Model-based control of hydraulically actuated manipulators

Model-based controllers have successfully been applied to many electric drive robotic manipulators to improve their tracking performance. The application to hydraulically actuated systems however is not straight forward, due to the nonlinear internal dynamics of the actuators. The paper presents the modelling of an experimental hydraulic robot arm and the implementation of a cascaded control scheme: a model-based motion controller that compensates for dynamic forces, such as friction and gravity, on top of underlying force controllers for the hydraulic actuators. Dynamic parameters, that are required by the position and the force controllers, are identified online using adaptation algorithms. Experimental results show the performance that this type of controller can achieve with the experimental hydraulic robot arms.