The spring allows you to connect two parts together
within your biomechanical model using a standard damped spring that you can
find described in any physics textbook. The mathematical description for this system is shown in equation 1.
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| Figure 1. Standard mass-spring-damper system |
K is the stiffness of the spring. Delta x is the displacement of the spring from its resting length.
B is the damping coefficient, and v is the velocity of the mass. So the spring exerts a force
that is proportional to the amount it is stretched or compressed. The damper produces forces
proportional to how fast the mass is moving. So the faster the block tries to move, the harder
the dashpot pushes back on it to resist that movement.
The spring connects to other body parts using
muscle attachments. It has two properties for the primary and secondary
muscle attachments.
When you select these properties they display a drop-down list that shows all attachment points in this body for you to
select the one you want. When you have set the two attachment points a colored line is drawn between the two attachment points.
Biomechanical springs can be enabled or disabled. You can set this feature directly using the Enable property. You can also do it by applying an
enabler stimulus to enable and disable the spring for specific periods of time. Another way to control whether a spring is enabled is
by using neural control. The default input into a spring controls whether it is enabled. Any input into a spring above 0 will cause
the setting of the enabled property to be flipped. So if the spring is initially set to be disabled and you have a positive input
go into the spring it will enable it while that positive input is maintained. If Enabled is initially set to true then any input into
the spring will disable the spring while the input is maintained.
For more information on how the spring works please see the
spring page of the mechanical tests section and watch the video tutorial.
Spring Properties
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| Figure 2. The properties of the spring. |
The color of the line drawn for this spring between the attachment points. This is only visible once attachment points have been selected.
Default value: Beige
Acceptable range: Any Color
The damping coefficient of the spring. This is B in equation 1 above.
Default value: 1 Kg/s
Acceptable range: 0 or greater
Determines if this spring is enabled or not. If it is disabled then it is as if the spring does not exist in the simulation.
Default value: True
Acceptable range: True/False
The name of this spring.
Default value: Blank
Acceptable range: Any string
The natural length of the spring. When the spring is stretched or compressed away from this length a force is produce that
is proportional to the spring constant.
Default value: 1 m
Acceptable range: Any value greater than 0.
The primary attachment that connects this spring to a part of the body. When you select this item a drop-down list shows
all the attachments in the body for you to choose one.
The secondary attachment that connects this spring to a part of the body. When you select this item a drop-down list shows
all the attachments in the body for you to choose one.
A read-only property that tells you how long the spring is between the two set attachment points. You can use this to determine the natural length of the spring.
The stiffness coefficient of the spring. This is K in equation 1 above.
Default value: 50 kN
Acceptable range: Any value greater than 0.
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