Boundary Representation Solid Models Research Articles

Modelling stiffeners of ship hull structures

In this study, the data associated with the definition of stiffeners on plate panels of ship structures are analysed and a data model is described. Then, methods to generate accurate representations of stiffeners as solid models are presented. First, a method is presented to create the parallel trajectory lines of the stiffeners computing geodesic offset paths on free-form parametric surfaces. Next, the generation of the boundary surfaces required to create boundary representation solid models of the stiffeners is described, and finally, this procedure is extended to produce the corresponding accurate edge cut-outs on any plates crossed.

A Feature Recognition Approach with Fuzzy ART Neural Network

This paper proposes a feature recognition approach from a boundary representation solid model with Fuzzy ART neural network. To recognize the feature efficiently, some key technologies in Fuzzy ART neural network are used. The influence of the vigilance parameter on feature recognition is studied, and two learning modes, fast learning and slow learning are adopted and compared in feature recognition. Finally, a case study is given to verify the proposed approach.

Combining Dynamic Modeling With Geometric Constraint Management to Support Low Clearance Virtual Manual Assembly

This research presents a novel approach to virtual assembly that combines dynamic modeling with geometric constraint-based modeling to support low clearance manual assembly of CAD models. This is made possible by utilizing the boundary representation solid model data available in most contemporary CAD representations, which enables (a) accurate collision/physics calculations on exact model definitions, and (b) access to geometric features. Application of geometric constraints during run-time, aid the designer during assembly of the virtual models. The feasibility of the approach is demonstrated using a pin and hole assembly example. Results that demonstrate the method give the user the ability to assemble parts without requiring extensive CAD preprocessing and without over constraining the user to arrive at predetermined final part orientations. Assembly is successful with diametral clearance as low as 0.0001 mm, as measured between a 26 mm diameter hole and pin.

A hybrid machining Feature Recognition system

This paper discusses a hybrid feature recognition system to recognise machining features in boundary representation solid model of 2.5D parts. It combines the strengths of graph-based and hint-based approaches. A pre-processor is used to validate the input part model. The graph-based system is used to extract and recognise isolated features of the part. The hint-based system decomposes the compound features into machinable features. It is capable of handling arbitrary interactions of features. The proposed integrated framework of the two approaches is tightly coupled with the machining environment to ensure manufacturability of the recognised features. [Received 10 June 2008; Revised 24 October 2008; Accepted 25 December 2008]

Towards a neutral specification of geometric features

The paper concerns the standardised exchange of feature data between CAD systems, or between CAD and downstream application systems. The international standard ISO 10303 (STEP) allows the exchange of CAD models expressed in terms of wireframe, surface or boundary representation solid models. Some published parts of this evolving standard additionally include representations of features suitable for various applications, and other such parts are under development. However, there is no unifying ISO 10303 resource for the general (application-independent) representation of features. Such a resource would enforce consistent feature modelling methodology throughout the standard, and avoid divergent representations that create difficulties in the automation and integration of feature-based applications. A three-level architecture is proposed for the representation of STEP features at an application-independent level. It is compatible with another important ISO standard that represents dimensions and tolerances in terms of the symmetries of feature configurations.

Recognition of cylindrical-based features using edge boundary technique for integrated manufacturing

A new technique called edge boundary classification (EBC) for recognition of features from boundary representation (B-rep) solid model to support integrated manufacturing is presented. Features are interpreted from patterns formed by identifying the solid and void ‘sides’ of a boundary entity using the spatial addressability information of solid models. The application of the EBC technique for recognising simple and interacting cylindrical-based features is explained and discussed. The type of features experimented are through-hole, blind-hole, boss and internal undercut. The results obtained show that cylindrical-based features can easily be recognised using the EBC technique.

Generating MODFLOW grids from boundary representation solid models.

Complex stratigraphy can be difficult to simulate in MODFLOW models. MODFLOW uses a structured grid that requires that each grid layer be continuous throughout the model domain. This makes it difficult to explicitly represent common features such as pinchouts and embedded seams in a MODFLOW model. In this paper, we describe a method for automatically generating MODFLOW-compatible grids from boundary-representation solid models. Solid models are data structures developed originally for computer-aided design applications that define the geometry of three-dimensional objects. Solid models can be used to represent arbitrarily complex stratigraphy. The elevations defined by the solids are then extracted from the solids in a manner that preserves the continuous-layer requirement imposed by MODFLOW. Two basic approaches are described: The first method adjusts the MODFLOW grid dimensions (layer elevations) to fit the solid model boundaries, and the second method creates a regular MODFLOW grid and adjusts the material properties to match the changes in stratigraphy. One of the main benefits of using solid models to define stratigraphy for MODFLOW models is that it provides a grid-independent definition of the layer elevations that can be used to immediately re-create the MODFLOW grid geometry after any change to the grid resolution.

CAD-based CMM dimensional inspection path planning – a generic algorithm

This paper describes a newly developed algorithm for CAD-based dimensional inspection path planning utilizing coordinate measuring machines (CMMs). The algorithm guarantees to provide optimum collision-free inspection probe paths by using the topological structure of the boundary representation (B-rep) solid CAD models of the inspected parts. A concept of automatic generation of optimum and collision free path in three dimensional space using available CAD database is proposed. The algorithm is generic for generating probe path over prismatic polyhedral parts. It serves as a principal part of the inspection path planning system. It is based on the modified ray tracing technique which uses a B-Rep data from any geometric modeling systems. Between start point and target point, an imaginary ray is established and if an intersection with part is encountered, an optimal detour path is created avoiding interference of the probe with the part. The generated path consists of linear segments joining start point and target point by various intermediate points. To locate these intermediate points in the consideration space, topological and geometrical structures of the part models are used at the time of decision making. To examine and implement the algorithm, a user-friendly application is developed employing AutoCAD Runtime Extension (ARX) development environment with object oriented programming (OOP) techniques, running on a Windows NT workstation. The effectiveness of the proposed algorithm is verified by the results of the implementation demonstrating optimum collision-free dimensional inspection path generation for four representative prismatic part models. All in all, this work contributes to the knowledge-base formation of automated dimensional inspection research area and paves a way for the integration of CMMs into a CAD/CAM environment, thus automate the process of design, manufacturing and quality assurance.

Manufacturing features recognition using backpropagation neural networks

A backpropagation neural network (BPN) is applied to the problem of feature recognition from a boundary representation (B-rep) solid model to facilitate process planning of manufactured products. It is based on the use of the face complexity code to represent the features and a neural network for the analysis of the recognition. The face complexity code is a measure of the face complexity of a feature based on the convexity or concavity of the surrounding geometry. The codes for various features are fed to the network for analysis. A backpropagation network is implemented for recognition of features and tested on published results to measure its performance. Any two or more features having significant differences in face complexity codes were used as exemplars for training the network. A new feature presented to the network is associated with one of the existing clusters, if they are similar, or the network creates a new cluster, if otherwise. Experimental results show that the network was consistent in recognizing features, hence is appropriate for application to the problem of feature recognition in automated manufacturing environment.

Delta-volume decomposition for multi-sided components

The subdivision of the removal, or delta-volume, of a machined component into meaningful volumes suitable for efficient machining is at present a complex and time-consuming task. An algorithm is presented for recognizing CNC machining volumes from 3D boundary representation solid models. The 2.5D volumes identified are associated with generic depressions and protrusions. The novelty of the algorithm lies in the fact that its success does not depend upon a pre-defined library of features and that it guarantees the accessibility of the volumes found.

Milling Process Simulation—A Generic Solid Modeller Based Paradigm

A generic solid modeller based milling process simulation system is developed for 3-axis milling of complex parts. Parts are described using a boundary representation solid model, and cutting edges are fitted with cubic Be´zier curves. For every completed tool path (i.e., one NC block), the tool swept volume is generated and intersected with the part, yielding the corresponding removed material volume. The tool cutting edges are then intersected with that volume to produce the tool-part immersion geometry. The mechanistic milling process model produces an accurate simulation of cutting forces, torque and power. Modelling of tool and tool holder dynamics is included. The system is based on a generic procedure for extracting geometric data required to accurately simulate milling of complex parts. Any tool shape can be represented, and extension to 4- and 5-axis machining is straightforward. Related processes such as turning and drilling can be modelled in a similar way. The capability of the system is demonstrated experimentally for ball end milling.

Feature recognition using ART2: a self-organizing neural network

A self-organizing neural network, ART2, based on adaptive resonance theory (ART), is applied to the problem of feature recognition from a boundary representation (B-rep) solid model. A modified face score vector calculation scheme is adopted to represent the features by continuous-valued vectors, suitable to be input to the network. The face score is a measure of the face complexity based upon the convexity or concavity of the surrounding region. The face score vector depicts the topological relations between a face and its neighbouring faces. The ART2 network clusters similar features together. The similarity of the features within a cluster is controlled by a vigilance parameter. A new feature presented to the net is associated with one of the existing clusters, if the feature is similar to the members of the cluster. Otherwise, the net creates a new cluster. An algorithm of the ART2 network is implemented and tested with nine different features. The results obtained indicate that the network has significant potential for application to the problem of feature recognition.

Automatic Determination of Feature Interactions in Design-for-Manufacturing Analysis

The current paper discusses a fundamentally new approach to defining and finding interactions in computer-aided design (CAD) forms or features. Feature classes are defined using a high-level abstract entity called a loop. Loops define features in a general manner and aid in the definition of feature boundaries as well. Interactions between features exist due to interactions between their boundaries. Several types of interactions are defined and automatically determined from the boundary representation solid model of the part subsequent to performing feature extraction.

Automatic Kinematic Analysis of Boundary Representation Mechanism Models

SUMMARY Traditional mechanism analysis packages require the user to define laboriously a dyad representation in terms of joint types, coordinates and link lengths. The resulting simulation is often limited in its usefulness, because many of the physical restrictions on the movement of the linkage cannot be determined. In contrast, this paper describes a kinematic analysis package that takes a boundary representation solid model of the mechanism as its sole input. The system uses feature recognition techniques to identify automatically individual joints and the overall structure of the linkage. Once the form of the mechanism has been determined, a kinematic analysis is carried out, which results in the animation of the solid model. The system demonstrates how automation of the mechanism definition step in kinematic analysis could produce a significant reduction in the design cycle time.

Topological and Geometric Consistency in Boundary Representations of Solid Models of Mechanical Components

This paper describes a method of verifying the consistency (i.e., agreement) between the topology and geometry of boundary representation (B-rep) solid models of mechanical components. This verification is well-suited for implementation as an algorithm and has been implemented as such in a polyhedral boundary representation solid modeling system (Jablokow, 1989). This technique and algorithm is important in the design of mechanical components for design documentation, integration with analysis and manufacturing applications, and design data exchange between solid modeling systems. Information regarding boundary representations has typically divided into the geometry and topology. It is important that the two are consistent for a valid solid model. In this work the genus of a solid model of an object is calculated topologically and geometrically and then compared to verify the consistency of the solid model. The genus of an object gives insight as to the geometric complexity of the object. This is equivalent to verifying the Gauss-Bonnet Theorem for the model, and is discussed in the paper.

Feature Extraction for Casting Core Development

Feature extraction techniques are presented for the generation of casting core patterns from a boundary representation (B-Rep) solid model. Techniques are presented which would allow for automatic extraction of three classes of core features (internal voids, single and multi-surface holes, and boundary perturbations). The task of extracting casting cores from solid models involves recognizing a collection of entities (i.e., slots, bosses, undercut surfaces, local and global concavities, etc.) from the set of lower level entities (i.e., the B-Rep structure). To this end, a combination of solid modeling B-Rep and graph structures and their associated methods will be used for casting core development. Appropriate local features are identified and extracted from the original object, and are grouped into one or more new object(s) (termed a core-object). If the core-object is multiply connected (i.e., composed of multiple objects), it is graph separated into global feature objects. Each of these global feature objects represents a core in the final pattern. Lastly, the geometry of the original part is augmented to add core prints where core geometries were extracted. The core print, as currently developed, combines the extracted core geometry and its convex hull.

Automated solid models from serial section images.

A new method for creating unambiguous and complete boundary representation solid models with a hybrid polygonal/nonuniform rational B spline representation was developed and tested using computed tomography scans of the wrist. Polygon surface approximation was applied to a sequence of parallel planar outlines of individual bone elements in the wrist. An automated technique for the transformation of edge contours into solid models was implemented. This was performed using a custom batch file command sequence generator coupled to a commercially available mechanical computer-aided design and engineering software system known as I-DEAS (Structural Dynamics Research Corporation, Milford, OH). This transformation software allows the use of biomedical scan slice data with a solid modeler.

Automated Flat Pattern Layout from Three-dimensional Wire-frame Data

SUMMARY Starting with a three-dimensional wire-frame data list, a shell-type boundary representation solid model is automatically created to represent sheet metal objects. This model contains the geometric data and topological relationships required to automate the flat pattern layout process and bend allowance calculation encountered in brakeforming. These features are incorporated into a software program called LAYOUT.LU, that uses a ring-type database structure to store data and uses real-time dynamic graphics to illustrate the layout and bend allowance process. Initial graphics exchange standard (IGES) formatted data can be provided as input and IGES output formats of the flat pattern are generated.