Optimization of fingernail sensor design based on fingernail imaging

摘要

This paper describes the optimization of fingernail sensors for measuring fingertip touch forces for human-computer interaction. The fingernail sensor uses optical reflectance photoplethysmography to measure the change in blood perfusion in the fingernail bed when the fingerpad touches a surface with various forces. In the original fingernail sensor, color changes observed through the fingernail have been measured by mounting an array of six LEDs (Light Emitting Diodes) and eight photodetectors on the fingernail in a laterally symmetric configuration. The optical components were located such that each photodiode had at least one neighboring LED. The role of each of the photodetectors was investigated in terms of the effect of removing one or more photodetectors on force prediction estimation. The analysis suggested designing the next generation of fingernail sensors with less than eight photodetectors. This paper proposes an optimal redesign by analyzing a photographic catalog composed of six different force poses, representing average fingernail coloration patterns of fifteen human subjects. It also introduces an optical model that describes light transmission between an LED and a photodiode, and predicts the optimal locations of the optoelectronic devices in the fingernail area.