Joris S. M. Vergeest

Freeform feature modelling: concepts and prospects

Abstract Much research has already been done on regular-shaped features, but more complicated, freeform features are now demanded by product designers. Freeform shapes are mostly represented by low-level representations, such as Bezier, B-Spline and NURBS patches. Freeform features provide a high-level interface to these low-level representations. The purpose of freeform features is faster and more intuitive modelling with more guarantees for a high-quality design. In contrast to the traditional ways of modelling with freeform surfaces, where low-level entities such as control points and weights are used to interact with a freeform surface, the user is offered a set of freeform features whose basic shape is fully defined by intuitive parameters. The design-by-features approach offers good opportunities for validity maintenance, by which only models that satisfy certain pre-defined validity conditions can be created. In this paper, the most important concepts in design by freeform features are surveyed, and issues such as classification and parameterisation of freeform features and freeform feature recognition are described. Wherever appropriate, promising research prospects are indicated.

A DISCRETE MECHANICS MODEL FOR DEFORMABLE BODIES

This paper describes the theory and implications of a discrete mechanics model for deformable bodies, incorporating behavior such as motion, collision, deformation, etc. The model is fundamentally based on inter-atomic interaction, and recursively reduces resolution by approximating collections of many high-resolution elements with fewer lower-resolution elements. The model can be viewed as an extended mass-spring model. We begin by examining the domain of conceptual design, and find there is a need for physics based simulation, both for interactive shape modeling and analysis. We then proceed with describing a theoretical base for our model, as well as pragmatic additions. Applications in both interactive physics based shape modeling and analysis are presented. The model is aimed at conceptual mechanical design, rapid prototyping, or similar areas where adherence to physical principles, generality and simplicity are more important than metric correctness.

Displacement feature modelling for conceptual design

Abstract Although the support of surface features, where a surface feature represents a local geometric detail imposed on a surface, is welldefined on prismatic objects, this is not the case for sculptured surface models. Current methods often lead to data-explosion, high polynomial results, or procedural solutions. In this paper a method is described that allows explicit modelling of protrusions and depressions in free-form B-spline surfaces. As this functionality is intended to be used by industrial designers during conceptual design, distinct requirements are formulated to allow its use in this early stage of design. A method is described that calculates a blending geometry approximating G 1 cross-boundary smoothness effectively. Using these requirements and approximations, protrusions and depressions can be modelled with real-time response, and with unprecedented flexibility.

Interactive simulation of robot milling for rapid shape prototyping

Abstract Rapid shape prototyping has become a prominent method to speed up the product development process in industry. Automatic robot milling, directly from CAD data, is an efficient technique to materialize the intended product shape quickly. There are a number of situations in which previewing of this process is required. The end-user, i.e. , the designer who intends to order a prototype, wishes to be informed about the quality of the result in terms of geometric appearance and accuracy, for example, by comparing it to the CAD model. Also, any systematic defects inherent in the prototyping process must be made visible. Furthermore, the developers of the prototyping system can take advantage of simulation in their efforts to improve the process. The major technical problem in simulating the milling process is to model the volume removal operations efficiently, so that the stock-in-progress can be visualized at any moment. This article presents a method to perform such simulation while meeting stringent requirements, including the ability to handle the large number of robot movements in a single milling process (up to 10 6 , depending on the required spatial accuracy), high speed, and user-interactivity. Both the block of material that is being machined and the milling tool are internally represented by a 3D voxel structure to achieve real-time volume-removal operations on the material. All other objects, such as the robot and the work cell, keep their original B-spline surface representation, to enable high-quality visualization. Implementation of the data structures and algorithms described here has resulted in a useful system for joint simulation of volume removal and robot motion.

New functionality for computer-aided conceptual design: the displacement feature

Abstract Conceptual design using conventional 3D CAD systems is a controversial issue among industrial designers. Although one can produce complex, accurate, finished 3D models using these CAD systems, it is still difficult to use them during early, creative product design. In this paper, a method is described that allows the design of protrusions and depressions in sculptured surfaces in a flexible and interactive manner. Through interviews with industrial designers, the basic requirements for support of such functionality during conceptual design have been formulated. An implemented method based upon these requirements has been extensively evaluated by industrial designers, and these evaluations show that industrial designers find this functionality extremely useful during conceptual shape design.

Tool profile and tool path calculation for free-form thick-layered fabrication

Abstract In several application fields, large sized, free-form objects of various soft materials are widely used. Available layered prototyping technologies cannot be applied for fabrication of these kinds of objects due to size limitations. The authors have developed a novel approach of layered manufacturing that is the most appropriate for physical concept modeling. This paper presents the algorithms for geometrically-based modeling of the profile curve of the flexible blade tool. It also describes the algorithm for direct slicing of the CAD model. The second part of the paper deals with the algorithms for slicing, tool positioning and tool path calculation. On the front surfaces of the layers G2, quasi G1 continuity can be implemented at the transition from one layer to another. In the circumferential direction G0 continuity exists.

Robot machines rapid prototype

Describes the application of an industrial robot to the rapid prototyping of 3D CAD‐defined products. Outlines the equipment and the major software issues of the fully automatic offline generation of the robot instructions. Presents performance, limitations and practical results.

Free-form thick layer object manufacturing technology for large-sized physical models

Abstract Large-sized free-form objects of different materials are widely used in various industrial applications. Currently, layered rapid prototyping technologies are not suitable for the fabrication of this kind of objects, due to the necessity of a large number of layers and the limitations in size. This paper reports a novel approach of layered manufacturing that is more appropriate for the fabrication of these large objects. A method of thick-layered object manufacturing is presented, which is based on a higher order approximation of the shape and application of a flexible curved cutting tool. The method allows the production of physical prototypes, which need little or no finishing. In order to meet the designers intend, as closely as possible, some feasible system characteristics are introduced. The process is ordered in a sequential way and provides a highly automated process. A hierarchical decomposition of the CAD geometry takes place into components, segments, layers and sectors, based on morphological analysis. This method enables the manufacturing and the re-assembly of the parts to produce the physical prototypes without affecting the requested functionality. Due to the possibility of obtaining multiple solutions in the physical model, much attention must be paid to the efficiency of the process.

CAD surface data exchange using STEP

Abstract In 1991, the International Standards Organisation will publicly present a technical proposal for a part of Version 1.0 of Step , the international standard for external representation of product data. Step provides advanced methods for product-model specification and for the realization of high-quality data-exchange processes. The main obstacles to the integration of CAD/CAM systems are the incompatibility of the individual data-type domains and the multiplicity of implementations of certain entities. The paper demonstrates that the latter problem can be ameliorated via the proposed Step specification. This is illustrated with reference to B-spline curves and B-spline surfaces. The geometry Part of Step is briefly outlined, and the definition of B-spline entities in the Express language is given. It is shown how these entities meet the requirements for Step data exchange. The multipurpose character of Step B-splines is illustrated with numerical examples.

Testing shape manipulation tools using abstract prototypes

Abstract Research in computer support to industrial design typically involves much experimentation. Proposals for new modeling methods are commonly evaluated using pilot software implementations. The experimentation tends to be lengthy and therefore expensive. We propose a faster way to evaluate the functionality of design tools. This evaluation method, called abstract prototyping, can be used in a very early stage of the development of a computer tool, prior to any software implementation. The evaluation focuses on how potential users appreciate new modeling functions by simulating their basic properties. The method aims at decreasing the risk of building a useless tool. We have applied abstract prototyping to make a selection among different candidate shape modeling techniques. The method proved to be feasible, fast and inexpensive,