GB2083321A

GB2083321A - A method of signalling along drill shafts

Info

Publication number: GB2083321A
Application number: GB8126555A
Authority: GB
Original assignee: Marconi Co Ltd
Current assignee: BAE Systems Electronics Ltd
Priority date: 1980-09-03
Filing date: 1981-09-02
Publication date: 1982-03-17

Abstract

A communication system particularly for drilling in mines in which information is required to be transmitted from the drill tip (2) to the surface (or base tunnel if the drilling is horizontal) and sometimes vice versa. A transmitter is mounted in the drill adjacent the tip and a radio frequency signal is coupled to the drill shaft for transmission to the surface. The r.f. signal is modulated by a sensor (3) at the drill tip to supply temperature or position information. Transmission in the opposite direction, e.g. to steer the drill tip, is also possible. <IMAGE>

Description

SPECIFICATION A method of signalling along drill shafts This invention relates to a method and apparatus for signalling information along a drill shaft, and particularly, although not exlusively, for signalling to and from the drill bit in a long-hole drilling situation.

In such situations, e.g. in connection with mines, the medium the drill is cutting through would normally attenuate radio frequency signals transmitted through the medium from the drill bit to a receiver on the surface. The use of cables to transmit information presents reliability problems resulting from the harsh environment.

An object of the present invention is to provide a signalling facility, for use in mine drilling for example, in which the above problems are overcome and in which signalling can be effected while drilling is in progress.

According to one aspect of the invention therefore, in a method of signalling between stations between which a length of drill shaft extends, a modulated radio-frequency signal is impressed upon the drill shaft at one of said stations and decoupled from the drill shaft at the other.

Where the drill shaft is hollow it may contain a radio-frequency transmitter at the one station, the transmitter signal being modulated by a sensor at that station.

The transmitter may be coupled to the drill shaft by conduction and the radio-frequency signal decoupled from the drill shaft by a stationary induction member.

According to another aspect of the invention, a signalling arrangement for an earth drilling system comprises transmitter means arranged to impress a modulated radio-frequency signal upon a drill shaft at one station, and receiver means for decoupling the radiofrequency signal from the drill shaft at another station.

Where the drill shaft is hollow the transmitter means may be mounted within the hollow drill shaft, sensor means being mounted at the one station and connected to the transmitter means, the sensor being arranged to modulate the transmitter radio-frequency signal.

The signalling arrangement may be duplicated to provide transmitter means and receiver means at each station and thereby permit two way signalling, the arrangement being such that each receiver means is responsive to signals from the remote transmitter means only.

A method and apparatus for signalling between stations in a drilling situation will now be described, by way of example, with reference to the accompanying block diagram of a drill shaft and transmitter and receiver stations.

A drill shaft 1, shown horizontally, but commonly vertical, consists of a steel tube in a number of sections according to the required depth of hole. At the bottom end of the drill shaft is a drill bit 2 which performs the cutting action as the drill shaft is rotated from the upper end by means not shown.

The drill shaft may be of substantial diameter and length, for example 70 mm diameter and 1 Km long.

It is sometimes desirable to know, while the drilling operation is proceeding, the conditions at the drill bit, its temperature for example. It is then necessary to provide a sensor at or in the vicinity of the drill bit and means for signalling the output data of the sensor to the operator on the ground surface.

The latter function is achieved according to the invention by radio transmission along the drill shaft. A radio frequency signal is impressed upon the drill shaft at one station along the shaft, the drill bit station, and picked off, or decoupled from, the shaft at the surface station.

However, it is important that the radio frequency employed is such that the wavelength is large compared to the length of the drill shaft. If the wavelength is smaller than the shaft length, standing waves will arise. Voltage maxima will coincide with current minima and if the latter coincide with the receiver (surface) station the current will be difficult to detect. In addition, high losses will occur at the voltage peaks due to ground conductivity.

Special precautions have therefore to be taken with higher radio frequencies if useful results are to be obtained. Clearly then, lower radio frequencies are preferable and, with drill shaft lengths such as mentioned above, a frequency of about 10 kHz would be suitable.

Mounted inside the drill shaft adjacent the drill bit, is a transmitter and sensor. The sensor 3 may be a temperature sensor indicating the bit temperature so that the work rate can be adjusted within temperature limits. The transmitter comprises an oscillator 4 of suitable radio frequency which feeds a transformer primary 5 by way of a modulator circuit 6. This provides 100% amplitude modulation, effectively switching the oscilltor on and off.

The pulse repetition rate is fixed but the modulator 6 is controlled by a code generator 7 which provides width modulation of the 'on' pulses, the pulse width being proportional to the sensor signal magnitude.

The secondary 9 of the transformer is connected by direct conduction to the drill shaft, the ends of the winding being connected at points on either side of an insulating portion 11 which isolates the drill bit from the rest of the drill shaft. The transmitter signal is thus effectively applied between earth (at the drill bit) and the main part of the drill shaft.

At the surface station a receiver 1 3 is positioned and is coupled to the drill shaft by means of a ferrite coupling ring 1 5 which surrounds the drill shaft but is not in contact with it. A winding 1 7 on the ferrite ring is connected to an R.F. amplifier 19, a mixer and l.F. amplifier 21 fed by a local oscillator 23, the mixer being followed by a decoder 25 and display 27 of the sensed condition.

In some situations it may be necessary to transmit signals from the surface station to the drill tip location. In this case a further receiver 29 is connected to the transformer winding 9, while a further transmitter 31 is connected to the winding 1 7 of the ferrite ring.

Transmission of signals to the drill tip may be required to steer the path of the drill, for example along a slightly undulating horizontal coal seam. Again, the transmitter at the drill tip may be switched on and off by signals transmitted from the surface, thus conserving the local power source.

Where there are a number of sensors at the drill tip, indicating temperature, position etc.

A particular sensor may be selected by appropriate signals transmitted.

Ciearly various well known modulation and coding systems other than that described above may be employed. For example, the radio frequency signal may be pulsed at a low frequency, the pulses then being transmitted or not according to a pulse code modulation to give a binary indication of the sensor signal magnitude.

Claims

1. A method of signalling between stations between which a length of drill shaft extends, wherein a modulated radio-frequency signal is impressed upon the drill shaft at one of said stations and decoupled from the drill shaft at the other.

2. A method according to Claim 1, wherein said drill shaft is hollow and contains a radio-frequency transmitter at said one station, the transmitter signal being modulated by a sensor at that station.

3. A method according to claim 2, wherein the transmitter is coupled to the drill shaft by conduction.

4. A method according to Claim 2 or Claim 3, wherein the radio-frequency signal is decoupled from the drill shaft by a stationary induction member.

5. A method according to any preceding claim, including a transmitter and a receiver at each of said stations for two-way signalling.

6. A signalling arrangement for an earth drilling system, and comprising transmitter means arranged to impress a modulated radiofrequency signal upon a drill shaft at one station, and receiver means for decoupling the radio-frequency signal from the drill shaft at another station.

7. A signalling arrangement according to Claim 6, wherein the drill shaft is hollow and said transmitter means is mounted within the hollow drill shaft, and sensor means is mounted at said one station said sensor means being connected to the transmitter means and being arranged to modulate the transmitted radio-frequency signal.

8. A signalling arrangement according to Claim 7, wherein said transmitter means is couple to the drill shaft by electrical conductor means.

9. A signalling arrangement according to any of Claims 6, 7 and 8, wherein said receiver means is stationarily mounted and is coupled to the drill shaft by electrical inductor means.

10. A signalling arrangement according to any of Claims 6 to 9, duplicated to provide transmitter means and receiver means at each station and thereby permit two way signalling, the arrangement being such that each receiver means is responsive to signals from the remote transmitter means only.

11. A method of signalling along a drill shaft substantially as hereinbefore described with reference to the accompanying drawing.

1 2. An arrangement for signalling along drill shafts, substantially as hereinbefore described, with reference to the accompanying drawings.