Variable structure methods in hydraulic servo systems control

In the general framework of hydraulic servo systems, this paper addresses t he problem of position control in the presence of important friction nonlin earities. The accent falls on the variable structure methodology, as we try to use its intrinsic robustness properties. Several friction observers, in cluding the one based on a variable structure approach, were incorporated a nd tested in an acceleration feedback control. Next, we present a novel imp lementation of a variable structure controller, which lumps friction and lo ad as an external disturbance. Results of extensive experimental testing en courage the use of variable structure methods in a class of highly nonlinea r hydraulic servo systems. (C) 2001 Elsevier Science Ltd. All rights reserv ed.