Design and Experiment of a Spraying System for Trellised Crops in Multi-Span Greenhouses

To address the high labor intensity, low level of automation, and insufficient uniformity of spray coverage in plant protection operations for trellised crops in multi-span greenhouses, an autonomous spraying system based on magnetic navigation and RFID node identification was developed. The system mainly includes a differential-drive chassis module, a control module, and a spraying module, with an STM32 microcontroller serving as the core controller. The CAN bus was used for information exchange between modules. Magnetic navigation was employed for continuous path tracking between crop rows, while RFID was used to identify key operation nodes. A fuzzy PID algorithm was adopted to correct path deviations by adjusting the motion states of the differential-drive wheels online. The system thereby achieved autonomous path tracking, steering, obstacle avoidance, and point stopping. To evaluate the performance of the system, tests were conducted on the trellised watermelon in a multi-span greenhouse. The results showed that, at an angular velocity of 0.6 rad/s, the average actual turning angle was 88.48°, corresponding to the smallest steering error. At a travel speed of 0.5 m/s, the average obstacle-avoidance braking distance and RFID point-stopping error were 7.50 cm and 14.44 cm, respectively. The spraying tests showed that, within the tested ranges, spray coverage and coverage uniformity exhibited clearer changes with travel speed than with spray pressure. Among the nine tested operating conditions, the highest observed mean canopy coverage was 40.98% at 0.8 m/s and 0.4 MPa, with a coverage coefficient of variation of 26.56%. These results demonstrate that the developed system can perform autonomous navigation, node-based control, and spraying operations in multi-span greenhouse environments. The findings provide a reference for automated spraying operations of trellised crops in greenhouse environments.