Stop

Sliding mass with hard stop and Stribeck friction

Library

Mechanics/Translational/Components

Description

This element describes the Stribeck friction characteristics of a sliding mass, i.e. the frictional force acting between the sliding mass and the support. Included is a hard stop for the position.

The surface is fixed and there is friction between sliding mass and surface. The frictional force f is given for positive velocity v by:

    f = F_Coulomb + F_prop * v + F_Stribeck * exp (-fexp * v)

The distance between the left and the right connector is given by parameter L. The position of the center of gravity, coordinate s, is in the middle between the two flanges.

There are hard stops at smax and smin, i.e. if

    flange_a.s >= smin and flange_b.s <= smax

the sliding mass can move freely. Where flange_a.s and flange_b.s are the positions of the left and right connector.

When the absolute velocity becomes zero, the sliding mass becomes stuck, i.e., the absolute position remains constant. In this phase the friction force is calculated from a force balance due to the requirement that the absolute acceleration shall be zero. The elements begin to slide when the friction force exceeds a threshold value, called the maximum static friction force: F_Coulomb + F_Stribeck.

Remark: Index reduction might eleminate position and velocity of this element as states and the model will not work. To avoid this any inertias should be connected via springs to the Stop element, other sliding masses or dampers must be avoided.

Parameters

    Stop_0

  • smax [m] : right stop for (right end of) sliding mass (smax): Scalar.
  • smin [m] : left stop for (left end of) sliding mass (smin): Scalar.
  • m [kg] : mass of the sliding mass (m): Scalar.
  • F_prop [N/(m/s)] : velocity dependent friction (F_prop): Scalar.
  • F_Coulomb [N] : constant friction: Coulomb force (F_Coulomb): Scalar.
  • F_Stribeck [N] : Stribeck effect (F_Stribeck): Scalar.
  • fexp [1/(m/s)] : exponential decay of Stribeck effect (fexp): Scalar.
  • mode_start [-] : Initial sliding mode (-1=Backward,0=Sticking,1=Forward) (mode_start): Scalar.
  • L [m] : length of component from left flange to right flange (= flange_b.s - flange_a.s) (L): Scalar.

Ports

  • Port 1 at left position: implicit input fixedport numbered 1.
  • Port 1 at right position: implicit output fixedport numbered 1.

See Also