GB1598590A - Explosive devices - Google Patents

Description

(54) EXPLOSIVE DEVICES (71) We, M. L. AVIATION COMPANY LIMITED., a British Company, of M. L.

Building, Ajax Avenue, Trading Estate, Slough SL1 4BQ, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to explosive devices.

Such explosive devices are commonly used for actuating or releasing mechanisms, such as, for example, ejector release mechanisms in aircraft.

In our British Patent Specification No.

1,235,844 there is disclosed an ignition circuit in which the explosive device comprises, besides the explosive charge, an electrical heating element for igniting the charge, and a first coil connected to the element and wound on a magnetic core. The device is received by a holder which contains a second coil which is wound on a second magnetic core and which becomes inductively linked with the first coil by proximity of the two cores, so that energisation of the second coil by an oscillator induces a continuous alternating current in the first coil which energises the heating element and ignites the charge. The cores are preferably pot cores which completely enclose the coils and thereby shield them from spurious radio frequency signals.

In order to initiate firing of the charge, the oscillator is energised by feeding a d.c.

supply to the oscillator.

In our British Specification No. 1,416,095 there is disclosed a somewhat similar transformer arrangement, but without the heating element. In this case the explosive material is, itself, electrically conductive and forms part of the secondary circuit.

It is an object of the present invention to provide an explosive device with an alternative ignition circuit.

According to the invention, an explosive device comprises electrically-conductive explosive material connected to a transformer secondary winding; a primary winding magnetically coupled to the secondary winding; a capacitive circuit; means to charge the capacitive circuit; and means to discharge the capacitive circuit into the transformer primary winding to cause ignition of the explosive material.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawing, in which: Fig. 1 is a schematic longitudinal crosssection through an explosive device in accordance with the invention, Figs. 2, 5 and 8 are diagrams of respective different ignition circuits for use in the invention, Figs. 3, 6 and 9 are graphs showing the approximate shape and magnitude of firing pulses generated by the circuits of Figs. 2, 5 and 8, respectively, and Figs. 4, 7 and 10 are graphs similar to Figs.

3, 6 and 9, respectively, but showing the approximate shape and magnitude of the firing pulses when the primary and secondary parts of the transformer are separated by a .02 inch gap and are misaligned axially by .03 inch.

Fig. 1 shows an example of an assembled explosive device with its ignition circuit. The explosive device 1 is contained within a casing 2 (only part of which is shown) and includes electrodes 3 and 4 connected to a transformer secondary winding 5 wound on a ferrite pot core. An electrically-conductive explosive material 6 is packed into the space between the electrodes 3 and 4.

A transformer primary winding 7 is encapsulated on a ferrite pot core contained within a casing 8 formed of an aluminium alloy, such as duralumin. The cores are arranged to be in axial alignment when the casing 8 is located relative to the device 1.

The cores are separated only by cupro-nickel diaphragms which close the ends of the device 1 and the casing 8, respectively. The casing 8 is spring loaded to give firm abutment between the transformer primary and secondary assemblies.

Also contained within the casing 8 is a circuit 9 of one of the forms described below.

The circuit 9 may also be encapsulated in a synthetic resin. A cable 10 feeds a power supply to the circuit 9.

Fig. 2 shows one example of a circuit 9 for use in the invention. A power supply, for example at 400 Hz, is fed via the cable 10 to a diode bridge 11. The output of the bridge is fed to a capacitor 12 via a charging resistor 13. The transformer primary winding 7 is connected in series with a thyristor 14 across the capacitor 12. A zener diode 15 is connected between the anode and the gate of the thyristor.

In operation of the circuit, when it is desired to fire the explosive the supply is connected to the cable 10. The capacitor 12 charges up from the diode bridge 11 until the break down voltage of the -zener diode 15 is reached. Current then flows into the gate, and the thyristor 14 fires, thereby discharging the capacitor through the transformer winding. The voltage pulse applied to the transformer is shown in Fig. 3 (and in Fig. 4 where the optimum transformer coupling is not achieved). It will be seen that the voltage rises to a peak, falls to zero, overshoots, reaches a reverse peak level, returns to zero, and finally overshoots again before settling at zero.

An alternative circuit is shown in Fig. 5. In this case a capacitor 16 is connected across the supply cable 10. A rectifier bridge 17 comprises two diodes 18, 19 and two thyristors 20, 21. Zener diodes 22 and 23 are connected, respectively, between the anode and the gate of the thyristors 20 and 21. A firing thyristor 24 with associated zener diode 25 is connected across the output of the bridge. A capacitor 26 is connected in series with the primary winding 7 across the thyristor 24.

In operation of the circuit, when the supply is connected to the cable 10 the capacitor 16 charges until the breakdown voltage of the zener diode 22 or of the zener diode 23, depending upon the polarity of the supply in that half cycle, is reached. The associated thyristor then fires and the capacitor 26 is charged through the transformer primary 7. When the combined voltage across the capacitor 26 and the primary winding 7 reaches the zener level of the diode 25, the thyristor 24 fires and discharges the capacitor 26 through the winding 7.

In the next supply half cycle the other of the thyristors 22 and 23 fires and the charge and discharge cycle of the capacitor 26 is repeated.

The voltage applied to the explosive material is shown in Fig. 6 (and in Fig. 7). In this case the voltage oscillates between positive and negative peaks.

Fig. 8 shows another alternative circuit. In this case, two capacitors 27 and 28 are used in a voltage doubler circuit. An a.c. supply is connected to the cable 10. One conductor of the cable 10 is connected to the junction of the capacitors 27 and 28, and the other conductor is connected to the ends of the capacitors via reverse-connected diodes 29 and 30. A charging resistor 31 is connected between the diode 29 and the capacitor 27. A thyristor 32, with an associated zener diode 33, is connected in series with the winding 7 across the capacitors 27 and 28.

The circuit operates in a similar manner to the Fig. 2 circuit, but a larger voltage is produced at the transformer secondary winding, the waveform (Fig. 9) being similar in shape to that shown in Fig. 3.

Other capacitance charge and discharge circuits may be used without departing from the scope of the invention.

For example, the circuit of Fig. 8 could be modified so that the transformer primary winding 7 is connected in series with the capacitor 28, the thyristor 32 then being connected across the circuit comprising the capacitors 27 and 28 and the winding 7. This circuit has an advantage over the Fig. 8 circuit in that the voltage oscillations continue for a longer period than those shown in Fig. 9.

Alternatively, the winding would be connected in series with the capacitor 27. This would enable a test to be carried out to check whether there is electrically-conductive explosive material connected to the secondary winding 5, or whether the device has already been fired. A constant current source is connected to the supply cable 10. The time taken to charge the capacitor 27 to a predetermined low level via the transformer winding 7 is checked, the charge level being selected so that it is insufficient to cause firing of the thyristor 32. There will be a considerable difference between the time taken for the capacitor to charge with a loaded transformer secondary winding than with an open-circuit transformer, or with badly aligned transformer primary and secondary windings.If the charge time is longer than the standard time expected for a properly-connected unused explosive device, a warning device, such as a lamp or a lightemitting diode, can be operated. The reaching of the predetermined charge level can be detected by monitoring the current through a resistor or a transformer connected in series with the supply.

A device for testing any of the abovedescribed ignition circuits can comprise a transformer secondary winding for coupling to the winding 7; a potentiometer connected across the winding; a zener diode connected between the potentiometer wiper and the gate of a thyristor, the cathode of which is connected to a d.c. negative supply line and to one end of the potentiometer; an audio sounder device connected between the d.c.

positive supply line and one pole of a flasher lamp having a bimetal contact which is heated by the lamp filament; the other pole of the lamp being connected to the anode of the thyristor.

If the ignition circuit under test produces an adequate output pulse, the zener diode will conduct, causing the thyristor to fire.

This will light the lamp and the audio sounder will operate until the bimetal contact opens, say 10 seconds later. The thyristor anode supply will then be interrtupted, and in the absence of any gate signal (since the ignition circuit output pulse has finished long before) the thryristor will not restrike on reclosing of the bimetal contact. If the connection between the potentiometer and the negative line is open-circulated, for example by opening a switch connected thereto, the thyristor will fire at very low gate signal levels. Hence, if spurious signals are present in the ignition circuit, the lamp will light and the audio sounder will operate without any proper ignition circuit output pulse having been generated, thereby warning of the presence of the potentially hazardous spurious signals.

WHAT WE CLAIM IS: 1. An explosive device comprising electrically-conductive explosive material connected to a transformer secondary winding; a primary winding magnetically coupled to the secondary winding; a capacitive circuit; means to charge the capacitive circuit; and means to discharge the capacitive circuit into the transformer primary winding to cause ignition of the explosive material.

2. A device as claimed in Claim 1, wherein the means to discharge the capacitive circuit comprises a discharge thyristor.

3. A device as claimed in Claim 2, including a zener diode connected between the anode and the gate of the discharge thyristor and operative to trigger the discharge thyristor when the charge on the capacitive circuit reaches a predetermined level.

4. A device as claimed in Claim 2 or Claim 3, wherein the discharge thyristor is connected in series with the transformer primary winding across the capacitive circuit.

5. A device as claimed in Claim 4, wherein the capacitive circuit comprises a voltage doubler circuit.

6. A device as claimed in Claim 4, wherein the means to charge the capacitive circuit comprises a bridge rectifier circuit.

7. A device as claimed in Claim 2 or Claim 3, wherein the means to charge the capacitive circuit comprises a bridge including two paths each comprising a diode and a thyristor, the two paths becoming conductive alternately when the bridge is connected to an a.c. supply; wherein the discharge thyristor is connected across the output of the bridge; and wherein the capacitive circuit is connected in series with the primary winding across the discharge thyristor.

8. A device as claimed in Claim 1 and substantially as hereinbefore described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. of the lamp being connected to the anode of the thyristor. If the ignition circuit under test produces an adequate output pulse, the zener diode will conduct, causing the thyristor to fire. This will light the lamp and the audio sounder will operate until the bimetal contact opens, say 10 seconds later. The thyristor anode supply will then be interrtupted, and in the absence of any gate signal (since the ignition circuit output pulse has finished long before) the thryristor will not restrike on reclosing of the bimetal contact. If the connection between the potentiometer and the negative line is open-circulated, for example by opening a switch connected thereto, the thyristor will fire at very low gate signal levels. Hence, if spurious signals are present in the ignition circuit, the lamp will light and the audio sounder will operate without any proper ignition circuit output pulse having been generated, thereby warning of the presence of the potentially hazardous spurious signals. WHAT WE CLAIM IS:

1. An explosive device comprising electrically-conductive explosive material connected to a transformer secondary winding; a primary winding magnetically coupled to the secondary winding; a capacitive circuit; means to charge the capacitive circuit; and means to discharge the capacitive circuit into the transformer primary winding to cause ignition of the explosive material.

2. A device as claimed in Claim 1, wherein the means to discharge the capacitive circuit comprises a discharge thyristor.

3. A device as claimed in Claim 2, including a zener diode connected between the anode and the gate of the discharge thyristor and operative to trigger the discharge thyristor when the charge on the capacitive circuit reaches a predetermined level.

4. A device as claimed in Claim 2 or Claim 3, wherein the discharge thyristor is connected in series with the transformer primary winding across the capacitive circuit.

5. A device as claimed in Claim 4, wherein the capacitive circuit comprises a voltage doubler circuit.

6. A device as claimed in Claim 4, wherein the means to charge the capacitive circuit comprises a bridge rectifier circuit.

7. A device as claimed in Claim 2 or Claim 3, wherein the means to charge the capacitive circuit comprises a bridge including two paths each comprising a diode and a thyristor, the two paths becoming conductive alternately when the bridge is connected to an a.c. supply; wherein the discharge thyristor is connected across the output of the bridge; and wherein the capacitive circuit is connected in series with the primary winding across the discharge thyristor.

8. A device as claimed in Claim 1 and substantially as hereinbefore described with reference to the accompanying drawings.