存在洋流时欠驱动水下机器人的动态定位和航路点跟踪外文翻译资料

 2022-08-02 14:00:33

Dynamic positioning and way-point tracking of underactuated AUVs in the presence of ocean currents

A. PEDRO AGUIARdagger;lowast; and ANTacute;ONIO M. PASCOALdagger;

dagger; ISR/IST Institute for Systems and Robotics, Instituto Superior Tacute;ecnico,

Torre Norte 8, Av. Rovisco Pais, 1049-001 Lisboa, Portugal

(January 2007)

This paper addresses the problem of dynamic positioning and way-point tracking of underactuated autonomous underwater vehicles (AUVs) in the presence of constant unknown ocean currents and parametric modeling uncertainty. A nonlinear adaptive controller is proposed that steers an AUV along a sequence of way-points consisting of desired positions (x, y) in a inertial reference frame, followed by vehicle positioning at the final target point. The controller is first derived at the kinematic level assuming that the ocean current disturbance is known. An exponential observer for the current is then designed and convergence of the resulting closed-loop system trajectories is analyzed. Finally, integrator backstepping and Lyapunov based techniques are used to extend the kinematic controller to the dynamic case and to deal with model parameter uncertainty. Simulation results with a dynamic model of an underactuated autonomous underwater shuttle for the transport of benthic1 labs are presented and discussed.

1 Introduction

The problem of autonomous underwater vehicle (AUV) control continues to pose considerable challenges to system designers, especially when the vehicles are underactuated and exhibit large parameter uncertainty. From a conceptual standpoint, the problem is quite rich and the tools used to solve it must necessarily borrow from solid nonlinear control theory. However, the interest in this type of problem goes well beyond the theoretical aspects because it is well rooted in practical applications that constitute the core of new and exciting underwater mission scenarios, as the following example shows.

Over the past few years, there has been renewed interest in the development of stationary benthic stations to carry out experiments on the biology, geochemistry, and physics of deep sea sediments and hydrothermal vents in situ, over long periods of time. However, classical methods of deploying and servicing benthic laboratories are costly and require permanent support from specialized crews resident on board manned submersibles or surface ships [9]. To overcome some of the above mentioned problems, a European team consisting of IFREMER (FR), IST (PT), THETIS (GER), and VWS (GER), developed a prototype autonomous underwater shuttle vehicle named Sirene to automatically transport and position a large range of stationary benthic laboratories on the seabed, at a desired target point, down to depths of 4000 meters [5]. In a typical mission scenario (see Figure 1), the Sirene vehicle and the laboratory are first coupled together and launched from a support ship. Then, the ensemble descends in a free-falling trajectory (under the action of a ballast weight) at a speed in the range from 0.5 to 1m/s. At approximately 100m above the seabed, the Sirene releases its ballast and the weight of the all ensemble becomes neutral. At this point, the operator onboard the support ship instructs the vehicle to progress at a fixed speed, along a path defined by a number of selected way-points, until it reaches a vicinity of the desired target point. Afterwards, Sirene maneuvers to acquire the final desired heading and lands smoothly on target, after which it uncouples itself from the benthic laboratory and returns to the surface. The benthic laboratory can be easily recovered at a later time by sending an acoustic signal to the vehicle that triggers the release of a weight and forces the laboratory to re-surface slowly.

The Sirene Autonomous Underwater Vehicle (AUV) – depicted in Figure 2 – has an open-frame structure and is 4.0m long, 1.6m wide, and 1.96m high. Its dry weight is 4000 Kg and its maximum operating depth is 4000 m. The vehicle is equipped with two back thrusters for surge and yaw motion control in the horizontal plane and one vertical thruster for depth control. Roll and pitch motion are left uncontrolled, since the metacentric height2 is sufficiently large (36 cm) to provide adequate static stability. The AUV has no side thruster, thus making it underactuated. In the figure, the vehicle carries a representative benthic lab which is cubic-shaped and has a volume of approximately 2.3m3.

The problem of steering an underactuated AUV like Sirene to a point with a desired orientation (i.e.,pose control) has only recently received special attention in the literature (cf., e.g., [14; 16; 17; 7; 8; 2] and references therein). This task raises some challenging questions in control system theory because, in addition to being underactuated, the vehicle exhibits complex hydrodynamic effects that must necessarily be taken into account during the controller design phase. Namely, the vehicle exhibits sway and heave

velocities that generate non-zero angles of sideslip and attack, respectively. This rules out any attempt to design a steering system for the AUV that would rely on its kinematic equations only.

In practice, an AUV must also be capable of operating in the presence of unknown ocean currents. Interestingly enough, even for the case where the current is constant, the problem of regulating an underactuated AUV to a desired point with an arbitrary desired orientation does not have a solution. In fact, if the desired orientation of the vehicle is such that its main x-axis is not aligned against the direction of the current, point stabilization controllers derived without taking the current into account will in general

yield one of two possible behaviors: i) the vehicle will diverge from the desired target position, or ii) the controller will kee

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Dynamic positioning and way-point tracking of underactuated AUVs in the presence of ocean currents

存在洋流时欠驱动水下机器人的动态定位和航路点跟踪

A. PEDRO AGUIARdagger;and ANT ONIO M. PASCOALdagger;

dagger;ISR/IST系统与机器人研究所，德国高等理工学院，

托瑞北8,Av. Rovisco Pais，葡萄牙里斯本1049-001

(2007年1月)

摘要: 本文研究了在恒定的未知洋流和参数化建模不确定性的条件下，欠驱动自主水下航行器的动态定位和航路点跟踪问题。提出了一种非线性自适应控制器，该控制器在惯性参照系中引导AUV在惯性参照系中通过一系列由期望位置(x, y)组成的点，然后在最终目标点进行车辆定位。在已知海流扰动的情况下，首先从运动学的角度推导了控制器。其次，设计了电流的指数观测器，分析了闭环系统轨迹的收敛性。最后，利用积分器反推，并基于李雅普诺夫的技术将运动控制器扩展到动态情形，并处理了模型参数的不确定性。介绍了一种用于benthic1实验室运输的欠驱动自主水下航天飞机动力学模型的仿真结果并进行了讨论。

1 背景介绍

自主水下航行器控制问题一直是系统设计人员面临的一大挑战，特别是在水下航行器欠驱动和参数不确定性较大的情况下。从概念上看，这个问题是相当丰富的，用来解决它的工具必须借用坚实的非线性控制理论。然而，如下面的例子所示，人们对这类问题的兴趣远远超出了理论方面，因为它植根于实际应用，构成了新的和令人兴奋的水下任务场景的核心。

在过去的数年，人们对发展固定底栖生物站重新产生了兴趣，以便长期在原地进行深海沉积物和热液喷口的生物、地球化学和物理实验。然而，部署和维护底栖生物实验室的传统方法是昂贵的，并且需要居住在有人潜水器或水面舰艇[9]上的专门人员的长期支持。为了克服上述问题,欧洲团队组成的IFREMER (FR), IST (PT), THETIS (GER), and VWS (GER),在所需深度4000米[5]的目标点，开发了一个原型自治水下穿梭车Sirene，自动传输和大范围的位置固定底栖生物实验室在海底。在一个典型的任务场景中(见图1)，Sirene车辆和实验室首先耦合在一起，从一艘支持舰发射。然后，整个系综以自由下落的轨迹(在压舱物的作用下)以0.5到1m/s的速度下降。在距海床约100米处，Sirene释放了它的压舱物，所有系综的重量变为中性。在这一点上，支援舰上的操作员指示车辆以一个固定的速度前进，沿着一个由许多选择的路径点定义的路径，直到它到达预期目标点附近。之后，Sirene进行机动以获得最终想要的航向并平稳降落在目标上，然后它从底栖生物实验室中分离出来，返回水面。底栖生物实验室可以在稍后的时间很容易地恢复，通过发送一个声音信号到车辆，触发释放的重量，迫使实验室慢慢地重新浮出水面。

Sirene自主水下航行器(AUV)——如图2所示——采用开放式框架结构，长4.0米，宽1.6米，高1.96米。干重4000公斤，最大作业深度4000米。车辆配备两个用于水平面上的浪涌和偏航运动控制的后推力器和一个用于深度控制的垂直推力器。横摇和俯仰运动不受控制，因为稳心高度2足够大(36厘米)，提供足够的静态稳定性。AUV没有侧推器，因此驱动不足。在图中，运载工具携带一个典型的底栖生物实验室，它是方形的，体积大约2.3立方米。

将一个像Sirene一样的欠驱动AUV转向到一个指定方向点的问题（位姿控制）。最近才在文献中受到特别关注(cf.， e.g.， [14;16;17;7;8;2]和其中的参考文献)。这一任务在控制系统理论中提出了一些具有挑战性的问题，因为除了欠驱动外，车辆还表现出复杂的流体动力效应，在控制器设计阶段必须加以考虑。即车辆表现出摇摆和升沉，并分别产生非零侧滑角和攻角的速度。这就排除了为水下机器人设计一个仅依赖其运动学方程的转向系统的任何尝试。

实际上，AUV还必须能够在未知洋流存在的情况下工作。有趣的是，即使在电流恒定的情况下，用任意的期望方向来调节欠驱动AUV到期望点的问题也没有解决的办法。事实上，如果车辆的期望方向是这样的，即它的主x轴不与电流方向对齐，则不考虑电流的点稳定控制器通常会产生两种可能的行为之一: （i）车辆将偏离期望的目标位置，或（ii）控制器将保持车辆在期望位置附近移动，试图坚持引导它到给定的点，从而导致振荡行为。因此，有必要明确指出洋流的存在。

另一个扩展了上述问题的实际问题是设计一个联合制导和控制系统来实现AUV在停在最终目标位置之前的航路点跟踪。然后，可以使AUV沿着由一系列航路点指定的预定义参考路径(指向最终目标点)航行。路点跟踪在原则上可以通过多种方式进行。他们中的大多数人都能凭直觉做出解释，但缺乏坚实的理论背景。也许最广为人知的是所谓的视线方案[11]。在这种情况下，车辆导航是简单地通过向车辆的转向系统发出航向参考命令来完成的，以便使车辆的主轴在车辆当前位置和要到达的航路点之间沿视线对齐。参考指令的跟踪是通过一个适当设计的自动驾驶仪来完成的。然而，众所周知，分离制导和自动驾驶仪的方式是相当不稳定的[15]。

基于上述考虑，本文研究了在恒定的未知洋流和参数化建模不确定性下，欠驱动自主水下航行器在水平面上的动态定位和航路点跟踪问题。这个问题是在一个严格的数学框架中提出和解决的。提出了一种非线性自适应控制器，该控制器控制AUV，使其在惯性参照系中通过一系列由期望位置(x, y)组成的点，然后在最终目标点进行车辆定位。为了解决定位问题，这里考虑的方法是放弃最终期望方向上的规范，并使用这种额外的空间来迫使车辆收敛到期望的点。很自然的，飞行器会顺着水流的方向调整方向。提出的非线性自适应控制器能使闭环系统在恒定的未知海流扰动下的轨迹收敛参数模型不确定性。控制器的设计依赖于原始状态空间的非光滑坐标变换，然后在新的坐标下推导出基于李亚普诺夫的自适应控制律和海流扰动的指数观测器。为了表述清楚，我们首先在运动层面推导控制器，假设洋流扰动是已知的。然后，设计了一个电流观测器，分析了闭环系统轨迹的收敛性。最后，利用积分器反推和李雅普诺夫技术，将运动控制器扩展到动态情形，并对模型参数不确定性进行处理，提出了一种非线性自适应控制器。给出了仿真结果并进行了讨论。

本文的组织结构如下:第2节阐述了恒定未知洋流和参数化建模不确定性情况下的车辆动态定位和航路点跟踪问题。在第三节中，提出了一种基于非线性自适应控制律的动态定位问题的求解方法。分析了所得闭环系统的收敛性。第4节扩展了上一节提出的策略，迫使AUV在收敛到最终的目标点之前，在惯性参照系中跟踪一系列由期望位置(x, y)组成的点。第5节评估使用计算机模拟开发的控制算法的性能。最后，第6节包含了一些结束语，并讨论了需要进一步研究的问题。

5 仿真结果

为了说明在参数不确定性和恒定海流干扰下所提出的车辆定位控制方案的性能，以Sirene水下机器人模型为例进行了计算机仿真。第2节简要描述了车辆动力学模型。读者可参阅[1;3]获取详细信息，包括AUV水动力参数列表。

6 结论

摘要针对未知海流干扰和参数化建模不确定性条件下，欠驱动自主水下航行器(AUVs)在水平面上的动态定位和航路点跟踪问题。提出的解决方案借鉴了非线性自适应控制理论，使控制器本身成为电流的观测器。给出了控制律收敛闭环系统轨迹的条件。通过对典型水下机器人非线性模型的仿真，验证了控制律的有效性。仿真结果还表明，虽然没有得到正式的证明，但是在测量噪声存在的情况下，控制律仍然具有良好的性能。在实际应用中，利用状态滤波估计器可以进一步减小传感器噪声对系统性能的影响。对这个问题的严格分析无疑是未来研究的一个主题。

本文避开了研究动力学中输入饱和和执行机构可能引起的问题。事实上，作为控制它只是显示了如何容易地处理输入饱和时的浪涌和偏航速度。我们回顾所采用的控制设计方法是基于Lyapunovbased的和倒退技术，原则上可以扩展到处理驱动器动力学，在成本上获得更复杂的控制律。另一种可能被证明更适合实践的方法，是对所采用的控制律采取内外结构。在这个框架下，并使用运动学战略设计一个内环来处理执行器和车辆动力学。而本文提出的控制律在外环中。证明收敛性所得到的反馈控制系统的轨迹是一个具有挑战性的任务。这些和相关的问题值得进一步研究。

致谢

部分研究由项目GREX / ceci - ist(合同编号035223)、项目ma - sub支持AdI、PT和FCT-ISR/IST年度资助计划(通过后经济复兴计划主动与FEDER合作)。

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[11] Anthony J. Healey and David Lie

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