flexible nightmare

[Anonymous]

Hi,

can someone explain why this is not working?

in attachment there everything, on video you can see what the problem is.

Cris.

[Anonymous]

next one

[mcgyvr]

Kind of difficult to follow your spastic mouse movements 

BUT.. Seems like you just need a few more constraints in the subassembly to keep it from flipping inside out on you..

Angle constraints with explicit vectors,etc...

Flexible subs have always seemed to go goofy every once and a while with me too.. But its usually because of how I have constrained something.. or the lack of proper (bulletproof) constraints. 

Like those 2 threaded knuckles.. I assume thats a mate (axis to axis).. well that can flip over on you and the axis constraint is still "valid"

also sometimes when that happens I will uncheck flexible (and it will snap back to being correct) then turn it on again..

[johnsonshiue]

Hi! It looks like the angular constraint in the flexible subassembly does not have explicit vector defined. As a result, it could flip in some situation. The original dataset you attached here has a few components missing. I have removed the missing components and fix up the constraints. What I did was quite straight forward. It is a bit like unwinding the process. First, I edit the angular constraint in the subassembly and select a logical explcit vector. Second, I go to the top level assembly and unsuppress all constraints. Next, uncheck Flexible option for all subassemblies. At this point, no constraints should fail. Lastly, reverse the order. Check Flexible option and unsuppress all constraints. Please take a look at the attached assembly. It seems to exhibit the desirable movement.

Thanks!

[Anonymous]

Hi,

Sorry but what you suggest dose not solve any of problems with this assembly.

1) I am sure that in my original assembly all angular explicit reference vector constrains have their vectors defined. They ware defined exactly the same as in assemblies you posted.

2) I have spend some time and prepared similar set of parts but not using flexible assemblies but placing them all in top level assembly and applying all constraints between them exactly in the same way they are constrained in subasemblies used as flexible.

As it is clearly seen although everything is constrained in perfectly reasonable manner Inventor is not capable of handing this set of parts and for example axis of central hole can not be aligned with work axis.

Furthermore it is not possible to reposition this middle element in controlled manner.

But there is one very significant difference in how inventor is behaving when not being able to create constrain.

In case you are applying constrain to flexible assembly Inventor forces this new constrain against constrains defined in flexible assemblies. This results in destruction of flexible assembly (shown on video above). After that whole assembly is destroyed.

In case you are applying constrain to the same element but in case all parts are placed in top level assembly (and are constrained exactly in the same way as thy are in flexible assemblies) in case inventor finds this constrain conflicting (although theoretically it is not) even if you choose to apply it, it dose not result in flipping assembly up side down but is rather marked as "corrupted".

As following video shows in presented assembly inventor is not handling constrains in stable way. One moments there are numerous constrains in conflict. And seconds after all is OK, although nothing was done. And again second after Inventor is reporting conflicting constrains.

So I wish to repeat my question:

Why this is not working and is there anything going on to finally fix this issue?

Cris.

In attachment you have everything so you can play. flex.iam is top level assembly.

[Anonymous]

Works like a charm for me. Just do what johnsonshiu explained to you. You have to constrain another angle, so it is no longer flipping.

When you work with flexible you have to make sure to not make the constraints to complicated. It will get very clunky anyway and you will expierience some performance problems.

If possible try to use display representation, like min / max Position.

[johnsonshiue]

Hi! I am sorry that you don't see the benefit of the workflow I proposed. I must have misunderstood something here. You raised quite a few points and the assembly has been recreated. I would like to take a look at the old assembly and the new one. Could you post or send me (johnson.shiue@autodesk.com) the complete flex.iam (the original) without missing component?

The general rule of thumb is assembly modeling, especially in assembly constraint, is to clean up existing errors as much as possible. Those lingering failed constraints can create confusing result. Like the video at the top shows, the flexible subassembly is already in failed solve state. It does not really matter if you add new constraints. I don't believe it will get better just by adding new constraints.

Regarding angular constraints, there are indeed a few places that explicit vector was not chosen (Angle:15, 16, and 17 in the new flex.iam; some in the flexible subassembly).

I am more than willing to help. If you can send me the complete datasets. I should be able to figure out where the problem is and how to change the behavior. If there is indeed a bug in the software, I will work with engineering team to correct it.

Many thanks for your patience!

[blair]

It could be that you have constrained the rod in the housing using the axis constraint. This will allow two solutions that will match the constraint. The rod in one direction as well as in the other direction. An angle/direction constrain will stop this from happening as posted in the previous posts.

This is a problem with Flexibility as Inventor attempts to loosen some constraint values to allow for motion.

[Anonymous]

Hi,

I did constrain this treder rods by flash/mate constrains in such a way that tthere is only one solution to this set.

I did try to use axis constrain but, as you say, I found it producing valid solutions I did not accept.

Cris.

[Anonymous]

Hi,

Thank you for your effort.

Please let me explain once again from the beginning.

1) original problem is that when using flexible assemblies it is often the case that when applying new constrains in top level assembly flexible assemblies are forced in to positions that are against their internal constrains set or some parts are misplaced against constrains they have in top level assembly.

This is illustrated on following video.

It is based on flex3.iam attached in flex3.zip.

In this case I have top level assembly (flex3) in witch I have a flexible assembly rama_conector2 (in grey) and set of assemblies constrained together rama_conector 2_bez lap and 3x Rama_connector_lapa. This are constrained in similar way that in flexible rama_conector2.

So this two sets represent basically the same deice (movable adjustable support).

This sets are constrained with work axis 1 so it goes threw axis of central hole of the connector.

On video I am attempting to apply constrain that by definition is in conflict with the other one already defined. In case of such situation if there is no flexibility in top level assembly inventor gives a massage that "constrain you are trying to apply is in conflict with ...., do you want to: edit, accept, delete..." and in case you do any of those things assembly is not destroyed.

But in case there is any flexibility in top level assembly instead of giving this warning and wait for your decision inventor first destroys whole assembly forcing flexible assemblies in ti positions that are against their internal constrains (situation shown for grey part), or destroys assembly by forcing flexible components in to positions that are against their constrains defined in top level assembly. You can observe this for red elements. When trying to apply this mate constrain all 3 legs are misplaced so they are no longer connected to holes (this is against mates 30, 33, 35).

Similar problem, that is errors in assemblies indicated by red cross in the top of the screan, also sometimes appear if there are additional constrains created that do not directly influence flexible constrains. It also happens if some other constrains in assembly are edited for example some translation is done.

In another assembly I have also problem with this connector that is that this connector gives error if it is shifted along this work axis going there central hole. Although this change in position should not in any case influence angels of the legs it dose and often forces them in to positions against their internal constrains.

2) here is an example of the second very common problem with flexible assemblies. I find it very often. Inventor gives and error (red cross) in top level assembly having flexible component. When examined error gives list of conflicting constrains that ware not conflicting a moment before. If I then go end "edit" all those constrains and go back to top level assembly original error is no longer signalized by inventor. Please note that "edit" is not realy an edit because I only go to edit this particular constrain but I am not changing anything, only clicking OK. So there is no change in the model resulting from this "pseudo edit operation"

This brings me to the obvious conclusion that this is some problem with the software if in the same situation it gives an error or does not give this error, that this is not stable behaviour.

If you wish to play with this assemble you can try to apply angular constrain to this leg and see if you will get the same behaviour.

Following video shows this process.

Please note how this flexible assembly is forced in to position against its internal constrains. And in following part how error is fixed by "not editing".

I consider this kind of behaviour a problem and definitely not stable.

3) as for angular constrains not having explicit reference vector. It is true some of constrains I use do not have explicit reference vector defined. This are constrains Angle: 15, 16 and 17 mentioned by johnsonshiue. I only use angular constrains without explicit reference vector if I want to constrain two planes at 0 deg angle. And that's the case for those. In all other cases I need angle other that 0 or may need such an angle in case of particular constrain I always use explicit reference vector. In case of this assembly I do not expect this constrains 15 16 17 to have any impact on possible problems.

4) As for proposed workflow basing mostly (as I understood) on suppressing flexibility and constrains and then turning them on again, in deed I do not think this is really an option for me because it is rather difficult to look for all flexibilities in assemblies and all related contains to suppress then and the then to unsuppress them. Especially that in some cases this can be constrains of totally different part than flexible assembly in question.

5) As for missing components this are content center part not relevant for this problem. I have removed all of them in latest project attached to this post.

So to narrow a little bit the subject I propose to stick to three key problems:

1) how to prevent inventor from destroying top level assembly when trying to apply new constrain being in conflict with previously existing once? So how to prevent this what is shown on video but in a way other than suppressing and unsuppressing flexibility and constrains or from the user not to apply such conflicting constrains.

2) how to prevent inventor from destroying top level assembly when some of already existing and not conflicting constrains are edited in such w way that this edit should not cause any conflict but it causes forcing (by the program) flexible assemblies in to positions against their internal constrains? Also a way other than suppressing and unsuppressing or expecting user not to perform any edits.

3) find the reason why inventor gives an error sign (red cross) in assembly with flexible member but after you go and select edit all constrains that are listed as conflicting, but you change nothing just click edit and OK there is nothing wrong with top level assembly that was reporting errors just before you started to edit (but not editing)? This is shown on second video.

In attachment you will find latest project flex. top level assemblies are flex.iam and flex3.iam. I used flex3 for video. flex is basically the same maybe some constrains are not applied at top level.

I have also fixed this screw so it was not overconstrained (I found this was causing top level to crash at some point), and so it could not flip.

Cris.

[blair]

You are Constraining using the Axis of the rod and Axis of the housing it travels in. This will provide 2 viable solutions as the rod can be pointed in either direction. You need to use the Angle Constraint and select directions as well. This will only allow a single direction solution to your problem.

[Anonymous]

Yes there is an axis constrain but this element in any case should not flip in the way that is flipping when trying to apply constrains in top level assembly.

Constrains "wysow flex" , "mate7", "flash 5" and "symetry 1" should define relative position of two threaded rods against each other. So rods in any case should not be able to flip in a way that contention holes would be inside and threads outside.

Only thing tat theoretically could happened is that red rod would meet grey nut, so rod set could be rotated 180 deg along global X but still they would be pointing connection holes outside and be metrically placed bout global XY.

Cris.

[blair]

Add the Angle Direction constraints as this will only allow a single solution.

[Anonymous]

Hi,

You insisted, I tried with angle constrain.

I had prepared new extension screw that is constrained using axial and angular constrains so it was only able to produce single solution and never be allowed to flip.

This however did not change anything in behaviour of the software. It is constantly giving inconsistent relationships error message. And as before if they are "edited" but not edited really, error is no longer present, until new update of geometry of flexible assembly.

I post two new assemblies of flex3 project. they use parts of flex3 so if you place them in this directory they should work.

Cris.

[blair]

IAM's are data-bases that only contain which IPT files, constraints and positions (and a coupld of other items) but no IPT files. You need to include all related IPT and IAM files. Do a Pack-and-Go of the primary IAM file.

[Anonymous]

Hi, these two iam files are new files for flex3 project that is attached 3 or 4 posts up.
Cris

[blair]

OK, I'll try and take a look at it this evening at home,

[blair]

I used the Explicit Angle/Direction Constraint on the adjustors and everything works fine. 

[Anonymous]

Hi,

I tried with this file you posted but it is not working in a stable way.

I am getting basically same errors as for all the time I use flexible assemblies.

Simple "drive constrain" command gives errors right away.

On video below you cam observe this behaviour.

On following picture I have marked an area where it can be seen how inventor forced this extension screw in to position against its internal constrains. In this case Mate 3 of internal constrains of sruba rzymska TR30_1.iam is violated.

Cris

[blair]

I'm out this evening and tomorrow evening and won't be able to look at the model until the weekend. I was only looking at the flipping issue and didn't realize that you had a "Drive" issue as well.