Disturbance-Observer-Based Admittance Control and Its Application to Safe Contact Regulation*

Robust force control systems guarantee robustness to disturbance, including external force. Few previous studies, however, clarify transitions between contact and non-contact. This paper considers an admittance control with the desired relation between force and velocity to achieve safety transitions. Also, the proposed admittance control keeps robust by disturbance observer (DOB). The DOB-based admittance control intrinsically contains robust force control, and a controller during non-contact and one during contact differ only in damping parameter settings. It allows simple contact regulation on transitions. Experiments adopt and validate the proposed method for workspace control of two-degree-of-freedom (2-DOF) manipulators. This paper indicates that the control-based approach, as well as the mechanism-based approach, is one of the effective strategies in human-robot coexisting situations.