Patent Publication Number: US-6981436-B2

Title: Electronic torque wrench

Description:
RELATED APPLICATIONS 
   This application is a division of copending U.S. application Ser. No. 10/293,006, filed Nov. 13, 2002 which, in turn, claims the benefit of the filing date of U.S. Provisional Application No. 60/333,033, filed Nov. 14, 2001. 

   BACKGROUND 
   This application relates to wrenching tools, and, in particular, to torque-measuring and recording wrenches. 
   Various types of torque wrenches are known. One common type of mechanical torque wrench is what is known as a “click”-type wrench which generates an audible sound, such as a “click,” when a predetermined value of applied torque is reached. Such wrenches are disclosed, for example, in U.S. Pat. No. 4,485,703. In this type of wrench, when a predetermined set force is transmitted by the wrench to a workpiece, certain parts within the wrench move rapidly from a normal position to an actuated position in a manner such as to generate an audible click-like sound and tactile sensation to signal the operator that a predetermined set torque has been reached. The predetermined torque is set by the operator by rotating coaxial, telescoping tubular parts, so that as one part is rotated relative to the other it advances axially relative to the other along scale indicia, in the nature of a micrometer. Such wrenches have the advantage that their manner of use is simple and highly intuitive, so that the wrenches can easily be used with little or no training. Additionally, with this type of wrench, the operator can always see where the scale is set so that he can always ascertain the predetermined set torque value while the wrench is in use. 
   Other types of mechanical torque wrenches have gauges with one or more pivoting dials. One such wrench has two dials, one of which tracks the applied torque both up and down, and the other of which tracks the applied torque only up, so that it registers the peak torque applied. 
   Various types of electronic torque wrenches are also known which utilize electronic circuitry for measuring and/or indicating torque values. Such electronic devices may have the advantage of being more precise or accurate in setting predetermined torque values and in measuring applied torque. However, such electronic torque wrenches are typically much less intuitive to use than the mechanical torque wrenches described above. Such wrenches typically have a keypad with multiple keys which are capable of a number of specialized functions, many of which may rarely, if ever, be used by a particular operator. Considerable training is required to master the operation of such wrenches and the basic operational functions may be very non-intuitive. Also, in order to simultaneously display both a pre-set torque value and an applied torque value, such electronic wrenches must have relatively complex and expensive displays. While wrenches with more simplified and inexpensive displays are known, they typically register a display of the preset torque while it is being set, but then, after the setting function is accomplished, the display returns to zero in preparation for recording the applied torque during use of the wrench. If the operator puts the wrench down after setting the predetermined torque and returns to it later for use, he will have to typically perform some keypad function in order to view the preset torque. Also, such electronic wrenches lack the familiar audible/tactile indication when the predetermined set torque value is reached, and may provide some other type of visible and/or audible indication, or even require that the user watch a display. 
   SUMMARY 
   There is described in this application an improved electronic torque wrench which is more intuitive to use than the previous electronic wrenches, simulating basic features of mechanical torque wrenches while maintaining advantages of prior electronic torque wrenches. 
   An embodiment of an electronic torque wrench includes a workpiece-engaging head carried by a housing which also carries torque measuring apparatus including a processor operating under stored program control. A user interface is coupled to the torque measuring apparatus and includes a data input device and annunciator apparatus. The processor program responds to the input device for selectively setting or changing a preset torque level at any time, and compares torque values measured by the torque measuring apparatus with the preset torque level for causing the annunciator apparatus to produce an indication when the measured torque value coincides with the preset torque level. 
   An embodiment also includes an electronic torque wrench, wherein the user interface includes a keypad having an on/zero key for powering up the wrench and setting a zero level, a units key for toggling among plural different units of torque measurement, an increment key for incrementing a preset torque level and a decrement key for decrementing a preset torque level. 
   A torque wrench embodiment also includes a housing assembly including telescoping tubular inner and outer housing portions with registered apertures therein and a bezel assembly disposable in the outer housing portion aperture and carrying torque measuring apparatus, the housing portions and the bezel assembly all being interconnected by a single fastener. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For the purpose of facilitating an understanding of the subject matter sought to be protected, there are illustrated in the accompanying drawings embodiments thereof, from an inspection of which, when considered in connection with the following description, the subject matter sought to be protected, its construction and operation, and many of its advantages should be readily understood and appreciated. 
       FIG. 1  is a top plan view of an embodiment of an electronic torque wrench having a four-key keypad; 
       FIG. 2  is a front elevational view of the torque wrench of  FIG. 1 ; 
       FIG. 3  is a slightly reduced, exploded, perspective view of the torque wrench of  FIG. 1 ; 
       FIG. 4  is an exploded view of the handle assembly of the wrench of  FIG. 1 ; 
       FIG. 5  is an enlarged, exploded, perspective view of the battery tray of the torque wrench of  FIG. 3 ; 
       FIG. 6  is an enlarged, exploded, perspective view of the end cap assembly of the torque wrench of  FIG. 3 ; 
       FIG. 7  is an enlarged, top-plan view of the sensory yoke and strain gauge of the torque wrench of  FIG. 3 ; 
       FIG. 8  is a front elevational view of the sensory yoke and strain gauge of  FIG. 7 ; 
       FIG. 9  is sectional view taken generally along the line  9 — 9  in  FIG. 7 ; 
       FIG. 10  is an enlarged, exploded, perspective view of the bezel assembly of the torque wrench of  FIGS. 2 and 3 ; 
       FIG. 11  is a top plan view of the bezel of  FIG. 10 ; 
       FIG. 12  is a sectional view taken generally along the line  12 — 12  in  FIG. 11 ; 
       FIG. 13  is a bottom plan view of the bezel of  FIG. 11 ; 
       FIG. 14  is a view similar to  FIG. 11  of a modified bezel; 
       FIG. 15  is a functional block diagram of the electronic circuitry of the torque wrench of  FIGS. 1 and 2 ; and 
       FIG. 16  is a flow chart diagram of the software for operating the circuitry of  FIG. 15 . 
   

   DETAILED DESCRIPTION 
   Referring to  FIGS. 1–3 , there is illustrated an electronic torque wrench, generally designated by the numeral  10 , having a housing  15  including an inner housing portion in the form of an elongated cylindrical body tube  11  with a large, elongated, rectangular aperture  12  in the upper portion thereof intermediate its ends and a rectangular notch  13  formed in the upper rear edge thereof. A circular hole  14  is formed in the bottom portion adjacent to the forward end of the notch  12 . Referring also to  FIGS. 7–9 , a sensor yoke  20  has a cylindrical base  21  which is fitted in the forward end of the body tube  11 , the base  21  having an axial bore  22  formed in the rear end thereof and a rectangular groove or channel  23  formed in the outer surface thereof and extending longitudinally from the rear end of the base  21  to about midway along its length. The forward half of the base  21  defines a reduced-diameter neck portion  24  having parallel flats  25  formed on opposite sides thereof, one of which defines a recess communicating with the channel  23 . Projecting forwardly from the front end of the base  21  are a pair of spaced clevis legs  26 , respectively having aligned pivot holes  27  therethrough. The base  21  has two internally threaded bores  28  formed radially therein for respectively receiving fasteners  29  (see  FIG. 3 ) to secure the yoke  20  in place in the body tube  11 . 
   A ratchet head  30  is coupled to the sensor yoke  20 . The ratchet mechanism of the head  30  may be of the type disclosed in U.S. Pat. No. 6,125,722. The head  30  has a neck  31  projecting rearwardly therefrom which is received between the clevis legs  26  of the yoke  20 , the neck  31  having a bore  32  therethrough which aligns with the pivot holes  27  for receiving a pivot screw  33  to allow pivotal movement of the head  30  relative to the yoke  20 , as indicated in phantom in  FIG. 2 . While a pivoting or indexible head  30  is illustrated, it will be appreciated that other types of ratcheting or non-ratcheting, pivoting or non-pivoting, fixed or removable heads could be mounted on the forward end of the body tube  11 , with suitable modifications to the sensor yoke  20 . 
   Referring also to  FIG. 4 , the housing  15  includes an outer housing portion in the form of a generally tubular handle assembly  40 , which is of fundamentally two-part construction, including a lower housing assembly  41  and an upper housing  50 , which are mateably joined and secured together, as by ultrasonic welding. The lower housing assembly  41  has a generally part-cylindrical body  42  with a reduced-diameter neck portion  43  at the forward end thereof provided with a circumferentially extending rectangular slot  44 . A circular hole  45  is formed through the body  42  adjacent to the neck portion  43  and is surrounded at the inner surface of the body  42  by a bushing  46 . A foot  47  projects downwardly from the body  42  intermediate its ends. The rear half of the body  42  is provided with upstanding, arcuate grip flanges  48 . Projecting rearwardly from the body  42  is a reduced-diameter, externally threaded part-cylindrical neck portion  49 . 
   The upper housing  50  has a generally part-cylindrical body  52  having a reduced-diameter neck portion  53  projecting from its forward end with a rectangular, circumferentially extending slot  54  therein. A large, elongated, generally rectangular aperture  55  is formed in the forward half of the body  52 . The lower edges of the body  52  are provided with large cutouts  56  in the rear half thereof for respectively accommodating the grip flanges  48 . An externally threaded, reduced-diameter part-cylindrical neck portion  59  projects rearwardly from the body  52 . 
   In assembly, the lower housing assembly  41  and the upper housing  50  are joined along their longitudinal edges, such as by ultrasonic welding, with the grip flanges  48  respectively received in the cutouts  56 , the neck portions  43  and  53  cooperating to form a forward neck and the neck portions  49  and  59  cooperating to form a rearward neck. A trim ring  58  ( FIG. 3 ) is fitted over the forward neck and has tabs (not shown) which respectively snap fit into the slots  44  and  54  to retain the trim ring  58  in place. The rear portion of the body  42 , including the grip flanges  48 , may be over molded with a grip  57  ( FIGS. 3 and 4 ) formed of a suitable elastomeric material, such as that sold under the trade name SANTOPRENE®. 
   Referring also to  FIG. 5 , the torque wrench  10  is provided with a battery support or tray assembly  60 , which is of fundamentally two-part construction, including a lower tray  61  and an upper tray  70 . The lower tray  61  has an elongated, part-cylindrical base  62 , provided along approximately the rearward two-thirds thereof with upstanding sides  63 , respectively provided at their upper edges with laterally outwardly extending flanges  64 , each having a plurality of longitudinally spaced rectangular notches  65  in the outer edge thereof. The sides  63  are joined at their forward ends by an upstanding partition  66 , integral with the base  62 . An arcuate, radially extending end flange  67  projects from the base  62  and sides  63  at their rearward ends. Projecting upwardly from the base  62  at its forward end is a cylindrical bushing  68 . 
   The upper tray  70  has a part-cylindrical base  72  with a length substantially equal to the distance between the partition  66  and the end flange  67  of the lower tray  61 . Formed in the forward end of the base  72  is an elongated rectangular notch  73 . Integral with the base  72  along its opposite side edges are laterally outwardly extending flanges  74 , respectively provided with depending, longitudinally spaced-apart posts or stakes  75 . Projecting upwardly from one of the flanges  74  are a plurality of longitudinally-spaced, short lugs  75   a . In assembly, the upper tray  70  is fitted over the lower tray  61 , with the flanges  74  respectively abutting the flanges  64  and the posts  75  respectively snap-fitted into the notches  65  (see  FIG. 3 ) to form a generally cylindrical compartment closed at the forward end by the partition  66  and open at the rearward end. A helical compression spring  76  is seated at the forward end of the compartment against the partition  66  and may rearwardly urge a suitable contact plate  69 . An elongated contact strip  78  lies along the outer surface of the one flange  75  and has a notch  78   a  for receiving a lug  75   a  to position the strip. The rear end of the contact strip  78  is bent to make contact with a rear contact plate  79 , which is biased forwardly by a helical compression spring  79   a  (see  FIG. 3 ). The battery tray assembly  60  is dimensioned to receive three series-stacked, standard “AA” alkaline cells, with a positive terminal contacting the contact plate  69  and a negative terminal contacting the contact plate  79 . A tab on the contact plate  69  and the forward end of the contact strip  78  will, respectively, be connected by suitable soldered ribbon wires  71  to the remainder of the circuitry, to be described more fully below. 
   Referring to  FIG. 3 , in assembly of the housing  15 , the rear end-of the body tube  11  is telescopically received in the forward end of the handle assembly  40  until the aperture  12  lies immediately beneath the aperture  55 , substantially in registry therewith. The forward end of the battery tray assembly  60  is then telescopically received in the rear end of the handle assembly  40  and into the rear end of the body tube  11  until the bushing  68  is in registry with the hole  14  in the body tube  11 . The notch  13  in the body tube  11  will then be in registry with a motor holder receptacle (not shown) formed at the rear end inside the upper housing  50 . 
   Referring now also to  FIGS. 10–13 , the housing  15  includes a bezel assembly  80 , the parts of which are illustrated in  FIG. 10 . The bezel assembly  80  includes a generally rectangular printed circuit board (“PCB”) assembly  82 . Mounted on the PCB assembly  82  is a buzzer  83 , provided with a seal  84 . A keypad plate  86  overlies the PCB assembly  82  and includes four keys. Formed in the keypad plate  86  is a longitudinally extending, narrow rectangular notch  87 . An elongated, thin, elastomeric connector  88  is received in the notch  87  and provides connection between terminals on the PCB assembly  82  and terminals on an LCD display  89 , which is provided with a lens  90 . 
   The bezel assembly  80  also includes a generally part-cylindrical bezel  91 , which is dimensioned to mateably fit in and close the aperture  55  in the handle assembly  40  (see  FIG. 3 ). The bezel  91  has a generally rectangular aperture  92  therein dimensioned to receive the upper portion of the lens  90 . Formed through the bezel  91  adjacent to the forward end thereof are a plurality of small apertures  93  for the buzzer  83 . Formed in the upper surface of the bezel  91  at the rear end thereof is a generally rectangular recess  94 , in the bottom wall of which are formed four keyholes  95 , respectively positioned and shaped to receive the keys of the keypad plate  86 . Depending from the front end of the bezel  91  is a cylindrical bushing  96 , which receives an internally threaded insert  97 . A generally rectangular tab  98  depends from and projects rearwardly from the rear end of the bezel  91 . 
   In assembly, the PCB assembly  82  is fixedly secured to the bezel  91  by suitable means, such as screws  99 , with the remaining parts of the bezel assembly  80  illustrated in  FIG. 10  sandwiched therebetween. The elastomeric connector  88 , which is a type of connector normally used to accommodate considerable flexing between connected parts is, in this case, very thin so as to provide a low-profile and rigidly-assembled bezel assembly  80  with minimal relative movement of internal parts. 
   The keypad plate  86  illustrated in  FIG. 10  is provided with four keys, the functions of which will be described below. In a modified form of the torque wrench  10 , additional keys may be provided, in which case a modified keypad plate would be used and the bezel  91  would be modified to provide an appropriate number of (e.g., six) keyholes. Such a modified bezel assembly is illustrated in  FIG. 14  and is designated  80 A and is substantially identical to the bezel assembly  80 , except for the number of keys and the fact that an output jack and output jack cover and associated port (not shown) may be provided. 
   The assembled bezel assembly  80  or  80 A is fitted into the aperture  55  in the handle assembly  40 , with the tab  98  slipped beneath the wall of the upper housing  50  at the rear end of the aperture  55 . When thus installed, the bushing  96  and threaded insert  97  will register with the bushing  68  of the battery tray assembly  60  and the hole  14  in the body tube  11  (see  FIG. 3 ), so that a single screw  100  may be received through the hole  14  and the bushing  68  and threaded into the insert  97  to hold the entire assembly together. 
   Referring to  FIGS. 3 and 6 , the rear end of the housing  15  is closed by an end cap assembly  101 , which includes a generally cup-shaped end cap  102  and a threaded insert  103  adapted for threaded engagement with the threaded neck portions  49 ,  59  of the handle assembly  40 . The contact plate  79  and spring  79   a  may be seated in the end cap  102  against an end surface of a post  106 , the spring receiving a centering lug  107  projecting from the end of the post  106 . Thus, when the end cap assembly  101  is mounted in place, the spring  79   a  resiliently urging the contact plate  79  against the rear end of the strip  78 . If desired, an alternative form of end cap assembly (not shown) could be provided with a transverse hanging hole formed therethrough. 
   Referring to  FIG. 10 , the four keys of the keypad plate  86  include an “on/zero” key  111 , a “units” key  112  for toggling among different torque-measurement units, an “increment” key  113  and a “decrement” key  114 . A storage key  115  and a download key  116  could also be provided in a six-key bezel assembly  80 A (see  FIG. 14 ). To further distinguish the keys, the key  111  is circular in shape, the key  112  is “U”-shaped, and the keys  113  and  114  are triangular to simulate arrows. The storage and download keys  115 ,  116  if provided, may be square. 
   The wrench  10  includes a strain gauge assembly  120 . Referring to  FIGS. 7 and 8 , the strain gauge assembly  120  includes  4  gauges arranged in a bridge network, including two deflection sensing gauges  121  and  122  and Poisson correction and temperature compensation gauges  123  and  124 . The strain gauge assembly  120  is physically mounted on one of the flats  25  of the sensor yoke  20 , the terminal strips thereof being connected to the PCB assembly  82  by ribbon wires  119  which extend through the channel  23  in the sensor yoke  20 . 
   The wrench  10  also includes a vibratory motor M, which is physically accommodated in a receptacle formed at the rear end inside the upper housing  50  (not shown) and in the notch  13  of the body tube  11 , and is connected by wires to the PCB assembly  82 . 
   Referring to  FIG. 15 , there is illustrated a functional block diagram of an electronic circuit  110  for controlling the operation of the torque wrench  10 . The circuit  110  includes a processor  125 , which may be in the nature of a suitable microcontroller, such as an NEC model 789456, which may have a crystal-controlled clock speed of 4.915 MHz. The processor  125  operates under control of a program, which may be stored within the processor. An EEPROM  126  may be provided to store setup, preset and calibration parameters. The output of the strain gauge bridge  120  is applied to the processor  125  through an analog-to-digital converter (ADC)  127 , which may be an Analog Devices model AD7705BR. The keypad plate  86  constitutes a data input device which is coupled to the processor  125  and forms part of a user interface, which also includes annunciator apparatus, which may include a buzzer  128 , the vibratory motor M and the LCD display  89 , all coupled to the processor  125 . The battery support assembly  60  carries a battery pack  129 , which includes the three “AA” alkaline cells to power the wrench  10 . The battery pack  129  is coupled to a voltage regulator  130 , which produces a V++ voltage, which may, for example, be 3.3 volts, and which is applied to the EEPROM  126 , the processor  125 , the keypad  86  and the buzzer  128 . The battery pack  129  is also coupled to a voltage regulator  131 , which produces a V+ supply voltage which may, for example, be 3.0 volts, and which is applied to the strain gauge bridge  120  and the ADC  127 , the regulator  131  being enabled under the control of the processor  125 . The battery pack  129  is also coupled to a motor regulator  132 , which produces a suitable supply voltage to the vibratory motor M, which may, for example, be 3.0 volts, the motor regulator  132  being enabled under the control of the processor  125 . 
   The strain gauge bridge  120  mounted on the sensor yoke  20  constitutes a sensing device in the nature of a bending-beam measurement transducer, the two deflection sensing gauges  121  and  122  being aligned with the primary bending plane of the beam, and the second pair of gauges  123  and  124  being aligned perpendicular to the primary bending plane. The strain gauge bridge  120  is excited by regulated V+ voltage and delivers a differential output, which may be approximately 6.5 mV at full-scale torque, which output signal is fed through the ADC  127  to the processor  125 . The buzzer  128  may be an electromagnetic buzzer, which is driven directly by the processor  125  and may provide audible keypush, preset and overload alerts to the wrench user. The vibratory motor M may be a DC motor rotating an off-axis weight, of the type typically used in personal pagers. The motor M is driven momentarily by the regulated output voltage of the regulator  132  and provides the user with a tactile preset coincidence alert. 
   In operation, when the user desires to utilize the torque wrench  10 , the wrench is turned on by pressing the on/zero key  111 . The first time that the wrench is powered up in this manner, the wrench will execute a self test and a zero set operation under the control of suitable program routines, followed by causing the display  89  to display flashing “0000”, indicating program mode. The wrench is capable of operation in different modes and these can be manually selected by the user by entering a suitable code number using the increment and decrement keys  113  and  114 . Then the units key  112  is pressed to accept or enter the code, whereupon the wrench shuts off. The program mode can be exited by pushing the on/zero key without leaving any changes. 
   The next time the unit is powered up the display will flash “UCAL” for ten seconds, indicating that the wrench is uncalibrated. The user must then proceed with a calibration procedure to establish full-scale range. After the wrench is calibrated, subsequent power-ups will take 1.5 seconds, during which the buzzer pulses for 0.2 second and the wrench executes self test and zero set routine followed by displaying “0000” for one second, and then displaying any previously-entered set point or predetermined torque level or, if none has been previously set, displaying 20% of full-scale torque as a default set point. 
   The user may select the units of torque measurement by scrolling through the several different available units, utilizing the units key  112 . The first time the units key is depressed the display  89  will display one of the several units selections available. Each push of the units key  112  shifts to the next measurement unit. 
   The operator can then select a preset torque level or alter a previously-set torque level by using the increment and decrement keys  113  and  114 , each push one of these keys incrementing or decrementing the currently-displayed value by one unit. Increment/decrement speed increases as the increment and decrement keys  113  and  114  are held down. The total time to traverse from the center of the measurement scale to either end is less than seven seconds. Once the predetermined torque level is set, the display  89  will continue to display that level until torque is applied by the wrench or until another key is pressed or an internal timer times out. 
   Once the predetermined torque level is set, the user then utilizes the wrench in a normal manner to apply torque. As soon as torque exceeds the minimum specified display range, the display  89  will begin to display the measured torque value and will track the applied torque, which may be from 5% of full scale up to 125% of full scale. When torque application is released, the display  89  will display the peak torque value applied with a flashing display for 10 seconds. If, during that 10-second interval, the torque is reapplied the display  89  will revert to its tracking mode. Pushing any key will cancel the 10-second peak display period and the display will revert to the function of whatever key was pressed. 
   When the applied torque reaches the predetermined torque level minus a 2% tolerance, the processor  125  will enable the motor regulator  132  to power the vibratory motor M, which will then run continuously until torque is released. Also, at this time, the buzzer  128  will sound an audible alert for 0.5 seconds. At and above 100% of full scale, the buzzer pulses at a 5-Hz rate. At 125% of full scale the display  89  locks up and displays “----”, indicating overload of the wrench. Pressing the on/zero key  111  will reinitiate a self test. 
   The user may, at any time, display the predetermined torque level by pushing the on/zero key  111 , which will momentarily show “0000” for one second and then display the predetermined torque level. 
   If the sensing apparatus has been damaged due to excessive torque applied, resulting in tare greater than 20% of full scale, then the display  89  will show “Err 0 .” The wrench  10  also will provide a low battery alert. Normally, the display will show a filled-in outline of a battery when it is fully charged, a half-filled outline when the battery is at about half-capacity and, when there is approximately 0.5 hours of battery life remaining, the LCD display  89  will display a flashing battery outline symbol. When this display is active, the accuracy of the wrench will not be affected by a vibratory motor loading. When the batteries are depleted, the display  89  will flash “BAtt”, whereupon the wrench will not operate unless the batteries are exchanged. 
   In calibrating the wrench  10 , the user employs the following procedure:
         1. Push ON/ZERO KEY to turn wrench on.   2. Momentarily apply full-scale torque three times in the CW direction.   3. Select UNITS (Nm, ft-lb, or in-lb)   4. While pushing the ON/ZERO key, push UP key once momentarily and then push DOWN key until display shows “CAL.”   5. With no torque applied, push UNITS key once to set zero into memory.   6. Apply continuous full-scale CW torque using certified torque source.   7. Use UP and DOWN keys to adjust wrench display to match applied torque.   8. Push UNITS key to set full scale into memory.   9. Push ON/ZERO key to accept new calibration parameters. Display momentarily reads “CAL” and then shuts down.   10. Verify calibration at 20%, 60% and 100% of full-scale in both CW and CCW directions.       

   If the on/zero key  111  is pushed anytime after step 4 and before step 8, the wrench will exit the calibration mode and retain the previous calibration parameters. If the wrench is left idle for two minutes, from any point in the calibration procedure, it will default to the previous calibration parameters and shut down. 
   If the wrench lies idle for two minutes, i.e., no keys are pushed and no torque is applied, a timer will time out and the wrench will automatically turn off 
   The foregoing description applies to a wrench configuration which is designed for automotive service technicians and the like. An alternate configuration might be utilized for industrial uses, such as in automobile assembly plants and the like. That configuration is similar, except that the wrench may also have user-adjustable tolerance values. 
   Referring to  FIG. 16 , there is illustrated a flow chart, illustrating a software program routine  140  for operating the torque wrench  10 . When the wrench is powered up, at  141 , it executes the power up routine described above, pulsing the buzzer for 0.2 second, executing the self test or display diagnostic function at  142  and the zero set function at  143 . Then, at  144 , it displays the previous set point or predetermined torque level or, if one has not been previously set, displays 20% of full-scale torque as a default preset. Then, at  145 , the program sets a two-minute timer and checks at  146  to see if the timer has timed out. If it has, the wrench is turned off at  147 . 
   After setting the timer at  145 , the program also checks at  148  to see if a keystroke has occurred, i.e., that one of the keypad keys has been pushed. If not, the program then, at  149 , measures torque applied by the wrench, as sensed by the strain gauge bridge  120 , and then checks, at  150 , to see if the measured torque is above a minimum value, e.g., 5% of full-scale. If the measured torque is above the minimum, the routine first, at  151 , triggers the track mode, causing the display  89  to track and display the measured torque, and then returns to  145  to reset the timer and goes to  152  to stop the ten-second delay for the peak hold display and returns to  144  to display the set point. At this point, the program also checks at  153  to see if set point coincidence has occurred, i.e., whether the measured torque is substantially equal to the predetermined torque level. If it is, the program, at  154 , triggers the preset alarm, causing the vibratory motor M and the buzzer  83  to generate their alarm signals in the manner described above and then returns to  145  and  152 . The program next checks at  155 , to see if the measured torque is above the full scale level. If so, it triggers the full scale alarm at  156 , causing the buzzer to give its appropriate alarm, as described above, and then returns to  145  and  152 . The program next checks at  157  to see if measured torque is above 125% of full scale. If so, it triggers the overload alarm at  158  and locks the display at  159 . The program next checks at  160  to see if torque application has been released. If so, it triggers the peak hold mode at  161 , causing the display  89  to display the peak torque value, and starts a ten-second delay period at  152  to display the peak value for ten seconds, after which it returns to  144  to resume displaying, the set point. If torque release has not occurred at  160 , the program returns to  149  to continue measuring torque. 
   If, at  148 , a keystroke has occurred, the program checks at  162 ,  163 ,  164  and  165 , respectively, to see if it is the on/zero key, the units key, the increment key or the decrement key which has been actuated to activate the zero/tare function at  166 , change the units at  167 , increment the set point at  168  or decrement the set point at  169 , in each case thereafter resetting the timer at  145  and stopping the ten-second delay period at  152  and returning to  144  to display the set point. 
   From the foregoing, it can be seen that there has been provided an improved electronic torque wrench which is characterized by intuitive functions which maintain the advantages of prior electronic torque wrenches while, at the same, time effectively simulating prior mechanical “click”-type torque wrenches. 
   The matter set forth in the foregoing description and accompanying drawings is offered by way of illustration only and not as a limitation. While particular embodiments have been shown and described, it will be apparent to those skilled in the art that changes and modifications may be made without departing from the broader aspects of applicants&#39; contribution. The actual scope of the protection sought is intended to be defined in the following claims when viewed in their proper perspective based on the prior art.