Flexibility not working properly in inventor - BUG that has been there for ever

[Cris-Ideas]

Hi,

I am trying to use flexibility feature but every time I give it a chance it fails me. There is a bug somewhere in inventor that makes it not capable of properly solving assemblies with flexible components.

This time I have run on to this issue with a very simple assembly, had been able to reproduce this buggy behaviour  tens of times, and had made video for you.

After unsuccessfully trying to post this I thought I will make another video for you so you could clearly see what is the difference when assembly is flat.

Here it is.

Here I have uploaded data set for you to play with :  http://a360.co/2fmTsvD

And in case you also think this is not working properly you can support idea to fix this: Fix flexible assemblies !

Cris.

[Cris-Ideas]

Hello again,

Still working and tried flexibility. Result as usual.

Cris.

[Cris-Ideas]

And another exmaple

Just an Ordinary day of "work" with Inventor.

Cris

[Cris-Ideas]

And another one ridiculous solution from the constrain solver.

It is clear BUG. How long will this last until Autodesk finally admits facts.

It is not my design concept. It is match in inventor that is failing here. CLEARLY!

It says pins and holes are aligned when clearly they are NOT!

It says angle in -50 when it is 0!

Cris.

[johnsonshiue]

Hi Cris,

Many thanks for recording the videos! I suggest you contact Product Support team and report these as issues and provide the files. The new videos show that you have added supporting components which are not present on the assembly you sent me earlier. Or, you can send me the updated files.

Thanks again!

[Cris-Ideas]

@johnsonshiue

Will of course do that once have time.

But I have documented and provided data sets for similar behaviours in the past.

This by far not the firs time I am experiencing this kind of behaviour.

This is the constrain solver not the data set.

Why it could not be fixed using precious examples?

I am sending them for at least 3 years now.

Is any of the previous examples working now? I didn't see any video that would prove they are.

I would probably be able to reproduce all documented cases now. Only I do not have the time to do that.

I did it once.

Now it is Autodesk turn to do the videos end explain what was the cause and how it was fixed.

Cris.

[karthur1]

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@Cris-Ideas wrote:

Hello All,

I have another example of DOFs analysis failing and constrain solver bug showing it self again.

This time it is one of assemblies I am currently working on so it is real life project.

This video documents what is causing the problem exactly, so I hope Autodesk developers will be able to track this bug down and remove it.

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As always data set available for download from: bug # 175 model

Or model and video: bug # 175 model & video

And for all of you interested Autodesk Support Case No.:  14381427

Hope for some response.

Cris

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Cris,

I first watched your videos on the flexible bolt assemblies and see your problem.  I am using Inventor 2018, and do not have that same problem with flexible fastener assemblies. My flexible bolt assemblies work as expected and I do not see any of the issues that you are showing.  I use iparts for my fasteners, not content center parts as you, but that really shouldn't make any difference.

I also downloaded your dataset for problem #175.  I see the exact same DOF issues and constraint errors as you show in the video.  I am using 2018.3.  Just for kicks, I also tried your assembly in 2019 and see exactly the same thing there as well.

Kirk

[Cris-Ideas]

@karthur1

Thanks for update.

I didn't have time, will, nor disk space to install anything above 2017 so far. I am most interested in flexibility and properly solving of the assemblies and this are not being fixed, as I expected. If this was the case I suppose people from Autodesk would post videos on this thread very fast.

Did you try exactly the same steps with bolt assemblies as I show in the videos? Do they really work?

Cris.

[karthur1]

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@Cris-Ideas wrote:

@karthur1

... 

Did you try exactly the same steps with bolt assemblies as I show in the videos? Do they really work?

Cris.

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Cris,

I only watched the first couple video and saw the issue that you were having.  Not sure what's going on with that because we have been using flexible assemblies for many years without issue. Most of the time, they are pretty stable with me unless it is really complicated.  I never loaded 2017.  I went from 2016 to 2018, but I dont remember that being an issue with 2016.

I recorded a screen cast video of the flexible bolt assemblies (click here for video).  I could share the model, but since it is done in Inv 2018, it would not work with Inv 2017.  When I assembled the bolt, I just grounded the bolt.  I always ground the first (or at least one) of the parts in the assembly.  Then the flat washers are constrained to the bolt.  You can see how its done in the video.

I am sure that you have already applied all the service packs to your Inv 2017, if not check to see what is out there.

Kirk

kelly.young has embedded your screencast for clarity.

[Cris-Ideas]

@karthur1

OK, got that.

Will rebuild my bolts and try. With this basic examples from the beginning.

Have you any good experience with flexible assemblies using range constrains and more then one DOF? like jacks?

Cris.

[karthur1]

Cris,

I use flexible assemblies all the time, but I can't think of one instance where that is mixed with range constraints....Sorry.

When I first looked at your model #175, I thought the patterned components may be causing an issue.  I looked at it closer this morning and noticed that if I delete the "component pattern 11" (Horizontal beams), then when I change the "fold" constraint, everything works and the DOF are shown correctly.  Even after I constrained the "DIN 1025 - IPE 80-2244,5 Steel S355:6" to "frame 1_pomost:1", the fold constraint can be changed without any errors.

I attached just my assembly (you should have the other files) so you can see what I did. I found 2017 on a different workstation, so you can see what I changed.

Take a look at this and see if it solves your issue.

Kirk

[Cris-Ideas]

@karthur1

This one I have already figured out. It is logged with Customer Support.

It should not work like that.

But even if I constrain as you describe, still there are problems.

Assembly in the next videos has this constrain redefined to the first occurrence in pattern.

Fold started to work, but DOFs are still not correct if I make range on fold (video).

Also once I placed flex jack everything start to go crazy on constrain solving. (other videos).

Do you use flexible so they can move or are constrained that once placed they do not change shape? (like those bolts).

Do you use flexible only as "fills" (they accommodate to the outer geometry) or as "controls of the assembly" for example to limit some movements?

Also I noticed that your bolts do not have any range constrain to limit position of the nut + have on extra DOF (nut and washer can flip.

Did you have any problems with range and removed it or you never used it?

Cris.

[Cris-Ideas]

@karthur1

Hi,

I have went back to the beginning and this simplest examples with only one bolt.

I have made another fresh approach, and redefined bolt assembly to be constrained exactly like yours.

I then tried the same situation as in the video in the beginning of the thread.

It failed as previously, after 4 clicks.

Can you try exactly the same on your system? and upload video?

@johnsonshiue

Johnson can you also try?

And if anyone else could do that as well that we would know if this is an issue on my system only, or not.

It should not take more than 30 seconds.

Dataset attached below.

Cris.

[karthur1]

Cris,

I agree, it should not have to work that way, but that is what I found to make it work.  I don't see any new video right now, but when I looked at the range of motion, it would work correctly even with the angle set to 45°. 

Normally, I just use flexible assemblies to change the position of the components in the sub.  I can't think of an instance where I used flexibility to drive position of other components, but I am sure I have done that.  As an example, I just tried setting a range on the bolt/nut assembly and used that to drive the location of one of the test plates in my assembly.  That worked as expected, but it is a really simple assembly (not other subs or array patterns.. etc). 

Here is a screencast of what I am seeing here.

Kirk

[karthur1]

Cris,

I just now saw your video.  I will look at it and reproduce it here.

Kirk

[swalton]

I took a quick look at your files using Inventor 2018.  I see the same behavior as the video if I constrain the bolt axis to the hole first.  The constraint solver seems to be getting tangled trying to flip the washers around the bolt axis.  Adding extra constraints to the bolt assembly to define the orientation of the moving washer does not seem to help.

If I make the constraints shown in the video, and disable flexibility, Inventor will solve the constraints, and I can re-enable flexibility.  This is true even if I add flush constraints to the moving washer in the bolt assembly to try to keep it from flipping.

If I wait to make the bolt assembly flexible until after I get the head washer and the bolt located on the hole, it works fine.  

If I constrain the fixed washer face to the block first, and then add the axis mate, it works with no issues.

If I use an insert constraint between the head washer and the plate, it works with no issues.  

[karthur1]

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@Cris-Ideas wrote:

@karthur1

Hi,

I have went back to the beginning and this simplest examples with only one bolt.

I have made another fresh approach, and redefined bolt assembly to be constrained exactly like yours.

I then tried the same situation as in the video in the beginning of the thread.

It failed as previously, after 4 clicks.

Can you try exactly the same on your system? and upload video?

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Cris.

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Cris,

Trying to see exactly the same as your video, but when I downloaded your dataset and opened the "simplified asy for flex.iam" file, there is no bolt assembly as shown in your video.  Please supply the subassembly and those components.

This is what I see in Inventor when I open it. Notice the missing component (nut i think) and the missing subassembly.

Below is what I see in your video.

[Cris-Ideas]

@swalton

basically what I found is exactly the same as you did.

Only when I tries insert it was failing depending on what component was selected fires.

Solutions with making component flexible at different stage also work but they are not an acceptable workaround because flexible component should work within the assembly while other components are being constrained and it is likely that during this process flexible component must be considered in the solve process and it can have applied constrains in any configuration.

The same for applying constrains in particular order.

So as for me process of solving assembly having flexible component, even so simple as in the example is not stable because it fails in various situations not caused by the user.

Isn't there anyone form Autodesk who could explain it to as how flexible assemblies are considered in the assembly solve process? Really no one?

Obviously they are different than flat assembly structure. If we know how exactly maybe there was a stable way of using them to find.

Cris

[Cris-Ideas]

Subassembly is in the zip only not inserted in to main assembly. you just need to place it.

nut was for CC I have added it to zip.

Cris.

[karthur1]

Cris,

Ok, I got the files now.  When I looked at it, I see the same thing about the nut flipping and then the problem when it errors out when changing faces with the mate constraint using your bolt assembly.  I agree, that it probably shouldn't give the error in that case, but rather, it should flip the direction of the bolt and mate the face of the washer and the plate.

When I use my bolt sub-assembly, I do not see the nut flip directions. I guess that I have never seen this issue because when I insert a bolt (or washer) into a hole, 99% of the time, I use the insert constraint. 

If I use the insert constraint with my bolt assembly or with yours, then I don't see any issues.

Here is another screencast.

Kirk

[johnsonshiue]

Hi Cris,

Regarding #119, I believe it is not directly related to Flexible. It is actually related to how Axial Mate constraint is solved. Axial Mate means as long as the two axes are mate together, it is a valid solution. The trouble here is that the user is unaware of the direction of the axes. On 2019, Axial Mate offers three options: Opposed, Aligned, and Undirected. This will help stabilize the mate direction. The legacy Axial Mate will be set to Undirected by default when being edited in 2019.

I just tried the case in 2019 by converting the Axial Mate to appropriate type. I am seeing the desirable result.

Many thanks!