Towards combined force and distance sensing using only optical sensors to aid in stroke rehabilitation

Authors: Christoph Wagner, Simon Stone, Peter Birkholz

Abstract:

In this paper, we present a systematic approach to characterize opti- cal sensors for their suitability to measure both distance and force, when pressed against with the tongue. For this task, a custom test station was developed that can simultaneously record both quantities. Seven different sensors were examined (4 analog, 3 digital, with respect to their output values) with force and distance ranging from 0.1N to 8N and 0mm to 30 mm, respectively, and averaged mea- surements were compared. Distance characteristics were mainly determined by the half-power angle of the light emitter (with wider half-power angles generally being worse). For force measurements, indicators for good performance (i.e., a monoton- ically increasing sensor output with increasing force) seem to be a wide half-power angle and no height difference between light source and photodetector. Allthough precise performance parameters for force measurements were not fully identified, using optical sensors for both distance and force sensing is generally possible.