Dynamic Charateristic And Control Method Research For High-Speed High-Precision Ball Screw Positioning System

With the rapid development of machine tool, surface mounting technology and 3D metal printing machine, the driving technology of servo motor+ball screw is becoming a huge demand as the core part of the intelligient manufacturing equipments. It plays a critical and decisive role in the development of China’s high-end manufacturing equipment. The positioning precision and efficiency of high-end manufacturing equipments are directly determined by the accuracy and speed of servo motor+ball screw drive platform.In the research background of surface mounting technology and in order to reduce the tracking error caused by the high-speed motion in the servo motor+ball screw drive system, a series of research works are conducted in this thesis. The theoretical analysis and experiment research of dynamic characteristic and closed-loop control algorithm for ball screw mechanism are presented in succession. The positioning accuracy and speed are improved in a large extent. This thesis provides an important theoretical significance and practical value for the developing of the high-end manufacturing equipments. The main work and research results in this thesis are as follows:1) The drive pattern of "rotating motor+ball screw mechanism" is designed and built as the positioning system. The rigid dynamic model of ball screw positioning system is acquired based on the physical property analysis. The piece-wise constant voltage signal is used as the input signal for the drive motor to generate the time-domain data. This data is used in the least-square method to identify the parameters in the rigid dynamic model. The rotating motor used in the ball screw positioning system is permanent magnet synchronous motor (PMSM). The mathematical model of PMSM is analyzed and deduced based on the space vector control principle. The bandwidth characteristic of servo amplifier for PMSM is obtained by the experiment. This builds the foundation for the control system design.2) Based on the vibration shape calculated from finite element model (FEM) and considering the influence to the dynamic characteristic by the variation location of working table, a set of hybrid basis function is used to generate the new Ritz series to build the system motion equation. The pitch of ball screw is also considered in the method. Through the numerical simulation, the modal characteristics and vibration shape of system under the circumstance of different worktable locations are given. The sine sweep experiment is conducted to acquire the real vibration mode frequencie of the system. The experiment result shows that the proposed modeling method can accurately predict the vibration characteristics for the ball screw drive system. It provides a theoretical basis for the control design of high frequency vibration suppress.3) A sliding mode control based on nonlinear sliding surface (NSMC) is researched for a class of system with matched parameter perturbation and disturbance which the upper bound is unknown. NSMC can improve the system transient performance with fast response and non-overshoot by changing the system damping ratio. The adaptive parameter estimation is used here for replacing the high switching gain. It can reduce the chattering caused by the switching term in the sliding mode control. In order to overcome the weakness of unrobust to the mismatched parameter perturbation and disturbance of the system above, the disturbance observer is designed to eliminate the mismatched disturbance and generate the novel nonlinear sliding surface. Finally, the improved control law which is named as adaptive sliding mode control with nonlinear sliding surface and disturbance observer (ANSMC-DOB) is acquired.4) From the perspective of traditional control method, PID and adaptive sliding mode control (ASMC) are presented according to the rigid body model of ball screw positioning system as the single position feedback control. In order to improve the precision of control system, the two-degree-of-freedom model of ball screw positioning system is built and identified by the frequency response of first axial vibration mode. On the basis of this model, the dual-position feedback control of ball screw positioning system is researched by the control law of ANSMC-DOB. Based on the dynamic characteristic analysis of the system, the corresponding notch filters are designed to control the high frequency vibration.5) The closed-loop control system for ball screw driven mechanism is built based on the real-time simulation platform of dSPACE. The reference trajectory is firstly researched before the control design for the ball screw positioning system. In order to reduce the vibration caused by the jumping acceleration and deceleration, a continuous jerk trajectory is designed. Then the simulation and experiment works are conducted based on the theory analysis above. The result shows that when the working table of ball screw positioning system is running under the condition of maximum speed of 1 m/s, the proposed controller of ANSMC-DOB can acquire the positioning precision as ±10μm while the positioning accuracy is within ±25μm by PID and ASMC. It can be obviously seen that the positioning accuracy is improved a lot by the proposed control method.