In a top-down design environment, component geometry can be created in the context of the assembly. The benefit of this technique is that references can be made between components to create the required geometry. However, as the number of references increase they can become difficult to organize and control. In this case, creating or copying cross-referenced geometry from the skeleton model creates a centralized location for exchanging information between assembly components. The reference geometry is easily distinguished from the final assembly geometry because it is located in a single location.
The solid model shown on the right-hand side of Figure 2–4 is created in the assembly, referencing datum points PNT0 and PNT1 from the skeleton model, as shown in the sketched section on the left-hand side. Additional components can be created in the assembly referencing the same skeleton.
Figure 2–4
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General Steps
Use the following general steps to create skeleton models:1. Create a skeleton model.
2. Define the skeleton geometry.
To create a skeleton model, click Insert > Component > Create or by selecting the button in the toolbar. Select the Skeleton Model option in the Component Create dialog box, enter a name for the skeleton, and select the button. The Creation Options dialog box appears as shown in Figure 2–5.
The default skeleton name consists of the parent assembly model name with
"skel" appended to it (e.g., crank_skel.prt). You can also enter a user-defined name for the skeleton.
Figure 2–5
Skeleton models can be created using one of the following three options:
• Copy From Existing
• Empty
• Create First Feature
The Copy From Existing option copies features from an existing model. This option is valuable when the skeleton model is created prior to the top-level assembly.
Step 1: Create a skeleton model
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The Empty option creates a blank part file where all features, including the default datum planes, must be created.
The Create First Feature option creates a feature in the skeleton model at the assembly level. This option can be used to create the default datum planes for the skeleton model by selecting three perpendicular planes in the assembly to copy into the skeleton.
The skeleton model always exists as the first component in the assembly model tree. Even if it is created after other components, the skeleton is placed before the assembly default datum planes and any previously assembled components. If there are existing components, an origin to origin constraint is added to align the origin (the point of intersection of the three default datum planes) of the first component to the origin of the skeleton model. This alignment may result in the reorientation of the first component and its children. You can manually redefine the component’s placement constraints to correct the
orientation. You can avoid this situation entirely by creating the skeleton model before any components are assembled.
Skeleton models appear with a unique icon in the model tree to distinguish them from other components. Figure 2–6 shows the model tree icons for parts, sub-assemblies and skeletons.
Figure 2–6
To define the geometry for a skeleton created within the assembly, use either of the following techniques:
• Activate the skeleton and create the geometry within the context of the assembly
• Open the skeleton in Part mode and create the geometry Any type of feature can be added to the skeleton model, including solid and sheet metal features; however, skeleton models typically only consist of surface and datum features.
Step 2: Define the skeleton geometry
Part
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2.2Skeleton Properties
Skeleton models in Pro/ENGINEER have the following properties:
• By default, only one skeleton model can be created for an assembly. By setting the configuration option
multiple_skeletons_allowed to "yes", you can have more than one skeleton belonging to an assembly.
• Skeleton models can exist in sub-assemblies but must be created at the subassembly level.
• Skeleton models are always given the default name of
assembly_name_skel.prt where assembly_name is the name of the parent assembly model. You can use an alternative name if desired. If you are creating multiple skeletons, the default name is incremented for each skeleton (assembly _name _ skel0002.prt).
• Skeleton models can be created at any time but are automatically reordered to appear before the first component and feature in the assembly.
• Assembly features such as cuts and holes do not intersect skeleton models.
• Skeleton models are not included in the mass property calculations.
• Skeleton models can be filtered out of assembly bill of material listings.
• The display of skeleton models can be removed from assembly drawings and simplified representations.
• By default, the color of all solid and surface geometry in the skeleton is medium blue (R=0, G=0, B=49). This color is controlled by the configuration option skeleton_model_default_color. The color is defined by three values (ranging between 0 and 100), specifying the percentages of red, green and blue. This option only applies to skeleton models created after the configuration option is set.
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