Limiting a constraint to only one direction.

[dpiagno]

Hi, I'm relatively new to Inventor, so please forgive me if this question seems ridiculous but it's doing my head in at the moment!

I want to somehow limit a constraint on a part to only 1 direction. For this example, lets say its the Z-direction - so I would like the part to be able to move in the positive Z-direction, but not in the negative Z-direction. Essentially I want to perform the analysis on the part as if it were resting on the ground, but could bend upwards if force was applied in the right place.

Hopefully there's an easy solution I haven't come across yet in all my googling.

Thanks in advance for any help!

[admaiora]

Hi Dpiagno,

something like this?

[JavaLodge]

Are you trying to use FEA to simulate this?  You'll have to use different tools that contraints to do what you want.  It would help if you could post your assembly and associated files or at least a picture of it.

[johnsonshiue]

Hi! I am sorry that I might misunderstand the requirement. It sounds that you only want the component to move in positive Z direction. Wouldn't the component just keep moving far away from origin in Z+? Or, it has to be confined within a range within Z+ coordinate?

Many thanks!

[dpiagno]

Thank you all for your quick replies, much appreciated.

I apologise for not being more clear in my initial post.. I am indeed trying to model this in the stress analysis 'environment'. I've attached the example part file I'm playing around with. I'm trying to find away to constrain the model for stress analysis so that the two short ends can deform upwards if enough force is applied downwards in the centre from the top of the part (as I've begun to do in the stress analysis environment. I need to somehow model the two curved surfaces as being in contact with the ground, yet let them slide/rotate outwards (along the longitudinal axis) and also upwards, with the two inner contact point always touching the ground. Sorry if this makes no sense at all, hopefully the pictures and attached file help!

[TheCADWhisperer]

What is the material?

What keeps the part from rotating about the cylindrical axis?  Balance?

Is the force evenly spread over the entire planar face - or is it concentrated in certain location(s) (Split Face)?

I think you might need to do this as an assembly.

What does the mating part look like?

[dpiagno]

Hi,

The material can be any type of plastic I guess, something relatively ductile - I've just made this shape up to try and explore what Inventor can do and teach myself a little.

I was trying to model the force as a point force in the centre (not distributed across the whole top face) and with balance keeping it from rolling/rotating, though I was reading about the frictionless constraint option in Inventor that will stop it from rotating, which I could apply to the longitudinal edges I think.

[JDMather]

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@dpiagno wrote:

Hi,

1. The material can be any type of plastic I guess, something relatively ductile - ....

2. I was trying to model the force as a point force in the centre (not distributed across the whole top face) .....

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1. Inventor FEA (linear) valid results limited to reletively small displacements.  I think your force might be too great.

2. P=F/A  As A approaches zero, P approaches infinity. In the real world how is the force distributed?

I will try to remember to post an example later today using your part (in an assembly with a "ground").

Check back - or try it yourself.  (You can use the Frictionless Constraint on one or two sides to balance.)

I will be doing a class on FEA at AU this year.  Anyone with simple problems like this one - please post problem description.

https://events.au.autodesk.com/connect/sessionDetail.ww?SESSION_ID=6583

[dpiagno]

Thanks! I'll check back in a day or so.

[clo-z-nuff]

Huh, I have the exact same question.  I would like to be able to let a table leg (for example) slide on the floor or lift off of the floor but not go "into" the floor.  In other words, the only direction it can be constrained from moving is down (or -Z).  Can this be done with the Fixed Constraint using Vector Components somehow?  I'm afraid I don't quite understand how the Vector functionality works in the Fixed Constraint Stress Analysis environment.

[swalton]

I think you could get what you need by adding a very stiff "floor" part to your analysis.  Use the separation constraints between the feet of your table and the "floor" part.  Use fixed constraints to hold the floor in place.  You can hide the "floor" in your results too.

The vector components of the fixed constraints let you specify how far those surfaces move.  You might use this to see the stresses on a cantilevered beam that is deflected by 12" at the free end.