Force control in internal/external modes for redundantly actuated systems using modal space observer

The methodology to independently control the internal/external force in redundantly actuated systems is presented. Actuation redundancy is frequently presented in various mechanisms like industrial positioning machines, cable-driven mechanisms, and biomimetic robots. However, the force control method for interacting with external environments is scarcely researched. The main challenge is to decouple the internal/external force. Internal force interferes with the motion and external force in the redundantly actuated systems. Such internal force should be controlled so as not to interfere with the external force and not to burden the mechanism. This paper explains the method to decouple them and control the position and force independently. The proposed method is based on the modal space, where the modal space observer (MOB) is used to realize the robustness of the control system. As a result, the proposed method realizes the position/force hybrid control in the decoupled internal/external modes. The proposed method is validated with a planar parallel robot with actuation redundancy. Trajectory tracking, control of the interacting force, and position/force hybrid control are achieved with the proposed method.