The future of autonomous underwater vehicle control

摘要

It is said generally that the history of autonomous underwater vehicles (AUVs) started with SPURV which was developed by APL of the University of Washington at the request of US Navy in 1957. This was an untethered underwater vehicle with a total length of 3.1 m and a displacement of 430 kg driven by a mono-axis motor and a silver-zinc battery. It was able to run with a maximum depth of 3600 m, a speed of 2–2.5 kt and a maximum cruising endurance of 5.5 h. For control, 12 bit preset command was used to change the steps of azimuth and depth, and hardwired logic circuit was used in the controller. The azimuth was controlled by the offset from the initial azimuth at launch. The roll is secured by the static stability of the body. The temperature and conductivity sensors were installed on the nose section, and the data was recorded on a tape recorder. This vehicle was used for wide-area ocean observation by US Navy.1 A modern AUV, for example, the REMUS 600 developed by Woods Hole Oceanographic Institution having the same size scale as SPURV, has an inertial navigation system of ring laser gyro fully integrated with a Doppler velocity log (DVL) and acoustic positioning system. Autopilot software enables independent control of fins providing yaw, pitch and roll control, altitude, depth, and track-line following. Furthermore, it can be equipped with optional forward fins available to maintain a straight heading in a cross current. This alignment and stability is essential for optimizing the performance of a synthetic aperture sonar. Various kind of sensors like synthetic aperture sonar (SAS), side scan sonar (SSS), and multibeam echo sounder (MBES) can be equipped as the payload sensor. This can run for up to 24 h with lithium-ion rechargeable batteries and it is also possible to avoid obstacles by using a front sonar.2 In a half century, due to the progress of digital technologies, sensor technology, and battery technologies, AUVs have made significant progress and they have been used widely for oceanography, industries, and defense. One of the most representative examples of AUV's strengths in wide-area subsea search was for Air France Flight 447 which crashed off the coast of Brazil in 2009. Multiple REMUS 6000, which is equipped with SSS and cameras, were used in this search activity, and after about 2 months of operation, they finally discovered the wreckage of an aircraft lying about 4000 m deep seabed and contributed to the recovery of the flight and voice recorders.3 From the perspective of industry, the AUV industry has moved from prototype development for research and development to mass production of systems now. However, the number of AUV manufactures is still limited, for example, “Husin” of Kongsberg in Norway,4 “Remus series” of Hydroid in United States (now a subsidiary of Huntington Ingalls Industries), and “Bluefin series” of Bluefin Robotics in United States (a subsidiary of General Dynamics Mission Systems).5 Mitsubishi Heavy Industries, Ltd. (MHI) had developed R&D AUV such as Urashima6 for JAMSTEC, and currently is manufacturing OZZ -5 AUV production model for the Ministry of Defense in Japan.7 This article mainly describes the expected future operation of AUVs to motivate AUV research and development in the academic world. This section describes the typical operation of an AUV, which is a prerequisite for a concrete view of the control system. As its name implies, AUV is an autonomous underwater vehicle that does not have a tether cable for power supply and communication. After it is launched from the surface vessel, it basically navigates autonomously according to a predetermined route plan because its underwater communication capacity is very limited. The first AUV, SPURV, traveled through the “empty” ocean to measure sea water temperature and conductivity. Therefore, it did not have sensors to detect the surrounding terrain. On the other hand, the main mission of the modern AUV is to survey the seafloor str