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1、sdarticle3In-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

2、,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 i

3、nspection of main gas pipelines with di?erent diameter series.Its physical design employs the scheme that three sets of parallelogram wheeled leg mechanism are circumferentially spaced out 120apart symmetrically.This structural design makes it possible to realize the adaptation to pipe diameter and

4、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 adaptabil

5、ity and tractive force adjusting of the robot,related ?eld 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

6、/doc/086f8ad676a20029bd642df7.htmlpared 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

7、 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.2006Elsevier Ltd.All rights reserved

8、.Keywords:In-pipe robot;Active pipe-diameter adaptability;Tractive force adjusting;Gas pipelines inspection1.IntroductionBecause of the defect of gas puri?cation apparatus,block and leakage often occur in the urban gas pipe-lines.Furthermore,as most urban gas pipelines are buried under the ground,cr

9、acks 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 2006Elsevier Ltd.All rights reserved.doi:10.1016/j.mechmachtheory.2006.12.004*Corresponding author.Address:Faculty of Modern Agricultural Engin

10、eering,Kunming University of Science and Technology,Bailongsi Village 296,Kunming 650093,China.Tel.:+868713801017;fax:+868713802108.E-mail address:zhangyunwei72/doc/086f8ad676a20029bd642df7.html (Y.Zhang).Available online at /doc/086f8ad676a20029bd642df7

11、.htmlMechanism and Machine Theory 42(2007)16181631and Machine TheoryY.Zhang,G.Yan/Mechanism and Machine Theory42(2007)161816311619 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

12、.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

13、 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,de?ned in Fig.4,Nc attitude angle of the inspection robot,de?ned in Fig.3,radz coordinate of center of gravity G at axis OZ,Fig.3,mh i

14、ncluded 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 coe?cient 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),

15、NU slope angle of pipe,Eq.(3),radT output torque of the adjusting motor,Eq.(6),N.mg transmission e?ciency 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 coe?cient between driving wheels and pipe wall,Eq.(10)y coordinate of

16、 point E at axis Y,Eq.(11),mR P additional pressure,Eq.(13),ND1pipe diameter,Fig.5,mI g weight use factor,de?ned 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

17、. 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-p

18、ipe robot have been reported125,and some prototypes of in-pipe robot have been developed based on di?erent motion mech-anism,such as wheeled type114,snaking type1517,walking type1820,worming type2123,and helical-drive type24,25.Pipe diameter,which is one of the important size parameters of gas pipel

19、ine,a?ects 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

20、1,2,46,810,1214,18,19,21,2325,and some of them were adaptable to small change of pipe diameter,but they widely contacted against the pipe wall by using spring4,5,24,25.This is a passive mode with feature of structure being simple.But the limitation of spring narrows the radial adjustable range of th

21、ose robots,and their tractive force can not be adjusted dynamically1620Y.Zhang,G.Yan/Mechanism and Machine Theory42(2007)16181631according 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 ro

22、bot 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-distan

23、ce inspection in main gas pipelines with di?erent 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 su?cient tractive force accord-ing to actual requirement dur

24、ing 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 robot

25、ic 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 syst

26、em,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 ma

27、gnetic?ux 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

28、communication,the gas pipeline inspection robotic system employs wired remote control.The tether cable,which is composed of two power lines and four optical?bers,is designed by a special /doc/086f8ad676a20029bd642df7.htmlrmation data and power can be transferred together in th

29、is photoelectric hybrid cable.Di?ered from other optical?ber 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 inte

30、rference between signal andFig.1.Overview of gas pipeline inspection robotic system.Y.Zhang,G.Yan/Mechanism and Machine Theory42(2007)161816311621power in remote hybrid transmission is well avoided.Through this cable,the inspection robot can establish a real-time communication with the ground workst

31、ation 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 giv

32、en 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

33、 three sets of parallelogram wheeled legs circumferentially spaced out120apart 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

34、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 betwee

35、n 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 axia

36、l 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 su?cient and stable tra

37、ctive 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 t

38、he 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 pa

39、ir and which can be measured by the pressure sensor.3.2.Mechanical model of active adaptation to pipe diameterIn order to be adaptive for di?erent diameters of pipelines,some bends,and some sections with specialmotorshape,the inspection robot needs to change its body size actively.To respond this ac

40、tion,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 par

41、allelogram 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

42、 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

43、 at its central axis.In Fig.3,symbol c denotes the attitude angle of the robot which can re?ect 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 O

44、Z 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 coe?cient of transverse friction between driving wheels and pipe wall.From Figs.2and 3,we have geometric relationships R ?r th tL sin a x ?L

45、 1cos a tL 2cos b L 1sin a ?L 2sin b s ?R 1h R sin /?R 1sin h z sin /?R 1sin e/h T8TFig.3.Forced diagram.1622Y.Zhang,G.Yan /Mechanism and Machine Theory 42(2007)16181631Ignoring frictional heating,considering a slope angle /of pipe,and according to equilibrium equation of forces and conservation of

46、energy,we can obtain P N ?N 1tN 2?mg cosu cos c ?mg cos u cos c R 1?R 21R 2sin 2/p F d x tf P N d s ?mg d z cos u cos c (e3Twhere P N is the sum of all supporting force.De?ning k 1?L 1eR r h TL 1?L 2eR r h T2p tL 1?L 2L 22L 21eR r h T2p !k 2?R 1sin /?R 21R 2sin 2/p k 3?cos /tR sin 2/?R 21R 2sin 2/p

47、k 4?R 1?R 21R 2sin 2/p 8F ?mg cos u cos c k 1ek 2k 4f tk 3Te5TThen,the output torque of the adjusting motor can be written asT ?p h 2p gF e6Twhere g denotes the transmission e?ciency of the ballscrew pair,P h denotes the lead of the ballscrew.3.3.Mechanism of tractive force adjusting A gas pipeline

48、inspection robot must obtain su?cient 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

49、by the adhesion force which depends on the normal pressure and adhesion coe?cient 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

50、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

51、 motion motor of the robot produces more driving force,the adhesion force only contributed by robot weight may be insu?cient,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 mechanis

52、m 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 p

53、ipe 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

54、adjusting motor.We de?ne 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)161816311623additiona

55、l 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 120apart symmetrically,any attitude angle of the robot

56、 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 de?ne that an attitude angle along counter-clockwise

57、 is positive,and an attitude angle along clock-wise is negative.Then we have N 3?06006c 660N 1?06006c 6180 N 2?018006c 63008N 2cos ec 60 TN 3cos c ?mg N 2sin ec 60 TN 3sin c ?0 60 6c 6180N 3cos c tN 1cos e60 tc T?mg N 3sin c tN 1sin e60 tc T?0180 6c 6300e8TSolving Eq.(8),and considering the slope an

58、gle /,we have X N ?2mg cos c cos u 60 6c 660 2mg cos ec 120 Tcos u 60 6c 6180 2mg cos ec 240 Tcos u 180 6c 63008e10Twhere l denotes the adhesion coe?cient.In Fig.2,we have geometricrelationships Fig.4.Supporting force distribution.1624Y.Zhang,G.Yan /Mechanism and Machine Theory 42(2007)16181631R ?r th tL sin a y ?R hx ?L 1cos a tL