17-08-2012, 10:57 AM
An Autonomous Underwater Vehicle
Autonomous Underwater Vehicle.docx (Size: 940.39 KB / Downloads: 138)
INTRODUCTION
An Autonomous Underwater Vehicle (AUV) is a robotic device that is driven through the water by a propulsion system, controlled and piloted by an onboard computer, and maneuverable in three dimensions. This level of control, under most environmental conditions, permits the vehicle to follow precise preprogrammed trajectories wherever and whenever required. Sensors on board the AUV sample the ocean as the AUV moves through it, providing the ability to make both spatial and time series measurements. Sensor data collected by an AUV is automatically geospatially and temporally referenced and normally of superior quality. Multiple vehicle surveys increase productivity, can insure adequate temporal and spatial sampling, and provide a means of investigating the coherence of the ocean in time and space.
Autonomous underwater vehicle fall in to mobile robotics sector and are of brilliant importance to the present world military and commercial requirements. The need to find cutting edge in military research induces the invention of AUVs. This paper gives a glimpse on autonomous underwater vehicles and its applications.
AUTONOMOUS UNDERWATER VEHICLES
AUVs are relatively small, self-propelled, untethered, and unmanned vehicles that can operate wholly underwater beyond the control and communication of any support facility. They are usually pre-programmed to conduct a variety of unattended underwater “missions” and may be launched and recovered from shore or at sea. They exist under a number of model-specific aliases and are sometimes also classed as untethered, unmanned vehicles or unmanned undersea vehicles (both UUV). Typically, they are torpedo-shaped of the order of 2–10 m in length and 0.2–1.3 m in diameter. Most of the internal space is taken up with the propulsion-energy source and command-and-control instrumentation, which naturally need waterproofing in housings that vary in design according to the operational depth. Most AUVs can operate to 200 m or so, with some operating beyond 5000 m. Autosub-2 of the UK (Figure 1) is typical of the design of many AUVs. Long-range gliders (Simonetti, 1998) can also be considered as AUVs, although for the purposes of this review they are excluded because of the high power and payload-space requirements of current acoustic instruments; gliders also have restricted horizontal movements which would make systematic surveying problematic.
AUV TECHNOLOGY
Over the years, the focus of technology development has changed as new ideas surfaced to address technology problems. Some of the problems have been solved, others remain that must be addressed, and other, previously unrecognized problems, have surfaced. It is hard to list those technologies that are needed for AUV systems. Any list that is developed will be incomplete. It could be suggested, however, that the following list represents many of the technologies that have been addressed over the past three decades.
ENERGY SYSTEMS / ENERGY MANAGEMENT
Endurance of AUVs has increased from a fewhours to 10s of hours. Some systems now contemplate missions of days and, a very few, ofyears. This extended endurance, however, is at the expense of sensing capability, as well as verylimited transit speeds. In the majority of early AUV systems, Lead Acid batteries were theworkhorse for energy systems. Some AUV designs included Silver Zinc batteries, but, for themost part, the cost was prohibitive. Some applications, such as the ABE vehicle, utilizedLithium primary batteries. A number of other chemistries were tried for different applications.Recent advances in NiMH batteries have provided new opportunities for AUV and thistechnology is being used in many of the current AUV systems. In 1987 the use of an Aluminum/ Oxygen “semi-cell” was proposed to DARPA for use in an AUV. A number of years later a similar system development was funded and dramatically increased the endurance of the DARPA UUV. Currently the ALTEX [altex] program is underway to utilize similar technology to allow an AUV to transit under the Arctic ice.
NAVIGATION
Early AUV systems relied on dead reckoning for their navigation. Acoustic Transponder navigation systems provided greater accuracy but at a significant logistics cost. Inertial navigation systems were available for more expensive AUVs, but costs were prohibitive for the non-military user. With advances in inertial platform technology, the cost has dropped significantly to a point where it is possible to utilize these systems for lower cost AUVs.
Navigation systems continue to improve in accuracy as well as precision. In the past few years, many AUVs have taken advantage of Global Positioning Systems (GPS). When the vehicle surfaces, it is possible to obtain an accurate position and update onboard inertial systems. Still, there is strong interest in being able to navigate relative to the environment within which the system exists. This environment referenced navigation utilizing bottom features, gravimetric variations or other similar characteristics is an objective to be attained. A successful system will provide a significant increase in AUV capability
SENSOR SYSTEMS AND PROCESSING / 3D IMAGING
An AUV is simply a platform on which to mount sensors and sensing systems. Initial efforts to develop AUV technology was more concerned about the basic technologies required to allow reliable vehicle operation. As that reliability was achieved, sensors were added to the vehicle system to acquire data from the ocean environment. Most of these efforts to date have been to integrate existing sensors and sensor processing to the sometimes unique constraints of the AUV. This paradigm has proven to work reasonably well. Recently it has been recognized that we must develop entirely new sensors based on the constraints imposed by an AUV. This would change the paradigm of sensor integration. It would encourage the development of sensors specifically for AUVs; smarter, lower power, highly reliable, smaller in size, etc.
COMMUNICATIONS
In the underwater environment acoustic communications is probably the most viable communication system available to the system designer. Some development programs have investigated and evaluated other technologies such as laser communication at short range and relatively noise free communications over larger ranges using RF current field density techniques. In the past 10 years there has been significant advances in acoustic communications such that relatively low error rate communications is possible over ranges of kms at bit rate of a few kbps [Comms]. This remains an active area of investigation.
Autonomous Underwater Vehicle.docx (Size: 940.39 KB / Downloads: 138)
INTRODUCTION
An Autonomous Underwater Vehicle (AUV) is a robotic device that is driven through the water by a propulsion system, controlled and piloted by an onboard computer, and maneuverable in three dimensions. This level of control, under most environmental conditions, permits the vehicle to follow precise preprogrammed trajectories wherever and whenever required. Sensors on board the AUV sample the ocean as the AUV moves through it, providing the ability to make both spatial and time series measurements. Sensor data collected by an AUV is automatically geospatially and temporally referenced and normally of superior quality. Multiple vehicle surveys increase productivity, can insure adequate temporal and spatial sampling, and provide a means of investigating the coherence of the ocean in time and space.
Autonomous underwater vehicle fall in to mobile robotics sector and are of brilliant importance to the present world military and commercial requirements. The need to find cutting edge in military research induces the invention of AUVs. This paper gives a glimpse on autonomous underwater vehicles and its applications.
AUTONOMOUS UNDERWATER VEHICLES
AUVs are relatively small, self-propelled, untethered, and unmanned vehicles that can operate wholly underwater beyond the control and communication of any support facility. They are usually pre-programmed to conduct a variety of unattended underwater “missions” and may be launched and recovered from shore or at sea. They exist under a number of model-specific aliases and are sometimes also classed as untethered, unmanned vehicles or unmanned undersea vehicles (both UUV). Typically, they are torpedo-shaped of the order of 2–10 m in length and 0.2–1.3 m in diameter. Most of the internal space is taken up with the propulsion-energy source and command-and-control instrumentation, which naturally need waterproofing in housings that vary in design according to the operational depth. Most AUVs can operate to 200 m or so, with some operating beyond 5000 m. Autosub-2 of the UK (Figure 1) is typical of the design of many AUVs. Long-range gliders (Simonetti, 1998) can also be considered as AUVs, although for the purposes of this review they are excluded because of the high power and payload-space requirements of current acoustic instruments; gliders also have restricted horizontal movements which would make systematic surveying problematic.
AUV TECHNOLOGY
Over the years, the focus of technology development has changed as new ideas surfaced to address technology problems. Some of the problems have been solved, others remain that must be addressed, and other, previously unrecognized problems, have surfaced. It is hard to list those technologies that are needed for AUV systems. Any list that is developed will be incomplete. It could be suggested, however, that the following list represents many of the technologies that have been addressed over the past three decades.
ENERGY SYSTEMS / ENERGY MANAGEMENT
Endurance of AUVs has increased from a fewhours to 10s of hours. Some systems now contemplate missions of days and, a very few, ofyears. This extended endurance, however, is at the expense of sensing capability, as well as verylimited transit speeds. In the majority of early AUV systems, Lead Acid batteries were theworkhorse for energy systems. Some AUV designs included Silver Zinc batteries, but, for themost part, the cost was prohibitive. Some applications, such as the ABE vehicle, utilizedLithium primary batteries. A number of other chemistries were tried for different applications.Recent advances in NiMH batteries have provided new opportunities for AUV and thistechnology is being used in many of the current AUV systems. In 1987 the use of an Aluminum/ Oxygen “semi-cell” was proposed to DARPA for use in an AUV. A number of years later a similar system development was funded and dramatically increased the endurance of the DARPA UUV. Currently the ALTEX [altex] program is underway to utilize similar technology to allow an AUV to transit under the Arctic ice.
NAVIGATION
Early AUV systems relied on dead reckoning for their navigation. Acoustic Transponder navigation systems provided greater accuracy but at a significant logistics cost. Inertial navigation systems were available for more expensive AUVs, but costs were prohibitive for the non-military user. With advances in inertial platform technology, the cost has dropped significantly to a point where it is possible to utilize these systems for lower cost AUVs.
Navigation systems continue to improve in accuracy as well as precision. In the past few years, many AUVs have taken advantage of Global Positioning Systems (GPS). When the vehicle surfaces, it is possible to obtain an accurate position and update onboard inertial systems. Still, there is strong interest in being able to navigate relative to the environment within which the system exists. This environment referenced navigation utilizing bottom features, gravimetric variations or other similar characteristics is an objective to be attained. A successful system will provide a significant increase in AUV capability
SENSOR SYSTEMS AND PROCESSING / 3D IMAGING
An AUV is simply a platform on which to mount sensors and sensing systems. Initial efforts to develop AUV technology was more concerned about the basic technologies required to allow reliable vehicle operation. As that reliability was achieved, sensors were added to the vehicle system to acquire data from the ocean environment. Most of these efforts to date have been to integrate existing sensors and sensor processing to the sometimes unique constraints of the AUV. This paradigm has proven to work reasonably well. Recently it has been recognized that we must develop entirely new sensors based on the constraints imposed by an AUV. This would change the paradigm of sensor integration. It would encourage the development of sensors specifically for AUVs; smarter, lower power, highly reliable, smaller in size, etc.
COMMUNICATIONS
In the underwater environment acoustic communications is probably the most viable communication system available to the system designer. Some development programs have investigated and evaluated other technologies such as laser communication at short range and relatively noise free communications over larger ranges using RF current field density techniques. In the past 10 years there has been significant advances in acoustic communications such that relatively low error rate communications is possible over ranges of kms at bit rate of a few kbps [Comms]. This remains an active area of investigation.