A carrying task for nonprehensile mobile manipulators

Manipulation is an essential capability for mobile robots to perform many useful tasks. Our focus has been on mobile robots with nonprehensile (i.e., nongrasping) manipulators. The robots are equipped with a flat "palm" with two degrees of freedom. We have tackled the problem of carrying an object using two such mobile manipulators. Since these manipulators cannot grasp an object, each robot must support one end. However, if errors cause the separation between robots to change, the robots will drop the object. In this paper, we describe an algorithm to maintain the object contact at a nominal position on the palms by performing corrective actions. We first present analysis of the system mechanics, formulate both a centralized and a distributed algorithm for this task, and then show results of our experimental implementation.