Guohua Xu

Path-Following Control of an AUV: Fully Actuated Versus Under-actuated Configuration

The problem of motion control of underwater vehicles in both the fully actuated and under-actuated configurations is often confronted by the marine technology community. This paper presents a nonlinear control method for autonomous underwater vehicles (AUVs) traveling along a planned planar path in both actuation configurations. The common objectives of path-following control for both fully actuated and under-actuated vehicles are described, and the differences in the necessary path-following control designs are analyzed, showing that the side-slip angle of the vehicle plays an important role in the evolution of the dynamics of AUVs with different actuation configurations. Based on the presented analysis, nonlinear controllers for the two types of AUV configurations are proposed, and the inherent characteristics of under-actuation and full actuation are revealed by a dedicated analysis of numerical simulation paradigms, the results of which will be instrumental in guiding marine technology engineers in the practical design and control of AUVs.

Trajectory tracking for underwater manipulator using sliding mode control

Considering variable payload and uncertainty of model, a sliding mode control scheme is proposed to realize a deep-sea manipulator control with high precision. The control principle is based on the exponential approach law. A saturation function is introduced to solve the problem of chattering. A novel and simple self-adaptive regulation method is used to improve the velocity of approaching. Under the constant load and variable load, the simulation results of trajectory tracking show the effectiveness of the improved controller. Finally, a practical sliding mode control system based VxWorks OS and PC104 is designed. Experiment results are presented at the end to show the control scheme has a good performance.

Coordinated control for multi-AUV systems based on hybrid automata

This paper presents a coordinated control strategy based on hierarchical control architecture for a team of Autonomous Underwater Vehicles (AUVs). The dedicated control structure is described by a four layered design for coordinated control, constituted with a global organizer and a local organizer modeled by a discrete-event system as two upper layers, an AUV controller modeled by a continuous-time system as a lower layer, and an AUV interpreter interconnecting the upper and lower layers as a middle interface. Such that the layered design for the coordination strategy is encoded as hybrid automata based techniques. As triggered by special events, the team organizer intermittently generates waypoints, then that the AUV controller generates commands which continuously move the AUVs between waypoints. Therefore, the team constituted even with heterogenous AUVs could implement a coordinated control as a whole using the proposed strategy. Simulation examples of AUVs in a flock demonstrate the results.

A Novel Acoustic Navigation Scheme for Coordinated Heterogenous Autonomous Vehicles

This paper addresses the navigation problem of coordinating a team of heterogenous vehicles including an autonomous surface vehicle (ASV) and several autonomous underwater vehicles (AUVs). Specially, a dedicated acoustic navigation scheme has been proposed in it. Utilizing the underwater DGPS concept, together with a set of intelligent surface sonobuoys, the precise position of the concerned AUV carrying an acoustic pinger, could be estimated by the measured time of arrival(TOA) of acoustic signals and the DGPS positions of sonobuoys, which were collected and computed by the central control ASV via radio link. Thus the ASV can generate and allocate the waypoints to the AUVs, and also move above the central of mass of the AUVs. As a result, the team constituted with heterogenous vehicles could implement a coordinated search or rescue scenario as a whole. Compared with INS/GPS navigation system, AUVs adopting such novel method, need not come to the surface to calibrate their positions periodically, which may seriously disturb the team coordination and existed formation. While compared with classical acoustic navigation systems (LBL, SBL, etc.), higher precise positions of AUVs are conveniently achieved. Furthermore, the paper demonstrates the simultaneous LS navigation algorithm for the coordinated control scheme in detail. The challenge is on the novel method in this paper that but also allows us to easily handle with heterogeneity in coordinated control task for underwater activities.

Adaptive Fuzzy Trajectory Tracking Control of an Under-Actuated Autonomous Underwater Vehicle Subject to Actuator Saturation

This paper focuses on vertical-plane trajectory tracking of an under-actuated autonomous underwater vehicle (AUV) subject to actuator saturation and external disturbances. A successive guidance and control frame is designed to avoid the cascade analysis between the kinematics guidance and the dynamics control, and the complete Lyapunov function is chosen to analyze the asymptotic stability of trajectory tracking system. In the guidance loop, the line-of-sight guidance law is applied to trajectory tracking of AUVs, which transforms the depth tracking error into the elevation angle tracking error and solves the problem of the under-actuated configuration in heave. In the control loop, direct adaptive fuzzy control is adopted to compensate for the effect of actuator saturation, which guarantees the system stability of trajectory tracking in the presence of actuator saturation. Finally, comparative numerical simulations are provided to illustrate the robust and bounded performance of the designed trajectory tracking control system.

Prospective research on coordinated control of multiple AUVS

This paper proposes some feasible ideas to improve research on coordinated control of multiple AUVS in the future. Firstly, there is a glancing overview about the state of the art of coordinated multi-AUVS, especially the drawbacks in concurrent research have been indicated, and then the aim of prospective research to derive distributed and scalable control laws is announced, which is based on stability criteria in global for multi-AUV systems. Secondly, there are four countermeasures addressed as prospective technology and possible improvements. The first issue is development of novel distributed algorithms in global but not in local case, secondly it is necessary to analyze the stabilization both on switching communication topology and switching formation topology. Thirdly, robust control is useful to deal with the unreliable acoustic communication system. Furthermore, complex vehicle dynamics should be highly regarded for coordinated control for heterogenous AUVS. At last, it is supposed that the gap between the scientific theory and commercial end users, could be bridged by dedicating appropriate efforts and prospective improvements mentioned above.

Cooperative Acoustic Navigation Scheme for Heterogenous Autonomous Underwater Vehicles

Oceans cover 71% of the earths surface and contribute the largest reservoir of life on the earth. With more and more concern about the abounding and valuable ocean resources, these years have witnessed a remarkable growth in the wide range of underwater commercial activities for ocean survey, especially focusing on undersea exploration and exploitation, and even extensively for salvage operations related with disastrous accidents occurred undersea (Lapierre, 2006). There are three main kinds of vehicles recruited for underwater activities. Manned Submersibles and Manned Underwater Vehicles with good abilities of directly manoeuvring and in-situ observation, have been widely utilized in commercial activity and scientific research, and reached the zenith in the late 1960s and early 1970s. However, this critical systems with vital importance of crew aboard and complex handling system significantly cost so much. Then, Remotely Operated Vehicles (ROVs) still with human in the loop but not in the vehicle are successful substitutes, being low-cost vehicles piloting in deep water greater than 1000ft. Today, ROV becomes a well-established technology frequently used in the offshore industry, most notably in the commercial offshore oil and gas, nuclear, pipeline and cable industries. Nevertheless, the long umbilical cable, linked with the mother ship, greatly inhibits the speed of the ROV, requiring the mother ship equipped with deck gear capable of winding up this cable and significantly restricting ship movement while deployed. More recently, with the development of advanced underwater technology, Autonomous Underwater Vehicles (AUVs) are steadily becoming the next significative step in ocean exploration due to their freedom from the constraints of an umbilical cable. Nowadays there has been gradually growth in the AUV industry worldwide which would be on an unprecedented scale and AUVs will carry out interventions in undersea structures in the future (Whitcomb, 2000). Moreover, recent applications using Intervention Autonomous Underwater Vehicles (IAUVs), have demonstrated the feasibility of autonomous underwater manipulations (Xu et al., 2007), controlled via acoustic links, thus removing the parasite effects of the umbilical cable (http://www.freesubnet.eu). With

Hovering control of submarine based on L1 adaptive theory via ballast tanks

This article proposed a novel method for submarine hovering control implement by ballast tanks based on L1 adaptive theory. The ballast tanks are able to provide submerge/emerge force by let in/out ballast tank water, and therefore adjust submarine position and altitude when low-speed maneuver largely limits rudder effect. After formulate and analysis models of ballast tanks as well as submarine dynamic, control scheme is determined as cascaded controller system. L1 adaptive theory is adopted for outer loop control, to deal with the nonlinearity and uncertainties of model, as well as environmental disturbance in hovering condition for the first time. Robustness of control system is tested through simulations based on Simscape. Large impact force is exerted on submarine to simulate missile launching and test restoring ability of ballast tanks control. Simulation results demonstrated that the submarine is able to maneuver and response precisely, despite of sudden impact.

Modelling and simulation for underwater hovering control based on ballast tank

This paper presents an integrated modelling method for submarine hovering system which equipped ballast tank to adjust vehicle position and altitude. Ballast system model including high pressure bottle and ballast tank is made first of all, and then the disturbance force considering compressibility and sea environment. Discharged coefficient of orifice is taken into account, and necessary linearity to avoid solver difficulties is made. To demonstrate the accuracy of model, numerical simulations in Matlab are run both for blowing and venting process only, and depth changing maneuver of hover system, multidomain physical system “Simscape” is introduced for more efficient simulation.