We investigate a case of multi-robot cooperation in a robotized greenhouse as presented in the SpECULARIA [1] project.
The use of robots in agricultural applications is not anew concept, but rather a fast-growing industry, mainly focused on large machines used for specific crops and applications. However, the main objective of the SpECULARIA project is to develop a heterogeneous robot system consisting of three agents: an Unmanned Aerial Vehicle (UAV), Unmanned Ground Vehicle (UGV), and a compliant manipulator with several degrees of freedom
The greenhouse consists of two tables with plants placed along the walls of the building. Each table is organized into five rows and two columns. The tables are enumerated, as are the specific positions within the table. The convention for addressing tray holders within the table is (row, column) and the indices begin with 0. The full address of each plant is defined by the triplet (table, row, column). The plants within the table can only be accessed only by row, starting with the positions at the aisle. Plants located by the wall of the structure can therefore only be accessed by removing previous plants in the same row of the table.
In addition to the two tables, there is a buffer table structure in the middle of the greenhouse. The structure of a buffer is very similar to the structure of tables, but the plants can be reached from both sides, so there is no priority relationship between the plant access tasks. The buffer is used to store plants that need to be put aside before the required plants are transported to the processing station (workspace station of the robot manipulator). Plants that are finished with the care procedure are also put back into the buffer.
Finally, at the bottom of the greenhouse structure is a workspace table with four plant tray holders. The idea of the four positions is to allow batch processing of the plants, which is especially advantageous for simpler tasks such as watering or spraying the plants.
Inputs for the planning procedure are, in addition to the greenhouse layout, the groups of plants to be cared for on that day, and the procedures to be carried out. In the given example from the figure above, the specific groups are A = {(1,0,1), (1,2,0), (1,3,0)}, in the figure marked violet, B = {(1,1,0), (2,1,1)} painted green, and C = {(1,4,1), (2,0,1), (2,2,0)} marked red. This means that to perform operation A, all three defined plants must be present in the workspace table. Same holds for the other two tasks.
The diagram of the final schedule is given in the figure below. Tasks of moving plants which do not require care to the buffer are marked in gray. Precedence relations are marked with arrows.
The video visualization of the obtained schedule:
[1] Specularia, http://specularia.fer.hr