Mass with stops

Mass with Coulomb and viscous friction and hard end stops.

  • translational
  • Modelica Standard Library
  • 2 ports
  • 7 parameters
BlockMass with stopsKindmassStopsLibraryTranslational

Description

A sliding mass with viscous, Coulomb, and Stribeck friction against the frame, limited to travel between two hard stops. The mass sticks at zero speed until the net force exceeds the breakaway force.

Reaching a stop is fully inelastic: the position is clamped to the stop and the velocity is reset to zero.

Example

End stops and motion sources A sliding mass that hits its stops, a mass pushed into an elastic stop, and masses driven by speed and position sources.

20 sin(πt) NForce sourceMass with stopsPosition (stops)Push 10 NMass 1 kgElastic stopStop at 0.1 mPosition (elastic stop)0.2 m/sSpeed sourceMass 1 kg (speed)Velocity (speed source)0.1 sin(πt) mPosition sourceMass 1 kg (position)Position (position source)
In Gradara, select a Mass with stops block and press F1, then choose Open example. It opens as a new model in My models, ready to run.

Also in this example:ConstantSine waveFixed (translational)MassHard stopForce sourceConstant forceVelocity sourcePosition sourcePosition sensorVelocity sensor

Ports

Conserving terminals 2

  • aflange_atranslational

    Flange a. Force into the flange is positive.

  • bflange_btranslational

    Flange b, at the same position as flange_a.

Parameters

  • Massm1 kg

    ≥ 0

    Mass, in kilograms. Zero or positive.

  • Upper stopsmax0.5 m

    Upper stop position, in meters. Must be greater than smin.

  • Lower stopsmin-0.5 m

    Lower stop position, in meters.

  • Viscous frictionF_prop1 N·s/m

    ≥ 0

    Viscous friction coefficient, in N·s/m. Zero or positive.

  • Coulomb frictionF_Coulomb5 N

    ≥ 0

    Constant (Coulomb) friction force while sliding, in newtons. Zero or positive.

  • Stribeck frictionF_Stribeck10 N

    ≥ 0

    Extra friction force at low speed, decaying with speed, in newtons. Zero or positive.

  • Stribeck decayfexp2 s/m

    ≥ 0

    Decay rate of the Stribeck term, in s/m. Zero or positive.

Equations

Modelica
m · dv/dt = flange_a.f + flange_b.f − f, with v = ds/dt
Sliding forward: f = F_prop · v + F_Coulomb + F_Stribeck · e^(−fexp·|v|)
Sliding backward: f = F_prop · v − F_Coulomb − F_Stribeck · e^(−fexp·|v|)
Stuck (v = 0): |f| ≤ 1.001 · (F_Coulomb + F_Stribeck); f follows from the force balance
At s = smin or s = smax: s is held at the stop and v is reset to 0

Implementation

Modelica Standard Library 4.1.0Modelica.Mechanics.Translational.Components.MassWithStopAndFriction
MSL documentation

Assumptions and limitations

  • The mass is a point; both flanges share its position.
  • Impacts at the stops lose all kinetic energy; there is no bounce. For an elastic stop, use Mass with Hard stop.
  • Initialization fails if the starting position lies outside smin…smax.

See also

Select a block in Gradara and press F1 to open its page offline.