Two relay control robustification by continuous switched integral sliding modes

Robust generation of self-oscillation for mechanical systems in the presence of matched uncertainties/perturbations based on a two-relay controller, which naturally has a switched structure, is presented. Two scenarios are considered: the case when all the system states are available and the case when only output information is measured. In both scenarios, a continuous switched integral sliding modes controller is implemented to guarantee theoretically exact compensation of matched uncertainties/perturbations before the first switching. The chattering attenuation in the presence of fast parasitic dynamics can be realised by a switched gain strategy of the super-twisting algorithm. In the output-based scenario, the observer and the controller are initiated sequentially. A super twisting-based observer is used, guaranteeing theoretically exact reconstruction of the states before the controller is activated. The observer gains are also switched to diminish the chattering. Once the observer has converged, the reconstructed state is used in the controller to achieve the control objective. The observer and controller are designed to attain convergence before the first switching.