Bearings and Gearbox Diagnostics
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Transcript of Bearings and Gearbox Diagnostics
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Review of Techniques forBearings & Gearbox Diagnostics
Suri Ganeriwala, PhdSpectraQuest, Inc.Richmond, Virginia 23228, [email protected]
IMAC Conference - Feb. 3, 2010Jacksonville FL
Rolling Element BearingFaults
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Rolling Element Bearing Faults
Ball damageInner race defectOuter race defectCage damage
Rolling Element Bearing Faults cos1
2 Dd nf
BPFO r
cos12 D
d nf BPFI r
cos12 D
d f FTF r
2cos1
2
D
d
d
D BSF
ball passing frequency outer race
ball passing frequency inner race
Ball spin frequency
fundamental train frequency
D = pitch dia; d = ball dia; = contact angle;n = no. of balls
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5
1. All balls/rollers are equal in diameter2. There in pure rolling contact between balls, inner race and outer
race.
3. There is no slipping between the shaft and the bearing
4. Outer race is stationary and inner race rotates
In practice there is always some sliding and slippage specially when abearing is under load and after some wear
Approximate formulas:
BPFI = 0.55-0.6 x No. of balls x RPM
BPFO=0.45 x No. of balls x RPM
BSF = 3.5 x RPM
Assumptions Made in Bearing Fault Frequencies Equations
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Bearing Defects
BSF
BPFI
BPFO
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Time Domain Impact Response
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Illustration of Sidebands
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How do we analyze vibration signature of bearing faults?How do we analyze vibration signature of bearing faults?& Issues& Issues
Observe the time waveform and the spectrum to see differencesbetween the good and bad bearing data
Compare the observed frequencies with the calculated frequencies.Are the peaks present ?
Signals are often masked by large amplitude periodic components
Direct Spectral analysis may not give sufficient information
Bearing faults create a series of impacts witch are amplified byresonances: bearing, sensors, structure etc
This creates envelopes of specific faults at high frequencies
Fault signals are not periodic; appear more like random
Some cases can be treated as cyclostationary
New techniques are still being developed
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Techniques Currently used in Industrial ProductsTechniques Currently used in Industrial Products
Time Waveform Analysis
Frequency Spectral Analysis
High Frequency Detection (HFD)
Stress Wave Analysis or Spike Energy
PeakView
Enveloping
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Typical Bearing Outer race Fault Waveform
Typical Bearing Outer race Fault Spectra
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Typical Bearing Outer race Fault Spectra
Bearing FaultBearing Fault
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Right-sideBearing onthe MFS
BearingLoader
BearingLoader
Left-side Bearingon the MFS
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Bearing Outer Race Faults
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Outer Race Fault Signal Example
The harmonics of BPFO show up clearly
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MB ER-10K bearing parameters:Number of rolling element: 8Rolling element diameter: 0.3125 InchesPitch diameter: 1.319 inchContact angle: 0 degree
)cos*1(*2
Pd
Bd Nb BPFO
Bearing Faults for MB ER-10K bearing at the Running Speed of 2,004 RPM
Notation FaultFrequencyMultiplier
FaultFrequency (Hz)
Harmonics of the RunningSpeed
HarmonicFrequencies(Hz)
DeltaFrequencies(Hz)
Resolution to Detectthe Fault Frequencies= Delta Frequencies/4(Hz)
BPFI 4.9480 165.3176 5 167.0570 1.7394 0.4349
BFPO 3.0520 101.9704 3 100.2340 1.7364 0.4341
BSF 1.9920 66.5547 2 66.8230 0.2683 0.0671
1 2 3 4 5 6 7 8
33.411 66.823 100.234 133.646 167.057 200.469 233. 880 267.291
1.674E-5 1.966E-5 1.014E-5 4.219E-5 1.309E-4 7.179E-5 9.206E-5 7.807E-5
RPM Harmonics
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Spectral Lines Resolution, Hz Resolution, RPM
100 50.0000 3,000.0000
200 25.0000 1,500.0000
400 12.5000 750.0000
800 6.2500 375.0000
1,600 3.1250 187.5000
3,200 1.5625 93.7500
6,400 0.7813 46.8750
12,800 0.3906 23.4375
25,600 0.1953 11.7188
51,200 0.0977 5.8594
102,400 0.0488 2.9297
Spectral Resolution for 5,000 Hz Maximum Frequency Setting
Resolution: 6400 FFT Lines using a Hanning Window
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Resolution: 25600 FFT Lines using a Hanning Window
Acceleration signals acquired from an outer race faulted bearingBPFO which is roughly 71 Hz (=1/0.014)
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Acceleration signals acquired from an outer race faulted bearingBPFO which is roughly 71 Hz (=1/0.014)
Envelope Spectra
Envelope spectrum of the faulted bearing (outer race) showing theBPFO demodulated in the frequency band of 2000Hz-4000Hz
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Effect of demodulation band
Envelope spectrum of the faulted bearing (outer race) not showing theBPFO demodulated in 10k-12k Hz band
Inner race Fault Time Waveform
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Inner Race Fault Spectra
Envelope Spectrum
Envelope spectrum of the inner race faulted bearing with a shaftspeed of 20 Hz showing the BPFI and sidebands with a 750 psi load
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Effect of load
Envelope spectrum of the inner race faulted bearing not showingthe BPFI under no load
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New Techniques under ResearchNew Techniques under Research
Adaptive Noise Cancellation (ANC)
Self-adaptive Noise Cancellation (SANC)
Spectral Kurtosis
Discrete Random Separation
Cyclostationary Signal Analysis
Julian
Hilbert-Huang Transform
Entropy
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Adaptive Noise Cancellation (ANC)Removes the random components from the periodic componentsRequires reference input along with primary inputSANC uses the delayed primary signal as reference signalIt uses the fact that bearing signals has a short correlation length
Ref: Prof. Bob Randall
Fault bearing signal with gear signal (b) Gear signal discrete components(c) Bearing components- random components
Spectral KurtosisCalculates Kurtosis for each frequency lineIdentifies the impulsiveness in the dataUses short time Fourier transformDetermines optimum band for demodulation
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Spectral Kurtosis showing the maximum excited frequency bands(fc=8800hz, bw=1600hz) using outer race faulted bearing
(a) Envelope spectrum showing the BPFO(34.4Hz) in freq. range 8000-9400 hz(b) Envelope spectrum showing harmonics of BPFO much clearly in 4000-5000hz band
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Gearbox Diagnostics
Techniques for Gearbox Vibration Analysis
Time Waveform AnalysisSpectral AnalysisOrder AnalysisTime synchronous averagingCepstrum Analysis
Amplitude and Phase DemodulationTransmission Error Analysis
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Gearbox Vibration
Transmission ratio: 1.5:1, (27 and 18 teeth)
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Gearbox Vibration
Missing of tooth
Gearbox Vibration
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Gearbox Vibration
of pinion
sidebands of gear
Baseline data
Spectrum of Fault Level 1 Data
Compared with baseline, more pinion sidebands emerge
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Spectrum of Fault Level 2 Data
Spectrum of Fault Level 3 Data
Compared with baseline, the amplitudes of pinion sidebandsIncrease significantly.
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Spectrum of Fault Level 4 Data
The amplitudes of pinion sidebands continually Increase.
Spectrum of Fault Level 5 Data
The amplitudes of pinion sidebands exceed that of the mesh frequencyFor the missing of a tooth.
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Gear vibration order analysisSpeed variation captured using encoder
Intact gear(small spikes arecaused by gearmeshing)
Fault level 5(impacts causedby missed tooth)
1 revolution
Speed Variation Order Spectrum - baseline
The number of teeth on gearbox output shaft is 27. The 27 th, 54 thand 81th orders have high amplitude. They correspond to themesh frequency and its 2 nd and 3 rd harmonics.
Gear vibration order analysis
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Gear vibration order analysis
Pinion sidebands emerge clearly for the missing of a tooth
Speed Variation Order Spectrum fault level 5
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Worn Gearbox Vertical, RMS Ave.
0.00
20.00
40.00
60.00
80.00
100.00
0.00 100.00 200.00 300.00 400.00 500.00 600.00 700.00 800.00
Frequency, Hz
M i n / s e c ^ 2
Time Synchronous Averaging
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0.00E+00
5.00E+00
1.00E+01
1.50E+01
2.00E+01
2.50E+01
3.00E+01
0.0 200.0 400.0 600.0 800.0 1000.0 1200.0 1400.0 1600.0 1800.0 2000.0
Time Synchronous Averaging
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0.00E+00
5.00E+00
1.00E+011.50E+01
2.00E+01
2.50E+01
3.00E+01
0.0 200.0 400.0 600.0 800.0 1000.0 1200.0 1400.0 1600.0 1800.0 2000.0
0.00E+00
5.00E+01
1.00E+02
1.50E+02
2.00E+02
2.50E+02
3.00E+02
0.00 200.00 400.00 600.00 800.00 1000.00 1200.00 1400.00 1600.00 1800.00 2000.00
Worn Gearbox data comparison, two Types of Averaging
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Worn Gearbox T ime SynchronousAveraging
0.0E+00
2.0E+01
4.0E+01
6.0E+01
8.0E+01
1.0E+02
1.2E+02
0.0 500.0 1000.0 1500.0 2000.0 2500.0 3000.0 3500.0Frequency, Hz
M i n / s e c ^ 2
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Worn Gearbox Syn. Ave. on Gear
0.0
5.0
10.0
15.0
20.0
25.0
30.0
0.0 200.0 400.0 600.0 800.0
Frequency
M i n / s e c ^ 2
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Worn Gearbox data comparison, TSA at Two Shafts
Worn Gearbox Syn. Ave. on Gear
0.0
5.0
10.0
15.0
20.0
25.0
30.0
0.0 200.0 400.0 600.0 800.0
Frequency
M i n / s e c ^ 2
Worn Gearbox Time SynchronousAveraging
0.0E+00
2.0E+01
4.0E+016.0E+01
8.0E+01
1.0E+02
1.2E+02
0 .0 5 00 .0 1 00 0.0 1 50 0.0 20 00 .0 2 50 0.0 3 00 0.0 3 50 0.0Frequency, Hz
M i n / s e c ^ 2
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Speed =
Side bands = 59.37, 23.7, 17.8 Hz
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Baseline Data
Chipped Tooth Data
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Chipped Tooth Data
Chipped Tooth Data
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Missing Tooth Data
Cepstrum AnalysisInverse Fourier transform of logarithmicspectrumUseful for detecting changes in sidebandfamiliesEcho, Transmission path, etcQuefrency, Rahmonic, Gamnitude, Lifter,Saphe
Where X(f) is the Fourier transform of x(t)
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Cepstrum Analysis
Ref: Prof. Bob Randall
Signal Separation with Cepstrum
Use of cepstrum to remove sideband patternsRef: Prof. Bob Randall
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Amplitude & Phase Demodulation
Amplitude and Phase Demodulation of raw acceleration signalsfrom a gearbox with chipped tooth ; note both phase and amplitude demodulation work
Ref: Prof. Bob Randall
Amplitude and Phase Demodulation of raw acceleration signals from aparallel shaft gearbox with chipped tooth (where phase demodulation did not work)
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Transmission Error
Amplitude & Phase Demodulation onTransmission Error Signal
Note that amplitude demodulation workedbut phase demodulation did not work
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Torsional Vibration Signals obtained from TVCwith zero degree deflection
Torsional Vibration Signals obtained from TVCwith 12.5 degree deflection