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Suspected bug in Inventor's sketch solver when using Reference parameters

5 REPLIES 5
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Message 1 of 6
DynamicObjects
495 Views, 5 Replies

Suspected bug in Inventor's sketch solver when using Reference parameters

Hello Autodesk and forum,

 

In this earlier post, here , we think we have identified a bug in the sketch solver which manifests itself as unstable geometry because the sketch in question toggles between alternative solutions with every call of .Rebuild of the part file (not Rebuild of the assembly it may or may not be added to).

 

Capture01.JPG

 

Capture02.JPG

 

To reproduce the behaviour requires TWO conditions to exist...

 

  1.      a model parameter, e.g. d4, must be a function that includes a reference parameter as one of its arguments e.g. d4 = d1 - ref1  

    and; 

  2. the function must always evaluate negative, 
    e.g. d1 < ref1

Attached is the simplest example I can think of as shown in the pictures above.  

Open the attached part file (Inventor 2020) and press the Rebuild button consecutively and notice how the sketch geometry toggles between solutions as per the pictures above...  It is unstable and can cause downstream issues if this part is used in assemblies.

 

Now change the formula in d4 so that it no longer uses a reference parameter, e.g. d4 = d1 - d2.  Note now that, even though d4 still always evaluates negative, the sketch is stable and yields the same solution on subsequent clicks of the Rebuild button.

 

@Anonymous  - could you please confirm if this is a bug as we suspect or whether in fact this is deliberate Inventor behaviour and if so could you clarify why it is desirable for Inventor to toggle between solutions on consecutive recomputes?

 

Thanks in advance for your time.

Dan

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Atkins Consultants Ltd UK
+19,000 staff (M&E, Civils, Structural, Geotechnical, Environmental and more)
5 REPLIES 5
Message 2 of 6

Hi! This is an interesting case. When inputting a dimension value, negative input is not allowed. However, when the equation is evaluated, negative number is accepted and it could trigger a flip. For this case, you can simply add a function to avoid the flip. For "d4", you can rewrite the equation to "abs(d1-ref1)" and then it will no longer flip. Would it work for you?

Many thanks!



Johnson Shiue (johnson.shiue@autodesk.com)
Software Test Engineer
Message 3 of 6

@johnsonshiue - that's not the point.  Of course we can re-define things to avoid the behaviour.

The question is - should Inventor behave this way?

 

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Atkins Consultants Ltd UK
+19,000 staff (M&E, Civils, Structural, Geotechnical, Environmental and more)
Message 4 of 6

Hi! No, absolutely not. Any inconsistent behavior is a bug. Rebuild All should produce consistent result no matter what. I was merely offering a workaround bypassing the issue. At the moment, we don't have a fix to the problem and I am not sure when the fix will be available. I cannot promise something I don't know.

Many thanks!

 



Johnson Shiue (johnson.shiue@autodesk.com)
Software Test Engineer
Message 5 of 6
johnsonshiue
in reply to: johnsonshiue

Hi! The issue has been reported as INVGEN-38836. Before the fix becomes available, the abs() function is a good workaround for now.

Many thanks!

 



Johnson Shiue (johnson.shiue@autodesk.com)
Software Test Engineer
Message 6 of 6

This is 3 years old now has this issue not been resolved yet? 

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