Tactile Perception of Roughness and Hardness to Discriminate Materials by Friction-Induced Vibration

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.

Humanoid Identification of Fabric Material Properties by Vibration Spectrum Analysis

“…There is a clear monotonic relationship between kv and the yarn weight of fabrics, because the fabric surface roughness is directly influenced by the yarn weight values. Then, S ( FFT ) frequency spectrum was conducted with an increasing normal load applied on the interface of fabrics in different yarn weight, as it is shown in Figure 4 d, six different curves—which represent six different hardness values as we presented in the previous study [ 14 ]—are able to discriminate the soft fabrics from the hard ones.…”

“… ( a ) Schematic illustrating the processes of human tactile perception by an index fingertip and a steel ball probe, when they are sliding on the surface of 1/1 plain weave fabrics consisting of weft and warp yarns in each direction. ( b ) A finger biological structure-inspired tactile sensor with cross configuration cantilever beams was designed and mounted on a reciprocating motion tribometer to access the tactile perception [ 12 , 14 ]. …”

“…Intensive research demonstrated that the tactile perception of various physical stimuli is generated by fingertip sliding along the surface, which permits identification and/or discrimination of textural properties. For instance, when the skin deformation and friction induced vibration stimulate the sensory receptors, the surface texture information is transmitted into a potential current and delivered to human brain by nerve fibers as we presented in the previous studies [ 14 ].…”

“…A simple and effective fabric humanoid identification method basing on the previous research [ 14 ] was proposed by characterizing the power spectrum integral S ( FFT 2 ) of the vibration signal in the frequency domain. Fabric textures were identified by the slope values of S ( FFT 2 ) and S ( FFT ) as a function of sliding velocity and normal load, which were defined as kv and kw respectively for surface roughness and hardness.…”

Evaluation of Electrovibration Stimulation with a Narrow Electrode

“…When a human touches the surface of an object, the contacting part of the fingertip deforms spatially [ 27 , 28 ]. Additionally, the textures of day-to-day surfaces are fine [ 29 ]. For example, wood surface has bumps with a pitch of a few micrometers.…”