CN1749723A - The accurate detecting method of random vibration of isolation mounting - Google Patents

Abstract

A kind of accurate detecting method of random vibration of isolation mounting may further comprise the steps: on earthquake isolating equipment to be detected, build an interferometer; 2. on described interferometer, take system's interferogram, 3., take the digital interference pattern of another system again through after the time interval with a digital camera; 4. two digital interferograms are read in the computing machine and go, through Fourier transform, first-order diffraction item and conjugation item thereof in that the spectrum space acquisition separates take out first-order diffraction item or its conjugation item with digital filtering method, can obtain the phase information of two interferograms again through inverse Fourier transform; 5. two positions will taking out distribute mutually and carry out digital subtraction, can obtain the phasic difference distribution plan of random vibration of isolation mounting; 6. differ amplifying method with digit order number again and amplify, the phasic difference distribution plan that has obtained to amplify, for amplifying N bar graph doubly, measuring accuracy can reach λ/N, obtains the size of device random vibration thus.

Description

The accurate detecting method of random vibration of isolation mounting

Technical field

The present invention relates to earthquake isolating equipment, particularly a kind of accurate detecting method that utilizes digital phase difference amplification to carry out random vibration of isolation mounting.

Background technology

In various accurate detections, particularly optical precision detects, (comprising electron interferometer, neutron interferometer, intervening atom art etc.), electron microscopy, photoetching technique, preparing grating or the like are measured in for example holographic detection, interference, all need the shockproof platform of high stability.

And this piece soil of our underfooting is all bearing outside various disturbances all the time.As the automobile that runs quickly outside window, the machine of heavy running, the hasty step of making a return journey, everything is all on the ground of shaking us, though what sensation they almost do not have for we crowd, for the detection of precision, it is destructive that this interference has just become, to such an extent as to can't work.In order to prevent this disturbance, various vibration abatements have been developed for many years.Vibration for these vibration abatements rises and falls, and measure with interferometer usually, yet measuring accuracy can only reach λ/20, and λ is a wavelength, and this still can not practical requirement.

Summary of the invention:

The problem to be solved in the present invention is to remedy the deficiency of above-mentioned technology formerly, and a kind of accurate detecting method of random vibration of isolation mounting is provided.This method should be simple and easy to do, and it is highly sensitive to survey magnitude of vibrations, its precision can reach nanometer scale or more than.

The essence of technical solution of the present invention is to utilize two digital interferograms, and fetch bit phase information from interferogram is carried out digital subtraction, carries out the numeral amplification again, thereby measures the size of random vibration of isolation mounting.

A kind of accurate detecting method of random vibration of isolation mounting is characterised in that this method may further comprise the steps:

1. on earthquake isolating equipment to be detected, build a Mach-Zehnder interferometer or other interferometer;

2. on described interferometer, take system's interferogram that the carrier fringe of certain space frequency is arranged with a digital camera, the spatial frequency of this carrier fringe should be adjusted to and can guarantee that image is when being converted into Fu Li leaf spectrum space, its frequency spectrum is not overlapping (referring to technology: Kou Leigang formerly, Chen Jianwen, the electronic holographic art,＜Proceedings in Physics 〉, 15 (4), 1995,330-390);

3. through after the time interval, take the digital interference pattern of another system again;

4. two digital interferograms are read in the computing machine and go, through Fourier transform, first-order diffraction item and conjugation item thereof in that the spectrum space acquisition separates take out first-order diffraction item or its conjugation item with digital filtering method, can obtain the phase information of two interferograms again through inverse Fourier transform;

5. two positions will taking out distribute mutually and carry out digital subtraction, can obtain the phasic difference distribution plan of random vibration of isolation mounting;

6. differ amplifying method with digit order number again and amplify, the phasic difference distribution plan that has obtained to amplify, for amplifying N bar graph doubly, measuring accuracy can reach λ/N, obtains the size of device random vibration thus.

The present invention compares the advantage that is had with technology formerly:

1) simple to operate, adopt digitalized intervention and digital amplifying method, avoid systematic error and the personal error introduced in the optics amplification process, and improved efficient.

2) do not have specific (special) requirements to measuring used optical element, just can obtain very high accuracy of detection with common interferometer.

Description of drawings

Fig. 1 is the phasic difference distribution plan without system's random vibration of amplifying.

Fig. 2 is after phasic difference is amplified 100 times, the phasic difference distribution plan of system's random vibration.

Embodiment

The invention will be further described below in conjunction with embodiment, but should not limit protection scope of the present invention with this.

The present invention is undertaken by following 6 steps:

1) on earthquake isolating equipment to be detected, builds a Mach-Zehnder (M-Z) interferometer;

2) on interferometer, take an interference pattern that has the certain frequency striped with a commercially available digital camera;

3) after process several seconds or a few minutes interval, take the interference pattern of another system again;

4) two digital interferograms are read in the computing machine go, through the Fourier transform process, diffraction terms at different levels and conjugation item thereof in that spectrum space can obtain to separate take out first-order diffraction item or its conjugation item, and it is carried out the phase information that inverse Fourier transform can obtain two interferograms.

The position phase distributed digital loop of two interferograms that 5) will take out is subtracted each other, and promptly obtains the phasic difference distribution plan of system's random vibration, as shown in Figure 1;

6) and then amplify, the phasic difference distribution plan after obtaining to amplify, as shown in Figure 2, enlargement factor reaches 100 times here.Can draw the random vibration error thus is 10 nanometers.

Principle of work of the present invention is as follows:

According to the interference strength formula, the intensity distributions of interferogram can be write as:

I(x，y)＝a(x，y)+b(x，y)cos(2πf ₀x+(x，y)) (1)

Here suppose that carrier fringe is parallel to the y axle.So-called carrier fringe is not exactly when placing testing sample, by the interference fringe that interferometer directly obtains, f ₀Be carrier frequency, f ₀=1/d, d are the spacing of carrier fringe.(x is the phase migration that the random vibration of system produces incident light wave y) to , and (x y) is bias light intensity to a, and (x y) is the contrast of image to b.By following formula as can be known, interferogram is that the position of the random vibration of system distributes mutually and is superimposed on carrier fringe and forms, and promptly the position of system vibration distributes mutually and makes carrier fringe generation deviation, the circle of equal altitudes that distributes mutually corresponding to device random vibration position.

Distribute mutually and the carrier fringe formation that is superimposed because interferogram is the position of device random vibration, the phase change digital subtraction with twice random vibration of different time causes just can draw the phasic difference distribution, draws the random vibration error amount of system thus.Provide a kind of Fourier transformation method below and achieve this end, this method is applicable to phase migration , and (x is y) less than the situation of 2 π.

We are rewritten into following exponential form with (1) formula:

I(x，y)＝a(x，y)+c(x，y)exp(i2πf ₀x)+c ^*(x，y)exp(-i2πf ₀x) (2)

Wherein,

(2) formula is carried out one-dimensional Fourier transform to be obtained:

$I_F(f,y)=a_F(f,y)+c_F(f-f_0,y)+c_F^{*}(f+f_0,y)---\left(4\right)$

From (4) formula as can be known, interference field forms three equidistant crests in Fourier's frequency domain, and their distances each other are f ₀The right and left crest correspond respectively to the 3rd and second of (2) formula, these two crests contain the position phase distributed intelligence of object under test.We can take out one of them crest separately, and it is made the one dimension inverse Fourier transform, and (x y), just can obtain the position distribution mutually of every interferogram again according to (3) formula to obtain c.Two interference fringe pictures that certain interval of time is taken carry out above-mentioned processing respectively, the phasic difference that two phase functions just can obtain system's random vibration as calculated behind the machine digital subtraction distributes, position phase distribution function be multiply by amplification factor N, just can obtain phasic difference and amplify N bar graph doubly, the desirable positive integer of N.Detection accuracy is λ/N, and λ is for interfering wavelength.

Claims (2)

1, a kind of accurate detecting method of random vibration of isolation mounting is characterised in that this method may further comprise the steps:

1. on earthquake isolating equipment to be detected, build an interferometer;

2. take system's interferogram that the carrier fringe of certain space frequency is arranged with a digital camera on described interferometer, the spatial frequency of this carrier fringe should be adjusted to and can guarantee image when being converted into Fu Li leaf spectrum space, and its frequency spectrum is not overlapping;

3. through after the time interval, take the digital interference pattern of another system again;

4. two digital interferograms are read in the computing machine and go, through Fourier transform, first-order diffraction item and conjugation item thereof in that the spectrum space acquisition separates take out first-order diffraction item or its conjugation item with digital filtering method, can obtain the phase information of two interferograms again through inverse Fourier transform;

5. two positions will taking out distribute mutually and carry out digital subtraction, can obtain the phasic difference distribution plan of random vibration of isolation mounting;

6. differ amplifying method with digit order number again and amplify, the phasic difference distribution plan that has obtained to amplify, for amplifying N bar graph doubly, measuring accuracy can reach λ/N, obtains the size of device random vibration thus.

2, the accurate detecting method of random vibration of isolation mounting according to claim 1 is characterised in that described interferometer is a Mach-Ceng Deer interferometer.

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