Often times I create designs which are necessary to have a certain heiarchy for documentation but at the same time it limits how I can control movement and positions at higher levels of my design. By default open degrees of freedom (DOFs) in lower level assemblies do not carry higher into the next level of the assembly. This can be the open degrees of freedom on an unconstrained component or a component with constrain limits (Inventor 2011 and newer). First iff we must decide if the movement is necessary at a higher level. So here is a common flowchart for use by engineers to help decide movement options.
Okay in all seriousness, if we do need to have movement at a higher level of the design we have to perform a status change to the subassembly called Flexible. Before we look at that, lets take a loot at Limiting Constraints.
Limiting Constraints are used in any of the Assembly type constraints such as Mate, Insert, Tangent, and Angle. The settings allow you to grant movement through a range of offset values and even set a resting value for the offset.
Once this particular example is applied there will be movement of 12 inches of travel between the 2 inch minimum and the 14 inch maximum. If the resting postion was set as the offset when ever the cylinder is moved it will snap back to 8 inches when released. A visual indicator will also let you know that the constraint is limiting with a +/- in the browser for the constraint.
Now in order to use this freedom at a higher level we have to make the assembly flexible to use this movement, otherwise when pulled on at the top level or when attempted to be used in a Positional Representation, the model would not move. (Note: Weldments cannot be made flexible, don't do it).
Right click on the assembly and choose the option in the list to make it flexible. A status icon will appear in front of the assembly letting you know that the setting has been enabled.
This has to be done for every level up you want the movement to be available. So in this next image you can see the CylinderAssembly is flexible in the Arm-Assembly but in order to use it at the top level the Arm-Assembly also has to be made flexible.
Now this design can be used in Positional Representations (we'll cover that another day) to show movement of the cylinder at different positions of the arm. We didn't even need to break out the WD-40!
Now if you need the Duct Tape, that is your Grounded status. That will remove all degrees of freedom and keep your design static in its current location. A nice advantage to grounding is that if a component never needs to move again, you can remove the constraints and Inventor will work a little faster. Some designs that use Origin based modeling use Grounded states exclusively and have 0 constraints! That is pretty awesome on the performance side.
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