Pro-Dex v. Intelligent Automation
`U.S. Patent 7,091,683
`Pro-Dex Ex. 1054
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`- 1 -
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`

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`US. Patent=Mar. 20, 1990 Sheet1 of 4 4,908,926
`
`FIG1
` GrarD-
`
`
`
`' S
`
`iS
`TART SIGNAL
`PRESENT ?
`
`YES
`TURN ON
`SOLENOID
`
`TART MOTOR
`SLOWLY
`
`ROTATE OUTPUT SHAFT
`WITH LOWER TORQUE
`AT HIGHER SPEED
`
`iS
`SWITCHING TORQ
`REACHED ?
`
`STOP MOTOR
`
`TURN OFF
`
`WITHMEDIUM.TORGUE
`AT MeBiun SPEED
`
`I
`SNUG TORQUE
`REACHED ?
`
`YES
`
`SOLENOIDnee
`STOP MOTORi"
`TORQUE REACHED ?;
`
`ROTATE OUTPUT SHAFT
`WITH HIGHER TORQUE
`AT LOWER SPEED
`
`|
`:
`TIGHTENING
`
`YES
`
`|
`
`STOP MOTOR
`
`ISSUE OK OR NG
`TIGHTENING
`TORQUE SIGNA
`
`END
`
`DISPLAY °
`TIGHTENING
`“TORQUE
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`- 2 -
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`U.S. Patent
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`Mar. 20, 1990
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`Sheet 2 of 4
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`4,908,926
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`- 3 -
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`THREE
`STAGES
`
`
`LOWER
`MEDIUM
`
`VOLTAGE
`VOLTAGE
`
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`
`
`
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`FINAL
`TORQUE TF
`
`TWO
`STAGES
`HIGHER
`VOLTAGE
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`NUMBER OF SPEED
`REDUCTION STAGE
`VOLTAGE APPLIED
`TO MOTOR
`
`Ic
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`TIGHTENING
`TORQUE
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`US. Patent—Mar. 20, 1990 - Sheet 3of 4 4,908,926
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`FIG.3
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`
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` SWITCHING
`
`SNUG
`
`TORQUE To
`TORQUE Tg
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`
`
`
`
` HIGHER
`
`
`ROTATIONAL
`SPEED Nw
`
`
`
`MEDIUM
`ROTATIONAL
`SPEED Nu
`
`OQUTPUT SHAFT
`ROTATIONAL
`SPEED
`
`
`
`
`
`LOWER
`ROTATIONAL
`SPEED NL
`
`SLOW-START
`ROTATIONAL
`SPEED Ns
`
`.
`
`TIME
`
`t
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`- 4 -
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`

`US. Patent
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`Sheet4 of4
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`4,908,926
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`Mar. 20, 1990
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`1
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`METHOD OF AND APPARATUS FOR
`CONTROLLING NUT RUNNER
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`4,908,926
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`2
`applied earlier to change the motor speed from the
`higher speed to the lower speed in order to avoid an
`excessive tightening of the fastener. Then, the motor
`speed may be switched to the lower speed too early
`because of a measured motor current, a motor speed
`fluctuation, or the like, with the result that the fastener
`may betightened at the lower speed for a certain period
`of time beforeit is seated, and the total tightening time
`required may be prolonged.
`it is necessary to
`To prevent the above problems,
`lowerthe rotational speed of the nut runneroutput shaft
`to reducethe inertial force thereof whenthe rotational
`speed is high. Typically, the rotational speed of the
`output shaft is reduced to about 300 rpm. Therefore,
`efforts to reduce the total tightening time are limited.
`U.S. Pat. No. 3,965,778 discloses a procedure for
`reliably switching the rotational speed of the output
`shaft ofa nut runner from a higher speed to a lower
`speed. According to the disclosed process, when a pre-
`scribed tightening torque is detected at a snug point
`immediately before a bolt or the like is seated on a sur-
`face, the motor is de-energized to stop the rotation of
`the output shaft so as to maintain an output shaft torque
`corresponding to a fastener seating torque.
`However,since a torque increase from the tightening
`torque at the snug pointto a final tightening torque is
`extremely abrupt, a certain response delay may never-
`theless occur and the fastener maystill be excessively
`tightened when the output shaft is stopped at the final
`tightening torque level.
`SUMMARYOF THE INVENTION
`
`It is an object of the present invention to provide a
`method of and an apparatus for controlling a nut runner
`by detecting a tightening torque of the output shaft of
`the nut runner, switching the rotational speed of the
`output shaft between three speed stages,i.e., higher, or
`predetermined speed medium, and lower speedsorfirst,
`second, and third speeds, temporarily stopping the out-
`put shaft upon speed switching to eliminate adverse
`effects of a response delay and an inertial force of the
`output shaft, and increasing the higher rotational speed
`to shorten a time required to tighten a fastener.
`To achieve the above object, there is provided a
`method of controlling a nut runner for tightening a
`fastener, including the following steps of: rotating an
`output shaft of the nut runner with a lower predeter-
`mined torque at a higher, predetermined speed; detect-
`ing a tightening torque of the output shaft, and inter-
`rupting the rotation of the output shaft when the de-
`tected tightening torque reaches a preset switching
`torque immediately before the fastener is seated on a
`surface. Thereafter, the output shaft is rotated with a
`medium torque relative to the lower, predetermined
`torque and at a medium speed relative to the higher,
`predetermined speed followed by; interrupting the rota-
`tion of the output shaft when the detected tightening
`torque reaches a preset snug torque whenthefasteneris
`seated on the surface. Finally, the output shaft is rotated
`with a higher torque relative to the lower, predeter-
`mined torque and at a lower speed relative to the
`higher, predetermined speed; and the rotation of the
`output shaft is stopped when the detected tightening
`torque reachesa preset final torque whenthefasteneris
`completely tightened. The lower, medium and higher
`torque, identified above and subsequently, may also be
`described as a first, second and third torque, respec-
`
`5
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`10
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`_
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`30
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`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`The present invention relates to a method of and an
`apparatus for controlling a nut runner which tighten a
`fastener such as a bolt, a nut, or the like by reducing
`step-wise the rotational speed of the output shaft of the
`nut runner.
`2. Description of the Background
`Nut runners are employedto tighten fasteners such as
`bolts, nuts, or the like. When tightening such a fastener
`with a nut runner, in order to reduce the time required
`to tighten the fastener, the fasteneris first tightened
`with a low torque andat a high speed until the tighten-
`ing torque reachesa prescribed level from the start of
`tightening the fastener. Then, when the prescribed
`torque level is reached, the fasteneris tightened with a 20
`higher torque at a low speed. Such a two-stage tighten-
`ing process is performed byrotating the output shaft of
`the nut runnerfirst at a higher speed and then at a lower
`speed.
`One knownfastener tightening process of the above 25
`type is disclosed in Japanese Patent Publication No.
`53-3840, for example. In the disclosed process, the fas-
`tener is tightened at a high speed by a nut runner driven
`by a DC motor until a prescribed torque level
`is
`reached.
`The current supplied to the DC motor and the torque
`produced by the DC motor are proportional to each
`other. Therefore, the torque of the DC motor can be
`detected by detecting the value of the current supplied
`thereto. When the torque thus detected of the nut run- 35
`ner output shaft reaches a certain switching torque
`level, the power supply that energizes the DC motoris
`switched from a higher-voltage unit to a lower-voltage
`unit to lower the voltage applied to the DC motor,
`thereby rotating the nut runner output shaft at a lower 40
`speed. Whenthe torque of the nut runner output torque,
`as detected by a separate torque sensor, reaches a pre-
`scribed tightening torque level, the DC motor is de-
`energized completing the tightening process.
`In the above tightening process, the rotational speed 45
`of the motoris switched from a higher speed to a lower
`speed immediately before the fastener, such as a bolt,is
`seated on a surface. Since the tightening torque of the
`output shaft increases abruptly just before the fasteneris
`seated, however, the rotational speed of the motor may 50
`not appropriately be switched from the higher speed to
`the lower speed on account of an error in the motor
`current measured for torque detection, a fluctuation in
`the rotational speed of the motor, a delay in the re-
`sponse to the switching between the motor speeds, an 55
`inertial force of a rotating member such as the output
`shaft, and other factors. If the motor speed is switched
`from the higher speed to the lower speedafter the fas-
`tener is seated, then the tightening torque is increased in
`excess of the desired torque level due to the response 60
`delay in the switching from the higher to the lower
`speed. Particularly, inasmuch as the fastener has been
`tightened at a high speed immediately beforeit is seated,
`the inertial force of the output shaft is large, and the
`fastener tends to be excessively tightened due to such 65
`large inertial force even after a switching signal to
`change the motor speed from the higher speed to the
`lower speed is issued. Such a switching signal may be
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`-4,908,926
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`3
`tively. Similarly, the higher, medium and lower speed,
`identified above and subsequently, may be described as
`a first, second and third speed, respectively.
`The method further includes the step of removing the
`tightening torque from the output shaft when interrupt-
`ing the rotation of the output shaft immediately before
`the fastener is seated on the surface and also when inter-
`tupting the rotation of the output shaft when the fas-
`tener is seated on the surface.
`The method further includes the step of reversing the
`rotation of the output shaft to brake the output shaft to
`remove the tightening torque from the output shaft.
`The snug torque is about 20% ofthefinal torque and
`the switching torque is about 70% of the snug torque.
`The higher speed ranges from 600 rpm to 800 rpm,
`the medium speed ranges from 100 rpm to 200 rpm, and
`the lower speed ranges from 10 rpm to 30 rpm.
`According to the present invention, there is also pro-
`vided an apparatus for controlling a nut runner for
`tightening a fastener, including a motor for rotating an
`output shaft of the nut runner, a speed reducer including
`a switching clutch shiftable selectively in higher and
`lower speed positions for rotating the output shaft in
`respective higher and lower speed ranges and a torque
`sensor for detecting a tightening torque of the output
`shaft. A master controller includes means for presetting
`a switching torque, a snug torque, a final torque, a
`higher speed, a medium speed, and a lower speed. A
`subcontroller includes comparator means for determin-
`ing whether the detected tightening torque reaches
`each of the preset switching, snug, and final torques,
`switching means responsive to a signal from the com-
`parator meansfor rotating the output shaft with a lower
`torque at the higher speed with the switching clutch in
`the higher speed position, interrupting the rotation of
`the output shaft and shifting the switching clutch into
`the lower speed position when the detected tightening
`torque reaches the preset switching torque. Thereafter,
`the output shaft is rotated with a medium torque at the
`medium speed, and interrupts the rotation of the output
`shaft when the detected tightening torque reaches the
`preset snug torque. Finally, the output shaft is rotated
`with a higher torque at the lower speed, and stop the
`rotation of the output shaft when the detected tighten-
`ing torque reaches the preset final torque. Motor driver
`means responsive to an outputsignal from the switching
`means as provided for controlling the motor and the
`output shaft through the speed reducer.
`With the method ofthe present invention, the switch-
`ing torque, the snug torque, and the final torque are
`preset. The output shaft of the nut runneris first rotated
`with the lower torque at the higher speed. The tighten-
`ing torque of the output shaft is detected and compared
`with the switching torque. When the tightening torque
`reaches the switching torque, the lower-torque higher-
`speed rotation of the output shaft is interrupted, and
`thereafter the output shaft is rotated with the medium
`torque at
`the medium speed. When the tightening
`torque reaches the snug torque, the medium-torque
`medium-speed rotation of the output shaft
`is inter-
`rupted, and thereafter the output shaft is rotated with
`the higher torque at the higher speed. Whenthe tighten-
`ing torque reaches the final torque, the higher-torque
`lower-speed rotation of the output shaft is stopped thus
`completing the tightening of the fastener.
`Eachtime the rotational speed of the output shaft is
`to be changed, the rotation of the output shaft is inter-
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`35
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`40
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`65
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`4
`rupted to prevent inertial forces of the output shaft from
`adversely affecting the tightening of the fastener.
`Each time the rotational speed of the output shaft is
`to be changed, the tightening torque is removed from
`the output shaft to relatively reduce an increase in the
`tightening torque from the time immediately before the
`fastener is seated to the time whenthefasteneris seated,
`thereby facilitating the control of the position in which
`the output shaft is stalled.
`The snug torque is about 20% of the final torque and
`said switching torque is about 70% of the snug torque,
`and the higher speed ranges from 600 rpm to 800 rpm,
`the medium speed ranges from 100 rpm to 200 rpm,and
`the lower speed ranges from 10 rpm to 30 rpm. With
`these numerical settings, the time period required for
`tightening the fastener is shortened, and the final tight-
`ening torque is of a desired torquelevel.
`With the control method ofthe present invention, the
`master controller is preset to the switching torque, the
`snug torque,the final torque, the higher speed, the me-
`dium speed, and the lower speed. The output shaft is
`rotated with the lower torque at the higher speed by the
`motor through the speed reducer with the switching
`clutch in the higher speed position. The tightening
`torque detected by the torque sensor is compared with
`the switching torque by the comparator means. When
`the tightening torque reaches the switching torque, the
`rotation of the output shaft is interrupted by the switch-
`ing means through the motor driver means, and the
`switching clutchis shifted into the lower speed position.
`Thereafter, the output shaft is rotated with the medium
`torque at the medium speed by the motor through the
`speed reducer. When the tightening torque reaches the
`snug torque, the rotation of the output shaft is inter-
`rupted by the switching means through the motor
`driver means. Thereafter the outputshaft is rotated with
`the higher torque at the lower speed by the motor
`through the speed reducer. When the tightening torque
`reachesthefinal torque, the rotation of the output shaft
`is stopped by the switching means through the motor
`driver means.
`The above and other objects, features and advantages
`of the present invention will become more apparent
`from the following description when taken in conjunc-
`tion with the accompanying drawings in which a pre-
`ferred embodimentof the present invention is shown by
`wayofillustrative example.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a flowchart of a control sequence of a nut
`runner control method according to the present inven-
`tion;
`FIG. 2 is a block diagram of a nut runner control
`apparatus according to the present invention;
`FIG. 3 is a diagram showing a time vs. tightening
`torque curve and a time vs. rotational speed curve; and
`FIG.4 is a cross-sectional view of a nut runner con-
`trolled by the method and the apparatus of the present
`invention.
`
`DETAILED DESCRIPTION OF THE
`EMBODIMENT
`
`A nut runner X shownin FIG.4is controlled by a nut
`runner control apparatus shown in FIG. 2 in accor-
`dance with a nut runner control method shown in FIG.
`1.
`
`As shownin FIG.2, the control apparatus includes a
`master controller A and a subcontroller B coupled
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`4,908,926
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`When the solenoid 6 is energized, it moves the switch-
`thereto for controlling the nut runner X electrically
`ing clutch 7 into a higher-speed position against the
`connected to the subcontroller B to tighten a fastener
`resiliency of a spring 11 to rotate the output shaft 4 with
`such as a bolt, a nut, or the like.
`a lowertorque at a higher speed through first and third
`The master controller A is set to a slow-start rota-
`planetary gear mechanisms 8, 10 of the speed reducer.
`tional speed Ns, a higher, predetermined rotational
`When the solenoid 6 is de-energized,
`it allows the
`speed Nz, a medium rotational speed Nyy, and a lower
`switching clutch 7 to be shifted into a lower-speed posi-
`rotational speed Nz for controlling the rotational speed
`tion under the bias of the spring 11 for rotating the
`of a motor 1 of the nut runner X, reverse rotational
`output shaft 4 through thefirst, second, and third plane-
`speeds Naw, Naw, Nar correspondingto the rotational
`tary gear mechanisms8, 9, 10 of the speed reducer.
`speeds Nu, Nas, Nz, respectively, for braking or stop-
`Operation of the control apparatus for tightening a
`ping the rotation of the motor 1, a switching torque Tc,
`fastener with the nut runner X will be described below
`a snug torque Ts, and a final torque Tr for selecting the
`with reference to FIGS.1, 2, and 4.
`rotational speeds or shutting off the motor 1, and an
`A start signal is applied from the master controller A
`upper limit tightening torque Tay and a lower limit
`to the latch RS1 to set the sameto close the switching
`tightening torque Tz for determining whetherthefinal
`circuit SS8 for energizing the solenoid 6 of the nut
`torque Tris appropriate or not whenthe tightening of
`runner X. The switching clutch 7 of the nut runner X is
`the fastener is completed. The master controller A also
`shifted into the higher-speed position to ready the nut
`displays a tightening torque To of an outputshaft 4 of
`runner X for low-torque high-speed operation in a two-
`the nut runner X.
`stage speed reduction mode achieved by the first and
`The subcontroller B comprises a D/A converter
`third speed planetary gear mechanisms8,10.
`means C for converting the variouspresetdigital signals
`After the switching clutch 7 has been shifted, the
`from the master controller A into corresponding analog
`delay circuit TM closes the switching circuit SS1 to
`signals. A detector means D is connected to a torque
`reset the latch RS1 andto set the latch RS2. When the
`sensor 2 of the nut runner X for applying a signal to and
`25
`switching circuit $S1 is closed, the digital signal repre-
`receiving a signal from the torque sensor 2 to detect the
`senting the preset slow-start rotational speed Ns is con-
`tightening torque To. A comparator meansEis pro-
`verted into an analog voltage signal by the D/A con-
`vided for comparing the detected tightening torque To
`verter C1, and the analog voltage is issued via the inte-
`withthe preset torques Tc, Ts, Tr. A decision means F
`grating circuit IS to the servoamplifier SA, which em-
`is provided for determining whether the final torque Tr
`ploys the applied voltage as a rotation control voltage
`is appropriate or not. A switching means G is respon-
`to control the voltage from a motor power supply
`sive to output signals from the comparator E for se-
`through a feedback control
`loop for smoothly and |
`quentially switching circuits for the preset rotational
`slowly starting to energize the motor 1. Then, upon
`speeds Ns, Nu, Nw, Nz and operating a switching
`elapse of a slow-start time, the delay circuit TM8 opens
`clutch 7 of a speed reducer of the nut runner X. A
`the switching circuit SS1 to stop the slow-start rotation
`motor driver means H having a servoamplifier SA re-
`of the motor 1. An output signal from the latch RS2is
`sponsive to an output signal from the switching unit G
`applied to the delay circuit TM2 which closes the
`is provided for driving the motor 1 to rotate the nut
`switching circuit SS2 at the same time that the slow-
`runner X selectively with a lower torque at a higher
`start rotation of the motor1 is stopped. An analog volt-
`speed, with a medium torque at a medium speed, and
`age converted from the digital signal representing the
`with a higher torque at a lower speed.
`higher rotational speed Naby the D/A converter C2is
`The comparator means E comprises comparators
`applied through the switching circuit SS2 to the servo-
`CS1, CS2, CS3 for comparing analog voltages con-
`amplifier SA, which controls the voltage applied to the
`verted respectively from digital input signals represent-
`motor 1 to rotate the motor 1 with a lower torque at a
`ing the preset torques Tc, Ts, Tr by D/A converters
`higher speed.
`C8, C9, C10 of the D/A converter means C with the
`The outputshaft 4 whichis rotated by the motor with
`measured tightening torque To to determine whether
`the lower torque at the higher speed generatesthe tight-
`the measured tightening torque To has reached the
`ening torque Tg for tightening the fastener. The gener-
`switching torque Tc, the snug torque Ts, and thefinal
`ated tightening torque To is detected by the torque
`torque T,, respectively, latches RS1 through RS7 for
`sensor 2 coupled to the output shaft 4, andits signal is
`switching the comparators CS1, CS2, CS3, and delay
`applied to the detector means D of the subcontroller B.
`circuits TM1 through TM7 for delaying operation
`times.
`The detector means D applies a carrier voltage from an
`oscillator OS through an amplifier AMP to the strain
`The switching means G comprises switching circuits
`gages 12 of the torque sensor 2. Thestrain gages 12 are
`SS1 through SS7 for applying, to the servoamplifier
`connected as a Wheatstone bridge which is kept in
`SA,analog voltages converted respectively from digital
`equilibrium unlessthe tightening torque Tois produced
`input signals representing the preset rotational speeds
`by the output shaft 4. When the tightening torque To is
`Ns, Na, Nat, Nz, Nag, Naw, Nar by D/A Converters
`generated by the output shaft 4, the Wheatstone bridge
`C1 through C7 of the D/A converter means C, a
`is brought out of equilibrium and detects the strain on
`switching circuit SS8 responsive to an output signal
`the output shaft 4. A signal representing the strain is
`from the comparator CS1 for applying an outputsignal
`applied from the torque sensor 2 to a synchronous de-
`to a solenoid. 6 of the nut runner X to operate the
`tector SY through an amplifier AMP. The. carrier of an
`switching clutch of the nut runner X, and an integrating
`output signal from the synchronous detector SY is cut
`circuit IS for starting the nut runner X slowly.
`off by a filter FT. The detector means D now produces
`The nut runner X shown in FIG.4 is driven by the
`a voltage signal representing the tightening torque To.
`motor 1 which has a pulse transmitter 5 (FIG. 2). The
`The detector means D applies the tightening torque
`torque sensor 2 having strain gages 12 is associated with
`voltage to the comparator means E. The tightening
`the output shaft 4 for issuing a signal indicative of the
`torque voltage from the detector meansDis applied to
`detected tightening torque Tg to the detector means D.
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`The maximum level of the tightening torque To de-
`the comparator CS1 for comparison with the analog
`tected by the torque sensor 2 is held by a peak hold
`voltage converted from the digital switching torque Tc.
`circuit PS of the decision means F. The analog voltage
`Whenthe tightening torque To reaches the switching
`indicative of the maximum tightening torque level is
`torque Tc, the latch circuit RS2 is reset and the switch-
`converted by an A/D converter into a digital voltage
`ing circuit SS2 is opened, and thelatch circuit RSS is set
`whichis then displayed as a digital value on a tightening
`and the switching circuit SS5 is closed. At this time, an
`torque display (not shown) in the master controller A.
`inverted voltage of the reverse rotational speed Nazis
`The peak hold circuit PS is initially reset by the start
`applied via the switching circuit SS5 to the servoampli-
`signal applied thereto through the latch RS1. The out-
`fier SA to forcibly reversing the motor 1 to quickly
`put signal from the peak hold circuit PS is also applied
`brakeorstop the rotation of the motor 1. The period of 10
`to a window comparator WC which compares the max-
`time for which the switching circuit SS5 is closed, i.e.,
`imum tightening torque level with the upperlimit tight-
`the rotation of the motor 1 is stopped, is preset in the
`ening torque T4y and the lowerlimit tightening torque
`delay circuit TM3. After elapse of this period of time,
`Tat which are supplied from the master controller A.If
`the switching circuit SS5 is opened and thelatch circuit
`the maximum tightening torquefalls between the upper
`RSSis reset. The output signal from the comparator
`and lowerlimit tightening torques Tau, Taz, then the
`CS1is also applied to open the switching circuit SS8 to
`window comparator WC applies an OK signal to the
`de-energize the solenoid 6 of the nut runner X,retract-
`master controller A. If the maximum tightening torque
`ing the speed reducerof the switching clutch 7 from the
`falls outside the range between the upper and lower
`higher-speed position.
`limit tightening torques Tay, Taz, then the window
`Since the switching clutch 7 is urged toward the
`‘comparator WC applies an NG signal to the master
`lower-speed position by the spring 11, the switching
`controller A. The decision means F thus determines
`clutch 7 is automatically shifted into the lower-speed
`whether the tightening torque is appropriate or not.
`position, and now the output shaft 4 can be rotated with
`A pulsed output signal from the pulse transmitter 5
`a medium torque at a medium speed or with a higher
`associated with the motor 1 is converted into a voltage.
`torque at a lower speed in a three-stage speed reduction
`by a pulse-to-voltage converter PC. The voltage is fed
`mode achieved by thefirst through three planetary gear
`back to the servoamplifier SA for controlling the rota-
`mechanisms8, 9, 10.
`tion control voltage from the switching means G to
`The output signal from the comparator CS1is also
`energize the motor at. a selected one of the rotational
`supplied to set the latch RS3 to energize the delaycir-
`speeds and producea selected one of the torques.
`cuit TM4. After elapse of the shutdown time of the
`In order to set the final torque Tr to an appropriate
`motor 1, the delay circuit TM4 closes the switching
`torque level, performing a tightening procedure effi-
`circuit SS3 to allow the analog voltage representing the
`ciently, and prevent excessive tighteningof the fastener,
`medium rotational speed Naz from the D/A converter
`the fastener is tightened with a lower, predetermined
`C3 to be applied via the switching circuit SS3 to the
`torque at a higher, predetermined speed immediately
`servoamplifier SA. The servoamplifier SA then con-
`before the fastener is seated on a surface since the tight-
`trols the voltage applied to the motor 1 to rotate the
`ening torque is not large, and when the tightening
`output shaft 4 with the medium torque at the medium
`torque reaches the preset switching torque Tc, the nut
`speed.
`runner output shaft is temporarily stopped. Then, the
`When the tightening torque Top detected by the
`fastener is tightened again with a medium torque at a
`torque sensor 2 reaches the snug torque Ts, a signal
`medium speed so that it
`is seated with the medium
`indicative of the tightening torque Tog is supplied from
`torque relative to the lower, predetermined torque and
`the detector means D and issued from the comparator
`at the medium speed relative to the higher, predeter-
`CS2. The output signal from the comparator CS2 resets
`mined speed. When the tightening torque reaches the
`the latch RS3 and opens the switching circuit SS3, and
`at the same time sets the latch RS6 and closes the
`preset snug torque Ts, the nut runner output shaft. is
`stopped again, after which the fastener is tightened
`switching circuit SS6. The medium-torque medium-
`again with a higher torque relative to the lower, prede-
`speed rotation of the motor 1 is now discontinued, and
`termined torque and at a higher speed relative to the
`upon elapse of a preset period of time, the switching
`higher, predetermined speed until the tightening torque
`circuit SS6 is opened by the delay circuit TMS and the
`latch RS6is reset.
`reaches thefinal torque Tr. The tightening time and the
`tightening condition are good by selecting the snug
`At this time, the output signal from the comparator
`torque Ts to be about 20% of the final torque Tr and
`CSz2sets the latch RS4 andis applied to the delay circuit
`also selecting the preset switching torque Tcto be about
`TM6.After the motor 1 is shut off for the preset period
`70% of the preset snug torque Ts.
`of time, the delay circuit TM6 closes the switching
`FIG. 3 shows a graph having a horizontal axis repre-
`circuit SS4 to enable the motor 1 to rotate the output
`shaft 4 with the higher torque at the lower speed.
`senting time and a vertical axis representing the de-
`Thetightening torque To is increased by the higher-
`tected tightening torque. An upper t-Tocurveindicates
`torque lower-speed rotation of the output shaft 4. When
`how the tightening torque To varies with time, and a
`lower t-N curve shows the manner in which the rota-
`the tightening torque To reaches the final torque Tr, a
`tional speed N of the output shaft 4 varies with time.
`signal indicating the tightening torque To is supplied
`Thet-Tocurve is plotted when the snug torque Ts is
`from the detector means D and issued from the compar-
`20% ofthe final torque Trand the switching torque Tc
`ator CS3 to reset the latch RS4 and opensthe switching
`circuit SS4. Simultaneously, the latch RS7is set and the
`is 70% of the snug torque Ts. With theillustrated t-To
`curve, the fastener such as a bolt is tightened in a high
`switching circuit SS7 is closed to discontinue the high-
`er-torque lower-speed rotation of the output shaft 4.
`speed range from 600 rpm to 800 rpm,preferably from
`700 rpm to 800 rpm, and then abruptly stopped by ap-
`In order not to reverse the motor 1, the switching
`circuit SS7 is opened and the latch RS7is reset by the
`plying an inverted voltage to the motor at the preset
`delay circuit TM uponelapse of a preset period of time.
`switching torque Tc immediately before the fastener is
`
`40
`
`45
`
`50
`
`35
`
`60
`
`65
`
`- 9 -
`
`

`

`4,908,926
`
`10
`
`Whatis claimedis:
`1. A method ofcontrolling a nut runnerfor tightening
`a fastener, comprising the steps of:
`rotating an output shaft of the nut runner with a pre-
`determined first torque at a predetermined first
`speed;
`detecting said predeterminedfirst torque of said out-
`put shaft;
`interrupting the rotating of said output shaft when
`said predetermined first torque reaches a preset
`switching torque immediately before said fastener
`is seated on a surface;
`thereafter, rotating said output shaft with a second
`torque, said second torque being greater thansaid
`predeterminedfirst torque, and at a second speed,
`said second speed being slower than said predeter-
`mined first speed;
`interrupting the rotation of said output shaft when
`said second torque reaches a preset snug torque
`whensaid fastener is seated on the surface;
`thereafter, rotating said output shaft with a third
`torque, said third torque being greater than said
`predeterminedfirst torque and said second torque,
`and at a third speed, said third speed being slower
`than said predeterminedfirst speed and said second
`speed; and
`stopping the rotating of said output shaft when said
`third torque reachesa preset final torque when said
`fastener is completely tightened.
`2. The method according to claim 1, further including
`the step of:
`removing torque from said output shaft when inter-
`rupting the rotation of said output shaft immedi-
`ately before said fastener is seated on the surface
`and also when interrupting the rotation of said
`output shaft when said fastener is seated on the
`surface.
`3. The method accordingto claim 2,further including
`the step of:
`reversing the rotation of said output shaft, thereby
`braking the output shaft, and thereby removing
`torque from said outputshaft.
`4. The method according to claim 1, wherein said
`snug torque is about 20% ofsaid final torque and said
`switching torque is about 70% ofsaid snug torque.
`5. The method according to claim 1, wherein said
`predetermined first speed ranges from 600 rpm to 800
`rpm,said second speed ranges from 100 rpm to 200 rpm,
`and said third speed ranges from 10 rpm to 30 rpm.
`x
`*
`*#
`&
`
`9
`seated. Therefore, the tightening torque is stable just
`before the fasteneris seated. Then, the fasteneris tight-
`ened in a medium speed range from 100 to 200 rpm,and
`the tightening torque is increased up to the preset snug
`torque Ts which is reachedin the fastener seated condi-
`tion. The motor 1 energized again to rotate the output
`shaft 4 in a low speed range from 10 to 30 rpm to tighten
`the fastener, which is abruptly stopped when the preset
`final torque Tr is reached. Since no response delay is
`experienced and the fastener is tightened from the
`stopped position, the tightening torque To, i.e., the final
`torque Ts,is made substantially constant, and hence the
`tightening procedure can easily be supervised. With t