Theory And Strategy Of NC Machining Tool-path Planning For Vector Chinese Characters

Chinese characters' engraving is often encountered in the mechanical processing. However, the module of Chinese characters engraving is often embedded in some of the CAD/CAM softwares which can only deal with planar Chinese characters' engraving. Moreover, the distortion problem of Chinese characters machined on curved surfaces has received more and more attentions. It is studied that the theory and strategy of NC machining tool-path planning for vector Chinese characters will be helpful to the development of domestic software.In order to get the NC machining tool-path of the planar Chinese characters, firstly, the data of the Chinese characters' control points in the TrueType files are read. Then, in order to ensure the curving parts of the characters can be naturally changed and the characters can be unlimitedly enlarged without distortion, the contours of the characters are described by line segments and cubic Bezier curves. Finally, the tool-path points are gotten by an intersecting process between the baseline of trajectory and the contours. Based on the moving mode of Zigzag tool-path planning, the tool-path points are linked according to a preferential criterion. The criterion gives the priority to an adjacent point which belongs to the same contour and in the following cutting path.The harmonic mapping which has a conformal property have been introduced to avoid the distortion of the vector Chinese characters machined on curved surfaces. In this dissertation, the basic theory of harmonic mapping is introduced. The harmonic mapping from a plane to a surface is emphasized and partial differential equations which the harmonic mapping must satisfy are achieved using the variation approach. The harmonic equation has to be changed to diffusion equations, the solution of which helps to obtain the harmonic mapping. In the mean time, the algorithm for the solution of the diffusion equations is intensively discussed and the stability and the convergence of the algorithm are also proved. Then using the harmonic mapping approach, the planar Chinese character's tool-path points are mapped to the curved surfaces getting the tool-path of Chinese characters machined on the curved surface.Interference is also an important problem in the machining of Chinese characters by flat-end cutter. The curvature matching method is put forward and used to determine the orientation of the cutter. Based on the theoretical analysis and discussion above, the corresponding Visual C++ procedure is programmed, and the tool-path points' data for the Chinese characters machined on planes and on curved surfaces can be gotten. The simulation results of UG NX4.0 software prove that the algorithms we have put out and discussed are right and feasible. It will be a fundamental job for NC machining development.