Open Cut Mine Machinery Automation: Going Beyond GNSS With Locata

Transcription

1 Open Cut Mine Machinery Automation: Going Beyond GNSS With Locata Chris Rizos School of Surveying & Spatial Information Systems University of New South Wales Brendon Lilly, Craig Robertson Leica Geosystems Nunzio Gambale Locata Corporation Pty Ltd Abstract Many of the new paradigms in mining and notions of sustainable mining have at their core the requirement for reliable, continuous centimetre-level positioning accuracy to enable increased automation of mining operations. The deployment of precision systems for navigating, controlling and monitoring machinery such as drills, dozers, draglines and shovels with real time position information increase their operational efficiency, and reduce the need for humans to be exposed to hazardous conditions. The Global Positioning System (GPS) is the best known, and only currently fully operational, Global Navigation Satellite System (GNSS) providing positioning capability anywhere in the globe, on a continuous 24/7 basis, with accuracies ranging from the dekametre-level to the sub-centimetre-level depending on hardware and operational configuration. Despite this versatility, GNSS cannot satisfy the high accuracy positioning requirements for many applications in mine surveying, and mine machine guidance and control. The reason is that increasingly open-cut mines are getting deeper, resulting in a reduction of the sky-view necessary for GNSS systems to operate satisfactorily. Yet to date their have been no viable alternatives to GNSS that can be deployed in mine environments that can meet the challenging requirements in open-cut mines. Locata Corporation, a Canberra-based company, has invented a terrestrial high accuracy positioning system known as Locata that can augment GNSS with extra terrestrial signals to permit cm-level positioning accuracy even when there are insufficient GNSS satellite signals for reliable positioning and navigation. Locata relies on a network of synchronised groundbased transceivers that transmit positioning signals that can be tracked by suitably equipped user receivers. Hence Locata can be considered a new type of local constellation, able to provide high accuracy positioning coverage where GNSS fails. This paper introduces some of the technical aspects of this Australian technology and describes tests conducted by Leica Geosystems over the last few years at the Newmont Boddington Gold Mine in Western Australia. A recent news announcement by Leica Geosystems (12 January 2011) has confirmed that their new mine management system will have combined GNSS+Locata positioning capability the first commercial product that integrates GNSS and Locata capabilities into a single high accuracy and high availability navigation device for open-cut mine machine automation applications. 1. INTRODUCTION

2 The Global Positioning System (GPS) is a reliable, versatile, generally available and comparatively accurate positioning technology, able to operate anywhere across the globe. GPS is, in fact, the most effective general-purpose navigation tool ever developed because of its ability to address a wide variety of applications: air, sea, land, and space navigation; precise timing; geodesy; surveying and mapping; machine guidance/control; military and emergency services operations; hiking and other leisure activities; personal location; and location-based services. These varied applications use different and appropriate receiver instrumentation, operational procedures, and data processing techniques. But all require signal availability from a minimum of four GPS satellites for three-dimensional fixes. Although GPS is currently the only fully operational Global Navigation Satellite System (GNSS), the Russian Federation s GLONASS is being replenished (fully operational by the end of 2011), the European Union s GALILEO is expected to be operational in the time frame , and China s COMPASS is likely to also join the GNSS Club by 2020 (after first deploying a regional navigation satellite system by 2012). Together with dozens more satellites from other countries and agencies in the form of augmentation satellite or regional systems, it is likely that the number of GNSS satellites useful for high accuracy positioning will increase to almost 150 with perhaps six times the number of broadcast signals on which carrier phase and pseudorange measurements can be made (Rizos, 2008). However, the most severe limitation of GPS/GNSS performance will still remain the accuracy of positioning deteriorates very rapidly when the user receiver loses direct view of the satellites, which typically occurs in deep open-cut mines. Locata s positioning technology solution is an option to either augment GNSS with extra terrestrial signals, or to replace GNSS entirely (Barnes et al, 2003). Locata relies on a network of synchronised ground-based transceivers (LocataLites) that transmit positioning signals that can be tracked by suitably equipped user receivers. These transceivers form a network (LocataNet) that can operate in combination with GNSS, or entirely independent of GNSS to support positioning, navigation and timing (PNT). This permits considerable flexibility in system design due to there being complete control over both the signal transmitters and the user receivers. One special property of the LocataNet that should be emphasised is that it is time-synchronous, allowing single receiver positioning with cm-level accuracy using carrier phase measurements. This paper introduces the technical aspects of this technology, and describes tests that Leica Geosystems have conducted in a real open-cut mine. 2. FROM PSEUDOLITES TO LOCATALITES 2.1 Background Pseudolites are ground-based transmitters of GPS-like signals (i.e. pseudo-satellite ). Most pseudolites that have been developed to date transmit signals at the GPS frequency bands (L1: MHz or / and L2: MHz). Both pseudorange and carrier phase measurements can be made on the pseudolite signals. The use of pseudolites can be traced back to the early stages of GPS development in the late 1970s, at the Army Yuma Proving Ground in Arizona, where the pseudolites in fact were used to validate the GPS concept before launch of the first GPS satellites (Rizos et al, 2010b). In the case of GALILEO, the GATE testbed ( serves the same purpose.

3 With the development of the pseudolite techniques and GPS user equipment during the last two decades, the claim has been made many times that pseudolites can be used to enhance the availability, reliability, integrity and accuracy of PNT in many indoor and outdoor applications. However, extensive research and testing by the authors has concluded that pseudolites have fundamental technical problems that are extremely difficult to overcome. The challenges of optimally siting pseudolites, controlling transmission power levels, overcoming near-far problems, trying to ensure extremely high levels of time synchronisation, configuring special antennas, and designing the field of operations such that GNSS and pseudolites can work together (or at least not interfere with each other) have been largely insurmountable in the real world. As far as the authors are aware the only pseudolitebased commercial product is the Terralite XPS multi-frequency integrated GPS+pseudolite system offered to the open-cut mining industry, now owned by the Trimble Company (ibid, 2010b). Pseudolite research at the University of New South Wales (UNSW) commenced in UNSW researchers have experimented with them in the unsynchronised mode, using the GPS L1 frequency, on their own or integrated with GPS and Inertial Navigation Systems, for a variety of applications. UNSW researchers have been working with Locata Corporation for over a decade on a new terrestrial-based positioning concept. (The reader is referred to the website for a full list of pseudolite-related and Locata papers by UNSW researchers.) 2.2 Locata Technology In 2003 Locata Corporation took the first steps in overcoming the technical challenges required to create a localised autonomous terrestrial replica of GNSS (Barnes et al, 2003). The resulting Locata positioning technology was designed to overcome the limitations of GNSS and other pseudolite-based positioning systems by using a time-synchronised transceiver called a LocataLite. The LocataLite is both a transmitter of positioning signals, but also can receive, track and process signals from other LocataLites. A network of LocataLites forms a LocataNet, and the first generation system transmitted signals using the same L1 frequency as GPS. Time-synchronised signals allow carrier phase single point positioning with cm-level accuracy for a mobile unit. In effect, the LocataNet is a new constellation of signals, analoguous to GNSS but with some unique features; such as having no base station data requirement, requiring no wireless data link from base to mobile receiver, and no requirement for measurement double-differencing (Barnes et al, 2003, 2004, 2005b). In 2005 a fundamental change was made to the first generation Locata design that affirms its claim to not being a pseudolite. Locata s new design incorporates a proprietary signal transmission structure that operates in the Industry Scientific and Medical (ISM) band ( GHz). Within the ISM band the LocataLite design allows for the transmission of two frequencies, each modulated with two spatially-diverse PRN codes. From the beginning the driver for the Locata technology was to develop a centimetre-level accuracy positioning system that could complement, or replace, conventional RTK-GNSS in classically difficult GNSS environments such as open-cut mines, deep valleys, heavily forested areas, urban and even indoor locations. 3. LOCATA APPLICATIONS Since 2005 the Locata technology has been refined through tests carried out at Locata

4 Corporation s Numerella Test Facility (NTF) outside of Canberra (Australia), at the UNSW campus (Australia), at the University of Nottingham campus (U.K.), at the Ohio State University campus (U.S.A.), at the USAF s Holloman AFB, and at several real world test sites including several bridges, in road tests, at two open-cut mines, on a dam site, and indoors. Some of these test results are described below (part of the text is taken from Rizos et al, 2010b). 3.1 Kinematic Positioning Extensive kinematic tests conducted at the NTF were reported in, e.g., Barnes et al (2005b, 2006). Figure 1 shows a typical setup, with the Locata receiver/antenna together with two GPS receivers/antennas (to provide ground truth ) fitted to a truck. Results confirmed cmlevel accuracy trajectories with LocataLite separations of the order of a few kilometres. Figure 1: Kinematic test, Locata antenna between two antennas of the Leica RTK-GPS ground truth system. The Locata technology s potential was confirmed in a recent (September 2010) announcement that Locata Corporation had been awarded a contract by the USAF 746th Test Squadron to deliver a system able to provide an independent high accuracy positioning (subdecimetre-level) capability over almost 6500 square kilometres of the White Sands Missile Range whenever GPS is undergoing jamming tests. In May 2011 first results of decimetrelevel accuracy aircraft positioning over wide areas, acquiring LocataLite signals from over 50km distant, were reported (GPSWorld, 2011). 3.2 Deformation Monitoring Another important application of Locata (on its own or in combination with GPS) is deformation monitoring of structures such as buildings, bridges or dams. Early Locata testing was conducted in Sydney (Figure 2a) and in Nottingham (Figure 2b), as reported in Barnes et al (2002, 2005a) and Meng et al (2004), which demonstrated the benefit of augmenting GPS with Locata signals in order to improve availability, and consequently improve the horizontal accuracy. Recently first Locata-only tests were conducted on a dam structure the Tumut Pond Dam (Figure 3a,b), and reported in Choudhury et al (2010). Comparison with 3D

5 coordinates derived from a Robotic Total Station confirmed sub-cm level repeatability, as well as sub-centimetre accuracy (under the assumption there was no dam wall movement). Figure 2a: Suspension bridge tests, Sydney. Figure 2b: Suspension bridge tests, Nottingham. Figure 3a: Tumut Pond Dam (Total View). Figure 3b: LocataLite and receiver installation. 3.3 Locata/GPS/INS Integration The determination of the position and orientation of a device (or platform to which it is attached), to high accuracy, in all outdoor environments, is something of a holy grail quest for navigation researchers and engineers. Two classes of applications that place stringent demands on the positioning/orientation device are: (a) portable mapping and imaging systems that operate in a range of difficult urban and rural environments, often used for the detection of underground utility assets (such as pipelines, cables, conduits), unexploded ordnances and buried objects, and (b) the guidance/control of construction or mining equipment in environments where good sky view is not guaranteed. The solution to this positioning/orientation problem is increasingly seen as being based on an integration of several technologies. Researchers from UNSW and The Ohio State University (OSU), Columbus (U.S.A.), assembled a working prototype of a hybrid system based on GPS, inertial navigation, and Locata receiver technology. The data processing methodology, based on a distributed Kalman filter, and the results obtained of tests conducted at the NTF, the UNSW campus (Figure 4) and the OSU campus, have been described in a number of recent papers (Rizos et al, 2008, 2010a).

6 Figure 4: Integrated GPS+INS+Locata test car on UNSW campus. 3.4 Indoor Positioning In April 2004 the first indoor tests were conducted at BlueScope Steel, one of BHP Billiton s steel producing companies located in Wollongong, south of Sydney (Australia), to assess the performance of the prototype Locata technology for tracking a large crane in a harsh multipath environment (Figure 5). A Total Station was used to provide independent ground truth. The results demonstrated cm-level accuracy (Barnes et al, 2004). However no further public demonstration of indoor positioning was conducted until 2010, at which time a radically new Locata indoor antenna design (trademarked as a small TimeTenna) was tested for the first time at the NTF (Rizos et al, 2010b). The 2010 indoor experiments were conducted inside a large metal shed, approximately 30 metres long and 15 metres wide (Figure 6). Such an environment guarantees severe multipath disturbance. A LocataNet consisting of five LocataLites was installed inside the shed. The

7 Locata receiver was placed on a small trolley. The TimeTenna was mounted on a pole attached to the trolley and was connected to the receiver. In order to compare reported receiver positions with the true position, a Robotic Total Station (RTS) was setup near the test area. A surveying prism was placed vertically above the phase centre of the TimeTenna. The RTS was programmed to track the location of the prism as it was moving and log the data internally for subsequent processing. Static (Locata receiver placed over known points marked on the ground) and kinematic tests were conducted. Apart from some initial convergence challenges, all static coordinates were determined to cm-level accuracy. The kinematic tests indicated that the trajectory was in almost all cases less than 3cm from that derived using the RTS (Rizos et al, 2010b). Impressive first results were obtained from this new multipath-mitigating antenna technology, and more tests will be conducted in the coming months (including a live demonstration at the 2011 U.S. Institute of Navigation s GNSS Conference in September 2011, in Portland, Oregan). Figure 6: Indoor test site, Locata receiver on trolley and RTS setup. 4. LOCATA & MINE MACHINERY AUTOMATION 4.1 Leica Geosystems Mining Background Leica Geosystems is part of the Hexagon Global Measurement Group. With close to 200 years of experience pioneering solutions to measure the world, Leica Geosystems products and services are trusted by professionals worldwide to help them capture, analyse, and present spatial information. Leica Geosystems is best known for its broad array of products that capture accurately, model quickly, analyse easily, and visualise and manage spatial information. Leica Geosystems Mining Solutions focuses on optimised dispatching fleet management systems and high precision guidance systems. These products include Jigsaw 360 fleet management system, high precison dozer, shovels, excavator, supervisor, drill systems and dragline monitoring systems (Figure 7). These systems improve productivity by measuring, monitoring and reporting on what is happening across an entire mine site.

8 Figure 7a: Dragline with dragline monitoring system and high precision guidance installed. Figure 7b: CAT D11 dozer with Leica fleet and high precision guidance system at work. 4.2 Leica Geosystems Tests at the Boddington Gold Mine Leica Geosystems has successfully begun to deploy a production version of its Locata integrated system at Newmont Boddington Gold in Western Australia. Expected to become the continent s largest gold producer, the mine consists of two pits each about 1.5km long and 800m wide. The more southern of the pits (Figure 8) is already over 200m deep and machines

9 are already experiencing positioning availability issues. It is anticipated that this pit will reach a depth of 800m during the life of the mine. Figure 8: South Pit of Newmont Boddington Gold. A single LocataNet consisting of 15 LocataLites has been designed to cover both of pits in the mine. These LocataLites are solar-powered and designed to be placed in the best locations to achieve the maximum benefit. Of the 15 LocataLites, five of them are fixed installations and 10 are Mobile LocataLites as shown in Figure 9. The Mobile LocataLites are designed to be easy to manoeuvre for blasting or relocation to another part of the mine. Once repositioned, the Mobile LocataLite self surveys its antennas and is transmitting signals to the navigating machines within minutes of powering up. Figure 9: Mobile LocataLite (left) and one of the drills installed with the Locata system. The installation on the drills contains two Leica GNSS and two Locata receivers. One GNSS and Locata receiver pair is connected to a co-located antenna on one side of the machine and the other GNSS and Locata receiver pair is connected to the other co-located antenna. The

10 system uses the signals from both pairs of receivers to determine the position and heading of the machine for navigation purposes. The GNSS receivers obtain their RTK corrections from the same RTK base station as the survey equipment. The Locata receivers do not require any corrections therefore there is no special requirement for another base station or a new corrections network. The only requirements for installation are positioning the LocataLites around the pit and the installation of the combined receiver on the machine. Machines are able to travel between the pits without the need for reconfiguration. They seamlessly search and synchronise onto the network. During the LocataNet deployment when only 5 LocataLites had been deployed, a dynamic test was conducted on the pit floor using a light vehicle (LV) (Figure 10). 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. Figure 10: Light vehicle installed with co-located antenna used in accuracy tests. The test trajectory (Figure 11) covered an area of about 140m by 120m. Figure 12 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 the Locata technology, including the ability to leverage the spatial and frequency diversity of the signals transmitted from each LocataLite in the navigation solution. Now that more LocataLites have been deployed, even greater robustness and higher levels of accuracy can be achieved.!

11 100 GPS Locata 80 ) m ( h t r o n east (m) 63.5 GPS Locata ) m ( h t r o n east (m) Figure 11: Test trajectory (top) and a zoomed in section of the trajectory (bottom). Subsequent verification tests onboard the drills demonstrated good results. In one test, both GNSS antennas were disconnected from their receivers and the system navigated on the LocataNet alone. The drill navigated for nearly an hour and a half, and drilled two holes using the LocataNet. Figure 13 shows that the availability of the system was significantly improved with the added benefit of the Locata system. The trough in the data is attributed to when the drill itself had significant downtime due to maintenance.

12 ) m ( 0.05 t s a e ) m ( h t r o n ) m ( t h g i e h epoch Figure 12: Difference between the RTK-GNSS position and Locata 3D positions. 5. CONCLUDING REMARKS Figure 13: Overall availabilty versus GNSS availability. Locata is a new type of localised constellation, able to provide high accuracy positioning coverage where GNSS fails. Locata is a technological solution to high accuracy indoor and outdoor positioning where GNSS cannot on its own provide the requisite positioning capability. This paper introduced some of the technical aspects of this technology, summarised the R&D highlights over the last decade or so, and described a variety of applications for Locata technology, including some recent results of high accuracy outdoor and indoor positioning. Extensive tests on the use GNSS+Locata at the Newmont Boddington Gold Mine has confirmed the improved PNT performance of this hybrid system. Over the next year several commercial positioning systems will be developed that incorporate the

13 ability to track Locata signals in addition to GNSS. Locata as a terrestrial augmentation to GNSS is particularly suited critical mine automation applications, where sky visibility is restricted due to high walls in open-cut mines, as indicated by a recent news announcement by Leica Geosystems (12 January 2011). Leica s new Jigsaw 360 mine management system will have combined GNSS+Locata positioning capability, and is the first commercial product that integrates GNSS and Locata capabilities into a single navigation device. REFERENCES Barnes, J., J. Wang, C. Rizos & T. Tsujii (2002). The performance of a pseudolite-based positioning system for deformation monitoring, 2nd Symp. On Geodesy For Geotechnical & Structural Applications, Berlin, Germany, May, Barnes, J., C. Rizos, J. Wang, D. Small, G. Voigt & N. Gambale (2003). Locatanet: A new positioning technology for high precision indoor and outdoor positioning, 16th Int. Tech. Meeting of the Satellite Division of the U.S. Institute of Navigation, Portland, Oregan, USA, 9-12 September, Barnes, J., C. Rizos, M. Kanli, D. Small, G. Voigt, N. Gambale, J. Lamance, T. Nunan & C. Reid (2004). Indoor industrial machine guidance using Locata: A pilot study at BlueScope Steel, 60th Annual Meeting of the U.S. Inst. of Navigation, Dayton, Ohio, USA, 7-9 June, Barnes, J., C. Rizos, H.K. Lee, G.W. Roberts, X. Meng, E. Cosser & A.H. Dodson (2005a). The integration of GPS and pseudolites for bridge monitoring, In "A Window on the Future of Geodesy", F. Sanso (ed.), IAG Symp. Vol.128, Spinger-Verlag, Barnes, J., C. Rizos, M. Kanli, A. Pahwa, D. Small, G. Voigt, N. Gambale & J. Lamance (2005b). High accuracy positioning using Locata's next generation technology, 18th Int. Tech. Meeting of the Satellite Division of the U.S. Institute of Navigation, Long Beach, California, USA, September, Barnes, J., C. Rizos, M. Kanli & A. Pahwa (2006). A solution to tough GNSS land applications using terrestrial-based transceivers (LocataLites), 19th Int. Tech. Meeting of the Satellite Division of the U.S. Inst. of Navigation, Fort Worth, Texas, USA, September, Choudhury, M., B.R. Harvey & C. Rizos (2010). Mathematical models and a case study of the Locata Deformation Monitoring System (LDMS), XXIV FIG Int. Congress "Facing the Challenges - Building the Capacity", Sydney, Australia, April, procs on website GPSWorld (2011). accessed 6 June Meng, X., G.W. Roberts, A.H. Dodson, E. Cosser, J. Barnes & C. Rizos (2004). Impact of GPS satellite and pseudolite geometry on structural deformation monitoring: Analytical and empirical studies, Journal of Geodesy, 77, Rizos, C. (2008). Multi-constellation GNSS/RNSS from the perspective of high accuracy users in Australia, Journal of Spatial Science, 53(2), Rizos, C., D. Grejner-Brzezinska, C.K. Toth, A.G. Dempster, Y. Li, A. Politi & J. Barnes (2008). A hybrid system for navigation in GPS-challenged environments: Case study, 21st Int. Tech. Meeting of the Satellite Division of the U.S. Inst. of Navigation, Savannah, Georgia, USA, September, Rizos, C., D. Grejner-Brzezinska, C.K. Toth, A.G. Dempster, Y. Li, A. Politi, J. Barnes, H. Sun & L. Li (2010a). Hybrid positioning: A prototype system for navigation in GPSchallenged environments, GPS World, 21(3), Rizos, C., G.W. Roberts, J. Barnes & N. Gambale (2010b). Locata: A new high accuracy

14 indoor positioning system, Proc. Int. Conf. on Indoor Positioning & Indoor Navigation, Zurich, Switzerland, September, , IEEE Xplore, 971 pp, IEEE Catalog Number: CFPI009J-ART, ISBN: , DOI: /IPIN