The Position Tracking Control of Precise Servo Systems with Nonlinear Dynamic Friction Using Variable Structure Control and Friction Observer

A position tracking control schemes on the precise servo system in the presence of nonlinear dynamic friction is proposed. A nonlinear dynamic friction is regarded as the bristle friction model to compensate effects of friction. The conventional VSC method that often has used as a non-model-based friction controller has a poor tracking performance in high-precision position tracking application since it completely cannot compensate the friction effect below a certain precision level. Thus to improve the precise position tracking performance, we propose the VSC method combined with the friction-model-based observer having tunable structure of the transient response. Then this control scheme has a good transient response as well as the high precise tracking performance compared with the conventional VSC system without observer and the control system with similar type of observer. The experiments on the ball-screw drive table with the nonlinear dynamic friction show the feasibility of the proposed control scheme.