A novel model for assessing sliding mechanics and tactile sensation of human-like fingertips during slip action

This paper presents a model for displaying friction and localized stick/slip of sliding inhomogeneous human-like fingertips, to understand how slippage occurs and its role in assessing tactile sensing mechanics. In the absence of friction, the fingertip slides, as on an ice surface, in the virtual world of haptic interfaces. Slippage of fingertip at very low velocity can reflect micro stick/slip on a contact area, which is challenging to represent in any friction model. To overcome these drawbacks, we propose that a Beam Bundle Model (BBM) can be used to model a human fingertip during pushing and sliding actions, especially during stick-to-slip transition. To construct its three-dimensional, non-homogeneous structure, we obtained a sequential series of magnetic resonance images, showing consecutive cross-sectional layers of a fingertip with distribution of skin, tissue, bone, and nail. Simulation results showed that this model could generate not only normal force distribution caused by pushing, but also response of friction during stick-to-slip transition. Secondly, and more interestingly, the model dynamically produced localized displacement phenomena on the contact area during stick-to-slip phase, indicating how slippage enlarges the contact area prior to total slippage of the fingertip. These findings may better assess the sliding processes of human fingertips, and how and when slippage occurs on the contact surface. This model may be a useful platform for studying tactile perception of fingertips.