| The main areas producing rape in the world are China, Canada, India, the European Union and Australia. Rape, as the largest oil crop in China, plays an important role in our national agricultural production with its planting area amounting 1/3 of the total world rape production, ranking first place in the world. According to 2015 China Statistical Yearbook, the majority sowing patterns are semi-mechanized or by hand and the ratio of mechanical seeding is only about 16.1%. Therefore, reliable and effective technique and equipment for precision sowing rapeseed would be a trend for development of seeding machine. In our study, a pneumatic cylinder-type centralized rapeseed precision metering device was proposed to realize function to sow with precision and multiply, meanwhile, it was simplified planter structure when comparing and analyzing on rapeseed mechanical seeding technology and equipment. The technique research and simulation analysis were conducted by using pneumatic cylinder-type centralized rapeseed precision metering device. Besides the detection system for miss-seeding which was integrated with the alarming system was designed to achieve precision sowing and multi-channel real-time miss-seeding detecting during seeder working. The contents of our study include:(1) Research of pneumatic cylinder-type centralized rapeseed precision metering device. Dynamic and kinematics models were established in the main metering processes at the absorbing, retaining and dropping stages. The volume of seedbox combination was 19.3L. The angle of inside box was more than 27.2°, 40 holes were radially distributed, and six rows were along the axis hole number 40, the diameter of seeding cylinder was 165 mm. The diameter and height of combination airbag were 280 mm and 60 mm, respectively. And the negative and positive pressure air chamber volume were 3.92×106mm3 and 7.84 ×105mm3, respectively. the vacuum tube radius should be not less than 5.85 mm and positive pressure pipe radius should be not less than 4.47 mm. In order to ensure filling performance in the absorbing process, the throwing velocity of rapeseed should be less than 0.3m/s; The displacement equation, the transmission ratio and power of planter were clear. Then the rapeseed metering device was adopted to conduct single factor experiments, which showed that the variation coefficient of the consistency of each line displacement was 3.23%, and stability of the total displacement was 1.38% under the rotational speed in 18 r/min, positive pressure in 1800 Pa and vacuum in-3400 Pa.(2) Simulation analysis on seeding process of pneumatic cylinder-type centralized rapeseed precision metering device. Extended Discrete Element Method software was used for simulation and calculation of absorbing process, based on which the mechanism and influence factors of rapeseed movement was study; the simulation analysis for centralized metering device was analyzed by using the ANSYS /CFX software. The influence rule of shape and structural parameters on adsorption properties was clarified. With average pressure and average flow velocity on the end face of centralized metering device as the main evaluation index, the single factor and orthogonal experiments used the arrangement of shape hole, diameter of hole, numbers of hole as the experiment factors. The results of simulation analysis showed that the shape of hole was stepped, the diameter of hole was 1.2mm, the numbers of hole were 40, and the arrangement was equally 30 mm-aligned. The error range of the pressure fluctuation was 0.19% with the combination of airbag. The four structural parameters were important factors which influenced distribution of air flow field. The shape of structure was a significant factor and the axial distance was not significant.(3) Pre-experiment of pneumatic cylinder-type centralized rapeseed precision metering device. The single factor experiments were conducted with qualified index, miss index and multiple index as evaluate metering performance, which showed that the quality index reached above 90.83% and the miss index was 4.35% under the condition of the rotational speed in 18 r/min, positive pressure in 1800 Pa and vacuum in-3400 Pa. The variation coefficient of consistency of each line displacement and stability of total displacement were taken as evaluation index to test with orthogonal experiments for pneumatic cylinder-type centralized rapeseed precision metering device, which showed that output way of negative pressure, transmission ratio and throttle of Dongfanghong 854 tractor were significant factors for displacement consistency. A2B1C2 was best optimizing combination for variation coefficient of consistency of each line displacement and stability of total displacement.(4) Design on performance test system for precision metering device. Given the possibility of miss-seeding and difficult to test performance of precision metering device, performance test system for precision metering device was designed and a test method based on the seeding frequency has been put forward. Measurement experiment could be done via frequency-measuring apparatus by checking the outlet of pneumatic seeding apparatus according to various rotational speed and hole clogging. And seeding situation could be defined and distinguished into different conditions under different rotational speed. They are no miss-seeding condition, less miss-seeding condition and serious miss-seeding condition. The frequency value of miss index could be defined via the interpolation operation when the tested value of rotating speed of metering device goes through smooth filtering. And the miss index could also be tested by the comparison of sowing frequency value via medium filtering and the threshold value. The tests on test-bed indicated that seeding frequency method could effectively check to what degree the miss-seeding could happen. When there was no miss-seeding, the accuracy was achieved to 100%. When more than 8 holes were clogged, miss-seeding was tested with the accuracy of 100%;Another test based on the seeding interval time has been put forward, and synchronous experiments were conducted between JPS-12 test-rig for performance of rapeseed metering device and performance test system based on MCU, which showed that average error and maximum error for detection miss index were 0.31% and 0.7% respectively, meanwhile, the average error and maximum error for detection multiple index were 0.33% and 0.55% respectively.(5) Analysis study and application for seeding technique of pneumatic cylinder-type centralized rapeseed precision metering device. It was Integrated study between centralized metering device and performance test system for metering device. And it was conducted on field experiment of seeding system. The preliminary field trials showed that the variation coefficient of the consistency of each line displacement and stability of the total displacement were 27.72%, 14.71% respectively. The average row spacing within six line was in the range of 11, and the uniformity coefficient of variation were 33.7%,34.7%,31.1%,35.8%,38.4% and 35.7% respectively. The serious miss-seeding condition was detected with miss-seeding test system based on MCU when there was no seed or the metering device broken down.Innovative points 1: The hybrid combination structure and one type of airbag combination structure were proposed;Innovative points 2: Methods of seeding frequency and interval time have been put forward, which realized to detect miss-seeding and performance of metering device;... |
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