Non contact acquisition of sonic emissions of bearings Assoc. Prof.: Kiril M. Alexiev, Petia D. Koprinkova-Hristova; Dr.: Vladislav V. Ivanov, Volodymyr V. Kudriashov, Iurii D. Chyrka

AComIn Technology Transfer Workshop on Advanced Techniques in NonDestructive Testing

Sozopol, June 18-19, 2015

Outline

• The Acoustic Camera overview and resolution enhancement

• Experiment description • Comparison of spectra estimates from single

microphone and from the focalized Acoustic Camera • Obtained spectra estimates for different bearings

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Acoustic Camera Applications: Acoustic Imaging and Signal Analysis

Pictures from WWW 3

The Acoustic Camera

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Software list: a) Acoustic Test Consultant - Type 7761; b) Beamforming - Type 8608; c) FFT Analysis - Type 7770; d) Time Data Recorder - Type 7708.

Manufacturer: Brüel & Kjær (Sound and Vibration Measurement A/S)

• PULSE LabShop Customized Solution Version 17.1.2 • Array Acoustics Post-processing ver.: 17.1.2.308

Frequency range: from 10Hz to 20kHz Wavelength range: from 34.3m to 17.15mm

Criteria: Half power (-3dB)

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Trg. 2 Trg. 1

Resolution Enhancement

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Resolution Enhancement

B&K “Array Acoustics Post-processing” 1 response Capon mod. 2 responses

dB

Center frequency fc =10 kHz. Frequency bandwidth ∆f ≈ 2.3 kHz. fc/∆f ≈23% Range ~0.8 m. Spacing between centers of the speakers ~0.1 m

Before After (Obtained result)

Trg. 1 Trg. 2 Trg.

( ) ( )[ ] ( )[ ] ( )[ ]222SESESESE zkzykyxkxkr −+−+−= ( ) ( ) ( ) ( )C

HSECSESE fXfFfXfQ ∆=∆ 0

( )( ) ( ) ( )C

HSEMCSE

SE fXfFfXfR

∆=∆

−11( ) ( ) ( ) ( )[ ] ( )[ ]ikjtifjiatkutks

N

i

,exp2exp,,1

ϕπ∑=

+=

( ) ( ) ( ) SSE vkrifik πϕ 2, =

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Beamforming based-on modified Capon algorithm

dB dB

Center frequency fc =5 kHz. Frequency bandwidth ∆f =0.5 kHz. fc/∆f =10% Range ~0.75 m; Spacing ~0.14 m

“Delay and Sum” Beamforming Capon mod.

Before After (Obtained result)

Trg. 1 Trg. 2 Trg.

Photo

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Spectra Estimates

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Parameters for SKF bearing SKF ”type” 6205.

Number of rolling elements N 9

Rolling element diameter B, mm 7.938

Pitch diameter P, mm 39.04

Contact angle Θ, deg. 0

Rotational speed F, rpm Unknown. Slightly variable.

Pitch diameter, P

Rolling element diameter, B

SKF old Opened

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Verified with SKF “Bearing Frequencies Calculator”. Bearing SKF ”type” 6205.

↓ Parameters on → Rotational speed F, rpm & Shaft speed frequency, Hz

Min: 1820 & 30.3(3) Max: 1830 & 30.5 Fundamental train frequency FTF, Hz 12.0828 12.1492

Ball pass frequency BSF, Hz 71.5076 71.9005

Ball pass frequency outer race BPFO, Hz 108.7455 109.343

Ball pass frequency inner race BPFI, Hz 164.2546 165.157

Rolling element defect frequency, Hz 143.015 143.801

Bearing Fundamental Frequencies SKF old Opened

The first bearing band

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SKF old Opened

Acquisition time, T = 0.25, [s] Frequency resolution, ∆f = 4, [Hz] Quantity of autospectra averages = 100

Good sample emission is more powerful

Bad sample emission is more powerful

Spectra estimates

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Acquisition time, T = 0.25, [s] Frequency resolution 1, ∆f1 = 4, [Hz] No averaging

Acquisition time is T Frequency resolution 2, ∆f2 = 256, [Hz] Quantity of autospectra averages = 64

Non-stationary signals

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The considered spectra difference is at higher frequency range. Thus, such peaks were not removed, yet.

Spatial Filtering

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An isotropic radiator,a theoretical point source of a waves

An irregular array of transducers

Normalized radiation patterns

0 dB–3 dB

0 dB–3 dB

-Mainlobe-Sidelobes-Grating Lobe(s)

Contrast

Angle

–10 dB

Enhancement of Spectra Difference

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The difference is not getting worse due

to application of the microphone array

Beamwidth ~60o

Beamwidth >~120o

The Generated Acoustic Map 1

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Lower Signal-to-noise ratio

- 55 dB

Center frequency, fС=10, [kHz] Bandwidth ∆f = 1, [kHz]

The Generated Acoustic Map 2

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Higher Signal-to-noise ratio

- 55 dB up grow, PSF

Center frequency, fС=10, [kHz] Bandwidth ∆f = 1, [kHz]

Spectra Estimates

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SKF old Opened

Hereinafter: Acquisition time, T = 0.25, [s] Frequency resolution, ∆f = 4, [Hz] Quantity of autospectra averages = 100

Spectra Estimates

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SKF old Opened

The difference is much lower than in previous Measurements Session due to greasing

Spectra Estimates

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SKF old Opened

At the room, the background varies at low freq.

Spectra Estimates

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2. WBF Good

Two “same” spectra

About 20 dB difference

Spectra Estimates

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3. NSK

Spectra Estimates

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4. KBS

Spectra Estimates

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5. HF

Spectra Estimates

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6. CNR

Spectra Estimates

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7. VMF

Spectra Estimates

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8. SKF

Spectra Estimates

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8. SKF

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Main goal is to find collaboration with industry/business. Project AComIn "Advanced Computing for Innovation“ FP7 Capacity Programme. Host – Institute of Information and Communication Technologies at the Bulgarian Academy of Sciences.

Aco

ustic

Cam

era

Appl

icat

ions

1. Noise pollution Airport noise

Urban/Street noise Instrument noise

2. Noise identification (Find the source of specific noise)

Sound quality analysis Data/music recording Multimedia product analysis

3. Diagnostic approaches Spectral analysis Time-frequency analysis Trend detection in sound intensity signals Noise intensity analysis Shock response analysis etc, including post-processing in third-party software

4. Occupational health Noise exposure Hearing protection Human vibration Noise reduction Factory hall acoustic

5. Military/security applications Noise barrier detectors Noise localization Noise recognition

6. Scientific tool for research in Beamforming Random antenna array development Acoustic signal analysis Acoustic holography Signal processing/filtering etc.

7. Educational Useful for experiments/demonstrations 30

Conclusions

• Frequency resolution of the Acoustic Camera is modified from 1/3 octave to 4 Hz.

• Comparison of the spectra shows opportunity to detect difference to good bearings.

• Non-contact diagnosis is implemented. Future Plan: Automatic detection of defects (using the spectra) will be implemented for priori unknown background noise.

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