Research On Contour Error Iterative Learning Algorithm Based On Modified Motion Command Sequence

In order to improve production efficiency,it is often necessary to increase the speed in the batch processing of a single product.While the contour error increases with the increased feed rate,limiting the ability of computer numerical control(CNC)machine tools to produce qualified products in high-speed machining.For existing commercial CNC machine tools with the closed CNC systems,the advanced controllers or the other online error-reduction approaches cannot be adopted because the interpolators and the feeddrive controllers are not allowed to be altered.Moreover,most online control methods respond after the error appears,and the compensation effect is often poor due to lag.Therefore,it is necessary to study practical methods that can balance processing efficiency and precision.In order to solve the contradiction of contour accuracy reduction caused by high feed rate in single-product batch processing,this dissertation proposes a contour error iterative learning algorithm based on the modified motion command sequence of servo system.The processing contour has the premise of repeatability in repeated processing,so the contour error of the current trajectory can be predicted through learning control,and then the next reference trajectory of the servo system can be actively corrected in advance.The main research content is as follows.Based on the digital curve composed of the command sequence,a three-dimensional contour error estimation method is proposed,which does not depend on the contour expression and is suitable for general contours.In terms of contour error compensation,the problem of compensation lag and speed change caused by error compensation is considered.Thus the repetitive disturbance model is linked with the contour error estimates of the previous points,and a filter-type iterative learning method is proposed to suppress repetition.Based on Lyapunov's theory,the stability of the algorithm is proved.In addition,for the local contour area where the control effect is still poor after using the iterative learning method,the speed of this area is re-optimized by the time scaling mechanism,and the contour compensation effect is adjusted by reducing the speed to achieve the improvement of the overall processing accuracy of the contour.Through the experimental results of the standard three-axis CNC machine tool experimental platform,the effectiveness and feasibility of the algorithm are analyzed,and the contour control effect and processing efficiency optimization of the algorithm are evaluated.The results show that the algorithm guarantees that the contour accuracy is still guaranteed with feed rate increased.