Ferruccio Mandorli

A reference kernel model for feature-based CAD systems supported by conditional attributed rewrite systems

According to the general design theory a design process is an evolutionary process which step by step transfers the model of the design object from the design specification to the design solution. In our framework, design object specification and iterating evaluation are performed over different contexts using featurebased design, and feature recognition/transmutation. These activities are integrated to achieve consistency between given design requirements and design objects. Features are used to relate elements of different domains, in order to represent design objects with shape and meaning within a context. The basic concept of topology and attributed entities is used to define a homogeneous architecture of the modeling space of our reference kernel. It is reflected in the uniform use and structure of an attributed feature graph, an attributed boundary representation, and a knowledge representation in form of conditional attributed rules. For design by feature and feature recognition we propose to use a conditional attributed rewrite system as a generative as well as a recognition device to represent knowledge of control and operationalization in a uniform way. Morphisms realize a bi-directional mapping between the entire modeling space of the reference kernel and an alphabet of attributed symbols, which together with rewrite rules define our rule-based design object specification. Knowledge representation for reflective functionality and strategies of design and recognition are specified with a conditional attributed rewrite system on a meta level. Central components of a prototype implementation, according to our proposed reference model kernel, will be introduced and discussed together with first results of modeled and evaluated objects.

Explicit 3D functional dimensioning to support design intent representation and robust model alteration

Design intent representation is a well-known issue in the MCAD domain, and is related to the readability, alterability, and usability of CAD models. The recent widespread introduction of functionality and commands in modern CAD systems, aimed at facilitating explicit modeling, introduces not only a new modeling paradigm supplementary to the feature-based approach, but also a new perspective on how the design intent can be captured and represented. Taking into account the traditional method of communicating design intent with functional dimensioning in mechanical drawings, in this paper a novel approach is presented, aimed at translating this traditional design intent representation from 2D into 3D. Objectives are directed towards the specification and implementation of dimensioning correspondence mapping and the identification as well as examination of shortcomings in current systems. This should help direct future improvements aimed at supporting 3D dimensioning within 3D explicit modeling systems.

Error classification and recovery within CAD model reconstruction

With ever increasing demands from international markets and responding industries for a quick transfer as well as processing of CAD and product data between different computer aided applications, within as well as between a products life cycle stages, activities dedicated to the development and standardization of data representations and exchange formats are more critical than ever before. However, in practice, before complete standards and developed models and systems succeed and become reality, interim solutions are required to bridge certain gaps. One application field, requiring such interim solutions until robust methods are found, to correct error causing processes, is the exchange and consequent repair of geometric models. Due to subtle errors in geometric models and their representations, caused by design mistakes, programming errors or model evaluation failures, irrational behavior of CAD systems and other, post design related systems exchanging as well as accessing CAD data, are becoming a frequently observed situation, causing a severe break in the process of computer aided product development. To recover from such a rather undesirable situation, we propose an interim solution, aimed at bridging the gap between generation of corrupted CAD data and model exchanging post design applications. An approach, that is based on an error classification driven systematic recovery of corrupted CAD data being subject to model reconstruction. The approach taken includes a classification scheme for face adjacency errors, missing faces and curve adjacency errors for which dedicated individual methods and solutions were developed and related to. Practical work used to support as well as provide parameters for validation and assessment of proposed solutions was carried out using an implemented testbed, which is based on spatial model point distance tolerances driven face sewing. During experimental work exchange format used for model import/export were limited to IGES. Investigated models imported through these standardized data exchange formats were mainly taken from mechanical engineering.

A Framework to Support 3D Explicit Modeling Education and Practice

ABSTRACTIn this paper a framework based on the concept of functional dimensioning features is presented. It is aimed at supporting a methodological approach to explicit modeling with a focus on issues related to its use in MCAD education and practice. The proposed framework is based on the assumptions that shape, dimensions, and required manufacturing precision of a mechanical component are designed to fulfill specific functionalities. Principle formation and development regarding geometric entities and associated functional meaning are approached with an orientation on the concepts and definitions introduced by the GPS system of standards. Application of the GPS standards requires that dimensions and tolerances of the functional elements are specified within the nominal representation of a part or component. The traditional method of representing such information is a 2D technical drawing. However, explicit modeling provides new perspectives and opportunities for approaching 3D modeling, since it allows ...

Integration of negative knowledge into MCAD education to support competency development for product design

ABSTRACTWith a steadily increasing use of CAD systems within digital prototypes in product design and development, the capacity to create viable geometric models that can be used in various computer-aided engineering processes is becoming an indispensable necessity. However, with the current trend of commercial CAD systems increasingly to promote hybrid geometric modeling environments, this requirement poses a new challenge for education, as it requires a teaching strategy that goes beyond the sum of subject learning in surface modeling and solid modeling. In this paper, a novel teaching approach is introduced, which integrates negative knowledge as one crucial element in combination with traditional teaching methods to support competency development that reaches beyond the acquisition of basic modeling skills and domain knowledge.

Integrating Life Cycle Aspects within Product Family Design: An Example for SMEs

Recent concern for the environment and high competition in globalized markets pose eminent requirements to the producing industry, including small and medium sized enterprises. Envisioned goals of a eco-design combined with a drastical reduction of product development time and increase of customized features of products require new strategies and tools. One solution subject to international investigation is the development of modular products. This approach we enhance by integrating life cycle assessment. Work done in this field was concentrated on developing methods to define either a products platform architecture or relationships between product modules and documented customer needs within the design analysis of product families. Unfortunately, all of these approaches failed to include a framework to enable also the integration of life cycle assessment. Within the scope of the work described in this paper, we target fundamental problems within the design of product families regarding the integration of life cycle assessment and economic application of information technology, suitable in terms of cost and performance for small and medium sized enterprises. The application field, where first case studies were undertaken and real product models implemented was within the design of parallel-shaft speed reducers.

A framework for negative knowledge to support hybrid geometric modeling education for product engineering

Abstract Due to the full integration of CAD systems into modern product development and engineering, the competency to create usable geometric models has become an essential requirement for current CAD users. To avoid serious repercussions for future engineering labor, the focus of CAD education needs to be raised from the teaching of knowledge that is merely aimed at operating a system, to the development of basic strategic knowledge. From a pedagogical point of view, this situation represents a challenging task that requires new, innovative teaching methodologies. These new methodologies must facilitate the development of know-how and cognitive ability to organize domain knowledge within a holistic mental model allowing for accurate perception of the significance of circumstances and the possible consequences of actions. In this paper a new direction for CAD education is presented, based on the integration of traditional teaching methods with an educational approach based on negative knowledge. Analysis of first empirical results of this newly developed and implemented approach showed promising results. Improvements were observed in a better understanding of issues related to the usability of CAD models and an increased capability to recognize critical modeling situations and thus prevent the mistakes typically made by novices. Also, successful autonomous attempts could be observed of recovery from situations caused either by an accumulation of small mistakes or by severe modeling errors, which usually require remedial intervention by academic supervisors.

Innovation in MCAD education toward competency development using negative knowledge: From theoretical framework to practical implementation

ABSTRACTWith the rising importance of CAD models for product development and the recent strong promotion of hybrid geometric modeling from within the industry, the focus of teaching methods in current CAD education, as practiced in most institutions of higher education, needs to be reconsidered. From a pedagogical point of view, this situation represents a challenge, as it requires new, innovative teaching methodologies which advance the development of competency going beyond basic domain knowledge and skills limited to operating a CAD system. In this paper, a new and innovative direction for CAD education is offered, which is based on the integration of traditional teaching methods with an educational approach using negative knowledge. Central aspects of framework development and concept translation are presented together with promising results obtained through a multi-method oriented empirical study of this newly developed and now fully implemented approach.

SOLID MODEL RECONSTRUCTION FROM TRIMMED SURFACES BASED ON B-REP FACE SEWING

Despite international efforts to support specification and exchange of CAD data through acknowledged standards and data interfaces, in practice several problems still remain. One type of problem is related to the reconstruction and verification of CAD data containing defects. Major problems causing such defects are related to differences in the internal modeling accuracy of systems. Generated models that sometimes contain degenerated edges and faces having either almost zero length or zero area exacerbate the situation. Defects in the topology and / or the geometry of such geometric models have a severe impact on computer-aided post-design processes such as finite element analysis, STL file generation, tool path generation, etc. In the meantime, until improvements can be made in the processes that generated those corrupted CAD data, correction of possible errors in CAD data can be achieved by introducing an intermediate post-processing step aimed at reconstructing an error-free, valid solid model. Within the given scope of this paper, we introduce and investigate the application of a face-sewing operator, which can be applied to CAD data based either on surface models or on solid models. Operation and quality of the model reconstruction are determined by the tolerances of spatial model space points located on the face boundaries and their distances apart. Due to the use of reference kernel architecture featuring a Brep scheme within an integrated multi-dimensional topology supporting both surface models and solid models, a CAD data interface based on a standard data exchange format and an internal translator that classifies, converts and correlates pure geometric entities, sub-setting geometric entities and topological entities, open and highly flexible system architecture in respect to considered CAD data and geometric models can be maintained.