| Reverse Engineering (RE) has become an effective tool for supporting complex product design, shortening product development cycles and improving innovation ability of the enterprise. It’s an important technical method to the advanced design and manufacture. Digitization, data processing and model reconstruction are the key technologies of the RE. With the development of RE, the single sensor can not meet the digitization increasing demands of the accuracy and efficiency any more. In the meantime, it’s also difficult for single sensor to obtain complete model information of the complex parts. Multiple-sensor integrated measurement provides a new idea for achieving high efficiency, high precision and complete measurement of RE. However, integration measurement present new requirements to the subsequent data processing, data merging and model reconstruction.Combined with respectively advantages and features between the line structured light vision measurement and three coordinate measuring machine (CMM), a new multiple-sensor integrated RE system is proposed, on the basis of the systematic analysis for the theory and application of the domestic and foreign multiple-sensor integrated measurement. The key technologies such as integrated measurement, data processing and data merging are researched in this thesis. The main contents are including:1. A new CMM and line structured light vision sensor integrated measuring program is proposed. Adopting the divide-and-rule method is applied to measure complex products, using CMM to drive line structured light sensor in order to obtain surface initial data. In the areas where vision measurement has great error or the blind areas, CMM measure fewer points in order to correct the initial surface. For the rule features, CMM measurement is used to get design parameters. This method makes full use of the rapidity of optical measuring system and the high accuracy of CMM, to realize the high-efficiency, high-accuracy and complete measurement.2. The mathematical model of the line structured light vision measuring is established. On the basis of Zhang’s camera calibration method, considering the tangential distortion and using nonlinear global optimization method, all the camera parameters can be calibrated with free-position planar pattern. Using the combination of cross ratio invariance theory and free-position planar pattern to obtain the numerous feature points in a light plane, the structural parameters of the vision sensor can be calibrated.3. The light strip centre extraction method based on deformable model is proposed. B-spline curve is set on the the strip skeleton as the initial model of the deformation model. Regarding the Gradient Vector Flow (GVF) as external force, the model is deformable operated by internal force and external force. The centre of light stripe can be found when energy of deformable model is least. The proposed approach not only takes advantage of the geometry information of the light strip skeleton but also calculates the energy of the entire light, so that it can restrain the effects of noise and branching efficiently, and also has a strong ability of repairing broken light stripe. The extracted centre of the light strip has single connectivity, smoothness as the free-form surface and subpixel accuracy. Meanwhile,2D B-spline curve is converted into3D B-spline curve space based on the3D measurement model. It can avoid storing and processing large amounts of scattered "point cloud" data, and also can simplify surface reconstruction. This approach can achieve the combination of digitization, data processing and model reconstruction, which improves the efficiency of RE.4. The two-step method of line structured light scanning adaptively is proposed, which will determine the steps of main scanning based on the curvate of the auxiliary scan line and transform the freefrom surface sampling into the curve sampling.A fast and efficient sampling approach based on the angle analysis of the curve is proposed, which will realize the points adaptive distribution with the curvature of curve. When combined with arc-length method, it can avoid the problem of less sampling points in the small curvature region. The approach can make scanning step change adaptively with the curvature of curve when the line structured light scans the unknown freeform surface. It can significantly reduce the number of scan lines and improve the efficiency and accuracy of vision measurement.5. The method of multiple-sensor data merging, based on surface deformation and hybrid modeling technology, is proposed. The line structured light sensor measure the free surface of the part as the initial surface, and transforming the small number of high-precision points got by CMM to the point constraint forms, in order to correct initial surface.Through the developed deformation modeling software on the ACIS platform, the initial surface is deformed to high-precision points based on the energy optimization method. The proposed approach of data merging can not only improve the utilization of measurement information by different sensors and the accuracy of the surface reconstruction, but also make reconstruction model has good conformality. It can also avoid the problems that the date got by different kinds of sensor can not be alignment due to the disparity of data density and data accuracy. For the rules elements, the hybrid modeling method based on the feature is used to fuse rules elements measured by CMM and freeform data into the complete CAD model. |
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