Tracking Accuracy Improvement Based on Adaptive Nonlinear Sliding Mode Control

Abstract

Oftentimes, due to mechanical wear and ambient environment variations, friction-related parameters may vary with respect to the position of the iron-core linear servomotor. In addition, cogging force is also a function of the iron-core linear servomotor's position. In order to cope with the adverse effects caused by friction and cogging force, this article proposes a disturbance compensation approach based on nonuniform rational B-spline (NURBS), in which the parameters of the proposed NURBS-based disturbance compensation approach are represented as a function of the linear servomotor's position. The parameters of the proposed NURBS-based friction model are updated using online adaptive laws designed based on the Lyapunov stability theory. Moreover, in order to attain excellent tracking performance for a motion stage actuated by iron-core linear servomotors, this article combines the proposed NURBS-based friction model and cogging force model with fast nonsingular terminal sliding mode control (FNTSMC) to develop adaptive nonlinear sliding mode control (ADNSMC). The proposed ADNSMC inherits the advantages of both FNTSMC and the proposed NURBS-based disturbance compensation approach. Experimental results indicate that the proposed ADNSMC exhibits satisfactory performance on tracking control and disturbance compensation.