Measurement System for Finger Skin Displacement on a Textured Surface Using Index Matching

Abstract

Understanding the relationship between the displacement of the skin when tracing a textured object and the resulting subjective sensations is essential in designing tactile displays. Previous studies observed skin displacement using flat glass plates or uneven surfaces that do not optically interfere with finger surface observations. In contrast, no direct method for observing skin surface displacement on a texture exists. We propose a system that enables observation of the interaction between a textured surface and the skin of the finger using an index-matching technique. In the proposed system, a texture plate is immersed in oil having the same refractive index as the plate, and measurements are made when the interface is nearly optically transparent. Further, printed markers are attached to the skin of the finger, and their movements analyzed using an image-processing algorithm. The system enables spatial measurement of the skin shear and the vibration of the contact area. Evaluation experiments conducted on a 1D textured surface having a pitch of 0.6 mm verify the feasibility of the proposed system. Optical misalignment simulation results indicate that the system is slightly less accurate than type-I mechanoreceptors but can measure skin deformation on a texture and also observe it spatially and temporally.