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Multiple sub-assembly connections failure.

pkane
1-Newbie

Multiple sub-assembly connections failure.

Hi All,

Apologies in advance, I am not sure if I am posting in the right category.

I am looking for some advice as to how to solve this problem I am experiencing with adding multiple sub-assemblies to an  assembly.

Please refer to picture for reference.

I have a master assembly with sub assembly A constrained in the default position in the top level. I have a second sub assembly B  fixed in position in the top level assembly aligned with sub assembly A. There is a drive rod ( C) which is constrained as a slider in the top level assembly as is connected at either end to  mechanisms within both A and B. The connections to A and B are defined as general coincidental constraint sets additional to the slider contstraint for C. ( Fig 1.)   The movement of C actuates mechanisms  within A and B (See Fig 2.) to have protusions extend out from A and B. This Assembly works as intended, moving C back and forth (by dragging)  lifts and lowers the blocks ( red triangles)  smoothly and without any issues.

The blocks have adjustable height ( amount they protrude) and this is controlled in the top level assembly  by adding a connection at part level in sub-assembly being a fixed height from the datum plane in the top level. Sub Assembly B also has a part level connection of fixed height to the top level datum plane. ( Fig. 3)  Modifying the the position of the the datum plane ( red line) adjusts the block height . This all works as intended.

The problems arise when I add a second sub-assembly B.( Fig.4)  It is the sames as B but just rotated 180° to the other output from A. Beacause of the part level constraints to top level constraints in the first Sub assembly B, when constraining the second sub-assembly B it throughs up a dialogue box " This feature has external dependancy created in another location of this assembly, with redefine feature in original or current location as options. Both  of these options if executed cause the model to fail. normally by disabling the one or both of the connections of B to the top level datum plane (red line.)

1.PNG
I dont want to create family table members of B and define different constraint sets for each, as I want the model tree and BOM to show the same sub assembly B being used. Also there could be an infinite number sub assembly B connected in line,

I have looked at making sub assembly B flexible, and calling up different part level ptc_constraint_set definitions but this hasnt been succesful in reaching the assembly intent.

Any assistance would be appreciated. Thanks.


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3 REPLIES 3
danderson
11-Garnet
(To:pkane)

Paul, the issues you are running into might be related to having a regen value set in a mechanism sub assembly. Multiple sub assemblies cannot regenerate at the top level assembly to 2 or more different states at the same time. Better to only use regen values in top level asseblies and use snap shots at the sub assembly levels.

Hope this helps,

Don Anderson

Hi Don, Thanks for the reply. There are no regen values set for the mechanisms, I have had issues before with setting regen values, they seem to make modelling less than stable. I can use snapshots but I would prefer to have the model be flexible due to the possibility of adding more(infinite) sub assembly B to the master. This would mean require infinite number of snapshots required.

danderson
11-Garnet
(To:pkane)

Paul,

If you are driving the sub assemblies with top level assembly features(assembly level created datum planes, etc.), make sure you are only driving from one assembly reference.  All sub assemblies need to balance out (positions need to have same dimension) and rounding of dimensions can cause an issue.

Example: you can't have all of the sub assemblies connected and driven from 2 different top level assembly datum's to control position at the same time.

Also verify that your limits for movement at the sub assembly allow movement in the required direction.

You can use one snap shot to everything, just have one state with everything active when you create (add joint axis) and update the snapshots.

You can use the snapshot as long as it's the same name as the rep. The missing joints just become inactive.

Hope this helps,
Don Anderson

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