Clamp

Abstract

A clamping apparatus (10) is provided with: a metallic detector (20) that is provided to a pivot shaft (90) pivotally moving integrally with a clamp arm (18) under the operation of a driving unit (12), in such a manner as to extend along the pivot shaft (90) so as to be around the axis thereof; and one proximity sensor (22) that is arranged so as to be opposed to the detector (20) and that detects the magnetic loss of the detector (20). The detector (20) is formed so that the area of a sensor opposing part (126) opposed to a detection surface (124) of the proximity sensor (22) changes in association with the pivotal moving of the pivot shaft (90).

Description

Clamping device The present invention relates to a clamping device that clamps a workpiece using a rotating clamping arm. Conventionally, in automated assembly lines for automobiles and the like, a welding process has been carried out in which multiple press-formed sheet metals are clamped together using a clamping device and then welded to each other. In this clamping device, the piston in the cylinder is displaced axially under the action of fluid pressure, thereby rotating the clamping arm via a toggle link mechanism connected to the piston rod. This switches the clamping arm between the clamped position and the unclamped position. Japanese Patent Publication No. 2001-113468 discloses a clamping device that detects the rotational position (clamped and unclamped states) of a clamping arm by detecting the position of a metal holding member that is displaced by stroke together with a piston rod using two induction-type proximity sensors. This clamping device accommodates changes in the rotational angle range of the clamping arm by replacing a plurality of holding members of different shapes. European Patent Application Publication No. 0636449 discloses a clamping device for detecting the position of a piston rod using two limit switches mounted on a switch holder. The switch holder is provided with multiple mounting holes for the limit switches along the axial direction of the piston rod, and the mounting position of the limit switches can be changed. In the case of Japanese Patent Publication No. 2001-113468, the rotational position (rotation angle) of the clamp arm is indirectly detected by detecting the position of the holding member that is displaced by the stroke together with the piston rod. Therefore, the accuracy of detecting the position of the clamp arm is affected by the machining accuracy and assembly accuracy of the toggle link mechanism. Consequently, it is not easy to improve the accuracy of detecting the rotational position of the clamp arm. Furthermore, the clamping device described in Japanese Patent Publication No. 2001-113468 has two proximity sensors, which increases the number of parts. In addition, changing the rotation angle range of the clamping arm requires replacing the holding member, making the work complicated. In European Patent Application Publication No. 0636449, when changing the rotation angle range of the clamp arm, it is necessary to change the limit switch to the position of the mounting hole corresponding to the arm opening degree, so the operation is complicated. The present invention has been made in consideration of such problems, and an object thereof is to provide a clamp device that can reduce the number of parts, directly and highly accurately detect the rotation position of the clamp arm, and easily perform the operation of changing the rotation angle range of the clamp arm. In order to achieve the above object, a clamp device according to the present invention is a clamp device that clamps a workpiece by a rotating clamp arm, and includes a clamp body, a drive unit provided on the clamp body, a rotation shaft that rotates integrally with the clamp arm under the action of the drive unit, a metal detector provided on the rotation shaft and extending along the axis of the rotation shaft, and one proximity sensor disposed so as to face the detector and generating eddy currents in the detector and detecting magnetic loss. The detector is formed such that the area of a sensor facing portion facing the detection surface of the proximity sensor in the detector changes as the rotation shaft rotates. According to such a configuration, the change in the area of the sensor facing portion accompanying the rotation of the rotation shaft is detected by one proximity sensor. Therefore, the number of parts can be reduced, and the rotation position of the clamp arm can be detected directly and highly accurately. In addition, when changing the rotation angle range of the clamp arm, it is not necessary to replace the detector or change the position of the proximity sensor, so the operation of changing the rotation angle range of the clamp arm can be easily performed. In the above clamp device, the detector may be formed in a plate shape. According to such a configuration, the detector can be easily manufactured by press molding. In the above clamp device, a long groove may be formed in the detector along the extending direction of the detector so that the area of the sensor facing portion changes as the rotation shaft rotates. With this configuration, the area of ​​the sensor-facing portion can be easily changed by using the long groove. In the clamping device described above, the side of the long groove may extend linearly in a direction intersecting the extension direction of the detection body. With this configuration, the resonant impedance and inductance of the proximity sensor can be changed nonlinearly. In the clamping device described above, the sides of the long groove may extend in a curved shape. With this configuration, the resonant impedance and inductance of the proximity sensor can be changed linearly. In the clamping device described above, the detection body may have one of the long grooves formed therein, and the sensor-facing portion may be provided spanning both sides of the long groove. This configuration allows for a simplification of the detection element's structure while suppressing a decrease in rigidity. In the clamping device described above, the detection body may have two elongated grooves arranged side by side in the width direction of the detection body, and the sensor-facing portion may be provided between the two elongated grooves. With this configuration, the area of ​​the sensor-facing part can be reliably changed by the rotation of the pivot axis. In the clamping device described above, the detection body has a communication groove that connects the ends of the two long grooves to each other, and the groove width of the communication groove may be greater than or equal to the diameter of the detection surface. With this configuration, the resonant impedance and inductance of the proximity sensor can be made discontinuous (changed abruptly) when the detection surface faces the communication groove. As a result, even if the resonant impedance and inductance of the proximity sensor fluctuate due to temperature changes in the operating environment of the clamping device, the clamped or unclamped state can be reliably detected. In the clamping device described above, the detection body may be fixed to the pivot shaft by a screw member. This configuration allows the detection element to be firmly fixed to the pivot axis. Therefore, it is possible to suppress fluctuations in the distance between the sensor-facing surface and the detection surface when the pivot axis rotates. In the clamping device described above, at least one end of the detection body in the extending direction may be provided with a mounting portion having an insertion hole through which the screw member is inserted. With this configuration, the detection object can be fixed to the pivot axis with a simple setup. In the clamping device described above, holding portions may be provided at both ends of the detection body in the extending direction for clamping the outer circumferential surface of the pivot shaft from the radially outward direction. With this configuration, the detection object can be fixed to the rotation axis with higher precision and more firmly. In the clamping device described above, a recess may be formed on the outer circumferential surface of the pivot shaft in the portion facing the detection surface. With this configuration, even if the pivot shaft is made of metal, the proximity sensor can suppress the generation of eddy currents in the pivot shaft. According to the present invention, since the change in the area of ​​the sensor-facing part accompanying the rotation of the pivot axis is detected by a single proximity sensor, the number of parts can be reduced, and the rotation position of the clamp arm can be detected directly and with high precision, making it easy to change the rotation angle range of the clamp arm. The above objectives, features, and advantages will become clearer from the following description of preferred embodiments in conjunction with the attached drawings. Figure 1 is a perspective view of a clamping device according to one embodiment of the present invention. Figure 2 is a partially exploded perspective view of the clamping device. Figure 3 is a longitudinal cross-sectional view showing the clamped state of the clamping device. Figure 4 is an exploded perspective view of the support lever and detection body constituting the clamping device. Figure 5 is an unfolded view of the detection body. Figure 6 is a block diagram of the main parts of the clamping device. Figure 7 is a longitudinal cross-sectional view showing the unclamped state of the clamping device. Figure 8 is a graph showing the relationship between the area of ​​the sensor-facing portion and the detection resonance impedance. Figure 9A is a perspective view of a detection body according to a first modified example, Figure 9B is an unfolded view of the detection body, and Figure 9C is a graph showing the relationship between the area of ​​the sensor-facing portion and the detection resonance impedance in the detection body. Figure 10A is a perspective view of a detection body according to a second modified example, Figure 10B is an unfolded view of the detection body, and Figure 10C is a graph showing the relationship between the area of ​​the sensor-facing portion and the detection resonance impedance in the detection body. Figure 11A is a perspective view of the detection body according to the third modification, Figure 11B is an unfolded view of the detection body, and Figure 11C is a graph showing the relationship between the area of ​​the sensor-facing part of the detection body and the detection resonance impedance. Figure 12A is a perspective view of the detection body according to the fourth modification, Figure 12B is an unfolded view of the detection body, and Figure 12C is a graph showing the relationship between the area of ​​the sensor-facing part of the detection body and the detection resonance impedance. Figure 13 is a perspective view showing the detection body according to the fifth modification mounted on a pivot shaft. Figure 14A is a perspective view of the detection body in Figure 13, and Figure 14B is an unfolded view of the detection body in Figure 14A. Hereinafter, preferred embodiments of the clamping device according to the present invention will be described with reference to the attached drawings. A clamping device 10 according to one embodiment of the present invention is used, for example, in an automated assembly line for automobiles, to clamp multiple press-formed steel plates or other sheet materials when welding them together. As shown in Figures 1 to 3, the clamping device 10 comprises a drive unit 12, a clamp body 14 connected to the drive unit 12, a link mechanism (power transmission mechanism) 16 disposed within the clamp body 14, a clamp arm 18 that rotates via the link mechanism 16 under the action of the drive unit 12, a detection body 20, a proximity sensor 22, and a control unit 24. The drive unit 12 is configured as a fluid pressure cylinder and has a cylinder tube 26 that is configured in the shape of a flattened cylinder. However, the drive unit 12 may also be configured as an electric actuator. In Figure 3, the opening at one end of the cylinder tube 26 (direction of arrow A) is closed by an end block 28, and the opening at the other end of the cylinder tube 26 (direction of arrow B) is closed by a rod cover 30. A piston 32 is disposed inside the cylinder tube 26 so as to be displaceable along its axial direction, and a piston rod 34 is connected to the piston 32. The cylinder tube 26 is not limited to a flattened cylindrical shape, but can take any shape such as a true cylindrical shape or an elliptical cylindrical shape. The cylinder tube 26 has a first port 38 that communicates with a first cylinder chamber 36 formed between the end block 28 and the piston 32, and a second port 42 that communicates with a second cylinder chamber 40 formed between the piston 32 and the rod cover 30. The first port 38 and the second port 42 are connected to tubes (not shown) for supplying and discharging compressed fluid (driving fluid) to cause the piston 32 to reciprocate. The end block 28, cylinder tube 26, and rod cover 30 are integrally connected by a plurality of fastening bolts 44. An adjustment bolt 46 is screwed into the approximate center of the end block 28 to adjust the rotation angle range (arm opening) of the clamp arm 18 by adjusting the stroke of the piston 32. The adjustment bolt 46 allows adjustment of the protruding length of the first cylinder chamber 36 under its screw action, and a damper 48 is attached to the head located inside the first cylinder chamber 36 to mitigate the impact and collision noise of the piston 32. An annular piston packing 50 is fitted to the outer surface of the piston 32 via an annular groove. One end of the piston rod 34 is fixed to the center of the piston 32. A rod hole is formed in the center of the rod cover 30 through which the piston rod 34 is inserted. An annular rod packing 52 is fitted to the wall surface constituting the rod hole via an annular groove. The clamp body 14 is connected to the other end of the rod cover 30 and is made of a metal material such as iron, stainless steel, or aluminum. The clamp body 14 is provided with a bracket 53 for attaching the clamp device 10 to a fixing member (not shown) (see Figure 1). As shown in Figures 1 and 2, the clamp body 14 has a pair of cover portions 54 and 56 with a U-shaped cross-section. These cover portions 54 and 56 are configured to be substantially symmetrical and are fastened to each other by a plurality of screw members 60 so as to form a chamber 58 (see Figure 3) in which the link mechanism 16 is housed. In Figures 2 and 3, a knuckle joint 62 is connected to the other end of the piston rod 34. The knuckle joint 62 has a base portion 66 with a hole 64 for holding the other end of the piston rod 34, two side plate portions 68 and 70 protruding from the base portion 66 in the direction of arrow B, and a knuckle pin 72 connecting these side plate portions 68 and 70. The two side plate portions 68 and 70 face each other in the thickness direction of the clamp body 14. An annular member 76 is provided on the knuckle pin 72 via a bearing 74. When the clamp arm 18 clamps the workpiece, the annular member 76 contacts the release pressing member 78 provided on the clamp body 14, causing the pressing member 78 to protrude a predetermined length outward from the clamp body 14 (in the direction of arrow B). The pressing member 78 is a pin member extending along the axial direction of the piston rod 34, and its ends are formed to be larger in diameter than the middle section, preventing it from coming out of the clamp body 14. The user can release the clamped state of the workpiece (put it in an unclamped state) by pressing the pressing member 78 in the direction of arrow A with a tool such as a hammer (see Figure 7). The link mechanism 16 converts the reciprocating motion of the piston 32 into the rotational motion of the pivot shaft 90, which will be described later. This link mechanism 16 has two link plates 80 and 82, a link pin 84, and a support lever 86. Link plate 80 is located between the annular member 76 and the side plate portion 68, and link plate 82 is located between the annular member 76 and the side plate portion 70. Each link plate 80, 82 extends in an arc shape (or semi-arc shape). A knuckle pin 72 is inserted through a hole formed at one end of each link plate 80, 82, and a link pin 84 is inserted through a hole formed at the other end of each link plate 80, 82. In other words, each link plate 80, 82 is rotatably supported with respect to the knuckle pin 72 and the link pin 84, respectively. As shown in Figures 3 and 4, the support lever 86 is made of, for example, a metal material. However, the support lever 86 may be made of a resin material or the like that does not generate eddy currents. The support lever 86 has a support portion 88 that is rotatably supported with respect to the link pin 84, a pivot shaft 90 integrally provided with the support portion 88 and extending in a direction perpendicular to the axis of the piston rod 34, and arm mounting portions 92 and 94 provided at both ends of the pivot shaft 90. The support portion 88 is located in the axial center of the pivot shaft 90 and includes a support portion body 96 with a hole through which a link pin 84 is inserted, and two leg portions 98 and 100 extending from the support portion body 96 so as to straddle the pivot shaft 90. The side surface of the leg portion 100 has a projection 102 that protrudes on the side opposite to the piston rod 34 and a screw hole 104 for attaching the detection body 20. A semicircular recess 106 is formed in the axial center of the outer surface of the pivot shaft 90, with a cross-section perpendicular to the axis Ax of the pivot shaft 90. The recess 106 is located on the opposite side of the support portion 88. The dimensions of the recess 106 along the axial direction of the pivot shaft 90 are smaller than the width dimension of the detection body 20 and larger than the diameter of the detection surface 124 of the proximity sensor 22, which will be described later. Both ends of the pivot shaft 90 are rotatably supported by bearings 107 and 109 provided on the clamp body 14 (see Figures 1 and 2). The arm mounting portions 92 and 94 are configured to allow the clamp arm 18 to be attached and detached. As shown in Figures 4 and 5, the detection body 20 is made of a metallic material such as pure iron, steel, copper, or aluminum. In other words, the detection body 20 is made of a material that generates eddy currents when the proximity sensor 22 is activated. The detection body 20 is integrally formed by press molding a thin metal sheet. The detection body 20 has a main body portion 108 that extends around the axis of the pivot shaft 90 and a mounting portion 110 provided at the end of the main body portion 108 in the R1 direction. The main body portion 108 is formed by bending a substantially rectangular metal plate into a substantially semi-circular arc and is provided to cover the recess 106 of the pivot shaft 90. In the center of the width direction of the main body portion 108, a long groove (long hole) 112 is formed that extends along the axis of the pivot shaft 90 (the direction in which the main body portion 108 extends). The elongated groove 112 is formed in a roughly triangular shape. Each side 112a and 112b of the elongated groove 112 extends linearly in a direction intersecting the extending direction of the main body portion 108. In other words, each side 112a and 112b of the elongated groove 112 extends linearly so as to be close to each other in the direction of arrow R1. That is, the groove width of the elongated groove 112 gradually widens from one end of the main body portion 108 to the other end (in the direction of arrow R2). The mounting portion 110 extends in a rectangular shape from the center of the width direction of one end of the main body portion 108, and has a screw insertion hole 116 through which a screw member 114 for fixing the detection body 20 to the support lever 86 (rotation shaft 90) is inserted. As shown in Figure 6, the proximity sensor 22 is configured as an inductive proximity sensor and includes a detection coil 118 provided close to the main body 108 of the detection body 20, an oscillation circuit 120 electrically connected to the detection coil 118, and a detection circuit 122 electrically connected to the oscillation circuit 120. The detection coil 118 is positioned so that its detection surface (coil surface) 124 faces the main body 108. Specifically, the detection coil 118 is positioned and fixed to the clamp body 14 so that the sensor facing portion 126 (see Figure 5) of the main body 108 that faces the detection surface 124 is located on both sides of the long groove 112. The oscillation circuit unit 120 drives the detection coil 118 to oscillate at a predetermined oscillation frequency. The detection circuit unit 122 detects the resonant impedance (parallel resonant impedance) based on the output signal of the oscillation circuit unit 120. That is, the proximity sensor 22 detects the rotation position (rotation angle) of the clamp arm 18 by detecting the change in the area of ​​the sensor-facing part 126 accompanying the rotation of the pivot shaft 90 as a change in resonant impedance. In Figures 3 and 6, the control unit 24 is housed in a casing provided on the clamp body 14, and the proximity sensor 22 is electrically connected by lead wires 128. The casing is provided with a setting button 130 that can be pressed by the user from the outside, a connector 132 to which a cable connected to an external device (power supply, etc.) can be connected, and a display unit 134 that is visible from the outside. As shown in Figure 6, the display unit 134 includes a power indicator light 136, a clamp indicator light 138, and an unclamping indicator light 140. The control unit 24 includes a determination unit 142, a threshold setting unit 144, and an output unit 146. The determination unit 142 determines whether the clamp state is active (whether the clamp arm 18 is in the clamp position) based on a comparison between the resonant impedance detected by the detection circuit unit 122 of the proximity sensor 22 (hereinafter referred to as the detected resonant impedance) and the clamp threshold Za. The determination unit 142 also determines whether the unclamped state is active (whether the clamp arm 18 is in the unclamped position) based on a comparison between the detected resonant impedance and the unclamped threshold Zb. The threshold setting unit 144 sets the clamp threshold Za based on the output signal (detection resonant impedance) of the detection circuit unit 122 when the setting button 130 is operated for the first time. The threshold setting unit 144 also sets the unclamping threshold Zb based on the detection resonant impedance when the setting button 130 is operated for the second time. The clamp threshold Za and unclamping threshold Zb set by the threshold setting unit 144 are stored in the controller. The output unit 146 turns on or off the power lamp 136, clamp lamp 138, and unclamping lamp 140. The clamping device 10 according to this embodiment is basically configured as described above, and its operation will now be explained. The unclamped state shown in Figure 7 will be described as the initial state. First, the user attaches the bracket 53 of the clamping device 10 to a fixing member (not shown). The clamping device 10 is then connected to an external device (power supply, etc.) by connecting the cable to the connector 132. This supplies power to the control unit 24, causing the power indicator light 136 to illuminate. In the initial state, the unclam lamp 140 is lit and the clamp lamp 138 is off, and the piston 32 is positioned on the end side of the cylinder tube 26 towards the end block 28 and in contact with the damper 48. At this time, as shown in Figure 5, the detection surface 124 of the proximity sensor 22 is at position P2 opposite to the end of the long groove 112 in the direction of arrow R2, and the sensor-facing portion 126 of the main body 108 that faces the detection surface 124 has an area of ​​S1. When clamping a workpiece, compressed fluid is supplied to the first port 38 with the second port 42 open to the atmosphere. As a result, the piston 32 is displaced toward the rod cover 30 (in the direction of arrow B), as shown in Figure 3. This linear motion of the piston 32 is transmitted to the link mechanism 16 via the piston rod 34 and the knuckle joint 62, and the clamp arm 18 rotates integrally in the direction of arrow R2 (clockwise in Figure 3) under the rotational action of the pivot shaft 90. At this time, the detection body 20 fixed to the support lever 86 also rotates integrally with the pivot axis 90, so that the detection surface 124 is displaced relative to the main body 108 in the direction of arrow R1, and the area of ​​the sensor-facing portion 126 increases, causing the detection resonance impedance to decrease nonlinearly (see Figures 5 and 8). If the detected resonant impedance is greater than the clamp threshold Za and less than the unclamping threshold Zb, the determination unit 142 determines that it is in an intermediate state (a transition state from the unclamped state to the clamped state). At this time, the output unit 146 turns off both the unclamping lamp 140 and the clamping lamp 138. This allows the user to confirm that it is in an intermediate state by visually observing that the unclamping lamp 140 and the clamping lamp 138 are turned off. Then, when the detection surface 124 is displaced to position P1, which is opposite the end of the long groove 112 in the direction of arrow R1, the area of ​​the sensor-facing portion 126 becomes S2. Note that area S2 is larger than area S1. At this time, the detection resonance impedance reaches the clamp threshold Za, so the determination unit 142 determines that it is in a clamped state. The output unit 146 also turns on the clamp lamp 138 while keeping the unclamp lamp 140 off. This allows the user to confirm that it is in a clamped state by visually checking the clamp lamp 138. At this time, the displacement of the piston 32 toward the rod cover 30 side stops. On the other hand, to release the clamped state of the workpiece, compressed fluid is supplied to the second port 42 with the first port 38 open to the atmosphere. As a result, the piston 32 is displaced toward the end block 28, as shown in Figure 7. This linear motion of the piston 32 is transmitted to the link mechanism 16 via the piston rod 34 and the knuckle joint 62, and the clamp arm 18 rotates integrally in the direction of arrow R1 (clockwise in Figure 7) under the rotational action of the pivot shaft 90. At this time, the detection body 20 fixed to the support lever 86 also rotates integrally with the pivot axis 90, causing the detection surface 124 to be displaced relative to the main body 108 in the direction of arrow R2, and the area of ​​the sensor-facing portion 126 to decrease, resulting in a nonlinear increase in the detection resonance impedance (see Figure 8). If the detected resonant impedance is greater than the clamp threshold Za and less than the unclamping threshold Zb, the determination unit 142 determines that it is in an intermediate state (a transition state from the clamped state to the unclamped state). At this time, the output unit 146 turns off both the unclamping lamp 140 and the clamping lamp 138. Then, when the detection surface 124 is displaced to position P2, which is opposite the end of the long groove 112 in the direction of arrow R2, the area of ​​the sensor facing portion 126 becomes S1. At this time, the detection resonance impedance reaches the unclamping threshold Zb, so the determination unit 142 determines that it is in an unclamped state. The output unit 146 also turns on the unclamping lamp 140 while keeping the clamp lamp 138 off. At this time, the piston 32 comes into contact with the damper 48, stopping the displacement of the piston 32 toward the end block 28, and stopping the rotation of the pivot shaft 90 and the clamp arm 18. In such a clamping device 10, the arm opening angle is adjusted and the clamp threshold Za and unclamping threshold Zb are set according to the shape and size of the workpiece. To set the arm opening angle, the length of the adjustment bolt 46 protruding into the first cylinder chamber 36 is changed by turning the adjustment bolt 46. This changes the stroke length of the piston 32, and thus changes the arm opening angle of the clamp arm 18, which rotates via the link mechanism 16 under the action of the linear motion of the piston 32. To widen the arm opening angle, the length of the adjustment bolt 46 protruding into the first cylinder chamber 36 is reduced, and to narrow the arm opening angle, the length of the adjustment bolt 46 protruding into the first cylinder chamber 36 is increased. Furthermore, when changing the clamp threshold Za, the clamp arm 18 is brought into contact with the workpiece and the workpiece is clamped by displacing the piston 32 toward the rod cover 30 under the action of fluid pressure. In this state, when the user continuously presses the setting button 130 for a predetermined time (for example, 3 seconds) or longer (performing the first operation), the value of the detected resonance impedance at this time is reset as the new clamp threshold Za and stored in the memory of the control unit 24. Furthermore, when changing the unclamping threshold Zb, the user presses the setting button 130 for less than a predetermined time (for example, about 1 second) while the clamp arm 18 is positioned at a predetermined rotation angle (unclamping angle). At this time, the value of the detected resonant impedance is reset as the new unclamping threshold Zb and stored in the memory of the control unit 24. Thus, even if the shape or size of the workpiece is changed, the clamp threshold Za and unclamping threshold Zb can be easily reset by pressing the setting button 130 while the clamp arm 18 is positioned at a predetermined angle. Furthermore, by changing the pressing time of the setting button 130, both the clamp threshold Za and unclamping threshold Zb can be set with a single setting button 130. In this embodiment, the change in the area of ​​the sensor-facing portion 126 accompanying the rotation of the pivot shaft 90 is detected by a single proximity sensor 22. Therefore, the number of parts can be reduced, and the rotational position of the clamp arm 18 can be detected directly and with high precision. Furthermore, when changing the rotational angle range (arm opening) of the clamp arm 18, there is no need to replace the detection body 20 or change the position of the proximity sensor 22, making it easy to change the arm opening. In this embodiment, since the detection body 20 is plate-shaped, the detection body 20 can be easily manufactured by press molding. Furthermore, the detection body 20 has a long groove 112 extending along the direction of extension of the detection body 20 so that the area of ​​the sensor-facing portion 126 changes with the rotation of the pivot axis 90. Therefore, the area of ​​the sensor-facing portion 126 can be easily changed by the long groove 112. Furthermore, since the sides 112a and 112b of the elongated groove 112 extend linearly in a direction intersecting the extending direction of the detection body 20, the resonant impedance of the proximity sensor 22 can be changed nonlinearly. Moreover, since the sensor-facing portion 126 is provided spanning both sides of the elongated groove 112, the configuration of the detection body 20 can be simplified and a decrease in rigidity can be suppressed. In this embodiment, a mounting portion 110 is provided at one end of the detection body 20 in the extending direction, through which a screw insertion hole 116 is formed for inserting a screw member 114. This allows the detection body 20 to be firmly fixed to the pivot shaft 90 (support lever 86) with a simple configuration. This suppresses fluctuations in the distance between the sensor-facing portion 126 and the detection surface 124 when the pivot shaft 90 rotates. Furthermore, since a recess 106 is formed in the part of the pivot shaft 90 that faces the detection surface 124 when the pivot shaft 90 rotates, even if the pivot shaft 90 is made of metal, the proximity sensor 22 can suppress the generation of eddy currents in the pivot shaft 90. Next, the detection body 150 according to the first modified example will be described with reference to Figures 9A to 9C. In this detection body 150, the same reference numerals are used for components identical to those of the detection body 20 described above, and their detailed explanations will be omitted. Furthermore, the same effects and functions are obtained for parts of the detection body 150 that are common to the detection body 20 described above. As shown in Figures 9A and 9B, the detection body 150 according to the first modified example has a main body portion 152 extending around the axis of the pivot shaft 90 and a mounting portion 110 provided at the end of the main body portion 152 in the direction of arrow R1. Two long grooves 154 and 156 are arranged side by side in the width direction of the main body portion 152, extending along the axis of the pivot shaft 90 (the direction in which the main body portion 152 extends). As a result, the main body portion 152 is formed with a rectangular outer frame portion 158 located outside the long grooves 154 and 156, and an intermediate portion 160 located between the long grooves 154 and 156. The intermediate portion 160 extends along the axis of the pivot shaft 90. Both ends of the intermediate portion 160 in the direction of extension are connected to the outer frame portion 158. Each of the elongated grooves 154 and 156 is formed in a roughly triangular shape. The sides 154a and 156a of each elongated groove 154 and 156 on the intermediate portion 160 side extend linearly in a direction intersecting the extending direction of the main body portion 152. In other words, the sides 154a and 156a of each elongated groove 154 and 156 extend linearly so that they are close to each other in the direction of arrow R1. That is, the width dimension of the intermediate portion 160 narrows in the direction of arrow R1. When such a detection body 150 is used, in the initial state, the detection surface 124 of the proximity sensor 22 is at position P2 opposite the end of the intermediate portion 160 in the direction of arrow R2, and the sensor-facing portion 126 has an area of ​​S4. Note that the clamp threshold Za is greater than the unclamping threshold Zb. As shown in FIGS. 9B and 9C, when clamping the workpiece, the detection surface 124 is displaced relative to the main body portion 152 in the direction of arrow R1, and the area of the sensor facing portion 126 becomes smaller, and the detected resonance impedance increases non-linearly. When the detected resonance impedance is greater than the unclamping threshold value Zb and less than the clamping threshold value Za, the determination unit 142 determines that it is in an intermediate state (a transition state from the unclamped state to the clamped state). Then, when the detection surface 124 is displaced to the position P1 facing the end portion of the intermediate portion 160 in the direction of arrow R1, the area of the sensor facing portion 126 becomes S3. Note that the area S3 is smaller than the area S4. At this time, since the detected resonance impedance reaches the clamping threshold value Za, the determination unit 142 determines that it is in the clamped state. On the other hand, when releasing the clamped state of the workpiece, the detection surface 124 is displaced relative to the main body portion 152 in the direction of arrow R2, and the area of the sensor facing portion 126 becomes larger, and the detected resonance impedance decreases non-linearly. When the detected resonance impedance is less than the clamping threshold value Za and greater than the unclamping threshold value Zb, the determination unit 142 determines that it is in an intermediate state (a transition state from the clamped state to the unclamped state). Then, when the detection surface 124 is displaced to the position P2 facing the end portion of the intermediate portion 160 in the direction of arrow R2, the area of the sensor facing portion 126 becomes S4. At this time, since the detected resonance impedance reaches the unclamping threshold value Zb, the determination unit 142 determines that it is in the unclamped state. According to this modification example, since the sensor facing portion 126 is provided in the intermediate portion 160 located between the two long grooves 154 and 156, the area of the sensor facing portion 126 can be reliably changed by the rotation of the rotation shaft 90. Next, the detector 170 according to the second modification will be described with reference to FIGS. 10A to 10C. In this detector 170, the same components as those of the above-described detector 150 are denoted by the same reference numerals, and detailed description thereof will be omitted. Further, in the detector 170, the same effects as those of the detector 150 can be obtained for the parts common to the above-described detector 150. The same applies to the detector 180 according to the third modification and the detector 200 according to the fifth modification described later. As shown in FIGS. 10A and 10B, the detector 170 according to the second modification includes a main body portion 172 extending around the axis of the rotation shaft 90, and a mounting portion 110 provided at an end portion of the main body portion 172 in the direction of arrow R1. In the main body portion 172, a communication groove 174 is formed that communicates the end portions in the direction of arrow R1 of the two long grooves 154 and 156 with each other. The groove width of the communication groove 174 is equal to or greater than the diameter of the detection surface 124. In other words, the detection surface 124 is not covered by the main body portion 172 in a state of facing the communication groove 174. In this modification, in the main body portion 172, one substantially U-shaped groove 176 is formed by the two long grooves 154 and 156 and the communication groove 174. As a result, an outer frame portion 158 and an intermediate portion 178 located between the long grooves 154 and 156 are formed in the main body portion 172. The intermediate portion 178 extends along the axis of the rotation shaft 90. The end portion of the intermediate portion 178 in the direction of arrow R2 is connected to the outer frame portion 158, and the end portion of the intermediate portion 178 in the direction of arrow R1 is separated from the outer frame portion 158. When such a detector 170 is used, in the initial state, the detection surface 124 of the proximity sensor 22 is at a position P2 facing the end portion of the intermediate portion 178 in the direction of arrow R2, and the sensor facing portion 126 has an area of S5. As shown in FIGS. 10B and 10C, when clamping the workpiece, the detection surface 124 is displaced relative to the main body portion 172 in the direction of arrow R1, the area of the sensor facing portion 126 becomes smaller, and the detection resonance impedance becomes larger. If the detected resonant impedance is greater than the unclamping threshold Zb and less than the clamping threshold Za, the determination unit 142 determines that it is in an intermediate state (a transition state from the unclamped state to the clamped state). When the detection surface 124 is displaced to position P1 facing the communication groove 174, the area of ​​the sensor facing portion 126 becomes zero. At this time, the detected resonant impedance reaches the clamping threshold Za, and the determination unit 142 determines that it is in the clamped state. On the other hand, when the clamped state of the workpiece is released, the detection surface 124 is displaced relative to the main body 172 in the direction of arrow R2, and the area of ​​the sensor-facing portion 126 increases, causing the detection resonance impedance to decrease. If the detected resonant impedance is less than the clamp threshold Za and greater than the unclamping threshold Zb, the determination unit 142 determines that it is in an intermediate state (a transition state from the clamped state to the unclamped state). When the detection surface 124 is displaced to position P2, which is opposite the end of the intermediate portion 178 in the direction of arrow R2, the area of ​​the sensor facing portion 126 becomes S5. At this time, the detected resonant impedance reaches the unclamping threshold Zb, and the determination unit 142 determines that it is in the unclamped state. According to this modified example, since the groove width of the communication groove 174 is greater than or equal to the diameter of the detection surface 124, the detection resonance impedance of the proximity sensor 22 can be made discontinuous (changed abruptly) when the detection surface 124 is displaced to a position P2 facing the communication groove 174. As a result, even if the detection resonance impedance of the proximity sensor 22 fluctuates due to temperature changes in the operating environment of the clamping device 10, the clamping state can be reliably detected. The detection body 170 in this modified example is not limited to the configuration described above. The communication groove 174 may connect the ends of the two long grooves 154 and 156 in the direction of arrow R2. In this case, even if the resonant impedance of the proximity sensor 22 fluctuates due to temperature changes in the operating environment of the clamping device 10, the unclamped state can be reliably detected. Next, the detection body 180 according to the third modified example will be described with reference to Figures 11A to 11C. As shown in Figures 11A and 11B, the detection body 180 according to this modified example has a main body portion 182 that extends around the axis of the pivot shaft 90 and a mounting portion 110 provided at the end of the main body portion 182 in the direction of arrow R1. The main body portion 182 has two elongated grooves 184 and 186 arranged side by side in the width direction of the main body portion 182, extending along the axis of the pivot shaft 90 (the direction in which the main body portion 182 extends). As a result, the main body portion 182 is formed with a rectangular outer frame portion 158 located outside the elongated grooves 184 and 186, and an intermediate portion 188 located between the elongated grooves 184 and 186. The intermediate portion 188 extends along the axis of the pivot shaft 90. Both ends of the intermediate portion 188 in the direction of extension are connected to the outer frame portion 158. The sides 184a and 186a of each of the long grooves 184 and 186 on the intermediate portion 188 side extend in a curved shape. In other words, the sides 184a and 186a of each of the long grooves 184 and 186 extend in a curved shape so that they approach each other in the direction of arrow R1. That is, the width dimension of the intermediate portion 188 narrows in the direction of arrow R1. When such a detection body 180 is used, in the initial state, the detection surface 124 of the proximity sensor 22 is at position P2 opposite the end of the intermediate portion 188 in the direction of arrow R2, and the sensor-facing portion 126 has an area of ​​S7. As shown in Figures 11B and 11C, when a workpiece is clamped, the detection surface 124 is displaced relative to the main body 182 in the direction of arrow R1, the area of ​​the sensor-facing portion 126 decreases, and the detection resonant impedance increases linearly. When the detection surface 124 is displaced to position P1, which is opposite the end of the intermediate portion 188 in the direction of arrow R1, the area of ​​the sensor-facing portion 126 becomes S6. Note that area S6 is smaller than area S7. At this time, the detection resonant impedance reaches the clamp threshold Za, so the determination unit 142 determines that the device is in a clamped state. On the other hand, when the clamped state of the workpiece is released, the detection surface 124 is displaced relative to the main body 182 in the direction of arrow R2, and the area of ​​the sensor-facing portion 126 increases, causing the detection resonant impedance to decrease linearly. When the detection surface 124 is displaced to position P2, which is opposite the end of the intermediate portion 188 in the direction of arrow R2, the area of ​​the sensor-facing portion 126 becomes S7. At this time, the detection resonant impedance reaches the unclamping threshold Zb, and the determination unit 142 determines that the device is in an unclamped state. According to this modified example, since the sides 184a and 186a of the long grooves 184 and 186 extend in a curved shape, the resonant impedance of the proximity sensor 22 can be changed linearly. This makes it possible to detect the rotation angle of the clamp arm 18. Next, the detection body 190 according to the fourth modified example will be described with reference to Figures 12A to 12C. In this detection body 190, the same reference numerals are used for components identical to those of the detection body 180 described above, and their detailed explanations are omitted. Furthermore, in the detection body 190, the same effects and functions as those of the detection body 180 are obtained for parts common to the detection body 180 described above. As shown in Figures 12A and 12B, the detection body 190 according to this modified example has a main body portion 192 extending around the axis of the pivot shaft 90 and mounting portions 110 provided at both ends of the main body portion 192. The main body portion 192 has a communication groove 194 formed in which the ends of two long grooves 184 and 186 in the direction of arrow R1 are connected to each other. The width of the communication groove 194 is greater than or equal to the diameter of the detection surface 124. In other words, the detection surface 124 is not covered by the main body portion 192 when facing the communication groove 194. In this modified example, the main body portion 192 has a roughly U-shaped groove 196 formed by two elongated grooves 184 and 186 and a connecting groove 194. As a result, the main body portion 192 has an outer frame portion 158 and an intermediate portion 198 located between the elongated grooves 184 and 186. The intermediate portion 198 extends along the axis of the pivot shaft 90. The end of the intermediate portion 198 in the direction of arrow R2 is connected to the outer frame portion 158, and the end of the intermediate portion 198 in the direction of arrow R1 is separated from the outer frame portion 158. When such a detection body 190 is used, in the initial state, the detection surface 124 of the proximity sensor 22 is at position P2 opposite the end of the intermediate portion 198 in the direction of arrow R2, and the sensor-facing portion 126 has an area of ​​S8. As shown in Figures 12B and 12C, when a workpiece is clamped, the detection surface 124 is displaced relative to the main body 192 in the direction of arrow R1, the area of ​​the sensor-facing portion 126 decreases, and the detection resonant impedance increases linearly. When the detection surface 124 is displaced to position P1 facing the communication groove 194, the area of ​​the sensor-facing portion 126 becomes zero. At this time, the detection resonant impedance reaches the clamp threshold Za, and the determination unit 142 determines that the workpiece is clamped. On the other hand, when the clamped state of the workpiece is released, the detection surface 124 is displaced relative to the main body 192 in the direction of arrow R2, and the area of ​​the sensor-facing portion 126 increases, causing the detection resonance impedance to decrease linearly. When the detection surface 124 is displaced to position P2, which is opposite the end of the intermediate portion 198 in the direction of arrow R2, the area of ​​the sensor-facing portion 126 becomes S8. At this time, the detection resonance impedance reaches the unclamping threshold Zb, and the determination unit 142 determines that the device is in an unclamped state. According to this modified example, since mounting portions 110 are provided at both ends of the main body portion 192 in the extending direction, the detection body 190 can be fixed even more firmly to the pivot shaft 90 (support lever 86). Next, the detection body 200 according to the fifth modified example will be described with reference to Figures 13 to 14B. As shown in Figures 13 to 14B, the detection body 200 according to this modified example has two first holding parts 202 provided at the end of the main body 192 in the direction of arrow R1, and two second holding parts 204 provided at the end of the main body 192 in the direction of arrow R2. The two first holding portions 202 are provided at both ends of the main body portion 192 in the width direction, sandwiching the mounting portion 110. A predetermined gap is formed between each first holding portion 202 and the mounting portion 110. Each first holding portion 202 is configured to be elastically deformable in the radial direction of the pivot shaft 90 (thickness direction of the detection body 200). In other words, each first holding portion 202 includes a first extension portion 202a extending from the main body portion 192 along the extending direction of the pivot shaft 90, and a first receiving portion 202b extending radially outward from the tip of the first extension portion 202a in the direction of arrow R1. The two second holding portions 204 are provided at both ends of the main body portion 192 in the width direction, spaced apart from each other. The second holding portion 204 is configured similarly to the first holding portion 202 described above, and includes a second extension portion 204a extending from the main body portion 192 along the extending direction of the pivot shaft 90, and a second receiving portion 204b extending radially outward from the tip of the second extension portion 204a in the direction of arrow R2. The distance between the first holding portion 202 and the second holding portion 204, which face each other when the detection body 200 is not attached to the pivot shaft 90, is set to be slightly smaller than the outer diameter of the pivot shaft 90. In this modified example, when the pivot shaft 90 is inserted between the first holding portion 202 and the second holding portion 204, the first receiving portion 202b and the second receiving portion 204b, which are in contact with the outer circumferential surface of the pivot shaft 90, are pressed radially outward, causing the first holding portion 202 and the second holding portion 204 to elastically deform in a direction that separates them from each other (in a direction that expands). Then, when the detection body 200 is fully attached to the pivot shaft 90, the first extension portion 202a and the second extension portion 204a are pressed against the outer circumferential surface of the pivot shaft 90 by the restoring force. According to this modified example, the first holding portion 202 and the second holding portion 204 hold the outer circumferential surface of the pivot shaft 90 from the radially outward direction, thereby enabling the detection body 200 to be fixed more firmly to the pivot shaft 90. This embodiment is not limited to the configuration described above. For example, mounting portions 110 may be provided at both ends in the extending direction of the detection bodies 20, 150, 170, 180, and 200. Also, first holding portions 202 and second holding portions 204 may be provided for the detection bodies 20, 150, 170, 180, and 190. Furthermore, the proximity sensor 22 may detect the rotational position of the clamp arm 18 based on the change in inductance rather than the resonant impedance. The above-mentioned detection bodies 20, 150, and 170 may be configured such that the area of ​​the sensor-facing portion 126 decreases when transitioning from the unclamped state to the clamped state, and increases when transitioning from the clamped state to the unclamped state. In this case, the detection resonant impedance increases when transitioning from the unclamped state to the clamped state, and decreases when transitioning from the clamped state to the unclamped state. Furthermore, the above-mentioned detection bodies 180 and 190 may be configured such that the area of ​​the sensor-facing portion 126 increases when transitioning from the unclamped state to the clamped state, and decreases when transitioning from the clamped state to the unclamped state. In this case, the detection resonant impedance decreases when transitioning from the unclamped state to the clamped state, and increases when transitioning from the clamped state to the unclamped state. Each of the detection units 20, 150, 170, 180, and 190 described above is attached to the support lever 86 by inserting a screw member 114 through a screw insertion hole 116 formed in the mounting part 110 and screwing it into the screw hole 104 of the support lever 86. In other words, each of the detection units 20, 150, 170, 180, and 190 has a mounting part 110 of the same dimensions. Therefore, the detection units 20, 150, 170, 180, and 190 can be easily replaced. That is, by replacing the detection units 20, 150, 170, 180, and 190 without changing the structure of the support lever 86 or the proximity sensor 22, it is possible to easily meet the requirements for various sensor characteristics. Specifically, for example, if the clamping device 10 requires high-precision detection of the detection resonance impedance in the clamped state, then detection bodies 150, 170, and 190 can be used in which the area of ​​the sensor-facing portion 126 in the clamped state becomes zero (the detection resonance impedance changes rapidly). Furthermore, for example, when changing the clamping characteristics (for instance, changing the power transmission mechanism from a toggle link mechanism to a wedge mechanism), the clamping force characteristics change. However, by using a detection element that matches these clamping characteristics, the clamped and unclamped states can be detected simply and with high accuracy. Furthermore, when changing the rotation angle range of the clamp arm 18, the clamped and unclamped states can be detected easily and with high accuracy by using a detection body such that the area of ​​the sensor-facing portion 126 changes over the entire range of that rotation angle. The clamping device according to the present invention is not limited to the embodiments described above, and can take various configurations without departing from the spirit of the present invention.

Claims

Page 1 of 2 pages Claims 1. Clamping device (10) which is arranged to clamp the workpiece by a rotatable clamping arm (18) which is incorporated with the clamp (14); a drive unit (12) which is provided on the clamp (14); a rotating shaft (90) which is arranged to rotate together with the clamping arm (18) in a single unit under the operation of the drive unit (12); detection targets (20,150,170,180,190,200) which are made of metal and are provided on the rotating shaft (90) to extend around the axis of the rotating shaft (90); and a sensor. A single (22) sensor is positioned facing the detection target (20,150,170,180,190,200) and arranged to generate an eddy current in the detection target (20,150,170,180,190,200) and detect magnetic loss; where the detection target (20,150,170,180,190,200) is plate-shaped, and includes long grooves (112,154,156,184,186) that extend in the direction in which the detection target (20,150,170,180,190,200) extends in this direction, so that the area of ​​the sensor facing (126) of the detection target (20,150,170,180,190,2. The clamping device (10) under claim 1 in which the sides (112a,112b,154a,156a) of the longitudinal groove (112,154,156) extend linearly in a direction which intersects the direction in which the detection target (20,150,170,180,190,200) extend in this direction.

3. The clamping device (10) under claim 1 in which the sides (184a,186a) of the longitudinal groove (184,186) extend in a curved manner.

4. The clamping device (10) under any one of claims 1, 2 and 3 in which: the longitudinal groove of the target The detection device (20) includes one long groove (112); and the sensor facing part (126) extends along both sides of the long groove (112). Page 2 of Number 2 of Page 5. The clamping device (10) according to one of claims 1 and 2 through 4, in which: the long grooves of the detection target (150,170,180,190,200) include long grooves (154,156,184,186) arranged side-by-side in the width direction of the detection target (150,170,180,190,200); and the sensor facing part (126) is arranged between two long grooves (154,156,184,186). Page 6. The clamping device (10) according to claim 5, in which the detection target (170,190,200) including the contact groove (174,194) through which the ends of two long grooves (156,184,186) pass through this section and are connected to each other; and the width of the contact groove (174,194) is greater than or equal to the diameter of the detector surface (124).

7. The clamping device (10) according to any one of the claims 1 and 2 to 6, in which the detection target (20,150,170,180,190,200) is firmly fixed to the rotating shaft (90) by a scaffolding assembly.

8. The clamping device (10) in accordance with claim 7, in which the attached part (110) which has a hole (116) into which the screw assembly (114) is inserted, such hole is provided at least one end of the detection target (20,150,170,180,190,200) in the direction in which the detection target (20,150,170,180,190,200) extends in this direction.

9. The clamping device (10) in accordance with claim 7 or 8, in which the clamping part (202,204) which is arranged to grip the surface along the outer circumference of the shaft(90) from the outside in the radial direction, is provided at both ends of the target(200) in the direction in which the target(200) extends.

10. The clamping device(10) under any one of claims 1 to 2 to 9, in which the recess(106) is formed in the area of ​​the surface along the outer circumference of the shaft(90) facing the detector surface(124);,