An Exploration of Sensorless Manipulation

The use of motion strategies to eliminate uncertainty, without the use of sensors, is considered. The approach is demonstrated within the context of a simple method to orient planar objects. A randomly oriented object is dropped into a tray. When the tray is tilted, the object can slide into walls, along walls, and into corners, sometimes with the effect of reducing the number of possible orientations. For some objects a sequence of tilting operations exists that leaves the object's orientation completely determined. An automatic planner is described that constructs such a tilting program, using a simple model of the mechanics of sliding. The planner has been implemented, the resulting programs have been executed using a tray attached to an industrial manipulator, and sometimes the programs work. The authors explore the issue of sensorless manipulation, tray tilting in particular, within the context of a formal framework described by T. Lozano-Perez, M.T. Mason, and Russ Taylor (1984). It is observed that sensorless motion strategies perform conditional actions using mechanical decisions in place of environmental inquiries.