Sliding controller design for non-linear systems

New results are presented on the sliding control methodology introduced by Slotine and Sastry (1983) to achieve accurate tracking for a class of non-linear time-varying multivariate systems in the presence of disturbances and parameter variations. An explicit trade-off is obtained between tracking precision and robustness to modelling uncertainty : tracking accuracy is sot according to the extent, of parametric uncertainty and the frequency range of unmodelled dynamics. The trade-off is further refined to account for time-dependence of model uncertainty.