NONLINEAR PROPORTIONAL INTEGRAL CONTROLLER

A method and apparatus for controlling a hydraulic manipulator defines a position error signal (~e), defining a first control signal (Up, UPD) based on t he position error (~e) and generating an improved position error integral signal (~I) based on a product of the position error (~e) integral signal and a velocity factor Fv. The velocity factor Fv is based on a derivative of the position error (~e) and a nonlinear fu nction. An integral control signal (UI) is produced based on the improved position error in tegral signal (~I) and is combined with the first signal (Up, UPD) to provide an output control signal U to control the manipulator. The invention also preferably includes a sy stem to further reduce overshoot by further modifying the position error signal (~e) dep ending on whether the velocity and acceleration of position are in the same direction a nd to accommodate stiction at deadband areas of the control by determining a stick ind uced velocity error signal (~e . stiction) and modifying the control signal when requ ired.