Digital adaptive control for servo system with unknown nonlinear friction

The authors consider the design of a discrete time model reference adaptive control system (MRACS) for motion control systems with unknown nonlinear friction. From a control system viewpoint, the static and Coulomb frictions are characterized by a nonlinear dead-zone element and constant value disturbance for the control input signal, respectively. The discrete MRACS is considered for a nonlinear system which is a cascade combination of an unknown dead-zone block and a linear dynamic block with disturbance. In order to verify the validity of the theory, the design method described is applied to a servo system influenced by friction. Experimental results show the high control performance of the constructed MRACS and the effectiveness of the proposed method