EP0057304A1

EP0057304A1 - A gun sighting and fire control system

Info

Publication number: EP0057304A1
Application number: EP81300469A
Authority: EP
Inventors: Shlomo Barak; Raffi Yizhar; Jacob Beutler
Original assignee: EL-OP ELECTRO-OPTICS INDUSTRIES Ltd
Current assignee: EL-OP ELECTRO-OPTICS INDUSTRIES Ltd
Priority date: 1981-02-04
Filing date: 1981-02-04
Publication date: 1982-08-11

Abstract

A gun sighting and fire control system having laser ranging means and including an assembly of rotatable optical wedges (32) located in the common axis (31) of the system subsequent to a common objective (30) thereof.

Description

This invention relates to a gun sighting and fire control system incorporating laser ranging means.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.

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.
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.'
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.
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.
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:
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.
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.
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.
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.
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.
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.
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.
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.
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'.
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).
(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'.
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.
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.

Claims

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.