Optimization of the groove wheel structural parameters of UAV-based fertilizer apparatus

Abstract: Agricultural spraying unmanned aerial vehicles (UAVs) have been emerging to promote mechanized fertilization in recent years. A fertilizer discharging device is one of the most important components in the fertilization machinery. Among them, a groove wheel-type fertilizer discharging device has been widely used, due to the simple structure and the adjustable range of displacement. However, the large fluctuation and low displacement accuracy often occur during fertilizer discharging of groove wheel type fertilizer discharging device for the fertilizing UAV. Harsh requirements also remain on the structure design and installation position of the fertilizer discharging device, where the fertilizing UAV has a small size and limited payload. Therefore, it is of great significance to explore the new groove wheel-type fertilizer discharging device. This study aims to design the groove wheels with different groove shapes and columns, thereby clarifying the interaction between the particles and the groove in a UAV-based fertilizer. A simulation software EDEM was also selected to optimize the fertilizer discharge process of each groove wheel at different rotational speeds. An analysis was then made to determine the influence of groove shape and columns number on the pulsation of fertilizer discharge from the perspective of the amplitude and time interval. The simulation results showed that when the rotational speed was 10-40 r/min, the groove shape and column presented a great influence on the pulsation of the fertilizer discharge, where the amplitude of the pulsation increased, whereas, the time interval decreased, as the rotational speed increased. There was an outstandingly larger pulsation of the groove wheel with the straight groove, compared with the other two kinds of groove wheel. A bench test was conducted to investigate the displacement range of compound fertilizer and urea discharged by each groove wheel, further to determine the accuracy of displacement and the interaction of each influencing factor on the displacement. The test results showed that when the rotational speed was 40-120 r/min, the discharge of the two fertilizers within the speed range of each groove wheel was more than 17 kg/min, meeting the discharge requirements of the fertilizing UAV. The analysis of variance showed that the main effect and interaction of groove shape and column posed a significant influence on the displacement at different rotational speeds (P<0.05), and interfered by rotational speed. In a compound fertilizer, the CVs of the groove wheels E-6, S-6, and E-5 fluctuated smoothly, basically within 1%; the CVs of the groove wheels I-4, I-6, and E-4 fluctuated in a large range, but all within 3%. In the urea, the CVs of the groove wheels I-4 and S-4 fluctuated in a large range, indicating a low accuracy of discharge rate; the CVs of the groove wheels S-5, I-5, E-4, E-5, and E-6 fluctuated within 1%-2%. An optimal fertilizer discharge was achieved at different speeds, considering the discharge pulsation at a low speed and the discharge accuracy at a high speed for the fertilizing UAV. Correspondingly, it was suggested that the E-4 groove wheel can be used for the discharging compound fertilizer, and the E-4 or I-5 groove wheels for discharging urea. Consequently, the structural parameters of the groove wheel in the fertilizer discharging device were optimized to achieve the optimal combination of small pulsation, as well as the accurate and stable discharge of fertilizer. The finding can provide a strong reference to optimize the performance of fertilizer discharging devices in the UAV agricultural spraying system.