Research On Cmm Measuring And Modeling For Free-form Surface Based On The Closed-loop Theory

Data acquisition and surface reconstruction are two key steps of reverse engineering. Data acquisition is usually precede surface reconstruction and the reconstruction is done offline. Such sequential and separate data acquisition and offline surface reconstruction essentially form an open loop process. Due not to timely feedback between the surface reconstruction and measurement, the open loop process may lead to invalid measurement, may also lead to potential data missing and outliers in the acquired point cloud.in order to acquire free-form surface data accurately and rapidly, it is proposed a continuous curvature adaptive measuring algorithm based on the fifth Bezier curve, and realiezd the actual measuring by DMIS programming. It can make the distribution of points with the change of curvature, try to make every measured points are feature points, reduce the redundancy of measuring information, and facilitate the follow-up measuring data processing and the surface reconstruction. Compared with other adaptive methods, such as the circular interpolation method, the polynomial prediction method, through actrual measuring, it is eventually proved the accuracy and effectiveness of the continuous curvature adaptive measuring algorithm based on the fifth Bezier curve.according to the characteristics of the acquired data by CMM, it is researched B-spline surface reconstruction based on the quads domain. According to the different distribution of measuring points, seperately compared the results of quasi-uniform and non-uniform B-spline surface reconstruction, found that using non-uniform B-spline surface reconstruction can get good effect for non-uniform measured points. Based on the non-uniform distribution of data in this paper, it is presented a non-uniform B-spline surface reconstruction algorithm, using Visual C++and OpenGL programming to realize the software module design of this algorithm. Through the examples of several free-form surface reconstruction, it is verified the efficacy, accuracy and quickness of the surface reconstruction algorithm.combined with the adaptive measuring algorithm and the non-uniform B-spline surface reconstruction algorithm, it is established the closed-loop system between measuring and modeling. The system is adopted the CMM adaptive measuring method to realize the rapid and efficient measurement for free form surface, acquiring the initial data of surface. Then using measuring and modeling software system to automatically generate the initial non-uniform B-spline surface, and automaticly acquie a certain number of check points, and generate CMM automatic detection program, then guid CMM to automatic detection, each measuring can gain a new accurate data, then make these data form a feedback to software to improve the quality of the surface model, until satisfy the requirement of accuracy. In order to prove the validity and practicability of the closed-loop system, it is done the practical experiments by using a free form surface and a mouse surface. From the experimental results, it is proved the quickness, accuracy and practicability of the closed-loop system in data acquisition and surface reconstruction.