| Reverse engineering is a combination of a series of advanced analysis methods and application technologies, which has been developed in recent years. It regards existing products or the technology as the research object, bases on modern design theory, production engineering, material theory, measuring theory and relevant professional knowledge, aims at dissecting and mastering the key technology of research object, finally realizes understanding in research object, reproduce and created developing. It is the information flow course with opposite to the traditional design- manufacture process. There are extensive application prospects in the field of industry at present. The technical application of the reverse project can shorten more than 40% of product development cycle, which is one of the important means to boost productivity. In the reverse engineering, digitization is a very important process. At present, the methods of digitization mainly include contact measurement and non-contact measurement. Contact measurement is that the probe is contacted with the object surface. The adopted equipments are Coordinate Measuring Machine, NC with measuring device, special digitizer etc. Among these digital equipments, the data of the object surface are acquired by bowstring or arc。At present, because the technique is mature and its realization by computer is easy, a great number of manufacturers use this approach to acquire the data of the object surface. The quality of digitization directly impacts the measuring precision. In the reverse engineering, describing measuring object with the least point cloud information is in expectation. Generally speaking, the larger curvature change is, the denser the point cloud is, and vice versa. So it is expected that the measuring object is accurately described through least point cloud. Thus a high-efficiency, high-quality method for digitizing the measured object is the object which is being pursued all the time. In this paper, the innovation is that the digitization strategy of Closed Scan Loop Scanning (CSLS), which is an iterative digitization strategy of continuous scanning the probe, is studied. The continuous scanning probe can be mechanically contact or optically non-contact. The Scanning strategy is described as follows. Firstly beginning to scan a sparse grid, thus the triangular grids point cloud can be come into being, and the triangular grids can be evaluated according to some certain arithmetic. Then the evaluating results may form a group of new regions which are needed to be digitized, scanning is automatically started and the new scanned points are inserted in the current triangular grids. Subsequently, the above process is repeated, and this process doesn't end until the digitization region which needs to be repeatedly digitized cannot be found or all terminating conditions have been met. In practical application, compared with bowstring or arc digitization strategy, this digitization strategy is difficult to be realized. But when this digitization strategy is used for object digitization, the efficiency and precision is very high. With the development of computer technology, and the enhancement of the speed and performance of computer, this digitization strategy will be widely applied. At the end of this paper, two measuring examples are presented to validate the precision and function of this digitization strategy software, one of the two examples is a raised sphere in the plane, another is a free surface object. For a raised sphere in the plane, the measuring point cloud follows the principle of curvature change. That is, point cloud density in the section of large curvature is larger than that in the section of small curvature. In addition, for the digitization of free surface object, the digitization strategy represents the powerful sampling capability of scanning line point cloud. By the NURBS method in the digitization strategy, the object surface is described with least point cloud and the higher precision is ensured.
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