Michael J. Pratt

Towards the standardized exchange of parameterized feature-based CAD models

The paper describes the status of work aimed at extending the international standard ISO 10303 (STEP) to permit the exchange of parameterized feature-based models between different CAD systems, in terms of the constructional history of the models concerned. Such procedural models have the advantage of being easy to edit following an exchange, by contrast with the models that can be exchanged using current STEP methodology, which prove to be difficult or impossible to edit in the receiving system. The use of the approach described has already been demonstrated in the exchange of realistic procedural shape models of mechanical parts, and the paper includes a brief account of some of the tests performed and the projected benefits of the use of this extension of STEP technology.

Cyclides in computer aided geometric design

Abstract Extensions are made to the methods of Pratt (1990) for the use of cyclides in solid modelling, with particular regard to their application as blend surfaces. New insights are given into the geometry and Bezier representation of cyclide surface patches. The existing theory of symmetric cyclide blends is extended and then generalised to cover asymmetric problems. Finally, some details are given of a wider class of surfaces which show great promise for CAD use in the future.

Automated feature recognition from 2D drawings

Abstract Automated feature recognition is likely to be an essential requirement for future integrated design and manufacturing systems. Most methods which have so far been proposed use as their input a solid model which represents only the purely geometric aspects of the design information. Much research is currently in progress on the augmentation of such models with technological and other lifecycle data to give what is referred to as a product model. The presence in such a model of design feature data, in particular, may make the recognition of manufacturing features easier in the future. On the other hand, little previous work has been reported on feature recognition from 2D drawings, which is the form in which the majority of design data currently exists. The paper describes an experimental system for this purpose. It has been designed to meet the automated process-planning requirements of today rather than tomorrow, and it has been demonstrated on a range of simple prismatic machined parts.

Solid Modeling and the Interface Between Design and Manufacture

Many challenges must be faced before an automatic process-planning system will be practical for individual application¿specifically, the recognition and simulation of a parts ¿form features.¿

Cyclides in surface and solid modeling

It is shown that Dupin cyclides (C.P. Dupin, 1822), as surfaces in computer-aided geometric design (CAGD), have attractive properties such as low algebraic degree, rational parametric forms, and an easily comprehensible geometric representation using simple and intuitive geometric parameters. Their alternative representations permit the transition between forms when one or the other is more convenient for a specific purpose. Cyclides provide is useful extension of geometric coverage in solid modeling, primarily as blending surfaces for many commonly occurring situations. The geometry, properties, and uses of the Dupin cyclide in free-form surface modeling and blending are discussed.<<ETX>>

Design techniques for the definition of solid objects with free-form geometry

Solid modellers and free-form surface systems have been evolving to a large extent separately for fifteen years or more. Free-form surface techniques must now be integrated into solid modelling systems, since many engineering parts involve this type of geometry. The present paper classifies free-form surfaces into four categories for design purposes, depending on the degree of geometric constraint involved in their definition. Proposals are then made for free-form design techniques suitable for use in solid modellers. A survey of existing solid modelling systems is included, with indications of the techniques currently available for the design of free-form solids.

Smooth parametric surface approximations to discrete data

Classical approximation theory is not ideally suited for application to parametric curves and surfaces. Some experiences are reviewed, and some suggestions for practical algorithms outlined. The paper raises a number of questions which could form the basis for useful research in this area.

Progress Towards an International Standard for Data Transfer in Rapid Prototyping and Layered Manufacturing

Abstract This paper discusses the informational requirements of rapid prototyping and layered manufacturing (RPLM). The study is motivated by the recent decision to embark on the development of a new Application Protocol for the international standard ISO 10303, specifically to handle layered manufacturing information. The most common industrial use of RPLM today is for rapid prototyping, but a wider view of it as a flexible fabrication technology is taken here, to allow for future developments. Its use in building functional metallic parts under computer control has already been demonstrated, and commercial RPLM machines for building production parts are already being marketed. The paper includes a survey of current and proposed data formats for communication between the various stages of the RPLM process. In comparing them, particular attention is given to the issue of extensibility to meet future needs. In this last respect, special emphasis is given to materials-related and other non-geometric information needed for fabricating multi-material objects and objects with graded material properties.

Quartic supercyclides I: basic theory

Abstract Various classes of algebraic surfaces have been examined as to their suitability for CAGD purposes. This paper contributes further to the study of a class of quartic surfaces recently investigated by Degen, having strong potential for use in blending, and possibly also in free-form surface design. These surfaces are here put in the context of a classification of quartic surfaces originally given more than one hundred years ago. An algebraic representation is provided for them, and a simple geometric interpretation given for their rational biquadratic parametric formulation. Their theory is established from an analytic geometry viewpoint which is more straightforward than Degens original approach and gives further useful geometric insight into their properties. A major subclass of Degens surfaces consists of projective transforms of the Dupin cyclides; for this reason (and others, explained in the text) the name supercyclides is proposed for them.

Conversion of dupin cyclide patches into rational biquadratic bézier form

This paper uses the symmetry properties of circles and Bernstein polynomials to establish a series of interesting barycentric properties of rational biquadratic Bezier patches. A robust algorithm is presented, based on these properties, for the conversion of Dupin cyclide patches into Bezier form. A set of conversion examples illustrates the use of this algorithm.