Characteristic Study And Optimization Design Of 2-DOF Direct Drive Induction Motor

The 2-DOF(two degrees of freedom) driving devices presented to this date were usually implemented by two or more conventional motors and complicated transmissions resulting in a higher cost. The 2-DOF motor without transmissions possesses a smaller volume, lower cost and higher operation efficiency, which has a broad application prospect. This paper proposed a 2-DOF DDIM(2-DOF direct drive induction motor), which is consisted of a rotary motion arc-shaped stator, a linear motion arc-shaped stator and a common hollow ferromagnetic mover coated with copper layer. The mover can move rotary, linear or helical motion. The main content are as following:The structure of hollow ferromagnetic mover coated with copper layer and multi-forms of motion made it difficult to analyze the characteristics of 2-DOF DDIM. The equivalent plate model was adopted to simplify the complex electromagnetic analysis. The 3-D electromagnetic governing equations were established to calculate the electro-magnetic field quantities using Maxwell equations. By adopting equivalent complex permeability to consider nonlinear magnetization of ferromagnetic material, the surface impedance of the medium was adopted to obtain rotor parameters and the single-phase equivalent circuit model was established. The proposed equivalent circuit model is not accurate without considering coupling effect between rotary motion part and linear motion part. Analytic models of two-dimensional(2-D) electromagnetic field for end-effect and 3-D motion coupling effect in the motor were established using Maxwell’s equations respectively. 3-D finite element model of 2-DOF DDIM was established to take account of the influence of motion coupling effect, magnetic field coupling effect and end-effect more accurately.There is a special phenomenon in 2-DOF DDIM whose no-load rotating(translational) speeds exceed the so-called synchronous speed. In this paper, the mathematical model of the motor was established to analyze the distribution of air gap and end region magnetic field considering dynamic longitudinal end effect. A new physical quantity "Equivalent electromagnetic pole pitch" considering the dynamic longitudinal end effects was proposed and correction coefficients corresponding to mechanical pole pitch with different number of poles was given. By comparing the results of 2-D, 3-D Finite Element Method(FEM) simulation and prototype testing, the rationality and feasibility of the equivalent circuit model as well as the equivalent plate model was verified. The existence of electro-magnetic coupling and motion coupling was verified. It can also be concluded that no-load speed does not exceed the synchronous speed calculated by "Equivalent electromagnetic pole pitch" and just exceeds the synchronous speed calculated by mechanical pole pitch.Keeping some parameters constant, the stator winding style, air gap thickness, copper thickness and steel thickness were optimized by adopting FEM and comparing with speed, electromagnetic torque and loss. It has some reference values to the theoretical research and application of the motors.