Research On Several Key Techniques Of High Performance NC System

Combined with the research project, several key techniques of high performance NC system are studied detailedly and systematically, which include flexible acceleration and deceleration control methods for high speed NC machining, adaptive look-ahead interpolation method for high speed machining of consecutive micro line blocks, contour error compensation method of the multi-axis motion control. On the basis of analysis for the research on several key techniques of high performance NC system, the multi-axes high speed micro fabrication machining system platform is developed and the above methods are validated on the system platform by experiments.In chapter one, the development of NC technology and the research status on several key techniques of high performance NC system are summarized detailedly. The main research contents of the dissertation are given.In chapter two, the flexible acc/dec control methods for high speed NC machining are studied. The commonly used methods in most domestic economical NC system are linear and exponential acceleration and deceleration control methods. But the vibration is easily caused by discontinuity of acceleration, which affects machining quality and equipment life. To satisfy the need of high speed NC machining, flexble acc/dec control methods, including 7-segment s-curve, cubic polynomial and quintic polynomial flexible acc/dec control method, are studied. The proposed methods are verified by examplification. The experimental result proves that the cubic polynomial flexible acc/dec control method has the characteristic of easily implementing, stable moving and low impact.In chapters three, an adaptive look-ahead interpolation method for high speed machining of consecutive micro line blocks is proposed. Since a complex contour machining program generated by CAD/CAM systems usually composes a lot of consecutive micro line blocks, actual feedrate is heavily reduced and the consequential machining efficiency becomes very low when the conventional interpolation velocity control method is used in NC machining. An adaptive look-ahead interpolation method for high speed machining of consecutive micro line blocks, including interpolation preprocess and real time parametric interpolation, is proposed. During interpolation preprocess, the high speed adaptive look-ahead control strategy is established by using path transfer point maximum velocity confirming, adaptive predetermination of deceleration point position and stride segment transfer point speed checking. During real time interpolation, stride multi-path parametric interpolation algorithm is set up based on the cubic polynomial flexible acc/dec control method. The experiment results demonstrated the proposed method realize high speed machining of consecutive micro line blocks and determination of deceleration point position in advance. The method achieved high speed machining and the productivity is improved significantly.In chapter four, a contour error compensation method of the multi-axis motion control is researched. In the contour machining, contour accuracy is an important accuracy criterion. The controller objective of cross-coupling control is to eliminate the contour error, rather than the reduction of the individual axial errors. The contour- error model for 2D straight line and circular arc contours is introduced, and the impact on contour error affected by dynamic characteristics of the servo system is analyzed. To satisfy the need of high precision NC machining, a contour error compensation method is proposed and the effectivity of the above method is verified by examplification. The simulation results demonstrate that the proposed method achieves high precision machining and the contour accuracy is improved greatly.In chapter five, the multi-axes high speed micro fabrication machining system platform is developed. The prototype system is designed firstly, then an open architecture NC system based on NC embedded into PC is proposed, the preemptive multitask scheduling strategy is presented, and the multi-axis motion control card based on serial communication is self-designed. Finally, a total introduction of the multi-axes high speed micro fabrication machining system platform is given and relative research results are validated on the system platform by experiments. The experiment results prove the better performance on flexible acc/dec control method, adaptive look-ahead interpolation method for high speed machining of consecutive micro line blocks and high accuracy positioning control algorithm.In chapter six, the main conclusions of this dissertation are summarized and the further research work is put forward.