Autodesk Inventor Tutorials

by Sean Dotsonwww.sdotson.comsean@sdotson.com

Adaptivity 103Part Three in a Series

Latest Revision: 1/15/03For R5, 5.3 & 6

© 2003 Sean Dotson (sdotson.com)Inventor is a registered trademark of Autodesk Inc.

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In this portion of the Adaptivity tutorial series we will be constructing the pipe flangespacer but this time in the context of an assembly. Drawing parts in the context of anassembly is an easy way to gain both the benefits of adaptivity and to use geometry fromother parts. However so thought must be given to the process to avoid the associatedpitfalls.

The data set for this tutorial can be downloaded from:http://www.sdotson.com/tutparts/adaptdata103.zip

Begin by double clicking on Adapt.103.ipj to open Inventor and set the project. Thenopen the assembly Adapt103.iam. In it you will find one part, the pipe flange. We shallstart construction of the spacer by selecting the Create Component button (right belowthe place component button) in the assembly panel.

In the resulting dialogue (see Figure 1) you will be asked to specify a new file name, filetype (and assembly or part), a location to store this new file, and a template to use (clickbrowser to select your custom templates). Name the file Spacer_001.ipt and save it inthe same directory as the rest of the files. Be sure to check the Constrain sketch plane toselected face or plane. When finished click OK. You will be returned to the model.

Figure 1 - Create Component Dialogue

Select the front face of the flange. Depending on the settings you have for componentopacity the flange may or may not turn opaque (see Figure 2). If it does not this can betoggled by the component opacity button on the main toolbar.

Before we go any further we need to address some settings of which you may not beaware. Select Tools/Application Options and then the Assembly tab (see Figure 3).

On this tab you will see a section named In-Place Features. Note the state of the optionlabeled Enable Associative Edge/Loop Geometry Projection During In-Place

Figure 2 - Flange is Opaque during In Context Editing

Figure 3 - Assembly Options Dialogue

Modeling. This turns on and off a feature that is know as Cross Part Association(CPA).

Simply, CPA is a way of making features of parts adaptive during in-context modeling.If CPA is turned on (which it is by default) then projected geomety while in-contextediting is adaptive. If it is off the projected geometry is non-adaptive. It’s that simple.

We’ll return to this discussion in a moment but let’s look at an example first. Close theAssembly Options dialogue and return to the model. Choose the project geometry tooland click on the OD and ID of the pipe.

This is where it get a bit confusing, as things changed (for the better) between R5.3 andR6. Reference Figure 4. In R6 if you project geometry and it is associative (i.e. CPA isturned on) it will be dark blue or whatever color you have selected for sketch geometrydepending on your color scheme. If CPA is turned off the geometry will project pink.

In 5.3 the geometry will project pink regardless of the state of CPA. The only way todetermine if CPA is on (other than looking in Application Options) is to look at thebrowser. If an adaptive sign appears next to the sketch, CPA is on. If no adaptive signappears then CPA is turned off. See Figure 5. Confusing for sure.

Inventor R6 Inventor R5.3 & 5

Figure 4 - Cross Part Association Colors

Figure 5 - Adaptive In-Context Sketch Signifies CPA is ON

Now extrude the sketch a distance of 0.375”. You will have a part that looks like Figure6. Notice that in the browser both the part and the extrusion have been tagged as adaptive(see Figure 7.) We can now start a new sketch on the face of the spacer and project theholes from the flange. You can choose to project the entire circle as shown or just thehole centers. See Figure 8 for an example. Note that this screenshot was done in R6. In5 and 5.3 the circles will be pink. Just make sure that the browser shows the sketch asadaptive.

After projecting the holes use the hole tool and select the center points of each projectedhole circle. Create 6 standard ¼” counterbored holes. (See Figure 9)

Figure 6 - Extruded In-Context Part

Figure 7 - Adaptive Part & Feature

Figure 8 - Projected Holes on Spacer (R6 screenshot)

Figure 9 - Counterbored Holes in Spacer

NOTE: An alternate way of creating these holes would be to project the hole in the pipethat was the base hole feature and then array the holes in the spacer. You have to besure to project the original hole however.

Your browser should now look like the one shown in Figure 10. Both the Extrusion andits sketch, as well as the Hole feature and its sketch should be adaptive. Click the Returnbutton or RMB and select Finish Edit. Your browser should reflect that Spacer_001.iptis adaptive.

Figure 10 -Browsers Showing Adaptive Features & Parts

Furthermore you will notice that if you expand each sketch there will be a series ofreference sketches. These reference sketches are references to the projected geometryfrom the pipe flange. These reference can be deleted (or broken) by RMB on thereference and selecting Break Link. Be aware that this also removes adaptivity betweenthe feature and parts.

So you now have an adaptive spacer. Let’s check to make sure it works. Open or in-context edit PipeFlange.ipt. Change the OD to 6” and the bolt circle for the hole featureto 5”. Return to the top-level assembly and click Update. The spacer will change shapeand the bolt circle will move to reflect the changes in the Pipe Flange. (See Figure 11).Restore the Pipe Flange to it’s original state and then save this assembly asAdaptiveSpacerAssy.iam we will be returning to it later.

Figure 11 - Spacer Adapts to Changes to Pipe Flange

That is the basis of in-context adaptivity. However that’s just half the story. OpenAdapt103_001.iam. (This is just a copy of the original Adapt103.iam assembly.) OpenTools/Application Options and go to the Assembly tab. Now turn off CPA.

TIP: You can toggle the state of CPA while projecting geometry. If you hold downControl while projecting a line or arc it inverts the current state of CPA. For example ifCPA is on and you project while holding down control, it is turned OFF for that line andvice-versa. This is a very handy trick to keep in mind.

Start a new in-context part and project the OD and ID. Notice that in R^ the lines arepink. In 5 & 5.3 they are pink as well. In all versions you should NOT see an adaptivesign next to the sketch in the browser. Extrude the sketch and then project the holes.Creates the hole features as well. Your browser should show no signs of adaptivity.

Return to the assembly via Return of by RMB Finish Edit Now edit the OD and boltcircle of the Pipe Flange. Return to the assembly and click Update. Notice that thespacer did not adapt to the flange. (See Figure 12)

Figure 12 - Non-Adaptive Spacer

The reader should now see the differences between adaptive and non-adpaptive featuresand how CPA is used in in-context part creation. All that remains is to explain whaterrors can occur through the use of CPA.

Reopen AdaptiveSpacerAssy.iam. Recall that the OD and positions of the holes on thespacer are adaptive to the pipe flange. Edit the Pipe Flange and change the pattern ofholes from 6 to 5 holes (Figure 13). Return to the top-level assembly and hit update.You will receive an error like the one in Figure 14.

Figure 13 - Editing the Hole Array

Figure 14 - Cross Part Association Error

This is the infamous Cross Part Association Error. I say infamous because many a userhas stumbled across this error and had no idea what caused it. When you install InventorCPA is turned on by default, so unwitting users who project geometry that subsequentlydisappears or drastically changes are presented with this error as the adaptive projectedgeometry has lost association to the feature from which it was projected.

A common action that can result in this error is projecting a feature (hole, extrusion, filletedge etc.) and then changing the base part such that the feature grossly changes ordisappears completely. Since the feature is gone the CPA fails and you get this error.

It is for this reason that I recommend users turn CPA OFF! This will prevent CPA errorsin the future. I believe that users should consciously make features and parts adaptive,not by default. Remember that even with CPA off you can turn it on temporarily byholding down control as you project geometry.

Figure 15 shows the resulting spacer if you accept the CPA error.

Figure 15 - CPA Error on Spacer

In the next tutorial in this series we will look at more in-context adaptivity and how toconstruct parts than can dynamically change shape as you drive related constraints. Ourexample will be constructing an air hose attached to a robot arm that can grow/shrink asthe robot arm moves. This technique can also be used to simulate springs or otherdeformable parts like rubber.