GB1564597A

GB1564597A - Sighting and aiming system

Info

Publication number: GB1564597A
Application number: GB4906272A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1971-10-25
Filing date: 1972-10-24
Publication date: 1980-04-10
Also published as: DE2252301C2; FR2432261A5; DE2252301A1

Description

(54) A SIGHTING AND AIMING SYSTEM (71) I, ALAIN ARNAUD, of French nationality, of 2, rue Alsace Lorraine, 65 TARBES - France, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed. to be particularly described in and by the following statement: This invention relates to the stabilizing of the sighting and aiming of devices such as guns or telescopes and is particularly applicable to firing on the move from armoured vehicles.

Firing on the move from armoured vehicles is a rather complex problem. In fact, it implies an aiming accuracy better than one mil of a radian whatever the vehicle movements, because of the turret inertia.

Although the problem could be solved using powerful aiming systems these would. in turn, raise threshold. band-pass of linearity problems difficult to be overcome.

For a specific application. the present invention can be implemented to achieve very accurate en route firing even if the turret is not perfectly stabilized.

According to the invention. there is provided a sighting and aiming system comprising a movable element to be aimed. sighting means carried by said element and having a movable line of sight, a first servosvstem for controlling the aiming of said element. and a second servosystem for controlling the line of sight of the sighting means in relation to the movable element. the second servosvstem having a wider band-pass than the first servosystem and being slaved to the first servosystem in such a manner that parasitic movement of the movable element produces movement of the line of sight in a direction opposite to that of the parasitic movement.

For a better understanding of the invention and to show how the same may be carried into effect. reference will now be made, by way of example. to the accompanying drawings in which: Figure 1 is a schematic view of the elevation aiming system of an armoured vehicle gun; and Figure 2 is a block diagram showing the control means for a sighting system of the gun.

Figure 1 shows an armoured vehicle gun 1 mounted on a turret la to tilt about a pivot 2 defining what is called the "elevation axis".

A toothed gear sector 3 integral with the gun l is actuated bv an aiming box 4 which is driven bv a motor-tvpe aiming device 5, e.g.

an electric motor which drives a magnetic clutch.

The gun carries a rate gyro 6 for measuring the angular speed of the gun in elevation with respect to predetermined absolute axes. It also features a sighting system 7 the optical axis of which can be angularly shifted in relation to the gun axis via a prism deflector controlled bv servo mechanism. In Figure l. a is the angle formed between the firing axis of the gun and an absolute radius and Q is the angle formed by the line of sight with that same absolute radius.

Gun stabilization is obtained using the rate gyro. the latter being also used for sighting stabilization. The resulting stabilization is arranged to be much better than that of the gun providing the sighting servomechanism with a wide band-pass which. in conjunction with the damped movements of the gun which supports the sighting system. allows the gunner to take aim at a target.

The gunner is able to hold a reticle of the sighting system onto a target while a level comparator system is used to authorize the gun to be fired onlv when the deviation between the firing and the sighting axes. as measured by repeater means of the sighting servomechanism. is below a predetermined value.

The sighting system incorporates servo units and detection or repeater elements, interconnected as shown in Figure 2.

A device 8, such as a potentiometer.

actuated by the gunner supplies the turret with an aiming signal, a voltage in this case, corresponding to a speed davit. This voltage is compared in a circuit 9 with a voltage issuing from the rate gyro 6 and representing davit. The difference voltage produced by circuit 9 is processed in an integrator 10 whose output voltage represents the deviation between the position the gun would be in if it had strictly followed the aiming signal and its effective position (av - ar); this voltage controls the aiming device 5 via a circuit 11 so that the gun continuously tends to assume the position assigned to it.

As a result, the arrangement so far described acts as a conventional position servo loop.

In addition, the system has been arranged so that the rate gyro signal is directlv returned, via circuit 11, to the aiming device 5 in order to make up a tachometer loop.

This loop is required for certain types of device 5 such as those involving magnetic clutches. The output voltage of integrator 10 is also applied to sighting servomechanism 12 for stabilization purposes discussed later on. Nevertheless it can be seen that, for tracking at constant speed. the integrator output voltage will be constant and equal to a lag error (speed quotient times open loop gain this would lead to an offset sighting which is not desirable. To cancel this offset ting, the aiming signal voltage is applied to an amplifier 13 for multiplication by a factor equal to the open loop gain: the amplifier output voltage is then fed to a comparator 14 where it is subtracted from the output voltage of integrator 10 before being applied to servomechanism 12.

Hence, the sighting offset at constant speed is substantiallv nil. Furthermore. it is advisable to insert a high-pass filter 15 between the comparator 14 and the servomechanism 12 so as to suppress any constant deviation factor which is independent of sighting. such as may be caused by an unbalance of the load of the gun due to gravity.

If the output voltage of amplifier 13 causes a sighting offset during transients. it may prove useful, as shown. to reinject this voltage into the circuit 11 with an appropriate calibration corresponding to the sighting offset and in opposition to the gun aiming direction.

There is also an adder 16. which allows firing corrections. in elevation. issuing from an element 17 to be introduced into the sighting. These corrections can he simultaneously applied to circuit 11. after a change of sign, by known means not illustrated.

For a better understanding of the stabilization process, let it be assumed that the aiming signal is equal to zero. The system is then normally stationary. If a disturbance now occurs. the gun will be displaced bv a spurious amount. The resulting spurious speed will almost immediately be detected by rate gyro 6. This deviation, reinjected by the speed loop via circuit 11 and by the position loop via circuit 9 to the aiming device 5. will accordingly correct the movement. However, the band-pass of the powerful servomechanism controlling device 5 being small, the correction takes place after a certain delay.

On the other hand, it is possible to pick up the output signal of integrator 10, this signal corresponding to the deviation be- tween gun position ar and initial zero position.

Due to the presence of comparator 14 and adder 16. this signal. after a change of sign, will be applied to the sighting servomechanism 12 causing the line of sight to be rotated bv an angle exactly opposite to that by which the gun has been rotated. As the band-pass of the sighting servomechanism 12 is very high, the sighting axis will rotate by an angle practically opposed to that of the gun and the reticle viewed by the gunner will seem to remain stationary. In other words. the sighting regulation obtained is verv efficient.

Position repeater elements of sighting servomechanism 12 deliver a voltage equal to the sum of the firing corrections plus the aiming random deviations. The firing corrections are subtracted from this voltage in circuit 18. whose residual output voltage corresponds to any deviation between the ideal firing line position and the actual gun position. This voltage. which varies according to the disturbances. is applied to a level comparator 19 which delivers a signal when its input voltage is below a given value.

The output voltage of comparator 19 is fed to an AND circuit 20 which is also supplied with a firing signal issuing from a contactor 21. If both signals are present. a firing control 22 will be actuated. A round is thus fired when the deviation between the sighting axis and the gun is equal to the corrections.

As a summarv of the system so far described, it is pointed out that, at an instant t. the servomechanism 12 receives a signal (ar - av) to control the sighting axis in such manner that the axis forms with the device to be aimed the angle (ar - av), which represents the angle between the sighting axis and the axis of the device to be aimed. However. since the sighting device is supported bv the device to be aimed. which is at this instant at the angular position ar (the absolute radius), the sighting device behaves as a mechanical comparator whose two inputs are the signal (ar - av) emanating from servomechanism 12 and the signal (-ar) given by the physical position of the device to be aimed.The result of the comparison is the angle (ay), which represents the position of the sighting axis in relation to the reference direction. The aimer closes an external loop by acting on the control device 8 in dependence upon his view along the sighting axis to align the sighting axis with the target.

The repeater element 6 of the gun aiming system may consist of a rate gyro or of any other inertial data generator producing a rate gyro signal. In one application. the repeater element 6 and the integrator 10 are combined in the form of a gyroscope. while the tachometer signal fed to circuit It is either absent or is supplied by a tachogenerator of a repeater element of the gyroscope.

The sighting servomechanism 12 may consist of a conventional offsetting system but it is preferable to use a reflecting mirror and, if a high accuracy is required. a prism deflector or "diasporameter" known per se.

i.e. a deflector comprising two prisms each having a small apex angle. these prisms being placed together along one of their surfaces. Relative rotation of the prisms deflects a light beam passing through them.

The element to be aimed may be a gun, a missile launching ramp or a telescope. In another application, servomechanism 12 is used for radiating a laser beam in a direction independent of any disturbances which may affect the movement of a telescope. Thus.

the element to be aimed is a telescope and the "firing signal" is a triggering order for the laser whose beam passes through the sighting system. The telescope is fitted with a position repeater element whose output signal is compared with the aiming signal.

representing a position. and then applied to the circuit 11.

As for stabilized sighting for a ground vehicle for instance, the gun aimer is influenced by the same accelerations as the vehicle and it will be difficult for him to maintain his eve in the centre of the ocular circle of sighi. Sighting is affected by a parallax error. To obviate this. the image might be collected by a television camera and displayed on a screen placed in front of the gun aimer. Such a system is particularly interesting if the TV camera used incorporates a low light level lens system allowing night firing to be performed.

With a view to simplifying and clarifying the description, an embodiment has been discussed for stabilization with a single degree of freedom.

However. the invention is applicable to stabilization of an element with several degrees of freedom. In that case, one provides as many rotation detectors (rate gyros) as there are rotational degrees of freedom.

WHAT I CLAIM IS: ]. A sighting and aiming system comprising a movable element to be aimed, sighting means carried by said element and having a movable line of sight, a first servosystem for controlling the aiming of said element. and a second servosystem for controlling the line of sight of the sighting means in relation to the movable element, the second servosystem having a wider band-pass than the first servosystem and being slaved to the first servosystem in such a manner that parasitic movement of the movable element produces movement of the line of sight in a direction opposite to that of the parasitic movement.

2. A system according to claim 1, wherein the first servosystem comprises detection means for sensing movement of the movable element. these means being carried bv the movable element.

3. A system according to claim 1 or 2, wherein the sighting means comprises a pair of prisms relatively rotatable to deflect the line of sight.

4. A system according to claim 1. 2 or 3.

wherein the first servosystem comprises a rate gyro to detect the movement of the movable element. a comparator to compare the output signal of the rate gyro with a speed aiming signal. and an integrator connected to receive the comparator output signal and to produce therefrom an output signal representing the deviation between the ordered position and the actual position of the movable element. the second servosystem being coupled to receive the integrator output signal to be controlled thereby in such a wav that the deviation between the line of sight and the axis of the movable element is directly opposed to the deviation between the ordered position and that of the movable element to be aimed.

5. A system according to claim 4. wherin a signal related to the speed aiming signal is also fed to the second servo system so as to compensate for the deviation inherent in the output signal of the integrator when the movable element is tracking at constant speed.

6. A system according to claim 5.

wherein the signal related to the speed aiming signal is also applied to the second servosvstem so as to act therein in the opposite sense to its action in the first servosystem.

7. A system according to any one of claims I to 6. and comprising means for introducing into the second servosystem a ballistic correction signal.

8. A system according to claim 7, and

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

(the absolute radius), the sighting device behaves as a mechanical comparator whose two inputs are the signal (ar - av) emanating from servomechanism 12 and the signal (-ar) given by the physical position of the device to be aimed. The result of the comparison is the angle (ay), which represents the position of the sighting axis in relation to the reference direction. The aimer closes an external loop by acting on the control device 8 in dependence upon his view along the sighting axis to align the sighting axis with the target.

The repeater element 6 of the gun aiming system may consist of a rate gyro or of any other inertial data generator producing a rate gyro signal. In one application. the repeater element 6 and the integrator 10 are combined in the form of a gyroscope. while the tachometer signal fed to circuit It is either absent or is supplied by a tachogenerator of a repeater element of the gyroscope.

The sighting servomechanism 12 may consist of a conventional offsetting system but it is preferable to use a reflecting mirror and, if a high accuracy is required. a prism deflector or "diasporameter" known per se.

i.e. a deflector comprising two prisms each having a small apex angle. these prisms being placed together along one of their surfaces. Relative rotation of the prisms deflects a light beam passing through them.

The element to be aimed may be a gun, a missile launching ramp or a telescope. In another application, servomechanism 12 is used for radiating a laser beam in a direction independent of any disturbances which may affect the movement of a telescope. Thus.

the element to be aimed is a telescope and the "firing signal" is a triggering order for the laser whose beam passes through the sighting system. The telescope is fitted with a position repeater element whose output signal is compared with the aiming signal.

representing a position. and then applied to the circuit 11.

As for stabilized sighting for a ground vehicle for instance, the gun aimer is influenced by the same accelerations as the vehicle and it will be difficult for him to maintain his eve in the centre of the ocular circle of sighi. Sighting is affected by a parallax error. To obviate this. the image might be collected by a television camera and displayed on a screen placed in front of the gun aimer. Such a system is particularly interesting if the TV camera used incorporates a low light level lens system allowing night firing to be performed.

With a view to simplifying and clarifying the description, an embodiment has been discussed for stabilization with a single degree of freedom.

However. the invention is applicable to stabilization of an element with several degrees of freedom. In that case, one provides as many rotation detectors (rate gyros) as there are rotational degrees of freedom.

WHAT I CLAIM IS: ]. A sighting and aiming system comprising a movable element to be aimed, sighting means carried by said element and having a movable line of sight, a first servosystem for controlling the aiming of said element. and a second servosystem for controlling the line of sight of the sighting means in relation to the movable element, the second servosystem having a wider band-pass than the first servosystem and being slaved to the first servosystem in such a manner that parasitic movement of the movable element produces movement of the line of sight in a direction opposite to that of the parasitic movement.
2. A system according to claim 1, wherein the first servosystem comprises detection means for sensing movement of the movable element. these means being carried bv the movable element.
3. A system according to claim 1 or 2, wherein the sighting means comprises a pair of prisms relatively rotatable to deflect the line of sight.
4. A system according to claim 1. 2 or 3.

wherein the first servosystem comprises a rate gyro to detect the movement of the movable element. a comparator to compare the output signal of the rate gyro with a speed aiming signal. and an integrator connected to receive the comparator output signal and to produce therefrom an output signal representing the deviation between the ordered position and the actual position of the movable element. the second servosystem being coupled to receive the integrator output signal to be controlled thereby in such a wav that the deviation between the line of sight and the axis of the movable element is directly opposed to the deviation between the ordered position and that of the movable element to be aimed.
5. A system according to claim 4. wherin a signal related to the speed aiming signal is also fed to the second servo system so as to compensate for the deviation inherent in the output signal of the integrator when the movable element is tracking at constant speed.
6. A system according to claim 5.

wherein the signal related to the speed aiming signal is also applied to the second servosvstem so as to act therein in the opposite sense to its action in the first servosystem.
7. A system according to any one of claims I to 6. and comprising means for introducing into the second servosystem a ballistic correction signal.
8. A system according to claim 7, and

comprising means for forming the difference between the value represented by the ballistic correction signal and the value of any position deviation between the line of sight and the movable element, as measured by the second servosystem, and a logic circuit for receiving the output of the difference forming means and for receiving the output of the difference forming means and for receiving an external command signal, the logic circuit being arranged to issue a command signal initiated by the external command signal onlv when the deviation between the movable element and the line of sight falls below a given value.
9. A system according to claim 8.

wherein the movable element is a gun and wherein the external command represents a gun firing command signal.
10. A system according to claim 8, wherein the movable element to be aimed is a telescope and the external command signal is a triggering signal for a laser the beam of which passes. upon radiation, through the sighting means, the first servosystem comprising means for comparing the position of the telescope with a desired position represented by an aiming signal.
11. A system according to any one of the preceding claims. wherein the image originating from the sighting means is picked up by a TV camera and projected on a screen viewable bv an operator.
12. A system according to claim 11, wherein the TV camera comprises electronic light-amplifying means.
13. A sighting and aiming system substantially as hereinbefore described with reference to the accompanying drawings.