Onboard networks of autonomous underwater vehicles

By Aleksandr Inzartsev and Oleg Lvov

Designing autonomous underwater vehicles (AUVs) is a basic line of activity at the Institute of Marine Technology Problems (IMTP), Far Eastern Branch, Russian Academy of Sciences. Compact vehicles developed at the IMTP are intended mainly for

1. solving economics problems (servicing of sea oil-gas fields, objects of mariculture, fishing and crabbing regions, etc.),
2. collecting oceanographic data from depths to 2 km (investigation of ocean flows, ocean floor composition and structure, as well as bathymetry and seismology problems),
3. monitoring the condition of underwater communications (pipelines and cables) and environmental water pollution, and
4. carrying out search-and-rescue operations (with an underwater object location accuracy of 5 m).

The cost effectiveness of AUVs stems from the fact that, in a number of cases, they may well replace expensive large ships intended for the same purposes or less accurate and less maneuver towed apparatuses.
The control system of AUVs provides the complex and adaptive behavior of the robot. The local-area network (LAN) structures the control system, which consists of the autopilot's computer and computer of the vision system, as well as of different (navigation, measuring, power-supply, search, sonar, engine-controlling, etc.) microcontroller-based onboard facilities. The LAN has a hybrid topology involving the star (Ethernet-TP, USB, or RS-232) and bus (RS-485 or CAN) configurations. Such a topology of the LAN, which results from a combination of serial data-exchange channels, provides a high reliability and survivability of the AUVs.

The SBCs used in the system must have small dimensions and a low energy consumption, meet service conditions (temperature range from -20 to +70°C, humidity to 95%, vibration to 5g, and shock to 20g), be functionally complete, and offer good repairability and reliability (MTBF).
Cool RoadRunner, Cool SpaceRunner, and Cool EcoRunner PC/104-format SBCs, which are produced by Lippert Co. and distributed in Russia, CIS, and Baltic countries by ProSoft Co., meet these requirements most fully. The above approaches used to construct the control system formed the basis for a new version of AUVs (MMT-2000) and modified versions of the currently available ones (such as MT-98).

In a modified MT-98 AUV, the module of the onboard computer of the vision system consists of a Cool SpaceRunner-II (300 MHz) SBC, 2.5" HDD with a heater, a DC/DC converter card, and a power supply supervisor. The module is compact (60 mm long and 150 mm in diameter). It performs real-time processing of digital images, which allows search at a cruising speed. The same SBC incorporated into the autopilot system solves all control tasks, including navigation, and reduces the overall dimensions and energy consumption of the system. In a new MMT-2000 AUV, Cool EcoRunner SBCs are used.

The software of the AUVs is realized in the QNX real-time operational system.
The AUVs mentioned above proved their wide functionality and high reliability during oceanic expeditions and search-and-rescue operations.

Modified MT-98 AUV before submerging to carry out search-and-rescue operations.

Module of the onboard computer (based on Lippert Cool SpaceRunner-II SBCs) mounted on the chassis of the vision system of a modified MT-98 AUV.

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