FR2743625A1 - SOLID STATE LASER ARMING / FIRED DEVICE - Google Patents

Abstract

A solid state laser arming / firing device is disclosed. This device comprises an electronic switch (34/36) for triggering the ignition of a pyrotechnic material (42) in response to a signal, laser means (38) electrically connected to the electronic switch to produce a laser pulse and a optical fiber (40) one end of which is optically coupled to the laser means and the other of which is inserted into the pyrotechnic material (42) so that the laser pulse concentrates heat on the inserted end of the optical fiber to initiate pyrotechnic material. Application in particular to arming / firing devices for activating explosive charges.

Description

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  The present invention relates to the field of arming / firing devices (hereinafter also referred to as AFD), and more particularly to a laser AFD device (hereinafter referred to as

LAFD).

  In conventional arming / firing devices (AFD)

  it is necessary to provide a mechanical barrier between the electronic device

  explosive (referred to as EED) and the output charge or pyrotechnic material. This mechanical barrier involves moving parts and therefore must have a structural capability to clear the output of the EED device. Moving parts reduce reliability and mechanical barriers increase the weight and dimensions of the device. Similarly, EED devices may be affected by electromagnetic pulses (hereinafter referred to as EMI) and a discharge.

  electrostatic (hereinafter referred to as ESD).

  An exemplary arming / firing device is disclosed in U.S. Patent No. 5,022,324 entitled "Piezoelectric Crystal Powered Ignition Device", which uses pyrotechnic flashlamps to trigger a solid state laser. The laser is formed by a neodymium glass laser bar, which is "pumped" when a light from the flashlamps penetrates the sides of the laser. As in conventional AFD devices, this device uses mechanical safety devices. In the preferred embodiment, the mechanical safety device is an assembly formed of a spring-loaded weight, which is used to mechanically open a shutter. In another embodiment, a rotary mechanical axis having a hole which is misaligned is used, except when

  hole is aligned with the laser and the pyrotechnic material.

  It is desirable to have an AFD device that does not have the mechanical barrier or the moving parts between the device

EED and the output load.

  The object of the invention is to provide an arming / firing device which eliminates the limitations indicated above. The present invention removes the limitations indicated above by providing a device for igniting a pyrotechnic material, and comprises electronic switch means for triggering the firing of the pyrotechnic material in response to a signal, connected laser means

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  electrically to the electronic switch means for producing a laser pulse in response to these electronic switch means, and an optical fiber, one end of which is optically coupled to the laser means and the other end of which is inserted into the pyrotechnic material so that the laser pulse concentrates heat at the level

  of the inserted end of the optical fiber, and initiates the pyrotechnic material.

  The laser means may be a laser diode. The pyrotechnic material contains a metal capsule and the optical fiber is sealed to the metal capsule with a copper or epoxy seal. The copper seal may be formed of a fine copper powder disposed in a sealing zone, which is consolidated by compression means to form the seal, or the copper seal may be constituted a copper sleeve disposed on the optical fiber in the sealing zone and which is compressed with compression means to form the seal. The wavelength of the laser pulse is about 860 nanometers. The optical fiber is inserted over a length of between 0,076 cm and 1,52 cm (0,030 and 0,60 in) in the pyrotechnic material which is a powder of B / KNO3 dimensioned so as to cross 100% a sieve having meshes of 25 micrometers, the pyrotechnic material containing 2% by weight of carbon black to improve the absorption of the energy of the laser. The B / KNO3 powder is consolidated around the inserted optical fiber, by applying a pressure of between 13790.103 Pa and 20684.103 Pa (2000 to 3000 psi) for an application time of 1 to 10 seconds. The laser pulse produces heat in a small area in a manner sufficient for initiation to occur in about 4 milliseconds. The optical fiber has a diameter of

micrometers.

  The AFD laser device can be used in military equipment, for commercial explosions or for the initiation of

  rocket engines with solid propulsion.

  A method of igniting a pyrotechnic material using the device described above consists in applying an electrical signal to

  means forming an electronic switch.

  Also provided is a solid laser arming / firing device which includes a first electronic switch for

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  arming the device in response to an ARM signal, a second electronic switch for firing the device and triggering

  initiating a pyrotechnic material in response to a FIRE signal.

  A laser diode electrically connected to the second electronic switch produces a laser pulse in response to the FIRE signal. This device also comprises an optical fiber whose end is optically coupled to the laser diode and the other end is inserted into the pyrotechnic material so that the laser pulse initiates the pyrotechnic material. This device comprises a visual indicator SURETE / ARMEMENT and a casing Faraday cage forming the housing of said device. The device comprises means for performing a diagnostic test to verify that the operation of the laser diode is

  correct, without priming the pyrotechnic material.

  A method of igniting a pyrotechnic material whose device is described above includes the steps of applying an ARM signal to the first electronic switch and applying a

  FIRE signal at the second electronic switch.

  Other features and advantages of the present invention

  will emerge from the description given below taken with reference to the drawings

  attached, in which: - Figure 1 is a cross-sectional view of a conventional AFD device of the prior art; FIG. 2 represents a cross-sectional view of a laser AFD device according to the invention; FIG. 3 is a diagram of a circuit of the AFD laser device according to the invention; FIG. 4 is a cross section showing how the optical fiber is sealed to a metal capsule; and - Figure 5 shows another embodiment of the scheme

  of the circuit of the AFD laser device according to the invention.

  Although the invention may be embodied in many different forms, there is shown in the drawings and specific preferred embodiments of the invention are described herein in detail. The

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  present description gives an example of the principles of the invention and is not

  intended to limit the invention to the particular embodiments shown.

  Referring now to FIG. 1, there is shown an AFD device of the prior art generally designated by the reference 10. The mechanical indicator SURETE / ARMEMENT is represented at 12 and the electromagnet, which is a moving mechanical part is designated by the reference 14. The detonator is designated by the reference 16 while the donor charge is designated by the reference 18, the receiving load is designated by the reference 20 and the output load formed of B / KNO3 is

designated by reference 22.

  Referring now to Figure 2, there is shown the AFD laser device (LAFD) according to the invention, generally designated by the reference 30. An electrical and visual indicator of SURETE / ARMEMENT is designated by reference 32. Two independent electronic switches are designated respectively by the references 34 and 36. A laser diode is shown at 38. A cable of an optical fiber, which is optically coupled to the laser diode 38, is designated by reference 40. The

  optical fiber cable 40 is inserted into the output load 42 at B / KNO3.

  The LAFD device has the same electrical inputs and the same pressure outputs as those of the conventional electromechanical AFD device shown in FIG. 1. The electrical interface accepts signals

  AFD standard for ARMING and FIREFIGHTING commands.

  Referring now to Figures 2 and 3, there is shown the electrical diagram of the device LAFD. When receiving an ARMING signal, represented at the terminal 7 with the reference numeral 50, the electrical and visual indicator 32 is lit by a high intensity red LED diode 52. This light is focused by a film that has a green background, a white letter "S" (SURETE) and a letter "A" (ARMEMENT). In the absence of input light, the indicator represents the green background on which the white "S" is superimposed. The red LED 52 is connected in series with two optical couplers 54 and 56. The optical coupler 54

  powers the electronic indicator SURETE / ARMEMENT, represented in 58.

  The optical coupler 56 represents the first electronic switch and validates the firing circuit. If either of the two components 52 or 56 fails, the arming function is not executed and the indicator

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  visual does not work. A wide range of ARMING signals can be received based on a selection of component values, and the choice of different values is considered part of the routine technique. The choices shown in Figure 3 set the LAFD device for a 30-volt ARM signal.

  When the LAFD device is armed, it is ready to be fired.

  Upon receiving a FIRE signal, terminals 4 and 1 at 60, the second electronic switch 64 is closed and a current flows through the laser diode 62. The emitting facet of the laser diode 62 produces a laser pulse at a wavelength of about 860 nanometers, this pulse being transmitted by the optical fiber 40 of 100 micrometers. The optical fiber 40 is inserted into the output load 42 formed of B / KNO3. The optical fiber 40 projects or extends over a distance of between 0.076 cm and 1.52 cm, in the

output load 42.

  The particle size of the output charge 42 is dimensioned such that it can pass 100% through a micron mesh screen. 2-3% by weight of carbon black is added from

  to improve the energy absorption of the laser.

  Referring now to Figure 4, there is shown a cross-sectional view of the seal. The optical fiber 40 is sealed to a metal cap 70 of the output load 42 by the use of a consolidated copper gasket 72. In the preferred embodiment of the consolidated gasket, a thin copper powder in the sealing zone 72 and the powder is compressed by tightening a clamping screw or the compression produced by a piston against the sealing zone. Another embodiment of the consolidated copper gasket resembles a copper compression fitting by the use of a small copper sleeve which is placed on the fiber and within the area of the copper. seal. A clamping screw is tightened or a piston is pushed against the sealing zone 72, which causes the sleeve to expand and seal. The seals of the embodiment are welded after compression to obtain an absolutely hermetic seal. An epoxy seal is added to prevent corrosion and contamination. In another embodiment, the copper gasket can be replaced by a pure epoxy gasket

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  for applications that do not require high temperature sealing

and for a long time.

  The powder of B / KNO3 is packed around the optical fiber 40 under the application of a pressure of 13790.103 Pa - 20684.103 Pa for an application time of 1 to 10 seconds. The amount of powder is adjusted to obtain the required outlet pressure, as is well known in the prior art. The cavity accommodating the charge is sealed by placing a non-conductive insulating disk 74, following which

  applies a stainless steel cup 76 (best seen in Figure 4).

  The cup is welded in place by means of TIG welding, and it is tested whether the assembly is leaking, so as to ensure its integrity. When the laser energy is received at the tip of the optical fiber 40, the temperature of the output charge 42 increases abruptly until priming begins. A first indication of pressure appears typically in

the space of 4 milliseconds.

  The inventors have found that the use of an inserted optical fiber suppresses the effect of the operating temperature on the firing delay. Although the load is more difficult to prime in extreme cold conditions, the electronic system is more efficient and delivers higher laser energy. Similarly, at high temperature, the charge is easier to prime, but the electronic system is less efficient. It turns out that the variables are in equilibrium and there is no statistically significant difference between start-up delays in the

tactical range of temperatures.

  Another advantage of inserting the fiber 40 directly into the output load 40 is that this makes it possible to satisfy the American MIL-STD-1901 standard, which eliminates the need to provide mechanical release systems of gas containment. The use of a conductive optical fiber 40 also eliminates the risk of an inadvertent initiation response due to electromagnetic EMI pulses or ESD electrostatic discharge. The AFD device can be housed in a complete Faraday cage to obtain additional protection against EMI / ESD phenomena, while obtaining the lowest weight of competing embodiments. Removal of moving parts in the

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  AFD device also reduces the size and weight of the device and

  also increases the reliability of the latter.

  Another advantage of the device LAFD according to the invention is that it allows to run diagnostic tests to verify that the diode is working properly. In devices with a filament, this feature is not available, since the excitation of a filament

leads to priming.

  Another advantage of the LAFD device according to the invention is that by using a high pressure and high temperature resistant copper gasket, the expensive and complicated manufacturing process for creating glass-on-metal sealing is eliminated. . The ability to use a pure epoxy seal for low temperature applications reduces

  additional way the manufacturing costs.

  Referring now to FIG. 5, there is shown another embodiment of the circuit according to the invention of FIG. 3, which additionally confers protection against electrostatic discharge (ESD) and protection against electromagnetic interference (EMI) at

  input connector due to the presence of respective filters 66 and 68.

  This completes the description of the preferred embodiment and

  other embodiments of the invention. It will be understood that although many features and advantages of the present invention

  indicated in the foregoing description, as well as the details of the

  structure and operation of the invention, this description is given

  only for illustrative purposes and that modifications of detail may be made, in particular as regards the shape, dimensions and

  the arrangement of parts within the scope of the invention.

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Claims (23)

  1. A device for igniting a pyrotechnic material, characterized in that it comprises: electronic switch means (56) for triggering the ignition of the pyrotechnic material (42) in response to a signal; laser means (62; 38) electrically connected to the electronic switch means (16) for producing a laser pulse in response thereto; an optical fiber (40), one end of which is optically coupled to the laser means (62; 38) and the other end of which is inserted into the pyrotechnic material (42) so that the laser pulse concentrates heat at the the inserted end of the optical fiber, and starts the pyrotechnic material.   2. Device according to claim 1, characterized in that the   laser means (62; 38) are a laser diode.   3. Device according to claim 2, characterized in that the pyrotechnic material includes a metal cap (70) and the optical fiber (40) is hermetically sealed to the metal cap (70) by means of   a copper gasket (72).   4. Device according to claim 3, characterized in that the copper seal (72) is constituted by a fine copper powder disposed in a sealing space (72) and which is consolidated by means   compression to form the joint.   5. Device according to claim 3, characterized in that the copper seal (72) consists of a copper sleeve disposed above the optical fiber (40) in the sealing space and which is   compressed by compression means to form the seal.   6. Device according to claim 2, characterized in that the pyrotechnic material (42) includes a metal cap (70) and that the optical fiber is hermetically sealed to said metal cap by a solder / epoxy seal. 7. Device according to claim 1, characterized in that the   wavelength of the laser pulse is equal to about 860 nanometers. 9 2743625   8. Device according to claim 1, characterized in that the optical fiber (40) is inserted over a distance of between 0.076 cm and 1, 52 cm in the pyrotechnic material.   9. Device according to claim 1, characterized in that the pyrotechnic material is a powder of B / KNO3. 10. Device according to claim 9, characterized in that the powder of B / KNO3 is dimensioned so as to cross 100% a sieve having meshes of 25 micrometers and that the pyrotechnic material contains   2-3% by weight of carbon black to increase the absorption of laser energy.   11. Device according to claim 10, characterized in that the powder of B / KNO3 is consolidated around the inserted optical fiber (40) at a pressure between 13790.103 Pa and 20684.103 Pa for a period of time. from 1 to 10 seconds.   12. Device according to claim 1, characterized in that the laser pulse sufficiently concentrates the heat at the inserted end of the optical fiber (40) so that the ignition occurs in about 4 milliseconds. 13. Device according to claim 1, characterized in that the   Pyrotechnic material is used in military equipment.   14. Device according to claim 1, characterized in that the   Pyrotechnic material is used for commercial explosions.   15. Device according to claim 1, characterized in that the pyrotechnic material is used for the priming of rocket motors to solid propellant.   Device according to claim 1, characterized in that the   optical fiber (40) has a diameter of 100 micrometers.   17. A method for initiating a pyrotechnic material, using the device according to claim 1, characterized in that it consists in applying   an electrical signal to the electronic switch means (56).   18. A solid state laser arming / firing device, characterized in that it comprises: a first electronic switch (54) for arming the device in response to a signal ARMEMENT; 2743625   a second electronic switch (64) for setting. firing the device and triggering the firing of a pyrotechnic material (42) in response to a FIRE signal; a laser diode (62; 38) electrically connected to the second electronic switch (64) for producing a laser pulse in response to the FIRE signal; an optical fiber (40), one end of which is optically coupled to the laser diode (62; 38) and the other end of which is inserted into the pyrotechnic material (42) so that the laser pulse produces heat in a small zone in a manner sufficient to prime the pyrotechnic material. 19. Device according to claim 18, characterized in that   has a visual indicator SURETE / ARMEMENT (32).   20. Device according to claim 19, characterized in that it comprises a Faraday cage housing forming a housing of said device 21. Device according to claim 18, characterized in that it comprises filters (66,68) for protection against electrostatic discharges.   (ESD) and against electromagnetic impulses (EMI).   22. Device according to claim 18, characterized in that it comprises means for performing diagnostic tests to check whether the   Laser diode works properly without priming the pyrotechnic material.   23. A method for initiating a pyrotechnic material, with the use of the device according to claim 18, characterized in that it comprises the steps of: applying an ARMING signal to the first electronic switch (56), and applying a signal from FIRST to the second switch electronic (62).