Page 251 - Handbook of Biomechatronics

Lower-Limb Prosthetics 247

SL SL
h h
L
r
L
L eff

(A) (B)

m

µ r(o)
r 1
c 2
k 1
k 2
c 1
q
h

(C) (D)
Fig. 2 (A) Compass-gait model, (B) rocker-based inverted pendulum model introduced
by Gard and Childress (2000), (C) stiffness-damper model of gait used from Siegler et al.
(1982), and (D) stiffness-damper-rocker model of gait used from Gard and Childress
(2000).

The Northwestern University Prosthetics Research Laboratory
(NUPRL) (Childress, 2002; Gard and Childress, 2002) believed that in
order to design the best lower-limb prostheses, a good able-bodied theory
of walking should be developed along with amputee deviations. Therefore,
the NUPRL developed a theory of walking so we can understand why the
body moves the way it moves during walking. An inverted pendulum model
with rockers was introduced (Fig. 2B). The characteristics of the rocker are
based on the “roll-over shape” which is the equivalent foot/ankle geometry
extracted from a person walking during the stance phase (Hansen, 1998;
Hansen et al., 2000). The “roll-over shape” functionally lengthens the leg
of the inverted pendulum model; thus, it is equivalent to a virtual leg
approximately 1.7 times the length of the anatomical leg but without rockers
(Fig. 2C). Both models, the leg with rockers or the virtual leg without
rockers produce similar center of mass trajectories. The rockers, or equiva-
lently the virtual leg, reduce the peak to peak of the vertical excursion of the
center of mass from what it would be otherwise (Gard and Childress, 2000).