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.     

Motion and force control with a nonlinear force error filter for underwater vehicle-manipulator systems

This paper deals with a control scheme for autonomous underwater robots equipped with manipulators. Several motion and force controllers have been developed. Most of them were designed in disregard of the dynamics of marine thrusters to develop a controller with a simple structure. However, the robot body propelled by thrusters generally has a considerably slower time response than the manipulator driven by electrical motors. Therefore, it may be difficult to construct a high-gain feedback control system to achieve a good control performance, because the high gain may excite the slow thruster dynamics ignored in the controller design, and the excitation will degrade the control performance. In this paper, we develop a motion and force controller for mathematical models with the dynamics of thrusters. It includes a nonlinear force error filter which allows us to construct a stable motion and force control system. To investigate its control performance, we conducted numerical simulations for comparing the proposed control scheme with an existing control scheme designed in disregard of the thruster dynamics. Simulation results demonstrate the usefulness of the proposed controller.     

基于强化学习的波动鳍推进水下作业机器人悬停控制

本文针对波动鳍推进水下作业机器人的悬停控制问题开展研究. 首先, 给出了波动鳍推进水下作业机器人 的运动学模型、动力学模型和波动鳍的参数–力映射模型, 建立了基于马尔可夫决策过程的悬停控制训练框架. 其 次, 基于模型结构和训练策略, 使用强化学习的方法进行网络训练, 得到最佳的悬停控制器. 最终, 在室内水池中完 成了波动鳍推进水下作业机器人的悬停控制实验, 实验结果验证了所提方法的有效性.     

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.     

Digital RAC for underwater vehicle-manipulator systems considering singular configuration

We have proposed continuous-time and discrete-time resolved acceleration control methods for underwater vehicle-manipulator systems and the effectiveness of the control methods has been shown by experiments. In this article, we propose a digital control method considering the singular configuration of manipulator. Experimental results show the effectiveness of the proposed method. This work was presented in part at the 10th International Symposium on Artificial Life and Robotics, Oita, Japan, February 4–6, 2005     

Adaptive control of underwater vehicle-manipulator systems using radial basis function networks

This paper deals with a control scheme for underwater vehicle-manipulator systems with the dynamics of thrusters in the presence of uncertainties in system parameters. We have developed two controllers that overcome thruster nonlinearities, which cause an uncontrollable system: one is a regressor-based adaptive controller and the other is a robust controller. However, the structure of the adaptive controller is very complex due to the feedforward terms including the regressors of dynamic system models, and the error feedback gains of the robust controller with a good control performance are excessively high due to the lack of feedforward terms. In this paper we develop an adaptive controller that uses radial basis function networks instead of the feedforward terms. The replacement leads to a moderately high gain controller whose structure is simpler than that of the regressor-based adaptive controller.     

Neural networks to determine task oriented dexterity indices for an underwater vehicle-manipulator system

A method for the fast approximation of dexterity indices for given underwater vehicle-manipulator systems (UVMS) configurations is presented. Common underwater tasks are associated with two well-known dexterity indices and two types of neural networks are designed and trained to approximate each one of them. The method avoids the lengthy calculation of the Jacobian, its determinant and the computationally expensive procedure of singular value decomposition required to compute the dexterity indices. It provides directly and in a considerably reduced computational time the selected dexterity index value for the given configuration of the system. The full kinematic model of the UVMS is considered and the NN training dataset is formulated by the conventional calculation of the selected dexterity indices. A comparison between the computational cost of the analytical calculation of the indices and their approximation by the two NN is presented for the validation of the proposed approach. This paper contributes mainly on broadening the applications of NN to a problem of high complexity and of high importance for UVMS high performance intervention.     

Fuzzy redundancy resolution and motion coordination for underwater vehicle-manipulator systems

The problem of redundancy resolution and motion coordination between the vehicle and the manipulator in underwater vehicle-manipulator systems (UVMSs) is addressed in this paper. UVMSs usually possess more degrees of freedom than those required to perform end-effector tasks; therefore, they are redundant systems and kinematic control techniques can be applied aimed at achieving additional control objectives besides tracking of the end-effector trajectory. In this paper, a task-priority inverse kinematics approach to redundancy resolution is merged with a fuzzy technique to manage the vehicle-arm coordination. The fuzzy technique is used both to distribute the motion between vehicle and manipulator and to handle multiple secondary tasks. Numerical case studies are developed to demonstrate effectiveness of the proposed technique.     

Sensor-based guidance control of a continuum robot for a semi-autonomous colonoscopy

Due to their compliance and high dexterity, biologically-inspired continuum robots have attracted much interest for applications such as medical surgery, urban search and rescue, de-mining etc. In this paper, we will present an application to medical surgery-colonoscopy by designing a pneumatic-driven flexible robotic manipulator, called ColoBot. The focus of this paper lies in the sensor-based position control of the ColoBot for guiding the advancement in a tubular, compliant and slippery environment. The kinematic model related the position of the distal end of the ColoBot to the actuator inputs which is firstly developed and formulated to control the shape of the ColoBot through position control of the distal tip. To achieve safe guidance, the ideal position of the tip should be in the central axis of the colon. A method based on a circumscribed circle is proposed to approximate the central position in real-time based on three sensor readings. This position will be used as reference position for the tip to adjust its shape in real time to avoid the contact with tube wall. This proposed approach can be extended to the control of continuum robots in the conditions of a dynamically confined space. The simulation results and experimental results with a curved tube will be presented in order to validate the proposed control strategy.     

混合驱动水下滑翔器主从互转式应急控制技术研究

水下滑翔器是一种长续航新型水下机器人,利用其高效的驱动方式能够航行数月,因而相比其他无人水下自主航行器,滑翔器控制系统的可靠性显得尤为关键。根据水下滑翔器长续航的工作需求,结合其分布式控制系统的架构形式,设计了一种主从互转式应急控制技术。通过CPU互监控以及建立公共存储区等手段,实现了控制器异常情况下的非复位式热切换,保证了滑翔器重要动作部件的正常运行。试验结果表明,利用主从互转式控制方式,可以极大的减小了控制系统中主CPU宕机对滑翔器自主运行的影响,增加水下滑翔器的安全性能。     

Multi-modal control framework for a semi-autonomous wheelchair using modular sensor designs

This paper presents the hardware and software control framework for a semi-auton omous wheelchair. The hardware design incorporates modular and reconfigurable sensors and corresponding low-level software architecture. Two control schemes are discussed. Assisted control that augments the user inputs by providing functionalities such as obstacle avoidance and wall following. And, semi-autonomous navigation which takes higher level destination goals and executes a simultaneous localization and mapping algorithm. We also propose an adaptive motion control with a online parameter estimation. The paper presents both experimental and simulation results.     

一种主从式多轴控制卡的设计

本文设计了一种基于PCI总线、以TMS320F2812为核心的主从开放式多轴控制系统,介绍了系统的功能、组成、硬件设计以及软件算法。该控制卡可独立或与计算机一同实现对目标的精稳控制,通过对三轴转台的控制,表明该控制系统具有实时、模块化的优点,控制精度满足系统要求,具有广阔的应用前景。     

Towards semi-autonomous operation of under-actuated underwater vehicles: sensor fusion,on-line identification and visual servo control

In this paper we propose a framework for semi-autonomous operation of an under-actuated underwater vehicle. The contributions of this paper are twofold: The first contribution is a visual servoing control scheme that is designed to provide a human operator the capability to steer the vehicle without loosing the target from the vision system’s field of view. It is shown that the under-actuated degree of freedom is input-to-state stable (ISS) and a shaping of the user input with stability guarantees is implemented. The resulting control scheme has formally guaranteed stability and convergence properties. The second contribution is an asynchronous Modified Dual Unscented Kalman Filter (MDUKF) for the on-line state and parameter estimation of the vehicle by fusing data from a Laser Vision System (LVS) and an Inertial Measurement Unit (IMU). The MDUKF has been developed in order to experimentally verify the performance of the proposed visual servoing control scheme.     

具有震颤抑制的微创机器人主从控制系统设计

详述了一种用于抑制微创手术机器人震颤现象的主从控制系统,提出了针对人手生理震颤的新型零相位滤波方法及针对从操作臂关节“粘滑行为”的前馈补偿PD伺服算法。新型零相位滤波避免了传统低通滤波器容易造成延时和传统零相位滤波无法在线使用的缺点,前馈补偿PD伺服算法通过摩擦补偿克服了非线性摩擦对从操作臂运动造成的影响。最后,对系统进行仿真及实验,结果表明该方法能有效地抑制机器人手术工具末端的震颤现象。     

时滞输出反馈非恒同主从耦合混沌系统一致同步的判据

当主从耦合混沌系统的参数之间非恒同时,一般意义上的混沌同步难以实现,因此,讨论了其具有一定误差界的一致同步问题.本文对一类包含Lur’e系统和Lipschitz系统在内的混沌系统,应用Lyapunov函数方法导出通过时滞输出反馈控制实现一致同步的充分条件,该判据用矩阵不等式的形式给出.进而讨论了同步的鲁棒性问题.最后结合Chua电路对结论进行了数值模拟,验证了结论的正确性与有效性.     

Study on formation control system for underwater spherical multi-robot

Microsystem Technologies - Aiming at multi robot cooperation application requirements of our small-scaled underwater spherical robots, a cooperative formation control system with static and dynamic...     

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.     

Vehicle-manipulator system dynamic modeling and control for underwater autonomous manipulation

Underwater autonomous manipulation is a challenging task, which not only includes a complicated multibody dynamic and hydrodynamic process, but also involves the limited observation environment. This study systematically investigates the dynamic modeling and control of the underwater vehicle-manipulator multibody system. The dynamic model of underwater vehicle-manipulator system has been established on the basis of the Newton–Euler recursive algorithm. On the basis of dynamic analysis, a motion planning optimization algorithm has been designed in order to realize the coordinate motions between AUV and manipulator through reducing the restoring forces and saving the electric power. On the other hand, a disturbance force observer including the coupling and restoring forces has been designed. An observer-based dynamic control scheme has been established in combination with kinematic and dynamic controller. Furthermore, from the simulations, although the disturbance forces such as restoring and coupling forces are time varying and great, the observer-based dynamic coordinate controller can maintain the AUV attitude stable during the manipulator swing and pitch motions. During the precise manipulation simulation, the stable AUV attitude and minimization of disturbance forces have been realized through combination of optimal motion planning and the observer-based dynamic coordinate controller.