| In recent years,the requirement of vegetable has increased with rising living standard.The vegetable industry in our country has flourished and China has become the largest vegetable producer and consumer in the world.Although the vegetable production is affected by the season,the use of greenhouse technology has changed the seasonal characteristics of vegetable cultivation.However,most of greenhouse vegetables are cultivated in way of nursery transplanting,and in view of small seed size,irregular shape,vegetables are still planted in semi-mechanized or manual way,in spite of low efficiency.Therefore,the development of a new kind of metering device,suitable for the characteristics of vegetable seed,is of much significance to promote the fully-mechanized planting of vegetable.Aimed at the characteristics of economic crops,a kind of pneumatic roller precision seed-metering device was put forward,with celery seed of ‘Liang feng' as research object.The contents and conclusions of this paper were listed as follows:(1)Based on the physical properties of seed material,‘Liang feng',a new kind of pneumatic roller precision seed-metering device was proposed,with its working principle and structural parameters explained and determined.Including the design of sucking hole structure,the structure of roller,the axial and circumferential space between seed holes.(2)The dynamic model of seed during seeding process was established,to achieve the influence of the diameter of seed roller,suction hole diameter and drum speed on the minimum negative pressure and the change of minimum adsorption force during the carrying-seed stage,as well as to study the impacts of rotational speed and positive pressure on the horizontal displacement of seeds.(3)To simulate the flow field of the pneumatic roller precision seed-metering device.The pressure distribution in the roller was studied and the results were shown as followed: there was a linear relationship between the pressure at the entry of the sucking hole and that at the inlet of the roller;the rotation speed of roller had no effect on the flow field distribution;Taking the three structural parameters of the suction hole as experimental factors,namely Diameter of entry,Diameter of transition and Diameter of end,flow field in the negative pressure and positive pressure region of the seeder was simulated to obtain the optimal sucking hole structure.(4)Coupling analysis to simulate the metering process was carried out to study the effect of operating parameters such as inlet pressure,rotation speed on seed movement.The results showed that the pressure at the entry of suction hole in the positive and negative pressure zones was approximately linear with inlet pressure of the positive and negative pressure zones.The effect of suction parameters on the flow field distribution in the positive and negative pressure zones of the seed metering device was studied,and the optimum set of suction hole structure parameters was obtained.(5)Both single-factor and orthogonal experiments were conducted on the self-made metering device,about the effect of the suction hole structure and the working parameters of the seed-metering device on the seeding performance.The results showed that: the seeding performance indexes of the pneumatic roller precision seed-metering device,such as qualified rate,single seed rate,multiply rate,missing index,were significantly affected by the experimental factors of diameter of entry,diameter of end,the pressure of at the inlet of positive and negative pressure region and the rotational speed of roller.The metering device worked in an optimal state with diameter of entry 0.7mm,diameter of transition 2mm,diameter of end 2mm,roller speed 12 r / min,the pressure at the inlet of positive and negative pressure region 1500 Pa and-4000 Pa,where the qualified rate reached 71.78%.and the ‘misses' was 16.82%. |
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