Hybrid positioning control using time-optimal feed-forwarding and sliding mode feedback

The positioning control in presence of nonlinearities can exhibit the limit cycles at settling when a simple integral co-action is included into the feedback. On the contrary, the sliding mode feedback allows attaining a robust convergence to the reference in presence of parametric uncertainties and nonlinearities like pre-sliding friction. In order to avoid the control chattering at higher gains, which can be required for fast positioning but are wearing for mechanical structures, the time-optimal feed-forwarding is applied before switching to the sliding mode. The criteria for robust control design and proper parameter selection are derived using the phase-plane analysis. The determined gain of discontinuous control depends mainly on friction uncertainties and does not impact the transient response. The analyzed dynamics with nonlinear friction and designed control are experimentally evaluated on a table drive system.