NC machine tool path generation from CSG part representations

In the past few years there has been a lot of interest and excitement generated by solid modeling. Numerous papers have been presented on the value and benefits of this technology. Many talented individuals have contributed to the state of the art. Solid modeling has played a larger role at SIGGRAPH in the past three years, with tutorials, panel discussions and technical papers. All this material has been presented for the most part by academics, researchers and developers of solid modeling systems. The users of solid modeling systems have yet to be heard from. The reason is that there have been very few of them out there in the past. However, that situation is slowly changing. Now that several CAD/CAM vendors are marketing solid modeling systems, a small cadre of users does exist. This panel will be composed primarily of users of solid modeling systems. They will discuss topics of interest to potential users (and also developers) of solid modelers. Questions to be addressed include: What is the status of solid modeling systems from a user standpoint? Can the present solid modelers be used in a production environment today? Should a solid modeling system replace the present wire frame and surface systems or be integrated with them? What are the problems associated with using a solid modeling system? How good is the user interface? Does the necessary application software exist? The primary intent of this Panel discussion is to give the potential user some idea as to whether the available solid modeling systems are useful for his applications. It is beginning to look like the next generation CAD/CAM system for mechanical design will be a solid modeler. The big question is “when will this occur?”

The investigation and implementation of product modeling methods are two of the most important research objectives in the field of computer-aided engineering design. Commercial product modeling systems go beyond geometric modeling systems in that they are adapted to user requirements through the addition of systems that aid in the generation of engineering models and methods. The embodiment design of a mechanical energy storage system serves as an example of future continuous and flexible computer-aided design (CAD). This example is implemented with GEKO, a user system for the layout of design elements. GEKO is coupled with a commercial geometric modeler (CATIA) and uses several programming interfaces.

Symbolic and numerical techniques are coupled together in a proposed geometric modeling system. The geometric modeling system is based on geometrical constraints. It is unnecessary to give constraints in the correct order and the ability of replacing incorrect constraints with their inverse constraints exists in the system itself. A new structure, a biconnected constraint description graph, is used. A triggering mechanism for controlling of the constraint propagation is developed for this structure. An algorithm for converting the biconnected constraint description graph into an acyclic constraint description graph is outlined.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The general objective of this work is to develop a description language for constructive 3D boundary representation [5] of neuroanatomical structures and connectivity at various levels of granularity (from coarse-resolution solids to fine meshes). This approach is motivated by a desire to capture regularities in neural circuitry as revealed by neuro-architectonic studies [4], while at the same time to explore hypotheses about anatomic variability of various origins, such as experimental uncertainties, cross species scaling factors, individual differences, and assess them for their impact on connectivity, and ultimately on network dynamics. Boundary representation is a general approach to describe 3D objects solely by their surface. Boundary representations consist of topological objects and their concrete geometrical representations in terms of enclosing boundaries. Topological elements include vertices, edges and faces, with corresponding geometrical elements being points, curves, and surfaces. The relationships between topological elements in a structure are expressed by means of a graph of topological connections. The description language is being implemented on top of the GNU Triangulated Surface library [3], and provides the ability to: • Specify compound topological objects with parametric geometry; • Specify geometric parameters for the instantiation of topological objects, such as coordinates for placement, or probability distributions for random placement of a group of identical objects; • Specify individual coordinate systems for different cell populations; • Define categories of topological objects, such as stellate, basket and Golgi cells, which may be part of a morphological continuum; • Define rules for connectivity between different categories of objects. We present the anisotropic cerebellar circuitry as a case study, and define boundary representations of the arrangement of Purkinje and Golgi cells in the cerebellar cortex. We use the hexagonal grid pattern suggested by Palkovits et al. in [1,2], while allowing for small variability in the placement of cells within a hexagon. The implementation of the language instantiates the topological objects, computes the intersections of the resulting surfaces, and given connectivity rules for the different categories of objects, computes the potential synaptic connectivity (producing graph theoretical measures, as well as connectivity histograms), and ultimately aims to generate connectivity descriptions for the NEURON simulator.

Ordinary triangular mesh model can be constructed from discrete point cloud. However, this kind of model contains large amount of data. It is not only difficult to split, but also lacks topological relation information. We proposed a CSG---BRep (Constructive Solid Geometry--Boundary Representation) topological model to overcome these problems. CSG---BRep model can record topological relationship of 3D model in great detail. We first introduced aspects of the topological model: location, orientation and sub-shape. Then we proposed two algorithms to access topological structure. We also proposed algorithms for performing Boolean operation on CSG---BRep models. Finally, we demonstrated CSG---BRep construction using LIDAR point cloud as a data source. We would show that, compared to ordinary triangular mesh model, CSG---BRep model is composable and can effectively reduce data volume. In addition, CSG---BRep model has detailed topological relation information, allowing further querying and analysis of 3D spatial topological information.

Although curved-surface solid modeling systems achieve a higher level of accuracy than faceted systems, they also introduce a host of topological, geometric, and numerical complications. A method for calculating accurate boundary representations of solid models is introduced that reduces the impact of these complications. The method uses a pair of bounding polyhedral approximations to enclose the boundary of each object. A structural analysis automatically determines where to make adaptive refinements to the polyhedrons to assure the topological validity of the results. Potential singularities are localized. The implementation is an experimental extension to the Geometric Design Processor (GDP) solid modeling system. >

For robot manipulators, it is nowadays necessary to know their surroundings. This knowledge consists at least of a world representation with recognized objects. During the reconstruction of scene objects from multiple views, changes, like positioning of the objects, or additional unwanted signals, like parts of a human co-worker, may occur. In this paper, we classify the possible changes for a specific type of representation (boundary representation models). Afterwards, we present an approach to detect and handle these changes to maintain a valid world model. To achieve this, we compare what should be visible in the world model reconstructed thus far with the actual information from the current view. The detected change is handled by using object hypotheses as well as geometric information from the world representation. Based on an evaluation, we show a proof of concept and the usefulness of our approach and suggest future work.

The design of a mould, which is manually performed, is time-consuming and quite complicated. This research presents a study on the procedures for automatic feature recognition to help in mould design. A hybrid representation approach is used in automatic feature recognition to extract geometric information from a feature to identify undercut features. Boundary representation is applied in the shape representation using topology and geometry. The proposed approach uses a face adjacency hypergraph to describe the shape of the undercut features by representing the relationships amongst the feature faces. Face-to-face composition is applied to represent the relationship between the main and the undercut features. Parts A, B, and C are created, and automatic feature recognition is used to classify the depression and protrusion features. Algorithms based on a heuristic rule are adopted to determine the optimal parting line and direction of the parts by comparing their feature’s geometric information. The automatic feature recognition approach identifies the shape of concave and convex features in accordance with the depression or protrusion of faces and the face adjacency relationship. This approach can be helpful in automatically creating the core and cavity. The proposed approach will help simplify the process and reduce the time for mould design. Therefore, this approach will significantly affect the increase in productivity in the manufacturing industry.

Fetuses are extremely radiosensitive and the protection of pregnant females against ionizing radiation is of particular interest in many health and medical physics applications. Existing models of pregnant females relied on simplified anatomical shapes or partial-body images of low resolutions. This paper reviews two general types of solid geometry modeling: constructive solid geometry (CSG) and boundary representation (BREP). It presents in detail a project to adopt the BREP modeling approach to systematically design whole-body radiation dosimetry models: a pregnant female and her fetus at the ends of three gestational periods of 3, 6 and 9 months. Based on previously published CT images of a 7-month pregnant female, the VIP-Man model and mesh organ models, this new set of pregnant female models was constructed using 3D surface modeling technologies instead of voxels. The organ masses were adjusted to agree with the reference data provided by the International Commission on Radiological Protection (ICRP) and previously published papers within 0.5%. The models were then voxelized for the purpose of performing dose calculations in identically implemented EGS4 and MCNPX Monte Carlo codes. The agreements of the fetal doses obtained from these two codes for this set of models were found to be within 2% for the majority of the external photon irradiation geometries of AP, PA, LAT, ROT and ISO at various energies. It is concluded that the so-called RPI-P3, RPI-P6 and RPI-P9 models have been reliably defined for Monte Carlo calculations. The paper also discusses the needs for future research and the possibility for the BREP method to become a major tool in the anatomical modeling for radiation dosimetry.For more information on this article, see medicalphysicsweb.org

A 3D engineering geology modeling and analyzing system is designed based on the complex data structure including BRep (boundary representation) and TIN by GIS. To fit the complex stratum interfaces, a few methods to build TIN are discussed on multi-source data, such as the discrete points, the contour line or the DEM, and the techniques of impacting detection, cutting, and mending methods between the TIN model are also discussed. The geological information also can be realistically represented by color and texture mapping. Furthermore, the basal analysis function of the 3D geological model is carried out in this paper, such as generation of geological section, calculating area and volume of the stratum body. Finally, the 3D engineering-geological modeling and analysis system is applied to simulate some projects, such as the coast, slope, hydraulic and hydroelectric project, and highway slope being dig, and the results show that the base theories and system have favorable reliability and practicability.

During design, a designer uses various computational tools, such as a geometric modeling system, analysis tools, and databases. To support these design processes, a system that can integrate such computational tools and support him/her to use the tools and to build, operate and modify models is required. For this purpose, we have been developing the Knowledge Intensive Engineering Framework (KIEF) system. This paper describes the structure of knowledge model used in a modeling process of engineering models. We analyzed engineering knowledge used for Finite Element Analysis (FEA), categorized it, and finally built an environment to support FEA on KIEF.Key wordsModel GenerationEngineering ModelOntologyKnowledge Intensive Engineering

Manufacturing industries have greatly emphasized the need to &quot;integrate&quot; various manufacturing functions-Design, Planning, and Business Operations- into a unified and well coordinated system, so as to increase productivity. In order to achieve this goal, the various CAD/CAM systems must have a common engineering and manufacturing knowledge base. We propose a Knowledge Based Manufacturing System(KBMS) that will help the Manufacturing Engineer(ME) to directly model the workcell environment. The system consists of two main modules: the Workcell Modelling Facility and the Task Planner. The Workcell Modelling Facility helps the ME to create workcell models using the workcell components, product parts, and manufacturing operations contained in a pre-defined knowledge base. The system also allows the manufacturing engineer to add information to the existing knowledge bases schemas. The Task Planner accesses these knowledge bases to generate a network of proposed actions from a given production goal. Integration of the proposed KBMS with a Geometric Modelling System will provide the ME with a tool to perform off-line animation of the Manufacturing Process in a particular workcell model. A prototype KBMS is currently being implemented at the University of Florida using the Object-oriented Semantic Association Model(OSAM*) as the underlying data model for the Knowledge Bases. OSAM* provides the object-oriented features of inheritance and encapsulation of data, as well as the ability to represent complex relationships between object classes in semantic nets.

A CAD-to-vision system with applications in robot guidance, docking and tracking, and inspection tasks is being developed. The goal of the system is to start with CAD models from a geometric modeling system, convert to models that are appropriate for object recognition in vision, and use these vision models for online vision tasks. The vision models consist of two parts: a three-dimensional component, and a set of two-dimensional structures called view classes, each of which relates back to the three-dimensional component. A view class represents a range of views of the object that have similar features in similar relationships. The definition of a view class, its representation as a relational pyramid, and an algorithm for rapidly selecting the view class that best matches an unknown view of the object are discussed. >

Computer-based systems for modehng the geometry of rigid solid objects are becoming increasingly important in mechanical and civil engineering, architecture, computer graphics, computer vision, and other fields that deal with spatial phenomena. At the heart of such systems are symbol structures (representations) designating abstract (subsets of Euclidean space) that model physical solids. Representations are the sources of data for procedures which compute useful properties of objects. The variety and uses of systems embodying representations of solids are growing rapidly, but so are the difficulties in assessing current designs, specifying the characteristics that future systems should exhibit, and designing systems t9 meet such specifications. This paper resolves many of these difficulties by providing a coherent view, based on sound theoretical principles, of what is presently known about the representation of solids. The paper is divided into three parts. The first introduces a simple mathematical framework for characterizing certain important aspects of representations, for example, their semantic (geometric) integrity. The second part uses the framework to describe and compare all of the major knownschemes fo~ representing solids. The third part briefly surveys extant geometric modeling systems and then applies the concepts developed in the paper to the high-level design of a multiple*representation geometric modeling system which exhibits a level of reliability and versatility supermr to that of systems currently used in industrial computer-aided design and manufacturing.

A domain-based fast feature modeling approach was proposed. Inspired by the approach of Domain Engineering in software engineering, for a particular field of feature modeling design, this approach is on how to use the knowledge of such field to improve geometric modeling system. As a result, the entire efficiency of the geometric modeling system was improved by optimizing software architecture and algorithm design. Base on this novel method, the demand of geometric modeling in Computer-Aided Architectural Design (CAAD) was discussed, and a system framework for domain-based geometric modeling was created. Several examples of this method in industry modeling design and digital entertainment fields prove the effective.