Experimental investigation of effect of fingertip stiffness on friction while grasping an object

In this study, we experimentally investigated the effect of robot fingertip stiffness on friction during grasping of an object. To make robots more human-friendly, robotic hands with soft surfaces have been developed. A soft fingertip, i.e., one with low stiffness, is considered desirable because it produces high friction. However, in our experiments, we were able to obtain high friction from a stiff fingertip under a certain condition. We initially investigated the maximum resistible force when solid objects with different angled surfaces were grasped by spherical fingertips of different stiffness. When the contact surface was flat, a stiffer fingertip produced larger frictional force. When the contact surface was highly convex, the maximum frictional force increased with decreasing fingertip stiffness. Secondly, we examined the relationships among the contact area, the load, and the maximum frictional force. We reformulated the relationship between the load and the maximum frictional force and, together with our experimental results, used it to determine the factor that increased the maximum frictional force.