GB2195420A - Detonation fuzes - Google Patents

Abstract

A detonation fuze comprises a detonation energiser element 27, e.g., the bridgewire of a detonator 28, an electrical power source 20, a control circuit 24,25,31 for supplying. when energised, electric current from the power source through the detonation energiser element, a first control switch 21 connected to the power source in a circuit in parallel with the control circuit, a second control switch 23 connected to the power source in a circuit in parallel with the first control switch and the first control circuit, a first timer (3) for producing a first timing signal arranged to control in operation the state of the first control switch 21 and a second timer (5) for producing a second timing signal arranged to control in operation the state of the second control switch 23, and switches and the control circuit being constructed and arranged such that the capacitor 25 in the control circuit is energised by the power source when both the first and second control switches are switched by the first and second timing signals from a conducting state into a blocking state. The capacitor discharges through the energiser element 27 when the second control switch 23 reverts to a conducting condition in response to a third timing signal. <IMAGE>

Description

SPECIFICATION Detonation fuzes The present invention relates to detonation fuzes.

Detonation fuzes incorporating a timer arranged to produce a trigger signal to activate the fuze after a given period of time are well known. The timer and activation systems in such fuzes generally comprise electronic circuitry and in prior art fuzes such circuitry can be damaged, e.g. by accidental mechanical shock, and the fuze can thereby be activated prematurely if the timer prematurely triggers the activation system.

According to the present invention a detonation fuze comprises a detonation energiser element, an electrical power source, a control circuit for supplying, when energised, electric current from the power source through the detonation energiser element, a first control switch connected to the power source in a circuit in parallel with the control circuit, a second control switch connected to the power source in a circuit in parallel with the first control switch and the first control circuit, a first timer for producing a first timing signal arranged to control in operation the state of the first control switch and a second timer for producing a second timing signal arranged to control in operation the state of the second control switch, the switches and the control circuit being constructed and arranged such that the control circuit is energised by the power source when both the first and second control switches are switched by the first and second timing signals from a conducting state into a blocking state.

The detonation energiser element may for example be a detonator bridgewire filament.

The fuze according to the present invention has the advantage compared with known systems that the control circuit is energised only when both the first and second control switches have been switched to provide energisation of the conrol circuit thereby improving the inherent safety of the system. If one of the control switches is switched prematurely the fuzes will not be activated since its operation requires switching of both switches.

The control circuit preferably comprises a capacitor which is arranged so as to be charged in operation when the first and second control switches in parallel with it are both switched into their blocking state. The capacitor may subsequently be discharged through the detonation energiser element by returning one of the first and second switches to its conducting state.

The first and second control switches may be transistor switches, e.g. field effect transistors. For example, the first and second timing signals may be signals which are respectively applied to the gates of field effect transistors comprising the first and second switches.

The first timing signal may comprise a voltage which falls from a high level to a low level after a pre-determined time causing switching of state of the first control switch.

The second timing signal may comprise a voltage which falls from a high level to a low level coinciding with the low level of the first timing signal after a pre-determined time causing switching of state of the second control switch. Preferably, the fall of the second timing signal takes place after the fall of the first timing signal the delay preferably being 0.1 to 1 second, preferably 0.1 to 0.3 second, and being provided to differentiate the two signals for safety reasons. Where the control circuit includes a capacitor the second timer signal may comprise 'a rise in voltage after the fall of the second timing signal. This rise may be a leading edge of a square wave of a part of a square-wave function provided after the initial fall and causes the state of the second switch to be further switched into a conducting state.

The first and second timing signals may be provided by first and second programmable timing chips, each incorporating a non-volatile memory, which may be pre-programmed by an electronic fuze setter, an external control device which provides basic input signals to the memories of the timing chips controlling the respective times when the timing chips will produce an output to change the state of the first and second control switches respectively. The first and second timing chips may be set to start timing when a voltage is sensed to be received from an internal voltage source. The voltage source, which may be the same voltage source as the power source arranged to be applied to the detonation energiser element via the control circuit, may be one which is brought into operation by firing of a projectile in which the fuze is incorporated.Such a source may, for example, be an energiser in which an ampoule is perforated upon firing of the projectile allowing electrolyte to come into contact with electrodes to provide an output potential difference, e.g. as described in UK Patent No. 2059672B.

Preferably, the fuze according to the present invention incorporates an upcounter which is arranged to convert the signals stored in the memories of the first and second timers, n1 and n2 respectively, when the timers are energised to start timing, into signals which are of the form M-n1, M-n2, where M is an arbitrary maximum. This ensures that any leakage of information from the stored signals does not cause premature changes to the output signal of the timers and premature activation of the detonator caused thereby.

An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a schematic block circuit diagram of a projectile fuze system; Figure 2 is a voltage waveform (voltage v time graph) of the output of timers incorporated in the system shown in Fig. 1.

Figure 3 is a schematic circuit diagram of an activating system incorporated in the system shown in Fig. 1.

In Fig. 1 a fuze electronics package, e.g.

circuit board, indicated by a broken line 1 comprises a first timer chip 3 and a second timer chip 5 mounted on a common substrate 8. The timer chips 3 and 5 are set prior to firing of the projectile incorporating the fuze by data from an external fuze setter 7 applied via a data interface 9. The power required to provide signals to set the timer chips 3, 5 is provided by an external power source 11 which may be part of the setter 7.

The timer chips 3 and 5 which incorporate non-volatile read/write memories 4, 6 respectively are set by recording in the memories 4, 6 different digital signals which carry information concerning the respective times when the timer chips 3, 5 are required to produce a change in the state of their output signals.

When the timer chips 3, 5 have been set by the setter 7 the setter 7 is arranged to read out the signals which have been recorded in the timer chips 3, 5. Ifthe recorded signals are outside a pre-determined tolerance level with regard to the required signals then the recording procedure is repeated or the malfunctioning causing the error is found and rectified thereby allowing the timer chips -3, 5 to be correctly set.

When the projectile incorporating the fuze is fired power is obtained from an internal power source 20 (see Fig. 1), e.g. by the breaking of an electrolyte-containing ampoule in an energiser as described in UK Patent No.

GB2059672B.

This is detected by a detector 13 which triggers up counters 10, 12 within the timer chips 3, 5 to start counting.

When the timer chips 3, 5 are first triggered in this way the contents of their non-volatile memories 4, 6 are transferred into upcounters 10, 12 respectively. The numbers M-n1 and M-n2 represent the times required to be counted by the upcounters 10, 12 of the timer chips 3, 5.

When the numbers respectively counted by eah of the upcounters 10, 12 of the timer chips 3, 5 reach those stored in the memories 4, 6 (after conversion by the upcounters 14, 16 as described above) the chips 3, 5 are triggered to produce a change in output which is supplied to a firing circuit 19.

The respective outputs from the timer chips 3, 5 are shown in Fig. 2. The output from the timer chip 3 is essentially at a high (typically 15V) level until it is triggered to change state at a time T1 after which it is at a low level (OV relative to the previous level). The output from the timer chip 5 is aiso at a high (typically 15V) level until it is triggered after a time T2 to change to a square wave function initially by falling to a low level. The output first returns to its high level as part of the square wave function at a time T3.

As shown in Fig. 3 the firing circuit 19 comprises a first transistor switch 21 of the MOSFET type (metal oxide semiconductor field effect transistor) and a second MOSFET switch 23 in parallel with the switch 21. The switches 21, 23 are connected across a capacitor 25 which is in a circuit containing the energiser element 27 of a detonator 28. The voltage from the power source 20, typically about 26V, is applied through the parallel arrangement of the switches 21, 23 and capacitor 25 to ground. The outputs of the timer chips 3, 5 are'applied to the gates of the switches 21, 23 respectively. When the outputs of the timer chips 3, 5 are both in their original high level state the switches 21, 23 are both conducting and prevent any charging of the capacitor 25.However, when the outputs of both of the timer chips 3, 5 have changed state to their low level state the switches 21, 23 are both switched to their blocking or high impedance state and the capacitor 25 is allowed to charge. When the output of the timer chip 5 rises to a high level once more at the time T3 the switch 23 is switched to a conducting state causing the capacitor 25 to discharge through the detonator energiser element 27 thereby activating its associated detonator 28. A rectifying diode 31 prevents activation of the element 27 directly via the power source 20.

The times T1 and T2 are typically 0.2 sec apart and the times T2 and T3 are typically 0.2 sec apart.

The signals recorded in the memories 4, 6 may incorporate a correction factor to take account of the delay, typically 10 msec, between instant of firing of the projectile and provision of an output voltage by the power source 20.

Claims (11)

1. A detonation fuze comprising a detonation energiser element, an electrical power source, a control circuit for supplying, when energised, electric current from the power source through the detonation energiser element, a first control switch connected to the power source in a circuit in parallel with the control circuit, a second control switch connected to the power source in a circuit in parallel with the first control switch and the first control circuit, a first timer for producing a first timing signal arranged to control in operation the state of the first control switch and a second timer for producing a second timing signal arranged to control in operation the state of the second control switch, the switches and the control circuit being constructed and arranged such that the control circuit is energised by the power source when both the first and second control switches are switched by the first and second timing signals from a conducting state into a blocking state.

2. A detonation fuze as claimed in claim 1 and wherein the detonation energiser element is a detonator bridgewire filament.

3. A- detonation fuze as claimed in claim 1 or claim 2 and wherein the conrol circuit comprises a capacitor which is arranged so as to be charged in operation when the first and second control switches which are in parallel with it are both switched into their blocking state, the capacitor subsequently being discharged through the detonation energiser element by returning one of the first and second switches to its conducting state.

4. A detonation fuze as claimed in any one of the preceding claims and wherein the first and second control switches comprise field effect transistors, the first and second timing signals being signals which are respectively applied to the gates of the field effect transistors comprising the first and second switches.

5. A detonation fuze as claimed in any one of the preceding claims and wherein the first timing signal comprise a voltage which falls from a high level to a low level after a predetermined time causing switching of state of the first control switch and the second timing signal comprises a voltage which falls from a high level to a low level coinciding with the low level of the first timing signal after a predetermined time causing switching state of the second control switch.

6. A detonation fuze as claimed in claim 5 and wherein the fall of the second timing signal takes place after the fall of the first timing signal the delay being 0.1 to 1 second.

7. A detonator fuze as claimed in any one of the preceding claims and wherein the second timing signal comprises a rise in voltage after the fall of the second timing signals and wherein the said rise is a leading edge of a square wave of a part of a square-wave function provided after the initial fall and causes the state of the second switch to be further switched into a conducting state.

8. A detonation fuze as claimed in any one of the preceding claims and wherein the first and second timing signals are provided by first and second programmable timing chips, each incorporating a non-volatile memory, which may be pre-programmed by an electronic fuze setter, an external control device which provides basic input signals to the memories of the timing chips controlling the respective times when the timing chips will produce an output to change the state of the first and second control switches respectively.

9. A fuze as claimed in any one of the preceding claims and wherein the first and second timing chips may be set to start timing when a voltage is sensed to be received from an internal voltage source which is brought into operation by firing of a projectile in which the fuze is incorporated.

10. A fuze as claimed in any one of the preceding claims and wherein the signals stored in the memories of the first and second timers are of the form M-n1, M-n2, where M is an arbitrary maximum and n1 and n2 represent the times at which the first and second timers respectively are required to function.

11. A detonation fuze as claimed in claim 1 and substantially as hereinbefore described with reference to the accompanying drawings.