Design And Research Of Vacuum Precision Seed-metering Device With Synchronously Rotating Plate And Chamber

With the speeding up of large scale production process,the cultivation of crop development direction is changing from pursuit of high yield to same status of production and efficiency,giving priority to benefits.Due to its advantage of saving cost and increasing benefit,precision seeding technology is highly valued.Seed-metering device,the key component of precision planting,faces new technical challenges.Low requirements of seeds shape,high operation precision and speed make vacuum seed-metering device widely used.The friction between seed plate and sealing gasket of vacuum chamber in traditional vacuum precision seed-metering device causes the problems of airtightness reduction,vacuum pressure demand increase and planting precision decline,planting costs increase.The way of changing the material of the gasket to improve the wear resistance is used abroad.It can only extend service life,but cannot avoid wear and tear.Aiming at this problem,a new metering method and a new seed-filling method were proposed;a new type of vacuum precision seed-metering device with synchronously rotating seed plate and vacuum chamber was designed.This seed-metering device utilizes a mechanical disturbance technique to increase activity and reduce interaction of seeds to be filled.And gravity-assisted filling principle is also used.Seeds,which are distributed by a tapered profile of a newly designed circular plate with rectangular embossment,fill into the cells with the help of self-gravity and mechanical disturbance.Seed plate and vacuum chamber are fixed together so that they rotate synchronously during the process of operation with no friction between each other,resulting in no pressure loss.It can save time and cost of replacing the sealing gasket.This metering device has compact structure and stable operation,and the operation effect meets the requirements of the national standard.The main research contents and conclusions of the paper are as follows.(1)A new gravity-assisted filling method for vacuum seed-metering device is proposed.New filling zone proposal is designed.The motion path of flow field and particle field of the seed-metering device are analyzed.The operation method of the new designed seed-metering device is optimized.A mathematical model of force condition of seeds to be filled under gravity-assisted is established.The synchronously rotating of plate and chamber,gravity-assisted filling are achieved.It is found that the radial component along plate of the to be filled seeds gravity and the pressure from upper seeds are in the same direction as the drag force,the radial component along plate of the filled seeds gravity are in the same direction as the pressure gradient force.A simulation study is conducted to determine the effect of the quantity of seeds to be filled and the filling position on the seed filling performance,simulation results shows:the impact of seeds quantity on the average normal force can be ignored when the seeds population is over 600.At this time,the change of the average normal force is related to the filling location,and the average normal force gradually increases with the change of the low,medium,and high positions of the filling position.(2)A new vacuum precision seed-metering device with synchronously rotating plate and chamber is designed.Taking the corn seeds size as reference,the key components feature parameters were determined through theoretical calculations.The structure and main parameters of seed storage box are designed and calculated with the goal of seeds successfully passing through it.The minimum size parameter of the seed storage box should be not less than 24.3 mm,and the adjustment range of seed inlet is(12.74°,30.78°).In order to improve the filling performance and reduce the air pressure requirement,the key parameters of the seed plate are designed and calculated:the maximum outside diameter of the seed plate is 180 mm,the diameter of the hole is 5.4 mm,and the number of holes is 26.Consider gravity-assisted filling and seed clearing comprehensively,the seed plate tilt angle is set to be?=64° and the thickness to be 29 mm.To reduce the interaction force between seeds to be filled,the structure and main parameters of the seed plate disturbing mechanism are determined by digital simulation software EDEM.Seeds kinetic energy is regard as an indicator and the seed dragging effect from seeds disturbance mechanism is taking into account in this simulation.in order to ensure that the path of clearing and retreating is smooth and to avoid mutual interference between seeds come and go,the seeds fall process is analyzed and a seed-falling trough is designed.The volume mathematical model of the seed-falling trough is established,and the maximum allowable seed amount is determined to be 74.Working method of scratching off by seed-removal plate is determined.The optimal design of seed-removal plate is performed to improve unloading result based on the analysis of test results.The effects of straight-type seed-removal plates and tilt-type seed-removal plates on the operation performance of the seed-metering device is compared and analyzed.Statistical analysis is performed on seed falling position and results shows that:the more concentrated the seed filling location area is,the higher the qualified index is;High speed camera technology was used to analyze the falling speed of seeds,the result shows that:the tilt-type seed-removal plates changes the direction of the seed,reduces the instantaneous loss of speed,and makes it easier to form a stable and orderly seed flow.The overall structural of the seed-metering device is determined and its working principle is summarized.Working area is divided into five zones:filling zone,clearing zone,carrying zone,unloading zone and transition zone.Those five zones are analyzed and calculated,the range of each area are ?1?(0°-45°),?2?(45°?63.2°),?3 ?(63.2°?205°),?4 ?(205°?235°),?5 ?(235°?360°),respectively.(3)Flow field of metering device is simulated and optimized by Fluent and EDEM.Fluent three-dimensional model of the flow field and the Bonding model of maize seeds are constructed.The simulation and analysis of the influence of pressure and number of holes on flow field is carried out.Air-solid two-way coupling simulation is performed on the operation process of the vacuum seed-metering device.Changing rules of speed,position and stress situation of seeds are clarified through the simulation data of particle velocity,position and force change over time.Based on the flow velocity of suction mouth,a simulation comparison is made on hole's structure.It is found that air flow velocity from the suction port range as follows:small straight type<outward convex type<inward concave type<chamfered type.Parameters of chamfer hole and flow field structure of air chamber are optimized.It is determined that small diameter,large diameter,and the height of hole extra are dk1=5.4 mm,dk2=7.5 mm,and h=2.6 mm,respectively.And the dip angle of air chamfer is 8d=8°.(4)Indoor bench tests and field tests are conducted to determine key job parameters of seed-metering device.Single-factor tests and two-factor comparison test were conducted.It is determined that the maximum operating speed of the seed-metering device is 12 km/h.-3.5 kPa is the minimum operating air pressure and the optimal value is-4.5 kPa.Compared with Kverneland seed-metering device,the new designed one has a lower demand for pressure and a wider adaptable speed range.Field performance test results show that when the theoretical seed spacing is 0.146 m,the seeder's operating index meets the national standard under operating speed of 9.48 km/h.The qualified index of the seeder increases first and then decreases as speed increasing.The maximum value is reached at 7.68 km/h.When the speed higher than 7.68 km/h,the missing index increases and double index decreases.