Research On Key Techniques Of Reverse Engineer Based On Feature Technology

Reverse Engineering (RE) technology is an advanced manufacturing technology which is used to design and exploit new product. Shape data acquisition and geometric reconstruction are two key technologies, and recreation of product's CAD is its soul in reverse engineering.Traditional surface reconstruction based on triangle model or rectangle model is easy to lost design intention of product. It leads to modify difficultly. And reverse engineering geometric modeling (REGM), referring to create CAD model from points cloud data, should be serving for recreation and machining etc. Feature technology is efficient approach to realize information share and system integration. In the dissertation, some key technologies of feature modeling based on section feature technology in RE are researched, the main conclusions of research read as follows.(1). Definition and data structures of features in RE and system model of RE CAD prototype are studied. Features in RE, such as points, curve, surface, are defined considering implementation STEP (the STandard for Exchange of Product model data) which is benefit to realize feature modeling. Based on the shortcoming analysis of three CAD system models, CAD system based of object oriented and group assembly is proposal to implement RE CAD prototype system. Classes and data structure of feature based on OOP and GA are also defined.(2). Data structure of points cloud and points reduction method are studied through analyzing the shortcoming of existing algorithms. It's important to reconstruct topology of points cloud to find the point quickly in points cloud, especially points cloud include points more and more larger with measuring technique more and more advanced. Firstly, the min-max box of points cloud is divided into a set of uniform grids, and then the indexes of points stored into appropriate cell for finding k-nearest neighbors. After reconstruction of topology, a new point's reduction method based of chord-arc distance estimation is used to reduce the points cloud. It can reduce points greater with near 90 percent reducing ratio, while keeping former shape. (3). Quick-implementation of arbitrary slice technology is studied on emphasis, and order reconstruction also discussed on emphasis. Slice technology is foundation of strategy of reverse engineering based of section feature. The intersection of an arbitrary plane and three-dimensional cube-cell is realized, and all the subordinate cells intersected with the plane are got rapidly and briefly. Base on it all the scattered points on the slicing plane are got quickly. Getting serial points data from scatter points calls curve reconstruction. At firstly, simplified Dijkstra algorithm for curve reconstruction is introduced and illustrated by experiments. Then, curve reconstruction implementation of Ant Colony Optimization (ACO) algorithm in reverse engineering is researched, emphasis on ACO parameters setting. After experimenting, the conclusion is that the curve reconstructed by ASO-curve reconstruction is better smooth and reflect better the shape of scatter points as other curve reconstruction, but needs more time.(4). A novel method for plane feature recognition is proposed, curve matching algorithm is also researched. It's difficulties of photography and geometry science that plane curve recognition and curve matching. Plane feature recognition method is by combining the angle-difference method and conicoid least square curve fitting method to recognize the curve feature. Firstly, comer points are extracted by angle-difference method, and then feature points are recognized from the corner points with conicoid least square curve fitting method. Fourier-Mellin image registration for curve matching and contract is presented based on analysis shorting of traditional curve matching which is invariant to rotation, scaling and translation (RST). It is effective and feasible illustrated by experiments.(5). Simple three-dimension (3D) feature recognition based on Fourier-Mellin curve matching method is discussed. Extracting algorithm that extruded surface, revolved surface and scanned surface are presented and some samples are given to illustrate the feasibility of feature extracting algorithm.(6). To make the theory research be used in practice, two surface reconstruction is given and the CAD model are got. The practicalities of two CAD model are made by FDM. From the results, the conclusion is drawn that the feature reconstruction software, TrSurf1.0 which programmed based on algorithms presents in the dissertation, is feasibly and efficiency.Combining feature technology in forward-engineering with reverse engineering geometric modeling, the reverse engineering feature modeling based on section feature technology is put forward. And the prototype RE-CAD system software, TrSurf1.0, is programmed by C++. The geometry model reconstructed by TrSurf1.0 includes high-level semantic information, serving for recreation and machining etc, which is according with the developing intent of modern production design.