Fig. 13. ALBAC Glider Schematics (Kawaguchi et al., 1993)
Another glider under development is a hybrid, which is designed to travel under power, glide mode or both. This vehicle, under development at Florida Institute of Technology, Melbourne Florida, is being designed to obtain water samples, make photographic/video images of specimens in the water column and specify the environmental characteristics of the data field. Furthermore, it is expected to possess a wide array of traditional oceanographic instruments that can be used by the vehicle's control system to make mission/navigational changes.
The vehicle's ability to obtain specimen/water samples and photographs directly affects the design of the vehicle more than the addition of oceanographic instruments. Water samples are to be collected using a series of small automatically closing specimen bottles, and two digital cameras are used to document what is floating through the water column. The AUV-Powered Glider was design using the following parameters:
• Mission applications to 6000-meter ocean depths.
• Modular design: to ship easily in small boxes and to have interchangeable scientific modules.
• Quick assembly & disassembly of AUV components.
• Easy battery access for replacement and recharging during missions.
• Reasonable space for scientific & instrument payload.
• Capable of landing
Unlike torpedo-shaped survey AUVs, the structure of the AUV-Powered Glider has a rectangular frame that is approximately 1.5 by 2-meters square. Figure 14 shows an overview of an AUV-Powered Glider prototype with the main components.
The vehicle is designed for easy assembly and disassembly, with easy access to the batteries and the two 17-inch diameter, 3/8-inch-thick vehicle control system and scientific pressure housings. The objective was to use cost-effective solutions to keep the overall budget of the vehicle reasonable. The version shown in figure 14 is for marine biologists, biological oceanographers and other scientists needing samples and photographs of organisms in the water column.
The main vehicle specifications for the AUV are:
• Dry weight: 293 kg (without instruments and drop weight system)
• Glass pressure housing depth: 6000 m
The AUV-Powered Glider is equipped with two 12-Volt longitudinal and two 12-Volt DC-brushless vertical thrusters mounted on the forward two corners of the frame.
• Longitudinal thrusters: asynchronous 3-phased, oil-filled design.
• Optimum running speed of 2-knots.
• Estimated power usage for the two thrusters at 2-knots, 12-Volts and 5-Amps = 50-Watts for each thruster.
• Vertical thrusters: Elcom ST N2312, coil-type 3-phase wye-wound, low speed, low operating voltage and high torque (Kt=5.30), 12-Volt DC-brushless motors from DC-brushless thrusters, are typically run up to 75% thrust and draw a total of 1.0-Amp for very short periods of time (e.g., one minute to raise the vehicle's bow from the ground in cases where the vehicle has landed).
Active Buoyancy Control - is used to make the vehicle's buoyancy either slightly positive or negative allowing the vehicle to glide up and down the water column in a saw-tooth pattern. The speed of the ascent or descent in glide mode depends on the buoyancy and glide angle and whether the vehicle is under power. The vehicle can be under power at any time, but energy consumption is high since the motors use more energy than any individual system on the AUV. A simple drop weight / drop float system is integrated currently for rapid prototype development allowing the vehicle 10 glide cycles. The design and development of a deep water buoyancy system is a primary task for future development of this vehicle.
Active Trim Control - is used to actively to control and stabilize the vehicle's trim. For example, when the buoyancy system has an unbalanced configuration (e.g., too much positive or negative buoyancy on one side) or when something foreign is tangled with the vehicle such as seaweed, the active trim control would attempt to align the vehicle. This control is handled by the rear control rudders and flaps. An automatic trim system using liquid mercury is under investigation that is similar to the trim systems on airplanes. Fluid Intake Channel - at the front of the vehicle focuses water and organisms from in front of the vehicle through the channel. Two camera systems document what passes through the channel: one mounted so the photos are made from the side of the channel; the other mounted facing directly into the channel. An optional mesh can be mounted in front of the camera to collect organisms over a specified distance. The vehicle would reverse direction to wash already documented samples from the screen using the vehicle's thrusters.
0.58 m 379 kg 4000 m
Sample Taking - is made through a limited number of small sample chambers mounted along the external frame allowing the scientist to obtain permanent samples of the water and biological organisms. The sample chamber is opened and closed by servo motors at pre-set times.
Communication - is via a 802.11b Wireless Ethernet (WLAN) card between the AUV and a host PC allowing wireless communications with the AUV while at the surface and via radio through a MaxStream 9Xstream-PKG-R low-speed, half-duplex radio modem, with an extended range at sea: 7 miles (11km). Information concerning the MaxStream can be found at: (MaxStream, Inc., http://www.maxstream. net/).
Navigation and Absolute Positioning - is made with a Spartan Electronics SP3000D digital compass, depth gage and speed vector/altitude generated by a Doppler Velocity Log (DVL) for dead reckoning. Like any integrating process, dead reckoning accumulates errors and requires periodic fixes to cancel resulting drift. This is done by GPS during surface navigation. Collision control is through two UA-2 altimeters from J.W. Fishers Mfg., Inc. The altimeters have the pulse generation and return detection circuitry potted into the transducer and return the information to the computer via a RS232 connection. The UA-2 altimeters provide height over ground and the distance to an object in front of the vehicle up to 100 feet (30 meters) at 200 kHz. An inertial measurement unit (IMU) will measure the vehicle's acceleration and will determine the vehicle's position while underwater. The position will be verified by GPS when the vehicle is on the surface.
Control System and Supervision (See Figure 15) - algorithms manage the entire vehicle with a combination of a traditional feedback system and an under-development neural-network control system is used standard grid pattern surveys and chemical or physical trace mapping.
The Sterne glider, developed at Ecole Nationale Superieure D'Ingenieurs in Brest, France is a hybrid glider having both a glider (buoyancy) and thruster mode. The 4.5 m long, 0.6 m in diameter, 900 kg in mass vehicle has buoyancy control and a thruster for forward propulsion and capable of gliding at 1.3 m/s.
The Sterne is designed to conduct surveys by gliding or by flying level using its thruster, which when powered has the range of an estimated 120 miles with an estimated speed of 3.5 knots (1.8 m/ s). The vehicle has 2.5 knots (1.3 m/s) when gliding. It has two fixed wings two actuated horizontal tail fins and a vertical tail with rudder and moves a battery pack to control pitch (Graver, 2005).
Was this article helpful?
Although we usually tend to think of the digital camera as the best thing since sliced bread, there are both pros and cons with its use. Nothing is available on the market that does not have both a good and a bad side, but the key is to weigh the good against the bad in order to come up with the best of both worlds.