Coupling mechanical design and control design for energy-efficient and stable walking of a compass-like biped

This paper aims at developing a highly efficient walking scheme for compass-like biped robots with feet. Towards this goal, a latch attached to the hip is introduced to lock the hip joint when the hip joint retracts to the desired value and spring devices are installed in the ankle joints to reduce the inputs of the ankles. Moreover, the stance foot allowed to rotate about the toe is considered. With these setups, a highly efficient limit-cycle walking gait is obtained by using the method of Poincaré shooting with the objective of minimizing the dimensionless specific mechanical cost of transport. However, this limit-cycle walking gait is unstable. To stabilize it, a new control strategy is proposed based on transverse coordinate linearization on moving Poincaré sections. A series of numerical simulations show that such a robot model under the proposed control law can walk stably and efficiently.