Rail contact element and dropout detection unit

Abstract

To provide an improved rail contact element and an improved rail monitoring element. [Solution] The present invention relates to a rail contact element (10, 10a, 10b, 10c, 10d, 10e, 10f, 10g) for detecting detachment, which is mountable to a rail (12) and comprises a spring element (14), a body (16) that holds the spring element, and an optical fiber (18), and the spring element (14) is in a tensioned or relaxed state depending on the mounting state of the rail contact element. The optical fiber (18) has an exit face (20) for emitting a light beam (22), and the rail contact element (10, 10a, 10b, 10c, 10d, 10e, 10f, 10g) further comprises a reflective element (24). The spring element (14), reflective element (24), and optical fiber (18) are arranged such that the effect of the reflective element (24) on the light beam (22) is different in a tensioned state than in a relaxed state.

Description

[Technical field]

[0001] The present invention relates to a rail contact element for dislodgment detection, the rail contact element being mountable on a rail and comprising a spring element, a body for holding the spring element and an optical fiber, the spring element being in a tensioned or relaxed state depending on the mounting state of the rail contact element.The present invention further relates to a dislodgment detection unit. [Background technology]

[0002] A corresponding rail contact element is disclosed in US Pat. No. 5,399,633.

[0003] To make railway systems safe and reliable, rail monitoring elements, e.g. axle counters, can be used to determine certain characteristics of the rail and / or trains running on the rail. In many cases, the rail monitoring elements are mounted on the rail and need to be in surface contact with the rail. To ensure proper determination of the required characteristics of the rail and / or trains running on the rail, it is necessary to detect a dislodged situation, i.e. a situation where the rail monitoring element has fallen off the rail or is only loosely connected.

[0004] Patent Document 2 describes a management device for monitoring the mounting state of a sensor element. The mounting state of the sensor element is monitored using an electrical contact, which is closed when the sensor element is mounted on a rail and is disconnected when the sensor element is removed. This solution is mechanically sophisticated and expensive.

[0005] Patent Document 1 describes a strain gauge device equipped with an optical fiber having a fiber Bragg grating (FBG) as a strain sensor element. When the strain gauge device is attached to a rail, the optical fiber is held in an elastically deformed state. Falling off can be detected by detecting a change in the frequency of the detection light of the FBG due to a change in strain acting on the FBG. Optical fibers are easily damaged during the manufacturing process, making them difficult and expensive to manufacture. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] EP 3459811 A1 (Reference [1]) [Patent Document 2] EP 2 962 915 A1 (Reference [2]) Summary of the Invention [Problem to be solved by the invention]

[0007] It is an object of the present invention to provide an improved rail contacting element and an improved rail monitoring element. [Means for solving the problem]

[0008] This object is solved by a rail contact element according to claim 1. This object is also solved by a dropout detection unit according to claim 11.

[0009] The rail contact element for detecting a dislodgment is mountable on the rail and comprises a spring element, a body for holding the spring element and an optical fiber. The rail contact element is an element mountable on the rail so as to be in contact with the rail, in particular via a surface contact or a fastening means (e.g. adhesive). The spring element is in a tensioned or relaxed state depending on the mounting state of the rail contact element.

[0010] A spring element is an elastic body capable of storing mechanical energy. Different types of spring elements can be used, e.g. leaf springs, coil springs also called helical springs. Springs can be, e.g., tension, extension or torsion type. The tensioned state of a spring element is the state when energy is stored in the spring element. The relaxed state is the state when there is no or less energy stored compared to the tensioned state of the spring element.

[0011] The mounting state of a rail contact element is either mounted on the rail, e.g. mounted and attached to the rail, or not mounted on the rail, e.g. dropped off or loosely mounted. A rail contact element is mounted on a rail when it is properly mounted on the rail. In such a situation, the rail contact element performs the function of monitoring the proper mounting state of, e.g., a larger unit comprising the rail contact element. The larger unit may be, e.g., a rail monitoring element for axle counting. If the rail contact element detects a proper mounting state, it can be assumed that the respective rail monitoring element is able to properly perform its function. On the other hand, if the rail contact element is not mounted, it may be unmounted on the rail, e.g. dropped off completely or incorrectly mounted, i.e. loosely mounted.

[0012] The spring element may be in a tensioned state when the rail contact element is in the mounted state and in a relaxed state when the rail contact element is in the unmounted state. It is also possible that the spring element is in a relaxed state when the rail contact element is in the mounted state and in a tensioned state when the rail contact element is in the unmounted state.

[0013] The optical fiber comprises an exit surface for emitting the light beam to the rail contact element. The rail contact element further comprises a reflective element. The reflective element may be a surface capable of reflecting incident light to at least some extent. The spring element, the reflective element and the optical fiber, particularly the one with its exit surface, are arranged such that the effect of the reflective element on the light beam is different in a tensioned state and in a relaxed state. The effect of the reflective element on the light beam may, for example, be a change in the direction in which the light beam is reflected and / or the degree of reflection of the light beam. The degree of reflection of the light beam may, for example, be a percentage of the overall intensity of the light that is reflected.

[0014] The body of the rail contact element is preferably made of an optically absorbing material, so that any light emitted towards the surface of the body can be absorbed rather than reflected.

[0015] The invention may also be implemented using several optical fibers emitting several light beams, which may then interact with one or more reflective elements.

[0016] In one embodiment of the invention, the position of the reflective element relative to the optical fiber and / or the orientation of the reflective element relative to the exit face of the optical fiber are different in the relaxed and tensioned states of the spring element. Different reflection behaviors can then be detected by the detection unit. The mounting state of the rail contact element influences the state of the spring element, which in turn influences the direction of reflection of the light beam and / or the degree of reflection of the light beam and / or the degree of absorption of the light beam.

[0017] In one embodiment of the invention, the spring element, the reflecting element and the optical fiber are arranged such that in either the tensioned or relaxed state of the spring element, the light beam can be reflected back into the optical fiber. The light beam reflected back into the optical fiber can then be detected, for example, using a detection unit. Preferably, in one state of the spring element (relaxed or tensioned), all or almost all of the light is reflected back into the optical fiber, and in the respective other state of the spring element, none or almost none of the light is reflected back into the optical fiber. It is also possible that in one state (relaxed or tensioned), more light is simply reflected back into the optical fiber than in the respective other state. If the difference is large enough to be detected, for example, by a detector, this can be used to detect the mounting state of the rail element.

[0018] Alternatively or additionally, the light beam may be reflected back into two or more optical fibers and detected, for example, by one common detector or by two or more detectors.

[0019] In one embodiment, the optical fiber is fixed to the spring element. The spring element and the optical fiber are arranged such that when the spring element is in a tensioned state, the light beam exiting the optical fiber through the exit face can be emitted in a first direction, and when the spring element is in a relaxed state, the light beam exiting the optical fiber through the exit face can be emitted in a second direction. The first direction is different from the second direction. The optical fiber is fixed to the spring element and is intended to remain fixed during operation. Even so, it may be possible to separate the optical fiber from the spring element when the rail contact element is removed. In this embodiment, the direction of light emitted from the optical fiber changes with the mounting state of the rail contact element.

[0020] In an alternative embodiment, the reflective element is mounted on the spring element. The spring element and the reflective element are arranged such that when the spring element is in a tensioned state, the light beam can be reflected (when it strikes the reflective element) in a third direction, and when the spring element is in a relaxed state, the light beam can be reflected (when it strikes the reflective element) in a fourth direction. The third direction is different from the fourth direction. In this embodiment, the direction of reflection by the reflective element changes with the mounting state of the rail contact element.

[0021] The reflective element may be mounted directly to the spring element. It is also possible for the reflective element to be indirectly mounted to the spring element, for example when another element is mounted between the reflective element and the spring element.

[0022] In one embodiment, the rail contact element comprises a light absorbing element. The light absorbing element, the reflecting element, the optical fiber, and the spring element are arranged such that when the spring element is in a tensioned state, a light beam can be reflected back into the optical fiber, and when the spring element is in a relaxed state, the light beam can be absorbed by the light absorbing element.

[0023] The light absorbing element may comprise a surface capable of absorbing incident light to at least a certain extent. The spring element, the reflective element, the light absorbing element and the optical fiber with its exit surface are arranged such that the effect of the light absorbing element and / or the reflective element on the light beam is different in a tensioned state than in a relaxed state. The effect of the light absorbing element on the light beam may be, for example, a degree of absorption of the light beam. The degree of absorption of the light beam may be, for example, a percentage of the overall intensity of the light that is absorbed.

[0024] In the context of the present disclosure, a light beam is "reflected back" if more of its light is reflected than is absorbed. In the context of the present disclosure, a light beam is "absorbed" if more of its light is absorbed than is reflected. Preferably, in one state of the spring element (relaxed or tensioned), all or nearly all of the light is reflected back to the optical fiber, and in the respective other state of the spring element, all or nearly all of the light is absorbed. It is also possible that in one state (relaxed or tensioned), more light is simply reflected back to the optical fiber than in the respective other state. This can be used, for example, to detect the mounting state of the rail element, if the difference is large enough to be detected by a detector.

[0025] The light absorbing element, which has the ability to absorb at least some of the incident light, may be a separate element attached to the body of the rail contact element. The light absorbing element may also be part of the body. The light absorbing element may be part of the body, for example, if the body itself is made of a light absorbing material.

[0026] In one embodiment, the light absorbing element is mounted on the spring element. The light absorber may be directly mounted on the spring element. It is also possible that the light absorbing element is indirectly mounted on the spring element. This is the case, for example, when another element is mounted between the light absorbing element and the spring element. The other element may be a reflective element.

[0027] In a highly preferred embodiment, the rail monitoring element comprises a sensor element, in particular a strain sensor element such as a sensor fiber with an inscribed Fiber Bragg Grating (FBG). Such a rail contacting element can be used as a rail monitoring element, e.g. as an axle counter for trains of a rail network. Such a rail monitoring element may comprise a rail contacting element as described above. The rail contacting element is capable of detecting when the rail monitoring element is no longer attached to the rail and thus the function of the rail monitoring element is impaired.

[0028] The present invention also relates to a dropout detection unit comprising a rail contact element as described above, and may further comprise a detector for detecting light reflected back into the optical fiber, which in some embodiments may be configured to detect light in a different fiber connected to the detector.

[0029] Further advantages can be extracted from the description and the attached drawings. The above and following features can be used according to the invention either individually or collectively in any combination. The mentioned embodiments should not be understood as being exhaustive but rather are embodiments of the invention.

[0030] Further features and advantages of the invention are shown in the drawings. [Brief description of the drawings]

[0031] [Figure 1] FIG. 2 is a schematic diagram of a rail contact element. [Diagram 2] FIG. 13 shows an embodiment of a rail contact element for dropout detection in a separated state with a fixedly mounted fiber and a reflective element attached to a spring element. [Diagram 3] FIG. 3 shows the embodiment of FIG. 2 mounted on a rail. [Figure 4] FIG. 13 shows an embodiment of a rail contact element for dropout detection in a separated state with a fixedly mounted fiber and a reflective element attached to a spring element. [Diagram 5] FIG. 5 shows the embodiment of FIG. 4 mounted on a rail. [Figure 6] 13A-13C show an embodiment of a rail contact element for dropout detection in a separated state with an optical fiber attached to a spring element. [Figure 7] FIG. 7 shows the embodiment of FIG. 6 mounted on a rail. [Figure 8] 13A-13C show an embodiment of a rail contact element for dropout detection in a separated state with an optical fiber attached to a spring element. [Figure 9] FIG. 9 shows the embodiment of FIG. 8 mounted on a rail. [Figure 10] 13A-13C show an embodiment of a rail contact element for off-axis detection in a separated state, with a fixedly mounted fiber, a reflective element indirectly attached to the spring element, and a light absorbing element directly attached to the spring element. [Figure 11] FIG. 11 shows the embodiment of FIG. 10 mounted on a rail. [Figure 12] 13A-13C show an embodiment of a rail contact element for off-axis detection in a separated state, with a fixedly mounted fiber, a reflective element attached directly to the spring element, and a light absorbing element attached indirectly to the spring element. [Figure 13] FIG. 13 shows the embodiment of FIG. 12 mounted on a rail. [Figure 14] 13A-13C show an embodiment of a rail contact element for off-axis detection in a separated state, with a fixedly mounted fiber, a reflective element attached directly to the spring element, and a light absorbing element attached indirectly to the spring element. [Figure 15] FIG. 15 shows the embodiment of FIG. 14 mounted on a rail. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] 1 shows a schematic diagram of a rail contact element 10. The rail contact element 10 has a body 16 with a spring element 14 attached to the front surface thereof. This front surface of the body 16 may be attached to a rail 12 (FIG. 2) so that the rail contact element 10 is "mounted" to the rail 12. The rail contact element 10 comprises an optical fiber 18 through which a light beam 22 may pass. The light beam 22 may be emitted through an exit face 20 of the optical fiber 18.

[0033] FIG. 2 shows an embodiment of a rail contact element 10a for dislodged detection in a state where it is not mounted on a rail 12. An optical fiber 18 is attached to a body 16 made of a light absorbing material. A spring element 14 is attached to the body 16. A reflective element 24 is attached to the spring element 14. When the rail contact element 10a is not mounted on a rail 12, the spring element 14 is in a relaxed state. The mounted state is "dislodged", which may also be called "dislodged". In this state, the orientation and / or position of the reflective element 24 is such that a light beam 22 emitted through the exit face 20 of the optical fiber is reflected in a direction other than back to the exit face. That is, the light beam 22 is not reflected by the reflective element 24 back to the optical fiber 18. A portion of the light is absorbed by the body 16.

[0034] 3 shows the embodiment of FIG. 2 when the rail contact element 10a is mounted on the rail 12. The mounting state is "mounted" and the spring element 14 is in tension. When the rail contact element 10a is mounted on the rail, the protrusion of the spring element 14 contacts the rail and is pressed in the cavity of the body 16 towards the body 16. This puts the spring element 14 in tension and causes the reflective element 24 to change its position and orientation. In this state, the orientation and position of the reflective element 24 are such that a light beam 22 emitted through the exit face 20 of the optical fiber is reflected by the reflective element 24 in the direction towards the exit face 20. That is, the light beam 22 is reflected by the reflective element 24 back to the optical fiber 18.

[0035] In the embodiment of Figures 2 and 3, when the spring element 14 is in a tensioned state, the light beam 22 is reflected in one direction, and when the spring element 14 is in a relaxed state, the light beam 22 is reflected in the other direction.

[0036] 4 shows an embodiment of a rail contact element 10b for dropout detection when not mounted on a rail 12. The optical fiber 18 and the spring element 14 are mounted on the body 16. The reflective element 24 is attached to the spring element 14. When the rail contact element 10b is not mounted on a rail 12, the spring element 14 is in a relaxed state. In this state, the orientation and / or position of the reflective element 24 is such that a light beam 22 emitted through the exit face 20 of the optical fiber is reflected in a direction towards the exit face 20. In this embodiment, the light beam 22 is reflected by the reflective element 24 back to the optical fiber 18.

[0037] FIG. 5 shows the embodiment of FIG. 4 when the rail contact element 10b is mounted on the rail 12. The mounting state is "mounted" and the spring element 14 is in tension. When the rail contact element 10b is mounted on the rail, the protrusion of the spring element 14 contacts the rail and is pressed in the cavity of the body 16 towards the body 16. This puts the spring element 14 in tension and causes the reflective element 24 to change its position and orientation. In this state, the orientation and / or position of the reflective element 24 is such that the light beam 22 emitted through the exit face 20 of the optical fiber is reflected by the reflective element in a direction other than back to the exit face 20. In this embodiment, the light beam 22 is not reflected by the reflective element 24 back to the optical fiber 18. A portion of the light is absorbed by the protrusion and / or the body.

[0038] In the embodiment of Figures 4 and 5, when the spring element 14 is in a tensioned state, the light beam 22 is reflected in one direction, and when the spring element 14 is in a relaxed state, the light beam 22 is reflected in the other direction.

[0039] 6 shows an embodiment of a rail contact element 10c for dropout detection when not mounted on a rail 12. The body 16 is made of a light absorbing material. The spring element 14 is mounted on the body 16 and the optical fiber 18 is attached to the spring element 14. The reflective element 24 is attached to the body 16. When the rail contact element 10c is not mounted on a rail 12, the spring element 14 is in a relaxed state. In this state, the orientation of the exit face 20 of the optical fiber 18 and the orientation of the reflective element 24 are such that a light beam 22 emitted through the exit face 20 of the optical fiber is emitted in a direction towards the reflective element and is reflected by the reflective element 24 back to the optical fiber 18.

[0040] Figure 7 shows the embodiment of Figure 6 when the rail contact element 10c is mounted on the rail 12. The mounting state is "mounted" and the spring element 14 is in tension. When the rail contact element 10c is mounted on the rail, the protrusion of the spring element 14 contacts the rail and is pushed towards the body 16 towards the cavity of the body 16. This puts the spring element 14 in tension and changes the orientation of the exit face 20. In this state, the orientation of the exit face 20 of the optical fiber relative to the position and orientation of the reflective element is such that the light beam 22 emitted through the exit face 20 of the optical fiber is not reflected back to the optical fiber 18 by the reflective element 24. A portion of the light is absorbed by the body 16.

[0041] In the embodiment of Figures 6 and 7, the light beam 22 is emitted in one direction when the spring element 14 is in a tensioned state and in the other direction when the spring element 14 is in a relaxed state.

[0042] 8 shows an embodiment of a rail contact element 10d for dropout detection when not mounted on a rail 12. The body 16 is made of a light absorbing material. The spring element 14 is mounted on the body 16 and the optical fiber 18 is attached to the spring element 14. The reflective element 24 is attached to the body 16. When the rail contact element 10d is not mounted on a rail 12, the spring element 14 is in a relaxed state. In this state, the orientation of the optical fiber exit face 20 relative to the position and orientation of the reflective element is such that a light beam 22 emitted through the optical fiber exit face 20 is not reflected by the reflective element 24 back to the optical fiber 18.

[0043] Figure 9 shows the embodiment of Figure 8 when the rail contact element 10d is mounted to the rail 12. The mounted state is "mounted" and the spring element 14 is in tension. In this state, the orientation of the exit face 20 of the optical fiber 18 and the orientation of the reflective element 24 are such that a light beam 22 emitted through the exit face 20 of the optical fiber is emitted in a direction towards the reflective element 24 and is reflected by the reflective element 24 back into the optical fiber 18.

[0044] In the embodiment of Figures 8 and 9, the light beam 22 may be emitted in one direction when the spring element 14 is in a tensioned state and in the other direction when the spring element 14 is in a relaxed state.

[0045] FIG. 10 shows an embodiment of a rail contact element 10e for dropout detection when not mounted on a rail 12. The optical fiber 18 and the spring element 14 are attached to the body 16. The light absorbing element 26 is directly attached to the spring element 14. The reflecting element 24 is indirectly attached to the spring element 14, i.e., the reflecting element 24 is attached to the light absorbing element 26, which is attached to the spring element 14. When the rail contact element 10e is not mounted on the rail 12, the spring element 14 is in a relaxed state. In this state, the positions of the reflecting element 24 and the light absorbing element 26 are such that the light beam 22 emitted through the exit face 20 of the optical fiber strikes the absorbing element 26 and is absorbed. The light beam 22 does not strike the reflecting element 24 and is therefore not reflected by the reflecting element 24 back to the optical fiber 18.

[0046] Figure 11 shows the embodiment of Figure 10 when the rail contact element 10e is mounted to the rail 12. The mounted state is "mounted" and the spring element 14 is in tension. In this state, the reflective element 24 and the light absorbing element 26 are positioned such that the light beam 22 emitted through the optical fiber exit face 20 strikes the reflective element 24 and is reflected by the reflective element 24 back into the optical fiber 18. Most of the light beams 22 do not strike the absorbing element 26.

[0047] 12 shows an embodiment of a rail contact element 10f for dropout detection when not mounted on a rail 12. The optical fiber 18 and the spring element 14 are attached to the body 16. The reflective element 24 is directly attached to the spring element 14. The light absorbing element 26 is indirectly attached to the spring element 14, i.e., the light absorbing element 26 is attached to the reflective element 24, which is attached to the spring element 14. When the rail contact element 10f is not mounted on the rail 12, the spring element 14 is in a relaxed state. In this state, the position of the reflective element 24 and the light absorbing element 26 is such that the light beam 22 emitted through the exit face 20 of the optical fiber strikes the reflective element 24 and is reflected by the reflective element 24 back to the optical fiber 18. The light beam 22 does not strike the absorbing element 26.

[0048] Figure 13 shows the embodiment of Figure 12 when the rail contact element 10f is mounted to the rail 12. The mounted state is "mounted" and the spring element 14 is in tension. In this state, the positions of the reflective element 24 and the light absorbing element 26 are such that the light beam 22 emitted through the exit face 20 of the optical fiber strikes the light absorbing element 26 and is absorbed. The light beam 22 does not strike the reflective element 24 and is therefore not reflected by the reflective element 24 back to the optical fiber 18.

[0049] FIG. 14 shows an embodiment of a rail contact element 10g for dropout detection when not mounted on a rail 12. The optical fiber 18 and the spring element 14 are attached to the body 16. In this embodiment, the spring element 14 is a helical spring. The reflective element 24 is attached directly to the spring element 14. The light absorbing element 26 is attached indirectly to the spring element 14, which is attached to the reflective element 24, which is attached to the spring element 14. When the rail contact element 10g is not mounted on the rail 12, the spring element 14 is in a relaxed state. In this state, the position of the reflective element 24 and the light absorbing element 26 is such that a light beam 22 emitted through the exit face 20 of the optical fiber strikes the reflective element 24 and is reflected by the reflective element 24 back into the optical fiber 18. Most of the light beams 22 do not strike the absorbing element 26.

[0050] Figure 15 shows the embodiment of Figure 14 when the rail contact element 10g is mounted to the rail 12. The mounted state is "mounted" and the spring element 14 is in tension. In this state, the positions of the reflective element 24 and the light absorbing element 26 are such that the light beam 22 emitted through the exit face 20 of the optical fiber strikes the light absorbing element 26 and is absorbed. The light beam 22 does not strike the reflective element 24 and therefore is not reflected back to the optical fiber 18 by the reflective element 24 in this mounted state of this embodiment.

[0051] A helical spring (or other type of spring element) may also be used in a configuration similar to the embodiment shown in Figures 2-13.

[0052] In the embodiment shown in Figures 10 to 15, the cavity in which the spring element 14 can be bent is designed such that the reflective element 24 and / or the light absorbing element 26 are guided by the body 16 or other guiding elements.

[0053] According to the invention, light is guided through the fiber inside the rail contact element and the spring element is used to guide the light emitted from the exit face of the fiber to the reflector element or to position the reflector element in the beam path of the light emitted from the exit face, either in the tensioned or relaxed state of the spring element, as well as to guide the light emitted from the exit face of the fiber below the reflector element or to position the reflector element out of the beam path of the light emitted from the exit face, in the respective other state of the spring element. [Explanation of symbols]

[0054] 10, 10a, 10b, 10c, 10d, 10e, 10f, 10g Rail contact elements 12 Rail 14 Spring elements 16 Main unit 18 Optical Fiber 20 Exit surface 22 Light Beam 24 Reflective elements 26 Light absorbing element

[0055] References [1] EP 3459811 A1 [2] European Patent Application Publication No. 2962915

Claims

1. A rail contact element (10, 10a, 10b, 10c, 10d, 10e, 10f, 10g) for detecting a dislodgment, the rail contact element (10, 10a, 10b, 10c, 10d, 10e, 10f, 10g) is mountable to a rail (12) and comprises a spring element (14), a body (16) for holding the spring element (14), and an optical fiber (18), the spring element (14) being in a tensioned or relaxed state depending on the mounting state of the rail contact element; The optical fiber (18) has an exit face (20) for emitting a light beam (22); The rail contact element (10, 10a, 10b, 10c, 10d, 10e, 10f, 10g) further comprises a reflective element (24); The spring element (14), the reflective element (24), and the optical fiber (18) are positioned such that the effect of the reflective element (24) on the light beam (22) is different in the tensioned state than in the relaxed state. A rail contact element comprising:

2. 2. The rail contact element of claim 1, wherein the position of the reflective element (24) relative to the optical fiber (18) and / or the orientation of the reflective element (24) relative to the exit face (20) of the optical fiber (18) is different in the relaxed state and in the tensioned state of the spring element (14).

3. 3. A rail contact element as claimed in claim 1 or 2, characterized in that the spring element (14), the reflective element (24) and the optical fiber (18) are arranged such that in either the tensioned or relaxed state of the spring element (14), the light beam (22) can be reflected back to the optical fiber (18).

4. 4. The rail contact element according to claim 1, wherein the optical fiber (18) is fixed to the spring element (14), and the spring element (14) and the optical fiber (18) are arranged such that the spring element (14) can emit the light beam (22) in a first direction when the spring element (14) is in the tensioned state, and the spring element (14) can emit the light beam (22) in a second direction when the spring element (14) is in the relaxed state.

5. 4. A rail contact element according to claim 1, characterized in that the reflective element (24) is mounted on the spring element (14), and the spring element (14) and the reflective element (24) are arranged such that when the spring element (14) is in the tensioned state, the spring element (14) can reflect the light beam (22) in a third direction, and when the spring element (14) is in the relaxed state, the spring element (14) can reflect the light beam (22) in a fourth direction.

6. 4. The rail contact element according to claim 1, further comprising a light absorbing element, the light absorbing element, the reflecting element, the optical fiber, and the spring element being arranged such that when the spring element is in the tensioned state, the light beam can be reflected back to the optical fiber, and when the spring element is in the relaxed state, the light beam can be absorbed by the light absorbing element.

7. 4. The rail contact element according to claim 1, further comprising a light absorbing element, the light absorbing element, the reflecting element, the optical fiber, and the spring element being arranged such that when the spring element is in the relaxed state, the light beam can be reflected back to the optical fiber, and when the spring element is in the tensioned state, the light beam can be absorbed by the light absorbing element.

8. Rail contact element according to claim 6 or 7, characterized in that the light absorbing element (26) is attached to or is part of the body (16).

9. Rail contact element according to claim 6 or 7, characterized in that the light absorbing element (26) is mounted on the spring element (14).

10. 10. Rail contact element according to any one of the preceding claims, further comprising a sensor element, in particular a strain sensor element.

11. A dropout detection unit comprising a rail contact element according to any one of claims 1 to 10 and a detector for detecting light reflected back into the optical fibre (18).

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