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cmerani10-Marble
10-Marble
January 24, 2016
Solved

Mechanism flexible wire tray issue, similar to a chain

  • January 24, 2016
  • 3 replies
  • 13729 views

Hello all,  I have been a Creo user since proENGINEER 2001.  I have never run into an issue where I needed to accomplish this task and I have exhausted every work around I can think of and am looking for some advice on how you all would attack this problem.  Moderators, if this belongs in a different category, please feel free to move as you feel suitable.  See the attached pictures for a better understanding.

Basically I have a linear actuator attached to a beam. This linear actuator moves with a stroke length of 1500mm driving a drill head.  I have some snap together flexible wire tray that I want to show in the model and have mechanism correctly reposition it as the carriage moves.  The bottom side is stationary as you will see in the photos.  The other end is attached to the carriage (some detail is missing but the end bracket is constrained to the carriage).  I have attempted to make the connection multiple ways.

I have assembled the links with all pin connections which works, sort of.  The carriage can move but the tray acts incorrectly and dips below the bracketry with collision detection off.  With detection on it causes the carriage to bind up.

After giving up on this approach I decided to use a sketch that dynamically updates using a perimeter dimension and relations so that the path is correctly displayed.  I then attempted to use a series of pin joints on one side of each link with a slot on the second, rinse, repeat.  This causes the mechanism to fail however as the sketch becomes part of the ground body and wont allow the carriage to move.

I then decided, if I cant get the mechanism to work, maybe I can just get it to display and update position on regen.  At least I could take snapshots and animate this way.... I used Leo Greene's approach found here‌.  This also worked.... sort of.  It also causes the mechanism to fail and I no longer can move the carriage.  This lead me to try using a second sketch parametrically updated with relations by the first one (requiring 2 regens) but this still causes odd performance.

Any help or recommendations would be greatly appreciated! I have wasted way too much time on such a simple, insignificant issue but now I am determined to make it work.

PS, I am using Creo 3.0, Build M060.  I do have AAX.

sincerely,

Losing hair by the minute, Chris


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Best answer by TomD.inPDX

It was about time someone made this available...

Again, this is my way, and certainly not the only way.  Linking each link with 2 sets of constraints is a real pain.  Repeat and temporary assembly references don't seem to work when you have two separate constraints.

One of the gotcha's is the ground body reference.  When installing the chain to the mechanism, be sure to only constrain it with only the end piece references.

Obviously the point on curve I referred to earlier is a slot constraint.  Each link therefore has a slot constraint and a pin constraint.  The slot path does not require the shift|select... it is one of the few that you can pick multiple curves.

Video Link : 6677

Creo 2.0 commercial version attached

If someone cam make this work with patterned links... POST UP!

3 replies

D
dschenken1-Visitor
1-Visitor
January 24, 2016

I like the Leo Greene method for quick and dirty; but it doesn't accurately represent the polygon shape of fixed length links going around a sprocket. The big problem is the chain straight path isn't tangent to the polygons. A minor problem is the sag should be a catenary, not an arc.

I'm not sure there are good solutions in the Creo toolbox without a lot of programming, either with relations or by driving it externally via trail/training file.

Perhaps if PTC adopts the Bullet Physics engine?

Real-Time Physics Simulation

Bullet (software) - Wikipedia, the free encyclopedia

C
cmerani10-MarbleAuthor
10-Marble
January 24, 2016

Hi David.  Thank you for the response.  The concerns you have raised don't really apply to this issue.  I'm not too concerned with 100% accurate depiction of the physics related to the "chain path".  I am only concerned with making the mechanism connections that do not fail upon regen.  Even if I use the Leo approach which is sufficient for displaying the chain, I have to suppress that entire subassembly before I can dynamically move the carriage again.  This becomes a problem when attempting to generate an animation for the customer.  I can't use snapshots with this method as it causes the mechanism to fail and Creo wont let me even take snaps...

As far as PTC adopting another physics engine.... dont hold your breath.  I remember some years ago there was a bunch of hype about them adopting a new photorendering package.  I haven't seen any improvement in photorendering since WF3.  I will say however that I spent the last year working with Autodesk Inventor and boy am I glad to be back with Creo.  Although the photorealism stuff in inventor is way better than Creo, the way it handles modeling data, sketches, and assemblies will make you want to puke.

D
dschenken1-Visitor
1-Visitor
January 24, 2016

I've done much more complex animations via trail file. Change a dim, regen, then save image, repeat. Then collect the images into a video. Since everything is handled in the trail file, base geometry and camera moves can be automated as can fades on component appearances.

T
TomD.inPDX17-Peridot
17-Peridot
January 24, 2016

It is possible to do this.  I've needed this in a few instances already.

You want to use paths to drag the chain along, however you make the chain assembly.

Behind the scene, you need to make the path "skeleton" (rotated U-shaped curve) move with one end of the chain fixed in the assembly.  This will push and pull the floating end.  Done properly, you can fix the moving end to your moving body and all will stay connected.

Make snapshots for quick resets.  Be patient... this is fairly CPU intensive.

C
cmerani10-MarbleAuthor
10-Marble
January 24, 2016

Antonius, Thank you for your reply.  I think what you are describing is one of the methods I attempted.  Would it be possible for you to elaborate on this a bit? I am quite patient with Creo.  I have a pretty stout system but over the years I have learned that sometimes its best to hit regen, get up and get a drink and come back.

Patriot_1776
Patriot_177622-Sapphire II
22-Sapphire II
January 25, 2016

Nice work! 

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