Note: Descriptions are shown in the official language in which they were submitted.
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WIRELESS DETONATING SYSTEM
BACKGROUND OF THE INVENTION
[0001] This invention relates to a detonating system.
[0002] US2008/0041261 relates to a wireless blasting system in which at least
two
components are adapted to communicate with each other over a short range
wireless radio
link. Use is made of so-called identification code carriers which are
associated with
respective detonators. The code carriers are capable of communication with
each other
and with a blast box.
[0003] Communication may be effected using various protocols, such as the
Bluetooth
protocol which operates at a frequency of about 2,45 gHz.
[0004] The specification of the aforementioned application also describes
certain
problems which are encountered when electronic blasting systems which are
interconnected by way of wires are used in diverse sites. The use of a short
range, high
frequency, wireless radio link is intended to address some of these problems.
However,
the amplitude of a high frequency radio signal in rock is rapidly attenuated.
It is then not
feasible to communicate directly with a detonator in a borehole. If the
equivalent of an
identification code carrier is used on a rock surface then the carrier is
exposed to the
prevailing environmental conditions and can easily be damaged and thereby
rendered
useless.
[0005] A magnetic signal at a frequency of, say, less than 20 kHz can however
penetrate
rock and soil without undue attenuation. It is then possible to make use of a
transmitting
antenna with a relatively large area which is positioned at a suitable
protected location and
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which transmits at a power of several tens of watts communication signals to
detonators
which have appropriate receivers and which are placed in boreholes in the
rock. This
approach, which enables the use of the identification code carriers or
equivalent devices to
be dispensed with, is essentially of a unidirectional nature. Reliable
communication links
can be established from the transmitter to the various antennas which are
associated with
the detonators in the boreholes, but due to physical limitations of magnetic
field
propagation, it is not feasible to transmit from each detonator a signal in
the reverse
direction, over the same distance, to a receiving antenna which may be the
same as a
transmitting antenna.
[0006] A direct drawback thus is that a one-way communication process does not
allow
an operator to establish whether all detonators are receiving signals
correctly from the
transmitter. This means that there is no way of determining whether commands
to the
detonators from a control mechanism are being properly received. The absence
of
feedback from a detonator to the control mechanism means that safety and
functional
requirements are, inevitably, compromised.
[0007] Another factor, if a single antenna is used to transmit to all of the
detonators in the
boreholes, is that the size of the antenna and its power demands may be
substantial,
particularly if the blast site extends over a large area. Other disadvantages
include the
practical problem of positioning and deploying a large antenna in an
underground situation
in which space may be limited and of then protecting the transmitting antenna
from damage
due to rock displaced in a subsequent blasting process.
[0008] An object of the present invention is to address at least to some
extent the
aforementioned situation.
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SUMMARY OF INVENTION
[0009] The invention is based on the use of a near-field magnetic induction
communication
technique in which a transmitter coil in one device is used to modulate a
magnetic field
which is measured by means of a receiver coil in another device.
[0010] The power density of a far-field magnetic transmission attenuates at a
rate which
is proportional to the inverse of the range to the 2nd power (-1.2) or -20db
per decade. By way
of contrast a near-field magnetic induction system is designed to contain
transmission
energy within a localised magnetic field which does not radiate into free
space. The power
density of a near-field transmission does, however, attenuate at a rate which
is proportional
to the inverse of the range to the 6th power (--1-6) or - 60 db per decade. A
cross over point
between a near-field transmission and a far-field transmission occurs at an
approximate
distance of (wavelength of operation) / (2u). Utilization of the
aforementioned factors
means that a relatively low powered transmitter functioning at a frequency of,
say, 4 kHz
which is associated with a detonator inside a borehole is capable of
transmitting a signal
through rock over a meaningful distance of say, several, or even tens of,
meters.
[0011] Against the aforementioned background the invention provides a
detonator which
includes a transmitter which, when actuated, transmits a first signal at a
known,
predetermined signal strength, a receiver which in operation, receives said
first signal from
another detonator which is the same as said detonator and which is displaced
by a distance
from said detonator, a comparator which compares the strength of the
transmitted first
signal to the strength of said received first signal, and a processor,
responsive to the
comparator, operable to provide a measurement of the degree of attenuation of
the first
signal, is received.
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[0012] The invention further extends to a detonator system which includes at
least a first
detonator which is located in a first borehole and which includes a first
transmitter and a
first receiver and a second detonator which is located in a second borehole
and which
includes a second transmitter and a second receiver, the first borehole being
spaced from
the second borehole, wherein the first transmitter is actuable to transmit a
first signal at a
first signal strength and the second receiver is configured to receive the
first signal, the
second detonator including a processor to measure the strength of the received
first signal
and to determine at least from the difference between the strength of the
transmitted first
signal and the strength of the received first signal a measurement of the
attenuation of the
.. first signal as it travels from the first borehole to the second borehole.
[0013] Each transmitter and receiver may be adapted to function in the ULF or
VLF bands
i.e. at a frequency of less than 30 kilohertz and preferably at a frequency of
the order of 4
kilohertz. As a signal at this frequency has the capability to travel through
rock or soil each
receiver and transmitter associated with a respective detonator can be wholly
contained
within a respective borehole and no part thereof would then be located on, or
exposed to,
an external rock surface. The likelihood of physical damage due to mining or
other
operations is therefore substantially eliminated.
[0014] The invention also extends to a blasting system which includes control
equipment
and a plurality of detonators, each detonator being of the aforementioned
kind, wherein
.. each detonator, via its respective transmitter and receiver, is adapted to
communicate in a
two-directional manner with a restricted number of detonators in adjacent
boreholes,
whereby a signal from the control equipment is relayed in succession via the
respective
transmitters and receivers of at least some of the plurality of detonators
along a plurality of
outbound paths to all the plurality of detonators and a signal from any
detonator is relayed
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in succession via the respective transmitters and receivers of at least some
of the plurality
of detonators along a respective inbound path to the control equipment.
[0015] Preferably each outbound path is along a path in which the sum of the
degrees of
attenuation of the signal between successive boreholes, in which the
respective detonators
5 .. are located and along which the signal is relayed from the control
equipment, has a minimal
value.
[0016] Similarly, each inbound path is along a path in which the sum of the
degrees of
attenuation of the signal between successive boreholes, in which the
respective detonators
are located and along which the signal is relayed to the control equipment,
which has a
minimal value.
[0017] Each detonator has a respective unique identifier. Thus each path
(inbound and
outbound) is precisely specified by the unique identifiers of the associated
detonators, and
by the sequence, or order, of these identifiers.
[0018] An objective in the aforementioned process is to enable a communication
path to
be determined, which is uniquely associated with a particular detonator, in
which the
attenuation of a signal to or from that detonator is minimised. If the body of
rock in which
the boreholes are formed is essentially of the same nature (homogeneous) then
this path
may be one of a minimum physical distance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The invention is further described by way of example with reference to
the
accompanying drawings in which:
Figure 1 is a block diagram representation of a detonator according to the
invention; and
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Figure 2 is a two-dimensional view of a plurality of detonators which are
included in a
blasting system which has a mesh network configuration, according to the
invention.
DESCRIPTION OF PREFERRED EMBODIMENT
[0020] Figure 1 of the accompanying drawings illustrates in block diagram form
a
detonator 10 according to the invention.
[0021] The detonator 10 includes detonating components 12, of known elements,
such as
an initiator, a primary explosive and the like. These aspects are not
individually shown nor
described herein for they are known in the art.
[0022] The detonator 10 further includes a timer 14, a memory 16 in which is
stored a
unique identifier for the detonator, a processor 18, a transmitter 20 which is
controlled by
the processor 18 and which emits a signal through a custom-designed coil
antenna 22, a
receiver 24 which is connected to the processor 18 and which is adapted to
receive a signal
detected by a custom-designed coil antenna 26, and a comparator 28.
[0023] A battery 30 is used to power the electronic components in the
detonator and to
provide energy to the initiator to fire the detonator when required.
[0024] In use, the transmitter 20 produces a magnetic field which is
transmitted by the
antenna 22. The magnetic field is modulated with information output by the
processor 18
in order to transmit information from the detonator. Similarly, the receiver
26 is adapted to
decode a modulated magnetic field signal which is received by the antenna 26
and to feed
information, derived from the demodulation process, to the processor 18. The
receiver and
transmitter function at a frequency of the order of 4 kHz.
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[0025] Figure 2 illustrates a detonator system 34 according to the invention
which includes
a plurality of boreholes 38 which are drilled in a body of rock in, say, an
underground
location. The spacings 40 between the boreholes 38, the depth of each
borehole, and the
position of each borehole, are determined by the application of known
principles which are
not described herein. Each borehole 38 is charged with an explosive
composition 42 and
is loaded with at least one detonator 10 of the kind described in connection
with Figure 1.
For ease of identification the detonators are labelled Al to A3, B1 to B3, Cl
to 03, D1 to
D3, El to E3 and Fl to F3.
[0026] The detonator system 34 also includes control equipment 50 which is
used to
establish and measure parameters of the blasting system in accordance with
operating and
safety techniques. The control equipment 50 is adapted to receive signals from
the various
detonators and to transmit signals to the various detonators as is described
hereinafter.
[0027] The control equipment 50 is connected to the detonator A2, referred to
herein for
ease of identification as a sink detonator, via a physical link 52 such as
conductive wires.
A signal generated by the control equipment 50 is transmitted via the link 52
to the sink
detonator A2. Information carried by this signal is extracted and that
information is used to
modulate a magnetic signal which is generated by the respective transmitter 20
in the
detonator A2. A resulting near-field modulated magnetic signal is then
transmitted from the
coil antenna 22 of the detonator A2.
[0028] As is explained hereinafter it is possible for a signal generated at
the control
equipment 50 to be transmitted via the mesh network to a particular
predetermined
detonator and for a signal to be returned from that detonator to the control
equipment 50.
In each instance the signal is relayed sequentially from one detonator to
another and is
guided to its particular destination. However, as the energy capability of
each battery 30 in
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each detonator 10 is limited it is important for this signal transfer
capability to be
implemented in an energy efficient manner.
[0029] Assume that the sink detonator A2 transmits a signal which is received
by a number
of adjacent detonators. In Figure 2 these adjacent detonators are illustrated
at least as the
detonators Al, B2 and A3. Referring only to the detonator B2, this detonator
contains
information, previously loaded in its memory 16, which is based on an accurate
measurement of the strength of each signal which might be transmitted by the
transmitter
20 in the detonator A2.
[0030] The signal from the detonator A2 is received by the receiver 24 in the
detonator B2
and the strength of the received signal is measured. The comparator 28 in the
detonator
B2 compares the strength of the received signal to the strength of the
transmitted signal ¨
the latter value is, as stated, known from the relevant data which are stored
in the memory
16 of the detonator B2. Due to the attenuating effect of the rock material
between the two
boreholes in which the detonators A2 and B2 are located, the received signal
has a lower
strength then the strength of the transmitted signal and, by using an
appropriate algorithm
which is executed by the processor 18 in the detonator B2, a measure of the
degree of
attenuation of the signal strength is determined. If the body of rock is
essentially
homogeneous this technique also provides a measure of the physical distance
between
the boreholes in which the detonators A2 and B2 are located.
[0031] It is also possible for the strength of the transmitted signal to be
given by a value
which is contained in the transmitted signal.
[0032] The signal which is emitted by the detonator A2 is also received by the
detonators
Al and A3. In each instance a measurement is determined of the degree of
signal
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attenuation between the borehole of the detonator A2 and the borehole of the
respective
receiving detonator (Al, A3).
[0033] Included in each modulated transmitted signal is the unique identifier
of the relevant
detonator, taken from the memory 16.
.. [0034] Each detonator 10 which receives a signal then transmits a
responsive signal.
Referring again by way of example only to the detonator B2 the respective
components in
the detonator B2 cause the generation of a modulated magnetic signal which is
transmitted
via the respective coil antenna 22. That transmitted signal carries
information identifying
the sequential path from the control equipment 50, to the detonator A2, and to
the detonator
B2, and is received at least by the adjacent detonators 02, B3, A2 and B1 . In
each instance,
a corresponding calculation is made of the extent of signal attenuation
between the
transmitting borehole and the receiving borehole.
[0035] Assume, referring to the detonator B3 (again only by way of example)
that the
detonator B3, in response to the received signal, emits a modulated magnetic
signal of the
.. nature which has been described. That signal is received at least by the
adjacent
detonators B2, C3 and A3.
[0036] The process continues in this manner until each detonator has received
a
corresponding signal which originated from the control equipment 50. It should
be borne in
mind that each transmitted signal travels in three dimensions. However, for
explanatory
.. purposes herein, signal propagation is described as taking place in two
dimensions.
[0037] Subsequently, a signal containing data of the respective distance
measurement
between each adjacent pair of boreholes, together with the identifiers of the
respective
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detonators, is propagated along various paths through the mesh network towards
the sink
detonator A2 which, in turn, transfers such signal to the control equipment
50.
[0038] The control equipment 50 is then capable of establishing a computer
representation of the configuration which is shown in Figure 2 i.e. of the
various boreholes
5 and the detonators, the identities of the detonators and the expected
extent of signal
attenuation between each adjacent pair of boreholes. Through the use of
appropriate
software the control equipment 50 determines how a signal which is intended
for any
particular detonator 10, which is identified uniquely by means of its identity
number, can be
sent through the mesh network of detonators in the most energy-efficient
manner i.e. along
10 the shortest path through the body of rock i.e. the path which has the
smallest degree of
signal attenuation. Additionally, the aforementioned process enables each
detonator to
establish the identity of each adjacent detonator with which it can
communicate in a bi-
directional manner.
[0039] It is apparent that a signal intended for a particular detonator must
carry in the
correct sequence the unique identifiers of the detonators which lie on the
signal propagation
path ¨ this is a requirement for each signal going to, or from, the sink
detonator.
[0040] Once the routing information has been established it is possible for
the control
equipment 50 to generate a message that is intended for any particular
detonator, as
identified by its identity number, and then to transmit an outbound message
which is
intended only for that detonator. In the return direction a detonator can, for
example after
carrying out integrity and functional capability tests, generate and transmit
an inbound
signal to the control equipment 50. In each instance, the signal goes along a
pre-
determined path which is determined primarily by the routing information
referred to. The
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control equipment 50 is then able to verify the integrity of the entire
blasting system before
initiating a fire signal.
[0041] The invention makes it possible for the establishment of an energy
efficient, reliable
and effective bi-directional communication facility between the control
equipment and each
detonator. This is achieved without the use of a large area primary antenna of
the kind
referred to in the preamble hereof.
