| Unmanned helicopter(UH)is flexible to control,and can realize automatic path planning and navigation flight,without a dedicated airport.The UH can flexibly land in the farm,out of limitation of topography and geomorphology,adapting to the complex environment,to work in the area beyond the reach of the ground mechanical and manned aircraft.Therefore,choosing UH for sowing can effectively solve the problem of mechanization in some areas.The research of domestic existing centrifugal disc type of unmanned aerial vehicle(uav)sowing device was reported,which was only suitable for seeding field where the sowing evenness coarse request was not high.There is little sowing device with high uniformity suitable for UH.In this paper,the advantages and disadvantages of common sowing technology were analyzed,the research and application status of the aircraft sowing technology at home and abroad were summarized,the possibility and reliability of the UH sowing technology were explored.The improvement design method of the current existing disc type sowing device was put forward,a new pneumatic type sowing device for UH was designed,and these two sowing devices in all kinds of operation parameters and operation effects were compared by doing the basic test and field experiments.The main research contents include:(1)simulation analysis of rotor wind field of UH was presented in the experiment.In this article,the multi-rotor unmanned helicopter rotor wind field was simulated in the Ansys software,and the changing rules of the rotor wind field concluded were as follow:when in hover state,the rotor wind field distribution of the multi-rotor unmanned helicopter was symmetrical.At the bottom of the fuselage,the rotor flow downward was spiral,and in the vertical direction,disturbance area produced by the rotor flow increased with the increase of the distance to the bottom of the fuselage,and the wind intensity gradually weakened at the same time.When it comes to the downward distance about 1 m,the disturbance areas of the airflow under different rotor interfered each other,and gradually expanded.Moreover,the air pressure directly under each rotor was smaller,and the air pressure increased with the increase of the horizontal distance from the bottom of fuselage,and the rice movement direction in the wind field tended to the downward of the rotors.the law aforesaid showed that rice trajectory was mainly affected by rotor wind field,gradually dispersed within the area,after leaving the sowing device export airflow into the rotor wind field disturbance area,which can get larger width;When the rice escaped the turbulence zone of the rotor wind field,its motion trajectory was mainly determined by the initial velocity and direction of the last time of the flight,and freely fell into the ground.In other words,if the flying height of the UH is less than the distance of its rotor wind field attenuation,the spread width is mainly affected by the rotor wind field.(2)The main factors affecting the uniformity of the centrifugal disc type sowing device for unmanned helicopter were analyzed.The key components and structures,and parameter optimization were improved through the analysis of metering institution characteristics and influence factors of disc type sowing device when considering the appropriation for unmanned helicopter.The test results showed that the rotation speed of the groove wheel of the metering device was 0~196 r/min,the filling capacity of each groove was about 8g,and the adjustable range was0~5.722kg/min.For the disc,the diameter was 200 mm,the thickness was 2 mm,leaf number was 3,linear,the height was 15 mm,no eccentric,the better falling down position for seed particles was 55 mm,no angle,the rotational speed of disc was about 1000 r/min.When in the condition above,the width and the radian of seed distribution area was better.The sowing control system was developed,and the variable control can be realized by combining with unmanned helicopter flight parameters.(3)For centrifugal disc type sowing device,the falling area was in circular arc form,sowing uniformity is not stable,the control in the width direction was difficult.Considering these problems,a pneumatic type sowing device for UH was designed.The relationship between the distribution box size and export airflow velocity,and diversion channel angle within the diversion channel on the effect of air flow and pressure distribution and width,and the influence of seeding uniformity for aeroplanes were studied.The test results showed that there is a strong negative correlation between the outlet size of the divider box and the outlet wind speed.According to the design requirements,the better diameter of the outlet of the air flow was selected as?32 mm.There is a strong linear correlation between the cone angle of the diversion channel and the sowing width,and the correlation coefficient R~2=0.999.comprehensively considering the air pressure and velocity distribution of channel,and the influence of cone angle on the width and uniformity,the cone Angle of 130°was optimized for the diversion channel.The sowing height to width and the influence of seeding uniformity was further studide,the results showed that in the range of 1~2.8 m,sowing height and width of the correlation coefficient was 0.359,significantly assignments and sowing uniformity of high correlation coefficient was0.197,significantly within a given the height of the unmanned aerial vehicle(uav)width height on aeroplanes,and the influence of seeding uniformity was not significant(significance level?=0.05),In actual sowing,incorporating the spread width and uniformity coefficient of variation and the field work environment factors,the sowing height of 2m was optimized for the unmanned aerial vehicle(uav)platform.(4)The prototype of the two sowing devices were tested and the corresponding sowing control systems were designed,which can be combined with the flight parameters of UH to control the sowing quantity and improve the uniformity of ssowing.The contrast tests and researches of the two sowing devices for unmanned helicopter were respectively carried out.Results showed that the left side of the disc type sowing method boundary fluctuation coefficient of variation is relatively smaller than the right side(6.53%),and the variation coefficient of the right boundary of the distribution is as high as 19.62%,and the overall distribution was not stable,boundary extremum was not so good as pneumatic type sowing device.Therefore,the regional boundary of the pneumatic sowing device was less volatile and the boundary was more stable.In actual field contrast experiment,the conventional Huang Huazhan was choosed to test,under the same operating condition and growth environment,from the point of the number of rice planting,the number of rice sowed by pneumatic type sowing device was stable,sowing uniformity was good. |
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