Proceedings of the 8th

World Congress on Intelligent Control and Automation July 6-9 2010, Jinan, China

978-1-4244-6712-9/10/$26.00 ©2010 IEEE

Research and Design of Railway Clearance Measurement System Based on Non-Contact Sensors

Liu Yu, Shi Hongmei, Zhu Liqiang, Xu Xining School of Mechanical, Electronic and Control Engineering

Beijing Jiaotong University Beijing, China

08121815@bjtu.edu.cn

Abstract - The measurement of railway clearance is the important guarantee way to the safety and the high-speed operation. A new scheme of non-contact clearance measurement method is proposed based on laser sensor in this paper. A high speed data acquisition card is designed based on FPGA, completing the laser data acquisition and clock synchronization. And an algorithm of vibration compensation is designed based on the displacement sensors for measure the error of car body vibration. The system is proved that it can complete the vibration compensation and judge the out-of-gauge point real-time under the speed of 160km/h through experiment.

Index Terms - checking of clearance, clock synchronization, vibration compensation.

I. INTRODUCTION

With the development of high-speed railway and municipal rapid orbital transportation, more requirements are put forward including the trains safety and comfort. Higher speed and heavier load will increase track damage, leading to the status of track deterioration and decreasing the safety and comfort of vehicles. Fast clearance measurement technology will be required for more new and existing lines. At the same time, with the advance of passenger dedicated line, a real time and rapid measurement system for the railways status, a fault diagnosis technology and an information feedback are the particularly important guarantee ways to safety and high speed operation of railway. The traditional clearance measurement system uses contact measurement method based on the mechanical tentacles, meaning that it is difficult for vibration compensation, low automation level and not suitable to high speed operation [1]. Recently, with the photoelectricity technology development, a rotary laser scanning range sensor based on the principle of light propagation time is widely used in the foreign high speed railway. This kind of sensors can measure the distance between sensor and the impediment by measuring the time interval between the emission of a laser pulse and receiving of the reflection laser pulse from impediments. The laser pulse can scan all impediments and get clearance size when the effluence angle is changed [2]. To getting the real-time clearance size, a new scheme of non-contact clearance measurement method is proposed based on laser sensor in this paper. A high speed data acquisition card is designed based on FPGA, completing the laser data acquisition and clock synchronization. And an algorithm of vibration compensation is designed based on the displacement sensor for measure error of car body vibration. A software is

developed for acquisition data uses VC++6.0 development environment. The function of acquisition, storage, query and data analysis are carried out. The system is proved that it is can complete vibration compensation and real-time out-of-gauge point judgment under the speed of 160km/h through experiment.

II. HARDWARE SCHEME

Measuring devices shown on Fig.1 is consisted of the clearance measurement system, the dynamic reference system, the speed and position measurement system, the data acquisition system and so on.

Fig.1 System scheme of the railway clearance measurement based on laser

sensor

A. Clearance Measurement System The high speed laser measurement device used in this system is LMS200 series from SICK Co. Ltd.. They have many advantages, such as small volume, convenient installation, anti-external light interference, harmless to eyes and it can be installed on the normal operation train or the inspecting car of the track. These laser sensors can scan 180 degree, their repetition measurement error is less than ±5 mm, sampling rate is up to 500kbps, and the distance between two samples is 0.25 degree. 30000 points can be sampled per second when the laser scanning frequency is 75Hz [3]. As shown on Fig.2, two LMS200 are installed in front of the train for getting clearance size, the high speed laser data is collected by data processing card based on FPGA, the sample data is transmitted to PC from FPGA by PCI interface, and the profile of clearance is drawn by software.

B. Dynamic Reference System There will be six DOF uncertainty posture between vehicles and ground when the train is running, which are the main error resource of the clearance measurement system.

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Inertial measurement technique are the traditional dynamic posture measurement method, for example, mechanical gyroscopes, laser gyroscopes and fiber gyroscopes can measure the change of the angle around the three-dimensional axis rotation of the dynamic object, accelerometers can measure the acceleration of the linear motion, at last the absolute change of the six DOF are calculated indirectly by integral [4]. The gyroscope have zero drift error, these systematic errors will be accumulated into the measurement results in the integration process. So the measurement errors will become lager with operation time. The inertial navigation is inappropriate for long distance measurement.

Fig.2 System device of clearance measurement

Due to the practically of the railway transit, the existing posture measurement technologies can’t simultaneously satisfy the requirement of range, accuracy, distance of detection and on-board installation. A low cost and high-accurate posture compensation arithmetic are proposed in this paper based on displacement sensors. The measurement device includes four displacement sensors and their data acquisition device. The displacement sensors are installed between the carriage and the bogie follow certain rules. The system uses YK176 series displacement sensors. There are four DOF of posture values can be obtained including rolling angle, hunting angle, bouncing and swaying. Finally, the posture compensation can be realized by rotation matrix.

C. Speed and Position Measurement System The traditional speed measurement system mainly relies on the axle tachometer, but there are idling and slipping phenomenons when the train is running. If the errors didn’t be eliminated in time it would result in unpredictable incidents. The speed and position measurement system is made up of

point-laser AR4000 and axle tachometer. The point-laser AR4000 is installed on the car body to check the characteristics of the environment symbol (e.g. turnout) when the train is running. The actual location information can be obtained from AR4000, as shown on Fig.3, which can compare with the standard line parameter and correct the output of the axle tachometer to decrease the accumulated error in real-time [5].

Fig.3 The track slope shape diagram by AR4000

D. Data Acquisition System The data acquisition part consists of hardware and software. As shown on Fig.4, hardware collections mainly depend on the high speed data processing card of PCI based on FPGA. An IP core is designed shown on Fig.5, to implement the high speed serial port send and receive the data from LMS200, to count pulse of the tachometer, to acquire A/D converter values of displacement sensor, and to achieve clock frequency. The data acquisition and cache of the gyroscope and GPS though the computer serial port. The pulse values of tachometer and the clock frequency of CLK noted by count IP core, these values are used as the synchronization clock label.

MAX490 TLP113

TLP113

EP1C12Q240C8N74LVTH16245

74LVTH16245

S29GL256N

PCI9052 PCI

93CS46

TachometerPulse

Fig.4 The system drawing of hardware sampling

Fig.5 FPGA inside designed drawing

P C I

256B Data send TTL—422

2K FIFO Data receive

First laser sensor

256B Data send TTL—422

2K FIFO Data

Second laser sensor

Displacement sensorA/D 1K FIFO

Tachpmeter Pulse Count IP core CLK

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The difficulties of software design consist of clock synchronization and the arithmetic of all sensors. When data from each sensor and the count value are read at the same time via computer, the synchronization clock came true through read data from the same PCI interface card, and save the count value to a global variable, so that the global variable as the clock label can be read when capture image and read data from the point laser AR4000, gyroscope and GPS. The arithmetic of each sensor contains judged the out-of-gauge point, run after GPS, vibration compensation and so on. The Ministry of Railway established the standard railway clearance size, which must be written to database and compared with the high speed laser data, to judge if the clearance have been intruded, if it is, the software will alarm, save the out-of-gauge data and capture out-of-gauge images. Then preparation the GIS system for run after the position information of train running by the longitude and latitude from GPS, and shown the figure of satellite navigation in the screen.

III. DATA PROCESS

A. Compensation Scheme of Car Body Vibration The movement of measurement system is simplified to six DOF transformations, when the deformation of the measurement framework can be ignored in the dynamic measurement system. The changes of fore-and-aft motion and bouncing angle have no obvious effect on the vibration compensation system, so 0, 0y α= = . Finally, the cay body posture is shown by four DOF. The traditional vibration compensation is based on the gyroscope measurement of the inertial standard, but it has accumulated error which is difficult to eliminate, and because its coordinate is geodetic coordinate system, the rotation matrix between the gyroscope coordinate and the reference coordinate is uncertain. The vibration compensation is achieved by the displacement sensor in the system. As shown on Fig.6, the displacement sensor is installed between the car body and the bogie，movement output values are d1, d2, d3, d4 corresponding the displacement sensor S1, S2, S3, S4, and the distance between S1 and S2 is L1, between S3 and S4 is L2.

Fig.6 The installation of displacement meter for car body vibration

compensation

B. Mathematical Model of Compensation The output values of displacement sensor can be changed when train is running as shown on Fig.7 1 1 2w d d= − ,

2 3 4w d d= − . So the rock-roll angle arctan( 1/ 1)w lθ = , the

rolling angle arctan( 2 / 2)w lβ = , the swaying value ( 1 2) / 2x d d= + and the bouncing value ( 3 4) / 2z d d= + .

The six DOF are obtained when the train is running.

θβ

Fig.7 Schematic diagram for displacement sensor variation

The compensated coordinates is obtained by rotation matrix method,

cos cos sin sin sin sin cos cos sin sin cos sin 'sin cos cos cos sin ' (1)

cos sin sin sin cos sin sin cos sin cos cos cos '

X X xY Y yZ Z z

α β α θ β α β α θ β θ βα θ α θ θ

α β α θ β α β α θ β θ β

− + −⎡ ⎤ ⎡ ⎤⎡ ⎤ ⎡ ⎤⎢ ⎥ ⎢ ⎥⎢ ⎥ ⎢ ⎥= − +⎢ ⎥ ⎢ ⎥⎢ ⎥ ⎢ ⎥⎢ ⎥ ⎢ ⎥⎢ ⎥ ⎢ ⎥+ −⎣ ⎦ ⎣ ⎦⎣ ⎦ ⎣ ⎦

as,

( ).

cos sin sin cos sin0 cos sin 2

sin sin cos cos sin

'' 0'

XYZ

X xYZ z

β θ β θ βθ θ

β θ β θ β

− ⎡ ⎤ ⎡ ⎤⎡ ⎤ ⎡ ⎤⎢ ⎥ ⎢ ⎥⎢ ⎥ ⎢ ⎥⎢ ⎥ ⎢ ⎥⎢ ⎥ ⎢ ⎥⎢ ⎥ ⎢ ⎥⎢ ⎥ ⎢ ⎥−⎣ ⎦ ⎣ ⎦ ⎣ ⎦ ⎣ ⎦

= +

In equation (2), (X', Y', Z') is coordinate before compensation, (X, Y, Z) is compensated coordinate.

IV. TESTS AND VALIDATION

The clearance measurement system is installed on the operating train. Before the installation of sensors, the reference coordination must be established at first. And the track center line is designed as y-axis, vertical direction on the track surface as x-axis. Fig.8 shows the coordinate of laser sensor is transformed to the reference coordinate by precise calibration platform when train is in still mode. The real-time compensation of car body posture is needed when the train is running. The status of vehicle is back to no-vibration status by compensation system, shown on Fig.9.

(a) Before calibration

S3

S4

S2 S1

L2 Car Body

Bogie

L1

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(b) After calibration

Fig.8 Compared the result of system calibration

(a) Before compensation

(b) The compensation result with displacement sensor

Fig.9 Schematic diagram of vibration compensation

V. CONCLUSIONS

A new method of on-board railway clearance measurement is proposed in this paper based on high accurate and non-contact sensors. And an effective compensation scheme is realized based on displacement sensor which has low cost and high precision. The existing compensation problem of on-board has been solved. The real-time position correction and the sensors synchronization are achieved. The judgment of the out-of-gauge point and the disposal of the alarm are realized. The system can be applied to the entire railway field including mass transit for its economy and maneuverability. The technology of non-contact measurement also can be used to the road transportation field, checking the deformation of freeways, monitoring the high limit and so on.

REFERENCES [1] D.K. MacKinnon, V. Aitken, F. Blais, A Comparison of Precision and

Accuracy in Triangulation Laser Range Scanners, 2006 Canadian Conference on Electrical and Computer Engineering, CCECE'06, 2007(2006), pp. 832-837.

[2] Li Ruying, Wu Jiqin, Zeng Ming, Metro Clearance Detection Based on Laser Measurement, URBAN RAPID RAIL TRANSIT, 2007, vol. 20, no.5, pp. 70-73.

[3] Yu Zujun, Zhu Liqiang, Zhao Jieting, Study on System Scheme for Vehicular Kinematical Measurement of Railway Complete Profile, Journal of Beijing Jiaotong University, 2007, vol. 31, no.5, pp. 1-5.

[4] J. Talaya, R. Alamus, E. Bosch, Integration of A Terrestrial Laser Scanner with GPS/IMU Orientation Sensors, ISPRS Istanbul Turkey, 2004, pp. 12-23.

[5] C. Krobb, M. Krauhausen, R. Priem, H.O. Katthöfer, M. Hülsmann, Measurement of rail profiles using 2D laser sensors, VDI Verlag GMBH, 2002, pp. 149-154.

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