Robust force control of a 6 link electro-hydraulic manipulator

In this paper, a robust force control method using a 6-link electrohydraulic manipulator is studied. An electrohydraulic manipulator using hydraulic actuators is superior to electrically driven manipulators in the viewpoint of power/mass density and electric insulation. Meanwhile it has many nonlinear elements, and its parameter fluctuations are greater than those of electrically driven manipulators. So it is relatively difficult to realize robust force control in order to realize autonomous assembly tasks using hydraulic manipulators such as high-voltage live line maintenance task. In this report, a force disturbance observer, which plays the role of estimating the force disturbance to realize the robust force control, is proposed. In designing the force disturbance observer, the H^∞ control theory is adopted. Experiments are performed with respect to the environments with 4 types of environments (steel, plastic, rubber and sponge) to demonstrate the effectiveness of the proposed force controller designed by the H^∞ control theory. Experimental results show that highly robust force tracking by a 6-link electrohydraulic manipulator can be achieved even if the stiffness of environment changes approximately 200(%) and without respect to the change of the shape of wall