Junichiro Tahara

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.

Preliminary research on the thruster assisted crawler system for a deep sea ROV

In order to reduce a tension on a cable, a deep sea ROV is designed to minimize the weight. However, the ROV having a lightweight is apt to wheelie when running by means of a crawler system. In order to run stably in counterpoise the combination of the center of gravity and the center of buoyancy should be in an adequate area called “stable area” which can be obtained corresponding to the weight and the buoyancy by the theory described in previous papers. The stable area becomes small as the weight is light. The center of gravity and the center of buoyancy is designed to be in the stable area. However, one of the important matters is that the ROV runs forward and also backward. It results in changing the discrimination of the stable area. And it sometimes makes the center of the gravity and the center of buoyancy sometimes to be outside of stable area. So, it is advantageous to increase the weight only when running by crawler system and to change the center of gravity meaningly. This paper proposes a method to virtually increase the weight and to change the center of gravity by using thrusters. And we conducted preliminary experiments using a small-size ROV having four thrusters and crawler system in a water tank to confirm the advantageous effect.

Sea Trial Results of ROV “ABISMO” for Deep Sea Inspection and Sampling

JAMSTEC (Japan Agency for Marine-Earth Science and Technology) has been developing the deep sea ROV ABISMO (Automatic Bottom Inspection and Sampling Mobile) having the capability to dive to the deepest sea. The purposes of ABISMO are to inspect on the seabed in the deep sea and to obtain sediment samples from there. ABISMO consists of a launcher and a vehicle which is launched from the launcher and surveys on the seabed to determine the place for sampling. Core sampling system, which is exchangeable with a gravity piston type or a grab type, is equipped in the launcher. The both of the launcher and the vehicle have cameras to observe. One of the features of ABISMO is that the vehicle has crawlers in addition to thrusters in order to advance mobility. ABISMO is operated with the support ship KAIREI and dived by means of its onboard equipment including a primary cable. We conducted sea trials in January and September 2007 at the areas with the water depths up to 1,300m in Sagami Bay as primary function tests. And we conducted the third sea trial at Izu-Ogasawara trench in December 2007 and made the successful results of diving to the depths up to 9707 m and obtaining a sediment sample from the seabed in 9760 m water depth. This paper describes the features and the outline of ABISMO as well as the sea trial results.Copyright

MR-X1 — An AUV equipped with a space distributed CPU system and a satellite telecontrol interface

JAMSTEC has planned development of a long-rang cruising AUV. This vehicle will enable over 20 days autonomous cruising. To achieve this vehicle, we need various basic technology developments. In this article, a space distributed CPU system development for achieving highly redundant system control and a stationary satellite control system for remote control of the vehicle are described. We carried out sea trial to make sure the each system function using a test bed vehicle. It was shown that the satellite communication system is more effective.

Buoy Platform Development for Observation of Tsunami and Crustal Deformation

We constructed a buoy system for real-time observations of tsunamis and crustal deformation in collaboration with the Japan Agency for Marine-Earth Science and Technology, Tohoku University, and the Japan Aerospace Exploration Agency. The most important characteristics of our system are resistance to the strong sea currents in the large-earthquake rupture zone around Japan (e.g., the Kuroshio maximum speed > 5 knots), and the capability to transmit data in real-time. Our system has four units: (1) a buoy station with a GPS/Acoustic station serving as a central base, (2) a wire-end station (WES) 1,000 m below the sea surface that serves as a staging base, (3) a pressure seafloor unit (PSU) comprising a pressure sensor, and (4) six GPS/Acoustic transponders to measure crustal deformation. The pressure data used to detect tsunamis and the vertical component of crustal deformation are sent to the land station via the wire-end and buoy stations at intervals of 1 h in normal mode and 15 s in tsunami mode. The data measured between the buoy and six transponders are also sent to the land station at 1-week intervals. The Iridium satellite is used for data transmission of all data to land station. The dynamic range for pressure observations is + ∕− 8 m with a fine resolution of 2 mm, and the accuracy of the crustal deformation measurements is less than 1 m. We tuned the system for an observation period of 5 months and carried out a sea trial. The length of the observation period influences the total system due to the weight of the battery. We rearranged the geometry of the total system to new one with heavier weight and a lot of batteries on the buoy considering long period observation and decided upon a slack ratio of 1.6. In addition, it is important for a long observation period to minimize electrical consumption. We used double pulses for acoustic data transmission between the PSU and WES. The time difference between two pulses indicates the observed pressure value. For the PSU, we designed a tsunami mode on the basis of data from the tsunami generated by the 2011 earthquake off Tohoku, which were recorded by cabled network system data and offline bottom pressure data. The results confirmed that a tsunami can be detected even if the first tsunami signals include strong-motion signals. In this case, the tsunami was detected 10–20 s after the first seismic arrival. During sea trials, we successfully tested the tsunami mode we designed. We succeeded real-time observation of pressure and crustal deformation using buoy system in strong sea current speed area for 5 months. However, there are some issues to be resolved at this moment. For acoustic data transmission, 1 ms step difference of the detection of acoustic signals at the WES, wrong detection of the multiple phases are issues to be resolved. We will consider assigned mapping of transmitted data to the time difference of the double pulses and take measures on the PSU and WES. In addition, we consider strategy to reduce slack ratio in the future. For data transmission from the WES to the buoy station, we experienced electrical unhealthy of the wire rope due to damages by the fisheries activities and the torsion brought by rotation of the buoy. We consider the countermeasure to reduce the rotation.

Research on Stability of Crawler System for Deep Sea ROV

A deep sea ROV is desired to be light from the viewpoints of reducing a tension on an underwater cable and possessing the adequate movability by thrusters in water. On the other hand, when moving by a crawler system on the seabed, such a lightweight will influence on its movability characteristics. As an initial investigation experiments using an actual ROV were conducted in a water tank. And it was observed that the ROV ran in wheelie in some cases and almost fell down in extreme case in spite of the fact that it could run stably on land. In order to clarify the results fundamental theory of stability of the ROV in steady running is presented. The theory gives the discriminant chart of stable running for the combination of the center of gravity and the center of buoyancy. Experiments using a model were conducted to verify the theory. In order to increase the stable area and also to change meaningly the center of gravity, this paper proposes a method to virtually increase the weight and to change the center of gravity by using thrusters. And preliminary experiments were conducted to confirm its advantageous effect.Copyright

Deployment of an ice buoy at 60 °S in the Southern Ocean

Performing oceanographic measurements from the sea surface to the sea bottom is technically challenging under rough or icy sea conditions. In 2011, we tested measures for protecting a buoy under such severe conditions, by incorporating anti-icing and tolerance to high winds and rough seas. Based on the results, we carried out detailed designs of a suitable buoy system. In January 2012, we succeeded in deploying the buoy in the Southern Ocean off the Adelie Coast at 60°S and 140°E. Some of the meteorological and oceanographic data being gathered by the buoy can now be monitored in real time. In this paper, we describe some details concerning the design of the sensor pole and mooring line, in addition to the data already received from the buoy.

Development of the visible light communication device for swarm using nonlinear synchronization

This paper describes development of a visible light 4 Pulse position modulation (4PPM) data communication device for underwater swarms using a nonlinear synchronizing system. SWARM—a group robot that uses intelligence as a group—do as ants and bees, is expected to be useful for marine resource exploration. Specifically, numerous SWARMs will be grouped to explore marine resources efficiently. An important difficulty is the change in electronic circuit characteristics because of high water pressure in the deep sea. Development of small and simple underwater SWARM communication devices must eliminate this problem without using large pressure-proof containers. As described herein, we considered nonlinear synchronizing systems as effective because they can be synchronized even if system time constants differ. Such systems resemble the glow mechanism used by fireflies. They have individuality, but they flash synchronously when in a group. We developed a visible light communication device using this nonlinear synchronization system based on the firefly concept. Test results confirmed that they are synchronized even if a time constant difference exists between them. Furthermore, we achieved 4PPM data communication using the nonlinear synchronization signal as a communication clock.

Full depth ROV “ABISMO” and its transponder

The Japan Agency for Marine-earth Science and Technology is now developing an automatic bottom inspection and sampling mobile, ABISMO, which is a full depth rating remotely operated vehicle for conducting research at the deepest sea bottom, observing the area with a camera, and sampling the bottom layer.

Conceptual Design and Key Technology Development of a Long-Range Underwater Vehicle Traveling Over Thousands Kilometers

The underwater platform which has enough ability to cruise globally and freely in vast deep sea will allow us to make the survey of entire oceans. We aim to develop an underwater platform which travels and surveys across entire oceans for the research into the global change, ocean-trench earthquake, and biodiversity and so on. We have developed the first prototype underwater platform or the long-range cruising autonomous underwater vehicle (LCAUV) named Urashima since 1998. The vehicle powered by a polymer electrolyte fuel cell system marked the world record of cruising distance of 317 kilometers in 2005. The vehicle has the following specifications: length; 10 m, weight; 10 tons, maximum depth ratings; 3500 m, maximum cruising speed; 3.2 knots, and endurance; 60 hours. This large vehicle has large user payload of a few hundreds kilograms. In 2007, we started research and development of the elemental technologies which will be utilizes for development of the second generation LCAUV to achieve cruising range of over 3000 kilometers. The technologies under research and development are power sources, navigation methods, communication methods, vehicle controllers, materials for body, and advanced sensors for highly resolution survey. The fuel cell and secondary battery hybrid system is had to improve at energy efficiency to generate electricity as possible for long time running with limited energy. A high accuracy inertial navigation system and an underwater positioning system being covered area of over 1000 km are under development. A synthesized aperture sonar is also under development.Copyright