Optical detection of finger pressure through utilization of nailbed color changes

Abstract

This thesis presents the theory and design of a sensor that detects a when a finger is pressed by visually examining a user's fingernail coloration. Unlike other finger-based controllers that primarily depend on covering the finger pad, this method of sensing allows for accurate measurements without impairing a user's tactile sense. First the color change of a fingernail is examined based on the underlying biological mechanisms of the finger. Then the hue, saturation, and value (HSV) coordinates of videos of the fingernails are analyzed in three different locations; the entire image, a segment of the rear of the fingernail, and a segment of the tip of the fingernail. The front of the fingernail, where a white band develops when pressure is applied to the finger, proved to have statistically significant increases in saturation and value for all test subjects. With these results a simple sensor was designed and tested that accurately sensed finger presses, however with a significant time lag. Finally, the mechanical design of such a sensor was proposed, leaving room for further study and development.