Help creating an assembly

[IbrahimTayyab]

I am trying to replicate a curved scissor mechanism from an old purse (image named open and closed below), I am having some trouble connecting the assembly particularly the translation for the curved parts (image named translation below) , it is working fine with the non-curved version as I selected the bottom and top surfaces respectively. With the curved versions even when I attempt to define unique planes for the translation it does not seem to work, I assume it is due to a problem with the geometry I have defined.

I would really appreciate it if the error that I have made can be pointed out, I am attaching the files below.

Best,
Ibrahim Tayyab

[IbrahimTayyab]

Fearing I might have not described the issue succinctly, I will summarise it here: I am unable to make a pin connection for the curved part on the end holes. Picture attached. I would appreciate any and all feedback.

[IbrahimTayyab]

As an update, I was able to make the assembly using a mixture of other constraints however they are not reliable. Some parts seem to overlap when I reopen the file and this was not the case when I defined the assembly.

 

Also when I view the sub-assemblies they no longer seem to hold their shape when the file is re-opened in a new session. (they should look like a section of the assembly above). 

The assembly does seem to work as I intended to however I think the method I applied is not reliable, I would appreciate methods to improve this. Files attached below.

As an addition, I defined each connection manually even though they were the same connections, I am not sure how I could have used creo to automate this, any and all suggestions for that are most welcome.

[pausob]

Not able to open your files as I am still using Creo 4.

But I had a quick go at this, and I defined the kinematic structure in this way:

Each link placed by a pin joint.

then the connecting links that complete the "x" are assembled, each with 2 additional spherical connections that link 2 of the previously laid out links above:

Note after this is all done, the whole assembly is not moveable.

But modifying the radial distance effectively closes or opens the "scissors":

So this construction requires regeneration to update, but you could build on this idea and devise a 1-input mechanism that makes it possible to "drag" the mechanism around.

However, I do suspect the actual device has slop in the "pin joints" which allows the extra degree of twist required (or the links themselves twist a little) - because the angle of the "pin" axis between the adjacent links changes as this device opens and closes - here it is illustrated by drawing the surfaces of the next link in the open position (green) vs closed position (red):

(this is done with straight links, so not sure whether using curved links would solve this)

Anyway, hope this gives you some clues, and thanks for showing this neat problem.

[IbrahimTayyab · Accepted solution]

Thank you very much, it definitely gave me a lot more think about and made me consider new approaches. 

For posterity, I figured out how to do the pin constraint for the curved features using a datum point, which works very well. 

 

http://support.ptc.com/help/creo/creo_pma/usascii/#page/assembly%2Fasm%2Fasm_four_sub%2FAbout_Predefined_Constraint_Sets.html%23

You are correct is seems it is not possible to change the diameter by dragging.

I am attempting to make a surface that curves in 2 axes instead of one and seeing how that affects the "dragging" and also because I realised my previous attempt was incorrect.

So far the problems that I hoped to resolve by posting this have been resolved, again thank you for your help. I will update this with the complete assembly once I am able to complete it.

Wishing you a great day,
Ibrahim Tayyab