**2. Dynamic walking model**

2 Will-be-set-by-IN-TECH

However, the effects of heel-strike and toe-strike during normal walking are ignored, which may influence the characteristics of bipedal walking [12]. In addition, the phase of rotation of the stance foot about the toe tip is ignored in this model, which makes the bipedal walking

Another area that can use segmented foot is rehabilitation robotics, e.g. lower-limb prostheses and exoskeletons. Although foot prosthesis was invented thousands of years ago, the development of foot prostheses is not as fast as people expect. Most of today's commercial foot prosthesis are passive and do not comprise segmented foot. In 1998, [17] first built a powered ankle-foot prosthesis which was powered by a pneumatic actuator. Then, several pneumatic actuated prostheses have been developed [18, 19]. Though the pneumatic actuator is lightweight, inherently compliant and capable of generating high forces, its control difficulties, large size and noise restrain the development of pneumatic driven prosthesis. Recently, [20] developed a powered ankle-foot prosthesis driven by a DC motor. The motor implemented compliant actuation and was placed on the ankle joint. The prosthesis can provide net positive work to propel the body upward and forward during the stance period. Experimental results show that the prosthesis can decrease the amputee's metabolic cost by 14% on average as compared to the conventional passive-elastic prosthesis. However, the prosthesis functionality is not comparable to that of the human foot because of the absence of segmented foot with toe joint. Similarly, although exoskeletons were invented several decades ago [21], there is no powered toe joint implemented in existing exoskeleton systems,

In this chapter, we discuss the effects and applications of adding segmented feet with compliant joints to lower-limb prostheses and exoskeletons. To analyze the effects of segmented foot and compliant joints on energetic efficiency and stability of bipedal walking, we first propose a passivity-based dynamic bipedal model which shows resemblance to human normal walking. Phase switching is determined by the direction of ground reaction force. The push-off phase includes rotation around toe joint and rotation around toe tip, which show a great resemblance to natural human gait. The effects of foot structure on motion characteristics including energetic efficiency and walking stability is investigated through simulation experiments. Starting from the theoretical analysis, we introduce segmented foot with toe joint in both ankle-foot prosthesis and exoskeleton prototypes. Both the ankle and toe joints are driven by two series-elastic actuators (SEA), which not only provide the required torque, but also shock tolerance and energy storage during walking. Preliminary studies on sensory based feedback control are carried out to improve the movement of the proposed systems. Experimental results validate the effectiveness of the proposed structure

The rest of the chapter is organized as follows. In section 2, we introduce the idea of adding segmented feet with compliant actuators placed on ankles and toes. Specifically, a theoretical model with segmented feet is proposed which is based on the simplest walking model. In Section 3, detailed investigations are presented to analyze the effects of segmented foot with joint compliance on dynamic walking. Then, starting from the theoretical analysis, the applications of segmented feet to lower-limb prostheses and exoskeletons are introduced in Section 4. After an overview of current compliant actuators in robotics, the development of a lower-limb prosthesis and an exoskeleton with powered compliant ankle and toe joints is presented. In section 5, the basic control method and related experiments on the prototypes are described. Experimental results validate the effectiveness of the proposed systems.

gait far from natural human-like gait.

e.g. [22, 23].

and actuation method.
