JP2020138305A - Robot control method, control device, program, storage medium, robot system and manufacturing method - Google Patents

Abstract

To shorten a time required for diagnosis by enabling diagnosis of a state of a speed reducer disposed in a joint of a robot device by one inspection operation per joint, for example, irrespective of an individual difference of a robot or state of the joint.SOLUTION: A control method for controlling a robot including a joint part that includes a motor and a speed reducer includes: a drive step of driving a joint while successively changing a drive parameter containing a condition that the joint part resonates; and an acquisition step of acquiring a resonance amplitude of the joint in the middle of operation in the drive step.SELECTED DRAWING: Figure 6

Description

The present invention relates to a robot control device having joints and a control method.

Conventionally, various robot devices have been used in factories and the like, and in recent years, robot devices equipped with robot arms having joints for performing more complicated movements have become widespread.

For example, a multi-axis, articulated robot arm has a high degree of freedom of movement, so the robot arm may come into contact with surrounding structures, for example, other objects such as workpieces and tools, and the robot arm may be damaged during work. is there. In particular, the speed reducer provided in the joint portion is a delicate part and is known to be easily damaged.

If the speed reducer is damaged, the operation accuracy of the robot arm deteriorates, so that the desired operation cannot be performed and the robot stops abnormally. Therefore, in recent years, various abnormality detection techniques for the speed reducer of the robot arm have been proposed. One of them is a method focusing on the magnitude of vibration when a robot is made to perform a predetermined motion.

For example, in Patent Document 1, the actuator of the joint is maintained at the speed at which the robot resonates most for a certain period of time, and the vibration of the arm generated at that time is detected. A technique has been proposed in which vibration of an arm is detected using a torque fluctuation value calculated from a motor torque value, and an abnormality is determined by comparing the fluctuation width with a threshold value.

Japanese Unexamined Patent Publication No. 2006-281421

However, it is known that the driving speed of the joint in which the robot resonates most varies depending on the individual difference of the robot and the state of the joint. Therefore, when the method of Patent Document 1 is actually performed, it is necessary to drive at a constant speed a plurality of times while changing the speed little by little, and to search for the point where the resonance is the largest from among them, which takes time for inspection. There was a problem called.

In view of the above problems, an object of the present invention is to provide a robot diagnosis method and a robot diagnosis device capable of diagnosing the speed reducer state of an articulated robot in a short time.

In order to solve the above problems, in the present invention, the control method for controlling a robot having a joint portion including a motor and a speed reducer changes drive parameters including conditions for resonance of the joint portion over time. It is characterized by including a driving step of driving the joint while driving the joint, and an acquisition step of acquiring the resonance amplitude of the joint during operation in the driving step.

By using this configuration, it is possible to diagnose the reducer with, for example, one inspection operation per joint, regardless of individual differences in the robot and variations due to joint conditions, and it is possible to shorten the diagnosis time. It becomes.

Diagram showing a 6-axis robot system Diagram showing the joint structure of a 6-axis robot Diagram showing the internal configuration of the controller Diagram showing the UI screen for diagnosis Diagram showing the configuration of the diagnostic function Diagram showing how to generate inspection motion Diagram showing the diagnostic flow The figure which shows the data processing method which calculates the judgment value A

In the present embodiment, the state of the speed reducer (including the state of deterioration) using the wave gear mechanism is diagnosed through the resonance phenomenon generated in the joint portion of the robot device. The detection of the state of the transmission of the joint through the resonance phenomenon of the joint of this robot device is based on the following principle.

When the speed reducer is damaged due to the above-mentioned buffering or collision, an angle transmission error occurs due to tooth skipping or biting of small pieces caused by the damage. This angle transmission error is, for example, an error between the input angle on the primary side of the speed reducer and the output angle obtained on the secondary side of the speed reducer via the gear ratio.

On the other hand, a resonance frequency f (Hz: natural frequency) as shown in the following equation (1) exists in a joint of a robot using a speed reducer using a wave gear.

Here, f is the resonance frequency (Hz: natural frequency) of the vibration system including the reduction gear, K is the spring constant of the reduction gear, and J is the load inertia (kgm2) of the load driven by the joint provided with the reduction gear. is there. Of these, the spring constant K is a constant term and is unique to each model of the reducer. Further, J corresponds to the moment of inertia applied to the joint axis of the target, and its size changes depending on the size and posture of the robot arm and the weight of the object attached to the hand.

Further, the speed reducer is a rotation drive system, and the above-mentioned resonance frequency f (Hz: natural frequency) corresponds to the rotation speed R (rpm: rotation speed per minute) as in the following equation (2).

Therefore, when the rotation speed on the input side of the speed reducer reaches the rotation speed R satisfying the equation (2), a resonance phenomenon occurs in the joint. That is, when the joint is driven, speed unevenness synchronized with the resonance frequency f occurs in the vicinity of the drive rotation speed of the equation (2).

There is a relationship between the angle transmission error of such a reducer and the magnitude of resonance. For example, an angle transmission error occurs when another tooth periodically bites a tooth piece of a reduction gear that has been chipped due to a sudden overload such as a collision. When the vibration system matches the resonance frequency in the state where the angle transmission error occurs, the arm resonates more than when it resonates in the normal state.

Even if the gears are not damaged, if the speed reducer (whole) is distorted in an elliptical shape, the web generator, which is one of the components constituting the wave gear mechanism of the speed reducer, is periodically deformed. When the vibration system matches the resonance frequency in the state where this deformation occurs, the arm resonates more than when it resonates in the normal state.

As described above, it can be considered that the resonance phenomenon generated in the joint of the robot is expressed in the form of the vibration of the joint due to the angle transmission error of the speed reducer. Therefore, the amplitude of resonance generated in the joint (reducer) of the robot arm is measured by, for example, an encoder, a current sensor, or a torque sensor, and this resonance amplitude is used as an index (reference) value according to the angle transmission error. The reducer can be diagnosed by comparing with the value. In particular, since the output shaft encoder can directly detect the rotation unevenness on the speed reducer output side, it is preferable to utilize the output shaft encoder in performing this diagnosis. Therefore, although an example using an output shaft encoder is shown in this embodiment, detection is also possible by using an input side encoder, a motor current value, a torque value, and an acceleration sensor.

In addition, in order to clarify which joint reducer is damaged in this diagnosis, it is desirable to stop other than the joint to be inspected and operate only the target joint. Therefore, when diagnosing all joints, an operation for inspection is performed for each joint.

Hereinafter, with reference to the examples shown in FIGS. 1 to 8, the measurement and diagnosis of the joints of the robot device will be specifically described based on the above principle. In this embodiment, a diagnostic example using an output shaft encoder is shown.

1 to 3 show an example of a configuration of a robot system in which the present invention can be implemented. FIG. 1 schematically shows the overall configuration of the robot system. FIG. 2 shows a cross-sectional structure in the vicinity of one joint of the robot system of FIG. Further, FIG. 3 shows the configuration of the control device 200 of the robot system of FIG.

As shown in FIG. 1, the robot system includes a robot device 100 for assembling and manufacturing a work W, a control device 200 for controlling the robot device 100, and a teaching pendant 300 connected to the control device 200.

The robot arm 100 includes a base portion 101 (base) fixed to a workbench, a plurality of links 102 to 107 that transmit displacement and force, and a plurality of joints that rotatably or rotatably connect the links 102 to 107. It includes 111 to 116. In the present embodiment, the configurations of the plurality of joints 111 to 116 are basically the same. Therefore, in the following, with respect to the configurations common to the joints 111 to 116, the configuration of the joint 112 between the link 102 and the link 103 will be described as a representative, and the other joints 111, 113 to 116 will be concretely described. The explanation will be omitted. It should be noted that this embodiment can be carried out as long as the joint having the same configuration as the joint 112 is provided at at least one of the plurality of joints 111 to 116 of the robot arm 100.

By operating this robot system and executing the control method described below, it is possible to contribute to the stable operation of the robot system, and by extension, the manufacturing of articles can be efficiently executed by this robot system.

As shown in FIG. 2, the joint 112 includes a servomotor (motor) 12 as a rotation drive source and a speed reducer 11 that reduces (shifts) the output of the servomotor 12 (transmission). Further, an input side encoder 8 as an input side angle sensor for detecting the rotation angle of the motor shaft 4 of the servomotor is provided. The output-side rotation angle (output-side rotation angle) of the speed reducer 11 of the joint 112 is detected by the output-side encoder 10 (rotary encoder) as the output-side angle sensor. The input side encoder 8 and the output side encoder 10 have the same configuration as a general rotary encoder, and are composed of an optical or magnetic rotary encoder device.

The servo motor 12 can be configured by, for example, an electromagnetic motor such as a brushless DC motor or an AC servo motor. If necessary, the servomotor 1 may be provided with a brake unit for holding the posture of the robot arm 100 when the power is turned off.

The speed reducer 11 includes a web generator 1 as an input unit, a circular spline 3 as an output unit, and a flex spline 2 arranged between the web generator 1 and the circular spline 3. The web generator 1 is connected to the other end side of the rotating shaft 4 of the servomotor 12. The circular spline 3 is connected to the link 103. The flex spline 2 is connected to the link 102. That is, the coupling portion between the rotating shaft 4 of the servomotor 12 and the web generator 1 is on the input side of the speed reducer 11, and the coupling portion between the flex spline 2 and the link 103 is on the output side of the speed reducer 11. Then, the rotating shaft 4 of the servomotor 12 is decelerated to 1 / N (decelerated at a reduction ratio N) via the speed reducer 11, and the link 102 and the link 103 rotate relatively. The rotation angle on the output side of the speed reducer 11 at this time is the actual output angle, that is, the angle of the joint 112.

The output side encoder (output side angle sensor) 10 is provided on the output side of the speed reducer 11 and detects the relative angle between the link 102 and the link 103. Specifically, the output side encoder 10 generates an output side pulse signal with the drive of the joint 112 (relative movement between the link 102 and the link 103) and outputs the output side pulse signal to the control device 200. A cross roller bearing 9 is provided between the link 102 and the link 103, and the link 102 and the link 103 are rotatably connected via the cross roller bearing 9.

FIG. 3 is an internal block diagram of a robot system centered on the control device 200. The control device 200 is composed of a portable computer or a stationary computer. There is a communication bus 210 inside, and a CPU 216 and a RAM 217 for various calculation processes and a ROM 218 for storing a control program 219 are connected by communication. As the control program 219, not only a program for controlling the entire robot system but also a program for enabling the inspection shown below to be executed by being read and executed by the CPU is stored. Further, the input side encoder 8 of the robot 100, the output shaft encoder 10, the servomotor 12, the operation button 312 of the teaching pendant 300, and the display unit 311 are connected via the I / F (211-215) by communication.

The medium for storing the control program 219 is not limited to the ROM 218, and may be a recording medium such as a hard disk, a semiconductor memory, an optical disk, or a magneto-optical disk.

The user inputs an instruction via the TP operation button 312, the program 205 is called accordingly, and the servomotor 12 of the robot 100 is controlled via the servo control device 201. At this time, the CPU 216 also plays the role of a drive control unit that controls the servo control device 201 and drives and controls the motor.

Next, the configuration and flow for performing the diagnosis will be described with reference to FIGS. 4 to 8.

FIG. 4 is a diagram showing a diagnosis mode UI in which the user sets the diagnosis when performing the diagnosis. The UI is displayed on the display unit 311 on the teaching pendant 300. When the "diagnosis" button on the screen (a) is pressed, the robot system shifts to the diagnosis mode, and the display unit 311 displays the screen (b) for setting the diagnosis. The user can select the axis on which the reduction gear diagnosis is to be performed, and presses the start button to start the diagnosis on the selected axis.

When finished, the diagnosis result screen (c) of each joint is displayed on the display unit 311. Here,% of the predetermined reference value is displayed in the center column, if it is within 100%, no abnormality (OK) is displayed, and if it exceeds 100%, there is more (NG) is displayed in the right column, and the diagnosis result is displayed for each axis. Can be understood. Further, when the "History reference" button on the screen for setting the diagnosis is pressed, the transition of the past diagnosis result is displayed on the graph screen (d), and the tendency of each axis diagnosis result can be understood at a glance.

FIG. 5 is a diagram showing a flow of data when performing a diagnosis. In FIG. 5, the rectangle in the control device 200 shows various control units that show the functions executed by the CPU 216 in terms of hardware, or actual hardware.

The diagnostic mode is activated by the input S312 from the TP operation button 312. Then, when the joint to be diagnosed is selected, the inspection motion generation unit 207 generates an inspection motion according to the joint, or reads the generated inspection motion, and the servo control device 201 and the resonance amplitude calculation unit 204 Is output to (S207). Here, the reason why the inspection operation information S207 is output to the resonance amplitude calculation unit 204 is that the inspection operation information S207 is used in the data processing in the resonance amplitude calculation unit. The servo control device 201 controls the current S201 based on the output inspection operation information S207 to drive the servomotor 12. At this time, the input side angle information S8 detected by the input side encoder 8 that detects the rotation position of the motor shaft 4 and the output side angle information S10 of the speed reducer 11 detected by the output shaft encoder 10 are periodically driven. Output to the data recording unit 203. It is desirable that this time interval be about 10 times or less the resonance frequency in order to accurately record the resonance amplitude of the robot. For example, when the resonance frequency is 20 Hz, the interval is 200 Hz = 5 msec cycle or less.

When the inspection operation is completed, the drive data recording unit 203 outputs the recorded series of angle information S8 and S10 as the inspection data S203 to the resonance amplitude calculation unit 204. The resonance amplitude calculation unit 204 obtains the determination value A from the obtained inspection data S203 and the inspection operation information S207, and outputs the determination value A to the speed reducer state determination unit 205 (S204). The speed reducer state determination unit 205 compares the reference value S206 read from the reference value storage unit 206 with the determination value A (S204), diagnoses the state of the reducer, and displays the diagnosis result S205 on the display unit 311 of the teaching pendant. indicate.

FIG. 6 is a diagram showing a method of generating an inspection motion for sweeping a speed range. In step S601, the moment of inertia m applied to the target joint is calculated in order to obtain the resonance frequency f. Since the resonance frequency f of the robot changes depending on the load and posture of the hand portion attached to the hand, it is calculated based on these. Next, in step S602, the resonance frequency f of the target joint is calculated from the above equation (1) using the obtained moment of inertia m. Further, the resonance frequency f may be obtained in advance by an experiment under the same conditions.

Next, in step S603, the speed reducer input side rotation speed R of the target joint that matches 1/2 or an integral multiple of the resonance frequency f obtained in step S602 is calculated, and the operating speed s of the joint corresponding to this is calculated. Here, it is desirable that the speed reducer input side rotation speed R has a value corresponding to 1/2 of the resonance frequency f. This is due to the structure of the strain wave gearing reducer. That is, since the flex spline 2 is in contact with the circular spline 3 at two points, two vibrations are generated for each rotation of the flex spline. This is because the resonance frequency and the excitation by the reducer are 1: 1, that is, the rotation speed at which the resonance frequency and the reduction gear input side rotation speed are 2: 1 is easy to measure because the resonance phenomenon occurs most.

In the next step S604, the speed range is set. It is desirable that this speed range be set within a range that can cover individual differences and variations due to joint conditions, provided that the joint operating speed s obtained in the previous step S603 is included. As the width of this range, a width determined in advance for the apparatus may be applied centering on the operating speed s. In the next step, an operating speed profile that changes the operating speed of the joint over time so as to cover the speed range set in the previous step S604 is set. At this time, it is necessary to adjust the operating time so that the movable range of the target joint does not exceed the allowable range. In addition, it is desirable to make the speed change as slow as possible so that the resonance can be measured reliably, and therefore it is preferable to take the operating time as long as possible.

Further, in the figure, the profile changes linearly from the low speed side to the high speed side of the speed range, but the profile may change from the high speed side to the low speed side, or may not change linearly. .. For example, in the vicinity of the joint speed s, the speed may be changed non-linearly, such as by slowing the speed change, or the speed may be changed stepwise discontinuously at regular intervals for a short period of time. That is, it is preferable that there is a period in which the speed can be changed without stopping the robot arm while moving the robot arm.

The inspection motion generated in this way includes the joint speed s at which the target joint resonates, and can cover a range including individual differences and variations due to the joint state with a single motion.

In the description of this embodiment, the operating speed of the joint when moved at the speed reducer input side rotation speed R is set to s, and a speed range including s is set as an inspection condition. Alternatively, you may define other parameters. For example, the number of rotations per unit time of a rotary motor or speed reducer may be used, or the rotation angle of joints per unit time may be used. That is, if the drive conditions and drive parameters that cause the joints to resonate can be read, and the joints are driven while changing the drive parameters over time so that the conditions for the joints to resonate are included in the operating range. Good.

FIG. 7 is a diagram showing a flow of measuring using the generated inspection operation.

When performing a diagnosis, the robot enters the diagnosis mode by pressing the "diagnosis" button on the UI screen of FIG. 4 (a). In step S701, the user specifies the joint to be diagnosed using the UI screen of FIG. 4B. In step S702, the reference value S206 of the joint selected in step S701 is read, and an operation for inspection is generated for each joint according to the flow of FIG. Alternatively, if the generated operation is memorized, it may be read.

Next, in step S703, the angle value S8 of the input side encoder 8 and the output shaft encoder while driving the joint while changing the drive parameters over time in parallel with the execution of the read operation (S703a). The angle value S10 of 10 is recorded in the drive data recording unit 203 (S703b). In S704, it is determined whether or not the joint to be inspected remains, and if the joint to be inspected remains, the process returns to step S703, and the execution of the inspection operation and the recording of the angle information are repeated in the same manner. When the inspection operation is completed for all the target joints, the data processing described later is performed in step S705 to obtain the determination value A. In step S706, the determination value A calculated in step S705 is compared with the reference value S206 to diagnose the state of the speed reducer. Finally, in step S707, the diagnosis result is displayed as shown in screen view 4 (c), and the diagnosis mode ends.

FIG. 8 is a diagram showing a method in which the CPU calculates and acquires the determination value A as the maximum value of the vibration amplitude in step S705.

The resonance amplitude calculation unit 204 calculates the determination value A from the inspection data S203 (that is, the difference between the angle information S8 of the input side encoder and the angle information S10 of the output shaft encoder) sent from the drive data recording unit 203.

When the angle information S8 of the input shaft is subtracted from the series of output shaft angle information S10 obtained when the target joint is operated according to the created velocity profile, the resonance amplitude as the angle transmission error of the reducer is obtained. Can be done (Fig. 8). From the above diagnostic principle, the angle transmission error at resonance can be regarded as proportional to the magnitude of damage generated in the reducer. Since the velocity profile includes the velocity at which the joint to be inspected resonates most, it is possible to forcibly express an angle transmission error in the vibration amplitude by resonance, and at the same time, the resonance velocity due to individual differences of the robot and the state of the joint. It can respond to changes. Therefore, of the calculated angle transmission errors, the larger of the plus side maximum value and the minus side maximum value (arrow portion in FIG. 8), that is, the maximum value of the vibration amplitude is set as the determination value A.

The determination value A obtained as described above and the corresponding reference value S206 are compared by the speed reducer state determination unit 205. As the reference value to be compared with the determination value A, for example, there is a method of using the specification value described in the catalog value of the speed reducer. That is, when the specification value set by the speed reducer manufacturer is exceeded, it is determined that an abnormality has occurred. Further, the position deviation required for the target joint may be calculated from the required position accuracy of the hand of the robot arm 101, and the position deviation may be used as a reference value.

As described above, according to the present embodiment, it is possible to diagnose the state of the speed reducer with one inspection operation per joint regardless of the individual difference of the robot and the variation due to the state of the joint, and the diagnosis time. Can be shortened.

12 Servo motor (motor)
11 Reducer (transmission)
1 Web generator 2 Flex spline 3 Circular spline 8 Input side encoder (motor shaft angle detection means)
10 Output axis encoder (output side angle detection means)
100 Robot device 111-116 Joint 200 Control device 216 CPU (Calculation unit)
217 ROM (storage unit)
300 Teaching pendant 311 Display unit 203 Drive data recording unit 204 Resonance amplitude calculation unit 206 Reference value storage unit 405 Reducer state judgment unit 207 Inspection operation generation unit s8 Input side encoder pulse s10 Output axis encoder pulse s203 Inspection data s204 Judgment value A
s206 Judgment reference value s207 Inspection operation information 1000 Robot system

Claims (18)

It is a control method for controlling a robot having a joint portion including a motor and a speed reducer.
A drive process that drives the joint while changing the drive parameters including the condition that the joint resonates over time.
An acquisition process for acquiring the resonance amplitude of the joint during operation in the drive process, and
A method of controlling a robot device, which is characterized by being equipped with. The control method according to claim 1, wherein the condition for the joint to resonate corresponds to a natural frequency that changes according to a change in the posture of the joint. The control method according to claim 1 or 2, further comprising a diagnostic step of diagnosing the state of the transmission according to the resonance amplitude of the joint obtained in the acquisition step. Any one of claims 1 to 3, wherein as a condition for the joint to resonate, the rotation speed of the drive source is set so that the rotation speed is an integral multiple of the resonance frequency at which the joint to be inspected resonates. The control method described in. The control method according to any one of claims 1 to 4, wherein a rotation speed that is ½ or several times the resonance frequency at which the joint to be inspected resonates is set as a condition for the joint to resonate. The control method according to any one of claims 1 to 5, wherein the motor is a rotary-driven motor. The joint is provided with an output side angle sensor that measures the rotation angle of the rotation shaft on the output side of the reduction gear and an input side angle sensor that measures the rotation angle of the rotation shaft on the input side of the reduction gear. ,
The control method according to claim 1 to 6, wherein in the acquisition step, the resonance amplitude is acquired based on the difference between the angle information output by the output side angle sensor and the input side angle sensor. A control device that controls a robot having joints equipped with a motor and a speed reducer.
A drive control unit that drives the joint while changing the drive parameters including the conditions under which the joint resonates over time.
An acquisition means for acquiring the resonance amplitude of the joint while the drive control unit is operating the joint,
A control device for a robot device, which is characterized by being equipped with. The control device according to claim 8, wherein the condition for the joint to resonate corresponds to a natural frequency that changes according to a change in the posture of the joint. The control device according to claim 8 or 9, further comprising a diagnostic step of diagnosing the state of the transmission according to the resonance amplitude of the joint obtained in the acquisition step. Any one of claims 8 to 10, wherein as a condition for the joint to resonate, the rotation speed of the drive source is set so that the rotation speed is an integral multiple of the resonance frequency at which the joint to be inspected resonates. The control device described in. The control device according to any one of claims 8 to 11, wherein a rotation speed that is ½ or several times a resonance frequency at which the joint to be inspected resonates is set as a condition for the joint to resonate. The control device according to any one of claims 8 to 12, wherein the motor is a rotary-driven motor. The joint is provided with an output side angle sensor that measures the rotation angle of the rotation shaft on the output side of the reduction gear and an input side angle sensor that measures the rotation angle of the rotation shaft on the input side of the reduction gear. ,
The control according to any one of claims 8 to 13, wherein the acquisition means acquires the resonance amplitude based on the difference between the angle information output by the output side angle sensor and the input side angle sensor. apparatus. A program for causing a computer to execute the control method according to any one of claims 1 to 7. A computer-readable recording medium, which stores a program capable of executing the inspection method according to any one of claims 1 to 7 when the computer reads and executes the program. A robot system including the control device and the robot device according to any one of claims 8 to 14. A method for manufacturing an article, which comprises manufacturing the article using the robot system according to claim 17.

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