Abstract:
In a clamping device, a detection mechanism detects a state of clamping/unclamping and includes: a detected body that moves together with a piston and a piston rod; a circuit board disposed to face the detected body and capable of detecting the position of the detected body; and an indicator lamp that is connected to the circuit board and is lit/extinguished depending on the state of clamping/unclamping. By pressing a setting button provided on the detection mechanism when the rotation angle of the arm is changed, the second detection position of the circuit board for detecting the unclamped state is changed, making it possible to detect the detected body at a newly set detection position.

Description:
TECHNICAL FIELD 
     The present invention relates to a clamping device which is capable of clamping a workpiece through a clamp arm rotated a predetermined angle under a displacement action of a piston. 
     BACKGROUND ART 
     Heretofore, for example, when welding together component parts of a vehicle or the like, a clamping device has been used for clamping the parts. The present applicant has proposed such a clamping device, having a main body portion, a cylinder connected to the main body portion, and a clamp arm, which is rotated a predetermined angle through a toggle link mechanism disposed in the interior of the main body portion under a driving action of the cylinder (see Japanese Laid-Open Patent Publication No. 2001-113468). 
     In such a clamping device, a piston and a piston rod of the cylinder are displaced in a axial direction under the action of a pressure fluid supplied to the cylinder, whereby a clamp arm is rotated through an operational angle based on a displacement amount of the piston via the toggle link mechanism that is connected to the piston rod, and the clamping device is switched between a clamped state, at which a workpiece can be clamped, and an unclamped state, at which the workpiece is released from the clamped state. 
     Further, in the clamping device, a detection member is connected with respect to a knuckle block, which is connected to the piston rod, whereby the rotational state of the clamp arm is detected by detecting the detection member by two proximity switches disposed at respective side portions of the body. 
     Recently, it has been desired to detect the rotational state of a clamp arm more easily and with greater accuracy. 
     SUMMARY OF INVENTION 
     The present invention is related to the aforementioned proposal, and has an object of providing a clamping device in which, even in the case that the angle of rotation of a clamp arm is changed, the rotational state of the clamp arm can be detected easily and with high accuracy. 
     To achieve the above object, the present invention is characterized by a clamping device for clamping a workpiece with a clamp arm, by converting linear motion in a cylinder into rotational motion through a toggle link mechanism, the clamping device comprising: 
     a main body portion; 
     a cylinder connected to the main body portion and having a piston and a piston rod therein which are displaced in an axial direction under a pressing action of a pressure fluid; 
     an adjustment mechanism disposed displaceably in the cylinder, and which is capable of adjusting a stroke displacement amount of the piston by regulating displacement of the piston; 
     a detecting mechanism having a detection body that is stroke-displaced together with the piston and the piston rod, and a detecting section, which is capable of detecting a position of the detection body, wherein the detecting mechanism detects clamped and unclamped states of the workpiece by the clamp arm by detecting, with the detecting section, a position at which the detection body is stroke-displaced; and 
     a position setting means for setting a detection position of the detection body by the detecting section, when the stroke displacement amount is adjusted by the adjustment mechanism. 
     According to the present invention, in the clamping device, in the case that the angle of rotation of the clamp arm is changed by adjusting the stroke displacement amount of the piston using the adjustment mechanism, since it is possible to change and set, with the position setting means, the detection position at which the detection body of the detecting mechanism is detected by the detecting section, for example, it is unnecessary for an adjustment operation to be carried out by removing the detecting mechanism from the main body portion every time that the angle of rotation of the clamp arm is changed, and thus the operation to change the detection position can be performed easily responsive to the change in the angle of rotation. As a result, adjustment of the angle of rotation of the clamp arm can be performed reliably and efficiently, and accordingly the rotational state of the clamp arm can be detected highly accurately. 
     Further, the position setting means may be constituted from a switch, which is connected electrically with respect to the detecting section, and which sets the detection position of the detecting section corresponding to the clamped state or the unclamped state, by being pressed in the case that the clamp arm is in the clamped state or the unclamped state. 
     Furthermore, the detection body may include: 
     a holder which is supported by a connecting arm that is connected to the piston rod; and 
     a detection element having magnetism and which is accommodated in the interior of the holder, 
     wherein the magnetism of the detection element is detected by the detecting section. 
     Further still, the detection element may be constituted from a coil. 
     Still further, the detecting mechanism may include a display lamp that is illuminated in the clamped state and the unclamped state of the workpiece, the display lamp being disposed in the detecting mechanism at a position where the display lamp can be perceived visually from the exterior. 
     Further, the display lamp may include: 
     a first display lamp that is illuminated in the clamped state; and 
     a second display lamp that is illuminated in the unclamped state, 
     wherein the first display lamp and the second display lamp have different colors respectively. 
     According to the present invention, the following advantages and effects are obtained. 
     More specifically, in the case that the angle of rotation of the clamp arm is changed by adjusting the stroke displacement amount of the piston using the adjustment mechanism, since it is possible to change and set, with the position setting means, the detection position at which the detection body of the detecting mechanism is detected by the detecting section, for example, it is unnecessary for an adjustment operation to be carried out by removing the detecting mechanism from the main body portion every time that the angle of rotation of the clamp arm is changed, and thus the operation to change the detection position can be performed easily responsive to the change in the angle of rotation. As a result, the adjustment of the angle of rotation of the clamp arm can be performed reliably and effectively, and the rotational state of the clamp arm can be detected with high accuracy. 
     The above and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an exterior perspective view of a clamping device according to an embodiment of the present invention; 
         FIG. 2  is a partial exploded perspective view showing a condition in which a first casing and a switch housing are removed from the clamping device of  FIG. 1 ; 
         FIG. 3  is an overall cross-sectional view with partial omission of the clamping device shown in  FIG. 1 ; 
         FIG. 4  is an enlarged cross-sectional view showing the vicinity of a detecting mechanism in the clamping device of  FIG. 3 ; 
         FIG. 5  is an enlarged perspective view showing the vicinity of the detecting mechanism as seen from a lower oblique perspective in the clamping device shown in  FIG. 1 ; 
         FIG. 6  is a bottom plan view of the switch housing constituting the detecting mechanism shown in  FIG. 5 ; 
         FIG. 7  is a perspective view of the detecting mechanism shown in  FIG. 2  as seen from a different direction; and 
         FIG. 8  is a vertical cross-sectional view with partial omission showing an unclamped state in which the arm is rotated through a predetermined angle in the clamping device of  FIG. 3 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A preferred embodiment of a clamping device according to the present invention will be described in detail below with reference to the accompanying drawings. In  FIG. 1 , reference numeral  10  indicates a clamping device according to an embodiment of the present invention. 
     As shown in  FIGS. 1 through 3 , the clamping device  10  is equipped with a cylinder  12  driven under a supply action of a pressure fluid, a body (main body portion)  18  connected to an upper end of the cylinder  12  and which is formed in a flat shape from first and second casings  14 ,  16 , an arm (clamp arm)  22 , which is connected to rectangular bearings  20  that project outwardly from the body  18 , and a detecting mechanism  24  disposed on a side of the body  18  for detecting clamped and unclamped states of a workpiece (not shown) by the arm  22 . On a side surface of the body  18 , plural attachment holes  26  are formed to facilitate attachment of the clamping device  10  to another member by non-illustrated attachment screws, which are screw-engaged therein. 
     The cylinder  12  includes a hollow cylinder tube  30  having a cylinder chamber  28  defined therein, an end block  32  connected to one end of the cylinder tube  30  for closing the cylinder chamber  28 , and an end plate  34  for closing and sealing the other end of the cylinder tube  30 . In this case, although the cylinder tube  30  is formed with a flat shape in cross section, the cylinder tube  30  is not limited to such a shape, and may be formed, for example, with an oval or circular cross-sectional shape. 
     Through holes (not shown) that penetrate in the axial direction (the direction of arrows A and B) are formed in the four corners of the end block  32 . By insertion of fastening bolts  36  (see  FIGS. 1 and 2 ) respectively in the through holes and tightening the fastening bolts  36  with respect to the body  18 , the cylinder tube  30  and the end plate  34  are sandwiched between the end block  32  and the body  18 , and the end block  32 , the cylinder tube  30 , and the end plate  34  are connected integrally with respect to the body  18 . 
     As shown in  FIG. 3 , on side surfaces of the cylinder tube  30 , a pair of first fluid ports  38   a ,  38   b  through which a pressure fluid (e.g., compressed air) is introduced and discharged are formed at positions in the vicinity of the end block  32 , and a pair of second fluid ports  40   a ,  40   b  through which the pressure fluid (e.g., compressed air) is introduced and discharged are formed at positions in the vicinity of the end plate  34 . 
     The first fluid ports  38   a ,  38   b  and the second fluid ports  40   a ,  40   b  are separated by a predetermined distance in the axial direction of the cylinder tube  30  (the direction of arrows A and B), and are formed on opposite side surfaces at substantially symmetrical positions with respect to the axis of the cylinder tube  30 . 
     In addition, in each of the pairs of the first and second fluid ports  38   a ,  38   b ,  40   a ,  40   b , only one of the two ports is used selectively, whereas, for example, the first and second fluid ports  38   b ,  40   b , which are not used, are blocked respectively by plugs  42  (see  FIG. 3 ). Moreover, each of the first and second fluid ports  38   a ,  38   b ,  40   a ,  40   b  communicates with the cylinder chamber  28 . 
     An adjustment bolt  44  is screw-engaged from below substantially in the center of the end block  32 , and an end of the adjustment bolt  44  projects a predetermined length into the interior of the cylinder chamber  28 . The adjustment bolt  44 , for example, is constituted from a stud bolt, with a damper  46 , which is formed, for example, from a rubber material, being mounted on the end thereof. Additionally, a connecting bolt  54 , which is fastened to a later-described piston  48  of the cylinder  12 , comes into abutment against the adjustment bolt  44 , whereby displacement of the piston  48  is regulated, and shocks and impact sounds, which are generated upon abutment, are suitably absorbed by the damper  46  (see  FIG. 8 ). 
     Further, under a screw-turning action of the adjustment bolt  44 , the adjustment bolt  44  is disposed while enabling displacement thereof along the axial direction (the direction of arrows A and B) of the cylinder tube  30 . A lock nut  49  is screw-engaged with the adjustment bolt  44  on the outside of the end block  32 . In addition, by changing the length at which the adjustment bolt  44  projects toward the side of the cylinder chamber  28  (in the direction of the arrow A), the displacement amount (stroke amount) in the axial direction (the direction of the arrow B) of the piston  48  is adjusted. Together therewith, after adjustment thereof, the lock nut  49  is screw-engaged with respect to the adjustment bolt  44 , and comes into abutment against the end surface of the end block  32 , whereby displacement of the adjustment bolt  44  in the axial direction (the direction of arrows A and B) is restricted and the adjustment bolt  44  is fixed in place. 
     More specifically, the adjustment bolt  44  functions as an adjustment mechanism that is capable of adjusting the angle of rotation of the arm  22  by adjustment of the displacement amount of the piston  48 . 
     The end plate  34  includes a hole  52  that penetrates substantially through the center thereof. A piston rod  50  of the later-described cylinder  12  is inserted through the hole  52 , and the end plate  34  supports the piston rod  50  for displacement along the axial direction (the direction of arrows A and B). 
     On the other hand, the piston  48 , which is displaceable along the cylinder chamber  28 , is disposed in the interior of the cylinder tube  30 . An end of the elongate piston rod  50  is connected by the connecting bolt  54  to a center portion of the piston  48 . A piston packing  56  is installed through an annular groove on the outer circumferential surface of the piston  48 . In this case, the piston  48  is displaced in a direction (the direction of the arrow B) away from the body  18 , and by the connecting bolt  54  coming into abutment against the damper  46  provided on the adjustment bolt  44 , displacement of the piston  48  is regulated at a displacement end position (lower limit position), and together therewith, shocks that occur upon abutment of the piston  48  are buffered by the damper  46 . Further, the piston rod  50  is arranged so as to extend (in the direction of the arrow A) toward the body  18 . 
     The body  18  is constituted from the first casing  14  and the second casing  16 , which are asymmetrically shaped, and the first casing  14  and the second casing  16  are assembled together integrally. 
     Guide grooves (not shown) are formed along the axial direction (the direction of arrows A and B) respectively on inner wall surfaces of the first casing  14  and the second casing  16 . A knuckle joint  58 , which is connected to the other end of the piston rod  50 , is slidably disposed in the guide grooves. 
     Further, a slit  60  that opens over a predetermined length in the axial direction (the direction of arrows A and B) is formed in a side surface of the body  18 . A connecting arm  95  of the later-described detecting mechanism  24  is inserted through the slit  60 . 
     The knuckle joint  58  is constituted from a knuckle block  64  having a forked member  62  that branches into two portions substantially in parallel while the two portions being separated a predetermined distance from each other, and a knuckle pin  66  that is inserted through holes formed in the forked member  62 . Further, a toggle link mechanism  68  is provided for converting linear motion of the piston rod  50  into rotational motion of the arm  22 . 
     Further, upwardly projecting release projections  70  are disposed on the forked member  62  of the knuckle block  64 . The release projections  70  are disposed so as to project a predetermined length from a substantially rectangular opening  72  formed on an upper portion of the first and second casings  14 ,  16  when a workpiece is clamped by the arm  22 . 
     The toggle link mechanism  68  is disposed in the interior of the body  18 , and includes a link plate  74 , which is connected via the knuckle pin  66  between the two portions of the forked member  62  of the knuckle joint  58 , and a support lever  76 , which is supported rotatably in openings formed respectively in the first and second casings  14 ,  16 . By providing the toggle link mechanism  68  in the interior of the body  18 , adhesion of spatter or the like, which is scattered throughout the atmosphere in the installation environment of the clamping device  10 , is prevented. 
     The link plate  74  is interposed between the knuckle joint  58  and the support lever  76  for carrying out a function to link the knuckle joint  58  and the support lever  76 . Two holes, which are separated by a predetermined distance, are formed in the link plate  74 . The link plate  74  is connected to the other end of the piston rod  50  through the knuckle joint  58  and the knuckle pin  66 , which is supported pivotally in one of the holes of the link plate  74 , and is connected to the support lever  76  through a link pin  78 , which is supported pivotally in the other hole of the link plate  74 . 
     The support lever  76  includes a fork-shaped support section  80  that pivotally supports the link pin  78 , and a pair of the bearings  20  that project in directions substantially perpendicular to the axis of the piston rod  50  and are exposed through openings to the exterior of the body  18 . The arm  22 , which clamps a non-illustrated workpiece, is mounted detachably to the bearings  20 . The arm  22  is disposed for rotation together with the support lever  76  (see  FIG. 1 ). 
     More specifically, linear motion of the piston rod  50  is transferred to the support lever  76  through the link plate  74  and the knuckle joint  58 , and by rotational displacement of the support lever  76  through a predetermined angle, the arm  22 , which is mounted on the support lever  76 , is rotated. 
     Furthermore, in the interior of the first and second casings  14 ,  16 , a guide roller  84  is disposed rotatably in a cavity on an upper side portion in the vicinity of the toggle link mechanism  68 . The guide roller  84  is pivotally supported through a pin member  86 , and in the interior of the guide roller  84 , a plurality of needle bearings  88  are mounted along the circumferential direction thereof. More specifically, under a rolling action of the needle bearings  88 , the guide roller  84  is disposed while enabling smooth rotation thereof. In addition, under a rotary action of the link plate  74  that constitutes the toggle link mechanism  68 , the guide roller  84  is rotatably displaced upon contact with the curved surface of the link plate  74 . 
     On the other hand, at the top portion of the body  18 , a top cover  90  is disposed detachably thereon that covers the release projections  70 . When the release projections  70  are to be operated, the top cover  90 , which is formed, for example, from a rubber material, is taken off from the body  18  so as to expose the release projections  70  to the exterior. In the case that the release projections  70  are not operated, the top portion including the release projections  70  that project from the opening  72  is covered completely by the top cover  90 . 
     As shown in  FIGS. 3 and 4 , the detecting mechanism  24  is mounted through bolts (not shown) on a side surface of the first and second casings  14 ,  16 , and includes a switch housing  92 , a circuit board (detecting section)  94  disposed in the interior of the switch housing  92 , a detection body  96  provided on an end of a connecting arm  95  that is connected to the knuckle block  64  and which is displaced along the circuit board  94 , and an output terminal  98  that outputs, to the exterior, a detection signal representing the position of the detection body  96 , which is detected by the circuit board  94 . 
     The switch housing  92  is formed, for example, from a resin material and into a box-like shape. The open end thereof is mounted with respect to the side surface of the body  18  on which the slit  60  is formed (see  FIGS. 2 and 3 ). The switch housing  92  is mounted in covering relation to the slit  60 . Additionally, a non-illustrated bolt is inserted into a through hole  100  that penetrates perpendicularly to the longitudinal direction (the direction of arrows A and B) of the switch housing  92 , and by screw engagement of the bolt with respect to the side surface of the body  18 , the switch housing  92  is fixed with respect to the body  18 . 
     Further, the switch housing  92  includes a bulging portion  102  that bulges outwardly in a direction (lateral direction) away from the body  18  in a position near a substantially central portion along the longitudinal direction (the direction of arrows A and B). The output terminal  98  is disposed on the bottom of the bulging portion  102 . The bottom of the bulging portion  102  is formed substantially perpendicular to the longitudinal direction (the direction of arrows A and B) of the switch housing  92 . 
     The output terminal  98  is connected electrically to the circuit board  94  in the interior of the switch housing  92 , and a portion thereof is exposed to the exterior. In addition, a connector  104  is connected to the output terminal  98  at a region of the output terminal  98  that projects outwardly to the exterior. The position of the detection body  96 , which is detected by the circuit board  94 , is output as an output signal to a non-illustrated controller through a lead wire  106  that is connected to the connector  104 . 
     Further, on the bottom of the bulging portion  102 , a display lamp  108 , by which the clamped/unclamped state of the arm  22  can be visually perceived, is disposed at a position that is distanced from the output terminal  98 . Together therewith, a setting button (position setting means)  110 , which is used when an unclamped state of the arm  22  is recognized, is disposed in the vicinity of the display lamp  108 . 
     Moreover, the display lamp  108  and the setting button  110  are both exposed externally of the switch housing  92 , and are connected electrically to the circuit board  94  through non-illustrated wiring or the like. 
     The display lamp  108  is disposed at a position on the switch housing  92  where the display lamp  108  can easily be seen, and is constituted from a clamped lamp (first display lamp)  112 , which is illuminated when the arm  22  is in a clamped state, an unclamped lamp (second display lamp)  114 , which is illuminated when the arm  22  is in an unclamped state, and a power source lamp  116 , which is illuminated when power is supplied. The clamped lamp  112 , the unclamped lamp  114 , and the power source lamp  116  are positioned on a straight line separated mutually by predetermined distances, and preferably are set to different colors, respectively, to facilitate visibility thereof. 
     On the other hand, in the interior of the switch housing  92 , the circuit board  94  is disposed in parallel and separated by a predetermined distance with respect to the body  18 . The circuit board  94  is fixed with respect to the switch housing  92 , and is formed with a predetermined length in the longitudinal direction of the switch housing  92 . 
     As shown in  FIGS. 1 through 7 , the detection body  96  is made up from a holder  118  made of resin and formed with a substantially rectangular cross section, and a coil (detection element)  122  (see  FIG. 4 ) housed in an accommodation hole  120  that opens in the holder  118 . The coil  122  is sealed by a sealing body  124  in the interior of the hole. 
     Further, one side surface of the detection body  96  is connected to an end of the connecting arm  95 , whereas the other side surface thereof opposite to the one side surface is disposed substantially in parallel with and separated a predetermined distance from the circuit board  94  (see  FIG. 4 ). In addition, in a condition in which the other end of the connecting arm  95  is connected by bolts  125  to the knuckle block  64 , the piston  48 , the piston rod  50 , and the knuckle block  64  are displaced in the axial direction (the direction of arrows A and B), whereby the detection body  96  is displaced along the circuit board  94  through the connecting arm  95 . 
     More specifically, by movement of the detection body  96  along the circuit board  94 , magnetism generated by the coil  122  is detected at first and second detection positions  126 ,  128 , which are set beforehand on the circuit board  94  (see  FIG. 4 ). The detected magnetism is output as a control signal to a non-illustrated controller through the output terminal  98  and the connector  104 , whereby the angle of rotation of the arm  22  is detected based on the position of the detection body  96  in the axial direction (the direction of arrows A and B). 
     The clamping device  10  according to the embodiment of the present invention is constructed basically as described above. Next, operations and effects of the clamping device  10  will be described. 
     At first, the clamping device  10  is fixed in a predetermined position through a non-illustrated fixing means, and non-illustrated tubes, which are connected to a pressure fluid supply source, are connected respectively to the first and second fluid ports  38   a ,  40   a . On the other hand, the connector  104 , which is connected to the output terminal  98  of the detecting mechanism  24 , is connected through the lead wire  106  to a non-illustrated controller, and a state is brought about in which the power source lamp  116  in the detecting mechanism  24  is energized and illuminated. 
       FIG. 3  shows a clamped state of the clamping device  10  in which a non-illustrated workpiece is clamped, and  FIG. 8  shows an unclamped state of the clamping device  10 . Below, the clamped state shown in  FIG. 3  will be described as an initial condition. 
     In the clamped state of the arm  22 , as shown in  FIGS. 3 and 4 , the detection body  96  is positioned upwardly inside the switch housing  92 , and the first detection position  126  is set beforehand with respect to the circuit board  94  in facing relation to the detection body  96 . More specifically, as shown in  FIG. 4 , when the detection body  96  is disposed in confronting relation to the first detection position  126 , a control signal indicative of the clamped state is output from the circuit board  94  to the controller (not shown), whereby the clamped lamp  112  is energized through the circuit board  94  and is illuminated. 
     In this manner, in the initial condition of the clamping device  10  in which the clamped lamp  112  is illuminated, the pressure fluid is supplied from a non-illustrated pressure fluid supply source to the second fluid port  40   a , and the pressure fluid is introduced into the cylinder chamber  28 . Under action of the pressure fluid introduced to the cylinder chamber  28 , the piston  48  is pressed in a direction (the direction of the arrow B) away from the body  18 , and descends along the cylinder chamber  28  toward the end block  32 . Additionally, upon displacement of the piston  48  and the piston rod  50 , the knuckle block  64  is slidably displaced while being guided by the guide grooves (not shown). At this time, the first fluid port  38   a  is open to atmosphere. 
     During this time, the detection body  96  together with the connecting arm  95 , which is connected to the knuckle block  64 , descends along the circuit board  94  in the interior of the switch housing  92 , and the detection body  96  separates away from the first detection position  126 , accompanied by the magnetism of the coil  122  no longer being detectable in the first detection position  126 . As a result, since the output signal to the controller becomes de-energized, it is confirmed in the controller that the clamped state of the clamping device  10  has been released. Simultaneously, energization from the circuit board  94  to the clamped lamp  112  of the display lamp  108  is terminated, and the illuminated state of the clamped lamp  112  is extinguished. Consequently, by extinguishing the illuminated state of the clamped lamp  112 , the fact that the clamped state of the clamping device  10  has been released can reliably be recognized from the exterior of the clamping device  10 . Moreover, at this time, the unclamped lamp  114  remains in a non-illuminated state. 
     Linear motion of the piston  48  is transmitted to the toggle link mechanism  68  through the piston rod  50  and the knuckle joint  58 , and is converted into rotational motion of the arm  22  under a rotary action of the support lever  76  that makes up the toggle link mechanism  68 . More specifically, in accordance with linear motion of the piston  48 , a force is brought about, which acts to pull the link plate  74  and the knuckle joint  58  connected to the piston rod  50  downwardly (in the direction of the arrow B). 
     In addition, the pulling force applied to the link plate  74  causes the link plate  74  to be rotated through a predetermined angle about the knuckle pin  66 , together with the support lever  76  being rotated in a clockwise direction under a linking action of the link plate  74 , whereby the arm  22  is rotated through a predetermined angle about the bearings  20  of the support lever  76 . Further, upon abutment of the connecting bolt  54  connected to the piston  48  against the damper  46  of the adjustment bolt  44  that is screw-engaged with the end block  32 , displacement of the piston  48  is regulated, and rotational displacement of the arm  22  through the piston rod  50  and the toggle link mechanism  68  is stopped. 
     As a result, as shown in  FIG. 8 , the clamping device  10  is placed in an unclamped state in which the arm  22  is rotated clockwise through a predetermined angle away from the clamped state, and the detection body  96  descends and is placed in a state at which the detection body  96  confronts the second detection position  128  of the circuit board  94 . 
     In addition, after magnetism from the coil  122  of the detection body  96  is detected at the second detection position  128 , the detected magnetism is output as a control signal to the non-illustrated controller, whereby the unclamped state of the clamping device  10  is confirmed, together with the unclamped lamp  114  of the display lamp  108  being energized through the circuit board  94  and becoming illuminated. 
     The second detection position  128  of the circuit board  94  is set beforehand at a position (refer to the two-dot dashed line in  FIG. 4 ) where the detection body  96  confronts the second detection position  128  in the unclamped state of the arm  22 . 
     On the other hand, in the unclamped state of the clamping device  10  shown in  FIG. 8 , under the action of a non-illustrated switching valve, pressure fluid is supplied to the first fluid port  38   a , and the piston  48  is displaced toward the body  18  (in the direction of the arrow A). At this time, the second fluid port  40   a  is open to atmosphere. In addition, upon displacement of the piston rod  50  together with the piston  48  toward the body  18  (in the direction of the arrow A), the support lever  76  is rotated in the opposite direction through the link plate  74  that constitutes the toggle link mechanism  68 , accompanied by the arm  22  being rotated toward the non-illustrated workpiece. 
     At this time, the detection body  96  is displaced upwardly (in the direction of the arrow A) along the circuit board  94  through the connecting arm  95  that is connected to the knuckle block  64 , and by the detection body  96  being brought to a position where the detection body  96  confronts the first detection position  126  of the circuit board  94 , magnetism from the coil  122  is detected and the detection body  96  is detected as having reached the first detection position  126 . As a result, the fact that the detection body  96  has reached the first detection position  126  is output as an output signal to the non-illustrated controller through the output terminal  98  and the connector  104 , and the clamped state of the clamping device  10  is confirmed. Further, the circuit board  94  suspends energization of the unclamped lamp  114  to turn off the unclamped lamp  114 , whereas the clamped lamp  112  is energized and illuminated. 
     Next, a case will be described in which, in the above-described clamping device  10 , the angle of rotation of the arm  22  is adjusted by the adjustment bolt  44 , accompanied by performing an adjustment of the detecting mechanism  24 . A case shall be explained in which the angle of rotation of the arm  22  is made smaller than that of the above-described clamping device  10 , and more specifically, wherein the unclamped position of the arm  22  is changed. 
     First, the adjustment bolt  44  is screw-rotated such that the length of the end of the adjustment bolt  44  that protrudes toward the body  18  (in the direction of the arrow A) is increased, and then the adjustment bolt  44  is fixed in place by the lock nut  49 . Accordingly, when the arm  22  is switched from the clamped state to the unclamped state, since the end of the adjustment bolt  44  is moved more toward the body  18  compared with the case of the above-described clamping device  10 , the amount by which the piston  48  is displaced downward is made shorter. Owing thereto, the angle of rotation of the arm  22 , which is rotationally displaced through the toggle link mechanism  68  upon displacement of the piston  48 , also becomes smaller. 
     Next, after the connecting bolt  54  fastened to the piston  48  is brought into abutment against the adjustment bolt  44  and the arm  22  is confirmed to be in the unclamped state, by an operator pressing the setting button  110  of the detecting mechanism  24 , in the circuit board  94 , the region thereof confronted by the detection body  96  is set as a new second detection position  128 . More specifically, since the unclamped position is changed by changing the angle of rotation of the arm  22  by way of the adjustment bolt  44 , by pressing the setting button  110 , the second detection position  128  at which the unclamped state is detected is reset on the circuit board  94 . 
     Consequently, even in the event that the angle of rotation of the arm  22  is changed, since the second detection position  128  with respect to the circuit board  94  can easily be reset by the setting button  110 , the unclamped position of the arm  22 , which has been changed, can be detected reliably and highly accurately by the detecting mechanism  24 . 
     In the foregoing manner, with the present embodiment, even in the case that the angle of rotation of the arm  22  is changed in the clamping device  10 , by pressing the setting button  110  of the detecting mechanism  24  in the unclamped state of the arm  22 , the second detection position  128  of the circuit board  94  confronting the detecting mechanism  24  can be reset. Owing thereto, for example, it is unnecessary for an adjustment operation to be carried out by removing the detecting mechanism  24  from the body  18  every time that the angle of rotation of the arm  22  is changed, and thus the adjustment operation of the detecting mechanism  24  with respect to changes in the angle of rotation can easily be performed. As a result, adjusting the angle of rotation of the arm  22  can be performed reliably and efficiently. 
     Further, since the clamped and unclamped states of the arm  22  can be detected electrically in the detecting mechanism  24 , the rotational state of the arm  22  can be confirmed with greater accuracy. 
     Furthermore, since the clamped and unclamped states of the arm  22  can be confirmed more easily and reliably from the exterior by the clamped lamp  112  and the unclamped lamp  114  in the display lamp  108 , for example, even in an installation environment where it may be difficult to visually perceive the rotational state of the arm  22  (for example, in a dark location), an advantage results in that the rotational state of the arm  22  can be confirmed reliably by confirming the state of the display lamp  108 . 
     Further still, in the above-described embodiment, although a case has been described in which resetting of the second detection position  128  for detecting the unclamped state of the arm  22  is performed by the setting button  110 , the invention is not limited to this feature. For example, an arrangement may be provided in which the first detection position  126  for detecting the clamped state of the arm  22  is reset by the setting button  110 . 
     The clamping device according to the present invention is not limited to the embodiments described above. It goes without saying that various alternative or additional structures could be adopted therein without departing from the essential scope of the present invention as set forth in the appended claims.