| With the promotion of national Land Circulation Policy, large-scale and intensive land operation will become the main form of agricultural activity. High-speed, high-efficiency and high-quality precision seeder is required by the agricultural scaled production. Precision planter with a function of coordinated profill has become the mainstream model of maize precision planter with uniform seeding depth and good spacing consistency. However, Limited by the structure of gauge wheel,There is some distance between seed meter and furrow. Aiming at overcoming the position deviation in seed-dropping process, a seed tube is used to deliver seeds to furrow from seed meter. Even though the seed tube performs well at the middle-low speed range, but the spacing uniformity becomes worse obviously at high speed. In order to improve the spacing consistency at high speed, foreign researchers have developed delivery systems applying brush belt and SpeedTube with high level automation,but there are certain disadvantages and shortcoming, such as complex structure and poor universality. To solve the above problems, a method of accurate seed-pocketing, stable seed-deliverying and preciseseed-dropping was proposed, a seed precise delivery mechanism with finger synchronous belt was innovative designed, which kept the movement of seed's movement under control from the seed-dropping point in seed meter to the furrow to avoid the the position deviation in seed-dropping process and improve the seed-spacing uniformity at high seeding speed.The main contents and conclusions of this PhD theis are as follows:(1) Aiming at proving the effect of travel speed on seed-spacing uniformity, took the following four seed meters an the research object: a finger pickup seed meter, a scope-wheel seed meter, an air-pressure type seed meter and an air-blowing type seed meter. The effects of sowing speed on the quality of feed index and coefficient of variation of seed spacing of four kinds of seed meter were analyzed in bench test and field experiment. Conclusions were drawn that the field experiment results show that travel speed have effect on the quality of feed index of four seed meters, which declines with the increase of travel speed. When the travel speed of maize precision planter is greater than 9.7 km/h,the decreasing amplitude of the quality of feed index and theincreasing amplitude of the coefficient of variation both increase rapidly. Test results indicated that the seed tube can not meet the requirement of seed precise delivery at high travel speed, so it is necessary to syudy a new seed delivery mechanism suitable for high-speed operation.(2) The key structure design and the calculation of parameters were made based on the install location and functional requirement of seed delivery system. Crucial parameters have been obtained as follows: the seed delivery device is 39 cm high, 10.2 cm wide, and 3.8 cm thick, the finger synchronous belt was made of polyurethane, its size is 16 mm long, 15 mm wide, and 1 mm thick. Through kinematics analysis of seed in seed-dropping phase and seed-dropping phase, conclusions were drawn that the spacing between two adjacent fingers is proportional to the rotate speed ratio between driving pulley and seed plate, and the spacing between two adjacent fingers is 21.43 mm when the rotate speed ratio is set at 5.77. Crucial operating parameters of the seed precise delivery machanism were calculated in seed-prefilling phase,and the following parameters were obtained: when the spacing between fingers is 21.43 mm, the seed-prefilling advance angle is 21.2°, the number of seed plate rotations are 0.563 and 0.60 in the first and third seed-prefilling phase, respectively . The number of driving pulley rotations are 3.52 at the third phase of seed-prefilling process.(3) The contact parameters between maize seed and synchronous belt were measured by friction coefficient tester, Results are as follows: the coefficient of static friction between maize seed and synchronous belt is 0.428, the coefficient of rolling friction is 0.0845, and the coefficient of restitution is 0.426. EDEM software was used to build models of seed delivery device and seed particle. The effect of vertical distance and horizontal distance between the seed-dropping point and the center of driving pulley on seed-pocketing performance of the seed delivery device was analyzed in simulation, and the influence of the shape & angle of seed pitching board on the seed discharge performance was also emulated. The simulation results showed that optimal seed-pocketing performance was obtained when the vertical distance and the horizontal distance between the seed-dropping point and the center of driving pulley is 40 mm and 20 mm, respectively. The optimal seed-dropping performance is obtained when the linear seed pitching board with seed-dropping angle of 73°is adopted.(4) According to the function requiremnt of the seed delivery device, hardware and software were designed based on the workflow of the seed delivery device accordingly. Rotary accuracy of seed plate is a crucial factor in determining steady rotation of seed plate,so is rotary accuracy of driving pulley,the above two parameters affect the seed pocketing and pitching effect. The rotary accuracy of seed plate and driving pulley were measured and calculated. Results are as follows: the error margin of revolving speed of seed plate is less than 1% between actual value and theoretical value, and the error margin of turning angle of seed plate is not more than 0.1‰, and the error margin revolving speed of driving pulley is less than 0.9% between actual value and theoretical value.(5) The optimal structural combination of seed delivery device was presented by three orthogonal tests of seed dropping position, the spacing between two adjacent fingers and the shape & angle of seed pitching board. The orthogonal tests indicated that the order of structural factors that affect the effect of seeding is the spacing between two adjacent fingers, the shape & angle of seed pitching board, and seed dropping position. The optimal levels are as follows: the spacing between two adjacent fingers is 42.86 mm, linear seed pitching board with seed-dropping angle of 73°. The quality of feed index is 94.1%,and the coefficient of variation is 9.3% when the optimal combination is adopted. The field experiment showed that the quality of feed indexes of seed delivery device are 93.96%, 88.43%, 85.74% at travel speed of 10.8 km/h, 11.9 km/h and 13.1 km/h, respectively. The quality of feed indexes in seed spacing of seed tube are 85.90%, 81.33%, 73.49% at travel speed of 10.8 km/h, 11.9 km/h and 13.1 km/h,respectively. It can be seen that drop margin of the quality of feed index in seed spacing of seed delivery device is significantly smaller than that of seed tube, and the quality of feed index in seed spacing of the seed delivery device is higher than that of seed tube at the same travel of maize precision planter.The coefficients of variation in seed spacing of seed delivery device increses from 13.37% at the travel speed of 10.8 km/h to 17.50% at the travel speed of 13.1 km/h, the increasing amplitude is 4.13%. The coefficients of variation decreases from 17.71% at the travel speed of 10.8 km/h to 28.00% at the travel speed of 13.1 km/h, the increasing amplitude is 10.29%. Bench test and field experiment indicated that the seed delivery device significantly improved the quality of feed index and seed spacing uniformity at high travel speed of maize seeder compared with seed tube. |
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