteristics of pulses or pulse trains; generating pulses or pulse trains
- G01D5/24404—Interpolation using high frequency signals
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
- B25B—TOOLS OR BENCH DEVICES NOT OTHERWISE PROVIDED FOR, FOR FASTENING, CONNECTING, DISENGAGING OR HOLDING
- B25B23/00—Details of, or accessories for, spanners, wrenches, screwdrivers
- B25B23/14—Arrangement of torque limiters or torque indicators in wrenches or screwdrivers
- B25B23/145—Arrangement of torque limiters or torque indicators in wrenches or screwdrivers specially adapted for fluid operated wrenches or screwdrivers
- B25B23/1453—Arrangement of torque limiters or torque indicators in wrenches or screwdrivers specially adapted for fluid operated wrenches or screwdrivers for impact wrenches or screwdrivers
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- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Details Of Spanners, Wrenches, And Screw Drivers And Accessories (AREA)
Abstract
IMPACT WRENCH
Ian E. Kibblewhite, John T. Boys & Angelo L. Tambini ABSTRACT OF THE DISCLOSURE
A self-contained impact wrench having an adaptive control system for determining the yield point or some similarly significant tightened condition of a fastener assembly by detect-ing a signal representative of the forward rotation angle of the fastener assembly is disclosed. One embodiment utilizes a com-puted signal of time over a fixed interval of forward rotation angle, as an estimate of the torque applied by the impact wrench, and the torque estimate vs. rotation angle curve is differentiated to obtain the gradient thereof. Successive gradient values are stored and compared, and when the present gradient value has attained a predetermined relationship relative to a stored value of a gradient in a tightening region of the curve, further tight-ening of the fastener assembly is discontinued. This ensures that the yield point or other similarly significant tightened condition of the assembly has been reached.
Ian E. Kibblewhite, John T. Boys & Angelo L. Tambini ABSTRACT OF THE DISCLOSURE
A self-contained impact wrench having an adaptive control system for determining the yield point or some similarly significant tightened condition of a fastener assembly by detect-ing a signal representative of the forward rotation angle of the fastener assembly is disclosed. One embodiment utilizes a com-puted signal of time over a fixed interval of forward rotation angle, as an estimate of the torque applied by the impact wrench, and the torque estimate vs. rotation angle curve is differentiated to obtain the gradient thereof. Successive gradient values are stored and compared, and when the present gradient value has attained a predetermined relationship relative to a stored value of a gradient in a tightening region of the curve, further tight-ening of the fastener assembly is discontinued. This ensures that the yield point or other similarly significant tightened condition of the assembly has been reached.
Description
~-- -This invention relates generally to the ield of tool driving or impacting, and more p~rticularly to a self-contained impact type wrench having a control system for accurately con-: trolling the tension in ~ ~stener assembly of a joint.
It is well known in the prior art that tightening a ¦¦f6stener to s yield point produces optimum joint efflciency.
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~ 1'155~25 A fastened joint having a greater preload value up to the ~ieldpoint of the material of the joint is more reliable and better fastener performance. High fastener preload further increases fatigue resistance due to the fastener feeling less added s~ress from external joint loading, and dynamically loaded joints have less tendency to slip and loosen.
The prior art reveals various types of impact wrench control systems for controlling the amount of preload in a fast-ener. ~ne commonly used type employs some form of torque control, in which the impact wrench tightenes a fastener to a maximum pre~
determined value of torque and thereupon shuts off. Examples of impact wrenches utilizing torque control can be found in United Stat~s Patents to Schoeps et al, No. 3,835,934; Hall No.
3,833,068; Schoeps, No. 3,703,933; Vaughn, No. 3,174,559;
Elliott et al, No. 3,018,866 and Maurer, No. 2,543,979. Another means of controlling impact wrenches found in the prior art is commonly known as a "turn-of-the-nut" system, in which a fastene is tightened to some preselected initial conditlon, such as a predetermined torque value or spindle speed, and thereupon ro-tated an additional predetenmined number of degrees before shut-ting off. Examples of various turn-of-the-nut impact wrench systems are found in United States P~tents to Allen, No.
3,623,557; Hoza et al, No. 3,318,390 and Spyradakis et al,No.
3,011,479. ~nother type of control comprises imparting a con-stant angular momentum of each impulse blow, such as found in the United stes Patent to Swtnson, No. 3,1Bl,672.
5~2 n 811 o the control systems de8crlbed in ehe cbove-noted patents, prior knowledg of the f~stener ~nd joint charac-teristics must be known or ~ss~med in order to determine either the exact predetermined final torque, the exact smount of addi-tional rot~tion, or the amount of constant angular momentum of each impact blow. It is well kno~n that tightenlng to a prede-tenmined preload condition, such as the yield point, is a func-tion of many variables~ among them being joint stiffness~ fasten-er stiffness, surface friction between mating threads and thread form of the mating threads. Therefore, if it is desired to tighten an sssembly to the yleld point with any of the systems described in the above-noted prior art patents, this point cannot ~lways be accurately determined because the conditions of each iastener assembly and joint can vary and may not be known in ad-vance. This consequence can lead to uneven tightening from joint to joint in the same structure, which, in tur~, can result in loosening of one or more fastener assemblies, especially in the presence of vibrations, and premature fatigue failure.
In the control system described in U.S. Patent No .
. 4,185!701 of Januarv 29, lq~n, I . the yield point of a fastener ¦¦ assembly is tained by a ti~htening epparatus which periodically~
applies a tightening moment to the fastener assembly, such as, ¦¦ or example n impsct wrench. Jhe yield point is ettained when ¦
sn lnstantaneous peak moment signal has not increased by more ¦¦ thsn a pred rmined smount over a K tored previous peak moment 11 ~ I
_ 3 _ .
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` 1~55~25 slgnal. While this control system works satisactorily in cer-taln applications~ the present invention is seen as being an improvement thereover.
SUMMARY OF THE INVE ION
Accordingly, it is a general purpose snd object of the present invention to provide apparatus for tightening a fastener assembly to the yield point or some similarly signifi-cant tightened condition in a joint. It is another object of the present invention ts provide a control system for tightening a fastener assembly to its yield point, which control system is particularly useful in a tightening system having a pulsed output for periodically applying a tightening moment. It is still anoth er object o~ thP present lnvention to provide an impact wrench having a self-contained, adaptive control system for accurately tightening a astener assembly to a predetermined preload condi-tion by the utilization of measured characteristics of the fast-ener assembly and joint being tightened. It is yet a further object of the pres~nt invention to provide an adaptive control system in an impact wrench for accurately tightening a fastener to a predetermined preload condition with minimum prior know-ledge of the fastener assembly and joint characteristics. It is yet another object of the present invention to provide an impact d~er~li~es wrench having an adaptive control system which ~ the yield point or similarly significant tightened condition by measuring a value representative of the orward rotation angle of the astener ~ssembly being tightened, and utilizes a comput-1 1S~525 ed function of this forward rotation angle to determine theyield point. It is still a further object of the present in-vention to provide an impact wrench having an adaptive control system which determines the yield point or similarly significant tightened condition of a member by utilizing a measurement of time over a fixed interval of forward rotation angIe as a para-meter representative of the torque applied to the member, and thereafter applies gradient comparison techniques to a curve of the parameter representative of torque vs. forward rotation angle to obtain the yield point. Finally, it is an object of `the present invention to provide an integral r self-contained impact wrench/control system ~hich is compact, reliable, relatively in expensive to manufacture and easily maintainable.
These and other objects are accomplished according to the present invention by apparatus for providing a parameter representative of torque in a tightening system having a pulsed output for periodically applying a tightening moment to a member, the parameter being derived from forward rotation angle measure-ment of the member being tightened.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a side elevational view of an impact wrench constructed according to the invention partially cut away and in cross-section, showing the entire wrench control system;
Fig. 2 is an elevational view of the rear portion of the wrench of Fig. 1 with the back cover removed;
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Fig. 3 is a top view of the wrench shown in Fig. l;
Figs. 4a-4d are views of the air/solenoid trip valve assembly shown in Figs . 1 and 2, in eleva tion and partially in cross section showing progressive operation of the assembly;
Fig. 5 is a schematic block diagram of the control ~ystem for the wrench shown in Fig. l;
Fig. 6a is a schematic illustration of the Fo~ward Ro~ation Sensing Circuit ~h~wn ln Fig. 5j Fig. 6b i~ an elevational view of the encoder and sensors shown in Figs. 1, 2 and 6a showing resolution of the orward rotation sensing system;
Fig. 6c is an illustration of the waveforms produced by the circui ~ of Fig . 6a;
Fig. 7 is a schematic block diagram of the Calculation o Time/Angle and Digital Filter blocks shown in Fig. 5;
Fig. 7~ is a schematic illustration of the Inhibit "N"
Pulses After Reset and Chord Length Setting blocks shown in Fig. 7; ~av~c~n~, Fig. 7b is an illustration of the produced by the blocks of Fig. 7;
Fig. 7c is a 8chematic illustration of the Timing Con-trol Logic block sh~wn in Fig. 7;
Fig. 8 is a graph of the parameters TIME/FORWARD
ROTATION ANGLE vs. ~.NGLE from the Calculation of Time/Angle block of Figs. 5 ~nd 7 before filtering; and Fig. 9 is ~ graph of TORQUE ESTIMATE vs. ANGLE from the Digital Filter block of Figs. 5 ~nd 7 after digital filtering in the ~ngle d~ aLn- G~_ 1 ~55r325 DESCRIPTION OF THE PREFERRED EMBODIMENT
~ efore proceeding with a descrlption of an apparatus ~nd control system in accordance with the present invention, a brief discussion ~bout the operation of impact wrenches will be presented. All impact wrenches operate by relea~ing a periodic build up of kinetic ener~y in the form of a series of torsional shock impulses transmitted to a fastener assembly, ~hich may typ-ically include a bolt and/or nut. As a result, considerable impact forces can be produced with little reactive torque.
Pneumatically driven impact wrenches are most common (as compared with electrically or hydraulically driven impact wrenches) and comprise a vane type air motor and a hammertanvil mechanism.
When the air motor gains sufficient speed, a high lnertia hammer on the motor shaft engages on an anvil on the wrench drive shaft.
The energy of the blow is (a) dissipated as a result of collision inelasticity and riction; (b~ stored as torsional strain energy in the impact mechanism, the wrench drive shaft and the coupling to the fastener; and (c) transferred to the fastener, and con-verted to the work of tightening. The hammer then disengsges from the anvil and the motor accelerates for a complete revolu-tion before delivering the next blow. While most impact wrenches deliver one blow per revolution, there are some which can deliver more than one blow per revolution of the motor. The above des-cription is for conventional pneumatically driven impact wrenches Unlike a continuous action power wrench system in which ~he torque ~pplied can be measured with a s~rain ~ ~reaction torque transducer, there is no convenient way to directly measure the torque ~pplied by an Lmpact wrench. Consequently, it is dificult to control tightening accurately with these wrenches. Because of the discontinuity of impact wrench dynamics which prevents continuous psrameter measurement, control of impact wrench tightening has relied largely on limiting the ener-gy transmitted to the fastener rather than the measurement of impact parameters for estimating applied torque. It has been found that a beneicial parameter for use as an estimate of tor-que in an impact wrench is based upon measurement of the forward rotation angle of the fastener ~ssembly~ The following three assumptions are made in deriving the torque estimate: (a) con-stant energy is transmitted by the impact mechanism (i.e. the air motor reaches full speed well before impact occurs~; (b) the torsional strain energy in the shafts and couplings i5 small;
and (c) the time between impacts is approximately constant.
Thexefore, the energy (E) transmitted to the wrench anvil on each impact is converted ~o the work done in rotating the bolt head through angle (~) against average torque (T). Then, E = T ~ .
Since E is assumed to be constant T
That is, the ~verage torque applied to the bolt during an impac~
is inversely proportional to the angle through which it is ro tated. Measurement of the bolt rotation angle per impact is possible ~ but difficult ln practice ~ because 1'~5'j~25 of the difficulty in making high resolution encoders necessary to detect the relatively small ~alues of Q ~ e. 2 - 3 at final tightening torques), and the difficulty in determining when an impact has occurred. In further explanation of the latter po~nt, it can be difficult to discriminate between actual rotations resulting from impacts and apparent rotations due to slight movements of the hand-held impact wrench ~uring tighten-ingO Since the time between impacts is assumed to be constant, the average applied torque will also be inversely proportional to the average rate of tightening. This can be expressed as Average Torque cy _ _ 1 Rotation~ le Time or, Average Torque c~ Time Rotation Angle By measuring time over a fixed interval of angle, the need for high resolution encoders and detenmining when an impact has occurred is eliminated.
Referring now to Figs. 1, 2, 3, 4a, 4b, 4c and 4d of the drawings, there is illustrated a preferred embodiment of an impact wrench in accordance with the present invention. While the invention will be described with reference to an impact wrench, it should be understood that the invention may be prac-ticed in any tightening system having a pulsed output for peri-odically applying a tightening moment to ~ member. Wrench 10 may be any conventional, pneumatically powered impact wrench de-1l55~5 signed to receive compressed air from an external source (notshown) in order to successively impact a hammer assembly 12 onto an anvil 14. The anvil is rotatably secured within the forward portion of a wrench housing 16 by a bearing 18. The forward end 20 of anvil 14 comprises, for example, a square drive for attach-ment to a drive socket (not shown) or some other suitably shaped wrenching member for driving a fastener assembly (not shown).
Hammer assembly 12, which is connected to and driven by a con-ventional air motor rotor 22, surrounds and contacts portions of anvil 14 imparting periodic impact blows thereto to rotate the anvil and drive the fastener assembly. Wrench 10 also in-cludes a conventional trigger mechanism 24 which, when depressed, allo~s air irom the external source (not shown) to enter the wrench at an inlet port 26 connected to the air motor, driving rotor 22 coupled ~o hammer assembly 12 which rotates anvil 14.
A bidirectional incremental encoder 28 used in a system for measuring angular rotation of the fastener assembly is mounted on a shaft 30 ~ithin the wrench, suitably fixed to anvil 14 for rotation therewith. The encoder disc is of a low inertia type which eliminates problems of fixing the encoder to the shaft in order to withstand the high shock loadings at im-pact. The low inertia disc also avoids errors in measuring angu-lar rotation due to twisting of the shaft on which it is mounted during the large accelerations encountered during operation.
While the encoder is illustrated as being located toward the rear portion of the wrench body, lt should be understood that it :~ ~55~25 may be located at any convenient place within the wrench. Since anvil 14 drives the wrenching member which tightens the fastener assembly, encoder 28 essentially rotates with the fastener assem-bly as it is tightened in a joint. Between impacts of hammer 12 against anvil 14, the anvil and encoder coupled thereto recoil, but the fastener assembly does not due to tolerances in the con-nection between the driving member and the fastener assembly Thus the rotation measuring system should be capable of detecting and disregarding any recoil of encoder 28. Encoder 28 includes a series of vanes or teeth 32 on its outer periphery, with the present embodiment including eighteen ~18) teeth having their respective center lines spaced 20 apart. However, it should be noted that the encoder could contain more or less teeth depending on the degree of accuracy ~esired, the only requirement being that the teeth axe spaced equally apart from each other. A pair of light emitting diodes (LED's) 34 (only one is visible in Fig.
1) are mounted on a board 36 suitably fixed to the wrench housing directly across from a pair of photo transistors 38 mounted on a board 40 which is coupled to board 26 by means-of a pair of electrically conducting spacers 42. The LED's 34 and corres-ponding photo transistors or sensors 38 are mounted at an angular spacing of 45 in the present embodiment providing angle resolu-tion of 5, but they could be spaced any odd multiple of the encoder resolution degrees (i.e. 5, 15, 25, 35, 45, 55 etc.). Seventy-two (72) counts :1~5~52~
per revolution of the encoder are produced wi~h this configura-tion. While optical angle sensing devices have been disclosed in the present embodiment, it is here noted that any other suita-ble proximity type sensing devices may be used instead to detect the passage of teeth 32 during operation of the wrench. These include, among other types, magnetic sensors which have an induc-tion coil whose output varies due to the presence or absence of metal.
The impact wrench control system electronics is con-tained completely within the wrench housing in the back portion thereof. The control system is powered by a battery 44 which is accessible by removing a cap 46. Preferably, but not neces-sarily, a 280 mA-hr nickel-cadmlum (8) cell battery, having a nominal voltage of 10 volts, is used. The battery is supported at each end by a pair of stiff springs 48, so that a good elec-trical contact is maintained during the severe vibration from the impacting action of the wrench. A pair of connectors 50 transmit power from batte~ 44 to boards 36 and 40, containing the angle measurement devices, as well as to thé remainder of the electronic control system. The electronics are contained on (3) boards 52 rigidly bolted together and mounted at the back of the wrench, which boards are accessible by removing cover 54 and are insulated from shock and vibration by any suit-able shock absorbing material 56. The remaining portion of the operating control system consists of an air/solenoid trip valve ~ssembly 58, which will be descr~bed in detail hereinbelow.
The solenoid receives po~er directly from b~ttery 44.
Mounted on one ide of trigger 24 is a permanent magnet 60, and on the ~nside of the handle 62 housing is a reed switch 64. Upon depressing trigger 24, in ~ddition t~ allowing air to pass to the air motor, reed switch 64 is closed by the magnet in order to direct power to the control system, as will also be described in detail hereinbelow.
Six ~6) indicator LED's comprising LED display 66 are mounted on top of the wrench housing and also receive their power from battery 44. Thes~ LED's are color coded and indicate to the operator the wrench/tightening condition and certain fault conditions. A RUN LED ~orange) indicates that the system is operating, and comes on almost immediately after trigger 24 is depressed. ~n OK LED (green) indicates that the tightening of the joint is complete and within preselected specifications;
NGLE LOW LED (red) indicates tha~ a yield point has been detected, but a minimum preselected angle value after reaching a snug point has not been attained; an ANGLE HIGH LED ~red) in-dicates that a maximum preselected angle value after reaching a snug point has been exceeded without detecting a yield point tthese (3) lights are part of a qu~lity eontrol system described more fully in U. S. Patent No. 3,973,434, but do not control the operation of the wrench). A TIGHTENING RATE SLOW LED (red) indi-cates that the wrench does not have sufficient power to yield the bolt (i.e. the bolt has either stopped rotating or else is ro~ating too 610wly for the control system to operate). FinallyJ
a BATTERY LOW LED ~red) indicates that the b~ttery needs re-charging if the battery voltage level is low when the trigger is îl55525 depressed, Referring to Figs. 4a, 4b, 4c and 4d, a unique air/solenoid trip valve ~ssembly 58 is shown. This valve assem-bly must be capable of shutting off the flow of air from the air source to the wrench air motor very rapidly ~hen the control system produces a signal indicating that tightening is complete, and must also require a minimum amount of power to operate.
Valve assembly 58 includes an electrically actuated solenoid valve 300, ~L~air valve 302 and a trip lever 304 biased by a return spring 306 into engagement with a plunger 308 in the air valve to keep the valve in an open position. A spring 310 with-in the air v~lve housing 312 bisses the plunger to a normally open position. Trip lever 304 is actuated by a plunger 314 in the solenoid valve.
As previously m~ tioned, before operation of the wrench as illustrated in Fig. ~,~ trip lever 304 engages a CUtQUt 316 on air valve plunger 308 keeping the plunger in an open position aided by the force of spring 310. Plunger 308 also includes an enlarged head portion 317 at its other end. When trigger mechan ism 24 is depressed, air flows from inlet port 26 through an outlet port 318 of ~ir valve 302 to the air motor operating the impact wrench. As can best be seen in Fig. 4c, the pressure exerted by the air flowing through air valve 302 causes an up-ward force against the surface of enlarged head 317 moving plunger 308 upwardly against spring 310 and trip lever 304. This ~ir pressure is designed to produce a greater force on the plunger in sn upward direction ~han the dow~ward force exerted 1~SS~5 by spring 310. When sn electric~l signal is produced by the control system indicating that tightening is complete, such as at the yield point of the fastener assembly being tightened, this signal actuates solenoid valve 300~ causing plunger 314 to rotate trip lever 304 out of engagement with air valve plunger 308. This occurs very rapidly, and once the solenoid valve is pulsed to actuate it, the electrical signal can be removed eliminating any b~ r~,/
further power drain from the ~ Since trigger mechanism 24 is still being depressed by the wrench operator, causing air to flow into air valve 302 9 the pressure exerted by the air overcomes the force of spring 313 and forces plunger 308 upwardly against ~lve body 312 cutting off flow through the air valve to the wrench air motor, AS shown in Fig. 4d. It should be noted that there is a differential pressure across the air valve from the inlet to the outlet port due to air flow, allowing rapid closure of the valve. At this point, the operator recognizes that tightening has been completed, and he releases trigger mechanism 24 cutting off furthex ~ir flow. Plunger 308 thereupon is forced downwardly to an open position by spring 310, and retur spring 306 rotates trip lever 304 back into engagement with cut-out 316 keeping it open and ready for the next tightening se-quence, as illustrated in Fig. 4b.
Referring now to Fig. 5, a control system is illustrat-ed for controlling the tightening of a fastener assembly by wrenc~
10. It should be clear from all of the foregoing that the entire control system is within the housing of wrench 10, which control 1 1 S55~ ~
system is illustrated as separate blocks outside of the wrench in Fig. 5 for convenience. Signals from photo transistors 38 are supplied to a forward rotation sensing circuit 66 in quadra-ture, as will be explained more Eully below with regard to Fig~.
6a, 6b and 6c. Circuit 66 produces angle pulses representing increments of forward angular displacement of the wrench output shaft 20 or the rotation angle of the fastener assembly being tightened. These incremental forward angle pulses are introduced into a circuit 68 for calculation of time per forward rotation angle and a circuit 70 for detectin~ the yield point of the as-sembly being tightened. Circuit 68 is illustrated in Fig. 7 and will be described below. The output signals from circuit 68 can be used to generate a curve as illustrated in Fig. 8, which can be seen to contain a high noise level due to the discontinu~
ities in the impact tightening process, and is generally unsatis-factory for use without further processing. Consequently, thls curve is then filtered in the angle domain in a digital filter 72 to produce the smoother curve illustrated in Fig. 9. The in-formation from this curve is used in yield detection circuit 70, which will be discussed hereinbelow. Once the yield point is detected by circuit 70, a signal is fed back to solenoid trip valve assembly 58 to cut off the flow of air to the air motor and stop tightening, as previously described with reference to Figs. 4a-4d.
Forward rotation sensing circuit 66 will now be des-cribed in detail with regard to Fig. 6~. As previously stated, the purpose of this circuit is to produce pulses representing incremPnts of forward rotation angle of the fastener during tightening. The reference for the angle measurements is the hand held impact wrench. Angular movement of the wrench by the operator during tightening is generally significantly less than the encoder resolution or the required accuracy for control system operation. The impact wrench drive shaft rotation angle is representative of the fastener rotation angle only for the duration of the impact. At all other ~Lmes the angle measure-ment of the drive shaft is subject to errors due to recoil and backlash in the couplings between the drive shaft and the fasten-er assembly after an impact. Hence the maximwm forward angular displacement of the drive s~aft represents the forward rotation angle of the ~astener assembly which is required.
Referring to Figs. 6a, 6b and 6c, enc~der 28 and sen-sors 38A and 38B are illustrated with the actual spacing between the sensors shown. This arrangement, having a resolution of /4 or 5, produces signals A and B shown in Fig. 6c for either forward or reverse rotation of the encoder. The sîgnals from sensors 38A and 38B are fed through grounded resistors 74 and 76, respectively, to a pair of Schmitt triggers 78 and 80, respectively. The Schmitt triggers are used to produce signals C and D w~th clearly defined transitions from the sensor signals A snd B . Two D-type latches 82 and 84 receive and 1 ~55~25 temporarily store the previous signal levels from Schmitt triggers 78 and 80, respectively. The output of latches 82 and 84 are introduced into one input of excluslve OR gates 86 and 88, respectively. The second input to yate 86 is from Schmitt trigger 80, and the second input to gate 88 is from Schmitt trigger 78. The outputs from gates 86 and 88 are introduced into inverters 90 and 92, respectively, and into one input to NOR gates 96 and 94, respectively. The other inputs to gates 94 and 96 are from inverters 90 and 92, respectively. The sig-nals stored in latches 82 and 84 are thus compared with the in-coming signals C and D to latches 84 and 82, respectively, causing the signals E or F from NOR gates 94 and 96, respec-tively, to change from a logical 0 to 1 for an increment in the forward or reverse direction, respectively. These signal level changes are then used to clock latches 82 and 84 so that they then store the present signal levels from Schmitt triggers 78 and 80, respectively, and are ready for the next signal change from the encoder. When latches 82 and 84 are clocked, the signal level at E or F changes back to a logical 0. The pulse lengt~
of signals E and F is determined by the dela~ in clocking the latches, and is controlled by introducing the output signals from NOR gates 94 and 96 into the inputs of an OR gate 98, whose output is fed to latches 82 and 84 through a grounded resistor/capacitor circuit 100 which provides the appropriate time constant.
An UP/DOWN counter 102, such as a National Semiconduc-tor part No. 74C193, is used to store the maximum forward angular displacement signals. Forward direction signals E are intro-duced into the Count Up input o counter 102 through a NAND gate 104 which receives another input from an inverter 106. Reverse direction signals F ~re introduced into the Count Down input of counter 102 through an inverter 108. During ~n impact, the forward angle pulses E are fed to the output G of circuit 66 through a NAND gate llO, which receives another input from a ~4) input AND gate 112. The t4) inputs to AND gate 112 are the binary output bits from countPr 102. The counter output bits are all logical l's 9 and the forward ~ngle pulses to the counter are inhibited when pulses representing reverse rotation of the drive shaft ~re produced between impacts due to recoil and backlash in the wrench. These reverse pulses F are subtracted from the preset count stored in counter 102~ and thus one or more of the output bit signals to AND gate 112 then become logical O's, caus-ing the output from gate 112 which is fed to NAND gate 110, to be-come 0. NAND gate 110 cannot output any further forward rotation pulses E until the reverse pulses F are ~ade up in counter 102. At the next impact, forward rotation pulses E are once again introduced into the Count Up input of counter :L02, and when the reverse pulses are made Up3 the counter output bits once again become logical lls allowing AND gate 112 to output a high signal to NAND gate 110 ~and inverter 106). ~ate llO then allows forward rotation signals E to pass to the output G of circuit 66, and inverter 106 inhibits ~he introduction of 6~gnals E
through gate 104 to counter 102. In this way the counter stores 1 155~2i the angular position of encoder 28 before any rotation in the reverse direction and inhibits all forward angle pulses until the encoder has returned to that position.
Referring now to Fig. 7, the circuit for calculating the time per forward rotation angle will be explained. At each sngle increment signal from circuit 66, the time is calculated for the bolt to rotate through the previous "n" angle increments ~where "n" = preset chord length, such as, for example (4) incre-ments of 5 per increment or 20~. Time is measured by a counter 114 driven by a simple astable multivibrator circuit 116.
Counter 114 may be typically made up of thxee 4~bit counters, such as,for example, Nation31 Semiconductor par~ No. 7493, for 12-bit resolution; and multivibrator 116 is a square-wave signal generator3 such as, for example, National Semiconductor part No.
~B~ This time is stored at each angle increment in a read-write random access memory (RAM) unit 117, which typically may consist of three 16 x 4-bit RAMS for 12-bit resolution such as, for ex-ample, National Semiconductor part No. 7489. The time to rotate the bolt through a value of "n" increments (equal to the pre-selected chord length~ is calculated by reading from RAM 117 the value of time which was stored "n" angle increments previous-ly, and subtracting this value of time from the value just stored in a subtraction circuit 118. The value of the output signal from subtr~ctlon circuit 118 is the time/angle signal illustrated in Fig. 8, which could be plotted, if desired, for th~ joint ~S~25 being tlghtened. Memory addressing of RAM 117 is accomplished by the outputs from two tri-state address counters 120 and 1220 These address counters are typically 4-bit counters with three state outputs, such as, for example, National Semiconductor part No. 8554. The output of read address counter 122 is equal to the output of write ~ddress counter less the chord length preset with switches in binary as a particular number of angle incre-ments. During normal processing, both of these address counters are clocked9 incrementing their addresses by "1" every angle increment. Counters 120 and 122 are initially preset by resettin, them to "O" and then inhibiting the first "N" clock pulses to read address counter 122 by means o cixcuits 124, which will now be described in greater detail with regard to Fig. 7a.
Circuit 124 includes a presettable counter ~ , such as, for example, National Semiconductor par~ No. 74197, and a series of logic gates to inhibit the number of read address counter 122 clock pulses preset by the chord length switches in circuit 126 after reset. The number in read address counter 122 therefore becomes the number in write address counter 120 minus the preset chord length. Counter 12~ receives a reset signal from the reset line and a series of preset chord length inputs from binary switches 127 in circuit 126. The output from counter 128 is fed into a 4-input NOR gate 130 whose output is fed into an inverter 132 and one input of an OR gate 134. The other input to OR gate 134 is from the output of an inverter 136 which 1~55S25 xeceives clock pulses from a timing control logic circuit 138.
The outputs of inverters 132 and 136 are :Eed into a NOR gate 140 whose output clocks read address counter 122, ~s previously described, The chord length is set in"l's" complement by switche , 127 (inverted logic signals), and ~ulses are enabled to pre-settable counter 128 and inhibited to read address counter 122 until presettable counter 128 output reaches "0000".
The processing sequence for calculation of time/angle, which is started with an angle pulse ~rom eircuit 66, is as foll-ows with reference to Figs. 7a and ~ ,1 . a) Multivibrator 116 is inhibited by signal B from circuit 138 so that the value of time cannot change during processing;
b) RAM 117 is put in the write mode by Signal D from circuit 138 and write address counter 120 is also enabled by signal D;
c) The current value of time is written in the RAM
memory location addressed by wrlte address counter 120 by signal E from circuit 138;
d) RAM 117 is put in the read mode by signal D from circuit 138, the write address is disabled, and the read address is enabled by enabling the output of read address counter 122 by signal C, and ~AM 117 is enabled for reading by signal E;
e) At that point in time the difference between the current time ~nd the time stored "N" sngle increments previously 1~552~
is then valid at the output of ~ubtraction circuit 118. This time/angle signal is then stored by clocking a data latch 142 connected to the output of subtraction cireuit 118 by means of signal F from circuit 138. Data latch 142 is used for storing binary data and typically consists of three 4-bit latches for 12-bit resolution, such as, for ex~mple, National Semiconductor p~rt ~o. 74175.
f) Multivibrator 116 is then enabled by driving signal B from circuit 138 high, write and read address counters 120 and 122 are incremented ready for the next angle pulse from circuit 66, and the leading edge of signal B indicates that a new time/
angle ignal is now valid at the output of data latch 142.
Timing control logic circuit 138 will now be described in greater det~il with reference to Fig. 7c. Circuit 138 gener-ates the timing control signals B - F previously re:Eerred to for calculation of time/angle following an angle pulse :Erom circuit 66, as shown in Fig. 7b. These signals are typically produced by a plurality of monostable multivibrators 144, 146, 148, 150, 152, 154 ~nd 156, such as, for example, National Semiconductor part No. 741~3. The respective time constants (e.g. lO~s, 3~s, l~s) of these multivibrators are chosen for the desired timing sequences, ~nd are built in by external RC circuits to the des~red values. Each of the multivibrators are designed to trigger on the tr~iling edge of ~n incoming signal, as illustrat-ed by the symbol ~ Aat the input of each multivibrator. Angle
It is well known in the prior art that tightening a ¦¦f6stener to s yield point produces optimum joint efflciency.
'~
.
~ 1'155~25 A fastened joint having a greater preload value up to the ~ieldpoint of the material of the joint is more reliable and better fastener performance. High fastener preload further increases fatigue resistance due to the fastener feeling less added s~ress from external joint loading, and dynamically loaded joints have less tendency to slip and loosen.
The prior art reveals various types of impact wrench control systems for controlling the amount of preload in a fast-ener. ~ne commonly used type employs some form of torque control, in which the impact wrench tightenes a fastener to a maximum pre~
determined value of torque and thereupon shuts off. Examples of impact wrenches utilizing torque control can be found in United Stat~s Patents to Schoeps et al, No. 3,835,934; Hall No.
3,833,068; Schoeps, No. 3,703,933; Vaughn, No. 3,174,559;
Elliott et al, No. 3,018,866 and Maurer, No. 2,543,979. Another means of controlling impact wrenches found in the prior art is commonly known as a "turn-of-the-nut" system, in which a fastene is tightened to some preselected initial conditlon, such as a predetermined torque value or spindle speed, and thereupon ro-tated an additional predetenmined number of degrees before shut-ting off. Examples of various turn-of-the-nut impact wrench systems are found in United States P~tents to Allen, No.
3,623,557; Hoza et al, No. 3,318,390 and Spyradakis et al,No.
3,011,479. ~nother type of control comprises imparting a con-stant angular momentum of each impulse blow, such as found in the United stes Patent to Swtnson, No. 3,1Bl,672.
5~2 n 811 o the control systems de8crlbed in ehe cbove-noted patents, prior knowledg of the f~stener ~nd joint charac-teristics must be known or ~ss~med in order to determine either the exact predetermined final torque, the exact smount of addi-tional rot~tion, or the amount of constant angular momentum of each impact blow. It is well kno~n that tightenlng to a prede-tenmined preload condition, such as the yield point, is a func-tion of many variables~ among them being joint stiffness~ fasten-er stiffness, surface friction between mating threads and thread form of the mating threads. Therefore, if it is desired to tighten an sssembly to the yleld point with any of the systems described in the above-noted prior art patents, this point cannot ~lways be accurately determined because the conditions of each iastener assembly and joint can vary and may not be known in ad-vance. This consequence can lead to uneven tightening from joint to joint in the same structure, which, in tur~, can result in loosening of one or more fastener assemblies, especially in the presence of vibrations, and premature fatigue failure.
In the control system described in U.S. Patent No .
. 4,185!701 of Januarv 29, lq~n, I . the yield point of a fastener ¦¦ assembly is tained by a ti~htening epparatus which periodically~
applies a tightening moment to the fastener assembly, such as, ¦¦ or example n impsct wrench. Jhe yield point is ettained when ¦
sn lnstantaneous peak moment signal has not increased by more ¦¦ thsn a pred rmined smount over a K tored previous peak moment 11 ~ I
_ 3 _ .
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` 1~55~25 slgnal. While this control system works satisactorily in cer-taln applications~ the present invention is seen as being an improvement thereover.
SUMMARY OF THE INVE ION
Accordingly, it is a general purpose snd object of the present invention to provide apparatus for tightening a fastener assembly to the yield point or some similarly signifi-cant tightened condition in a joint. It is another object of the present invention ts provide a control system for tightening a fastener assembly to its yield point, which control system is particularly useful in a tightening system having a pulsed output for periodically applying a tightening moment. It is still anoth er object o~ thP present lnvention to provide an impact wrench having a self-contained, adaptive control system for accurately tightening a astener assembly to a predetermined preload condi-tion by the utilization of measured characteristics of the fast-ener assembly and joint being tightened. It is yet a further object of the pres~nt invention to provide an adaptive control system in an impact wrench for accurately tightening a fastener to a predetermined preload condition with minimum prior know-ledge of the fastener assembly and joint characteristics. It is yet another object of the present invention to provide an impact d~er~li~es wrench having an adaptive control system which ~ the yield point or similarly significant tightened condition by measuring a value representative of the orward rotation angle of the astener ~ssembly being tightened, and utilizes a comput-1 1S~525 ed function of this forward rotation angle to determine theyield point. It is still a further object of the present in-vention to provide an impact wrench having an adaptive control system which determines the yield point or similarly significant tightened condition of a member by utilizing a measurement of time over a fixed interval of forward rotation angIe as a para-meter representative of the torque applied to the member, and thereafter applies gradient comparison techniques to a curve of the parameter representative of torque vs. forward rotation angle to obtain the yield point. Finally, it is an object of `the present invention to provide an integral r self-contained impact wrench/control system ~hich is compact, reliable, relatively in expensive to manufacture and easily maintainable.
These and other objects are accomplished according to the present invention by apparatus for providing a parameter representative of torque in a tightening system having a pulsed output for periodically applying a tightening moment to a member, the parameter being derived from forward rotation angle measure-ment of the member being tightened.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a side elevational view of an impact wrench constructed according to the invention partially cut away and in cross-section, showing the entire wrench control system;
Fig. 2 is an elevational view of the rear portion of the wrench of Fig. 1 with the back cover removed;
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Fig. 3 is a top view of the wrench shown in Fig. l;
Figs. 4a-4d are views of the air/solenoid trip valve assembly shown in Figs . 1 and 2, in eleva tion and partially in cross section showing progressive operation of the assembly;
Fig. 5 is a schematic block diagram of the control ~ystem for the wrench shown in Fig. l;
Fig. 6a is a schematic illustration of the Fo~ward Ro~ation Sensing Circuit ~h~wn ln Fig. 5j Fig. 6b i~ an elevational view of the encoder and sensors shown in Figs. 1, 2 and 6a showing resolution of the orward rotation sensing system;
Fig. 6c is an illustration of the waveforms produced by the circui ~ of Fig . 6a;
Fig. 7 is a schematic block diagram of the Calculation o Time/Angle and Digital Filter blocks shown in Fig. 5;
Fig. 7~ is a schematic illustration of the Inhibit "N"
Pulses After Reset and Chord Length Setting blocks shown in Fig. 7; ~av~c~n~, Fig. 7b is an illustration of the produced by the blocks of Fig. 7;
Fig. 7c is a 8chematic illustration of the Timing Con-trol Logic block sh~wn in Fig. 7;
Fig. 8 is a graph of the parameters TIME/FORWARD
ROTATION ANGLE vs. ~.NGLE from the Calculation of Time/Angle block of Figs. 5 ~nd 7 before filtering; and Fig. 9 is ~ graph of TORQUE ESTIMATE vs. ANGLE from the Digital Filter block of Figs. 5 ~nd 7 after digital filtering in the ~ngle d~ aLn- G~_ 1 ~55r325 DESCRIPTION OF THE PREFERRED EMBODIMENT
~ efore proceeding with a descrlption of an apparatus ~nd control system in accordance with the present invention, a brief discussion ~bout the operation of impact wrenches will be presented. All impact wrenches operate by relea~ing a periodic build up of kinetic ener~y in the form of a series of torsional shock impulses transmitted to a fastener assembly, ~hich may typ-ically include a bolt and/or nut. As a result, considerable impact forces can be produced with little reactive torque.
Pneumatically driven impact wrenches are most common (as compared with electrically or hydraulically driven impact wrenches) and comprise a vane type air motor and a hammertanvil mechanism.
When the air motor gains sufficient speed, a high lnertia hammer on the motor shaft engages on an anvil on the wrench drive shaft.
The energy of the blow is (a) dissipated as a result of collision inelasticity and riction; (b~ stored as torsional strain energy in the impact mechanism, the wrench drive shaft and the coupling to the fastener; and (c) transferred to the fastener, and con-verted to the work of tightening. The hammer then disengsges from the anvil and the motor accelerates for a complete revolu-tion before delivering the next blow. While most impact wrenches deliver one blow per revolution, there are some which can deliver more than one blow per revolution of the motor. The above des-cription is for conventional pneumatically driven impact wrenches Unlike a continuous action power wrench system in which ~he torque ~pplied can be measured with a s~rain ~ ~reaction torque transducer, there is no convenient way to directly measure the torque ~pplied by an Lmpact wrench. Consequently, it is dificult to control tightening accurately with these wrenches. Because of the discontinuity of impact wrench dynamics which prevents continuous psrameter measurement, control of impact wrench tightening has relied largely on limiting the ener-gy transmitted to the fastener rather than the measurement of impact parameters for estimating applied torque. It has been found that a beneicial parameter for use as an estimate of tor-que in an impact wrench is based upon measurement of the forward rotation angle of the fastener ~ssembly~ The following three assumptions are made in deriving the torque estimate: (a) con-stant energy is transmitted by the impact mechanism (i.e. the air motor reaches full speed well before impact occurs~; (b) the torsional strain energy in the shafts and couplings i5 small;
and (c) the time between impacts is approximately constant.
Thexefore, the energy (E) transmitted to the wrench anvil on each impact is converted ~o the work done in rotating the bolt head through angle (~) against average torque (T). Then, E = T ~ .
Since E is assumed to be constant T
That is, the ~verage torque applied to the bolt during an impac~
is inversely proportional to the angle through which it is ro tated. Measurement of the bolt rotation angle per impact is possible ~ but difficult ln practice ~ because 1'~5'j~25 of the difficulty in making high resolution encoders necessary to detect the relatively small ~alues of Q ~ e. 2 - 3 at final tightening torques), and the difficulty in determining when an impact has occurred. In further explanation of the latter po~nt, it can be difficult to discriminate between actual rotations resulting from impacts and apparent rotations due to slight movements of the hand-held impact wrench ~uring tighten-ingO Since the time between impacts is assumed to be constant, the average applied torque will also be inversely proportional to the average rate of tightening. This can be expressed as Average Torque cy _ _ 1 Rotation~ le Time or, Average Torque c~ Time Rotation Angle By measuring time over a fixed interval of angle, the need for high resolution encoders and detenmining when an impact has occurred is eliminated.
Referring now to Figs. 1, 2, 3, 4a, 4b, 4c and 4d of the drawings, there is illustrated a preferred embodiment of an impact wrench in accordance with the present invention. While the invention will be described with reference to an impact wrench, it should be understood that the invention may be prac-ticed in any tightening system having a pulsed output for peri-odically applying a tightening moment to ~ member. Wrench 10 may be any conventional, pneumatically powered impact wrench de-1l55~5 signed to receive compressed air from an external source (notshown) in order to successively impact a hammer assembly 12 onto an anvil 14. The anvil is rotatably secured within the forward portion of a wrench housing 16 by a bearing 18. The forward end 20 of anvil 14 comprises, for example, a square drive for attach-ment to a drive socket (not shown) or some other suitably shaped wrenching member for driving a fastener assembly (not shown).
Hammer assembly 12, which is connected to and driven by a con-ventional air motor rotor 22, surrounds and contacts portions of anvil 14 imparting periodic impact blows thereto to rotate the anvil and drive the fastener assembly. Wrench 10 also in-cludes a conventional trigger mechanism 24 which, when depressed, allo~s air irom the external source (not shown) to enter the wrench at an inlet port 26 connected to the air motor, driving rotor 22 coupled ~o hammer assembly 12 which rotates anvil 14.
A bidirectional incremental encoder 28 used in a system for measuring angular rotation of the fastener assembly is mounted on a shaft 30 ~ithin the wrench, suitably fixed to anvil 14 for rotation therewith. The encoder disc is of a low inertia type which eliminates problems of fixing the encoder to the shaft in order to withstand the high shock loadings at im-pact. The low inertia disc also avoids errors in measuring angu-lar rotation due to twisting of the shaft on which it is mounted during the large accelerations encountered during operation.
While the encoder is illustrated as being located toward the rear portion of the wrench body, lt should be understood that it :~ ~55~25 may be located at any convenient place within the wrench. Since anvil 14 drives the wrenching member which tightens the fastener assembly, encoder 28 essentially rotates with the fastener assem-bly as it is tightened in a joint. Between impacts of hammer 12 against anvil 14, the anvil and encoder coupled thereto recoil, but the fastener assembly does not due to tolerances in the con-nection between the driving member and the fastener assembly Thus the rotation measuring system should be capable of detecting and disregarding any recoil of encoder 28. Encoder 28 includes a series of vanes or teeth 32 on its outer periphery, with the present embodiment including eighteen ~18) teeth having their respective center lines spaced 20 apart. However, it should be noted that the encoder could contain more or less teeth depending on the degree of accuracy ~esired, the only requirement being that the teeth axe spaced equally apart from each other. A pair of light emitting diodes (LED's) 34 (only one is visible in Fig.
1) are mounted on a board 36 suitably fixed to the wrench housing directly across from a pair of photo transistors 38 mounted on a board 40 which is coupled to board 26 by means-of a pair of electrically conducting spacers 42. The LED's 34 and corres-ponding photo transistors or sensors 38 are mounted at an angular spacing of 45 in the present embodiment providing angle resolu-tion of 5, but they could be spaced any odd multiple of the encoder resolution degrees (i.e. 5, 15, 25, 35, 45, 55 etc.). Seventy-two (72) counts :1~5~52~
per revolution of the encoder are produced wi~h this configura-tion. While optical angle sensing devices have been disclosed in the present embodiment, it is here noted that any other suita-ble proximity type sensing devices may be used instead to detect the passage of teeth 32 during operation of the wrench. These include, among other types, magnetic sensors which have an induc-tion coil whose output varies due to the presence or absence of metal.
The impact wrench control system electronics is con-tained completely within the wrench housing in the back portion thereof. The control system is powered by a battery 44 which is accessible by removing a cap 46. Preferably, but not neces-sarily, a 280 mA-hr nickel-cadmlum (8) cell battery, having a nominal voltage of 10 volts, is used. The battery is supported at each end by a pair of stiff springs 48, so that a good elec-trical contact is maintained during the severe vibration from the impacting action of the wrench. A pair of connectors 50 transmit power from batte~ 44 to boards 36 and 40, containing the angle measurement devices, as well as to thé remainder of the electronic control system. The electronics are contained on (3) boards 52 rigidly bolted together and mounted at the back of the wrench, which boards are accessible by removing cover 54 and are insulated from shock and vibration by any suit-able shock absorbing material 56. The remaining portion of the operating control system consists of an air/solenoid trip valve ~ssembly 58, which will be descr~bed in detail hereinbelow.
The solenoid receives po~er directly from b~ttery 44.
Mounted on one ide of trigger 24 is a permanent magnet 60, and on the ~nside of the handle 62 housing is a reed switch 64. Upon depressing trigger 24, in ~ddition t~ allowing air to pass to the air motor, reed switch 64 is closed by the magnet in order to direct power to the control system, as will also be described in detail hereinbelow.
Six ~6) indicator LED's comprising LED display 66 are mounted on top of the wrench housing and also receive their power from battery 44. Thes~ LED's are color coded and indicate to the operator the wrench/tightening condition and certain fault conditions. A RUN LED ~orange) indicates that the system is operating, and comes on almost immediately after trigger 24 is depressed. ~n OK LED (green) indicates that the tightening of the joint is complete and within preselected specifications;
NGLE LOW LED (red) indicates tha~ a yield point has been detected, but a minimum preselected angle value after reaching a snug point has not been attained; an ANGLE HIGH LED ~red) in-dicates that a maximum preselected angle value after reaching a snug point has been exceeded without detecting a yield point tthese (3) lights are part of a qu~lity eontrol system described more fully in U. S. Patent No. 3,973,434, but do not control the operation of the wrench). A TIGHTENING RATE SLOW LED (red) indi-cates that the wrench does not have sufficient power to yield the bolt (i.e. the bolt has either stopped rotating or else is ro~ating too 610wly for the control system to operate). FinallyJ
a BATTERY LOW LED ~red) indicates that the b~ttery needs re-charging if the battery voltage level is low when the trigger is îl55525 depressed, Referring to Figs. 4a, 4b, 4c and 4d, a unique air/solenoid trip valve ~ssembly 58 is shown. This valve assem-bly must be capable of shutting off the flow of air from the air source to the wrench air motor very rapidly ~hen the control system produces a signal indicating that tightening is complete, and must also require a minimum amount of power to operate.
Valve assembly 58 includes an electrically actuated solenoid valve 300, ~L~air valve 302 and a trip lever 304 biased by a return spring 306 into engagement with a plunger 308 in the air valve to keep the valve in an open position. A spring 310 with-in the air v~lve housing 312 bisses the plunger to a normally open position. Trip lever 304 is actuated by a plunger 314 in the solenoid valve.
As previously m~ tioned, before operation of the wrench as illustrated in Fig. ~,~ trip lever 304 engages a CUtQUt 316 on air valve plunger 308 keeping the plunger in an open position aided by the force of spring 310. Plunger 308 also includes an enlarged head portion 317 at its other end. When trigger mechan ism 24 is depressed, air flows from inlet port 26 through an outlet port 318 of ~ir valve 302 to the air motor operating the impact wrench. As can best be seen in Fig. 4c, the pressure exerted by the air flowing through air valve 302 causes an up-ward force against the surface of enlarged head 317 moving plunger 308 upwardly against spring 310 and trip lever 304. This ~ir pressure is designed to produce a greater force on the plunger in sn upward direction ~han the dow~ward force exerted 1~SS~5 by spring 310. When sn electric~l signal is produced by the control system indicating that tightening is complete, such as at the yield point of the fastener assembly being tightened, this signal actuates solenoid valve 300~ causing plunger 314 to rotate trip lever 304 out of engagement with air valve plunger 308. This occurs very rapidly, and once the solenoid valve is pulsed to actuate it, the electrical signal can be removed eliminating any b~ r~,/
further power drain from the ~ Since trigger mechanism 24 is still being depressed by the wrench operator, causing air to flow into air valve 302 9 the pressure exerted by the air overcomes the force of spring 313 and forces plunger 308 upwardly against ~lve body 312 cutting off flow through the air valve to the wrench air motor, AS shown in Fig. 4d. It should be noted that there is a differential pressure across the air valve from the inlet to the outlet port due to air flow, allowing rapid closure of the valve. At this point, the operator recognizes that tightening has been completed, and he releases trigger mechanism 24 cutting off furthex ~ir flow. Plunger 308 thereupon is forced downwardly to an open position by spring 310, and retur spring 306 rotates trip lever 304 back into engagement with cut-out 316 keeping it open and ready for the next tightening se-quence, as illustrated in Fig. 4b.
Referring now to Fig. 5, a control system is illustrat-ed for controlling the tightening of a fastener assembly by wrenc~
10. It should be clear from all of the foregoing that the entire control system is within the housing of wrench 10, which control 1 1 S55~ ~
system is illustrated as separate blocks outside of the wrench in Fig. 5 for convenience. Signals from photo transistors 38 are supplied to a forward rotation sensing circuit 66 in quadra-ture, as will be explained more Eully below with regard to Fig~.
6a, 6b and 6c. Circuit 66 produces angle pulses representing increments of forward angular displacement of the wrench output shaft 20 or the rotation angle of the fastener assembly being tightened. These incremental forward angle pulses are introduced into a circuit 68 for calculation of time per forward rotation angle and a circuit 70 for detectin~ the yield point of the as-sembly being tightened. Circuit 68 is illustrated in Fig. 7 and will be described below. The output signals from circuit 68 can be used to generate a curve as illustrated in Fig. 8, which can be seen to contain a high noise level due to the discontinu~
ities in the impact tightening process, and is generally unsatis-factory for use without further processing. Consequently, thls curve is then filtered in the angle domain in a digital filter 72 to produce the smoother curve illustrated in Fig. 9. The in-formation from this curve is used in yield detection circuit 70, which will be discussed hereinbelow. Once the yield point is detected by circuit 70, a signal is fed back to solenoid trip valve assembly 58 to cut off the flow of air to the air motor and stop tightening, as previously described with reference to Figs. 4a-4d.
Forward rotation sensing circuit 66 will now be des-cribed in detail with regard to Fig. 6~. As previously stated, the purpose of this circuit is to produce pulses representing incremPnts of forward rotation angle of the fastener during tightening. The reference for the angle measurements is the hand held impact wrench. Angular movement of the wrench by the operator during tightening is generally significantly less than the encoder resolution or the required accuracy for control system operation. The impact wrench drive shaft rotation angle is representative of the fastener rotation angle only for the duration of the impact. At all other ~Lmes the angle measure-ment of the drive shaft is subject to errors due to recoil and backlash in the couplings between the drive shaft and the fasten-er assembly after an impact. Hence the maximwm forward angular displacement of the drive s~aft represents the forward rotation angle of the ~astener assembly which is required.
Referring to Figs. 6a, 6b and 6c, enc~der 28 and sen-sors 38A and 38B are illustrated with the actual spacing between the sensors shown. This arrangement, having a resolution of /4 or 5, produces signals A and B shown in Fig. 6c for either forward or reverse rotation of the encoder. The sîgnals from sensors 38A and 38B are fed through grounded resistors 74 and 76, respectively, to a pair of Schmitt triggers 78 and 80, respectively. The Schmitt triggers are used to produce signals C and D w~th clearly defined transitions from the sensor signals A snd B . Two D-type latches 82 and 84 receive and 1 ~55~25 temporarily store the previous signal levels from Schmitt triggers 78 and 80, respectively. The output of latches 82 and 84 are introduced into one input of excluslve OR gates 86 and 88, respectively. The second input to yate 86 is from Schmitt trigger 80, and the second input to gate 88 is from Schmitt trigger 78. The outputs from gates 86 and 88 are introduced into inverters 90 and 92, respectively, and into one input to NOR gates 96 and 94, respectively. The other inputs to gates 94 and 96 are from inverters 90 and 92, respectively. The sig-nals stored in latches 82 and 84 are thus compared with the in-coming signals C and D to latches 84 and 82, respectively, causing the signals E or F from NOR gates 94 and 96, respec-tively, to change from a logical 0 to 1 for an increment in the forward or reverse direction, respectively. These signal level changes are then used to clock latches 82 and 84 so that they then store the present signal levels from Schmitt triggers 78 and 80, respectively, and are ready for the next signal change from the encoder. When latches 82 and 84 are clocked, the signal level at E or F changes back to a logical 0. The pulse lengt~
of signals E and F is determined by the dela~ in clocking the latches, and is controlled by introducing the output signals from NOR gates 94 and 96 into the inputs of an OR gate 98, whose output is fed to latches 82 and 84 through a grounded resistor/capacitor circuit 100 which provides the appropriate time constant.
An UP/DOWN counter 102, such as a National Semiconduc-tor part No. 74C193, is used to store the maximum forward angular displacement signals. Forward direction signals E are intro-duced into the Count Up input o counter 102 through a NAND gate 104 which receives another input from an inverter 106. Reverse direction signals F ~re introduced into the Count Down input of counter 102 through an inverter 108. During ~n impact, the forward angle pulses E are fed to the output G of circuit 66 through a NAND gate llO, which receives another input from a ~4) input AND gate 112. The t4) inputs to AND gate 112 are the binary output bits from countPr 102. The counter output bits are all logical l's 9 and the forward ~ngle pulses to the counter are inhibited when pulses representing reverse rotation of the drive shaft ~re produced between impacts due to recoil and backlash in the wrench. These reverse pulses F are subtracted from the preset count stored in counter 102~ and thus one or more of the output bit signals to AND gate 112 then become logical O's, caus-ing the output from gate 112 which is fed to NAND gate 110, to be-come 0. NAND gate 110 cannot output any further forward rotation pulses E until the reverse pulses F are ~ade up in counter 102. At the next impact, forward rotation pulses E are once again introduced into the Count Up input of counter :L02, and when the reverse pulses are made Up3 the counter output bits once again become logical lls allowing AND gate 112 to output a high signal to NAND gate 110 ~and inverter 106). ~ate llO then allows forward rotation signals E to pass to the output G of circuit 66, and inverter 106 inhibits ~he introduction of 6~gnals E
through gate 104 to counter 102. In this way the counter stores 1 155~2i the angular position of encoder 28 before any rotation in the reverse direction and inhibits all forward angle pulses until the encoder has returned to that position.
Referring now to Fig. 7, the circuit for calculating the time per forward rotation angle will be explained. At each sngle increment signal from circuit 66, the time is calculated for the bolt to rotate through the previous "n" angle increments ~where "n" = preset chord length, such as, for example (4) incre-ments of 5 per increment or 20~. Time is measured by a counter 114 driven by a simple astable multivibrator circuit 116.
Counter 114 may be typically made up of thxee 4~bit counters, such as,for example, Nation31 Semiconductor par~ No. 7493, for 12-bit resolution; and multivibrator 116 is a square-wave signal generator3 such as, for example, National Semiconductor part No.
~B~ This time is stored at each angle increment in a read-write random access memory (RAM) unit 117, which typically may consist of three 16 x 4-bit RAMS for 12-bit resolution such as, for ex-ample, National Semiconductor part No. 7489. The time to rotate the bolt through a value of "n" increments (equal to the pre-selected chord length~ is calculated by reading from RAM 117 the value of time which was stored "n" angle increments previous-ly, and subtracting this value of time from the value just stored in a subtraction circuit 118. The value of the output signal from subtr~ctlon circuit 118 is the time/angle signal illustrated in Fig. 8, which could be plotted, if desired, for th~ joint ~S~25 being tlghtened. Memory addressing of RAM 117 is accomplished by the outputs from two tri-state address counters 120 and 1220 These address counters are typically 4-bit counters with three state outputs, such as, for example, National Semiconductor part No. 8554. The output of read address counter 122 is equal to the output of write ~ddress counter less the chord length preset with switches in binary as a particular number of angle incre-ments. During normal processing, both of these address counters are clocked9 incrementing their addresses by "1" every angle increment. Counters 120 and 122 are initially preset by resettin, them to "O" and then inhibiting the first "N" clock pulses to read address counter 122 by means o cixcuits 124, which will now be described in greater detail with regard to Fig. 7a.
Circuit 124 includes a presettable counter ~ , such as, for example, National Semiconductor par~ No. 74197, and a series of logic gates to inhibit the number of read address counter 122 clock pulses preset by the chord length switches in circuit 126 after reset. The number in read address counter 122 therefore becomes the number in write address counter 120 minus the preset chord length. Counter 12~ receives a reset signal from the reset line and a series of preset chord length inputs from binary switches 127 in circuit 126. The output from counter 128 is fed into a 4-input NOR gate 130 whose output is fed into an inverter 132 and one input of an OR gate 134. The other input to OR gate 134 is from the output of an inverter 136 which 1~55S25 xeceives clock pulses from a timing control logic circuit 138.
The outputs of inverters 132 and 136 are :Eed into a NOR gate 140 whose output clocks read address counter 122, ~s previously described, The chord length is set in"l's" complement by switche , 127 (inverted logic signals), and ~ulses are enabled to pre-settable counter 128 and inhibited to read address counter 122 until presettable counter 128 output reaches "0000".
The processing sequence for calculation of time/angle, which is started with an angle pulse ~rom eircuit 66, is as foll-ows with reference to Figs. 7a and ~ ,1 . a) Multivibrator 116 is inhibited by signal B from circuit 138 so that the value of time cannot change during processing;
b) RAM 117 is put in the write mode by Signal D from circuit 138 and write address counter 120 is also enabled by signal D;
c) The current value of time is written in the RAM
memory location addressed by wrlte address counter 120 by signal E from circuit 138;
d) RAM 117 is put in the read mode by signal D from circuit 138, the write address is disabled, and the read address is enabled by enabling the output of read address counter 122 by signal C, and ~AM 117 is enabled for reading by signal E;
e) At that point in time the difference between the current time ~nd the time stored "N" sngle increments previously 1~552~
is then valid at the output of ~ubtraction circuit 118. This time/angle signal is then stored by clocking a data latch 142 connected to the output of subtraction cireuit 118 by means of signal F from circuit 138. Data latch 142 is used for storing binary data and typically consists of three 4-bit latches for 12-bit resolution, such as, for ex~mple, National Semiconductor p~rt ~o. 74175.
f) Multivibrator 116 is then enabled by driving signal B from circuit 138 high, write and read address counters 120 and 122 are incremented ready for the next angle pulse from circuit 66, and the leading edge of signal B indicates that a new time/
angle ignal is now valid at the output of data latch 142.
Timing control logic circuit 138 will now be described in greater det~il with reference to Fig. 7c. Circuit 138 gener-ates the timing control signals B - F previously re:Eerred to for calculation of time/angle following an angle pulse :Erom circuit 66, as shown in Fig. 7b. These signals are typically produced by a plurality of monostable multivibrators 144, 146, 148, 150, 152, 154 ~nd 156, such as, for example, National Semiconductor part No. 741~3. The respective time constants (e.g. lO~s, 3~s, l~s) of these multivibrators are chosen for the desired timing sequences, ~nd are built in by external RC circuits to the des~red values. Each of the multivibrators are designed to trigger on the tr~iling edge of ~n incoming signal, as illustrat-ed by the symbol ~ Aat the input of each multivibrator. Angle
2 ~
signal A is introduced into inputs to multivi.brators 144, 146 and 148. Output singal B is generated by multivi.brator 144, and out-put signals C and D are both generated by multivibrator 146.
Output signal C from multivibrator 146 is introduced into multi-vibrators 152 and 154. The output from multivibrator 148 is in-troduced into the input to multivibrator 150, and the respective outputs rom multivibrators 150 and 152 are fed into a NOR yate 158, whose output is signal E. The output from multivibrator 154 is introduced into the input to multivibrator 156, whose output is signal F.
Since the impact tightening process is discontinuous, the timejangle signals generated by circuit 68 produce a curve illustrated in Fig. ~ having a great deal of noise. ~ filtering or averaging process is thus required to make use of this time/
angle information. Such processes inevitably introduce delays in real time systems. Filtering in the time domain is unsatis-factory because the rate of tightening varies considerably during the tightening process and therefore so does the amount of neces-sary filtering or "smoothing" of the curve of Fig. 8. This problem is eliminated by digital filtering in the angle domain.
Not only does this technique ensure consistent filtering, but also, since the range of tightening angles for most fasteners is between 90 and 180, the filter constant does not require alter-ation for di~ferent joints. It need only be altered to compen-sate for changes in angle encoder resolution.
11~55~
Referring again to Fig. 7, digital filter circuit 72, shown ~ n Fig. 5, will now be described in greater detail, The digital filter used to filter the time/angle signal from circuit 68 in order to produce a torque estimate signal usable in yield detection circuit 70, is a first order low pass recursive filter defined by the filter difference equation Yk - aXk ~ bYk-l where, Yk ~ the present filter output Xk = the present filter input Yk 1 = the previous filter output For a 5 resolution encoder, for example, the constants "a" and "b" are chosen as 1/4 and 3/4~ respectively, and the difference equation is, Yk = 1/4 Xk + 3/4 Yk_ or, ~ k Yk-l ~ ~Xk Yk-l) /4 The filter described by this equation is illustrated in Fig. 7 as follows. Yk and Yk 1 are respectively stored in data latches 160 and 162, which are similar to data latch 142. The output signal; Yk 1' from data latch 162 is introduced along with the time/angle signal, Xk, from data latch 142 in circuit 68~ into a subtraction circuit 164, whose output is the difference signal (Xk Yk-l). Division by 4 is accomplished by shifting the binar ~ ~ 5 5~2 :j data lines 2-bits to the right by a hard~wired shift designated as 166. This is accomplished, for example, by connecting each output data line from subtraction circuit 164 to a corresponding input data line two significant bits lower on addition circuit 168. That is, the output binary data line representing the deci-mal value "8" on circuit 164 is connected to the input binary data line representing the decimal value "2" on circuit 168, and ! correspondingly, "4" on circuit 164 is connected to "1" on cir-cuit 168. The output signal, Yk 1' from data latch 162 is added to the output signal, (Xk - Yk 1)/4' from shift register 166 in an addition circuit 168. Subtraction and addition circuits 164 and 168 typically comprise three binary full adders for 12-bit resolution, similar to subtraction circuit 11~. Data latches 160 and 162 are clocked by monostable multivibrators or one-shots 170 and 172, respectively, which output signals G and H illustrated in Fig. 7b. Multivibrators 170 and 172, such as, for example, National Semiconductor part No. 74123~ are triggered respectively from the leading edge of signal B representing the new time/angle signal valid line, and the trailing edge of the output signal Erom multivibrator 170. The trailing edge of the signal from multivibrator 172 indicates that a new torque estimate has been calculated following an angle pulse. The output, Yk, from data latch 160 of digital filter 72 is the tor~ue estimate which is introduced along with the incremental angle pulses from circuit 66 into yield detection circuit 70.
Yield detection circuit 70 may be any of a number of systems for tightening to the yield point of the fastener f -26-~5~25 ~ssembly, such as, for example, the systems described in ~. S.
P~tent Nos. 3,974,~83, 4,023,406, 4,027~530, 4,104,779, 4,104,780 and others. However, ~ preferred 8ystem is that disclosed in U. S. PatPnt No. 3,982,419, particularly Fig. 7 thereof.
~ Briefly describing the function of yield detection, circuit 70, the grfldient or slope of the Torque Estimate vs. Angle curve illustrated in Fig. 9 is determined, ~nd the characteristic (e.g. maximum) slope in the tightening (e.g. linear) region of the curve is stored. The in-stantaneous gradient signal is then compared with the stored gradient signal, and a control signal is provided to solenoid trip valve assembly 58 indicating that the yield point has been reached when the instantaneous gradient signal is a predetermined percentage of the stored gr~dient Qignal. The solenoid trip valve assembly then operates to cut off the flow of air to the air motor discontinuing tightening of the fastener ~ssembly.
While the control system has been described with ref-erence to integrated circuit logic elements, it is to be under-stood that the functions of rirCuits 68, 70 and 72 could be accom-plished by an appropriately programmed microprocessor, such as9 for example, an Intel Model No. 8748, or other similar micro-processors. The results obtained with ~ programmed microprocessor version o the control system are fully equivalent to those ob-tained with the control system previously described. An impact wrench using a programmed Intel Model No. 8748 microprocessor - 27 - ~
.
1i5552.~
has been built, as lllus trated in Figs . 1 and 3, and successfully tes ted .
Having thus described the impact wrench and control circuitry, operstion of the wrench will now be described with reference to the drawlngs. Upon depression of trigger mechanism 24, reed switch 64 is closed by magnet 60 providing power to the electronic control system The "RUN" LED immediately indicates that the control ~ystem is operating. If the battery is low,a re BATTFR~ LOW LED is energized instead, indicating that the battery requires recharging. Depression of the trigger also opens the valve (not shown) admitting air from inlet port 26 through air valve 302 to the air motor driving rotor 22 and inltiating ~he tightening sequence. When tightening is complete, a signal from the control system actuates solenoid trip valve assembly 58 which shuts off the air supply to the air motor. A number of checks are carried out on the torque estimate/angle data during the tightening sequence. If the tightening is within specifications~
the "OK" LED is turned on and remains on until the system is de-energized by releasing the wrench trigger mechanism 24 and open-ing reed switch 64~ If the tightening is not within specifica-tions, a number of fault LED's indicate the specific fault condi-~r~
tion. ~ Lnclude ANGLE LOW, ANGLE HIGH and TIGHTENING RATE SLOWLED's. If any of these fault LED's should light, the operator would then check the joint just tightened to see if there are any problems, or the wrench for possible malfunction.
~1 ~115S525 While in the foregoing there have been disclosed alternate embodiments of a tightening system in accordance with the present invention, it should be readily apparent that various changes and modifications could be made by one skilled in the art without departing from the true spirit and scope of the invention as recited in the claims.
signal A is introduced into inputs to multivi.brators 144, 146 and 148. Output singal B is generated by multivi.brator 144, and out-put signals C and D are both generated by multivibrator 146.
Output signal C from multivibrator 146 is introduced into multi-vibrators 152 and 154. The output from multivibrator 148 is in-troduced into the input to multivibrator 150, and the respective outputs rom multivibrators 150 and 152 are fed into a NOR yate 158, whose output is signal E. The output from multivibrator 154 is introduced into the input to multivibrator 156, whose output is signal F.
Since the impact tightening process is discontinuous, the timejangle signals generated by circuit 68 produce a curve illustrated in Fig. ~ having a great deal of noise. ~ filtering or averaging process is thus required to make use of this time/
angle information. Such processes inevitably introduce delays in real time systems. Filtering in the time domain is unsatis-factory because the rate of tightening varies considerably during the tightening process and therefore so does the amount of neces-sary filtering or "smoothing" of the curve of Fig. 8. This problem is eliminated by digital filtering in the angle domain.
Not only does this technique ensure consistent filtering, but also, since the range of tightening angles for most fasteners is between 90 and 180, the filter constant does not require alter-ation for di~ferent joints. It need only be altered to compen-sate for changes in angle encoder resolution.
11~55~
Referring again to Fig. 7, digital filter circuit 72, shown ~ n Fig. 5, will now be described in greater detail, The digital filter used to filter the time/angle signal from circuit 68 in order to produce a torque estimate signal usable in yield detection circuit 70, is a first order low pass recursive filter defined by the filter difference equation Yk - aXk ~ bYk-l where, Yk ~ the present filter output Xk = the present filter input Yk 1 = the previous filter output For a 5 resolution encoder, for example, the constants "a" and "b" are chosen as 1/4 and 3/4~ respectively, and the difference equation is, Yk = 1/4 Xk + 3/4 Yk_ or, ~ k Yk-l ~ ~Xk Yk-l) /4 The filter described by this equation is illustrated in Fig. 7 as follows. Yk and Yk 1 are respectively stored in data latches 160 and 162, which are similar to data latch 142. The output signal; Yk 1' from data latch 162 is introduced along with the time/angle signal, Xk, from data latch 142 in circuit 68~ into a subtraction circuit 164, whose output is the difference signal (Xk Yk-l). Division by 4 is accomplished by shifting the binar ~ ~ 5 5~2 :j data lines 2-bits to the right by a hard~wired shift designated as 166. This is accomplished, for example, by connecting each output data line from subtraction circuit 164 to a corresponding input data line two significant bits lower on addition circuit 168. That is, the output binary data line representing the deci-mal value "8" on circuit 164 is connected to the input binary data line representing the decimal value "2" on circuit 168, and ! correspondingly, "4" on circuit 164 is connected to "1" on cir-cuit 168. The output signal, Yk 1' from data latch 162 is added to the output signal, (Xk - Yk 1)/4' from shift register 166 in an addition circuit 168. Subtraction and addition circuits 164 and 168 typically comprise three binary full adders for 12-bit resolution, similar to subtraction circuit 11~. Data latches 160 and 162 are clocked by monostable multivibrators or one-shots 170 and 172, respectively, which output signals G and H illustrated in Fig. 7b. Multivibrators 170 and 172, such as, for example, National Semiconductor part No. 74123~ are triggered respectively from the leading edge of signal B representing the new time/angle signal valid line, and the trailing edge of the output signal Erom multivibrator 170. The trailing edge of the signal from multivibrator 172 indicates that a new torque estimate has been calculated following an angle pulse. The output, Yk, from data latch 160 of digital filter 72 is the tor~ue estimate which is introduced along with the incremental angle pulses from circuit 66 into yield detection circuit 70.
Yield detection circuit 70 may be any of a number of systems for tightening to the yield point of the fastener f -26-~5~25 ~ssembly, such as, for example, the systems described in ~. S.
P~tent Nos. 3,974,~83, 4,023,406, 4,027~530, 4,104,779, 4,104,780 and others. However, ~ preferred 8ystem is that disclosed in U. S. PatPnt No. 3,982,419, particularly Fig. 7 thereof.
~ Briefly describing the function of yield detection, circuit 70, the grfldient or slope of the Torque Estimate vs. Angle curve illustrated in Fig. 9 is determined, ~nd the characteristic (e.g. maximum) slope in the tightening (e.g. linear) region of the curve is stored. The in-stantaneous gradient signal is then compared with the stored gradient signal, and a control signal is provided to solenoid trip valve assembly 58 indicating that the yield point has been reached when the instantaneous gradient signal is a predetermined percentage of the stored gr~dient Qignal. The solenoid trip valve assembly then operates to cut off the flow of air to the air motor discontinuing tightening of the fastener ~ssembly.
While the control system has been described with ref-erence to integrated circuit logic elements, it is to be under-stood that the functions of rirCuits 68, 70 and 72 could be accom-plished by an appropriately programmed microprocessor, such as9 for example, an Intel Model No. 8748, or other similar micro-processors. The results obtained with ~ programmed microprocessor version o the control system are fully equivalent to those ob-tained with the control system previously described. An impact wrench using a programmed Intel Model No. 8748 microprocessor - 27 - ~
.
1i5552.~
has been built, as lllus trated in Figs . 1 and 3, and successfully tes ted .
Having thus described the impact wrench and control circuitry, operstion of the wrench will now be described with reference to the drawlngs. Upon depression of trigger mechanism 24, reed switch 64 is closed by magnet 60 providing power to the electronic control system The "RUN" LED immediately indicates that the control ~ystem is operating. If the battery is low,a re BATTFR~ LOW LED is energized instead, indicating that the battery requires recharging. Depression of the trigger also opens the valve (not shown) admitting air from inlet port 26 through air valve 302 to the air motor driving rotor 22 and inltiating ~he tightening sequence. When tightening is complete, a signal from the control system actuates solenoid trip valve assembly 58 which shuts off the air supply to the air motor. A number of checks are carried out on the torque estimate/angle data during the tightening sequence. If the tightening is within specifications~
the "OK" LED is turned on and remains on until the system is de-energized by releasing the wrench trigger mechanism 24 and open-ing reed switch 64~ If the tightening is not within specifica-tions, a number of fault LED's indicate the specific fault condi-~r~
tion. ~ Lnclude ANGLE LOW, ANGLE HIGH and TIGHTENING RATE SLOWLED's. If any of these fault LED's should light, the operator would then check the joint just tightened to see if there are any problems, or the wrench for possible malfunction.
~1 ~115S525 While in the foregoing there have been disclosed alternate embodiments of a tightening system in accordance with the present invention, it should be readily apparent that various changes and modifications could be made by one skilled in the art without departing from the true spirit and scope of the invention as recited in the claims.
Claims (67)
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS.
1. Apparatus for providing a parameter representative of torque in a tightening system having a pulsed output for peri-odically applying a tightening moment to a member, said parameter being derived from forward rotation angle measurement of the member being tightened.
2. Apparatus in accordance with Claim 1 wherein said parameter representative of torque is derived from a measurement of time over a fixed interval of forward rotation angle of the member being tightened.
3. Apparatus in accordance with Claim 1 wherein said parameter representative of torque is derived from a measurement of forward rotation angle of the member being tightened over a fixed interval of time.
4. Apparatus in accordance with Claim 1 wherein said parameter representative of torque is derived from a measurement of forward rotation angle of the member being tightened per im-pact of the tightening system.
5. Apparatus in accordance with Claim 1 wherein said parameter representative of torque is derived from a measurement of impacts over a fixed interval of forward rotation angle of the member being tightened.
6. Apparatus in accordance with Claim 2 including means for determining the forward rotation angle of the member being tightened and providing a signal indicative thereof and means for calculating the time over a fixed interval of said for-ward rotation angle and providing a signal indicative thereof.
7. Apparatus in accordance with Claim 6 further in-cluding means receiving said forward rotation angle signal and said signal indicative of time over a fixed interval of said for-ward rotation angle for developing a control signal when the member has been tightened to its yield point or some similarly significant point.
8. Apparatus in accordance with Claim 6 further in-cluding filtering means receiving said signal indicative of time over a fixed interval of said forward rotation angle for providing a filtered signal thereof.
9. Apparatus in accordance with Claim 8 wherein said filtering means is a digital filter.
10. Apparatus in accordance with Claim 9 wherein said digital filter filters in the angle domain.
11. Apparatus in accordance with Calim 10 further in cluding means receiving said forward rotation angle signal and said filtered signal for developing a control signal when the member has been tightened to its yield point or some similarly significant point.
12. Apparatus in accordance with Claim 11 including means adapted to receive said control signal for discontinuing tightening of the member.
13. Apparatus for tightening an assembly including a fastener, to a predetermined tightened condition said apparatus comprising:
wrench means having a pulsed output for periodically applying a tightening moment to a fastener in a joint assembly;
first means for determining the forward rotation angle of the fastener being tightened and producing an output signal indicative thereof;
second means receiving said first means output signal for pro-viding an output signal representative of time over a fixed interval of said forward rotation angle; and third means receiving said first and second means output signals for developing a control signal when the predetermined tightened condition is reached.
wrench means having a pulsed output for periodically applying a tightening moment to a fastener in a joint assembly;
first means for determining the forward rotation angle of the fastener being tightened and producing an output signal indicative thereof;
second means receiving said first means output signal for pro-viding an output signal representative of time over a fixed interval of said forward rotation angle; and third means receiving said first and second means output signals for developing a control signal when the predetermined tightened condition is reached.
14. Apparatus in accordance with Claim 13 further in-cluding filter means interposed between said second and third means receiving said second means output signal for filtering spurious noise from said signal and outputting a filtered signal to said third means for use in developing said control signal when the predetermined tightened condition is reached.
15. Apparatus in accordance with Claim 14 wherein said predetermined tightened condition is the yield point or some similarly significant point of the assembly being tightened.
16. Apparatus in accordance with Claim 15 wherein said control signal is developed by developing a signal representative of the instantaneous gradient of a curve which could be plotted for said first and second means output signals through which the joint assembly is being tightened, and determining a significant change in slope following a tightening region on said curve by storing a signal representative of the gradient of said curve in the tightening region thereof and developing said control signal when said instantaneous signal is a predetermined percentage of said stored signal.
17. Apparatus in accordance with Claim 15 wherein said control signal is developed by developing a signal representa-tive of the instantaneous gradient of a curve which could be plotted for said first means and said filter means output sig-nals through which the joint assembly is being tightened, and de-termining a significant change in slope following a tightening region on said curve by storing a signal representative of the gradient of said curve in the tightening region thereof and de-veloping said control signal when said instantaneous signal is a predetermined percentage of said stored signal.
18. Apparatus in accordance with Claim 16 wherein said stored signal is representative of the maximum gradient of the curve of said first and second means output signals.
19. Apparatus in accordance with Claim 17 wherein said stored. signal is representative of the maximum gradient of the curve of said first means and said filter means output signals.
20. Apparatus in accordance with Claim 14 wherein said first means includes encoder means, sensor means and circuit means for producing said signal indicative of forward rotation angle of the fastener being tightened.
21. Apparatus in accordance with Claim 13 wherein said second and third means comprise programmed microprocessor means.
22. Apparatus in accordance with Claim 14 wherein said second, third and filter means comprise programmed microprocessor means.
23. Apparatus in accordance with Claim 14 wherein said third means control signal is operative to discontinue the appli-cation of the tightening moment.
24. Apparatus in accordance with Claim 23 further in-cluding shutoff means and wherein said third means control signal is introduced to said shutoff means to discontinue the applica-tion of the tightening moment.
25. Apparatus in accordance with Claim 24 wherein said wrench means is fluid operated and wherein said shutoff means in-cludes actuating means, lever means and valve means, said ac-tuating means receiving said third means control signal and dis-placing said lever means, which is initially biased into engage-ment with said valve means in an open position, out of engagement with said valve means causing said valve means to move to a closed position stopping the flow of fluid to said wrench means.
26. Apparatus in accordance with Claim 25 wherein said actuating means is a solenoid actuating device.
27. Apparatus in accordance with Claim 25 wherein said lever means is pivotable out of and into engagement with said valve means.
28. In an impact wrench including a hammer impacting with an anvil to rotate an output shaft operative to tighten an assembly including a fastener to its yield point by applying a tightening moment thereto, a control system comprising:
first means for determining the forward rotation angle of the fastener being tightened and producing an output signal indicative thereof;
second means receiving said first means output signal for pro-viding a signal representative of time over a fixed in-terval of said forward rotation angle; and third means receiving said first and second means output signals for developing a control singal when the predetermined tightened condition is reached.
first means for determining the forward rotation angle of the fastener being tightened and producing an output signal indicative thereof;
second means receiving said first means output signal for pro-viding a signal representative of time over a fixed in-terval of said forward rotation angle; and third means receiving said first and second means output signals for developing a control singal when the predetermined tightened condition is reached.
29. A control system in accordance with Claim 28 further including filter means interposed between said second and third means receiving said second means output signal for filtering spurious noise from said signal and outputting a filtered signal to said third means for use in developing said control signal when the predetermined tightened condition is reached.
30. A control system in accordance with Claim 29 wherein said predetermined tightened condition is the yield point or some similarly significant point of the assembly being tight-ened.
31. A control system in accordance with Claim 30 where-in said control signal is developed by developing a signal repre-sentative of the instantaneous gradient of a curve which could be plotted for said first and second means output signals through which the joint assembly is being tightened, and determining a significant change in slope following a tightening region on said curve by storing a signal representative of the gradient of said curve in the tightening region thereof and developing said con-trol signal when said instantaneous signal is a predetermined percentage of said stored signal.
32. A control system in accordance with Claim 30 where-in said control signal is developed by developing a signal repre-sentative of the instantaneous gradient of a curve which could be plotted for said first means and said filter means output signals through which the joint assembly is being tightened, and deter-mining a significant change in slope following a tightening region on said curve by storing a signal representative of the gradient of said curve in the tightening region thereof and developing said control signal when said instantaneous signal is a predetermined percentage of said stored signal.
33. A control system in accordance with Claim 31 where-in said stored signal is representative of the maximum gradient of the curve of said first and second means output signals.
34. A control system in accordance with Claim 32 where-in said stored signal is representative of the maximum gradient of the curve of said first means and said filter means output signals.
35. A control system in accordance with Claim 28 or 29 wherein said first means includes encoder means, sensor means and circuit means for producing said signal indicative of forward rotation angle of the fastener being tightened.
36. A control system in accordance with Claim 28 where-in said second and third means comprise programmed microprocessor means.
37. A control system in accordance with Claim 29 where-in said second, third and filter means comprise programmed micro-processor means.
38. A control system in accordance with Claim 29 where-in said third means control signal is operative to discontinue the application of the tightening moment.
39. A control system in accordance with Claim 38 where-in said impact wrench further includes shutoff means and wherein said third means control signal is introduced to said shutoff means to discontinue the application of the tightening moment.
40. A control system in accordance with Claim 39 where-in said impact wrench is fluid operated and wherein said shutoff means includes actuating means, lever means and valve means, said actuating means receiving said third means control signal and displacing said lever means, which is initially biased into engagement with said valve means in an open position, out of en-gagement with said valve means causing said valve means to move to a closed position stopping the flow of fluid to said impact wrench.
41. A control system in accordance with Claim 40 where-in said actuating means is a solenoid actuating device.
42. A control system in accordance with Claim 40 where-in said lever means is pivotable out of and into engagement with said valve means.
43. An impact wrench for tightening an assembly inclu-ding a fastener comprising:
a motor;
a hammer assembly adapted to be driven by said motor;
an anvil adapted to be rotatingly impacted by said hammer assembly;
wrenching means operatively attached to said anvil and adapted to drive the fastener by applying torque thereto;
first means for determining the forward rotation angle of the fastener being tightened and producing an output signal indicative thereof;
second means receiving said first means output signal for pro-viding a signal representative of time over a fixed in-terval of said forward rotation angle; and third means receiving said first and second means output signals for developing a control signal when the predetermined tightened condition is reached.
a motor;
a hammer assembly adapted to be driven by said motor;
an anvil adapted to be rotatingly impacted by said hammer assembly;
wrenching means operatively attached to said anvil and adapted to drive the fastener by applying torque thereto;
first means for determining the forward rotation angle of the fastener being tightened and producing an output signal indicative thereof;
second means receiving said first means output signal for pro-viding a signal representative of time over a fixed in-terval of said forward rotation angle; and third means receiving said first and second means output signals for developing a control signal when the predetermined tightened condition is reached.
44. An impact wrench in accordance with Claim 43 further including filter means interposed between said second and third means receiving said second means output signal for fil-tering spurious noise from said signal and outputting a filtered signal to said third means for use in developing said control signal when the predetermined tightened condition is reached.
45. An impact wrench in accordance with Claim 44 where-in said predetermined tightened condition is the yield point or some similarly significant point of the assembly being tightened.
46. An impact wrench in accordance with Claim 45 where-in said control signal is developed by developing a signal repre-sentative of the instantaneous gradient of a curve which could be plotted for said first and second means output signals through which the joint assembly is being tightened, and determining a significant change in slope following a tightening region on said curve by storing a signal representative of the gradient of said curve in the tightening region thereof and developing said con-trol signal when said instantaneous signal is a predetermined percentage of said stored signal.
47. An impact wrench in accordance with Claim 45 where-in said control signal is developed by developing a signal repre-sentative of the instantaneous gradient of a curve which could be plotted for said first means and said filter means output signals through which the joint assembly is being tightened, and deter-mining a significant change in slope following a tightening region on said curve by storing a signal representative of the gradient of said curve in the tightening region thereof and developing said control signal when said instantaneous signal is a predeter-mined percentage of said stored signal.
48. An impact wrench in accordance with Claim 46 where-in said stored signal is representative of the maximum gradient of the curve of said first and second means output signals.
49. An impact wrench in accordance with Claim 47 where-in said stored signal is representative of the maximum gradient of the curve of said first means and said filter means output signals.
50. An impact wrench in accordance with Claim 43 or 44 wherein said first means includes encoder means, sensor means and circuit means for producing said signal indicative of forward rotation angle of the fastener being tightened.
51. An impact wrench in accordance with Claim 43 where-in said second and third means comprise programmed microprocessor means.
52. An impact wrench in accordance with Claim 44 where-in said second, third and filter means-comprise programmed micro-processor means.
53. An impact wrench in accordance with Claim 44 where-in said third means control signal is operative to discontinue the application of the tightening moment.
54. An impact wrench in accordance with Claim 53 further including shutoff means and wherein said third means con-trol signal is introduced to said shutoff means to discontinue the application of the tightening moment.
55. An impact wrench in accordance with Claim 54 where-in said impact wrench is fluid operated and wherein said shutoff means includes actuating means, lever means and valve means, said actuating means receiving said third means control signal and dis-placing said lever means, which is initially biased into engage-ment with said valve means in an open position, out of engagement with said valve means causing said valve means to move to a closed position stopping the flow of fluid to said impact wrench.
56. An impact wrench in accordance with Claim 55 where-in said actuating means is a solenoid actuating device.
57. An impact wrench in accordance with Claim 55 where-in said lever means is pivotable out of and into engagement with said valve means.
58. A method of tightening an assembly including a fastener to a predetermined tightened condition by periodically applying a tightening moment to the fastener with wrench means having a pulsed output, comprising the steps of:
determining the forward rotation angle of the fastener being tightened and producing a first output signal indica-tive thereof;
providing from said first output signal a second output signal representative of time over a fixed interval of said forward rotation angle; and developing from said first and second output signals a control signal when the predetermined tightened condition is reached.
determining the forward rotation angle of the fastener being tightened and producing a first output signal indica-tive thereof;
providing from said first output signal a second output signal representative of time over a fixed interval of said forward rotation angle; and developing from said first and second output signals a control signal when the predetermined tightened condition is reached.
59. A method of tightening an assembly in accordance with Claim 58 further comprising the step of filtering said second output signal to remove spurious noise therefrom and thereafter developing from said first output signal and said filtered second output signal said control signal when the pre-determined tightened condition is reached.
60. A method of tightening an assembly in accordance with Claim 59 wherein the predetermined tightened condition is the yield point or some similarly significant point of the as-sembly being tightened.
61. A method of tightening an assembly in accordance with Claim 60 wherein said control signal is developed by develo-ping a signal representative of the instantaneous gradient of a curve which could be plotted for said first and second means out-put signals through which the assembly is being tightened, and determining a significant change in slope following a tightening region on said curve by storing a signal representative of the gradient of said curve in the tightening region thereof and deve-loping said control signal when said instantaneous signal is a predetermined percentage of said stored signal.
62. A method of tightening an assembly in accordance with Claim 60 wherein said control signal is developed by develo-ping a signal representative of the instantaneous gradient of a curve which could be plotted for said first means and said filter means output signals through which the assembly is being tightened, and determining a significant change in slope following a tight-ening region on said curve by storing a signal representative of the gradient of said curve in the tightening region thereof and developing said control signal when said instantaneous signal is a predetermined percentage of said stored signal.
63. A method of tightening an assembly in accordance with Claim 61 wherein said stored signal is representative of the maximum gradient of the curve of said first and second means out-put signals.
64. A method of tightening an assembly in accordance with Claim 62 wherein said stored signal is representative of the maximum gradient of the curve of said first means and said filter means output signals.
65. A method of tightening an assembly in accordance with Claim 58 wherein the steps of providing said second output signal and developing said control signal are accomplished by programmed microprocessor means.
66. A method of tightening an assembly in accordance with Claim 59 wherein the steps of providing said second output signal, filtering said second output signal to remove spurious noise therefrom and developing said control signal are accom-plished by programmed microprocessor means.
67. A method of tightening an assembly in accordance with Claim 58 or 59 wherein said control signal is operative to discontinue the application of the tightening moment.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/027,127 US4316512A (en) | 1979-04-04 | 1979-04-04 | Impact wrench |
| US027,127 | 1979-04-04 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1155525A true CA1155525A (en) | 1983-10-18 |
Family
ID=21835850
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000349144A Expired CA1155525A (en) | 1979-04-04 | 1980-04-03 | Impact wrench |
Country Status (13)
| Country | Link |
|---|---|
| US (1) | US4316512A (en) |
| JP (1) | JPS55164483A (en) |
| AU (1) | AU533695B2 (en) |
| BR (1) | BR8001997A (en) |
| CA (1) | CA1155525A (en) |
| DE (1) | DE3012734A1 (en) |
| ES (2) | ES8104933A1 (en) |
| FR (1) | FR2452997B1 (en) |
| GB (1) | GB2048494B (en) |
| IT (1) | IT1143129B (en) |
| MX (1) | MX151493A (en) |
| SE (1) | SE458181B (en) |
| ZA (1) | ZA801998B (en) |
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-
1979
- 1979-04-04 US US06/027,127 patent/US4316512A/en not_active Expired - Lifetime
-
1980
- 1980-04-01 SE SE8002505A patent/SE458181B/en not_active IP Right Cessation
- 1980-04-01 BR BR8001997A patent/BR8001997A/en not_active IP Right Cessation
- 1980-04-01 DE DE19803012734 patent/DE3012734A1/en active Granted
- 1980-04-02 ES ES490267A patent/ES8104933A1/en not_active Expired
- 1980-04-02 GB GB8011143A patent/GB2048494B/en not_active Expired
- 1980-04-02 MX MX181832A patent/MX151493A/en unknown
- 1980-04-03 CA CA000349144A patent/CA1155525A/en not_active Expired
- 1980-04-03 JP JP4403580A patent/JPS55164483A/en active Pending
- 1980-04-03 AU AU57199/80A patent/AU533695B2/en not_active Ceased
- 1980-04-03 FR FR8007615A patent/FR2452997B1/en not_active Expired
- 1980-04-03 ZA ZA00801998A patent/ZA801998B/en unknown
- 1980-04-03 IT IT48337/80A patent/IT1143129B/en active
- 1980-12-16 ES ES497818A patent/ES8204633A1/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| DE3012734A1 (en) | 1980-10-16 |
| AU5719980A (en) | 1980-10-09 |
| ES490267A0 (en) | 1981-05-16 |
| ES497818A0 (en) | 1982-05-01 |
| US4316512A (en) | 1982-02-23 |
| GB2048494B (en) | 1983-05-25 |
| IT8048337A0 (en) | 1980-04-03 |
| SE8002505L (en) | 1980-10-05 |
| AU533695B2 (en) | 1983-12-08 |
| JPS55164483A (en) | 1980-12-22 |
| SE458181B (en) | 1989-03-06 |
| DE3012734C2 (en) | 1989-03-16 |
| MX151493A (en) | 1984-12-04 |
| ES8104933A1 (en) | 1981-05-16 |
| IT1143129B (en) | 1986-10-22 |
| FR2452997A1 (en) | 1980-10-31 |
| ZA801998B (en) | 1981-04-29 |
| ES8204633A1 (en) | 1982-05-01 |
| FR2452997B1 (en) | 1986-03-07 |
| BR8001997A (en) | 1980-11-25 |
| GB2048494A (en) | 1980-12-10 |
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| MKEX | Expiry |