Robust Sliding Mode Control for Robots Driven by Compliant Actuators

Compliant actuators can offer many attractive features over stiff actuators in real human-robot interaction applications, such as low output impedance, smooth force transmission, and shock tolerance. This brief focuses on a robust sliding mode control (SMC) methodology for robotic systems with compliant actuators. First, a continuous SMC design is introduced due to its advantages of strong robustness and chattering attenuation. However, this continuous SMC structure cannot guarantee a high tracking performance in the presence of mismatched disturbances in compliantly actuated robots. Meanwhile, in many application fields, compliantly actuated robots are affected by different kinds of time-varying disturbances, including external environmental disturbances, internal parameter uncertainties, and frictions, which may be in the form of constant, ramp, and parabolic disturbances. To estimate such unknown disturbances, a generalized proportional integral observer (GPIO) technique is employed. By designing a new sliding surface with the help of disturbance estimation, a GPIO-based continuous SMC method is synthesized, which is used to deal with matched/mismatched time-varying disturbances. A detailed stability analysis of the closed-loop system is also presented. Experimental results under three different test conditions are provided to illustrate the promising tracking performance of the proposed control strategy.