Patent Publication Number: US-7213805-B2

Title: Clamping device

Description:
FIELD OF THE INVENTION 
     The present invention relates to a clamping device for clamping a workpiece at a predetermined position, which device is installed on a clamping jig for an assembly line or a welding operation of several types of products, or installed on the upper surface of a table supporting a workpiece for a machine tool. 
     BACKGROUND OF THE INVENTION 
     In the prior art, a toggle clamp disclosed in Japanese Laid-Open Utility Model Publication 63-136838 has been proposed. The toggle clamp of the above publication has a tightening force adjustment mechanism, which includes a base bracket, a workpiece pressing arm, and a handle. The workpiece pressing arm and the handle are designed to operate in cooperation via a toggle mechanism. The workpiece pressing arm is formed of a pair of strip-shaped arm plates to sandwich a vertical pin receiver of the base bracket. A slit is formed in each arm plate to extend in the longitudinal direction in parallel to the lower rim of the arm plate. 
     The slits receive the ends of a plate nut so that the plate nut slides freely. The plate nut includes rotation restricting steps, each of which is engaged with the rim of the corresponding slit. Furthermore, a U-shaped washer fitted to the lower rims of the arm plates has a central hole through which an adjustment bolt is inserted and screwed to the plate nut so that a lock nut on the adjustment bolt is tightened to the washer. 
     The tightening force adjustment mechanism of the toggle clamp adjusts the clamp position by moving the plate nut along the slits. However, since the adjustment bolt is fixed by the lock nut after adjusting the height of the adjustment bolt, the pressing force cannot be adjusted easily while clamping the workpiece. 
     That is, the height of the adjustment bolt needs to be adjusted by loosening the lock nut in a narrow space surrounded by the base bracket, the arm plates, and the workpiece. Thus, adjusting the pressing force applied to the workpiece is very troublesome. 
     Accordingly, it is an objective of the present invention to provide a clamping device that solves the problems of the prior art and finely and easily adjusts the pressing force while actually clamping a member that is to be clamped. 
     SUMMARY OF THE INVENTION 
     To solve the above problems, a clamping device of the present invention includes a support member for supporting a member to be clamped at a predetermined position, a mounting member attached to the support member, a clamp arm attached to the mounting member to be able to reciprocate with respect to the mounting member, a pressure applying mechanism, which is located between the mounting member and the clamp arm and applies pressure to the clamp arm, and a clamp bolt, which is located on the clamp arm and clamps the member to be clamped between the clamp bolt and the support member. Further, a threaded cylinder having an external thread portion on the outside and an internal thread portion on the inside is attached to the clamp arm such that the height of the threaded cylinder is adjustable by utilizing the external thread portion. The clamp bolt is screwed to the internal thread portion of the threaded cylinder. A manipulation portion is provided for rotating the clamp bolt in a state where the member to be clamped is clamped between the clamp bolt and the support member. 
     Therefore, the pressure applied to the member to be clamped is appropriately adjusted by the manipulation portion while the member to be clamped is actually clamped. 
     According to a clamping device of a modified embodiment of the present invention, the crank bolt is provided on the crank arm such that the position of the crank bolt is adjustable along the crank arm. A manipulation portion is provided on the clamp bolt above the clamp arm. The manipulation portion is used for rotating the clamp bolt in a state where the member to be clamped is clamped between the clamp bolt and the support member. Therefore, the pressure applied to the member to be clamped is easily adjusted by the clamp bolt by utilizing a wide space above the clamp bolt. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front view illustrating a toggle clamp of the present invention clamping a workpiece; 
         FIG. 2  is a plan view illustrating the toggle clamp of  FIG. 1 ; 
         FIG. 3  is an enlarged cross-sectional view taken along line  3 — 3  of  FIG. 1 ; 
         FIG. 4  is a front view illustrating a toggle clamp according to a modified embodiment of the present invention; 
         FIG. 5  is a longitudinal cross-sectional view illustrating the toggle clamp of  FIG. 4 ; 
         FIG. 6  is a front view illustrating a substantial part of the toggle clamp according to a modified embodiment of the present invention; 
         FIG. 7  is a longitudinal cross-sectional view illustrating the toggle clamp of  FIG. 6 ; 
         FIG. 8  is a longitudinal cross-sectional view illustrating a substantial part of the toggle clamp according to a modified embodiment of the present invention; 
         FIG. 9  is a longitudinal cross-sectional view illustrating a substantial part of the toggle clamp according to a modified embodiment of the present invention; and 
         FIG. 10  is a longitudinal cross-sectional view illustrating a substantial part of the toggle clamp according to another modified embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A toggle clamp according to one embodiment of the present invention will now be described with reference to  FIGS. 1 to 3 . 
     As shown in  FIG. 1 , a pair of left and right mounting members, which are fixed mounting plates  12  in this embodiment, are arranged on an upper surface of a support member, which is a base bracket  11  in this embodiment. The mounting plates  12  are fixed to a predetermined position with four bolts  13 , which are inserted through the base bracket  11  from below and upward, and nuts  14  screwed to the bolts  13 . A pressure applying mechanism, which is a toggle mechanism  15  in this embodiment, is attached to upper ends of the mounting plates  12 . 
     A clamp arm  17  extends substantially horizontally. The proximal end of the clamp arm  17  is rotatably coupled between the upper ends of the mounting plates  12  with a coupling pin  16 . Therefore, the distal end of the clamp arm  17  can rotate back and forth in the vertical direction. A pair of manipulation levers  19  extends in a substantially vertical direction. The lower ends of the manipulation levers  19  are coupled to the outer surfaces of the upper end of the mounting plates  12  with a coupling pin  18  so that the manipulation levers  19  rotate forward and rearward and the direction of rotation alternates. A resin grip  20  is formed at the upper ends of the pair of manipulation levers  19  through insert molding. A toggle link  21  is located between the intermediate portion of the clamp arm  17  and the intermediate portion of each manipulation lever  19 . Each toggle link  21  is coupled to the clamp arm  17  and the corresponding manipulation lever  19  with coupling pins  22 A and  22 B. 
     The clamp arm  17  is branched into a pair of left and right arm pieces  23  as shown in  FIG. 2 . A guide groove  24  is formed between the arm pieces  23  and perforates the arm pieces  23  in the vertical direction. A clamp bolt unit  25  is attached to the clamp arm  17  using the arm pieces  23  and the guide groove  24 . The clamp bolt unit  25  includes a threaded cylinder  26 , which is vertically inserted through the guide groove  24 . A first lock nut  27  and a second lock nut  28  are screwed to an external thread portion  26   a  formed on the outer circumferential surface of the threaded cylinder  26 . 
     An upper washer  29  is located between the upper surfaces of the arm pieces  23  and the lower surface of the first lock nut  27 . A lower washer  30  is located between the lower surfaces of the arm pieces  23  and the upper surface of the second lock nut  28 . The lower washer  30  and the second lock nut  28  are fixed by welding. As shown in  FIG. 3 , the left and right sides of each of the upper washer  29  and the lower washer  30  are bent to form a rotation restricting rib  29   a  or  30   a  to restrict rotation of the upper washer  29  or the lower washer  30  by engaging with the upper rim or lower rim of the arm pieces  23 . 
     An internal thread portion  26   b  is formed vertically through the center of the threaded cylinder  26 . A clamp bolt  31  is screwed to the internal thread portion  26   b  so that the vertical position of the clamp bolt  31  is adjustable. A head portion  31   a  is formed at the upper end of the clamp bolt  31 . A hexagonal manipulation portion, which is an engaging hole  31   b  in this embodiment, is formed in the upper surface of the head portion  31   a  to be engaged with the distal end of a hexagonal wrench. A spherical portion  31   c  is formed at the lower end of the clamp bolt  31  and is engaged with a pad  32 . The spherical portion  31   c  and the pad  32  are rotatable relative to each other. A third lock nut  33  is screwed to the outer circumference of the clamp bolt  31 . The third lock nut  33  is securely tightened to the lower surface of the threaded cylinder  26  after the height of the clamp bolt  31  is adjusted so that the clamp bolt  31  is secured to the threaded cylinder  26 . 
     In this embodiment, the guide groove  24  of the clamp arm  17 , the first lock nut  27 , the second lock nut  28 , the upper washer  29 , and the lower washer  30  constitute position adjusting means, which adjusts the clamp position of the threaded cylinder  26  and the clamp bolt  31 . 
     Operation of the toggle clamp having the above structure will now be described. 
     As shown by a solid line in  FIG. 1 , when the manipulation levers  19  of the toggle mechanism  15  are rotated clockwise about the coupling pin  18 , the toggle mechanism  15  is maintained inoperative. In this state, a workpiece W is placed at a predetermined position on the upper surface of the base bracket  11 . 
     The clamp position is adjusted by moving the clamp bolt unit  25  horizontally along the guide groove  24  to match the position of the workpiece W with the first lock nut  27  loosened. After that, the first lock nut  27  is rotated in the tightening direction to secure the threaded cylinder  26  at the predetermined position of the clamp arm  17 . 
     In this state, the height of the clamp bolt  31  is roughly adjusted by rotating the threaded cylinder  26  so that the pad  32  at the lower end of the clamp bolt  31  contacts the upper surface of the workpiece W. In this state, the manipulation levers  19  of the toggle mechanism  15  are rotated counterclockwise about the coupling pin  18  to press the clamp bolt  31  and the pad  32  against the upper surface of the workpiece W. Accordingly, the coupling pin  22 A is located slightly on the right side of a dead line L, which connects the center of the coupling pin  18  and the center of the coupling pin  22 B. Therefore, the workpiece W is clamped by a predetermined pressure. However, it is often the case that a desired pressure is not obtained by only rotating the toggle mechanism  15 . Therefore, while the workpiece W is actually clamped, the distal end of the hexagonal wrench is engaged with the engaging hole  31   b  in the head portion  31   a  of the clamp bolt  31 . When the hexagonal wrench is rotated, the clamp bolt  31  is rotated and the pressure is adjusted to an appropriate level. 
     The preferred embodiment has the following advantages. 
     (1) In the preferred embodiment, the threaded cylinder  26  is attached to the arm pieces  23  formed at the distal end of the clamp arm  17  so that the threaded cylinder  26  is horizontally adjustable along the guide groove  24 . The clamp bolt  31  is screwed to the internal thread portion  26   b  formed at the center of the threaded cylinder  26  so that the clamp bolt  31  is vertically adjustable. Therefore, by engaging the hexagonal wrench with the engaging hole  31   b  in the head portion  31   a  of the clamp bolt  31  and rotating the hexagonal wrench while the workpiece W is clamped by the toggle mechanism  15  between the base bracket  11  and the pad  32 , an operator is allowed to clamp the workpiece W with an appropriate pressure while perceiving the actual pressure with a hand. If a torque wrench is used instead of a normal hexagonal wrench to rotate the clamp bolt  31 , the pressure is more accurately detected by a numerical value. 
     (2) In the preferred embodiment, the first lock nut  27  and the second lock nut  28  are screwed to the threaded cylinder  26 , which is then moved in the guide groove  24 . After that, the first lock nut  27  is tightened to secure the threaded cylinder  26 . Therefore, the clamp position of the threaded cylinder  26  is easily adjusted with a simple structure. 
     (3) In the preferred embodiment, the pad  32  is provided at the outer end of the clamp bolt  31  via the spherical portion  31   c . Therefore, when the clamp bolt  31  is rotated, the pad  32  does not rotate on the upper surface of the workpiece W. This prevents the upper surface of the workpiece W from being damaged. 
     (4) In the preferred embodiment, the second lock nut  28  is secured to the lower surface of the lower washer  30  by welding, and the rotation restricting rib  30   a  of the lower washer  30  is engaged with the lower rims of the arm pieces  23 . Therefore, it is unnecessary to prevent rotation of the second lock nut  28  with, for example, fingers while rotating the threaded cylinder  26 . This facilitates adjusting the height of the threaded cylinder  26 . 
     (5) In the preferred embodiment, since the toggle mechanism  15  is used as the pressure applying mechanism, the pressure is easily applied to the workpiece W. 
     The preferred embodiment may be modified as follows. 
     In a modified embodiment shown in  FIGS. 4 and 5 , a tubular body  41  having a rectangular cross-section is fitted to the outer circumference of the arm pieces  23  to be slidable in the lateral direction. A bolt  42  is screwed to an internal thread portion formed in a side plate of the tubular body  41 . The distal end of the bolt  42  is pressed against the side surface of one of the arm pieces  23  so that the tubular body  41  is secured to the side surface of the arm piece  23 . The upper and lower plates of the tubular body  41  function as the upper and lower washers  29 ,  30 . Other structures are the same as the preferred embodiment. 
     In this modified embodiment, the clamp position of the threaded cylinder  26  and the clamp bolt  31  is adjusted by reciprocating the tubular body  41  along the arm pieces  23  with the bolt  42  loosened. Then, the height of the threaded cylinder  26  is adjusted by loosening the first lock nut  27 . Therefore, the height of the threaded cylinder  26  is adjusted in a stable manner. Other operations are the same as the preferred embodiment. 
     In a modified embodiment shown in  FIGS. 6 and 7 , the shape of the two lock nuts  27 ,  28  of the preferred embodiment shown in  FIGS. 1 to 4  is changed to a disk-like form, and the diameter is increased as compared to that of the lock nuts of the preferred embodiment of  FIG. 1 . A knurl is formed on the outer circumferential surface of each lock nut to prevent slipping. Also, a manipulation knob  31   d  for rotational manipulation is integrally or separately formed on the upper end of the clamp bolt  31 . Furthermore, the third lock nut  33  is also formed as a large diameter disk and a knurl is formed on its outer circumferential surface to enable manipulation of the third lock nut. The second lock nut  28  and the lower washer  30  are formed separately. 
     In this modified embodiment, the first lock nut  27 , the second lock nut  28 , the clamp bolt  31 , and the third lock nut  33  are easily rotated. 
     In a modified embodiment shown in  FIG. 8 , the internal thread portion  26   b  is formed at the lower section of the threaded cylinder  26  and a cylindrical accommodating bore  26   c  is formed at the upper section of the threaded cylinder  26 . The head portion  31   a  formed at the upper portion of the clamp bolt  31  is accommodated in the accommodating bore  26   c . In this modified embodiment, since the head portion  31   a  is not exposed outside the threaded cylinder  26 , the appearance is simplified. 
     In a modified embodiment shown in  FIG. 9 , the threaded cylinder  26  is screwed to an internal thread portion  17   a  formed at the distal end of the clamp arm  17 . The first lock nut  27  is screwed to the external thread portion  26   a  of the threaded cylinder  26 . A manipulation piece  26   d  is screwed to the upper end of the threaded cylinder  26  and is secured to the threaded cylinder  26  by welding. The threaded cylinder  26  and the manipulation piece  26   d  may be integrally formed with each other. 
     In this modified embodiment, the clamping force is roughly adjusted by adjusting the height of the threaded cylinder  26  by rotating the manipulation piece  26   d  formed at the upper end of the threaded cylinder  26  with the first lock nut  27  loosened. The clamping force is then finely adjusted by rotating the clamp bolt  31  via the engaging hole  31   b  formed at the upper end of the clamp bolt  31  while the workpiece W is clamped. 
     In the preferred embodiment shown in  FIG. 1  or the modified embodiments shown in  FIGS. 4 and 6 , a rotational manipulation knob (not shown) may be formed at the upper end of the threaded cylinder  26 . In this case, the height of the threaded cylinder  26  is easily adjusted. 
     A modified embodiment shown in  FIG. 10  differs from the preferred embodiment of  FIG. 1  in that a solid clamp bolt  26   a  is provided instead of a combination of the hollow threaded cylinder  26  and the small diameter clamp bolt  31 . The pad  32  that is the same as the preferred embodiment is attached to the lower end of the clamp bolt  26   a  via the spherical portion  31   c.    
     Also, the upper end of the clamp bolt  26   a  is located above the arm pieces  23 . The hexagonal engaging hole  31   b  for being engaged with the distal end of the hexagonal wrench is formed in the upper end face of the clamp bolt  26 . The engaging hole  31   b  functions as a manipulation portion. 
     Therefore, in this modified embodiment, while the workpiece W is clamped by the toggle mechanism  15  between the base bracket  11  and the pad  32 , the hexagonal wrench is engaged with the engaging hole  31   b  of the clamp bolt  26   a  and rotated. Thus, the workpiece W is clamped with an appropriate pressure while finely and easily adjusting the pressure of the clamp bolt  26   a . Since a wide space above the clamp bolt  26   a  is used when adjusting the pressure, the operation is easily performed. 
     In addition to the above advantages, advantages are provided that are the same as the preferred embodiment of  FIG. 1 . Furthermore, the number of parts can be reduced to simplify the structure. 
     In the preferred embodiment, the second lock nut  28  and the lower washer  30  are coupled to each other. However, the second lock nut  28  and the lower washer  30  may be separated from each other. 
     Besides a workpiece that is processed by a machine tool, for example, a height detector may be a member to be clamped. 
     The pressure applying mechanism need not be formed by the toggle mechanism, but may be formed by a cam mechanism. 
     Instead of the base bracket  11 , a support table for a workpiece for a machine tool may be used as the support member. 
     The clamping device may be used as a clamping jig for an assembly line or a welding operation of several types of products.