Electric gripping device

Abstract

To provide an electric gripping device that can perform self-locking appropriately.SOLUTION: An electric gripping device 10 can perform self-locking which a pair of gripping claws 55 can keep on gripping a work-piece W by compressing a coil spring 23 between: a contact place between the coil spring 23 and a follower 28; and a first end 23a of the coil spring 23. When a friction coefficient of when the coil spring 23 contacts the follower 28 is defined as μ and an angle between a direction of force which the follower 28 receives from the coil spring 23 when the pair of gripping claws 55 grips the work-piece W and a direction of normal force at the contact place between the coil spring 23 and the follower 28 is defined as θ, the electric gripping device 10 is configured to satisfy a relational expression of μ>tan θ in a state of self-locking. The electric gripping device 10 makes the angle θ to be zero by inclining the coil spring 23, accompanying compression of the coil spring 23 between the contact place and the first end 23a of the coil spring 23.SELECTED DRAWING: Figure 8

Description

[Technical field]

[0001] The present invention relates to an electric gripping device. [Background technology]

[0002] As shown in FIG. 15, for example, an electric hand 90 disclosed in Patent Document 1 has a first finger 91, a second finger 92, a housing 93, a nut 94, a drive shaft 95, a first oscillating arm 96, a second oscillating arm 97, a spring member 98, and an electric motor 99.

[0003] The housing 93 is provided with a guide rail 93a. The guide rail 93a guides each of the first finger 91 and the second finger 92. The nut 94 is accommodated in a sliding hole 93b provided in the housing 93 so as to be freely reciprocable. The outer peripheral surface of the nut 94 and the inner peripheral surface of the sliding hole 93b are formed with flat surfaces facing each other. These flat surfaces serve as a rotation prevention mechanism for the nut 94 and also constitute a feed nut mechanism. The female thread portion 94a provided in the nut 94 is coupled to a male thread portion 99b of a screw shaft 99a rotated by an electric motor 99. The drive shaft 95 is accommodated in a guide hole 94b provided in the nut 94 so as to be freely reciprocable in the axial direction.

[0004] The drive shaft 95 forms a spring chamber 100 together with the nut 94. The first swing arm 96 is supported in the housing 93 so as to be able to swing freely. One end of the first swing arm 96 engages with the drive shaft 95, and the other end engages with the first finger 91. The second swing arm 97 is supported in the housing 93 so as to be able to swing freely. One end of the second swing arm 97 engages with the drive shaft 95, and the other end engages with the second finger 92.

[0005] The spring member 98 is accommodated in a spring chamber 100. The spring member 98 drives the drive shaft 95 together with the nut 94 until each of the first and second fingers 91, 92 contacts the workpiece. The spring member 98 elastically deforms and biases the first and second fingers 91, 92 when each of the first and second fingers 91, 92 grips the workpiece. Since the workpiece is gripped by the biased first finger 91 and second finger 92, the workpiece can be gripped and transported by the first finger 91 and the second finger 92 with the electric motor 99 stopped. In other words, the male thread portion 99b and the female thread portion 94a form a self-lock when the first finger 91 and the second finger 92 grip the workpiece. Due to the self-lock, the position of the drive shaft 95 does not change due to the reaction force that the first finger 91 and the second finger 92 receive from the workpiece. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6277119 Summary of the Invention [Problem to be solved by the invention]

[0007] In the electric hand 90 of Patent Document 1, for example, galling or the like may occur at the contact points between the male thread portion 99b and the female thread portion 94a due to the impact force received when gripping a workpiece. Such galling or the like changes the coefficient of friction that occurs at the contact points between the male thread portion 99b and the female thread portion 94a during self-locking. If the coefficient of friction changes, it may become difficult to maintain self-locking, and there is also a risk that the change in the coefficient of friction may make it impossible to release the self-locking. [Means for solving the problem]

[0008] An electric gripping device for solving the above problems includes a motor having a motor shaft, a coil spring formed by winding a wire material in a spiral shape and fixed to a rotating member that rotates integrally with the motor shaft, an operating shaft that is arranged inside the coil spring and moves in an axial direction along a central axis of the coil spring, a follower that protrudes from a peripheral surface of the operating shaft, the follower being provided so that the central axis of the follower intersects with the central axis of the operating shaft and is supported by the operating shaft to be rotatable about the central axis of the follower, and a protruding portion from the peripheral surface of the operating shaft is arranged in a gap between adjacent wire materials in the axial direction, and a gripping jaw opening and closing mechanism connected to an end of the operating shaft, the gripping jaw opening and closing mechanism opening and closing a pair of gripping jaws by movement of the operating shaft in the axial direction and rotating the operating shaft about the central axis of the operating shaft. The gripping jaws have a gripping jaw opening / closing mechanism that regulates the force applied to the gripping jaws and a control device that controls the motor, and the coil spring is compressed between the contact point between the coil spring and the follower and the fixed end of the rotating member, thereby enabling self-locking that maintains grip of the workpiece by the pair of gripping jaws, and is configured to satisfy the relationship μ>tan θ in the self-locked state, where μ is the coefficient of friction when the coil spring and the follower come into contact, and θ is the angle between the direction of the force that the follower receives from the coil spring when the workpiece is gripped by the pair of gripping jaws, and θ is the angle between the direction of the normal force at the contact point.The gripping jaws are configured to satisfy the relationship μ>tan θ in the self-locked state, and the coil spring is tilted as the coil spring is compressed between the contact point and the fixed end, thereby setting the angle θ to zero.

[0009] In the electric gripping device, the actuation shaft may have a bearing that rotatably supports the follower. In the electric gripping device, the rotating member may be a cylindrical protective member that surrounds the coil spring from the outside, a first end of the coil spring is fixed to a first end of the protective member as the fixed end and a second end of the coil spring is made a free end, an attachment member is fixed to the inside of the second end of the protective member, and the motor shaft is connected to the attachment member.

[0010] In the electric gripping device, the operating shaft may be formed by connecting an operating shaft main body that supports the follower and a rod that is connected to the gripping claw opening / closing mechanism, and may have a unit portion that integrates the mounting member, the protective member, the coil spring, and the operating shaft main body.

[0011] In the electric gripping device, a support member may be fixed to the operating shaft, and the support member may be in sliding contact with an inner circumferential surface of the protection member. In the electric gripping device, the coil spring may be compressed in the axial direction between the protection member and the support member.

[0012] In an electric gripping device, a driver that operates the motor is signal-connected to the control device, and a position detection sensor that detects the position of the working shaft in the axial direction is signal-connected to the control device, and the position detection sensor outputs a gripping start signal to the control device indicating that the position of the working shaft in the axial direction has been detected at the time when the pair of gripping jaws start to grip the workpiece, and when the control device inputs the gripping start signal, it may control the driver to increase the gripping force of the pair of gripping jaws on the workpiece.

[0013] For an electric gripping device, the control device may control the driver to decelerate the motor when the gripping start signal is input, and to stop the motor after the motor has operated at a predetermined rotation amount.

[0014] In the electric gripping device, the control device may be signal-connected to a deceleration acceleration setting unit that adjusts the rotation speed when decelerating the motor to a plurality of deceleration accelerations. For an electric gripping device, the control device may output an error signal indicating that the workpiece is not present if a signal indicating that the position of the working axis in the axial direction has been detected is not input at the time the motor stops.

[0015] The electric gripping device may further include a gripping jaw operating unit that manually rotates the motor shaft to adjust the opening degree of the pair of gripping jaws. Effect of the Invention

[0016] According to the present invention, self-locking can be achieved advantageously. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is a cross-sectional view showing an electric gripping device according to an embodiment. [Diagram 2] FIG. 1 is a perspective view showing an electric gripping device according to an embodiment. [Diagram 3] FIG. 4 is a partially enlarged front view showing the follower and the coil spring in the initial position. [Figure 4] FIG. [Diagram 5] FIG. [Figure 6] FIG. [Figure 7] FIG. 4 is a cross-sectional view showing the electric gripping device at a gripping start position. [Figure 8] FIG. 4 is a cross-sectional view showing the electric gripping device in the gripping position. [Figure 9] 5A to 5C are diagrams illustrating the operation of the electric gripping device. [Figure 10] FIG. 4 is a partially enlarged front view showing the follower and the coil spring in the gripping position. [Figure 11] FIG. 4 is a diagram showing an inner gripping unit part. [Figure 12] FIG. 13 is a diagram showing a unit portion according to another example. [Figure 13] FIG. 13 is a diagram showing a unit portion in which a coil spring is compressed and accommodated. [Figure 14] FIG. 4 is a cross-sectional view showing an electric gripping device having a support member. [Figure 15] FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, one embodiment of an electric gripping device will be described with reference to Figs. <Overall electric gripping device> As shown in Figures 1 and 2, the electric gripping device 10 has a body 11, a motor 14, a rod guide 15, a first position detection sensor 16a and a second position detection sensor 16b, a drive mechanism 20, a gripping jaw opening / closing mechanism 50, a control device 60, a driver 61, and a deceleration acceleration setting unit 63.

[0019] The body 11 is in the shape of a substantially rectangular block. The body 11 has a main body 11a, a pair of extending walls 11b extending from the main body 11a, and a guide plate 52. The direction in which the central axis L1 of the main body 11a extends is defined as an axial direction Z. In a plan view of the body 11 seen from the axial direction Z, a direction perpendicular to the axial direction Z of the body 11 is defined as a first direction X. In addition, in a plan view of the body 11 seen from the axial direction Z, a direction perpendicular to the axial direction Z of the body 11 and the first direction X is defined as a second direction Y.

[0020] The body main body 11a is formed with an axial hole 12. The axial hole 12 is a circular hole penetrating the body main body 11a in the axial direction Z. Each of the pair of extension walls 11b extends from the body main body 11a in the axial direction Z. The pair of extension walls 11b face each other at a distance in the first direction X. A space S is defined between the pair of extension walls 11b. A first end of the axial hole 12 in the axial direction Z opens into the space S, and a second end of the axial hole 12 in the axial direction Z is closed by the motor 14. A guide plate 52 is connected to a tip of each extension wall 11b in the axial direction Z. The space S is closed from the tip side of the extension wall 11b by the guide plate 52. The space S opens to both ends of the body 11 in the second direction Y.

[0021] A tool hole 11d is formed in the end of the main body 11a on the motor 14 side. A first end of the tool hole 11d opens into one end face of the outer surface of the main body 11a in the second direction Y, and a second end of the tool hole 11d opens into the shaft hole 12. The tool hole 11d is a hole into which the tip side of a tool can be inserted. A part of the tool hole 11d is female-threaded. A closure member 17 is screwed into the female thread of the tool hole 11d.

[0022] The rod guide 15 is attached to the extension wall 11b side inside the main body 11a. The rod guide 15 is annular. The rod guide 15 is disposed inside the shaft hole 12. Mounting grooves 11c are formed on both end faces in the second direction Y of the outer surface of the main body 11a. The longitudinal direction of the mounting grooves 11c extends in the axial direction Z.

[0023] The first position detection sensor 16a is inserted into one of the pair of mounting grooves 11c, and the second position detection sensor 16b is inserted into the other of the pair of mounting grooves 11c. The first position detection sensor 16a and the second position detection sensor 16b are attached to the body 11. The side surface of the first position detection sensor 16a and the side surface of the second position detection sensor 16b are exposed from the mounting groove 11c. Therefore, in a side view of the electric gripping device 10 seen in the second direction Y, the first position detection sensor 16a or the second position detection sensor 16b can be seen. The mounting positions of the first position detection sensor 16a and the second position detection sensor 16b in the mounting groove 11c can be changed along the axial direction Z. The functions of the first position detection sensor 16a and the second position detection sensor 16b will be described later.

[0024] The motor 14 is connected to an end face of the main body 11a opposite to the extending wall 11b. The motor 14 is a stepping motor. The motor 14 has a motor shaft 14a. The motor shaft 14a is inserted into the shaft hole 12.

[0025] A driver 61 for operating the motor 14 is signal-connected to the motor 14. A control device 60 is signal-connected to the driver 61. The control device 60 generates a pulse signal or stops generating the pulse signal. In response to the pulse signal generated by the control device 60, the driver 61 causes a motor current corresponding to the pulse signal to flow through the motor 14. This causes the motor 14 to operate. The motor 14 can be switched between rotating in a forward direction and rotating in a reverse direction.

[0026] The motor 14 has a gripping claw operation unit 14b. The gripping claw operation unit 14b protrudes from the outer surface of the motor 14. The gripping claw operation unit 14b is connected to the motor shaft 14a. By rotating the gripping claw operation unit 14b in the forward or reverse direction, the motor shaft 14a can be manually rotated in the forward or reverse direction. Therefore, the electric gripping device 10 is equipped with the gripping claw operation unit 14b that manually rotates the motor shaft 14a. An operation member 14c is attached to the gripping claw operation unit 14b, but the operation member 14c may be omitted.

[0027] As shown in FIGS. 1, 7 and 8, the drive mechanism 20 includes a mounting member 21, a protective member 22, a coil spring 23, an operating shaft 24, and a follower . The mounting member 21 is cylindrical. A connecting hole 21a is formed in the mounting member 21. A first end of the connecting hole 21a opens to the outer circumferential surface of the mounting member 21. A second end of the connecting hole 21a opens to the inner circumferential surface of the mounting member 21. The connecting hole 21a is a female threaded hole. The connecting member 18 is screwed into the connecting hole 21a. The connecting member 18 screwed into the connecting hole 21a presses the motor shaft 14a against the inner circumferential surface of the mounting member 21. This connects the mounting member 21 to the motor shaft 14a. The mounting member 21 rotates integrally with the motor shaft 14a. The mounting member 21 is disposed in the shaft hole 12. The outer diameter of the mounting member 21 is smaller than the hole diameter of the shaft hole 12.

[0028] The protective member 22 is cylindrical. The direction in which the central axis L2 of the protective member 22 extends coincides with the axial direction Z of the body 11. Therefore, the direction in which the central axis L2 of the protective member 22 extends is also defined as the axial direction Z. The dimension of the protective member 22 in the axial direction Z is smaller than the dimension of the main body 11a in the axial direction Z. In detail, the dimension of the protective member 22 in the axial direction Z is slightly larger than half the dimension of the main body 11a in the axial direction Z.

[0029] The coil spring 23 is disposed inside the protective member 22. That is, the protective member 22 surrounds the coil spring 23 from the outside. The first end 22a in the axial direction Z of the protective member 22 is an end for attaching the coil spring 23. The mounting member 21 is fixed to the inside of the second end 22b of the protective member 22. The protective member 22 extends cylindrically from the mounting member 21 toward the rod guide 15. The protective member 22 rotates integrally with the mounting member 21. Therefore, the protective member 22 is a rotating member that rotates integrally with the motor shaft 14a. The protective member 22 is also a transmission member that positions the coil spring 23 on the opposite side of the motor shaft 14a and transmits the rotation of the motor shaft 14a to the coil spring 23 from the opposite side. The first end 22a in the axial direction Z of the protective member 22 is separated from the rod guide 15 toward the motor 14 along the axial direction Z.

[0030] A magnet arrangement space S1 is defined between an end face of the protective member 22 on the first end 22a side, an end face of the rod guide 15 on the protective member 22 side, and an inner circumferential surface of the main body 11a. The magnet arrangement space S1 is disposed inside the first position detection sensor 16a and the second position detection sensor 16b in the radial direction of the protective member 22.

[0031] The inner diameter of the protective member 22 at the first end 22a is smaller than the inner diameter at any other portion than the first end 22a. The outer diameter of the protective member 22 is constant in the axial direction Z. The outer diameter of the protective member 22 is smaller than the hole diameter of the shaft hole 12. There is a clearance between the outer peripheral surface of the protective member 22 and the inner peripheral surface of the body main body 11a that defines the shaft hole 12.

[0032] 3 and 4, the coil spring 23 is formed by winding a metal wire 23c in a spiral shape around a central axis L3. When the coil spring 23 is in a non-compressed state, the extension direction of the central axis L3 of the coil spring 23 coincides with the axial direction Z of the body 11 and the protective member 22. The extension direction of the central axis L3 of the coil spring 23 is also defined as the axial direction Z.

[0033] The coil spring 23 is formed by winding the wire 23c so as to have a constant pitch P in an uncompressed state. The pitch P is the size of the interval between adjacent wires 23c in the axial direction Z. In the uncompressed state of the coil spring 23, the pitch P is constant at any position in the axial direction Z. In the uncompressed state of the coil spring 23, the wire 23c is inclined at a constant angle with respect to the central axis L3 of the coil spring 23 at any position. When the coil spring 23 is compressed in the axial direction Z, the interval between the wires 23c becomes narrower and the wire 23c approaches the axial direction Z, so that the pitch P becomes narrower. As the coil spring 23 is compressed in the axial direction Z, the pitch P becomes narrower, so that the angle approaches zero.

[0034] As shown in FIG. 1, FIG. 7, and FIG. 8, the first end 23a of the coil spring 23 in the axial direction Z is fixed to the first end 22a of the protective member 22. In other words, the first end 23a of the coil spring 23 is fixed to the first end 22a of the protective member 22 as a fixed end. The second end 23b of the coil spring 23 in the axial direction Z is a free end. In other words, the second end 23b of the coil spring 23 is not fixed. The protective member 22 surrounds the coil spring 23 from the outside. The coil spring 23 rotates integrally with the protective member 22. Therefore, when the motor shaft 14a rotates by the motor 14, the coil spring 23 rotates integrally with the motor shaft 14a in the same direction via the mounting member 21 and the protective member 22.

[0035] Since the coil spring 23 is separated from the inner circumferential surface of the protective member 22 except for the first end 22a, the coil spring 23 can tilt with respect to the central axis L3 when compressed in the axial direction Z. However, when the tilted coil spring 23 comes into contact with the inner circumferential surface of the protective member 22, the tilt of the coil spring 23 is restricted.

[0036] The operating shaft 24 is cylindrical. The operating shaft 24 is disposed inside the coil spring 23. The direction in which the central axis L4 of the operating shaft 24 extends coincides with the axial direction Z of the body 11, the mounting member 21, the protective member 22, and the coil spring 23. Therefore, the direction in which the central axis L4 of the operating shaft 24 extends is also defined as the axial direction Z. The operating shaft 24 is formed by connecting an operating shaft main body 25 and a rod 26.

[0037] The working shaft body 25 has a first end face 25a on one end face in the axial direction Z, and a second end face 25b on the other end face in the axial direction Z. The first end face 25a of the working shaft body 25 is disposed on the rod guide 15 side in the axial direction Z, and the second end face 25b is disposed on the motor 14 side in the axial direction Z.

[0038] The working shaft body 25 has a female thread 25c recessed from the first end face 25a. In addition, an attachment hole 25d is formed in the working shaft body 25. The attachment hole 25d is provided closer to the second end face 25b than the center of the working shaft body 25 in the axial direction Z. The attachment hole 25d penetrates the working shaft body 25 in the radial direction.

[0039] As shown in FIG. 4, the working shaft body 25 is provided with a bearing 27. The bearing 27 is a ball bearing. The bearing 27 is attached to the attachment hole 25d. Thus, the bearing 27 is provided on the working shaft 24. The bearing 27 has an outer ring 27a, an inner ring 27b, and a plurality of balls 27c. The outer ring 27a is attached to the inner peripheral surface of the working shaft body 25 that defines the attachment hole 25d. The outer ring 27a is non-rotatable. The inner ring 27b is located on the inner peripheral side of the outer ring 27a. The plurality of balls 27c roll between the inner peripheral surface of the outer ring 27a and the outer peripheral surface of the inner ring 27b. The inner ring 27b is rotatable relative to the outer ring 27a.

[0040] The follower 28 has a shaft portion 28a and a head portion 28b. The shaft portion 28a is attached to the inner ring 27b. The follower 28 rotates integrally with the inner ring 27b. The head portion 28b is disk-shaped. The head portion 28b protrudes from the circumferential surface of the operating shaft 24. Therefore, the head portion 28b is a protruding portion that protrudes from the circumferential surface of the operating shaft 24. An annular groove 28c is formed in the circumferential surface of the head portion 28b. The wire rod 23c of the coil spring 23 faces the annular groove 28c. The follower 28 is rotatably supported by the operating shaft 24 via the bearing 27. In other words, the operating shaft 24 has the bearing 27 that rotatably supports the follower 28.

[0041] The follower 28 rotates about a central axis M. The central axis M of the follower 28 is perpendicular to the central axis L4 of the operating shaft 24. The central axis M of the follower 28 extends in the radial direction of the operating shaft 24. Therefore, the follower 28 is provided such that the central axis M of the follower 28 intersects with the central axis L4 of the operating shaft 24, and is supported by the operating shaft 24 so as to be rotatable about the central axis M of the follower 28 as the rotation center. A head 28b of the follower 28 protrudes from the peripheral surface of the operating shaft 24 in the radial direction of the operating shaft 24.

[0042] The diameter of the annular groove 28c in the head 28b is smaller than the gap between adjacent wire rods 23c in the axial direction Z in the coil spring 23 in an uncompressed state. The head 28b is disposed in the gap between adjacent wire rods 23c in the axial direction Z. Therefore, the protruding portion of the follower 28 protruding from the peripheral surface of the operating shaft 24 is disposed in the gap between adjacent wire rods 23c in the axial direction Z. A portion of the wire rod 23c fits into the annular groove 28c in the head 28b.

[0043] As shown in FIG. 6, the drive mechanism 20 includes a unit part 201. The unit part 201 is formed by previously integrating the mounting member 21, the protective member 22, the coil spring 23, and the working shaft body 25 of the working shaft 24. The bearing 27 and the follower 28 are previously integrated with the working shaft body 25. Therefore, the electric gripping device 10 has the above-mentioned unit part 201. The outer shape of the unit part 201 is formed almost entirely by the protective member 22. The outer shape of the unit part 201 is cylindrical. The unit part 201 is inserted into the shaft hole 12 of the body 11. The unit part 201 is integrated with the motor shaft 14a by connecting the mounting member 21 to the motor shaft 14a with the connecting member 18. As a result, the unit part 201 is integrated with the body 11 and is rotatable within the shaft hole 12.

[0044] As shown in Figs. 1, 7 and 8, the rod 26 has a first rod portion 31, a second rod portion 32 and a pair of shaft supports 33. The first rod portion 31, the second rod portion 32 and the pair of shaft supports 33 are arranged in the axial direction Z in the above order. The first rod portion 31 has a smaller diameter than the second rod portion 32. The first rod portion 31 is located on the motor 14 side, and the pair of shaft supports 33 are located on the rod guide 15 side. The first rod portion 31 has a male thread 31a at its tip. The male thread 31a is screwed into the female thread 25c of the operating shaft main body 25. By screwing the male thread 31a into the female thread 25c, the operating shaft main body 25 and the rod 26 are integrated together, and the operating shaft 24 is formed.

[0045] A magnet holder 34 is attached to the first rod portion 31 other than the male thread 31a. The magnet holder 34 is annular. The magnet holder 34 holds a magnet 35. The magnet 35 is annular. The magnet 35 surrounds the rod 26. The magnet 35 is arranged in the magnet arrangement space S1. In the magnet arrangement space S1, the magnet 35 moves in the axial direction Z together with the operating shaft 24.

[0046] The magnetic field generated from the magnet 35 in the magnet arrangement space S1 is detected by the first position detection sensor 16a and the second position detection sensor 16b. The position of the magnet 35 that can be detected by the first position detection sensor 16a and the position of the magnet 35 that can be detected by the second position detection sensor 16b are shifted in the axial direction Z. The positions of the first position detection sensor 16a and the second position detection sensor 16b in the axial direction Z are adjusted so that the magnetic field of the magnet 35 can be detected by the first position detection sensor 16a and the second position detection sensor 16b.

[0047] Of both surfaces of the magnet holder 34 in the axial direction Z, a cushion rubber 37 is attached to the surface on the second rod portion 32 side. The operating shaft 24 can move toward the rod guide 15 until the cushion rubber 37 contacts the rod guide 15. On the other hand, the operating shaft 24 can move toward the motor 14 until the magnet holder 34 contacts the end face of the protective member 22 on the first end 22a side.

[0048] The second rod portion 32 is inserted into the rod guide 15. The rod guide 15 guides the movement of the second rod portion 32, and therefore the operating shaft 24, in the axial direction Z. A portion of the second rod portion 32 near the shaft support portion 33 protrudes from the shaft hole 12 and is located in the space S.

[0049] 5, the pair of shaft supports 33 protrude from the second rod portion 32 in the axial direction Z. The pair of shaft supports 33 face each other with a gap therebetween in the first direction X. A rotating shaft 36 is attached to the pair of shaft supports 33.

[0050] 1 and 5, the gripping jaw opening / closing mechanism 50 has a rotating shaft 36, a pair of master jaws 51, a pair of levers 53, and a pair of support shafts 54. The gripping jaw opening / closing mechanism 50 opens and closes a pair of gripping jaws 55. The gripping jaw opening / closing mechanism 50 is connected to the shaft support portion 33 which is the end of the operating shaft 24 via the rotating shaft 36.

[0051] The unit part 201 is rotatably inserted into the shaft hole 12. For this reason, a rotation prevention mechanism for the operating shaft 24 included in the unit part 201 is not built into the unit part 201. On the other hand, the gripping jaw opening / closing mechanism 50 serves as a rotation prevention mechanism for the operating shaft 24 by holding each lever 53 supported by a pair of support shafts 54 between a pair of shaft supports 33 of the operating shaft 24.

[0052] The guide plate 52, which is a part of the body 11, is formed with a guide recess 52a and a pair of lever through holes 52b. The guide recess 52a is formed on the end face of the guide plate 52 opposite to the connecting face with the pair of extending walls 11b. The guide recess 52a extends over the entire second direction Y of the guide plate 52. The pair of lever through holes 52b are provided on both sides of the center of the guide plate 52 in the second direction Y. Each of the pair of lever through holes 52b penetrates the guide plate 52 in the plate thickness direction. The pair of lever through holes 52b open into the guide recess 52a. The pair of lever through holes 52b are formed along the guide recess 52a. The plate thickness direction of the guide plate 52 coincides with the axial direction Z.

[0053] A ball 52c is interposed between the outer surface of each of the pair of master jaws 51 and the inner surface of the guide plate 52 defining the guide recess 52a. Each of the pair of master jaws 51 is connected to the guide plate 52 via the ball 52c. Each of the pair of master jaws 51 is supported so as to be movable in the second direction Y by the rolling of the ball 52c.

[0054] Each of the pair of levers 53 is substantially L-shaped. A part of each lever 53 is disposed in the space S. A U-shaped hook groove 53a is formed in a first end of each lever 53. The first end of each lever 53 is disposed between a pair of shaft supports 33. A rotating shaft 36 is inserted into each hook groove 53a. A support shaft 54 ​​penetrates the L-shaped bent portion of each lever 53. Each support shaft 54 ​​is bridged across a pair of extension walls 11b. Each lever 53 is supported by the support shaft 54 ​​so as to be able to swing.

[0055] The second end side of each lever 53 is inserted into each lever through hole 52b and protrudes from the end face of the guide plate 52 opposite to the pair of extending walls 11b. An engagement piece 53b is provided at the second end of each lever 53. The engagement piece 53b of each lever 53 is connected to each master jaw 51. The master jaw 51 is connected to the second end of the lever 53 by the connection between the engagement piece 53b and the master jaw 51. The gripping claws 55 are connected to the master jaw 51. Each of the pair of gripping claws 55 is rectangular plate-shaped. The gripping claws 55 are connected to the outer surface of the master jaw 51 in the second direction Y. The gripping claws 55 protrude from the master jaw 51 to the opposite side to the body 11 in the axial direction Z.

[0056] Here, a method for assembling the electric gripping device 10 will be described. First, with the rod 26 assembled to the grip jaw opening / closing mechanism 50, the grip jaw opening / closing mechanism 50 is assembled to the guide plate 52. Therefore, the body 11, the grip jaw opening / closing mechanism 50, and the rod 26 are assembled together.

[0057] Then, the female thread 25c of the operating shaft main body 25 of the unit part 201 is screwed into the male thread 31a of the rod 26. Then, the body 11, the gripping jaw opening / closing mechanism 50, and the drive mechanism 20 are assembled together. Next, the motor 14 is attached to the body main body 11a. At this time, the motor shaft 14a is inserted into the mounting member 21. Next, the closing member 17 is removed from the tool hole 11d, and the tool hole 11d is opened at the end face of the body main body 11a. Note that the closing member 17 may be removed from the tool hole 11d before the electric gripping device 10 is assembled.

[0058] Then, the connecting member 18 is inserted into the connecting hole 21a, and the connecting member 18 is operated with the tool inserted into the tool hole 11d to screw the connecting member 18 into the connecting hole 21a. As a result, the motor shaft 14a and the mounting member 21 are connected by the connecting member 18. Then, the body 11, the motor 14, the gripping jaw opening / closing mechanism 50, and the unit part 201 are integrated to form the electric gripping device 10.

[0059] Conversely, by screwing the connecting member 18 back from the connecting hole 21a and then releasing the connection between the mounting member 21 and the motor shaft 14a, the mounting member 21, the protective member 22, the coil spring 23, the operating shaft body 25, the bearing 27, and the follower 28 can be removed all at once from the motor 14.

[0060] In the electric gripping device 10, the rod 26 is connected to the operating shaft body 25 of the unit part 201. A first end of a pair of levers 53 is connected to the pivot support part 33 of the rod 26 by a rotating shaft 36, and a master jaw 51 is connected to a second end of each lever 53 by an engaging element 53b. By connecting the rod 26 to the operating shaft body 25 of the unit part 201, the operating shaft 24 and the gripping jaw opening / closing mechanism 50 are integrated. Therefore, the operating shaft 24 is formed by connecting the operating shaft body 25 that supports the shaft part 28a of the follower 28 and the rod 26 that is connected to the gripping jaw opening / closing mechanism 50.

[0061] <Operation of the electric gripping device> In the electric gripping device 10, when the motor 14 rotates in the forward or reverse direction, the mounting member 21 and the protective member 22 rotate in the forward or reverse direction together with the motor shaft 14a. At the same time, the coil spring 23 rotates in the forward or reverse direction. As the coil spring 23 rotates, the operating shaft 24 is sent out toward the motor 14 side or the rod guide 15 side via the follower 28 by the spiral of the coil spring 23. The follower 28 rotates about the central axis M as a rotation center due to contact with the coil spring 23. The follower 28 rotates smoothly due to the bearing 27, and the rotation of the follower 28 in the circumferential direction is restricted.

[0062] The working shaft 24 tries to rotate in the circumferential direction due to contact between the coil spring 23 and the follower 28. At this time, as described above, the rotation prevention mechanism of the gripping jaw opening / closing mechanism 50 restricts the rotation of the working shaft 24 in the circumferential direction. In other words, the gripping jaw opening / closing mechanism 50 restricts the rotation of the working shaft 24 about the central axis L4.

[0063] The actuating shaft 24 moves in the axial direction Z along the central axis L3 of the coil spring 23. That is, the actuating shaft 24 moves linearly in the axial direction Z so as to approach the motor 14 or the rod guide 15 along the axial direction Z. As the actuating shaft 24 moves in the axial direction Z, the pair of levers 53 receive a force from the rotating shaft 36 and swing around the support shaft 54 ​​as a swing center. At this time, the pair of levers 53 swing in the second direction Y by the lever through hole 52b. As the pair of levers 53 swing, the master jaw 51 moves in the second direction Y along the guide recess 52a, and the gripping claws 55 connected to the master jaw 51 move in the second direction Y. That is, the gripping claw opening / closing mechanism 50 opens and closes the pair of gripping claws 55 by the movement of the actuating shaft 24 in the axial direction Z.

[0064] 1, in the electric gripping device 10, the position where the pair of gripping claws 55 are furthest apart in the second direction Y is set as an initial position P1. The cushion rubber 37 is in contact with the rod guide 15 at the initial position P1.

[0065] When the electric gripping device 10 is in the initial position P1, when the motor 14 rotates in the forward direction, the mounting member 21 and the protective member 22 rotate in the forward direction together with the motor shaft 14a. At the same time, the coil spring 23 rotates in the forward direction. With the rotation of the coil spring 23 in the forward direction, the operating shaft 24 is sent out toward the motor 14. In a state before the gripping jaws 55 come into contact with the workpiece W, the pair of levers 53 swing in a direction that brings the pair of master jaws 51 closer to each other, and the pair of gripping jaws 55 approach each other. In other words, the opening degree of the pair of gripping jaws 55 becomes smaller. Then, when the pair of gripping jaws 55 come into contact with the workpiece W, the swinging of the pair of levers 53 stops. The position where the pair of gripping jaws 55 come into contact with the workpiece W is set as the gripping start position P2. When the workpiece W is not placed, the pair of gripping jaws 55 do not stop at the gripping start position P2, but approach further to reduce the opening degree.

[0066] 7, when the pair of gripping jaws 55 contact the workpiece W at the gripping start position P2 and the swing of the pair of levers 53 stops, if the motor 14 continues to rotate in the forward direction, the operating shaft 24 does not move in the axial direction Z. In other words, the follower 28 does not move in the axial direction Z. On the other hand, the coil spring 23 rotates in the forward direction.

[0067] Therefore, as shown in FIG. 8, the coil spring 23 enters between the contact point with the head 28b and the first end 23a which is the fixed end of the coil spring 23 and the protective member 22. As a result, the coil spring 23 is compressed between the contact point between the head 28b and the coil spring 23 and the first end 23a. With the compression of the coil spring 23, a force is applied to the operating shaft 24 via the follower 28 in a direction approaching the motor 14. This force applies a force to the pair of levers 53 in a direction approaching each other, and therefore a force is applied to the pair of gripping jaws 55 in a direction approaching the workpiece W. As a result, the pair of gripping jaws 55 grip the workpiece W with a predetermined gripping force. The position where the workpiece W is gripped with the predetermined gripping force is defined as a gripping position P3.

[0068] The predetermined gripping force is a force that allows the workpiece W to be transported without coming off between the pair of gripping jaws 55 when the workpiece W is gripped by the pair of gripping jaws 55 and moved together with the electric gripping device 10. Such a predetermined gripping force is set by verifying that the workpiece W is moved together with the electric gripping device 10 while being gripped by the pair of gripping jaws 55.

[0069] The gripping force can be set by the amount of compression displacement of the coil spring 23 in the axial direction Z. The greater the amount of compression displacement of the coil spring 23 in the axial direction Z, the greater the gripping force. The gripping force is maximum when the coil spring 23 is compressed to the maximum extent in the axial direction Z. The amount of compression displacement of the coil spring 23 can be controlled by the amount of rotation of the motor 14 from the point when the pair of gripping jaws 55 are brought into contact with the workpiece W.

[0070] When the electric gripping device 10 is at the gripping position P3, if the motor 14 rotates in the reverse direction, the mounting member 21 and the protective member 22 rotate in the reverse direction together with the motor shaft 14a. At the same time, the coil spring 23 rotates in the reverse direction. As the coil spring 23 rotates in the reverse direction, the operating shaft 24 is sent out toward the rod guide 15. The pair of levers 53 swing the pair of master jaws 51 in a direction away from each other, and the pair of gripping claws 55 move away from each other. In other words, the opening degree of the pair of gripping claws 55 increases. Then, when the operating shaft 24 moves until the cushion rubber 37 contacts the rod guide 15, the swinging of the pair of levers 53 stops, and the electric gripping device 10 is disposed at the initial position P1.

[0071] <Grip jaw position> As shown in FIG. 9, when the electric gripping device 10 is at the initial position P1, when a motor current flows through the motor 14, the motor 14 operates at an acceleration where the rotation speed increases linearly from the minimum speed from the initial position P1 toward the gripping start position P2. After reaching the maximum speed, the motor 14 operates at a constant maximum speed up to the gripping start position P2. The motor 14 operates at a decelerating acceleration where the rotation speed is linearly decelerated from the gripping start position P2. The motor 14 stops when a predetermined operation time has elapsed from the gripping start position P2. The control of the rotation speed of the motor 14 from the initial position P1 toward the gripping position P3 is performed by the control of the driver 61 by the control device 60.

[0072] The initial position P1 is a fixed position, but the gripping start position P2 and the gripping position P3 are each changed depending on the dimension of the workpiece W in the second direction Y. The gripping start position P2 and the gripping position P3 are each set appropriately according to the dimension of the workpiece W in the second direction Y.

[0073] 7 and 8, when paying attention to the positions of the pair of gripping claws 55, grip start position P2 and gripping position P3 are the same position, but the length of coil spring 23 from the contact point between coil spring 23 and head 28b to first end 23a is different between grip start position P2 and gripping position P3. Hereinafter, of the length of coil spring 23, the length along wire rod 23c from the contact point between coil spring 23 and head 28b to first end 23a is referred to as the "effective spring length."

[0074] As shown in FIG. 7, the grip start position P2 is a position at the time when the pair of gripping jaws 55 contact the workpiece W. At the grip start position P2, the cushion rubber 37 is slightly away from the rod guide 15 toward the motor 14. In the gripping jaw opening / closing mechanism 50, the pair of master jaws 51 are closer to each other along the second direction Y than at the initial position P1. The effective spring length at the grip start position P2 is longer than the effective spring length at the initial position P1, but the compression displacement amount of the coil spring 23 at the grip start position P2 is zero. Therefore, the gripping force of the pair of gripping jaws 55 is zero at the grip start position P2. Then, the compression displacement amount of the coil spring 23 increases from the grip start position P2 toward the gripping position P3.

[0075] As shown in Fig. 8, the gripping position P3 is a position at the time when the pair of gripping jaws 55 contact the workpiece W and grip the workpiece W with a predetermined gripping force. At the gripping position P3, the cushion rubber 37 is slightly separated from the rod guide 15. In the gripping jaw opening / closing mechanism 50, the pair of master jaws 51 are closer to each other in the second direction Y than the initial position P1. These parts are shown in Fig. 7 This is the same as the gripping start position P2 shown in FIG.

[0076] At the gripping position P3, the coil spring 23 is inserted further between the contact point between the coil spring 23 and the head 28b and the first end 23a than at the gripping start position P2. As a result, the amount of compression displacement of the coil spring 23 at the gripping position P3 is greater than the amount of compression displacement of the coil spring 23 at the gripping start position P2. The greater the amount of compression displacement of the coil spring 23, the longer the effective spring length becomes. The amount of compression displacement at the gripping position P3 is greater than the amount of compression displacement at the initial position P1 and the gripping start position P2. At the amount of compression displacement at the gripping position P3, the gripping force of the pair of gripping jaws 55 is greater than zero. At the gripping position P3, the workpiece W is gripped by the pair of gripping jaws 55 with the above-mentioned predetermined gripping force. The gripping start position P2 and the gripping position P3 can be adjusted according to the dimensions of the workpiece W.

[0077] As described above, the predetermined gripping force at the gripping position P3 can be set by the rotation angle of the motor 14 from the gripping start position P2. The rotation angle of the motor 14 is determined according to the step angle of the motor 14 and the number of pulse signals. The rotation angle of the motor 14 increases in proportion to the number of pulse signals. The number of pulse signals per unit time is the pulse rate. The higher the pulse rate, the faster the rotation speed of the motor 14. In order to obtain a desired rotation angle of the motor 14 at the gripping position P3, the faster the rotation speed of the motor 14 is, the shorter the operation time of the motor 14 from the gripping start position P2 is. In other words, in order to obtain a desired rotation angle of the motor 14 at the gripping position P3, the slower the rotation speed of the motor 14 is, the longer the operation time of the motor 14 from the gripping start position P2 is.

[0078] 9, the longer the operation time of the motor 14 from the grip start position P2, the greater the amount of compressive displacement of the coil spring 23 and the longer the time that the pair of gripping jaws 55 fastens the workpiece W. This increases the gripping force of the pair of gripping jaws 55. The operation time of the motor 14 is the time that the motor 14 operates from when it starts to decelerate at the grip start position P2 until it stops.

[0079] The control device 60 controls the motor 14. Since the motor 14 is a stepping motor, the motor 14 is controlled by open loop control. The control device 60 has a processor and a storage unit. The storage unit includes a random access memory (RAM) and a read only memory (ROM). The storage unit stores program codes or instructions configured to cause the processor to execute processes. In this embodiment, the storage unit stores program codes for operating the electric gripping device 10. The storage unit, i.e., the computer readable medium, includes any available medium accessible by a general-purpose or dedicated computer. The control device 60 may be configured by a hardware circuit such as an application specific integrated circuit (ASIC) or a field programmable gate array (FPGA). The control device 60, which is a processing circuit, may include one or more processors operating according to a computer program, one or more hardware circuits such as an ASIC or an FPGA, or a combination thereof.

[0080] As shown in Fig. 1, the control device 60 is signal-connected to the driver 61 and the deceleration acceleration setting unit 63. The control device 60 has a pulse oscillator (not shown). The control device 60 uses the pulse oscillator to generate a pulse signal for controlling the operation of the motor 14, or to stop the generation of the pulse signal. The pulse signal generated by the control device 60 is input to the driver 61. When the pulse signal is input to the driver 61, the magnetic pole through which the current of the motor 14 flows is switched for each pulse, and the motor 14 is positioned.

[0081] As shown in the graph of the rotation speed in Fig. 9, the motor 14 operates under acceleration / deceleration operation control. When the motor 14 is controlled under acceleration / deceleration operation control, the motor 14 starts operating at the minimum speed from a stopped state. After accelerating at a constant acceleration, the motor 14 operates at the maximum speed when it reaches the maximum speed. When the motor 14 starts decelerating from the maximum speed, it decelerates at a constant deceleration acceleration and stops when it reaches the minimum speed.

[0082] In acceleration / deceleration operation control, the minimum speed is the rotational speed of motor 14 when motor 14 begins to operate and the rotational speed just before motor 14 stops. The minimum speed is obtained by operating motor 14 at the minimum pulse rate. In acceleration / deceleration operation control, the maximum speed is the maximum value of the rotational speed of motor 14. The maximum speed is obtained by operating motor 14 at the maximum pulse rate.

[0083] In the acceleration / deceleration operation control, when the motor 14 operates at a constant acceleration, the pulse rate is gradually increased. The increase rate of this pulse rate is set to a constant value. In the acceleration / deceleration operation control, when the motor 14 operates at a constant deceleration, the pulse rate is gradually decreased. A plurality of decrease rates of this pulse rate are set.

[0084] In the acceleration / deceleration operation control, when the maximum speed, minimum speed, pulse rate increase rate, and pulse rate decrease rate are set, the acceleration time and deceleration time of the motor 14 are determined. The control device 60 generates pulse signals at calculated intervals so that the motor 14 operates at the calculated acceleration time and deceleration time. Then, the motor 14 is subjected to acceleration / deceleration operation control by the driver 61. The acceleration / deceleration operation control is a so-called trapezoidal control. Moreover, in the acceleration / deceleration operation control, the current rotation position is not grasped when the motor 14 is rotated by the driver 61. The minimum speed and maximum speed can be set by the control device 60. Moreover, the pulse rate increase rate can be set by the control device 60.

[0085] A plurality of deceleration accelerations at which the motor 14 stops rotating are stored in advance in the storage unit of the control device 60. The deceleration acceleration is set as a reduction rate of the pulse rate. The deceleration acceleration setting unit 63 can select and set one of the plurality of deceleration accelerations. The deceleration acceleration is an acceleration at which the rotation of the motor 14 is decelerated from the grip start position P2 in order to stop the motor 14. The larger the deceleration acceleration is, the shorter the operation time required for the motor 14 to stop from the grip start position P2 becomes. In other words, the smaller the deceleration acceleration is, the longer the operation time required for the motor 14 to stop from the grip start position P2 becomes. In other words, the rotation angle of the motor 14 from the grip start position P2 to the motor 14 stopping becomes larger. The control device 60 outputs a pulse signal to the driver 61 using the deceleration acceleration selected by the deceleration acceleration setting unit 63. Specifically, the deceleration acceleration setting unit 63 is a rotary switch.

[0086] The control device 60 is signal-connected to a host control device 62 that is separate from the control device 60. The host control device 62 outputs a start signal to the control device 60. The start signal is a signal that instructs the pair of gripping jaws 55 to start the gripping operation of the workpiece W.

[0087] When the control device 60 receives a start signal from the upper control device 62, it outputs a pulse signal to the driver 61. When the driver 61 receives the pulse signal from the control device 60, a motor current flows in the motor 14 in response to the pulse signal, and the phase of the excited coil advances.

[0088] The control device 60 is signal-connected to the first position detection sensor 16a and the second position detection sensor 16b. Each of the first position detection sensor 16a and the second position detection sensor 16b detects magnetism from the magnet 35 integrated with the operating shaft 24. By detecting this magnetism, each of the first position detection sensor 16a and the second position detection sensor 16b detects the position of the operating shaft 24 in the axial direction Z.

[0089] The first position detection sensor 16a and the second position detection sensor 16b output a magnetic detection signal when they detect a magnetic field. The first position detection sensor 16a and the second position detection sensor 16b do not output a magnetic detection signal when they are no longer able to detect a magnetic field. The magnetic detection signal is input to the control device 60.

[0090] 9, in the initial position P1, the first position detection sensor 16a outputs a magnetic detection signal to the control device 60 and is turned on. The first position detection sensor 16a that is turned on is illuminated. The on and off state of the first position detection sensor 16a can be visually confirmed from the end face of the main body 11a.

[0091] When the operating shaft 24 moves and the gripping jaws 55 move from the initial position P1 toward the gripping start position P2, the magnet 35 moves away from the first position detection sensor 16a. Then, the first position detection sensor 16a is turned off and does not output a magnetic detection signal before reaching the gripping start position P2. The first position detection sensor 16a that has been turned off goes out. At this time, no magnetic detection signal is input to the control device 60. Therefore, at the gripping start position P2 and the gripping position P3, the first position detection sensor 16a is turned off and does not output a magnetic detection signal.

[0092] In the initial position P1, the second position detection sensor 16b does not output a magnetic detection signal and is turned off. When the operating shaft 24 moves and the gripping jaws 55 move from the initial position P1 toward the gripping start position P2, the magnet 35 approaches the second position detection sensor 16b. When the gripping jaws 55 reach the gripping start position P2, the second position detection sensor 16b outputs a magnetic detection signal and is turned on. When the second position detection sensor 16b is turned on, it is illuminated. The on and off state of the second position detection sensor 16b can be seen from the end face of the main body 11a.

[0093] When the pair of gripping claws 55 reach the grip start position P2 and the control device 60 inputs a magnetic detection signal, the control device 60 starts a deceleration operation to decelerate the motor 14 at a deceleration acceleration selected by a deceleration acceleration setting unit 63, operates the motor 14 at a predetermined rotation angle, and then stops the motor 14 at the grip position P3. In other words, when the pair of gripping claws 55 reach the grip start position P2 and inputs a grip start signal (magnetic detection signal), the control device 60 controls the driver 61 to decelerate the motor 14 at a deceleration acceleration selected by the deceleration acceleration setting unit 63, operates the motor 14 at a predetermined rotation amount, and then stops the motor 14 at the grip position P3.

[0094] Therefore, in the electric gripping device 10, the second position detection sensor 16b outputs a magnetic detection signal that detects the position of the operating shaft 24 in the axial direction Z as a gripping start signal to the control device 60 at the time when the pair of gripping jaws 55 starts gripping the workpiece W. When the control device 60 receives the magnetic detection signal, it controls the motor 14 to increase the gripping force of the pair of gripping jaws 55 on the workpiece W.

[0095] The control device 60 starts the deceleration acceleration control from the point when the pair of gripping jaws 55 reach the grip start position P2. The motor 14 starts the deceleration operation with the start of the deceleration acceleration control. The trigger for the control device 60 to start the deceleration acceleration control is that a magnetic detection signal (gripping start signal) from the second position detection sensor 16b is input to the control device 60. When the control device 60 inputs the magnetic detection signal from the second position detection sensor 16b, the pulse rate is reduced in the deceleration acceleration control from the maximum pulse rate until it reaches the minimum pulse rate. The reduction rate of the pulse rate at this time is set to the deceleration acceleration selected by the deceleration acceleration setting unit 63. When the pulse rate is reduced to the minimum pulse rate by the deceleration acceleration control, the control device 60 stops generating the pulse signal. Then, at that position, the motor 14 stops with the holding current flowing, and the deceleration operation of the motor 14 ends. Here, if the self-lock condition is satisfied, the holding current can be stopped.

[0096] Then, the deceleration acceleration control causes the pulse rate to decrease from the grip start position P2, and the motor 14 continues to operate at a deceleration speed and the coil spring 23 is compressed until the pulse signal is no longer output. In other words, the gripping force increases from the grip start position P2 to the grip position P3. Note that, since the gripping jaws 55 come into contact with the workpiece W, the operating shaft 24 does not move in the axial direction Z, and the position of the magnet 35 does not move in the axial direction Z either. For this reason, from the grip start position P2 to the grip position P3, the second position detection sensor 16b remains on and continues to be illuminated.

[0097] When the gripping start position P2 and the gripping position P3 are adjusted in accordance with the dimensions of the workpiece W, the position of the magnet 35 at the gripping start position P2 and the gripping position P3 is also changed. When the position of the magnet 35 is changed, the position of the second position detection sensor 16b is adjusted so that the gripping start position P2 and the gripping position P3 are detected by the second position detection sensor 16b. The position of the second position detection sensor 16b is adjusted by moving the second position detection sensor 16b along the mounting groove 11c of the body 11.

[0098] The control device 60 outputs a gripping completion signal to the upper control device 62. The gripping completion signal is output from the control device 60 when the pulse rate decreases and the motor 14 stops, and the magnetic detection signal is output by the second position detection sensor 16b. In other words, when the deceleration acceleration control is completed from the gripping start position P2 and the gripping position P3 is maintained, the control device 60 judges that the gripping state is reached and outputs the gripping completion signal. Therefore, when the pair of gripping jaws 55 is located at the gripping position P3, the control device 60 outputs the gripping completion signal to the upper control device 62. The time when the gripping completion signal is output is the time when the deceleration operation of the motor 14 ends and the rotation speed of the motor 14 becomes zero. Also, when the gripping completion signal is output, the motor 14 switches to a holding current. When the self-locking condition is satisfied, the holding current of the motor 14 can be stopped.

[0099] As shown by the dashed lines of different line types in Figure 9, the rotation angle at which the motor current stops flowing and the motor 14 stops varies depending on the deceleration acceleration selected by the deceleration acceleration setting unit 63, and therefore the point in time at which the grip completion signal is output also varies.

[0100] <Alarm processing> Next, a case where the workpiece W is not placed between the pair of gripping jaws 55 will be described. When the gripping jaws 55 move from the initial position P1 toward the gripping start position P2 to a position where the gripping jaws 55 are scheduled to come into contact with the workpiece W, the second position detection sensor 16b outputs a magnetic detection signal and is turned on.

[0101] Even if the workpiece W is not placed, the deceleration operation starts as the gripping force control start point. The motor 14 performs the deceleration operation under the set conditions. At this time, the operating shaft 24 moves in the axial direction Z, and the pair of gripping jaws 55 approach each other. Therefore, the position of the follower 28 also approaches the motor 14, so that the coil spring 23 is not compressed. In other words, the compression displacement amount of the coil spring 23 is zero. As a result, as shown by the two-dot chain line in FIG. 9, the second position detection sensor 16b that has been turned on is turned off without outputting a magnetic detection signal. The second position detection sensor 16b that has been turned off is turned off.

[0102] Then, from the grip start position P2 to the grip position P3, the second position detection sensor 16b remains off and the second position detection sensor 16b continues to be turned off. Then, when the set operation is completed from the time when the second position detection sensor 16b outputs the magnetic detection signal at the grip start position P2, the control device 60 stops the generation of the pulse signal by the driver 61. Then, the motor 14 is positioned at the stop position by the holding current. After that, the control device 60 stops the holding current of the motor 14. If the magnetic detection signal is not input from the grip start position P2, the control device 60 outputs an error signal to the upper control device 62. In other words, if the signal detecting the position of the working shaft 24 in the axial direction Z is not input at the time when the motor 14 stops, the control device 60 outputs an error signal indicating that the workpiece W is not present. The upper control device 62 issues an alarm using a notifying means (not shown).

[0103] <Self-locking and action> The self-locking state of the electric gripping device 10 is a mechanism that maintains gripping of the workpiece W by the pair of gripping jaws 55 when motor current stops flowing to the motor 14 at the gripping position P3. The electric gripping device 10 compresses the coil spring 23 between the contact point between the coil spring 23 and follower 28 and the first end 23a of the coil spring 23, thereby enabling a self-locking state in which the pair of gripping jaws 55 maintain gripping of the workpiece W.

[0104] In the electric gripping device 10, when the pair of gripping jaws 55 opens and closes, the head 28b is in contact with the coil spring 23. The head 28b is in contact with the surface of the coil spring 23 from the axial direction Z. With the head 28b in contact with the coil spring 23, the operating shaft 24 moves in the axial direction Z together with the rotation of the coil spring 23.

[0105] Then, when the pair of gripping jaws 55 contact the workpiece W at the gripping start position P2, the movement of the operating shaft 24 in the axial direction Z stops. After that, the coil spring 23 is compressed from the gripping start position P2 toward the gripping position P3.

[0106] 8 and 10, the angle of the coil spring 23, which corresponds to the lead of the screw, gradually decreases in the coil spring 23. Note that the angle does not become zero when the coil spring 23 is simply compressed in the axial direction Z.

[0107] In this embodiment, when moving from gripping start position P2 to gripping position P3, coil spring 23 tilts from the contact point between head 28b and coil spring 23 as a starting point so as to approach the tip of head 28b.

[0108] As shown in FIG. 8, the coil spring 23 tilts so as to deform the central axis L3 into an arc shape. With such tilt of the coil spring 23, the contact point between the coil spring 23 and the head 28b moves toward the inner diameter side of the coil spring 23. At the gripping position P3, the angle between the direction of the force F1 that the follower 28 receives from the coil spring 23 and the direction of the normal force F2 at the contact point between the coil spring 23 and the head 28b is defined as "θ". Then, as shown in FIG. 10, at the gripping position P3, the positive and negative of the angle θ are reversed at the contact point between the head 28b and the coil spring 23, so that the angle θ can be set to zero. When the angle θ is zero, the self-locking condition is satisfied, and a reliable self-locking state is achieved.

[0109] At gripping position P3, the friction coefficient when the coil spring 23 and head 28b come into contact and the follower 28 slides or rotates about its axis is "μ". When self-locking at gripping position P3, the relational expression "μ>tan θ" is satisfied. Note that the angle θ becomes smaller as one moves from gripping start position P2 to gripping position P3. In other words, as one moves from gripping start position P2 to gripping position P3, one approaches a state where μ>tan θ is satisfied, and at gripping position P3, one reaches a state where μ>tan θ is satisfied.

[0110] As shown in FIG. 3, in the uncompressed state of the coil spring 23, the angle θ is almost the same as the direction in which the spiral of the coil spring 23 extends, and is constant like a feed screw mechanism. In other words, the angle θ is greater than zero. In this case, it can be seen that in order to achieve a self-locking state in the relational expression "μ>tan θ", it is necessary to use the coil spring 23 under conditions in which friction occurs between the coil spring 23 and the head 28b. For this reason, self-locking using a ball screw mechanism that does not generate friction cannot be used, and self-locking using a sliding screw mechanism must be used. When using a self-locking using a sliding screw mechanism, there is a risk that energy loss will occur due to friction loss, and that it will be difficult to release the self-locking due to the change in the friction coefficient μ associated with the change in the angle θ.

[0111] In this embodiment, the follower 28 is rotatably supported by the operating shaft 24. Furthermore, the follower 28 is supported by the operating shaft 24 by the bearing 27 so as to be smoothly rotatable. Therefore, compared to the case where the follower 28 is non-rotatable, the energy loss due to friction at the contact point between the head 28b and the coil spring 23 is minimized. In other words, compared to the case where the follower 28 is non-rotatable, the friction coefficient μ is kept small. Then, as the coil spring 23 is compressed from the grip start position P2 toward the grip position P3, the angle θ approaches zero.

[0112] 10, as the compression of the coil spring 23 continues, the coil spring 23 tilts toward the contact point between the coil spring 23 and the head 28b, and the angle θ becomes zero. In other words, as the compression of the coil spring 23 continues between the contact point between the coil spring 23 and the head 28b and the first end 23a, the coil spring 23 tilts and the angle θ becomes zero. Note that the angle θ being zero includes a case where the angle θ is slightly different from zero by ± due to a manufacturing error of the coil spring 23, etc.

[0113] Therefore, even if the friction coefficient μ is small, μ>tanθ can be maintained. In other words, even if the friction coefficient μ is small, the self-locked state can be maintained. The coil spring 23 is maintained in a compressed state between the contact point between the head 28b and the coil spring 23 and the first end 23a of the coil spring 23, and the coil spring 23 is prevented from rotating in the non-compressed direction. In other words, the coil spring 23 is prevented from unwinding from the compressed state. As a result, the self-locked state is maintained. Therefore, the pair of gripping claws 55 can be prevented from being displaced from the gripping position P3 to the gripping start position P2 as the coil spring 23 rotates. Therefore, the self-locked state can be maintained even under low friction conditions due to rolling bearings that cannot be achieved by self-locking using a sliding screw mechanism.

[0114] On the other hand, when releasing the self-locked state in order to release the gripping of the workpiece W by the pair of gripping jaws 55, the motor 14 is rotated in the reverse direction by the control device 60. Then, since the angle θ is zero, the coil spring 23 quickly rotates in the non-compressed direction, and the self-locked state is released.

[0115] According to the above embodiment, the following effects can be obtained. (1) The follower 28 is rotatably supported by the operating shaft 24. At the gripping position P3, the coil spring 23 is compressed in a state inclined toward the follower 28 with respect to the central axis L3 of the coil spring 23. This inclination of the coil spring 23 allows the angle θ at the contact point between the follower 28 and the coil spring 23 to be zero. Therefore, even if the friction coefficient μ is small, μ>tan θ can be maintained at the gripping position P3, so that the self-locked state can be maintained. Also, in the self-locked state, since the angle θ is zero, the friction coefficient μ between the coil spring 23 and the follower 28 is kept small. Therefore, energy loss due to friction between the follower 28 and the coil spring 23 can be suppressed. As a result, it is possible to suppress the occurrence of a case in which it is difficult to release the self-locked state due to a change in the friction coefficient μ. Therefore, the electric gripping device 10 can preferably self-lock.

[0116] (2) The follower 28 is rotatably supported by the bearing 27. Therefore, the energy loss due to friction between the follower 28 and the coil spring 23 can be further suppressed. (3) The coil spring 23 is disposed inside the protective member 22. The coil spring 23 comes into contact with the inner circumferential surface of the protective member 22, thereby restricting excessive inclination of the coil spring 23, i.e., buckling. This makes it possible to prevent the coil spring 23 from inclining until the angle θ becomes a numerical value significantly different from zero. In addition, since the inclination of the coil spring 23 can be adjusted by adjusting the inner diameter of the protective member 22, the gripping force of the electric gripping device 10 can be easily adjusted by changing the protective member 22.

[0117] (4) The coil spring 23 is disposed inside the protective member 22. Therefore, the protective member 22 can widen the range of application of the coil spring 23, such as the buckling condition of the coil spring 23.

[0118] (5) The second position detection sensor 16b detects the gripping start position P2. When the control device 60 receives a magnetic detection signal from the second position detection sensor 16b, it operates the motor 14 at a decelerating acceleration in accordance with the detection of the gripping start position P2. Therefore, one of the second position detection sensors 16b can detect the gripping start position P2 and switch from position control to force control of the gripping jaws 55. Compared to a case where the detection of the gripping start position P2 and the switch from position control to force control of the gripping jaws 55 are performed by separate sensors, the configuration of the electric gripping device 10 can be simplified and the control load of the control device 60 can be reduced.

[0119] (6) The deceleration acceleration setting unit 63 can set the reduction rate of the pulse rate, i.e., the deceleration acceleration, to multiple values. By setting the deceleration acceleration selected by the deceleration acceleration setting unit 63, the gripping force of the pair of gripping jaws 55 can be adjusted. Therefore, the gripping force can be adjusted by the deceleration acceleration of the motor 14 set by the deceleration acceleration setting unit 63, making it easy to adjust the gripping force. In other words, since it is not necessary to change the control program of the control device 60, the versatility of the electric gripping device 10 is improved.

[0120] Furthermore, the deceleration acceleration setting unit 63 allows the selection of a preset deceleration acceleration, making it easy to set the gripping force. When the electric gripping device 10 is at the gripping position P3 and the workpiece W falls due to the acceleration during transportation, the deceleration acceleration setting unit 63 makes it easy to make a post-adjustment such as increasing the deceleration acceleration by one step, and adjustment is also possible at the site where the electric gripping device 10 is used.

[0121] (7) When the second position detection sensor 16b detects a magnetic detection signal, the control device 60 starts deceleration / acceleration control of the motor 14, and stops the motor 14 when the pulse rate drops to the minimum pulse rate. Then, the gripping jaws 55 are located at the gripping position P3. When the motor 14 is stopped, if the pair of gripping jaws 55 grips the workpiece W, the second position detection sensor 16b outputs a magnetic detection signal and is turned on and illuminated. Therefore, for example, it is possible to detect the gripping of the workpiece W by the pair of gripping jaws 55 without using a device that detects the number of rotations of the motor 14. In addition, when the pair of gripping jaws 55 grips the workpiece W, the second position detection sensor 16b is illuminated, so that it can be visually confirmed.

[0122] (8) When the motor 14 is stopped, if the workpiece W is not gripped by the pair of gripping jaws 55, the second position detection sensor 16b does not output a magnetic detection signal and is turned off and unlit. Therefore, it is possible to detect a state in which the workpiece W is not being gripped by the pair of gripping jaws 55, for example, without using a device that detects the number of rotations of the motor 14. In addition, when the workpiece W is not being gripped by the pair of gripping jaws 55, the second position detection sensor 16b is unlit, so that it can be visually confirmed.

[0123] Furthermore, when the motor 14 is stopped, if the workpiece W is not gripped by the pair of gripping jaws 55, the control device 60 outputs an error signal to the host control device 62. When the host control device 62 receives the error signal, it issues an alarm indicating that the workpiece W is not being gripped. Therefore, the operator can easily confirm that the workpiece W is not being gripped by the pair of gripping jaws 55.

[0124] (9) The electric gripping device 10 has a gripping jaw operation unit 14b. The gripping jaw operation unit 14b can manually rotate the motor shaft 14a to adjust the opening degree of the pair of gripping jaws 55. Therefore, the gripping start position P2 and the gripping position P3 can be adjusted manually. As a result, adjustment of the gripping start position P2 and the gripping position P3 does not require program changes to the control device 60, and can be easily set at the site where the electric gripping device 10 is used. In addition, adjustment of the gripping start position P2 and the gripping position P3 can be easily performed according to the dimensions of the workpiece W.

[0125] (10) The electric gripping device 10 grips the workpiece W with a pair of gripping jaws 55 by rotating one coil spring 23. Therefore, the pair of gripping jaws 55 open and close synchronously. For example, if the electric gripping device uses two coil springs and opens and closes the gripping jaws by rotating each coil spring, the pair of gripping jaws move individually to open and close. Compared to this case, it is possible to improve centering accuracy when gripping the workpiece W, and it is easier to control the gripping force.

[0126] (11) The gripping jaw opening / closing mechanism 50 includes the rotating shaft 36 of the actuating shaft 24, a lever 53, a support shaft 54, a guide plate 52, and a master jaw 51. With such a gripping jaw opening / closing mechanism 50, the centering accuracy of the pair of gripping jaws 55 can be improved.

[0127] (12) The drive mechanism 20 includes a unit part 201. The unit part 201 is formed by previously integrating the mounting member 21, the protective member 22, the coil spring 23, the working shaft body 25 of the working shaft 24, the bearing 27, and the follower 28. Therefore, by connecting the unit part 201 to the rod 26 and the motor shaft 14a, the mounting member 21, the protective member 22, the coil spring 23, the working shaft body 25, the bearing 27, and the follower 28 can be collectively provided in the body 11. Conversely, by releasing the connection between the mounting member 21 and the motor shaft 14a, the motor 14 can be removed from the body 11, and by releasing the connection between the rod 26 and the working shaft body 25, the mounting member 21, the protective member 22, the coil spring 23, the working shaft body 25, the bearing 27, and the follower 28 can be collectively removed from the body 11.

[0128] This embodiment can be modified as follows: This embodiment and the following modifications can be combined with each other to the extent that there is no technical contradiction. 11, in the unit part 201, the first end 23a of the coil spring 23 may be a free end, and the second end 23b of the coil spring 23 may be a fixed end and fixed to the mounting member 21. In this case, the direction in which the spiral of the coil spring 23 extends is opposite to that in the embodiment. Also, the mounting member 21 serves as a rotating member to which the coil spring 23 is fixed.

[0129] In the electric gripping device 10 having the unit part 201 shown in Fig. 11, the pair of gripping jaws 55 are in contact with each other at the initial position P1 where the workpiece W is not gripped. In the electric gripping device 10, when the motor 14 is rotated in the forward direction, the pair of gripping jaws 55 in the initial position P1 move in the second direction Y so as to move away from each other. Then, at the gripping position P3, the outer surfaces of the pair of gripping jaws 55 come into contact with the workpiece W to grip it. The workpiece W is gripped by so-called inner gripping.

[0130] When the motor 14 is rotated in the forward direction from the gripping start position P2, the coil spring 23 enters between the mounting member 21 and the follower 28 and is compressed. At the gripping position P3, the compressed coil spring 23 applies a force in a direction that separates the pair of gripping jaws 55.

[0131] 11, the protective member 22 may be omitted. In this case, the coil spring 23 rotates integrally with the motor shaft 14a and the mounting member 21. As shown in Fig. 12, in the unit part 201, the first end 23a of the coil spring 23 may be fixed to the first end 22a of the protective member 22, and the second end 23b of the coil spring 23 may be fixed to the mounting member 21. In this case, the protective member 22 and the mounting member 21 become rotating members to which the fixed end of the coil spring 23 is fixed. The direction in which the spiral of the coil spring 23 extends may be the same as that of the embodiment, or may be the opposite. In other words, when the pair of gripping jaws 55 are moved from the gripping start position P2 to the gripping position P3, the direction of the spiral of the coil spring 23 is selected depending on whether the coil spring 23 is compressed on the motor 14 side or on the rod guide 15 side.

[0132] Therefore, in the electric gripping device 10 having the unit portion 201 shown in FIG. 12, the direction in which the workpiece W is gripped can be selected. 13, in an embodiment, the second end 23b of the coil spring 23 may be in a compressed state and in contact with the mounting member 21. With this configuration, the coil spring 23 is pre-compressed, so that the time required to operate the motor 14 to exert a gripping force at the gripping position P3 can be shortened.

[0133] As shown in FIG. 14, the electric gripping device 10 may have a support member 29 integral with the operating shaft 24. The support member 29 is fixed to the second end surface 25b of the operating shaft body 25 in the operating shaft 24. The support member 29 is disk-shaped. A sliding ring 29a is attached to the peripheral surface of the support member 29. The sliding ring 29a is in contact with the inner peripheral surface of the protective member 22. When the operating shaft 24 moves in the axial direction Z, the sliding ring 29a of the support member 29 slides against the inner peripheral surface of the protective member 22. Due to the sliding contact of the support member 29, it is possible to suppress inclination of the operating shaft 24 when the operating shaft 24 moves in the axial direction Z.

[0134] In addition, in the initial position P1, the second end 23b of the coil spring 23 is in contact with the support member 29. In the initial position P1, the coil spring 23 is compressed. Therefore, it is possible to suppress the vibration of the coil spring 23 due to the vibration of the motor 14. Therefore, when the operating shaft 24 is moved by the rotation of the coil spring 23, it is possible to suppress the influence of the vibration of the motor 14 from interfering with the movement of the operating shaft 24. In addition, since the coil spring 23 is compressed in advance, it is possible to shorten the time required to generate a gripping force when moving from the gripping start position P2 to the gripping position P3.

[0135] Furthermore, when the coil spring 23 is compressed, it tends to tilt with respect to the central axis L3. The tilt of the coil spring 23 causes the operating shaft 24 to tilt. However, the support member 29 can suppress the tilt of the operating shaft 24 even when the coil spring 23 is compressed. As a result, the load applied to the motor 14 due to the tilt of the operating shaft 24 can also be reduced. This makes it possible to accommodate an increase in the travel distance of the gripping jaws 55 due to an increase in the size of the workpiece W.

[0136] In the embodiment shown in FIG. 14, the first end 23a of the coil spring 23 may be fixed to the protective member 22, and the second end 23b of the coil spring 23 may be fixed to the support member 29.

[0137] In this case, the coil spring 23 is supported at both ends, increasing the apparent spring constant. This allows a high gripping force to be generated with a small coil spring 23, making it possible to miniaturize the electric gripping device 10. In addition, the reduction in size of the coil spring 23 allows the amount of rotation of the motor 14 to be reduced, thereby shortening the operating time of the motor 14 required to grip the workpiece W.

[0138] There may be three gripping claws 55. In this case, the gripping claw opening / closing mechanism 50 employs a sliding cam mechanism for opening and closing the three gripping claws 55. The gripping jaw operation unit 14b and the operation member 14c may be omitted. In this case, the gripping start position P2 and the gripping position P3 are adjusted by changing the control program.

[0139] The deceleration from the grip start position P2 to the grip position P3 does not have to be adjustable. In this case, the deceleration setting unit 63 is omitted. If the follower 28 is rotatably supported by the operating shaft 24, the bearing 27 may be omitted.

[0140] The follower 28 may be cylindrical. In this case, the follower 28 is formed only with the shaft portion 28a. That is, the follower 28 does not have the head portion 28b. In this case, the portion of the shaft portion 28a protruding from the peripheral surface of the operating shaft 24 fits between the wires 23c. In the follower 28 having only the shaft portion 28a, the portion protruding from the peripheral surface of the operating shaft 24 may or may not have an annular groove 28c formed therein.

[0141] Although the gripping start position P2 is set to the point at which the pair of gripping jaws 55 come into contact with the workpiece W, the gripping start position P2 may be set to immediately before the pair of gripping jaws 55 come into contact with the workpiece W. In this configuration, the motor 14 can be decelerated immediately before the gripping jaws 55 come into contact with the workpiece W. As a result, the gripping speed immediately before gripping starts is reduced, and the workpiece W can be gripped softly.

[0142] The central axis M of the follower 28 may be oblique to the central axis L3 of the coil spring 23. One or both of the first position detection sensor 16a and the second position detection sensor 16b may be, for example, a photosensor that detects the movement of the operating shaft 24.

[0143] When the workpiece W is not positioned between the pair of gripping jaws 55, the control device 60 does not need to output an error signal. The control of the motor 14 from the gripping start position P2 to the gripping position P3 at which the motor 14 is stopped may be controlled by the rotation speed of the motor 14.

[0144] After inputting the gripping start signal at the gripping start position P2, the control device 60 may operate the motor 14 at a constant rotational speed without decelerating the motor 14, and then stop the motor 14 without decelerating.

[0145] Although the embodiment shows the motor 14 being controlled by open loop control, the motor 14 may be controlled by closed loop control using rotation angle detection by a rotary encoder or the like.

[0146] In the electric gripping device 10, the operating shaft 24 does not have to be separable into the operating shaft body 25 and the rod 26. The electric gripping device 10 does not have to include the unit portion 201.

[0147] The electric gripping device 10 does not need to have the protective member 22. In this case, the mounting member 21, the coil spring 23, and the operating shaft 24 are directly inserted into the shaft hole 12. [Explanation of symbols]

[0148] 10...electric gripping device, 14...motor, 14a...motor shaft, 14b...gripping claw operation unit, 16b...second position detection sensor, 21...mounting member as rotating member, 22...protective member as rotating member, 22a...first end, 22b...second end, 23...coil spring, 23a...first end, 23b...second end, 23c...wire, 24...operating shaft, 25...operating shaft main body, 26...rod, 27...bearing, 28...follower, 29...support member, 50...gripping claw opening / closing mechanism, 55...gripping claw, 60...control device, 61...driver, 63...deceleration acceleration setting unit, 201...unit unit.

Claims

1. a motor having a motor shaft; a coil spring formed by winding a wire in a spiral shape and fixed to a rotating member that rotates integrally with the motor shaft; an actuation shaft disposed inside the coil spring and movable in an axial direction along a central axis of the coil spring; a follower protruding from a circumferential surface of the operating shaft, the follower being provided so that a central axis of the follower intersects with a central axis of the operating shaft, the follower being supported by the operating shaft so as to be rotatable about the central axis of the follower as a rotation center, and the follower having a protruding portion from the circumferential surface of the operating shaft disposed in a gap between the wire rods adjacent to each other in the axial direction; a gripping claw opening / closing mechanism connected to an end of the operating shaft, the gripping claw opening / closing mechanism opening and closing a pair of gripping claws by moving the operating shaft in the axial direction and restricting rotation of the operating shaft about a central axis of the operating shaft; A control device for controlling the motor, By compressing the coil spring between a contact point between the coil spring and the follower and a fixed end between the coil spring and the rotating member, a self-locking mechanism is enabled that maintains the grip of the workpiece by the pair of gripping jaws, an electric gripping device configured to satisfy the relational expression μ>tan θ in the self-locking state, where μ is the coefficient of friction when the coil spring and the follower come into contact with each other, and θ is the angle between the direction of the force that the follower receives from the coil spring when the workpiece is gripped by the pair of gripping jaws, and the direction of the normal force at the contact point, and wherein the angle θ is set to zero by tilting the coil spring as the coil spring is compressed between the contact point and the fixed end.

2. The electric gripping device according to claim 1 , wherein the actuation shaft has a bearing that rotatably supports the follower.

3. the rotating member is a cylindrical protective member that surrounds the coil spring from the outside, a first end of the coil spring is fixed to a first end of the protective member as the fixed end, and a second end of the coil spring is a free end; 3. The electric gripping device according to claim 1, wherein an attachment member is fixed to an inner side of the second end portion of the protection member, and the motor shaft is connected to the attachment member.

4. The actuating shaft is formed by connecting an actuating shaft main body that supports the follower and a rod that is connected to the gripping jaw opening / closing mechanism, The electric gripping device according to claim 3 , further comprising a unit portion in which the mounting member, the protection member, the coil spring, and the operating shaft body are integrated.

5. The electric gripping device according to claim 3 , wherein a support member is fixed to the operating shaft, and the support member is in sliding contact with an inner circumferential surface of the protection member.

6. The electric gripping device according to claim 5 , wherein the coil spring is compressed in the axial direction between the protection member and the support member.

7. The control device is connected by signal to a driver that operates the motor, and to a position detection sensor that detects the position of the working shaft in the axial direction, and the position detection sensor outputs a gripping start signal to the control device indicating that the position of the working shaft in the axial direction has been detected at the time when the pair of gripping jaws start to grip the workpiece, and when the gripping start signal is input, the control device controls the driver to increase the gripping force of the pair of gripping jaws on the workpiece.

8. The electric gripping device according to claim 7, wherein the control device controls the driver to decelerate the motor when the gripping start signal is input, and to stop the motor after the motor has operated by a predetermined rotation amount.

9. The electric gripping device according to claim 8 , wherein the control device is signal-connected to a deceleration acceleration setting unit that adjusts the rotation speed when decelerating the motor to a plurality of deceleration accelerations.

10. The electric gripping device according to claim 8, wherein the control device outputs an error signal indicating that the workpiece is not present if a signal indicating that the position of the working shaft in the axial direction has been detected is not input at the time the motor is stopped.

11. 3. The electric gripping device according to claim 1, further comprising a gripping jaw operation unit that manually rotates the motor shaft to adjust an opening degree of the pair of gripping jaws.

Images