4 Modelling and Controlling the Compliance of a Robotic Hand with Soft Finger-pads

Abstract

Compliant pads greatly contribute to increase the robustness and the stability of grasps of robot hands, because of their conformability to the objects’ surfaces, the capability to damp dynamic effects and to dissipate repetitive strains, the enlarged contact areas they allow. On the other hand, besides the difficulty to obtain a precise model of soft pads, they appears not suitable to achieve stiff and accurate grasps in those tasks that require high stiffness and precision. In this chapter, the normal and tangential stiffnesses of soft materials have been experimentally investigated in order to demonstrate their suitability with the development of compliant pads for robotic hands. Since these stiffnesses strongly depends on the applied load, a control approach , exploiting such relation, is proposed in order to “arbitrarily” change the overall stiffness of the hand. In this sense, the perspective of this control strategy, differently from the traditional one that “makes more compliant a stiff system” , is to use the internal forces of the grasp to “make stiffer a compliant system”.