Experimental verification of infinity norm approach for precise force control of manipulators driven by bi-articular actuators

In recent years there has been increasing interest in manipulators presenting animal musculoskeletal characteristics such as bi-articular actuators. Manipulators driven by bi-articular actuators usually have more actuators than joints, resulting in actuator redundancy. In this paper, our approach based on infinity norm to resolve actuators redundancy is implemented on Biwi, Bi-articularly actuated and Wire driven robot arm, and compared with the Phase Different Control (PDC) approach, which is based on human muscle activation level patterns. It is shown that the infinity norm approach produces no error in calculation of output force, while the PDC approach produces non-zero error. Such error is not significant when the angle between the manipulator links is about 120 degrees, but increases as the manipulator moves towards singular configurations. The experimental results agrees with the calculation.