Utilization of skin color change for image-based tactile sensing

Measurement of pressure distribution applied to a fingertip is crucial for the teleoperation of robots and human computer interface. Previous studies have acquired pressure distribution by affixing a sensor array to the fingertip or by optically recording the deformation of an object. However, these existing methods inhibit the fingertip from directly contacting the texture, and the pressure applied to the fingertip is measured indirectly. In this study, we propose a method to measure pressure distribution by directly touching a transparent object, focusing on the change in skin color induced by the applied pressure, caused by blood flow. We evaluated the relationship between pressure and skin color change when local pressure is applied, and found a correlation between the pressure and the color change. However, the contact area and the color change area did not align perfectly. We further explored the factor causing the spatial non-uniformity of the color change, by accounting for the stress distribution using finite element analysis. These results suggest that the proposed measurement method can be utilized to measure the internal stress distribution, and it is anticipated to serve as a simple sensor in the field of human computer interface.