Pose Estimation of Grasped Object from Contact Force or Joint Data of Manipulator

Abstract

It is necessary to estimate a grasping pose when a robot changes its grasping state.This paper proposes a new technique for estimating 3-D position and orientation of a grasped object with respect to the hand coordinate system using contact information. It is assumed that the grasped objects are polyhedron. In this paper, two techniques to estimate the grasping pose are described. One uses force data as contact information, and the other uses joint angles of a manipulator.The estimation process is as follows. First, the system contacts a vertex of the grasped object with external environment. Then, the contact point with respect to the hand coordinate system is detected by using contact force data or joint angles of the manipulator. This contact point with respect to the hand coordinate system is transformed to the point with respect to the grasped object coordinate system from the internal model. The above-mentioned process is repeated several times changing the contact vertex of the grasped object. Relative rotation and translation between hand coordinate frame and grasped object coordinate frame are computed from these data using Newton method.In the case of a parallel-jaw gripper, consideration of geometrical constraints of polyhedral model reduces the number of transformation parameters from hand coordinate frame to grasped object coordinate frame and the calculation time. Experimental results of estimating the grasping pose with the DD robot ETA-3 is also described.