1,721,055 research outputs found
A Preliminary Test on Agent based Docking System for Autonomous Underwater Vehicles
No full textThis paper addresses an automation method of underwater tasks using AUV (Autonomous Underwater Vehicles). An AUV has a small agent vehicle to connect to an underwater docking station which is connected with operators. If the agent docks, the operator can fully monitor and control the AUV as an ROV (Remotely Operated Vehicles). Under human supervision, it can carry out complicated tasks such as underwater manipulations. If the agent undocks and is recovered, the AUV navigates as an untethered vehicle. In order to evaluate the proposed docking system, an experimental agent and a docking device were developed. For efficient and reliable docking, a visual landmark and a smart cable-based docking method were developed. A preliminary docking test was carried out at an indoor tank to evaluate the proposed docking system.X112sciescopu
Real-time sonar image enhancement for AUV-based acoustic vision
No full textSonar imaging is considered the only feasible sensing solution for underwater investigations by autonomous underwater vehicles (AUVs) in zero-visibility water conditions. State-of-the-art forward-looking imaging sonars can acquire high resolution images at high frame rates, making the acquired images nearly similar to video images acquired using optical cameras. However, the sonar images are corrupted with speckle noise. In this paper, a speckle noise reduction algorithm is proposed for AUV operation. Unlike the conventional algorithms, the proposed algorithm is adequate for real-time treatment. In order to evaluate the performance of the proposed algorithm, an experiment was conducted by using a forward-looking imaging sonar. Based on the experimental results, it was confirmed that the proposed algorithm can effectively reduce the noise. (C) 2015 Elsevier Ltd. All rights reserved.1166sciescopu
Robust Sonar-Based Underwater Object Recognition Against Angle-of-View Variation
No full textUnderwater object recognition based on deployed mobile nodes (underwater vehicles) is difficult, because the shape of an object in a sonar image is significantly changed depending on the direction from which the object is approached. The approaching directions of deployed mobile nodes cannot be predicted in advance. To solve the problem, the conventional underwater recognition algorithms use realistic template images generated by sonar image simulators, and compare the template images to the actual sonar image. However, the realistic sonar image simulation is computationally complex, and the comparison requires some preprocessing methods, such as image segmentation. To solve the problem, this paper proposes a sonar image simulator-based underwater object recognition algorithm. The proposed algorithms that is motivated by the generation mechanism of a sonar image can directly compare the actual sonar image and the simulation image generated by a simple sonar image simulator.113Nsciescopu
Armless underwater manipulation using a small deployable agent vehicle connected by a smart cable
No full textConventional underwater manipulation is performed by a remotely operated vehicle (ROV) equipped with a rigidly connected multi-link arm. However, accurate manipulation requires the ROV to have excellent maneuverability, which limits the design flexibility and capabilities of the vehicle. This paper instead proposes the use of a small, deployable, and highly maneuverable agent ROV as an end effector, which is connected to the main vehicle by a flexible smart cable. This cable tracks the relative position of the agent, thus eliminating the need for additional positioning sensors and allowing significant size reduction for the agent. In addition, to compensate for the limited lifting capability of the small agent, it is equipped with active buoyancy control. The proposed system can be applied to common autonomous underwater vehicles (AUVs) with minimal modification for coarse station-keeping. The whole system is operated as a conventional AUV under normal operating conditions, but the agent is deployed when manipulation or precise monitoring is necessary. Numerical simulations were performed for dynamic analysis and prototype design of the agent vehicle, and this design was implemented as a model-scale system for experiments in a test tank. This implementation confirmed the feasibility and potential capabilities of the proposed manipulation system concept. (C) 2013 Elsevier Ltd. All rights reserved.X111617sciescopu
Modeling of High-Resolution 3D Sonar for Image Recognition
No full textAutomated underwater 3D sonar image recognition has great potential to simplify many underwater tasks. Sonar modeling is necessary to recognize 3D object images. We propose a 3D sonar model that can predict what an object is based on by recognizing similarities to objects that pre-exist in a database. The sonar's displaying mechanism and characteristics of the 3D sonar image are studied. Due to the nature of acoustics, a sonar image is not necessarily always an accurate depiction of an object. The proposed model enables mapping of a 3D world onto a 2D sonar screen. This modeling framework enables the implementation of various optical vision techniques for recognition. Recognition experiments were conducted to evaluate the model's accuracy.X116sciescopu
Integral sliding mode controller for precise manoeuvring of autonomous underwater vehicle in the presence of unknown environmental disturbances
No full textWe propose an integral sliding mode controller (ISMC) to stabilse an autonomous underwater vehicle (AUV) which is subject to modelling errors and often suffers from unknown environmental disturbances. The ISMC is effective in compensating for the uncertainties in the hydrodynamic and hydrostatic parameters of the vehicle and rejecting the unpredictable disturbance effects due to ocean waves, tides and currents. The ISMC is comprised of an equivalent controller and a switching controller to suppress the parameter uncertainties and external disturbances, and its closed-loop system is exponentially stable. Numerical simulations were performed to validate the proposed control approach, and experimental tests using Cyclops AUV were carried out to demonstrate its practical feasibility.11139sciescopu
Real-Time 2D Height Mapping Method for an Unmanned Vehicle using a Stereo Camera and Laser Sensor Fusion
No full textThis paper proposes a method for mapping the height information on an area around a vehicle and of identifying a drivable area by fusing a stereo camera and a laser sensor. A SUM (Self Organizing Map) clustering algorithm obtained from the depth information of the stereo camera is used to analyze the front part area of a vehicle in forms of several candidate planes. In addition, an IMU indicating the current pose of a vehicle is applied to detect a drivable plane. A laser sensor installed on a vehicle's roof scans the front part with a single line and informs a distance value. A drivable plane detected is utilized to calculate height value in the normal direction detected by the laser scan data. Additionally, when the height already mapped has a value higher than that of the threshold, it is regarded as an obstacle and the vehicle is prevented from coming into contact with it. Regarding the vehicle position estimation, a Kalman filter method is used for real-time mapping during driving. The moving location of the vehicle is dead reckoned based on steering angle and velocity, and this value is compensated using the position value received from the GPS. The vehicle's position and mapping coordinates are converted into latitude and longitude values. This study demonstrates that it is possible to generate a precise 2D height map by conducting a test in a real road environment with various slope angles and obstacles.X1122sciescopuskc
Development of hovering type AUV "Cyclops" and its performance evaluation using image mosaicing
No full textIn this paper, a hovering-type autonomous underwater vehicle called Cyclops is introduced. Because of the symmetric body structure and thruster configuration of Cyclops, it is specially designed to utilize a lawnmower trajectory without changing its heading direction. This movement is effective at reducing the dead reckoning error and obtaining source images with homogeneous optical characteristics for underwater image mosaicing. (C) 2015 Elsevier Ltd. All rights reserved.1116sciescopu
Second-order sliding-mode controller for autonomous underwater vehicle in the presence of unknown disturbances
No full textWe propose the use of a second-order sliding-mode controller (2-SMC) to stabilize an autonomous underwater vehicle (AUV) which is subject to modeling errors and often suffers from unknown environmental disturbances. The 2-SMC is effective in compensating for the uncertainties in the hydrodynamic and hydrostatic parameters of the vehicle and rejecting the unpredictable disturbance effects due to ocean waves, tides, and currents. The 2-SMC is comprised of an equivalent controller and a switching controller to suppress the parameter uncertainties and external disturbances, and its closed-loop system is exponentially stable in the presence of parameter uncertainties and unknown disturbances. We performed numerical simulations to validate the proposed control approach, and experimental tests using Cyclops AUV were conducted to demonstrate its practical feasibility. The proposed controller increased the accuracy of trajectory tracking for an AUV in the presence of uncertain hydrodynamics and unknown disturbances.X114541sciescopu
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