Biomedical Engineering Reference
In-Depth Information
z
i+6
z
i+5
Joint (
k+
1)
z
i+4
Link (
j
+1)
Kinematics
Dynamics
z
i+3
z
i+2
Joint (
k
)
z
i+1
Link (
j
)
FIGURE 7.3
Mass and inertia allocation for joint pairs.
7.6
Gait model
7.6.1
One-step gait model
We shall present a modeling method for a complete gait cycle that includes two
continuous steps (also called one stride). In the present formulation, normal walk-
ing is assumed to be symmetric and cyclic; therefore only one step of the gait
cycle needs to be modeled and simulated. Each step is divided into two phases:
single support phase and double support phase.
The single support phase occurs when one foot contacts the ground while the
other leg is swinging; it starts from the rear foot toe-off and ends when the swing-
ing foot lands on the ground with a heel strike; the time duration for this phase is
denoted as
T
SS
.
Considering the ball joint of foot, the single support phase can be divided into
two basic supporting modes: rear foot single support and forefoot single support.
The double support phase is characterized by both feet contacting the ground. This
phase starts from the front foot heel strike and ends with the contra-lateral foot toe-
off. The time duration of double support is denoted as
T
DS
. In this work, a walking
step starts from the left heel strike, then goes through left foot flat, right toe-off,
right leg swing, left heel off, and finally comes back to right heel strike as shown
in
Figure 7.4
. The foot support polygon is plotted in
Figure 7.5
. The foot contact-
ing conditions are summarized in
Table 7.2
.
Symmetry conditions for the gait cycle are needed so that only one step can
be modeled to simulate gait. The successive step repeats the motion of the previ-
ous step by swapping the roles of the legs and arms. The initial and final joint
angles and velocities (at left heel strike and subsequent right heel strike) should
satisfy symmetry conditions so as to generate continuous and cyclic gait motion.
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