CN1271086A - Schileren instrument for the measurement of body surface appearance - Google Patents

Abstract

The schlieren instrument includes a light source assembly and an optical imaging assembly; the light source assembly consists of a laser, a micropore filter and a beam expanding lens; and the optical imaging assembly consists of a spectroscope, a reflector, a collimating lens, a spatial filter and a CCD video camera, with the spatial filter being a two-dimensional Langchi grating. The present invention obtain the profile data in both x and y directions, has simplified struture and can be used to measure surface appearance of both static object and varying object.

Description

The schlieren of Measuring Object surface topography

The invention belongs to the object surface appearance field of measuring technique, relate in particular to the schlieren of the gradual surface topography of Measuring Object.

The light and shade of schlieren mensuration by optical projection changes the variation of indicating refractive index, reflectivity and transmissivity that testee surface irregularity or interior condition produced, therefore often is used to carry out rate of flow of fluid field analysis, solution concentration analysis, surface flatness analysis etc.Existing a kind of schlieren that is used to measure reflecting surface comprises: a pointolite, a spectroscope, a collimating mirror and an edge of a knife spatial filter.The light that pointolite sends is after the spectroscope beam split, and one the tunnel is radiated on the testee surface behind the collimating mirror collimation, and another road is imaged on the film viewing screen after then assembling.The light beam that reflects from measured surface is looking like on the plane through the spectroscope post-concentration again, if measured surface is a plane, folded light beam will be converged to an infinitesimal hot spot on as the plane.If reflecting surface is an irregular surface, its imaging then or be higher than or be lower than focus.Place an edge of a knife at the focus place, then this edge of a knife can block the folded light beam of a part.That part of light that is blocked can form dark fringe on film viewing screen, unbroken that part of light then forms bright fringes on film viewing screen, thereby just forms light and dark conoscope image on film viewing screen.Just can detect the partial parameters of measured surface from this figure.In essence, what schlieren detected is that surface elevation changes the graded on a direction (x), for obtaining on the other hand the variation on (y), the testee or the edge of a knife need rotate 90 degree, therefore the graded on x, the y direction must separately be measured, and its direction be can not determine.The disadvantage of this knife edge type schlieren method is: it is a kind of semiquantitative measuring method.

Contact and noncontact two classes are adopted in the measurement of object surface appearance usually, the most typical with the interference of light and deflection of light method in non-cpntact measurement.What interferometric method was measured is optical path difference, and the light intensity of each point and optical path difference are the relations of one-to-many on the interferogram, can not determine the pattern of measured surface according to an interferogram fully, therefore introduce phase-shifting technique in the interferometric method of being everlasting, calculate the phase place of each point with many interferograms, final reconstruct measured surface profile.The measurement of gradual surface topography also is an important measurement problem, and some crystal often need research and observe the variation of its concentration and the macroscopic view variation of surface topography in its growth course.Therefore the phase shift interference method is not suitable for measuring the surface topography of variation.Schlieren method and More's deflectometry are the deflection of light angles owing to what measure, it has not only comprised the size information of this slope, and comprised the slope symbolic information, therefore be suitable for measuring the pattern of dynamic surface, but need obtain the surface graded change information of two directions simultaneously.And as previously mentioned, no matter be the gradient information that schlieren method or More's deflectometry all can not obtain two directions simultaneously.

At W.L. Hao Weisi, " the rainbow formula is put the comparison of shadow instrument and Mach one Ceng Deer interferometer ", " applied optics ", 1985, the 24th volume, the 6th phase, a kind of schlieren that is used to detect the measured object surface flatness has been described in the 816-822 page or leaf, spatial filter wherein substitutes the edge of a knife with a color dish.The central area of dish is transparent, and first lap has first kind of color, and second circle is second kind of color, and other circle respectively has different colors.If measured surface is the plane, then the picture on the film viewing screen is a white; Otherwise then be different colors.Although can detect the graded that measured surface makes progress in Different Diameter simultaneously with this method, the shortcoming of this method be can not responsive measured surface tangential graded, be a kind of semiquantitative analytical approach therefore.

United States Patent (USP) the 4th, 854, introduced a kind of More's deflectometry in No. 708, it also is a kind of schlieren mensuration in essence, and its basic device is still the device of a schlieren, just substitute the knife edge device on the picture plane, and after as the plane, place two blocks of parallel Ronchi gratings, two blocks of gratings are at a distance of a talbot distance d, and the angle 0 that tilts mutually, thereby after light beam is through two blocks of gratings, then on film viewing screen, form light and dark Moire fringe.Measure the internal feature of measured surface scrambling or phase object thus.The amount that this method is measured concerning reflecting surface is the single order partial derivative of surface undulation height in essence, therefore for obtaining the derivative on two directions, needs two gratings or measured object half-twist.Therefore can not be used to measure the surface that changes medium or variation to bring some inconvenience part, especially this method of surface measurement.

At S. Ke Laien etc., " be used for the details in a play not acted out on stage, but told through dialogues formula schlieren microscope of in situ quantitation shadow " according to solution concentration profile around the grown crystal, " crystal growth magazine " 1997, the 179th phase, introduced a kind of quantitative measurment grown crystal dark field type schlieren microscope of solution concentration profile on every side in the 240-248 page or leaf, the basic device of this method is a schlieren, and an edge of a knife is set on the focal plane equally.The shortcoming of this method also is to obtain the concentration gradient of x, y direction simultaneously, therefore can not be used for the measurement of the very fast diffusion that changes,

The objective of the invention is for overcoming the weak point of prior art, a kind of schlieren of Measuring Object surface topography is provided, can obtain the face deformation gradient information on x, y two directions simultaneously, thereby simplified the structure of whole device, pattern that can not only the Measuring Object static surface, and can measure the pattern of surface variations.

The schlieren of a kind of Measuring Object surface topography that the present invention proposes, comprise light source part, the optical imagery parts, said light source part is made up of laser instrument and the small filter and the extender lens that are arranged on its output beam, said optical imagery parts are by the spectroscope that will carry out beam splitting through the light beam after extender lens expands bundle, receive the catoptron of this spectroscope beam reflected, receive the collimation lens of the light beam of this mirror reflects, and the spatial filter and the ccd video camera that receive the light beam of this spectroscope transmission are formed, it is characterized in that said spatial filter is a two-dimentional Ronchi grating.

Said laser instrument can be He-Ne laser instrument or semiconductor laser.Said collimation lens can adopt the anaberration non-sphere collimation mirror.Said two-dimentional Ronchi grating can be placed on the focal plane; Also can be placed on the appropriate location before, focal plane.Said ccd video camera can be the CCD area array camera.The present invention also can comprise and also comprise and be used for image acquisition and disposal system that picture signal is handled, said ccd video camera obtains the high speed image acquisition board of information of measured surface pattern and the microcomputer that this view data is handled is constituted by being used to gather in this system, said high speed image acquisition board links to each other with the interface of this microcomputer, and said microcomputer stores graphics process and Control Software.

Principal feature of the present invention is to substitute knife-edge method on as the spatial filter position on plane and place a two-dimentional Ronchi grating at traditional schlieren, be used to obtain at x, the gradient information of deformationization above y two directions, and can further adopt high speed image acquisition board that graphical information is carried out real-time sampling, thereby come the pattern of reconstruct measured surface, apparatus structure of the present invention is simple, but the pattern of Measuring Object static surface not only, and can measure the pattern on dynamic gradual surface.

Brief Description Of Drawings

Fig. 1 is a measuring method schematic diagram of the present invention,

Fig. 2 is the schematic diagram of measurement mechanism of the present invention,

Fig. 3 is the example structure synoptic diagram of measurement mechanism of the present invention,

Fig. 4 is the bidimensional Ronchi grating structural representation of present embodiment,

Fig. 5 is the PaintShop process flow diagram of present embodiment.

The structure embodiment of the formation of the schlieren of Measuring Object surface topography of the present invention, principle of work and device thereof is described in detail as follows in conjunction with each accompanying drawing.

The measuring principle that the present invention is based on Ronchi grating realizes by sampling with grating pair light the measurement at light deflection angle as shown in Figure 1.When measured surface 31 was the plane, reflection ray converged at a F through collimation lens 32, Ronchi grating 33, has according to triangle relation $\frac{\stackrel{\&OverBar;}{A^{\&prime;}{B}^{\&prime;}}}{\stackrel{\&OverBar;}{\mathrm{AB}}}=\frac{\stackrel{\&OverBar;}{B^{\&prime;}{C}^{\&prime;}}}{\stackrel{\&OverBar;}{\mathrm{BC}}},$ If the dutycycle of Ronchi grating 33 is 50%, what then obtain on 34 battle arrays of ccd video camera is that dutycycle is 50% square-wave signal, can be written as $I\left(x\right)={\mathrm{<figure-callout\; id="0"\; label="b"\; filenames="A0010737100101.png"\; state="\{\{state\}\}">b</figure-callout>}}_0+\underset{k=1}{\overset{\&infin;}{\mathrm{\&Sigma;}}}{b}_k\sin \mathrm{k\&omega;x}$ 。When measured surface had a tiltangle, reflection ray projected P point on the focal plane, met at the D point with CCD face battle array, and light and CCD face battle array meet at the D point during bias free, this moment can get Δ=D ' D " deviation, according to the diagram geometric relationship, have: $\frac{\stackrel{\&OverBar;}{E^{\&prime;}{E}^{\&prime;\&prime;}}}{\stackrel{\&OverBar;}{P^{\&prime;}{P}^{\&prime;\&prime;}}}=\frac{\stackrel{\&OverBar;}{D^{\&prime;}{D}^{\&prime;\&prime;}}}{\stackrel{\&OverBar;}{F^{\&prime;}P}},$

Δ=D ' D is then arranged "=Ztg (1)

Since =2 θ, then

Δ=Ztg2 θ (2) is so the grating projection just is converted to the tiltangle of measured surface the variation delta of fringe spacing in the optical grating projection.For asking the θ angle, adopt combined synchronous demodulation technique.

With the optical grating projection signal indication be $I\left(x\right)={\mathrm{<figure-callout\; id="0"\; label="b"\; filenames="A0010737100101.png"\; state="\{\{state\}\}">b</figure-callout>}}_0+\underset{k=1}{\overset{\&infin;}{\mathrm{\&Sigma;}}}{b}_k\sin [\mathrm{k\&omega;x}+{\mathrm{\&psi;}}_k\left(x\right)]$ ψ in the formula _k(x) for grating space changes the spatial frequency phase angle change that causes, I (x) is got fundamental frequency signal I through low-pass filtering ₁(x)=b ₁Sin[ω x+ ψ ₁(x)], ψ in (3) formula ₁(x) at sampled point x _iValue be ${\mathrm{\&psi;}}_1\left(x_1\right)=\frac{2\mathrm{\&pi;}}{d}\mathrm{\&Delta;}\left(x_1\right)----\left(4\right)$ D is the optical grating projection cycle in the formula.Formula (3) normalization is got:

I ₁(x)=sin[ω x+ ψ ₁(x)] (5) get synchronizing signal I _SynC (x)=cos ω x (6) multiplies each other formula (5) and formula (6): $I_1\left(x\right)I_{\mathrm{sync}}\left(x\right)=\frac{1}{2}\left\{\sin \right[2\mathrm{\&omega;x}+{\mathrm{\&psi;}}_1\left(x\right)]+\sin [{\mathrm{\&psi;}}_1\left(x\right)\left]\right\}----\left(7\right)$ Product is removed through low-pass filtering after the carrier signal of 2 frequencys multiplication $F\left(x\right)=\frac{1}{2}\sin \left[{\mathrm{\&psi;}}_1\left(x\right)\right]----\left(8\right)$ Formula (2) and formula (4) substitution formula (8) can be got: $\frac{2\mathrm{\&pi;}}{\mathrm{<figure-callout\; id="2"\; label="d\; ztg"\; filenames="A0010737100091.png"\; state="\{\{state\}\}">d</figure-callout>}}\mathrm{ztg}2\mathrm{\&theta;}=\arcsin \left[2F\left(x\right)\right]$ That is $\mathrm{\&theta;}\left(x\right)=\frac{1}{2}\left\{\frac{\mathrm{<figure-callout\; id="2"\; label="d"\; filenames="A0010737100091.png"\; state="\{\{state\}\}">d</figure-callout>}}{2\mathrm{\&pi;Z}}\arcsin \right[2F\left(x\right)\left]\right\}----\left(9\right)$ Can get the pitch angle of the pairing measured surface of optical grating projection signal of delegation thus along the x direction.Whole measured surface is then had $\mathrm{\&theta;}(x,y)=\frac{1}{2}\mathrm{arctg}\left\{\frac{\mathrm{<figure-callout\; id="2"\; label="d"\; filenames="A0010737100091.png"\; state="\{\{state\}\}">d</figure-callout>}}{2\mathrm{\&pi;Z}}\mathrm{arcSin}\right[2F(x,y)\}----\left(10\right)$ In like manner can get the pitch angle of the expression formula cotype (10) of y direction.Obtaining the broken tiltangle of surveying the pairwise orthogonal direction on surface _xAnd θ _yAfterwards, can obtain its slope tg[θ _x(x, y)] and tg[θ _y(x, y)], and then can obtain the relative height value of measured surface each point, i.e. surface topography by integration.

The composition of measurement mechanism of the present invention and principle are as shown in Figure 2, the laser beam of being sent by He-Ne laser instrument 1 expands bundle by extender lens 2, after small filter 3 is eliminated parasitic light, change the direction of propagation of its a part of light by spectroscope 4, change light path through plane mirror 7, behind aspheric surface collimation lens 8 collimations, be radiated on the tested liquid level 9 then, after this directional light is reflected by tested liquid level, return through spectroscope 4 by former road and once more light to be divided into two-way, wherein one the tunnel be focused on the focal plane, project to through spatial filter 5 on the photosensitive array of ccd video camera 6.

The general structure of a kind of embodiment of the present invention is made up of upper bush 12, lower sleeve 13, horizontal sleeve 14, upper pillar stand 15, lower pillar stand 16, intermediate plate 17, base plate 18, laser assembly 19 and guide rail 20 as shown in Figure 3.Each light path element shown in Figure 2 is installed in respectively in upper bush 12, lower sleeve 13, the horizontal sleeve 14.Upper pillar stand 15, lower pillar stand 16, intermediate plate 17 are used to connect upper bush 12 and lower sleeve 13 ' make it in aggregates.Ccd video camera 6 is placed on the guide rail 20.Regulate the horizontality of measured object with set screw 21.Whole instrument is fixed with gib screw 11.

Because measured object is gradual surface, therefore to obtain the variable signal of surface on x, y two directions simultaneously, the present invention adopts the bidimensional Ronchi grating to be used as spatial filter for this reason, a kind of example structure of bidimensional Ronchi grating as shown in Figure 4, this grating is the alternate bidimensional direct light grid of rectangular node shape, point.In one embodiment of the invention, the crystal growing surface of surface of surveying for slowly changing, its change frequency is about 1HZ, according to the signal sampling theorem, the length of side a of rectangular unit grid can be decided to be 0.25mm.

The present invention also can further comprise and is used for image acquisition and disposal system that picture signal is handled, this system is made of video camera, microcomputer and graphics process and Control Software, in one embodiment of the invention, video camera adopts the CCD B, and output signal is the CCIR standard.Camera speed was 25 frame/seconds continuously.Image pick-up card is the Pulsar black-white image grabbing card of Matrox company, and its picking rate is 8 A/D, 45MHZ; 10 A/D, 30MHZ, gathering full-size is 2048 * 2048 * 8.Adopt PaintShop to handle and to be used for controlling the whole operation process to the view data of gathering, the three-dimensional appearance of the last tested liquid level of reconstruct also is added on demonstration on display.

Fig. 5 is the PaintShop process flow diagram of present embodiment, is the pattern of reconstruct measured surface, and the present invention has taked a kind of technology of synchronous demodulation to obtain the pitch angle of surperficial each point, and then obtains surface topography.Concrete treatment step is as follows:

1, image pick-up card is made initialization process;

2, obtain optical image information with image pick-up card from ccd video camera:

3, use synchronizing signal I _Sync(x, y)=cos ω (x, y) respectively to x, the optical grating projection image of y two directions do synchronous demodulation with the surface tilt angle θ that obtains two directions (x, y);

4, obtain surperficial x, the slope of y two directions;

5, make integration by this slope information, try to achieve three-dimensional surface shape.

Claims (7)

1, a kind of schlieren of Measuring Object surface topography, comprise light source part, the optical imagery parts, said light source part is made up of laser instrument and the small filter and the extender lens that are arranged on its output beam, said optical imagery parts are by the spectroscope that will carry out beam splitting through the light beam after extender lens expands bundle, receive the catoptron of this spectroscope beam reflected, receive the collimation lens of the light beam of this mirror reflects, and the spatial filter and the ccd video camera that receive the light beam of this spectroscope transmission are formed, it is characterized in that said spatial filter is a two-dimentional Ronchi grating.

2, schlieren as claimed in claim 1 is characterized in that, said laser instrument is He-Ne laser instrument or semiconductor laser.

3, schlieren as claimed in claim 1 is characterized in that, said collimation lens adopts the anaberration non-sphere collimation mirror.

4, schlieren as claimed in claim 1 is characterized in that, said two-dimentional Ronchi grating is placed on the focal plane.

5, schlieren as claimed in claim 1 is characterized in that, said two-dimentional Ronchi grating is placed on the appropriate location before, focal plane.

6, schlieren as claimed in claim 1 is characterized in that, said ccd video camera is CCD and array camera.

7, as claim 1,2,3,4,5 or 6 described schlierens, it is characterized in that, also comprise and be used for image acquisition and disposal system that picture signal is handled, said ccd video camera obtains the high speed image acquisition board of information of measured surface pattern and the microcomputer that this view data is handled is constituted by being used to gather in this system, said high speed image acquisition board links to each other with the interface of this microcomputer, and said microcomputer stores graphics process and Control Software.

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