Trajectory Tracking of Robot Manipulators by a New Chattering-Reduced Sliding Mode Controller

Robot motion control is challenging due to the ever- demanding requirements on precision and agility under highly nonlinear dynamics, large uncertainties, and unknown disturbance. Sliding mode control (SMC) is well-known for its good robustness, but suffers from chattering. Thus, many chattering-reduced SMCs were explored at a price of compromised tracking performance. However, they are either not accurate enough or too complicated. To enhance tracking performance of robot manipulators, this paper proposes a modified SMC that establishes the sliding surface in the joint state space of the plant and the controller to filter the switching term and achieve high tracking accuracy. Furthermore, by analyzing the equivalent systems in the sliding mode of various SMCs, we point out that dynamic SMCs contain a feedback loop around the input gain matrix uncertainty in the sliding mode. Therefore, closed-loop stability of the whole system requires not only convergence of the sliding variable but stability of the equivalent system in the sliding mode. Then experimental comparisons among the first-order SMC with sliding layers (FOSMC), two types of second-order SMC (SOSMC), and the proposed SMC on a 6-axis industrial robot show that the proposed one effectively reduces chattering and outperforms the others.