The Research Of Avoidance And Spraying Test For Four-rotor Plant Protection UAV

Plant protection UAVs have developed rapidly in recent years because of their high efficiency,good prevention and control effect,and good terrain adaptability.With the wide application of drones,the problem of drones flying in farmland environment has gradually appeared.Among them,the farmland environment is uncontrollable factors,such as wind speed,temperature,relative humidity,etc.in natural factors,power poles,signal towers,water towers and other cylindrical obstacles and high-voltage electric towers,houses and other rule obstacles.Plant protection UAV operation is limited by non-natural factors,it have a great impact on the flight path and operation of UAV,so barrier-avoidance spray technology and experimental research is of great significance.There are two main points of work in this article:1)Research on obstacle avoidance and flight height controlEstablishing a plant protection UAV dynamic model,using sensors to detect and identify obstacles,and establishing obstacle models.Obtaining the obstacle avoidance threshold according to the parameters of the UAV and the sensitivity of the laser sensor in order to plan and implement three obstacle avoidance paths of circle,diamond,and square.After the sensor detects the crop’s pose,the control height is calculated to adjust the height.The two methods of obstacle avoidance and near-crop flight are tested: the errors of three modes about the obstacle avoidance starting point and obstacle avoidance characteristic value are all within ±500 mm,but the area of the obstacle avoidance region of the circle method is smaller,which proves path circle is more conducive to spraying operations.Besides,when the UAVs takes the path circle,its yaw and roll angle are 5° and 50° respectively.When the flying speed is 2 m/s,its shape is a circle;it proves that the method circle can avoid obstacles feasibly.The fluctuation amplitude of the pitch angle is proportional to the height adjustment frequency,which means that the height adjustment frequency of 0.5 Hz is suitable for the height control of the plant protection drone.2)Obstacle avoidance spraying testThe reliability of the spray system was verified with two indicators,namely,the operating time of a single aircraft and the operating area.The test results are as follows:the spray system can meet the operating time of 10 minutes for sorties,and the operating area is 10 mu.Outdoor spray operation test: At a temperature of 29°C and relative humidity of 72%,the droplet coverage rate is the highest at the center of the flight trajectory,and the coverage rate on both sides of the trajectory decreases with the increase of the distance.At a wind speed of 0.4 m/s,the average coverage rate at the center of the trajectory of multiple sorties is 48%,and the average coverage rate at 1.5m to the right is 4%.Under different wind speed conditions,the coverage rate at the center of the trajectory decreases with the increase of wind speed.As the distance from the center of the track increases,the change in coverage decreases gradually.Field test:The overall average coverage of the three operations was 23.63%,42.27%,and 30.18%,which was consistent with the deposition law of the outdoor simulated obstacle spray operation test.The coefficient of variation of the uniformity of the droplet distribution was 7.23-11.55%.Outdoor simulated obstacle spraying test: in an environment with a temperature of27°C,a humidity of 76%,and a wind speed of 0.7 m/s,the coverage rate near the obstacle increases with the increase of the distance to the obstacle.The collection point is 0.5 m,and the coverage rate is 25% at 2.5 m;comparing the spray effect at 0.5-2 m away from the obstacle,the average coverage of circle at 0.5 m and 1.0 m is larger than that of rhombic and square on average,and circle is 12% and 16.91%.Mode rhombic is 9.9%,16.67%,Mode square is 7.68%,15.26%.Field test of obstacle avoidance mode circle: The overall average coverage under circle is 115% of rhombic and 126% of square.Therefore,circle in three modes is the best obstacle avoidance spraying route.Outdoor simulated obstacle spraying operation test: in an environment with a temperature of 27°C,a humidity of 76%,and a wind speed of 0.7 m/s,the average coverage of obstacles between 0.5 and 2 m will increase with The distances are 11.68%,18.02%,30.88%,37.56%,42.25%,and the coverage rate at 0.5 m has increased by 4%.Field test after height control: After height control,the average coverage is increased by 5% compared to before control.In terms of uniformity of droplet distribution,the coefficient variation is larger than before,so the uniformity of droplet distribution is worse.