In the specific engineering design, several softwares are generally used in combination with each other to learn from each other. For example, the reverse engineering project undertaken by Shanghai Jiaotong University Mould Technology Research Institute adopts the combination of Surfacer and UG and Pro/E functions. In the specific operation, Surfacer is used for point and line processing to obtain the basic control curve, and then UG and Pro/E introduces data from the control line for surface modeling. Among them, the modules of Pro/E application mainly include ICEM Surf, Pro/DESIGNER (CDRS), etc. The modules used by UG are mainly UG/Modeling and UG/Surface modules. These design modules are commonly used in general CAD design.

It is worth noting that not all points are selected during the design process. Therefore, when determining the control curve of the basic surface, it is necessary to find out which points or lines are available, and which points or lines are fine. The characteristics need to be used in future designs, rather than in the overall design. In fact, some features such as cylinders, bosses, etc. are generated after the overall contour is determined, and the solid model is measured and combined with the scan data. At the same time, try to select some points or lines with better scanning quality and fit them.

Fifth, smooth processing of curved surfaces

Since the measured point data is discrete point data, lacking the necessary feature information, there are often digitized errors, and the surface and curve need to be smoothed. Smoothness is an engineering concept that includes both smooth and pleasing meanings. Smooth refers to the continuous order of the space curve and the surface. The mathematically first-order reciprocal continuous curve is a smooth curve; and the pleasing eye is the subjective sensory evaluation of the human. For the plane curve, the smoothing needs to satisfy the following points: the curve C2 is continuous; there is no extra inflection point; the curvature changes evenly. In the reverse design, the smoothness adjustment of the curve is very important. It is generally difficult to ensure the smoothness of the curve obtained by scanning or fitting. In order to construct a smooth interpolation curve, it is necessary to correct the sequence of the original value points and adjust with the relevant functional modules of the software. The current curve smoothing methods are mainly energy method and round rate method. The criterion for design is that the curvature extreme points on the curve are as small as possible; the curvature between adjacent two extreme points is as close as possible to a linear change.

The smoothness of the surface often comes down to the smoothness of the mesh. The so-called smoothing of the mesh means that each curve of the mesh is smooth, and the smooth surface should be free of convex and concave regions. Mathematically, the basis for judging whether a surface satisfies the above conditions is Gaussian curvature. In general CAD software, the Gaussian curvature method can be used to analyze the surface in the analysis module. When the curvature of the surface changes more evenly, the design requirements can be met. If the surface quality is poor, you need to re-adjust the resulting curve until the surface is satisfactory.

Reverse engineering must ensure the quality of the surface and ensure the design accuracy. In addition to smoothing the original value points, it is sometimes necessary to control the coordinate deviation between the modified value points and the original value points. The deviation should not be too large to ensure that the indicators given by the design department are not too large. Impact.

Sixth, the conclusion

Reverse engineering is a pioneering, practical and comprehensive technology. Reverse engineering technology has been widely applied to the development of new products, the restoration of old parts and the detection of products. It not only digests and absorbs physical prototypes, but also Modify the redesign to create a new product. However, at the same time, the degree of system integration is relatively low in the design process, and the ratio of manual intervention is significant. It is expected that an integrated reverse engineering system will be formed in the future, and the intelligence of the software will replace the shortage of manual intervention.

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