[0001] This invention relates to a control device for use with a detonator which enables the detonator to be responsive to wireless signals from a controller in a blasting system.

[0002] Wireless detonators employed in a blasting system can facilitate automated mining processes and eliminate problems associated with damage to a harness of the type used in a wired detonator system.

[0003] A wireless detonator in which communication is effected at a radio frequency typically needs an antenna or receiver/antenna combination that is placed outside a borehole in which the detonator is positioned. This is necessary as an electric field does not penetrate deeply into rock around the borehole. On the other hand a receiver which operates in response to a magnetic field has the advantage that the field can propagate through rock and, although some attenuation of the magnetic field is experienced, typically no external antenna or external receiver is required to be positioned outside of the borehole.

[0004] The applicant's patent application number ZA2010/07921 entitled WIRELESS BLASTING MODULE relates inter alia to a wireless detonator. The content of the specification of that patent application is hereby incorporated into this specification.

[0005] Other approaches to the field of wireless detonators are disclosed in US2008/0307993A1 and US2010/17041 1A1.

[0006] A magnetic field-based system does however suffer from the disadvantage that the strength of the magnetic field decreases rapidly as the distance between a transmitter and a receiver increases. To address this the receiver is typically required to have an antenna with a large number of turns and a high effective coil area to ensure adequate reception of signals transmitted from a blast controller's antenna.

[0007] The transmitting and receiving antennas may be tuned to a specific frequency by means of a parallel or series capacitor to obtain Q-factors for the resulting resonant circuits that improve the transmitted and received signal strengths respectively. For the receiver, the coil antenna is a limiting factor because it is physically bulky, relatively heavy and expensive. It is also difficult to fabricate as thin wires are normally used over a large number of turns to improve the required signal level. Additionally, a receiver that is required to be omnidirectional requires three antennas disposed at a right angle to one another. These factors hamper the adoption of this type of coil-based, wireless electronic receiver, for use with a detonator.

[0008] An object of the present invention is to provide an alternative arrangement for establishing wireless communication between a detonator and a controller.

SUMMARY OF THE INVENTION

[0009] The invention provides a control device for use with a detonator which includes an electrical energy source, a magnetoresistive sensing arrangement which, in response to a predetermined wireless signal, produces a control signal, and processor means which extracts data from the control signal and which inputs the data to a control circuit of the detonator.

[0010] The electrical energy source may be of any appropriate kind and preferably includes a battery. The electrical energy source may provide energy at a fixed voltage to the magnetoresistive sensing arrangement. Alternatively the energy source acts as a constant current source to provide energy to the magnetoresistive sensing arrangement.

[0011] The magnetoresistive sensing arrangement may include any appropriate magnetic field sensor or sensors. A sensor of this type displays the characteristic of a change in resistance when exposed to a magnetic field. The change in resistance may be due to an ordinary magnetoresistive effect (OMR), an anisotropic magnetoresistive effect (AMR), a giant magnetoresistance effect (GMR), a colossal magnetoresistance effect (CMR), a magnetic tunnel effect or tunnel magnetoresistance effect (TMR), an extraordinary magnetoresistance effect (EMR) or any combination thereof. GMR may include a multi-layered GMR, spin-valve GMR, pseudo spin-valve GMR, granular GMR or an extension of the spin-valve GMR. These effects are referred to herein collectively as the "magnetoresistive effect".

[0012] The magnetoresistive effect is particularly suitable for use in a system in which communication is unidirectional i.e. a signal is transmitted from a coil-or loop- based magnetic transmitter, possibly tuned with at least one capacitor, to a receiver, associated with or incorporated in a detonator, that embodies at least one magnetoresistive sensor. To enable the receiver to display an omnidirectional receive capability a plurality of sensors may be used, orientated at a right angle to one another.

[0013] The magnetoresistive sensing arrangement may be separate to, or combined with, a receiver circuit or the control circuit of the detonator and, when fabricated as an integrated circuit, may be manufactured on a common substrate to the receiver circuit or, the detonator control circuit preferably together with the processor means. [0014] The magnetoresistance effect has been employed in diverse applications. EP0950871 B1 describes the effect to assess the spin rate of a round or to sense the exit of a round from a gun barrel. WO2002/0307052 describes the use of the effect in borehole measurements.

[0015] US71 12957 describes a proximity sensor which is based on the use of magnetoresistive resistors which are used together with flux concentrators.

[0016] US2008/0299904 relates to a wireless communication system in which a transmitter generates a modulated magnetic field and a receiver includes a solid magnetic field sensor, which incorporates a magnetoresistive sensor, to sense the magnetic field.

[0017] These documents do not disclose nor suggest the adaption of magnetic communication techniques which are based on the use of a plurality of magnetoresistive sensors which are respectively associated with detonators included in a detonator system which, in turn, is responsive to a blast controller.

[0018] The magnetoresistive sensing arrangement of the invention preferably is configured to be responsive to small resistive changes, and so that the arrangement is substantially temperature-insensitive. To achieve this it is preferable to make use of a Wheatstone bridge configuration which is formed from magnetoresistive sensors.

[0019] Within the bridge some magnetoresistive sensors may be shielded from magnetic fields and act primarily as temperature drift compensation means. A flip coil may be used for offset correction or to cause the bridge to recover from exposure to high magnetic field strengths. Reference is made in this respect, for example, to the data sheet "Magnetic Field Sensors" issued by Phillips under the title Discrete Semiconductors SC17 of 12 June 1998.

[0020] An output of the magnetoresistive sensing arrangement may be applied to a signal processing module which may include at least one of the following: an amplifier and a filter. The filter may be a low pass or a band pass filter, and may include a plurality of filtering stages. Similarly, use may be made of a plurality of amplifying stages and of automatic gain techniques or offset compensation to enable the sensing arrangement to be responsive in an accurate manner to widely varying dynamic or static magnetic fields.

[0021] The processor means may be a microcontroller, asic, fpga or other logic device of any appropriate kind. The processor means may be operable to generate an offset signal which compensates for the effect of the earth's magnetic field, determined during a period in which an input signal i.e. from the blast controller, is absent.

[0022] The control device may be provided as a standalone device for use with a detonator, or as an assembly which is contained in a housing to which the detonator is attached or in which the detonator is located. Components of the control device, where appropriate, may be formed as part of an integrated circuit in combination with components from the detonator or the control circuit which is associated with the detonator.

[0023] The invention also extends to a blasting system which includes a plurality of detonators, a plurality of control devices, each control device being of the aforementioned kind and being associated with a respective detonator, and a blast controller which generates and transmits at least one wireless signal to which the respective control devices are responsive.

[0024] Each control device may be associated with a respective identifier or code which enables a signal from the blast controller to be associated uniquely with a target detonator or control device. For example a signal from the blast controller may be encoded with data which is uniquely associated with a target detonator. In an alternative application a signal from the blast controller, transmitted in broadcast fashion, is intended to be received and acted upon by each of the detonators or control devices in the blasting system.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The invention is further described by way of example with reference to the accompanying drawings in which:

Figure 1 schematically depicts a plurality of detonators, each of which includes a control device according to the invention, incorporated in a blasting system; and Figure 2 depicts in block diagram form a control device according to the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0026] Figure 1 of the accompanying drawings illustrates a blasting system 10 which includes a blast controller 12 and an array of detonators 14A, 14B... respectively positioned in boreholes 16A, 16B...

[0027] Each detonator is associated with a respective control circuit 8A, 18B... and a control device 20A, 20B... according to the invention.

[0028] The blast controller 12 includes a control unit 30 of a kind which is known in the art and which for this reason is not further described herein. The control unit 30 functions in a known way to produce a plurality of control signals. Each control signal is applied to a magnetic field generator and transmitter 32 which in turn is connected to a transmitting coil 34 which consists of at least one winding. The transmitting coil may surround the detonators in the area to be blasted or may be contained within this area or overlap the area as desired.

[0029] Each detonator 14 is an electronic detonator which includes a respective control circuit 18 of a kind which is known in the art. The control circuit typically embodies a unique identifier or code for the associated detonator. The function of the code is to enable the detonator to be targeted in a unique manner by a control signal from the blast controller. If a coded signal is however not emitted by the blast controller then all the detonators are responsive, in broadcast manner, to the control signal. The detonators could then be directly fired, possibly after a predetermined delay period.

[0030] The control device 20, associated with a detonator, is shown in block diagram form in Figure 2.

[0031] The control device includes a magnetoresistive sensor 40, a signal processor 42, a controller 44 and an energy source 46.

[0032] The magnetoresistive sensor arrangement 40 may be configured in any appropriate form and preferably includes a Wheatstone bridge formed from a plurality of magnetoresistive sensors. The use of a bridge structure reduces the temperature sensitivity of the arrangement and enables small resistive changes to be detected. Some of the magnetoresistive sensors may be shielded from external magnetic fields, as is known in the art. It may be necessary to employ a flip control circuit 48 for offset correction or to reset the sensors to facilitate recovery from an exposure to a magnetic field of a high strength.

[0033] The current consumption of the Wheatstone bridge and associated electronic elements is typically low and the components are readily powered by an on-board energy source in the form of one or more batteries 46 which provide an electrical supply at a fixed voltage. Alternatively use is made of a constant current source 50 to provide energy to the sensing arrangement while other components of the control device may be powered conventionally at a fixed voltage. The constant current source helps to compensate for bridge resistance variations due, inter alia, to temperature changes.

[0034] Optionally a flux concentrator 52 is coupled to the sensing arrangement 40 in order to increase the sensitivity of the arrangement. Due care is taken to avoid nonlinear effects which are attributable to saturation of the flux concentrator to particular magnetic field values in the range of operation.

[0035] It is possible to provide the magnetoresistive bridge elements and the flip control coils in a single package and preferably at least the controller 18, bridge 40 and the controller 44 are fabricated as part of an integrated circuit on a common substrate.

[0036] The magnetoresistive effect is particularly suitable for use in a blasting system of the kind shown in Figure 1 in which communication is unidirectional i.e. from the blast controller 12 to the detonators. The individual control devices 20, in order to be omnidirectional, may each include a plurality of magnetoresistive sensors orientated at a right angle to one another. [0037] The directionality and number of sensors used depend on the type of sensors. A wide range of magnetoresistive sensors is available. These include sensors which respond to the ordinary magnetoresistive effect (OMR), the anisotropic magnetoresistance effect (AMR), the giant magnetoresistance effect (GMR), the colossal magnetoresistance effect (CMR), the magnetic tunnel effect or the tunnel magnetoresistance effect (TMR), the extraordinary magnetoresistance effect (EMR), or any combination of the aforegoing. The giant magnetoresistive effect may encompass the multilayer GMR, the spin valve GMR, the pseudo-spin valve GMR, the granular GMR or an extension of the spin GMR.

[0038] For example an AMR sensor is sensitive primarily to signals along one axis while some types of GMR sensors exhibit little directionality. GMR sensors also usually require a magnetic bias field to improve linearity.

[0039] The earth's magnetic field creates an offset for the readings from the sensor arrangement 40. This may be countered from a signal from an offset arrangement 56. The required offset may vary dynamically as there are small variations in the earth's magnetic field over time which may influence reception. In an alternative approach use is made of AC coupled gain stages to avoid the offset problem. Temperature shifts and component tolerances can also create offsets which must be compensated for. The orientation of the sensors relative to the earth's magnetic field is also a consideration which may require compensation. A good reference for these issues, when using an AMR sensor, is Application Note 218 from Honeywell.

[0040] An output of the sensor arrangement 40 is input to the signal processor 42 which includes one or more amplifiers and one or more filters. The filters are structured to provide a low pass or band pass characteristic or otherwise as may be appropriate in accordance with communication and modulation requirements. A number of amplification and filtering stages may be required due to the low magnitude of the signals which are received. The use of automatic gain techniques (58) or offset compensation may be necessary to enable the sensor arrangement to function accurately through a range of dynamic or static magnetic fields. As is indicated by means of a dotted line 62 electric and magnetic shielding may be necessary to prevent background signals from creating interference in the sensing circuit.

[0041] The output of the signal processor 42 is a voltage-based signal which varies in a manner which is dependent on the applied magnetic field which, in turn, is the field produced by the controlled generation and transmission of signals from the blast controller 12. The demodulation of the output signal from the signal processor is accomplished using a demodulator, not shown, which may be a separate circuit or which may be incorporated in the controller 44, or in an application specific integrated circuit. The kind of modulation required matches the modulation technique used in the signal generation and transmission process at the blast controller. Different modulation techniques have various advantages or disadvantages in terms of noise performance, bandwidth requirements, reliability and complexity.

[0042] The controller 44 is adapted to receive a signal from the processor 42 and to validate the signal. In response thereto the controller generates an output signal which is applied to the detonator control circuit 18 which controls arm, disarm, programming, firing and other phases of the detonator 14. Alternatively the detonator control circuit 18 supplies firing voltage and current to the respective electric detonator. These aspects are not further described herein. [0043] In use of the blasting system control signals generated by the blast controller are transmitted via the transmitter coil 34 to the various detonators. Each detonator is associated with a respective control device which embodies an arrangement of the kind shown in Figure 2. The signals transmitted by the blast controller can be transmitted on a broadcast basis in that each control device would detect and then respond to a transmitted signal. Alternatively signals from the blast controller can be uniquely encoded so that each signal is destined for subsequent action only by a targeted detonator or control device. Alternatively the signals from the blast controller are destined only for a selected set of devices, the set ideally being chosen under user control.

[0044] For communicating through rock, transmission frequencies are typically low, in a range of several hertz to several kilohertz. The invention however is not limited in this respect.

[0045] The controller 44 is preferably capable of detecting the absence of a transmitted signal from the blast controller and during this period of generating offset control signals to compensate for background magnetic fields.

[0046] The blast controller thus, through the use of suitable encoding techniques, is able to address each detonator and control device in turn. Validation techniques are implemented at each detonator and, once on-board testing at each detonator has been carried out and the functionality of the detonator has been validated, the detonator is placed in a state in which an encoded signal from the blast controller can be used to program the detonator with a required time delay. Thereafter, subject to further validation and control techniques, a broadcast signal from the blast controller can be sent to all of the detonators to cause firing thereof. [0047] In the described arrangement each control device 20 is not capable of directing a signal to the blast controller. Thus communication is unidirectional only. Each detonator however is a standalone device and has substantial on-board processing capability which enables the functionality of the detonator to be verified so that it can then be placed in a mode in which it is receptive to programming and firing commands.

[0048] In the described arrangement, a single processor is shown but the teachings of ZA2010/07921 may be selectively employed for improving the security and reliability of the device by using a plurality of processors, repeated commands, forward error correction et. al.