Effect of roughness on vibration of human finger during a friction test

To study the effect of a rough texture on tactile perception, the human finger was equipped with a sensor very sensitive to the vibration generated during a touch test. The range of vibrational frequencies is well consistent with the frequency of Pacini. To analyze the vibrational characteristics of the human finger under different experimental conditions, our experimental results are based on two quantitative parameters: a parameter which measures the amplitude of the average vibration level Lv (dB), and a parameter related to the spatial resolution of the human finger and which is identified as the characteristic wavelength corresponding to the maximum of the power spectral density (PSD) in the Pacinian frequency band (1–500 Hz).For a constant normal force, the parameter Lv (dB) allowed us to compare the received vibration with the finger as a function of the nature of the surface scanned, the scanning speed, the amplitude and wavelength of roughness. Depending on the scan rate used, it was possible to identify the wavelength filter of the human finger, which can be defined as the ratio of the scanning speed to the frequency corresponding to the maximum PSD: λf (mm)=v/ω. This result allowed us to set a lower speed 10 mm/s for better spatial resolution that can be achieved in the case of abrasive paper: 0.2 mm.To understand the role of texture morphology on finger deformation and vibration, a 3D contact model has been developed. Assuming the finger elastic deformation, the results of the contact model show the way the roughness is printed on the human fingerprint and the effect it produces on the contact pressure and give Von Mises stress for various textures.