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ISSN 0308-6631 October 2010 www.miningmagazine.com

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To meet unprecedented demand for minerals and energy resources, open-pit mines are getting deeper

and potentially steeper, presenting many challenges that can have an adverse affect on productivity and safety. One challenge is the reduction of ‘sky-view’, which dimin-ishes the availability of satellites used for positional information for mine machinery.

Acceptable real-time kinematic (RTK) GNSS (global navigation satellite system) performance is heavily dependent on a relativity unobstructed sky-view, where there are a minimum of five satellites with good geometry available, and on the reliability of the wireless data link used for differential corrections (in this article the more generic term, GPS, will be used to cover all systems).

In a deep mine, high pit walls have a vignette effect on the sky, resulting in ‘satellite masking’. Machinery operating at the bottom of the pit or next to the walls will have a reduced angle from which they can clearly receive signals from the satellites necessary to obtain positioning, which affects availability and accuracy.

This reduced availability and accuracy affects machine control systems (MCS) and fleet management systems (FMS). To optimise productivity and improve safety on site, modern mines rely on the accuracy provided by high-precision GPS machine-control systems for drills, dozers, shovels and draglines, and the efficiency offered by automated truck and shovel optimisation.

Leica Geosystems’ Jigsaw360 fleet management system provides productivity gains through efficient use of equipment and reduced shovel hang time. Along with Leica’s high-precision machine-control systems on loading and auxiliary equipment, the rise in safety systems such as proximity detection, collision avoidance and asset tracking all require high GPS availability for optimum performance. Poor GPS reduces productivity and can affect safety.

INCORPORATING LOCATATo overcome the issue of obstructed GPS signals, inherent in satellite position technology, Leica has sought to reduce the dependence of its machine-control and fleet-management systems on satellites by incorporating technology developed by Locata Corp. Leica’s Jigsaw360 system has been integrated with Locata’s positioning technology, combined with the use of a GPS-Locata co-located antenna, which Leica developed specifically for mining.

The integration consists of a network of terrestrially-based ‘beacons’ (LocataLites) which transmit positioning signals that augment or replace satellite GPS entirely. These LocataLites form a positioning network called a LocataNet, which can operate in combination with GPS or entirely independent of GPS (for indoor applications). A time-synchronisation technology developed by Locata, called TimeLoc, allows the LocataNet to replicate GPS satellites locally.

This invention allows completely autonomous ‘better than nanosecond’ wireless synchronisation, which allows the LocataNet to give the mine high-accuracy RTK survey grade positioning without using any of the reference base stations, differential corrections or data links traditionally needed by RTK GPS. Locata’s technology is the only one in the world that can do this.

In the current system design, the LocataLites transmit their own proprietary signal structure in the 2.4GHz ISM band (licence-free globally). This ensures complete interoperability with GPS, and allows enormous flexibility due to total control over both the signal transmitter and receiver. Further details of the current system design can be found in Barnes et al 2005 (see references), together with positioning results showing RTK-level performance independent of GPS.

Locata, just like GPS, can be used for many different applications. The company is working with a number of global partners on industry specific implementations.

Leica was the first company to recognise the potential of Locata’s emerging technology. In July 2006, the two firms signed a technology co-operation agree-ment for the distribution and support of Locata technology in open-cut mining for machine automation and mine monitoring.

Leica’s early adoption allowed it to be the first to trial, refine and then develop new mine-specific Locata implementations that are tightly integrated with its machine-automation systems. Leica is the first company to bring Locata technology to

In a follow-up to the mining GPS article in the September 2010 issue, a new approach to reduce satellite dependence in accurate positioning is outlined by Leica Geosystems and Locata Corp

GPS augmentation for mining

Figure 2: LocataLite installation

Figure 1: first stage of LocataNet installation at Boddington gold mine

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market, with the first Locata-integrated Leica product that is designed specifically for mining.

In 2006, a proof-of-concept trial was undertaken at De Beers’ Venetia diamond mine in South Africa, with positive results. A LocataNet gave centimetre-level positioning without differential corrections or reference stations. This gave Leica and Locata the confidence to look at developing a GPS guidance

application integrated with Locata local positioning technology for mining.

BODDINGTON GOLD MINELeica has successfully begun to deploy a production version of its Locata integrated system at Newmont’s Boddington Gold Mine (BGM) in Western Australia. Expected to become the continent’s largest gold producer, the mine is currently at a depth of 170m. It is anticipated that the pit will

reach a depth of 800m during the life of the mine. BGM found holes in standard satellite-based GPS coverage at the current depth and is embracing Leica’s solution, which offers complete position-ing coverage for its machinery fleet throughout the life of the mine.

The Locata integrated machines currently consist of four drills and one shovel, running Leica’s high-precision machine-control systems, DrillNav Plus and DigNav JS. Five semi-permanent LocataLites are positioned around the rim of the pit and transmit unobstructed signals to machinery mounted receivers.

Augmenting GPS coverage with the LocataNet is already delivering real benefits by relieving machine control systems from GPS satellite dependence. The technology has reduced GPS downtime, and can be relied upon to keep machinery operating with the accuracy and efficiency only possible with Locata integrated positioning technologies.

LOCATANET SET-UPIn March, a LocataNet consisting of five LocataLites was deployed around the rim of the southern pit of BGM (figure 1). Each LocataLite site (figure 2) is installed with an antennae mast, solar panels to charge batteries, and a LocataLite housed within

and environmental protective enclosure. The antennae mast contains two spatially separated transmit antennae and a receive antenna. The receive antenna is used to perform TimeLoc – Locata’s proprietary precise and continuous time synchronisation procedure (see Barnes et al 2003), while the transmit antennae broadcasts the precise dual-frequency ranging and carrier signals used by the rovers.

The two transmit antenna are typically separated by a 1.5-2m vertical offset, and each transmit a different frequency to ensure measurement redundancy and robustness against multipath fading (Barnes et al 2006).

DRILL APPLICATION/INSTALLATIONLeica Geosystems’ DrillNav Plus is a high-precision blasthole navigation system for drill rigs, which improves drill accuracy, efficiency and safety. The system graphically provides navigation guidance to operators, allowing them to follow drill patterns designed in the office.

Operators can execute plans accurately and drill to the correct depth, day or night, in all weather conditions, thanks to accurate GPS guidance. This lowers blasting costs through a reduction in ‘over’ and ‘under’ drilling, and improved fragmentation. Position and orientation

Figure 3: integrated Leica/Locata system

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information is provided via two Leica 1200 series RTK GPS receivers.

In the Locata integrated Leica DrillNav Plus system installed at BGM, the two existing Leica 1200-series GPS receivers have been augmented with two Locata receivers. Each GPS receiver shares a GPS/Locata co-located antenna with one of the Locata receivers (figure 3).

During operation, if the GPS solution fails to meet specification (due to poor satellite geometry, satellite availability, losing carrier ambiguities or wireless data link failure), the Locata receivers continue to deliver centimetre-level, accurate positioning information to Leica DrillNav Plus, so drill operations are unaffected.

LIGHT VEHICLE INSTALLATIONDuring the LocataNet deployment in March, a dynamic test was conducted on the pit floor using a light vehicle (LV) (figure 4). The aim was to confirm the performance of the BGM Locata network against a survey grade RTK system. A GPS/Locata co-located antenna was mounted on the roof of the LV and connected to an integrated Leica/Locata rover system.

PERFORMANCE RESULTSThe test trajectory (figure 5) covered an area of about 140m by 120m. Figure 6 shows the difference in 3D-position components between the Locata and Leica System 1200 RTK solutions. The differences between the GPS RTK and Locata positions were 2.4cm in the horizontal and 6.7cm in the vertical (RMS 95%). These remarkable results fall well within the positioning requirements of BGM. They are particularly impressive considering they are achieved with only

five LocataLites. The better performance in the horizontal, in comparison to the vertical, is due to the relatively shallow pit depth, which imposes considerable constraint on the ‘vertical geometry’ of the Locata solution.

The success of the test highlights some key, unique characteristics of Locata technology, including the ability to leverage the spatial and frequency diversity of the signals transmitted from each LocataLite in the navigation solution. Furthermore, a ‘Stage 2’ deployment of more LocataLites will ensure even greater robustness and greater levels of accuracy in the vertical as the pit deepens and changes shape.

SUMMARYAn integrated Leica/Locata system product for fleet management in open-cut mining has been deployed successfully and is operating on a continuous basis at Boddington Gold Mine. A LocataNet, consisting of five LocataLites, provides ranging signals to Locata rovers integrated with Leica’s high-precision machine-control systems on four drills and one shovel. This provides accurate positioning and orientation for the equipment during the significant RTK-GPS outages.

Over the coming months, the integrated Leica/Locata system will be expanded to include self-surveying mobile LocataLites, covering two pits and servicing the site’s high-precision equipment of drills, shovels and dozers.

Leica Geosystems’ Locata integrated Jigsaw360 fleet-management system overcomes the hurdle of obstructed satellite GPS coverage. Reliable and complete coverage improves productivity and allows future innovative products to be built on reliable positional information. For example, proximity awareness and collision-avoidance systems significantly increase safety on mine sites, and benefit from complete GPS coverage and availability.

Guaranteed positioning coverage will give more assurance for remote-controlled or autonomous machine control. In another key achievement and a validation of the technology, the US Air Force has awarded a new contract to expand an existing LocataNet system to cover a vast area of New Mexico for the purpose of testing GPS under jamming conditions.

For Hexagon, the owner of Leica

Geosystems and the world’s largest supplier of measurement software and hardware, Locata is a fundamental part of its strategy to offer a complete mining solution that covers survey to machine control to fleet management to safety systems, and beyond.

The landscape has changed forever with the advent of the Locata technology and Hexagon will deliver this mining innovation for measurable success as part of its life-of-mine relationship with customers.

References:Barnes J, Rizos C, Wang J, Small D, Voight G and Gambale N, 2003. High-precision indoor and outdoor positioning using LocataNet. 2003 International Symposium on GPS/GNSS, Tokyo, Japan, 15-18 November, 9-18. Barnes J, Rizos C, Kanli M, Pahwa A, Small D, Voight G, Gambale N and Lamance J, 2005. High-accuracy positioning using Locata’s next generation technology. 18th International Technical Meeting of the Satellite Division of the US Institute of Navigation, Long Beach, California, 13-16 September, p2049-2056. Barnes J, Rizos C, Kanli M and Pahwa A, 2006. A positioning technology for classically difficult GNSS environments from Locata. IEEE/ION PLANS, San Diego, California, 25-27 April, p715-721. Barnes J, Lamance J., Lilly B, Rogers I, Nix M and Balls A, 2007. An integrated Locata and Leica Geosystems positioning system for open-cut mining. 20th International Technical Meeting of the Satellite Division of the US Institute of Navigation, Applications Institute of Navigation Conference (ION), Fort Worth Texas, September 2007

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Figure 4: light vehicle used to conduct dynamic tests

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