Pro-Dex v. Intelligent Automation
`U.S. Patent 7,091,683
`Pro-Dex Ex. 1051
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`U.S. Patent
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`Jun, 16,1981
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`Sheet 1 of 6
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`4,273,198
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`TORQUE
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`U.S. Patent
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`Jun. 16, 1981
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`Sheet 2 of 6
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`4,273,198
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`Fig.2
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`U.S. Patent
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`Jun. 16, 1981
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`Sheet 3 of 6
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`4,273,198
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`U.S. Patent
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`Jun. 16, 1981
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`Sheet 4 of6
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`4,273,198
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`Fig. 7
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`MOTORSPEED
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`US. Patent
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`Jun. 16, 1981
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`Sheet 5 of 6
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`4,273,198
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`Fig. 8
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`U.S. Patent
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`Jun. 16, 1981
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`Sheet 6 of 6
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`4,273,198
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`G3AL
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`1
`MOTOR-DRIVEN CLAMPING METHOD AND >
`DEVICE
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`FIG.2isa timing chart of a. torque during the use of
`the tool shown in- FIGS. 1Aand 1B;°
`“FIGS. 3 and5.are circuit diagrams illustrating exam-
`'
`ples of the circuit construction‘of a control part of the
`device embodying this invention;
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`BACKGROUND OF THE INVENTION
`FIG. 4 is a motor torque variation characteristic dia-
`1. Field of the Invention .
`gram;FIG. 6 shows waveforms at respective parts of the
`This invention relates to a motor-driven clamping
`method for drivinga bolt or the like with a constant
`_ Circuit in FIG. 5;
`©
`“FIG. Tisa characteristic diagram showing the torque
`torque.
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`2. Description of the Prior Art.
`shownin FIG.4 in terms of the motor speed;
`Forexample, in the assembling ofan automobile or an
`FIG.8 is an elévation including alongitudinal section
`internal combustion engine, an operation of driving a
`of the tool part; and
`bolt into a workpiece and clamping it for rigidity is
`FIG.9 is a circuit diagram illustrating an example of
`carried out at an extraordinary frequency and is very
`a detailed control part of the device embodying this
`invention.
`laborious; hence,
`it is achieved 'in many cases by an
`automatic clamping tool utilizing compressed air or
`" DESCRIPTION OF THE PREFERRED
`electric power. A motor-driven tool, though usually
`‘EMBODIMENTS
`heavy as compared with a pneumatic tool,
`is easy to
`handle and less noisy, and hence ‘is widely employed.
`With a prior art motor-driven tool,the head of a bolt is
`inserted in a socketof a rotary shaft affixed to the tip of
`the tool and the bolt is rapidly driven into a workpiece
`by. the rotary shaft: (driven via a reduction gear, for
`example, at 500 rpm) with the rotation (for instance,
`5000rpm) of a motor. Whenthe driving operation’ is
`almost complete and:a load on the motorstarts to in-
`crease suddenly, a mechanical ‘clutch between the
`motor and the rotary shaft is disengaged to switch the
`rotaryshaft to a low speed (for example, 5 rpm) and,
`whenit is detected bya torque detectorbuilt in the tool
`thatthe torque applied to the rotary shaft has reached a
`certain value, the motoris stopped; in this manner, the
`bolt is clamped to the workpiece with a constant torque.
`As a.consequence,. the clamping torque can be made
`uniform but the weights of the built-in clutch, the de-
`vice for mechanically detecting the torque to disengage
`the clutch and so forth are added to the weight of the
`motor, so that the total becomes heavy and inconve-
`nient to handle.
`SUMMARY OF THE INVENTION
`An object of this invention isto provide a motor-
`drivenclamping method and device overcoming, the
`above defects of the priorart.
`A motor-driven clamping methodofthis inventionis
`characterized by a.two-step control operation. When a
`torque applied to a member to be clamped reaches a
`first set value smaller than a referenceset value, a drive
`motor is once decelerated and rapidly stopped. The
`drive. motor is then, re-started immediately and con-
`trolled so that the torque applied to the memberto be
`clamped increases along a predetermined torque in-
`creasing characteristic. Thereafter,: when. the torque
`applied to the member to be clamped reached a second
`set value corresponding to the reference value,
`the
`drive motor is braked to be rapidly stopped.
`A handy motor-driven clamping device of light
`weight can be prepared in accordance with the above
`method ofthis invention.
`BRIEF DESCRIPTION OF THE DRAWING
`This invention will be hereinafter described in details
`with reference to the accompanyingdrawing, in which:
`FIGS. 1A and 1B show an external appearance of.a
`tool part of a device embodying this invention and a
`front view ofits rotary shaft;
`
`‘With reference to FIGS. 1A and 1B, reference nu-
`meral 1 indicates a drive motor (having an input of 0.9
`to several kVA,for example); and 2 designates the top
`end portion of the rotary shaft, which has a square
`configuration and is formed to receive and fixedly sup-
`port a socket for engagement with a bolt. This top end
`portion is adapted to move into and out of a case 3.
`within a certain range of stroke. Referencé numeral 4
`identifies a reduction gear portion arid 5 denotes a
`torque. detecting portion for detecting the torque ap-
`plied to a rotary shaft in it. In FIGS. 1A and 1B, only
`one clamping tool is shownbut, in practice, a plurality
`of (for example, twenty) ‘such tools are arranged in
`parallel and their operations and settings and control of
`the clamping torque are effected by a control panel (not
`shown) provided separately of the tools. Reference
`numeral6 represents a connectorofconnecting lines for
`connecting the torque detector and the motor 1 to the
`control panel. The construction of the tool will be de-
`scribed in details with reference to FIG.8.
`Next, the basic operation of this invention will be
`described... As mentioned above,
`the tool shown in
`FIGS. 1A and:1B does not employa clutch used in the
`prior art; therefore, a movable part between the motor
`and the rotary shaft is only reduction gears. This ar-
`rangementis very advantageousin that the tool is made
`small-sized, lightweight, more durable and simple in
`maintenance but, on the other hand,variouscircuits are
`required, since control by the clutch is replaced by
`speed control of the drive motor by electrical circuits.
`FIG. 2 is a timing chart of'a torque whenthe tool
`shownin FIG.1Ais in use. A bolt is driven and tight-
`ened by a two-step operation. The torque applied to the
`rotary shaft of the tool is set to five values, b to e anda,
`d being a reference torque value for.completion oftight-
`ening the bolt. In practice, the bolt to be tightened is
`slightly screwed in a tap:hole (or a nut) of a workpiece
`in advance andthe boltis tightened bya first-step oper-
`ation to an intermediate torque value and-then further
`tightened by a second-step up to a predetermined value.
`Thefive torque values shown in FIG..2 are set- by a
`potentiometer of the control panel and the: motor. 1 is
`started. At this time,
`the rotary’ shaft has no load
`thereon and is driven at.ahigh speed (for example, of
`300 rpm) andits torque has the-small value a, but when
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`the bolt:is seated on the clamped bed, the rotation speed
`of the rotary shaft decreases but its torque incréases
`abruptly. This torque is detected by the torque detector
`3 and whenthe torquereachesthe first-step torque set
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`value b, a reverse current is applied to the drive motor
`1 to stop its rotation rapidly. This reverse current is cut
`off when the torque detector output reachesa first-step
`brake set value c. When the drive motor 1 is thus put
`into a completely or substantially standstill state, the
`second-step operation is immediately started. In a case
`of a plurality of such tools being used, however, the
`second-step operation is started after making sure that
`the rotary shafts of all the tools have finished thefirst-
`step operation, and in a case of only onetool being used,
`the first-step operation is immediately followed by the
`second-step operation. In the second-step, the rotation
`speed and outputof the motorare controlled by feeding
`back thereto the torque detected output so that
`the
`torque of the rotary shaft increases to reach the refer-
`ence clamping torque d along an inclined characteristic
`curve of a present torque increasing angle a. Upon
`detection of the torque value reaching d, a reverse cur-
`rent is applied to the drive motor 1 to stop it rapidly.
`This reverse current is cut off when the torque reaches
`the second-step brake set value e.
`The arrangements of the torque detector, a circuit for
`selectively switching currents on the basis of a compari-
`son between the detector output and the torque set
`values, a sequential circuit and so forth, will be hereinaf-
`ter described except knowncircuits.
`Next, a description will be made of the construction
`and operation of a circuit for achieving the abovesaid
`torque control. Before entering into such a description,
`reference is made to advantagesof the two-step control
`described above. (1) The two-step control of the torque
`value prevents damageto the tool by seating of the bolt
`and ensures to prevent application of an excessive
`torque to the bolt even when the torque of the rotary .
`shaft increases abruptly after seating of the bolt. (2) The
`cutting off of the reverse current is accomplished in
`dependence on the amount of feedback of the torque
`detected value, ensuring smooth disengagement of the
`socket 2 from the bolt to prevent excessive reverse-cur-
`rent braking from loosening the bolt after being tight-
`ened. (3) In the second step, the torque increasing rate
`on the time axis is controlled with the amountof feed-
`back of the torque valueitself; this ensures to provide
`constant clamping conditionsat all times. (4) Since the
`torque value can easily be switched from the final
`clamping speed (proportional to a) or a high-speed to a
`low-speed operation, optimum clamping is possible
`according to use. According to an experiment con-
`ducted on the tool of FIG. 1A,in the case of a=45° the
`time required for tightening a bolt was about 2.5 sec.
`after seating of the bolt and,in this case, the number of
`rotations of the rotary shaft was 10 before seating of the
`bolt.
`FIGS. 3 to 5 are diagrams showing the circuit con-
`struction of the principal part of a motor output control
`panel using the torque detector output and explanatory
`of its operation. In FIGS, 3 to 5, each reference charac-
`ter IC indicates an operational amplifier. FIG. 3 illus-
`trates a setting circuit for providing the torque charac-
`teristic in the second step with a gradient of a. In FIG.
`3, a set voltage Vs for the reference torque d is applied
`to the input of an operational amplifier IC;. If a transis-
`tor T; is arranged so that it is switched from the ON
`state to the OFF state when the bolt is seated and the
`second step operation is started (This arrangement can
`easily be achieved by comparing the output voltage of
`the detector for detecting the torque applied to the
`rotary shaft of the tool with a voltage corresponding to
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`a set torque, for example, by means of a comparator or
`the like to detect that the both voltages are equal to
`each other.), when the transistor T) is in the OFFstate,
`a capacitor C; is charged in accordance with time con-
`stants of Ri and C, and the charged voltage is amplified
`by an operational amplifier IC2, whose output E; varies
`as indicated by E) in FIG. 4. This characteristic is to
`provide the torque characteristic of the gradient a in
`the second-step operation. A torque value E7 by the
`detector is inverted by an operational amplifier IC3 in
`polarity, and its output E2 and the output E; from the
`operational amplifier [C2 are respectively subtracted by
`resistors R2 and R3 and amplified by an operational
`amplifier IC4. If the output from the operational ampli-
`fier [C4 is positive (if E; > E7), an input voltage E3 to an
`operational amplifier IC¢ of the next stage is prevented
`by diodes D; and D2 from being affected by the output
`from the operational amplifier IC, but, if the output
`from the operational amplifier IC, is negative (if E}-
`>E7), the input voltage E3 drops in proportion to the
`magnitude of this output. In other words, as shown in
`FIG. 4, when the output Ev-.exceeds the value of the
`output E1, the input voltage E3 is lowered by — AE,
`with the result that the output Ey is made to approach
`the output E;. The reason for this is that an output
`voltage E4 from the amplifier IC¢, in which the output
`E; is amplified, controls the output (torque) of the
`motor 1 in the following manner.
`FIG. 5 shows an example of the construction of a
`circuit for controlling the motor speed with the control
`voltage E4, and FIG. 6 shows waveforms appearing in
`various parts of the circuit. In FIG. 5, reference charac-
`ter Tyo indicates a commercial power source trans-
`formerandoneportion of the output from its secondary
`winding is full-wave rectified to produce a voltage Es
`for synchronization use. The waveform of the voltage
`Es is depicted in FIG. 6. From this voltage Es, an out-
`put voltage Es from an operational amplifier ICs is
`transformed into such a sawtooth wave as shownin
`FIG.6 in accordance with a time constant by a resistor
`R4and a capacitor C2. A voltage obtained by adding the
`abovesaid voltage E4 to the voltage Eg is applied via a
`voltage-follower operational amplifier IC7 and a transis-
`tor T2 to an oscillator made up of a unijunction transis-
`tor T3and a transistor Tq andis used as a trigger voltage
`synchronized with the power source of the oscillator.
`Its output voltage E7 becomes an oscillation voltage
`which occurs only during a phase angle ao, as depicted
`in FIG.6. It is evident that the phase angle ag is propor-
`tional to the voltage Es. The output voltage E7 is pro-
`vided to a transformer T,: and the resulting rectified
`voltages are applied to trigger electrodes of thyristors
`S, and S2, so that the waveform ofa voltage Eg supplied
`to a motor M ofthe tool from each thyristor becomes a
`waveform of the same phase as the voltage E4 and the
`output from the motor M increases in proportion to ao.
`Since the voltage E4 is proportional to the voltage E}, it
`mayalso be considered that ao is proportional to ag and
`that ag=a.
`In short, the operations of the circuits of FIGS. 3 and
`5 are to producefirst an ideal waveform E, close to the
`secondstep torque increasing characteristic in FIG. 2
`and to control the motor M in such a mannerthat the
`torque value increase along the characteristic E,. This
`can be achieved as described above.If full-waverectifi-
`cation takes place when ao is 180°, it is necessary that
`the motor M can yield an output larger than the set
`torque value d. After seating of the bolt,
`the torque
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`usually reaches the set value with the small angle ag;
`it can be considered from the above principle of this
`therefore, if the E) increasing characteristic. (FIG.4)is
`invention that decision circuits for the upper or lower
`assumed suchthat the set value of the reference clamp-
`limits and the indication lamps may be unnecessary.
`ing torque d is close to the upperlimit of the charging
`However, these monitoring means are provided to de-
`characteristic of the RC time constantcircuit, there is
`tect rare falts or erroneous operations of constructive
`obtained a reference curve in which the torque increas-
`elements in the above embodimentofthis invention.-
`ing rate is reduced as the set value is approached.If a
`Ashas been described in detail in the foregoing, since
`torque exceeding the reference curve occurs,it is equiv-
`the present invention eliminates the use of a mechanical
`alent
`to a negative feedback of the torque detected
`clutch which has posed problemsin the art, the drive
`value Evitself, making the torque increasing character-
`unit becomes small and lightweight and, further, the
`istic approach to the E characteristic, as set forth previ-
`advantages of the two-step control can be obtained. On
`ously.
`top of that, as the low-speed rotation of the motorafter
`Asdescribed above, in the present invention all con-
`seating ofa bolt can be electrically adjusted at will, the
`trol operations are accomplished by the feedback of
`bolt can be tightened in a short time comparableto that
`torque values but, as a result, the numberof rotation
`obtainable with a pneumatic tool. Moreover, reversible
`(speed) of the motor1 of the motor-driven tool is con-
`rotation of the:motoris also possible. Accordingly, this
`trolled. FIG. 7 is a-motor speed characteristic rede-
`invention is of particular utility when employed -in a
`scribed from the torque characteristic shown in FIG.2.
`case of using a large numberof tools in gangedrelation-
`When the torque becomesclose to the set value d in the
`ship.
`WhatI claim is:
`second step, the number of rotations of the motor 1 is
`made very small; therefore, the motor 1 can be accu-
`1. A motor-driven clamping method comprising the
`rately stopped at the reference torque value d.
`steps of:
`With reference to FIG. 8, the tool structure of an
`once decelerating and rapidly stopping a drive motor
`embodimentof this invention comprises a DC motor A,
`whena torque applied to a memberto be clamped
`a shaft B of the DC motor A having a gear B’ at the top
`reachesa first set value smaller than a reference set
`portion, and a planetary gear C engaged with the gear
`value; :
`B’ of the shaft B and an internal gear E formed on the
`re-starting immediately and controlling the drive
`inner wall of a case F. The revolution of the planetary
`motor so that the torque applied to the memberto
`gear C is transferred to a pinion gear G through a pin D.
`be clampedincreases along a predetermined torque
`Therotation of the pinion gear G is transferred to plan-
`increasing characteristic; and
`etary gears H, which act revolutions by the internal
`braking the drive motor to be rapidly stopped when:
`gear E. The revolutions of the planetary gears H are
`the torque applied to the memberto be clamped
`transferred through pins J to a drive shaft K for driving
`reaches a second value correspondingto therefer-
`a bolt and nut. As mentioned above, the high speed
`enceset value.
`rotation of the DC motor A is reduced to an optimum
`2. A motor-driven clamping device comprising:
`low speed rotation through the gears B’, C, E,H,etc. to
`a Case;
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`be suitable for driving the bolt and the nut.
`a drive motor seated in the case;
`On a torquetransducerL,a strain gaugeMis fixed by
`a drive shaft rotatably held in the case;
`an adhesive. When the drive shaft K drives the bolt or
`a socketfixedly supported to the top end ofsaid drive
`the nut, the fastening torque raises so that a reaction of
`shaft
`for engagement with a member
`to be
`the fastening torque is applied to the drive shaft K. The
`clamped;
`reaction applied to the drive shaft is transferred to the
`transmission means mechanically transmitting the
`entire part of the tool through the internal gear E to
`high speed rotation of said drive motor to said
`give a torsional momentto the torque transducer L, so
`drive shaft as an optimum low speed rotation;
`that a stress caused by the torsional momentvaries. the
`torque transducer means operatively connected to
`resistance value of the strain gauge M.
`said drive shaft to produce a DC voltage propor-
`Thestrain gauge M formsa bridge circuit G; shown
`tional the fastening torque ofsaid drive shaft;
`in FIG. 9, the output of which is amplified, through a
`first detection means connected to said torque trans-
`connector N,by an operational amplifier IC, to obtain a
`ducer for receiving said DC voltage to produce a
`commoninput voltage Eyofa gate G2 and of the opera-
`first detection output when a torque appliedto said
`tional amplifier IC3. The gate G2 forms an analog mem-
`member to be clamped reaches a first set value’...
`ory circuit, in which the peak output signal of a torque
`smaller than a reference set value;
`:
`transducer charged in a capacitor Cq is held at a stable
`second detection means connected to said torque
`value for a long time period by the use of a FETtransis-
`transducer for receiving said DC voltage to pro-
`tor F, of high impedance and an operational amplifier
`1Cjo.
`duce a second detection output when the torque
`applied to the member to be clamped reaches a
`A potentiometer E; is employedto establish a voltage
`second value corresponding to. said reference. set
`corresponding to an upperlimit of the fastening torque,
`value;
`while a potentiometer E, is employed to establish a
`first control means operatively connected tosaid first
`voltage corresponding to a lowerlimit of the fastening
`detection means and said drive motor for at. once
`torque.
`decelerating and rapidly stopping said drive motor
`The stored signal from the gate G2 is compared with
`in response to said first detection output and for
`these established voltages by comparators ICi; and
`re-starting immediately and controlling the drive
`IC}2, so that lamps L; and L2 are lightened by transis-
`motor so that the torque applied to the- member to
`tors T5 and Tin accordance with the comparedresults.
`be clamped increases along a predetermined torque
`Moreover,since the IN limit of the fastening torqueis
`increasing characteristic; and -
`detected by a gate G3 so that a lamp L;3of IN limit is
`lightened by a transistor T7.
`second control means operatively connected to said
`second detection means and said drive motor for
`Theprinciple of this invention resides in continuously
`comparing the fastening torque with respective refer-
`braking the drive motor to be rapidly stopped in
`response to said second detection output.
`ence values and in controlling the rotation speed of a
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`DC motorto raise the fastening accuracy. Accordingly,
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