U.S. patent application number 15/711670 was filed with the patent office on 2018-01-11 for system for monitoring the condition of structural elements.
The applicant listed for this patent is CSIR. Invention is credited to Philip Wayne Loveday.
Application Number | 20180011063 15/711670 |
Document ID | / |
Family ID | 47023034 |
Filed Date | 2018-01-11 |
United States Patent
Application |
20180011063 |
Kind Code |
A1 |
Loveday; Philip Wayne |
January 11, 2018 |
SYSTEM FOR MONITORING THE CONDITION OF STRUCTURAL ELEMENTS
Abstract
A system for monitoring the condition of elongate structural
elements, for example, railway rails, and a method of designing and
manufacturing the system is disclosed. The method includes
identifying and selecting suitable modes of propagation and signal
frequencies that can be expected to travel large distances through
an elongate structural element; designing a transducer that will
excite the selected mode at the selected frequency; numerically
modelling the transducer as attached to the elongate structural
element; validating the transducer design by analysing a harmonic
response of the selected mode of propagation to excitation by the
transducer, and manufacturing one or more transducers for use in
the system.
Inventors: |
Loveday; Philip Wayne;
(Midrand, ZA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CSIR |
Brummeria |
|
ZA |
|
|
Family ID: |
47023034 |
Appl. No.: |
15/711670 |
Filed: |
September 21, 2017 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
14239666 |
Apr 14, 2014 |
9797869 |
|
|
PCT/IB2012/054264 |
Aug 23, 2012 |
|
|
|
15711670 |
|
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01N 29/4472 20130101;
G01N 2291/106 20130101; G06F 30/20 20200101; G01N 2291/048
20130101; G01N 2291/2623 20130101; G01N 29/04 20130101; G01N
2291/102 20130101; G01N 29/043 20130101; G01N 2291/042 20130101;
G01N 29/34 20130101 |
International
Class: |
G01N 29/34 20060101
G01N029/34; G01N 29/44 20060101 G01N029/44; G06F 17/50 20060101
G06F017/50; G01N 29/04 20060101 G01N029/04 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 23, 2011 |
ZA |
2011/06192 |
Claims
1. A system for monitoring and detecting cracks or breaks in rails
of a railway track, the system including a plurality of transducers
defining transmitting and receiving stations of the system,
characterised in that the transducers are located on the inner
sides of the rails.
2. The system of claim 1 in which the plurality of transducers is
in the form of a series of transducers located at predetermined
spaced apart positions, with at least one transducer provided at
each predetermined position, and with ultrasonic waves periodically
being transmittable along the rail from one transducer used as a
transmitter to a spaced apart transducer used as a receiver.
3. The system of claim 2 in which an array of the transducers is
located at each predetermined position.
4. The system of claim 1 in which the plurality of transducers is
in the form of a series of transducers located at predetermined
spaced apart positions, with at least one transducer provided at
each predetermined position, with ultrasonic waves periodically
being transmittable along the rail from one transducer used as a
transmitter, and reflected by a crack in the rail to the same
transducer, which is also used as a receiver.
5. The system of claim 4 in which an array of the transducers is
located at each predetermined position.
6. The system of claim 1, claim 2 or claim 4 in which the
predetermined spaced apart positions are spaced apart by a distance
of about 1 to 3 kilometres.
7. The system of claim 6 in which the predetermined spaced apart
positions are spaced apart by a distance of about 2 kilometres.
8. The system of claim 6 in which an array of the transducers is
located at each predetermined position.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application of patent
application Ser. No. 14/239,666, which is a U.S. national stage
application of International Application No. PCT/IB2012/054264
entitled "A System for Monitoring the Condition of Structural
Elements and a Method of Developing Such a System", which has an
international filing date of Aug. 23, 2012, and which claims
priority to South African Patent Application No. 2011/06192, filed
23 Aug. 2011.
BACKGROUND OF THE INVENTION
Field of the Invention
[0002] This invention relates to a system for monitoring the
condition of elongate structural elements and more particularly but
not exclusively, to a system for monitoring and detecting cracks
and breaks in railway rails. The invention furthermore extends to
the methodology of designing and developing such a system.
Related Art
[0003] There are several methods and systems which have been
proposed for monitoring the integrity of elongate structural
elements, and in particular railway rails. These methods and
systems are aimed at detecting cracks in the rails before they
develop into complete breaks, and also to detect breaks in a
railway network where they have already occurred. If a crack or
break in the rail is not detected beforehand, it could result in
the derailment of the railway vehicle travelling on the track. It
will be appreciated that such derailments cause financial loss and
can also result in injury and loss of life. Also, it should be
noted that although reference is made to railways, these systems
are equally applicable to other applications where lengths of
structural steel are utilised, such as for example mine shafts and
bridges.
[0004] One method of detecting cracks and breaks in the rails of
railway tracks is disclosed in South African patent 99/6936, the
contents of which is incorporated herein by reference. The method
includes the step of providing a number of autonomous acoustic
transmitter units, and a number of acoustic receiver units located
between the transmitter units. The various units are spaced apart
from one another by predetermined distances. The transmitter units
introduce a series of acoustic pulses with specific frequency
composition into the rails and the receiver units detect and
analyse the pulses to monitor any unwanted condition concerning the
rail. This method requires the use of transmitters and the use of
receivers in order to monitor the condition of the rail.
[0005] Development of transducers for this method of detecting and
monitoring cracks and breaks in railway rails is discussed in
"Development of piezoelectric transducers for a railway integrity
monitoring system", Philip W. Loveday, Smart Structures and
Materials 2000: Smart Systems for Bridges, Structures, and
Highways, Proceedings of SPIE Vol. 3988, 2000, Newport Beach, pp.
330-338. The system makes use of piezoelectric transducers which
are mounted (clamped) under the crown of the rail on the outside of
the track. The method of clamping the piezoelectric transducers is
described in PCT patent application WO 2004/098974, the content of
which is incorporated herein by reference.
[0006] The piezoelectric transducers are spaced along the length of
the railway network and they periodically transmit ultrasonic waves
through the rails. The waves propagate through the track from one
transducer towards a downstream transducer which acts as a
receiving station. Typically, the transducers are spaced about 1 km
apart. If the ultrasonic signal is not detected at the receiver
station, the receiver station activates an alarm indicating that
the rail either has a crack or is broken.
[0007] A disadvantage associated with the above system is that the
piezoelectric transducers are attached (clamped) under the crown of
the rail on the outside of the track. The piezoelectric transducers
are large and cannot be attached under the crown on the inside of
the track because they would interfere with the train wheels. The
piezoelectric transducers have to be removed from the rail during
routine track maintenance because a `tamping` machine used to
re-pack the ballast under the sleepers has wheels that engage the
outside of the crown. The removal and re-attachment (which requires
re-tightening of the clamps two weeks after re-attachment) of the
piezoelectric transducers increases the maintenance cost of the
system and results in periods of time when the system is
inoperable.
[0008] In addition, the existing system is not suited for distance
in excess of 1 km, as the transmitted signal is not strong enough,
and because the transducer is also not accurately matched to the
particular structural element to which it will be attached from a
propagation and operating frequency point of view.
[0009] The detection systems described above have generally been
developed using design methodologies that do not optimally
incorporate the use of mathematical modelling techniques in which
the transducer and rail response is mathematically modelled, and in
which the transducer is then designed in an iterative manner. This
resulted in the selection of transducers that are not necessarily
optimized for a particular application, and which may result in the
transducers being larger than required in practice, whilst also not
performing optimally insofar as transmission and receiving of
signals are concerned.
[0010] It is therefore an object of the invention to provide a
system for monitoring and detecting cracks and breaks in railway
rails that will address the disadvantages described above.
[0011] It is also an object of the invention to provide a
piezoelectric transducer for use in the system according to the
present invention.
[0012] It is a further object of the invention to provide a method
for developing a transducer-based failure detection system, which
will at least partially overcome the above disadvantages, and which
will also be a novel and useful alternative to existing design
methodologies.
SUMMARY OF THE INVENTION
[0013] According to a first aspect of the invention there is
provided a method of developing a transducer-based failure
detection system, the method including the steps of: [0014]
identifying modes of propagation and signal frequencies that can be
expected to travel large distances through an elongate structural
element; [0015] selecting a suitable mode of propagation and
frequency of operation; [0016] designing a transducer that is
adapted to excite the selected mode at the selected frequency;
[0017] numerically modelling the transducer as attached to the
elongate structural element; and [0018] analysing a harmonic
response of the selected mode of propagation to excitation by the
transducer in order to validate the transducer design.
[0019] The step of identifying modes of propagation and frequencies
that can be expected to travel large distances through an elongate
structural element preferably comprises the use of a numerical
model of a particular rail profile having predetermined material
properties.
[0020] The selection of a suitable mode of propagation and
frequency of operation preferably entails selecting a mode of
propagation having low attenuation over a large range of
frequencies, and which is relatively insensitive to small changes
in rail profile.
[0021] The method may include the further steps of iteratively
changing dimensions of transducer components in order to achieve an
optimal response of the selected mode of propagation at the
frequency of operation, and computing a predicted displacement time
response of the rail to an electrical excitation of the
transducer.
[0022] The method may further include a verification phase
including the steps of: [0023] manufacturing a prototype in
accordance with the modelled transducer; [0024] measuring free
electrical transmittance of the transducer, and comparing the
measured free electrical transmittance with transmittance predicted
by the model described above.
[0025] The verification phase may also include the steps of: [0026]
attaching the transducer to a predetermined length of the
structural element; [0027] measuring a displacement response on a
surface of the structural element; and [0028] comparing the
measured response to the predicted displacement time response.
[0029] The verification phase may still further include the steps
of performing in-use field measurements in order to confirm
excitation of the selected mode, as well as propagation with low
attenuation.
[0030] According to a second aspect of the invention there is
provided a system for monitoring and detecting cracks or breaks in
rails of a railway track, the system including a plurality of
transducers defining transmitting and receiving stations of the
system, characterised in that the transducers are preferably
located on the inner sides of the rails.
[0031] There is provided for the plurality of transducers to be in
the form of a series of single transducers located at predetermined
spaced apart positions, with ultrasonic waves periodically being
transmitted along the rail from one transducer used as a
transmitter to a next transducer used as a receiver.
[0032] There is also provided for the plurality of transducers to
be in the form of a series of single transducers spaced apart at
predetermined intervals, with ultrasonic waves periodically being
transmitted along the rail from one transducer used as a
transmitter, and reflected by a crack in the rail to the same
transducer, which is also used as a receiver.
[0033] There is further provided for a plurality of transducers to
be located at each predetermined position so as to define an array
of transducers. A number of arrays may be provided, with the arrays
of transducers spaced apart at predetermined intervals.
[0034] In one embodiment the transducers are permanently attached
to the rails on the inner sides of the rails.
[0035] Preferably, the rails include a web and a crown, and there
is provided for the transducers to be attached underneath the
crown, or alternatively to the web of the rails.
[0036] Advantageously, the transducers are of a geometrical size,
shape and configuration enabling the attachment thereof to the
rails without interfering with a wheel of a railway vehicle
travelling on the rails.
[0037] In one embodiment the system is configured such that an
upstream transducer transmits an ultrasonic wave along the rail
which is received by a downstream transducer if there are no cracks
or breaks in the rail. The system is furthermore configured such
that if the downstream transducer does not receive the ultrasonic
wave transmitted by the upstream transducer, an alarm is triggered,
warning of the possible presence of a crack or break in the
rail.
[0038] In another embodiment the system is configured such that a
transducer transmits and ultrasonic wave along the rail, and the
same transducer receives the ultrasonic wave if it is reflected by
a crack in the rail. The system is furthermore configured such that
if the transducer receives the reflected ultrasonic wave, an alarm
is triggered, warning of the possible presence of a crack in the
rail.
[0039] In a still further embodiment the system comprises both the
functionalities described above.
[0040] In one embodiment, the transducers are spaced apart by
distances of about 1 to 3 kilometres. Preferably, the transducers
are spaced apart by distances of about 2 kilometres.
[0041] Preferably, the transducer is a piezoelectric
transducer.
[0042] According to another aspect of the invention there is
provided a transducer suitable for use in a system for monitoring
and detecting cracks or breaks in rails of a railway track, the
system including a plurality of transducers defining transmitting
and receiving stations of the system, characterised in that the
transducers are located on the inner sides of the rails.
BRIEF DESCRIPTION OF THE DRAWINGS
[0043] A preferred embodiment of the invention is described by way
of a non-limiting example, and with reference to the accompanying
drawing in which:
[0044] FIG. 1 shows a system in accordance with one embodiment of
the present invention, the system including two piezoelectric
transducers which are attached to the rails of the railway track,
for monitoring and detecting cracks or breaks in the rails;
[0045] FIG. 2 shows the output of an initial modelling process used
to select an appropriate mode of propagation and operating
frequency for a particular rail profile; and
[0046] FIG. 3 shows the experimental comparison between the
performance of a prior art system and the system in accordance with
the invention.
EXAMPLE OF DESIGN METHODOLOGY
[0047] The methodology and development procedure used to develop a
transducer-based failure detection system in accordance with the
invention is described with reference to FIG. 2. The method is a
computer implemented method.
1. Analysis of Dispersion of Rail Profile on Damped Support.
[0048] This step involved developing a numerical (semi-analytical
finite element method) model of the rail profile that also
incorporated the material properties of the rail. The development
of semi-analytical finite element models is a methodology known in
the art, but which has not heretofore been applied in this
particular application. The model was analysed to determine which
modes of propagation and frequencies could be expected to travel
large distances. Some modes of propagation and frequencies that
were expected to travel with low attenuation are indicated by the
arrows in FIG. 2. The size of the dots represents the expected
propagation performance. The dots form curves describing different
modes of propagation. The arrows indicate three modes that could be
suitable and it was accordingly decided to use a signal with a
frequency centred at the arrow location.
2. Selection of Appropriate Mode of Propagation and Frequency.
[0049] Based on the results from step 1 a mode of propagation and
frequency of operation were selected. The selected mode had low
attenuation over a reasonably large range of frequencies so that it
could be expected to work over a range of temperatures. This
analysis is a qualitative procedure in which modes and frequencies
with the lowest relative attenuation were considered. The analysis
did not attempt to quantify the actual attenuation. Any person
skilled in the art will be able to understand and correctly apply
this qualitative approach. In essence, if the system is required to
detect a particular type of crack the selected mode of propagation
should contain energy in the region where the cracks occur. The
mode of propagation and range of frequencies was chosen to be
relatively insensitive to changes in the rail geometry due to for
example rail profile grinding or changes in the axial load in the
rail. In this particular example, a mode with wavenumber of 82
rad/m at 35 kHz was selected, and additional analyses were
performed to ensure that the selected point was insensitive to rail
grinding, temperature changes and axial load.
3. Conceptual Design of Transducer Configuration.
[0050] A transducer configuration suitable for permanent attachment
to a rail was subsequently conceptualized. In this example, a
sandwich-type transducer suitable for being attached under a crown
of the rail was designed. The transducer design was not
fundamentally different in structure and configuration to existing
transducer designs, but was expected to be better matched with the
system as a whole due to the integrated design methodology.
4. Numerical Modelling of Transducer Configuration Attached to Rail
and Sizing to Achieve Large Response at Required Frequency.
[0051] A numerical model (3-D finite element method) of the
piezoelectric transducer was prepared, and was coupled to the
numerical model (semi-analytical finite element method) of the
rail. The harmonic response of the selected mode to electrical
excitation of the transducer was subsequently analysed. The
dimensions of the transducer components were then iteratively
changed in order to achieve an optimal response of the selected
mode at the operating frequency. This methodology was previously
developed by the inventor, and is described in more detail in
"Simulation of Piezoelectric Excitation of Guided Waves Using
Waveguide Finite Elements", Loveday P W, IEEE Transactions on
Ultrasonics, Ferroelectrics, and Frequency control; vol. 54 no. 10;
October 2007, the contents of which is incorporated herein by
reference. Finally, the predicted displacement time response of the
rail due to tone-burst electrical excitation of the transducer was
determined for use in a later verification phase. This methodology
was also previously developed by the inventor, and is described in
more detail in "Analysis of Piezoelectric Ultrasonic Transducers
Attached to Waveguides Using Waveguide Finite Elements", Loveday P
W, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency
control; vol. 55 no. 9; September 2008, the contents of which is
incorporated herein by reference.
5. Transducer Prototype Manufacture and Measurement in Lab.
[0052] Based on the above modelling, a number of prototype
transducers were manufactured. The free electrical admittance of
each transducer was measured and compared with modelled predictions
to verify correct manufacture. A transducer was subsequently
attached to a short rail length in a lab environment and electrical
tone-burst excitation was applied thereto. The displacement
response on the rail surface at a distance of 1 m or more was
measured using a laser vibrometer. The measured results were then
compared to the predicted displacement time response from step
4.
6. Field Measurements to Confirm Transducer Performance and
Propagation Mode in Rail.
[0053] The transducer was subsequently attached to an actual rail
in the field, and was driven electrically. Scanning laser
vibrometer measurements were performed on the rail surface at
different distances from the transducer (e.g. 5 m, 300 m, 500 m).
Modes present in the measured data were extracted to confirm that
the selected mode was being excited and that it does indeed
propagate with low attenuation. Long-range transmit-receive
measurements were performed with the new transducers and compared
to the same measurements performed with the prior art
transducers.
7. Industrialization of Transducer.
[0054] Subsequent to the transducer design process described above,
the transducer was industrialised, which process included the
preparation of manufacturing data packs and qualification and
acceptance test procedures.
[0055] The above process yielded an optimised transducer design,
which meets the required design criteria, whilst also being of a
relatively small size compared to existing transducers used in
similar failure detection applications.
[0056] The design methodology can furthermore be used in the
optimised design of transducers that are application and profile
specific, and will therefore result in more accurate design of
transducers for use in failure-detection systems.
DESCRIPTION OF AN EMBODIMENT OF THE SYSTEM
[0057] The relative small size of the transducer designed using the
above design methodology enables the use of a new configuration,
which is now generically described in more detail with reference to
FIG. 1.
[0058] Typically, railway tracks include two parallel rails 11 that
are mounted on sleepers 12. The rails 11 typically have a profile
including a base 13 which rests on the sleepers 12, a web 14
extending upwardly from the base 13, and a crown 15 extending
transversely from the web 14, on which the wheels 16 of a railway
vehicle travel. It will however be appreciated that the system of
the present invention, with modifications, can be used on any rail
profile. It will be appreciated that the described embodiment
relates to one particular use in a railway application, but that
the system can likewise be utilised in any application involving
lengths of structural steel, for example bridges and mine
shafts.
[0059] In accordance with the present invention, the system 10
includes transducers 17 for detecting cracks and breaks in the
rails. The transducers used in the present system are piezoelectric
transducers 17. The piezoelectric transducers 17 can be permanently
attached underneath the crown 15 of the rails, or attached to the
web 14 of the rails 11. The piezoelectric transducers 17 are of
such a geometrical size, shape and configuration that they can be
attached to the rails 11 without interfering with the wheels 16 of
the railway vehicle utilising the rails 11. In the preferred
embodiment of the invention, these piezoelectric transducers 17 are
located on the rails 11 on the inner sides of the rails 11.
[0060] The piezoelectric transducers 17 transmit ultrasonic waves
which travel along the rails 11, and also operate as receivers for
receiving the ultrasonic waves transmitted along the rails 11.
These piezoelectric transducers 17 periodically transmit ultrasonic
waves along the rails 11 to monitor the condition of the rails 11
i.e. to detect cracks and breaks in the rails 11.
[0061] The piezoelectric transducers 17 are spaced apart from one
another at predetermined distances along the rails 11. Typically,
the piezoelectric transducers 17 are spaced apart from one another
by distances of about 1 to 3 kilometres.
[0062] The system 10 is configured such that a transducer 17
located upstream on the rail 11 transmits a signal in the form of
an ultrasonic wave along the rail 11, which is received by a
transducer 17 located downstream of the upstream transducer 17. If
the ultrasonic wave transmitted by the upstream transducer 17 is
received by the downstream transducer 17, the system 10 determines
that there are no cracks or breaks in the rail 11. However, if the
upstream transducer 17 transmits an ultrasonic wave which does not
reach the downstream transducer 17, the system 10 determines that
there is a possibility that there is a crack or break in the rail
11.
[0063] In the event that the transducer 17 located downstream does
not receive the ultrasonic wave transmitted by the upstream
transducer 17, the system 10 is configured to generate a signal
indicating the possible presence of a crack or break in the rail
11. The signal triggers an alarm warning of the possible presence
of the crack or break in the rail 11. The alarm is transmitted to a
base station or the railway vehicle utilising the railway
track.
[0064] In the above example the system is utilised as a signal
transmission system. However, in another embodiment (not shown) the
same transducers can also be used in a pulse-echo configuration
where the same transducer transmits and receives a signal. The
signal is transmitted by the transducer, and if there is a crack in
the rail the signal will be reflected back to the same transducer,
which will then also act as the receiver. The transducers developed
using the design methodology described above will also be
particularly suitable for this type of pulse-echo monitoring system
due to the enhanced signal strength.
[0065] Irrespective of the system configuration (pulse-echo or
transmission), an array of transducers (for example 4) can be
provided at each predetermined location to improve the performance
of the system because the additional transducers allow better
control of the modes to be excited and transmission in one
direction along the rail and receiving from one direction.
[0066] It will be appreciated that a combination of the
transmission and pulse-echo systems would be an optimal solution.
This is now possible due to the new design methodology resulting in
transducers that are much better matched to the operating
conditions, thus resulting in stronger signal strengths whilst also
significantly reducing the size of the transducers used. In the
past, larger transducers with robust designs were used to propagate
the waves through the rails. This was due in part to a lack of
detailed modelling of the system, and over above the physical sizes
of the transducers, the design methodology used did not allow for
optimal signal strength and propagation of such signal through the
rails. Now, as a result of the methodology described above, the
system has been optimised and one can more accurately predict the
results of the wave propagation. Surprisingly, as a result of the
mathematical modelling and experimentation it has been found that
the transducers can be smaller than originally thought, and that
the smaller transducers perform better than the older, larger and
robust transducers. As a result of the smaller geometrical size,
shape and configuration of the transducers, the system is optimised
and has improved functionality, and in particular addresses the
disadvantages mentioned above.
[0067] A comparison between the performance of a prior art system
and the new system was performed on a particular length of railway
track. It was concluded that the transmit performance and receive
performance of the new transducers were both 20 dB improved over
the prior art transducers. The above is graphically illustrated in
FIG. 3. In FIG. 3, the two bars on the left hand side of the graph
represents the performance of a prior art system secured to two
adjacent rails of a railway. The transmission voltage was 1300 Vp.
The two bars in the middle represent the results from a combined
system where the transmitters of the olds system were used, whereas
the receivers were transducers designed in accordance with the new
design methodology. The transmission voltage was again 1300 Vp. The
two bars on the right hand side represent the results of the new
system--i.e. both the transmitting and receiving transducer were
designed using the new design methodology. In this case the
transmission voltage was however 280 Vp. It will be noted that a 40
dB improvement was observed.
[0068] As a result of this 40 dB transmit-receive performance, it
was found that the while the prior art system could only operate at
900 m spacing, on this particular rail section, the new transducers
enabled operation at 2000 m spacing.
[0069] The system of the present invention addresses the problems
discussed above. Firstly, the need to remove the piezoelectric
transducers during routine track maintenance and the need to
re-attach piezoelectric transducers after the track maintenance is
eliminated. Advantageously, the piezoelectric transducers of the
present invention are attached under the crown, or attached to the
web of the rail on the inner sides of the rails, and thus there is
no need to remove them during routine track maintenance. Moreover,
the need to re-tighten the clamps after two weeks of re-attachment,
according to the previous system, is eliminated. Secondly, the
system performs much better than the prior art system, and can
successfully be implemented for operational distances of 2000 m, on
poor condition rail, where only 900 m was previously possible. This
is a direct result of the new design methodology that results in
larger signal transmission and improved receive sensitivity.
[0070] It will be appreciated that the above is only one embodiment
of the invention and that there may be many variations without
departing from the spirit and/or the scope of the invention.
* * * * *