Manipulation Planning for Redundant Robots: A Practical Approach

An emerging paradigm in solving the classical motion- planning problem (among static obstacles) is to capture the connectivity of the configuration space using a finite (but pos sibly large) set of landmarks (or nodes) in it. In this paper, we extend this paradigm to manipulation-planning problem, where the goal is to plan the motion of a robot so that it can move a given object from an initial configuration to a final configuration while avoiding collisions with the static obstacles and other movable objects in the environment. Our specific approach adapts Adriadne's clew algorithm, which has been shown effective for classical motion-planning prob lems (Mazer et al. 1994; Ahuactzin 1994). In our approach, landmarks are placed in lower dimensional submanifolds of the composite configuration space. These landmarks repre sent stable grasps that are reachable from the initial con figuration. From each new landmark, the planner attempts to reach the goal configuration by executing a local plan ner, again in a lower (but different) dimensional submani fold of the composite configuration space. The approach is probabilistically resolution complete, does not assume that a closed-form inverse-kinematics solution for the manipulator is available, and is particularly suitable for redundant manip ulators. We also demonstrate that our approach is practical for realistic problems in three-dimensional environments with manipulator arms having fairly large numbers of degrees of freedom. We have experimented with this approach for a 7- DOF manipulator in 3-D environments with one movable ob ject, and computation times range between a few minutes and a few tens of minutes-in our experiments, between 3 min to 15 min, depending on the task difficulty.