Fast track for rail surveys

Fraunhofer researchers are developing an optical measuring system that travels along rail tracks at night detecting obstacles far faster than current survey trains.

Survey trains carry out regular inspections to detect large and small obstacles on and near the rails, such as leaning masts or overhanging branches that constitute a potential hazard. Regular inspections are essential as the track operators are responsible for the safety of passenger trains and extra-wide loads as well as for trains operated by other rail companies. However, many of these track maintenance vehicles are not authorised to travel on high-speed routes and have to creep along at 30km/h.

On behalf of German rail operator Deutsche Bahn, researchers at the Fraunhofer Institute for Physical Measurement Techniques (IPM) joined forces with FIT Engineering Network and Metronom Automation to develop a measurement system capable of working much more quickly and precisely than any available so far.

Named LIMEZ III, the German rail operator’s new optical-measurement survey train no longer holds up traffic on the tracks, as it inspects the route at 100km/h. The system is not only designed to perform measurements at high speed but is also extremely precise, recording and classifying objects with a minimum diameter of one millimetre.

Two laser scanners are mounted like short feelers at the front of the train, which measure clearance profiles at a frequency of one megahertz, which is higher than ever before.

A forerunner of the system currently in development is already in use in Singapore’s metro network.

Gerhard Stasek, Manager of New Technologies and Patents at the IPM, said: ‘A mirror rotating at lightning speed projects two laser beams that scan the track in a spiral motion. This allows two cross-sections of the area to be recorded simultaneously with each rotation. If the beams hit an obstacle, they are reflected back and registered by a detector. If there is an object overhanging the track, the beam travels a shorter distance and the light signal delay is altered.’

The measurement system analyses these time delays and deduces from them how far away the obstacle is. In addition, a number of scanners register the area adjacent to the track, as well as the neighbouring track. Four video cameras record the journey, and the system matches these images against the measured data.

The train also has 14 onboard computers that pre-process the vast quantities of data being gathered. This combination of optical sensors and new tools for data analysis and management is not only suitable for use in a rail environment, but can also be used to survey roads and waterways.