Feedforward control apparatus for a servomotor

Electricity: motive power systems – Positional servo systems

Patent

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Details

318610, 318615, 318616, G05B 1300, G05D 312

Patent

active

051071932

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Technical Field
The present invention relates to a feedforward control apparatus capable of smoothly stably operating a servomotor.
2. Background Art
Generally known is a servo system for controlling a servomotor mounted as a drive source on various machines, such as machine tools, robots, etc., so that the deviation between a command motor position and an actual motor position is brought into zero. If there occurs a follow-up delay with respect to a position command in this servo system, the positional deviation increases. In machine tools, for example, this entails errors in work shape. Particularly, at the time of high-speed machining in which the position command quickly changes, such errors are liable to be caused.
In this respect, it is conventionally known to perform phase-lead compensation for the position command, i.e., position feedforward control, by adding a differential value of the position command to a speed command corresponding to the positional deviation, so as to eliminate a response delay of the servo system with respect to the position command, thereby preventing control errors, e.g., the work shape errors entailed in the high-speed machining.
The speed command, however, contains more high-frequency components when it is phase-lead-compensated than when it is not. On the other hand, a speed control loop of the conventional servo system for delivering a current command corresponding to the deviation between the speed command and an actual speed is not responsive enough to the high-frequency components of the speed command. According to the conventional servo system, therefore, the positional deviation changes in undulations. In other words, the action of the servomotor, and hence, of a mechanical system which uses the motor as its drive source, becomes unstable, and their vibration cannot be easily damped.
Also known is a servo system of another type in which a position command delivered from a numerical control apparatus is subjected to acceleration/deceleration processing so that the position command can change smoothly. Despite such acceleration/deceleration processing, however, the positional deviation is still subject to undulations, so that the motor may possibly be shocked.


DISCLOSURE OF THE INVENTION

The object of the present invention is to provide a feedforward control apparatus capable of smoothly stably operating a servomotor used as a drive source for various machines.
In order to achieve the above object, according to one aspect of the present invention, a feedforward control apparatus comprises: a position control loop for obtaining a first controlled variable on the basis of a position command and an actual servomotor position; first feedforward control means for differentiating the position command to obtain a first feedforward controlled variable; first addition means for adding the first feedforward controlled variable to the first controlled variable to obtain a speed command; a speed control loop for obtaining a second controlled variable on the basis of the speed command and an actual servomotor speed; second feedforward control means for differentiating the first feedforward controlled variable to obtain a second feedforward controlled variable; and second addition means for adding the second feedforward controlled variable to the second controlled variable to obtain a current command.
According to another aspect of the present invention, a feedforward control apparatus comprises: a position control loop for obtaining a controlled variable on the basis of a position command and an actual servomotor position; feedforward control means for differentiating the position command to obtain a feedforward controlled variable; acceleration/deceleration means for subjecting the feedforward controlled variable to acceleration/deceleration processing; and addition means for adding the feedforward controlled variable after the acceleration/deceleration processing to the controlled variable obtained by the position control loop to obtain a spe

REFERENCES:
patent: 4956594 (1990-09-01), Mizuno et al.
patent: 4992715 (1991-02-01), Nakamura et al.

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