Study On The Design And Optimization Of The Detent Force Of The Permanent Magnetic Synchronous Linear Motors

With the development of advanced manufacturing industry, CNC machine tools trend to high-speed, high-precision, fast-response and long stroke. Owing to inherent drawbacks of traditionaltransmission, it is difficult for “traditional serve motor with ball-screw” to meet the demands.Therefore, direct drive linear motors are used to replace mechanical transmission mechanismincreasingly in the machine tool industry year by year. However， the detent force resulted fromthe magnetic circuit discontinuity of linear motors deteriorates the servo performance of theprecision motion systems, especially squirming (crawling) at low speed. This paper describes thedesign of linear motors and optimization of detent force through systematical analysis onelectromagnetic parameters, air-gap flux density and magnetic resistances. Fabricating processesand prototyping of the permanent magnet linear synchronous motor (PMLSM) are conducted toverify the effectiveness of techniques proposed by the paper. Experiments show excellentconsistence between design and the prototype.Main contents in this paper are configured as below.1. An overview of the development and current status of linear motors is presented. Differentoptimization techniques taken to minimize the detent force of the linear motors are alsosummarized.2. Based on the theory of rotating permanent magnet motors, a set of electromagneticformulas for permanent magnet synchronous linear motors are derived. Therefore, initialparameters including the main dimensions of the linear motor, the air gap size, and permanentmagnet size, and notch, no-load operating point of the permanent magnet and the configuration ofwindings are determined according to the requirements for the motor in the task.3. By using Equivalent Magnetizing Current (EMC) methods, a physical model with smootharmature is established. Analytical solutions of magnetic field and flux density in air gap arederived. S-c transformation is applied further to analyze the slot effect due to lamination stacknotching.4. Through the study on the principle of the detent force in the PMLSM, mathematical modelsof end force versus primary displacement are established and optimal length of the primarylamination stack is worked out to minimize the end force. Eventually, fractional pole-slotconfiguration of linear motor with28poles24slots and optimal teeth-slot ratio are employed in prototype to reduce the cogging force. Final results show that the detent force is decreased by56.4%comprised with that of the initial design and overall fluctuation of thrusting force iscontrolled within3.4%.5. In the experimental, key processes are introduced in prototyping of PMLSM. Mainparameters (detent force, force linearity, back EMF, etc.) of the prototype are measured, whichshow excellent accordance between simulation results and the prototype.