Biomedical Engineering Reference
In-Depth Information
double support
single support
L
R
R
L
R
L
L
R
L
R
y
z
x
FIGURE 7.4
Basic feet supporting modes in a step (side view: R denotes right leg; L denotes left leg).
left
x
z
y
right
FIGURE 7.5
Foot support polygon (dash area) in a step.
7.6.2 Ground reaction forces (GRF)
It is necessary to calculate GRFs in the gait formulation for multiple purposes.
Ground reaction forces provide rigorous validation criteria for whether the walk
prediction is realistic and whether it does indeed simulate a natural human walk.
To include the GRF in the formulation, we have two challenges: not only is the
GRF value transient but also the GRF position is variable. To solve for the GRF,
a two-step algorithm is developed.
Initially we will distinguish forces into two categories: active forces and GRF.
Active forces include inertia, Coriolis, gravity, and external forces and moments.
The main idea of the algorithm is to first calculate the resultant of the active
forces and ZMP location from the equations of motion, and then calculate GRF
using the global equilibrium conditions between the active forces and GRF. After
that, the obtained GRF are applied as external loads at the ZMP, together with the
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