| The vegetable industry plays an imperative role in China’s economy.Since Seeding and transplantation has been adopted for over two thirds of the vegetable.Consequently,there is a desperate need for plug precision seeders in our country.The gas-powered rolling precision seeders featured by less strict requirement for the size of the seeds,lower chance of breaking seeds,higher seeding productivity,lower energy consumption etc.,which has become publicized and promoted nationwide.Our country has comprehensive range of vegetables;the planting of the vegetable is characterized by multiple types for one season,types varying from season to season.Thus developing advanced and original gas-powered rolling precision seeding technology with low cost,stable seeding discharging,high productivity to achieve the goal of one seeder sowing most leaf and fruit vegetables would be significant to the mechanization of grow seeding production.The paper is grounded in the character of succession to the past for seeding device,revolves around the study of seed suction theory,then establishes the model for the evaluation of seeding performance to study each phase including seeds suction,seeds supply,seeds removal,seed metering.Moreover,the study lays foundation for the consequent seeding test on the seeds of China flowering cabbage,broccoli,radish,eggplants,tomatoes,pod peppers as well as sweet peppers.In order to calculate an evaluation value for each and every seeding result,the paper aims to establish a model for the evaluation of seeding performance on the basis of the major factors named as single index and miss index.The performance of the seeding device goes in line with the evaluation value,the larger the value is,the better the performance will be.If the values are equal,then the performance will be equally good.The model can also be utilized as a way to rate the seeding performance level for different seeders.Suppose that the transformation process between positive and negative process occurs in ideal condition,the flow condition of the gas outside the seed suction hole is steady and uneven,the flow velocity for any fluid particle is in reverse proportion to the square of the distance from the center of the airflow field,In the meanwhile,it is also in proportion to the quantity of flow through the seed suction pore.Then a force analysis is conducted in regard with the critical moving condition for the seeds in the airflow field,moreover,a mathematic model for absorption boundary is established and a mathematic analysis is performed accordingly.The suction boundary along with its moving area are the representation for the analysis of this model,the model not only manifests the longest distance between the seeds and suction boundary area,but reflects the degree of the suction moving area’s accommodating seeds.That is to say,the model represents both the suction capability and suction performance.The physical properties of seeds as well as the quantity of gas flowing into the seed suction pore prove to be two major factors that affect the suction boundary,which comprises the size,shape,thousand kernel weight,density,friction factor of the seeds,the vacuum degree of seeding device,and the diameter of the seed suction hole.The paper suggests the suction boundary of the seeds actually should be an imaginary limit contained in airflow field,which reflects two key conclusions: Firstly,the seeds will only be absorbed when they get into the boundary,otherwise they will remain static.Secondly,if the suction boundary area is expanded,seeds longer distance away from the seed suction pore will be absorbed.Meanwhile,the number of seeds that suction boundary area can accommodate will be increased accordingly.The suction performance of seeding device is in connection with the absorption boundary area as well as the arrangement of seeds around the seed suction hole.The study indicates that,suction boundary areas with the same size will possibly accommodate different numbers of seeds,which is related to the arrangement of the seeds;the suction boundary contains only one seed,the size of the boundary areas may vary due to various arrangements of the seeds.The paper considers that the suction pressure will reach the minimum value when the seed suction pore absorbs only one seed.Under this circumstance,the suction boundary will contain 1 to 5 seeds according to the arrangement of the seeds.By means of analyzing the motion and force of the seeds in the airflow field with flat shape,It is discovered that the force taken by the seeds i will vary due to different conditions.High-speed camera also provides a testimony to the fact that the distribution and arrangement of flat seeds the surface of the roller is extensively complicated,thus only the seeds close to the seeds suction hole can be absorbed.After one seed is absorbed,the seeds suction hole is able to absorb the seeds repeatedly as long as they are close enough to the hole.Compared to the spherical seeds,the arrangement,posture,force,absorption of flat seeds around the seeds suction pore prove to be more complex.During the process of seeding,flat seeds will be more likely to fail,but also have greater chance to achieve “multiple seeds”.The precision seeding for a single flat seed is more difficult than a single spherical seed.During the interval between seed layers rolled out by the roller,at least one seed will flow into the seed suction boundary,to ensure that the seeds suction hole has seeds to absorb,Which is considered to be a requirement for successful seeding of the seeding device.To guarantee the seeds suction pore not to fail in seeding,the seeds around the hole must have fluidity.The vibration suction experiment indicates that the seeds of cabbage,broccoli as well as sweet pepper reflect better fluidity at 40% of vibration intensity,Moreover,the seeds suction pore have better absorption ability.Therefore,the failure rate of cabbage and broccoli seeds is almost 0,and the failure rate of sweet pepper seeds is lower than 3%.Consequently,rate of empty seed will be reduced by adopting certain approach such as vibrating seeds-supplying to improve fluidity.With regard to the requirements of clearing up seeds after seeds are absorbed,a scraping airflow seed-removing device has been developed.The study indicates that the pressure for seed absorption is less than the minimum reasonable pressure,the vibration intensity is 40%,and adopting the measure of seed-removing will reduce “multiple seeds” rate as well as promote percentage of pass,consequently improves seeding accuracy.A 2BS-800 D pneumatic roller-type sample seeder is set up on the basis of the theoretical study of each phase including seed absorption,seed supplying,seed-removing,seed metering,then an experiment is conducted on the seeds of cabbage,radish,eggplant,tomato,and pod pepper to test their seeding effects in the condition that the diameter of the seeds suction hole is 0.5 mm,at speed of 90 mm/s and 135 mm/s respectively.The result indicates that the sample seeder is suitable for precision seeding of single small spherical seeds,and is also appropriate for precision seeding of 1-2 small flat seeds.The study shows that,with the vibration seed-supply device and Collision and Air Blowing device,chose the right suction pressure,pneumatic roller-type metering not only can fulfill the high production rate requirement with the small ball-shape seeds but also can meet the high production rate requirement of the small Flat vegetable seeds ’seeding process. |
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