A New Absolute Position Measurement Method for Encoders Using Characterized Magnetic Fields
In recent years, the number of industrial robots sold has been increasing, and robots are required to achieve a variety of movements. And for high-precision control, the accuracy of encoders that acquire angle information plays an important role. Magnetic encoders are resistant to dust and oil and are expected to find a wide range of applications as devices that can withstand harsh environments. On the other hand, they are inferior to optical encoders in terms of resolution, so improving resolution is an issue.
To improve the resolution of magnetic encoders, it is effective to increase the number of poles of magnets. However, with multipolarity, the absolute angle cannot be calculated. Therefore, we are developing a new magnetic absolute encoder that uses a characterized magnetic field. We have proposed an eccentric type that rotates a magnet by shifting it from the central axis and a magnetic force difference type that rotates a magnet with a different magnetic flux density for each pole pair, aiming at highly accurate absolute angle calculation with a magnetic encoder.
山本 航大, 大友 一輝, 橋本 秀紀, 偏心構造を用いた磁気式アブソリュートエンコーダの開発, 電気学会論文誌Ｄ（産業応用部門誌）, 2018, 138 巻, 12 号, p. 920-925, 公開日 2018/12/01, Online ISSN 1348-8163, Print ISSN 0913-6339
Shota Komatsuzaki, Akishi Takeyama, Keita Sado, Yuki Nagatsu and Hideki Hashimoto(小松崎翔太, 竹山耀之, 佐渡啓太, 長津裕己, 橋本秀紀),“Absolute Angle Calculation for Magnetic Encoder Based On Magnetic Flux Density Difference”, IECON2021-47th Annual Conference of the IEEE Industrial Electronics Society
Kodai Yamamoto, Kazuki Otomo, Hideki Hashimoto, Development of Absolute Magnetic Rotary Encoder with Eccentric Rotation, IEEJ Journal of Industry Applications, 2019, 8 巻, 6 号, p. 991-996, 公開日 2019/11/01, Online ISSN 2187-1108, Print ISSN 2187-1094
Eccentric Magnetic Absolute Encoder
The accuracy of encoders that acquire angle information plays an extremely important role in high-precision control of motors. Magnetic encoders are resistant to dust and oil and are expected to find a wide range of applications as devices that can withstand harsh environments. On the other hand, their resolution is inferior to that of optical encoders, so improving resolution is an issue.
To improve the resolution of magnetic encoders, it is effective to increase the number of poles of magnets. However, the absolute angle cannot be calculated with multipolarity. Therefore, we are developing an eccentric absolute magnetic encoder. By rotating the magnet eccentrically, the signal can be characterized and the absolute angle can be calculated from the characteristics.
In addition, further accuracy was achieved by estimating and removing disturbances online using a neural network. In addition, by modeling eccentric signals, we proposed a method that enables absolute angle calculation even when the number of internal sensors is reduced.
Akishi Takeyama, Shota Komatsuzaki, Takashi Ohhira, Hideki Hashimoto, “Levenberg-Marquardt method based Precise Angle Estimation for Eccentric Magnetic Absolute Encoders,” IEEE International Conference On Mechatronics (ICM2023), March 2023.
竹山耀之, 小松崎翔太, 大平峻, 橋本秀紀, “ADALINE Neural Network を用いた偏心型磁気式アブソリュートエンコーダの開発”, 第23回計測自動制御学会システムインテグレーション部門講演会（SI2022）, 3P2-A17, 2022.12, 千葉.
Research on Higher Torque Motor
Motor technology is constantly evolving as a key element of electrical-mechanical energy conversion, and today it is used in a wide range of fields such as robotics and automobiles. With the development of these applications, the demands placed on motors have increased, and high torque is an important element of motor technology. In this laboratory, we have focused on the temperature of the motor coils, and by setting a temperature-dependent limit, more current can flow in the motor than before, resulting in higher torque. On the other hand, there is a problem that more heat is generated inside the motor, which leads to motor damage. Therefore, it is necessary to obtain the coil temperature in real time. Although temperature information can be obtained by installing a temperature sensor inside the motor, it is difficult to place a temperature sensor directly near the rotor and stator inside the motor. Therefore, a temperature sensor is installed outside the motor, and using thermal conduction and heat transfer, real-time temperature information can be acquired without installing a temperature sensor inside the motor.
Research on Improving the Accuracy of PMSM Sensorless Control
Permanent magnet synchronous motors (PMSM) are used in a variety of products such as home appliances and automobiles because of their features such as high efficiency, high power density, and low noise. Since it is necessary to control the current and voltage according to the magnetic pole position of the rotor, position sensors are usually used to measure the magnetic pole position. However, the use of position sensors causes problems such as increased cost, poor reliability due to faulty installation or failure, and increased space requirements.
To solve these problems, we are studying a sensorless control method that estimates the magnetic pole position based on the differential value information of the current instead of a position sensor. To reduce errors in magnetic pole position estimation, a neural network-based filter is used to remove disturbance components to achieve higher accuracy in sensorless control.