U.S. patent application number 15/863973 was filed with the patent office on 2018-05-10 for systems and methods for controlling rotation and twist of a tether.
The applicant listed for this patent is X DEVELOPMENT LLC. Invention is credited to Bryan Christopher GilroySmith, Brian Hachtmann, Elias Wolfgang Patten, Damon Vander Lind.
Application Number | 20180127113 15/863973 |
Document ID | / |
Family ID | 54929681 |
Filed Date | 2018-05-10 |
United States Patent
Application |
20180127113 |
Kind Code |
A1 |
Patten; Elias Wolfgang ; et
al. |
May 10, 2018 |
Systems and Methods for Controlling Rotation and Twist of a
Tether
Abstract
A system may include a tether, a slip ring, a tether gimbal
assembly, a drive mechanism, a control system. The tether may
include a distal tether end coupled to an aerial vehicle, a
proximate tether end, and at least one insulated electrical
conductor coupled to the aerial vehicle. The slip ring may include
a fixed portion and a rotatable portion, where the rotatable
portion is coupled to the tether. The tether gimbal assembly may be
rotatable about at least one axis and is coupled to the fixed
portion of the slip ring. The drive mechanism may be coupled to the
slip ring and configured to rotate the rotatable portion of the
slip ring. And the control system may be configured to operate the
drive mechanism to control twist in the tether.
Inventors: |
Patten; Elias Wolfgang;
(Seattle, WA) ; Vander Lind; Damon; (Alameda,
CA) ; GilroySmith; Bryan Christopher; (San Francisco,
CA) ; Hachtmann; Brian; (San Martin, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
X DEVELOPMENT LLC |
Mountain View |
CA |
US |
|
|
Family ID: |
54929681 |
Appl. No.: |
15/863973 |
Filed: |
January 7, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14586909 |
Dec 30, 2014 |
9884692 |
|
|
15863973 |
|
|
|
|
62019273 |
Jun 30, 2014 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F05B 2240/921 20130101;
Y02E 10/723 20130101; B64F 3/02 20130101; F03D 7/02 20130101; B64C
39/022 20130101; Y02E 10/72 20130101 |
International
Class: |
B64F 3/02 20060101
B64F003/02; F03D 7/02 20060101 F03D007/02 |
Claims
1. A system comprising: a tether comprising: a distal tether end
coupled to an aerial vehicle; a proximate tether end; and at least
one insulated electrical conductor coupled to the aerial vehicle,
wherein the tether has an amount of twist between the distal tether
end and the proximate tether end; a tether gimbal assembly, wherein
the tether gimbal assembly is coupled to the tether and is
rotatable about at least a horizontal axis or an azimuth axis; a
drive mechanism coupled to the tether at the proximate tether end,
wherein the drive mechanism rotates the tether about a long axis of
the tether that extends between the distal tether end and the
proximate tether end; and a control system, wherein the control
system operates the drive mechanism to change the amount of twist
in the tether.
2. The system of claim 1, wherein the control system operates the
drive mechanism in a lag mode.
3. The system of claim 1, wherein the control system operates the
drive mechanism in a lead mode.
4. The system of claim 1, wherein the control system operates the
drive mechanism by activating and deactivating the drive
mechanism.
5. The system of claim 1, wherein the control system operates the
drive mechanism by causing the drive mechanism to rotate the tether
at a constant rate.
6. The system of claim 1, wherein the control system operates the
drive mechanism by causing the drive mechanism to rotate the tether
at a variable rate.
7. A system comprising: a tether comprising: a distal tether end
coupled to an aerial vehicle; a proximate tether end; and at least
one insulated electrical conductor coupled to the aerial vehicle; a
tether gimbal assembly, wherein the tether gimbal assembly is
coupled to the tether and is rotatable about at least a horizontal
axis or an azimuth axis; and a resistive bearing system coupled to
the tether gimbal assembly, wherein the resistive bearing system is
configured to allow the proximate tether end to rotate when a
torque at the proximate tether end exceeds a slip limit, and
further configured to inhibit the rotation of the proximate tether
end when the torque does not exceed the slip limit.
8. The system of claim 7, wherein the resistive bearing system
comprises a brake.
9. The system of claim 7, wherein the resistive bearing system
comprises a friction brake.
10. The system of claim 7, wherein the slip limit is based at least
in part on a tension of the tether.
11. The system of claim 7, wherein the tether further comprises a
torque layer having at least one fiber, wherein the at least one
fiber is helically wound around a length of the tether over the at
least one insulated conductor, and wherein the at least one fiber
is configured to provide a torque to drive the resistive bearing
system.
12. The system of claim 7 further comprising a slip ring comprising
a fixed portion and a rotatable portion, wherein the rotatable
portion of the slip ring is coupled to the tether.
13. The system of claim 7 further comprising: a ground station; and
a slip ring comprising a fixed portion and a rotatable portion,
wherein the fixed portion of the slip ring is coupled to the ground
station.
14. The system of claim 7 further comprising a slip ring comprising
a fixed portion and a rotatable portion, wherein the fixed portion
of the slip ring is coupled to the tether gimbal assembly.
15. A system comprising: a tether comprising: a distal tether end
coupled to an aerial vehicle; a proximate tether end; and at least
one insulated electrical conductor coupled to the aerial vehicle,
wherein the tether has an amount of twist between the distal tether
end and the proximate tether end; a tether gimbal assembly, wherein
the tether gimbal assembly is coupled to the tether and is
rotatable about at least a horizontal axis or an azimuth axis; and
a resistive bearing system coupled to the tether gimbal assembly,
wherein the resistive bearing system is configured to allow the
proximate tether end to rotate and to provide a resistance to the
rotational torque of the tether so as to maintain the amount of
twist in the tether within a determined range of values.
16. The system of claim 15, wherein the resistive bearing system
comprises a brake.
17. The system of claim 15, wherein the resistive bearing system
comprises a friction brake.
18. The system of claim 15 further comprising a slip ring
comprising a fixed portion and a rotatable portion, wherein the
rotatable portion of the slip ring is coupled to the tether.
19. The system of claim 15 further comprising: a ground station;
and a slip ring comprising a fixed portion and a rotatable portion,
wherein the fixed portion of the slip ring is coupled to the ground
station.
20. The system of claim 15 further comprising a slip ring
comprising a fixed portion and a rotatable portion, wherein the
fixed portion of the slip ring is coupled to the tether gimbal
assembly.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 14/586,909, filed Dec. 30, 2014, which claims priority to U.S.
Provisional Application No. 62/019,273, filed Jun. 30, 2014. The
entire disclosure contents of U.S. application Ser. No. 14/586,909
and U.S. Provisional Application No. 62/019,273 are herewith
incorporated by reference into the present application.
BACKGROUND
[0002] Unless otherwise indicated herein, the materials described
in this section are not prior art to the claims in this application
and are not admitted to be prior art by inclusion in this
section.
[0003] Power generation systems may convert chemical and/or
mechanical energy (e.g., kinetic energy) to electrical energy for
various applications, such as utility systems. As one example, a
wind energy system may convert kinetic wind energy to electrical
energy.
SUMMARY
[0004] Systems and methods for controlling rotation and twist of a
tether are described herein. More specifically, example embodiments
generally relate to systems that incorporate a ground station for
tethering aerial vehicles. During certain flight modes, the tether
connecting the aerial vehicle to the ground station may twist as
the aerial vehicle orbits about an axis relative to the ground
station. Beneficially, embodiments described herein may control
rotation and twist of the tether so as to avoid breaking components
of the tether and/or improve a fatigue life of the tether.
[0005] In one aspect, an example system may include a tether that
includes a distal tether end coupled to an aerial vehicle, a
proximate tether end, and at least one insulated electrical
conductor coupled to the aerial vehicle; a slip ring that includes
a fixed portion and a rotatable portion, where the rotatable
portion is coupled to the tether; a tether gimbal assembly, where
the tether gimbal assembly is rotatable about at least one axis and
is coupled to the fixed portion of the slip ring; a drive mechanism
coupled to the slip ring and configured to rotate the rotatable
portion of the slip ring relative to the fixed portion; and a
control system configured to operate the drive mechanism to control
twist in the tether.
[0006] In another aspect, a system may include a ground station; a
tether that includes a distal tether end coupled to an aerial
vehicle, a proximate tether end, and at least one insulated
electrical conductor coupled to the aerial vehicle, a slip ring
that includes a fixed portion and a rotatable portion, where the
fixed portion is coupled to the ground station and the rotatable
portion is coupled to the tether; a tether gimbal assembly, where
the tether gimbal assembly is rotatable about at least one axis,
and where the tether passes through the tether gimbal assembly; a
drive mechanism coupled to the slip ring and configured to rotate
the rotatable portion of the slip ring relative to the fixed
portion; and a control system configured to operate the drive
mechanism to control twist in the tether.
[0007] In another aspect, a system may include a tether that
includes a distal tether end coupled to an aerial vehicle; a
proximate tether end; and at least one insulated electrical
conductor coupled to the aerial vehicle; a slip ring comprising a
fixed portion and a rotatable portion, where the rotatable portion
is coupled to the tether; a tether gimbal assembly, where the
tether gimbal assembly is rotatable about at least one axis; and a
resistive bearing system coupled to the slip ring, where the
resistive bearing system is configured to allow the rotatable
portion of the slip ring to rotate relative to the fixed portion
when a torque provided by the tether exceeds a slip limit, and
further configured to inhibit the rotation of the rotatable portion
of the slip ring relative to the fixed portion when the torque
provided by the tether does not exceed the slip limit.
[0008] In another aspect, a system may include a tether that
includes a distal tether end coupled to an aerial vehicle; a
proximate tether end; and at least one insulated electrical
conductor coupled to the aerial vehicle; a slip ring comprising a
fixed portion and a rotatable portion, where the rotatable portion
is coupled to the tether; a tether gimbal assembly, where the
tether gimbal assembly is rotatable about at least one axis; and a
resistive bearing system coupled to the slip ring, where the
resistive bearing system is configured to allow the rotatable
portion of the slip ring to rotate relative to the fixed portion
and to provide a resistance to the rotational torque of the tether
so as to maintain the twist in the tether within a determined range
of values.
[0009] In another aspect, a method may involve launching an aerial
vehicle connected to a tether, transitioning the aerial vehicle to
crosswind flight, and controlling, by a control system, an amount
of twist in the tether during crosswind flight.
[0010] In yet another aspect, a system may include means for
launching an aerial vehicle connected to a tether, means for
transitioning the aerial vehicle to crosswind flight, and means for
controlling an amount of twist in the tether during crosswind
flight.
[0011] In another aspect, a system may include a tether that
includes a distal tether end coupled to an aerial vehicle; a
proximate tether end; and at least one insulated electrical
conductor coupled to the aerial vehicle; a tether gimbal assembly,
where the tether gimbal assembly is coupled to the tether and is
rotatable about at least one axis; a drive mechanism coupled to the
tether and configured to rotate the tether; and a control system
configured to operate the drive mechanism to control twist in the
tether.
[0012] In another aspect, a system may include a tether that
includes a distal tether end coupled to an aerial vehicle; a
proximate tether end; and at least one insulated electrical
conductor coupled to the aerial vehicle; a slip ring comprising a
fixed portion and a rotatable portion, wherein the rotatable
portion is coupled to the tether; a tether gimbal assembly, wherein
the tether gimbal assembly is rotatable about at least one axis and
is coupled to the fixed portion of the slip ring; a drive mechanism
coupled to the slip ring and configured to rotate the rotatable
portion of the slip ring relative to the fixed portion; and a
control system configured to operate the drive mechanism to control
twist in the tether.
[0013] In another aspect, a system may include a tether that
includes a distal tether end coupled to an aerial vehicle; a
proximate tether end; and at least one insulated electrical
conductor coupled to the aerial vehicle; a tether gimbal assembly,
where the tether gimbal assembly is coupled to the tether and is
rotatable about at least one axis; and a resistive bearing system
coupled to the tether gimbal assembly, where the resistive bearing
system is configured to allow the proximate tether end to rotate
when a torque at the proximate tether end exceeds a slip limit, and
further configured to inhibit the rotation of the proximate tether
end when the torque does not exceed the slip limit.
[0014] In yet another aspect, a system may include a tether that
includes a distal tether end coupled to an aerial vehicle; a
proximate tether end; and at least one insulated electrical
conductor coupled to the aerial vehicle; a tether gimbal assembly,
where the tether gimbal assembly is coupled to the tether and is
rotatable about at least one axis; and a resistive bearing system
coupled to the tether gimbal assembly, where the resistive bearing
system is configured to allow the proximate tether end to rotate
and to provide a resistance to the rotational torque of the tether
so as to maintain the twist in the tether within a determined range
of values.
[0015] These as well as other aspects, advantages, and
alternatives, will become apparent to those of ordinary skill in
the art by reading the following detailed description, with
reference where appropriate to the accompanying drawings.
BRIEF DESCRIPTION OF THE FIGURES
[0016] FIG. 1 depicts an Airborne Wind Turbine (AWT), according to
an example embodiment.
[0017] FIG. 2 is a simplified block diagram illustrating components
of an AWT, according to an example embodiment.
[0018] FIG. 3 depicts an aerial vehicle, according to an example
embodiment.
[0019] FIGS. 4a-c illustrate twist in a tether, according to an
example embodiment.
[0020] FIG. 5a depicts an aerial vehicle coupled to a ground
station via a tether, according to an example embodiment.
[0021] FIG. 5b depicts an aerial vehicle coupled to a ground
station via a tether, according to an example embodiment.
[0022] FIG. 6a depicts a system for controlling rotation and twist
of a tether, according to an example embodiment.
[0023] FIG. 6b depicts a foreshortened view of a tether section,
according to an example embodiment.
[0024] FIG. 7 depicts a system for controlling rotation and twist
of a tether, according to an example embodiment.
[0025] FIG. 8 depicts a tether in cross-section, according to an
example embodiment.
[0026] FIG. 9 depicts a tether in cross-section, according to an
example embodiment.
[0027] FIG. 10 depicts a tether in cross-section, according to an
example embodiment.
[0028] FIG. 11 is a flow chart illustrating a method, according to
an example embodiment.
DETAILED DESCRIPTION
[0029] Exemplary systems and methods are described herein. It
should be understood that the word "exemplary" is used herein to
mean "serving as an example, instance, or illustration." Any
embodiment or feature described herein as "exemplary" or
"illustrative" is not necessarily to be construed as preferred or
advantageous over other embodiments or features. More generally,
the embodiments described herein are not meant to be limiting. It
will be readily understood that certain aspects of the disclosed
systems and methods can be arranged and combined in a wide variety
of different configurations, all of which are contemplated
herein.
I. OVERVIEW
[0030] Illustrative embodiments relate to aerial vehicles, which
may be used in a wind energy system, such as an Airborne Wind
Turbine (AWT). In particular, illustrative embodiments may relate
to or take the form of systems for controlling rotation and twist
of a tether that connects an aerial vehicle to a ground
station.
[0031] By way of background, an AWT may include an aerial vehicle
that flies in a closed path, such as a substantially circular path,
to convert kinetic wind energy to electrical energy. In an
illustrative implementation, the aerial vehicle may be connected to
a ground station via a tether. While tethered, the aerial vehicle
can: (i) fly at a range of elevations and substantially along the
path, and return to the ground, and (ii) transmit electrical energy
to the ground station via the tether. (In some implementations, the
ground station may transmit electricity to the aerial vehicle for
take-off and/or landing.)
[0032] In an AWT, an aerial vehicle may rest in and/or on a ground
station (or perch) when the wind is not conducive to power
generation. When the wind is conducive to power generation, such as
when a wind speed may be 3.5 meters per second (m/s) at an altitude
of 200 meters (m), the ground station may deploy (or launch) the
aerial vehicle. In addition, when the aerial vehicle is deployed
and the wind is not conducive to power generation, the aerial
vehicle may return to the ground station.
[0033] Moreover, in an AWT, an aerial vehicle may be configured for
hover flight and crosswind flight. Crosswind flight may be used to
travel in a motion, such as a substantially circular motion, and
thus may be the primary technique that is used to generate
electrical energy. Hover flight in turn may be used by the aerial
vehicle to prepare and position itself for crosswind flight. In
particular, the aerial vehicle could ascend to a location for
crosswind flight based at least in part on hover flight. Further,
the aerial vehicle could take-off and/or land via hover flight.
[0034] In hover flight, a span of a main wing of the aerial vehicle
may be oriented substantially parallel to the ground, and one or
more propellers of the aerial vehicle may cause the aerial vehicle
to hover over the ground. In some implementations, the aerial
vehicle may vertically ascend or descend in hover flight. Moreover,
in crosswind flight, the aerial vehicle may be oriented, such that
the aerial vehicle may be propelled by the wind substantially along
a closed path, which as noted above, may convert kinetic wind
energy to electrical energy. In some implementations, one or more
rotors of the aerial vehicle may generate electrical energy by
slowing down the incident wind.
[0035] During crosswind flight, the tether connecting the aerial
vehicle to the ground station may twist as the aerial vehicle
orbits about an axis relative to the ground station. In some
implementations, the amount of twist between the ground station end
of the tether and the aerial vehicle end of the tether may vary
based on a number of parameters during crosswind flight. Twist in
the tether may have beneficial or detrimental effects on the
system, depending on the system design and operating
parameters.
[0036] Embodiments described herein may allow for controlling the
rotation and twist of the tether for maximum benefit. In an
illustrative implementation, a system may control the rotation, and
amount of twist, of the tether when the tether is orbiting during
crosswind flight of the aerial vehicle. In the case of a tether
with electrical conductor(s), it may be desirable to maintain the
twist in the tether within a certain range to reduce a strain of
the conductors. Beneficially, such a reduction of the strain may
avoid breaking the conductors and/or may improve a fatigue life of
the tether.
[0037] In some implementations, a system may include a tether, a
tether gimbal assembly, a slip ring, a drive mechanism, and a
control system. In an example embodiment, the control system may be
configured to operate the drive mechanism to rotate the slip ring
and the tether in order to control the amount of twist in the
tether. With this arrangement, the amount of twist in the tether
during crosswind flight of the aerial vehicle may be actively
controlled.
[0038] Moreover, in some implementations, a system may include a
tether, a tether gimbal assembly, a slip ring, and a resistive
bearing system. In an example embodiment, the resistive bearing
system may be used to passively control tether twist during
crosswind flight of the aerial vehicle. For example, the resistive
bearing system may inhibit or prevent rotation of the slip ring and
tether when the applied torque from a twisted tether is below a
threshold level (which may be referred to as a slip limit). When
the applied torque from a twisted tether is above the slip limit,
the bearing system may allow the slip ring and tether to
rotate.
[0039] As another example, the resistive bearing system may be
configured to allow the rotatable portion of the slip ring to
rotate relative to the fixed portion and to provide a resistance
(e.g., friction) to the rotational torque of the tether so as to
maintain the twist in the tether within a determined range of
values.
[0040] Other embodiments may relate to methods for controlling
rotation and twist of a tether. For instance, some implementations
may involve launching an aerial vehicle connected to a tether,
transitioning the aerial vehicle to crosswind flight, and
controlling, by a control system, an amount of twist in the tether
during crosswind flight.
II. ILLUSTRATIVE SYSTEMS
[0041] A. Airborne Wind Turbine (AWT)
[0042] FIG. 1 depicts an AWT 100, according to an example
embodiment. In particular, the AWT 100 includes a ground station
110, a tether 120, and an aerial vehicle 130. As shown in FIG. 1,
the tether 120 may be connected to the aerial vehicle on a first
end and may be connected to the ground station 110 on a second end.
In this example, the tether 120 may be attached to the ground
station 110 at one location on the ground station 110, and attached
to the aerial vehicle 130 at three locations on the aerial vehicle
130. However, in other examples, the tether 120 may be attached at
multiple locations to any part of the ground station 110 and/or the
aerial vehicle 130.
[0043] The ground station 110 may be used to hold and/or support
the aerial vehicle 130 until it is in an operational mode. The
ground station 110 may also be configured to allow for the
repositioning of the aerial vehicle 130 such that deploying of the
device is possible. Further, the ground station 110 may be further
configured to receive the aerial vehicle 130 during a landing. The
ground station 110 may be formed of any material that can suitably
keep the aerial vehicle 130 attached and/or anchored to the ground
while in hover flight, crosswind flight, and other flight modes,
such as forward flight (which may be referred to as airplane-like
flight). In some implementations, a ground station 110 may be
configured for use on land. However, a ground station 110 may also
be implemented on a body of water, such as a lake, river, sea, or
ocean. For example, a ground station could include or be arranged
on a floating off-shore platform or a boat, among other
possibilities. Further, a ground station 110 may be configured to
remain stationary or to move relative to the ground or the surface
of a body of water.
[0044] In addition, the ground station 110 may include one or more
components (not shown), such as a winch, that may vary a length of
the tether 120. For example, when the aerial vehicle 130 is
deployed, the one or more components may be configured to pay out
and/or reel out the tether 120. In some implementations, the one or
more components may be configured to pay out and/or reel out the
tether 120 to a predetermined length. As examples, the
predetermined length could be equal to or less than a maximum
length of the tether 120. Further, when the aerial vehicle 130
lands in the ground station 110, the one or more components may be
configured to reel in the tether 120.
[0045] The tether 120 may transmit electrical energy generated by
the aerial vehicle 130 to the ground station 110. In addition, the
tether 120 may transmit electricity to the aerial vehicle 130 in
order to power the aerial vehicle 130 for takeoff, landing, hover
flight, and/or forward flight. The tether 120 may be constructed in
any form and using any material which may allow for the
transmission, delivery, and/or harnessing of electrical energy
generated by the aerial vehicle 130 and/or transmission of
electricity to the aerial vehicle 130. The tether 120 may also be
configured to withstand one or more forces of the aerial vehicle
130 when the aerial vehicle 130 is in an operational mode. For
example, the tether 120 may include a core configured to withstand
one or more forces of the aerial vehicle 130 when the aerial
vehicle 130 is in hover flight, forward flight, and/or crosswind
flight. The core may be constructed of any high strength fibers. In
some examples, the tether 120 may have a fixed length and/or a
variable length. For instance, in at least one such example, the
tether 120 may have a length of 140 meters.
[0046] The aerial vehicle 130 may be configured to fly
substantially along a closed path 150 to generate electrical
energy. The term "substantially along," as used in this disclosure,
refers to exactly along and/or one or more deviations from exactly
along that do not significantly impact generation of electrical
energy.
[0047] The aerial vehicle 130 may include or take the form of
various types of devices, such as a kite, a helicopter, a wing
and/or an airplane, among other possibilities. The aerial vehicle
130 may be formed of solid structures of metal, plastic and/or
other polymers. The aerial vehicle 130 may be formed of any
material which allows for a high thrust-to-weight ratio and
generation of electrical energy which may be used in utility
applications. Additionally, the materials may be chosen to allow
for a lightning hardened, redundant and/or fault tolerant design
which may be capable of handling large and/or sudden shifts in wind
speed and wind direction.
[0048] The closed path 150 may be various different shapes in
various different embodiments. For example, the closed path 150 may
be substantially circular. And in at least one such example, the
closed path 150 may have a radius of up to 265 meters. The term
"substantially circular," as used in this disclosure, refers to
exactly circular and/or one or more deviations from exactly
circular that do not significantly impact generation of electrical
energy as described herein. Other shapes for the closed path 150
may be an oval, such as an ellipse, the shape of a jelly bean, the
shape of the number of 8, etc.
[0049] The aerial vehicle 130 may be operated to travel along one
or more revolutions of the closed path 150. As shown in FIG. 1, the
number of revolutions of the closed path 150 that the aerial
vehicle 130 has traveled along may be represented by N.
[0050] B. Illustrative Components of an AWT
[0051] FIG. 2 is a simplified block diagram illustrating components
of the AWT 200. The AWT 100 may take the form of or be similar in
form to the AWT 200. In particular, the AWT 200 includes a ground
station 210, a tether 220, and an aerial vehicle 230. The ground
station 110 may take the form of or be similar in form to the
ground station 210, the tether 120 may take the form of or be
similar in form to the tether 220, and the aerial vehicle 130 may
take the form of or be similar in form to the aerial vehicle
230.
[0052] As shown in FIG. 2, the ground station 210 may include one
or more processors 212, data storage 214, and program instructions
216. A processor 212 may be a general-purpose processor or a
special purpose processor (e.g., digital signal processors,
application specific integrated circuits, etc.). The one or more
processors 212 can be configured to execute computer-readable
program instructions 216 that are stored in a data storage 214 and
are executable to provide at least part of the functionality
described herein.
[0053] The data storage 214 may include or take the form of one or
more computer-readable storage media that may be read or accessed
by at least one processor 212. The one or more computer-readable
storage media can include volatile and/or non-volatile storage
components, such as optical, magnetic, organic or other memory or
disc storage, which may be integrated in whole or in part with at
least one of the one or more processors 212. In some embodiments,
the data storage 214 may be implemented using a single physical
device (e.g., one optical, magnetic, organic or other memory or
disc storage unit), while in other embodiments, the data storage
214 can be implemented using two or more physical devices.
[0054] As noted, the data storage 214 may include computer-readable
program instructions 216 and perhaps additional data, such as
diagnostic data of the ground station 210. As such, the data
storage 214 may include program instructions to perform or
facilitate some or all of the functionality described herein.
[0055] In a further respect, the ground station 210 may include a
communication system 218. The communication system 218 may include
one or more wireless interfaces and/or one or more wireline
interfaces, which allow the ground station 210 to communicate via
one or more networks. Such wireless interfaces may provide for
communication under one or more wireless communication protocols,
such as Bluetooth, WiFi (e.g., an IEEE 802.11 protocol), Long-Term
Evolution (LTE), WiMAX (e.g., an IEEE 802.16 standard), a
radio-frequency ID (RFID) protocol, near-field communication (NFC),
and/or other wireless communication protocols. Such wireline
interfaces may include an Ethernet interface, a Universal Serial
Bus (USB) interface, or similar interface to communicate via a
wire, a twisted pair of wires, a coaxial cable, an optical link, a
fiber-optic link, or other physical connection to a wireline
network. The ground station 210 may communicate with the aerial
vehicle 230, other ground stations, and/or other entities (e.g., a
command center) via the communication system 218.
[0056] In an example embodiment, the ground station 210 may include
communication systems 218 that allows for both short-range
communication and long-range communication. For example, the ground
station 210 may be configured for short-range communications using
Bluetooth and for long-range communications under a CDMA protocol.
In such an embodiment, the ground station 210 may be configured to
function as a "hot spot"; or in other words, as a gateway or proxy
between a remote support device (e.g., the tether 220, the aerial
vehicle 230, and other ground stations) and one or more data
networks, such as cellular network and/or the Internet. Configured
as such, the ground station 210 may facilitate data communications
that the remote support device would otherwise be unable to perform
by itself.
[0057] For example, the ground station 210 may provide a WiFi
connection to the remote device, and serve as a proxy or gateway to
a cellular service provider's data network, which the ground
station 210 might connect to under an LTE or a 3G protocol, for
instance. The ground station 210 could also serve as a proxy or
gateway to other ground stations or a command center, which the
remote device might not be able to otherwise access.
[0058] Moreover, as shown in FIG. 2, the tether 220 may include
transmission components 222 and a communication link 224. The
transmission components 222 may be configured to transmit
electrical energy from the aerial vehicle 230 to the ground station
210 and/or transmit electrical energy from the ground station 210
to the aerial vehicle 230. The transmission components 222 may take
various different forms in various different embodiments. For
example, the transmission components 222 may include one or more
conductors that are configured to transmit electricity. And in at
least one such example, the one or more conductors may include
aluminum and/or any other material which allows for the conduction
of electric current. Moreover, in some implementations, the
transmission components 222 may surround a core of the tether 220
(not shown).
[0059] The ground station 210 could communicate with the aerial
vehicle 230 via the communication link 224. The communication link
224 may be bidirectional and may include one or more wired and/or
wireless interfaces. Also, there could be one or more routers,
switches, and/or other devices or networks making up at least a
part of the communication link 224.
[0060] Further, as shown in FIG. 2, the aerial vehicle 230 may
include one or more sensors 232, a power system 234, power
generation/conversion components 236, a communication system 238,
one or more processors 242, data storage 244, and program
instructions 246, and a control system 248.
[0061] The sensors 232 could include various different sensors in
various different embodiments. For example, the sensors 232 may
include a global positioning system (GPS) receiver. The GPS
receiver may be configured to provide data that is typical of
well-known GPS systems (which may be referred to as a global
navigation satellite system (GNNS)), such as the GPS coordinates of
the aerial vehicle 230. Such GPS data may be utilized by the AWT
200 to provide various functions described herein.
[0062] As another example, the sensors 232 may include one or more
wind sensors, such as one or more pitot tubes. The one or more wind
sensors may be configured to detect apparent and/or relative wind.
Such wind data may be utilized by the AWT 200 to provide various
functions described herein.
[0063] Still as another example, the sensors 232 may include an
inertial measurement unit (IMU). The IMU may include both an
accelerometer and a gyroscope, which may be used together to
determine the orientation of the aerial vehicle 230. In particular,
the accelerometer can measure the orientation of the aerial vehicle
230 with respect to earth, while the gyroscope measures the rate of
rotation around an axis, such as a centerline of the aerial vehicle
230. IMUs are commercially available in low-cost, low-power
packages. For instance, the IMU may take the form of or include a
miniaturized MicroElectroMechanical System (MEMS) or a
NanoElectroMechanical System (NEMS). Other types of IMUs may also
be utilized. The IMU may include other sensors, in addition to
accelerometers and gyroscopes, which may help to better determine
position. Two examples of such sensors are magnetometers and
pressure sensors. Other examples are also possible.
[0064] While an accelerometer and gyroscope may be effective at
determining the orientation of the aerial vehicle 230, slight
errors in measurement may compound over time and result in a more
significant error. However, an example aerial vehicle 230 may be
able to mitigate or reduce such errors by using a magnetometer to
measure direction. One example of a magnetometer is a low-power,
digital 3-axis magnetometer, which may be used to realize an
orientation independent electronic compass for accurate heading
information. However, other types of magnetometers may be utilized
as well.
[0065] The aerial vehicle 230 may also include a pressure sensor or
barometer, which can be used to determine the altitude of the
aerial vehicle 230. Alternatively, other sensors, such as sonic
altimeters or radar altimeters, can be used to provide an
indication of altitude, which may help to improve the accuracy of
and/or prevent drift of the IMU. In addition, the aerial vehicle
230 may include one or more load cells configured to detect forces
distributed between a connection of the tether 220 to the aerial
vehicle 230.
[0066] As noted, the aerial vehicle 230 may include the power
system 234. The power system 234 could take various different forms
in various different embodiments. For example, the power system 234
may include one or more batteries for providing power to the aerial
vehicle 230. In some implementations, the one or more batteries may
be rechargeable and each battery may be recharged via a wired
connection between the battery and a power supply and/or via a
wireless charging system, such as an inductive charging system that
applies an external time-varying magnetic field to an internal
battery and/or charging system that uses energy collected from one
or more solar panels.
[0067] As another example, the power system 234 may include one or
more motors or engines for providing power to the aerial vehicle
230. In some implementations, the one or more motors or engines may
be powered by a fuel, such as a hydrocarbon-based fuel. And in such
implementations, the fuel could be stored on the aerial vehicle 230
and delivered to the one or more motors or engines via one or more
fluid conduits, such as piping. In some implementations, the power
system 234 may be implemented in whole or in part on the ground
station 210.
[0068] As noted, the aerial vehicle 230 may include the power
generation/conversion components 236. The power
generation/conversion components 236 could take various different
forms in various different embodiments. For example, the power
generation/conversion components 236 may include one or more
generators, such as high-speed, direct-drive generators. With this
arrangement, the one or more generators may be driven by one or
more rotors. And in at least one such example, the one or more
generators may operate at full rated power wind speeds of 11.5
meters per second at a capacity factor which may exceed 60 percent,
and the one or more generators may generate electrical power from
40 kilowatts to 600 megawatts.
[0069] Moreover, as noted, the aerial vehicle 230 may include a
communication system 238. The communication system 238 may take the
form of or be similar in form to the communication system 218. The
aerial vehicle 230 may communicate with the ground station 210,
other aerial vehicles, and/or other entities (e.g., a command
center) via the communication system 238.
[0070] In some implementations, the aerial vehicle 230 may be
configured to function as a "hot spot"; or in other words, as a
gateway or proxy between a remote support device (e.g., the ground
station 210, the tether 220, other aerial vehicles) and one or more
data networks, such as cellular network and/or the Internet.
Configured as such, the aerial vehicle 230 may facilitate data
communications that the remote support device would otherwise be
unable to perform by itself.
[0071] For example, the aerial vehicle 230 may provide a WiFi
connection to the remote device, and serve as a proxy or gateway to
a cellular service provider's data network, which the aerial
vehicle 230 might connect to under an LTE or a 3G protocol, for
instance. The aerial vehicle 230 could also serve as a proxy or
gateway to other aerial vehicles or a command station, which the
remote device might not be able to otherwise access.
[0072] As noted, the aerial vehicle 230 may include the one or more
processors 242, the program instructions 246, and the data storage
244. The one or more processors 242 can be configured to execute
computer-readable program instructions 246 that are stored in the
data storage 244 and are executable to provide at least part of the
functionality described herein. The one or more processors 242 may
take the form of or be similar in form to the one or more
processors 212, the data storage 244 may take the form of or be
similar in form to the data storage 214, and the program
instructions 246 may take the form of or be similar in form to the
program instructions 216.
[0073] Moreover, as noted, the aerial vehicle 230 may include the
control system 248. In some implementations, the control system 248
may be configured to perform one or more functions described
herein. The control system 248 may be implemented with mechanical
systems and/or with hardware, firmware, and/or software. As one
example, the control system 248 may take the form of program
instructions stored on a non-transitory computer readable medium
and a processor that executes the instructions. The control system
248 may be implemented in whole or in part on the aerial vehicle
230 and/or at least one entity remotely located from the aerial
vehicle 230, such as the ground station 210. Generally, the manner
in which the control system 248 is implemented may vary, depending
upon the particular application.
[0074] While the aerial vehicle 230 has been described above, it
should be understood that the methods and systems described herein
could involve any suitable aerial vehicle that is connected to a
tether, such as the tether 220 and/or the tether 120.
[0075] C. Illustrative Aerial Vehicle
[0076] FIG. 3 depicts an aerial vehicle 330, according to an
example embodiment. The aerial vehicle 130 and/or the aerial
vehicle 230 may take the form of or be similar in form to the
aerial vehicle 330. In particular, the aerial vehicle 330 may
include a main wing 331, pylons 332a, 332b, rotors 334a, 334b,
334c, 334d, a tail boom 335, and a tail wing assembly 336. Any of
these components may be shaped in any form which allows for the use
of components of lift to resist gravity and/or move the aerial
vehicle 330 forward.
[0077] The main wing 331 may provide a primary lift force for the
aerial vehicle 330. The main wing 331 may be one or more rigid or
flexible airfoils, and may include various control surfaces, such
as winglets, flaps (e.g., Fowler flaps, Hoerner flaps, split flaps,
and the like), rudders, elevators, spoilers, dive brakes, etc. The
control surfaces may be used to stabilize the aerial vehicle 330
and/or reduce drag on the aerial vehicle 330 during hover flight,
forward flight, and/or crosswind flight.
[0078] The main wing 331 and pylons 332a, 332b may be any suitable
material for the aerial vehicle 330 to engage in hover flight,
forward flight, and/or crosswind flight. For example, the main wing
331 and pylons 332a, 332b may include carbon fiber and/or e-glass,
and include internal supporting spars or other structures.
Moreover, the main wing 331 and pylons 332a, 332b may have a
variety of dimensions. For example, the main wing 331 may have one
or more dimensions that correspond with a conventional wind turbine
blade. As another example, the main wing 331 may have a span of 8
meters, an area of 4 meters squared, and an aspect ratio of 15.
[0079] The pylons 332a, 332b may connect the rotors 334a, 334b,
334c, and 334d to the main wing 331. In some examples, the pylons
332a, 332b may take the form of, or be similar in form to, a
lifting body airfoil (e.g., a wing). In some examples, a vertical
spacing between corresponding rotors (e.g., rotor 334a and rotor
334b on pylon 332a) may be 0.9 meters.
[0080] The rotors 334a, 334b, 334c, and 334d may be configured to
drive one or more generators for the purpose of generating
electrical energy. In this example, the rotors 334a, 334b, 334c,
and 334d may each include one or more blades, such as three blades
or four blades. The rotor blades may rotate via interactions with
the wind and be used to drive the one or more generators. In
addition, the rotors 334a, 334b, 334c, and 334d may also be
configured to provide thrust to the aerial vehicle 330 during
flight. With this arrangement, the rotors 334a, 334b, 334c, and
334d may function as one or more propulsion units, such as a
propeller. Although the rotors 334a, 334b, 334c, and 334d are
depicted as four rotors in this example, in other examples the
aerial vehicle 330 may include any number of rotors, such as less
than four rotors or more than four rotors.
[0081] A tail boom 335 may connect the main wing 331 to the tail
wing assembly 336, which may include a tail wing 336a and a
vertical stabilizer 336b. The tail boom 335 may have a variety of
dimensions. For example, the tail boom 335 may have a length of 2
meters. Moreover, in some implementations, the tail boom 335 could
take the form of a body and/or fuselage of the aerial vehicle 330.
In such implementations, the tail boom 335 may carry a payload.
[0082] The tail wing 336a and/or the vertical stabilizer 336b may
be used to stabilize the aerial vehicle 330 and/or reduce drag on
the aerial vehicle 330 during hover flight, forward flight, and/or
crosswind flight. For example, the tail wing 336a and/or the
vertical stabilizer 336b may be used to maintain a pitch of the
aerial vehicle 330 during hover flight, forward flight, and/or
crosswind flight. The tail wing 336a and the vertical stabilizer
336b may have a variety of dimensions. For example, the tail wing
336a may have a length of 2 meters. Moreover, in some examples, the
tail wing 336a may have a surface area of 0.45 meters squared.
Further, in some examples, the tail wing 336a may be located 1
meter above a center of mass of the aerial vehicle 330.
[0083] While the aerial vehicle 330 has been described above, it
should be understood that the systems and methods described herein
could involve any suitable aerial vehicle that is connected to an
airborne wind turbine tether, such as the tether 120 and/or the
tether 220.
[0084] D. Illustrative Tether Twist
[0085] FIGS. 4a-c depict twist in a tether 420, according to an
example embodiment. The tether 120 and/or the tether 220 may take
the form of or be similar in form to the tether 420. Referring to
FIG. 4a, the tether 420 includes a bridal portion 421, a proximate
tether end 422, a distal tether end 424, and a long axis 426 that
extends between the proximate tether end 422 and the distal tether
end 424. In the illustrated example, the distal tether end 424 is
coupled to the aerial vehicle 330. The proximate tether end 422 may
be coupled to a ground station (not shown), such as the ground
station 110 and/or the ground station 210. In addition, the tether
420 may include at least one insulated electrical conductor (not
shown) coupled to the aerial vehicle 330. FIGS. 4a-c, and remaining
Figures depicting tethers, are for illustrative purposes only and
may not reflect all components or connections. Further, as
illustrations the Figures may not reflect actual operating
conditions, but are merely to illustrate embodiments described. For
example, while a straight cylinder may be used to illustrate the
described tether embodiments, during orbiting crosswind flight the
tether may in practice exhibit some level of droop between the
ground station and the aerial vehicle. Further still, the relative
dimensions in the Figures may not be to scale, but are merely to
illustrate the embodiments described.
[0086] FIGS. 4a-c illustrate twist in the tether 420 between the
proximate tether end 422 and the distal tether end 424 as the
aerial vehicle 330 travels along a closed path, such as the closed
path 150. In some embodiments, an amount of twist in the tether 420
may be measured as an angular distance between a point .alpha. on
the tether 420 at the distal tether end 424 and a point .alpha.' on
the tether 420 at the proximate tether end 422. Other measurement
points are also possible. For example, an amount of twist may be at
two or more points located between the distal tether end 424 and
the proximate tether end 422. As shown in FIGS. 4a-c, an amount of
twist in the tether 420 may increase as the number of revolutions
of the closed path, N, that the aerial vehicle 330 has traveled
along increases.
[0087] For example, as shown in FIG. 4a, when N=0, an illustrative
reference line 428 on the tether 420 may extend between the point
.alpha. and the point .alpha.' that is substantially parallel to
the long axis 426. With this arrangement, the angular distance
between the point .alpha. and the point .alpha.' may be
substantially zero. Accordingly, the amount of twist in the tether
420 may be substantially zero.
[0088] The term "substantially parallel," as used in the
disclosure, refers to exactly parallel or one or more deviations
from exactly parallel that do not significantly impact controlling
rotation and twist of a tether as described herein. In addition,
the term "substantially zero," as used in this disclosure, refers
to exactly zero or one or more deviations from zero that do not
significantly impact controlling rotation and twist of a tether as
described herein.
[0089] As shown in FIG. 4b, after the aerial vehicle 330 completes
one orbit, and thus N=1, the tether may twist about the long axis
426. Thus reference line 428 may form a helix around the long axis
426. With this arrangement, when N=1, the angular distance between
the point .alpha. and the point .alpha.' may be greater than the
angular distance between the point .alpha. and the point .alpha.'
when N=0. Accordingly, when N=1, an amount of twist in the tether
420 may be greater than an amount of twist in the tether 420 when
N=0.
[0090] Further, as shown in FIG. 4c, after the aerial vehicle 330
completes two orbits, and thus N=2, the tether may further twist
about the long axis 426. In the illustrated example, the helical
pitch of reference line 428 may be greater than the helical pitch
of the reference line 428 in FIG. 4b. With this arrangement, when
N=2, the angular distance between the point .alpha. and the point
.alpha.' may be greater than the angular distance between the point
.alpha. and the point .alpha.' when N=1. Accordingly, when N=2, an
amount of twist in the tether 420 may be greater than an amount of
twist in the tether 420 when N=1.
[0091] E. Aerial Vehicle Coupled to a Ground Station Via a
Tether
[0092] FIG. 5a depicts the aerial vehicle 330 coupled to a ground
station 510 via the tether 420, according to an example embodiment.
Referring to FIG. 5a, the ground station 510 may include a winch
drum 512 and a platform 514. The ground station 110 and/or the
ground station 210 may take the form of or be similar in form to
the ground station 510. FIG. 5a is for illustrative purposes only
and may not reflect all components or connections.
[0093] As shown in FIG. 5a, the tether 420 may be coupled to a
tether gimbal assembly 542 at the proximate tether end 422 and to
the aerial vehicle 330 at the distal tether end 424. Moreover, as
shown in FIG. 5a, the tether gimbal assembly 542 may also be
coupled to the winch drum 512 which in turn may be coupled to the
platform 514. A slip ring 544 located between the tether 420 and
the tether gimbal assembly 542 may allow the tether 420 to rotate
about the long axis 426 of the tether 420 (as shown in, and
described with respect to, FIGS. 4a-c) relative to the ground
station 510.
[0094] In some embodiments, the tether gimbal assembly 542 may be
configured to rotate about one or more axes, such as a horizontal
axis 552 and an azimuth axis 554, in order to allow the proximate
tether end 422 to move in those axes in response to movement of the
aerial vehicle 330. Moreover, in some embodiments, the slip ring
544 may include a fixed portion 544a, a rotatable portion 544b, and
one or more insulated electrically conductive pathways (not shown).
The rotatable portion 544b may be coupled to the tether 420. The
fixed portion 544a may be coupled to the tether gimbal assembly
542. The one or more insulated electrically conductive pathways may
provide an electrical connection between one or more electrical
conductors in the tether, and one or more ground-side electrical
connections (not shown).
[0095] The use of the word fixed in the fixed portion 544a of the
slip ring 544 is not intended to limit fixed portion 544a to a
stationary configuration. In this example, the fixed portion 544a
may move in axes described by the tether gimbal assembly 542 (e.g.,
the horizontal axis 552 and azimuth 554), and may rotate about the
ground station 510 as the winch drum 512 rotates, but the fixed
portion 544a will not rotate about the tether 420, i.e., with
respect to the long axis 426 of the tether. Moreover, in this
example, the rotatable portion 544b of the slip ring 544 may be
coupled to the tether gimbal assembly 542 and configured to
substantially rotate with the rotation of tether 420.
[0096] As shown in FIG. 5a, a drive mechanism 546 may be coupled to
the rotatable portion 544b and configured to rotate the rotatable
portion 544b (and consequently the proximate tether end 422)
relative to the stationary portion 544a. As an example, the drive
mechanism 546 may include a servo motor.
[0097] Via the slip ring 544, the tether 420 may rotate about its
centerline along the long axis 426 as the aerial vehicle 330
orbits. The distal tether end 424 may rotate a different amount
than the proximate tether end 422, resulting in an amount of twist
along the length of the tether 420. With this arrangement, the
amount of twist in the tether 420 may vary based on a number of
parameters during crosswind flight of the aerial vehicle 330.
[0098] In a further aspect, the slip ring 544 may not be coupled to
the tether gimbal assembly 542. For example, as shown in FIG. 5b,
the slip ring 544 may be near the platform 514. As such, the tether
420 may pass through the tether gimbal assembly 542. In the
illustrated example, the fixed portion 544a of the slip ring 544
may be coupled to platform 514, the winch drum 512, or another
component of the ground station 510 and the tether 420 may be
coupled to the rotatable portion 544b of the slip ring 544 at the
proximate tether end 422. The other connections of the aerial
vehicle 330, the winch drum 512, the platform 514, the tether
gimbal assembly 542, and the drive mechanism 546, as well as other
connections, may be described with respect to FIG. 5a.
[0099] In some embodiments, a flexible coupling 548 may be used to
route the tether 420 from the tether gimbal assembly 542 to the
slip ring 544. As shown in FIG. 5b, the flexible coupling 548
includes a first end 548a and a second end 548b. The first end 548a
of the flexible coupling 548 may be coupled to the tether gimbal
assembly 542 and the second end 548b of the flexible coupling 548
may be coupled to the rotatable portion 544b of the slip ring
544.
[0100] Moreover, in some embodiments, the tether 420 may be coupled
to the tether gimbal assembly 542 at the proximate tether end 422,
and one or more cables (or wires) may be connected to the proximate
tether end 422. The one or more cables may connect the tether 420
to the slip ring 544.
[0101] F. Systems for Controlling Rotation and Twist of a
Tether
[0102] FIG. 6a depicts a system 600 for controlling rotation and
twist in the tether 420, according to an example embodiment. In
particular, the system 600 includes a control system 650. Referring
to FIG. 6a, the tether 420 may be coupled to a tether gimbal
assembly 542 at the proximate tether end 422 and to the aerial
vehicle 330 at the distal tether end 424. Additionally or
alternatively, the tether 420 may pass through the tether gimbal
assembly 542. Moreover, as shown in FIG. 6a, the tether gimbal
assembly 542 may be coupled to the winch drum 512 which in turn may
be coupled to the platform 514, the rotatable portion 544b of the
slip ring 544 may be coupled to the tether 420, the fixed portion
544a of the slip ring 544 may be coupled to the tether gimbal
assembly 542, and drive mechanism 546 may be coupled to the
rotatable portion 544b. For example, the tether 420, the slip ring
544, the tether gimbal assembly 542 connections, as well as other
connections, may be as described with respect to FIG. 5a.
[0103] Alternatively, the fixed portion 544a of the slip ring 544
may be coupled to the platform 514, the winch drum 512, or another
component of the ground station 510 as described with reference to
FIG. 5b. For example, the tether 420, the slip ring 544, the tether
gimbal assembly 542 connections, as well as other connections, may
be described with respect to FIG. 5b.
[0104] The control system 650 is configured to control operation(s)
of the system 600 and its components. In some embodiments, the
control system 650 may be configured to perform one or more
functions described herein. For example, in some embodiments, the
control system 650 may be configured to operate the drive mechanism
546 to control twist in the tether 420. In the illustrated
embodiment, the control system 650 is connected to at least the
drive mechanism 546, though other alternative or additional
connections are possible, including but not limited to the tether
420, the slip ring 544, and the aerial vehicle 330. With this
arrangement, an amount of twist in the tether 420 during crosswind
flight of the aerial vehicle 330 may be actively controlled. In
some examples, the control system 650 may be connected to at least
one component by a wired connection or a wireless connection.
[0105] The control system 650 may be similar in form to the control
system 248. For instance, the control system 650 may be implemented
with mechanical systems and/or with hardware, firmware, and/or
software. As one example, the control system 650 may take the form
of program instructions stored on a non-transitory computer
readable medium and a processor that executes the instructions. The
control system 650 may be implemented in whole or in part on the
ground station 510 and/or at least one entity remotely located from
the ground station, such as the aerial vehicle 330. Generally, the
manner in which the control system 650 is implemented may vary,
depending upon the particular application.
[0106] FIG. 6b depicts a foreshortened view of the tether 420,
according to an example embodiment. As noted, in some embodiments,
an amount of twist T in the tether 420 may be measured as an
angular distance between a point .alpha. on the tether 420 at the
distal tether end 424 and a point .alpha.' on the tether 420 at the
proximate tether end 422. Alternatively or additionally, the amount
of twist in the tether may be measured between points along the
tether other than a and .alpha.'. For example, the amount of twist
may be measured along a portion of the tether 420 near the
proximate end 422 or the distal end 424, or over multiple portions
of the tether 420. In any case, the control system 650 may be
configured to operate the drive mechanism 546 to control the amount
of twist.
[0107] Further, in some embodiments, it may be desirable for the
twist in the tether 420 to be positive. This may be accomplished by
maintaining a rate of rotation in the proximate tether end 422 via
the drive mechanism 546 such that the proximate tether end 422 is
twisted a fixed or variable amount towards the direction of aerial
vehicle 330 orbit beyond a natural state of the tether 420 (for
example, when no torque or tension is applied via a drive mechanism
and the proximate end 422 is allowed to rotate freely via a
free-running slip ring). This may be referred to as a lead mode. In
such embodiments, the control system 650 may be configured to
operate the drive mechanism 546 in the lead mode.
[0108] Further still, in some embodiments, it may be desirable for
the twist in the tether 420 to be negative. This may be
accomplished by maintaining a rate of rotation in the proximate
tether end 422 via the drive mechanism 546 such that the proximate
tether end 422 is twisted a fixed or variable amount away from the
direction of rotation, although the proximate tether end 422 may
still be rotating in the direction of the aerial vehicle 330 orbit.
This may referred to as a lag mode. In such embodiments, the
control system 650 may be configured to operate the drive mechanism
546 in the lag mode.
[0109] In addition, in some embodiments, the control system 650 may
be configured to operate the drive mechanism at variable speeds,
fixed speeds, or in an on/off fashion in order to maintain the
desired twist within a certain operating range. For example, the
control system 650 may be configured to maintain the tether 420
twist within a range of values by activating and deactivating the
drive mechanism 546 (e.g., pulsing a drive motor attached to the
slip ring). As another example, the control system 650 may be
configured to maintain the tether 420 twist within a range of
values by causing the drive mechanism 546 to rotate the rotatable
portion 544b at a constant rate. As yet another example, the
control system 650 may be configured to maintain the tether 420
twist within a range of values by causing the drive mechanism 546
to rotate the rotatable portion 544b at a variable rate. In such
examples, the variable rate may be determined in reference to at
least the rotational rate of the tether 420. For instance, in at
least one such example, the variable rate may be determined in
reference to at least the rotational rate of the distal tether end
424 or a rotational speed of the aerial vehicle 330. Further, in at
least one such example, the variable rate may be determined in
reference to at least the rotational rate of the proximate tether
end 422.
[0110] Moreover, in some embodiments, the control system 650 may be
configured to determine one or more operational or environmental
parameters that affect an AWT, such as AWT 100 and/or AWT 200, and
then control the amount of twist in the tether 420 based at least
in part on the determined parameter. As examples, the parameters
may include tether 420 tension, position of the aerial vehicle 330,
load(s) on the aerial vehicle 330, velocities of the aerial vehicle
330, wind speed(s), temperature of a tether 420 conductor,
environmental temperature, conductor resistance, and/or current
flowing in a conductor. For example, by increasing or decreasing
the twist in the tether 420, tension in the tether 420 can be
increased or decreased. And in at least one such embodiment, when
the tether 420 includes two or more layers, it may desirable to
maintain a relative tension between the layers of the tether 420.
The control system 650 may determine the parameters at least in
part by information provided by any of the sensors 232 of the
aerial vehicle 230.
[0111] Although system 600 has been described above, other example
systems are possible as well. For example, although the drive
mechanism 546 is coupled to the rotatable portion 544b of the slip
ring 544 in the system 600, in other example systems the drive
mechanism 546 may not be coupled to the rotatable portion 544b.
Instead, in some embodiments, the drive mechanism 546 may be
coupled to a portion of the tether 420. In such embodiments, the
drive mechanism 546 may be configured to rotate the coupled portion
of the tether 420.
[0112] Although in system 600 the slip ring 544 is coupled to the
tether gimbal assembly 542 or the ground station 510, in other
example systems the slip ring 544 may be coupled instead to the
aerial vehicle 330. For instance, in some embodiments, the fixed
portion 544a of the slip ring 544 may be coupled to the aerial
vehicle 330, the rotatable portion 544b of the slip ring 544 may be
coupled to the distal tether end 424, and the drive mechanism 546
may be coupled to the rotatable portion 544b. Moreover, in an
example system where the slip ring 544 is coupled to the aerial
vehicle 330, the system may not include the tether gimbal assembly
542. Instead, in some embodiments, the proximate tether end 422 may
be coupled to the winch drum 512.
[0113] As yet another example, although system 600 includes the
drive mechanism 546, other example systems may include two or more
drive mechanisms coupled to the slip ring 544. Beneficially, such
redundancy may improve the reliability of the system. In some
embodiments, each drive mechanism of the two or more drive
mechanisms may take the form of or be similar in form to the drive
mechanism 546.
[0114] FIG. 7 depicts another system 700 for controlling rotation
and twist of the tether 420, according to an example embodiment. In
particular, the system 700 includes a resistive bearing system 760.
The resistive bearing system 760 may passively control an amount of
twist in the tether 420 during crosswind flight. Referring to FIG.
7, the tether 420 may be coupled to the tether gimbal assembly 542
at the proximate tether end 422 and to the aerial vehicle 330 at
the distal tether end 424. Additionally or alternatively, the
tether 420 may pass through the tether gimbal assembly 542.
Moreover, as shown in FIG. 7, the tether gimbal assembly 542 may be
coupled to the winch drum 512 which in turn is coupled to the
platform 514, the rotatable portion 544b of the slip ring 544 may
be coupled to the tether 420, the fixed portion 544a of the slip
ring 544 may be coupled to the tether gimbal assembly 542, and the
resistive bearing system 760 may be coupled to the slip ring 544
and/or the tether gimbal assembly 542.
[0115] Alternatively, the fixed portion 544a of the slip ring 544
may be coupled to the platform 514, the winch drum 512, or another
component of the ground station 510. For example, the tether 420,
the slip ring 544, the tether gimbal assembly 542 connections, as
well as other connections, may be described with respect to FIG.
5b.
[0116] In some embodiments, the resistive bearing system 760 may be
configured to allow the rotatable portion 544b to rotate relative
to the fixed portion 544a when a torque provided by the tether 420
exceeds a slip limit, and may be further configured to inhibit the
rotation of the rotatable portion 544b relative to the fixed
portion 544a when the torque provided by the tether 420 does not
exceed the slip limit. In other embodiments, the resistive bearing
system 760 may be configured to allow the proximate tether end 422
to rotate when a torque at the proximate tether end 422 exceeds a
slip limit, and may be further configured to inhibit the rotation
of the proximate tether end 422 when the torque does not exceed the
slip limit.
[0117] Moreover, in some embodiments, the slip limit may be based
on any of the parameters of the tether 420, the aerial vehicle 330,
and/or the environment as described herein. Further, in some
embodiments, the tether 420 may include fibers (not shown) at a lay
angle that is less than any helical lay angle of conductor(s) of
the tether 420. As such, the fibers may provide torque to drive or
assist driving the resistive bearing system 760. Further still, in
some embodiments, the tether 420 may include fibers at a lay angle
that is equal to or greater than any helical lay angle of
conductor(s) of the tether 420. As such, the fibers may provide
torque to drive or assist driving the resistive bearing system
760.
[0118] Further, in some embodiments, the resistive bearing system
760 may include a brake (not shown) and the brake may be configured
to inhibit the rotation of the rotatable portion 544b relative to
the fixed portion 544a, for example, when the torque provided by
the tether 420 does not exceed the slip limit.
[0119] Further still, in some embodiments, the resistive bearing
system 760 may be configured to allow the rotatable portion 544b of
the slip ring 544 to rotate relative to the fixed portion 544a and
to provide a resistance to the rotational torque of the tether 420
so as to maintain the twist in the tether 420 within a determined
range of values. Moreover, in some embodiments, the resistance to
the rotational torque of the tether 420 provided by the resistive
bearing system 760 may be based on any of the parameters of the
tether 420, the aerial vehicle 330, and/or the environment as
described herein. In other embodiments, the resistive bearing
system 760 may be configured to allow the proximate tether end 422
to rotate and to provide a resistance to the rotational torque of
the tether 420 so as to maintain the twist in the tether 420 within
a determined range of values.
[0120] In addition, in some embodiments, a resistance of the
resistive bearing system 760 may vary based on any parameters of
the tether 420, the aerial vehicle 330, and/or the environment as
described herein. For example, a friction brake may be used to vary
the resistance of the resistance bearing system 760.
[0121] Although system 700 has been described above, other example
systems are possible as well. For example, although the resistive
bearing system 760 is coupled to the slip ring 544 and/or the
tether gimbal assembly 542 in the system 700, in other example
systems the resistive bearing system 760 may not be coupled to the
slip ring 544 and/or the tether gimbal assembly 542. Instead, in
some embodiments, the resistive bearing system 760 may be coupled
to a portion of the tether 420. In such embodiments, the resistive
bearing system 760 may be configured to allow the coupled portion
of the tether 420 to rotate when a torque at the coupled portion of
the tether 420 exceeds a slip limit, and may be further configured
to inhibit the rotation of the coupled portion of the tether 420
when the torque does not exceed the slip limit. Alternatively, in
such embodiments, the resistive bearing system 760 may be
configured to allow the coupled portion of the tether 420 to rotate
and to provide a resistance to the rotational torque of the tether
420 so as to maintain the twist in the tether 420 within a
determined range of values.
[0122] G. Illustrative Tethers
[0123] FIG. 8 depicts a cross-section of a tether 820, according to
an example embodiment. The tether 120, the tether 220, and/or the
tether 420 may take the form of or be similar in form to the tether
820. The tether 820 includes a core 872, at least one compliant
layer 874, and at least one conductor 876. As shown in FIG. 8, the
compliant layer 874 is located between the core 872 and the
conductor 876. The core 872 may be configured to withstand a strain
load, for example, of between 0.8% and 1.0%. In some embodiments,
the conductor 876 may be configured to withstand less strain than
the core 872.
[0124] The conductor 876 may be helically wound around a length of
the core 872. With this arrangement, strain on the conductor 876
may be reduced during normal operation. In addition, when the
tether 820 is twisted, the conductor 876 may compress into the
compliant layer 874. With this arrangement, strain on the conductor
876 may be further reduced.
[0125] When the tether 820 is twisted, a helically wound conductor
876 may be in tension or compression. For example, when the
direction of twist of the tether 820 corresponds to the conductor's
876 helical winding, the conductor 876 may be in tension. And when
the direction of the twist is in opposition to the conductor's 876
helical winding, the conductor 876 may be in compression.
[0126] Although the tether 820 has been described above as
including the conductor 876, other example tethers may include a
conductor layer having two or more conductors. In some embodiments,
each conductor of the two or more conductors may take the form of
or be similar in form to the conductor 876. Moreover, in some
embodiments, each conductor of the two or more conductors may be
helically wound around a length of the core 872.
[0127] Further, although the tether 820 has been described above as
including the compliant layer 874, other example tethers may not
include a complaint layer.
[0128] FIG. 9 depicts a cross-section of another tether 920,
according to an example embodiment. The tether 120, the tether 220,
and/or the tether 420 may take the form of or be similar in form to
the tether 920. In particular, the tether 920 includes a core layer
972 having two or more core elements 973. The tether 920 may
include the core layer 972, a complaint layer 974, and at least one
conductor 976. The compliant layer 974 may take the form of or be
similar in form to the compliant layer 874, and the conductor 976
may take the form of or be similar in form to the conductor
876.
[0129] As shown in FIG. 9, the complaint layer 974 is located
between the core layer 972 and the conductor 976. The conductor 976
may be helically wound around a length of the core layer 972 in the
same or similar way as the conductor 876 may be helically wound
around a length of the core 872 in the tether 820. In addition, the
tether 920 may include two or more conductors in the same or
similar way as the tether 820 may include two or more
conductors.
[0130] As noted, the core layer 972 includes two or more core
elements 973. In the illustrated example, the two or more core
elements 973 may include seven core elements: a first core element
973a, a second core element 973b, a third core element 973c, a
fourth core element 973d, a fifth core element 973e, a six core
element 973f, and a seventh core element 973g. However, in other
examples, the two or more core elements 973 may include more than
seven core elements or less than seven core elements. Moreover, in
some embodiments, each core element may be the same or similar.
However, in some embodiments, at least one core element may have a
different material, thickness, length, lay angle, etc.
[0131] Further, in some embodiments, at least one core element may
be helically wound around a length of the tether 920. With this
configuration, the core layer 972 may have a lower polar moment of
inertia than a polar moment of inertia of the core 872.
Beneficially, the core layer 972 may allow for a greater amount of
twist in the tether 920 than allowed by core 872 in tether 820.
Further still, in some embodiments, at least one core element may
include a carbon rod and the core layer 972 may be configured to
provide torque to drive a resistive bearing system, such as the
resistive bearing system 760.
[0132] FIG. 10 depicts a cross-section of yet another tether 1020,
according to an example embodiment. In particular, the tether 1020
includes a torque layer 1078 having at least one fiber 1079. The
tether 120, the tether 220, and/or the tether 420 may take the form
of or be similar in form to the tether 1020. The tether 1020
includes a core 1072, a complaint layer 1074, a conductor layer
1076, and the torque layer 1078. The conductor layer 1076 may
include at least one conductor 1077. The core 1072 may take the
form of or be similar in form to the core 872 or the core layer
972, the complaint layer 1074 may take the form of or be similar in
form to the complaint layer 874 and/or the complaint layer 974, and
the conductor 1077 may take the form of or be similar in form to
the conductor 876 and/or the conductor 976.
[0133] As shown in FIG. 10, the complaint layer 1074 is located
between the core 1072 and the conductor layer 1076. Moreover, as
shown in FIG. 10, the core 1072, the complaint layer 1074, and the
conductor layer 1076 may be located inside of the torque layer
1078. The conductor 1077 may be helically wound around a length of
the core 1072 in the same or similar way as the conductor 876 may
be helically wound around a length of the core 872 in the tether
820 and the conductor 976 may be helically wound around a length of
the core layer 972 of the tether 920. In addition, the tether 1020
may include two or more conductors in the same or similar way as
the tether 820 may include two or more conductors and the tether
920 may include two or more conductors.
[0134] As noted, the tether 1020 includes the torque layer 1078
having the fiber 1079. In some embodiments, the fiber 1079 may be
helically wound around a length of the tether 1020 over the
conductor layer 1076. With this configuration, the fiber 1079 may
be configured to provide torque to drive a resistive bearing
system, such as the resistive bearing system 760. As an example,
the fiber 1079 may include carbon or any suitable material
configured to drive the resistive bearing system.
[0135] In such embodiments, the fiber 1079 may be helically wound
in the direction that an aerial vehicle, such as the aerial vehicle
130, the aerial vehicle 230, and/or the aerial vehicle 330, rotates
during crosswind flight (e.g., right-handed direction). As the
tether twists, the helically wound fiber 1079 will create torque by
virtue of a winding/unwinding force. Further, in such embodiments,
a lay angle of the fiber 1079 may be based at least in part on one
or more parameters, including friction in the resistive bearing
system, stiffness of the fiber 1079, the compressibility (e.g.,
bulk modulus) of the tether 1020, allowable strain in the conductor
1077, and alternating tension of the tether 1020. Further still, in
such embodiments, a lay angle of the fiber 1079 may be less than a
lay angle of the conductor 1077.
[0136] Moreover, in some embodiments, at least one parameter of the
torque layer 1078 may be selected so as to increase or decrease a
tensile strength of the tether 1020. In such embodiments, at least
one parameter of the fiber 1079 may be selected so as to increase
or decrease a tensile strength of the tether 1020. Further, in some
embodiments, at least one parameter of the torque layer 1078 may be
selected so as to increase or decrease a stiffness of the tether
1020. In such embodiments, at least one parameter of the fiber 1079
may be selected so as to increase or decrease a stiffness of the
tether 1020.
[0137] Although the torque layer 1078 has been described above as
having the fiber 1079, other example tethers may have two or more
fibers. In some embodiments, each fiber of the two or more fibers
may take the form of or be similar in form to the fiber 1079.
Moreover, in some embodiments, each fiber of the two or more fibers
may be helically wound around a length of the tether 1020. Further,
in such embodiments, a corresponding lay angle of each fiber of the
two or more fibers may be less than a lay angle of the conductor
1020.
[0138] Moreover, although the tether 1020 has been described above
with the core 1072, the compliant layer 1074, and the conductor
layer 1076 being located inside of the torque layer 1078, in other
example tethers, the torque layer 1078 may be located between the
core layer 1072 and the conductor layer 1076 (e.g., between the
compliant layer 1074 and the conductor 1077). In some embodiments,
the fiber 1079 may be helically wound around a length of the tether
1020 over the core 1072.
III. ILLUSTRATIVE METHODS
[0139] FIG. 11 is a flowchart illustrating a method 1100, according
to an example embodiment. Illustrative methods, such as method
1100, may be carried out in whole or in part by a component or
components of an AWT, such as by the one or more components of the
AWT 100 shown in FIG. 1, and the AWT 200 shown in FIG. 2.
[0140] As shown by block 1102, the method 1100 may involve
launching an aerial vehicle connected to a tether. The aerial
vehicle may take form of or be similar in form to the aerial
vehicle 130, the aerial vehicle 230, and/or the aerial vehicle 330.
The tether may take the form of or be similar in form to the tether
120, the tether 220, the tether 420, the tether 820, the tether
920, and the tether 1020.
[0141] As shown by block 1104, the method 1100 may involve
transitioning the aerial vehicle to crosswind flight. In some
embodiments, the aerial vehicle may transition to crosswind flight
via hover flight and/or forward flight.
[0142] As shown by block 1106, the method 1100 may involve
controlling, by a control system, an amount of twist in the tether
during crosswind flight. The control system may take the form of or
be similar in form to the control system 248 and/or the control
system 650.
[0143] In some embodiments, a drive mechanism is coupled to the
tether, and controlling, by the control system, the amount of twist
in the tether during crosswind flight may involve operating a drive
mechanism in a lag mode. Moreover, in some embodiments, a drive
mechanism is coupled to the tether, and controlling, by the control
system, the amount of twist in the tether during crosswind flight
may involve operating a drive mechanism in a lead mode. Further, in
some embodiments, a drive mechanism is coupled to the tether, and
controlling, by the control system, the amount of twist in the
tether during crosswind flight may involve activating and
deactivating the drive mechanism.
[0144] Further still, in some embodiments, a rotatable portion of a
slip ring is coupled to the tether, a drive mechanism is coupled to
the rotatable portion, and controlling, by the control system, the
amount of twist in the tether during crosswind flight may involve
causing the drive mechanism to rotate a rotatable portion of the
slip ring coupled to the tether at a constant rate.
[0145] Moreover, in some embodiments, a rotatable portion of a slip
ring is coupled to the tether, a drive mechanism is coupled to the
rotatable portion, and controlling, by the control system, the
amount of twist in the tether during crosswind flight may involve
causing the drive mechanism to rotate the rotatable portion of the
slip ring at a variable rate. And in at least one such embodiment,
the variable rate may be determined in reference to at least the
rotational rate of the tether.
[0146] Further, in some embodiments, a drive mechanism is coupled
to a tether, and the method 1100 may further involve determining
the value of an operational or environmental parameter and
operating the drive mechanism to control tether twist based at
least in part on the determined operational or environmental
parameter. And in at least one such embodiment, the operational or
environmental parameter comprises a tension on the tether, a load
on the aerial vehicle, a position of the aerial vehicle, a velocity
of the aerial vehicle, a wind speed, a temperature of the at least
one conductor, an environmental temperature, a resistance of the at
least one conductor, or the amount of electrical current carried by
the at least one conductor.
IV. CONCLUSION
[0147] The particular arrangements shown in the Figures should not
be viewed as limiting. It should be understood that other
embodiments may include more or less of each element shown in a
given Figure. Further, some of the illustrated elements may be
combined or omitted. Yet further, an exemplary embodiment may
include elements that are not illustrated in the Figures.
[0148] Additionally, while various aspects and embodiments have
been disclosed herein, other aspects and embodiments will be
apparent to those skilled in the art. The various aspects and
embodiments disclosed herein are for purposes of illustration and
are not intended to be limiting, with the true scope and spirit
being indicated by the following claims. Other embodiments may be
utilized, and other changes may be made, without departing from the
spirit or scope of the subject matter presented herein. It will be
readily understood that the aspects of the present disclosure, as
generally described herein, and illustrated in the Figures, can be
arranged, substituted, combined, separated, and designed in a wide
variety of different configurations, all of which are contemplated
herein.
* * * * *