Abstract
The human fingertip is an exquisitely powerful bio-tactile sensor in perceiving different materials based on various highly-sensitive mechanoreceptors distributed all over the skin. The tactile perception of surface roughness and material hardness can be estimated by skin vibrations generated during a fingertip stroking of a surface instead of being maintained in a static position. Moreover, reciprocating sliding with increasing velocities and pressures are two common behaviors in humans to discriminate different materials, but the question remains as to what the correlation of the sliding velocity and normal load on the tactile perceptions of surface roughness and hardness is for material discrimination. In order to investigate this correlation, a finger-inspired crossed-I beam structure tactile tester has been designed to mimic the anthropic tactile discrimination behaviors. A novel method of characterizing the fast Fourier transform integral (FFT) slope of the vibration acceleration signal generated from fingertip rubbing on surfaces at increasing sliding velocity and normal load, respectively, are defined as kv and kw, and is proposed to discriminate the surface roughness and hardness of different materials. Over eight types of materials were tested, and they proved the capability and advantages of this high tactile-discriminating method. Our study may find applications in investigating humanoid robot perceptual abilities.
Highlights
Tactile perception through finger touch plays an essential role in our interaction with the external environment
Based on a large number of experiments’ data frequency analyses, we proposed a new method to distinguish the surface roughness and hardness properties of different materials by the frequency spectral integral of the vibration acceleration signal generated from the interface between the fingertip and the surface, which was defined as S(FFT) by the following relationship: S( Fourier transform integral (FFT) ) =
The acceleration signals and FFT spectral analysis of the 200 mesh ground glass sample are presented as a sample in the first two columns
Summary
Tactile perception through finger touch plays an essential role in our interaction with the external environment. Slowly-adapting (SA) receptors, such as Merkel and Ruffini corpuscles, respond to sustained touch and pressure on the skin, and rapid-adapting (RA) receptors, for example, Meissner and Pacinian corpuscles, respond to dynamic touch and vibration stimuli [11,12,13,14]. All of these mechanoreceptors enable humans to precisely perceive and discriminate mechanical and thermal stimuli. Studies in the field of Sensors 2017, 17, 2748; doi:10.3390/s17122748 www.mdpi.com/journal/sensors
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