A Computational Model for Frictional Effects Applied To Dexterous Hands with Soft Pads

Currently, the design of many robotics hands integrates soft pads as mechanical interface between fingers and manipulated objects. There are several good reasons for introducing soft pads, ranging from increasing safety in manipulation tasks to aesthetic issues. Among the advantages brought by soft pads, one has to mention the significant increase of friction between fingers and the object in contact, and consequently the capability of exert tangential forces with respect to the contact normal. These forces play a fundamental role in grasping and fine manipulation tasks. In this paper we propose a mathematical model able to render the tangential forces due to friction and soft pad elasticity that a finger (represented here with cylindrical and hemispherical surfaces) exerts at the contact, with the aim of simulating the interaction of a soft pad with an object. The main characteristics that this model takes into account are: the tangential elasticity of the soft pad, the relative rolling of the phalanx and the object, and the stick and slip phases. This computational model can also be adapted to haptic applications.