Note: Descriptions are shown in the official language in which they were submitted.
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REMOTE ACOUSTIC DETONATOR 5Y
The instant invention relates to explosive detonator systems in general, and
more
particularly, to acoustically activated detonators.
BACKGROUND ~,T
Explosives have been a necessary evil in the mining, demolition, tunneling,
quarrying, oil, gas, construction and related industries for years. Over time,
explosives
technology has advanced arm-in-arm with safety considerations. The current
state of the
art generally consists of, in simplified fashion, a detonator, fuse, primer,
and explosive.
The detonator is usually energized via a hardwired clectrical signal. By
activating the
detonator, the fuse is blown which sets offthe primer. As the primer ignites,
the charge
subsequently explodes. For safety and efficiency reasons, the long daisy chain
of firing
components are strung together to (1) ensure no inadvertent firing and (2)
affirmatively
place and sequentially time the explosives for full effect.
Current blasting practice in most underground mines utilizes the non-electric
shock tube system. This system involves the sequencing of the blast as it is
loaded and/or
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following a pre-planned sequence pattern. A novel is inserted into the
explosive column
of the hole being loaded. The novel's end is attached to a length of
detonating cord. All
novel detonators involved in the blast are attached to the detonating cord
trunkline. The
trunkline in turn has an instantaneous electric detonator attached. The
electric detonator
is attached to a length of lead wire that runs back to the blasting box. The
blasting box
may be part of the mine's central blasting system.
Novels come in two separate timing sequences. Long delay periods (LP) and
short period delays (SP). Both delay s~uences have a color code on the
connector
because the timing of the sequences is not compatible. Problems anise when
people have
visual impairments, are hurried or have not been properly trained to
differentiate between
the two sequences. Hole lengths can vary greatly which requires novels to have
many
different lengths. Insuring that the proper length of shock tube an the
detonator for the
application is a must. Too long and the expensive shock tube is being wasted;
and too
short does not allow for proper detonator placement which results in the shock
tube
remaining inside the hole collar.
Packaging and transportation of detonators with shock tubes is bulky and
expensive. Multiple trips down a shaft are required to deliver the detonators.
When
placed into underground storage or finally used at the stops or face, the
packaging must
be removed, cleaned and returned to the surface. Inventory and storage
requires large
inefficient storage capacity because of the bulkiness of the product.
In production blasts where long lead novels are used, the spent shock tube
must
be cleaned up and removed after the blast. This is time consuming and costly.
Portions
of spent shock tube that are left after the blast get into the muck circuit.
The shock tubes
end up in the subsequent milling process because most of the existing scrap
manipulator
systems are designed for the removal of steel, not plastic.
Hardwired systems suffer from the need to tie numerous detonators together and
connect the entire array to a remote initiator site. It is often difficult,
labor intensive,
expensive and time consuming to run long lengths of electrical wires from the
blast site to
the remotely situated initiation site. This is particularly true in
underground mining
applications using sequential blast patterns.
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There have been attempts to remotely activate blasting systems.
U.S. patent 5,159,149 to Marsden discloses a remote detonator system employing
untethered radio frequency (1tF) transmitters and receivers. Each detonator
must be
physically coupled and uncoupled with a combined charging energy storage means
and a
programmable delay time means prior to shot initiation.
Canadian patent 1,309,299 to Beattie et al., discloses a wireless system
including
detonation means capable of receiving ItF signals from a remote source
hardwired to a
fuse via connecting wires.
Canadian patent 1,298,899 to Beattie et al., discloses a dual detonation
system
employing RF and a steerable laser beam.
Wired designs include U.S. patent 5,295,438 to Hill et al, and U.S. patent
5,520,114 to Guimard et al. The former patent discloses a transportable
programming
tool and a control loop. Each detonator is affixed to a split core which is
hooked to the
loop. The latter patent discloses a feedback programming unit and an
integrated
electronic delay detonator.
Current commercially available detonation systems still ultimately require
physically connecting wires to each detonator regardless of the mode of
initiation.
The purpose of the present invention is to provide a remote wireless
untethered
acoustic blast initiation system. The need for such a system comes from a
greater
requirement to automate the entire mining process. A key part of the
underground hard
rock mining process is blasting. In order to automate blasting, a technique is
needed to
allow for the wireless initiation of a blast. Wiring a blast is a labor
intensive manual
process requiring a person to physically connect wires to each detonator. As
well, many
different time delays are required for the blast. Since development blasts can
have a blast
pattern containing 80 or more detonators, the possibility for human error is
high. These
errors occur in the placement of a detonator with the wrong timing in a hole.
Incorrect
placement and timing of the blast pattern creates poor break" bootlegs, loose
rock, varying
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muck size and damage to the opening. This in turn raises safety issues and
creates higher
mining costs.
Assignee has developed a successful prototype 1tF remote detonator system
wherein a coded 1iF triggering signal is transmitted from an RF transceiver to
one or
more wireless 1tF detonators. The 1tF signal programs the RF detonators' time
delay and
initiates the blast.
The difficulty with RF initiated remote systems relates to the problematic
transmission and reception of the 1tF signals through underground rock and
ore.
Electrical signals are attenuated and do not travel through these mediums very
far. To
ensure that the detonators receive programming and initiation signals, the
detonators
require antennae that protrude out of the blasthole. Antennae are relatively
fragile and are
subject to damage. Moreover, they pose handling and loading problems,
particularly
when utilized with automatic loading devices. The spider web of antennae is
easily
dislodged.
As an alternative, acoustic triggering was considered. Mindful that
structures,
especially mines, are subject to a bewildering array of noise and vibration
from numerous
sources-blasting, hauling, drilling, machinery, etc., the safety of acoustic
based detonator
systems was carefully considered.
It is known that noise is capable of traveling great distances underground
through
solid and liquid mediums such as rock, ore and water. The instant inventors
believed that
by harnessing, modulating and analyzing vibration within rock, a safe
dependable
acoustic-based detonating system could be developed. Alteration of acoustic
signals can
be calculated and physically measured to initiate an explosive charge.
The present invention allows data from a computerized blasting design program
to be transferred directly to the detonators and the automatic machine
installing them.
This reduces error and allows for a machine to automatically install the
detonators. The
elimination of wires greatly reduces the complexity of the automated machine
required to
install the detonators. The elimination of wires or other tethers such as
shock tubes also
eliminates the chance of the tethers being cut by the blast before the
initiation signal can
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propagate to the other detonators. This creates a poor blast i.e. oversize
chunks, poor
perimeter contour and bootlegs. All of these factors create additional worker
hazards,
decrease e~ciency and raise costs. Efficiency and safety of the process is
also improved
since the blast design data is immediately available to the blast operator and
is transferred
by computer file instead of being read and acted upon by a person.
In summary, conventional detonators come with preset times, creating the need
to
stock many dii~erent detonators, each with individual time delays. In
contrast, the present
acoustic system allows one detonator to be stocked and allows for much finer
control of
the blast by allowing a higher resolution and greater number of delay times.
The
detonators may be timed in I millisecond (ms) increments up to 10,000 ms,
giving total
timing control. These times are determined by measuring rock properties.
Matching the
timing to the rock properties gives consistent fragmentation, which is
required in
automated mining.
An advantage of using acoustic communication as opposed to ItF initiation is
that
there are no cumbersome antenna wires. They are easily damaged and may also be
easily
pulled out of the detonator causing failure to fire the detonator resulting in
undetonated
explosives remaining in the blasthole. Moreover, the initiating acoustic
signal to the
acoustic detonators can be sent over relatively long distances underground
through solid
materials.
,SUMMARY OF THE INVENTION
Accordingly, there is provided an acoustic detonator system that is adapted to
initiate a timed sequential blast pattern by an acoustic signal transmitted to
each
individual detonator.
A remote central processing unit (CPU) programmed with detonator
programming software communicates with an acoustic base transceiver. The
acoustic
base transceiver communicates with at least one remote dedicated acoustic
detonator
affixed to an individual charge. The acoustic detonator interprets the signal,
disregards
extraneous and potentially dangerous "noise" and fires off an internal fuse
directly setting
off the associated charge.
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B~tIEF DESCRIPTION OF'~~ D,~~~TGS
Figure 1 is an overall schematic diagram of an embodiment of the invention.
Figure 2 is a schematic diagram of an embodiment of the invention.
Figure 3 is a schematic diagram of an embodiment of the invention.
Figure 4 is a schematic diagram of an embodiment of the invention.
Figuro 5 is a schematic diagram of an embodiment of the invention.
Figure 6 is a schematic diagram of an embodiment of the invention.
Figure 7 is a schematic diagram of an embodiment of the invention.
Figure 8 is a schematic diagram of an embodiment of the invention.
Figure 9 is a schematic diagram of an embodiment of the invention.
Figure 10 is a schematic diagram of an embodiment of the invention.
Figure 11 is a sample waveform.
Figure 1 depicts a schematic representation of the remote acoustic detonating
system 10. A programmable controller 12, preferably a computer, ultimately
communicates via acoustic energy or sound waves 18 through a medium such as
solid
ground 20 to one or more discrete explosive charges 14 or 14(A) ("A" equaling
1, 2,
3,....).
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Each explosive charge 14 includes its own si~x~ and ~dicated microacoustic
detonator 16 or 16A ("A" equaling 1, 2, 3,....). For non-limiting simplicity,
any
reference to an individual component will include multiple iterations unless
indicated to
the contrary.
Acoustic transmitting transducers 22, such as piezoelectric devices,
microphones,
sonic transducers, speakers, flat panels, pingers, etc. generate the sound
waves 18 of
appropriate wavelength, amplitude, frequency and duration to travel to and
safely trigger
the explosive charges 14. Similarly, acoustic receiving transceivers 24, which
may be
identical to the transducers 22, receive the transmitted sound waves 18 for
interpretation
and detonation. The receivers 24 are generally small enough to be integrated
into or
affixed to the detonator 16 so as to be easily fit into a blast hole.
By virtue of the controller's 12 software, once a firing program has been
initiated,
13 an acoustic trigger will target each batch of detonators 16. By reducing or
eliminating
wired connections between the controller 12 and the blast site, the
difficulties posed by
the prior art direct hardwired or wireless antenna based systems are reduced.
In the embodiment depicted, the inventors utilized Inco Limited's preexisting
broadband CATV communications network 32 connecting surface structures to
underground mine locations. However, as will become apparent, any
communication
system bridging the controller 12 and the blast site may be used.
The system 10 includes the controller/computer 12 (preferably equipped with
Microsoft Windows~ 95 or NT~ (or later), and Inco Limited's proprietary
Telebiast AT"~ blast control software [copyrighted copies are available from
Inco
Limited]), a local acoustic detonator base transmitter 26 ("acoustic
transmitter") and one
or more remote acoustic detonators 16.
The computer 12 communicates with the acoustic transmitter 26 using its serial
communications port (COM 1 ). The acoustic transmitter 26 modulates the data
stream
coming from the computer 12 onto the acoustic wave signal 18. The acoustic
wave signal
18 is received by the acoustic detonator 16 and is demodulated to provide data
for a
central processing unit 36 located in the acoustic detonator 16. See Figure 3.
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As briefly stated previously, Figure 1 demonstrates Inco Limited's
abovegound/undergound communications system in an abbreviated fashion. The
controller 12, which may be stand-alone or part of a larger comprehensive
mining control
system and may be disposed above ground 28 or in any secure remote location,
is
connected to a conventional serial to ethernet converter 30 via a RS-232
serial bus 104.
The signal is passed through the conventional network 32 to a first standard
modem 34.
The modem 34 in turn is connected to the acoustic transmitter 26 conveniently
disposed
underground, that is, below ground 28. The communications link is passed
underground
through a main broadband underground communications trunk system 100.
A branch line 102 offthe trunk 28 is diverted to the modem 34. The modem 34
in turn communicates with the acoustic base transmitter 26.
As one skilled in the art will readily appreciate, the means for communicating
and transmitting a signal from the controller 12 to the acoustic transmitter
26 may be as
varied as desired depending on site considerations, available equipment,
permanence,
finances, etc. It is within the realm of this invention that in non-mining
situations such as
construction, oil, gas, demolition, quarrying, etc., the distance and
communication system
may be relatively short, line of sight, wireless and simple. In other
situations, such as
underground or under water, the communication system traversing the controller
12 and
the acoustic ddonator base transmitter 26 may be sophisticated and greatly
spaced.
Whatever the conditions, one skilled in the art is capable of causing the
controller 12 to
communicate with the acoustic transmitter 26.
In particular, the instant system 10 allows for easy integration onto a
conventional two-way network 32 such as one typically installed in underground
mines.
The system 10 takes advantage of existing cable and network infrastructure
already
installed thereby reducing cost. The cost of installing dedicated wiring is
eliminated.
Security of communications is ensured by using blast control software
employing a
mathematical coding scheme, cyclic redundancy check ("CRC"), addressable
detonators
16, a dedicated broadband CATV channel and a distinctive acoustic signal.
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The system 10 unabashedly takes advantage of the ever increasing and amazing
reductions in electronic component size and cost. The components making up the
acoustic detonator 16 can be made so small and cheaply that they are literally
expendable.
By physically mating the acoustic donator 16 to each specific charge 14, the
safety and
efficiency of explosive blasting is considerably camped up.
In the present discussion, particular manufacturers' components may be
referenced for convenience. However, it should be understood that comparable
alternatives may be substituted for the particular identified components. What
must be
t0 borne in mind is that a remote safety-triggering signal is transmitted from
a remote
initiation site to a transmitter 26. The transmitter 26 in tum generates an
acoustic signal
18 to a distinct explosive charge 14. Each charge 14 includes its own stand-
alone
dedicated acoustic detonator 16. The acoustic detonator I6 interprets the
signal from the
transmitter 26 and, if conditions are appropriate, initiates the explosive
sequence.
In Figure 2, the controller 12 is shown connected to the acoustic detonator
base
transmitter 26 (minus intermediate connections). Figure 3 is a schematic of an
acoustic
detonator 16.
The controller 12 is programmed with the appropriate software and commands
the system 10. The Telebfast AT"' blast control software:
a) computes the CRC for communication verification and integrity.
This is a method for checking the accuracy of a digital
transmission over a communications link. The computer 12
performs a calculation on the data and attaches the resulting CRC
value to the communication data stream; the transmitter CPU 38
performs the same calculation and compares its result to the
original value in anticipation of a hand shake confirmation. If
they do not match, a transmission error has occurred and the
receiving CPU 38 requests retransmission of the data;
b) allows an operator to program: a blast batch identification
number, a detonator identification number and detonator delay
time in milliseconds (0 to 10000) into each detonator;
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c) allows an operator to initiate a common fire command to start a
countdown from each individual detonator delay setting for all
detonators within a batch;
d) allows programming and initiation over a secure networked
communication system via the modem 34.
The acoustic detonator base transmitter 26:
l0 a) transmits coded acoustic signals. It communicates with the
detonator CPU 36.
The CPU 38:
a) encodes the batch identification number, detonator identification
number, detonator delay times, CRC, arm and fire codes.
The transmitter (Tx} 48 includes:
a) modulation circuitry which modulates encoded transmit data. It
uses a FSK (frequency shift keying) modulation format.
b) driver circuitry which takes the tow voltage and low current
signal of the modulation circuit and provides enough current and
voltage to drive the acoustic transducer 22.
The transducer 22 converts modulated electrical energy into modulated
acoustical
energy. For underground applications it is preferably coupled to solid ground
or rock 20.
The acoustic detonating system 10 may be used in non-gaseous mediums such as
solid-like earth formations, rock, underground mines, quarries, tunnels,
construction and
demolition sites, etc.. It may be also used in liquid environments such as
bodies of water,
rivers, liquid conduits, pools, etc. As long as the non-gaseous medium is
capable of
effectively transmitting an acoustic energy (sound) wave to the ultimate
destination, the
instant system 10 may be employed in many situations. Naturally in water
environments
the components need to be sufficiently waterproofed.
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The acoustic detonator 16 receives and decodes coded acoustic signals:
a) The acoustic receiver 24 is an acoustic signal sensor such as a
microphone (piezoelectric sensor in the prototype). The acoustic
receiver 24 converts acoustic energy to electrical energy which it
receives acoustic energy transmitted through rock and explosive
emulsion.
b) The receiver (Rx) 50 consists of a receive buffer and
demodulation circuit. The receive buffer amplifies the signal
from the acoustic receiver 24 for use by the demodulation circuit.
The demodulation circuit demodulates the FSK signal into a data
stream for use by the CPU 36.
c) The CPU 36 decodes coded data from receiver 50 consisting of
batch identification number, detonator identification number,
detonator delay times, arm command, fire command and CRC.
If appropriate, it outputs a fire command to relay 40.
d) The energy source 42, which may be a battery and/or capacitor,
powers the acoustic detonator 16 including the receiver 50, the
CPU 36, the relay 40 and the fuse 44 circuits. Discharge 98
begins upon turning on the roceiver 50 and the CPU 36.
A prototype acoustic detonating system 10 was built and successfully tested as
shown in Figures 4-10. The following discussion relates to the prototype in
greater detail.
For both the transmitter 26 and detonator 16, a MicrochipTM CPU PIC 16C63A
programmable microcontroller ("PIC") 52, 80 was chosen based on its low cost,
functionality and ease of programming. The PIC 52, 80 is essentially a
complete
computer in a small, low cost package, with a central processor, random access
memory
(RAM) for temporary storage and programmable read only memory (PROM) for
permanent storage of a software program.
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To acoustically transmit and receive the binary sequence, several modulation
schemes were identified including impulsive (hammer type), on-off keying
(pinging) and
frequency shift keying ("FSK", two separate frequencies representing on and
off. For
the prototype, FSK was used.
The transmission circuitry 56 was programmed to generate a binary 8-bit
transistor-transistor logic ("TTL") (on-oil sequence. As shown in Figure 4,
the TfL
signal is transformed by FSK modulating circuit 58 to an FSK signal large
enough to
drive via piezo driver circuit 60 the acoustic transducer 22. Piezoelectric
devices were
used for the acoustic transducer 22 and receiver sensor 24 simply due to their
availability
and the ease with which they may be interfaced. For demonstration purposes, a
4-foot
( I .22m) high cylindrical column of concrete 54 was used to simulate
transmission
through rock. The driver circuit 60 amplifies the FSK signal to an appropriate
level for
the piezoelectric device 22.
The acoustic signal, after passing through the concrete 54, is received by the
second piezoelectric device 24 also affixed to the concrete 57. In order to
receive an
adequate signal level, a buffer circuit 62 is used to provide signal gain from
the
piezoelectric device 24 to the remaining receiver system. The received FSK
signal is then
passed through an FSK demodulation circuit I 08, resulting in the reproduction
of the
original TTL signal. The TTL signal is then inputted to the receive circuit 64
including
PIC 80, where it is decoded to an 8-bit value. A valid detonation code is
determined if
the 8-bit value matched a predetermined value that was stored in the receiver
PIC 80.
Upon reception of a valid detonation code, the receive circuit 108 energizes a
LED 68
thus simulating a detonation. If the data is not a valid detonation code, the
LED remains
de-energized and the receive circuit 108 continues to await another
transmission.
The receive circuit 108 can be programmed with a variable time delay. Thus,
the
LED 68 can be programmed to energize after a programmed time delay, which
simulates
a delayed detonation signal to a detonator cap.
To control the acoustic detonator 16 circuits, software performs the following
tasks:
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a) on the transmit PIC 52 (see Figure S) the software, transmits one
of two possible 8-bit binary numbers selectable by an electronic
switch;
b) on the receive PIC 80 (see Figure 10), the software receives and
decodes the 8-bit binary signal and determines whether it is a
valid detonation command; and
c) on the receive PIC 80, if the received code is valid, it simulates
detonation by energizing the LED 68 after a determined time
delay.
Turning now to the details of the prototype in greater detail.
The PIC 52 is used on the transmitter 26 to store and generate the detonation
codes. Two separate 8-bit codes were required to demonstrate successful
operation of the
acoustic detonator 16 prototype. The ftrst code is a valid detonation code,
which, when
transmitted, will result in a simulated detonation. The srcond is an invalid
detonation
code, which, does not result in a simulated detonation, thus demonstrating
that a specific
8-bit number is required to trigger a detonation. The 8-bit codes were chosen
arbitrarily
and can be assigned any value.
For brevity, in Figures 5 to 10, a number of the components such as resistors,
capacitors, power supplies, amplifiers, etc. known to those skilled in the art
will not be
discussed.
Figure 5 is a schematic drawing of the transmit circuit 56. The transmit PIC
52
outputs the 8-bit code serially on pin 22 (RB1, Port B). This binary TTL
signal is then
passed to the FSK modulation circuit 58. An electronic switch SW I is used to
allow the
user to select which 8-bit code was to be transmitted (i.e. the valid or
invalid code). The
switch SW 1 is connected to pin 23 (ltB2, Port B) and pin 24 (RB3, Port B).
When
toggled, the switch S W I places on either RB2 or ltB3, thus selecting which
code is to be
transmitted. Two LEDs D1 (valid code) and D2 (invalid code) are connected in
line with
the switch SW 1 to display which code had been selected for transmission. A
momentary
close switch SW2 is connected to pin 21 (RBO/INT). Pressing this switch
asserts an
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interrupt on the PIC 52 resulting in the selected code being transmitted once
(i.e. one shot
operation).
The PIC 52 is powered by a SV regulated power supply. A 20MHz crystal 70 is
placed across pin 9 (CLKIN) and pin 10 (CLKOUT), resulting in a SMIPS
instruction
rate. An additional LED D3 is placed on pin 2 (RAO, Port A) which is energized
when
the PIC 52 is under normal operation.
The TTL binary signal from the transmit circuit 56 is FSK modulated by the
circuitry shown in Figure 6. FSK modulation was chosen for its simplicity to
implement
and the control it allows over the frequency content of transmitted signals.
FSK was also
chosen in order to reduce the risk of a narrow band interference source from
initiating a
detonation by virtue of it's frequency diversity. For ~monstration purposes, a
center
frequency of 2.SkHz was chosen arbitrarily with mark/space frequencies of
2kHz/3kHz.
IS Thus, binary 0 results in a 2kHz sine wave, while binary 1 produces a 3kHz
sine wave.
To achieve this modulation technique, the FSK modulation circuit 58 was
designed using
a XR-2206T"' function generator integrated circuit 72 manufactured by EXART"~.
The
circuit 58 is capable of converting a TTL keying signal (the 8-bit code) to a
frequency-
modulated sine wave. The mark/space frequencies are set by a combination of
external
resistors and capacitors.
The TTL signal from the transmit circuit 56 is input to pin 9 of the
integrated
circuit 72. Capacitor C1 (across pins 5 & 6) along with R1 (pin 7) and R2 (pin
8)
determine the mark/space frequencies. The amplitude of the output sine wave
may be
adjusted by changing the resistor value of R3 connected to pin 3. However, for
this
demonstration the value was chosen to pmduce a 6V peak-peak sine wave. The FSK
output is located on pin 2 and is capacitively coupled to the driver circuit
60. The
integrated circuit 72 was powered by a l OV regulated supply for the
demonstration.
However, it is capable of operating over a range of 1 OV-26V. Frequency of
operation
3o may be anywhere between 0.01 Hz - I MHz.
Turning now to Figure 7, there is shown a driver circuit 60. Due to the
inefficiency of the piezoelectric material as a transmitter, a large voltage
is required to
successfully transmit an acoustic signal through several feet of concrete. The
output from
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the circuit 58 in the modulation circuitry only provides a 6V peak-peak
signal. It was
required to boost this signal to roughly 400V peak-peak to achieve a
successful
transmission. A step-up transformer 74 is used to achieve the boost. However,
a buffer
circuit is also required to provide the current to drive the transformer 74
and the
transducer 22.
The transformer 74 is a simple wire wound iron core. The buffer circuit is
comprised of an OF183TM operational amplifier 76 configured for unity gain.
The
amplifier 76 was chosen for its high output capability arid fast skew rates.
The
transformer 74 drives the acoustic transmitter 22.
A detonator 16 was assembled with three main subsystems:
1 ) Receiver buffer 62;
2) FSK demodulation circuit 64; and
3) Receive circuit 108.
For demonstration purposes, two detonators were assembled ( 16 and 16A - see
Figure 4), on a single circuit board and, for simplicity, shared the receiver
buffer 62 and
FSK demodulator 64 subsystems. See Figure 8.
The buffer circuit 62 is required to provide signal gain from the
piezoelectric
sensor 24 for use by the FSK demodulation circuit 64. A second or mirror
OP183T"~
operational amplifter 78 was chosen and configured as a unity gain amplifier.
The buffed
signal is routed to the FSK demodulation circuit 64.
In Figure 9, the demodulation circuit 64 was designed to perform FSK
demodulation based on mark/space frequencies of 2kHzi3kI-Iz. This design
incorporated
a XR-221 I FSK demodulation integrated circuit 106 ("1C"). The mark/space
frequencies
are selected by setting external resistors and capacitors. The FSK signal from
the input
buffer 62 is capacitively coupled to pin 2 of IC 106. The signal must be
between l OmV-
3V to be recognized by the IC 106.
The iC l 06 is configured to output two signals. The first is a carrier detect
(CD)
signal that is used to indicate whether or not the IC 106 has locked on a
valid carrier
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frequency (i.e. between 2kHz and 3kHz). If a valid frequency is detected, the
CD signal
is to I~ set to OV. Otherwise, a SV signal indicates that a valid frequency is
not found
and hence no data is received. The second output signal is the data output
(DATA). The
DATA signal is TTL level and is derived from the raceiv~ FSK signal. It should
be
noted that as long as the CD signal is high (i.e. no carrier detected), the
DATA output
signal is un-defined. The CD and DATA signals are sent to the receive circuit
108 for
interpretation. The IC 106 is powered by a l OV (Vcc) regulated supply.
Figure 10 depicts the receive circuit 108. The receive circuit 108 having the
PIC
16C 63A programmable microcontroller 80 ("receive PIC 80") on the detonator 16
is
required to perform three functions. First, the receive PIC 80 determines
whether the data
it is receiving from the FSK demodulation circuit 64 is valid or noise
induced. It does
this through analysis of the carrier detect signal (GD). If the CD signal from
the FSK
demodulation circuit 64 is logic high (i.e. 5V indicating no carrier due) the
receive
t 5 PIC 80 ignores the data signal it received. If the CD signal is logic low,
then the receiver
PIC 80 accepts the data signal as a transmitted code. The second function
roquired of the
receive PIC 80 is to transform the received data back into an 8-bit cod and
LED 110 is
lit. The third function is to ddermine whether or not the received code
matches the
expected detonation code. If a match is found, the receive PIC 80 simulates
detonation
through energizing LED 68 after a predetermined time delay. For the
demonstration, the
two detonators 16 and 16A were implemented. This allowed the user to
demonstrate that
one transmitted code would result in two separate time delayed detonations.
The cagier detect (CD) sigaal is input to pin 13 (RC2, Port C) of the PIC 80
and
the data (DATA) signal is input to pin 12 (RC1, Port C). The LED 68 is
connected to pin
4 (RA2, Port A). This LED 68 is energized to simulate a detonation. The PIC 80
is
powered by a SV regulated power supply. A 20MHz crystal 112 is placed across
pin 9
(CLKIN} and pin 10 (CLKOUT), resulting in a SMIPS instruction rate. An
additional
LED 82 is placed on pin 2 (RAO, Port A) which is energized when the PIC 80 is
under
normal operation. Several of these detonators 16 may be constructed, each
simulating a
detonator with a different blast time delay.
The PIC 80 for the detonator 16 is programmed as a serial communications
receiver. When powered up, the PIC 80 initializes itself and immediately
starts waiting
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for the caurier detect (CD) signal from the demodulator circuit 64. When the
CD makes
the transition from high to low, it is known that the IC 106 is recxiving data
so the
processor waits for the start bit. If no information is being sent from the
transmitter, the
default data sent is stop bits. The start bit is detected when the FSK data
pin makes the
transition from high to low. This activates TIMER1 in the PIC 80 and all
subsequent
samples of the FSK data pin 12 are taken based on this timer. The data format
that the
PIC 80 re~nizes is 7 data bits, 1 parity bit and 2 stop bits. The program then
verifies
that the data is in the proper format and that the parity is cornet. If the
detonate code is
valid, then the software times out and turns on the LED 68 which represents
the detonate
signet. If during any part of the data gathering process the PIC 80 stops
detecting the CD
signal, the PIC 80 reverts back to its waiting for carrier detect state. If
the data received
is determi~d to be invalid, the program reverts back to its start-bit wait
state. Invalid
data can be caused by an invalid parity bit, insufficient stop bits, or an
invalid detonate
code.
The baud rate use in the serial communications was ar6ritrarily set to 62.5
BPS.
At an instruction cycle spend of 5 MHz and a timer pre-sealer of 8:1 for the
TIMER 1
module, one bit length corresponds to 10000 TIMER1 increments. This is the
delay time
that is used with the TIMERI interrupt to control the sampling of serial data.
The program is designed to work like a state machine, with clearly defined
states
and statatrnnsitions that govern the flow of the program. The machine advances
states
depending ~ the 2 external or 1 internal interrupt. These are the carrier
detect (CD)
signal coming from the PIC 80, the data detect (DD) interrupt coming from the
PIC 80 or
the TIMERI interrupt generated by the PIC 80. If the data received is invalid,
the
program flow will return to the start bit wait state.
The program for the transmit circuit 56 works as follows. On startup, the
transmit PIC 52 is initialized and immediately starts sending out stop bits
(logic high) to
the FSK modulating circuit 58. The only external inputs to the circuit 58 are
a button
(switch SW2) connected to pin RBO, and a toggle switch SW 1 connecting either
pin RB2
or RB3 to logic high. When the button on switch SW2 is pressed, an RBO
interrupt is
created and depending on whether RB2 or RB3 is high a different code is sent
to the FSK
modulating circuit 58. The signal is sent at 62.5 BPS to pin RB 1. This signal
is timed
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out exactly as it is in the receiver using TIMERI . Once the transmission is
complete
another transmission can be started if desired.
In summary, the acoustic detonator system 10 demonstrates the feasibility of
acoustically triggering the detonation of a blast area. The objectives of the
acoustic
detonator system 10 demonstrates the following: .
a) to acoustically transmit a unique binary code;
b) to acoustically receive and recognize a unique binary code
through rock;
c) to process the unique code as a detonation trigger and perform
the function of a programmable time-delayed detonation source;
and
d) to perform the detonator functions in a small autonomous
package that can be reproduced simply and cheaply in large
quantities.
To accomplish these objectives, the prototype detonator 16 and transmitter 26
were constructed using an inexpensive microcontrollers and piezoelectric
sensors. The
transmitter unit was programmed to send two different "detonation codes": an
invalid and
valid code. The prototype detonators were programmed to receive and recognize
a
unique code, designated as the "valid code" by the transmitter. The prototype
detonators
were successfully demonstrated; they recognized the detonation code, delayed
by a
preprogrammed period, and asserted a detonation signal.
In a fully operational system 10, the output from the receive circuit 108
would be
routed, not to the LED 68, but the relay 40. The cascade of events from the
receipt of the
acoustic signal 18 will discharge 98 the explosive charge 14.
By employing the FSK paradigm, a customized signal 18 may be generated
thereby causing the most efficient signal propagation through the various rock
and ground
conditions in a mine.
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CA 02367161 2002-O1-09
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Two typical non-limiting signal characteristic cases are outlined below. A 31
bit
code and a 63 bit wave packet code are contemplated. The 63 bit code can carry
additional intelligence. Other wave packets may be acceptable.
Center fl Q Chip 31-Bit 63-Bit Chip 31-Bit 63-Bit
Freq. (Hz) (Hz) DnratioCode Code DuratioCode Code
(Tiz) n Length Length n Length Length
(mSec) (mSec) (mSec) (mSec) (mSec) (mSec)
Case Case Case Case Case Case 2
1 1 1 2 2
2500 2294 2725 5 155 315 10 310 630
1250 1157 1350 10 310 630 20 620 1260
625 574 680 20 620 1260 40 1240 2520
312.5 2 342 4 1240 252 80 248 5040
85 0 0 0
1546.25_ 171 _ _ _ ~ 160 __ 10080
142 ~ _ _ __ ~ _
80 ~ 2480 r 5040 4960
~
Figure 11 shows a 31 bit detonator coding code excerpt. Each acoustic
detonator
26 will respond to a particular code sequence and duration. For example, the
following
code characteristics may apply to the excerpt shown in Figure 11.
F~(Hz) F=(JEIz) Tc(msec)
2294 2725 5 or 10
1157 1350 10 or 20
574 680 20 or 40
285 342 40 or 80
142 171 80 or 160
The amplitude of the signal is a function of the medium and the range.
However,
preliminary indications for hard rock mines, such as those found in Sudbury,
Ontario,
Canada appear to be somewhere between 110-120 db re 1 uPa 1 m, where the
sensitivity
of receiver device 24 is about 85db re 1 uPa. Under perfect conditions this
translates to a
range of about 50 meters. However, it should be apparent that different
mediums will
require different signal characteristics, and the above parameters are non-
limiting
examples.
The design components are easily miniaturized for use in blast holes.
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The acoustic detonating system 10 need not be static. Returning to Figure 1, a
communications junction box 84 including a modem 86 and wireless modem 88 are
connected to a leaky coax cable 90. The leaky coax cable 90 may be disposed
throughout
a mine and on different levels, drafts and stopes.
An acoustic detonator mobile base transmitter 92 mounted on a mobile vehicle
94
is capable of being brought into close proximity to a blast site. It is
contemplated that the
transmitter 92 may be coupled with a remotely operated automatic explosives
loader that
can both load the holes with an exposure charge 14 / detonator 16 combination
via an
explosures vehicle processor 96 and then remotely detonating the blast face
safely and
economically. A wireless modem 114 receives the initiation signal from the
leaky coax
cable 90. The acoustic detonator mobile base transmitter 92 operates in a
similar manner
as does the previously discussed acoustic detonator base transmitter 26.
While in accordance with the provisions of the statute, there are illustrated
and
described herein specific embodiments of the invention, those skilled in the
art will
understand that changes may be made in the form of the invention covered by
the claims
and that certain features of the invention may sometimes be used to advantage
without a
corresponding use of the other features.
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