1 0.5 L. V c V b. V a. A rc A B. A rc P D A. D riv in g ra n g e. N o m in a l p ip e, e lb o w, re d u c e r, b ra n c h, e tc.

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ctively Steerable Inpipe Inspection Robots for Underground Urban Gas ipelines S G Roh, S Ryew, J H Yang, H R hoi School of echanical Engineering, Sungkyunkwan University 300, honchon dong, Jangan gu,

1 ctively Steerable Inpipe Inspection Robots for Underground Urban Gas ipelines S G Roh, S Ryew, J H Yang, H R hoi School of echanical Engineering, Sungkyunkwan University 300, honchon dong, Jangan gu, Suwon, Kyonggi do, Korea, , hrchoi@mechaskkuackr Seoul ity Gas R&D enter bstract In this paper we introduce robots called RINSET (ultifunctional Robotic crawler for INpipe inse- Tion) III and IV which are under development for the inspection of urban gas pipelines The proposed robots can freely move along the basic configuration of pipelines such as horizontal or vertical pipelines oreover it can travel along reducers, elbows, and steer in the branches by using steering mechanisms Especially, their three dimensional steering capability provides outstanding mobility in navigation that is a prerequisite characteristic in urban gas pipelines Their critical points in the design and construction are introduced with preliminary results of experiments 1 Introduction Thereareawidevariety of pipelines such as urban gas, sewage, chemical plant, nuclear power plant etc, which are indispensable in our life lso, pipelines are the major tools for transportation of oils and gases and anumber of countries employ pipelines as the main facilities for transportation In our country, the urban gas pipelines currently goupto 13,000 Km long but since most of them have been constructed in 1980's, there happen a lot of troubles caused by aging, corrosion, cracks, and mechanical damages from third parties ontinuous activities for inspection, maintenance and repair should be performed from now on However, those activities need enormous budgets that may not be easily handled by gas companies as they are mostly small and medium in size Efficient equipments for inspection and integrated maintenance program are required in gas industries Figure 1: RINSET III Up to nowvarious inpipe robots have been reported [1,2] but those robots just have the capability oftraveling along straight pipelines with elbows Few of them have been designed under the consideration of branched pipelines In fact branched pipelines are one of the most popular configuration in underground urban gas pipelines and thus to conduct efficient traveling inside those pipelines steering capability is prerequisite For last several years, we have developed several inpipe inspection robots with steering capability, and this paper introduces the robots named RIN- SET III and IV among them which have been recently developed( refer to [3] as for RINSET I and II) oth robots have totally different features in steering that may be regarded as the original ones, respectively In this paper RINSET III is briefly overviewed and a new robot RINSET IV is described in detail Several specific features are addressed concentrating on the steering and preliminary results of experiments are outlined This paper is organized as follows In the next sec-

tion we briefly introduce RINSET III Section 3 cover the issues related to the development of RIN- SET IV and preliminary experiments Finally we conclude with summary in section 4 2 RINSET III lable

legs employ a pantograph mechanism with a sliding base that ensures natural folding and unfolding of the body With the proposed mechanism the legs just contract or expand along the radial direction

protrusions inside the pipelines The driving motor of the vehicle is included in the rear articulated body which gives the major driving force to the system The front bodydoesnothave anypower and it

2 tion we briefly introduce RINSET III Section 3 cover the issues related to the development of RIN- SET IV and preliminary experiments Finally we conclude with summary in section 4 2 RINSET III lable two dof joint and it makes it possible to control the compliance of active joints in steering [4] Each articulated body of the robot has three wheeled legs located circumferentially 120 ffi apart The legs employ a pantograph mechanism with a sliding base that ensures natural folding and unfolding of the body With the proposed mechanism the legs just contract or expand along the radial direction when they are pressed It is a quite advantageous feature because undesirable forces causing distortion does not exert on the body when the robot goes over obstacles such as steps,reducers, protrusions inside the pipelines The driving motor of the vehicle is included in the rear articulated body which gives the major driving force to the system The front bodydoesnothave anypower and it just guides the motion The wall pressing forces are obtained by the reflective forces of the spring that supports the moving base of the pantograph mechanism Thus, the wall pressing forces can be easily preset depending on the payload by adjusting the spring constant and initial deflection Fig 2 shows the whole inspection system utilizing RINSETION III which is composed of two RINSET III's, control modules, and inspection tools 3 RINSET IV 31 echanism Overview s illustrated Fig 1 RINSET III consists of two vehicle segments and a steering mechanism called Double ctive Universal Joint(DUJ) between the segments This robot is configured as an articulated type where two independent vehicles are connected via a double active universal joint providing omni directional steering capability DUJ acts like a stiffness control- ' H J D I J * =? D IJ, & # ' E # &# + +, D I J Figure 3: onstruction and specification of RIN- SET IV Figure 2: Inpipe Inspection System RINSET IV shares several aspects with RIN- SET III but most of the mechanism has been renewed to miniaturize the robot as shown in Fig 3 The robot is largely composed of 1) a body frame that mounts a D camera assembly and driving modules with foldable linkages, 2) a camera assembly which is for the navigation and the visual inspection of the pipelines, and 3) three modularized driving modules illustrated in Fig 4 which are located circumferentialy with 120 ffi apart 5K>9 D ) N EI H >=? / =HIJ 1@ 9 5FKH/ =H 9 H 9 D 9 D J H-? H@H D 9 H Figure 4: Driving module driving module consists of a D motor with an encoder and a reducer, several wheels and casings s it can be easily disassembled from the body frame, it ensures the convenience in maintenance The driving units can be controlled independently and thus they amplify the tractive forces as well as provide steering capability To provide the sufficient tracting forces and flexibility innavigation we designed a body frame illustrated in Fig 5 t the end of the legs on the

body frame three driving modules are xed 120Æ apart circumferentially y L 1 0 5 L 1 3 0 6 0 Æ S p r in g G x y, y o v in g d ir e c tio n o f W h e e l a x is x, x Figure 5: Link mechanism Two wheels

the wall Distance between the main shaft of the robot and the wheel changes according to the link construction, and it makes the wheel have e ective contact with the wall inside the pipelines

3 body frame three driving modules are xed 120Æ apart circumferentially y L L Æ S p r in g G x y, y o v in g d ir e c tio n o f W h e e l a x is x, x Figure 5: Link mechanism Two wheels of the driving module move independently along the radial direction due to constraints of links and interaction between elastic force at the main spring of the body frame and the reaction forces of the wall Distance between the main shaft of the robot and the wheel changes according to the link construction, and it makes the wheel have e ective contact with the wall inside the pipelines whatever diameters changes It assures stable traveling as long as providing suæcient traction forces Front wheel of each driving module have been synchronized each other s shown in Fig 3, wheels in front and back of each driving module are named the front wheel set and the back wheel set, respectively onstraint of the wheels inside each wheel set makes the robot capable of neglecting the e ect of gravity, which makes the central axis of the robot always coincide with that of the pipelines D r iv in g V e h ic le D r iv in g V c D o u b le c tiv e U n iv e r s a l J io n t V b o d u le SET IV does with speed di erences of each driving module Fig 6 illustrates the distinction of the steering action between RINSET III and IV RINSET III turns the front body by using DUJ like a manipulator In this case the robot should not rotate along the driving direction due to the contact constraint between the wheels of the robot and the wall, which is coped with DUJ On the contrary RINSET IV steers its own body with the velocity differences among the driving modules Thus, though it does not require complicated mechanisms, its control becomes quite diæcult The analysis related to the steering control is addressed in the later Se c ti o n - L in k e c h a n is m o n tro lle r O p e ra tio n D riv in g ra n g e R I o n w ith a N S tro l D n to g 32 Navigation in Elbow asically the size of the robot is the critical points in the design in realizing the movement in the elbow The basic relations and analysis can be found in the reference [3] and in this section we focus on the additional features in the navigation along the elbow R V a R IN S E T IV (fo r 4 in c h ) o n tro l u s in g d iffe re n tia l s p e e d o f d riv in g m o d u le s E T III(fo r 8 in c h ) o f d irc tio n v e h ic le U J ra p h m e c h a n is m a n to g ra p h m e c h a n is m m o u n te d w ith ro b o t E x te rn a l J o y s tic a n d k e y b o rd Figure 7: Straight to elbow D ir e c tio n V e h ic le S te e rin g O rc rc s e p a ra te d, d Figure 8: Robot in elbow To travel smoothly along the elbow it should be considered the curvature of the elbow varies depending upon the inner area of the pipelines having contact with the robot When speeds of all of the wheels are same, the wheels in the outer side may be caused to slide, which K e y b o rd N o m in a l p ip e, e lb o w, re d u c e r, b ra n c h, e tc Figure 6: omparision of RINSET III and IV RINSET IV has upgraded RINSET III in many aspects, especially in the steering mechanism RINSET III performs three-dimensional steering with a double active universal joint, while RIN763

33 S tr a ig h t ip e S e c ti o rc rc R n - s shown in Fig 11 branches can be considered to consist of two elbows and V-shaped area between the elbows The V-shaped area has a at surface rather E lb

but it is a control work requiring careful observation When the robot turns to the elbow from the straight pipelines the front wheel set of the robot is to be placed at inner area of the elbow, while

angle Æ with the cross section of straight pipeline s the robot enters the elbow, the angle Æ increases When the robot R rc E lb o w E lb o w re a V N o r m a l ip e (a) Elbows (b) Flat area Figure

has been designed to be suitable for the curved surface To travel in the branch the robot basically follows the method similar to the method in the elbow but there are several characteristic features

4 33 S tr a ig h t ip e S e c ti o rc rc R n - s shown in Fig 11 branches can be considered to consist of two elbows and V-shaped area between the elbows The V-shaped area has a at surface rather E lb o w Navigation in ranch S e c tio n - Figure 9: oving trajectory in elbow gives overload to the driving system Thus each driving module of the robot can adjust its speed according to the curvature but it is a control work requiring careful observation When the robot turns to the elbow from the straight pipelines the front wheel set of the robot is to be placed at inner area of the elbow, while back wheel set is to be located at the straight pipeline shown in Fig 7 The cross section connecting contact points between rear wheel of the robot and walls with the axis of the pipeline has an angle Æ with the cross section of straight pipeline s the robot enters the elbow, the angle Æ increases When the robot R rc E lb o w E lb o w re a V N o r m a l ip e (a) Elbows (b) Flat area Figure 11: Formation of branch than curved one and the at surface can be found out only in the V-shaped area throughout the pipeline onsequently, the V-shaped area may be an obstacle to the robot because it has been designed to be suitable for the curved surface To travel in the branch the robot basically follows the method similar to the method in the elbow but there are several characteristic features that makes it diæcult to control its motion Those can be summarized as follows First, as the robot moves along the branch, it meets a variety of cross sections depending on the posture of the wheel as shown in Fig 12 In the second, the robot has rc, d S tra ig h t D riv e Figure 10: Dependence on posture completely gets into the elbow, its center moves along rc having the curvature R from the center of the curvature, and has the o set d with the center of curvature depicted in Fig 8 Section - in Fig 9 is the range where the center of the robot moves between the straight pipeline and the elbows, while section is the range where the robot is completely placed in the elbow rc R is the route where the center of the robot moves as depicted in Fig 10 ecause the robot is driven by the independent driving modules located 120Æ apart, the contact area varies depending on the posture the robot Thus o set distance between the center of the robot and the pipeline axis varies depending on Æ ased on the those observations we should calculate the route of travel, which is the basic for modulating the speed di erences 764 rc R T u rn D riv e T rc (a) ranch (b) ross section - Figure 12: hange of cross section been designed to move while making six wheels have contact with the inner side of the pipe radially Nevertheless when the robot enters a branch, some of the wheels may not have contact with the wall ccording to Fig 12 the cross section does not have a circular shape any more in the branch and some of the wheels may carry idle rotations In this case the robot loses its degree of motion and consequently we may not able to

control its travel route exactly When the robot turns in a branch, its center is assumed to move along the curve like rc RT as illustrated in Fig 12 that has di erent meaning from rc R, rc and rc of

the pipeline does not change a lot until the front wheel set reaches section - after passing through section - illustrated in Fig 13, but the robot cannot rotate in this region whatever speed di

that each wheel contacts the points) D S e c tio n D -D S e c tio n - Figure 13: onstraint space in branch When the front wheel set comes to the section, the diameter of the pipeline changes greatly

drive space because the front wheel set is still placed close to inner side of the pipeline lso, the front wheel set of the robot has still contact with the inner side of the pipeline and as the

5 control its travel route exactly When the robot turns in a branch, its center is assumed to move along the curve like rc RT as illustrated in Fig 12 that has di erent meaning from rc R, rc and rc of the elbow because these rcs of the elbow are a deterministic path produced by the robot while its wheels keep contact with the inner walls When the robot enter the branch, initially the diameter of the pipeline does not change a lot until the front wheel set reaches section - after passing through section - illustrated in Fig 13, but the robot cannot rotate in this region whatever speed di erences are given S e c tio n - S tr a ig h t D r iv e S p a c e S e c tio n - T u r n D r iv e S p a c e z b a 8 x ) y c ) D D r iv e h o ic e S p a c e the pipeline(this is based on the assumption that each wheel contacts the points) D S e c tio n D -D S e c tio n - Figure 13: onstraint space in branch When the front wheel set comes to the section, the diameter of the pipeline changes greatly to let the robot travel toward turn drive space represented in Fig 13 Even at this region, the robot can not rotate by itself with speed di erences In this region, the robot travels toward the turn drive space because the front wheel set is still placed close to inner side of the pipeline lso, the front wheel set of the robot has still contact with the inner side of the pipeline and as the wheel set is con ned absolutely up to this section, it cannot rotate by using speed di erences In fact, despite speed di erence of the robot wheel only slip is produced between the wheels and inner sides of the pipelines, and the robot cannot rotate to the direction that it has to move s a result, in this region the robot can still select either straight travel or rotation and thus this space is said to be drive choice space When the front wheel set is close to section D-D, either one or two wheels, which are placed at the turn drive space, do not contact inner side of the pipe Such a phenomenon indicates that there exists no inner side of the pipe contacting the wheel, which may prevent the robot from moving to the turn drive space In this region, the robot can turn along the desired direction with speed di erences Thus as soon as the robot enters the branch, it decides the direction of rotation using D camera attached in the front of the robot, and then adjusts the rotational speed of each three driving modules In Fig 14 a, b and c indicate the points where each wheel contacts the inner side of 765 Figure 14: Three dimensional representation of related velocity vectors It also shows the rotational direction of the robot when only the wheel at a rotates while two wheels remain without rotating When speeds at a is V and speeds at b, c are 0 respectively, the robot turns with! of angular speed along the direction of the vector connecting b and c s explained, the robot actually starts to rotate at section D-D, and the speed di erences does not have a lot of in uence on the rotation in front of the section D-D Thus, we just need to start modulating the speeds of the wheels at the section D-D and to turn the robot to the desired direction, the rotation speed should be controlled accordingly as shown in Fig 15 To turn the robot, rst V at c assuming that it is the place closest to the rotational direction z, is set to be 0 Using theæ D camera we already know the angles, + 120, and + 240Æ between z -axis and wheels, respectively! z b G o c = 0 a x a b c c = 0 b p a Figure 15: Turning at section D-D of the angular speed can be freely selected to let the robot rotate, but V, and V have to be decided to select the robot's travel speed at contact points between each wheel and inner wall of the pipeline The

following equation can be used to derive V, and V!a = V 23 a (1)!b = V 32 b (2) b!b = 0 (3) Æ b!a = j b jj!

in the branch F ro n t v ie w S id e v ie w S te p 1 S te p 2 Figure 18: Steering in branch other robots The steering is very important in underground pipelines, especially in urban gas pipelines and

reliminary Experiments In the experiments we demonstrated the movement in the elbow with 90Æ and the steering in the branch Fig 16 shows the scene of the robot running along the elbow and Figs 17 and

Structural Integrity Research enter at the Sung Kyun Kwan University References Figure 16: Robot in elbow F ro n t v ie w S te p 1 S te p 2 Figure 17: Straight drive in branch 5 onclusion In this

6 following equation can be used to derive V, and V!a = V 23 a (1)!b = V 32 b (2) b!b = 0 (3) Æ b!a = j b jj!a j cos150 (4) Those are the basic equations for navigation in the branch and in reality a lot of unexpected patterns of movements can be met It need further research to completely analyze the motion in the branch F ro n t v ie w S id e v ie w S te p 1 S te p 2 Figure 18: Steering in branch other robots The steering is very important in underground pipelines, especially in urban gas pipelines and the proposed robots proves their e ectiveness through real implementations s the further work, we are going to implement NDT inspection tools on our robot and related works will be continued 4 reliminary Experiments In the experiments we demonstrated the movement in the elbow with 90Æ and the steering in the branch Fig 16 shows the scene of the robot running along the elbow and Figs 17 and 18 depicts the steering in the branch which has 90Æ of the curvature angle cknowledgments The authors are grateful for the support provided by a grant from Seoul ity gas R&D center and the Safety and Structural Integrity Research enter at the Sung Kyun Kwan University References Figure 16: Robot in elbow F ro n t v ie w S te p 1 S te p 2 Figure 17: Straight drive in branch 5 onclusion In this paper we introduces two inpipe inspection robots, RINSET III and IV The system with RINSET III has already been developed as shown in Fig 2 but the system for RINSET IV is under development oth robots has the characteristic features in steering which are not discussed in the 766 [1] Y Kawguchi, I Yochida, H Kurumatani, and T Kikuta, \Development of an In{pipe Inspection Robot for Iron ipes," J of the Robotics Society of Japan, Vol 14, No 1, pp 137{143, 1996 [2] S Hirose, H Ohno, T itsui, and K Suyama, \Design of In{pipe Inspection Vehicles for 25; 50; 150 pipes", roc of IEEE Int onf on Robotics and utomation, pp , 1999 [3] H R hoi, S Ryew, S W ho, \Development of rticulated Robot for Inspection of Underground ipelines", Trans of the 15th Int onf on Structural echanics in Reactor Technology(SiRT-15), Vol3, pp , 1999 [4] S Ryew, S H aik, S W Ryu, K Jung, S G Roh, H R hoi, \Inpipe Inspection Robot System with ctive Steering echanism" IEEE Int onf on Intelligent Robot and Systems(IROS 2000), pp , 2000

Navigation Inside Pipelines with Differential Drive Inpipe Robot

Navigation Inside Pipelines with Differential Drive Inpipe Robot avigation Inside Pipelines with Differential Drive Inpipe Robot Se-gon Roh School of Mechanical Engineering, Sungkyunkwan University 300, Chonchon dong, Jangan gu, Suwon, Kyonggi do, Korea, 440 746, robotian@mecha.skku.ac.kr