Lossless contact type rail fastener bolt loosening length detection system and detection method

Abstract

The invention discloses a nondestructive contact type rail fastener bolt loosening length detection system and detection method. The system comprises a detection vehicle and a detection sensor arranged on the detection vehicle. The detection vehicle runs along the track, the detection sensor comprises a contact probe and a sliding variable resistor, the contact probe is elastically arranged in a telescopic mode and comprises a contact part and a telescopic moving part, and the contact part of the contact probe touches fastener bolts on the two sides of the track in the process that the detection sensor runs along with the detection vehicle; the telescopic moving part is connected with a resistance value regulator of the sliding variable resistor, the contact probe changes the resistance value of the sliding variable resistor in the process of touching the fastener bolt, the specific loosening length value of the fastener bolt is detected according to the current signal change caused by the resistance value change during contact, and automatic detection of the loosening length of the rail fastener bolt is achieved. The method has the advantages of being high in detection efficiency, reliable in detection result, low in detection cost and high in environmental adaptability.

Description

Technical Field

[0001] The invention discloses a non-destructive contact type rail fastener bolt loose length detection system and detection method, belonging to rail transportation detection technology. Background Art

[0002] The rail fastening system plays a role in stabilizing the rails during railway operation and is an important component to ensure the safe and reliable operation of the railway system. Bolts (also known as spiral spikes) are the core components of the fastening system. Only when the bolts are firm can the fastening system function normally. Therefore, whether the bolts in the fastening system are firm is the focus of the railway inspection process.

[0003] Ballastless tracks account for more than 90% of the total high-speed railway lines in my country, and slab tracks account for more than 50% of the ballastless tracks, while about 75% of the slab tracks use the WJ-8 fastener system. In addition, each rail contains thousands of fastener systems. Bolt loosening is a major test item for fastener system testing, and the large number of fasteners leads to a huge demand for testing this project.

[0004] At present, most rail systems still rely on manual inspection to detect loose fastener bolts. Whether the fastener bolts are loose is judged by manual visual inspection. Relying on manual inspection is not only inefficient and costly, but the test results are also easily affected by human factors and external environmental factors, resulting in missed judgments and misjudgments, and the test results are unreliable.

[0005] With the further development of artificial intelligence, a series of technologies have emerged that use visual image technology to assist in the detection of rail fastener system bolts, such as a dual-spectral imaging rail and fastener anomaly detection method disclosed in the Chinese patent application with application number CN201710949482.9, and a high-speed dynamic real-time detection method and device for loose rail fasteners disclosed in the Chinese patent application with application number CN201310159000.1. This type of detection technology usually uses a camera to obtain rail and fastener image data, and uses image processing and recognition technology to perform abnormal detection of fasteners and fastener bolts. However, this type of detection technology is greatly affected by the environment. In rainy, snowy or windy and sandy environments, it will produce large image acquisition noise, causing misjudgment in subsequent image recognition, affecting the accuracy of the final detection results. Summary of the invention

[0006] The technical problem solved by the present invention is: in view of the problem that the existing rail fastener detection technology based on visual image processing has reduced accuracy in harsh environments, a direct and non-destructive contact rail fastener bolt loosening length detection system and detection method that can achieve rapid initial screening is provided.

[0007] The present invention is implemented by the following technical solutions:

[0008] The present invention firstly discloses a non-destructive contact type rail fastener bolt loose length detection system, comprising a detection vehicle 1 and a detection sensor 2 arranged on the detection vehicle; the detection vehicle 1 travels along a track, the detection sensor 2 comprises a contact probe 201 and a sliding variable resistor 204, the contact probe 201 is elastically telescopically arranged, comprising a contact portion and a telescopic moving portion, the contact portion of which touches the fastener bolts on both sides of the track in the process of the detection sensor traveling with the detection vehicle, the telescopic moving portion is connected to a resistance adjuster of the sliding variable resistor 204, the contact probe 201 changes the resistance value of the sliding variable resistor in the process of touching the fastener bolt, and the fastener bolt loose length detection is realized by detecting the resistance change value of the sliding variable resistor.

[0009] In the non-destructive contact type rail fastener bolt loosening length detection system of the present invention, further, the detection sensor 2 also includes a protective shell 21, a limiting guide tube 202 is provided inside the protective shell 21, the telescopic movable part of the contact probe 201 is slidably assembled inside the limiting guide tube 202, and a return spring 203 for extending the contact probe is provided at the bottom of the limiting guide tube.

[0010] In the non-destructive contact type rail fastener bolt loose length detection system of the present invention, further, the contact probe 201 is telescopically arranged in the vertical direction, and its contact head touches the fastener bolt downward, and the contact surface of the contact head facing the fastener bolt is arranged as an inclined surface.

[0011] In the non-destructive contact type rail fastener bolt loose length detection system of the present invention, further, the detection sensor 2 is connected to the frame of the detection vehicle through an adjustable bracket 22.

[0012] In the non-destructive contact rail fastener bolt loose length detection system of the present invention, further, the sliding variable resistor 204 is a resistance wire coil arranged along the telescopic movement direction of the contact probe, and the resistance adjuster thereon is an adjustment slide sliding on the resistance wire coil, and the telescopic moving part of the contact probe 201 is connected to the adjustment slide.

[0013] In the non-destructive contact rail fastener bolt loose length detection system of the present invention, further, the sliding variable resistor 204 is connected to the current detection circuit, and the current detection circuit is provided with a current recorder 311. The current recorder 311 detects the current passing through the sliding variable resistor in real time and records the change of the current value.

[0014] In the non-destructive contact type rail fastener bolt loose length detection system of the present invention, further, a fastener position recorder 312 is connected in series to the current detection circuit, and the fastener position recorder 312 is equipped with a Beidou positioning chip, and the fastener position information is located in real time through the Beidou positioning chip. The fastener position recorder 312 is feedback-connected to the current recorder 311, and the current recorder 311 detects the resistance change of the sliding variable resistor and records the corresponding fastener position information at the same time.

[0015] In the non-destructive contact type rail fastener bolt loose length detection system of the present invention, further, the current recorder 311 and the fastener position recorder 312 are communicatively connected with the information storage module 31, and the information storage module 31 calculates and stores the detected fastener bolt loose length information and the corresponding fastener position information, and transmits them to the host computer through the communication module.

[0016] The present invention also discloses a non-destructive contact type rail fastener bolt loose length detection method, using the non-destructive contact type rail fastener bolt loose length detection system of the present invention, and performing detection according to the following steps:

[0017] In the early stage of debugging, the detection sensor is installed on the detection vehicle, and the bottom end of the contact part of the contact probe is adjusted to contact with the standard fastener bolt through the adjustable bracket, and calibrated as the standard detection position of the contact probe;

[0018] Mid-term inspection: start the inspection vehicle to inspect the looseness of all the fastener bolts of the track and obtain the loosening length of the fastener bolts;

[0019] In post-processing, when an abnormal bolt whose loose length exceeds the safety threshold is detected, the loose length information and fastener position information of the abnormal bolt are recorded, saved and uploaded through the information storage module, and the maintenance personnel are fed back to the designated fastener position to inspect and repair the abnormal bolt. The maintenance personnel will feedback the inspection and repair results and remove the abnormal bolt loosening information at the fastener position;

[0020] If the loose length of the abnormal bolt is within the safety threshold, the test result will be retained and the bolt will be the focus of the next test.

[0021] In the detection method of the non-destructive contact type rail fastener bolt loose length detection system of the present invention, the bolt loosening information is the bolt loosening length, and the bolt loosening length is calculated by the following formula:

[0022] L=R / (ρ·πr 2 ·πr1 2 ),

[0023] Wherein, L is the loose length of the bolt that increases in the vertical direction due to loosening of the fastener bolt, ρ is the resistivity of the resistance wire used in the sliding variable resistor, r is the cross-sectional radius of the resistance wire used in the sliding variable resistor, r1 is the radius of the resistance wire winding coil of the sliding variable resistor, R is the real-time resistance change value of the sliding variable resistor connected to the current detection circuit, R=V / A-(R1+R2), when the fastener bolt increases without loosening, R is 0, R1 is the resistance value of the fixed resistor set in the current detection circuit, R2 is the resistance value of other electrical appliances in the current detection circuit, V is the detection power supply voltage of the current detection circuit, and A is the current passing through the current detection circuit detected by the current recorder.

[0024] The present invention adopts the above technical solution to achieve the following beneficial effects:

[0025] (1) The detection system of the present invention adopts a detection method based on sensor technology. The resistance value of the sliding variable resistor is changed by the contact between the contact probe and the fastener bolt, and the change in the current value is detected, thereby judging whether the fastener bolt is loose and obtaining the loose length of the bolt. The response speed is extremely fast. During the detection process, the detection vehicle runs at a high speed. The detection efficiency is much higher than that of manual detection one by one, which greatly improves the detection efficiency, avoids the misjudgment and missed judgment of manual detection, improves the detection accuracy, and makes the detection efficient and accurate.

[0026] (2) The contact probe of the present invention is made of a suitable flexible material, and uses an inclined surface to contact the fastener bolt. The vertical component force generated by the decomposition of the inclined surface is used to push the contact probe to change the resistance value of the sliding variable resistor, thereby avoiding direct frontal impact and realizing non-destructive contact detection of the fastener bolt.

[0027] (3) The detection system of the present invention detects abnormal fastener bolts by detecting sensors touching them. Compared with visual image acquisition, it is basically not affected by external environmental factors and has stronger anti-interference ability. Combined with the protective shell wrapping structure of the detection sensor, inspection can be carried out even in severe weather conditions, and the inspection results are more stable and reliable. The detection equipment has a simple structure, does not require expensive manufacturing costs, is easy to operate, and effectively reduces the detection cost and labor cost.

[0028] (4) The detection method of the present invention utilizes the contact probe of the detection sensor to contact the upper surface of the screw head of the loose fastener bolt, and detects the specific loose length value of the fastener bolt according to the change of the current signal caused by the change of the resistance value during contact, and combines the Beidou positioning technology to locate the fastener position information in real time, thereby realizing the automatic detection of the loose length of the rail fastener bolt.

[0029] In summary, the non-destructive contact type rail fastener bolt loose length detection system and detection method provided by the present invention have the characteristics of high detection efficiency, reliable detection results, low detection cost and strong environmental adaptability, etc., which realize the automation and informatization of rail fastener bolt loose length detection, and provide a more efficient and reliable detection technology for rail fastener bolt loose length detection.

[0030] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a schematic diagram of the overall structure of a non-destructive contact type rail fastener bolt loose length detection system according to Example 1.

[0032] Figure 2 It is a side schematic diagram of the detection sensor in the first embodiment.

[0033] Figure 3 It is a front view schematic diagram of the detection sensor in the first embodiment facing the fastener screw.

[0034] Figure 4 This is a schematic diagram of installing the adjustable bracket of the detection sensor in Example 1.

[0035] Figure 5 This is a schematic diagram of the contact detection principle between the detection sensor and the fastener bolt in the first embodiment.

[0036] Figure 6 Schematic diagram of the current detection circuit in Example 1.

[0037] Numbers in the figure: 100-track, 110-fastener, 111-fastener bolt;

[0038] 1-test vehicle, 11-frame, 12-wheels, 13-power unit;

[0039] 2-detection sensor, 201-contact probe, 202-limiting guide tube, 203-return spring, 204-sliding variable resistor, 205-resistance adjuster, 21-protective housing, 22-adjustable bracket, 221-vertical rod, 222-cross rod, 223-locking knob, 224-bracket base;

[0040] 300-detection power supply, 301-fixed resistor, 302-detection system switch, 310-information storage module, 311-current recorder, 312-fastener position recorder. DETAILED DESCRIPTION

[0041] Embodiment 1

[0042] See also Figure 1, the figure shows a specific implementation scheme of the non-destructive contact rail fastener bolt loosening length detection system of the present invention, which includes a detection vehicle 1 and a detection sensor 2, wherein the detection vehicle 1 uses wheels 12 with the same chassis wheelbase as the rail train to travel on the track 100, and a power device 13 for driving the detection vehicle 1 to move is provided on the frame 11, and the power device 13 uses the same electric drive method as the rail train, or an independent internal combustion engine drive method. The detection sensor 2 is arranged on the frame 11 of the detection vehicle 1. The main body of the detection sensor 2 is a contact probe 201 and a sliding variable resistor 204. The contact probe 201 is elastically retractable. The contact probe 201 is divided into a contact part and a retractable moving part. The contact part touches the fastener bolts of the fasteners 110 on both sides of the track 100 when the detection sensor 2 moves with the detection vehicle 1. The retractable moving part of the contact probe 201 is connected to the resistance adjuster of the sliding variable resistor 204. When the contact probe 201 touches the fastener bolt, it drives the resistance adjuster 205 to change the resistance value of the sliding variable resistor 204. The fastener bolt loosening information detection is realized by detecting the resistance change value of the sliding variable resistor 204. .

[0043] See also Figure 2 and Figure 3 The detection sensor 2 also includes a protective shell 21 and an adjustable bracket 22. The main body of the detection sensor 2 is arranged in the protective shell 21 and is connected to the adjustable bracket 22 through the protective shell 21. The entire detection sensor 2 is connected to the frame 11 of the detection vehicle through the adjustable bracket 22, and the height and position of the detection sensor can be adjusted through the adjustable bracket 22.

[0044] Specific as Figure 4 As shown, in this embodiment, the adjustable bracket 22 for installing the detection sensor 2 includes a vertical rod 221, a horizontal rod 222, a locking knob 223 and a bracket base 224. The detection sensor is connected to the horizontal rod 222 through a snap-fit ​​of the protective shell 21. One end of the horizontal rod 222 slides on the vertical rod 221, and the horizontal rod 222 is locked at different height positions on the vertical rod 221 through the locking knob 223, so as to realize the height change of the horizontal rod 222 and the sensor thereon in the vertical direction. The bottom of the vertical rod 221 is fixedly connected to the frame of the detection vehicle through the bracket base 224, and can be fixed by bolts or magnetic adsorption.

[0045] The frame 11 of the inspection vehicle 1 is generally made of stainless steel, which has good structural strength and is durable and corrosion-resistant. The adjustable bracket 22 is made of aluminum alloy, which is stable and lightweight. The protective shell 21 is loaded on the inspection vehicle through the adjustable bracket 22, and can be made of aluminum alloy, which has good plasticity and corrosion resistance, and has a streamlined shape to reduce wind resistance and further improve the stability of the inspection results.

[0046] The entire detection sensor 2 only retains the contact part of the contact probe 201 exposed outside the protective shell. The protective shell 21 can also protect the internal detection sensor, prevent the detection sensor body from being exposed to the external environment, and realize the functions of preventing rain, snow, wind and sand. Specifically, a limiting guide tube 202 is provided inside the protective shell 21, and the telescopic movable part of the contact probe 201 is slidably assembled inside the limiting guide tube 202, and a return spring 203 for extending the contact probe is provided at the bottom of the limiting guide tube 202. The return spring 203 is located inside the limiting guide tube 202, one end of which is connected to the telescopic movable part of the contact probe, and the other end is connected to the inner wall at the bottom of the limiting guide tube 202, so as to ensure that the contact head of the contact probe 201 rebounds and extends to the initial position in time after being touched and retracted by the loose bolt. This embodiment takes the WJ-8 type fastener bolt detection commonly used in the rail system as an example. The length of the WJ-8 type fastener bolt increased in the vertical direction after rotating 360° is 12.5mm. It is necessary to ensure that the maximum compression deformation of the return spring 203 is at least not less than 12.5mm. In actual applications, it can be set to 30mm.

[0047] The contact probe 201 is telescopically arranged in the vertical direction, and the limit guide tube 202 is arranged in the vertical direction inside the protective shell 21. The contact head of the contact probe 201 extends downward from the protective shell 21 to touch the fastener bolt for detection. When the contact head of the contact probe 201 faces the fastener bolt 111, the contact surface is set as an inclined surface. During the contact between the fastener bolt 111 and the contact surface of the contact head, an upward vertical component force is generated by decomposing the inclined surface to push the contact probe 201 toward the inside of the limit guide tube 202. Figure 5 As shown in , the contact head can be extended and retracted in the vertical direction to avoid direct frontal collision. The contact probe 201 is made of insulating, hard, wear-resistant and low-cost materials, such as nylon. The outer surface of the contact surface of the contact head is smoothed and grease is applied to the contact surface to reduce the friction when it touches the fastener bolt head, which is conducive to the vertical displacement of the contact probe. In practical applications, the contact head of the contact probe 201 can be set to a conical head, or a triangular cross-section cylinder with a certain length. The triangular cross-section cylinder is arranged horizontally to ensure that the contact head of the contact probe 201 can accurately touch all fastener bolts on both sides of the track that have a certain installation error in the horizontal position.

[0048] When the detection vehicle 1 drives the contact probe 201 of the detection sensor 2 to contact the abnormal fastener bolt 111, the contact probe 201 produces a vertical displacement, thereby driving the resistance adjuster 205 of the sliding variable resistor 204, resulting in a change in the resistance value, which brings about a change in the current value in the current detection circuit. At this time, the return spring 203 is squeezed, so that the contact probe 201 is close to the upper surface of the screw head of the fastener bolt 111, ensuring the accuracy of the detection result. After the detection vehicle 1 continues to drive the contact probe 201 of the detection sensor 2 away from the abnormal bolt, the return spring 203 loses the squeezing force and rebounds quickly, driving the contact probe 201 and the resistance adjuster of the sliding variable resistor 204 back to the initial position.

[0049] The contact probe 201 adopts a detachable structure for easy replacement. The contact probe 201 and its telescopic movable part are connected by threaded connection, magnetic connection or snap connection, so as to facilitate replacement after being damaged during long-term use.

[0050] The sliding variable resistor 204 in this embodiment adopts a resistance wire coil, and the resistance adjuster thereon is an adjustment slider sliding on the resistance wire coil. The resistance wire coil of the sliding variable resistor 204 is arranged along the telescopic movement direction of the contact probe, and the adjustment slider on the resistance wire coil is directly connected to the telescopic moving part of the contact probe 201, ensuring that the resistance adjuster of the sliding variable resistor 204 and the displacement of the contact probe 201 are synchronized. The movement of the resistance adjuster of the sliding variable resistor 204 will change the resistance value of the connected current detection circuit.

[0051] like Figure 6As shown, the current detection circuit connected to the sliding variable resistor 204 includes a detection power supply 300, a fixed resistor 301, a detection system switch 302, a sliding variable resistor 204 and a current recorder 311 connected in series. The detection power supply 300 provides a constant voltage for the entire current detection circuit and adopts a low-voltage DC power supply to avoid the current value being too large and exceeding the range, causing a detection error. The detection system switch 302 controls the opening and closing of the detection circuit. The current recorder 311 detects the current passing through the sliding variable resistor 204, and calculates the real-time resistance change value of the sliding variable resistor through Ohm's law. The current value in the current detection circuit should be controlled within the range of the current recorder 311, and the specific current value can be selected from 100mA-400mA. Furthermore, a fastener position recorder 312 is also connected in series to the current detection circuit. The fastener position recorder 312 is feedback-connected to the current recorder 311. The current recorder 311 detects the resistance change of the sliding variable resistor and records the corresponding fastener position information at the same time. The fastener position recorder 312 and the current recorder 311 are connected in series in the current detection circuit to ensure that there is no time difference in the information recorded by the two instruments. When the current recorder 311 records the current change in the circuit, the fastener position recorder 312 records the fastener position information. The current recorder 311 and the fastener position recorder 312 are connected in communication with the information storage module 31. The information storage module 31 calculates and stores the detected fastener bolt loosening information and the corresponding fastener position information, and transmits them to the host computer through the communication module.

[0052] The fastener position recorder 312 in this embodiment is equipped with a Beidou positioning chip, which uses the Beidou positioning chip to locate the inspection vehicle in real time to obtain and record the position signal of the track where the fastener is located, and assist the maintenance personnel to quickly locate the fastener with abnormal detection. The Beidou navigation and positioning technology is a mature existing technology, and this embodiment does not explain the specific method of Beidou navigation and positioning of the inspection vehicle.

[0053] Embodiment 2

[0054] This embodiment further describes the non-destructive contact type rail fastener bolt loosening length detection method of the present invention. The detection method uses the contact type rail fastener bolt loosening detection system in the first embodiment to perform detection according to the following steps:

[0055] In the early stage of debugging, the detection sensor is installed on the detection vehicle, and the bottom end of the contact part of the contact probe is adjusted to contact with the standard fastener bolt through the adjustable bracket, and calibrated as the standard detection position of the contact probe;

[0056] Mid-term inspection: start the inspection vehicle to inspect the looseness of all the fastener bolts of the track and obtain the loosening length of the fastener bolts;

[0057] In post-processing, when an abnormal bolt whose loose length exceeds the safety threshold is detected, the loose length information and fastener position information of the abnormal bolt are recorded, saved and uploaded through the information storage module, and the maintenance personnel are fed back to the designated fastener position to inspect and repair the abnormal bolt. The maintenance personnel will feedback the inspection and repair results and remove the abnormal bolt loosening information at the fastener position;

[0058] If the loose length of the abnormal bolt is within the safety threshold, the test result will be retained, the fastener position information will not be reported temporarily, and the bolt will be the focus of attention for the next test.

[0059] The safety threshold is selected as the axial movement distance corresponding to one circle loosening of the fastener bolt. For example, in this embodiment, the safety threshold of bolt loosening is set at 12.5 mm for the pitch parameter of the WJ-8 type fastener bolt.

[0060] The bolt loosening information in this embodiment is reflected by the bolt loosening length. The specific bolt loosening length is calculated by the following formula:

[0061] L=R / (ρ·πr 2 ·πr1 2 ),

[0062] Wherein, L is the loose length of the bolt that increases in the vertical direction due to loosening of the fastener bolt, ρ is the resistivity of the resistance wire used in the sliding variable resistor, the resistivity depends on the selected material, and this embodiment uses nickel-chromium alloy-K as the material, and the resistivity is 1.09Ω·mm2 / m; r is the cross-sectional radius of the resistance wire used in the sliding variable resistor, r1 is the radius of the resistance wire winding coil of the sliding variable resistor, R is the real-time resistance change value of the sliding variable resistor connected to the current detection circuit, R=V / A-(R1+R2), when the fastener bolt is not loosened and increases, R is 0, R1 is the resistance value of the fixed resistor 301 set on the current detection circuit, R2 is the resistance value of other electrical appliances in the current detection circuit, V is the detection power supply voltage of the current detection circuit, and A is the current passing through the current detection circuit detected by the current recorder.

[0063] The specific process of post-processing includes that the manager calculates, analyzes and visualizes the test results by storing all uploaded fastener bolt test results. The processing results include the proportion of abnormal bolts, the overall loosening rate of bolts, the location information of abnormal bolts and their corresponding loosening lengths. Through the management platform, managers can obtain the real-time location of on-site maintenance personnel on duty in real time, and intelligently plan the optimal personnel scheduling plan based on the distance between the maintenance personnel and the abnormal bolts to improve maintenance efficiency. Managers can issue an alarm with one click on the management platform, and automatically notify on-site maintenance personnel to go for maintenance according to the personnel scheduling plan. After receiving the alarm, on-site maintenance personnel carry out maintenance work based on the location information of the abnormal bolts, and promptly feedback the maintenance results through smart devices to lift the alarm.

[0064] In this document, the directions or positional relationships indicated by terms such as "up", "down", "front", "back", "left", "right", "top", "bottom", "inside", "outside", "vertical", and "horizontal" are based on the directions or positional relationships shown in the accompanying drawings and are only for the clarity of expressing the technical solutions and the convenience of description, and therefore should not be understood as limitations of the present invention.

[0065] In this document, the terms "comprises," "comprising," or any other variations thereof, are intended to cover a non-exclusive inclusion of elements other than those listed and may also include additional elements not expressly listed.

[0066] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art who is familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. Non-destructive contact rail fastener bolt loose length detection system, characterized by: It comprises a detection vehicle (1) and a detection sensor (2) arranged on the detection vehicle; The detection vehicle (1) travels along a track. The detection sensor (2) comprises a contact probe (201) and a sliding variable resistor (204). The contact probe (201) is elastically telescopically arranged and comprises a contact portion and a telescopic moving portion. The contact portion touches the fastener bolts on both sides of the track when the detection sensor travels with the detection vehicle. The telescopic moving portion is connected to a resistance adjuster of the sliding variable resistor (204). When the contact probe (201) touches the fastener bolt, the telescopic moving portion moves up and down, causing the resistance adjuster to move up and down synchronously, thereby changing the resistance value of the sliding variable resistor. The loose length of the fastener bolt is detected by detecting the resistance change value of the sliding variable resistor.

2. The non-destructive contact rail fastener bolt loose length detection system according to claim 1 is characterized in that: The detection sensor (2) further comprises a protective shell (21), a limiting conduit (202) is provided inside the protective shell (21), the telescopic movable part of the contact probe (201) is slidably mounted inside the limiting conduit (202), and a return spring (203) for extending the contact probe is provided at the bottom of the limiting conduit.

3. The non-destructive contact rail fastener bolt loose length detection system according to claim 2 is characterized in that: The contact probe (201) is telescopically arranged in the vertical direction, with its contact head facing downward to contact the fastener bolt, and the contact surface of the contact head facing the fastener bolt is arranged as an inclined surface.

4. The non-destructive contact rail fastener bolt loose length detection system according to claim 1, characterized in that: The detection sensor (2) is connected to the frame of the detection vehicle via an adjustable bracket (22).

5. The non-destructive contact rail fastener bolt loose length detection system according to claim 1, characterized in that: The sliding variable resistor (204) is a resistance wire coil arranged along the telescopic movement direction of the contact probe, and the resistance value adjuster thereon is an adjustment slide that slides on the resistance wire coil. The telescopic moving part of the contact probe (201) is connected to the adjustment slide, and the upward and downward telescopic movement of the telescopic moving part causes the adjustment slide to move synchronously upward and downward.

6. The non-destructive contact type rail fastener bolt loose length detection system according to any one of claims 1 to 5, characterized in that: The sliding variable resistor (204) is connected to a current detection circuit, and a current recorder (311) is provided on the current detection circuit. The current recorder (311) detects the current passing through the sliding variable resistor in real time and records the change in the current value.

7. The non-destructive contact rail fastener bolt loose length detection system according to claim 6, characterized in that: A fastener position recorder (312) is connected in series to the current detection circuit. The fastener position recorder (312) is equipped with a Beidou positioning chip, and fastener position information is located in real time through the Beidou positioning chip. The fastener position recorder (312) is feedback-connected to a current recorder (311). The current recorder (311) detects the resistance change of the sliding variable resistor and simultaneously records the corresponding fastener position information.

8. The non-destructive contact rail fastener bolt loose length detection system according to claim 7, characterized in that: The current recorder (311) and the fastener position recorder (312) are communicatively connected to the information storage module (31); the information storage module (31) calculates and stores the detected fastener bolt loosening length information and the corresponding fastener position information, and transmits them to the host computer via the communication module.

9. A non-destructive contact method for detecting the loose length of rail fastener bolts, characterized in that: The non-destructive contact type rail fastener bolt loose length detection system according to claim 8 is used to perform detection according to the following steps: In the early stage of debugging, the detection sensor is installed on the detection vehicle, and the bottom end of the contact part of the contact probe is adjusted to contact with the standard fastener bolt through the adjustable bracket, and calibrated as the standard detection position of the contact probe; Mid-term inspection: start the inspection vehicle to inspect the looseness of all the fastener bolts of the track and obtain the loosening length of the fastener bolts; In post-processing, when an abnormal bolt whose loose length exceeds the safety threshold is detected, the loose length information and fastener position information of the abnormal bolt are recorded, saved and uploaded through the information storage module, and the maintenance personnel are fed back to the designated fastener position to inspect and repair the abnormal bolt. The maintenance personnel will feedback the inspection and repair results and remove the abnormal bolt loosening information at the fastener position; If the loose length of the abnormal bolt is within the safety threshold, the test result will be retained and the bolt will be the focus of the next test.

10. The non-destructive contact type rail fastener bolt loosening length detection method according to claim 9, characterized in that: The bolt loosening length is calculated by the following formula: L=R / (ρ·πr 2 ·πr1 2 ), Wherein, L is the loose length of the bolt that increases in the vertical direction due to loosening of the fastener bolt, ρ is the resistivity of the resistance wire used in the sliding variable resistor, r is the cross-sectional radius of the resistance wire used in the sliding variable resistor, r1 is the radius of the resistance wire winding coil of the sliding variable resistor, R is the real-time resistance change value of the sliding variable resistor connected to the current detection circuit, R=V / A-(R1+R2), when the fastener bolt increases without loosening, R is 0, R1 is the resistance value of the fixed resistor set in the current detection circuit, R2 is the resistance value of other electrical appliances in the current detection circuit, V is the detection power supply voltage of the current detection circuit, and A is the current passing through the current detection circuit detected by the current recorder.

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