• 한국기계가공학회지
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• 제17권3호
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• pp.78-86
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• 2018

The 3D mesh model is used in various fields, such as virtual reality, shape-based searching, 3D simulation, reverse engineering, 3D printing, and laser scanning. There are various formats for the 3D mesh model, but STL and OBJ are the most typical. Since application systems support different 3D mesh formats, developing technology for converting 3D mesh models from one format into another is necessary to ensure data interoperability among systems. In this paper, we propose a method to convert a 3D mesh model in STL format into the OBJ format. We performed the basic design of the conversion system and developed a prototype, then verified the proposed method by experimentally converting an STL file into an OBJ file for test cases using this prototype.

• 대한기계학회논문집A
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• 제31권7호
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• pp.739-746
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• 2007

Recently, models in STL files are widely used in reverse engineering processes, CAD systems and analysis systems. However the models have poor geometric quality and include only triangles, so the models are not suitable for the finite element analysis. This paper presents a general method that generates finite element mesh from STL file models. Given triangular meshes, the method estimates triangles and makes clusters which consist of triangles. The clusters are merged by some geometric indices. After merging clusters, the method applies plane meshing algorithm, based on domain decomposition method, to each cluster and then the result plane mesh is projected into the original triangular set. Because the algorithm uses general methods to generate plane mesh, we can obtain both tri and quad meshes unlike previous researches. Some mechanical part models are used to show the validity of the proposed method.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 추계학술대회 논문집
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• pp.595-598
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• 2002

Laser scanners are getting used more and more in reverse engineering and inspection. For CNC-driven laser scanners, it is important to automate the scanning operations to improve the accuracy of capture point data and to reduce scanning time in industry. However, there are few research works on laser scan planning system. In addition, it is difficult to directly analyze multi-patched freeform models. In this paper, we propose an STL (Stereolithography) mesh based laser scan planning system for complex freeform surfaces. The scan planning system consists of three steps and it is assumed that the CAD model of the part exists. Firstly, the surface model is approximated into STL meshes. From the mesh model, normal vector of each node point is estimated. Second, scan directions and regions are determined through the region growing method. Also, scan paths are generated by calculating the minimum-bounding rectangle of points that can be scanned in each scan direction. Finally, the generated scan directions and paths are validated by checking optical constraints and the collision between the laser probe and the part to be scanned.

• 한국정밀공학회지
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• 제22권9호
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• pp.202-211
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• 2005

This paper introduces and illustrates the results of a new method fer offsetting triangular mesh by moving all vertices along the multiple normal vectors of a vertex. The multiple normal vectors of a vertex are set the same as the normal vectors of the faces surrounding the vertex, while the two vectors with the smallest difference are joined repeatedly until the difference is smaller than allowance. Offsetting with the multiple normal vectors of a vertex does not create a gap or overlap at the smooth edges, thereby making the mesh size uniform and the computation time short. In addition, this offsetting method is accurate at the sharp edges because the vertices are moved to the normal directions of faces and joined by the blend surface. The method is also useful for rapid prototyping and tool path generation if the triangular mesh is tessellated part of the solid models with curved surfaces and sharp edges. The suggested method and previous methods are implemented on a PC using C++ and illustrated using an OpenGL library.

• 한국정밀공학회지
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• 제13권10호
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• pp.46-55
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• 1996

As industrial standard data, the STL format which approximates three dimensional CAD model to triangular facets, is used for RP(Rapid Prototyping) system in recent days. Because most RP system take the only form of two dimensional line segments as an input stream inspite of its imperfectness while converting into STL format, a CAD model is converted into a standard industrial format which is composed of many triangular facets. The error verifying process is composed of four main steps, and these are 1) Remove facets with two or more vertices equal to each other. 2) Fix overlapping error such as more than three facets adjacent to anedge. 3) Fill holes in the mesh by using Delaunay triangulation method. 4) Correct the wrong direction and normal vectors. This paper is concerned with serching the mentioned errors in advance and modifying them.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1996년도 춘계학술대회 논문집
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• pp.597-601
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• 1996

Nowadays, the STL format, industrial standard data, which approximates three dimensional CAD model to triangular facets, is used for RP(Rapid Prototyping) system. Because most RP machine is accpted to only two dimensional line segments, but some STL translators are sometimes poorly implemented. The error verifying process is as follows. 1) Remove facets with two or more vertices equal to each other. 2) Fix overlapping error such as more than three facets adjacent to an edge. 3) Fill holes in the mesh by using Delaunay triangulation method. 4) Repair wrong direction and value of normal vectors. This paper is concerned with searching the mentioned errors in advance and modifying them.

• 한국멀티미디어학회:학술대회논문집
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• 한국멀티미디어학회 2002년도 춘계학술발표논문집(하)
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• pp.901-906
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• 2002

본 논문은 신속조형(RP: rapid prototyping) 시스템에서 사용되며 3D 기하학적 형상 모델을 가지고 있는 STL(standard transform language)에 워터마크를 삽입하는 방법에 관한 연구이다. 제안된 알고리즘은 3D 형상 데이터의 왜곡이 전혀 없이 패싯(facet, mesh)의 버텍스(vertex) 영역에 워터마크를 삽입한다. 기존의 알고리즘으로 STL에 워터마크를 삽입할 경우, 패싯의 저장순서를 변경하는 단순한 공격으로도 워터마크가 제거된다. 제안된 알고리즘은 패싯의 저장 순서 변경과 같은 공격에 대한 강인성을 가질 뿐만 아니라, 비가시성(invisibility)도 충족한다. 제안된 알고리즘으로 STL 3D 형상에 워터마크를 삽입하고 추출하는, 실험 결과들은 3D 원형상을 전혀 왜곡하지 않고 워터마크의 삽입과 추출이 가능함을 보여준다.

• International Journal of CAD/CAM
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• 제2권1호
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• pp.55-67
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• 2002

In many areas of industry, it is desirable to have fast and reliable systems in order to quickly obtain suitable solid models for computer- aided analyses. Nevertheless it is well known that the data exchange process between CAD modelers and CAE packages can require significative efforts. This paper presents an approach for geometrical data exchange through triangulated boundary models. The proposed framework is founded on the use of STL file specification as neutral format file. This work is principally focused on data exchange among CAD modelers and FEA packages via STL. The proposed approach involves the definition of a topological structure suitable for the STL representation and the development of algorithms for topology and geometry data processing in order to get a solid model suitable for finite element analysis or other computer aided engineering purposes. Different algorithms for model processing are considered and their pros and cons are discussed. As a case study, a prototype modeler which supports an exporting filter for a commercial CAE package has been implemented.

• 한국통신학회논문지
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• 제32권12C호
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• pp.1194-1202
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• 2007

본 논문에서는 쾌속조형시스템(Rapid Prototyping System)에 적용 가능한 블라인드 워터마킹 알고리즘을 제안한다. 3차원 메쉬 모델은 쾌속조형시스템의 시제품 제작 전 단계인 CAD 모델링 단계에서 사용된다. STL 형태의 메쉬 모델을 이용하여 제작할 시제품의 오류를 확인하고 수정하여 정밀도를 높이고 데이터의 오류를 줄인다. 모델링 단계의 메쉬 모델 오류는 시제품의 정밀도와 직접 연결되기 때문에 시제품 제작 전 단계에서는 이동, 회전과 같은 모델의 형태를 변형시키지 않는 변환은 사용하지만 데시메이션, 평활화 등의 변환은 사용되지 않는다. 기존의 대부분 워터마킹 알고리즘은 모델에 특정 노이즈를 추가하는 방법으로 워터마크 정보를 표현한다. 이런 알고리즘은 쾌속조형시스템에 사용할 경우 시제품의 정밀도를 저하시키기 때문에 사용이 극히 제한적이다. 제안한 알고리즘은 워터마크 삽입 전후 모델의 형태가 변하지 않으며 쾌속조형시스템과 같은 고정밀도를 요구하는 기계공학 분야에서 제작자 정보의 표현, 데이터의 무결성 인증 등 목적으로 사용할 수 있으며, 가상현실 등 다른 분야에서는 정보은닉 용도로도 사용할 수 있다.

• 한국정밀공학회지
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• 제23권7호
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• pp.187-193
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• 2006

This paper introduces and illustrates the results of a new method for offsetting the triangular mesh generated from multiple surfaces. The meshes generated from each surface are separated each other and normal directions are different. The face normal vectors are flipped to upward and the lower faces covered by upper faces are deleted. The virtual normal vectors are introduced and used to of feet boundary. It was shown that new method is better than previous methods in offsetting the triangular meshes generated from multiple surfaces. The introduced offset method was applied for 3-axis tool path generation system and tested by NC machining.