Analysis of cogging torque in dual-stage magnetically geared devices considering magnetic flux coupling
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ORIGINAL PAPER
Analysis of cogging torque in dual-stage magnetically geared devices considering magnetic flux coupling Jin Zhang1,2 · Qiuju Zhang1,2 Received: 30 April 2020 / Accepted: 6 October 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The dual-stage magnetically geared machine (DSMGM) has a high gear ratio. The first stage is a Vernier machine (VM), and the second stage is a coaxial magnetic gear (CMG). These two components share a common rotor (CR), and they are partially flux coupled. Two DSMGMs with different PM arrangements are fabricated and tested. The DSMGM-I with gear ratio 34 can work smoothly, while the DSMGM-II with gear ratio 14.875 is hard to be started up. The purpose of this paper is to reveal the failure of the DSMGM-II. Due to the magnetic flux coupling, there is a recessive CMG in DSMGM structure. The recessive CMG in DSMGM-II prototype is activated and results in high cogging torque and high torque ripple. The thickness of CR yoke controls the portion of flux penetrating through stator. When the thickness of CR yoke is large enough, the cogging torque of the DSMGM-II can be improved. Moreover, another effective method to improve the cogging torque is designing a flux barrier to magnetically decouple the VM and CMG components. For direct-drive robotic application, a DSMGM with Halbach-PM-array is presented. It has a high gear ratio, high torque capability and low cogging torque. Keywords Cogging torque · Magnetic flux coupling · Coaxial magnetic gear (CMG) · Vernier machine (VM) · Dual-stage magnetically geared machine (DSMGM)
1 Introduction Magnetic gears (MGs) with non-contact transmission can increase the torque capability and decrease the output speed of power train systems. They have promising applications in robotics [1, 2]. Among the MGs, the coaxial MGs (CMGs) receive more attention. A typical CMG consists of a high-speed rotor (HSR), a low-speed rotor (LSR) and a ferromagnetic modulator [3–8]. Due to all the permanent magnets (PMs) participating in torque transmission simultaneously, the CMG exhibits a high torque density. The torque density of the CMG proposed by Atallah and Howe [3] exceeded 70 Nm/L. To further improve the torque capability, CMGs with Halbach [4] and spoke-type (ST) [5, 6], etc., PM rotors
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Qiuju Zhang [email protected]
1
School of Mechanical Engineering, Jiangnan University, Wuxi 214122, Jiangsu, China
2
Jiangsu Key Laboratory of Advanced Food Manufacturing Equipment and Technology, Jiangnan University, Wuxi 214122, Jiangsu, China
have been presented. The torque density of the ST-CMG proposed by Uppalapati et al. [6] was up to 239 Nm/L. Moreover, CMGs with consequent-pole (CP) [7] and pure-reluctance [8] rotors can greatly reduce the PM volume. The CMG can be integrated with the brushless electrical machine to form a magnetically geared machine (MGM). Based on the operation principle of CMG, multiple MGMs have been proposed. A straight forward method is integrating a brushless electrical machine into the inside or out
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