Digital RAC with a disturbance observer for underwater vehicle-manipulator systems

Most control methods of underwater vehiclemanipulator systems (UVMS) are based on the computed torque method that is used for underwater robotic vehicles. We have proposed a resolved acceleration control (RAC) method for UVMS. In this article, we propose a disturbance compensation control method for both vehicle and manipulator based on the RAC method. Experimental results using an underwater robot with a vertical planar 2-link manipulator show that the proposed control method has good control performance.     

Development of a real-time control architecture for a semi-autonomous underwater vehicle for intervention missions

The need for autonomous underwater vehicles (AUVs) for intervention missions becomes greater as they can perform underwater tasks requiring physical contacts with the underwater environment, such as underwater plug-in/plug-out, construction and repair, cable streaming, mine hunting, munitions retrieval, and scientific sampling. This paper describes a semi-autonomous underwater vehicle for intervention missions that has multiple on-board CPUs, redundant sensors and actuators, on-board power source and a robotic manipulator for dextrous underwater performance. Such a complex robotic vehicle system requires advanced control software architecture for on-board intelligence with a wide range of sensors and actuators to carry out required missions. In this paper, AUV control architectures are reviewed and a sensor data bus based control architecture (SDBCA) is presented. SDBCA is a modified hierarchical architecture that offers good controllability and stability while sensor data bus increases flexibility of system design, making it possible to have a prompt response from high-level control with respect to low-level sensor data. The overall sensor input mechanism of SDBCA becomes similar to the sensor input mechanism of subsumption architecture.     

Disturbance observer-based robust control for underwater robotic systems with passive joints

Underwater exploration requires mobility and manipulation. Underwater robotic vehicles (URV) have been employed for mobility, and robot manipulators attached to the underwater vehicle (i.e. rover) perform the manipulation. Usually, the manipulation mode takes place when the rover is stationary. The URV is then modeled as a passive joint and joints of the manipulator are modeled as active joints. URV motions are determined by inherent dynamic couplings between active and passive joints. Furthermore, the control problem becomes complex since there are many hydrodynamic terms as well as intrinsic model uncertainties to be considered. Tocope with these difficulties, we propose a disturbance observer-based robust control algorithm for underwater manipulators with passive joints. The proposed control algorithm is able to treat an underactuated system as a pseudo-active system in which passive joints are eliminated. Also, to realize a robust control method, a non-linear feedback disturbance observer is applied to each active joint. A four-jointed underwater robotic system with one passive joint is considered as an illustrative example. Through simulation, it is shown that the proposed control algorithm has good position tracking performance even in the presence of several external disturbances and model uncertainties.     

Development and Experimental Tests of a ROS Multi-agent Structure for Autonomous Surface Vehicles

Robotic structures that couple autonomous surface vehicles and unmanned underwater vehicles in integrated systems with various levels of cooperation provide interesting solutions to the problem of developing efficient, versatile and cost effective tools for exploration, monitoring and exploitation of the underwater environment. In this paper we describe the development and preliminary field testing of an autonomous surface vehichle that can automatically track, deploy and recover a small remotely operated vehicle, which is guided from a shore-ground station. This goal is achieved by exploiting two-ways transmission of data and commands through the umbilical and a wireless link with a shore-ground station. In this way, pilots can experiment telepresence in the underwater environment, avoiding the need of expensive and logistically demanding manned supply vessel. The vehicle is a small aluminum hull boat, equipped with a steering outboard electric motor. A multi-agent system in the ROS framework is proposed for the robotic structure. The use of commercial-off-the-shelf components and the choice of a multi-agent ROS architecture are a mean to reduce costs and to assure performances, modularity and versatility. Field tests in both supervised and autonomous guidance mode have been performed in order to assess the basic functionalities of the system and their results are illustrated and discussed.     

Experimental study on a learning control system with bound estimation for underwater robots

Underwater robotic vehicles (URVs) have become an important tool for numerous underwater tasks due to their greater speed, endurance, depth capability, and a higher factor of safety than human divers. However, most vehicle control system designs are based on simplified vehicle models and often result in poor vehicle performance due to the nonlinear and time-varying vehicle dynamics having parameter uncertainties. Conventional proportional-integral-derivative (PID) type controllers cannot provide good performance without fine-tuning the controller gains and may fail for sudden changes in the vehicle dynamics and its environment. Conventional adaptive control systems based on parameter adaptation techniques also fail in the presence of unmodeled dynamics.This paper describes a new vehicle control system using the bound estimation techniques, capable of learning, and adapting to changes in the vehicle dynamics and parameters. The control system was extensively wet-tested on the Omni-Directional Intelligent Navigator (ODIN)-a six degree-of-freedom, experimental underwater vehicle developed at the Autonomous Systems Laboratory, and its performance was compared with the performance of a conventional linear control system. The results showed the controller's ability to provide good performance in the presence of unpredictable changes in the vehicle dynamics and its environment, and it's capabilities of learning and adapting.     

An experimental remote handling system

An experimental robotic remote handling system is described which has been constructed in order to investigate various engineering problems in advanced remote handling such as the man-machine interface, system control and communication. The device consists of a mobile and a control station. The mobile station comprises an electrical manipulator having seven degrees of freedom, a TV camera, a control sub-computer, a servo-control unit, radio transmitters and receivers, batteries, etc., which are mounted on a crawler-type vehicle. The control station is equipped with the master arm of the manipulator, radio transmitters and receivers, a TV monitor, a main control computer and its peripheral devices, etc. The manipulator can be operated in either a master-slave, a playback or a programmed control mode with the assistance of control computers. Communication between the mobile and the control stations is made using optical fibres or a radio link.     

Development of the Omni Directional Intelligent Navigator

The Autonomous Systems Laboratory is in the midst of developing an advanced underwater robotic technology test platform. The platform consists of the Omni-Directional Intelligent Navigator (ODIN) and the Integrated Graphic Workstation (IGW). ODIN is a six degree-of-freedom (dof) underwater vehicle with dual operational modes (autonomous and tethered) and a single dof mechanical manipulator. IGW is a real-time, 3-dimensional graphic monitoring, testing, and evaluation workstation. This paper presents ODIN's mechanical and electrical specifications; its vehicle dynamics and depth control system; its recent simulation and experimental results; and IGW's specifications     

Shared autonomy for low‐cost underwater vehicles

This field report presents an overview of the development and testing of a semi‐autonomous underwater vehicle (sAUV). The work presented here is aimed at bridging the gap between current remotely operated vehicles and autonomous research platforms by developing shared autonomy capabilities for low‐cost underwater vehicles. We use commercially available components and open‐source software interfaces to provide a wider range of capabilities for underwater autonomy research at a lower cost than previously available systems. We describe the overall structure of the system, discuss its capabilities, and provide results demonstrating system performance. We place particular emphasis on shared autonomy, where a human operator is assisted in controlling an underwater tethered vehicle. We present three capabilities developed for the sAUV: (a) an assisted control mode that provides a variable level of assistance using an on‐line estimate of user skill level, (b) a planner to generate paths that avoid tether entanglement, and (c) a sonar processing algorithm that identifies informative sonar images for selecting features for 3D scene reconstruction. The vehicle has been deployed on five off‐shore and near‐shore marine field deployments since 2015, and this report includes selected results from four of those trials to demonstrate the capabilities and limitations of the sAUV system.     

水下机器人多功能作业工具包

本文首先阐述了水下机器人作业工具包的重要性，重点研究了水下机械手的原理、 功能及两种主要结构．并以沈阳自动化所研制的缆控水下机器人为背景，讨论了水下作业工 具包的一些专用工具的原理及其结构．     

Robust feedback stabilization of underwater robotic vehicles

The controlled motion of an underwater vehicle is very likely to be affected by arbitrary disturbances with considerable magnitudes. In this paper, we develop a simple approach for optimal robust control design of underwater robotic vehicles having decentralized input-output structure. Our design method is based on an explicit condition on the control input matrix which has been found to be necessary and sufficient for a decentralized control system to be robust against arbitrary, but otherwise, bounded disturbances. That makes it possible to get optimal trade-off relations between the bounds of disturbances, the system output accuracy, and the control force limits. For the robust control design purpose, we apply decentralized sliding-mode control the stability of which can be easily verified using Lyapunov theory. In order to show the effectiveness of the design method, the controlled planar motion of an underwater robotic vehicle is taken as an illustrative example.     

Adaptive nonsingular fast terminal sliding mode control for underwater manipulator robotics with asymmetric saturation actuators

In this paper, an adaptive nonsingular fast terminal sliding mode control (ANFTSMC) is proposed for underwater manipulator robotics with asymmetric actuator saturations and unknown time-varying (TV) external disturbances. Firstly, the nonsingular fast terminal sliding mode (NFTSM) control scheme is conducted for the underwater manipulator robotics, which guarantees the boundedness of all the signals in the control system. Secondly, the adaptive method and the smooth hyperbolic tangent (tanh) function are introduced to address the unknown TV external disturbances and the input saturation errors. Thus the prior knowledge about the upper bounds of the system uncertainties is not needed in this paper. To deal with the nonlinear asymmetric input saturation issue, a Gaussian error function is employed in the asymmetric saturation module so that the discontinuous input signals can be transformed into smooth forms. Thirdly, the rigorous mathematical verification is conducted to demonstrate the stability and finite-time convergence of the closed-loop control system via the Lyapunov theory. Finally, numerical simulations are performed on a two-link underwater manipulator robotic system to illustrate the effectiveness of the proposed controller.     

Visual inspection of sea bottom structures by an autonomousunderwater vehicle

This paper describes a vision-based system for inspections of underwater structures, e.g., pipelines, cables, etc., by an autonomous underwater vehicle (AUV). Usually underwater inspections are performed by remote operated vehicles (ROVs) driven by human operators placed in a support vessel. However, this task is often challenging, especially in conditions of poor visibility or in presence of strong currents. The system proposed allows the AUV to accomplish the task in autonomy. Moreover, the use of a three-dimensional (3-D) model of the environment and of an extended Kalman filter (EKF) allows the guidance and the control of the vehicle in real time. Experiments done on real underwater images have demonstrated the validity of the proposed method and its efficiency in the case of critical and complex situations.     

An adaptive fuzzy sliding mode controller for remotely operated underwater vehicles

Sliding mode control is a very attractive control scheme because of its robustness against both structured and unstructured uncertainties as well as external disturbances. In this way, it has been widely employed for the dynamic positioning of remotely operated underwater vehicles. Nevertheless, in such situations the discontinuities in the control law must be smoothed out to avoid the undesirable chattering effects. The adoption of properly designed boundary layers has proven effective in completely eliminating chattering, however, leading to an inferior tracking performance. This work describes the development of a dynamic positioning system for remotely operated underwater vehicles. The adopted approach is primarily based on the sliding mode control strategy and enhanced by an adaptive fuzzy algorithm for uncertainty/disturbance compensation. Using the Lyapunov stability theory and Barbalat’s lemma, the boundedness and convergence properties of the closed-loop signals are analytically proven. The performance of the proposed control scheme is also evaluated by means of numerical simulations.     

A comparative study of control techniques for an underwater flight vehicle

Unmanned, underwater vehicles have been developed considerably in recent years. Remotely operated vehicles (ROVs) are increasingly used for routine inspection and maintenance tasks but have a range that is limited by the umbilical cable. For long range operations, such as oceanographic exploration and surveying, autonomous underwater vehicles (AUVs) are emerging which haveon-board power and are equipped with advanced control capabilities to carry out tasks with the minimum of human intervention. AUVs typically resemble torpedoes in that mosthave control surfaces and a single propulsion unit, and must move forwards to manoeuvre. Such vehicles are called flight vehicles. This paper describes techniques which are candidates for control of a flight AUV and identifies controllers used on some existing vehicles. Since underwater vehicle dynamics are nonlinear, fuzzy logic and sliding mode control were felt to have promise for autopilot application due to their potential robustness. Following development using a comprehensive simulation programme, the controllers were tested using the experimental vehicle, Subzero II, and their performance compared with that of a classical linear controller. The relative merits of the methods for practical implementation are discussed.     

UNION: underwater intelligent operation and navigation

The main goal of the UNION ESPRIT Basic Research Action is to develop methods for increasing the autonomy and intelligence of underwater remotely operated vehicles (ROVs). The project focuses mainly on the development of coordinated control and sensing strategies for combined manipulator and vehicle systems. Both fundamental theories and methods for the design of these heterogeneous systems are investigated. A complex canonical mission in the field of offshore inspection maintenance and repair tasks was chosen as an integration guideline of all the results     

Adaptive Fuzzy Sliding Mode Controller for the Kinematic Variables of an Underwater Vehicle

This paper address the kinematic variables control problem for the low-speed manoeuvring of a low cost and underactuated underwater vehicle. Control of underwater vehicles is not simple, mainly due to the non-linear and coupled character of system equations, the lack of a precise model of vehicle dynamics and parameters, as well as the appearance of internal and external perturbations. The proposed methodology is an approach included in the control areas of non-linear feedback linearization, model-based and uncertainties consideration, making use of a pioneering algorithm in underwater vehicles. It is based on the fusion of a sliding mode controller and an adaptive fuzzy system, including the advantages of both systems. The main advantage of this methodology is that it relaxes the required knowledge of vehicle model, reducing the cost of its design. The described controller is part of a modular and simple 2D guidance and control architecture. The controller makes use of a semi-decoupled non-linear plant model of the Snorkel vehicle and it is compounded by three independent controllers, each one for the three controllable DOFs of the vehicle. The experimental results demonstrate the good performance of the proposed controller, within the constraints of the sensorial system and the uncertainty of vehicle theoretical models.     

作业型水下机器人姿态调节控制研究

为了解决在作业时水下机器人载体上的机械手伸展过程将会引起载体重心发生变化,导致水下机器人发生纵横倾运动,影响作业效率的问题,考虑到水下机器人控制系统较为复杂,因此引入模糊滑模控制,根据要求设计出一款模糊滑模控制器。利用计算机和MATLAB技术,将水下机器人姿态运动方程与常规PID控制和模糊滑模控制分别结合起来进行仿真分析。仿真结果表明,模糊滑模控制相比于常规PID控制,在机械手关节正弦运动过程中,姿态角下降了20%以上,横倾姿态角度误差减小了30%以上,纵倾姿态角误差也超过了8%以上。在悬停作业过程中,纵横倾姿态角度都下降了30%以上。通过两种不同控制方式的仿真,验证了模糊滑模控制的控制效果要优于常规PID控制,能够取得更好的控制效果,同时利用计算机技术缩短了研究时间、提高了研究效率。     

Dual-eyes Vision-based Docking System for Autonomous Underwater Vehicle: an Approach and Experiments

A critical challenge for autonomous underwater vehicles (AUVs) is the docking operation for applications such as sleeping under the mother ship, recharging batteries, transferring data, and new mission downloading. The final stage of docking at a unidirectional docking station requires the AUV to approach while keeping the pose (position and orientation) of the vehicle within an allowable range. The appropriate pose therefore demands a sensor unit and a control system that have high accuracy and robustness against disturbances existing in a real-world underwater environment. This paper presents a vision-based AUV docking system consisting of a 3D model-based matching method and Real-time Multi-step Genetic Algorithm (GA) for real-time estimation of the robot’s relative pose. Experiments using a remotely operated vehicle (ROV) with dual-eye cameras and a separate 3D marker were conducted in a small indoor pool. The experimental results confirmed that the proposed system is able to provide high homing accuracy and robustness against disturbances that influence not only the captured camera images but also the movement of the vehicle. A successful docking operation using stereo vision that is new and novel to the underwater vehicle environment was achieved and thus proved the effectiveness of the proposed system for AUV.     

基于VxWorks的水下机器人通信系统设计

针对水下机器人（ROV）在深海高噪声干扰环境中工作的特点,设计了一套基于VxWorks实时操作系统的ROV整体通信系统,实现了水下核心控制器对水下分系统快速高效的信息采集和数据分配,水下系统和水面控制器稳定实时的数据交换;硬件方面设计了以CAN总线为基础的水下通信系统,通过FPGA实现了CAN总线和PC104总线之间的时序逻辑转换,软件方面设计了基于TCP/IP协议栈的水面操控台和ROV之间的网络通信方式和水下各系统之间的CAN总线通信方式,着重介绍了基于缓冲队列的网络通信编程;通信系统数据测试实验表明：CAN总线通信和网络通信均具有良好的实时性和可靠性,满足最初的设计需求,而且采用模块化设计,便于维护和移植。     

随控布局AUV动力定位系统综合模型研究

采用随控布局的新型水下航行器配备了多个不同方向的推进器,实现了直接升力控制、直接侧向力控制.能够完成水下动力定位、三维轨迹跟踪以及地形跟随等精确的水下作业.建立了新型水下航行器在动力定位模式下的低频和高频运动模型,以及推进器系统和波浪、海流等海洋环境的模型,最后给出了航行器动力定位系统的综合状态空间模型,进行了计算机仿真.仿真结果证明了建模方法的有效性,为动力定位综合控制系统的设计奠定了基础.