Learning energy-efficient walking with ballistic walking

This paper presents a method for energy efficient walking of a biped robot with a layered controller. The lower layer controller has a state machine for each leg. The state machine consists of four states: 1) constant torque is applied to hip and knee joints of the swing leg, 2) no torque is applied so that the swing lea can move in a ballistic manner, 3) a PD controller is used so that the certain posture can be realized at the heel contact, which enables a biped robot to walk stably, and 4) as the support leg, hip and knee joints are servoed to go back and the torque to support upper leg is applied. With this lower layer controller, the upper layer controller can search parameters that enable the robot to walk as energy efficiently as human walking without paying any attention to fall down.