Mechanical Responses of the Fingerpad and Distal Phalanx to Friction of a Grooved Surface: Effect of the Contact Angle

The fingertip angle of incidence at contact in lateral touch is a determinant of its mechanical responses at different scales. In the experiment, we made use of a grooved pulley to stress regions of the finger pulp defined by the contact angle at a 1N applied force. Non-contact measurement of velocities were first performed with a LASER Doppler Vibrometer focused on an adjacent zone. Using wavelets to process signals, we experimentally identified three different kind of vibration which amplitudes were functions of the index finger posture. Additional measurements with an accelerometer glued on the nail permitted to discover that the composite material structure of the fingerpad was not able to damp the tribologic shocks at high angles. This resulted in an actuation of the distal interphalangeal joint.