Electricity: motive power systems – Positional servo systems – 'reset' systems
Patent
1993-01-08
1995-01-24
Ip, Paul
Electricity: motive power systems
Positional servo systems
'reset' systems
318609, 3185681, 364160, 364165, G05D 312
Patent
active
053845250
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to a method of controlling a servomotor for driving various machines such as a robot and a machine tool, and more particularly, to a sliding mode control.
2. Description of the Related Art
A variety of sliding mode control techniques are used for controlling servomotors in various machines to improve disturbance suppressing ability and achieve good follow-up with respect to commands. Such sliding mode control techniques are disclosed, for example, in Unexamined Japanese Patent Publications No. 2-297611 and No. 3-118618.
These conventional sliding mode control techniques, however, have no relevance to P control (proportional control) for a position loop or to PI control (proportional-plus-integral control) for a speed loop, which have conventionally been employed for controlling servomotors. Thus, conventional linear control techniques elaborated for the P and PI controls cannot be utilized at all for the control of a servomotor.
Thus, the application of the sliding mode control has been hindered mainly due to that the selection of various parameters is so time consuming and some other reasons.
SUMMARY OF THE INVENTION
The object of this invention is to permit easy introduction of sliding mode control, and to utilize conventional linear control techniques.
According to this invention, the phase surface of the sliding mode is set to be in proportion to a mode of obtaining a torque command when carrying out a proportional control for a position loop and a proportional-plus-integral control for a speed loop, and a switching input is added to the torque command obtained by a linear control process including the position loop process according to the proportional control and the speed loop process according to the proportional-plus-integral control, to obtain a corrected torque command. The servomotor is controlled in accordance with the corrected torque command.
The phase surface of the sliding mode is made to be equivalent to the mode of obtaining a torque command by a linear control in which the position loop is subjected to proportional control and the speed loop is subjected to proportional-plus-integral control. Thus, by adding the switching input to the torque command obtained by the linear control process, a torque command for the current loop is obtained, and the sliding mode control can be easily applied.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram illustrating a servomotor control method according to one embodiment of this invention;
FIG. 2 is a block diagram of a principal part of a servomotor control unit for carrying out the control method illustrated in FIG. 1;
FIG. 3 is part of a flowchart showing a feedforward process, position loop process, speed loop process, and sliding mode process, which are executed by a processor of a digital servo circuit shown in FIG. 2; and
FIG. 4 and FIG. 5 are individually the subsequent part of the flowchart shown in FIG. 3.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
First, a phase surface (switching surface) Suf is defined as expressed by the following equation (1): ltidot..epsilon.) (1)
In equation (1), Kp is a position gain of a position loop according to P control, and K1 and K2 are an integral gain and a proportional gain, respectively, of a speed loop according to PI control. .epsilon. represents a position deviation, while .epsilon. represents the derivative of the position deviation, i.e., a speed deviation. In the following, symbols with one dot give above denote first-time derivatives, and symbols with two dots given above denote second-time derivatives.
For the Liapunov function V, the following formula (2) is defined:
The derivative of the Liapunov function V is given by the following equation (3):
If a servomotor is supplied with such an input that the resulting value of equation (30 is always negative, then the Liapunov function V is always positive, and the derivative thereof is negative, showing a monotonic decrease, so that the Liapunov function
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Fanuc Ltd.
Ip Paul
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