GB2077400A

GB2077400A - Air-to-air or ground-to-air automatic fire control system

Info

Publication number: GB2077400A
Application number: GB8032165A
Authority: GB
Original assignee: Societe de Fabrication dInstruments de Mesure SFIM SA
Current assignee: Societe de Fabrication dInstruments de Mesure SFIM SA
Priority date: 1980-04-11
Filing date: 1980-10-06
Publication date: 1981-12-16
Also published as: GB2077400B; FR2480424A1; FR2480424B1; DE3044348A1

Abstract

This invention relates to an automatic fire control unit for aircraft- mounted weapons. It includes a swivelling television camera coupled with one or several gyroscopes, and a television automatic tracking system using a processor to maintain the camera permanently focussed on a target and to steer the laying of the weapon mounted on the aircraft according to the direction of the axis of the camera, this direction being determined by sensors associated with the gyroscopes. The target acquisition takes place on a television screen on which an image of the automatic tracking system lock-on window is shown by an indicator. The pilot's functions are thus simplified and the influence of the aircraft instability is excluded. <IMAGE>

Description

SPECIFICATION Air-to-air or ground-to-air automatic fire control system This invention relates to an automatic fire control system for weapons mounted on aircraft and particularly flat-trajectory weapons mounted on helicopters.

Whether the crew of helicopter or aircraft consists of only one man acting both as a pilot and as a gunner, or includes a pilot and a co-pilot or gunner, the problem always comes from the difficulty to fire accurately because of the instability of the aircraft: aiming and keeping the target in the line of sight proves to be very difficult, especially for a helicopter, in spite of the pilot's expertise and even if the aircraft is in the autopilot mode, because of the instability of the aircraft attitude and vibrations: even with the most advanced helicopters flying in the autopilot mode, a residual oscillation will still remain.Moreover, most of the time the helicopter must be used in an air-to-air or air-to-ground (antitank) fight and the pilot, whether he uses the autopilot or not must also steer and fly the aircraft depending on the motions of the target he strives to hit, which makes it difficult for him to aim if he is also the gunner, or for a separate crew-member manning the weapon to aim.

This invention provides an automatic fire control system ensuring, in lieu of the gunner, a number of functions that the gunner had to fulfill for each firing, and above all rendering fire independent of the in-flight instability and vibrations of the helicopter.

For this purpose, this invention provides a combination of devices intended to serve the function of laying an aircraft borne weapon on to the line of sight of a target noted by the gunner, such that once the gunner has sighted the target the system locks onto the target and tracks it, automatically causing the weapon to follow, until the opening of fire, a direction enabling it to hit the target, i.e. a direction either exactly in alignment with the target or offset in view of the corrections to be applied to the trajectory of the projectile fired by the weapon.

The automatic fire control system of the invention includes - a television (TV) camera with the associated mechanical or optical devices for setting its optical axis with regard to the aircraft; means to control the setting devices, including at least one stabilizing gyroscope and means to apply one or two precession torques to each gyroscope, the gyroscope(s) being fitted with orientation sensors which provide control signals to the devices setting the optical axis of the television camera;; - a television automatic tracking system using a signal processor to generate, in the form of television signals synchronized with those of the camera, an acquisition window located in the field of vision of the camera, and to displace the window within this field, either by means of a control device, or in response to variations of the signals sent by the images detected by the camera, inside the window, to keep the window centred on a given image sector by moving the optical axis of the camera; means for displaying the acquisition window on a TV screen optionally with its variable location superimposed on a TV image of the background detected in the field of vision of the camera;; - control means arranged to change the location of the acquisition window within the field of vision of the camera and on the TV screen so as to make it enclose the target to be acquired, and switching means for activating the automatic tracking system to keep the window automatically centred on the target; means for laying the weapon mounted on the aircraft; - a processor capable of using the signals specific to the direction of the optical axis of the camera and the signals specific to the direction of the acquisition window and of the target in the field of vision of the camera and, if any, of the ,,signals specific to other parameters having an influence on the line of fire, to generate two groups of control signals: one group for setting the optical axis of the camera. and the other group for laying the weapon.

The TV screen may be integrated either into a so-called "head-up display" firing sight or into a helmet sight, using well-known optical means, so that the image of the acquisition window will be seen by the gunner against the actual background he will observe, projected to infinity. The TV image display superimposed on the actual image of the background will be normally used only for matching the directions of the reference mechanical and/or optical axes of the television camera on the one hand, the head-up display firing sight or the helmet sight on the other hand.

The control means may be a manual one. It may alternatively be a helmet sight the optical axis of which is co-axial to the gunner's line sight.

These two means can be mounted simultaneously and used separately by means of a switching device.

In the target-acquisition mode, the manual control is actuated to bring the acquisition window around the target; in the tracking mode, the optical axis of the camera undergoes an angular displacement so that the window brought on to the target remains automatically centred on the target even if the target is fluctuating either because of its own movement or because of movement of the firing aircraft.

The processor lays the weapon, having regard to the direction of the acquisition window, and therefore to the direction of the optical axis of the camera, which is known because of the above mentioned angular sensors, and inputs the weapon aiming corrections according to other parameters such as the target speed and the target range, the type of ammunition, the aerologic data relating to the firing envelop, etc.

The speed of the target is measured by TV tracking signals such as those applied to the control means controlling the devices for setting the optical axis of the camera. The use of linear precession control gyroscopes makes it possible, to obtain a parameter representing the target speed, the measurement of the gyroscope precession control currents, which are smoothed by the inertia of the gyroscope responding to these currents. The range is preferably measured by means of a laser range-finder or radar the optical axis of which is set and stabilized by the same means as those of the camera. In the specific case of a neodyme laser range-finder, the laser and TV camera optics may be to a large extent common.

The fire control system operates as follows: the pilot steers his helicopter towards the target to be engaged, so that this target enters the TV camera field of vision at a given time. This field of vision can advantageously be displayed on the above-mentioned television screen, which enables the pilot or the gunner to check that the target has entered the camera field of vision by means of the above-mentioned head-up display firing sight or the helmet sight.

Once the target has been so located, the gunner actuates one of the two above-mentioned control means to displace the acquisition window generated in the form of TV signals and displayed on the above-mentioned TV screen(s) until the window encloses the target. The target is then acquired and the operator, using a push-button switch, changes the fire control system from the "acquisition" mode (in which an external agent can change the position of the window) to the "tracking" mode in which the tracking system takes it upon itself to act through the processor in order to displace the optical axis of the TV camera in such a way that the window is kept centred on the acquired target.

In the "tracking" mode the processor of the tracking system receives the television signals from the camera, therefore the target image signals. Having generated the TV signals corresponding to the acquisition window it knows these signals and therefore the coordinates of the target X and Y. It compares with reference to-two rectangular axes the amplitude variations of the television signal (brightens variations) of the spot representing the target inside the acquisition window using the brightness ratio directly or using the shapes they represent (image correlation) and it determines the control signals of the devices for setting the optical axis of the camera to keep this optical axis centred on the target in spite of the relative motions of the aircraft and target.

On the other hand, the direction of the weapon carried on board the aircraft must reproduce at every moment the direction of the optical axis of the camera to enable the gunner to open fire without having to worry about the direction of the weapon. The weapon can be permanently laid in the direction of the target or offset by a quantity depending on such parameters as the relative speeds of the aircraft and the target or the shape in space and time of the trajectory of the projectile that has been fired, etc.

In order to carry out this automatic laying of the weapon, two solutions are theoretically applicable, although the first one may seem more reliable and more convenient than the other.

a) in the first solution, the above-mentioned slaving processor discriminates a tendency of the target, therefore of the acquisition window, to deviate from the optical axis of the camera, and then it gives immediate commands to change the direction of the optical axis of the camera to bring the position of the optical axis of the camera back on to the target by actuating the above-mentioned controls especially the stabilizing gyroscope(s); as'- far as the weapon is concerned, it is layed by means of at least two follow-up systems which receive from the processor control signals taking into account both the position of the optical system of the camera and the above-mentioned other fire parameters. Then the weapons follows (fire corrections apart) the direction of the TV camera optical axis.

b) in the second solution, the processor measures the deviation of the target direction from the optical axis of the camera, i.e. it locates the coordinates of the target in relation to two perpendicular axes describing the field of vision of the camera.

From this measurement and that of the direction of the optical axis of the camera, and from the measurement of the other parameters (fire corrections) it determines the direction in which the weapon must be laid in relation to the optical axis of the camera. In the simplest case, this axis could remain invariable (fixed camera), the pilot having to keep the target within the field of vision of the camera by steering the aircraft; but in the most usual case, the camera or its optical sight is mobile, controlled by one or two gyroscopes which enable the direction of its axis to be stabilized independently of the motions of the aircraft; in such a case the processor is permanently informed of the direction of the optical axis of the camera and it combines such an information with the deviation measurement of the target p6sition and with the other parameters in order to inform the devices for laying the weapon of the direction which must be taken by the weapon. This system, because of its static nature, can present advantages, but it is less reliable, as far as measurements are concerned, than the system which consists in bringing and keeping the optical axis of the camera on to the target by means of a slave control.

Moreover, in both cases, the weapon is stabilized in direction since it is slaved in direction to a gyroscopic device.

By way of example there now follows some detailed information on the various preferred components of the fire control system according to the invention.

The television camera is a camera with electronic and/or mechanical scanning operating either in visible light or in invisible light (especially in the infrared band, even for infrared). It is equipped with an optical sight system which may be a complex system and include dioptric, catadioptric or mixed magnifying optics, with a fixed or continuously or discontinuously variable focus so that the field of vision can be varied as necessary.

The visual display can be mounted independently of the camera and when reference is made in this specification to setting of the camera or of its optical axis, it must be understood that the aim is to set the optical axis of the camera and therefore that it is possible to set either the camera itself, or an optical system or part of an optical system located in front of the lens of the camera, even though such a system does not necessarily have an output optical system coincident with the optical axis of the camera itself.

In particular, it will be possible in many cases to arrange a set of mirrors, prisms, and lenses capable of deflecting the light rays received or transmitted along a determined optical axis, so as to direct them to the camera along a different optical axis.

In these circumstances, it is quite possible to envisage three arrangements for stabilizing and setting the line of sight of the camera.

First, the camera and its optical sight may be mounted on a common support, mechanically coupled or slaved in direction by means of motors with one or more gyroscopes capable of receiving the electric signals controlling the angular positioning, by applying precession torques to these gyroscopes; Secondly, the camera can be directly mounted on the structure of the aircraft, and the optical system be mechanically coupled with or slaved to the gyroscopic device; or Thirdly, the optical system can be directly mounted on the structure of the aircraft and then be coupled or slaved to the gyroscopic device.

In the first case, the elements for example, the camera or range-finder to be set and stabilized may be carried on a platform gimbal-mounted on the structure of the aircraft, which can be oriented in various directions by means of positioning motors, said elements receiving for this purpose signals controlling the angular positioning, particularly when the optical axis of the camera has to be set so as to be permanently in the direction of the target.

In the second case, the optical system will advantageously include one or more mirrors and/or one or more mobile diasporameter(s). The movable elements, either the camera and sight assembly or the sight alone, are equipped with angular sensors which give information on the direction of these elements and therefore of the emerging optical axis, with respect to the structure of the aircraft, this information being used as a feedback and for the above-described fire calculations.

The mentioned processor is preferably a microprocessor programmable to fulfill a number of measurement, calculation and system management functions, incorporating in particular generation functions in the form of TV signals of indicators such as the acquisition window indicator which must be displayed on a television screen in a variable position which is adjustable and measureable, or other indicators used as firing and steering aids, for example an indicator showing the direction in which the weapon is laid (a direction which is usually different from the direction represented by the position of the lockon window) one or more indicators determining the maximum possible sphere of action (maximum clearance of the sight and of the weapon) in the field of vision of the camera, an indicator representing the firing "future point" i.e., the theoretical impact point which is the converging point in space of the projectile and the target, one or more indicators for flying the aircraft such as, available power, position in space, line of flight and/or one more system management indicators showing such functions as: in or out of service; ready for firing; alarm(s); or target range, target speed, etc.

All these indicators can be continuous or blinking, with variable frequencies, and different colours can be used. Processors can presently be programmed so as to generate all these indicators and incorporate them in a single TV circuit. The TV screen which displays these indicators may, for harmonization purpose, receive television signals and TV images directly from the camera, to superimpose on the indicators (and particularly on the lock-on window indicator) an image of the background as seen by the camera and changed into a TV picture.For a normal use of the system, the gunner is equipped with a helmet sight or uses a "head-up display" sight incorporating both in the TV screen and which enables him to see the background and therefore the target directly through a semi-reflecting mirror which projects the superimposed TV images of the various indicators generated by the processor and, in particular, in accordance with its actual direction, the acquisition window. Helmet sights fitted with a TV screen, either built-in or offset by optical fibers, can achieve this image superimposition through a monocular lens in which the indicators appear projected to infinity and superimposed on the background.

The direction of the helmet sight is measured at every moment to establish a relationship between the positions of the indicators and the position of the TV camera, i.e. substantially a coincidence, subject to harmonization, as stated hereabove, between the field of vision of the helmet sight and the field of vision of the camera. The direction of the optical axis of the helmet sight and therefore the glance direction of an observer wearing such a helmet sight can be determined and this factor can be used in the invention, especially to displace the acquisition window within the field of vision of the camera or to bring the optical axis of the camera on to the target with a view to its acquisition, through the rotation of the observer's head glancing at the target.

If a "head-up display" sight, which is stationary with respect to the aircraft, is used, its semireflecting mirror enables the observer to see the background and therefore the target directly and additionally to project, superimposed on the mirror, the synthetic images of the lock-on window and other indicators, and the TV image of the background, for harmonization purposes. The use of a helmet sight revolving with the gunner's head is more favourable because "head-up display" sights have a field of vision and syntheticimage projection limited to some twenty degrees.

Television tracking circuits, coupled with the camera and the processor, or forming an integral part of the processor, are now sufficiently perfected to track a target through a lock-on window which moves within the field of vision of the camera while remaining centred on the designated target. In a given procedure, this target is located through the analysis of its basic brightnesses.

The average brightnesses in the vicinity of the spot, on both sides of the spot, in two or more perpendicular directions, are measured as soon as the target is acquired, and the acquisition window is displaced along these two directions to keep these brightnesses (or at least their ratios) to their measured values, in spite of target movement within the field of vision.In reality, the window is a sequence of electric time plateaus, generated at the rate of one per line on certain lines of television scanning by a generator synchronized with the camera scanning, the position of this plateau on the line of scanning, i.e. its phase shift with regard to the scanning start, and the position of the lines showing a plateau being adjustable from the outside in the target acquisition mode or automatically in the tracking mode owing to the slaving loops which move the plateau in elevation (line position) and in traverse, while centring it permanently on an area showing a given brightness ratio.

In another procedure, the target outline is determined by the basic brightness. This target outline is stored and compared with the new outline, then a correlation calculation gives the deviation signals necessary for the tracking.

The weapon laying calculation function at every moment during the tracking is performed especially through the use of information on the range of the target in relation to the aircraft, and on the speed of the target in relation to the aircraft, in order to offset the weapon in relation to the target by such a quantity that the projectile fired by the weapon hits the target in spite of its movement.

To illustrate the principle of the invention, the drawing shows schematically an example of the application of the invention. This example is a block diagram and is drawn so as to explain the function fulfilled by the fire control system. In view of the complexity of each sub-assembly used, and as these sub-assemblies are well known, the invention has not been represented in more detail and the lines connecting the blocks of the diagram represent functional relations and not real connections between sub-assemblies.Moreover, some elements have been purposefully dissociated to clarify the representation of the functions but it must be realized that, in practice, these sub-assemblies can be grouped together, for example, the television tracking circuits can be an integral part of the processor, the generators of indicators to be displayed on the television screen and the lock-on window generator can be integral parts of the same assembly arid be closely coupled with the processor or be integral parts of the processor, etc.

Lastly, although only two television screens have been mentioned so far and represented in the diagram, one or more other TV screens can also be used, for example there may be a screen in the aircraft cockpit, at the disposal of a second operator. It is also possible for the equipment to include one or more tape recording, or similar devices.

Several examples of operation of the invention, either with a single gunner, the pilot, or with the pilot plus one or more operators or gunners, will now be described.

The operating procedure includes a phase of target acquisition and a phase of tracking prior to firing.

Phase O Prepare for filing by storing the previous permanent or semi-permanent data.

Achieve harmonization by displaying the image of a characteristic landmark in the background and actuate the harmonization adjusting devices for this landmark to coincide with the acquisition window, or for the purpose of storing the observed deviations.

Phase 1 Acquisition 1 sot case: use of head-up display sight placed in front of the pilot's head.

If necessary, switch the fire control system to "head-up display" sight position; actuate the appropriate control to bring the optical axis of the camera into the aircraft centreline; discover a target by sight; steer the aircraft so as to bring the target into the field of vision of the head-up display sight (usually the acquisition field of the camera sight is larger than the field of vision of the head-up display sight); observe the so-called "window" indicator displayed in the head-up display sight (and also the adequate service and flight indicators, if any); move the "window indicator towards the target by actuating the corresponding control (joy-stick or two-way button) by keeping the aircraft approximately in line; ; frame the target with the window by manually adjusting its dimensions in accordance with the reaction of the target and its environment if need be, or rely upon an automatic window readjusting device; activate the television automatic tracking; and check that activation has been achieved by observing the movement of the optical axis of the camera, the tracking, or warning light, or a corresponding service indicator in the head-up display sight.

The acquisition is completed.

2nd case: use ofa helmet sight switch the fire control system to "helmet sight" which, in particular, slaves the direction of the optical axis of the camera to the optical axis of the helmet, i.e. to the direction of the operator's glance; discover a target visually by moving the head; if necessary, steer the aircraft so as to keep the target within the field of vision of the camera sight; observe the so-called "window" indicator in the helmet sight (television screen projected in the operator's eye); and then proceed as above to move the acquisition window up to the target, enclose the target and switch the system to automatic tracking.

The acquisition is completed.

Phase 2 Preparation for firing and firing observe the appearance of the "future point" indicator as soon as fire calculations are completed; steer the aircraft so as to bring, if necessary, and maintain the "future point" indicator within the firing envelope of the weapon, this firing envelope being displayed either in the head-up display sight, or in the helmet sight; press the trigger of the weapon.

The weapon will start firing after automatically checking that all conditions for firing satisfactorily are met. In case of emergency, it will be possible to use a switch to transgress this provisional interdiction.

Following phases observe the results of the firing with the naked eye by displaying the TV image either in the headup display sight or in the helmet sight, or on a TV screen; repeat, if necessary, from the start the acquisition phase and the preparation-for-firing phase.

Claims

1. An automatic fire control system for aircraft mounted weapons, comprising: a television (TV) camera having an optical sight system and devices for setting the optical axis of the sight system in relation to the aircraft; means for controlling said setting devices including at least one gyroscope and means for applying one or two precession torques to each gyroscope the gyroscopes being equipped with orientation sensors providing control signals to the devices for setting the optical axis of the camera;; an automatic television tracking system using a signal processor to generate, in the form of television signals synchronized with those of the camera, an acquisition window located in the field of vision of the camera, a) either to move the window within the field of vision by means of an external control, or in response to the variations of video signals delivered by the camera inside the lock-on window to keep the window centred on a given image sector in spite of the displacements of the optical axis of the camera, b) or to move the optical axis of the camera so as to slave this optical axis to the direction in which a target is detected; means for displaying, in its actual direction, the acquisition window or a TV screen, optionally superimposed on a natural image of the background corresponding to the field of vision of the camera (harmonization);; external control means for manually changing the position of the acquisition window or the optical axis of the camera so as to bring it on to a target visible in the natural image of the background, and a switch to activate then the automatic tracking system in order to maintain the window or the optical axis of the camera automatically centred on this target; means for laying a weapon mounted on the aircraft; and a processor capable of using the signal specific to the optical axis of the TV camera setting the axis of the camera, and the signals specific to other parameters having an influence on the weapon laying means.

2. A system according to claim 1, wherein the processor measures the deviation of the window position within the field of vision of the camera.

3. A system according to claim 2, wherein the processor generates signals for applying precession torque to the or each gyroscope during the camera in proportion to the deviation of the lock-on window position from a central position, such as to bring back the optical axis of the camera, to a position in which the acquisition window is in its axial position.

4. A system according to any one of claims 1 to 3 wherein an optical range-finder is mounted together with the camera on a common support and the range-finder receiving a beam along the same axis as the camera and being coupled with the processor to provide a fire correction parameter.

5. A system according to any one of claims 1 to 4, wherein the rotation speeds of the optical axis of the camera, estimated by the precession currents of the gyroscope(s) are fed into the processor to provide a fire correction parameter.

6. A system according to claim 4 or claim 5 wherein the processor is capable of continuously generating on the screen a specific visual indicator representing the future point of impact.

7. A system according to any one of claims 1 to 7 wherein the camera-and/or its optical sight system are installed on a gimbal-mounted platform provided with positioning motors along at least two axes, said motors being controlled by ,the direction sensors of the gyroscopic device.

8. A system according to any one of claims 1 to 7 wherein a TV screen is incorporated in a "headup display sight" or a helmet sight.

9. A system according to claim 1, substantially as described herein with reference to and as shown in the drawing.