In the railway sector, it is essential to carry out infrastructure inspection and maintenance tasks in order to ensure safe and efficient railway operation. In general, it is the infrastructure manager (the entity owning or directly managing the track) who must carry out these tasks in order to guarantee a contractually agreed standard, while the train operating companies must pay a fee for the use of the infrastructure, which finances the aforementioned tasks.

When the infrastructure managers implement an strategy based on corrective maintenance, the results and conclusions derived from track inspection activities allow determining the values of each of its geometry parameters (i.e., vertical profile, alignment, cant, twist and gauge), defining whether there are significant defects or deviations on which it is necessary to intervene (i.e. where maintenance activities need to be carried out on the railway infrastructure). For this reason, inspection operations for the detection of track defects are essential on a regular basis on railway lines in operation.

However, as will be discussed further in the next section, due to the limitations of existing track inspection technologies, these tasks are often very costly, especially if high performance is needed, and involve disrupting or modifying traffic on the line or working during night-time periods.

In addition, the current approach to track inspection and maintenance implies that the limitations of inspection systems are not the only problem, as a paradigm shift is also necessary to move from a corrective approach (acting when the damage is at an advanced stage) to a predictive maintenance strategy, through the implementation of technological solutions that provide information on the prediction of the onset of defects, allowing action to be taken at early stages in the evolution of the deterioration.

This technological breakthrough is vital, as the focus of railway infrastructure managers must be on achieving significant reductions in maintenance costs of increasingly ageing infrastructure while not compromising safety. In fact, the implementation of these new predictive maintenance approaches in the industrial sector has led to cost savings of up to 70% compared to traditional corrective strategies.

Therefore, in order to optimize inspection and maintenance tasks and reduce the high costs associated with them, COREAL’s team has developed an innovative track monitoring system designed to be installed easily and economically on any in-service train vehicle. While in service this train becomes a continuous, real-time register of data related to the condition of the track, that is advanced processed in order to generate predictive maintenance plans, specific and customized to the railway infrastructure on which it is operating.

Our solution to the problem: technology for track geometry inspection based on equipped in-service trains, using inertial methods and mathematical processing

Common methods of track inspection can be grouped into two main categories:

• Manually operated track measuring devices
• Dedicated track inspection trains

Manually operated track measuring devices are cost-effective manually operated tools used to inspect rail and track infrastructure. The most relevant technology in this category is the track geometry measuring trolley.

• Track geometry measuring trolleys consists of a trolley equipped with high-precision sensors capable of measuring all the significant geometry parameters. The position is generally obtained by means of control points with a known position and by measuring distances with a built-in odometer.

  

  As can be seen in the image above, it is a manually operated system (low speeds, need for a specialised technician), which usually has a screen on which the different variables are selected for correct measurement. . Furthermore, trolleys can be combined with GPS or robotised station to store collected data and determine the exact location of measured data.

  Derived from its own nature, the main limitations of this system are its low performance (the equipment circulates at human speed) and the need for the inspection work to be carried out at night or for the railway service to be interrupted.

On the other hand, dedicated track inspection trains are becoming increasingly popular. These vehicles are designed to inspect the track under a circulating load, i.e. the track measuring system consists of a measuring axle which is mounted underneath the vehicle. These inspection vehicles allow numerous analyses and can be grouped into:

• Contact monitoring systems. In this method, a movable roller object, which has constant contact with rails, is used to indicate track geometry parameters. The most common equipment currently used to carry out these tasks are vehicles incorporating contact sensors mounted on track recording vehicles, track tamping-inspection vehicles and draisine-inspection vehicles.

  Thus, vehicles incorporating contact sensors are based, as already mentioned, on physical contact methods, since the sensors are elements placed on the bogies of the inspection trains so that they are in contact with the rails in order to detect defects in the geometry of the track. These contact sensors can be of two types: horizontal sensors (whose function is to measure the inner side of the rails to characterise the alignment and the track gauge) and vertical sensors (whose objective is to measure the running surface to characterise the elevation by taking measurements of longitudinal levelling or profile, cant and twist).

  The main purpose of track tamping machines is to pack the tack ballast. However, some of them can also be levelling-tamping and aligning-tamping machines. These machines, in addition to tamping, measure the defects in the track layout and correct them, placing it in its exact position, grouping these operations in a single machine. The inspection methodology is based on track geometry measuring devices, such as contact sensors.

  A draisine is a self-propelled vehicle fitted with the necessary equipment to carry out maintenance work on the track or catenary, designed to transport operators carrying out maintenance work and the corresponding goods. In addition, it allows the inspection of all geometric parameters as it moves along the track.

  

  One of the main limitations of these systems is that the speed of circulation of this equipment is lower than that of the trains in operation, which makes it necessary to schedule specific periods of time to carry out the work, interrupting the normal operation of the system.

  In addition, by their very nature, the sensors are in continuous contact with the rail at a certain pressure so that they do not separate, which causes continuous wear on the sensors and on the rail, which on the one hand affects the quality of the measurements and on the other the deterioration of the rail.

• Techniques based on non-contact methods. In an attempt to overcome the limitations of contact-based inspection systems, non-contact inspection vehicles were developed in the 1990s. Laboratory cars, which integrate different technologies, are driven by a locomotive or coupled to trains running commercial services.

  They can also be specific self-propelled vehicles.The technologies they incorporate may include such as ultrasonic, thermal sensors or eddy current,  among which those based on optical measurements would stand out. The non-contact optical laser-based measurement system generally operates based on the time of flight principle. To calculate distances and track geometric parameters, the sensor emits a narrow beam light towards the desired object and measures the time taken by the pulse to reflect off the target and return to the device.

  These dedicated vehicles are very sophisticated and expensive, reason why they are limited in number and only can be found in countries with large railway networks. This is the case in Spain, where we find the SENECA laboratory train of Adif for the inspection of the infrastructure of high-speed lines, or the VAI (Installation Inspection Vehicle) of Metro Madrid.

  

  Therefore, we would highlight that their main limitation lies in the fact that they are sophisticated vehicles that are few in number and very expensive, which makes their use very complicated due to the long distance they have to travel to reach from one inspection site to another.
  Another disadvantage, as with tamping machines, is that they occupy the track as they are not commercial train vehicles, which reduces the capacity of the infrastructure, with the consequent added cost.

Given the situation described above, COREAL identified the need to develop an innovative solution capable of solving all the problems described previously, providing results, in terms of track inspection, of equal or superior accuracy to those of the existing systems.
Our technical team focused the strategy on developing a solution based on the concept of non-contact track monitoring vehicle systems, but without having to use dedicated, high-cost track monitoring vehicles.

Thus, the development and validation of an innovative inspection system based on inertial methods and mathematical processing was carried out, which, with the use of sensors located on in-service vehicles, is capable of providing real-time data on the state of the track, on the basis of which predictive maintenance can be implemented.

Our methodology for developing the solution

Once our methodology was implemented, after analysing the technological challenge and the potential client’s objectives, we carried out an research that allowed us to define the best approach to solve the problem, specifying features and assessing their suitability from a cost-benefit point of view.

Thus, we propose to develop an advanced inspection system which, although it consists of a subsystem for capturing and transmitting track records, including the vibrations produced by the different track defects to be measured, its main advantage lies in the mathematical process capable of converting the captured signal to the parameter of interest (track geometry).

This is because the defects are captured indirectly, so the most important technological challenge during the creation of the solution was the development and validation of an advanced mathematical algorithm for data processing, since only through a process of transformation of the digital signal recorded by the inertial sensors as a function of time is it possible to achieve the results and precision that characterizes our system.

With regard to the track acquisition and registration subsystem, the purpose of the inertial sensors is to capture the vibrations produced by the interaction of the vehicle wheel with the track for subsequent analysis. Regarding the location of the sensor, special attention must be paid to signal interference caused by the possible occurrence of resonance phenomena of the system, which is why accelerometers should be installed in those parts of the vehicle with higher eigenfrequencies, such as unsprung masses.

In addition, these sensors must be connected to the data acquisition system by wiring, so their location must be such that the cables can be routed inside the vehicle without excessive difficulty, so as to avoid damage due to the relative movement between the different vehicle masses. For all these reasons, it is determined that the ideal place to install the accelerometers is the vehicle’s axle box. The location of the accelerometers on the axle box of a train is shown below:

As shown in the figure above, the sensor is installed on the metal structure by means of a magnetised joint reinforced with an industrial adhesive. This allows the sensor to be positioned without the need to modify the vehicle’s elements or perform mechanical operations on it, as well as allowing quick and easy assembly/disassembly.

The sensor is connected to the recording unit by means of cables which are anchored to the vehicle’s components by means of cable ties, thus ensuring that they cannot come into contact with moving parts. In addition, the cable is provided with an insulating protective barrier to prevent wear or breakage caused by the projection of stones or other particles.

On the other hand, a GPS geolocation system is implemented which, as acceleration records are made, associates global coordinates of the exact place where these records have been made. The GPS module together with its antenna shall be installed in the vehicle cab. The installation of the antenna can be carried out by magnetic connection with the body of the vehicle or by fastening it by means of cable ties to some element of the vehicle.

Once the data have been collected, they are analysed using the signal processing algorithm. The aim of this processing is to characterise the parameters of the track and its elements from the vibration signal recorded by the inspection system placed in the vehicle, and to be able to relate this information by associating these records with the GPS coordinates.

The algorithm will process the acceleration (vibration) data obtained in the time domain. By means of the acceleration, the displacements that have produced it can be obtained via integration and, by filtering and transforming them to the frequency domain, the signal can be correlated with the cause by means of an analysis based on a mathematical model of the interaction of the vehicle’s axle with the track.

Once this process has been completed, it is possible to return to the time domain to finally obtain in the space domain the correlation of the defects and characteristics of the track with the coordinates of the points where they have been recorded.

The results of this analysis are presented to the client via a web platform, where all track geometry track parameters are displayed, indicating the condition of the track. In this way, it will be able to quantify and predict the moment at which degradation is going to occur, i.e., it will make it possible to anticipate as far as possible, preventing maintenance tasks from being carried out at advanced stages of deterioration.

Conclusions

Our team has developed a system with the capacity to characterise the track condition that can be integrated into any in-service vehicle, so that it is able to monitor all the geometry parameters as the vehicle runs during its normal operation.

Our innovative solution makes it possible to monitor the condition of the network and implement predictive maintenance techniques without affecting track service, so that railway infrastructure managers have a tool that makes it possible to optimise maintenance operations while improving the safety, quality and service level of their infrastructures.

For more information on this innovative solution, do not hesitate to download our specific brochure.

In addition, if you are interested in improving the productivity of your industrial sector, do not hesitate to check out other solutions developed by our team or contact us to jointly develop a tailor-made technological solution to meet your specific needs.

References

Falamarzi, A., Moridpour, S., & Nazem, M. (2019). A review on existing sensors and devices for inspecting railway infrastructure. Jurnal Kejuruteraan, 31(1), 1-10.

Real, J., Salvador, P., Montalbán, L., & Bueno, M. (2011). Determination of rail vertical profile through inertial methods. Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit, 225(1), 14-23.7

Real Herráiz, J. I., Montalbán Domingo, M. L., Real, T., & Puig, V. (2012). Development of a system to obtain vertical track geometry measuring axle-box accelerations from in-service trains. Journal of Vibroengineering, 14(2), 813-826.

Real, T., Montrós Monje, J., Montalbán Domingo, M. L., Zamorano, C., & Real Herráiz, J. I. (2014). Design and validation of a railway inspection system to detect lateral track geometry defects based on axle-box accelerations registered from in-service trains. Journal of Vibroengineering, 16(1), 234-248.