Air-Gap Magnetic Density Characteristic Analysis And Robust Optimization Of Structure Parameters For Permanent Magnet Brush DC Micro-motor

Permanent magnet brush DC micro-motors are widely used in automobiles, household appliances, medical equipment, and aeromodelling toys etc. However, in the process of large-scale manufacture for Permanent magnet brush DC micro-motors, its output torque characteristic don’t have a good uniformity because of the influence factors, such as, processing and assembly, material properties, working conditions etc. Therefore, taking permanent magnet brush DC micro-motor as the object of study, the method and theory, which include robust design, electromagnetics, mechanical optimization design, and finite element analysis and so on, is used synthetically. Air-gap flux density characteristic is analyzed with different magnetization patterns. Analytic model of the air-gap flux density for PM motor is researched under the condition of cogging effect. Optimization of Structure Parameters for permanent magnet brush DC micro-motor is developed in order to reach the target of output torque fluctuation minimization. The main research contents are as follows:Firstly, analytic model of air-gap flux density for permanent magnet motors is researched under the condition of non-cogging effect. For four different permanent magnet magnetization, analytic model of air-gap flux density of permanent magnet excitation and electrification winding excitation are built respectively under the condition of non-cogging effect. Radial component and tangential component of air-gap flux density are analyzed, and, comparing to finite element analysis, the result of analytic calculation is validated.Secondly, analytic model of air-gap flux density for permanent magnet motors is researched under the condition of cogging effect. Air-gap permeance, pole shifting and different magnetization patterns are considered synthetically, and, synthetic air-gap flux density and calculation method of cogging torque are researched considering cogging effect. Based on this, analytic model of output torque are derived with different magnetization patterns. The synthetic air-gap flux density and cogging torque are analyzed by examples calculation. What’s more, the effectiveness of analytic calculation is validated by comparing with finite element analysis.Thirdly, finite element analysis of output torque for permanent magnet brush DC micro-motors are carried. The influence of residual magnetic flux density, relative permeability, pole arc coefficient, permanent magnet thickness, pole arc offset distance, stator thickness, tooth width, tooth wedge angle, height of slot bottom and slot opening width on motor output torque are analyzed further by means of Ansoft Maxwell software. Comparing to finite element analysis, the validity of calculation result is affirmed.Finally, robust optimization of structural parameters for permanent magnet brush DC micro-motors is carried. Using robust design method, stator thickness, pole arc offset distance, pole arc coefficient, residual magnetic flux density, relative permeability and shaft material are chosen as controlling parameters, and, stator thickness deviation, pole arc offset distance deviation, pole arc coefficient deviation, residual magnetic flux density deviation, rotor dynamic eccentric and pole position shifting are chosen as noise factors. Then, orthogonal test is arranged. Using torque fluctuation factor as an optimization target, the best combination level of each design parameters is obtained and simulation test is carried via noise-signal ratio analysis. The result show that mean value of torque fluctuation factor is reduced by 76.8% and the variance is decreased by 89.5%. The method provides a new way to design low cost and high quality for permanent magnet brush DC micro motor.