Dynamic analysis of a tactile device for mimicking mechanical stimuli responsible for texture perception

Friction-induced vibrations are one of the main mechanical stimuli at the origin of tactile perception, allowing perception and discrimination of surface textures. While acoustic waves and electromagnetic waves are successfully reproduced for mimicking the auditive (loudspeakers) or visual (monitors) stimuli, the stimuli at the origin of tactile perception are still not fully understood and are still not reproduced. This work presents the development and the dynamic analysis of a device, allowing the reproduction of vibrations induced by the sliding of the finger on a surface. The overall bio-electro-mechanical transfer function, including the fingertip, mechanical device and its control electronics, has been first characterized. The system is highly nonlinear, due to the contact nonlinearities and the nonlinearities proper of the tissues of the fingertip, and a parametrical analysis has been developed for investigating the effect of the contact parameters (contact force, subject, etc.) on the transfer function of the overall biomechanical system. Then, the vibrations measured on the nail of the subject, during the exploration task of different surfaces, have been reproduced by the tactile device. A first validation is obtained by the comparison of the original and the simulated vibration spectra. Then, a discrimination campaign has been developed to verify the ability in discriminating different textures, both during the exploration of real textures and when mimicking the respective vibrational stimuli. The obtained spectra can be correlated with both correct discrimination results and discrimination errors, allowing the identification of the spectral features responsible for texture perception and discrimination.