Note: Descriptions are shown in the official language in which they were submitted.
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TITLE: EL CTRO -OPTICAL DETONATOR.
FIELD OF INVENTION
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This invention is concerned with a detonator for explosive composit- . -
-ions and in particular is concerned with a detonator which employes as - ;~
a fail safe device , an opti~ally actuated switching means to close an
electrical energizing circuit.
Electrically actuated detonators comprising a thermo-resistive element
coated with an initiating "flashing" pyrotechnic compound are well known.
Such devices are inexpensive to manufacture and are known to be extremely
lO.reliable in use as well as relatively safe in storage and handling.
Electrical detonators have a major disadvantage in that they require
connection via electrically conductive cables to a remote detonating device
providing a source of electrical energy. Accidental explosions have been
attributed to spurious electrical currents induced or conducted in the
electrical conductors by electrical machinery, static earth charges,
lightning, high voltage transmission line corona discharge, radio frequ-
-ency transmission and the like.
In an endeavour to overcome the dangers associated with conventional
electrically actuated detonators of the type described above, various
20.non-electric systems have been proposed.
One type of non-electrically actuated detonator described in the
known patent specifications relating to blasting detonators systems
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employs a tubular lead, the inner surface of which i5 coated with a
deflagrating material. When the deflagrating material is fired at a
remote end of the tubular lead, a shock wave is propagated down the
interior of the tubular lead to detonate the explosive composite of the
detonator. A non-electrical blssting initiating system of this type is
described in United States patent number 4,757,764.
While generally effective for its purpose and relatively safe
in use such non-electric initiating systems have been the cause of a
number of large blast project failures and are limited to a short shelf
life. lhe system is complicated to systemize with a shock wave speed ot
1.8 kilometers per second compared to 300,000 kilometers per second for
optic initiation.
Swedish patent application number 8,503,595 describes a fibre-
optic ignition system for explos~e compositions wherein optical energy
is converted by a photo-voltaic cell into electrical energy. The elect-
rical energy is amplified and stored in a capacitor for selective release
via electrical conductors to a conventional electric detonator. While
this system avoids the necessity for long electrical conductors between
tho dutonator and the remote initiating position (with the attendant
2û riaks described above) the requirement of expensive fibre-optic cables
capable of transmitting a large amount of energy to charge the capacitor,
with its ability to hold the full charge for only a short period. The
firing of the detonator would require a further signal from the remote
triggering station.
The formation of a continuous electrically conductive circuit
between the electrical switching means of the optical initiating device
and the detonator is considered to pose an unacceptable risk of premature
detonation from spurious induced or conductive currents in the electrical
conductors. 2
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United States Patent Numbers 3812783,4403143 and 3408937 are illust-
-rative of non-electric blast initiation systems employing high intensity
laser radiation transmitted via an optical fire cable to a detonating
device.
Prior art blast initiating systems employing Laser energy as a sole
energizing source are relatively safe in use but currently uneconomical
in use and of dubious reliability.
It is an aim of the present invention to overcome or alleviate the
problems of prior art blast initiation systems and to provide a safe,
10. reliable and economic explosives detonator and initiation system therefore.
BROAD DESCRIPTION OF THE INVENTION
According to one aspect of the invention there is provided a deton-
-ator comprising:-
a hollow body portion containing adjacent a closed end thereof
a quantity of explosive material;
a electrical resistance element spaced from a said quantity of
explosive material, which may be combined with an optional deflagrating
chemical time-delay charge to fire the main detonating charge; said elect-
-rical resistance element having associated therewith a quantity af therm-
20.-ally energizable initiating pyrotechnic material; and, a switching means
responsive to electromagnetic radiation.
a contained primary battery means as the electrical energizing
source.
a terminal socket located wlthin the proximal end of the deton-
-ator hollow body portion to securely accept the terminal plug attached
to the distal end of the fibreoptic light guide cable.
Switching means responsive to electromagnetic radiation is coupled
with a primary battery means and the electrical resistance element .
Said switching means when actuated by the correct radiation signal closes
30-an electrical circuit associated with said resistance element and primary
battery means whereby the pyrotechnic fusehead is thermally ignited.
Preferably said electromagnetic radiation responsive switching means
comprises a photo-conductive device.
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DETAILED DESCRIPTION OF THE INVENTION.
In order that the invention may be more clearly understood ,refer-
-ence will now be made to a preferred embodiment illustrated in the
accompanying drawings. Figure 1 shows a typical embodiment of the device `
of the invention.
The drawings illustrate in cross-section a detonator l and portion
of a free end of a fibreoptic light guide 2, as a schematic projection.
Detonator 1 comprises a hollow body portion 3 having a closed distal
end 4 adjacent which is located a quantity of explosive chemical material
10. 5. Chemical time-delay deflagrating material 10 may be optionally incorp-
-orated adjacent to the detonating material 5.
A insulating means 9 supports the electrical resistance element 7
which is coated with a chemical deflagrating pyrotechnic material 8 of
the type commonly employed in prior art electric detonators to initiate
fusion of the detonating material 10 and 5.
Said electrical resistance element 7 coated with a thermally ignit-
-able pyrotechnic material 8 as the "fusehead",is spaced from a quantity
of chemical explosive material lO and 5 placed adjacent to closed end 4
of detonator l elongated body portion 3. Quantity of chemical explosive
20. material lO and 5 may consist of more than one part compounded as a quant-
-ity of deflagrating pyrotechnic chemical time-delay material lO placed
adjacent to a quantity of detonating chemical explosive material 5 ,said
quantity of deflagrating pyrotechnic chemical time-delay material lO
would be spaced from the pyrotechnic fusehead 8.
A primary battery means 20 contained adjacent to the electrical
resistance element 7 would provide the electrical energy source to power
the device. Activation of the circuit would occur when a electromagnetic
radiation signal sent down the fibreoptic light guide engaged within
the proximal end ll of the detonator casing 3 to impinge at 15 on an adj-
30. -acent placed photo-conducter device 16 such as a photo-diode or as a
photo-transister switching means responsive to electromagnetic radiation.
Said primary battery means 20 will have a energy capacity level suff-
-icient to heat the electrical resistance element 7 to provide thermal
energizing of the resistance element 7 chemical pyrotechnic coating 8 to
cause ignition of the adjacent explosive materials lO and 5 contained
within the detonator casing 3.
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Primary battery means 20 may have an isolating switch means 17
incorporated in the electric circuitry layout . Said switching means
would be separate and additional to the electromagnetic radiation respon-
-ive switching means.
A terminal socket placed within the mouth at the proximal end of the
elongated hollow body portion of the detonator casing is arranged to
accept the mating terminal plug encasing the distal end of the fibreoptic
light guide cable 24 .
Isolating switch means incorporated in the primary battery means 20
10. circuit may be located within the socket terminal 12 placed within the
proximal end 11 of the detonator casing 3.
Isolating switch 17 would be in the normallynopen~state and would be
"closed"by the insertion of the fibreoptic light guide cable terminal
plug 14 into the terminal socket 12 of the detonator.
The photo-conductor device 16 as the electromagnetic radiation respon-
-sive switching means is mounted within the hollow body portion 3 of the
detonator near its proximal end 12 adjacent to the rear of the terminal
socket 12 whereby the radiation sensing area 15 of the photo-conductor
switching means is in axial alignment with the optic fibres encased by
20. the terminal plug 14 of the light guide cable when inserted into said
terminal socket means 12 of the detonator.
In operation the photo- conducter device 16 of the detonator on
receiving an electromagnetic radiation signal from the external radiation
source by way of the connected fibreoptic light guide cable , triggers
the electromagnetic switching means to allow a conductive circuit to be
formed to pass an electric current from the primary battery means 20
through the electrical resistance element 7, thereby to ignite the thermal
pyrotechnic chemical coating 8 to fire the detonator .
Preferably the external electromagnetic radiation source would be a
30. laser device producing a radiation signal as a coherent monochromatic
collimated energy beam. Due to the need only for low powered energy by
photo-conductive switching means within the detonator a low cost fibre
-optic light guide cable would suffice.
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Fibre optic light guide can be arranged as a suitable plug-
in/adaptor means or be crimp sealed into the body portions 3 at prox-
imal end 11 of the detonator case.
It is understood the distal end of the fibre optic light guide
would align with the optic sensing means of the photo-conductor switching
means 16 to allow electromagnetic radiation energy such a infra-red
radiato~to imping on sensitive area of ~hoto-conductor 16 such as a
photo-diode or transistor to close the electrical circuit between the
adjacent mounted primary battery and the circuit of the resistance element
to fire the fusing means. This would only occur when the correct pre-
selected radiation energy signal was sent down the fibre optic light
guide from the firing station to the detonator. : ~
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In use the detonator 1 is connected to free end of optical
conductor, the opposite ends of conductor is connected at a remote position
to a source of electromagnetic radiation energy respectively controlled
by the remote firing means.
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It will be appreciated by a skilled addressee that even though
the detonator according to the present invention i5 structurally and
otherwise functionally identical to a prior art electric detonator, the
inherent dangers associated with spurious electrical charges are avoided
by the incorporation in detonator of ~a switching means responsive to
electromagnetic radiation to close the detonator in-housed electrical
circuit of the primary battery means and the electrical element of the
fusing means, g4~ranteeing no-risk of premature detonation of the device.
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The detonator may be manufactured with a suitable length of
fibre optic cable attachedthereto, the free end of the fibre optic
cable terminating in an optical coupling device.
Alternatively the detonator may be manufactured without a fibre
optic cable attached. The plug 13 may be made of a resilient poly-
meric material or other deformable material with a central cable receiv-
ing aperture. Dver the end of the plug 13 is a thin piercable closure
such as a plastics film or aluminium foil to protect the detonator
against ingress of contaminants such as waterl dirt etc.
In use the frse end of a fibre optic-cable is pushed against
the closure to pierce an aperture therein and the cable is then pushed
through the aperture in plug 13 until the free end abuts against the
inner wall. The resilient plug 13 firmly retains the fibre-optics
cable.
In the variation described above, the use of expensive fibre
optics couplers may be avoided.
The detonators according to the present invention thus possess
the advantages of prior art electrical detonators in terms of relia-
bility and economy but otherwise avoid the dangers inherent therein.
It will be clear to a qkilled addressee that many modifications
nnd variations may be made to the present invention without departing
from the ~.pirit and scope thereof.
DATED this ~ day of ~ ~oL~ , ~ , / 9 9 o
ARTHUR GEûRGE YARRINGTON
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