Control Of Slow Tool Servo Turning And Contour Error Compensation

In recent decades,because of the great development of science and technology,optical technology has played a key role in the development of military,medicine,aerospace and other fields.Therefore,optical components have been researched by many research workers.Among many machining methods,Slow Tool Servo(STS),which has many advantages such as high precision,long stroke,and high stiffness,has attracted a large number of researchers and is one of the most popular machining technologies currently.In order to improve the cutting accuracy,in this thesis,the methods to improve the single-axis tracking accuracy,to suppress the disturbance and to control the multi-axis contour error of the slow tool lathe were studied respectively.Specific studies as follows:Firstly,lots of references were collected and consulted to master the structure and working principle of slow tool lathe.According to the different characteristics and requirements,the motors driving each axis were selected.After established the mathematical models,a simple mathematical modeling of the slow tool lathe was constructed.Secondly,the design of tracking controller of slow tool lathe was carried out.For the sake of meet the high-precision tracking requirements of slow tool lathe,a fast non-singular terminal sliding mode controller was designed.The ideal switching function was replaced with a continuous function to weaken the chattering phenomenon of sliding mode control,but the robustness of the system was reduced inevitably.Therefore,it was necessary to design a disturbance observer to track the load disturbance,and introduce the observed value into the control law to offset the load disturbance to gratify the robustness of the system.To this end,the thesis designed an extended observer to observe the load disturbance.Finally,the control algorithm designed in this chapter was simulated in MATLAB/Simulink,and the superiorities of the controller were reflected by the comparison with the traditional nonsingular terminal sliding mode algorithm.It was worth noting that,according to the actual cutting conditions,the system's dynamic response to the Z-axis was much higher than that of the C-axis and X-axis.In order to prevent the simulation process from being too cumbersome,only the Z-axis tracking performance was simulated and verified.Finally,due to the single-axis tracking error and multi-axis coordination,contour errors occurred between the three axes of the slow-tool lathe.A cross-coupled control based on three-dimensional standard expansion was proposed to settle the contour error,and the three-dimensional standard expansion method was used to approximate the desired curve at the desired trajectory in real time.The shortest displacement from the actual position to the approximation curve was defined as the contour error vector,and the contour error value and cross-coupling gain were calculated in real time.After theoretical analysis,the theoretical research and design of the controller in this chapter would be simulated and verified in MATLAB/Simulink,then compared and analyzed the effect of the cross-coupled controller designed in this chapter.