Development of a nonlinear PI controller for accurate positioning of an industrial hydraulic manipulator

Abstract Designing a quick, very accurate and robust position controller for industrial hydraulic manipulators is a challenging problem. The controller must contend with many nonidealities that exist in such systems—nonlinear 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) controller, each displaying improved performance over the last. The final NPI controller is shown to improve position tracking accuracy by a factor of five, relative to a conventional PI controller, without sacrificing regulation accuracy or robustness. The experiments are performed on the up-down revolute axis of an instrumented Unimate MK-II hydraulic manipulator.