Estimation of joint angles with capacitive accelerometers

In neurorehabilitation of individuals with sensory-motor deficit it is of interest to estimate the joint angles during movement. We designed and tested a system by using a system of micro-machined capacitive accelerometers. The major difficulty was the intrinsic property of the capacitive transducer outputting the total acceleration caused by both gravity and other forces. We developed a method for estimating the absolute angular acceleration and angular velocity of the rigid body by using a combination of two accelerometers fixed along the same axis on the rigid body. By low-pass filtering of outputs from two sensors on the same segment, and subtracting the differences calculated for the two neighboring segments we estimated the joint angle. The experimental verification was done by using the pendulum. The measurement uncertainty in the experiments was comparable with the commercially available goniumeter (+/- 2 degrees). The system developed and tested does not require calibration, the mounting of the system is simple, and the sensory system is light and robust.