An Improved Tactile Sensing Device for Material Characterization via Friction-Induced Vibrations

Abstract We report an improvement of an instrument used to correlate perceived material surface characteristics to vibrations induced in a transducer via surface profile tracing by addition of stick-slip vibration and stochastic measurements. Our instrument utilizes an inductive transducer and turntable stage to measure and characterize induced vibrations, and additionally incorporates an elastic bead of poly(ethylene-co-vinyl acetate) (EVA) on the stylus tip to simulate the slight tackiness and elasticity of skin, when in contact with certain types of materials. It is thus able to tease vibrational frequencies out of the measurement through stick-slip friction from the polymer’s elasticity and tackiness. The result is a larger range of measurable frequencies of vibration from both normal and tangential forces, for use in classification of selected materials, that vary uniquely with roughness, speed of measurement, contact forces, and material compositions. Additionally, to simulate varying pressure during stroking of a material surface with a finger-tip, the turntable was warped to induce a periodic wobble. This wobble produces variations in contact friction over each period of the measurement by varying contact area and contact force, and thus increases consistency of measurements via statistical distributions of contact force and area. The distributions that manifest are high frequencies over a single period of measurement that can be parsed for classification purposes. The results of this work show that the improved instrument has significantly more data characteristics to utilize and can identify subtle differences between similar materials in identical environments.