Research on Continuous Two-stage Visual Servo Control for Robotic Arm in Fruit and Vegetable Harvesting

Abstract:

In order to improve the picking speed and stability of picking manipulator, a continuous two-stage image-based visual servo control method combined monocular camera and laser distance sensor was proposed. The YOLOv5s network was used to detect the target fruit, and then threshold segmentation was performed on the detected target to obtain the target area. In the visual servo process, the center point of the target fruit was taken as the image feature, and the velocity control law of the manipulator joint was established combined with PD control. The visual servo process was divided into alignment stage and approach stage, and the target depth information in the two stages was obtained from the radius estimation of the target in the image and the measurement data of the laser ranging sensor, respectively. In order to ensure the continuity of longitudinal velocity during phase switching, the dynamic weight method was used to smooth the velocity in the transition zone. The joint velocity was calculated by the dynamic damping least squares method to avoid the out-of-control of the manipulator when approaching the singular configuration area. The apple picking experiment was carried out. The results showed that the proposed continuous two-stage control method reduced the movement time of the manipulator from 4.52s to 2.56s, the maximum absolute positioning error without disturbance was 4.00mm, and it could stably pass through the singular configuration area of the manipulator, which verified the high speed and strong robustness of the method.