Der-Baau Perng

Automatic 3D machining feature extraction from 3D CSG solid input

Abstract A method for automatically extracting the machining features from 3D CSG solid input is proposed. The method involves converting a parts CSG tree representation into its equivalent DSG tree representation and then identifying the types of machinable features from the DSG tree. A DSG tree is a special case of CSG tree in which all geometric operations are of ‘difference’ type. The method is proposed for recognizing prismatic part features and its outputs contain feature attributes and possible tooling entrance faces, etc. Computer simulation is provided to illustrate the proposed method.

A systematic approach for developing a foot size information system for shoe last design

Abstract The property of a shoe last design significantly impacts the fitness of the shoes thus produced. Traditionally, a shoe last is designed by using numerous foot measure data. Among all the items of foot measure information, the foot length and joint girth are further identified as principle factors affecting shoe last design. In this paper, foot length and joint girth are analyzed by using a bi-variate normal distribution to obtain a more efficient foot size grading system. A set of 2486 adult male samples collected in Taiwan area are used in this analysis to establish the norm for the foot length and joint girth. A foot size information system (FSIS) providing shoe last related information such as the percentage of population that a last can fit in is established from the analysis results. This study contributes designers the grading information that is helpful for shoe last design. Relevance to industry Shoe last design is the basis for footwear design. The foot size information system derived in this paper provides shoe making industry with a more efficient and economical size grading system to design shoe lasts. This grading system also promotes customer satisfaction with better fitness in foot size.

Automatic reconstruction of 3D solid objects from 2D orthographic views

Abstract An algorithm which can automatically construct 3D solid objects from 2D orthographic views is proposed. The views contain geometric information of lines, circles or circular arcs. The reconstructed objects may be polyhedra, cylinders, partial cylinders and their composites. The reconstruction process consists of three phases: decomposition, reconstruction and composition. First, the inputted drawing is decomposed into several predefined types of subviews, then a translation sweep operation, perhaps followed by a plane-cutting operation, is used to reconstruct the corresponding subpart for each set of subviews. Finally, the volume enclosure relationships between these subparts are utilized to compose the final part.

Directional textures auto-inspection using discrete cosine transform

This paper describes a global image restoration scheme using a discrete cosine transform (DCT) that can be used to detect defects in directional textured surfaces automatically. The input spatial domain image is first transformed into the DCT domain so that the dominant directions of the texture in the input image will be compacted into the orthogonal straight lines or impulses through the direct current (DC) component of the spectrum. The linear primitives associated with the high-energies in the DCT domain are eliminated by reducing them to zero before transforming back to the spatial domain. Finally, the defects, if any, are extracted by the thresholding method. Experiments on a variety of product surfaces with directional textures such as straight, slanted, orthogonal, slanted orthogonal, and oblique linear primitives were conducted in this paper. The proposed scheme would blur directional textures and preserved only local defects if they were initially embedded in the image. Furthermore, some preliminary experiments were also conducted to demonstrate the proposed scheme was insensitive to horizontal and vertical shifting, changes in illumination, and image rotation.

Resolving feature interactions in 3D part editing

Feature-based design approach has been regarded as a promising approach for 3D parts design. However, the critical issues of modifying a part design by 3D features have not yet evoked sufficient discussion. This paper aims to address issues of feature interaction, especially for enclosure and intersection, among the modified feature and the other existing features. An efficient new approach to solve the feature interaction problems encountered in part-editing is proposed. The parts are assumed to consist of subtractive volume-features only. A set of rules that facilitate updating the B-rep data and feature-based representation of the part are devised. Computer simulation examples are given to show that the proposed approach is both feasible and effective. This research contributes to several aspects of feature-based design research, especially to the area of providing simple feature-based commands.

Automatic form feature recognition and 3D part reconstruction from 2D CAD data

Abstract In this paper, a method which can recognize form features and reconstruct 3D part from 2D CAD data automatically is proposed. First, we use the divide-and-conquer strategy to extract the vertex-edge data from each 2D engineering drawing of IGES format. Then, a set of production rules are developed to facilitate the form feature matching process. A new structure of form feature adjacency graph (FFAG) is devised to record the related attibutes of each form feature. Finally, to avoid the combinatorial subparts composition problem, a sweeping operation and volumetric intersection approach is used to rapidly reconstruct the remaining 3D objects. The last reconstructed 3E object is used as the base of the FFAG. All the recognized form features in the FFAG can be classified as depression or protrusion features on the 3D part base. The FFAG structure can be easily transformed into CSG/DSG structure, which is readily integrated with the downstream CAPP/CAM systems. A detailed example is provided to illustrate the feasibility and effectiveness of the proposed system.

Feature-based process plan generation from 3D DSG inputs

Abstract A method that can automatically generate a process plan from 3D input data for a prismatic part is proposed. The 3D input data are the machining features represented in the DSG tee model [1]. A DSG tree is a special case of CSG tree in which all geometric operations are of difference type. The proposed method can (a) transfer the DSG-represented input data into refined machinable features, (b) determine the machinability of features, and (c) determine the cutting directions of all features of a prismatic part. This information is used to determine the machines, tools, and machining sequences that are required to manufacture a part. The NC paths are also generated. Computer simulations are provided to illustrate the proposed method. The major contribution of this paper is that the process plan of a CSG represented prismatic part can be generated automatically through the proposed method. It, therefore, extends the application domain of the CSG tree model and fully integrates CAD/CAM systems.

Assembly-part automatic positioning using high-level entities of mating features

Abstract We present a new and convenient method for automatically positioning parts in an assembly. High-level entities of mating features and mating relations are used to describe the composed state of parts in an assembly. The characteristics of volume, reference origin, and boundary face of mating features and parts are used to determine automatic part-positioning operations. Using the proposed approach, a hierarchical model of the assembly can be constructed more easily with fewer input data. This approach thus makes computer-aided assembly design systems more user-friendly and greatly reduces the amount of input data required. An example is presented to demonstrate the simplicity and effectiveness of the proposed approach.

A NOVEL VISION SYSTEM FOR CRT PANEL AUTO-INSPECTION

The defects of a 3-D translucent hull CRT panel may include scratches, blemishes, cracks, bubbles, or collapsed portions. Defects may occur on the inside surface, outside surface, or interior of the glass. We designed and developed three sets of vision systems which can automatically inspect defects in CRT panels. The first system inspects the front-surface and two turn-segments, the second system inspects the other two turn-segments, while the third system inspects the side-wall defects. Two different kinds of lighting environments were developed to highlight the CRT panels and to simplify the image-capturing process. Meanwhile, a set of image processing methods were devised which can reliably detect the defects within the expected processing time. Experimental results demonstrate that the developed vision systems can be used to inspect CRT panels in the production line.

Analysis of changes to the anterior chest wall after the Nuss procedure—an objective measurement of pectus excavatum

INTRODUCTION We report a noninvasive method for recording the deviation of the anterior chest wall (ACW) in patients with pectus excavatum before and after the insertion and removal of a Nuss bar. PATIENTS AND METHOD All patients undergoing the Nuss procedure at our institutions between June 2008 and February 2009 were enrolled in this study. A thermal plastic strip was used to cast the ACW at the skin level along the area corresponding to the tract of the inserted bar. The height of the ACW was defined as the perpendicular length from the xiphoid process to the transverse line drawn between the 2 midaxillary points. RESULTS Bar insertion caused a significant increase in ACW height and width. Bar removal reduced the corrective effects in terms of a significant decrease in ACW height; at the same time, an increase in ACW width was noted. CONCLUSION Feature extraction and analyses of permanent contour casts of the ACW help to understand immediate changes in the ACW after the Nuss procedure and may assist in the design of the bar at insertion. The Nuss bar in situ helped to maintain cosmetic benefits to the ACW.