TRACKING CONTROL OF AN ELECTROHYDRAULIC MANIPULATOR IN THE PRESENCE OF FRICTION

Analysis and estimation of friction and compensation for its effects i n the control of an electrohydraulic manipulator is addressed in this paper. The specific hydraulic manipulator is an integral part of an au tomated fish processing machine which has been developed in our labora tory. The analysis reveals that considerable static and dynamic fricti on exists in the system. An available nonlinear observer for Coulomb f riction, is modified to simultaneously estimate friction, velocity, an d acceleration. A novel observer-based friction compensating control s trategy is developed for improved tracking performance of the manipula tor. The approach is based on acceleration feedback control. Experimen tal investigations show that this controller significantly outperforms a conventional, proportional-plus-derivative (PD) controller. The gen eral approach presented in this paper, may be applied to compensate fo r friction in any servomechanism, particularly when the actuator dynam ics is not negligible.