Microcontroller-based mobile robot positioning and obstacle avoidance

Microcontroller-based

mobile

robot

positioning

and

obstacle

avoidance

Aziza

M.

Zaki

,

Osama

Arafa,

Sanaa

I.

Amer

PowerElectronicsandEnergyConversionDepartment,ElectronicsResearchInstitute,El-TahrirStreet,Dokki,Cairo,Egypt Availableonline4April2014

Abstract

Theuseofmobilerobotsisgrowinginmanufacturingfacilities,hazardousmaterialshandling,etc.Usually,severalsensorsystems areusedincombination.Thetaskofcombiningtheinformationintoausableform,suitableformakingnavigationdecisions,is knownassensorfusion.Inthispaper,thenavigationsystembuiltonamobilerobotoperatinginawarehouseispresentedfocusingon thesensorysystemused.Hybridnavigationsystemthatcombinestheperceptionanddeadreckoningisusedandgivessatisfactory operation.Amicrocontrollersystemisdesignedtocontrolthenavigationofamobilerobotwhileavoidingobstacles.Asystemof 24ultrasonicsensorswasdesignedandtheoperationalgorithmsweredescribed.Theencoderandtheultrasonicsensorsusedare presentedindetailtogetherwiththenavigationsystemdesignedbasedontheiroperation.

©2014ProductionandhostingbyElsevierB.V.onbehalfofElectronicsResearchInstitute(ERI).

Keywords:Mobilerobot;Navigationcontrol;Odometry;Ultrasonicsensors;Microcontroller

1. Introduction

Robotnavigationmeanstheabilitytowonderintheenvironmentwithoutcollidingwithobstacles,theabilityto determineone’sownposition,andtheabilitytoreachcertaingoallocations.So,navigationsystemmayimplythe followingcomponents:robotpositioningsystem,pathplanningandmapbuilding.Thesearefourpopularpositioning systems:

1. Odometry(deadreckoning)-basednavigation. 2. Activebeacons-basednavigationsystem. 3. Landmark-basednavigationsystem. 4. Map-basednavigationsystem.

∗_{Correspondingauthor.}

E-mailaddress:[email protected](A.M.Zaki).

PeerreviewundertheresponsibilityofElectronicsResearchInstitute(ERI).

http://dx.doi.org/10.1016/j.jesit.2014.03.009

istoocomplicatedformanyapplications.

Inthispaper,thenavigationsystembuiltonamobilerobotoperatinginawarehouseispresented.Hybridnavigation systemthatcombines theperception anddead reckoningwasfoundtobecomplementaryandgivesasatisfactory operation of the mobilerobot. If environmentcontainsconfusing informationor few perceptuallydistinguishable landmarks,the performanceof thesesystems decline.Theperceptualaliasing problemcanbesolvedbyincluding theodometrydatatodiscriminatebetweenthesimilarplaces.Theuseofultrasonicsensorsinmostapplicationsis easier,cheaperandcomputationallysimpler.Ultrasonictransducersarepreferablyusedtoobtainthree-dimensional informationof theenvironment (Bak, 2002;Everett, 1995;Borenstein andKoren,1988; Benitz-Readand Rojas-Ramirez,2010).Theymeasureanddetectdistancestomovingobjects,areimpervioustotargetmaterials,surfaceand color,solid-stateunitshavevirtuallyunlimitedmaintenance-freelifespan.Ultrasonicsensorsarenotaffectedbydust, dirtorhigh-moistureenvironment.

In Section2 of thiswork,the odometryandthe odometry errorswerepresented.Section 3presents ultrasonic systems,thesourceoferrorsthatcouldbeencounteredandthesensorstypespeciallythesensorusedinthiswork. Section4presentsthe robotdescriptionandthesensors,decodersandencodersbuilt onthe robotwhileSection5 describestherobotcontrollerdesignedforrobotoperationwiththeultrasonicsensorsusedclusteringandthecontroller hardwareandsoftware.Section6detailstheproposedrobotnavigationinsideandoutsidethewarehousewhileSection 7presentstheexperimentaltestingtogetherwiththeinterfaceboardused.Sections8and9givetheresultsdiscussion andconclusions.

2. Odometryandodometryerrors

Odometryisthemostwidelyusednavigationmethodformobilerobotpositioning.Itiswellknownthatodometry providesgoodshorttermaccuracy,isinexpensiveandallowsveryhighsamplingrates.However,thefundamentalidea ofodometryistheintegrationofincrementalmotioninformationovertime,whichleadsinevitablytotheaccumulation oferrors.Odometryisusedinalmostallmobilerobotsforvariousreasons:Odometrydatacanbefusedwithabsolute positionmeasurementstoprovidebetterandmorereliablepositionestimation(ChenavierandCrowley,inpress;Evans, 1994).Odometrycanbeusedinbetweenabsolutepositionupdateswithlandmarks.

Odometry is based on simple equations that are easily implemented and that utilize data from inexpensive incremental wheel encoders. However, odometry is also based on the assumption that wheel revolutions canbe translatedinto lineardisplacementrelativetothe floor.Thisassumptionisof limitedvalidity.Oneextreme exam-ple is wheelslippage: – if onewheelwas toslipon, sayan oil spill, thenthe associated encoder would register wheel revolutions even though these revolutions would not correspond to a linear displacement of the wheel. Therearealso,severalothersubtlereasonsforinaccuraciesinthetranslationofwheelencoderreadingsintolinear motion.

To correct the errors inpositioning resulting from the odometry system andfor safe navigation and obstacle avoidance,ultrasonicsensorsarefrequentlyusedastheycanprovidegoodrangeinformationbasedonthetimeofflight (TOF)principle.Theyhavebeenwidelyusedinmobilerobotapplications(Elfes,1987;LeonardandDurrant-Whyte, 1992;BorthwickandDurrant-Whyte,1994).

Fig.1.Angularerrorofanultrasonicsensorαisthehalfopeningangleofsonarcone,Risasonarresponse.

3. Ultrasonicsystems

UltrasonicTOFrangingistodaythemostcommontechniqueemployedonindoormobileroboticsystems,primarily duetothereadyavailabilityoflow-costsystemsandtheireaseofinterface.

3.1. Ultrasonicsensors

Ultrasonictransducersarepreferablyusedtoobtainthree-dimensionalinformationoftheenvironment.Butsome problemsappearinsonarresponse.Ultrasonicsensorssufferfromunreliablesonarresponsesfromtheenvironment. Forsonar-basedmobilerobotinconfined space, special attentionshould bepaid totheseproblems. Thespace is normallyaclosedenvironment.

Twomajorproblemsarediscussedinthefollowing(Kumari,2012). 3.1.1. Angularuncertainty

WhenanultrasonicsensorgetsarangeresponseofRmeters,theresponsesimplyrepresentsaconewithinwhich theobjectmaybepresent.Thereisnowaytopin-pointexactlywherethepositionoftheobjectis.Fig.1conveysthe idea.Theopeningangleoftheultrasonicsensoris2αandtheobjectcanbeanywhereintheshadedregionforthe responseR.

3.1.2. Specularreflection

Specularreflectionreferstothesonarresponsethatisnotreflectedbackdirectlyfromthetargetobject.Inspecular reflection,theultrasoundisreflectedawayfromthereflectingsurface,whichresultsinlongerrangereportingormissing thedetectionofobjectalltogether,Fig.2(Drumheller,1987;LimandCho,1994).

3.2. Typesofultrasonicsensor

Beforeweselectorinstallanultrasonicsensor,weshouldbefamiliarwiththeseterms: 1. Deadzone.

2. Beamangle.

3. Beamconediameter. 4. Maximumsensingrange. 5. Backgroundsuppression. 6. Switchingfrequency. 7. Inclinationoftarget.

8. Environmentalconsiderations.

Afterstudyingsometypesofultrasonicsensors,weselectedthe(DevantechSRF04RangerCompactHigh Perfor-manceUltrasonicRanger(Polaroid,1987))foruseinthiswork.Fig.3representstheSRF04ultrasonicsensor.

Fig.2.Specularreflections.

Fig.3.DevantechSRF04range.

3.2.1. Specifications

The specificationsof SRF04UltrasonicRangerare shownintheAppendix.Thebeam pattern ofthe SRF04is conicalwiththewidthofthebeambeingafunctionofthesurfaceareaofthetransducersandisfixed.Thebeampattern ofthetransducersusedontheSRF04,takenfromthemanufacturer’sdatasheet,isshowninFig.4.

Therangerworksbytransmittingapulseof soundoutsidetherangeofhumanhearing.Thispulsetravelsatthe speedofsound(roughly0.9ft/ms)awayfromtherangerinaconeshapeandthesoundreflectsbacktotherangerfrom anyobjectinthepathofthissonicwave,Fig.5.

4. Robotdescription

The mechanical design for the robot plays a critical role in the success of the robot facility. The following specificationsshouldbemet:

1. Movingforwardandbackwardwithoutrotation. 2. Movingaside(rightandleft)withoutrotation. 3. Havethefacilitytorotateinacompletecircle.

4. Therobotwilluseabatteryassemblywithtotalvolt48V. 5. Thecontrolunitandbatterychargershouldbeontherobotitself.

Fig.4.Beampattern.

100µse c: object detected very close 18 msec: no object detected

Pulse sound to generate at the falling ed ge 10µsec min. Pulse Trigg er input

Min. width 10µsec to initiate the sonic pulse

Sonic burst SRF 04 (ba ck) Echo output Pulse Trigger input

G

+5v

Fig.5.SRF04typicalwaveformsandconnections.

Thedrivingsystemoftherobotiscomposedof4wheelseachofthemequippedwithaseparateelectricmotor.A frontandrearsteeringsystemwereaddedtogiveflexibilityinthemotionplanningforsmoothnavigation.Themobile robotconfigurationisshowninFig.6.Therobotisequippedwithasimplearmusedduringloadingandunloadingthe components.

Fig.6.Mobilerobotconfiguration.

4.1. Robotpositioning

Methodsforrobotpositioningcanberoughlycategorizedintotwogroups:relativeandabsoluteposition measure-ments.Becauseofthelackofasinglegoodmethod,developersofmobilerobotsusuallycombinetwomethods,one fromeachcategory.

Inthiswork,therelativemethodusedisodometry.Thismethodusesencoderstomeasurewheelrotationand/or steeringorientation.Odometryistotallyself-containedanditisalwayscapableofprovidingthevehiclewithanestimate ofitsposition,butthepositionerrorgrowswithoutboundunlessanindependentreferenceisusedperiodicallytoreduce theerror.Naturallandmarkrecognitionwasusedasanabsolutepositioningmeasurementsystemtocorrectperiodically therightpositionoftherobot.

4.2. Encoder,decodercontrollerandmotioncontrolused

Opticalincrementalencodersareameanforcapturingspeedandtraveleddistanceonamotor.Rotationvelocitycan bedeterminedfromthetimeintervalbetweenpulses,orbythenumberofpulseswithinagiventimeperiod.Because theyare digital devices,incrementalencoders will measuredistance andspeedwithperfect accuracy.Quadrature encodershavedualchannels,AandB,whichare electricallyphased 90◦ apart.Thus,directionof rotation canbe determinedbymonitoringthephaserelationshipbetweenthetwochannels.Inaddition,withadual-channelencoder,a fourtimesmultiplicationofresolutioncanbeachievedbycountingtherisingandfallingedgesofeachchannel(A&B). Inthiswork,theHEDS5540,3channelshighperformanceopticalincrementalencodersareused.ThisICconsists ofmultiplesetsofphotodetectorsandthesignalprocessingnecessarytoproducethedigitalwaveforms.Thedigital outputofchannelAisinquadraturewiththatofchannelB(90◦outofphase).Theencoderstandardresolutionis1024 countsperrevolution.

ThegeneralpurposemotioncontrolIC,HCTL-1100,isemployed.Itfreesthehostprocessorforothertasksby performingallthetimeintensivefunctionsofdigitalmotioncontrol.TheHCTL-1100providespositionandvelocity controlforDC,DCbrushlessandsteppermotors.

5. Theproposedcontroller

Atdesigningamotioncontrollerforanautonomousmobilerobot,amainproblemmustbehandledwhichisthe obstacleavoidanceproblem.

Inthecaseconsidered,therobotismovingtotransportelectroniccomponentsfromawarehousetooneofthree productionlines.Themissionoftherobotintheinnerwarehouseistopickupcomponentsfromthetargetpoint.So,it willbealwaysmovingnexttooneofthewallsastheshelvesinthiswarehousearelocatednexttothewalls.Outside thewarehouse,thepathwillbeprescribedaccordingtothetargetproductionline.Thesensorsshouldbearrangedsoas toachievesafenavigationinsideandoutsidethewarehouse.Weuseasystemof24ultrasonicsensorsarrangedaround thevehicleasshowninFig.7.

Fig.7.Sensorsclustering.

5.1. Sensorsclustering

Groupingthesensorsismadetofacilitatedecisionmaking.Thesensorsinacertaingroupactasonesensor(grouped sensor).Sothesensorsineachgroupmustbeselectedcarefully.

Theclusteringproceduresareasfollows: 1. Scanthereadingsofthesensorsofthegroup.

2. Theminimumreadingisthedominantoneandtheothersareneglected.

TheclusteringshowninFig.7isthesuggestedoneforourcontroller.FrontLeft(FT):Sensors(So,S1)andFront (F):Sensors(S2,S3,S4andS5).Therobotsensestheobstaclesusingitssonarsensors.Inthiswork,weconsider onlythestaticobstacles.Theshapeandmaterialdonothavegreatimpactinourcase.Thesonarsensorscannotdetect obstaclesthathaveheightsmallerthancertainvalue(indicatedinthedatasheet),soweconsideronlyobstaclesthat canbedetectedbythesonarsensors.

Thereadingsofthegroupedsensorsareassignedoneoftwolabelswhicharefaranddangerous.Eachgrouphas differentinterpretationtothemeaningoffaranddangerous.Forexampleforthefrontsensorsgroup,thereadingof thegrouprangingfrom1mto3misfar,whilethereading3cmto1misdangerousrangingfrom1mto3misfar, whilethereading3cm–1misdangerous.

Theselectionoftherangeaffectsonthesensitivityofthesensorsorinothermeaningtheevaluationtothedistance betweentherobotandtheobstaclefromthepointofviewifitisdangerousornot.Weneedthefrontsensorstobe moresensitivethantheFront-Right(FR-RT)andFront-Left(FR-LT)toprotecttherobotfromcollisionwiththewalls orobstaclesduringturningatthewallscornerorturningaroundtheobstacletoavoidit.Thesethreegroupshelpthe robottoavoidthefrontobstaclesandtoturninthecornersandstarttoalignagaintoanewwall.Duringbackward navigation,Back(B),BackLeft(BL)andBackRight(BR)arethesensorgroupsused.

thedecisionofwhatisthenextstep.Thepositionestimateprovidedbydeadreckoningiscorrectedbymatchingthe perceptionagainstastoredworldmap.Landmark-basednavigationdependsmainlyontheagent’sperceptiontoits environment.Iftheenvironmentcontainsconfusinginformationorfewperceptuallydistinguishablelandmarks,the performanceofthesesystemsdecline.Theperceptualaliasingproblemcanbesolvedbyincludingtheodometrydata todiscriminatebetweenthesimilarplaces.

6. Proposedrobotnavigation

6.1. Robot’smotiontrajectory

Thevehiclewillmoveinsideandoutsidethewarwarehouse.Navigationofthevehicleisdividedintothreemain parts:

1. Insidewarehouse. 2. Outsidewarehouse.

3. Maneuveringatthewarehousedoor.

Robotcanfigure outfrom theodometer systemif it insideor outsidewarehouse. There areseveral rulebases accordingtosensorsreadingsandodometerthatmaketherobotswitchfromonecontrollertotheother.

6.2. Robotsmotiontypes

Therobotvehicleisdesignedtoperformonlytwodistinctkindsofmotioninthewarehouse: (1) Straight-linemotion,wherebothmotorsarerunningatthesamespeedandinthesamedirection.

(2) Rotationaboutthevehicle’scenter-point,wherebothmotorsarerunningatthesamespeedbutinoppositedirections. Thisapproachisadvantageousforseveralreasons:

1. Wheelslippageisminimizedbecauseofthesimultaneousactionorrestofbothwheelsandbecauseofthe “on-the-spot”rotationactionforturns.

2. Arelativelysimplecontrolsystemmaybeused,sinceineithercasetheonlytaskofthecontrolleristomaintain equalangularvelocities.

3. Thevehiclepathisalwayspredictable,unlikeothermotionstrategieswhichsmoothsharpcornersbyan unpre-dictablycurvedpath.Apredictablepathisadvantageouswhenglobalpathplanning,toavoidobstacles,isemployed. 4. Thevehiclealwaystravelsthroughtheshortestpossibledistance(straight-lineor“on-thespot”rotation).

6.3. Theproposedcontroller

Atdesigningamotioncontrollerforanautonomousmobilerobotthereisamainproblemthatmustbehandled whichistheobstacleavoidanceproblem.Therobotsensestheobstaclesusingitssonarsensors.

6.3.1. Controllerinsidethewarehouse

Inthislocationofthewarehouse,itisrequiredfromtherobottogotocertainshelftopickupsomecomponents andthenmovetowardthedoorasafirststeptodrivethesecomponentstotherequiredassemblylines.

Asthemissionoftherobotintheinnerwarehouseistopickupcomponents,sothetargetpointwillbealwaysnext tooneofthewalls.Sowesuggestthattherobotwillmoveparalleltothewallsuntilarrivingtothetargetpointtopick uptherequiredcomponents.

Thereadingsofthegroupedsensorsareassignedoneoftwolabelswhicharefaranddangerous.Eachgrouphas differentinterpretationtothemeaningoffaranddangerous.Forexampleforthefrontsensorsgroupthereadingofthe grouprangingfrom1mto3misfarwhilethereadingfrom3cmto1misdangerous.Theexpertsystemrulebaseis presentedinTable1.

6.3.2. Motioninsidethewarehouse

ThedifferencebetweenthereadingsofthetwosidesensorsL=SL1−SL2areusedtohelptherobottoalignto theleftwall.Wewanttherobottokeepcertaindistancetothewallwhichisestimatedinourworktobe50cm.The selectionofthisvalueistargetedtohelptherobottoturnsmoothlyatthecornerswithoutgettingstuckwiththewalls. Whiletheothergroupedsensorsallowtherobottodetecttheobstaclesinhiswayandavoidcollisionbyrotatingaround it.TheusedalgorithmisshowninFig.8.Thisalgorithmiscalledonceentrancetothewarehouseisacknowledged andrepeatedduringnavigationinsidethewarehouse.

7. Experimentaltesting

7.1. TestingofSRF04sensoroperation

InFig.9,thephotographshowstheURFboard,asingleSRF04sensor,thetestingboardandapowersupply.They wereconnectedtogetherinasuccessfultestingtrial.Line1isusedtodisplaytherangingresultandline2isusedto displaythesensorIDwhoserangingresultsisdisplayedinline1.Line1isusedtodisplaytherangingresultandline 2isusedtodisplaythesensorIDwhoserangingresultsisdisplayedinline1.Thesensorconnectionwasmadewith eachofthe24channelsandallthesechannelsgivesatisfactoryresult.

7.2. Theinterfaceboard

Sinceultrasonicrangingdependsonmeasuringthetimedurationtakenbytheultrasonicwavetotravelgoandback betweenthetransceiverandthenearestobject,itisessentialtohaveaprecisemeansoftimemeasuringwhichshould meetthefollowingrequirements:

1. Toput aminimumloadingonthe mastermicrocontrollerof the robottopreserve its processingpowerfor the navigationandobjectshandlingtasks.

Send grouped sensors to master

Call expert sysems

(If robot away from or close to wall align. If obstacle in front detected turn around then align

to wall)

Apply O/P for t

Traverse

the door Return Yes

No

Fig.8.Algorithmforinnernavigation.

2. To provide sufficient number of independent time measuring devices that can serve simultaneously as many transceiversasneededbythemobilerobotvehicle.

3. Rangingistobeinitiatedbythemaster.Therangingsubsystemshouldacknowledgethemasteruponcompletion ofeachindividualrangingtask.

Thefirst requirementismetbyofferingaseparatemicrocontrollerthatcancollecttherangingresultsfromthe available timemeasuringdevices andconvertthemfromtimeunits tosuitabledistance units(centimeters,meters orfoots),thenstoretheminanarrayform.Themastermicrocontrollercanacquirethesedataas neededthrougha master/slaveserialcommunicationlink.

Thesecondrequirementismetbyprovidingsufficientnumberofindependentcountersthatcanindividuallyand simultaneouslycountthepulsesofahighfrequencyclocksharedbyallcounters.Theplannednumberofchannelsin thisstageis24channels.

Fig.9.Rangertestingboard,SRF04sensorandURFboardduringtest.

Thethirdrequirement ismetbyestablishing ahandshakinglink betweenthemastercontrollerandtheranging controller.Throughthislinkastartrangingcommandisissuedbythemasterandarangingcompletedsignalisissued bytheslavewhenthelatestechosignalofthe24transceiversiscaptured.

ThemainbuildingblockbesidetheAtmelAVR90S8515microcontrollerisaprogrammableTTLcounterchip8254 whichhas3independentcounters.

Thismainbuildingblockisrepeatedeighttimestoprovideatotalof24timingchannels.

ATMELAVRmicrocontrollersareeasilyprogrammedusingtheATMELintegrateddevelopmentenvironmentAVR studio4.

7.3. Controlarchitectureoverview

Themobilerobotcontrolsystemisamulti-inputmulti-outputlargeandcomplexonethatmayrequireadedicated controllerforeachofitsmultiplesubsystems.Forexampletherobot’swheelsneedadedicatedmotioncontrolsystem whichcanreceiveandexecutethefollowinghighlevelmotioncommandsandreportexecutionerrorsincaseoffault incidence:

• Setforwardspeed. • Setbackwardspeed.

• MoveforwardXcentimeters. • MovebackwardXcentimeters. • Stopimmediately.

• TurnrightYdegrees. • TurnleftYdegrees. • Resetodometer. • Getodometer.

AssemblyLine:pointBothenpointB1.Eachpathissavedasaconsequencenumberof(x,y)pointsstartingfromjust thewarehousedoor.So,alook-uptableisestablishedtomatchbetweentheassemblyline’snumberandthesequence ofpointsrepresentingit.Inorderthattherobotcanfollowacertainpath,ithastotraceitspointsinorderuntilreaching itstarget.Thecompositebehaviorwillbedividedintofourprimitivebehaviorswhichare:

Path1: 1. Moveforward1.5m. 2. Turnright90◦. 3. Moveforward6m. 4. Stop. Path2: 1. Moveforward1.5m. 2. Turnleft90◦. 3. Moveforward17m. 4. Stop. Path3: 1. Moveforward1.5m. 2. Turnleft90◦. 3. Moveforward4m. 4. Turnleft90◦. 5. Moveforward8m. 6. Turnright90◦. 7. Moveforward17m. 8. Stop

Theareaoftheplacewasdividedasamapofx,ypoints.Point(0,0)isjustatthemidpointofthewarehousedoor. Thestepwassettobe0.5m.

Whentherobotterminatestherequiredjobatanyoftheassemblylines,it willtakethereversedirectiontohis pathreturningbacktothedoorofthewarehouse(point(0,0)).Duringitsnavigation,therobotreadscontinuouslythe sensorsreadings.Iftherobotdetectsanobstacleinfrontofhim,itwillstopandstoreitspositiontoavoidthecollision andatthesametimenottoloseitspath.

Fig.10.Schematicdiagramoftheworkingarea.

Path1x,y Path2x,y Path3x,y

0,0 0,0 0,0 0,3 0,3 0,3 12,3 −34,3 −8,3 Stop Stop −8,−13 −42,−13 Stop

AschematicdiagramoftheworkingareaisshowninFig.10. 7.5. Maneuveringatthewarehousedoor

Therobotsystemabilitytodetectobstaclesduringnavigationwastestedduringmaneuveringatthewarehousedoor whilegettinginoroutthewarehouse.

Thereadingsoftheultrasonicsensorsindicateifitisintherightpositiontoenter,forexample,ornot.Iftherobot detectsapartofthewallintheleftorright,dependingonthesetofsensorsthatdetectsanobstacle,hehastomaneuver toputitselfintherightpositioninfrontofthedoorbeforegettingin:

First,hehastogobackwardforabout50cm.

Thenmovingrightorleftdependingonthepositiondetectedbythesensorsuntilaligningtothecenterofthedoor. Duringitsroutetotheproductionline,inmanyplacestheailesareverynarrow,sotherobotwillstopwhenhedetects anobstacleandgivesanalarm,sotheobstaclecouldberemoved.

Thisprocesswastestedsuccessfullyduringtestingtherobotoperation.

8. Resultsanddiscussion

Duringtestingoftherobotoperation,therobothadtogotooneoftheassemblylinesandgetbacktothewarehouse, itmaneuverstoputitselfintherightpositionatthedoor,gotothetargetAssemblyLineandgetbacktothewarehouse enteringsafelyfromthedoor.Someproblemswereencounteredconcerningthemaneuveringatthedoorandtheerrors wereadjusted.Thesepathsweretraveledsuccessfullyattheend.

9. Conclusions

Thepaperpresentsthecontrolsystemofamobilerobotoperatingtotransportcomponentsfromawarehouseto productionlinesaccordingtoprescribedpathsavoidingcollisiontoanyobstacleduringitsnavigation.Therobothasto followthedesignedalgorithmduringmovinginsidethewarehousetogettherequireditems.Thentransportingthese itemstotheprescribedassemblyline,ithastofollowanotheralgorithm.

Amicrocontrollersystemwasdesignedtoaccomplishthistask.Anultrasonicrangerslavemicrocontrollersystem wasdesignedandprogrammedtoaccomplishthistask.Theultrasonicsensorusedspecificationswaspresentedand

thenumberofsensorsandtheirpositioningaroundtherobotwasdesignedandillustrated.Thesystemwastestedin eachstep.Theultrasonicsensorswastestedfirsttobesureof theconsistingofthereadingsandthecorresponding sensors.Alsothepathstothethreeassemblylineswereprogrammedandstoredtobefollowedbytherobot.Obstacle detectionwasexamined.Therobotstopswhendetectinganobstacleandgivesanalarminordertoremoveit.

Inthispaper,thenavigationofamobilerobotinawarehousewaspresented.Therobothastonavigateinsidethe warehousetopickthecomponentsneededfortheindustrialoperation.Overtheouterpath,therobotwillmoveinone ofthreepredeterminedpathstoreachoneofthethreeassemblylinesinoperation.Thesepathsweresavedintherobot memory.Thesensorysystemusediscomposedofwheelencodersandultrasonicsensorstocorrectthepositionofthe robotresultingfromodometrysystemandtoavoidanyobstaclesduringnavigation.

Thenavigationsystemwasdescribedandthesensorysystemdescription,positioningandoperationwaspresented. Thecontrolofthenavigationsystemwasalsodetailed.

Appendix.

SeeTable2.

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