Dynamics of Rotating Structures Relealed

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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.

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Dynamics of Rotating Structures Relealed

  1. 1. Dynamics of Rotating Structures Revealed Using Non-Contact Laser Vibrometers 8/24/2012
  2. 2. Presentation OutlineRotationalvibrations  Technology behind rotational vibrometer  Why use lasers?  Application examplesDerotation  Derotator  Description  Derotated measurements 8/24/2012
  3. 3. Vibration in Rotating ObjectsVibrations in horizontal, vertical and axial planesare easy to measure with a single point sensor 8/24/2012
  4. 4. Vibration in Rotating ObjectsAs shafts transmit power they createand are subjected to torsional vibrations 8/24/2012
  5. 5. Goal – Find critical resonances – Map operational deflection shapes – Verify finite element simulationsUnder real operational conditionsWithout altering the data! 8/24/2012
  6. 6. The Contact Approach: EncodersDisadvantage : – requires mounting on shaft end – instrumentation time – Location is fixed – Changes moment of inertia pulley adaptor encoder 8/24/2012
  7. 7. Vibration in Rotating ObjectsRotational pulses are due to changes in angularvelocity, and must be measured with a rotationalvibrometer. 8/24/2012
  8. 8. RLV-5500 Rotational VibrometerConsists of – Optical Sensor Head (RLV-500) Compact Contains two Laser Doppler Interferometers IP67 protection – Demodulation Electronics (RLV-5000) 8/24/2012
  9. 9. Rotational Vibrometer Dual Beam Sensor HeadIntegrated meter shows centerline balanceand light return signal strength 8/24/2012
  10. 10. Aligning Lasers with Shaft Balance Indicator: Symmetric Asymmetric One SidedThe measurement result is independent of the alignment, however,asymmetry reduces the rpm measurement range. 8/24/2012
  11. 11. Rotational VibrometerThe shape of the object is irrelevant,and the measurement is insensitive to any lateral vibrations. 8/24/2012
  12. 12. Rotational Vibrometerf DA = 2V A λ Doppler Frequency Beam A V A = ω R A cos αf 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 8/24/2012
  13. 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 8/24/2012
  14. 14. Signal Processing Angular Velocity Angular Displacement RPMDC 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 8/24/2012
  15. 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 pointvibrometer• Contains a Bragg cell allowing measurement ofpositive and negative rotations as well as vibrationsaround zero RPM 8/24/2012
  16. 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 8/24/2012
  17. 17. Belt Pulley of Crankshaft Single Point Vibrometer: Axial VibrationsRotational Vibrometer: Rotational Vibrations 8/24/2012
  18. 18. Crankshaft Results 2 4 6 8 Engine Running Speed Frequency Spectrum 8/24/2012
  19. 19. Crankshaft Results Order Spectrum of the Rotational Vibrations 8/24/2012
  20. 20. Drive Shaft ApplicationsDrive Shaft Torsional Response 8/24/2012
  21. 21. Drive Shaft (Order Analysis) Applications Constant Velocity Joint Universal Joint TorsionsDrive Shaft Torsional Response 8/24/2012
  22. 22. Drive Train Testing Measure events on high-dynamic dynamometers 8/24/2012
  23. 23. Drive Train Testing Dual Mass FlywheelTwo flywheel masses that are linked by elastic springs 8/24/2012
  24. 24. Drive Train Testing Dual Mass Flywheel Results 8/24/2012
  25. 25. Supercharger Order AnalysisIf orders excited with too high of an amplitude, failures can occurVery small hub requires non-contact method 8/24/2012
  26. 26. Application: Pump ShaftTorsional vibration limit related to pump failure 8/24/2012
  27. 27. Application: RPM Ramp Test on Clutch Dyno Absorber Drive 1/RPM signal Data RLV-500 Acquisition ∆ϖ 8/24/2012
  28. 28. Drivability Motor CycleTuning torsionalvibration dampers – test crank shaft vibration under driving conditions measurement with crank shaft adapter Source: InFocus 2008/2 courtesy BMW Group 8/24/2012
  29. 29. Performing Linear MeasurementsWith two beams anytranslational movement iscanceled out in the signalWhen terminating one beamwith a mirror, linearmovements can be detected 8/24/2012
  30. 30. Performing Linear Measurements RLV-500In the “II” position two beams are emitted and the unit is in rotationalmode.In the “I” position one beam is emitted and the unit is in single pointmode.In the “0” position both beams are shut off 8/24/2012
  31. 31. Accessories90 degree deflectionAir Wipe 8/24/2012
  32. 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 filtersAngular Displacement Measurement – Measurement Range: 0.01°/V, 0.1°/V, 1°/V – Analog Output: + 10V – Frequency: 1 Hz up to 10 kHz 8/24/2012
  33. 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 filtersAngular Displacement Measurement – Measurement Range: 0.01°/V, 0.1°/V, 1°/V – Analog Output: + 10V – Frequency: 1 Hz up to 10 kHz 8/24/2012
  34. 34. FeaturesBandwidth – (0) 0.5 Hz – 10 kHz – 30th order at max. speedResolution – 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 8/24/2012
  35. 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. 8/24/2012
  36. 36. Scanning Vibrometer PrincipleExample: 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 referencegrid after measurement deflection shape @ 36kHz spectrum MPn+a 8/24/2012
  37. 37. Drive Train Vibrationsscanning at fixed rpm along shaft – bending modes are visible 20 Hz 262 Hz 8/24/2012
  38. 38. Measurements on rotating partsAxial measurement on tireDeflection shape of rotating tireat 50 mph 8/24/2012
  39. 39. Measurements on rotating partsRadial measurement on tireDeflection shape of rotating tire at 16 mph – Scan area limited by speed on circumference 8/24/2012
  40. 40. Decoder saturationRadial measurements Tangent. velocity r sensor vtangent = ωr Radial velocity +v 0 vtangential t -v Time-signal 8/24/2012
  41. 41. Measuring Rotating Structures –The Goals:Measure under real operating conditionsTrack deflection shapes rotating withstructure to avoid smearing of dataAvoid the drawbacks of telemetry and/or slipringsAnd…..Can we achieve all of this while enjoying thebenefits of laser vibrometry? 8/24/2012 # 41
  42. 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 8/24/2012
  43. 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° 8/24/2012
  44. 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 driveVertical telescopic drive Base frame 8/24/2012
  45. 45. Shift of Resonances During Run-up • Curved plot of Eigen resonances – Stiffening ofRPM material – Centrifugal forces – Excited by orders Frequency – Important for composites and plastics 8/24/2012
  46. 46. Run-up and shift of resonances actual resonance at order calculated resonance eigenfrequency at standstill 8/24/2012
  47. 47. Bladed Disk: 10900 rpm 8/24/2012
  48. 48. Bladed Disk: 10900 rpm 725 Hz 800 Hz 845 Hz 895 Hz 8/24/2012
  49. 49. ApplicationsElectronic industry – Noise reduction in cooling systems for consumer products, trouble shootingAerospace – Durability and FE update on blisk and fansAutomobil – Cooling fans – Tires – Turbo Chargers (@ reduced rpm levels) 8/24/2012
  50. 50. Benefits of Vibrometry with OpticalDerotation• Whole field measured…..stress analysis, modalanalysis, FEM validation• Acquire reliable FEM validation data under realoperating conditions• Obtain operating deflection shapes rotating withstructure• No added mass, change in flow dynamics• No potentially noisy telemetry or slip rings 8/24/2012
  51. 51. ConclusionOptical 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 8/24/2012
  52. 52. Engineering Services and Rental ProgramAdvanced 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

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