| Potato was both grain and vegetable,which was nutrient rich and versatility. The development of potato industry was of great significance for ensuring food security. By 2015, the ministry of agriculture took the work of potato as staple food on the agenda, intended to expand the potato planting areas by current 5.573 million hectares to 10 million hectares,which the effective measure to expand planting areas was made full use of the 6.67 million hectares southern winter idle paddy planting winter potato.In the process of potato production, the harvest was an important link which affected the quality and production efficiency of potato. And mechanized harvest had to be the inevitable choice to realize large-scale potato production. However, for increasing the soil temperature to ensure the production of potato, straw or plastic film was used to cover the soil and double row high ridging cultivation method has been adopted when planting winter potato. The special planting mode brought a lot of problems to most existing potato harvester, and the rainy season at harvest time led to too much soil moist and made the problems more serious. The plastic film was decomposed fully or removed by artificial at harvest time, so that the plastic film mulching way had no obvious effect on the harvest operation, which the mechanization of potato harvest could be realized by using the harvester of small digging resistance and good desorption performance. While the residual rate of straw was nearly 50% under the straw mulching cultivation at harvest time, which brought the problems to the existing harvesters such as big digging resistance, easy to be jam, could not separate straw, low excavation rate and high injury rate of potato. Currently, the implementation of potato as staple food strategy was restricted because potato harvested by the way of artificial or animal digging, which was labour-intensive and low efficiency. Therefore, a harvester for straw mulching winter planting potato was developed in this research. The theory research, design method, field test of the key component and the overall unit were implemented,and the results were as follows:(1) The planting technology and agronomic requirements of winter potato were verified. The growth characteristics and related material properties of winter potato were studied. The planting technology and agronomic requirements of winter potato were obtained by investigating the cultivated land of winter potato, which laid the foundation for determination of the harvesting operation scheme. By investigating the growth characteristics of winter potato, found that the maximum distribution depth and width of potato tubers were 183 mm and 338 mm, which were helped to determine the digging width and depth of the harvester. Obtained the minimum and maximum structure size of potato tubers were 38.2mm and 133.8mm, and the average quality of potato tubers was 0.21 kg,which were helped to design the separating screen of harvester and provided support for the stress analysis of potato. For finding the theories of potato collision damage, the impact property test was carried out, and the results showed that the potato was not damaged when the impact energy exerted on it was less than 0.7 J.(2) The overall unit of harvester for straw mulching winter planting potato was designed by using virtual prototype technology. A harvester for straw mulching winter planting potato was developed, which was composed of combined digging shovel, chain-lever elevator, straw separating mechanism and vibrating screen. The drive way and working principle of the potato harvester were elaborated, and it also came to a conclusion that the harvester could working under the traction of tractor above 29.8kw.The working width of the harvester was 1000 mm, the operating depth was 150~300mm, and the production efficiency was 0.2~0.3hm2/h.(3)A combined type of digging component was designed and the digging resistance were calculated. According to the requirement of operation and the dynamic conditions, a kind of combined digging shovel was designed. For reducing the digging resistance, the theorems of force vector projection and kinetic energy were used to determine the main parameters of the digging shovel. Calculated to obtain the digging resistance of digging shovel was 8192.84~9254.58 N, which provide the gauge for the selection of matching tractor.(4)The detach component for potato, soil and straw separation was designed, the action mechanisms were discussed, the mechanism parameters were identified,and test was used to detect and analyze the performance of key parts of detach components. The detach components of potato harvester were composed of chain-lever elevator, straw separating mechanism and vibrating screen, which the action mechanism of jitter, pluck and swing were used to realize the separation of potato, soil and straw. On the condition of straw layer relative to the chain-lever elevator was stably moved up, defined the linear velocity and lift angle of chain-lever elevator were 1.5m/s and 24°, the protrusion height of shaking wheel was 22 mm. Aimed at swimmingly separating straw and ensuring the potato without damage, finger tip velocity and sieve plate installation position were identified. To ensure the potato backward transported on the vibrating screen and effective separated of potato and soil, defined the incline angle and swing direction of vibrating screen were 12°and 18°, the offset distance and velocity of eccentric was 22 mm and 25rad/s. Simulated separation experiment of potato, soil and grass was carried out and the results showed that the fingers of detach component were able to effectively separate the straw, the design of vibrating screen met the requirements of potato-soil effective separation and potato backward transportation.(5)The field harvest experiment was carried out to test the performance of harvester for straw mulching winter planting potato and to select the optimal working parameters combination. The field experiment of potato harvester was designed by orthogonal test, in which the velocity of harvester, the tilt angle of sieve plate and the number of lifting levers of detach component were considered as test factors while the potato obvious rate, potato injury rate and straw separation rate were considered as test indexes. Comprehensive score of each combination of factors was calculated using the weighted scoring algorithm. The results showed that the potato harvester had the optimum comprehensive performance when the velocity of harvester was 0.4m/s, the tilt angle of sieve plate was 8°and the number of lifting lever were 6. In this working parameters combination the field experiment data of potato harvester showed the potato obvious rate was 99.5%,the potato injury rate was 4.2% and the straw separation rate was 80.4%, which were in line with the technical requirements for harvest of winter potato. |
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