Continuous Friction Feedforward Sliding Mode Controller for a TriMule Hybrid Robot

This paper presents a continuous friction feedforward sliding mode controller (CFSMC) for a TriMule hybrid robot to improve its trajectory-tracking performance. The dynamic model depicts that the TriMule robot is a multivariable system with nonlinearity and strong coupling, which poses significant challenges in controller design. Hence, a novel CFSMC that consists of a friction feedforward control loop and a continuous sliding mode feedback control loop is specially developed. The feedforward control item calculated with a speed related function is used to handle discontinuous friction disturbance and achieve good transient performance. The feedback control item designed with a continuous sliding mode algorithm is applied to cope with other nonlinear dynamics and assure zero steady-state error. The robustness of the proposed hybrid control scheme is validated in the sense of Lyapunov. Comparative experimental studies with the double closed-loop controller, the sliding mode controller, and the continuous sliding mode controller are conducted, confirming that the CFSMC with the superior control accuracy is an effective and practical robust control scheme for the TriMule hybrid robot. Taking advantages of the CFSMC, a high-precision circular motion is achieved by the TriMule hybrid robot.