Improved Pivot Grasping Using Friction Plane Contacts

A four degree-of-freedom (DOF) robotic mechanism can be used to manipulate objects in six DOF by using a gripper altered for two-point pivot grasping where the force of gravity is used for six DOF reorientation. We show that one pivot grasp is sufficient to rotate an ashlar-shaped object from known initial stable configuration into arbitrary final stable configuration. If the initial configuration is not given, robotic vision and a series of two consecutive pivot grasps are needed to achieve the desired final configuration. Two frames of different stable configurations of the same object suffice to perform the required reorientation of the object. A pivot gripper can be further modified by replacing its contact points with rotating contact planes which improves the gripping performance and stability considerably. The effectiveness of the reorientation algorithm along with determining position and orientation of objects lying in the robot workspace with robotic vision is tested in a work cell comprising a SCARA robot and a standard industrial FireWire camera.