Part models features

The text and illustrations in this book have outlined the application of the advanced method of shape modification for the construction of part models. Feature based part modeling describes information about form features and the construction process. Features may be retrieved from feature libraries, created on site, or defined as modifications or combinations of existing features. Features can be grouped at different levels in order to give structure to the design. The sequence of shape modifications can be reordered when a new sequence is more appropriate for the subsequent steps of construction or modification of the part model, as illustrated by the example of Figure 5-7. Feature suppression makes it possible to inactivate then activate features or groups of features. 

A typical process of feature driven part modeling is illustrated in Figure 8-2. Base feature FF/, is created as a tabulated solid, starting from contour Cpph, sketched in its place in the reference plane RPj. Feature FFi, is modified by volume adding features FFp and FFr starting from contours Cppp and Cppr, respectively. Rib feature FFr needs reference plane RP2 outside of the part. RP2 is not included in the boundary of the part, but it is included in the part model. Features FFp and FFr are modified by draft conditioning features FFd2 and FF u, respectively. 

For spherical micelles, one of the more commonly accepted models for the micellar structure is that proposed by Gruen (Fig. 1). This model features a rather sharp interface between a dry hydrophobic hydrocarbon core and a region filled with surfactant headgroups, part of the counterions (for ionic surfactants), backfolding surfactant tails, and water, namely, the Stern region. In the remainder of this chapter, intramicelle volumes with specific features such as the Stern region and the hydro-phobic core will be referred to as zones. ... 

Since in pharmacophore-based VS only a part of the database molecules matches the model and therefore obtains an alignment score, a limited number of Se and 1-Sp values can be calculated and plotted. Thus, a selective model would result in an ROC curve that starts at the origin and finishes before it reaches the upper right comer where all active and inactive molecules are scored. However, to simplify the explanation of the ROC curve method, we suggest that the model would retrieve and score all database molecules, either because all database molecules are very similar or because partial matching of model features is allowed. In this case, an ideal pharmacophore model will score all actives higher than inactive database molecules. 

Papadakis, S. E. and King, C. J. 1988a. Air temperature and humidity profiles in spray drying, part 1 Features predicted by the particle source in cell model. Ind. Eng. Chem. Res. 27 2111-2116. 

A large step was the integration of assembly and kinematics design with part modeling. Instead of the construction of individual part models, the connection-related design of parts proceeds in an assembly space where the part is constructed and represented in connection with other parts in the actual assembly. The assembly model consists of a structure of connected parts and a set of relationship definitions for part placement in relation to parts that are connected to it. One of the advantages of this method is that connections of parts are defined by form features common for two or more parts. 

The basic concept of modification of a shape by form features is volume adding and removing. The shape is then adjusted by fillet and other treatment features. While solid primitives are geometric oriented shapes, form features can be application orientated. In other words, form features can be defined according to their purpose and function in the modeled part and use in a part model. At the same time, form features are often defined as pure geometry. 

The purpose of reference elements is not a shape modification but the assistance of the construction of feature based part models. 

They are simple geometric entities such as points, lines, and planes and relate form features to the modified sections (Figure 4-16). For given steps of model construction, reference elements can be selected from existing entities in a part model under construction. When appropriate reference elements are not available in the part model, they must be constructed and then placed in the model as an entity that is included in the model but is not included in the shape of the part. 

Tolerancing forced definition of features when they cannot be extracted from the part model. 

Modeling tools in part modeling systems are included for the creation, integration, design analysis, model analysis, shape related modification, positional modification, application sequence modification (reordering), removal, and suppression of form features. 

Inertia and mass properties such as the absolute and relative inertial axis and center of gravity are calculated using geometry and density information. These calculations are based on the closed volume of a solid. Estimation of the cost for a part can be involved in part modeling by defining appropriate formulas and relating them with features. 

Customer expandable choices of form features are available for part modeling in industrial modeUng systems. Part modeling is a sequence of shape modifications. This process is based on a concept or modification steps are sequenced intuitively. Anyway, most of the sequence of modifications is governed by fundamental construction rules for each typical part. A form feature can be included in the model when its contextual elements such as existing form features to be modified or conditioned, as well as construction planes and other reference geometry, are available. 

Construction of a contour for a form feature in a part model and its validation by use of checks is explained in Figure 8-9. Contour C is sketched for form feature FFj. Validation of contour C revealed three errors and communicated them to the engineer. Contour C contained a break point This is not allowed for the selected type of form feature solid modeling requires a closed contour. Contour C was found to be open at point P, i.e., the gap is larger than the specified tolerance. Note that certain form features such as solid sweeps allow an open contour. Finally, the upper limit specified for the length L was exceeded. After correction, the modified contour was applied at the creation of form feature FFj. Construction of the part model can be continued by form feature FF2 because form feature FFj was proved correct during its repeated validation. 

The modeling environment where a given change of a part model causes changes, is called the effect zone of that modification. On the other hand, a feature can be isolated when its geometry is needed alone. In this case, the designer takes care that it is appropriately placed in its environment. There are several basic modifications associated with feature driven part models as follows. 

Figure 8-10 Modification of a feature based part model.

The unfolded state of a part, or in other words the flat pattern, is fully associative with the part model. This is necessary because the part is cut together with punched features from a sheet metal table. Flattened parts are arranged on a sheet metal... 

Top-entry models feature the inlet connection as an integral part of the lid. The inlet can be equipped widi different types of quick disconnects for fiist basket removal. 

We selected five examples for hands-on evaluation, as listed in Table 3. Among the five examples, two are given as polygon meshes and the other three are point clouds. These five parts represent a broad range of applications. Parts like the block, tubing, and door lock are more traditional mechanical parts with regular solid features. In contrast, sheetmetal part (Model 3) is a formed part with large curvature, and the blade is basically a free-form object. 

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