Constrain solving - as complicated as that

[Cris-Ideas]

Hello All,

I have started this thread to bring up and hopefully explain problems related to constrain solver and gain knowledge on how exactly constrain solver handles the assembly.

This is because I am experiencing many problems related to assembly solving that should not be expected.

Originally I was discussing this issues in the thread related to problems with flexible assemblies but I decided to split this topics and this thread is intended to focus on constrain solver it self.

I would like to encourage especially people from Autodesk who have the knowledge about constrain solver it self to participate and help us understand better how this works to make our lives easier.

I will be posting videos and data sets, so anyone could try the same what I do and see if is getting the same outcome.

I also would like to ask you to do the same, and if possible use videos with comment rather than long posts, as this is more easy to follow and understand the intent.

I will be also giving each example a name, so it was easy to track replays. So when posting please make it obvious what you are referring to. 

If you are interested in problems related to flexible assemblies please visit this thread Flexibility not working properly in inventor - BUG that has been there for ever

Cris.

[Cris-Ideas]

So here is the first example

# 172 bug - Constrain solver - simple case 0

Please watch this video.

data set available for download: https://autode.sk/2M1tKwI

Cris

[SBix26]

It works perfectly for me-- using Inventor 2017.4.5, I opened your assembly, edited constraint Mate:10 and selected the opposite side of the grounded part.  Constraint solved instantly in preview (with the appropriate sound effect).  No error.

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Sam B
Inventor Pro 2019.1 | Windows 7 SP1
LinkedIn

[Anonymous]

I saw the green nut move together with the red bolt, so these 2 also have a relation. It could be that the nut is preventing the bolt to swap sides. Always consider the entire set of constraints to understand how it works - or doesn't.

[Cris-Ideas]

@Anonymous

yes they have obviously, but nut has no constrains on the top level so it is totally free to rotate.

I am installing the update @SBix26 mentioned. My desktop app obviously does not work as indicates no new updates.

Cris.

[Cris-Ideas]

I have installed the update.

I see no change in the behaviour.

Cris.

[Curtis_Waguespack]

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@ SBix26 wrote:

It works perfectly for me-- using Inventor 2017.4.5, I opened your assembly, edited constraint Mate:10 and selected the opposite side of the grounded part.  Constraint solved instantly in preview (with the appropriate sound effect).  No error.

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@Cris-Ideas

Thanks for the clean and simple data set!

I followed the same steps that SBix26 described, and I had the same results using Inventor 2017.4.

I am not sure what the issue would be that would cause you to see different results?

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

[Cris-Ideas]

@Curtis_Waguespack@SBix26

There must be something though.

What are your application options for assembly?

Can you save this whole set on your machine and post. I will then try on the other data set.

Cris.

[Curtis_Waguespack]

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@Cris-Ideas wrote:

What are your application options for assembly?

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Ahhh-ha! 

When you said that it made me think about these 2 settings. I always have both of these off, but when I turned them on and tested your assembly I saw the same results as you. You can un-check them both and try your test again. But it seems to be the top one the is causing the warning in this case.

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

[SBix26]

I, too, have that option unchecked, and when I turn it on, I get the error message.  Note, however, that if I accept the conflicting relationship, and then drag on the assembly in any way, it immediately solves correctly and all is well.

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Sam B
Inventor Pro 2019.1 | Windows 7 SP1
LinkedIn

[Cris-Ideas]

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@SBix26 wrote:

I, too, have that option unchecked, and when I turn it on, I get the error message.  Note, however, that if I accept the conflicting relationship, and then drag on the assembly in any way, it immediately solves correctly and all is well.

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Yes I know this behaviour even too well. Dragging makes constrain solver to solve assembly while you drag. This probably gives new boundary conditions for solve and than it works. Unless assembly is destroyed before.

When I unchecked "Enable relationships redundancy analysis" it solves.

Will make other attempts with different data sets.

So this makes me wonder what exactly this option does during assembly solve?

Any ideas?

Cris.

[Curtis_Waguespack]

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@Cris-Ideas wrote:

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So this makes me wonder what exactly this option does during assembly solve?

Any ideas? 

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Hi @Cris-Ideas,

I'll take a stab at the explanation, and then someone can correct me on any of it that I get wrong.

There are situations where you can apply a constraint that does the same thing as an existing constraint. Maybe something like an mate constraint to the center of a bolt shaft and the center axis of a hole, when there was already an insert constraint between the hole and bolt... I don't know if that example is a real example that this setting catches without testing... but it illustrates the idea of redundant constraints.

So why is this problematic? New users often do this as they learn, and it can cause them problem later down the line when they try to update one of the constraints... using the previous example, let's say they attempt to offset the axis to axis mate for some reason... the Insert constraint will not allow it. And so by having this on, they user is alerted to the issue before they create it. 

The other part of redundant constraints that is of concern is the impact they have on performance as the solver tries to do all of these redundant solves.

In any case I think you would best served by disabling both of the options I showed, since you have a good sense of assembly constraints.

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

[Cris-Ideas]

@Curtis_Waguespack

Thank you for the explanation.

I however know that all.

What I meant in my question "what this option does during assembly solving" was rather to concern entirely different level. So I would like to know how this influences sequence of assembly solve from the programming point of view.

In this particular case this behaviour indicates that there is something that inventor does not like in constrain set for this assembly.

For us humans this situation is perfectly understandable as we know that no matter how nut is constrained with the bolt (btw. it is the nut that's making trouble, once deleted this error message disappears) it can be rotted and moved freely with the bolt in the context of the top level assembly. 

But obviously solves sees some problem in this.

What is interesting that if you delete the nut all is solving.

Also if you directly demote whole set all is solving

Also if you try to constrain washer under the nut first all is solving

.....

btw. this assembly is over constrained and inventor does not indicate that by showing redundant constrains. Which in my opinion it should do.

So what is exactly the condition that stops inventor from successfully solve in case this option is checked while allowing for successful solve once it is unchecked?

I believe we need Inventor engineer to explain this.

Cris.

[Curtis_Waguespack]

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@Cris-Ideas wrote:

I believe we need Inventor engineer to explain this.

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Yep, maybe @johnsonshiue can help

[Cris-Ideas]

Juts to update on # 172

Cris

[Frederick_Law]

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@Cris-Ideas wrote:

So I would like to know how this influences sequence of assembly solve from the programming point of view.

Cris.

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I don't think constrain is resolve in any particular order.  Same goes to parameter and dimension.

[Cris-Ideas]

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@Frederick_Law wrote:

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I don't think constrain is resolve in any particular order.  Same goes to parameter and dimension.

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I have example showing order does matter.

Yet to come.

Cris.

[Cris-Ideas]

So having made signiffcant progress on # 172 I fought I will bring up another one queuing.

Here is # 166 bug

data set available for download: https://autode.sk/2MdQFS0

Please try to remember mark witch problem you are referring to in the begging of the post.

Cris

[johnsonshiue]

Hi Cris,

Since you have access to Beta site, you may want to try the workflow on the latest Inventor Beta, which also contains the Opposed and Aligned Axial-Axial Mate like in 2019. Please note that Inventor Beta is under NDA so do not share any video or behavioral based on the Beta build.

I could be wrong as always, but I believe this case could use same help from Opposed and Aligned Axial-Axial Mate.

Many thanks!

[Cris-Ideas]

Hi @johnsonshiue

Witch case are you referring to?

Cris