Mechanical and optical evaluation of a vision-based tactile sensor inspired by human fingernail and bone structures

Vision-based tactile sensors (VBTS) that leverage low-cost, high-resolution cameras and advanced computer vision algorithms hold great promise for robotic manipulation, yet their physical designs remain largely task-specific and underexplored. In this work, we introduce a human-inspired nail structure into a soft VBTS fingertip – termed With-Nail VBTS (w-VBTS), which comprises compliant skin, a rigid ‘bone’ and a nail layer. We quantitatively assess the nail’s contribution by comparing w-VBTS against a nail-free prototype (wo-VBTS) on two metrics: (1) holding force, defined as the downward reaction force during object lifting, and (2) planar contact area. Our results show that the nail structure increases mechanical resistance, yielding higher lifting forces and larger contact areas than the nail-less design. Furthermore, optical marker analysis during planar contact reveals that the nail layer imposes a geometric constraint on skin deformation, elucidating its mechanical role. These findings demonstrate the potential of nail-inspired architectures to enhance the performance of future VBTS solutions.