State Torque Synergy-Based Comprehensive Design Method for Wire-Driven Flexible Robot Hands

This letter presents a novel design method for wire-driven flexible robot hands. Conventional methods generally focus on the correlation patterns of desired postures called postural synergy. In contrast, the proposed method introduces state torque aggregating the influence of posture, contact force, and gravity. Utilizing the correlation patterns of state torques, referred to as state torque synergy, we achieve a comprehensive design for reproducing the desired postures and contact forces, including gravity compensation. First, based on an analytical model, the equilibrium equation of the torque acting on the hand is derived. The components of the equation are clearly separated into two torques: the mechanism torque depending on the wire routings and natural posture, and the state torque depending on the posture and contact forces. Next, giving multiple desired states as a design index, a design method for the hand mechanism is developed. Each desired state is converted to the desired state torque, and the state torque synergy is derived by principal component analysis. Based on the isomorphism of the mathematical structure in the state torque synergy and the mechanism torque, the mechanism parameters are analytically determined. Finally, through the design and development of a hand, the proposed method is validated.