Page 269 - Handbook of Biomechatronics

Lower-Limb Prosthetics 263

Fig. 15 The Ohio Willow Pathfinder foot system. (Courtesy of WillowWood.)

shock absorption action is limited to heel loading and there is no limb short-
ening problem to address” (Gard, 2002).

5.4 Prosthetic Feet
Versluys et al. (2009) classify the recent timeline of prosthetic feet into three
categories: (a) conventional feet, (b) energy storing and returning (ESR)
feet, and (c) bionic feet.
The desire of transtibial amputees to participate in sports led to the devel-
opment of the early ESR feet, which stored energy during early stance by
loading a spring with the body weight and then releasing a portion during
late stance. The energy lost in the system in the form of friction is high and is
dissipated as heat and sound. Early ESR feet include the Seattle foot, the
Dynamic Plus foot, the C-Walk, and the Carbon Copy foot.
Advanced ESR feet have better properties than early ESR feet and are
shown in Fig. 16.
Hansen et al. (2004) have shown that there is net power generation by
the ankle at speeds higher than 1.2m/s. The need for power generation has
led to the design of the so-called “bionic feet,” which are active pneumat-
ically or electrically driven feet with objective to generate the above-
mentioned net power at the ankle during gait. Different bionic feet have
been designed (Fig. 17). This can enable amputees to walk faster and also
ascend/descend stairs and walk on slopes.