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Inspection Systems Monitor Trains

Photonics Spectra
Feb 2003
Anne Fischer Lent

The Intercity Express trains in Germany travel at speeds up to 330 km/h, faster than a jet at takeoff. To support such speeds, inspection of the wheels is crucial so that defects may be detected early and remedied immediately, but until recently, this was a time-consuming procedure performed by a team of engineers.

An optical inspection system integrated into the railroad tracks at Intercity Express maintenance facilities in Berlin monitors the wheels of the high-speed trains for defects. Courtesy of Hegenscheidt-MFD GmbH & Co. KG.

Now researchers at three Fraunhofer institutes in Germany, in cooperation with Deutsche Bahn AG and other partners, have developed optical and ultrasonic testing systems that offer speed and precision.

The optical system scans the wheels for signs of wear as a train slowly rolls over a measurement station integrated into the tracks at the inspection site. A laser projects a pattern of lines onto the rolling surface of the wheels. A camera records the reflected pattern, which is sent to a signal processing and evaluation unit. The geometric profile of the contact surface and the wheel diameter can be calculated from this pattern in 250 ms.


The laser projects a pattern of lines on the surface of the wheels, enabling the users to calculate the geometric profile of the contact surface in 250 ms.

The laser system is installed at nine locations worldwide. It has demonstrated the ability to withstand trains rumbling overhead as well as differing weather conditions.

The mobile ultrasound system inspects the wheels from underneath, employing up to 42 ultrasonic units to examine the rims and discs for surface cracks and for internal planar and volumetric flaws. Three of these systems are in use by Deutsche Bahn.

The two systems perform separate but equally important functions: The ultrasound system analyzes the state of the wheel interior and its surface, while the laser system reveals any wear on the wheel profile. When used in conjunction, they complement each other to give complete feedback on the wear of the wheels.


GLOSSARY
camera
A light-tight box that receives light from an object or scene and focuses it to form an image on a light-sensitive material or a detector. The camera generally contains a lens of variable aperture and a shutter of variable speed to precisely control the exposure. In an electronic imaging system, the camera does not use chemical means to store the image, but takes advantage of the sensitivity of various detectors to different bands of the electromagnetic spectrum. These sensors are transducers...
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