Design and parameter optimization of pneumatic rice sowing device for unmanned aerial vehicle

Abstract: Unmanned aerial vehicles are widely used in agriculture because of the advantages of flexible landing, no contact with plots, and wide adaptability of terrain. Currently, the unmanned aerial vehicle sowing operation is mainly based on the centrifugal sowing device, which mainly relies on the disc to sowing, forming the circular-shape falling area, causing the unstable uniformity of sowing, and it is difficult to control in the direction of the sowing width. In order to meet the needs of unmanned aerial vehicle low-altitude and high-velocity sowing operations, and to ensure the uniformity of the sowing, a pneumatic unmanned aerial vehicle sowing device was designed in this paper, making use of the air-flow to blow the seeds out in different directions. The basic working principle was that the seed particles discharged from the metering device were mixed with the high-velocity air flow in the flow-spitting box, forming a gas-solid two-phase flow, and then separated into a few streams of seed particles along the diversion channels. The high-spread streams of seed particles, released from the outlet of the diversion channels, cause the formation of a larger width, achieving satisfying sowing presentation. Meanwhile, the key components of the sowing device were simulated and tested. In this paper, the rotor wind field of the multi-rotor unmanned aerial vehicle was simulated and analyzed. The wind field distribution was summarized from two aspects of the vertical plane and the horizontal plane of different heights, and the movement and reasons of the particles in the rotor wind field were analyzed. Three main aspects (the relationship between the outlet size and the wind velocity of the air-flow outlets, and the influence of the cone angles of the diversion channel on the airflow, and air pressure distribution in the diversion channel) were studied. The reasons for doing these tests were that the wind velocity at the air-flow outlets was the key factor to determine whether the seed can be blown out or not. The design of the diversion channel affected the trajectory of the internal seed particles flow, and the most important thing was the effect on the velocity of the seed when leaving the diversion channel in the size and direction. The effect of the cone angle of the diversion channel on the sowing width and the sowing uniformity was tested. The test results showed that there was a strong negative correlation between the outlet size of the flow-spitting box and the outlet wind velocity, and thus, the air outlet size can be determined according to the required wind velocity. There was a strong linear correlation between the cone angle and the sowing width of the diversion channel. The correlation coefficient (R2 = 0.999) can be used to determine the appropriate cone angle according to the requirement of sowing width. Considering the distribution of pressure and flow velocity in the diversion channel and the influence on the width and uniformity, 130° was preferred as the cone angle of the diversion channel. Finally, the effects of sowing height on sowing width and sowing uniformity were studied. The correlation analysis method was used to analyze whether the working height in a certain range had an effect on the sowing width. By analyzing the uniformity variation coefficient in the sample areas the effect of working height on sowing uniformity was determined. The results showed that, in the range of 1-2.8 m, the correlation coefficient of height and width was 0.359, greater than 0.05, and the variation coefficient of sowing uniformity was above 15%, and the significance of height and coefficient of variation was 0.197, greater than 0.05, both of which mean that the height of unmanned helicopter had no significant effect on sowing width and sowing uniformity in the range of 1-2.8 m. Therefore, in this range, it is not necessary to consider the effect of the working height fluctuation on the sowing width and uniformity when sowing by this device. In the actual operation, taking into account the sowing width and uniformity coefficient of variation and energy consumption and other factors, the optimal height of 2 m was preferred on the unmanned aerial vehicle. This study provides the basic reference for further optimization of the prototype.