Research On The Control Of The Position Servo System Of CNC Machine Tools

CNC machine tools are widely used in the manufacturing area because of their good stability and high processing efficiency,their performance is increasingly developing towards high precision and high reliability.The CNC machine tool position servo system is an important part of the CNC machine tool.The accuracy of its position determines the accuracy of the CNC machine tool to a great extent.However,the position servo system is a complex electromechanical system.It is impacted by the disturbance torque of the system,damping of mechanical transmission devices.Other factors,such as the friction and external interference,can also cause the difficulties of system control and bring negatively effect on the position accuracy.The position servo system of CNC machine tool is studied in this paper,the system performance is mainly increased by improving the algorithm.The specific work is as follows:(1)The mathematical models of permanent magnet synchronous motor and mechanical drive system of position servo system are carried out.For the permanent magnet synchronous motor,the voltage equation,torque equation,flux linkage equation and coordinate transformation process of the permanent magnet synchronous motor model are analyzed.For the mechanical transmission system model,the angular displacement of the motor is taken as the input,and the displacement of the workbench is taken as the output.(2)The position servo system of CNC machine tools based on PI control is designed.PI control scheme is adapted to design the position loop,speed loop and current loop.After the analysis of vector control principle and space vector pulse width modulation,a PI-based position servo system simulation module is established.The details of current,torque,speed and position response are analyzed,and the results show that the control effects of PI control is not good,the control scheme is not proper for position servo system of CNC machine tools.(3)Two kinds of position servo systems of CNC machine tools are designed based on model-free adaptive control.The position loop and speed loop are improved by MFAC,the equivalent dynamic linear data model for nonlinear systems is built,by using the current and position data of the system to online estimate the pseudo partial derivative of the system,a weighted one-step forward controller is designed,and the data-driven model-free adaptive control of servo system is realized.The model-free adaptive control method is improved by adding time-varying proportional and integral control terms to the algorithm,and the application scope of the model-free adaptive control method is expanded as a result.The stability of bounded-input bounded-output based on improved model-free adaptive controllers before and after is proved.Then,simulation is implemented in Matlab/Simulink software,and the details of current,torque,speed and position response are compared.The results show that the control effects of the two model-free adaptive control schemes are better than PI scheme.The improved model-free adaptive scheme not only can guarantee the advantages of the original model-free adaptive scheme,but also make the position following performance stronger.