Eye-in-hand stereo visual servoing of an assistive robot arm in unstructured environments

Abstract

We document the progress in the design and implementation of a motion control strategy that exploits visual feedback from a narrow baseline stereo head mounted in the hand of a wheelchair mounted robot arm (WMRA) to recognize and grasp textured ADL objects for which one or more templates exist in a large image database. The problem is made challenging by kinematic uncertainty in the robot, imperfect camera and stereo calibration, as well as the fact that we work in unstructured environments. The approach relies on separating the overall motion into gross and fine motion components. During the gross motion phase, local structure on an object around a user selected point of interest (POI) is extracted using sparse stereo information which is then utilized to converge on and roughly align the object with the image plane in order to be able to pursue object recognition and fine motion with strong likelihood of success. Fine motion is utilized to grasp the target object by relying on feature correspondences between the live object view and its template image. While features are detected using a robust real-time keypoint tracker, a hybrid visual servoing technique is exploited in which tracked pixel space features are utilized to generate translational motion commands while a Euclidean homography decomposition scheme is utilized for generation of orientation setpoints for the robot gripper. Experimental results are presented to demonstrate the efficacy of the proposed algorithm.