Our 2000 ICRA paper paper describe new experiments with a distributed manipulation system. We study a system in which multiple robots cooperate to move large objects such as furniture and boxes using a constrained prehensile manipulation mode, by wrapping ropes around them. The system consists of three manipulation skills: tieing ropes around objects, affecting translations using a flossing manipulation gait, and affecting rotations using a ratcheting manipulation gait. We present experimental data and discuss the non-holonomic nature of this system.
Manipulating objects with ropes has several advantages over the direct manipulation of an object using a team of robots. First, the method allows for the parallel and synchronized manipulation of multiple objects. (That is, several objects can be wrapped together). Second, wrapping a rope around an object permits constrained prehensile manipulation with non-prehensile robots. The rope can conform to any object geometry on-line, in that the same wrapping protocol works for all geometries and there is no need to specify a model in advance. Finally, the rope can be viewed as a tool that allows the robot system to exert torques that are larger than the torque limit of each individual robot. Our notion of constrained prehensile manipulation is different than the classical definition of prehensile manipulation, which usually denotes a force closure grasp. In constrained prehensile manipulation, perturbations along any differential direction can be resisted (in our case, due to the taut rope) but the object can be moved only along certain lower dimensional degrees of freedom. Thus, constrained prehensile manipulation systems are non-holonomic.