AU622871B2 - An ignition system and a method for the initiation thereof - Google Patents

Description

Signaure.

To: THE COMMISSIONER OF PATENTS.

Ber4--'3nsson i;I AU-AI-22642/881 WORLD INTELLECTUAL PROPERTY ORGANIZATION International Bureau 0

PCT

INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT) (51) International Patent Classification 4 (11) International Publication Number: WO 89/ 01601 F42C 11/06, C06C 5/04 Al (43) International Publication Date: 23 February 1989 (23.02.89) (21) International Application Number: PCT/SE88/00409 Published With international search report.

(22) International Filing Date: 12 August 1988 (12.08.88) In English translation (filed in Swedish).

(31) Priority Application Number: 8703157-1 (32) Priority Date: 14 August 1987 (14.08.87) 6 2 2 8 (33) Priority Country: SE A.O.J.P. 27 APR 1989 (71X72) Applicant and Inventor: JONSSON, Bert [SE/SE]; 7 APR 1989 Sk6rdevagen 42, S-713 00 Nora (SE).

(74) Agent: FALK, Bengt; Nobel Corporate Services, S-691 AUSTRAIAN 84 Karlskoga

AUSTRALIAN

-9 MAi 1989 (81) Designated States: AU, BR, DE, FI, US.

PATENT OFFICE (54) Title: AN IGNITION SYSTEM AND A METHOD FOR THE INITIATION THEREOF (57) Abstract The disclosure relates to a method for initiating, i.e. starting, an electronically delayed-action ignition system for explosive charges, the system being entirely protected against disturbance by electromagnetic waves. According to the invention, at least a part of the pressure, heat or light energy generated from, for example, a detonating fuze upon a primary detonation, is utilized for starting the time igniter which in turn after a preset time-lag initiates the explosive main charge. The present invention also includes devices adapted thereto including, for instance, photocells electrolytes (11) or piezoelectric transducers r WO 89/01601 PCT/SE88/00409 TITLE OF INVENTION: AN IGNITION SYSTEM AND A METHOD FOR THE INITIATION THEREOF TECHNICAL FIELD The present invention relates to a method of initiating, i.e.

starting, an electronically delayed ignition system for explosive charges, the ignition system being entirely protected from disturbance by electromagnetic waves. The present invention also relates to an ignition system functioning in accordance therewith and being of a specific design.

BACKGROUND ART In the employment of electric ignition systems for initiating explosive charges, nearby radio and radar stations as well as other sources of radiation constitute potential risks, since they could give rise to sufficiently powerful induced currents in the ignition wiring to cause accidental initiation of the charges.

This is a serious drawback which is inherent in all electric ignition systems and which has entailed that, in electrical ignition systems intended for military applications, it has been necessary to incorporate complex anti-disturbance systems, since, in field-service use it cannot be anticipated as in civilian blasting operations using electrical ignition systems that all use of radio, radar or other radiation transmitters in the vicinity of the explosion site can be prevented.

WO 89/01601 PCT/SE88/00409 2 It has previously been common for electrically initiated blasting cartridges (blasting caps) also to be provided when necessary with pyrotechnical delay charges of conventional type.

However, electronic delayed action igniters with very good performance as regards precise and well-known ignition intervals and small outside dimensions have recently become available at highly attractive prices.

These electronic delayed action igniters constitute a further argument in favour of choosing an electric instead of a nonelectric ignition system in the initiation of explosive charges.

However, as soon as an electric ignition system is employed in which the electric wires are of sufficient length to run the risk of induced currents in the wires, there will be the additional requirement of accurate and therefore also complex and expensive disturbance shielding of the entire ignition system.

Consequently, it would in many cases be desirable to have access to a non-electric ignition system which could offer the same exact time lag as the electronic time igniters and which could never be achieved using even the best pyrotechnical delay charge.

SUMMARY OF THE INVENTION The present invention relates to a disturbance-shielded, electronically delayed ignition system for explosive charges in which the ignition system is initiated by detonation, or high-energy combustion, for instance of a pyrotechnical charge or the like, triggered in the immediate vicinity of the ignition system. According to a primary variant of the present invention, the initiating effect on the ignition system is achieved by means of a detonating fuze fired in its vicinity. The effect initiating the ignition system may then, in accordance with the secondary variant of the present invention, be amplified by or replaced by, for instance, a more slowly burning pyrotechnical charge.

According to the present invention, at least a portion of the energy generated on detonation or combustion is converted into electric current of sufficient power to energize an electronic WO 89/01601 PCT/SE88/00409 time igniter which, in turn, initiates the desired detonation after a preset interval.

By employing a detonating fuze such as a pentyl fuze or a low-energy fuze of the type which consists of a tube interiorly coated with a primary explosive for initiating electrically delayed the igniter, access will thus be created according to the present invention to an ignition system which is entirely free of disturbance in respect of induced currents in the ignition system, at the same time as the electronic delayed action with its extraordinarily high precision gives an ignition precision in time which today is impossible to achieve using exclusively pyrotechnical igniters.

Detonating fuzes of the pentyl fuze type, or the low-energy fuze briefly described in the foregoing will, on firing, always give rise to a greater or lesser extent both to a shock wave and to heat and light generation. According to the present invention, all of these forms of energy may be utilized for initiating different variants of the igniter designed according to the present invention. The difference between these igniter variants lies in which of the energy forms generated by the detonating fuze is utilized for initiating the electronic time igniter, and how this initiation is implemented. As already intimated, other types of detonations or combustion giving rise to sufficient shock waves, light or heat generation may also be employed for initiation of the ignition system according to the present invention.

According to a first variant embodiment of the invention, use is made of that shock wave which, for instance, a detonating fuze generates to influence a proximally disposed piezoelectric transducer to generate an electric pulse which may charge a capacitor connected to the transducer to a sufficient voltage in order that this, in turn, discharge across an electronic delayedaction igniter interconnected therewith, the igniter, after a preset delay interval initiating, via very short electric wires, a conventional electric igniter. All of the components included in

A

WO 89/01601 PCT/SE88/00409 4 this igniter variant are of per se known type. Moreover, state-of-the-art technology makes it possible to miniaturize all 4 the components, with the possible exception of the electric igniter. Since the miniaturized components require no other I external supply of energy than the shock wave which is to activate the piezoelectric transducer, the entire igniter may advantageously be moulded in some suitable plastic and be given a practicable outer configuration with, for example, a tunnel or groove for guiding a detonating fuze to sufficient proximity to the piezoelectric transducer. The electric igniter and its detonator (if any) may either be incorporated together with the other components in the thus obtained igniter body or be connected, in a conventional manner, with conductors which are sufficiently short that they could not be influenced induced currents.

The above generally described igniter contains only very short electric conductors which may advantageously be grouped on a circuit board. This means that the risk of induced currents in the electric conductors may be disregarded. Consequently, the igniter according to the present invention will be completely free of disturbance in respect of electromagnetic waves etc. from nearby radio or radar transmitters.

According to a second variant of the present invention, use is made of the heat generated by the detonating fuze to melt down, and thereby start, current emission from an electrolyte of the type which only emits current when the electrolyte is in the molten state but not when it is in the solid state. The current emitted by the molten electrolyte is now utilized to initiate the same type of electronic time igniter as that employed in conjunction with the first variant of the present invention. Also according to this second variant of the present invention, the entire igniter may be of extremely compact form, with the whole of the ignition system well encapsulated and entirely protected from disturbance in respect of electromagnetic waves. When a detonating fuze is utilized to.emit heat, the effect thereof may be amplified by an extra pyrotechnical charge.

WOv 89/01601 PCT/SE88/00409 The detonating fuze is suitably led through a channel or a groove through the igniter separated from the electrolyte by, for instance, a metal wall of good thermal conductivity and suitably also good thermal storage capacity so that the heat generated on detonation of the fuze may be utilized to maximum benefit in the electrolyte.

According to a third variant of the present invention, use is made of the light generated on detonation of the detonating fuze to act on a photocell which, in turn, starts an electronic time igniter of the same type as was employed in the previouslymentioned variants of the present invention. In this variant of the present invention, the needle flame formed on detonation of the fuze possibly amplified by an extra pyrotechnical charge may also be used to burn off a safety layer which wholly screens the photocell from all surrounding light up to the detonation of the fuze. The safety layer may, for instance, consist of an aluminium coating on a glass panel or glass lens which screens off the photocell and the electronic time igniter from the detonating fuze. In this variant of the present invention, use may advantageously be made of a detonating low-energy fuze for the initiation.

Such a low-energy fuze can thus consist of a plastic tube interiorly coated with minor amounts of primary explosive, for example of the octogen type. In such low-energy fuzes as are started by means of a normal detonating high-energy fuze, for example a pentyl fuze, the detonation wave follows the explosive coating along the interior of the tube. In this third variant of the present invention, such a tubular low-energy fuze could thus be terminated by a conventional pyrotechnical charge which is defined by an aluminium-foil coated glass lens behind which the photocell and the electronic time igniter connected therewith are placed. Finally, the time igniter is connected by suitable means to a blasting cap or detonator of conventional type.

WO 89/01601 PCT/SE88/00409 b BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS The present invention has been defined in the appended Claims and will now be described further with particular reference to the accompanying Drawings. In the accompanying Drawings: Fig. 1 shows a schematic section taken through a shock-wave initiated igniter variant; Fig. 2 is a schematic section of a thermally initiated igniter variant; and Fig. 3 is a schematic section of a light-initiated igniter variant.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring to the Drawings, the igniters illustrated in Figs.

I, 2 and 3, which are elaborated in accordance with the three different main variants of the present invention, all include a number of identical components and these have all been given corresponding reference numerals.

All igniters thus include an electronic time igniter 1. This, in turn, is disposed, after a preset time interval on being itself initiated, to initiate the final ignition function. In the Figures, this final ignition function is marked by an electric ignition bead 2 supplied via leads 3 and 4. The final ignition function may, however, be elaborated in any other per se known manner, or even in accordance with hitherto unknown ignition technol.ogy, since this does not form an embodied part of the present invention.

The ignition bead 2 shown in the Figures may, for example, be combined with a detonator of per se known type. The time igniter, Sin turn, is started by a current which is supplied to the time igniter via leads 5 and 6 from a transducer which is capable of transforming at least parts of the energy generated on detonation in the vicinity of the transducer into an electric current.

According to the variant shown in Fig. 1, the transducer which is to convert energy from the detonation into electric current is a piezoelectric transducer 8 disposed close to a detonatable fuze 7. A protective foil 9 is disposed between the ii WO 89/01601 PCT/SE88/00409 transducer 8 and the fuze 7. When the fuze 7 is detonated, the transducer 8 receives a shock wave that generates an electric pulse which, in turn, charges a capacitor 10 which discharges across the time igniter 1, thereby starting the igniter. When the delay interval preprogrammed into the time igniter has expired, the time igniter initiates the ignition function 2. When the transducer is initiated by a detonatable fuze, this may either be drawn transversally past the transducer as shown in Fig. 1, or endwise to the transducer as in Fig. 2. Other detonating charges may also be employed to initiate the transducer.

In the variant illustrated in Fig. 2, use is made of the heat which is generated upon detonation of the fuze 7 to melt down an electrolyte disposed near the fuze 7, the electrolyte being of the type which emits battery current only in the molten state but not in its solid state at normal temperature. The electrolyte is designated 11. It is separated from the fuze by a protective wall 9 so as not to be burst and spread upon detonation of the fuze.

From the electrolyte, two electric leads 5 and 6 run to the electronic clock 1. From the time igniter 1 and start thereof, all components and function are identical with the system according to Fig. 1.

In the variant of the present invention illustrated in Fig.

3, the time igniter 1 is started by a photocell 12 which is connected to the electronic time igniter 1 by means of leads 5 and 6. A protective lens of glass 13 is disposed between the photocell and the detonating fuze. This protective lens is, in turn, coated with a safety layer facing towards the fuze and consisting of a material which may be burnt off, in this particular case, an aluminium foil 14. This thus constitutes a safety function which effectively prevents all light from reaching the photocell 12. In the embodiment shown in Fig. 3, use is made of a detonating lowenergy fuze of the type which consists of a plastic tube 7a interiorly coated with a primary explosive charge 15. Since this does not possess sufficient combustion energy to burn off the protective layer 14, a special pyrotechnical charge 16 has been WO-89/01601 PCT/SE88/00409 disposed in conjunction with the protective layer. The pyrotechnical charge 16 also serves to provide a longer light impulse so that the photocell will have time to react. The low-energy fuze 7a may be replaced by a pentyl fuze of normal quality.

When the fuze 7a detonates and the pyrotechnical charge 16 is combusted, the protective layer 14 will be combusted at the same time, the light generated by the flame influencing the photocell 12 which, via leads 5 and 6, starts the electronic time igniter which, after the preprogrammed time lag, thus initiates the ignition function 2 via ignition leads 3 and 4.

Claims (7)

1. An apparatus for detonating at least one explosive charge at a given location in response to an initiation at a remote location and after a preselected time delay, said apparatus comprising: a) non-electrical initiation means comprising means for generating a non- electrical energy input by detonation or by pyrotechnical combustion at said given location and initiated at said remote location; and b) an electrical igniting nmeans also provided at said given location and responsive to said initiation means for time-delayed ignition of said explosive charge, said electrical igniting means including: 1 transducer means for generating an electrical output signal in response to said non-electrical energy input; 2) an electronic variable time delay means in close proximity to said transducer means for setting a preselected time delay and for generating in resporse to said electrical output signal from said transducer means a time delayed electrical output signal whose time delay corresponds to said preselected time delay value and is substantially independent of the magnitude of said electrical input signal from said transducer means; co o:i 3) igniter means also in close proximity to said electronic time delay means and responsive to the electrical output signal from said electronic time delay means for initiating the ignition of said explosive charge; and S4 a first pair of short electrical conductors for interconnecting the output of said transducer means with the input of said electronic time delay means and a second pair of short electrical conductors for interconnecting the output of said electronic time delay means with the input of the igniter means, said i first and second pair of conductors constituting the only electrical conductors in said detonating apparatus; o. ~whereby the initiation of the explosive charge requires the transmission S. of electronic signals over said short pairs of electrical conductors, said short pairs of electrical conductors thereby minimizing the possibility of a spurious signal being generated in said short pairs of electrical conductors which could result in the inadvertent detonation of the explosive charge.

2. An apparatus for detonating at least one explosive charge at a given location in response to an initiation at a remote location and after a preselected time delay, said apparatus comprising: a) non-electrical initiation means comprising means for generating and supplying non-electrical energy input by detonation or pyrotechnical combustion at said given location upon initiation at said remote location; and b) an electrical igniting means also provided at said given location for time- delayed ignition of said explosive charge responsive to said initiation means including: 1 transducer means for generating an electrical output signal in response to said non-electrical energy input; 2 an electronic variable time delay means in close proximity to said transducer means for setting a preselected time delay and for generating in response to said electrical output signal from said transducer means a time delayed electrical output signal whose time delay corresponds to said preselected time delay value and is substantially independent of the magnitude of said electrical input signal from said transducer means; 3) igniter means also in close proximity to said electronic time delay means and responsive to the electrical output signal from said electronic time delay means for initiating the ignition of said explosive charge; 4 a first pair of short electrical conductors for interconnecting the output of said transducer means with the input of said electronic time delay means and a second pair of short electrical conductors for interconnecting the output of said electronic time delay means with the input of the igniter means, said first and second pair of conductors constituting the only electrical conductors in said detonating apparatus, thereby minimising the possibility of a spurious signal being generated in said short pair of electrical conductors which could result in the inadvertent detonation of the explosive charge; and 5) a passage means for said means for supplying non-electrical energy :.:input provided in connection with said electrical igniting means for transmitting said non-electrical energy input past said electrical igniting means to further detonating apparatus.

3. An apparatus for detonation according to claim 1, wherein said means for supplying non-electrical energy input includes a detonating cord and wherein a passage is provided in S0 t said electrical igniting means for running said detonation cord past said electrical igniting means whereby said non-electric energy input is supplied to a further detonating apparatus.

4. An apparatus for detonation according to claim 3, wherein said means for supplying non-electrical energy input includes a plastic tube interiorly coated with a primary explosive and wherein a passage is provided in said electrical igniting means for running said detonation cord past said electrical igniting means, whereby said non-electrical energy input is supplied to a further detonating apparatus.

A method for detonating at least one explosive charge at a given location in response to an initiation at a remote location and after a preselected time delay, said method comprising the steps of: 1 generating a non-electrical energy input by detonation or by pyrotechnical combustion at said given location, upon initiation at said remote location; T0 Ii., 2) generating an electrical output signal in response to said non-electrical energy input by transducer means also provided at said given location; 3) setting a preselected time delay and generating, in response to said electrical output signal from said transducer means, a time delayed electrical output signal by an electronic variable time delay means in close proximity to said transducer means, said time delay corresponding to said preselected time delay value and being substantially independent of the magnitude of said electrical input signal from said transducer means; 4) initiating the ignition of said explosive charge by igniter means also in close prcximity to said electronic time delay means in response to the electrical output signal from said electronic time delay means; transmitting said electrical signals over a first pair of short electrical conductors between the output of said transducer means and the input of said electronic time delay means and over a second pair of short electrical conductors between the output of said electronic time delay means and the input of the igniter means, said first and second pair of short electrical conductors constituting the only electrical conductors in said detonating apparatus, whereby minimizing the possibility of a spurious signal being generated in said pairs of electrical conductors which could result in the inadvertent detonation of the explosive charge; and 6) transmitting said non-electrical energy input past said transducer means 0 through a passage formed in connection with said transducer means to another Sdetonating apparatus.

6. An apparatus for detonating at least one explosive charge at a given location in o• response to an initiation at a remote location and after a preselected time delay, substantially as hereinbefore described with reference to the accompanying drawings.

7. A method for detonating at least one explosive charge at a given location in response to an initiation at a remote location and after a preselected time delay, substantially as hereinbefore described with reference to the accompanying drawings. DATED THIS 10TH DAY OF FEBRUARY, 1992. BERT JONSSON WATERMARK PATENT TRADEMARK ATTORNEYS FLOOR 2, "THE ATRIUM", 290 BURWOOD ROAD, HAWTHORN, VIC 3122. ORL4i