1. Data preprocessing
Because the point cloud data of the involute cylindrical spur gear measured by the three coordinate machine is regular and the part coordinates are consistent with the software, in the preprocessing stage, only the noise data caused by the influence of the measuring equipment and the surrounding environment needs to be eliminated, and the obvious noise points are manually deleted with circle selectpoint. The preprocessed point cloud of the involute cylindrical spur gear is shown in Figure 1.
2. Construction of characteristic lines and main surface patches
At present, the combination of general-purpose CAD / CAM software and reverse engineering software to realize the approximation between surface and point cloud data by establishing curve and surface models that have no direct mathematical relationship with point cloud data is an important method to effectively solve the problem of reverse engineering of surface reconstruction. At the same time, the surface model has good modifiability and can meet the requirements of redesign.
Imageware is a famous reverse engineering software. Its unique advantage is that it has strong ability of point cloud preprocessing, curve and surface fitting and error analysis, and can directly display the difference between the constructed characteristic surface and the measured point cloud in real time, and issue an error report; However, there is still a gap between the surface modeling means and auxiliary functions provided by it and the commercial CAD / CAM software with complete functions. The flexible application of Pro / E can establish most models that meet the needs of reverse engineering, but it is very difficult to deal with huge point cloud data.
Combining the advantages of Imageware and Pro / E, we use Imageware to preprocess the point cloud, construct the necessary feature lines and surface patches for subsequent Pro / E modeling, and analyze the error between the surface patches and the point cloud; Then Pro / E accepts the point cloud, curve and surface in IGS format from Imageware software, and realizes the mirroring, merging and materialization of the surface through the surface and solid modeling functions, and finally completes the reconstruction of the model.
For subsequent model reconstruction, it is necessary to construct the feature lines and feature surfaces required by the proposed modeling method. The steps are as follows:
(1) Fitting cylinder: the shaft hole is fitted into a cylindrical surface by the construct surface form cloud fit cylinder. The fitting command is adopted because the axis line of involute cylindrical spur gear to be precipitated later must use the cylinder obtained by fit.
(2) Find out the central axis of involute cylindrical spur gear: separate the central axis of involute cylindrical spur gear with construct curve from surface line form cylinder / cone axis to facilitate subsequent modeling operations.
(3) Construction of tooth profile surface and tooth root circular arc surface: because there are enough point clouds in the tooth profile and tooth root, the point cloud can be directly fitted into the surface, and the tooth profile surface and tooth root circular arc surface can be fitted with construct surface form cloud uniform surface.
(4) Create the connection surface between the tooth profile and the tooth root arc: in order to connect the part where the tooth profile is not connected with the tooth root arc, section the point cloud, use the point cloud of the section to construct the tooth profile curve and the tooth root arc curve, and then use cre Ate-3d curve-3d B-spline construct the connecting line to ensure that the constructed connecting line is continuous with the curvature of tooth profile curve and tooth root arc; Then the connecting line is stretched into a connecting surface, and finally the tooth profile surface on one side is formed, as shown in Figure 2.
(5) Use construct surface form cloud fit plane to fit the plane where the end face and boss of involute cylindrical spur gear are located.
(6) Trim each surface piece: mainly extend the tooth profile surface and cut the top circle of involute cylindrical spur gear to obtain a complete tooth profile; Then extend and cut the constructed surface patches, write and save them in IGS format selected, and select the output point cloud, curve and surface, as shown in Figure 3.
In the process of involute cylindrical spur gear tooth profile surface reconstruction, there may be surface wrinkles, unsmooth and large error with the original point cloud. In order to achieve the required accuracy, there will be many parameter choices that need to be adjusted and tried repeatedly, which requires a certain degree of proficiency and skills.
3. Create the whole large surface and final CAD model with Pro / E
Pro / E accepts the point cloud, curve and surface in IGS format from Imageware software. Based on a reconstructed tooth profile surface and based on the central axis of involute cylindrical spur gear, the whole large surface is generated through mirroring and merging, as shown in Figure 4. Then remove the material materialization and cut off the outer part of the curved surface in the tooth top circular entity to obtain Fig. 5.
Finally, stretch the boss to the selected surface, remove the material, stretch the shaft hole, and chamfer to obtain the CAD model of the final involute cylindrical spur gear, as shown in Figure 6.
