Research On Key Techniques Of MPF-oriented Reverse Engineering And Application

Reverse Engineering(RE) is a new technology based on computer technology ,measuring technology and CAD/CAM in recent years. Multi-point forming(MPF) may substitute the traditional mould using discrete element to realize 3D flexible forming, which is integrated CAD/CAM/CAE technology and which has been a new research direction in the area of 3D sheet metal parts manufacture . In the field of reversing manufacture for sheet metal parts, the general method is that measuring the die or sample parts by some 3d measuring tool firstly, and the die is manufactured by the surface model which is reconstructed from 3D measuring data, at last ,the parts is formed by this die . The disadvantage of this method is the cost of production is too high and the cycle of product is too long, so it cannot meet the demand of actual industrial need. In this dissertation, Author takes advantage of the character of which MPF and RE have the same key technique so as to realize the reversing manufacture from sample parts to final products .The feasibility and reliability of this method is proved via some samples. The following is the main content: 1.Multi-way measuring method is studied which includes stereo visual measurement based on double CCD ,laser scanning measurement and the edge detection for CT photograph. In stereo visual measurement, author make use of fuzzy method to extract the outline of parts and calculate the 3d coordinate of the measuring data via the result of non-linear calibration. The matching points between the left and right image shotten by camera is found by using the pole line.In the laser scanning measurement, the equipment based on triangle principle is developed. According to the purpose of measurement, we take the different measuring way. To the measurement of sample parts in RE, because the model of CAD is no available,so we take the method that stereo vision is used firstly to calculate the outline of surface,then sampling the data by self-adaptive method from measuring points. In the detection of forming precision for MPF parts, we take the method that sampling the data based on curvature. In the measurement for CT photograph, we take the method based on wavlet tranformation to detect the edge of parts for skull remedy. 2. To pre-processing of measuring data, we establish the method for denoise and multi-view match . In the denoise area ,we make use of the soft threshold of wavlet to multi-layer decompose the measuring information. The denoise function is realized and the high frequency information is analysed through Matlab tool . In the multi-view match, we match the data from different view based on three shared points and fulfil the function by program. To the matching result, we analysed the factor influence the matching precision and proposed the way of improvement. 3. To the surface reconstruction of pre-processing measuring data, we proposed the method based on both NURBS and triangular mesh. In the surface reconstruction based on NURBS, we take the function of Modified Quadratic Shepard to construct the rectangular mesh from scattered points.Then NURBS curve approximation in one direction is employed. After that, we interpolate the NURBS surface through having constructing NURBS curve. The algorithm of calculation of contacting points for MPF is proposed . Another reconstructing method by using triangular mesh is studied and the algorithm of contacting points is also proposed. 4. To the calculation of precision of MPF for sheet metal parts,we give the registrating algorithm based on two step method. At first step, the self adaptive GA is employed to aligning the data in different coordinate system, then ICP algorithm based on outline error is employed to registered the data precisely by using the result of GA as the initial value. Finally, we prove the feasibility via example. 5. To the problem of MPF springback control, we established the modified BP algorithm of ANN to predict the springback value, and modified the data of model according to the springback value. By the method of iteration of prediction and modification, the simulating closed loop forming is realized. In order to improve the precision of forming ,the actual closed loop forming is employed by making use of flexible character of MPF. The springback sample data sets is established according to the existence of edge press and non edge press.Through example,we give the result of analysis. 6. The special software to RE applying in MPF is developed. The software...