Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BORESIGHTING DEVICE AND METHOD
Subject-matter of the invention
The present invention relates to a method and device for aligning the line
of sight with the firing line, commonly called boresighting device, for
weapons
systems, preferably large caliber (75 mm to 140 mm).
Technological background and state of the art
On a weapons system, a misalignment between the firing line and the line
of sight is detrimental to hit a target with precision. There are two main
sources of
misalignments. A first misalignment source is the physical deformation of the
barrel,
commonly called deflection, which appears naturally and inevitably, both
horizontally
and vertically, as a result of the relatively heavy weight of the barrel and
the outside
conditions (rain, wind, sun, etc.). This deformation causes a parallelism flaw
between
the firing line from the shaft of the barrel and the firing line from the
muzzle of the
barrel. A second source of misalignment lies in the impacts and vibrations
experienced
during driving and shot firings that cause a deviation relative to the
alignment
previously calibrated.
Different devices exist for aligning the firing line with the line of sight,
or in
other words, boresighting a weapons system.
There are traditional boresighting techniques where the device is based on
the cooperation between two operators, the first being located in the turret
while the
second, outside the turret, stays close to the muzzle of the barrel. The
principle is
based on optical collimator and described in document US 1,994,177. The
collimator is
placed inside the tube of the barrel by the second operator and gives the
first operator
a view aligned with the firing line. In other words, the second operator
informs the first
operator how it is necessary to move the barrel so that he can see, through
the
observation hole, how the reference target is positioned. One major drawback
of this
device is that it requires two operators, including one outside the vehicle,
i.e., directly
exposed to an outside threat. Furthermore, it requires a ladder in order for
the second
operator to be able to reach the muzzle brake.
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There are also devices of the "Muzzle Reference System" (MRS) type. These
devices, described inter alla in document US 4,665,795, are generally made up
of a
laser transceiver situated at the base of the barrel and a mirror placed at
the muzzle of
the barrel. The transmitter sends an infrared laser ray toward the mirror,
which is next
reflected toward the receiver. Based on the position of the laser received by
the
receiver, a piece of electronic equipment allows the automatic calculation of
the
azimuth and elevation corrections, which are next added to the ballistic
corrections at
the shot firing control system. One drawback of these devices is that the
mechanical
stability of the mirror is very complex to provide. Furthermore, detecting the
arc lines
of the barrel via laser measurements can make the system detectable by the
enemy.
Next, although devices of the MRS type make it possible to correct the
variations in the
arc lines of the barrel, an initial alignment remains necessary.
Similarly, the document FR 2 505 477 discloses a boresighting device which
comprises on the barrel a deflection target formed by a mirror on which a
crosshairs is
projected, a housing comprising optics systems and an image sensor, the images
are,
on the one hand, the reflected image of the crosshairs and, on the other hand,
in the
presence of a filter, the reflected image of a distant object. It is again a
precarious
system wearing out with low stability and with the risk of deterioration of
the precision
of the optics systems in the long run.
Other, less widespread devices may also be cited.
Document EP 1,510,775 describes a device with a camera having two
focusing levels. This camera is inserted in the chamber of the barrel during
the
boresighting operations. A first focusing at the muzzle of the barrel makes it
possible
to estimate its angular deviation (X,Y). A second infinity focusing makes it
possible to
observe an object situated at a far distance, and therefore to bring the view
of the
optical system back onto the same reference. The boresighting is done by
combining
these two ope rations.
Document EP 1,616,145 discloses a boresighting device done by a single
operator located inside the turret. A camera is pushed to the muzzle of the
barrel from
the inside of the latter. Since this camera is situated at the muzzle of the
barrel, it
implicitly takes the arc line of the barrel into account.
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These two devices have the drawback of having to position a camera inside
the barrel. In the case of document EP 1,616,145, deploying the camera is a
time-
consuming and tedious operation, especially if it must be done by a single
operator
situated in the turret. Furthermore, it is not possible to guarantee that the
orientation
of the camera pushed to the muzzle will systematically be the same upon each
boresighting operation.
Aims of the invention
The present invention aims to provide a boresighting device and method
that require only one operator located inside the turret.
It further aims to develop a device not requiring an optics system inside the
barrel. It thus aims to develop a device which is stable and precise.
It also aims to develop a boresighting method that is quick, while also being
repeatable.
Brief description of the figures
The present invention will be better understood in light of the following
description, referring, as an example, the Figures 1 to 3.
Figure 1 schematically shows a turret provided with the boresighting device
according to the invention, in the presence of the shaft, the barrel and the
sighting
optics, as well as the optical axes of the two cameras of the boresighting
device.
Figure 2 schematically shows the optics systems inside the housing
according to the invention.
Figure 3 illustrates the movement of the geometric figure over the
deflection target following deflection of the barrel.
Legend
(1) Turret
(2) Housing
(3) Deflection target
(4) Barre!
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(5) Shaft
(6) Muzzle brake of the barrel
(7) Optics system provided with the deflection camera
(8) Optics system provided with the boresighting camera
(9) Geometric figure on the deflection target
(10) Optics of a sight system of the turret
Main features of the invention
The present invention relates to a boresighting device to equip a turret
provided
with a barrel and one or several sight system(s) each with an optical system,
said
device comprising:
- a deflection target intended to be positioned outside the barrel, at the
muzzle brake
of said barrel,
- a housing intended to be positioned outside the barrel, at the shaft of
said barrel,
said housing including:
- a first optics system provided with a deflection camera, said first system
being used
to determine a parallelism error between a firing line from the shaft and that
from the
muzzle brake,
- a second optics system provided with a boresighting camera, said second
system
being used to determine a parallelism error between the firing line from the
shaft and
an optics line from the sight system(s).
According to specific embodiments of the invention, the device includes at
least one or a suitable combination of the following features:
- each camera has fixed focusing, the boresighting camera having infinity
focusing and
the deflection camera being configured to have focusing adjusted on the
deflection
target;
- the deflection target includes any geometric material figure serving as a
reference
point for the first optics system, said geometric figure preferably being a
circle.
The present invention also relates to a weapons system comprising the
boresighting device as described above, wherein the housing is positioned on
the shaft
of the barrel and said deflection target is positioned near or on the
perimeter of the
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muzzle brake of the barrel. Furthermore, in this weapons system, the
deflection target
can be attached or integrated with respect to the muzzle brake.
The present invention also relates to an armored vehicle provided with this
weapons system.
5 The present invention also relates to a boresighting method using the
device described above, said method comprising the following steps:
- Calculating the displacement AX and AY of the geometric figure relative to a
reference position of said figure, said calculation being done based on image
processing from the deflection camera, the parallelism error between the
firing line
from the shaft and that from the muzzle brake next being determined via a
mathematical model based on calculated AX and AY values,
- Comparing an image taken by the boresighting camera with an image taken
by an
optical system of the sight system(s) in order to determine the parallelism
error
between the firing line from the shaft and the optics line from the sight
system(s),
- Accumulation of two parallelism errors and displacement of said optics line
accordingly.
According to specific embodiments of the invention, the method includes
at least one or a suitable combination of the following features:
- the calculation of AX and AY is done using an algorithm based on a contour
detection
according to the Canny method and using a Hough transform;
- the reference position of the geometric figure is calculated during a
calibration
following an installation of the boresighting device on a weapons system;
- the calibration is done using a muzzle bezel, said calibration comprising
a step for
aligning a position of a crosshairs of the boresighting camera with a point
observed
.. through the muzzle bezel;
- after the step for calculating the parallelism error between the firing
line from the
shaft and that from the muzzle brake, the crosshairs of the boresighting
camera is
moved by a same angle along the X and Y coordinates;
- the method can be implemented during a mission.
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Lastly, the present invention relates to a computer program suitable for
implementing the method described above and by recording data readable by a
computer comprising this program.
Detailed description of the invention
The present invention relates to a boresighting device and the method
implemented using said device. The device according to the invention is
preferably
intended for large caliber weapons systems (75 mm to 140 mm). It could
nevertheless
be used for small and/or medium caliber weapons systems subject to certain
developments related to the steric bulk in the riggings associated with said
calibers.
The boresighting device according to the invention is shown in Figure 1 on
a turret 1. The device is made in two parts positioned in separate locations.
It includes
a housing 2 on the one hand, and a deflection target 3 on the other hand. The
housing
2 is positioned outside the barre! 4, and preferably mounted on the shaft 5 of
the
barrel 4. The housing 2, visible in more detail in Figure 2, includes two
optics systems
7, 8 each provided with a camera. A first camera 7, called deflection camera,
is
intended to correct the misalignment resulting from the deflection of the
barrel, i.e.,
the misalignment between the firing line from the shaft and that from the
muzzle of
the barrel. A second camera 8, called boresighting camera, is intended to
correct the
misalignment between the firing line from the shaft of the barrel and the
optical axis of
the sight system. In the housing, the two cameras are mounted in a single
block. The
boresighting and deflection cameras have the feature of having fixed focusing,
respectively infinity focusing and focusing at the muzzle brake, as
illustrated in Figure
1. Mounting in a single block with fixed focusing for each camera has the
advantage
that no moving part is required in the housing, which makes it possible to
ensure
mechanical stability thereof relative to the impacts and vibrations related to
shot
firings. Furthermore, the housing is designed athermally so that the position
of the
optics axis of the cameras is not sensitive to temperature variations. In
addition to the
housing, the device includes the deflection target 3, which is located at the
muzzle
brake 6, i.e., at the end of the barrel where the ammunition exits. This
deflection
target 3 can be either an additional part that is placed at the fastening of
the muzzle
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brake, or it can be integrated directly on the perimeter thereof. The latter
alternative is
favored to guarantee the mechanical stability of the device. The deflection
target is
provided with any geometric figure serving as a reference point for the optics
system
7. This figure is physical, or tangible in other words, on the target which
means that it
is integrated on the target. It is thus not a projected figure on a mirror
acting as a
deflection target.
The boresighting method according to the invention takes into account
both of the aforementioned misalignment causes, i.e., the deflection of the
barrel and
the deviation between the firing line and the sight line following impacts
caused by the
use of the vehicle and its weapons system.
To that end, the method is based on three steps.
In a first step, the optics system provided with the deflection camera is
used to determine the parallelism error between the firing line from the shaft
and that
from the muzzle brake. More specifically, the first optical system 7 of the
housing
detects the position of the deflection target via image processing such that
the system
can deduce, vertically and horizontally, the deflection of the barrel relative
to a
reference position obtained during calibration of the device. The movement
along X
and Y, i.e., the delta X (AX) and delta Y (AY), is calculated relative to a
reference
ennbodied by the geometric figure that is preferably a circle 9 on the
deflection target
3 (see Figure 3). It is possible to consider other geometric forms, having
previously
made several specific modifications to the algorithms used. A AX and AY are
thus
calculated relative to the starting position of the center of the circle.
Through a
mathematical model, the system produces the parallelism error therefrom
between
the firing line at the shaft and the firing line at the muzzle brake. The
algorithm used to
detect a geometric figure is based on a contour detection according to the
Canny
method. A Hough transform makes it possible to obtain a first estimate of the
position
of the reference circle. Next, an algorithm makes it possible to refine the
obtained
results at the sub-pixel level.
In a second step, the optics system provided with the boresighting camera
is used to determine the parallelism error between the firing line at the
shaft and the
sight line. The camera whose axis is parallel to the firing line at the shaft
and which
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uses infinity focusing provides an image of a distant object that is directly
compared to
the image provided by the optics system(s) 10 of the sight system(s) of the
turret
(Figure 1). It is thus possible to deduce the parallelism error between the
firing line at
the shaft and the optics line of the sight system(s).
In a third step, the two parallelism errors are accumulated and sent directly
to the sight system(s) of the turret.
Prior to these steps, the device must be calibrated. This calibration is done
when the housing and the target are mounted on the turret. Subsequently, no
new
calibration is required as long as the housing and the deflection target are
not moved.
The calibration is done from a conventional muzzle bezel. This calibration
consists of
aligning the position of the crosshairs in the boresighting camera with the
point
observed by the muzzle bezel. This operation is done by one of the occupants
of the
turret via his control monitors. When this alignment is achieved, the
reference position
of the geometric figure is calculated and stored by the device. During
subsequent
boresighting operations, in the first step, the device measures the
displacement of the
geometric figure relative to that obtained during the calibration. This
difference is next
reflected in the boresighting camera by moving the position of its crosshairs
thereto.
Advantages of the invention
The precision of the boresighting in the presence of the device according to
the invention is equivalent to that encountered with the prior art devices,
but without
the drawbacks.
Thus, the boresighting is done by a single operator located inside the
turret, without deploying any tools. There is therefore no heavy, and
therefore slow,
manipulation. This absence of manipulation also guarantees better
repeatability of the
measurements. Furthermore, this allows the boresighting to be done mid-
mission.
According to the invention, the deflection target and its geometrical figure
are physical. It is not a mirror on which a crosshairs is projected. Thus, the
device
according to the invention does not require layers of mirrors causing
desynchronization risks and requiring systematic calibrations.
