Shape-Based Compliance in Locomotion

Abstract

Having many degrees of freedom is both a blessing and a curse. A mechanism with a large number of degrees of freedom can better comply to and therefore better move in complex environments. Yet, possessing many degrees of freedom is only an advantage if the system is capable of coordinating them to achieve desired goals in realtime. This work supports the belief that a middle layer of abstraction between conventional planning and control is needed to enable robust locomotion of articulated systems in complex terrains. The basis for this abstraction is the notion that a system’s shape can be used to capture jointto-joint coupling and provide an intuitive set of controllable parameters that adapt the system to the environment in real time. This paper presents a generalizable framework that specifies desired shapes in terms of shape functions. We show how shape functions can be used to link low-level controllers to high-level planners in a compliant control framework that directly controls shape parameters. The resultant shape-based controllers produce behaviors that enable robots to robustly feel their way through unknown environments. This framework is applied to the control of two separate mechanisms, a snake-like and a hexapod robot.