Electricity: motive power systems – Positional servo systems – 'reset' systems
Patent
1991-11-25
1993-03-02
Ip, Paul
Electricity: motive power systems
Positional servo systems
'reset' systems
318610, 318560, 364176, 364178, H02P 500, G05B 1132, G05B 1302
Patent
active
051912724
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of adjusting a gain for motor control for a robot or the like, and more particularly to a method of automatically adjusting the feedback gain of a motor control loop.
2. Background of the Related Art
It is highly difficult to effect a feed-forward control process on a system, such as a robot, in which the inertia of a load varies to a large extent depending on whether the arm of the system is extended or contracted, and which has servomotors and mechanical movable parts with large speed-reduction ratios of mechanisms. This is because a feed-forward gain, which is not in a feedback loop, is ineffective unless parameters are in exact conformity with each other.
Heretofore, it has been impossible to calculate a feed-forward gain if the value of inertia is unknown. In the event that the inertia is subjected to a variation, it is very difficult to calculate an average inertia value, and highly cumbersome to do so when such a calculation is carried out.
One solution is disclosed in a patent application entitled "Method of learning a feed-forward gain for motor control", filed on Feb. 21, 1990 by the applicant. In the disclosed method, a feed-forward gain is determined according to a learning process.
A feedback gain of a feedback loop, i.e., a proportional gain or the like, is determined in view of a step response, etc., of the system.
When a feedback gain is determined in view of a step response, etc., however, it takes considerable time to measure the step response, etc. Since determination of a feedback gain requires a lot of skill on the part of the operator, difficulty has been experienced in objectively determining a proper value of feedback gain.
SUMMARY OF THE INVENTION
In view of the aforesaid drawbacks of the conventional method, it is an object of the present invention to provide a method of automatically adjusting a feedback gain for motor control.
Another object of the present invention is to provide a method of adjusting a motor control feedback gain by calculating it from a feed-forward gain.
To accomplish the above objects, there is provided a method of adjusting a feedback gain for motor control for a control system in which the inertia of a load is greatly variable, said method comprising the steps of determining a first feed-forward gain according to a learning process with a first feedback gain in a feedback system, calculating a second feedback gain from said first feed-forward gain, and determining a second feed-forward gain with said second feedback gain according to a learning process, thereby establishing a motor control loop.
A first feedback gain is determined. The value of feedback gain is calculated from a servomotor itself or the like, and selected so that the control loop will not oscillate. A first feed-forward gain is determined according to a learning process using the first feedback gain. Then, a second feedback gain is calculated from the first feed-forward gain thus determined. Thereafter, a second feed-forward gain is determined again according to a learning process based on the second feedback gain. The second feed-forward gain and the second feedback gain are used to establish a control system. In this manner, a control system having an optimum feed-forward gain and an optimum feedback gain can be established.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a flowchart of the processing sequence of a method of adjusting a gain for motor control according to the present invention;
FIG. 2 is a block diagram of the hardware arrangement of a robot system exemplifying the present invention; and
FIG. 3 is a block diagram of a speed loop for motor control.
DESCRIPTION OF THE PREFERRED EMBODIMENT
An embodiment of the present invention will hereinafter be described with reference to the drawings.
FIG. 2 shows in block form the hardware arrangement of a robot system exemplifying the present invention. The robot system has a host processor (CPU) 1 for controlling a robot in its entir
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patent: 4841208 (1989-06-01), Itoh
patent: 4885676 (1989-12-01), Zweighaft
patent: 4940924 (1990-07-01), Mizuno et al.
patent: 5032777 (1991-07-01), Ogawa
patent: 5049796 (1991-09-01), Seraji
Astrom, K. J., and B. Wittenmark, Adaptive Control, Addison-Wesley, 1989, pp. 372-379 (Reading, Massachusetts).
Kato Tetsuaki
Nihei Ryo
Torii Nobutoshi
Fanuc Ltd.
Ip Paul
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