Weird constraint behavior

[Neil_Cross]

Tried to reproduce this but so far can't.

Using 2018.2 a user has a big assembly, in that assembly there was two broken/sick constraints which is perfectly normal.

User drops in a new part and constrains it to another part, the constraint solves but the user is given a warning that the constraint interferes with the sick constraints (it doesn't, the sick constraints are completely unrelated and do not interfere with this).

The constraint is applied, the new constraint is not sick, but the user is unable to free drag the part...

If the two sick constraints are suppressed, the assembly behaves normally.

So basically, until these sick constraints are suppressed, no parts in that assembly can be free dragged and all new constraints are told that they clash with the sick ones.

Anyone else seen this?

[-niels-]

Yes, i've also seen that.
Broken constraints also interfere with iMate placement if i recall correctly.
And, not 100% sure, i think they interfere with placing CC parts as well.
(thought that might be because of the iMates...)

[jtylerbc]

I've seen all sorts of odd behavior when there are sick constraints in an assembly, and occasional inability to drag parts is definitely one of them.  I don't think it's a 2018-specific thing.  I'm still on 2016 at my office, and have seen similar behavior (seemingly at random) with assemblies that have sick constraints, going back several years.

I usually point out to my users that things are going to act a bit screwy if their model has issues, and tend to suggest fixing the broken constraints before doing much else with the assembly.  If something is messed up, adding more constraints on top of that rarely makes the situation better.

[kelly.young]

@Neil_Cross I've seen this a few times in customer posts, typically it's from the sick constraint making the rest of the assembly confused and limiting further placement or motion.

Here is a good example assembly like you are seeing, part file in post 9:

Inventor 2018 Cannot Rotate Assembly Parts

They were frustrated the same way but once the sick constraint is fixed it is all good.

I always just try to make sure the red plus sketch doctor symbol is not lit up before moving forward.

Sometimes it limits movement and others it doesn't mind, haven't been able to discern what exactly makes it angry.

Please select the Accept as Solution button if a post solves your issue or answers your question.

[Neil_Cross]

It's not just the inability to free drag parts which is frustrating, but Inventor 2018 also gives the user the "can't solve the constraint" dialog with the "edit, accept etc" prompts every time they attempt to place a new constraint from that point on.

I'll not ramble on about the ins and outs of the nature of the assembly today, but the last thing the user needed to be told was he had to go on a clean up mission on a 7 year old assembly done by someone who doesn't work here any more!

If I get a spare few minutes I'll try and reproduce the issue from scratch.

[Curtis_Waguespack]

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@Neil_Cross wrote:

...also gives the user the "can't solve the constraint" dialog with the "edit, accept etc" prompts every time they attempt to place a new constraint from that point on. 

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Hi @Neil_Cross,

I see this in Inventor 2017 also. 

I think the intended workflow, is to choose the Diagnose option, and then find the problem constraint and use the keep/ break buttons (yellow or grey bubble buttons) to suppress or delete the problem constraint(s). You can use the Check button to verify the constraints in the Conflict Analysis too.

If anyone wants to reproduce this, you can:

• create a cube with a hole in it, place 2 instances of that cube in an assembly,
• use an insert constraint to constraint between the holes,
• then edit the cube and move the End of Part marker above the hole feature.
• then return to the assembly, accept the constraint error,
• and then attempt to create another constraint.

I hope this helps.
Best of luck to you in all of your Inventor pursuits,
Curtis
http://inventortrenches.blogspot.com

[johnsonshiue]

Hi Neil,

Yes, I have seen it before. It is like the assembly is totally locked up. Essentially, the assembly is in fail-solve state. The solver simply could not find a good solution. Sometimes, Rebuild All can help. Sometimes, reordering constraints may help. Sometimes suppressing constraints will do the job. Try this and see if you can still reproduce it. Go to Tools -> Application Options -> Assembly -> check Enable Redundant Relationship Analysis. Checking this will disable "quick solve" which is supposed to be super fast but it may not solve the full system.

Many thanks!