Biomedical Engineering Reference
In-Depth Information
1
0.05
0.9
0.04
Left foot
Right foot
Left foot
Right foot
0.8
0.03
0.7
0.02
0.6
0.01
0.5
0
0.4
-0.01
0.3
-0.02
0.2
-0.03
0.1
-0.04
0
-0.05
0102030405060708090100
0102030405060708090100
% Lifting motion
% Lifting motion
(A)
(B)
FIGURE 8.12
Ground reaction forces for dynamic box-lifting using the weighted sum performance
measure: (A) vertical GRF, (B) fore-aft GRF.
effort performance measure predicts a more natural back-lift lifting motion as
shown in
Figure 8.10(B)
. Knee, spine
,
and shoulder flexions occur simulta-
neously, and the ZMP trajectory moves in a relatively larger area in the support
polygon in
Figure 8.11(B)
. Finally, the weighted sum performance measure pro-
duces a lifting motion that is quite similar to the one predicted using the dynamic
effort as the performance measure as seen in
Figure 8.10(C)
. However, the predicted
ZMP trajectory varies in a small area in the support polygon in
Figure 8.11(C)
.Itis
evident that the MOO approach shows the combination effects of the two objective
functions and also predicts a more natural lifting motion.
The GRF and joint torque profiles for the box-lifting motion are also obtained by
solving the optimization problem. The GRFs on both feet are similar in both trends and
magnitudes, as shown in
Figure 8.12
(GRF is shown as a fraction of the body weight).
In addition, the vertical GRF on each foot takes about half of the body and box
weights. The fore-aft GRF has small values for a symmetric box-lifting motion. The
predicted joint torques for the right knee, hip, shoulder, and elbow are also similar to
the values on the left counterparts as depicted in
Figure 8.13
. This is quite reasonable
because the initial and final box locations are symmetric in the sagittal plane so that
the predicted lifting motion is also symmetric. However, the torque values on the left
and right sides of the skeletal model are not exactly the same. This is expected because
of the uneven locations of ZMP where GRF are applied as shown in
Figure 8.11(C)
.
8.8
Validation
In order to ensure the accuracy of the proposed method, motion capture is used to
validate the results experimentally. The lifting motion experimental data were col-
lected from five healthy male subjects. The mean height of the subject population
was 5
0
7
v
with a mean weight of 143 lbs. The average age of the participants was
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