The benefit of trolley truck systems is the substitution of the diesel fuel by the cheaper and more ecological electrical energy. Trolley trucks are powered by electricity fromtwo overhead contact lines, where one is the supply and the other the return conductor. Such trolley trucks are used for haulage at open pit mining sites but could also be used for freight traffic at roadways in the future. Automatic guidance prevents the trolley-powered trucks fromleaving the track and thus allows higher operating speeds, higher loading capacity, and greater efficiency. Radar is the ideal sensing technique for automatic guidance in such environments.The presented radar systemwith two-dimensional digital beamforming capability offers a compact measurement solution as it can be installed on top of the truck. Besides the distance measurement, this radar system allows to detect the location and inclination of the overhead contact lines by digital beamforming in two dimensions. Besides automatic guidance, the knowledge of the inclination of the overhead contact lines could allow automatic speed adaption, which would help to achieve maximum speed especially in hilly terrain

Harter, M.

Schipper, T.

Ziroff, A.

Zwick, T.

Zwirello, L.

English

KITopen

Hindawi Publishing CorporationInternational Journal of Vehicular TechnologyVolume 2013, Article ID 914351, 5 pageshttp://dx.doi.org/10.1155/2013/914351Research ArticleDetection of Overhead Contact Lines witha 2D-Digital-Beamforming Radar System forAutomatic Guidance of Trolley TrucksMarlene Harter,1 Tom Schipper,1 Lukasz Zwirello,1 Andreas Ziroff,2 and Thomas Zwick11 Institut für Hochfrequenztechnik und Elektronik (IHE), Karlsruher Institut für Technologie (KIT), Kaiserstraße 12,76128 Karlsruhe, Germany2 Siemens AG, Corporate Technology, CT RTC ELE RFT-DE, Otto-Hahn-Ring 6, 81739 München, GermanyCorrespondence should be addressed to Marlene Harter; marlene.harter@kit.eduReceived 19 October 2012; Accepted 21 January 2013Academic Editor: Kuo-Kun TsengCopyright © 2013 Marlene Harter et al.This is an open access article distributed under the Creative Commons Attribution License,which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.The benefit of trolley truck systems is the substitution of the diesel fuel by the cheaper andmore ecological electrical energy. Trolleytrucks are powered by electricity from two overhead contact lines, where one is the supply and the other the return conductor. Suchtrolley trucks are used for haulage at open pit mining sites but could also be used for freight traffic at roadways in the future. Auto-matic guidance prevents the trolley-powered trucks from leaving the track and thus allows higher operating speeds, higher loadingcapacity, and greater efficiency. Radar is the ideal sensing technique for automatic guidance in such environments. The presentedradar system with two-dimensional digital beamforming capability offers a compact measurement solution as it can be installed ontop of the truck. Besides the distance measurement, this radar system allows to detect the location and inclination of the overheadcontact lines by digital beamforming in two dimensions. Besides automatic guidance, the knowledge of the inclination of the over-head contact lines could allow automatic speed adaption, which would help to achieve maximum speed especially in hilly terrain.1. IntroductionThe benefit of trolley truck systems is the substitution ofthe diesel fuel by the cheaper and more ecological electricalenergy [1]. Trolley trucks are powered by electricity fromtwo overhead contact lines, where one is the supply andthe other the return conductor. Such vehicles are oftenused for haulage at open pit mining sites in order to savefuel and increase productivity [2, 3]. Recently, Siemens AGstarted the eHighway project [4] for electrification of freighttraffic. The system can be installed with only limited alter-ations to current roadways.These diesel-hybrid driven truckswould help to cut the fossil fuel use and reduce pollutionin residential and agricultural areas. Adding an automaticguidance feature to trolley truckswould help to keep the truckon track under the overhead contact lines. Thus, it wouldprovide an increased driving safety and therefore it couldallow for higher loading capacities and higher operatingspeeds. Besides automatic guidance, the knowledge about theinclination of the overhead contact lines allows automaticspeed adaption, which would help to achieve maximumspeed especially in hilly terrain.Due to its day and night operability and robustness inharsh environments, radar is the ideal sensing technique forsuch an application.In this proposed guidance solution, radar is used todetect the location and inclination of overhead contact lines.Compared to other existing guidance systems described in[5], neither fixed installations in the surrounding area norchanges on the current collectors are required, as the radarsystem can be installed on top of the truck as shown inFigure 1. Besides the distance measurement of the overheadlines, the presented radar system [6] provides angular infor-mation in two dimensions by applying digital beamforming(DBF) [7].In the first part, a short overview of the realized radarsystem and its characteristic features is given. The measure-ment setup and signal processing aspects for the detection of2 International Journal of Vehicular TechnologyTable 1: Settings of the system parameters.Frequency Bandwidth Sweep duration Measurement cycle Sampling frequency𝑓0𝐵 𝑇𝑆𝑇𝑐𝑓𝑎24GHz 270MHz 2.5ms 20ms 250 kHzTable 2: Parameters of the two different measurement setups.Setup Contact line Height [m] Height [m] Antenna height [m] Distance [m] Length [m] Angle [∘]ℎ1ℎ2𝑒 𝑑 𝑙 𝛼1 1/2 3 3 0.38 0.6 1.9 02 1/2 3 2.5 0.38 0.6 1.9 15.3Reflection pointReflection point𝑑𝑦𝑧ℎ𝑥𝜃𝜓𝑟DBF radarTx antenna arrayRx antenna arrayDriving directionFigure 1: Drawing of the trolley truck with 2D-DBF radar on top.TransmitterarrayReceiverarrayFigure 2: Realized 2D-DBF radar system with orthogonallyarranged transmit and receive antenna arrays.overhead contact lines are treated afterwards. In the final part,measurement results of twometal bars verify the applicabilityof the proposed sensing technique.2. DBF Radar SystemThe realized DBF radar system is a 24GHz frequency modu-lated continuous wave (FMCW) radar system with a sweepbandwidth of 270MHz. It comprises eight transmitter andeight receiver channels [6]. As shown in Figure 2, the trans-mitter and receiver antenna arrays are arranged orthogonallyto each other in the form of an inverted T. This arrangementof the antenna arrays enables to measure the angles, denotedby 𝜃 and𝜓, of the reflected signals in two dimensions by DBF.For the transmitter and the receiver antenna array, the samedesign consisting of four vertical polarized subpatches perantenna element is used in the same orientation. The singlepatch antenna provides a half-power beamwidth (HPBW)of 42∘ in azimuth and 50∘ in elevation. The HPBW of thetransmitter array in elevation is determined by measurementto 5.8∘ and the HPBW of the receiver array in azimuthto 6∘, respectively. Besides the distance provided by theFMCW measurement principle, the location and inclinationof the two overhead contact lines can be determined byDBF. Since the radar is laid down (Figure 1), the radar’selevation is now equal to 𝜃 and its azimuth to 𝜓, respectively.The DBF radar system is realized on several modules forwhich a detailed description can be found in [6, 8]. DBFon transmit is performed by time-division multiplexingwith eight independently switchable transmitters, whereaseight receiver channels allow simultaneous acquisition andprocessing of the radar signal. Ameasurement cycle in whichthe transmit signal is switched from transmit antenna one toeight takes 20ms. In Table 1 the system parameter settings ofthe radar system are given.3. Measurement SetupFor demonstration of the presented 2D-DBF radar systemand its suitability for detection of overhead contact lines,a measurement setup with two metal bars with a diameterof 2 cm is chosen. As shown in Figures 3(a) and 3(b), thetwo metal bars are mounted in parallel with a distance 𝑑and a height ℎ above the radar system. The 2D-DBF radarsystem is oriented on the floor with the transmit antennaarray along the driving direction (z-axis) and the receiverarray orthogonal to it (y-axis). The angular positions of theoverhead contact lines in y-direction can be determined byDBF on receive, whereas the inclination of the overheadcontact lines is obtained by DBF on transmit.Two different measurement setups are investigated withthe parameters given in Table 2. The first measurement setupwith two parallel overhead contact lines, both mounted inthe same height, represents the usual case and is shownInternational Journal of Vehicular Technology 3Reflection pointReflection point𝑑𝑦𝑧𝑥𝜃𝜓𝑟DBF radarDriving directionℎ1ℎ2𝑒𝑙(a) Drawing of setup 1𝛼DBF radar(b) Photograph of setup 2Figure 3: Setup for measurement of the overhead contact lines with the 2D-DBF radar system.Table 3: Comparison of theoretical and measured ranges and angles.Setup Contact line Theoretical range [m] Measured range [m] Theoretical angle [∘] Measured angle [∘]𝑟 𝑟 𝜓 𝜃 𝜓 𝜃1 1 2.64 2.66 6.5 0 +6.1 02 2.64 2.66 −6.5 0 −6.1 02 1 2.39 2.36 7.2 15.3 +7.5 15.42 2.39 2.36 −7.2 15.3 −7.5 15.4in Figure 3(a). The photograph in Figure 3(b) shows themeasurement setup 2, in which the two metal bars are hungup with an inclination of 𝛼 = 15.3∘.4. Signal ProcessingThe distance from the radar system to the overhead contactlines is obtained by the FMCW principle. The location andinclination of the two metal bars are determined by digitalbeamforming in two dimensions [6]. For angular processingof the measured data the conventional delay-and-sum (DS)beamformer based on the fast fourier transform and themultiple signal classification method (MUSIC) are used.MUSIC is the so-called super resolution technique and wasfirstly introduced in [9]. Range and azimuth processing canbe directly started after one FMCW sweep as the reflectedsignal of one transmitter is measured by all receiver channelssimultaneously. After one complete transmit cycle, in whichthe transmitters are switched successively, digital beamform-ing on transmit can be performed in order to determine theinclination of the metal bars.5. Measurement ResultsAfter range processing of the measured data, 2D-DBF isapplied onto the range cell in which the overhead contactlines are located. The angular spectra for measurement setup1 are shown in Figures 4(a) and 4(b), respectively. The twooverhead contact lines can be discriminated in the angularspectrum lateral to the driving direction, and their locationsare measured to 𝜓 = ±6.1∘. In Table 3 the measured rangesand angles are given in comparison to the theoretical values,which are calculated from the parameters of themeasurementsetups in Table 2. As the overhead contact lines are mountedhorizontally above the floor, the peak in the angular spectrumalong the driving direction is located at 𝜃 = 0∘. In the secondconfiguration the overhead contact lines aremountedwith aninclination of 𝜃 = 15.3∘, which is determined to 𝜃 = 15.4∘ bythe radar in Figure 5(b).Due to the inclination, the two metal bars have a shorterdistance to the radar system. Thus, the angles acquired byDBF on receive increase to 𝜓 = ±7.5∘ (Figure 5(a)) comparedtomeasurement setup 1 (Figure 4(a)).The slight deviations inthe presented measurement results can be explained due tothe nonideal measurement setup and inaccurate placementof the DBF radar system under the overhead contact lines.Comparing the two angular processingmethods, broaderpeaks and higher side lobes can be observed for the DS. Insome situations it can bemore difficult to detect the overheadcontact lines by using DS. On the other hand, applyingMUSIC presupposes knowledge of the exact number of tar-gets. In real-world environments, where more objects beside4 International Journal of Vehicular TechnologyRelative power (dB)DSMusic−25 −20 −15 −10 −5 0 5 10 15 20 25Angle 𝜓 (deg)−100−90−80−70−60−50−40−30−20−100(a) Angular spectrum lateral to driving directionRelative power (dB)DSMusic−25 −20 −15 −10 −5 0 5 10 15 20 25−100−90−80−70−60−50−40−30−20−100Angle 𝜃 (deg)(b) Angular spectrum along driving directionFigure 4: Measurement results of setup 1.Relative power (dB)DSMusic−25 −20 −15 −10 −5 0 5 10 15 20 25Angle 𝜓 (deg)−100−90−80−70−60−50−40−30−20−100(a) Angular spectrum lateral to driving directionRelative power (dB)DSMusic−25 −20 −15 −10 −5 0 5 10 15 20 25Angle 𝜃 (deg)−100−90−80−70−60−50−40−30−20−100(b) Angular spectrum along driving directionFigure 5: Measurement results of setup 2.the two overhead lines may be existing, additional estimatingtechniques could be required [10, 11]. Even further signalprocessing as, for example, tracking of the overhead contactlines or range gating could be implemented to discriminatethe overhead contact lines from other targets [12].6. ConclusionIn this paper a radar-based measurement technique for thedetection of overhead contact lines of electrically poweredtrolley vehicles is presented. It is shown by measurementsof two metal bars that the realized DBF radar system allowsone to detect their location lateral to the driving direction aswell as their inclinations. Two different spectrum estimationmethods are applied and compared for angular processing ofthe measured data, and the same angular values are obtainedwith both. The proposed DBF radar offers an ideal measure-ment system which can be used for automatic guidance andautomatic speed control of trolley vehicles. Further, it offers arobust and compact solution particularly for open pit miningsites as no further installations are required.References[1] http://www.hutnyak.com/Trolley/trolleyhistory.html.International Journal of Vehicular Technology 5[2] W. G. Koellner, G. M. Brown, J. Rodŕıguez, J. Pontt, P. Cortés,andH.Miranda, “Recent advances inmining haul trucks,” IEEETransactions on Industrial Electronics, vol. 51, no. 2, pp. 321–329,2004.[3] http://www.industry.usa.siemens.com/verticals/us/en/mining/mobile-mining-solutions/simine-tr/trolley-assist/pages/trol-ley-assist.aspxmining/mobile-mining-solutions/simine-tr/trol-ley-assist/pages/trolley-assist.aspx.[4] http://www.mobility.siemens.com/mobility/global/en/interur-ban-mobility/road-solutions/electric-powered-hgv-traffic-ehighway/pages/electric-powered-hgv-traffic-ehighway.aspx.[5] R. R. Obaid and R. H. Ahmad, “Automatic guidance system fortrolley-powered mining haul trucks,” in Proceedings of the IEEEIndustry Applications Society AnnualMeeting (IAS ’09), October2009.[6] M. Harter, T. Schipper, L. Zwirello, A. Ziroff, and T. Zwick,“24GHz Digital Beamforming radar with T-shaped antennaarray for three-dimensional object detection,” InternationalJournal of Microwave andWireless Technologies, vol. 4, no. 3, pp.327–334, 2012.[7] W. Mayer, S. Buntz, H. Leier, and W. Menzel, “Imaging radarsensor front-end with a large transmit array,” in Proceedings ofthe 1st European Radar Conference (EuRAD ’04), pp. 153–156,October 2004.[8] M. Harter and T. Zwick, “An FPGA controlled Digital Beam-forming radar sensor with three-dimensional imaging capabil-ity,” in Proceedings of the International Radar Symposium (IRS’11), pp. 441–446, 2011.[9] R. O. Schmidt, “Multiple emitter location and signal parameterestimation,” IEEE Transactions on Antennas and Propagation,vol. 34, no. 3, pp. 276–280, 1986.[10] P. Stoica and Y. Selen, “Model-order selection: a review ofinformation criterion rules,” IEEE Signal Processing Magazine,vol. 21, no. 4, pp. 36–47, 2004.[11] P. Chen, T. J. Wu, and J. Yang, “A comparative study of modelselection criteria for the number of signals,” IET Radar, Sonarand Navigation, vol. 2, no. 3, pp. 180–188, 2008.[12] D. Oprisan and H. Rohling, “Tracking systems for automotiveradar networks,” in Proceedings of IEE Radar, pp. 339–343,October 2002.International Journal ofAerospaceEngineeringHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014RoboticsJournal ofHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014 Active and Passive  Electronic ComponentsControl Scienceand EngineeringJournal ofHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014 International Journal of RotatingMachineryHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014Hindawi Publishing Corporation http://www.hindawi.com Journal ofEngineeringVolume 2014Submit your manuscripts athttp://www.hindawi.comVLSI DesignHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014Shock and VibrationHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014Civil EngineeringAdvances inAcoustics and VibrationAdvances inHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014Electrical and Computer EngineeringJournal ofAdvances inOptoElectronicsHindawi Publishing Corporation http://www.hindawi.comVolume 2014The Scientific World JournalHindawi Publishing Corporation http://www.hindawi.com Volume 2014SensorsJournal ofHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014Modelling & Simulation in EngineeringHindawi Publishing Corporation http://www.hindawi.com Volume 2014Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014Chemical EngineeringInternational Journal of  Antennas andPropagationInternational Journal ofHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014Navigation and  ObservationInternational Journal ofHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014DistributedSensor NetworksInternational Journal of

Detection of Overhead Contact Lines with a 2D-Digital-Beamforming Radar System for Automatic Guidance of Trolley Trucks

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Detection of Overhead Contact Lines with a 2D-Digital-Beamforming Radar System for Automatic Guidance of Trolley Trucks

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