Pre-grasp Interaction for Object Acquisition in Difficult Tasks

In natural manipulation activities of daily living, actions for object grasping must respect several constraints for successful task completion. For example, grasping actions must satisfy at a minimum the reachability of grasp contacts on the object surface, collision avoidance with obstacles, as well as kinematic and strength limits of the hand. In challenging manipulation scenarios with high constraints, direct reaching actions to grasp the object in place may not be sufficient for object acquisition. We have observed that humans use pre-grasp interaction to adjust the object placement during the grasping process. For example, an object may be slid or tumbled on its support surface before the final grasp contacts are achieved. In this chapter we provide an overview of the variety of pre-grasp actions that we have observed from a video survey of human manipulation activities in natural home and occupational environments. We also present our studies of object reorientation by rotation, as a particular type of human pre-grasp interaction. Finally we also examine the utility of pre-grasp rotation for increasing object reachability and grasp reuse for a robot manipulator.