Abstract
An axle-counting method for railbound vehicles includes the following method steps: coupling light into at least one sensor fiber, wherein the sensor fiber includes at least one fiber Bragg grating mounted on a rail, wherein each fiber Bragg grating has a reflection spectrum having a reflection peak which is at a Bragg wavelength and has a full width at half maximum; generating a difference signal from two shear stress signals through detection and filtering the temporal intensity course of the light power reflected by two Fiber Bragg gratings which are arranged at a separation from one another; and generating a wheel signal if the difference signal exceeds a predetermined shear stress difference limiting value.
Claims
1. An axle-counting method for railbound vehicles, the method comprising the steps of: coupling light into at least one sensor fiber, wherein the sensor fiber comprises at least two fiber Bragg gratings mounted on a rail intersecting and arranged obliquely with respect to a neutral axis of the rail, wherein each fiber Bragg grating has a reflection spectrum having a reflection peak which is at a Bragg wavelength and has a full width at half maximum; detecting the light reflected by two fiber Bragg gratings spaced apart from one another and obtaining from the two fiber Bragg gratings a respective shear stress signal of the rail; generating a shear stress difference signal from the two respective shear stress signals from the two fiber Bragg gratings; and generating a wheel signal within a signal-processing unit if the shear stress difference signal exceeds a predetermined first upper limiting value or falls below a predetermined second lower limiting value.
2. The axle-counting method according to claim 1, wherein sensor fibers each having two fiber Bragg gratings that are arranged in a row and have different Bragg wavelengths are used at two sensor positions that are spaced apart from one another in the rail direction, and wherein the shear stress difference signal is generated optically within a signal-processing unit by means of an optoelectronic component by the temporal intensity profile of the light output reflected in the sensor fiber being filtered at two filter edges of a wavelength filter of the optoelectronic component by means of the optoelectronic component, the filter edges each being in the range of one of the Bragg wavelengths of the fiber Bragg grating and having gradients having different algebraic signs, and wherein the filtered intensity profile is detected as the difference signal, and wherein wheel signals are generated by processing the difference signal within a signal-processing unit.
3. The axle-counting device for performing the method according to claim 2, comprising: a light source; at least one counting unit, wherein each counting unit comprises two rail-contacting halves for mounting to a rail, wherein each rail-contacting half comprises: a sensor fiber comprising a first fiber Bragg grating having a first Bragg wavelength and a second fiber Bragg grating having a second Bragg wavelength, wherein the fiber Bragg gratings are designed to be mounted on the rail obliquely with respect to the neutral fiber; a signal-processing unit having an optoelectronic component for performing an optical subtraction of the light output reflected by the two fiber Bragg gratings of a sensor fiber, wherein the optoelectronic component comprises a wavelength-dependent filter having two filter edges, wherein the filter edges are each in the range of one of the Bragg wavelengths of the fiber Bragg grating and have gradients having different algebraic signs.
4. The axle-counting device according to claim 3, wherein the gradients of the filter edges are of the same absolute value.
5. The axle-counting device according to claim 4, wherein the fiber Bragg gratings of the two rail-contacting halves of a counting unit are arranged within a common sensor fiber.
6. The axle-counting method according to claim 2, wherein the full widths at half maximum of the reflection peaks of the two fiber Bragg gratings differ by less than 0.5 nm, and the reflectivity's of said gratings differ by less than 20%.
7. The axle-counting method according to claim 2, wherein a reference signal is detected from the temporal intensity profile of the light output reflected in the sensor fiber, without said reference signal being filtered by means of the optoelectronic component, and wherein the difference signal is compared with the reference signal.
8. Axle-counting device for performing the method according to claim 7, comprising: a light source; at least one counting unit, wherein each counting unit comprises two rail-contacting halves for mounting to a rail, wherein each rail-contacting half comprises: a sensor fiber, comprising two fiber Bragg gratings arranged in a row, at two sensor positions that are spaced apart from one another, wherein the fiber Bragg gratings are designed to be mounted on the rail obliquely with respect to the neutral fiber, and wherein the Bragg wavelengths of the two fiber Bragg gratings and the distance between the two sensor positions are selected such that the reflection peaks of the two fiber Bragg gratings overlap when the rail is subjected to a predetermined load between the two sensor positions; a signal-processing unit for detecting and subsequently processing the light reflected by the fiber Bragg grating.
9. The axle-counting device according to claim 8, wherein the full widths at half maximum of the reflection peaks of the two fiber Bragg gratings differ by 1 to 2 orders of magnitude.
10. The axle-counting device according to claim 9, wherein the Bragg wavelengths of the two fiber Bragg gratings do not differ by more than 5 nm, and in that the full width at half maximum of one fiber Bragg grating is at least 0.05 nm and the full width at half maximum of the other fiber Bragg grating is at most 5 nm.
11. The axle-counting method according to claim 1, wherein sensor fibers having two fiber Bragg gratings that are arranged in a row and have different Bragg wavelengths are used at two sensor positions that are spaced apart from one another in the rail direction, and wherein the shear stress difference signal is generated optically by a spectral overlap of the reflection peaks of the two fiber Bragg gratings during the transition from an unloaded state to a loaded state.
12. The axle-counting method according to claim 11, wherein the reflection peaks overlap in the loaded state.
13. The axle-counting method according to claim 1, wherein two sensor fibers each having one fiber Bragg grating are used, the fiber Bragg gratings of different sensor fibers being arranged at sensor positions that are spaced apart from one another in the rail direction, and wherein, for each sensor fiber, a filtered signal of the temporal intensity profile of the light output reflected by the fiber Bragg grating in the sensor fiber is generated as a shear stress difference signal within a signal-processing unit by filtration at each filter edge of a wavelength filter of an optoelectronic component, and wherein the shear stress difference signal of the two fiber Bragg gratings is generated electronically by means of a microcontroller.
14. The axle-counting device for performing the method according to claim 13, comprising: a light source; wherein each counting unit comprises two rail-contacting halves for mounting on a rail, wherein each rail-contacting half comprises: a sensor fiber comprising a fiber Bragg grating having a Bragg wavelength, wherein the fiber Bragg grating is designed to be mounted on the rail obliquely with respect to the neutral fiber; a signal-processing unit for generating shear stress signals, wherein the signal-processing unit comprises an optoelectronic component having a filter edge; and comprising a microcontroller for generating a difference signal of the shear stress signals emitted by the signal-processing units.
15. The axle-counting device according to claim 14, wherein the fiber Bragg gratings are attached to the rail in parallel with one another at an angle of from 30 to 60, in particular 45, with respect to the neutral fiber.
16. The axle-counting device according to claim 15, wherein the fiber Bragg gratings intersect the neutral fiber of the rail.
17. The axle-counting device according to claim 16, wherein the fiber Bragg gratings are equipped with a converter structure for compensating for temperature expansion of the rail.
18. The axle-counting device according to claim 17, wherein the fiber Bragg gratings are fastened to the rail under pretension.
19. The axle-counting device according to claim 18, wherein a trimming device is provided for adjusting the pretension under which the fiber Bragg gratings are mounted onto the rail.
20. The axle-counting device according to claim 19, wherein the signal-processing unit comprises a fiber-optic beam splitter.
21. The axle-counting method according to claim 13, wherein a reference signal is detected from the temporal intensity profile of the light output reflected in the sensor fiber, without said reference signal being filtered by means of the optoelectronic component, and wherein the shear stress signal is determined from the ratio of filtered signal to reference signal.
22. The axle-counting method according to claim 1, wherein a fault is identified if the reference signal falls below a predetermined third limiting value.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) The accompanying drawings illustrate the invention. In such drawings:
(2) FIG. 1 shows the schematic structure of a rail-contacting half of an axle-counting device according to the invention according to the EOC concept;
(3) FIG. 2 is a block wiring diagram of the processing of an optical signal received by the rail-contacting half from FIG. 1 (EOC concept);
(4) FIG. 3 shows the profile of the reflection peak relative to the filter edges (EOC concept);
(5) FIG. 4 shows the temporal profile of the photocurrent of the difference signal detected by the photodiodes according to the OEC concept and the portion of the detected photocurrent assigned to the individual fiber Bragg gratings;
(6) FIG. 5 shows the schematic structure of a rail-contacting half of an axle-counting device according to the invention according to the RR concept;
(7) FIG. 6 is a block wiring diagram of the processing of an optical signal received by one of the rail-contacting halves from FIG. 5 (RR concept);
(8) FIG. 7a, b shows the arrangement of the reflection peak in an unloaded and in a loaded state;
(9) FIG. 8 shows the temporal profile of the difference signal according to the RR concept;
(10) FIG. 9 shows the schematic structure of two rail-contacting halves of an axle-counting device according to the invention according to the EO2 concept;
(11) FIG. 10 is a block wiring diagram of the processing of signals received by the two rail-contacting halves according to FIG. 9 (OE2 concept);
(12) FIG. 11 shows the arrangement of a reflection peak relative to the filter edge in an unloaded state of the rail;
(13) FIG. 12a shows the temporal profile of the shear stress signals of the two rail-contacting halves according to the OE2 concept;
(14) FIG. 12b shows the temporal profile of the difference signal according to the OE2 concept;
(15) FIG. 13a shows fiber Bragg gratings of two rail-contacting halves fastened to a rail ac-cording to the OEC and RR concepts with separate sensor fibers;
(16) FIG. 13b shows fiber Bragg gratings of two rail-contacting halves fastened to a rail ac-cording to the OEC and RR concepts with a common sensor fiber;
(17) FIG. 13c shows fiber Bragg gratings of two rail-contacting halves fastened to a rail ac-cording to the OE2 concept;
(18) FIG. 14 is a cross section of a rail with a fiber Bragg grating fastened to the rail ac-cording to FIG. 13a-c; and
(19) FIG. 15 shows the general structure of an axle-counting device according to the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
(20) FIG. 1 shows the structure of a rail-contacting half SK1 of an axle-counting device according to the invention according to the EOC concept. The rail-contacting half SK1 comprises a sensor fiber SF having two fiber Bragg gratings FBG1, FBG2, which are spaced apart from one another and are preferably pre-assembled on a bracket T such that they can be mounted on a rail S simply in the desired orientation (see FIG. 13a, b). The fiber Bragg gratings FBG1, FBG2 have different Bragg wavelengths 1, 2 and accordingly reflect light of the relevant Bragg wavelength 1, 2. Light is coupled into the sensor fiber SF by means of a light source L. The light reflected by the fiber Bragg gratings FBG1, FBG2 is transmitted to an optoelectronic component OEC by means of a fiber coupler FK, within which optoelectronic component the reflected light is processed. In the present case, the optoelectronic component OEC and the light source L are part of a signal processing unit SV.
(21) FIG. 2 shows how the reflected light is subsequently processed within the signal processing unit SV. The reflected light is transmitted from the sensor fiber SF into the optoelectronic component OEC, in which the light is split by means of a beam splitter ST. In a first channel, the reflected light is filtered by means of a wavelength filter F and detected as an electrical difference signal SD by means of a first photodiode PD1. In a second channel, the reflected light is transmitted directly onto a second photodiode PD2 and detected there as a reference signal SR, the reference signal SR being proportional to the total reflected light output. Ac-cording to the invention, the wavelength filter F has two filter edges K1, K2, the two filter edges K1, K2 having gradients that have different algebraic signs. Owing to the different algebraic signs, shifts of the Bragg wavelengths 1, 2 of the two fiber Bragg gratings FBG1, FBG2, for example to larger wavelengths, are evaluated differently, i.e. due to an increase in the detected light output in the case of the first fiber Bragg grating FBG1, and due to a reduction in the detected light output in the case of the other fiber Bragg grating FBG2.
(22) Transimpedance amplifiers V1, V2 convert the difference signal SD and reference signal SR into stress signals. Said stress signals can now be subsequently processed (for example, by low pass filtering). In order to determine the actual measured variable, the ratio between the difference signal SD and the reference signal SR is provided. Path neutrality is thus achieved and measurements which are independent of damping effects are made possible. The signal generated thus is proportional to the axle load, which can be analyzed separately. The analogue signal can be converted into a digital wheel signal (wheel pulse RI1) with the aid of a comparator.
(23) FIG. 3 shows a possible profile of the filter edges K1, K2 relative to the reflection peak P1, P2 of the fiber Bragg grating FBG1, FG2. The two filter edges K1, K2 have the same absolute value of gradient, but are inclined in different directions in the diagram shown (different algebraic signs). The reflection peaks P1, P2 of the fiber Bragg gratings FBG1, FBG2 are selected so as to be symmetrical to the filter edges K1, K2. The filter edges K1, K2 extend through the reflection peaks P1, P2 such that shifts of the reflection peaks to larger and to smaller wavelengths lead to a change in light intensity, a shift of the first reflection peak P1 to larger wavelengths causing an increase in intensity, whereas a shift of the second reflection peak P2 to larger wavelengths brings about a reduction in intensity.
(24) FIG. 4 is a diagram of the profile of the difference signal SD (solid curve) and of the portions of the light reflected by the fiber Bragg grating FBG1, FBG2 in each case from the difference signal (FBG1: dashed curve, FBG2: dotted curve). In the example shown, the first fiber Bragg grating is compressed owing to an approaching load and the Bragg wavelength 1 of the first fiber Bragg grating FBG1 is shifted to larger wavelengths, i.e. along the rising filter edge K1. An increase in the intensity of the light output is brought about as a result of this. If the load moves over the first fiber Bragg grating FBG1 towards the second fiber Bragg grating FBG2, the first fiber Bragg grating FBG1 is stretched, the Bragg wavelength 1 of the first fiber Bragg grating FBG1 is therefore shifted to smaller wavelengths (along the falling filter edge K1) while the second fiber Bragg grating FBG2 is compressed, the Bragg wave-length 2 of the second fiber Bragg grating FBG2 is therefore shifted to larger wavelengths (along the falling filter edge K2). This results in the difference signal SD in the profile shown in FIG. 4. A wheel pulse RI1 is detected if the difference signal SD falls below a predetermined limiting value G.
(25) FIG. 5 shows the structure of a rail-contacting half SK1 of an axle-counting device according to the RR concept. The rail-contacting half SK1 comprises a sensor fiber SF having two fiber Bragg gratings FBG1, FBG2, which are spaced apart from one another and are prefer-ably preassembled on a bracket T such that they can be mounted simply on a rail S in the desired orientation (see FIG. 13a, b). The fiber Bragg gratings FBG1, FBG2 have different Bragg wavelengths 1, 2 and accordingly reflect light of the relevant Bragg wavelength 1, 2. Light is coupled into the sensor fiber SF via a light source L. The light reflected by the fiber Bragg gratings FBG1, FBG2 is transmitted into a signal processing unit SV, in which the reflected light is processed. The light source L in the present case is part of the signal processing unit SV.
(26) FIG. 6 shows how the reflected light is subsequently processed within the signal processing unit SV. The reflected light is detected as an electrical difference signal SD by means of a photodiode PD. Shifts of the Bragg wavelengths 1, 2 of the two fiber Bragg gratings FBG1, FBG2. A transimpedance amplifier V converts the difference signal SD into a stress signal. Said stress signal can now be subsequently processed (for example, by low pass filtering). The analogue signal can then be converted into a digital wheel signal (wheel pulse RI1) with the aid of a comparator.
(27) FIG. 7a, b show a particularly advantageous example of the reflection peaks P1, P2 of the two fiber Bragg gratings FBG1, FBG2 in an unloaded state (FIG. 7a) and in a loaded state (FIG. 7b). The reflection peaks P1, P2 have different full widths at half maximum FWHM. In the unloaded state, the reflection peaks P1, P2 overlap slightly in the example shown such that shifts of the reflection peaks to larger and also to smaller wavelengths lead to a change in light intensity, a shift of the reflection peaks P1, P2 away from one another causing an increase in intensity whereas a shift of the reflection peaks P1, P2 towards one another brings about a decrease in intensity since an overlapping of the reflection peaks P1, P2 reduces the bandwidth of the reflected light. A difference signal SD is generated by the over-lapping of the reflection peaks P1, P2 since part of the light to be reflected by the second fiber Bragg grating FBG2 is already reflected by the first fiber Bragg grating FBG1 and therefore does not reach the second fiber Bragg grating FBG2 and consequently cannot be reflected by the second fiber Bragg grating FBG2.
(28) FIG. 8 is a diagram of the profile of the difference signal SD. In the example shown, the first fiber Bragg grating is compressed owing to an approaching load and the first reflection peak P1 of the first fiber Bragg grating FBG1 is shifted to larger wavelengths, i.e. towards the second reflection peak P2. As a result of this, the overlapping of the reflection peaks P1, P2 increases, which leads to a reduction in intensity of the light output. If the load moves over the first fiber Bragg grating FBG1 towards the second fiber Bragg grating FBG2, the first fiber Bragg grating FBG1 is stretched, the Bragg wavelength 1 of the first fiber Bragg grating FBG1 and therefore the first reflection peak P1 is shifted to smaller wavelengths, while the second fiber Bragg grating FBG2 is compressed, the second reflection peak P2 of the second fiber Bragg grating FBG2 is therefore shifted to larger wavelengths. The reflection peaks P1, P2 therefore move away from one another. As a result of this, the overlap of the reflection peaks P1, P2 reduces, which leads to a rapid increase in the intensity of the light output. This results in the profile of the difference signal SD shown in FIG. 8. A wheel pulse RI1 is detected if the difference signal SD exceeds a predetermined limiting value G.
(29) FIG. 9 shows the structure of two rail-contacting halves SK1, SK2 of an axle-counting device according to the invention according to the EO2 concept. The rail-contacting halves SK1, SK2 each comprise one sensor fiber SF having one fiber Bragg grating FBG1, FBG2. The fiber Bragg gratings FBG1, FBG2 of the two rail-contacting halves SK1, SK2 have Bragg wavelengths 1, 2 and accordingly reflect light of the relevant Bragg wavelength 1, 2. In this variant, the Bragg wavelengths 1, 2 can be the same. Light is coupled into the sensor fibers SF via a light source L in each case. In principle, however, just one single light source can be provided which supplies light into the two sensor fibers SF. The light reflected by the fiber Bragg gratings FBG1, FBG2 is transmitted by means of a fiber coupler FK to an optoelectronic component OEC within each rail-contacting half SK1, SK2, in which optoelectronic component the reflected light is processed. The optoelectronic components OEC and the light source L are parts of the signal-processing unit SV in the present case. The optoelectronic components OEC convert the detected signals into electrical currents, process said currents and subsequently conduct them to a microcontroller MC in which a difference signal is generated. Within the microcontroller MC, a digital signal is generated from the difference signal by means of establishing the threshold value, which digital signal is emitted as a wheel pulse.
(30) FIG. 10 shows how the reflected light is subsequently processed in the signal-processing units SV. The light reflected in the two sensor fibers SF is transmitted from the sensor fibers SF into the optoelectronic components OEC, in which the light is split by means of a beam splitter ST. The reflected light is filtered within a first channel in each case by means of wavelength filters F having a filter edge K and detected as shear stress signals S1, S2 by means of first photodiodes PD1. The reflected light is transmitted directly onto second photodiodes PD2 within a second channel in each case and detected there as reference signals SR1, SR2, the reference signals SR1, SR2 being proportional to the total light output reflected in the relevant sensor fiber SF1, SF2. Transimpedance amplifiers V1, V2 convert the shear stress signals S1, S2 and the reference signals SR1, SR2 into stress signals. Said stress signals can now be subsequently processed (for example, by low pass filtering). In order to determine the actual signals to be subsequently processed, the ratio between the difference signal SD and the reference signal SR is provided. These ratio signals are then transmitted to the microcontroller MC, which generates a difference signal by subtracting the electrical signals.
(31) FIG. 11 shows a possible profile of the first filter edge K relative to the first reflection peak P1 of the first fiber Bragg grating FBG1. The filter edge K extends through the reflection peak P1 such that shifts of the reflection peak to larger and also to smaller wavelengths lead to a change in light intensity, a shift of the first reflection peak P1 to larger wavelengths causing a reduction in intensity, whereas a shift of the first reflection peak P1 to smaller wavelengths causes an increase in intensity. The profile of the second filter edge K relative to the second reflection peak P2 of the second fiber Bragg grating FBG2 is preferably the same.
(32) FIG. 12a shows the temporal profile of the shear stress signals of the two rail-contacting halves according to the OE2 concept.
(33) If the difference of the two shear stress profiles is formed, this is at a maximum when the load transfer into the rails by the wheel takes place precisely between the two sensors, as shown in FIG. 12b.
(34) FIG. 13a, 13b show fiber Bragg gratings FBG1, FBG2, which are fastened to a rail S, of two rail-contacting halves SK1, SK2 according to the OEC and RR concepts. A first fiber Bragg grating FBG1 and a second fiber Bragg grating FBG2 are each arranged together on a bracket T at two sensor positions SS1, SS3 which are spaced apart from one another in the rail direction, which bracket is mounted on the rail S under pretension. In FIG. 13a, a separate sensor fiber SF is provided for each rail-contacting half SK1, SK2 into which sensor fiber the first fiber Bragg grating FBG1 and the second fiber Bragg grating FBG2 are written, the two fiber Bragg gratings FBG1, FBG2 being spaced apart from one another. FIG. 13b shows an-other embodiment, in which the fiber Bragg gratings FBG1, FBG2 of the two rail-contacting halves SK1, SK2 are part of one single sensor fiber SF. The signals are transmitted by means of a frequency-separating filter FW to the signal processing units SV of the corresponding rail-contacting halves SK1, SK2. The four fiber Bragg gratings FBG1, FBG2 must, however, have different Bragg wavelengths for this purpose.
(35) FIG. 13c shows fiber Bragg gratings of two rail-contacting halves fastened to a rail according to the OE2 concept. Each fiber Bragg grating FBG1, FBG2 is written into its own sensor fiber SF1, SF2 and preassembled on a bracket T in each case.
(36) In FIG. 13a and FIG. 13c, the fiber Bragg gratings FBG1, FBG2 are fastened to the rail at a 45 angle relative to the neutral fiber NF. FIG. 13b on the other hand shows an embodiment in which the fiber Bragg gratings FG1, FBG2 are fastened to the rail at an angle of 45 relative to the neutral fiber NF. The two attachment options are possible with all three concepts described here. The different orientations of the fiber Bragg gratings FBG1, FBG2 in FIG. 13a, c on the one hand and FIG. 13b on the other hand have the effect that the shear stress signals and also the difference signal having different algebraic signs are emitted. Preferably, an orientation is selected such that the wheel signal is emitted as a minimum. Preferably, the two fiber Bragg gratings are arranged at a spacing of about 150 mm from one another. If the two sensor elements are located close enough to one another (preferably closer than 150 mm), they also both experience the same temperatures such that a varying temperature behavior of the fiber Bragg gratings does not occur. Torsions of the rail as a result of lateral input of force into the rail head can also be compensated in this manner.
(37) FIG. 14 is a cross section of a rail S, having a fiber Bragg grating attached to the rail S by means of a bracket T according to FIG. 13a-c.
(38) FIG. 15 shows the general structure of an axle-counting device according to the invention. The axle-counting device shown comprises two counting units ZP each having two rail-contacting halves SK1, SK2, each rail-contacting half SK1, SK2 generating a wheel pulse RI1, RI2 which is transmitted to a counting device within each counting unit. The direction of travel can be determined within each counting unit using the wheel pulse RI1, RI2. The detected information (wheel pulses RI1, RI2, direction of travel) are transmitted to an evaluation unit ACE.
LIST OF REFERENCE SIGNS
(39) ACE evaluation unit
(40) F wavelength filter
(41) FBG1, FBG2 fiber Bragg gratings
(42) FK fiber coupler
(43) FW frequency separating filter
(44) FWHM full width at half maximum
(45) G limiting value
(46) K, K1, K2 filter edges
(47) L light source
(48) MC microcontroller
(49) NF neutral fiber
(50) OEC optoelectronic component
(51) P1, P2 reflection peaks
(52) PD, PD1, PD2 photodiodes
(53) RI1, RI2 wheel pulse
(54) SK1, SK2 rail-contacting halves
(55) S rail
(56) SF sensor fiber
(57) SS1, SS2 sensor positions
(58) ST beam splitter
(59) SV signal processing unit
(60) SD difference signal
(61) SR, SR1, SR2 reference signal
(62) S1, S2 shear stress signals
(63) T bracket
(64) V, V1, V2 transimpedance amplifier
(65) ZP counting unit
(66) 1, 2 Bragg wavelengths
