Design And Analysis Of Electromagnetic Systems Of A Novel 3-DOF Composite Drive Type PM Motor

With the development of the complex industrial control systems and artificial intelligence, the requirement of flexibility and precision performance for the drive devices is more and more stringent. So, the actuators which can achieve multiple-degree-of-freedom motion are used more and more widely. However, the traditional multi-DOF actuators are composed by a number of single degree of freedom actuators, which reduces the position accuracy, response speed and operation efficiency. To solve these problems, relying on their appealing advantageous characteristics of small size, light weight, high power index and simple control, etc., the multi-DOF motors have attracted more and more widespread attention. Based on the initial 3-DOF deflection type PM motor, this paper proposes a novel 3-DOF composite drive type PM motor. Compared with the initial design, this new type motor not only effectively improves the magnetic field and torque, but also introduces the magnetic suspension technology, which can achieve the suspension control on the basis of the 3-degrees-of-freedom motion. This design successfully reduces the problems of the bearing loss caused by the mechanical friction for extending the life of the motor and has become a new development direction of the multi-degree-of-freedom motor field. The specific contents of this dissertation are summarized as follows.1) This paper proposes a kind of novel 3-DOF composite drive type PM motor with three-layer “butterfly type” PM rotor and three-layer stator coils structure. The structure parameters and working principle of this motor has been introduced in details.2) Based on the analytical and finite element methods, the magnetic field and torque models are established in this paper. And the three-dimensional distribution of the magnetic field and torque with the novel 3-DOF deflection type PM motor are analyzed and calculated by the variable separation method in the spherical coordinates and the Lorentz force law, respectively. The affects of the motor structure parameters on the magnetic field and torque are given out by MTLAB simulation. The finite element method uses ANSOFT MAXWELL electromagnetic analysis software to model and simulate. By comparing the two methods, the correctness of the analytical method model has been verified.3) The back electromotive force model of the 3-DOF composite drive type PM motor is established and its distribution properties during the spin rotation movement are derived, which realizes the prediction to the rotor position. The steady-state and transient-state thermal analysis are calculated by ANSYS WORKBENCH software, and the influences of different electric currents and simulation time on the temperature rise of this motor are presented, which lays the foundation for the subsequent studies of the motor’s structure optimization design combined with the structure parameters of the motor.4) The levitation mechanism of the 3-DOF composite drive type PM motor has been described in this paper. Aiming at solving the unbalanced radial force problem with rotor eccentricity, the models of the change of gap-length, air-gap flux density and the radial electromagnetic force are simulated and calculated based on the analytical method and FEM, respectively. According to the principle of the coordinate transformation and levitation force synthesis method, the MATLAB current control model of the levitation force is established. The relationships between the coil currents with the levitation force, offset size, air-gap length and rotation Euler angles of the rotor are presented, and the real-time control of the suspension current has been completed in theory, which provides the foundation for the subsequent studies of the motor levitation control system design.5) The rotor magnetic field model, torque model and back electromotive force models have been detected by the experiments of the motor prototype. By comparing the experimental results with theoretical analysis, the correctness of the theory and simulation models has been further verified.