Dynamic Modeling Of The Ball Screw Test Bench's Joint And Modal Analysis

When the machine tool is in a high speed machining state,the uncontrollable vibration of the feed system has a great influence on the machining quality of work-piece.In order to improve the stability of machine tool structure and reduce vibration,dynamic research is necessary.In the commonly used finite element simulation method,the rolling joints of the structure are usually simply defined as bonding contact,and the complex contact form between the rolling joints are ignored.In particular,the finite element calculation may have a great error in the study of the dynamic characteristics of a complex assembly,who has a large number of rolling joints.In this paper,the ball screw test bench with typical screw feed system is chosen as the object of the research.Considering the static state and the operation state,the comprehensive research of the dynamic and vibration characteristics of the ball screw test bench are finished by using dynamics modeling,finite element simulation and modal experiment.The details are shown as follows:Firstly,the composition of the electromechanical system,structure characteristics and installation method of the ball screw test bench are briefly described to prepare the following calculation,simulation and experiment.Secondly,The Hertz contact theory are used to calculate the contact stiffness of the ball screw,bearing and liner guide according to the contact characteristics of the rolling joints in the test bench's feed system.After the contact stiffness is assigned to the spring element in the finite element software,the modified dynamic model of the system is set up by finite element software.Thirdly,the finite element modal analysis of the test bench is carried out.Based on the results of finite element analysis,the test bench was analyzed by using impact hammer modal test.Then the suitable vibration pick-up points are determined by the finite element mode.And the number of modal measurement points that can fully display the mode of vibration is determined by comparing the mode shapes of multiple tests.Furthermore,base on change the material of the hammer head and test,the hammer head which can achieve structure's fully excitation is determined.At this point,the experimental modal analysis is completed and the exact modal parameters of the system are obtained.At last,the accuracy of this model is verified by comparing the results of three methods.Fourth,aiming at the characteristics that this kind of equipments always do continuous work for a long term,the operation mode analysis of the test bench is carried out.The natural frequency of the system under different working conditions is obtained,and the influence trends of rotational speed and axial load on the vibration and natural frequency is obtained by analysing the experimental results.In this paper,the dynamic characteristics of the ball screw test bench are studied from two aspects: the static state and the working state.It provides a reasonable dynamic model and a comprehensive research method for the dynamic characteristics of the complex assemble structures like machine tools,and also provides the basis for modal analysis,structure optimization and fault diagnosis of machine tools.