Modeling And Analysis Of Ball Screw Mechanics And Electromechanical Coupling Characteristics

The feed system structure and servo system in CNC machine tools are an important part of modern CNC machine tools,and also the focus and hotspot of research in recent years.The ball screw joint is a typical representative rolling joint in the movable joint.It is widely used in the feed system of CNC machine tools.It has many advantages such as large load,large stroke and high efficiency.The feed system is It is the direct participation part of the machining process,so it is of great research significance to study the ball screw joint to improve the performance of the machine.The servo system serves the feed behavior of the workpiece.Dynamic stability,operational stability and adjustable speed are several important basic functions of the servo system.Among them,the linear servo motor has become a popular research object by omitting the simplicity of the transmission link between the traditional CNC machine tool motor and the workbench.CNC machine tools are typical mechatronic systems,in which electromechanical coupling is quite common.The output command of the servo motor becomes the input command of the mechanical structure,the state variable of the mechanical structure is transformed into the input variable of the control system,and the information conversion between the two "subsystems" has a direct electromechanical coupling effect.The mechanical structure part and the servo control system are separately modeled and analyzed,and then they are integrated into the simulation model through mathematical relationship to analyze the influence of the axial stiffness of the ball screw pair of the mechanical structure on the servo feed behavior.The influence of the mechanical structure parameters is taken into account in the electromechanical coupling function to form a complete set of ball screw static and dynamic characteristics and electromechanical coupling characteristics modeling and analysis methods.The theoretical model of the ball screw is based on the three-dimensional solid model under the assumption of rigid body.The static stiffness is calculated by the theory of Hertz contact mechanics.The kinematic equation is added by the spring damping element method and the finite element software dynamics calculation can be used to analyze the joint.Affected ball screw pair static and dynamic characteristics.In order to verify the correctness of the model,the ball screw of the horizontal machining center of the model W5032 is used to perform the hammering frequency response function extraction experiment.The experiment adopts the principle of collecting the average value of multiple hammers.The mathematical model of the permanent magnet synchronous motor established by the coordinate transformation principle of the vector control method is simplified on the basis of the Laplace transform to obtain the transfer function of the permanent magnet synchronous motor.The servo speed regulation system is decomposed into current loop,speed loop and position loop,and the current loop is regarded as the innermost loop in the three-loop control,and the outer layer is the speed loop and the position loop in turn.Write the transfer function of the inverter and the filter in the current loop,and adjust the PID regulator parameters to be equivalent to the first-order system.The outer two rings are equivalently simplified and then stabilized by the boundary method.The mechanical transmission part contained in the position loop must also be equivalent to the transfer function.After the system is built,the Bode plot generated by the linear analysis function in Matlab/simulink detects the system stability of each loop.In order to investigate the influence of the axial stiffness of the ball screw on the servo system on the feed response speed and stability of the mechanical structure,the axial stiffness of the ball screw is compared with the output results under the two conditions of no-load condition and load disturbance state.Experiments show that the axial stiffness of the ball screw is very important to the speed response of the system,regardless of the no-load or load disturbance,which will affect the stability and machining accuracy of the system.Therefore,it is necessary for the system to select a reasonable axial stiffness of the ball screw.