Alternative Measurement by Laser Doppler Vibrometry

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1 Alternative Measurement by Laser Doppler Vibrometry Polytec South-East Asia Pte Ltd Prepared for: APMP 4 th TCAUV Workshop Nov Polytec 1

2 Vibration Measurement? Accelerometers Microphones Well established conventional sensors utilizing different measurement technology. Proximity Sensor Strain Gauges AE Sensors NO BEST SENSOR only the most suitable for your needs! Different technologies addresses different needs. Combination of sensors to enable the most complete solution!!! Polytec 2

3 Drawbacks of Conventional Sensors Samples lightly damped/light-weight? Mass Loading of Contact Sensors Meddlesome cablings? Concerns on contact measurement resulting in defects on sample? Unable to localize actual vibration at specific point? Unable to attain high point density Operational Deflection Shapes (ODS)? Required to setup measurement sensor in close proximity to sample? Polytec 3

4 What if you could measure... Without contacting the surface Without setting cabling and connection to the sensor/surface Without using multiple sensors to attain multi-point measurement? Also enabling you to measure on Hot/Difficult/Sensitive surfaces Light structures without causing mass loading With pico-meters resolution Polytec 4

5 Laser Doppler Vibrometer Polytec 5

6 The Doppler Effect Sound or light waves emitted or back-scattered from a moving object are shifted in frequency relative to the motion of the object. The amount of the frequency shift is in proportion to the object s velocity Polytec 6

7 Laser Doppler Vibrometry Polytec 7

8 Why no contact? light has no mass no additional damping no shift of Eigen frequencies light is robust high temperatures exhaust systems, engine components light is flexible stand-off distance arbitrary points by scanning by mirrors and optical fibers Polytec 8

9 Expanding on Light Capitalizing on the technology, we have created solutions to enable some of the toughest measurement requirements: a) Long Distance Measurement b) Micro-structure / Sensitive Surface Measurement c) High Point Density Measurement - ODS d) Surface / Ultrasonic Wave Visualization e) Dynamic Stress / Strain Limitless potential of utilizing LDV along your current measurement techniques Polytec 9

10 a) Calculate tension force in stay-cables Excitation of the cables Tension force calculated on the basis of vibration data Measurement with Laser- Doppler- Vibrometer Much faster than conventional contact sensors: 10 cables per hour thanks to RSV-150! see SCHMIEDER, M.;TAYLOR-NOONAN, A.; HEERE, R. (2011): Rapid Non-Contact Tension Force Measurements on Stay Cables CONFERENCE AND EXHIBITION OF THE TRANSPORTATION ASSOCIATION OF CANADA Polytec 10

11 a) Structural Dynamics Railway Bridge Steel framework ca.107 m high Working distance > 140m Excitation: Train (ca. 240 t) Measurement of displacement Displacement when train crosses bridge Polytec 11

12 b) 3 Axis Measurement on MEMS Cantilever 3D vibration data set x-direction: amplitude ~ 8pm y-direction: amplitude ~ 4pm z-direction: amplitude ~ 8pm Polytec 12

13 Scanning Laser Doppler Vibrometry (SLDV) non-contact full-field sequential = scanning from point to point full bandwidth (- 25 MHz) frequency response measurement deflection shapes measurement practically unlimited # of locations operational or excited vibrations no mass loading requirement: repeatable conditions Polytec 13

14 Limitations of contact transducers Spacial Aliasing deflection shape at 514 Hz low point density: amplitude error distorted shape low point density = location is crucial = preparation time 19 point profile 19 MP 9 MP 5 MP 3.00E E E E E E E E E E E E E E E E E points -3.00E-08 9 points -1.50E-08 5 points -4.00E E E E Polytec 14 14

15 Video image of the measurement object Measurement grid with video overlay MP1 MP2 MP3... Sequential: excitation per meas. point Spectrum MPn Phase reference measurement grid after scan Polytec 15 Spectrum MPn+a ODS

16 Shaker Results Shaker Vibration Acquisition: accelerometer - Scanning LDV object under test object under test Amp. Signal conditioning Amp Acquisition + Signal generation Post-processing: ODS, modal analysis etc. Set of FRF Accelerometer 1D or 3D data Demodulation/acquisition/Signal Generation Post-processing: ODS, modal analysis etc. Scanning LDV 1D or 3D data Polytec 16

17 c) High Point Density ODS 612.5Hz for Washing Machine Drum FEM Correlation Polytec 17

18 c) High Point Density ODS Electronics Manufacturing Equipment Wire Bonders 63KHz Polytec 18

19 d) Surface Wave Propagation Lamb Wave Propagation 200KHz Defect Detection on Aluminum Plate Polytec 19

20 d) Ultrasonic Wave Visualization Parking Sensors - Refractometry Polytec 20

21 e) Dynamic Stress/Strain Turbine Blade Polytec 21

22 3D geometry 3D vibration In-Plane strains stresses Polytec Polytec GmbH # 22

23 3D 7000 nm in-plane 350 nm e xx D = 35 nm (Grid: 3 mm) e yy D = 6 nm (Grid: 2 mm) Polytec Polytec GmbH # 23

24 Key Notes Polytes s LDV provides a true contactless vibration measurement method with key benefits: Zero Mass Loading Disregard Surface Conditions Precise, Digital Vibration measurement Point and Shoot easy setup Complete Measurement & Acquisition package A solution for every application be it production testing with single point or ODS Scanning measurement for FEM, Modal Analysis. And a significant expansion to your current measurement technique Polytec 24

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