Rail tracks are undoubtedly the most heavily loaded structural components in the railway industry. With increasing train speed, axle load, and traffic density, rail defects are becoming more severe than ever. According to the European Railway Safety Agency, there was, on average, a derailment or collision at least every two days in the European Union because of defects in the track.

The rail network open to traffic in Canada is about 41,000 km (25,477 miles). This is constantly increasing with passenger and freight demand growth, which means that railway track inspection is a significant concern to the industry. In recent decades, numerous non-contact techniques have been used for rail inspection. These techniques are based on measuring technologies such as ultrasound, eddy currents, and lasers. A comprehensive survey of the existing rail inspection techniques indicated that laser-based inspection is the most applicable technology for detecting surface defects. Compared with conventional rail inspection methods, laser-based inspection methods are truly non-contact, with laser equipment up to 100 mm above the rail line.

Below, you can access the headings of this article:

• What is the 3D laser-based rail inspection?
• Applications of laser-based rail inspection
• What are the most common railway track defects?
• System description of laser-based rail profile inspection
• Conclusion

What is the 3D laser-based rail inspection?

Numerous studies about laser-based approaches to assist rail inspection have been carried out as a form of machine vision technology. For example, some new trains are equipped with laser track scanners to get a detailed 2D rail-head profile to ensure a 2D full-rail shape and evaluate the rail surface conditions by comparison with the standard profile. 2D imaging has its advantages, such as high resolution and high efficiency with the capability to inspect at train speed; however, the geometrical characteristics of some defects like the particular cracks, squats, and partial deformation of crossing noses are longitudinal in nature, and thus difficult to detect using 2D techniques.

In recent years, the quality of 3D imaging techniques has improved substantially with the development of sensor technology and processing capabilities. This article's proposed 3D laser-based system explores the feasibility of applying 3D techniques to rail inspection. The main goal is that the system can not only measure the 2D transverse profile but also allow common longitudinal surface defects with different geometrical characteristics to be detected and characterized more comprehensively than 2D techniques.

Applications of laser-based rail inspection

Track measurements are necessary for the rail industry to ensure safety. Trolleys for short sections of track, And for longer rail routes, locomotives are used to carry these laser sensors. With micrometer precision, manual and small locomotives use four 2D/3D profile sensors to check for bare or rusted steel rails. Via laser triangulation, the sensors provide width, inclination, irregularities, or damage values. The sensors reliably measure in all weather conditions, high levels of ambient light, such as sunlight, and any temperature.

The laser-based rail profile measurement Artificial Intelligence algorithms automatically measure and detect changes related to gauge, cross-level, alignment, spikes, clips, tie plates, joint gap, joint bar bolting, rail surface wear, and tie grade.

What are the most common railway track defects?

Dedicated rail components consist of plain track and crossing noses. A rail profile consists of a rail foot, a rail web, and a railhead.

Rail defects can be divided into three categories: rail manufacturing defects, defects resulting from improper handling, use, and installation, and defects because of rolling contact fatigue (RCF) crack growth. Defects belonging to the first two categories have significantly been reduced globally with the improvement of materials and rail-making industries. However, defects in the third category are difficult to control and prevent because they usually originate from the cyclical loading and long-term impact of rolling stock. In railway systems, RCF describes a range of defects caused by the development of excessive shear stresses at the rail contact interface. It is known that the gauge corner region, the running surface, and the field corner regions are the areas that make contact with the wheel, thus defects in the third category that endanger the movement of the train are mostly centered in these regions.

As one of the most critical components of the railway infrastructure, switches and crossings are used to guide trains from one track to another and enable lines to cross paths. It can be fabricated from two machined rails joined together or cast as a single unit. Modern crossings are now released from manganese steel, an advanced alloy that gets harder with use. However, an increase in axle loads and train speed creates larger lateral forces as they change course, and these forces can cause wear, RCF, and deformation. Flaws in crossings may eventually lead to grave consequences such as train derailments.

System description of laser-based rail profile inspection

A laser generally refers to a device that emits light utilizing optical amplification based on stimulated emission. The property of optical coherence allows laser light to be focused on a tight spot and makes a laser beam stay highly collimated even after long-distance transmission. According to the geometrical characteristics of the laser light, laser scanners can be categorized as 1D, 2D, or 3D.

Laser-based inspection methods often incorporate vision-based inspection. For example, profile data are analyzed using image processing methods or combining what the camera sees with laser inspection to improve accuracy. The system can detect missing clips with 2D depth images using 2D template-matching algorithms, but the measurement is implemented in 2D, while with the 3D model discrete in the longitudinal direction, There exist some opportunities to improve the performance of laser-based rail inspection.

Conclusion

This article has presented an innovative approach for applying laser-based inspection systems in railway track and crossing-nose inspection to improve the capability of existing inspection methods, which are usually implemented on a 2D/3D basis. In addition, the applications of laser-based inspection, the description of laser-based systems, and the defects that arise for railway tracks have been reviewed.

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