Chong-Moo Lee

Discrete-time quasi-sliding mode control of an autonomous underwater vehicle

This paper presents a discrete-time quasi-sliding mode controller for an autonomous underwater vehicle (AUV) in the presence of parameter uncertainties and a long sampling interval. The AUV, named VORAM, is used as a model for the verification of the proposed control algorithm. Simulations of depth control and contouring control are performed for a numerical model of the AUV with full nonlinear equations of motion to verify the effectiveness of the proposed control schemes when the vehicle has a long sampling interval. By using the discrete-time quasi-sliding mode control law, experiments on depth control of the AUV are performed in a towing tank. The controller makes the system stable in the presence of system uncertainties and even external disturbances without any observer nor any predictor producing high rate estimates of vehicle states. As the sampling interval becomes large, the effectiveness of the proposed control law is more prominent when compared with the conventional sliding mode controller.

A docking and control system for an autonomous underwater vehicle

Autonomous underwater vehicles are unmanned underwater vessels to investigate sea environments, oceanography and deep-sea resources autonomously. Docking systems are required to increase the capability of the AUVs to recharge the batteries and to transmit data in real time underwater. This paper presents a docking system for an AUV to dock into underwater station with a camera. To make a visual servo control system, this paper derives an optical flow model of a camera mounted on AUV, where a CCD camera is installed at the nose center of the AUV to monitor the docking condition. This paper combines the optical flow equation of the camera with the AUVs equation of motion, derives a state equation for the visual servoing AUV. This paper also proposes a MIMO controller minimizing a cost function. The control inputs of the AUV are automatically generated with the projected target position on the CCD plane and with the AUVs motion. To demonstrate the effectiveness of the modeling and the control law of the visual servoing AUV, simulations of docking the AUV to a target station are performed with the 6-dof nonlinear equations of REMUS of WHOI and a CCD camera.

Improvement on an inertial-Doppler navigation system of underwater vehicles using a complementary range sonar

This work presents an improvement of an inertial-Doppler underwater navigation system for unmanned underwater vehicles (UUV) using a complementary range sonar. The inertial-Doppler navigation system is generally based on an inertial measurement unit (IMU) and a Doppler velocity log (DVL) accompanying a magnetic compass and a depth sensor. Although conventional navigation systems update bias errors of the inertial sensors, scale effects of the DVL, the estimated position slowly drifts as time passes. This paper proposes a measurement model with additional range sonar to improve the performance of the IMU-DVL navigation system for underwater vehicles. The proposed navigation model based on inertial navigation systems includes the scale effects, the bias errors of the DVL, and the error model of the range sonar, where the order of the system states is 21. An extended Kalman filter was adopted to propagate the error covariance, updated the measurement errors and correct the state equation when the external measurements are available. Simulation conducted with the 6-d.o.f. equations of motion of an AUV in lawn-mowing survey mode illustrates the effectiveness of the IMU-DVL navigation system assisted by the additional range measurement.

System design of an ROV with manipulators and adaptive control of it

A remotely operated vehicle (ROV) equipped with two manipulators and an underwater stereo camera is being developed in KRISO (Korea Research Institute of Ships and Ocean Engineering) for seabed working. This paper describes the preliminary design of the ROV. An underwater stereo camera has been developed to enhance the working efficiency of the ROV with the manipulator in seabed operation. This paper presents the operational principle and the structure of the underwater stereo camera. The stereo camera consists of two CCD cameras and horizontally moving base, and it is embedded in a small pressure canister for underwater application. This paper also evaluates the implementation of an adaptive controller to the tracking control of the ROV/manipulator system.

Navigation and Control System of a Deep-sea Unmanned Underwater Vehicle 'HEMIRE'

This paper presents a hybrid underwater navigation and control system for positioning, guidance and control of a deep-sea unmanned underwater vehicle (UUV), HEMIRE. For precise navigation of the UUV, the hybrid navigation system is designed based on strap-down IMU (inertial measurement unit) accompanying with USBL (ultra-short base line), DVL (Doppler velocity log), range sonar, depth and heading sensors. Initial localization and position reference of the UUV are performed with the USBL when the vehicles are in stationary condition. This paper also presents the characteristics of the UUV and the system constitution of the surface control unit. HEMIRE is equipped with two hydraulic manipulators, ORION, which are remotely controlled at the surface vessel via fiber optic communication. An operator can control the manipulators with a workspace-controlled master arm as well as a parallel-type master arm. This paper describes the task-oriented control of the tele-operated robotic arms mounted on HEMIRE and its application to task-oriented joint configurations.

A study on the design and manufacture of a deep-sea unmanned underwater vehicle based on structural reliability analysis

The reliability analysis tool provided with the commercial structure-analysis package, ANSYS 9.0, is relatively easy to use and allows solutions to be rapidly obtained. However, the tool cannot guarantee the results of the reliability analysis since it can only provide an outline tendency of the probability of failure without giving an accurate numerical value of the probability of failure at the regions that a designer requires. The independent commercial reliability analysis code, NESSUSS 7.0, also has problems in that it may not necessarily converge and can waste computation time from having to undertake unnecessary repetitive structure analyses for design variables that have little significance to the structural integrity of the object being designed. A design methodology and a software module, which can make up for the current deficiencies in these commercial packages, have been developed by the authors and are presented in this paper. This paper describes how the methodology and the software module were applied to the design and manufacture of a stiffened pressure vessel, which can be mounted on a 6000 m class deep-sea unmanned underwater vehicle.

An integrated DVL/IMU system for precise navigation of an autonomous underwater vehicle

Summary form only given. This paper describes a hybrid navigation system for an autonomous underwater vehicle (AUV) equipped with a Doppler Velocity log (DVL) and an inertial measurement unit (IMU). The navigation system additionally employed a conventional magnetic heading compass, a depth sensor, and gravitational roll and pitch sensors. A dynamic filter is developed to predict the motion of the AUV, where the hydrodynamic coefficients of the AUV are derived from planar motion measurement (PMM) tests. A data fusion algorithm based on the Kalman filter fuses the various data from the DVL, the IMU, and the other motion sensors and corrects the measurement error to conduct precise navigation. This paper also presents the architecture of the navigation system including the filter algorithm and the extensive data fusion methods. Experiments were performed with a semi-autonomous underwater vehicle (SAUV) and compared with a conventional acoustic navigation system.

Preliminary study on the inertial-Doppler localization of a deep-sea launcher hanging on a cable

This paper presents a localization method of a deep-sea launcher with a hybrid underwater navigation system. The under water navigation system mainly composed of an inertial measurement unit (IMU) and a Doppler velocity log (DVL). The implementation of DVL can improve the navigational performance of the IMU when an underwater vehicle works near sea bottom. A dynamic error model of a DVL-aided inertial navigation system is designed to implement an indirect feedback Kalman filter, and a measurement model is also designed. This paper demonstrates the enhanced performance of the DVL-aided hybrid navigation by conducting rotating arm test in ocean engineering basin at KRISO. The IMU and the DVL are embedded in a small fish attached at the rotating arm. Additional depth sensor and a magnetic compass are introduced in the measurement model. In addition, this paper also conducts a dead-reckoning navigation using the DVL and the magnetic compass. The dead-reckoning navigation system also shows better performance than the IMU-only navigation system.

A study on the pressure vessel design, structural analysis and pressure test of a 6000 m depth-rated unmanned underwater vehicle

MOERI-KORDI (Maritime and Ocean Engineering Research Institute—Korea Ocean Research and Development Institute) has conducted the development of an unmanned underwater vehicle (UUV) for 6000 m deep-sea exploration, which was completed in 2006. Several pressure vessels were mounted on the UUV frame for loading electric and electronic equipment. The pressure vessels were constructed with titanium alloy Ti–6Al–4V for two main cylindrical canisters and with aluminium alloy Al6061–T6 for several hemispherical housings of electric motor drivers, respectively. This article presents the design process of the pressure vessels and experimental results acquired by high-pressure tests, which were conducted with the cooperation between MOERI-KRISO and Japan Agency for Marine-Earth Science and Technology (JAMSTEC). The pressure vessels were designed on the basis of the buckling analysis as well as structural yielding analysis, and checked the safety by the finite-element analysis (FEA) and analytical (empirical) formula. Moreover, by structural reliability analysis, the cylindrical part and the end plates of the main pressure vessels made of Ti–6Al–4V were designed with a safety of 99.98% under circumstance of 75 MPa. The pressure housings made of Al6061–T6 were also designed by the same procedure. Pressure test was performed with the large high-pressure environment simulation unit of JAMSTEC. The pressure vessels made of the titanium–aluminium alloy were safe even when they were under pressure of 75.46 MPa. Test results show that there are less than 5% difference between the FEA and the high-pressure tests. In this research, the pressure test was conducted up to 75 MPa, which corresponds with a safety factor of 1.25. Even though this is lower than the usual safety factor of 1.5–2.5, this study shows that the pressure vessels are safe if we consider the reliability analysis.

Attitude estimation using depth measurement and AHRS data for underwater vehicle navigation

This paper proposes a method for attitude estimation that utilizes the depth measurement as well as the MEMS-AHRS (Micro-electromechanical systems Attitude Heading Reference System). Estimating attitude in real-time is crucial for navigation of an unmanned underwater vehicle since path planning, trajectory tracking, and collision-avoidance is based on the attitude information. Many of the attitude estimation methods usually use the measurements from IMU(Inertial Measurement Unit) and three axis magnetic field measurements. However, the IMU measurement leads accumulated drift in attitude estimation and the magnetic field measurements are affected by bias and disturbance by electromagnetic field sources around the sensor. The method that makes use of the depth measurement whose accuracy and robustness is superior to the measurements by IMU and magnetic field sensors, can improve the performance of the attitude estimation. The method uses quaternion to explicitly relate the depth to the attitude including the yaw. The method is tested and evaluated using simulated data and the data from test tank and sea trial experiment. The results show explicit improvement especially when the depth changes with time.