Railway track fastening bolt pre-tightening state monitoring system and method

Abstract

This application discloses a monitoring system and method for the pre-tightening state of railway track fastener bolts, relating to the field of rail transit safety inspection. In this system, one end of a first inductor is connected to the positive terminal of a diode and the input terminals of each LC resonant circuit. The LC resonant circuits are set inside the resonant cavity. The upper plate of a capacitor is set on the top surface of the resonant cavity, and the lower plate is set on the bottom surface of the resonant cavity. An intelligent wireless transmitter transmits an excitation signal with a frequency that changes according to a preset step to a passive wireless detection device for bolt fasteners at a set time interval within one transmission cycle. After receiving the excitation signal, the passive wireless detection device for bolt fasteners generates an echo response signal. The bolt state analysis unit determines the pre-tightening state of each bolt to be tested based on the echo response signal. This application can automatically monitor multiple bolts simultaneously without relying on manual operation or environmental conditions. It requires no external power supply, is easy to install, and has high detection accuracy.

Description

Technical Field

[0001] This application relates to the field of rail transit safety inspection, and in particular to a railway track fastener bolt preload monitoring system and method for in-service condition assessment and remote monitoring of key fastening components such as rail bolts, fasteners, and fishplate clamps in railway track scenarios. Background Technology

[0002] Bolted connections, as crucial mechanical fastening units in rail transit equipment, are widely used in key areas such as rail-sleeper connections, fasteners, and fishplate connections. Their reliability directly impacts the overall stability of the rail structure and the safety of track operation. With prolonged train operation and continuous exposure to complex conditions, rail bolts, fasteners, and fishplates are prone to loosening, fatigue, or breakage. Failure to detect and address these issues promptly can lead to serious problems such as fastener failure, deterioration of rail geometry, and even track structure misalignment, directly threatening track safety. Therefore, establishing an efficient and accurate method for detecting bolt preload is of paramount importance for ensuring the safe operation of rail transit systems.

[0003] Current rail bolt inspection methods primarily rely on manual inspection. One common method is foot inspection, where maintenance personnel visually inspect key connecting components such as rail bolts, fasteners, and fishplates along the track to determine if they are loose, broken, or missing. Another common method is the baseline marking method, which involves drawing lines between the nut and the rail base and observing whether the lines are aligned to determine if the bolt has rotated or loosened. Some railway departments have also experimented with machine vision-based inspection methods, using image recognition technology to photograph and analyze track connection points to identify missing or obviously loose rail bolts. However, all of the above inspection methods have certain limitations. Manual inspection and the marking method rely on manual operation, resulting in low inspection efficiency, high labor intensity, high cost, and inaccurate results due to human factors. While machine vision methods offer a certain level of automation, their recognition accuracy is limited by lighting conditions, track environment, and complex operating conditions, resulting in insufficient adaptability and reliability.

[0004] Therefore, the existing methods for detecting the preload of rail bolts have the following two main problems: 1. They rely heavily on manual operation, resulting in low detection efficiency, high cost, and difficulty in achieving large-scale, continuous monitoring.

[0005] 2. Machine vision methods are highly dependent on the environment, and the stability and reliability of detection results are insufficient.

[0006] There is an urgent need for a railway track fastener bolt preload monitoring device that can automatically monitor multiple bolts simultaneously without relying on manual operation and is independent of the environment. Summary of the Invention

[0007] The purpose of this application is to provide a monitoring system and method for the pre-tightening status of railway track fastener bolts, which can automatically monitor multiple bolts simultaneously without relying on manual operation or environmental conditions, requires no external power supply, is easy to install, and has high detection accuracy.

[0008] To achieve the above objectives, this application provides the following solution: In the first aspect, this application provides a railway track fastener bolt preload status monitoring system, including: an intelligent wireless transmitter, a bolt status analysis unit, and multiple passive wireless detection devices for bolt fasteners, with one passive wireless detection device for bolt fasteners corresponding to one bolt to be tested.

[0009] The passive wireless testing device for bolt fasteners includes: a gasket and a frequency receiving and transmitting circuit; n resonant cavities are formed on the side of the gasket, where n is a positive integer greater than or equal to 3; the frequency receiving and transmitting circuit includes an antenna, a first inductor, a diode, and n parallel LC resonant circuits, with the antenna connected to one end of the first inductor, the positive terminal of the diode, and the input terminal of each LC resonant circuit; the LC resonant circuits are arranged inside the resonant cavities, with one LC resonant circuit corresponding to one resonant cavity; the upper plate of the capacitor in the LC resonant circuit is arranged on the top surface of the resonant cavity, and the lower plate of the capacitor is arranged on the bottom surface of the resonant cavity; the gasket is placed on the bolt to be tested.

[0010] For any passive wireless testing device for bolt fasteners, an intelligent wireless transmitter transmits excitation signals with frequencies varying in preset steps to the passive wireless testing device at set time intervals within a transmission cycle. The passive wireless testing device generates echo response signals corresponding to each excitation signal. The resonant frequencies of the echo response signals generated by different passive wireless testing devices for bolt fasteners are within different preset frequency ranges. Different bolts under test correspond to different preset frequency ranges. The bolt state analysis unit plots the time-frequency curves corresponding to each passive wireless testing device for bolt fasteners based on the resonant frequencies of the echo response signals generated by each passive wireless testing device for bolt fasteners. Based on the time-frequency curves, the resonant frequencies of the echo response signals generated by each passive wireless testing device for bolt fasteners, and the preset frequency ranges, the preload state of each bolt under test is determined.

[0011] Secondly, this application provides a method for monitoring the pre-tightening state of railway track fastener bolts, applied to the aforementioned railway track fastener bolt pre-tightening state monitoring system. The method includes: for any passive wireless detection device for bolt fasteners, transmitting an excitation signal with a frequency that changes according to a set step at a set time interval within a transmission cycle to the passive wireless detection device for bolt fasteners.

[0012] Obtain the echo response signals corresponding to each excitation signal generated by the passive wireless detection device for bolt fasteners.

[0013] Based on the resonant frequency of the echo response signal generated by the passive wireless detection device for each bolt fastener, the time-frequency curve corresponding to each passive wireless detection device for bolt fastener is plotted. Based on each time-frequency curve, the resonant frequency of the echo response signal generated by each passive wireless detection device for bolt fastener, and each preset frequency range, the pre-tightening state of each bolt to be tested is determined. The resonant frequency of the echo response signal generated by different passive wireless detection devices for bolt fasteners is within different preset frequency ranges. Different bolts to be tested correspond to different preset frequency ranges.

[0014] According to the specific embodiments provided in this application, this application has the following technical effects: This application provides a railway track fastener bolt pre-tightening state monitoring system and method. An intelligent wireless transmitter automatically transmits excitation signals with preset frequency variations to each bolt fastener passive wireless detection device. The antenna receives the excitation signal, generates an AC voltage through magnetization, and the equivalent capacitance of the diode continuously changes with the AC voltage. This causes the resonant frequency of the echo response signal generated by each bolt fastener passive wireless detection device to be within a frequency band. Due to pressure, the capacitance in the n parallel LC resonant circuits changes, causing the resonant frequency of the generated echo response signal to change with the pressure. The bolt state analysis unit then... The resonant frequency of the echo response signal determines the preload state. The resonant frequencies of the echo response signals generated by the passive wireless detection device for different bolts fall within different preset frequency ranges. Different bolts to be tested correspond to different preset frequency ranges. It can automatically monitor multiple bolts simultaneously without manual operation. The entire process is based on the electromagnetic response principle of resonance characteristics for information acquisition. It can stably identify the preload state of the bolts to be tested without relying on external visual conditions, is unaffected by the environment, improves detection accuracy, and requires no external power supply. The passive wireless detection device for bolts to be tested can be directly installed as a shim on the bolts to be tested, making installation simple. It can meet the intelligent and high reliability requirements of rail transit systems for the status perception of key connecting components. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of a passive monitoring system for bolt preload status based on frequency step excitation and adaptive reception, provided as an embodiment of this application.

[0017] Figure 2 This is a schematic diagram of the structure of a gasket provided in one embodiment of this application.

[0018] Figure 3 This is a circuit diagram of a frequency receiving and transmitting circuit provided in an embodiment of this application.

[0019] Figure 4 This is a schematic diagram of the structure of an intelligent wireless transmitting device provided in an embodiment of this application.

[0020] Figure 5 This is a schematic diagram of the structure of a frequency adaptive wireless receiving device provided in an embodiment of this application. Detailed Implementation

[0021] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0022] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] When a bolt is tightened, the applied preload is relatively large, resulting in a correspondingly large pressure on the washer. When the bolt loosens, the preload gradually decreases, and the pressure on the washer also decreases. Based on this, this application provides a railway track fastener bolt preload monitoring system, such as... Figure 1 As shown, the railway track fastener bolt pre-tightening status monitoring system includes: an intelligent wireless transmitter, a bolt status analysis unit, and multiple passive wireless detection devices for bolt fasteners, with one passive wireless detection device for a bolt fastener corresponding to one bolt to be tested.

[0024] like Figure 2As shown, the passive wireless testing device for bolt fasteners includes: a gasket and a frequency receiving and transmitting circuit; n resonant cavities are formed on the side of the gasket, where n is a positive integer greater than or equal to 3; the frequency receiving and transmitting circuit includes an antenna E1, a first inductor L1, a diode D1, and n parallel LC resonant circuits. The antenna E1 is connected to one end of the first inductor L1, the positive terminal of the diode D1, and the input terminal of each LC resonant circuit. The LC resonant circuits are arranged inside the resonant cavities, with one LC resonant circuit corresponding to one resonant cavity; the upper plate of the capacitor in the LC resonant circuit is arranged on the top surface of the resonant cavity, and the lower plate of the capacitor is arranged on the bottom surface of the resonant cavity; the gasket is arranged on the bolt to be tested as a functional gasket for the bolt to be tested. Each LC resonant circuit consists of a pressure-sensitive variable capacitor (varistor) connected in series with a fixed inductor. Multiple LC resonant circuits are connected in parallel to form a multi-resonant network structure with independent electrical parameters and structural distribution characteristics. Each bolt fastener passive wireless detection device has an independent number. It responds to changes in axial preload through the varistor in its embedded LC resonant circuit to achieve resonant frequency modulation.

[0025] For any passive wireless testing device for bolt fasteners, an intelligent wireless transmitter transmits excitation signals with frequencies varying in preset steps to the device at set time intervals within a transmission cycle. The passive wireless testing device generates echo response signals corresponding to each excitation signal. The resonant frequencies of the echo response signals generated by different passive wireless testing devices fall within different preset frequency ranges. Different bolts under test correspond to different preset frequency ranges. The bolt state analysis unit plots the time-frequency curves corresponding to each passive wireless testing device based on the resonant frequencies of the echo response signals generated by each device. Based on these time-frequency curves, the resonant frequencies of the echo response signals generated by each device, and the preset frequency ranges, it determines the preload state of each bolt under test. The preload state includes the preload level and bolt number information.

[0026] In another exemplary embodiment of this application, the railway track fastener bolt preload status monitoring system further includes: a frequency-adaptive wireless receiver, through which the echo response signal is transmitted to the bolt status analysis unit. The frequency-adaptive wireless receiver is communicatively connected to the bolt status analysis unit.

[0027] In another exemplary embodiment of this application, the gasket includes a main load-bearing area and a sensitive element area; the resonant cavity is disposed in the sensitive element area; the main load-bearing area has a frustum structure; the sensitive element area has a cylindrical shape; the bottom area of ​​the main load-bearing area is larger than the top area of ​​the main load-bearing area; the bottom surface of the main load-bearing area is in contact with the top surface of the sensitive element area, forming a non-uniform pressure slow-release gasket. The sloping concave structure of the main load-bearing area, which gradually thins in the axial direction, makes the gasket exhibit a gradient transition characteristic of gradually decreasing thickness from the main load-bearing area to the sensitive element area. Through the sloping thinning design, the gasket makes the force on the sensitive element area less than that on the main load-bearing area, thus improving the sensing sensitivity while ensuring mechanical strength.

[0028] The main load-bearing area is used to contact the nut and bear most of the axial preload. The sensitive element area forms a flexible contact with the nut through the main load-bearing area, and the axial pressure it receives is lower than that of the main load-bearing area. Thus, while maintaining the continuity of the force path, the mechanical stress borne by the sensitive element area is effectively relieved.

[0029] In practical applications, the resonant cavity is formed by opening a cavity groove on the side of the gasket. The LC resonant circuit is embedded through the side opening and sealed and fixed by filling with insulating material. Since the cavity on the side wall is potted and encapsulated, the varistor installed in the resonant cavity will form an initial contact relationship with the side wall of the resonant cavity when the gasket is not subjected to pre-tightening force. When the bolt is pre-tightened, the sensitive element area deforms with the axial clamping force, causing the capacitor's pressure state to change accordingly, thereby achieving a sensitive response to the bolt's stress state, and then modulating the resonant frequency for passive detection.

[0030] In another exemplary embodiment of this application, such as Figure 4 As shown, the intelligent wireless transmitting device specifically includes a frequency control module and a resonant transmitting circuit module. The frequency control module generates multiple tuning signals with frequencies varying according to a set step within one transmission cycle. The resonant transmitting circuit module generates excitation signals corresponding to each tuning signal and transmits these excitation signals to the passive wireless detection device for bolt fasteners at set time intervals within one transmission cycle. The intelligent wireless transmitting device is equipped with a tunable resonant transmitting circuit module, which, in conjunction with the frequency control module, enables the excitation signal frequency to vary according to a preset step pattern, forming a frequency domain excitation signal covering the resonant frequency band of each passive wireless detection device for bolt fasteners.

[0031] In practical applications, the intelligent wireless transmitting device further includes: a first main control module and a signal output interface module; wherein, the first main control module sets the start frequency, end frequency, and stepping strategy of the tuning signal generated by the frequency control module, and sends a tuning signal generation command to the frequency control module; the frequency control module is used to generate a frequency-progressive tuning signal according to the generation command and the preset start frequency, end frequency, and stepping strategy, so as to drive the resonant transmitting circuit module to generate an excitation signal with equally spaced resonant frequencies; the resonant transmitting circuit module is used to output an excitation signal of the corresponding frequency under the action of the tuning signal; the signal output interface module is used to transmit the excitation signal to the passive wireless detection device for bolt fasteners.

[0032] In practical applications, such as Figure 5 As shown, the frequency adaptive wireless receiving device specifically includes: a second main control module, a receiving tuning module, a weighted control module, and a signal output module.

[0033] The second main control module generates frequency scanning instructions, sets the starting frequency and stepping strategy of the receiving frequency, the target frequency range and weighting strategy (frequency weighting control function) corresponding to each bolt fastener passive wireless detection device, so as to uniformly regulate the receiving tuning logic.

[0034] The nonlinear dynamic adjustment is not random; rather, it differentiates the scanning time and step size based on the common operating frequency distribution of passive wireless detection devices for various bolts and fasteners. This allows for encrypted reception within the main response frequency band (common frequency band) and simplified scanning in extreme frequency bands, achieving efficient and accurate matching. The common frequency band is determined by the resonant frequency measured during the assembly of the passive wireless detection device for bolts and fasteners under tight conditions, and a scanning priority zone is set around this frequency. The receiving tuning module adjusts the center frequency of the receiving channel in real time according to the starting frequency and stepping strategy set by the second main control module. This enables the receiving tuning module to perform encrypted sampling in the set frequency band and rapid scanning in the edge frequency band during the scanning process, thereby achieving nonlinear dynamic tuning based on measured characteristics.

[0035] The weighted control module, based on the weighting strategy set by the second main control module, determines where to perform intensive sampling and where to perform sparse sampling, and jointly controls the receiving tuning module. Specifically, for any passive wireless detection device for bolt fasteners, the sampling resolution is increased and the frequency step size is reduced near the typical resonant frequency band of the passive wireless detection device (the target frequency band range corresponding to the passive wireless detection device for bolt fasteners set earlier), thereby achieving narrowband high-brightness reception of the resonant echo of the passive wireless detection device for bolt fasteners.

[0036] The signal output interface module transmits the received echo response signal to the bolt status analysis unit.

[0037] The frequency adaptive wireless receiver is equipped with a receiver tuning module that dynamically adjusts the receiver channel frequency according to the excitation frequency. It also optimizes the sampling density of the target frequency band by combining the frequency weighting control function in the weighting control module, thereby improving the receiver sensitivity and signal recognition accuracy in the key frequency band and achieving narrowband high-brightness reception.

[0038] In practical applications, the specific form of the frequency-weighted control function is as follows: , It can be seen that the scanning time is longest at the center frequency. The frequency response weight function represents the frequency of occurrence of a certain frequency point, and exp() represents an exponential function with the natural constant e as the base. This indicates the current scanning frequency point. This indicates that the center frequency measured by the passive wireless detection device for bolt fasteners under the assembled and tightened state is the center of the commonly used frequency band. This represents the frequency distribution broadening parameter, which controls the width of the peak of the function; the larger the value, the wider the commonly used frequency band. Indicates the receiving module at frequency The scanning dwell time at the location. Indicates the system's shortest dwell time (used for edge or extreme frequency bands). The adjustment coefficient representing the dwell time is used to control the magnitude of the time difference between the center frequency band and the edge frequency band.

[0039] In another exemplary embodiment of this application, such as Figure 3 As shown, the passive wireless detection device for bolt fasteners further includes: a second inductor L2 and a third inductor L3; an antenna E1 is connected to one end of the second inductor L2, and the other end of the second inductor L2 is connected to the input terminals of n parallel LC resonant circuits, one end of the first inductor L1, and the positive terminal of the diode D1; one end of the third inductor L3 is connected to the output terminals of the n parallel LC resonant circuits; and a signal transmitting and receiving device is used to receive excitation signals and send echo response signals to the bolt state analysis unit.

[0040] In another exemplary embodiment of this application, the bolt state analysis unit includes a time-frequency curve determination subunit, a bolt to be tested determination subunit, and a preload state determination subunit.

[0041] The time-frequency curve determination subunit is used to plot the time-frequency curve corresponding to any passive wireless detection device for bolt fasteners, with the resonant frequency of each echo response signal generated by the passive wireless detection device for bolt fasteners as the vertical axis and the time when the passive wireless detection device for bolt fasteners transmits each echo response signal for bolt fasteners as the horizontal axis.

[0042] The test bolt determination subunit is used to determine the test bolt corresponding to any passive wireless detection device for bolt fasteners based on a preset frequency range corresponding to the resonant frequencies of all echo response signals generated by the passive wireless detection device for bolt fasteners and a first preset mapping relationship; the first preset mapping relationship is the mapping relationship between the preset frequency range and the test bolt.

[0043] The preload state determination subunit is used to obtain the preload force of each bolt to be tested based on the bolt to be tested corresponding to the passive wireless detection device for each bolt fastener and the time frequency curve corresponding to the passive wireless detection device for each bolt fastener, and to obtain the preload state of each bolt to be tested based on the preload force of each bolt to be tested.

[0044] In practical applications, the preload of each bolt is determined based on the test bolt corresponding to each passive wireless bolt fastener detection device and the corresponding time-frequency curve of each device. Specifically, for any passive wireless bolt fastener detection device, the preload corresponding to the device is determined based on the translation distance between the time-frequency curve of the device and the initial time-frequency curve, as well as a second mapping relationship. The second mapping relationship is the mapping relationship between preload and translation distance (determined through preliminary experiments). The initial time-frequency curve is the time-frequency curve plotted based on the resonant frequency of the echo response signal generated by the passive wireless bolt fastener detection device when it is placed on the bolt without any force.

[0045] The preload of each bolt to be tested is obtained based on the corresponding bolt and the preload of each bolt fastener passive wireless detection device.

[0046] In another exemplary embodiment of this application, the resonant cavities on the side of the gasket are uniformly arranged along the circumferential direction of the gasket. Their structural positions are equiangularly distributed along the axial direction of the gasket to enhance the uniformity of force perception. If three resonant cavities are provided, they are respectively positioned at three equiangularly distributed locations on the gasket, with the circumferential angle between any two adjacent resonant cavities being 120 degrees, and the center points of all three located on the same circumference centered on the center of the gasket, i.e., possessing an equidistant radial distribution characteristic.

[0047] In another exemplary embodiment of this application, the inductance values ​​of the inductors in the n parallel LC resonant circuits within the same passive wireless detection device for bolt fasteners are different. Each passive wireless detection device for bolt fasteners is provided with a separately configured resonant circuit structure so that the resonant frequency of each bolt falls within a preset frequency bandwidth range that is distinct from each other. The inductance values ​​of the inductors in each LC resonant circuit are differentiated according to a preset frequency difference rule, so that the resonant frequencies generated by each passive wireless detection device for bolt fasteners under axial load have slight offsets from each other, thereby forming three adjacent but distinguishable resonant peaks in the frequency domain response, which naturally superimpose to form a single main response frequency peak. The slight difference in inductance between each LC resonant circuit can form a multi-peak response with a slightly offset frequency under changes in axial load. After frequency domain superposition, a single main response frequency is presented, enhancing detection stability and recognition accuracy.

[0048] In practical applications, to achieve parallel passive identification of multiple bolts, the inductance parameters of n parallel LC resonant circuits are configured according to a preset frequency difference rule. This ensures that the total resonant frequencies of the passive wireless detection devices for different bolts form non-overlapping frequency bands on the frequency axis. Sufficient frequency isolation bandwidth is reserved between each frequency band to prevent the resonant frequency from drifting into the frequency range of other passive wireless detection devices for bolts during bolt pre-tightening due to changes in the varistor capacitance with the bolt pre-tightening force. This ensures that the frequency division passive identification of each bolt in the same detection system does not cause cross-interference.

[0049] In practical applications, to achieve spectral distinguishability of passive wireless detection devices for different bolt fasteners, the inductors in n parallel LC resonant circuits are used to separate the main peak centers of each device: the frequency difference rule is configured as follows: the center frequency of the first device is set to be... Its theoretical range of variation is ,make The second device is set to have a center frequency of . , range ,make And it does not overlap with the first device, that is, it satisfies Generally, the first Each device is set in the center ,scope , And satisfy the adjacency constraint ( This ensures that the possible peak ranges of all devices do not overlap. Here, L... pn Let represent the inductance in the nth LC resonant circuit out of n parallel LC resonant circuits. This indicates the calculation of the arithmetic mean.

[0050] The intelligent wireless transmitter of the railway track fastener bolt preload monitoring system provided in this application can generate an excitation signal with a frequency that changes in preset steps. The passive detection device uses multiple sets of LC resonant circuits to achieve resonant frequency changes coupled with the bolt's stress state, and passively radiates the echo signal through an antenna. The frequency-adaptive wireless receiver achieves high-sensitivity response to specific frequency points based on a frequency conversion receiving mechanism. The bolt state analysis unit extracts changes in the echo curve and determines the corresponding preload force based on the mapping relationship. The system requires no manual intervention or power supply and supports separate identification of multiple bolts. The working process of the railway track fastener bolt preload monitoring system provided in this application is as follows: The intelligent wireless transmitter generates an excitation signal with a frequency that changes in preset steps. When the passive wireless detection device for the bolt fastener receives this excitation signal, its internal resonant frequency shifts with the capacitance change caused by the bolt's stress state, forming an echo response signal at its corresponding frequency point, which is radiated to the frequency-adaptive wireless receiver through an antenna. The bolt status analysis unit is used to perform narrowband frequency domain scanning on the echo signal, plot the time-frequency curve corresponding to the passive wireless detection device for each bolt fastener, and then, based on each time-frequency curve, the resonant frequency of the echo response signal generated by each passive wireless detection device for each bolt fastener, and each preset frequency range, determine the current preload status of each numbered bolt, where the preload status includes the preload force level and bolt number information.

[0051] The detection principle of this application is as follows: For any passive wireless detection device for bolt fasteners, let the frequency of the excitation signal transmitted in a certain instance be F; the selected element in the circuit is diode D1, and a resonant frequency is generated between diode D1 and the first inductor L1. Because the equivalent capacitance of diode D1 is constantly changing, the resonant frequency generated between diode D1 and the first inductor L1 is a frequency band range. The resonant frequency f generated by the three parallel LC resonant circuits is... c Within this frequency band, the resonant frequencies of the echo response signal are F and f. c The difference, F, varies with time; when the pressure changes, f... c Only then will it change, otherwise f c It is a constant.

[0052] Under no pressure, the passive wireless detection device for bolt fasteners performs a measurement to obtain the initial time-frequency curve (slope k1, intercept b1, specifically expressed as: y = k1x + b1, where x is time and y is F minus f). c In subsequent measurements, a second time-frequency curve is obtained. The preload is determined by whether there is an up-down shift between the two curves. The specific value of the preload is obtained based on the distance of the shift and the second mapping relationship.

[0053] This application also provides an embodiment of applying the railway track fastener bolt preload status monitoring system provided in the above embodiments to railway track inspection operations. An inspection drone equipped with the system runs along the track to monitor the status of the bolts under test, with specific steps as follows: steps S1 to S3.

[0054] Step S1: Install the passive wireless detection device for bolt fasteners onto the bolt to be tested on the rail.

[0055] Step S2: The inspection drone performs inspections sequentially along the planned path along the longitudinal direction of the track. The drone is equipped with an intelligent wireless transmitter, a frequency-adaptive wireless receiver, and a bolt status analysis unit. For a specific inspection section along the track, the drone positions itself and hovers in the middle of that section. The intelligent wireless transmitter then transmits frequency-stepping excitation signals to all passive wireless bolt detection devices within that section. Simultaneously, the frequency-adaptive wireless receiver receives the electromagnetic echo signals (echo response signals) returned by each passive wireless bolt detection device.

[0056] Step S2-1: The passive wireless detection device for each bolt fastener receives a frequency-stepped excitation signal via an antenna. This signal is sequentially input through a front-end inductor and then enters a multi-channel resonant unit at the back end, composed of multiple LC resonant circuits with slightly different inductance values. The capacitors in the LC resonant circuits are varistor capacitors, whose capacitance values ​​change slightly with the bolt's stress state, causing a shift in the corresponding resonant frequency. Multiple resonant channels form superimposed main response frequency peaks on the resonant frequency axis, which are ultimately transmitted back via the antenna to the frequency-adaptive wireless receiver of the inspection drone.

[0057] Step S2-2: The passive wireless detection device for bolts at each location is equipped with inductors in n parallel LC circuits with differentiated parameters, so that the resonant frequencies of each detection unit are distributed within a preset, non-overlapping frequency bandwidth. Specifically, the inductance values ​​of each LC resonant circuit are different and configured according to a predetermined frequency difference rule, so that each detection unit forms a segmented distribution structure on the frequency axis that does not interfere with each other. In addition, sufficient frequency isolation bandwidth is reserved between each frequency band to cope with the resonant frequency drift caused by the change in varistor capacitance due to the bolt stress state, and to prevent this frequency shift from falling into the frequency range of other detection units, thereby effectively improving the frequency domain resolution capability of the system and realizing frequency-division passive identification and independent status monitoring of multiple bolts in the same railway track monitoring section and within the same excitation cycle.

[0058] Step S3: The echo response signal is input from the frequency adaptive wireless receiver to the bolt state analysis unit. The bolt state analysis unit plots the time-frequency curve of each passive wireless detection device for bolt fasteners, and determines the number of the passive wireless detection device for bolt fasteners according to the preset frequency range of the passive wireless detection device for bolt fasteners. It compares the result with the preset time-frequency curve and determines the change in preload force on the passive wireless detection device for bolt fasteners by the slope and intercept change of the time-frequency curve.

[0059] This application has the following technical advantages: Compared with existing manual inspection methods, which suffer from low detection efficiency, limited coverage, and subjective bias due to reliance on human experience, this application constructs a fully passive, multi-bolt parallel frequency response monitoring system, which can achieve efficient and automated detection of bolt status, significantly reduce the degree of human intervention, and improve the reliability and consistency of system detection.

[0060] This application addresses the shortcomings of traditional machine vision methods, which are susceptible to interference from factors such as changes in lighting conditions at the track site, rain and snow, oil pollution, and obstruction by foreign objects. It adopts an electromagnetic response principle based on resonance characteristics for information acquisition, which can stably identify the pre-tightening state of the bolt under test without relying on external visual conditions, effectively overcoming the limitation of insufficient detection accuracy of traditional methods in complex environments.

[0061] This application is based on the physical mechanism of resonant frequency shift caused by changes in the varistor capacitance due to bolt stress. It combines frequency step excitation and narrowband high-brightness adaptive reception to receive the frequency of the passive wireless detection device for bolt fasteners, plot the corresponding time-frequency curve, and compare it with its preset time-frequency curve. By analyzing the mapping relationship between the slope and intercept change of the time-frequency curve and the bolt preload, the actual preload value of the target bolt can be deduced, thus realizing the quantitative detection of the bolt preload state, which is different from the limitation of traditional methods that can only make qualitative judgments.

[0062] After the frequency adaptive wireless receiver acquires the echo response signals returned by the passive wireless detection devices of each bolt fastener, the bolt status analysis unit analyzes and judges them. The bolt status analysis unit plots the time-frequency curve corresponding to the passive wireless detection device of each bolt fastener, and based on the frequency domain range of the received frequency and the changes between the time-frequency curve and the preset time-frequency curve, combined with the preset curve changes and the mapping relationship between the preload, the current preload state of each bolt is obtained, realizing passive, disassembly-free and non-contact structural health assessment.

[0063] In an LC resonant circuit, the varistor is coupled to a pressure-sensitive membrane structure. As the bolt preload changes, the capacitor deforms, thus altering the resonant frequency. Multiple LC resonant circuits work together to form a stable, single peak value of the main response frequency in the frequency domain.

[0064] To achieve parallel identification of multiple bolts within the same system, this application introduces inductors with differentiated parameters into n parallel LC resonant circuits of each bolt fastener passive wireless detection device, constructing separately configured resonant frequency bands. This ensures that different units have non-overlapping response bandwidths in the frequency domain, and reserves sufficient isolation bandwidth to accommodate frequency drift, thereby improving the overall system's anti-interference capability and frequency division identification performance.

[0065] Based on the same inventive concept, this application also provides an application to the above-mentioned railway track fastener bolt pre-tightening state monitoring system. The railway track fastener bolt pre-tightening state monitoring method includes: for any bolt fastener passive wireless detection device, transmitting an excitation signal with a frequency that changes according to a set step at a set time interval within a transmission cycle to the bolt fastener passive wireless detection device.

[0066] Obtain the echo response signals corresponding to each excitation signal generated by the passive wireless detection device for bolt fasteners.

[0067] Based on the resonant frequency of the echo response signal generated by the passive wireless detection device for each bolt fastener, the time-frequency curve corresponding to each passive wireless detection device for bolt fastener is plotted. Based on each time-frequency curve, the resonant frequency of the echo response signal generated by each passive wireless detection device for bolt fastener, and each preset frequency range, the pre-tightening state of each bolt to be tested is determined. The resonant frequency of the echo response signal generated by different passive wireless detection devices for bolt fasteners is within different preset frequency ranges. Different bolts to be tested correspond to different preset frequency ranges.

[0068] As an optional implementation, based on the resonant frequency of the echo response signal generated by each passive wireless detection device for bolts and fasteners, a time-frequency curve corresponding to each passive wireless detection device for bolts and fasteners is plotted. Based on each time-frequency curve, the resonant frequency of the echo response signal generated by each passive wireless detection device for bolts and fasteners, and each preset frequency range, the pre-tightening state of each bolt to be tested is determined. Specifically, for any passive wireless detection device for bolts and fasteners, a time-frequency curve corresponding to the passive wireless detection device for bolts and fasteners is plotted with the resonant frequency of each echo response signal generated by the passive wireless detection device for bolts and fasteners as the vertical axis and the time when the passive wireless detection device for bolts and fasteners transmits each echo response signal as the horizontal axis.

[0069] Based on the preset frequency range corresponding to the resonant frequencies of all echo response signals generated by the passive wireless detection device for bolt fasteners and the first preset mapping relationship, the bolt to be tested corresponding to the passive wireless detection device for bolt fasteners is determined; the first preset mapping relationship is the mapping relationship between the preset frequency range and the bolt to be tested.

[0070] Based on the test bolts corresponding to the passive wireless detection devices for each bolt fastener and the corresponding time-frequency curves of the passive wireless detection devices for each bolt fastener, the preload of each test bolt is obtained, and the preload state of each test bolt is obtained based on the preload of each test bolt.

[0071] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0072] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. Furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A monitoring system for the pre-tightening status of railway track fastener bolts, characterized in that, The railway track fastener bolt pre-tightening status monitoring system includes: The system includes an intelligent wireless transmitter, a bolt status analysis unit, and multiple passive wireless detection devices for bolt fasteners, with one passive wireless detection device for a bolt fastener corresponding to one bolt to be tested. A passive wireless testing device for bolt fasteners includes: a gasket and a frequency receiving and transmitting circuit; n resonant cavities are formed on the side of the gasket, where n is a positive integer greater than or equal to 3; the frequency receiving and transmitting circuit includes an antenna, a first inductor, a diode, and n parallel LC resonant circuits, with the antenna connected to one end of the first inductor, the positive terminal of the diode, and the input terminal of each LC resonant circuit; the LC resonant circuits are housed within the resonant cavities, with one LC resonant circuit corresponding to one resonant cavity; the upper plate of the capacitor in the LC resonant circuit is located on the top surface of the resonant cavity, and the lower plate is located on the bottom surface of the resonant cavity; the gasket is placed on the bolt to be tested; the gasket includes a main load-bearing area and a sensitive element area; the resonant cavity... The main load-bearing area is located in the sensitive element area; the bottom surface of the main load-bearing area contacts the top surface of the sensitive element area to form a non-uniform pressure-relieving gasket; the sloping concave structure of the main load-bearing area gradually thins in the axial direction, so that the gasket as a whole presents a gradient transition feature where the thickness gradually decreases from the main load-bearing area to the sensitive element area; the main load-bearing area is used to contact the nut and bear most of the axial preload, and the sensitive element area forms a flexible contact with the nut through the main load-bearing area, and the axial pressure it receives is lower than that of the main load-bearing area; the inductance values ​​of the inductors in the n parallel LC resonant circuits in the same bolt fastener passive wireless detection device are different; the inductance values ​​of the inductors in each LC resonant circuit are differentiated according to a preset frequency difference rule; For any passive wireless testing device for bolt fasteners, the intelligent wireless transmitter transmits excitation signals with a frequency that varies in a set step at set time intervals within a transmission cycle. The passive wireless testing device for bolt fasteners generates echo response signals corresponding to each excitation signal. The resonant frequencies of the echo response signals generated by different passive wireless testing devices for bolt fasteners are within different preset frequency ranges. Different bolts to be tested correspond to different preset frequency ranges. The bolt state analysis unit is used to plot the time-frequency curve corresponding to each passive wireless detection device for bolts based on the resonant frequency of the echo response signal generated by each passive wireless detection device for bolts. Based on the time-frequency curves, the resonant frequency of the echo response signal generated by each passive wireless detection device, and each preset frequency range, the preload state of each bolt under test is determined. Specifically, the preload force corresponding to each passive wireless detection device is determined based on the translation distance between the time-frequency curve corresponding to the passive wireless detection device and the initial time-frequency curve corresponding to the passive wireless detection device, and a second mapping relationship. The second mapping relationship is the mapping relationship between the preload force and the translation distance. The railway track fastener bolt preload status monitoring system further includes: a frequency adaptive wireless receiver, through which the echo response signal is transmitted to the bolt status analysis unit; the frequency adaptive wireless receiver is equipped with a receiving tuning module, which dynamically adjusts the receiving channel frequency according to the excitation frequency, and optimizes the sampling density of the target frequency band by combining the frequency weighting control function in the weighting control module; the specific form of the frequency weighting control function is: ， ； In the formula, represents the frequency response weighting function; exp() represents an exponential function with the natural constant e as the base; Indicates the current scan frequency point; This indicates the center frequency measured by the passive wireless detection device for bolt fasteners under assembled and tightened conditions. Indicates the frequency distribution broadening parameter; Indicates the receiving module at frequency The scanning dwell time at the location; Indicates the system's shortest dwell time; The adjustment coefficient representing the dwell time.

2. The railway track fastener bolt pre-tightening status monitoring system according to claim 1, characterized in that, The intelligent wireless transmitting device specifically includes: The system includes a frequency control module and a resonant transmission circuit module. The frequency control module generates multiple tuning signals with frequencies varying in a set step within one transmission cycle. The resonant transmission circuit module generates excitation signals corresponding to each tuning signal and transmits the excitation signals corresponding to each tuning signal to the passive wireless detection device for bolt fasteners at set time intervals within one transmission cycle.

3. The railway track fastener bolt pre-tightening status monitoring system according to claim 1, characterized in that, The passive wireless detection device for bolt fasteners further includes: a second inductor and a third inductor; an antenna is connected to one end of the second inductor, and the other end of the second inductor is connected to the input terminal of n parallel LC resonant circuits, one end of the first inductor, and the positive terminal of the diode; one end of the third inductor is connected to the output terminal of the n parallel LC resonant circuits.

4. The railway track fastener bolt pre-tightening status monitoring system according to claim 1, characterized in that, The bolt state analysis unit includes a time-frequency curve determination subunit, a bolt under test determination subunit, and a preload state determination subunit. The time-frequency curve determination subunit is used to plot the time-frequency curve corresponding to any passive wireless detection device for bolt fasteners, with the resonant frequency of each echo response signal generated by the passive wireless detection device for bolt fasteners as the vertical axis and the time when the passive wireless detection device for bolt fasteners transmits each echo response signal as the horizontal axis. The test bolt determination subunit is used to determine the test bolt corresponding to any passive wireless detection device for bolt fasteners based on the preset frequency range corresponding to the resonant frequency of all echo response signals generated by the passive wireless detection device for bolt fasteners and a first preset mapping relationship; the first preset mapping relationship is the mapping relationship between the preset frequency range and the test bolt. The preload state determination subunit is used to obtain the preload force of each bolt to be tested based on the bolt to be tested corresponding to the passive wireless detection device for each bolt fastener and the time frequency curve corresponding to the passive wireless detection device for each bolt fastener, and to obtain the preload state of each bolt to be tested based on the preload force of each bolt to be tested.

5. A method for monitoring the pre-tightening state of railway track fastener bolts, characterized in that, The railway track fastener bolt preload monitoring system applied to any one of claims 1-4, wherein the railway track fastener bolt preload monitoring method comprises: For any passive wireless detection device for bolt fasteners, an excitation signal with a frequency that changes according to a set step is transmitted to the passive wireless detection device for bolt fasteners at a set time interval within a transmission cycle. Obtain the echo response signals corresponding to each excitation signal generated by the passive wireless detection device for bolt fasteners; Based on the resonant frequency of the echo response signal generated by the passive wireless detection device for each bolt fastener, the time-frequency curve corresponding to each passive wireless detection device for bolt fastener is plotted. Based on each time-frequency curve, the resonant frequency of the echo response signal generated by each passive wireless detection device for bolt fastener, and each preset frequency range, the pre-tightening state of each bolt to be tested is determined. The resonant frequency of the echo response signal generated by different passive wireless detection devices for bolt fasteners is within different preset frequency ranges. Different bolts to be tested correspond to different preset frequency ranges.

6. The method for monitoring the pre-tightening state of railway track fastener bolts according to claim 5, characterized in that, Based on the resonant frequency of the echo response signal generated by the passive wireless detection device for each bolt fastener, a time-frequency curve corresponding to each passive wireless detection device for the bolt fastener is plotted. Then, based on each time-frequency curve, the resonant frequency of the echo response signal generated by each passive wireless detection device for the bolt fastener, and each preset frequency range, the pre-tightening state of each bolt to be tested is determined, specifically including: For any passive wireless detection device for bolt fasteners, plot the time-frequency curve corresponding to the passive wireless detection device for bolt fasteners with the resonant frequency of each echo response signal generated by the passive wireless detection device for bolt fasteners as the vertical axis and the time when the passive wireless detection device for bolt fasteners transmits each echo response signal as the horizontal axis. Based on the preset frequency range corresponding to the resonant frequencies of all echo response signals generated by the passive wireless detection device for bolt fasteners and the first preset mapping relationship, the bolt to be tested corresponding to the passive wireless detection device for bolt fasteners is determined; the first preset mapping relationship is the mapping relationship between the preset frequency range and the bolt to be tested. Based on the test bolts corresponding to the passive wireless detection devices for each bolt fastener and the corresponding time-frequency curves of the passive wireless detection devices for each bolt fastener, the preload of each test bolt is obtained, and the preload state of each test bolt is obtained based on the preload of each test bolt.

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