A Hybrid Models Deformation Tool for Free-Form Shapes Manipulation

2008 ◽  
Author(s):  
J.-P. Pernot ◽  
B. Falcidieno ◽  
F. Giannini ◽  
J.-C. Le´on
Keyword(s):  
Geometric Constraints ◽  
Free Form ◽  
Geometric Models ◽  
Nurbs Curves ◽  
Characteristic Points ◽  
Deformation Behaviors ◽  
Geometric Representations ◽  
Different Dimensions ◽  
Simple Deformation ◽  
Prototype Software

This paper addresses the way models mixing various types of geometric representations (e.g. NURBS curves and patches, polylines, meshes), potentially immersed in spaces of different dimensions (e.g. NURBS patch and its 2D trimming lines), can be deformed simultaneously. The application domains range from the simple deformation of a set of NURBS curves in a 2D sketcher to the simultaneous deformation of meshes, patches as well as trimming lines lying in parametric spaces. The deformation itself results from the solution of an optimization problem defined by a set of geometric constraints and deformation behaviors. This new breakthrough on how geometric models can be manipulated has been made possible thanks to our linear mechanical model of deformation that can be coupled to manifolds of dimension zero (e.g. points, vertices) and one (e.g. edges, segments) whatever the spaces dimension. An extended constraints toolbox is also proposed that enables the specification of both characteristic points/curves and continuity conditions between the various geometric models. The link between the semantics of the deformation behaviors and the geometric models is ensured through the use of multiple minimizations. The approach is illustrated with several examples coming from our prototype software.

Fully Free-Form Deformation Features (δ-F4) Incorporating Discontinuities

2004 ◽  
Author(s):  
Vincent Cheutet ◽  
Jean-Philippe Pernot ◽  
Jean-Claude Leon ◽  
Bianca Falcidieno ◽  
Franca Giannini
Keyword(s):  
Surface Deformation ◽  
Geometric Constraints ◽  
Free Form ◽  
Initial Surface ◽  
Cad Systems ◽  
Free Form Deformation ◽  
Deformation Features ◽  
Generate Surface ◽  
Prototype Software ◽  
Free Form Surfaces

To limit low-level manipulations of free-form surfaces, the concept of Fully Free Form Deformation Features (δ-F4) have been introduced. They correspond to shapes obtained by deformation of a surface area according to specified geometric constraints. In our work, we mainly focused on those features aimed at enforcing the visual effect of the so-called character lines, extensively used by designers to specify the shape of an object. Therefore, in the proposed approach, 3D lines are used to drive surface deformation over specified areas. Depending on the wished shape and reflection light effects, the insertion of character lines may generate surface tangency discontinuities. In CAD systems, such kind of discontinuities is generally created by a decomposition of the initial surface into several patches. This process can be tedious and very complex, depending on the shape of the deformation area and the desired surface continuity. Here, a method is proposed to create discontinuities on a surface, using the trimming properties of surfaces. The corresponding deformation features produce the resulting surface in a single modification step and handle simultaneously more constraints than current CAD systems. The principle of the proposed approach is based on arbitrary shaped discontinuities in the parameter domain of the surface to allow the surface exhibiting geometric discontinuities at user-prescribed points or along lines. The proposed approach is illustrated with examples obtained using our prototype software.

Representing and Recognizing Features in Mechanical Designs

1990 ◽  
Author(s):  
Susan Finger ◽  
Scott A. Safier
Keyword(s):  
Graph Grammars ◽  
Design Environment ◽  
Geometric Models ◽  
Feature Based ◽  
Geometric Representations ◽  
Design Systems ◽  
High Level ◽  
Feature Based Design ◽  
Structural Engineers ◽  
Rough Surface Finish

Abstract When experts view an object, they perceive it in terms of their own expertise. For example, manufacturers see features that affect the processes used to fabricate a part, while structural engineers see sources of stresses and other features that tend to reduce the life of a part. Features can be geometric, such as slots or chamfers; they can be quantitative, such as distances between holes; they can be functional, such as alignment; or they can be qualitative, such as a rough surface finish. Research in feature-based design systems for mechanical designers has been motivated by the realization that geometric models represent the design in greater detail than can be utilized by designers, process planners, assembly planners, or by systems that emulate these activities. Features provide abstractions to facilitate the creation, representation, and analysis of designs. Our goal is to enable designers to compose mechanical designs from high-level features that embody functional and geometric properties. In addition, we want to provide designers with feedback on the manufacturability, assemblability, functionality, cost, etc. of the design as it evolves. To support this process in an intelligent CAD environment requires the integration of geometric models, analysis tools, and synthesis tools so that all aspects of the design can be considered while it is in progress. We are developing a design environment based on a shared representation of the design in which we can extract and reason about features of the design from different perspectives. Our approach is to represent both the design and the features using graph grammars. By representing the features using the same grammar as the design, we can recognize features by parsing a feature against the graph that represents the design. We are exploring grammars for behavior as well as geometry in order to provide a link between behavioral and geometric representations. In this paper, we focus on the representation and recognition of features.

scholarly journals Enriching Assembly CAD Models With Functional and Mechanical Informations to Ease CAE

2010 ◽  
Author(s):  
Gilles Foucault ◽  
Jean-Claude Le´on
Keyword(s):  
Product Development ◽  
Geometric Constraints ◽  
Geometric Models ◽  
Bill Of Materials ◽  
Starting Point ◽  
Cad Models ◽  
Development Processes ◽  
Mechanical Information ◽  
Standard Components ◽  
Assembly Models

Assembly models can be regarded as a kernel for product development processes where they can efficiently contribute to many product simulation behaviors. Assembly models are often containing 3D B-Rep CAD models, possibly with geometric constraints between the components and bill of materials. However, these models are often difficult to process for simulations because algorithms often face a very large diversity of configurations. One origin of such difficulties can be found in companies’ practice where components may be represented differently from one company to another and their interfaces as well. In any case, interfaces between components are not explicit, which leads to tedious model processing tasks. This paper illustrates preparation of assembly models to ease CAE through an analysis of company practices, showing that a concept of conventional representations is an important starting point to efficient treatments of assemblies. In addition, it is described how interfaces and conventional representations can be combined to derive functional and mechanical information from geometric models of components. Illustrations of the proposed approach is given throughout the paper using various standard components.

MACHINE VISION TOOLS FOR CAGD

1996 ◽  
Vol 10 (02) ◽  
pp. 165-182 ◽  
Author(s):  
V. KOIVUNEN ◽  
J.-M. VEZIEN
Keyword(s):  
Iterative Closest Point ◽  
Free Form ◽  
Shape Estimation ◽  
Data Set ◽  
Computer Aided Geometric Design ◽  
Multiple Images ◽  
Geometric Models ◽  
Surface Representations ◽  
Imaging Sensors ◽  
Rapid Modeling

In this paper, the problem of constructing geometric models from data provided by 3-D imaging sensors is addressed. Such techniques allow for rapid modeling of sculptured free-form shapes and generation of geometric models for existing parts. In order for a complete data set to be obtained, multiple images, each from a different viewpoint, have to be merged. A technique stemming from the Iterative Closest Point (ICP) method for estimating the relative transformations among the viewpoints is developed. Computational solutions are provided for estimating shape from noisy sensory measurements using representations that conform with commonly used representations from Computer Aided Geometric Design (CAGD). In particular, NURBS and triangular surface representations are applied in shape estimation. The surface approximations are refined by the algorithms to meet a user-defined tolerance value.

Rational Motion Interpolation Under Kinematic Constraints of Spherical 6R Closed Chains

2008 ◽  
Vol 130 (6) ◽  
Author(s):  
Anurag Purwar ◽  
Zhe Jin ◽  
Q. J. Ge
Keyword(s):  
Ordered Set ◽  
Extreme Points ◽  
Rational Curves ◽  
Geometric Constraints ◽  
Free Form ◽  
Constrained Motion ◽  
Kinematic Constraints ◽  
Cartesian Space ◽  
Rational Spline ◽  
Closed Chain

The work reported in this paper brings together the kinematics of spherical closed chains and the recently developed free-form rational motions to study the problem of synthesizing rational interpolating motions under the kinematic constraints of spherical 6R closed chains. The results presented in this paper are an extension of our previous work on the synthesis of piecewise rational spherical motions for spherical open chains. The kinematic constraints under consideration are workspace related constraints that limit the position of the links of spherical closed chains in the Cartesian space. Quaternions are used to represent spherical displacements. The problem of synthesizing smooth piecewise rational motions is converted into that of designing smooth piecewise rational curves in the space of quaternions. The kinematic constraints are transformed into geometric constraints for the design of quaternion curves. An iterative algorithm for constrained motion interpolation is presented. It detects the violation of the kinematic constraints by searching for those extreme points of the quaternion curve that do not satisfy the constraints. Such extreme points are modified so that the constraints are satisfied, and the resulting new points are added to the ordered set of the initial positions to be interpolated. An example is presented to show how this algorithm produces smooth spherical rational spline motions that satisfy the kinematic constraints of a spherical 6R closed chain. The algorithm can also be used for the synthesis of rational interpolating motions that approximate the kinematic constraints of spherical 5R and 4R closed chains within a user-defined tolerance.

Approximate Geometric Methods in Application to the Modeling of Fiber Placed Composite Structures

2004 ◽  
Vol 4 (3) ◽  
pp. 251-256 ◽  
Author(s):  
Kurt Schueler ◽  
James Miller ◽  
Richard Hale
Keyword(s):  
Composite Structures ◽  
Modern Method ◽  
Geometric Constraints ◽  
Free Form ◽  
Curved Surfaces ◽  
Fiber Placement ◽  
Geometric Methods ◽  
Offset Curves ◽  
Free Form Surface ◽  
Placement Machine

Fiber placement is a modern method of constructing composite structures with complex curved surfaces. Modeling individual tows in a fiber placed part constitutes the challenge addressed by methods presented in this paper. One method is presented to approximate offset curves on a free form surface using the geometric constraints of the fiber placement process. A second method is presented to approximate a curve on a free form surface that can be used to generate a laminate family ply. We demonstrate that these approximation methods are sufficient for the accuracy of the fiber placement machine.

Sign in / Sign up

Export Citation Format

Share Document