【正文】 。最后通過這次畢業(yè)設計有一次鍛煉了我學習的認真態(tài)度，注意每一個細節(jié)，在學習和工作上沒有可能只有肯定。這樣的學習態(tài)度對我以后的工作和學習有很大的好處。參考文獻[1] 鄭福祿. UG NX6中文版逆向造型設計經(jīng)典實例解析 清華大學出版社 2009.[2] NX 5+ .[3] 浙江大學現(xiàn)代制造工程研究所 .[4] 張偉、. 浙江工業(yè)大學 .[5] ―原理方法及應用. 機械工業(yè)出版社 .[6] . 北京大學出版社 .[7] 王文廣、 .[8] ， Molds 130 Proven . .[9] .[10]李麗華、 .[11] [12] 譚海林、．2006．5.[13] 1997．12.[14] .[15] .[16] 鄭大中、 1998．3.[17] 2004．9.附 錄The PreProcessing of Data Points for Curve Fitting in Reverse Engineering Reverse engineering has bee an important tool for CAD model construction from the data points, measured by a coordinate measuring machine (CMM), of an existing part. A major problem in reverse engineering is that the measured points having an irregular format and unequal distribution are dif?cult to ?t into a Bspline curve or surface. The paper presents a method for preprocessing data points for curve ?tting in reverse engineering. The proposed method has been developed to process the measured data points before ?tting into a Bspline form. The format of the new data points regenerated by the proposed method is suitable for the requirements for ?tting into a smooth Bspline curve with a good shape. The entire procedure of this method involves ?ltering, curvature analysis, segmentation, regressing, and regenerating steps. The method is implemented and used for a practical application in reverse engineering. The result of the reconstruction proves the viability of the proposed method for integration with current mercial CAD systems.1. IntroductionWith the progress in the development of puter hardware and software technology, the concept of puteraided technology for product development has bee more widely accepted by industry. The gap between design and manufacturing is now being gradually narrowed through the development of new CAD technology. In a normal automated manufacturing environment, the operation sequence usually starts from product design via geometric models created in CAD systems, and ends with the generation of machining instructions required to convert raw material into a ?nished product, based on the geometric model. To realise the advantages of modern puteraided technology in the product development and manufacturing process, a geometric model of the part to be created in the CAD system is required. However, there are some situations in product development in which a physical modelor sample is produced before creating the CAD model.1）. Where a clay model, for example, in designing automobile body panels, is made by the designer or artist based on conceptual sketches of what the panel should look like.2）. Where a sample exists without the original drawing or documentation de?nition.3）. Where the CAD model representing the part has to be revised owing to design change during manufacturing.In all of these situations, the physical model or sample must be reverse engineered to create or re?ne the CAD model. In contrast to this conventional manufacturing sequence,everse engineering typically starts with measuring an existing physical object so that a CAD model can be deduced in order to exploit the advantages of CAD technologies. The process of reverse engineering can usually be subdivided into three stages, . data capture, data segmentation and CAD modeling and/or updating. A physical mockup or prototype is ?rst measured by a coordinate measuring machine or a laser scanner to acquire the geometric information in the form of 3D measured results are then segmented into topological egions for further processing. Each region represents a single geometric feature that can be represented mathematically by a simple surface in the case of model reconstruction. CAD modelling reconstructs the surface of a region and bines hese surfaces into a plete model representing the measured part or prototype . In practical measuring cases, however, there are many situations where the geometric information of a physical prototype or sample cannot be measured pletely and accurately to reconstruct a good CAD model. Some data points of the measured surface may be irregular, have measurement errors,or cannot be acquired. As shown in Fig. 1, the main surface of measured object may have features such as holes, islands,or roughness caused by manufacturing inaccuracy, consequentlythe CMM probe cannot capture the plete set of data points to reconstruct the entire surface. Fig. 1. The general problems in a practical measuring case.Measurement of an existing object surface in reverse engineering can be achieved by using either contact probing or noncontact sensing probing techniques. Whatever technique is applied, there are many practical problems with acquiring data points, for examples, noise, and inplete data. Without extensive processing to adjust the data points, these problems will cause the CAD model to be reconstructed with an undesired shape. In order to rebuild the CAD model correctly and satisfactorily, this paper presents a useful and effective method to preprocess the data points for curve ?tting. Using the proposed method, the data points are regenerated in a speci?ed format, which is suitable for ?tting into a curve represented in Bspline form without the problems previously ?tting all of the curves, the surface model can be pleted by connecting the curves.2. The Theory of BsplineMost of the surfacebased CAD systems express shape required for modelling by parametric equations, such as in Be 180。zier or Bspline forms. The most used is the Bspline form Bsplines are the standard for representing freeform curves and surfaces in current mercial CAD systems. Bspline curve and Be 180。zier curves have many advantages in mon Control points in?uence the curve shape in a predictable natural way, making them good candidates for use in an interactive environment. Both types of curve are variation diminishing, axis independent, and multivalued, and both e