An angle displacement sensor using a simple gear

This paper presents an angle displacement sensor that consisting of a specified gear, permanent magnets, pairs of tunnel magnetoresistance (TMR) magnetic sensors, and a shaft. The shaft and the gear fixed on it move together with the object under measurement. TMR magnetic sensors with the permanent magnet behind it are placed beside the gear. The gear is made up with high magnetic permeability, which constitutes the magnetic circuit with the permanent magnet. With the rotation of the gear, an alternating magnetic field with displacement information is generated. Pairs of TMR sensors separated by 90° electrically angle and applied with sine and cosine voltages respectively are used to perceive the changing magnetic field. So, the angle displacement detection can be realized by analyzing the output signals of TMR sensors. That is, the phase shift of the signals is proportional to the displacement and the phase detection can be realized by serve high frequency time pulses as standard. Thus, the displacement is measured by counting the time pulses. Finite element stimulation and experiment are performed using a prototype of the angular sensor. The proposed scheme is proven to be feasible. The proposed angle displacement sensor can reach up to ±5″ stability with 0.1° resolution.