Human tactile perception of screen-printed surfaces: self-report and contact mechanics experiments

Polyester sheets were screen-printed with 16 different patterns formed from one of two different types of polymer-based ink. The patterns were arrays of bumps or pockets with different pitch and per cent coverage of ink. People stroked their fingers over the sheets and reported their resulting feelings in terms of 15 prechosen word pairs, ranging from the psycho-physical smooth-coarse to the more impressionable or affective artificial-natural and happy-sad. It has been possible partially to relate feelings to the printed surfaces' roughnesses and sliding friction coefficients against a fingertip. But the measure of roughness is resolvability of the bumps or pockets by a fingertip and that of friction coefficient is maximum value of the coefficient, on surfaces of mixed materials that showed different coefficients for each material. However, because not all aspects of the results have been explained, these conclusions are tentative. Apparent and real contact areas were observed between both static and sliding fingertips and smooth and printed surfaces. Simple contact and sliding friction models were introduced to explain observed friction coefficients between a sliding fingertip and the printed surfaces and, from comparison with experiments, to derive fingertip skin elastic moduli for future contact mechanics simulations. These moduli are so highly dependent on assumed skin thickness that it is argued that calibration of simulations against experiment will always be essential. A simple test is proposed.