Sea Technology

JUL 2013

The industry's recognized authority for design, engineering and application of equipment and services in the global ocean community

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Autonomous AUV Navigation In a Partially Known Environment P-SURO Detects Obstacles, Moves Autonomously in KIRO Water Tank By Ji-Hong Li I n April 2009, the Korea Institute of Robot & Convergence ters height. Two pressure hulls, each for a battery system (KIRO), formerly Pohang Institute of Intelligent Robotics, and electronics system, are designed for maintenance and (PIRO), launched a project to develop a test-bed AUV called reliability. To increase its hydrodynamic mobility, the open P-SURO (PIRO-Smart Underwater Robot) to demonstrate frame of the vehicle is wrapped by two pieces of fber-reinvarious AUV technologies, such as vision-based underwater forced plastic shell. localization, obstacle avoidance and underwater simultaneThere are only two horizontal thrusters to steer the vehious localization and mapping (SLAM). cle at 3 degrees of freedom (DOF) horizontal motion. From a Four SeaBotix Inc. (San Diego, California) SBT150 thrustcontrol point of view, this is a typical underactuated system. ers, two vertical and two horizontal, are mounted on the How to design a stable tracking scheme for this system has vehicle. Throughout its underwater mission, the vehicle is been one of most interesting research topics in the nonlinear always forced to keep zero pitch angles. With this kind of control community of the past decades. thrust confguration, the vehicle's horizontal and heavy moAn InnaLabs (Dublin, Ireland) AHRS (attitude and headtions can be easily decoupled. ing reference system) is mounted on the vehicle. This is a There are three communication channels connecting the microelectromechanical systems device, with three axes vehicle and the surface unit. Ethernet cable is used in the magnetometers installed to measure the geomagnetic feld early stage of development and to upload and download vector to correct the drift of calculated heading. However, fles. On the surface, radio frequency is used to exchange KIRO's water tank is surrounded by a steel structure, and information, while LinkQuest Inc.'s (San Diego, California) there is a considerable magnetic-feld distortion in the tank UWM2000H acoustic modem is used underwater. Tritech environment. Consequently, AHRS could not output proper International Ltd. (Aberdeen, Scotland) Super SeaSpy camattitude value. era is mounted in front of the vehicle and used for visionHowever, there is a one-axis InnaLabs CVG-25 gyrobased localization. A total of three Tritech Micron Echoscope, with random walk less than 0.05°/√h, mounted on sounders are used for environment recognition, including the vehicle's horizontal plane. By integrating this gyro output obstacle detection. Since August 2010, various water-tank tests have been carThe P-SURO AUV and its open frame. ried out to demonstrate the developed AUV technologies. Vehicle Overview P-SURO's experimental tests are carried out mostly in a 12-by-8-by-7-meter concrete cuboid water tank at KIRO. The underwater acoustic link is vulnerable in the tank, so the vehicle must possess a relatively high level of autonomy. P-SURO was designed to be compact at 1.1 meters length, 0.5 meters width and 0.3 July 2013 / st 39

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