Field test of different end-effectors for robotic harvesting of sweet-pepper

This paper focusses on field experiments with two different types of endeffectors for robotic harvesting of sweet-pepper fruits. One of the major issues is to reach, grasp and detach the fruit efficiently, without damaging it, while avoiding obstacles in the environment. End-effectors for harvesting fruit must be able to adapt to different fruit sizes and geometries. Two types of end-effectors were designed and realized. The first one had four fingers which utilized the "Fin Ray" effect to grip the fruit. A scissor-like cut mechanism on top of the fingers was used to cut through the fruit peduncle. The second, a lip-type end-effector first stabilized the fruit using a suction cup after which two rings enclosed and cut the peduncle with a circular blade integrated in the upper lip. Both end-effectors had integrated miniature cameras with a LED illumination system: one Time of Flight camera and the other a colour camera. To study the performance of the end-effectors a number of harvesting experiments were performed in commercial sweet-pepper greenhouses. Special attention was paid to the following aspects: positioning at the target fruit, separation of the fruit from the plant, fruit damage, leaf damage and plant stem damage. Both end-effector designs had their strengths and weaknesses. The Fin ray type end-effector harvested a maximum of 80% of the fruits on the plant, the lip-type end-effector a maximum of 76% of the fruits. In none of the experiments more than 64% of the fruit could be harvested without fruit damage.