毕业设计(论文)翻译 学生姓名： 学院： 机电工程学院 专 业： 机械设计制造及自动化 设计(论文)题目： 小型蔬菜播种机的设计 指导教师： 年4月10日Mathematical Modelling of Vacuum Pressure on a Precision SeederAbstractThe purpose of this research was to determine the optimum vacuum pressure of a precision vacuum seeder and to develop mathematical models by using some physical properties of seeds such as one thousand kernel mass, projected area, sphericity and kernel density. Maize, cotton, soya bean, watermelon, melon, cucumber, sugarbeet and onion seeds were used in laboratory tests. One thousand kernel mass, projected area, sphericity and kernel density of seeds varied from 4.3 to 372.5g, 577mm2, 38.485.8% and 4401310kgm3, respectively. The optimum vacuum pressure was determined as 4.0kPa for maize I and II; 3.0kPa for cotton, soya bean and watermelon I; 2.5kPa for watermelon II, melon and cucumber; 2.0kPa for sugarbeet; and 1.5kPa for onion seeds. The vacuum pressure was predicted by mathematical models. According to the results, the final model could satisfactorily describe the vacuum pressure of the precision vacuum seeder with a chi-square of 2.51103, root mean square error of 2.74102 and modelling efficiency of 0.99. Nomenclature Nomenclature a, b, c, d, e regression coefficients Em modelling efficiency Erms root mean square error kexp experimental vacuum pressure, kPa kexp, mean mean value of experimental vacuum pressure, kPa kpre predicted vacuum pressure, kPa L length, mm m1000 one thousand kernel mass, g N number of observation n number of constants in the model P projected area, mm2 Pv vacuum pressure, kPa p probability R2 coefficient of determination T thickness, mm W width, mm sphericity, % 2 chi-square k kernel density, kgm3Article OutlineNomenclature 1. Introduction 2. Literature review 3. Materials and methods 4. Results and discussion 5. Conclusions Acknowledgements References1. IntroductionPrecision sowing has been a major thrust of agricultural engineering research for many years; however, most of the research and development work has dealt with seeders for agronomic crops. The main purpose of sowing is to place the seed to a certain space and a depth in the seedbed. Precision seeders place seeds at the required spacing and provide a better growing area per seed. There are two common types of precision seeders: belt and vacuum. Precision vacuum seeders have a metering plate with metering holes on a predetermined radius. A vacuum is applied to these metering holes by means of a race machined in a backing plate. As the plate rotates, the vacuum applied to the metering holes enables them to pick up seeds from the seed hopper. Precision vacuum seeders have the following advantages over the mechanical seeders: better working quality, more precise seed rates with lower rate of seed damage, better control and adjustment of upkeep and drift of seeds, and broader spectrum of applicability (Soos et al., 1989). A seeder should place a seed in an environment in which the seed will reliably germinate and emerge. A number of factors affect the spacing of plants. The seed selection mechanism may fail to select or drop a seed resulting in large spacing between seeds. The mechanism may select and drop multiple seeds resulting in small spacings between seeds. Seed quality, soil conditions, seeder design and the skill of the operator all play a part in determining the final plant stand. The physical properties of seeds are essential for the design of equipment for handling, processing, storing and sowing the kernels. Various types of cleaning, grading, separation and sowing equipment are designed on the basis of the physical properties of seeds. However, no model has been found to describe seeder parameters such as vacuum pressure related with physical properties of seeds. The physical properties of the seeds are the most important factors in determining the optimum vacuum pressure of the precision vacuum seeder. In this study, using some of these, e.g. one thousand kernel mass, projected area, sphericity and kernel density, mathematical models were developed to predict optimum vacuum pressure. The experimental values of vacuum pressure were determined from laboratory test procedure. 2. Materials and methodsThe laboratory test procedure involved testing the metering uniformity of the seeder at the different vacuum pressure with the different seeds: two different maize varieties (maize I and maize II), cotton, soya bean, two different watermelon varieties (watermelon I and watermelon II), melon, cucumber, sugarbeet and onion. These seeds repres