Biomedical Engineering Reference
In-Depth Information
Table 2.2
Link Length and Mass Properties
Link
Length (cm)
Mass (kg)
L 1
8.51
4.48
L 2
38.26
9.54
L 3
39.46
3.74
L 4
5.0
0.5
L 5
9.01
0.7
L 6
7.56
0.23
L 7
9.0
2.32
L 8
5.63
2.32
L 9
5.44
2.32
L 10
6.0
2.32
L 11
17.39
3.0
L 12
16.76
5.78
L 13
20.0
4.22
L 14
17.1
1.03
L 15
4.41
2.8
L 16
25.86
1.9
L 17
24.74
1.34
L 18
16.51
0.5
branch: three at the lower neck and two at the upper neck. The anthropometric
data for the skeletal model representing a 50-percentile male, generated using
commercial software, are shown in Table 2.2 .
It is noted here that the foregoing 55-DOF skeletal model has been developed to
simulate many human activities, such as symmetric and asymmetric walking, running,
stairs climbing, lifting objects, throwing, etc. For simulating each of these activities,
some DOF that do not participate in the activity in a significant manner are frozen to
their neutral angles. The formulation presented here is quite flexible allowing any
DOF to be frozen to a specified value. In addition, limits on the range of motion of
any DOF can be imposed. A general-purpose software is being developed that can be
used to simulate these activities using the same skeletal model. For the symmetric
gait simulation problem, the following DOFs are frozen: wrist joint, clavicle joint,
neck joint, and two spine joints (shown as red dashed enclosures in Figure 2.26 ).
Therefore, the skeletal model used for gait simulation has 38 active DOFs. The other
way to accomplish this objective would be to redefine the skeletal model for each
activity. However, this would require redefinition of the body segments and recalcula-
tion of their mass and inertial properties, which would be quite tedious.
2.14 Global DOFs and virtual joints
The six global DOFs generate rigid body motion for the entire spatial skeleton
model. The three translations are represented by three prismatic joints, and the
three rotations by three revolute joints in the DH method. These joints are named
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