PSI - Issue 54

Francisco Afonso et al. / Procedia Structural Integrity 54 (2024) 545–552 Francisco Afonso / Structural Integrity Procedia 00 (2019) 000 – 000

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bearings, rail profile, rail wear and RCF as well as track geometry irregularities. To detect such defects, several types of sensors may be implemented, in this case the objective is the detection of surface defects, which may be observed through the following sensor types: optical laser measurement, cameras, accelerometers and other NDT sensors (Falamarzi et al., 2019). Optical laser measurement sensors are suitable to detect surface defects and can also operate while moving over 100 km/h (Falamarzi et al., 2019). Additionally, as indicated by Jing et al. (2022), these sensors display fast measurement speeds, in addition to not requiring contact with the railway track. Several inspection platforms already successfully implement optical laser measurement sensors, such as the self-propelled inspection kart, TRV and the train-borne system (Jing et al., 2022). As written by Alemi et al. (2017), when it comes to the analysis of train wheels, various defects may influence the wheel’s shape, such as eccentricities, discrete defects, periodic non -roundness, non-periodic (stochastic) non roundness, corrugation, roughness, flat, spalling and shelling. Optical laser measurement sensors have been implemented to measure train wheel dimensions, these systems are usually placed on the tracks, capturing the dimensions of the passing wheels (Alemi et al., 2017). Since the wheel monitoring system will be implemented in a maintenance context, there is ample space and conditions to implement an optical laser measurement sensor. As indicated by Falamarzi et al. (2019) in their review, and by Ye et al. (2021) through their integration of sensors for the noncontact measurement of a rail profile, optical laser measurement sensors usually operate either through the time-of-flight principle or through the triangulation principle. The time-of-flight principle, when applied to laser scanning, usually either involves pulse or phase-shift methods for measuring distances. In the case of pulse-based laser scanners, the light travel time from the sensor to the object to be measured is used to determine their distance, the maximum measurable range of this type of sensors is about six kilometers. The phase-shift method correlates the phase difference between the emitted and received laser light, as well as the laser modulation frequency, to the distance between the sensor and the object to be detected (Altuntas, 2021). On the other hand, the triangulation principle, when applied to laser scanning sensors, effectively creates a triangle between the object to be detected, a camera and a laser; the camera and the laser being part of a compact sensor, and their distance and relative angle, known. The camera detects the laser light and the tridimensional location of the laser can be determined (Altuntas, 2021). This way, the distance between the sensor and the object is able to be calculated, the measurement data is scaled according to the base length which corresponds to the distance between the camera and the laser, this means that the maximum range is dependent on the base length, for about 15 cm of base length, the maximum range is around 8 m (Altuntas, 2021). Additionally, as indicated by Berkovic and Shafir (2012), triangulation laser sensors may also have a lower price, and display a fast measurement. Therefore, two different optical laser measurement sensors were chosen, one to monitor the railway tracks and the other the train wheel, both sensors work using the triangulation principle. 3. Track defect detection This system was developed to be implemented on a fully assembled train, as aforementioned, and a laser line sensor was used, together with a support structure, to capture and process the profiles of railway tracks. As the train moves, the system can continuously acquire the tracks’ profiles, communicating with a maintenance platform and warning the maintenance crew when a defect is detected. The developed software must also allow the technician to define the tolerance for several metrics which will be used in the profile analysis. The laser line sensor included in this system is the Gocator 2350D-3R-R-01-T. It should be noted that the sensor is able to capture profiles between 300 mm and 700 mm of distance to its reference point, it has a 0.019 mm depth resolution and 0.15 mm resolution along the laser line (LMI Technologies, 2022). External custom electronics allow this sensor to communicate via MQTT with the maintenance platform.