Akihisa Ishikawa

Accuracy Improvement of an Inertial Navigation System Brought about by the Rotational Motion

An autonomous underwater vehicle (AUV) is equipped with an inertial navigation system (INS) in order to understand its own position in real time while it cruises without the communication with the external environment such as a support ship and GPS. Japan Agency for Marine-Earth Science and Technology has the cruising AUV URASHIMA, and it is also equipped with the INS. However the INS outputs its own absolute position containing the error that increases with time. It means, it is very difficult for URASHIMA to cruise dependent only on the position data outputted by the INS for a long time. So we have proposed the method to improve the performance of the INS, and its effect was confirmed in experiments. In the method, it was put on a turntable with assumption that it is fixed inside URASHIAM and the INS has been rotated by it around one rotation axis according to some rules. Consequently, the INSs position error was decreased by the rotational motion. In order to cause this effect, a precondition had to be met. It was that URASHIMA keeps its own posture to near-horizontal while cruising. However URASHIMA usually cruises with the roll motion which is caused by its shape. So the roll motion such as URASHIMAs one in a sea trial was applied to the turntable, and the INS was rotated in the situation. As the result, the INSs position error was decreased about half of the original one.

The Rotation Control System to Improve the Accuracy of an Inertial Navigation System Installed in an Autonomous Underwater Vehicle

An Autonomous Underwater Vehicle (AUV) is equipped with an Inertial Navigation System (INS) in order to detect its own current position for the autonomous cruise. It has a sensor part and an arithmetical part. The sensor part is composed of three gyros and three accelerometers, and the three-dimensional coordinate system (INS coordinate system) is defined in the arithmetical part. And an accelerometer and a gyro are set on each axis in the coordinate system. The INS calculates AUVs position using outputs of the sensors. So the position accuracy of it depends strongly on the precision of the sensors. However they have drift-bias errors which increase with the passage of the time. So, a method, which applies the rotational motion to the INS, is proposed in order to reduce the errors. In this method, the INS is put on the turntable and the INS is rotated by it around an axis of the INS coordinate system. And the errors of sensors, which are set on non-rotation axis, were reduced on average. This causes the position accuracy improvement. As the experimental results, the position error of the INS is reduced up to four times if suitable methods are given to it.

The PEM Fuel Cell System for Autonomous Underwater Vehicles

Various types of autonomous underwater vehicles (AUVs) have been developed and are used for conventional surveys due to their small size. Large AUVs are also being developed that are equipped with high technology computers, high-precision navigation systems, and efficient power sources. One ocean-going AUV powered by a polymer electrode membrane fuel cell system was completed by The Japan Agency for Marine-Earth Science and Technology. Its fuel cell system generates 4kW of electric power for the control electronics and propulsion system. Hydrogen gas is stored under low pressure in the metal hydride. Heat generated by the fuel cell is used to discharge hydrogen gas into the metal hydride. This article proposes one method in which to equip the proton exchange membrane fuel cell with storage devices for fuel and oxidizer, and a heat transfer device using the new generation AUV as its power source. Test results of the fuel cell, storage system and the 317 km Suruga Basin sea test are presented in this article.

Autonomous Underwater Vehicle for surveying deep ocean

There are concerns about the impact that global warming will have on our environment, and which will inevitably result in expanding deserts and rising water levels. AUVs (Autonomous Underwater Vehicle) were considered and chosen, as the most suitable tool for conduction survey concerning these global environmental problems. JAMSTEC has started to build a long range cruising AUV. The plan for its development is in several steps. As the first step an AUV, named URASHIMA was built in 1999, and sea trials have been held since 2000. URASHIMA dived to 3,518m depth in 2001. At the end of February 2005, the vehicle was able to cruise autonomously and continuously for 317km. This paper describes outline of the vehicle, presents some experimental results.

Results of a long distance experiment with the AUV "Urashima"

Japan Agency for Marine-Earth Science and Technology (JAMSTEC) has advanced the development of an ocean going Autonomous Underwater Vehicle (AUV). Technical problem on an AUV is to develop instruments for highly accurate positioning, an efficient power source and digital telemetry in the sea. The AUV in JAMSTEC has accurate positioning system, fuel cell and digital telemetry. Sea test started in 2000, results were fed back to instruments to improve AUV performances. Its energy source was replaced to closed-cycle fuel cell system from lithium-ion battery in 2002. The AUV was successfully cruised 220 km range in 2003 along the pre-programmed route while having submerged. This paper presents result and navigational data obtained in a long distance test with the AUV

Energy Storage for Autonomous Underwater Vehicles

Energy storage is one of the key technology for underwater vehicles. Many kind of batteries have been developed for underwater systems. An ocean-going autonomous underwater vehicle powered by a polymer electrode membrane fuel cell system was completed by Japan Agency for Marine-Earth Science and Technology. The fuel cell system generates 4 kW of electric power for the control electronics and propulsion system. Hydrogen gas is stored under low pressure in the metal hydride. Heat generated by the fuel cell is used to discharge hydrogen gas into the metal hydride. This paper presents the test results of the fuel cell, storage system and 5,600 mol discharge result in the underwater cruise.