Physical connection that enables tension transfer
Simscape / Driveline / Couplings & Drives
The Rope block represents an element that transfers tension between two contact points. You can treat it as an arbitrary tension transfer device to simulate a variety of situations, including pulley networks, cable drives, and serpentine belts. You can choose whether the block exhibits slack upon loss of tension. The block has a base port, B, and a follower port, F. The rope stretches in tension when the base port leads the follower port.
The block considers only the longitudinal translational motion and force of the rope ends. For the ideal case, the block is equivalent to the spring-damper or spring-mass-damper systems illustrated in the figures, depending on whether you choose to model the mass. These figures do not necessarily apply when you simulate slack.
Confirm that your model performs correctly with Rope model set to
Ideal - No tension. While in this mode, verify that
the B and F ports are oriented properly by
viewing the tension plots of each rope in the Simscape Results
Viewer and looking for unexpected negative values.
You simulate a rope with arbitrary physical properties by adjusting the block parameters. The Rope block can act as a belt, cable, or any other device that has tensile strength and transmits tension between two contact points. A contact point can be a pulley, a drum, or an ideal source.
The block is useful for modeling stationary or travelling pulley networks. You can drive the Rope block with sources like the Ideal Translational Velocity Source block, or a Rope Drum block attached to an Ideal Force Source block.
For greater fidelity or numerical stability, you can choose to model the effect of mass on
the system. When you set Model mass to
On, the block distributes half of the total mass to
either end of the rope. Adding even a small amount of mass can improve the
initialization of your model. You can also specify the initial conditions of the rope.
If you choose to simulate slack, the block will stop applying stiffness and damping when
the rope is no longer in tension.
The Rope block characterizes the external load at the base port as
and at the follower port,
where . The forces vary as functions of time and the stretch deformation, xs. Here, K and B are functions of xs, such that when there is no slack or you are not simulating slack. Otherwise, when slack occurs. That is, when . The same logic applies for B. Ignore the mass terms unless you are modeling mass.
The variables have the following meanings:
F is the tension force, where
K is the spring stiffness coefficient. when you set Rope model to
Model rope slackand .
D is the damping coefficient.
m is the total mass. This is equivalent to the Mass parameter. The block distributes half of the total mass to each end.
xB is the position of the base node.
xF is the position of the follower node.
xs is the deformation due to stretching. This is equivalent to the Stretch variable.
ẋs is the stretch velocity.
Use the Variables tab to set the priority and initial target values for the block variables before simulating. For more information, see Set Priority and Initial Target for Block Variables.
B — Base end of rope
Mechanical translational conserving port associated with the leading end of the rope.
F — Follower end of rope
Mechanical translational conserving port associated with the following end of the rope.
Rope model — Slack behavior
Ideal - no slack (default) |
Model rope slack
Option to model slack. By default, the rope will transfer force while in tension or
compression. When you select
Model rope slack,
the block stops transferring spring force when it is not in tension. The
Rope block in slack is equivalent to a
Translational Hard Stop block with
Upper bound set to
Lower bound set to
more information, see Translational Hard Stop.
Model mass — Mass parameterization option
Off (default) |
Option to parameterize mass. Setting this to
will cause the block to consider the mass of the rope segment that it
represents. Simulating mass can help initialize some models but can also be
more computationally costly.
Mass — Rope segment mass
kg (default) | positive scalar
Mass of the rope segment that the block represents. The block distributes half of the total mass to each end of the rope.
To enable this parameter, set Model mass to
On or set Rope model
Stiffness — Resistance to deformation
N/m (default) | positive scalar
Effective translational spring stiffness of the rope segment.
Damping — Tendency to dissipate energy in the system
N/(m/s) (default) | positive scalar
Effective translational damping of the rope segment. When you set Rope
Model slack and , the block ignores damping.
Slack model — Slack transition behavior
Stiffness and damping applied smoothly through
transition region, damped rebound (default) | ...
Stiffness and rebound options for the slack model. The slack model is equivalent to a Translational Hard Stop block. You can choose from the following options:
Stiffness and damping applied smoothly through transition region, damped rebound
Full stiffness and damping applied at bounds, undamped rebound
Full stiffness and damping applied at bounds, damped rebound
To enable this parameter, set Rope model to
Model rope slack.
Transition region — Region of partial slack effects
mm (default) | positive scalar
Distance from full compression or full extension where the effects of
stiffness and damping are partially applied. When you set Slack
Stiffness and damping applied smoothly
through transition region, damped rebound, the block will
smoothly transition the onset of stiffness and damping as the spring
approaches full extension or full compression.
To enable this parameter, set Rope model to
Model rope slack.
Maximum tension — Tension limit model
No maximum tension (default) |
Specify maximum tension
Option to constrain the maximum tensile force in the rope.
No maximum tension— Tension can be arbitrarily large during simulation.
Specify maximum tension— Tension must remain lower than a maximum value. If the tension exceeds this value, the simulation generates an error and stops.
Rope maximum tension — Maximum allowable tension force in rope segment
N (default) | positive scalar
Tension value error target. When the tension in the rope segment exceeds this parameter, the block will generate an error.
To enable this parameter, set Maximum tension to
Specify maximum tension.
Tension warning — Slack threshold notification
Do not check tension (default) |
Warn if rope loses tension
Generate a warning when the rope segment is no longer in tension. This setting can help you discover if your system experiences instances of slack.