View Full Version : modelling joints with springs and dampers

John D Finan (university College Dublin)
07-21-2000, 02:21 AM

I'm a research assistant working to develop (very)
simple rigid body linkage to model the human body in a
fall. The work is part of a wider project concerning
head injury. The objective of my model is to yield a
velocity vector for the head at the time of impact in a
simple fall, initially a fall from a standing
position. I started by representing the body as a
simple rigid bar and now I've moved on to representing
it as two links joined at the hip or three links with a
neck joint included.

It seems to be common to take the joints as pin joints
in car crash models, even quite advanced ones. This is
valid for a car crash model because, in the sitting
position, most of the main joints are in the middle of
their range of motion and therefore reasonably free to
move plus the forces generated in a car crash dwarf
anything generated by human muscles. In the case of a
fall from a standing height, neither of these
arguements hold and pin joints lead to impossible
configurations. Therefore, I will be representing
muscle action on joints using torsional springs and
dampers. My question is this: what values of torionsal
stiffness and damping should I use. I know that muscle
action has been represented sucessfully in this way by
fitting curves to motion analysis data. I wonder does
anybody know of studies which have done that kind of
analysis on the hip or neck. I am especially
interesteed in the hip in its relaxed state. Ideally,
I would like three quadratic torisonal springs, one
modelling the action of a relaxed hip in a fall
forward, backward and to the side. I realise few
people work with such crude approximations but any help
would be appreciated.


John D. Finan

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