WO2005003698A1

WO2005003698A1 - Monitoring the performance of a system by measuring a time-variant acoustic signal from the system

Info

Publication number: WO2005003698A1
Application number: PCT/GB2003/002845
Authority: WO
Inventors: Roger Todd
Original assignee: Tekgenuity Limited
Priority date: 2003-07-01
Filing date: 2003-07-01
Publication date: 2005-01-13
Also published as: AU2003304286A1

Abstract

A method of monitoring the performance of a system. The method comprises the steps of measuring an acoustic signal from the system and analysing the signal using chromatic processing techniques so as to obtain values indicative of the system. A corresponding apparatus is disclosed.

Description

MONITORING THE PERFORMANCE OF A SYSTEM BY MEASURING A TIME-V_ARIAN_{T ACOUSTIC} SIGNAL FROM THE SYSTEM

Field of the Invention

5 This invention relates to methods and apparatus for monitoring acoustic signals from systems. Acoustic signals can, for example, be caused by the interaction, between a moving surface and a stationary surface or second moving surface, or by atomic or molecular movement0 within a body.

Background to the Invention

In many applications, it is desirable to monitor wear and5 tear of various component parts of apparatus used in those applications. In particular, it is desirable to monitor degradation of moving parts, which are arranged to move over a stationary part or parts, to determine whether the moving part has developed unacceptable friction-derived 0 damage.

Examples of moving parts which may need monitoring to determine frictional wear and tear include vehicle wheels and tyres which rotate over a stationary surface such as5 roads and rails, bearings, brakes and gears.

Furthermore, it may be desirable to monitor a stationary surface, which undergoes frictional wear and tear from a moving surface or other means. For example, railway 0 tracks may need to be monitored for wear induced by rolling stock or the elements. Monitoring of any of the moving or stationary parts may be performed visually, electronically or the like and especially for vehicles, may form part of an electronic monitoring system for that vehicle.

However, each application is different and each needs a different type of monitoring system to accurately monitor the wear and tear of components. This problem means that for any one application, many different monitoring systems may be needed. For example in an automobile, tyre wear, brake wear and bearings wear may all need to be monitored regularly, and each requires a separate monitoring system utilising different monitoring techniques. For railway applications, multiple monitoring systems may be needed to monitor wheel wear, brake wear and wear of railway tracks. The need for multiple monitoring systems increases the costs in monitoring and may be prone to individual monitoring systems malfunctioning.

Furthermore, the wear and tear on some vehicle components may still be monitored visually or manually, such as tyre wear. This type of monitoring suffers from the disadvantage that the component being monitored may have become dangerously worn before visual or manual inspection is commenced, and therefore the component may endanger the user of the vehicle.

It is therefore an aim of preferred embodiments of the present invention to overcome or mitigate at least one of the disadvantages of the prior art, whether expressly stated herein or not . Summary of the Invention

In a first aspect, the present invention provides a method of monitoring the performance of a system, the method comprising the steps of: measuring an acoustic signal from the system to provide a time-variant representation thereof; and analysing the time-variant signal using chromatic processing techniques so as to obtain values indicative of said system.

Typically, signals with frequency content will be analysed using Fourier analysis techniques. Fourier Transform analysis is complex, and requires a relatively large amount of computing power to perform. Fast Fourier Transform (FFT) is a simpler method that requires less computational power but has the drawback that it is only able to carry out a frequency analysis of a signal, and is thus unable to provide other information that might characterise the signal being analysed.

However it has been realised that by utilising chromatic processing techniques to analyse acoustic signals (in very much the same way as applied to an optical signal) , sufficient information can be obtained so as to characterise the performance of the source of the signal without the need for a computationally expensive Fourier transform.

The chromatic processing technique can comprise evaluating the Gabor transform of the signal. Such a transform can be applied to analyse a signal in the time and frequency domain, so as to determine the values indicative of the performance of the system. The acoustic signals can be caused by the movement of atoms or molecules within a structure. For instance, this could be caused by the stressing or relaxation of the structure .

The system may comprise two or more surfaces in contact, at least one of the surfaces being a moving surface, with the acoustic signal caused by the interaction of the surfaces.

The surfaces may be at a molecular level, with the acoustic signals caused by the interaction of molecular surfaces .

Preferably, one of the surfaces comprises a wheel. The analysed signal can then be utilised so as to determine at least one of the performance of the wheel and the performance of the surface in contact with the wheel .

The method may further comprise the step of determining the performance of the system by comparing the obtained values with a database mapping values to different system performances. Additionally, the method may also comprise the step of providing a warning signal if the values indicate abnormal operation, or alternatively a continuous output indicative of the ongoing operation of the system.

Suitably, the acoustic signal can be filtered in the time- domain. Suitably, the acoustic signal is filtered to a contiguous frequency range. Alternatively, the acoustic signal is filtered to a plurality of discrete frequency ranges . Suitably, the acoustic signal is normalised.

In a second aspect, the present invention provides an apparatus for monitoring the performance of a system, the apparatus comprising: measuring means arranged to measure an acoustic signal from the system to generate a time-variant representation thereof; and analysing means arranged to analyse the time- variant signal using chromatic processing techniques so as to obtain values indicative of the performance of the system.

The system can comprise two or more surfaces in contact. At least one of the surfaces can be a moving surface. The measuring means can be arranged to measure -an acoustic signal caused by the interaction of the surfaces.

The measuring means can be arranged to either pick up sound waves transmitted through the air, or alternatively arranged for connection to one or more of the surfaces so as to pick up at least one of the surface vibrations and the sub-surface vibrations.

The apparatus may further comprise position tracking means arranged for use in determining the location of the apparatus. Such position tracking means may be a direct location determining system such as GPS (Global Positioning System) . Alternatively, the position tracking means may simply be arranged to monitor distance travelled. By either actively or later comparing the distance travelled with a knowledge of the route of the apparatus, the location of the apparatus may easily be determined. Such a position tracking means is particularly useful in analysing surfaces over which vehicles move e.g. roads or rail tracks, as it permits values relating to the surface performance (e.g. the condition of the surface) to be mapped to the corresponding surface location.

The measuring means can comprise an acoustic transducer. The analysing means can comprise sampling means arranged to sample the filter with three filters having non- orthogonal Gaussian responses with respect to time and frequency. Such filters can be utilised in conjunction with Gabor transforms so as to analyse properties of the signal, which correspond to the optical properties of Hue, Lightness and Saturation. These three properties have been determined to be sufficient to characterise the performance of most systems .

Suitably, the apparatus further comprises a filter for filtering the acoustic signal in the time-domain. Suitably, the apparatus comprises a plurality of filters for filtering the acoustic signal to a contiguous frequency range. Alternatively, the apparatus comprises a plurality of filters for filtering the acoustic signal into a plurality of discrete frequency ranges. A filter providing filtering into two frequency ranges is therefore considered to be a plurality of filters.

Suitably, the apparatus further comprises a normalisation unit for normalising the acoustic signal.

In a third aspect, the present invention comprises a vehicle mounting an apparatus as described above. Brief Description of the Drawings

Embodiments of the invention will now be further described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 shows an apparatus in accordance with the first embodiment of the present invention,

Figure 2 shows a first configuration of the sensors utilised in figure 1, in use with a six wheel vehicle,

Figure 3 shows an alternative configuration of the sensors utilised in figure 1, again with a six wheeled vehicle,

Figure 4 shows a second embodiment of the present invention in use with rolling stock,

Figure 5 shows a third embodiment of the present invention being utilised to monitor rails.

Detailed Description of Preferred Embodiments

Figure 1 shows a monitoring system 10 being used to monitor the noise 3 originating from a tyred wheel 2 to travelling over a road surface 1. The wheel 2 is mounted on an axle 4 and underneath a wheel arch 5.

The monitoring system 10 comprises an acoustic measuring device 11 coupled to an analysis unit 12. The measuring device is arranged to detect the time-variant acoustical noise originating from the interaction between the road surface 1 and the tyre 2. The detected acoustical signal is passed to the analysis unit 12, where the time-variant signal is analysed in real time using chromatic processing techniques .

Chromatic processing techniques are well known, and are typically used to characterise an optical signal by describing the signal in terms of values of Hue, Saturation, and Lightness. It is known to apply such chromatic processing techniques to analyse, and hence characterise, non-optical signals. For instance, the article "The Gabor transform basis of chromatic monitoring" by G R Jones et al . , Meas . Sci . Technol . 11 (2000) 1-8, describes how chromatic processing techniques may be applied to analysing, and hence characterising, non-optical signals.

The analysis unit 12 comprises a filtering unit 13, a chromatic processing unit 14, a post processing unit 15, and an alarm annunciation unit 16.

The signal from the measuring device 11 is passed to the filtering unit 13, which incorporates at least one bandpass filter for use in the time-domain. That is the filters restrict the real-time passage of bandwidth to the chromatic processing unit 14. The band-pass filter defines the bandwidth of the signal for analysis, with the bandwidth being selected in dependence on the type of signal/system the sensing system is detecting, and the defects/operational criteria the sensing system is optimised to detect. The actual bandwidth passed can typically be from 0Hz up to an upper value of 100 kHz for audio signals, but can range from 50 kHz to 5 MHz for acoustic emissions generated by stresses in the molecular structure of the object. There may be several contiguous or discrete band-pass filters used. Thus, frequency ranges that are of no interest could be omitted.

The filtered acoustic signal is then passed through an analogue to digital converter (ADC) to generate a time- variant digital representation of the acoustic signal, and then to the chromatic processing unit 14. The ADC conversion rate is typically at least twice the bandwidth, and where applicable anti-aliasing measures are taken. Additionally, the monitoring system may include a normalisation unit 50 for normalising the signal to suppress dominant signals that might otherwise swamp the results. Thus, a threshold may be set for how strong a signal is permitted to be if it is to be passed for analysis .

The chromatic processing unit analyses the signal using chromatic processing techniques to provide outputs that would (in an optical signal) correspond to Hue (H) , Saturation (S) and Lightness (L) . For instance, the signal could be evaluated using the Gabor transform so as to obtain these values.

The output from the chromatic processing unit 14 is then routed to the post-processing unit 15.

The post-processing unit 15 compares the values output from the chromatic processors (i.e. values of H, L, S) with the analysis templates. The templates map the values of H, L and S to different performance criteria, to determine whether or not the source of the acoustic signal is performing correctly.

The sound signature made by a tyre rotating on a road surface will contain information about the state of the tyre and surface against which it is moving. The sound signature alters as the state of the tyre changes e.g. if the tyre slowly deflates, starts to suffer tread deformities or other tyre defects. By analysing the signal by using chromatic processing techniques, characterising values of Hue, Saturation and Lightness are obtained that indicate the performance of the tyre. The correct performance of the tyre corresponds to the normal safe operational envelope as determined by any of experimentation, calculation, industrial/commercial standards and manufacture, or health and safety specifications or recommendations. The post-processing unit 15 analyses the determined values, to detect whether or not the values differ from the values that correspond to the correct performance.

The post-processing unit is arranged to determine the rate of change of the values from the correct performance criteria for each parameter being monitored, and includes algorithms used to determine the level of urgency to be assigned to the parameter change. For instance, this can range from a low-level warning for a slight drop in tyre pressure, to a high-level warning (take immediate action) if the pressure drop is more rapid.

The output of the post-processing unit 15 is passed to the alarm and annunciation unit 16, which acts as the man/- machine interface. The annunciation of any trends in the changes of values of the parameters indicating system performance can be made visually, audibly or simply logged for future reference. The system algorithms will determine the threshold of when a driver needs to be informed of a trend at the time of system configuration.

It will be apparent that the system can be realised in a number of configurations. For instance, whilst the above embodiment has described the apparatus as comprising a separate filter and ADC, it will be appreciated that these can be combined into a single unit and arranged in any order. For instance, the filtering unit 13 can be arranged to first pass the acoustic signal through an ADC, and then to band pass filter the resultant. Such a filtering operation can be performed in hardware or software .

The acoustic measuring device 11 can take the form of a transducer, or indeed any device that can reliably detect the required frequency range and provide the necessary signal levels. Preferably, however, sound signals are converted directly to electronic signals as this is most convenient .

The acoustic measuring device can be located in a number of positions, such as under an axle 4, or within a wheel arch 5. The location for the measuring device 11 will dependent on the desired system performance criteria to be monitored.

Preferably, a separate measuring device 11 is located near each position that is to be monitored. If the axle is run with a pair of tyres, rather than a single tyre, a single sensor can still be used but should be positioned so approximately equal sound levels are received from each tyre. This can be achieved by the use of a hollow axle, so that the acoustic sensor can be positioned between the two tyres, or alternatively the sensor could be positioned in front or behind the tyre pair to gain the best possible monitoring location.

In sensing systems 10 located on vehicles, it is preferable that sound signatures are collected from each wheel or wheel pair. The data can be collected in a number of ways, examples which are shown in figures 2 and 3.

Figure 2 shows an omnibus system that uses a daisy chain cabling system 20 to link acoustic sensors 11 in turn, and that connects to the analysis unit 12 at each end. The detected acoustic signals can be processed by the analysis unit 12 using TDM (Time Division Multiplexing) techniques to identify which tyre 2 is generating the respective sound signature. Alternatively, each sensor 11, can be arranged to communicate individually with the analysis unit 12 using a token ring system. The advantage of the omnibus system is that it requires only a single cable for all sensors to communicate with the analysis unit.

Alternatively, as shown in figure 3 each sensor 11 can be individually connected to the analysis unit 12 via a separate connection 22. This has the disadvantage of requiring more cabling than an omnibus system, but has the advantage of being more robust and less prone to total system failure due to a single break within the connecting cabling. Experimentation has shown that, with the appropriate signal profiles being defined within the templates stored in the post processing unit 15, it is possible to distinguish between a wide range of differing performances within the tyre system, including but not limit to: a drop in tyre pressure; a change in the rolling resistance of the tyre; an abnormality that alters the rolling circumference of the tyre in a linear or non-linear manner; an abnormality that alters the tyre profiles so that eccentric rotation (a wobble) is produced; a change in the normal angular directional rotation of the tyre, other than that due to normal turning, which will cause increased wear of the tyre fabric; a change in the rotational speed of tyre; a foreign object becoming embedded in the tyre and determining if this body poses a threat to the integrity of the tyre casing; a brake binding causing loss of rolling efficiency; and a wheel bearing starting to fail .

It will be appreciated that the sensing system is not limited to just tyres on vehicles, but can be utilised in any situation in which a system (which may include a body or structure) generates an acoustic signal. This includes systems where two surfaces are in contact and at least one of the surfaces is a moving surface. The surfaces can be those at the macro level, for example a wheel/rail interface. Alternatively, the surfaces can be those at an atomic or sub-atomic level where the movement is that of the atoms and molecules in a structure, for example the movement of the molecules in a steel bar exposed to strain causing the generation of acoustic emissions. Examples of such other uses include the monitoring of fixed structures, for integrity and fatigue such as buildings, bridges, pressure vessels, industrial machines and plants, and the monitoring of moving structures such as ships, submarines, road vehicles, air and spacecraft. Other examples include railway rolling stock wheels, brakes and bearings, aircraft wheels, brakes and bearings; static wheels and moving surfaces, where either or both could be motion, and the surfaces over which moving wheels are travelling e.g. for monitoring the condition of road or rail surfaces.

For instance, figure 4 shows a sensing system 10 arranged to monitor the performance of railway rolling stock. The acoustic measuring device 11 is located to detect the sound signature 103 originating from the interaction between the rolling stock wheel 102 and the running rail 101. The measuring device 11 can be placed in front, behind or to the rear of the rolling stock wheel 102, it's position being determined by looking for the point of best signal level and where it is least likely to sustain damage .

The operation of the system shown in figure 4 is very similar to the operation shown in figure 1. As the system is being utilised to monitor rolling stock, it will be configured to monitor different performance criteria. For example, the system could be configured to monitor any of the combination of development of flats on the rim; deterioration of the wheel due to cracking; running out of true; wheel/rail adhesion; wheel rotational speed; increase/decrease in rolling resistance; and wheel locking or skidding. The sensing system 10 can be utilised to monitor the brake 106 and bearing (not shown) as well as the wheel 102. If the braking is carried out on the rolling wheel 102, then a single sensing device 11 could be utilised to monitor simultaneously the wheel, the break and the bearing. Alternatively, particularly if the rolling stock employs inboard braking discs 107, a separate sensing device 11 can be used. In such an application, the algorithms applied to process the signals, as well as the relevant templates used in determining the operation of the various parts of the system, are optimised for brake and bearing monitoring as well as rolling stock wheels.

The running rail (track) 101 on which the rolling stock travels is subjected to heavy stresses and strains. Over a period of time this can induce fatigue-cracking 23 of various types which will ultimately lead to failure of the track. Although hitherto the sensing system 10 has been described as monitoring the performance of the moving surfaces (e.g. wheels 2, 102), it will be appreciated that the present invention can also be used to monitor the static surfaces such as the track 101. Figure 5 shows how the analysis unit 12 can be adapted to perform such running rail monitoring.

As shown in the upper portion of figure 5, the analysis unit 12 in this embodiment incorporates three additional units - a GPS system 117, a data processing unit 118 and a data storage unit 119. The lower portion of figure 5 shows how such a sensing system 10 would be configured on a carriage using an omnibus configuration to connect each of the sensors (a to h) via a single connecting cable 20 to the analysis unit 12, each sensor being mounted above a separate wheel 102. The wheels run along the track 101, with a carriage 21 moving in the direction indicated by the arrow 25.

Each of the carriage 21 wheels 102 will produce a sound signature, the sound signatures of sensing devices e to h being indicated in figure 5. In passing over rail defect 23, the signatures of sensors g and h indicate the defect as a spike. Wheel defects are cyclical in nature, whilst a defect in a track will not be. Thus, track defects are relatively easy to detect, e.g. in the example shown in figure 5 the defect will be detected on the four signatures as each of the wheels pass over the defect in turn.

To determine the location of the defect, a position tracking device such as a GPS system 117 is located within the analysis unit 12. The data processing system 118 will be used to log the defect and its position to the data storage system 119. The recorded track defect information can then be extracted 120 from the data storage unit 119 either on journey completion, or in real time e.g. via a radio link.

Sound signatures from potential track defects and from track joints can be differentiated either by a comparison template of the different sound signatures, and /or via a location map of expected joints and junctions.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings) , and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) , may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment (s) . The invention extend to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings) , or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

CLAIMS :

A method of monitoring the performance of a system, the method comprising the steps of: measuring an acoustic signal from the system to provide a time-variant representation thereof; and analysing the time-variant signal using chromatic processing techniques so as to obtain values indicative of said system.

A method as claimed in claim 1, wherein the chromatic processing technique comprises evaluating the Gabor transform of the signal .

3. A method as claimed in claim 1 or claim 2 , wherein the acoustic signals are caused by the movement of atoms or molecules within a structure.

4. A method as claimed in any one of the above claims, wherein the system comprises two or more surfaces in contact, at least one of the surfaces being a moving surface, with the acoustic signal caused by the interaction of the surfaces.

5. A method as claimed in claim 4, wherein the surfaces are at a molecular level, with the acoustic signals caused by the interaction of molecular surfaces.

6. A method as claimed in claim 4, wherein one of the surfaces comprises a wheel.

7. A method as claimed in claim 6, wherein the analysed signal can then be utilised so as to determine at least one of the performance of the wheel and the performance of the surface in contact with the wheel .

8. A method as claimed in any of the above claims, in which the method further comprises the step of determining the performance of the system by comparing the obtained values with a database mapping values to different system performances.

9. A method as claimed in any one of the above claims, in which the method further comprises the step of providing a warning signal if the values indicate abnormal operation, or alternatively a continuous output indicative of the ongoing operation of the system.

10. A method as claimed in any of the above claims, the method further comprising filtering the acoustic signal in the time-domain.

11. A method as claimed in claim 10, in which the acoustic signal is filtered to a contiguous frequency range.

12. A method as claimed in claim 10, in which the acoustic signal is filtered to a plurality of discrete frequency ranges.

13. A method as claimed in any preceding claim, wherein the acoustic signal is normalised.

14. An apparatus for monitoring the performance of a system, the apparatus comprising: measuring means arranged to measure an acoustic signal from the system to generate a time-variant representation thereof; and analysing means arranged to analyse the time-variant signal using chromatic processing techniques so as to obtain values indicative of the performance of the system.

15. An apparatus as claimed in claim 14, wherein the system comprises two or more surfaces in contact.

16. An apparatus as claimed in claim 14 or claim 15, wherein the measuring means is arranged to either pick up sound waves transmitted through the air, or alternatively is arranged for connection to one or more of the surfaces so as to pick up at least one of the surface vibrations and the sub-surface vibrations.

17. An apparatus as claimed in any one of claims 14 to 16, wherein the apparatus further comprises a position tracking means arranged for use in determining the location of the apparatus.

18. An apparatus as claimed in claim 17, wherein the position tracking means comprises at least one of a direct location determining system such as a Global Positioning System, and a device arranged to monitor distance travelled.

19. An apparatus as claimed in any one of claims 14 to 18, wherein the analysing means comprises sampling means arranged to sample the filter with three filters having non-orthogonal Gaussian responses with respect to time and frequency.

20. An apparatus as claimed in any one of claims 14 to 18, further comprising a filter for filtering the acoustic signal in the time-domain.

21. An apparatus according to claim 20, in which the apparatus comprises a plurality of filters for filtering the acoustic signal to a contiguous frequency range .

22. An apparatus according to claim 20, in which the apparatus comprises a plurality of filters for filtering the acoustic signal into a plurality of discrete frequency ranges.

23. An apparatus according to any one of claims 14 to 22, further comprising a normalisation unit for normalising the acoustic signal.

24. A vehicle mounting an apparatus as described in any one of claims 14 to 23.