Nonlinear control methods for disturbance rejection on a hydraulically driven flexible robot

For robots that are used to operate in wide ranges or to carry heavy loads the elastic deformations of the links have to be taken into account since undesired vibrations can be observed frequently. For these kind of manipulators hydrostatic differential cylinders are often applied for the actuation because of their simple construction and their high power density. This paper presents two nonlinear controllers-a disturbance rejecting controller and a flatness based controller-for the task of rejecting the influence of the disturbance force on the hydraulically driven flexible robot. Both controllers are investigated in a simulation study of a differential cylinder/servo valve system that is an important subsystem of these flexible robots. The simulation results yield good tracking performance for each control method up to a certain disturbance force margin which is typical for the disturbance rejection problem.