Electromagnetic Characteristics And Optimization Of High Thrust Density Cylindrical Voice Coil Motor

Voice Coil Motor(VCM)is a special permanent magnet motor designed based on the principle of Lorentz force.It has the advantages of simple structure,small size,fast response,convenient control,high efficiency,and no cogging effect.Voice coil motor is faced with the problem of small output thrust density,a large electrical load will overheat the motor windings and permanent magnet,resulting in problems such as winding insulation damage and permanent magnet material demagnetization.In this paper,for the purpose of improving the thrust density of the motor,the structure of the voice coil motor is reasonably optimized,and an improved adaptive genetic algorithm is used to optimize the structural parameters of the motor.Firstly,the working principle of the voice coil motor and the structure of different types of motors were introduced.A cylindrical voice coil motor suitable for high thrust density applications was established combined with the relevant research foundation and practical engineering requirement.Then,the equivalent magnetic circuit model of the motor was established,and the working air gap magnetic flux density of the motor was calculated by the nonlinear magnetic circuit,thereby further calculating the thrust density of the motor.The finite element simulation software was used to establish a two-dimensional simulation model of the motor.The static magnetic field distribution of the motor was analyzed,verifying the validity of the mathematical model of the motor.Through the simulation results,it was found that the error of the thrust density calculation of the motor based on the equivalent magnetic circuit model is small,which can be used in the optimization algorithm as the target function for calculation.Secondly,to improve the thrust density,the structure optimization of the cylindrical voice coil motor was studied.This paper proposed a semi-closed structure applied to a cylindrical voice coil motor.The finite element model of the motor was established to verify the effectiveness of the new structure.Compared with the original model,it was found that the semi-closed structure can improve the magnetic circuit at the end of the motor,and constrain the reverse magnetic flux at the end of the motor.As a result,the air gap magnetic flux density of the motor and the thrust density of the motor were increased.Then,using the semi-closed voice coil motor as the model and the thrust density of the motor output as the target,the sensitivity analysis of the key structural parameters of the motor was carried out,and the influence of each structural size on the performance of the motor was studied.A prototype of a semi-closed voice coil motor was fabricated,and an experimental platform was built to conduct static thrust testing.The experimental results show that the static thrust of the mover of the semi-closed voice coil motor at different positions is close to the theoretical calculation result,and the thrust density of the motor is significantly increased compared with that before the improvement.Finally,the genetic algorithm and adaptive improvement strategy were studied.Since the traditional method for changing single structural parameters of motors has the defect of local convergence,genetic algorithm was used for global optimization of structural parameters of motors.Aiming to solve the problem that the basic genetic algorithm is easy to locally converge in the optimization process,linearly and nonlinearly adjustment of the crossover and mutation probability of the basic genetic algorithm was used to improve the performance of the algorithm.The improved adaptive genetic algorithm was used to globally optimize the semi-closed voice coil motor to find the optimal solution.Through multiple calculations,the performance of various algorithms were compared.It was found that the improved adaptive genetic algorithm had better stability and calculation results.Substituting the optimization scheme into the finite element method,the thrust density of the motor calculated by simulation has been improved to some extent compared to the motor before optimization.