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글 편집
글 편집 (이전 에디터)
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*The joint friction equation is very complex. So in this article, the joint friction will be explained intuitively rather than precisely. (So the explanation in this article can be a little different from the equation which is really used.) You can refer to the manual for the detailed joint friction equation.
In RecurDyn, there are check boxes to select sliding and stiction in Joint Friction dialog (Sliding & Stiction type).
Usually, it is okay to use the default setting, but some users may be curious what they are for.
It's better to show joint friction graph than to explain it in detail.
In the below graph, each option corresponds to curve of different color.
Blue: Sliding & Stiction are checked both
Green: Only Stiction is checked
Red: Only Sliding is checked
In other words
1. Sliding & Stiction use both of static friction coefficient and dynamic friction coefficient. So the friction coefficient changes according to the velocity.
2. If only Stiction is checked, only static friction coefficient is used. (For the continuity of the curve, the friction coefficient can change in the very slow period.)
3. If only Sliding is checked, only dynamic friction coefficient is used when the velocity is faster than Absolute Threshold Velocity, and the static friction coefficient is not used.
(Velocity means the relative velocity between base marker and action marker of a joint.)
Below graph has the adjoint lines to help your understanding.
Only velocity was considered to decide the friction coefficient above.
But the distance between action/base markers of the joint is used to decide the friction coefficient.
In an extreme case, the friction coefficient curve can be shown as the below left curve.
(But usually, it is shown as the below right curve.)
Basically, the static friction coefficient is used when the velocity is reached to Absolute Threshold Velocity.
But this parameter, Maximum Stiction Deformation is used to use the static friction coefficient even if the velocity is slower than the absolute threshold velocity.
In reality, the velocity of the stationary body must be 0..
But in numerically, it it very difficult to achieve the zero velocity, so the distance between action and base marker of a joint cannot be zero.
Conceptually speaking, if the distance between them increases while the velocity is slow (slower than the absolute velocity), the maximum friction (Static friction coefficient) is applied to control it. (of course, the velocity affects the friction coefficient.)
You can refer to the below paper. Even if it is about contact friction, it is very similar to the algorithm of joint friction.
https://link.springer.com/article/10.1007/s12206-011-0504-y
