Feature-based validation reasoning for intent-driven engineering design

Feature based modelling represents the future of CAD systems. However, operations such as modelling and editing can corrupt the validity of a feature-based model representation. Feature interactions are a consequence of feature operations and the existence of a number of features in the same model. Feature interaction affects not only the solid representation of the part, but also the functional intentions embedded within features. A technique is thus required to assess the integrity of a feature-based model from various perspectives, including the functional intentional one, and this technique must take into account the problems brought about by feature interactions and operations. The understanding, reasoning and resolution of invalid feature-based models requires an understanding of the feature interaction phenomena, as well as the characterisation of these functional intentions. A system capable of such assessment is called a feature-based representation validation system. This research studies feature interaction phenomena and feature-based designer's intents as a medium to achieve a feature-based representation validation system. [Continues.

Structured multi-level feature interaction identification

Features are an established means of adding non-geometric information and extra geometric semantics to conventional CAD systems. It has been already realised that although feature-based modelling is necessary for the next generation of integrated design and manufacturing systems, inherent feature interactions pose a difficulty in representing and manipulating geometric design. This paper presents a structured multi-level geometric feature interaction classification scheme implemented within a Design-by Feature (DbF) system for representation validation analysis. Various feature interaction definitions and classification methods are first surveyed. The elements and the tests used for the identification process are presented. The classification encompasses existing feature interference cases found in the literature, uses a clear structure for the classification and, is applied at three different levels

Operating invalid feature-based models

A valid feature-based representation is one where instantiated features in a model agree with the features' expected behaviours, available and defined as a library. Invalid feature-based models happen when manipulations on the model change the interrelationship among features therefore changing the behaviour of an instantiated feature. Freedom of manipulation is an intrinsic advantage of using a CAD system and it is taken for granted. However, even the most basic manipulation, such as "adding" a feature to a model, is capable of disrupting the validity of a representation. Furthermore, invalid models could compromise the usefulness of any following analysis on it. Thus, identifying means to operate on an invalid model to make it valid, through "revalidation operations", is a necessity in Feature-based CAD systems. It allows conventional CAD systems (usually more preoccupied with representing and producing feature-like shapes within a geometrically constrained environment) to interface more easily for example with CAPP systems (usually more preoccupied with planning problems than with the correctness of the representation). The framework of a feature-based validation system, called FRIEND (Feature-based Reasoning system for Intent-driven Engineering Design), and a discussion on representation validity analysis is presented with emphasis on identifying and discussing "revalidation operations”

An intent-driven paradigm for feature-based design

A very important advantage of a feature-based modelling (FBM) system is claimed to be its ability to capture and carry designer’s intents (DI’s), although this last term is rarely clearly defined. Feature’s extra nongeometrical semantics, that are closely related to such designer’s intents, are used by many applications but never related back to designer’s intents. Therefore, adopting the approach of defining of designer’s intents helps define the role of features in the geometric design and, indeed, allows future feature-based modelling systems to better represent, store and reuse such information. Moreover, it allows a more formal approach for manipulating, verifying and maintaining DI’s throughout the design process, which is an invaluable support for really intelligent CAD systems. This paper presents Designer’s Intents in the feature-based modelling context and exposes a methodology used to effectivelly capture and manage and verify this extra information

Evaluation of a feature modelling validation method

Geometric modelling techniques for computer-aided design are provided with formal validation methods to ensure that a valid model is made available to applications such as interference checking. A natural and popular extension to geometric modelling is to group geometric entities into features that provide some extra meaning for one or more aspects of design or manufacture. These extra meanings are typically loosely formulated, in which case it is not possible to validate the feature-based model to ensure that it provides a correct representation for a downstream activity such as process planning. Earlier research established that validation methods can be based on the capture of designers' intents related to functional, relational and volumetric aspects of component geometry. This paper describes how this feature-based validation method has itself been validated through it's application to a series of test parts which have been either drawn from the literature or created to demonstrate particular aspects. It is shown that the prototype system that has been developed is indeed capable of meaningful featurebased model validation and additionally provides extensive information that is potentially useful to a range of engineering analysis activities

Morphological and volumetrical feature-based designer's intents

Features are claimed to be the carriers of Designer's Intents (DI's) which are seldom defined, identified and represented in Design-by-Features (DbF) systems. This paper presents an interpretation of Designer's Intents for the Feature-based Modelling (FBM) context and emphasis will be given to the Morphological Functional and Volumetrical Geometrical DI’s which express the basic behaviour of a DbF system. DI's are also an important part of a validation system capable of reasoning about the semantics of using features in a particular design. If features' characterisations via DI's are well established and measurable the representation could be assessed as to its conformity with feature's meaning and their semantics could be validated. It is considered that the better Designer's Intents are understood and specified, the more useful Feature-based Modelling will become

Feature-based interaction: an identification and classification methodology

Features are an established means of adding non-geometric information and extra geometric semantics to conventional computer aided design (CAD) systems. For some time it has been realized that, although feature-based modelling is necessary for the next generation of integrated design and manufacturing systems, the inherent feature interactions pose a difficulty in representing and manipulating geometric designs. This paper presents a structured geometric spatial feature interaction identification method based on a broad multilevel classification. Feature interaction definitions and classifications have been surveyed and it is evident that, although many feature interaction classifications have been proposed, there is a lack of a general framework. The classification presented here encompasses existing feature interference cases found in the literature and defines a singular framework that leads to a general classification structure. The framework is presented and applied at three different levels and each interaction case is defined by feature parameters rather than just geometric entities. The restrictions often found in other research concerning contact:non-contact and concave:convex situations are avoided. The resulting classification is easy to understand and implement because it uses simple rules based on commonly available Boolean operators. Finally, an example component is presented and the advantages, uses and applications of the classification scheme are discussed

Intent-driven reasoning priorities in a feature-based validation system

Feature-based representation validation seeks to find means to verify feature-based representations in order to guarantee that feature's expected behaviours are met and that applications that use the representation can be sure of the correctness of the feature-related data. To achieve this, a clear definition of features and their behaviour is needed but cannot be found in the literature. Instead of proposing yet another feature definition, an attempt was made to define some basic common-sense characteristics for (prismatic) features that could be tested, analysed and manipulated. These characteristics are called Intents because features are said to be the carriers of designer's intents. Feature-based Designer's Intents (DI's) proved to be essential to the validation framework because they define the scope of the Feature-based Modelling (FBM) utilisation. Also, some DI's establish clearly the geometric-dependent behaviour of features and were found to be closely related to validation. A prototype system called FRIEND, an acronym to Feature-based Reasoning system for Intent-driven ENgineering Design, was implemented to perform feature-based representation validation. This paper details Designer's Intents (DI's) in the context of deign-by-feature representation validation, presents Morphological Functional and Volumetrical DI's, their semantics and their priority organisation inside the validation mechanism, as it was implemented within FRIEND

Feature modelling: a validation methodology and its evaluation

Geometric modelling techniques for computer-aided design are provided with formal validation methods to ensure that a valid model is made available to applications such as interference checking. A natural and popular extension to geometric modelling is to group geometric entities into features that provide some extra meaning for one or more aspects of design or manufacture. These extra meanings are typically loosely formulated, in which case it is not possible to validate the feature-based model to ensure that it provides a correct representation for a downstream activity such as process planning. This paper presents a methodology used to validate the feature-based representation which is based on the capture of designer’s intents related to functional, relational and volumetric aspects of the component geometry. The feature-based validation method has itself been validated through its application to a series of test parts which have been either drawn from the literature or created to demonstrate particular aspects. It is shown that the prototype system that has been developed is indeed capable of meaningful feature-based model validation and additionally provides extensive information that is potentially useful to a range of engineering and manufacturing analysis activities

Feature-based designer's intents

Feature-based modelling is considered an improvement on existing CAD systems. Features are considered to be a medium that carries designer’s intents, but neither features nor designer’s intent have widely accepted definitions. Morphological functional designer’s intents, defined as common-sense behaviours of the (form) feature’s concept, have been defined and presented within a feature-based representation validation system [4]. The process of “feature elicitation”, frequently implied to identify and categorise features, comprises “featurization” and “featurization validation” processes which help specify an appropriate feature library to be used in a particular application. In the research reported here a similar approach, called “intent elicitation”, has been performed to identify and categorise meaningful and measurable designer’s intents from the integrated CAD/CAM and Computer Aided Process Planning (CAPP) domains. The resulting classification and taxonomy is presented in this paper. It can be observed that the classification encompasses morphological feature-based designer’s intents (FbDI’s), because of the feature’s concept, and is application dependent. The identified FbDI’s have been used in a feature-based reasoning system which has led to an intent-driven approach for feature-based modelling where designer’s intents are an explicit and central aspect