Robust control design for uncertain flexible-joint manipulators: a singular perturbation approach

A robust composite control law is proposed for flexible-joint manipulators which contain uncertainties. The uncertainty considered is nonlinear and (possibly fast) time-varying. Therefore, the uncertain factors such as imperfect modeling, friction, payload change, and external disturbances are all addressed. Based only on the possible bound of the uncertainty, a robust control law is constructed for the rigid counterpart of the flexible-joint robot. A velocity feedback control term is then added to the robust control law to stabilize the elastic vibrations at the joint. To show that the proposed robust composite control law is indeed applicable to flexible-joint robots, a singular perturbation approach for the stability study is proposed. Practical stability is proven. The size of the uniform ultimate boundedness ball can be manipulated to be arbitrary small