Synergy-based control of anthropomorphic robotic hands with contact force sensors

A study on the synergy-based control of an anthropomorphic hand is proposed in this paper. The robotic hand is equipped with three-axis optical force sensors placed on thumb, index, and middle fingertips in order to obtain a better grasping quality in terms of adaptability and contact forces with respect to the physical object properties. A fully-actuated hand is used in the experiments since this allows to select different postural synergies and explore how the hand behaves in case of decoupled finger motion. Therefore, the proposed method can be extended to two different application cases: purely synergy-based contact force control and synergy-based contact force control with decoupled fingers. While the first control strategy allows to simplify the grasping by selecting only the synergy weights in order to obtain the desired value of the mean contact forces among the fingers, the second allows both to control the contact force individually on each finger in order to better adapt the hand to the object and to preserve the simplicity in the grasp design provided by the synergy-based approach. Experimental tests have been performed in both the cases to show the performance of the proposed methods and to highlight the capability of the proposed control strategies to regulate the contact forces properly.