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TECHNICAL PAPERS

Rotor Vibration Measurements Using Laser Doppler Vibrometry: Essential Post-Processing for Resolution of Radial and Pitch/Yaw Vibrations

[+] Author and Article Information
Ben J. Halkon

Wolfson School of Mechanical and Manufacturing Engineering, Loughborough University, Loughborough, Leicestershire, LE11 3TU, UK

Steve J. Rothberg1

Wolfson School of Mechanical and Manufacturing Engineering, Loughborough University, Loughborough, Leicestershire, LE11 3TU, UKs.j.rothberg@lboro.ac.uk

1

Corresponding author.

J. Vib. Acoust 128(1), 8-20 (Jul 07, 2005) (13 pages) doi:10.1115/1.2149389 History: Received October 21, 2004; Revised July 07, 2005

Laser Doppler vibrometry is now a well established technique enabling noncontact vibration measurements in the most challenging of environments. Rotor vibration measurements are often highlighted as a major application of laser vibrometers due to their noncontact operation and inherent immunity to shaft runout. In such measurements, resolution of the individual axial and torsional vibration components is possible via particular arrangement of the laser beam(s). Resolution of the radial or pitch/yaw vibration components, however, can only be achieved by essential post-processing of the data from simultaneous orthogonal measurements. This paper describes the principle and rigorous examination of a novel, dedicated resolution algorithm enabling, for the first time, real-time post-processing of the outputs from standard commercial instruments. The system performed well, even in the presence of noise and other typical measurement errors, and was implemented successfully in an engine vibration study.

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Copyright © 2006 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

(a) Definition of axes and the point P on a vibrating and rotating shaft. (b) Laser beam orientation, defining angles β and α.

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Figure 2

(a) Constant angular velocity resolution algorithm block diagram. (b) Correction algorithm block diagram.

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Figure 3

Simulated x and y vibration velocities in the time domain ((a) and (b)) and frequency domain ((c) and (d)) (ẋ=20cos(0.5ΩT¯t+0.5π)mm∕s, ẏ=10cos(1.5ΩT¯t)mm∕s, ΩT¯=100πrad∕s)

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Figure 4

Simulated ac coupled laser vibrometer outputs for the x and y directions in the time domain ((a) and (b)) and frequency domain ((c) and (d)): Resolved outputs for simulated measurements in the x and y directions ((e) and (f)) (ẋ=20cos(0.5ΩT¯t+0.5π)mm∕s, ẏ=10cos(1.5ΩT¯t)mm∕s, ΩT¯=100πrad∕s)

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Figure 5

Simulated ac coupled laser vibrometer output for a measurement in the x direction in the presence of 0.015mm∕s random and 0.1mm∕s pseudo-random noise

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Figure 6

Resolved output for a simulated measurement in the x direction in the presence of 0.015mm∕s random and 0.1mm∕s pseudo-random noise and a −2% speed measurement error: (a) spectral line at ΩT¯ eliminated and (b) spectral lines at ΩT¯±0.1ΩT¯ eliminated

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Figure 7

Simulated ac coupled laser vibrometer output for a measurement in the x direction in the presence of broadband torsional oscillation (ẋ=20cos(0.5ΩT¯t+0.5π)mm∕s, ẏ=10cos(1.5ΩT¯t)mm∕s, ΩT¯=100πrad∕s, ΔΩT=0.67×10−3ΩT¯ rms (arbitrary phase), x0=y0=0mm)

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Figure 8

Resolved output for a simulated measurement in the x direction in the presence of broadband torsional oscillation (a) first, (b) second, and (c) fourth estimates of the x vibration velocity (spectral lines at ΩT¯±0.1ΩT¯ eliminated)

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Figure 9

Simulated ac coupled laser vibrometer output for a measurement in the x direction in the presence of 0.02mm∕s random noise, a −2% speed measurement error and alignment offsets (ẋ=20cos(0.5ΩT¯t+0.5π)mm∕s, ẏ=10cos(1.5ΩT¯t)mm∕s, ΩT¯=100πrad∕s, ΔΩT=0.67×10−3ΩT¯ rms (arbitrary phase), x0=0.25mm, y0=0.5mm)

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Figure 10

Resolved output for a simulated measurement in the x direction in the presence of 0.02mm∕s random noise, a −2% speed measurement error and alignment offsets. (a) First and (b) fourth estimates of the x vibration velocity (spectral lines at ΩT¯±0.1ΩT¯ eliminated).

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Figure 11

Engine crankshaft radial vibration measurements experimental arrangement

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Figure 12

(a) Resolved x radial vibration vs loaded engine speed. (b) Resolved yaw vibration vs loaded engine speed.

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