GB2356048A - Acoustic on-line condition monitoring of a machine part - Google Patents

Abstract

A method of on-line condition monitoring of a moving machine part is described, comprising the steps of beaming an impulse of energy onto, and/or into and/or across the moving machine part at predetermined time intervals, detecting either or both of the resulting transmitted or reflected energy, and interpreting the state of the part from a study of signals derived from the detected energy. Typically the energy is ultrasound, and the method is especially useful in relation to monitoring the state of gearwheels in gear boxes. Apparatus for performing the method typically comprises at least one transmitter probe for directing bursts of energy at the moving part which probe is mounted on an assembly which allows adjustment in azimuth and pitch of the probe and at least one receiver probe for detecting energy reflected from or transmitted by the said moving part. Typically the probes are immersed in a fluid which also surrounds the moving part. Advantageously, there is provided means for directing fluid at the moving part and the transmitter probe is directed into the stream of fluid, and the stream of fluid serves as a waveguide. Two or more detectors may be provided for receiving different energies from one or more moving parts under investigation such as for example reflected and transmitted energies from one moving part.

Description

2356048 Title: Testing and monitoring systems

Field of invention

The present invention relates to methods and apparatus for assessing the mechanical integrity of machines and machine parts, including machines and machine parts which are actually in-service, and more specifically to the testing of gears in transmission systems such as gearboxes.

Background to the invention

Assessing the state of gears in motion leads to the benefits of "oncondition monitoring" in providing on-line information and reducing unnecessary removals and downtime while equipment is taken out of service for inspection and checking.

Ultrasound is used widely as a non-destructive testing technique for the off-line detection of flaws in materials, and it is an object of the present invention to apply aspects of those techniques to the testing of machines and machine parts when in service.

Summary of the invention

According to one aspect of the present invention on-line condition monitoring may be achieved by beaming an impulse of energy onto, into and across revolving machine parts, such as meshing gear wheels, at predetermined time intervals, detecting the resulting transmitted or reflected energy, and interpreting the state of the parts from a study of signals derived from the returning energy.

Thus the present invention provides a method for monitoring the integrity of gears in motion using ultrasound to map their 2 working quality, by periodic assessment.

In contriving to monitor gear integrity on-line, the present invention proposes to direct bursts of energy at their revolving surfaces from probes carried on an assembly giving movement in azimuth and pitch.

The probes may be immersed in a fluid which also surrounds the gears.

Detection may be by echo from, passage through, or transfer across, surfaces, junctions, and structures.

The presdht invention can detect flaws in revolving gear teeth in at least three ways.

In one method, the contour of each tooth is mapDed by amassing reflections of a beam directed onto its movinc surface.

In a second method the near-surface passage of a beam of energy along the length of each tooth face is logged.

In a third method the quantity of energy transferred across teeth in contact is noted.

Beam-paths may be contrived, either by surrounding the machine part(s) and probe assembly in a fluid, or by injection of fluid, using the fluid stream as a wave-guide.

Readings, interleaved over a number of revolutions, may be compiled and mapped by timing the incidence and coordinate of each transition around the circumference and across the breadth of a rotating part.

Anomalies in surface contour may be detected by overlaying the plots as a topographical picture of the reflected pulses, while details of the efficiency of each passage, either across their 3 near working surfaces or at their meshing may be noted in statistical form.

An iterative process may be employed to interpret the results and deduce mechanical integrity, centering upon comparison. Manual or automatic learning processes may be employed.

According to another aspect of the invention, there is provided a method of assessing the surface and sub-surface integrity of gear-teeth during their normal operation, comprising the following steps:

(1). Ascertain the speed of the gearwheel (2) Det4-rmine angular position (3) Note probe coordinates in pitch and azimuth (4) Set datum period and position (5) Add tooth spacing period (6) Trigger a pulse of ultrasound (7) Trigger time-base (8) Trigger pulse toward rotating surface (9) Reduce noise and "ringing" for example by filtering or thresholding (10) Convert reflected pulses to an electrical signal (11) Convert transmitted pulses to an electrical signal (12) Note time of return (13) Calculate and enter distance with coordinates into matrix (14) Compare with earlier readings (15) Move to next coordinate, and (16) Return to step (i) and repeat.

The method may also comprise the following steps:

(1) Map the working surface contour of each tooth face (2) outline the contact between teeth (3) Probe for sub-surface discontinuity along each tooth-face skin, and (4) Set or do not set an alarm, depending on the results of 4 step (3) Another aspect of the invention lies in a method of data acquisition from a constantly rotating surface, comprising the following steps:

(1) Interface ultrasound in a fluid stream with the moving surface (2) Sweep-interleave recordings at mapped coordinates (3) Engage angular rates to determine period, position and record (4) Revert to tick-over as necessary, and (5)..Apply repetition-logic modelling to determine validity.

Another aspect of the invention lies in a method of measuring involving a rotating source, comprising the following steps:

(1) Determine speed of rotation (2) Derive coordinates (3) Record distance travelled in pitch-echo to working surface (4) Note disruptions between oitch-catch transitions nearsurface (5) Quantify signal transfer through pitch-catch and across mesh (6) Accommodate related dynamic effects, and (7) Reduce "ringing" and noise for example by filtering or thresholding.

Data may be interpreted in accordance with the invention by a method involving the following steps, namely:

(1) Examine voltage versus time throughout each rotation, (2) Convert analogue values to digital format (3) Map changes (4) List events, and (5) Equate check-sums.

S Data may be analysed in accordance with the invention by the following steps, namely:

(1) Collate by short-term comparison (2) Identify changes by pattern recognition (3) Model long-term trends, and (4) overlay archives.

Brief description of the drawings

Figure 1 provides a schematic representation of apparatus comprising the present invention; Figure 2-"outlines the equipment in block diagram form; Figure 3 introduces a cut-away view of the surface probe assembly used to transmit ultrasound in a jet of fluid; Figure 4 is an end-on aspect of the gearwheel presenting a view of the interleaved measurement and recording process; Figure S depicts the timing sequence used to create the interleaving process and outlines the timing algorithm; Figure 6 gives examples of the contour mapping process; Figure 7 lists an example of the continuity matrix; and Figure 8 shows the contact monitoring process.

Detailed description of the illustrated apparatus

In the drawings similar numerals represent similar components in the different views.

6 Keywords:

integrity refers to the judgement of condition. in motion is contingent upon rotation.

working qualit is assessed with three primary investigative tools; one groups surface echoes for each tooth as contours on a map to show shape; the second accounts for the passage of a given signal across teeth under load to assess their quality of contact; and the third checks integrity of each face by monitoring the continuity of a near-surface signal passing along their length.

periodic assessment relates to the assembly and comparison of interleaved readings recorded at co-ordinates during sequential rotations.

Referring to Figure 1, a system embodying the invention comprises a probe (12) which monitors echoes (11) for contour mapping, while a second probe (7) introduces a pitch-catch configuration to observe the contact between meshing teeth using contact beam path (8). Re-orientating the first probe assembly (12) to the position (12a) so as to face the gear side and mount4 -ng another probe opposite at (10), allows the continuity of path (9) along the near surface length of each tooth, to be tested.

Each probe is mounted on a linkage allowing movement in pitch over coarse and fine ranges of 160 and 15 degrees and has a set-screw collar (42) (see Figure 3) to adjust the separation distance between the crystal face and the teeth. A stepper motor (39) is used to nod the probe in pitch through small changes of incidence and as with each probe, the complete part is mounted on an azimuth drive assembly comprising a lead-screw (25) and tracking motor (4) combination, to sweep the surface of each gear. Further, each assembly is fitted with a calibration block (5) opposite the drive motor gearbox. The whole assembly is preferably built to operate in a damp or immersed environment.

7 Other parts making up the system comprise a laser (24) and marker (54) fixed to a primary gear (40) and six industry standard computer boards outlined in the block diagram of Figure 2. The laser provides a precise angular datum and rate signal for timing circuits on one of six boards mounted in a computer. The remaining five include an input-output 32bit counter-timer (49), a motor controller (28) and back-plate (29), a signal conditioner (43) to distribute ultrasound pulses, a signal processor (44) to measure, record and convert the data, and an oscilloscope or video card (36). Adapted software tools (48) control the laser (24), oil switch (32), pressure regulator and filter (34). The probe assembly motors (4) _(39) are controlled by controller (28) through the backplate (25) The method The preferred method of operation is to present a signal comprising several MHz of high voltage, low power, pulses from a signal conditioning card (43), over periods of time and at intervals determined by the counter-timer unit (49) - to the wave sender crystal along wire (64), to create a compression wave. A parallel signal is fed via wires (55) and (60) to size and trigger a spike at the oscilloscope or video card (36), to appear as a trace on the computer display.

After a period, determined by the nature of the interfacing medium, the focused compression wave meets the tooth surface whereupon, depending on its angle of incidence, some energy enters the material while the remainder is dispersed as refracted and reflected energy. With the angle of incidence at, or near normal, a proportion of the compression wave enters the material as a shear wave, while smaller angles with respect to the surface, set-up surface waves. A significant proportion of the reflected energy scatters randomly but some returns to the crystal.

8 In its first investigative mode, the system is activated by switching the probe into a "receive', mode, in which the crystal converts each returning ultrasound wave back to an electrical signal, passing it to the signal processor unit (44) along wire (65). The amplified signal is fed along wire (56) to the oscilloscope card and represented on a time-base, delayed by a period proportional to the transmi ss ion- receive cycle. Some returns during the waiting period are noise - caused by earlier refractions and reflections for example - but the primary return signal is of sufficient size to be detected amongst these random perturbations. Thus knowing the speed of sound in the interfacing material and noting the time taken for the ultrasound to pass from, and return to, the probe between the two point-s on the trace, enables the distance travelled to he deduced, and therefore the separation distance at that instant.

Differentials in the rates of change between the high operational frequencies of ultrasound and that of rotating machinery ensure that, at any instant, a passing tooth can be bombarded with many pulses. By employing fractional millimetre wavelengths, and with separation distances set to give repetition frequencies of the order of 5-KHz, the process is of such a high speed compared with the physical limitations of machinery for example turbo-shaft jet speeds usually only reach 10OHz - many measurements can be made during every rotation. Thus traces in the form shown in Figure 6 outline a broken tooth (14) by a shorter and wider illumination than the others, while the equally sized missing section represents a worn root (15) and a proportional build up indicates side wear (16). This "damage" can therefore be seen by inspecting the computer display.

In its second investigative mode, another probe is configured to intercept the passage of energy along the working surface of each tooth. The method takes up the phenomena that a wave entering a material will continue in a straight line until it meets another barrier and, depending upon the nature of that 9 interface will echo, or transfer and continue penetrating a second material. Thus by moving the contour probe to a side-on position (12a) as a pitcher, and arranging for another to be placed diametrically opposite at (10) to intercept the signal along path (9) as a catcher, creates the means to monitor changes in the sub-surface condition of each tooth. Using the circuits, techniques and equipment described earlier, the method requires the same parallel signal from conditioning unit (43) to be routed along wire (64) to the pitch probe (12a) via the wave sender and wire (69), to be intercepted at the catch probe (12). This is wired back to the wave receiver via (68) and (70) and via (65) to the processor (44). All other functions are the same except that in this mode subsurface integrity is monitored by a pattern of the passage of each transmission.

Similarly in its third investigative mode the system employs a pitchcatch configuration to assess the passage of a wave crossing the interface between working teeth, as shown in Figure 8. With the pitch probe (12) set to create and transmit -a series of surface waves (8) around the perimeter of the primary gear (41) a part of the ultrasound wave bridges the tooth interface (b to 3) and is intercepted by a second probe (10). The acquisition process is completed by adding the number of transmissions during a given transfer to a matrix where in this mode integrity is assessed by the pattern and quantity of waves crossing the interface.

In its "wet", immersed configuration, the lubricating fluid provides a bridging medium between the ultrasound beam and the subject. Special provision may be needed however to ensure constant immersion and prevent aeration.

where such provisions cannot be met the system may include an injector probe, shown in Figure 3. This device forms a jet of fluid (20) as a waveguide to focus the ultrasound beam (6) at selected coordinates on the moving surface of each tooth (13) from crystal (s) (19) lapped into the forward face of the probe assembly described earlier. The stream is created, and air eliminated, by forcing fluid into a cylindrical enclosure (21) having a conical extension from which it emits. The fluid is introduced via port (22) and connector fitting (33). Thus the fluid is forced against the crystal in the larger diameter cylindrical region (21) and ejects from the smaller orifice (21a) opposite. The crystal transmits pulses which are carried by the stream of fluid in a focused pencil beam (6) The larger umbrella receptor crystal (23) allows for minor deviations during interception of the returning signal. Oil is filtered, piped, and switched through the injector from a reservoir at pressures, temperatures and times controlled by local circuits.

Interleaving The acquisition method used in the illustrated system involves the interleaving of readings transmitted from, through, or across each tooth at coordinates determined by reference to the speed of rotation. These readings are taken at the same spot on each tooth, usually during one revolution, after the spot coordinates are moved on, down or across, as depicted in Figure 4. This process sweeps each surface, either to map the contour of the face of every tooth, or as a check of their near-surface integrity, or in a series of continuity passes to note the presence and duration of each contact.

Expanding, the sequence begins with noting the regularity of the rising edge of a signal created by the wheel mounted marker (54) interrupting the laser (24) over several revolutions, to determine the probability of constant speed during the relatively short measurement period. A background assessment of speed change continues throughout, to ensure measurements are taken within specified limits in variation; otherwise the system resets to the beginning of its sequence.

As illustrated in Figure S, mapping coordinates are selected by arranging an appropriate time delay. With each reading made at constant speed the signal from the timer (49) directs an ultrasound wave towards the required spot on each surface, albeit delayed by a proportion of the speed of rotation, the number of teeth, the coordinate, and the tooth to be measured at that instant. Thus the f irst record trl is taken at coordinate pitch 1 and azimuth 1 (1:1), at an instant ( (1/number of teeth) x (1/rpm)) after the datum time. The next follows at the same coordinate but twice the ratio of the angular rate for the second tooth, and so on throughout the revolution. The ratio then adjusts to the next coordinate (2:1) either by adding an incremental time element or by nodding --the pitch motor (39) one "click". When all the readings for the pitch coordinate (38) have been recorded, the probe is repositioned to the next azimuth coordinate (13) by a signal from motor control stepper via wire (57, 58 or 59), and the process is repeated.

Interpretation The preferred solution employs an automated process to convert the analogue signals to digital form, and present the outcome for summation, and for visual assessment via a screen display for each of the three investigative processes.

In the contour mode each tooth profile is outlined by converting the time taken for the ultrasound beam to reflect from every tooth surface into distance readings at each coordinate and mapping each as a gradient in the topographical format given in Figure 6.

The several continuity measurements, recorded at coordinates along the length of each tooth near its working surface, shown as a, b, c and d in Figure 7, are assembled in columns in a matrix showing the outcome of each attempted pass. Short-term assessments are made by checking the sum of each row of 12 successful transitions and compared against archived values, to note trends.

Similarly, the passage of energy at each tooth contact is represented in a statistical form but with the emphasis on the number of pulses passed between the driving and driven teeth. Slotting these figures in rows and columns, in a matrix such as shown in Figure 8, shows the intensity of each contact as a footprint for comparison by signal averaging and check sum.

The analysis software (1) may include intelligent sieving and sorting methods including active filters, morphology and prob.ability, wave-let and maths transform analysis techniques and inspjEction procedures incorporating rain-flow, neuralnetworks and the application of so-called fuzzy logic.

Both long and short-term contrasts are made, comparing normal events with deviations from the standard at build and/or installation, and at acceptable levels in normal operations, where there should be equivalence with their immediate past and.its neighbour. Long-term records are evolved from theory, design and specification, and the quality standard during manufacture, including records attributed to specific items on acceptance, and their type history in service. Other less long-term milestones include, monitoring trends by noting gradual changes in readings from the same area, relating predictable with unexpected patterns of wear, and searches for anomalies in the performance of the overall system. Short-term records differentiate between readings taken in the same vicinity on the same tooth, and are contrasted with similar readings taken on other teeth, both immediately before and over the complete complement.

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Claims (26)

Claims

1. A method of on-line condition monitoring of a moving machine part comprising the steps of beaming an impulse of energy onto, and/or into and/or across the moving machine part at predetermined time intervals, detecting either or both of the resulting transmitted or reflected energy, and interpreting the state of the part from a study of signals derived from the detected energy.

2. A method as claimed in claim I wherein the energy is ultrasound.

3. A method as claimed in claim I or 2 wherein the machine part is a gear wheel.

4. A method as claimed in claim 3 wherein the gear wheel is meshed with another gear wheel and both are revolving.

5. Apparatus for performing the method of any of claims I to 4 comprising at least one transmitter probe for directing bursts of energy at the moving part which probe is mounted on an assembly which allows adjustment in azimuth and pitch of the probe and at least one receiver probe for detecting energy reflected from or transmitted by the said moving part.

6. Apparatus as claimed in claim 5 wherein the probes are immersed in a fluid and the same fluid surrounds the moving part.

7. Apparatus as claimed in claim 5 or 6 wherein the energy is ultrasound and further comprising ultrasound detector means adapted to detect ultrasound echoes from, or ultrasound which has passed through, or transferred across surfaces, junctions and structures associated with the moving part.

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8. A method of detecting a flaw in revolving gear teeth wherein the contour of each tooth is mapped by amassing reflections of a beam of energy directed onto its moving surface.

9. A method of detecting a flaw in revolving gear teeth wherein the nearsurface passage of a beam of energy along the length of each tooth face is logged.

10. A method of detecting a flaw in revolving meshing gear teeth wherein the quantity of energy transferred across teeth in contact is noted.

11. A method as claimed in any of claims I to 4 or 8 to 10 wherein the energy is directed into a stream of fluid which is directed at the part to be monitored and the fluid stream serves as a wave-guide for the energy.

12. Apparatus as claimed in any of claims 5, 6 or 7 further comprising means for directing fluid at the revolving part and the transmitter probe is directed into the stream of fluid, which serves as a waveguide and conveys the energy in the transmission to the port

13. Apparatus as claimed in claim 12 wherein two or more detectors are provided for receiving different energies from the moving part or parts under investigation.

14. Apparatus as claimed in claim 12 wherein a first detector receives energy transmitted through or across the surface of a machine part and a second detector is positioned to receive energy reflected from that part by way of echo.

15. A method of checking the circumference of a revolving machine part as claimed in any of claims I to 4 or 8 to 11, wherein readings, interleaved over a number of revolutions, are compiled and mapped by timing the incidence and coordinates of each energy transition around the said circumference.

16. A method of checking a revolving machine part as claimed in claim 15 wherein the readings are compiled and mapped for each transition across the breadth of a rotating part.

17. A method of detecting flaws in revolving gear teeth comprising the steps of overlaying the plots obtained by the method of claims 15 and/or 16 as a topographical picture of the reflected pulses and noting details of the efficiency of each passage, either across their near working surfaces or at their meshing, in statistical form.

18. A method as claimed in any of claims I to 4, 8 to I I or 15 to 17, wherein an iterative process is employed to interpret the results and deduce mechanical integrity of a part, based upon comparison with predetermined or preloaded data about the part.

19. A method as claimed in claim 18 wherein a manual or automatic learning process is employed.

20. A method of assessing the surface and sub-surface integrity of the teeth of a gear wheel during its normal rotational operation, whilst meshing with another gear wheel comprising the following steps:

(1) Ascertain the speed of the gearwheel to be checked, (2) Determine the angular position of the gearwheel, (3) Note probe coordinates in pitch and azimuth, (4) Set datum period and position, (5) Enter tooth spacing period, (6) Trigger a pulse of ultrasound, (7) Convert transmitted pulses to electrical signals, (8) Trigger a titne-base, (9) Transmitting a pulse toward the rotating gearwheel and detect any reflected signal, 16 (10) Reduce noise and "ringing" in the reflected signal by filtering or thresholding, (11) Convert reflected pulses to electrical signals, (12) Note time of return, (13) Calculate and enter distance with coordinates into a matrix, (14) Compare with earlier readings for the same angular position of gearwheel, (15) Move to next coordinate, and (16) Return to step (1) and repeat for next and subsequent angular positions.

21. The method of claim 20 comprising in addition the following steps:(1) Mapping the working surface contour of each tooth face, (2) Outlining the contact between teeth, (3) Probing for sub-surface discontinuity along each tooth face skin, and (4) Generating an alarm, depending on the results of step (3).

22. A method of data acquisition from a constantly rotating surface, comprising the following steps: (1) Interfacing ultrasound in a fluid stream with the moving surface, (2) Sweep-interleaving recordings at mapped coordinates, (3) Utilising angular rates to determine period and position, and record, (4) Reverting to tick-over as necessary, and (5) Applying repetition logic-modelling to determine validity.

23. A method of measuring surface or subsurface condition of material forming a rotating part, comprising the following steps:(1) Determining speed of rotation, (2) Deriving coordinates, (3) Recording distance travelled in pitch-echo to working surface, (4) Noting disruptions between pitch-catch transitions near-surface, (5) Quantifying signal transfer through pitch- catch and across mesh, (6) Accommodating related dynamic effects, and 17 (7) Reducing "ringing" and noise by filtering and/or thresholding signals derived from reflected or transmitted energy.

24. Interpreting data obtained by a method as claimed in any of claims I to 4, 8 to I I or 15 to 23 by: (1) Examining voltage versus time throughout each rotation, (2) Converting analogue values to digital format, (3) Mapping changes, (4) Listing events, and (5) Equating checksums.

25. A method of analysing data obtained by a method as claimed in any of claims I to 4, 8 to 11 or 15 to 24, involving the steps of:(1) Collating by short term comparison, (2) Identifying changes by pattern recognition, (3) Modelling long-term trends, and (4) Overlaying archives.

26. Apparatus and methods for monitoring the condition of revolving parts substantially as herein described with reference to and as illustrated in the accompanying drawings.