EP0033282A1 - Missile guidance system using a modulated optical beam - Google Patents

Abstract

System for guiding a machine in a viewing direction, comprising, on emission, an emission source producing a light beam whose axis defines the viewing direction and a device for modulating the emitted beam, and on the machine, at least one photo-detector and a processing circuit for determining, from the detector output signal, the coordinates of the machine relative to the direction of sight, said coordinates being applied to the control surfaces of the machine in order to control the trajectory of the machine on the direction of sight. The modulation device comprises a strip-shaped target having repeating patterns, a translational movement at constant speed being created between the beam and the target, in a direction perpendicular to the axis of the beam, each pattern comprising opaque parts and transparent, the opaque and / or transparent parts having a length (dimension according to the direction of movement) which varies according to the height considered.

Description

The present invention relates to a system for guiding a machine in a direction of sight, comprising, on emission, an emission source producing a light beam whose axis defines the direction of sight and a device for modulating the emitted beam, and on the machine, at least one photo-detector and a processing circuit for determining, from the detector output signal, at least one coordinate of the machine with respect to the sighting direction, said coordinate being applied to the control surfaces of the machine in order to control the trajectory of the machine on the direction of sight.

In known systems of this type, a generally complicated rotating target is generally used for the modulation of the beam, and the modulated beam thus produced is highly subject to diffraction.

The invention relates to a guidance system in which the modulation device operates according to an entirely different principle and is very simple in its design.

In the guidance system according to the invention, the modulation device comprises a strip-shaped target having repeating patterns, a translational movement at constant speed being created between the beam and the target in a direction perpendicular to the axis of the beam, each pattern comprising opaque and transparent parts, the opaque and / or transparent parts having a length (dimension according to the direction of movement) which varies according to the height considered, and a time base is provided for determining the two coordinates of the craft.

The realization of the modulation device in the form of a moving pattern formed of repeating patterns allows to give the target, that is to say, to each pattern, a very simple drawing and the modulated beam obtained is consequently not very subject to diffraction.

The target is suitably a hollow drum driven in rotation around its axis and a reflecting member is placed in the center of the target so as to reflect the beam, arriving along the target's axis, in a radial direction relative to to the crosshairs.

In a simple embodiment, the opaque and transparent parts of the pattern have sides inclined at 45 ° relative to the edges of the pattern and, in a particularly advantageous manner, the opaque parts (respectively transparent) are parallelograms, the two parts transparent (respectively opaque) adjacent to such a parallelogram being triangles or trapezoids in head-to-tail arrangement.

In this embodiment of the target, the average illumination rate is constant and equal to 50% whatever the position of the detector. This value is optimal for the system link budget.

Advantageously, the time base necessary to determine the coordinates of the detector on the basis of the signal emitted by the latter is provided by a second traveling test pattern trained in synchronism with the modulation pattern, but decoupled from the latter for the detector.

The invention will be clearly understood on reading the following description, made with reference to the accompanying drawings.

• - la figure 1 illustre le principe de guidage d'engin par faisceau lumineux.
• - la figure 2 montre de façon schématique l'émetteur du système de guidage.
• - la figure 3 représente les dispositifs de modulation de l'émetteur de la figure 1.
• - les figures 4a, 4b, 4c montrent, à l'état développé, plusieurs formes de réalisation de la mire de modulation.
• - la figure 5 montre le signal de sortie du détecteur de l'engin obtenu avec la mire de la figure 4c.
• - la figure 6 illustre le traitement dudit signal de sortie en vue de la détermination des coordonnées de l'engin.
• - la figure 7 est un schéma du récepteur placé sur l'engin.
• - la figure 8 illustre le mode de détermination du roulis absolu dans le récepteur de la figure 7.
• - la figure 9 représente le circuit de détermination du roulis absolu.

In the drawings:

• - Figure 1 illustrates the principle of machine guidance by light beam.
• - Figure 2 shows schematically the transmitter of the guidance system.
• - Figure 3 shows the modulation devices of the transmitter of Figure 1.
• - Figures 4a, 4b, 4c show, in the developed state, several embodiments of the modulation pattern.
• - Figure 5 shows the output signal of the machine detector obtained with the test pattern of Figure 4c.
• - Figure 6 illustrates the processing of said output signal for the purpose of determining the coordinates of the machine.
• - Figure 7 is a diagram of the receiver placed on the machine.
• FIG. 8 illustrates the method of determining the absolute roll in the receiver of FIG. 7.
• - Figure 9 shows the circuit for determining the absolute roll.

Figure 1 illustrates the principle of machine guidance by modulated light beam. A transmitter 1 coupled to the firing station of the machine E emits a modulated light beam whose axis is directed at the target C. The machine carries detectors D sensitive to the wavelength of the beam emitted, and a circuit processing capable of determining the coordinates of the machine with respect to an absolute reference frame linked to the axis of the beam from the output signals of the detectors. The signals emitted by this processing circuit are applied to the control surfaces of the machine in order to control its trajectory on the axis of the beam.

FIG. 2 shows the general structure of the transmitter 1, in an exemplary embodiment. A laser source 2, of preferably with continuous emission, emitting for example on a wavelength of 10.6 _I xm, produces a beam which is modulated by a modulation device 3 described in detail below. Block 4 represents the supply of the laser source 2 and block 5 the primary supply which includes a battery.

The beam has a rectilinear polarization, for a purpose which will be explained later.

The modulated beam transmitted by the optics 6 is returned by a mirror 7 to a parabolic mirror 8 which acts as an objective.

The optics 6 comprises an afocal with variable magnification, or zoom, the adjustment of which is controlled in such a way that the beam section at the level of the machine remains substantially constant, this having the aim of keeping the light power received by the lens substantially constant. detectors. A circuit 9 having in memory the information "distance traveled by the machine" controls the positioning motor of the optics 6 appropriately.

We will now describe in more detail the modulation device 3.

This device comprises a hollow cylindrical drum 10, the lateral surface of which has parts transparent to laser radiation and opaque parts, formed according to a design obtained by repeating a simple pattern, examples of which will be described below.

The drum 10 is driven in rotation by a motor 11, and a control device of known type, comprising an opto-electronic source-sensor assembly 12 is provided to keep the speed of the drum constant.

The drum 10 thus constitutes a moving target which modulates the beam. The motor 11 also drives a drum 13 coaxial with the drum 10 and whose lateral surface has a design quite different from that of the drum 10 and which, as will be seen, makes it possible to define a time base.

The laser beam from the source 2 passes radially through the drum 13 and is reflected by a mirror 14, located in the center of the drum, so that the axis of the reflected beam coincides with the axis of the drums 13 and 10. The beam passes through a Wollaston prism 15 mounted in a hollow axis driven by the motor 11, and falls on a mirror 16 placed in the center of the drum 10. The beam is thus reflected in a radial direction relative to the rotary drum 10.

Figures 4a, 4b, 4c show, in the developed state, different embodiments of the modulation pattern which correspond to different basic patterns. In all cases, the opaque and transparent sectors are delimited by lines a inclined at 45 ° relative to the edges b of the target. In the case of FIG. 4a, the opaque and transparent sectors all have the form of isosceles right triangles, and in the case of FIG. 4b, the sectors are constituted by isosceles trapezoids.

In these two embodiments, two consecutive delimitation lines are always perpendicular.

In the embodiment of FIG. 4c, the two consecutive lines delimiting a transparent sector are, on the contrary, parallel, so that the transparent sectors are parallelograms and that the opaque sectors are isosceles right triangles whose arrangement is reversed each time. This embodiment has the advantage over the previous ones that the relative illumination duration is equal to 50%, which is the optimal value in terms of of the system link budget, whatever the distance between the machine and the beam axis. This is due to the fact that parallelograms always have the same dimension parallel to their sides. Of course, it would be equivalent if the opaque sectors were constituted by parallelograms and the transparent sectors by triangles.

The principle of calculating the coordinates is as follows.

In FIG. 4c, on the left, the field defined by the target is represented, the detector being at D. It is noted that a system of axes has been chosen which is suitable for drawing the target, that is to say that the axes Ox and Oy are respectively parallel to the sides has triangles constituting the opaque sectors.

In the following explanation, we will reason for clarity as if the detector was moving relative to a beam passing through a fixed target. The opposite occurs, but the two cases are equivalent with regard to operation.

The horizontal passing through D is then the geometric location of the detector and the one passing through 0 the geometric location of the trace of the beam axis.

The signal emitted by the detector is shown in FIG. 5, the rising edges corresponding to the passages from an unlit area to an illuminated area and the falling edges with reverse transitions.

.The measurement of the time between two transitions provides a first relation depending on the x and y coordinates, namely a function of

.

, etTo get a second relationship, you have to take consider the illumination rate over a given reference period T, function of the offset due to the fact that the point D is not on the line x + y = O. We find that this offset is a function of

, and

for this, the processing circuit on the machine produces pulses called + x, -y, + y, -x from the time base component supplied by the transmitter, more particularly by the drum 13 in the present example of realization.

. Dans ce cas, leThe signal of FIG. 5 is integrated over a period delimited by two consecutive pulses. The signal of FIG. 6 is thus obtained, in which the coordinates x, y are given by the amplitudes at each reset, the amplitudes successively providing -x, + x, -y, + y. Indeed, the line x = O, coincides with the first sides rising from isosceles triangles at the instants of triggering of the measurement of x increased by

. In this case, the

detector delivers a signal whose algebraic surface, obtained by integration, is zero. For a nonzero value of x, equal for example to k, the detector delivers a signal whose two positive and negative surfaces are respectively proportional to (1 + k) and (1 - k). Consequently, the algebraic surface of the signal during the reference or measurement period is proportional to 2k, therefore to k. This is how we get x. The same reasoning is applicable to y, considering the first descending sides of the isosceles triangles, to demonstrate how to obtain y.

We see that this is an extremely simple calculation principle.

As regards the time base, it has been seen that in the present example, a drum 13 driven by the motor 11 was used as the time base target. If we chooses as angular speed of the motor a speed of 50 r / s and it is assumed that the developed test pattern has 10 triangles, arranged with their hypotenuse alternately on one edge then on the other of the test pattern, the frequency of the pulses, with two pulses per triangle, is 50 x 10 x 2 = 1000 Hz.

To avoid the risks of interference or intermodulation between the various components of the composite signal received by the detector, the time base signal must be developed in an appropriate manner.

In this development, it must be taken into account that the Wollaston 15, by its rotation linked to the movement of the time base target, ensures a decoupling between the time base signal, by means of a judicious choice of this signal, and the signal received by the detector resulting from the rotation of the drum 10, so that the instants of triggering of measurement do not depend on the position of the image of the moving target projected on the detector. In other words, the moving target must not be the carrier of the time base, the instants of triggering having to occur at the times when the axis x + y = 0 of the detector field passes through the points of the isosceles triangles of the moving target, whatever the position of the detector in its field.

This double action - that of the drum 13 and that of the Wollaston 15 - however causes on the time base component detected a phase modulation effect at 100 Hz which increases with the distance of the detector from the beam axis and which, when the detector is far from the axis, could result in somewhat disturbing the sorting of the different information on reception.

The harmonic analysis shows that it is advantageous for example to constitute the time base component from of two components, one at 450 Hz, the other at 550 Hz. The drum 13 is etched in a corresponding manner with more or less wide lines defining more or less transparent zones according to the amplitude of the basic component of time, as shown by way of example in Figure 3 on a part of the drum., Of course, the entire target 13 is etched in this way.

However, the invention is not limited to this solution, and the time base can be obtained by any other appropriate means, in particular by modulating the beam with a high frequency which is modified, either continuously or by discontinuously, in a specific manner.

We will now describe, with reference to the diagram in FIG. 7, the receiver present on the machine.

The machine carries two detectors D ′, D ″ arranged symmetrically with respect to its axis, and a third detector R associated with a polarizer P, for calculating the absolute roll. Each of the detectors is associated with an appropriate input optic 18 ', 18 "and 19.

Each detector D ′, D ″ is associated with an amplifier device 20 ′, 20 ″ followed by an appropriate bandpass filter 21 ′, 21 ″. The filtered signals are applied to an adder 22 whose output is connected to the entry of a time base elaboration circuit 23.

The circuit 23 extracts from the input signal the time base component produced by the drum 13 by appropriate filtering in a band encompassing 450 Hz and 550 Hz. The two components of 450 Hz and 550 Hz are then isolated by new filterings and, from these components, we find the basic frequency of 50 Hz corresponding to the rotation speed of the sights.

The signals from the filters 21 ', 21 ", which are as shown in FIG. 5, are applied to integrators 23', 23" which also receive a signal of frequency 1000 Hz from the time base circuit 23, this signal controlling the resetting of the integrators.

The signals produced by the integrators 23 ' _t 23 "are illustrated in FIG. 6. We have seen that these signals alternately provide the coordinates ± x and ± y at the end of the integration periods. We therefore go up to the output of each integrator a 24 ', 24 "switching device with one input channel and two output channels, which is controlled by a frequency signal 250 Hz produced by the time base circuit 23. This gives one output channel the coordinate x '(respectively x ") and on the other channel the coordinate y' (respectively y") of the detector D '(respectively D ").

The coordinates x 'and x "are added in an adder 25 which provides the mean X = x' + x" / 2 and the adder 26 provides the mean Y = y '+ y "/ 2. These means correspond to the central coordinates of the machine, since the detectors D 'and D "are placed symmetrically with respect to the axis of the machine.

The signals representative of these coordinates X and Y are applied to the circuit 27 for controlling the control surfaces of the machine. The circuit 27 acts on the control surfaces so as to bring the trajectory of the machine closer to the ideal path defined by the axis of the beam, that is to say in the direction of the cancellation of X and Y.

Furthermore, it is necessary, in the case of an autorotation vehicle, to know the absolute roll - that is to say the instantaneous angular position - of the vehicle to act at the desired moment on the control surfaces.

The device comprises, as has been said, a detector P with which a polarizer is associated. The beam emitted by the source 2 has a linear polarization and the Wollaston 15 rotates its plane of polarization at a speed of 2 x 50 = 100 r / s. Detection by the P detector would occur with a frequency of 2 x 100 = 200 Hz if the missile was not in autorotation.

But as the missile turns on itself at a speed n (in r / s), the detection frequency is in fact (200 + 2n) Hz.

The detector P is associated with an amplifier 30 and a bandpass filter 31 adapted to the above frequency.

By comparing the signal thus obtained with a signal at the frequency of 200 Hz produced by the time base circuit 23 from the base frequency of 50 Hz, one can determine the absolute roll with very good precision, but the value obtained is defined to within π and it is necessary to remove this indeterminacy.

To do this, the coordinates x ', y' and x ", y" of the detectors D 'and D "are used. The coordinates x', x", y ', y "are only known with average precision. However, this precision is sufficient to remove the indeterminacy which affects the value calculated by the above method from the output signal of the detector P.

These calculations are carried out in the circuit 40 for determining the absolute roll, which supplies the roll value to the control circuit for the control surfaces.

The principle of determining absolute roll is illustrated in Figure 8.

avec le vecteur origine

.The position of detectors D 'and D "as can be determined determining on board the craft is marred by an imprecision illustrated by the hatched circular zones surrounding the points D 'and D ". The absolute roll ϕ is the angle made by the real vector

with the original vector

.

faisant l'angle ϕ avec

et le vecteur -

.We saw above that we obtained, from the output signal of the detector P, this angle ϕ with very good precision but to within π. If we refer to Figure 8, we obtain the vector

making the angle ϕ with

and the vector -

.

.

et on fait en sorte que le produit calculé soit positif.To remove this indeterminacy, we calculate the dot product

.

and we make sure that the calculated product is positive.

This principle supposes that the uncertainty zones of D 'and D "do not overlap. This condition is satisfactory without difficulties in practice.

. V vaut (x"-x') cos ϕ + (y"-y') sin ϕ. Le circuit 40 représenté à la figure 9 effectue le calcul de cette expression et comprend un inverseur 41 sur lequel on agit pour maintenir cette expression à une valeur positive.The dot product

. V is (x "-x ') cos ϕ + (y"-y') sin ϕ. The circuit 40 shown in Figure 9 performs the calculation of this expression and includes an inverter 41 on which one acts to maintain this expression at a positive value.

Circuit 40 receives on input A the frequency signal 200 Hz coming from the time base circuit 23 and on input B the frequency signal (200 + 2n + 2 ϕ) Hz coming from filter 31.

The signal arriving at terminal A is of the form cos 21r f _o t with f _o = 200 Hz. It is applied to a circuit 42 dividing the frequency by 2, which provides the signals cos (π f _o t + k π) and -cos (π f _o t + k π), which are applied to the two inputs of the inverter 41 which, depending on its position, transmits one or the other of these signals.

The signal arriving at terminal B is of the form cos (2 π f _R t + 2 ϕ) with f _R = (200 + 2n) Hz. This signal is applied to a circuit 43 dividing the frequency by 2, which delivers a signal cos (π f _R t + ϕ + k π).

This signal is applied to the multipliers 44 and 45. The multiplier 44 also receives the signal + cos (π f _o t + k π) from the inverter and the multiplier 45 receives the signal + sin (π f _o t + k π) obtained after phase shift of π / 2 in a circuit 46 connected to the output of the inverter.

Low-pass filters 47 and 48 are respectively connected to the outputs of multipliers 44 and 45, so that at the output of filters 47 and 48 signals are obtained whose frequency is the difference of the frequencies of the input signals and which are therefore representative of the trigonometric functions cos ϕ and sin ϕ of the absolute roll angle Q.

.

précité.On the other hand, the signals representative of the coordinates x ', x "and y', y", coming from the circuits 24 'and 24 ", are applied to subtractors 49 and 50 which deliver the differences x" - x' and y "- y '. The outputs of subtractors 49 and 50 are connected to multipliers 51 and 52 - which receive the signals cos ϕ and sin ϕ from filters 47 and 48. The products (x" - x) cos ϕ and (y " - y ') sin ϕ are added in circuit 53 which delivers the scalar product

.

cited above.

The output signal of the adder 53 is applied as a control signal to the inverter 41 (link shown in dotted lines) so that the latter is always in the position which results in a positive dot product.

The values cos ϕ and sin ϕ obtained at outputs C and D are applied as indicated to the control circuit for the control surfaces.

Claims (8)

1. System for guiding a machine in a direction of sight, comprising, on emission, an emission source producing a light beam whose axis defines the direction of sight and a device for modulating the emitted beam, and on the machine, at least one photo-detector and a processing circuit for determining, from the detector output signal, at least one coordinate of the machine with respect to the direction of sight, said coordinate being applied to the control surfaces of the machine in order to control the trajectory of the machine on the direction of sight, characterized pa: the fact that the modulation device comprises a strip-shaped target with repetitive patterns, a translational movement at constant speed being created between the beam and the target, in a direction perpendicular to the axis of the beam, each pattern comprising opaque and transparent parts, the opaque and / or transparent parts having a length (dimension along the direction of dep lacing) which varies according to the height considered, and a time base is provided to determine the two coordinates of the machine. 2. System according to claim 1, characterized in that the target is a hollow drum driven in rotation about its axis and a reflection member is placed in the center of the target so as to reflect the beam arriving along the axis of the test pattern, in a radial direction relative to the test pattern. 3. System according to one of claims 1 and 2, characterized in that the opaque and transparent parts of the target have sides inclined at 45 ° relative to the edges of the target. 4. System according to claim 3, characterized by the the fact that the opaque parts (respectively transparent) are parallelograms, the two transparent parts (respectively opaque) adjacent to such a parallelogram being triangles or trapezoids in head-to-tail arrangement. 5. System according to claim 2, characterized in that the time base necessary to determine the coordinates of the detector from the signal emitted by the latter is provided by a second scrolling test pattern driven in synchronism with the modulation test pattern but decoupled of it for the detector. 6. System according to claim 5, characterized in that the second target is a drum coaxial with the modulation target in the center of which is placed a reflection member, which reflects the beam from the source and having passed radially through the second target towards the reflection device placed in the center of the modulation pattern. 7. System according to one of claims 1 to 6, characterized in that the beam has a linear polarization, means are provided on emission to rotate the beam and therefore its plane of polarization, and the machine carries two photodetectors placed symmetrically with respect to the axis of the machine, a third photodetector, associated with a polarizer and a calculation circuit providing the absolute roll q of the machine from the output signal of the third photodetector and coordinates ( x ', y') (x ", y"), supplied by the processing circuits associated with the first two photodetectors. 8. System according to claim 7, characterized in that the calculation circuit comprises means for forming the difference between the frequency of the output signal from the third photodetector and that corresponding to the speed of rotation of the plane of polarization, said said means providing the roll angle ϕ to within π, said means including an inverter which can take two positions, corresponding to the two possible values for ϕ, and means for calculating the expression (x "-x ') cos ϕ + (y "- y ') sin ϕ, the inverter being controlled so that this expression is constantly positive.

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