Survival Test of RFID UHF Tags in Timber Harvesting Operations

Originalscientificpaper

Croat. j. for. eng. 36(2015)2 165

Survival Test of RFID UHF Tags in Timber

Harvesting Operations

Gianni Picchi, Martin Kühmaier, Juan de Dios Diaz Marques

Abstract

Traceability of wood products is more and more relying on high technology systems. Among them the Radio-Frequency IDentification with Ultra High Frequency (RFID UHF ) tags are probably the most flexible and promising tools. Several studies address their use in timber logistics, but the possibility to mark standing trees and maintain intact the information along a whole-tree extraction system is still not explored. Under this perspective one of the main challenges is the capacity of UHF RFID tags to survive the harsh conditions of timber harvest-ing. Different tag models and different placement positions on the tree may lead to diverse ratio of tags arriving intact up to the landing. Particularly extracting operations may play a major role in damaging or removing the tags from the trees. In the present study, two tag models and two fixing modalities were compared during three commercial hauling and one transport operation in mountain conditions. Over a total of 239 tracked tags, just 5 were lost, proving a good reliability for this traceability system. This preliminary result will serve for addressing the electronic tree/log marking method in the frame of the project SLOPE, co-funded by the EC.

Keywords: RFID UHF, tree marking, hauling, survival test, cable yarder

of such data requires a traceability system that relates the digital information generated for the single stand-ing tree to the actual item being harvested and trans-mits this data to the forest machines, making available in real time the bucking instructions for each tree. The same traceability architecture can be used to assign an IDtoeachlogproducedandlinkthistoalltheavail-ableinformation(measures,quality).Forthispurposeseveral solutions have been used for actual marking oftreesandlogsinforestoperationsortimberlogis-tics, such as color marking, barcodes, QR codes and Radio-Frequency IDentification technology (RFID)(TzoulisandAndreopoulou2013).The latterhasawiderangeofapplicationsinthefieldoflogistics,live-stock and warehouse management among others (Fer-reretal.2010,Zhuetal.2012)andseemstobethemostpromisingtoolforsupplychainmanagement,particu-larlyforthecapacitytoberedatconsiderabledistanc-es:UltraHighFrequency(UHF)RFID,operatingatafrequency of 868 MHz, can be detected at distances of over10minoptimalconditions.AccordingtotheEPCstandard, RFID tags have an internal memory that al-

1. IntroductionInthenearfuture,theproductivityandprofitabil-

ityofforesttimbersupplychainsareexpectedtoin-creaserapidlybyimplementingthetoolsandmethodsofprecision forestry (Holopainenetal. 2014).Thistrendisalsoexpectedinmountainforestry,wherefor-estoperationsaremainlybasedoncableyardingsys-tems, but the relatively low degree of mechanization ofthesesystemsrepresentsapotentialconstrainttotheapplicationofhighprecision technologies (Ca-valli2012).ThisspecificchallengeisaddressedbytheprojectSLOPE,co-fundedbytheEC,withthegoaltosetupan integratedand innovative timbersupplychaininmountainareas.Intheplannedworkflow,differentdigitaldatasources,suchasaerialsensorsandterrestriallaserscanners(LiDAR),areusedfortheacquisitionofgeoreferenced3Ddataonthestandingtrees.Thisiselaboratedwithdedicatedsoftwarere-turningtheoptimaltreebuckingsuggestions(Dassotetal.2011,Murphy2008),whichareusedbythepro-cessorformaximizingthevalueoftheextractedtim-ber according to the market demand. The transmission

G. Picchi et al. Survival Test of RFID UHF Tags in Timber Harvesting Operations (165–174)

166 Croat. j. for. eng. 36(2015)2

lowsacontentof96bits(EPCClass1),includedinastringof14characters,providingauniqueIDtoeachtag.Suchinformationcanbeusedforautomaticallytagging an item (log or tree) in a database.Inforestryapplications,RFIDtechnologyhasbeen

mostlytestedforcontrolandoptimizationoftimberlogistics(KortenandKaul2008).Anotherapplicationarea is the traceability of timber throughout the whole supplychain,wheretheuseofRFIDforlogmarkingmay increase the degree of automation of the log in-ventory,reducetheneedforrepeatedmeasurementsofthetimberandincreasetheoverallefficiency,withevidenteconomicbenefits(Haklietal.2010).Never-theless, thepotentialofelectronicmarkingof treesmaybeextendedbeyondthetraceabilityofgoods,whichcouldbecoupledwithothercontentsaimingattheoptimizationoftheforestoperations.ThetestsperformedsofarwithUHFRFIDtagsin

timberlogisticsprovethatthistechnologyisreliable,andthat,intheappropriateconditions,tagsmaybereadevenatrelatively longdistances (2–4meters).Kaul(2010)testedtheperformanceofseveralRFIDtagmodels both in bulk reading (e.g. a full truckload of taggedlogs)andsingleitemsidentification.WiththeappropriateselectionofRFIDtagmodelandreader/antennalayout,bulkreadingcanreturn92%ofreadratesatmillgateentrance,whilesinglelogidentifica-tioninoptimalconditions(e.g.atthebeltconveyorofthesawmill)provided100%ofreadrate.Björk(2011)claimsthataneconomicbenefitcanbe

detectedalongthesupplychainevenwithpartialtag-ging of the whole load of logs, which still allows for a certain degree of traceability of the loads. This would alsomakelesscriticaltheimpactofalowautomatedreadrateand/oralowphysicalsurvivalrate.Never-theless,thefullpotentialofRFIDmarking,particu-larlywhenusedfortransmittinginstructions,canbeexpressedonlyifthereliabilityofthesystemishigh.Thisisrelatedtothereadrate,butmainlytothecapac-ityofRFIDtagstosurviveallalongtheproductionprocessmaintainingintactitsoperationalcapacity.Inthissense,forestoperationsareaverychallengingen-vironment.Inthecaseofcableyardingoperations,thefrequentshocks,frictionsandimpactsoftheextractedmaterial against ground, standing or felled trees and piledtimbermakeitreasonabletoexpectthatpartoftheappliedRFIDtagscouldbelostordestroyedinthephases of bunching, extraction and landing of themarkedwholetreesandthesubsequentlogisticsop-erations of logs.Fig.1depictstheapplicationplanned,whereUHF

RFIDtagsarefirstplacedatbreastheightonstandingtreesbytheforesterduringthemarkingphase(1).

Only trees to be felled are marked and related to the digitalforestdatabasepreviouslygeneratedbyLiDARtechnology.ThechainsawoperatorinchargeoffellingthetestsitewillbeequippedwithalightRFIDreaderconnectedviaBluetooth to theservicesmartphone(always carried for security reasons) and before felling thetreewillreadthetagonit(2).Thiswillallowhimtorelatethefelledtree,andthecorrespondingID,toanewtag,tobeplacedonthecrosssectionsurface(thebuttofthefelledtree).Thispositionisconsideredasoptimal for thedesignedsupplychain, in fact it ismoreprotectedagainstfrictionduringskiddingop-erations than the tangential surface (on the bark) and leadstoanoptimalreadingangle(perpendicular)withantennasplacedonthecableyardercarriageandontheprocessorhead.ByreadingtheRFIDtagofthetree,thislattermachinewillgatherinrealtimethecuttinginstructionsfromthedigitalforestdatabase(3),guaranteeingapreciseandfastbuckingoperation,andmaximizingthevalueoftimberassortments.Fi-nally,theprocessordesignedintheframeoftheproj-ectwillapplyanewUHFRFIDtagtoeachlogpro-duced(4),linkingtheIDtoanewdatabasefeaturingthe measured dimensions (diameters and length) and the commercial quality class assessed with dedicated sensors(Sandak2015).Timberwouldnowbereadytomakepartofadedicatedmanagementsystem,wheretheapplicationofRFIDtagsmayleadtocostreduc-tionsestimatedintherangeof70%comparedtothecurrent systems of industrial wood procurement(Björketal.2011).TheactualcapacityofUHFRFIDtagstoendure

theseconditionsisstillunexplored,particularlyforthephasesofconcentrationandhaulingoftreesintheforest.Theaimofthisstudywastoevaluatetheper-formanceoftwotagmodelsandtwofixingoptionsthoroughthetimbersupplychaininsteepterraindur-ingcableyardingandlogisticoperations.Thestudyalsoaimedatidentifyingthemostcriticalstandorop-erationalparametersthatcouldhaveaninfluenceonthesurvivalrateoftheappliedtags(e.g.diameterorlengthoftheextractedpiece;distanceofconcentration;etc.)andpossiblemitigationactionsforreducingitsnegativeimpactonthereliabilityofinformationflowand traceability system.

2. Material and Methods2.1 RFID tags usedThebasicstructureofRFIDtagsisthetransponder,

ametallicelementbuiltindifferentshapes,accordingtothepurposeandthemanufacturer,andtheinte-gratedcircuit.Theseelementsarefixedonasimple

Survival Test of RFID UHF Tags in Timber Harvesting Operations (165–174) G. Picchi et al.

Croat. j. for. eng. 36(2015)2 167

plastictapestructure(possiblywithoneadhesivesur-faceforapplication),orprotectedandsupportedwithdifferenttypeofcases,accordingtothefinalapplica-tion.Clearly,thecomplexityofthefinalRFIDstructureisreflectedinthesizeandtheunitarycost.Inapreviousscreeningphase,alargenumberof

commercial UHF RFID tag models had been com-paredinordertoidentifythemostsuitabletypesforthespecificpurposesoftheproject,andingeneralfortreeandlogmarking.Aselectionof10tagmodelshadbeentestedinstandingtreeandmarkingoperations,gatheringtheopinionsandsuggestionsofexpertpro-fessionals. Finally, two models were selected for the actualsurvivaltestoverthewholeproductionprocess(Table 1):

ÞWintagFlexytagUHFD7040S.Thistagmodelwasselectedbecauseitwasconsideredparticu-larly suitable for the forest environment. In fact it was originally designed for laundry uses, with a waterproof polyurethane cover (IP68) de-signedformaintainingtheoperativecapacityattemperatures ranging from–40°C to80°Cas

well as resistant to UV, acids and salt solutions. Thistagmodelwasavailablejustinalimitednumber(n.=31),thusitwasonlyusedinapartofthesurvivaltests;

ÞSmartracShortdipoleMonza5.Alogisticdedi-cated model with long reading range. This is a verysimpletagmodelbasicallyconstitutedbythetransponderandtherelativediecutappliedinplasticcoloredstickersprovidedinreels.In

Fig. 1 Schematic representation of the timber supply chain process with RFID tag based transmission of information

Table 1 Main characteristics of the RFID tags tested

RFID

tag

mod

el

Tras

pond

er s

ize, m

m

Over

all si

ze, in

cludin

g pla

stic

cove

r, m

m

Read

ing ra

nge

in lab

orat

ory

cond

itions

with

high

pow

er

read

ers (

2 W

), m

Aver

age

unita

ry w

eigh

t, g

Wintag Flexytag UHF D7040S 47x13 64x45 2–3 4.9

Smartrac Shortdipole Monza 5 93x11 120x25 10 1.1


168 Croat. j. for. eng. 36(2015)2

ordertomakeitsuitableforthepurposesoftim-bertraceabilitythismodelwasmodifiedbyap-plyingaPETEVAplasticcoverwiththermaltreatment(110°C).

The selected UHF RFID tags are designed for being manuallyfixedonthetreesorlogsbymeansofacom-monmechanicalstaplerdeploying6mmlongalumi-numstaples.Thissystemwaschosenforitssimplicity,costeffectivenessandthenegligibleeffectofthealu-minumstaplesincaseofimpactwiththesharptoolsat the sawmill. Furthermore, the selected tags have verylowunitaryweight,animportantaspectconsid-ering that at the sawmill the tags are discarded to-getherwiththeexternalpartsofthelog,whichentersthe stream of industrial residual wood. This raw mate-rialiscommonlyusedforpulporenergyproduction,andinbothcasestheshareofimpurities(plasticandmetal of the tags) should be reduced to a minimum if thissystemistobeacceptedbyendusers.

The second treatment was the method of RFID tag fixingonthelogs:

ÞAdoublestaplingwasregardedasthestandardsolution, being theoretically more reliable, given thedoublegripofthestaplesonthewoodandthe tags and the total adherence of the tag on the log surface, reducing the risk of being caught andrippedbybranchesandslash;

ÞSinglestaplingwascomparedbecauseitpres-entstwopotentialadvantages:staplingthetagonasinglespot,insteadoftwo,simplifiesgreatlytheapplicationoftheRFIDtagonthelog,particularlywhenthisisautomationsystemfortagplacingonaproto-typetimberprocessorhead,

apparentlythepreliminarytestsconductedinmore controlled conditions (timber yard) sug-gestthat,bynotadheringcompletelytothewood surface, the tag becomes more readable becausetheantennaresultsarelessexposedto the loss due to the dielectric constant of wood(Ghahfarokhietal.2011).Inthissense,it should be taken into consideration that, by adoptingthissolution,itwillnotbepossibleto fully control the reading angle in the fol-lowingautomaticoperations,thusacircularantennaanddirectioninsensitivetranspon-dersaretobeusedifthissolutionispreferred.

ThecombinationofRFIDtagmodelandfixingsys-temresulted in three treatments:WintagRFID tagwithdoublestapling(DW),ShortdipoleRFIDtagwithdoublestapling(DS)andsinglestapling(SS).Dueto

thelimitednumberofWintagRFIDsavailable,thesewerenottestedwiththesinglestaple(Fig.2–3).Electronicreadingwasperformedbymeansofa

handheldUHFRFIDreaderCAENqID1240within-builtdoubleperpendicularantennas.ThereaderwasinterfacedviaBluetoothtoamobilephone,re-turningtheIDofidentifiedtags,andtheaveragenum-beroftagsredpersecond.Powersettingsweread-justedtolowlevel(140mW)foravoidingtheriskofmultipletagsreturnsignal.Incaseofdifficultaccessto the logpile, it couldbe set tomaximumpower (500mW),allowinginthebettercasesareadingdis-tanceofabout80–60cminoperativeenvironment.Thesame reader was used in laboratory for testing the tags tobeusedpriortothefieldstudy.

In the forest, the trees and logs were measured and markedbeforeextraction.Aprogressivenumberwasassignedtoeachtreeandlogpaintedwithforestspray

Fig. 2 Marking method with Wintag RFID and double stapling (DW)

Fig. 3 Marking method with Shortdipole RFID and single stapling (SS), note the uplifted position


Croat. j. for. eng. 36(2015)2 169

colorandaRFIDtagwasapplied.Tagmodelandap-plicationtypewasvariedrandomly.Duringextrac-tion,afurthersetofparameterswererecorded,de-scribingeachsingleload(Table2).Notesweretakenforanyparticularevent,suchasimpactofthetaggedarea against standing trees or friction with slash and ground.Suchdescriptiveandnumericalparameterswere

consideredasthemostrepresentativeforafollowingfactorial analysis of the results.

2.2 Cable yarder extractionThecapacity toenduretheoperationsof lateral

yardingandextractionofRFIDtagswastestedinthreecommercial cableyardingoperations in the ItalianApennines(Table3).Inaproperlyplannedandcon-ductedcablecraneextraction,thetreesarefelledina

directionalmostoppositetothepositionofthecableline,withananglefacilitatingtheextractionoftrees.Inthislayout,theoperatorfixesthetreeorthetreesectionsbyapplying thechokers to thebuttof theplant.Thispositionreducestheeffortforthecablecranetoconcentratebyskiddingorpartialskiddingthetreeclosetotheline,whereitisfinallyliftedandtransportedalongthecorridor.Thisworkconditionminimizes the damage to the remaining trees (Marchi etal.2014)and,giventhereducedimpacts,shouldalsobe the less dangerous for the RFID tags survival.All the hauling operations studied were per-

formedinconiferdominatedstands,butdifferedfora number of details, among which the dominant was relatedtospecies. Inallcasestheconditionswereparticularlychallengingcomparedtoacommonop-eration,andahighnumberoffactorsaffectingthereliability of the tagging system could be evaluated, while in case of high rate of survival, the robustness ofthesystemcouldhavebeenconfirmed:Site1:wasamixedforestdominatedbyfir(Abies

alba Mill.)withoccasionalAustrianPine(Pinus nigra Arnold)andbroadleaves (beech, chestnut,maple,cherry).Thesilviculturalworkwaspartiallyanemer-gencyoperationduetostormdamageonanalreadyplannedselectivecut,withthedominantlayerofco-nifers (broadleaveswereprocessed and extractedonly in case of damage). Most of the trees were felled overtwomonthsbeforetheextractionoperations,which were postponed for weather conditions(snow).Theterrainpresentedaregularprofileandslope.Alltheactivitieswereperformedbyacrew

Table 2 Parameters collected in the forest prior and during cable yarder operations

Measured parameters Description

Tree/log parameters

Maximum diameter, cm

Tags were applied at the butt of the felled tree or at the main diameter side of logs and the corresponding diameter measured. If this was not accessible, measurement and tag application were performed on the minor diameter side

Length, m Measured or estimated

Species, descriptor The tree species were noted

Type of section descriptor

Log (processed) Top (with branches) Whole tree

Load parameters

Choker position descriptor

Top of the tree or minor diameter of the log/tree section

Butt of the tree or main diameter of the log/tree section

Hauling distance, m Distance travelled by the carriage loaded

Concentration distance, m

Distance from the original position to the vertical of the carriage

Type of load descriptor

Single item per load

Multiple item per load (two or more trees, sections or logs)

Electronic marking parameters

Tag type descriptorDW, Flexytag fixed with two staples DS, Shortdipole fixed with two staples SS, Shortdipole fixed with one staple

Table 3 Main characteristics of the cable yarding lines studied during the tests

Site 1 Site 2 Site 3

AreaFirenzuola (Firenze)

Montepiano (Prato)

Firenzuola (Firenze)

Altitude above sea level, m 953 843 1079

Coordinates of the cable yarder tower

N44 06.719

E11 16.721

N44 05.830

E11 09.572

N44 08.887

E11 19.353

Average slope, % 35–45 30–40 40–50

Average mainline height, m 12 6-8 14

Direction of extraction Uphill Uphill Downhill

Average extraction distance, m 185 235 215

Average concentration length, m 12.3 15.4 12.6

Average log/tree diameter, cm 41 37 42

Minimum log/tree diameter, cm 27 22 20

Maximum log/tree diameter, cm 56 57 80


170 Croat. j. for. eng. 36(2015)2

experiencedinforestharvestingandcableyarderex-traction(alsooperatinginsite3).Theunloadingareawaslimited,posingafurther

challengetotagsurvival,sincetheprobabilityofcol-lisionamongtreesunloadedorhandledandthepiledtimberishigher(Fig.4).Thisalsoledtoamorecom-plicatecontrolofRFIDtagssurvivalwiththehand-heldreader.Forthisreason,itwasnotpossibletocheck electronically all of the trees, even if the tag and thetreenumberwasvisible.Inthesecases,thepres-enceofthetag,theapparentcondition(damagedornot) and the relative tree number were recorded. Clearly,thisissuewouldnotoccurifforestmachinesequippedwithRFIDreaderswillbeused,sinceeachtree would be grabbed and read individually.

Site2:wasapinedominatedsite(Pinus nigra Ar-nold)ofafinalregenerationcut for facilitating thenatural renovation of broadleaves. Very few standards wereleft,reducingtheinterferencewiththeconcentra-tionoftrees.Thisareawasnotaffectedbystormdam-age.Theterrainprofilehadanunfavorableconvexslope,whichledtoalowaverageheightoftheskylineinspiteofthethreeintermediatesupportsinstalled.Thecrewwascomposedofprofessionalchainsawop-erators,butinexperiencedintheuseofcableyardersfortimberextraction.Forthisreason,mostoftheloadswereskiddedforalmost50%ofthedistance,withlogscompletelylyingontheground,inconditionsverysimilartowinchextraction.Inseveraloccasions,thebuttofthetreeimpactedagainststandingtrees,pro-trudingstones,alreadyprocessedlogsandtheabun-dantslashleftontheground.Site3:Thesitewasdominatedbyfir(Abies alba

Mill.) with occasional beech. The whole area had been affectedbyawindstorm,whichdamagedover50%oftheoriginalstandingtrees(completelyuprootedtopartiallydamagedbythefallofothertrees),andtheforestry activity can be described as an emergency in-tervention.Terrainprofilewasquiteirregular,withtwochangesofconvexity/concavityoverstretches.Insuch conditions, trees were hooked to the chokers ei-theratthebuttorthetop,accordingtotheirpositionand the easiest solution for untangling trunks and crowns.Thismadethelateralyardingquitedifficult,with frequent scratching against standing and lying trees(Fig.5).Forthesamereason,thespecificworkconditionsofthisforestoperationwereconsideredaschallengingforthesurvivaloftags,whichwereex-posedtoadditionalfrictionsandshockscomparedtoaproperlyplannedextraction.

2.3 Intermediate Transport of logs by tractorIn timber logistics, the most critical conditions for

thesurvivalofRFIDtagsareexpectedtooccurduringloghandling,mainlyrepresentedbyloadingandun-loadingoperations.Theenduranceoftagstotheseac-tivitieswasobservedinasinglecommercialoperationatthepreviouslymentionedsite1,wheretimberwastransportedfromthelandingareaofthecableyardertoanintermediatestorageareaoveradistanceofap-proximately 300meters on a steepdownhill forestroad.Thetractortowedasmallsingleaxeforesttrailer,with tilting unloading system, which was loaded at the cableyarderlandingbytheprocessoringrapplemode.Before loading, the dimensions of each log were mea-sured by the crew, involving additional handling.Onthetimberpiledatthelanding,RFIDtagswere

appliedonthelogsidefacingtheroad,whileloading

Fig. 4 Landing of cable yarder with limited operational size. In such conditions post extraction handling may cause further impacts on the tagged surfaces

Fig. 5 Cable yarder concentration in a storm damaged forest is very challenging for the survival of tags due to the abundance of debris, deadwood and uprooted stumps, which could rip or damage the transponder (the white arrow indicates the position of the RFID tag on the log)


Croat. j. for. eng. 36(2015)2 171

onthetrailerwasmadeinordertooptimizeandmakestable the load, thus the tagged sides were randomly distributed in front and on the back of the trailer. At the storage area, logs were unloaded by tilting the trailerandslidingtheloadagainstthetimberpiles.Alsointhiscase,theworkconditionswereparticu-larly challenging for the survival of tags (Fig. 6).Inthistest,onlyDSandSStaggingsystemswere

used.Notallofthelogsinthepileweremarked,eitherbecausebelowthediameterof24cm,setasminimumthreshold, or because not safely accessible.

Logswithadiameterlowerthan24cmwerenotconsidered for the study (not tagged) but counted on theloadsincetheirpresencecouldbeoneofthefactorsinfluencingthesurvivaloftagsonthemarkedlogs.Inthestudy,7roundtripsofthetractorfollowed,trans-portingatotalof198logs,ofwhich86carriedaUHFRFID tag.

3. Results3.1 Extraction operationsThegeneralperformanceofRFIDtagsalongthe

extractionprocessoftreesorlogswaspositive(Table4).Overall5RIFDtagswerelostduringtheextractionof153markeditems,resultinginamortalityof3.3%.Noneofthetagsarrivedatthelandinghadbeenmadeinoperative,evenwhenthewholeofthehostingcross-cutareapresentedevidencesofshocks,abrasionorimpacts.Insomecases,thetagwasnotvisiblefortheadherence of mud or soil on the crosscut section, but still itwaspossible todetect itwith thededicatedreader.Apartialremovalwasobservedfor2DStags,i.e.oneof thestaplingareaswasripped,while theotherstillkeptthetagmoreorlessfirmly.Inanycase,these tags were successfully read at the landing, and thus accounted within the survived. Given these proofsof resistance, the6RFID tags that couldbecheckedonlyvisuallybytheoperator,andpresentedno signs of damage, were added to the total of success-

Table 4 Results of the reading test at landing (cable yarding) and at the storage area (tractor transport)

Cable yarding RFID tag type MarkedElectronic/visual control Just visual control1

Operative Removed Destroyed Not damaged Not visible

Site 1SS 19 16 0 0 3 –

DS 23 20 0 0 3 –

Site 2

DW 16 16 0 0 – –

SS 19 19 0 0 – –

DS 18 18 0 0 – –

Site 3

DW 15 14 1 0 – –

SS 23 21 2 0 – –

DS 20 18 2 0 – –

TOTAL 153 142 5 0 6 –

Tractor transportSS 44 32 0 0 8 4

DS 42 31 0 0 8 3

TOTAL 86 63 0 0 16 7

Fig. 6 Unloading was performed by tilting the trailer against already piled logs, causing further impacts potentially lethal for the tags


172 Croat. j. for. eng. 36(2015)2

fullylandedtags.Itshouldbeemphasizedherethatin the work system envisaged, each RFID tag will be readautomaticallybytheprocessorwhengrabbingsingle trees, thus averting the case of tags out of reach. In any case, even if the tags out of reach for manual readingareexcludedfromtheanalysis,themortalityrateincreasesjustto4.3%.

Due to the very low number of lost tags, it is not possibletoperformastatisticalanalysisoftheresultsagainsttherecordedparameters.Ontheotherhand,thisispersearesult,provingthehighreliabilityofthesystem.

3.2 Transport of logsTheresultsforthetransporttesthavetobeconsid-

eredaspreliminaryfortherelativelyreducednumberoflogs.Nevertheless,duetoparticularlyharshcondi-tions,theresultscanberegardedasparticularlyen-couraging.Infact,overthefullyverifiedtags(visuallyandelectronically),nonehadsuffereddamageorwasremoved.Apartofthetagswasvisibleunderthepile,but not reachable by means of the RFID reader. Two tagshadvisiblysufferedanimpactduringunloading.Electroniccheck(bymeansoftheRFIDreader)waspossiblejustforoneofthese(singlestapling),whichresultedunharmedandperfectlyoperating.Itisthusreasonabletoaddthetags(visuallyidentified)amongthe survived tags, since during all of the trials the eventofatagstillattachedbutmadeinoperativebyshocks never occurred, and it can be considered as extremelyunlikelyintagsthatdonotevenshowsignofimpactsorscratches.Inanycase,evenconsideringthis last tag as destroyed, the overall survival rate wouldbeabove98%.

4. Discussion

4.1 Extraction operationsConsideringthefactorsevaluatedandthedirect

observationsoftheoperators,itispossibletoidentifythemaincauseoftagremoval:thepositionofchokerwithrespecttothecrosscutsection,wheretheRFIDtagisapplied.Ofthe5missingtags,4wereplacedonthesideoppositetothechokerposition.Furthermore,allofthemissingtagswerelostinsite3,themostaf-fectedbystormdamage.Thisforcedtheoperatorstosetthechokersatthemostaccessibleposition,ratherthanthemostappropriateforthecableyardingextrac-tion itself.Asa result,over31%of logs/treeswerehookedfromthetoporminordiameterend,oppositetotheRFIDtagposition.However,thisfactoralonecannotexplainthetagremovalsinceinsites1and2

thehookingpositionoppositetotagplacingoccurredin19and17%ofcases,respectively.Whenthetagsarelost,thechokersettingpositionappearstocombinewithotherfactors,themainbeingthespecificlayoutofthecableline.Infact,theextractioninSite3wasperformedindownhilldirection,andthecombinationofskylineheightandterrainprofilecausedthehang-ingtrees/logstobrushviolentlyandrepeatedlyagainstthe ground with the crosscut surface hosting the RFID tags.Thishappenedmostlyatthelanding,butalsooccurredinotherspots,accordingtothelengthoftheextractedtrees/logs.Thiscombinationoffactors(loadshooked from the minor diameter or the crown and a convexunloadingarea)canberegardedasquiteun-usualandparticularlyunfavorabletoRFIDsurvival.Nevertheless,thesurvivalrateforthisspecificsitewasstillabove90%,confirmingthereliabilityofthetagmarking system.TheRFIDtagmodelandthemethodofapplication

seemtohavenoinfluenceonthefinalsurvivalrate.Infact2,2and1werelost,respectively,ofthetypesDW,SSandDS.Inthisscenario,themethodSS,represent-ingthesimplestUHFRFIDtagsandthefastestap-plicationsystem,shouldbepreferred.

4.2 Transport of logsThetestsuggeststhatnodifferencecanbefound

insingleordoublestaplingfixingofthetags,thusthefirstshouldbepreferred.Thisresult isparticularlyencouraging for thedevelopmentofanautomatedRFIDtagapplicationsystemtobeinstalledonthetim-berprocessor.Infact,thepossibilitytofixthetagwithjustasinglestaplesimplifiesgreatlythedesignofthemachine.Byobserving theoperations, the loadingphase

doesnotappeartobeadangerousoperationforthetagsurvivalinthespecifictestedposition,evenifac-cidents,suchasimpactagainstotherlogsorthetrailerposts,dooccasionallyhappen.Onthecontrary,inthegivencaseunloadingseemstobeaparticularlychal-lengingoperation,sincelogsarelandedbytiltingthetrailer, thusslidingdownthetimber,whichpoten-tiallyhitsthegroundwiththeradialfaceorthepileoflogspreviouslyunloaded.Itisimportanttonotethatallalongthelogisticsof

logs,thepositionofthetaggedextremecannotbecer-tain.TheRFIDtagisnecessarilyappliedtooneex-tremeofthelog:duringloadingandunloadingop-erationsthisextremecanbepositionedontheloadingcageofthetrailer/forwarder/truckandonthepileinacasualposition.Asaresult,thetagswillbepartlyfac-ingonesideofthearrangementandpartlytheoppo-site side. This issue shall be taken into account when


Croat. j. for. eng. 36(2015)2 173

designing the following traceability systems for auto-matic detection of UHF RFID tags in the load, and particularlywhenplanningthepositionoffixedan-tennas for bulk reading.

5. ConclusionsTheresultsofthetestareverypositive.Theoverall

survivalrateofRFIDtagsinforestoperationsandtim-berlogisticswascloseto98%.Consideringjustthecableyardingoperations,thesurvivalratedecreasedslightly toalmost 97%. In the single cableyarding operation,whereRFIDtagcasualtieswererecorded,thesurvivalratewas91%,while100%oftagssuccess-fully arrived at the landing in the other two sites ob-served.Tractortransportationandtimberpilingledtono

detectable damage or losses to the RFID tags, never-theless, due to the limits of the manual RFID reading systemused for this test,28%of the tagscouldbeverifiedjustvisually,orthetaggedareacouldnotbefoundatallinthepiledtimber,leavingadegreeofuncertainty.Thiswouldnothappeninthefullymech-anizedreadingsystemunderdevelopment,sinceeachtagwouldbeautomaticallyredduringextractionandprocessingofthetrees.ThestudyconfirmsthatlargeRFIDtagmodels,

with longer read range, can be used without incurring a higher risk of information loss. Furthermore, a single staplingpositionisenoughtoassureastablegriponthecrosscutsurface,simplifyingthetaggingopera-tions in forest (manual) and in the subsequent auto-matedprocesses.ItcanbeconcludethatsimpleRFIDtagsfixedon

thetreeswithcommonaluminumstaplescanbere-gardedasareliabletoolfortracingortransmittinginformationallalongtheextractionprocessoftimberfrom the forest to the landing and from there to the enduser.Thissystemprovidesapowerfulandrela-tivelyinexpensivedeviceforcontrolandoptimizationofforestoperationsandtimberlogisticsanditsap-plicationsshouldbefurthertestedindifferentworkconditionsandextractionsystems.

AcknowledgementsThis work has been conducted within the frame-

workoftheprojectSLOPEreceivingfundingfromtheEuropeanUnion’sSeventhFrameworkProgrammeforresearch,technologicaldevelopmentanddemon-stration under theNMP.2013.3.0-2 (Grant number604129).TheauthorswishtothankDr.MirandoDi

PrinzioforhisessentialroleintheorganizationofthefieldstudyandMrs.CarolinaLombardiniforhervalu-ablesupportandsuggestionsindatacollection.

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174 Croat. j. for. eng. 36(2015)2

Received:May29,2015Accepted:July31,2015

Authors’address:

GianniPicchi,PhD.* e-mail:[email protected] CNR-IVALSA viaMadonnadelPiano10 50019SestoFiorentino ITALY

MartinKühmaier,PhD.* e-mail:[email protected] UniversityofNaturalResourcesandLifeSciences, Vienna DepartmentofForestandSoilSciences InstituteofForestEngineering PeterJordanStrasse82 1190Vienna AUSTRIA

JuandeDiosDíazMarqués,PhD.* e-mail:[email protected] ITENE-InstitutoTecnológicodelEmbalaje, TransporteyLogística Area:AdvancedIntelligentSystems C/AlbertEinstein,1 46980Paterna,Valencia SPAIN

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Survival Test of RFID UHF Tags in Timber Harvesting Operations