Time-Delay Sliding Mode Control for Trajectory Tracking of Robot Manipulators

Sliding mode control strategies have been widely used for tracking robot manipulators and have demonstrated their effectiveness. However, certain issues still persist. One of them is that tracking error may converge to a bounded region surrounding the origin, due to the sliding surface failing to reach zero. This can be so because system's motion depends on the designed sliding surface. In this article, a new sliding surface is proposed to enhance tracking performance with a fast convergence rate and minimum steady-state error. The sliding surface is formulated using the sliding variable value at the previous sampling instant, and the technique is therefore referred to as time-delay sliding mode control. The proposed control strategy offers several advantages: first, it achieves better precision without the need for increasing the number of tunable parameters; second, it can be readily extended to different types of sliding surfaces, without the need for complex architectures to decrease the steady-state error; third, it is robust against unknown dynamics and payload. Numerical simulations and practical experiments are reported to demonstrate the effectiveness of the proposed approach in enhancing tracking performance.