Effects of Distributed Friction Actuation During Sliding Touch

Abstract

Friction modulation allows for a range of different sensations and textures to be simulated on flat touchscreens, yet is largely unable to render fundamental tactile interactions such as path following or shape discrimination due to lack of spatial force distribution across the fingerpad. In order to expand the range of sensations rendered via friction modulation, in this paper we explore the possibility of applying spatial feedback on the fingerpad via differing friction forces on flat touchscreens. To this end, we fabricated six distinct flat surfaces with different spatial distributions of friction and observed deformation of the fingerpad skin in response to motion along these physical samples. In our study, friction changes that occur sequentially along the sliding direction introduced little transitory spatial warping such as compression or stretching to the fingerpad, suggesting limited perceptual differences in comparison to 'classic' friction modulation. Distributing friction across the direction of motion, however, showed pattern-dependent shearing of the fingertip skin, opening avenues for new sensations and illusions heretofore unachievable on flat touchscreen surfaces.

Figures (9)

• Figure 1: Different Friction Rendering Strategies. Illustration comparing real textured surfaces, classic friction modulation, and discretization of a friction modulating surface. (a) a finger slides over a real surface with physical ridges, (b) a finger slides over a friction modulating screen simulating the leftmost real surface by applying a 'High' or 'Low' friction force onto the fingerpad, (c) a finger slides over a friction modulating screen, which is segmented into discrete sections to simulate the sensation of the fingerpad as it is sliding on the border between two distinct friction states.
• Figure 2: Sample Configurations (a) Geometries and distribution of friction for each of the six samples evaluated in this study; (b) Coefficient of Friction (COF) measurements for all four participants. Average COF for the high and low friction samples was calculated to be $\mu_1=0.886$ and $\mu_2=0.376$, respectively.
• Figure 3: Marker Application (a) finger with stencil, (b) participant fingers post-tattoo application.
• Figure 4: Experimental Setup Illustration of final experimental setup. (a) Top view, (b) Side View. (1) Motorized Linear Stage, (2) Sample, (3) Finger Brace, (4) Sample Reservoir/Mount, (5) Camera. We only record data as the reservoir moves to the right, relative to the reader.
• Figure 5: Marker Tracking (a) Visualization for Image Processing and labelling of 2-by-2 dot grid. (b) Visualization of total dot displacement values used in absolute and relative displacement calculations