View Full Version : Re: Summary: force plate issue

10-17-2005, 01:20 PM
Dear all,

The following is what Chris Kirtley sent me but I believe he meant to send
it to Biomch-L.

>Dear Kwon, Tomislav and all,
>It is worth noting that in AMTI plates (and Bertec, I think?) the total net
forces and moments on the plate: Fx,y,z and Mx,y,z (6 variables) are derived
by suitable manipulation (in hardware), and ouput directly. The equations
then simplify: see my scan of an AMTI manual:
>The 'c' of your equations is here called Zoff - I have also often (e.g.
Dave Winter's books) seen it signified by Dz.

Probably, one of the best places to see a complete set of CP & Tz equations
for the AMTI (Bertec) plates and Kistler plates will be my webpage:
http://kwon3d.com/theory/grf/cop.html. Or if you are interested in the
force-plate-related issues in general, I recommend
http://kwon3d.com/theory/grf/grf.html. The CP (X and Y) & Tz equations for
an AMTI plate are actually more complex than what Chris scanned because it
has something called the 'true origin':

X = [ My + c*Fx ] / Fz + a [1]

Y = [ Mx - c*Fy ] / Fz + b [2]

Tz = Mz - ( x - a )*Fy + ( y - b )*Fx [3]

where ( a, b, c ) = true origin of the plate (c < 0). 'a' and 'b' for a
Bertec plate are equal to 0 but those for an AMTI plate are not. Consult the
manual and the calibration sheet of the AMTI plate for the true origin

Young-Hoo Kwon, Ph.D.
Biomechanics Laboratory
Texas Woman's University
Phone & Fax: (940) 898-2598
ykwon@mail.twu.edu / kwon3d@kwon3d.com