System Characteristic Analysis And Heat Dissipation Research Of Slotless Permanent Magnet Linear Motor For Punching Application

The slotless permanent magnet linear motor(SPMLM)performing a direct linear motion,and is characterized by space saving,high thrust density,zero detent force and fast dynamic response.Therefore,the SPMLM is an attractive candidate for the lowpower leather punching system.However,the long electromagnetic air-gap length of the SPMLM leads to an inevitable increase of copper loss and a poor cooling condition of the motors,and thus constricting the safe and reliable operation for the system.In order to find methods to reduce motor losses and improve the motor cooling condition,the system characteristics,magnetic field distribution and the lumped parameter thermal network model of the SPMLM are studied through theoretical calculation,finite element analysis and prototype experiments.The main contents of this thesis are as follows:Firstly,the electromagnetic characteristics and structural characteristics of various short-stroke permanent magnet linear motors are compared,and the characteristics of the leather punching system are combined to demonstrate the rationality of SPMLM applied to leather impact systems.Then,an analytical calculation model for the air gap flux density and electromagnetic force of the SPMLM was established.Secondly,The mathematical model of the impact motion was established and solved by analytical method and numerical method respectively to present a comprehensive analysis of the system characteristics.The result shows that both reducing the mover mass and increasing the average thrust coefficient are conducive to reducing the resistive energy consumption and the increasing system dynamic performance.Besides,the system efficiency will decrease as the mover kinetic energy increases.Based on the system characteristics research results and the magnetic field distribution of SPMLM,the specialshaped yoke structure is proposed to reduce the mover mass.According to the the finite element analysis and the prototype experiment results,the special-shaped yoke structure can reduce the mass of the mover while keeping the thrust performance of the motor unaffected,thereby reducing the resistive energy consumption and shortening the impact time.Moreover,the dynamic experiment also verifies the relevant conclusions about the relationship between impact kinetic energy and impact efficiency.Thirdly,the temperature rise and heat dissipation of the SPMLM are analyzed based on the lumped parameter thermal network,the results indicated that the winding heat is mainly dissipated through the coil bobbin in the axial direction and the yoke surface in the radial direction.The small heat dissipation coefficient of the yoke surface is an important factor that limits the radial heat dissipation capacity。The high temperature and low emissivity of the yoke provide conditions and space for improving the surface radiation capacity.Therefore,a carbon nano-coating material with high emissivity is used to cover the yoke surface.The results of the thermal network model and the temperature rise experiment show that this approach can significantly enhance the surface radiation heat dissipation,thereby effectively reducing the temperature rise of each part of the motor,and extending the safe and reliable operation range of the motor.