Rotational joint friction issue

Greetings,

I have a technical question regarding SimMechanics 2G rotational joints.

We are modeling a mechanical unit with help of the Contact Forces library, and on several spots, we would like to model a spherical roller bearing joint between two frames. From the bearing's technical sheet, we know its dimensions and its coefficient of dynamic friction. However, while configuring the rotational joints in SimMechanics, we found out that the internal mechanics only allows us to specify a stiffness and damping parameter.

So the question stands, how do we "translate" the coefficients of friction into the damping and/or stiffness parameters correctly?

Thanks in advance.

Answer 1

[Sebastian Castro]

Friction is not quite the same as pure damping, and is usually a slightly more complicated function of velocity -- especially if you're considering static and dynamic friction.

The most common thing would be for you to measure the velocity of the joint, perform the friction computation with Physical Signals blocks, and apply the force/torque back in as an input to the same joint primitive. I saw Physical Signals blocks because if you use Simulink blocks you'll get algebraic loops.

If you want, you can even interface the joint in this way to the Simscape Translational or Rotational Friction blocks using the Simscape-SimMechanics Interface blocks.

If you're concerned more with coefficient of friction under variable loading, then that would become another factor in your computation that you can probably measure from your joint's constraint forces (forces that act outside the allowable direction of motion). Similarly to the friction case above, there is a SimDriveline block for modeling Loaded-Contact Friction.

- Sebastian

[N/A]

Hi Sebastian, is there any tutorial/example on rotary friction block implementation in SimMechancis 2G?

[Sebastian Castro]

Yes, you can use the Simscape-SimMechanics Interface blocks on the File Exchange to do this.

The simplest case would look as follows, where you can leverage the Simscape Rotational Friction block.

- Sebastian

[mohamed omar]

@Sebastian Castro

Hello, please if I want to model friction of revolute joint but between two moving links, with actuation