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为农业机械提供位置数据测量 Herman Speckmann 原文来源:Federal Agricultural Research Centre Braunschweig (FAL), Institute for Biosystems Engineering, Bundesallee 50, D-38116 Braunschweig, Germany 摘要农业机械、车辆需要位置数据来指导和控制执行最佳工作位置。位置数据也被需要用在像精细农作这样的应用上。位置数据的必要的准确性、分辨率和频率依照不同的应用而变化。只有一个系统,安装在中央车辆(例句、拖拉机),应该提供对每项任务的位置数据。提出的关于中央系统的基本概念是位置数据按照特定应用程序计算并且直接被传送到它需要被应用到的那个点上。这片论文阐述了测量的基本原理和位置数据的计算,还对现有的传送数据的农业网络进行了简要介绍。它集中建议了一个提供和转移位置数据的网络服务。被讨论的解决方案是以农业BUS(总线)系统为基础(DIN 9684, ISO 11783). 2000 Elsevier Science B.V. 版权所有.1.前言 位置指导的目的是给生长在农田里一个固定的区域上的庄稼带来增产的方法。庄稼或者它们在农田里所处的位置是指导的重要参照。位置数据被用来指导农用车、实现控制和支持精耕农业。准确性、分辨率和频率取决于他们的具体应用。必须强调的是本文没有合适的解决这个问题的传感器来产生数据。更确切的说,这里研究的问题是参照移动单位的一定的位置进行了一个位置信号产生,但是这个位置和需要的位置数据并不是完全一致的。此外,位置信息有可能在同一时间被需要用于几种目的, 车辆和工具组合的结构可能会经常改变。正如 Freyberger 和 Jahns (1999), Wilson (1999)所提到的, 测量系统可以是一个绝对定位系统,比如Bell(1999)描述的卫星系统,或者是一个相对的系统,比如Debain et al. (1999), Hague et al. (1999)描述的机器视觉系统。它可能也包括辅助传感器。传感器只有在参考具体位置情况下测量位置,比如相机的安装点、天线的底部。在接下来的描述中,这个位置被称为测量点。由于各种原因,这位置测点的是预先设定好的,意味着卫星天线将尽可能安装在拖拉机的车顶上以便减少测量不到的区域。摄像机将会安装在有保障最佳视觉的位置。粗糙或倾斜的表面引起的运动可能导致测量位置和运动表面的位置不同。例如,一辆车顶上装有卫星天线的车辆,大约3.5m,驾驶在10的斜坡表面,倾斜方向造成的区别相差60cm。图1阐述了这个情形。在这个例子中,计算一个参考点的位置可能更适当一些。贝尔(1999)提出把拖拉机的后方轴的中点作为参考点。表面上的一个点,例如,后方轴中间的下垂直面似乎显得更适合与某些应用。像一些应用,比如控制实现,工具的一定点的位置可能最终重要。这个点将被称作目标点。在某些情况下位置数据需要用于不同的目的,分别为每个目的以一种独立的测量系统测量位置不是很有效。当位置测量只有一次时多个硬件可以避免,同时工具上其他点的位置或者工具也被计算。假如位置和方法被测量,实验测量和空间向量之间的地点测点的计算是众所周知的,那么这种情况是可能的。如果两个点严格耦合,这意味着两点都在拖拉机上、两点之间的向量是常数,一个简单的矩阵运算就能产生结果。如果这些点没被严格耦合,这意味着,例如,一处拖拉机,另一个是在附加工具上,矢量是可变的。额外的测量成为必要用来建立两点之间的向量或必须应用其他原理计算目标点的位置。2.数据处理和数据转移通过计量点上的测量位置和方法,在车辆或工具上任何点的位置数据可以被计算出来。计算结果可以被测量系统(中央数据处理)或由请求目标位置数据的各个系统(分布式数据处理)计算出来。2.1 分布式数据处理在分布式数据的情况下,测量系统仅作为智能传感器服务。它测量需要的位置和计算,和提供这些未经处理的数据。频率和精度等特点取决于请求的单位。这个单位执行所有处理来计算位置。单位必须知道测点的位置和各有关参数。这样处理的好处是测量装置可以相对简单。另一方面,每个请求的单位需要的充分的能力来履行这一运算。2.2 中央数据处理测量单位被扩展包括计算目标位置的各个组件。这个测量和处理系统形成了一个所谓的位置和导航服务的单元,这个单元提供任何目标点的最终位置数据。在这种情况下,只有一个测量与处理系统是必要的,即使位置数据必须被更多的用户要求。这样做,只有PNS必须知道所有相关的参数来进行计算。2.3 数据传送 无论数据在哪里处理,一个数据传输是必要的。对于这样一个数据传输,一个标准的网络是适当的。为了用于农业领域,存在一个在移动单位和固定农场电脑之间传输数据的汽车。农业总线系统(LBS)也已被标准化以便能在网路的各个电子单元(LBS节点或BUS节点)之间进行信息交换。这个标准定义了物理层网络,网络协议,系统管理,数据对象和常见任务的服务程序(Speckmann andJahns, 1999)。LBS以DIN9684(DIN,19891998)作为标准。目前,正在努力建立一个国际标准(Nienhaus,1993),ISO 11783,为了这个目的,像LBS,ISO 11783也将定义一个农业BUS作为一个农业机械交换数据的开放系统,特别是在拖拉机-执行工具的组合和从移动单位到静止不动的农场计算机。这个标准是基于控制器区域网络数据协议(CAN; BOSCH, 1991)。市场上有相应的硬件设备。在LBS中,为一般位置数据(地理位置:经度、纬度、高度,或轨道位置)的传输定义了数据对象。这标准允许定义的额外的数据对象,例如多维的距离,方向和速度。没有几何实施参数的数据对象目前存在在LBS中。ISO 11783提供,在第7部分(信息实现应用层),实施航行偏移的第一个定义。现行标准没有定义数据在哪里进行处理。因此,关于BUS中哪个单元计算目标点的数据,哪个或那些单元测量数据不具体。LBS提供所谓的LBS服务来执行常见任务。LBS服务是为LBS的参与者频繁地执行复发的任务的功能单元。LBS用户站就是这样的一项服务。这是一个为用户提供输入和输出BUS上节点(BUS参与者)处置的数据中央接口。另一项服务提供在移动单位和固定的电脑,农场的电脑之间的数据交换。一些服务在LBS中被定义但尚未有详细的标准,例如诊服务断或“Ortung und Navigation”(位置和导航),将在下面作为PNS被讨论。在图2中,一个典型的农业网络的简化方案展示了一个拖拉机-喷雾器的组合。这个图表包括物理BUS线路,即骨干网络。在这个BUS上,参与单元如拖拉机的电子控制单元(ECUs)、雾化器被连接协作起来。另外,两项LBS服务也被连接到BUS上。一项服务代表LBS用户站。另外一项是位置和导航服务,即位置数据的测量和处理系统。2.4 分布式和中央数据处理的比较一个分布式数据处理,农业BUS,根据DIN 9684 或者ISO 11783, 定义了在测量系统和任何参赛者之间必要的数据交换;独自地,任何一个ECU。每一个ECU怎样得到计算机位置数据计算必要的几何和运动参数的问题保持开放。每一个ECU知道从各自的结合点到目标点的参数,但它不知道从结合点到测量点的参数。这些参数必须由其他ECU提供。没有标准定义相应的数据对象或请求数据的程序。对于分布式数据处理,这些定义必须补充。另外,对于中央数据处理,一定要知道测量点和目标点之间所有的运动参数。此外,方法必需被定义以便使用中央服务计算目标点的位置数据。一个位置和导航服务需要扩展标准,但以下的优点在实际使用中是至关重要的。 为了确定目标点的位置数据,相应的控制单元(ECU)只有一个对话伙伴网络。它独立工作于各自的网络配置,仅仅发送自己的参数和只接受它特定位置数据。 PNS从所有的ECU上接受参数。它知道所有一切几何条件和车辆-工具组合的运动参数。因此,任何目标点位置的确定是可能的。 这个标准的定义了计算程序和明确的提出了目标点的位置数据。 计算位置数据的计算性能完全由PNS提供。没有计算能力需要用于这个目的。在前一节提到,提供位置和导航数据的服务已经在LBS的计划中。在下文中,将提到PNS的一个试例解决方案。3.一项定位和导航服务的提议此时,应当指出,下面的PNS的介绍是一项建议。它提供了一个平台进行讨论,这可能导致这个服务标准化。3.1 PNS的主要特征PNS的特征首先依赖于它的使用目的。从前面所讲的,很明显的是,测量的位置数据在一个地点,用在不同的地点。为了提供需要的数据来指导车辆,控制工具的位置和协助任何一种精耕农业,下面的条件必须满足: PNS提供有关测量点的数据。 PNS提供有关参考点的数据。 PNS提供有关目标点的数据。这项服务的特点如下:1.数据的请求和传播的方式已经标准化,数据被LBS (DIN 9684)定义和将被ISO 11783标准化。因此,它将不会在此讨论。在下面,LBS将作为一种标准化的农业BUS系统被使用。2.数据的容量、准确性、频率和范围是由数据的目的决定的。3.满足这些要求的硬件和软件不应被规范,应该取决于生产厂家。3.2关于位置数据测量和计算方法标准的影响各种测量系统和PNS中用于决定位置数据的方法不再标准的范围之内。基于卫星,机器视觉、惯性导航、地磁或这些情况的组合可能被应用。作为一种结果,生产企业可以决定如何产生位置数据,只要他满足了规定的要求和准确性。3.3 PNS在农业BUS系统中的整合在LBS中整合定位和导航服务存在一些好处,因为许多特性已经被定义。LBS已经包括在PNS的选项作为试验的标准。它允许实现服务作为一个独立的物理单位或者为另外一个物理单位的逻辑单位。BUS接口和BUS协议的物理性能(DIN 9684, part 2)已经被标准定义。为LBS中服务的集成,系统的功能的定义是果断的(DIN 9684,part3)。他们在LBS中定义节点的性能。第三部分也给了LBS服务一般的定义。一项LBS服务形成与LBS参与者点对点的连接。LBS参与者使用服务时不会被其它使用者影响,一个LBS参与者也不能影响其他参与者对服务的使用。所有进一步PNS的定义还不规范。3.4 PNS操作的一般模式PNS设计应用以下的基本假设:1.每一个ECU的只知道它自己的参数,包括参考点、目标点、结合点位置、车辆类型或轴距的坐标和数量。2.只有ECU根据工作条件可以定义必要的时间间隔,准确度和位置数据的分辨。3.每一个ECU的可以选择不同的任意时刻的位置数据。4.参数和计算和提供的位置数据的方法将会在田野机械开始运作过程之前被定义。5.PNS提供了一些程序为实施标准和车辆类型计算位置数据。6.位置数据自动(周期性)地或根据需求被提供。 为了满足这些要求,服务窗口提供适当的工具,同时 ECUs 决定如何使用及使用哪个工具。这意味这它们定义一个或者多个任务。这样一项任务基本上代表了一个命令表,包括激活具体工具使用的命令。这些任务被送到PNS,随后PNS执行这些任务。一个ECU的不同的任务相互独立的被执行。图3阐明了PNS与一个ECU之间的数据传递。同时,也显示了PNS的主要部分。PNS的这些工具包括位置测量系统和测量点的数据,以及一系列处理这些数据的程序方法。程序如下:1. 计算位置数据(位置程序);2. 计算位置数据值的平均值,最大值、最小值和积分的方法(算术程序);3. 输入和输出数据(传输程序);4. 传递数据到ECU(传递程序);5. 控制数据处理(数据控制程序);为了这些方法的执行,ECU必须定义相应的参数。它同时也定义位置数据的数据对象。PNS的主要工具是一项执行ECU定义的任务的程序系统。简而言之,程序系统解释任务指令,调动相应的方法,计算要求的位置以及把数据送到ECU(电子控制单元)。为了一项任务的定义,ECU生成一个任务库。一个务库主要是一系列调动PNS的程序法或者调动内嵌的任务库的指令。各种参数被定义并且放置在参数库里。为了存储被计算的位置数据,ECU必需定义数据库。数据库必需在激发相应任务程序之前通过BUS从ECU传送到达PNS。3.5 PNS预定义的程序PNS预定义的程序是一些处理位置数据或者控制数据处理的程序。不同的程序执行不同的功能。不同的程序被一些独特的标识符区别。这些程序被称为“内部任务”(任务库)。他将会成为标准的一部分用来定义标识符,功能规格和调用程序规格。3.5.1 位置程序位置程序(计算位置数据的程序)是计算目标点位置数据的数据。这些方法计算从最初的位置(输入位置数据、资料的参考点的数据或以前计算的数据)到一种新的点的位置(输出的位置数据、数据的目标点或作为中间结果)。位置程序能够满足不同结构位置的计算(考虑一、二或三维模型,严格耦合点,几个基本类型车辆的不严格耦合点,工具和车辆-工具的结合)。这些程序从有关ECU执行定义的参数库得到他们的实际参数(目标点的坐标,车辆的长度、宽度、高度、类型或轴距)这是确定的有关实施ECU的。图4显示了使用一个位置程序的一段任务库。PNS的程序系统执行这个程序库。在任务库的某一点上,它发现调用位置程序的指令。这个调用指令包括特定程序的标识符和有关参数库的引用。这时,程序系统拥有由以上的操作产生的实际位置数据。现在它使用这些实际数据作为输入数据,和引用参数库用于位置程序。然后,它执行特定的程序。该程序使用指定的参数计算输出的位置数据。然后,它返回到程序系统。位置程序的输出数据成为新的实际位置数据。程序系统继续执行下面的指令。3.5.2 算术程序算术方法被用来计算位置数据的平均值,最大值、最小值或者积分值。一个算术程序从程序系统的实际位置数据或从特定数据库得到位置输入数据。它使用在调用指令里决定的参数库中的参数计算输出位置数据。然后,计算结果数据被存储在一个被定义的数据库里。图5展示了一个算术程序使用的例子。在任务库的某一点上,它发现调用算术程序的指令。这个调用包括具体程序的标识符,一个有关参数库的引用,一个目的数据库的引用和源数据库选择性的引用。这个程序系统采用实际数据和参考数据用于程序计算。根据调用规格,算术程序从程序系统(没有定义的数据库参考)或一种数据资源(数据资源I)得到输入数据。它计算被要求的值并把计算结果存储在一个数据库里(数据库II)。计算参数是从定义的参数库中得到的。程序发挥到程序系统并继续执行。实际的位置数据没有被改变。3.5.3 传输程序 PNS定义了三种类型的传输程序。输入程序是用来装载作为实际位置数据的确定的数据库位置数据到PNS的程序系统。输出程序存储实际位置数据到一个在调用指令里预先定义了的数据库。输入/输出程序被用来从一个源数据库到目的数据库之间传输数据。 图6显示了一个使用输入和输出程序的例子。输入程序的调用指令包括具体程序的标识符和源数据库的引用。在执行输入程序之前,程序系统为程序提供源数据库的引用。然后,程序执行和得到位置数据,并将它作为实际位置数据返回给程序系统。以前的实际位置数据被损坏。系统继续进行。对于输出程序的使用,实际位置数据与目的位置数据库提供参考。输出程序将实际数据放到目的数据库并返回到程序系统。实际位置数据仍然有效。3.5.4 传递程序 传递程序发送具体的位置数据到ECU。源数据在调用指令(或一个数据库或程序系统的实际数据)里被定义。当执行一个传递程序时,它得到具体的位置数据并传送到ECU。3.5.5 数据控制程序数据控制程序控制一个任务库的执行。程序流程是控制时间或距离。PNS的程序系统调查任务库。假如确定的时间间隔已过期或已超出距离限制,程序将执行下列指令。否则,程序系统跳到数据库的结尾。Computers and Electronics in Agriculture25 (2000) 87106Providing measured position data foragricultural machineryHermann SpeckmannFederal Agricultural Research Centre Braunschweig(FAL), Institute for Biosystems Engineering,Bundesallee50, D-38116Braunschweig, GermanyAbstractAgricultural machinery and vehicles require position data for guidance and to controlimplements for optimal working positions. Position data are also needed for such applica-tions as precision farming. The necessary accuracy, resolution and frequency of position datavary according to the specific application. Only one system, installed at a central vehicle (e.g.the tractor), should provide position data for each task. The basic concept for the proposedcentral system is that position data are calculated in accordance with the application andtransferred directly to the point at which they will be used. The paper describes thefundamentals of measurement and calculation of position data, and gives a short introduc-tion to the existing agricultural networks to transfer these data. It concentrates on a proposalfor a network service to provide and transfer position data. The solution discussed is basedon the agricultural BUS (DIN 9684, ISO 11783). 2000 Elsevier Science B.V. All rightsreserved.Keywords:Local area network; Controller area network; Agricultural BUS system; LBS; Calculation ofposition; Calculation of direction; LBS service/locate/compag1. IntroductionThe purpose of position guidance is to bring the means of production to theplants, which grow at a fixed location on the field. The plants, or rather theirlocation on the field surface, are the reference for guidance. Position data areneeded to guide agricultural vehicles, to control implements and to supportprecision farming. Accuracy, resolution and frequency depend on their application.E-mail address:hermann.speckmannfal.de (H. Speckmann)0168-1699/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved.PII: S0168-1699(99)00057-5H. Speckmann/Computers and Electronics in Agriculture25 (2000) 8710688It must be emphasized that this paper does not address the problem of suitablesensors to generate the data. Rather, the problem studied here is that a positionsignal is generated with reference to a certain location on the mobile unit, but thisposition is not identical with the location where the position data are needed.Moreover, position information may be needed for several purposes at the sametime, and the configuration of the vehicleimplement combination may changefrequently.As mentioned by Freyberger and Jahns (1999), Wilson (1999), the measuringsystem can either be an absolute position system, such as the satellite systemdescribed by Bell (1999), or a relative system, such as the machine vision systemsdescribed by Debain et al. (1999), Hague et al. (1999). It may also include auxiliarysensors.Sensor systems measure position only in reference to a specific location, such asthe mounting point of the camera or the foot of the aerial. In the followingpresentation, this location is called the measuring point. For various reasons, thelocation of this measuring point is predetermined, meaning the satellite antenna willbe mounted as high as possible on the roof of the tractor cab to minimize shading.A camera will be mounted where optimal view is guaranteed. Movement caused byrough or sloping field surfaces may cause the measured position and the position onthe field surface to differ widely. For example, for a vehicle with a satellite antennamounted on top of the cab, at about 3.5 m, driving on a sloping surface of 10, thedifference in direction of the inclination will be about 60 cm. Fig. 1 illustrates thisscenario for one dimension. In this example, it may be appropriate to calculate theposition of a reference point. Bell (1999) proposes the middle rear axes of theFig. 1. Difference in position for two locations due to sloping terrain.H. Speckmann/Computers and Electronics in Agriculture25 (2000) 8710689tractor as a reference point. A point in the field surface, for example, vertical underthe middle of the rear axis seems more appropriate for some applications. Forcertain applications, such as the control of implements, the position of a certainpoint of the implement may be of final importance. This point will be called thetarget point.In cases where position data are needed for different purposes, it is not veryefficient to measure the position for each purpose separately with an independentmeasuring system. Multiple hardware can be avoided when the position is measuredonly once, and the positions of the other points on the vehicle or implements arecalculated. This is possible if position and attitude are measured, and the spatialvector between the measuring point and the point to be calculated is known. If bothpoints are rigidly coupled, meaning that both points are on the tractor, the vectorbetween these points is constant, and a simple matrix calculation yields the result.If these points are not rigidly coupled, meaning, for example, that one point is onthe tractor and the other is on an attached implement, the vector is variable.Additional measurements become necessary to establish the vector between thesetwo points or other principles to calculate the position of the target point must beapplied.2. Data processing and data transferPosition data of any point on the vehicle or implement can be calculated fromthe position and attitude measured at a measuring point. This calculation can bemade by the measuring system (central data processing) or by each systemrequesting target position data (distributed data processing).2.1. Distributed data processingThe measuring system serves only as an intelligent sensor in the case ofdistributed data. It measures position and attitude on request, and provides thesedata without any processing. Characteristics such as frequency and accuracy aredetermined by the requesting unit. This unit performs all processing to calculate theposition. The unit must know the position of the measuring point and all relevantparameters to do this. The advantage of this procedure is that the measuring devicecan be relatively simple. On the other hand, each requesting unit needs the fullcapacity to perform this calculation.2.2. Central data processingThe measuring unit is extended by components to calculate the position of targetpoints for any user. This measuring and processing system forms one unit of aso-called position and navigation service (PNS), which provides final position dataof any target point. In this case, only one measuring and processing system isnecessary even when position data are requested by more than one user. To do so,only the PNS must know all of the relevant parameters for the calculation.H. Speckmann/Computers and Electronics in Agriculture25 (2000) 87106902.3. Data transferA data transfer is necessary no matter where the data are processed. For such adata transfer, a standardized network is appropriate. For agricultural purposes, aBUS for data transfer between mobile units and stationary farm computers exists.The agricultural BUS system (LBS) has been standardized to exchange informationbetween the electronic units (LBS participants or BUS nodes) in a network. Thestandard defines the physical layer of the network, network protocol, systemmanagement, data objects and central services for common tasks (Speckmann andJahns, 1999).The LBS has been standardized as DIN 9684 (DIN, 19891998). Currently,efforts are being made to establish an international standard (Nienhaus, 1993),ISO 11783, for such purposes. Like LBS, ISO 11783 will also define an agri-cultural BUS as an open system to exchange data on agricultural machinery,particularly on tractorimplement combinations and from the mobile units tothe stationary farm computer. The standards are based on the controller areanetwork data protocol (CAN; BOSCH, 1991). Corresponding hardware is on themarket.In the LBS, data objects are defined for the transmission of general position data(geographical positions: longitude, latitude, altitude, or position in a tramline). Thestandard allows definition of additional data objects such as multidimensionaldistances, directions and speeds. No data objects exist presently in the LBS forgeometric implement parameters. ISO 11783 provides, in Part 7 (Implement Mes-sages Application Layer), the first definitions of implement navigational offsets.Current standards do not define where which data are processed. Therefore, it isimmaterial on which unit the BUS calculates the data for the target point, andwhich unit or units measure the data.The LBS provides so-called LBS services to execute common tasks. LBSservices are functional units, which perform frequently recurring tasks forLBS participants. Such a service is the LBS user station. This is a centralinterface to the user (operator) for input and output of data which is at thedisposal of any node (LBS participant) on the BUS. Another service providesthe data exchange between the mobile unit and the stationary computer, thefarm computer. Some more services are named in the LBS but not yet stan-dardizedindetail,suchasfordiagnosisservicesortheserviceOrtungund Navigation (position and navigation), which will be discussed in the followingas PNS. In Fig. 2, an exemplary simplified scheme of an agricultural networkis shown for a tractorsprayer combination. This scheme includes the physicalBUS line, which is the backbone of the network. At this BUS, participantssuchaselectroniccontrolunits(ECUs)ofthetractorandsprayerarecoupled. Additionally, two LBS services are connected on the BUS. Oneof these services represents the LBS user station. The other is the LBS serviceposition and navigation, with the measuring and processing system for positiondata.H. Speckmann/Computers and Electronics in Agriculture25 (2000) 8710691Fig. 2. Scheme of an agricultural network in a tractorsprayer combination.2.4. Comparison of distributed and central data processingFor a distributed data processing, the agricultural BUS, according to DIN 9684or ISO 11783, defines the necessary data exchange between the measuring systemand any participant; respectively, any ECU. The question how each ECU getsgeometric and kinematic parameters that are necessary to compute position dataremains open. Each ECU knows its own parameter from its coupling point to thetarget point, but it does not know the parameter from the coupling point to themeasuring point. These parameters must be provided from other ECUs. None ofthe standards define corresponding data objects or procedures requesting the data.For distributed data processing, these definitions have to be supplemented.Also, for central data processing, all kinematic parameters between the measur-ing point and the target point must be known. In addition, methods are to bedefined for the use of the central service with regard to the calculation of positiondata of target points. A position and navigation service requires an extension of thestandards, but the following advantages in practical use are essential:?To determine the position data of a target point, the corresponding ECU hasonly one dialogue partner in the network. It works independently from therespective network configuration, delivers only its own parameters and receivesonly its specific position data.?The PNS receives parameters from all ECUs. It knows all geometric conditionsand kinematic parameters of the vehicleimplement combination. Thereby, anunambiguous determination of the position of any target point is possible.H. Speckmann/Computers and Electronics in Agriculture25 (2000) 8710692?The standard defines the procedures to calculate and present the position data ofa target point unambiguously.?The computing performance to calculate the position data is provided solely bythe PNS. No computing capacity is needed for this purpose from the ECUs.As mentioned in the previous section, a service to provide position and naviga-tion data is already planned in the LBS. In the following, a sample solution of aPNS is presented.3. Proposal for a positioning and navigation serviceAt this time, it should be mentioned that the following description of a PNS isa proposal. It provides a platform for discussion, which may lead to the standard-ization of such a service.3.1. Main features of a PNSThe features of a PNS depend, first of all, on the purpose for which it will beused. From the foregoing, it is clear that position data are measured at one locationand used at different locations. The following requirements must be fulfilled toprovide the data needed to guide a vehicle, to control positions of implements andto assist any kind of precision farming:The PNS provides data related to the measurement point(s).The PNS provides data related to the reference point(s).The PNS provides data related to the target point(s).The characteristics of such a service are as follows:1. The way the data are requested and transmitted is already standardized anddefined by the LBS (DIN 9684) and will be standardized by ISO 11783.Therefore, it will not be discussed here. In the following, LBS will be used as astandardized agricultural BUS system.2. The volume, accuracy, frequency and range of the data are determined by thepurpose of the data.3. The hardware and software to fulfil these demands should not be standardized,but be determined by the manufacturers.3.2. Influence of the standard on measuring and calculation methods for positiondataThe kinds of measuring systems and methods used to determine position data bythe PNS is not in the scope of the standard. Systems based on satellites, machinevision, inertial navigation, geomagnetics or a combination of these may be applied.As a consequence, the manufacturer may determine how to generate the positiondata as long as he meets the stated requirements and accuracy.H. Speckmann/Computers and Electronics in Agriculture25 (2000) 87106933.3. Integration of the PNS into an agricultural BUS systemThere are some benefits of integrating the positioning and navigation service intothe LBS, because many characteristics are already defined. The LBS alreadyincludes the option of a PNS as part of the standard. It allows the realization of aservice either as an independent physical unit or as a logical unit inside of anotherphysical unit. The physical properties of the BUS interface and the BUS protocol(DIN 9684, part 2) are defined by the standard. For integration of the service intothe LBS, the definitions of the system functions are decisive (DIN 9684, part 3).They define the performance of the nodes at the LBS. Part 3 also gives the generaldefinitions of LBS services.An LBS service forms a point-to-point link with LBS participants. The use of aservice by an LBS participant can neither be influenced by other users, nor can anLBS participant influence links between the service and other participants. Allfurther definitions of the PNS are not yet standardized.3.4. General mode of operation of the PNSFor the design of the PNS, the following basic assumptions apply:1. Each ECU knows only its parameters, meaning coordinates and numbers ofreferencepoints,targetpoints,positionsofcouplings,vehicletypesorwheelbases.2. Only the ECU can define necessary time intervals, accuracy and resolution forposition data, depending on the working conditions.3. Each ECU can get different position data at arbitrary times.4. Parameters and the way of calculating and providing position data will bedefined before the working processes of the field machinery are started.5. The PNS provides a library of procedures to calculate position data forstandard implement and vehicle types.6. Position data are provided automatically (cyclically) or on demand.To meet these requirements, the service provides the tools, and the ECUsdetermine how and which tools are used. This means they define one or severaltask(s). Such a task basically represents a list that includes commands to activatethe specific tools. These tasks are sent to the PNS, which subsequently performsthese tasks. Different tasks of one ECU are executed independently of each other.Fig. 3 illustrates the data transfer between the PNS and one ECU. It also showsthe main parts of the PNS. The tools of the PNS include the system for measuringthe position and attitude data of the measuring point, and a library of methods toprocess these data. Methods exist:?to calculate position data (position methods);?to calculate mean, maximum, minimum and integral values of position data(arithmetic methods);?to export and import data (transport methods);?to send data to the ECU (transmission methods); and?to control the data processing (data control methods).H. Speckmann/Computers and Electronics in Agriculture25 (2000) 8710694For some of these methods, the ECU has to define corresponding parameters. Italso defines data objects for position data.The central tool of the PNS is the program system to execute the tasks definedby the ECU. Simplified, the program system interprets the instructions of the task,calls the corresponding methods, calculates the demanded position and sends thedata to the ECU.For the definition of a task, the ECU generates a task resource. A task resourceis mainly a list of instructions to call methods of the PNS or to call nested taskresources. Parameters are defined by the ECU and placed in parameter resources.To store calculated position data, the ECU has to define data resources. Theresources have to be transmitted from the ECU via the BUS to the PNS beforeactivating corresponding tasks.Fig. 3. Strcture of a PNS and its data exchange with one ECU.H. Speckmann/Computers and Electronics in Agriculture25 (2000) 8710695Fig. 4. Example of the use of a position method in the course of a task resource.3.5. Predefined methods of the PNSPredefined methods of the PNS are procedures to process position data or tocontrol this data processing. Methods exist to perform different functions. Thedifferent methods are distinguished by a unique designator. They are called withintasks (task resources). It will be a part of the standard to define the designators,function specifications and calling specifications of the methods.3.5.1. Position methodsPosition methods (methods to calculate position data) are the basis for calculat-ing position data of target points. These methods calculate from an initial position(input position data, data of a reference point or previously computed data) theposition of a new point (output position data, data of a target point or as aninterim result). Position methods exist for different configurations (one-, two- orthree-dimensional model considerations, rigidly coupled points, non-rigidly coupledpoints for several basic types of vehicles, implements and vehicleimplementcombinations). These methods get their actual parameters (coordinates of the targetpoint, vehicle length, width, height, type or wheelbases) from parameter resourceswhich are defined by the concerned implement ECU.Fig. 4 shows a section of a task resource using a position method. The programsystem of the PNS executes this task resource. At a certain part of the taskresource, it finds a calling instruction for a position method. This calling instructionincludes the designator of the specific method and a reference to a relevantparameter resource. At this moment, the program system owns actual positiondata, which result from previous operations. Now it uses these actual data as inputdata, and the parameter resource reference for the position method. Then, itexecutes the specified method. This method calculates the output position datausing the specified parameters. It then returns to the program system. The outputposition data of the position method become the new actual position data. Theprogram system continues and executes the following instructions.3.5.2. Arithmetic methodsArithmetic methods are used to compute mean, maximum, minimum or integralvalues of position data. An arithmetic method gets its input position data eitherfrom the actual position data of the program system or from a specified dataH. Speckmann/Computers and Electronics in Agriculture25 (2000) 8710696resource. It computes the output position data using the parameters of a parameterresource determined in the calling instruction. Then it stores the results in a defineddata resource.Fig. 5 shows an example of the use of an arithmetic method. At a certain part ofthe task resource, the program system of the PNS finds a calling instruction for anarithmetic method. This calling instruction includes the designator of the specificmethod, a reference to a relevant parameter resource, a reference to a destinationdata resource and, optionally, a reference to a source data resource. The programsystem uses the actual data and the references for this method. Depending upon thecalling specification, the arithmetic method receives its input data either from theprogram system (dashed line, no reference to a source data resource defined) orfrom a data resource (dashed dotted line, Data Resource I). It calculates thedemanded values and stores the result in a data resource (Data Resource II). Theparameters for the calculations are taken from the defined parameter resource. Themethod returns to the program system and continues. The actual position data arenot altered.3.5.3. Transport methodsThree types of transport methods are defined in the PNS. The import method isused to load the position data of a determined data resource as actual position datainto the program system of the PNS. An export method stores the actual positiondata into a data resource predefined in the calling instruction. Import/exportmethods are needed to transfer position data from a source data resource to adestination data resource.Fig. 6 shows an example of the use of an import and an export method. Thecalling instruction for an import method includes the designator of the specificmethod and a reference to a source data resource. Before executing an importmethod, the program system provides the reference of the source data resource forthe method. The method is then operated and gets the position data, and returns itas actual position data to the program system. The previous actual position dataare corrupted. The system continues. For the use of an export method, the actualposition data and the destination data resource reference are provided. The exportmethod puts the actual data into the destination data resource and returns to theprogram system. The actual position data are still valid.Fig. 5. Example of the use of an arithmetic method in the course of a task resource.H. Speckmann/Computers and Electronics in Agriculture25 (2000) 8710697Fig. 6. Examples of the use of transport methods in the course of a task resource. (a) Import method;(b) export method.3.5.4. Transmission methodsTransmission methods (transmit methods) serve to send specified position data tothe ECU. The source of the data is defined in the calling instruction (either a dataresource or the actual data of program system). When a transmit method isexecuted, it gets the specified position data and sends it to the ECU.3.5.5. Data control methodsData control methods control the execution of a task resource. The flow is eithertime or distance controlled. The program system of the PNS polls the task resource.If the determined time interval has expired or distance limits have been exceeded, itprocesses the following instructions. Otherwise, the program system skips to theend of the resource.3.6. Definition of resources for the PNSWhile methods are mostly predefined by the standard, resources are defined bythe ECUs to use the tools of the PNS. Three types of resources exist.H. Speckmann/Computers and Electronics in Agriculture25 (2000) 87106983.6.1. Task resourcesThe first type of resources is task resources, data objects to describe tasks of thePNS. A task resource consists, at the very least, of the instructions Task ResourceBeginning and Task Resource End. In between can be arbitrary sequences of anarbitrary number of Call Method and Call Resource instructions. The instructionsTask Resource Beginning and Task Resource End include a unique designator ofthe resource. The calling instructions include the designators of the demandedmethods or resources and controls or references to relevant parameter or dataresources.To perform a task by the PNS, the ECU has to activate a resource. This meansthe ECU selects a resource that shall be operated by the PNS. After the activation,the program system, of the PNS, processes all instructions called in the specificresource. The program system keeps temporal data during the operation, transfersit to the called methods or nested resources (on demand), and receives data fromthe called methods or nested resources.The following sequence shows how the foregoing is expressed in a modifiedBackusNaur format (BNF) syntax.Task Resource :=BTask Resource BeginningBCall Method?BCall ResourceBTask Resource EndBelow is a syntax describing the structure of a task resource, a modified BNFsyntax:MeaningSymbolInstructionBsymbol:=consists ofContents can appear from 0 to repeated timesInstruction 1 or Instruction 2Instr1?Instr23.6.2. Data resourcesIn the PNS, data resources are needed to store position data for input and outputpurposes. The members of position data structures (data resources) include coordi-nates (longitude, latitude, altitude), directions (spatial angles), speeds or accelera-tions. The minimum definition of a data resource consists of the instructions DataResource Beginning and Data Resource End. These instructions include a dataresource type and a unique designator. An empty data resource provides a dataobject at which the PNS or the ECU can store position data. Otherwise, the ECUcan set each data structure member with the instruction Set Data StructureMember. This instruction includes a member designator to specify the demandedstructure member. Additionally, a position data structure includes the originalposition of the point for which the data are valid.H. Speckmann/Computers and Electronics in Agriculture25 (2000) 8710699The following sequence shows a data resource in BNF syntax:Data Resource :=BData Resource BeginningBSet Data Structure MemberBData Resource End3.6.3. Parameter resourcesParameter resources serve to contain parameter structures for different methodsof the PNS. The members of parameter structures (parameter resources) depend onthe type of methods that use the parameters. For position methods, parameterresources include members such as vehicle length, width, height and wheelbase. Forarithmetic methods, parameter resources contain time intervals for averaging andintegration or equivalent distances. Data control methods need parameters such astime intervals or working distances to start measurement and calculation ofposition data. Parameter resources are similar to data resources and defined byBNF syntax as follows:Parameter Resource :=BParameter Resource BeginningBSet Parameter Structure MemberBSet Parameter Structure MemberBParameter Resource End3.7. Basic rules and definitions of the PNSFor the operation of tasks, the following basic rules apply:?Tasks are assembled in task resources.?Task resources are defined by the requesting ECU (LBS participant).?Task resources are distinguished by a unique ECU specific designator.?An ECU loads its task resources into the PNS.?An ECU can operate only its own resources.?Task resources are an assemblage of calls of predefined methods of the PNS.?Task resources can call other task resources.?At the calling of a task resource, the source of input position data (either froman addressed data resource, inherited from the calling task resource or no inputdata) and the destination of output position data (either to an addressed dataresource, returned to the calling resource or no destination) are established. Atthe beginning of the called task resource, actual position data are generated fromthe input position data. At the end of a task resource, actual position data of theresource are stored as output position data if a destination address is determinedand/or is returned to the calling resource if needed.?At the return from a called task resource, the actual position data of the callingresource are restored, except the returned data from the called task resource aredemanded by the calling resource.?Multiple nestings of task resources are allowed.?Task resources have to be defined before their first use.H. Speckmann/Computers and Electronics in Agriculture25 (2000) 87106100?Task resources can be activated and deactivated.?All tasks included directly in a task resource and all tasks referenced in calledtask resources are executed after the activation.?After deactivation, all tasks of a task resource are terminated. Tasks of refer-enced task resources may be active elsewhere.?Task resources can be changed to their defined extent.For the methods of the PNS, the following basic rules apply:?There exists a pool of predefined methods in the PNS.?Methods are distinguished by a unique designator.?Methods are called inside of task resources.?At the calling of a method, the source of parameters (address of selectableparameter resources) is determined. The method uses these parameters and thevalid actual position data of the calling task resource (as input data) to calculateits output data.?At the return from a called method, the output data become the actual positiondata of the calling resource.For parameters, the following definitions are valid:?Parameters represent a structure.?Parameters are contained in parameter resources.?Parameter resources are distinguished by a unique designator.?Parameter structure members are distinguished by a unique designator.?Parameters can be changed. After the amending of parameters, methods areexecuted with the new parameters.For position data, the following definitions are valid:?Position data represent a structure.?A position data structure consists of several members (coordinates, directions,speed, acceleration, etc.).?Position data are contained in data resources.?Data resources are distinguished by a unique designator.?Data structure members are distinguished by a unique designator.?Data resources serve for the import and export of position data.3.8. Operating task resources in the PNSTo start the operation of a task resource, a requesting ECU sends a singlecommand to the PNS. This command specifies the demanded task resource with theresource designator. This task resource is the top-level resource, which will beoperated by the program system of the PNS. Because it is not nested in a callingtask resource, some special issues have to be regarded. If this entire task should bestarted cyclically, then a control method has to be put on the top of this resource.To get input data (no source is determined), the top-level resource has to call atransport method (import method). This import method has to get position datafrom a specific initial reference point. This is a virtual coupling point between thePNS and any ECU. The original task of the PNS is to provide this special referencedata.H. Speckmann/Computers and Electronics in Agriculture25 (2000) 87106101Now the program system is prepared to operate. At the call of a positionmethod, the system transfers its actual position data to the method. This returns thecomputed data, now the new actual position data. At the call of an inserted taskresource, the system either inherits the actual position data, transfers position datafrom a specified data resource to the called task resource or transfers no data,depending on the conditions in the calling instruction. After the return from aninserted task resource, the system accepts the returned data as actual position dataor restores its own actual position data, also depending on the conditions in the callinstruction. With the help of export methods, the actual position data or data froma determined source can be stored in a data resource, specified by the designator inthe call instruction. Data can also be transmitted to the requesting ECU by callinga transmit method.At the end of a resource, the actual data of the resource can be stored in a dataresource defined by the destination designator in the call instruction. This is notpossible for a top-level task resource, because in this situation no address isspecified.4. Example of the employment of the PNSFig. 7 shows a scheme of a tractor with a towed sprayer. In a first example, theposition data of the front wheels shall be provided by the PNS. In a secondexample, the PNS shall provide the position data for a site-specific application ofchemicals according to a task map.Fig. 7. Two-dimensional scheme of a tractor with a towed sprayer.H. Speckmann/Computers and Electronics in Agriculture25 (2000) 87106102Fig. 8. Structure of an exemplary task resource for the tractor.4.1. Example1:position of the front wheelsThe tractor has its coordinates with the origin at the point 0, 0. Additionally,the measuring point (A) and the reference points for the front wheels (FTLand FTR)are defined for the tractor. The position data for the front wheels of the tractor areprocessed and cyclically transmitted in a time interval of 40 ms to the tractor ECU.For this task, the ECU of the tractor has defined the resources. This is depictedin Fig. 8. These are the task resources (task resource 1100, 2300, 2301) and theparameter resources (para 2000, para 2100, para 2101). The task resource 1100 isthe top-level resource. The task resource 1100 begins with a control method (I),which refers to a parameter resource (para 2000) and obtains parameters from it.The method controls the data processing of the task resource 1100 and restarts itH. Speckmann/Computers and Electronics in Agriculture25 (2000) 87106103cyclically every 40 ms; this means if the time interval has not expired, the taskresource is skipped.Otherwise, the following instructions of the resource are executed. Importmethod (II) imports from the PNS the position data (data 000) of its coupling pointto the PNS. In this example, the origin 0, 0 of the tractors coordinates is definedas coupling point between tractor and PNS. These position data are set to theprogram system as actual position data (Position data 0, 0) inside the taskresource 1100.The program system of the PNS is responsible for calculating these position dataautomatically. In an internal operation, the PNS gets the position data of themeasuring point. Then it computes the position data of the coupling point 0, 0.Necessary parameters such as the relative coordinates of the measuring point, e.g.antennas (A), have to be defined at the installation of the hardware of the PNS.In task resource 1100, the task resource 2300 and 2301 are called. Task resource2300 inherits the actual position data (Position data 0, 0) from the callingresource (task resource 1100). The called position method (III) calculates theposition data for the reference point of the left front wheel (FTL) using theconcerning parameters contained in the parameter resource (para 2100). Themethod returns its results to the calling task resources as new actual data. Thefollowing transmit method (IV) sends these data directly to the tractor ECU asposition data for the left front wheel. The nested task resource 2300 ends andreturns.Task resource 1100 restores its actual position data for the next called taskresource 2301. This task resource provides the position data for the right frontwheel with an analogous procedure. The operation stops at the end of task resource1100 until the next cycle.4.2. Example2:position of sprayer sectionsThe first example only uses a small part of the functionality of a PNS. Thesecond example is a little more complex. In addition to the coordinates of the firstexample, some more reference or target points (Fig. 7) have to be considered. Veryimportant is the point of the coupling (C=CT=CS) which is owned by the sprayeras well as by the tractor. The position data of this point are the starting data forall tasks that can be defined by the sprayer (requesting ECU). The secondimportant point is the middle of the sprayer axle (WS). Its position and attitudedata describe the movement of the sprayer completely. On this basis, it is verysimple to calculate the position data of any rigidly coupled point of the sprayersuch as sections of the sprayer boom or wheels.To specify the locations of reference or target points, the sprayer has also itscoordinates with the origin at the point (0, 0=WS) (grey background). Referencepoints exist for the wheels (WSLand WSR) and the sections of the spray boom (BL3,BL2, BL1, BR3, BR2, BR1,).The basic task definitions of this example are as follows:H. Speckmann/Computers and Electronics in Agriculture25 (2000) 87106104Averaged position data for the origin (WS) of the sprayer have to be transmittedto the sprayer in a predefined time interval of 10 s. The sampled position data ofthe boom sections have to be transmitted every second.The program system of the PNS provides in an internal operation the positiondata of the coupling automatically (Fig. 9). In addition to example 1, the PNS hasto know the parameters of the coupling (CT) of the tractor. This information mustbe provided by the tractor ECU.For the demanded tasks, the requesting ECU of the sprayer has defined severalresources. The structure of these task resources with the called resources is shownin Fig. 9. The ECU has defined the task resources (task resource 100, 200, 210, 313,312, 311, 321, 322, 323), the parameter resources (para 1000, para 0900, para 0910,para 1010, para 1100, para 0113, para 0112, para 0111, para 0121, para 0122, para0123) and the data resources (data 000, data 0800).In this implementation task, resource 100 is the top-level resource. The sprayerhas activated this resource. The task resource 100 begins with a control method (1).This method refers to a parameter resource (para 1000) and obtains necessaryparameters from it. The method control
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本文标题:叶菜收获机设计【含8张CAD图纸和文档资料】
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