An accelerometer-based embedded system-on-chip for measuring human-body joint angles

Joint angular sensors are widely used in industry, from highly effective robots in product lines and heavy construction machines to different home appliances. Likewise in the medical field, parameters of human motion, especially the orientations of lower limb segments, are crucial in clinical evaluations and therapeutic treatments in the orthopedic and rehabilitation fields. This paper presents the design and implementation of an embedded system-on-chip for measuring human-body joint angles using MEMS accelerometers and PSoC mixed-signal circuits. It focuses on two algorithms, one called CMR and another DCMR, and utilizes the property of rigid body kinematics to explain their advantages and weaknesses. Unlike CMR algorithm, DCMR algorithm has no requirement on placing the sensors close to the joint center. This provides greater flexibility for the sensor installation. An auto-adjustment procedure is described and both algorithms are characterized on a rigid body robot arm model and compared with a reference system. Experimental results showed that the algorithms were able to measure joint angles in real time, and their accuracy was high enough to be used in ambulatory human-body joint angle measurements and feedback control systems for gait assistance.