FIRING ARRANGEMENT

Abstract

A firing arrangement for an initiator (1) includes a capacitor (16), an arming arrangement (6, 11, 14) for charging the capacitor (16) on receipt of an arming instruction and a trigger device (13). When a trigger condition is achieved which indicates sufficient charge on the capacitor (16), a trigger signal is automatically generated by the trigger device (13) to trigger discharge of the capacitor (16) through the initiator (1) to activate the initiator (1). The trigger condition may be a predetermined time after receipt of the arming instruction.

Claims

1. A firing arrangement for an initiator comprising: a capacitor; an arming arrangement for charging the capacitor on receipt of an arming instruction; and a trigger device which, when a trigger condition is achieved indicating sufficient charge on the capacitor, automatically generates a trigger signal to trigger discharge of the capacitor through the initiator to activate the initiator.

2. The firing arrangement as claimed in claim 1 wherein the trigger condition is a predetermined time from when charging the capacitor begins.

3. The firing arrangement as claimed in claim 2 and including a pulse counter to count a series of pulses to determine when the predetermined time is reached.

4. The firing arrangement as claimed in claim 1 wherein the trigger condition is when the voltage across the capacitor reaches a threshold value.

5. The firing arrangement as claimed in claim 1 wherein the arming arrangement includes a sequence validator having a first input, a second input and an output, the sequence validator generating the arming instruction at its output only when a first arming signal is received on the first input followed by a second arming signal received on the second input.

6. The firing arrangement as claimed in claim 5 and including a first static switch and a second static switch each of which, in an open state, interrupts the firing arrangement such that arming is not possible and, in a closed state, completes part of the firing arrangement, the first static switch and the second static switch being connected to close on receipt of the first and second arming signal respectively.

7. The firing arrangement as claimed in claim 2 and including a low voltage capacitor arrangement, a dynamic switch and a transformer, the dynamic switch being operative during arming to discharge the low voltage capacitor arrangement via a transformer to charge the capacitor.

8. The firing arrangement as claimed in claim 7 wherein the dynamic switch is operative during arming at a frequency in the range 100 kHz to 1 MHz.

9. The firing arrangement as claimed in claim 7 and including a dynamic pulse generator connected to receive the arming instruction and to output a series of pulses to operate the dynamic switch when the arming instruction is received.

10. The firing arrangement as claimed in claim 9 wherein the pulse counter is connected to receive the series of pulses from the dynamic pulse generator.

11. The firing arrangement as claimed in claim 1 wherein the time period from receiving the arming instruction to generating the trigger signal is 1 ms or less.

12. A firing system comprising a firing arrangement as claimed claim 1 and an initiator.

13. The firing system as claimed in claim 12 wherein the initiator is one of: an Exploding Foil Initiator (EFI); a Pyrotechnic Igniter; a Bridge Wire (BW); a Film Bridge (FB); a Conducting Composition (CC); a Semiconductor Bridge (SCB); and a Semiconductor Initiator (SCI).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Some embodiments of the present invention will now be described by of example only, and with reference to the accompanying drawings, in which:

[0018] FIG. 1 schematically illustrates a firing arrangement in accordance with the invention;

[0019] FIG. 2 is a schematic timing diagram relating to the operation of the firing arrangement shown in FIG. 1; and

[0020] FIG. 3 schematically illustrates operation of a prior art firing arrangement and the firing arrangement of FIG. 1.

DETAILED DESCRIPTION

[0021] With reference to FIG. 1, a firing arrangement for activating an initiator, which in this case is an EFI detonator 1, includes power supply lines 2 and 3 and a low voltage capacitor bank 4 connected across them. To activate the EFI detonator 1, a first arming signal is applied to a first input 5 of a sequence validator 6 and a second arming signal is applied to a second input 7 of the sequence validator 6. The sequence validator is latched to only generate an arming instruction at 8 when an arming signal is received at both the first and second inputs and in the correct order. If the arming signal on the second input 7 arrives before or simultaneously with that on the first input 5 then no arming instruction signal is generated. FIG. 2 shows the first and second arming signals at 2(a) and 2(b) respectively when they arrive in the correct sequence at the validator 6.

[0022] The first arming signal is also applied to a first static FET switch 9 to close it and complete that part of the circuit. Similarly, the second arming signal is also applied to a second FET switch 10 to complete another part of the circuit. In the absence of an arming signal, the relevant static FET switch remains open, providing a safety break in the circuit and preventing the EFI detonator 1 from being activated.

[0023] The arming instruction from the sequence validator 6 is applied to a dynamic pulse generator 11. On receipt of the arming instruction, the dynamic pulse generator 11 starts to produce a series of pulses, shown at FIG. 2 (c) and continues to generate pulses providing the arming instruction is present at the sequence validator output 8. The series of pulses is applied to a dynamic FET switch 12 and also to a pulse counter 13. The dynamic FET switch 12 repeatedly opens and closes in response to the received pulses. This causes the low voltage capacitor bank 4 to discharge via the primary winding of a transformer 14 at a frequency set by the pulse frequency with a typical frequency of operation of between 100 kHz and 1 MHz. The secondary winding of the transformer 14 is connected via a rectifier 15 across a high voltage capacitor 16 such that the charge on the high voltage capacitor 16 builds as shown in FIG. 2(d). The use of low voltage storage capacitors of capacitor bank 4 enable extremely high local peak current to be achieved through the transformer 14 and subsequent rapid charging of the high voltage capacitor 16. The low voltage capacitor bank capacitance is in the order of a few thousand micro-Farads (or a few milli-Farads) and the peak current delivered during charging is in the order of a few hundred amps. The dynamic pulse generator 11, dynamic FET switch 12 and transformer 14 can be considered to form a high voltage converter circuit which may operate in a high frequency mode, tuned for efficient conversion through the high voltage transformer 14.

[0024] If either or both of the first and second arming signals are removed, the sequence validator 6 ceases to provide an arming instruction to the dynamic pulse generator 11 which no longer generates pulses and the arming procedure is thus halted.

[0025] The pulse counter 13 counts the number of pulses generated by the dynamic pulse generator 11. When a pre-determined number of pulses has been counted by the pulse counter 13, a trigger condition is reached. The trigger condition thus represents a fixed time period from when the arming instruction is received by the dynamic pulse generator 11. It also is indicative of the number of times the dynamic FET switch 12 has operated and thus the amount of charge discharged through the primary winding of the transformer 14 and accumulated at the high voltage capacitor 16. When the trigger condition is reached, the pulse counter 13 generates a trigger signal shown at FIG. 2 (e). The trigger signal is applied to a trigger circuit 17 which in response closes a switch 18, causing the high voltage capacitor 16 to be discharged through the EFI detonator 1 to activate it, as shown at FIG. 2(e). The trigger signal is thus generated automatically after a predetermined time from receipt of the arming instruction and requires no separate external input. Due to the relatively short period of time that is taken to accumulate sufficient energy to fire reliably, it is not necessary to start the arming sequence until firing is required.

[0026] FIG. 3 provides a comparison in general terms of the operating stages of a prior conventional arrangement, and that of the arrangement shown in FIG. 1. In the conventional arrangement shown at FIG. 3(a), following application of power, there is a first safety break or switch which must be activated before arming can be initiated. During this period, the system is considered to be safe. When an arming signal is received, a second safety break must be activated to allow arming to begin and charge is built up in the system. During arming, the system is not deemed safe and the system is then held in an armed state without any further safety breaks until and if a separate firing signal is received. The system may thus be held in an unsafe condition for a relatively long time and indeed, the firing signal may never be received. In contrast, the arrangement shown in FIG. 1, as shown at FIG. 3(b), remains in a safe state until an arming signal is received. The second safety break is activated at the same time as arming is begun and then firing occurs automatically a known time thereafter. Thus it provides a rapid arming and firing circuit that essentially eliminates the armed state but instead transitions rapidly from the safe state to the fired state, maintaining the safe state for almost all of a mission. Firing/arming times of less than 1 ms are readily achievable. A firing arrangement in accordance with the invention also has the advantage of an extremely consistent activation time, independent of temperature variation. Furthermore, the system can be immediately returned to the safe state if any safety breaks are removed as no charge is accumulated in the high voltage capacitor prior to the arming instruction.

[0027] In another firing arrangement, the pulse counter 13 is omitted. A voltage monitor is applied across the high voltage capacitor 16, shown as a broken line at 19, and the trigger condition is when the voltage and hence charge exceeds a pre-determined threshold value. In this embodiment, the trigger signal is also automatically generated following receipt of an arming instruction.

[0028] The firing arrangement of FIG. 1 is used with an EFI detonator but could be used with, for example, a pyrotechnic ignitor, bridge wire detonator or any electro-explosive device.

[0029] Previous approaches to arming and firing generally involve a separate arming phase after which the device is held in the armed state until required to fire. FIG. 2 shows part of the arming circuit that takes an input to cause arming and a separate input to cause firing. A separate circuit is used to control provide a fire pulse after a fixed number of pulses have been applied to the arming input. This achieves firing after a consistent time period. Due to the relatively short period of time that is taken to accumulate sufficient energy to fire reliably, it is not necessary to start the arming sequence until firing is required. It enables the system to remain in the safe state for the majority of the operational sequence. This is particularly advantageous for systems that have a long operational life during which the system must be ready to fire at short notice. The advantage is both for safety of the system and also reliability of the high voltage circuit as it spends almost all of its operational life in the dormant, unpowered state.

[0030] The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.