GB2375385A

GB2375385A - Weapon fire control system

Info

Publication number: GB2375385A
Application number: GB0204894A
Authority: GB
Inventors: Bernard Boehm
Original assignee: Sagem SA
Current assignee: Sagem SA
Priority date: 2001-03-09
Filing date: 2002-03-01
Publication date: 2002-11-13
Anticipated expiration: 2022-03-01
Also published as: GB2375385B; DE10208102A1; FR2821928A1; GB0204894D0; FR2821928B1; IL148539A; DE10208102B4; IL148539A0

Abstract

A fire control system for the aiming of a weapon by an operator is capable of stabilising a camera-captured image and determining an error representative of the deviation between a position which corresponds to a control command and the actual position of the weapon where a translation inverse 3 to that of the deviation is applied to the image. The system comprises a motorisation device 5 which drives the weapon and has an input corresponding to a velocity error arising from summator S3 which itself receives as input a velocity command. This input velocity is the sum of that commanded by the operator via aiming stick 1 and that as corrected by the assembly in relation to summator S1. The velocity is communicated as output from the device 5 to the weapon. The weapon velocity, as measured by sensor 6 (eg. a rate gyro), is then subtracted from the S3 input velocity command. The system inherently comprises observation and sighting means and the images captured by the camera are transmitted to the operator on a sighting channel.

Description

WEAPON FIRE CONTROL SYSTEM

.. The present invention relates to weapon fire control systems. GENERAL TECHNICAL FIELD

Fire controls are conventionally known, comprising: - a weapon mobile about two axes, elevation and 10 bearing, the aiming of which is effected with regard to each of the two axes by way of a velocity servocontrol achieved on the basis of a facility for motorization of the weapon and of an angular velocity measurement sensor; 15 - a video camera mounted securely with the weapon and whose sighting axis is parallel to that of the weapon; this sighting axis is defined by a reticle inlaid into the video image; 20 The operator then uses the video image supplied by the camera to sight a target by aligning this target with the reticle inlaid into the image. To do this, he acts on an aiming stick which supplies the servocontrol of the weapon with the elevational and bearing velocity 25 commands required for the tracking of the target.

In the case where the above system is used on a mobile vehicle it is necessary to ensure the stabilization of the weapon about both axes, elevation and bearing, so 30 as to eliminate the angular disturbances of aim which are caused by the movement of the vehicle.

Stabilization of the weapon is then generally achieved by using a gyroscopic facility (rate gyro) as the 35 weapon's angular velocity measurement sensor.

For an example of an automatic target tracking device, reference may advantageously be made to Patent Application FR 2 484 626.

In this document, the television camera which constitutes the observation and sighting means is mobile with respect to the turret of the tank.

According to two degrees of freedom there are provided processing means allowing it to undertake target tracking to which the aiming of the weapon is servocontrolled. In such a system the following problems appear: 1) The camera being secured to the weapon, the aiming of the sight is obtained directly by the aiming of the weapon. However, having regard: 15 - to the generally considerable mass and inertia of the weapon, - to the numerous disturbing torques (unbalances, friction, etc.) which intervene in the servocontrol, - to the technical solutions generally employed for 20 this type of motorization (geared reduction motor inevitably exhibiting some play and limited mechanical stiffness), the performance of the weapons aiming servocontrol is itself limited.

This results in mediocre quality of aiming of the weapon which is experienced directly by the operator with regard to his sight and which impedes the obtaining of fine, continuous and well-centred tracking of the sight onto the target.

2) The stabilization of the sight (decoupling from the movements of the vehicle) is obtained directly by stabilization of the weapon. However, having regard to 35 the difficulties recalled above, the quality conventionally obtained in weapon stabilization is likewise limited and generally insufficient so as not to significantly degrade the intrinsic quality of the image supplied by the camera. Specifically, the

residual movements of the weapon which are transmitted directly to the camera are generally of a much larger order of magnitude than the camera's own resolution, thereby creating blur on the image observed and 5 resulting in a loss of observation range.

3) In the case where firing is requested, there is reason, as in any conventional fire control, to shift prior to firing the axis of the weapon with respect to 10 the direction of the target by an angular correction in elevation and bearing (fire correction). This fire correction takes account in particular of the effects of the ballistic trajectory of the munition (lift correction) and of any relative displacement of the 15 target with respect to the marksman during the time of flight of the munition (kinematic correction).

The calculation of the fire correction requires in particular the knowledge of the distance of the target 20 and of the target/marksman relative angular velocity.

These parameters are generally acquired during a preliminary phase of target tracking by the use of a telemeter coupled to the video camera and the acquisition of the measurements of angular velocity of 25 aim of the weapon during the target tracking phase.

In the type of system alluded to, the introduction of

the fire correction is performed by shifting the sighting reticle in the video image by an angular 30 deviation corresponding to the calculated fire correction. The firing sequence is then performed thus: - acquisition of the target by the operator in the 35 field of the camera.

- Fine tracking of the target by the operator using his sighting reticle.

- Acquisition of the parameters required for the calculation of the fire correction.

- 4 - Translation of the sighting reticle in the video image so as to allow the introduction of an angular

shift equal to the fire correction between the direction of the weapon and the direction of the 5 sighting reticle once displaced.

- Re-aiming by the operator at the target with the sighting reticle, the latter occupying its new position. 10 In such a sequence, the operatoIwhilst track the target a first time and then re-aim at it accurately a second time after introduction of the fire correction by shift

of the reticle.

15 This two-stage method is prejudicial to the total reaction time of the system before firing having regard in particular to the need for the operator to accurately re-aim at the target a second time with his reticle. In order to eliminate the various drawbacks stated above a conventional solution is to introduce an aiming and stabilization device specific to the video channel (in addition to the weapon's aiming and stabilization 25 device) based either on the interposition of a two-axis stabilized mirror downstream of the camera, or on the mounting of the camera directly on a two-gimbal stabilized platform.

30 By virtue of these means which are specific thereto, the aiming and stabilization of the sight become independent of that of the weapon, the latter generally being feedback controlled by duplication of the position of the sight.

The aiming and stabilization performances obtained with regard to sighting are generally very good.

The introduction of the fire correction is achieved by

- 5 - shifting the weapon with respect to the sight, this shift possibly being effected automatically by introducing the shift directly into the feedback control of the weapon with regard to the sight. The 5 sight which is stabilized independently is not disturbed by this introduction of the fire correction

and the operator has no operation of re-aiming at the target to be performed. The ergonomics of the system are improved and the total reaction time of the system 10 before firing is minimal.

This solution offers numerous technical advantages but it results unfortunately in a very considerable increase in the complexity and cost of the system, 15 thereby greatly limiting its use.

PRESENTATION OF THE INVENTION AND STATE OF THE ART

The objectives of the present invention are to afford 20 the same improvements as the previous solution in terms of performance, ergonomics and reaction time but by proposing a much more economical and physically much less complex and bulky solution.

25 It is already known practice to restore video images degraded by angular deflection movements undergone by a camera by applying to these images a translation inverse to the translation undergone by the image, together with, as appropriate, a blur restoration 30 processing.

Reference may for example be made in this regard to French Patent Application No. 92 03871, which describes only image restoration in the case of a camera mounted 35 on a mobile craft undergoing angular destabilizations.

For its part, the invention proposes a fire control system for the aiming of a weapon by an operator, comprising:

6 - - means of motorization able to drive the weapon, -- means able to control the means of motorization so as to displace the weapon as a function of a control command 5 - aiming means allowing the operator to generate this control command, - observation and sighting means which comprise a camera whose observation axis is parallel to the weapon, an image captured by this camera being 10 transmitted to the operator on a sighting channel, - means able to stabilize the image supplied to the operator on the sighting channel, characterized in that the observation axis of the observation and sighting means is fixed with respect to 15 the weapon and in that the stabilization means comprise means which determine an error representative of the deviation between the position corresponding to the control command and the actual position of the weapon and which apply to the image captured by the camera a 20 translation inverse to that corresponding to this position deviation.

Advantageously, the means of control of the motorization means comprise means for summing with a 25 control command generated by the aiming means a correction dependent on the position deviation for which a translation is applied to the image captured by the camera, the sum of the control command generated by the aiming means and of this correction being used as 30 control command to control the displacement of the weapon. In particular, the correction summed with the control command generated by the aiming means is furthermore 35 dependent on a fire correction to be applied to the weapon. Especially, in an especially preferred manner, the correction summed with the control command generated by

the aiming means is dependent on the sum between the fire correction and a displacement corresponding to the inverse of the translation applied to the image captured by the camera.

Other characteristics and advantages of the invention will emerge further from the description which follows

and which is purely illustrative and nonlimiting.

10 DESCRIPTION OF A POSSIBLE EMBODIMENT OF THE INVENTION

Architecture The architecture of a system in accordance with a 15 possible embodiment of the invention is represented in Figure 1, which diagrammatically illustrates the servocontrols which are applied individually to each of the two elevation and bearing axes of the weapon system. The system represented in this figure comprises an aiming stick 1 allowing the operator to generate velocity, elevation or bearing aiming commands.

25 It also comprises a device 5 for motorization of the weapon in terms of elevation or bearing. This device 5 has as input a velocity error arising from a summator S3 and as output the velocity communicated to the weapon. The summator S3 receives as input a velocity command.

It subtracts the velocity of the weapon therefrom, which is measured by a sensor 6 which measures the 35 angular velocity of the weapon in terms of elevation or bearing. This sensor 6 is for example a rate gyro in the case of a stabilized system.

The motorization device 5, the sensor 6 and the

- 8 summator S3 constitute the weapon's velocity servocontrol loop.

The velocity command received as input by the summator 5 S3 is the sum of the velocity commanded by the operator on the basis of the aiming stick 1 and of a velocity correction determined by the assembly which will now be described. 10 This assembly comprises a summator S1 which subtracts from the velocity commanded by the operator with the aid of the aiming stick and the velocity of the weapon as measured by the sensor 6+ 15 The output signal from this summator S1 is transmitted to means 2 which carry out the time integration of the velocity error corresponding to the signal output by the summator S1.

20 The velocity error thus integrated is transmitted to means 3 which carry out a restoration of the degraded image by implementing a processing of the type of that described in Patent Application FR-92 03871, consisting in applying to the current image a translation inverse 25 to the value supplied by the integrator 2 (the sampling of the output of the integrator 2 being done in a manner synchronized with the acquisition of the video images). 30 The integrated velocity error arising from the means 2 is furthermore transmitted as input to a summator S2.

The summator S2 forms the sum between this integrated velocity error arising from the means 2 and a value of 35 the fire correction, which is calculated elsewhere independently, and which has to be introduced into the system. The fire correction processing may be very diverse (ballistic lift corrections, anticipations of target movement, weather, etc.) and is in itself

- 9 - conventionally known to the person skilled in the art.

The output signal from the summator S2 is transmitted to means 4 which generate on this signal a velocity 5 control gain making it possible to transform a position deviation arising from the summator S2 into a velocity command for the servocontrol of the weapon.

Manner of operation The various functionalities offered by the architecture just described are presented in a progressive manner independently of one another hereinbelow: 15 Stabilization of the image in the absence of commanded aiming velocity and of fire correction to be introduced: The sensor 6 measures the residual velocity of the 20 weapon (which is not completely zero having regard to the imperfect stabilization of the weapon).

The output of the integrator 2 reconstructs the positional movement of the weapon and hence of the 25 camera (successive positions of the camera at each image). The means 3 carry out on each image a translation inverse to the camera's residual movement supplied by 30 the integrator 2, thereby allowing compensation of this movement. The image presented to the operator is therefore thus stabilized.

Independent control of the velocity sighting in the 35 absence of stabilization (vehicle stationary and of fire correction to be introduced: The aiming stick 1 supplies the instructed velocity aiming command on sighting. This command is sent to the

- 10 weapon's velocity servocontrol (anticipation control).

The weapon duplicates this velocity command only imperfectly. The summator S1 takes the difference between the velocity instructed on sighting and the 5 velocity achieved by the weapon as measured by the sensor 6. The output of the integrator 2 represents the deviation in position between the position instructed on sighting and the measured position of the weapon and hence of the camera. The means 3 perform on each image 10 a translation inverse to that corresponding to the position deviation supplied by the integrator 2. The image presented to the operator is then decoupled from the weapon's own movement. As far as the operator is concerned, this amounts to having direct control of 15 sighting independent of the weapon which nevertheless carries the camera.

Introduction of the fire correction in the absence of

stabilization (vehicle stationary) and of instructed 20 aiming velocity: The fire correction (elevational or bearing angular shift command) is introduced by way of the summator S2.

25 This command is transformed into a velocity control for the servocontrol of the weapon by the gain 4.

The servocontrol of the weapon reacts and the weapon is driven. The sensor 6 measures the velocity achieved by 30 the weapon and feeds the integrator S2 which brings about the progressive translation of the image.

When the translation effected on the image is equal to the fire correction to be introduced the velocity 35 command arising from the summator S2 is cancelled out and the weapon comes to a standstill.

The weapon is then shifted with respect to the sighting by the value of the fire correction, the image

- 11 presented to the operator having remained still.

In practice the various modes of operation analysed independently above are overlaid.

A system is thus obtained which simultaneously has: Stabilization of the image presented to the operator (image decoupled from the movements of the vehicle and the weapon).

10 Independent control of velocity sighting (not constrained by the quality of the servocontrol of the weapon).

Automatic introduction of the fire correction

without disturbance with regard to sighting (thus 15 allowing a minimal reaction time before firing).

Variant embodiments other than that just described are of course possible. In particular the video camera may be a television camera or a 20 thermal camera.

e The invention applies as a priority to systems using cameras equipped with matrix detectors which are therefore not furnished with an internal device for line or column scanning. However the invention may be 25 applied to cameras equipped with a linear-array detector which require an internal device for line scanning. In this case the stabilization of the image will be satisfactorily obtainable only with regard to a limited zone of the image for which the image-by 30 image acquisition of the movement of the camera is perfectly synchronized with the acquisition of this zone of the image.

The camera might not be mounted directly on the weapon but integrated into a viewfinder which has an 35 aiming mirror linked mechanically to the weapon allowing the camera sight to be secured to (fixed) and coaxial with this weapon (case of a turret roof viewfinder with mechanical feedback duplication of the weapon).

- 12 The stabilization of the weapon can be achieved by means of lootings different from that described in the invention (for example: open-loop stabilization of the weapon on the basis of a chassis rate gyro for 5 bearing and of a turret rate gyro for elevation). The proper operation of the invention requires only the ability on the one hand to control the weapon in terms of displacement and on the other hand to have available the measurement either of the velocity or 10 of the position achieved by the weapon (in the latter case, the summator S1 is placed downstream of the integrator 2 in diagram 1).

o If the case of a stationary vehicle is considered, the servocontrol of stabilization of the weapon can 15 be replaced by a simple servocontrol of velocity based on the use of tachometers allowing measurement of the relative velocity of the weapon with respect to its support. The functions of independent control of the line of sight and of automatic introduction of

20 the fire correction are still available in such a configuration.

Claims

- 13 CLAIMS

1. Fire control system for the aiming of a weapon by an operator, comprising: 5 - means of motorization able to drive the weapon, - means able to control the means of motorization so as to displace the weapon as a function of a control command - aiming means allowing the operator to generate 10 this control command, - observation and sighting means which comprise a camera whose observation axis is parallel to the weapon, an image captured by this camera being transmitted to the operator on a sighting channel, 15 - means able to stabilize the image supplied to the operator on the sighting channel, characterized in that the observation axis of the observation and sighting means is fixed with respect to the weapon and in that the stabilization means comprise 20 means which determine an error representative of the deviation between the position corresponding to the control command and the actual position of the weapon and which apply to the image captured by the camera a translation inverse to that corresponding to this 25 position deviation.

2. System according to Claim 1, characterized in that

the means of control of the motorization means comprise means for summing with a control command generated by 30 the aiming means a correction dependent on the position deviation for which a translation is applied to the image captured by the camera, the sum of the control command generated by the aiming means and of this correction being used as control command to control the 35 displacement of the weapon.

3. System according to Claim 2, characterized in that the correction s D ed with the control command generated by the aiming means is furthermore dependent

- 14 on a fire correction to be applied to the weapon

4. System according to Claim 3, characterized in that the correction summed with the control command

5 generated by the aiming means is dependent on the sum between the fire correction and a displacement corresponding to the inverse of the translation applied to the image captured by the camera.

10 5. System according to one of the preceding claims, characterized in that it comprises an angular velocity or position sensor which supplies measurements of angular velocity or of position of the weapon on the one hand to the means of stabilization of the image 15 supplied to the operator on the sighting channel and on the other hand to the means which control the motorization means.

6. System according to one of the preceding claims, 20 characterized in that the means of stabilization of the image supplied to the operator on the sighting channel receive as input on the one hand a command representative of an angular velocity of command and on the other hand an angular velocity measurement and in 25 that the stabilization means comprise means for integrating over time the deviation between this command and this measurement.

7. System according to one of the preceding claims, 30 characterized in that the camera is one which employs matrix detectors.

8. Fire control system for the aiming of a weapon by an operator, substantially as hereinbefore described with reference to and as shown in the accompanying drawing.