From rolling-in to enveloping: An active gripper for efficient handling of spherical fruits in agriculture

Robotic grippers enable robots to perform agricultural product handling tasks, such as grasping, holding, and lifting, reducing the reliance on human labor. Currently, most agricultural grippers adopt force or form closure modes, which are sensitive to the position of product. In this paper, an active rolling gripper is proposed for spherical fruit handling. It utilizes an innovative rolling-in and enveloping mode, with advantages in terms of high efficiency and high position offset tolerance. The gripper is equipped with three fingers and an elastic membrane, with active rollers at the fingertips. The active roller allows the fruit to be guided into the gripper with only a gentle touch. The elastic membrane, together with the fingers, provides support and restraint when the fruit is fully inside the gripper. To demonstrate the working principle of the gripper, the gripper-fruit interaction model was derived. Then, three experiments were conducted to evaluate its actual fruit handling capability. The results proved that the proposed gripper had high vertical and horizontal offset tolerance when handling tomatoes, oranges, and apples with different orientations. The gripper could complete the rolling-in and enveloping process within 0.5 s once it contacted the fruits. The effectiveness of the gripper was also verified in real-field citrus picking scenarios.