Research On Intelligent Metrology With Multiple-Sensor In Reverse Engineering

Reverse engineering plays an increasing important role in creative product design. At present, how to acquire 3D coordinate points of complicated objects efficiently and accurately is a critical issue to be solved. Single sensor cannot satisfy complex measurement requirements increasingly, and the multiple-sensor integrated system becomes a new development direction.This dissertation proposes an intelligent measurement theory of multiple-sensor integrated system. The coordinate-measuring system integrates vision sensor, laser scanner, contact probe and CNC machine. The integrated-system can take advantage of multiple-sensor to measure the complex objects in a fast and intelligent way. The main contents include the following aspects.1. Basic principles and measurement methods of CCD vision-sensor, laser scanner and contact probe are researched. A single CCD sensor is utilized to realize stereo-vision surface measurement. For the contact measurement, the triangle-division measurement way is analyzed first, and then a new method with the rectangle-division technique is proposed to measure unknown free-form surface adaptively. For the laser scanner, an edge measurement method based on sample points is put forward to measure object edges effectively, and a new measurement-planning method based on change-curvature is brought forward to measure unknown free-form surface adaptively.2. Several data-preprocess methods, burr elimination, filter, and compression, are studied. And a new area-growth method is presented to construct an optimized triangulated-surface model for unorganized data. A simple way of eliminating burr and a data-smooth principle is presented, and median-filter method is studied though emulation experiments. A compressing technology based on division-cube is presented to reduce the data number. To construct the topology relation of adjacent points, a new region-growing method is proposed to generate a triangulated-surface model from massive unorganized points. In the region-growing process of triangulated surfaces, a minimum-edge-angle-product algorithm is presented to select an appropriate point to form a new triangle.3. A theory of intelligent feature-detection for unorganized point-cloud is provided. It includes three steps: recovery of differential geometry property for unorganized points, data segmentation and feature detection. The first step is the base of the other two steps. The algorithm from Taubin is adjusted to estimate the principal curvatures and the local Darboux frame of unorganized noisy data. Using the differential geometry property of edge points, an automatic segmentation algorithm is presented to extract the D~0, D~1 and D2 edge strips from noisy data. For each segmented point-cloud patch, a principal curvature histogram is constructed to identify its surface feature effectively.4. Based on the detected feature of point-cloud patch, an intelligent measurement method with multiple sensors is proposed. The feature of point-cloud patch includes surface feature and edge feature. To plan surface measurement path from the surface feature, first sample a few points from the quadratic surface, or sliver the point-cloud and compute measuring steps foreach slivered curve. Then compute Zigzag path to acquire optimal measurement path. The edge of object is very important for measurement. An adaptive surface and hole measurement method directed by edge feature is provided. Based on the planned measurement path, high-precision sensors, touch probe or laser scanner, can be guided to measure the object in a fast and intelligent mode.5. The information fusion technique of multiple-sensor measurement is studied. The measured points of multiple views are registered firstly. Then surface reconstruction and surface accuracy assessment are performed. Surface patches that satisfy the accuracy requirements are used to recover surface feature. A type-specified least-square method is developed to reconstruct quadratic surface. To reconstruct free-form surface, B-spline curves fitting is performed and NURBS representation is generated. The measured points and surface representation are transformed into standard IGES format, which can be imported into commercial CAD/CAM software. The massive unorganized points can be used to generate optimal STL file directly through data compression based on triangulated surfaces.6. The intelligent measurement system that integrates multiple sensors is researched. The hardware frame of the multiple-sensor integrated measurement system includes motion controller system, accurate servo system, accurate mechanical system and multiple-sensor. The main functions of measurement software are introduced, in which intelligent measurement module is the key of the whole system. The intelligent measurement system that integrates multiple sensors are testified and verified by practical experiments.