Yuwen, Sun, Dongming, Guo, Zhenyuan, Jia, and Weijun, Liu
International Journal of Advanced Manufacturing Technology. Feb2006, Vol. 27 Issue 9/10, p918-924. 7p. 3 Diagrams.
SURFACES (Technology), RAPID prototyping, MACHINING, MANUFACTURING processes, REVERSE engineering, and SPLINE theory
The issue of surface reconstruction and slicing from point clouds has been receiving extensive attention recently. When using the B-spline surface fitting technique, the difficulty of parameterization exists. At the same time, for interfacing between reverse engineering and rapid prototyping, the point clouds are usually converted to an stereolithography (STL) model. This leads to a huge file size and requires expert modeling skills. The objective of this work is to establish a base surface parameterization and direct slicing strategy for scattered data based on a cross-sectional design technique. We first present a new method of directly extracting sectional contours from point clouds. Then, we create a base surface by skinning the primary boundary curves and interior sectional curves. Based on a good parameterization, the final surface is achieved with tight tolerance. Several practical examples have demonstrated the feasibility of the proposed method. It can be widely used in Number Control (NC) machining and rapid prototyping. [ABSTRACT FROM AUTHOR]
In the design of complex parts involving free-form or sculptured surfaces, the design is usually represented by a B-rep model. But in production involving rapid prototyping (RP) or solid machining, the B-rep model is often converted to the popular STL model. Due to defects such as topological and geometric errors in the B-rep model, the resulting STL model may contain gaps, overlaps, and inconsistent orientations. This paper presents the extension of a surface reconstruction algorithm to the global stitching of STL models for RP and solid machining applications. The model to be stitched may come from the digitization of physical objects by 3D laser scanners, or the triangulation of trimmed surfaces of a B-rep model. Systematic procedures have been developed for each of these two different but equally important cases. The result shows that the proposed method can robustly and effectively solve the global stitching problem for very complex STL models. [Copyright &y& Elsevier]
Journal of Engineering Design. Oct2007, Vol. 18 Issue 5, p475-488. 14p. 7 Color Photographs, 3 Black and White Photographs, 4 Diagrams, 2 Charts.
PROSTHETICS, COMPUTER-aided design, ORTHOPEDIC implants, COMPUTER simulation, and MATHEMATICAL models
Currently, the production of a high-quality and highly aesthetic prosthesis is still mainly based on handwork and subjective comparison to get the proper shape and colour of the prosthesis, likely not by a first attempt. This article describes a case study whose goal was to investigate the possibilities of computer-aided surface reconstruction and supplementation to improve the quality and reduce the manufacturing time for an orthopaedic prosthesis. For this purpose, a model of human finger made of plaster had been scanned with the high fidelity laser triangulation scanner. The result was a set of very dense point clouds, representing the surface of the finger model in all its complexity. The main target of this work was to create a water-tight, high resolution computer model of a human finger, which would be ready for further manipulation, such as scaling, mirroring or stretching in arbitrary dimensions. A larger amount of such models could represent a virtual database of human shapes, which would be suitable for prosthesis production and many other (medical) purposes. The first steps after scanning were done in an attempt to reorient several scans, taken from different viewpoints, relative to each other in order to get the proper shape of a finger. This was done by applying an ICP algorithm, integrated in commercial software, and its comparison to the results of reorientation, based on information about finger's position transformation during the scanning process. This information proved to be vital for a fast and accurate alignment of the scans and successful surface generation. This paper also discusses the possibilities of avoiding the influences of geometric errors, generated by a triangulation scanner on surface alignment and the creation of a 3D model. The surface was created by applying Delaunay triangulation to the point cloud. Afterwards, it was followed by manual and automatic refining and reconstruction of a triangular mesh. The final result is a 3D computer model of a human finger with all its details, such as fingerprints and wrinkles. Additional measurements showed that the arithmetical average of deviation between a computer and a physical model was less than 0.3 mm, which is a good result for the desired purposes. The study also showed the possibilities for acceleration of scan alignment while the accuracy could be increased. [ABSTRACT FROM AUTHOR]
REVERSE engineering, PRODUCT management, PROTOTYPES, and COATING processes
Abstract: Laser range-scanners are used in fields as diverse as product design, reverse engineering, and rapid prototyping to quickly acquire geometric surface data of parts and models. This data is often in the form of a dense, noisy surface mesh that must be simplified into piecewise-smooth surfaces. The method presented here facilitates this time-consuming task by automatically segmenting a dense mesh into regions closely approximated by single surfaces. The algorithm first estimates the noise and curvature of each vertex. Then it filters the curvatures and partitions the mesh into regions with fundamentally different shape characteristics. These regions are then contracted to create seed regions for region growing. For each seed region, the algorithm iterates between region growing and surface fitting to maximize the number of connected vertices approximated by a single underlying surface. The algorithm finishes by filling segment holes caused by outlier noise. We demonstrate the algorithm effectiveness on real data sets. [Copyright &y& Elsevier]
EUCLID'S elements, HEART, HEART valves, and AORTIC valve
Abstract: This paper describes the measurement and reconstruction of the leaflet geometry for a pericardial heart valve. Tasks involved include mapping the leaflet geometries by laser digitizing and reconstructing the 3D freeform leaflet surface based on a laser scanned profile. The challenge is to design a prosthetic valve that maximizes the benefits offered to the recipient as compared to the normally operating naturally-occurring valve. This research was prompted by the fact that artificial heart valve bioprostheses do not provide long life durability comparable to the natural heart valve, together with the anticipated benefits associated with defining the valve geometries, especially the leaflet geometries for the bioprosthetic and human valves, in order to create a replicate valve fabricated from synthetic materials. Our method applies the concept of reverse engineering in order to reconstruct the freeform surface geometry. A Brown & Shape coordinate measuring machine (CMM) equipped with a HyMARC laser-digitizing system was used to measure the leaflet profiles of a Baxter Carpentier-Edwards® pericardial heart valve. The computer software, Polyworks was used to pre-process the raw data obtained from the scanning, which included merging images, eliminating duplicate points, and adding interpolated points. Three methods, creating a mesh model from cloud points, creating a freeform surface from cloud points, and generating a freeform surface by B-splines are presented in this paper to reconstruct the freeform leaflet surface. The mesh model created using Polyworks can be used for rapid prototyping and visualization. To fit a freeform surface to cloud points is straightforward but the rendering of a smooth surface is usually unpredictable. A surface fitted by a group of B-splines fitted to cloud points was found to be much smoother. This method offers the possibility of manually adjusting the surface curvature, locally. However, the process is complex and requires additional manipulation. Finally, this paper presents a reverse engineered design for the pericardial heart valve which contains three identical leaflets with reconstructed geometry. [Copyright &y& Elsevier]