Abstract:
A device for calibrating a torque wrench includes a base plate, a strain gauge, a display, a cup, a rod and a ring. The strain gauge is non-rotationally connected to the base plate. The display is electrically connected to the strain gauge. The cup is non-rotationally connected to the base plate. The rod is non-rotationally connected to the cup. The ring is inserted in the cup so that the ring and the cup together define an annular gap for tightly receiving a socket.

Description:
BACKGROUND OF INVENTION 
     1. Field of Invention 
     The present invention relates to a torque wrench and, more particularly, to a device for calibrating a torque wrench. 
     2. Related Prior Art 
     A mechanical device for calibrating a torque wrench is disclosed in Taiwanese Patent Publication No. 538859. The mechanical device includes a shell 10, an axle 21, a block 23, an elastic bar 24, a positioning element 25 and a meter 40. The axle 21 includes a middle section inserted in the shell 10 and two ends 22 located out of the shell 10. The block 23 is attached to the middle section of the axle 21. The elastic bar 24 includes an upper end inserted in the axle 21 and a lower end in contact with the positioning element 25 located in and attached to the shell 10. The meter 40 includes a probe 42, an indicator 43 and a scale (not numbered). The probe 42 includes a lower end in contact with the block 23 and an upper end connected to the indicator 43. The indicator 43 is rotatable with respect to the scale. In operation, a boxed or open end 51 of a torque wrench 50 is engaged with one of the ends 22 of the axle 21 while the shell 10 is secured to a workbench or held by a user. The axle 21 is rotated by the torque wrench 50. The block 23 is rotated while the elastic bar 24 is deformed. The probe 42 is lifted so that the indicator 43 is rotated relative to the scale. Thus, the torque exerted on the axle 21 is measured by the calibrating device. However, the reading of the torque is affected by the angle of the observation of the indicator 43 relative to the scale. Moreover, there are errors in such a mechanical configuration so that the reading of the torque might not reflect the real value of the torque exerted on the axle 21 by the torque wrench 50. 
     An electric device for calibrating a torque wrench is disclosed in Taiwanese Patent I341235. The electric device includes a shell 20, a rod 30, an elastic bar 40, a sensor 60 and an electric display unit 70. The rod 30 includes a middle section (not numbered) inserted in the shell 20 and two ends 34 located out of the shell 20. The elastic bar 40 includes an end inserted in the axle 21 and another end in contact with a rotating element 54 attached to a frame 52 located in and attached to the shell 20. The sensor 60 is a strain gauge attached to the elastic bar 40. The electric display unit 70 includes a display 72 electrically connected to the sensor 60. In operation, a boxed or open end of a torque wrench is engaged with one of the ends 34 of the rod 30 while the shell 20 is secured to a workbench or held by a user. One of the ends 34 of the rod 30 is rotated by the torque wrench via the rod 30, which is accordingly rotated. Thus, the elastic bar 40 is deformed. The sensor 60 senses the deformation of the elastic bar 40 and accordingly sends a signal to the electric display unit 70 which accordingly calculates the value of the torque exerted in the rod 30 and shows the value on the display 72. The pivoting of the torque wrench is however not smooth. 
     Therefore, the present invention is intended to obviate or at least alleviate the problems encountered in prior art. 
     SUMMARY OF INVENTION 
     It is the primary objective of the present invention to provide a smooth device for calibrating a torque wrench. 
     To achieve the foregoing objective, the device includes a base plate, a strain gauge, a display, a cup, a rod and a ring. The strain gauge is non-rotationally connected to the base plate. The display is electrically connected to the strain gauge. The cup is non-rotationally connected to the base plate. The rod is non-rotationally connected to the cup. The ring is inserted in the cup so that the ring and the cup together define an annular gap for tightly receiving a socket. 
     Other objectives, advantages and features of the present invention will be apparent from the following description referring to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The present invention will be described via detailed illustration of two embodiments referring to the drawings wherein: 
         FIG. 1  is an exploded view of a device for calibrating a torque wrench according to the first embodiment of the present invention; 
         FIG. 2  is a perspective view of the device shown in  FIG. 1 ; 
         FIG. 3  is a partial, cross-sectional view of the device shown in  FIG. 2 ; 
         FIG. 4  is a partial, side view of a torque wrench engaged with the device shown in  FIG. 3 ; and 
         FIG. 5  is a partial, cross-sectional view of a device for calibrating a torque wrench according to the second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Referring to  FIGS. 1-4 , a device  10  for calibrating a torque wrench includes a base plate  12 , a shell  16 , a cup  20 , a rod  30 , a bearing  40 , a ring  50  and an electronic unit  60  according to a first embodiment of the present invention. The base plate  12  includes an opening  14 . 
     The shell  16  includes a brim  11  and a crown  18 . The brim  11  extends around the crown  18 . The crown  18  is made with a window  13  and an opening  15 . 
     The cup  20  includes a lower portion  22 . A square opening  24  is made in the lower portion of the cup  20 . The cup  20  includes a space  26  in communication with the square opening  24 . The space  26  is made of a stepped shape so that an annular shoulder  28  is formed on an internal side of the cup  20 . 
     The rod  30  includes a circular section  31 , a square section  34 , a lower annular flange  38 , an upper annular flange  36  and a hexagonal section  32 . The square section  34  is formed on the circular section  31 . The lower annular flange  38  is formed on the square section  34 . The upper annular flange  36  is formed above the lower annular flange  38 . The hexagonal section  32  is formed on the upper annular flange  36 . 
     The bearing  40  can be a ball bearing or a roller bearing. 
     The ring  50  includes an opening  52  and an annular lip  56 . The opening  52  is centrally made in the ring  50 . The annular lip  56  extends from a lower side of the ring  50 . 
     The electronic unit  60  includes a circuit board (not numbered), a strain gauge  62  and a display unit  64 . The display unit  64  includes a display  66  and a glass panel  68 . 
     The cup  20  is supported on the base plate  12 . Three screws (not numbered) are driven in screw holes made in the lower portion  22  of the cup  20  through apertures (not numbered) made in the base plate  12 . Thus, the cup  20  is secured to the base plate  12 . 
     The circular section  31  of the rod  30  is inserted in the opening  14  of the base plate  12 . A screw  17  is driven in a screw hole (not numbered) made in the circular section  31  of the rod  30  through an aperture made in a washer  21 . The aperture of the washer  21  is made of a diameter marginally larger than that of the screw  17 . The washer  21  expands larger than the opening  14 . Thus, the rod  30  is kept in position. The square section  34  of the rod  30  is inserted in the square opening  24  of the cup  20 . The lower annular flange  38  is supported on the lower portion  22  of the cup  20 . The upper annular flange  36  is inserted in the space  26  of the cup  20 . The hexagonal section  32  of the rod  30  is located out of the space  26  of the cup  20 . 
     The bearing  40  is supported on the annular shoulder  28  of the cup  20 . The bearing  40  is flush with the upper annular flange  36 . 
     The annular lip  56  is inserted in and supported on the bearing  40  so that the ring  50  is allowed to smoothly rotate on the bearing  40 . The upper annular flange  36  and the hexagonal section  32  of the rod  30  are inserted in the opening  52  so that an annular gap  54  is defined between the rod  30  and the ring  50 . 
     The circuit board and the strain gauge  62  are supported on the base plate  12 . The strain gauge  62  is secured to the base plate  12  so that the strain gauge  62  can be deformed with the base plate  12 . The strain gauge  62  is electrically connected to the circuit board. 
     The glass panel  68  is fit in the window  13 . The display  66  is attached to the crown  18  so that the display  66  is observable through the window  13 . The display  66  is protected by the glass panel  68 . The display  66  is electrically connected to the circuit board. 
     The brim  11  is secured to the base plate  12  by screws (not shown). Thus, the circuit board and the strain gauge  62  are closed by the base plate  12  and the shell  16 . 
     In calibration of a torque wrench  72 , a socket  74  connected to the torque wrench  72  is placed on the hexagonal section  32  of the rod  30 . A force is exerted on the torque wrench  72  so that a torque is exerted on the socket  74 . Hence, the torque is transferred into the rod  30 . Then, the torque is transferred to the cup  20 . Finally, the torque is transferred to the base plate  12  so that the base plate  12  is deformed, and so is the strain gauge  62 . The strain gauge  62  sends a signal corresponding to the deformation. Thus, the value of the torque is calculated and shown on the display  66 . The value of the torque shown on the display  66  is compared with a reading of the torque shown on the torque wrench  72 . Thus, the torque wrench  72  is calibrated. 
     Advantageously, the socket  74  is inserted in the annular gap  54 . That is, an internal side of the socket  74  is in contact with the hexagonal section  32  of the rod  30  and an external side of the socket  74  is in contact with the ring  50 . That is, the socket  74  is guided by both of the rod  30  and the ring  50 . The ring  50  is allowed to smooth rotate as it is supported on the bearing  40 . Hence, the rotation of the socket  74  is smooth, and so is the pivoting of the torque wrench  72 . Moreover, the socket  74  is supported on the upper annular flange  36 . 
     Referring to  FIG. 5 , there is a device for calibrating a torque wrench according to a second embodiment of the present invention. The second embodiment is identical to the first embodiment except including an axially longer ring  50 . 
     The present invention has been described via the detailed illustration of the embodiments. Those skilled in the art can derive variations from the embodiments without departing from the scope of the present invention. Therefore, the embodiments shall not limit the scope of the present invention defined in the claims.