3 research outputs found
Representation validation in feature-based modelling: a framework for design correctness analysis and assurance
Feature-based Modelling allows extra meaning to be added to geometry, but lacks the
equivalent geometric formalism usually found in computer-aided design (CAD) and
Geometric Solid Modelling (GSM) systems. CAD systems have been evolving into
constraint-based design environments instead of intent-driven ones where the designer can
use whatever manipulation is available in the system without been afraid of messages like
"manipulation not permitted". These messages usually restrain the user in order to avoid
representation changes and faulty or "unknown" situations.
A Design-by-Feature system with a representation validation framework is presented that
supports "Design for X", intent-driven modelling, encompasses existing low-level geometric
verifications, adds high-level rules to analyse and enrich the design and incorporates
operations to assure its correctness. Also it alleviates the designer from specifying each and
every geometric detail/relationship (improving productivity)
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.
An incremental constraint-based approach to support engineering design.
Constraint-based systems are increasingly being used to support the design of products. Several commercial design systems based on constraints allow the geometry of a product to be specified and modified in a more natural and efficient way. However, it is now widely recognised the needs to have a close coupling of geometric constraints (i.e. parallel, tangent, etc) and engineering constraints (Le. performance, costs, weight, etc) to effectively support the preliminary design stages. This is an active research topic which is the subject of this thesis. As the design evolves, the size of the quation set which captures the constraints can get very large depending on the complexity of the product being designed. These constraints are expected to be solved efficiently to guarantee immediate feedback to the designer. Such requirement is also necessary to support constraint-based design within Virtual Environments, where it is necessary to have interactive speed. However, the majority of constraint-based design systems re-satisfy all constraints from scratch after the insertion of a new design constraint. This process is time consuming and therefore hinders interactive design performance when dealing with large constraint sets. This thesis reports research into the investigation of techniques to support interactive constraint-based design. The main focus of this work is on the development of incremental graph-based algorithms for satisfying a coupled set of engineering and geometric constraints. In this research, the design constraints, represented as simultaneous sets of linear and non-linear equations, are stored in a directed graph called Equation Graph. When a new constraint is imposed, local constraint propagation techniques are used to satisfy the constraint and update the current graph solution, incrementally. Constraint cycles are locally identified and satisfied within the Equation Graph. Therefore, these algorithms efiiciently solve large constraint sets to support interactive design. Techniques to support under-constrained geometry are also considered in this research. The concept of soft constraints is introduced to represent the degrees of freedom of the geometric entities. This is used to allow the incremental satisfaction of newly imposed constraints by exploiting under-constrained space. These soft constraints are also used to support direct manipulation of under-constrained geometric entities, enabling the designers to test the kinematic behaviour of the current assembly. A prototype constraint-based design system has been developed to demonstrate the feasibility of these algorithms to support preliminary desig