topic Gasspring simulation and force calculation in Inventor Forum

Gasspring simulation and force calculation

Wapster — Sat, 04 Feb 2017 17:29:51 GMT

Hi,

I've been on this all day with Wasim's books, tutorials and so on but can't figure it out

I'm working on a hinge system, with a panel that needs to be lifted up by a gasspring.

The centerline of the gasspring is placed behind the pivot point of the rod which connects to the panel.

This way, the panel is kept in place (down) by the gasspring as well

To let the gasspring lift the rod (panel), the centerline needs to get past the pivot point.

To make this happen, the panel needs to be pulled out by hand first. Not much, just enough to get past the pivot.

Than the gasspring needs to take over and push the panel up.

To order the correct gasspring (pressure) and to find out if the force needed to pull out the panel by hand is not to big, I tryed to use Dynamic Simulation.

I'm sure i'm doing something wrong cause i'm not getting the results i need.

Is there someone here who can tell me the best approach, or point me in the right direction.

All help is appreciated.

I broke it all down to a very simple assembly and attached the files (IV 2016)

So where i'm after is the force (pressure) needed to lift the rod (panel) and the force (hand pull) to overcome this pressure (and the weight of the panel (200N)) in the gasspring.

Thanks in advance.

Wap

Re: Gasspring simulation and force calculation

TheCADWhisperer — Sat, 04 Feb 2017 21:44:08 GMT

I keep running into an issue that I think is more of a geometry/mathematics anomaly where everything is perfectly aligned, but not possible in the real world.

To bad there isn't anyone from Autodesk who will enter discussions on professional use of their software anymore (they are all too enamored with their Fusion infant to get involved in professional software discussions).

Re: Gasspring simulation and force calculation

Wapster — Sun, 05 Feb 2017 20:33:52 GMT

Thank you JD for taking the time to respond to my question.

I watched your screencast and it helped me out a lot.

I've been working on the problem all day again and i think i have a found (sort of) a solution.

If we use the unkown force option with the revolution1 angles for kinematics, at a certain moment the gasspring comes in line with the pivot point.

I understand that the straight axial force becomes so high (your spike in the grapher) that IV has a problem with it.

This indeed is imposible in real life because the force can not be applied to the gasspring this way (for the system to work)

I tryed to do an imposed motion (position) on the prismatic joint using the input grapher going for A to B (inward) and then from B to C (outward).

This also doesn't work because when the straight line is reached, the rod then can go either left or right (and of course it goes the wrong way) and you still end up with a spike because it's impossible to drive the system this way in real life.

So what did i do.....

It's all an approximation but i think (hope) i'm doing it right.

First i position the rod out a bit as one would do when pulling the panel towards you in real life.

The straight line of the gasspring is now past the pivot point.

I do this by setting the revolution1 joint to -120 degrees.

I then use the unkown force option and drive it back to zero degrees using the revolution1 kinematics or 285 mm using the prismatic6 kinematics.

The outcome for both is the same (under 650 N)

I then use revolution1 to set the panel back to it's start position. -143 degrees.

I then put a 650 N force on the gasspring, which should be enough to push the panel up (from the 120 degree angle)

Then i apply the unknow force again using the revolution1 angle from -143 to to -120

The outcome is about 94 N.

Next i apply this force to the panel (bracket), give the the prismatic6 joint a small damping and run the simulation.

So.... I applied 3 forces.

1 force of 100N pulling the bracket to the side (in real life this is done by hand)

1 force of 650N pushing the gasspring out (the gasspring takes over when de angle reaches -120 degrees)

1 force of 160N pulling down (the weight of the panel)

My question to you...

Is this a correct approach (assuming you follow me of cource )

I've put 2 extra part in the assembly, making it more clear.

I also made a screencast (have to buy a good mic. so no sound sorry)

Hope to hear from you.

Thanks again,

Wap

Re: Gasspring simulation and force calculation

Wapster — Sun, 05 Feb 2017 21:07:20 GMT

Sorry, wrong files....

These are the correct ones