Design And Research Of Cylindrical Giant Magnetostrictive Automatic Preload System For Ball Screw

The preload force is the main factor for generating the frictional torque of the ball screw.It can improve the axial rigidity and positioning accuracy.If only the rigidity and positioning accuracy of the ball screw pair are considered,the larger the preload force is,the better the axial clearance caused by the elastic deformation can be eliminated.However,excessive preload force will increase the driving torque,reduce the transmission efficiency,increase the temperature,increase the contact fatigue and wear between the ball and the raceway,and shorten the working life.Therefore,the development of the automatic preload system with adjustable output force is of great significance to improve the transmission performance of the ball screw pair.Precision micro-displacement actuators based on functional materials such as piezoelectric ceramics and giant magnetostrictive materials(GMM)have the advantages of high resolution,fast response speed,adjustable output force,etc.Accordingly,real-time control of preload force is the direction to improve transmission performance of the ball screw in the industry.According to this research idea,a novel cylindrical giant magnetostrictive actuator(CGMA)is developed by using the GMM,a cylindrical giant magnetostrictive automatic preload system for ball screw is proposed,the structure analysis and optimization of cylindrical giant magnetostrictive automatic preload system for ball screw are carried out,multi-field simulation and output characteristic analysis of the CGMA are done,modeling and control of automatic preload system are conducted,and the main performance of the ball screw with preload system based on CGMA is discussed in this paper.(1)To realize the automatic adjustment of the preload force,a magnetostrictive automatic preload system is proposed based on the spacer preload principle of double-nut ball screw.A novel actuator(CGMA),which is the core component of the preload system.is developed by using the cy’lindrical giant magnetostrictive material(CGMM).Based on the measured data,the pre-tightening force of the CGMA is determined.The internal magnetic field model of the CGMA is established to analyze the influence of magnetic yoke permeability,air gap thickness and screw shaft on magnetic field intensity.The temperature control structure which directly cools the heating source is proposed.The equivalent thermal circuit model,steady temperature model and thermal displacement model of the CGMA are established,and the main factors affecting cooling effect are analyzed.The structure design of the preload connector is determined by considering the factors such as the adjustment of the initial preload force and the transmission of the driving torque.(2)Static electromagnetic field,temperature field and structural statics simulations are conducted to verify the rationality of the structure analysis and design of the preload system.The magnetic field simulation shows that the calculated magnetic field intensity based on the magnetic circuit model is in good agreement with the simulated value under different driving current;the magnetic field intensity of the CGMA through a screw shaft is reduced by less than 1%,and the magnetic flux density is reduced by less than 4.9%,which meets the requirements of automatic preload;the magnetic field evenness of electromagnetic bias is obviously better than that of permanent magnet bias,and different stress has little effect on the evenness.The temperature field simulation shows that the oil cooling method has excellent cooling effect and the temperature field distribution is uniform.Choosing appropriate oil temperature and flow velocity can keep CGMA in the optimum working temperature range.The 2504 series ball screw is used as the preload object.The structural static simulation shows that when the maximum preload force is applied to the automatic preload system,its total axial deformation is within the allowable range,and the CGMA can realize the adjustment of the output preload force.(3)A test platform is established with self-developed CGMA,then the static and dynamic output characteristics are respectively studied.The experiment results indicate that the CGMA has good linearity and no double-frequency effect under the action of the bias magnetic field.Although the output decreases with screw shaft through the actuator,the performance of CGMA meets the design requirements for ball screw preload.The thermal characteristics are tested and analyzed.The results show that the forced oil cooling method can effectively suppress the thermal deformation error caused by temperature rise,so that the magnetostrictive output characteristics of CGMA are stable;the measured steady-state temperature is consistent with the simulation value,the relative error is less than 5%,which verifies the rationality of the temperature control system design.(4)Based on the Jiles-Atherton hysteresis nonlinear model and quadratic domain model,a quasi-static model of CGMA output displacement is established.Differential evolution algorithm is used to realize the model parameter identification.Compared with genetic algorithm and particle swarm optimization algorithm,it has fast convergence speed,stable identification result and high identification precision.The calculated output value of the identified displacement model is compared with the measured value and the average relative error is less than 6.2%.The results show that the differential evolution algorithm is effective and reliable for the parameter identification of nonlinear model.Based on the piezo-magnetic equation and Newton’s law,the transfer function model in the linear region of cylindrical giant magnetostrictive automatic preload system is established,and the influence of design parameters on its dynamic performance is analyzed.(5)For cylindrical giant magnetostrictive automatic preload system,it is difficult to express with a fixed mathematical model due to factors such as temperature and magnetic field.A data-driven tight format model-free adaptive control(MFAC)method is proposed,and the nonlinear model of preload system is replaced with the dynamic linear time-varying model.Through the simulation and experiment of MFAC control and PID control of automatic preload system,the rationality and effectiveness of MFAC algorithm are verified.The results show that the automatic preload system based on MFAC algorithm has fast response speed,small tracking error and strong anti-interference ability.(6)By analyzing the axial deformation of the ball screw based on CGMA preload,the relationship between the axial deformation and the magnetostrictive preload force is obtained.When the size parameter is fixed and the axial load remains unchanged,it appears positively correlated.The preload force and the axial displacement of nuts of the ball screw based on CGMA preload are experimentally studied.The results show that different initial preload force can be preset by adjusting the preload connector,and timely adjustment can be made to the preload force by changing the drive current of CGMA.As a result,the axial rigidity can be improved by preload adjustment,which is in accordance with the theoretical analysis results.The torque and vibration test results are analyzed.The results show that the friction torque is positively correlated with the drive current,the amplitude of the ball screw depends on rotating speed,and the force output by the automatic preload system has no obvious influence on the main frequency of the running ball screw.