Understanding the Effects of Tactile Grating Patterns on Perceived Roughness Over Ultrasonic Friction Modulation Surfaces

Abstract

Objective Our study aims to investigate the effects of grating patterns of perceived roughness on surfaces with ultrasonic friction modulation, and also to examine user performance of identifying different numbers of grating patterns. Background In designing grating-based tactile textures, the widths of low- and high-friction zones are a crucial factor for generating grating patterns that convey roughness sensation. However, few studies have explored the design space of efficient grating patterns that users can easily distinguish and identify via roughness perception. Method Two experiments were carried out. In the first experiment, we conducted a magnitude estimation of perceived roughness for both low- and high-friction zones, each with widths of 0.13, 0.25, 0.38, 0.5, 1.0, 1.5, 2.0, 3.5, and 5.5 mm. In the second experiment, we required participants to identify 5 pattern groups with 2–6 patterns respectively. Results Perceived roughness fitted a linear trend for low- or high-friction zones with widths of 0.38 mm or lower. Perceived roughness followed an inverted U-shaped curve for low- or high-friction zones with widths greater than 0.5 mm but less than 2.0 mm. The peak points occurred at the widths of 0.38 mm for both low- and high-friction zones. The statistical analysis indicates that both low- and high-friction zones had similar effects on human perception of surface roughness. In addition, participants could memorize and identify up to four tactile patterns with identification accuracy rates higher than 90% and average reaction time less than 2.2 s. Conclusions The relation between perceived roughness and varying widths of grating patterns follows linear or inverted U-shape trends. Participants could efficiently identify 4 or fewer patterns with high accuracy (>90%) and short reaction time (<2.2 s). Application Our findings can contribute to tactile interface design such as tactile alphabets and target-approaching indicators.