Variable structure methods in hydraulic servo systems control

In the general framework of hydraulic servo systems, this paper addresses the problem of position control in the presence of important friction nonlinearities. The accent falls on the variable structure methodology, as we try to use its intrinsic robustness properties. Several friction observers, including the one based on a variable structure approach, were incorporated and tested in an acceleration feedback control. Next, we present a novel implementation of a variable structure controller, which lumps friction and load as an external disturbance. Results of extensive experimental testing encourage the use of variable structure methods in a class of highly nonlinear hydraulic servo systems. (C) 2001 Elsevier Science Ltd. All rights reserved.