Balancing High-Speed Rotors at Low Rotation Speeds Using Parametric Excitation
Presented is a novel method allowing to perform mass balancing of flexible vibration modes, while rotating at low speeds. Through special external excitation, the projection of imbalance forces on vibration modes corresponding to high rotation speed can be found. The main merit of this method is that it uses measurements taken at low speeds, which anticipate the imbalance effects at considerably higher speeds. Standard mass balancing procedures of flexible bending modes, require the rotor to be rotated up to its operating speed. High speed rotors such as small jet engines and turbochargers cannot be rotated to such high speeds at laboratory conditions, and therefore are usually balanced using commercial balancing machines that are limited to low speeds. At low speeds it is impossible to detect the projection of imbalance forces on high frequency modes and thus low-speed balancing can worsen vibrations once the system is operational.
The present paper outlines a method whereby parametric excitation is employed to selectively amplify the imbalance response, and find the projection of the imbalance on any desired mode of vibration while rotating at low speeds. This means that the effect of imbalance at any critical speed, can be found without the need to actually rotate the device at these speeds.
In order to perform the proposed procedure, the system to be balanced is driven by actuators with signals containing several frequencies. These signals create an excitation pattern that creates large sensitivity to the forces caused by imbalance at low-speeds.
KeywordsDynamic balancing Parametric excitation Non linear vibration
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