Pro-Dex v. Intelligent Automation
`U.S. Patent 7,091,683
`Pro-Dex Ex. 1046
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`U.S. Patent—Jan. 13, 1981 Sheet 1 of 6 4,244,213
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`TYPICAL
`RETORQUE SIGNAL
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`%6
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`IST POS.
`PEAK
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`wrote LIL
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`PEAK MEMORY 58
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`9
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`INPUT TO POSITIVE
`PEAK MEMORY 58
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`SHIFTER 60 OUTPUT 0
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`—
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`FLIPFLOP. |FLIP FLOP 66 0
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`;
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`(D)
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`NEGATIVE SLOPE DETECTED
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`FJ
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`OUTPUT
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`INVERTER 78
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`SECOND
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`: NEGATIVE VALLEY
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`(E)
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`NEGATIVE PEAK
`MEMORY 80 OUTPUT
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`SECOND POSITIVE
`PEAK MEMORY 90
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`U.S. Patent
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`Jan. 13, 1981
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`Sheet 2 of 6
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`YOLVYEVdIWOD
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`4,244,213
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`U.S. Patent
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`Jan. 13, 1981
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`Sheet 3 of 6
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`30A
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`FIG.4A
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`U.S. Patent
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`Jan. 13,
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`1981
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`U.S. Patent
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`Jan. 13
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`Sheet 5 of 6
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`4244,213
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`TORQUE DISPLAY
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`a
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`tL —— ——
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`—_~————J4
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`BRE AKAWAY
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`FIG.4C
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`U.S. Patent
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`Jan, 13, 1981
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`Sheet 6 of 6
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`Od!
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`4,244,213
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`4,244,213
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`2
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`RETORQUE MEASURING APPARATUS
`
`BACKGROUNDOF THE INVENTION
`
`This invention relates to apparatus for measuring
`torque. More particularly,
`it
`involves apparatus for
`sensing the amount of previously applied torque to a
`fastener.
`Ina variety of manufacturing applications,it is imper-
`ative that the correct amount of torque be applied to a
`fastener. For example, in automotive applications,it is
`necessary to make sure that bolts have been tightened
`within a certain prescribed range of torque in order to
`properly fasten two parts together. It has been common
`procedure for a memberof the quality control depart-
`ment to use a hand torque wrench to approximate the
`prior torque level by viewing the movement of the
`torque indicator just prior to the “give” or breakaway
`of the fastener. Later improvements of such a test in-
`cluded the use of a wrench which would maintain the
`position of the indicator at the maximum torque experi-
`enced.
`Unfortunately, these prior art methodsof sensing the
`applied torque were not very precise and not capable of
`being accurately reproduced from operator to operator.
`Even under ideal conditions the torque sensed was the
`“breakaway” torque which caused further
`relative
`movementof the fastener and not the torque delivered
`to the fastener in the first instance. Undertrue operating
`conditions even this breakaway torque could not be
`accurately sensed because the operator was not capable
`of instantaneously stopping the level of applied torque
`as soon as he noticed the fastener motion.
`OBJECT AND SUMMARY OF THE INVENTION
`
`Therefore, it is the primary object of this invention to
`provide an apparatus for accurately measuring the
`amount of previously applied torque to a fastener.
`The present invention is based upon the discovery
`that the negative valley torque is a more accurate indi-
`cation of the previously applied torque to the fastener.
`This negative valley torque is the minimum torquelevel
`which occurs immediately after the first positive peak
`or breakaway torque level and before the torque level
`begins to again increase with further applied torque. A
`transducer provides an output signal representative of
`the subsequently applied torque to the fastener whichis
`applied until motion of the fastener is obtained. A posi-
`tive peak detector senses the maximum positive output
`of the transducer before the signal decreases. A nega-
`tive peak detector senses the minimum negative output
`signal of the transducer before the signal again in-
`creases. The negative peak detector is energized by a
`switching network upon detection of the negatively
`sloped signal from the transducer. A display device jis
`utilized to provide a visual indication of the output of
`the negative peak detector thereby providing a mea-
`surement which is more closely associated with the
`amountof torque originally applied to the fastener than
`previously known methods.
`Otherfeatures of this invention include the provision
`for additionally displaying the first positive peak signal
`from the transducer representative of the breakaway
`torque and the maximum amount of. torque applied
`during the entire retorquing operation. This latter indi-
`cation insures that an excessive amount of torque has
`not been applied during thetest.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
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`These and other advantages of the present invention
`will become more apparent upon reading the following
`specification and by reference to the drawings in which:
`FIG.1is a perspective view showing the apparatus of
`the present invention in typical use;
`FIG.2 (A-H)is a series of waveforms showing sig-
`nals normally encountered in the circuitry of the pres-
`ent invention;
`FIG. 3 is a block diagram ofthe electrical circuitry of
`the present invention;
`FIG. 4 (A-C)is a detailed schematic of the compo-
`nents shown in block diagram form in FIG.3; and
`FIG.5 is a block diagram along the lines of FIG. 3
`whichillustrates another feature of this invention.
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
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`25
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`40
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`45
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`FIG. 1 illustrates one example of a torque wrench
`testing apparatus which may incorporate the concepts
`of the present invention. Torque wrench 10 includes
`handle 12 on which housing 14 is mounted on interme-
`diate portions thereof. Housing 14 includes an LED
`display 16 which is coupled to internally mounted cir-
`cuitry which will be more fully described later in this
`description. Housing 14 includes an indicator lamp 18, a
`multi-position display selection switch 20, and a reset
`control switch 22. A shaft 24 attached to an opposite
`end of handle 12 includes a cylindrical head 26 atits free
`end. Head 26 includes suitable strain gages or other
`transducers therein for sensing the amount of torque
`applied by wrench 10. A more detailed description of a
`suitable transducer and torque wrench maybe had by
`reference to U.S. Pat. No. 4,125,016 to Lehoczkyet al
`issued Nov.14, 1978, and assigned to the assignee of the
`present invention.
`In a typical application of this apparatus,it is used to
`test the amount of previously applied torque to a fas-
`tener such as bolts 28. Head 26 of torque wrench 10
`includes a suitable socket on its lower end for receiving
`the head of bolt 28. The wrench 10 is then rotated by
`the operatorin the fastening direction until further rota-
`tional movementof bolt 28 is noted. This is commonly
`referred to in the industry as the “breakaway” of the
`fastener under test. FIG. 2A shows a typical torque
`level signal that may be encountered in this retorquing
`operation. The torque level increases with increasingly
`_ applied force by the operator until point 30 at which
`time the fastener begins further rotational movement.
`This point shall be referred to as the breakaway torque
`level.
`Immediately after the breakaway torque,
`the
`torque level sensed decreases to a minimum level 32.
`This point shall be referred to as thevalley torque.It is
`not completely understood why the torque signal will
`decrease even though the operatoris still applying force
`to the wrench 10. However,it is believed that this mo-
`mentary decrease is due to the frictional forces being
`overcome between the bearing surfaces of the fastener
`and the fastened part. After a short period of time, the
`torque signal again increases to a maximum level 34
`until the operator ceases to apply any more force to
`wrench 10. The maximum level 34 will, of course, de-
`pend upon how soon the operator ceases applying fur-
`ther torque after noticing the motion of the fastener.
`Accordingly, there are three torque levels of interest;
`namely, the breakawaytorque 30, the valley torque 32,
`and the maximum torque 34. It is important to realize
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`20
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`3
`4
`that the valley torque level 32 has been discovered to be
`yet allow sensing of slope reversal at the earliest possi-
`a more accurate indication of the originally applied
`ble moment. By comparing FIGS. 2A to 2D,it can be
`torqueto the fastener. This level is shown in FIG. 2A as
`seen that as long as the torque signalis increasing, the
`point 36. Thus,it can be readily appreciated that previ-
`signal inputs to comparator 62 will be unequal. How-
`ous methods of detecting either torque levels 30 or 34
`ever, when the torque signal begins to decrease, the
`did not provide an accurate indication of the previously
`inputs to comparator62 will become equalat the certain
`applied torque to the fastener. Instead, all that can be
`point determined by the level of offset. When coinci-
`ascertained from such a measurementis. that at least a
`dence is detected by comparator 62, it provides an out-
`certain prescribed force has been applied, but even this
`put signal to the set input of an RSflip-flop 66 indicat-
`was hard to consistently verify due to the inherent oper-
`ing detection of a negatively sloped transducer signal.
`ator error factor. In constrast, the apparatusof the pres-
`At the beginning of the retorquing process,flip-flop 66
`ent invention provides a capability of sensing all three
`is reset via switch 22 thereby resulting in a positive
`torque levels.
`.
`voltage level on controlline 56 for coupling transducer
`FIG. 3 showsa functional block diagram ofthe cir-
`signals to peak memory 58. However, whenflip-flop 66
`cuitry of the present invention. A strain gage torque
`is set, control line 56 goes low, thus opening switch 54
`transducer 40 is powered by a regulated power supply
`and preventing any subsequent storage of positive
`42 which supplies the necessary voltagelevels to other
`torque in peak memory 58. Accordingly, the output of
`portionsof the circuitry ‘as well. Plug 44 introduces on
`positive peak memory 58 can be coupled to display
`line power to the power supply 42. Transducer 40 can
`device 16 via switch 20 to display the breakaway torque
`level.
`be a variety of suitable transducers for sensing the
`amount of applied torque. In this embodiment, strain
`Focusing attention now onthe detection ofthe valley
`gages in torque wrench head 26 are connected into a
`torque 32, control line 68 has been in a low state due to
`bridge network which provides a differential signal to
`the initial reset of flip-flop 70 during the beginning of
`amplifier 46 representative of the applied torque.
`the retorquing process in the same mannerasflip-flop
`A zeroing network48 is provided to adjust the output
`66. After the Q output offlip-flop 66 goes low upon
`of amplifier 46 to a zero level when no torqueis being
`detection of a negative going transducer outputsignal,
`applied by wrench 10. Zeroing network 48 may simi-
`the output of OR gate 72 goes low. The low output
`larly take a multiplicity of forms such as a manually
`signal from OR gate 72 is coupled to semiconductor
`zeroing potentiometer, semi-automatic zeroing by the
`switch 74 and to semiconductor switch 76 through
`pushing ofa button switch, or even via a timing circuit
`inverter 78. Inverter 78 produces a high signal for
`based upon prior conditions when the apparatus is used
`switch 76 which turns it on and allows the transducer
`in an automated machine environment. A properly am-
`signal to enter the negative peak memory circuit 80
`plified and zeroed signal from transducer 40 is entered
`upon detection of a negatively sloped transducersignal.
`into a scaling potentiometer 50.
`FIG. 2F showsthe output signal of inverter 78. Con-
`The conditioned transducer outputsignalis then split
`versely, switch 74 assumes a non-conductive state. The
`into five paths, all of which are coupled to node 52. The
`purpose of switch 74is to initially set the input to nega-
`first path is into a semiconductor switching device 54
`tive peak memory 80 at a preselected positive voltage
`controlled by signals on control line 56. With a positive
`level during the reset of the circuit at the beginning of
`voltage or high signal on control line 56, device 54
`the test. When terminals Y and Y’ are shorted atreset,
`conducts and passes signals from node 52 to an input
`the input to negative peak detector80 will be broughtto
`terminal of a positive peak memory 58. The purpose of
`a voltage level of about + V through switch 74 whichis
`peak memory58is to store the breakaway torque level
`conducting at that time. Resistor 83 and capacitor 85
`30 shown in FIG. 2A. A simple peak detection device
`filter some of the switching transients when switch 76 is
`could not differentiate between the breakaway torque
`first turned on. FIG. 2G showsthe output of negative
`45
`signal 30 and the maximum torque level 34. Accord-
`peak memory 80. The value of +Vis not particularly
`ingly, provision is made for detecting a.negative going
`importantas longasit is higher than the normally ex-
`torque signal and turning off or de-energizing switch 54.
`pected negative peak level. As should now beclear to
`A representative example of an input signal to memory.
`one skilled in the art, the less positive transducer signal
`58 is shown in FIG. 2C andits output is shownin FIG.
`values cause the previously stored value to be succes-
`2B.
`sively reduced such thatthefinal output of detector 80
`The output of memory 58 is coupled to a DC level
`is the least positive or most negative value detected
`shifter 60. The output of DC level shifter 60 iscoupled
`when switch 76 is turned on. The minimum level of the
`to a comparator 62 which compares the virgin torque
`torque signal or valley torqueis thusstored in the nega-
`signal on line 64 coupled to node 52 with the adjusted
`tive peak memory 80 which, in turn, can be displayed
`signal from shifter 60. As shownin FIG.2D,theshifter
`on display 16 by moving switch 20 to the appropriate
`contact.
`60 provides a negative offset with respect to the peak
`memory 58 outputsignal. Without the DC levelshifting
`The output of negative peak memory80 is coupled to
`circuit 60, both inputs to comparator 62 would be the
`one input of a comparator 82 through potentiometer 84.
`same, thereby resulting in an indeterminate condition
`It should be noted that negatively sloped signal values
`for comparator 62. While this latter problem could be
`are stored in the memory 80 which will continue to
`solved by reducing (attenuating) one ofthe signals to
`store such signals until comparator 82 senses a positive
`the comparator 62 via a simple voltage dividing net-
`slope on line 86 which is coupled to the virgin trans-
`work, such a solution may make the comparatorsensi-
`ducer output. Potentiometer. 84 establishes the neces-
`tive to ihe level at which the slope reversal of the trans-
`sary offset similar to the DC level shifter 60. A constant
`ducersignal takes place. On the other hand, the DC
`offset which would be provided by such a DC level
`level shifter 60 provides a constant shift of the trans-
`shifter would be advantageous, but it has been found to
`ducer signal to establish the level of offset required to
`be an unnecessary expense andsatisfactory results are
`circumvent inherent noise excursionsof the signal and
`obtainable by the use of a simple potentiometer. In this
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`5:
`embodiment, the gain of memory 80'is adjusted so that
`its output is more positive with réspect to the transducer
`signal on line 86 during its negatively sloping portion.
`Whenthe transducer torque signal on line 86 begins to
`again increase, the signal on lines 86 and 84 become
`substantially equal thereby providing an output signal
`from comparator 82 whichsets flip-flop 70. The high
`output signal on the Q terminalofflip-flop 70 activates
`indicator lamp. 18 via amplifier 88 to provide a visual
`indication that the valley torque has been detected and
`that the operator should cease applying further torque.
`The high signal from flip-flop 70 is also coupled to the
`input of OR gate 72. Thus, the output of OR gate 72
`goes high, thereby reversing the conductivity states of
`switches 74 and 76.
`,
`Ofcourse,it is practically impossible for the operator
`to immediately stop supplying any further torque to
`wrench 10 when valley torque lamp 18 is activated. For
`whatever reasons, an excessive amount of torque may
`be ultimately applied to the fastener. According to an-
`other feature of this invention, the maximum positive
`force applied to the fastener throughout the entire span
`of operation is also detected and displayed. The trans-
`ducer signal from node 52 is coupled to a second posi-
`tive peak memory 90 whichis substantially identical to
`positive peak memory 58. A-semiconductor switch 92 is
`conducting during the entire testing operation except
`for the time at which the valley torque is being de-
`tected. The output of OR gate 72 is coupled to the
`control line 94 of switch 92 such that a low signal on
`line 94 will cause switch 92 to block the entry of the
`transducer signal to memory90. It can be remembered
`that the only time that OR gate 72 has a low output
`signal is during the time of the negative slope of the
`transducersignal. Accordingly, memory 90 detects and
`stores the signal such as signal 34 which is representa-
`tive of.the maximum applied torque during the entire
`span of operation. The output of the second positive
`peak memory 90 is shown in FIG. 2H. The output of
`memory 90 is coupled to display 16 via switch 20 where
`a visual indicationofits output can be displayed by the
`appropriate setting of switch 20.
`the breakaway
`Accordingly,
`it can be seen that
`torque 30, the valley torque 32, and maximum torque 34
`can each beselectively displayed. Trim potentiometers
`96, 98, 100, and resistor 102 are used for scaling the
`signals to make them compatible with display 16 in a
`manner well-knownin theart.
`FIG.4 showsthe details of the functional blocksjust
`described in connection with FIG. 3. The components
`making up these functional blocks are circumscribed by
`dotted lines in FIG. 4. Accordingly,it is believed that a
`detailed description describing the connection of each
`component would be superfluous and unnecessaryfor a
`person skilled in the art to construct the circuit dis-
`closed in detail in FIG.4.
`Briefly amplifier 46 comprises operational amplifier
`1C3 and associated resistors to establish its gain as is
`well-known in the art. The output of amplifier 46 is
`coupled to zeroing network 48 in which the output
`thereof is regulated by potentiometer P1 to provide a
`zero output signal when the torque wrenchis not being
`utilized. The first positive peak detector 58 employs a
`series of components IC5, Q3, Q4, and IC6 whosefunc-
`tion is to store a charge on capacitor C1 representative
`of the first peak in the torque signal without letting the
`capacitor discharge on signals of lesser magnitude. The
`DC level shifter 60 employs integrated circuit
`IC7
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`whose outputis regulated by thesetting of potentiome-
`ter P5 to determine the level of offset. The non-invert-
`ing (+) input of comparator 62 is coupled to the output
`of level shifter 60 whereas the inverting (—) input is
`coupled to the transducersignal via node 52. When the
`signal from shifter 60 exceeds the transducersignal, it
`sets flip-flop 66 which is comprised of two cross-cou-
`pled NOR gates. OR gate 72 is comprised of two diodes
`D2 and D3 which control the activation of switches 74
`and 76 comprised of integrated circuits IC-11C and
`IC-11B, respectively. Negative peak detector 80 em-
`ploys a serial connection of components IC2B,transis-
`tors Q5 and Q6, and IC2C. When the deviceis first
`reset, capacitor C9 is charged to about +V. Upon re-
`ceipt of less positive signals,
`the capacitor C9 dis-
`charges. Accordingly, capacitor C9 maintains the mini-
`mum negative output or valley torque signal 32. The
`inverting (—) input of comparator 82 is coupled to the
`outputof negative peak memory80 through potentiom-
`eter 84. The non-inverting (+) input is coupled to the
`transducer signal via node 52. The ‘gain of the compo-
`nents making up negative peak detector 80 is set to a
`high level so as to provide a positive offset with respect
`to the transducer signal. Accordingly, when the trans-
`ducer signal becomes morepositive with respect to the
`negative peak signal comparator 82 will provide an
`output which is coupled to flip-flop 70 comprised of
`two cross-coupled NORgates. An output from flip-flop
`70 causes diode D3 to conduct thereby. turning switch
`92 back on to allow the second positive peak memory
`90 to sense the maximum positive peak throughout the
`entire span of operation. The second positive peak
`memory 90 is substantially identical to the first positive
`peak memory 58. The output of the:first positive peak
`memory 58, the negative peak memory 80, and second
`positive peak memory 90 are coupledto a three-position
`switch 20 through trim potentiometers 98, 100 and 96,
`respectively.
`;
`oa,
`Accordingly, to utilize this device, power is applied
`to the device and the reset switch 22 is pushed thereby
`resetting the flip-flops and generally initializing the
`peak detector circuit components. The display 16 is
`then zeroed to provide a zero output. This can be ac-
`complished by a variety of means and it is envisioned
`that an automatic zeroing network can be employed in
`an automated system. The torque wrenchis then in-
`serted overthe fastener to be tested and rotated until the
`valley detection indicating lamp 18 is lit. Then, by the
`appropriate positioning of switch 20, the breakaway
`torque 30, the valley torque 32, and the maximum ap-
`plied torque 34 throughout the entire operation can be
`selectively displayed.
`The circuit components are preferably mounted and
`interconnected by printed circuit boards which are
`suitably mounted in housing 14. However,alternative
`embodiments, including fabrication of integrated circuit
`chips incorporating large blocksof the circuitry are also
`possible. Similarly, various types of displays may be
`utilized and, along with the associated circuitry, need
`not necessarily be mountedas an integral fixture on the
`torque wrench 10.
`FIG. 5 discloses another feature of this invention
`which automatically distinguishes those transducer out-
`put signals which are generated during the testing pro-
`cedure and those which are not or merely preliminary
`to it. For example, during the insertion of torque
`wrench head 26 over bolt 28 the operator may acciden-
`tally be applying a small amount of torque to the fas-
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`tener which may cause the test apparatus to believe this
`sensed torque was due to a bonafide test and thus pro-
`vide an erroneous output.
`.
`To alleviate this possibility,
`threshold comparator
`circuit 110 is provided which compares the transducer
`signal on line 112 with a preselected voltage level sup-
`pled on line 114 by a voltage divider network com-
`prised of resistor 116 and potentiometer 118 coupled to
`a voltage supply + V. Potentiometer 118 is adjusted to
`provide a voltage level which is greater than the trans-
`ducer outputsignal that may be generated underprelim-
`inary set up or other non-test conditions. By way of a
`simplified example, assumethat the fastener undertestis
`supposed to be torqued to 100 ft/lbs and that the trans-
`ducersignal at this torque level would be about 10 volts.
`Thus, a transducer signal of at least 5 volts certainly
`would be encountered during the testing procedure
`since the operator must apply at least 100 ft/Ibs of
`torque to reach the breakawaylevel. On the other hand,
`a transducersignal of less than 5 volts may be generated
`during initial set up. Accordingly,
`the potentiometer
`118 may be adjusted to provide voltage level on line 114
`of 5 volts. Comparator 110 will thus provide an output
`on line 120 only when the transducersignal on line 112
`exceedsthis level.
`The output of comparator 110 on line 120 and the Q
`outputofflip-flop 66 are coupled to two inputs of AND
`gate 122, the output of which is connected to control
`line 56. It will be remembered that the Q outputis at a
`HIGHlevel whenthecircuitis initially reset. However,
`control line will be LOW,thus turning off switch 54,
`until.a HIGH signal is received on line 120 from com-
`parator 110. Accordingly, the entire remaining circuit
`operation previously described is thus disabled until the
`transducer signal exceeds the preset
`threshold level
`thereby preventing erroneous readings which may be
`caused by extraneous factors not related to the testing
`operation.
`:
`The embodiments of the invention in which an exclu-
`sive property or privilege is claimed are defined as
`follows:
`1. Apparatus for measuring the amount of previously
`applied torque to a fastener comprising:
`transducer meansfor providing an output signal rep-
`resentative of the amount of subsequently applied
`torque to the fastener, such torque being applied
`until motion of the fastener is obtained;
`first positive peak detector means for sensing the
`maximumpositive output of said transducer before
`said signal decreases;
`negative peak detector means for sensing the mini-
`mum negative output signal of the transducer be-
`fore said signal again increases;
`switching network means coupled to the output of 55
`said first positive peak detector for energizing said
`negative peak detector upon detection of a nega-
`tively sloped signal from the transducer; and
`display means for displaying the outputof said nega-
`tive peak detector, said output being closely associ-
`ated with the amount of torque originally applied
`to the fastener.
`2. The apparatus of claim 1 wherein said switching
`networkincludes:
`first comparator means for comparing the transducer
`signal with the output of said positive peak detec-
`tor, said comparator providing an output signal
`when the output from the positive peak detector
`
`45
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`8
`fails to track the transducersignal thereby indicat-
`ing a negatively sloping transducersignal.
`3. The apparatus of claim 2 wherein said switching
`network means further comprises a. DC level shifter
`means coupled between the positive peak detector and
`said comparatorfor offsetting the signal from the posi-
`tive peak detector from said transducersignal, with said
`comparator providing an output signal when said sig-
`nals substantially coincide.
`4. The apparatus of claim 2 which further comprises:
`first bistable means coupled to the output ofthe first
`comparator;
`a first switch means coupled between said transducer
`and the positive peak detector;
`second switch means coupled between said trans-
`ducer and said negative peak detector;
`said first and second switch means being coupled to
`the output ofsaid first bistable means wherein said
`first switch means is rendered non-conductive to
`block further transducer signals to the positive
`peak detector and rendering said second switch
`means conductive thereby energizing said negative
`peak detector upon detection of a negatively
`sloped transducer signal.
`5. The apparatus of claim 4 which further comprises:
`third switch means coupled between a potential
`source and said negative peak detector, said third
`switch means applyingan initialization potential to
`said negative peak detector; and
`said third switch means being coupled to the output
`of said first bistable means wherein said third
`switch. means is rendered non-conductive upon
`detection of a negatively sloped transducersignal.
`6. The apparatus of claim 4 which further comprises:
`second comparator means for comparing the output
`of said negative peak detector and said transducer
`signal, with said second comparator providing an
`output signal indicative of said transducer signal
`again increasing with a positive slope.
`7. The apparatus of claim 6 which further comprises:
`offset means coupled between said negative peak
`detector and said second comparator for providing
`a positive offset with respect to said negatively
`sloped transducersignal such that said second com-
`parator provides an output signal when the trans-
`ducer signal and negative peak detector signal sub-
`stantially coincide.
`8. The apparatus of claim 7 which further comprises:
`second bistable means coupled to the output of said
`second comparator means, said second bistable
`means having an output coupled to said second
`switch means wherebysaid second switch meansis
`rendered non-conductive upon detection of the
`transducer signal again positively increasing.
`9. The apparatus of claim 1 which further comprises
`indicator means coupled to the output of said negative
`peak detector for providing a visual indication of the
`detection of the negatively sloped signal thereby signal-
`ing an operatorto cease further torquing ofthe fastener.
`10. The apparatus of claim 1 which further comprises:
`second positive peak detector means for sensing the
`maximum positive output of said transducer during
`the entire span of application of torque to the fas-
`tener.
`
`11. The apparatus of claim 16 which further com-
`prises:
`:
`fourth switch means coupled between said transducer
`and said second positive peak detector; and
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`9
`means for coupling the output of said switching net-
`workto said fourth switch meansfor de-energizing
`said second positive peak detector upon detection
`of a negatively sloped signal from the transducer.
`12. The apparatus of claim 10 which further com-
`prises:
`means for selectively displaying the output of said
`first positive peak detector, said negative peak
`detector, and said second positive peak detector.
`13. The apparatus of claim. 1 which further comprises:
`discriminator means for preventing energization of
`said first positive peak detector until the transducer
`signal exceeds a predetermined level thereby elimi-
`nating detection of transducersignals not related to
`a bona fide test of the fastener.
`14. The apparatus of claim 13 wherein said discrimi-
`nator means comprises:
`_
`an adjustable voltage source;
`threshold comparator means for comparing the trans-
`ducersignal with the outputofsaid voltage source,
`
`10
`said-comparator providing an output signal when
`said transducer signal exceeds the output of said
`adjustable voltage source; and
`first switch means coupled between the transducer
`meansandthefirst positive peak detector,said first
`switch means being rendered conductive upon
`receipt of the threshold comparator output signal
`to thereby couple the transducersignalto the first
`positive peak detector.
`15. The apparatus of claim 14 which further com-
`prises:
`gating means having one input coupled to the thresh-
`old comparator output and another input coupled
`to an output of said switching network means, with
`the output of said gating means being coupled to
`said first switch means wherein the conductive
`states ofsaid first switch means is dependent upon
`the output signals from said threshold comparator
`and said switching network means.
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