Key Techniques Research About Reverse Engineering Based On CMM Measuring Data

At present, reverse engineering has been in appliance, automotive, aerospace, and other fields with a wide range of application. Reverse engineering is carried under the circumstance which has only entity withous engineering drawings. It obtains 3D datas by 3D measuring machine, then generates the geometric model of entities by 3D reconstruction software, and generate NC programme to control CNC machine, or process sample by applicating Rapid Prototype Technique. Reverse engineering can reduce cost of product, shorten time of consignment in the market, improve quality of productand market competition of enterprise. It plays an important role in the process of product research. On the base of summarized the actuality and existing problems of Reverse engineering, both at home ang abroad, key techniques were studied and discussed deeply in this paper.The workflow of reverse engineering includes three key parts : data measuring equipment and Probe radius compensation ,data processing and surface reconstruction , each part was studied in detail in this paper .Layout of measuring route was summed up according to outer surface characters of specimen .The principle about how to choose methods of data acquisition was putted forward on the base of studying, contrasting, analyzing kinds of measuring method.Introduced mainfram structure and software components of coordinate measuring machine used in the paper whose tye was MISTRAL070705. Reseach the factor of measuring precision, and put forward measure of eliminating interfere. At the same time, according to the measuring points and information of ambient points, trigonal gridding was structured by the melodic data points, then elicit vector gridding. This method is simple .It is unnecessary to structure B-spline surface and parameter surface to calculate the derivative vetor. This method is carried after measuring. When it is used in software, it is very efficient.. From the practical application of reverse engineering, the correlative contents how to process scanning datas measured by CMM were studied. Data compositor,data filter,data compression,datamerging,data interpolation data block were studied. In the aspect of data filter, interactive filtering technology was realized.At the same time, the algorithm of data reducing which combines distance threshold with angle warp is researched. The method not only achieve data reducing but effectively avoid deleting useful feature points, and raise the processing speed of the intensive scan lines.Data block was researched. Close wireframes were obtained by connecting curve. Also, it was discussed to how to select data processing methods to different datas .The principle of data processing was putted forward.At first development status of surface reconstruction were researched and compared. Improved algorithm was putted forward to reconstruct NURBS surface with measurement points after processed .This algorithm fit nonlinear multivariable variables into a single optimization problem by modification of the objective function, iteration method. Thus easily obtained control point coordinates, and the right of the measurement point and the corresponding parameter values, and achieve optimal number of control points through dichotomy in order to effectively reduce the measurement point data and the complexity of NURBS surface reconstruction. The method overcomes the existing methods for the needs of the non-linear multi-variable optimization problem, can not obtain the optimal number of control points, and measurement data point defects. After Computer simulation, the results show the effectiveness of the algorithm and seek to surface IGES format output. Make use of existing CAD / CAM software for further its editorial changes, the processing path generation, such as finite element analysis and follow-up treatment. In addition, the method was studied to assess the accuracy of surface reconstruction methods. And computer simulation results show that the reconstructed surface meet the requirements of precisionFinally main results and conclusions of this dissertation have been summarized the prospects and study emphases of the future research work have been discussed and forecast .