SUMMARYInspired by the agility of animal and human locomotion, the number of researchers studying and developing legged robots has been increasing at a rapid rate over the last few decades. In comparison to multilegged robots, single-legged robots have only one type of locomotion gait, i.e., hopping, which represents a highly nonlinear dynamical behavior consisting of alternating flight and stance phases. Hopping motion has to be dynamically stabilized and presents challenging control problems. A large fraction of studies on legged robots has focused on modeling and control of single-legged hopping machines. In this paper, we present a comprehensive review of developments in the field of single-legged hopping robots. We have attempted to cover development of prototype models as well as theoretical models of such hopping systems.

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Energy efficiency is an important consideration for the success of many portable as well as other energetic systems. One way to improve the efficiency of an engineering system is through regeneration. A regenerative actuator returns some of the otherwise dissipated energy required for passive operation. A regenerative actuator can plow back part of energy normally lost in the passive operation of the actuator into useful energy. The amount of regenerated energy will depend on the dissipation characteristics of the actuator and the regenerative potential of the process itself. In order to analyze regeneration a bond graph model of a generalized regenerative actuator is developed. The regenerative potential is analyzed in the power phase plane trajectory. By superimposing such a trajectory with the dissipation characteristics of the actuator, a framework is developed to study the feasibility of regeneration. A possible way of optimizing the regenerated energy is also considered in some depth.

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