文献翻译-除草的四轮农业机器车

1Agricultural 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 2implementation 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 electronics3This 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: 4where: 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;5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6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%-