马铃薯播种机的性能评估-机械外文资料翻译.doc

中国地质大学长城学院本科毕业论文外文资料翻译系 别： 工程技术系 专 业：机械设计制造及其自动化姓 名： 学 号： 2010 年 03月 10 日外文资料翻译译文马铃薯播种机的性能评估 大多数马铃薯播种机都是通过勺型输送链对马铃薯种子进行输送和投放。当种植精度只停留在一个可接受水平的时候这个过程的容量就相当低。主要的限制因素是：输送带的速度以及取薯勺的数量和位置。假设出现种植距离的偏差是因为偏离了统一的种植距离，这主要原因是升运链式马铃薯播种机的构造造成的.一个理论的模型被建立来确定均匀安置的马铃薯的原始偏差，这个模型计算出两个连续的马铃薯触地的时间间隔。当谈到模型的结论时，提出了两种假设，一种假设和链条速度有关，另一种假设和马铃薯的形状有关。为了验证这两种假设，特地在实验室安装了一个种植机，同时安装一个高速摄像机来测量两个连续的马铃薯在到达土壤表层时的时间间隔以及马铃薯的运动方式。结果显示：（a）输送带的速度越大，播撒的马铃薯越均匀；（b）筛选后的马铃薯形状并不能提高播种精度。主要的改进措施是减少导种管底部的开放时间，改进取薯杯的设计以及其相对于导种管的位置。这将允许杯带在保持较高的播种精度的同时有较大的速度变化空间。介绍说明升运链式马铃薯种植机（图一）是当前运用最广泛的马铃薯种植机。每一个取薯勺装一块种薯从种子箱输送到传送链。这条链向上运动使得种薯离开种子箱到达上链轮，在这一点上，马铃薯种块落在下一个取薯勺的背面，并局限于金属导种管内.在底部，输送链通过下链轮获得足够的释放空间使得种薯落入地沟里。 图一，杯带式播种机的主要工作部件：（1）种子箱；（2）输送链；（3）取薯勺；（4）上链轮；（5）导种管；（6）护种壁；（7）开沟器；（8）下链轮轮；（9）释放孔；（10）地沟。 株距和播种精确度是评价机械性能的两个主要参数。高精确度将直接导致高产以及马铃薯收获时的统一分级(McPhee et al, 1996；Pavek & Thornton, 2003)。在荷兰的实地测量株距（未发表的数据）变异系数大约为20%。美国和加拿大早期的研究显示，相对于玉米和甜菜的精密播种，当变异系数高达69%(Misener, 1982；Entz & LaCroix, 1983；Sieczka et al, 1986)时，其播种就精度特别低。输送速度和播种精度显示出一种逆相关关系，因此，目前使用的升运链式种植机的每条输送带上都装备了两排取薯勺而不是一排。双排的取薯勺可以使输送速度加倍而且不必增加输送带的速度。因此在相同的精度上具有更高的性能是可行的。该研究的目的是调查造成勺型带式种植机精度低的原因，并利用这方面的知识提出建议，并作设计上的修改。例如在输送带的速度、取薯杯的形状和数量上。为了便于理解，建立一个模型去描述马铃薯从进入导种管到触及地面这个时间段内的运动过程，因此马铃薯在地沟的运动情况就不在考虑之列。由于物理因素对农业设备的强烈影响(Kutzbach, 1989)，通常要将马铃薯的形状考虑进模型中。两种零假设被提出来了：（1）播种精度和输送带速度无关；（2）播种精度和筛选后的种薯形状（尤其是尺寸）无关。这两种假设都通过了理论模型以及实验室论证的测试。材料及方法2.1 播种材料几种马铃薯种子如圣特、阿玲达以及麻佛来都已被用于升运链式播种机测试，因为它们有不同的形状特征。对于种薯的处理和输送来说，种薯块茎的形状无疑是一个很重要的因素。许多形状特征在结合尺寸测量的过程中都能被区分出来(Du & Sun, 2004； Tao et al, 1995； Zdler, 1969)。在荷兰，马铃薯的等级主要是由马铃薯的宽度和高度（最大宽度和最小宽度）来决定的。种薯在播种机内部的整个输送过程中，其长度也是一个不可忽视的因素。形状因子S的计算基于已经提到的三种尺寸： 此处l是长度，w是宽度，h是高度（单位：mm），且hw001 m时，这种关系是线性的。 ，测量数据；，数学模型的数据； ，延长到R 0 01米； -，线性关系；R2，决定系数。3.2 马铃薯的尺寸和形状 实验数据由表三给出。显示固定进料率为每分钟400个种薯的时间间隔的标准偏差。这些结果与期望值刚好相反，即高的标准偏差将使得形状因子增加。球状马铃薯的结果尤其令人吃惊：球的标准偏差高过阿玲达马铃薯50%以上。时间间隔的正态分布如图七所示，球和马铃薯之间的差异明显。两个不同品种的马铃薯之间的差异不明显。 表三 马铃薯品种对种植间距的精确度的影响 品种 标准偏差，ms CV, % 阿玲达 8.60 30 麻佛来 9.92 35 高尔夫球 13.24 46 图七，固定进料率下不同形状的沉积的马铃薯时间间隔的正态分布。球状马铃薯的这种结果是因为球可以以不同的方式在取薯勺背部定位。临近杯中球的不同定位导致沉积精度降低。杯带的三维视图显示了取薯勺与导种管之间的间隔的形状，显然获得不同大小的开放空间是可行的。图八，取薯勺呈45度时的效果图；马铃薯在护种壁的位置对其释放具有决定性影响。阿玲达块茎种薯在沉积时比麻佛来的精度高。通过对记录的帧和马铃薯的分析，结果表明：阿玲达这种马铃薯总是被定位平行于最长的轴线的护种壁。因此，除了形状因子外，宽度与高度的高比例值也将造成更大的偏差。阿玲达的这个比例是1.09，麻佛来的为1.15。3.3 实验室对抗模型测试平台该数学模型预测了不同情况下的流程性能。相对于马铃薯，该模型对球模拟了更好的性能，然而实验测试的结果却恰然相反。另外实验室试验是为了检查模型的可靠性。在该模型里，两个马铃薯之间的时间间隔被计算出来。起始点出现在马铃薯开始经过A点的时刻，终点出现在马铃薯到达C点的时刻。通过实验平台，从A到C点的马铃薯的时间间隔被测出。每个马铃薯的长度、宽度和高度也通过测量获得，同时记录了马铃薯的数量。测量过程中马铃薯在取薯杯上的位置是已经确定好的。这个位置和马铃薯的尺寸将作为模型的输入量，测量过程将阿玲达与麻佛来以400个马铃薯每分的速率下进行。测量时间间隔的标准偏差如表四所示。测量的标准误差与模型的标准误差只是稍稍不同。对这种不同现象的解释是：（1）模型并没有把图八中出现的情况考虑进去；（2）从A点到C点的时间不一致。块状马铃薯如阿玲达可能从顶部或者最远距离下落，这将导致种薯到达C点底部的时间增加6ms表四 通过实验室测量和模型计算出来的开放时间的标准误差的差异 品种 形状因子 标准偏差, ms 测量值 计算值 阿玲达 326 8.02 5.22 麻佛来 175 6.96 4.404. 总结这个模拟马铃薯从输送带开始释放的运动的数学模型是一个非常有用的证实假设和设计实验平台的工具。模型和实验室的测试都表明：链速越高，马铃薯在零速度水平沉积得更均匀。这是由于开口足够大使得马铃薯下降得越快，这对马铃薯的形状和种薯在取薯杯上的定位有一定的影响，与链条速度的关系也就随之明确，因此，在保持高的播种精度时，应该提供更多的空间以减小链条的速度。建议降低链轮的半径，直至低到技术上的可行度。该研究显示，播种机的取薯勺升运链链对播种精度（播种的幅宽）有很大的影响。更规格的形状（形状因子低）并不能自动提高播种精度。小球（高尔夫球）在很多情况下沉积的精度低于马铃薯，这是由导向的导种管和取薯勺的形状决定的。因此建议重新设计取薯勺和导种管的形状，要做到这一点还应该将小链轮加以考虑。外文原文Assessment of the Behaviour of Potatoes in a Cup-belt PlanterThe functioning of most potato planters is based on transport and placement of the see potatoes by a cup-belt. The capacity of this process is rather low when planting accuracy has to stay at acceptable levels. The main limitations are set by the speed of the cup-belt and the number and positioning of the cups. It was hypothesized that the inaccuracy in planting distance, that is the deviation from uniform planting distances, mainly is created by the construction of the cup-belt planter. To determine the origin of the deviations in uniformity of placement of the potatoes atheoretical model was built. The model calculates the time interval between each successive potato touching the ground. Referring to the results of the model, two hypotheses were posed, one with respect to the effect of belt speed, and one with respect to the inuence of potato shape. A planter unit was installed in a laboratory to test these two hypotheses. A high-speed camera was used to measure the time interval between each successive potato just before they reach the soil surface and to visualize the behaviour of the potato. The results showed that: (a) the higher the speed of the cup-belt, the more uniform is thedeposition of the potatoes; and (b) a more regular potato shape did not result in a higher planting accuracy. Major improvements can be achieved by reducing the opening time at the bottom of the duct and by improving the design of the cups and its position relative to the duct. This will allow more room for changes in the cup-belt speeds while keeping a high planting accuracy. 1. Introduction The cup-belt planter (Fig. 1) is the most commonly used machine to plant potatoes. The seed potatoes are transferred from a hopper to the conveyor belt with cups sized to hold one tuber. This belt moves upwards to lift the potatoes out of the hopper and turns over the upper sheave. At this point, the potatoes fall on the back of the next cup and are confined in a sheet-metal duct. At the bottom, the belt turns over the roller, creating the opening for dropping the potato into a furrow in the soil. Capacity and accuracy of plant spacing are the main parameters of machine performance.High accuracy of plant spacing results in high yield and a uniform sorting of the tubers at harvest (McPhee et al., 1996; Pavek & Thornton, 2003). Field measurements (unpublished data) of planting distance in The Netherlands revealed a coefficient of variation (CV) of around 20%. Earlier studies in Canada and the USA showed even higher CVs of up to 69% (Misener, 1982; Entz & LaCroix, 1983; Sieczka et al., 1986), indicating that the accuracy is low compared to precision planters for beet or maize. Travelling speed and accuracy of planting show an inverse correlation. Therefore, the present cup-belt planters are equipped with two parallel rows of cups per belt instead of one. Doubling the cup row allows double the travel speed without increasing the belt speed and thus, a higher capacity at the same accuracy is expected. The objective of this study was to investigate the reasons for the low accuracy of cup-belt planters and to use this knowledge to derive recommendations for design modifications, e.g. in belt speeds or shape and number of cups. For better understanding, a model was developed, describing the potato movement from the moment the potato enters the duct up to the moment it touches the ground. Thus, the behaviour of the potato at the bottom of the soil furrow was not taken into account. As physical properties strongly inuence the efficiency of agricultural equipment (Kutzbach, 1989), the shape of the potatoes was also considered in the model. Two null hypotheses were formulated: (1) the planting accuracy is not related to the speed of the cup-belt; and (2) the planting accuracy is not related to the dimensions (expressed by a shape factor) of the potatoes. The hypotheses were tested both theoretically with the model and empirically in the laboratory. Fig 1. Working components of the cup-belt planter: (1) potatoes in hopper; (2) cup-belt; (3) cup; (4) upper sheave; (5) duct; (6) potato on back of cup; (7) furrower; (8) roller; (9) release opening; (10) ground level 2 .Materials and methods 2.1. Plant material Seed potatoes of the cultivars (cv.) Sante, Arinda and Marfona have been used for testing the cup-belt planter, because they show different shape characteristics. The shape of the potato tuber is an important characteristic For handling and transporting. Many shape features, usually combined with size measurements, can be distinguished (Du & Sun, 2004; Tao et al., 1995; Zodler,1969).In the Netherlands grading of potatoes is mostly done by using the square mesh size (Koning de et al.,1994),which is determined only by the width and height (largest and least breadth) of the potato. For the transport processes inside the planter, the length of the potato is a decisive factor as well. A shape factor S based on all three dimensions was introduced: (1)Where/ is the length, w the width and h the height of the potato in mm, with hwl. As a reference, also spherical golf balls (with about the same density as potatoes), representing a shape factor S of 100 were used. Shape characteristics of the potatoes used in this study are given in Table 1. 表一 实验中马铃薯及高尔夫球的形状特征 品种 方形网目尺寸，毫米 形状因子 圣特 2835 146 阿玲达 3545 362 麻佛来 3545 168 高尔夫球 42.8 1002.2. Mathematical model of the process A mathematical model was built to predict planting accuracy and planting capacity of the cup-belt planter. The model took into consideration radius and speed of the roller, the dimensions and spacing of the cups, their positioning with respect to the duct wall and the height of the planter above the soil surface (Fig. 2). It was assumed that the potatoes did not move relative to the cup or rotate during their downward movement. The field speed and cup-belt speed can be set to achieve the aimed plant spacing. The frequency fpot of potatoes leaving the duct at the bottom is calculated as (2)where v c is the cup-belt speed in m s1and xc is in the distance in m between the cups on the belt. The angular speed of the roller r in rad s1 with radius r r in m is calculated as (3)The gap in the duct has to b e large enough for a potato to pass and be released .This gap xrelease in m is reached at a certain angle release in rad of a cup passing the roller. This release angle release (Fig.2) is calculated as where: rc is the sum in m of the radius of the roller, the thickness of the belt and the length of the cup; and xclear is the clearance in m between the tip of the cup and the wall of the duct. When the parameters of the potatoes are known, the angle required for releasing a potato can be calculated. Apart from its shape and size, the position of the potato on the back of the cup is determinative. Therefore, the model distinguishes two positions: (a) minimum required gap, equal to the height of a potato; and (b) maximum required gap equal to the length of a potato. The time trelease in s needed to form a release angle a0 is calculated as Calculating trelease for different potatoes and possible positions on the cup yields the deviation from the average time interval between consecutive potatoes.Combined with the duration of the free fall and the field speed of the planter, this gives the planting accuracy. When the potato is released, it falls towards the soil surface. As each potato is released on a unique angular position, it also has a unique height above the soil surface at that moment (Fig. 2). A small potato will be released earlier and thus at a higher point than a larg