Field of the invention

The present invention refers to the technical field of the methods and devices for the control of railway lines status and in particular to the technical field of the methods and devices for the detection of the state of occupation of railroad sections.

State of the art

The present invention relates generally to railway safety, and more particularly to a system detecting in real time the state of occupation of railroad sections.

To prevent crashes on the railroad track, it is important to avoid that 2 or more vehicles occupy the same track section in the same time slot.

Several techniques are used to detect the presence of vehicles on a track section, some of them use mechanical switches, arranged in close proximity of the rail and adapted to be pushed by the train wheel passing on them; others use magnetic devices triggered by the steel material of the vehicle wheels.

Those old techniques make use of electromagnetic devices that generally are not immune to electrical interference coming from external power sources like electric engine of locomotives or lightning during a thunderstorm. The interference following such events may be able to trigger the axle counter devices, causing false detections and inducing troubles on trains traffic or dangerous conditions. Moreover, the detection of the presence of a vehicle on a track section is related to the safety rules and requirements to be guaranteed on the railroad, particularly when a false negative event is detected: the vehicle is present on the track but not detected.

Recently, new techniques aimed to detect the presence of vehicles on a track section introduced fiber optics as wheel detector. The employed detector is based on Fiber Bragg Gratings (FBG) sensors, which are implemented into a fiber optics, and placed strictly in contact with the rail. The FBG sensors manage to reflect a particular optical wavelength related to the stress grade induced by the wheel weight on the rail. Different technical solutions and implementations have been disclosed, depending on the position of the FBG sensors on the rail, and on the way said FBG sensors is connected to the rail track, glued or fixed through a particular support.

For safety reasons, it is important to check continuously if the sensor is working and able to detect the train wheels, or if it is at fault or out of order. While is easy to establish if the fiber is broken, because in this case no signal is received by the FBG sensors, an important issue is to establish if the FBG sensors are properly locate on the rail to detect its deformation. In fact, to detect the wheel, the FBG sensors need to stay strictly in contact with the rail track, because they need to sense the deformation of the rail due to wheel weight to perform a reliable detection. If, for any reasons, the sensor is removed from the rail surface, it will keep on working correctly but it will no longer be able to detect the wheel passage on the track section and this is an unacceptable dangerous condition.

It's an aim of the present invention to disclose a method and a device for the real time detection of the state of occupation of railroad sections based on FBG sensors wherein the correct placement of said FBG sensors is continuously monitored.

Summary of the invention

Method and device, for the real time detection of the state of occupation of railroad sections based on FBG sensors, further adapted to continuously check and monitor its own correct placement on the rail track and its own state of functionality.

Brief description of the attached drawings

Figure 1 shows a rail track with a hole on the web where the Fiber Bragg Grating (FBG) based sensor according to the present invention is arranged in order to detect the passage of the vehicle wheels.

Figure 2 shows a first preferred embodiment of the device for the real time detection of the state of occupation of railroad sections based on FBG sensors. Figure 3 shows a second preferred embodiment of the device for the real time detection of the state of occupation of railroad sections based on FBG sensors. Detailed description of the invention The present invention discloses a method and a device for the real time detection of the state of occupation of railroad sections based on FBG sensors wherein the correct placement of said FBG sensors is continuously monitored in order to make sure that said FBG sensors is strictly in contact with the railway track to be monitored.

The present invention is based on the technique of detecting the deformation of the rail, caused by the wheel transit, by detecting the deformation of a hole made on the web of the rail itself.

In fig.1 the hole 1 of radius R1 located on the web 2 of the rail is shown; when the rail is charged and flexed by the vehicle wheel weight, the hole 1 is deformed and its curvature changes point by point with respect to its nominal value;

To detect the presence of a vehicle on the monitored rail section, we need to detect the curvature change of said hole 1 .

With reference to figures 2 and 3, the device according to the present invention comprises an elastic holder 4, preferably shaped as a closed ring or as an open ring, and an FBG sensor 3 fixedly attached to said elastic holder 4. The FBG sensor 3 is furthermore associated to an electronic measurement device 5 by means of a fiber optic link 6.

The measurement device 5 is adapted to interrogate the FBG sensors to evaluate their strain state. The measurement device 5 is adapted to send light signals to the fiber optic 6, said light signals having a frequency spectrum tuned with the frequency spectrum of the FBG sensors to interrogate. Depending on the strain condition, each FBG sensor interrogated reflects back, toward the measurement device 5, a certain optical wavelength. Measuring the reflected wavelength value, the measurement device 5 establishes the strain condition and correct placement of the FBG sensor and the presence of the vehicle wheel on the monitored rail track.

Said elastic holder 4 can be made of metal, fiberglass, composite or plastic material.

The optical wavelength reflected by the FBG sensor and acquired by said electronic measurement device 5 is directly related to its length variation, and thus it is related to the mechanical stress induced on the support. When the holder 4 is not fixed to the rail, said holder is in its relaxed state and its radius is R2 as indicated in enclosed figure 2. In the relaxed state the light reflected by the FBG sensor 3 is characterized by a well defined optical wavelength L2. When the holder 4 is compressed in radial direction, the curvature of its surface changes. The change of the surface of the holder 4 forces the FGB sensor length to change and, consequently, the optical wavelength reflected by said FGB sensor changes as well.

In order to detect the deformation of the rail track during the transit of a wheel, the holder 4 is inserted in a hole 1 arranged in the rail web, in order to detect its deformation.

The hole is arranged having a radius R1 slightly smaller than the nominal, relaxed state radius R2 of said holder 4.

When the holder 4 is forced to fit inside the hole 1 , its radius R2 tends to reduce to the value R1 ; this deformation causes a curvature change, that imply a length variation of the FBG sensor, The wavelength reflected by the FBG sensor changes accordingly, switching from L2 to L1 .

The device according to the present invention is characterized by two bi-stable states, L1 and L2, and a third measurement state L3.

When a wheel transits on the rail, both the hole 1 and the holder 4 are further deformed, resulting in a variation of the FBG sensor wavelength from L1 to L3.

The two bi-stable wavelength values are continuously checked by said electronic device 5 to assess if the holder 4 is properly inserted in the hole 1 and then able to detect the wheel transits.

When the electronic device 5 detects the wavelength L2, an alarm signal is sent to the signaling network that ensure that no trains have access to the checked railway section.

The electronic device 5 can be easily and directly connected to a common railway signaling plant, replacing the present electromagnetic devices and thus allowing for easy retrofitting of the existing signaling systems.