Touching the void

A new remote control laser scanner will allow underground mine surveyors to inspect voids without endangering their safety. Michael Mills writes.

Unstable voids and cavi ties in underground shafts can pose serious risks to the safety of workers as well as the viability of whole minesites.

After drilling and blasting is carried out in shafts and tun nels, an authorised surveyor is required to accurately assess the structure of the voids and cavities.

MDL Australia general manager Kevin Jacobson told Australian Mining conventional survey techniques can be costly, dangerous, time consuming and, in some cases, impractical.

To scan these difficult and dangerous areas, the company has developed the Voidscanner Mark II VS150 remote control laser measurement system.

“If the surveyor is not allowed near the void, then the unit can be deployed on a boom to carry out a 360 degree scan,” he said.

“It can give the surveyors a good understanding of the void without putting them in harm’s way.”

According to Jacobson, oper ators can program the scanning procedures remotely through a computer and view a three- dimensional model of the data in real-time as it is recorded.

“The system can also be used in tunnel profiling and underground volumetric surveys as well as to gather informa tion about drill and blast effec tiveness, ventilation and drain age,” he said.

“The unit can also be de ployed to scan the voids from different angles to counter the problems that can be caused by shadows.

“Shadows can cause inac curacies in the data, so this facil ity can ensure the correct data is obtained.”

The unit operates on the pulse time-of-flight distance measurement principle, in which the time it takes for a laser beam to reflect and return to the source is calculated into a distance value.

The device’s laser module features two windows; one to transmit the laser beam and another to receive it.

The module is mounted inside a motorised yoke, which allows the device to scan along horizontal and vertical axes.

Vertical and horizontal encoders are included to measure the respective angles.

According to Jacobson, the device can scan 360 degrees horizontally and 270 degrees vertically and has a maximum range of 150 m.

“With a scanning accuracy of 5 cm, the device can provide a comprehensive model of the void,” he said.

“A typical one-degree scan will take about half an hour, but the actual initialisation of the product should only take around one minute.”

The system also comes with IP-65 certification and is rated to operate in temperatures between 10 and 45ºC.

According to Jacobson, the mounting booms can be very heavy and difficult to transport.

“They are also very expen sive, at around $11,000 to $13,000. Because many sites have their own booms, the oper ators can use an accompany ing third-party boom adaptor to attach the scanner without having to buy a new one and ship it up to the site,” he said.

The Voidscanner Mk I comes with a surface box, which acted as a central processing unit for the attached power and data cables.

The Mk II unit has been redesigned with a smaller junc tion box to reduce the total weight to five kilograms.

“The idea is to make the equipment more user-friendly by making it possible for a single person to carry it all,” Jacob son said.

The unit’s junction box is connected to the source power and a PC.

According to Jacobson, the user can input all of the XYZ co-ordinates into the Voidscan operating software during scan ning. This means that the device can be controlled by the oper ator in real-time.

“A cable telemetry system transmits all measured data back to the surface control unit,” he said.

“The data dot points are transmitted back to the PC and plotted onto the software window.

“Because it is operated in real-time, the surveyors can restart the scanning if they are not happy with the model that is being displayed.

“Later on, the user can examine the model, put refer ence points at certain XYS co- ordinates and then export it all to third-party mine software.”

“The first Australian sale was to BHP Billiton’s Canning ton project in north-west Queens land,” Jacobson said.

“Endeavour Operations’ Cobar site in New South Wales has been so pleased with per formance of a hired unit.”

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