Method and system for synchronously inhibiting subcritical vibrations of magnetic levitation molecular pump rotor

Patent metadata

Field	Value
Publication number	US-9644634-B2
Application number	US-201214363725-A
Country	US
Kind code	B2
Filing date	Nov 22, 2012
Priority date	Dec 8, 2011
Publication date	May 9, 2017
Grant date	May 9, 2017

Abstract

A method for synchronously inhibiting subcritical vibrations of magnetic levitation molecular pump rotor, by use of synchronously sampling signals of subcritical vibrations of the rotor generated after the rotor of the magnetic levitation molecular pump touches down so as to obtain the amplitude and the phase of subcritical vibrations of the rotor, based on which a compensation force is output for inhibiting subcritical vibrations of the rotor. Through using the present method, an accurate synchronous for signals of subcritical vibrations and fast inhibition for subcritical vibrations of the rotor is achieved.

First claim

The invention claimed is:

1. A method for synchronously inhibiting subcritical vibrations of a magnetic levitation molecular pump rotor, wherein the method sequentially comprises the following steps of:
step 1: controlling a digital signal processor through a controller of said magnetic levitation molecular pump after said rotor of said magnetic levitation molecular pump falls off due to instability of the rotor, so as to obtain a displacement signal of said rotor; executing a Fast Fourier Transformation of said displacement signal, and then analyzing a spectrum of vibrations of said rotor to obtain a frequency f 0 and amplitude A 0 of the subcritical vibrations of said rotor;
step 2: establishing a Cartesian coordinate system by taking an inner center of a stator of a radial magnetic bearing as an origin, and setting a position A on a track of the subcritical vibrations of said rotor as an origin point synchronous with the subcritical vibrations of said rotor; then obtaining a phase φ 0 of the subcritical vibrations of said rotor, when a positive angle formed by a vector of a displacement of said rotor and the coordinate X axis reaches a predetermined angle Φ, which indicates said rotor reaches said position A; outputting a compensation force so as to inhibit the subcritical vibrations of said rotor according to the frequency f 0 , the amplitude A 0 and the phase φ 0 of the subcritical vibrations of said rotor, based on the sine rule, when said rotor reaches said position A;
step 3: when said rotor reaches said position A again, enabling said digital signal processor for executing a single frequency Fast Fourier Transformation of the displacement of said rotor during a next period of the subcritical vibrations of said rotor, so as to obtain amplitude A i and a phase φ i of the subcritical vibrations of said rotor, wherein, setting a frequency of said single frequency Fast Fourier Transformation as a current subcritical frequency f i of said rotor; comparing the amplitude A i and the phase φ i of the current subcritical vibrations of said rotor with the amplitude A i-1 and the phase φ i-1 of a previous period of the subcritical vibrations through said controller of said magnetic levitation molecular pump, and making corresponding revisions to an amplitude and a phase of a compensation force of the next period of the subcritical vibrations; repeating this step till a predetermined period is passed;
step 4: executing a Fast Fourier Transformation of a displacement signal of said rotor at an interval of a predetermined period T through said digital signal processor, so as to obtain an updated frequency f i of the subcritical vibrations of said rotor, and setting the updated frequence f j as the frequency of the compensation force for the next period of the subcritical vibrations;
step 5: determining if the amplitude of the subcritical vibrations of said rotor decreases to a value below a predetermined threshold in every period of the subcritical vibrations through said controller of said magnetic levitation molecular pump; completing inhibition to the subcritical vibrations of said rotor, when a detected amplitude of the subcritical vibrations of said rotor is lower than said predetermined threshold and meanwhile said rotor is entirely disengaged with a protective bearing, otherwise, repeating step 3 to step 4.

2. The method of claim 1 , wherein said positive angle formed by said displacement vector of said rotor and said coordinate X axis is zero degrees.

3. The method of claim 2 , wherein in said step 3, the frequency of said compensation force equals the frequency of said subcritical vibrations; said compensation force is proportional to the amplitude of said subcritical vibrations, with contrary phase.

4. The method of claim 3 , wherein in said step 4, said predetermined period T may be equivalent to 5-15 periods of the subcritical vibrations of said rotor.

5. The method of claim 4 , wherein said predetermined period T may be equivalent to 10 periods of the subcritical vibrations of said rotor.

6. A system for synchronously inhibiting subcritical vibrations of a magnetic levitation molecular pump rotor, adapted for executing the method of claim 1 , wherein the system comprises:
a position sensor;
a controller of said magnetic levitation molecular pump, adapted for controlling said position sensor for obtaining a displacement signal of said rotor of said magnetic levitation molecular pump and controlling the working of components of said system;
a digital signal processor, adapted for obtaining a frequency, an amplitude and a phase of the subcritical vibrations of said rotor through receiving and analyzing said displacement signal of said rotor obtained by said controller, and for transmitting the frequency, the amplitude and the phase to said controller;
a magnetic bearing, adapted for being controlled by said controller so as to output a compensation force for inhibiting the subcritical vibrations of said rotor according to the frequency, the amplitude and the phase;
after said rotor of said magnetic levitation molecular pump falls off due to instability of the rotor, the digital signal processor is controlled by the controller to:
obtain a displacement signal of said rotor; execute a Fast Fourier Transformation of said displacement signal, and then analyze a spectrum of vibrations of said rotor to obtain a frequency f 0 and amplitude A 0 of the subcritical vibrations of said rotor;
establish a Cartesian coordinate system by taking an inner center of a stator of a radial magnetic bearing as an origin, and set a position A on a track of the subcritical vibrations of said rotor as an origin point synchronous with the subcritical vibrations of said rotor; then obtain a phase φ 0 of the subcritical vibrations of said rotor, when a positive angle formed by a vector of a displacement of said rotor and the coordinate X axis reaches a predetermined angle Φ, which indicates said rotor reaches said position A; cause the magnetic bearing to output a compensation force so as to inhibit the subcritical vibrations of said rotor according to the frequency f 0 , the amplitude A 0 and the phase φ 0 of the subcritical vibrations of said rotor, based on the sine rule, when said rotor reaches said position A;
execute a single frequency Fast Fourier Transformation of the displacement of said rotor during a next period of the subcritical vibrations of said rotor after said rotor reaches said position A again, so as to obtain amplitude A i and a phase φ i of the subcritical vibrations of said rotor, wherein, a frequency of said single frequency Fast Fourier Transformation is set as a current subcritical frequency f i of said rotor; compare the amplitude A i and the phase φ i of the current subcritical vibrations of said rotor with the amplitude A i-1 and the phase φ i-1 of a previous period of the subcritical vibrations, and make corresponding revisions to an amplitude and a phase of a compensation force of the next period of the subcritical vibrations; repeat this step till a predetermined period is passed;
execute a Fast Fourier Transformation of a displacement signal of said rotor at an interval of a predetermined period T, so as to obtain an updated frequency f j of the subcritical vibrations of said rotor, and setting the updated frequency f j as the frequency of the compensation force for the next period of the subcritical vibrations;
determine if the amplitude of the subcritical vibrations of said rotor decreases to a value below a predetermined threshold in every period of the subcritical vibrations; complete inhibition to the subcritical vibrations of said rotor, when a detected amplitude of the subcritical vibrations of said rotor is lower than said predetermined threshold and meanwhile

Assignees

• Kyky Technology Co Ltd
• Univ Tsinghua

Inventors

• Zhang Kai
• Wu Han
• Li Qizhi
• Zhang Xiaozhang
• Zou Meng

Classifications

• F04D27/00 Primary

  Control, e.g. regulation, of pumps, pumping installations or pumping systems specially adapted for elastic fluids · CPC title

• F04D19/048

  comprising magnetic bearings · CPC title

• F04D29/58

  Cooling (of machines or engines in general F01P); Heating; Diminishing heat transfer {(for the motor of air-pump units F04D25/082; cooling of shafts or bearings F04D29/04)} · CPC title

• F04D27/001 Primary

  Testing thereof; Determination or simulation of flow characteristics; Stall or surge detection, e.g. condition monitoring · CPC title

• F04D29/058

  magnetic; electromagnetic · CPC title