A Simple Optical Angular Sensors to Measure the Human Joint Angle

Medical practioners usually measure dorsiflection of the human joint angle for medical assessment purpose. In order to measure the joint angle, a more or less standard mechanical or electro-mechanical goniometer is used. But mechanical construction has many problems. This research is originated from the lack of user-friendly, versatile and not expensive apparatus which are commercially available. In this paper, we present new design concepts of goniometer utilizing the light refraction characteristics of optical fiber in order to measure angular displacement of the human joints. In order to form an asymmetrical beam profile at the end of fiber tips, we cut the end of fiber tip at an angle of 35 degrees. Phototransistor is used to measure beam intensity as a function of optical fiber angle with respect to optical axis of fiber. Thus the sensed signal represented an indirect measure of curvature angle. The result showed that asymmetrical beam profile provide wider linear relationship than symmetrical one. Eventually, overall performance of the proposed sensor is quite suitable for measurement of the human joint angle