GB2309770A - Elevation compensating gun sight - Google Patents

Abstract

An elevation mirror 12 is mounted on stub shafts 14, 16 to determine the elevational field of view of the sight. A rotor assembly including a respective winding and a shaft 24 is coupled to the mirror via a tape drive 28. Elevational movement of a gun causes another winding 20 to rotate via a linkage 32. An optical encoder coupled to a computer 40 detects movement of the winding 20 relative to the shaft 24, and the computer generates drive signals for the windings. When the gunner lays an aiming mark onto a target the phase relationship between the two windings is maintained so that the mirror accurately follows the gun, but when a ranging laser 42 is fired, the computer 40 deflects the aiming mark downwards and varies the phase angle in such a way that when the gunner elevates the gun to lay the mark back onto the target the mirror remains on target.

Description

GUN SIGHTS TECHNICAL FIELD OF THE INVENTION This invention relates to gun sights.

BACKGROUND Vehicles provided with a gun sometimes have a periscopic sight through which the gunner views his target. The sight will often include a mirror which is coupled to the gun via a mechanical linkage so that the two move together. Thus, the gunner's view is dictated by the elevation of his gun.

Modern vehicles are often also equipped with a laser range finder. If the gunner identifies a target he positions an aiming mark on the target by moving his gun, and he then fires the laser to determine the range. A computer uses the range information to move the aiming mark downwards by a calculated amount to compensate for the anticipated trajectory. Thus, when the gunner puts the aiming mark back onto the target the gun should be elevated to the correct position to fire.

Generally, the elevational field of view through the periscope is sufficiently wide that the gunner is still able to see the target when the gun has been elevated in response to the adjusted aiming mark. In some circumstances however, the amount of correction may be sufficiently large to take the target out of the field of view when the gun is placed in a super elevated position.

An aim of the present invention may be viewed as being to overcome this problem.

SUMMARY OF THE INVENTION According to a first aspect the present invention proposes a gun sight comprising an elevation mirror, a gun, sensor means for sensing the angular position of the gun relative to another body, drive means for moving the mirror in elevation, and control means for controlling the drive means and being responsive to the sensor means such that the mirror moves with the gun in an initial sighting mode, but in a range compensation mode the gun moves independently of the mirror.

The sensor means is preferably arranged to sense the relative angular position between the gun and the mirror, since this allows the system to compensate for any errors in movement of the mirror. The sensor means may comprise an optical or inductive encoder, for example.

The drive means preferably comprises an electromagnetic device such as an electric motor. The device may thus comprise first and second relatively moveable parts having respective windings. The device may be arranged to drive the mirror relative to a fixed body, or the device may act between the gun and the mirror, in effect acting as a variable angle electromagnetic coupling. Preferably the angle of the coupling can be varied by changing the phase angle of power supplied to the two windings.

According to a second aspect, the invention further proposes a gun sight comprising an elevation mirror which is coupled to a gun via a linkage, the linkage including a release coupling which is fixed in an initial sighting mode such that the mirror moves with the gun, but in a range compensation mode the release coupling allows the gun to move independently of the mirror.

The release coupling preferably comprises an electromagnetic coupling. The coupling preferably comprises first and second parts having respective windings, e.g. concentric rotors. The angle of the electromagnetic coupling is preferably variable by changing the phase angle of power supplied to the two windings.

In the range compensation mode the release coupling me be operated to lock the mirror in position. Preferably however, the sight includes sensor means for detecting movement of the gun and means for adjusting the coupling so as to maintain the position of mirror. The sensor means preferably comprises an optical encoder. The sensor means is preferably associated with the release coupling rather than the gun.

BRIEF DESCRIPTION OF THE DRAWINGS The following description and the accompanying drawings referred to therein are included by way of non-limiting example in order to illustrate how the invention may be put into practice. In the drawings: Figure 1 is a diagrammatic side view of a gun sight in accordance with the invention, and Figure 2 is a modified detail of the gun sight of Fig. 1.

DETAILED DESCRIPTION OF THE DRAWINGS The head 10 of a periscopic sight1 which may include an image intensifier or thermal imager system for night vision, incorporates a mirror 1 2. The mirror is mounted on stub shafts 14 and 16 which are in turn journalled in high quality bearings to rotate about a horizontal axis and allow the elevational field of view of the sight to be varied.

An outer body assembly 18 including a first winding 20 is mounted to rotate relative to the sight head 10 in a further set of high quality bearings. The outer body contains a relatively rotatable inner rotor assembly which includes a shaft 24 and a second winding (not shown) positioned concentrically inside the body 18 and arranged such that the two windings are mutually electromagnetically coupled when energised. A projecting portion of the shaft 24 carries a drive pulley 26 which drives the mirror 1 2 via an endless tape drive 28 and a pulley 30.

A linkage 32 couples a gun (not shown) to the outer body 18 so that as the gun is moved in elevation the linkage 32 causes the body 18 to rotate relative to the sight head 10. An optical encoder (not shown) is housed in the outer body 18 to detect movement of the body relative to the shaft 24, and hence detects relative movement between the gun and the mirror, and generates electrical signals indicative of the amount of such relative movement. These signals pass along a cable 34 to a control card 36 which is connected via a two-way RS232 link 38 to a computer 40. The card 36 also generates drive signals which supply the first and second windings via the cable 34.

A laser range finder indicated generally at 42 sends range information to the computer via a cable link 44.

When the gunner lays an aiming mark onto a target the mirror accurately follows the gun since the computer uses the signals generated by the optical encoder to vary the drive signals to the two windings in order to maintain the phase relationship between the two windings at 00. The inner and outer assemblies are thus, in effect, rigidly coupled by the magnetic flux generated by the two windings.

When the ranging laser is fired, the computer 40 deflects the aiming mark as in existing sights, but when the gunner elevates the gun to lay the mark back onto the target the computer uses the angle information from the optical encoder to generate a difference in the phase angle between the drive signals sent to the windings to accurately keep the mirror on the target as the gun moves.

Since the optical encoder always provides a true and accurate indication of the angular relationship between the gun and the mirror, the computer can automatically compensate for any error in the position of the mirror (e.g. due to unpredictable mechanical influences) by making appropriate compensatory changes to the position of the aiming mark.

Fig. 2 shows an alternative form of mirror drive and encoder arrangement.

The gun linkage 32 drives an input shaft 50 which is journalled in bearings 52 to rotate relative to the sight head 10. The input shaft 50 is coupled to one section 54 of an inductive angular resolver, the other section 56 of the resolver being coupled to a rotor shaft 24. The angular information signals from the resolver 54, 56 are again fed via cable 34 to the control card 36 to indicate the precise angular relationship between the gun and the mirror.

The shaft 24 forms part of the inner rotor of a limited angle electrical torque motor 60, the outer body of which is fixed relative to the housing 10. The shaft 24 drives the mirror via pulley 26 in accordance with analogue drive signals sent from the card 36 via cable 34.

The computer again 40 uses the angular information from the resolver 54, 56 to control the motor 60 such that the mirror accurately tracks the gun during the initial aiming procedure. When the ranging laser is fired, the computer 40 again deflects the aiming mark, but when the mark is laid back onto the target the computer drives the motor 60 according to the angle information from the resolver to hold the mirror on the target.

It should be appreciated that the drive motor 60 or other electromagnetic mirror compensating arrangement can be coupled to any of the shafts 14, 1 6 or 24, via a suitable gear box if necessary.

In the described embodiments the optical or inductive sensor always provides a true and accurate indication of the angular relationship between the gun and the mirror, so that the computer can automatically compensate for any error in the position of the mirror (e.g. due to unpredictable mechanical influences) by making appropriate compensatory changes to the position of the aiming mark.

Claims (10)

1. A gun sight comprising an elevation mirror, a gun, sensor means for sensing the angular position of the gun relative to another body, drive means for moving the mirror in elevation, and control means for controlling the drive means and being responsive to the sensor means such that the mirror moves with the gun in an initial sighting mode, but in a range compensation mode the gun moves independently of the mirror.

2. A gun sight according to Claim 1, in which the sensor means is arranged to sense the relative angular position between the gun and the mirror.

3. A gun sight according to Claim 1 or 2, in which the sensor means comprises an optical encoder.

4. A gun sight according to Claim 1 or 2, in which the sensor means comprises an inductive encoder.

5. A gun sight according to any preceding claim, in which the drive means comprises an electromagnetic device.

6. A gun sight according to Claim 5, in which the drive means comprises first and second relatively moveable parts having respective windings.

7. A gun sight according to Claim 6, in which the relative angular orientation between the first and second parts is varied by changing the phase angle of power supplied to the two windings.

8. A gun sight according to any preceding claim, in which the drive means is arranged to drive the mirror relative to a fixed body.

9. A gun sight according to any of Claims 1 to 7, in which the drive means is arranged to act between the gun and the mirror.

10. A gun sight substantially as described with reference to the drawings.