Claims:We Claim
1. A system for real time detection of vertical strain on the rail, in connection with a passing of a rail vehicle, the system comprising:
one or more packaged structure100 incorporating one or more Fiber Bragg Grating (FBG) sensor 101, to obtain stress;
an optoelectronic instrument 104 to analyze the change in Bragg wavelength of sensor, wherein said change in wavelength are generated based on stress variations on the sensor;
a data processing unit(DPU) 105 to process change in Bragg wavelength and generate corresponding strain on the rail; and
GUI 106 of the authorized person to display the strain corresponds to change in Bragg wavelength of the FBG sensor.
2. The system as claimed in claim 1, wherein the packaged structure 100 is metallic packaged Fiber Bragg Grating (FBG) sensor structure.
3. The system as claimed in claim 2, wherein the packaged structure 100 is mounted underneath the rail in between two sleepers.
4. The system as claimed in claim 1, wherein an authorized person includes driver, station master, or any other competent railway personnel that remotely monitors vertical strain with respect to change in stress on the sensor.
5. The method for real time detection of vertical strain on the rail, in connection with a passing of a rail vehicle, the method comprising:
providing one or more packaged structure 100 incorporating one or more bare Fiber Bragg Grating (FBG) sensor 101 for producing a signal corresponding to stress on the rail;
mounting said packaged structure 100 underneath the rail;
obtaining stress variations due to movement of vehicle and shift in Bragg wavelength of said FBG sensor 101;
analyzing shift in Bragg wavelength of said FBG sensor 101;

converting shift in Bragg wavelength of said FBG sensor 101 to the strain applied vertically on the rail; and

displaying the vertical strain on the rail at GUI 106 of authorized user.

6. A metallic packaged structure 100 incorporating Fiber Bragg Grating (FBG) sensor comprising:
two or more fixtures 103;
a sensor element 102 , a metallic plate fixed on plurality of fixtures; and
a bare fiber Bragg grating (FBG) sensor 101 with armoured fiber optic cable, embedded on the surface of sensor element 102.
7. The metallic packaged structure100 incorporating Fiber Bragg Grating (FBG) sensor as claimed in claim 6, wherein bare FBG sensor 101 is coated at least one of acrylate, polyimide material.
8. The metallic packaged structure100 incorporating Fiber Bragg Grating (FBG) sensor as claimed in claim 6, wherein the sensor element 102 is constructed in at least one of rectangular, DOG BONE/I-shaped metallic plate.
9. The metallic packaged structure100 incorporating Fiber Bragg Grating (FBG) sensor as claimed in claim 8, wherein the sensor element 102 is made of at least one of stainless steel, brass, aluminium, EN-24 and Hastelloy C-22 material.
10. A manufacturing method of a metallic packed structure100 for detecting vertical strain, the method comprising the steps of:
fixedly mounting a sensor element 102 on plurality of fixtures103 wherein the fixtures are metallic;
obtaining one or more bare Fiber Bragg Grating (FBG) sensor 101 with fiber optic cable;
pasting of said FBG sensor101 with fiber optic cable on the surface of sensor element 102 to obtain metallic packed structure 100; and
fastening of the structure 100 using clamps with the rail.
11. The manufacturing method for a metallic packed structure 100 for detecting vertical strain as claimed in claim 10, wherein the sensor element 102 is mounted on the plurality of fixtures 103 using at least one of welding, fastening, crimping, etc.
12. The manufacturing method for a metallic packed structure 100 for detecting vertical strain as claimed in claim 10, wherein bare FBG sensors 101 is pasted on sensor element using at least one adhesive material includes M bond 200, glue, steel tape etc.
13. The manufacturing method for a metallic packed structure 100 for detecting vertical strain as claimed in claim 12, wherein the metallic sensor element with FBG sensor 101 and fiber optic cable is covered with M-Coat protective coating to protect from the external environment.
14. The manufacturing method for a metallic packed structure 100 for detecting vertical strain as claimed in claim 13, wherein the fiber optic cable is armoured cable.

, Description:A system for measuring vertical strain using packaged structure and the method thereof
TECHNICAL FIELD

[0001] The present invention relates to a kind of optical fiber sensing technology, relate in particular to a kind of Fiber Bragg Grating (FBG) sensor. The present invention discloses a system for measuring vertical strain on the rail, in connection with a passing of a rail vehicle using metallic packaged Fiber Bragg Grating sensor structure, and the method for the same. The invention also discloses about metallic packaged Fiber Bragg Grating (FBG) sensor structure as monitoring device and the method of manufacturing this device.

BACKGROUND

[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0003] The fiber optic sensor is a photo-electric sensor which uses optical fiber as sensing element. The principle of fiber optic sensor is that the light form a laser or any super luminescent source is transmitted through optical fiber result in changes in its parameters. Further detectors measure those changes. The optical fiber detects certain parameters such as mechanical strain or temperature, concentrations of chemical species, acceleration, rotations, pressure, vibrations and displacements etc. The sensor has an optical fiber connected to a light source to allow for detection in tight spaces. Fibers have so many uses in the field of remote sensing because they require no electrical power at the remote location and they have tiny size. Optical fiber sensors are widely used in various industries due to their many advantages, such as small size, light weight, resistant to high temperature, high accuracy and sensitivity, excellent range and resolution, immunity to electromagnetic interference and radiation, corrosion resistance, fire prevention, explosion proof, multiplexing capabilities and long service life etc.
[0004]Fiber Bragg grating is the reflector in optical fiber that reflect particular wavelength of light and transmit all other wavelength. The reflected wavelength, called Bragg wavelength, depends on the effective refractive index of the fundamental mode propagating through the fiber and period of the grating/modulation. Fiber Bragg gratings can then be used as direct sensing elements for strain and temperature. Fiber grating sensor is a type of fiber optic sensors having gratings to monitor shift in wavelength corresponds to the changes in strain and temperature. According to Maxwell's equations and the coupled-mode theory, the Bragg wavelength ?B can be expressed as
?B=2neff? (1)
where neff is the effective refractive index of fiber core, and ? is the grating pitch.
According to the equation (1), the Bragg wavelength ?B depends on the effective refractive index neff of the fiber core and the periodicity of the grating A. The effective refractive index, as well as the periodic pitch between the Bragg grating planes, will be affected by changes in temperature and strain. The change in the effective refractive index neff is related to the thermo-optic effect and stain-optic effect induced by changes in temperature and strain, as well as the change in grating pitch ?, which is related to thermal expansion and mechanical deformation induced by changes in temperature and strain. Accordingly, the measurement of temperature and stress/strain can be achieved by monitoring the changes in the Bragg wavelength ?B.
[0005]FBG sensors have multiple applications in the field of civil and geotechnical engineering, Security and perimeter monitoring, Medical and biotech, Industrial, Telecommunications, Commercial transportation etc. But FBG sensors have some limitations also. The limitation of FBG sensors includes high sensitivity, expensive to build and maintain, difficulty in discriminating wavelength shift due to temperature and strain separately, difficulty in demodulation of wavelength shift and decaying of reflectivity at high temperature, etc.
[0006]The two types of strain which are applied by the passing train on the rail at rail-wheel contact include Vertical strain and lateral strain. Vertical strain is the strain vertically applied by the train on the rail and lateral strain is the strain applied horizontally or at certain angle to the baseline of the rail. The FBG sensors are mounted on the rail to detect vertical strain on the rail due to each wheel, number of axles, dead load, bad wheels etc.
[0007]Accordingly, for effectively monitoring the strain, a packaged sensor for protecting the fragile bare FBG sensors from outer environment and to amplify the signals, is highly desirable. Also, there is enormous scope of accurate, reliable and real time assembly of fiber optical sensors which can measure various forms of strain at rail-wheel contact point.
[0008]Patent Application No. CN103309002A, entitled “Capillary sensitivity enhancing packaging device capable of applying pre-stress to fiber grating” relates to a compact system that apply pre-stressed capillary type enhanced sensitivity packaging system to fiber grating. But the system is too complex and does not provide information regarding sensitivity of the sensor and sensors protection.
[0009]Therefore, there exists need for sensors protection, pre-tensioning issues during sensor installation due to high sensitivity, sensor stability at high temperature and real time strain monitoring.

OBJECTS OF THE INVENTION

[0010] An object of the present disclosure is to resolve problems and disadvantages of conventional technologies as described above.
[0011] An object of the present disclosure is to provide a metallic packaged Fiber Bragg Grating sensor structurethat is easy to install, use, and configure underneath the rail.
[0012] It is an object of the present disclosure to characterize the change in Bragg wavelength of FBG sensors due to strain.
[0013] Another object of the present disclosure is to provide a method of manufacturing of metallic packaged Fiber Bragg Grating sensor structure.
[0014] It is an object of the present disclosure to provide a system that can protect the sensor from external environment.
[0015] It is also an object of the present discloser to detect real time vertical strain on the rail.

SUMMARY

[0016]The present invention fulfils the foregoing needs by providing a system for real time detection of vertical strain on the rail, during movement of a rail vehicle. The system includes a sensor structure incorporating assembly of fiber optical sensors, inserted under the rail to obtain stress. Further, an optoelectronic instrument analyzes the change in Bragg wavelength due to stress variations on the sensor. Also the data processing unit (DPU) processes the variations in Bragg wavelength and generate corresponding load. The GUI of the user displays the load to authorized personnel.
[0017] The invention also discloses metallic packaged Fiber Bragg Grating (FBG) sensor structure for vertical strain sensing on the rail in real time. The packaged structure includes pair of fixtures, a bare fiber Bragg Grating (FBG) sensor with armoured fiber optic cable and a metallic sensor element. This metallic packaged Fiber Bragg Grating Structure act as a monitoring device and mounted underneath the rail for vertical strain sensing.
[0018]The invention also provides a method for manufacturing of metallic packed Fiber Bragg Grating sensor structure for vertical strain sensing on the rail, during movement of a rail vehicle. The method includes pair of fixtures on which a sensor element is welded. Here, the sensor element can be I-shaped/DOG BONE shaped or rectangular shaped metallic plate. Further, the metallic plate is made of Hastelloy C-22, stainless steel, aluminium, EN-24 etc. Additionally, the method includes obtaining metallic packaged FBG sensor structure from bare Fiber Bragg grating (FBG) sensor with armoured fiber optic cable. Here, the clamps are fastened with fixture to attach the structure to the rail.
[0019] Hence, the present invention provides a sensor package structure which is designed to allow a good mechanical contact between the FBG sensor and the rail surface while providing sufficient protection to the fiber. The package structure is easy to install, simple design, increase efficiency, cost saver, saves from multiple tuning of FBG sensor. The invention also provides real time monitoring of vertical strain using said sensor package structure for various applications like load detection on each wheel, dead load, bad wheel, axle count etc.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.
[0021] FIG. 1 illustrates Fiber Bragg Grating (FBG) sensor structurein accordance with an embodiment of the present disclosure.
[0022] FIG. 2(a, b) illustrates I shaped/bone shaped Sensor element (top view, bottom view), FIG.2(c) illustrate sensor element design in accordance with embodiments of the present disclosure.
[0023] FIG. 3(a) illustrates rectangular Sensor element (top view, bottom view), FIG. 3(b) illustrate sensor element design in accordance with embodiments of the present disclosure.
[0024] FIG. 4 is a schematic view of the installation of packaged Fiber bragg Grating (FBG) sensor structure underneath the rail when the packaged structure is fixed in between two sleepers of the rail, in accordance with an embodiment of the present disclosure.
[0025] FIG. 5(a, b, c)is a schematic view (side, front, bottom) of the Packaged structure with the rail. FIG. 5c(i, ii) shows respective bottom view of DOG BONE shaped and rectangular shaped sensor element based packaged structure with the rail section.
[0026] FIG.6 is a strain plot of a sensor located under a wheel as the wheel occupies the track, in accordance with an embodiment of the present disclosure.
[0027] Fig. 7 is a wavelength shift vs time plot with Fiber Bragg Grating (FBG) sensor structure installed under the rail, during train movement for train axle counting, weight measurement in motion, bad wheel detection, speed measurement, etc., in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION

[0028]Unless the context requires otherwise, throughout the specification and claims which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense that is as “including, but not limited to.”
[0029] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.
[0030] As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise. It should also be noted that the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise.
[0031] The headings and abstract of the disclosure provided herein are for convenience only and do not interpret the scope or meaning of the embodiments. Reference will now be made in detail to the exemplary embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.
[0032] The following discussion provides many example embodiments of the inventive subject matter. Although each embodiment represents a single combination of inventive elements, the inventive subject matter is considered to include all possible combinations of the disclosed elements. Thus if one embodiment comprises elements A, B, and C, and a second embodiment comprises elements B and D, then the inventive subject matter is also considered to include other remaining combinations of A, B, C, or D, even if not explicitly disclosed.
[0033] Embodiments of present disclosure described herein relate to a monitoring device, having metallic packaged Fiber Bragg Grating (FBG) Structure for vertical strain sensing on the rail in real time for real time train traffic control based on Fiber Bragg Grating (FBG) sensors. FBG sensor is configured to transduce vibrations into strain and generate corresponding signal that are interpreted and recorded by an optoelectronic instrument and data processing unit (DPU) for further analysis.
[0034]As depicted in FIG.1, the present invention is achieved like this, it comprises bare sensor 101 with fiber optic cable, metallic sensor element 102 and plurality of fixture 103.
[0035]In an embodiment, the sensor element 102 is welded to the fixtures103. A bare sensor 101with fiber optic cable is embedded on the surface of sensor element 102 to obtain sensor structure thatoffer good mechanical contact between the sensor structure and rail for capturing the rail deformation due to rail wheel contact.
[0036]The sensor is fiber Bragg grating sensor 101 for the assembling of sensor. The bare sensor 101 is acrylate or polyimide coated FBG sensor.Further, acrylate coated FBG sensor 101 is preferred for strain based applications and polyimide is preferred for temperature based application.And the fiber optic cable is preferably armoured fiber cable.
[0037]Further in fig. 1, the sensor element 102 is a metallic plate and aligned to the direction of rail. Further, the metallic plate 102 is constructing in rectangular, DOG BONE shaped etc. for detecting strain on the rail section, where the weight of rail sections (Kg/meter) is following International Union of Railways (UIC), Indian Railway Standard (IRS), and Revised British Standard (RBS) etc. Additionally, the plate is made of various metals like stainless steel, brass, aluminium, EN-24 and Hastelloy C-22 etc. Wherein, DOG BONE/I-shaped metallic plate is preferred to make with Hastelloy C-22 material. Hastelloy C-22 material is Nickel-chromium-molybdenum alloy,anti-corrosion specially localized corrosion and also stress corrosion cracking and corrosion of weldments with good material memory and sensing characteristics. And rectangular metallic plate is preferred to make with stainless steel material.
[0038]Further in fig. 1, the packaged structure 100 which is a robust metal structure mounted underneath the rail in between the sleepers in connection with a passing of a rail vehicle. In other embodiment, the fixture103 is made up of stainless steel, EN-24, any alloy metal or plastic etc. The sensor element 102 is (which is placed horizontally/ align with the rail) welded at both side with fixtures 103 (which is placed vertically) and clamps are helping in holding the structure to the rail using fasteners. The system further includes a sensor structure 100 incorporating assembly of fiber optical sensors 101, inserted under the rail to obtain stress. Further, an optoelectronic instrument 104 analyzes the change in Bragg wavelength due to stress variations on the sensor. Also the data processing unit (DPU) 105 processes the variations in Bragg wavelength and generate corresponding load on rail section. The GUI 106 of the user displays the load to authorized person. Here, the authorized person can be driver, station master, or any other competent railway personnel.
[0039]As shown in Fig. 2, another embodiment of one of the technology of the present invention solution is sensor element 102 (shown in Fig.1). The sensor element is metallic plate having shape similar to English Alphabet “I” shaped cross-section or DOG BONE shaped. Fig. 2(a, b) shows the top view and bottom view of sensor element. The bare sensor is aligned to sensor element and fixed on the surface of sensor element. Fig. 2(c) shows the design of the I-Shaped metallic sensor element. The length of metallic plate is 150mm, width is 30mm and the thickness of the plate is 3mm. The groove of size 20*3mm is cut, at both end of metallic plate for fixing fiber optical cable.
[0040] Fig. 3, shows another design of metallic plate having rectangular shape. Fig. 3a, shows the sensor element with tube at both ends. Further, the tube is made of stainless steel and fixed using strain gauge adhesive. The bare sensor is aligned to sensor element and fixed on the surface of sensor element. Fig. 3 (b) shows the design of the rectangular shaped metallic sensor element. The length of metallic plate is 100mm, width is 30mm and the thickness of the plate is 0.5mm. The stainless steel tube is fixed with sensor element for placing fiber optical cable. This steel tube also saves the sensor from cutting at the corner of metallic plate.
[0041]Quick fix, Mbond 200 etc. are the installation strain gauge adhesive used for fixing bare sensor with optical cable on the metallic sensor element. At last, the sensor element with sensor and optical cable is coated with M-Coat (A, B, W, J….) protective coating. Where, M-Coat F is preferred for outdoor applications, specifically shielding from rain, snow. The sensor element coated with M-Coat F is added with Aluminum foil to protect from moisture or other natural activities.
[0042] The installation of packaged Fiber bragg Grating (FBG) sensor structure 100 on rail is shown in Fig. 4. The structure includes bare sensor 101, sensor element 102 and plurality of fixtures 103 as disclosed in Fig.1. The packaged structure 100 is installed using fasteners like nut, bolt, screw etc on the foot of the rail. Here, the clamps are helping to hold the structure to the rail. Also, the packaged structure 100 is installed in between two sleepers of the rail for measuring vertical strain, during train operations.
[0043]In other embodiment, one or more packaged structure 100 can be installed in between the sleeper of the rail. When the train moves over the rail, the rail obtains stress due to vertical strain. The train includes goods trains/freight trains or passenger trains, etc.
[0044]Further in Fig.5, the view of positioning of packaged structure 100down the rail. Fig. 5 (a,b,c) shows the side view, front view and bottom view of packaged structures 100 positioned down the rail. The structure 100 is robust metal protective casing and the fixture is fastened using clamps to the foot of the rail. Also, the sensor element having bare sensor is positioned as ground facing and aligned to the rail section. Fig. 5c (i, ii) shows the bottom view of packaged structure with DOG BONE shaped and rectangular shaped sensor element respectively.
[0045]Fig. 6 shows strain plot on the rail. Fig. 6 (a, b) shows vertical strain transmitted from the wheel to the rail during operations. During train operations, when the vertical strain is applied, it results in both upward and downward forces on the rail leads to deformation in its structure. The sensor installed under the rail inside packaged structure, obtains stress due to rail deformation and leads to change in Bragg wavelength. The change in Bragg wavelength generates vertical strain on the rail.
[0046]The invention discloses a packaged structure for sensing vertical strain on the rail. The solution can be used for any application for measuring vertical strain transmitted from the wheel to the rail during train operations. The Applications includes Axle counting System, Wheel impact load Detector (WILD) etc.
[0047] For example Fig.7 is showing the axles of a running train. Each peak indicates each axle of the train. The plot shows the change in wavelength (in Pico meter) of the sensor with respect to time (in seconds), when a train is running over rail instrumented with the packaged structure described above. The sensor of the structure obtains stress and corresponding change in Bragg wavelength of the sensor. Fig.7 shows the value of vertical strain with respect to each axle of the train in Pico meter. As expected, it is observed that strain caused by the movement of locomotive is higher than that caused by the movement of the coaches. Hence, the strain of locomotive is about 300 pm and of coaches are 100-200 pm range.
[0051]Hence, the proposed structure provides real time information regarding vertical strain on the rail. The real time information to authorized personnel and train operation management increases efficiency and safety for railways. Also, the packaged structure improves the sensor stability, safety, efficiency during train operations.
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