Optical Measurement System for Monitoring Railway Wheel Tread Surfaces During Train Motion

The need to measure the geometric dimensions of a railway wheel during train motion at a speed of 120–150 km/h with an error below ±0.25 mm and to identify defects on the tread surface and flange is justified. A new optical measurement system that provides this measurement accuracy was developed. The wheel geometric parameters were measured, and defects were identified using square-wave pulsed laser radiation with a plane-parallel wavefront in the form of a 4 mm wide and 280 mm long line, with a pulse duration of 14 μs, formed using a newly designed collimator. A method was developed for selecting the laser pulse duration so that image blur would have an insignificant influence on the measurement results. Under these conditions, the wheel surface could be considered locally flat with respect to the incident laser radiation. The receiving modules were positioned relative to the rail surface so that the CMOS field of view covered a wheel-surface sector of 10°12′ from both sides and recorded the reflected radiation as a point cloud. To reduce stray illumination and reflections, a filter with a 12.6 nm bandwidth centered at 638.2 nm with a transmittance of 0.71 was installed in front of the CMOS matrix. A point-cloud processing algorithm was developed. Of 236 recorded profiles, 232 were processed successfully, corresponding to a successful-processing rate of 98.3%. Defects were detected in seven processed profiles and confirmed by control measurements. The geometric parameters were determined with a calculated error not exceeding 0.25 mm at 150 km/h. Complete wheel monitoring required 36 sequentially installed optical measurement modules developed in this work, approximately 1.4 times fewer than in comparable systems, for which the measurement error at 150 km/h was approximately ±0.6 mm and the reported defect identification reliability was 95%.