1 Adpted Mgneti Wheel Unit for Compt Roots Inspeting Complex Shped Pipe Strutures Fien T he, Wolfgng Fisher, Rolnd Moser, Frneso Mondd, Rolnd Siegwrt Systems (http://www.sl.ethz.h), Eidgeno ssishe Tehnishe Hohshule Zu rih (ETHZ), 8092 Zu rih, Switzerlnd ASTOM (Switzerlnd) td, ASTOM Power Servie (http://www.lstom.om), 5401 Bden, Switzerlnd ortoire de Syste mes Rootiques (http://lsro.epfl.h), Eole Polytehnique Fe de rle de usnne (EPF), 1015 usnne, Switzerlnd Emil: fthe@ethz.h, wfisher@ethz.h, rsiegwrt@ethz.h, rolnd.moser@power.lstom.om, frneso.mondd@epfl.h Autonomous Astrt This pper desries novel mgneti wheel unit integrting mehnism tht n e used for lifting nd stilizing the unit. The mehnism onsists of 2 tive lever rms mounted on eh side of the wheel nd rotting oxilly with the wheel. This mehnism llows slightly lifting the mgneti wheel t ny desired position on the wheel irumferene nd onsequently deresing the mgneti fore t this speifi lotion. The sme mehnism n lso e used to stilize the wheel, when externl fores re unfvorle. This pper lso desries the potentil of this onept for in-pipe inspetion tehnologies. Indeed it n e used to inrese the moility of mgneti wheels roots whih re urrently not le to negotite omplex ostles. At the sme time, it llows uilding smller roots, sine the self stilizer system llows reduing the mount of required mgneti wheels to only two units. negotited thnks to differentil-drive steering (for single ody systems) or rtiulted strutures. When liming ility is required, the most ommon solution is to use spreding systems [3] [9] s for roots depited in Figure 1. Index Terms Mgneti wheel, in-pipe inspetion, liming, ostle pssing. Fig. 1. oomotion systems for in-pipe inspetion roots: Toshi s root [8], MORITZ [4], MRINSPECT IV [3], Explorer [9] nd HEI-PIPE [6] I. I NTRODUCTION Typil pipe onstrutions suh s sewers, gz/oil trnsmission pipelines, gz/oil distriution pipes re suffering from severl diseses when getting old. Aging, orrosion nd mehnil stress generlly led to the loss of mteril thikness or genertion of rks tht n use lekges or sometimes the destrution of the pipe onstrution. Thus, periodi inspetion of the pipe system is required in order to prevent suh dmges. Sine mny of these onstrutions hve not een designed to optimize utomti inspetion nd repir tsks, inspetion nd mintenne generte huge osts, espeilly if disssemling or even exvting is neessry. Inspetion nd mintenne tehnology hs then eome growing industry mrket nd lrge vriety of systems hve een developed. Severl reent reports [1], [2] hve lredy estlished stte of the rt of the existing industril nd demi systems, y lssifying nd ompring their performnes. As summry, Roh [3] proposes lssifition of the possile loomotion strtegies used to solve the in-pipe inspetion prolems: roots my e pig type (pssively driven y the fluid pressure), wheel type, terpillr type, wll-pressed type, wlking type, inhworm type or srew type. Bends re usully However, none of these systems n del with nrrow pipe environments whih integrte high rupt dimeter hnges, ends nd lso requires liming ility. In this se, it is interesting to omine the loomotion system with tthment elements suh s grsps, sution ups [10], dhesive polymers [11] or (eletro)mgneti elements. These tehnis re typilly used in wll liming roots for tnk inspetion [12] or wll lening tsks [10]. Sine the first onepts usully imply omplex mehnis nd tht the onsidered environment is ferromgneti, mgneti tthment systems were seleted for this pplition. This overview of existing systems then fouses on mgneti wheel solutions. The ide of using mgneti elements or wheels on moile roots is not new, sine Guy [13] ptented onepts for mgneti wheels systems in 1972 lredy. Roots using mgneti elements for loomotion (wheels for Mgneots [14], Tripod [15] nd Osk Gs inspetion root [16] or trks for Nnomg [17]) lredy exist. These roots tke dvntge of the mgneti fore in order to trvel on surfes with ny inlintion regrding the grvity vetor. Their moility is however limited to smooth ostle-free surfes. By smooth, we refer to surfes with high rdii of urvture.
2 In omprison, Kwguhi [18], Yukw [19] nd Fisher [12] roots implemented speil mehnisms to negotite speifi ostles. The root desried in [12] nd [19] re designed for vertil wlls or the outer surfes of pipes. These mehnisms im for pssing very diffiult ostles, ut require lot of spe nd mny DOF. The root from Kwguhi [18] is more relted to our pplition, sine it is designed for inspeting the interior surfes of pipes nd uses pssive mehnism to overpss 90 trnsitions. Due to very restritive environment onstrints, the existing loomotion systems nnot e used in our speifi pplition. This pper then desries novel mgneti wheel unit tht llows for designing ompt nd simple roots for inspeting nrrow pipes with very omplex shped strutures. The pper is orgnized s follows. Setion II introdues the hllenging environment for whih moile inspetion root hs to e uilt nd the speifi requirements of the pplition. Setion III nlyzes existing solutions nd shows their limittions. The neessity to use mgneti element integrting lifter mehnism is then explined in setion IV. While severl onepts nd their limittions re desried in setion V, n innovtive dpted mgneti wheel unit is proposed in setion VI. Finlly this pper shows how this dpted mgneti wheel unit n help inresing the moility of ompt mgneti wheel roots. II. A PPICATION REQUIREMENTS As lredy mentioned in the introdution, mong the existing in-pipe inspetion systems, there does not exist ny ompt root tht n dpt to extreme dimeter hnges. As strting point for the disussion, this setion first gives n overview of speifi pplition nd the ritil onstrints of the environment. Tripple step 50 mm Tripple step 200 mm Fig. 2. Gp g 3D CAD model of typil environment Even if dmges tend to pper in preferred lotions, n effiient inspetion root needs loomotion system tht llows for ringing the inspetion sensors to ny lotion tht might e dmged. The 3D CAD model represented on Figure 2 helps understnding the requirements of the loomotion system: the root hs to negotite different trnsitions of 90 onvex nd onve surfes. For instne, the profile ontins triple step nd gp type ostle. In ddition to the ostle omplexity, the loomotion mehnism hs to e independent of the grvity vetor orienttion. Indeed the sme profile n e extrted from severl points of view regrding grvity. III. A NAYSIS : MOBIITY, SIZE AND COMPEXITY At first, it hs to e verified tht the ssumption of using mgneti wheels s loomotion nd tthment system is the est for this pplition. For this reson, existing systems re deeper nlyzed nd their limittions re presented. A. Environment Constrints Figure 2 shows the 3D CAD model of typil environment tht requires non destrutive inspetion (NDI). Here is list of the most ritil dimensions nd hrteristis of this environment: the wide rnge of inner dimeters: the dimeter vries from 200mm (this defines the mximum root spe envelope) to 700mm spe envelope. the lol rupt inner dimeter hnges: up to 50mm on Figure 2. it is omposed of horizontl pipe elements, s well s vertil elements. Generlly ny inlintion n e enountered. it is uilt out of ferromgneti mteril. B. Root purpose nd required moility Sine the root is intended for NDI, it hs to emed typil NDI sensors suh s mers, Eddy urrent proes or eletromgneti ousti trnsduer proes. Thus the root should e le to rry its own weight plus some extr pylod orresponding to the weight of NDI sensor nd some mnipultion tools. A. Neessity nd optimlity of mgneti wheels Sine the root hs to work in nrrow in-pipe environment with vertil elements nd 90 ends, this drstilly restrits the rnge of possile loomotion systems. As mentioned in the introdution, spreding systems is ommon solution when liming ility is required. An exmple is MORITZ [4] (Fig. 3), rwler root equipped with eight legs eh equipped with two driven joints. MORITZ root is le to rwl in tues of ny inlintion nd to mnge urved pipes with dimeter of 60-70m. This root weighs 20kg. Another exmple is Explorer [9] (Fig. 1), seven-element rtiulted ody root, four of them eing equipped with set of three tive deploying legs. This root is le to drive in 6-in. nd 8-in. pipe elements nd negotite 45 nd 90 ends. It n lso drive on slightly inlined nd short vertil pipe elements. Tking into ount the mehnil nd ontrol omplexity of legged roots nd the omplexity of implementing highly extensile legs in restrited spe envelope, these solutions hve een disrded. Anlyzing the remining tthment solutions, grsping is not n option in this environment, dhesive elements still hve prolems to keep their effiieny on long runs nd sution
3 ups do not seem optiml to work on urved surfes. It seems rther ovious tht omplexity nd size n e sved y tking dvntge of the ferromgneti environment nd onsequently using (eletro)mgneti elements for tthment. Indeed, insted of hving root tht uses the whole ville spe in the pipe, it n e ompt unit tht follows the profile of the pipe s illustrted in Fig. 3. Fig. 3. MORITZ legged root ompred to the sheme of ompt mgneti wheel root ostle (flnge, vlve or ridge) without rolling on it. These strutures whih hve een developed for externl pipe nd gs tnk inspetion re not suitle for this pplition, sine they re very omplex (26, respetively 10 tive degrees of freedom) nd not ompt enough for in-pipe inspetion. IV. A NAYSIS OF OBSTACE NEGOTIATION As pointed out in the previous setion, mgneti wheel liming roots do not only hve to del with the grvity fore, ut lso with the mgneti fores, espeilly when wheel is in ontt with 2 different surfes. As illustrted in Figure 5 (left), the root hs to get rid of the mgneti fore Fmg 1 when it drives wy from the the vertil wll; wheres it hs to get rid of the mgneti fore Fmg 1 when it drives wy from the horizontl wll. Tr_1 B. Mgneti wheels on pssive rtiultion strutures Given the prolem of negotiting diffiult ostles, good soure of inspirtion is the reserh on rough terrin explortion rovers. An exellent solution is to use root struture tht pssively dpts to the terrin shpe nd is le to negotite ostles lrger thn the wheel dimeter. One ould then first imgine equipping Shrimp-like rtiulted struture [20] (Fig. 4) with mgneti wheels. Fmg_1 Fmg_1 Tr_1 µ1 µ1 T1 Tr_1 Fmg_1 R 1 mg_1 T1 R1 r_1 r_1 CM mg R1mg_1 r_1 mg_1 1 1 Fmg_1 µ1 mg_1 1 1 1 r T2 µ2 R2 Tr_2 Fmg_2 1 r R2 Fmg_2 r_2 2 Fig. 5. eft: externl2 foresmg_2 nd torques ting on 2 pirs of motorized mg_2 2 wheels system. Right: sme model for system with only front wheel trtion. At the moment the wheel gets lifted, the trtion Tr 1 nd retion R1 fores tend to 0 Fig. 4. d Shrimp-like root equipped with mgneti wheels This type of solution does however not seem promising for severl resons: the omplexity of downsling nd inresing the power to mss rtio of strutures whih integrte high numer of tuted wheels. on strutures with high numer of wheels, wheel slippge is neessry for turning. Due to the high frition fores generted y mgneti wheels, these rtiulted strutures re oviously not optiml. wheres the mehnisms in rough terrin roots only hve to del with the grvity, mgneti wheel liming roots lso hve to get rid of the mgneti fores tht re severl times higher thn the grvity. C. Mgneti wheels on tive strutures Ative strutures equipped with mgneti elements re proposed in [19] nd [12]. They use tive liner mehnisms, in order to lift off one or severl wheels tht pss over the A stti model of the fores nd torques (Fig. 5 left) ting on 2 mgneti wheel-pirs system llows omputing the frition oeffiient nd torques tht re neessry to negotite this 90 onve ostle. The neessity of using n dpted wheel n lredy e demonstrted y doing some simplifitions (Fig. 5 right). First, it is ssumed tht the root with two pirs of wheels hs only front wheel trtion (T2 = 0). Seondly the weight (mg) n e negleted, sine mgneti wheel roots require mgneti fores severl times higher thn the root s weight in order to ensure good seurity ginst flling. Getting rid of the unwnted mgneti fore (Fmg 1 ) requires trtion fore (Tr 1 ) igger thn Fmg 1 /( + r), respetively frition oeffiient µ1 igger thn /( + r). Indeed we ssume tht the trtion Tr 1 nd retion R1 fores tend to zero t the moment the wheel lifts off. Consequently, for optimiztion, /r rtio hs to e deresed s muh s possile. Figure 6 shows the se of = r for whih the required µ1 would e 0.5. Detiled lultions (omputer simultion) without this simplifition show similr results. The system length should however not e too short, in order to void the singulr se, for whih the system gets loked on onvex ostle. Indeed trtion fore nnot e provided,
4 r Fig. 6. : 2 pirs of wheels onfigurtion with = r, : singulrity on onvex ostle, : ground lerne prolem for long system sine the effetive distne etween wheel ontt points is zero. hs then to e igger thn 2 r to void this singulrity on onvex edges. Inresing too muh this dimension hs lso drwk regrding ground lerne (Fig. 5). From these 2 simple exmples, we lredy notie the diffiulty to implement unique system dpted to different senrios. This prolem hs even no solution, if the rrngement nd size of these ostles gets more omplex s illustrted on Figure 7, espeilly in se for whih ll wheels hve two ontts with the terrin. This lerly shows the neessity to use system whih dereses or nels the unwnted mgneti fore, in order to go towrds the implementtion of universl system le to fe ny omintion of 90 surfe trnsitions. Fig. 7. Complex shped ostles: doule steps (), gp shorter thn the root length (), doule steps, ll wheels with doule ontt points () d e Fig. 8. Pssive wheel mehnis s proposed in [18]. Arrows show the movement of the inner wheel (lue) nd outer tire (red) s well s the evolution of the mgneti fore (green) 1) Glol fore modultion: Repling the entrl ring mgnet y n tive oil llows modulting the mgneti fore of the wheel. A first drwk of this eletromgneti solution is tht it does modulte the fore in the sme wy on the whole wheel irumferene: this is kind of glol fore modultion system. Not only the unwnted mgneti fore is redued, ut lso the mgneti fore tht is neessry for trtion nd dhesion: the root my fll when pssing ostles on the eiling. Another mjor drwk is tht filure on the power supply would nel the mgneti fore nd would use the root s fll. 2) ol fore modultion: Due to the drwks of glol fore modultion systems mentioned ove, lol fore modultion systems re nlyzed in more detils. The most promising onepts for suh systems re illustrted in Figure 9. In onept, the permnent mgnet is repled y tive oils distriuted on the wheel irumferene. Deresing the urrent in the orret oil llows for diminishing the unwnted mgneti fore. Conept onsists in using liner mehnism tht moves xilly in order to lift the wheel. Yukw [19] implemented this solution on the Type III root. Conept onsists in using rotry mehnism, rotting oxilly with the wheel, whih gets tngentilly into ontt with the terrin. V. C ONCEPTS FOR ADAPTED WHEE UNIT After hving disussed the neessity of hving n dpted wheel, this setion proposes onepts for suh mgneti wheel units: first pssive onepts, s well s tive ones. A. Pssive mgneti wheel By pssive mgneti wheel, we refer to wheels tht pssively dpt their mgneti property regrding the shpe of the terrin. An exmple is the wheel proposed in [18]. Piture 8 reminds the mehnil priniple of the inner mgneti wheel whih rolls on the outer ferromgneti tire. The mgneti fore is then smoothly trnsferred from one surfe to the other. In this pper, the reliility of the system (risk of loosing ontt on the eiling) is however not disussed. Indeed position, for whih the mgneti fore is spred etween the two ontt points (one eing n edge), my e ritil. B. Ative mgneti wheel On the ontrry, y tive mgneti wheel, we refer to wheels whih tively modify their mgneti property in order to dpt to the terrin. Systems on Coil mg1 Systems off Fig. 9. Ative mgneti wheel: eletromgneti (), liner lifter () nd rotry lifter () The liner lifter only works when the unwnted mgneti ontt point is lwys loted t the sme position. Sine in our omplex shped environment, the ontt point with the terrin n e nywhere on the wheel irumferene, this onept does not mke sense. Due to the omplexity (wiring) nd low effiieny of eletromgneti wheels (lower energy density thn powerful mgnets), this onept is disrded. Conept seems to e the most promising nd is further investigted.
5 VI. A DAPTED MAGNETIC WHEE UNIT This hpter desries the innovtive mgneti wheel unit integrting n tive rotry lifter mehnism. Figure 10 shows CAD model of possile implementtion of the mehnism. The lifter mehnism onsists in two powered rotting lever rms mounted on eh side of the wheel. The rottion xis of these rms is ommon to the wheel rottion xis, ut is independently tuted. These rms hve two omplementry funtions: they n either e used to lift off the wheel in order to derese the fore t the unwnted ontt point ( lifter ) or to stilize it lterlly ( stilizer ). movement (Figure 12), it n e remrked tht the lifters of the front nd rer wheels re not pplied t the sme position, regrding the root ( referene position is mrked y dshed line). Fig. 12. Root negotiting step ostle This mehnism does not only llow for negotiting simple step ostles, it even helps negotiting the most diffiult type of ostles (Fig.2), respetively when ll wheels re in doule ontt with the terrin. This is illustrted in Figure 13, on whih 2 wheel-pirs root uses the lifter mehnism on oth wheel pirs t the sme time. Fig. 10. CAD model of rotry lifter mehnism. Wheel nd lifter re independently tuted through two different gers mounted on ommon xis Fmg1 Fmg1 Fmg2 Fmg2 mg1 Fig. 13. Root negotiting doule step ostle B. Wheel rms s stilizer As mentioned, the 2nd funtionlity of this mgneti wheel lifter implementtion is tht the two lever rms n lso e used s wheel stilizer when the grvity vetor is unfvorle, s shown on Figure 10. This feture might e seen s useless, if one thinks to 4 wheels roots with Akermnn steering geometry or differentil-drive type roots tht re lterlly self stilized. However we lim tht this new system hs gret dvntge onsidering mgneti wheel roots minituriztion, thnks to the possiility to redue the loomotion onept to 2 ligned dpted wheel units. α=15 mg1 Fig. 11. The lever rm mehnism is pplied, in order to slightly lift off the wheel nd derese the mgneti fore t the unwnted ontt point mg2 mg2 The unwnted mgneti fore (Fmg2 in this exmple) n even e fully neled if the wheel is suffiiently lifted off. It is however sfer to design it, so tht n offset fore remins when the lifter is pplied perpendiulrly to the surfe. Indeed it prevents the wheel to fully lose mgneti ttrtion fore, in se the lifter is pplied, when the wheel is in ontt with only one ferromgneti surfe. Sine the lifter n reh ny position on the wheel irumferene, this dpted mgneti wheel llows for 2 wheelpirs root negotiting step ostles. In the sequene of Fmg_ref Fig. 14. 0.45 * Fmg_ref Remining fore [%] A. Wheel rms s lifter As mentioned, these rms n e used to lift off the wheel, in order to derese the mgneti fore t the unwnted ontt point on the irumferene s illustrted on Figure 11. The imlne etween the mgneti fores Fmg1 nd Fmg2 then solves the prolem pointed out in setion IV. This imlne n e modulted, depending if the lifter is pplied perpendiulrly (Fig.11 left) to the ground or not (Fig.11 right). 100% 80% 60% 40% 20% 0% 0 3 6 9 12 15 18 Wheel tilt ngle α [ ] Mgneti fore of the mgneti wheel regrding wheel tilt ngle When deling with the urved surfes of internl pipes, n importnt onstrint is to tke re tht the wheel provide their mximl mgneti fore. For stndrd wheel, this ondition
6 is rehed when it stnds perpendiulrly to the surfe. Indeed some tests showed tht the mgneti fore dereses more thn 50% when the wheel is only tilted 15 from its optiml orienttion (Fig.14). A prtil solution to this prolem is to uild wheels with n dpted geometry tht fit ertin rnge of pipe dimeters s proposed y Kwguhi [18]. Nevertheless the optiml solution onsists in implementing mehnil system tht llows pssively dpting the wheel orienttion to the terrin onfigurtion. Front view Side view Fig. 15. 2 to 4 wheels onfigurtions: mtrix of top view regrding side nd front views By nlyzing stndrd wheel onfigurtions for roots with t most 4 wheels (Figure 15), we notie tht rrngements 2, 3 nd 4 require this type of mehnism. The dvntge of this lifter rm implementtion is then ovious: using them s lterl stilizer llows designing system with 2 ligned wheels 1 whih is ompt nd simple. VII. CONCUSION AND FUTURE WORK After hving presented n overview of the existing loomotion onepts for in-pipe inspetion, this pper first desries n pplition tht requires ompt system tht n del with high rupt dimeter hnges nd vertil liming. It shows tht mgneti wheels re the est onept for this ferromgneti environment. It is then shown why n dpted mgneti wheel is neessry in order to negotite the omplex ostles of the onsidered pplition. A promising solution to this loomotion prolem is then presented: n innovtive tive mgneti wheel unit inorporting n tive lifter-stilizer mehnism. It is shown how this loomotion onept n e used in order to negotite omplex shped strutures. The pper finlly presents its dvntges towrds root downsizing nd simplifition, y explining tht 2 ligned wheels struture is suffiient. Ongoing work onsists in implementing prototype root integrting this mehnism, in order to vlidte the onept. Then ontrol strtegy will hve to e proposed in order to ontrol the tive system. 1 2 3 4 ACKNOWEDGMENTS We would like to thnk ASTOM for supporting this work s explortion reserh. REFERENCES [1] B.Brue, R.Gordon, M.Sullivn, nd C.Nery, Internl repir of pipelines - tehnology sttus ssessment report, Edison Welding Institute, Columus, USA, Teh. Rep. DE-FC26-02NT4163, Nov. 2002. [2] H.Shempf, In-pipe-ssessment root pltforms - phse I - stte-ofthe-rt review, Cnergie Mellon University, Pittsurgh, USA, Report to Ntionl Energy Tehnology ortory REP-GOV-DOE-20041102, Nov. 2004. [3] S. Roh nd H. R. Choi, Differentil-drive in-pipe root for moving inside urn gs pipelines, IEEE Trnstions on Rootis, vol. 21, no. 1, pp. 1 17, Fe. 2005. [4] A. Zgler nd F. Pfeiffer, MORITZ pipe rwler for tue juntions, in Pro. of the 2003 IEEE Interntionl Conferene on Rootis & Automtion (ICRA 03), Tipei, Tiwn, Sept. 2003, pp. 2954 2959. 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