Table of Contents

FP Type 2

Channels

A Type 2 force platform records 6 ANALOG channels containing the following information: 

[Original Analog] = [Fx, Fy, Fz, Mx, My, Mz]

Note that a Type 4 force platform has the same analog channels as a Type 2 force platform but also includes a CalMatrix. Alternatively, a Type 2 force platform can be thought of as a Type 4 force platform where the CalMatrix is the identity matrix.

Calculating the Force Signals

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 the Ground Reaction Force
  4. Apply a threshold
  5. Transform the signals into the Laboratory Coordinate System

Force Vector

The Force vector for a Type 2 force platform is calculated as follows: 

Force[X]= Fx
Force[Y]= Fy
Force[Z]= Fz

Compute Centre of Pressure

The COFP signal for a Type 2 force platform is calculated as follows: 

COP[X]= (ORIGIN[Z]*Force[X] - M[Y]) / Force[Z]
COP[Y]= (M[X] + ORIGIN[Z]*Force[Y]) / Force[Z]
COP[Z]= ORIGIN[Z]

Where 

M[X]= Mx*LengthConversion
M[Y]= My*LengthConversion
M[Z]= Mz*LengthConversion

and where 

LengthConversion = Point units conversion to meters

for example, if the POINT units are millimetres then the LengthConversion term is 0.001.

Note: When comparing Type 2 and Type 4 force platforms, the LengthConversion term for Type 4 force platforms is always 1 because this conversion is part of the CalMatrix.

Compute Free Moment

The FreeMoment signal for a Type 2 force platform is calculated as follows: 

FreeMoment[X]= 0
FreeMoment[Y]= 0
FreeMoment[Z]= M[Z] - ( COP[X]*Force[Y] - COP[Y]*Force[X] )

Transforming Signals into the Laboratory Coordinate System

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