Research On Detent Force Of Tubular Permanent Magnet Linear Motors

Linear motor is widely applied in several occasions,as a special type of motor,it can directly convert electrical energy into linear motion without the intermediate conversion mechanism such as ball screw.Compared to traditional rotary motor,it has advantages such as small volume,high efficiency,fast response,high accuracy and so on.As one of the linear motor types,the tubular permanent magnet linear motor(PMLM)has both advantages from linear motor and permanent magnet motor.Because of its slotted primary core,cogging force will be produced.The primary core is discontinuous,so the magnetic field in the left and right sides of the core is distorted,which will result in end force.Cogging force and end force are called detent force together.Detent force will result in thrust fluctuation which will deteriorate the performance of servo control system.This project is fund by National Natural Science Foundation of China—study on thrust ripple and material iron loss character of tubular PMLM made of soft magnetic composite materials.In this paper,the main research is concentrated on the structure of tubular PMLM.For the problems mentioned above,a tubular PMLM is designed and its detent force is studied.The work mainly including the following several aspects:Firstly,the basic structure and working principle of tubular PMLM were introduced in details.Based on the theoretical analysis and calculation,the electromagnetic structure of tubular PMLM is designed.The main structure of the motor is basically determined.The mechanism of detent force of tubular PMLM is studied,and the influence of the factors such as the length of primary core,the air gap,the width of the slot and the pole-arc coefficient on the detent force of tubular PMLM were analyzed by the finite element method.Secondly,a tubular PMLM with skewed core end is proposed to reduce detent force and the analytical expression of the end force of the motor is derived.According to the analytical expression,the optimal length of the skewed core end is determined and verified by the finite element method,the prototype is manufactured for experimental verification.Applied skewed core slot of rotary motor to the tubular one,the influence of the angles of the skewed core slot on the detent force is studied and analyzed by the finite element.Finally,a tubular PMLM with auxiliary teeth is proposed to reduce detent force.Based on lateral force method,the end force is derived and on the basis of the end force of the core,the end force expression of auxiliary teeth and the total end force are obtained,according to the total end force expression,the size of optimal auxiliary tooth is obtained,and verified by the finite element simulation.