EP0090713B1 - Fire control system with a sighting telescope controlled by an automatic tracking device - Google Patents

Description

The present invention relates to a fire control system, and more precisely to an automatic target targeting and tracking system, particularly suitable for use on aircraft (combat helicopter in particular).

In a known fire control system, an operator must first search for a target to be destroyed, in particular by using a magnifying observation scope for which it provides orientation in elevation and in bearing by means of a remote control handle acting on bezel orientation motors.

The operator sends to an automatic tracking device, during this search phase or at the end of this phase, an order of forced orientation of the tracking device along the axis of the telescope; then he decides to go into the automatic tracking phase and sends the tracking device an automatic orientation order on a spotted target. The tracking device comprises, in order to ensure the execution of this last point, on the one hand an aiming optic providing an image (video for example) of the target, and on the other hand ecartometry circuits operating for example by contrast or by correlation, which locate the displacements of the image of the target in the field of the optical sight and which ensure the adequate orientation of the tracking device to bring back this image of target in the axis of aimed.

Information on the direction taken by the tracking device is continuously transmitted, with appropriate fire corrections, to a destruction weapon which therefore targets the target as long as it remains centered in the line of sight of the tracking device. pursuit, and the operator can send a firing order at any time.

It is desirable that the magnifying telescope follow the movements of the tracking device when the latter is performing an automatic tracking phase, so that the operator can use the telescope as a means of visual control of the proper execution of the tracking. For example, in case of loss of the target by the tracking device (passage behind a curtain of trees etc ...), the operator must be able to regain control immediately or verify that the tracking device catches the target by itself lost (at the exit of the curtain of trees for example).

On the other hand, when the operator aims at a target with the telescope, and asks the tracking device to aim at the same target, the optics of the telescope and the optics of the tracking device must aim at the same point. otherwise the operator must perform an additional phase of checking or resetting the image given by the tracking device before entering the tracking phase.

As the telescope is magnifying, an error of angle even small between the two optics can have very troublesome practical consequences.

However, several reasons combine to create such errors and in particular the parallax error between the telescope and the optics of the tracking device which, from two close but different positions, aim at the same point, or even angular errors due mechanical deformation of the structure of the helicopter carrying the fire control system.

The object of the invention is to remedy these drawbacks.

On the other hand, a combined sighting and tracking device for a missile guidance system is known from French patent 2,230,247. It includes a pivotally mounted telescopic sight and a pivotally mounted tracking device rigidly coupled to the telescope for pivoting with the latter, the optical axes of the telescope and of the tracking device being approximately collimated. The tracking device has a photoelectric screen and a projection system capable of projecting onto said screen a real image of a light source to which the tracking device is directed. The screen produces electrical signals of coordinates dependent on the offset coordinates of the projected image relative to the electrical center of the screen. In order to improve the harmonization of the tracking device and the aiming device, it further comprises a point light source, optical means for injecting a light brush from this point source into the optical systems of the telescope and of the tracking device, so that an image of the point source appears in the center of the field in the lens of the telescope and that a real image of the point source is projected on the tracking screen. it includes electrical cancellation means which generate electrical control voltages which suppress the electrical output signals from the screen produced by the projected image of the point source so as to compensate for any shift of said image with respect to the electrical center of the screen.

This solution does not prove to be effective enough and can only be very difficult to adapt to a system where the tracking device and the telescope are separate.

• - un dipositif optique de poursuite automatique de cible pourvu de moteurs d'orientatioi en site et en gisement et de capteur angulaires repérant l'orientation de son axe de visée en site et en gisement;
• - une lunette grossissante d'observation pourvue également de moteurs d'orientation en site et en gisement et de capteurs angulaires repérant l'orientation de son axe de visée en site et en gisement, caractérisé par le fait que:
  • a) le dispositif de poursuite porte un moyen d'illumination laser émettant un rayonnement laser parallèlement à l'axe de visée de ce dispositif;
  • b) la lunette porte un détecteur de rayonnement laser couplé à un circuit d'écartométrie associé susceptible de fournir un couple de signaux d'erreur représentant l'écart en site et en gisement entre le centre du détecteur correspondant à l'axe de visée de la lunette et le point de focalisation du rayonnement laser reçu après réflexion sur un obstacle;
  • c) une mémoire est prévue pour recevoir et enregistrer ces signaux d'erreur dans une phase de recalage préliminaire pendant laquelle le moyen d'illumination laser émet un rayonnement laser.
  • d) un circuit électrique est prévu pour recevoir des informations issues des capteurs angulaires du dispositif de poursuite et de la lunette, et pour fournir aux moteurs d'orientation de la lunette, dans une phase de poursuite automatique, des signaux de commande pour asservir la lunette aux mouvements en site et en gisement du dispositif de poursuite, le circuit électrique étant connecté pendant la phase de poursuite à la mémoire pour recevoir les signaux d'erreur enregistrés pendant la phase de recalage, ledit circuit électrique comportant des moyens pour apporter- aux signaux de commande une correction correspondant aux signaux d'erreur.

The present invention provides a fire control system comprising:

• - an optical device for automatic target tracking provided with orientation motors in elevation and in bearing and angular sensor locating the orientation of its aiming axis in elevation and in bearing;
• - a magnifying observation scope also provided with orientation motors in elevation and in bearing and angular sensors locating the orientation of its aiming axis in elevation and in bearing, characterized in that:
  • a) the tracking device carries a laser illumination means emitting laser radiation parallel to the line of sight of this device;
  • b) the telescope carries a laser radiation detector coupled to an associated deviation circuit capable of supplying a pair of er signals ror representing the difference in elevation and in bearing between the center of the detector corresponding to the line of sight of the telescope and the focal point of the laser radiation received after reflection on an obstacle;
  • c) a memory is provided for receiving and recording these error signals in a preliminary registration phase during which the laser illumination means emits laser radiation.
  • d) an electrical circuit is provided for receiving information from the angular sensors of the tracking device and of the telescope, and for supplying the telescope orientation motors, in an automatic tracking phase, with control signals for controlling the telescope with elevation and bearing movements of the tracking device, the electrical circuit being connected during the tracking phase to the memory for receiving the error signals recorded during the registration phase, said electrical circuit comprising means for providing control signals a correction corresponding to the error signals.

This registration makes it possible to effectively overcome parallax errors and errors due to deformations of the structure of the aircraft. It has the advantage of being able to be done by using as a means of laser illumination the laser rangefinder which is often provided in a fire control system (to work out ballistic corrections of shooting according to the distance from the target), provided that this laser rangefinder effectively emits parallel to the axis of the sighting device or even precisely along the axis thereof.

• - la figure 1 représente un schéma de principe de l'invention,
• - la figure 2 représente schématiquement une possibilité d'agencement d'un moyen d'émission laser émettant parallèlement à l'axe optique d'un dispositif de poursuite automatique.

Other characteristics and advantages of the invention will appear on reading the detailed description which follows and which is given with reference to the appended drawings in which:

• FIG. 1 represents a block diagram of the invention,
• - Figure 2 schematically shows a possibility of arrangement of a laser emission means emitting parallel to the optical axis of an automatic tracking device.

The fire control system, mounted for example on a helicopter, comprises a certain number of elements of which only those which are necessary for the understanding of the invention will be described. For example, we will not describe all the display systems with which the fire control system can be provided to assist the operator or the pilot.

Among the elements represented in FIG. 1, there is a magnifying observation telescope 10, adjustable in elevation and in bearing by motors which are preferably couple-motors with electromagnetic drive to avoid the presence of gears in the transmission of the movement. The telescope 10 can moreover be gyrostabilized, that is to say that orientation control signals are applied to these motors not directly but by means of gyrometers (simple or integrating gyrometers or two-axis gyroscopes with suspension granted) fixed on the telescope, these gyrometers having for axes the axes of rotation in elevation and in bearing.

To simplify the description of the invention, there has been shown in FIG. 1 only a bearing orientation motor 12 for the telescope; the whole description will moreover be made only with reference to the axes of rotation in the deposit, it being understood that two similar independent circuit paths are necessary respectively for the orientation in elevation and the orientation in the deposit.

The axis of rotation in bearing of the telescope 10 is designated by the reference 14. The axis of rotation in elevation would be perpendicular to the plane of the figure.

An amplifier 16 supplies control signals to the motor 12 (directly or via a gyro-stabilization system). We will see below where these signals come from.

An angular sensor 18 makes it possible to locate the orientation in bearing of the telescope; of course, another sensor is provided for the orientation in elevation.

Furthermore, an automatic tracking device 20 constitutes another important element of the fire control system. It is also orientable in elevation and in bearing (orientation motor in bearing 22) around an axis of rotation in bearing 24 and it is preferably gyrostabilized, that is to say that it receives control signals from an amplifier 26 not directly but by means of a gyro-stabilization system (not shown here) comprising gyrometers or integrating gyrometers or a gyroscope with tuned suspension whose sensitive axes are the axis of rotation in bearing 24 and a axis of rotation in elevation perpendicular to the plane of Figure 1. The drive motors of the automatic tracking device are preferably electromagnetic drive. Angular orientation sensors in bearing (28) and in elevation (not shown) are provided on the tracking device 20 to identify its orientation at any time.

The tracking device comprises an objective for forming on an image detector 30 the image of a target situated in the field of view of this objective; the optical axis of this objective is called the line of sight of the device 20 and is designated by the reference 32.

The image detector 30, which can be a vidicon tube supplying a video signal or a matrix of photosensitive detectors, supplies electrical signals representing the image of the field of view (and in particular of the target being tracked) to a deviation circuit 34 and possibly to display screens (television monitor, etc.).

The deviation circuit 34, which provides tracking, generates elevation and bearing deviation signals representing the difference between the position of the target in the image and a reference position (for example the center of the picture); these signals are intended for the amplifier 26 which controls the orientation motors of the aiming device so as to bring the image of the target back to the reference position when it tends to deviate from it.

The deviation circuit can operate by contrast (the edge of the target image defines a line of contrast whose position can easily be detected and compared to a reference position to generate deviation signals), or even by image correlation: when the operator decides to enter the automatic tracking phase after having manually centered the target in the field of view, the image of this field obtained on the detector 30 is saved in memory as a reference image and the subsequent images are correlated with the image in memory, with a correlation function involving lateral and vertical shifts of the image, in order to define correlation peaks which make it possible to know the offset in elevation and bearing of the subsequent images compared to the original recorded image.

A bearing deviation signal is transmitted by the circuit 34 to the amplifier 26 and an elevation deviation signal is provided in the analog path not shown in elevation orientation.

The angular sensors (28 for orientation in range) send signals to a computer 36 which also receives other information, and the latter processes orientation control signals of a firing weapon, to give to this weapon the same orientation as the aiming device (in the pursuit phase) possibly corrected according to ballistic data such as wind speed, distance from target, type of shell, etc.

The angular bearing sensor 18 of the telescope 10 and the angular bearing sensor 28 of the tracking device 20 are connected to the two inputs of a subtractor 38 which generates an error signal used to align the orientations of the telescope and the device of pursuit. This error signal is applied to an input of another subtractor 40 which receives on another input a signal called "harmonization error" coming from a memory 42.

The output signal from subtractor 40, which corresponds to the difference between the orientations of the sighting axes of the telescope and of the tracking device, affected by a harmonization correction, is directed either to the input of the amplifier. 26, in target acquisition phase, ie towards the input of amplifier 16, in automatic tracking phase.

A switch 44 having a position "A" (for acquisition phase) and "P" (for tracking phase) is provided for this purpose to connect to the input of amplifier 26, ie the output of subtractor 40 ( acquisition position A), or the output of the deviation circuit 34 (tracking position P).

Similarly, a switch 46 makes it possible to direct to the input of the amplifier 16, either the signals from a remote control stick 48 in the acquisition phase (position "A"), or the signals from the subtractor 40 in tracking phase (position "P").

Thus, in the target acquisition phase, the tracking device automatically follows the orientation of the telescope which is manually controlled, while in the tracking phase the telescope automatically follows the orientation of the tracking device which is controlled by its distance measurement circuit.

Provision may also be made for the switch 44 to have a third position, M, for directing signals from another hand control stick 49 to the input of the amplifier 26.

A third switch 50 is inserted between the input of the amplifier 16 and the switch 46, this switch having a normal position "N" and a so-called setting position "C"; in the normal position N, the signals from the remote control stick 48 or the subtractor 40 are transmitted to the input of the amplifier 16; but, in setting position C, these signals are interrupted and other signals are applied to the input of the amplifier 16 which are output signals from a deviation circuit 52 whose input comes from a detector of the laser beam 54 carried by the telescope 10.

The detector 54 is advantageously of the four quadrant type. It is placed on the telescope behind a focusing and possibly selective filtering optics of a particular laser wavelength, so that if a laser beam arrives in the axis or parallel to the line of sight of the telescope, this beam falls in the center of the detector 54, while if the laser beam does not arrive completely parallel to the axis, it falls on a non-central portion of the detector, which then provides signals corresponding to the deviation in elevation and in bearing from the center of the detector; these signals are processed by the deviation circuit 52 and applied to the input of the amplifier 16 but only in the so-called stall position (switch 50 in position C).

The laser beam received comes from the reflection on an obstacle of a beam emitted by a laser illuminator 56 arranged to emit parallel to the line of sight 32 (or along this line) of the tracking device; thus, the differential measurement signals of the circuit 52 are an indication of the offset of the points targeted by the telescope and the tracking device.

The deviation signals of the circuit 52 are also applied to an input of a subtractor 58 which also receives the output of the subtractor 38; the output of the subtractor 58 is applied, optionally through a switch 60 having a setting position C in which it is closed (and a normal open position), to the input of the memory 42 for recording there, in the setting phase, the signal supplied by the subtractor 58 and which represents the harmonization difference between the telescope and the tracking device.

Finally, a switch 62 can be provided for connect the output of memory 42 to the input of subtractor 40 (normal position N: switch closed, setting position C: switch open).

As for memory 42, if it is to be commanded in writing, a corresponding control signal must be provided during the setting phase during which the switches 50, 60 and 62 are toggled to position C.

The circuit which has just been described with reference to FIG. 1 makes it possible to execute a target acquisition phase and an automatic tracking phase. In addition, the operator can carry out an action of resetting the orientation of the telescope as follows: he chooses an obstacle situated at a distance corresponding to a normal target distance and he points the tracking device 20 at this obstacle, preferably using the remote control handle 49 (switch 44 in position M).

It then gives an order to switch to the setting phase, which has the effect of switching the switches 50, 60 and 62 from the normal position N to the setting position C, and causing laser radiation to be emitted by the illuminator 56, then authorize writing to memory 42.

The telescope is then oriented so as to center, if possible, on the detector 54 the laser beam received after reflection on the target obstacle, and a so-called harmonization error value corresponding to the angular difference is recorded in the memory. which must exist between the angular sensors 18 and 28 so that the tracking device and the telescope aim at the same point (which in this case is the obstacle targeted during the setting phase).

This harmonization error takes into account the parallax and other positioning or adjustment errors of the sensors, as well as the deformation of the structure of the carrier helicopter.

When we return to the normal position N of the switches 50, 60 and 62, this harmonization error is restored by the memory 42 and transmitted as a correction signal to the amplifier 26 in the acquisition phase or to the amplifier 16 in the phase of pursuit.

FIG. 2 shows by way of indication how the optical path of a laser beam can be arranged so that it leaves the tracking device 20 parallel to the line of sight 32 thereof: the tracking device carries, as a means of 'laser illumination, several deflection mirrors, the actual laser illuminator, 66, being fixed and able to be deported. A first mirror M1, secured to a mobile support rotating around the axis of rotation in elevation (68), returns the laser beam to a second mirror M2, then a third mirror M3, secured to the same support. The beam received by M3 is directed towards a fourth mirror M4 mounted on the optical sighting assembly (movable in elevation and in bearing) of the tracking device 20. The laser beam exits parallel to the sighting axis 32 whatever the orientation in elevation and in bearing, in particular because the mirrors M1, M3 and M4 are placed so as to return the beam either on the axis of rotation in elevation or on the axis of rotation in bearing. The optical elements of the tracking device 20 have not been shown to simplify the figure.

Claims (5)

1. A fire control comprising: -

- an optical device (20) for automatically tracking a target, including motors (22) for the orientation in the azimuth and elevation directions, and angular probes (28) detecting the orientation of its tracking axis (32) in the azimuth and elevation directions;

- an observation telescope (10) having a blow- up factor and being also provided with orientation motors (12) in the azimuth and elevation diretions, and with the angular probes (18) detecting the orientation of its tracking axis in the azimuth and the elevation directions, characterized in that:

a) the tracking device (20) bears a laser illumination means (56) emitting a laser radiation parallelly to the tracking axis (32) of said device;

b) the telescope bears a laser radiation detector (54) coupled to an associated divergence meter circuit (52) which is able to supply a couple of error signals representative for the azimuth and elevation divergence between the center of the detector (54) corresponding to the tracking axis of the telescope and the focalisation point of the laser radiation received after reflection on an obstacle;

c) a memory (42) is provided for receiving and recording these error signals in a preliminary readjustment phase during which the laser illumination means (56) emits a laser radiation;

d) an electrical circuit (38, 40, 16) is provided for receiving informations supplied by the angular probes (28, 18) of the tracking device (20) and the telescope (10) and for supplying to the orientation motors (12) of the telescope, in a phase of automatic tracking, control signals for adjusting the telescope to the azimuth and elevation movements of the tracking device, the electrical circuit (38, 40, 16) being connected during the tracking phase to the memory (42) in order to receive the error signals recorded during the readjustment phase, said electrical circuit comprising means (40) for submitting the control signals to a correction in accordance with the error signals.

2. A system according to claim 1, characterized in that the detector (54) is a four-quadrant detector located behind a focalisation objective and behind a selective filter which is a pass filter for the wavelength of the laser radiation.

3. A system according to any one of claims 1 and 2, characterized in that the error signals supplied by the divergence meter circuit (52) are supplied to the orientation motors (12) of the telescope during the readjustment phase in order to bring the telescope into such a direction that the reflected laser beam strikes the center of the detector (54).

4. A system according to any one of claims 1 to 3, characterized in that the electric circuit comprises a first subtractor (38), the inputs of which are connected to the angular probes (18, 28) of the telescope (10) and of the tracking device (20), and that said means comprise a second subtractor (40), the inputs of which are respectively connected to the output of the first subtractor (38) and to the output of the memory (42).

5. A system according to claim 4, characterized in that the electrical circuit comprises a third subtractor (58) used during the readjustment phase and connected by a first input to the output of the first subtractor (38), by a second input to the output of the divergence meter circuit (52) and by an output to the input of the memory (42).

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