DEVELOPMENT OF A NONLINEAR PI CONTROLLER FOR ACCURATE POSITIONING OF AN INDUSTRIAL HYDRAULIC MANIPULATOR

Designing a quick, very accurate and robust position controller for in dustrial hydraulic manipulators is a challenging problem. The controll er must contend with many nonidealities that exist in such systems-non linear dynamics, hydraulic flow deadband, and stiction are all present . This paper documents step-by-step development and implementation of a novel nonlinear proportional-integral (NPI) controller in an attempt to deal with these issues. A number of modifications are performed on the integral portion of a conventional proportional-integral (PI) con troller, each displaying improved performance over the last. The final NPI controller is shown to improve position tracking accuracy by a fa ctor of five, relative to a conventional PI controller, without sacrif icing regulation accuracy or robustness. The experiments are performed on the up-down revolute axis of an instrumented Unimate MK-II hydraul ic manipulator. (C) 1997 Elsevier Science Ltd.