Sensing Mechanism of a Rotary Magnetic Encoder Based on Time Grating

This paper presents a sensing mechanism of a rotary magnetic encoder based on the time grating approach. The relationship between spatial displacement and time standard is built by the orthogonal alternating magnetic field in the rotational motion. Time pulses serve as measurement standard and are counted to measure the angular displacement. Therefore, this displacement detection method is called time grating. The alternating magnetic field is generated using the magnetic ring rotating with the shaft. Pairs of tunnel magneto resistance sensors are separated by 90° electrically angles to induce the alternating magnetic field and output orthogonal voltage signals. The travelling wave would be generated by signal processing, which has the phase shift with the rotating shaft. Thus, the rotation angle is measured by counting the time pluses corresponding to the phase difference. A rotary magnetic encoder has been fabricated to evaluate the proposed method. Experimental results indicate that the measurement has high resolution and stability.