An angle measurement system of high resolution for the upper limbs using a low-cost servomotor

In the here presented study, the biomechanical design and coupling of a servomotor as measuring element for determining the angle of elbow flexion in humans is presented. This task requires a digital servomotor with a 12-bit low charge encoder type ''contactless absolute", which makes the holding torque negligible. Because the servomotor is used as a sensor and not as an actuator, and is expected to produce the least possible resistance to the movement of the elbow, this is a crucial point. Additionally, the biomechanical design of the structure for coupling the servomotor was carried out considering the different movements of the arm and forearm, and the necessity to not interfere with the natural movement of the arm. The measurement resolution allows obtaining the flexion angle to an accuracy of 0.088; and integrated into the embedded system used to communicate with the servomotor, that allows obtaining and analyzing data and temporarily integrating information for counting repeats or measuring the speed of movements, among others. This system will also be useful to calibrate and compare other compatible biomechanical analysis models, where the same movement is analyzed.