Pan-Mook 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.

Control of underwater manipulators mounted on an ROV using base force information

This paper presents a control scheme for obtaining high manoeuvrability of underwater robot manipulators mounted on a remotely operated vehicle (ROV). The motions of an underwater manipulator can affect the attitude and position of the ROV which should remain stationary in seabed operation. To compensate for the dynamic effect of the underwater manipulator on the ROV, the force-torque (F/T) information between the manipulator and the vehicle is used to regulate the states of the ROV. When an F/T sensor is practically unavailable, a disturbance observer can fill the role of the F/T sensor. This paper proposes a disturbance observer for estimating the interaction forces between the ROV and the manipulator. A two-link manipulator mounted on an ROV is considered and numerical simulations are performed to demonstrate the improvement on the manoeuvrability of the proposed controller.

Design of a teleoperation controller for an underwater manipulator

A robust teleoperation controller design method for an underwater manipulator is proposed considering the master and the underwater slave separately. To achieve transparency and stability for a teleoperation of an underwater manipulator in unknown environments with time-varying uncertainties such as added mass, buoyancy, hydraulic drag and friction effect, an adaptive sliding mode control scheme is proposed for robust position tracking control of slave manipulator. To guarantee a force transparency in the master side, disturbance observer is used as a local controller for compensating a friction and coupled nonlinear dynamic effects of the master manipulator. Numerical simulations are performed to demonstrate the transparency and robustness of the proposed controller.

An integrated navigation system for autonomous underwater vehicles with two range sonars, inertial sensors and Doppler velocity log

This work presents an integrated navigation system for autonomous underwater vehicles with inertial and acoustic sensors. The integrated navigation system is based on a strap-down inertial measurement unit (IMU), where auxiliary navigation sensors are two range sonars, a Doppler velocity log (DVL), a magnetic compass and a depth sensor. The main idea of the paper is to improve the performance of the IMU-DVL navigation system by introducing additional range information. The range sonars can measure the distance and the incident angle from a reference transponder on an underwater station. The range sonars are modeled to improve the navigation algorithm, which could provide valuable information for the IMU-DVL navigation to reduce estimation error, especially when the DVL cannot detect the bottom reflection. Simulation was conducted with the 6-d.o.f. nonlinear numerical model of an AUV in lawn-mowing survey mode at tidal flow, where the bottom reflected DVL information is unavailable. Simulations illustrate the effectiveness of the integrated navigation system assisted by the additional range measurements.

Visual servoing for underwater docking of an autonomous underwater vehicle with one camera

Docking systems are required to increase the capability of autonomous underwater vehicles (AUVs) to recharge the batteries and to transmit data in real time in underwater. This paper presents a docking system for an AUV to dock into an underwater station with one camera installed at the nose center of the AUV. To make a visual servo controller, this paper presents an optimal control algorithm based on a state equation composed of the AUV dynamics and the optical flow equation. The control inputs of the AUV are generated with the projected target position on the CCD plane of the camera and with the AUVs motion. This paper introduces a test bed AUV for underwater docking developed in Korea Research Institute of Ships and Ocean Engineering (KRISO), KORDI of Korea. The AUV is propelled with one thruster and controlled with two horizontal planes and two vertical planes. Experiments will be performed in Ocean Engineering Basin of KRISO to demonstrate the effectiveness of the modeling and control law of the visual servoing AUV. The AUV identifies target position with processing the captured image of the lights mounted around the entrance of the dock. This paper also presents a strategy to identifier the target with lights arrays.

Multivariable optimal control of an autonomous underwater vehicle for steering and diving control in variable speed

This paper describes a multivariable optimal control for a Semi-Autonomous Underwater Vehicle (SAUV) developed in Korea Ocean Research and Development Institute (KORDI). The SAUV is a test-bed for evaluation of navigation algorithms and manipulator technologies for a mine disposal vehicle (MDV) in military use and for a light working underwater vehicle in scientific application. The vehicle was designed to control its cruising speed, heading and depth with 4 horizontal thrusters installed at the rear of the hull. The decoupled control methods are limited to be applied to the SAUV because the thrust forces are highly coupled with the surging, yawing, and pitching motion of the vehicle. The multivariable Linear Quadratic (LQ) control method is chosen to control steering and diving in variable speed motion automatically. This paper presents the results of tank-test with the controller and compares them with the simulation results to validate the performance.

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.

Path tracking control for underactuated AUVs based on resolved motion acceleration control

In contrast with man-operating underwater vehicles, autonomous underwater vehicles (AUVs) should find a proper trajectory, control to follow the trajectory, avoid static or moving obstacles, and home safely to their mother ship or launching device by themselves. As a consequence, lots of newly introduced problems have to be solved compared to man-operating underwater vehicle case. In these works we focus on path following control problems. Most AUVs are usually designed to be under-actuated or non-holonomic constrained system. In this paper, we propose a method of resolved motion and acceleration control (RMAC) to solve the path following control problems of an underactuated AUV. Simulations were done to verify the effectiveness of the proposed control method for underactuated AUV and results are discussed.

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.

Self-tuning control of autonomous underwater vehicles based on discrete variable structure system

This paper presents a discrete-time quasi-sliding mode controller and a self-tuning controller of autonomous underwater vehicles with parameter uncertainties and long sampling interval, which are based on the variable structure system. The proposed control systems are designed to track the desired path and each component of the switching gain can be determined separately one another. The discrete quasi-sliding mode controller is robust to the uncertainties, and reaching condition of the control system is satisfied for any initial condition. The self-tuning controller based on discrete VSS prevents the fluctuation of the estimated parameters which can occur during the parameter adaptation. These controllers with the reduced switching region are actually applicable to the tracking control of an AUV having discrete measurements and parameter uncertainties in deep sea environments. Simulation results for motion control of an autonomous underwater vehicle which acquires position informations with a discrete interval show the effectiveness of the proposed technique.