Abstract:
An output part is provided to the left end of a clamp arm that is supported by a housing so as to be slidable in the vertical direction. At the left end of the housing, a first hole for spring fitting opens obliquely upward towards the output part. A through hole that links the upper surface and the lower surface of the clamp arm is disposed obliquely upward at a left-leaning part of the clamp arm. A second hole for spring fitting and a female screw hole are formed, in that order, upwards in the through hole. A return spring that is installed through the first hole and the second hole impels the output part upwards. A push bolt that is screwed into the female screw hole rom above compresses the return spring.

Description:
TECHNICAL FIELD 
     The present invention relates to a clamp device which fixes an object to be fixed such as a mold or a workpiece to a support stand such as a table, and more specifically relates to a clamp device of a type in which a middle portion of a clamp arm in a longitudinal direction thereof is swingably supported. 
     BACKGROUND ART 
     As such a type of conventional clamp device, there is a clamp device disclosed in Patent Literature 1 (Japanese Laid-Open Patent Publication No. H08-177814). The clamp device of the conventional art is configured as follows. 
     A middle portion of a clamp arm in a longitudinal direction thereof is mounted on a housing (clamp arm receiving stand) via a fulcrum shaft so as to be swingable in an up-down direction. A leading end portion of the clamp arm is provided with an output portion (working point) which presses an object to be fixed, and a rear end portion of the clamp arm is provided with an input portion (power point) which is pressed up by a piston. 
     A first hole for mounting a spring is formed at the leading end side of the housing so as to be opened obliquely upward toward a leading end-adjacent portion of the clamp arm. In addition, a second hole for mounting a spring is formed at the leading end side of the clamp arm so as to be opened obliquely downward toward the first hole. A return spring for returning the clamp arm is installed in the first hole and the second hole. 
     In fixing the object to be fixed by means of the conventional clamp device, a pressure fluid is supplied into a working chamber located at the lower side of the piston. Accordingly, the input portion of the clamp arm is pressed up by the piston, the clamp arm swings, and the output portion presses the object to be fixed. In this lock state, the return spring is compressed between the housing and the clamp arm. 
     In return-driving the clamp device from the lock state to a release state, the pressure fluid in the working chamber is discharged therefrom. Accordingly, the output portion of the clamp arm is pressed up by a biasing force of the return spring, and the input portion of the clamp arm presses down the piston. Thus, the lock state of the object to be fixed is released. 
     [PTL 1] Japanese Laid-Open Patent Publication No. H08-177814 
     SUMMARY OF THE INVENTION 
     In the above-described conventional art, since the return spring for returning the clamp arm is installed so as to be tilted, it is possible to increase an arm length between the fulcrum shaft and a location at which the biasing force of the return spring is applied to the clamp arm. Thus, the return spring is allowed to increase a rotary force thereof with respect to the clamp arm to immediately return the clamp arm. However, with the conventional clamp device, there is room for improvement in assembling or maintenance as follows. 
     Specifically, in the above-described conventional art, in order to further immediately return-drive the clamp arm, a return spring having a great biasing force is required. In the case where such a powerful return spring is used, in assembling or maintenance of the clamp device, a working operation using a special tool is required in order to mount or dismount the return spring in or from the first hole and the second hole for mounting a spring. Thus, the assembling or maintenance of the clamp device takes much time and labor. 
     An object of the present invention is to allow a powerful spring to be used as a return spring for a clamp arm and also allow the powerful spring to easily be mounted and dismounted. 
     In order to attain the above object, according to the present invention, a clamp device is configured as follows, for example, as shown in  FIGS. 1 to 5 . 
     A clamp arm  14  extending along a housing  12  in a horizontal direction includes a fulcrum portion  14   a  which is swingably supported by the housing  12  at a middle portion in the horizontal direction, an input portion  14   b  which is provided at a base end thereof in the horizontal direction, and an output portion  14   c  which is provided at a leading end thereof in the horizontal direction. A cylinder hole  16  is formed in the housing  12  and below the input portion  14   b  so as to extend in an up-down direction and be opened in an upper surface of the housing  12 . A piston  18  is inserted into the cylinder hole  16  and configured to advance to above an opening end of the housing  12  to move the input portion  14   b  upward. A working chamber  20  which a pressure fluid is supplied into and discharged from is formed between a bottom wall  16   a  of the cylinder hole  16  and the piston  18 . A first hole  22  for mounting a spring is formed near a leading end portion of the housing  12  so as to be opened obliquely upward toward a leading end-adjacent portion of the clamp arm  14 . A through hole  24  is provided between the output portion  14   c  and the fulcrum portion  14   a  so as to extend obliquely upward and provide communication between an upper surface and a lower surface of the clamp arm  14 . A second hole  24   a  for mounting a spring and a female screw hole  24   b  are formed in the through hole  24  in this order so as to extend upward. A return spring  26  is mounted in the first hole  22  and the second hole  24   a  and biases the output portion  14   c  upward. A pressing bolt  28  is screwed into the female screw hole  24   b  from above and compresses the return spring  26 . 
     The present invention exerts the following advantageous effects. 
     In assembling the clamp device, when the return spring is mounted on the clamp arm, first, the return spring in a free state is disposed between the first hole of the housing and the second hole of the clamp arm. Next, the pressing bolt is screwed into the female screw hole from above and rotated to be fastened to compress the return spring. Thus, the mounting of the return spring is completed. In addition, in disassembling the clamp device, the pressing bolt is rotated relative to the female screw hole to be loosed, thereby returning the return spring from the compressed state described above to the free state or a state close to the free state. Thus, it is possible to easily dismount the return spring from the first hole and the second hole. 
     As described above, in assembling or disassembling the clamp device, the return spring is caused to come into the free state or a state close to the free state, whereby it is possible to make a biasing force thereof zero or decrease the biasing force. Thus, unlike the conventional art described above, a special tool for mounting and dismounting the return spring is unnecessary. As a result, in assembling or maintenance of the clamp device, it does not take much time and labor to mount or dismount the return spring. In addition, it is also possible to use a powerful spring as the return spring. 
     In the present invention, preferably, at least an upper half portion of the cylinder hole  16  is formed so as to extend straight in the up-down direction; and at least an upper half portion of the piston  18  is formed so as to extend straight in the up-down direction. 
     In this case, it is possible to efficiently produce the cylinder hole of the housing and the piston. 
     In addition, in each invention described above, an inclination angle θ of an axis C 2  of the first hole  22  with respect to an axis C 1  of the cylinder hole  16  is set preferably within a range of 30 degrees to 45 degrees and more preferably within a range of 35 degrees to 45 degrees. 
     Furthermore, in the present invention, it is preferred to add a specific configuration described in an embodiment described later. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional elevation view of a release state in a clamp device according to an embodiment of the present invention. 
         FIG. 2  is a left side view of the clamp device shown in  FIG. 1 . 
         FIG. 3  is a right side view of the clamp device shown in  FIG. 1 . 
         FIG. 4  is a plan view of the clamp device shown in  FIG. 1 . 
         FIG. 5  is a cross-sectional elevation view showing a lock state of the clamp device. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, an embodiment of the present invention will be described with reference to  FIGS. 1 to 5 . First, the structure of a clamp device  10  will be described with reference to  FIGS. 1 to 4  showing a release state prior to fixing an object to be fixed. 
     The clamp device  10  according to the present invention is mounted on a support stand  1  such as a table when being used. A T-leg  30  is formed at a lower portion of a housing  12  and fitted into a T-groove  32  formed in the support stand  1 , so as to be movable in a horizontal direction (a right-left direction in  FIG. 1 ). 
     At the left end side (leading end side) of the housing  12  in  FIG. 1 , a pair of right and left side walls  34   a  are provided in a standing manner as shown in  FIG. 2 . A groove  34  having a U shape in a side view is formed between the side walls  34   a . A pivotal support shaft  36  is provided to both side walls  34   a  and at a middle portion of the housing  12  in the right-left direction, and a fulcrum portion  14   a  provided at a middle portion of a clamp arm  14  in a longitudinal direction thereof is rotatably supported by the pivotal support shaft  36 . In addition to the fulcrum portion  14   a , the clamp arm  14  includes: an input portion  14   b  which is provided at the right end side (base end side) of the clamp arm  14 ; and an output portion  14   c  which is provided at the left end side (leading end side) of the clamp arm  14 . 
     Meanwhile, at the right end side (base end side) of the housing  12  in  FIG. 1 , a cylinder hole  16  is formed at a position corresponding to the input portion  14   b  so as to be opened in an upper surface of the housing  12  and extend straight over the entirety thereof in an up-down direction. A piston  18  is hermetically inserted into the cylinder hole  16  via a sealing member  38 . The piston  18  is formed so as to extend straight over the entirety thereof in the up-down direction, and advances to above the opening end of the cylinder hole  16  to move the input portion  14   b  upward. In addition, a scraper  40  is mounted at an opening edge portion of the cylinder hole  16 . 
     A working chamber  20  is formed between the piston  18  and a bottom wall  16   a  of the cylinder hole  16 . A pressure oil as a pressure fluid is supplied into or discharged from the working chamber  20  through a supply/discharge port  42 . 
     A first hole  22  for mounting a spring is formed near a left end portion of the housing  12  so as to be opened obliquely upward toward a left end-adjacent portion of the clamp arm  14 . An inclination angle θ of an axis C 2  of the first hole  22  with respect to an axis C 1  of the cylinder hole  16  is set preferably within a range of 30 degrees to 45 degrees and more preferably within a range of 35 degrees to 45 degrees. When the inclination angle θ is set within such a range, an arm length between an axis of the pivotal support shaft  36  and a location at which a biasing force of a later-described return spring  26  is applied to the clamp arm  14 , is increased. Thus, the return spring  26  is allowed to increase a rotary force with respect to the clamp arm  14 . As a result, it is possible to further rapidly return-drive the clamp arm  14  without increasing the size of the housing  12 , the return spring  26 , or the like. 
     Meanwhile, a through hole  24  is formed in the clamp arm  14  and between the output portion  14   c  and the fulcrum portion  14   a  so as to extend obliquely upward and provide communication between an upper surface and a lower surface of the clamp arm  14 . The through hole  24  is provided so as to be substantially coaxial with the axis C 2  of the first hole  22  in the release state. A second hole  24   a  for mounting a spring and a female screw hole  24   b  are formed in the through hole  24  in this order so as to extend upward. As described later, the return spring  26  is mounted in the first hole  22  and the second hole  24   a  in a free state, and is compressed by a pressing bolt  28  screwed into the female screw hole  24   b  from above, thereby biasing the output portion  14   c  upward. It should be noted that in order to prevent the pressing bolt  28  from being loosed, the pressing bolt  28  is preferably rotated to be fully fastened. 
     In addition, a projection  14   d  formed on a left end side lower surface of the clamp arm  14  and a left end side upper surface  12   a  formed in the housing  12  so as to receive the projection  14   d  serve as a stopper which prevents the piston  18  from coming out of the cylinder hole  16 . 
     The return spring  26  includes: an outer spring  26   a  which has a large diameter; and an inner spring  26   b  which has a small diameter and is inserted into the outer spring  26   a . Each of the outer spring  26   a  and the inner spring  26   b  is composed of a compression coil spring. A lower end portion of the return spring  26  is received by a bottom wall of the first hole  22  of the housing  12 . An upper end portion of the return spring  26  is received by the pressing bolt  28  via a spring receiver  44  inserted into the second hole  24   a  of the clamp arm  14 . 
     As shown in  FIGS. 1 and 5 , the clamp device  10  having the above configuration operates as follows. 
     In the release state of  FIG. 1 , the pressure oil in the working chamber  20  is discharged therefrom, and the output portion  14   c  of the clamp arm  14  is pressed up and the input portion  14   b  is pressed down by the biasing force of the return spring  26 , thereby moving the piston  18  downward. 
     In lock-driving the clamp device  10 , the pressure oil is supplied into the working chamber  20  in the release state of  FIG. 1 . 
     Accordingly, as shown in  FIG. 5 , the pressure oil in the working chamber  20  moves the piston  18  upward, the piston  18  presses up the input portion  14   b  of the clamp arm  14 , and the output portion  14   c  is pressed down against the return spring  26 . Thus, the output portion  14   c  presses a mold D against an upper surface of the support stand  1 . 
     In switching the clamp device  10  from the lock state of  FIG. 5  to the release state of the  FIG. 1 , the pressure oil in the working chamber  20  is discharged therefrom in  FIG. 5  described above. 
     Accordingly, the output portion  14   c  of the clamp arm  14  is pressed up by the biasing force of the return spring  26 , and the input portion  14   b  moves the piston  18  downward, thereby returning to the release state of  FIG. 1 . Thus, fixing of the mold D is released. 
     The clamp device  10  according to the embodiment described above has the following advantages. 
     In assembling or disassembling the clamp device  10 , when the clamp arm  14  is mounted in or dismounted from the groove  34  of the housing  12 , the pressing bolt  28  is rotated to be loosed to decrease the biasing force of the return spring  26 , thereby allowing the pivotal support shaft  36  to easily be inserted into or pulled out from the housing  12 . 
     In addition, since the stopper for the piston  18  is composed of the projection  14   d  provided on the left end side lower surface of the clamp arm  14  and the left end side upper surface  12   a  of the housing  12  which is formed so as to receive the projection  14   d , it is unnecessary to provide a stopper portion at an upper portion of the cylinder hole  16 . Thus, it is possible to simplify the structure of the cylinder hole  16  or the piston  18 . As a result, the clamp device  10  is excellent in productivity and maintainability. 
     Moreover, by changing the machining dimensions of either one of the projection  14   d  on the left end side lower surface of the clamp arm  14  or the left end side upper surface  12   a  of the housing  12 , it is possible to handle pistons  18  having various strokes. Thus, it is possible to share components. As a matter of course, the machining dimensions of both the projection  14   d  on the left end side lower surface of the clamp arm  14  and the left end side upper surface  12   a  of the housing  12  may be changed. 
     The embodiment described above can be changed as follows. 
     The pressure fluid which is supplied into or discharged from the working chamber  20  is not limited to the exemplified pressure oil, and may be compressed air, another compressed gas, or the like. 
     Although the clamp device  10  is not equipped with moving means, positioning means, and the like, the clamp device  10  may be reciprocated between a predetermined advance position and a predetermined retreat position on the support stand  1  by an actuator such as an electric motor or a hydraulic cylinder. 
     The case has been shown in which a dual spring composed of the outer spring  26   a  and the inner spring  26   b  is used as the return spring  26 . However, for example, the return spring  26  may be composed of a single spring. 
     In addition, the case has been shown in which the spring receiver  44  is mounted at the upper end of the return spring  26 . However, in the case where the return spring  26  can be compressed by only the pressing bolt  28 , it is possible to omit the spring receiver  44 . 
     In the embodiment described above, the case has been shown in which as a mounted attitude of the clamp device  10 , the longitudinal direction of the clamp arm  14  is directed in the horizontal direction. However, the longitudinal direction of the clamp arm  14  may be directed in a vertical direction or an oblique direction. 
     In addition, the case has been shown in which the clamp device  10  is movably mounted on the support stand  1  by means of the T-leg  30  and the T-groove  32 . However, a manner in which the clamp device  10  is mounted on the support stand  1  is not limited thereto, and the clamp device  10  may be fixed to the support stand  1  by means of a bolt. 
     The case has been shown in which the cylinder hole  16  and the piston  18  are formed so as to extend straight over the entirety thereof in the up-down direction. However, at least of an upper half portion of each of the cylinder hole  16  and the piston  18  may be formed so as to extend straight in the up-down direction. 
     DESCRIPTION OF THE REFERENCE CHARACTERS 
       10  clamp device 
       12  housing 
       14  clamp arm 
       14   a  fulcrum portion of clamp arm  14   
       14   b  input portion of clamp arm  14   
       14   c  output portion of clamp arm  14   
       16  cylinder hole 
       18  piston 
       20  working chamber 
       22  first hole 
       24  through hole 
       24   a  second hole 
       24   b  female screw hole 
       26  return spring 
       28  pressing bolt 
     C 1  axis of cylinder hole  16   
     C 2  axis of first hole  22   
     θ inclination angle