Animal walking is thought to be driven by rhythmic signals sent through the spinal cord. These signals are translated to motions of the limbs. For a bipedal walker, such patterns would force leg swings and foot contacts to be alternated so as to achieve stable walking. By using similar mechanisms, roboticists hope to generate walking gates that do not require any complex modeling or computation.
Along these lines, Aoi et al. consider stable walking with a five-link biped robot. The links represent the femur and tibia of both legs and torso as shown in the video below. The robot is driven by a Central Pattern Generator (CPG) that uses one oscillator to generate the rhythmic signals. As a first step, they investigate what parameters lead to stable walking when no sensory feedback is used (open-loop). Important parameters include walking speed, knee amplitude, and distribution of mass. In a second step, the robot is able to detect when its foot hits the ground and use that information to reset the oscillator. By reacting to its environment, the robot is therefor able to adapt its walking and achieve better stability. Finally, controller parameters for the walker are optimized to fully exploit the interactions between robot dynamics, oscillator dynamics and the environment.