Magnetic Absolute Encoder with Magnet of Different Magnetic Flux Densities and AMR Sensors
Yusuke Sakuma, Kohei Takashima, Takashi Ohhira, Hideki Hashimoto · 2023
In this study, we developed a novel magnetic absolute encoder with different magnetic flux densities. Magnetic encoders can be created with a simple structure consisting of a magnet magnetized in a sinusoidal shape and a sensor that detects the magnetic field. They are known for their compact design and excellent environmental resistance. A method of obtaining even higher resolution signals while maintaining absolute accuracy is to use a magnet with different magnetic flux densities and Hall sensors. However, there are physical limitations in improving the accuracy of a multi-polarizing magnet with different magnetic flux densities. In this study, we developed a magnetic encoder with a new structure using a magnet with different magnetic flux densities and anisotropic magnetoresistive(AMR) sensors. The developed system can calculate the absolute angles and output angular frequency signals twice as high as those of AMR sensors, thereby improving the resolution without requiring a multipole magnet. In the past, distortion was considered to occur because AMR sensors were used outside the saturation sensitivity region to capture the amplitude characteristics of a magnet with different magnetic flux densities; however, this was solved by correction using a look-up table. Finally, an actual device was created and validated by comparing the measured values obtained in the experiment with those obtained using a Hall sensor.