FP Type 7

A Type 7 force platform records information according to its four corners, which are named 1, 2, 3, and 4.

A Type 7 force platform records 8 ANALOG channels containing the following information:

[Original Analog] = [Fx12_original, Fx34_original, Fy14_original, Fy23_original, Fz1_original, Fz2_original, Fz3_original, Fz4_original]

A Type 7 force platform also includes an 8×8 CalMatrix (or an Inverse Sensitivity Matrix) such that:

[Fx12, Fx34, Fy14, Fy23, Fz1, Fz2, Fz3, Fz4]= [CalMatrix][Tared Analog]

Calculating the desired force signals in the force platform's coordinate system consists of the following steps:

1. Compute baselines by averaging the analog signals for the specified FP_ZERO frames
2. Subtract each channel's baseline from its recorded signal
3. Calculate the Ground Reaction Force
4. Apply a threshold
5. Transform the signals into the Laboratory Coordinate System

The Force vector for a Type 7 force platform is calculated as follows:

Force[X] = Fx12+Fx34
Force[Y] = Fy14+Fy23
Force[Z] = Fz1+Fz2+Fz3+Fz4

The COFP signal for a Type 7 force platform is calculated as follows:

COP[X] = ((az0*Force[X] - M[Y])/Force[Z]) + a
COP[Y] = ((M[X] + az0*Force[Y])/Force[Z]) + b
COP[Z] = az0

Where

a = Origin[X]
b = Origin[Y]
az0 = Origin[Z]

M[X] = b*( Fz1 + Fz2 - Fz3 - Fz4) - az0*(Fy14 + Fy23)
M[Y] = a*(-Fz1 + Fz2 + Fz3 - Fz4) + az0*(Fx12 + Fx34)
M[Z] = b*(-Fx12 + Fx34) + a*(Fy14 + Fy23)

The FreeMoment signal for a Type 7 force platform is calculated as follows:

FreeMoment[X] = 0
FreeMoment[Y] = 0
FreeMoment[Z] = M.Z - (COP[X]-a)*Force[Y] + (COP[Y]-b)*Force[X]

The transformation is defined by the location of the force platform corners, and is common to all force platforms.