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]

Hi,

last night I was walking carrying my new born son and thinking about this flexibility example I show in this post.

I come up with another Idea how I can constrain flexible sub-assembly internally to see if this makes any difference. I was expecting it might and it does.

In my opinion this is an indication where to look for bug.

Here is a video:

and I also updated data set for your convenience:  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,

I have received an e-mail from one of Autodesk inventor engineers. in this e-mail there is a suggestion to avoid constraining to the origin planes of the sub assembly that is to be flexible.

Well I must make a remark on that first.

So from what I showed on videos in previous posts it seems that flexible sub assembly where parts are constrained to origin planes of the flexible sub assembly works best (of not working). Also please note that the only one flexible assembly that was solved properly had ALL parts constrained to origin planes and origin axis of sub assembly.

Also in recently publishes article about that (link) it is said " Constrain to the origin instead of using grounded status"

From the same e-mail I also got an impression that my previous videos may not be clear enough in exposing bad behaviour as he wrote "I do not see a bug in this cases"

So I have prepared another set of videos that are more concern on exact bad behaviours rather than on describing this issue in general

Below you will find this videos.

Please back me up if you also see a bug here by awarding this post a kudos or adding to this thread.

Here you also can support idea to fix this "Fix flexibility"

(Watching videos please make sure you have sound on)

In this video I explain what is the design intent and how I am going to achieve that.

In 4 following videos I present how in different situations inventor is not capable of solving simplest cases when using flexible assembly.

All 4 videos are for different layouts.

I clearly see BUG here.

How about you?

Cris.

data set available for download: http://a360.co/2eSIdJH

[Cris-Ideas]

Hello,

Isn't there anyone from Autodesk who would like to join this thread?

I think your input is expected.

Cris

[pball]

Cris, this forum is a user forum where users help other users. Autodesk staff do visit and help but their support should not be expected. If you are looking for feedback straight from Autodesk going through one of the official support channels is a much better option.

Bugs and feedback can be sent here.

http://www.autodesk.com/company/contact-us/product-feedback

For actual support if you have a subscription there is a way in your account to request support. I personally am not familiar with this so I don't have any links.

[Cris-Ideas]

Hello pball.

Thank you for posting. I could write pages about how Autodesk is handling bugs and support cases but I would not like this thread to go of subject.

I will then just quote Inventor Senior Principal Engineer Steven Dennis from this post (link) 

answering my question "Why Autodesk does not provide any place dedicated for reporting bugs?" he wrote:

"We do, call your product support numbers or use this forum (this is not Ideas forum). Staff (product support, QA, and Development) monitor these forums regularly. ..."

Autodesk employees are on this forum, trust me, I had many threads where they ware the only once participating.

As for the subject of this thread I am curious if you consider behaviour showed on videos correct or buggy?

Cris.

[Cris-Ideas]

Hi

I thought I have to refresh this video blog about flexibility failing in most basic cases.

Here you have another video showing most basic and most common problem related to using flexible components.

still hoping for some replies or comments.

Cris.

[johnsonshiue]

Hi Cris,

I am very sorry that I reply to you late. My availability can be affected by other urgencies and travel plans. Since you have access to Subscription Support, please contact our support team if you have issues requiring immediate attention.

This particular topic is about flexible solve or under-constrained solve behavior. As I have mentioned before, assembly constraints can be confusing sometime. In real world on the earth, objects are grounded by gravity. Only when there is force big enough to overcome the gravity or friction, an object can move. But, in constraint world, this is not the case. All the components, though look stationary, are free to move with 6 degrees of freedom. They have to be constrained if you want to restrict its movement. Each constraint is like an equation restricting movement of two participating components. Inventor assembly constraint solver simply finds the quickest solution to satisfy the equations (constraints). Sometime the solve result is not what you expect, mostly because the constraints are not set up consistently with your design intent (there are bugs from time to time for sure). If you look at the solve result and compare it to the constraints, more than likely you will see the constraints are satisfied. Then it is a valid solution.

Regarding flexible solve, we have been discussing on and off for two years. You think flexible subassembly should behave exactly like flattened components. To certain degree, it is true. But, there is major difference. For flattened components, the constraint participants are all solved in the global (top assembly) coordinate system. For flexible subassembly, there is a local subassembly coordinate system in play. This local coordinate system in the flexible assembly can introduce confusing behavior, particularly when the components within the subassembly are constrained to the local origin planes. To minimize the influence from local coordinate system, it is better to avoid constraining to the local origin planes in the flexible subassembly. To further reduce degree of freedom, you can ground the flexible subassembly. By doing so, the flexible subassembly itself is just like an invisible wrapper container hosting the components. It does not participate in the solve process. This will truly identical to flattened components.

Attached is an example of such technique using the files you provided here. Please take a look and let me know if it works better.

Many thanks!

[Cris-Ideas]

Hi Johnson,

Yes in deed we are discussing on and off for about a period you mention.

I do not insist flexible assemblies should work exactly as flatten once.

I insist that behaviour of the software is consistent and stable. And behaviour of flexible components can be different from flatten once if designed this way.

Problem I am constantly binging up over and over again is that constrain solver and design doctor do not work in stable reliable way.

My problem is NOT, as you imply, that constrain solver gets solution that is mathematically valid but no following my design intent.

Problem is that constrain solver gets solutions that DO NOT meet boundary conditions, that are defined constrains, and in many cases design doctor does not bring en error message about this.

Other problem is that design doctor brings up many ridiculous constrain inconsistency errors even thought this constrains are met in obvious way.

This problems I show in my videos in this thread. So if you could refer to those documented once it would be appreciated.

As I have showed in one of first videos in this thread when trying to use grounded flexible assembly with ungrounded components in it it got me same errors as for other types of flexible components.

As I also showed in one of the videos only flexible assembly that did not produced any errors when constrained was the one where there ware no constrains defined between its components and everything was constrained to flexible assembly (container as you call it).

I will download data set you provided and will get back with it.

In the meantime I have prepared two additional videos showing inconsistent design doctor behaviour. Please watch those in the next post.

Cris.

[Cris-Ideas]

Hi,

I have prepared two additional videos documenting design doctor incorrect behaviour.

here you have a data set for those: http://a360.co/2hhK7Ce

And please do not tell me it is not following my design intent. I just want it to work stable and give proper solutions, and not an error messages when assembly is perfectly fine.

Cris.

[johnsonshiue]

Hi Cris,

These are very good cases. The second one is a bug. Design Doctor "forgot" to clear out the error status. Basically, it becomes out of sync with the assembly status. The first one has something to do with "quick solve" behavior. By default, Inventor solves constraints using "quick solve" mode, meaning the solver detects the constraints need to be solved and only solve those constraints and related geometry. It does not go through full solve. The mode is for performance purpose. For a large assembly, we don't want to solve each constraint when the user adds a new constraint or edit an existing one.

You can turn off the mode by checking "Enable relationship redundancy analysis" option in Tools -> Application Options -> Assembly. I would suggest you turn it on. Repeat the workflow and you will see the problematic behavior shown in first video will be gone.

Many thanks!

BTW, congratulations to the new baby!

[Cris-Ideas]

Hi

This issue that you confirm is a bug has been there for ever and this behaviour was reported many, many times (it is easy to find threads about hits + there must have been numerous support cases from subscription customers (I have submitted few my self)).

Can we expect this bug to be removed in next SP? (I heard one should be available in February).

Cris.

[Cris-Ideas]

So having agreed there is one bug.

I propose to deal with the next one.

Please try to explain why constrain solver is not capable of obtaining solution for a very simple case when I try to apply first top level constrain to a flexible component?

How I understand this:

It should be simple. Since there are not restrictions for a flexible component, it should be possible to apply any constrain as a first one on the top level as there is no possible conflict with anything since nothing restricts (constrains) this component.

But in case I show this turns out to be not possible. Therefore there is a bug either in constrain solver (which I do not belie) or what I consider most likely in algorithm responsible for data preparation for constrain solver or algorithm responsible for validating solution obtained from constrain solver, or in logic connecting this two.

Please analyse this video, and try to follow. It is really simple concept. I just want to apply ordinary, most basic mate constrain. I wane this to be possible as it is most basic and easy case.

data set available for download from previous posts of this thread.

Cris.

[bob_holland]

@Cris-Ideas

Thank you for bringing this to my attention and we are sorry for your inconvenience.
I have sent this to our development staff for them to resolve in an upcoming release or service pack.

I have created a web page and the investigation have been documented in the article published here:

http://knowledge.autodesk.com/article/Flexibility-not-working-properly-in-Inventor

We will keep the article updated with the findings from the investigation, as they become available. You may look up the article by searching Autodesk Knowledge Network using the Incident Id: 166160 for the status of the investigation any time.

The above webpage should be live tomorrow (Friday) morning PST.

Thank you for your patience while we work to get this resolved.

[Cris-Ideas]

---

@johnsonshiue wrote:

Hi Cris,

I am very sorry.....

.....

Attached is an example of such technique using the files you provided here. Please take a look and let me know if it works better.

Many thanks!

---

Hi Johnson,

As promised I have downloaded your model, and sadly it failed just as all other flexible once, after just 2 or 3 minutes.

This brings me to the same conclusion as I have stated many times.

There is a bug somewhere, witch makes it not possible to use flexible components.

Please see video made with your assembly.

Cris

[bob_holland]

@Cris-Ideas

Hi Cris,

I wanted to let you know that Johnson i on holiday until sometime in January.

I did not want you to think that he was being rude for ignoring you.

As stated before, I have logged this with our development staff and have created a tracking page so that when the status changes you can be made aware of this.

Thank you again for your patience while we work to get this resolved for you and the rest of our users.

[mcgyvr]

Nice job Cris.. Way to keep on it!!!..

Too many users run out of patience/time,etc... when attempting to work with Autodesk to find/nail down bugs. (its not an easy process many times for either side)

Good job Johnson/Bob for sticking with him too!!!

Hopefully this gets cleared up.. There are certainly issues with what Cris has reported here and I've had numerous problems with flexible on occasion too.. 

[Cris-Ideas]

Hello Everyone,

While working on my design I have run on to a very interesting case of flexible component and problems related to using it.

I have been able to narrow down cause to a single constrain that if turned on or suppressed is causing a problem.

I therefore had made a video documenting this and prepared data set for you.

I would like to ask guys from Autodesk to consult this case with development.

This is a clean, build from scratch assembly thought in such a way so it was used as flexible. So all constrains are thought over to allow only needed DOFs to stay free.

here you have data set available for download: http://a360.co/2h20zJG

Cris.

[Cris-Ideas]

@bob_holland

Hi Bob,

Thanks for info.

I hope there are other inventor team members that will participate in this thread.

Cris.

[Cris-Ideas]

Hello again.

I have found some surprising facts about using flexible components. I am sure this findings are specially interesting for development.

@bob_holland Bob can I ask you to review this video and interest development with it.

Maybe someone from team could join this thread?

Conclusion in short:

It turns out that in order to make assembly using flexible component to be solved in stable way some irrational requirements must be met, that cannot in any case be met in real life projects.

I am hoping for some feedback.

Here you have a video with extensive comment & data set for download.

http://a360.co/2ht9pNO

Cris.