Optical sensor system surveys railway tracks

Railway operators should obtain several track parameters in regular intervals to make sure that track infrastructures are safe. Since steel rails are always under high tensions, irregularities in the rail geometry can cause sudden cracks in them. These cracks can then cause domino effects with rails and railway sleepers tearing over large stretches.

An innovative optical sensor system scans the tracks quickly and safely. A laser scanner acquires geometrical irregularities and transforms them into 3D images.

Today the state of the art in surveying a railway track infrastructure is camera-based systems. These systems however have a number of drawbacks: The quality of the results heavily depends on the lighting conditions, and they require a rather complex processing of image data. In addition, the image data are demanding a very large memory space.

In its Rail Track Scanner (RTS), Fraunhofer IPM for the first time utilises a laser scanner to measure rails, railheads, sleepers, and rail bed. The specific optical design allows the scanner to be mounted just 1.2m above the rail bed. The device scans the tracks transversely to the measurement vehicle movement at a track width of some 1.7m. With up to two million single measurements per second, the instrument generates up to 800 profiles, providing a detailed three-dimensional image of the tracks and the infrastructure that is associated directly to it.

Out of the cluster of points generated, appropriate algorithms extract parameters such as distance, height, and tilt of the rails as well as the exact geometry of the railheads. These parameters then are compared with set values. The scan frequency can be adapted to the respective task. Topographic structures and deviations are identified at an exactness of less than 1mm.

The scanner has the size of a shoebox and thus can be mounted to any rail vehicle. Thus, the RTS offers a cost-effective option to automatically survey the rail infrastructure without the need to acquire a specific measurement vehicle. Utilising an eye-safe infrared laser (class I), the scanner can be deployed in the public space without any restrictions. The instrument, which will be introduced to the public at the Innotrans trade fair in September, will be utilised by Swiss mobile mapping services company iNovitas to survey narrow-gauge lines in Switzerland.

- Christoph Hammerschmidt
  EE Times Europe