Improving Continuous Approximation of Sliding Mode Control

This paper proposes a continuous approximation of Sliding Mode Control (SMC) designed to fully reject constant disturbances. The main advantage of standard continuous approximation is knew to be chattering reduction while main- taining the state in a well defined boundary of the sliding surface. However, in classical implementations, the effect of even a simple constant disturbance causes the state to leave the sliding surface and move unpredictably in the boundary layer. The proposed solution is a first order SMC approximation, presented with a theoretical proof for the rejection of constant disturbances. The efficacy of the control law is demonstrated in a real-life implementation and comparisons with higher order SMC are carried on. Despite the simplicity of the proposed law, experiments in a robotic application show performances comparable with state of the art second order SMC.