Chapter 56 — Robotics in Agriculture and Forestry

An autonomous cucumber harvester

The video demonstrates an autonomous cucumber harvester developed at Wageningen University and Research Centre, Wageningen, The Netherlands. The machine consists of a mobile platform which runs on rails, which are commonly used in greenhouses in The Netherlands for the purpose of internal transport, but they are also used as a hot- water heating system for the greenhouse. Harvesting requires functional steps such as the detection and localization of the fruit and assessment of its ripeness. In the case of the cucumber harvester, the different reflection properties in the near infrared spectrum are exploited to detect green cucumbers in the green environment. Whether the cucumber was ready for harvest was identified based on an estimation of its weight. Since cucumbers consist 95% of water, the weight estimation was achieved by estimating the volume of each fruit. Stereo-vision principles were then used to locate the fruits to be harvested in the 3-D environment. For that purpose, the camera was shifted 50 mm on a linear slide and two images of the same scene were taken and processed. A Mitsubishi RV-E2 manipulator was used to steer the gripper-cutter mechanism to the fruit and transport the harvested fruit back to a storage crate. Collision-free motion planning based on the A* algorithm was used to steer the manipulator during the harvesting operation. The cutter consisted of a parallel gripper that grabbed the peduncle of the fruit, i.e., the stem segment that connects the fruit to the main stem of the plant. Then the action of a suction cup immobilized the fruit in the gripper. A special thermal cutting device was used to separate the fruit from the plant. The high temperature of the cutting device also prevented the potential transport of viruses from one plant to the other during the harvesting process. For each successful cucumber harvested, this machine needed 65.2 s on average. The average success rate was 74.4%. It was found to be a great advantage that the system was able to perform several harvest attempts on a single cucumber from different harvest positions of the robot. This improved the success rate considerably. Since not all attempts were successful, a cycle time of 124 s per harvested cucumber was measured under practical circumstances.
Elder J. van Henten, Jochen Hemming, Bart A.J. van Tuijl, J.G. Kornet, Jan Meuleman, Jan Bontsema, Erik A. van Os