Predicting the compliance of soft fingertips with differentiated layer design: A numerical and experimental investigation

This paper describes the nonlinear finite elements analysis (FEA) of soft fingertips for robotic hands in contact conditions. The purpose is to test the reliability of FEA when designing fingertips with differentiated layer design, that is the adoption of a single elastic material, dividing the overall thickness of the pad into layers with different structural design (e.g. a continuous skin layer coupled with an internal layer with voids). The pads are shaped around a rigid core and their behavior is investigated under compressive contact loads. The applicability of various nonlinear hyperelastic constitutive models for predicting the pad behavior is explored under the hypothesis of large deflections. Two materials have been tested whose mechanical properties are determined experimentally. One of these materials can be used in rapid prototyping printers and its properties are presented for the first time. Experimental activity fully validates the proposed FEA models concerning homogeneous pads. At last two different and innovative pad geometries are proposed showing that FEA confirms to be a powerful tool for predicting the compliance of soft fingertips if the right hypothesis and simplifying assumptions are made.