Static Characteristics And Finite Element Analysis Of Permanent-magnet Spherical Motor

The permanent magnet (PM) spherical motor can take the place of the traditional multiple DOF transmission system to achieve the three-DOF motion. Therefore, the mechanical structure is greatly simplified, the position accuracy and the response speed of transmission systems are improved, and the application range of the motor is developed. At present, the research on this kind of motor is still in theoretical exploration stage. Thus, the research results in this dissertion can provide theoretical basis and experimental reference for the further study on this kind of motors.A novel PM spherical motor is proposed. Its mechanical structure and working principle are introduced. The simulation model of the PM spherical motor is established. Based on the model, the electromagnetic torque characteristics and reluctance torque characteristics of the motor are derived. Through comparing and analyzing the variation of the torque characteristics of the spherical motor with different magnetizing methods of rotor poles, different stator iron core permeabilities and different materials applied in the stator shell respectively, an effective way which can enhance the output torque of the spherical motor is obtained. The variation rules of the maximum static torque of the motor with the main configuration parameters are obtained and analyzed.In order to simplify the torque calculation, the torque calculation method based on the 2-demensional (2-D) conversion model is proposed. This method equivalently simplifies the magnetic field of the spherical PMs, the shape and the current of cylindrical stator windings. The equivalent conversion parameters are obtained to establish the 2-D conversion FE model of the PM spherical motor. With the electro-magnetic field quantity obtained from the 2-D conversion model, the virtual work torque calculation formula of the PM spherical motor is derived, and three different integral paths of Maxwell stress tensor method are selected to calculate the spinning torque. The calculation results are compared with those of the 3-dimensional (3-D) FE model to prove the validity of the proposed torque calculation method.In order to further study the performance of the PM spherical motor, the 3-D simulation model is established and analyzed, from which the stator flux linkage distribution characteristic curves are obtained. The effects of the magnetizing methods of the permanent magnets, the air gap length and the variation of the configuration parameters of the stator and the rotor on the stator flux linkage characteristics are analyzed. Based on the stator flux linkage data, the spinning back-EMF characteristic curve of the PM spherical motor is obtained. The effects of the main parameters of the motor on the back-EMF characteristics are analyzed.The end-effect of the permanent magnets is validated throught establishing both the 2-D FE model and the 3-D FE model of the PM spherical motor, and its effects on the spinning back-EMF waveform of the motor are analyzed. Due to the special configuration of the PM spherical motor, a novel analyzing method to quantize the end-effect of the PM spherical motor is proposed, that is, the shape of the stator winding is simplified first, and then the end-effect coefficient of the PM spherical motor is calculated to modify the back-EMF waveform obtained from the 2-D FE model. The revised 2-D back-EMF waveforms are verified by those obtained from the 3-D FE model and the experimental waveform.Based on the theoretical analysis, the mechanical structural design and the electromagnetic design about the PM spherical motor are conducted. The experimental motor is produced, and based on the DSP system, its control system is successfully built. Considering the operation characteristics of the PM spherical motor, both the hardware design and the software design are conducted to achieve the spinning motion of the PM spherical motor.