EP0292383B1 - Photopyrotechnic priming device, and photopyrotechnic chain using such a device - Google Patents

Abstract

A photopyrotechnical detonating device and a photopyrotechnical chain using this device are disclosed. A pyrotechnical charge, which can be actuated by a laser beam, is placed in a solid body. The beam is conveyed by an optical fiber which penetrates a connector mounted on the body. The beam, which is divergent when it leaves the fiber, is made parallel by a first lens. A second lens, mounted on the body, makes the beam converge and works with a transparent barrier to focus the beam on a given point. Tight-sealilng means are provided between the transparent barrier and the body of the device, thus ensuring the containment of the charge. The transparent barrier is shaped like a truncated cone which maintains its integrity within a tapered cylinder after firing of the actuating and boosting charges. The tightness of the transparent barrier within the tapered cylinder is enhanced by the sealing means and prevents fragments from entering the detonating device after firing of the charges.

Description

The present invention relates to the field of initiation of pyrotechnic substances by light beams produced by laser and transported by fibers or optical cables.

• un laser comme source d'énergie,
• une fibre ou un câble optique pour transporter l'énergie, et
• une amorce détonateur ou un inflammateur pyrotechnique.

It is recalled that, by the expression "pyrotechnic substances", is meant primary explosives (such as azides, fulminates, tetrazene, etc.) secondary explosives (such as: PETN, RDX, HNS, etc. ..) and pyrotechnic compositions such as ignition compositions, illuminating, tracing compositions, smoke bombs, etc. The different elements used form what is called a photopyrotechnical functional chain. This chain generally consists of three elements:

• a laser as an energy source,
• an optical fiber or cable to transport energy, and
• a detonator primer or a pyrotechnic igniter.

As the laser source, it is preferably possible to use a triggered pulsed laser. Such a laser is described in the article by MM. C. CAREL and A.P. JOSSE of Aerospace and MM. M. MORISSON, P. BALDY and J. REFOUVELET from the Tarbes Construction Workshops entitled "Initiation of Explosives by Laser" (communication made at the "international symposium on fundamental and applied pyrotechnics: substances and systems" held on 5 on October 7, 1982 in Arcachon (France)).

A photopyrotechnic detonator primer is a device charged with primary or secondary explosives which can be initiated under the action of an energy beam such as a laser beam and make it possible to obtain a shock wave. sufficient to initiate another pyrotechnic component charged with explosive. As for pyrotechnic igniters, these are devices containing a pyrotechnic substance capable of igniting when it receives a calorific contribution, for example in the form of a laser beam, this flame possibly causing the ignition of another composition. pyrotechnic.

Document US-A-4 391 195 describes an explosive initiation system with a laser source and optical fibers for transporting energy from the laser to photopyrotechnic initiators. In this document, the end of the optical fiber opposite the laser is in direct contact with a substance capable of igniting, the energy of the flame being used to ignite charges of explosives. However, in most of the current photopyrotechnical initiation devices, these have a poor seal vis-à-vis the outside, which has two drawbacks: first, the pyrotechnic initiation substance is poorly protected external influences (humidity or more or less corrosive atmospheres), which can affect its functioning. On the other hand, when the charge is ignited, there is a risk of yield losses due to the leakage of the gas released during the detonation as well as the risks of pollution of the surrounding equipment.

American patent US-A-4 600 472 describes a pyrotechnic detonator which uses a lens focusing parallel radiation on a booster. However, no mechanical barrier is introduced at this level and even less means for sealing this barrier.

As for the US patent US-A-3 911 823, it does not describe a pyrotechnic ignition device, but a method of attaching optical fibers to a pyrotechnic element operating using laser radiation. In this document, the element has no focusing function on the radiation used. The seal is not used for sealing this element.

The object of the present invention is to remedy these drawbacks by proposing a photopyrotechnical initiation device in which the pyrotechnic initiation substance is protected from external aggressions before and during operation.

• une cavité pour loger une charge pyrotechnique ;
• une entrée pour un faisceau énergétique de longueur d'onde donnée servant à initier cette charge ; et
• un passage pour le faisceau énergétique entre ladite entrée et la cavité.

More specifically, the subject of the invention is a photopyrotechnic device comprising a body having, in a manner known in document US-A-4 391 195:

• a cavity for housing a pyrotechnic charge;
• an input for an energy beam of given wavelength used to initiate this charge; and
• a passage for the energy beam between said entrance and cavity.

• une barrière transparente placée dans le passage sur le trajet du faisceau, cette barrière résistant aux effets mécaniques engendrés lors du fonctionnement de la charge et étant réalisée en un matériau transparent à la longueur d'onde de ce faisceau et ayant une première face du côté de l'entrée et une deuxième face du côté de la charge pyrotechnique, son emplacement et la forme de ses deux faces sont déterminés de manière à focaliser en un point donné un faisceau énergétique parallèle ayant ladite longueur d'onde donnée et pénétrant dans cette barrière transparente par sa première face ; et
     des moyens d'étanchéité entre cette barrière et le corps du dispositif.

According to the invention, this device also comprises:

• a transparent barrier placed in the passage on the path of the beam, this barrier resistant to the mechanical effects generated during the operation of the load and being made of a material transparent to the wavelength of this beam and having a first face on the side of the entry and a second face on the side of the pyrotechnic charge, its location and the shape of its two faces are determined so as to focus at a given point a parallel energy beam having said given wavelength and penetrating this transparent barrier by its first face; and
  sealing means between this barrier and the body of the device.

Preferably, the transparent barrier is made of sapphire.

Thus, the presence of a transparent barrier made of a material transparent to the wavelength of the beam used and of sealing means between this barrier and the body of the device makes it possible to protect the pyrotechnic charge from external aggressions while allowing passage the beam used to initiate this charge. In addition, as the constitution of this barrier allows it to resist the mechanical effects generated during the operation of the load, it remains intact after it has been ignited and any gas leaks are avoided through the passage for the laser beam.

Optionally, the device may further comprise a thin cover placed between the transparent barrier and the pyrotechnic charge, this cover having a face in contact with the pyrotechnic charge.

The presence of this seal is especially useful in the case where the pyrotechnic charge is a substance which can explode under the action of a shock wave. It is used when the device includes means for focusing the laser beam. As we will see later, these are arranged so as to focus the beam on this operculum or to obtain on it the image of the exit face of the optical fiber: in this way the energy concentration is created in the mass of the operculum capable of creating a wave of shock. This shock wave is transmitted to the pyrotechnic substance which then explodes.

According to another aspect of the invention, when the body of the pyrotechnic device is mounted on a support, sealing means are also provided between the body of the device and this support.

The latter can be a device containing the main explosive charge which must be initiated by the photopyrotechnic device. Thus, the main load is itself protected from external aggressions.

• une source laser émettant un faisceau de longueur d'onde donnée ;
• un dispositif d'amorçage photopyrotechnique ; et
• un câble optique transportant le faisceau de la source laser au dispositif d'amorçage.

Finally, the invention also relates to a photopyrotechnical functional chain comprising, in a known manner:

• a laser source emitting a beam of given wavelength;
• a photopyrotechnical initiation device; and
• an optical cable transporting the beam from the laser source to the ignition device.

According to the invention, the initiating device conforms to what is described above and the laser source is preferably constituted by a pulsed pulsed laser. As for the expression "optical cable", it designates either an optical fiber alone, or a set of optical fibers.

• la figure 1 est un schéma de principe illustrant l'allure générale d'un système d'amorçage photopyrotechnique ;
• la figure 2 est une vue schématique en coupe d'un mode de réalisation du dispositif d'amorçage photopyrotechnique objet de l'invention ;
• les figures 3a à 3c et 4a à 4c sont des vues schématiques montrant divers modes de réalisation possibles du dispositif objet de l'invention lorsqu'il n'y a pas de système optique associé et lorsqu'il y a un système optique associé ; et
• la figure 5 est une vue schématique en coupe d'un laser utilisable dans une chaîne fonctionnelle photopyrotechnique selon l'invention.

The invention will appear better on reading the description which follows, given by way of purely illustrative and in no way limiting, with reference to the drawings annexed in which:

• Figure 1 is a block diagram illustrating the general appearance of a photopyrotechnic initiation system;
• Figure 2 is a schematic sectional view of an embodiment of the photopyrotechnical initiation device of the invention;
• Figures 3a to 3c and 4a to 4c are schematic views showing various possible embodiments of the device object of the invention when there is no associated optical system and when there is an associated optical system; and
• Figure 5 is a schematic sectional view of a laser usable in a photopyrotechnical functional chain according to the invention.

FIG. 1 schematically represents a photopyrotechnical functional chain comprising a laser source 10 and an optical fiber 12 transmitting the beam produced by the laser to a photopyrotechnical initiation device 14. This can be placed on a support 16 shown schematically in phantom in FIG. 1. The latter can be, for example, the wall of a container or of an apparatus containing the main charge which must be initiated by the device 14.

This first consists of a body 18 fixed on the support 16 by any suitable means, for example by screwing. The body 18 has, at one of its ends, a cavity 20 for housing a pyrotechnic charge. In the example illustrated here, this charge consists of an initiating charge 22 in contact with a reinforcing charge 24. The cavity 20 can be formed inside a load carrier constituted by a spacer 26 held against a shoulder provided inside the body 18 by a cap 28. The latter is fixed to the body 18 by any known means, for example by screwing as illustrated in Figure 2, the seal being provided by a seal 30. However, one can consider other methods of attachment, for example by laser welding.

The cap 28 has a thinned part or cover 32 which is destroyed during the explosion of the charge 24. When the charge 22 is ignited under the effect of the laser beam emitted by the source 10, it is the seat of a shock wave. This wave propagates through the load 22, then through the load 24 where it is reinforced. The explosion of the charge 24 leads to the destruction of the cover 32 and the shock wave can thus ignite the main charge 34 contained inside the support 16 (the latter is shown diagrammatically in phantom on the figure 2).

The body 18 of the device which is the subject of the invention also has a passage 36 allowing the laser beam 38 to penetrate inside the device. A transparent barrier 40 is mounted inside the passage 38, upstream of the cavity 20 relative to the direction of propagation of the beam. It should be noted that, in the example shown here, all the elements of the device have a symmetry of revolution about a common axis. The transparent barrier 40 has the shape of a truncated cone widening in the direction of the cavity 20 and limited at its two ends by circular faces. It is housed in a part of the passage 40 having the same seal between the barrier 40 and the body 18 being provided by sealing means 42, for example a rubber O-ring. As for the seal between the body 18 and the support 16, it can be ensured by an O-ring 46 or any other equivalent device.

Tests have shown that the best results have been obtained with a transparent sapphire barrier having the shape of a truncated cone limited by two circular faces of diameter 4 mm and 6 mm respectively and the length of which was 10 mm. Good results have also been obtained with a sapphire truncated cone 8 mm in length and the end faces of which had diameters of 4 and 6 mm respectively.

Sapphire, which is a particular aluminum oxide crystal (Al₂O₃), is well suited for this use because it has a very high Young's modulus (3.7.10⁵ MPa). In addition, its softening point is at 1800 ° C, which gives it good temperature resistance (for comparison, it can be noted that B1664 glass has a processing temperature of 559 ° C).

We also see in Figure 2 a thin cover 44 interposed between the transparent barrier 40 and the initiating charge 22. In the example shown here, this cover is in the form of a thin coating deposited on the rear face of the barrier 40. The thickness of this coating is between a few hundred and a few thousand Angstroms and its constituent material can be a metal such as, for example, aluminum, gold, silver, niobium or indium. However, it would not go beyond the scope of the invention to use another material (for example an organic material) or another arrangement, the coating being for example deposited on the initiating charge 22. This seal finds its usefulness when using a secondary explosive as the initiating charge. Indeed, to initiate such an explosive, you need a powerful shock wave. This can be obtained by the breakdown of a thin metallic layer and the breakdown of the cover 44 can be obtained by focusing the beam 38 on the cover 44.

The device illustrated in Figure 2 further comprises means for focusing the laser beam. The latter essentially consist of an optical connector in the form of a hollow housing which can be threaded over the end of the body 18 opposite the cavity 20. The optical fiber 12 transmitting the beam of the laser 10 to the device 14 passes through a wall of the connector 48 and its end is inside the latter. The laser beam leaving the fiber 12 passes through a lens 50 mounted inside the connector 48. This can be held on a shoulder or a support using a spacer 52 screwed inside the connector 48 The shape of the lens 50 is determined so that the beam 38, which is divergent when it leaves the fiber 12, is parallel after passing through the lens 50, its optical axis being coincident with the axis of revolution of the device 14 .

The front face 41 of the barrier 40 is convex in shape when viewed from the entrance to the device. So the face front of the barrier 40 behaves like a plano-convex lens making the parallel beam coming from the lens 50 converge. The shape of the face 41 and the length of the barrier 40 are determined, as a function of the wavelength of the beam , so that it is focused at a given point, for example to obtain the image of the exit face of the fiber 12 on the cover 44. It is therefore the front face 41 of the barrier 40 which constitutes a second lens of the device.

Thus, the device which is the subject of the invention has particularly advantageous advantages, the main one of which is good confinement of the pyrotechnic charge before operation and of the products of the detonation after operation. This is obtained by the presence of the transparent barrier 40 which is fixed in leaktight manner inside the body 18, and is made of a material resistant to the effects of detonation. On the other hand, the mounting, adjustment and positioning operations are facilitated by the use of an optical system which makes the laser beam 38 parallel over part of its path. The distance between the barrier 40 and the lens no longer needs to be determined with precision since, even if this distance varies, the beam remains parallel when it arrives at the optical barrier. However, care must be taken to center the various elements, which is relatively easy insofar as the components of the device have a symmetry of revolution.

Finally, it is understood that the invention is not limited to the single embodiment which has just been described, but that one can imagine many variants without departing from the scope of the invention. Thus it is possible to use or not the cover 44 or replace the initiating charge 22 with a substance which ignites under the effect of the energy provided by the laser beam, this flame causing the explosion of another pyrotechnic substance. It is thus possible to replace the two charges 22 and 24 with a single charge.

It is also possible to modify the shape of the barrier 40 and to associate or not with the device of the invention an optical system, as illustrated in FIGS. 3 to 4.

They illustrate the case where the front face 41 of the barrier 40 is of convex shape and cut so as to focus a parallel beam arriving on this face 41 at a given point of the device. In FIG. 3a, the barrier 40 has the shape of a truncated cone widening towards the load 23 while, in the case of FIG. 3b, it narrows in the direction of this load. Finally, in the case of FIG. 3c, the barrier 40 has the shape of a cylinder.

Figures 4 illustrate variants in which the device of the invention is associated with an optical system.

They relate to the case where the front face 41 of the barrier 40 is convex in order to constitute the second lens. In FIG. 4a, the lens 50 is mounted on an independent connector 48, while, in the case of FIG. 4b, the lens 50 is permanently mounted on the body 18. Finally, it should be noted that in the figures 4, the transparent barrier 40 is in the form of a truncated cone widening towards the pyrotechnic charge 23. However, it would not go beyond the scope of the invention to give other forms to the transparent barrier, by example the shape of a truncated cone tapering towards the load 23 or of a cylindrical bar as illustrated in FIGS. 3.

FIG. 5 represents a preferred embodiment of a laser which can be used in the invention.

The laser 10 comprises an amplifier bar 62, a straight flash tube 64, two mirrors 66 and 68, a trigger 70 (with dye or Pockels cell) and electronics 72.

The bar 62 is composed of a neodymium doped glass working at a wavelength 1.06 μm corresponding to an optical window of the optical figure 12. The operation in triggered mode is ensured by the interposition between the two mirrors. the optical cavity of the saturable absorbent 70 (triggering of the passive type) or of a Pockels cell (triggering of the active type). The laser pulse, approximately Gaussian in shape, has a pulse duration of the order of 10 ns at mid-height.

The optical energy is of the order of 75 mJ with a saturable absorbent as a trigger system and of the order of 150 mJ with a Pockels cell.

Claims (9)

1. Photopyrotechnic detonating device comprising a body (18) with:
   a cavity (30) to house a pyrotechnic charge (22, 24),
   an output for an energy beam of a given wavelength, used to actuate this charge (22, 24) and
   a passage (36) for the energy beam between said input and the cavity,
   characterized in that it also comprises:
   a transparent barrier (40) placed in the passage (36), said barrier withstanding the mechanical effects generated during the operation of the charge and made from a material which is transparent to the wavelength of the beam used and having a first surface (41) on the input side and a second surface on the side of the pyrotechnic charge (22, 24), its position and the shape of its two surfaces being defined so as to focus, on a given point, a parallel energy beam, having said given wavelength and penetrating this transparent barrier (40) through its first surface (41), and
   sealing means (42) between this barrier (40) and the body of the device.
2. Device according to claim 1, characterized in that the transparent barrier (40) is made of sapphire.
3. Device according to claim 2, characterized in that the transparent barrier (40) has the shape of a truncated cone that widens towards the cavity (20), and in that the sealing means (42) are formed by an O-ring.
4. Device according to claim 1, characterized in that it comprises a thin percussion cap (44) placed between the transparent barrier (40) and the pyrotechnic charge and has one side in contact with the latter.
5. Device according to claim 1, characterized in that the body (18) being mounted on a support (16), said device comprises sealing means (46) between the body (18) and said support (16).
6. Device according to claim 1, characterized in that it comprises a lens (50) cut so as to make the high energy beam entering the device parallel, so that the high energy beam (38) successively passes through the lens (50) and the transparent barrier (40), the position and shape of the transparent barrier (40) being determined so that the parallel energy beam passing out of the lens (50) is focused at a given point.
7. Device according to claim 6, characterized in that the lens (50) is installed on an optical connector (48), which can be dismantlably fixed to the body (18) of the device.
8. Photopyrotechnic functional chain comprising a laser source (10) emitting a beam having a given wavelength, a pyrotechnic detonating device (14) and an optical cable (12) carrying the beam from the laser source (10) to the detonating device (14), characterized in that the detonating device (14) is in accordance with claim 1.
9. Functional chain according to claim 8, characterized in that the laser source (10) is a triggered, pulsed laser.

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