Tilt Angle Sensor Picture Book 7_Railway Engineering

F. Railway Engineering

Gyroscopes are used in track detection vehicles to detect tracks, and their main functions include monitoring track gauge, height, direction, level, triangular pits, vibration acceleration, etc. The uneven state of the track is a key factor that directly restricts the improvement of train speed in terms of the line.

Case 1: Gyroscope Track Inspection Vehicle

Track inspection vehicle, also known as track inspection vehicle or track inspection instrument, is abbreviated as track inspection vehicle. The use of track inspection vehicles to check the geometric status of the track is an important link in ensuring the safety of railway operation. The main content of track deformation detection by track inspection vehicles includes track gauge, height, track orientation, level, triangular pits, vibration acceleration, etc. The uneven state of the track is a key factor that directly restricts the improvement of train speed in terms of the line. Track irregularity refers to the deviation of two steel rails from the ideal position geometric dimensions of the rails in the height, left and right directions.

There are four types of track irregularities:

1) The height of the track is uneven. It refers to the vertical geometric position deviation between the actual track centerline and the ideal track centerline along the length direction.

2) The track level is not smooth. It refers to the vertical height difference between the left and right rails along the length direction.

3) The track direction is not smooth. It refers to the horizontal geometric position deviation between the actual track centerline and the ideal track centerline along the length direction.

4) Uneven track gauge. It refers to the deviation between the actual gauge and the nominal gauge.

Track irregularity can be divided into periodic track irregularity, random irregularity, and local irregularity. Periodic track irregularity is caused by the irregularity formed by track joints with track length as the wavelength. Random unevenness is caused by errors in track laying, maintenance, and wheel rail wear, which varies from time to place. Local unevenness is caused by specific structures of the line (such as switches, transfer lines, sidings, transition curves, branching lines, bridges, etc.) or accidental locations (such as local diseases of the line). The unevenness of the track causes significant wheel rail force, which not only damages the track structure itself, but also directly affects or endangers the safety of high-speed driving. Track irregularity is an external disturbance to the locomotive and vehicle system, which is the main source of vibration in the locomotive and vehicle system. The functional description of the random variation law of track irregularity is an important basic data for the dynamic analysis of locomotives, vehicles, and track systems. This dynamic analysis is an important means for the design, maintenance, and quality evaluation of modern locomotives, vehicles, and tracks.

This article mainly discusses the irregularity of track direction in track irregularity (see Figure 1). The unevenness of the track direction is caused by the positioning deviation of the track centerline during track laying and major repair operations, the accumulation of lateral residual deformation of the track panel, uneven wear on the side of the track head, failure of fasteners, and inconsistent lateral elasticity of the track.

There are two main methods for detecting the smoothness of track direction:

1. Inertial reference method

2. Short string measurement method

The inertial reference method is an orbit measurement method based on the principle of inertial navigation to describe the trajectory of the orbit and determine the geometric state of the orbit. This method requires the use of high-precision strapdown inertial navigation systems, typically used for high-speed track inspection vehicles. Its principle is the same as that of strapdown inertial navigation system, and details can be referred to relevant literature of strapdown inertial navigation system. When using this system, initial alignment is usually required to determine the directional matrix between the geographic coordinate system and the carrier coordinate system, and then navigation calculations begin. The advantage of using inertial reference method to detect track conditions is rapid measurement, while the disadvantage is expensive price.

The string measurement method is an earlier method for measuring the smoothness of track direction, which is usually used for track detection cars. Among them, the track irregularity detection technology based on fiber optic gyroscope (FOG) is currently the most advanced track detection method in string measurement. The core issue of using gyroscopes to measure track direction is precision angle measurement. Based on this, the transfer function relationship between the angle change of the track inspection instrument and the track direction is established, and the track irregularity information is extracted from it.

The measurement of track irregularity is based on several chord lengths, such as 10m chord, 20m chord, 30m chord, 70m chord, 300m chord, etc. This is also known as wavelength, and each wavelength has a corresponding allowable deviation for track irregularity. The deviation of short wavelength has a significant impact on low-speed driving, while the deviation of long wavelength has a significant impact on high-speed driving.

Case 2: Application of inclination sensor in railway monitoring

Railway transportation is one of the most important modes of transportation, and in recent years, it has been continuously developing, with high-speed trains, intercity trains, and train speeds becoming faster and faster. However, faster speed also comes with greater danger, and accidents occur everywhere. How to ensure driving safety and create a stable and efficient driving environment is currently the most urgent demand.   

A train is a special type of transportation that operates on railway tracks, with a complex and ever-changing operating environment. It is often affected by various factors such as wind, snow, earthquakes, mudslides, landslides, tunnel foreign objects, geological mutations, etc. It is easy to cause deformation of the railway tracks and be covered by foreign objects, seriously threatening the safety of train travel.

The sensor designed and produced by Mai Xinmin Micro Company has a maximum measurement accuracy of ± 0.01 ° @ 25 ° C. It can not only accurately measure the tilt and deformation of iron objects, but also monitor the tilt changes of the surrounding environment of the track in real time. Especially in some inaccessible areas, preventive alarms are made in advance to avoid major accidents.

Case 3: Application of sensors in monitoring settlement of railway track subgrade

To ensure the high-speed and healthy development of railways, a remote automatic monitoring system for roadbed settlement is developed based on technologies such as laser measurement, advanced sensing, and wireless networks. The monitoring system includes four subsystems: laser automatic measurement of surface settlement, simultaneous automatic measurement of roadbed layered settlement and lateral displacement, automatic measurement of roadbed lateral profile settlement, and data acquisition and wireless transmission. The automatic measurement of surface settlement is achieved using laser measurement and automatic calibration technology; The simultaneous automatic measurement of layered settlement and lateral displacement of the roadbed is achieved using Hall sensors, laser ranging, and inclination sensors; The automatic measurement of the settlement of the transverse section of the roadbed is achieved by driving the inclination sensor by the master and slave motors. The monitoring system has been validated in the laboratory and designed for engineering purposes, and has been tested on-site at a high-speed railway station.

The inclination sensor can be well applied in the control system to achieve real-time monitoring of the overall settlement, local settlement, and settlement of different layers in the cross-section of the roadbed. The signal output from the inclination sensor is transmitted to the computer through wireless transmission or various wired networks, and then processed, analyzed, and stored by computer software.

Case 4: Static level and inclinometer for monitoring and warning of subway deformation

In cities in China that already have subways, there are more and more deep excavations along the subway line (very close to subway tunnels). How to protect the running subway tunnels during excavation is a very practical problem. The use of information technology construction and monitoring methods can effectively guide the construction process of foundation pits. The methods of time and space effect, reverse construction, grouting, and foundation pit reinforcement used in construction can all achieve the goal of protecting adjacent tunnels and controlling deformation. However, conventional subway deformation monitoring methods are quite difficult to monitor in running subway tunnels, mainly because the subway operation interval is very short and measurement personnel are absolutely not allowed to enter during operation. Therefore, there must be a simple, unmanned, and automatic dynamic monitoring method that can quickly complete the deformation monitoring of the tunnel in a short time interval and submit monitoring data for the construction of adjacent foundation pits. To ensure the safe operation of the subway, it is necessary to continuously monitor the deformation of the tunnel during the excavation process of the foundation pit.

Monitoring requirements

Due to the fact that subway tunnels are in a fully enclosed operating state for more than two-thirds of the day, monitoring personnel are absolutely not allowed to enter the tunnel to work. Therefore, it is necessary to set up an automated monitoring system in the tunnel to replace manual operation and achieve continuous and accurate monitoring of horizontal and vertical displacement of the tunnel. Considering the short interval between subway operations, the monitoring system used should be able to complete deformation monitoring of the tunnel (affected section) within 3-5 minutes, in order to grasp the deformation laws and characteristics of the subway tunnel caused by foundation pit excavation construction.

Composition of automated monitoring system

A complete automated monitoring system refers to the realization of functions such as automatic observation, recording, processing, storage, report preparation, early warning and prediction without the intervention of operators. It consists of a series of software and hardware, and the entire system configuration includes: foundation pit inclinometer, pressure differential static level, laser rangefinder, surface strain gauge, measurement and control terminal (GPRS), communication cable and power cable, computer and specialized software.

Case 5: Subway Rail Transit Roadbed Settlement Inclination Monitoring

Project Background

With the rapid development of the economy, many cities in China have gradually increased their efforts in urban subway construction. The underground excavation tunnel engineering of urban subways must be constructed inside the rock and soil. Regardless of the burial depth, excavation tunnel construction will inevitably disturb the underground rock and soil, leading to the destruction of the original equilibrium state and gradually shifting to a new equilibrium state. Excavation of underground rock and soil will inevitably lead to surface settlement and deformation, and local surface settlement to a certain extent will have an impact on the normal use of underground pipelines and the safety of ground buildings. During the construction period, effective measures should be taken according to requirements to reduce settlement and deformation, so as to prevent damage to buildings such as ground houses, roads, pipelines, and the ecological environment from deteriorating. During the operation period of the subway, it is even more important to accurately grasp the safety situation of the tunnel and ensure the safety of the subway and important facilities.

Maixinminwei developed static level (settlement monitoring) and inclination sensor (inclinometer) can provide online monitoring and warning of subway settlement deformation indicators. The vertical direction can detect a minimum elevation change of 0.2mm, with an inclination of 0.001 °.

The system reflects the settlement and deformation of subway tunnels in real-time through static level sensors installed on site. The data acquisition instrument collects, analyzes, and summarizes data from each sensor, and transmits the data to the monitoring room through optical fiber or other transmission methods. The monitoring and warning software arranged on the server of the room manages the system data.

Once the monitoring value reaches or exceeds the warning value, corresponding measures shall be taken to deal with it, stop the operation of fixed lines or take reinforcement measures to ensure the safe operation of subway tunnels.

Solution

The monitoring system mainly consists of three parts: sensor acquisition system, data communication system, and monitoring and early warning system. According to the on-site situation, a static level is used to monitor the settlement of the subway tunnel.

1. Sensor part: Static level monitoring, instruments are installed on one side of the tunnel wall, with one monitoring point every 100 meters. A reference point needs to be set up in the stable starting point area.

2. Data transmission part: Considering the real-time and stability of communication, and considering the on-site situation, optical fiber communication method is adopted. The specific method to be used can be determined on-site. GPRS communication can be used for distances exceeding 3KM, and optical fiber can be considered for distances below 3KM. Transmit sensor data to the monitoring center through various transmission methods for unified calculation and processing.

3. Data processing and control subsystem: composed of a small computer system, server system, and software system arranged in the monitoring center

4. Auxiliary support system: including subsystems such as external cabinets, external chassis, power distribution and UPS, and lightning protection.

By installing the Mai Xinmin micro online monitoring system to provide services for the daily safety management and safe operation of subway rail transit, we can greatly improve our understanding of the mechanism of settlement disasters, comprehensively improve the level of subway safety supervision and daily management, and enhance the early warning and response capabilities of enterprises, society, and governments to settlement disasters, Establish a comprehensive evaluation method for settlement deformation risk that is more convenient for safety management and risk control during subway operation.