Rail Short Pitch Corrugation Measurement Using Division of Focal Plane Camera

The long known problem of rail corrugation has a strong impact on the maintenance costs of train lines and underground lines. In fact, the interaction between the train and the corrugated rail generates noise that produces discomfort for the passengers, as well as vibrations. Assessing the state of rail surfaces is a fundamental step for correctly planning the maintenance activities. Measurements are performed with specialized equipment, dedicated for the purpose, and often require a stop of the line. Hence, the possibility to mount a measurement device on board a line train is appealing. In this article, a novel approach for the measurement of rail corrugation is described focusing on short pitch corrugation. The proposed method relies on the analysis of the light polarization state using a division of focal plane (DoFP) polarimeter camera. In particular, the angle of polarization (AoP) change due to the interaction between light coming from an illuminator and the corrugated rail surface is used to retrieve the original rail shape by numerical integration. Unlike other measurement systems, the use of a camera allows for the estimation of several profiles along the whole rail width. The performance of the experimental system in laboratory conditions on a real underground line rail is analyzed. Results show a good correspondence between the test results and the ground truth, measured with a more corroborated measurement technique (i.e., a laser displacement sensor).