Design of a Mobile Mechanism Possessing Driving Ability and Detecting Function for In-Pipe Inspection

Transcription

1 2008 IEEE Internatonal Conference on Robotcs and Automaton Pasadena, CA, USA, May 19-23, 2008 Desgn of a Moble Mechansm Possessng Drvng Ablty and Detectng Functon for In-Ppe Inspecton Peng L, Shugen Ma, Member, IEEE, Bn L and Yuechao Wang Abstract In ths paper, a moble mechansm wth drvng capablty and detectng functon s proposed for n-ppe nspecton task. Based on ths mechansm, a robot s desgned and fabrcated. The advantage of ths robot s that t has moble ablty n the ppe and detectng functon for nspecton, whle only one DC motor s nstalled. Ths results n low energy consumpton and low cost to make. The robot propels tself n the ppe under a drvng mode, and t s used for fndng the defect of the ppe under a detectng mode. By swtchng these two workng modes, the robot performs the nspecton task wthout other extra DC motors. Moreover, a velocty change mechansm s ntroduced to adapt the change of the payload through adjustng the nclne angle of the roller. The characterstcs of ths mechansm are analyzed by comparson wth a classcal screw drve robot and a drect drve robot. Fnally, basc experments are conducted to testfy the moblty and effcency of ths robot. P I. INTRODUCTION IPELINES have been used n many countres for the transportaton of lquds and gases for decades. Now, the ppelnes should be montored snce they are agng. Some problems, such as cracks, leakages and damages by other reasons, should be detected as early as possble n order to prevent serous accdents. Many ppe nspecton robots have been developed for the nspecton tasks. Hayash et al. developed a ppe robot that employed an external motor to drve tself [1], [2]. Hrose et al. reported the THES seres robots for the nspecton of gas ppes [3]. Toshba Corporaton developed a mcro robot equpped wth a hgh resoluton camera and a par of pneumatc hands for checkng the 1-n ppe [4]. MRINPECT3 developed by Cho and Ryew employed the lnk-type confguraton [5]. Roh developed MRINSPECT4, a wheel type robot based on dfferental drve [6]. A wheel type robot developed by Oya had steerng ablty by addng drvng motors to the wheel jonts [7]. Zhu reported hs ppe robot used for samplng n the sewage ppe [8]. Manuscrpt receved August 18, Ths work s supported by The Natonal Hgh Technology Research and Development Program of Chna (863 Program) (2006AA04Z230). Peng L s wth the State Key Laboratory of Robotcs, Shenyang Insttute of Automaton, Chnese Academy of Scences, Shenyang , Chna. He s also wth the Graduate School of the Chnese Academy of Scences, Bejng , Chna. (e-mal: lpeng@sa.cn; lpeng.brd@gmal.com). Shugen Ma s wth the Organzaton for Promoton of the COE Program, Rtsumekan Unversty, Shga-ken , Japan. He s holdng professor poston at Shenyang Insttute of Automaton, Chnese Academy of Scences, Shenyang , Chna. (e-mal: shugen@fc.rtsume.ac.jp). Bn L and Yuechao Wang are wth the State Key Laboratory of Robotcs, Shenyang Insttute of Automaton, Chnese Academy of Scences, Shenyang , Chna. (e-mal: lbn@sa.cn ycwang@sa.cn). Zagler and Peffer developed a walkng type ppe robot that equpped sxteen motors on eght legs for movng [9]. As seen, the ppe robots are usually equpped wth many motors that have dfferent functons to execute the nspecton task. For example, some motors are used for drvng the robot, whle other motors may be used for postonng the sensor or other devces for detectng the nner surface of the ppe. Because so many motors are used, the robots consume too much energy. For ths reason, the operaton tme to perform a task s reduced and the cost of makng a robot ncreased. In ths paper, we propose a new moble mechansm that reduces the number of the drvng motors, whle the robot stll has the moble ablty and nspectng functon. That s, we are tryng to ncrease the workng effcency of the drvng motor and decrease the cost of the ppe nspecton robot. Moreover, a velocty change mechansm that endows the robot wth adaptablty to the payload on the robot body s ntroduced. Thus, the new robot mposes low requrements to the power supply, and t s a low cost robot. The followng secton ntroduces the concept of the new robot. Secton III shows the desgn of the robot, and the mechansm of the new robot s analyzed n secton IV. Secton V gves the results and experments. Fnally, we offer the concluson at present. II. CONCEPT OF THE NEW MOBILE MECHANISM Snce the ppe envronment s not always fxed, a ppe robot needs adaptablty to the envronment. Furthermore, the ppe robot should not only have the moblty but also carry devces for nspecton. The narrow space constrans the robot s sze, so the robot must make full use of the capacty of the motor. Therefore, an n-ppe robot should possess the characterstcs: multfuncton, adaptablty and effcency. The speed of the wheel type robots s easy to reach a hgh level, and ther tracton force can be ncreased through enhancng the normal force and the adheson coeffcent between the wheel and the nner surface of the ppe. The wheel type drve s thus always employed as the man drvng method for n-ppe robot and s wdely used from small to large ppes, compared to other drvng methods. Wheel type robots can also be dvded nto Drect Drve Wheel type robots (DDW) and Screw Drve Wheel type robots (SDW). As shown n Fg.1, the wheel orentaton of the DDW s parallel to the axs of the ppe. The motors drve the wheels drectly or va the transmsson mechansm. The transmsson s used to reduce the speed of the motor or change the orentaton of the velocty produced by the motors /08/$ IEEE. 3992

2 As shown n Fg.1, the Screw Drve Wheel type robot s usually composed of a rotator, elastc support arms, rollers and a motors for drvng. The rollers have an nclne angle wth respect to the cross secton of the ppe. When the motor turns, the rollers rotate not only wth ther own axes but also around the axs of the ppe. Then the whole body moves forward. If the motor turns reversely, the body moves backward. the ppe s problems. One drvng motor s attached on the stator and support arms that prevent the stator from rollng around the axs of the ppe. The only one motor fxed on the stator provdes both torque of the drvng rotator and that of the detectng rotator. Therefore, the number of the drvng motor s reduced but the robot stll has the moble ablty and detectng functon, and the VCM endows the robot wth adaptablty to the payload. Drvng Motor Drvng Wheel Elastc Support Arm Transmsson Ppe Rotator Fg. 1. Wheel type ppe robot. Drect drve wheel type robot. Screw drve wheel type robot. α Drvng Motor Elastc Support Arm The Screw drve wheel type robot needs less drvng motors, whch results n less power consumpton and more workng tme to operate tasks. Ths type of robot also smplfes the control complexty, compared wth other drvng methods. The proposed robot shown n Fg. 2 s based on the screw drve prncple, and the robot not only has the moble ablty but also has the nspecton ablty n the ppe, whle only one DC motor s used. Ths moble mechansm s composed of a drvng rotator, drvng arms, rollers, a detectng rotator, a stator, support arms and a drvng motor. Top Vew Ppe Axs α Drvng Rotator Stator Detectng Camera Motor Support Arm Head Camera Detectng Rotator Ppe Drvng Arm Fg. 2. Concept of the new robot. Structure of the robot. Top vew of the roller. The drvng arms are fxed each 60 degrees on the perphery of the drvng rotator. The rollers on the drvng arms have an nclne angle wth respect to the axs of the ppe and are pressed onto the nner surface of the ppe. The advantage of the drvng arm s that the roller changes ts nclne angle when the resstance force s altered, and the speed of the robot changes due to the change of the nclne angle. Ths s a Velocty Change Mechansm (VCM). The detectng rotator rotates wth respect to the axs of the ppe and s mounted wth cameras that are used for executng the nspecton task. When the detectng rotator turns, the cameras wll montor the perphery of the ppe s nner surface to fnd III. MECHANICAL DESIGN OF THE ROBOT A. Mechansm wth Drvng and Detectng Functons Because the new robot only uses one motor to drve n the ppe and executes nspecton task, the transmsson mechansm should be consdered carefully before the mechansm s desgned. The requrements are as follows: 1) Moble mechansm for travelng n ppe s necessary. 2) Part of the robot can be used as the base of the electronc devces that are used for nspecton. 3) One DC motor s used to acheve moble and detectng ablty of the robot. The mechansm desgned for the robot should satsfy the above requrements. Fg. 3 llustrates the confguraton of the mechansm n detal. The prncple of ths mechansm s that the power of the motor s transmtted va a couplng to the spur gear 1 and the gear 2. When the motor and the spur gear rotate, the couplng elmnates the offset between them. The spur gear 2 and the sun gear are fxed on the central axs. When the central axs turns, the power of the motor s transmtted to the rng gear, and then the rng gear rotates the drvng arms that are fxed on the perphery of the rng gear. Ths s one route of the power output. Another power output route s that when the motor s actvated, the power s transmtted to the central axs and turns the sun gear, whch turns the planet gears. Fnally, the power of the motor s transferred to the planet gear carrer, whch s used as the base of the detectng devces. The rollers mounted on the drvng arms and the supportng arms are pressed by the force of the compressed sprngs. Moreover, the roller on the drvng arms has an nclne angle wth respect to the axs of the ppe, and ths angle changes when the payload of the robot vares. Rng gear Carrer Head Camera Ppe Sun gear Planet gear Velocty Change Mechansm Detectng Camera ω 3 ω 1 ω H Fg. 3. Moble mechansm of the robot. ω 6 ω 5 represent the Power Flow Route DC Motor Spur Gear Stator Electromagnet Support Arm A swtchng electromagnet that s on the stator always 3993

3 exerts constrans to the planet carrer. As a result, f the motor works, the drvng arms are actvated, whle the planet carrer s not. On the contrary, f the electromagnet s electrfed, the constraned force on the planet carrer dsappears. When the motor rotates, the planet carrer turns, and the drvng arms keep stll. Letω 6, ω3 andω H denote the angular velocty of the spur gear 1, the rng gear and the planet gear carrer of the mechansm n Fg. 3 respectvely. 16 denotes the reducton rato from the sun gear to the spur gear 1, whle K s the rato of teeth of the rng gear to that of the sun gear. We thus obtan the followng equaton 16ω6 + Kω3 = ( K + 1) ωh From, fω H = 0, we obtan the reducton rato from the spur gear 1 to the rng gear, 63, s equal to 61 K ; whenω 3 = 0, the rato from the spur gear 1 to the planet gear carrer, 6H, s equal to 61 ( K + 1). Here, 61 = ω6 / ω1 = z5 / z6 63 = ω6 / ω3 = 61K 6H = ω6 / ωh = 61( K + 1) K = z / z 3 1 Where j denotes the transmsson rato from the th part to the jth part, whle ω and z represent the angular velocty and number of teeth of the th gear respectvely. Consequently, the moble mechansm has two workng modes, whose ratos of transmsson are dfferent from each other. B. Velocty Change Mechansm As mentoned above, the drvng arm fxed on the rng gear can change ts nclne angle accordng to the payload of the robot. The drvng arm s realzed by the mechansm n Fg. 4.Ths mechansm s composed of a rollng block, a rollng rod, a sldng rod, pns, fender blocks, a contaner, a sprng, a gasket, an adjustve blot, and wheels. The sldng rod has a concave, whle the rollng rod has a convex. The sldng rod, whch can only move along wth the slot on the contaner, s pressed on the rollng rod, on whch the rollng block s fxed, by the sprng. When the rollng rod rotates aganst the sldng rod, a resstant torque that s generated by the convex/concave set prevents ths moton trend. That s, to slant the rollng rod an angle(change the nclne angle), there must exst a moment to conquer the resstant torque, otherwse, the nclne angle does not change. A pn and a fender block are attached on the rollng rod and the sldng rod, whch are used to lmt the relatve poston between the rollng rod and sldng rod. A gasket and an adjustve blot that are used for settng the ntal force of the sprng are arranged at the bottom of the sprng. Zhu used trapezod shape wheels to keep the robot from rotatng around the axs of the ppe [8]. Here, we use the trapezod shape wheels for ncreasng the contact area, when the robot surmounts the obstacle. The nclne angle of the roller on the drvng arm has nfluence on the translated velocty of ths type robot (see next secton). If the angle vares, whch means the concave/convex set relatve poston changes, accordng to the payload exerted on the robot, the velocty of the robot wll change wth the payload. That means f the payload ncreases, the velocty of the robot wll decrease. Concave/Convex Set (c) Compressed Sprng Wheel Gasket Adjustve Blot Fender Block Slot Slder Contaner Pn Sldng Rod Rollng Rod Rollng Block Fender Block Fg. 4. Velocty change mechansm. Detaled structure of the VCM. Prototype of the VCM. (c) Zoom n the concave/convex set. C. Workng Mode of The Robot The proposed robot has two typcal workng modes, as seen Fg. 5. 1) Drvng Mode: Under the drvng mode, the drvng motor rotates the drvng arms, whle the planet carrer does not turn because of the constraned force exerted by the swtchng electromagnet. Thus, the rotatng arms generate tracton force to propel the robot forward or backward. The rato of the drvng mode 63 s less than 6H, so the robot travels quckly under ths mode, as shown n Fg. 5. 2) Detectng Mode: When electromagnet s electrfed, the constrant actng on the planet carrer dsappears. The motor turns the planet carrer rather than the drvng arms. Therefore, the robot uses the detectng devce to check the defects of the nner surface of the ppe, as shown n Fg. 5. Movng Drecton Defects Drvng Mode (c) Fg. 5. Two workng modes of the robot. Detectng Mode Detectng After checkng the area, the robot s back to the drvng mode agan and goes on movng to reconnotre other suspcous area, as shown n Fg. 5(c) and (d). Although the robot s equpped wth one DC motor, t has both moble ablty and nspecton ablty. Wth the drvng motors number decreasng, the power consumpton and the cost of the robot drop and the workng effcency of the (d) 3994

4 drvng motor s ncreased. D. Front Camera Installaton A CMOS camera module s nstalled at the head of the robot for nspecton. The posture of robot body s changng more or less for most of n-ppe robots, so the camera module can not be nstalled to the robot body drectly. To solve ths problem, a mechansm n Fg.6 s proposed. The gear1 s fxed on the central axs of the robot, and the camera frame can rotate around the central axs, and the gear 2 can rotate around ts own axs that s fxed on the camera frame. When ths mechansm s dsturbed by other factors and slants a small angleθ, the mechansm returns to ts balance poston all by tself. Thus, the change of the robot s posture does not affect that of the orentaton of the camera. The camera s wreless, whch avods the problem of twstng the sgnal cable. Fg. 7 shows the raw mage captured from the head camera and Fg. 7 shows that a hole wth 2mm s detected by the detectng camera. A prototype based on the proposed mechansm has been fabrcated, whch s shown n Fg. 8. Man parameters of the robot are lsted n table I. IV. ANALYSIS OF THE NEW ROBOT WITH THE DIRECT DRIVE ROBOT A. Knematcs The nner dameter of ppe s D, as shown n Fg. 9. C denotes the centrod of the robot, and O denotes the center of the roller on the drvng arms or the drvng wheel. Pont C 1 denotes the rollng centre of O wth respect to the axs of ppe. Orthogonal unt vector, j and k are defned at the centrod of the robot, and Q denotes the contact pont between the rollers or wheels and ppe. Orthogonal unt vectors h, g and k are fxed to the centre of the roller or drvng wheel, and α denotes the nclne angle of h wth respect to the cross secton of ppe. g h α L Q k o C 1 j k C D k Q h o Drvng Wheel j k C Camera Frame Central Axs Gear1 Gear2 Wreless Camera Battery for θ The Camera Unbalance Poston Balance Poston Fg. 6. Installaton of the camera system. Front vew. Back vew. Fg. 7. Raw mage from the cameras. Image from the head camera. Image from the detectng camera. Drvng Arm Head Camera Detectng Camera Trapezod Wheel Fg. 8. Prototype of the proposed robot. Electromagnet Drvng Motor Stator Support Arm TABLE I SPECIFICATIONS OF THE NEW ROBOT Max-Mn Dameter 205~175mm Total Weght(wth camera) 1.95Kg Rato of Transmsson 2(drvng mode), 3(detectng mode) r w w r Fg. 9. Knematc model. Model of the screw drve type ppe robot. Model of the drect drve type ppe robot. In Fg. 9, r c and o denote the velocty of C, and O. vcc 1 and v s the relatve velocty of C wth respect to C 1 and the relatve velocty of C 1 wth respect to O. ω12 s the relatve angular velocty of the drvng arm wth respect to the stator, ω3 s the scalar angular velocty of the drvng arm, andϕ s the th scalar angular velocty of the roller on the drvng arm, respectvely. If the drecton of the angular velocty s clockwse looked from the head of the robot, t wll be a negatve value. Otherwse, t wll be postve. r w s the radus of the roller. The velocty relatons of the robot are as follows r = o + v + v (3) c cc 1 ( ϕ ) o = ω + g r (4) 12 w = 12 OC 1 v ω (5) ω 12 = ω3 (6) The relatonshp between h, g and, j s h snα cosα = cosα snα g j (7) From (3) to (7), the velocty of screw drve type s gven by rc = ω3( rw + L) tanα (8) In Fg.9, when the drect drve robot s movng n the straght ppe, ts velocty r c s r = ω r c w w (9) Whereω s the scalar angular velocty of the drvng wheel. w 3995

5 B. Velocty-load Relatonshp In Fg.10, F dj represents the frcton force along the normal drecton, and F rj represents the frcton force along the tangental drecton. The superscrpt, such as and, denotes the correspondng value at dfferent postons or postures. Fre denotes the sum of all the other resstant forces, and M drve s the drvng torque actng on the robot. n s the number of the drvng arms. Now, we obtan n F cosα F snα = F (10) ( ) ( α α) dj rj re dj rj drve n F sn + F cos = M / 0.5D (11) From (10) and (11), fn cosα ft snα 0.5DFre = (12) fnsnα + ft cosα Mdrve Where f n and f t s the frcton coeffcent n the normal drecton and tangental drecton respectvely. F dj α 0 F rj M drve F re F N F dj e γ F N F rj F dj F F n n γ r F fn F sp F sp F fn F rj (c) Fg. 10. Forces actng on the robot. Forces a on the man body. Forces on the drvng arm. (c) The forces slant the wheel an angle of Δ α. In Fg. 10, 2( cosγ snγ) ( γ γ) F F = F (13) n fn sp n fn r dj 2 F sn + F cos r = F e (14) Where F n s the contact force between the rollng rod and the sldng rod, Ffn s the frcton force due to F n, Fsp s the force of sprng, γ s the angle of the contact mate, r s the radus of the rod, e s the offset, and f c s the frcton coeffcent of the contact mate, respectvely. ( cosγ fc sn γ) Fsp = (15) ( snγ + fc cosγ) r Fdj e Fg. 10(c) shows that the rollng rod turns an angle of Δ α. So Fsp = Fsp + 2krr tan( γ ) Δ α / π (16) Then, the nclne angle at ths tme s α = α0 Δ α (17) Thus, equaton (8), (10)-(12) should be updated by (17). Consderng of the drven character of a DC motor, we obtan nm = n0 gmm (18) Where n m s the speed of the motor, and n0 s the speed under free load. M m s the torque generated by the motor, whle g s defned as Δnm / Δ Mm. Let total = mt and η = ηη m t. Here, and m t denote the transmsson rato of the motor reduce head and transmsson of the robot respectvely. η m andη t denote the effcency of the motor reducer head and transmsson of the robot. n drve and M drve are the speed and torque actng on the drvng arms and the drvng wheels. 2 n / / drve = n0 total gmdrve totalη (19) Now, we substtute (19) nto (8), the velocty- load character of the new robot s derved as 2 rc = π( rw + L)tan( α0 Δα)( n0 / total gmdrve / totalη)/30 (20) For the drect drve ppe robot, the torque actng on the wheel can be wrtten as M drve / rw = F re (21) Substtute (19) and (21) nto (9) 2 r c = πrw ( n0 / total gm drve / totalη)/30 (22) Equaton (22) s the velocty-load character of the drect drve type ppe robot. C. Computer Smulaton The parameters are set as follows: n=3, γ = 20, r r =4mm, e=3mm, k=0.5n/mm, F sp =5N, whle same parameters of motor and transmsson are used for dfferent knds of robots. The drvng motor parameters are lsted n table II [10]. Other parameters are set as: t =3, η t =0.75, r w =10mm, and the envronment parameters are D=190mm, f n =0.5, f t =0.01, f c =0.25. TABLE II PARAMETERS OF THE MOTOR V rated =24v n 0 =5390rpm n max =7300rpm g=103rpm/mnm η m =0.8 m =199 Fg. 11 gves the comparson of the robot wth velocty change mechansm (VCM) and the classcal screw drve robot, where the angle of the roller s 20. It s known that the angle decrease wth respect to the payload ncrease n the proposed mechansm, whle there s no any change n the classcal screw drve robot. Fg. 11. Payloads-nclne angle relaton. Fg. 12, and (c) gve the comparsons of the screw drve robot wth velocty change mechansm, the screw drve robot wth a constant angle of 20, and a drect drve robot, whle Fg.12(d) shows velocty-payload calculaton at dfferent speed of the proposed screw drve robot. From the 3996

6 results, t s known that when the same payload acts on the robots, robot wth velocty change mechansm moves faster. (c) (d) Fg. 12. Comparsons of the screw drve type and the drect drve type robots. Velocty-payload relaton of the screw drve robot wth VCM and the drect drve robot, whle Δα vares from 0 to Velocty-payload relaton of the screw drve robot wth a constant nclne angle of 20 and the drect drve robot. (c) Drvng characterstcs of the drect drve robot. (d) Velocty-payload calculaton at dfferent speed of the screw drve robot wth VCM. V. EXPERIMENTS To confrm the moblty of the proposed mechansm, experments have been conducted. The envronment s a ppe wth dameter of 200mm that has a hole defect. The head camera and the detectng camera are attached on the robot as the vson system for nspecton. Fg.13 shows that the robot propels n ppe under the drvng mode, whle the robot stops to check the defect area usng the camera on the detectng rotator n Fg.13. The robot goes on propellng, as seen n Fg.13(c) and (d). Fg. 13(e) shows the robot s examnng a small hole whose mage s n Fg. 7. In Fg. 14, the envronment s composed of ppes wth dfferent dameters and a concentrcally step s formed at the conjuncton of the two ppes. Fg. 14 and shows that the robot moves n the larger ppe, and the robot s checkng the suspcous area n Fg.14(c) under the detectng mode. In Fg.14(d), the robot s overcomng the concentrc step wth the heght of 5mm usng ts trapezod shape wheels. Fnally, the robot entered n the smaller ppe entrely. VI. CONCLUSION A new moble mechansm for n-ppe nspecton robot has been proposed n ths paper. The prototype has both moble ablty and checkng functon for nspecton whle only one DC motor s equpped. Ths makes the robot be effcent n low energy consumpton and low cost to make. The robot moves n the ppe under the drvng mode, and t can fnd the defect of the ppe under the detectng mode wthout usng any extra motors. Furthermore, velocty change mechansm has also been ntroduced and the performance of the robot equpped wth ths mechansm has been analyzed. Smulaton shows the mechansm has the adaptablty to the payload. Fnally, the moblty of the robot and ts effcency have been confrmed by the experments as well. REFERENCES [1] S. Iwashna, I. Hayash, N. Iwatsuk, and K. Nakamura, Development of In-Ppe Operaton Mcro Robots, n Proc. Int. Symp. Mcro Machne, Human Scence, 1994, pp [2] I. Hayash, N. Iwatsuk, and S. Iwashna, The runnng characterstcs of a screw-prncple mcrorobot n a small bent ppe, n Proc. Int. Symp. Mcro Machne, Human Scence, 1995, pp [3] S. Hrose, H. Ohno, T. Mtsu, and K. Suyama, Desgn of n-ppe nspecton vehcles forφ25,φ50,φ150 ppes, n Proc. IEEE Int. Conf. Robotcs, Automaton, 1999, pp [4] K.Suzumor, T.Myagawa, M.Kmura, Y.Hasegawa, Mcro Inspecton Robot for 1-n Ppes, IEEE/ASME Trans. Mechatroncs, vol. 4, no. 3, pp , [5] H.R. Cho, and S.M. Ryew, Robotc system wth actve steerng capablty for nternal nspecton of urban gas ppelnes, Mechatroncs, vol. 12, pp , [6] S.G. Roh, and H.R. Cho, Dfferental-drve n-ppe robot for movng nsde urban gas ppelnes, IEEE Trans. Robotcs, vol. 21, no. 1, pp. 1-17, [7] T. Oya, and T. Okada, Development of a steerable, wheel-type, n-ppe robot and ts path plannng, Advanced Robotcs, vol. 19, no. 6, pp , [8] C. Zhu, In-ppe robot for nspecton and samplng tasks, Industral Robot: An Internatonal Journal, vol. 34, no. 1, pp , [9] A. Zagler, and F. Pfeffer, "MORITZ" a ppe crawler for tube junctons, n Proc. IEEE Int. Conf. Robotcs, Automaton, 2003, pp [10] Maxon Motor Catalog, Maxon motor Co., Ltd. 2004, p.115. Hole 200mm Detectng The Hole Fg. 13. Test of the proposed mechansm. 195mm Defect Drvng Mode 200mm Concentrc Step Defect Fg. 14. Concentrc step surmountng experment. Detectng Mode Detectng Mode (c) (d) (e) Drvng Mode (c) (d) (e) 3997