Method and arrangement for aligning a gun barrel

Abstract

 The present invention relates to a method and an arrangement for aligning the gun barrel (1) in a primarily direct-shooting barrelled weapon with the weapon's sight (11). The invention is characterized in that it permits a direct measurement of the deflection or angling (x, v) of the gun barrel (1) that normally occurs as a result of the effect of the force of gravity, uneven heating, etc. The method according to the invention is based on the utilization of a video camera (5) inserted in the breech of the gun barrel, which can be focused on long distances as well as on the muzzle of the gun barrel.

Description

[0001] The present invention relates to a method and an arrangement for aligning the gun barrel with the weapon's sight in a primarily direct-shooting barrelled weapon. By aligning is meant that the alignment of the sight is coordinated with the actual alignment of each projectile fired out of the gun barrel at the time when the projectile leaves the gun barrel. It is well known in this connection that it is the actual alignment of the centre line of the gun barrel at the part of the gun barrel closest to the muzzle that determines the initial direction of flight of the projectile. The aligning procedure can be used with medium- and large-calibre barrelled weapons, but can also be used with smaller calibre weapons. By medium- and large-calibre barrelled weapons are meant here all such weapons with a calibre of 20 mm and above.

[0002] Guns on, for example, various types of armoured vehicle need to be aligned at regular intervals with the fire control system (the sight) in order to be able to achieve maximal accuracy. The alignment needs to be carried out due, for example, to distortion of the gun barrel as the result of unevenly distributed increases in temperature, play in the gun barrel bearings or the like. In particular, the alignment is important in the case of direct shooting at great distances towards small targets with, for example, trajectory ammunition, where long gun barrels are normally used. In weapons with long barrels, the alignment of the centre line of the gun barrel can vary a good deal along the length of the barrel for the reasons mentioned above.

[0003] Several different ways of aligning the gun barrel and the sight are currently known. Perhaps the oldest and most usual way is to use a so-called muzzle reference telescope (called a Pi-Watson device in USA) that is inserted into the muzzle of the gun barrel and by means of which it is possible, from a location at the muzzle, to determine the alignment of the centre line of the gun barrel in the area closest to the muzzle. The use of a muzzle reference telescope thus makes it possible to take comparative readings to a target at a suitable distance with the muzzle reference telescope and with the sight and to combine these. With this method, it is necessary, however, for a person to leave the vehicle and for this person to work with the gunner inside the vehicle during the aligning operation, as they must give each other directions until the centre line of the gun barrel and the sight line coincide at the selected target. This is thus primarily a method that can be used in situations other than frontline situations where there is no pressure regarding time.

[0004] Another method for aligning gun barrel and sight is based on arranging a mirror at the muzzle of the gun barrel. This mirror is directed towards a special sensor in the breech end of the gun or in the turret, or alternatively directly in the sight. By sending, for example, a laser beam towards the mirror and measuring the change in the position of the reflection, the direction of the muzzle in relation to the sensor/sight can be calculated and compensated for. In a real-time system, it is thereby possible to compensate continually for changes in the direction of the muzzle.

[0005] In addition to someone having to leave the safety of the vehicle and go out in front of the vehicle and corrections having to be carried out by this person and the gunner inside the vehicle giving each other directions, the use of a muzzle reference telescope thus means that during this operation a reference target must also be available at a sufficiently long distance. In frontline situations, this type of alignment would thus perhaps be able to be carried out once a day, while at the same time a muzzle reference telescope, which is a relatively expensive precision instrument, is normally shared between several guns. In the course of one and the same day, however, for example strong sun, wind or rain can change the strike point of the gun to such an extent that, even with very accurate shooting, the target will be missed.

[0006] The second type of aligning system with the mirror reference on the muzzle of the gun barrel can be subject to several different types of problem. The measuring sensor that is used (some kind of light source) can be detected by the enemy using the right kind of reconnaissance equipment and the mechanical environment at the muzzle of the gun barrel is extremely harsh and therefore imposes very high requirements concerning the fixings and material of the mirror, as the angular alignment of the mirror relative to the centre line of the muzzle must, in principle, remain unchanged. In addition, the mirror can become very dirty, as a result of wind and weather, surrounding terrain, etc, and also from residues from fired shots. An additional limitation of this technique is that the system does not permit any absolute measurement to a sufficiently distant target, for which reason this must, in any case, be carried out using a muzzle reference telescope, although the technique enables the length of time between the muzzle reference telescope measurements to be extended considerably as a result.

[0007] A third method for aligning gun barrel and sight is described in US-A-4 879 814 in which the use is proposed of a laser source arranged in the gun's breech or chamber, which laser source is designed as a dummy shell and which, when it is activated, sends a laser beam coordinated with the centre line of the gun barrel which gives a sufficiently sharp reflection at a long distance (1200 metres is stated in the text) to make possible alignment of the gun barrel and sight at the strike point of the laser beam. This method does not provide any actual ability to correct for such important sources of error as deflection of the gun barrel caused by the force of gravity and/or uneven heating up of the gun barrel, etc., but it must rather be regarded as a way of achieving a fairly rough alignment of the average centre line of the gun barrel with the sight. Another disadvantage of the method is that the target that is illuminated by the laser must have certain characteristics of a flat mirror in order for the method to be able to be applied. Thus, it is proposed, for example, in the patent document that, for example, buildings with a stucco facade, large flat rocks or other vehicles are selected as illuminated targets, and such objects that are suitable for carrying out the method are not always available. In situations other than frontline situations, the use is proposed quite simply of a flat mirror and method claims 1-3 refer, in fact, to the use of a flat mirror.

[0008] An additional method for aligning a gun barrel and sight in direct-shooting barrelled weapons is described in our own Swedish patent application 0203721-6, in which it is proposed that a direction marker in the form of a video camera looking in the direction of fire of the gun barrel is used as a reference for the centre line of the gun barrel in the end part of this towards the muzzle, which direction marker is propelled through the gun barrel from its breech up to the muzzle, with the centre line of the gun barrel included in the field of vision of the video camera and with the video camera being fixed in the gun barrel during the aligning operation in such a way that its optical axis coincides with the alignment of the centre line of the gun barrel at the muzzle. The image shown by the video camera is thereafter coordinated with the sight image of the weapon's sight. This way of utilizing a video camera for aligning gun barrel and sight has the obvious advantage that the whole aligning procedure can be carried out without any of the crew having to leave the vehicle upon which the weapon in question is mounted. Another advantage of the method is that the aligning is carried out completely between the sight and the end part of the gun barrel that is critical for the strike result. The method in question thus takes directly into account the previously discussed gun barrel distortions which occur to a greater or lesser extent. A disadvantage of the method in question is, however, that it necessitates that the video camera utilized for this purpose be passed through the whole gun barrel from the breech right up to its muzzle. While this is an operation that can easily be carried out from the loader's position inside the vehicle concerned, at the same time it still takes a certain amount of time to carry out and, similarly, it takes time to retrieve the video camera. These time aspects could prove to be a considerable disadvantage if the problem were to arise of suddenly needing to open fire immediately.

[0009] In accordance with the present invention, a new method and arrangement are now proposed instead for aligning a gun barrel and sight in particular for medium- and large-calibre barrelled weapons intended for direct shooting at long distances, which method and arrangement utilize a video camera. The method according to the invention is based on the video camera being arranged inside the gun barrel on a level with the breech or chamber, with the line of sight of the camera coinciding with the direction of fire of the gun barrel and with its optical axis precisely centred with the centre line of the gun barrel on a level with its position in the gun barrel. The video camera is then used for aligning the sight with the centre line of the gun barrel on a level with the breech and also for determining gun barrel distortions and compensating the sight setting accordingly. According to the invention, the projected image of the muzzle of the barrel which is obtained by the camera is measured and the alignment of the centre line of the gun barrel at the muzzle is calculated from the deviations between this image and the actual cross section of the gun barrel, using a calculation unit interacting with the camera or incorporated into the camera, after which the sight setting can be compensated accordingly.

[0010] The video camera can thus be a part of an optical measuring system, which must be able to measure the muzzle geometry of the gun barrel very accurately, that is the muzzle geometry as such and the centre line position of the muzzle in relation to the centre line of the chamber. In addition, the camera is to be designed in such a way that, in addition to being able to be focused on the muzzle of the gun barrel, it is also able to be focused on infinity, that is it is able to look at an object a long distance beyond the muzzle of the gun barrel, that is it can be directed towards a point or target in the terrain. The latter function also makes it possible to align the gun barrel and sight directly on a distant target and, in frontline situations when the sight function has been lost, for example due to external damage, the video camera would be able to replace the sight by first using this to direct the gun towards an enemy target and then by replacing it immediately afterwards by a live shell to attack the target.

[0011] The characteristic location of the video camera according to the invention means that the camera can either have the external shape of a dummy shell that fits the gun's chamber and is loaded into the gun's chamber in the same way as a live shell, or can quite simply be built into the end or rear part of the gun and is thus, in the latter case, ready for taking measurements, provided the gun is not loaded with a live shell. In accordance with the first variant, it is necessary for a shell to be removed and for a shell to be loaded before the weapon can be ready to be fired, and in the second case it is only necessary for the weapon to be loaded, that is in both cases standard operations that are carried out very quickly and that do not significantly delay a sudden need that has arisen to open fire.

[0012] By observing in an accurate way a target located a sufficiently long distance away, via a video camera placed in the gun barrel, a single person, for example the gunner, can thus align the fire control system with the gun, without needing to leave his ordinary position in the vehicle which contains the gun. According to a development of the system according to the invention, the measurement data that is obtained from the optical measuring system is able to be transferred directly to the fire control system. In order to obtain reliable information, this type of measurement to objects in the terrain must, however, be supplemented by measurements that define the angling of the muzzle of the gun barrel, in most cases in the form of a deflection at the muzzle. According to the invention, this angling or deflection is determined by the shape of the image of the muzzle of the gun barrel projected on the image plane of the video camera being compared with the actual shape of the muzzle. Each angling or deflection of the muzzle of the gun barrel gives an image of the muzzle projected on the image plane of the video camera that has a more or less elliptical shape instead of the actual circular shape of the muzzle. This is because the deflected part of the inner wall of the gun barrel delimits the image of the muzzle in the video camera. The degree of deviation from a circle is thus a measurement of the angle of the muzzle in relation to the alignment of the gun barrel on a level with the breech. On the basis of the image thus projected, a suitably programmed microprocessor or the like can easily calculate the actual alignment of the centre line of the gun barrel at the muzzle. As pointed out above, it is the alignment of this part of the centre line that primarily determines the direction of the shot fired out of the gun barrel when it leaves the gun barrel. The fact that the image plane of a video camera is divided into a large number of pixels, each of which is either part of an image or not part of an image when the camera is focused towards the muzzle of the gun barrel, makes the comparison between the image received and the actual shape of the gun barrel and hence also the determination of the angling of the gun barrel at the muzzle and the alignment of the centre line of the gun barrel at the muzzle considerably easier. The method according to the invention thus also comprises an indirect method of measuring the alignment of the gun barrel and, by this means, of obtaining information about the displacement of the muzzle in relation to the sight line.

[0013] In practice, the application of the invention involves the optical detecting unit in the form of the video camera being caused to send information that it has gathered to an image processing unit that can be integrated with the fire control system or can be a free-standing unit. In the image processing unit, the geometry is measured of the image of the muzzle of the gun barrel recorded in the optical detecting unit (the video camera) in the form of the number of pixels comprised in the image and their position in the image. By this means, positional displacements, changes in geometry and the like can be calculated and converted to information relating to data required by the fire control system concerning changes in angle, etc. Alarm functions can also be included in the same system, that give warnings or prevent the opening of fire in the event of the discovery of major damage or wear to the gun barrel.

[0014] As already pointed out above, in the event of serious damage to the sight, the optical measuring system can be used as a provisional sight, by means of the gun barrel being first aimed at the target using the video camera in the arrangement according to the invention, after which loading and firing are carried out. By the utilization of either video-superimposed cross hairs in the video image or a video target tracker, the target can be measured and its position when the projectile reaches it can be determined with relatively good precision. In this reserve mode, the information is sent via the video target tracker to the fire control system, if this has not been completely put out of action, or is sent straight out to a video monitor to be dealt with directly by the gunner.

[0015] Special means can be arranged to determine the orientation of the video camera relative to the vertical axis of the gun barrel. These can be in the form of direction-sensing sensors arranged in association with or on the video camera. There can also be a mechanical link with, for example, recesses in the gun barrel and projecting parts on the video camera.

[0016] The invention will be defined in greater detail in the following patent claims and it will now be described in additional detail in connection with the attached drawings, in which:

Figure 1 shows schematically the complete arrangement according to the invention.

Figure 2 shows, in exaggerated large scale, the image of the muzzle of the gun barrel projected on the image plane of the video camera.

[0017] In Figure 1, 1 indicates the sectioned gun barrel of a gun mounted in an armoured vehicle (not shown). The figure also shows the centre line 2 of the gun barrel 1 and its breech end 3. The video camera 5 in the arrangement according to the invention is arranged in the breech or chamber 4 of the gun barrel 1. In the example shown, this has suitably the external shape of a dummy shell and is inserted in the chamber without clearance. The dummy shell can be provided with projecting parts (not shown) that interact with recesses in the gun barrel to achieve well-defined orientation of the video camera. Alternatively, the design can comprise direction-sensing sensors. The measurement values measured by the video camera or measuring camera 5 are sent via the cable 6 to an image processing unit 7 which is linked by cables 8 and 9 respectively to a video target tracker 10 and to the gun's ordinary fire control system 11, which in turn can be linked to the turret and gun barrel servo system via a cable 12. The image processing unit 7 can also be integrated with the video camera in the dummy shell. It can be emphasized here that the video target tracker is an option in our system and does not necessarily need to be included in the invention in its most general form. As the component functions in the whole of this system only involve normal technical fire control technology that is not covered by the invention, these components will not be discussed here in greater detail. As shown in Figure 1, the image processing unit 7 is also linked via a cable 13 directly to a monitor 15 arranged at the position of the gunner 14. The monitor also has a direct link 16 to the video target tracker 10 which, in turn, has a direct link 17 to the fire control system 11.

[0018] As shown in Figure 1, the gun barrel 1 is angled downwards by the force of gravity, uneven heating or the like, which has resulted in the centre line 2 of the gun barrel being displaced by the distance x at the muzzle 19 of the gun barrel in comparison with the centre line at the breech 4, where the video camera 5 is located. This deflection can also be given solely as an angle, in the form of the angle v.

[0019] As shown in Figure 2, the image plane 20 of the video camera 5 shows a projected image 21 of the muzzle of the gun barrel 1 which is elliptical. This is because the image is delimited at its upper edge by the edge of the muzzle of the deflected gun barrel and is delimited at its lower edge by the lower internal wall of the gun barrel. The position of the centre line of the gun barrel at the muzzle has been marked 2y in Figure 2, while the direct linear projection of the centre line of the gun barrel on a level with the breech, that is where the video camera 5 is located, has been marked by 2i. The deflection of the gun barrel is thus calculated from this elliptical image of the muzzle of the gun barrel by a comparison with the actual circular cross section of the muzzle. The actual direction of the centre line of the gun barrel at the muzzle can then be calculated using the same data.

Claims

1. Method for aligning a gun barrel (1), with the gun's fire control system (the sight) (11) for direct-shooting barrelled weapons, utilizing a video camera (5) for determining the distortion (v, x) of the gun barrel (1) at the muzzle (19) brought about by the force of gravity, uneven heating or the like, characterized in that a video camera (5), arranged inside the gun barrel (1) on a level with the breech or chamber (4) with the line of sight of the camera coinciding with the direction of fire of the gun barrel (1) and with its optical axis precisely centred with the centre line (2) of the gun barrel on a level with its position in the gun barrel (1), is used for measuring the projected image (20) of the muzzle (19) of the gun barrel which is available to the video camera (5) and in that the alignment of the centre line (2) of the gun barrel (1) at the muzzle (19) is determined from the deviations between this image and the gun barrel's actual circular cross section, and in that the alignment of the sight (11) with this calculated alignment of the centre line (2y) of the gun barrel (1) at the muzzle (19) is corrected.

2. Method according to Claim 1, characterized in that the video camera (5) for recording the projected image (20) of the shape of the muzzle of the gun barrel and means for determining the deviations (x, v) in the centre line (2) of the gun barrel on a level with the muzzle are coordinated in an optical measuring system comprising or coordinated with requisite calculating units in which functions for determining and giving warning about wear in the gun barrel and indications and alarm functions in the event of any damage to the gun barrel (1) are included.

3. Method according to any one of the preceding claims, characterized in that the division of the image of the video camera (5) into a very large number of light-sensitive pixels is utilized when determining the deviations between the alignment of the centre line of the gun barrel on a level with the breech and at the muzzle.

4. Method according to any one of the preceding claims, characterized in that, in addition to the video camera (5) being utilized for recording the shape (20) of the muzzle of the gun barrel with subsequent determination of the deviations (x, v) between the alignment of the centre line of the gun barrel on a level with the breech or chamber (4) and the alignment of the centre line (2) at the muzzle (19), it is also utilized for directly observing and aligning the gun barrel towards a distant target by focusing at a long distance beyond the muzzle of the gun barrel, while at the same time the sight is aligned towards the same target.

5. Arrangement for aligning the gun barrel (1), primarily for direct-shooting barrelled weapons, with the gun's fire control system (the sight) (11) comprising a video camera (5), characterized in that the video camera (5) is arranged inside the gun barrel (1) on a level, with the breech or chamber (4) and with its line of vision in the direction of fire of the gun barrel, which video camera is so designed that its optical axis coincides with the alignment of the centre line (2) of the gun barrel on a level with the position of the video camera (5) inside the gun barrel (1), and in that this video camera and requisite peripherals form an optical measuring system that comprises or is coordinated with requisite calculating units that can calculate the deviations in displacement or angle (x, v) between the alignment of the centre line of the gun barrel on a level with the chamber or breech (2i) and on a level with the muzzle (2y) from the image (21) of the muzzle (19) of the gun barrel projected on the video camera's image plane and from the deviations in the image from the actual circular shape of the cross section of the gun barrel.

6. Arrangement according to Claim 5, characterized in that the video camera/fire control system in the form of an optical detecting unit is linked to an image processing unit (10) which measures the geometry of the image (21) of the muzzle (19) of the gun barrel projected by the video camera's imaging function and converts the number of pixels or areas of pixels concerned into angular deviations (x, v) of the centre line (2i-2y) of the gun barrel that are sent to the gun's fire control system for aligning the centre line of the muzzle of the gun barrel with the sight.

7. Arrangement according to any one of Claims 5-6, characterized in that, in addition to being able to be focused on the muzzle of the gun barrel, the video camera (5) can also be focused on targets a long distance beyond the muzzle of the gun barrel.

8. Arrangement according to any one of Claims 5-7, characterized in that the video camera (5) is permanently mounted in the breech end of the gun and is designed to be able to look through the gun barrel, provided there is no shell in the gun's chamber or breech (4).

9. Arrangement according to any one of Claims 5-8, characterized in that the video camera (5) is designed as a dummy shell that is inserted into the breech (4) of the gun barrel.

10. Arrangement according to any one of Claims 5-9, characterized in that the optical measuring system comprises monitoring functions for determining the presence of damage, wear or similar indications of impaired function of the gun barrel and for giving warning of this.

11. Arrangement according to any one of Claims 5-10, characterized in that the arrangement comprises means for determining the orientation of the video camera relative to the vertical axis of the gun barrel.

12. Arrangement according to Claim 11, characterized in that the means for determining the orientation of the video camera comprises direction-detecting sensors arranged in association with the video camera.

13. Arrangement according to Claim 11, characterized in that the means for determining the orientation of the video camera comprises a mechanical connection.

14. Arrangement according to Claim 13, characterized in that the mechanical connection comprises recesses in the gun barrel and projecting parts on the video camera that interact with these.

Drawing