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es E DeVault

very bridge depends on its physicalintegrity, the preservation of whichrequires adequate inspection, mainte-E ance, and repair. The United States

has approximately 575,000 highway bridgesin the National Bridge Inventory; 85 areover streams or rivers. Underwater inspec-tion is important, as emphasized by the 80flood-related failures that occurred over a re-cent three-year period [6].

The objective of m y research is to developan automated robotic system that will enablesafe and cost-effective underwater inspec-tion of bridge substructures.

Underwater BridgeInspectionInspecting bridge piers underwater is moredifficult than inspecting the other parts. Theharsher environment affects the inspectors Photo: Andrew allmobility and vision and limits cleaning and sampling. Notonly do inspectors work under adverse conditions, such asdeep, cold water with poor visibility, they must also havecomprehensive knowledge of the design and const ruction fea-tures of bridge substructures.

Most state agencies in the United States have recognizedthat competent engineering inspections of underwater struc-tural elements are essential and have as sumed the responsibil-ity for these inspections. Many agencies use commercialdivers supervised by professional engineers.

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Visual and Tactile inspectionVisual and tactile examinations are the primary methods usedto inspect the underwater portions of a bridge. The most obvi-ous limitation to visual inspection is water clarity. Often,bridges are built in turbid water that severely limits visibility.In these cases, the diver must touch and feel the piers to detectflaws, damage, or deterioration.

Divers inspect piers using only tactile methods in zero visi-bility, but it is difficult or impossible to quantify this tech-nique. The task is made more difficult by cold water, strongcurrents, or marine deposits. Presently, about half of all un-derwater inspection jobs have limited visibility and dependon tactile detection.

When visibility allows, the standard practice is to docu-ment observations with videotape. Underwater cameras maybe handheld or mounted on the divers headgear. Video offersa real-time display at the surface along with convenient dateand location stamping.

Other MethodsRecently, more sophisticated instruments, including fathom-eters and sonar imaging devices, have become available. Fa-thometers are effective for checking scour (deep erosion) inthe streambed adjacent to a bridge pier. They are not effective,however, when used very close to the pier, because substruc-tural elements or accumulated debris are likely to give errone-ous returns. Undermining of piers or abutments cannot beadequately detected. When undercutting or undermining issuspected, visual inspection of the pier is necessary.

Sonar imaging is useful in low-visibility environments. Itprovides structural data over and above that which is attain-able through video imaging alone because sonar can seethrough silt and algae covering the concrete surfaces. Com-bining both video and sonar technologies in a single inspec-tion process may give more comprehensive results.obots and ROVs

Remotely operated vehicles (ROVs)have proved useful in themarine industry. Offshore petroleum and salvage operationsincreasingly rely on information supplied by ROV site investi-gations to aid in planning a nd executing tasks underwater.However, these systems cannot operate under strong currents(more than four knots) in streams and rivers, which seriouslylimits their ability to perform underwater bridge inspections.

Currently, robotic apparatus is used to inspect and main-tain large pipes, storage tanks, and cargo ship hulls 111.Char-acteristics common to these applications include anontechnical operator interface, task specificity, and a degreeof autonomy. Although robotic inspection systems have widemarket potential, no system is available that can inspectbridge piers underwater.The Experimental SystemThe System ConceptMy colleagues and I are developing a semiautonomous ro-botic system that can carry a sensor platform underwater to

Fig 1 System concept for robotic inspection of bridge piers.detect scour, deterioration, or damage to support columns. Itprovides positional data and sensor information (video im-ages) to the system operator; these can be verbally annota tedwhile being recorded. The operator initiates basic commandsand transmits them to the underwater apparatus. Onboardmicroprocessor-based controllers automatically accomplishthe detailed control.

The primary underwater apparatus has a team of twoidentical mobile robots designed to travel along opposite sur-faces of the pier while connected to each another by a cableand winch system (Fig. 1 .Each robot has rubber tracks orwheels with cleats and is driven by internal motors. Ten-sioning the cables that connect the two robots provides trac-tion. The robots can move both vertically and horizontally.While each robot operates its own drive motors and cablewinches, coordination of movement and cable tensioning oc-curs automatically through feedback between the robots andthe control console. Multiple robots, evenly spaced around asupport column, may inspect larger structures.

Either robot may carry a video camera and a halogen light,or other sensors, and position them approximately 1 ft fromthe surface under inspection. They can provide auxiliary fea-tures, such as a rotary scrubbing brush, which may engage thesurface before inspection. The use of cables to suppo rt the ro-bots allows other testing systems to be fitted to them. For ex-ample, it is possible that the robots could be outfitted forultrasonic testing or core sampling. This robot pair, attachedby cables, will be able to function effectively in high currentsand turbulent waters (Fig.1 .

A compliant wheel adjacent to the drive tracks and at-tached to a digital encoder provides continuous positionaldata to the operators console. An integral bum per detects thebottom of the river or lake and can establish a positional refer-ence point. The robots have a rolling sensor that detects anysurface voids on the structure between the robots tracks orwheels.

Composite cables conduct power, control, video, and datasignals to each robot and return them to the control console.The cables lower the robots into the water and serve as emer-gency tethering.

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A serial data link communicates between the control con-sole and the robots. The operator may issue single keystrokecommands either to indiv idua l robots or to the robot team. Thegraphical user interface displays the robots position, directionof motion, and detection of bottom or end-of-travel, as well asstatu s for brush engagement , ights, camera, and cable tension.

Each robot contains a microprocessor system that receivesand interprets operator commands and sequences and con-

trols the onboard equipment. The coordination of movementand cable tension is transparent to the operator. Fig. 2illus-trates the block diagram of the robots command and controlstructure.

Early Work: Feasibility ExplorationThe preliminary work on this project explored the feasibilityof us ing a tethered team of robots in this application. We con-

Fig 2 Block diagram of a robots command and control structure.

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structed a nd tested two identical robots capable of traversinga vertical concrete struc ture representative of bridge piers.We did not atte mpt unde rwater operation. Each robot con-tained a drive unit a nd a cable unit. The drive units had rub-ber tracks fitted with cleats driven by geared servomotors,microcontroller boards, electronic interface boards, poweramplifiers, and power supplies. The cable units had servomo-tor-driven cable spools and were free to pivot atop.the driveunits.

The robots responded to commands generated by a PC.Microcontrollers resident on the robots interpre ted each com-mand and executed assembly language code to control thehardware. We developed a rudimentary graphical user inter-face for the system. Through this in terface, the robots could beindividually or jointly commanded to move. orward or back-ward and to turn either left or right. The user also had controlof the tensioning of each of the two cables by w hch the robotsattached themselves to the column. An operator had to coor-dinate the robot motion and cable tensioning manually, whichrequired substantial skill.

Two automotive batteries powered the robotic system.Onboard power supplies generated all necessary operatingvoltages for the control electronics and sensors.

We set a 6-ft length of 5-ft diameter concrete pipe on endfor convenient testing of the robots. This test fixture repre-sented many bridge piers for which this system might be ap-plied. The system successfully operated both vertically andhorizontally over the surface of the test structure (Fig.3 . Wedemonstrated the feasibility of this approach sufficiently tosuppor t issuance of a patent [3]. The testing identified theneed for several mechanical modifications; in particular, wefound we had to reduce substantially both the profile and theweight of the robot units.

Imaging Test System and ExperimentsAfter establishing the feasibility of the system, we divided theactivities between fabricating a prototype robotic system andevaluating the performance of an underwater video cameraand lighting system in turbid water conditions.

Work began with an evaluation of an underwater videocamera and high-intensity lighting systems ability to provideimages of a quality sufficient to detect structural damage atvarious levels of water turbidity. We prepared a test appara-tus for positioning a video camera along a concrete block in anunderwater environment of variable turbidity . The concretetest block had several structural defects that included cracks,spalls, and exposed rebar. We measured turbidity with aDRT-100 research turbiditimeter manufactured by HF Scien-tific Inc., of Fort Meyers,FL. Historical turbidity data collectedat seven locations on four major rive rs in Kansas establishedthe appropriate test levels. Turbidi ty levels of 0 to 60 NTU rep-resent a typical range of conditions.

We used a consumer-grade digital camera (Hitachi modelVM-H100LA) capable of underwate r operation to record im-ages representing over 200 combinations of turbidity, dis-tance, and lighting intensity. This method of inspection and

data collection proved viable under conditions of low to mod-erate turbidity.

The addition of a clear-water bag to the camera apparatusextended video viewing to the higher turbidity conditions of-ten encountered in rivers of this region. When fully imple-mented, a flexible, clear plastic bag mounts in anaccordion-like structure attached to the camera with rollersthat support the unit against the concrete surface. The cameraunit provides tactile feedback information about the surfacethrough a spring-loaded linear potentiometer. This tactilefeedback allows the clear-water bag to track an irregular sur-face without rubbing directly against it. As an additional ben-efit, the output of the potentiometer provides a surface profile.

With a simplified version of this system in place, we re-corded underwater imaging up to a maximum turbidity valueof 60 NTU (Fig.4). The quality of these images was judged ad -equate by an advisory team of regional experts including De-partment of Transportation officials from neighboring states.

Fig 3 arly prototype of the Robotic Inspection System

Fig 4 Camera image of exposed 5 rebar in water of NTU turbidity usinga clear-water bag


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Evolution of the Robot i c pparatusMechanical ComponentsWe have designed and constructed a second-generation robotsystem capable of submerged operation. Each robot includestwo powered drive wheels and a pair of passive outriggersthat both provide lateral support and channel the tethering ca-bles that hold the robots in contact with the bridge supportstructure. A motor-driven lead screw drives a chain that si-

Fig 5 Second-generation robo t.

Fig 6 Third-generation robot with a pneumatic motor and cylinder-actuatedsteering system.

Fig 7 Third-generation robot: view of chain and sprocket drive system

multaneously turns the two-wheel assemblies to providesteering (Fig.5).

The outriggers accommodate various structure dimen-sions as well as surface irregularities. The motors and amplifi-ers that control cable tension are also located within the bodyof the robot. The cable reels are driven through a worm gearthat provides a braking function, requiring that the motors beactivated to either increase or decrease cable tension. Changesin cable tension are made in response to variations indrive-wheel motor torque demands .

The rectangular upper body of each robot provides spacefor the mounting of drive amplifiers for the motors, micropro-cessor board assemblies, power supplies, and sensor controlrelays. The chassis is primarily aluminum, but a commercialimplementation may use an injection-molded plastic shell andmake substantial effort to reduce the weight below 40 lb.

The final size and weight of these robots precluded situ-ated operation, therefore, we developed an alternative systemof a significantly different design (Fig. 6). This system incor-porates pneumatic motors on an aluminum open frame.

A pneumatic motor drives a single wheel through adual-chain and sprocket system (Fig. 7). A separate air cylin-der steers the drive wheel in tricycle fashion through a leverarm. Outrigger arms guide a single tensioning cable. Thepneumatic drive-system supply can inflate individual air bagsand make the robots neutrally buoyant.

The control electronics are rudimentary and separatelyhoused in a remote location pending refinement of the me-chanical system. The robots are waterproof a nd sized to allowdeployment. This system has been tested under manual con-trol on the concrete test pipe.

Electrical ComponentsThe microcomputer boards are based on the AMD AMi88ESprocessor and provide 11 channels of 12-bit analog-to-digitalconversion, six channels of 12-bit digital-to-analog conver-sion, and 30 digital input/output lines. They also have twoRS-232 serial ports, six solenoid drivers, an d an onboard regu-lated power supply. The analog-to-digital converters readsensor information and digital-to-analog converters providecontrol voltages for the amplifiers that drive the motors. TheRS-232 serial ports communicate between robots as well aswith the PC that serves as the operators console.

The servo amplifiers provide pulse-width modulation thatcontrol the drive, steering, and cable tensioning motors; theservo amplifiers use power MOSFETs and surface-mounttechnology to produce high power in a small package thatweighs only 10 oz All motors are dc servo with integral ta-chometers that provide velocity feedback to the servo amplifi-ers. Shaft-position encoders mount on the drive motors a ndprovide positional feedback.

Two 12-Vmarine batteries supply power to the robotic sys-tem. The motors, used for locomotion, cable tensioning, andsteering, operate at 24V. The microprocessor systems requireseveral lower voltage levels that are derived onboard from the12-v supply.

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Communication and Control StructureWe constructed each member of the robot team identicallyand configured each with dupli-cate resident software. However,at the time of deployment, one of

the base of bridge substruc tures. Our long-te rm response tothis advice will be to moun t sonar equipment on the robots

sensor platform, initially pointeddownward. The robot apparatusand controls will be optimized toh e s y s t ~ ~o u l daccommodate vertical travel di-rectly to the riverbed followed byt i a ~ ~ ye t e c the robots was designated themaster and the second robot the

slave. All communications be-tween the operators console andthe robots channels were through

c a t a s t r ~ p ~ i ca i l u re s ofs h e lp sa ve co s tcircumnavigation of the base ofthe pier while scanning the imme-diate area around the base.

the master robot. This automated system for un-The master robot receives global preventative derwater bridge inspection will

commands identifying the varioustasks to be performed via serialcommunications channel. Its soft-

~ a ~ n t e n a n c end be beneficial for highway, rail-road, turnpike, toll, and bridgeagencies. The system could poten-u b l i c sa fe ty .

ware partitions and translates thisinformation into local parametersand instructions before transmission to the slave robot. Duringthe execution of these instructions, each robot inserts local statusinformation to the inter-robot communicationschannel.

Global operator commands that request a change in posi-tion expand into a set of local motor commands for both mas-ter and slave robots. These commands execute in anincremental fashion with continuous coordination betweenrobot movements, as well as with necessary changes in cabletension. Sensor control commands such as those that operatethe video camera and flood lights are interpreted by the mas-ter and either used by that robot or sent to the slave for execu-tion as required. While sensor data such as the video signalmay transmit directly to the operators console, sensor statuschannels to the master robot where it is assembled into an in-formation status packet prior to transmission to the operator.Future WorkThis is a work in progress. Autonomous local operation of therobot units in response to global operator commands requiressignificant additional engineering effort. This work will in-volve both computer simulation and the construction ofsmall-scale robot models tha t will duplicate the essential func-tions of the system robots. These models will facilitate labora-tory experimentation with alternative control structures andalgorithms.

A second area of emphasis will be the design and fabrica-tion of an improved robotic appara tus based on experiencegained through previous research and three generations ofprototype construction. Once we settle on a suitable mechani-cal apparatus, then we can install the full complement of con-trol and communications electronics.

The final area of effort is the user interface. The win-dows-based software will provide graphical control of the ro-bots and camera equipment, indication of robot position andorientation, and full data-logging support.

Bridge inspection experts have recently advised that in-creased emphasis should be placed on the detection of scour at

tially detect catastrophic failuresof bridges, help save cost through

preventative maintenance, and enhance public safety.

cknowledgementsThe author, in collaboration with William Hudson (now withSprint Corporation), and Mustaque Hossain, conducted thisresearch at Kansas State University. The Transportation Re-search Board of the National Research Council and the Ad-vanced Manufacturing Institute of Kansas State Universityboth provided funding.References[1]S Asami, Robots in Japan: present and future, I Robot

Automat Mag. vol. 1, pp. 22-26, June 1994.underwat er bridge inspection and scour evaluation, in IDEAProgram Final Report, Transportation Research Board, NationalResearch Council, Washington, D.C., 1998.

[Z] J. DeVault, W. Hudson, and M. Hossain, Robotic system for

[3] , DeVault,W. Hudson, and M. Hossain, Robotic inspectionapparatus and method, US. Patent 5,857,534 12 Jan. 1999.

[4] J. Engleberger,Robotics n Service Cambridge, MA MIT Press,1989.

[5]H.C. Lamberton, Jr.,A J Sainz, R.A. Crawford, W.B. Ogletree,and J.E. Gunn, U nderwater inspection and repair of bridgesubstructures:National Cooperative Highway Research Programsynthesis of highway practice, National Cooperative HighwayResearch Program Project 88, Washington, D.C., 1981.

[6] Underwa ter bridge maintenance and repair, problemstatement, National Cooperative Highway Research ProgramProject 22-04, Washington, D.C., 1993.

JamesE DeVuult is Professor of Electrical and Computer En-gineering at Kansas State University. His current areas of in-terest include mobile autonomous robotics, embeddedcontrols, and instrumentation. Prior to joining Kansas State,he was a Senior Engineering Specialist with the Electronicsand Space Division of Emerson Electric Company in St. Louis,MO He is a Senior Member of the IEEE.


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