# Design and Implementation of an Autonomous Charging Station for Agricultural Electrical Vehicles
## 1 Introduction
Thus when trying to adapt this to the agricultural context as previously stated, a major problem is that the fleet is not necessarily homogeneous, and it will be not feasible to have a dedicated docking area for each AEV coming from a different manufacturer. In contrast to this issue, the automotive industry or their partners focusing on electrical vehicles, and have begun to inspect the solutions that can be deployed in parking places belonging to airports, malls, or offices, where the drivers can be away from their EVs for relatively long periods of time, usually enough to top-up the batteries of the EVs. These companies [17; 18; 19] begun to investigate the possibility of having an autonomous charging station that does not require a dedicated docking area, and that instead navigates to where the EV is parked, and plug the charging cable autonomously into the vehicle. Building upon this idea, we present in this paper an autonomous charging station (ACS) composed of a holonomic mobile platform and a collaborative robot arm. The ACS navigates freely inside the garage where the AEV are parked, and plugs the power cable into the vehicles when they send a recharging request to the ACS. Nevertheless, the main challenge that hinders the implementation of such an idea is that AEV producers lacks standardization when it comes to charging ports. To this end, we present in this paper a simple, but unique, idea that consists of bringing the wall outlet to the AEV, instead of using a different plug for each AEV. The idea behind this is that, no matter the manufacturer of the AEV, it always comes with a common wall adapter, which in the case of this study, is the standard European type F Schuko plug [20]. This means that there will be no need for any special customization of the AEV in order to be compatible with the charging station mechanism. To make the whole process possible, we implemented machine-to-machine (m2m), and machine-to-server (m2s) communication paradigm, which allows the ACS to communicate directly with the concerned AEV in order to perform the plugging sequences, while updating the status of the operation to a central server for human supervision, mainly for security concerns, as there is no need for any human intervention in the whole process. A machine-state-based paradigm is used in order to create the sequence of actions required to fulfill the task of recharging the batteries of the AEV. Vision is used to detect the wall outlet, AEV socket, and to align both the mobile platform whether to the wall or to the AEV, and to perform the plug and unplug processes of the robotic arm. The novelty of the work presented in this paper is threefold:  
1. Holistic charging mechanism that is independent of the manufacturer of the vehicles. 2. Decision-tree-based scheme for controlling a combination of a robotic arm and an omnidirectional mobile platform. 3. To the best knowledge of the author, this is the first proof-of-concept of a dedicated autonomous charging solution for agricultural electrical vehicles. The remainder of the paper is organized as follows: we present in Section 2 the hardware configuration of the ACS, the used plugs, and the decision-tree-based scheme. We also present the different controllers for the collaborative robotic arm and the mobile platform. In Section 3, we present the experimental results of the proposed platform. We give details on the different plug/unplug sequences. Section 4 is dedicated to the conclusion of the work presented in this paper.