Application of the Earth's Magnetic Field and Accelerometry to the Measurement of Net Knee Extensor Torque
This paper presents a new angle measurement and torque estimation scheme. The angle of the shin is measured with a light, inexpensive two-axis magneto resistive bridge, sensing the swing of the leg through the Earth's magnetic field. The plane of swing is magnetic north-south. The transducer is currently hard-wired to a computer, but it is planned to couple it via a miniature radio transmitter. A single-axis accelerometer is mounted on the leg, below the knee at a specific distance, based on anthropomorphic data. This enables the gravity nonlinearity in the equation of leg swing to be cancelled out.