【作者】 龚智强；

【导师】 陈进；

【作者基本信息】 江苏大学 ， 机械设计及理论， 2013， 博士

【摘要】 精密排种装置是实现精密播种作业的关键设备,其性能优劣直接关系到作物生产的产量和品质。目前,超级稻穴盘育苗精密排种装置还处于探索研究阶段,现有的水稻排种装置大都属机械式,伤种较严重,且每穴播种达3-5粒,难以满足超级稻种植对播种技术的农艺要求(2±1粒／穴,低伤种率),因此,急需开展超级稻穴盘育苗精密排种装置的理论与试验研究。本文以设计的新型气吸振动盘式精密排种装置为研究对象,通过振动理论、计算流体动力学、离散元法、机构学、实验优化等理论,并结合先进的计算机仿真技术深入研究播种过程中排种装置机构运动、振动激励和气力对超级稻种子的作用机理及种群的运动规律、连续播种过程最佳吸种效果的参数组合,提出了精密播种理论,主要研究工作包括：(1)采用专业测量仪器对三个品种超级稻芽种基础物理特性参数进行测试和分析,得到芽种的三轴几何尺寸分布概率、千粒重、密度、摩擦系数、休止角、恢复系数和力-位移变化关系,为离散元仿真和排种装置吸种部件设计提供依据。(2)运用FLUENT对排种装置气流场进行研究：①分析吸种盘气流场分布规律,得出影响气流场的主要因素为吸孔孔径、真空负压值,得到均匀稳定流场的最佳结构及工作参数；②分析气流场中种子颗粒受力影响因素,得出其主次顺序为种子与吸孔的距离、种子姿态、真空负压值、吸孔孔径；建立种子受力数学模型,分析得出：真空负压值与孔径应合理匹配,小孔径需较大的真空负压值,高度方向的种子最容易被吸附；真空负压值为3～5kpa范围内,吸孔孔径为1.5mm～2.0mm时,吸孔吸附距离范围为0.34mm～1.90mm;③对吸种盘正压气流场进行模拟,得出流量对吸种盘正压气流场影响大,随着流量增加,吸孔口气流流速急剧增大,种子受到气流吹力增大,内板厚度对正压气流场分布和流量几乎无影响；④进行气流场流量测定及种子颗粒吸附试验,试验结果与FLUENT模拟值基本吻合,表明数值模拟结果的正确性。(3)进行排种装置的机构运动分析：①采用ADAMS对振动种盘机构运动进行分析,得到机构动力源的变化规律：随着频率和振幅的增大,最大驱动扭矩逐渐增大；②基于机构学理论,研究符合水平调节要求的并联机构,对一平移两转动并联机构进行型综合,设计水平调节机构,获得机构位置关系和精度模型；③建立携种过程种子颗粒受力数学模型,推导带动吸种盘运动的机械手动力学特性要求。随着负压值的增大,机械手临界加速度增加。长度方向吸附的种子最容易发生掉落,机械手设计时应满足长度方向不发生掉落的条件；④建立种子颗粒与吸种盘的碰撞运动数学模型,得出种子颗粒不被碰离吸种盘面板的弹回临界速度与负压值的关系。随着负压值增大,种子颗粒弹回临界速度增加。长度方向碰撞的种子最容易发生弹回掉落,当碰撞弹回速度大于临界弹回速度时,种子将脱离气流场约束并弹离吸孔。(4)基于离散元理论,研究振动种盘内种群运动,得出：①单颗粒种子运动具有波动性,受种群颗粒间约束力的相互作用,种群的运动呈规律性变化；②随着振动种盘振动频率和振幅的增加,种群竖直方向平均位移、平均速度和颗粒受力逐渐增大,种群抛掷运动的激烈程度增加,相对空间分布密度逐渐变小,增大频率和振幅能有效增大种群抛掷高度。单层种群抛掷高度、颗粒平均法向力和平均切向力大于其他种层厚度种群,其他种层厚度种群的竖直方向平均位移和平均速度、颗粒间平均受力及种群空间离散程度受种层厚度的影响较小。种子颗粒受到的作用力最大值小于0.03N,得出振动种盘的运动对种子损伤极小；③分析连续播种过程振动种盘内种子逐渐减少的变质量系统种层厚度与振动种盘振动参数的关系,建立排种装置工作参数与吸种距离(吸种盘面板与种层表面之间距离)之间的数学模型。得出影响种群抛掷高度的因素主次顺序为：振动频率、振幅、种层厚度,振动频率与振幅应合理匹配；仿真模拟倾斜状态振动种盘内种群运动,振动种盘倾角越大时种群运动均匀性越差,倾角越小对振动种群空间分布均匀性越有利；④基于CFD-DEM耦合理论,应用FLUENT-EDEM耦合方法仿真模拟了排种装置吸种过程,得出了参数变化规律。(5)研制一种新型气吸振动盘式精密排种装置试验台,并开展台架试验。①进行单因素试验和正交试验,着重分析真空负压值、吸孔孔径、振动种盘振动频率、振幅、吸种距离等因素对播种性能指标的影响,得出影响合格率的因素主次顺序为：吸种距离、振动频率、振幅、真空负压值、吸孔孔径；影响重播率的因素主次顺序为：真空负压值、吸孔孔径、吸种距离、振动频率、振幅；影响空穴率的因素主次顺序为：吸种距离、真空负压值、吸孔孔径、振动频率、振幅；吸种距离和频率对播种合格率有显著影响,真空负压值和吸孔孔径对重播率有显著的影响,吸种距离和负压真空值对空穴率有显著影响。②建立排种装置工作参数与播种性能指标之间的数学模型,进行遗传算法的多目标优化,得到最优解：真空负压值3.68kPa,吸孔孔径1.84mm,振动频率10.90Hz,振幅4.09mm,吸种距离3.92mm,并进行试验验证。③对不同品种超级稻进行播种试验,证明排种装置对不同品种超级稻芽种具有较好适应性。采用排种装置对芽种进行播种育苗试验,证明排种装置不损芽。通过对播种后的穴盘进行育苗后发现,该排种装置能满足超级稻种植的育苗要求。试验结果与理论分析相一致,为精密排种装置的设计提供理论依据。更多还原

【Abstract】 Seeding device is the key equipment to precision seeding, the quality of seeding is related to high quality and high yield directly. Presently, the seeding device of super rice is still at the exploratory stage, the seeding device of rice used wildly are mechanical type, which cause a more serious seeds injury, only meet seeding3-5seeds per hole,and difficultly to meet the super rice planting on seeding agronomic requirements(2±1seeds per hole, little seeds injury). Therefore, study on theory of super rice plug seedling precision seeding device is become a more urgently needed. The research takes new designed vacuum-vibration tray precision seeding device as object, through vibration theory, computational fluid dynamics, discrete element method, mechanism, experimental optimization theory, deeply study mechanism motion, the law of seed group vibration excitation and pneumatic strength to super rice particle in seeding process, combined with advanced computer simulation technology, parameter combination in the continuous seeding process of optimal suction seeds effect, put forward to precision seeding theory, the major research work as follows:(1) Make measurement and analysis three types of super rice sprout basic physical parameters change by professional measurement instruments:get three-axis geometry size distribution probability, thousand-grain weight, density, friction coefficient, repose angle, the recovery restitution and force-displacement changing process of super rice sprout. Provided the basis for the discrete element simulation and suction component designing of seeding device.(2) Study flow field of seeding device by FLUENT:①Analysis flow field distribution law of suction plate, get main factors which affecting flow field are suction hole’s aperture, vacuum negative pressure value, obtain the optimal structure and working parameters of the uniform stability flow field.②Analysis influence factors of seed particle force in flow field, the primary-secondary order is:the distance seed and suction hole, seed attitude, vacuum negative pressure value, suction hole’s aperture; set up seed force mathematical model, and then get:vacuum negative pressure value and suction hole’s aperture should be reasonable matching, small aperture need larger vacuum negative pressure, height direction of seed is most easily adsorbed; vacuum negative pressure value is in the range of3-5kPa, when suction hole’s aperture is1.5mm～2.0mm, suction pore distance range is from0.34mm to1.90mm.③Simulate the suction plate of air flow field, get flow effect to the suction plate air flow, with increasing of flow, with the seed force increasing by air blowing,suction orifice flow velocity increases rapidly, effect of inner plate thickness on the positive pressure air flow distribution and flow is little.④Test flow of field flow and seed particles adsorption, test results and FLUENT simulation results are in good agreement, which shows that the correctness of numerical simulation results.(3) Carry out mechanism kinematic analysis of seeding device.①Study on vibration plate motion by ADAMS, get the change of mechanism’s power:with the increasing of frequency and amplitude, maximum driving torque increases.②Based on mechanism theory of parallel mechanism, study parallel mechanism with level adjustment requirements, carry out type synthesis of a translation two rotation parallel mechanism, design a horizontal adjusting mechanism, get the relationship between the position and the accuracy model.③Analysis seed particle force and build the seed particle force model, get the dynamic characteristics of suction disc movement requirements. With the increasing of pressure, the critical acceleration of manipulator increases. Seed most easily falling at the length of seed adsorption, manipulator design should satisfy the length direction falling condition that does not occur.④Study on seed particles and suction plate collision movement, establishing collision motion model, get the relationship between seed particles is not touched off the bounce of critical velocity and negative pressure suction panel values. With the pressure increase, the critical velocity of seed particles increase. The length of seed is most likely to occur collision bounce off, when the impact velocity is greater than the critical speed, the seed will be out of flow field constraints and bounce off suction hole.(4) Based on the theory of discrete element method, study seed group movement in vibration plate, get:①Movement of the single seed has fluctuation, seed group movement changes regularly without obvious fluctuations, the reason is that the formation of constraint forces between seeds particles.②With the increase of vibration frequency and amplitude of plate, the average displacement of seeds, the average velocity and the particle force of Z direction gradually increases, throwing motion of seeds increase fiercely, relative spatial distribution density becomes smaller gradually, increasing frequency and amplitude can increase throwing height of seeds effectively. Average normal force and average tangential force of single layer thickness, is larger than other kinds of thickness seeds which Z direction average displacement, average velocity and particle force is closed, spatial discrete of seeds is similar. Maximum force of seed particles are less than0.03N, vibration plate has minimal damage to seed.③Study on parameters relationship between thickness and vibration of seeds that seed of variable mass system gradually reduce in seeding process, establish mathematical models between device parameters and suction distance(the distance between the panel and layer surface). The effect order throwing height of seeds is: vibration frequency, amplitude, layer thickness. get vibration frequency and amplitude shoould be reasonable matching; simulation for plate tilt state seeds movement, when the plate angle is large, seeds movement uniformity is worse, tilt angle is smaller, the space vibration of seeds distribution uniformity is more favorable.④Based on the theory of CFD-DEM coupling, simulate suction process of seeding device, get the variation of parameters.(5) Designing a new type of vacuum-vibrating tray precision seeding device test bed, carrying out bench test①Single factor test and orthogonal experiment, emphatically analysis vacuum negative pressure value, suction hole’s aperture, vibration frequency of plate, amplitude,the suction distance on effects of seeding performance. Get the primary-secondary order of the factors affecting qualified rate are:the suction distance, vibration frequency, amplitude, vacuum negative pressure value, suction hole’s aperture Get the primary-secondary order of the factors affecting rebroadcast rate are: vacuum negative pressure value, suction hole’s aperture, the suction distance, vibration frequency, amplitude. Get the primary-secondary order of the factors affecting cavity rate are:the suction distance, vacuum negative pressure value, suction hole’s aperture, vibration frequency, amplitude. The suction distance and frequency had significant effects on the pass rate of seeding, vacuum negative pressure value and suction hole’s aperture had significant effects on rebroadcast rate, the suction distance and vacuum negative pressure value had a significant effects on cavity rate.②Establishing a mathematical model between seeding device parameters and seeding performance index, made multiobjective optimization genetic algorithm, get the optimal solution:vacuum negative pressure value is3.68KPa, suction hole’s aperture is1.84mm, vibration frequency is10.90Hz, amplitude is4.09mm, the suction distance is3.92mm, and which verified by experiments.③Through seeding test of different kinds of super rice, which showed that the seeding device has a good adaptability to different varieties of super rice, which are suitable for different varieties of super rice seeding. Through seeding seedling test which showed that the seeding device can meet the requirements of super rice plant. Seeding test by seeding device, statistics after sowing budding condition. The seeding device does not hurt bud, and meet requirements of super rice planting seedling.The results are consistent with theoretical analysis, and provide a theoretical basis for precision seeding device’s designing.更多还原