Reach then see: A new adaptive controller for robot manipulator based on dual task-space information

It is interesting to observe from human visually guided tasks that visual feedback is not used for the entire movement, but only at end phases when our hand is near the target. We are able to move our hand from an initial position that is not within our field of view and transit smoothly and easily into visual feedback when the target is near. Inspired by this natural action, this paper presents a new task-space adaptive controller with dual feedback information. The proposed controller consists of a Cartesian-space region reaching controller at the initial stage and a vision based tracking controller that is only activated when the end effector enters an image region. A new potential energy function is proposed such that the image region can be fixed as the field of view of the camera and does not have to vary with the desired trajectory. The proposed task-space controller can transit smoothly from Cartesian-space reaching to vision-space tracking control. The stability of the closed-loop system is analyzed with consideration of the nonlinear dynamics. The proposed adaptive controller is implemented on an industrial robot and experimental results are presented to illustrate the performance of the proposed controller.