Control system, control method, and non-transitory storage medium

Abstract

The invention relates to a control system, a control method, and a non-transitory storage medium. The control system includes: a torque command generator configured to generate a torque command value to an actuator; an inertia compensation calculator configured to calculate an inertia compensation command value based on a differential value of a q-axis current of the actuator; and a drive command calculator configured to calculate a drive command value by adding the torque command value generated by the torque command generator to the inertia compensation command value calculated by the inertia compensation calculator, and output the drive command value to the actuator.

Description

Technical Field

[0001] The present disclosure relates to a control system, a control method, and a non-transitory storage medium that control an actuator of a robot or the like. Background Art

[0002] There is a control system that performs inertia compensation through feedback control using an acceleration sensor and an observer in order to improve back-drivability (for example, refer to Japanese Patent No. 6097174 (JP 6097174 B)). Summary of the invention

[0003] Some control systems perform inertia compensation by, for example, performing machine learning. The above control systems require additional sensors such as acceleration sensors to perform inertia compensation, which may complicate the configuration.

[0004] The present disclosure provides a control system, a control method, and a non-transitory storage medium that can improve reverse driving capability while simplifying a configuration.

[0005] The first aspect of the present disclosure is a control system. The control system includes: a torque command generator configured to generate a torque command value for an actuator; an inertia compensation calculator configured to calculate the inertia compensation command value based on a differential value of a q-axis current of the actuator; and a drive command calculator configured to calculate a drive command value by adding the torque command value generated by the torque command generator to the inertia compensation command value calculated by the inertia compensation calculator, and output the drive command value to the actuator.

[0006] In the control system according to the first aspect of the present disclosure, the inertia compensation calculator may be configured to calculate the inertia compensation command value based on the q-axis current and the following expression. In the following expression, T a * is the inertia compensation command value, I q is the q-axis current, I an is the inertia compensation coefficient, and τ a is used to pseudo-differentiate the q-axis current I q The time constant.

[0007]

[0008] A second aspect of the present invention is a control method. The control method includes: generating a torque command value for an actuator; calculating an inertia compensation command value based on a differential value of a q-axis current of the actuator; and calculating a drive command value by adding the torque command value to the inertia compensation command value, and outputting the drive command value to the actuator.

[0009] A third aspect of the present disclosure is a non-transitory storage medium storing instructions that can be executed by one or more processors and cause the one or more processors to perform functions. The functions include: generating a torque command value for an actuator; calculating an inertia compensation command value based on a differential value of a q-axis current of the actuator; and calculating a drive command value by adding the torque command value to the inertia compensation command value, and outputting the drive command value to the actuator.

[0010] According to the present disclosure, a control system, a control method, and a non-transitory storage medium that can improve a reverse driving capability while simplifying a configuration can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, wherein like symbols represent like elements, and wherein:

[0012] Figure 1 shows a schematic configuration of a robot arm according to an embodiment;

[0013] Figure 2 is a block diagram showing a schematic system configuration of a control system according to an embodiment;

[0014] Figure 3 is a control block diagram of a control system according to an embodiment;

[0015] Figure 4 is a flow chart of a control method according to an embodiment; and

[0016] Figure 5 Experimental results of a control system according to an embodiment are shown. DETAILED DESCRIPTION

[0017] Embodiments will be described below with reference to the accompanying drawings. In order to coexist with humans, robots that can perform flexible movements are required. In order to increase the flexibility of the robot, it is very important to improve the back-driving capability of the actuators at the joints of the robot.

[0018] There is a trade-off between improving the back-driving capability of an actuator and achieving a smaller, lighter, higher torque actuator. Therefore, it is useful to improve the back-driving capability of an actuator through a compensation control proportional to acceleration.

[0019] On the other hand, a control system that performs inertia compensation by feedback control using an acceleration sensor and an observer requires an additional sensor such as an acceleration sensor to perform inertia compensation, which may complicate the configuration. In addition, since the control system uses an observer to perform feedback control, it does not have sufficient responsiveness.

[0020] The control system according to the present embodiment uses the differential value of the q-axis current instead of the acceleration, and performs inertia compensation by providing a torque command of inertia to the actuator using feedforward control.

[0021] This eliminates the need for an additional sensor such as an acceleration sensor, thereby simplifying the configuration, thereby achieving cost and size reduction while improving the reverse driving capability. In addition, performing inertia compensation by feedforward control without using an observer (rather than feedback control using an observer) provides sufficient responsiveness.

[0022] The control system according to this embodiment controls, for example, Figure 1 The robot arm 10 is shown. The robot arm 10 is configured as an articulated arm having a plurality of joints 11. Each joint 11 is configured to rotate around a plurality of axes. The joints 11 are connected to each other via links or the like.

[0023] A plurality of actuators 12 drivingly rotating each joint 11 are centrally mounted on a base of the robot arm 10. Each actuator 12 drivingly rotates a corresponding joint 11 via a belt 13, a wire 14, etc. This configuration can reduce the main body weight of the robot arm 10 and improve the reverse driving capability.

[0024] For example, the actuator 12 includes a motor such as a servo motor and a speed reducer that reduces the driving force of the motor. An end effector 15 capable of grasping an object is installed at a distal end of the robot arm 10 .

[0025] Figure 2 2 is a block diagram showing a schematic system configuration of a control system according to the present embodiment. A control system 1 according to the present embodiment includes a torque command generation unit 2 , an inertia compensation calculation unit 3 , and a drive command calculation unit 4 .

[0026] The control system 1 has a general computer hardware configuration, including, for example, processors such as a central processing unit (CPU) and a graphics processing unit (GPU), internal memories such as a random access memory (RAM) and a read-only memory (ROM), storage devices such as a hard disk drive (HDD) and a solid-state drive (SSD), an input and output interface (I / F) for connecting peripheral devices such as a display, and a communication I / F for communicating with external devices.

[0027] The torque command generation unit 2 is a specific example of a torque command generator. The torque command generation unit 2 generates a torque command value for the actuator 12. The torque command generation unit 2 outputs the generated torque command value to the drive command calculation unit 4.

[0028] The inertia compensation calculation unit 3 is a specific example of an inertia compensation calculator The inertia compensation calculation unit 3 calculates an inertia compensation command value based on a differential value of a q-axis current of the actuator 12 .

[0029] A method for calculating the inertia compensation command value will be described in detail. The reverse driving capability is defined as the ease of movement of the actuator 12 when the actuator 12 is moved by an external force, for example. In the robot, the actuator 12 (especially its reducer) is the main reason for reducing the reverse driving capability.

[0030] Reverse drive torque T representing reverse drive capability f It is generally defined by the following expression (1).

[0031]

[0032] In the above expression (1), T s is the static friction force, θ is the output shaft angle of the actuator 12, K a is the stiffness coefficient, and C a is the viscosity coefficient. a is the coefficient of inertia and is, for example, the nominal value of the moment of inertia of the electric motor.

[0033] In the present embodiment, the following assumptions can be made for the above expression (1).

[0034] Since the actuator 12 is a hardware configuration consisting of a motor and a reducer, the K a Item.

[0035] Since the actuator 12 is in working state, T can be ignored. s item.

[0036] -With I a Compared with the torque in the term, the cogging torque is very small and can be ignored.

[0037] -With C a The term can be ignored because it is compensated by a different method.

[0038] Based on the above assumption, the above expression (1) can be rewritten as the following expression (2).

[0039]

[0040] Due to the reverse driving torque T f The torque constant K t and q-axis current I q Given, the above expression (2) can be rewritten as the following expression (3).

[0041]

[0042] The following expression (4) is derived by transforming the above expression (3), and the following expression (5) is derived by transforming the expression (4).

[0043]

[0044] The third-order differential of the angle is a jerk physically, but when the angle in the above expression (5) is actually differentiated, pseudo-differentiation is performed using a low-pass filter (LPF), thereby deriving the following expression (6).

[0045]

[0046] By appropriately selecting the time constant τ of the LPF, the differential of the q-axis current, that is, the change of the q-axis current with time can be used instead of the acceleration. The following expression (7) can be derived from the above expression (6), and the inertia compensation command value T a * can be calculated using the expression (7).

[0047]

[0048] In the above expression (7), τ a is used for the pseudo-differential q-axis current I q The time constant of I an is the inertia compensation coefficient, and through the expression I an =K t / I a The above calculated values ​​are actually adjusted to non-divergent values.

[0049] Adjust τ a , so that the phase is consistent with the second-order differential of the angle in the speed range that requires inertia compensation. At this time, the amplitude may become smaller depending on the size of the gain. an The value is also determined taking into account the magnitude of the gain.

[0050] Figure 3is a control block diagram of the control system 1 according to the present embodiment. The inertia compensation calculation unit 3 calculates the differential value of the q-axis current based on the current value output from the motor amplifier. The inertia compensation calculation unit 3 calculates the inertia compensation command value T based on the calculated differential value of the q-axis current and the above expression (7). a *. The inertia compensation calculation unit 3 calculates the inertia compensation command value T a * Output to the drive instruction calculation unit 4.

[0051] The drive instruction calculation unit 4 is a specific example of a drive instruction calculator. The drive instruction calculation unit 4 calculates the inertia compensation instruction value T calculated by the inertia compensation calculation unit 3 by adding the torque instruction value generated by the torque instruction generation unit 2 to the inertia compensation instruction value T calculated by the inertia compensation calculation unit 3. a * to calculate the drive command value. The drive command calculation unit 4 outputs the calculated drive command value to the actuator (motor) 12 via the motor amplifier. The actuator 12 is driven to rotate according to the drive command value from the drive command calculation unit 4.

[0052] Next, a control method executed by the control system 1 according to the present embodiment will be described. Figure 4 is a flow chart of the control method according to this embodiment.

[0053] The torque command generation unit 2 generates a torque command value for the actuator 12 and outputs the generated torque command value to the drive command calculation unit 4 (step S101 ).

[0054] The inertia compensation calculation unit 3 calculates the differential value of the q-axis current based on the current value output from the motor amplifier, etc. (step S102). The inertia compensation calculation unit 3 calculates the inertia compensation command value based on the calculated differential value of the q-axis current and the above expression (7), and outputs the calculated inertia compensation command value to the drive command calculation unit 4 (step S103).

[0055] The drive command calculation unit 4 calculates a drive command value by adding the torque command value generated by the torque command generation unit 2 to the inertia compensation command value calculated by the inertia compensation calculation unit 3, and outputs the calculated drive command value to the actuator 12 (step S104). The actuator 12 is driven and rotated according to the drive command value from the drive command calculation unit 4 (step S105).

[0056] Next, the results of an experiment comparing the operation of the motors of the control system 1 of this embodiment performing inertia compensation and the operation of the motors not performing inertia compensation will be described. The experiment compared the changes in the motor speeds when the motors were rotated by applying an external force such as a hand.

[0057] Figure 5 Experimental results of the control system 1 according to the present embodiment are shown. Figure 5 The line (1) in the lower left portion of shows the change in the rotation speed of the electric motor of the control system according to the present embodiment which performs inertia compensation. Figure 5 The line (1) in the lower right portion of shows the change in the rotation speed of the motor without performing inertia compensation. Figure 5 The thin line (2) in the upper part of represents the compensation command value, and Figure 5 The bold line (3) in the upper part of represents the q-axis current value.

[0058] from Figure 5 It can be seen that the motor of the present embodiment that performs inertia compensation accelerates more when the speed changes (i.e., when accelerating) than the motor that does not perform inertia compensation. This indicates that increasing the torque during acceleration by inertia compensation helps the rotation of the motor when the motor is rotated by applying an external force with a hand or the like. Therefore, the results show that the inertia compensation of the control system 1 according to the present embodiment works effectively.

[0059] As described above, the control system 1 according to the present embodiment includes: a torque instruction generating unit 2, which generates a torque instruction value for the actuator 12; an inertia compensation calculation unit 3, which calculates the inertia compensation instruction value based on the differential value of the q-axis current of the actuator 12; and a drive instruction calculation unit 4, which calculates the drive instruction value by adding the torque instruction value generated by the torque instruction generating unit 2 to the inertia compensation instruction value calculated by the inertia compensation calculation unit 3, and outputs the calculated drive instruction value to the actuator 12.

[0060] This eliminates the need for an additional sensor such as an acceleration sensor, thereby simplifying the configuration, thereby achieving cost and size reduction while improving the reverse driving capability. In addition, performing inertia compensation by feedforward control without using an observer (rather than feedback control using an observer) provides sufficient responsiveness.

[0061] Although an embodiment of the present disclosure is described above, the embodiment is presented only by way of example and is not intended to limit the scope of the present disclosure. This novel embodiment can be implemented in various other modes, and various omissions, substitutions, and changes can be made without departing from the scope of the present disclosure. The above-mentioned embodiment and its variations are included in the scope and spirit of the present disclosure, and are included in the scope of the present disclosure described in the claims and their equivalents.

[0062] In this disclosure, Figure 4 The processing shown can also be realized by, for example, causing a processor to execute a computer program.

[0063] The program can be stored and provided to the computer by using various types of non-transitory computer-readable media. Non-transitory computer-readable media include various types of tangible recording media. Examples of non-transitory computer-readable media include magnetic recording media (e.g., floppy disks, magnetic tapes, and hard disk drives), magneto-optical recording media (e.g., magneto-optical disks), compact disk read-only memories (CD-ROMs), recordable compact disks (CD-Rs), rewritable compact disks (CD-RWs), and semiconductor memories (e.g., mask ROMs, programmable ROMs (PROMs), erasable PROMs (EPROMs), flash ROMs, and random access memories (RAMs)).

[0064] The program can be provided to the computer through various types of temporary computer-readable media. Examples of temporary computer-readable media include electric signals, optical signals, and electromagnetic waves. Temporary computer-readable media can provide the program to the computer via a wired communication path such as an electric wire and an optical fiber or a wireless communication path.

[0065] The components constituting the control system 1 according to the above-described embodiment do not have to be realized by a program. Some or all of the components constituting the control system 1 may be realized by dedicated hardware such as an application specific integrated circuit (ASIC) or a field programmable gate array (FPGA).

Claims

1. A control system, characterized in that include: a torque command generator configured to generate a torque command value for the actuator; an inertia compensation calculator configured to calculate an inertia compensation command value based on a differential value of a q-axis current of the actuator; and A drive command calculator configured as calculating a drive command value by adding the torque command value generated by the torque command generator to the inertia compensation command value calculated by the inertia compensation calculator, and The drive command value is output to the actuator.

2. The control system according to claim 1, characterized in that: The inertia compensation calculator is configured to calculate the inertia compensation command value based on the q-axis current and the following expression: Where T a * is the inertia compensation command value, I q is the q-axis current, I an is the inertia compensation coefficient, and τ a is used to pseudo-differentiate the q-axis current I q The time constant.

3. A control method, characterized in that include: generating a torque command value for the actuator; calculating an inertia compensation command value based on a differential value of a q-axis current of the actuator; as well as A drive command value is calculated by adding the torque command value to the inertia compensation command value, and the drive command value is output to the actuator.

4. A non-transitory storage medium storing instructions, the instructions being executable by one or more processors and causing the one or more processors to perform functions, the functions being characterized by: generating a torque command value for the actuator; calculating an inertia compensation command value based on a differential value of a q-axis current of the actuator; as well as A drive command value is calculated by adding the torque command value to the inertia compensation command value, and the drive command value is output to the actuator.

Images