Nonlinear Robust Visual Servo Control for Robotic Citrus Harvesting

In this paper, a cooperative visual servo controller is presented for autonomous citrus harvesting. A fixed camera provides a global view of a tree canopy for the camera-in-hand, attached to the end-effector, to servo to a target fruit. The paper focuses on the development of a robust, image-based, nonlinear visual servo controller to regulate the end-effector to the fruit location in the presence of unknown fruit motion. A robust feedback term is included in the controller to compensate for the bounded fruit motion, for example, due to wind gusts and robot-tree contact. Lyapunov-based stability analysis guarantees uniformly ultimately bounded regulation of the end-effector. The presented work differs from the existing methods in that the fruit motion in the form of unknown disturbance dynamics are included in the control formulation to actively compensate for the motion without the need for high-frequency image feedback.