| As the core functional component of NC machine tool,ball screw is the key to ensure the accuracy and stiffness of industrial machine tool.At present,China is in the transition stage to advanced manufacturing.The localization matching rate of domestic ball screws for the highend CNC machine tools is still insufficient,and there is still a large gap with the foreign products in the performance indicators of high-end products such as high precision and high load.The profile parameters with the raceway arc radius and contact angle as the main parameters are the decisive factors for the accuracy and bearing performance of ball screw.Domestic rolling functional component manufacturers do not consider the difference of profile parameters and tolerances under different applications during the design stage,and have weak control ability on the raceway profile during the processing stage.Most of them only focus on the evaluation of the pitch diameter and lead during the measurement stage.The lack of theoretical research on raceway profile is the key to restricting domestic ball screws from catching up with the foreign high-end products.Supported by the National major science and technology project "Research on the common technology and the capacity building of functional component testing"(2016ZX04004008),this research carries out the theoretical and experimental research on the raceway profile parameters of ball screw in three aspects of design,processing and testing.Firstly,the calculation model of key performance considering raceway profile parameters is established,and the influence of different profile errors on the key performance is analyzed.Secondly,the design method of profile parameters under different requirements is considered.Then,the relationship between the geometric errors and raceway profile errors in raceway high-precision grinding is studied,and the targeted control measures are carried out.A perfect measuring method of profile parameters for internal and external helical raceways is established,and the machining error is fed back through profile measurement.The closed-loop control system of raceway profile based on the theory,design,machining and measurement is established.The specific research contents are as follows:(1)onsidering the balanced contact angle of screw and nut,the contact load model of ball screw under different loading conditions is established,and the load heterogeneity under different loading and profile parameters is compared.Based on this,the friction torque model considering bearing and viscosity is established,and the axial stiffness model considering series and parallel connection of contact deformation elements is established.The main influencing parameters of key performance are analyzed through the global sensitivity.(2)Aiming at the influence of raceway profile error,the influence of the normal section error,lead error and pitch diameter error on the load fluctuation is analyzed according to the contact load model.Based on this,the influence of profile error on the fluctuation of friction torque is analyzed,and the friction torque and fluctuation under different tolerance balls are verified by experiments.The influence of the profile error on the stiffness are analyzed,and the comparison with the stiffness calculation method using accuracy and load correction coefficient in the national standard is carried out.The axial stiffness under different loads is verified by experiments,and the relationship between axial stiffness and friction torque is established.Considering the axial travel error caused by the profile error,installation error and deformation error,the travel error model of ball screw is established.The period and fluctuation amplitude of the simulation curve are verified by experiments to be close to the measuring results.The influence theory of the profile error on the performance provides a theoretical basis for the design of high-performance products.(3)Aiming at the design of raceway profile parameter,considering the error influence theory and processing technology,a design method of the raceway profile parameter including contact angle optimization,adaptation ratio design,travel error determination and profile parameter classification requirements is proposed,which further improves the design theory of ball screw.On this basis,according to the characteristics of high-precision ball screw,R40-10 ball screw is designed,and the relevant test shows that the products controlled by profile can ensure the accuracy and reduce the performance fluctuation.According to the characteristics of high bearing ball screw,R16-04 ball screw is designed.Through the finite element analysis,the bearing capacity of the designed profile parameters is improved compared with the traditional parameters.(4)Aiming at the control of raceway profile machining,the topological analysis of the thread grinder is carried out based on the theory of multi-body system kinematics.Mapping the dressing error of the grinding wheel to the geometric errors of the virtual axis,the machining accuracy model of the thread grinder containing 36 geometric errors is established,which unifies the two-time profile replication process of grinding wheel grinding and dressing during the raceway forming of the thread grinder.According to the principle of raceway forming,after solving the difference between the actual and ideal raceway profile and corresponding to the profile parameters,the raceway profile grinding error model of ball screw is established.Finally,the relationship between geometric error of thread grinder and raceway profile error is established,and the key geometric errors corresponding to four profile parameters are obtained through the global sensitivity analysis.Combined with the grading requirements of raceway profile parameters,the accuracy requirements for the key geometric errors of thread grinder in the grinding of screw and nut raceway are further obtained,which provides a basis for the machining control of raceway grinding error.(5)Aiming at the measurement of raceway profile parameter,according to the raceway modeling,the basic theory of helical raceway profile measurement containing axial data conversion and normal data processing is proposed.Based on the optical measuring principle,the measuring methods are proposed respectively.The screw raceway profile measuring method is obtaining the normal section by axial scanning after rotating the LED sensor by the lead angle,and the nut raceway profile measuring method is converting the image obtained by axial scanning of the point laser reflected by the triangular prism to the normal section.And a complete set of special detection devices are developed.It has successively completed the optical path analysis and the sensor selection,the analysis of the system key errors,and the comparison and verification of the measuring accuracy,and finally realized the rapid and highprecision detection of the raceway profile for the different types of ball screws,which provides a guarantee for the closed-loop control of the product profile parameters.The development of the research and the establishment of the closed-loop control system for the raceway profile make up for the shortcomings of the relevant theories of ball screw,and provide the theoretical and technical support for improving the performance of domestic ball screw products. |
PDF Full Text Request