| Peanut in China is an important oil crop and a protein resource being of great international competitive advantage. For many years, China has been the first largest peanut productive country of the international total production and the second largest one in peanut planting area in the world, which plays a leading and dominant role in the industrial development of international peanut production. However, the development of peanut mechanization in China has lagged seriously far behind its industrial requirements. Especially the peanut harvesting in China, having a labor-cost and high-intensity operation, is still mainly relying on labor, which has become a major bottleneck of peanut industrial development. Combine harvesting is the development orientation for Chinese peanut harvest mechanization. It can complete all the operation procedure of peanut harvest just only depending on one equipment, with many advantages including high efficiency, low cost and saving farming season. But the study on peanut combine harvesting technology is very few, it is still in an infant stage, and far from meeting the requirements of practical production and marketing. Therefore, the development of an innovative combine harvester according with national situations is not only the urgent need of Chinese peanut industry, but also the key point to enhance the mechanization level of peanuts production.This dissertation was to develop a peanut combine harvester which can complete all the harvest operations at one time including digging, vine clamping and conveying, clod cleaning, pods picking, air-screen cleaning, pods connecting and vine throwing, hoping to provide some reference for the development of similar combine harvester. The study was firstly based on the reference, absorption and systemic analysis of the advanced combine harvesting technology and equipments of underground-fruit crops in the developed countries. During the study, Chinese national situations and actual practices were widely considered, including the peanut varieties, planting agronomy, operation conditions, management scale and patterns etc. Either basic research or product development, components optimization or the whole machine research, and absorbing advanced technology or independent innovation were all conducted in close combination. The study especially conformed to the technical path of strengthening independent innovation and market-driven design, focusing the major breakthroughs and key technology, enhancing the entireness. And the combinative methods of theoretical analysis, bench test, field test, optimization and promotion were all taken into account all through the dissertation’s study.The main study tasks and results were as follows:(1) According to Chinese planting agronomy and peanut biological characteristics, the design foundation and requirements of the combine harvester were proposed, and the design schemes of the whole machine were completed. The harvester employed the tracked self-propelled chassis and the principle of semi-feed picking pods. It can complete all the harvest operations at one time including digging, vine clamping and conveying, clod cleaning, pods picking, air-screen cleaning, pods connecting and vine throwing. And it was composed of chassis, driven system, vine detaching device, vine uprearing device, digging device, clamping and conveying device, clod cleaner, pods picking device, air-screen separation system, pods collecting system and other devices. All the operating components were configured on the right-hand orientation of the chassis from the front view of the harvester.(2) By employing the digging-pulling plant lifting technology and the combinative methods of theoretical analysis, bench test and field test, the configuration of vine detaching device, digging device, vine uprearing device, clamping and conveying device were optimized to ensure good coordination for the operation of all the parts, and to achieve best state for underground lifting, clamping and conveying of peanut plants, which can create advantageous conditions for the follow-up operations and can minimize resistance, reduce losses, improve operational smoothness as possible. When adopting the design parameters of vine uprearing device in obliquity80°, clamping chain in obliquity35°, vine uprearing speed ratio1.5, chain speed ratio1.2etc., peanut plants were nearly perpendicular with the clamping chain, and the pulling force on peanut plants was nearly directed in up-vertical orientation. Based on the analysis of the peanut vine lifting motion process, the calculation methods of the vine lifting times and the maximum active uprearing fingers for individual peanut plant were determined, and the separation distance of lifting fingers was optimized to be150mm. The optimization results of relative position parameters of the vine uprearing device, digging shovel, clamping chain in the left-side view were H1170mm, L1325mm, H2290mm, L225mm. And the field experiments showed that peanut plant lifting operation under the optimized configuration achieved a regular, orderly and smooth performance.(3) Based on the systemic analysis on the types, theories and characteristics of clod cleaners of peanut harvesters, the clod cleaner was designed adopting the structure of a pair of transverse swinging plates. The motion property of peanut plants and the computational method of flapping times during the clod cleaning were analyzed and defined. According to the combinative methods of theoretical analysis and experimental verification, some design parameters were determined as follows:the exit-entrance distance of flap plate is600mm, the width of flap plate is160mm,4mm soft rubber is fixed on the inboard side of the flap plate, the distance between the flap plate and the clamping chain is300mm. Subsequently, vibration frequency and angular amplitude of flap plates were optimized by field tests. The results showed that higher vibration frequency and smaller angel amplitude are suitable during the cold cleaning operation.(4)In order to reduce peanut breakage rate, unpicked peanut content and improve pods cleanliness, the structural configuration, structure parameters and motion parameters of the picking rollers were optimized. The optimized results were as follows:Adopting the oblique configuration of the picking rollers and the clamping chain, the constrictive angle configuration of the pair of picking rollers, and6backward curved blades, was fixed on each roller, the blade radius is35mm, the blade radian is70°. Based on the above design scheme, single-factor tests were respectively performed in terms of the five factors including the roller length z1, the roller diameter Z2, overlap distance at roller exit Z3, roller rotate speed Z4and chain conveying speed Z5. And the quadratic polynomial regression models of peanut breakage rate Y1and unpicked peanut content Y2and the optimal combination of factor parameters were obtained by Response Surface Method. The models were as follows:Y1=11.23205-0.025872z2-0.1243z3-0.059118z4+9.333×10-5Z2z4+5.67×10-4z3z4+7.0167×10-5z42, Y2=14.0744-0.005722z1-0.00575z2-0.04768z4+2.875z5+1.2778×10-5ziz4-0.006z4z5+4.4074×10-5Z42. The optimal parameters were:the roller length z1in1200mm, the roller diameter z2in152.5mm, overlap distance at roller exit z3is5mm, roller rotate speed z4is371rpm and chain conveying speed z5is1.025m/s(when the machine speed of going forward is0.854m/s). To obtain a good performance (for the low peanut breakage rate and unpicked peanut content), the high frequency and medium intensity of pods picking were preferred. Based on the optimal parameters combination, the maximum velocity of the picking blade was5.93m·-1, the theoretical picking times was86. The picking rollers were covered with static shield, and the shield-roller configuration of "static inside motion" was employed at entrance and exit of the roller, which can overcome the intertwist of the mulch film.(5) The effect factors of the operation of peanut vine throwing were analyzed and studied. The main parameters of the clamping chain and the vine throwing chain were optimized through the bench tests, determining the addendum angle and addendum height as90°and10mm, respectively. Based on the angular configuration of the clamping chain and the vine throwing chain, the motion properties of silent chain and peanut vines were analyzed, and the velocity ratio k3, the angle λ between the clamping chain and the vine throwing chain were determined as1.2and15°respectively. The design principle of the triangle area formed by vine throwing chain, clamping chain and binder plate should ensure that the peanut vines can be hold according the program of "strongâ†'looseâ†'strong" from the entrance to the exit. Two circulations of design schemes in the configuration of the triangle area were tested by bench experiments, which proved that the triangle area of the first circulation design scheme was too large resulting in the problems of backward conveying, intertwist and low smoothness of vine throwing. And the improved second circulation design scheme solved those problems by reducing the distance among the binder plate, clamping chain and vine throwing chain.(6)Based on the design and optimization of the key operation parts, the whole machine was designed and manufactured by effectively assembling all the parts. The field experiments on the operation performance of the whole machine were conducted to make certain how the performance indexes were influenced by the condition and operation parameters including harvest time, soil moisture content, soil hardness, forward speed of the machine, rotate speed of the engine, and the angular amplitude of the clod cleaner etc. The growth period of the tested peanut variety was ascertained to be130days, and the peanuts should be harvested before2to3days or so of its growth period. Soil moisture content had significant effect on the total loss rate and the clod content, and the optimal one for peanut harvesting was proved to be in the range of8-15%. The orthogonal tests in field showed that:in terms of the operational parameters of forward speed of the machine(A), rotate speed of the engine(B), and angular amplitude of the clod cleaner(C), there were no interaction effects on the performance of total loss rate, breakage rate and clod content. The optimal parameters combinations for total loss rate, breakage rate and clod content were A2B3C3, B1A1C2and A1B3C3, respectively. In order to obtain the optimum levels for all the three indexes, the weighted scoring method was employed to optimize the combination of the factors of A,B and C. The result of the comprehensive optimization was A1B2C2. And the optimized operational parameters were:forward speed of the machine0.8m/s, rotate speed of the engine2100r/min, angular amplitude of the clod cleaner24.5°, vibration frequency of the clod cleaner315times/min, clamp conveying speed0.96m/s, picking roller rotate speed365r/min. |
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