U.S. patent application number 12/242995 was filed with the patent office on 2009-01-29 for navigating uavs in formation.
This patent application is currently assigned to INTERNATIONAL BUSINESS MACHINES CORPORATION. Invention is credited to William Kress Bodin, Jesse Redman, Derral Charles Thorson.
Application Number | 20090030566 12/242995 |
Document ID | / |
Family ID | 39795770 |
Filed Date | 2009-01-29 |
United States Patent
Application |
20090030566 |
Kind Code |
A1 |
Bodin; William Kress ; et
al. |
January 29, 2009 |
Navigating UAVs In Formation
Abstract
Navigating UAVs in formation, including assigning pattern
positions to each of a multiplicity of UAVs flying together in a
pattern; identifying a waypoint for each UAV in dependence upon the
UAV's pattern position; piloting the UAVs in the pattern toward
their waypoints in dependence upon a navigation algorithm, where
the navigation algorithm includes repeatedly comparing the UAV's
intended position and the UAV's actual position and calculating a
corrective flight vector when the distance between the UAV's actual
and intended positions exceeds an error threshold. The actual
position of the UAV may be taken from a GPS receiver on board the
UAV.
Inventors: |
Bodin; William Kress;
(Austin, TX) ; Redman; Jesse; (Cedar Park, TX)
; Thorson; Derral Charles; (Austin, TX) |
Correspondence
Address: |
INTERNATIONAL CORP (BLF)
c/o BIGGERS & OHANIAN, LLP, P.O. BOX 1469
AUSTIN
TX
78767-1469
US
|
Assignee: |
INTERNATIONAL BUSINESS MACHINES
CORPORATION
Armonk
NY
|
Family ID: |
39795770 |
Appl. No.: |
12/242995 |
Filed: |
October 1, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11041919 |
Jan 24, 2005 |
|
|
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12242995 |
|
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Current U.S.
Class: |
701/5 ;
701/8 |
Current CPC
Class: |
G05D 1/0027 20130101;
G08G 5/0069 20130101; G05D 1/0044 20130101; G08G 5/0052
20130101 |
Class at
Publication: |
701/5 ;
701/8 |
International
Class: |
G05D 1/10 20060101
G05D001/10 |
Claims
1. A method for navigating UAVs in formation, the method
comprising: assigning pattern positions to each of a multiplicity
of UAVs flying together in a pattern; identifying a waypoint for
each UAV in dependence upon the UAV's pattern position; piloting
the UAVs in the pattern toward their waypoints in dependence upon a
navigation algorithm, the navigation algorithm including:
repeatedly comparing the UAV's intended position and the UAV's
actual position, the actual position taken from a GPS receiver; and
calculating a corrective flight vector when the distance between
the UAV's actual and intended positions exceeds an error
threshold.
2. The method of claim 1 wherein: assigning pattern positions to
each of a multiplicity of UAVs flying together in a pattern further
comprises designating an anchor position for the pattern and
assigning pattern positions to the other UAVs relative to the
anchor position; and identifying a waypoint for each UAV in
dependence upon its pattern position further comprises designating
a waypoint for the anchor position and calculating each UAV's
waypoint in dependence upon the waypoint for the anchor and in
dependence upon the UAV's position in the pattern.
3. The method of claim 1 wherein each UAV's intended position is
specified by the UAV's position in the pattern, a cross track to
the UAV's waypoint, and a flight schedule.
4. The method of claim 1 wherein piloting the UAVs in dependence
upon a navigation algorithm further comprises: identifying a cross
track to a waypoint for each UAV, the cross track having a cross
track direction; piloting the UAV to a starting point on the cross
track; calculating an airspeed for flying from the starting point
to the waypoint on schedule; calculating a heading in dependence
upon wind speed, wind direction, airspeed, and the cross track
direction; and flying the UAV on the heading at the airspeed.
5. The method of claim 1 wherein calculating a corrective flight
vector further comprises: selecting a corrective waypoint on a
cross track between a UAV's intended position and its waypoint;
calculating a corrective airspeed for arriving at the corrective
waypoint on schedule; and calculating a corrective heading in
dependence upon the calculated airspeed.
6. The method of claim 5 wherein selecting a corrective waypoint on
a cross track between a UAV's intended position and its waypoint
further comprises selecting a corrective waypoint at a
predetermined portion of the distance between a UAV's intended
position and its waypoint.
7. The method of claim 5 wherein calculating a corrective airspeed
for arriving at the corrective waypoint on schedule further
comprises calculating a groundspeed needed to bring the UAV to the
remedial waypoint on schedule, including dividing the distance from
the actual position to the corrective waypoint by the difference
between the current time and the schedule time for the corrective
waypoint
8. A system for navigating UAVs in formation, the system
comprising: means for assigning pattern positions to each of a
multiplicity of UAVs flying together in a pattern; means for
identifying a waypoint for each UAV in dependence upon the UAV's
pattern position; means for piloting the UAVs in the pattern toward
their waypoints in dependence upon a navigation algorithm; means
for repeatedly comparing the UAV's intended position and the UAV's
actual position, the actual position taken from a GPS receiver; and
means for calculating a corrective flight vector when the distance
between the UAV's actual and intended positions exceeds an error
threshold.
9. The system of claim 8 wherein: means for assigning pattern
positions to each of a multiplicity of UAVs flying together in a
pattern further comprises means for designating an anchor position
for the pattern and assigning pattern positions to the other UAVs
relative to the anchor position; and means for identifying a
waypoint for each UAV in dependence upon its pattern position
further comprises means for designating a waypoint for the anchor
position and calculating each UAV's waypoint in dependence upon the
waypoint for the anchor and in dependence upon the UAV's position
in the pattern.
10. The system of claim 8 wherein means for piloting the UAVs in
dependence upon a navigation algorithm further comprises: means for
identifying a cross track to a waypoint for each UAV, the cross
track having a cross track direction; means for piloting the UAV to
a starting point on the cross track; means for calculating an
airspeed for flying from the starting point to the waypoint on
schedule; means for calculating a heading in dependence upon wind
speed, wind direction, airspeed, and the cross track direction; and
means for flying the UAV on the heading at the airspeed.
11. The system of claim 8 wherein means for calculating a
corrective flight vector further comprises: means for selecting a
corrective waypoint on a cross track between a UAV's intended
position and its waypoint; means for calculating a corrective
airspeed for arriving at the corrective waypoint on schedule; and
means for calculating a corrective heading in dependence upon the
calculated airspeed.
12. The system of claim 11 wherein means for selecting a corrective
waypoint on a cross track between a UAV's intended position and its
waypoint further comprises means for selecting a corrective
waypoint at a predetermined portion of the distance between a UAV's
intended position and its waypoint.
13. The system of claim 11 wherein means for calculating a
corrective airspeed for arriving at the corrective waypoint on
schedule further comprises means for calculating a groundspeed
needed to bring the UAV to the remedial waypoint on schedule,
including means for dividing the distance from the actual position
to the corrective waypoint by the difference between the current
time and the schedule time for the corrective waypoint.
14. A computer program product for navigating UAVs in formation,
the computer program product comprising: a recording medium; means,
recorded on the recording medium, for assigning pattern positions
to each of a multiplicity of UAVs flying together in a pattern;
means, recorded on the recording medium, for identifying a waypoint
for each UAV in dependence upon the UAV's pattern position; means,
recorded on the recording medium, for piloting the UAVs in the
pattern toward their waypoints in dependence upon a navigation
algorithm; means, recorded on the recording medium, for repeatedly
comparing the UAV's intended position and the UAV's actual
position, the actual position taken from a GPS receiver; and means,
recorded on the recording medium, for calculating a corrective
flight vector when the distance between the UAV's actual and
intended positions exceeds an error threshold.
15. The computer program product of claim 14 wherein: means,
recorded on the recording medium, for assigning pattern positions
to each of a multiplicity of UAVs flying together in a pattern
further comprises means, recorded on the recording medium, for
designating an anchor position for the pattern and assigning
pattern positions to the other UAVs relative to the anchor
position; and means, recorded on the recording medium, for
identifying a waypoint for each UAV in dependence upon its pattern
position further comprises means, recorded on the recording medium,
for designating a waypoint for the anchor position and calculating
each UAV's waypoint in dependence upon the waypoint for the anchor
and in dependence upon the UAV's position in the pattern.
16. The computer program product of claim 14 wherein each UAV's
intended position is specified by the UAV's position in the
pattern, a cross track to the UAV's waypoint, and a flight
schedule.
17. The computer program product of claim 14 wherein means,
recorded on the recording medium, for piloting the UAVs in
dependence upon a navigation algorithm further comprises: means,
recorded on the recording medium, for identifying a cross track to
a waypoint for each UAV, the cross track having a cross track
direction; means, recorded on the recording medium, for piloting
the UAV to a starting point on the cross track; means, recorded on
the recording medium, for calculating an airspeed for flying from
the starting point to the waypoint on schedule; means, recorded on
the recording medium, for calculating a heading in dependence upon
wind speed, wind direction, airspeed, and the cross track
direction; and means, recorded on the recording medium, for flying
the UAV on the heading at the airspeed.
18. The computer program product of claim 14 wherein means,
recorded on the recording medium, for calculating a corrective
flight vector further comprises: means, recorded on the recording
medium, for selecting a corrective waypoint on a cross track
between a UAV's intended position and its waypoint; means, recorded
on the recording medium, for calculating a corrective airspeed for
arriving at the corrective waypoint on schedule; and means,
recorded on the recording medium, for calculating a corrective
heading in dependence upon the calculated airspeed.
19. The computer program product of claim 18 wherein means,
recorded on the recording medium, for selecting a corrective
waypoint on a cross track between a UAV's intended position and its
waypoint further comprises means, recorded on the recording medium,
for selecting a corrective waypoint at a predetermined portion of
the distance between a UAV's intended position and its
waypoint.
20. The computer program product of claim 18 wherein means,
recorded on the recording medium, for calculating a corrective
airspeed for arriving at the corrective waypoint on schedule
further comprises means, recorded on the recording medium, for
calculating a groundspeed needed to bring the UAV to the remedial
waypoint on schedule, including means, recorded on the recording
medium, for dividing the distance from the actual position to the
corrective waypoint by the difference between the current time and
the schedule time for the corrective waypoint.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation application of and claims
priority from U.S. patent application Ser. No. 11/041,919, filed on
Jan. 24, 2005.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The field of the invention is data processing, or, more
specifically, methods, systems, and products for navigating UAVs in
formation.
[0004] 2. Description of Related Art
[0005] Many forms of UAV are available in prior art, both
domestically and internationally. Their payload weight carrying
capability, their accommodations (volume, environment), their
mission profiles (altitude, range, duration), and their command,
control and data acquisition capabilities vary significantly.
Routine civil access to these various UAV assets is in an embryonic
state.
[0006] Conventional UAVs are typically manually controlled by an
operator who may view aspects of a UAV's flight using cameras
installed on the UAV with images provided through downlink
telemetry. Navigating such UAVs from a starting position to one or
more waypoints requires an operator to have specific knowledge of
the UAV's flight, including such aspects as starting location, the
UAV's current location, waypoint locations, and so on. Operators of
prior art UAVs usually are required generally to manually control
the UAV from a starting position to a waypoint with little aid from
automation. There is therefore an ongoing need for improvement in
the area of UAV navigations.
SUMMARY OF THE INVENTION
[0007] Exemplary methods, systems, and products are described for
efficient, automated navigation of UAVs, including navigating UAVs
in formation. That is, exemplary methods, systems, and products are
described for navigating UAVs in formation, including assigning
pattern positions to each of a multiplicity of UAVs flying together
in a pattern; identifying a waypoint for each UAV in dependence
upon the UAV's pattern position; piloting the UAVs in the pattern
toward their waypoints in dependence upon a navigation algorithm,
where the navigation algorithm includes repeatedly comparing the
UAV's intended position and the UAV's actual position and
calculating a corrective flight vector when the distance between
the UAV's actual and intended positions exceeds an error threshold.
The actual position of the UAV may be taken from a GPS receiver on
board the UAV.
[0008] Assigning pattern positions to each of a multiplicity of
UAVs flying together in a pattern may include designating an anchor
position for the pattern and assigning pattern positions to the
other UAVs relative to the anchor position, and identifying a
waypoint for each UAV in dependence upon its pattern position may
be carried out by designating a waypoint for the anchor position
and calculating each UAV's waypoint in dependence upon the waypoint
for the anchor and in dependence upon the UAV's position in the
pattern. Each UAV's intended position may be specified by the UAV's
position in the pattern, a cross track to the UAV's waypoint, and a
flight schedule.
[0009] Piloting the UAVs in dependence upon a navigation algorithm
may include identifying a cross track to a waypoint for each UAV,
the cross track having a cross track direction; piloting the UAV to
a starting point on the cross track; calculating an airspeed for
flying from the starting point to the waypoint on schedule;
calculating a heading in dependence upon wind speed, wind
direction, airspeed, and the cross track direction; and flying the
UAV on the heading at the airspeed.
[0010] Calculating a corrective flight vector may be carried out by
selecting a corrective waypoint on a cross track between a UAV's
intended position and its waypoint; calculating a corrective
airspeed for arriving at the corrective waypoint on schedule; and
calculating a corrective heading in dependence upon the calculated
airspeed. Selecting a corrective waypoint on a cross track between
a UAV's intended position and its waypoint may include selecting a
corrective waypoint at a predetermined portion of the distance
between a UAV's intended position and its waypoint. Calculating a
corrective airspeed for arriving at the corrective waypoint on
schedule may be carried out by calculating a groundspeed needed to
bring the UAV to the remedial waypoint on schedule, including
dividing the distance from the actual position to the corrective
waypoint by the difference between the current time and the
schedule time for the corrective waypoint.
[0011] The foregoing and other objects, features and advantages of
the invention will be apparent from the following more particular
descriptions of exemplary embodiments of the invention as
illustrated in the accompanying drawings wherein like reference
numbers generally represent like parts of exemplary embodiments of
the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 sets forth a system diagram illustrating relations
among components of an exemplary system for navigating a UAV.
[0013] FIG. 2 is a block diagram of an exemplary UAV showing
relations among components that includes automated computing
machinery.
[0014] FIG. 3 is a block diagram of an exemplary remote control
device showing relations among components that includes automated
computing machinery.
[0015] FIG. 4 sets forth a flow chart illustrating an exemplary
method for navigating a UAV that includes receiving in a remote
control device a user's selection of a GUI map pixel that
represents a waypoint for UAV navigation.
[0016] FIG. 4A is a data flow diagram illustrating an exemplary
method for receiving downlink telemetry.
[0017] FIG. 4B sets forth a data flow diagram illustrating an
exemplary method for transmitting uplink telemetry.
[0018] FIG. 5 sets forth a block diagram that includes a GUI
displaying a map and a corresponding area of the surface of the
Earth.
[0019] FIG. 6 sets forth a flow chart illustrating an exemplary
method of navigating a UAV in accordance with a navigation
algorithm.
[0020] FIG. 7 sets forth a line drawing illustrating a flight path
produced by application of the method of FIG. 6.
[0021] FIG. 8 sets forth a flow chart illustrating an exemplary
method of navigating a UAV in accordance with a navigation
algorithm.
[0022] FIG. 9 sets forth a line drawing illustrating a flight path
produced by application of the method of FIG. 8.
[0023] FIG. 10 sets forth a flow chart illustrating an exemplary
method of navigating a UAV in accordance with a navigation
algorithm.
[0024] FIG. 11 sets forth a line drawing illustrating a flight path
produced by application of the method of FIG. 10.
[0025] FIG. 12 sets forth a flow chart illustrating an exemplary
method for navigating a UAV that includes receiving in a remote
control device a user's selection of a GUI map pixel that
represents a waypoint for UAV navigation.
[0026] FIG. 13 sets forth a flow chart illustrating an exemplary
method of piloting in accordance with a navigation algorithm.
[0027] FIG. 14 sets forth a line drawing illustrating a method of
calculating a heading with a cross wind to achieve a particular
ground course.
[0028] FIG. 15 sets forth a line drawing illustrating a flight path
produced by application of the method of FIG. 13.
[0029] FIG. 16 sets forth a flow chart illustrating an exemplary
method of piloting in accordance with a navigation algorithm.
[0030] FIG. 17 sets forth a line drawing illustrating a flight path
produced by application of the method of FIG. 16.
[0031] FIG. 18 sets forth a flow chart illustrating an exemplary
method for navigating UAVs in formation.
[0032] FIGS. 19A and 19B are line drawings illustrating exemplary
relations among UAVs flying in formation.
[0033] FIG. 20 sets forth a flow chart illustrating an exemplary
method of piloting the UAVs in dependence upon a navigation
algorithm.
[0034] FIG. 21 sets forth a line drawing illustrating an exemplary
method of calculating airspeed and heading according to the method
of FIG. 21.
[0035] FIG. 22 sets forth a flow chart illustrating an exemplary
method of calculating a corrective flight vector.
[0036] FIG. 23 is a line drawing illustrating application of the
method of FIG. 22, showing relations among an intended position, an
error threshold, an actual position, a corrective flight vector,
and a cross track to a waypoint.
[0037] FIG. 24 sets forth a line drawing illustrating an exemplary
method of calculating corrective airspeed and corrective heading
according to the method of FIG. 22.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
Introduction
[0038] The present invention is described to a large extent in this
specification in terms of methods for navigating UAVs in formation.
Persons skilled in the art, however, will recognize that any
computer system that includes suitable programming means for
operating in accordance with the disclosed methods also falls well
within the scope of the present invention. Suitable programming
means include any means for directing a computer system to execute
the steps of the method of the invention, including for example,
systems included of processing units and arithmetic-logic circuits
coupled to computer memory, which systems have the capability of
storing in computer memory, which computer memory includes
electronic circuits configured to store data and program
instructions, programmed steps of the method of the invention for
execution by a processing unit.
[0039] The invention also may be embodied in a computer program
product, such as a diskette or other recording medium, for use with
any suitable data processing system. Embodiments of a computer
program product may be implemented by use of any recording medium
for machine-readable information, including magnetic media, optical
media, or other suitable media. Persons skilled in the art will
immediately recognize that any computer system having suitable
programming means will be capable of executing the steps of the
method of the invention as embodied in a program product. Persons
skilled in the art will recognize immediately that, although most
of the exemplary embodiments described in this specification are
oriented to software installed and executing on computer hardware,
nevertheless, alternative embodiments implemented as firmware or as
hardware are well within the scope of the present invention.
Definitions
[0040] "Airspeed" means UAV airspeed, the speed of the UAV through
the air.
[0041] A "cross track" is a fixed course from a starting point
directly to a waypoint. A cross track has a direction, a `cross
track direction,` that is the direction straight from a starting
point to a waypoint. That is, a cross track direction is the
heading that a UAV would fly directly from a starting point to a
waypoint in the absence of wind.
[0042] "GUI" means graphical user interface, a display means for a
computer screen.
[0043] "Heading" means the compass heading of the UAV. "Course"
means the direction of travel of the UAV over the ground. In the
absence of wind, or in the presence of a straight tailwind or
straight headwind, the course and the heading are the same
direction. In the presence of crosswind, the course and the heading
are different directions.
[0044] "Position" refers to a location in the air or over the
ground. `Position` is typically specified as Earth coordinates,
latitude and longitude. A specification of position may also
include altitude.
[0045] A "waypoint" is a position chosen as a destination for
navigation of a route. A route has one or more waypoints. That is,
a route is composed of waypoints, including at least one final
waypoint, and one or more intermediate waypoints.
[0046] "TDMA" stands for Time Division Multiple Access, a
technology for delivering digital wireless service using
time-division multiplexing. TDMA works by dividing a radio
frequency into time slots and then allocating slots to multiple
calls. In this way, a single frequency can support multiple,
simultaneous data channels. TDMA is used by GSM.
[0047] "GSM" stands for Global System for Mobile Communications, a
digital cellular standard. GSM at this time is the de facto
standard for wireless digital communications in Europe and
Asia.
[0048] "CDPD" stands for Cellular Digital Packet Data, a data
transmission technology developed for use on cellular phone
frequencies. CDPD uses unused cellular channels to transmit data in
packets. CDPD supports data transfer rates of up to 19.2 Kbps.
[0049] "GPRS" stands for General Packet Radio Service, a standard
for wireless data communications which runs at speeds up to 150
Kbps, compared with current GSM systems which cannot support more
than about 9.6 Kbps. GPRS, which supports a wide range of speeds,
is an efficient use of limited bandwidth and is particularly suited
for sending and receiving small bursts of data, such as e-mail and
Web browsing, as well as large volumes of data.
[0050] "EDGE" stands for Enhanced Data Rates for GSM Evolution, a
standard for wireless data communications supporting data transfer
rates of more than 300 Kbps. GPRS and EDGE are considered interim
steps on the road to UMTS.
[0051] "UMTS" stands for Universal Mobile Telecommunication System,
a standard for wireless data communications supporting data
transfer rates of up to 2 Mpbs. UMTS is also referred to W-CDMA for
Wideband Code Division Multiple Access.
Navigating a UAV with Telemetry through a Socket
[0052] Methods, systems, and products for navigating a UAV are
explained with reference to the accompanying drawings, beginning
with FIG. 1. FIG. 1 sets forth a system diagram illustrating
relations among components of an exemplary system for navigating a
UAV. The system of FIG. 1 includes UAV (100) and UAV (126), flying
in formation, each of which includes a GPS (Global Positioning
System) receiver (not shown) that receives a steady stream of GPS
data from satellites (190, 192). For convenience of explanation,
only two GPS satellites are shown in FIG. 1, although the GPS
satellite network in fact includes 24 GPS satellites. For
convenience of explanation in the example of FIG. 1, only two UAVs
are shown, but in fact any number of UAVs may be navigated together
in formation according to embodiments of the present invention.
[0053] The system of FIG. 1 operates to navigate a UAV by receiving
in a remote control device a user's selection of a GUI map pixel
that represents a waypoint for UAV navigation. Each such pixel has
a location on a GUI map, typically specified as a row and column
position. Examples of remote control devices in FIG. 1 include
mobile telephone (110), workstation (104), laptop computer (106),
and PDA (Personal Digital Assistant) (120). Each such remote
control device is capable of supporting a GUI display of a map of
the surface of the Earth in which each pixel on the GUI map
represents a position on the Earth.
[0054] Each remote control device also supports at least one user
input device through which a user may enter the user's selection of
a pixel. Examples of user input devices in the system of FIG. 1
include telephone keypad (122), workstation keyboard (114),
workstation joystick (112), laptop keyboard (116) and PDA touch
screen (118).
[0055] The system of FIG. 1 typically is capable of operating a
remote control device to map the pixel's location on the GUI to
Earth coordinates of a waypoint. The remote control device is often
capable of receiving downlink telemetry including starting position
from a GPS receiver on the UAV through the socket. In fact, the
remote control device is often receiving downlink telemetry that
includes a steady stream of GPS positions of the UAV. Receiving a
starting position therefore is typically carried out by taking the
current position of the UAV when the user selects the pixel as the
starting position. In the example of FIG. 1, the remote control
device generally receives the starting position from the UAV
through wireless network (102). The remote control device is often
capable of transmitting uplink telemetry including the coordinates
of the waypoint, flight control instructions, or UAV instructions
through a socket on the remote control devices.
[0056] Wireless network (102) is implemented using any wireless
data transmission technology as will occur to those of skill in the
art including, for example, TDMA, GSM, CDPD, GPRS, EDGE, and UMTS.
In a one embodiment, a data communications link layer is
implemented using one of these technologies, a data communications
network layer is implemented with the Internet Protocol ("IP"), and
a data communications transmission layer is implemented using the
Transmission Control Protocol ("TCP"). In such systems, telemetry
between the UAV and remote control devices, including starting
positions, UAV instructions, and flight control instructions, are
transmitted using an application-level protocol such as, for
example, the HyperText Transmission Protocol ("HTTP"), the Wireless
Application Protocol ("WAP"), the Handheld Device Transmission
Protocol ("HDTP"), or any other data communications protocol as
will occur to those of skill in the art.
[0057] The system of FIG. 1 typically is capable of calculating a
heading in dependence upon the starting position, the coordinates
of the waypoint, and a navigation algorithm, identifying flight
control instructions for flying the UAV on the heading, and
transmitting the flight control instructions from the remote
control device to the UAV.
[0058] UAVs according to embodiments of the present invention
typically include, not only an aircraft, but also automated
computing machinery capable of receiving GPS data, operating
telemetry between the UAV and one or more remote control devices,
and navigating a UAV among waypoints. FIG. 2 is a block diagram of
an exemplary UAV showing relations among components that includes
automated computing machinery. In FIG. 2, UAV (100) includes a
processor (164), also typically referred to as a central processing
unit or `CPU.` The processor may be a microprocessor, a
programmable control unit, or any other form of processor useful
according to the form factor of a particular UAV as will occur to
those of skill in the art. Other components of UAV (100) are
coupled for data transfer to processor (164) through system bus
(160).
[0059] UAV (100) includes random access memory or `RAM` (166).
Stored in RAM (166) is an application program (152) that implements
inventive methods according to embodiments of the present
invention. Among other things, application program (158) includes
computer program instructions capable of navigating UAVs in
formation according to embodiments of the present invention,
including computer program steps that execute generally by
assigning pattern positions to each of a multiplicity of UAVs
flying together in a pattern; identifying a waypoint for each UAV
in dependence upon the UAV's pattern position; piloting the UAVs in
the pattern toward their waypoints in dependence upon a navigation
algorithm, where the navigation algorithm includes repeatedly
comparing the UAV's intended position and the UAV's actual
position, the actual position taken from a GPS receiver, and
calculating a corrective flight vector when the distance between
the UAV's actual and intended positions exceeds an error threshold.
This capability of navigating UAVs in formation is described in
more detail below in this specification.
[0060] In some embodiments, the application programming runs on an
OSGi service framework (156). OSGi Stands for `Open Services
Gateway Initiative.` The OSGi specification is a Java-based
application layer framework that provides vendor neutral
application layer APIs and functions. An OSGi service framework
(156) is written in Java and therefore typically runs on a Java
Virtual Machine (JVM) (154) which in turn runs on an operating
system (150). Examples of operating systems useful in UAVs
according to the present invention include Unix, AIX.TM., and
Microsoft Windows.TM..
[0061] In OSGi, the framework is a hosting platform for running
`services`. Services are the main building blocks for creating
applications according to the OSGi. A service is a group of Java
classes and interfaces that implement a certain feature. The OSGi
specification provides a number of standard services. For example,
OSGi provides a standard HTTP service that can respond to requests
from HTTP clients, such as, for example, remote control devices
according to embodiments of the present invention. That is, such
remote control devices are enabled to communicate with a UAV having
an HTTP service by use of data communications messages in the HTTP
protocol.
[0062] Services in OSGi are packaged in `bundles` with other files,
images, and resources that the services need for execution. A
bundle is a Java archive or `JAR` file including one or more
service implementations, an activator class, and a manifest file.
An activator class is a Java class that the service framework uses
to start and stop a bundle. A manifest file is a standard text file
that describes the contents of the bundle.
[0063] The service framework in OSGi also includes a service
registry. The service registry includes a service registration
including the service's name and an instance of a class that
implements the service for each bundle installed on the framework
and registered with the service registry. A bundle may request
services that are not included in the bundle, but are registered on
the framework service registry. To find a service, a bundle
performs a query on the framework's service registry.
[0064] In the UAV (100) of FIG. 2, software programs and other
useful information may be stored in RAM or in non-volatile memory
(168). Non-volatile memory (168) may be implemented as a magnetic
disk drive such as a micro-drive, an optical disk drive, static
read only memory (`ROM`), electrically erasable programmable
read-only memory space (`EEPROM` or `flash` memory), or otherwise
as will occur to those of skill in the art.
[0065] UAV (100) includes communications adapter (170) implementing
data communications connections (184) to other computers (162),
which may be wireless networks, satellites, remote control devices,
servers, or others as will occur to those of skill in the art.
Communications adapter (170) advantageously facilitates receiving
flight control instructions from a remote control device.
Communications adapters implement the hardware level of data
communications connections through which UAVs transmit wireless
data communications. Examples of communications adapters include
wireless modems for dial-up connections through wireless telephone
networks.
[0066] UAV (100) includes servos (178). Servos (178) are
proportional control servos that convert digital control signals
from system bus (160) into actual proportional displacement of
flight control surfaces, ailerons, elevators, and the rudder. The
displacement of flight control surfaces is `proportional` to values
of digital control signals, as opposed to the `all or nothing`
motion produced by some servos. In this way, ailerons, for example,
may be set to thirty degrees, sixty degrees, or any other supported
angle rather than always being only neutral or fully rotated.
Several proportional control servos useful in various UAVs
according to embodiments of the present invention are available
from Futaba.RTM..
[0067] UAV (100) includes a servo control adapter (172). A servo
control adapter (172) is multi-function input/output servo motion
controller capable of controlling several servos. An example of
such a servo control adapter is the "IOSERVO" model from National
Control Devices of Osceola, Mo. The IOSERVO is described on
National Control Devices website at www.controlanything.com.
[0068] UAV (100) includes a flight stabilizer system (174). A
flight stabilizer system is a control module that operates servos
(178) to automatically return a UAV to straight and level flight,
thereby simplifying the work that must be done by navigation
algorithms. An example of a flight stabilizer system useful in
various embodiments of UAVs according to the present invention is
model Co-Pilot.TM. from FMA, Inc., of Frederick, Md. The Co-Pilot
flight stabilizer system identifies a horizon with heat sensors,
identifies changes in aircraft attitude relative to the horizon,
and sends corrective signals to the servos (178) to keep the UAV
flying straight and level.
[0069] UAV (100) includes an AVCS gyro (176). An AVCS gryo is an
angular vector control system gyroscope that provides control
signal to the servos to counter undesired changes in attitude such
as those caused by sudden gusts of wind. An example of an AVCS gyro
useful in various UAVs according to the present invention is model
GYA350 from Futaba.RTM..
[0070] Remote control devices according to embodiments of the
present invention typically include automated computing machinery
capable of receiving user selections of pixel on GUI maps, mapping
the pixel to a waypoint location, receiving downlink telemetry
including for example a starting position from a GPS receiver on
the UAV, calculating a heading in dependence upon the starting
position, the coordinates of the waypoint, and a navigation
algorithm, identifying flight control instructions for flying the
UAV on the heading, and transmitting the flight control
instructions as uplink telemetry from the remote control device to
the UAV. FIG. 3 is a block diagram of an exemplary remote control
device showing relations among components that includes automated
computing machinery. In FIG. 3, remote control device (161)
includes a processor (164), also typically referred to as a central
processing unit or `CPU.` The processor may be a microprocessor, a
programmable control unit, or any other form of processor useful
according to the form factor of a particular remote control device
as will occur to those of skill in the art. Other components of
remote control device (161) are coupled for data transfer to
processor (164) through system bus (160).
[0071] Remote control device (161) includes random access memory or
`RAM` (166). Stored in RAM (166) an application program 152 that
implements inventive methods of the present invention. Among other
things, application program (158) includes computer program
instructions capable of navigating UAVs in formation according to
embodiments of the present invention, including computer program
steps that execute generally by assigning pattern positions to each
of a multiplicity of UAVs flying together in a pattern; identifying
a waypoint for each UAV in dependence upon the UAV's pattern
position; piloting the UAVs in the pattern toward their waypoints
in dependence upon a navigation algorithm, where the navigation
algorithm includes repeatedly comparing the UAV's intended position
and the UAV's actual position, the actual position taken from a GPS
receiver, and calculating a corrective flight vector when the
distance between the UAV's actual and intended positions exceeds an
error threshold. This capability of navigating UAVs in formation is
described in more detail below in this specification.
[0072] In some embodiments, the application program (152) is OSGi
compliant an therefore runs on an OSGi service framework installed
(not shown) on a JVM (not shown). In addition, software programs
and further information for use in implementing methods of
navigating a UAV according to embodiments of the present invention
may be stored in RAM or in non-volatile memory (168). Non-volatile
memory (168) may be implemented as a magnetic disk drive such as a
micro-drive, an optical disk drive, static read only memory
(`ROM`), electrically erasable programmable read-only memory space
(`EEPROM` or `flash` memory), or otherwise as will occur to those
of skill in the art.
[0073] Remote control device (161) includes communications adapter
(170) implementing data communications connections (184) to other
computers (162), including particularly computers on UAVs.
Communications adapters implement the hardware level of data
communications connections through which remote control devices
communicate with UAVs directly or through networks. Examples of
communications adapters include modems for wired dial-up
connections, Ethernet (IEEE 802.3) adapters for wired LAN
connections, 802.11b adapters for wireless LAN connections, and
Bluetooth adapters for wireless microLAN connections.
[0074] The example remote control device (161) of FIG. 3 includes
one or more input/output interface adapters (180). Input/output
interface adapters in computers implement user-oriented
input/output through, for example, software drivers and computer
hardware for controlling output to display devices (185) such as
computer display screens, as well as user input from user input
devices (182) such as keypads, joysticks, keyboards, and touch
screens.
[0075] FIG. 4 sets forth a flow chart illustrating an exemplary
method for navigating a UAV that includes receiving (402) in a
remote control device a user's selection of a GUI map pixel (412)
that represents a waypoint for UAV navigation. The pixel has a
location on the GUI. Such a GUI map display has many pixels, each
of which represents at least one position on the surface of the
Earth. A user selection of a pixel is normal GUI operations to take
a pixel location, row and column, from a GUI input/output adapter
driven by a user input device such as a joystick or a mouse. The
remote control device can be a traditional `ground control
station,` an airborne PDA or laptop, a workstation in Earth orbit,
or any other control device capable of accepting user selections of
pixels from a GUI map.
[0076] The method of FIG. 4 includes mapping (404) the pixel's
location on the GUI to Earth coordinates (414) of the waypoint. As
discussed in more detail below with reference to FIG. 5, mapping
(404) the pixel's location on the GUI to Earth coordinates of the
waypoint (414) typically includes mapping pixel boundaries of the
GUI map to corresponding Earth coordinates and identifying a range
of latitude and a range of longitude represented by each pixel.
Mapping (404) the pixel's location on the GUI to Earth coordinates
of the waypoint (414) also typically includes locating a region on
the surface of the Earth in dependence upon the boundaries, the
ranges, and the location of the pixel on the GUI map.
[0077] The method of FIG. 4 also includes receiving (408) downlink
telemetry, including a starting position from a GPS receiver on the
UAV, from the UAV through a socket on the remote control device. In
fact, the remote control device is receiving downlink telemetry
that includes a steady stream of GPS positions of the UAV.
Receiving a starting position therefore is typically carried out by
taking the current position of the UAV when the user selects the
pixel as the starting position.
[0078] A socket is one end-point of a two-way communication link
between two application programs running on a network. In Java,
socket classes are used to represent a connection between a client
program and a server program. The java.net package provides two
Java classes--Socket and ServerSocket--that implement the client
side of the connection and the server side of the connection,
respectively. In some embodiments of the present invention, a Java
web server, is included in an OSGi framework on a remote control
device. Often then, a socket on the remote control device would be
considered a server-side socket, and a socket on the UAV would be
considered a client socket. In other embodiments of the present
invention, a Java web server, is included in an OSGi framework on
the UAV. In such embodiments, a socket on the UAV would be
considered a server-side socket, and a socket on a remote control
device would be considered a client socket.
[0079] Use of a socket requires creating a socket and creating data
streams for writing to and reading from the socket. One way of
creating a socket and two data streams for use with the socket is
shown in the following exemplary pseudocode segment:
TABLE-US-00001 uavSocket = new Socket( "computerAddress", 7);
outStream = new PrintWriter(uavSocket.getOutputStream( ), true);
inStream = new BufferedReader(new
InputStreamReader(uavSocket.getInputStream( )));
[0080] The first statement in this segment creates a new socket
object and names it "uavSocket." The socket constructor used here
requires a fully qualified IP address of the machine the socket is
to connect to, in this case the Java server on a remote control
device or a UAV, and the port number to connect to. In this
example, "computerAddress" is taken as a domain name that resolves
to a fully qualified dotted decimal IP address. Alternatively, a
dotted decimal IP address may be employed directly, as, for
example, "195.123.001.001." The second argument in the call to the
socket constructor is the port number. Port number 7 is the port on
which the server listens in this example, whether the server is on
a remote control device or on a UAV.
[0081] The second statement in this segment gets the socket's
output stream and opens a Java PrintWriter object on it. Similarly,
the third statement gets the socket's input stream and opens a Java
BufferedReader object on it. To send data through the socket, an
application writes to the PrintWriter, as, for example: [0082]
outStream.println(someWaypoint, macro, or Flight Control
Instruction);
[0083] To receive data through the socket, an application reads
from the BufferedReader, as show here for example: [0084] a
Waypoint, GPS data, macro, or flight control instruction=in
Stream.readLine( );
[0085] The method of FIG. 4 also includes calculating (410) a
heading in dependence upon the starting position, the coordinates
of the waypoint, and a navigation algorithm. Methods of calculating
a heading are discussed in detail below in this specification.
[0086] The method of FIG. 4 includes identifying (418) flight
control instructions for flying the UAV on the heading. Flight
control instructions are specific commands that affect the flight
control surfaces of the UAV. That is, instructions to move the
flight control surfaces to affect the UAV's flight causing the UAV
to turn, climb, descend, and so on. As an aid to further
explanation, an exemplary method of identifying flight control
instructions for flying on a calculated heading is provided: [0087]
receive new calculated heading from navigation algorithms [0088]
read current heading from downlink telemetry [0089] if current
heading is left of the calculated heading, identify flight control
instruction: AILERONS LEFT 30 DEGREES [0090] if current heading is
right of the calculated heading, identify flight control
instruction: AILERONS RIGHT 30 DEGREES [0091] monitor current
heading during turn [0092] when current heading matches calculated
heading, identify flight control instruction: FLY STRAIGHT AND
LEVEL
[0093] The method of FIG. 4 includes transmitting (420) uplink
telemetry, including the flight instructions, through the socket to
the UAV. Transmitting (420) the flight control instructions from
the remote control device to the UAV may be carried out by use of
any data communications protocol, including, for example,
transmitting the flight control instructions as form data, URI
encoded data, in an HTTP message, a WAP message, an HDML message,
or any other data communications protocol message as will occur to
those of skill in the art.
[0094] FIG. 4A is a data flow diagram illustrating an exemplary
method for receiving downlink telemetry. The method of FIG. 4A
includes listening (450) on the socket (456) for downlink data
(458). Listening on a socket for downlink data may be implemented
by opening a socket, creating an input stream for the socket, and
reading data from the input stream, as illustrated, for example, in
the following segment of pseudocode:
TABLE-US-00002 uavSocket = new Socket( "computerAddress", 7);
inStream = new BufferedReader(new
InputStreamReader(uavSocket.getInputStream( ))); String
downLinkData = inStream.readLine( );
[0095] This segment opens a socket object named "uavSocket" with an
input stream named "inStream." Listening for downlink data on the
socket is accomplished with a blocking call to in Stream.readLine(
) which returns a String object name "downLinkData."
[0096] The method of FIG. 4A includes storing (452) downlink data
(458) in computer memory (166) and exposing (454) the stored
downlink data (458) through an API (462) to a navigation
application (460). Downlink data typically is exposed through an
`API` (Application Programming Interface) by providing in a Java
interface class public accessor functions for reading from member
data elements in which the downlink data is stored. A navigation
application wishing to access downlink data then may access the
data by calling a public accessor methods, as, for example: String
someDownLinkData=APIimpl.getDownLinkData( ).
[0097] In the method of FIG. 4A, the downlink telemetry (470)
further comprises flight control instructions. It is
counterintuitive that downlink telemetry contains flight control
instruction when the expected data communications direction for
flight control instructions ordinarily is in uplink from a remote
control device to a UAV. It is useful to note, however, that flight
control instructions can be uplinked from a multiplicity of remote
control devices, not just one. A flight line technician with a
handheld PDA can issue flight control instructions to a UAV that is
also linked for flight control to a computer in a ground station.
It is sometimes advantageous, therefore, for downlink telemetry to
include flight control instructions so that one remote control
device can be advised of the fact that some other remote control
device issued flight control instructions to the same UAV.
[0098] FIG. 4B sets forth a data flow diagram illustrating an
exemplary method for transmitting uplink telemetry. The method of
FIG. 4B includes monitoring (466) computer memory (166) for uplink
data (464) from a navigation application (460). When uplink data
(464) is presented, the method of FIG. 4B includes sending (468)
the uplink data through the socket (456) to the UAV (100). Sending
uplink data through a socket may be implemented by opening a
socket, creating an output stream for a socket, and writing the
uplink data to the output stream, as illustrated, for example, in
the following segment of pseudocode:
TABLE-US-00003 uavSocket = new Socket( "computerAddress", 7);
outStream = new PrintWriter(uavSocket.getOutputStream( ), true);
outStream.println(String someUplinkData);
[0099] This segment opens a socket object named "uavSocket" with an
output stream named "outStream." Sending uplink data through the
socket is accomplished with a call to outStream.println( ) which
takes as a call parameter a String object named
"someUplinkData."
Macros
[0100] Although the flow chart of FIG. 4 illustrates navigating a
UAV to a single waypoint, as a practical matter, embodiments of the
present invention typically support navigating a UAV along a route
having many waypoints, including a final waypoint and one or more
intermediate waypoints. That is, methods of the kind illustrated in
FIG. 4 may also include receiving user selections of a multiplicity
of GUI map pixels representing waypoints, where each pixel has a
location on the GUI and mapping each pixel location to Earth
coordinates of a waypoint.
[0101] Such methods for navigating a UAV can also include assigning
one or more UAV instructions to each waypoint and storing the
coordinates of the waypoints and the UAV instructions in computer
memory on the remote control device. A UAV instruction typically
includes one or more instructions for a UAV to perform a task in
connection with a waypoint. Exemplary tasks include turning on or
off a camera installed on the UAV, turning on or off a light
installed on the UAV, orbiting a waypoint, or any other task that
will occur to those of skill in the art.
[0102] UAV instructions to perform tasks in connection with a
waypoint may be encoded in, for example, XML (the eXtensible Markup
Language) as shown in the following exemplary XML segment:
TABLE-US-00004 <UAV-Instructions> <macro>
<waypoint> 33.degree. 44' 10'' N 30.degree. 15' 50'' W
</waypoint> <instruction> orbit </instruction>
<instruction> videoCameraON </instruction>
<instruction> wait30minutes </instruction>
<instruction> videoCameraOFF </instruction>
<instruction> nextWaypoint </instruction>
</macro> <macro> </macro> <macro>
</macro> <macro> </macro>
<UAV-instructions>
[0103] This XML example has a root element named
`UAV-instructions.` The example contains several subelements named
`macro.` One `macro` subelement contains a waypoint location
representing an instruction to fly to 33.degree. 44' 10'' N
30.degree. 15' 50'' W. That macro subelement also contains several
instructions for tasks to be performed when the UAV arrives at the
waypoint coordinates, including orbiting around the waypoint
coordinates, turning on an on-board video camera, continuing to
orbit for thirty minutes with the camera on, turning off the video
camera, and continuing to a next waypoint. Only one macro set of
UAV instructions is shown in this example, but that is not a
limitation of the invention. In fact, such sets of UAV instructions
may be of any useful size as will occur to those of skill in the
art.
[0104] Exemplary methods of navigating a UAV also include flying
the UAV to each waypoint in accordance with one or more navigation
algorithms and operating the UAV at each waypoint in accordance
with the UAV instructions for each waypoint. Operating the UAV at
the waypoint in accordance with the UAV instructions for each
waypoint typically includes identifying flight control instructions
in dependence upon the UAV instructions for each waypoint and
transmitting the flight control instructions as uplink telemetry
through a socket. Flight control instructions identified in
dependence upon the UAV instructions for each waypoint typically
include specific flight controls to move the flight control
surfaces of the UAV causing the UAV to fly in accordance with the
UAV instructions. For example, in the case of a simple orbit, a
flight control instruction to move the ailerons and hold them at a
certain position causing the UAV to bank at an angle can effect an
orbit around a waypoint.
[0105] Operating the UAV at the waypoint in accordance with the UAV
instructions for each waypoint typically includes transmitting the
flight control instructions as uplink data from the remote control
device to the UAV. Transmitting the flight control instructions as
uplink data from the remote control device to the UAV may be
carried out by use of any data communications protocol, including,
for example, transmitting the flight control instructions as form
data, URI encoded data, in an HTTP message, a WAP message, an HDML
message, or any other data communications protocol message as will
occur to those of skill in the art.
Pixel Mapping
[0106] For further explanation of the process of mapping pixels'
locations to Earth coordinates, FIG. 5 sets forth a block diagram
that includes a GUI (502) displaying a map (not shown) and a
corresponding area of the surface of the Earth (504). The GUI map
has pixel boundaries identified as Row.sub.1, Col.sub.1; Row.sub.1,
Col.sub.100; Row.sub.100, Col.sub.100; and Row.sub.100, Col.sub.1.
In this example, the GUI map is assumed to include 100 rows of
pixels and 100 columns of pixels. This example of 100 rows and
columns is presented for convenience of explanation; it is not a
limitation of the invention. GUI maps according to embodiments of
the present invention may include any number of pixels as will
occur to those of skill in the art.
[0107] The illustrated area of the surface of the Earth has
corresponding boundary points identified as Lat.sub.1, Lon.sub.1;
Lat.sub.1, Lon.sub.2; Lat.sub.2, Lon.sub.2; and Lat.sub.2,
Lon.sub.1. This example assumes that the distance along one side of
surface area (504) is 100 nautical miles, so that the distance
expressed in terms of latitude or longitude between boundary points
of surface area (504) is 100 minutes or 1.degree. 40'.
[0108] In typical embodiments, mapping a pixel's location on the
GUI to Earth coordinates of a waypoint includes mapping pixel
boundaries of the GUI map to Earth coordinates. In this example,
the GUI map boundary at Row.sub.1, Col.sub.1 maps to the surface
boundary point at Lat.sub.1, Lon.sub.1; the GUI map boundary at
Row.sub.1, Col.sub.2 maps to the surface boundary point at
Lat.sub.1, Lon.sub.2; the GUI map boundary at Row.sub.2, Col.sub.2
maps to the surface boundary point at Lat.sub.2, Lon.sub.2; the GUI
map boundary at Row.sub.2, Col.sub.1 maps to the surface boundary
point at Lat.sub.2, Lon.sub.1.
[0109] Mapping a pixel's location on the GUI to Earth coordinates
of a waypoint typically also includes identifying a range of
latitude and a range of longitude represented by each pixel. The
range of latitude represented by each pixel may be described as
(Lat.sub.2-Lat.sub.1)/N.sub.rows, where (Lat.sub.2-Lat.sub.1) is
the length in degrees of the vertical side of the corresponding
surface (504), and N.sub.rows is the number of rows of pixels. In
this example, (Lat.sub.2-Lat.sub.1) is 1.degree. 40' or 100
nautical miles, and N.sub.rows is 100 rows of pixels. The range of
latitude represented by each pixel in this example therefore is one
minute of arc or one nautical mile.
[0110] Similarly, the range of longitude represented by each pixel
may be described as (Lon.sub.2-Lon.sub.1)/N.sub.cols, where
(Lon.sub.2-Lon.sub.1) is the length in degrees of the horizontal
side of the corresponding surface (504), and N.sub.cols is the
number of columns of pixels. In this example, (Lon.sub.2-Lon.sub.1)
is 1.degree. 40' or 100 nautical miles, and N.sub.cols is 100
columns of pixels. The range of longitude represented by each pixel
in this example therefore is one minute of arc or one nautical
mile.
[0111] Mapping a pixel's location on the GUI to Earth coordinates
of a waypoint typically also includes locating a region on the
surface of the Earth in dependence upon the boundaries, the ranges,
and the location of the pixel on the GUI map. The region is the
portion of the surface corresponding to the pixel itself. That
region is located generally by multiplying in both dimensions,
latitude and longitude, the range of latitude and longitude by
column or row numbers of the pixel location on the GUI map. That
is, a latitude for the surface region of interest is given by
Expression 1.
Lat.sub.1+P.sub.row((Lat.sub.2-Lat.sub.1)/N.sub.rows) (Exp. 1)
[0112] In Expression 1: [0113] Lat.sub.1 is the latitude of an
origin point for the surface area (504) corresponding generally to
the GUI map, [0114] P.sub.row is the row number of the pixel
location on the GUI map, and [0115]
((Lat.sub.2-Lat.sub.1)/N.sub.rows) is the range of latitude
represented by the pixel.
[0116] Similarly, a longitude for the surface region of interest is
given by Expression 2.
Lon.sub.1+P.sub.col((Lon.sub.2-Lon.sub.1)/N.sub.cols) (Exp. 2)
[0117] In Expression 2: [0118] Lon.sub.1 is the longitude of an
origin point for the surface area (504) corresponding generally to
the GUI map, [0119] P.sub.col is the column number of the pixel
location on the GUI map, and [0120]
((Lon.sub.2-Lon.sub.1)/N.sub.cols) is the range of longitude
represented by the pixel.
[0121] Referring to FIG. 5 for further explanation, Expressions 1
and 2 taken together identify a region (508) of surface area (504)
that corresponds to the location of pixel (412) mapping the pixel
location to the bottom left corner (506) of the region (508).
Advantageously, however, many embodiments of the present invention
further map the pixel to the center of the region by adding one
half of the length of the region's sides to the location of the
bottom left corner (506).
[0122] More particularly, locating a region on the surface of the
Earth in dependence upon the boundaries, the ranges, and the
location of the pixel on the GUI map, as illustrated by Expression
3, may include multiplying the range of longitude represented by
each pixel by a column number of the selected pixel, yielding a
first multiplicand; and multiplying the range of longitude
represented by each pixel by 0.5, yielding a second multiplicand;
adding the first and second multiplicands to an origin longitude of
the GUI map.
Lon.sub.1+P.sub.col((Lon.sub.2-Lon.sub.1)/N.sub.col)+0.5((Lon.sub.2-Lon.-
sub.1)/N.sub.cols) (Exp. 3)
[0123] In Expression 3, the range of longitude represented by each
pixel is given by ((Lon.sub.2-Lon.sub.1)/N.sub.cols), and the first
multiplicand is P.sub.col((Lon.sub.2-Lon.sub.1)/N.sub.cols). The
second multiplicand is given by
0.5((Lon.sub.2-Lon.sub.1)/N.sub.cols).
[0124] Similarly, locating a region on the surface of the Earth in
dependence upon the boundaries, the ranges, and the location of the
pixel on the GUI map, as illustrated by Expression 4, typically
also includes multiplying the range of latitude represented by each
pixel by a row number of the selected pixel, yielding a third
multiplicand; multiplying the range of latitude represented by each
pixel by 0.5, yielding a fourth multiplicand; and adding the third
and fourth multiplicands to an origin latitude of the GUI map.
Lat.sub.1+P.sub.row((Lat.sub.2-Lat.sub.1)/N.sub.rows)+0.5((Lat.sub.2-Lat-
.sub.1)/N.sub.rows) (Exp. 4)
[0125] In Expression 4, the range of latitude represented by each
pixel is given by ((Lat.sub.2-Lat.sub.1)/N.sub.rows), and the third
multiplicand is P.sub.row((Lat.sub.2-Lat.sub.1)/N.sub.rows). The
fourth multiplicand is given by
0.5((Lat.sub.2-Lat.sub.1)/N.sub.rows). Expressions 3 and 4 taken
together map the location of pixel (412) to the center (510) of the
located region (508).
Navigation on a Heading to a Waypoint
[0126] An exemplary method of navigating in accordance with a
navigation algorithm is explained with reference to FIGS. 6 and 7.
FIG. 6 sets forth a flow chart illustrating an exemplary method of
navigating a UAV in accordance with a navigation algorithm, and
FIG. 7 sets forth a line drawing illustrating a flight path
produced by application of the method of FIG. 6.
[0127] The method of FIG. 6 includes periodically repeating (610)
the steps of, receiving (602) in the remote control device from the
GPS receiver a current position of the UAV, and calculating (604) a
new heading from the current position to the waypoint. The method
of FIG. 6 also includes identifying (606) flight control
instructions for flying the UAV on the new heading, and
transmitting (608), from the remote control device to the UAV, the
flight control instructions for flying the UAV on the new heading.
In this method, if Lon.sub.1, Lat.sub.1 is taken as the current
position, and Lon.sub.2, Lat.sub.2 is taken as the waypoint
position, then the new heading may be calculated generally as the
inverse tangent of
((Lat.sub.2-Lat.sub.1)/(Lon.sub.2-Lon.sub.1)).
[0128] FIG. 7 shows the effect of the application of the method of
FIG. 6. In the example of FIG. 7, a UAV is flying in a cross wind
having cross wind vector (708). Curved flight path (716) results
from periodic calculations according to the method of FIG. 6 of a
new heading straight from a current location to the waypoint. FIG.
7 shows periodic repetitions of the method of FIG. 6 at plot points
(710, 712, 714). For clarity of explanation, only three periodic
repetitions are shown, although that is not a limitation of the
invention. In fact, any number of periodic repetitions may be used
as will occur to those of skill in the art.
Navigation with Headings set to a Cross Track Direction
[0129] A further exemplary method of navigating in accordance with
a navigation algorithm is explained with reference to FIGS. 8 and
9. FIG. 8 sets forth a flow chart illustrating an exemplary method
of navigating a UAV in accordance with a navigation algorithm, and
FIG. 9 sets forth a line drawing illustrating a flight path
produced by application of the method of FIG. 8. The method of FIG.
8 includes identifying (802) a cross track between the starting
point and the waypoint. A cross track is a fixed course from a
starting point directly to a waypoint. If Lon.sub.1, Lat.sub.1 is
taken as the position of a starting point, and Lon.sub.2, Lat.sub.2
is taken as the waypoint position, then a cross track is identified
by Lon.sub.1, Lat.sub.1 and Lon.sub.2, Lat.sub.2. A cross track has
a direction, a `cross track direction,` that is the direction
straight from a starting point to a waypoint, and it is often
useful to characterize a cross track by its cross track direction.
The cross track direction for a cross track identified by starting
point Lon.sub.1, Lat.sub.1 and waypoint position Lon.sub.2,
Lat.sub.2 may be calculated generally as the inverse tangent of
((Lat.sub.2-Lat.sub.1)/(Lon.sub.2-Lon.sub.1)).
[0130] The method of FIG. 8 includes periodically repeating (810)
the steps of receiving (804) in the remote control device from the
GPS receiver a current position of the UAV, and calculating (806) a
shortest distance between the current position and the cross track.
If the shortest distance between the current position and the cross
track is greater than a threshold distance (808), the method of
FIG. 8 includes transmitting (812) flight control instructions that
pilot the UAV toward the cross track, and, when the UAV arrives at
the cross track, transmitting (814) flight control instructions
that pilot the UAV in a cross track direction toward the
waypoint.
[0131] FIG. 9 illustrates calculating a shortest distance between
the current position and a cross track. In the example of FIG. 9,
calculating a shortest distance between the current position and a
cross track includes calculating the distance from a current
position (912) to the waypoint (704). In the example of FIG. 9, the
distance from the current position (912) to the waypoint (704) is
represented as the length of line (914). For current position
Lon.sub.1, Lat.sub.1 and waypoint position Lon.sub.2, Lat.sub.2,
the distance from a current position (912) to the waypoint (704) is
given by the square root of
(Lat.sub.2-Lat.sub.1).sup.2+(Lon.sub.2-Lon.sub.1).sup.2.
[0132] In this example, calculating a shortest distance between the
current position and a cross track also includes calculating the
angle (910) between a direction from the current position (912) to
the waypoint (704) and a cross track direction. In the example of
FIG. 9, the direction from the current position (912) to the
waypoint (704) is represented as the direction of line (914). In
the example of FIG. 9, the cross track direction is the direction
of cross track (706). The angle between a direction from the
current position to the waypoint and a cross track direction is the
difference between those directions.
[0133] In the current example, calculating a shortest distance
between the current position and a cross track also includes
calculating the tangent of the angle between a direction from the
current position to the waypoint and a cross track direction and
multiplying the tangent of the angle by the distance from the
current position to the waypoint.
[0134] FIG. 9 also shows the effect of the application of the
method of FIG. 8. In the example of FIG. 9, a UAV is flying in a
cross wind having cross wind vector (708). The flight path (904)
results from periodic calculations according to the method of FIG.
8 of a shortest distance between a current position and the cross
track (706), flying the UAV back to the cross track and then flying
in the direction of the cross track whenever the distance from the
cross track exceeds a predetermined threshold distance (916).
Headings Set to Cross Track Direction with Angular Thresholds
[0135] A further exemplary method of navigating in accordance with
a navigation algorithm is explained with reference to FIGS. 10 and
11. FIG. 10 sets forth a flow chart illustrating an exemplary
method of navigating a UAV in accordance with a navigation
algorithm, and FIG. 11 sets forth a line drawing illustrating a
flight path produced by application of the method of FIG. 10.
[0136] In the method of FIG. 10, piloting in accordance with a
navigation algorithm includes identifying (1002) a cross track
having a cross track direction between the starting point and the
waypoint. As described above, a cross track is identified by a
position of a starting point and a waypoint position. For a
starting point position of Lon.sub.1, Lat.sub.1 and a waypoint
position of Lon.sub.2, Lat.sub.2, a cross track is identified by
Lon.sub.1, Lat.sub.1 and Lon.sub.2, Lat.sub.2. In addition, it is
often also useful to characterize a cross track by its cross track
direction. The cross track direction for a cross track identified
by starting point Lon.sub.1, Lat.sub.1 and waypoint position
Lon.sub.2, Lat.sub.2 may be calculated generally as the inverse
tangent of ((Lat.sub.2-Lat.sub.1)/(Lon.sub.2-Lon.sub.1)).
[0137] In the method of FIG. 10, navigating a UAV in accordance
with a navigation algorithm includes periodically repeating (1010)
the steps of receiving (1004) in the remote control device from the
GPS receiver a current position and a current heading of the UAV,
and calculating (1006) an angle between the direction from the
current position to the waypoint and a cross track direction. If
the angle is greater than a threshold angle (1008), the method of
FIG. 10 includes transmitting (1012) flight control instructions
that pilot the UAV toward the cross track, and, upon arriving at
the cross track, transmitting (1014) flight control instructions
that pilot the UAV in the cross track direction toward the
waypoint.
[0138] Transmitting (1012) flight control instructions that pilot
the UAV toward the cross track is carried out by transmitting
flight control instructions to turn to a heading no more than
ninety degrees from the cross track direction, turning to the left
if the current position is right of the cross track and to the
right if the current position is left of the cross track.
Transmitting (1014) flight control instructions that pilot the UAV
in the cross track direction toward the waypoint transmitting
flight control instructions to turn the UAV to the cross track
direction and then flying straight and level on the cross track
direction.
[0139] FIG. 11 shows the effect of the application of the method of
FIG. 10. In the example of FIG. 11, a UAV is flying in a cross wind
having cross wind vector (708). The flight path (1104) results from
periodically transmitting flight control instructions to fly the
UAV, according to the method of FIG. 10, back to the cross track
and then in the direction of the cross track whenever an angle
between the direction from the current position to the waypoint and
a cross track direction exceeds a predetermined threshold
angle.
[0140] In many embodiments of the method of FIG. 10, the threshold
angle is a variable whose value varies in dependence upon a
distance between the UAV and the waypoint. In typical embodiments
that vary the threshold angle, the threshold angle is increased as
the UAV flies closer to the waypoint. It is useful to increase the
threshold angle as the UAV flies closer to the waypoint to reduce
the risk of excessive `hunting.` That is, because the heading is
the cross track direction, straight to the WP rather than cross
wind, if the angle remains the same, the distance that the UAV
needs to be blown off course to trigger transmitting flight control
signals instructing the UAV to return to the cross track gets
smaller and smaller until the UAV is flying to the cross track,
turning to the cross track direction, getting blown immediately
across the threshold, flying back the cross track, turning to the
cross track direction, getting blown immediately across the
threshold, and so on, and so on, in rapid repetition. Increasing
the threshold angle as the UAV flies closer to the waypoint
increases the lateral distance available for wind error before
triggering the transmission of flight instructions to return to the
cross track, thereby reducing this risk of excessive hunting.
[0141] FIG. 12 sets forth a flow chart illustrating an exemplary
method for navigating a UAV that includes receiving (402) in a
remote control device a user's selection of a GUI map pixel (412)
that represents a waypoint for UAV navigation. The pixel has a
location on the GUI. Such a GUI map display has many pixels, each
of which represents at least one position on the surface of the
Earth. A user selection of a pixel is normal GUI operations to take
a pixel location, row and column, from a GUI input/output adapter
driven by a user input device such as a joystick or a mouse. The
remote control device can be a traditional `ground control
station,` an airborne PDA or laptop, a workstation in Earth orbit,
or any other control device capable of accepting user selections of
pixels from a GUI map.
[0142] The method of FIG. 12 includes mapping (404) the pixel's
location on the GUI to Earth coordinates of the waypoint (414). As
discussed in more detail above with reference to FIG. 5, mapping
(404) the pixel's location on the GUI to Earth coordinates of the
waypoint (414) typically includes mapping pixel boundaries of the
GUI map to corresponding Earth coordinates and identifying a range
of latitude and a range of longitude represented by each pixel.
Mapping (404) the pixel's location on the GUI to Earth coordinates
of the waypoint (414) also typically includes locating a region on
the surface of the Earth in dependence upon the boundaries, the
ranges, and the location of the pixel on the GUI map.
[0143] The method of FIG. 12 also includes transmitting (406)
uplink telemetry, including the coordinates of the waypoint, to the
UAV through a socket on the remote control device. Transmitting
(406) uplink telemetry, including the coordinates of the waypoint,
to the UAV through a socket on the remote control device may be
carried out by use of any data communications protocol, including,
for example, transmitting the coordinates as form data, URI encoded
data, in an HTTP message, a WAP message, an HDML message, or any
other data communications protocol message as will occur to those
of skill in the art. Transmitting uplink telemetry through a socket
may be implemented by opening a socket, creating an output stream
for the socket, and writing uplink telemetry data to the output
stream, as illustrated, for example, in the following segment of
pseudocode:
TABLE-US-00005 uavSocket = new Socket( "computerAddress", 7);
outStream = new PrintWriter(uavSocket.getOutputStream( ), true);
outStream.println(String someUplinkData);
[0144] This segment opens a socket object named "uavSocket" with an
output stream named "outStream." Transmitting uplink telemetry
through the socket is accomplished with a call to
outStream.println( ) which takes as a call parameter a String
object named "someUplinkData."
[0145] The method of FIG. 12 also includes receiving (408) downlink
telemetry, including a starting position from a GPS receiver, from
the UAV through the socket and piloting (410) the UAV, under
control of a navigation computer on the UAV, from the starting
position to the waypoint in accordance with a navigation algorithm.
Methods of piloting a UAV according to a navigation algorithm are
discussed in detail below in this specification.
[0146] Receiving downlink telemetry through a socket may be
implemented by opening a socket, creating an input stream for the
socket, and reading data from the input stream, as illustrated, for
example, in the following segment of pseudocode:
TABLE-US-00006 uavSocket = new Socket( "computerAddress", 7);
inStream = new BufferedReader(new
InputStreamReader(uavSocket.getInputStream( ))); String
downLinkTelemetry = inStream.readLine( );
[0147] This segment opens a socket object named "uavSocket" with an
input stream named "in Stream." Receiving downlink telemetry
through the socket is accomplished with a blocking call to in
Stream.readLine( ) which returns a String object name
"downLinkTelemetry."
[0148] In the method of FIG. 12, downlink telemetry may include
Earth coordinates of waypoints as well as one or more UAV
instructions. It is counterintuitive that downlink telemetry
contains waypoint coordinates and UAV instructions when the
expected data communications direction for waypoint coordinates and
UAV instructions ordinarily is in uplink from a remote control
device to a UAV. It is useful to note, however, that waypoint
coordinates and UAV instructions can be uplinked from a
multiplicity of remote control devices, not just one. A flight line
technician with a handheld PDA can issue waypoint coordinates and
UAV instructions to a UAV that is also linked for flight control to
a computer in a ground station. It is sometimes advantageous,
therefore, for downlink telemetry to include waypoint coordinates
or UAV instructions so that one remote control device can be
advised of the fact that some other remote control device issued
waypoint coordinates or UAV instructions to the same UAV.
Macros
[0149] As mentioned above, embodiments of the present invention
often support navigating a UAV along a route having many waypoints,
including a final waypoint and one or more intermediate waypoints.
That is, methods of the kind illustrated in FIG. 12 may also
include receiving user selections of a multiplicity of GUI map
pixels representing waypoints, where each pixel has a location on
the GUI and mapping each pixel location to Earth coordinates of a
waypoint.
[0150] Such methods of navigating a UAV can also include assigning
one or more UAV instructions to each waypoint and transmitting the
coordinates of the waypoints and the UAV instructions in the uplink
telemetry through the socket to the UAV. A UAV instruction
typically includes one or more instructions for a UAV to perform a
task in connection with a waypoint. Exemplary tasks include turning
on or off a camera installed on the UAV, turning on or off a light
installed on the UAV, orbiting a waypoint, or any other task that
will occur to those of skill in the art. Such exemplary methods of
navigating a UAV also include storing the coordinates of the
waypoints and the UAV instructions in computer memory on the UAV,
piloting the UAV to each waypoint in accordance with one or more
navigation algorithms, and operating the UAV at each waypoint in
accordance with the UAV instructions for each waypoint.
Navigation on a Course to a Waypoint
[0151] A further exemplary method of navigating in accordance with
a navigation algorithm is explained with reference to FIGS. 13, 14,
and 15. FIG. 13 sets forth a flow chart illustrating an exemplary
method of piloting in accordance with a navigation algorithm. FIG.
14 sets forth a line drawing illustrating a method of calculating a
heading with a cross wind to achieve a particular ground course.
And FIG. 15 sets forth a line drawing illustrating a flight path
produced by application of the method of FIG. 13.
[0152] In the method of FIG. 13, piloting in accordance with a
navigation algorithm comprises periodically repeating (1212) the
steps of reading (1202) from the GPS receiver a current position of
the UAV; calculating (1204) a direction to the waypoint from the
current position; calculating (1206) a heading in dependence upon
wind speed, wind direction, airspeed, and the direction to the
waypoint; turning (1208) the UAV to the heading; and flying (1210)
the UAV on the heading.
[0153] FIG. 14 illustrates calculating a heading in dependence upon
wind speed, wind direction, airspeed, and the direction to the
waypoint. FIG. 14 sets forth a line drawing illustrating relations
among several pertinent vectors, a wind velocity (1222), a
resultant velocity (1224), and a UAV's air velocity (1226). A
velocity vector includes a speed and a direction. These vectors
taken together represent wind speed, wind direction, airspeed, and
the direction to the waypoint. In the example of FIG. 14, the angle
B is a so-called wind correction angle, an angle which subtracted
from (or added to, depending on wind direction) a direction to a
waypoint yields a heading, a compass heading for a UAV to fly so
that its resultant ground course is on a cross track. A UAV
traveling at an airspeed of `a` on heading (D-B) in the presence of
a wind speed `b` with wind direction E will have resultant
groundspeed `c` in direction D.
[0154] In FIG. 14, angle A represents the difference between the
wind direction E and the direction to the waypoint D. In FIG. 14,
the wind velocity vector (1222) is presented twice, once to show
the wind direction as angle E and again to illustrate angle A as
the difference between angles E and D. Drawing wind velocity (1222)
to form angle A with the resultant velocity (1224) also helps
explain how to calculate wind correction angle B using the law of
sines. Knowing two sides of a triangle and the angle opposite one
of them, the angle opposite the other may be calculated, in this
example, by B=sin.sup.-1(b(sin A)/a). The two known sides are
airspeed `a` and wind speed `b.` The known angle is A, the angle
opposite side `a,` representing the difference between wind
direction E and direction to the waypoint D. Calculating a heading,
angle F on FIG. 14, is then carried out by subtracting the wind
correction angle B from the direction to the waypoint D.
[0155] FIG. 15 shows the effect of the application of the method of
FIG. 13. In the example of FIG. 15, a UAV is flying in a cross wind
having cross wind vector (708). Curved flight path (1316) results
from periodic calculations according to the method of FIG. 13 of a
new heading straight whose resultant with a wind vector is a course
straight from a current location to the waypoint. FIG. 15 shows
periodic repetitions of the method of FIG. 13 at plot points (1310,
1312, 1314). For clarity of explanation, only three periodic
repetitions are shown, although that is not a limitation of the
invention. In fact, any number of periodic repetitions may be used
as will occur to those of skill in the art.
Navigation on a Course Set to a Cross Track Direction
[0156] A further exemplary method of navigating in accordance with
a navigation algorithm is explained with reference to FIGS. 16 and
17. FIG. 16 sets forth a flow chart illustrating an exemplary
method of piloting in accordance with a navigation algorithm, and
FIG. 17 sets forth a line drawing illustrating a flight path
produced by application of the method of FIG. 16.
[0157] The method of FIG. 16 includes identifying (1402) a cross
track and calculating (1404) a cross track direction from the
starting position to the waypoint. In the method of FIG. 16,
piloting in accordance with a navigation algorithm is carried out
by periodically repeating the steps of reading (1406) from the GPS
receiver a current position of the UAV; calculating (1408) a
shortest distance between the cross track and the current position;
and, if the shortest distance between the cross track and the
current position is greater than a threshold distance, piloting
(1412) the UAV to the cross track. Upon arriving at the cross
track, the method includes: reading (1414) from the GPS receiver a
new current position of the UAV; calculating (1416), in dependence
upon wind speed, wind direction, airspeed, and the cross track
direction, a new heading; turning (1418) the UAV to the new heading
(1502, 1505, and 1506); and flying (1420) the UAV on the new
heading.
[0158] FIG. 17 shows the effect of the application of the method of
FIG. 16. In the example of FIG. 17, a UAV is flying in a cross wind
having cross wind vector (708). Curved flight path (1504) results
from periodic calculations according to the method of FIG. 16 of a
shortest distance between a current position and the cross track
(706), flying the UAV back to the cross track, and, upon arriving
at the cross track, calculating a new heading and flying the UAV on
the new heading.
Navigating UAVs in Formation
[0159] It is also advantageous to have an ability to navigate UAVs
together in a flight formation or pattern. Exemplary methods,
systems, and products for navigating UAVs together in a flight
formation or pattern are described with reference to the
accompanying drawings, beginning with FIGS. 18, 19A, and 19B. FIG.
18 sets forth a flow chart illustrating an exemplary method for
navigating UAVs in formation. FIGS. 19A and 19B are line drawings
illustrating exemplary relations among UAVs flying in
formation.
[0160] The method of FIG. 18 includes assigning (302) pattern
positions to each of a multiplicity of UAVs flying together in a
pattern. The examples of FIGS. 19A and 19B includes two exemplary
flight patterns for UAVs. FIG. 19A illustrates a pattern having two
pattern positions occupied by UAV (226) and UAV (100). FIG. 19B
illustrates a pattern having four pattern positions occupied by
UAVs (226, 100, 234, and 142). Assigning pattern positions to each
of a multiplicity of UAVs flying together in a pattern may be
carried out by designating an anchor position for the pattern and
assigning pattern positions to the other UAVs relative to the
anchor position. In the pattern of FIG. 19A, for example, the
pattern position occupied by UAV (226) may be designated an anchor
position and UAV (100) may be assigned to a pattern position one
mile to the right of the position of UAV (226). Similarly in the
pattern of FIG. 19B, the position of the pattern position occupied
by UAV (226) may be designated an anchor position and: [0161] UAV
(100) may be assigned to a pattern position one mile to the right
of the position of UAV (226), [0162] UAV (234) may be assigned to a
pattern position one mile behind the position of UAV (226), and
[0163] UAV (142) may be assigned to a pattern position one mile to
the right and one mile behind the position of UAV (226).
[0164] The method of FIG. 18 also includes identifying (304) a
waypoint for each UAV in dependence upon the UAV's pattern
position. Identifying a waypoint for each UAV in dependence upon
its pattern position may be carried out by designating a waypoint
for the anchor position and calculating each UAV's waypoint in
dependence upon the waypoint for the anchor and in dependence upon
the UAV's position in the pattern. In the pattern of FIG. 19A, for
example, the pattern position occupied by UAV (226) may be
designated an anchor position and assigned the waypoint (230). If
UAV (100) is assigned to a pattern position one mile to the right
of the position of UAV (226), a waypoint (210) is calculated for
UAV (100) as one mile to the right of the waypoint (230) assigned
to the anchor position.
[0165] Similarly, if in the pattern of FIG. 19B: [0166] the
position of the pattern position occupied by UAV (226) is
designated an anchor position and assigned the waypoint (230),
[0167] UAV (100) is assigned to a pattern position one mile to the
right of the position of UAV (226), [0168] UAV (234) is assigned to
a pattern position one mile behind the position of UAV (226), and
[0169] UAV (142) is assigned to a pattern position one mile to the
right and one mile behind the position of UAV (226), then: [0170]
waypoint (210) is calculated for UAV (100) as one mile to the right
of the waypoint (230) assigned to the anchor position, [0171]
waypoint (238) is calculated for UAV (234) as one mile behind the
waypoint (230) assigned to the anchor position, and [0172] waypoint
(248) is calculated for UAV (142) as one mile to the right and one
mile behind the waypoint (230) assigned to the anchor position.
[0173] The method of FIG. 18 also includes piloting (306) the UAVs
in the pattern toward their waypoints in dependence upon a
navigation algorithm (312). The method of FIG. 18 also includes an
exemplary navigation algorithm that is implemented to repeatedly
compare (308) the UAV's intended position and the UAV's actual
position. In this example, the actual position is taken from a GPS
receiver on board the UAV.
[0174] Each UAV's intended position may be specified by the UAV's
position in the pattern, a cross track to the UAV's waypoint, and a
flight schedule. The intended position is a conceptual position, an
ideal used to navigate UAVs in formation. The intended position is
the position on the cross track where the UAV would be if it flew
precisely on schedule directly along the cross track.
[0175] A flight schedule is a time limitation upon travel from a
starting point to a waypoint. A flight schedule may be established
by assigning an arrival time at the waypoints of the pattern, from
which a groundspeed may be inferred. Or a flight schedule may be
established by assigning a groundspeed for the formation, from
which an arrival time can be inferred. Either way, the schedule
established an intended position for the formation for every moment
of the flight. If the groundspeed is taken as the governing
parameter, then the arrival time is the groundspeed multiplied by
the distance between the starting point and the waypoint. If the
arrival time is taken as the governing parameter, then the
groundspeed is the distance between the starting point and the
waypoint divided by the difference between the arrival time and the
start time. Either way, the groundspeed is known and the intended
position of the pattern at any point in time is the groundspeed
multiplied by the time elapsed after the start time. Similarly, for
each UAV in a pattern, the UAV's intended position at any point of
time elapsed after the start time is a position on a cross track
where the UAV would be if the UAV's course were directly over the
cross track at that point in time.
[0176] The exemplary UAVs of FIGS. 19A and 19B are shown flying
directly over their cross tracks. As a practical matter, actual
flight courses are rarely directly over cross tracks. Nevertheless,
for flying in formation, a course for each UAV that approximates a
cross track is adequate if a UAV's actual position in its actual
course does not vary too much from its intended position. What is
`too much` is defined by an error threshold. The navigation
algorithm of FIG. 18 includes calculating (310) a corrective flight
vector when the distance between the UAV's actual and intended
positions exceeds an error threshold. Calculating a corrective
flight vector is explained in more detail below.
[0177] Piloting UAVs in dependence upon a navigation algorithm,
together in a flight formation or pattern, usefully includes
startup and continuation of normal flight to UAV waypoints, that
is, flight when a UAV is within its error threshold. An exemplary
algorithm for such flight is described with reference to FIGS. 20
and 21. FIG. 20 sets forth a flow chart illustrating an exemplary
method of piloting the UAVs in dependence upon a navigation
algorithm. FIG. 21 sets forth a line drawing illustrating an
exemplary method of calculating airspeed and heading according to
the method of FIG. 21.
[0178] FIG. 20 sets forth a flow chart illustrating an exemplary
method of piloting the UAVs in dependence upon a navigation
algorithm that includes identifying (340) a cross track to a
waypoint for each UAV, where the cross track has a cross track
direction. In FIG. 21, cross track (212) has cross track direction
indicated by angle D. The method of FIG. 20 includes piloting (342)
the UAV to a starting point on the cross track. (222 on FIG. 21).
In subsequent iterations, the method may be implemented any time
the UAV returns to the cross track by moving the starting point to
the point where the UAV returns to the cross track.
[0179] The method of FIG. 20 includes calculating (344) an airspeed
for flying from the starting point to the waypoint on schedule. The
airspeed may be calculated from the wind speed, the groundspeed,
and the angle between the wind direction and the ground course
direction by use of the law of cosines according to the
formula:
a= {square root over (b.sup.2+c.sup.2-2ab cos A)},
where: [0180] a is the airspeed needed for flying from the starting
point to the waypoint on schedule, indicated on FIG. 21 as the
length (280) of the flight vector (250), [0181] b is the wind
speed, indicated on FIG. 21 as the length (282) of the wind vector
(208), [0182] c is the course groundspeed for flying from the
starting point to the waypoint on schedule, indicated on FIG. 21 as
the length (284) of the course vector (212), and [0183] A is the
angular difference between the wind direction and the ground course
direction along the cross track, indicated on FIG. 21 as the angle
`A.`
[0184] The wind direction is indicated on FIG. 21 as the angle E,
and the ground course direction along the cross track is indicated
on FIG. 21 as the angle D.
[0185] The method of FIG. 20 includes calculating (346) a heading
in dependence upon wind speed, wind direction, airspeed, and the
cross track direction. The heading may be so calculated by use of
the law of sines according to the formula:
B=sin.sup.-1(b(sin A)/a),
where: [0186] B is the wind correction angle, which in combination
with a direction to a waypoint yields a heading, indicated on FIG.
21 as angle `F,` [0187] b is the wind speed, indicated on FIG. 21
as the length (282) of the wind vector (208), [0188] A is the
angular difference between the wind direction and the ground course
direction along the cross track, indicated on FIG. 21 as the angle
`A,` and [0189] a is the airspeed needed for flying from the
starting point to the waypoint on schedule, calculated by use of
the law of cosines as described above, and indicated on FIG. 21 as
the length (280) of the flight vector (250).
[0190] Having the wind correction angle B, calculating the heading,
angle F on FIG. 21, is then carried out by subtracting the wind
correction angle B from the direction to the waypoint D.
[0191] The method of FIG. 20 includes flying (348) the UAV on the
heading at the airspeed. That is, starting from a starting point on
the cross track and flying a heading and airspeed so calculated,
results in a ground course that approximates the cross track
direction.
[0192] Calculating a corrective flight vector is further explained
with reference to FIGS. 22, 23, and 24. FIG. 22 sets forth a flow
chart illustrating an exemplary method of calculating a corrective
flight vector. FIG. 23 is a line drawing illustrating application
of the method of FIG. 22, showing relations among an intended
position, an error threshold, an actual position, a corrective
flight vector, and a cross track to a waypoint. FIG. 24 sets forth
a line drawing illustrating an exemplary method of calculating
corrective airspeed and corrective heading according to the method
of FIG. 22.
[0193] As mentioned above, an actual flight course is rarely
directly over a cross track. For flying in formation, a course for
each UAV that approximates a cross track is adequate if a UAV's
actual position in its actual course does not vary too much from
its intended position. What is `too much` is defined by an error
threshold. The navigation algorithm of FIG. 18 includes calculating
(310) a corrective flight vector when the distance between the
UAV's actual and intended positions exceeds an error threshold.
FIG. 23 shows a UAV whose actual position (218) is outside an error
threshold (202) around the UAV's intended position (220). That is,
for this exemplary UAV, the distance (290) between the UAV's actual
(218) and intended (220) positions exceeds an error threshold
(202).
[0194] The method of FIG. 22 includes selecting (360) a corrective
waypoint (214) on FIG. 23) on a cross track (212) between a UAV's
intended position (220) and its waypoint (210). Selecting a
corrective waypoint on a cross track between a UAV's intended
position and its waypoint may be carried out by selecting a
corrective waypoint at a predetermined portion of the distance
between a UAV's intended position and its waypoint. In the example
of FIG. 23, a corrective waypoint (214) on a cross track (212)
between a UAV's intended position (220) and its waypoint (210) is
selected as a corrective waypoint at the predetermined portion of
one-half of the distance between the UAV's intended position and
its waypoint.
[0195] The method of FIG. 22 also includes calculating (362) a
corrective airspeed for arriving at the corrective waypoint on
schedule. Calculating a corrective airspeed for arriving at the
corrective waypoint on schedule may include calculating a
groundspeed needed to bring the UAV to the remedial waypoint on
schedule. Calculating a groundspeed needed to bring the UAV to the
remedial waypoint on schedule may be carried out by dividing the
distance from the actual position to the corrective waypoint by the
difference between the current time and the schedule time for the
corrective waypoint. The schedule time for the corrective waypoint
is the time when the UAV would reach the corrective waypoint if the
UAV's ground course were over the cross track. With the groundspeed
to the remedial waypoint known, calculating a corrective airspeed
for arriving at the corrective waypoint on schedule may be
calculated from the wind speed, the groundspeed to the remedial
waypoint, and the angle between the wind direction and the ground
course to the corrective waypoint by use of the law of cosines
according to the formula:
a= {square root over (b.sup.2+c.sup.2-2ab cos A)},
where: [0196] a is the corrective airspeed for arriving at the
corrective waypoint on schedule, indicated on FIG. 24 as the length
(292) of the corrective flight vector (204), [0197] b is the wind
speed, indicated on FIG. 24 as the length (294) of the wind vector
(208), [0198] c is the groundspeed to the remedial waypoint,
indicated on FIG. 24 as the length (296) of the ground course to
the corrective waypoint (216), and [0199] A is the angular
difference between the wind direction and the ground course
direction to the corrective waypoint, indicated on FIG. 24 as the
angle `A.`
[0200] The wind direction is indicated on FIG. 24 as the angle E,
and the ground course direction to the corrective waypoint is
indicated on FIG. 24 as the angle D.
[0201] The method of FIG. 22 includes also calculating (364) a
corrective heading in dependence upon the calculated airspeed. The
corrective heading may be so calculated by use of the law of sines
according to the formula:
B=sin.sup.-1(b(sin A)/a),
where: [0202] B is the wind correction angle, which in combination
with a direction to a corrective waypoint yields a heading,
indicated on FIG. 24 as angle `B,` [0203] b is the wind speed,
indicated on FIG. 24 as the length (294) of the wind vector (208),
[0204] A is the angular difference between the wind direction and
the ground course to the corrective waypoint, indicated on FIG. 24
as the angle `A,` and [0205] a is the airspeed needed to fly from
the actual position (218) to the corrective waypoint so as to
arrive at the corrective waypoint on schedule, calculated by use of
the law of cosines as described above, and indicated on FIG. 24 as
the length (292) of the corrective flight vector (204).
[0206] Having the wind correction angle B, calculating the
corrective heading, angle F on FIG. 24, is then carried out by
subtracting the wind correction angle B from the direction to the
corrective waypoint D. Upon arriving at the corrective waypoint
(214), the UAV may be piloted by the method of FIG. 20, for
example, on a heading and with an airspeed calculated to fly a
course along a cross track (212 on FIG. 23) and arrive at its
waypoint on schedule.
[0207] All the navigational calculations for navigating UAVs in
formation according to embodiments of the present invention may be
carried in computers located either in the UAVs or in one or more
ground stations. In systems that carry out navigational
calculations in a UAV, uplink telemetry may provide starting
points, waypoints, and other flight parameters to the UAV, and
downlink telemetry may provide GPS locations for the UAV to the
ground station. In systems that carry out navigational calculations
in ground stations, downlink telemetry may provide GPS locations,
and uplink telemetry may provide flight control instructions.
[0208] It will be understood from the foregoing description that
modifications and changes may be made in various embodiments of the
present invention without departing from its true spirit. The
descriptions in this specification are for purposes of illustration
only and are not to be construed in a limiting sense. The scope of
the present invention is limited only by the language of the
following claims.
* * * * *
References