Sensor systems for lower limb functional electrical stimulation (FES) control

Two sensor systems comprising clusters of accelerometers, magnetic sensors, a rate gyroscope, and a strain gauge were designed. For one system, the clusters were located at the belt and AFO. In the other system, the clusters were located at the AFO and the thigh. The maximum cluster size was 14 cm(3) and 75 g. The clusters of each sensor system were interconnected by a single flexible wire bus, which minimized the effects of cabling. The sensors detected five phases of normal gait to a resolution of 40 ms in an able bodied test. Using a threshold method, the sensor system repeatedly predicted an incipient knee buckle in a paraplegic individual by a minimum of 30 ms. One system detected knee flexion angle analytically to an accuracy of 3.2 degrees during sit to stand trials. The second system determined knee and hip flexion angle to an accuracy of 3.8 degrees during sit to stand trials through neural networks. The signal processing of the acquired sensor signals in each system was performed on a MC68332 microcomputer in conjunction with the data sampling, and suggested the possibility for each sensor system to be used in real time control of FES.