Tamaki Ura

Development of motion control system for AUV using neural nets

A self-organizing neural-net-controller system is developed as an adaptive motion control system for AUVs (autonomous underwater vehicles). The system can generate autonomously an appropriate controller according to some evaluations of motion of the vehicle. To construct the system in practical environment, an organizing process of the controller is proposed, which is initiated by a premature fuzzy controller. This process enables the system to generate the controller with minimum prior knowledge of the effect of control actions. The system was applied to the longitudinal motion control of an AUV and succeeded in self-organization of the controller through free-swimming tank tests.<<ETX>>

An adaptive neural-net controller system for an underwater vehicle

Abstract This paper describes the concept and an example of an adaptive neural-net controller system for an underwater vehicle. The system consists of two parts, a real-world part and an imaginary-world part. The real-world part is a feedback control system for the actual robot. In the imaginary-world part, the model of robot and the controller are adjusted continuously in order to deal with changes of dynamic properties caused by disturbances and so on. The system is designed to be suitable for a computer system with parallel processing ability. In this paper, the adaptability of the controller system is investigated by heading-keeping and path-following experiments in conditions where unpredictable disturbances are applied to the robot.

Neural network system for online controller adaptation and its application to underwater robot

Describes a neural network system which executes identification of robot dynamics and controller adaptation in parallel with robot control. The system consists of two parts: real-world part and imaginary-world part. The real-world part is a feedback control system for the actual robot. In the imaginary-world part, the model of robot and the controller are adjusted continuously in order to deal with the change of dynamic property caused by disturbance and so on. The system is designed to be suitable for a computer system with parallel processing ability. In the paper, adaptability of the controller system is investigated by heading keeping and path following experiments on the condition that unknown disturbances are given to the robot.

Discovery of New Hydrothermal Activity and Chemosynthetic Fauna on the Central Indian Ridge at 18°–20°S

Indian Ocean hydrothermal vents are believed to represent a novel biogeographic province, and are host to many novel genera and families of animals, potentially indigenous to Indian Ocean hydrothermal systems. In particular, since its discovery in 2001, much attention has been paid to a so-called ‘scaly-foot’ gastropod because of its unique iron-sulfide-coated dermal sclerites and the chemosynthetic symbioses in its various tissues. Despite increasing interest in the faunal assemblages at Indian Ocean hydrothermal vents, only two hydrothermal vent fields have been investigated in the Indian Ocean. Here we report two newly discovered hydrothermal vent fields, the Dodo and Solitaire fields, which are located in the Central Indian Ridge (CIR) segments 16 and 15, respectively. Chemosynthetic faunal communities at the Dodo field are emaciated in size and composition. In contrast, at the Solitaire field, we observed faunal communities that potentially contained almost all genera found at CIR hydrothermal environments to date, and even identified previously unreported taxa. Moreover, a new morphotype of ‘scaly-foot’ gastropod has been found at the Solitaire field. The newly discovered ‘scaly-foot’ gastropod has similar morphological and anatomical features to the previously reported type that inhabits the Kairei field, and both types of ‘scaly-foot’ gastropods genetically belong to the same species according to analyses of their COI gene and nuclear SSU rRNA gene sequences. However, the new morphotype completely lacks an iron-sulfide coating on the sclerites, which had been believed to be a novel feature restricted to ‘scaly-foot’ gastropods. Our new findings at the two newly discovered hydrothermal vent sites provide important insights into the biodiversity and biogeography of vent-endemic ecosystems in the Indian Ocean.

Effects of Pressure on the Optical Emissions Observed from Solids Immersed in Water Using a Single Pulse Laser

The effects of pressure on the optical emissions of a laser ablated zinc plate immersed in water have been investigated. Well defined emission spectra were observed from plumes generated directly underwater after excitation using a single laser pulse of duration <10 ns. It was demonstrated that an increase in water pressure from 0.1 to 30 MPa (300 atm) does not have any significant effect on the intensity, broadness, or fluorescence lifetime of the observed spectra. The results suggest that laser-induced breakdown spectroscopy is, in principle, a technique suitable for in situ elemental analysis of deep sea minerals.

ER Fluid Applications to Vibration Control Devices and an Adaptive Neural-Net Controller

This article describes several applications of electro-rheological (ER) fluid to vibra tion control actuators and an adaptive neural-net control system suitable for the controller of ER ac tuators. ER fluid is a kind of colloidal suspension, and has a notable characteristic feature in that its apparent viscosity can be controlled in response to applied electric field strength. Viscosity can be varied in a wide range and the response time is very short, as short as several milliseconds. Accord ing to previous studies, one promising application is a controllable damper. In the present article, four applications are proposed: a shock absorber system for automobiles, a squeeze film damper bearing for rotational machines, a dynamic damper for multi-degree-of-freedom structures and a vibration isolator. Furthermore, an adaptive neural-net control system, composed of a forward model network for structural identification and a controller network, was introduced for the control system of these ER actuators. As an example study of intelligent vibration control systems, an experi ment was conducted in which the ER dynamic damper was attached to a beam structure and con trolled by the present neural-net controller so that the vibration in several modes of the beam was reduced with a single dynamic damper.

Positioning method for an AUV using a profiling sonar and passive acoustic landmarks for close-range observation of seafloors

Real-time accurate positioning is a key technology for autonomous underwater vehicles to perform close-range seafloor observations such as photo mosaicing. This paper proposes a real-time positioning method that realizes robust and drift-free positioning in a local area based on a passive acoustic landmarks set in the environment and a profiling sonar (profiler) mounted on the vehicle. The method stochastically updates the vehicles position based on all the sensory data available. Although the position of landmarks is generally unknown, this paper assumes the position is known without error for simplification. As an observation model of the profiler we propose a radial-angular representation with a non-Gaussian distribution based on experimental data. The performance of the proposed method is verified through tank experiments using the AUV Tri-Dog 1. The effects of the number of landmarks and observation model on the positioning accuracy is discussed. Through comparison with ground truth and off-line estimations based on actual data obtained during the experiments, the positioning accuracy of the proposed method remains within 5 centimeters at all times during the 2 hour duration of the experiment with a traveled distance of 600 meters, with two landmarks at a distance of 10 meters.

Terrain based localization for pinpoint observation of deep seafloors

Real-time accurate localization is essential for in many underwater vehicle applications. In particular, close-range seafloor observation requires precise positioning in relation to bottom structures or to coordinates on a map. This paper proposes a real-time terrain based localization method that realizes robust positioning that does not require any artificial landmarks. The method stochastically determines vehicles position relative to the map using the Particle Filter method, based on an inertial navigation system (INS) and a profiling sonar mounted on the vehicle. The reference bathymetric map is constructed a prior, either by the vehicle itself, or by other platforms. The proposed method is implemented on the hovering type AUV TUNA-SAND and sea trials were carried out. We succeeded in the real-time localization and verified the performance of the proposed method.

Approaching whales by autonomous Underwater vehicle

There are few studies on the ecology of whales in underwater except for small whales (Baird, R., 1996, Otani, S., 1998). It is hoped that through the use of Autonomous Underwater Vehicles (AUVs) new knowledge about whales can be gained. The whale makes sounds, and especially the humpback whale (Megaptera novaeangliae) makes a specific sound called a song. We started our project to develop the technology for AUVs to follow and observe humpback whales by analyzing their songs and locating them underwater. A small size passive SONAR was designed, fabricated, and fitted on the AUV AQUA EXPLORER 2000. An observation experiment was conducted in March 2001 off the Kerama Islands, Okinawa. Prior to our studies, there were no examples of AUV observations on whales anywhere in the world. This experimental observation was conducted as a joint project of the Underwater Technology Research Center at the Institute of Industrial Science in the University of Tokyo, KDDI Co. Research Institute, and the Okinawa EXPO Aquarium. The AUV succeeded in detecting a humpback whale underwater and approaching it within 50m in this experiment.

Navigation Method for Underwater Vehicles Based on Mutual Acoustical Positioning With a Single Seafloor Station

In this paper, we propose a novel navigation method for underwater vehicles based on a single seafloor station (SS), with which the vehicles can estimate their positions and orientations with respect to the SS without the need of expensive inertial navigation system or time-consuming calibration. This method is suitable for near-seafloor applications requiring real-time and accurate positioning, such as seafloor imaging and sampling. The method is also suitable for autonomous underwater vehicles (AUVs) since no other external aid is necessary other than SS. The key idea is to utilize mutual acoustical measurements between the vehicle and the SS. Simply explained: 1) the vehicle starts by interrogating the SS acoustically and measures the range between the two units as well as the bearing of the SS with respect to the vehicle in the vehicle reference frame; and then, 2) the SS computes the bearing of the vehicle with respect to the SS and transmits this information back to the vehicle using a similar acoustical device. By combining this information and inputting it into a nonlinear filter structure that includes measurements of the vehicles ground velocity and yaw angular velocity, the vehicle computes its position and heading estimates. A pair of acoustical devices named acoustical localization and communication (ALOC) devices that can communicate and calculate their relative positions have been built. Sea trials were carried out in October 2011 using the AUV Tri-Dog1 (TD) and a trial SS at Kagoshima Bay in Japan. The AUV successfully navigated around the SS based on the measurements of the ALOC device mounted on both the AUV and the SS. The performance of the method was verified through simulations based on the experimental results.