Biomedical Engineering Reference
In-Depth Information
q
i+1
Joint
i
+ 1
q
i
Link
i
Joint
i
α
i
z
i
x
i
a
i
z
i-1
d
i
θ
i
x
i-1
FIGURE 7.1
Joint coordinate systems using the DenavitHartenberg representation methodology.
joint (
z
11
,
z
12
), and finally, one to characterize the forefoot (
z
13
). At the clavicle,
there are two orthogonal revolute joints (
z
33
,
z
34
). Each arm consists of an upper
arm, a lower arm, and a hand. There are seven DOFs for each arm: three at the
shoulder, two at the elbow, and two at the wrist. In addition, there are five DOFs
for the head branch: three at the lower neck and two at the upper neck. The
anthropometric data for the skeletal model representing a 50
th
percentile male,
generated using GEBOD software (Cheng et al., 1994), are shown in
Table 7.1
.
Note that
these dimensions represent a specific human model—it
is not a
percentile-based anthropometry.
This 55-DOF skeletal model has been developed to simulate many human
activities, including symmetric and asymmetric walking, running, climbing stairs,
lifting objects, throwing, and many other tasks. For simulating each of these
activities, some DOFs that do not participate in the activity in a significant man-
ner are frozen to their neutral angles. The formulation presented here is quite flex-
ible, 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 has
been developed that can be used to simulate these activities using the same skele-
tal model. For the symmetric gait simulation problem, the following DOFs are
frozen: wrist joint, clavicle joint, neck joint, and two spine joints (shown as
dashed enclosures in
Figure 7.2
). Therefore, the skeletal model used for gait simu-
lation 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 recalculation of their mass and inertial
properties, which would be quite tedious.
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