CN1438468A - Equal-rise coefficient-comparison digital damage-free detection system for detecting large curvature radius - Google Patents

Abstract

The invention is a non-contact measurement technology, and the digital non-destructive detection system of the iso-sagittal coefficient comparison method is especially suitable for the measurement of various wide-range and large-curvature radii. Using the laser polarization interference system to produce non-contact Newton rings, combined with CCD image processing technology, the measurable radius of curvature is 1-25 meters, with a wide measurement range, non-contact measurement will not damage the high Precision surface, and can test concave and convex spherical surfaces with arbitrary reflectivity, and the test architecture is very compact. Interference fringes can be automatically and quickly obtained measurement results after computer data processing.

Description

Etc. rise coefficient relative method digitizing Non-Destructive Testing larger radius of curvature detection system

Technical field

The present invention is a kind of optical detection system of novelty, is specially adapted to the measurement of all kinds of wide region larger radius of curvature etc. rise coefficient relative method digitizing nondestructive detection system.

Background technology

The measurement of sphere curvature radius has contact and contactless with regard to its measuring method.Generally the measurement to small curvature radius has sphere template method, ball warp instrument method and auto-collimating microscope method, and the curvature of general laser resonant cavity is partly all bigger, and especially the scope of radius-of-curvature variation is also increasing, as from 1-25 rice or bigger.Measure for larger radius of curvature, have generally that auto-collimator method, knife method, newton are around-France, laser spherical interferometer method and a More's deviation art method.These methods can be measured the radius-of-curvature of a certain scope, though some method has degree of precision, more limitation is arranged, and structure are all huger.

The mathematic(al) mode that Newton ring is measured is to measure the radius of its interference ring, for larger radius of curvature, test can reach higher precision, have and utilize non-contacting Newton's Ring method for testing, it is to adopt image apart from 1: the 1 optical interference imaging system that satisfies 2f, and Newton ring is carried out artificial interpretation, precision is 0.5%, though it has reached non-contacting measurement purpose, measuring speed is slow, and efficient is low.Want the fast digital processing then must have and the corresponding high resolving power of tested bore, bigbore digital imaging device as 1: 1 imaging system, still having any problem at present.

Summary of the invention

The objective of the invention is to study a kind of brand-new measuring system, is prerequisite with the measurement of noncontact Newton ring, utilize one be skillfully constructed, succinct scanning system, with CCD imaging and computer data is handled and interpretation combines new method.Not only measurement range is big for it, and can non-contact detecting the concave, convex sphere, be not too harsh to environment requirement simultaneously, be simple in structure, easy to use, a novel non-contacting measuring system of radius-of-curvature real-time.

The optical principle of larger radius of curvature measuring system

As shown in Figure 1, the He-Ne laser beam is vertically injected a polarization spectroscope (PBS) behind beam-expanding collimation, reflected light is injected reference surface, transmitted ray is behind a pentaprism, return after vertically injecting plane was seized, dredge the close donut in limit in behind polarization spectroscope PBS, forming, again through the imaging system imaging on the CCD array, for adapting to the tested surface of different reflectivity, use polarized systems, rotate the light intensity of 1/2 wave plate scalable twin-beam, be i.e. P, S component by PBS, make to obtain better fringe contrast, the measurement equation is: $R=\frac{r^2}{\mathrm{N\λ}}$ Or $R=\frac{{r_2}^2-{r_1}^2}{(N_2-N_1)\mathrm{\λ}}----\left(1\right)$

R in the formula _i---the radius of corresponding a certain Crape ring;

N---the fringe order at this relative center of Crape ring;

λ---wavelength.

Because the non-cpntact measurement center may not be zero level, therefore must calculate with the back formula of two Crape ring radiuses.In the test, at first debug out desirable interference fringe, Fig. 2 (a) is to utilize Fig. 1 system to resemble the noncontact Newton ring image that obtains on the face at CCD (b), data acquisition system (DAS) is carried out image acquisition and storage to first width of cloth interferogram shown in Fig. 2 (a) earlier, determine the O point by computer interpretation, the pentaprism scanning system moves along being parallel to the incident light axis direction then, light beam is along tested spherical scanning, this moment, fringe center O point moved on to that O ' locates shown in Fig. 2 (b), in like manner computer interpretation is determined O ' point, and the number of picture elements between the OO ' is P _lSimultaneously, the precision length measurement system measures the actual displacement l of pentaprism system in scanning.Equation (1) can be written as thus: $R=\frac{{r_2}^2-{r_1}^2}{(N_2-N_1)\mathrm{\λ}}=\frac{K^2({P_{r_2}}^2-{P_{r_1}}^2)}{(N_2-N_1)\mathrm{\λ}}$ $=\frac{{\left(\frac{l}{p_1}\right)}^2({P_{r_2}}^2-{P_{r_1}}^2)}{(N_2-N_1)\mathrm{\λ}}----\left(2\right)$ In the formula: l---the distance of OO ', corresponding CCD number of picture elements P _l

K---object plane length value with resemble the scale-up factor that the face prime pair is answered ---the number of picture elements between i corresponding Crape ring

Scanning can have two kinds of forms: one is the described pentaprism scanning system of Fig. 1 (a).Also can use the form of Fig. 1 (b).Replace pentaprism with catoptron, and sample is scanned and measure displacement l.Adopting the prerequisite of sample scanning is to have a precision to move guiding systems, otherwise the nonlinearity of guide rail will make sample inclination, can not return along former road thereby make along the reflection ray at plane was seized center, on the CCD imaging surface, introduce error, also make simultaneously the metering of l introduce the single order Abbe error, and the characteristics of pentaprism scanning system are: to go into, emergent ray (this mainly is to be decided by the precision of the machining angle of pentaprism) basically all the time at an angle of 90.Therefore in the scanning process, influence is insensitive to the guide rail nonlinearity along the reflection ray at plane was seized center, and then the reflection ray at center returns along former road all the time.So just can avoid in accurate the calculating because the single order Abbe error that the guide rail nonlinearity is introduced the measuring accuracy of assurance l.

The characteristics of this interference testing system are that reference surface and plane was seized place same direction, and lean on very closely as far as possible, to suppress external environmental interference effectively, the contact of Newton method is modified into non-cpntact measurement, in order to avoid face shape is impaired, simultaneously can survey concave surface again, pentaprism scanning precision length measurement system combines with CCD fringe location technology, can make a series of data processing and interpretation with computing machine.

In the measurement, press the definite tested surface bores of rise measurement such as approaching according to different radius-of-curvature, make and be projected in CCD and resemble an amount of striped is arranged on the face, mainly be to handle for the discretize of following interference image to satisfy sampling theorem and fitting of a polynomial, like this for the tested sphere of different radii, imaging system is varifocal to have an amount of fringe number to satisfy on the CCD, so that the data processing of the analytical method of interference fringe and interpretation.As to R=25 rice the time, when beam size is 25mm, nearly 10 stripe are arranged then in the visual field, help the data processing of image.

The digitized processing of stripe image

After the interference image CCD sampling and A/D conversion that above-mentioned optical system produces, along the resulting ideal curve in interferogram center.This group is dredged the discrete pattern that the limit changed by the cosine rule in each close cycle in directions X stretches.By (2) formula as can be known, must obtain the radius of any two Crape rings.Observe pattern, similar with parabolical shape in each cycle.Consideration is in the interference fringe by stages at adjacent Feng Yifeng and carries out fitting of a polynomial, makes discrete pattern serialization, ask after the extreme value can with the exact value to N Crape ring, finally try to achieve R.

In the actual measurement, resulting data also include noise except that information.This shows as fluctuation and burr in the gray-scale map of interference fringe.Fig. 3 (a) is the discrete data figure that measures.As seen bigger noise is arranged, therefore can't determine fit interval in the above-mentioned data fitting, and interval wrong, will influence fitting of a polynomial, make the extreme point displacement of Crape ring.In the data processing, utilize the digital filter of gliding smoothing method, the elimination random noise obtains more smooth discrete data figure, and its equation is: $Y_j\left(n\right)=\frac{1}{N}\underset{i=-m}{\overset{m}{\mathrm{\Σ}}}{X}_{j+i}\left(n\right)----\left(3\right)$

Counting of N in the formula---average data point, N=2m+1;

X _J+i(n)---the data value that different j are ordered;

Y _j(n)---the mean value that i=0 is ordered.In the processing to Y _j(n) adopt at 9 smoothly, obtain transport function by transform, its frequency response: $H\left(e^{\mathrm{j\ω}}\right)=\frac{1}{5}[\cos 4\left(\mathrm{\ω}\right)+\cos 3\left(\mathrm{\ω}\right)+\cos 2\left(\mathrm{\ω}\right)+\cos \left(\mathrm{\ω}\right)+1]----\left(4\right)$

As seen be equivalent to a low-pass filter, it is that the smoothing effect of noise is very obvious to high fdrequency component.And Newton ring is the low frequency variations rule, is not subjected to the influence of wave filter.Fig. 3 (b) be with digital filter obtain smooth after discrete data figure, this figure meets the para-curve Changing Pattern in one-period.Interpretation interval in data processing is used in each is interval: Y (x)=a ₀+ a ₁X+a ₂x ²(5) formula (5) match in each cycle, corresponding normal equation (being weighted to 1) is: $\left[\begin{array}{ccc}9& {\mathrm{\Σx}}_i& {{\mathrm{\Σx}}_i}^2\\ {\mathrm{\Σx}}_i& {{\mathrm{\Σx}}_i}^2& {{\mathrm{\Σx}}_i}^3\\ {{\mathrm{\Σx}}_i}^2& {{\mathrm{\Σx}}_i}^3& {{\mathrm{\Σ}}_i}^4\end{array}\right]\left[\begin{array}{c}{a}_0\\ a_1\\ a_2\end{array}\right]=\left[\begin{array}{c}{\mathrm{\Σy}}_i\\ {\mathrm{\Σx}}_i{y}_i\\ {{\mathrm{\Σx}}_i}^2{y}_i\end{array}\right]----\left(6\right)$ The summation ∑ is in the formula

Write a Chinese character in simplified form.Separating this system of equations with elimination method can be in the hope of a ₀, a ₁, a ₂Fringe center is at light distribution minimal value place.Order $\frac{\mathrm{dy}}{\mathrm{dx}}=0,$ Can get certain interval dark line centre coordinate: $x_i=-\frac{a_1}{{2a}_2}i=\mathrm{1,2,3},K----\left(7\right)$

Then encircle radius:

r _i＝|x _i-x ₀|·K (8)

X in the formula (7) (8) ₀Be the coordinate of central point, X _iBe through the exact position of the extreme point on continuous function of over-fitting, can be accurate to 1/5～1/10 pixel, final radius-of-curvature can be obtained by the average of M permutation and combination after any two the ring radius calculation in N in the visual field the ring: $\stackrel{\‾}{R}=\frac{1}{M}\underset{i=1}{\overset{M}{\mathrm{\Σ}}}{R}_i=\frac{1}{M}\underset{1}{\overset{M}{\mathrm{\Σ}}}\left(\frac{{r_i}^2-{r_j}^2}{(N_i-N_j)\mathrm{\λ}}\right)----\left(9\right)$

Fringe order i, j=1,2,3, Λ N i ≠ j;

Because radius-of-curvature is the average of a plurality of R, aforementioned calculation can also reduce because the measuring error of the radius-of-curvature that local deformation is introduced.

The error analysis of system

The main source of error of this method of testing and final relative accuracy Δ R/R can carry out differential to (2) formula and (annotate: r ₁With r ₂Measuring error be identical) obtain: $\mathrm{\ΔR}=\±\sqrt{2}\sqrt{{\left(\frac{\∂R}{\∂l}\right)}^2{\mathrm{\Δl}}^2+{\left(\frac{\∂R}{{\∂P}_l}\right)}^2{{\mathrm{\ΔP}}_l}^2+{\left(\frac{\∂R}{{\∂P}_r}\right)}^2{{\mathrm{\ΔP}}_r}^2+{\left(\frac{\∂R}{\∂\mathrm{\λ}}\right)}^2{\mathrm{\Δ\λ}}^2}----\left(10\right)$ Because the error of wavelength is a second order a small amount of, ignores, and then can derive: $\frac{\mathrm{\ΔR}}{R}=\±2\sqrt{2}\sqrt{{\left(\frac{1}{l}\right)}^2{\mathrm{\Δl}}^2+{\left(\frac{1}{P_r}\right)}^2{{\mathrm{\ΔP}}_r}^2+{\left(\frac{1}{P_l}\right)}^2{{\mathrm{\ΔP}}_l}^2}----\left(11\right)$

Can find out that from (11) formula the parameter relevant with relative error has: the degree of accuracy Δ l of displacement l; With dark line radius r and the relevant parameter P of displacement l _r, P _lWith their bearing accuracy Δ P _r, Δ P _lAs seen, l, P _r, P _lGetting greatly then, error can reduce.

Owing to utilized the pentaprism scanning system, go into, the angle of emergent ray decide by the machining precision of pentaprism, so requires greatly to reduce for the nonlinearity that moves guiding systems.As control the error delta l=1 μ m of precision length measurement system, with image digitization sampling grid N ₁* N ₁Relevant pixel value is got p _r=p _l=320, the positioning error of dark line ${\mathrm{\ΔP}}_r={\mathrm{\ΔP}}_l=1/5~1/10$ Pixel.With above-mentioned parameter substitution (11) Shi Kede

R＝3m $2l=3\mathrm{mm},\frac{\mathrm{\ΔR}}{R}=0.00156$

R＝25m $2l=10\mathrm{mm},\frac{\mathrm{\ΔR}}{R}=0.00128$ Can get all the other R's

All less than 0.2%, theoretical analysis has higher relative accuracy.

Preliminary experiment result and analysis

The bore of CCD face battle array is 1/3 inch, adopts the picture dot behind image digitization to count p _r=p _l〉=320.To the radius-of-curvature of a laser resonant cavity with Fig. 1 (a) (b) two kinds of scanning systems measure and relatively.Fig. 2 (a) (b) be scanning before and after two width of cloth interferograms.Fig. 2 (c) is the desirable curve map in Newton ring center excessively along X-axis.Fig. 3 (a) is the discrete data figure along the Newton ring center that measures.Fig. 3 (b) utilizes the digital filter elimination random noise of gliding smoothing method to obtain smooth discrete data figure.On the basis of Fig. 3 (b), utilize equation (5)～(9) formula to carry out data processing.Table 1 is that two kinds of systems are respectively the measurement result of radius-of-curvature of the laser resonant cavity of 1m and 2m to nominal size.

The measurement result of table 1 radius-of-curvature and comparison

The scanning of sample scanning R=1m pentaprism

1.044 1.941

Measured value (m) 1.137 2.070

1.181 2.004

Average R (m) 1.112 2.004

Relative error 11.2 0.2

ΔR/R(％)

As seen from Table 1, plane mirror is fixed and the radius-of-curvature value of its measurement of system that sample scanning is moved is all bigger than normal, this is because the influence of single order Abbe error, promptly moves the nonlinearity of guiding systems and causes the direction of guide rail moving direction and tested standard flat inconsistent, and a tiny inclination angle is arranged.Then the value of l is always greater than the OO ' of reality, make the measurement result of radius-of-curvature also bigger than normal, and scanning system is when scanning, the amount of movement of pentaprism is consistent with being projected on the tested surface, and this is that the moving direction of length measurement system is consistent with pentaprism incident ray direction by the character decision of pentaprism, eliminated Abbe error, the value of measuring of relative theory as a result varies, and meets the regularity of distribution of error in the metering, with accord with theoretical analysis.

This system combines with the around-France and modern CCD interference fringe of noncontact newton analytical method measurement technology, has higher relative accuracy, it is big to survey range of curvature radius, not limited by the concave, convex face, the apparatus structure compactness, especially do not need with radius isometric move guiding systems and dark room conditions, the not harsh sampled data of utilizing repeatedly of environmental requirement is handled, reduction system random noise, the automaticity height.Be specially adapted to the especially measurement of high precision laser resonator cavity of all kinds of larger radius of curvature.

Embodiment

Embodiment 1

The optical system of radius measurement of the present invention as shown in Figure 1, the He-Ne laser beam is vertically injected a polarization spectroscope PBS after expanding bundle, reflected light is injected reference surface, transmitted ray is behind a pentaprism, return after vertically injecting plane was seized, dredge the close donut in limit in behind PBS, forming, again through the imaging system imaging on the CCD array.For adapting to the tested surface of different reflectivity, use polarized systems, the light intensity of scalable twin-beam, rotate 1/2 wave plate, can regulate P, S component, make to obtain better treaty contrast, can carry out the high precision non-contact detecting the concavo-convex spherical radius of 1～25 meter of long radius-of-curvature by PBS.

Rise coefficient relative method digitizing Non-Destructive Testing larger radius of curvature systems such as utilization, the Newton ring that optical system is produced combines with the least square method fitting of a polynomial technology of computer data image processing, utilize computing machine according to measuring principle establishment automatic interpretation software, finally try to achieve larger radius of curvature R.

Embodiment 2

The combination of polarization light path system and sample scanning system is as Fig. 1.0.6328 the He-Ne linearly polarized laser bundle of μ m is behind rotatable 1/2 wave plate, behind collimator and extender, inject polarization spectroscope PBS again, rotate the P of 1/2 wave plate scalable light beam, the size of S component, perpendicular to the S component of principal section vibration along the path quarter wave plate---reference mirror---again through quarter wave plate, polarized component half-twist and see through polarization spectroscope PBS, in like manner---plane was seized---reflected by PBS through quarter wave plate rear polarizer component half-twist the P component again through quarter wave plate along the road.Two vertical components form interference behind analyzer, interferogram is accepted by CCD behind imaging lens.In the detection, shown in Fig. 1 (b), only need mobile plane was seized, move guiding systems and correctly write down the length l that sample moves, data handling system calculates the number of picture elements that CCD goes up corresponding amount of movement, according to formula, just can obtain corresponding scale-up factor K.This system moves guiding systems and will have rectilinearity preferably for reducing Abbe error.

Embodiment 3

The combination of polarization light path system and pentaprism scanning system.Same in the polarization light path of embodiment 2, replace sample scanning with pentaprism scanning, shown in Fig. 1 (a), promptly sample is fixed, and mobile pentaprism scans sample, equally can be in the hope of scale-up factor K.Because the going into of pentaprism, emergent ray are basically all the time at an angle of 90, therefore insensitive to the nonlinearity that moves the guiding systems guide rail, can improve measuring accuracy.

Embodiment 4

The combination of unpolarized light path system and sample scanning system.In embodiment 2, when the reflectivity of plane was seized and reference surface near the time can adopt unpolarized system, promptly can save these polarizers of 1/2 wave plate, quarter wave plate and analyzer, substitute polarization spectroscope with common spectroscope.0.6328 the He-Ne laser beam of μ m is injected common spectroscope BS behind collimator and extender, the one tunnel sees through BS after the reference mirror reflection; In like manner another road is reflected by BS after the plane was seized reflection again, and two-beam is assembled the back and formed interference, and the radius-of-curvature interferogram is accepted by CCD behind imaging lens.In the detection, shown in Fig. 1 (b), only need mobile plane was seized, move guiding systems and correctly write down the length l that sample moves, data handling system calculates the number of picture elements that CCD goes up corresponding amount of movement, according to formula, just can obtain corresponding scale-up factor K.

Embodiment 5

The combination of unpolarized light path system and pentaprism scanning system.Same in the unpolarized light path of embodiment 4, replace sample scanning with pentaprism scanning.Be that sample is fixed, mobile pentaprism scans sample, equally can be in the hope of scale-up factor K.Because the going into of pentaprism, emergent ray are basically all the time at an angle of 90, therefore insensitive to the nonlinearity that moves the guiding systems guide rail, can improve measuring accuracy.

Claims (8)

1, a kind of optical detection system of radius measurement, as shown in Figure 1.It is characterized in that after expanding bundle, vertically injecting a polarization spectroscope PBS with the He-Ne laser beam, reflected light is injected reference surface, transmitted ray is behind a pentaprism, return after vertically injecting plane was seized, dredge the close donut in limit in behind polarization spectroscope PBS, forming, resembling on face (CCD) array through the imaging system imaging again, utilize polarized systems, the light intensity of scalable twin-beam, rotate 1/2 wave plate, regulate P by polarization spectroscope PBS, the S component, make and obtain better fringe contrast, the Newton ring that optical system is produced combines with computer data image processing and least square method fitting of a polynomial technology, utilizes computing machine according to measuring principle establishment automatic interpretation software, and rise coefficient relative method digitizing nondestructive detection systems such as utilization are finally tried to achieve radius of curvature R.

2, detection system according to claim 1 is characterized in that detection system utilizes optics two-beam interference method to produce the noncontact Newton ring.

3, detection system according to claim 1 is characterized in that the long radius-of-curvature of rise coefficient relative method detection such as utilization.

4, according to claim 1 or 3 described detection systems, it is characterized in that the plane was seized of different radii can go up the interference Newton ring that forms suitable equivalent at imaging surface (CCD), be convenient to data processing.

5, according to claim 1 or 4 described detection systems, it is characterized in that utilizing scanning system to ask for object plane scanning movable length l and the corresponding scale-up factor K of the face of resembling (CCD) number of picture elements, foundation as interpretation interference ring Crape ring position not at the same level time is used for the calculating of radius of curvature R.

6, detection system according to claim 1 or 5 is characterized in that adopting two kinds of scanning systems to ask for scale-up factor K.

7, detection system according to claim 6 is characterized in that one is the scanning system that sample directly moves, and another is fixed for sample, five rib rib motion scan systems.

8, detection system according to claim 1 is characterized in that and can carry out the high precision non-contact detecting to the concavo-convex sphere of 1～25 meter of long radius-of-curvature.

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