On the common-mode and configuration-dependent stiffness control of multiple degrees of freedom hands

Object manipulation using hands is a compelling topic in which the interaction forces play a key role. These influence the stability of the grasp and the dexterity of the hand manipulation. A well-known technique to modulate these forces is through the grasp stiffness. Inspired by the observations on human motor behaviour, this paper proposes a novel control method that exploits the dominant contribution of the finger poses to the major axes directions of the grasp stiffness ellipsoid. This is achieved by the optimisation of the hand/fingers posture minimizing the error between the desired orientation of the grasp stiffness ellipsoid and the obtained one. The adjustment of the volume of the ellipsoid is achieved through the adaptation of the fingers joint stiffness in a coordinated way. The performance of the proposed technique is evaluated in transferring desired grasp stiffness features from an anthropometric hand model to two different robotic hand models. Results show that the method is able to obtain a new grasp configuration approximating the desired grasp stiffness. Moreover, it is capable of adapting the orientation of the achieved grasp stiffness to the required variations of the task.