Optimal design and implementation of an energy-efficient biped walking in semi-active manner

In this paper, a biped that combines the merits of both powered and passive bipeds is proposed. The semi-activeness of the biped is due to the fact that during most of a walking cycle, only half of the joints are actuated to follow specific trajectories, and the other half of joints remain unactuated but have passive springs connected between adjacent links. It is expected that by having unactuated joints, the biped can preserve the power-saving feature of the passive biped, and by having actuated joints under active control, the biped can also achieve the stability and performance of the powered biped. To devise a systematic design methodology for the biped, its dynamics as well as the walking constraints are carefully studied. Furthermore, an optimization procedure is also proposed to compute the optimal trajectories for the actuated joints and spring constants, which can lead to minimum energy consumption. The feasibility of the proposed biped, including the system design and the control strategy, is verified by hardware implementation. Experiments indicate that the biped walking in the semi-active manner consumes 80% less the electrical power than the fully powered biped that performs the same gait and is more energy-efficient than several state-of-the-art bipeds.