On Soft Fingertips for In-Hand Manipulation: Modeling and Implications for Robot Hand Design

Contact models for soft fingertips are able to precisely compute deformation when information about contact forces and object position is known, thus improving the traditional soft finger contact model. However, the functionality of these approaches for the study of in-hand manipulation with robot hands has been shown to be limited, since the location of the manipulated object is uncertain due to compliance and closed-loop constraints. This letter presents a novel, tractable approach for contact modeling of soft fingertips in within-hand dexterous manipulation settings. The proposed method is based on a relaxation of the kinematic equivalent of point contact with friction, modeling the interaction between fingertips and objects as joints with clearances rather than ideal instances, and then approximating clearances via affine arithmetic to facilitate computation. These ideas are introduced using planar manipulation to aid discussion, and are used to predict the reachable workspace of a two-fingered robot hand with fingertips of different hardness and geometry. Numerical and empirical experiments are conducted to analyze the effects of soft fingertips on manipulation operability; results demonstrate the functionality of the proposed approach, as well as a tradeoff between hardness and depth in soft fingertips to achieve better manipulation performance of dexterous robot hands.