High spatial resolution tactile sensors are essential for robots to perform delicate and highly accurate tasks. To achieve sub-millimeter-order high spatial resolution, a tactile image sensor using mechanical-optical materials was fabricated using strain-sensing polymers. Strain-sensing polymers are polymer materials whose light reflection wavelength characteristics change depending on the magnitude of the applied strain. This tactile image sensor has a structure in which a strain-sensing polymer sheet is placed on a transparent acrylic substrate, and the sheet is photographed from the back with a color camera. By mapping the hue value to the pressure at each pixel using the color image of the strain-sensing polymer acquired by the camera, the pressure distribution on the sensor surface was estimated with sub-millimeter-order high spatial resolution. The developed sensor was able to estimate the pressure distribution with a spatial resolution of at least 0.4 mm and a measurement range of up to approximately 0.7 MPa. Furthermore, experiments confirmed that the high spatial resolution of the proposed tactile image sensor is also effective in accurately estimating the orientation of the object being contacted. This sensor is useful for robot hand to estimate the gripping state of minute or thin objects and perform manipulation tasks with high precision.

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