FR2593907A1 - Electrical igniter with a pyrotechnic charge and corresponding firing system - Google Patents

Abstract

The invention relates to an electrical igniter of a pyrotechnic or explosive charge. The igniter comprises a priming head 1 consisting of a pyrotechnic composition supported by an igniter body 2 having two ducts 21, 22 allowing the passage of electrical conductors 3, 4 connected to the primer 1. The priming head 1 is connected to the electrical conductors 3, 4 by means of a conduction threshold circuit 5. The invention is used in blasting techniques, for pyrotechnics and in sequential firing control in the abovementioned techniques.

Description

 The present invention relates to an electric igniter with pyrotechnic charge and to the corresponding ignition system.

 At present, electrical igniters with pyrotechnic charge commonly used essentially comprise a primer head constituted by a pyrotechnic composition supported or contained in an igniter body. The igniter body includes two bushings allowing the passage of electrical conductor wires connected to the primer head. An electrical resistance connecting the two conductive wires is disposed in the pyrotechnic composition constituting the primer head, so as to cause the electrical resistance to ignite by heating when the latter is supplied with electrical energy.

 If this type of igniter has hitherto been satisfactory from the point of view of safety and reliability of operation, it appears however that the triggering by all or nothing of this type of igniter does not make it possible to have a significant variety of different firing time models, except to fundamentally modify the internal structure of the latter and in particular the resistive element or to add external elements of the electrical circuit to the igniter.

 In addition, the current elements are, due to their triggering of firing by all or nothing, unsuitable for use under various firing conditions such as, in particular, the sequential fires implemented in pyrotechnics , or during military or blasting operations.

 The object of the present invention is to remedy the aforementioned drawbacks by using an electric igniter capable of exhibiting at least one triggering threshold for firing.

 Another object of the present invention is the use of an electric igniter having a degree of reliability at least equal to that of current electric igniters.

 Another object of the present invention is the implementation of an electric igniter, which, due to the existence of at least one triggering threshold for firing it, can be easily used for carrying out stakes. sequential fire according to a determined program.

 Another object of the present invention is also the implementation of a system for igniting pyrotechnic charges specially adapted for controlling the sequential ignition of a plurality of electric igniters in accordance with the invention.

 The electric igniter which is the subject of the present invention comprises a primer head constituted by a pyrotechnic composition supported by an igniter body, which comprises two bushings allowing the passage of electrical connection conductors connected to the primer head.

It is remarkable in that the primer head is connected to the connection conductors through a conduction threshold circuit.

 The sequential firing system of a plurality of pyrotechnic charges is remarkable in that it comprises a programmable voltage generator making it possible to generate a firing voltage which is variable over time, a plurality of electric igniters being connected at the output of the voltage generator.

 The invention finds application in very diverse fields of industry such as, in particular, the guiding of missiles, the control of gyroscopic systems for satellites or missiles, the firing of explosive charges in the field of public works, the 'mining or quarrying and blasting civil and military as well as of course, the sequential programmed control of firing in pyrotechnics.

It will be better understood on reading the description and observing the following drawings, in which
FIG. 1 represents, in section along a longitudinal plane of symmetry, an electric igniter according to the present invention,
FIG. 2 represents a block diagram of a system for igniting pyrotechnic charges in accordance with the present invention,
FIG. 3 represents an advantageous embodiment of a system for igniting pyrotechnic charges capable of ensuring the sequential ignition of any given number of electric igniters, in accordance with the invention,
FIGS. 4a and 4b represent an advantageous embodiment of one of the means of FIG. 3 and, by way of nonlimiting example, waveforms applied to an igniter Ii of order i of FIG. 3 as a function the state of the system.

 The invention will first be described in connection with FIG. 1.

 In accordance with this figure, which represents in longitudinal section an electric igniter according to the invention, it comprises a primer head noted 1, constituted by a pyrotechnic composition supported by an igniter body noted 2. The body of igniter 2 comprises two bushings 21, 22, allowing the passage of electrical connection conductors denoted 3 and 4. The primer head comprises an electrical resistance embedded in the pyrotechnic composition, this resistance noted 10 being connected to electrical conductors 3 and 4 above. In accordance with the invention, the primer head, and of course the electrical resistance 10, is connected to the connection conductors by means of a conduction threshold circuit denoted 5.

 Advantageously, the conduction threshold circuit can be constituted by at least one diode. In FIG. 1, two diodes denoted 51 and 52 are shown.

Preferably, at least one of the diodes 51, 52 is constituted by a diode of the diode type
Zener.

 As it also appears in FIG. 1, the pyrotechnic composition constituting the primer head can be an explosive composition of the conventional type normally used in electric igniters. The igniter body 2 can be made of a plastic material and obtained by overmolding. The bushings 21 and 22 are made directly during the production of the igniter body by overmolding and the electrical conductors 3 and 4 can be introduced into the bushings and protected mechanically and electrically by protective sheaths, for example polychloride sheaths of vinyl rated 30, 40.

 According to an advantageous characteristic, the igniter object of the invention is produced so that the conduction threshold circuit is constituted by two Zener diodes 51, 52 mounted in opposition. Thus, and advantageously, the two aforementioned Zener diodes being chosen so as to present different values of Zener voltage, the igniter object of the invention has two conduction thresholds of different nominal voltage according to the direction of polarization connection conductors.

When a supply voltage Va is applied to the connection conductors 3, 4, a direct voltage for example, according to the direction of polarization of this supply voltage, the conduction threshold of the electric circuit as shown in FIG. 1 s 'written
V51 = VZ1 + Vs or
VS2 = VZ2 + Vs relations in which Vzî and VZ2 represent the Zener voltages of the Zener diodes 51 and 52, and where Vs represents the conduction threshold voltage in the passing direction of each Zener diode 51, 52.

 Thus, the igniter advantageously has two conduction thresholds of different nominal voltage for different values of Vzi and Vz2. The electric power actually applied to the resistor 10 intended to cause the latter to heat up is then of the form (Va - Vs) 2 / R or R represents the value of the resistor 10.

 It was possible to produce electric igniters as shown in FIG. 1, in which Zener diodes of the BZX 55 C series distributed by the company THOMSON SEMICONDUCTORS were used. By way of example, and without limitation, an igniter comprising Zener diodes of the aforementioned type of Zener voltage of 6.8 volts could be produced so as to have an average ignition time of the order of 3.43 ms for a supply voltage Va = 10 volts.

Of course, the ignition time and the deviation from the average time for a series of igniters considered, can be reduced on the one hand by selection of the components constituting the igniter, and on the other hand, by the judicious choice of the supply voltage Va. Thus, for the same type of igniter supplied with a voltage Va of 15 volts, the average ignition time is reduced substantially to 0.8 ms, the difference for each igniter of this type compared to the average time being reduced Consequently.

 It has also been found that for the igniter as described above, a supply voltage Va of less than or equal to 8 volts did not allow any igniters of a sample consisting of a plurality of them to be ignited.

 In Figure 1, the connection conductors are shown by wires. Of course, the latter outside the igniter body 2 can advantageously be constituted by connection pins.

 The electric igniter as described is particularly advantageous in that it has a one-piece structure, the diode or diodes constituting the conduction threshold circuit being directly integrated into the igniter body 2 during the molding operation.

 As it appears advantageously, the diodes 51, 52 can be chosen of different value from the diodes of the same series having Zener voltage values included by way of nonlimiting example between 2.4 volts and 50 volts for example. The electric igniters thus obtained can advantageously have conduction thresholds of different nominal voltage stepped over the above-mentioned value range, so as to constitute a set of igniters capable of various applications. In particular, this set of electric igniters can advantageously be used for the sequential firing of a plurality of pyrotechnic or explosive charges and in particular for the programmed control of pyrotechnic parts.

 A sequential firing system of a plurality of pyrotechnic or explosive charges particularly suitable for triggering the igniters as described above will now be described in connection with FIG. 2.

 According to this figure, the system advantageously comprises a programmable voltage generator, denoted 20, making it possible to generate a firing voltage which varies over time. A plurality of igniters as previously described, and therefore each having conduction thresholds of different nominal voltage stepped for example over the range 2.8 volts to 50 volts mentioned above is connected to the output of the programmable voltage generator 20. In FIG. 2, each igniter is noted Ii. Of course, the igniters are connected in parallel to the output of the programmable voltage generator 20. By way of nonlimiting example, the programmable generator 20 can be arranged, at the operator's choice, so as to deliver, for example, voltage pulses of value corresponding to the nominal conduction threshold voltage of a given igniter Ii of order i. In this way, the operator chooses the value of the corresponding pulse as a function of the space-time order of the igniter to be triggered so as to ignite a given pyrotechnic setting. Thus, in a simple case in which the igniters Ii must be triggered successively at firing times separated by substantially equal time intervals, the operator may choose, as shown in FIG. 2, igniters whose threshold voltages will be distributed substantially linearly in depending on the order of the igniters, the programmable generator 20 then being adapted so as to deliver a substantially linear voltage of the sawtooth type. In this way, each igniter li is triggered successively.

The programmable voltage generator 20 can be constituted for example either by an analog generator of signals with adjustable parameters, or by a microprocessor assembly making it possible to generate signals in digital form, which are then converted into corresponding analog signals, by a suitable digital-to-analog converter.

 The previously described sequential firing system allows firing of a given plurality of igniters li, but the number of igniters capable of being effectively used appears reduced for the following reasons. On the one hand, the total amplitude of the time-varying ignition voltage is necessarily limited and can hardly exceed fifty volts without the implementation of more complex and more expensive additional power circuits.

On the other hand, in order to ensure proper operation of the set of ignitors Ii considered, it is necessary that the triggering threshold voltage, that is to say the nominal voltage for which 100% of triggering of a considered igniter is obtained, and the non-triggering threshold voltage of the successive igniter Ii + 1, for which no triggering of this igniter is obtained, are of course disjoint with a separation interval sufficient to avoid simultaneous triggering or almost simultaneous of two successive igniters for the same value of the ignition voltage. Consequently, the number of igniters that can actually be used with the system described above is necessarily reduced.

 In order to remedy the aforementioned drawbacks, and in particular to allow the implementation of a sequential firing system of a plurality of pyrotechnic or explosive charges comprising a larger number of these, a preferred variant of a system sequential firing will be described in conjunction with Figures 3 and 4a, 4b.

 According to FIG. 3, the above-mentioned sequential firing system comprises a programmable voltage generator, making it possible also to generate a firing voltage which varies over time. This generator is for example constituted by a microprocessor denoted 100, provided with its peripherals, not shown, connected by a link BUS, data BUS, to a digital-analog converter 101.

The digital-analog converter 101 has an analog output directly connected to a multiple connection terminal denoted 105. Each of the igniters Ii is connected to the programmable voltage generator, via a circuit denoted 106i for conditional tripping inhibition. In fact, as it appears in FIG. 3, each igniter Ii has one of its connection conductors connected to the terminal 105, and the other of the connection conductors is connected to the muting circuit 106i which is associated with it . The inhibition circuit 106i, and each of these, is connected to the microprocessor 100 via a
Link BUS, Address BUS. Each of the muting circuits 106i, in response to a preset program loaded in the microprocessor 100, is arranged so as to deliver to the igniter Ii considered, ie a supply voltage equal to the firing voltage variable over time, so as to inhibit the firing of the igniter Ii considered, ie a different supply voltage in absolute value from the firing voltage, the difference in value between the supply voltage and the ignition voltage being capable of causing the ignition of the pyrotechnic composition of the igniter Ii considered.

Of course, the switching between one or the other voltage value delivered by the muting circuit 106i is ensured by the microprocessor 100.

For this purpose, as it appears in FIG. 3, the signal delivered by the digital-analog converter 101, that is to say the ignition voltage, is delivered directly to each of the inhibition circuits 106i, and indirectly by means of a subtractor circuit, subtractor amplifier 104, to each of the aforementioned 1O6i circuits. The subtracting amplifier 104 is supplied on its positive terminal by the firing voltage and on its negative terminal by a predetermined reference voltage. The microprocessor 100 can for example be constituted by any microprocessor normally available on the market and for example by an 8 bit microprocessor, of CMOS type, with low current consumption.

 A more detailed description of a conditional inhibition circuit 106i will be given in connection with FIG. 4a, with reference to the test points A and B in FIG. 3.

 By way of nonlimiting example, each circuit 106i may include a circuit 1060, address reader, directly connected by the address bus previously described to the microprocessor 100. The address reader circuit 1060, may for example include a first assembly, address generator, denoted C, triggering on reception of the corresponding address transmitted by the microprocessor 100, a circuit of the bistable circuit type, denoted D, with two states, a low state denoted 0, and a high state denoted 1.

The two-state circuit 1060D, allows switching between two switching states denoted I and II, of a two-state switch system 1061. The switch system 1061 is connected to a contact terminal 1062, to which the conductor of corresponding connection of igniter Ii. In its state I, that is to say, when the two-state circuit 1060D is in its low state 0, ie in the absence of transmission of the corresponding address by the microprocessor 100, the switch system 1061 delivers at terminal 1062 the firing voltage, as shown in test point A, thereby inhibiting the firing of the corresponding igniter Ii. On transmission of the corresponding address by the microprocessor 100, the two-circuit states 1060D is switched to its I state and the switch system 1061 is switched to its il state and supplies the supply voltage to terminal 1062
VB different from the ignition voltage VA, this difference, constituted by the reference voltage VN, supplying the subtracting amplifier 104 being able to ensure the ignition of the igniter Ii considered. Of course, the reference voltage VN is advantageously chosen to be equal to the nominal voltage of the igniter considered. The link formed by the address BUS between the microprocessor 100 and each inhibition circuit 106i can advantageously be constituted for example by a link of the current loop type, each inhibition circuit 106i being connected substantially in cascade, on the current loop in the usual way. This type of connection allows in particular the connection of a large number of inhibition circuits 106i, and consequently, the use and connection of a corresponding number of ignitersIi. In FIG. 4a, the switch system 1061 has been represented schematically according to the usual electrotechnical representation, it is understood that this switching system can advantageously be constituted by a transistorized system. In addition, the address reader circuit 1060C and the two-state circuit 1060D are conventional circuits normally available commercially.

The signals at the test points A and B in FIG. 3 are represented in FIG. 4b, the voltage actually applied Vii equal to the difference of the voltages VA and VB being also represented as a function of the two switching states.
I, II, of the switch system 1061.

 Advantageously and as it appears in FIG. 4b, the time-varying ignition voltage, ie the voltage VA, and of course consequently the voltage VB is periodic. It can be constituted by way of nonlimiting example, either by a tension of the sawtooth tension type, or by a tension in the staircase step. The supply voltage different from the ignition voltage present relative to the latter, a difference in value corresponding to the nominal voltage VN of the igniter Ii considered. By nominal voltage of course is meant not only the voltage capable ensure, for a given type of igniter, 100% tripping, on a given test sample of igniters, but preferably a voltage capable of ensuring the ignition of a type of igniter, with a tripping time and an average deviation from the minimum mean tripping time for each igniter. Thus, it is possible to use a single type of igniter having a single triggering threshold.

 Advantageously, the periodic variable firing voltage can be generated by a program managed by the 1GO microprocessor. This program can for example advantageously consist of two nested counting loops, a first order k loop being adapted to generate any corresponding order k period of the ignition voltage, and a second order j corresponding in fact to a temporal subdivision of each period of order k. The existence at each instant of the firing voltage and correlatively of the supply voltage VB, for each period of order k and the transmission by the microprocessor 1OO, for one or more subdivisions of order j of the period of order k considered, corresponding addresses of one or more inhibition circuits 106i, allows the corresponding triggering or firing of the information. igniter Ii considered. Thus, the user or operator speaks only choice of the corresponding values of k and j, can of course program the ignition of an igniter ii considered, with a delay compared to the origin of launching of the sequence , substantially equal to the sum of the corresponding delays. Advantageously, the period of the periodic variable firing voltage, may, by way of nonlimiting example, be taken equal to 30 seconds and the maximum number of elementary intervals in each period, that is to say the maximum value of j, can be taken equal to 30, so as to obtain in each period, successive triggers from second to second.

Of course, the simultaneous triggering of several igniters Ii can be achieved without difficulty, insofar as the successive transmission of a given number of addresses of inhibition circuits 106i can be carried out by the microprocessor 100 in a time interval n '' not exceeding, for example, one tenth of the elementary interval of 1 second for each period, or ultimately 1 tenth of a second. In the case of the realization of a system comprising an 8-bit microprocessor, it is thus possible, without difficulty, to address under the aforementioned conditions up to 256 iritibition circuits and therefore to control 256 different igniters. the waveform of the firing voltage variable over time can be arbitrary, and in particular the amplitude of this firing voltage can be chosen to be constant over a period.

 An electric igniter has thus been described, the particular structure of which has made it possible to define a very efficient sequential firing system and very flexible in use, the latter allowing in particular the use of the most varied artistic pyrotechnic compositions .

 Of course, the igniter of the invention can advantageously be used in firing elements or components, such as igniters, detonators, chokes or gas generators.

 It will be recalled that in the pyrotechnic or blasting technique, an igniter designates the assembly constituted by an igniter associated with black or spherical powder, a detonator designates an igniter associated with an explosive, a gas generator or generator designates a igniter mounted on a screwable metal support.

Claims (12)

 1. Electric igniter comprising a primer head (1) constituted by a pyrotechnic composition supported by an igniter body (2) comprising two bushings (21), (22) allowing the passage of electrical connection conductors (3), (4) electrically connected to the primer head, characterized in that said primer head is connected to the connection conductors by means of a circuit (5) with conduction threshold.  2. igniter according to claim 1, characterized in that said conduction threshold circuit consists of at least one diode (51), (52).  3. igniter according to claim 2, characterized in that one of the diodes (51), (52) constituting the conduction threshold circuit is a diode of the Zener diode type.  4. Inflammateurselon claim 3, characterized in that the conduction threshold circuit consists of two Zener diodes (51), (52) mounted in opposition.  5. igniter according to claim 4, characterized in that the two Zener diodes (51), (52) have different Zener voltage values, the igniter having two conduction thresholds of different nominal voltage depending on the direction of polarization of the connection conducteus.  6. Sequential firing system for a plurality of pyrotechnic charges, characterized in that it comprises  - a generator (20) of programmable voltage making it possible to generate a firing voltage variable over time,  - A plurality of igniters (Ii) according to one of the preceding claims 1 to 5, connected at the output of said voltage generator.  7. Firing system according to claim 6, characterized in that said igniters (Ii) are connected in parallel to the output of said voltage generator.  8. Firing system according to claim 7, characterized in that each of the igniters (Ii) is connected to said generator via a circuit (106i) of conditional trigger inhibition, said circuit in response to the program aforementioned pre-established being arranged so as to deliver, to the considered igniter, either a supply voltage equal to the firing voltage variable over time so as to inhibit the firing of the latter, or a supply voltage which is different, in absolute value, from the ignition voltage, the difference in value between the supply voltage and the ignition voltage being capable of causing the pyrotechnic composition of the igniter considered.  9. System according to claim 8, characterized in that the firing voltage variable over time is periodic.  10. System according to claim 9, characterized in that the ignition voltage is constituted by a staircase voltage, the supply voltage different from the ignition voltage having with respect thereto a difference in value corresponding to the nominal voltage of the igniter (Ii).  11. System according to claim 9, characterized in that the amplitude of the ignition voltage is constant over a period.  12. Use of an igniter according to one of the preceding claims 1 to 5, in firing elements or components such as an igniter, detonator, choke or gas generator.