Discrete-time based sliding-mode control of robot manipulators

Purpose – The purpose of this paper is to develop sliding mode control with linear and nonlinear manifolds in discrete-time domain for robot manipulators. Design/methodology/approach – First, a discrete linear sliding mode controller is designed to an n-link robot based on Gao’s reaching law. In the second step, a discrete terminal sliding mode controller is developed to design a finite time and high precision controller. The stability analysis of both controllers is presented in the presence of model uncertainties and external disturbances. Finally, sampling time effects on the continuous-time system outputs and sliding surfaces are discussed. Findings – Computer simulations on a three-link SCARA robot show that the proposed controllers are robust against model uncertainties and external disturbance. It was also shown that the sampling time has important effects on the closed loop system stability and convergence. Practical implications – The proposed controllers are low cost and easily implemented in practice in comparison with continuous-time ones. Originality/value – The novelty associated with this paper is the development of an approach to finite time and robust control of n-link robot manipulators in discrete-time domain. Also, obtaining an upper bound for the sampling time is another contribution of this work.