An Introduction to Scanning Laser Vibrometry for Non-Contact Vibration Measurement
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Transcript of An Introduction to Scanning Laser Vibrometry for Non-Contact Vibration Measurement
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# 1# 1
An Introduction to Scanning Laser Vibrometry for Non-Contact Vibration
Measurement
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# 2
Presentation Outline Deflection Shape and Experimental Modal
Analysis used in the product development cycle
Traditional test methods versus Scanning laser vibrometry
Principles of 1-D and 3-D laser vibrometry Applications examples Accessories Conclusions
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# 3
Why Can’t We Rely 100% on the Computer Model?
Material properties Tolerances in manufacturing
Complex joint dynamics Damping Boundary conditions Changes in stiffness during rotation
→ → → FEM Validation and Updating
Uncertainties in:
Impossible or Difficult to Model:
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# 408.04.2023 # 4
PSV-500-3D
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# 5
Other Examples of the Need to Perform an Experimental Modal Test
Build an experimental model Compute structural modifications
Understand the dynamics of a structure (of a competitor for example) for which we do not have a finite element model
Troubleshooting:
Benchmarking:
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# 6
Full Field - Traditional Approach Issues with Contact Transducers
Mass loading Damping and stiffness errors
Time consuming Limited working environments Complicated cabling Safety Coarse spatial resolution Coordinate correlation to FEM
geometry cumbersome Transducer calibration Limited bandwidth Poor Modal Assurance Criteria
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# 7
A Better SolutionScanning Laser Vibrometer
Laser has no mass Faster - laser can be scanned Long standoffs, through windows,
fluids, hi temps No cabling on structure Spot dia typically 10s of µm FEM geometry import for easy
point definition One (3) transducer(s) to calibrate
(no book keeping) Wide bandwidth – no accel rolloff or
resonance - to 1.2GHz!! Reduced chance of spatial aliasing
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# 8
Spatial Aliasing19 MP
-4.00E-08
-3.00E-08
-2.00E-08
-1.00E-08
0.00E+00
1.00E-08
2.00E-08
3.00E-08
0.23
4668
0.18
6155
0.13
7642
0.08
9129
0.04
06156
-0.00
7897
-0.05
641
-0.10
4923
-0.15
3436
-0.20
1949
9 MP
-4.00E-08
-3.00E-08
-2.00E-08
-1.00E-08
0.00E+00
1.00E-08
2.00E-08
3.00E-08
0.23467 0.1619 0.08913 0.01636 -0.05641 -0.12918 -0.20195
5 MP
-2.00E-08
-1.50E-08
-1.00E-08
-5.00E-09
0.00E+00
5.00E-09
1.00E-08
0.234668 0.113385 0.0163594 -0.104923 -0.201949
19 point profile
19 points
9 points
5 points
Low point density:amplitude errordistorted shape
514 Hz
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# 9
PSV Configurations
1D Scanning
Simple structuresODS
Acoustics – noise source identification
Rotating
08.04.2023 # 9
3D Scanning
Complex structuresStructural Dynamics
Modal analysis
FEM validation
Stress & strain
Robot-integrated
Polytec Scanning Vibrometer (PSV)
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# 10
Front-end Data ManagementSystem
HD Video
LDVSensor
ScanningMirrors
ScanElectronics
Stitched data
Sensor Head Test Object
Test Object
1-D Scanning Vibrometry (PSV)
Up to 250,000 locations scanned point-by-point – vibration velocity or displacement
Software for exciter signal generation, data acquisition, display & manipulation
Geometry file imported or measured
Animated data visualization
Data export for modal analysis or FEM validation
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# 11
Operational steps:Define measurement points
using video image and draw programby geometry import
Excite structureusing internal or external function generator signal
Scan to acquire vibration response at each point time history orFFT spectrum
Visualizeanimated operating deflection shapes at selected frequencies of interesttime domain animations
Export for post-processing (e.g. modal analysis or FEM validation)
PSV Operational Steps
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# 12
PSV Working Principle
Measure V and at many points relative to a reference signal Amplitude and relative phase at each scan point
Spatial vibration pattern of measurement surface
Scan signal
Ref signal
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# 13
Operating Deflection Shapes
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# 14
Wide Ranging Applications
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# 15
Typical 1-D Scanning Vibrometer
PSV-500-H 4 (or 8) channel data
acquisition with 80 kHz bandwidth
4 or 8 reference channels 50° x 40° scan angle 13 velocity ranges up to 10
m/s Resolution to <0.01 µm/s/√Hz Autofocus MIMO with multi-shaker
excitation, 4 independent generator channels; Principal Component Analysis
Ethernet connection to DMS Coherence Optimizer
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# 16
Example measurement on black loudspeaker cone
480 pm deflection1775 Hz
8 averages
New Technology - New Quality
08.04.2023 # 16
Digital Broadband Decoder
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# 17
Scan Modes
Time
Frequency
FFT
Zoom FFT
Time Domain
FastScan
Time
Frequency
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# 18
Time Domain Animations
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# 19
Acoustics
Acoustics Configuration50 kHz vibrometer bandwidth digital
7 or 10 measurement ranges
1 channel for reference sensor (digital)
VibroLink Ethernet connection
Optional signal generator
Geometry Scan Unit optional
Software for acoustic measurements – live or stored data – headphones include
Configuration Examples
08.04.2023 # 19
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# 20
Requirements for Quiet Products
Sound propagationFrom source to receiver
Transmission (structure-borne noise)
Leakage (airborne noise)
Secondary noise (structure-borne noise)
08.04.2023 # 20
PSV-500 and its Applications
F
Structural dynamics
EmissionSurface velocity
Sound pressure
Fluid-structure-coupling Courtesy : P. Zeller; Handbuch
Fahrzeugakustik
Operating Load
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# 21
Laser vibrometers measure vibration in laser direction only
Data needs careful interpretation due to different vibration directions, surface shape and varying scan angles
Modal analysis software expects 3-D data
FE models produce 3-D data
Limitations of a 1-D Scanning Vibrometer
Test ObjectLaser Vibrometer Θ
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# 22# 22
3-D Scanning Laser Vibrometry
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# 23
x
yz
3-D object coordinate system defined by means of a minimum of 3 known reference points
Laser beam unit vectors for all scan heads are determined using the transformation matrix:
Principles of 3-D Laser Vibrometry
3
2
1
1
333
222
111
v
v
v
lll
lll
lll
v
v
v
zyx
zyx
zyx
z
y
x
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# 24
If the object geometry is known, all 3 lasers intersect for all (accessible) scan points
3 simultaneously acquired vibration signals are transformed into the object‘s coordinate system by software
x
y z
Principles of 3-D Laser Vibrometry
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# 25
Data import (via UFF):
a) Other test software packages
b) Finite Element Model Geometry File
c) Extracted from other methods such as CAT scan
What if there is no geometry file?
Options for Obtaining Geometry File
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# 26
Options for Obtaining Geometry File
When there is no geometry file:
a) Alignment of all 3 laser beams manually for every scan point
b) Measure geometry for every scan point
GEOMETRY SCAN UNIT
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# 27
PSV-500 Geometry Scan Unit
More compact, more stable, no moving parts, fasterFor eg: 844 points in 3mins 30secs
Higher sensitivity and wider optical dynamic range Handles larger range of surfaces and variations in surface finish
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# 28
Beam Positioning Accuracy
Reasons for poor overlap: Inaccurate “3D-Alignment” during set up procedureImperfect geometry data
Why must beams overlap?Lasers must measure at same point for optimal lateral resolutionMore critical for strain measurements - geometry must be known for transformation to in-plane and out-of-plane data
standard
with triangulation during scan
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# 29
Modifies the 3D coordinates by overlapping the 3 beams at one point.
Result: Impoved geometry as input data L for strain calculation
Result: accurate geometry
PSV-S-TRIA Video Triangulation
][m
m
L
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# 30
PSV-S-TRIAVideo Triangulation during Scan
before triangulation
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# 31
PSV-S-TRIAVideo Triangulation during Scan
after triangulation
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# 32
Structural Dynamics (3D)
3D Structural Dynamics Configuration100 kHz vibrometer bandwidth (digital)
13 measuring ranges
8 reference channels (integrated)
MIMO with multi-shaker excitation up to 4 shakers (integrated)
Principal Component Analysis (PCA)
Geometry Scan Unit
Coherence Optimizer
VibroLink Ethernet connection
StrainProcessor optional
Configuration Examples
08.04.2023 # 32
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# 33
Deflection shape at 82 Hz showing individual measurement points
Station Wagon 3-D Vibration Data
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# 34
Faster set-up According to a European car manufacturer just the mounting and cabling of the accels and dummy
masses plus the coordinate definitions for a car body usually takes around 4 – 5 days
FEM mesh (coarsened) can be imported Manual identification of points relative to FEM nodes not necessary All points correlate exactly with FE model
Faster data acquisition No moving of dummy masses, accels and retesting
Spatially more detailed data Important for FEM correlation, model updating, and acoustics
Benefits compared to Accelerometers Insensitive to crosstalk when rotational vibration is present Calibration not affected by temperature Flat frequency response
Software is easy to learn and system easy to use
Other time savings for design (FEM) department No modeling of dummy masses necessary
A major European car manufacturer estimates total time savings of > 50%
Benefits of Scanning Vibrometry for Modal Analysis
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# 35
RoboVib
CA
E w
ork
flow
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# 37
Results Exampledeflection shape at 38 Hz
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# 38
Case Study – Transmission Case
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# 39
Element type Tetrahedral (solid 185)
Number of nodes 19994
Number of elements 69019
Material Aluminum casting alloy
Case Study – Finite Element Model
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# 40
Results
Example: deflection shape at 592 Hz
Case Study – Polytec Data
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# 41
Frequency Response Functions
Case Study – Test Data
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# 42
Circle Fitting
Resonant Frequency
Damping
Case Study – Curve Fitting
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# 43
Case Study – Polytec MAC Data
Accel Data < 0.64
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# 44
Am
plit
ude (
dB
)
Frequency (Hz)
Frequency Shift
Density (% Change) = -1.3 %Elasticity Modulus (% Change) = -5.7 %
EMA
Case Study – Model Update
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# 45
Traditional - Fixed CostsAerospace GVT Example
Large Size >400 Channels 2-8 Reference Channels (MIMO)
Medium Size 100-400 Channels 2 Reference Channels (MIMO)
Small Size <100 Channels 1 or 2 Reference Channels
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# 46
Number of Channels
Time & Complexity
$$$
Small Medium Large
Total Cost of Modal Test Add in the variable cost of personnel on a daily rate
Add in time delay, impacts on production schedule!
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# 47
Many Accessories Enable New Applications
Rotating Structures
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# 48
Bladed Disk: 10,900 rpm
725 Hz 800 Hz
845 Hz 895 Hz
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# 49
Many Accessories Enable New Applications
Small parts at high spatial resolution, high frequencies, strain
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# 50
Stress distribution across the surface of a turbine blade in the X direction
Dynamic Stress and Strain
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# 51
FEA / Experimental Correlation
Strain in x direction
Strain in y direction
Shear Strain
Results courtesy of the University of Adelaide ME DepartmentPSV data
PSV data
PSV data
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# 52
Many Accessories Enable New Applications
Brake squeal studies
Entomology
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# 53
More comprehensive vibration testing in a fraction of the time and effort with enhanced detail and accuracy compared to traditional techniques easily integrated with CAE/FEM
FE Model Validations can be made using non-contact 3-D (and 1-D) laser measurement
Many accessories are available to extend the range of applications
Engineering services and rentals are available
Conclusions
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# 54
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