This paper studies high-precision motion control of linear motor servo systems. A model reference discrete-time sliding mode control is constructed, which converts servo problems to simple regulator problems. Moreover, based on one-step delayed disturbance approximation, unknown disturbances, including friction, can be well compensated without using any complicated friction modelling and corresponding on-line identification techniques, hence the design of the controller is simple and satisfactory performance is easy to achieve. For tracking control, the overall tracking errors can be further reduced by introducing an extra integral action, although it is not possible to completely eliminate the friction effect in the case that reference trajectories cross zero velocity. Since friction is a complicated non-smooth disturbance, detailed investigation on the influence of choice of sampling period on friction compensation performance is performed through simulation analysis. Experimental results are presented to illustrate the effectiveness and achievable control performance of the proposed scheme.
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