(斜拉桥缆索机器人的发展)Development of cable maintenance robot for cable-stayed bridges

Research articleDevelopment of cable maintenance robotfor cable-stayed bridgesJun Luo,Shaorong Xie and Zhenbang GongCollege of Mechatronics Engineering and Automation,Shanghai University,Shanghai,People’s Republic of China,andTiansheng LuCollege of Mechanical Engineering,Shanghai Jiaotong University,Shanghai,People’s Republic of ChinaAbstractPurpose–In order to replace the conventional human maintenance of cable-stayed bridges,a robot is designed and constructed for tasks such as cleaning,painting and rust-detecting.Design/methodology/approach–Adopting a modular approach,two kinds of climbing mechanisms,plus a painting mechanism and a rust-detecting method are designed.Findings–A robot that can climb and maintain the cables of cable-stayed bridges has been designed and constructed.It has been proved by experiment that the robot can overcome many disadvantages of conventional human bridge-maintenance,and drastically improve efficiency,cost,and safety.Research limitations/implications–The robot is of industrial size,but a new mechanism requiring less installing time will be designed for the future. Practical implications–The robot has been applied to cables of the Nanpu Bridge and Xupu Bridge in Shanghai.More than80cable-stayed bridges and six suspension bridges have been built or are being constructed across large rivers in China alone.This gives an enormous potential market. Originality/value–The cable maintenance robot developed in this paper is the world’sfirst special robot for the cables of cable-stayed bridges.Keywords Robotics,Cable bridges,ChinaPaper type Research paperIntroductionCable-stayed bridges are developing rapidly because of their anti-seismic characteristics,low cost and elegant appearance. Since,the construction of Shanghai’s Nanpu Bridge in1987 with a main span of423m,China has begun a new wave of constructing long-span cable-stayed bridges.Currently,more than80cable-stayed bridges and six suspension bridges have been built or are being constructed over the country’s large rivers.According to incomplete statistics,400cable-stayed bridges have been built in the world from the Stromsunel Bridge to the Xupu Bridge(Lin,1994).These cable-stayed bridges play an important role in economic development and city enhancement.With the development of these cable-stayed bridges,many challenging technical problems have emerged concerning design,construction and maintenance.Cables are the main supporting components of cable-stayed bridges,and since they are exposed over a long period to air,wind,rain and sunshine,the polyethylene sleeves on the cable surface harden and crack to different extents.This can cause serious problems such as rust spots and breaking of the steel wires within the sleeve.Therefore, regular cleaning and painting of the cables is necessary not just for enhancing the bridge with colourful cables,but also for its protection.Some countries began to clean and paint the cables of cable-stayed bridges using manual methods,for example on the Golden Bridge,USA and the Xupu Bridge in China.So far two methods have been adopted:hydraulic lifts for small cable-stayed bridges,or hanging brackets for the workers,tools,paint and so on,dragged with steel wire by a fixed pulley installed on the top of the bridge,as shown in Figure1.The latter method has low efficiency,high cost,and is less safe.T o address these problems,it is important to develop a cable maintenance robot(CMR)to clean,protect and improve the appearance of the cables with higher efficiency,lower cost and better safety.At present,there is no report of a CMR being applied to a cable-stayed bridge,but there are reports of some special robots which are similar in concept.Fukuda designed a series of external-pipeline diagnostic robots,Mark I-IV,consisting of three linked modules.These robots are capable of straightThe current issue and full text archive of this journal is available at /0143-991X.htmIndustrial Robot:An International Journal34/4(2007)303–309q Emerald Group Publishing Limited[ISSN0143-991X] [DOI10.1108/01439910710749627]This project is supported by National Natural Science Foundation of China(No.5040504660605028),Program for Excellent Y oung T eachers of Shanghai(04Y0HB094)State Leading Academic Discipline Fund (Y0102)and Shanghai Leading Academic Discipline(BB67).and spiral movements along the outside of a pipeline,and freely pass over obstacles such asflanges and T-joints,and they can move along vertical pipelines(Fukuda and Hosokai, 1992a,b).Higuchi and Maeda(1991)developed a mobile inspection robot for power transmission lines.This is equipped with four crawlers,two arms with pulleys,and four actuators that run on the earth wire stretched over the top of the pylons.However,this robot cannot climb power transmission lines with a large gradient.Almonacid et al. (2003),proposed a novel application of the Stewart-Gough parallel platform as a climbing robot that can climb through long structures describing unknown spatial trajectories,such as palm trunks and tubes.T avakoli et al.(2005)designed a hybrid four-degree-of-freedom mechanism and a unique gripper for pole-climbing robots.These devices are able to climb through spatial trajectories such as cylinders,tubes and so on,but it is difficult for these robots to climb the spiral hexed-prism shaped cables of cable-stayed bridges.Therefore, new mechanisms have been designed for a series of cable maintenance missions including cleaning,painting and rust-detecting.ModularizationBefore designing the new CMR system,the authors decided on a modular approach:the CMR is designed separately in two modules,a climbing module and maintenance module, linked by a standard mechanical interface.This method has high efficiency and low cost in terms of design and assembly. Using the same climbing mechanism,we can interchange different maintenance modules with different functions of cleaning,painting and inspecting cables.Climbing mechanismAfter studying the various mechanisms for climbing external pipelines,tree trunks,power transmission lines and so on,we designed a new climbing mechanism,called the electric climbing mechanism(shown in Figure2)which can climb arbitrary-gradient cables with diameters ranging from80to 200mm,and also climbs someflexible cables.In order to climb cables with a steep gradient,the climbing mechanism must minimise wind resistance,friction drag and other resistances,and maximise the climbing force.However,the sectional shape of most cables in cable-stayed bridges is spiral hexed-prism,so the climbing mechanism tends to rotate the cable along its axis because of the deflection produced by gravity and the force between the wheels and the cable.The maintenance mechanism must work in a stable way,so we designed a rotary device consisting of inner and outer frames. The inner frame connects to the climbing mechanism,and the outer frame to maintenance mechanism.Vertical and horizontal smooth-rolling bearings are set between the inner frame and the outer frame.This produces a climbing mechanism with an inner frame that moves spirally along the cable,and a maintenance mechanism mounted on the outer frame by a standard interface,that remains stable because of the hanging weight of a painting bucket or storage battery,etc.The umbilical cable linking to the inner frame needs to rotate around the cable,so a brush is used to facilitate this.T o cope with cables of different diameters,we designed two grades of clamping mechanism,a rough-tuning one for adapting to cables with a large diameter difference, and afine-tuning mechanism for adapting to cables with a small diameter difference.T o reduce the influence of wind-induced vibration,the CMR has a cylindrical structure, shown in Figure3.In order to install the climbing mechanism on cables with different gradients,an installing vehicle was designed,as shown in Figure4.In addition,the climbing mechanism has a safety device to allow the CMR to slip slowly from the high-altitude cable to the bridgefloor if there is a power failure or other unexpected condition.The technical specification of the electrical climbing mechanism with all-driven wheels is as follows:Dry weight:190kgPay load:180kgPower:3£0.4kWVelocity:0.5,8m/minSize:f1,100£1,000mmWe developed another climbing mechanism for rust-detection in cables,and this is shown in Figure5.This mechanism, called the pneumatic climbing mechanism,has14cylinders and is divided into an upper part and a lower part.Each part includes three clamping cylinders and three steerable cylinders.In addition to the12cylinders,there are two elevating cylinders allowing the mechanism to climb along the cable.As the lower part of the mechanism clamps the cable Figure2Figure1with its three clamping cylinders,the upper part of the mechanism moves upwards a certain distance along the cable using the two elevating cylinders.Then when the upper part of the mechanism is clamping the cable with its three clamping cylinders,the lower part of the mechanism moves upwards a certain distance along the cable by means of its two elevating cylinders.Continually repeating this movement like a worm,the mechanism travels a long distance along the cable.The extended state of the pneumatic robot is shown in Figure 6.The technical specification for the pneumatic worming climbing mechanism is as follows:Dry weight:160kg Pay load:140kgElevating cylinder:80£1,000mm Clamping cylinder:100£35mmFigure5Figure3Figure4Steerable cylinder:80£35mmVelocity:0.5,5m/minSize:600£600£1,280mmPainting mechanismPainting a cable requires fully painting its cambered surface with a uniform coat.So it is quite difficult to design a circular painting technique for the cable at high altitude.Figure7 shows a structural diagram of the painting mechanism of the CMR.On the left of the right-hand picture of the painting mechanism is the standard interface that links it to the climbing mechanism,and on the right is the painting mechanism.A hybrid four-bar linkage rocks the painting guns back and forth.The painting motor turns the crank,and the linkage makes the internal groove rock back and forth at an angle of708to external groove.The internal and external grooves are linked by vertical and horizontal bearings similar to those between the inner and outer frames of the climbing mechanism.The external groove links to the external frame of the climbing mechanism,and three spray guns arefixed symmetrically on the internal groove to paint the cambered surface of the cables.The wind-proof cover of the painting mechanism protects it from high-altitude winds.The CMR must apply a continuous coating to the cable, with no unpainted areas between the guns.So we now calculate the continuity requirement.Given that the distance between the nozzle of the spray gun and the surface of the cable is h,and the scatter angle is b,and that the rocking of the paint gun and robot’s climbing are driven by different motors,then the condition for continuity of painting is as follows:n1n2,4hitgðb=2Þp dð1Þwhere n1is the rotational speed of the climbing motor,i is the reduction ratio of the climbing mechanism,d is the wheel diameter of the climbing mechanism,n2is the rotational speed of the painting motor.Therefore,we must ensure that the rotational speeds of the climbing motor and the painting motor satisfy equation(1),to guarantee continuity of painting.A prototype painting mechanism is shown in Figure8.Examining internal wiresRust can cause wires to break within the cable,so it is important to detect rusting of the internal wires.A broken internal wire causes non-uniform tensile behaviour and changes in cross section.We have adopted a magnetic leakagefield method for testing internal wires non-destructively.The working principle is shown in Figure9.T o detect the leakagefield from defects,the wire is thoroughly magnetized in the axial direction to produce a constant residual magneticfield.Because of its change in permeability,the defective wire has a characteristic leakagefield,allowing the relevant information to be obtained from a distribution analysis of the leakagefield.The following is a brief analysis of the nature of the leakagefield of defective wires.Wire defects can be classified into two types:one is LF(localized faults)resulting from damage such as wire breakage,wire crack,and spot corrosion.The other is LMA(loss of metallic cross section) from wire drawing and wearing,etc.When a wire is thoroughly magnetized,the distribution of leakagefield,orflux density,is changed at the point of defect,no matter which type of fault is present.The leakagefield at a defect is not evenly distributed, but has a variable spatial vector.Hall elements test forflaws in wires inside the cable by detecting the change influx density. Figure9shows a new sensor for examining the internal wires of cables.This sensor includes Hall elements,a permanent magnet,and magnetic concentrating equipment,and detects LF and LMA faults.We used this sensor to examine two cable samples which simulate a broken wire and partial wearing of cables, respectively,shown in Figure10.The leakagefield of LF defects is shown in Figure11(a,b,c of curve1)and the leakagefield of LMA defects is shown in Figure10(e of curve2).Point d of curve2is random interference.ApplicationThe CMR can be applied to painting and rust-detecting on the cables of cable-stay bridges.Both were tested on the Xupu Bridge and the Nanpu Bridge in Shanghai.The installation position of the electric robot used for painting is shown in Figure12,while the position of the contracting/extending pneumatic robot is shown in Figure13.The electrical robot with all-driven wheels and the pneumatic worming robot developed in this paper can operate simultaneously on different cables of the same cable-stayed bridge.Figure6The painting and inspecting performances of the cable robot are much better than from manual work,with a higher quality,higher efficiency,lower cost and better safety.ConclusionAddressing the very difficult problem of detecting and painting the cables of cable-stayed bridges,this paper describes the design of two climbing mechanisms.One is an electrical climbing mechanism with all-driven wheels,and the other is a pneumatic worming climbing mechanism.In addition,a painting mechanism and a rust-detectingmechanism are designed.The CMR developed in this paper is the first special robot for the cables of cable-stayed bridges.The cable-stayed bridge has been of intense popular interest in modern middle-span bridge construction for 20years.The cost of manual maintenance per bridge per year amounts to millions of dollars.Besides,painting the cables of cable-stayed bridges,CMRs can also paint pipelines at high altitude.Therefore,CMRs have a large potential market and will create economic and social benefits.Figure8Figure9Figure12Figure13Figure11ReferencesAlmonacid,M.,Saltare´n,R.J.,Aracil,R.and Reinoso,O. (2003),“Motion planning of a climbing parallel robot”, IEEE Transactions On Robotics And Automation,Vol.19 No.3,pp.485-9.Fukuda,T.and Hosokai,H.(1992a),“A study on an autonomous pipeline maintenance robot(3rd Report, Structure and Control Mark III and Obstacle Sensing)”, JSME International Journal,Series C,Vol.53No.492, pp.1788-94.Fukuda,T.and Hosokai,H.(1992b),“A study on an autonomous pipeline maintenance robot(4th Report,Joint Control and its Trajectory Generation for Mark II)”,JSME International Journal,Series C,Vol.53No.495,pp.2325-30. Higuchi,M.and Maeda,Y.(1991),“Development of a mobile inspection robot for power transmission lines”, JRSJ,Vol.9No.4,pp.457-63.Lin,Y.(1994),Cable-Stayed Bridge,People’s Jiao T ong Press, Beijing.Tavakoli,M.,Zakerzadeh,M.R.,Vossoughi,G.R.and Bagheri,S.(2005),“A hybrid pole climbing and manipulating robot with minimum DOFs for constructionand service applications”,Industrial Robot,Vol.32No.2, pp.171-8.Further readingHosokai,H.and Fukuda,T.(1992),“A study on an autonomous pipeline diagnostic robot(2nd report,control method of manoeuvrability of robot mark II)”,JSME International Journal,Series C,Vol.53No.586,pp.399-405. Nishi, A.and Miyagi,H.(1993),“A wall-climbing robot using propulsive force of a propeller(mechanism and control in a mild wind)”,JSME International Journal,Series C,Vol.36No.3,pp.361-6.Nishi, A.and Miyagi,H.(1994),“A wall-climbing robot using propulsive force of a propeller(mechanism and control system in a strong wind)”,JSME International Journal,Series C,Vol.37No.1,pp.172-8.Schempf,H.,Mutschler,E.,Chemel,B.and Boehmke,S. (1998),“A robotic pipe-asbestos insulation removal system”,Industrial Robot,Vol.25No.3,pp.196-200. Corresponding authorJun Luo can be contacted at:wqlj1228@T o purchase reprints of this article please e-mail:reprints@ Or visit our web site for further details:/reprints。