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MR_107757274-Participant
4-Participant
January 27, 2025
Question

Partially Constrained vs Fully Constrained in Assembly

  • January 27, 2025
  • 2 replies
  • 1883 views

Tried to research this and found other posts but no results listed.  Using CREO Parametric 10.0.4.0


In an assembly, I have 10+ components assembled and always try to fully define the constraints.  As I am adding additional components and constraints towards the end of the design (hardware) I start getting "Confirm Package Reference" which to me indicates another assembly component is not fully defined.  I can click "Use Ref" and move on but want to resolve the unconstrained component that I am assembling new parts to.

 

Looking back at the assembly tree, I see component #10 has a small box indicating it is not fully constrained.  I click to edit constraints, and the Set Status says "partially constrained".  Yet I have three constraints (coincident/distance/distance) that should fully constrain the part/subassembly.  So I uncheck "Set Enabled" and create a new set.  Using similar constraints, I get the status to read "Fully Constrained". Close out the component placement and the assembly tree still treats this as an under constrained component.


I finally deleted both sets of constraints and redefined 3 constraints identical to the first set.  The part now displays as fully constrained as expected.  Now I have a handful of other components in this assembly with similar issues. 

I also see several shafts with two constraints and "Allow Assumptions" checked that are displaying as under defined.  I know this is not normal, it should be fully defined with two constraints and the system accepting that the axial orientation does not require a third constraint.

 

One other point of interest, in cases where I see enough constraints to fully constrain a part, there is typically a distance constraint that has a fixed value, either zero or some numeric value greater than zero.  However, the display dagger allows me to move in that axis as though a distance constraint was never set and displaying the component out of place.  Clicking OK will moved the component to the correct distance, but still suggest that this component is not fully constrained.  Most of the time that I setup constraints this way, they perform as expected.  Now I am beginning to see where I am getting mixed results when I use the same work flow to constrain these parts.

Why are CREO assemblies so inconsistent with how they compute fully defined vs under defined?  This is really annoying, and wastes hours of my time attempting to resolve.  For all I know, the "fixes" I made today will be under constrained again tomorrow.

2 replies

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MikeBennett16-Pearl
16-Pearl
January 27, 2025

Hi @MR_10775727 

 

I think some visual components or data examples will help the community to better understand your post and to help address the inconsistencies in the constraints.  Surely this is more complicated than cube-cube 3 coincidents or peg in hole insert-coincident-assumed align.  The component 3D dragger (3 axes/planes/rotations) should help to indicate any underconstrained components during assembly.

 

I strongly recommend against the Allow Assumptions box.  It allows you to put trust into a program and when it fails to assume what you want it to assume, the program gets blamed and requires more time to correct than it would originally take to place that constraint.  It is especially important when there are more components depending on the assumed constraints.  Hardware may be ok to assume, but I have experienced assembled fuel tanks which have a desired upward orientation become flipped upside down when assumed assembly on different sides of the vehicle.

M
MR_107757274-ParticipantAuthor
4-Participant
January 27, 2025

Thanks for your explanation.  I could add screen shots but after spending hours finding a work around I can't currently supply them.

This was very basic prismatic constraints like planes being coincident-distance-coincident.  When I would edit constraints to look for solutions, the dragger would show one degree of freedom.  I could drag the position as if one degree of freedom existed and the part would freely move in one axis only and remain 4" out of place.  Once I clicked OK to accept the original constraints, the component would pop back into the constrained position but still showed up as Partially Constrained.

Thanks for the feedback on Allow Assumptions.  I only use this for things like pins and bolts that don't required a fixed position along one axis (ie bolt centerline).

tbraxton
22-Sapphire II
tbraxton22-Sapphire II
22-Sapphire II
January 27, 2025

Creo is most likely constraining exactly as the user has instructed via the UI. As mentioned previously assumptions can be unpredictable (e.g. normal directions get flipped). Use the drag components options and look at the dragger in the graphics window, it will indicate what DOF remains unconstrained for any given constraint set.

 

tbraxton_0-1737993421968.png

 

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MR_107757274-ParticipantAuthor
4-Participant
January 27, 2025

Thanks for taking time to respond.  The dragger would indicate a DOF in one axis and allow the component to move (even thought three prismatic constraints should have eliminated all DOF).  Once I clicked OK, the part would snap back into position like all DOF had been defined.  However it would continue to show up as Partially Constrained.  If I see this in the future I can attempt to grab screen shots.

Catalina
CatalinaCommunity Manager
Community Moderator
February 11, 2025

Hi @MR_10775727,

I wanted to see if you got the help you needed.

If so, please mark the appropriate reply as the Accepted Solution or please feel free to detail in a reply what has helped you and mark it as the Accepted Solution. It will help other members who may have the same question.
Please note that industry experts also review the replies and may eventually accept one of them as solution on your behalf.

Of course, if you have more to share on your issue, please pursue the conversation.

Thanks,

Catalina | PTC Community Moderator
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