多轴转向系统的设计的外文翻译

外 文 翻 译毕业设计题目： 多轴转向系统的设计 原文 1： Agricultural Robotic Platform with Four Wheels Steering for Weed Detection 译文 1：除草的四轮农业机器车 原文 2： Turning characteristics of multi-axle vehicles 译文 2：多轴车辆的转向特性 Agricultural Robotic Platform with Four Wheels Steering for Weed DetectionThomas Bak; Hans JakobsenDepartment of Agricultural Engineering, Danish Institute of Agricultural Sciences, Schoottesvej. 17, DK-8700 Horsens, Denmark;e-mail of corresponding author: tbcontrol.auc.dk(Received 10 January 2003; accepted in revised form 14 October 2003; Published online 23 December 2003)A robotic platform for mapping of weed populations in fields was used to demonstrate intelligent concepts for autonomous vehicles in agriculture which may eventually result in a new sustainable model for developed agriculture. The software implements a hybrid deliberate software architecture that allows a hierarchical decomposition of the operation. The lowest level implements a reactive feedback control mechanism based on an extension of simple control for car-like vehicles to the four wheel case. The controller design forces the front and rear of the vehicle to follow a predetermined path and allows the vehicle to maintain a fixed orientation relative to the path. The controller rationale is outlined and results from experiments in the field are presented.1. IntroductionAdvances in mechanical design capabilities, sensing technologies, electronics, and algorithms for planning and control have led to a possibility of realizing field operations based on autonomous robotic platforms The need for such systems is driven by increasing financial pressure on farmers combined with public concern about the environment and working conditions. Efficient deployment of autonomous robotic platforms in the field will allow care and management of crops in a very different way from what is known today (Belasco et al., 2002; Cho et al,2002). Robotic platforms and implements may sense and manipulate the crop and its environment in a precise manner with minimal amount of materials and energy making them potentially more efficient than traditional machinery. This is likely to reduce the environmental impact while increasing precision and efficiency (Kondo De Baerdemaekr et al, 2001). The result is a new sustainable model for developed agriculture.This paper presents an overview of the system and approach. Section 2 provides a system description. This includes a description of modular mechanical concepts well as the Techtronic implementation of the system. Everything is tied together in hierarchical hybrid software architecture. In Section 3, the focus is on a specific mobility control strategy that extends simple controllers to 4WS. The result is a system that allows the vehicle to track a given path, while maintaining the front and rear implement bars on the path. Results from experiments in the field are summarized in Section 4 and demonstrate the effectiveness of the proposed 4WS solution. Finally, conclusions are drawn and discuss further research. This paper concentrates on the engineering aspects of the research and evaluation of the experimental system.2. System descriptionThe robotic platform described here is meant to demonstrate novel sensing capabilities (Sgaard &Olsen, 2000) and semi-autonomous operation of a robotic platform for agriculture. The immediate agronomic aim of the project is to demonstrate efficient measurement of spatial and temporal crop and weed measurements. Given that the variability in weeds is measured and mapped, inputs can be varied according to a defined strategy providing environmental and economic benefits. Studies show that 5080% of the costs for herbicides can be saved when treating only patches where weeds actually grow (Green et al., 1997; Nordmeyer et al., 1997). Fundamental for the success of such a system is the integration into farm management systems, e.g. job creation and path planning (Srensenet al., 2002).2.1. Robotic platformThe basis for the robotic platform is the mobility capability provided by the wheel module mechanism shown in Fig. 1. Each of the four identical wheel modules include a brushless electric motor for propulsion that provide direct drive without gearing. Motor, amplifier and microcontroller are all mounted in the wheel hub. Steering capability is achieved by a separate steering motor mounted on top of the wheel module shaft to create a two-degree-of-freedom mechanism. The steering motor amplifier and the control electronics are mounted next to the steering motor. The control electronics (wheel node) are based on a commercial agricultural job computer and handle the local position servo control for the steering and provide torque control of the drive motors. The driver motor electronics allow speed and current (torque) feedback while the steering servo system provide a steering angle feedback derived from motor shaft encoders.2.2. Platform electronicsThis allows programs to be built automatically and subsequently execute in near real-time on the platform computer. The solution supports transmission control protocol/internet protocol (TCP/IP) sockets for remote communication with the running code which allow monitoring and modification of parameters during development.2.3. System architectureThe system architecture adopted is similar to the hybrid deliberate approach (Arkin, 1990) that is now common in mobile robotics systems (Orebaack. & Christensen 2003). The three-layer architecture consists of: (1) a reactive feedback control mechanism that handles stabilization and tracking, (2) a plan-execution mechanism that deals with e.g. trajectory generation and task decomposition, and (3) a mechanism for performing time-consuming deliberative computations and interaction with human operators, i.e. job creation. The hierarchical structure is shown in Fig.4.3 Mobility controlThe motion of the robot can always be viewed as an instantaneous rotation around a time varying point called the instantaneous centre of rotation (ICR). Hence, at each instant, the velocity vector of any point. Of the frame is orthogonal to the straight line joining this point and the ICR. Controlling the vehicle position in the field implies controlling the two-dimensional location of the ICR, which may be achieved by specifying the direction of travel of two points of the vehicle. To get experimental results with the 4WS system, a simple controller that controls two steering points was implemented, one at the front end and one at the rear of the vehicle. The 4WS is then utilized to minimize the distance to the desired path for both steering points independently as indicated in Fig. 5. This approach with two independent controllers allows us to switch between 2WS and 4WS without having to change the controller structure. As front and rear controllers are identical so without loss of generality, the description here is focused on the front steering controller. Its control objective is to minimize the perpendicular distance to the path df. The sign of df indicates the side of the path on which the steering point is located. From df it calculates a commanded direction of the front steering point (FSP) relative to the vehicle f , using: where: h is a positive scalar converting the control signal to motor voltage.This simple distribution actually works very well in practice and in addition it also has an anti-spin effect. If a wheel slips, it will of course rotate a little faster as the EMF will grow to compensate for the missing torque, but the torque distribution among the wheels is not changed. A slipping wheel has a minor influence on the measured vehicle speed as it is based on the rotation speed of all wheels, but this can be solved by omitting a wheel if a slip detection indicates that it is slipping. 作者：Thomas Bak; Hans Jakobsen国籍：Danish出处：Department of Agricultural Engineering, Danish Institute of Agricultural Sciences, Schoottesvej. 17, DK-8700 Horsens, Denmark;除草的四轮农业机器车机器人平台测绘杂草种群的领域是用来展示智能概念车辆，这最终将为高度发达的农业引进一种可持续的模式，现有的车辆适用于 0.25 米和 0.5 米行距的作物，这种车辆装备了适用于行间向导和搜寻杂草的相机。携带有四个特备的轮子的组合方法，允许转向装置和推进力。这种结果被改进了，允许机器在转向时平行移动，是通过去耦合装置来调节方向的。机器的控制是通过工具系统和基于控制的系统，这种软件工具混合了成熟的建构软件，这种农业软件混合有机的操作。最低水准是运用反馈系统，这种反馈系统基于汽车简单控制的延伸，这种控制设计使得前后轮服从以设计的路径，允许机器维持复杂的相关路径，这种控制方法正在试验中。1. 引言在控制方面的机械设计能力，传感技术，电子学和运算学的进步已经使得自动化的机器人操作的可能性。这种系统的需要正被逐渐增加的财政压力，公众对环境和工作条件的关注而驱动着。机器平台和工具或许能精确的感觉到和控制到农作物和他所处的环境从而使其比传统的机器更有效。这能够在提高精度和效率的同时降低对环境的反作用，这种结果对于高度发达的农业是一种新的可持续模式，农业机器向导已经成为一种积极地研究领域好多年了，最初的商业导向系统已经普及，拖拉机被提前预设的路径控制，这种路径是基于GPS系统。这些自动向导机器解决了以上许多问题，但是在土壤，压实，能源使用、排放物和精密等方面不是最好的解决方案。把重心集中到能不断操作和最小误差的机器，能让我们想到一系列的更小更特殊更精确更有效的机器。这种机器能够以更低的频率来工作更长的时间，同时比以往机器提供同样甚至是更多的输出。机器在无人的情况下更长时间的操作时一项重大挑战。最近在机械手工程的区域农业者有很大的贡献。给在田里的杂草数量进行草绘的机器人平台在农业里被用来示范自动车辆的智能观念，这最终将为高度发达的农业引进一种可持续的模式，现有的车辆适用于0.25米和0.5米行距的作物，指导与农作物相关的车辆线使用指导照相机提高工作率，减到最少的同时提供有价值的局限输入对农作物的伤害。四轮转向（4WS）的引进为这次研究提供了一种更灵活的平台，但改善的变动性也提供了一个数量更多的实际利益。四轮转向系统允许车辆在转向中平行的位移，从而调整位移取向。鉴于有车辆的四个非线性性质的独立控制车轮的控制问题不是小事情，然而，那样的控制系统在一种低速的情况下也能给出很好的结果。一种已经成功被使用的方法就是在车辆的前头安上比例控制器，这些结果解决了传统的轿车般的车辆在两个转向车轮的问题，当时四轮转向的模糊控制被讨论中。这里采用的方法建立在两轮转向成功的试验的基础上的，同时引进了一种简单的4WS案例。2. 系统描述这里描述的机器人平台。旨在展示新型传感功能和一种农业机器人半自动化操作。农业经济项目的目的是控制有效的测量时间和控制的作物和杂草测量，考虑到杂草的测量方法和映射，输入的不同，参照一个提供环境和经济效益的明确方法。研究表明50%-80%的除草剂费用可以节省。2.1 机器人平台机器人平台的基础是车轮模块提供的流动性能力如图1，每个特定功能的车轮模块包括无刷电机提供无齿轮直接驱动推进，电机，放大器和微控制器都安装在轮毂上。通过在车轮模块安装具有独立转向电机轴轮模块来创建两个自由度的机制。转向电机放大器和控制电子器安装在方向盘马达上，控制电子系统是基于商业农业工作电脑和处理具体情况的控制系统。车轮模块有一个简单的机械接口允许它可以安装在几乎任何车辆上，电器接口包括一个电源接口和一个控制器区域网络（CAN）的总线接口控制模板如图二。该平台是专门为农业0.5米间隙作物的使用，具有良好的离地间隙，较小的车轮和0.25米行的驾驶区间。实现由被动稳定三点悬挂系统，确保所有车轮与地面接触。该平台为车辆提供细密的前面车厢电子系统，车厢后部的电池和可能的用户界面。2.2 平台电子系统通过提供控制平台机电一体化系统，包括刚才所描述的机械概念和汽车电子控制系统来正确驱动机械子系统。电子架构是围绕平台计算机（pc/104系统），如图3所示。该平台计算机软件实现Linux操作系统，该发展是由MathWorks公司的支持实行车间。允许带定制C代码直接来源于仿真模型，这使得程序将自动建立和随后在近实时的平台上执行。本地化是实现冗余的传感器集是连接到计算机使用平台RS232系列动力通信协议以及一个CAN2.0b 协议。主导航传感器是旧拓普康双频载波相位差GPS接收能够优于2厘米的标准偏差的绝对精度，一个KVH 的E-CORE2000光纤陀螺仪精确测量的标题率，包括测量控制陀螺漂移从磁轮和转向编码器。相结合，与绝对位置编码器，磁强计和陀螺仪的可靠性，标题绝对的唯一参考磁铁烁效应，但该计划包括该行的指导在融合过程中，以抵消这些问题的相机磁测量的灵敏度。2.3 系统构架系统架构采用的是类似混合蓄意的做法（阿金，1990年） ，现在是常见的移动机器人系统。三层建筑是由以下部分组成：（1）无反馈控制机制处理稳定和跟踪， （2）计划执行如轨迹生成和处理机制任务分解和（3）执行费时审议计算和机制与人类的运营商的互动，即创造就业机会。层次结构如图4.作者：汤姆斯 贝克；汉克斯 杰克森 国籍：丹麦出处：农业工程学部，农业科学丹麦学会（2003 年 1 月 10 日收到，2003 年十月 14 日以修正的形式接受，2003 年十月 23 日网上发表）Turning characteristics of multi-axle vehiclesAbstract：This paper presents a mathematical model for multi-axle vehicles operating on level ground. Considering possible factors related to turning motion such as vehicle configuration and tire slip velocities, equations of motion were constructed to predict steer ability and driving decency of such vehicles. Turning radius, slip angle at the mass center, and each wheel velocity were obtained by numerically solving the equations with steering angles and average wheel velocity as numerical inputs. To elucidate the turning characteristics faulty-axle vehicles, the eject of fundamental parameters such as vehicle speed, steering angles and type of driving system were examined for a sample of multi-axle vehicles. Additionally, field tests using full-scale vehicles were carried out to evaluate the basic turning char-ataractics on level ground. Keywords: Multi-axle vehicles; Turning maneuverability; Mathematical model1. IntroductionTrack laying running gear has been mainly used in the fields of military and construction for heavy vehicle applications. Recently, running gear with pneumatic tires has been expanding to heavy vehicles in such fields, since tire equipped vehicles excel in speed, silence and energy e?-cogency. Several papers have been published on the subject of tractability and maneuverability of multi-axle vehicles 1,2. A theoretical study to evaluate the turning motion of skid steering vehicles was also developed by Renoir and Cravat 3. More recent army vehicles, such as theMODIX, are designed to be equipped with independent wheel drive and steering, and load control suspensions 4. The MODIX can turn by normal steering, skid steering, or a mixture of both. Additionally, the conversion from mechanical drive to an electric drive unit controlled by each in-hub motor has been examined 57. A hybrid wheel steer system is being developed to complement the independent drive capability of the in-hub wheel motors. However, there has not been a paper or technical publication dealing with the subject comprehensively and in a logical sequence because the phenomenon of dynamic motions of the multi-axle vehicle is complex. This paper describes a computer simulation model to predict turning characteristics of multi-axle vehicles. The equations of motion for the vehicles are constructed for level ground. Tractate and side forces acting under pneumatic tires due to interaction with the ground are of fundamental importance to predict the motion of vehicles. In the numerical simulation, the brush model based on a physical approach was adopted for the tire model 8. The brush model is an idealized representation of tires in the region of contact. In order to determine the turning motion of multi-axle vehicles, the ejects of fundamental parameters such as vehicle speed, steering angles and type of driving system are examined by using specification of an example vehicle. Field tests on multi-axle vehicles were also conducted and compared to the predicted results with the data numerically obtained by the model. The results demonstrated that the proposed mathematical model could accurately assess the turning characteristics of multi-axle vehicles.2. Mathematical model of multi-axle vehicles2.1. Coordinate system and kinematics of the vehicleFig. 1 shows coordinate systems used to describe a multi-axle vehicle with velocity vector V and yaw angular velocity h at the mass center. The coordinate system (X1, X2) is fixed on the level ground with unit base vectors E1, E2. A moving coordinate system (x1, x2) is attached to the vehicle, whose origin is located at the mass center, with unit base vectors e1, e2. 2.2. Equations of motionNewtons second law applied to the vehicle yields:where m and I are the mass and the moment of inertia for the vehicle, respectively. The frictional force Q is defined under the itch wheel, and xi denotes the position vector of the itch wheel. In a steady state turn, the equilibrium equations for the vehicle are obtained by setting V and zero.2.3. Tire slip and frictional forcesModeling of shear force generation for pneumatic tires has been reviewed by Pacifica and Sharp 8 who covers physical and empirical models. The brush model, an analytical model physically derived, has been widely used for vehicle dynamics studies. The relation between deformations of tire treads and shear forces, i.e., side force and tractate force, is simplified and the model idealizes the representation of tires in the region of contact. The horizontal shear forces acting under the tire due to interaction with the ground are assumed to be linearly dependent on the tread displacement from the tread base.In this paper, the brush model has been adopted to the vehicle model. A schematic slip motion of a tire with slip angle is shown in Fig. 2. The slip velocity vector ViS is defined by the relative velocity of tread surface and the ground as follows:Where Vi and ViR denote the traveling velocity vector and the peripheral speed vector, respectively, of the itch wheel. A non-dimensional slip ratio S is defined by the ratio of the norm of slip velocity with the magnitude of the peripheral velocity:Frictional force yields at the limit of the adhesion and the coincident of yielding friction is expressed as a function of slip ratio as follows:where K is a positive constant dependent on the staidness of the tire, and l0 is the maximum coincident of friction. The limit of slip ratio Sm represents the full sliding state of the tire throughout the tread, expressed by Sm =1/K.Fig. 4 shows the lateral force versus the longitudinal force (braking or traction force) plotted at given values of slip angles (rod) for a tire with the property of K= 5.0.As the driving power from the engine is transmitted to the wheel through the deferential, the driving force and the rotational speed of each wheel are influenced by power train types. The general type of driving system for multivalve vehicles is illustrated in Fig. 5. Deferential are mounted in each axle to distribute equal tractate force to both side wheels and the rotational speeds of the wheels depend on the path length of the tires. The property of differential is mathematically expressed as constraint equations:where Qli is the tractate force or the longitudinal shear force on the ith tire, and VR0 is the average peripheral velocity of the tires.3. Experimental evaluationField tests were conducted by using two full-scale vehicles. The low speed turning performance of the vehicles was evaluated on a concrete test ground and on sandy ground. One vehicle was an eight-wheel-vehicle with front-four-wheel-steering, which is identified by vehicle A. The other was a TADANO ALL TERRAIN VEHICLE or vehicle B, which is an eight-wheel-vehicle with all-wheel-steering shown in Fig. 6. The maximum coincident of friction l0 depends on the ground condition. The coercions were measured in the field and l0 =0.6 was obtained with vehicle B on the concrete ground and l0 = 0.8 with vehicle A on the sandy ground. In the field tests, two steering types were examined. One was steering by the front four wheels, and the other by all the wheels.Fig. 7 shows the experimental and predicted results of the turning radius versus steering angles. The parameter indicates the average steering angle of the front wheels and, for all-wheel steering; the angles of the rear four wheels are fixed at a maximum in its steering capability. It is clear th