Inventor General

## Inventor General

Valued Contributor
Posts: 95
Registered: ‎02-08-2011
Message 1 of 6 (305 Views)

# Positional Representation Assembly - Flippin' Problem

305 Views, 5 Replies
10-05-2012 07:42 AM

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

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

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Posts: 871
Registered: ‎02-16-2006
Message 2 of 6 (297 Views)

# Re: Positional Representation Assembly - Flippin' Problem

10-05-2012 08:07 AM 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.

Valued Contributor
Posts: 95
Registered: ‎02-08-2011
Message 3 of 6 (284 Views)

# Re: Positional Representation Assembly - Flippin' Problem

10-05-2012 01:25 PM 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!

Mentor
Posts: 177
Registered: ‎12-27-2003
Message 4 of 6 (261 Views)

# Betreff: Positional Representation Assembly - Flippin' Problem

10-06-2012 04:02 AM 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:

Valued Contributor
Posts: 95
Registered: ‎02-08-2011
Message 5 of 6 (254 Views)

# Re: Positional Representation Assembly - Flippin' Problem

10-06-2012 04:46 AM in reply to: pompeo79

Great reply Walter ! ! !    thank you ! !

That's the answer that i was wainting !

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

Valued Contributor
Posts: 95
Registered: ‎02-08-2011
Message 6 of 6 (250 Views)

# Re: Positional Representation Assembly - Flippin' Problem

10-06-2012 04:56 AM in reply to: pompeo79

Nice paper-style inv background

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