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

Abstract

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.

The contributions of skin structural properties to the friction of human finger-pads

“…As expected, there was no significant difference among them except for the thumb which compares well with the data in Childs et al [25]. Most tested regions of the hand had similar frictional behaviours, particularly when they experienced high loads (> 2 N).…”

Quantifying touch–feel perception: tribological aspects

“…This range covers the normal pressures that people exert when trying to make touch-feel assessments. Other studies of the engineering tribology of skin have recommended that typical loads for friction tests should be from 0.3 to 3 N [14]. In our experience the loading force produced during finger stroking movements has rarely exceeded 1 N. The capacitive sensor used to measure the frictional force was calibrated against standard weights.…”

Understanding the Friction Mechanisms Between the Human Finger and Flat Contacting Surfaces in Moist Conditions

“…This involved applying ink and then pressing down onto a sheet of paper placed on the finger friction rig so that the normal load applied could be measured (see [33] for full details of method). This approach is the same as that used by Childs & Henson [34]. Scans of the images were post-processed using a It is evident from the calculations here that the "liquid bridges" theory is not likely to account for all the increase in friction force seen as moisture levels are increased.…”