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`Pro-Dex v. Intelligent Automation
`U.S. Patent 7,091,683
`Pro-Dex Ex. 1021
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`U.S. Patent
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`June 20, 1978
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`Sheet 1 of 3
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`4,095,325
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`U.S. Patent
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`June 20,1978
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`Sheet 2 of 3
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`4,095,325
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`U.S. Patent
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`June 20,1978
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`Sheet 3 of 3
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`4,095,325
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`1
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`4,095,325
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`METHOD FOR TIGHTENING BOLTS
`
`BACKGROUNDOF THE INVENTION
`
`2
`Further, the invention provides a method which ena-
`bles the operation to be carried out accurately and
`quickly.
`In order to achieve these objects, the invention ef-
`(a) Field of the Invention
`fects bolt tightening operation in such a mannerthat the
`The present invention relates to a method and a de-
`operation starts with turning the bolt at high speed and
`in course of the operation the rotative speed ofthe bolt
`vice for automatically tightening bolts (or nuts) under
`is switched to a low speed soasto obtaina fixed tighten-
`optimum conditions.
`ing completion condition. Such switching of the rota-
`(b) Description of the Prior Art
`tive speed of a bolt to a low speed in course of the
`Asfor tightening of bolts, the torque method and the
`operation is effective to reduce overrun dueto the iner-
`rotative angle method have heretofore been generally
`known.
`tia force whentherotation of the bolt is to be stoppedat
`the tightening completion point. In addition,if the oper-
`The torque method, which is based on the assumption
`ation is started with low speed rotation, the rotation
`that the axial force on the bolt is proportional to the
`could be stopped accurately at the tightening comple-
`torque required to turn the bolt; is adapted to continu-
`tion point, but this would extremely prolong the opera-
`ously detect the torque so as to control the tightening
`tion time.
`due to the axial force on the bolt.
`Said switching from high to low speed rotation is
`However, the proportional relationship between the
`effected by detection of the torque exerted on the rotary
`axial force on the bolt and the torque considerably
`shaft or detection of the forwardly moved position of
`changes owing to other factors than the bolt such as the
`the bolt or by meansofa timer. In this case, if an electric
`characteristics of the tightening tool and variations in
`(dc) motoris used as a rotative drive source in connec-
`the friction coefficient between the bolt and the member
`tion with detection of the torque, the torque detected
`to be clamped due to deposition of dirt or oil. There-
`can be expressed in termsof an electric current by mak-
`fore, such axial force varies from bolt to bolt and it is
`ing useofthe fact that current is proportional to torque.
`difficult to obtain a predetermined axial force.
`The present invention provides various methods of
`It
`is the above mentioned rotative angle method
`accurately stopping the rotation after the rotative speed
`which has improved the torque method. Thus, it makes
`is switched as described above.
`use of the fact that the amountof elongation of the bolt
`One of the methodsis to turn a bolt through a fixed
`is proportional to the angle through which the bolt is
`angle from the snug point (after which pointthe elonga-
`turned. According to said second method, the bolt is
`tion of the bolt is proportional to the angle through
`turned through a fixed predetermined angle after bolt
`which it is turned). Another is to detect the tightening
`head comesin contact with the tightening bearing sur-
`completion point in terms of torque. In the former
`face of a member to be clamped, in order to reduce
`method, in order to determine the tightening comple-
`variations in the axial force on the bolt proportional to
`tion point more accurately, the snug point is detected
`the elongation of the bolt.
`during low speed rotation. Concrete examples of such
`Even with this method, however, since it is very
`methods will be later described. To be brief,
`in one
`difficult to ascertain whether or not the bolt comesin
`method, the snug point is detected in terms of torque.
`accurate contact with the tightening bearing surface of
`Moreparticularly, a touch point is once detected during
`the memberto be clamped, the usual practice is to de-
`high speed rotation, whereupon some amount ofre-
`tect the time when about4 of the tightening completion
`verse rotation is effected at low speed in consideration
`torque is reached (which is referred to as the snug
`of overrun incidental to high speed rotation and then
`point), followed by further turning ofthe bolt through
`forward rotation is effected at low speed, in course of
`a fixed angle to complete the tightening.
`45
`which the snug point is detected and thenceforth low
`Further, the tightening tools generally used in carry-
`speed rotation throughafixed angle is effected to reach
`ing out said methods comprise a motor to turn a bolt at
`the tightening completion point. In another method,the
`high speed to reduce the tightening operation time.
`switching point from high to low speed rotation is
`With such high speed rotation of the motor, however,
`somewhat short of the touch point. This is made possi-
`evenif a stop signal indicating the completion oftight-
`ble either by setting it by means of a timer or by detect-
`ening is given, the inertia of the motor shaft prevents
`ing a position just short of the touch point, i.e., a posi-
`instantaneous stoppageofthe operation, resulting in the
`tion just prior to the bolt coming in contact with the
`disadvantage of the bolt being over-tightened. In this
`tightening bearing surface, by reference to the for-
`case, the idea might be conceived of giving a stop signal
`wardly movedposition of the bolt.
`to the motora little earlier in consideration of the inertia
`Once the snug point is detected during low speed
`of the motor shaft. Even with such a measure taken,
`rotation in the manner described above, the tightening
`however,it is difficult to obtain the desirable tightening
`completion point can be easily madefixed by low speed
`force, since such error-producing factors as variations
`rotation through a fixed angle from the snug point.
`in the frictional resistance of the tightening bearing
`Further, in the case of a method of detecting the
`surface and in the motor rpm are invloved.
`tightening completion point in terms of torque,
`the
`tightening completion point can be easily made fixed by
`SUMMARYOF THE INVENTION
`incorporating a method of detecting the time when
`switching from high to low speed rotation is made; in
`terms of a torque exerted when the touch point is
`reached.
`Further, the present invention is arranged so that a
`bolt is tightened beyondits yield point according to the
`rotative angle method, whereuponthebolt is turned in
`
`The present invention has for its object to provide
`improvements in a method and device for tightening
`bolts.
`Particularly, the invention has for its object to accu-
`rately reproducethe desired bolt tightening completion
`condition.
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`4,095,325
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`3
`the reverse direction througha fixed angle at low speed,
`thereby obtaining the proper tightening force.
`The invention will now be described in more detail
`with reference to concrete examples thereof shown in
`the accompanying drawings.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a block diagram showing the outline of a
`device according to the present invention,
`FIG. 2 is a schematic side view of the device;
`FIG.3 is a more detailed side view showing the prin-
`cipal portions of the present device;
`FIG.4 is a front view taken in the direction ofthe line
`IV—IV of FIG.3,
`FIG. 5 is an output vs. time graph showing some
`control characteristics of the bolt tightening method of
`the present invention;
`FIG.6 is an output vs. time graph showing other
`control characteristics of the bolt tightening method of
`the present invention;
`FIG.7 is an outputvs. time graph showingstill other
`control characteristics of the bolt tightening method of
`the present invention;
`FIG.8 is a stress vs. strain graph showing another
`control method in the bolt tightening method of the
`present invention; and
`FIG.9 is a graph in which the relationship shownin
`FIG.8 is shownas the stress corresponding to the angle
`through which the bolt is turned.
`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`
`4
`neously restore the speed change unit C to the high
`speed side.
`Tightening of another bolt may be effected by repeat-
`ing the operation described above.
`From the above description, it will be understood
`that bolts can be tightened with the proper tightening
`force at all times.
`FIGS.3 and 4 illustrate a concrete example ofa tight-
`ening device, wherein 1 designates a motor; 2,
`the
`motorshaft; and 3 designates a slitted disc fixed to said
`motor shaft 2. In this concrete example, the rotative
`angle detector is in the form of an optical encoder 4
`comprising a rotative angle detecting section consti-
`tuted by a set of a light emitter 5 and a light receiving
`element 6 opposed to each other and disposed on either
`side ofthe slitted disc 3, which is provided with angu-
`larly equispacedslits 7, the arrangement being such that
`a ray of light from the light emitter 5 disposed on one
`side of the slitted disc 3 is received by the light receiv-
`ing element 6 disposed on the other side of the slitted
`disc 3. Therefore, when the slitted disc 3 is rotated, a
`ray oflight emitted from the light emitter 5 toward the
`light receiving element 6 is intermittently received by
`the latter. The output signal from the light receiving
`element 6 is processed through an amplifier circuit, a
`shaping circuit, etc. to provide a pulse signal, which is
`then plus-minus discriminated by a plus-minus discrimi-
`nating circuit and counted by a counter to indicate the
`rotative angle.
`Further, in the above concrete example, the torque
`detector is arranged in the following manner.
`A de motoris used as the motor 1. The dc motor has
`a characteristic such that its current is proportional to
`its torque. By making use of this characteristic,
`the
`torque is detected by detecting the current.
`In addition, the use of an ac series-wound commuta-
`tor motor instead of said dc motor also enables similar
`torque detection.
`The bolt tightening machine in the above concrete
`example makes torque detection by the current through
`the motor 1 in such a manner that when the torque
`reaches about 4 ofthe tightening completion torque (or
`the snug point ), the voltage across the motor 1 is re-
`duced to reduce the rpm, while the optical encoder 4
`counts the numberof pulses until a value corresponding
`to a predetermined angle is reached, whereupon the
`rotation of the motor1 is stopped. Since rotative speed
`of the tightening machinejust prior to the stoppage has
`been reduced to about 10 rmp,instantaneous stoppageis
`First of all, the front end of the bolt I is lightly
`50
`achieved without overrun due to inertia force, so that
`screwedinto a bolt hole in the member H by hand and
`bolt tightening with high accuracy is assured. In addi-
`the spanner headGis then fitted over the bolt head. In
`tion, in FIG. 3, 8 designates a socket box.
`this case, if the spanner head G has the function of
`Instead of the optical encoder 4 in the above concrete
`firmly gripping the bolt head when simply fitted over
`example, Sony Magnescale (trade name) or other suit-
`the bolt head, then there is no need to manually acrew
`the bolt into the bolt hole in the member H in advance.
`able rotative angle detectors may be used.
`In the above concrete example,
`in order to more
`The spanner head G thusfitted over the bolt headis
`accurately determine the axial force on the bolt upon
`then rotated at high speed by the motor A to screw the
`bolt into the bolt hole in the member H, and when the
`completion of bolt tightening operation,it is desirable to
`detect the snug point during low speed rotation. To
`magnitudeof the torque reaches a predetermined value,
`realize this, the following methods are advisable.
`this is detected by the torque detector E, which causes
`One of the methods is by rotating the bolt at high
`the control section D2 to give instructions to the speed
`speed until a point of time for touch is reached, where-
`change unit C to change the speed from high to low
`uponthe bolt is slightly rotated in the reverse direction,
`value, so that the speed change unit C is rotated at low
`followed by rotation in the forward direction at low
`speed, the angle through which the motoris rotated at
`speed during which the bolt is allowed to pass by the
`this low speed being detected by the rotative angle
`snug point. The bolt is rotated at low speed through a
`detector F. When a predetermined rotative angle is
`fixed angle from the snug point, to complete the tighten-
`reached, the detector F gives the control sections Di
`and D2 instructions to stop the motor A and simulta-
`ing operation.
`
`According to the present invention, as shown in
`FIGS. 1 and 2, the motor A of a tightening machine
`rotating at high speed and a speed change unit C con-
`nected directly to the rotary shaft B of said motor A are
`given control instructions by control sections Di and
`D2 in accordance with output signals from a torque
`detector E and rotative angle detector F so asto effect
`bolt tightening operation on the basis of the rotative
`angle method. Connected directly to the motor output
`shaft B are the speed change unit C, torque detector E,
`rotative angle detector F and spanner head G.
`In FIG. 2, H designates a member to be clamped
`(plate or the like) and I designates a bolt.
`Bolt tightening operation by the above described
`tightening machineis carried out in the following man-
`ner.
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`Bythe point oftime for touch is meant a point of time
`rpm with time are as shownbyb; and the mannerofthe
`whenthe bolt head comesin contact with the tightening
`rotative angle detector counting the numberofpulses is
`bearing surface of the member to be clamped.
`shownby c. Further, a point B on the curvea indicates
`Changes in torque T with time in the above method
`the tightening completion point. The value of torque
`are as shown by a curvee in FIG. 5, wherein a point Al
`TO at the snug pointA is set to about 4 ofthe tightening
`designates the point of time for touch; a point A2, the
`completion torque.
`snug point; and a point B designatesthe tightening com-
`In the methods described so far, the rotation to be
`pletion point. Detection of the point A1 is effected by a
`imparted to the bolt is at high speedin thefirst stage and
`torque detector. Thus, the torque which will be exerted
`slowed down in the middle stage and after the snug
`whenthe bolt head comesin contact with the tightening
`point is reached the rotative angle method is employed
`bearing surface of the member to be clamped is prede-
`to impart a tightening force with high accuracy to the
`termined. The bolt is screwed into the bolt hole in the
`bolt. The present invention, however, may also be em-
`member at high speed, and when the torque exerted
`bodied in the following manner.
`becomesequal to said present torque, the rotation of the
`Switching from high to low speedis effected at the
`motor is stopped. The torque at the point A1is indi-
`touch point, and the tightening completion point is set
`cated at TO in FIG. 5. When the torque detector de-
`in terms of torque. In the case where an electric motor
`tects said TO,a pulse signal /-1 is emitted, whereby the
`is used, the detection of torqueis effected by detecting
`rotation of the motor is stopped. When the rotation of
`motor current with a detector by making useofthe fact
`the motoris completely stopped, the motoris rotated in
`that torque and current are in correspondencerelation-
`the reverse direction. In a region m from the start of the
`ship, as described above. It is, of course, possible to
`bolt tightening operation to the point Al, the motoris
`directly detect torque, but in that case, a torque detector
`is required. As compared therewith, the detection of
`rotated at high speed as shown at g-1. The emission of
`the pulse signal /-1 stops the rotation of the motor, but
`torque in terms of current has the advantage that there
`at this time, since the motor has inertia dueto its high
`is no need to provide such torque detector, as described
`25
`above.
`speed rotation, it is rotatedalittle too much beforeit is
`stopped. As a result, the torque exceeds the point A1.
`FIG. 7 shows changes in the motor current and rpm
`The motoris then rotated in the reverse direction at low
`in the above described method.In this Figure, a point A
`speed g-2 in a region P. This reverse rotation reduces
`designates the touch point and a point B designates the
`the torque and the motoris stopped in the vicinity of
`tightening completion point.
`TO andis then rotated in the forward direction at low
`The points A and B are set in the manner described
`above.
`speed g-3 through a region x. In this case, after detec-
`tion of the point A1, the start and stoppage of the re-
`Another methodoftightening bolts according to the
`verse rotation and the start and stoppage of the low
`present invention will now be described.
`speed forward rotation may be present byatimer or the
`In this method, the bolt is further tightened from the
`35
`like. Further, the amount of reverse rotation may be
`yield point until a region is reached where the tighten-
`detected by utilizing an angle detector so as to find the
`ing force is no longer proportional to the elongation of
`excess angle beyond the point A1, and this excess angle
`the bolt, whereupon the bolt is turned through a fixed
`alone or plus something may be controlled.
`angle in the reverse direction, thereby obtaining the
`During said low speed forward rotation, the snug
`proper tightening force.
`point A2 is detected. This detection is also effected by
`in,e.g.,
`Therelationship betweenstress o andstrain
`the torque detector. That is, the torque T1 at the snug
`a high tensile strength bolt is shown in FIG.8, in which
`point is preset to about 4 of the tightening completion
`a point O on the solid line curveis the so-called touch
`torque. And upon detection of the troque T1, a pulse
`point of the bolt, until which no stress o or strain €
`signal/-2 is emitted, thereby actuating the rotative angle
`appears owing to the absence of sufficient intimacy
`detector. After the point A2 is reached, the boltis tight-
`betweenthe bolt and the memberto be clamped. As the
`ened by an amountcorrespondingto the preset angle to
`bolt is tightened from this point O, the stress o and
`complete the tightening. In this way, tightening with
`strain €
`are increased approximately proportionally
`high accuracy is made possible. Thus, the pulse signal
`until a point P is reached which corresponds to about
`J-2 at the point A2 causes a rotative angle detector, e.g.,
`80% (whichfigure differs according to the place where
`an optical encoder, to begin counting, using pulses such
`the bolt is tightened) of the yied point. The stress o 1 at
`as those shown at /# in FIG. 5, and when the preset
`this point P corresponds to the optimum tightening
`numberofpulses is reached, the rotation of the motoris
`force andit is desirable to stop the tightening.If the bolt
`stopped.
`is further tightened from the yield point Q, the rate of
`The other method of detecting the snug point at low
`increase of stress o* becomesgentle and atlast the maxi-
`speedis illustrated in FIG. 6, wherein the time m for
`mum tensile strength point X is reached where any
`imparting high speed rotation to the bolt is set by a
`further tightening will break the material. Therefore,
`timer. In this case, however,the setting of the time m is
`even after the tightening proceeds to the maximum
`such that switching from high to low speed is effected a
`tensile strength point X, if the stress is brought back
`little short of the snug point A.
`again to o 1 or thereabouts, the tightening becomes
`60
`effective.
`With this arrangement, the snug point A is detected at
`low speed,andif the bolt is turned throughafixed angle
`Thus, the present invention, using the rotative angle
`from the point A by help ofa rotative angle detector,it
`method, is intended to turn the bolt through a fixed
`is possible to ensure that the axial force on thebolt, ie.,
`angle in the reverse direction after the bolt is tightened
`bolt tightening force,
`is equal to the predetermined
`to a region between A and B, to thereby obtain the
`value.
`optimum tightening force. FIG. 9 showsthe principles
`Changes in the torque T with time during the bolt
`of the method, showingtensile stress in (or tightening
`tightening operation according to the above described
`force on) a boit relative to tightening angle. The snug
`method are as shownby a curve a; changes in the motor
`point is detected during high or low speed operation
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`the bolt head to the bearing surface, thereafter slightly
`and the bolt is turned through a fixed angle, but the
`reversing the rotation of said bolt head engaging means
`tightening force varies between points As and Bs owing
`at low speed to reduce the torque over-run ofsaid bolt
`to errors in torque detection or variations in coefficient
`head engaging means and thereafter rotating the bolt
`of friction. If, however, the bolt is turned through a
`head engaging means forwardly at low speed through
`fixed angle from the point As or Ad to be tightened to
`its plastic range, it will reach the point A or B. At the
`the snug point.
`points A and B the increase oftensile stress relative to
`4. A methodfor tightening a bolt in accordance with
`the tightening rotative angle,i.e., the elongation of the
`claim 1, wherein the selected point is just short of the
`bolt is gentle, so that the difference between the tighten-
`snug point, said selected point being predetermined by
`10
`ing forces at these points A andBis small. Therefore, if
`timing means, and thereafter rotating said bolt head
`the bolt is turned back through a fixed angle 8 from the
`engaging means at low speed, said snug point being
`point A or B, a permanentstrain will result, and a tight-
`detected by a predetermined torque value.
`ening force with the same tightening accuracy as at the
`5. A methodfor tightening a bolt in accordance with
`point A orBis obtained with a stress approximating to
`claim 4, wherein electric motor meansare used to rotate
`15
`the optimum stress o 1.
`said bolt head engaging means and the snug point is
`Weclaim:
`detected in terms of the motorcurrent or voltage value.
`1. A methodfor tightening a bolt to a memberto be
`6. A methodfor tightening a bolt to a member to be
`clamped comprising applying rotatable bolt head en-
`clamped comprising applying an electric motor actu-
`gaging meansto the head ofthe bolt, rotating the bolt
`ated rotatable bolt head engaging means to the head of
`head engaging means at a high speed for a period of
`the bolt, rotating the bolt head engaging meansat high
`time sufficient for the bolt head to reach a particular
`speed ofrotation for a period of time sufficient for the
`pointin relation to the bearing surface of the member to
`bolt head to reach a selected point in relation to the
`be clampedthat is not beyond the snug pointof the bolt
`bearing surface of the memberto be clampedthatis not
`head to the bearing surface, reducing the speed of rota-
`beyond the snug point of the bolt head to the bearing
`tion of the bolt head engaging means whensaid particu-
`surface, changing the motor current or voltage value of
`lar point has been reached to a low speed, continuing
`the electric motor actuating th bolt head engaging
`the rate of rotation of the bolt head engaging means at
`means when the selected point has been reached to
`a low rate of speed from said particular point until said
`switch from a high rotational speed to a low rotational
`bolt is tightened beyond the yield point thereon and
`speed, thereafter continuing the rate of rotation ofbolt
`thereafter rotating said bolt head engaging means in a
`head engaging meansat a low rate of speed from said
`reverse direction at said low rate of speed through a
`selected point until the tightening completion point of
`fixed angle to obtain the proper tightening force.
`the bolt has been reached.
`2. A methodfor tightening a bolt in accordance with
`7. A methodfor tightening a bolt in accordance with
`claim 1, wherein the rate of rotation of the bolt head
`claim 6, wherein the tightening completion point is
`engaging means is continued at a high speed until the
`given by the current or voltage value.
`bolt head reaches the touch point with respect to the
`8. A method for tightening a bolt in accordance with
`bearing surface of the member to be clamped and the
`claim 6, wherein the selected point is short of the snut
`rate of rotation is thereafter continued at a low speed
`point.
`from said touch point.
`9, A methodfor tightening a bolt in accordance with
`3. A methodfor tightening a bolt in accordance with
`claim 6, wherein the selected point is the snug point.
`claim 1, wherein the rate of rotation is continued at a
`*
`*
`*
`*»
`*
`high speed until the bolt head reaches the snug point of
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