This paper proposes a novel dynamic walker capable of walking with heel, ankle, and toe rocker motions. The heel and toe rocker motions are obtained by using inelastic stoppers between leg and foot, which limit the range of rotation of the foot about the ankle joint. A generalized set of equations of motion and associated transition equations applicable for multiple foot segments is derived. Passive dynamic walking is studied with equal heel and toe strike angles for the case of symmetric foot walking. It is shown that by including the ankle joint, low-speed walking is made possible. The energy efficiency of the proposed walker is studied theoretically and through numerical simulations. Finally, three different underactuated modes of active walking that do not require toe and heel actuation are presented. In order to implement these modes of walking, the proposed walker can be constructed with little modification from an existing flat-foot walker that uses ankle rocker motion alone. Results show that substantial benefits can be obtained in efficiency and stability compared to point/flat-foot walker of the same leg length and mass distribution.
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