Thousands of bridges are inspected in Germany every year. Many of them were built in the last century and are not designed for modern traffic volumes. Heat, frost, moisture and constant load gradually destroy the structures. Cracks in concrete are especially hard to spot: they can be as thin as a hair and are not visible from a distance.
Inspectors usually work on site with a tablet and a camera. According to engineer Patrick Herbers of Ruhr University Bochum, this method requires great effort and is prone to errors. A team of four researchers offers a solution: David Mueller and Dr. Raphael Dirska from the Chair of Automatic Control and Systems Theory, Herbers from the Chair of Civil Engineering and Dr. Marcel Neuhausen from the Chair of Artificial Intelligence and Formal Methods. The university's science magazine Rubin reported on the project.
Their drone is small enough to fly into narrow hollow bridge girders - internal channels in the structure. There, using artificial intelligence, it scans the walls and looks for cracks. The robot plots its own route and saves the results to an SD memory card. SLAM technology (simultaneous localization and mapping) helps it navigate the dark, winding voids: the device understands in real time where it is and builds a map of the space.
The drone is currently being tested in the flight laboratory of the Chair of Automatic Control and Systems Theory at the Center for Intelligent Product-Service Engineering Systems (ZESS) of Ruhr University. The next step is a test on a real bridge. "We want to show that our drone works not only in laboratory conditions but also in practice," Neuhausen says.
The robot will not replace people but help them: it will mark dangerous areas and collect data, and a human will make the final assessment. The researchers are confident that their development will speed up the digitalization of structural inspection. "The number of bridge inspectors is shrinking, requirements are growing, and bridges are not getting any younger," Mueller notes. "Our drone can make inspections safer, faster and cheaper."