Research On Two-dimensional Contour Error Estimation And Control Method Of CNC Machine Tools

The position servo system of high-speed and high-precision CNC machine tools is always restricted by the problems of coupling and nonlinearity.Tracking error and contour error are caused by this kind of problem.At present,only single-axis tracking error compensation is considered to improve indirectly the contour processing performance in most control algorithms,and then the control of contour error is neglected.At present,the problem of contour error control is that the precision of existing contour error estimation model is not accurate enough.The existing estimation model which relies on tracking error has no direct closed-loop control for contour error.To solve the above problems,an improved contour error estimation and control scheme is proposed and verified by theoretical analysis and experiments.The specific work is as follows:The causes of two-dimensional contour error of CNC machine tools and the existing methods of contour error estimation are analyzed.A direct contour error estimation method based on Newton search algorithm is proposed and its convergence is proved.The contour error estimation accuracy of the proposed method is compared with that of the existing methods.In this method,the actual machining position of the machine tools and the given position of the servo system are taken as the input of the system to calculate directly the contour error.The contour error estimation is classified as an optimization problem..In the improved method,the loss function is set to search the result,and the optimal result of the contour error is obtained.Therefore,the problem of contour error being indirectly calculated by tracking error is solved.The existing two-dimensional contour error cross-coupling control principle and defects are analyzed,and an improved cross-coupling control framework is proposed.Firstly,the contour error component and the tracking error are added as the input of the controller.Secondly,the conventional PID algorithm is combined with the single neuron algorithm.Fuzzy control theory is introduced to adjust the output gain coefficient of single neuron.Finally,the conventional PID controller is replaced by single neuron fuzzy PID controller.Through simulation experiments,the performance of single neuron fuzzy PID controller and conventional PID controller in single axis control and contour control are compared and analyzed.The simulation results show that the single neuron fuzzy PID controller is better than the conventional PID control model.It is shown that the improved cross-coupling control method has better contour error control effect and is better than the existing cross-coupling algorithm.In order to obtain the precise coordinate position of CNC machine tools,the motor encoder signal is subdivided.The output signal of the encoder is a sine-cosine signal,and based on this characteristic,the subdivision method of amplitude division is designed.The Xilinx Spartan-6 series FPGA chip XC6SLX25T is selected for the experimental verification of position detection module.The output signal with 120 times resolution is obtained by this method,which means the position detection precision of CNC machine tool is improved,and the contour error estimation precision and control precision are improved.In this paper,the experimental platform is XY two-dimensional motion control platform,and the DSP+FPGA+PC architecture is selected as the hardware scheme of the motion controller.Under the CCS6.0 software environment,the control program has been written and debugged,and the motion control function of the XY coordinate axis has been realized.Finally,the contour error control effect of the improved algorithm is verified by the given processing of the circle contour,the parabola contour and the star contour.The experimental results show that the single neuron fuzzy PID controller has faster response performance and better tracking performance than the conventional PID controller.Compared with the existing cross-coupling method,the contour error can be reduced by the improved cross-coupling method.When machining circular arc and sharp angle,the good contour machining performance is shown by the improved method.