| Precision planting of maize can improve maize yield.The seed spacing uniformity and depth stability of maize precision planting need to be guaranteed by the corresponding technology.The seed depth of no-tillage drills is effected easily by external factors such as unit quality,soil texture,field topography and so on.Therefore,the study on method for controlling the seed depth uniformity was conducted and the seeding unit downforce control system was developed.Wheat wreckage and surface straw increase the skid rate of land wheel,which will result in poor uniformity of seed spacing in maize seeding operation.The study on maize seeding control technology was conducted and the seed and fertilizer application rate control system was developed.Based on this,tests and analyses were conducted.The main research contents and conclusions are as follows:(1)The affect of the coupling of terrain and operation speed on the stability of seed depth was studied.In order to ensure the repeatability of the test terrain and improve the efficiency,the farmland terrain simulation system suitable for ups and downs of terrain is designed.The impact of coupling of topography and operation speed on the consistency of seed depth was studied with depth-limiter and surface pressure as objects.Through bench tests at low,medium,and high operating speeds,it was found that the probability that the seed depth is less than the set value is 0.39%、0.94%and 4.20%,respectively.The test results show that the terrain mainly affects the rate of seed depth and the coefficient of variation,and the higher operation speed,the more significant the influence of the terrain.(2)The depth stability control method was studied.Aiming to the deficiencies of passive acting mechanical profiling mechanism,the consistency control method of active action seed depth.Based on the 2BQX-6 maize no-tillage drilling machinery,the seeding unit downforce control system was developed.Through the digital modeling and simulation of the system,the PID controller parameters were determined and the dynamic characteristics of the system were studied.The system performance field static test results show that the system overshoot ≤29.00%,the error ≤5.00%,to meet the general control system accuracy requirements.The dynamic test results show that the downforce is consistent with the target downforce value,the depth-limiter keeps close contact with the ground surface,and the seed depth is little affected by the topographic change.(3)The application rate control system for maize seed and fertilizer was designed.For the land wheel driven drills,there is a problem that the skid rate of land wheel is large and the seeding space uniformity is reduced.Therefore,the study on maize seeding control technology was conducted and the application rate control system for maize seed and fertilizer was developed.Aiming at the problem of poor uniformity of seed space caused by large variation range of wheel slip in wheel-driven seeder,the research on maize seeding control technology was carried out.The research focused on the speed measurement method of agricultural machinery.A combined speed measurement method based on GNSS/IMU technology was proposed and the corresponding speed measurement device was developed.The delay test was performed on application rate control system for maize seed and fertilizer.The results show that the maximum distance the land wheel driven,electronic control system based on single point GNSS,and electronic control system based on GNSS/IMU combined speed measurement is 56.4 cm,191.2 cm,97.6 cm,respectively.The delay distance index of the electronic control system based on GNSS/IMU combined speed measurement is better than the electronic control system based on single point GNSS speed measurement.Static and dynamic verification tests were performed on the application rate control system for maize seed and fertilizer.The errors of static fertilizer application rate and dynamic fertilizer application rate were 2.79%and 4.91%,respectively.The static seeding application rate error and dynamic seeding application rate error are 1.64%and 3.44%,respectively.The test results show that the control system meets the control accuracy requirements of the general control system.(4)Field testing of the seeding quality control system was conducted.When the seed depth criterion is 5.0±1.0 cm,the average quality rate of seed depth of mechanical control of downforce and electric control downforce is 77.04%and 90.37%,respectively.After increasing the seed depth criterion to 5.0±0.5 cm,the corresponding seed depth quality rate were 31.11%and 56.30%,respectively.According to the seeding test on the land wheel driven and the seed application rate control system,the average seed spacing quality index were 87.25%and 96.00%,respectively.With the 40%increase in the seed spacing criterion,the corresponding seed space quality index were 63.23%and 90.01%,respectively.The control system can improve the seed depth stability and the seed space uniformity. |
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