CN104515482A - Interference fringe widening method for white-light interferometer - Google Patents

Abstract

The invention relates to an automatic interference fringe widening method for a white-light interferometer in the field of optical detection. Operation difficulty is lowered, workload is relieved, and measurement efficiency is improved. The method includes implementation steps: firstly, adjusting the white-light interferometer until fringes are positioned at the center of a screen; secondly, calculating fringe strength of four subareas of the screen; calculating fringe directions of the subareas with higher-strength fringes; making a virtual straight line along the fringe direction of each of the two areas through the center, and calculating a screen coordinate of an intersection point; converting the screen coordinate into practical position deviation, and controlling a lens swing angle according to a curvature radius of an element; repeating the process until the fringes meet measurement requirements. By adoption of the image processing techniques, no extra sensor is needed, and simplicity in calculation and short adjusting period are realized; for general fringes, measurement requirements can be met after adjustment for 3-5 times.

Description

White light interferometer interference fringe method for widening

Technical field

The present invention relates to technical field of optical detection, be specifically related to a kind of white light interferometer interference fringe method for widening.

Background technology

Optics light part surfaceness adopts white light interferometer to detect usually.But because the sensing range of white light interferometer is very little, usually at a mm, so in order to obtain more real optical surface roughness information, usually getting multiple sampled point on surface and being averaging processing, and as final surperficial roughness measurement result.

So, each surface all needs measurement tens to tens sampled points, if when measured surface is curved surface (sphere, aspheric surface, free form surface), each point has needed the links such as contraposition, striped broadening, repetitive measurement, thus causes the measurement inefficiency of optical surface roughness.

At this wherein, interference fringe broadening is a very important link.Usually, in white light interferometer, striped broadening has been come by manual adjustments.Tester is by observing the stripe information such as shape, density, position of interference fringe, then the two-dimentional inclination angle (for objective table tilting white light interferometer) of manual adjustments objective table or the pendulum angle (for object lens inclining formula white light interferometer) of camera lens, thus gradually striped broadening is measured after being adjusted to zero striped.But this process is not only consuming time longer, and depend critically upon the operating experience of tester.For beginner, this operation is very loaded down with trivial details, is often difficult to striped entirely on the center in both direction.Even if for skilled operator, completing tens striped broadenings on a surface is also huge workload, and in striped spreading process, takes the change of carving and paying close attention to striped, easily causes eyes uncomfortable.

Summary of the invention

For solving the usual manual adjustments of existing interference fringe method for widening, there is adjustment process loaded down with trivial details in the present invention, and workload is large and cause the problems such as eyes discomfort, provides a kind of white light interferometer interference fringe method for widening.

White light interferometer interference fringe method for widening, the method is realized by following steps:

Step one, adjustment white light interferometer camera lens and the measured optical unit surface between Distance geometry angle, make interference fringe be presented on screen;

Step 2, screen is evenly divided into four regions, calculates the fringe intensity in each region respectively;

Obtain the threshold value of fringe intensity in step 3, setting procedure two, the fringe intensity judging whether to exist two or more regions exceedes described threshold value, if not, then points out fringe intensity too low, and returns step one; If so, then step 4 is performed;

Step 4, ask for the stripe direction in two the highest regions of fringe intensity, and using the center in described two regions as the reference point of corresponding region, by making straight line along stripe direction respectively to two reference point, obtain the screen coordinate of two straight-line intersections;

Whether the screen coordinate of two straight-line intersections that step 5, determining step four obtain and the distance of screen center are less than predetermined value, if not, then calculate the angle that white light interferometer camera lens needs adjustment, and carry out angular setting, return step 2; If so, then determine that striped broadening meets the demands.

Beneficial effect of the present invention: the striped spreading process that the present invention is directed to white light interferometer, have employed image processing method, is calculated the correlation parameter of interference fringe, and is realized the automatic broadening of striped by the two-dimentional pivot angle of adjustable lens.This process has broken away from the use experience of operator, the efficiency of the striped broadening greatly improved and stability, also reduces use difficulty and the workload of instrument, more proper operation person's long-time operation simultaneously.

Embodiment

Embodiment one, white light interferometer interference fringe method for widening, the method is realized by following steps:

One, white light interferometer is adopted to measure the surfaceness of sphere.

1, first determine position, measured point, then regulate the Distance geometry angle between white light interferometer camera lens and measured surface, make interference fringe be presented in screen and mediate as far as possible.

2, then screen is evenly divided into upper left, lower-left, upper right, four, bottom right square region, and obtains the gray-scale map of each sub regions.Gray-scale map for each region does following computing:

A) for this region any point: its coordinate for (x, y), then the coordinate of its neighbouring 8 points, and, be respectively in the counterclockwise direction using wherein right-hand point as starting point: (x+1, y), (x+1, y-1), (x, y-1), (x-1, y-1), (x-1, y), (x-1, y+1), (x, y+1), (x+1, y+1), then this o'clock is along 0 °, 45 °, 90 °, the gray variance of 135 ° of four directions is:

d ₁₃₅(x，y)＝[I(x-1，y-1)-I(x+1，y+1)] ²×0.5

Wherein I (x, y) represents the gray scale at (x, y) some place.

B) in zoning, each point, along the variance sum of above-mentioned four direction, can carry out search with every behavior unit and add up.Then whole region is along 0 °, 45 °, 90 °, and the gray variance of 135 ° of four directions is:

$D_0(x,y)=\underset{(x,y)\∈S}{\mathrm{\Σ}}{d}_0(x,y)$

$D_{45}(x,y)=\underset{(x,y)\∈S}{\mathrm{\Σ}}{d}_{45}(x,y)$

$D_{90}(x,y)=\underset{(x,y)\∈S}{\mathrm{\Σ}}{d}_{90}(x,y)$

$D_{135}(x,y)=\underset{(x,y)\∈S}{\mathrm{\Σ}}{d}_{135}(x,y)$

Wherein S represents the region that will calculate.

C) then the fringe intensity in this region is: C (x, y)=(D ₀-D ₉₀) ²+ (D ₄₅-D ₁₃₅) ²;

3, set fringe intensity threshold value, if there are two or more region fringe intensities to exceed this threshold value, then select two regions that fringe intensity is the highest, go to step 4; If there are not two or more region fringe intensities to exceed this threshold value, then point out fringe intensity too low, and return step 1, the distance between adjustable lens and surface, make striped near the center of screen.

4, record two regions that in step 3, fringe intensity is the highest, be set to a-quadrant, B region.In A, B region, calculate the stripe direction in two subregions respectively, the computing method of stripe direction are as follows:

wherein D ₀, D ₄₅, D ₉₀, D ₁₃₅calculate in step 2, do not needed to recalculate herein.

The stripe direction that can obtain A, B region is like this respectively: θ _a, θ _b.If the central point of A, B square region is M, N, then M point does direction is excessively θ _avirtual line, crossing N point, to do direction be θ _bvirtual line, then calculate the screen coordinate (P of two straight-line intersections relative to screen centre position by elementary geometry _x, P _y).

5, the screen coordinate (P of this intersection point is judged _x, P _y), if this intersection point is to the distance of screen center be less than setting value, then can think that the work of striped broadening terminates.If this intersection point is greater than setting value to the distance of screen center, then regulate according to following steps:

A, the horizontal direction physical length l measured according to length in pixels L and the white light interferometer in screen level direction, the actual range obtaining the corresponding optical element surface of unit screen pixel is: this parameter is constant under identical object lens condition, can calculated in advance being stored among program.

B, be true origin with screen center, record the screen coordinate (P of two straight-line intersections _x, P _y), and the actual range calculating element surface corresponding to this intersection point screen coordinate is: R _x=kP _x, R _y=kP _y

C, radius-of-curvature r according to the measured optical unit, obtaining white light interferometer camera lens along the pendulum angle of A, B axle is:

6, send steering order to white light interferometer control system, camera lens is swung along A, B axle respectively and return step 1, continue to judge that whether striped is adjusted and put in place.Described A, B axle is that its direction meets the right-hand rule respectively around the turning axle that X, Y-axis rotate.

Method described in present embodiment calculates simple, and regulating cycle is shorter, for the striped of generalized case, can meet measurement requirement through 3 ~ 5 adjustments.

Claims (5)

1. the method for widening of white light interferometer interference fringe, is characterized in that, the method is realized by following steps:

Step one, adjustment white light interferometer camera lens and the measured optical unit surface between Distance geometry angle, make interference fringe be presented on screen;

Step 2, screen is evenly divided into four regions, calculates the fringe intensity in each region respectively;

Obtain the threshold value of fringe intensity in step 3, setting procedure two, the fringe intensity judging whether to exist two or more regions exceedes described threshold value, if not, then points out fringe intensity too low, and returns step one; If so, then step 4 is performed;

Step 4, ask for the stripe direction in two the highest regions of fringe intensity, and using the center in described two regions as the reference point of corresponding region, by making straight line along stripe direction respectively to two reference point, obtain the screen coordinate of two straight-line intersections;

Whether the screen coordinate of two straight-line intersections that step 5, determining step four obtain and the distance of screen center are less than predetermined value, if not, then calculate the angle that white light interferometer camera lens needs adjustment, and carry out angular setting, return step 2; If so, then determine that striped broadening meets the demands.

2. white light interferometer interference fringe method for widening according to claim 1, it is characterized in that, screen is evenly divided into four regions in described step 2, being specially and making level, vertical two straight lines along screen center, is upper left, lower-left, upper right, four, bottom right square region by screen divider.

3. white light interferometer interference fringe method for widening according to claim 1 and 2, is characterized in that, striped strength calculation method in described step 2, is specifically realized by following steps:

Any point coordinate of step 2 one, the arbitrary region set in four regions is as (x, y), the then coordinate of neighbouring eight points of this point, and, be respectively in the counterclockwise direction using wherein right-hand point as starting point: (x+1, y), (x+1, y-1), (x, y-1), (x-1, y-1), (x-1, y), (x-1, y+1), (x, y+1), (x+1, y+1), then this o'clock is along 0 °, 45 °, 90 °, the gray variance of 135 ° of four directions is:

d ₀(x，y)＝[I(x-1，y)-I(x+1，y)] ²

d ₄₅(x，y)＝[I(x-1，y+1)-I(x+1，y-1)] ²×0.5

d ₉₀(x，y)＝[I(x，y-1)-I(x，y+1)] ²

a ₁₃₅(x，y)＝[I(x-1，y-1)-I(x+1，y+1)] ²×0.5

Described in step 2 two, calculation procedure 21, region is along 0 °, 45 °, and the gray variance of 90 ° and 135 ° four directions, is formulated as:

$D_{\mathrm{angle}}(x,y)=\underset{(x,y)\∈S}{\mathrm{\Σ}}{d}_{\mathrm{angle}}(x,y)$

Wherein, angle is 0 °, 45 °, and 90 ° or 135 °, this region fringe intensity C (x, y) is: C (x, y)=(D ₀-D ₉₀) ²+ (D ₄₅-D ₁₃₅) ².

4. white light interferometer interference fringe method for widening according to claim 3, is characterized in that, the computing method of stripe direction in described step 4, are specially:

5. white light interferometer interference fringe method for widening according to claim 1, is characterized in that, described step 5 calculates the angle that white light interferometer camera lens needs adjustment, and detailed process is:

Step May Day, the horizontal direction physical length l measured according to length in pixels L and the white light interferometer in screen level direction, the actual range obtaining the corresponding optical element surface of unit screen pixel is:

Step 5 two, be true origin with screen center, record the screen coordinate (P of two straight-line intersections _x, P _y), and the actual range calculating element surface corresponding to this intersection point screen coordinate is: R _x=kP _x, R _y=kP _y

Step 5 three, radius-of-curvature r according to the measured optical unit, obtaining white light interferometer camera lens along the pendulum angle of A, B axle is: