AN AXLE COUNTING SYSTEM FOR RAILWAY TRANSIT AND DEMODULATION METHOD THEREFOR

Abstract

 The present invention provides a rail transit axle counting system and a demodulation method thereof. The system comprises a sensor component and a fastener. The sensor component is connected to the fastener; N fiber grating sensors are fixed in the sensor component; and the N fiber grating sensors at least comprise a second fiber grating sensor and a fourth fiber grating sensor; the second fiber grating sensor and the fourth fiber grating sensor are arranged at both ends inside the sensor component; and the second fiber grating sensor and the fourth fiber grating sensor are both configured to collect a strain signal of a passing train. The axle counting system provided by the present invention is highly integrated, which is beneficial to simplifying installation steps, reducing the difficulty and cost of engineering construction, easy to maintain and replace, and high in safety.

Description

TECHNICAL FIELD

[0001] The present invention belongs to the technical field of rail transit safety monitoring, and in particular relates to a rail transit axle counting system and a demodulation method thereof.

BACKGROUND ART

[0002] After years of development, railway transportation technology has been extremely influential both in application fields and coverage areas. Therefore, more stringent requirements are put forward for the safety of rail transit. Nowadays, there are two main ways for rail axle counting, namely, electrical and magnetic axle counting schemes and fiber grating axle counting schemes.

[0003] The track circuit mainly is an electrical loop mainly consisting of axles and rails, and is a set of equipment formed by a conductor, a steel rail insulator, power transmission equipment, power receiving equipment and a current-limiting resistor, and is configured to determine whether a to-be-tested section is occupied by the train or not. When the electromagnetic axle counter is used for axle counting, a transmitting coil and an induction coil need to be arranged on both sides of the rail respectively so as to make an axle counting point located in a magnetic field. When the train passes the axle counting point, induced electromotive force on the induction coil changes with respect to the induced electromotive force when there are no wheels, it is determined that there is a train passing by to achieve axle counting, and then the function of monitoring the occupation of the rail is achieved.

[0004] In conclusion, both the track circuit and the electromagnetic axle counter are implemented with equipment arranged outdoors and are highly dependent on their excellent electrical transmission characteristics.

[0005] In the article Analysis oƒ Lightning Impact on Track circuit (CLC: U284.2), it is proposed that, especially in the thunderstorm season, the axle counting equipment is easy to be damaged by thunder and lightning, leading to damage to the equipment, which brings great impact on traffic transportation, makes the train be not able to run safely, and may cause serious accidents in severe cases. In the article Research on Common Interference Sources and Anti-interference Methods of Electromagnetic Induction type Axle Counting Equipment (CLC: U284.47), it is proposed that interference faults of most axle counting equipment of Chinese railway are caused by electromagnetic interference such as lightning damage, surge, over-voltage, etc.. Although the axle counting technology has been introduced in China for more than 10 years and has been widely used in a plurality of railway bureaus, the electromagnetic interference problem is still not effectively solved.

[0006] Since the birth, the fiber grating sensing technology has been widely used in the environments with strong electromagnetic interference and variable humidity due to its characteristics of electrical insulativity, electromagnetic interference resistance, corrosion resistance, strong chemical stability, long distance and the like. Axle counting products developed based on the fiber gratings, without placing electromagnetic sensitive equipment in the outdoor environment, can avoid the problems faced by the above electric equipment, such that the products are no longer tired of dealing with the impact of electromagnetic interference and the like of the application scenario.

[0007] In utility model patent CN200920088856.3, a train axle counting and direction determining scheme based on two independent fiber grating sensors is disclosed. When a train runs over two fiber grating sensors in sequence, wavelength drift values of the two sensors each generate a pulse at the adjacent moment, and a running direction of the train is determined according to the pulse coming order. Such scheme has the shortcomings that only the first pulse measured by the two fiber gratings in sequence can be used to determine the running direction of the train. If the coming order of the first pulse is determined mistakenly, the system may obtain the wrong running direction, seriously affecting the safety of the rail transport. In the invention patent CN201610956103.4, two fiber gratings are adhered to two faces of a strain gauge, and then the strain gauge is entirely fixed to the bottom of the steel rail, when there is a train passing by, the wavelength changes of the two fiber gratings are equal and opposite to play a role of sensitivity enhancement. As the two fiber optic gratings are in the same temperature environment, they can compensate for each other to eliminate temperature effects. According to such method, a mechanical structure is integrally adopted, which takes a spring as one of main strain transmission equipment. The mechanical structure is easy to displace along with the vibration of the rail, leading to the generation of noise. The rail is easy to generate high-frequency vibration, the mechanical structure used in such scenario for a long time is easy to age, which threatens the safety of the rail transport.

[0008] The installation mode of the sensor for the axle counting point in accordance with the existing patent is complex, each axle counting points requires a plurality of sensors to be installed.

[0009] Therefore, there is an urgent need of rail transit axle counting scheme with high integration and easy construction.

SUMMARY

[0010] For the problem above, the present invention provides a rail transit axle counting system, which includes:

a sensor component and a fastener, wherein the sensor component is connected to the fastener;

N fiber grating sensors are fixed in the sensor component;

the N fiber grating sensors at least include a second fiber grating sensor and a fourth fiber grating sensor;

the second fiber grating sensor and the fourth fiber grating sensor are arranged at both ends inside the sensor component; and

the second fiber grating sensor and the fourth fiber grating sensor are both configured to collect a strain signal of a passing train.

[0011] Further, the second fiber grating sensor and the fourth fiber grating sensor are spaced by a certain distance in a horizontal axial direction of the sensor component.

[0012] Further, the fastener includes a first fastener and a second fastener.

[0013] Further, the N optical fiber grating sensors further includes a first fiber grating sensor and a fifth fiber grating sensor which are respectively fixed to the first fastener and the second fastener;
the first fiber grating sensor and the fifth fiber grating sensor are respectively configured to monitor loosening situations of the first fastener and the second fastener.

[0014] Further, the first fastener and the second fastener are both bolts.

[0015] Further, the system further includes a third fiber grating sensor is fixed into the sensor component, and the third fiber grating sensor is perpendicular to the horizontal axial direction of the sensor component.

[0016] Further, the system further includes a demodulator which is connected to the N fiber grating sensors.

[0017] Further, the demodulator includes:

a broadband light source module, a first demodulation system and a second demodulation system redundant to each other, a primary coupler, N optical isolators, N optical circulators, N secondary couplers, and 2N tertiary couplers;

the secondary couplers and the tertiary couples are both one-to-two couplers;

the primary coupler is a one-to-N coupler;

where the primary coupler is connected to the broadband light source module;

the primary coupler is respectively connected to N optical isolators;

each of the optical isolators is connected to a respective optical circulator;

each of the optical isolators is connected to a respective secondary coupler;

each of the secondary couplers is connected to two respective tertiary couplers; and

two tertiary couplers connected to the same secondary coupler are respectively connected to a first demodulation system and a second demodulation system.

[0018] The present invention further provides a rail transit axle counting method. The method includes: collecting strain signals of the N fiber grating sensors based on the rail transit axle counting system above, and performing axle counting based on the strain signals.

[0019] Further, performing axle counting based on the strain signals includes:

determining a train passing condition by using two sets of demodulation systems redundant to each other; and

when two sets of demodulation systems both determine that there is an axle passing by under a designated condition, outputting axle counting information and direction information.

[0020] Further, determining the train passing condition by using two sets of redundant demodulation systems includes:
using a dynamic strain parameter threshold value and/or a dynamic time threshold value as the designated condition for the two sets of demodulation systems to determine that there is an axle passing by.

[0021] Further, using a dynamic strain parameter threshold value as the designated condition for the two sets of demodulation systems to determine that there is an axle passing by includes:

notifying the second demodulation system in the two sets of demodulation systems when the first demodulation system in the two sets of demodulation systems calculates that there is an axle passing by;

dynamically setting, by the second demodulation system, an upper limit value and/or a lower limit value of a strain parameter for determining that there is an axle passing by;

determining, by the second demodulation system, whether there is an axle passing by or not according to the dynamically set upper limit value and/or lower limit value of the strain parameter.

[0022] Further, using a dynamic time threshold value as the designated condition for the two sets of demodulation systems to determine that there is an axle passing by includes:

notifying the second demodulation system in the two sets of demodulation systems when the first demodulation system in the two sets of demodulation systems calculates that there is an axle passing by;

dynamically setting, by the second demodulation system, a time threshold value according to a change speed of a wavelength variation of the strain signal; and

when the second demodulation system calculates, within the dynamically set time threshold value, that there is an axle passing by , outputting axle counting information.

[0023] Further, the method includes: demodulating the strain signal by means of edge filtering.

[0024] Further, demodulating the strain signal by means of edge filtering includes:

dividing the strain signal into two paths, wherein one path of the strain signal is subjected to edge filtering modulation to obtain a reflected light modulated signal;

converting the reflected light modulated signal into a corresponding reflected light modulated electric signal;

directly converting the other in the two paths of strain signals into a reflected light reference electric signal; and

taking a ratio of the reflected light modulated electric signal to the reflected light reference electric signal as a basis for wavelength demodulation.

[0025] Further, the method includes:

calibrating a grating central wavelength and an electric signal ratio, wherein the electric signal ratio is the ratio of the reflected light modulated electric signal to the reflected light reference electric signal;

performing edge filtering demodulation on the strain signal, and amplifying the reflected light modulated electric signal and the reflected light reference electric signal based on optical transmission loss of the rail transit axle counting system; and

determining whether there is an axle passing by or not by using redundant demodulation systems, and outputting axle counting information and direction information when there is an axle passing by.

[0026] The rail transit axle counting system and demodulation method thereof provided by the present invention have the following advantages:
The axle counting system is highly integrated, which is beneficial to simplifying installation steps and reducing the difficulty and cost of engineering construction, easy to maintain and replace, and difficult to damage, such that the safety of a train axle counting product is effectively improved.

[0027] The accuracy and reliability of train axle counting and train running direction determining functions may be effectively improved, and self-inspection of the axle counting system may be achieved.

[0028] The redundant demodulation systems included in the system may perform data processing and output separately and perform comparison on the outputs, such that the reliability is improved.

[0029] In accordance with the demodulation method of the rail transit axle counting system, an effective solution is provided for the main problems of poor accuracy, poor universality, poor stability and the like when a rail transit axle counting demodulation system based on edge filtering is specifically implemented and used in the engineering field, such that the demodulation system is suitable for complex use environments, and the reliability and universality of the product are improved.

[0030] Additional features and advantages of the present invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the present invention. The objectives and other advantages of the present invention will be realized and attained by the structure particularly pointed out in the specification, the claims as well as the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] To describe the technical solutions in the embodiments of the present invention or in the prior art more clearly, the following briefly introduces the accompanying drawings required for describing the embodiments. Apparently, the accompanying drawings in the following description show merely some embodiments of the present invention, and a person of ordinary skill in the art may still derive other drawings from these accompanying drawings without creative efforts.

FIG. 1 illustrates a structure diagram of a rail transit axle counting system in accordance with the embodiments of the present invention;

FIG. 2 illustrates a schematic diagram of an optical path module of a demodulator in accordance with the embodiments of the present invention;

FIG. 3 illustrates a structure diagram of a demodulator in accordance with the embodiments of the present invention;

FIG. 4 illustrates a principle diagram of edge filtering demodulation in accordance with the embodiments of the present invention;

FIG. 5(a) illustrates a schematic diagram of the effect of reflectance of different gratings on an electrical signal ratio in accordance with the embodiments of the present invention;

FIG. 5(b) illustrates a schematic diagram of the effect of 3dB bandwidths of different gratings on an electrical signal ratio in accordance with the embodiments of the present invention;

FIG. 6 illustrates a schematic diagram of wavelength variation results of two demodulation systems in accordance with the embodiments of the present invention;

[0032] In the drawings:

1-Sensor component

11-First fiber grating sensor

12-Second fiber grating sensor

13-Third fiber grating sensor

14-Fourth fiber grating sensor

15-Fifth fiber grating sensor

2-demodulator

21-Broadband light source module

22-One-to-five coupler

23-Optical isolator

24-Optical circulator

25-One-to-two coupler A

26-One-to-two coupler B

27-One-to-two coupler C

28-Linear filter A

29-Linear filter B

3-Fastener

31-First fastener

32-Second fastener.

DETAILED DESCRIPTION

[0033] In order to make the objective, technical solutions and advantages of the embodiments of the present invention more clearly, the following clearly and completely describes the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are merely a part rather than all of the embodiments of the present invention. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention

[0034] An embodiment of the present invention provides a rail transit axle counting system. As shown in FIG. 1, the system includes: a sensor component 1 and a fastener 3, and the sensor component 1 is connected to the fastener 3. N fiber grating sensors are fixed into the sensor component 3, the N fiber grating sensors form a fiber grating sensor group. The N fiber grating sensors at least include a second fiber grating sensor 12 and a fourth fiber grating sensor 14. The second fiber grating sensor 12 and the fourth fiber grating sensor 14 are arranged at both ends inside the sensor component. Further, the second fiber grating sensor 12 and the fourth fiber grating sensor 14 are spaced at a certain distance in a horizontal axial direction of the sensor component 1; and fixing directions of the second fiber grating sensor 12 and the fourth fiber grating sensor 14 are parallel to an axial direction of the sensor component 1, i.e., the fixing direction of each fiber grating sensor is consistent with the horizontal axial direction. The horizontal axial direction of the sensor component 1 is the horizontal axial direction shown in FIG. 1, i.e., a long side direction of the rectangle, which is also a direction parallel to the track when the sensor component 1 is arranged on the track.

[0035] Specifically, the second fiber grating sensor 12 and the fourth fiber grating sensor 14 are packaged in the sensor component and are spaced at a certain distance in the horizontal axial direction of the sensor component 1. That is, when the sensor component is arranged at the bottom of the track, distribution directions of the second fiber grating sensor 12 and the fourth fiber grating sensor 14 are parallel to the rail direction, and an arrangement direction of each fiber grating sensor itself is parallel to the rail direction, such that the fiber grating sensors are configured to collect strain signals of a train passing through the track. Without loss of generality, at least one side surface of the sensor component is a strip-shaped hard substrate, such as a rectangular steel plate, the second fiber grating sensor 12 and the fourth fiber grating sensor 14 are distributed on a horizontal axial line, such as a horizontal central axis, of the substrate of the sensor component, and the two fiber grating sensors are fixed at a certain distance. Therefore, strain signals collected by the two sensors when a train passes through may be analyzed and then configured to determine a running direction of the train. These two sensors are respectively configured to modulate the light intensity corresponding to the gratings in the wavelength of the continuous light in the C waveband, when the train passes through and the strain is transmitted to the fiber grating sensor group via the steel rail, the central wavelength of the reflected light of the grating shifts, and the reflected light intensity of the continuous light in the C waveband regularly changes accordingly, and therefore the axle counting and direction determination of the train are achieved according to this change rule.

[0036] The fastener 3 includes a first fastener 31 and a second fastener 32. The N fiber grating sensors further includes a first fiber grating sensor 11 and a fifth fiber grating sensor 15 which are respectively fixed to the first fastener 31 and the second fastener 32 and are respectively configured to monitor loosening situations of the first fastener 31 and the second fastener 32. In accordance with the embodiment of the present invention, the first fastener 31 and the second fastener 32 are both bolts. In accordance with other embodiments, the fastener may also employ a welding stud or a rivet. In accordance with the embodiment of the present invention, preferably, adjustable and easy-to-replace bolts are employed. That is, the first fastener 31 is a fixing bolt A, and the second fastener is a fixing bolt B.

[0037] The first fiber grating sensor 11 and the fifth fiber grating sensor 15 are respectively packaged in the fixing bolt A and the fixing bolt B for fixing the sensor. Specifically, one end of the fixing bolt A and one end of the fixing bolt B are respectively provided with holes, and the fiber grating sensors are fixedly arranged in the holes. The hole may be formed by punching at the end face of the side, away from the threads, of the fixing bolt. Without loss of generality, the hole and the fixing bolt have the same central axis. After the fiber grating sensors are installed, the system records the wavelengths corresponding to the respective gratings of the first fiber grating sensor 11 and the fifth fiber grating sensor 15 at the moment. When the bolts are loosened, the wavelengths of the gratings may change, and thus the system gives an alarm. Specifically, when the wavelength change of each grating exceeds a certain threshold value or a change state of the wavelength is maintained to exceed a certain time threshold value, the system gives an alarm, and maintenance personnel may fasten or replace and maintain the bolt according to alarm information.

[0038] The N fiber grating sensors further include a third fiber grating sensor 13. The third fiber grating sensor 13 is fixed in the sensor component 1, and is perpendicular to the second fiber grating sensor 12, that is, perpendicular to the horizontal axial direction of the sensor component 1. The third fiber grating sensor 13 is packaged in the sensor component. When the sensor component is installed, the direction of the third fiber grating sensor 13 is perpendicular to the rail direction, such that the third fiber grating sensor is not affected by the strain generated by the train passing through, and can be configured to perform temperature compensation.

[0039] In accordance with the embodiment of the present invention, the five fiber grating sensors are packaged in one sensor component, and the sensor component is installed at the bottom of the rail during use. As the five fiber grating sensors are packaged in one sensor component, the sensor component may be installed in one sleeper, and one axle counting point only needs one sensor to achieve all functions of axle counting, such that the cost is saved, and the steps for engineering installation are simplified. By employing the integrated sensor component, the installation direction accuracy and stability of the sensors may be better guaranteed, and the installation stability of the sensor component is monitored in real time (which is achieved by the first fiber grating sensor 11 and the fifth fiber grating sensor 15), such that the reliability of acquiring the strain signals is improved. The third fiber grating sensor 13 which is not affected by strain is configured to perform temperature compensation to further improve the demodulation accuracy.

[0040] In accordance with the embodiment of the present invention, the sensor component 1 includes a substrate for transferring the strain signal, the third fiber grating sensor 13, the second fiber grating sensor 12 and the fourth fiber grating sensor 14 are fixed (such as adhered, welded) to the substrate, and a cover plate is configured to cover and package the fiber grating sensors so as to play a role in protection and fixation. The sensor component may also include a housing, the bottom wall of the housing is a hard substrate, such as a steel plate, for transferring the strain signal. The third fiber grating sensor 13, the second fiber grating sensor 12 and the fourth fiber grating sensor 14 are packaged in the housing and attached to the bottom wall. Without loss of generality, the housing is rectangular. The substrate may be fixed to the bottom of the rail by the fasteners (the fixing bolt A, the fixing bolt B) through fixing perforations on the sensor component 1. For the sensor component 1 of a housing structure, the sensor component 1 is fixed to the bottom of the rail by the fasteners penetrating through the housing.

[0041] The system further includes a demodulator 2. The demodulator 2 is connected to the N fiber grating sensors and configured to acquire wavelength signals of the N fiber grating sensors. In accordance with the embodiment of the present invention, the demodulator employs a 2-vote-2 redundancy architecture, as shown in FIG. 2, which is an optical path module of the demodulator. The demodulator includes a power supply board, a first demodulation system (demodulation system A), a second demodulation system (demodulation system B), a broadband light source module (specifically, an ASE light source (amplified spontaneous radiation light source)), a primary coupler, N optical isolators, N optical circulators, N secondary couplers and 2N tertiary couplers, wherein the secondary couplers and the tertiary couplers are all one-to-two couplers, i.e., 3N one-to-two couplers are provided.

[0042] The first demodulation system and the second demodulation system are redundant to each other. The secondary couplers and the tertiary couplers are all one-to-two couplers. The primary coupler is a one-to-N coupler, where the primary coupler is connected to the broadband light source module; the primary coupler is respectively connected to N optical isolators. Each of the optical isolators is connected to a respective optical circulator, and each of the optical isolators is connected to a respective secondary coupler. Each of the secondary couplers is connected to two respective tertiary couplers. The two tertiary couplers connected to the same secondary coupler are respectively connected to the first demodulation system and the second demodulation system.

[0043] The primary coupler is configured to divide the light source into N paths, such that each path of light sources may reach one of the N fiber grating sensors. The light sources divided into N paths are respectively transmitted to respective fiber grating sensors through the respective optical isolators and optical circulators. Reflected light of the N fiber grating sensors is output through respective optical circulators. The N secondary couplers respectively divide corresponding reflected light into two paths of optical signals (namely, strain signals of the fiber grating sensors are fed back in the form of optical signals), and then the two paths of optical signals are respectively input into the first demodulation system and the second demodulation system. In the first demodulation system, N tertiary couplers divide N paths of received optical signals into two paths, where one path of optical signals is subjected to edge filtering modulation. Similarly, in the second demodulation system, the N tertiary couplers divide the N paths of received optical signals into two paths, where one path of optical signals is subjected to edge filtering modulation. The two demodulation systems are configured to demodulate signals separately and then to perform information interaction so as to achieve a 2-vote-2 redundancy structure.

[0044] In accordance with the embodiment, N=5, that is, five fiber grating sensors are provided in the sensor component, is taken as an example for illustration. As shown in FIG. 2, the demodulator 2 includes a primary coupler (i.e., a one-to-five coupler 22), five optical isolators 23, five optical circulators 24, fifteen one-to-two couplers, ten (2N) linear filters, twenty (4N) photoelectric converters, where the fifteen one-to-two couplers include five secondary couplers, i.e., one-t-two coupler A 25, configured to input the reflected light into the two demodulation systems after dividing the reflected light into two paths; five tertiary couplers, i.e., one-to-two coupler B 26, configured to transmit the reflected light to the demodulation system A after dividing the reflected light into two paths; and five tertiary couplers, i.e., one-to-two coupler C 27, configured to transmit the reflected light to the demodulation system B after dividing the reflected light into two paths.

[0045] In accordance with other embodiments, it may also be N=2, that is, only the data of the second fiber grating sensor and the fourth fiber grating sensor are configured to perform data processing of axle counting and direction determination. It may be N=4, that is, the data of the second fiber grating sensor, the fourth fiber grating sensor, the first fiber grating sensor and the fifth fiber grating sensor are configured to perform data processing of axle counting and direction determination. It may also be N=3, that is, the data of the second fiber grating sensor, the fourth fiber grating sensor and the third fiber grating sensor are configured to perform data processing of axle counting and direction determination; or, more fiber grating sensors may be employed to perform data collection and processing.

[0046] The power supply board is configured to supply power to the broadband light source module 21 to make the broadband light source module output continuous light in the C waveband. The continuous light in the C waveband is divided into five paths through the one-to-five coupler 22, and then is respectively transmitted to the first fiber grating sensor 11, the second fiber grating sensor 12, the third fiber grating sensor 13, the fourth fiber grating sensor 14 and the fifth fiber grating sensor 15 through the optical isolators 23 and the optical circulators 24 in sequence.

[0047] These five paths have the same structure. The grating of each path of the fiber grating sensor is configured to modulate the light intensity corresponding to the grating in the wavelength of continuous light in the C waveband. When the wavelength of the grating changes, the central wavelength of the grating reflected light shifts. The reflected light is output through the path reflected and output by the corresponding optical circulator 24 and is divided into two same paths of optical signals by the one-to-two coupler A. That is, the signal reflected by the fiber grating sensor is divided into two same paths of signals, and the two same paths of signals are respectively output to the demodulation system A and the demodulation system B. The two demodulation systems are configured to demodulate the signals separately, and then to perform information interaction to achieve the 2-vote-2 redundancy structure.

[0048] The system performs demodulation by means of edge filtering. For the demodulation system A 25, five paths of reflected light each are further divided into two paths by the one-to-two coupler B 26, thereby forming ten paths of reflected light modulated signals: A 1 a, A_1_b, A_2_a, A_2_b, A_3_a, A_3_b, A_4_a, A_4_b, A_5_a, A_5_b. Illustratively, one path of reflected light is subjected to edge filtering modulation by a linear filter A 28 to obtain the reflected light modulated signal A 1 a, the light intensity of the reflected light modulated signal is in direct proportion to the grating wavelength, and the reflected light modulated signal is converted, by the photoelectric converter converts, into a corresponding reflected light modulated electric signal. The other path of reflected light modulated signal A 1 b directly enters the photoelectric converter without passing through the linear filter, the reflected light emitted by the fiber grating sensor is converted into a reflected light reference electric signal, a ratio of the reflected light modulated electric signal to the reflected light reference electric signal is used as a basis for wavelength demodulation, and errors caused by common mode factors are eliminated at the same time.

[0049] For the demodulation system B, five paths of reflected light received by the demodulation system B each are further divided into two paths by the one-to-two coupler C 27, thereby forming ten paths of reflected light modulated signals: B_1_a, B_1_b, B_2_a, B_2_b, B_3_a, B_3_b, B_4_a, B_4_b, B_5_a, B_5_b. Illustratively, one path of reflected light is subjected to edge filtering modulation by the liner filter B 29 to obtain the reflected light modulated signal B_1_a, the light intensity of the reflected light modulated signal is in direct proportion to the grating wavelength, and the reflected light modulated signal is converted, by the photoelectric converter converts, into a corresponding reflected light modulated electric signal. The other path of reflected light modulated signal B_1_b directly enters the photoelectric converter without passing through the linear filter, the reflected light emitted by the fiber grating sensor is converted into a reflected light reference electric signal, a ratio of the reflected light modulated electric signal to the reflected light reference electric signal is used as a basis for wavelength demodulation, and errors caused by common mode factors are eliminated at the same time.

[0050] As shown in FIG. 3, the strain signal reflected back by the first fiber grating sensor is converted, by the optical path module of the system, into four paths:A_1_a, A_1_b,B_1_a, B_1_b, where A_1_a and A_1_b are correspondingly equivalent to B_1_a and B_1_b; A_1_a and A_1_b are output to demodulation system A for demodulation, and B_1_a and B_1_b are output to demodulation system B for demodulation; A_1_a and B_1_a are reflected light modulated optical signals modulated by the linear filter, and A_1_b and B_1_b are reflected light reference optical signals without being modulated by the linear filter. The other four paths are the same. The demodulation system A and the demodulation system B are in communication connection. The power supply module supplies power to the demodulation system A, the demodulation system B and the optical path module.

[0051] The grating in each of the first fiber grating sensor 11, the second fiber grating sensor 12, the third fiber grating sensor 13, the fourth fiber grating sensor 14 and the fifth fiber grating sensor 15 is configured to modulate the light intensity corresponding to the grating in the wavelength of continuous light in the C waveband. When the central wavelength of grating reflected light shifts, the reflected light intensity of the continuous light in the C waveband regularly changes accordingly, the larger the grating wavelength shift is, the larger the reflectance of the corresponding filter is, the stronger the light intensity after filtering of the filter is, and transmittance of the linear filter is monotonously increased in the selected waveband. In accordance with the characteristic, the reflected light is subjected to edge filtering (belonging to linear filtering) modulation. As shown in FIG. 4, a dotted fold line is a filter transmission spectrum, the two peak-shaped curves are grating reflection spectra, where a solid curve (left) is an initial reflection spectrum of the grating, and a dotted curve (right) is a reflection spectrum of the grating subjected to external changes (such as strain or temperature).

[0052] The demodulation system A converts five reflected light modulated optical signals A 1 a, A_2_a, A_3_a, A_4_a and A_5_a (each fiber grating sensor corresponds to one reflected light modulated optical signal and one reflected light reference optical signal) and five corresponding reflected light reference optical signals A_1_b, A_2_b, A_3_b, A_4_b and A_5_b into five reflected light modulated electric signals and five corresponding reflected light reference electric signals by the photoelectric converter, and then solves the ratios of the five reflected light modulated electric signals and the five corresponding reflected light reference electric signals to obtain five electric signal ratios (the electric signal ratios may eliminate the influence of light source jitter and additional loss of other optical equipment on signals so as to improve a signal-to-noise ratio). The wavelength values corresponding to the five fiber grating sensors at the moment are demodulated through the five electric signal ratios, and then the states of the five fiber grating sensors at the moment are analyzed. Whether sensor installing bolts are loosened or not is determined according to the wavelength variations of the first fiber grating sensor 11 and the fifth fiber grating sensor 15. The train axle counting is carried out according to the strain signals of the second fiber grating sensor 12 and the fourth fiber grating sensor 14 when the train comes and the sequence of the strain signals. The temperature change of the external environment is calculated according to the wavelength variation of the third fiber grating sensor 13, and then temperature compensation is carried out.

[0053] In the technical solutions above, the demodulation system B converts five reflected light modulated optical signals B_1_a, B_2_a, B_3_a, B_4_a and B_5_a (each fiber grating sensor corresponds to one reflected light modulated optical signal and one reflected light reference optical signal) and five corresponding reflected light reference optical signals B_1_b, B_2_b, B_3_b, B_4_b and B_5_b into five reflected light modulated electric signals and five corresponding reflected light reference electric signals by the photoelectric converter, and then solves the ratios of the five reflected light modulated electric signals and the five corresponding reflected light reference electric signals to obtain five electric signal ratios (the electric signal ratios may eliminate the influence of light source jitter and additional loss of other optical equipment on signals so as to improve a signal-to-noise ratio). The wavelength values corresponding to the five fiber grating sensors at the moment are demodulated through the five electric signal ratios, and then the states of the five fiber grating sensors at the moment are analyzed. Whether the sensor installing bolts are loosened or not is determined according to the wavelength variations of the first fiber grating sensor and the fifth fiber grating sensor. The train axle counting is carried out according to the strain signals of the second fiber grating sensor and the fourth fiber grating sensor when the train comes and the sequence of the strain signals. The temperature change of the external environment is calculated according to the wavelength variation of the third fiber grating sensor, and then temperature compensation is carried out.

[0054] In accordance with the technical solutions above, the first fiber grating sensor, the second fiber grating sensor, the third fiber grating sensor, the fourth fiber grating sensor and the fifth fiber grating sensor all have a central wavelength of 1550 nm, a 3dB bandwidth of 0.3 mm, and the reflectance of 80%. The transmittance of the linear filter is monotonically increased within the wavelength range of 1550-1556 nm, and the liner filter has good consistency. The linear filter employs a high-precision filter, with the linearity not greater than 0.0165%.

[0055] Based on the rail transit axle counting system above, the embodiment of the present invention further provides a rail transit axle counting method. The method includes collecting strain signals of N fiber grating sensors, and performing axle counting based on the strain signals. In accordance with the embodiment of the present invention, two sets of redundant demodulation systems are configured to determine a train passing condition. When the two sets of demodulation systems all determine that there is an axle passing by under a designated condition, axle counting information and direction information are output. The axle counting information and direction information includes axle counting information and direction information. The axle counting information represents that there is a train passing by, and the direction information represents a direction in which the train passes. The embodiments of the present invention do not limit the representation of the axle counting information and direction information. Illustratively, the axle counting information and direction information may be represented by a numerical value that is added by 1 when the train passes in a designated direction (e.g., forward) and subtracted by 1 when the train passes in a direction opposite to the designated direction (reverse). Determining the train passing condition by using two sets of redundant demodulation systems includes: using a dynamic strain parameter threshold value and/or a dynamic time threshold value as the designated condition for the two sets of demodulation systems to determine that there is an axle passing by.

[0056] Further, using a dynamic strain parameter threshold value as the designated condition for the two sets of demodulation systems to determine that there is an axle passing by includes: notifying the second demodulation system in the two sets of demodulation systems when the first demodulation system in the two sets of demodulation systems calculates that there is an axle passing by; dynamically setting, by the second demodulation system, an upper limit value and/or a lower limit value of a strain parameter for determining that there is an axle passing by; and determining, by the second demodulation system, whether there is an axle passing by or not according to the dynamically set upper limit value and/or lower limit value of the strain parameter.

[0057] Using a dynamic time threshold value as the designated condition for the two sets of demodulation systems to determine that there is an axle passing by includes:
notifying the second demodulation system in the two sets of demodulation systems when the first demodulation system in the two sets of demodulation systems calculates that there is an axle passing by; dynamically setting, by the second demodulation system, a time threshold value according to a change speed of a wavelength variation of the strain signal; and when the second demodulation system calculates, within the dynamically set time threshold value, that there is an axle passing by , outputting axle counting information; otherwise, reporting an error. The dynamically set time threshold value is a period of designated time from the receipt of the notification, that there is an axle passing by, from the first demodulation system.

[0058] In accordance with the embodiment of the present invention, the strain signal is demodulated by means of edge filtering. Specifically, the strain signal is divided into two paths, where one path of the strain signals is subjected to edge filtering modulation to obtain a reflected light modulated signal; the reflected light modulated signal is converted into a corresponding reflected light modulated electric signal. The other path in the two paths of strain signals is directly converted into a reflected light reference electric signal; and a ratio of the reflected light modulated electric signal to the reflected light reference electric signal is used as a basis for wavelength demodulation.

[0059] The rail transit axle counting method in accordance with the embodiment of the present invention includes the following steps:

calibrating a grating central wavelength and an electric signal ratio, wherein the electric signal ratio is the ratio of the reflected light modulated electric signal to the reflected light reference electric signal;

performing edge filtering demodulation on the strain signal, and amplifying the reflected light modulated electric signal and the reflected light reference electric signal based on optical transmission loss of the rail transit axle counting system; and

determining whether there is an axle passing by or not by using redundant demodulation systems, and outputting axle counting information and direction information when there is an axle passing by.

[0060] The first demodulation system and the second demodulation system perform signal processing and output separately. According to the output axle counting information and direction information, the occupation and idle states of a certain section are determined by an upper-level train control system according to the axle counting information and direction information collected by the whole section.

[0061] The first, second and other serial number in the present invention are only used to differentiate different systems or components.

[0062] The following illustratively describes various steps in detail.

[0063] Step one, wavelength demodulation is carried out by means of edge filtering, and a one-to-one corresponding linear relation is formed between the grating central wavelength and the electric signal ratio (the ratio of a reflected light modulated electric signal to a reflected light reference electric signal) by utilizing the edge filtering modulation effect of a linear filter on the grating reflected light. A demodulation result of the wavelength variation is mainly influenced by the linear filter. However, in accordance with this embodiment of the present invention, due to the adoption of the electric signal ratio which is a division operation, the influence of the 3dB bandwidth and reflectance of the fiber grating sensor and the flatness of an ASE (amplified spontaneous emission) light source on the demodulation may be eliminated in the division operation process, and thus the universality of the demodulation system is improved. As shown in FIG. 5(a), different grating reflectance has less influence on the electrical signal ratio. Taking the 3dB bandwidth of 600 pm and the central wavelength of 1552 nm as an example, the electrical signal ratio on the ordinate changes from 0.401 to 0.4014 in the process that the reflectance changes from 20% to 80% (there are 6,000 sampling points in total, as shown on the horizontal axis, which are the sampling points with a change rate of 20% to 80%), with less change. Therefore, the influence of the reflectance of the linear filter may be reduced by using the electric signal ratio as the reference for wavelength variation. Correspondingly, FIG. 5(b) illustrates a schematic diagram of the effect of 3dB bandwidths of different gratings on an electrical signal ratio in accordance with the embodiments of the present invention. Taking the central wavelength of 1552 nm and the reflectance of 80% as an example, the 3dB bandwidth changes from 100 pm to 2 nm (as shown in abscissa in the figure, the 3dB bandwidth is divided into 300 sampling points), the fluctuation range of the electric signal ratio is between 0.4014 to 0.4017, with less change.

[0064] According to such characteristic, the demodulation system may calibrate the grating central wavelength and the ratio before use, and the demodulation system A and the demodulation system B calibrate the same signal at the same time so as to reduce a demodulation error between the two sets of systems. The system employs the linear filter with the good consistency, the calibration process may be reused in a plurality of demodulators only through one-time calibration. The sensor component 1 and the demodulator 2 are independent of each other to facilitate the maintenance in the middle and later periods of engineering application.

[0065] Step two, the demodulator performs demodulation by means of edge filtering, such that the system is sensitive the light intensity, and may perform loss analysis aiming at unequal laying distances between the sensors and the demodulator and various complex installation environments in engineering application. In order to meet the demands of the system, the demodulation system A and the demodulation system B may perform self-adaptive amplification on various paths of reflected light reference electric signals by means of a program-controlled amplifying circuit. Based on the optical transmission loss of the rail traffic axle counting system, the reflected light modulated electric signal and the reflected light reference electric signal are amplified to close to the maximum voltage value acquired by the system ADC, and meanwhile, each reflected light reference electric signal and the corresponding reflected light modulated electric signal are controlled to have the same magnification times so as to guarantee the accuracy and resolution of the wavelength demodulation. Therefore, the universality and stability of the demodulation system in the engineering field may be improved to avoid demodulation error caused by different light intensity loss due to the different optical fiber transmission distances in the field installation.

[0066] Step three, five beams of reflected light output by the first fiber grating sensor, the second fiber grating sensor, the third fiber grating sensor, the fourth fiber grating sensor and the fifth fiber grating sensor include wavelength signals for acquiring the axle counting information and direction information. These five beams of reflected light are divided into five groups of same signals by means of five one-to-two couplers, and the five groups of same signals are respectively output to the demodulation system A and the demodulation system for demodulation at the same time. For an alarm error designated by the system, the whole system may perform alarm output as long as one demodulation system detects that there is an alarm error. For the axle counting and direction information, one demodulation system notifies the other demodulation system when calculating that there is an axle passing by, and outputs the axle counting information and direction information to the upper-level system only when the feedback information that there is an axle passing by calculated by the other demodulation is received within a period of time t; otherwise, the one demodulation system reports an error. In a similar way, when receiving that the other demodulation system has calculated that there is an axle passing by, one demodulation system must calculate, within a period of time (the time threshold value), that there is an axle passing by and informs the other demodulation system, and then outputs the axle counting information and direction information to the upper-level system, otherwise, the one demodulation reports an error. The upper-level system is a common upper-level system of the demodulation system A and the demodulation system B, such as a master control system.

[0067] Due to the fact that there is an error of wavelength absolute values when the two demodulation systems process the same signal, when the train speed is very slow or the train just stop running, a system response time difference of the two demodulation systems is possibly caused to be greater than a set time threshold value, leading to system misjudgment. Therefore, the system performs axle counting logic determination by means of a dynamic strain parameter threshold value or a dynamic time threshold value, or may perform axle counting logic determination by means of the dynamic strain parameter threshold value and the dynamic time threshold value at the same time.

[0068] The dynamic strain parameter threshold value is as follows: as the demodulator 2 determines the axle counting logic by employing a relative value, the equipment error or calibration error may both cause the two demodulation systems to have different demodulation results for the unified strain signal. As shown in FIG.6, a dotted curve is a demodulation result of the demodulation system A, and a solid curve is a demodulation result of the demodulation system B. In the demodulation result of the demodulation system A, the moment that the wavelength variation reaches a threshold value for determining that there is an axle passing by is a point A of the dotted curve, and corresponds to time 11, and at the moment, the wavelength variation of the curve is at a point B and does not reach the threshold value. In the demodulation result of the demodulation system B, the moment when the wavelength variation reaches the threshold value for determining that there is an axle passing by is a point C of the dotted curve, and corresponds to time t2. There is a certain deviation between t1 and t2, that is, the wavelength variations demodulated by the two demodulation systems have a certain error value, which may cause that the time that there is an axle passing by calculated by the two demodulation systems exceeds a default time threshold value of the system. To this end, by means of the dynamic strain parameter threshold value, one demodulation system notifies the other demodulation system when first calculating that there is an axle passing by using the set strain parameter threshold value, and the other demodulation system adjusts an upper limit threshold value and a lower limit threshold value of its own strain parameter to extend the determination condition appropriately, such as, reducing the upper limit threshold value by N pm and increasing the lower limit threshold value by N pm, thereby guaranteeing that the other demodulation system may make determination and feeds back the determination result to the demodulation system making the axle counting at first within the designated time of the system. Illustratively, the demodulation system A calculates a result that there is an axle passing by according to the default strain parameter threshold value S pm set by the system, and notifies the demodulation system B. If the demodulation system B has not calculated the result that there is an axle passing by when receiving the notification, the demodulation system B adjusts its own strain parameter threshold value as a difference value between the strain parameter threshold value and a designated tolerance, such as, S pm+/-L pm. The addition or subtraction of the designated tolerance to, or from, the default strain parameter threshold value may be determined according to whether the wavelength change stage is in a rising stage or in a falling stage, or the strain parameter threshold value may be directly set to be an interval range after the default parameter threshold value plus or minus the designated tolerance without considering the change stage. When the strain parameter enters the interval range, it is considered that there is an axle passing by. Afterwards, the strain parameter threshold value of the demodulation system B is restored to a default strain parameter threshold value. Similarly, if the demodulation system B firstly calculates that there is an axle passing by using a default system threshold value, the demodulation system A may set its own strain parameter threshold value to be the default strain parameter threshold value plus or minus the designated tolerance after receiving the notification.

[0069] The strain parameter refers to parameters reflecting rail strain signals collected by the system when a train passes by, such as the reflected light wavelength and wavelength variation of the fiber grating sensor. In accordance with the embodiment of the present disclosure, the strain parameter is the wavelength variation.

[0070] The dynamic time threshold value is as follows: if the train speed is very slow, the wavelength variation within the allowed system time threshold value range may not reach a strain parameter threshold value that there is an axle passing by, which may cause an error report of the normal axle counting. To this end, the demodulation system A and the demodulation system B perform dynamical demodulation for the set of the time threshold value t according to the change speed of the wavelength variation, the demodulation systems may record a derivative of the wavelength variation relative to the change time when performing axle counting determination, and thus the derivative is used as the setting condition of the time threshold value t. When the train speed is very slow, the change speed of the wavelength variation is also slow, the time threshold value is correspondingly set to be longer to prevent false error report. When the train is static, t may be set to be infinite, that is, the axle counting determination is carried out by means of only the dynamic strain parameter threshold value instead of the dynamic time threshold value.

[0071] Step four: the demodulation system A and the demodulation system B perform signal processing and output separately, the upper-level train control system determines the occupation and idle states of a certain section according to the axle counting information and direction information collected by the whole section.

[0072] If output results of the demodulation system A and the demodulation system B are the same, the master control system considers that the axle counting result is reliable and performs idle occupation determination for the next section, and if the output results are different, the master control panel gives an alarm.

[0073] In the step 3 of the technical solution, the demodulation system converts strain signals (specifically, strain values) sensed by the second fiber grating sensor and the fourth fiber grating sensor into grating central wavelength variations of the second fiber grating sensor and the fourth fiber grating sensor. The grating central wavelength and the electric signal ratio have a corresponding relation, the wavelength may be obtained through the electric signal ratio, and the grating central wavelength variation may be obtained according to a difference between a wavelength demodulated in real time and the wavelength in an initial static state, which is referred to as the wavelength variation.

[0074] The demodulation system acquires the sequence of the grating central wavelength variation of the second fiber grating sensor and the grating central wavelength variation of the fourth fiber grating sensor reaching a set threshold value, thereby determining a running direction of the train.

[0075] What is not described in detail in this specification belongs to the prior art well known to those skilled in the art.

[0076] Although the present disclosure has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that the technical solutions described in the foregoing embodiments may be modified or equivalents may be substituted for some of the technical features thereof. These modifications or substitutions do not make the essence of the corresponding technical solutions depart from the spirit and scope of the technical solutions of various embodiments of the present disclosure.

Claims

1. A rail transit axle counting system, characterized in that it comprises:

a sensor component and a fastener, wherein the sensor component is connected to the fastener;

N fiber grating sensors are fixed in the sensor component;

the N fiber grating sensors at least comprise a second fiber grating sensor and a fourth fiber grating sensor;

the second fiber grating sensor and the fourth fiber grating sensor are arranged at both ends inside the sensor component; and

the second fiber grating sensor and the fourth fiber grating sensor are both configured to collect a strain signal of a passing train.

2. The rail transit axle counting system according to claim 1, characterized in that,
the second fiber grating sensor and the fourth fiber grating sensor are spaced by a certain distance in a horizontal axial direction of the sensor component.

3. The rail transit axle counting system according to claim 1, characterized in that,
the fastener comprises a first fastener and a second fastener.

4. The rail transit axle counting system according to claim 2, characterized in that, the N fiber grating sensors further comprise a first fiber grating sensor and a fifth fiber grating sensor which are respectively fixed to the first fastener and the second fastener; and
the first fiber grating sensor and the fifth fiber grating sensor are respectively configured to monitor loosening situations of the first fastener and the second fastener.

5. The rail transit axle counting system according to claim 3, characterized in that, the first fastener and the second fastener are both bolts.

6. The rail transit axle counting system according to claim 1, characterized in that, the N fiber grating sensors further comprise a third fiber grating sensor fixed into the sensor component, and the third fiber grating sensor is perpendicular to the horizontal axial direction of the sensor component.

7. The rail transit axle counting system according to any one of claims 1 to 6, characterized in that it further comprises a demodulator, which is connected to the N fiber grating sensors.

8. The rail transit axle counting system according to claim 7, characterized in that, the demodulator comprises:

a broadband light source module, a first demodulation system and a second demodulation system redundant to each other, a primary coupler, N optical isolators, N optical circulators, N secondary couplers, and 2N tertiary couplers;

the secondary couplers and the tertiary couples are both one-to-two couplers;

the primary coupler is a one-to-N coupler;

wherein the primary coupler is connected to the broadband light source module;

the primary coupler is respectively connected to N optical isolators;

each of the optical isolators is connected to a respective optical circulator;

each of the optical isolators is connected to a respective secondary coupler;

each of the secondary couplers is connected to two respective tertiary couplers; and

two tertiary couplers connected to the same secondary coupler are respectively connected to a first demodulation system and a second demodulation system.

9. A rail traffic axle counting method, characterized in that it comprises: collecting strain signals of the N fiber grating sensors based on the rail transit axle counting system according to any one of claims 1 to 8, and performing axle counting based on the strain signals.

10. The rail traffic axle counting method according to claim 9, characterized in that, performing axle counting based on the strain signals comprises:

determining a train passing condition by using two sets of demodulation systems redundant to each other; and

when two sets of demodulation systems both determine that there is an axle passing by under a designated condition, outputting axle counting information and direction information.

11. The rail traffic axle counting method according to claim 10, characterized in that, determining a train passing condition by using two sets of demodulation systems redundant to each other comprises:
using a dynamic strain parameter threshold value and/or a dynamic time threshold value as the designated condition for the two sets of demodulation systems to determine that there is an axle passing by.

12. The rail traffic axle counting method according to claim 11, characterized in that, using a dynamic strain parameter threshold value as the designated condition for the two sets of demodulation systems to determine that there is an axle passing by comprises:

notifying the second demodulation system in the two sets of demodulation systems when the first demodulation system in the two sets of demodulation systems calculates that there is an axle passing by;

dynamically setting, by the second demodulation system, an upper limit value and/or a lower limit value of a strain parameter for determining that there is an axle passing by;

determining, by the second demodulation system, whether there is an axle passing by or not, according to the dynamically set upper limit value and/or lower limit value of the strain parameter.

13. The rail traffic axle counting method according to claim 11, characterized in that, using a dynamic time threshold value as the designated condition for the two sets of demodulation systems to determine that there is an axle passing by comprises;

notifying the second demodulation system in the two sets of demodulation systems, when the first demodulation system in the two sets of demodulation systems calculates that there is an axle passing by;

dynamically setting, by the second demodulation system, a time threshold value according to a change speed of a wavelength variation of the strain signal; and

when the second demodulation system calculates, within the dynamically set time threshold value, that there is an axle passing by, outputting axle counting information.

14. The rail traffic axle counting method according to claim 9, characterized in that it comprises: demodulating the strain signal by means of edge filtering.

15. The rail traffic axle counting method according to claim 14, characterized in that, demodulating the strain signal by means of edge filtering comprises:

dividing the strain signal into two paths, wherein one path of the strain signal is subjected to edge filtering modulation to obtain a reflected light modulated signal;

converting the reflected light modulated signal into a corresponding reflected light modulated electric signal;

directly converting the other in the two paths of strain signals into a reflected light reference electric signal; and

taking a ratio of the reflected light modulated electric signal to the reflected light reference electric signal as a basis for wavelength demodulation.

16. The rail traffic axle counting method according to any one of claims 9 to 15, characterized in that, the method comprises:

calibrating a grating central wavelength and an electric signal ratio, wherein the electric signal ratio is the ratio of the reflected light modulated electric signal to the reflected light reference electric signal;

performing edge filtering demodulation on the strain signal, and amplifying the reflected light modulated electric signal and the reflected light reference electric signal based on optical transmission loss of the rail transit axle counting system; and

determining whether there is an axle passing by or not, by using redundant demodulation systems, and outputting axle counting information and direction information when there is an axle passing by.

Drawing