Brake based on Coulomb friction
Mechanics/Rotational/Components
This component models a brake, i.e., a component with two rigidly connected flanges (left, right) where a frictional torque is acting between these flanges and a housing (bottom). A controlled normal force (top) presses the flanges to the housing in order to increase friction.
The normal force fn has to be provided as input signal f_normalized (top) in a normalized form (0 <= f_normalized <= 1), fn = fn_max * f_normalized, where fn_max has to be provided as parameter. Friction in the brake is modelled as COULOMB friction.
When the relative angular velocity of the flanges with respect to the housing is not zero, the friction torque is a function of the friction coefficient mue_pos, of the normal force fn, and of a geometry constant cgeo which takes into account the geometry of the device and the assumptions on the friction distribution:
friction_torque = cgeo * mue_pos * fn .
When the relative angular velocity of the flanges becomes zero, the elements connected by the friction element become stuck, i.e., the absolute angular position of the flanges remains constant. In this phase the friction torque is calculated from a torque balance due to the requirement, that the absolute acceleration shall be zero. The elements begin to slide when the friction torque exceeds a threshold value, called the maximum static friction (stiction) torque, computed as:
stiction_torque = peak * cgeo * mue_pos * fn ,
where peak >= 1 is another parameter to be defined by the user.