WO2021033067A1

WO2021033067A1 - Identifying potential misfires in an electronic blasting system

Info

Publication number: WO2021033067A1
Application number: PCT/IB2020/057483
Authority: WO
Inventors: Andries Willem Posthumus; Anthony John Rorke
Original assignee: Omnia Group Pty Ltd
Current assignee: Omnia Group Pty Ltd
Priority date: 2019-08-16
Filing date: 2020-08-07
Publication date: 2021-02-25
Anticipated expiration: 2022-02-16
Also published as: ZA202101306B

Abstract

An electronic blasting system includes a plurality of detonators connected to at least one blaster unit via a wire network. The detonators are, in use, positioned according to a blast design. Prior to firing of the detonators, the system collects or obtains data from a detonator. The system determines whether a charged voltage of the detonator is sufficient to sustain a programmable electronic module of the detonator in a blasting countdown for the duration of a programmed firing time of the detonator so as to permit firing of a fuse head of the detonator at the programmed firing time. If it is determined that the charged voltage is insufficient to sustain the electronic module of the detonator so as to permit firing of the fuse head at the programmed firing time, the system identifies and/or reports a potential misfire in respect of the detonator.

Description

IDENTIFYING POTENTIAL MISFIRES IN AN ELECTRONIC BLASTING SYSTEM

Field of the invention

The invention relates to an electronic blasting system and to a method of identifying potential misfires in an electronic blasting system. The invention also relates to a detonator for use in such a system and/or method.

Background to the invention

Detonators are employed in the blasting of rock for the extraction of minerals or other valuable components, the quarrying of rock and in civil engineering projects that require rock blasting. Blasting is generally done by drilling a pattern of boreholes, priming each borehole with a detonator and a booster and filling the hole, in accordance with the design, with commercial explosives. Types of detonators used include those attached to a pyrotechnic fuse (fuse head), electric detonators, shock-tube initiated detonators and, in the last 20 years or so, electronic detonators.

Wired electronic blasting depends on electrical leads from a blaster unit (usually near the blast) to every hole that has been supplied with an electronic detonator. The surface wiring system may comprise a lead-in line which connects to lines running along each row of holes. Connectors, usually insulation displacement connectors (IDCs), are used to connect the lead-in line or trunk line electrically to the row lines. Similar connectors may be used to connect the detonator leg wires to the row lines.

Each detonator typically comprises a metal tube containing a sealing plug, a crimp, an electronic module, a fuse head connected to the electronic module and an explosive charge.

The electronic module of modern detonators typically comprises a microprocessor, a power supply to supply regulated power to the microprocessor, a firing capacitor and a bleed resistor which acts as a shunt and drains the firing capacitor to safe voltage levels after a period of time. During preparations for a blast, one or more detonators is/are placed in each hole. The detonators are then logged, during which the operator applies a hand-held device, commonly referred to as a “logger” to the detonator to generate an association between the detonator’s unique electronic identity and the borehole into which it is deployed. Logging commonly also includes programming the detonator by writing a firing time for the hole in question into the detonator’s memory, testing the detonator for its readiness to fire, and recording all relevant details of the detonator in the memory of the logger.

At this or any other time during blast preparation, a detonator or a circuit of connected detonators may be tested. The purpose of circuit testing is (a) to confirm that every detonator is ready to fire and (b) assess the amount of current leakage between the wires of the circuit. Leakage is commonly caused by water ingress at a connector or at a point of damage to wire insulation. Current leakage lowers the voltage at those detonators furthest from the blaster unit and often adversely affects two-way communication between the blaster unit and the detonators.

Once a blast command is sent out from the blaster unit, the wire connecting the detonators to the blaster unit is switched off / deactivated and the detonators must thus live off the charge in the capacitors which act as internal batteries for the duration of the countdown.

At the time of firing, the detonator functions by essentially “counting down” its firing time using the energy stored in the capacitor. It will be appreciated that this term does not refer to literal counting but to the pre-blast delay built into the detonator by means of the stored energy. It will be appreciated that the residual energy after countdown must be sufficient to fire the fuse head. The predefined energy threshold is defined by the maximum firing time designed into the system.

Firing capacitors typically require their full charge to ensure that they are capable of sustaining the electronic circuitry in the countdown for the maximum firing time required and still have enough energy to fire the fuse head. If there is leakage and the capacitor is unable to reach its full charge, the likelihood of the detonator not being able to fire increases, as by the time the firing time is reached, the voltage in the capacitor may well have dropped too low. This issue leads to potential misfires. Current systems typically allocate a common charge level threshold to all detonators, based on the maximum firing time designed into the system. Any detonator whose voltage is below this threshold will be reported as a misfire or potential misfire. The mine or other blasting site would then investigate whether a misfire actually happened.

Unreliable reporting could result in detonators becoming unknown misfires or could result in an overly cautious approach which reports detonators as potential misfires when in fact they have a high probability of firing. It is desirable to provide a reliable method of assessing whether a troublesome detonator is likely to be a potential misfire in an electronic blasting system.

Other causes of misfires include lightning, broken leg-wires or excessive current leakage. Some systems are capable of detecting such potential misfires before blasting and are able to flag these as “known misfires”. These are addressed by re-priming holes before the blast or by careful excavation at the known misfire location after the blast. Another class of misfires is referred to as “unknown misfires”, not reported to the operator before the fire command is sent. A major purpose of testable electronic detonators is to detect all potential misfires and therefore to avoid unknown misfires. However, the latter still do occur in practice and are particularly troublesome.

Embodiments of the present invention aim to address or alleviate the issues identified above, at least to some extent.

Summary of the invention

In accordance with a first aspect of the invention, there is provided a method of identifying potential misfires in an electronic blasting system, the blasting system including a plurality of detonators connected to at least one blaster unit via a wire network and positioned according to a blast design, and the method comprising, prior to firing of the detonators, for at least one of the detonators: collecting or obtaining data from the detonator, the data including at least a charged voltage of a firing capacitor of the detonator; determining whether the charged voltage is sufficient to sustain a programmable electronic module of the detonator in a blasting countdown for the duration of a programmed firing time of the detonator so as to permit firing of a fuse head of the detonator at the programmed firing time; and if it is determined that the charged voltage is insufficient to sustain the electronic module of the detonator so as to permit firing of the fuse head at the programmed firing time, identifying and/or reporting a potential misfire in respect of the detonator, or if it is determined that the charged voltage is sufficient to sustain the electronic module of the detonator so as to permit firing of the fuse head at the programmed firing time, allowing blasting to continue normally in respect of the detonator.

The method may include carrying out arming of the plurality of detonators, including charging of the firing capacitors of the detonators, prior to collecting or obtaining the data from each detonator.

The method may include transmitting an instruction to each detonator to measure the charged voltage of its firing capacitor and to report the measurement if the charged voltage is below a nominal standard charged value. The data collected or obtained may thus be the reported measurements from these detonators.

The nominal standard charged value may be between about 15 V and about 17 V.

Each detonator’s programmable electronic module may be programmed with a firing time relating to the detonator’s position in the blast design. The data collected or obtained may further include, for each detonator, the detonator’s programmed firing time. The charged voltage may be a measured voltage before the detonator receives a blast command.

The system (e.g. control unit or blaster unit) may be configured correlate the reported measurement with the detonator’s programmed firing time. The charged voltage of the firing capacitor of each detonator must be sufficient to sustain the detonator’s electronic module in the countdown to blasting for the length of its programmed firing time and still fire the fuse head. Where the correlation indicates sufficient voltage in the firing capacitor to fire the detonator at its programmed firing time, no potential misfire will be reported by the system and the sequence of firing the blast will continue as normal. Where the correlation indicates insufficient voltage in the firing capacitor to fire the detonator at its programmed firing time, a potential misfire will be reported by the system. The method may include, subsequent to identifying and/or reporting a potential misfire in respect of a particular detonator, reprogramming the detonator with a shorter firing time so as to avoid a misfire of the detonator. Reprogramming may be carried out by or occur under the authority/instruction of an operator.

The method may include the step of analysing a correlation between the detonator’s charged voltage and its programmed firing time in order to determine whether the detonator has the potential to misfire.

The system may be configured to calculate and/or propose a maximum firing time based on a reduced charge curve associated with the detonator and the detonator may be reprogrammed with the maximum firing time (which is less than the originally programmed firing time).

In short, the method/system thus enables, prior to the firing of the detonators, data to be collected from each detonator and analysed to determine the probability of the detonator misfiring.

The electronic blasting system may further include a control unit configured to control the detonators through their powering, arming, calibration and/or firing processes. Each blaster unit may communicate with the control unit for controlling the charging, arming, calibration and firing processes of the detonators.

The wire network may be a surface harness wire network.

Each detonator may include the programmable electronic module which may include an integrated circuit and the chargeable firing capacitor. Each detonator may further include a fuse head and an explosive charge.

According to a second aspect of the invention, there is provided an electronic blasting system comprising: at least one blaster unit; a plurality of detonators connected or connectable to the at least one blaster unit via a wire network and positioned or positionable according to a blast design, each detonator including a programmable electronic module having an integrated circuit and a chargeable firing capacitor, and each detonator further including a fuse head and an explosive charge; a control unit configured to communicate with the at least one blaster unit for controlling the charging, arming, calibration and/or firing processes of the detonators, wherein the system is configured to identify potential misfires by, prior to firing of the detonators, for at least one of the detonators: collecting or obtaining data from the detonator, the data including at least a charged voltage of the firing capacitor of the detonator; determining whether the charged voltage is sufficient to sustain the programmable electronic module of the detonator in a blasting countdown for the duration of a programmed firing time of the detonator so as to permit firing of the fuse head of the detonator at the programmed firing time; and if it is determined that the charged voltage is insufficient to sustain the electronic module of the detonator so as to permit firing of the fuse head at the programmed firing time, identifying and/or reporting a potential misfire in respect of the detonator, or if it is determined that the charged voltage is sufficient to sustain the electronic module of the detonator so as to permit firing of the fuse head at the programmed firing time, allowing blasting to continue normally in respect of the detonator.

The system may be configured to carry out any of the method steps described above.

The programmable electronic module may include an application specific integrated circuit (ASIC), containing non-volatile memory, in which certain parameters relating to a state of the detonator are recorded to its non-volatile memory for post-blast evaluation.

The recorded parameters may comprise at least the voltage of the firing capacitor after countdown, and before firing of the detonator, and whether or not the detonator received a blast command.

According to a third aspect of the invention, there is provided a detonator comprising a programmable electronic module including an integrated circuit and a firing capacitor, wherein the programmable electronic module of the detonator is configured to interrogate itself and report an exception if a charged voltage of the firing capacitor is below a nominal standard charged value.

According to a fourth aspect of the invention, there is provided a detonator comprising a programmable electronic module including an application specific integrated circuit (ASIC), containing non-volatile memory, in which certain parameters relating to a state of the detonator are recorded to its non-volatile memory for post-blast evaluation.

The recorded parameters may be chosen so as to optimize diagnostics on misfired detonators.

According to a fifth aspect of the invention, there is provided detonator comprising a programmable electronic module having an application specific integrated circuit (ASIC) and a firing capacitor, wherein the programmable electronic module is configured to interrogate itself and report an exception if a charged voltage of the firing capacitor is below a nominal standard charged value, and wherein the ASIC contains non-volatile memory in which certain parameters relating to a state of the detonator are recorded for post-blast evaluation.

Brief description of the drawings

An embodiment of the invention is described below, by way of example only, and with reference to the following drawings, in which:

Figure 1 is a schematic diagram of an electronic blasting system according to the invention; Figure 2 is a schematic drawing of a detonator of the electronic blasting system;

Figure 3 is a schematic drawing of a logger connected a detonator of the electronic blasting system;

Figure 4 is a schematic drawing of logger connected to a number of detonators of the electronic blasting system;

Figure 5 is a flow diagram depicting steps in a process implemented by the electronic blasting system; and

Figure 6 is a graph depicting an exemplary detonator’s charge voltage over time. Detailed description with reference to the drawings

The following description is provided as an enabling teaching of the invention, is illustrative of principles associated with the invention and is not intended to limit the scope of the invention. Changes may be made to the embodiment/s depicted and described, while still attaining results of the present invention and/or without departing from the scope of the invention. Furthermore, it will be understood that some results or advantages of the present invention may be attained by selecting some of the features of the present invention without utilising other features. Accordingly, those skilled in the art will recognise that modifications and adaptations to the present invention may be possible and may even be desirable in certain circumstances and may form part of the present invention.

Referring to Figure 1 , an example embodiment of an electronic blasting system (10) is shown. The system (10) comprises multiple detonators (12) connected via connectors (14) to a surface harness wire network (16) and to a blasting machine, also known as a blaster unit (18) or (19). Multiple blaster units (18, 19) are connected wirelessly, via suitably configured modems and antennas (21 ), to a control unit (20) that controls the detonators (12) through their powering, arming, calibration and firing processes. In some cases, blaster units (18, 19) may be connected to each other via a two-wire cable (22), e.g. for signal integrity and synchronization between units.

In use, at a blast site, a pattern of boreholes is drilled according to a blast design, where the parameters of each hole, including its position and firing time, are pre-assigned. Each borehole is then primed with one or more detonators (12). The detonator (12) may be inserted into a booster (not shown) to create a primer that initiates the explosive charge, alternatively the detonator (12) may directly initiate certain explosives itself. The detonator (12) is then lowered into the borehole and the hole is filled with a predetermined quantity of explosives.

Referring to Figures 1 and 2, each detonator (12) in the network is connected to the surface harness wire (16) via a two-core cable (24) and a connector (14). Each detonator (12) comprises a sealing plug (26), a crimp (28), an electronic module (30), a fuse head (32) and an explosives charge (34) which are contained inside a metal shell (36). In this example embodiment, each electronic module (30) comprises electrostatic discharge and over-voltage barriers (38), a low-voltage power supply (40) to supply regulated power to an application-specific integrated circuit (ASIC) (42) containing non-volatile memory and a firing switch, a bleed resistor (44) and a firing capacitor (46). The bleed resistor (44) acts as a shunt to drain the firing capacitor (46) to safe voltage levels after a period of time.

The ASIC (42) has non-volatile memory that allows data to be written to and read from it during manufacturing, during programming, during testing and during the initiation of the detonator. Certain information is written into the ASIC’s non-volatile memory during manufacture. This information includes a unique detonator identifier (ID), detonator cable length, date of manufacture, and quality control test results.

Referring to Figure 3, detonators (not shown in Figure 3) are programmed by writing a firing time and relative position into the detonator’s non-volatile memory by means of a portable logger (60) connectable to the detonator, either via the connector (14) which connects to the logger’s connector port (62) or directly from the cable (24) to the cable ports (64) on the logger (60) (connection not depicted). The logger (60) registers each detonator’s unique ID, and other details already stored in the detonator’s ASIC, and programs a firing time into the detonator, based on the detonator’s position in the blast design.

Additional information, including detonator position, date and time and logger ID may also be recorded on the detonator’s non-volatile memory. The logger (60) also tests each detonator for current consumption, and confirmation that it has been successfully programmed, and may request any other information from the detonator, including environmental measurements.

Referring now to Figure 4, once the logging of the detonators is complete, the harness wire (16), that connects all the detonators, is connected to the logger (60) at the cable ports (64) to verify that all logged detonators are present and functioning. This test also involves searching for detonators that have accidentally not been logged.

In this embodiment of the invention, the blasting units and the control unit (18, 19 and 20) are physically identical and are initialised as either a control unit or a blaster unit during preparation for undertaking a blast. Blaster units are initialised from a logger (60) via short-range wireless communication or cable between logger and blaster unit. During initialisation, data recorded in the logger (60) during logging of the detonators is transferred to the blaster unit via either one of these two communication methods. This information includes the identities and firing times of each detonator (12).

Once the control unit (20) has been initialized, the system (10) is armed. During arming, the detonators (12) receive power from the blaster unit (18 or 19) that they are connected to via the surface harness wires (16) and the detonators’ firing capacitors (46) are charged. Once a blast command has been issued by the control unit (20), and then communicated to each detonator (12) from their respective blaster units (18,19), the wire (16) connecting the detonators (12) to the blaster units (18,19) is switched off (deactivated), meaning that they no longer supply power to the detonators (12), and the detonators (12) must survive off the charge in their firing capacitors (46), which act as temporary internal batteries, for the duration of the count down.

The detonator (12) then counts down to the firing time assigned to it by the logger (60) using the charge stored in the firing capacitor (46). The residual charge in the firing capacitor (46) after countdown must be sufficient to fire the fuse head (32).

Referring to the flow diagram (70) of Figure 5, once the detonators (12) have been armed and their firing capacitors charged (46) by the blaster units (18,19) at stage (72), the blaster units (18, 19) issue/transmit repeating test sequences to the detonators. During testing, a detonator will only respond to the test if one of its test parameters is not met, for example, the firing capacitor’s charged voltage being below the nominal standard charged value.

Referring to line (1) in Figure 6, firing capacitors (46) require their full charge (in this embodiment being approximately 16V) to ensure that they are capable of sustaining the detonator’s ASIC (42) in the countdown to blasting for the possible maximum firing time reflected at “B” (in this example 40 seconds) and still have enough energy to fire the fuse head (in this case approximately 9V). This allows for the capacitor (46) to slowly discharge over time, and still have sufficient voltage to fire when the time is right. If there is leakage and the capacitor is unable to reach its full charge, the likelihood of the detonator (12) not being able to fire is high, as by the time the firing time is reached, the voltage in the capacitor (46) will have dropped too low. This leads to a potential misfire. The most likely reasons that a capacitor (46) does not take its full charge is nearby leakage in the cable system (16) usually caused by cable damage. Leakage will drop the voltage from the blaster unit (18,19) to the detonator (12) and therefore prevent a detonator (12) from achieving its full capacitor charge.

If a capacitor does not take its full charge during the arming process, the system (10) will warn the user that a problem exists. The system (10) is configured to calculate/determine whether the capacitor has sufficient charge to fire the detonator (12) at its programmed firing time or not. If not, it will warn the operator of a potential misfire.

Referring to Figures 5 again, the system (10) instructs each detonator (12) to measure its charged voltage at stage (74). If the charge voltage is normal, i.e. at or above the nominal standard charged value at stage (76), no potential misfire is reported (78) and blasting can proceed to completion at stage (80).

However, the system (10) is configured to report the measurement if the voltage is below the nominal standard charged value, at stage (82). In this example, this nominal standard charged value is between 15 V and 17 V. The system (10) then correlates this reported measurement with the detonator’s programmed firing time and decides whether to report the detonator as a potential misfire. For example, referring to line (2) in Figure 6, if a detonator’s charged voltage is 13 V, but the detonator is programmed with a firing time of less than the time reflected at “A”, the system (10) determines that the capacitor will still fire (see stages (84) and (56) in Figure 5), as the charge left in the capacitor at firing time will be sufficient to fire the fuse head. If however the detonator is programmed with a firing time in excess of “A”, then the system (10) will report a potential misfire and propose a maximum firing time based on the reduced charge curve (see stages (84), (86) and (88) in Figure 5.

This allows the system (10) to avoid unnecessarily reporting potential misfires and provides a method for the operator to ensure that a detonator that is reported as a potential misfire is guaranteed to fire. However, if the proposed maximum firing time is not accepted by the operator, a potential misfire is still reported at stage (90). The detonator (12) is also capable of recording the firing parameters to the non-volatile memory of its ASIC (42). These parameters include the voltage on the firing capacitor (46) after countdown and just before firing, whether or not the detonator (12) received its blast command, as well as the switching of the firing capacitor (46) to release the charge into the fuse head (32).

These parameters are chosen to optimise diagnostics on misfired detonators. If for some reason the detonator (12) does not fire, the information can be retrieved from the detonator’s non-volatile memory.

Embodiments of the invention may therefore provide an effective system for and method of determining a detonator’s fitness to fire or likelihood to misfire, and also of collecting and analyzing data from a detonator to determine the probability of the detonator misfiring or not. The invention may thus assist in reducing or preventing unknown misfires, at least to some extent.

The invention may also provide a detonator comprising a programmable electronic module including non-volatile memory which is capable of interrogating itself and reporting any exceptions/issues, and which is further capable of storing certain parameters about its state to its non-volatile memory for post-blast evaluation.

Claims

1 . A method of identifying potential misfires in an electronic blasting system, the blasting system including a plurality of detonators connected to at least one blaster unit via a wire network and positioned according to a blast design, and the method comprising, prior to firing of the detonators, for at least one of the detonators: collecting or obtaining data from the detonator, the data including at least a charged voltage of a firing capacitor of the detonator; determining whether the charged voltage is sufficient to sustain a programmable electronic module of the detonator in a blasting countdown for the duration of a programmed firing time of the detonator so as to permit firing of a fuse head of the detonator at the programmed firing time; and if it is determined that the charged voltage is insufficient to sustain the electronic module of the detonator so as to permit firing of the fuse head at the programmed firing time, identifying and/or reporting a potential misfire in respect of the detonator, or if it is determined that the charged voltage is sufficient to sustain the electronic module of the detonator so as to permit firing of the fuse head at the programmed firing time, allowing blasting to continue normally in respect of the detonator.

2. The method according to claim 1 , which includes carrying out arming of the plurality of detonators, including charging of the firing capacitors of the detonators, prior to collecting or obtaining the data from the at least one detonator.

3. The method according to claim 1 or 2, which includes transmitting an instruction to each detonator to measure the charged voltage of its firing capacitor and to report the measurement if the charged voltage is below a nominal standard charged value.

4. The method according to any one of the preceding claims, wherein the data collected or obtained further includes the detonator’s programmed firing time.

5. The method according to any one of the preceding claims, which includes analysing a correlation between the detonator’s charged voltage and its programmed firing time in order to determine whether the detonator has the potential to misfire.

6. The method according to any one of the preceding claims, which includes, subsequent to identifying and/or reporting a potential misfire in respect of a particular detonator, reprogramming the detonator with a shorter firing time so as to avoid a misfire of the detonator.

7. The method may according to claim 6, which includes calculating and/or proposing a maximum firing time based on a reduced charge curve associated with the detonator and reprogrammed the detonator with the maximum firing time.

8. An electronic blasting system comprising: at least one blaster unit; a plurality of detonators connected or connectable to the at least one blaster unit via a wire network and positioned or positionable according to a blast design, each detonator including a programmable electronic module having an integrated circuit and a chargeable firing capacitor, and each detonator further including a fuse head and an explosive charge; a control unit configured to communicate with the at least one blaster unit for controlling the charging, arming, calibration and/or firing processes of the detonators, wherein the system is configured to identify potential misfires by, prior to firing of the detonators, for at least one of the detonators: collecting or obtaining data from the detonator, the data including at least a charged voltage of the firing capacitor of the detonator; determining whether the charged voltage is sufficient to sustain the programmable electronic module of the detonator in a blasting countdown for the duration of a programmed firing time of the detonator so as to permit firing of the fuse head of the detonator at the programmed firing time; and if it is determined that the charged voltage is insufficient to sustain the electronic module of the detonator so as to permit firing of the fuse head at the programmed firing time, identifying and/or reporting a potential misfire in respect of the detonator, or if it is determined that the charged voltage is sufficient to sustain the electronic module of the detonator so as to permit firing of the fuse head at the programmed firing time, allowing blasting to continue normally in respect of the detonator.

9. The system according to claim 8, which is configured to transmit an instruction to each detonator to measure the charged voltage of its firing capacitor and to report the measurement if the charged voltage is below a nominal standard charged value.

10. The system according to claim 8 or 9, wherein the data collected or obtained further includes the detonator’s programmed firing time.

11 . The system according to any one of claims 8 to 10, which is configured to analyse a correlation between the detonator’s charged voltage and its programmed firing time in order to determine whether the detonator has the potential to misfire.

12. The system according to any one of claims 8 to 11 , which is further configured, subsequent to identifying and/or reporting a potential misfire in respect of a particular detonator, to calculate and/or propose a maximum firing time based on a reduced charge curve associated with the detonator such that the detonator can be reprogrammed with the maximum firing time to avoid a misfire of the detonator.

13. The system according to any one of claims 8 to 12, wherein the programmable electronic module of the detonator includes an application specific integrated circuit (ASIC), containing non-volatile memory, in which parameters relating to a state of the detonator are recorded for post-blast evaluation.

14. The system according to any one of claims 8 to 13, wherein the programmable electronic module of the detonator is configured to interrogate itself and report an exception if a charged voltage of the firing capacitor is below a nominal standard charged value.

15. A detonator comprising a programmable electronic module having an application specific integrated circuit (ASIC) and a firing capacitor, wherein the electronic module is configured to interrogate itself and report an exception if a charged voltage of the firing capacitor is below a nominal standard charged value, and wherein the ASIC contains non volatile memory in which parameters relating to a state of the detonator are recorded for post-blast evaluation.