Artificial SA-I, RA-I and RA-II/Vibrotactile Afferents for Tactile Sensing of Texture

TL;DR

This paper develops biomimetic tactile channels inspired by human afferents using a soft sensor, demonstrating effective texture classification through spatial, temporal, and vibrational cues, advancing robotic tactile sensing capabilities.

Contribution

It introduces artificial SA-I, RA-I, and RA-II channels based on the TacTip sensor, and evaluates their effectiveness in speed-invariant texture classification.

Findings

Spatial frictional cues are highly salient for texture representation.

Transforming spatial features enhances temporal coding accuracy.

Vibrational harmonic structures enable speed-invariant texture classification.

Abstract

Robot touch can benefit from how humans perceive tactile textural information, from the stimulation mode to which tactile channels respond, then the tactile cues and encoding. Using a soft biomimetic tactile sensor (the TacTip) based on the physiology of the dermal-epidermal boundary, we construct two biomimetic tactile channels based on slowly-adapting SA-I and rapidly-adapting RA-I afferents, and introduce an additional sub-modality for vibrotactile information with an embedded microphone interpreted as an artificial RA-II channel. These artificial tactile channels are stimulated dynamically with a set of 13 artificial rigid textures comprising raised-bump patterns on a rotating drum that vary systematically in roughness. Methods employing spatial, spatio-temporal and temporal codes are assessed for texture classification insensitive to stimulation speed. We find: (i) spatially-encoded frictional cues provide a salient representation of texture; (ii) a simple transformation of spatial tactile features to model natural afferent responses improves the temporal coding; and (iii) the harmonic structure of induced vibrations provides a pertinent code for speed-invariant texture classification. Just as human touch relies on an interplay between slowly-adapting (SA-I), rapidly-adapting (RA-I) and vibrotactile (RA-II) channels, this tripartite structure may be needed for future robot applications with human-like dexterity, from prosthetics to materials testing, handling and manipulation.