Abstract: Based on the theories of the Variable Structure Control System, the paper puts forward a new design scheme for high-precision and extremely-low-speed servo systems. In order to overcome the low-speed jerking motion and get rid of the system's stationary position error under the action of the slope input signals, the scheme takes the whole servo system for a position and velocity follower, and synthesizes the system control law according to a stable sliding mode equation, which is formed by the system position error and velocity error. The paper also proposes an on-line method for the identification of the nonlinear friction torque, so as to make an effective compensation to the disturbances. The schems proposed here results in not only a convenient system design process but also a simple control algorithm which is suitable for realization on line. Finally, the simulations present encouraging results.

Key words: variable structure control, low-speed jerking motion, servo system, nonlinear friction torque