| The permanent magnet coupling acts as a magnetic drive device to achieve the torque transmission between the motor and the load.It is based on the principle of electromagnetic induction.Induction eddy current produced by cutting conductor lines of a permanent magnet in a conductor plate,and by the ampere force induced by the eddy current,it provides the transmission torque to drive the load operation.During the entire torque transmission,there is no mechanical connection between the input side and the output side.The permanent magnet coupling has the characteristics of simple structure,low installation accuracy,low maintenance cost,strong environmental applicability,and excellent vibration isolation effect.It can realize the functions of load rotation speed adjustment,overload protection,soft start,etc.It has certain application in ships,petroleum,power generation,chemical industry and other fields,however it is less used in coal mines.Due to the poor production environment of the coal mine and the high work intensity,the above advantages of the permanent magnet coupling have certain advantages in the application of coal mines and have a good application prospect.At present,the research of the domestic permanent magnet coupling is in the computer simulation analysis,imitating the foreign product stage,The related theoretical analysis is not mature enough and have a shortage of products with independent intellectual property rights.Therefore,the study of the theory of the transmission of the permanent magnet coupling is of great significance.The analysis of the relevant characteristics has a high practical value.This paper uses magnetic drive technology,material technology,based on electromagnetic theory,electrical power drive theory,using theoretical analysis,finite element simulation and experimental verification methods,the permanent magnet coupling transmission theory and transmission characteristics are systematically studied.A permanent magnet coupling analysis model was established.Based on the electromagnetic field theory,the permanent magnets' own characteristics and their recovery curves were analyzed.The relationship between the magnetic induction intensity and the magnetic field strength at the working point of the permanent magnet is obtained.Equivalent surface current method is used to make the permanent magnet equivalent to a series connection of magnetomotive force and magnetic resistance;The magnetic circuit characteristics of the permanent magnet coupling are obtained from the magnetic circuit theorem analysis.Use magnetic field division method to divide the external magnetic circuit of the permanent magnet coupling reasonably,the air gap of the permanent magnet coupling is divided into multiple regular flux tubes,and the magnetic resistance of each flux tube is calculated.The equivalent magnetic circuit model of the permanent magnet coupling is constructed according to the equivalent magnetic circuit method,and the relationship between the characteristics of the external magnetic circuit and the magnetic properties of the permanent magnet is obtained,in conjunction with the permanent magnet recovery curve equation,the analytical expression of the magnetic induction intensity at the working point of the permanent magnet is obtained.And from this we can calculate the magnetic flux of each flux tube,according to the principle of electromagnetic induction,the amperage force that each magnetic flux pipe mapped to the conductor plate area is calculated,and the amperage force of each area is integrated to finally obtain the equation of the permanent magnet coupling transmission torque and slip.The analytical expression of the maximum transmission torque and the maximum adjustable rotation speed of the permanent magnet coupling is obtained from this equation.The analytical expression of the eddy current loss of the permanent magnet coupling is calculated according to the law of conservation of energy.Based on the equation of the permanent magnet coupling transfer torque and the slip,combined with finite element simulation and experimental research,a single factor analysis of the influence of various material parameters and structural parameters of the permanent magnet coupling on its performance was performed.In the case of only changing the permanent magnet coupling permanent magnet material,air gap thickness,conductor disc material,and conductor disc thickness,the mechanical characteristics of the permanent magnet coupling under different parameters are obtained,the influence of the permanent magnet coupling's rated torque,the maximum transmission torque,the maximum adjustable speed,and the eddy current loss is obtained.The permanent magnet coupling has a positive correlation between the remanent magnetization and the permanent magnet coupling,which is not related to the maximum adjustable speed;The air gap thickness of the permanent magnet coupling is negatively related to the rated torque and the maximum transmission torque,and is not related to the maximum adjustable speed;the conductivity of the permanent magnet coupling conductor plate is positively correlated with the rated torque,and is not related with the maximum transmission torque,with the maximum adjustable negative correlation;permanent magnet coupling thickness of the conductor plate is positively correlated with the rated torque,with the maximum transmission torque and maximum adjustable speed are negatively related to the conclusion.Use ANSYS Maxwell software to analyze the transmission performance of the permanent magnet coupling,simplify the actual model of the permanent magnet coupling rationally,establish the finite element analysis model,set the material and parameters of each part rationally,and set the boundary conditions and excitation conditions according to the actual situation.According to the actual precision requirements,the grid is divided reasonably,and the three-dimensional transient field simulation of the transmission torque and the axial force of the permanent magnet coupling is analyzed by using the slip as a variable,and the transmission torque of the permanent magnet coupling varies with different parameters.The curve of the transmission torque of the permanent magnet coupling with the slip and axial force with the slip under different parameters is obtained.Combined with ANSYS Workbench software,the finite element analysis of the temperature field of the permanent magnet coupling is performed.The heat source power of each component obtained by the torque finite element analysis is used to introduce the heat dissipation coefficient to describe the heat exchange capacity of each component of the permanent magnet coupling and the air.Reasonably set the heat transfer parameters of various components and air,simulate and analyze the temperature field distribution of the permanent magnet coupling to obtain the steady-state temperature of each part of the permanent magnet coupling and the temperature rise curve under overload conditions.The area where the permanent magnet is mapped to the conductor plate has the highest temperature,the outer steel plate that is in direct contact with it is followed by,and the temperature of the permanent magnet decreases as the thickness of the air gap increases.Under the rated conditions,the temperature of the permanent magnets of the sector-shaped permanent magnet prototype and the circular permanent magnet prototype can be maintained below the allowable temperature.The temperature of the permanent magnet increases rapidly when overloaded,and the temperature of the permanent magnet prototype exceeds the allowable value after the overload exceeds approximately 20 seconds.Based on the theoretical analysis results,combined with simulation analysis and experimental research,the mechanical characteristics of the permanent magnet coupling are obtained.The transmission torque of the permanent magnet coupling increases rapidly as the slip increases,when the slip reaches a certain value(Square permanent magnet prototype is 220 rpm,circular permanent magnet prototype is 500 rpm),the transmission torque reaches the maximum value,and the permanent magnet coupling can work stably when the slip is less than the fixed value,and after the slip exceeds this certain value,The permanent magnet coupling is overloaded,the output side stops operating quickly,the transmission torque drops,the permanent magnet coupling slips and does not work,the motor power is completely converted into the eddy current loss of the permanent magnet coupling,and the permanent magnet coupling temperature rises rapidly.For common mining loads,the permanent magnet coupling has a certain speed control function.Change the air gap thickness to obtain the mechanical characteristics of the permanent magnet coupling under different air gap conditions.It can be seen that the maximum adjustable speed of the permanent magnet coupling does not change under different air gap conditions.The maximum transmission torque decreases with the increase of air gap thickness.In any rated speed motor,for constant torque load and quadratic law load,the fan-shaped and circular permanent magnet prototype can reduce the load rotation speed of 220 rpm and 500 rpm at most.The resulting power loss is equal to the load torque multiplied by the reduced rotational speed,and therefore does not have an energy saving effect for constant torque loads;since the power of the secondary law load is proportional to the third power of the rotational speed,for the quadratic law load,permanent magnet coupling can have a certain energy-saving effect.The fan-shaped and circular permanent magnet prototypes can reduce the rotation speed by 12% and 31% respectively,and it can reduce the power of the motors by up to 31.9% and 67.1% when the operating conditions require.After installing a permanent magnet coupling,there is a certain soft start effect for a constant torque load.For the circular permanent magnet permanent magnet coupling in this paper,the peak current of the motor is reduced by 9.8% after installation,and the motor start time is reduced by 5.9%.For quadratic law load,the permanent magnet coupling does not have a soft start effect.The permanent magnet coupling has the function of overload protection.Increasing the air gap of the permanent magnet coupling can reduce the maximum transmission torque of the permanent magnet coupling and reduce the overload factor.The axial force of the permanent magnet coupling is initially attractive.As the slip increases from zero,the attractive force gradually decreases,and when the permanent magnet coupling reaches the maximum adjustable speed,the axial force becomes zero,the axial force changes from attraction to repulsion,the repulsive force increases as the slip continues to increase,when the load is stalled,the axial force forms a huge repulsive force due to the huge slip.This repulsive force increases the air gap thickness of the limit-limited permanent magnet coupling,which disconnects the motor from the load and protects the motor.In order to verify the results of theoretical analysis and finite element simulation,a finite element experiment platform was established to test the torque and slip condition of the permanent magnet coupling in the stable working condition using the existing sector permanent magnet permanent magnet coupling experimental platform.Improve the permanent magnet coupling experimental platform,install reducer,electric actuator to test the full mechanical characteristics of the permanent magnet coupling,equipped with a data acquisition system to record the permanent magnet coupling torque,slip,temperature changes,accurately obtain the permanent magnet coupling drive data and temperature conditions.The mechanical characteristics of the permanent magnet coupling obtained from the experiment are compared with the analytical expressions obtained by theoretical calculations and the finite element simulation results.It can be seen that the error between the finite element simulation result and the experimental data is within 5%,and the theoretical formula is less than the maximum adjustable slip.When the speed is low,the error is within 10%.If the error is greater than the slip,the error of the theoretical formula also increases when the air gap increases. |
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