Download Technical Note How does the BMS Software Calculate Velocity

Technical Note
How does the BMS Software Calculate Velocity, Force and Power from Cable Transducer
and Force plate data?
Problem: BMS can use displacement, force or both data sources to perform calculations.
Diagnosis: Following is an explanation of the three methods by which additional data sets
are derived.
Most Recent Revision Date: 17 October 2006
The BMS calculates power in three different ways depending on what raw data is
available:
a)
Measurement of vertical ground reaction force only – based on subject/system mass
and force time data, velocity-time data set is derived using the impulse momentum
relationship. That is:
displacement-time data is then calculated as:
Power-time data is then calculated as the product of force and velocity at each sample
point. Average power output between the cursors is calculated by averaging all the
POSITIVE power values. Peak velocity is simply the highest single power value measured
between the cursors. Acceleration-time data is derived by dividing the force-time data by
the system mass.
b)
Measurement of displacement only – based on displacement-time data and input
system mass, velocity-time and acceleration-time data are calculated using the inverse
dynamics approach using finite difference technique as described in David Winter’s
book. Raw displacement data is filtered prior to differentiation using a 4th order
Butterworth digital filter. Separate filter cutoff frequencies can be applied prior to
deriving velocity or acceleration data. Force-time data is calculated as the product of
acceleration-time data and system mass. Power is calculated as product of force-time
and velocity-time data.
c)
Measurement of both force and displacement – velocity-time data is derived as in b).
Acceleration-time data is derived as in a). Power-time data is derived as product of
velocity-time data and force-time data.