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(11) | EP 0 172 620 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Gun sighting arrangement |
| (57) A gun sighting arrangement in which a telescope (11) is mounted on the gun barrel
(1) and is pre-aligned with the gun barrel and the normal gunnery sight (9) on a standard-
distance target. Relative movement between the gun muzzle and the normal gunnery sight
(9), due, for example, to shock displacement of the sight or temperature distortion
of the barrel, causes an error in barrel/target alignment when the gunnery sight (9)
is on target. This error has two components (a) between gunnery sight sightline and
barrel mounting, due to shocks etc and (b) between barrel mounting and muzzle, due
to wear, temperature distortion of the barrel etc. Both of these effects can be compensated
by mounting the telescope (11) at the muzzle end of the barrel (1). Muzzle displacement
due to either effect causes displacement of the target image in the telescope (11),
which is produced by flashing the target with the standard range finding laser. The
displacement indicates the alignment error. Partial compensation can be provided by
mounting the telescope (11) at the barrel mounting (14) and otherwise taking account
of basic distortion. |
[0001] This invention relates to gun sighting arrangements particularly for large calibre guns employed in direct gunnery, i.e., where there is a direct line of sight to the target.
[0002] Such guns employ a gunnery sight having a sightline which has to be aligned with the gun barrel boresight, that is to say, the sightline has to be directed at the point, at a suitable standard distance, at which the gun is pointing, despite the practical necessity of displacing the boresight and the gunnery sight laterally. The process of lining up the sight with the gun barrel is referred to as boresighting. The first stage in this process is to determine the lie of the barrel boresight. According to one common method, a barrel telescope is mounted concentrically in the gun barrel and the boresight aligned with a suitable target of standard distance, say 1000 metres, by means of a right-angled eyepiece accessible from a position beside the gun muzzle. The gunnery sight is lined up with this same target which will then appear on the MBS (muzzle boresight) mark of the sight.
[0003] The sight will have a series of range marks; zero metres, 1000, 2000, 3000 metres etc, providing successively greater barrel elevation, and the MBS mark constitutes the zero range mark.
[0004] It will be clear that, as thus set up, the gunnery sight is correct only at the standard 1000 metre range, the error at other ranges being predictable and taken into account accordingly.
[0005] This method of boresighting can be very accurate, but is a lengthy procedure. Typically in a tank or anti tank gun, the gunner and his sight eyepiece are under armour. The boresight telescope can only be used when a second person leaves the protection of the armour and the gun cannot be fired while the telescope is in use. Thus, in practice, the boresight telescope cannot be used in battle, but only prior to action in a safe area.
[0006] Modern gunnery sights for large calibre guns are usually one of two types, telescopic and periscopic. A telescopic sight is mounted on the gun barrel directly, behind armour and moves integrally with the gun. A periscopic sight is also mounted under armour but relatively remote from the gun. The gun movement is relayed to the sight by a lever system which in one arrangement moves the whole sight and in another merely a mirror arrangement within the sight,
[0007] A problem that arises in maintaining a gunnery sight accurate, i.e., such that its sightline (MBS mark) is always aligned with the gun barrel boresight, is that use (firing) of the gun generally produces an upset in the predetermined relation that has been set up by boresighting, between the muzzle boresight and the sight sightline. Heating of the barrel by firing of the gun causes bending of the barrel. Also, differential heating due to sunlight, shadow and wind can produce a significant distortion in the barrel axis so that no matter how accurate the original boresighting the muzzle may no longer point accurately at the same target as the sight sightline.
[0008] In addition to movement of the muzzle relative to the gunnery sight, the sight itself may be disturbed by shock due to violent movement of the tank. Disturbance of the sight is even more likely in the case of a periscopic sight where the linkages are subject to vibration and shock.
[0009] In a known attempt at a solution to this problem, a light source is mounted either on the armour or on the muzzle. In the first case the source directs a beam of light at a mirror on the muzzle which reflects the beam to the gunnery sight. In the second case the light source, mounted on the muzzle, is itself directed at the gunnery sight. In both cases an expensive high precision prism and lens arrangement is associated with the sight to redirect the beam of light on to the sightline and to re-focus it at infinity. A spot of light then appears in the sight on the MBS mark. Any movement in the muzzle boresight relative to the sight sightline is shown as a displacement of the dot away from the MBS mark. The sight can then be adjusted to re-align the MBS mark with the light spot.
[0010] One such arrangement using an armour-mounted light source is shown in the accompanying Figure 1. A light source 3 is mounted on the gun armour 5 to direct a beam of light at a mirror 7, the mirror being mounted at the muzzle end and thus highly susceptible to bending of the barrel. The beam is then re-directed to the remotely mounted periscopic sight 9 (by way of example) which includes the prism and lens arrangement.
[0011] While this system works well to a certain extent there are disadvantages. Thus the prism and lens arrangement for re-aligning and focussing the reflected beam are of high quality and are correspondingly expensive.
[0012] A further disadvantage is that, because of the re-directing of the light beam by the prism,.correct alignment is obtained for only one incident angle of the light beam at the prism and thus for only one (index) position of the gun. There can therefore be no continuous assessment or correction of relative displacement between sight and muzzle pointing directions. In addition, the index position must be set up with great accuracy.
[0013] In the case of a periscopic sight, geometric errors in the sight-gun link system which vary with gun position cannot be corrected.
[0014] It is an object of the present invention to provide a sighting arrangement which provides an indication of relative displacement between gunnery sight sightline and gun axis at all gun positions and without the necessity for the presence of personnel adjacent the gun barrel, and thus exposed to enemy fire.
[0015] According to the present invention, a gun sighting arrangement comprises a gunnery sight having a sightline in predetermined relation with the gun axis, the sightline being arranged to move with the gun to maintain said relationship, focussing means fixedly mounted with respect to the gun so as to move with it and be subject to any differential movement between the gun at the focussing means and the sightline, the focussing means being arranged to receive radiation from the target and to focus it at a position which is dependent upon the target position relative to the axis of the focussing means, displacement of the focussed position of the received radiation providing information as to the above differential movement for correction of any gun/sightline misalignment.
[0016] The focussing means may be mounted at the muzzle end of the gun so that the above differential movement includes differential movement between the sightline and the barrel axis at the barrel mounting and differential movement between the barrel axis at the barrel mounting and the muzzle boresight.
[0017] Alternatively, the focussing means may be mounted adjacent the mounting of the gun barrel so that the above differential movement consists of differential movement between the sightline and the barrel axis at the barrel mounting, the arrangement further comprising means for determining differential movement between the barrel axis at the barrel mounting and the muzzle boresight, the sum of the two differential movements constituting the total muzzle-boresight/sightline misalignment.
[0018] In this case, the means for determining differential movement between the barrel axis at the barrel mounting and the muzzle boresight may comprise means for transmitting an electromagnetic beam between a position adjacent and fixed with respect to the muzzle and a position adjacent and fixed with respect to the barrel mounting, and receiver means for detecting displacement of the beam. There may then be transmitting and receiving means fixedly mounted adjacent the barrel mounting and reflecting means fixedly mounted at the muzzle end of the barrel, the receiving means being adapted to detect movement of the reflected beam from a datum position corresponding to alignment of the barrel axis at the barrel mounting of the muzzle boresight.
[0019] The electromagnetic beam may be provided by a laser incorporated in the transmitting and receiving means.
[0020] A laser local to the gun may be arranged to illuminate the target to provide by reflection radiation received from the target. Preferably, this laser is incorporated in a rangefinder associated with the gunnery sight, the laser beam path being aligned with the sight sightline or fixedly spaced from it.
[0021] The focussing means may consist of a telescope incorporating a positional detector operative in a focal plane of the telescope.
[0022] The gunnery sight may comprise a telescope mounted on the gun barrel directly, or may comprise a periscope mounted independently of the gun barrel and linked to it by a mechanical linkage.
[0023] Two gun sighting arrangements in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, of which:
Figure 1 is a diagram of a known muzzle reference system;
Figure 2 is a diagram of one sighting arrangement according to the invention.
Figure 3 is a diagrammatic illustration of 'focussing means', a telescope and positional detector, featuring in Figure 2;
and Figure 4 is a diagram of an alternative sighting arrangement.
[0024] As explained above, Figure 1 shows a system which has certain disadvantages in providing a check on errors of alignment between sight and muzzle.
[0025] Figure 2 shows a gun barrel 1 mounted in armour 5 and having, in this instance, a periscopic gunnery site 9 associated with it and mounted with its sightline in at least initial alignment with the boresight. The sight 9, as commonly used on modern tanks, incorporates a laser rangefinder as standard equipment. Such a rangefinder produces pulses of laser light prior to firing the gun which illuminate and effectively select the target on the gunnery sight sightline. The laser is aligned accurately with the sightline so that, as the gun is laid on any target that target can be illuminated with laser light. The rangefinder also includes a receiver for laser light which times the return of a reflected pulse, a processor 13 then calculating the distance to target, i.e., range. This information is passed to a fire control system 15 for use in known manner as one of the basic factors determining ballistic offsets.
[0026] Rigidly mounted on the muzzle end of the barrel 1 is a telescope 11 which is initially aligned with the gun barrel boresight so that the telescope axis intersects the boresight at the standard target distance.
[0027] This telescope 11, shown very diagrammatically in Figure 3, has a filter 21 passing the laser light frequency and a focussing lens system 19 (shown for simplicity as a single lens) which focusses reflected light from the illuminated target into a focal plane. On initial setting up of the system the position of the focussed spot of light corresponds to the MBS mark in the gunnery sight. In other words when the MBS mark in the gunnery sight 9 is 'on' a particular target and that target is illuminated by a laser flash, the position of the reflected spot of light in the focal plane represents the MBS mark. The telescope may then be adjusted until the spot of light falls on the axis. An array 23 of light-sensitive elements (or a positional detector) is mounted in or near this focal plane to indicate in two dimensions movement of the spot from the boresight (MBS) position. The light spot is shown illuminating a light sensitive element 25 in the Figure. Only a limited number of elements are shown, for simplicity : there will in general be many more.
[0028] It will be clear that any transverse movement of the gun muzzle, due to any of the causes mentioned above, i.e. differential barrel heating, will cause the telescope 11 to be effectively twisted about a transverse axis relative to the reflected laser beam. The focussed spot of light will then move off centre (as shown) by an amount corresponding to the movement of the muzzle. The elements of the array produce signals according to the amount of incident light and the signals are decoded in muzzle/ gunsight error processor 27 to produce an error signal. The error in muzzle pointing direction may be corrected in isolation by the gunner but may, alternatively, be incorporated as one more factor in the overall fire control system (15) determination of the required pointing direction of the muzzle.
[0029] It will then be clear that if, instead of the muzzle moving relative to the sight sightline the sight moves relative to the gun, e.g., as a result of vibration, firing shock etc, then sight sightline and laser will effectively select a displaced distant target point from that at which the muzzle is pointing. The focussed spot of light will move on the array thus again indicating an error of alignment.
[0030] In this arrangement the measurement of the total misalignment between the muzzle boresight 16 and the gunners sight (9) sightline is divided into two components:
(a) The bending of the gun barrel relative to the barrel mounting (at axis 14) is measured by a conventional electronic autocollimating (or equivalent) system consisting of a transmitter/receiver 12 which transmits a narrow beam of light, or other electromagnetic radiation to a mirror 7 rigidly mounted on the muzzle end of the barrel. The receiver 12 receives the reflected light from the mirror 7 and measures any displacement from the centre in a two- axis frame. The transmitter/receiver 12 is rigidly mounted to the gun barrel close to its pivot point.
(b) The misalignment between the pointing of the gun barrel, i.e., the barrel axis 14, near to its pivot-point, and the gunners sight (9) sightline is measured by the laser receiving telescope 11 previously described. The telescope 11 is rigidly mounted to the gun barrel close to the transmitter/receiver (12), ensuring that there can be no misalignment between the two measuring systems.
[0031] The total misalignment between the muzzle boresight 16 and the gunner's sight sightline is formed simply as the sum of the errors as measured by the two systems. The barrel distortion error is determined in block 18 from the spot displacement in receiver 12 : the gun/sightline misalignment is determined in block 20 from the spot displacement in telescope 11 : and the two errors summed (22) and passed to the fire control system 15.
[0032] This alternative arrangement has an advantage over the first arrangement described (Figure 2), namely that the receiving telescope 11 is removed from the severe shocks and dirty environment suffered by any forward- facing optical device mounted on the gun muzzle. The muzzle-end device becomes a backward-facing small mirror as used in the conventional system (Figure 1).
[0034] The laser rangefinder provides a ready made source of target illumination and operates automatically before firing for range finding purposes. The alignment error can thus be determined and compensated prior to each firing operation.
[0035] The positional displacement, or error, signal provided by the muzzle telescope takes account of barrel bend, sight-gun link errors, gun mounting displacements and sightline - gun line parallax.
[0036] The measurement of sightline - gun parallax is inherent in the new method. Parallax can be predicted and allowed for if various contributing factors are accurately measured. Measurement may, however, be expensive thus the inclusion of automatic parallax compenstion in the new method gives a cost advantage.
[0037] It should be noted that the system is equally effective at all gun positions and does not require standardisation at an index position.
[0038] Additionally, the system may be used after the manner of a conventional boresight telescope, but without the need for any person to leave the protection of armour. The gunner aims his sight sightline at any convenient target at or near the standard boresighting range (say 1000 metres). By firing his laser rangefinder 9 the telescope system 11 will generate misalignment error signals which allow the gunner to re-align his sight sightline to the gun barrel boresight. Sight alignment can thus be rapidly checked, corrected and re-confirmed by a few repeated uses of the system over a few seconds.
[0039] The initial alignment of the laser receiving telescope can be accomplished using conventional boresighting techniques, and, by firing the ranging laser, any misalignment between the sight MBS mark and the line of the laser beam can also be calibrated out.
[0040] While the existing presence of a laser source in the standard range finder greatly facilitates the application of the invention it will be apparent that any means that can illuminate the target with any form of electromagnetic radiation selectively would be sufficient for a target image to be presented to a suitably sensitive detector array. In fact, if radiation emanating from the target, whether primary (as in the case of infra-red) or secondary (constituting reflection of incident-radiation) can be sensed by the muzzle telescope in contrast to background radiation, then an alignment error signal can be produced.
[0041] There will, incidentally, be the possibility of providing a direct visual display of the alignment error in an eyepiece of the muzzle telescope but this would not in general be a practical arrangement since the gun muzzle could be inaccessible and the operator would be vulnerable to enemy fire.
1. A gun sighting arrangement comprising a gunnery sight (9) having a sightline in
predetermined relation with the gun axis the sightline being arranged to move with
the gun (1) to maintain said relationship, characterised by focussing means (11) fixedly
mounted with respect to the gun (1) so as to move with it and be subject to any differential
movement between the gun (1) at the focussing means (11) and the sightline, the focussing
means (11) being arranged to receive radiation from the target and to focus it at
a position (25) which is dependent upon the target position relative to the axis of
the focussing means, displacement of the focussed position (25) of the received radiation
providing information as to the above differential movement for correction of any
gun/sightline misalignment.
2. A gun sighting arrangement according to Claim 1, characterised in that said focussing
means (11) is mounted at the muzzle end of the gun (1) so that said differential movement
includes differential movement between the sightline and the barrel axis at the barrel
mounting and differential movement between the barrel axis at the barrel mounting
and muzzle boresight.
3. A gun sighting arrangement according to Claim 1, characterised in that said focussing
means is mounted adjacent the mounting of the gun barrel (1) so that said differential
movement consists of differential movement between the sightline and the barrel axis
(14) at the barrel mounting, the arrangement further comprising means (7, 12) for
determining differential movement between the barrel axis (14) at the barrel mounting
and the muzzle boresight (16), the sum of the two differential movements constituting
the total muzzle-boresight/sightline misalignment.
4. A gun sighting arrangement according to Claim 3, characterised in that said means
for determining differential movement be between the barrel axis at the barrel mounting
and the muzzle boresight comprises means (12) for transmitting an electromagnetic
beam between a position adjacent and fixed with respect to the muzzle and a position
adjacent and fixed with respect to the barrel mounting, and receiver means (12) for
detecting displacement of said beam.
5. A gun sighting arrangement according to Claim 4 characterised in that said means
for determining differential movement between the barrel axis (14) at the barrel mounting
and the muzzle boresight (16) comprises transmitting and receiving means (12) fixedly
mounted adjacent the barrel mounting and reflecting means (7) fixedly mounted at the
muzzle end of the barrel, said receiving means (12) being responsive to movement of
the reflected beam from a datum position corresponding to alignment of the barrel
axis (14) at the barrel mounting and said muzzle boresight.
6. A gun sighting arrangement according to Claim 5, wherein said electromagnetic beam
is provided by a laser incorporated in said transmitting and receiving means.
7. A gun sighting arrangement according to any preceding claim, wherein a laser local
to the gun (1) is arranged to illuminate the target to provide by reflection said
radiation received from the target.
8. A gun sighting arrangement according to Claim 7, wherein said laser is incorporated
in a rangefinder associated with the gunnery sight (9), the laser beam path being
aligned with the sight sightline or fixedly spaced from it.
9. A gun sighting arrangement according to any preceding claim wherein said focussing
means (11) consists of a telescope incorporating a positional detector (23), operative
in or near a focal plane of the telescope.
10. A gun sighting arrangement according to any preceding claim wherein said gunnery
sight (9) comprises a telescope mounted on the gun barrel directly.
11. A gun sighting arrangement according to any of Claims 1 to 9, wherein said gunnery
sight comprises a periscope mounted independently of the gun barrel and linked to
it by a mechanical lineage.