How a caterpillar-like robot inches up bridge cables to check for defects

Every day, an average of 26,000 tourists ride a San Francisco cable car and 280,000 vehicles cross the Bay Bridge. Every one of them relies on a network of support cables to keep them safe, illustrating the importance of regular maintenance to battle degradation from corrosion, stress and general wear.
A recently patented robot known as FluxCrawler provides a new way to spot flaws in cables before they become a problem. About two feet long and thin like a ruler, FluxCrawler inches around and up the entire cable. It moves on two wheels and sticks to the cable with magnets. Existing tools are clamped to wires, meaning they only work for a specific range of cable sizes. They are also fixed in place, which means they can’t determine the exact angle of a flaw. FluxCrawler can work with cables 1.5 to 8 inches in diameter and can map flaws at any angle.
FluxCrawler bridge cable monitoring robot
Like existing defect detection techniques, FluxCrawler uses a magnetic field. When the field is applied to a cable, any flaws will cause a disruption that can be picked up by the device’s sensors. FluxCrawler connects to a computer via Bluetooth and beams back an image of the magnetic field, highlighting any problem areas. This could be a fissure on the outside of the cable or more serious corrosion or cracks deep within it.
Researchers think FluxCrawler could also be used for elevators, cranes, ski lifts and any other machinery that relies on support cables. It is the work of researchers at the Fraunhofer Institute for Nondestructive Testing in Dresden, Germany. It is currently being tested on a bridge in Mettlach, Germany and will next undergo more testing in a laboratory.