Rock-and-Walk Manipulation: Object Locomotion by Passive Rolling Dynamics and Periodic Active Control

This study presents the method of robotic
rock-and-walk
manipulation for dynamic, nonprehensile object locomotion. The object, which is in contact with an environmental surface, is basically manipulated to rock from side to side about the contact point periodically by the robot system. In the meantime, the passive dynamics due to gravity enables the object to roll along a zigzag path that leads to a forward walk. Rock-and-walk is a special-purpose method that enables the transport of a certain class of objects, which are too large, heavy to apply other primary methods such as grasping- or pushing-based operations. Our work is motivated by an interesting question in archaeology, how the giant statues of Easter Island (known as “moai”) were transported several hundred years ago, and a recent demonstration performed by archaeologists that it is possible to walk the statue by periodic rocking. We present a detailed study of the dynamics, kinematics, and mechanics of the object-robot-environment system, and devise a feedback control strategy for rock-and-walk gaiting through the effective regulation of the object’s energy and posture. An extensive set of experiments demonstrate the viability and practicality of our approach in diverse settings: Caging-based single-robot manipulation and cable-driven dual-robot manipulation using manipulator arms and aerial robots.