Abnormality detection device for detecting abnormality of power transmission mechanism that transmits rotational force of motor output

Abstract

An abnormality detection device includes a first encoder for detecting a rotation angle of an input shaft of a speed reducer, and a second encoder for detecting a rotation angle of an output shaft of the speed reducer. An operation control section controls a servo motor in such a manner that a position acquired from an output of the second encoder corresponds to a position decided in an operation program. A detection section calculates an angle difference which is a difference between a rotation angle acquired from an output of the first encoder and a rotation angle acquired from an output of the second encoder. The detection section determines whether the speed reducer is abnormal based on the angle difference.

Description

Technical Field

[0001] This invention relates to an anomaly detection device for detecting anomalies in a power transmission mechanism that transmits the rotational force output by an electric motor. Background Technology

[0002] The rotational force output from the electric motor is transmitted to other components via a power transmission mechanism. For example, a speed reducer is known as a mechanism that amplifies the rotational force output from the electric motor and transmits it to other components.

[0003] When power transmission mechanisms such as speed reducers are used for a long time, the internal components deteriorate and fail. In the prior art, there is a known technique that detects abnormalities in the power transmission mechanism by analyzing the sensor installed in the mechanical part for detecting faults or by analyzing the command value output by the control device for driving the motor (e.g., Japanese Patent Application Publication No. 63-145507, Japanese Patent Application Publication No. 2013-152166, and Japanese Patent Application Publication No. 2006-102889).

[0004] Furthermore, in the prior art, a control method is known in which the rotation angle is obtained from an encoder mounted on the motor, and the skipping of gears arranged inside the reducer is detected based on the rotation angle (e.g., Japanese Patent Application Laid-Open No. 2020-104177 and International Patent Application Laid-Open No. 2014 / 098008). Additionally, as a method of using an encoder mounted on the motor, a control method is known in which the encoder is arranged on the output shaft of the reducer to correct positional deviations caused by torsion occurring in the reducer (e.g., Japanese Patent Application Laid-Open No. 2012-171069).

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 63-145507

[0008] Patent Document 2: Japanese Patent Application Publication No. 2013-152166

[0009] Patent Document 3: Japanese Patent Application Publication No. 2006-102889

[0010] Patent Document 4: Japanese Patent Application Publication No. 2020-104177

[0011] Patent Document 5: International Publication No. 2014 / 098008

[0012] Patent Document 6: Japanese Patent Application Publication No. 2012-171069 Summary of the Invention

[0013] The problem the invention aims to solve

[0014] Electric motors and power transmission mechanisms are incorporated into most machines. For example, in multi-joint robots, a mechanism is known that uses speed reducers at each joint to slow down the rotational force output by the electric motor, thereby rotating components such as the arm.

[0015] The internal components of a power transmission mechanism are driven in a state of mutual contact. Sometimes, these internal components wear down. As a result, the clearance between the internal components increases. For example, the backlash between gears increases due to gear wear. When the wear of the internal components intensifies, the power transmission device malfunctions and becomes unusable.

[0016] Machinery is sometimes used in production lines for manufacturing products. In such cases, a sudden malfunction of the machinery can have a significant impact on the production line using it. Alternatively, in the case of motors and power transmission mechanisms used in conveyors, a failure of the conveyor can prevent the desired conveying from occurring. Preferably, the machinery equipped with motors and power transmission mechanisms should not fail unexpectedly. Preferably, any abnormalities in the power transmission mechanism can be detected before a failure such as the machinery becoming unusable occurs.

[0017] Solution for solving the problem

[0018] The first aspect of this disclosure discloses an anomaly detection device for detecting anomalies in a power transmission mechanism that transmits the rotational force output by an electric motor. The anomaly detection device includes: a first rotary position detector for detecting the rotation angle of the input shaft of the power transmission mechanism; a second rotary position detector for detecting the rotation angle of the output shaft of the power transmission mechanism; and an operation control unit for controlling the operation of the electric motor. The anomaly detection device further includes a detection unit that detects anomalies in the power transmission mechanism based on the outputs of the first and second rotary position detectors. The operation control unit controls the electric motor in a manner that corresponds the position obtained based on the output of the second rotary position detector to a position determined in an operation program. The detection unit includes a variable setting unit that sets a variable including an angle difference based on the outputs of the first and second rotary position detectors and the reduction ratio of the power transmission mechanism. This angle difference is the difference between the rotation angle obtained based on the output of the first and second rotary position detectors. The detection unit also includes a determination unit that determines whether the power transmission mechanism is abnormal based on the variable.

[0019] The second aspect of the present disclosure discloses an anomaly detection device for detecting anomalies in a power transmission mechanism that transmits the rotational force output by an electric motor. The anomaly detection device includes: a first rotary position detector for detecting the rotation angle of the input shaft of the power transmission mechanism; a second rotary position detector for detecting the rotation angle of the output shaft of the power transmission mechanism; and an operation control unit for controlling the operation of the electric motor. The anomaly detection device further includes a detection unit that detects anomalies in the power transmission mechanism based on the output of the first rotary position detector. The operation control unit controls the electric motor in a manner that corresponds the position obtained based on the output of the second rotary position detector to a position determined in an operation program. The detection unit includes a variable setting unit that sets a variable that includes the rotation angle obtained based on the output of the first rotary position detector but not the rotation angle obtained based on the output of the second rotary position detector. The detection unit also includes a determination unit that determines whether the power transmission mechanism is abnormal based on the variable.

[0020] The effects of the invention

[0021] According to the present disclosure, an anomaly detection device can be provided for detecting anomalies in a power transmission mechanism with high precision. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the robot in the implementation method.

[0023] Figure 2 This is a block diagram of the robot device in the implementation method.

[0024] Figure 3 This is a partially enlarged cross-sectional view of the joint of the robot in the embodiment.

[0025] Figure 4 It is a graph showing the operating modes of a servo motor.

[0026] Figure 5 It is a graph of the rotation angle based on the encoder output when the speed reducer is new.

[0027] Figure 6 It is a graph of the rotation angle based on the encoder output when the wear of the gears in the reducer intensifies.

[0028] Figure 7 yes Figure 6 An enlarged view of part A in the image.

[0029] Figure 8 This is a first enlarged cross-sectional view of the contact area between the teeth of the two gears.

[0030] Figure 9 This is a second enlarged cross-sectional view of the contact area between the teeth of the two gears.

[0031] Figure 10 It is the first curve of the variable used to determine the abnormality of the reducer, corresponding to the number of times the robot device performs its operation.

[0032] Figure 11 This is the second graph of the variable corresponding to the number of times the robot device performs its tasks.

[0033] Figure 12 It is a graph showing the increase in the variable corresponding to the number of times the robot device performs its tasks.

[0034] Figure 13 It is a graph illustrating the control method for predicting periods of abnormality in a speed reducer based on changes in variables.

[0035] Figure 14 This is a graph showing other operating modes of the servo motor.

[0036] Figure 15 This is a side view of a robot illustrating the action used to calculate the proportional constant between the torque acting on the reducer and the torsional angle of the reducer.

[0037] Figure 16 This is a graph illustrating the control method for detecting anomalies based on the output of the first encoder.

[0038] Figure 17 yes Figure 16 An enlarged view of part B.

[0039] Figure 18 It is a graph showing the rotation angle of the initial state obtained from the output of the first encoder and the rotation angle after a long drive.

[0040] Figure 19 This is a side view illustrating the mechanism of other power transmission mechanisms in the implementation method. Detailed Implementation

[0041] Reference Figures 1 to 19 The following describes the anomaly detection device for detecting abnormalities in the power transmission mechanism according to the embodiment. The power transmission mechanism transmits the rotational force output by the electric motor to other components. Electric motors and power transmission mechanisms are used in various machines, such as machines for conveying objects, machines for moving objects, or machines for manufacturing objects. In this embodiment, a robot will be used as an example of a machine. Furthermore, a speed reducer configured in the joint of a robot will be used as an example of a power transmission mechanism.

[0042] Figure 1 This is a schematic diagram of the robot device in this embodiment. Figure 2 This is a block diagram of the robot device according to this embodiment. (Refer to...) Figure 1and Figure 2 The robot device 5 of this embodiment is used for transporting workpieces. The robot device 5 includes a hand 2 as a working tool for holding the workpiece and a robot 1 for moving the hand 2. The robot 1 of this embodiment is a multi-joint robot including multiple joints 18a, 18b, and 18c.

[0043] Robot 1 includes a base portion 14 fixed to a mounting surface and a rotating base 13 supported on the base portion 14. The rotating base 13 rotates relative to the base portion 14. Robot 1 includes an upper arm 11 and a lower arm 12. The lower arm 12 is supported on the rotating base 13 via a joint portion 18a. The upper arm 11 is supported on the lower arm 12 via a joint portion 18b. Robot 1 includes a wrist 15 connected to the end of the upper arm 11. The wrist 15 is supported on the upper arm 11 via a joint portion 18c. The wrist 15 includes a flange 16 for securing a hand 2.

[0044] Each component, such as the upper arm 11 and the lower arm 12, is configured to rotate around a predetermined drive axis. The robot 1 of this embodiment has six drive axes. The robot 1 includes a servo motor 27, which serves as an electric motor for driving each component, and a speed reducer 30. In this embodiment, a servo motor 27 and a speed reducer 30 are configured for each drive axis.

[0045] In this embodiment, the hand 2 includes a hand drive motor 21 for driving the hand 2. The hand drive motor 21 drives the claw portion of the hand 2 to open or close. Furthermore, the claw portion can also be configured to operate using pneumatic pressure. Additionally, any work tool can be mounted on the robot depending on the task being performed.

[0046] The robot device 5 includes a robot control unit 4 for controlling the robot 1 and the hand 2. The robot control unit 4 includes an arithmetic processing unit (computer) with a CPU (Central Processing Unit) as a processor. The arithmetic processing unit has RAM (Random Access Memory) and ROM (Read Only Memory) connected to the CPU via a bus. The robot control unit 4 is input with a pre-made motion program 41 for controlling the robot 1 and the hand 2. The robot 1 and the hand 2 are controlled based on the motion program 41.

[0047] The robot control device 4 includes a storage unit 42 for storing predetermined information. The storage unit 42 stores information related to the control of the robot 1 and the hand 2. The storage unit 42 can be constructed from a non-transitory recording medium capable of storing information, such as volatile memory, non-volatile memory, or a hard disk. The robot control device 4 includes a display 46 for displaying arbitrary information related to the robot device 5. The display 46 can be constructed from a display panel such as a liquid crystal display panel.

[0048] The robot control device 4 includes a motion control unit 43 that sends motion commands to the robot 1 and the hand 2. The motion control unit 43 controls the motion of the servo motor 27 and the hand drive motor 21. The motion control unit 43 is equivalent to a processor that drives the robot according to the motion program 41. The motion control unit 43 is configured to read information stored in the storage unit 42. The processor functions as the motion control unit 43 by reading the motion program 41 stored in the storage unit 42 and implementing the controls determined in the motion program 41.

[0049] The motion control unit 43 sends motion commands to the robot drive unit 45 for driving the robot 1 based on the motion program 41. The robot drive unit 45 includes circuitry for driving the servo motor 27. The robot drive unit 45 supplies power to the servo motor 27 based on the motion commands. Additionally, the motion control unit 43 sends motion commands to the hand drive unit 44 for driving the hand 2 based on the motion program 41. The hand drive unit 44 includes circuitry for driving the hand drive motor 21. The hand drive unit 44 supplies power to the hand drive motor 21 based on the motion commands.

[0050] In the robot device 5 of this embodiment, a reducer 30, serving as a power transmission mechanism, is disposed at the joint of the robot 1. The robot device 5 includes an anomaly detection device for detecting anomalies in the reducer 30. The anomaly detection device of this embodiment includes: a robot control device 4; a first encoder 23 serving as a first rotational position detector for detecting the rotation angle of the output shaft of the servo motor 27; and a second encoder 24 serving as a second rotational position detector for detecting the rotation angle of the output shaft of the reducer 30. In this embodiment, the rotation angle of the output shaft of the servo motor 27 corresponds to the rotation angle of the input shaft of the reducer 30.

[0051] The robot control device 4 includes a detection unit 51 that detects abnormalities in the reducer 30 based on the outputs of the first encoder 23 and the second encoder 24. The detection unit 51 includes a status acquisition unit 52 that acquires the robot's motion status. The detection unit 51 includes a variable setting unit 53 that sets variables used to determine if the reducer 30 is abnormal. The detection unit 51 includes a determination unit 54 that determines whether the reducer 30 is abnormal based on the variables. The detection unit 51 includes an estimation unit 55 that estimates the number of operations or drive time at which future abnormalities may occur. The detection unit 51 includes a torsion angle calculation unit 56 that calculates the torsion angle between the input and output shafts of the reducer 30 based on the torque applied to the reducer 30.

[0052] The detection unit 51 described above is equivalent to a processor that operates according to the action program 41. Furthermore, each unit within the detection unit 51—including the state acquisition unit 52, variable setting unit 53, determination unit 54, estimation unit 55, and torsion angle calculation unit 56—operates as a processor that operates according to the action program 41. Each unit functions by reading the action program 41 into the processor and implementing the controls determined within the action program 41.

[0053] In this embodiment, the servo motor 27, which serves as an electric motor, and the reducer 30, which serves as a power transmission mechanism, are described in the joint 18a, which is located between the rotating base 13 and the lower arm 12 in the plurality of joints 18a, 18b, and 18c.

[0054] Figure 3 This is a partially enlarged cross-sectional view of the joint between the rotating base and the lower arm. The lower arm 12 rotates relative to the rotating base 13 via the joint 18a of this embodiment. The joint 18a is equipped with a servo motor 27 that drives the lower arm 12 relative to the rotating base 13, and a speed reducer 30 for increasing the output torque of the servo motor 27.

[0055] The servo motor 27 is fixed to the slewing base 13 by bolts 29. The servo motor 27 includes an output shaft 28 protruding toward the reducer 30 for outputting rotational force. The reducer 30 includes an input shaft 32 into which the rotational force is input to the output shaft 28 of the servo motor 27.

[0056] The speed reducer 30 increases the rotational torque by reducing the rotational speed of its input shaft 32. The speed reducer 30 includes multiple gears for transmitting the rotational force of the input shaft 32 and an output shaft 33 supporting the gears. The speed reducer 30 includes a speed reducer housing 31 formed to surround the output shaft 33. The speed reducer housing 31 is cylindrical. The input shaft 32 is rotatably supported on the output shaft 33. The output shaft 33 is supported on the speed reducer housing 31 in a manner that allows relative rotation with respect to the speed reducer housing 31.

[0057] The reducer housing 31 is fixed to the slewing base 13 by bolts 37. Additionally, the output shaft 33 of the reducer 30 is fixed to the lower arm 12 by bolts 36. The input shaft 32 of the reducer 30 is connected to the output shaft 28 of the servo motor 27. The output shaft 28 and the input shaft 32 rotate about the rotation axis RA. The rotation axis RA is the rotation axis of the joint 18a.

[0058] In this example of the reducer 30, the reducer housing 31 is stationary. When the input shaft 32 rotates, the output shaft 33 rotates relative to the reducer housing 31 through the transmission of rotational force via the gears. The lower arm 12 rotates together with the output shaft 33. For example, an eccentric oscillating planetary gear reducer can be used as such a reducer 30. Furthermore, the reducer is not limited to this method; any reducer with an arbitrary mechanism that allows for variation of rotational force can be used.

[0059] Reference Figure 2 and Figure 3 A first encoder 23 is installed on the servo motor 27 to detect the rotational position of the output shaft 28 of the servo motor 27. The rotational position of the output shaft 28 of the servo motor 27 corresponds to the rotational position of the input shaft 32 of the reducer 30. That is, the first encoder 23 is configured to detect the rotational position of the input shaft 32 of the reducer 30.

[0060] In the robot device 5 of this embodiment, in addition to the first encoder 23, a second encoder 24 is also provided for detecting the rotational position of the output shaft 33 of the reducer 30. The second encoder 24 has a scale 24a and a detection part 24b arranged facing the scale 24a. The scale 24a is fixed to the surface of the lower arm 12. The scale 24a has a shape that extends circumferentially around the rotation axis RA.

[0061] The detection unit 24b is supported on the rotating base 13 via the support member 25. In the second encoder 24, a magnetic ring can be used as the scale 24a, and a magnetic sensor can be used as the detection unit 24b. For example, on the surface of the scale 24a facing the detection unit 24b, S poles and N poles can be magnetized at a certain interval so that changes in magnetic flux can be detected by the detection unit 24b. As a second encoder, it is not limited to this method, and an optical encoder can also be used.

[0062] Furthermore, in the second encoder 24 of this embodiment, the scale 24a is mounted on the surface of the lower arm 12, but this is not a limitation. The second encoder can be configured at any position to detect the rotational position of the reducer's output shaft. For example, the scale can also be mounted on the reducer's output shaft. Moreover, the first and second encoders can be either incremental or absolute encoders.

[0063] In this embodiment, the motion control unit 43 controls the rotational position of the servo motor 27 to control the position of the robot 1. The position of the robot 1 is, for example, the position of the tool tip of the working tool. The position of the tool tip is determined by the position and posture of the rotary base 13, the lower arm 12, the upper arm 11, and the wrist 15.

[0064] Generally, the control of the rotational position of the servo motor 27 is based on the rotational position output from the first encoder 23. However, in a reducer, there are gaps between the internal components (such as gear backlash). Furthermore, the components of the reducer are subjected to forces generated during drive, causing deformation or strain. As a result, torsion sometimes occurs between the input and output shafts of the reducer. Therefore, the rotational position of the output shaft 33 of the reducer 30 sometimes deviates from the rotational position of the output shaft 28 of the servo motor 27. In this embodiment, a second encoder 24 is provided for detecting the rotational position of the output shaft 33 of the reducer 30 in order to accurately detect the position of the robot 1.

[0065] Reference Figure 2 In this embodiment, the motion control unit 43 controls the position and posture of the robot 1 based on the rotational position output from the second encoder 24. The motion control unit 43 generates position commands for the servo motor 27 based on the motion program 41. At this time, the motion control unit 43 obtains the rotational position from the second encoder 24. The motion control unit 43 generates position commands in a manner that corresponds the rotational position output from the second encoder 24 to the position determined in the motion program 41. In this way, position feedback control can be performed.

[0066] Furthermore, the motion control unit 43 generates a speed command based on the position command. For the speed command, the motion control unit 43 also calculates the rotational speed based on the rotational position output from the second encoder 24. The motion control unit 43 generates the speed command in a manner that corresponds the actual rotational speed to the rotational speed based on the motion program 41. In this way, speed feedback control is possible.

[0067] By controlling the position and posture of robot 1 based on the output of the second encoder 24 used to detect the rotational position of the output shaft 33 of reducer 30, the accuracy of robot 1's position and posture is improved. Furthermore, the accuracy of the movement path of robot 1 is improved.

[0068] The detection unit 51 of the anomaly detection device determines anomalies in components housed inside the reducer 30. In particular, the detection unit 51 detects anomalies caused by component wear. Gears housed inside the reducer 30 wear due to the operation of the robot 1. Additionally, bearings housed inside the reducer 30 sometimes wear. For example, in the case where rolling bearings are installed in the reducer, the rolling elements or bearing races of the rolling bearings sometimes wear due to the robot's movement.

[0069] Due to wear and tear on components, the gaps between components increase. For example, when gears wear out, tooth skipping or other abnormalities can occur, causing the reducer to malfunction. Alternatively, when components wear out significantly, it may become impossible to accurately control the position and posture of the robot 1. The detection unit 51 of this embodiment detects abnormalities such as increased gaps between components that occur before a major abnormality like tooth skipping occurs.

[0070] exist Figure 4 The diagram illustrates one operating mode of the servo motor in this embodiment. Robotic device 5 repeatedly performs the task of conveying workpieces. Robot 1 changes position and posture in various modes. Figure 4 The diagram shows the action of the servo motor 27 corresponding to one action of the robot 1. After starting at time ts, the servo motor 27 reaches a predetermined rotational speed. The servo motor 27 continues to operate at a constant rotational speed and then stops at time te. This operating mode of the servo motor 27 is pre-selected to detect abnormalities in the reducer 30.

[0071] Figure 5 The middle shows Figure 4 The diagram shows a graph of the rotation angle based on the encoder output when the servo motor is driven in the operating mode shown. The action begins at time ts and ends at time te. The rotation angle represents the amount of rotation achieved by the motor. For example, when the output shaft rotates one revolution, the rotation angle is 360°. As time progresses, the rotation angle obtained from the output of each encoder increases as shown by arrow 92.

[0072] exist Figure 5The diagram shows the rotation angle based on the output of the first encoder 23 and the rotation angle based on the output of the second encoder 24 during one motion of the robot. Here, the rotation angle of the input shaft 32 of the reducer 30 is calculated based on the rotational position output from the first encoder 23. Then, the rotation angle of the input shaft 32 is divided by the reduction ratio of the reducer 30. Then, it is compared with the rotation angle based on the rotational position output from the second encoder 24. Alternatively, the rotation angle based on the output of the second encoder can be multiplied by the reduction ratio and compared with the rotation angle based on the output of the first encoder.

[0073] In the first anomaly detection control of this embodiment, whether the reducer 30 is abnormal is determined based on the output of the first encoder 23 and the output of the second encoder 24. (Refer to...) Figure 2 During the period when the servo motor 27 is driven, the status acquisition unit 52 of the detection unit 51 detects the rotational position output from the first encoder 23 and the rotational position output from the second encoder 24. The status acquisition unit 52 stores the acquired rotational positions of each encoder in the storage unit 42.

[0074] exist Figure 5 The diagram shows the rotation angle of the reducer 30 when it is operating normally. Here, the rotation angle is shown in the initial state when the reducer 30 is new. There is almost no clearance between the components of the reducer 30. Therefore, if there is almost no torsion between the input and output shafts of the reducer 30, the rotation angle obtained from the output of the first encoder 23 is approximately the same as the rotation angle obtained from the output of the second encoder 24. In this embodiment, the difference between the rotation angle obtained from the output of the first encoder 23 and the rotation angle obtained from the output of the second encoder 24 is called the angle difference. For example, the angle difference is equivalent to the value (θ1-θ2) obtained by subtracting the rotation angle θ2 obtained from the output of the second encoder 24 from the rotation angle θ1 obtained from the output of the first encoder 23. Figure 5 In the meantime, there is a small angle difference Δθ12i in the rotation angle.

[0075] exist Figure 6 The graph shows the rotation angle based on the encoder output as wear of the reducer components accelerates. Figure 7 The middle shows Figure 6 An enlarged view of part A. Figure 7 This is a graph showing the curve around the moment ts when the rotation angle is first measured. (Refer to...) Figure 6 and Figure 7 In this embodiment, the rotational position (phase) output from the second encoder 24 relative to the rotational position (phase) output from the first encoder 23 when there is no wear on the components is determined in advance. Therefore, it is possible to calculate the change in the angle difference during the period from the moment ts when the servo motor 27 is rotated to the moment te when wear intensifies.

[0076] Furthermore, in this embodiment, the position of robot 1 is controlled based on the output of the second encoder 24. Figures 5 to 7 In the curve diagram, at the moment when the robot 1 begins to perform the predetermined action, the rotation angle obtained from the output of the second encoder 24 is set to 0.

[0077] When the drive time of the reducer 30 increases, components such as gears or bearings experience wear. As a result, the difference between the rotation angle obtained from the output of the first encoder 23 and the rotation angle obtained from the output of the second encoder 24 increases. That is, the absolute value of the angle difference increases. Figure 6 and Figure 7 In this process, an angle difference Δθ12 is generated based on the rotation angle θ1 obtained from the output of the first encoder 23 and the rotation angle θ2 obtained from the output of the second encoder 24. Here, when the angle difference Δθ12 is defined by (θ1-θ2), the angle difference Δθ12 may become a positive number or a negative number depending on the contact state of the gear teeth.

[0078] Figure 8 The image shows a first enlarged cross-sectional view of the tooth contact portion of the two gears. Figure 9 The image shows a second enlarged cross-sectional view of the tooth contact portion of the two gears. Figure 8 and Figure 9 These are schematic diagrams illustrating different contact states of the teeth of gears facing each other. Figure 8 and Figure 9 In the middle, the input side gear 71 rotates in the direction shown by arrow 98. Figure 8 The tooth surface of the input-side gear 71, shown, contacts the tooth surface of the output-side gear 72 on the side of the rotation direction. On the other hand, in... Figure 9 In this process, the teeth of the input-side gear 71 contact the teeth of the output-side gear 72 on the tooth surface opposite to the direction of rotation. The different contact states of these teeth are caused by gravity, the inertial force of the robot's movement, or other external forces.

[0079] In such Figure 8 When the teeth of the input-side gear 71, as shown, contact the teeth of the output-side gear 72 on one side of the rotation direction, the rotation angle θ1 becomes larger than the rotation angle θ2 in order to obtain the orientation of the lower arm 12 on the output side. As a result, the angle difference Δθ12 becomes a positive value. Furthermore, in the case of… Figure 9 When the tooth of the input-side gear 71, on the side opposite to the direction of rotation, contacts the tooth of the output-side gear 72, the rotation angle θ1 becomes smaller than the rotation angle θ2. As a result, the angle difference Δθ12 becomes negative.

[0080] Furthermore, the angle difference is not limited to the value (θ1-θ2) obtained by subtracting the rotation angle θ2 obtained from the output of the second encoder 24 from the rotation angle θ1 obtained from the output of the first encoder 23; the value (θ2-θ1) obtained by subtracting the rotation angle θ1 from the rotation angle θ2 can also be used. Alternatively, the absolute value of the value obtained by subtracting the rotation angle of one of the rotation angles obtained from the output of the first encoder 23 and the rotation angle obtained from the output of the second encoder 24 can also be used. In this embodiment, for the angle difference Δθ12 being (θ1-θ2) and the gear as Figure 8 The example shown illustrates the contact as depicted.

[0081] In the first anomaly detection control, anomalies in the reducer 30 are detected based on a variable including the angle difference. In this embodiment, the variable is an evaluation variable used to assess whether the reducer 30 is abnormal. The variable setting unit 53 calculates the angle difference Δθ12 as the first variable. The variable setting unit 53 divides the rotation angle obtained from the output of the first encoder 23 by the reduction ratio of the reducer 30. The variable setting unit 53 calculates the angle difference Δθ12 obtained by subtracting the rotation angle obtained from the output of the second encoder 24 from this rotation angle. Next, the determination unit 54 determines whether an anomaly has occurred in the reducer 30.

[0082] The variable setting unit 53 can use the maximum value of the angle difference Δθ12 during the period from time ts to time te as the angle difference Δθ12 used when judging an anomaly. Alternatively, multiple times can be set and the average value of the variable at multiple times can be used. In addition, the angle difference Δθ12 can be converted to an absolute value before calculating the maximum or average value. In this way, the variable used when judging an anomaly can adopt the maximum or average value when the servo motor 27 is in its operating mode.

[0083] exist Figure 10 The graph shows the variable corresponding to the number of times the robot's actions were performed. The horizontal axis represents the number of times the predetermined robot 1's actions were performed. For example, the horizontal axis corresponds to the number of times the servo motor 27 performed its actions. Figure 4 The horizontal axis represents the number of predetermined actions. Additionally, the horizontal axis can also represent the drive time for robot 1 to execute the predetermined actions. The vertical axis is a variable used to determine whether an anomaly has occurred in the reducer 30.

[0084] In the first determination control of this embodiment, when the variable VX deviates from the predetermined determination range, it is determined that the reducer 30 is abnormal. As the number of executions increases, the variable VX gradually increases. Figure 10In the example shown, after N execution cycles, the variable VX exceeds a predetermined determination value. When the variable VX exceeds the determination value, the determination unit 54 determines that an anomaly has occurred. Here, the determination unit 54 determines that an anomaly has occurred when the N execution cycles have ended. For example, it can determine that the reducer 30 is malfunctioning when the angle difference Δθ12, which is the first variable, exceeds the determination value. Alternatively, the determination unit 54 can determine that gear wear is accelerating.

[0085] exist Figure 11 Other graphs showing the variables corresponding to the number of times the robot's actions are performed are also shown. In the second determination control of this embodiment, when the rate of change of variable VX relative to the number of times the task is performed deviates from a predetermined determination range, the determination unit 54 determines that the reducer 30 is abnormal. In this example, the slope between variable VX when the number of executions (N-1) and variable VX when the number of executions N is calculated is shown.

[0086] If the slope of variable VX exceeds a predetermined judgment value, the judgment unit 54 determines that the reducer 30 is malfunctioning. That is, if the slope of straight line 80 exceeds the judgment value, the judgment unit 54 determines that the reducer 30 is malfunctioning. For example, if the rate of change of the angle difference Δθ12, which is the first variable, exceeds the judgment value, the reducer 30 is determined to be malfunctioning. The calculation of the rate of change is not limited to two variables; it can also be based on three or more variables.

[0087] Alternatively, the drive time for the robot 1 or servo motor 27 to perform a predetermined action can be used instead of the number of executions. In this case, the determination unit can determine that the reducer is malfunctioning when the rate of change of the variable relative to the drive time deviates from a predetermined determination range.

[0088] exist Figure 12 The graph shows the increase in the variable corresponding to the number of times the robot's actions are performed. In the third determination control of this embodiment, similar to the second determination control, the abnormality of the reducer is determined based on the rate of change of the variable relative to the number of times the task is performed or the drive time.

[0089] The determination unit 54 calculates the increase in variable VX based on the number of times a predetermined action is performed. Here, the increase in variable VX is calculated every 10,000 actions of robot 1. As the number of executions increases, the increase in variable VX increases. When the increase in variable VX deviates from a predetermined determination range, the determination unit 54 determines that the reducer is malfunctioning. For example, the determination unit 54 can determine that the reducer 30 is malfunctioning when the increase in angle difference Δθ12 exceeds a predetermined determination value every 10,000 executions. In this example, the determination unit 54 can determine that the reducer is malfunctioning when the number of executions reaches N. Furthermore, when calculating the rate of change of the variable relative to the drive time, the increase in variable can be calculated based on the length of a predetermined drive time.

[0090] Next, the estimation unit 55 of the detection unit 51 in this embodiment will be described. The estimation unit 55 performs estimation control, in which it estimates the number of times an abnormal operation will be performed or the driving time of an operation in the future based on the value of a variable corresponding to the number of times an operation will be performed or the driving time of an operation in the past.

[0091] exist Figure 13 The graph shows the variables corresponding to the number of times the robot's actions are performed. Figure 13 This is a graph illustrating the control of the number of times the estimation unit 55 estimates the operation will be performed if an anomaly occurs. As shown by arrow 93, the variable VX increases with the number of executions. The estimation unit 55 calculates an approximate line 81 representing the trend of the variable's change based on the value of the variable corresponding to the number of executions of past operations. For example, an approximate line related to the angle difference Δθ12, which is the first variable, can be calculated.

[0092] The estimation unit 55 can generate an approximate line representing the trend of change through arbitrary control. Figure 13 In the example shown, all past values ​​of the variable VX are used to generate an approximate line 81 using the least squares method. The approximate line is not limited to a straight line; it can also be a curve. Furthermore, when generating an approximate line, a predetermined number of variables can be selected.

[0093] The estimation unit 55 estimates the number of times an operation where the approximate line deviates from a predetermined judgment range will be executed as the number of times an operation will be executed in the future that will cause an anomaly. In this example, the number of times the approximate line 81 exceeds a predetermined judgment value is estimated as the number of times an anomaly will occur. Alternatively, the estimation unit 55 may use the driving time instead of the number of executions. That is, the estimation unit may also calculate an approximate line representing the trend of change of a variable corresponding to the driving time, and estimate the driving time when the approximate line deviates from the judgment range as the driving time when an anomaly will occur.

[0094] Reference Figure 2Information related to abnormalities detected by the detection unit 51 can be displayed on the display 46. The operator can check the abnormality-related information displayed on the display 46 to plan the maintenance or inspection of the reducer 30. As a result, sudden failure of the reducer 30 can be avoided.

[0095] Next, the variables used to determine the abnormality of the reducer 30 will be explained. The variable VX is not limited to the angle difference as the first variable; any variable that includes the angle difference can be used. (See reference...) Figure 5 and Figure 6 The variable setting unit 53 can calculate the difference (Δθ12-Δθ12i) between the angle difference Δθ12i of the reducer 30 when it is in normal operation and the current angle difference Δθ12 of the reducer 30 as the second variable VX. Alternatively, the variable setting unit 53 can calculate the ratio (Δθ12 / Δθ12i) between the predetermined angle difference of the reducer 30 when it is in normal operation and the current angle difference of the reducer 30 as the third variable VX. Here, the angle difference of the reducer 30 in its initial state when it is a new product is used as the predetermined angle difference of the reducer 30 when it is in normal operation. The variable setting unit 53 can calculate the angle difference of the reducer 30 when it is a new product and store it in the storage unit 42.

[0096] Furthermore, the variable setting unit 53 can calculate the value (Δθ12-Δθ12i) / Δθ12i) obtained by dividing the difference between the angle difference (Δθ12i) of the reducer 30 when it is in normal condition and the current angle difference (Δθ12) of the reducer 30 by the angle difference of the reducer 30 when it is in normal condition, as the fourth variable VX.

[0097] Regardless of which variable is used, it is possible to achieve this through... Figure 10 The first determination control of the value of the variable shown, based on Figure 11 The second judgment control of the rate of change of the variable shown, or based on Figure 12 The third determination control, which measures the increase in the variable, determines whether the reducer 30 is malfunctioning. Furthermore, the estimation unit 55, by performing the aforementioned estimation control using each variable, can estimate the period during which an malfunction might occur.

[0098] exist Figure 14 The diagram shows other operating modes of the servo motor used to determine whether a malfunction has occurred in the reducer. In these other operating modes, the servo motor 27 is temporarily stopped during the period from time ts to time te. In this example, the servo motor 27 stops at time th1 and starts at time th2. The variable setting unit 53 can also calculate variables based on the encoder output during the period when the servo motor 27 is stopped. For example, when calculating the angle difference Δθ12 as the first variable, the variable setting unit 53 can also calculate the angle difference Δθ12 during the period when the servo motor 27 is stopped.

[0099] Furthermore, regarding the second to fourth variables mentioned above, the variables include the angle difference of the reducer 30 when it is operating normally. For example, the second variable is the current angle difference of the reducer 30 minus the angle difference of the reducer 30 when it is operating normally. Therefore, the effect of torsion in the reducer 30 is eliminated. However, regarding the first variable, the variable does not include the angle difference of the reducer 30 when it is operating normally. When using the first variable to implement judgment control, the effect of torsion in the reducer 30 is included. Next, the control that eliminates the effect of torsion in the reducer 30 when using the first variable to determine the abnormality of the reducer 30 or when estimating the period when an abnormality will occur will be explained.

[0100] Reference Figure 2 The torsion angle calculation unit 56 of the detection unit 51 calculates the torsion angle between the input shaft 32 and the output shaft 33 based on the torque applied to the output shaft 33 of the reducer 30. The relationship between the torque T acting on the output shaft 33 of the reducer and the torsion angle θt in the reducer 30 can be expressed by the following formula using the proportionality constant k.

[0101] T=k×θt…(1)

[0102] According to equation (1) above, the torsion angle θt can be expressed by equation (2).

[0103] θt=T / k…(2)

[0104] The torque T can be calculated using pre-calculated inertia and the angular velocity of the servo motor 27 when driving the robot 1. Inertia can be calculated based on the weight and center of gravity of the robot 1's constituent components, as well as the weight and center of gravity of the workpiece. When the robot 1 stops, the torque T related to the weight of the constituent components used to maintain the position of the robot 1 can be calculated. Alternatively, the torque T can also be calculated using the current value of the servo motor 27. That is, the torque applied to the output shaft 28 of the servo motor 27 is calculated using the current value. The torque T can be calculated by multiplying the torque applied to the output shaft 28 by the reduction ratio.

[0105] Next, the calculation method of the proportional constant k will be explained. The relationship between the angle difference Δθ12 between the output of the first encoder 23 and the output of the second encoder 24 and the component BL of backlash such as tooth backlash caused by wear of the gears of the reducer 30 is expressed by the following equation (3).

[0106] Δθ12=θt+BL…(3)

[0107] Next, the operator actually drives robot 1. An action is set where the direction of the backlash does not change relative to the gears inside the reducer 30. The angle difference Δθ12 and torque T are calculated for multiple postures of robot 1 during this action.

[0108] exist Figure 15 The diagram shows a schematic representation of the robot's motion used to calculate the proportional constant between torque and torsion angle. Here, at joint 18a, the lower arm 12 is rotated as indicated by arrow 95. The robot 1 is stopped midway through this rotation. That is, the servo motor 27 disposed at joint 18a is temporarily stopped.

[0109] When the lower arm 12 rotates from the moving point MPa to the moving point MPb as shown by arrow 96, the robot 1 is stopped. The torque Ta and the angle difference Δθ12a are calculated at the moving point MPb. Further, as shown by arrow 97, the lower arm 12 is rotated from the moving point MPb to the moving point MPc, and the robot 1 is stopped. The torque Tb and the angle difference Δθ12b are calculated at the moving point MPc. At the two moving points MPb and MPc, the following equations (4) and (5) hold.

[0110] Δθ12a=Ta / k+BL…(4)

[0111] Δθ12b=Tb / k+BL…(5)

[0112] Here, the void component BL can be considered constant at the moving points MPb and MPc. Based on equations (4) and (5), the proportionality constant k can be obtained by equation (6) below.

[0113] k=(Ta-Tb) / (Δθ12a-Δθ12b)…(6)

[0114] The proportional constant k can be pre-calculated for each reducer using this method. The torsion angle calculation unit 56 can use the proportional constant k, the position and posture of the robot 1 obtained by the state acquisition unit 52, and the angular velocity of the servo motor 27 to calculate the torsion angle θt using equation (2).

[0115] The variable setting unit 53 can set the value (Δθ12-θt), obtained by subtracting the torsion angle θt from the angle difference Δθ12 based on the output of the first encoder 23 and the output of the second encoder 24, as a variable. The determination unit 54 can use the calculated variable to perform first determination control to third determination control. By using the variable obtained by subtracting the torsion angle from the angle difference as a variable for determining abnormalities, the influence of torsion in the reducer can be eliminated. Abnormalities in the reducer can be determined with high accuracy. Furthermore, the estimation unit 55 can use the calculated variable to estimate the period when an abnormality will occur. The estimation unit 55 can estimate the period when a failure will occur more accurately.

[0116] Next, the second anomaly detection control for detecting anomalies in the reducer 30 in this embodiment will be described. In the second anomaly detection control of this embodiment, an anomaly in the reducer 30 is determined using a variable that includes the rotation angle obtained from the output of the first encoder 23 but not the rotation angle obtained from the output of the second encoder 24. The first to third determination controls for determining anomalies in the reducer 30 are the same as the first anomaly detection control. Furthermore, the estimation control for estimating the time when an anomaly in the reducer 30 occurs is also the same as the control described above.

[0117] exist Figure 16 The graph shown illustrates the rotation angle corresponding to time for the second anomaly detection control in this embodiment. Figure 16 The diagram illustrates an example where servo motor 27 stops during the movement of robot 1. The vertical axis is the rotation angle based on the output of each encoder. Figure 17 The image shows an enlarged view of the curve near the moment when the rotation angle was first measured. Figure 17 yes Figure 16 An enlarged view of part B in the image. Figure 16 and Figure 17 The diagram records the rotation angle of the reducer 30 when it is in its initial state (when it is new) based on the output of the first encoder 23. It also records the rotation angle based on the output of the first encoder 23 when the reducer 30 is worn out due to prolonged operation.

[0118] Reference Figure 16 and Figure 17 In this embodiment, the rotational position of the servo motor 27 is controlled based on the rotational position output from the second encoder 24. Therefore, even if wear increases in the components of the reducer 30, the rotational angle θ2 based on the output of the second encoder 24 when the robot 1 performs a predetermined action remains substantially unchanged. Conversely, as wear increases in the components of the reducer 30, the rotational angle θ1 based on the output of the first encoder 23 gradually changes in a manner that the difference between it and the rotational angle θ2 based on the output of the second encoder 24 increases. Figure 16 and Figure 17 In the example shown, the rotation angle θ1 increases relative to the rotation angle θ2.

[0119] In the second anomaly detection control, an anomaly of the reducer 30 is determined based on the rotation angle θ1 obtained from the output of the first encoder 23. In this second anomaly detection control, the variable setting unit 53 sets a variable including the rotation angle θ1 obtained from the output of the first encoder 23. Then, the determination unit 54 determines whether the reducer 30 is abnormal based on the variable determined by the variable setting unit 53, through the aforementioned first determination control to third determination control.

[0120] The first variable in the second anomaly detection control is the rotation angle θ1, obtained by dividing the rotation angle acquired from the output of the first encoder 23 by the reduction ratio. The determination unit 54 determines the anomaly of the reducer 30 based on the rotation angle θ1. For example, in Figure 10 In the first judgment control shown, when the rotation angle θ1 exceeds the predetermined judgment value, it can be determined that the reducer 30 is abnormal.

[0121] As the second variable in the second anomaly detection control, the difference Δθ11 between the predetermined rotation angle θ1i obtained from the output of the first encoder 23 when the reducer 30 is operating normally and the current rotation angle θ1 obtained from the output of the first encoder 23 can be used. In this example, the difference Δθ11 is the value (θ1-θ1i) obtained by subtracting the rotation angle θ1i when the reducer 30 is operating normally from the current rotation angle θ1. The predetermined rotation angle based on the output of the first encoder 23 when the reducer 30 is operating normally can be the rotation angle based on the output of the first encoder 23 in the initial state when the reducer 30 is new. The determination unit 54 determines the anomaly of the reducer 30 based on the difference Δθ11 of the rotation angles. In this way, the change in the rotation angle obtained from the output of the first encoder 23 can also be used as a variable.

[0122] exist Figure 18 The graph shows the rotation angle based on the output of the first encoder. Figure 18 The rotation angle shown is the difference in rotational position (phase) output from the first encoder 23. In the second anomaly detection control, it is not necessary to divide the rotation angle by the reduction ratio to make a judgment based on the output of the first encoder 23. Figure 18 In the diagram, the rotation angle is not divided by the reduction ratio. The diagram shows the predetermined rotation angle θ1i' based on the output of the first encoder 23 when the reducer 30 is operating normally, and the rotation angle θ1' based on the output of the first encoder 23 when component wear intensifies.

[0123] In the second anomaly detection control, the variable setting unit 53 can set the rotation angle θ1' output from the first encoder 23 as a third variable. The determination unit 54 determines the anomaly of the reducer 30 based on the rotation angle θ1'. Alternatively, the variable setting unit 53 can set the difference (θ1'-θ1i') between the normal rotation angle θ1i' of the reducer 30 and the current rotation angle θ1' as the rotation angle difference Δθ11', and set it as a fourth variable. The determination unit 54 determines the anomaly of the reducer 30 based on the rotation angle difference Δθ11'. In this way, in the second anomaly detection control, anomaly determination can be performed without using the output from the second encoder.

[0124] Furthermore, in the second anomaly detection control, the difference between the normal rotation angle of the reducer 30 and the current rotation angle can be either positive or negative. Moreover, the difference between the normal rotation angle of the reducer 30 and the current rotation angle is not limited to the methods described above; it can also be the absolute value obtained by subtracting the current rotation angle from the normal rotation angle of the reducer 30, or by subtracting one rotation angle from the other.

[0125] This embodiment illustrates a device for detecting abnormalities in the speed reducer at the joint between the slewing base and the lower arm, but it is not limited to this method. The abnormality detection device of this embodiment can be applied to the detection of abnormalities in the speed reducer at any joint.

[0126] The anomaly detection device of this embodiment can detect anomalies in power transmission mechanisms such as speed reducers at an earlier stage. In particular, it can detect gaps caused by wear of components with high precision. Alternatively, it can detect anomalies caused by deformation of components. For example, it can determine a maintenance or inspection plan for the speed reducer before a failure such as tooth skipping occurs. In addition, it can determine a maintenance or inspection plan for the speed reducer before the accuracy of controlling the robot's position and posture deteriorates. Furthermore, when a second encoder is provided to control the position of the mechanical components with high precision, anomalies in the power transmission mechanism can be detected without additional sensors.

[0127] The anomaly detection device of this embodiment can be applied to any machine having an electric motor and a power transmission mechanism. The power transmission mechanism for transmitting the rotational force of the electric motor to other components is not limited to a speed reducer; any mechanism that transmits the rotational force of the electric motor can be used. For example, in addition to gear mechanisms, belt-driven mechanisms, mechanisms including universal joints, or linkage mechanisms can be used as the power transmission mechanism. Next, a power transmission mechanism including pulleys and belts will be described.

[0128] Figure 19 The diagram shows a schematic side view of the electric motor and other power transmission devices. Figure 19 In the example shown, a driven mechanism is used to supply rotational force to a specified part of the machine. The machine includes a servo motor 27 and a power transmission mechanism 59 for transmitting the rotational force of the servo motor 27. The servo motor 27 is fixed to the support portion 67 of the base 60.

[0129] The power transmission mechanism 59 includes an input shaft 63 connected to the output shaft 28 of the servo motor 27, and an output shaft 64 that transmits rotational force to other components. The input shaft 63 is supported by bearings 65 on the support portions 67 and 68 of the base 60. The output shaft 64 is supported by bearings 66 on the support portions 67 and 68 of the base 60.

[0130] A pulley 61 is mounted on the input shaft 63. A pulley 62 is mounted on the output shaft 64. A belt 69 engages with pulleys 61 and 62. Driven by a servo motor 27, the belt 69 moves in the direction indicated by arrow 94. The rotational force of the input shaft 63 is transmitted to the output shaft 64 via the belt 69. The rotational speed varies based on the sizes of pulleys 61 and 62.

[0131] To detect the rotation angle of the input shaft 63 of the power transmission mechanism 59, a first encoder 23 is installed on the servo motor 27. Additionally, to detect the rotation angle of the output shaft 64 of the power transmission mechanism 59, a second encoder 24 is installed on the output shaft 64.

[0132] In the power transmission mechanism 59, for example, the phase of the output shaft 64 may deviate from the phase of the input shaft 63 due to deterioration of the belt 69. For example, the rotation angle of the input shaft 63 may deviate from the rotation angle of the output shaft 64 due to deflection of the belt 69. Alternatively, bearings 65 and 66 may sometimes wear. For such a power transmission mechanism 59, the anomaly detection device can also detect the anomaly of the power transmission mechanism 59 by implementing the same control as the first and second anomaly detection controls described above. Furthermore, by implementing the estimation control described above, the period in which an anomaly will occur can be estimated.

[0133] The above-described embodiments can be appropriately combined. In the various figures above, the same or equivalent parts are labeled with the same reference numerals. Furthermore, the above-described embodiments are illustrative and do not limit the invention. Additionally, variations of the embodiments shown in the claims are included in the embodiments.

[0134] Explanation of reference numerals in the attached figures

[0135] 4: Robot control device; 23: First encoder; 24: Second encoder; 27: Servo motor; 28: Output shaft; 30: Reducer; 32: Input shaft; 33: Output shaft; 41: Action program; 43: Action control unit; 51: Detection unit; 53: Variable setting unit; 54: Judgment unit; 55: Estimation unit; 56: Torsion angle calculation unit; 59: Power transmission mechanism; 63: Input shaft; 64: Output shaft; 65, 66: Bearings; 81: Approximate line.

Claims

1. An anomaly detection device for detecting anomalies in a power transmission mechanism that transmits the rotational force output by an electric motor, the anomaly detection device comprising: The first rotary position detector is used to detect the rotation angle of the input shaft of the power transmission mechanism; The second rotary position detector is used to detect the rotation angle of the output shaft of the power transmission mechanism; The motion control unit controls the operation of the electric motor; and The detection unit detects abnormalities in the power transmission mechanism based on the outputs of the first and second rotary position detectors. in, The motion control unit controls the motor in such a way that the position obtained from the output of the second rotary position detector corresponds to the position determined in the motion program. The detection unit includes a variable setting unit and a determination unit. The variable setting unit sets a variable including an angle difference based on the outputs of the first rotary position detector, the second rotary position detector, and the reduction ratio of the power transmission mechanism. The angle difference is the difference between the rotation angle obtained from the output of the first rotary position detector and the rotation angle obtained from the output of the second rotary position detector. The determination unit determines whether the power transmission mechanism is abnormal based on the variable. The variable setting unit calculates the difference between the current angle difference of the power transmission mechanism and the predetermined angle difference when the power transmission mechanism is in normal operation, or the ratio of the current angle difference of the power transmission mechanism to the predetermined angle difference when the power transmission mechanism is in normal operation, as the variable.

2. The anomaly detection device according to claim 1, wherein, The detection unit includes a torsion angle calculation unit, which calculates the torsion angle between the input shaft and the output shaft based on the torque applied to the power transmission mechanism. The variable setting unit calculates the value obtained by subtracting the torsion angle from the angle difference as the variable.

3. An anomaly detection device for detecting anomalies in a power transmission mechanism that transmits the rotational force output by an electric motor, the anomaly detection device comprising: The first rotary position detector is used to detect the rotation angle of the input shaft of the power transmission mechanism; The second rotary position detector is used to detect the rotation angle of the output shaft of the power transmission mechanism; The motion control unit controls the operation of the electric motor; and The detection unit detects abnormalities in the power transmission mechanism based on the outputs of the first and second rotary position detectors. in, The motion control unit controls the motor in such a way that the position obtained from the output of the second rotary position detector corresponds to the position determined in the motion program. The detection unit includes a variable setting unit and a determination unit. The variable setting unit sets a variable including an angle difference based on the outputs of the first rotary position detector, the second rotary position detector, and the reduction ratio of the power transmission mechanism. The angle difference is the difference between the rotation angle obtained from the output of the first rotary position detector and the rotation angle obtained from the output of the second rotary position detector. The determination unit determines whether the power transmission mechanism is abnormal based on the variable. The variable setting unit calculates the value obtained by dividing the difference between the current angle difference of the power transmission mechanism and the predetermined angle difference when the power transmission mechanism is in normal operation by the predetermined angle difference when the power transmission mechanism is in normal operation, and uses the value as the variable.

4. The anomaly detection device according to claim 3, wherein, The detection unit includes a torsion angle calculation unit, which calculates the torsion angle between the input shaft and the output shaft based on the torque applied to the power transmission mechanism. The variable setting unit calculates the value obtained by subtracting the torsion angle from the angle difference as the variable.

5. An anomaly detection device for detecting anomalies in a power transmission mechanism that transmits the rotational force output by an electric motor, the anomaly detection device comprising: The first rotary position detector is used to detect the rotation angle of the input shaft of the power transmission mechanism; The second rotary position detector is used to detect the rotation angle of the output shaft of the power transmission mechanism; The motion control unit controls the operation of the electric motor; and The detection unit detects abnormalities in the power transmission mechanism based on the output of the first rotary position detector. in, The motion control unit controls the motor in such a way that the position obtained from the output of the second rotary position detector corresponds to the position determined in the motion program. The detection unit includes a variable setting unit and a determination unit. The variable setting unit sets a variable that includes the rotation angle obtained from the output of the first rotation position detector but not the rotation angle obtained from the output of the second rotation position detector. The determination unit determines whether the power transmission mechanism is abnormal based on the variable. The variable setting unit calculates the difference between the current rotation angle obtained from the output of the first rotation position detector and the predetermined rotation angle obtained from the output of the first rotation position detector when the power transmission mechanism is normal, as the variable.

6. The anomaly detection device according to claim 5, wherein, The variable setting unit calculates the rotation angle obtained by dividing the rotation angle obtained from the output of the first rotation position detector by the reduction ratio as the variable.

7. The anomaly detection device according to claim 5, wherein, The variable setting unit sets the rotation angle output from the first rotation position detector as the variable.

8. The anomaly detection device according to any one of claims 1 to 7, wherein, When the variable deviates from the predetermined judgment range, the judgment unit determines that the power transmission mechanism is abnormal.

9. The anomaly detection device according to any one of claims 1 to 7, wherein, When the rate of change of the variable relative to the number of times the operation is executed or the driving time deviates from the predetermined judgment range, the judgment unit determines that the power transmission mechanism is abnormal.

10. The anomaly detection device according to any one of claims 1 to 7, wherein, The detection unit includes an estimation unit that estimates the number of times or drive time of operations that are likely to cause future anomalies. The estimation unit calculates an approximate line representing the trend of the variable's change based on the value of the variable corresponding to the number of times the approximate line is executed or the driving time of the operation when it deviates from a predetermined judgment range, and estimates the number of times the operation is executed or the driving time of the operation that will cause an anomaly in the future.

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