Method for recognizing blends in solid models

Details Method for recognizing blends in solid models Method for recognizing blends in solid models

2001-10-31

2004-07-06

Nguyen, Phu K. (Department: 2671)

Computer graphics processing and selective visual display system

Computer graphics processing

Graphic manipulation

Reexamination Certificate

active

06760038

ABSTRACT:

FIELD OF INVENTION
The invention relates generally to recognizing features in three-dimensional solid models and more particularly to a system and method for recognizing blends in a solid model of a part.
BACKGROUND OF THE INVENTION
Solid Modeling
Solid modeling is a term that refers to a set of techniques that can be used to create and store computer based representations of physical objects. A number of techniques have evolved over the years for providing computer-based representations of three-dimensional parts. One of these techniques is Boundary Representation, commonly referred to as B-rep.
A B-rep model of a mechanical part consists of a set of “faces,” “edges” and “vertices,” which are connected together to form a topological structure of the part. By using such a representation, it is possible to evaluate many properties of the part from its computer model. These include the mass, the volume, the moments of inertia and products of inertia. Additionally, such models enable computer-based analysis of stress and strains in the part under different loading conditions. B-rep based computer models can also be “cut” and examined in a manner similar to an actual part. For these reasons, a B-rep model of a part is known as a “solid” model.
Software based on solid modeling is widely used by engineers to create models of parts that are intended to eventually be manufactured. Software such as SolidWorks™ (SolidWorks Inc.), Pro/Engineer™ (Parametric Technology), I-DEAS™ (Structural Dynamics Research Corp.), Mechanical Desktop™ (AutoDesk) are examples of solid modeling software.
Feature recognition is the art of evaluating a B-rep (or other type) model of a part that is missing information regarding certain features of the model, recognizing those features and creating a database of those recognized features. A feature recognition system is used in these situations to aid in finding the design intent of the model from the B-Rep information and blend recognition is one of the important steps in the process of feature recognition.
The purpose of feature recognition is to recognize various features in a B-Rep model that typically does not have explicit feature information. The feature information may either be absent initially itself or may be lost due to translation of data from one CAD system to another. U.S. patent application Ser. No. 09/676,471, filed Oct. 2, 2000, discloses methods for recognizing another type of feature in B-rep solid models: holes, specifically, sets of complex, interacting holes. U.S. application Ser. No. 09/676,471 was commonly owned with the present invention at the time that the present invention was made.
Certain solid models also have blends as part of their design. Blends are mainly used to smoothen sharp edges and vertices of a part in order to improve their strength, the aesthetics, and to ensure the manufacturability of the part.
FIG. 2
shows an example of blending the part shown in FIG.
1
. Blend recognition can be used to detect all the blend features in the model along with the blend parameters. Blend recognition can also be used to detect the blend sequence that describes the order in which the blend features were created in a model.
One application of blend recognition is to aid in blend suppression or blend deletion. The blend recognition method disclosed herein detects the sequence in which blend chains were created in the model. The reverse of this sequence can be used to delete the blends in the model. Blend deletion helps in simplifying the part for downstream applications. Blend deletion also facilitates recognition of other volumetric features such as pockets/slots in the model. Deletion of the blend chains results in a model with sharp edge and vertices.
FIG. 1
shows the solid model that is obtained after suppressing the blends in the solid model shown in FIG.
2
.
Blend recognition can also be used to extract important parameters for manufacturing applications. For example, the blend parameters can provide information that will aid in selection of tools during machining.
Another application of blend recognition and suppression is for clean up operations in Finite Element Analysis (FEA). For example, it is often necessary to suppress blends that are less than a specific radius to simplify the model for further analysis. This facility for selective blend suppression can be implemented by utilizing the blend sequence generated by the blend recognizer of the present invention.
The present invention provides methods for automatic detection of blends in the model, for deducing the sequence in which the blends were created in the model and, these can eventually be used, if desirable, for deleting a set of recognized blends from the model.
Overview of Blends
Blends are typically introduced in solid modeling to smoothen sharp edges and vertices in the part. In this operation, called blending or filleting, new faces are introduced in place of the sharp edges to create smooth transitions from one surface to another. When creating solid model representations of parts, designers use various techniques provided by CAD systems to model fillets and blends.
Blends are of interest to engineers during all stages of the design-to-manufacturing cycle. While editing a part model, designers may be interested in modifying blend parameters such as the radius of the blend. In the analysis stage, an engineer may prefer to ignore some blends since they are not expected to contribute significantly to stresses and strains in the part. During manufacturing planning, the blend radii govern the selection of some of the manufacturing processes, the machine tools, the cutting tools and even the part stock itself.
The most common blend is the so-called face—face blend, which replaces a sharp edge by a face tangent to the two faces adjoining the sharp edge. The blend surface usually has a circular cross section, and the plane of the cross section is always perpendicular to both the faces. When three or more blended edges meet at a common vertex, a vertex blend is formed that connects all the neighboring blends smoothly. In simple blending, the geometry of a vertex blend is usually a sphere; however, in the general case, the geometry is described by an n-sided vertex blend surface.
In special cases, blending can also take place between a face and an edge. Such blends are called face-edge blends or cliff blends, and may occur as boundary cases of face-face blends.
FIG. 2
shows an example that contains a few kinds of blend surfaces created while blending the simple part shown in FIG.
1
. Blend K is a face-face blend on the top block of the part that essentially rounds the edge between the top face A and the face B. Blend P is a vertex blend that is made at one corner of the top block of the part and blend D is a face-edge blend between face B and edge E
5
.
In many situations, blends created in different blending operations interact with each other forming a blend network. The knowledge of the blend sequence is essential to understand the design intent of the model. This sequence also aids in post-recognition operations such as blend suppression. Frequently in real parts, a number of blends interact with each other to form a complex blend network. A blend network formed in multiple blending operations is shown in the solid model in FIG.
2
.
SUMMARY OF THE INVENTION
The invention is a method implemented by a computer program, and a computer running the same, for recognizing complex blends in solid B-Rep models. In addition to recognizing individual blend faces, the method according to the invention can also group the set of blends created as a single feature (a chain), detect the sequence in which the blend chains got created. This sequence can be used to delete some or all of the blends—if required.
The invention comprises several software modules that, in a preferred embodiment, operate on B-rep solid models. The modules may be implemented in any computer programming language, such as C or C++, and may use local operators from known geometric modeling ker

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