# Research Progress on Synergistic Technologies of Agricultural Multi-Robots
## 3 Research Progress on Synergistic Technologies of Agricultural Multi-Robots
### Architecture of Agricultural Multiple Robot Systems  
A reasonable architecture can guarantee information flow and control flow in the agricultural multi-robot system and make effective cooperation among multiple robots possible [22]. At present, the architecture of agricultural multi-robots can be divided into centralized architecture and distributed architecture. It is found that the earliest recorded structure of agricultural multiple robot systems comes from hay harvesting and transportation robots in farmland [23; 24], for which these multi-robot systems were operated under the principle of centralized architecture. As shown in Figure 2a, in leader-follower mode, a relatively powerful robot is selected as the \"leader\" of the swarm robots, performing specific motion planning for the remaining robots after analyzing and processing the sensory information, but these remaining robots are just executors, without the ability to choose their actions or coordinate with each other. Alternatively, as shown in Figure 2b, in the central controller mode, each robot can perform tasks independently and is commanded by a central controller [25]. The advantage of this centralized architecture is that the theoretical background is clear, and the implementation is intuitive, but the flexibility, fault tolerance, and adaptability are poor [26].  
Compared with the operating environment of UGVs, the operating area of UAVs has the advantage of no obstacles, so these systems generally adopt the distributed structure [28]. As shown in Figure 3, the three UAVs in the multi-robot system carry out agricultural situation monitoring in the individual workspaces independently; each robot  
Figure 2: The centralized architecture of an agricultural mobile multi-robot system. (**a**) One of the guided following modes, where the slave robot follows the travel path taken by the active robot [27]. (**b**) Another of the guided following modes, where the slave robot is ordered by the master robot to go the other way [27]. (**c**) The centralized control mode is usually a back-end computer that monitors, plans, and controls the robot’s tasks and operating paths.  
of this system had a high degree of autonomous operation ability and can complete a given task according to its aims; robots can communicate with each other, exchange information, and coordinate their behaviors equally and independently to complete a given task [28]. This structure has strong scalability and certain advantages in real-time operation, fault tolerance, and reliability, etc. [29] and is suitable for handling tasks related to spatial states [30]. However, \"it costs a lot in terms of the coordination mechanism, such as task allocation and motion planning\" [29].  
The centralized architecture that can be divided into a leader and follower robots is suitable for highly coordinated tasks and is advantageous in a fully known environment. The distributed architecture, in which there is no affiliation among robots, is suitable for weakly coordinated tasks and is advantageous in large-scale, complex, and varying environments.