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Positional Representation Assembly - Flippin' Problem

11 REPLIES 11
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Message 1 of 12
pompeo79
1858 Views, 11 Replies

Positional Representation Assembly - Flippin' Problem

Hi,


i have  a problem to manage some pos representation  in this assembly )see link below).

 

The max vertical rep, (using angle constraint third type too) give me some problem with a cylinder and his rod, they just flip.

 

 

Any idea?

 

Thanks to all

 

To download the assembly:

 

http://dl.dropbox.com/u/63643836/Excavator%20Positional%20rep.rar

11 REPLIES 11
Message 2 of 12
harco
in reply to: pompeo79

I haven't opened your assembly so I'm not sure this answers your question but this is a common problem with hydraulic cylinders.

I assume you used axis/axis and angle constraints, I found this unstable.

If you have drawn the rod and the cylinder centred on their origins then use the origin workplanes to constrain the sliding.

This is a robust approach and should not flip.

Message 3 of 12
pompeo79
in reply to: harco

I have tried already, the problematic cylinder....fixed in the orientation with the 3 origin plan, angle constraints.

 

Thanks for support!Smiley Happy

 

Message 4 of 12
WHolzwarth
in reply to: pompeo79

This is another example of Inventor's buggy constraint handling.

 

I've seen many flexible cylinders loosing their constraints and setting them bad, for no visible reason. This happens often with cylinder/rod combinations with +/- insert constraints. You can open the cylinder sub-assy, move the rod by mouse, and the constraint is back again.

 

With this excavator, all attempts with the cylinder near the boom were not successful. I only could get it stable, after moving it up into the main assy. Thus, I could get rid of the problems in Main and Free posrep, but not with Max vertical position.

 

This position simply can't be handled. The four bar linkage at the bucket assy flips and can't be set up, as needed.

As a remedy, I added Begrenzungswinkel and Begrenzungswinkel 2 as limits for the angular position of the bucket and the bucket link. But although the bucket angle was limited as +/- 30°, it's juming to about 105°. This should never happen, and results in flipping of the 4-bar linkage.

 

You can see this method working well in the minor assy Constraints ok.iam. But Inventor can't handle it in the still rather simple main assy.

 

I think, this should be improved. I don't need another UI change, but I'll have to do my job with tasks like that.

Walter

 

Files (only the changes) can be downloaded because of filesize for some time here:

www.holzwarth-cad.net/Joomla/media/download/Excavator_changes.zip

Walter Holzwarth

EESignature

Message 5 of 12
pompeo79
in reply to: pompeo79

Great reply Walter ! ! !    thank you ! !   Smiley HappySmiley Wink

 

That's the answer that i was wainting !

 

I have already downloaded your assembly, so you can drop off the rar,  thank you for your time and your patience to solve, change and upload !

 

At the end of the story just  a limit that need to be solved in Inventor Constraint with positional rep !

 

 

Message 6 of 12
pompeo79
in reply to: pompeo79

Nice paper-style inv background Smiley Very Happy

Message 7 of 12
lkrenzler
in reply to: pompeo79

I see this was brought up years ago but the problem persists even in 2014.  Positional representations are a bit like I imagine hell to be.  Holy.

 

Inventor can't seem to tell the difference between -30deg and +30deg half the time for example.  Cylinders and other objects flip for no reason.

 

Angles are a huge issue in 2014 in general.  It seems Inventor just randomly decides to ignore clockwise or counterclockwise, depending on how it's feeling that hour.

 

This assembly for example worked perfectly for weeks, but not this morning.  Nothing changed but now the **** thing won't update by itself.  If I drag the cylinder manually it snaps back into position.  A similar assembly does not!  I had to change the angle setting to - and it works again (for now).  I run into this same nonsense every day.  I can count on the fact that any positional representations will at some point destroy themselves.

 

Another issue is that when I finally get it the way I want, Inventer often doesn't save the changes.  It says it does.  It saves.  But when I re-open it, the changes aren't saved at all.  This I run into constantly.

 

Does anyone know if any of this has been addressed in 2015?  Any improvements?  Just wondering.

 

 

Const.jpg

 

 

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Inventor Pro 2019 - Win. 10 - GeForce GTX 1080 .
Message 8 of 12
andrewiv
in reply to: lkrenzler

I used to have this problem as well.  Then they added a third option to the angle constraint dialog.  Now Inventor can distinquish between clockwise and counter clockwise.  I have not had these issues when using this option.

Andrew In’t Veld
CAD Administrator

Message 9 of 12
lkrenzler
in reply to: andrewiv

OK, thanks, I'll give that a try.

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Inventor Pro 2019 - Win. 10 - GeForce GTX 1080 .
Message 10 of 12
lkrenzler
in reply to: lkrenzler

Thanks for the suggestion.  I tried this extensively, but seems to make no difference.  Positional representations in Inventor are beyond stupid.  I'll have it working perfectly, and then without making a single change, they quit working, flip over, fly apart, sit at angles they're not set to be at, etc. etc.  Holy, what a mess.

 

Then try to animate it in Studio, and you get nothing but jerky motion for no reason.  Autodesk, wake up and get your act together.

 

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Inventor Pro 2019 - Win. 10 - GeForce GTX 1080 .
Message 11 of 12
sumayo
in reply to: pompeo79

Still doing this in 2015, C'mon surely you can fix this!!!!!!

SolidWorks 2016
Message 12 of 12
Curtis_Waguespack
in reply to: sumayo


@sumayo wrote:

Still doing this in 2015, C'mon surely you can fix this!!!!!!


The OP's dropbox link no longer works. We need a detail, and a data set to look at, otherwise....?

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