A novel RISE-based adaptive feedforward controller for redundantly actuated parallel manipulators

A novel adaptive controller based on the Robust Integral of the Sign of the Error (RISE) is proposed. The RISE feedback strategy yields semi-global asymptotic tracking despite the presence of unstructured additive disturbances provided some limited assumptions on the system. To achieve better tracking performance, the RISE controller is extended with a model-based adaptive feedforward term. The addition of the feedforward term compensates for the structured uncertainties yielding reduced tracking errors and reduced control effort. The proposed controller is experimentally implemented on a 3-DOFs redundantly actuated parallel manipulator. The computed control inputs are projected using a kinematics based projector in order to remove the internal efforts that may damage the mechanical structure of the manipulator. Experimental results show a better performance of the proposed adaptive controller compared to the basic RISE controller in terms of tracking accuracy and energy consumption.