Screw fastening device, control system for screw fastening device, and control method for multiple screw fastening devices

Abstract

To provide a screw fastening device capable of detecting torque acting between a bit and a screw, as well as, downsizing the whole of the device.SOLUTION: A screw fastening device includes: a work mechanism including a bit disposed on a distal end side of an arm; and a drive device for driving the work mechanism. The drive device includes a motor, and wave gear speed reducer. The wave gear speed reducer includes: a wave generator which is rotatable about a central axis together with a rotating portion of the motor; an external gear which is disposed at least partially radially outside the wave generator, and has multiple external teeth protruding radially outward; and an internal gear including multiple internal teeth at least a portion of which is disposed radially outward of the external gear, and which extend in an annular shape about the central axis, protrude radially inward, and partially mesh with the multiple external teeth. The bit is rotatable together with the output portion which is one of the external gear and the internal gear. Multiple strain gauges are disposed on at least one of the external gear and the internal gear.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a screw fastening device, a control system for a screw fastening device, and a control method for a plurality of screw fastening devices. [Background technology]

[0002] In recent years, devices have been known in which a mechanism for screw tightening is attached as an end effector to the tip of a robot arm (for example, Patent Document 1). In the screw tightening device of Patent Document 1, a bit is attached to the tip of the device for engaging with the screw and rotating the screw to attach it to a workpiece. In addition, a force sensor for detecting a reaction force from the screw, i.e., a force pressing the bit, is disposed between the flange, which is driven by a motor and rotates while supporting the bit, and the bit. In addition, a motor and a torque sensor for detecting a torque generated around the rotation axis are disposed inside the wrist including the flange. In addition, a control device controls the robot based on force information detected by the force sensor and the torque sensor.

[0003] [Patent Document 1] JP 2017-127908 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the screw fastening device of Patent Document 1, a sensor needs to be arranged in addition to the driving source of the robot, making it difficult to reduce the size of the entire device.

[0005] An object of the present invention is to provide a technique for reducing the size of a screw fastening device while enabling detection of the torque acting between a bit and a screw. [Means for solving the problem]

[0006] The first invention is a screw tightening device comprising: a working mechanism having a bit arranged at the tip side of an arm; and a drive unit for driving the working mechanism, wherein the drive unit comprises a motor; a wave generator having a non-circular cross section perpendicular to a central axis and rotatable around the central axis together with a rotating part of the motor; an external gear having a plurality of external teeth protruding radially outward, at least a portion of which is arranged radially outward from the wave generator; and an internal gear having a plurality of internal teeth protruding radially inward and partially meshing with the plurality of external teeth, wherein the bit is rotatable together with an output unit which is either the external gear or the internal gear, and wherein a plurality of strain gauges are arranged in the output unit.

[0007] The second invention is a control system for screw fastening devices, comprising a plurality of screw fastening devices, each having a working mechanism with a bit arranged at the tip of an arm and a drive device that rotates and drives the bit, and a control device that controls the multiple drive devices in response to output signals from a plurality of strain gauges arranged in the drive device of each of the plurality of screw fastening devices, and the control device stops the operation of all of the working mechanisms when the output signal from at least one of the plurality of strain gauges falls outside a predetermined range.

[0008] The third invention is a control method for multiple screw fastening devices, each of which has a working mechanism with a bit arranged at the tip of an arm and a drive device that rotates the bit, and when an output signal from at least one of a plurality of strain gauges arranged in the drive device of each of the multiple screw fastening devices falls outside a predetermined range, the drive of all of the working mechanisms is stopped. Effect of the Invention

[0009] According to the first, second, and third inventions, by placing a strain gauge in the drive device itself to detect the torque applied to the bit, the entire screw fastening device can be made smaller than in the case where a torque sensor is placed separately from the drive device. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram of a screw fastening device according to a first embodiment. [Diagram 2] FIG. 2 is a diagram conceptually showing the configuration of the motor and reducer of the second driving device, the working mechanism, and the control unit according to the first embodiment. [Diagram 3] FIG. 3 is a vertical sectional view of the reducer according to the first embodiment. [Figure 4] FIG. 4 is a cross-sectional view of the reducer according to the first embodiment. [Diagram 5] FIG. 5 is a partial vertical sectional view of the sensor board and the external gear according to the first embodiment. [Figure 6] FIG. 6 is a plan view of the sensor substrate according to the first embodiment. [Figure 7] FIG. 7 is a partial plan view of the sensor substrate according to the first embodiment. [Figure 8] FIG. 8 is a partial plan view of the sensor substrate according to the first embodiment. [Figure 9] FIG. 9 is a circuit diagram of the first bridge circuit of the first torque sensor according to the first embodiment. [Figure 10] FIG. 10 is a circuit diagram of the second bridge circuit of the second torque sensor according to the first embodiment. [Figure 11] FIG. 11 is a schematic diagram for explaining a control system of the screw fastener device according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, exemplary embodiments of the present application will be described with reference to the drawings. In the following description, expressions such as vertical direction may be used, but these expressions are intended to express exemplary attitudes of each embodiment and do not limit the attitudes when the present invention is implemented. The attitudes can be changed as appropriate within the scope of the present invention.

[0012] <1. First embodiment> <1-1. Configuration of the screw tightening device> FIG. 1 is a schematic diagram of a screw fastening device 100 according to the first embodiment. The screw fastening device 100 is a collaborative robot that fastens a screw 71 to a workpiece 72 by rotating the screw 71 with the rotation output by a second driving device 3 described later. As shown in FIG. 1, the screw fastening device 100 has a base 1, a first driving device 2, a second driving device 3, an arm 4, a control unit 5, and a working mechanism 6. The second driving device 3 is a device that drives the working mechanism 6. The second driving device 3 is an example of a "driving device" of the present invention. That is, the screw fastening device 100 has a working mechanism 6 and a driving device. The driving device drives the working mechanism 6.

[0013] The base 1 is a stand placed on a support surface such as a desk or a floor on which the screw fastening device 100 is placed. The base 1 rotatably supports one end of the arm 4. A stand 101 for supporting a workpiece 72 into which a screw 71 is screwed is placed adjacent to the base 1 on the support surface.

[0014] The arm 4 is supported at one end to be rotatable relative to the base 1. The arm 4 has a plurality of joints 41. In this embodiment, the arm 4 has three joints 41. Of the three joints 41, the two joints 41 closest to one end each have a first drive device 2 built in. On the other hand, of the three joints 41, the joint 41 closest to the other end of the arm 4 does not have the first drive device 2 built in. Hereinafter, the joint 41 closest to the other end of the arm 4 will be referred to as the "joint 411." The wrist 45, which is a part of the arm 4 located further toward the other end than the joint 411, extends vertically downward from the joint 411.

[0015] A flange portion 46 is fixed to the other end of the arm 4 via a bearing (not shown). The flange portion 46 extends in a cylindrical shape in the vertical direction. However, as long as the working mechanism 6 is rotatably supported with respect to the wrist portion 45 of the arm 4, the flange portion 46 does not necessarily have to be provided.

[0016] As described above, in this embodiment, the two first driving devices 2 are respectively incorporated in the joints 41 of the arm 4. Each of the first driving devices 2 has a motor 21 and a reducer 22. The motor 21 in this embodiment has a structure equivalent to that of the motor 31 of the second driving device 3 described later. Also, the reducer 22 in this embodiment has a structure equivalent to that of the reducer 32 of the second driving device 3 described later. However, the motor 21 and the reducer 22 may have a structure different from that of the motor 31 and the reducer 32 of the second driving device 3. When a driving current is supplied to the motor 21, a rotational motion is output from the rotating part of the motor 21. The reducer 22 reduces the speed of the rotational motion output from the rotating part of the motor 21 and transmits it to the arm 4. As a result, the arm 4 rotates at a reduced speed relative to the base 1 and each joint 41. As a result, the other end of the arm 4 can be moved to a desired position.

[0017] The second drive device 3 has a motor 31 and a reducer 32. When a drive current is supplied to the motor 31, a rotational motion about a central axis 9 is output from a rotating part of the motor 31. Here, the central axis 9 is a central axis of rotation extending in the vertical direction. The reducer 32 reduces the speed of the rotational motion output from the rotating part of the motor 31 and transmits it to a bit 61 (described later) of the working mechanism 6. As a result, the bit 61 rotates at the reduced rotational speed. The detailed structure of the reducer 32 will be described later.

[0018] A holding member 62 for holding a bit 61 is fixed to the lower surface of the flange portion 46. The bit 61 is held vertically downward by the holding member 62. The bit 61 in this embodiment is supported rotatably about a vertical axis 91 together with the holding member 62 and the flange portion 46 via the bearing. Here, the vertical axis 91 is a central axis of rotation extending in the vertical direction. In this embodiment, the vertical axis 91 completely coincides with the central axis 9. However, the vertical axis 91 does not have to coincide with the central axis 9. The bit 61 and the holding member 62 constitute a working mechanism 6 as an end effector in this embodiment. That is, the working mechanism 6 has the bit 61 arranged on the tip side of the arm 4.

[0019] The bit 61 can also engage at its lower end with the screw 71 that is screwed into the workpiece 72. As described above, the bit 61 can rotate about the vertical axis 91 at a rotational speed reduced by the reducer 32. Therefore, when the bit 61 is engaged with the screw 71, the bit 61 rotates, thereby fastening the screw 71 to the workpiece 72.

[0020] The control unit 5 is a device that controls the operation of each part of the screw fastening device 100. The control unit 5 is configured by a computer or an electric circuit. As shown in FIG. 1, the control unit 5 has a processor 51 such as a CPU, a memory 52 such as a RAM, and a storage unit 53 such as a hard disk drive. The storage unit 53 also stores a program P for controlling the operation of each part of the screw fastening device 100. The function of the control unit 5 is realized by the processor 51, the memory 52 such as a RAM, and the storage unit 53 such as a hard disk drive operating in accordance with the program P. The control unit 5 is an example of the "control unit" of the present invention. That is, the screw fastening device 100 further has a control unit. However, the control unit 5 may be provided outside the screw fastening device 100.

[0021] 2 is a conceptual diagram showing the configuration of the motor 31 and reducer 32 of the second driving device 3, the working mechanism 6, and the control unit 5. As shown in FIG. 2, a torque sensor 8 for detecting the torque applied to the bit 61 is disposed in the reducer 32. The control unit 5 is electrically connected to the torque sensor 8 and the motor 31. The control unit 5 controls the motor 31 based on the detection value of the torque sensor 8 disposed in the reducer 32.

[0022] 1 and 2, in this embodiment, the motor 31 is controlled based on the detection value of the torque sensor 8 disposed closer to the bit 61 than the motor 31. This makes it possible to control the motor 31 while accurately detecting the state of the bit 61. As a result, the bit 61 can be operated with high accuracy.

[0023] The configuration of the torque sensor 8 will be described in more detail later.

[0024] <1-2. Detailed configuration of the reduction gear of the second driving device> Next, a more detailed configuration of the reducer 32 of the second driving device 3 will be described.

[0025] In the following description, the direction parallel to the central axis 9 is referred to as the "axial direction", the direction perpendicular to the central axis 9 is referred to as the "radial direction", and the direction along the arc centered on the central axis 9 is referred to as the "circumferential direction". In the following description, the shape and positional relationship of each part will be described with the direction of the central axis 9 of the reducer 32 as the left-right direction, the left side as the "one axial side", and the right side as the "other axial side" in Figs. 3 and 5, which will be described later. In Figs. 3 to 6, which will be described later, the "radial direction" is referred to as "r0", and in Figs. 4 and 6, the "circumferential direction" is referred to as "c0".

[0026] However, this definition of the left-right direction is not intended to limit the orientation of the screw fastening device according to the present invention during manufacture and use. In addition, in this application, a "parallel direction" is not limited to being geometrically strictly parallel. In other words, it is sufficient that a direction that is approximately parallel to a certain direction has a relationship that is approximately parallel to the extent that the effects of the invention are achieved. In addition, in this application, a "perpendicular direction" is not limited to being geometrically strictly perpendicular. In other words, it is sufficient that a direction that is approximately perpendicular to a certain direction has a relationship that is approximately perpendicular to the extent that the effects of the invention are achieved.

[0027] Fig. 3 is a vertical cross-sectional view of the reducer 32 of the second driving device 3 according to the first embodiment. Fig. 4 is a horizontal cross-sectional view of the reducer 32 as seen from the position AA in Fig. 3. To avoid complicating the drawing, hatching indicating a cross section and the like are omitted in Fig. 4.

[0028] The reducer 32 is a wave gear reducer. The reducer 32 reduces the rotational motion of a first rotational speed output from the motor 31 to a second rotational speed slower than the first rotational speed. As shown in Fig. 3 and Fig. 4, the reducer 32 includes an input shaft 33, an internal gear 34, an external gear 35, and a wave generator 36. That is, the second drive device 3 has the motor 31, the wave generator 36, the external gear 35, and the internal gear 34.

[0029] The input shaft 33 is a member that extends axially and cylindrically along the central axis 9, centered on the central axis 9. The input shaft 33 is connected to a rotating part of the motor 31, and rotates together with the rotating part of the motor 31 at a first rotation speed before deceleration. Note that the input shaft 33 may be the same member as the rotating part of the motor 31.

[0030] The internal gear 34 is a gear fixed to the wrist portion 45 of the arm 4. The internal gear 34 is disposed radially outward from a portion of the external gear 35 near an external tooth 352, which will be described later. In other words, at least a portion of the internal gear 34 is disposed radially outward from the external gear 35. The rigidity of the internal gear 34 is sufficiently higher than the rigidity of a body portion 351, which will be described later, of the external gear 35.

[0031] The internal gear 34 is annular about the central axis 9. That is, the internal gear 34 expands in an annular shape about the central axis 9. The internal gear 34 has a plurality of internal teeth 341. The plurality of internal teeth 341 protrude radially inward from the inner peripheral surface of the internal gear 34. The plurality of internal teeth 341 are arranged at a constant pitch in the circumferential direction on the inner peripheral surface of the internal gear 34. Some of the plurality of internal teeth 341 mesh with some of a plurality of external teeth 352 (described later) of the external gear 35. That is, the internal gear 34 has a plurality of internal teeth 341 that protrude radially inward and partially mesh with the plurality of external teeth 352.

[0032] The external gear 35 is a flexibly deformable annular gear. The external gear 35 is connected to the bit 61 of the working mechanism 6 directly or via another member. In this embodiment, the external gear 35 is connected to the bit 61 via a connecting member (not shown) so as to be non-rotatable relative to the bit 61. As shown in Figs. 3 and 4, the external gear 35 has a body portion 351, a plurality of external teeth 352, a diaphragm portion 353, and a thick portion 354. However, the structure of the external gear 35 may be different from the structure described below.

[0033] The body portion 351 is a portion that extends cylindrically along the central axis 9, centered on the central axis 9. One axial end of the body portion 351 is connected to the diaphragm portion 353. The body portion 351 extends from a radially inner end of the diaphragm portion 353 toward the other axial side. The other axial end of the body portion 351 is located radially outward of the wave generator 36 and radially inward of the internal gear 34. In other words, at least a portion of the external gear 35 is disposed radially outward of the wave generator 36. The body portion 351 is flexible and therefore capable of bending and deforming in the radial direction.

[0034] The multiple external teeth 352 protrude radially outward from the radially outer surface of the body 351. That is, the external gear 35 has multiple external teeth 352 protruding radially outward. The multiple external teeth 352 are also arranged on the radially outer surface of the body 351 near the other axial end. The multiple external teeth 352 are arranged at a constant pitch in the circumferential direction. As described above, some of the multiple external teeth 352 and some of the multiple internal teeth 341 of the internal gear 34 mesh with each other. The number of internal teeth 341 that the internal gear 34 has and the number of external teeth 352 that the external gear 35 has are slightly different.

[0035] Diaphragm portion 353 surrounds central axis 9 and expands in a direction intersecting central axis 9. Diaphragm portion 353 preferably expands along a plane perpendicular to central axis 9. Diaphragm portion 353 expands radially outward from one axial end of body portion 351. Diaphragm portion 353 is annular and surrounds central axis 9. Diaphragm portion 353 is thin-walled and therefore capable of slight flexural deformation.

[0036] The thick portion 354 is an annular portion located radially outward of the diaphragm portion 353 and centered on the central axis 9. The axial thickness of the thick portion 354 is thicker than the axial thickness of the diaphragm portion 353. In this embodiment, the thick portion 354 is connected to the bit 61 via a connecting member (not shown) so as not to rotate relative to the bit 61. The thick portion 354 is rotatably supported by the cross roller bearing 150 relative to the internal gear 34. The cross roller bearing 150 has an outer ring 152, an inner ring 151, and rollers 161. In this embodiment, the outer ring 152 is fixed to the other axial side of the thick portion 354, and the outer ring 152 is rotatably supported by the inner ring 151 fixed to the wrist portion 45 of the arm 4 via the rollers 161. That is, in this embodiment, the external gear 35 including the thick portion 354 is supported rotatably about the central axis 9 with respect to the wrist portion 45 of the arm 4 .

[0037] The wave generator 36 is a mechanism that generates periodic bending deformation in the external gear 35. The wave generator 36 is disposed radially inward of the external teeth 352. The wave generator 36 has a cam 361 and a flexible bearing 362. In this embodiment, the input shaft 33 and the cam 361 are formed as a single part. However, the cam 361 may be a part separate from the input shaft 33. In that case, it is sufficient that the cam 361 is fixed to the input shaft 33. As a result, the input shaft 33 and the cam 361 rotate together with the rotating part of the motor 31 at the first rotation speed before deceleration. That is, the wave generator 36 can rotate around the central axis 9 together with the rotating part of the motor 31. Furthermore, in addition to the input shaft 33 and the cam 361, the rotating part of the motor 31 may be formed as a single part.

[0038] The cam 361 is a component that gives a displacement at a period of 180° to the external gear 35. The radially outer surface of the cam 361 is an ellipse centered on the central axis 9. In other words, the cross section of the wave generator 36 perpendicular to the central axis 9 is non-circular.

[0039] The flexible bearing 362 is a bearing that can be flexibly deformed. The flexible bearing 362 is disposed between the radially outer surface of the cam 361 and the radially inner surface of the body 351 of the external gear 35. The inner ring of the flexible bearing 362 contacts the radially outer surface of the cam 361. The outer ring of the flexible bearing 362 contacts the radially inner surface of the body 351. Therefore, the body 351 is pushed from the radially inner side by the cam 361, and is deformed into an elliptical shape along the radially outer surface of the cam 361. As a result, the external teeth 352 of the external gear 35 and the internal teeth 341 of the internal gear 34 mesh with each other at two points corresponding to both ends of the major axis of the ellipse. At other positions in the circumferential direction, the external teeth 352 and the internal teeth 341 do not mesh with each other.

[0040] When the motor 31 is driven, the cam 361 rotates at a first rotation speed around the central axis 9 together with the rotating part of the motor 31 and the input shaft 33. As a result, the major axis of the ellipse of the external gear 35 also rotates at the first rotation speed. Then, the meshing position between the external teeth 352 and the internal teeth 341 also changes in the circumferential direction at the first rotation speed. Also, as described above, the number of the internal teeth 341 of the internal gear 34 is slightly different from the number of the external teeth 352 of the external gear 35. Due to this difference in the number of teeth, the meshing position between the external teeth 352 and the internal teeth 341 changes slightly in the circumferential direction for each rotation of the cam 361.

[0041] Here, the internal gear 34 having the internal teeth 341 is fixed to the wrist 45 of the arm 4 and does not rotate. On the other hand, as described above, the external gear 35 having the external teeth 352 is supported rotatably around the central axis 9 with respect to the wrist 45 of the arm 4. As a result, in this embodiment, the external gear 35 rotates around the central axis 9 relative to the internal gear 34 at a second rotation speed slower than the first rotation speed. As a result, the bit 61 connected to the external gear 35 rotates around the vertical axis 91 at the second rotation speed. That is, the external gear 35 of this embodiment is an example of the "output section" of the present invention.

[0042] <1-3. Detailed configuration of the torque sensor> Next, the configuration of the torque sensor 8 will be described in more detail.

[0043] As described above, the torque sensor 8 is disposed in the reducer 32. As shown in Fig. 3, the torque sensor 8 has a sensor substrate 80. The sensor substrate 80 is fixed to the surface of the diaphragm portion 353.

[0044] Fig. 5 is a partial vertical sectional view of the sensor substrate 80 and the external gear 35. Fig. 6 is a plan view of the sensor substrate 80. As shown in Fig. 5, the sensor substrate 80 has an insulating layer 801 and a conductor layer 802.

[0045] The insulating layer 801 is a portion that is flexibly deformable. The insulating layer 801 is made of an insulating resin or an inorganic insulating material. The insulating layer 801 extends in a direction intersecting the central axis 9. The insulating layer 801 has an annular shape centered on the central axis 9. The insulating layer 801 is disposed on a surface of the diaphragm portion 353 that faces one axial side.

[0046] The conductor layer 802 is a portion formed on a surface of the insulating layer 801 facing one axial side. The material of the conductor layer 802 is a metal that is a conductor. Specifically, the material of the conductor layer 802 is, for example, a copper alloy, a chromium alloy, or copper. The conductor layer 802 has a plurality of strain gauges. That is, a plurality of strain gauges are arranged in the output section that is the external gear 35 of this embodiment. The function of the torque sensor 8 is mainly realized by using the plurality of strain gauges.

[0047] The torque sensor 8 can detect the torque applied to the bit 61 by detecting the torque applied to the diaphragm portion 353 using the multiple strain gauges. Specifically, the output signal of the torque sensor 8 changes according to the torque applied to the diaphragm portion 353. This makes it possible to detect the torque applied to the bit 61 to which the external gear 35 having the diaphragm portion 353 is connected based on the output signal from the torque sensor 8. As a result, it is possible to detect the rotational torque applied to the screw 71 with which the bit 61 engages. This will be explained in more detail below.

[0048] As shown in FIG. 6, the torque sensor 8 includes a first torque sensor W1 and a second torque sensor W2. The second torque sensor W2 is disposed radially outward from the first torque sensor W1. The first torque sensor W1 and the second torque sensor W2 each have a plurality of strain gauges. Hereinafter, the plurality of strain gauges of the first torque sensor W1 will be referred to as "first strain gauges," and the plurality of strain gauges of the second torque sensor W2 will be referred to as "second strain gauges." That is, the plurality of strain gauges that realize the function of the torque sensor 8 include a plurality of first strain gauges and a plurality of second strain gauges. The plurality of second strain gauges are disposed radially outward from the plurality of first strain gauges.

[0049] The first torque sensor W1 also has four strain gauges Ra, Rb, Rc, and Rd. That is, the first strain gauges include four strain gauges Ra, Rb, Rc, and Rd. Of the four strain gauges Ra, Rb, Rc, and Rd, two strain gauges Ra and Rb are arranged at intervals from each other in the circumferential direction. In this embodiment, the two strain gauges Ra and Rb are each provided in a semicircular arc shape within a range of approximately 180° centered on the central axis 9. The radial distance from the central axis 9 to the strain gauge Ra and the radial distance from the central axis 9 to the strain gauge Rb are approximately the same.

[0050] Of the four strain gauges Ra, Rb, Rc, and Rd, the other two strain gauges Rc and Rd are disposed radially outward from the above two strain gauges Ra and Rb. The two strain gauges Rc and Rd are disposed at a circumferential distance from each other. In this embodiment, the two strain gauges Rc and Rd are each provided in a semicircular arc shape within a range of approximately 180° centered on the central axis 9. The radial distance from the central axis 9 to the strain gauge Rc is approximately the same as the radial distance from the central axis 9 to the strain gauge Rd.

[0051] As described above, the two strain gauges Rc, Rd are disposed radially outward from the two strain gauges Ra, Rb. Therefore, the two strain gauges Ra, Rb can be referred to as "inner strain gauges", and the two strain gauges Rc, Rd can be referred to as "outer strain gauges". That is, the multiple strain gauges that realize the function of the torque sensor 8 include multiple inner strain gauges Ra, Rb and multiple outer strain gauges Rc, Rd. The multiple inner strain gauges Ra, Rb are arranged in the circumferential direction. The multiple outer strain gauges Rc, Rd are arranged in the circumferential direction radially outward from the multiple inner strain gauges Ra, Rb.

[0052] Furthermore, two inner gap regions Gi are arranged between the circumferentially adjacent inner strain gauges Ra, Rb. That is, an inner gap region Gi is arranged between the circumferentially adjacent inner strain gauges Ra, Rb. When viewed from the axial direction, the two inner gap regions Gi are arranged at an angular interval of 180° around the central axis 9. That is, the multiple inner gap regions Gi are arranged at angular intervals of 180° around the central axis 9.

[0053] Furthermore, two outer gap regions Go are arranged between the circumferentially adjacent outer strain gauges Rc, Rd. That is, an outer gap region Go is arranged between the circumferentially adjacent outer strain gauges Rc, Rd. When viewed from the axial direction, the two outer gap regions Go are arranged at an angular interval of 180° around the central axis 9. That is, the multiple outer gap regions Go are arranged at angular intervals of 180° around the central axis 9. Furthermore, the inner gap region Gi and the outer gap region Go are adjacent to each other in the radial direction.

[0054] Moreover, the two strain gauges Ra, Rc and the two strain gauges Rb, Rd are arranged concentrically and line-symmetrically.

[0055] The strain gauges Ra, Rb, Rc, and Rd each have a pattern that extends in the circumferential direction while winding in a zigzag pattern. Figures 7 and 8 are partial plan views of the sensor substrate 80. As shown in Figures 7 and 8, each of the strain gauges Ra, Rb, Rc, and Rd has a plurality of resistance wires r1 arranged in the circumferential direction and substantially parallel to each other. Each resistance wire r1 extends in a direction having both radial and circumferential components.

[0056] The resistance wires r1 of the strain gauges Ra and Rd are inclined toward one circumferential side with respect to the radial direction. The resistance wires r1 of the strain gauges Rb and Rc are inclined toward the other circumferential side with respect to the radial direction. The inclination angle of the resistance wires r1 with respect to the radial direction is, for example, 45°. The ends of the resistance wires r1 adjacent to each other in the circumferential direction are alternately connected radially inward or radially outward. As a result, the multiple resistance wires r1 are connected in series as a whole.

[0057] Fig. 9 is a circuit diagram of a first bridge circuit C1 including four strain gauges Ra, Rb, Rc, and Rd of the first torque sensor W1. As shown in Fig. 9, the four strain gauges Ra, Rb, Rc, and Rd are connected to each other to form the first bridge circuit C1. That is, the first strain gauges constituting the first torque sensor W1 constitute the first bridge circuit C1. That is, the first bridge circuit C1 is constituted by the inner strain gauges Ra, Rb and the outer strain gauges Rc, Rd constituting the first torque sensor W1.

[0058] The strain gauges Ra and Rb are connected in series in this order. The strain gauges Rc and Rd are connected in series in this order. Then, between the positive and negative poles of the power supply voltage, a row of two strain gauges Ra, Rb and a row of two strain gauges Rc, Rd are connected in parallel. In addition, a first voltmeter V1 is connected between a midpoint M11 of the two strain gauges Ra, Rb and a midpoint M12 of the two strain gauges Rc, Rd.

[0059] The resistance value of each resistance wire r1 changes according to the torque applied to the area in which the resistance wire r1 is disposed. For example, when a torque is applied to the diaphragm portion 353 in one circumferential direction around the central axis 9, the resistance value of each resistance wire r1 of the two strain gauges Ra, Rd increases, and the resistance value of each resistance wire r1 of the other two strain gauges Rb, Rc decreases. On the other hand, when a torque is applied to the diaphragm portion 353 in the other circumferential direction around the central axis 9, the resistance value of each resistance wire r1 of the two strain gauges Ra, Rd decreases, and the resistance value of each resistance wire r1 of the other two strain gauges Rb, Rc increases. In this way, the two strain gauges Ra, Rd and the other two strain gauges Rb, Rc show resistance value changes in opposite directions with respect to torque.

[0060] When the resistance values ​​of the four strain gauges Ra, Rb, Rc, and Rd change, the potential difference between the midpoint M11 of the two strain gauges Ra, Rb and the midpoint M12 of the two strain gauges Rc, Rd changes, and the measurement value of the first voltmeter V1 also changes.

[0061] Here, as shown in FIG. 3, the second drive device 3 further includes a signal processing circuit 85. The signal processing circuit 85 is configured by an electric circuit equipped with a microprocessor. The signal processing circuit 85 is electrically connected to the first bridge circuit C1 of the torque sensor 8. The signal processing circuit 85 detects the direction and magnitude of the torque applied to the diaphragm portion 353 based on the measurement value of the first voltmeter V1. Furthermore, the signal processing circuit 85 transmits data related to the detected direction and magnitude of the torque applied to the diaphragm portion 353 to the control unit 5.

[0062] Then, the control unit 5 controls the driving of the motor 21 of the first drive device 2 and the motor 31 of the second drive device 3 based on the data on the direction and magnitude of the torque applied to the diaphragm portion 353 received from the signal processing circuit 85. For example, when the magnitude of the torque applied to the diaphragm portion 353 exceeds a predetermined value, the control unit 5 determines that an excessive rotational driving force is applied to the bit 61 and the screw 71. In this case, the control unit 5 temporarily stops the driving of the motor 31 of the second drive device 3. This makes it possible to prevent the screw 71 and the workpiece 72 from being damaged. Also, for example, when the magnitude of the torque applied to the diaphragm portion 353 is zero, the control unit 5 determines that the bit 61 is not properly engaged with the screw 71. In this case, the control unit 5 controls the driving of the motor 21 of the first drive device 2 to move the other end of the arm 4 to an appropriate position.

[0063] As described above, the first torque sensor W1 of this embodiment is provided with a plurality of inner strain gauges Ra, Rb arranged in the circumferential direction on the radially inner side, and a plurality of outer strain gauges Rc, Rd arranged in the circumferential direction on the radially outer side. The plurality of inner strain gauges Ra, Rb and the plurality of outer strain gauges Rc, Rd form a first bridge circuit C1. This reduces the effect on the measurement result of the torque applied to the diaphragm portion 353 even when the angular position of the major axis of the cam 361 of the wave generator 36 about the central axis 9 changes, so that the torque can be measured more accurately.

[0064] Next, the second torque sensor W2 has four strain gauges Re, Rf, Rg, and Rh. That is, the plurality of second strain gauges includes four strain gauges Re, Rf, Rg, and Rh. Of the four strain gauges Re, Rf, Rg, and Rh, two strain gauges Re and Rf are arranged at intervals from each other in the circumferential direction. In this embodiment, the two strain gauges Re and Rf are each provided in a semicircular arc shape within a range of about 180° centered on the central axis 9. The radial distance from the central axis 9 to the strain gauge Re and the radial distance from the central axis 9 to the strain gauge Rf are approximately the same.

[0065] Of the four strain gauges Re, Rf, Rg, Rh, the other two strain gauges Rg, Rh are disposed radially outward from the above two strain gauges Re, Rf. The two strain gauges Rg, Rh are disposed at a circumferential distance from each other. In this embodiment, the two strain gauges Rg, Rh are each provided in a semicircular arc shape within a range of approximately 180° centered on the central axis 9. The radial distance from the central axis 9 to the strain gauge Rg is approximately the same as the radial distance from the central axis 9 to the strain gauge Rh.

[0066] As described above, the two strain gauges Rg, Rh are disposed radially outward from the two strain gauges Re, Rf. Therefore, the two strain gauges Re, Rf can be referred to as "inner strain gauges", and the two strain gauges Rg, Rh can be referred to as "outer strain gauges". That is, the multiple strain gauges that realize the function of the torque sensor 8 include multiple inner strain gauges Re, Rf and multiple outer strain gauges Rg, Rh. The multiple inner strain gauges Re, Rf are arranged in the circumferential direction. The multiple outer strain gauges Rg, Rh are also arranged in the circumferential direction radially outward from the multiple inner strain gauges Re, Rf.

[0067] Furthermore, two inner gap regions Gi are arranged between the circumferentially adjacent inner strain gauges Re, Rf. That is, an inner gap region Gi is arranged between the circumferentially adjacent inner strain gauges Re, Rf. When viewed from the axial direction, the two inner gap regions Gi are arranged at an angular interval of 180° around the central axis 9. That is, the multiple inner gap regions Gi are arranged at angular intervals of 180° around the central axis 9.

[0068] In addition, two outer gap regions Go are arranged between the circumferentially adjacent outer strain gauges Rg, Rh. That is, an outer gap region Go is arranged between the circumferentially adjacent outer strain gauges Rg, Rh. When viewed from the axial direction, the two outer gap regions Go are arranged at an angular interval of 180° around the central axis 9. That is, the multiple outer gap regions Go are arranged at an angular interval of 180° around the central axis 9. In addition, the inner gap region Gi and the outer gap region Go are adjacent in the radial direction. This allows the inner strain gauges Re, Rf and the outer strain gauges Rg, Rh to be arranged in as wide an area as possible in the circumferential direction, thereby improving the torque detection accuracy, while simplifying the configuration of the sensor board 80 or the wiring of the second bridge circuit C2 described later.

[0069] Moreover, the two strain gauges Re, Rg and the two strain gauges Rf, Rh are arranged concentrically and line-symmetrically.

[0070] The strain gauges Re, Rf, Rg, and Rh each have a zigzag pattern extending in the circumferential direction. As shown in Figures 7 and 8, each of the strain gauges Re, Rf, Rg, and Rh has a plurality of resistance wires r2 arranged in the circumferential direction and substantially parallel to each other. Each resistance wire r2 extends in a direction having both radial and circumferential components.

[0071] The resistance wires r2 of the strain gauges Re and Rh are inclined toward one circumferential side with respect to the radial direction. The resistance wires r2 of the strain gauges Rf and Rg are inclined toward the other circumferential side with respect to the radial direction. The inclination angle of the resistance wires r2 with respect to the radial direction is, for example, 45°. The ends of the resistance wires r2 adjacent to each other in the circumferential direction are alternately connected radially inward or radially outward. As a result, the multiple resistance wires r2 are connected in series as a whole.

[0072] Fig. 10 is a circuit diagram of a second bridge circuit C2 including four strain gauges Re, Rf, Rg, and Rh of the second torque sensor W2. As shown in Fig. 10, the four strain gauges Re, Rf, Rg, and Rh are connected to each other to form the second bridge circuit C2. That is, the second strain gauges constituting the second torque sensor W2 constitute the second bridge circuit C2. That is, the second bridge circuit C2 is constituted by the inner strain gauges Re and Rf and the outer strain gauges Rg and Rh constituting the second torque sensor W2.

[0073] The strain gauges Re and Rf are connected in series in this order. The strain gauges Rg and Rh are connected in series in this order. Then, between the positive and negative poles of the power supply voltage, a row of two strain gauges Re, Rf and a row of two strain gauges Rg, Rh are connected in parallel. In addition, a second voltmeter V2 is connected between a midpoint M21 of the two strain gauges Re, Rf and a midpoint M22 of the two strain gauges Rg, Rh.

[0074] The resistance value of each resistance wire r2 changes according to the torque applied to the area where the resistance wire r2 is arranged. For example, when a torque is applied to the diaphragm portion 353 in one circumferential direction around the central axis 9, the resistance value of each resistance wire r2 of the two strain gauges Re, Rh increases, and the resistance value of each resistance wire r2 of the other two strain gauges Rf, Rg decreases. On the other hand, when a torque is applied to the diaphragm portion 353 in the other circumferential direction around the central axis 9, the resistance value of each resistance wire r2 of the two strain gauges Re, Rh decreases, and the resistance value of each resistance wire r2 of the other two strain gauges Rf, Rg increases. In this way, the two strain gauges Re, Rh and the other two strain gauges Rf, Rg show resistance value changes in opposite directions with respect to torque.

[0075] When the resistance values ​​of the four strain gauges Re, Rf, Rg, and Rh change, the potential difference between the midpoint M21 of the two strain gauges Re, Rf and the midpoint M22 of the two strain gauges Rg, Rh changes, and the measurement value of the second voltmeter V2 also changes.

[0076] The signal processing circuit 85 is also electrically connected to the second bridge circuit C2 of the torque sensor 8. Based on the measurement value of the second voltmeter V2, the signal processing circuit 85 detects the direction and magnitude of the torque applied to the diaphragm portion 353. Furthermore, the signal processing circuit 85 transmits data relating to the detected direction and magnitude of the torque applied to the diaphragm portion 353 to the control unit 5.

[0077] The control unit 5 can control the driving of the motor 21 of the first driving device 2 and the motor 31 of the second driving device 3, based on data relating to the direction and magnitude of the torque applied to the diaphragm portion 353, which is detected based on the measurement value of the second voltmeter V2 and received from the signal processing circuit 85. That is, the control unit 5 receives output signals from the multiple first strain gauges and output signals from the multiple second strain gauges, and controls the driving devices.

[0078] As described above, the second torque sensor W2 of this embodiment is provided with a plurality of inner strain gauges Re, Rf arranged in the circumferential direction on the radially inner side, and a plurality of outer strain gauges Rg, Rh arranged in the circumferential direction on the radially outer side. The plurality of inner strain gauges Re, Rf and the plurality of outer strain gauges Rg, Rh form a second bridge circuit C2. This reduces the effect on the measurement result of the torque applied to the diaphragm portion 353 even when the angular position of the major axis of the cam 361 of the wave generator 36 about the central axis 9 changes, so that the torque can be measured more accurately.

[0079] As described above, in this embodiment, a plurality of strain gauges are arranged in the second driving device 3 itself, and the torque applied to the diaphragm portion 353 and the rotational torque applied to the bit 61 and the screw 71 can be detected based on the output of the plurality of strain gauges. This allows the entire screw fastening device 100 to be made smaller in size than when a torque sensor is arranged separately from the second driving device 3.

[0080] As described above, the screw fastening device 100 of this embodiment has two torque sensors W1 and W2. Therefore, the control unit 5 can compare data detected based on the measurement value of the first voltmeter V1 of the first torque sensor W1 with data detected based on the measurement value of the second voltmeter V2 of the second torque sensor W2. As a result, if either one of the data is excessively large, the control unit 5 can easily determine which sensor is experiencing an abnormality.

[0081] That is, in this embodiment, when an abnormality occurs in either the first strain gauge constituting the first torque sensor W1 or the second strain gauge constituting the second torque sensor W2, the abnormality can be easily detected.

[0082] Furthermore, when the difference between the data detected based on the measurement value of the first voltmeter V1 of the first torque sensor W1 and the data detected based on the measurement value of the second voltmeter V2 of the second torque sensor W2 is excessively large, the control unit 5 can also stop the operation of the screw fastening device 100 until the cause is identified and a countermeasure is taken. That is, when the relationship between the output signals from the multiple first strain gauges and the output signals from the multiple second strain gauges falls outside a predetermined range, the control unit 5 stops the operation of the working mechanism 6. This makes it possible to stop the operation of the screw fastening device 100 when an abnormality occurs.

[0083] <2. Second embodiment> Next, a control system 200B for controlling a screw fastener 100B according to a second embodiment of the present invention will be described. In the following, differences from the screw fastener 100 of the first embodiment will be mainly described, and duplicated descriptions of parts equivalent to those of the first embodiment will be omitted.

[0084] FIG. 11 is a schematic diagram for explaining a control system 200B according to this embodiment. The control system 200B according to this embodiment is applied to a space in which a plurality of screw fastening devices 100B are arranged as collaborative robots that cooperate with workers, for example, in a manufacturing line of a factory. As shown in FIG. 11, the control system 200B has a plurality of screw fastening devices 100B and one control device 210B. The control device 210B is an example of the "control device" of the present invention. In addition, in the control system 200B according to this embodiment, a "control device 5B" corresponding to the "control device 5" of the first embodiment is provided in each of the plurality of screw fastening devices 100B. However, the "control device 5B" corresponding to the "control device 5" of the first embodiment may not be provided, and the control device 210B may also function as the "control device 5B". In addition, the control device 210B may be provided outside the control system 200B.

[0085] Each of the screw fasteners 100B of this embodiment has the same configuration as the screw fastener 100 of the first embodiment. That is, each of the screw fasteners 100B has a working mechanism 6B having a bit 61B arranged on the tip side of the arm 4B, and a second drive unit 3B which is a drive unit for rotating the bit 61B. A torque sensor consisting of a plurality of strain gauges is arranged on the external gear which is the output part of the reducer of each of the second drive units 3B. The control unit 5B and the control device 210B of each screw fastener 100B are electrically connected to the torque sensor and the motor of the second drive unit 3B. As in the first embodiment, the torque sensor detects the direction and magnitude of the torque applied to the diaphragm part of the external gear, and transmits data related to the detection result to the control unit 5B. In this embodiment, the torque sensor further transmits data related to the detection result of the direction and magnitude of the torque applied to the diaphragm part of the external gear to the control device 210B.

[0086] The control device 210B is a device that receives output signals from a plurality of strain gauges arranged in the second drive devices 3B of the plurality of screw fastening devices 100B and controls the plurality of second drive devices 3B. The control device 210B is configured with a computer or an electric circuit. As shown in FIG. 11, the control device 210B has a processor 211B such as a CPU, a memory 212B such as a RAM, and a storage unit 213B such as a hard disk drive. A program 214P for controlling the operation of the control system 200B is stored in the storage unit 213B. The control device 210B operates according to the program 214P.

[0087] The control device 210B of this embodiment stops the driving of the working mechanisms 6B of all the screw fastening devices 100B in the control system 200B when the output signal from at least one of the multiple strain gauges arranged in the second drive device 3B of each of the multiple screw fastening devices 100B falls outside a predetermined range. That is, when an abnormality occurs, the driving of all the screw fastening devices 100B can be stopped. As a result, when an abnormality is found in any one of the screw fastening devices 100B, the driving of all the screw fastening devices 100B can be stopped until the cause is identified and countermeasures are completed. As a result, the safety of the workers can be ensured and the occurrence of uneven progress of the work process in a production line or the like can be suppressed.

[0088] That is, the control method for multiple screw fastening devices 100B of this embodiment relates to multiple screw fastening devices 100B each having a working mechanism 6B having a bit 61B arranged on the tip side of an arm 4B and a second driving device 3B which is a driving device that rotates and drives the bit 61B. When an output signal from at least one of multiple strain gauges arranged on the second driving device 3B which is a driving device of each of the multiple screw fastening devices 100B falls outside a predetermined range, the driving of all the working mechanisms 6B is stopped. In this way, in the same manner as above, the driving of all the screw fastening devices 100B can be stopped when an abnormality occurs.

[0089] <3. Modifications> Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment.

[0090] In the above embodiment, the internal gear 34 having the internal teeth 341 is fixed to the wrist 45 of the arm 4 and does not rotate, while the external gear 35 having the external teeth 352 is rotatable around the central axis 9 together with the bit 61. However, the external gear 35 having the external teeth 352 may be fixed to the wrist 45 of the arm 4 and does not rotate, while the internal gear 34 having the internal teeth 341 may be rotatable around the central axis 9 together with the bit 61. In this case, the internal gear 34 is an example of the "output part" of the present invention. That is, it is sufficient that the bit 61 is rotatable together with the output part, which is either the external gear 35 or the internal gear 34.

[0091] In the above embodiment, the multiple strain gauges are disposed on the diaphragm portion 353 of the external gear 35, which is the output portion. However, the multiple strain gauges may be disposed on the internal gear 34, which is fixed to the wrist portion 45 of the arm 4. Even in this case, the torque applied to the diaphragm portion 353 and the rotational torque applied to the bit 61 and the screw 71 can be detected from the reaction force applied to the internal gear 34 according to the law of action and reaction. Furthermore, even in the case where the external gear 35 is fixed and the internal gear 34 serves as the output portion as in the above modified example, the multiple strain gauges may be disposed on the internal gear 34 or on the external gear 35. That is, it is sufficient that the multiple strain gauges are disposed on at least one of the external gear 35 and the internal gear 34.

[0092] However, as described above, while the external gear 35 has flexibility, the internal gear 34 has sufficient rigidity and is not easily bent. Therefore, it is desirable to place multiple strain gauges on the flexible external gear 35. This increases the change in the output signal from the strain gauge, making it possible to detect torque with greater sensitivity and accuracy.

[0093] In the above embodiment, each of the first torque sensor W1 and the second torque sensor W2 has two inner strain gauges and two outer strain gauges. However, each of the first torque sensor W1 and the second torque sensor W2 may have inner strain gauges that are a multiple of four and outer strain gauges that are a multiple of four so as to configure a bridge circuit. The inner strain gauges and outer strain gauges may be arranged at intervals in the circumferential direction.

[0094] The external gear 35 in the above embodiment is a so-called "hat-shaped" gear in which the diaphragm portion 353 expands radially outward from the body portion 351. However, the external gear 35 may be a so-called "cup-shaped" gear in which the diaphragm portion 353 expands radially inward from the body portion 351.

[0095] In addition, the detailed configurations of the screw fastening device and the control system for the screw fastening device may be appropriately modified without departing from the spirit of the present invention. Furthermore, the elements appearing in the above-described embodiment and modified examples may be appropriately combined without causing any contradiction.

[0096] <4. Summary> The present technology can have the following configurations.

[0097] (1): A screw tightening device, A working mechanism having a bit disposed on a tip side of the arm; A drive device that drives the working mechanism; having The drive device is A motor; a wave generator having a non-circular cross section perpendicular to a central axis and rotatable about the central axis together with a rotating portion of the motor; an external gear having at least a portion disposed radially outward of the wave generator and having a plurality of external teeth protruding radially outward; an internal gear having a plurality of internal teeth, at least a portion of which is disposed radially outward of the external gear, extending annularly about the central axis, and protruding radially inward to partially mesh with the plurality of external teeth; having The bit is rotatable together with an output portion that is one of the external gear and the internal gear, A screw tightening device, wherein a plurality of strain gauges are arranged on at least one of the external gear and the internal gear.

[0098] (2): A screw fastening device as described in (1), A screw tightening device, wherein the plurality of strain gauges are disposed on the external gear.

[0099] (3): A screw fastening device according to (1) or (2), The plurality of strain gauges include A plurality of inner strain gauges arranged in a circumferential direction; a plurality of outer strain gauges arranged in a circumferential direction radially outward of the plurality of inner strain gauges; having A screw tightening device, wherein the plurality of inner strain gauges and the plurality of outer strain gauges form a bridge circuit.

[0100] (4): A screw fastening device as described in (3), An inner gap region is disposed between the inner strain gauges adjacent to each other in the circumferential direction, The inner gap regions are arranged at angular intervals of 180° about the central axis, An outer gap region is disposed between the outer strain gauges adjacent to each other in the circumferential direction, The outer gap regions are arranged at angular intervals of 180° about the central axis, A screw fastening device, wherein the inner gap region and the outer gap region are adjacent in a radial direction.

[0101] (5): A screw fastening device according to any one of (1) to (4), The plurality of strain gauges include A plurality of first strain gauges forming a first bridge circuit; a plurality of second strain gauges arranged radially outward from the plurality of first strain gauges and constituting a second bridge circuit; A screw tightening device having a screw fastening mechanism.

[0102] (6): A screw fastening device according to (5), a control unit that receives output signals from the plurality of first strain gauges and output signals from the plurality of second strain gauges and controls the driving device; and The control unit stops driving the working mechanism when a relationship between output signals from the plurality of first strain gauges and output signals from the plurality of second strain gauges falls outside a predetermined range.

[0103] (7): A control system for a screw fastening device, A plurality of screw tightening devices each including a working mechanism having a bit disposed on a tip side of an arm and a driving device that rotates the bit; a control device that receives output signals from a plurality of strain gauges disposed in the drive devices of the plurality of screw fastening devices and controls the plurality of drive devices; having The control device is a control system for a screw tightening device, and stops driving all of the working mechanisms when an output signal from at least one of the plurality of strain gauges falls outside a predetermined range.

[0104] (8): A method for controlling a plurality of screw tightening devices, each of which has a working mechanism having a bit disposed at the tip side of an arm and a driving device that rotates the bit, comprising: A control method for a screw fastening device, which stops the drive of all of the working mechanisms when an output signal from at least one of a plurality of strain gauges arranged in the drive device of each of the plurality of screw fastening devices falls outside a predetermined range. [Industrial Applicability]

[0105] INDUSTRIAL APPLICABILITY The present invention can be used in a screw fastening device, a control system for a screw fastening device, and a control method for a plurality of screw fastening devices. [Explanation of symbols]

[0106] 2. First Drive Unit 3,3B Second drive unit 4,4B Arm 5,5B Control section 6,6B Working mechanism 8 Torque Sensor 9 Center axis 31 (Second drive unit) motor 32 (Second drive unit) reducer 33 Input shaft 34 Internal gear 35 External gear 36 Wave Generator 41 (Arm) Joint 45 (Arm) Wrist 61,61B bits 71 Screw 72 Work 80 (torque sensor) sensor board 85 (Torque sensor) signal processing circuit 100,100B Screw tightening device 200B Screw tightening device control system 210B Control device for screw tightening device 341 (of an internal gear) 351 (External gear) body 352 (of an external gear) 353 (External gear) diaphragm part 354 (External gear) thick part 361 (Wave Generator) Cam 362 Flexible bearing (for wave generators) C1 First bridge circuit C2 Second bridge circuit Gi inner gap area Go Outer gap area Ra (of the first torque sensor) inner strain gauge Rb (first torque sensor) inner strain gauge Rc (first torque sensor) outer strain gauge Rd Outer strain gauge (of first torque sensor) Re: Inner strain gauge (of second torque sensor) Rf (of the second torque sensor) inner strain gauge Rg Outer strain gauge (of second torque sensor) Rh Outer strain gauge (of second torque sensor) W1 First torque sensor W2 Second torque sensor

Claims

1. A screw fastening device, comprising: A working mechanism having a bit disposed on a tip side of the arm; A drive device that drives the working mechanism; having The drive device is A motor; a wave generator having a non-circular cross section perpendicular to a central axis and rotatable about the central axis together with a rotating portion of the motor; an external gear having a plurality of external teeth protruding radially outward, at least a portion of the external gear being disposed radially outward from the wave generator; an internal gear having a plurality of internal teeth, at least a portion of which is disposed radially outward of the external gear, extending annularly about the central axis, and protruding radially inward to partially mesh with the plurality of external teeth; having The bit is rotatable together with an output portion which is either the external gear or the internal gear, A screw tightening device, wherein a plurality of strain gauges are arranged on at least one of the external gear and the internal gear.

2. The screw fastening device according to claim 1, A screw tightening device, wherein the plurality of strain gauges are disposed on the external gear.

3. The screw fastening device according to claim 1 or 2, The plurality of strain gauges include A plurality of inner strain gauges arranged in a circumferential direction; a plurality of outer strain gauges arranged in a circumferential direction radially outward of the plurality of inner strain gauges; having A screw tightening device, wherein the plurality of inner strain gauges and the plurality of outer strain gauges form a bridge circuit.

4. The screw fastening device according to claim 3, An inner gap region is disposed between the inner strain gauges adjacent to each other in the circumferential direction, The inner gap regions are arranged at angular intervals of 180° about the central axis, An outer gap region is disposed between the outer strain gauges adjacent to each other in the circumferential direction, The outer gap regions are arranged at angular intervals of 180° about the central axis, A screw fastening device, wherein the inner gap region and the outer gap region are adjacent in a radial direction.

5. The screw fastening device according to claim 1 or 2, The plurality of strain gauges include a plurality of first strain gauges forming a first bridge circuit; a plurality of second strain gauges arranged radially outward from the plurality of first strain gauges and constituting a second bridge circuit; A screw tightening device having the above structure.

6. The screw fastening device according to claim 5, a control unit that receives output signals from the plurality of first strain gauges and output signals from the plurality of second strain gauges and controls the driving device; and The control unit stops driving the working mechanism when a relationship between output signals from the first plurality of strain gauges and output signals from the second plurality of strain gauges falls outside a predetermined range.

7. A control system for a screw fastening device, comprising: A plurality of screw tightening devices each including a working mechanism having a bit disposed on a tip side of an arm and a driving device that rotates the bit; a control device that receives output signals from a plurality of strain gauges disposed in the drive devices of the plurality of screw fastening devices and controls the plurality of drive devices; having The control device is a control system for a screw fastening device, wherein the control device stops driving all of the working mechanisms when an output signal from at least one of the plurality of strain gauges falls outside a predetermined range.

8. A method for controlling a plurality of screw tightening devices, each of which has a working mechanism having a bit disposed at a tip side of an arm and a driving device that rotates the bit, comprising: A method for controlling multiple screw fastening devices, which stops the drive of all of the working mechanisms when an output signal from at least one of multiple strain gauges arranged in the drive device of each of the multiple screw fastening devices falls outside a predetermined range.

Images