This invention relates to monitoring of the convergence of excavation surfaces in underground working areas in a mine. In particular the invention relates to a convergence meter and to a method of measuring relative movement between mine walls.

BACKGROUND TO THE INVENTION

The inventor is aware of a convergence meter, which has a telescopic measurement element. The convergence meter can be fitted between a footwall and a hanging wall in a stope. However, the telescopic element is limited in the range that can be measured by the length to which the telescopic element can extend. The present invention aims to address some of these shortcomings.

SUMMARY OF THE INVENTION

According to one aspect of the invention, there is provided a convergence meter, which includes a body having attachment means for attaching to a first reference point; a measurement element being extendible from the body of the convergence meter, in use to a second reference point; electronic measurement means, operable to measure movement of the measurement element, attached to the second reference point relative to the body of the convergence meter attached to the first reference point; a wireless transceiver operable to transmit measurements taken by the electronic measurement means to a remote receiver and to receive commands issued from a remote controller. The body may define an enclosure in which the electronic measurement means and the wireless communications interface is mountable.

The attachment means may be in the form of a mounting bracket to which the enclosure is mountable. The enclosure and mounting bracket may be mountable to the first reference point by means of mounting means. In particular, the mounting means may be in the form of at least one expansion bolt or the like.

The measurement element may be in the form of any one of a tape, a cable, a wire or the like. In particular, the measurement element may be in the form of a stainless steel tape.

The convergence meter may include a take-up arrangement from which the measurement element can be deployed and retracted. The take-up arrangement may be in the form of a reel onto which, and from which, the measurement element can be rolled. The take-up arrangement may include bias means for biasing the measurement element in a retracted condition. In the deployed condition, the measurement element may be deployed against a retracting force of the bias means. The bias means may be in the form of a coil- spring connected to the reel.

In use, the measurement element may be extendible from the take-up arrangement to a deployed condition in which the measurement element extends from the body, being attached to a first reference point, to a second reference point of which the relative movement to the first reference point is to be measured over a period of time.

In use, the electronic measurement means may thus measure movement of the deployed measurement element over an extended period of time. The measurement means may be in the form of a free-running wheel arrangement drivingly connected to the measurement element.

The free-running wheel arrangement may include a pair of wheels running against each other with the measurement element running between them. In particular, the pair of wheels may comprise a first wheel having an elastic circumferentially extending outer surface and a second wheel having a rigid circumference, with the measurement element running tangentially between the first and the second wheels, being pressed against the wheels.

The free-running wheel arrangement may include a rotary/angle encoder coupled to one of the pair of wheels. The rotary encoder may be operable to measure rotation of the wheels. The rotary encoder may be in the form of any one of a magnetic encoder, an optical encoder, or the like. For example, the encoder may be an AS5046 magnetic encoder from Austria Micro Systems.

In use, movement of the measurement element between the wheels will cause the wheels to rotate, which rotation can be measured by the rotary encoder. Tangential movement of the measurement element will cause angular movement of the rotary encoder, which can be calibrated to measure linear displacement of the measurement element.

In the embodiment in which the rotary encoder is a magnetic encoder, a magnet may be connected to one of the pair of wheels. The encoder may then be magnetically coupled to the magnet.

The magnet may be a disc shaped magnet, axially connected to one end of the axle of one of the pair of wheels. The wireless transceiver may be in the form of a radio frequency

(RF) transceiver, such as a ZigBee transceiver, or the like.

The wireless transceiver may be in the form of a two-way wireless RF transceiver, operable to receive commands from a matched remote transceiver and to transmit measurements to the remote transceiver.

It is to be appreciated that ZigBee is a registered trade mark of the ZigBee Alliance. This specification refers to methods implemented in accordance with the ZigBee Alliance's "ZigBee Cluster Library".

The convergence meter may include a motion sensor for sensing disturbance of the convergence meter body. For example, the motion sensor may be in the form of a mercury switch, or the like.

The convergence meter may include an on/off switch for switching the convergence meter on or off. The convergence meter may include a power supply for supplying power to the convergence meter.

The convergence meter may include processing means connected to the electronic measurement means and to the wireless transceiver. The processing means may be programmable with any one or both of reportable attributes and configurable attributes in accordance with the

"ZigBee Cluster Library".

More particularly, the processor may be programmable with any one or more of the following clusters from the "ZigBee Cluster Library":

- Profile wide commands;

- Basic cluster;

- Groups cluster; - Identification cluster;

- Location cluster; - Motion cluster;

- On/Off cluster;

- Power cluster; and

- Manufacturer specific Analog cluster.

The invention extends to a method of measuring convergence between mine walls, the method including electronically measuring relative movement between a measurement element and a body of the convergence meter; wirelessly transmitting the relative movement to a remote monitoring station.

The invention may further extend to a method of measuring convergence between mine walls, the method including deploying a number of convergence meters in an area where convergence between mine walls is to be measured; transmitting measured convergences from the convergence meters to a central recorder; measuring a convergence profile by spatially collating the measured convergences.

The invention will now be described, by way of example only with reference to the following drawing(s):

DRAWING(S)

In the drawing(s):

Figure 1 shows a body of a convergence meter in accordance with one aspect of the invention;

Figure 2 shows a component card of the convergence meter in Figure 1 in more detail; Figure 3 shows an electronic circuit of the convergence meter, of Figure

1 ;

Figure 4 shows a state diagram of a processor in the electronic circuit of Figure 3; and

Figure 5 shows a convergence meter in accordance with the invention.

EMBODIMENT OF THE INVENTION

In Figure 1 , a convergence meter 10 is shown. The convergence meter 10 has a body in two moulded halves 12.1 , 12.2. Circular apertures 14.1 to 14.4 are provided to attach the two body halves 12.1 , 12.2 to each other.

A component card 16 (see Figure 2) is mounted inside the body half 12.2 with electronic components (not shown for clarity) mounted on the card.

In Figure 2 the component card 16 is shown with a measurement element, in the form of a stainless steel tape 18 rolled onto a reel 20. The reel has a coil spring (not shown) for biasing the tape 18 in a retracted condition onto the reel.

The tape 18 is guided between two wheels 22, 24, mounted on two axels 26, 28, respectively. The wheel 22 has a knurled outer circumference 22.1 and the wheel 24 has an elastic wheel, in the form of an O-ring 24.1 with a grooved defined therein on its outer circumference. In operation, the O-ring 24.1 presses the tape 18 into the knurled outer circumference 22.1 and prevents slippage between the tape and the wheel 22.

A magnetic/angle rotary encoder 30 is axially aligned with the axle 26. A circular disc shaped magnet 32 (shown in broken line) is connected to a sleeve 34, which is rotatably mounted on the axle 26 to rotate in unison with the wheel 22. The magnet 32, being spaced above the encoder 30 produces a rotation signal measurable by the encoder 30.

As can be seen, linear movement of the tape 18, being frictionally connected to the wheel 22 will cause the wheel 22 and the magnet 32 to rotate, which rotation can be measured by the encoder 30.

In Figure 3 a processor 36 is connected to a Human Machine

Interface and Sensing module (HMIS) 42 sensing the rotation of the magnet 32 via the encoder 30. The processor 36 is calibrated to measure the rotations and to represent the rotation of the magnet 32 in terms of linear movement of the tape 18.

The processor 36 is programmed with reportable attributes and configurable attributes in accordance with the "ZigBee Cluster Library".

The attributes with which the processor 36 is programmed include the following clusters from the ZigBee Cluster Library:

- Profile wide commands; - Basic cluster;

- Groups cluster;

- Identification cluster;

- Location cluster;

- Motion cluster; - On/Off cluster;

- Power cluster; and

- Manufacturer specific Analog cluster.

The processor 36 includes a wireless transceiver for transmitting linear movement of the tape 18 to a remote receiver. The wireless transceiver is a ZigBee radio frequency (RF) transceiver. The wireless transceiver is operable to receive commands from a matched remote transceiver and to transmit measurements to the remote transceiver.

The convergence meter 10 further includes a power supply 46 for supplying a regulated 3V to the processor 36.

The electronic components mentioned above are all mounted on the component card 16, which is a multi -layer electronic circuit board.

An electrical interface 44 is provided to interface with the processor 36 for programming of the processor or for fault finding of the component card 16.

Operation of the processor is shown schematically in Figure 4. Execution starts at 100 where after the processor 36 initializes and then initializes the ZigBee transceiver and other input/output components at 102.

The processor 36 then searches for a wireless network at 104 and, if any network is within reception range, the processor joins the network, via a network access point, also referred to as an aggregator, at 106.

The operational algorithms are executed at 108. The algorithms include the transmission of data messages; the checking of measurement intervals; the measurement of linear movement of the tape 18 via the HMIS 42; the transmission of attributes; checking if the component card 16 should be placed in a sleep mode; calculating the sleep interval of the component card 16; and setting of a timer to wake up the processor 36.

At 110, the component card 16 is placed in a sleep mode. The sleep mode can be ended immediately by the activation of any one of several switches, including a full rotation measurement by the HMIS 42. In Figure 5, the convergence meter 10 is shown in use between a hanging wall (roof) 120 and a footwall (floor) 122 of a mine stope 130.

The convergence meter 10 is attached via a screw-in bracket to an expansion bolt 126 which is fixed in the hanging wall 120. The tape 18 is deployed from the convergence meter 10 towards the footwall 122 of the mine.

The tape 18 is fastened with an expansion bolt 128 extending into the footwall

122 of the mine stope 130.

Once installed, the convergence meter 10 is electronically initialized as indicated in Figure 4, and is then ready for operation.

Advantageously, the convergence meter can be used over a broad measurement range because of the tape being able to extend over any practicable opening which is to be measured.

The ZigBee wireless transceiver makes the convergence meter 10 versatile and easy to install without the need of external electrical connections.

In an installation where at least one convergence meter 10 is installed in a mine, the invention provides a method of measuring convergence between mine walls, which includes the steps of electronically measuring relative movement between a hanging wall 120 and a footwall 122 of a mine stope 130 and wirelessly transmitting the relative movement to a remote monitoring station (not shown).

In an installation where a number of convergence meters 10 are installed in a mine, the invention provides a method of measuring convergence at a number of positions along mine walls, by deploying a number of convergence meters in an area where convergence between mine walls is to be measured, by transmitting measured convergences from the convergence meters to a central data acquisition system (not shown) and by measuring a convergence profile by spatially collating the measured convergences.

The inventors believe that the invention as described provides an easy to install, modular and robust convergence meter which provides a significant improvement over existing technology.