# Patent

## Title
System for automatically landing aircraft using image signals and method of controlling the same

## Abstract

Disclosed herein are a system for automatically landing an aircraft using image signals and a method of controlling the system. The system includes an altimeter installed on the aircraft; a landing mark placed at a landing location on a landing runway; a camera installed on the aircraft, oriented toward the front of the aircraft, and configured to detect the shape of the landing mark in image information form; and a FCC configured to calculate the angle between the aircraft and the ground, the ground range and the slant range between the aircraft and the landing location using the altitude information measured by the altimeter, the image information of the landing mark captured by the camera, angle information composed of the pitch, roll and yaw angles of the aircraft, and the angle of entry into the landing runway, and configured to control the automatic landing of the aircraft.

## Background
This is a Divisional of U.S. application Ser. No. 12/363,185, filed Jan. 30, 2009, the subject matter of which is incorporated herein by reference.


BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a system for automatically landing an aircraft using image signals, and, more particularly, to a system for automatically landing an aircraft using image signals and a method of controlling the system, which are capable of automatically landing an aircraft at a landing location using a landing mark provided at the landing location and imaging equipment configured to detect the landing mark.
2. Description of the Related Art
In order to land an aircraft, particularly an unmanned aircraft, a landing method based on an external pilot's control, a landing method using a parachute or a net and an automatic landing method using an Instrument Landing. System (ILS) have been used.
However, the landing methods require the maintenance of additional manpower and the provision of additional facilities. In order to solve these problems, a way of automatically landing an unmanned aircraft by radar has been used.
In detail, this prior art system for automatically landing an aircraft uses a technique of radiating radar waves from the ground to the unmanned aircraft by radar, calculating the distance between the unmanned aircraft and a landing runway by determining the time of arrival of the radar waves, and controlling the unmanned aircraft so that it can safely land at a landing location with the distance to the landing runway and the altitude of the unmanned aircraft integrally taken into consideration.
However, the system for automatically landing an aircraft having the above-described construction has a defect in that high cost equipment needs to be installed on the ground so as to radiate the radar waves.
Furthermore, there is a problem in that radar waved are easily exposed to disturbances which interrupt the radio waves.
SUMMARY OF THE INVENTION
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a system for automatically landing an aircraft using image signals, which is capable of detecting, using image signals, the deformation of the shape of a landing mark at a landing location on the ground that occurs as the attitude and location of the aircraft vary and automatically landing the aircraft at the landing location, and a method of controlling the system.
In order to accomplish the above object, the present invention provides a system for automatically landing an aircraft using image signals, including an altimeter installed on the aircraft, and configured to measure the altitude of the aircraft; a landing mark placed at a landing location on a landing runway; a camera installed on the aircraft, oriented toward the front of the aircraft, and configured to detect the shape of the landing mark in the form of image information; and a FCC(Flight Control Computer) configured to calculate the angle between the aircraft and the ground, the ground range between the aircraft and the landing location and the slant range between the aircraft and the landing location using the altitude information measured by the altimeter, the image information of the landing mark captured by the camera, angle information composed of the pitch, roll and yaw angles of the aircraft, and the angle of entry into the landing runway, and configured to control automatic landing of the aircraft.
The image information may include the horizontal and vertical lengths of the landing mark captured by the camera.
The altimeter may include a radio wave altimeter.
The landing mark may be painted with luminous paint.
The camera may include an infrared camera.
In order to accomplish the above object, the present invention provides a method of controlling a system for automatically landing an aircraft using image signals, including an altitude measurement step of a FCC of the aircraft receiving the altitude information of the aircraft from an altimeter; a landing mark recognition step of a camera installed in the aircraft and oriented toward the front of the aircraft capturing a landing mark at a landing location and transmitting it to the FCC; a landing mark measurement step of the FCC measuring the lateral and vertical lengths of the landing mark captured by the camera; a flight information calculation step of the FCC of the aircraft calculating the angle between the aircraft and the ground, the ground range between the aircraft and the landing location and the slant range between the aircraft and the landing location using the altitude information, the horizontal and vertical lengths of the landing mark measured at the landing mark measurement step, angle information composed of the pitch, roll and yaw angles of the aircraft and the angle of entry to a landing runway; and a flight control step of controlling the flight and attitude of the aircraft using the calculated flight information.
At the flight information calculation step, the angle θ between the aircraft and the ground may be calculated using Equation 1, the ground range GR between the aircraft and the landing location may be calculated using Equation 2, and the slant range SR between the aircraft and the landing location may be calculated using Equations 3 or 4:

θ=tan−1(y′′ cos(δ)cos(α)/(x′ cos(β)))  (1)

GR=h*x′ cos(β)/(y′′ cos(δ)cos(α))  (2)

SR=h/sin(tan−1(y′′ cos(δ)cos(α)/(x′ cos(β))))  (3)

SR=GR/cos(tan−1(y′′ cos(δ)cos(α)/(x′ cos(β))))  (4)

where α: the pitch angle,

β: the roll angle,
δ: the yaw angle,
x: the horizontal length of the landing mark measured from the image information recognized by the camera,

x′=x/cos(β),

y: the vertical length of the landing mark measured from the image information recognized by the camera,

y′=y/cos(α),

y′′=y′/cos(δ), and

h: the altitude information measured by the altimeter
At the flight information calculation step, calculating a ground range d1 to a nearest point that makes the angle of entry into the landing runway ψ zero at a current location using Equation 5 may be further included:

d1=(GR−D/2)*sin(ψ)  (5)

where ψ: the angle of entry into the landing runway, and

D: the actual diameter of the circle of the landing mark



BREIF DESCRIPTION OF THE DRAWINGS
The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
FIG. 1 is a plan view showing a landing mark for a system for automatically landing an aircraft using image signals according to the present invention;
FIG. 2 is a plan view showing the shape of the landing mark that is captured by the camera of an aircraft;
FIGS. 3 to 6 are diagrams showing methods of calculating the angle between an aircraft and the ground, the ground range between the aircraft and a landing location and the slant range between the aircraft and the landing location on the basis of a pitch angle (FIG. 4), a roll angle (FIG. 5), a yaw angle (FIG. 6), and the angle between the direction of movement of the aircraft and the direction of entry into a landing runway in a method of controlling the system for automatically landing an aircraft using image signals; and
FIG. 7 is a diagram showing a method of calculating a ground range to the nearest point that makes the angle of entry into a landing runway zero at a current location on the basis of the angle between the direction of movement of an aircraft and the direction of entry into the landing runway in a method of controlling the system for automatically landing an aircraft using image signals according to the present invention.



DESCRIPTION OF THE PREFERRED EMBODIMENTS
Reference now should be made to the drawings, in which the same reference numerals are used throughout the different drawings to designate the same or similar components.
Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Prior to the description, it should be noted that the terms and words used in the present specification and the attached claims should not be interpreted as having common meanings or meanings in a dictionary but should be interpreted as having meanings suitable for the technical spirit of the present invention on the basis of the principle in which an inventor can appropriately define the concepts of terms in order to describe his or her invention in the best way.
FIG. 1 is a plan view showing a landing mark for a system for automatically landing an aircraft using image signals according to the present invention, and FIG. 2 is a plan view showing the shape of the landing mark that is captured by the camera of the aircraft.
The system for automatically landing an aircraft using image signals according to the present invention includes an altimeter installed on the aircraft, and configured to measure an altitude of the aircraft; a landing mark placed at a landing location on a landing runway; a camera installed on the aircraft, oriented toward the front of the aircraft, and configured to detect the shape of the landing mark in the form of image information; and a FCC(Flight Control Computer) configured to calculate the angle θ between the aircraft and the ground, the ground range GR between the aircraft and the landing location and the slant range SR between the aircraft and the landing location using the altitude information measured by the altimeter, the image information of the landing mark captured by the camera, angle information composed of the pitch, roll and yaw angles of the aircraft, and an angle of entry into the landing runway, and configured to control automatic landing of the aircraft.
In the present embodiment, the aircraft may include an unmanned aircraft.
The altimeter may be a radio wave altimeter. That is, in order to provide a precise altitude value even when the altitude is reduced, the radio wave altimeter may be installed. In the present embodiment, it is possible to purchase MK5 (transmission frequency: 76 GHz, resolution: 0.02 m) or MK4 (transmission frequency: 13 GHz, resolution: 0.2 m) manufactured by Roke Manor Research Ltd. in the United Kingdom and use it as the radio wave altimeter.
The landing mark may be provided in a circular form. That is, it is preferred that the landing mark be a target plate on which a circle with a diameter of 10 m has been drawn, as shown in FIG. 1. Furthermore, it is preferred that the landing mark be painted with luminous paint so that it can be recognized at nighttime.
In the present embodiment, the camera may be a monochrome camera having a 480*640 specification. It will be apparent that the camera may be an infrared camera in order to improve precision, even though the target plate is painted with the luminous paint. Furthermore, the camera must be installed such that it is oriented toward the front of the aircraft in order to reduce errors.
The image information includes the horizontal and vertical lengths of the landing mark captured by the camera. That is, when an image of the landing mark is captured in the direction of movement of the aircraft, the circular shape of the landing mark on the ground looks like an elliptical shape, as shown in FIG. 2, and the horizontal length x and vertical length y of the landing mark measured by the camera vary with the distance between the aircraft and the landing mark, and the pitch angle, roll angle and yaw angle of the aircraft. However, if x<y, that is, θ>45°, in FIG. 3, error can be increased.
The operation and effect of the system for automatically landing an aircraft using image signals according to the present invention will be described below.
FIGS. 3 to 6 are diagrams showing methods of calculating the angle between an aircraft and the ground, the ground range between the aircraft and a landing location and the slant range between the aircraft and the landing location on the basis of a pitch angle (FIG. 4), a roll angle (FIG. 5), a yaw angle (FIG. 6), and the angle between the direction of movement of the aircraft and the direction of entry into a landing runway in a method of controlling the system for automatically landing an aircraft using image signals. FIG. 7 is a diagram showing a method of calculating a ground range d1 to the nearest point that makes the angle of entry into a landing runway zero at a current location on the basis of the angle between the direction of movement of an aircraft and the direction of entry into the landing runway in a method of controlling the system for automatically landing an aircraft using image signals according to the present invention.
In FIGS. 3 to 7, dotted line F indicates the direction of movement of an aircraft.
The method of controlling a system for automatically landing an aircraft using image signals according to the present invention includes an altitude measurement step of a FCC of the aircraft receiving altitude information of the aircraft from an altimeter; a landing mark recognition step of a camera installed in the aircraft and oriented toward the front of the aircraft capturing a landing mark at a landing location and transmitting it to the FCC; a landing mark measurement step of the FCC measuring the horizontal and vertical lengths of the landing mark captured by the camera; a flight information calculation step of the FCC of the aircraft calculating the angle between the aircraft and the ground, the ground range between the aircraft and the landing location and the slant range between the aircraft and the landing location using the altitude information, the horizontal and vertical lengths of the landing mark measured at the landing mark measurement step, angle information composed of the pitch, roll and yaw angles of the aircraft and the angle of entry to a landing runway; and a flight control step of controlling the flight and attitude of the aircraft using the calculated flight information.
The angle of entry into the landing runway ψ is the angle between the direction of movement of the aircraft and the direction of entry into the landing runway.
At the flight information calculation step, the angle θ between the aircraft and the ground is calculated using Equation 1 with reference to FIGS. 3 and 4, the ground range GR between the aircraft and the landing location is calculated using Equation 2, and the slant range SR between the aircraft and the landing location is calculated using Equations 3 or 4.

θ=tan−1(y′′ cos(δ)cos(α)/(x′ cos(β)))  (1)

GR=h*x′ cos(β)/(y′′ cos(δ)cos(α))  (2)

SR=h/sin(tan−1(y′′ cos(δ)cos(α)/(x′ cos(β))))  (3)

SR=GR/cos(tan−1(y′′ cos(δ)cos(α)/(x′ cos(β))))  (4)

In Equations 1 to 4,
α: the pitch angle,
β: the roll angle,
δ: the yaw angle,
x: the horizontal length of the landing mark measured from the image information recognized by the camera,

x′=x/cos(β),

y: the vertical length of the landing mark measured from the image information recognized by the camera,

y′=y/cos(α),

y′′=y′/cos(δ), and

h: the altitude information measured by the altimeter
Furthermore, at the flight information calculation step, if the angle of entry into the landing runway ψ is not 0, calculating the ground range to the nearest point d1 that makes the angle of entry into the landing runway ψ zero at a current location using Equation 5 is further included.

d1=(GR−D/2)*sin(ψ)  (5)

where ψ: the angle of entry into the landing runway, and

D: the actual diameter of the circle of the landing mark
As shown in FIG. 3, in the case where y=0.5 cm and x=1 cm when D=10 m, the pitch angle α=0°, the roll angle β=0°, the yaw angle δ=0°, the angle of entry into the landing runway ψ=0° and h=300 m,

y/x=0.5

θ=tan−1(y/x)=26.57°

GR=h*x/y=300/0.5=600 m, and

SR=h/sin(θ)=300/sin(26.57)=670.70 m

As shown in FIG. 4, in the case where y′=0.5 cm and x=1 cm when D=10 m, the pitch angle α=+10°, the roll angle β=0°, the yaw angle δ=0°, the angle of entry into the landing runway ψ=0° and h=300 m,

y=y′ cos(α)=0.5*cos(10)=0.4924 cm

y/x=0.4924/1=0.4924

θ=tan−1(y/x)=26.22°

GR=h*x/y=300/0.4924=609.26 m, and

SR=h/sin(θ)=300/sin(26.22)=679.01 m

As shown in FIG. 5, in the case where y′=0.5 cm and x′=1 cm when D=10 m, the pitch angle α=+10°, the roll angle β=+5°, the yaw angle δ=0°, the angle of entry into the landing runway ψ=0° and h=300 m,

y=y′ cos(α)=0.5*cos(10)=0.4924 cm

x=x′ cos(β)=1*cos(5)=0.9962 cm

y/x=0.4924/0.9962=0.4943

θ=tan−1(y/x)=26.30°

GR=h*x/y=300/0.4943=606.92 m, and

SR=h/sin(θ)=300/sin(26.30)=677.09 m

As shown in FIG. 6, in the case where y′′=0.5 cm and x′=1 cm when D=10 m, the pitch angle α=+10°, the roll angle β=+5°, the yaw angle δ=+5°, the angle of entry into the landing runway ψ=0° and h=300 m,

y=y′′ cos(δ)cos(α)=0.5*cos(5)cos(10)=0.4905 cm

x=x′ cos(β)=1*cos(5)=0.9962 cm

y/x=0.4905/0.9962=0.4924

θ=tan−1(y/x)=26.22°

GR=h*y/x=300/0.4924=609.26 m, and

SR=h/sin(θ)=300/sin(26.22)=679.01 m

As shown in FIG. 7, in the case where y′=0.5 cm and x=1 cm when D=10 m, the pitch angle α=+10°, the roll angle β=+5°, the yaw angle δ=+5°, the angle of entry into the landing runway ψ=20° and h=300 m,
d1=(GR−D/2)*sin(ψ)=(609.26−10/2)*sin(20)=206.67 m, θ, GR and SR are the same as those of FIG. 6, but the angle of entry into the landing runway ψ must be made zero using calculating ground range d1 to the nearest point that makes the angle of entry into the landing runway zero. It is apparent that the distance d2 can be obtained using d2=(GR−D/2)*cos(ψ).
Since the system for automatically landing an aircraft using image signals and the method of controlling the system according to the present invention are capable of calculating the angle between the aircraft and the ground, the ground range between the aircraft and the landing location and the slant range between the aircraft and the landing location using a camera for recognizing a landing mark provided at a landing location on the ground and an altimeter for obtaining altitude information, they are advantageous in that the equipment thereof is simple and the cost thereof is reduced.
Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

## Claims

1. A method of controlling a system for automatically landing an aircraft using image signals, comprising:
an altitude measurement step of a Flight Control Computer (FCC) of the aircraft receiving altitude information of the aircraft from an altimeter;
a landing mark recognition step of a camera installed in the aircraft and oriented toward a front of the aircraft capturing a landing mark at a landing location and transmitting it to the FCC;
a landing mark measurement step of the FCC measuring horizontal and vertical lengths of the landing mark captured by the camera;
a flight information calculation step performed by the FCC of the aircraft, calculating an angle between the aircraft and a ground, a ground range between the aircraft and the landing location and an slant range between the aircraft and the landing location using the altitude information, the horizontal and vertical lengths of the landing mark measured at the landing mark measurement step, angle information composed of pitch, roll and yaw angles of the aircraft and an angle of entry to a landing runway; and
a flight control step performed by the FCC of the aircraft, of controlling flight and attitude of the aircraft using the calculated flight information,
wherein:
the angle θ between the aircraft and the ground is calculated using Equation 1,
the ground range GR between the aircraft and the landing location is calculated using Equation 2, and
the slant range SR between the aircraft and the landing location is calculated using Equations 3 or 4:


θ=tan−1(y′′ cos(δ)cos(α)/(x′ cos(β)))  (1)



GR=h*x′ cos(β)/(y′′ cos(δ)cos(α))  (2)



SR=h/sin(tan−1(y′′ cos(δ)cos(α)/(x′ cos(β))))   (3)



SR=GR/cos(tan−1(y′′ cos(δ)cos(α)/(x′ cos(β))))   (4)



where α: the pitch angle,
β: the roll angle,
δ: the yaw angle,
x: the horizontal length of the landing mark measured from the image information recognized by the camera,


x′=x/cos(β),


y: the vertical length of the landing mark measured from the image information recognized by the camera,


y′=y/cos(α),



y′′=y′/cos(δ), and


h: the altitude information measured by the altimeter.

2. The method as set forth in claim 1, further comprising calculating a ground range d1 to a nearest point that makes the angle of entry into the landing runway ψ zero at a current location using Equation 5:


d1=(GR−D/2)*sin(ψ)  (5)


where ψ: the angle of entry into the landing runway, and
D: the actual diameter of the circle of the landing mark.