Operational flow of an autonomous sweetpepper harvesting robot

Samenvatting

Advanced automation is required for greenhouse production systems due to the lack of skilled workforce and increasing labour costs [1]. As part of the EU project SWEEPER, we are working on developing an autonomous robot able to harvest sweet pepper fruits in greenhouses. This paper focuses on the operational flow of the robot for the high level task planning.

In the SWEEPER project, an RGB camera is mounted on the end effector to detect fruits. Due to the dense plant rows, the camera is located at a maximum of 40 cm from the plants and hence cannot provide an overview of all fruit locations. Only a few ripe fruits at each acquisition can be seen. This implies that the robot must incorporate a search pattern to look for fruits. When at least one fruit has been detected in the image, the search is aborted and a harvesting phase is initiated. The phase starts with directing the manipulator to a point close to the fruit and then activating a visual servo control loop. This motion approach ensures that the fruit is grasped despite the occlusions caused by the stems and leaves. When the manipulator has reached the fruit, it is harvested and automatically released into a container. If there are more fruits that have already been detected, the system continues to pick them. When all detected fruits have been harvested, the system resumes the search pattern again. When the search pattern is finished and no more fruits are detected, the robot base is advanced along the row to the next plant and repeats the operations above.

To support implementation of the workflow into a program controlling the actual robot, a generic software framework for development of agricultural and forestry robots was used [2]. The framework is constructed with a hybrid robot architecture, using a state machine implementing the following flowchart.