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In-pipe inspection robot with active pipe-diameteradaptability and automatic tractive force adjustingYunwei Zhanga,b,*,Guozheng Yan a a Department of Instrumentation Engineering,Shanghai Jiaotong University,Huashan Road 1954,Shanghai 200030,Chinab Faculty of Modern Agricultural Engineering,Kunming University of Science and Technology,Bailongsi Village 296,Kunming 650093,ChinaReceived 27March 2006;accepted 10December 2006Available online 31January 2007AbstractAn in-pipe robot with active pipe-diameter adaptability and automatic tractive force adjusting is developed for long-distance inspection of main gas pipelines with different diameter series.Its physical design employs the scheme that three sets of parallelogram wheeled leg mechanism are circumferentially spaced out 120°apart symmetrically.This structural design makes it possible to realize the adaptation to pipe diameter and tractive force adjusting together.On the basis of analyzing the mechanical actions of the adaptation to pipe diameter and tractive force adjusting,the related mechanical models are established,and their control system structure and control strategy are discussed.To verify the pipe-diameter adaptability and tractive force adjusting of the robot,related field experiments are implemented in actual underground gas pipeline.The experimental results show that the theoretical analysis in this paper is valid and the prototype of this robot can work well in actual underground gas pared with other similar robots,this robot,which employs active mode for its adaptability to pipe diameter,can be adaptable to the wide range of gas pipeline diameters from B 400mm to B 650mm and automatically provide a stable and reliable tractive force with strong capacity of tractive force adjusting.As a mobile carrier for visual inspection and nondestructive testing to monitor block,corrosion,crack,defect,and wall thick-ness of main gas pipelines,its inspection range of one-time job in pipelines is extended beyond 1000m.Ó2006Elsevier Ltd.All rights reserved.Keywords:In-pipe robot;Active pipe-diameter adaptability;Tractive force adjusting;Gas pipelines inspection1.IntroductionBecause of the defect of gas purification apparatus,block and leakage often occur in the urban gas pipe-lines.Furthermore,as most urban gas pipelines are buried under the ground,cracks and damages in the welded region of pipelines may be caused by the third party such as construction,electricity,and sewage 0094-114X/$-see front matter Ó2006Elsevier Ltd.All rights reserved.doi:10.1016/j.mechmachtheory.2006.12.004*Corresponding author.Address:Faculty of Modern Agricultural Engineering,Kunming University of Science and Technology,Bailongsi Village 296,Kunming 650093,China.Tel.:+868713801017;fax:+868713802108.E-mail address:zhangyunwei72@ (Y.Zhang).Available online at Mechanism and Machine Theory 42(2007)1618–1631and Machine TheoryY.Zhang,G.Yan/Mechanism and Machine Theory42(2007)1618–16311619 NomenclatureR radius of inspection robot,Fig.2,mR1pipe radius,Fig.2,mL length of link CD,Fig.2,mL1distance between point M and point D,Fig.2,mL2length of the link MN,Fig.2,mr radius of a driving wheel,Fig.2,ma included angles between link CD and axis X,Fig.2,radb included angles between link MN and axis X,Fig.2,radh height from the central axis of the inspection robot to supporting point D,Fig.2,mF thrust force,Fig.2,NN1supporting force acting on the driving wheels by the gravity,Figs.3and4,NN2supporting force acting on the driving wheels by the gravity,Figs.3and4,NN3supporting force acting on the driving wheels by the gravity,defined in Fig.4,Nc attitude angle of the inspection robot,defined in Fig.3,radz coordinate of center of gravity G at axis OZ,Fig.3,mh included angle between axis OZ and the line from the supporting point of a driving wheel to thepipe center,Eq.(1),rads arch length of h,Fig.3,mf coefficient of transverse friction between driving wheels and pipe wall,Fig.3x coordinate of point N at axis X,Eq.(1),mR N sum of all supporting force,Eq.(3),NU slope angle of pipe,Eq.(3),radT output torque of the adjusting motor,Eq.(6),N.mg transmission efficiency of the ballscrew pair,Eq.(6)P h lead of the ballscrew,Eq.(6),mF T tractive force of the inspection robot,Eq.(10),Nl adhesion coefficient between driving wheels and pipe wall,Eq.(10)y coordinate of point E at axis Y,Eq.(11),mR P additional pressure,Eq.(13),ND1pipe diameter,Fig.5,mI g weight use factor,defined in Eq.(18)F Td desired tractive force,Fig.7,NF d desired thrust force,Fig.7,Nproject.This may disturb the daily life of inhabitants,and increase their risk of losing life and losing money. Therefore,inspection,maintenance and repair for gas pipeline are demanded strongly.Since inspection for urban gas pipelines is a special task,employing robots to complete inspection and maintenance for pipelines appears to be one of the most attractive solutions now.Up to date,some studies on in-pipe robot have been reported[1–25],and some prototypes of in-pipe robot have been developed based on different motion mech-anism,such as wheeled type[1–14],snaking type[15–17],walking type[18–20],worming type[21–23],and helical-drive type[24,25].Pipe diameter,which is one of the important size parameters of gas pipeline,affects its transportation capa-bility,and limits the working space occupied by the inspection robot.Therefore,it is necessary to be consid-ered that a robot is designed for what size of pipe diameter.In common,many prototypes of existing in-pipe robots were designed for one size of pipe diameter[1,2,4–6,8–10,12–14,18,19,21,23–25],and some of them were adaptable to small change of pipe diameter,but they widely contacted against the pipe wall by using spring[4,5,24,25].This is a passive mode with feature of structure being simple.But the limitation of spring narrows the radial adjustable range of those robots,and their tractive force can not be adjusted dynamically1620Y.Zhang,G.Yan/Mechanism and Machine Theory42(2007)1618–1631according to the actual requirement during inspection.Therefore,with weak tractive capacity,they can not pull the tether cable and inspection instruments as well as the robot itself while executing a long-distance inspection inside the pipeline,and their inspection range of one-time job in pipeline is limited.In this paper,a new style of in-pipe inspection robot with active pipe-diameter adaptability and automatic tractive force adjusting is developed for long-distance inspection in main gas pipelines with different diameter series.This robot can change its radial size actively in a wide range to move inside gas pipelines with various diameters from B400mm to B650mm,and automatically provide stable and sufficient tractive force accord-ing to actual requirement during inspection.As a mobile carrier for visual inspection and nondestructive test-ing to monitor block,corrosion,crack,defect,and wall thickness of main gas pipelines,its inspection range of one-time job in pipelines is extended beyond1000m.2.Overview of the robotic systemAs shown in Fig.1,this robotic system for gas pipeline inspection is composed of two parts,which are the inspection robot running inside the pipeline,and the ground workstation monitoring the state of the inspec-tion robot.The in-pipe inspection robot consists of running mechanism,pipe diameter adaptive mechanism, sensing system,control system and lighting system etc.The lighting source and CCD camera,transformer, switching power supply,step motor driver,and embedded computer system are all mounted on the inspection robot.The nondestructive testing module,such as the pipe wall thickness sensor developed by us based on magneticflux leakage method,can be connected to the inspection robot by an universal joint.The ground workstation consists of engineering vehicle,control cabin,industrial control computer,automatic cable winder,and vehicular generator etc.In view of the technical feasibility of remote power supply and communication,the gas pipeline inspection robotic system employs wired remote control.The tether cable,which is composed of two power lines and four opticalfibers,is designed by a special rmation data and power can be transferred together in this photoelectric hybrid cable.Differed from other opticalfiber cables,this cable with excellent abrasion resis-tance can bear tractive load more than3000N.This feature is very suitable for the application in gas pipelines. Because information data is transferred by optical signal in the cable,the interference between signal andFig.1.Overview of gas pipeline inspection robotic system.Y.Zhang,G.Yan/Mechanism and Machine Theory42(2007)1618–16311621power in remote hybrid transmission is well avoided.Through this cable,the inspection robot can establish a real-time communication with the ground workstation based on TCP/IP protocol,and transfer video infor-mation,environmental parameters,running status of the robot,control instructions,and detecting data.Dur-ing the inspection inside a gas pipeline,the robot can be operated by two modes.One is the autonomous mode that the robot is guided by a given inspection task automatically,another is the manual mode that the robot is controlled by the operator on-line.3.Modeling3.1.Pipe diameter adaptive mechanismThe pipe diameter adaptive mechanism is the actuator of active adaptation to pipe diameter and adjustment of tractive force.It is composed of three sets of parallelogram wheeled legs circumferentially spaced out120°apart symmetrically.Each parallelogram wheeled leg has a front driving wheel and a rear driving wheel.Fig.2 illustrates the one of three sets.The operation of the pipe diameter adaptive mechanism is driven by a step motor with convenience to be controlled.This motor is called the adjusting motor.Under the control of motor driver,the adjusting motor drives rotation of the ballscrew pair which can push three sets of parallelogram wheeled legs to make driving wheels contact to inner wall of pipe,or adjust the pressure between driving wheels and pipe wall.This structural design makes it possible to realize the adaptability to pipe diameter and tractive force adjusting together,and the pipe diameter adaptive mechanism with this structure can realize adjustment in a wide range.The nut of ballscrew,pressure sensor and axial sliding bush are connected together by screw bolts.The pressure sensor,which may test the sum of pressures between all the driving wheels and pipe wall indirectly,is useful for the control of pressing the driving wheels against the pipe wall with a stable pressure to obtain sufficient and stable tractive force,and on the other hand,can provide overload protection to prevent the mechanism overloading.As in Fig.2,R is the radius of the robot,R1is the radius of a pipe,h denotes the height from the central axis of the inspection robot to supporting point D,r is the radius of a driving wheel,L is the length of link CD,L1is the distance between point D and point M,L2is the length of link MN,a is the included angles between link CD and axis X,b is the included angles between link MN and axis X,and F denotes the thrust force of mechanism motion,which is caused by the rotation of the ballscrew pair and which can be measured by the pressure sensor.3.2.Mechanical model of active adaptation to pipe diameterIn order to be adaptive for different diameters of pipelines,some bends,and some sections with specialmotorshape,the inspection robot needs to change its body size actively.To respond this action,the adjusting Array Fig.2.A parallelogram wheeled leg of pipe diameter adaptive mechanism.drives rotation of the ballscrew with an output torque T and produces a thrust force F which can drive trans-lation of parallel linkage ABCD to change the radial size of the robot,and other two sets of parallelogram wheeled leg perform same action synchronously.At the beginning of this process,because the central axis of the robot does not overlap the central axis of pipe as shown in Fig.3,an additional torque is required to overcome the opposition caused by the transverse friction between surface of pipe wall and the wheels supporting the gravity.This may result over loading of the adjust-ing motor.Therefore,we need to analyze this process,and establish its mechanics model to guide the design.Since the structure of the robot is symmetric,its center of gravity denoted by symbol G can be assumed at its central axis.In Fig.3,symbol c denotes the attitude angle of the robot which can reflect its rotation round the central axis of a pipe,N 1and N 2respectively denote the supporting force acting on the two sets of driving wheels by the gravity of the robot,h is the included angle between axis OZ and the line from the supporting point of a driving wheel to the pipe center,s is the arc length of h ,z is the coordinate of G at axis OZ ,and f denotes the coefficient of transverse friction between driving wheels and pipe wall.From Figs.2and 3,we have geometric relationships R ¼r þh þL sin a x ¼L 1cos a þL 2cos b L 1sin a ¼L 2sin b s ¼R 1h R sin /¼R 1sin h z sin /¼R 1sin ð/Àh Þ8>>>>>>>><>>>>>>>>:ð1Þwhere x is the coordinate of point N at axis X .Differentiating both sides of Eq.(1)yields d x ¼ÀL 1ðR Àr Àh Þ1ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiL 2ÀðR Àr Àh Þ2p þL 1ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiL 2L 22ÀL 21ðR Àr Àh Þ2p !d R d s ¼R 1sin /ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiR 21ÀR 2sin 2/p d R d z ¼Àcos /þR sin 2/ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiR 21ÀR 2sin 2/p d R 8>>>>>>><>>>>>>>:ð2ÞFig.3.Forced diagram.1622Y.Zhang,G.Yan /Mechanism and Machine Theory 42(2007)1618–1631Ignoring frictional heating,considering a slope angle /of pipe,and according to equilibrium equation of forces and conservation of energy,we can obtain P N ¼N 1þN 2¼mg cosu cos c ¼mg cos u cos c R 1ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiR 21ÀR 2sin 2/p F d x þf P N d s ¼mg d z cos u cos c (ð3Þwhere P N is the sum of all supporting force.Defining k 1¼L 1ðR Àr Àh ÞL 1ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiL 2ÀðR Àr Àh Þ2p þL 1ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiL 2L 22ÀL 21ðR Àr Àh Þ2p !k 2¼R 1sin /ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiR 21ÀR 2sin 2/p k 3¼cos /þR sin 2/ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiR 21ÀR 2sin 2/p k 4¼R 1ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiR 21ÀR 2sin 2/p 8>>>>>>>>>><>>>>>>>>>>:ð4Þand substituting Eq.(2)into Eq.(3),we haveF ¼mg cos u cos c k 1ðk 2k 4f þk 3Þð5ÞThen,the output torque of the adjusting motor can be written asT ¼p h 2p gF ð6Þwhere g denotes the transmission efficiency of the ballscrew pair,P h denotes the lead of the ballscrew.3.3.Mechanism of tractive force adjusting A gas pipeline inspection robot must obtain sufficient tractive force to pull its tether cable and other equip-ments while traveling inside a gas pipeline to complete inspection,maintenance,and repair tasks.When the motion motor of a wheeled robot can produce an enough driving force,its tractive force is determined by the adhesion force which depends on the normal pressure and adhesion coefficient between driving wheels and pipe wall.Thus,a wheeled robot with the pipe diameter adaptive mechanism,which can produce an addi-tional normal pressure to change the adhesion force between driving wheels and pipe wall,is capable of adjust-ing its tractive force in a certain range.Along with the increase of inspection distance in pipeline,more tractive force of the robot is demanded to overcome increasing friction resistance of the tether cable,or an additional kinetic resistance caused by pipe slope.However,when the motion motor of the robot produces more driving force,the adhesion force only contributed by robot weight may be insufficient,and its driving wheels may slip on the surface of pipe wall.Therefore,an additional pressure enhancing adhesion force should be produced by the pipe diameter adaptive mechanism to improve the tractive capacity of the robot.This is realized as the way that the action of the adjusting motor drives rotation of the ballscrew pair with the output torque T and produces the thrust force F which drives parallel linkage ABCD to press the driving wheels against inner wall of the pipe with an addi-tional pressure.3.4.Mechanical model of tractive force adjustingTo realize the control of the adjustment of tractive force,we should establish its mechanical model on the basis of analyzing relationships among tractive force,additional pressure,thrust force,and output torque of the adjusting motor.We define the sum of all pressures applied to driving wheels by the robot weight as total supporting force denoted by symbol P N ,and the sum of pressures produced by pipe diameter adaptive mechanism actively as Y.Zhang,G.Yan /Mechanism and Machine Theory 42(2007)1618–16311623additional pressure denoted by symbol P P .As shown in Fig.4,the central axis of the robot nearly overlapsthe central axis of the pipe during the adjustment of tractive force.Since three sets of parallelogram wheeled legs are circumferentially spaced out 120°apart symmetrically,any attitude angle of the robot will results that only one or two sets of driving wheel at the bottom are contributors which support the gravity of the robot.In Fig.4,N 1,N 2,and N 3are used to denote the supporting force applied to three sets of driving wheels respec-tively.We define that an attitude angle along counter-clockwise is positive,and an attitude angle along clock-wise is negative.Then we have N 3¼0À6006c 660N 1¼06006c 6180 N 2¼018006c 63008><>:ð7ÞAccording to equilibrium of forces,we obtain N 1cos ðc þ60 ÞþN 2cos ð60 Àc Þ¼mg N 1sin ðc þ60 ÞÀN 2sin ð60 Àc Þ¼0 À60 6c 660N 2cos ðc À60 ÞÀN 3cos c ¼mg N 2sin ðc À60 ÞÀN 3sin c ¼0 60 6c 6180ÀN 3cos c þN 1cos ð60 þc Þ¼mg ÀN 3sin c þN 1sin ð60 þc Þ¼0180 6c 6300ð8ÞSolving Eq.(8),and considering the slope angle /,we have X N ¼2mg cos c cos u À60 6c 660 2mg cos ðc À120 Þcos u 60 6c 6180 2mg cos ðc À240 Þcos u 180 6c 63008><>:ð9ÞIf the driving force of the motion motor is sufficient,the tractive force of the robot can be written as F T ¼X N þX P lð10Þwhere l denotes the adhesion coefficient.In Fig.2,we have geometricrelationships Fig.4.Supporting force distribution.1624Y.Zhang,G.Yan /Mechanism and Machine Theory 42(2007)1618–1631R ¼r þh þL sin a y ¼R Àhx ¼L 1cos a þL 2cos b L 1sin a ¼L 2sin b 8>>><>>>:ð11Þwhere x is the coordinate of point N at axis X ,y is the coordinate of point E at axis Y .Differentiating both sides of Eq.(11)yieldsd y ¼d R d x ¼Àk 1d Rð12ÞApplying principle of virtual displacement yields X N þX P d y þF d x ¼0ð13ÞSubstituting Eq.(12)into Eq.(13),we obtainF ¼1k 1X N þX P ¼1k 1lF T ð14ÞThen,the required output torque of adjusting motor can be written asT ¼p h 2p g F ð15ÞThe mechanical model of the tractive force adjusting is composed of Eqs.(9),(10),(14)and (15)which can describe variations of the thrust force F ,output torque T of the adjusting motor,additional pressure R P ,and tractive force F T .4.Discussion4.1.Active adaptation to pipe diameterFrom above mechanical model of active adaptation to pipe diameter,it is known that both the required thrust force F and the required output torque T change as R 1and R change in the behaviour that the inspec-tion robot adjusts its size to fit variation of pipe diameter,and both F and T have different variation in the case of the pipe diameter being different as shown in Fig.5,where D =2R and D 1=2R 1.The required F and T are more in pipelines with small diameter than in pipelines with large diameter.In order to prevent the adjusting motor overloading,we place a speed reducer with reduction rate of 10:1between the adjusting motor and ball-screw,and verify the strength and rigidity of the related components bearing load.4.2.Tractive force adjustingFrom Eq.(4),the first derivative of k 1with respect to R equals d k 1d R ¼L 1L 1ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiL 2ÀðR Àr Àh Þ2q þL 1ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiL 2L 22ÀL 21ðR Àr Àh Þ2q 0B @1C A þL 1ðR Àr Àh ÞL R Àr Àh ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiL 2ÀðR Àr Àh Þ2q þL 1ðR Àr Àh ÞffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiL 2L 22ÀL 21ðR Àr Àh Þ2q 0B @1C A >0ð16ÞSubstituting Eq.(16)into the first derivative of Eq.(14)with respect to R yieldsY.Zhang,G.Yan /Mechanism and Machine Theory 42(2007)1618–16311625d F d R ¼d Fd k 1d k 1d R ¼ÀP N þP P ðÞk 21d k 1d R <0d T ¼p h d F<08<:ð17ÞSince we have R %R 1in the process of tractive force adjusting,Eq.(17)reveals that producing a same tractive force needs a different thrust force F and output torque T of the adjusting motor in the case of the pipe diam-eter being different,and both F and T decrease as pipe diameter increase.According to above mechanical model of tractive force adjusting,it is easy to know that the inspection robot can adjust its tractive force in fact through adjusting the additional pressure.Enhancing the additional pressure is an efficient way to improve the tractive capacity of the robot,but as the additionalpressureFig.5.Variations of F and T versus robot radial size in different pipe diameter:(a)pipe diameter D 1=450mm,(b)pipe diameter D 1=550mm and (c)pipe diameter D 1=650mm.1626Y.Zhang,G.Yan /Mechanism and Machine Theory 42(2007)1618–1631increases,the load distributed in the related components and motor of the robot also increases.Therefore,it is necessary to restrict this adjusting in a reasonable range according to the actual demand in the design.4.3.Optimal attitude angleSince the inspection robot is heavy,its own weight may be an important contributor to improve its tractive capacity.We define the ratio of the total supporting force R N to the weight of the robot mg as the weight use factor I g,which reveals how much the weight of the robot contributes to its tractive capacity.Then we haveI g¼PNmg¼2cos c cos uÀ60 6c6602cosðcÀ120 Þcos u60 6c61802cosðcÀ240 Þcos u180 6c63008><>:ð18ÞEq.(18)shows that the weight use factor I g is determined by the attitude angle c of the inspection robot.This relationship is illustrated in Fig.6.It is obvious that the traveling attitude of the robot inside pipelines may affects its tractive capacity in a certain degree.This effect is dependent on the weight use factor of the inspec-tion robot.Therefore,the inspection robot should keep one optimal attitude angle of c=0°,c=120°,and c=240°to efficiently utilizes its weight to improve its tractive capacity as more as it can while traveling inside pipelines.4.4.Control strategyAfter modeling,we should pay attention to the control strategy of the pipe diameter adaptive mechanism of the inspection robot to realize its active adaptability to pipe diameter and automation of tractive force adjust-ing.The control system structure is illustrated in Fig.7,where F Td denotes the desired tractive force,and F d denotes the desired thrust force.The control behavior largely involves two aspects.Firstly,the inspection robot adjusts its radial size to press the driving wheels against the inner wall of pipe.When the pipe radius R1changes,it will be captured by a pipe diameter sensor.Then,the control system compares current R1with current radial size of the inspec-tion robot R.If the difference between R1and R is more than a desired value D,the PD controller operates the pipe diameter adaptive mechanism to change the radial size of the robot until the difference is less than D.In this procedure,it is known from above theoretic analysis that the actuating mechanism must overcome the transverse friction between the driving wheels and the pipe wall.Secondly,the control system adjuststheFig.6.Variation of weight use factor versus attitude angle.Y.Zhang,G.Yan/Mechanism and Machine Theory42(2007)1618–16311627actual tractive force F T of the inspection robot to track the desired tractive force F Td by operating the pipe diameter adaptive mechanism.Given a desired tractive force F Td ,the desired value of the thrust force F d can be calculated by using the mechanical model of tractive force adjusting.Therefore,with the input of the difference from real-time feedback comparison between the actual thrust force F tested by the pressure sen-sor and F d ,the PID controller actuates the adjusting motor to keep the actual thrust force F tending to F d .Adopting this control strategy,the inspection robot can automatically adjust itself to the variation of pipe diameter while moving inside the pipeline,and provide a stable and sufficient tractive force according to a desired value.5.Experiments5.1.Testing for adjustment of tractive forceTo verify the tractive force adjusting of the inspection robot in pipelines with different diameters,three tests are implemented in horizontal pipelines with diameters of B 500mm,B 550mm,B 600mm respectively,and each test is repeated three times.In each test,given a desired tractive force of 1200N,let the inspectionrobotFig.7.Block diagram of control system.Testing scheme for tractive force adjusting.Table1Testing results of tractive force adjustingPipe diameter (mm)Desired tractive force(N)Desired thrust force(N)No.Tractive force testing(N)Average of tractive force testing(N)B50012001665.51122812302121931242B55012001207.21122112172123331198B6001200788.31120612142121531223Fig.9.Field experiment inside underground gas pipeline:(a)put the inspection robot into underground gas pipeline and(b)adjust the radial size to pass through Z-shape pipe joint.automatically adjust its output of tractive force under the control of above strategy;then,according to the scheme illustrated in Fig.8,we can test its actual tractive force with a standardized force transducer connected to a digital measuring apparatus which can display the measured value on screen.The peak tractive force is recorded when the drive wheels slip on the surface of pipe wall.The measured values are given in Table1.The experimental result shows that the inspection robot can provide a stable and sufficient tractive force in pipe-lines with different diameters,and this result also proves that above theoretical analysis is valid.5.2.Field experiment inside underground gas pipelineAfield experiment was implemented to observe the running state of the inspection robot inside the actual gas pipeline under Longquan Road nearby Kunming normal school.This gas pipeline,which is a main line of Kunming Gas Company,is connected with the helical-weld pipes12m in length,and there are a slope angle around10°and Z-shape pipe joints along this pipeline.Fig.9is two pictures of thefield experiment.Infigure(a),the inspection robot was put into the underground gas pipeline from the valve in a drainage shaft;infigure(b),the inspection robot adjusted its radial size to pass through a Z-shape pipe joint.The result of thefield experiment shows that the inspection robot can work well inside the underground gas pipeline,and smoothly pass through pipelines with slope angle and Z-shape pipe joints.6.ConclusionsThis paper presents a new style of in-pipe inspection robot with active adaptability to pipe diameter and automatic tractive force adjusting for long-distance inspection in main gas pipelines with different diameter pared with other similar robots,this robot,which employs active mode to resolve its adaptability to pipe diameter,can adjust itself to gas pipelines with a wide range of diameters from B400mm to B650mm and provide a stable and reliable tractive force with strong capacity of tractive force adjusting.This can help the inspection robot to extend its inspection range of one-time job in pipeline.Field experiments prove that the inspection robot can work well inside the underground gas pipeline,and smoothly pass through pipelines with slope angle and Z-shape pipe joints.AcknowledgementsThis project is supported by the National High-Tech Research and Development Program of China(863 Program)(Grant No.2002AA422110)and the Key Project of Science and Technology of Shanghai(Grant No.021111117)and Yunan Province-University Cooperation Fund(Grant No.2001KABAA00A025).We thank the Foundation Committees.References[1]H.T.Roman,B.A.Pellegrino,Pipe crawling inspection robots:an overview,IEEE Transactions on Energy Conversion8(3)(1993)576–583.[2]M.Beller,E.Holden,N.Uzelac,Cracks in pipelines and how tofind them,Pipe and Pipelines International25(6)(2001)26–34.[3]Y.Kawaguchi,I.Yoshida,H.Kurumatani,Internal pipe inspection robot,In:Proc.IEEE International Conference on Robotics andAutomation,1995,pp.857–862.[4]H.R.Choi,S.M.Ryew,Robotic system with active steering capability for internal inspection of urban gas pipelines,Mechatronics16(12)(2002)713–736.[5]S.G.Roh,H.R.Choi,Differential-drive in-pipe robot for moving inside urban gas pipelines,IEEE Transactions on Robotics21(1)(2005)1–17.[6]J.Okamoto,J.C.Adamowski,M.S.G.Tsuzuki,Autonomous system for oil pipelines 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