Presentation Information
[P1-41]Development of 200,000rpm SPM small motor using rare earth anisotropic bonded magnets
Takenobu Yoshimatsu1, *Chisato Mishima1, Eiki Kikuchi1, Yoshinobu Honkura1, Junichi Asama2 (1. MagDesign corporation (Japan), 2. Shizuoka University (Japan))
Keywords:
SPM motor,anisotropic bonded magnet,High speed rotation
1.Background
With the expansion of the robotics and medical industries, increasing the efficiency and weight reduction of small SPM (Surface Permanent Magnet) motors has become an important issue. High speed rotation of motors is an important to achieve this, but when NdFeB-based sintered magnets are used, it is difficult to achieve high speeds due to the large eddy currents loss. We have found that a coreless distributed winding SPM motor using rare earth anisotropic bonded magnets with a motor structure of 200,000rpm, can achieve twice the performance of a conventional motor.
2.Experiment method
1) Prototype SPM type rotor
Rare earth anisotropic bonded magnets were integrally molded into a steel rotor shaft using a vertical injection molding machine and a magnetic molding die. The molding temperature was 275℃ and the molding pressure was 1425Pa. Polar anisotropic orientation and magnetization of anisotropic bonded magnets were performed simultaneously during injection molding using polar anisotropic molds made from permanent magnets. To improve the centrifugal force resistance, the rotor shaft surface was knurled, shot blasted, and coated with adhesive. The 200,000rpm test was performed using a high-speed rotary tester with an air turbine.
2)Computer design of SPM motors
The motor diameter, magnet diameter, magnet length, rotation speed, current density, and clearance were set to 18mm,8mm, 15mm,200,000 rpm, 6Arms/mm2 and 0.3 mm, respectively, and the motor structure (with and without core, winding method), yoke material, and rare earth anisotropic bonded magnetic material were examined for the optimum combination and optimal motor performance was investigated.
3.Experimental results
3.1 Shaft surface processing and integral molding
The rotor shaft surface used in this study was knurled to withstand centrifugal force at high-speed rotation, followed by shot blasting and adhesive coating (Fig.1). Figure 2 shows the results of surface observation by SEM (scanning electron microscope). An anisotropic bonded magnet was integrally molded into this rotor shaft and investigated in a high-speed rotation test apparatus (Fig.3).
3.2 Polar Anisotropic Molds Using Permanent Magnets
Figure 4 shows a pole-anisotropic mold designed with Nd sintered magnets. The number of poles is four, and the magnetic circuit is designed so that the magnetic field flows pole-anisotropically. The distribution of the magnetic flux density of the magnet after integral molding was evaluated, and a roughly sinusoidal flux density was obtained (Fig.5).
3.3 High-speed Rotation Results
Figure 6 shows the results of a 200,000rpm high-speed rotation test of the above integrally molded rotor shaft. As a result, it was found that the shaft maintained a rotation speed of more than 200,000 rpm.
3.4Computer design result of motor
The calculation results show that a small SPM motor with a motor output of 140 W and a motor efficiency of 97% can be realized by using a coreless partial winding, a rare earth anisotropic bond magnet with a (BH)max of 12 MGOe(3mm thick, 4 pole anisotropic magnetization)for the magnet, and an amorphous ribbon for the yoke material. Note, the size of a commercial motor with the same output using Nd sintered magnets is twice, with a diameter of 18mm and a length of 30mm.
4.Summary
1)The performance of 200,000rpm rotation type SPM motor using rare earth anisotropic bonded magnets((BH)max12MGOe) instead of Nd sintered magnets((BH)max50MGOe) was found to achieve twice the torque for the same size.
2)A four-pole anisotropic magnetized magnet was successfully molded into the rotor.
3)We succeeded in creating a rotor that can withstand the centrifugal force of 200,000 rotations.
4)Future plan: We will fabricate a motor and confirm consistency with simulation results, and aim for practical application.
Acknowledgements: This development was supported by the NEDO Energy Saving Technology Development Program (JPNP21005), and we would like to express our gratitude.
With the expansion of the robotics and medical industries, increasing the efficiency and weight reduction of small SPM (Surface Permanent Magnet) motors has become an important issue. High speed rotation of motors is an important to achieve this, but when NdFeB-based sintered magnets are used, it is difficult to achieve high speeds due to the large eddy currents loss. We have found that a coreless distributed winding SPM motor using rare earth anisotropic bonded magnets with a motor structure of 200,000rpm, can achieve twice the performance of a conventional motor.
2.Experiment method
1) Prototype SPM type rotor
Rare earth anisotropic bonded magnets were integrally molded into a steel rotor shaft using a vertical injection molding machine and a magnetic molding die. The molding temperature was 275℃ and the molding pressure was 1425Pa. Polar anisotropic orientation and magnetization of anisotropic bonded magnets were performed simultaneously during injection molding using polar anisotropic molds made from permanent magnets. To improve the centrifugal force resistance, the rotor shaft surface was knurled, shot blasted, and coated with adhesive. The 200,000rpm test was performed using a high-speed rotary tester with an air turbine.
2)Computer design of SPM motors
The motor diameter, magnet diameter, magnet length, rotation speed, current density, and clearance were set to 18mm,8mm, 15mm,200,000 rpm, 6Arms/mm2 and 0.3 mm, respectively, and the motor structure (with and without core, winding method), yoke material, and rare earth anisotropic bonded magnetic material were examined for the optimum combination and optimal motor performance was investigated.
3.Experimental results
3.1 Shaft surface processing and integral molding
The rotor shaft surface used in this study was knurled to withstand centrifugal force at high-speed rotation, followed by shot blasting and adhesive coating (Fig.1). Figure 2 shows the results of surface observation by SEM (scanning electron microscope). An anisotropic bonded magnet was integrally molded into this rotor shaft and investigated in a high-speed rotation test apparatus (Fig.3).
3.2 Polar Anisotropic Molds Using Permanent Magnets
Figure 4 shows a pole-anisotropic mold designed with Nd sintered magnets. The number of poles is four, and the magnetic circuit is designed so that the magnetic field flows pole-anisotropically. The distribution of the magnetic flux density of the magnet after integral molding was evaluated, and a roughly sinusoidal flux density was obtained (Fig.5).
3.3 High-speed Rotation Results
Figure 6 shows the results of a 200,000rpm high-speed rotation test of the above integrally molded rotor shaft. As a result, it was found that the shaft maintained a rotation speed of more than 200,000 rpm.
3.4Computer design result of motor
The calculation results show that a small SPM motor with a motor output of 140 W and a motor efficiency of 97% can be realized by using a coreless partial winding, a rare earth anisotropic bond magnet with a (BH)max of 12 MGOe(3mm thick, 4 pole anisotropic magnetization)for the magnet, and an amorphous ribbon for the yoke material. Note, the size of a commercial motor with the same output using Nd sintered magnets is twice, with a diameter of 18mm and a length of 30mm.
4.Summary
1)The performance of 200,000rpm rotation type SPM motor using rare earth anisotropic bonded magnets((BH)max12MGOe) instead of Nd sintered magnets((BH)max50MGOe) was found to achieve twice the torque for the same size.
2)A four-pole anisotropic magnetized magnet was successfully molded into the rotor.
3)We succeeded in creating a rotor that can withstand the centrifugal force of 200,000 rotations.
4)Future plan: We will fabricate a motor and confirm consistency with simulation results, and aim for practical application.
Acknowledgements: This development was supported by the NEDO Energy Saving Technology Development Program (JPNP21005), and we would like to express our gratitude.
