Learn how dynamic torsional motion found in rotating bodies can be measured using non-contact angular velocity and displacement sensors. Controlling torsional vibrations is critical to designing reliable vehicles, electric power generators and aircraft propulsion systems. Rotational vibration data, used in the early stages of product development, has enabled design and test engineers to reduce noise, vibration felt by the passenger/operator, and to substantially increase durability. Classic examples of products with dynamic torsional motion are: drive shafts, universal joints, CV joints, electric motors, combustion engines, turbines, pumps, gearboxes / transfer cases. Discover how vibrometers can be used to measure the vibration at fixed points and scanned to characterize the entire surface even when the structure is rotating. Our experts in the field of vibrometry will be on hand to answer any questions you have about your current and future measurement needs and requirements.

1. Dynamics of Rotating Structures Revealed
Using Non-Contact Laser Vibrometers
8/24/2012

2. Presentation Outline
Rotationalvibrations
 Technology behind rotational vibrometer
 Why use lasers?
 Application examples
Derotation
 Derotator
 Description
 Derotated measurements
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3. Vibration in Rotating Objects
Vibrations in horizontal, vertical and axial planes
are easy to measure with a single point sensor
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4. Vibration in Rotating Objects
As shafts transmit power they create
and are subjected to torsional vibrations
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5. Goal
– Find critical resonances
– Map operational deflection shapes
– Verify finite element simulations
Under real operational conditions
Without altering the data!
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6. The Contact Approach: Encoders
Disadvantage :
– requires mounting
on shaft end
– instrumentation
time
– Location is fixed
– Changes moment
of inertia
pulley adaptor encoder
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7. Vibration in Rotating Objects
Rotational pulses are due to changes in angular
velocity, and must be measured with a rotational
vibrometer.
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8. RLV-5500 Rotational Vibrometer
Consists of
– Optical Sensor Head
(RLV-500)
Compact
Contains two Laser Doppler Interferometers
IP67 protection
– Demodulation Electronics
(RLV-5000)
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9. Rotational Vibrometer
Dual Beam Sensor Head
Integrated meter shows centerline balance
and light return signal strength
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10. Aligning Lasers with Shaft
Balance
Indicator:
Symmetric Asymmetric One Sided
The measurement result is independent of the alignment, however,
asymmetry reduces the rpm measurement range.
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11. Rotational Vibrometer
The shape of the object is irrelevant,
and the measurement is insensitive to any lateral vibrations.
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12. Rotational Vibrometer
f DA = 2V A
λ
Doppler Frequency Beam A
V A = ω R A cos α
f DB = 2VB
λ
Doppler Frequency Beam B
V B = ω R B cos β
d = RA cos(α) + RB cos(β)
f D = 2d ω fDλ
f D = f DA + f DB => ω =
λ 2d
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13. Rotational Vibrometer
fDλ
ω =
2d
From the equation you can see that the rotational velocity ω
is only dependant on:
- λ (laser wavelength)
- f D (measured)
- d (beam separation)
The radius, lateral position, out-of-plane and in-plane shaft vibrations
are automatically cancelled out of the equation therefore:
 The measurement is insensitive to any lateral vibrations in x, y or z
 The measurement is insensitive to shape of object
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14. Signal Processing
Angular Velocity
Angular Displacement
RPM
DC and AC components are separated from one another
Complete separate decoding for RPM and dynamic component
Very small angular vibrations can be detected even at high RPM
Displacement is integrated velocity signal
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15. Advantages
• No special fixtures or prepared surfaces
• Shaft doesn’t have to be machined or even round
• Has a dual interferometer = better sensitivity
• Displays RPM without linear speed or radius info
• Switch turns rotational vibrometer into a single point
vibrometer
• Contains a Bragg cell allowing measurement of
positive and negative rotations as well as vibrations
around zero RPM
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16. Sample Applications
Measurement of Rotational Vibrations on:
– Crank Shafts
– Drive Shafts
– Clutches
– CV / Universal Joints
– Optimization of Tuned Mass Damper
– Paper and Printing webs
Ramp Up – Ramp Down Characterizations:
– Crank Shafts
– Electric Motors
– Coupled Machine Components
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17. Belt Pulley of Crankshaft
Single Point Vibrometer:
Axial Vibrations
Rotational Vibrometer: Rotational Vibrations
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18. Crankshaft Results
2 4 6 8
Engine Running Speed
Frequency Spectrum
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19. Crankshaft Results
Order Spectrum of the Rotational Vibrations
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20. Drive Shaft Applications
Drive Shaft Torsional Response
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21. Drive Shaft (Order Analysis) Applications
Constant Velocity Joint
Universal Joint Torsions
Drive Shaft Torsional Response
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22. Drive Train Testing
Measure events
on high-dynamic dynamometers
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23. Drive Train Testing
Dual Mass Flywheel
Two flywheel masses that are linked by elastic springs
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24. Drive Train Testing
Dual Mass Flywheel Results
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25. Supercharger Order Analysis
If orders excited with too high of an amplitude, failures can occur
Very small hub requires non-contact method
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26. Application: Pump Shaft
Torsional vibration limit related to pump failure
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27. Application: RPM Ramp Test on Clutch
Dyno Absorber
Drive
1/RPM
signal Data
RLV-500 Acquisition
∆ϖ
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28. Drivability Motor Cycle
Tuning torsional
vibration dampers
– test crank shaft
vibration under
driving conditions
measurement
with crank shaft
adapter
Source: InFocus 2008/2
courtesy BMW Group
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29. Performing Linear Measurements
With two beams any
translational movement is
canceled out in the signal
When terminating one beam
with a mirror, linear
movements can be detected
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30. Performing Linear Measurements
RLV-500
In the “II” position two beams are emitted and the unit is in rotational
mode.
In the “I” position one beam is emitted and the unit is in single point
mode.
In the “0” position both beams are shut off
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31. Accessories
90 degree deflection
Air Wipe
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32. Measurement Specifications (7.5 mm beam)
RPM Measurement:
– Range: from -8,000 to +20,000 rpm
– Analog Output: -4V …+10V
– Error: <0.3%
Angular Velocity Measurement
– Range: from << 10°/s/V up to 6,000°/s/V
– Frequency Range: 0.5Hz to 10kHz
– High pass and low pass filters, order and variable band pass filters
Angular Displacement Measurement
– Measurement Range: 0.01°/V, 0.1°/V, 1°/V
– Analog Output: + 10V
– Frequency: 1 Hz up to 10 kHz
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33. Measurement Specifications (24 mm beam)
RPM Measurement:
– Range: from -2,500 to +6,500 rpm
– Analog Output: -2.5V …+6.5V
– Error: <0.3%
Angular Velocity Measurement
– Range: from << 10°/s/V up to 12,000°/s/V
– Frequency Range: 0.5Hz to 10kHz
– High pass and low pass filters, order and variable band pass filters
Angular Displacement Measurement
– Measurement Range: 0.01°/V, 0.1°/V, 1°/V
– Analog Output: + 10V
– Frequency: 1 Hz up to 10 kHz
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34. Features
Bandwidth
– (0) 0.5 Hz – 10 kHz
– 30th order at max. speed
Resolution
– 0.01 °/s = 0.00017 rad/s
– sufficient for
• combustion engines and gears
• gas turbines (special mode for
constant speed)
• pumps
• printers
– limitation
• steam turbines require 100 x
resolution
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35. Rotating the RLV Sensor Head
If we reduce the beam separation either side of the rotational axis from
d to d‘, we gain RPM range:
d‘=d * cos Υ
d d'
Rotating the sensor head and reducing the beam separation (d‘)
allows us to not only measure higher rpm‘s but also on smaller
shafts.
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36. Scanning Vibrometer Principle
Example: piezo motor
MP1 MP2 MP3 ...
sequential measurement at all points.
video image object meas. points in video image Excitation for all points
spectrum MPn
phase reference
grid after measurement
deflection shape @ 36kHz
spectrum MPn+a
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37. Drive Train Vibrations
scanning at fixed rpm along shaft
– bending modes are visible
20 Hz 262 Hz
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38. Measurements on rotating parts
Axial measurement on tire
Deflection shape of rotating tire
at 50 mph
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39. Measurements on rotating parts
Radial measurement on tire
Deflection shape of rotating tire at 16 mph
– Scan area limited
by speed on
circumference
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40. Decoder saturation
Radial measurements
Tangent. velocity
r sensor
vtangent = ωr
Radial velocity
+v
0
vtangential t
-v Time-signal
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41. Measuring Rotating Structures –
The Goals:
Measure under real operating conditions
Track deflection shapes rotating with
structure to avoid smearing of data
Avoid the drawbacks of telemetry and/or slip
rings
And…..
Can we achieve all of this while enjoying the
benefits of laser vibrometry?
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42. Vacuum Pump Counterweight
• Failing during operation
• Strain not predicted
• Vibrometer revealed
• 9th order of rotation
excites bending @
~3875 rpm
• Deflection shape
• FE model updated
• Part redesigned
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43. PSV-A-440 Optical Derotator
• Scanning Laser
Vibrometer
– ODS
• Single Point Laser
– Phase reference
• Object speed
– Max. 24,000 rpm
• Acceleration
– Max. 700 rpm/s
• For Order Analysis
• Scan angle
– Max. +/- 4°
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44. Reference LDV Adjustable
(OFV-505, IVS, PDV) mirror for
reference LDV
positioning
Derotator unit
PSV Scan
head
Adjustable base (for
Co-axial unit for alignment of rotating
reference LDV axis)
Derotator Controller for motorized
controller telescopic drive
Vertical telescopic
drive
Base frame
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45. Shift of Resonances During Run-up
• Curved plot of
Eigen resonances
– Stiffening of
RPM
material
– Centrifugal forces
– Excited by orders
Frequency
– Important for
composites and
plastics
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46. Run-up and shift of resonances
actual
resonance at
order
calculated
resonance
eigenfrequency at
standstill
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47. Bladed Disk: 10900 rpm
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48. Bladed Disk: 10900 rpm
725 Hz 800 Hz
845 Hz 895 Hz
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49. Applications
Electronic industry
– Noise reduction in cooling systems for
consumer products, trouble shooting
Aerospace
– Durability and FE update on blisk and fans
Automobil
– Cooling fans
– Tires
– Turbo Chargers (@ reduced rpm levels)
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50. Benefits of Vibrometry with Optical
Derotation
• Whole field measured…..stress analysis, modal
analysis, FEM validation
• Acquire reliable FEM validation data under real
operating conditions
• Obtain operating deflection shapes rotating with
structure
• No added mass, change in flow dynamics
• No potentially noisy telemetry or slip rings
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51. Conclusion
Optical vibration measurement
– reduces limitations
– avoids mass loading and added moment of
inertia
– allows assessment of resonances of
• shafts (torsional and bending)
• axial measurements of rotation objects
– fans, tires ..
– Optical Derotation delivers
• order analysis
• operational deflection shapes
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52. Engineering Services and Rental Program
Advanced non-contact vibration and surface metrology measurements available for
every budget
 Measurements using Polytec’s latest, non-contact measurement technology
 Skilled and experienced applications engineers to operate the measurement
system to its fullest potential
 Convenience of testing at the customer’s facility or in a Polytec lab
 Short-notice, critical measurements
 Scheduled, occasional measurements
 Build justification prior to purchase
 Save cost by renting instead of buying
 Budget flexibility, rent-to-buy
8/24/2012