[0001] This invention relates to a gun sighting and fire control system incorporating laser
ranging means.
[0002] With any conventional fire control system, the line of sight of an aiming telescope
is first adjusted so as to coincide with a cannon bore center line for a predetermined
range (for example, in the case of tank guns, about 1,000 meters). External factors
have to be taken into consideration, when aiming the cannon, so as to increase to
a maximum the likelihood that the projectile will hit its target. Such external factors
include, for example, wind forces, movement of the target, etc. In addition, intrinsic
factors have to be accounted for such as for example the ballistic curve of the projectile
and projectile speed, etc. In order to take these factors into account certain corrections
have to be introduced in the form of angular deviations between the line of sight
and the bore center line. Thus, for example, in order to correct for the external
factors referred to above the bore center line will have to be deflected horizontally
whilst in order to correct for the intrinsic factors a vertical super-elevation of
the bore center line is called for. The conventional manner of effecting these corrections
has-involved displacing an aiming reticle across the field of view, within the image
plane of the aiming telescope, by the required amount and then moving the bore until
the reticle is again centered on the target.
[0003] It is known to provide such systems with laser ranging means so as to facilitate
the precise measurement of the range to a specific target. In order to ensure that
the ranging laser beam hits the target seen through the aiming sight and that only
the laser light returning from the target is sensed by the range detector, the laser
beam, the range detector and a laser aiming point provided in the sight have all to
be perfectly aligned. The triaxial adjustment required in order to ensure such alignment
is effected during the assembly of the system in the assembly plant. In order to aim
the gun exactly at the target an aiming point is provided in the sight which is boresighted
to the gun when the sight is mounted in a tank. There are thus in effect two aiming
points in the sight - one a laser aiming point which is direction adjusted in the
assembly plant, and the other being the gun aiming point which is aligned with gun
direction. These two aiming points do not usually or necessarily coincide.
[0004] Furthermore, seeing that the gun has to be adjusted for the required deflection and
super-elevation whilst the laser is fixed to the sight the displacement between the
two aiming points could vary considerably from one target setting to another.
[0005] In order to cope with this situation the sighting system is usually provided with
two reticles within the telescope, one being a so-called "fixed" reticle being employed
for laser ranging whilst the other, being an adjustable "moving" reticle is used for
fire control. In order to lay the gun with respect to the target the range must first
of all be measured using the fixed reticle whereupon with the effecting of the various
adjustments the moving reticle is centered on the target. The location of the moving
reticle is determined on each occasion by the data fed into a computer associated
with the gun or, alternatively, can be manually effected. It is clear that once the
moving reticle is centered on the target it is no longer possible to measure the range
seeing that the fixed reticle of the laser ranging means is no longer centered on
the target and in consequence on each occasion the "fixed" and "moving" reticles must
be successively centered on the target.
[0006] It is an object of the present invention to provide a new and improved gun sighting
and fire control system in which the above referred to disadvantages are substantially
reduced or overcome.
[0007] According to the present invention there is provided, in a gun sighting and fire
control system having laser ranging means, an assembly of rotatable optical wedges
located in the common axis of the system subsequent to a common objective thereof.
[0008] The properties of rotating optical wedges in general and their use for ranging in
fire control systems in particular are well known and for a discussion thereof reference
can be made to the publication "Design of Fire Control Optics" ORDM2-1 page 100 and
following. At least a pair of such rotating optical wedges are employed in the present
system. In this inventive system, however, the wedges are rotated after ranging responsive
to the external and intrinsic factors. The rotation is effective in displacing the
target image as viewed through the telescope eyepiece. Thus, instead of displacing
a moving reticle either on the basis of data fed into a computer or manually, the
image of the target is displaced by appropriate relative rotation of the wedges. The
rotation is effected either on the basis of the data fed into the computer or manually.
The gun is subsequently laid by centering the reticle vis-a-vis the displaced image.
[0009] It will be readily appreciated that the relative positions of the reticle in the
field of view and of the laser aiming point are maintained throughout and if these
points are made to coincide in the assembly plant this coincidence will be maintained
at all deflections and elevations. Thus, by virtue of the use of the optical wedges
whenever the reticle is on target, the laser beam is also optically on target. When
the gun is laid the ranging laser beam is still in position to measure the range.
Therefore, there is no longer any need for successive centering utilizing respectively
the fixed and moving reticles and, in point of fact only a single reticle is employed
constantly positioned at the center of the field of view.
[0010] The system in accordance with the present invention, in addition to eliminating the
necessity of realigning the laser beam with the target for subsequent ranging on the
same target, is also particularly advantageous for use in overcoming the problems
of providing coordinated or linked collimating reticles for use in a complete modern
tank fire control system. For such a system four aiming stations are involved, namely:
(1) the daytime aiming sight for the gunner; (2) the night image intensified aiming
sight for the gunner; (3) the daytime aiming sight for the tank commander; and (4)
the night image intensified aiming sight for the tank commander. According to the
present invention only one reticle or less is required per station.
[0011] It will be realized that all four stations must be exactly bore sighted and corrected
so as to aim at exactly the same target and that all adjustments required (so as to
compensate for external and intrinsic factors) must simultaneously affect all four
sights and to the highest possible degree of accuracy. It has hitherto been attempted
to ensure that such adjustments simultaneously affect all four sights by using mechanical
links combined with various optical and electrical means. Such proposals however have
suffered from errors arising out of tolerances, backlash, stresses and indexing errors
and, in consequence, the tendency has been for designers to concentrate on the daytime
aiming sight of the gunner (this being the main fire control sight of the tank crew)
whilst reducing the demands for accuracy for the remaining sights.
[0012] In accordance with.an aspect of the present invention however, this problem is overcome
not only by the reduction of the maximum number of aiming reticles required per station
from two to one but also by the provision of means for projecting the aiming reticle
into one or more additional sights from a single collimator and via said assembly
of rotatable optical wedges. Thus, for example the aiming reticle collimator is physically
part of the main daytime gunner's aiming sight, optically part of the night image
intensified.sight for the gunner and optically part of the commander's corresponding
sights.
[0013] With this preferred embodiment all angular adjustments (bore sighting, deflection
and super-elevation) carried out in the sight using the optical wedge assembly across
the triaxial line of sight, automatically and simultaneously effect that part of the
aiming sight which serves as the common collimator and the adjustments are therefore
simultaneously and automatically accomplished in all the remaining sights. It will
be appreciated that the various deflecting mirrors necessary for such simultaneous
projection are of course critically adjusted during the initial assembly of the system
while elevation of the gun and the aiming sights is electrically controlled by servo-mechanisms
having suitable angle sensors.
[0014] The only really high precision link required is between the mechanical emergency
elevation tilting mechanism of the gunner's periscope head mirror and the commander's
collimator reflection device. With this exception, the coincidence of the day and
night sights both as far as deflection and as far as super-elevation are concerned
are not reduced as a result of emergency manual operation.
[0015] For a better understanding of the present invention and to show how the same may
be carried out in practice reference will now be made to the accompanying drawings
in which:
Fig. 1 is a schematic representation showing the essential optical constituents of
a gun sighting and fire control system in accordance with the present invention, and
Figs. 2 and 3 show schematically and respectively two embodiments of daytime and nighttime
sights incorporating the present invention.
[0016] As seen in Fig. 1 of the drawings the gun sighting and fire control system in accordance
with the present invention comprises an optical assembly shown schematically at 1
and a triaxial arrangement comprising an emerging laser beam 2 emanating from a laser
emitter 3, a returning laser beam 4 detected by a laser range detector 5 and the sighting
beam 6 viewed by an operator 7. As can be seen the triaxial system combines these
into a common optical axis 8 which passes through a common objective 9, an optical
wedge assembly 10 and iminges on an object 11.
[0017] It will be readily seen that the triaxial adjustment of the beam directions 2,4,6
with respect to the common axis 8 is maintained.invarient irrespective of the corrections
which have to be introduced in the form of angular deviations in the line of sight
and the bore center line. This is in view of the fact that these corrections are effected
as a result of the displacement of the image by the optical wedge assembly 10 and
the subsequent centering of the single reticle on the target. The laser ranging beam
is optically on target while the single reticle is on target. Thus, as distinguished
from the hitherto known arrangements employing two reticles, the repeated centering
of separate reticles for range sighting and laying is obviated.'
[0018] As indicated above, the provisions of the system with the optical wedges simplifies
and increases the accuracy of the simultaneous adjustment and correction for all the
constituent aiming stations of a fire control system, for example for a tank.
[0019] Reference will now be made in this connection to Fig. 2 of the drawings which is
a schematic representation of a gunner's aiming peritelescope having an elbow 21 constituting
a daytime sight and an elbow 22 constituting an image intensified night sight. A main
head mirror 23 which can be rotated about a horizontal axis 24 is common to the day
and night sights and is tiltable for elevation. The daytime sight 21 comprises an
eyepiece 25, a shutter 26, a reticle 27 indirectly illuminated via its edge by means
of a light source 28, a penta roof prism 29 and an objective 30. Located in the optical
axis 31 of the daytime sight 21 is a pair of optical wedges 32 which are mutually
rotatable about this optical axis in opposite senses. Also located along this optical
axis is a relay prism 33 and a shutter or filter member 34.
[0020] The laser transmitter and receiver are attached in a manner well known to those skilled
in the art, so that the laser ranging beam (not shown) and laser light returning beams
(not shown) are parallel with the axis 31 and pass through objective 30 and wedges
32 but the ranging beams do not pass through prism 33. The laser beams thus are also
effected by rotation of the wedges as indicated in Fig. 1:
[0021] The night sight 22 comprises an eyepiece 35, an image intensifier tube 36, a folding
mirror 37 and an objective 38 located along the optical axis 39. Also located along
the optical axis subsequent to the objective 38 is a reticle projection injection
prism 40.
[0022] In use light coming from a target (not shown) is folded by the mirror 23 downwardly
into both sights 21 and 22. Folding is effected by the tilting of the mirror 23 about
its axis 24, the rest of the aiming system being fixed. Light from the target passes
through the pair of optical wedges 32 entering the day sight 21 through an objective
30 and being deflected by the prism 29. An image of the target is formed in the focal
plane of the objective, this focal plane coinciding with the reticle 27. By virtue
of the indirect illumination of the reticle by the light source 28 the reticle lines
stand out brightly against a dark background and the reticle and the target image
superimposed on it are observed through the eyepiece 25.
[0023] In effect the illuminated reticle 27, the prism 29 and the objective 30 form a collimator
and light originating from the reticle 27 passes through the objective 30 and is collimated.
After passing through the optical wedges 32 some of the light is deflected by the
reticle projection relay prism 33 into the other reticle projection prism 40 and therefrom
deflected into the night sight 22.
[0024] It will be appreciated that, in order to ensure that there is no reversal of the
image of the reticle projected into the night sight one of the deflecting prisms 33
or 40 must be a roof prism.
[0025] Light from the target (not shown) is deflected by the main mirror 23 into the night
sight objective 38 and is guided by the lower folding mirror 37 onto the front face
of the image intensifier 36 where an image of the target is formed. The collimated
light entering the objective 38 from the reticle projection injection prism 40 forms
an image of the reticle 27 superimposed on the target image at the front face of the
image intensifier. At the other, output end of the intensifier 36 an intensified image
of the target and of the reticle is formed and can be observed through the eyepiece
35.
[0026] In order to ensure that ghost images and stray lights are not collected from the
eyepiece 25 of the day sight 21 in the collimator, the shutter 26 is interposed between
the eyepiece 25 and the reticle 27. The further shutter 34 at the front end of the
daylight sight 21 serves to obscure telltale illumination from the reticle that may
otherwise be detected by hostile forces. This shutter 34 may momentarily be opened
if required whilst both shutters can of course remain open during daytime.
[0027] It will be readily appreciated that, with the arrangement just described, the projection
of the reticle from the day sight into the night sight is at exactly the same point
on the viewed target in both sights. Therefore when the reticle is on target and when
the wedges are rotated to take into account the extraneous and intrinsic factors involved
in the laying of the gun the target image moves in the day sight 21 while the reticle
moves in the night sight 22, but the relative positions df the target and the reticle
remain the same.
[0028] In an alternative embodiment shown in Fig. 3 of the drawings the daytime and nighttime
sights are essentially similar to those previously described with reference to Fig.
2 of the drawings but in this case, in addition to the reticle 27' and its illuminating
means 28' being located between the eyepiece 25' and a prism 29' a separate collimator
45 is provided comprising a housing 46 rigidly fixed to the daylight sight 21' and
having a reticle 47 which is directly illuminated by a light source 48. Located subsequently
to the reticle 47 of this collimator 45 is a collimating lens 49. A pair of optical
wedges 51 extends across the optical axes of the collimator 45 and the daylight' sight
21' whilst a reticle projection relay prism 52 is located along the optical axis of
the collimator 45.
[0029] The collimated light emerging from the collimator 45 passes through the optical wedges
51 and from there into the night injection prism 52 and 40' into the night sight objective
38'. After passing through the night sight objective 38' and being deflected by the
mirror 37' it forms an image of the reticle 47 on the front face of the image intensifier
36'.
[0030] If the prism 52 is converted to a beam splitter (as shown by the dashed lines) then
another portion of the collimated light originating from the collimator 45 is arranged
to pass through an opening 53 in the upper mirror 23' and is deflected by a commander's
reticle prism 54 into the commander's sight (not shown).
[0031] (The prism 54 and sight are rotated 90° from the position shown). The commander's
projection mirror (not shown) can be linked mechanically and electrically with the
elevation mechanism of the main head mirror 23'.
[0032] The reticle transfer scheme just described can be used as an optical relay from the
day sight to the night sight alone or it may be extended to the commander's sight
where it may be further split up into the day and night channels.
[0033] While the principles of the invention have been described above in connection with
specific apparatus and applications, it is to be understood that this description
is made by way of example only and not as a limitation on the scope of the invention.
1. A gun sighting and fire control system having laser ranging means, objective lenses
used with said laser ranging means, said system characterized in that an assembly
of rotatable optical wedges is located in the common axis of the system subsequent
to said objective lenses, for sighting with and correcting the alignment of said system.
2. A gun sighting and fire control system comprising:
at least one aiming sight means for use in aiming at a target by providing a view
of the target,
laser ranging means for ranging said target, objective lens means common to said one
aiming sight means and said laser ranging means,
reticle means associated with said one aiming sight means for providing a reticle
for use in aiming said gun at said target, said reticle being optically aligned with
said laser ranging means whereby when said reticle is on target said laser ranging
means is on target,
the system characterized in this, that: .
a rotatable optical wedge assembly is located subsequent to said objective lens for
moving said view of said target relative to said reticle responsive to external and
intrinsic factors,
and further means for again setting said reticle on said target.
3. A system according to claim 2 further characterized in this, that said system comprises
a plurality of aiming sight means, said one aiming sight means being a daylight sight,
said reticle means comprising a reticle collimator and
reticle injection projection means located subsequent to said optical wedge assembly
for projecting an image of said reticle into at least another of said plurality of
aiming sights.
4. A system according to claim 3 further characterized in this, that said reticle
collimator forms an integral part of said daytime sight and includes an indirectly
illuminated reticle.
5. A system according to claim 3 further characterized in this, that said reticle
collimator is separate from said daytime sight and includes a directly illuminated
reticle, and wherein one or more further images of the reticle are projected via said
optical wedge assembly and reticle injection projection means into one or more additional
sights.