MechDesigner Reference & User Interface > Dialogs > Dialog: Function-Block: Spring

Spring FB

See Add Spring FB

Use a Spring FB to apply a force between two Points. The name that we use for the two Points is Anchor-Points.

Force units are defined in the Machine-Settings dialog > Engineering Units - default Force units are Newtons (N).

How to open the Spring FB dialog

MD-GA-Spring-Edit

In Mechanism-Editor:

1.Double-click the Spring-FB in the graphics-area

1.See How to Open a dialog

Note: It is not necessary to connect a wire to the input-connector or from the output-connectors of the Spring FB. The input and output-connectors provide extra functionality - see Here

The Spring dialog is now open.

Spring dialog

Spring FB dialog

Spring Parameters

☑ Check-box to enable the Spring FB.

Spring-Rate:

Force Contribution:

= Spring-Rate × | Spring-Length – Free-Length |

Spring-Length is the distance between the two anchor-points.

The Force always tries to move the anchor-point to the Free-Length (They cannot, of course).

Free-Length:

The natural length of the Spring, when it is not joined to the Anchor-Points.

Constant-Force:

A positive force PULLS the Anchor-Points together (o>>> + <<<o)

A negative force PUSHES the Anchor-Points apart (o<<< — >>>o)

Velocity Parameters

Coulomb (Constant) Friction Force (Ff = μ.Fn )

A Constant Force that is opposite to the direction of the motion.

You can use it to approximate a Friction-Force.

Note: Friction Force is NOT constant in general. Friction-Force is proportional to the Contact-Force between two bodies, and the Contact-Force is not generally constant.

Viscous Coefficient (Fv α V ( N/(mm/s) )

A Force that is proportional to the relative velocity between the Points.

The Force is opposite to the direction of motion.

For example, if the Damping Coefficient = 4 and the Velocity is +100mm/s, (anchor points moving away from each other), the force pulling the points together is a force of 400N.

Drag Factor (Fd α V2) ( N/((mm/s)2 ) )

A Force that is proportional to square of the relative velocity between the Points. For example, air resistance.

The Force is opposite to the direction of motion.

For example, if the Drag Factor = 4, and the Velocity = +100mm/s (anchor-points are moving apart), then the force pulling the anchor-points together is a force of 40000N.

Input and output-Connectors

Output-Connectors

The Spring-FB has two output-connectors.

Top :

Distance, Velocity, Acceleration of the dimension between the anchor-points.

Bottom :

Total Force, Force-X, Force-Y acting on anchor-points.

Driving-Force = Linear Motive Force, if you configure the Spring FB as a Linear Motor - see Configure Power Source

Input-Connector - see more at Spring FB dialog

The Spring-FB has one input-connector.

Connect a wire to the input-connector of a Spring FB to add a Force-Function to the Total-Force that is exerted by the Spring-FB.

The units of the data-values at the input-connector must be Force, for example, Newtons.

If necessary, use a Math FB to convert values and units to Force units.

For example: To convert 100mm at the input to a Math FB to 100N, you must:

1.Change the Output Data Type to Force (N) - see Math FB dialog > Output data-type

AND

2.Multiply the input-value by 1000 to convert 0.1m to 100N