Examining the Frictional Behavior of Primitive Contact Geometries for use as Robotic Finger Pads

Prosthetic and robotic grippers rely on soft finger pads to better acquire objects of varying size, shape and surface. However, the frictional behavior of soft finger pads of different designs and geometries have yet to be quantitatively compared, in large part due to the difficulty in modeling soft contact mechanics. In this letter, we experimentally examine the frictional behavior of several common primitive contact geometries in terms of their performance under shear loads that would tend to cause the contact to slip and the grasp to potentially fail. The effective static and kinetic coefficients of friction were recorded for each finger pad under a range of common grasping loads. The results show that the variance in contact curvature, contact patch geometry and pressure distribution have influences on key parameters for grasping at low forces. The advantages and disadvantages of these simple geometries are discussed for design of single finger, multi-finger and manipulation-based robotic hands.