Patterned compliance in robotic finger pads for versatile surface usage in dexterous manipulation

The design of finger pads for robotic and prosthetic hands is often overlooked, with relatively simple shapes and mechanical properties typically used. The finger pad geometry and mechanical properties are especially important for within-hand dexterous manipulation, and human finger usage patterns suggest extending robotic finger pad usage onto side surfaces could enable a wider range of manipulation motion. In this work, we propose a novel finger pad design that combines a ridged stiff inner structure with air gaps and a flexible outer skin to facilitate both grasp stability and versatile usage of the finger surface. The air gaps enable objects to displace the outer skin and stably settle between two adjacent ridges. During manipulation, the ridges can also serve as predictable pivot points. Experimental results comparing three ridged finger designs to a conventional solid core design show that the ridged designs consistently outperform the reference solid core design for all objects, in terms of the ability to stably manipulate objects through a large motion range without ejection (losing grip on the object). Designs with larger spaces between ridges performed better overall than designs with closer spacing, showing that larger “wells” allow objects to more stably settle into the space between ridges. We anticipate the novel finger pad designs and the analysis of their behavior will inform future robotic hand designs, especially designs which aim to incorporate side finger usage.