Sliding Mode Controller with Nonlinear Sliding Surface for Two-Link Planar Manipulator

The objective of this paper is to propose a method to control a two-link planar manipulator using a sliding mode controller with higher order sliding surface. Earlier approaches of varying sliding surface are time dependent and this may not yield optimal performance as the rotating surface does not depend on the dynamic states of the system. In this paper, the proposed control law alters the sliding surface based on the error states to drive the trajectory approaching the sliding phase quicker. A new sliding manifold is established and tuned until error decreases to zero. Stability is ensured through Lyapunov theorem and the trajectory is driven towards a designed sliding surface. The performance of the proposed controller is evaluated and compared against the conventional sliding mode controller as well as the previous approach of rotating sliding surface controller. Results showed that the proposed controller improved the respond speed and shortened the reaching phase. Although the chattering phenomenon remains, it enhanced the flexibility to adapt to the variation of system settings (e.g. torque limit).