Electricity: motive power systems – Positional servo systems – Program- or pattern-controlled systems
Patent
1991-01-02
1993-06-01
Ip, Paul
Electricity: motive power systems
Positional servo systems
Program- or pattern-controlled systems
31856811, 318561, 318615, 318609, G05D 312, G05B 1304
Patent
active
052163423
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a sliding mode control method with a feedforward compensation function capable of achieving a control response characteristic adapted to varying system parameters, and more particularly, to a control method in which a manipulated variable affecting a controlled object can always be kept proper.
2. Description of the Related Art
A conventional control system for controlling the operation of a robot, machine tool, etc. is generally arranged to carry out proportional-plus-integral control using a fixed gain. In this case, if a system parameter greatly varies, the response characteristic of the control system is likely to become maladapted. In this respect, sliding mode control, etc. have recently been proposed. The conventional sliding mode control, however, entails a drawback such that a steady-state deviation from a control target value is likely to occur.
If the conventional sliding mode control is applied to a control system, which is provided with a feedforward compensation function for improvement of the control response characteristic, the manipulated variable (control input to a controlled object) is likely to become maladapted to the operating state of the controlled object, due to a compensation effect of a feedforward term associated with a nonlinear parameter (e.g., inertia, dynamical friction force, or gravitational term of the robot), when the nonlinear system parameter varies. If the manipulated variable is maladaptive, the controlled variable to be adjusted to a target value oscillates around the target value. In other words, an energy loss occurs in the controlled object. For example, the torque command (manipulated variable) supplied to the controlled object including a servomotor as a drive source oscillatorily varies with a change of the nonlinear parameter. Thus, a driving current flowing through the servomotor periodically becomes excessive, thereby heating the motor.
According to the conventional method neglecting a variation of the nonlinear system parameter in determining the manipulated variable as described above, the manipulated variable is likely to become maladaptive, causing inconveniences.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a sliding mode control method with a feedforward compensation function, which is capable of achieving a control response characteristic adapted to varying system parameters, and of permitting a manipulated variable which affects a controlled object to be always kept proper.
In order to achieve the above object, an object is controlled using a sliding mode control method with a feedforward compensation function according to the present invention, comprising the steps of: selecting a value of an operation parameter representative of an operating state of a controlled object and a value of a nonlinear system parameter which varies in dependence on the operating state of the controlled object, respectively; calculating a manipulated variable which permits a characteristic of a control system to be converged on a switching plane in accordance with the selected values of the operation parameter and the nonlinear system parameter; and controlling the controlled object using the control system.
According to the present invention, as described above, when the sliding mode control with the feedforward compensation function is carried out, a manipulated variable which permits the characteristic of the control system to be converged on the switching plane is calculated in accordance with the detected value of the operation parameter, which represents the operating state of the controlled object, and the detected value of the nonlinear system parameter, which varies in dependence on the operating state of the controlled object. Accordingly, control stability achieved by the sliding mode control and control response characteristic achieved by the feedforward compensation function can be enjoyed. Moreover, it is possible to eliminate the malada
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Kato Tetsuaki
Nihei Ryo
Torii Nobutoshi
Fanuc Ltd
Ip Paul
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