Semi-degeneracy in stiffness generation and optimal muscle attachment of an anthropomorphic robot

This paper presents the semi-degeneracy in stiffness generation and the optimal attachment of bi-articular muscles of an anthropomorphic robot. The semi-degeneracy is referred to here as the sign-dependent failure in generating the operational stiffness incurred due to the constraint that the muscle stiffness should be positive. First, the cause of the semi-degeneracy is identified as the sign inconsistency of the actual and the desired coupling joint stiffness. Second, the spacing of single bi-articular muscles is optimized for the maximal dynamic range of the coupling joint stiffness. Third, the attachment of multiple bi-articular muscles is optimized for the reduced semi-degeneracy over the entire joint stiffness. Finally, the allowable operational stiffness in the presence of the semidegeneracy is quantified both algebraically and geometrically.