A Type 4 force platform is similar to a Type 2 force platform except that a CalMatrix is specified.

A Type 4 force platform records 6 ANALOG channels containing the following information:

[Original Analog]= [Fx_original, Fy_original, Fz_original, Mx_original, My_original, Mz_original]

A Type 4 force platform also includes a 6×6 CalMatrix (or Inverse Sensitivity Matrix) for pre-multiplying the recorded analog signals before calculating the Ground Reaction Force such that:

[Fx, Fy, Fz, Mx, My, Mz] = [CalMatrix][Original 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. Pre-multiply the tared analog signals by the CalMatrix
4. Calculate the Ground Reaction Force
5. Apply a threshold
6. Transform the signals into the Laboratory Coordinate System

The Force vector for a Type 4 force platform is calculated as follows:

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

The COFP signal for a Type 4 force platform is calculated as follows:

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

The FreeMoment signal for a Type 4 force platform is calculated as follows:

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

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