U.S. patent application number 13/890939 was filed with the patent office on 2013-09-19 for underwater vehicle bouyancy system.
This patent application is currently assigned to iRobot Corporation. The applicant listed for this patent is IROBOT CORPORATION. Invention is credited to Jason Isaac Gobat, Edison Thurman Hudson, Robert Eugene Hughes, Timothy James Osse, Frederick Roland Stahr.
Application Number | 20130239870 13/890939 |
Document ID | / |
Family ID | 49156487 |
Filed Date | 2013-09-19 |
United States Patent
Application |
20130239870 |
Kind Code |
A1 |
Hudson; Edison Thurman ; et
al. |
September 19, 2013 |
Underwater Vehicle Bouyancy System
Abstract
A multiple stage buoyancy changing system, or variable buoyancy
device, for an underwater vehicle. The multiple stage buoyancy
changing system comprises: a pressure hull containing a
flexibly-sized internal fluid reservoir; a flexibly-sized external
fluid reservoir attached to the pressure hull and connected to the
internal reservoir; a system of devices and channels configured to
move fluid between the internal fluid reservoir and the external
fluid reservoir to change a displaced volume of the vehicle. Each
stage of the variable buoyancy device can be optimized for maximum
energy efficiency while changing the vehicle's displaced volume
within an ambient pressure range. A control system for the variable
buoyancy device engages different stages depending on ambient
external pressure such that maximum energy efficiency is achieved
over a large range of pressures/depths.
Inventors: |
Hudson; Edison Thurman;
(Chapel Hill, NC) ; Hughes; Robert Eugene; (Chapel
Hill, NC) ; Stahr; Frederick Roland; (Seattle,
WA) ; Gobat; Jason Isaac; (Burien, WA) ; Osse;
Timothy James; (Sarzana, IT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
IROBOT CORPORATION |
Bedford |
MA |
US |
|
|
Assignee: |
iRobot Corporation
Bedford
MA
|
Family ID: |
49156487 |
Appl. No.: |
13/890939 |
Filed: |
May 9, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13038373 |
Mar 1, 2011 |
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13890939 |
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12890584 |
Sep 24, 2010 |
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13038373 |
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61309420 |
Mar 1, 2010 |
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Current U.S.
Class: |
114/333 |
Current CPC
Class: |
B63G 8/24 20130101; B63G
2008/004 20130101; B63G 8/08 20130101; B63G 8/001 20130101; B63G
8/18 20130101; B63G 8/22 20130101; B63G 2008/002 20130101 |
Class at
Publication: |
114/333 |
International
Class: |
B63G 8/22 20060101
B63G008/22 |
Claims
1. A multi-stage buoyancy changing system for an autonomous
underwater vehicle, the system comprising: an internal reservoir
configured to hold a fluid; an external bladder connected to the
internal reservoir via one or more channels and configured to
exchange fluid with the internal reservoir via the one or more
channels; a first device configured to move fluid through a first
channel from the internal reservoir to the external bladder at an
optimized efficiency for an ambient pressure of a first segment of
a dive profile to increase an apparent displacement and a buoyancy
of the autonomous underwater vehicle; a second device configured to
move fluid through a second channel from the internal reservoir to
the external bladder at an optimized efficiency for an ambient
pressure of a second segment of the dive profile to increase an
apparent displacement and a buoyancy of the autonomous underwater
vehicle, wherein the first channel and the second channel are
arranged in parallel rather than in series; and a third channel
configured to allow fluid to move from the external bladder to the
internal reservoir, the third channel including a solenoid valve
that can be selectively opened to allow water to pass from the
external bladder to the internal reservoir, wherein the first
segment of the dive profile includes a different ambient pressure
range than the second segment of the dive profile, and wherein a
check valve is located in each of the first channel and the second
channel and is configured to prevent fluid from moving from the
external reservoir to the internal reservoir through either of the
first channel and the second channel.
2. The system of claim 1, further comprising a mass distribution
mechanism configured to shift a center of gravity of the autonomous
underwater vehicle to allow a portion of the autonomous underwater
vehicle to surface when a buoyancy of the underwater vehicle is
positive.
3. The system of claim 2, wherein the autonomous underwater vehicle
remains surfaced by maintaining positive buoyancy and a shifted
center of mass, so that a tail end of the autonomous underwater
vehicle is held above a surface of the water while information is
transmitted and received.
4. The system of claim 2, wherein the autonomous underwater vehicle
is configured to shift its center of mass to travel horizontally in
a neutrally buoyant state.
5. The system of claim 1, wherein the autonomous underwater vehicle
comprises an expandable internal reservoir that is capable of
withstanding ambient pressures of surrounding water up to a
predetermined depth.
6. The system of claim 5, wherein the autonomous underwater vehicle
displaces a volume of water and is configured to expand or contract
the internal reservoir to increase or decrease, respectfully, the
displaced volume of water to control a buoyancy and a center of
gravity of the autonomous underwater vehicle.
7. The system of claim 1, wherein the autonomous underwater vehicle
comprises a nose and a tail, the tail comprising a portion
configured to rise above a surface of the water that includes one
or more of an antenna for radio communication and a GPS locator
configured to communicate data that the autonomous underwater
vehicle has collected while submerged and obtain a geographical
location of the autonomous underwater vehicle.
8. The system of claim 1, further comprising one or more sensors
that collect data while the underwater vehicle is submerged.
9. The system of claim 1, wherein the autonomous underwater vehicle
has a front and a rear, and is configured to shift its center of
buoyancy and center of mass toward the front or the rear while
decreasing and increasing its buoyancy, respectfully.
10. A method for employing a multi-stage buoyancy changing system
for an autonomous underwater vehicle having an internal reservoir
connected to an external bladder via one or more channels, the
method comprising: in a first segment of a dive profile, increasing
an apparent displacement and buoyancy of the autonomous underwater
vehicle by moving water from the internal reservoir to the external
bladder using a first device configured to move fluid through a
channel from the internal reservoir to the external bladder at an
optimized efficiency for an ambient pressure of the first segment
of the dive profile; and in a second segment of the dive profile,
increasing an apparent displacement and buoyancy of the autonomous
underwater vehicle by moving water from the internal reservoir to
the external bladder using a second device configured to move fluid
through a channel from the internal reservoir to the external
bladder at an optimized efficiency for an ambient pressure of the
second segment of the dive profile, wherein the first segment of
the dive profile includes a different ambient pressure range than
the second segment of the dive profile, wherein the first device
moves fluid from the internal reservoir to the external bladder
through a first channel and the second device moves fluid from the
internal reservoir to the external bladder through a second channel
that is different than the first channel and is arranged in
parallel with the first channel, and wherein a check valve is
located in each of the first channel and the second channel and is
configured to ensure that fluid does not move from the external
reservoir to the internal reservoir through the first channel and
the second channel.
11. The method of claim 10, further comprising shifting a center of
mass of the autonomous underwater vehicle so that a nose portion of
the underwater vehicle is raised before increasing the apparent
displacement and a buoyancy of the autonomous underwater
vehicle.
12. A multi-stage buoyancy changing system for an
autonomous'underwater vehicle, the system comprising: an internal
reservoir configured to hold a fluid; an external bladder connected
to the internal reservoir via one or more channels and configured
to exchange fluid with the internal reservoir via the one or more
channels; a pump motor in combination with a continuous variable
transmission that can adapt to a torque-speed curve to obtain an
optimal pressure/pumping rate needed for a current ambient pressure
of the autonomous underwater vehicle, the pump motor and continuous
variable transmission being configured to move fluid through a
first channel from the internal reservoir to the external bladder
at an optimized efficiency for an ambient pressure of more than one
segment of a dive profile to increase an apparent displacement and
a buoyancy of the autonomous underwater vehicle; and a third
channel configured to allow fluid to move from the external
reservoir to the internal reservoir, the third channel comprising a
solenoid valve that can be selectively opened to allow water to
pass from the external bladder to the internal reservoir.
Description
RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 13/038,373, filed Mar. 1, 2011, which claims
the benefit of and priority from U.S. Provisional Patent
Application Ser. No. 61/309,420, filed Mar. 1, 2010, and which is a
continuation-in-part of U.S. patent application Ser. No.
12/890,584, filed Sep. 24, 2010, the disclosures of which are
incorporated herein by reference in their entireties.
FIELD
[0002] The present teachings relate to a multiple stage buoyancy
changing system for underwater vehicles.
BACKGROUND
[0003] Autonomous underwater vehicles that are propelled by changes
in buoyancy have become commercial in recent years and demonstrated
the ability to operate at sea for long periods. Such vehicles,
known in the trade as underwater gliders, are in an early stage of
deployment for oceanic research, coastline monitoring, and other
applications. While such vehicles have shown viability for many
desirable applications/missions, the existing designs are
specialized to performing in limited ranges of depths that are
optimized to the design of their "buoyancy engine" or buoyancy
system. As a result, existing designs are typically optimized for
shallow water (e.g., less than 200 meters), deep water (e.g., 200
meters to 1000 meters), or very deep water (e.g., 1000 to 6000
meters). This limits the operation of existing underwater gliders
to a specific domain of underwater depth profiles that any specific
vehicle can traverse.
[0004] Underwater gliders can work, for example, as described in
U.S. Pat. No. 3,157,145 to Farris et al., the entire disclosure of
which is incorporated herein by reference. A glider can comprise a
main body, wings, and an adjustable portion such as an external
bladder for changing the apparent displacement of the glider. The
external bladder can initially be filled with a fluid such as oil
to maximize the buoyancy of the glider when the glider is initially
launched in the water. A valve can initially be set in a closed
position to prohibit the fluid in the bladder from leaving the
bladder. To begin the glider's descent, the valve can be opened,
allowing fluid to escape the bladder (for storage in, for example,
an internal storage reservoir). As fluid leaves the bladder, the
apparent displacement of the glider decreases while the glider's
mass stays the same, causing the glider to begin its descent into
the water.
[0005] When the vehicle has reached the deepest point of its
desired path, a pump system is used to move fluid from the internal
reservoir back out to the external reservoir. As the glider
descends, the wings of the glider cause it to move forward.
Similarly, the wings cause the glider to move forward as it ascends
through the water. To move forward, the glider must typically be
ascending or descending in the water. The glider moves forward
through its intended path by changing its buoyancy to move up and
down through the water, propelling it forward. Because more
vertical movement is possible in deeper waters, a greater
horizontal distance can be traversed by a glider for a single
descent and ascent in deeper waters. Thus, it may be possible to
traverse 10 kilometers horizontally in a single dive in deeper
water, whereas 10-20 dives can be required to traverse 10
kilometers in shallower water. If the same pump is used in both
shallow and deep water, the 10-20 dives can use far more energy
(e.g., pumping fluid into the bladder to cause the glider to
ascend) than the single dive in deep water. Thus, smaller and more
efficient devices such as pistons moving fluid in and out of the
external bladder are typically used for gliders used in shallow
water.
SUMMARY
[0006] The present teachings provide a multi-stage buoyancy
changing system for an autonomous underwater vehicle comprising: an
internal reservoir configured to hold a fluid; an external bladder
connected to the internal reservoir via one or more channels and
configured to exchange fluid with the internal reservoir via the
one or more channels; a first device configured to move fluid
through a channel from the internal reservoir to the external
bladder at an optimized efficiency for an ambient pressure of a
first segment of a dive profile to increase an apparent
displacement and a buoyancy of the autonomous underwater vehicle;
and a second device configured to move fluid through a channel from
the internal reservoir to the external bladder at an optimized
efficiency for an ambient pressure of a second segment of the dive
profile to increase an apparent displacement and a buoyancy of the
autonomous underwater vehicle. The first segment of the dive
profile includes a different ambient pressure range than the second
segment of the dive profile.
[0007] The present teachings also provide a method for employing a
multi-stage buoyancy changing system for an autonomous underwater
vehicle having an internal reservoir connected to an external
bladder via one or more channels. The method comprises: in a first
segment of a dive profile, increasing an apparent displacement and
buoyancy of the autonomous underwater vehicle by moving water from
the internal reservoir to the external bladder using a first device
configured to move fluid through a channel from the internal
reservoir to the external bladder at an optimized efficiency for an
ambient pressure of the first segment of the dive profile; and in a
second segment of the dive profile, increasing an apparent
displacement and buoyancy of the autonomous underwater vehicle by
moving water from the internal reservoir to the external bladder
using a second device configured to move fluid through a channel
from the internal reservoir to the external bladder at an optimized
efficiency for an ambient pressure of the second segment of the
dive profile. The first segment of the dive profile includes a
different ambient pressure range than the second segment of the
dive profile.
[0008] The present teachings further provide a multi-stage buoyancy
changing system 400 for an autonomous underwater vehicle
comprising: an internal reservoir configured to hold a fluid; an
external bladder connected to the internal reservoir via one or
more channels and configured to exchange fluid with the internal
reservoir via the one or more channels; a pump motor in combination
with a continuous variable transmission that can adapt to a
torque-speed curve to obtain an optimal pressure/pumping rate
needed for a current ambient pressure of the autonomous underwater
vehicle, the pump motor and continuous variable transmission being
configured to move fluid through a first channel from the internal
reservoir to the external bladder at an optimized efficiency for an
ambient pressure of more than one segment of a dive profile to
increase an apparent displacement and a buoyancy of the autonomous
underwater vehicle; and a third channel configured to allow fluid
to move from the external reservoir to the internal reservoir, the
third channel comprising a solenoid valve that can be selectively
opened to allow water to pass from the external bladder to the
internal reservoir.
[0009] Additional objects and advantages of the present teachings
will be set forth in part in the description which follows, and in
part will be obvious from the description, or may be learned by
practice of the present teachings. The objects and advantages of
the teachings will be realized and attained by means of the
elements and combinations particularly pointed out in the appended
claims.
[0010] The present teachings provide a multiple stage buoyancy
changing system, or variable buoyancy device, for an autonomous
underwater vehicle. The system or device comprises: a pressure
hull; a flexible sized internal reservoir configured to hold a
fluid; and a flexible sized external reservoir, or bladder,
connected to the internal reservoir via one or more channels, each
channel having multiple valves and pumps. The one or more channels
are configured to exchange fluid between the reservoirs as variable
buoyancy device stages which are specifically optimized for energy
efficiency at a range of ambient external pressures for multiple
segments of a dive profile.
[0011] The first segment of the dive profile can be handled by a
first stage of the variable buoyancy device, the second segment of
the dive profile can be handled by the second stage of the variable
buoyancy device, et cetera, up to an Nth stage corresponding to a
maximum depth or pressure to which the vehicle is designed to
dive.
[0012] The present teachings also provide a method for controlling
a multiple stage buoyancy changing system, or variable buoyancy
device, for an autonomous underwater vehicle having an external
pressure sensor and a volume measurement system for either, or
both, of an internal reservoir and an external reservoir. The
external pressure sensor and the volume measurement system are
connected to an internal processor and electronics that control the
valves and pumps of the variable buoyancy device. The present
teachings include logic for selecting which stage of the variable
buoyancy device is used at any given depth.
[0013] The present teachings further provide a multiple stage
variable buoyancy device for an autonomous underwater vehicle that
includes a pump and motor combination with a continuous variable
transmission that can electronically adapt to a torque-speed curve
to rapidly obtain an optimal pumping rate for changing
buoyancy.
[0014] Additional objects and advantages of the present teachings
will be set forth in part in the description which follows, and in
part will be obvious from the description, or may be learned by
practice of the present teachings. The objects and advantages of
the teachings will be realized and attained by means of the
elements and combinations particularly pointed out in the appended
claims.
[0015] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory only and are not restrictive of the present
teachings, as claimed.
[0016] The accompanying drawings, which are incorporated in and
constitute a part of this specification, illustrate embodiments of
the present teachings and, together with the description, serve to
explain the principles of the teachings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 illustrates an exemplary path of an autonomous
underwater vehicle such as a glider descending and ascending
through multiple depth ranges.
[0018] FIG. 2 schematically illustrates an exemplary embodiment of
a multiple stage fluid pump and valve system for an underwater
vehicle in accordance with the present teachings, the system being
optimized for one to "N" stages to be energy efficient at all
ranges of pressure (or depth) underwater.
[0019] FIG. 3 illustrates an exemplary embodiment of a decision
scheme used by an electronic control system for a multiple stage
variable buoyancy device (VBD), wherein each stage is designed to
pump at a particular output pressure range for maximum energy
efficiency throughout an underwater dive profile. The illustrated
decision scheme uses information from an external pressure sensor
and an internal volume sensor to know if a target volume has been
achieved. Other system of the underwater vehicle can determine
whether a change in vehicle volume is needed.
[0020] FIG. 4 is a flow chart outlining the basic steps of an
exemplary algorithm for implementing a multi-stage system to
achieve efficiency at various depth profiles.
[0021] FIG. 5 is a schematic diagram illustrating an exemplary
embodiment of a hydraulic multi-stage buoyancy system in accordance
with the present teachings.
[0022] FIG. 6 is a schematic diagram illustrating another exemplary
embodiment of a multi-stage buoyancy system in accordance with the
present teachings.
[0023] FIG. 7 is an exemplary embodiment of an energy storage
system onboard an autonomous underwater vehicle for powering fluid
displacement mechanisms.
[0024] FIG. 8 is an exemplary embodiment of an energy storage
system onboard an autonomous underwater vehicle for powering fluid
displacement mechanisms.
[0025] FIG. 9 is a cross section of an exemplary embodiment of an
energy storage system onboard an autonomous underwater vehicle for
powering fluid displacement mechanisms.
[0026] FIG. 10A is a top view of an exemplary embodiment of the
autonomous underwater vehicle of the present invention.
[0027] FIG. 10B is a perspective side view of the autonomous
underwater vehicle of FIG. 10A.
[0028] FIG. 11A illustrates an autonomous underwater vehicle
descending into a deep depth range of a universal glider range.
[0029] FIG. 11B illustrates an exemplary dive profile having three
distinct depth ranges for which multiple pump stages are utilized
during ascent.
[0030] FIG. 12 is a chart illustrating pressure versus depth
underwater.
[0031] FIG. 13 illustrates an exemplary underwater dive profile
with time represented on the horizontal axis and depth represented
on the vertical axis.
DESCRIPTION OF THE EMBODIMENTS
[0032] The present invention now will be described more fully
hereinafter with reference to the accompanying drawings, in which
illustrative embodiments of the invention are shown. In the
drawings, the relative sizes of regions or features may be
exaggerated for clarity. This invention may, however, be embodied
in many different forms and should not be construed as limited to
the embodiments set forth herein; rather, these embodiments are
provided so that this disclosure will be thorough and complete, and
will fully convey the scope of the invention to those skilled in
the art.
[0033] It will be understood that when an element is referred to as
being "coupled" or "connected" to another element, it can be
directly coupled or connected to the other element or intervening
elements may also be present. In contrast, when an element is
referred to as being "directly coupled" or "directly connected" to
another element, there are no intervening elements present. Like
numbers refer to like elements throughout.
[0034] In addition, spatially relative terms, such as "under",
"below", "lower", "over", "upper" and the like, may be used herein
for ease of description to describe one element or feature's
relationship to another element(s) or feature(s) as illustrated in
the figures. It will be understood that the spatially relative
terms are intended to encompass different orientations of the
device in use or operation in addition to the orientation depicted
in the figures. For example, if the device in the figures is turned
over, elements described as "under" or "beneath" other elements or
features would then be oriented "over" the other elements or
features. Thus, the exemplary term "under" can encompass both an
orientation of over and under. The device may be otherwise oriented
(rotated 90 degrees or at other orientations) and the spatially
relative descriptors used herein interpreted accordingly.
[0035] The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting of
the invention. As used herein, the singular forms "a", "an" and
"the" are intended to include the plural forms as well, unless the
context clearly indicates otherwise. It will be further understood
that the terms "comprises" and/or "comprising," when used in this
specification, specify the presence of stated features, integers,
steps, operations, elements, and/or components, but do not preclude
the presence or addition of one or more other features, integers,
steps, operations, elements, components, and/or groups thereof. As
used herein, the expression "and/or" includes any and all
combinations of one or more of the associated listed items.
[0036] Unless otherwise defined, all terms (including technical and
scientific terms) used herein have the same meaning as commonly
understood by one of ordinary skill in the art to which this
invention belongs. It will be further understood that terms, such
as those defined in commonly used dictionaries, should be
interpreted as having a meaning that is consistent with their
meaning in the context of the relevant art and will not be
interpreted in an idealized or overly formal sense unless expressly
so defined herein.
[0037] It is noted that any one or more aspects or features
described with respect to one embodiment may be incorporated in a
different embodiment although not specifically described relative
thereto. That is, all embodiments and/or features of any embodiment
can be combined in any way and/or combination. Applicant reserves
the right to change any originally filed claim or file any new
claim accordingly, including the right to be able to amend any
originally filed claim to depend from and/or incorporate any
feature of any other claim although not originally claimed in that
manner. These and other objects and/or aspects of the present
invention are explained in detail in the specification set forth
below.
[0038] Reference will now be made in detail to embodiments of the
present teachings, examples of which are illustrated in the
accompanying drawings.
[0039] In many implementations, an autonomous underwater vehicle
(hereafter interchangeably called "AUV") 100 uses most (e.g., about
75%) of its energy to pump fluid (e.g., hydraulic fluid, water,
seawater, or other non-compressible fluids or fluids having low
compressibility) into an external bladder 405 from an internal
storage reservoir to increase the AUV's 100 apparent displacement
and buoyancy to cause the AUV 100 to ascend to move forward and/or
to reach the surface of the water for data receipt and
transmission. The amount of pressure required to pump fluid into
the external bladder typically varies by depth. For example, in
shallow water (e.g., less than about 200 meters) the required
pressure can have a magnitude of hundreds of psi, whereas in deep
water (e.g., about 200 meters to about 1000 meters) the required
pressure can have a magnitude of thousands of psi.
[0040] This difference in pressures required to pump fluid into the
autonomous underwater vehicle's external bladder has created a
design dilemma, because existing pumps that are powerful enough to
create enough pressure to pump fluid into the external bladder in
deeper water with high ambient pressure are typically inefficient
for use in shallower waters with low ambient pressures and in
certain dive profiles where the pump must cause the autonomous
underwater vehicle to ascend more frequently to cover a given
horizontal distance. The pressure that must be generated by
existing deep water glider pumps makes those pumps less energy
efficient. Low pressure pumps are more energy efficient but
typically do not provide sufficient pumping force in deeper waters.
This design dilemma causes existing autonomous underwater vehicles
to be optimized for a limited range of depths.
[0041] As stated above, this pump design dilemma is imposed by the
existence of increasing hydrostatic pressure with increasing depth,
which is illustrated in FIG. 12. For example, as shown in FIG. 11A,
a system required to compensate for the hydrostatic pressures that
are encountered in water that is typically considered shallow 200,
for example from the surface to a depth of 100 meters, must
overcome ambient pressures ranging from 1 atmosphere (14.7 psi) to
about 14 atmospheres (200 psi). By comparison, the pressure change
that must be overcome by a deep diving vehicle (i.e. an AUV 100
deployed in a deep AUV range 250) can range from a surface pressure
of about 1 atmosphere (14.7 psi) to nearly about 102 atmospheres
(1500 psi). FIG. 12 is a chart illustrating pressure versus depth
underwater, where the vertical axis represents hydrostatic pressure
in pounds per square inch (psi) and the horizontal axis represents
depth in meters. A single pumping system that can overcome 1500 psi
in the deep AUV range 250 will not be as energy efficient for
pumping lower psi that occurs in shallower depths 200. In contrast,
a buoyancy system designed to handle a smaller range of pressure
compensation will use significantly less energy to do so. Thus, as
stated above, existing autonomous underwater vehicles are offered
to be efficient in, generally, one of four ranges: 0 to 30 meters;
10 to 100 meters; 40 to 200 meters; and 200 to 1000 meters.
[0042] A pump capable of producing enough pressure to move fluid
into an autonomous underwater vehicle's external bladder in deep
water 250 is far less efficient than a pump that is capable of
producing enough pressure to move fluid into the external bladder
in shallow water 200. A deep water pump can use, for example, nine
times more energy than a shallow water pump. An example of a
commercial pump used in deep diving gliders is the Hydro LeDuc
model PB32.5 which can pump against 100 atmospheres and requires 14
ft lbs (20 nm) of energy to drive. By comparison a hydraulic pump,
such as the MicroPump GB models, requires about 1.25 ft lbs energy
to pump against the pressure at 100 meters, about 11 atmospheres.
When the Hydro LeDuc is used to pump against the lower pressure
(e.g., 11 atmospheres), it uses nearly the same amount of energy as
it does when pumping against 100 atmospheres.
[0043] Turning to FIG. 10A, the present teachings provide a
universal or increased depth range autonomous underwater vehicle
100 comprising a multi-stage buoyancy system 400 and a control
system 105 that can plan the travel of an autonomous underwater
vehicle using a depth profile plan (See FIG. 1) and depth sensors
110 (e.g., one or more pressure sensors and/or one or more acoustic
altimeters). In one embodiment, the AUV 100 may determine a range
and heading by, for example, an acoustic modem 107 USBL message to
determine which portions of the multi-stage buoyancy system to use
to achieve the profile plan while utilizing the least amount of
onboard stored energy. By sensing the depth and/or the position of
the underwater vehicle 100 in its dive profile (e.g., via sensors
including depth/pressure sensors 110 and/or acoustic altimeters
112), a control system 105 and buoyancy system 400 in accordance
with the present teachings allow a single autonomous underwater
vehicle to produce efficient motion covering a broad range of
depth, including shallow coastal waters 200 to deep ocean domains
250.
[0044] As depicted in FIGS. 2 and 6, the present teachings provide
a multiple stage buoyancy changing system 400, or variable buoyancy
device, that can make an autonomous underwater vehicle 100 energy
efficient over a large range of depths 200, 250. Multiple stages
including a channel, a pump, a motor, and a valve can be optimized
to each cover a portion of an external pressure range that the
vehicle will encounter in a typical dive cycle. By sensing the
depth or ambient pressure surrounding the underwater vehicle in a
given dive profile, and engaging the correct stage for pumping
fluid for that ambient pressure, a system in accordance with the
present teachings allows a single autonomous underwater vehicle 100
to produce energy efficient vertical motion covering a broad range
of depths, including shallow coastal waters 200 to deep ocean
domains 250.
[0045] FIGS. 2, 5 and 6 schematically illustrates an exemplary
embodiment of a multiple stage buoyancy system 400 in accordance
with the present teachings. The embodiment of FIG. 5, for example,
illustrates a multiple stage buoyancy system 400 having a first
channel 420 including a bypass channel 422, a second channel 415,
and a third channel 425. By utilizing multiple channels within the
device, including bypass channels 422, a multiple stage buoyancy
system 400 of the present teachings achieves high efficiency in
buoyancy changes without allowing one stage to compromise or
restrict the performance of any other stage. Check valves 450 can
be provided to prevent fluid from returning to previous pump
stages. In the embodiment of FIG. 2, a filter is shown, which can
protect the system 400 from contaminants in the fluid that would
decrease the flow or clog the valves, but is not essential to
operation.
[0046] An autonomous underwater vehicle 100 having a multi-stage
buoyancy system 400 in accordance with the present teachings, an
exemplary embodiment of which is illustrated schematically in FIG.
11A, can traverse a dive profile ranging from shallow coastal water
200 to deep water 250 with a single vehicle 100, without a
significant compromise of energy consumption or reliability that
might occur in a design optimized for a narrow range of depths.
[0047] The present teachings contemplate an underwater vehicle
including as many stages as are deemed necessary and expedient to
produce the best trade-off between energy use for pumping and (a)
the mass of parts needed for each stage, (b) the volume occupied by
each stage within the pressure hull, and (c) the complexity of
controls and plumbing.
[0048] FIGS. 1 and 11B illustrate an exemplary dive profile having
one or more distinct depth (or pressure) ranges (hereafter
interchangeably called depth "stages") for which different variable
buoyancy device pump stages are utilized. As indicated in the flow
chart of FIG. 3, the choice 500 of which pump stage 505, 510, 515
to utilize can be made, for example, by the vehicle's on-board
processor 105 with input from various sensors 110, 112 and command
files. In accordance with certain embodiments, the autonomous
underwater vehicle 100 can abort a dive when a problem (e.g., a
system error) is detected. When a dive is aborted, the autonomous
underwater vehicle 100 can, for example, pump as much fluid into
the external reservoir 405 as possible to reach the surface 205 for
retrieval, preferably using the most efficient stages of the
variable buoyancy system.
[0049] The fluid displacement systems (e.g., the pump 460a, 460b,
460n, motor, and valve systems) of the present teachings need not
be of the same type. Different dive stages 260a, 260b, 260n can
comprise different components. Exemplary fluid displacement systems
that can be used in accordance with the present teaching include,
for example, a piston-driven pump, a systolic pump, a Stirling
engine, and/or other suitable devices that can move fluid.
[0050] A multiple stage buoyancy system 400 in accordance with the
present teachings can be implemented using a variety of approaches
that embody the principle of depth/pressure dependent selection of
the most efficient pump stage 505, 510, 515 corresponding to the
dive stages 260a, 260b, 260n. An example of an implementation and
decision process 500 is illustrated in FIG. 3. By using a pressure
sensor 112 that detects the surrounding water pressure at a given
depth 260a, 260b, 260n, and a volume sensor 114 that detects the
vehicle's 100 displacement volume, the control system 105 and/or
electrical logic of the vehicle 100 can enable a pumping stage 505,
510, 515 that is most energy efficient for the detected
environmental pressure if a change in external volume is needed. In
principle, a system of many ("N") stages can be employed, wherein
two is the simplest case and may be adequate for many different
vehicles. The present teachings illustrate in FIG. 2, however, that
more than two stages can be utilized to achieve high efficiency
across the entire depth of the ocean.
[0051] As depicted in FIG. 5 as an optional element (dashed lines),
another embodiment of the present teachings contemplates utilizing
a pump 260 and motor 261m in combination with a continuous variable
transmission 261t that can adapt to a torque and speed curve,
resulting in different pumping rates at different depths to
efficiently change the buoyancy of an autonomous underwater vehicle
100. Continuously variable transmissions can provide an effective
continuum of torque-speed ratios over a predetermined range, with
slower speeds corresponding to higher torque output and higher
speeds corresponding to lower torque output.
[0052] The illustrated exemplary embodiment of FIG. 2 places the
stages (or channels) 415, 420, of the multiple stage buoyancy
system in parallel with each other to eliminate a potential
negative impact of serial placement. Serial placement can impede
optimal performance by restricting the downstream pump's access to
the internal reservoir.
[0053] Certain embodiments of the present teachings can combine two
or more stages to increase the rate of pumping and thus change of
buoyancy.
[0054] During an underwater vehicle's 100 descent, fluid can move
from the external reservoir (or bladder) 405 to the internal
reservoir 410 when a high-pressure return valve 452 between the
external reservoir and the internal reservoir is opened. In one
embodiment the external bladder 405 and/or the internal reservoir
are expandable. Ambient pressure can be used to push fluid from the
external reservoir 405 to the internal reservoir 410 by pressing on
the external reservoir 405. In addition, the autonomous underwater
vehicle 100 can have a reduced internal pressure (e.g., a vacuum)
that encourages fluid flow from the external reservoir 405 to the
internal reservoir 410. Certain embodiments of the present
teachings also contemplate using one or more pumps to drive fluid
from the external reservoir to the internal reservoir if more speed
is required in that process.
[0055] In accordance with certain embodiments of the present
teachings, a connection can exist from the output of one pump stage
to the intake of another pump stage. This series-like plumbing can
function as a safety path for any pump stage that needs
priming.
[0056] An autonomous underwater vehicle 100 employing control and
buoyancy systems 400 in accordance with the present teachings can
travel long distances (e.g., thousands of kilometers) over
durations of many months using buoyancy changes that combine
algorithms and multiple stage buoyancy control to conserve onboard
stored energy by utilizing an optimized fluid displacement
strategy, selecting the most energy efficient fluid displacement
mechanism(s) to traverse all desired diving profiles.
[0057] FIGS. 1, 11B and 13 illustrate an exemplary dive profile of
an embodiment of the AUV 100 having three distinct depth ranges (or
stages) for which three pump stages are utilized during ascent,
Pressure Range 1 260a, Pressure Range 2 260b and Pressure Range n
260n. Many depth (pressure) ranges may exist between Pressure Range
1 260a and Pressure Range n 260n. As shown, the dive profile
includes a single deep dive having five segments: first SURFACE
265; DIVE 270; APOGEE 275; CLIMB 280, and second SURFACE 285. In a
first SURFACE 265 segment, the autonomous underwater vehicle 100, a
position of which is indicated by various dots 290a-290n, starts a
surface phase 265 and transmits information including, for example,
vehicle health (e.g., all systems self-test and indicate that they
are working normally), available onboard energy, a dive log, data
from onboard instruments 113 (e.g., chemical compounds in water,
optical backscatter, sound detection, salinity, predominant
currents, images, other physical properties of the ocean, etc.),
and receives information including a dive plan having waypoints
(e.g., latitude, longitude, depth, descent rate, and ascent rate),
instrument sampling rates, and other parameters associated with
controlling instruments (turning them off or when to turn them
off). After a dive plan is received, the vehicle 100 can calculate
a correct rate and angle of descent based at least in part on the
new dive plan. An initial GPS location is taken (GPS1) with an
onboard GPS sensor 114 when the vehicle 100 surfaces or is
initially placed in the water and then, after data transmission and
receipt of a new dive plan (which presently typically takes about
10-15 minutes (using, e.g., about 10 Watts of energy), another GPS
location is taken (GPS2) because the vehicle 100 may have moved
during data transmission and receipt. Movement of the vehicle 100
from GPS1 to GPS2 can provide information regarding predominant
currents affecting the vehicle 100. A dive log can comprise data
indicating how each dive profile step went. The dive log can also
record errors and error mitigation attempts, and can collect
instrument data.
[0058] Certain embodiments of the autonomous underwater vehicle 100
can remain surfaced without using an electro-motive force, while
radio communications and electro-optics perform the above mentioned
tasks.
[0059] During a second dive plan segment, labeled DIVE 270, the
autonomous underwater vehicle's 100 nose 155, or front, is pointed
downward and the vehicle 100 begins its dive phase by beginning a
descent into a first depth range 260a (typically without using a
pump but rather by letting fluid bleed out of the external bladder
405 to an internal reservoir 410). After descending through the
first depth range 260a, the autonomous vehicle enters a second
depth range 260b of the DIVE segment 270 that can be identified,
for example, by external pressure sensor 112 readings indicating a
depth of the vehicle 100 based on the ambient pressure. In
accordance with certain embodiments, during descent, the underwater
vehicle can change its angle of descent by changing its pitch angle
as needed to follow the requested dive profile 255.
[0060] After descending through the second depth range 260b, the
autonomous vehicle 100 enters a third depth range 260n of the DIVE
segment 270 that can be identified, for example, by external
pressure sensor 112 readings indicating a depth of the vehicle 100
based on the ambient pressure. In certain embodiments of the
present teachings in which a bathometric map has been stored, the
autonomous underwater vehicle 100 can make sure it has reached a
maximum depth set forth in the dive profile 255 and/or avoid
collision with the bottom 210 (e.g., using acoustic pings to find
the bottom) before beginning an APOGEE dive plan segment 275. As
the underwater vehicle 100 reaches the bottom of its dive, for
example in the third depth range 260n, it enters an APOGEE dive
plan segment 275. The APOGEE dive plan segment 275 can include a
transition from descent to ascent, wherein the autonomous
underwater vehicle 100 levels out (becomes horizontal) and changes
its inclination (by, e.g., turning its nose 115 upward for an
ascent by shifting a mass 117 within the vehicle 100) before
changing buoyancy by pumping fluid from the internal reservoir 410
to the external bladder 405 to begin its ascent and begin a CLIMB
segment 280 of the dive plan 255.
[0061] The CLIMB segment 280 of the illustrated dive plan 255
begins in the third depth range 260n, where a Pump Stage (channel)
3 515 is utilized to pump fluid into the external bladder 405 of
the autonomous underwater vehicle 100, which requires a pumping
force sufficient to overcome the ambient external pressure at the
underwater vehicle's depth 260n. Pump Stage 3 515 can comprise one
or more pumps 460a, 460b, 460n, optimized for the third depth range
(i.e., deep water 250). As the external bladder 405 fills with
fluid, the surface area and thus the buoyancy of the underwater
vehicle 100 increase, causing the underwater vehicle to ascend. In
accordance with certain embodiments, only a nominal amount of fluid
is move to the external bladder 405--just enough to get a desired
rate of rise. As the autonomous underwater vehicle 100 begins to
ascend, it may need to change the amount of fluid in the external
bladder 405 because, for example, the density (e.g., the salinity)
of the water may not be what was originally predicted. Thus, more
fluid can be pumped into the external bladder 405 or some fluid can
be allowed to bleed from the external bladder 405 to alter the rate
of ascent. Adding and removing water from the external bladder 405
can be performed, for example, in a PID loop type of arrangement.
In certain embodiments, the system 400 may not allow fluid to be
bled from the external bladder 405 to slow the underwater vehicle's
100 ascent, because the vehicle 100 typically eventually hits an
area of water in its ascent that slows the vehicle down and makes
up for a too-rapid rise. Ocean water density tends to be more
uniform near the ocean's bottom 210. Toward the ocean's surface
205, the density is more likely to vary, for example due to varying
temperature or salinity. Salinity may vary due to, for example,
fresh water sources such as rivers, streams, runoff, and rain
water.
[0062] The underwater vehicle ascends through the third depth range
260n to the second depth range 260b. In the second depth range
260b, the depth and thus the ambient pressure decrease, and a Pump
Stage 2 510 can be used to pump fluid into the external bladder 405
if needed to maintain a desired rate of ascent. Pump Stage 2 510
can comprise one or more pumps 460a, 460b, 460n optimized for the
second depth range 260b. In accordance with certain embodiments,
during ascent, the underwater vehicle 100 can change its angle of
ascent by changing its pitch angle as needed to follow the
requested dive profile. The underwater vehicle 100 ascends through
the second depth range 260b to the first depth range 260a. In the
first depth range 260a, the depth and thus the ambient pressure
decrease, and a Pump Stage 1 505 can be used to pump fluid into the
external bladder 405 if needed to maintain a desired rate of
ascent. Pump stage 1 505 can comprise one or more pumps 460a, 460b,
260n optimized for the first depth range 260a (i.e., shallower
water 200). Within the first depth range 260a, for example at about
10 meters or less, a second SURFACE segment 285 can begin as
illustrated. At surfacing 285, more fluid can be pumped into the
external bladder 405 and the vehicle's mass 117 may be shifted to
get the vehicle's tail (or rear) 120 up to allow an antenna 135
located at the tail 120 to rise for communication.
[0063] During the second SURFACE segment 285, the autonomous
underwater vehicle 100 can transmit information including, for
example, vehicle health (e.g., all systems self-test and indicate
that they are working normally), available onboard energy, a dive
log, data from onboard instruments (e.g., chemical compounds in
water, optical backscatter, sound detection, salinity, predominant
currents, images, other physical properties of the ocean, etc.),
and can receive information including a dive plan having waypoints
(e.g., latitude, longitude, depth, descent rate, and ascent rate),
instrument sampling rates, and other parameters associated with
controlling instruments (turning them off or when to turn them
off). After a dive plan 255 is received, the vehicle 100 can
calculate a correct rate and angle of descent based at least in
part on the new dive plan 255. An initial GPS location is taken
(GPS1) with an on board GPS 114 when the vehicle 100 surfaces and
then, after data transmission and receipt of a new dive plan 255
(which presently typically takes about 10-15 minutes (using, e.g.,
about 10 Watts of energy), another GPS location is taken (GPS2)
because the vehicle 100 may have moved during data transmission and
receipt. Movement of the vehicle from GPS1 to GPS2 can provide
information regarding predominant currents affecting the vehicle. A
transmitted dive log can comprise data indicating how each dive
profile step went. The dive log can also record errors and error
mitigation attempts, and can collect instrument data. Certain
embodiments of the underwater vehicle 100 can remain surfaced
without using any energy. The underwater vehicle 100 can also be
retrieved after a single dive.
[0064] In accordance with certain embodiments, the autonomous
underwater vehicle 100 can abort a dive 255 when a problem (e.g., a
system error) is detected. When a dive 255 is aborted, the
autonomous underwater vehicle 100 can pump as much fluid into the
external bladder 405 as possible to reach the surface for
retrieval.
[0065] When the dive plan 255 requires the vehicle 100 to re-dive
without surfacing, the vehicle 100 typically levels out and shifts
a mass 117 within the vehicle to point its nose 115 downward before
the vehicle 100 allows bleeding from the external bladder 405 to
begin to dive again.
[0066] To provide an autonomous underwater vehicle 100 that can
efficiently traverse a dive profile 255 ranging from shallow
coastal water 200 to deep water 250, the present teachings
contemplate a multi-stage buoyancy system c400 omprising, for
example, a system employing multiple fluid displacement mechanisms
(e.g., a multi-pump system or a system employing a combination of
pumps and other fluid displacement systems) to provide efficient
movement of fluid at a variety of depths. The fluid displacement
systems need not all be the same type of fluid displacement system
and can comprise, for example, a piston-driven pump, a systolic
pump, a Stirling engine, and/or other suitable devices that can
move fluid.
[0067] Various embodiments of the present teachings provide a
system for changing the apparent displacement or incorporated mass
of an autonomous underwater vehicle by displacing fluid within an
underwater vehicle comprising two or more stages or subsystems of
displacement mechanisms as set forth hereinabove, and a control
system that determines an appropriate stage to utilize in the
environment that is ambient to the underwater vehicle at any given
segment of the underwater vehicle's dive profile.
[0068] As stated above, an autonomous underwater vehicle must
descend and ascend in the water to move forward and traverse its
intended path. FIG. 13 illustrates an exemplary underwater dive
profile with time represented on the horizontal axis and depth
being represented on the vertical axis. FIG. 3 shows that the
ascent phase of the underwater vehicle's dive profile is where the
multi-stage control of the present teachings is effective in
allowing the underwater vehicle to employ more than one fluid
displacement mechanism to move fluid to the external bladder with
maximum efficiency while providing the pressure needed to fill the
bladder based on the ambient pressure at the underwater vehicle's
depth.
[0069] At the end of the ascent phase, the autonomous underwater
vehicle can reach a surface level (or at least come close enough to
the surface) where it can send data (e.g., via satellite
transmission) regarding its preceding path and/or begin a new
decent and ascent cycle. Upon surfacing, the underwater vehicle can
reconcile its location by receiving its current GPS location and
inputting that location into its dive profile.
[0070] A multi-stage buoyancy system in accordance with the present
teachings can be implemented in a number of ways using a variety of
approaches that embody the principle of depth-driven and
pressure-driven selection of the most efficient stage. For example,
by using a pressure sensor that detects the surrounding water
pressure at a given depth, the control system or electrical logic
of the vehicle can enable the pumping stage that is most efficient
for the detected environmental pressure. In principle, a system of
many stages can be employed, wherein two is the simplest case for
use as an exemplary embodiment herein and may be adequate for many
coastal to deep water oceanic missions for autonomous underwater
vehicles. The present teachings contemplate, however, more than two
stages being used to achieve high efficiency across the entire
depth of the ocean from a few meters to 6000 meters or more.
[0071] The design principle driving selection of different pumps
and pump drive motors for differing depth ranges can be such that
the pumping energy for predefined depth ranges and associated
pressure is minimized on the basis of balancing the rate of pumping
against the torque and hence energy consumption required to resist
and overcome the range of pressures within a depth range and move
enough fluid to achieve a required buoyancy offset. For example, a
depth range of from 0 to 100 meters typically has a corresponding
pressure range of from about 1 atmosphere to about 11 atmospheres,
and this would dictate that a pump and drive motor capable of most
efficiently overcoming the 11 atmospheres maximum value would be
selected for this depth range. For a range of 100 meters to 500
meters, having a pressure range of from 12 atmospheres to 50
atmospheres, a stronger pump/motor drive combination is needed,
preferably having the best energy efficiency for that range. This
design criteria can continue until a maximum depth demanded by the
vehicle is serviced by a pump and motor drive stage that meets the
maximum pressure demand, while using the minimum energy to achieve
buoyancy change by volume of expelled fluid to overcome pressure at
any given depth.
[0072] Using the above design approach for very large depth ranges
can, in certain instances, produce a sub-optimal match of pumping
stage to the encountered pressure at some depths, or can produce a
design with an excessive number of stages and thus excessive
complexity and a significant number of parts lending toward failure
modes. Thus, another embodiment of the present teachings
contemplates utilizing a pump motor in combination with a
continuous variable transmission (CVT) that can adapt to a
torque--speed curve resulting in an optimal pressure/pumping rate
needed at any given depth of the autonomous underwater vehicle.
CVTs can provide an effective continuum of torque-speed ratios over
a predetermined range, with slower speeds corresponding with higher
torque output. A continuous variable transmission would effectively
allow a pump to work across an entire pressure range efficiently by
virtue of operating at a faster rate (using a low gear ratio for
shallower water, lower ambient pressure, lower torque requirements)
or slower rate (using a high gear ratio for deeper water, higher
ambient pressure, higher torque requirements) of fluid displacement
as needed to minimize the torque and hence the energy required to
change buoyancy as needed to allow the underwater vehicle to follow
its dive profile.
[0073] A CVT-based implementation of the present teachings is
practical for increased dive durations associated with increased
dive depths. For example, dives to 50 meters will typically take
from 15 to 20 minutes, whereas dives to 1000 meters can take up to
5 hours, affording a far longer time frame for the pumping system
to move the fluid to achieve ascent velocity when ascending from a
1000 meter depth. In other words, a CVT-based embodiment would pump
slowly, using less energy when at greater depths by employing a
high gear ratio in the CVT, resulting in low pumping speed but high
enough torque to overcome external pressure. Given the longer
duration of deeper dives, this can produce an acceptable and
optimized result with a single pump design. Where pressures are low
in shallow dives, the amount of torque required by the pump to
overcome the external water pressure is much lower, but rapid
pumping to achieve rapid ascent is typically desirable, so the CVT
would then be set to a low gear ratio between the drive motor and
the output pump, achieving a higher pumping rate with the lower
torque demand. The best effective gear ratio of the CVT for a given
ambient pressure can be automatically selected by reading the
pressure sensor, then applying an algorithm or other analog control
scaling to cause the control arm or other mechanisms that
determines the CVT's effective gear ratio to react proportionally
or in steps to pressure changes, in a relationship that decreases
the effective gear ratio as depth (and hence pressure)
increases.
[0074] An exemplary embodiment of the present teachings that
employs a CVT can utilize a NuVinci.TM.. Model N360 continuously
variable planetary drive train transmission or another continuously
variable or step gearbox mechanism that can vary the pump-to-drive
motor effective gear ratio based on a proportional algorithm that
is keyed to pressure. As will be understood by those skilled in the
art, low gear ratios can be used at shallower depths with lower
external pressures, and high gear ratios can be used in deeper
waters to produce the extra torque needed to push fluid into the
external bladder and against the higher external pressure exerted
on the external bladder.
[0075] A flow chart outlining the basic steps of an exemplary
algorithm for implementing a multi-stage buoyancy system to achieve
efficiency at various depth ranges is illustrated in FIG. 4. The
flow chart of FIG. 4 illustrates the basic concept of a two-stage
system, one stage being for shallow dive segments of the autonomous
underwater vehicle's dive profile and the other stage being for
deep dive segments of the underwater vehicle's dive profile. The
present teachings contemplate using either the profile sequence or
the actual pressure to determine which of the fluid displacement
mechanisms (e.g., which pump) is used for a given segment of a
dive. In certain embodiments, two or more fluid displacement
mechanisms (e.g., two pumps or two stages) can be used for a single
segment. In certain embodiments, only the ascent phase of a dive,
as illustrated in FIG. 3, uses the underwater vehicle's fluid
displacement mechanisms to change the underwater vehicle's
buoyancy.
[0076] As shown in FIG. 4, after a dive sequence begins, the
autonomous underwater vehicle performs a next segment of the dive
profile, which can be the initial dive profile segment. Each time a
new segment of the dive profile begins (e.g., based on a reading of
the depth, compass, attitude, or other sensors, singularly or in
combination), the algorithm determines whether the profile is an
ascent segment (in which one or more fluid displacement mechanisms
may need to be employed to displace fluid into an external
bladder). If the next segment of the dive profile is not an ascent
segment, pressure can be bled from the external bladder to reduce
buoyancy, as needed, and the underwater vehicle can begin a descent
through the water until a next segment of the dive profile is
reached. If the next segment of the dive profile is an ascent
segment, the algorithm determines whether the depth of the next
segment and the current ambient conditions are less than "Stage 2,"
which means that the depth of the next segment and the current
ambient conditions are less than a predetermined depth that is
optimal for the pump/motor combination currently being utilized,
and thus the ambient pressure is below a predetermined value. To
determine the ambient pressure, the algorithm can utilize input
from a pressure/depth sensor employed on the underwater vehicle. If
the depth of the next segment and the current ambient conditions
are less than Stage 2, a high pressure fluid displacement mechanism
(referred to herein as a "Stage 1 pump") can be disabled to improve
efficiency of the overall system. Thereafter, the system can
perform a buoyancy change with just the Stage 2 fluid displacement
mechanism and then move on to perform a next segment of the dive
profile.
[0077] If either the depth of the next segment or the current
ambient conditions are greater than or equal to "Stage 2," which
means that the depth of the next segment or the current ambient
conditions are greater than or equal to a predetermined depth that
is optimal for the next range of pressure and thus the ambient
pressure is above a predetermined value, the high pressure fluid
displacement mechanism (the Stage 1 pump) can be enabled to provide
the pressure needed to move fluid to the external bladder against
higher ambient pressures. When the Stage 1 pump is enabled, it can
be used alone (by disabling the stage 2 pump as shown), or in
conjunction with the Stage 2 pump. The algorithm then performs a
next segment of the dive profile. In certain embodiments, two fluid
displacement mechanisms can be employed to create a three-stage
buoyancy system when each fluid displacement mechanism can be used
alone or the two mechanisms can be used together.
[0078] In certain embodiments, the control system for the
autonomous underwater vehicle uses stored dive profile information,
such as the profile illustrated in FIG. 11B or a profile including
more than one dive segment such as the segments in FIG. 13, to
determine at what time (or distance) an appropriate stage should be
used--based on a profiled desired depth. Since this method depends
on an accurate assessment of the vertical distance traversed by the
underwater vehicle 100, which can be significantly affected by
currents and density structure of the dive environment, certain
embodiments of the present teachings can employ a secondary method
for selecting the buoyancy stage, such as by reading an external
pressure sensor 112 or another method to determine actual depth
(e.g., by an acoustic altimeter or by a range and heading
determined by an acoustic modem USBL message). The depth and/or
depth analog such as pressure can then be used to select the
appropriate stage 505, 510, 515 to be used for the desired buoyancy
changes in that segment of the dive profile 255. The terms stages,
pumps, and fluid displacement mechanisms are used interchangeably
herein.
[0079] FIG. 5 is a schematic diagram illustrating an exemplary
embodiment of a hydraulic multi-stage buoyancy system in accordance
with the present teachings. The exemplary embodiment of FIG. 5
includes, among other elements: a first stage (Stage 1) pump for
high pressure depths; a second stage (Stage 2) pump for lower
pressure depths; an internal reservoir for fluid (e.g., hydraulic
fluid) used to change buoyancy; and a buoyancy chamber or external
bladder mounted on an external surface of the underwater vehicle
that changes in size and displacement when hydraulic fluid is
pumped into it or expressed from it by ambient pressure as the
underwater vehicle enters deeper water. The external bladder is
preferably at least somewhat elastic.
[0080] FIG. 5 illustrates an exemplary embodiment of paths fluid
can take between the internal reservoir 410 and the external
bladder 405. In the illustrated embodiment, three paths 415, 420,
425 exist between the accumulator/reservoir 410 and the external
buoyancy chamber or bladder 405, two of which contain a fluid
displacement mechanism. One path 420 runs fluid through a low
pressure "Second Stage" (Stage 2) pump 460b and through a check
valve 450 such as the illustrated bypass (check) valve that
prevents movement to fluid in an unwanted direction. Another path
415 runs fluid through a bypass (check) valve 450 and through a
high pressure "First Stage" (Stage 1) pump 460a. The parallel
channels having bypass check valves 450 can combine to eliminate
unproductive loads on a stage that is currently operating, by
providing a direct path to the internal reservoir 410, without the
fluid needing to be pushed or pulled through any non-operating
elements (e.g., non-operating stages). The third path 425 allows
fluid to return from the external bladder 405 to the internal
reservoir 410 through a valve 452 such as, for example, a solenoid
valve (e.g., a Skinner valve).
[0081] To cause the autonomous underwater vehicle 100 to descend,
the Skinner valve 452 can be opened between the external bladder
405 and the internal reservoir 410, allowing fluid to be driven by
ambient pressure from the external bladder 405 to the internal
reservoir 410. In the illustrated embodiment of FIG. 5, a return
valve such as an electronically actuated solenoid valve (e.g., a
Skinner valve) 452 is located between the external bladder 405 and
the internal reservoir 410, although those skilled in the art will
appreciate that other suitable types of valves can alternatively or
additionally be used. The valve 452 between the external chamber
405 and the internal reservoir 410 should remain selectively closed
while the external buoyancy chamber 405 is being filled to cause
the underwater vehicle 100 to ascend.
[0082] In the illustrated embodiment, a check valve 450 is provided
between the line returning fluid from the external bladder 405 to
the internal reservoir 410 and the Stage 1 pump 460a. This check
valve can prevent fluid returning to the internal reservoir 405
from being diverted to the Stage 1 pump 460a.
[0083] While atmospheric pressure can be sufficient to drive fluid
from the external bladder 405 to the internal reservoir 410,
certain embodiments of the present teachings also contemplate using
one or more of the pumps 460a, 460b, 460n to drive fluid from the
external bladder 405 to the internal reservoir 410, for example if
fluid is not moving therebetween or if fluid is not moving fast
enough therebetween to achieve a desired rate of descent.
[0084] The illustrated exemplary embodiments of the present
teachings eliminate the impact of serial placement of stages 415,
420, 425, by placing the stages in parallel. Serial placement of
the stages can impede an optimal performance of stages downstream
or upstream in the system 400. If, for example, a smaller pump was
positioned between a larger pump and the reservoir 410, the smaller
pump could restrict the larger pump's access to the reservoir,
making it less efficient and/or slower for the larger pump to move
fluid from the reservoir 410 to the external bladder 405. Pumps
arranged in series between the reservoir 410 and the bladder 405,
rather than in parallel as illustrated in FIG. 5, would tend to add
frictional and orifice (size) restrictions that can impede fluid
flow.
[0085] Certain embodiments of the present teachings can combine two
or more stages 415, 420, 425, to achieve either greater total
pressure output to overcome pressures at deeper depths 250 or to
increase the rate of change of buoyancy by pumping more fluid into
the bladder 405 to increase a rate of ascent. Certain embodiments
of a control system 400 for an embodiment utilizing two stages to
increase a rate of change in buoyancy can, for example, sense the
rate at which buoyancy of the underwater vehicle 100 is being
changed, which in some embodiments can be determined by the
displacement of an internal plate inside the fluid reservoir 410,
and in other embodiments by, for example, measuring a reservoir
pressure. When the rate of buoyancy change reaches or exceeds a
level required to achieve the underwater vehicle ascent or descent
rate desired in the dive profile, one of the stages can be halted
to save energy. The stage to be halted can depend, for example, on
the underwater vehicle's 100 depth. For example, if the underwater
vehicle 100 is in deeper water 250 requiring use of a stage 1 pump
460a, the stage 2 pump 460b would be halted. Otherwise, if the
underwater vehicle 100 is in shallower water 200 requiring use of a
stage 2 pump 460b, the stage 1 pump would be halted. If less than
all of the stages 415, 420, 425, of the system 400 are being
utilized and the rate of buoyancy change falls below a desired
level, one or more additional stages can be switched on to provide
additional buoyancy fluid flow.
[0086] FIG. 6 is a schematic diagram illustrating another exemplary
embodiment of a multi-stage buoyancy system 400 in accordance with
the present teachings. The exemplary embodiment comprises a main
pump 462a and a boost pump 462b for pumping fluid from an internal
reservoir 410 to an external bladder 405. The main pump 462a can
comprise, for example, a high pressure pump. The boost pump 462b
can comprise, for example, a lower pressure pump. As shown, fluid
can travel from the internal reservoir 410 to the external bladder
405 to cause ascent via a first path 415 and/or a second path 420.
The first path 415 includes the boost pump 462b, a filter 455, and
a check valve 450, the check valve ensuring that fluid flows
through this path only in the desired direction. A filter 455 is
not essential, but can protect the system from contaminants in the
fluid that would decrease the flow or clog the valves. The second
path comprises the main pump 462a with a check valve 450 on either
side thereof, each check valve ensuring that fluid flows through
the second path 420 only in a desired direction.
[0087] During a descent, movement from the external bladder 405 to
the internal reservoir 410 is called `bleeding` and the ambient
underwater pressure is used to push fluid from the external bladder
405 into the underwater vehicle's internal reservoir 410 by
pressing on the external bladder 405. In addition, the autonomous
underwater vehicle 100 can have a negative internal pressure that
assists the bleeding process and encourages fluid flow back to the
internal reservoir 410 when a high pressure (h.p.) return valve 452
between the external bladder 405 and the internal reservoir 410 is
opened.
[0088] In certain embodiments, the check valve 450c in the second
path 420, located outside the pressure hull 320, is located within
the external bladder 405 and can prevent fluid from flowing back
into the pump(s) 462a, 462b. Because the external bladder 405 is
both elastic and exposed to the ambient pressure of the surrounding
water, it will experience an internal pressure that tends to push
fluid back toward the pump(s). The check valve 450c located outside
the hull 320 (e.g., inside the external bladder 405) serves as a
backflow preventer, making the return valve 452 the only outlet
from the external bladder 405. The return valve 452 is selectively
openable and only opened when it is desirable to allow fluid to
bleed from the external bladder 405.
[0089] In certain embodiments of the present teachings, a
flow-through connection can exist through an intake reservoir 463
of the main pump 462a. Pressure from the boost pump 462b can flow
to the external bladder 405 until a predetermined ambient pressure
of, for example, 200 psi exists. When the predetermined ambient
pressure is reached, fluid from the boost pump 462b can be sent
(circuitously but effectively) through the main pump's 462a intake
reservoir 463 via a flow-through connection 464 and back to the
internal reservoir 410. The flow-through connection 464 thus can
function as a safety path.
[0090] A 425 path exists for fluid to flow from the external
bladder 405 to the internal bladder 410 to cause the underwater
vehicle 100 to have a decreased apparent displacement and a
decreased buoyancy, and therefore to descend, the path including a
return valve 452 such as an electronically actuated solenoid valve
(e.g., a Skinner valve) 452 as shown in the embodiment of FIG.
5.
[0091] The autonomous underwater vehicle 100 can comprise a
variable buoyancy displacement chamber or variable volume enclosure
that can be offset from the center of gravity CG of the underwater
vehicle 100, providing a means to change the displacement volume or
the mass of the underwater vehicle 100 relative to its center of
gravity CG, for example to tip the nose 115 of the underwater
vehicle up or down. For example, such a mass distribution mechanism
117 can comprises a vehicle battery or another defined mass 117
within the underwater vehicle that can be adjusted within the
underwater vehicle to tip the nose 115 of the underwater vehicle
100 up or down, or to roll the underwater vehicle 100 to its left
or right. Movement of the mass distribution mechanism 117 can be
controlled by the control system 105, allowing the control system
105 to steer the underwater vehicle 100 as needed to cause the
underwater vehicle 100 to descend to desired depths 200, 250, 260a,
260b, 260n, ascend to the water surface 205, roll/steer left or
right, or keep station as might be determined by the buoyancy of
the underwater vehicle 100 relative to the surrounding ambient
water and the center of buoyancy CB of the underwater vehicle
100.
[0092] The present teachings provide a multi-stage buoyancy engine
or system 400 in which two or more stages 415, 420, 425, can be
combined to increase the rate of buoyancy change as determined by
the control system 105 to maintain a desired rate of horizontal
and/or vertical velocity for the vehicle 100 in accordance with a
predetermined dive profile plan. A bypass system such as the bypass
valves 450 disclosed above for the multiple stages 415, 420, 425,
of the buoyancy engine or system 400 enables use of one or more
stages to obtain optimal energy consumption at a given depth, with
no significant impedance or degradation of efficiency imposed by
any other stage of the system 400.
[0093] Various embodiments of the present teachings provide an
arrangement of multiple stages 415, 420, 425, such that they can be
combined to provide a higher rate of buoyancy change or higher
torque, whereby a bypass system allows the stages to be provided in
parallel. Various embodiments can also comprise a mechanism to
change the center of gravity of the autonomous underwater vehicle
to cause the underwater vehicle to roll (rotation about the
longitudinal axis of the vehicle) and pitch (rotation about the
lateral axis of the vehicle), such that the attitude of the vehicle
can be changed to provide a desired glide angle relative to forward
motion. The external bladder 405 can be used to cause the
underwater vehicle 100 to roll and pitch, and can change the center
of gravity of the autonomous underwater vehicle 100.
[0094] As depicted in FIGS. 7-9, one or more known energy storage
systems 600a, 600b onboard the autonomous underwater vehicle 100
can power the fluid displacement mechanisms 460a, 460b, 460n, the
sensors 110, 112, 114, and the control system 105. In certain
embodiments, the energy storage systems 600a, 600b can comprise one
or more rechargeable (e.g., lithium) batteries.
[0095] As set forth above, various embodiments of the present
teachings comprise a control system 400 for an autonomous
underwater vehicle 100, the control system 105 comprising a control
computer, sensors to determine depth, heading angles, and rate of
descent, and a buoyancy system 400 for changing the apparent
displacement or mass of the underwater vehicle using fluid
displacement mechanisms 460a, 460b, 460n to move fluid between an
internal reservoir 405 and an external bladder 410.
[0096] Certain embodiments of the present teachings provide an
algorithm for determining the appropriate fluid displacement
mechanism to use to achieve a desired change in buoyancy to
maintain ascent or descent at a specified velocity through a
specific range of depths. The fluid displacement mechanisms can
comprise a hydraulic system configured with multiple pumping stages
or alternate gearing ratios that can efficiently transfer work from
one stage to another without significant impairment of a selected
stage, and can work in concert or separately to produce changes in
buoyancy with respect to the ambient pressure in effect at the time
of execution of buoyancy change.
[0097] The present teachings provide a configuration of controls,
sensors, and fluid displacement mechanisms that can include motors,
pistons, or similar mechanisms that enable a change of buoyancy of
the autonomous underwater vehicle in accordance with its
environment, to minimize its expenditure of stored energy. An
advanced method uses a continuously variable transmission to
effectively obtain the benefits of a large number of physically
separate stages by employing a single stage having continuously
changeable torque, flow rate, and pressure outputs.
[0098] The present teachings also comprise a control algorithm for
execution by the controller 105 that can store a desired path 255
of the autonomous underwater vehicle 100 including a depth profile
and bathymetric information about the intended path of travel 255
of the vehicle 100, such that appropriate buoyancy control actions
can be programmed to use the most efficient employment of fluid
displacement mechanisms to minimize utilization of onboard stored
energy.
[0099] An autonomous underwater vehicle 100 employing control and
buoyancy systems in accordance with the present teachings can
travel across long distances (e.g., thousands of kilometers) over
durations of many months using buoyancy changes that combine
algorithms, controls, and multi-stage buoyancy control 400 to
conserve onboard stored energy by utilizing an optimized fluid
displacement strategy, selecting the most efficient fluid
displacement mechanism(s) to traverse both shallow water 200 and
deep water diving profiles 250.
[0100] Other embodiments of the present teachings will be apparent
to those skilled in the art from consideration of the specification
and practice of the teachings disclosed herein. It is intended that
the specification and examples be considered as exemplary only,
with a true scope and spirit of the present teachings being
indicated by the following claims.
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