Complex Assembly Temporary Sick Constraint Issues

[MechMachineMan]

We have a complex assembly that will have random constraints get sick, except as soon as you go in to edit them through the Doctor and Accept that there are errors, the sick disappears.

This is for an assembly of over 1000 parts and 3900 instances of those parts/documents.

Is there any reason it would do this?

I have worked my way to the 2nd level assembly from the lower ones i found obvious issues in, rebuilding, updating, and saving along the way. By the time I am at the 2nd level, everything looks fine and there is no constraint issues.

I will open up the top level, and the re-open the 2nd level and all of a sudden there are sick constraints all over the place. 

Some assemblies are flexible, some are weldments.

Any idea of what is going on here?

[Anonymous]

Sounds like the cure to your ailment would be to find ways to simplify your model. I tend to tell my co-workers that "Inventor gets confused" when they have an extreme amount of singular instances and a very high number of constraints.

Using Substitutes may help and I've also heard (though haven't thoroughly tested) that if you have an assembly that is finished and will be used elsewhere, grounding the parts prior to saving/closing will help with performance when the sub-assembly is placed later on. I've been told that if a part is grounded, inventor will remember where it is at but neglect it's constraints for checking/processing/whateverit'sdoing. Again, that's kind of a theory, but it's something you could explore.

Ultimately, Inventor is behaving strangely because there's too much going on. I've had similar behaviours in large models before and in some cases, there's simply nothing I can do. And if you've got parts/assemblies that are flexible, adaptive, patterned - all of those things can weigh it down too.

Simplification through substitutes, grounded parts in sub assemblies, and the generation/use of new sub-assemblies where possible is the best way I know of to remedy the problem (assuming that I'm correct in my diagnosis).

Sorry there's not a better answer (to my knowledge).

Hope this helps.

[johnsonshiue]

Hi! Justin,

The behavior sounds dataset specific. I have seen this behavior before but I need to take a look at the files in order to tell where the exact problem is and how to resolve it. Could you send me an email so I can set up a secure account for you to upload the files?

Many thanks!

[mcgyvr]

I've had that MANY times.. Mostly with angle constraints without an explicit vector.. 

It just leaves Inventor having to "think" too much and it can get confused..

A rebuild all or even just attempting to move parts can clear it up but it will usually come back again...

[swalton]

I've had this happen if I try to nest flexable sub-assemblies more than 2 levels down from my top level assembly. 

My solution is to make explicit position reps for those sub-assemblies and avoid nesting flexable subs.

[Anonymous]

Hi,

This problem is often and it is there regardless of whether assembly is small or large.

see this. Just three components 6 constrains and inventor gets confused.

Also this thread contains more

http://forums.autodesk.com/t5/inventor-general-discussion/flexible-nightmare/td-p/5514888/page/4

Cris.

[MechMachineMan]

The data isn't data secure, I just haven't found the time to access the
files with the behavior. I will try to do that by the end of today.

[Thermeco-Cad]

Inventor is great when you want to put few parts together as soon as you add some sub-assemblies and constraints in gets confused, useless and hopeless. I am just wondering if you get the same problem with Solidworks or not.

[Anonymous]

Hi,

I tried solid works to see if this problem is also present in that software.

I only was able to use trial for a short period of time, so was not able to get very deep in the matter.

Generally my impression was that in solid works this problem can be smaller.

I have however been able to prepare assembly that crushed the software.

But as for flexibility of assemblies solid works seems to behave much more stable.

As for Inventor. Flexibility doe's not work at all. Give up hope Autodesk will fix this at all.

As far as I know problem is in that how constrains of sub assemblies are treated in top level assembly. There is a bug somewhere that makes constrain solver to crash because (probably) it is forces some explicit assumptions. Very same constructions work and are solved fine when all constrain and elements are on top level.

I tried to make Autodesk aware of that, I struggled for a long time.

Now I am sure they just do not care. This policy is hopeless.

Cris.

[pistonrod8]

Manage Tab -> Rebuild All

This will usually fix those pesky, unruly flexible assemblies. It doesn't keep it from happening, but it will update the constraints that are sick without you having to go through each one.