FluxCrawler Robot Inspects Steel Cables To Check Defects

CAD model of the FluzCrawler robot inspecting a wire cable

Researchers at the Fraunhofer Institute for Nondestructive Testing (IZFP) have developed a robot called Fluxcrawler that can detect fissures (strain, wear and corrosion) in stay cables, wire ropes, bridges, elevators, ski lifts and cable cars on a regular basis before they pose a danger or threat.

The detection system was designed as a cooperative effort between the Fraunhofer Institute’s “FilameNDT” project and the French Carnot Institute’s VITRES-IFFSTAR project that seeks to further develop magnetic leakage testing as well as other non- destructive testing methods.

Slowly, very slowly, the robot climbs up the wire cable. As it crawls upward with caterpillar-like movements, it scans the steel surface and detects whether it has any defects.

By conducting a magnetic flux leakage test, the robot not only identifies tiny fissures in the cable surface, it also recognizes deeper cracks. This process exposes the cable to a magnetic field that is “disrupted” in the event of a defect. A measurable leakage field is created wherever defects are located.

Measuring around 70 cm (27.5 in) long, the Fluxcrawler can inspect cables from four to 20 cm (1.6 to 7.9 in) in diameter. The robot is powered by batteries and controlled via Bluetooth by a computer that displays a graphical representation of the magnetic field along the cable’s entire surface. Any suspicious spots are highlighted in high resolution on the screen.A permanent magnet prevents slipping and holds FluxCrawler to the cable. At the same time, it generates the magnetization required to make measurements.

FluxCrawler Robot crawls upward with caterpillar-like movements

Fraunhofer has already patented the robot, which the researchers say has successfully been tested on cables in the lab. They will now conduct further tests as a cable testing facility at DMT GmbH in Bochum, Germany and have already received interest from industry, giving the team confidence the FluxCrawler will soon be crawling cables and hunting for defects on bridges, elevators and cable cars.


The FluxCrawler cannot be used in all situations. For instance, the robot cannot recognize defects in covered areas, for instance in the area where the cable is anchored.

To detect defects in such cases, we apply another non-destructive testing method, namely, EMAT,” says Kurz. To do this, the researchers create a guided ultrasound wave with a transducer that is placed directly on the cable. The wave penetrates the material and is reflected when it hits a flaw. The signals that are sent back to the computer are used to reconstruct an image. The computer uses this image to analyze the physical changes that the wave perceives in the material, and can thus determine the situation in the material’s interior. As a result, the seriousness of even the smallest of flaws can be determined.
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Write by: RC - Friday, July 5, 2013

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