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非开沟式插条机构的理论与实验研究

Theoretical and Experimental Research of Non-ditched Cuttings Transplanting Machine

【作者】 姚立红

【导师】 王乃康; 茅也冰;

【作者基本信息】 北京林业大学 , 机械设计及理论, 2008, 博士

【摘要】 开沟式插条机,先开沟,后插条,插条不受土壤阻力,不会断裂。但开沟深度大,当株距较大时,在插条之间的空地也开出不必要的深沟,浪费发动机动力,又破坏了地表植被。为了节约能源,保护地表植被,需要设计不整地、不开沟的非开沟式插条机,使插条直接插入土壤。如果土壤太硬,必须开沟时,则应开窄短沟。非开沟式插条机面临的主要问题是插条在土壤中运动时受土壤阻力而变形,变形太大则会断裂。所以应尽量减小插条在土壤中的位移量,使插条在土壤中运动轨迹在行驶方向最窄,并求出与之相应的机构参数;另外,通过设计实验装置,对理论研究所获得插条最佳运动轨迹进行实验验证;测试土壤阻力引起插条的应变,掌握插条的受力、破坏和变形规律;通过直径不同的实际插条在紧实度不同的土壤中进行插土试验,统计插土深度、插条直径、插条端部削尖与否等因素与土壤紧实度之间的关系,确定其对插条插入土壤难易程度的影响。所有这些都为插条机的设计打下理论与实践基础。本研究所采用的研究方法是利用计算机CAXA软件对各个不同参数条件下插条运动轨迹的模拟,然后通过数学推导论证并结合编写计算机程序对插条运动轨迹及插条机构参数进行优化,最后通过自行设计的实验装置、电阻应变仪、土壤紧实度仪等对插条运动轨迹、插条应变、土壤紧实度进行测试,并在插条试验机上用实际插条进行插土试验。对径向插条机构,当中心高H、插深A、虚轮半径R等发生改变时,插条运动轨迹在水平方向的宽度M也发生改变。当A和R一定,H较大或较小时,都会使M较大;R越大,M越小;A越小,M值越小;当插深一定时,如果保持插条运动轨迹所包络的轮廓水平宽度上下一致时,即采用本作者提出的“虚实地面轮廓宽度一致法”进行优化,插条在土壤中运动的轮廓宽度最窄。对垂直插条机构,其插条犁上各点的运动轨迹完全由曲柄最外端点的运动轨迹来决定,在虚轮半径一定时,插条犁在土壤中运动轨迹的纵截面形状及其尺寸、插条犁在土壤中水平运动方向,与曲柄长度相对于虚轮半径的取值大小有关;在曲柄长度正好等于虚轮半径时,插条犁在土壤中运动方向朝前,轨迹的纵截面下面最尖,较瘦,面积较小,因而动力消耗小,插条犁在土壤中运动过程中消耗功率较均衡。对直接插种的垂直插条机构,用本作者首次提出的“超两点法”的优化方法,可使插条在土壤中运动轨迹的水平宽度达到最小,由此决定了最佳的曲柄设计长度;当虚轮每转一周插条根数分别为3、4、5,而株距都是1m,插深A从100~250mm时,通过优化,得到最佳曲柄的各个长度值及插条机构的中心高。采用自行设计的实验装置,对径向插条运动轨迹进行实验验证,证明了计算机模拟、数学推导及计算机程序计算的最佳参数的准确性;经过对实际插条进行三点弯曲实验,对测定插条弯曲应变所用钢插条进行了研究;通过对插条进行破坏性弯曲试验,发现插条是在弯矩最大的夹持部位破坏,而且插条是被弯矩引起的正应力拉断,说明插条的抗拉强度低于其抗压强度,另外,插条在破坏前,加载端挠度变形均较大;土壤的紧实度是一个很难模拟的量,提出土壤的等效紧实度概念及其计算方法,便于评价土壤的紧实度对插条受力的影响;通过对插条的速度及受力分析,得知插条在土壤中受到土壤对插条杆部的挤压力及摩擦分力是引起插条破坏的主要因素,并结合钢试件插条插入土壤进行弯曲应变测试,得知试件的应变值沿着插条长度方向线性增加,最大值位于插入最深时试件的夹持端,土壤等效紧实度值越大,应变值越大。分析与实践证明,实际插条插入土壤时,若土壤等效紧实度大,则插条的破坏会发生在夹持端;若土壤紧实度较小,则插条不会破坏,但插条在夹持端会有些弯曲,留在土壤中的部分基本保持直线状态并倾斜,当插条夹放松后,插条为倾斜状态。通过插条试验机,用实际插条进行插土实验,插深越小,越容易插入土壤;插条端头削尖与否没有多大区别;直径为12-16mm的插条,插入土壤的难易程度几乎一样。本研究采用CAXA软件对不同参数时的插条运动轨迹进行模拟,用数学方法对径向插条机构、垂直插条机构的插条犁或直接插植的插条运动轨迹及其影响规律进行了严格的推导和论证,提出了“虚实地面轮廓宽度一致法”及“超两点法”的观点,结合编制计算机程序对插条机构参数进行优化方法,从而得出最佳机构参数;通过自行设计的插条机构试验设备及土壤紧实度仪,对插条插植的运动轨迹进行了实验验证,并结合实验提出“土壤等效紧实度”的概念及其计算方法,进而通过实验研究插条的弯曲应变,提出插条“压土点”和“推土点”的概念,分析插条的受力、破坏及变形规律;在插条试验机上用实际插条进行插土实验,统计并分析插条直径、插土深度、插条端部削尖与否与土壤紧实度的关系。以上这些研究方法及研究成果在国内未见报导,具有创新性。

【Abstract】 Ditch-cutting machine’s work step is first furrowing and then cutting.The cuttings have not resistance from the soil and cannot be broken.But the deep and wide furrow in the soil of larger spacing between two plants is unnecessary and results in a waste of engine power and the destruction of surface vegetation.In order to save energy and to protect the surface vegetation, non-furrow-cutting machines need to be designed so that the cuttings can be directly inserted into soil. If the soil is too hard for the cuttings to be directly inserted into,a narrow and short ditch should to be open.The main problem faced by non-furrow-cutting machine is deformation of the cuttings because of their moving in the soil and soil resistance.Excessive deformation will cause cuttings to be broken. Therefore the displacement of the cuttings in the soil should be minimized,and the moving track of the cuttings in the soil will be the narrowest in the direction of level.The corresponding mechanism parameters calculated in this paper is for the reason.In addition,the experimental device is designed to validate the best path,got by theoretical study,of the cuttings in the soil,to test the cuttings’ strain caused by soil resistance and to master the law of cuttings’ force,destruction and deformation. Through different diameters of the actual cuttings inserting into different compaction of soil,the relationships of soil depth,diameter of cuttings,and cuttings tip’s sharpness with the soil compaction can be get.All of this lay a foundation for the theory and practice of non-furrow-cutting machine designing.The methods used in the research are the cutting path simulation on various parameters by computer software CAXA,mathematical proof in conjunction with the writing of computer programs on the cutting path and cutting parameters to optimize mechanism,using self-designed experimental equipment,resistance strain gauge,soil compaction meter to test the cuttings’ movement track,cutting strain,soil compaction testing,and inserting the actual cuttings into the soil with the cuttings’ test machine.On the radial cutting mechanism,when the height H of the center,depth A of cutting,radius R of the imaginary wheel etc.changes,the width M of the cutting path in the direction of the level will change.When the radius R and depth A keep invariable,the height H to a greater or lesser,the width M will make more.The greater the radius R is,the smaller the width M is.The smaller the depth A is, the smaller the width M.When inserting a certain depth,if keep the outline formed by the path of the cuttings the same width on the actual and the imaginary ground,the width of the outline in the soil will be the narrowest.This approach,brought up by the author for the first time,is known as imaginary-and-actual-same-ground-outline-width-method.On the vertical cutting mechanism,the movement track of all points on the cutting plow is decided by the movement track of outside end of the crank set in the mechanism.In a certain radius of the imaginary wheel,the size and shape of the longitudinal section of the movement track of the cutting plow in the soil,the level direction of the cutting plow movement in the soil,relate to the difference of the crank length relative to the radius of imaginary wheel.In the crank length is equal to the radius of imaginary wheel,the movement of cutting plow in the soil is in the forward direction, and the vertical cross-section of the track is sharp and thin and therefore small in area,small in power consumption.The power consumption in the process of cutting plow movement in the soil is of approximately equality.On the vertical cutting mechanism which Inserted cuttings directly into the soil without cutting plow,with super-two-point optimization methods brought up by the author first, the level width of the profile of the cuttings movement in the soil is of minimum,and the best design of the crank length is determined.Inserting cuttings into the soil with the cutting mechanism,the number of cuttings respectively being 3,4,5 when the mechanism rotating every turn,the spacing between two plants being 1m,cuttings depth A into the soil being from 100~250mm,through the optimization,the best value in all of crank length and the mechanism’s center height are calculated.With the device self-designed,the radial cutting track is verified being exactly the same with the theory deduced.Using the data of three-point bending experiment of the actual cuttings,steel cutting specimen is designed to test cuttings’ bending strain.By cuttings’ destructive bending test,it is found that cuttings’ destruction happened at the cross-section next to where the cutting is gripped,and cuttings were pulling off by the normal stress caused by bending moment,and the tensile strength of the cuttings is lower than the compressive strength.In addition,the load end deflection of the cuttings before damage is larger than 100mm.Soil compaction is a very difficult to simulate,the concept of the soil equivalent compaction and its method of calculating is proposed for the evaluation of soil compaction.By cuttings’ speed and force analysis,it is known that the pressure and friction of soil on the cuttings’ bar is the main factors that cause the damage of the cuttings.Inserting the steel sample into the soil for bending strain,it shows that strain of the sample along the length of the cuttings linear increases,and the maximum is at the gripping end of the specimen when inserting to the deepest.The greater the soil compaction,the greater the strain is.Analysis and practice has proved that,when the actual cuttings inserting into soil,if the soil equivalent compaction being enough great,the cuttings’ damage occurs in the gripping end.If the soil compaction being smaller,the cuttings will not be damaged,but there will be some bending at the holding end,the remains part of cuttings in the soil will maintain a straight line and tilt.By cutting test machine,inserting the actual cuttings into soil,it is clear that the smaller the inserting depth,the easier it is inserted into the soil.Cuttings’ end,whether sharpened or not,has not much difference.12-16mm diameter of the cuttings,when inserting into the soil,have almost the same degree of difficulty. CAXA software is used in this study to simulate the cuttings path of the cutting mechanism when it dealing with different parameters.Mathematical methods are used for strict derivation and demonstration of the track and its changing law of cuttings in radial cutting mechanism,of the cutting plow or cuttings in vertical cutting mechanism.Proposed the point of view of ’Same Contour Width on Imaginary and Actual Ground Optimization’ and ’Super-Two Optimization’.In conjunction with the methods of preparation of the computer program to the cutting mechanism parameters optimization,the best mechanism parameters are arrived at.With the experimental equipment designed for the cutting mechanism as well as soil compaction meter,the track of the cuttings movement in the soil has experimental verification.Combind with experiment,’soil equivalent compaction’ and its method of calculating is proposed.Through the experimental study of cuttings’ bending strain,the conception of cuttings’ ’soil-pressure-point’ and ’soil-push-point’ are proposed to analyse the cuttings’ force,deformation and destruction.With the cutting machine,inserting actual cuttings into soil,the relation of the cutting diameter,inserting depth of soil,and the cuttings end sharpness with the soil compaction can be got.All of the methods and the results of the research in China have not been reported innovative.

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