Design of a robust force control system for an automatic live-line maintenance robot using a force disturbance observer

Abstract

Uninterrupted power supply has become indispensable during the maintenance task of high-voltage live lines as a result of today's highly information-oriented society and increasing demand of electric utilities. This maintenance task has the risk of electric shock and needs skilled workers. Therefore it is necessary to realize an autonomous robot system using an electrohydraulic manipulator because hydraulic manipulators have the advantage of electric insulation and high power/mass density. Meanwhile an electrohydraulic manipulator using hydraulic actuators has many non-linear elements, and its parameter fluctuations are greater than those of an electrically driven manipulator. Therefore it is relatively difficult to realize not only stable contact work but also accurate force control for the autonomous assembly tasks using hydraulic manipulators. In this paper, the robust force control of an automatic live-line maintenance robot used in the real maintenance task of an active electric line is examined in detail. A nominal model for the system is obtained from experimental frequency responses of the system, and the deviation of the manipulator system from the nominal model is derived by a multiplicative uncertainty. Robust force disturbance observer is designed using this information in an H∞ framework and implemented on two different set-ups. Experimental results show that highly robust force tracking by the automatic live-line maintenance robot could be achieved even if the stiffness of environment and the shape of wall change.