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Research Papers

Active Control of Rotor Vibrations by Two Feedforward Control Algorithms

[+] Author and Article Information
Kari Tammi

 VTT–Technical Research Centre of Finland, P.O. Box 1000, FI-02044 VTT, Finlandkari.tammi@vtt.fi

J. Dyn. Sys., Meas., Control 131(5), 051012 (Aug 19, 2009) (10 pages) doi:10.1115/1.3155015 History: Received September 19, 2008; Revised March 05, 2009; Published August 19, 2009

Resonance vibrations (critical speeds) play a significant role in rotor vibration control. Active vibration control methods for rotors are studied to develop solutions to enhance machines’ dynamic behavior, durability, and operating range. This paper reports rotor vibration attenuation with a supplementary electromagnetic actuator located outside the rotor bearing span. Feedback and feedforward control system design are shown, and comparative experiments on two active vibration control methods for mass unbalance compensation are reported. The methods compared are adaptive FIR filter with the least mean squares (LMS) algorithm and convergent control (CC) method with a frequency-domain adaptation algorithm. The methods were experimentally validated on the rotor test rig (rotor weight 2.7 kg, length 560 mm, and first critical speed about 50 Hz). The feedback system provided wideband damping in the sub- and supercritical regions. The feedforward systems attenuated vibratory responses at the speed of rotation and its harmonic. The attenuation achieved was about 20 dB depending on the rotor speed. Also, discrete-time CC algorithm is shown to have a feedback equivalent circuit. The significance of feedback control lies in making the system phase-characteristics sufficiently smooth for feedforward control methods. Then, feedforward algorithms provided a good vibration damping performance over the operating range. CC was found to be a more effective and simpler algorithm for the purpose than the adaptive FIR filter with the LMS algorithm. The equivalent feedback circuit derived for CC, and systems similar to CC, facilitates their stability and robustness analysis.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 12

Comparison of radial responses at the rotor midpoint with CC and with the adaptive FIR working

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Figure 1

The feedback and feedforward controllers with the rotor system

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Figure 2

The general working principle of feedforward systems

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Figure 3

An adaptive feedforward controller (a) and the equivalent feedback system (b) (adopted from Ref. 15)

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Figure 4

Extraction of the Fourier coefficients at the frequency of rotation and return to the time domain

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Figure 5

The rotor layout: the displacement sensors at “S1” and “S2” and the actuator at “A.” The dimensions are in millimeters.

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Figure 6

The driving motor (left), the rotor with the disks, and the actuator (right)

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Figure 7

The three lowest mode shapes of the rotor. The nondeformed shape, the disk center lines, and the bearing positions are shown by the straight black lines.

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Figure 8

The control systems: feedback above and CC below

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Figure 9

The rotor midpoint radial response when running at a constant speed of 25 Hz

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Figure 10

The radial responses during a ramp down at the rotor midpoint with the feedback controller working alone, and together with CC

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Figure 11

The rotor midpoint responses at 25 Hz

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