Analysis of actuator redundancy resolution methods for bi-articularly actuated robot arms

Bi-articular actuators - actuators that span two joints - are rising interest in robot application because they increase stability, optimize force production, and reduce the nonlinearity of the end effector force as a function of force direction. In this paper, we propose an approach to resolve actuator redundancy for bi-articularly actuated robot arms in which the three actuators produce maximum joint actuator torques that differs among each other. A closed form solution based on the infinity norm is derived. The proposed infinity norm based approach is compared with the conventional 1-norm and 2-norm based methods. Under the same actuator limitations, the maximum end effector force produced with the proposed method is significantly greater than the one produced by the conventional methods. The proposed closed form solution is suitable for redundant systems with three inputs and two outputs, bringing the advantage of an higher maximum output without the need for iterative algorithms.