JPH0455915A - Robot servo controller - Google Patents

Abstract

PURPOSE:To prevent the uneven rotation of a robot arm by inferring instantaneously the optimum gain and an optimum phase is response to the change of the transmission characteristic of the robot servo system and adding an optimum position correcting signal to a position command signal. CONSTITUTION:When a servo motor 12 revolves, a speed detector 15 detects the revolving speed, the revolving direction, and the variation width of the uneven rotation of the motor 12. A gain/phase inference processor 18 infers the gain and a phase based on the inputted speed signal, revolving direction, and variation width of the uneven rotation respectively. Then the processor 18 reads a pattern coincident with the obtained conclusion of a gain/phase storage 19 and inputs it to a position correcting signal generator 17. Thus the generator 17 produces a position correcting signal based on the inputted gain/ phase signal and outputs the signal to an adder 16. The adder 16 compares the received position correcting signal with a position command signal and outputs the division between both signals to a position/speed controller 11 to control the revolution of the motor 12. Thus the uneven rotation produced to a robot arm can be prevented in real time.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a servo system for a robot having a position transmission mechanism with uneven rotation, particularly a servo control device for smoothly operating a robot arm of an articulated industrial robot. It is related to.

2. Description of the Related Art A position transmission mechanism in a conventional multi-joint industrial robot generally has some kind of nonlinear characteristic. In order to correct such nonlinear characteristics, conventionally, a value obtained by subtracting the nonlinear characteristics was directly added to the position command signal. This method is used when dealing with relatively rigid machines or machines that operate at relatively low speeds. For example, in precision lathes, it is known that the feed pitch error of a ball screw is measured in advance and corrected.

Figure 3 shows the reduction gears (H, D,
An example of a robot servo control device having a function of correcting the position transmission error in C) is shown. In Figure 3,
1 is a position/speed control device, 2 is a servo motor, 3 is a speed detector, 4 is a reducer (H, D, C), 5 is a robot arm, 6 is an adder, and 7 is a position correction signal generator. .

There are various possible rotational irregularities that appear in the robot arm 5, but here we will consider the speed reducer (H).

Let us consider only the rotational unevenness of D and C). H
, D, and C are reducers called harmonic drives.
It has a position transmission error with a period twice the motor rotation speed. For this reason, if rotational unevenness of H, D, and C exists, the rotational unevenness that appears in the robot arm is expressed by K as the amplitude.
If φ is the phase, it is expressed as θν=−5in(2θ−+φ). Therefore, robot arm 5
If the position correction signal generator 7 generates a signal that is an opposite phase signal, and this signal is input to the adder 6 and added to the position command signal, the robot arm 5 will operate smoothly. .

Problems to be Solved by the Invention However, the conventional servo control device for robots simply adds a pre-measured position correction signal to the position command signal. Conversely, rotational irregularities occurring in the robot arm may increase. Another problem is that it takes too much time to adjust the position correction signal.

The present invention solves these conventional problems, and aims to provide a robot servo control device that can constantly suppress rotational irregularities occurring in a robot arm.

Means for Solving the Problems In order to achieve the above object, the present invention calculates the speed signal of the servo motor, its direction, rotational unevenness variation width, gain and phase when determining the gain and phase of the position correction signal. The relationship between the two is created as a rule base and stored in the gain/phase storage device in advance, and the gain/phase inference processing device performs rule-based inference on the optimal gain and phase based on data such as the measured motor speed signal. A position correction signal is generated based on the inferred gain and phase, and this is added to the position command signal.

According to the present invention, even if the transmission characteristics of the servo system change, the optimal gain and phase can be immediately inferred and the optimal position correction signal can be added to the position command signal. It is possible to always suppress uneven rotation in the robot arm.

Embodiment FIG. 1 shows a control block of a robot servo control device in an embodiment of the present invention. In Figure 1,
11 is a position/speed control device, 12 is a servo motor, 13
is a speed detector, 14 is a reducer (H, D, C), 15 is a robot arm, 16 is an adder, 17 is a position correction signal generator, 18 is a gain/phase inference processing device, 19 is a gain/phase inference processing device, and 19 is a gain/phase inference processing device.
It is a phase memory device. This embodiment employs a digital servo system in which position and speed control is realized by a high-speed CPU.

As mentioned above, the reducer 14 is a harmonic drive (
H, D, C), there is a position transmission error with a period twice the motor rotation speed, so the position correction signal generator 17 generates an opposite phase signal of the rotational unevenness that appears in the robot arm 15. If this is manually added to the position command signal in the adder 16, it is possible to suppress uneven rotation of the reducers (H, D, C) and to smoothly operate the robot arm 15.

The issue at this time is whether the gain and phase of the position correction signal are always appropriate. In this embodiment, the gain and phase are determined using a rule-based inference method from a rule base constructed using production rules. That is, first, gain and phase data for the speed signal, its direction, and rotational unevenness variation width are measured in advance, and this data is stored in the gain/phase storage device 1.
9, the patterns are classified into rule-based patterns and stored.

The input method is IP-TH as shown in Figure 3.
The production rules in the natural language format of EN~ are inputted, and each pattern is stored in the gain/phase storage device 19. In the illustrated example, “If the speed is 1
0. If the direction is + and the fluctuation width is 0.5, the gain is 5 and the phase is 20. ”, and a knowledge base is created by creating a rule base for all possible combinations of such patterns. Further, the gain/phase inference processing device 18 includes an inference engine that infers the rule base pattern stored in the gain/phase storage device 19 in a forward or backward direction.

The servo motor 12 rotates, and the speed detector 13 detects its rotation speed, its direction, and rotation unevenness fluctuation range,
A portion is manually input to the position/velocity control device 11 to perform speed control, and a portion is input to the gain/phase inference processing device 18.

The gain/phase inference processing device 18 infers the gain and phase based on the input speed signal, direction, and rotational unevenness variation width, and reads out a pattern that matches the obtained conclusion from the gain/phase storage device 19. Position correction signal generator 17
Enter. The position correction signal generator 17 generates a position correction signal based on the input gain/phase signal and outputs it to the adder 16. The adder 16 compares this with the position command signal and calculates the amount of deviation. is output to the position/speed control device 11 to control the rotation of the servo motor 12. In reality, the gain is set such that the fluctuation range of rotational unevenness of the speed detector 13 is reduced.
A type of learning control method is used in which a phase pattern is estimated within a short time by repeating several trials using data stored in the gain/phase storage device 19.

Effects of the Invention As described above, according to the present invention, when determining the gain and phase of the position correction signal, the relationship between the speed signal of the servo motor, its direction, rotational unevenness variation width, and gain and phase is determined in advance. The gain/phase inference processing device determines the optimal gain and phase based on data such as the measured motor speed signal using rule-based inference. A position correction signal is generated based on the inferred gain, in, and phase, and this is added to the position command signal, so it is possible to always suppress rotational irregularities that occur in the robot arm in real time. , the robot arm can be operated smoothly without being affected by individual differences between robots or fluctuations due to aging of the machine.

[Brief explanation of the drawing]

FIG. 1 is a control block diagram of a robot servo control device according to an embodiment of the present invention, FIG. 2 is an explanatory diagram showing a description method in a rule-based pattern in the same device,
The figure is a control block diagram showing an example of a conventional robot servo control device. 11...Position/speed control device, 12...Servo motor, 13...Speed detector, 14...Reducer (H, D
. C), 15... robot arm, 16... adding machine,
17... Position correction signal generator, 18... Gain/phase inference processing device, 19... Gain/phase storage device. Name of agent: Patent attorney Masaaki Kura 2nd figure

Claims (1)

[Claims] A servo motor, a speed detector attached to the servo motor, a position/speed control device that controls the position and speed of the servo motor, and a position/speed control device coupled to the servo motor to detect nonlinear position transmission errors between input and output. A servo system including a speed reducer having a characteristic and a robot arm coupled to the speed reducer, a position correction signal generator that generates a signal having the same period as rotational unevenness occurring in the robot arm, and the speed detector. a gain/phase storage device that stores in advance a rule-based relationship between gain and phase for the magnitude of the speed signal from the motor, the rotational direction of the motor, and the variation range of rotational unevenness of the speed signal; The optimum gain and phase are determined using rule-based reasoning using the magnitude of the speed signal, the rotational direction of the motor, the variation range of rotational unevenness of the speed signal, and the gain and phase storage data from the gain and phase storage device. A gain/phase inference processing device that outputs to the position correction signal generator, adds the position correction signal from the position correction signal generator, and the position command signal, and outputs the amount of deviation to the position/speed control device. A robot servo control device equipped with an adder.