The Study On Dynamics Characteristics And Stability Of Feeding System In Big-inertia

The ball screw system of big inertia is the key function components of the feed system of high speed, high precision and heavy CNC machine tools, is a damping system of multiple-degree of freedom. Because of the thin and hollow bar of the ball screw special structure, and the influence of different support form of both ends of a ball screw, the ball screw system in high speed rotating is actually a nonlinear dynamic system, this view has been identified by many scholars. At present the research work of mainstream of the ball screw system are mostly based on the theory of linear vibration to check into the vertical, horizontal and torsional vibration a the system, ignore the nonlinear factors, makes the large deviation compared with the theoretical results and experimental conclusion. When the machine tool put up the strong cutting, and high-speed cutting, cutting difficult-to-machine materials, or the structure of cutting tools, fixture, workpiece are relative complex, it’s going to produce the incentive of various order of frequency, make the state of motion of system happen bifurcation, may enter chaos state. So this article will be main research the nonlinear dynamic behavior of the ball screw in big inertia at high speed based on the linear vibration of system.This subject adopts the research approaches of "theory derivation-simulation analysis-experiment test" to promote the research for the feeding system of numerical control machine. It mainly includes the following aspects:First of all, by the use of Lagrange equation to establish linear vibration model of feed system, identificated the four parameters that influent the system inertia, the orthogonal test are used to analysis the influence degree of the stiffness coefficient and inertia parameters to the positioning accuracy of the table.The study focuses on the nonlinear characteristic of the stiffness based on the ball screw’s four supporting scheme, so the dynamic stiffness of ball screw pair is changed with nonlinear characteristics, and make reasonable simplify in the process of theoretical derivation, then identify the stiffness nonlinear dynamics equation of the small errors. The L-P method is used to solve the approximate analytical solution of the equations and compared with the result of numerical simulation with MATLAB; Draw the phase diagram, bifurcation diagram, Poincare section graph, etc, study the chaos characteristics and regularity of the dynamic equation. Focuses on the analysis of the nonlinear systems movement stability and the bifurcation and chaos characteristics of system, and find out the relationship and match rule between the dynamics characteristic and the system parameters of the feeding system.Then, this paper introduces the Stribeck friction theory and friction model. The nonlinear characteristic of the friction was detailed discussed. It present that the changing law of nonlinear friction in the four characteristics of Stribeck friction curve, the response of nonlinear friction within the range comply with the different laws respectively. The dynamic equation of nonlinear was set up consider friction factors, and was given the analytical solution analysis, numerical simulation and parameter identification. Further through the bifurcation diagram and Poincare section graph, the bifurcation and chaos characteristics were analysised of the nonlinear system.After that, taking into account the nonlinear function of spring force and friction damping in the meantime, that is considering the nonlinear dynamic characteristics of friction coupling stiffness, establish dynamics equation, thus identify coupling nonlinear structure model. The approximate analytical solution of the equation was solved, and the numerical simulation analysis to the response, and programming with the software MAPLE, by changing the related parameters, study the bifurcation and chaos characteristics of the coupled system.As the foundation of the feeding system of single axis CNC milling machine and horizontal processing center, set up the experiments table for testing the dynamic characteristics of ball screw vice. Make a series of analysis for the collecting the acceleration time series, make the nonlinear judgment of the dynamic property of the system, and checking the effectiveness of the conclusion of the theoretical analysis from different angles. In a horizontal machining center, the vibration experiments were conducted of the feed system. It conclude that the trend that the changes of the inertia parameters, screw and nut contact stiffness, table and rail contact stiffness influence on the longitudinal, transverse and torsional vibration of ball screw and the tool working point. So the theoretical analyse of second chapter were validated.Finally, according to the results of theory analysis and experimental research, this paper puts forward the control strategy of Hopf bifurcation and chaos movement, and analyze the influence and control measures of nonlinear stiffness and friction factors, and discussed the effectiveness of the control measures from the optimization of the control strategy and improvement of the mechanical device of the CNC machine tools.