| In order to obtain a desired wheat yield,wheat seeds need to be sown at an accurate sowing amount and are uniformly distributed in the sown field.The conventional seeding rate control system of the wheat drill controls the seeding rate indirectly by regulating the rotation speed of the seeding shaft.However,when the seed metering device is interfered with the disturbances,such as the decrease of the seeds' mass in the hopper and the change of the working length of the flute roller.The seeds' mass discharged per rotation of the flute roller will be changed.Although the conventional roller speed control system can enable the roller speed to approach to the theoretical value,the error of the seeding rates caused by the interference of the flute roller cannot be eliminated.In order to solve the aforementioned problems,a seeding rate regulating technology based on the real-time monitoring information of seeding flow rates was studied.Specific research contents and results are listed as follows:(1)Seed flow reconstruction technique for large wheat-seed flow rateConventional photoelectric sensors will miss the detection,if more than one seed pass through the monitoring beam together.Thus,a reconstruction technique of seed flow rate was proposed for reducing the overlap phenomenon.A dispersing board structure and a parallel-channel structure were designed.They were used to separate the dense seed flow and then reconstruct several intermittent seed flows.When the dispersing uniformity of the seeds was set as the assessment criterion,the dispersing performance of the single-dispersing-board structure and that of the double-dispersing-board structure were compared.Combining the numerical simulations of the discrete element method and the experimental design of response surface method,the optimized structural parameters of the aforementioned two dispersing structures were obtained.The simulation results showed that the coefficient of variation of seeds' number in every channels was 26.32% when using the single-dispersing-board structure,while the coefficient of variation of seeds' number in every channels was 21.63% when the double-dispersing-boards structure was used to separate the seed flow,and thus the double-dispersing-boards structure was ascertained as the seed flow dispersion structure of the seed flow rate sensor.(2)The seed flow rate monitoring method based on the seed flow reconstruction techniqueIn order to provide the accurate seeding rate to the seeding rate control system,the seed flow rate monitoring technique needs breakthrough.Based on the double-dispersing-boards structure and signal processing circuit,a seed flow rate sensor was developed.The passing time of a single seed and double seeds through the monitoring beam was measured.According to the passing time of seeds of a different number,a threshold of passing time,for judging the number of seeds,was ascertained.Experiments were carried out to compare the accuracies of the proposed seed-number counting method and a conventional seed-mass estimating method.When the interval of the theoretical seed flow rate was from 50 particles per second to 185 particles per second,all of the accuracies of results of the proposed seed-number counting method were more than 95%.While only 57.7% accuracies of the results of the conventional seed-mass estimating method was more than 95%.At any theoretical level of the seed flow rate,the average absolute percentage error of monitored values by the seed-number counting is lower than that of the predicted values by the seed-mass estimating method,are 1.89% and 5.91% respectively.The comparison experimental results revealed that the proposed seed-number counting method can be used to monitor the seed flow rate at the condition of the large seeding rate.(3)The seeding rate control technique based on the real-time seed flow rate monitoring informationA seeding rate control system,which integrated the self-designed seed flow rate sensor,was developed.Also,a seeding rate control method based on the real-time monitoring values of the seed flow rates was proposed.The core part of the control method was a modified expert control algorithm which can compensate the seeding rate in the(i+1)th feedback distance according to the error of the seeding rate in the ith feedback distance.The seeding performances of the developed control system with the feedback distances of 2.5 m,5 m and 7.5 m were compared.The results showed that 7.5 m was the optimal feedback distance.Under this condition,the accuracy(SA)and the coefficient of variation(SCV)of the seeding rate of the developed seeding control system were 94.12% and 6.77%,respectively.Under the same condition,the SA and the SCV of the conventional roller speed control(RSC)system were 89.00%and 8.95%,respectively.When the wheat drill travelled at various velocities,the SA and SCV of the proposed system were 91.58% and 11.08%,respectively,while the SA and SCV of the conventional roller speed control system were 88.48% and 13.08%,respectively.The aforementioned results indicated that no matter under the constant-velocity or various-velocity conditions,the performance of the proposed seeding rate control method was better than that of the conventional RSC method.(4)The field experiments for the validation of the performance of the developed seeding rate control systemIn the field condition,the performance of the self-designed seed flow rate sensor and the developed seeding rate control system may be affected by the vibrations of the wheat drill.Therefore,at first,the developed sensor and control system were modified for obtaining a better performance of anti-vibration.Afterwards,the verification experiments for seed flow rate sensor were conducted and the average accuracy of the two tested sensors were 92.39% and 93.44%,respectively.If the monitoring results of two sensors were viewed as a total one,the average accuracy of the results was92.91%.Moreover,the comparison experiment of the developed seeding rate control system and the conventional roller speed control(RSC)system were carried out.Concerning the seeding amount in the holistic sown field,the SA values of the developed system and the RSC system were 97.71% and 96.33%,respectively.In each feedback distance,the SA value of the developed system and that of the RSC system were 92.88% and 90.46%,respectively.The number of seeds in 10 cm was taken as a sowing unit,the SCV of the developed system and the RSC system were30.19% and 32.63%,respectively.In conclusion,the developed seeding rate control system can effectively improve the sowing accuracy and sowing uniformity,which laid the foundation of desired crop yield. |
PDF Full Text Request