外文资料--Design and control method for a high-mobility

Research articleDesign and control method for a high-mobilityin-pipe robot with flexible linksWoongsun JeonDepartment of Mechanical Engineering, Texas A&M University, College Station, Texas, USA, andInho Kim, Jungwan Park and Hyunseok YangDepartment of Mechanical Engineering, Yonsei University, Seoul, Republic of KoreaAbstractPurpose The purpose of this paper is to propose a high-mobility in-pipe robot platform and its navigation strategy for navigating in T-branch pipesefficiently.Design/methodology/approach For high mobility, this robot is developed based on inchworm locomotion. An extensor mechanism with flexiblelinks and clamper mechanisms enable the robot to conduct both steering and inchworm locomotion. The locomotion of the robot is modeled based on apseudo-rigid-body model. From the developed model, this paper introduces a navigation strategy based on defining relay points and generating a pathfrom a main pipe to a T-branch pipe.Findings With this navigation strategy, the robot can avoid collisions and enter T-branch pipes effectively. The path generation algorithm is verified byexperiment. In addition, both the navigation strategy and mobility of the robot are demonstrated by experiments conducted in a commercial pipe configuration.Originality/value This paper describes the mechanism of an inchworm-type in-pipe robot that is able to steer and adapt to pipe diameter changes.This paper also describes navigation strategy that enables a robot to avoid collisions and enter T-branch pipes effectively. This research will help theconstruction of a fully autonomous in-pipe robot that can navigate through various types of pipes.Keywords Robots, Pipes, In-pipe robot, Inchworm locomotion, Navigation strategy, Path planningPaper type Research paper1. IntroductionPipesystemsarewidelyusedfor transferringwater,gas,orotherfluids.Pipes can bedamaged byphysicalimpact, corrosion,anderosion. Such damage can cause tremendous loss and eventhreaten the safety of humans in industrial fields. For thesereasons, the importance of pipe system maintenance andinspection has increased. However, the maintenance andinspection of pipes can be challenging because pipelines areusually installed in areas that are difficult to access(e.g. underground, inner walls of buildings). Furthermore, it isvery difficult to evaluate in-pipe conditions.In order to solve the above problems, many researchers havestudiedin-piperobots.Therearevarioustypesofpipes,andin-pipe configurations can be quite restrictive. In-pipe robotsshould be able to navigate not only insimple straight pipes, butalso in curved and branch pipes, which are installed bothhorizontally and vertically. The robots should also have theability to navigate and perform tasks in restrictiveconfigurations, such as cylindrical or rectangular spaces.Thus, in-pipe robots must have high-mobility. Many travelingmechanisms for in-pipe robots have been researched for high-mobility. According to the traveling mechanism, robots can beclassified into wheel (Roh and Choi, 2005), track (Park et al.,2009； Kim et al., 2009, 2010； Mirats Tur and Garthwaite,2010),screw(Horodincaetal.,2002；Lietal.,2007),inchworm(Limetal.,2008；OnoandKato,2010),snake,andleggedtypes(Neubauer and Siemens, 1994； Zagler and Pfeiffer, 2003；Streich and Adria, 2004； Kuwada et al., 2006). Most in-piperobots can successfully navigate through straight and curvedpipes. However, most robots have trouble navigating throughbranch pipes and adapting to changes in the pipe diameter.Whileafewin-piperobotscanmaneuver throughbranchpipesusingdifferentialdrivingoranarticulatedactivejoint,therearestill limitations due to the shape of the pipe (Roh and Choi,2005)andtoadaptabilitywithrespecttopipediameterchanges(Yu-xia et al., 2009； Yu et al., 2005； Kim et al., 2010). Whilesnake- and legged-type robots have high-mobility and cansuccessfully navigate through branch pipes, most suffer fromcontrol difficulties and require many actuators (Neubauer andSiemens, 1994； Zagler and Pfeiffer, 2003； Streich and Adria,2004； Kuwada et al., 2006).InadditiontomobilityinT-branchpipes,thedevelopmentofasuitable control algorithm for maneuvering through T-branchpipes is challenging. In order to efficiently navigate in T-branchpipes, control algorithms based on mathematical modeling orsensor feedback are necessary. A few studies have beenconducted on control algorithms for T-branch pipes accordingThe current issue and full text archive of this journal is available /0143-991X.htmIndustrial Robot: An International Journal40/3 (2013) 261274q Emerald Group Publishing Limited ISSN 0143-991XDOI 10.1108/01439911311309960261to movement mechanism of the robot (Roh and Choi, 2005；Zagler and Pfeiffer, 2003). However, in the case of inchworm-type in-pipe robots, such research has not yet been performed.We developed a steerable inchworm-type in-pipe robot(Jeonetal.,2011).Therobotcannavigatethroughawiderangeof commercial pipes, including vertical, curved, and branchpipes with both circular and rectangular cross sections.Inchworm locomotion based on a flexible link mechanismmade steering possible, and the robot is able to navigate invarious types of pipes.In addition, wemodeled the locomotionofarobotbasedonapseudo-rigid-bodymodel(Howell,2001).From the previous modeling results, we now propose anavigation strategy based on defining relay points andgenerating a path from a main pipe to a T-branch pipe. Forgiven pipe configurations, this navigation strategy enables arobot to avoid collisions and enter to branch pipes effectively.This paper is organized as follows. The mechanisms of therobotaredescribedinSection2,andthesteeringlocomotionoftherobotisanalyzedandmodeledinSection3.InSection4,thenavigation strategy is introduced and the path generationalgorithm is verified by experiment. Finally, the navigationstrategy and mobility of the robot are experimentallydemonstrated in Section 5.2. The proposed robotAs shown in Figure 1, the robot is mainly composed of oneextensor module and two clamper modules. The two clampermodules are attached to both ends of the extensor module.2.1 Extensor moduleAs shown in Figure 2(a), the extensor largely consists of aframe, four flexible links that are attached to a timing belt,pulleys, bevel gear sets, passive wheels, and two actuators.Urethane rubber (SeoulUrethane company), which can befound commonly and has no special properties, is used as thematerial of flexible links. Two pulleys are connected to a shaftand driven with one actuator via a bevel gear set as shown inFigure2(b).Idlersareusedforgeneratingenoughnormalforceto prevent the disengagement and slipping between flexiblelinksandpulleysasshowninFigure2(a).Throughtheuseofanopen-endedtimingbeltattachedtoaflexiblelink,therotationofthe pulleys creates linear motion of the flexible link as showninFigure 2(c). The flexible link and its linear motion are the keyfactorstothestraightandsteeringlocomotionoftherobot.Thestraight and steering locomotion with flexible links aredescribed in Section 2.3 in detailed. The passive wheels helpthe robot traveling in pipelines smoothly.2.2 Upper and lower clamper moduleAs shown in Figure 3(a), the clamper module consists of fourcrank-slider mechanisms placed in a circular arrangementwith a 908 spacing between each mechanism； the four cranksare connected to an actuator. As a result, the four cranks arerotated by the same number of degrees at the same time usingonly one actuator. The rotary motion induced by the actuatoris converted to reciprocating linear motion of the sliders alonga guide, as shown in Figure 3(c). This crank-slidermechanism makes the robot adaptable to pipe diameters inthe range of 205-305mm. The slider is connected to a leg andthe connector that contains a spring acts as a suspensionsystem as shown in Figure 3(c) and (d). This suspensionstructure guarantees that the robot is able to adapt and exert aforce normal to an uncertain in-pipe surface. In order toimprove the adherence of the clamp to interior of the pipe,thin natural rubber plate is used on sole of feet.The extensor module can steer only two directions, so themechanism that allows the robot to change its steeringdirection is necessary. An upper clamper module hasadditional servo motor and it works for changing steeringdirection as shown in Figure 3(a) and (b). When the robot isclamped in the pipe using only the upper clamper module, theextensor module can be rotated a full 3608 by the servomotor. Therefore, the robot is steerable in any direction. Theupper clamper module is fixed such that it is perpendicular toeach of the four flexible links.A lower clamper module has exactly the same mechanismsas the upper clamper module, and it is connected to the frameof the extensor module.2.3 Movement mechanismInchworm locomotion is composed of extension and clampingmotions. Initially, the lower clamper module adheres to theinner surface of the pipe and the robot is set to a position at thecenter ofthe pipe.Theextensor module thenstrokes theupperclampermodule.Aftertheupperclampermoduleisclampedinthepipe,thelowerclamper modulewithdrawsitslegsthatwereadhered to the pipe. Lastly, the extensor module pulls in thelower clamper module. The robot is able to move forward orbackward through repeated cycles of the above steps.Straight locomotion is easily performed by driving twoactuators of the extensor at the same velocity. Consequently,every flexible link can move straight without any deflections.This straight locomotion strategy with clamper modules allowsthe robot to navigate through both horizontal and verticalstraight pipes as shown in Figure 4(a).Figure 1 In-pipe inspection robotDesign and control method for a high-mobility in-pipe robotWoongsun Jeon, Inho Kim, Jungwan Park and Hyunseok YangIndustrial Robot: An International JournalVolume 40 Number 3 2013 261274262By driving two actuators of the extensor at different velocities,the flexible links undergo a deflection. The robot can steer invarious directions by adjusting the length of the flexible links.This steering locomotion scheme with clamper modulesallows the robot to navigate not only in straight pipes, but alsoin curved and branch pipes as shown in Figure 4(b).Figure 3 Upper clamper module(a) (b)(c) (d)Notes: (a) Main components of clamper module； (b) direction change； (c) crank-slider mechanism； (d) suspensionmechanismFigure 2 Extensor module(a) (b) (c)Notes: (a) Main components of extensor module； (b) power transmission； (c) flexible links and its linear motionDesign and control method for a high-mobility in-pipe robotWoongsun Jeon, Inho Kim, Jungwan Park and Hyunseok YangIndustrial Robot: An International JournalVolume 40 Number 3 2013 2612742633. Modeling of locomotionWhentherobotconductsstraightlocomotion,thepositionoftheupper clamper moduleis thesameasitsstrokelength. However,theposition of the robot can hardly beknown because the upperclamper module does not move along its orientation when therobot is steering. The modeling of steering locomotion requirescontroloftherobotinordertoefficientlynavigatethroughbranchor curved pipes.3.1 Analysis of steering locomotionSince each side of the two links act in an identical manner, thesteeringmechanism, whichmainlyconsists offlexible linksandpulleys, can be represented by a half-model as shown inFigure 5(a). In case of the steering locomotion, every motionoccurs instantaneously when a flexible link on one sidelengthens whereas the other flexible link remains fixed.Therefore, the fixed flexible link can be considered as a simplecantilever beam that is forced by the motion of the oppositeflexiblelinkasshowninFigure5(b).Thefixedlinkandmovinglink are denoted as links 1 and 2, respectively, in Figure 5(c).When the robot is steering, link 1 undergoes deflection. Theorientation u of the robot is then coincident with the angle ofrotationattheendoflink1.Asuequalsu0,theposition(xm,ym)oftherobotinFigure5(c)isdefinedbythedeflection(a,b)oflink1:xmb d212cosuym a d212sinu1where d is the shortest distance between the two ends of theflexible links as shown in Figure 5(b). It is worth noting thatthe deflection and angle of rotation at the end of the beam arethe keys to determining the position and orientation of therobot as it steers.3.2 Pseudo-rigid-body modelIt is quite difficult to find a closed-form solution of thedeflection and orientation because complicated forces andmoments, such as tensile load and gravitational force, act onlink1.Inaddition,thefiniteelementmethodcannotbeadaptedto mobile robots due to the excessive time required forcalculations. The pseudo-rigid-body model (Howell, 2001) isusedinthisworktoanalyzelargedeflectionsoflink1.Specially,the model was used to describe the deflection of flexible linksusing rigid-body components that have equivalent deflectioncharacteristics.The advantageof the pseudo-rigid-body modelis that material properties are not needed to describe thebehavior of a flexible link. This method assumes the flexiblematerialasarigidlinkandobtainsthedeflectionapproximately.Figure 4 Navigation in T-branch pipe(a)(b)Notes: (a) Simple model of upper clamper module and its geometry； (b) initial and final position of upperclamper modelDesign and control method for a high-mobility in-pipe robotWoongsun Jeon, Inho Kim, Jungwan Park and Hyunseok YangIndustrial Robot: An International JournalVolume 40 Number 3 2013 261274264Apseudo-rigid-bodymodelofalarge-deflectioncantileverbeamis shown in Figure 6. The flexible link is substituted by a rigid-bodycomponentwithacharacteristicpivotlocatedatalengthglfrom the free end of the link, where g is called the characteristicradius factor. The pseudo-rigid-body angle Q is the anglebetweenthepseudo-rigid-bodylinkanditsundeflectedposition.The coordinates of the end of a beam can be expressed as(Howell, 2001):al12g12cosQbl gsinQ2The end angle for link1 has the following linear relationshipwith the pseudo-rigid-body angle (Howell, 2001):u cuQ 3where cuis called the parametric angle coefficient.In order to find a suitable g for the steering locomotion,we experimentally obtained the deflection of link 1 at severalanglesfromtheendofthelinkforaspecificlinklength.Theanglesare obtained by adjusting the length of link 2 and measuredin terms of inertial measurement unit (IMU). Since the angleof rotation is the same as the inclination of the connector,Figure 5 Steering mechanismConnectorLinkIdlerPulleyUpper clampermoduleLink 2Link 1(xm, ym)U (xu, yu)huO (o, 0)0qqyabd2xl2l1d(a) (b)(c) (d)Notes: (a) Simple half-model； (b) cantilever model； (c) instantaneous steering motion；(d) instantaneous steering motion with upper clamper moduleDesign and control method for a high-mobility in-pipe robotWoongsun Jeon, Inho Kim, Jungwan Park and Hyunseok YangIndustrial Robot: An International JournalVolume 40 Number 3 2013 261274265theinclinationismeasuredbyanXsensMTi(/en/general/mti), Micro-Electronic-Mechanical-System IMU,attached to the connector. From the data, an acceptable valueof g and cuwere found by determining the maximum acceptableerror in deflection as showninFigure 7. By combining equations(2) and (3), the deflection of link 1 canbe expressed as:a l112g 12cosucuC18C19C18C19C26C27b l1gsinucuC18C19 4where l1is the length of link 1 as shown in Figure 5(b). Thedeflection at a certain angle u about any length of link 1 can becalculatedfromequation(4).Weverifiedthisexperimentallyforthreecases,asshowninFigure8.Foreachcase,wemeasuredandcalculated the deflection of link 1 at 158 intervals from 0 to 908.The maximum error was 2.268mm and the root mean squareerror (RMSE) was 1.233mm.3.3 Position of upper clamper moduleBy substituting equation (4) into equation (1), the position(xm, ym) of the robot can be obtained as:xm l1gsinucuC18C19d212cosuym l112g 12cosucuC18C19C18C19C26C27d2sinu5The trajectory of the upper clamper module is quite importantwhen navigating through T-branch pipes. A point U is apartfrom the connecter as huin Figure 5(d). Finally, the position Uof the upper clamper module is:xu l1gsinucuC18C19d212cosuhusinuyu l112g 12cosucuC18C19C18C19C26C27d2sinu hucosu6Equation (6) tells us that the position of the upper clampermodule about any length and orientation of link 1 can becalculated.Finally,themodelingoflocomotioncanbeobtained.4. Navigation strategyThe navigation strategy shown in Figure 9 is proposed in thiswork. The scheme is based on defining relay points, checkingallowable pipe diameters, and generating paths for T-branchpipes. Through modeling of the robot locomotion via thepseudo-rigid-body model, motion and path planning of therobot can be conducted for a given pipe configurations.Figure 6 Pseudo-rigid-body modelSource: Howell (2001)Figure 7 Flow chart for determining pseudo-rigid-body modelDesign and control method for a high-mobility in-pipe robotWoongsun Jeon, Inho Kim, Jungwan Park and Hyunseok YangIndustrial Robot: An International JournalVolume 40 Number 3 2013 2612742664.1 Decision of a relay pointA relay point may be defined as a position of the lowerclamper module from which the robot can steer its upperclamper module into the branch at a proper location as shownin Figure 10. In order to find the relay point, the origin is setwith respect to a branch that the robot might enter as shown inFigure 11(a). The desired x-axis position xU,fof the upperclamper module in Figure 11(b) is determined. Then, lengthof link 1 at its final position can subsequently be calculatedfrom (6) as:l1；fxU； f2d=22hugsinp=2cu7Bysubstitutingequation(7)intoequation(6),they-axisdistanceYdbetween the extensor module and upper clamper module asshown in Figure 11(b) is:Figure 8 Comparison between measured and estimated deflection of link 1 on three cases (40, 50, and 60 mm)10 0 10 20 30 40 50 60010203040506070x (mm)y (mm)Measured & Estimated Deflection of Link 1Measured deflection of link1 (40 mm)Measured deflection of link1 (50 mm)Measured deflection of link1 (60 mm)Estimated deflection of link1 (40 mm)Estimated deflection of link1 (50 mm)Estimated deflection of link1 (60 mm)Figure 9 Flowchart of navigation strategyStartCalculate next relaypointCalculate next relaypointCurrent position= Next relay pointnonono noIs diameter acceptablerange?Is diameter acceptablerange?YesYesYes YesCase1:path generationCase2: Achieverelaypoint positionCase3:FalseEndEnter intoBranch?Design and control method for a high-mobility in-pipe robotWoongsun Jeon, Inho Kim, Jungwan Park and Hyunseok YangIndustrial Robot: An International JournalVolume 40 Number 3 2013 261274267Figure 10 Example of relay pointsrelay point*relay pointFigure 11 Navigation in T-branch pipe(a)(b)(c)(d)Notes: (a) Simple model of upper clamper module and its geometry； (b) initial and finalposition of upper clamper model； (c) entering to branch from main pipe； (d) procedure ofentering into branch from main pipeDesign and control method for a high-mobility in-pipe robotWoongsun Jeon, Inho Kim, Jungwan Park and Hyunseok YangIndustrial Robot: An International JournalVolume 40 Number 3 2013 261274268Ydd2 l1；f12g 12cosp2cuC18C19C18C19C26C278By considering the margin mLas shown in Figure 11(b), theinitial position of both the upper and lower clamper modules(xU,i, yU,i)and(xL,i, yL,i) can be, respectively, calculated as:xU；i 0yU；idleg=22Yd mL hu(9xL；i 0yL；i yU；i2hu2h(10where dlegis the distance between two legs when the upperclampermoduleisfullyfolded,andhisthedistancebetweentheextensor module and lower clamper module as shownin Figure 11(a). Through the above procedure, the relay point(xL,i, yL,i) can be obtained. The final position of the upperclampermodulecanbethecenterofthepipesection,butsmoothpath for steering could be obtained by setting the final positionslightly lower than the center of the pipe section. Due to thesuspension system in the clamper module, this robot cansustain its position even though a little distortion occurs.Therefore, a little lower position than the center of the pipesection should be recommended as a final position of the upperclamper module for steering.From the distance between the relay point and the currentposition of the robot, the stroke distance and the number ofinchworm locomotion cycles can be defined. Once the robotreaches the relay point, the robot makes a decision to either gostraight or enter a branch. If the robot decides to go straightinto the main pipe, the next relay point can be determinedthrough the procedure outlined above.4.2 Path generationBy making a decision regarding relay points, the initial and finalposition of the upper clamper module for entering branch pipesfrom main pipes can be determined. In order to enter branchpipesefficiently,aproperpathfor theupperclamper moduleforsteeringshouldbegenerated.Fromtheinitialtofinalsequenceofsteering,thegeneratedpathmustsatisfythefollowingconditions:.the upper clamper module must follow the generated pathby adjusting the length of the flexible links； and.the upper clamper module must not collide with the pipewall at all regions.Algorithm 1. Navigation for T-branch pipeProcedure PathGenerationmu；interval；interval*yUE；0 D mu 1while yUE；02D2mu . 0 don 1For u 0 to p/2 doxUE l1；fgsinucuC16C17d212cosuhusinu2dleg2cos2uyUE l1；f12g 12cosucuC16C17C16C17nod2sinuyU；ihucosu212dleg2sin2un n 1end forxUEj min(jxUE2 D/2j)yUE,0 yUE, jl1,f l1,f2 1end whilel1,m l1,f 1um ujn um/interval 1n* (p/2 2 um)/interval* 1inter_L l1,m/ninter_L* (l1,f2 l1,m)/n*For j 1 to n douj interval(j 2 1)l1,j inter_L(j 2 1)xUpath；j l1；jgsinujcuC16C17d212cosujhusinujyUpath；j l1；j12g 12cosujcuC16C17C16C17nod2sinuj yU；ihucosu021end forFor j 1 to n*doujn un interval*(j 2 1)l1,jn l1,n inter_L*(j 2 1)xUpath；jn l1；jngsinujncuC16C17d212cosujnhusinujnyUpath；jn l1；jn12g 12cosujncuC16C17C16C17nod2sinujnyU；i hucosu021end forreturn u1； .；unn*；l1；1； .；ll；nn*；xUpath；1； .；xUpath；nn*；yUpath；1； .；yUpath；nn*end procedureWe propose a path generation algorithm to fulfill conditions (1)and(2)asshowninAlgorithm1.Inordertosatisfycondition(1),a path should be generated according to the length of link 1 andthe orientation of the upper clamper module. The orientationcan be adjusted by changing the length of link 2. For thefulfillment of condition (2), it is important to check the positionof the upper clamper module at the junction between the mainand branch pipe. The coordinates (xU, yU)and(xUE, yUE)indicate the center and end positions of the upper clampermodule, respectively, when the upper clamper module is fullyfoldedasshowninFigure11(c).Whenthex-axispositionxUEofthe end of the upper clamper module is located at the junctionbetweenthemainandbranchpipe,itsy-axispositionyUEshouldbe lower than the pipe diameter D； a margin concerning thelengthofthefootisalsoneededtopreventthefootfromhittingonthe corner of branch. The function min(X) returns the indicesof the minimum values and its vector at line 10 in Algorithm 1.Through an iterative process, a value of xUEthat is close to thedesired position which is as far from the pipe wall as the marginmUat the junction in Figure 11(c), can be obtained.Consequently, the length of link 1 and the orientation of theupper clamper module can be calculated. The procedure forentering a branch pipe from the main pipe is divided in twophases,asshowninFigure11(d).Anoperatorsetsdiscretizationsizes as interval and interval*for the two phases. Finally, a pathcan be generated by discretizing the length of link 1 and theorientation for the two phases.4.3 Verification of path generation algorithm forT-branch pipeUsing the proposed algorithm, the path shown in Figure 12(a)for a T-branch pipe with a diameter of 244mm was generated.In order to verify the proposed navigation algorithm forT-branch pipes, a test bed that consists of a main and branchDesign and control method for a high-mobility in-pipe robotWoongsun Jeon, Inho Kim, Jungwan Park and Hyunseok YangIndustrial Robot: An International JournalVolume 40 Number 3 2013 261274269pipe was set up as shown in Figure 13(a). The inner diameterof the pipes are 244mm while the inner dimensions of theacrylic joint for observation is 250mm 250mm 250mm.When the lower clamper module of the robot was located at(xU,i, yU,i), the robot was controlled by the link length and itsorientation, which were calculated from the proposednavigation algorithm. By marking discretized link length onlinks, the robot can be manually controlled as the calculatedlink lengths and orientation which is monitored from IMU.The operation of the robot is filmed to measure positions by afixed camera. From the images, the position of the upperclamper module was measured at 158 intervals from 08 to 908.The robot followed the proposed path and successfullyentered into a branch from the main pipe as shown inFigure 12(a) and (b). The maximum error was 4.77mm andthe RMSE was 3.06mm. Because the robot has a suspensionmechanism to clamp the pipes (as described in Section 2), theerror is allowable for navigation in the pipes.5. Experiments5.1 T-branch pipeWe verified the proposed navigation strategy and the mobilityin commercial T-branch pipes. The experimental environmentwas set up as shown in Figure 13(b). The inner diameter of thepipeswas244mm.TheexperimentalprocessconsistedofthreeFigure 12 Verification of algorithm for T-branch pipe(b)100 50 0 50 100 150 20050050100150200250Verification of Navigation Algorithm for T-branch pipex-aixs position (mm)(a)y-axis position (mm)PipeGenerated PathPoints at 15 degree intervalsExperimental valuesNotes: (a) Comparison between measured and generated path； (b) experiment in T-branch pipeDesign and control method for a high-mobility in-pipe robotWoongsun Jeon, Inho Kim, Jungwan Park and Hyunseok YangIndustrial Robot: An International JournalVolume 40 Number 3 2013 261274270steps: locating initial position for steering invertical main pipe,entering the branch, ansd going forward into the horizontalbranch pipe.In this experiment, the robot is manually controlled. Byusing DSP, an operator sends signal to each actuator as shownin Figure 14 in the same manner in Section 4.3. From thecalculated initial position of the robot for steering, the robotsuccessfully entered into the branch from the main pipe usingthe suggested navigation strategy for T-branch pipes as shownin Figure 15. After entering the horizontal branch pipe, therobot can navigate the branch pipe using inchwormlocomotion as shown in Figure 15.5.2 Steering direction changeIn general, branch pipes can be installed in any direction withrespect to the main pipe. However, the steering mechanism ofthe extensor module can only move the upper clamper modulefromsidetoside.Forthesereasons,therobotisequippedwithamotor that can rotate its body and thus, adjustments in thesteering direction can be made.Figure 13 T-branch pipe test bed(a) (b)Notes: (a) Acrylic T-branch joint； (b) commercial T-branch pipeFigure 14 Control schemaDesign and control method for a high-mobility in-pipe robotWoongsun Jeon, Inho Kim, Jungwan Park and Hyunseok YangIndustrial Robot: An International JournalVolume 40 Number 3 2013 261274271The experimental environment was the same as that usedfor the verification of Algorithm 1. Initially, the posture ofthe robot is twisted by 458 with respect to the direction ofthe branch. The robot then rotates the upper clamp module sothat it coincides with the direction of the branch beforesteering. Next, the robot rotates its extensor module andnavigates to the initial position for steering as shown inFigure 16. The red arrows in Figure 16 shows the steerabledirection in that posture. After these steps, the remainder ofthe process is the same as that introduced in the abovesubsection.5.3 Adaptation for pipe diameter changesIn-pipe robots must be able to adapt to various pipe diametersfor high-mobility. The test bed was setup for three pipediameters: 210, 244, and 305mm (Figure 17). The obtainedresults shown in Figure 18 demonstrate the feasibility ofadaptation to pipe diameter changes.Figure 15 Experiment in T-branch pipeFigure 16 Experiment for changing robot position for any direction of branchDesign and control method for a high-mobility in-pipe robotWoongsun Jeon, Inho Kim, Jungwan Park and Hyunseok YangIndustrial Robot: An International JournalVolume 40 Number 3 2013 261274272Figure 17 Experiment setup for adaptation of pipe diameter changesFigure 18 Experiment for adaptation of pipe diameter changesDesign and control method for a high-mobility in-pipe robotWoongsun Jeon, Inho Kim, Jungwan Park and Hyunseok YangIndustrial Robot: An International JournalVolume 40 Number 3 2013 2612742736. Conclusion and future workInthispaper,wedescribedthemechanismofaninchworm-typein-pipe robot that is able to steer and adapt to pipe diameterchanges. We also suggested a navigation strategy based onmodeling of the robot locomotion. By defining relay points,the robot can reach a position suitable for navigation in both amainpipeandaT-branchpipe.InthecaseofenteringT-branchpipes, we introduced a path generation algorithm and verifiedthat the algorithm is effective. Additional experimentsdemonstrating the mobility of the robot were also conducted.Here,wefocusedonanavigationstrategyforenteringT-branchpipes,throughwhichin-piperobotsoftenhavedifficultytraveling.In future research, we will address navigation strategies forvarious types of pipes, including curved and Y-branch pipes. Inaddition, sensor systems for recognizing in-pipe configurationswill be installed for achieving a more reliable system. We will alsofocus on the construction of a fully autonomous in-pipe robotthat can navigate through various types of pipes.ReferencesHorodinca, M., Dorftei, I., Mignon, E. and Preumont, A.(2002),“Asimplearchitectureforin-pipeinspectionrobots”,Proc. Int. Colloq. Mobile, Autonomous Systems, pp. 61-64.Howell, L.L. (2001), Compliant Mechanisms,Wiley,New York, NY, pp. 135-196.Jeon, W., Park, J., Kim, I., Kang, Y.-K. and Yang, H. (2011),“Development of high mobility in-pipe inspection robot”,ProceedingsoftheIEEE/SICEInternationalSymposiumonSystemIntegration, Kyoto, Japan, 20-22 December,pp.479-484.Kim, D.-W., Park, C.-H., Kim, H.-K. and Kim, S.-B. (2009),“Force adjustment of an active pipe inspection robot”,Proceedings of the ICROS-SICE International Joint Conference2009.Kim, J.-H., Sharma, G. and Iyengar, S.S. (2010), “FAMPER:a fully autonomous mobile robot for pipeline exploration”,Proceedings of the IEEE-ICIT 2010 International Conferenceon Industrial Technology, Vina del Mar, Chile, 14-17 March.Kuwada, A., Tsujino, K., Suzumori, K. and Kanda, T.(2006), “Intelligent actuators realizing snake-like smallrobot for pipe inspection”, MHS 2006 Micro-Nano COE,MP1-2-1, November, p. 20.Li,P.,Ma,S.,Li,B.,Wang,Y.andYe,C.(2007),“Anin-pipeinspection robot based on adaptive mobile mechanism:mechanical design and basic experiments”, Proceedings ofthe 2007 IEEE/RSJ International Conference on Intelligent Robotsand Systems, San Diego, CA, USA, 29 October-2 November.Lim,J.,Park,H.,An,J.,Hong,Y.-S.,Kim,B.andYi,B.-J.(2008),“Onepneumaticlinebasedinchworm-likemicrorobotforhalf-inchpipeinspection”,Mechatronics,Vol.18No.7,pp.315-322.Mirats Tur, J.M. and Garthwaite, W. (2010),