Registration of point cloud with its CAD model can be used to detect products. To register point cloud with its CAD model, feature characters are used. In this article, a registration method based on line contour matching is proposed. The registration process includes two parts. The one is to extract line contour points (LCPs) from point cloud. The other is to match LCPs of point cloud with LCPs of CAD model. To extract LCPs from point cloud, a slice set is constructed to extract section line data (SLD) containing LCPs from point cloud. Then LCPs are identified by judging the feature end of SLD and analyzing normal angle sequence (NAS) of SLD. LCPs of CAD model are non-uniformly distributed. So to make the matching process more efficient and robust, two groups of LCPs are uniformly sampled. Then best fitting method is used to match the two groups of sampled LCPs to obtain transformation parameters. Verification experiments are conducted on three line contours. And the calculated transformation parameters are compared with reference values. The results show that the deviations of rotation angle are within (-0.9°~0.3°). And deviations of translation elements are within ±0.4mm.
Minimal distance between engine assembled pipes is an important parameter for evaluating the assembling quality. Feeler gauge is a traditional method, which is time-consuming and low accuracy. In this article, a new approach is proposed which employs an accurate 3D scanner to obtain the surface cloud points of pipes, then extracting the pipe center lines to calculate the minimal distance of two pipes. Firstly, points belonging to the same pipe were picked up. Then equal-interval grids were built along a coordinate direction in which the pipe stretched longest. Point cloud was divided into grid according to its coordinates. Center points of all grids constituted rough tendency points of a pipe. Then, a vertical plane was built on each tendency point passing through it. Then point cloud of the pipe was projected onto the nearest plane. And on each plane, the projected points were fitted into a circle. The center points of all circles constituted center-line points of a pipe. Then traversing method was used to calculate rough minimal-distance (RMD) between two center lines. Then a searching process is conducted around the minimal-point-pair to further calculate minimal distance of two center lines. And minimal-distance of two pipe surfaces was calculated by subtracting radii of two pipes from the minimal-distance of center-line points. Four groups of pipes were examined to verify the proposed strategy. The results showed that the deviations of minimal-distance of two pipe surfaces were within -0.35mm~0.46mm. And the deviations of pipe radius were within-0.1mm~0.29mm.
This paper proposes a new strategy of extracting boundary points from scanning point cloud (SPC) data of sheet metal parts (SMPs). This strategy is suitable for bending SMPs with slowly changing surfaces. To cope with the problem that the SMP is too thin to have enough points of its lateral surface to be calculated for the boundary outline, the boundary points are obtained by moving ridge points which is the maximum curvature points on the marginal of parts along theoretical position direction. In this article, the strategy is explained firstly and then carried out on two different experimental SMPs. The strategy contains several steps. Firstly, we construct a slice set called multiple direction slices (MDS) along a curve fitted by boundary points of SPC. Then marginal point data (MPD) is obtained completely and accurately by MDS. And then the chamfer arc data is extracted from MPD by setting identification model of chamfer arc’s two endpoints. Then the ridge points which are the maximal curvature points of chamfer arc data are picked out from chamfer arc data. Finally, by moving the ridge points along a certain direction for a fixed distance, the boundary points are calculated out. Two experiments are carried out to identify position error and form error of the extracted boundary points. The measurement results of boundary outlines of a 6mm thick SMP from a three coordinate measuring machine (CMM) is taken as reference in the first experiment. The second experiment regards theoretical boundary outline as reference. Both two experiments demonstrate the effectiveness of the strategy.
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