Noncontact Sesnsing of Rotating Structures with ... Noncontact Sensing with Rotary Optical Radial...

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  • Noncontact Sensing with Rotary OpticalNoncontact Sensing with Rotary Optical Radial Coupler (RORC) using CRadial Coupler (RORC) using C--lenslensRadial Coupler (RORC) using CRadial Coupler (RORC) using C lenslens

    Khazar Hayat Prof Sung Kyu HaKhazar Hayat, Prof. Sung Kyu Ha

  • Motivation

    Structural Health Monitoring (SHM) of Critical Rotary Components

    Rotating Structure SHM Goals:SHM Goals:


    Components Sensing Mechanism

    Data acquisition &

    SHM Goals: SHM Goals:

    Condition Assessment

    Damage Evaluation

    Service Life Prediction

    Management Catastrophic Failure Prevention

    os ts

    Cost Savings trend 




    SHM Advantages:

    • Ensure Structural Integrity  Scheduled




    Unscheduled (Today)

    PredictivePredictive SHMg y

    •“Maintenance on demand” • Lower unscheduled inspections

    Slide 2

    < SHM Benefits (Source: Holger Speckmann, AIRBUS)>

  • Motivation

    Composite Rotating Structures

    SHM A li ti

    < Wind Turbine blade > ( Model: GE90-115B)>

    H li t Bl d (S Sik k Ai ft C )

    Slide 3


  • Problem Statement

    Structural integrity can be assessed by monitoring strainsStructural integrity can be assessed by monitoring strains

    Difficult to receive strain data from Rotating Structure

    “Development of a Noncontact Strain MeasurementDevelopment of a Noncontact Strain Measurement Method using Rotary Optical Radial Coupler


    Slide 4

  • Previous Strain Measurement Methods

    Strain Gauges with Slip Ring / Telemetry system

    •High signal to noise ratio

    •Data transmission limitation

    •Not applicable to higher speedNot applicable to higher speed

    •Need power supply

    •Sensitive to electromagnetic (EM) interference

    Slide 5

  • Previous Strain Measurement Methods

    FBG Sensor with Telemetry System •Power Supply Problempp y

    •Imbalance of Rotating Structure at Higher Speed

    < Wireless signal transmission between Signal Process Unit (SPU) & FBG sensors attached on wind turbine blade>

    Slide 6

    Ref: Kerstin S., Wolfgang E., Jorg A., Elfrum L. and Gerhard L. A fibre bragg grating sensor system monitors operational load in a wind turbine blade. Meas. Sci. Technol. 2006: (17) 1167-1172

  • Previous Strain Measurement Methods

    Fiber Optic Rotary Joint

    •Optical signal transmissionOptical signal transmission

    •Insensitive to EM interference

    •Tight mechanical tolerance for optical alignment•Tight mechanical tolerance for optical alignment

    •Limited speed & durability due to mechanical parts

    < Working Principle of Fiber Optic Rotary Joint >

    Slide 7

    Ref: Jing W., Jia D., Tang F., Zhang H., Zhang Y., Zhou G., Yu J., Kong F. and Liu K. Design and implementation of a broadband optical rotary joint using C-lenses. Opt. Express: (2004) 12 4088–93

  • Previous Strain Measurement Methods

    Fiber Optic Coupler •Free-space coupling

    •Require machining of for installation, weakening the Shaft

    • Space Installation Problems in real structuresSpace Installation Problems in real structures

    < Arrangements of a rotary optical coupler and FBG sensors >

    Radial Optical Rotary Coupler (RORC)

    (Over come above problems associate with Fiber Optic Coupler)

    Slide 8

    ( p p p )

  • Theory

    Fiber Bragg Grating (FBG) Sensor •Reflect particular (i.e. Bragg) wavelength of light and transmits others

    Strain-included shift =

    n0 : refractive index of the air n1 : refractive index of the cladding n2 : refractive index of the core n3 : refractive index of the grating


    •Strain & Temperature Measurements

    Slide 9

  • Theory

    Wavelength Division Multiplexing (WDM)

    •Many FBG sensors on single optical fiber can be address simultaneously•Many FBG sensors on single optical fiber can be address simultaneously

    •Sensing Network

    < Representation of a WDM interrogation of FBG sensor array >

    Slide 10

  • Experiment

    Experimental Arrangement for RORC Feasibility

    Slide 11

    < Sketch of experiment test fixture to show feasibility of rotary optical radial coupler (RORC) >

  • Experiment

    Alignment of Collimators

    •Tedious and Time Consuming (i e 06 DOF’s )•Tedious and Time Consuming (i.e. 06 DOF s )

    •Use of marked Collimators < 06 DOF manipulation >

    V-groove block pre-alignment for marking

    < Optical alignment b/t stationary side and rotary side collimators >

    Fi l li t ith k d lli t (i k t hi )

    < Circumferential marking of C-lens Collimators pair at proper optical alignment position >

    Slide 12

    Final alignment with marked collimator (i.e. mark matching)

  • Experiment

    Equipment Specification & Setup FBG Sensor Spec.:

    • Qty: 01 l l h• Central Wavelength: 1552.10 nm

    < Pair of C-lens Collimators used as RORC >

    Slide 13

    < Experimental setup >

  • Preliminary Results & Conclusions

    • Optical signal pike per each rotation of disk appeared on si-425 Optical Sensing Interrogator (as expected )


    • As speed increases, the time space between wavelength signal spikes decreases and vice versa (see region A & C )

    W av

    el en


    • Increase in speed sometimes causes misalignment that result in


    missing signal spikes (see region B)

    Slide 14

    < Signal spikes appearing on si-425 interrogator > Time

  • Preliminary Results & Conclusions

    • For max. test speed of 1350 RPM, strain modulated wavelength signal was observed

    Wavelength Signal

    Strain Measurement

    •Wavelength signal value (i.e. 1552 10 nm) remained constant up

    Strain Measurement

    1552.10 nm) remained constant up to 1350 rpm, because negligible deformation / strain of steel disk

    Slide 15

    < Wavelength signal measurement on si-425 optical sensing interrogator at different rotating disk speeds >

  • Future Work

    • Multiple points strain signal measurement ( i.e. For 0o ~ 360o varying strains)

    • High Sampling Data Acquisition System < signal measurement four times per revolution

    at required rotation angles >

    • Optical Loss across RORC

    Minimize by precise alignment & use of better quality Collimators

    Overcome by Higher Laser Source

    • Real-time applications (i.e. on wind turbine blade, composite flywheel rotor, helicopter blade, Composite fan blades etc.)

    Slide 16

  • Thank You for Your Attention khazarhayat@yahoo com

    Slide 17