Abstract:
A torque wrench including a handle attached to a drive member and a transducer that senses the torque transferred from the handle to the drive member and outputs a first signal corresponding to the transferred torque. An analog mechanical input device disposed on the handle that simultaneously defines a set point and indicates the set point. A comparator receives the first signal from the transducer, receives the set point, compares the first signal from the transducer to the set point, and outputs a second signal. The mechanical input device does not display a real time measurement of the torque transferred to the work piece prior to reaching the set point.

Description:
CLAIM OF PRIORITY 
       [0001]    This application claims priority to U.S. Provisional Patent Application No. 61/093,658, filed Sep. 2, 2008, entitled “Electronic Torque Wrench With A Manual Input Device,” the entire disclosure of which is incorporated by reference herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to torque application and measurement devices. More particularly, the present invention relates to an input device for manually selecting a set point torque value for an electronic torque wrench. 
       BACKGROUND OF THE INVENTION 
       [0003]    Often, fasteners used to assemble performance critical components are tightened to a specified torque level to introduce a “pretension” in the fastener. As torque is applied to the head of the fastener, beyond a certain level of torque the fastener begins to stretch. This stretch results in the pretension in the fastener which then holds the components together. A popular method of tightening these fasteners is to use a torque wrench. Accurate and reliable torque wrenches help insure the fasteners are tightened to the proper torque specifications. 
         [0004]    Torque wrenches vary from simple mechanical types to sophisticated electronic types. Mechanical type torque wrenches are generally less expensive than electronic ones. There are two common types of mechanical torque wrenches, beam and clicker types. With a beam type torque wrench, a beam bends relative to a non-deflecting beam in response to the torque being applied with the wrench. The amount of deflection of the bending beam relative to the non-deflecting beam indicates the amount of torque applied to the fastener. Clicker type torque wrenches work by preloading a snap mechanism with a spring to release at a specified torque, thereby generating a click noise. 
         [0005]    Electronic torque wrenches (ETWs) are typically more accurate than mechanical torque wrenches, but they tend to be more expensive than mechanical torque wrenches and less rugged in their construction. Typically, when applying torque to a fastener with an electronic torque wrench, the torque readings indicated on the display device of the electronic torque wrench are proportional to the pretension in the fastener due to the applied torque. Because the display devices on electronic torque wrenches often include liquid crystal displays, or similar devices, they are often the “weak link” of the torque wrenches construction. 
         [0006]    Drawbacks present in prior art electronic torque wrenches may leave them susceptible to being easily damaged through normal usage and, subsequently, may lead to the over or under-torquing of fasteners, which can contribute to reduced performance, and eventual failure, of the fasteners. 
         [0007]    The present invention recognizes and addresses the foregoing considerations, and others, of prior art constructions and methods. 
       SUMMARY OF THE INVENTION 
       [0008]    One embodiment of the present invention provides a torque wrench including a drive member with a surface configured to attach to a work piece to transfer torque to the work piece and a handle attached to the drive member so that force applied to the handle transfers torque to the drive member. A transducer is disposed operatively between the handle and the drive member so that the transducer senses the torque transferred from the handle to the drive member and outputs a first signal corresponding to the transferred torque sensed by the transducer. An analog mechanical input device is disposed on the handle that simultaneously defines a set point and indicates the set point. A comparator receives the first signal from the transducer, receives the set point, compares the first signal from the transducer to the set point, and outputs a second signal based on a predetermined relationship between the first signal and the set point. A detection mechanism receives the second signal from the comparator and generates a human recognizable output in response to the second signal. The mechanical input device does not display a real time measurement of the torque transferred to the work piece prior to reaching the set point. 
         [0009]    Another embodiment of the present invention provides a torque wrench including a drive member with a surface configured to attach to a work piece to transfer torque to the work piece and a handle attached to the drive member so that force applied to the handle transfers torque to the drive member. A transducer is disposed operatively between the handle and the drive member so that the transducer senses the torque transferred from the handle to the drive member and outputs a first signal corresponding to the transferred torque sensed by the transducer. A variable output circuit outputs a set point signal corresponding to a desired set point and includes a hand-actuable control that simultaneously defines the set point signal and indicates the desired set point. A comparator receives the first signal from the transducer, receives the set point signal, compares the first signal from the transducer to the set point signal, and outputs a second signal based on a predetermined relationship between the first signal and the set point signal. A detection mechanism receives the second signal from the comparator and generates a human recognizable output in response to the second signal. 
         [0010]    The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate one or more embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended drawings, in which: 
           [0012]      FIG. 1  is a perspective view of a preferred embodiment of an electronic torque wrench in accordance with the present invention; 
           [0013]      FIG. 2  is an exploded perspective view of the electronic torque wrench as shown in  FIG. 1 ; 
           [0014]      FIGS. 3A and 3B  are left side and right side plan views of the electronic torque wrench shown in  FIG. 1 ; 
           [0015]      FIGS. 4A and 4B  are top and bottom plan views, respectively, of the electronic torque wrench shown in  FIG. 1 ; 
           [0016]      FIG. 5  is a front plan view of the electronic torque wrench shown in  FIG. 1 ; 
           [0017]      FIG. 6  is a side plan view of the electronic torque wrench as shown in  FIG. 1  with the battery door removed; 
           [0018]      FIG. 7  is a perspective view of a resistive element of the electronic torque wrench as shown in  FIG. 1 ; 
           [0019]      FIG. 8  is a block diagram representation of the electronic torque wrench as shown in  FIG. 1 ; 
           [0020]      FIG. 9  is an electrical circuit diagram of the electronics unit of the electronic torque wrench as shown in  FIG. 1 ; 
           [0021]      FIGS. 10A and 10B  are a flow chart of the control algorithm of the electronic torque wrench as shown in  FIG. 1 ; and 
           [0022]      FIG. 11  is a perspective view of an alternate embodiment of an electronic torque wrench in accordance with the present invention. 
       
    
    
       [0023]    Repeat use of reference characters in the present specification and drawings is intended to represent same or analogous features or elements of the invention according to the disclosure. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0024]    Reference will now be made in detail to presently preferred embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. Each example is provided by way of explanation, not limitation, of the invention. In fact, it will be apparent to those skilled in the art that modifications and variations can be made in the present invention without departing from the scope and spirit thereof. For instance, features illustrated or described as part of one embodiment may be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
         [0025]    Referring now to  FIGS. 1 through 6 , an electronic torque wrench  10  including an analog mechanical input device in accordance with the present invention is shown. Electronic torque wrench  10  includes a wrench body  12 , a drive member  14 , a housing  16 , and an electronics unit  18  with a user interface. Preferably, wrench body  12  is of unitary construction, made of steel or other rigid material, and pivotably receives drive member  14  at a first end and a grip handle  24  at a second end. Housing  16  is mounted therebetween and carries electronics unit  18 . As shown, a yoke  22  is formed at the first end of wrench body  12 , yoke  22  defining a pair of mounting apertures  32  that are configured to receive a mounting pin  33  therein, thereby forming a pivot joint. A detent  34  including a ball and a biasing spring is received in an aperture (not shown) that is formed in a front face of body  12  between the arms of yoke  22 . A central portion  30  of wrench body  12  is disposed between a front flange  26  and a rear flange  28  of the body. Central portion  30  includes a rectangular cross-section defined by a top wall  36 , a bottom wall  38 , and a pair of substantially parallel opposed side walls  40 . The cross-sectional dimensions of central portion  30  are selected dependent upon the desired amount of flexural movement of the central portion over the operating range of the torque wrench. 
         [0026]    A strain gauge assembly  42  is disposed on one of opposed side walls  40  and is connected to electronics unit  18  by a wire set  43  that is similarly disposed on the corresponding side wall  40 . In the preferred embodiment, the strain gauge assembly is a full-bridge assembly including four (4) separate strain gauges on a single film that is secured to the desired side wall  40 . An example of one such full-bridge strain gauge assembly is Model No. N2A-S1449-lKB manufactured by Vishay Micromeasurement. Together, the full-bridge strain gauge assembly mounted on side wall  40  of wrench body  12  is referred to as a strain tensor. 
         [0027]    As shown, yoke  22  of wrench body  12  pivotably receives drive member  14 . Drive member  14  includes a body  44  at a first end and a boss  46  at a second end. Body  44  defines a mounting aperture  48  therethrough that corresponds to mounting apertures  32  defined by yoke  22 . Drive member  14  is pivotably mounted to yoke  22  by passing mounting pin  33  through aligned mounting apertures  32  and  48 . A plurality of transverse grooves  50  are formed about the outer surface of body  44  and are configured to selectively receive detent  34  that projects outwardly from body  12 . As shown, three transverse grooves  50  are formed in body  44  such that drive member  14  can be selectively secured either in alignment with the longitudinal axis of body  12  (as shown in  FIG. 1 ) or in one of two positions in which drive member  14  is transverse to the longitudinal axis of wrench body  12  (as shown in  FIGS. 3A and 3B ). Boss  46  of drive member  14  is configured to receive variously sized sockets, extensions, etc., and includes a detent  47  to assist in maintaining the desired fitting on boss  46 . 
         [0028]    Housing  16  includes a top portion  78  and a bottom portion  80  that are received about central portion  30  of wrench body  12  and house electronics unit  18 . Electronics unit  18  provides a user interface for the operation of electronic torque wrench  10 . Electronics unit  18  includes a first printed circuit board  52  that is configured to receive a plurality of batteries  54  ( FIG. 6 ) and has an annunciator  56  mounted thereon. Electronics unit  18  also includes a second printed circuit board  58  including two light-emitting diodes (LEDs)  62  and  64  and a power button  59  that is operated by a switch  60 . LEDs  62  and  64  are green and red, respectively, when activated. The user interface also includes an analog mechanical input device for simultaneously defining and indicating a set point torque value, as discussed in greater detail below. In the preferred embodiment shown, the mechanical input device is a resistive element assembly  66  that includes a resistive element  68 , a graduated panel  74  and a manually operated input slider  76 . 
         [0029]    Referring additionally to  FIG. 7 , in the preferred embodiment shown, the resistive element is a sliding potentiometer that includes a linear resistor  69 , a wiper assembly  70  configured for motion along linear resistor  69 , and an adjustment pin  72  extending outwardly from wiper assembly  70 . Terminal leads are provided for receiving wires from electronics unit  18 . The motion of wiper assembly  70  along linear resistor  69  causes the overall resistance of sliding potentiometer  68  to vary, as discussed in greater detail below. As shown, graduated panel  74  includes two different sets of units disposed along its upper half and bottom half such that the user of electronic torque wrench  10  can select either of the sets of units when manually selecting the desired set point torque value with input slider  76 . As shown, input slider  76  indicates that the upper set of units are in inch-pounds whereas the lower set of units are Newton-meters. Note, however, various other sets of units can be utilized by merely replacing the existing graduated panel  74  with a graduated panel including the desired sets of units. 
         [0030]    As best seen in  FIG. 2 , electronics unit  18  is disposed on wrench body  12  between top portion  78  and bottom portion  80  of housing  16 . Top portion  78  and bottom portion  80  each include a pair of longitudinal slots  84 , a plurality of corresponding access apertures  86 , corresponding input device recesses  88 , and a plurality of corresponding fastener apertures  90 . The corresponding pairs of longitudinal slots  84  are configured to slidably receive central portion  30  of wrench body  12  such that top portion  78  and bottom portion  80  of housing  16  are received between front and rear flanges  26  and  28  of wrench body  12 . Threaded fasteners are received in corresponding fastener apertures  90  to secure the two portions of housing  16  in place. So connected, corresponding input device recesses  88  of top and bottom portion  78  and  80  form a single input device recess for receiving graduated panel  74  of resistive element assembly  66 . Also, as best seen in  FIG. 6 , corresponding access apertures  86  form a plurality of apertures through which batteries  54  can be installed on first printed circuit board  52 . Additionally, aperture  86   a  allows annunciator  56  that is disposed on first printed circuit board  52  to extend outwardly from housing  16  so that it may be more easily heard. Top portion  78  of housing defines recess  82  that is configured to receive a top plate  65  of the user interface. 
         [0031]    A battery door  94  is removably secured to housing  16  so that batteries  54  are securely held within housing  16 . Bottom portion  80  of housing  16  defines a door aperture  96   a  that is configured to receive an arm  96  that extends inwardly from a first end of battery door  94  and a fastener aperture  97   a  that is configured to receive a fastener that passes through a corresponding fastener aperture  97  on a second end of battery door  94 . As best seen in  FIG. 3B , battery door  94  defines a plurality of annunciator slots  98  that correspond to the position of annunciator  56  so that the annunciator can be more easily heard. Additionally, bottom portion  80  of housing  16  defines a plurality of apertures  92  ( FIG. 4B ) through which central portion  30  of wrench body  12  is visible. An O-ring  91  is disposed between front flange  26  of wrench body  12  and housing  16  to help keep dust, dirt, debris, etc., out of housing  16  while the electronic torque wrench  10  is in use. 
         [0032]    A block diagram representation of the electronics unit of the preferred embodiment, showing various inputs and outputs, is shown in  FIG. 8 . Prior to using electronic torque wrench  10  to apply torque, a set point torque value is selected using the analog mechanical input device. Referring additionally to  FIG. 9 , a sensor electrical circuit  67  that determines the resistance of the resistive element of resistive element assembly  66  in order to create an electrical signal for use by the microcontroller, is shown. Sensor electrical circuit  67  provides a fixed DC excitation voltage (Vcc) in the range of three to five volts that corresponds to a base torque value for the torque wrench. The output voltage  67   a  of sensor electrical circuit  67  is proportional to the resistance of the resistive element of resistive element assembly  66 . As input slider  76  ( FIG. 1 ) is manipulated, the resistance of the resistive element changes, which in turn changes the output voltage  67   a  of sensor electrical circuit  67 . Because the output voltage  67   a  is proportional to the resistance of the resistive element, it is also proportional to the desired set point torque value. 
         [0033]    The analog output voltage  67   a  from sensor electrical circuit  67  is converted to an equivalent digital value by an analog to digital converter and is then fed to a microcontroller  63  (for example, Model No. ADuC843 manufactured by Analog Devices, Inc.). A control algorithm  110  ( FIGS. 10A and 10B ) residing in microcontroller  63  converts the equivalent digital value into an equivalent set point torque value. A unit conversion algorithm converts the torque value to the units indicated on graduated panel  74  of resistive element assembly  66 , in the present case inch-pounds and Newton-meters. The choice of units can be increased to cover all possible units by changing the appropriate algorithms, and changing the units shown on graduated panel  74  of resistive element assembly  66 . 
         [0034]    When electronic torque wrench  10  is used to apply torque, the strain gauges of the strain tensor sense the actual torque applied and send a proportional electrical signal  42   a  to a strain gauge signal conditioning unit  45  that amplifies the signal, and adjusts for any offset of the signal. Adjusting for the offset of the signal increases the accuracy of the wrench by compensating the signal for any reading that may be present before torque is actually applied to the fastener. An amplified and conditioned electrical signal  45   a  is then fed to microcontroller  63  that compares electrical signal  45   a  to electrical signal  67   a  that corresponds to the desired set point torque value to determine if the current torque level value is within a pre-selected range of the set point torque value. Furthermore, microcontroller  63  generates alarm signals in the form of audio signals and light displays of appropriate color once the current actual torque value is within the pre-selected range of the preset set point torque value, as discussed in greater detail hereafter. 
         [0035]    Referring now to  FIGS. 8 ,  9 ,  10 A and  10 B, a flow chart of the algorithm  110  used with the electronics unit is shown. Prior to initiating torquing operations, the control system of the present invention allows for calibration of the wrench. To initially calibrate the torque wrench, the voltage output signals  45   a  and  67   a  of strain gauge signal conditioning unit  45  and sensor electrical circuit  67 , respectively, are measured for two known torque values. Because the values of the two voltage output signals  45   a  and  67   a  are known to correspond to the two known torque values, the “slope” of the voltage output of the strain gauge signal conditioning unit  45  and the sensor electrical circuit  67  with regard to the potential range of set point torque values can be calculated. These slopes are then recorded into the memory of microcontroller  63 . 
         [0036]    To initiate torquing operations, a user manually inputs a set point torque value using an analog input device into the electronic torque wrench that equals the maximum desired torque to be applied. As seen in  FIG. 1 , the user slides input slider  76  along graduated panel  74  of resistive element assembly  66  to select the desired set point torque value. Note, the user may set the desired set point torque value either prior to, or after, powering on the electronic torque wrench. However, the torque wrench should be powered on using operating switch  60  prior to actually applying torque. 
         [0037]    When powered on, the electronics unit goes through various system initialization processes. For example, the slopes and offset for the resistive element are retrieved from the memory of microcontroller  63  as are the slopes for the strain tensor. Additionally, the electronics unit also reads from memory whether or not the electronic torque wrench was subjected to an overload condition during previous uses. The electronics unit determines whether or not the battery level is sufficient for proper operation of the electronic torque wrench. If not, microcontroller  63  causes green LED  62  to flash ten times prior to initiating a power off sequence for the wrench. If the battery level is deemed adequate for proper operation, microcontroller  63  switches green LED  62  on continuously, sets the enunciator buzzer to off, and sets red LED  64  to off, unless a previous overload condition was determined to have existed, in which case red LED  64  is switched to continuously on. As well, microcontroller  63  reads an offset voltage value for the strain tensor in the no-load condition. 
         [0038]    As previously noted, electronic signal  67   a  from sensor electrical circuit  67  is read by microcontroller  63  and converted to the set point torque value utilizing the aforementioned slopes and offset values from memory. As torque is applied with the wrench, microcontroller  63  converts electrical signal  45   a  provided by the strain tensor into an actual torque value (Tact) that is being applied by the electronic torque wrench by using the aforementioned slope values. 
         [0039]    Next, microcontroller  63  ensures that the actual torque value (Tact) is a positive value so that it can be compared to the set point torque value (Tset). If microcontroller  63  determines that the actual torque value exceeds 125% of the rated capacity of the torque wrench, the microcontroller causes green LED  62  and red LED  64  to flash and annunciator  56  buzzer to activate. This condition continues until the actual torque value is reduced to less than 125% of rated capacity. If the actual torque value being applied is less than 125% of rated capacity, microcontroller  63  sets its memory to reflect that no overload condition currently exists. 
         [0040]    As torque is applied by the wrench, microcontroller  63  continuously switches green LED  62 , red LED  64  and annunciator  56  on or off depending on the actual torque value applied by the wrench up until that time. Preferably, green LED  62  remains in a steadily on condition as long as the actual torque value remains below 125% of the torque wrench&#39;s rated capacity. If the actual torque value exceeds 106% of the set point torque value, microcontroller  63  causes red LED  64  to begin flashing and activates annunciator  56 , in addition to maintaining green LED  62  in a continuously on condition. If the actual torque value is less than 106% of the set point torque value, yet greater than 101% of the set point torque value, microcontroller  63  causes green LED  62  and red LED  64  to remain in a continuously on condition, and causes annunciator  56  to buzz continuously. If the actual torque value is determined to be less than 101% of the set point torque value yet greater than 100% of the set point torque value, microcontroller  63  causes green LED  62  and red LED  64  to remain in a continuously on condition, while annunciator  56  remains silent. 
         [0041]    For actual torque values that are less than the set point torque value yet greater than five inch-lbs of torque, microcontroller  63  causes green LED  62  to remain in a continuously on condition. For actual torque values that are less than five inch-lbs., microcontroller  63  initiates a timing sequence in which the electronic torque wrench will go through a power off sequence if it is determined that the actual torque value being applied is less than five inch-lbs for three minutes. By keeping track of the activity of the torque wrench, the algorithm prevents inadvertently draining the batteries. 
         [0042]    While one or more preferred embodiments of the invention are described above, it should be appreciated by those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope and spirit thereof. For example, as seen in  FIG. 11 , an alternate embodiment of an electronic torque wrench  10   a  in accordance with the present invention includes a graduated knob  75  as the analog mechanical input device for selecting a set point torque value, rather than a linear resistor as previously discussed. It is intended that the present invention cover such modifications and variations as come within the scope and spirit of the appended claims and their equivalents.