Rendering variable-sized lump sensations on a softness tactile display

This paper describes a new tactile rendering technique to produce lump sensations in virtual soft surfaces. Most softness displays reported so far reproduced only simple and uniform soft objects; nevertheless many real objects around us provide complicated softness. To reproduce various different softness sensations, we have previously developed a softness display utilizing a flexible sheet that wraps around a fingertip to stimulate fingertip cutaneous sensations. The device controls the softness sensations by changing tension of the flexible sheet, as well as the contact area between the sheet and a fingertip. During our pilot experiments, we found that users feel lump sensations from the softness display in particular conditions. Based on the findings, this paper proposes a technique to reproduce sensations of soft objects that contain lumps beneath their surfaces. The proposed technique can vary the size of the rendered virtual lumps through tension control; larger tension produces smaller size of lump sensation, and vice versa. Results of experiments using human subjects confirmed the validity of the proposed method.