Control system for industrial equipment and rotation angle estimation device

Abstract

This rotation angle estimation device is provided in industrial equipment comprising a strain wave gear device and a drive unit. The strain wave gear device comprises: an annular rigid internally toothed gear having internal teeth formed on an inner peripheral surface; a flexible externally toothed gear disposed inside the rigid internally toothed gear and having external teeth capable of meshing with the internal teeth; and a wave generator that is provided inside the flexible externally toothed gear, and flexes the flexible externally toothed gear in a radial direction to partially mesh the external teeth with the internal teeth and move a meshing position of the rigid internally toothed gear and the flexible externally toothed gear in a circumferential direction. The drive unit rotates the wave generator in the circumferential direction. The rotation angle estimation device has a plurality of strain gauges that are attached to the flexible externally toothed gear and positioned at different locations in the circumferential direction, and an estimation unit that identifies magnitude relationships among output signals from the plurality of strain gauges and estimates the rotation angle of the wave generator from the identified magnitude relationships.

Description

Control system for industrial equipment and rotation angle estimation device

[0001] The present disclosure relates to a control system for industrial equipment and a rotation angle estimation device applied to industrial equipment.

[0002] Some industrial equipment such as industrial robots used in factories and the like are equipped with a wave gear device as a speed reducer. The wave gear device is composed of a rigid internal gear, a flexible external gear disposed inside the rigid internal gear, and a wave generator. The wave generator radially deflects the flexible external gear to partially mesh with the rigid internal gear, and moves the meshing position in the circumferential direction. In the flexible external gear, periodic strain unrelated to the transmission torque is generated by the rotation of the wave generator due to the structure of the wave gear device. In recent years, the following technologies have been proposed focusing on such periodic changes in strain. That is, a technology has been proposed in which a strain gauge is attached to the flexible external gear, and the rotation angle of a rotating portion such as a joint portion (specifically, the wave generator) is estimated based on an output signal from the strain gauge. For example, in the system disclosed in Patent Document 1, the safety of the equipment is improved by comparing a signal from a rotation angle detection sensor configured using a strain gauge with a signal from an encoder to perform failure diagnosis.

[0003] Here, the output signal from the strain gauge basically changes in a sinusoidal manner in accordance with the rotation of the wave generator. That is, a fixed relationship arises between the value of the output signal (i.e., the voltage value) and the rotation angle of the wave generator. In view of such circumstances, for example, by preparing in advance a function table or relational expression that associates the value of the output signal with the rotation angle, and inputting the acquired value of the output signal into the function table or relational expression, the rotation angle of the wave generator can be easily estimated (see Patent Document 1).

[0004] Japanese Unexamined Patent Application Publication No. 2021-143987

[0005] However, in such estimation methods, if the resistance value of the strain gauge or wiring changes due to aging or other factors, the value of the acquired output signal may fall outside the input range (i.e., the upper to lower limit of the amplitude) of the function table or relational equation. If the voltage value falls outside the input range, estimating the rotation angle may become difficult or impossible. This can hinder improvements in the stability or reliability of the operation of industrial equipment. In light of these circumstances, there is still room for improvement in the configuration for estimating the rotation angle using strain gauges attached to flexible external gears in industrial equipment equipped with harmonic drive gears.

[0006] This disclosure has been made in view of the problems exemplified above, and its primary purpose is to contribute to improving the stability or reliability of the operation of industrial equipment equipped with harmonic drive gears.

[0007] A rotation angle estimation device according to one aspect of the present disclosure is provided in an industrial machine comprising a harmonic drive gear and a drive unit, wherein the harmonic drive gear comprises: an annular rigid internal gear having internal teeth formed on its inner circumferential surface; a flexible external gear disposed inside the rigid internal gear and having external teeth formed that can mesh with the internal teeth; a wave generator provided inside the flexible external gear and partially meshing the external teeth with the internal teeth by radially bending the flexible external gear, and moving the meshing position between the rigid internal gear and the flexible external gear in the circumferential direction; the drive unit rotates the wave generator in the circumferential direction; the rotation angle estimation device comprises: a plurality of strain gauges attached to the flexible external gear and each having a different position in the circumferential direction; and an estimation unit that identifies the magnitude relationship of the output signals from the plurality of strain gauges and estimates the rotation angle of the wave generator from the identified magnitude relationship.

[0008] A schematic diagram showing the robot system in the first embodiment. A block diagram showing the configuration of the robot system. A plan view of the wave drive gear. A cross-sectional view along line A-A in Figure 3. A schematic diagram for explaining the problem. A plan view of a flexible external gear showing the arrangement of strain gauges. A block diagram showing the configuration related to the detection of rotation angle. A schematic diagram showing the waveforms of each detection signal. A schematic diagram showing the relationship between multiple detection signals. A schematic diagram showing a correlation table for detecting the rotation angle of the wave generator. A schematic diagram showing an example of rotation angle detection. A schematic diagram showing another example of rotation angle detection. A schematic diagram showing a plan view of a flexible external gear showing the arrangement of strain gauges in the second embodiment and a schematic diagram showing the waveforms of the detection signals. A schematic diagram showing the relationship between multiple detection signals. A schematic diagram showing a table for detecting the rotation angle of the wave generator. A schematic diagram showing the positional relationship of strain gauges in the third embodiment. A schematic diagram showing the positional relationship of the first strain gauge. A schematic diagram showing the positional relationship of the second strain gauge. A block diagram showing the configuration related to the detection of rotation angle and torque. A schematic diagram showing an example of the relationship between the waveforms of multiple detection signals and a combined waveform. A schematic diagram showing another example of the relationship between the waveforms of multiple detection signals and the combined waveform.

[0009] <First Embodiment> Hereinafter, a robot system 10 according to the first embodiment will be described with reference to the drawings. The robot system 10 includes a vertical articulated industrial robot (i.e., robot 15) that works in cooperation with humans on a factory production line or the like.

[0010] As shown in Figure 1, the main body of the robot 15 (i.e., the robot body 21) has a base portion 22, a shoulder portion 23, a lower arm portion 24, a first upper arm portion 25, a second upper arm portion 26, a wrist portion 27, and a flange portion 28. The base portion 22 is fixed to a pedestal or the like. The shoulder portion 23 is supported by the base portion 22. The lower arm portion 24 is supported by the shoulder portion 23. The first upper arm portion 25 is supported by the lower arm portion 24. The second upper arm portion 26 is supported by the first upper arm portion 25. The wrist portion 27 is supported by the second upper arm portion 26. The flange portion 28 is supported by the wrist portion 27.

[0011] A first joint is formed in the base portion 22 and the shoulder portion 23, connecting the base portion 22 and the shoulder portion 23. The shoulder portion 23 is rotatable horizontally around the connecting axis of the first joint (i.e., the first axis AX1). A second joint is formed in the shoulder portion 23 and the lower arm portion 24, connecting the shoulder portion 23 and the lower arm portion 24. The lower arm portion 24 is rotatable vertically around the connecting axis of the second joint (i.e., the second axis AX2). A third joint is formed in the lower arm portion 24 and the first upper arm portion 25, connecting the lower arm portion 24 and the first upper arm portion 25. The first upper arm portion 25 is rotatable vertically around the connecting axis of the third joint (i.e., the third axis AX3). A fourth joint is formed in the first upper arm portion 25 and the second upper arm portion 26, connecting the first upper arm portion 25 and the second upper arm portion 26. The second upper arm portion 26 is rotatable in a twisting direction about the connecting axis of the fourth joint portion (i.e., the fourth axis AX4). The second upper arm portion 26 and the wrist portion 27 have a fifth joint portion that connects the second upper arm portion 26 and the wrist portion 27. The wrist portion 27 is rotatable in the vertical direction about the connecting axis of the fifth joint portion (i.e., the fifth axis AX5). The wrist portion 27 and the flange portion 28 have a sixth joint portion that connects the wrist portion 27 and the flange portion 28. The flange portion 28 is rotatable in a twisting direction about the connecting axis of the sixth joint portion (i.e., the sixth axis AX6).

[0012] The shoulder portion 23, lower arm portion 24, first upper arm portion 25, second upper arm portion 26, wrist portion 27, and flange portion 28 are arranged in a continuous sequence. This forms the arm of the robot body 21. An end effector 29 is attached to the flange portion 28, which is the tip of the arm. If the end effector 29 is, for example, a hand type, it can grip a workpiece or the like.

[0013] Each joint of the arm is equipped with a servo motor, rotary encoder, torque sensor, motor unit, and transmission mechanism. The servo motor is an electrically operated actuator for driving the joints. The rotary encoder detects the rotation angle of the joint (i.e., the axis). The torque sensor detects the rotational torque of the joint. The motor unit has an electromagnetic brake that operates without excitation. The transmission mechanism transmits the power generated to the servo motor and includes a harmonic drive gear, which will be described later. The harmonic drive gear is equipped with a rotation angle detection sensor to detect the rotation angle of the arm joint using a method different from that of the rotary encoder. The servo motor, rotary encoder, torque sensor, and rotation angle detection sensor are connected to a robot controller 42, which is a control device for controlling the robot 15. Now, with reference to Figure 2, the configuration of the robot system 10 will be described.

[0014] The robot controller 42 is connected to the servo motor 31 and the higher-level controller 41 (for example, a teaching pendant or PC). Data communication takes place between the robot controller 42 and the higher-level controller 41 via a communication interface. The higher-level controller 41 has an application installed for creating a control program that defines the work content and work sequence of the robot 15. Specifically, a setting support application is installed to assist the user in setting the movements of the robot 15 (including so-called teaching). The user creates the control program by directly inputting drive control code into the higher-level controller 41 or by manually operating the robot 15. The higher-level controller 41 sends operation commands to the robot controller 42 according to the created control program.

[0015] The robot controller 42 is equipped with a control unit 51 and an input / output unit 52. The control unit 51 performs drive control of the servo motor 31, etc. The input / output unit 52 performs input and output of signals from the servo motor 31 and the higher-level controller 41, etc. When the control unit 51 receives an operation command from the higher-level controller 41, it performs drive control of the robot body 21 and the end effector 29 based on the operation command.

[0016] Specifically, the input / output unit 52 is connected to a rotary encoder 32 and a rotation angle detection sensor 36. The rotation angle detection sensor 36 is provided on the wave drive gear unit 35. The control unit 51 receives operation instructions from the higher-level controller 41 and identifies the target operation position. The control unit 51 identifies the current rotation angle of each joint based on information from the rotary encoder 32 (i.e., encoder value) and information from the rotation angle detection sensor 36 (rotation angle of the wave generator described later). The control unit 51 controls the drive of the servo motor 31 based on the identified target operation position and the current rotation angle (i.e., position data).

[0017] Here, the configuration for determining the rotation angle of each joint will be explained. The configuration for determining the rotation angle is duplicated by using both a rotary encoder 32 and a rotation angle detection sensor 36. Specifically, the control unit 51 determines the rotation angle of the joint based on information from the rotary encoder 32 (more specifically, information indicating the rotation angle of the servo motor 31's axis (i.e., the encoder value)). The control unit 51 determines the rotation angle of the joint based on information from the rotation angle detection sensor 36 (more specifically, information indicating the rotation angle of the wave generator, which will be described later (i.e., the judgment value)). The control unit 51 calculates the difference in rotation angles by comparing the rotation angle of the joint determined based on the information from the rotary encoder 32 with the rotation angle of the joint determined based on the information from the rotation angle detection sensor 36. If the difference in rotation angles is within the reference range, the control unit 51 performs the above drive control based on the rotation angle of the rotary encoder 32. On the other hand, if the difference in rotation angles exceeds the reference range, there is a possibility that a malfunction has occurred in at least one of the rotary encoder 32 and the rotation angle detection sensor 36. In this case, the control unit 51 restricts the movement of the robot body 21 (for example, by stopping it). As described above, the configuration that allows monitoring of the rotation angle of the wave generator makes it possible to effectively prevent overlooking malfunctions such as failures in the wave gear device 35.

[0018] Furthermore, if the difference in rotation angles is within the reference range, the control unit 51 may perform the drive control based on the rotation angle of the rotation angle detection sensor 36, or it may perform the drive control based on a calculated value (for example, an average value) calculated from both rotation angles.

[0019] One of the features of this embodiment is the configuration of the rotation angle detection sensor 36 provided in the harmonic drive gear 35. The basic structure of the harmonic drive gear 35 will be described below with reference to Figures 3 and 4. Figure 3 is a plan view of the harmonic drive gear 35, and Figure 4 is a cross-sectional view taken along line A-A in Figure 3.

[0020] As shown in Figure 3, the wave drive gear 35 (i.e., the speed reducer) is equipped with an annular rigid internal gear 60 (a so-called circular spline) with internal teeth 61 formed on its inner circumferential surface. The rigid internal gear 60 has a plurality of through holes 62 and a plurality of positioning holes 63. Bolts for fixing it to a mating member (for example, the frame of the first upper arm portion 25) are inserted through the plurality of through holes 62. Positioning pins and the like are inserted through the plurality of positioning holes 63.

[0021] As shown in Figure 4, a flexible external gear 70 (a so-called flex spline) made of spring steel is arranged inside the rigid internal gear 60. The flexible external gear 70 has a gear main portion 71 and a flange portion 72. The gear main portion 71 is formed in a thin-walled cylindrical shape. The flange portion 72 (a so-called diaphragm) is formed at one end of the gear main portion 71. That is, the flexible external gear 70 is a so-called top hat type. External teeth 73 that mesh with the internal teeth 61 of the rigid internal gear 60 are formed on the outer circumferential surface of the gear main portion 71 near the other end.

[0022] The flange portion 72 protrudes radially from one end of the gear main portion 71, is coaxial with the gear main portion 71, and is disc-shaped. The thickness of the flange portion 72 is relatively small at the base end and relatively large at the tip end. Multiple bolt holes 77 and multiple positioning holes 78 are formed in the thicker portion 76 at the tip end of the flange portion 72. Bolts for fixing to a mating member (for example, the frame of the second upper arm portion 26) are inserted through the multiple bolt holes 77. Positioning pins are inserted through the multiple positioning holes 78. One plate surface of the thin portion 75 at the base end (specifically, the plate surface opposite to the gear main portion 71 side) is an area for attaching a strain gauge 91 and a fixing device (not shown), which will be described later. The fixing device secures the lead wires connected to the strain gauge 91.

[0023] A wave generator 80 is fitted inside the main gear portion 71 (specifically, where the external teeth 73 are formed). The wave generator 80 has an annular wave bearing 81 and an elliptical rigid cam 85. The outer circumference of the wave bearing 81 faces the inner surface of the flexible external gear 70 (i.e., the main gear portion 71). The rigid cam 85 is housed inside the wave bearing 81. The wave bearing 81 deforms to match the outer shape of the rigid cam 85, making the whole structure elliptical.

[0024] Specifically, the wave bearing 81 consists of an outer ring 82, an inner ring 83, and a plurality of balls 84. The outer ring 82 abuts against the inner circumferential surface of the gear main portion 71. The inner ring 83 is fixed to a rigid cam 85. The plurality of balls 84 are arranged between the outer ring 82 and the inner ring 83. A connecting portion 87 for connecting the shaft of the servo motor 31 is formed in the central part of the rigid cam 85. In accordance with the rotation of the shaft of the servo motor 31, the rigid cam 85 rotates together with the inner ring 83. As a result, the outer ring 82 elastically deforms via the balls 84, and the flexible external gear 70 abutting the outer ring 82 also elastically deforms to follow the movement of the outer ring 82.

[0025] Of the external teeth 73 of the flexible external gear 70, those located at both ends of the major axis of the elliptical wave generator 80 (i.e., at two locations in the major axis direction) partially mesh with the internal teeth 61 of the rigid internal gear 60. When the wave generator 80 rotates, the meshing position of the external teeth 73 with respect to the internal teeth 61 shifts in the circumferential direction. The number of external teeth 73 is set to be, for example, two fewer than the number of internal teeth 61. As a result, relative rotation occurs between the flexible external gear 70 and the rigid internal gear 60. Therefore, by fixing the rigid internal gear 60, for example, a reduced rotation output can be obtained from the flexible external gear 70 as an output unit.

[0026] In this embodiment, the rigid internal gear 60, the flexible external gear 70, and the wave generator 80 (i.e., the rigid cam 85) are coaxial and rotate around the central axis CL. As described above, the wave generator 80 is elliptical and two-lobe. That is, gear meshing occurs at two different locations in the rotational direction around the central axis CL. Specifically, the gears mesh on both sides of the central axis CL in the cross-section. In other words, the gears mesh at approximately 180° intervals in the rotational direction around the central axis CL.

[0027] The flexible external gear 70 is bent into an elliptical shape by the wave generator 80. As the wave generator 80 rotates, each part of the flexible external gear 70 undergoes repeated forced deformation in a direction perpendicular to the central axis CL (i.e., moving towards or away from the central axis CL). Therefore, periodic strain unrelated to the transmitted torque is generated in the flexible external gear 70. Specifically, each part of the flexible external gear 70 reciprocates twice with a constant stroke in a direction perpendicular to the central axis CL for each rotation of the wave generator 80. As a result, the strain unrelated to the transmitted torque appears in the detection signals of each strain gauge as a sine wave corresponding to two periods for each rotation of the wave generator 80 (so-called rotational ripple). In other words, the detection signal (i.e., voltage value) from the strain gauge 91 is a sinusoidal curve on a graph where the vertical axis is the voltage value and the horizontal axis is the rotation angle of the wave generator 80 (i.e., the rotation angle of the axis in the servo motor 31). There is a correlation between the voltage value related to the strain gauge 91 and the rotation angle of the wave generator 80.

[0028] Here, we focus on the correlation between the voltage value and the rotation angle described above. If a function table or function formula that associates the voltage value with the rotation angle is prepared in advance, the rotation angle of the wave generator 80 (i.e., the rotation angle of the servo motor 31 shaft) can be detected (i.e., estimated) by inputting the voltage value obtained from the strain gauge 91 into the function table, etc. However, in this method using a function table, etc., if the resistance value of the strain gauge changes due to the effects of aging, etc., a discrepancy may occur between the voltage value that should be obtained and the voltage value that is actually obtained. If the voltage value falls outside the input range of the function table, etc. due to such a discrepancy, it may become difficult or impossible to detect the rotation angle. For example, Figure 5 illustrates the cases where the amplitude of the detection signal has increased due to the effects of aging, etc., and where the detection signal has shifted to the positive side. In these examples, the actual rotation angle is rotation angle ANG(Va), and the corresponding voltage value should be voltage value Va. However, because the voltage value exceeds the input range due to the above effects (i.e., voltage values ​​Vb, Vc), it is impossible to detect the rotation angle using the function table, etc.

[0029] When the above-described event occurs, it becomes impossible to compare the rotation angle of the joint determined based on the information from the rotation angle detection sensor 36 with the rotation angle of the joint determined based on the information from the rotary encoder 32. This is undesirable for improving the operational stability (i.e., smooth operation) or reliability of the robot 15. In this embodiment, measures have been taken to address these circumstances. The rotation angle detection sensor 36 will now be described with reference to Figures 6 and 7. Figure 6 is a plan view of the flexible external gear 70, and Figure 7 is a block diagram showing the configuration related to rotation angle detection.

[0030] As shown in Figure 6, the rotation angle detection sensor 36 has a plurality of strain gauges 91 arranged in a line on a virtual circle FC centered on the central axis CL. Specifically, there are three strain gauges 91. The plurality of strain gauges 91 are arranged to surround the central axis CL.

[0031] Each of the multiple strain gauges 91 is a stacked type in which two linear element pieces 93a and 93b are stacked so as to be perpendicular to each other. Furthermore, the element pieces 93a and 93b share common specifications such as overall length (i.e., gauge length), overall width (i.e., gauge width), and material. The arrangement angle of each element piece 93a with respect to the central axis CL is standardized. The arrangement angle of each element piece 93b with respect to the central axis CL is also standardized.

[0032] As shown in Figure 7, each of the strain gauges 91 is connected to the detector 96 via a lead wire. The detector 96 is provided with a bridge circuit section 96a (for example, a Wheatstone bridge) and an amplifier section 96b. The bridge circuit section 96a is an electrical circuit suitable for detecting minute changes in resistance. The amplifier section 96b amplifies each signal detected by the bridge circuit section 96a. The detector 96 is also provided with an angle detection section 96c that detects the rotation angle of the wave generator 80 by determining the relative magnitudes of all (i.e., three) signals amplified by the amplifier section 96b.

[0033] The rotation angle of the wave generator 80 detected by the angle detection unit 96c is output to the robot controller 42. The input / output unit 52 of the robot controller 42 identifies the rotation angle of the joint based on this information. The control unit 51 of the robot controller 42 performs the above-mentioned monitoring, etc., based on the identified rotation angle of the joint.

[0034] Now, referring again to Figure 6, we will explain the positional relationship of the three strain gauges 91. For convenience in the following explanation, the three strain gauges 91 will also be referred to as "strain gauge 91A," "strain gauge 91B," and "strain gauge 91C."

[0035] The strain gauges 91A to 91C are located on a virtual circle FC centered on the central axis CL. The strain gauges 91A to 91C are arranged at equal intervals in the rotational direction (i.e., circumferential direction) of the flexible external gear 70 centered on the central axis CL. In other words, the strain gauges 91A to 91C are arranged at 120° intervals with respect to the central axis CL. To put it another way, the strain gauges 91A to 91C are positioned such that the angle between the virtual half-line L1A connecting the center point CP and strain gauge 91A and the virtual half-line L1B connecting the center point CP and strain gauge 91B is 120°, the angle between the virtual half-line L1B and the virtual half-line L1C connecting the center point CP and strain gauge 91C is 120°, and the angle between the virtual half-line L1C and the virtual half-line L1A is 120°. The center point CP is located at the position corresponding to the central axis CL on the same plane as the strain gauges 91A to 91C. Multiplying any of the angles formed by the virtual half-lines by an integer does not result in a period of one cycle (i.e., 180°) of the sine wave described above.

[0036] As shown in Figure 8, the detection signals of the three strain gauges 91A to 91C, arranged as described above, have different phases but similar amplitudes and periods. The phase difference between the detection signal of strain gauge 91A (hereinafter also called signal A) and the detection signal of strain gauge 91B (hereinafter also called signal B), the phase difference between the detection signal of strain gauge 91B and the detection signal of strain gauge 91C (hereinafter also called signal C), and the phase difference between the detection signal of strain gauge 91C and the detection signal of strain gauge 91A are all 60°. There is a correlation between the magnitudes of the detection signals of strain gauges 91A to 91C (i.e., signals A, B, and C) and the rotation angle of the wave generator 80.

[0037] Here, with reference to Figure 9, the method for detecting the rotation angle in the angle detection unit 96c will be explained. The angle detection unit 96c has a correlation table (see Figure 9B) pre-stored, which is a table showing the correlation between the magnitude relationship of the detection signals of strain gauges 91A to 91C (i.e., signals A, B, and C) and the rotation angle of the wave generator 80. The angle detection unit 96c compares the input signals A, B, and C, and detects the rotation angle of the wave generator 80 by comparing the comparison results with the correlation table.

[0038] Specifically, in the correlation table, the first angle (i.e., 0° or 180°) is the rotation angle of the wave generator 80 when the voltage value of signal B is maximum and the voltage value of signal C is minimum (i.e., first section S1), the second angle (i.e., 30° or 210°) is the rotation angle of the wave generator 80 when the voltage value of signal A is maximum and the voltage value of signal C is minimum (i.e., second section S2), and the third angle (i.e., 60° or 2) is the rotation angle of the wave generator 80 when the voltage value of signal A is maximum and the voltage value of signal B is minimum (i.e., third section S3). A fourth angle (i.e., 90° or 270°) is defined as the rotation angle of the wave generator 80 when the voltage value of signal C is maximum and the voltage value of signal B is minimum (i.e., fourth section S4), a fifth angle (i.e., 120° or 300°) is defined as the rotation angle of the wave generator 80 when the voltage value of signal C is maximum and the voltage value of signal A is minimum (i.e., fifth section S5), and a sixth angle (i.e., 150° or 330°) is defined as the rotation angle of the wave generator 80 when the voltage value of signal B is maximum and the voltage value of signal A is minimum (i.e., sixth section S6).

[0039] For example, consider a case where, after comparing the voltage values ​​of acquired signals A to C, the relationship is: voltage value of signal A < voltage value of signal B < voltage value of signal C. In this case, by comparing the comparison results with the correlation table, it is determined that the rotation angle of the wave generator 80 is equal to the fifth angle.

[0040] As described above, each of the first to sixth angles consists of two angles, one large and one small. The angle detection unit 96c in this embodiment stores past detection history and determines from the detection history which of the two angles, the current angle, is large or small. For example, if the rotation angles are detected in the order of first angle (0°), second angle (30°), third angle (60°), and fourth angle (90°), and the relationship between the detection signals is such that the voltage value of signal A < the voltage value of signal B < the voltage value of signal C, then the fifth angle is determined to be 120°. If the rotation angles are detected in the order of first angle (180°), second angle (210°), third angle (240°), and fourth angle (270°), and the relationship between the detection signals is such that the voltage value of signal A < the voltage value of signal B < the voltage value of signal C, then the fifth angle is determined to be 300°. Note that the specific configuration for determining which of the two angles, the current angle, is large or small, is arbitrary.

[0041] According to the configuration described above, even if the amplitude of the detection signal changes due to aging or other factors, or if a shift occurs in the waveform, it is possible to suppress the inability to detect the rotation angle of the wave generator 80. The reason for this will be explained below with reference to Figure 10. Figure 10 illustrates the case where the waveform of the detection signal is shifted to the negative side (i.e., downwards). However, the same applies to the detection result when the amplitude becomes larger.

[0042] In the example shown in FIG. 10A, the waveforms of any of signal A, signal B, and signal C are exactly the waveforms assumed as defaults. Therefore, for example, at timing t1 where the magnitude relationship of the voltage values satisfies signal A < signal B < signal C, the current rotation angle of the wave generator 80 detected with reference to the correlation table (see FIG. 9B) is the fifth angle. In contrast, in the example shown in FIG. 10B, the waveform of signal A is shifted to the negative side, and the voltage value of signal A is lower than that of the default waveform. However, in the present embodiment, the rotation angle of the wave generator 80 is not detected directly from the voltage value itself using the aforementioned function table or the like. The rotation angle of the wave generator 80 is detected by comparing the magnitude relationship of the voltage values of the detection signals against the correlation table. That is, there is no limitation on the input range as shown in FIG. 5. For this reason, even if the actual voltage value is a value lower than the minimum value (i.e., the lower limit value) in the default waveform, the rotation angle of the wave generator 80 will not become undetectable. For example, at the same timing as timing t1 shown in FIG. 10A, although the difference between the voltage value of signal A (i.e., the minimum value) and the voltage value of signal C (i.e., the maximum value) is large, the magnitude relationship of the voltage values is signal A < signal B < signal C. In other words, the magnitude relationship of the voltage values is the same as in the case of FIG. 10A. Therefore, by referring to the correlation table (see FIG. 9B), the current rotation angle of the wave generator 80 is determined to be the fifth angle.

[0043] According to the first embodiment described in detail above, the following excellent effects can be expected.

[0044] The detection signal (i.e., output signal) from each strain gauge 91 attached to the flexible external gear 70 basically changes in a sinusoidal manner in accordance with the rotation of the wave generator 80. For this reason, the magnitude relationship of the detection signals from each strain gauge 91 switches in a predetermined order as the wave generator 80 rotates. That is, there is a correlation between the magnitude relationship of the detection signals and the rotation angle of the wave generator 80. Therefore, as shown in the present embodiment, by specifying the magnitude relationship of the detection signals from each strain gauge 91 and estimating the rotation angle of the wave generator 80 from the specified magnitude relationship, the estimation of the rotation angle can be easily realized.

[0045] Furthermore, the resistance values ​​of the strain gauge 91 and the leads attached to the strain gauge 91 may change due to aging or other factors. Changes in resistance values ​​may cause the magnitude of the detection signal to deviate from its original magnitude. For example, by preparing a function table or relational expression in advance that associates the value of the detection signal (i.e., voltage value) with the rotation angle, and inputting the acquired value of the detection signal into the function table or relational expression, the rotation angle of the wave generator can be easily estimated. However, in such an estimation method, the value of the acquired detection signal may fall outside the input range (i.e., upper to lower limit of amplitude) of the function table or relational expression due to the effects of aging or other factors mentioned above. There is a concern that if the value of the detection signal falls outside the input range, it may become difficult or impossible to estimate the rotation angle. However, in the configuration shown in this embodiment, a correlation table, which is correlation information showing the correlation between the magnitude relationship of the detection signal from the strain gauge 91 and the rotation angle of the wave generator 80, is stored in advance. The magnitude relationship of the detection signal from the strain gauge 91 is identified. Based on the identified magnitude relationship and the correlation table, the rotation angle of the wave generator 80 is estimated. Here, the stored correlation table merely identifies the magnitude relationship of the detected signals. Therefore, as long as the magnitude relationship of the detected signals can be identified, it is possible to suppress the difficulty or inability to estimate the rotation angle due to detected signals exceeding the amplitude of the waveform assumed as a reference. Thus, it is possible to suppress the effects of aging deterioration and other factors as described above, and contribute to improving the stability or reliability of the robot 15's operation.

[0046] In the case of a two-lobe type harmonic drive gear as shown in this embodiment, the strain gauges 91A to 91C are arranged asymmetrically with respect to the central axis CL. This suppresses the overlapping of the waveforms of the detection signals from the strain gauges 91A to 91C. This is preferable for setting the relative magnitudes of the detection signals with a simple configuration.

[0047] When detecting (i.e., estimating) the rotation angle using the method described above, it is preferable to suppress bias in the relative magnitudes of the detected signals. Here, as shown in this embodiment, by attaching all of the strain gauges 91 to the flange portion 72, the strain gauges 91 are arranged on the same virtual circle FC centered on the central axis CL. This makes it possible to suppress the bias mentioned above.

[0048] In the present embodiment, the largest detection signal and the smallest detection signal among the plurality of detection signals are identified. Such a configuration is advantageous in making the estimation of the rotation angle less susceptible to the influence of deviation of the detection signal due to the above-described aged deterioration or the like.

[0049] <Second Embodiment> In the above-described first embodiment, three strain gauges 91 are arranged in the circumferential direction of the flexible external gear 70 on the flange portion 72 of the flexible external gear 70. In the present embodiment, the number and arrangement of the strain gauges 91 are different from those in the above-described first embodiment. Further, comparing the detection signals from the strain gauges 91 and detecting (that is, estimating) the rotation angle of the wave generator 80 based on the magnitude relationship of the detection signals is the same as in the first embodiment. However, part of the configuration related to the detection is different. Hereinafter, the rotation angle detection sensor 36X in the present embodiment will be described with reference to FIG. 11. FIG. 11 is a schematic diagram showing a plan view of the flexible external gear 70X and waveforms of detection signals.

[0050] In the present embodiment, the number of strain gauges 91 constituting the rotation angle detection sensor 36X is four. The four strain gauges 91 (that is, the strain gauge 91A, the strain gauge 91B, the strain gauge 91C, and the strain gauge 91D) are arranged in the circumferential direction of the flexible external gear 70X. The distances from the central axis line CL to each of the four strain gauges 91 are the same. Here, the strain gauges 91 are not arranged uniformly over the entire circumference of the flexible external gear 70X (that is, the flange portion 72), and are arranged only on one side (for example, the left side portion) of the flange portion 72.

[0051] Specifically, strain gauges 91A to 91D are positioned such that the angle between the virtual half-line connecting the center point CP and strain gauge 91A and the virtual half-line connecting the center point CP and strain gauge 91B is 45°, the angle between the virtual half-line connecting the center point CP and strain gauge 91B and the virtual half-line connecting the center point CP and strain gauge 91C is 45°, the angle between the virtual half-line connecting the center point CP and strain gauge 91C and the virtual half-line connecting the center point CP and strain gauge 91D is 45°, and the angle between the virtual half-line connecting the center point CP and strain gauge 91D and the virtual half-line connecting the center point CP and strain gauge 91A is 225°. The center point CP is the position corresponding to the central axis CL on the same plane as the strain gauges 91A to 91D. Multiplying the angle formed by any of the virtual half-lines by an integer does not result in a period of one sine wave (i.e., 180°) as described above.

[0052] As shown in Figure 11, the detection signals of the four strain gauges 91A to 91D, arranged as described above, have different phases but similar amplitudes and periods. The phase difference between the detection signal of strain gauge 91A (hereinafter also called signal A) and the detection signal of strain gauge 91B (hereinafter also called signal B), the phase difference between the detection signal of strain gauge 91B and the detection signal of strain gauge 91C (hereinafter also called signal C), the phase difference between the detection signal of strain gauge 91C and the detection signal of strain gauge 91D (hereinafter also called signal D), and the phase difference between the detection signal of strain gauge 91D and the detection signal of strain gauge 91A are all 45°. There is a correlation between the magnitude relationship of the detection signals of strain gauges 91A to 91D (i.e., signals A, B, C, and D) and the rotation angle of the wave generator 80.

[0053] Next, with reference to Figure 12, the method for detecting the rotation angle in the angle detection unit 96c will be described. The angle detection unit 96c has a correlation table (see Figure 12B) pre-stored, which is a table showing the correlation between the magnitude relationships of the detection signals of the strain gauges 91A to 91D (i.e., signals A, B, C, and D) and the rotation angle of the wave generator 80. The angle detection unit 96c compares the input signals A, B, C, and D, and detects the rotation angle of the wave generator 80 by comparing the comparison results with the correlation table.

[0054] Specifically, in the correlation table, the first angle of rotation of the wave generator 80 when the voltage value of signal B is maximum and the voltage value of signal A is second largest (i.e., first section S1) is 11.25° or 191.25°, the second angle of rotation of the wave generator 80 when the voltage value of signal A is maximum and the voltage value of signal B is second largest (i.e., second section S2) is 33.75° or 213.75°, the third angle of rotation of the wave generator 80 when the voltage value of signal A is maximum and the voltage value of signal D is second largest (i.e., third section S3) is 56.25° or 236.25°, and the fourth angle of rotation of the wave generator 80 when the voltage value of signal D is maximum and the voltage value of signal A is second largest (i.e., fourth section S4) is 78.75° or 258.7 The following angles are defined: 5°), the fifth angle (i.e., 101.25° or 281.25°) which is the rotation angle of the wave generator 80 when the voltage value of signal D is maximum and the voltage value of signal C is second largest (i.e., fifth section S5); the sixth angle (i.e., 123.75° or 303.75°) which is the rotation angle of the wave generator 80 when the voltage value of signal C is maximum and the voltage value of signal D is second largest (i.e., sixth section S6); the seventh angle (i.e., 146.25° or 326.25°) which is the rotation angle of the wave generator 80 when the voltage value of signal C is maximum and the voltage value of signal B is second largest (i.e., seventh section S7); and the eighth angle (i.e., 168.75° or 348.75°) which is the rotation angle of the wave generator 80 when the voltage value of signal B is maximum and the voltage value of signal C is second largest (i.e., eighth section S8).

[0055] For example, consider a case where, after comparing the voltage values ​​of acquired signals A to D, the relationship is: voltage value of signal B < voltage value of signal A < voltage value of signal C < voltage value of signal D. In this case, by comparing the comparison results (specifically, the detection signal with the largest voltage value and the detection signal with the second largest voltage value) with the correlation table, it is determined that the rotation angle of the wave generator 80 is equal to the fifth angle.

[0056] According to the second embodiment described in detail above, the angular resolution of the rotation angle detection sensor can be increased.

[0057] When magnitude relationships are determined by comparing detected signals, the processing load is high if all magnitude relationships are identified and all of them are compared. In particular, when the rotation angle estimation is repeated at short intervals, there is a concern that the drawbacks such as delays due to the high processing load will become significant. However, as shown in this embodiment, the correspondence between a combination of a detection signal of a predetermined rank (i.e., the first) and a detection signal of a specific rank (i.e., the second) in the magnitude order of the detected signals and the rotation angle of the wave generator 80 is stored in advance. As a result, the number of magnitude relationships identified and compared is reduced compared to the case where all magnitude relationships are identified and all of them are compared, thus reducing the processing load.

[0058] <Third Embodiment> In the first embodiment described above, a torque sensor for detecting the rotational torque of the joint (i.e., the shaft) and a rotational angle detection sensor 36 for detecting the rotational angle of the joint are used in combination. In this embodiment, by devising the rotational angle detection sensor and related configurations, both the detection of the rotational torque and rotational angle of the joint are realized using the rotational angle detection sensor. Hereinafter, with reference to Figures 13 to 15, the characteristic configuration of this embodiment will be described, focusing on the differences from the first embodiment. Configurations common to the first embodiment will be omitted from explanation as appropriate.

[0059] When the harmonic drive gear 35Y is rotationally driven, torque is generated in the harmonic drive gear 35Y. The generated torque is detected by a rotation angle detection sensor 36Y attached to the rigid internal gear 60. As shown in Figure 13A, the rotation angle detection sensor 36Y has a plurality of strain gauges 91 and an additional plurality of strain gauges 92 arranged in a line on a virtual circle FC centered on the central axis CL. In this embodiment, the number of strain gauges 91 and strain gauges 92 are both three. The central axis CL is surrounded by a total of six strain gauges 91 and 92. The specific configuration related to strain detection of the strain gauge 92 is the same as that of the strain gauge 91, so a detailed explanation is omitted.

[0060] In the rotation angle detection sensor 36Y shown in this embodiment, a first group G1 is formed by three strain gauges 91, and a second group G2 is formed by three additional strain gauges 92. In the following description, the three strain gauges 91 that constitute the first group G1 (hereinafter also referred to as the first strain gauge 91) will be referred to as "first strain gauge 91A," "first strain gauge 91B," and "first strain gauge 91C," and the three strain gauges 92 that constitute the second group G2 (hereinafter also referred to as the second strain gauge 92) will be referred to as "second strain gauge 92A," "second strain gauge 92B," and "second strain gauge 92C."

[0061] As shown in Figure 13B, the first strain gauges 91A to 91C are located on a virtual circle FC centered on the central axis CL. The first strain gauges 91A to 91C are arranged at equal intervals in the rotational direction (i.e., circumferential direction) of the flexible external gear 70 centered on the central axis CL. That is, the first strain gauges 91A to 91C are arranged at 120° intervals with respect to the central axis CL. In other words, the first strain gauges 91A to 91C are positioned such that the angle between the virtual half-line L1A connecting the center point CP and the first strain gauge 91A and the virtual half-line L1B connecting the center point CP and the first strain gauge 91B is 120°, the angle between the virtual half-line L1B and the virtual half-line L1C connecting the center point CP and the first strain gauge 91C is 120°, and the angle between the virtual half-line L1C and the virtual half-line L1A is 120°. The center point CP is located at the position corresponding to the central axis CL on the same plane as the first strain gauges 91A to 91C. Multiplying any of the angles formed by the virtual half-lines by an integer does not result in a period of one cycle (i.e., 180°) of the sine wave.

[0062] As shown in Figure 13C, the second strain gauges 92A to 92C are located on a virtual circle FC centered on the central axis CL. The second strain gauges 92A to 92C are arranged at equal intervals in the rotational direction (i.e., circumferential direction) of the flexible external gear 70 centered on the central axis CL. That is, the second strain gauges 92A to 92C are arranged at 120° intervals with respect to the central axis CL. In other words, the second strain gauges 92A to 92C are positioned such that the angle between the virtual half-line L2A connecting the center point CP and the second strain gauge 92A and the virtual half-line L2B connecting the center point CP and the second strain gauge 92B is 120°, the angle between the virtual half-line L2B and the virtual half-line L2C connecting the center point CP and the second strain gauge 92C is 120°, and the angle between the virtual half-line L2C and the virtual half-line L2A is 120°. The center point CP is located at the position corresponding to the central axis CL, which lies on the same plane as the second strain gauges 92A to 92C. Multiplying any of the angles formed by the virtual half-lines by an integer does not result in a period of one cycle (i.e., 180°) of the sine wave described above.

[0063] As shown in the block diagram of Figure 14, each of the multiple first strain gauges 91 is connected to the first detector 96 via lead wires. The first detector 96 is provided with a bridge circuit section 96a (e.g., a Wheatstone bridge) and an amplifier section 96b. The bridge circuit section 96a is an electrical circuit suitable for detecting minute changes in resistance. The amplifier section 96b amplifies each signal detected by the bridge circuit section 96a. In addition to the angle detection section 96c described above, the first detector 96 is provided with a combining section 96d that combines all (i.e., three) signals amplified by the amplifier section 96b. The first signal (i.e., the combined result), which is the detection signal combined by the combining section 96d, is output to the robot controller 42.

[0064] Each of the multiple second strain gauges 92 is connected to the second detector 97 via a lead wire. The second detector 97, like the first detector 96, is also provided with a bridge circuit section 97a (e.g., a Wheatstone bridge) and an amplifier section 97b. The bridge circuit section 97a is an electrical circuit suitable for detecting minute changes in resistance. The amplifier section 97b amplifies each signal detected by the bridge circuit section 97a. The second detector 97 is also provided with an angle detection section 97c and a combining section 97d. The angle detection section 97c detects the rotation angle of the wave generator 80 by determining the relative magnitudes of all (i.e., three) signals amplified by the amplifier section 97b. The combining section 97d combines all (i.e., three) signals amplified by the amplifier section 97b. The second signal (i.e., the combined result), which is the detection signal combined by the combining section 97d, is output to the robot controller 42.

[0065] The combining units 96d and 97d shown in this embodiment combine the detection signals by adding the three detection signals together. As will be described in detail later, the robot controller 42 detects abnormalities such as noise based on the input first signal and second signal, and determines whether protective stop or other action is necessary based on the first signal.

[0066] Here, we will explain the technical effects brought about by the synthesis of the detection signals. As mentioned above, the rigid cam 85 is elliptical and has a two-lobe shape. That is, the gears of the wave generator 80 mesh at two different locations in the rotational direction around the central axis CL (see Figure 3). Specifically, the gears mesh on both sides of the central axis CL in the cross-section. In other words, the gears mesh at approximately 180° intervals in the rotational direction around the central axis CL.

[0067] As described above, the flexible external gear 70 is bent into an elliptical shape by the wave generator 80. As the wave generator 80 rotates, each part of the flexible external gear 70 undergoes repeated forced deformation in a direction perpendicular to the central axis CL (i.e., in a direction approaching or moving away from the central axis CL). Therefore, periodic strain unrelated to the transmitted torque is generated in the flexible external gear 70. Specifically, each part of the flexible external gear 70 reciprocates twice with a constant stroke in a direction perpendicular to the central axis CL for each rotation of the wave generator 80. As a result, the strain unrelated to the transmitted torque appears in the detection signals of each strain gauge 91 and 92 as a sine wave corresponding to two periods for each rotation of the wave generator 80.

[0068] Here, although the phases of the detection signals from the three first strain gauges 91A to 91C arranged as described above differ, the amplitudes and periods of these detection signals are the same. By combining these three detection signals, rotational ripple can be suppressed. Rotational ripple is a periodic strain component that occurs in the flexible external gear 70 independently of the transmitted torque as the wave generator 80 rotates (see Figure 15A). Specifically, the amplitude of the first signal is proportional to sin(α) + sin(α + 120 × 2) + sin(α - 120 × 2) + β, where α is the rotation angle of the rigid cam 85, and sin(α) + sin(α + 60 × 2) + sin(α - 60 × 2) = 0. Therefore, theoretically, rotational ripple is canceled out. In other words, the waveform of the first signal (i.e., the result of the combination) is theoretically a flat waveform.

[0069] The amplification factor of each detection signal by the amplifier section 96b may be any value that can suppress the rotational ripple. For example, the amplification factor may be common to all detection signals, or it may be set individually to account for individual differences, etc.

[0070] As described above, the detection signals of the three second strain gauges 92A to 92C, although having different phases, have the same amplitude and period. By combining these three detection signals, the rotational ripple described above can be suppressed (see Figure 15B). Specifically, the amplitude of the second signal is proportional to sin(α) + sin(α + 120 × 2) + sin(α - 120 × 2) + β, where α is the rotation angle of the rigid cam 85, and sin(α) + sin(α + 60 × 2) + sin(α - 60 × 2) = 0. Therefore, theoretically, the rotational ripple is canceled out. In other words, the value of the combined second signal is constant, and theoretically, the waveform of the second signal is flat.

[0071] The amplification factor of each detection signal by the amplifier section 97b may be any value that can suppress the rotational ripple. For example, the amplification factor may be common to all detection signals, or it may be set individually to account for individual differences, etc.

[0072] Next, referring again to Figure 13A, the positional relationship between the first strain gauge 91 and the second strain gauge 92 will be explained.

[0073] The first strain gauge 91 and the second strain gauge 92 are arranged alternately on the virtual circle FC. That is, the second strain gauge 92 is adjacent to the first strain gauge 91, and the first strain gauge 91 is adjacent to the second strain gauge 92. The first strain gauge 91 and the second strain gauge 92 are arranged point-symmetrically with respect to the central axis CL. In other words, if the position where the first strain gauge 91 is placed in the flange portion 72 is shifted by 180° around the central axis CL, their positions coincide with the position where the second strain gauge 92 is placed in the flange portion 72.

[0074] More specifically, the angles formed by the virtual half-line L1A connecting the center point CP and the first strain gauge 91A and the virtual half-line L2A connecting the center point CP and the second strain gauge 92A, the angles formed by the virtual half-line L1B connecting the center point CP and the first strain gauge 91B and the virtual half-line L2B connecting the center point CP and the second strain gauge 92B, and the angles formed by the virtual half-line L1C connecting the center point CP and the first strain gauge 91C and the virtual half-line L2C connecting the center point CP and the second strain gauge 92C are all 180°. This coincides with the angle equivalent to one period defined by 360° / lobe number (i.e., the reference angle: 180°).

[0075] With the arrangement described in detail above, it is possible to match the waveform of the first signal, which is obtained by combining the detection signals from the first strain gauges 91A to 91C, with the waveform of the second signal, which is obtained by combining the detection signals from the second strain gauges 92A to 92C (see Figure 15). Both the first and second signals are input to the robot controller 42. The input / output unit 52 of the robot controller 42 compares the first and second signals to detect noise and other issues.

[0076] Specifically, it is determined whether the difference between the value of the first signal and the value of the second signal exceeds a preset judgment criterion value (i.e., the first judgment criterion value). If the difference between the value of the first signal and the value of the second signal does not exceed the first judgment criterion value, it is determined that no noise is being generated, and the value of the first signal is output directly to the control unit 51. The control unit 51 calculates the torque generated based on the value of the first signal. If the torque is of a magnitude corresponding to the protective stop of the robot 15, the control unit 51 performs a protective stop process, and if it is of a magnitude corresponding to the deceleration of the robot 15, it performs a deceleration process.

[0077] Here, even if the difference between the value of the first signal and the value of the second signal is less than or equal to a preset first judgment criterion value, if it exceeds a second judgment criterion value which is smaller than the first judgment criterion value, a fault detection process is performed. Specifically, the number of consecutive times the second judgment criterion value has been exceeded is identified. If that number exceeds a predetermined number, a process is performed to notify the user that there is a possibility that a fault has occurred in one of the strain gauges.

[0078] If the difference between the value of the first signal and the value of the second signal exceeds the first judgment threshold, noise may be present. Therefore, the most recent value of the first signal, which is below the first judgment threshold, is output to the control unit 51. The control unit 51 calculates the torque generated based on the most recent value of the first signal, and if the torque exceeds the threshold, it performs protective shutdown or other processing.

[0079] Furthermore, if the difference between the value of the first signal and the value of the second signal exceeds the first judgment criterion value, the control unit 51 does not need to output a value. Alternatively, the control unit 51 may output the value of the first signal or the second signal that has changed less from the previous value.

[0080] Furthermore, since the torque generated at the joint is detected using the rotation angle detection sensor 36, the rotation angle detection sensor 36 may also be called a torque detection sensor 36.

[0081] In the harmonic drive gear 35Y shown in this embodiment, the rotation of the rigid cam 85 periodically generates strain in the flexible external gear 70 that is unrelated to the transmitted torque. Therefore, the detection signals from the strain gauges 91 and 92 attached to the flexible external gear 70 change sinusoidally in amplitude according to the rotation angle of the rigid cam 85. For this reason, using multiple strain gauges in combination and synthesizing the detection signals from these strain gauges is preferable in suppressing rotational ripple, which is a cause of error in torque detection. In the robot 15, there is a possibility that noise from the power supply line for supplying drive power to the built-in servo motor 31 or the power supply line of other industrial equipment may be applied to the signal line. As mentioned above, increasing the number of strain gauges is preferable in suppressing rotational ripple. However, if the number of strain gauges increases, the opportunities for noise to be applied to the signal line (i.e., lead wire) attached to the strain gauge also increase.

[0082] However, as shown in this embodiment, a first signal, which is a composite of detection signals from multiple first strain gauges 91, and a second signal, which is a composite of detection signals from multiple second strain gauges 92, are compared. As a result, noise is applied to either the detection signal from the first strain gauges 91 or the detection signal from the second strain gauges 92. Consequently, the first signal and the second signal diverge significantly, and the relationship between the first signal and the second signal is disrupted. In other words, by comparing the first signal and the second signal, it is possible to detect that noise has been applied to at least one of the detection signals. This is preferable for suppressing malfunctions caused by noise. As described above, the configuration shown in this embodiment can contribute to suppressing rotational ripple and enhancing noise immunity.

[0083] The harmonic drive gear 35 shown in this embodiment is of the two-lobe type. The first strain gauge 91 and the second strain gauge 92 are arranged point-symmetrically with respect to the central axis CL. With this configuration, the difference between the waveform of the combined first signal and the waveform of the second signal can be reduced. In other words, it is possible to suppress large fluctuations in the difference between the first signal and the second signal depending on the timing of the comparison. This is preferable for realizing a simple comparison between the first signal and the second signal and for simplifying the configuration related to the determination of noise, etc.

[0084] If the comparison result between the first signal and the second signal is below the first judgment criterion value (i.e., it is presumed that no noise is being applied), the torque generated in the harmonic drive gear 35 is detected based on the first signal. Then, a decision such as protective stop or deceleration is made according to the detected torque. After the comparison between the first signal and the second signal, the first signal is used directly for torque detection. This makes it possible to suppress the time lag until control (i.e., deceleration or stopping of industrial equipment) is performed according to the detected torque.

[0085] Increasing the number of detection signals that are synthesized is advantageous in suppressing rotational ripple. However, when synthesizing detection signals, it is undesirable for local changes such as noise to be masked by the synthesis, as this hinders the early detection of signs of abnormalities due to degradation, etc. For example, the masking of local changes by synthesis hinders the detection of local changes. However, as shown in this embodiment, the first signal and the second signal are generated by adding the detection signals together. This is desirable for the early detection of signs of abnormalities.

[0086] Each strain gauge 91 and 92 is attached to the flange portion 72, and the distance from the central axis CL to each strain gauge 91 and 92 is the same. This suppresses differences in how strain appears depending on the placement of the strain gauges 91 and 92. This is preferable for aligning the waveforms of the first signal and the second signal.

[0087] The first strain gauges 91 are arranged at equal intervals in the circumferential direction. The second strain gauges 92 are also arranged at equal intervals in the circumferential direction. As described above, in the comparison between the first signal and the second signal, the values ​​of both signals are constant or approximately constant. This suppresses large fluctuations in the difference between the waveforms of the first signal and the waveform of the second signal depending on the timing of the comparison. This is preferable for realizing a simple comparison process, such as unifying the judgment criteria in the comparison.

[0088] The first strain gauge 91 and the second strain gauge 92 are arranged alternately in the circumferential direction. This is preferable in order to achieve the point-symmetrical positional relationship described above while suppressing any bias in the arrangement of the strain gauges 91 and 92.

[0089] As shown in this embodiment, rotation angle detection (i.e., estimation) and torque detection are performed using rotation angle detection sensors 36Y (i.e., strain gauges 91 and 92). This contributes to the consolidation and simplification of the sensing configuration.

[0090] <Other Embodiments> This disclosure is not limited to the embodiments described above, and may be modified as follows, for example. Each of the following configurations may be applied individually to each of the embodiments described above, or some or all of them may be applied to each of the embodiments described above. It is also possible to arbitrarily combine all or some of the various configurations shown in each of the embodiments described above. The technical effects of each combined configuration are guaranteed. Furthermore, each of the following configurations may be applied individually to a new configuration consisting of a combination of embodiments, or some or all of them may be applied in combination.

[0091] (1) In the first embodiment described above, a plurality of strain gauges 91 are arranged at equal intervals in the rotational direction about the central axis CL. On the other hand, the plurality of strain gauges 91 may be arranged at different intervals. However, since the rotation angle of the wave generator 80 is detected (i.e. estimated) from the relative magnitudes of the detection signals from the strain gauges 91, it is preferable to have as large a phase difference as possible in order to improve detection accuracy. For this reason, there is a technical advantage to arranging the strain gauges 91 at equal intervals.

[0092] (2) In the first and third embodiments described above, detection signals from three strain gauges 91 are compared, and in the second embodiment described above, detection signals from four strain gauges 91 are compared. However, the number of detection signals to be compared (i.e., the number of strain gauges 91) does not necessarily have to be three or four. For example, the number of detection signals may be five or six or more. Also, although the resolution will decrease, it is possible to use two strain gauges 91.

[0093] (3) In the correlation table shown in the first embodiment above, the rotation angle of the wave generator 80 is associated with the combination of the largest and smallest of the three detection signals. However, the correlation table is not limited to this. For example, the rotation angle of the wave generator 80 may be associated with the combination of the largest and the second largest of the three detection signals, or with the combination of the smallest and the second smallest.

[0094] Similarly, in the correlation table shown in the second embodiment above, the rotation angle of the wave generator 80 is associated with a combination of the largest and second largest of the four detection signals. However, the correlation table is not limited to this. For example, the rotation angle of the wave generator 80 may be associated with a combination of the largest and third largest of the four detection signals, or with a combination of the largest and smallest. Alternatively, the rotation angle of the wave generator 80 may be associated with a combination of the largest, second largest, and third largest of the four detection signals.

[0095] (4) In the correlation table shown in the first embodiment above, the rotation angle of the wave generator 80 is associated with a combination of the largest and smallest of the three detection signals. However, the correlation table is not limited to this. For example, the rotation angle of the wave generator 80 may be associated with the largest of the three detection signals, or with the smallest of the three detection signals.

[0096] (5) In the third embodiment described above, the magnitude relationship of the detection signals from the strain gauges 91 constituting the first group G1 is determined, and the rotation angle of the wave generator 80 is detected (i.e., estimated) based on the determination result. However, this may be changed as follows: The magnitude relationship of the detection signals from the strain gauges 92 constituting the second group G2 is determined, and the rotation angle of the wave generator 80 may be detected based on the determination result.

[0097] (6) In each of the above embodiments, the rotation angle detection sensor 36 determines the magnitude relationship of the detection signals from the strain gauge 91. However, the main detection is not limited to this. It is also possible for the detection signals to be input to the robot controller 42, and for the robot controller 42 (for example, the input / output unit 52) ​​to determine the magnitude relationship. However, in order to suppress the influence of disturbances such as noise, it is preferable to determine the magnitude relationship of the detection signals from the strain gauge 91 using the rotation angle detection sensor 36.

[0098] (7) The strain gauges 91 and 92 provided on the flange portion 72 of the flexible external gear 70 can also be positioned on the same virtual circle (i.e., a virtual circle centered on the central axis CL) as the bolt holes 77 and positioning holes 78 formed in the flange portion 72.

[0099] (8) In each of the above embodiments, strain gauges 91 and 92 are arranged on the flange portion 72 of the flexible external gear 70. However, the arrangement of strain gauges 91 and 92 is not limited to this. The arrangement of strain gauges 91 and 92 is arbitrary as long as rotation angle detection is possible. For example, strain gauges 91 and 92 can also be arranged on the gear main portion 71 of the flexible external gear 70 (more specifically, on the outer or inner circumferential surface of the cylindrical portion).

[0100] (9) In each of the above embodiments, the strain gauge 91 is constructed by combining two element pieces 93a and 93b so as to be orthogonal. However, the gauge pattern of the strain gauge 91 (i.e., the arrangement or number of element pieces) can be arbitrarily changed as long as it is possible to detect the strain generated in the harmonic drive gear 35 and to identify the magnitude relationship of the detected signals. For example, when a strain gauge is constructed by combining two element pieces, the two element pieces can be arranged spaced apart. Also, for example, a strain gauge may be constructed by one element piece, or by combining three or more element pieces. However, it is preferable to align the gauge pattern because the magnitude relationship of the detected signals is compared.

[0101] (10) In each of the above embodiments, a two-lobe type wave generator 80 is exemplified. However, the wave generator is not limited to this. For example, the wave generator can be a three-lobe type using a triangular rigid cam, a four-lobe type using a quadrangular rigid cam, or a five-lobe type using a pentagonal rigid cam.

[0102] (11) In each of the above embodiments, a so-called top hat type flexible external gear 70 is exemplified. However, the shape of the external gear is not limited thereto. For example, the shape of the external gear may be a so-called cap type or pancake type.

[0103] (12) The configurations for detecting rotation angles shown in each of the above embodiments can also be applied to robots other than robots that work in collaboration with humans. Other robots are robots installed in other processes that are equipped with a harmonic drive gear reducer. Furthermore, the configuration for detecting torque can be applied to robots other than industrial robots used in factories (for example, robots used in restaurants or hospitals). Moreover, the configuration for detecting rotation angles can also be applied to other industrial equipment equipped with a harmonic drive gear reducer (for example, machine tools such as NC (numerical control) machine tools).

[0104] <Features extracted from each of the above embodiments> Below, the features extracted from each of the above embodiments will be explained, showing the effects and other details as necessary. For ease of understanding, the corresponding configurations in each of the above embodiments will be shown in parentheses as appropriate, but the invention is not limited to the specific configurations shown in parentheses.

[0105] (Feature 1) A wave drive gear device (wave drive gear device 35) having an annular rigid internal gear (rigid internal gear 60) with internal teeth (internal teeth 61) formed on its inner circumferential surface, a flexible external gear (flexible external gear 70) disposed inside the rigid internal gear and having external teeth (external teeth 73) that can mesh with the internal teeth, and a wave generator (wave generator 80) provided inside the flexible external gear which partially meshes the external teeth with the internal teeth by flexing the flexible external gear radially and moves the meshing position between the rigid internal gear and the flexible external gear in the circumferential direction, a drive unit (servo motor 31) for rotating the wave generator in the circumferential direction, and a rotation angle estimation device (for example, a rotation angle detection sensor 36) for estimating the rotation angle of the wave generator, is applied to industrial equipment (robot 15). An industrial equipment control system (control system 40) that controls the industrial equipment (e.g., drive control, stop control) based on the rotation angle estimated by the rotation angle estimation device, wherein the rotation angle estimation device comprises a plurality of strain gauges (e.g., strain gauges 91A to 91C) attached to the flexible external gear and having different positions in the circumferential direction, and an estimation unit (angle detection unit 96c) that identifies the magnitude relationship of the output signals from the plurality of strain gauges and estimates the rotation angle of the wave generator from the identified magnitude relationship.

[0106] (Feature 2) The control system for industrial equipment according to Feature 1, wherein the estimation unit pre-stores correlation information (correlation table) showing the correlation between the magnitude relationship of the output signals from the plurality of strain gauges and the rotation angle of the wave generator, and estimates the rotation angle of the wave generator based on the identified magnitude relationship and the correlation information.

[0107] (Feature 3) The control system for industrial equipment according to Feature 1 or Feature 2, wherein the plurality of strain gauges include a first strain gauge (strain gauge 91A) and a second strain gauge (strain gauge 91B), the first strain gauge and the second strain gauge are positioned such that an integer multiple of the angle between a first virtual half-line (e.g., virtual half-line L1A) and a second virtual half-line (e.g., virtual half-line L1B) does not coincide with a reference angle (e.g., 180° in the case of a two-lobe type, 120° in the case of a three-lobe type), the first virtual half-line is a half-line extending from the rotation center of the wave generator through the first strain gauge, the second virtual half-line is a half-line extending from the rotation center through the second strain gauge, and the reference angle is the angle obtained by dividing 360° by the number of lobes of the wave gear device.

[0108] As shown in this feature, by devising the positional relationship between the first strain gauge and the second strain gauge, it is possible to suppress the overlap between the waveform of the output signal from the first strain gauge and the waveform of the output signal from the second strain gauge. This is preferable for setting the relative magnitudes of the output signals with a simple configuration.

[0109] (Feature 4) The harmonic drive gear is a two-lobe type harmonic drive gear in which the rigid cam (rigid cam 85) fixed to the shaft of the drive unit is elliptical, and the plurality of strain gauges include a first strain gauge (strain gauge 91A) and a second strain gauge (strain gauge 91B), and the first strain gauge and the second strain gauge are arranged asymmetrically with respect to the rotation center (central axis CL) of the wave generator, as described in any one of Features 1 to 3.

[0110] (Feature 5) The control system for industrial equipment according to any one of Features 1 to 4, wherein the flexible external gear has a cylindrical body portion (gear main portion 71) on which the external teeth are formed on its outer circumferential surface, and an annular flange portion (flange portion 72) formed at one end of the body portion, and the plurality of strain gauges are attached to the flange portion and arranged on the same virtual circle (virtual circle FC) centered on the rotation center.

[0111] (Feature 6) The control system for industrial equipment according to any one of Features 1 to 5, wherein the strain gauges include a first strain gauge (strain gauge 91A), a second strain gauge (strain gauge 91B), and a third strain gauge (strain gauge 91C), and the spacing between the first strain gauge and the second strain gauge in the circumferential direction is equal to the spacing between the second strain gauge and the third strain gauge in the circumferential direction.

[0112] When estimating the rotation angle using the method described in Feature 1, etc., it is preferable to suppress bias in the relative magnitudes of the output signals. As shown in this feature, in a configuration that includes first to third strain gauges, it is advantageous in suppressing the above-mentioned bias if the distance between the first strain gauge and the second strain gauge in the circumferential direction is equal to the distance between the second strain gauge and the third strain gauge in the circumferential direction.

[0113] The above feature may be modified as follows: The strain gauge includes a first strain gauge (strain gauge 91A), a second strain gauge (strain gauge 91B), and a third strain gauge (strain gauge 91C), and the industrial equipment control system according to any one of Feature 1 to Feature 5, wherein the distance between the first strain gauge and the second strain gauge in the circumferential direction is equal to the distance between the second strain gauge and the third strain gauge in the circumferential direction and the distance between the third strain gauge and the first strain gauge in the circumferential direction.

[0114] (Feature 7) The number of strain gauges is three or more, and the strain gauges are arranged at equal intervals in the circumferential direction. This is the control system for industrial equipment according to any one of Features 1 to 6.

[0115] When estimating the rotation angle using the method described in Feature 1, it is preferable to suppress bias in the relative magnitudes of the output signals. As shown in this feature, in a configuration in which three or more strain gauges are used in combination, arranging the strain gauges at equal intervals in the circumferential direction is advantageous in suppressing the above-mentioned bias.

[0116] Furthermore, by combining this with the configuration shown in Feature 3, it is possible to suitably avoid increasing the number of strain gauges that do not contribute to improving estimation accuracy.

[0117] (Feature 8) The control system for industrial equipment according to any one of Feature 1 to Feature 7, wherein the estimation unit stores a correspondence between a combination of an output signal of a predetermined rank (e.g., the first, i.e., the largest) and an output signal of a specific rank (e.g., the second, i.e., the smallest) in the order of magnitude of the output signals from the plurality of strain gauges, and the rotation angle of the wave generator.

[0118] (Feature 9) The control system for industrial equipment according to Feature 8, wherein the predetermined order is the order in which the output signals from the plurality of strain gauges are the largest, and the specific order is the order in which the output signals from the plurality of strain gauges are the smallest.

[0119] (Feature 10) The plurality of strain gauges include a first strain gauge (strain gauge 91A) that outputs a first output signal (signal A), a second strain gauge (strain gauge 91B) that outputs a second output signal (signal B), and a third strain gauge (strain gauge 91C) that outputs a third output signal (signal C), and the estimation unit estimates the rotation angle of the wave generator to be a first rotation angle (first angle: 0° / 180°) when the first output signal is greater than the third output signal and the second output signal is greater than the first output signal, and estimates the rotation angle of the wave generator to be a second rotation angle (second angle: 30° / 210°) when the second output signal is greater than the third output signal and the first output signal is greater than the second output signal, A control system for industrial equipment according to any one of features 1 to 9, wherein the rotation angle of the wave generator is estimated to be the third rotation angle (third angle: 60° / 240°) when the third output signal is greater than the second output signal and the first output signal is greater than the third output signal; the rotation angle of the wave generator is estimated to be the fourth rotation angle (fourth angle: 90° / 270°) when the first output signal is greater than the second output signal and the third output signal is greater than the first output signal; the rotation angle of the wave generator is estimated to be the fifth rotation angle (fifth angle: 120° / 300°) when the second output signal is greater than the first output signal and the third output signal is greater than the second output signal; and the rotation angle of the wave generator is estimated to be the sixth rotation angle (sixth angle: 150° / 330°) when the third output signal is greater than the first output signal and the second output signal is greater than the third output signal.

[0120] According to the configuration shown in this feature, the configuration shown in Feature 1, etc., can be suitably realized using three strain gauges.

[0121] (Feature 11) A wave drive gear device (wave drive gear device 35) having an annular rigid internal gear (rigid internal gear 60) with internal teeth (internal teeth 61) formed on its inner circumferential surface, a flexible external gear (flexible external gear 70) disposed inside the rigid internal gear and having external teeth (external teeth 73) that can mesh with the internal teeth, and a wave generator (wave generator 80) provided inside the flexible external gear which partially meshes the external teeth with the internal teeth by bending the flexible external gear radially and moves the meshing position between the rigid internal gear and the flexible external gear in the circumferential direction, and a drive unit (servo motor 31) that rotates the wave generator in the circumferential direction, The industrial equipment (robot 15) is equipped with a detection device (e.g., a rotation angle detection sensor 36Y) that detects the rotation angle of the wave generator and the torque generated in the wave gear device based on output signals from strain gauges (strain gauges 91 and 92) attached to the flexible external gear, and the industrial equipment control system (control system 40) controls the industrial equipment (e.g., drive control, stop control) based on the rotation angle and torque detected by the detection device, wherein the strain gauges attached to the flexible external gear include a plurality (e.g., three) of first-type strain gauges (first strain gauges 91) and a plurality (e.g., three) of second-type strain gauges (second strain gauges 92), the plurality of first-type strain gauges and the plurality of second-type strain gauges are arranged to surround the rotation center (central axis CL) of the flexible external gear, and the industrial equipment control system is A combining unit (combining unit 96d of detectors 96, 97) generates a first signal by combining the output signals from the plurality of first-type strain gauges, and generates a second signal by combining the output signals from the plurality of second-type strain gauges.A control system for industrial equipment comprising: 97d) a comparison unit (comparison function in the robot controller 42) for comparing the first signal and the second signal, and if the comparison result by the comparison unit corresponds to the absence of an abnormality, the system detects the torque generated in the wave drive gear based on the first signal, controls the industrial equipment according to the detected torque, identifies the magnitude relationship of the output signals from the plurality of first-type strain gauges or the magnitude relationship of the output signals from the plurality of second-type strain gauges, and estimates the rotation angle of the wave generator from the identified magnitude relationship; and an estimation unit (angle detection unit 96c).

[0122] (Feature 12) The control system for industrial equipment according to Feature 11, wherein the number of first-type strain gauges and second-type strain gauges are the same, and the first-type strain gauges and second-type strain gauges are arranged alternately in the circumferential direction.

[0123] To suppress rotational ripple that occurs over long periods, it is preferable to arrange strain gauges in a balanced manner around the rotation center. On the other hand, as mentioned above, to clarify the relative magnitudes of the output signals, it is preferable to introduce a certain phase difference between the output signals. For this reason, as shown in this feature, first-type strain gauges and second-type strain gauges are arranged alternately in the circumferential direction. This is advantageous in suppressing rotational ripple during torque detection while clarifying the relative magnitudes of the output signals.

[0124] (Feature 13) A wave drive gear device (wave drive gear device 35) having an annular rigid internal gear (rigid internal gear 60) with internal teeth (internal teeth 61) formed on its inner circumferential surface, a flexible external gear (flexible external gear 70) disposed inside the rigid internal gear and having external teeth (external teeth 73) that can mesh with the internal teeth, and a wave generator (wave generator 80) provided inside the flexible external gear which partially meshes the external teeth with the internal teeth by flexing the flexible external gear radially and moves the meshing position between the rigid internal gear and the flexible external gear in the circumferential direction, and a drive unit (servo motor 31) that rotates the wave generator in the circumferential direction, is applied to an industrial machine (robot 15) having, A rotation angle estimation device comprising: a plurality of strain gauges (e.g., strain gauges 91A to 91C) attached to the flexible external gear and each having a different position in the circumferential direction; and an estimation unit (angle detection unit 96c) that identifies the magnitude relationship of the output signals from the plurality of strain gauges and estimates the rotation angle of the wave generator from the identified magnitude relationship.

[0125] (Feature 14) The rotation angle estimation device according to Feature 13, wherein the estimation unit pre-stores correlation information (correlation table) showing the correlation between the magnitude relationship of the output signals from the plurality of strain gauges and the rotation angle of the wave generator, and estimates the rotation angle of the wave generator based on the identified magnitude relationship and the correlation information.

Claims

1. A rotation angle estimation device provided in an industrial machine comprising a harmonic drive gear and a drive unit, wherein the harmonic drive gear comprises: an annular rigid internal gear having internal teeth formed on its inner circumferential surface; a flexible external gear disposed inside the rigid internal gear and having external teeth formed that can mesh with the internal teeth; a wave generator provided inside the flexible external gear and causing the flexible external gear to bend radially, thereby partially meshing the external teeth with the internal teeth and moving the meshing position between the rigid internal gear and the flexible external gear in the circumferential direction; the drive unit rotates the wave generator in the circumferential direction; and the rotation angle estimation device comprises: a plurality of strain gauges attached to the flexible external gear and each having a different position in the circumferential direction; and an estimation unit that identifies the magnitude relationship of the output signals from the plurality of strain gauges and estimates the rotation angle of the wave generator from the identified magnitude relationship.

2. The rotation angle estimation device according to claim 1, wherein the estimation unit pre-stores correlation information showing the correlation between the magnitude relationship of the output signals from the plurality of strain gauges and the rotation angle of the wave generator, and estimates the rotation angle of the wave generator based on the identified magnitude relationship and the correlation information.

3. The rotation angle estimation device according to claim 1 or claim 2, wherein the plurality of strain gauges include a first strain gauge and a second strain gauge, the first strain gauge and the second strain gauge are positioned such that an integer multiple of the angle between the first virtual half-line and the second virtual half-line does not coincide with the reference angle, the first virtual half-line is a half-line extending from the rotation center of the wave generator through the first strain gauge, the second virtual half-line is a half-line extending from the rotation center through the second strain gauge, and the reference angle is the angle obtained by dividing 360° by the number of lobes of the wave gear device.

4. The rotation angle estimation device according to claim 2, wherein the correlation information is a correspondence between a combination of the output signals of a first rank and the output signals of a second rank in the order of magnitude of the output signals from the plurality of strain gauges, and the rotation angle of the wave generator.

5. The plurality of strain gauges include a first strain gauge that outputs a first output signal, a second strain gauge that outputs a second output signal, and a third strain gauge that outputs a third output signal, and the estimation unit estimates the rotation angle of the wave generator as a first rotation angle when the first output signal is greater than the third output signal and the second output signal is greater than the first output signal, estimates the rotation angle of the wave generator as a second rotation angle when the second output signal is greater than the third output signal and the first output signal is greater than the second output signal, estimates the rotation angle of the wave generator as a third rotation angle when the third output signal is greater than the second output signal and the first output signal is greater than the third output signal, and estimates the rotation angle of the wave generator as a fourth rotation angle when the first output signal is greater than the second output signal and the third output signal is greater than the first output signal. A rotation angle estimation device according to claim 1 or 2, wherein the rotation angle of the wave generator is estimated to be the fifth rotation angle when the second output signal is greater than the first output signal and the third output signal is greater than the second output signal, and the rotation angle of the wave generator is estimated to be the sixth rotation angle when the third output signal is greater than the first output signal and the second output signal is greater than the third output signal.

6. An industrial equipment control system applicable to the industrial equipment comprising the rotation angle estimation device described in claim 1, wherein the industrial equipment is controlled based on the rotation angle estimated by the rotation angle estimation device.

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