on the rail track as described in the previous section. The local vibrations such as those in Cars 4 and 10. (counting from the left) of Fig. 8 have been found to be.
QUT Digital Repository: http://eprints.qut.edu.au/
This is the author version published as: This is the accepted version of this article. To be published as :
This is the author’s version published as: Ho, S.L. and Lee, K.K. and Lee, K.Y. and Tam, H.Y. and Chung, W.H. and Liu, S.Y. and Yip, C.M. and Ho, T.K. (2006) A comprehensive condition monitoring of modern railway. In: Proceedings of The Institution of Engineering and Technology International Conference on Railway Condition Monitoring, 2006, 29‐30 November 2006, Brimingham. Catalogue from Homo Faber 2007
Copyright 2006 IEEE
A Comprehensive Condition Monitoring of Modern Railway S.L. 101, K.K. Lee', K.Y. Lee2, H.Y. Tam1, W.H. Chungt, S.Y. Liul, C.M. Yip1, T.K. Ho1
'Dept. of Electrical Engineering, Hong Kong Polytechnic University, Hong Kong 2Kowloon-Canton Railway Corporation, Kowloon, Hong Kong
(excluding the mechanical reinforcement, of course), one can therefore easily understand why the authors believe that the future railway sensors should be optical rather than electrical.
Keywords: Condition Monitoring, FBG Sensors
Abstract The demand for high quality rail services in the twentyfirst century has put an ever increasing demand on all rail operators. In order to meet the expectation of their patrons, the maintenance regime of railway systems has to be tightened up, the track conditions have to be well looked after, the rolling stock must be designed to withstand heavy duty. In short, in an ideal world where resources are unlimited, one needs to implement a very rigorous inspection regime in order to take care of the modem needs of a railway system [1]. If cost were not an issue, the maintenance engineers could inspect the train body by the most up-to-date techniques such as ultra-sound examination, x-ray inspection, magnetic particle inspection, etc. on a regular basis. However it is inconceivable to have such a perfect maintenance regime in any commercial railway. Likewise, it is impossible to have a perfect rolling stock which can weather all the heavy duties experienced in a modem railway. Hence it is essential that some condition monitoring schemes are devised to pick up potential defects which could manifest into safety hazards. This paper introduces an innovative condition monitoring system for track profile and, together with an instrumented car to carry out surveillance of the track, will provide a comprehensive railway condition monitoring system which is free from the usual difficulty of electromagnetic compatibility issues in a typical railway environment [2].
2 Measurements using Optical Sensors A Fibre Bragg Grating (FBG) sensor is an optical device that measures strains by means of detecting changes in the wavelength of light. A FBG sensor can be fabricated by exposing the sensors to ultra-violet light through a face mask as shown in Fig. 3. UV beams
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Phase Mask
Optic Fibre
Fig. 3 Fabrication of Optical Sensors using Ultra-violet lights and masks
The FBG sensor consists of a short length of periodic refractive-index changes inside an optical fibre which is as thin as human hair. A light source is used to pass a band of light spectrum into the sending end of the optical fibre. Without the FBG sensor, the light passes through the optical fibre un-obstructed. When there is a FBG sensor, a narrowband of wavelength of the light spectrum is reflected back to the sending end and these reflected wavelengths are analyzed by an optical interrogator. The light reflected back has a spectrum that characterizes the pitch (e.g. the separation between two periodic marks) of the periodic refractive-index variation. The pitch is changed when the FBG is subjected to strain (i.e. the pitch becomes longer, when the FBG sensor is being extended, and becomes shorter when the FBG sensor is being compressed), resulting in a corresponding change in the reflected wavelength. As the parameter of measurement is the wavelength of light, the process is immune to electromagnetic interference and hence is intrinsically more stable than any electrical monitoring system in an electromagnetically noisy environment which is typical in an electrified railway.
1 Detection System There are many aspects in trains that needs condition monitoring. The paper describes two essential aspects, one on the rails and one on the trains. Both systems to be described monitor the strains using optical sensors. It is well known that the use of conventional strain gauges can be highly corrupted by noise. However, optical sensors are immune to electromagnetic fields. Furthermore, many optical sensors can be fabricated onto one single optical fibre and this is different from conventional sensors which require two independent wires and a pre-amplifier for each sensor [3]. In other words, if one needs to monitor twenty points on the track (Fig. 1), one needs only one single optical fibre linking all twenty sensors. The same argument is applicable to the optical sensors installed on the train body (Fig. 2). For conventional strain gauges one would require forty wires and twenty pre-amplifiers if 20 sensors are installed. Notwithstanding the fact that the optical fibre and the sensors are as thin as human hair
Fig. 4 shows a typical pickup from a sensor installed on the track with the passage of a 12-cars train. It is noted that there are 4 wheels in one car and hence the first 4 peaks on
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investigation revealed that there were roundness problems
the left-hand side correspond to the first car. It can be seen that there are more vibrations in Car 9 (when counting from the left hand side) and such observation guides the engineer to pay attention to the cars. Subsequent
in the wheels of Car 9 and this will be described in details in subsequent sections of this paper.
Seve al t B(.W Sensort w tahric ated onto one single
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Strain Signals of a noisy tirain in Car 9 (counted from left-hand side)
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from being immune from electromagnetic interference, these sensors could be made very small and hence a string of these sensors could be connected together in a string to measure how the strain patterns are varying in the vicinity of cracks or points suspected to be suffering from high strains. Figs. 5 to 7 show the strain Apart
22
measurement of 3 FBG sensors in the vicinity of a weld
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Strain on the metal case which is about 9 - 5 mm) from the welded bracket
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which is suspected to be suffering from high strains in a typical train. All these 3 FBG sensors are connected in series in one single optical fibre and many measurements have indeed been carried out. The length of each sensor in this 3-senor pack is around 4 mm and each sensor is separated from each other by another 5 mm. In other words, the total length of the three sensors is (4+5+4+5+4) mm or 22 mm.
4
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The local vibrations such as those in Cars 4 and 10 (counting from the left) of Fig. 8 have been found to be higher than those of the other cars in the same train.
3 Applications 3.1 Monitoring of Imperfections in Train Wheels
It can be seen from Fig. 9 that the vibration index for most cars are below 2. However the vibration index for Cars 4 and 10 are higher than 4.
With the installation of the sensors on the tracks, a wealth of investigations could be carried out readily. For example, from the strain measurements at the track it was confirmed that there were some noisy trains. It was suspected that these noisy trains might have relatively imperfect wheels. Hence a series of tests were carried out. The first test is to identify a noisy train (a train producing strains as shown similar to the one in Fig. 4) using a FBG sensor installed on the rail track as described in the previous section.
The wheel out-of-roundness of the noisy cars (car No.4 & 10) were measured and the results are shown in Table. 1. Table. I Wheel out-of-roundness measurement for the noisy investigation.
The principle of wheel imperfection detection by FBG strain sensors installed at track is based on the fact that wheel defects such as flange pits, wheel flats and particularly out-of-round wheels which are also known as polygonal wheels, will exert periodic impact force on the track. In this work, it was founded that an imperfect wheel will produce an uneven strain impulse on the track. In contrary, a newly turned wheel will produce a symmetrical strain impulse. In another approach, one attempts to relate the inter-axial vibrations as shown in Fig. 8 with wheel out-of-roundness. In order to compare parameters from two different systems, the inter-axial vibrations were quantified by a vibration index which is obtained arithmetically by considering the train speed, vibration frequency and magnitude as a whole. Fig. 9 shows the vibration indexes obtained from a noisy train. Strain Pattern 0.1
for a
under
cars
Wheel out of roundness (mm) Left Right
Car no.4
Axle 1 2 3 4
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The wheels on car No.10 were turned right after the outof-roundness measurement while the wheels on car no.3 were kept unturned as a control. The wheels out-ofroundness after tuming were between 0.05 to 0.07mm. The strain pattern and vibration indexes of the serviced train are shown in Fig. 11.
Noisv Car
Noise
From Fig. 11 it can be observed that the vibration at car 10 was eliminated after wheel turning while the vibration at car no. 4 persisted. By comparing Fig.9 with Fig. 11, it can be seen that the vibration index of Car No. 4 (unturned wheels) is around 4.4 while the index of Car No. 10 (turned wheels) was greatly reduced from 4.7 to 1.8. This shows that the vibration index, which is deduced from the FBG strain sensor measurement results, is an effective means to distinguish out-of-round wheels from good wheels. no.
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Fig. 8 Strains picked up on the track due to the passage of a noisy Train V1ibatloll IiOCdex
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Fig. 9 Vibration index of the 12
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128
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Fig. 14 Strain picked up on the sole bar with old suspension system
Fig. 11 Vibration index of the train with the wheels car 3 turned
For a typically healthy train the strain measurements picked up and the corresponding vibration index are shown in Fig. 12 and 13, respectively.
Normal Strain Pattern 07~~~~~~~~~~~~~~~~~~~~-
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Fig. 15 Strain picked up on the sole bar with new suspension system
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4 Conclusion
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Fig. 12 Strains picked up on the track due to the passage of a normal Train
powerful condition monitoring system using FBG to monitor the conditions of rail tracks and train borne equipment have been developed and tested on a heavily used mainline railway.
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very sensors
Vibration Index b
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5 Acknowledgement
4
The authors wish to express their grateful to KCRC for supporting the investigations and allowing the authors to publish the work as described in this paper.
2-
6 Reference
:
0~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -I 1 2 -. ;4 Fr 7 8 9 10 11i Ntth Snnti [1] Weston, P.F., Goodman, C.J., Li, P., Goodall, R.M., Fig. 13 Vibration index of a healthy train Ling, C.S., Roberts, C., Track and Vehicle Condition Monitoring During Normal Operation Using 3.2 Monitoring of Strain on Train Borne Equipment Reduced Sensor Sets, HKIE Transactions, Special Issue on Railway Development in the 21' Century, 0
------I
t
5
The strains of the various equipment on another train were measured with i) the old suspension system and ii) a totally new suspension system. The spectral density of the strains measured as given in Figs. 14 and 15.
March, 2006, pp. 47-53. [2] Lee, K.Y., Lee, K.K., Ho, S.L., Exploration of Using FBG Sensor for Axle Counter in Railway Engineering, WSEAS Transactions on Systems, Issue 6, Vol. 3, August, 2004, pp. 2440-2447. [3] Lee, K.K., Ho, S.L., Unconventional Method of Train Detection Using Fibre Optic Sensors, HKIE Transactions, Special Issue on Railway Development in the 21st Century, March, 2006, pp. 16-21.
It can be seen from these two figures that there were improvements after changing the suspension system and hence a very thorough investigation with new components being replaced one at a time was carried out. Very useful conclusions could be drawn from the measurement data although the authors cannot reproduce such results here due to commercial considerations.
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