intech-design_and_optimal_research_of_a_non_contact_adjustable_magnetic_adhesion_mechanism_for_a_wall_climbing_welding_robot.pdf...

International Journal of Advanced Robotic Systems Design and Optimal Research of a Non-Contact Adjustable Magnetic Adhesion Mechanism for a Wall-Climbing Welding Robot Regular Paper

Minghui Wu1, Gen Pan1, Tao Zhang2, Shanben Chen2, Fu Zhuang1 and Zhao Yan-zheng1,* 1 State Key Laboratory of Mechanical System and Vibration - School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai, P.R. of China 2 Institute of Welding Engineering - School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai, P.R. of China * Corresponding author E-mail: [email protected]

Received 20 Apr 2012; Accepted 2 Oct 2012 DOI: 10.5772/54008 2013 Wu et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract Wallclimbing welding robots (WCWRs) canreplace workers in manufacturing and maintaininglarge unstructured equipment, such as ships. Theadhesionmechanism is thekeycomponentofWCWRs.As it isdirectlyrelated to therobotsability inrelationto adsorbing,moving flexibly and obstaclepassing. Inthis paper, a novel noncontact adjustably magneticadhesionmechanism is proposed.Themagnet suckersaremountedundertherobotsaxilsandthesuckerandwall are innoncontact. Inorder topassobstacles, thesuckerandthewheelunitcanbepulledupandpusheddown by a liftingmechanism. Themagnetic adhesionforce can be adjusted by changing the height of thegap between the sucker and the wall by the liftingmechanism. In order to increase the adhesion force,the value of the suckers magnetic energy density(MED)ismaximizedbyoptimizingthemagnetsuckersstructure parameters with a finite element method.Experiments prove that the magnetic adhesionmechanism has enough adhesion force and that the

WCWRcancompletewallclimbingworkwithinalargeunstructuredenvironment.Keywords WallClimbing Welding Robot, NonContactAdhesion, Adjustable Magnetic Adhesion Mechanism,MagneticEnergyDensity1.IntroductionWith the development of economies and industrialtechnology, the demand for large unstructuredequipment such as ships and oil tankers is increasing.These require that a large amount of welding andinspectionwork be accomplished in themanufacturingandmaintenanceofthem.Wallclimbingrobotscanmoveonaslopeandonverticalsurfacesandsoreplaceworkersin carrying out suchwork. In view of safety, cost andefficiency, etc., the demand for wallclimbing weldingrobots (WCWRs) isgrowingrapidly.During theprocess

1Minghui Wu, Gen Pan, Tao Zhang, Shanben Chen, Fu Zhuang and Zhao Yan-zheng: Design and Optimal Research of a Non-Contact Adjustable Magnetic Adhesion Mechanism for a Wall-limbing Welding Robot

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ARTICLE

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ofwork,WCWRsoftenneed tocarryheavydevicesandpassobstacles,andsotheabilitytoadherewhilemovingis crucial. A permanent magnet has the advantage ofgreatadhesion forcewhilenotbeingaffected in thecaseof a power failure.Magneticwheeltype (Fischer, 2008;Tacheetal.,2009)andtracktypemechanisms(KalraandGu, 2007; Gao et al., 2009) are used in many steelenvironments.Thewheeltypemechanismcanmoveandturn flexiblybut thecontactsurfacebetween thewheelsandthewallissmall(Fischer,2010;Tacheetal.,2007)andso the energyuse ratio is low; as a result, it ismainlyapplied by small detection robots. The tracktypemechanismhasalargecontactarea(Love,2007;Yi,2010)and so the adsorptive force is great and it can moveflexibly;however,itishardtochangedirections.To overcome these disadvantages of wheeltype andtracktypemechanisms,anoncontactmagneticadhesionmechanism is designed. Magnets are installed under achassisandthereisgapbetweenthemagnetandthewallsurface so as to adsorb in a noncontact manner. Theadsorptivearea isbigenough togenerategreat force sothat therobotcancarryaheavy load.Anondestructivetesting (NDT)wheeltype robot is designed in order toinspect a long weld line (Shang, 2008). Magnets areinstalledunder thechassis.The robotconsistsofa frontpart and a back part so that it canmove on a curvedsurface. A wheeltype robot for detection andmaintenance is alsodesignedbyGui et al. (2006, 2008).These adsorption mechanisms cannot adjust theadsorptiveforceandsoitishardtouseanddismounttherobot.The adjustment of the adsorption force of themagneticmechanism is realizedbyeither changing thegaporbyadjustingtheanglebetweenthemagnetsandthewall.Atracktype robot was designed by Xue et al. (2011) toconductasurfacetreatmentwithitsmagneticadsorptionforcebeingmodulatedthroughtheformerapproach.Anadjustable magnetic adhesion wallclimbing robot wasdesigned by Wen et al. (2011) with the magneticadsorption force being modulated through the latterapproach.Theliterature(Wang,2003)changesadsorptionforcebymeansofmodulatingthetotalmagneticflowinaclosedloop.Thesemechanismscanonlychangetheforcemanually, so they cannot realize online automaticadjustment.Asa result, the robots safetyandability topassobstaclesareinfluenced.In this paper, the design and optimization ofmagneticcircuitswith finite elementmethods (FEMs) of a novelnoncontactpermanentmagneticadhesionmechanism(amagnetsucker)fortheWCWRareproposed.Themagnetsuckersareinstalledunderaxlesandthegapbetweenthemagnets and the wall can be adjusted to change themagnetic adsorption force. The WCWR has a largepayload capacity and gives a good performance in

passing obstacles. The structure of this paper is asfollows: a brief introduction of the WCWR and themagneticadhesionmechanism isproposed inpart2.Ananalysis of the balance condition of the wallclimbingprocess for WCWR and the optimized target for thedesignofamagnetsuckerarepresentedinpart3.Part4proposes an optimal design process for the magnetsucker utilizing FEM approaches. Finally, theeffectiveness of this noncontact magnetic adhesionmechanism in improving the robots payload capabilityand safety during wallclimbing work is proven byexperimentsinpart5.2.StructuraldesignoftheWCWRandthenoncontactmagneticadhesionmechanism2.1BriefintroductionoftheWCWRsmobileplatformTheadhesionmechanismandthelocomotionmechanismare key to wallclimbing robots. The structure of largeequipmentisverycomplex.Inordertomeetthedemandsofweldingandmaintenance, theWCWR shouldhaveabig adhesion force and a good obstaclepassing ability.Furthermore, inorder to carryout complicatedweldingtasks, the WCWR needs a dexterous manipulator withmultipledegreesof freedom tohold the torch.Tomeetthesedemands, thispaperpresents a noveldesign of awheeled wallclimbing robot (figure 1). The robotcomprisesamobileplatform,a5DOFmanipulatorandasensor system. Sixwheels and three groups ofmagnetsuckersaremountedunderamobileplatformandcanbelifteduptopassobstacles.Atthesametime,themagneticadhesion force can be regulated to meet the need forlocomotion. The detail is introduced in the followingparts. Each wheel is independently driven and thedifferencevelocityprincipleisadoptedinordertorealizethe turn. The robot exhibits good locomotionperformanceandpayloadcapacityenablingittomoveinabigunstructuredenvironment.Itcanfreeworkersbothfrom carrying out welding work when the weldingequipment is installed and from finishing maintenanceworkwhentheNDT(nondestructivetesting)equipmentofotherdevicesisinstalled.

Figure1.PrototypeoftheWCWR

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ThemobileplatformisthecoreoftheWCWRandisdirectlyboundupwith therobotsperformance.Theconfigurationoftheplatformisshowninfigure2suchthatitiscomposedof three identicalgroupsofwheeledmobileand adhesionparts.Thus, themobileplatformhas9DC servomotors intotal (six for the driving wheels, three for the liftingmechanisms).Eachpartincludesawheelunit,apermanentmagnetsuckerandaliftingmechanism.Themagnetsuckersaremountedunderthewheelaxels.The liftingmechanismconsists of a leadscrew, an actuatorwith an encoder andsometransmissionparts.Themobileandadhesionpartscanbemovedupanddownbytheliftingmechanism.Whentherobotconfrontsanobstacle,thethreegroupsofmobileandadhesion parts are pulled up and pushed down, in turndrivenbytheliftingmechanisms.Itcanpassobstacleswithdimensionsofnomorethan70mm*250mm.Theprocessofpassingobstaclesispresentedinfigure3.Atthesametime,themagneticforcebetweenthemagnetsuckerandthewallcan be adjusted by the lifting mechanism changing theheightofthegap.Eachwheelunitincludestwoindependentlydrivingwheelsandanaxle.ThewheelsdiameterisR=133mmandcoveredwithalayerofpolyurethanerubbertoincreasethefriction;thedrivingactuator,whichconsistsofaDCservomotor,aplanetary gearbox and an encoder, is installed inside thewheel.Theoutputforceofthemotoris78Wandthespeeddown ratio of the gearbox is 608 ( The normaloutputtorqueandspeedafterthegearboxare18Nmand9.5rpm. We can calculate the motion speed of the robot: .This speed seemssufficient fortherobottoimplementweldingandotherwork.

Figure2.Modelofthemobileplatform

(a)(b)(c)Figure3.Obstaclepassingprocess

2.2DesignoftheliftingandadjustmentmechanismforthewheelunitandmagnetsuckerDuring the process of wallclimbing, the WCWR isalways required to carry heavy equipment and passobstacles.Itisveryimportanttoensuretherobotssafety.Adjustingtheadhesionforcetomeettherequirementsofwallclimbingwork isagoodway to improve thesafetyof the robot. However, judging from previous studies,most wallclimbing robots do have not both obstaclepassing and magnetic adhesion force adjustmentcapabilities.Anovelmechanismwhich canpullupandpush down the wheel units and the magnet sucker isproposed in thispaper,whereby themagneticadhesionforceisadjustedbychangingthegapwidthbetweenthemagnetandthewall.

1Frame2Linearguiderail3Spring4Guidebar5Axle6Magnetsucker7Belt8Actuator9Leadscrew10Net111Net212WheelFigure4.Structureoftheliftingandadjustmentmechanism

Thestructureoftheliftingandadjustmentmechanismispresented in figure4. Itconsistsofanactuator (withanencoder),abelt,a leadscrew, two linearguide railsandtwo nutswhose pitches are different.Net1with 3mmpitch ismountedontheaxleofthewheelunitandNet2with 5mm pitch is fixed on the magnet sucker. Theleadscrewhas twosegmentsofscrewwhosepitchesare3mmand5mminordertofitthetwonuts,respectively,and forms the kinematic joint. The magnet sucker isinstalledundertheaxlebyfourguidebarsandspringsthe guide bar and axle forms a sliding pair.When theleadscrewrotatesbybeingdrivenbytheactuatorviathebelt,thewheelunitandthemagnetsuckeraremovedupordownalongthelinearguiderailtogether.Becausethepitchesofthetwonutsaredifferent,therewillberelativemotion between themagnet sucker and thewheelunit.Asaresult, thegapbetween thesuckerand thewall,aswellasthemagnetadhesionforce,ischanged.Thegapisadjustedwitharangeof2~20mm.Thegapinfluencesthemagnetic force greatly, so the adhesion force can bechanged within a large range. Figure 5 shows theoperating principle of the lifting and adjustmentmechanism. The increase or decrease of the adhesionforce is realizedby eitherpushingdown (figure 5b)orpullingupthewheelunitandthemagnetsucker(figure


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5a; figure 5c). Photos of the magnetic adhesion forceadjustment are shown as figure 6. Accordingly, theadhesion force can be adjusted in realtime by theactuatorunder thecontroloftherobotschiefcontroller.ADC servomotorwith a threestage planetary gearbox(speed down ratio i=84) is selected. The normal outputtorqueandspeedare10Nmand69rpm.Theliftingcanreachaspeedof .

(a)(b)(c)Figure5.Operatingprincipleoftheliftingandadjustmentmechanism

(a)(b)

Figure6.Photosofthemagneticadhesionforceadjustment

3.Forceanalysisandthebasictheoryofthemagneticforcecalculation3.1ForceanalysisoftherobotwallclimbingprocessWhentherobotismovingonaverticalsurface,theremaybe capsizing or slipping. The robots safety must beensured.Theadhesionforceofamagnetsuckermustbestrongenoughtopreventtherobotdroppingorslippingfrom the wall. The analysis of the WCWRs forceconditionisgiveninwhatfollows.Therearethreecaseswheretherobotmightbemovingandpassingobstaclesonaverticalsurface,asshowninfigure3.The cases shown in figure3aand figure3crepresent the two most dangerous situations. Therobot needs a larger adhesion force than in thesituationshown in figure3b.Thecaseof figure3c isanalysed as an example. The forces applied on therobotareshown in figure7.Themainparametersare:robot weight G 800N ; the height of the centre ofgravity h 250mm ; the front andmiddlewheel axisdistance L 260mm ; the acceleration less thana=0.5m/s2; the friction coefficient between the wheeland the surface 0.5 . F1 and F2 are the adhesionforces,whichareproducedbythefrontmagnetsuckerandthemiddleone,respectively.Besidesthis,inordertoensure therobotssafety, the1.5 timessafety factor(s=1.5)isadopted.

Figure7.Forceanalysisoftherobotonaverticalwall

1. Toavoidtherobotslippingfromtheverticalwall,thefrictionforce f whichisproducedbyF1andF2mustbe larger than the totalof the robotsweightGandtheacceleratingforcema:

1 2 1 2f F 0.5 F F G ma s F F 2520N (1)Generally,thetwoforcesF1andF2areequivalent.Assuch,theresultcanbeattained: 1F 1260N

1F 1260N

2. Toavoidcapsizingfromtheverticalwall,thetorqueinducedbyF1shouldbelargerthanthatinducedbyG;thus,F1canbecalculated:

1 1F L G h s F 1150N (2)

In order to avoid capsizing and slipping, the adhesionforceproducedbyeachmagnetsuckershouldbegreaterthan 1260N .3.2ThebasictheoryofmagneticforcecalculationThe adsorbing mechanism is the key component of awallclimbing robot. The performance of the magnetsucker can be improved by optimizing the magneticcircuitofmagnetsucker.Theanalysisandcalculationofthe electromagnetic field is complicated. The rationalebehind the electromagnetic field calculation followsMaxwellsTheoryofElectromagneticFields.Itincludes4equation sets, such as theAmpere circuit law, three ofwhich are independent. The equation to calculate theelectromagnetismusingFEMisinducedasbelow:

H J D / tE B / t

DB 0

(3)


Here, isadifferentialoperator,Histhemagneticfieldintensity, J is the current density, D is the electricdisplacementvector,Eistheelectricfieldintensity, isthe charge density and B is the magnetic inductionintensity.The relationships between the field vectorsE,D,BandHinthemediumare:

D EB HJ E

(4)

Here, is thedielectric constantof themedium istheconductivityof themediumand is themagneticpermeabilityofthemedium.Themagneticpermeabilityof ferromagnetics such as steel and iron is nonlinear,which decreases as the magnetic field intensityincreases.The magnetic adhesion mechanism is applied in thisrobot. While the robot is working, the magnetic fieldgenerated by the adhesion mechanism is regarded asstatic. The electromagnetic field generates a unitarymagnetic field effect in this situation. The field vectorsandsourcevectorsinequation(4)areallspacecoordinatefunctionsthatdonotchangewithrespecttotime,whichcanbeexpressedas:

H JB 0

(5)

Thefieldgeneratedbythepermanentmagneticadhesionmechanismisastaticmagneticfield.Thedoublerotationequation of the equivalent vector magnetic potentialfunctionis:

1 A J (6)

TheFEMdivides the solutionarea into smallareasviathe discretization method. Based on the variationprinciple, the boundary conditions of the differentialequationmathematicalmodel can be translated into avariation problem and an extremevalue problem of afunction.The magnetic adhesion mechanism includes manypermanentmagnetswhichhaveasymmetricalstructure.InordertoreducethecalculatedamountintheFEM,thefundamental equation can be induced to solve theDirichletboundaryvalueproblemoftheaxialsymmetryofthemagneticfield:

22AA J

(7)

Thisboundaryvalueproblemis:

0 bL

1 ( A) 1 ( A) Jz z

A( ,z) A (r )

(8)

4.OptimaldesignofthemagnetsuckerwiththeFEMThe magnet sucker consists of permanent magnets, ayokeandan interval.Inaddition, there ismagnetizationwhich is nonlinear with respect to the material andmagnetic leakage and the magnetic displacementasymmetry.Thesuckersmagneticcircuit iscomplicatedand it is difficult to establish an accuratemathematicalmodel and calculate accurately. The finite elementmethod (FEM) is an efficient method to address thesecomplicatedcalculations.Inthispaper,thefiniteelementsoftware Ansoft Maxwell V10 is used to optimize thestructureparametersofthemagnetsucker.4.1OptimizedtargetofthemagnetsuckerThe structure parameters of the magnet sucker aredirectlyrelatedtothesuckersperformance.Forthewallclimbing robot, it is hoped that the suckerwill have asmaller, lighter but bigger adhesion force.The value ofthe magnetic energy density (MED, the ratio of theadhesionforcetothesuckersweight) directlyreflectsthe suckersperformance.Theoptimized target is togetas large an adhesion force as possible with the lowestpossibleweightof themagnet sucker i.e., tomaximize .Theexpressionoftheratiois: m mF / G (9)

Here,Fm isamagneticadsorptive forcegeneratedby theadsorptive unit and Gm is the weight of the magnetsucker.4.2OptimaldesignofthemagnetsuckerstructurewithFEMThematerialofthepermanentmagnetandyokedirectlyrelatetothemagnetsuckersadhesionforceandweight.AthirdgenerationrareearthpermanentmagnetmaterialsinteringNdFeB waschosenas themagnetwhile thematerials mark is NdFeB 45SH. The performanceparameters are shown in table 1. The yoke ismade ofelectricianpure iron DT4 whichhasahighmagneticpermeabilityandmagneticinduction.

Parameters ValueMagneticinductionintensity rB (mT) 1320~1380

Coerciveforce cbH (KA / m) 1003Intrinsiccoerciveforce ciH (KA / m) 1592

Max.remaindermagneticenergyproduct3(KJ / m ) 342~366

Relativepermeability( r ) 1.068~1.113Table1.MainpropertyparametersofNdFeB45SH


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The magnet sucker is comprised of several groups ofmagnetunits.Thestructureofthemagnetunit isshownin figure 8. A magnet unit includes two pieces ofpermanentmagnets and a plate of yoke. Themagnets,yoke, steel plate and gap constitute amagnetic circuit.The main parameters are: the thicknesses Hy and thewidthWyof theyoke, the thicknessesHmand thewidthWmofthemagnet,theheightHgandthewidthWgofthegapand the thicknessesHsof thesteelplate (Q235).Thepermanentsareassignedwithinitialvaluessuchthat:Hy=Hm= Hg= Hs= Wg=10mm, Wm=25mm, Wy=60mm and thelengthof themagnetunit isL=100mm. In thesimulationexperiments, only one parameter is allowed to bechanged at each simulation instance. One set ofsimulation results for the magnetic flux densitydistributionisshownbyfigure9.

Figure8.Sketchofthemagnetunit

Figure9.Distributionofthemagneticfluxdensity

1.TheinfluenceofmagnetthicknessandyokethicknessThethicknessesofthemagnetandtheyokearechosenasvariables so as to analyse their influence on theperformanceof the adsorptive structurewhile theotherparameters constants. Figure 10 shows the influence ofthemagnetthicknessandtheyokethicknessontheMED(). When the magnets thickness is regarded as aconstant, the MED would increase greatly at the verybeginningwiththeincreaseoftheyokesthicknessanditwould increase with a lower rate when the thicknessreached a certain value. However, the force no longerchanges and begins to decrease instead. The mainreasonforthis isthatwhentheyokethicknessreachesacertainvalue, themagnetic leak is toosmall to influencetheadhesion.Itcanbeobservedfromfigure10thatwhenthemagnet thickness is4mm,6mm,8mm,10mm,12mmor15mm, theyoke thickness inorder tomaximize themagneticenergyproductis5mm,6.5mm,7.5mm,8mm,9mm and 10mm.When the yoke is 9mm thick and themagnet is 12mm thick, the magnetic energy density

reaches peak54.As a result,when the gap is fixed, inorder to maximize the yoke thickness changesaccordingtothemagnetthickness.Assuch,themagneticdisplacementoftheyokemustbeappropriate.

Figure10.Theinfluenceofthethicknessofthemagnetandtheyoke

2.TheinfluenceofthemagnetwidthWhen other parameters stay the same, increasing themagnetwidth pw ,themagneticadsorptiveforcewouldincrease accordingly. The weight of the magnet alsoincreases and the relationshipbetweenmagnetic energydensityand themagnetwidth isshown in figure11.Asthewidth increases, increases significantly;however,when reachesthepeak,itdecreasesinstead.When pw increasesto25mm, reachesthemaximumvalue.

Figure11.Theinfluenceofmagnetwidth

Figure12.Theinfluenceofthegapbetweenofmagnets

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3.TheinfluenceofthegapbetweenmagnetsWhen the height of the gap between the magnetsincreases with other parameters being unchanged, theadsorptive force becomes greater but the yoke widthincreases; thus, the weight of the whole magnet unitincreases.The influenceof thegapbetween themagnetson isshown infigure12.Whenthegap gw is11mm, reaches itsmaximumvalue.However,when thegapcontinues to increase, the adsorptive forcewill increaseslowlywhile willdecreaseinstead.4.3OptimizationanalysisofthemagneticcircuitcouplingTheinfluenceofthemagneticstructureparametersontheperformanceofthemagnetwasanalysedinthepreviousparagraphs.Themagnetsuckerismadeofseveralgroupsofmagnet units and so the coupling between the unitsinfluences theperformanceof the suckerdirectly.Thereare threecommonstylesofcoupling,asshown in figure13.

(a)(b)(c)Figure13.Sketchofthecouplingstructure

The magnetic poles of the adjacent two magnets areoppositetoeachother.Theyokethicknessis9mm,andthemagnetthicknessis12mmwhilethegapbetweenmagnetsis11mm.Themagnetsareall100mmlongandcoupleonlyintheXdirectioninstructures(a)and(b).Instructure(a),each magnet has the same width25mm and the wholewidthofthesuckeris133mm.Themagnetsonthesidesofthesuckerare25mmwideinthestructure(b),themiddleone is 50mmwide and thewholewidthof the sucker is122mm.TherearecouplingsinboththeXandYdirectionsinstructure(c),wherethesizeoftheXdirectionisthesameasthatinstructure(b)whilethemagnetintheYdirectionis50mm;thus,thewholelengthis111mm.

Figure14.Couplingresult

Theresults in figure14demonstrate thatwhen thegapis shorter than 4mm, structure (b) generates a smallerforcethanstructure(c).However,whenthegapislargerthan 4mm, structure (b) generates a larger force thanstructure (c). Under different heights of the gap,structure (b)generatesa larger force thanstructure (a).The forcegeneratedby structure (b)hasa largervalueof MED () than that generated by the other twostructurestyles.5.ExperimentsofthemagnetsuckerandtheWCWRAccordingtotheresultsoftheanalysisinpart4,thesizeparameters of the magnet sucker are: yoke thickness9mm, magnet thickness12mm, magnet width of twosides25mm,middlemagnetwidth50mm, gap betweenthe magnets11mm, the whole width W 120mm , thewhole length L 244mm ,thesizeofthewholemagnet

3244 120 21mm ,, the whole weight of the magnetsucker mG 4.33kg . The magnet sucker is shown byfigure15.Thereisaholeinthemiddlefortheleadscrewtopass through themagnetsuckerwhen it ispulledupandpusheddown.

Figure15.Theobjectofthemagnetsucker

A testdevicewasdesigned to test theperformance ofthe magnet sucker (Figure 16). The device and therobotsliftingmechanismwhichispresentedinpart2workinmuchthesameway.Themagnetsuckercanbepulledupandpusheddownbyanactuatorturningtheleadscrew through thebelt.A force sensor ismountedunder the steelplate tomeasure the suckersmagneticforce.Acomputerwithadataacquisitioncardisusedtodeal with the test result. The adhesion force of themagnet sucker was tested for different heights of airgap.The test resultsare shown in figure17.When theheight of the gap changes from 5mm to 15mm, theadhesion force changes accordingly from about 5,000Nto 1,000N. The adhesion force can reach about 2,250Nwhen the gap is high at 10mm. Compared with theanalysis results in part 2, themagnet sucker canmeettherequirementofsecurity.2 4 6 8 10 12 14 16

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Figure16.Magneticadhesionforcetestdevice;(a)Structureofthetestdevice(b)Experimentofthemagneticforce

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Figure17.Testresultsofthemagnetsucker

Inorder to test theperformanceof themagnetadhesionmechanism and the WCWR, a simulation platform isdesigned toperformobstaclepassing andwallclimbingwelding experiments. The platform simulates themanufacturing environment of large unstructuredequipment (figure 19a). Experiments are performed onthe platform to provewhether theWCWRworkswell.Figure18 shows theexperimentphotographsofpassingobstacles the experiment results show that the liftingmechanismworkswellandthattherobotcanovercomea70mmhighobstacle. In theprocessofpassingobstacles,the obstaclepassing sequence is: while the robot ismoving on a vertical orhorizontal surface andmeets aobstacle, the actuatorof the front liftingpartdrives theleadscrewand lifts the frontwheelunitand themagnetsuckertoapositionatasufficientheight;next,therobotmoves forward and the first wheel unit passes the

obstacle; finally, the frontwheelunit is lifteddown.Themiddle and tail wheel units are controlled to passobstacles in the same way. The adjustment of themagneticadhesionforceisasdescribedearlierinSection2.2.

Figure18.Experimentofpassinganobstacle

Figure 19 shows thewallclimbing experimentsonboththesimulationplatformandtheworkshop.Figure19aisthe experiment on the simulation platform: the robotstartedmoving from thehorizontal surface, turned andclimbed onto the verticalwall through the circular arcsurface; then, the robot overcame the obstacle andclimbed down the simulation platform. Meanwhile,experiments of theWCWR carrying a load of 30kg andpassingobstaclesonthewallhavealsobeencarriedout.To ensure the robots safety, a rope is attached to theWCWR. Nevertheless, we performed a furtherexperimenton the application spot formanufacturing agastank(figure19b).TheWCWRcanclimbonacirculararc tank surface and implementwelding.The resultsofthe experiments demonstrate that the magnet suckergives a good performance and that its adhesion forcemeets the requirements of thewallclimbingwork. Therobot possesses good payload ability and can replaceworkers in carrying out welding work on largeunstructuredenvironments.

Figure19.Experimentsofwallclimbingwork;(a)Experimentonthesimulationplatform(b)Experimentintheapplicationspot

6.ConclusionOwing to the fact that the magnet sucker is mountedunder the robotchassisanddoesnotmakecontactwiththewall,theWCWRexhibitsgoodpayloadabilityandasmall turning resistance, which brings good flexibility.Thenovel liftingmechanism can lift thewheelunitandmagnetsuckertogetherusingonlyamotor.Atthesame


time, the adhesion force of the magnet sucker can beadjustedbyadjusting theheightof thegapbetween thesucker and the wall. Thus, the WCWR gives anoutstandingperformance in termsof safety, itspayloadanditsobstaclepassingcapacity.Inourproject,theWCWR is intendedtobeapplied inalargeunstructuredenvironment,suchaswithships.Therobot is required to carry cable and other additionalpipelinesduringmovinginalargescale.Thegreaterthedistance therobotmoves, theheavier the load the robothas to carry. To turn the WCWR into a practicalapplication,thisisaproblemthatmustbesolved.Inournextwork,we plan to design awallclimbing robot tocarry thecableandotherauxiliaryequipments suchaselectrical force while the robot moves following theWCWR.Moreover,itisveryimportanttoensuretherobotssafetyduring theprocess ofwallclimbingwork, although theWCWR has a good adsorptive ability. During theexperiments,aropewasattachedwiththerobotinorderto ensure its safety. It is also a goodway to solve theprobleminapracticalapplication.7.AcknowledgmentsThe support of theNationalHighTechnologyResearchand Development Programme of China, through theMinistryofScienceandTechnologyofChinaGrantNo.2009AA04Z221,isgratefullyacknowledged.8.References[1] Fischer, W., Tache, F., Caprari, G. and Siegwart, R.

(2008),Magneticwheeled robotwith highmobilitybut only 2DOF to Control, Proc. of the 11thInternationalConference onClimbing andWalkingRobots and the Support Technologies for MobileMachines(CLAWAR),Coimbra,Portugal.

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[3] Gao,X.,Xu,D.,Wang,Y.,Pan,H.andShen,W.(2009),Multifunctional robot to maintain boiler watercoolingtubes,Robotica,Vol.27,No.6,pp.9418.

[4] Gui, Z., Chen, Q., Sun, Z., Zhang, W. and Liu, K.(2006), Optimization of permanentmagneticadhesion device forwallclimbing robot, DiangongJishuXuebao/TransactionsofChinaElectrotechnicalSociety,Vol.21,No.11,pp.406.

[5] Gui,Z.,Chen,Q. and Sun,Z. (2008),Wall climbingrobot employing multibody flexible permanentmagnetic adhesion system, Chinese Journal ofMechanicalEngineering,Vol.44,pp.17782.

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[13] Yi,Z.,Gong,Y.,Wang,Z.,Wang,X.andXu,J.(2010),Analysisonturningstressstatesofmagneticsuckingmechanismunitofa large loadwallclimbingrobot,in International Conference on MeasuringTechnologyandMechatronicsAutomation,ICMTMA2010, March 13, 2010 March 14, 2010. Changsha,China:IEEEComputerSociety.


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welding andinspectionwork

adhesion force

walllimbing welding

magnetic adhesionmechanism

mechanical engineering

shanghai jiao tong university

optimal research

zhao yanzheng1