Evaluation of Tomato Fruit Harvestability for Robotic Harvesting

Harvestability is a quantitative index of how easy tomato fruits are to harvest using a robot. Previous studies on tomato harvesting robots have focused on tomato fruit detection methods, harvesting mechanisms, harvesting success rates, and harvesting times. However, tomato fruit harvestability using robots has not been quantitatively assessed. In this paper, we propose a method for evaluating the tomato fruit harvestability using a tomato harvesting robot. We first evaluated the harvestability qualitatively, based on the results of harvesting experiments conducted in a tomato greenhouse. Harvestability was then quantitatively evaluated using a camera (hereinafter referred to as a hand camera) attached to an end-effector of the tomato harvesting robot developed. The hand camera consists of an RGB camera and a depth camera. The occlusion ratio of obstacles (stems, peduncles, and other fruits) to a target fruit is calculated using the RGB image and depth image acquired by the hand camera. The larger the occlusion ratio was, i.e., the more obstacles there were in front of the target fruit, the more difficult the target fruit was to harvest. Conversely, if the occlusion ratio is low, the harvestability is high. This study shows that the occlusion ratio is effective as a quantitative indicator of the tomato fruit harvestability.