Sliding mode control method for a machine having an operating section

Abstract

A sliding mode control method is provided capable of improving the following ability of a control system with respect to a command at the time of change in the operating condition of a machine, and preventing vibration which tends to occur by the action of a spring element of the machine at the time of change in the operating condition. The processor of a servo circuit derives position deviation (.epsilon.) and speed deviation (.epsilon.) based on a command position (.theta.r) and an actual position (.theta.), estimates an torsion amount (.epsilon.n) and torsion speed (.epsilon.n) by effecting observer processing (Steps 100 to 101), and derives a switching variable (s) (102). The processor derives each of the first to fourth terms of the switching input in dependence on the positive or negative sign of the switching variable, and the positive or negative sign of a corresponding one of the position deviation, the second derivative of the command position, the torsion amount, and the torsion speed (103 to 129), and then derives, on the basis of the switching input derived by adding the four terms together, a torque command (T) sufficient to cause the switching variable to converge on 0 (130, 131). The servo system properly follows the command even when nonlinear parameters associated with the spring element of the machine have varied, thereby preventing vibration of the machine.