Friction coefficient dynamic simulation

[alessandro.plebaniFM42P]

Hello everyone!

I have a question about the friction coefficient in a dynamic simulation. I'm trying to simulate a very basic example to understand all the parameters involved. The scenario is a simple cube sliding on a fixed base with a prismatic joint. I add a force perpendicular to the sliding plane of 100N and apply a dry friction coefficient of 0.5. I set a constant speed movement.

After the simulation, I expect to find an imposed driving force (U_imposed) equal to 50N (100 * 0.5), but instead, I find a value of 1.4N.

...I don't understand it...

[JoshuaNAM]

If all is well inventor also creates a spatial joint. Define all settings in the spatial joint and keep the settings of the prismatic joint all empty. The prismatic joint also only gives one DOF but you you need at least two. The downforce of 100N and a constant horizontal movement. Therefor the prismatic joint is not giving you the options you need. I rebuilt your model and I get a 50N U_imposed as expected.

I hope this helps you out a bit.

Kind regards, Joshua

[alessandro.plebaniFM42P]

Dear Joshua, thanks for your feedback!

I followed your instructions but I get a U_imposed of 0N. I added a spatial joint and set the dry friction coefficent, I set all the prismatic joint parameters to 0, but the result is a U_imposed of 0N

How did you set the spatial joint?

Thanks!!!

[JoshuaNAM]

Hi Alessandro,

You need to have the orientation arrows of both parts pointing in the same direction. Of the square block your Z-direction is pointing downwards, try to flip this so that it also points upwards.

I hope you'll get it to work now. Good luck.

[alessandro.plebaniFM42P]

Nothing... I haven't had any luck. I've tried everything. Any orientation... nothing changes. I'm starting to think there might be a bug... I'm using Inventor 2025.

Thank you very much for your information!

[JoshuaNAM]

I can have a look at your model if you want? I'm running 2024 so then we can see if that makes a difference.

[alessandro.plebaniFM42P]

Hi Joushua,

I tried to do the assembly with Inventor 2024. In the attachment, you can see the file. The result, with a dry friction coefficient of 0.5 and a force of 100N, shows that the U_imposed force from the joint is 25N.....I really not understand....

[JoshuaNAM]

Hi Alessandro,

I tried to find where you had put your force of 100N downwards but couldn't find it.

Then I tried to find the iam I previously made but couldn't find it either. Please find enclosed a new built assembly with your parts in it. I just used normal constraints in the assembly environment as I am more familiar with them.

When entering the DS environment first I go to the simulation settings and turn off "Automatically Convert....Joints" then when prompted I choose "remove automatic generated joints"

Then I add a spatial joint and a planar joint manually. The planer joint I don't edit, it just keeps the parts from moving through each other.

By the spatial joint I define the dry friction of 0,5 by dof6(T) and the imposed motion (see pictures).

Then by dof4(T) I set the downforce of -100N.

The simulation player is set to 1 sec. Then run simulation and in the output grapher you can see the U-imposed6 of the spatial joint giving you the expected 50N.

I hope this helps you out.

Kind regards,

Joshua

[JoshuaNAM]

Also don't forget to always define the gravity direction