# Reduction of Pesticide Use in Fresh-Cut Salad Production through Artificial Intelligence
## 2 Materials and Methods
### Main Subsystems of the Machine  
The main subsystems of the designed machine are: data gathering, spraying circuit, boom structure and actuation, rover structure and motion, and navigation computing/electronics. The aim of the data gathering subsystem is to acquire information regarding the plant and the treatment, carried out thanks to a 3D camera, a pressure sensor and a flow sensor. The 3D camera is by far the most important component, both in terms of information output and cost; its core function is to determine the type and growth stage of the plant, while allowing a visual odometer to measure the speed of the rover, a fundamental parameter for the treatment. The water pressure and flow sensors instead allow a closed-loop control of the droplet size and product amount. While in theory the pressure-flow curve of the nozzles is known, and therefore only one of these sensors would be needed, the presence of both allows to detect faults (clogged nozzles, disconnected pipes, air in the pump, etc.) and consequently stop the treatment, thus allowing the user to solve the problem immediately. The spraying circuit is the subsystem with the more traditional architecture. The water line starts from the plastic tank and, through a high-pressure (up to 8 bar) variable speed membrane pump, delivers the water to the nozzles. To allow different spacing, two rows of nozzles were installed, driven by an electrovalve to allow using only one row, so resulting in a 50 cm distance between active nozzles, or both, reducing this distance to 25 cm. The 50 cm distance was considered because it is the standard generally adopted on sprayer booms, while the addition of the second row allows multiangle treatment and lower dispersion of the droplets when reducing the boom height from the ground. A low-pressure (0.2 bar) agitation pump recirculates the water in the tank, to avoid sedimentation when a powder-based of PPP is used. The air line is composed only of a variable speed fan and a flexible plastic air sleeve to direct the flow over the treatment area. The boom structure is an aluminum body-on-frame. The selection of aluminum as the main material, despite the higher cost, is due to the necessity to keep this component as light as possible since the overhang outside the track and the height from the ground have to be adjustable. To change the height, within a range of 30 cm, a linear electric actuator was used, to cover the optimal settings for both the defined nozzle distances. The rover structure is a mild steel body-on-frame, coated with high-temperature powder paint to increase durability. Due to the low working speed, no suspension system was implemented. The rear wheels have independent in-hub motors, while the front wheels are free-pivoting. This configuration allows controlling the motion without a steering system, by imposing the speed of the right and left wheel. The motors are driven from two independent power drives that implement a closed-loop speed control and are directly connected to the battery. The battery is a 48 V Li-ion pack with a waterproof casing. For a suitable safety of the operations, an emergency switch is put on the battery for the disconnection. The navigation system is based on a differential real-time kinematic GPS. This system consists of three sensors and antennas, two on the rover and one in a fixed reference position on the ground. Thanks to the real-time kinematic algorithm the relative position of the antennas can be known with precision in the subcentimetric range. The two antennas on the rover allows to determine differentially its spatial orientation, with a typical uncertainty of 0.2\({}^{\circ}\). The data coming from the GPS are fused with those obtained from the inertial measurement unit (IMU) and the 3D camera, to allow excellent accuracy and to stop safely the system in case of malfunctions.