EP0033279B1 - Missile quidance system by means of an optical beam - Google Patents

Description

The present invention relates to a machine guidance system comprising a source emitting a light beam whose axis defines the direction of sight, a modulation pattern placed on the path of the beam, means for producing a relative rotational movement between the target and beam, means arranged to provide an angular reference on the machine, and, on the machine, at least one detector and a calculation circuit for determining, from the detector output signal, the coordinates of the detector relative to the direction of sight, the control surfaces of the machine being actuated according to said coordinates in order to control the trajectory of the machine on the direction of sight.

French patent 2 339 832 discloses such a guidance system comprising, for the modulation of the beam, a rotating target in the form of a spiral. Measuring the illumination times of each detector makes it possible to determine the distance from the detector to the beam axis, since, given the shape of the target, the lighting duration is a function of the distance to the axis.

But in this known system, the duration of illumination is very variable compared to the total duration of measurement and in particular the duration of relative illumination is close to 100% on the axis of the beam and decreases as one s 'deviates from the axis until it is close to 0 at the edge of the field. This is very disadvantageous in terms of the link budget because in this regard, the optimal value of the relative illumination duration is equal to 50%.

The present invention relates to a guidance system of the type described above, in which the relative illumination duration of the detector remains equal to 50% regardless of the position of the detector.

To this end, the present invention relates to a system of the type defined above, characterized in that the target is formed as the superposition of a first target divided into a transparent sector and a partially transparent semi-circular sector, and d '' a second target divided into four equal sectors, namely two transparent sectors and two partially transparent sectors, by two curves symmetrical with respect to the center of the target, of equation f (p, σ modulo n) - 0, where p varies monotonically as a function of σ, your modulation pattern thus comprising transparent, partially transparent and opaque sectors, delimited by symmetrical curves with respect to the center of the pattern and defining equal angles at the center whatever the radius considered of so that the relative illumination duration of the detector remains equal to 50% whatever its position.

The present invention also relates to a system of the type defined above, characterized in that two modulation patterns are provided which are axially symmetrical and phase-shifted with respect to each other by a given angle and occupy at in turn an active beam interception position, each target being divided into two identical sectors, one transparent the other opaque, respectively by a curve of equation f (p, a modulo π) = 0 and a curve with equation f (p, - σ modulo π) = 0, where p varies monotonically as a function of a, these curves being symmetrical with respect to the center of the pattern and defining angles at the center equal whatever the radius considered so that the relative illumination duration of the detector remains equal to 50% whatever the position.

The invention will be clearly understood on reading the following description of embodiments shown in the drawings.

• - La figure 1 est une vue schématique du système de guidage selon l'invention;
• - La figure 2 montre la section du faisceau de guidage au niveau du détecteur de l'engin;
• - La figure 3 représente une première forme de réalisation de la mire de modulation;
• - les figures 4a et 4b montrent les dessins de mire dont la superposition donne la mire de la figure 3.
• - la figure 5 est un diagramme de signaux illustrant le principe de modulation.
• - les figures 6a et 6b illustrent une autre forme de réalisation des moyens de modulation.

In the drawings:

• - Figure 1 is a schematic view of the guidance system according to the invention;
• - Figure 2 shows the section of the guide beam at the detector of the machine;
• - Figure 3 shows a first embodiment of the modulation pattern;
• FIGS. 4a and 4b show the target drawings, the superposition of which gives the target in FIG. 3.
• - Figure 5 is a signal diagram illustrating the modulation principle.
• - Figures 6a and 6b illustrate another embodiment of the modulation means.

The guidance system shown diagrammatically in FIG. 1 comprises a light source 1, for example a laser source emitting in the infrared such as a CO ₂ laser. Preferably, a continuous emission laser is used in the invention. However, it is also possible to envisage using a light-emitting diode of the AsGa type as a source.

The beam emitted by the source 1 is amplitude modulated at a high frequency by an electro-optical modulator 2 which is designed to provide an angular reference. To this end, the modulation frequency of the beam is modified in a determined manner, in synchronism with the rotation of the target described below.

The beam from the modulator 2 is modulated by a rotating target 3 driven in rotation at an angular speed o by a mechanism 4 and described in more detail below. The important thing is that a relative rotational movement takes place between the test pattern 3 and the beam, one could also leave the test pattern fixed and rotate the beam for example by means of a Wollaston prism. The resulting beam then passes through an emission optic 5.

The machine E goes towards the target C on which the beam is pointed. It carries one (or more) detector D which transforms the light radiation which it receives coming from source 1 into an electrical signal. Because the light beam is modulated, so is the electrical signal and the modulation principle, set out below, is such that the polar coordinates (p, 9) of detector D relative to the beam axis can be derived from the detector output signal.

The signals representing said coordinates are applied to the control circuit for the control surfaces provided on the vehicle, so as to control the trajectory of the vehicle on the beam axis.

It should be noted that the emission optics 5 is designed to keep the section of the beam projected at the detector substantially constant, and therefore the light power received by the detector. Optics 5 is provided for this purpose with a zoom type device.

The test pattern 3 shown in FIG. 3 can be considered as the superposition of two test patterns 6 and 7 shown respectively in FIGS. 4a and 4b.

The first is made up of a transparent sector and a semi-transparent sector of semi-circular shape. The resulting modulation component in the output signal of the detector D is the signal S ₁ (ω t) (see fig. 5).

Thanks to the frequency variation carried out by the modulator 2 in synchronism with the rotation of the test pattern 3, the processing circuit provided on the machine produces a reference signal R ₁ (ω t) of the same frequency corresponding to the axis x _H and it is clear that the polar angle 6 can be easily determined by measuring the phase shift between S ₁ (ω t) and R ₁ (ωt).

The test chart 7 represented in FIG. 4b defines four identical sectors, alternately transparent and semi-transparent which are delimited by sections of Archimedes spiral of equations p = a (θ modulo π) and

modulo n). The corresponding modulation component is represented by the signal S ₂ (mt) and it is easy to understand that the phase shift of S ₂ (ot) with respect to a reference signal R ₂ (ω t), whose frequency is double that of R ₁ (ω t), is a function of the vector radius p. This phase shift is given by the relation

and as we can determine 0 by the phase shift between S ₁ (ωt) and R ₁ (ωt), it is also easy to determine p.

The signals S, and S ₂ are easily deduced from the signal S (ωt) which is obtained at the output of the detector D after amplification and appropriate shaping.

It should be noted, with regard to the target represented in FIG. 3, that it comprises transparent sectors (100% illumination), semi-transparent sectors (50% illumination), represented in spaced hatching, and sectors opaque (illumination at 0%), represented in tight hatching. In terms of opacities, the test pattern in Figure 3 should not be considered as formed by the superposition of the patterns in Figures 4a and 4b, since the superposition of two semi-transparent sectors would not give complete opacity. The patterns of Figures 4a and 4b are fictitious and are shown only for the purpose of explanation.

It should be emphasized that, for each of the fictitious targets in FIGS. 4a and 4b, the duration of total illumination, corresponding to the total of the angles at the center defined by the transparent sectors would be equal to the duration of semi-illumination, corresponding to the total of the angles in the center defined by the semi-transparent sectors, whatever the radius considered. It follows that the relative illumination duration of the target of FIG. 3 is equal to 50% whatever the radius considered, this relative duration being equal to 100. Σ ET + 50. Σ _SE, Σ _ET and Σ _SE denoting the total of the center angles defined respectively by the transparent sectors and the semi-transparent sectors of the target.

As indicated above, this is a very advantageous characteristic in terms of the system link budget.

In addition, and still in terms of the link budget, the invention makes it possible to obtain a maximum signal variation, as well as a variation of the parameters p and σ in also maximum measurement ranges.

Figures 6a and 6b illustrate another embodiment of the modulation means. In this case, two patterns 14a and 14b are provided which are moved in a clocked fashion by a switching mechanism, not shown, so that the beam is modulated in turn by the pattern 14a and by the pattern 14b.

The patterns 14a and 14b are axially symmetrical and each formed by two identical sectors delimited by a curve 15a, 15b, formed by two sections of Archimedes' spiral p = a θ and p = - a σ symmetrical with respect to the center of the pattern . The two patterns are phase shifted by a given angle, which is equal to 90 ° in the example shown. Means are of course provided for creating a rotational movement between the beam and the targets, for example an optical member rotating the beam or a mechanism for driving the targets in rotation in the same direction at the same angular speed ω.

As indicated above, the components attributable to the respective patterns are deduced from the output signal of the detector D and their phase shift ϕa, ϕb is determined with respect to a reference signal.

et

On en tire

et

The phase shifts are given by the relations

and

We get it

and

The processing circuit allowing the calculation of p and θ is not described here, because it is entirely within the reach of those skilled in the art.

The embodiment shown in Figs. 6a and 6b requires only one reference signal R (ω t) instead of two in the embodiment of figs. 3a and 3b. It is also more advantageous in terms of diffraction.

It is also possible, as a variant, to rotate the sights 14a and 14b at the same speed, but in opposite directions.

In the embodiments described, the curves delimiting the sectors are sections of Archimedes' spiral, which provides a linear relationship between p and 0. But the invention is not limited to this type of curves and it is possible to envisage in a way more general any curve with equation f (p, θ) = O where p varies monotonically as a function of θ.

Claims (5)

1.- System for guiding a missile, comprising a source emitting a light beam of which the axis defines the direction of sight, at least one modulation sight placed in the path of the beam, means for producing a relative movement of rotation between the sight and the beam, means for furnishing, on the missile, an angular reference, and, on the missile, at least one detector and a calculating circuit for determining, from the output signal from the detector, the coordinates of the detector with respect to the direction of sight, the control surfaces of the missile being actuated as a function of said coordinates with a view to controlling the path of the missile on the direction of sight, characterized in that the sight is formed as the superposition of a first sight divided into a transparent sector and a semi-transparent sector, which are semi-circular, and of a second sight divided into four equal sectors, namely two transparent sectors and two semi-transparent sectors, by two curves symmetrical with respect to the center of the sight, having for equation f(p,a modulo π) = 0, whese p varies monotonically as a function of σ, the modulation sight this comprising transparent, semi-transparent and opaque sectors, defined by curves symmetrical with respect to the center of the sight, and defining angles at the center which are equal whatever the radius in question, so that the duration of relative illumination of the detector remains equal to 50 %, whatever its position.

2.- System for guiding a missile, comprising a source emitting a light beam of which the axis defines the direction of sight, at least one modulation sight placed in the path of the beam, means for producing a relative movement of rotation between the sight and the beam, means for furnishing, on the missile, an angular reference and, on the missile, at least one detector and a calculating circuit for determining, from the output signal from the detector, the coordinates of the detector with respect to the direction of sight, the control surfaces of the missile being actuated as a function of said coordinates with a view to controlling the path of the missile on the direction of sight, characterized in that two modulation sights are provided for, which are axially symmetric and one another phase shifted of a given angle and occupy in turn an active position of beam interception, each sight being divided into two identical sectors, one transparent and the other opaque, respectively by a curve of equation f(p, θ modulo π) = 0 and a curve of equation f(p-θ modulo π) = 0, where p varies monotonically as a function of θ, these curves being symmetrical with respect to the center and defining angles at the center which are equal whatever the radius in question, so that the duration of relative illumination of the detector remains equal to 50 %, whatever its position.

3.- The system of claim 2, characterized in that the two sights rotate in the same direction.

4.- The system of claim 2, characterized in that said two sights rotate in opposite directions.

5.- The system of one of claims 1 to 4, characterized in that each of said curves is formed by two sections of Archimedes' spirel of equations p = a θ and p - -a 0.

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