Research On The Crawling Mechanism And Dynamic Analysis Of Linear Feed System

The crawling phenomenon of machine tool feed system will cause the instability flutter of machine tool, and it will make workbench work quickly or slowly, walking or stopping. It reduces location accuracy and sensitivity, dropping the processing precision and surface quantity of workpiece, and also result in machine tool transmission system to generate additional load which intensify tool wear. Therefore, studying the low-speed crawl and high-speed start-braking problems is of vital significance to improving the quality of machining and the study of linear motion dynamics.This paper takes linear motion platform with ball screw as research object, rigid-flexible coupling model is established, and then simulation of dynamic characteristic is made under low speed crawl and high speed start-braking, Finally the correctness of the theory of finite element analysis is verified through the modal test. In this paper, the concrete research content is as follows:(1) The present situation of crawl vibration is summarized through consulting relevant references at home and abroad. And the working principle of machine tool feed system and crawling mechanism are expounded briefly.(2) The model of linear motion platform is established, and then the numerical analysis is done, finally the critical speed of crawling is obtained. For the "low speed crawl" phenomenon of feed system, mechanics model and the mathematical model are established. According to the mathematical model, the crawling phenomenon of critical speed of feed system is concluded, and it is concluded that the factors influencing crawling including moving parts quality, damping coefficient, the stiffness of the transmission system, the difference between the static friction coefficient and driving speed, etc.(3) The rigid-flexible coupling model of linear motion platform is established. The screw is made flexible with the finite element analysis software ANSYS, and then it generates the modal neutral file which is imported to ADAMS to build rigid-flexible coupling model, and the correctness of the model is verified.(4) Dynamics simulation of Machine under two kinds of limit state, low speed crawling and high speed start-braking. The simulation under the working condition of low speed crawl is finished, and the influence factors, feeding speed, moving parts mass, damping, and the system stiffness, the difference of the static-kinetic friction is studied. Finally, theoretically restrain and reduce the crawling measures put forward; Simulation of the feed system under high speed start-braking is done, stress on node of screw in the braking phase is the largest, and the platform in Z axis generates vibration.(5) The finite element and experimental modal analysis of linear motion platform is Completed and the comparison is made. According to the theory of Hertz, ball screw nut surface and rolling guide joint surface contact stiffness are obtained, Then the modal analysis of linear motion platform is done with ANSYS. Finally, modal test analysis of the feed system is made to verify the correctness of the finite element analysis.