CN101408478B - Method and apparatus for measuring cofocal combined ultra-long focal distance - Google Patents

Abstract

The invention belongs to the technical field of optical precision measurement, and relates to a method for measuring super long focal length of a confocal combination lens and a device thereof. The method is as follows: firstly determining the focal position of a reference lens and the focal position of the combination of the measured lens and the reference lens according to the confocal focusingprinciple, measuring the distance delta between the two focal points and the distance d0 between the two lenses, and substituting the delta and the d0 into a formula to calculate the focal length value of the measured lens, a pupil filtering technique can also be used in the measurement to enhance the sensitivity of focal length measurement. The invention proposes that accurate focusing is realized by the characteristics that an object corresponds to the microscope objective focus when the confocal point responds to the maximum curve value, and extends the confocal microscopy principle to thesuper long focal length measurement field, and proposes the confocal focusing principle. The method combines the confocal focusing principle with the combination lens method, has the advantages of high measurement precision and strong anti-environment interference ability, and can be used for high-precision focal length measurement during the detection and assembly of the super-long focal length lens.

Description

Confocal combination ultra-long focal length measuring method and device

Technical field

The invention belongs to technical field of optical precision measurement, can be used for the detection of overlength focal length lenses and the high precision focometry in the assembling process.

Technical background

In recent years, the overlength focal length lenses is widely used in large-scale field of optical systems such as high-energy laser, astronomical telescope, and the processing of these type of large scale lens, detection and assembling have very high difficulty.As the important parameter of overlength focal length lenses, its focometry is a difficult point in optical measurement field always, and principal element is: numerical aperture is little, depth of focus is long, is difficult to realize accurately focusing; Focal length is long, is difficult to precision length measurement; Optical path length is measured and is subjected to environmental interference easily.Therefore, traditional method that focuses such as magnification method or pentaprism method is difficult to realize the high-acruracy survey of overlength focal length.

At ultra-long focal length measuring, domestic scholars has proposed new measuring method, and the document of delivering mainly comprises: " Taibo-Moire technique is measured the focal length of long-focus system " of " Chinese measuring technology "; " the accuracy limit research that Ronchi grating Talbot effect long-focus is measured " of " photon journal ".This type of technology has mainly adopted Taibo-Moire technique, utilizes Ronchi grating, Talbot effect to realize focusing, by the Digital Signal Processing focal length measurement.The sensitivity of such measuring method is compared classic method and is increased, but the parameter of optical path length, measuring process complexity, need measurement is many.

The long-focus measuring technique of comparing external, among " the Focal length measurements for the NationalIgnition Facility large lenses " that in " The Optical Society ofAmerica ", delivered in 2002, adopt Feisuo to interfere compound lens ultra-long focal length measuring technology to carry out long-focus and measured, and reached very high measuring accuracy.This measuring method is utilized the compound lens method to reduce optical path length, has been simplified measuring process.But in the method measuring process, adopt interference fringe to focus, interference figure is subject to the interference of ambient condition factors such as temperature, air-flow, vibration, and measurement environment has been proposed harsh requirement.

More than the general character of several measuring methods also be: its opinion scale all is based on the axial image information of hanging down.Since the object distance of optical system change the logitudinal magnification that causes change be hang down the axle magnification change square, if can choose a kind of axial information, then can further improve the sensitivity of focometry as opinion scale.

In recent years, the confocal microscopy fast development in micro-imaging field both at home and abroad, this technology with axial light intensity response curve as opinion scale, highly sensitive in vertical axial evaluation method, and, compare image processing method and have higher anti-environmental interference ability owing to adopt light intensity as data message.For example Chinese patent " confocal microscope " (patent No. 01122439.8) has proposed confocal microscopy, and this technology mainly is applicable to microcosmic micrometering field.Up to now, do not see as yet this technology is directly applied to the report that the overlength focal length focuses.

Summary of the invention

The objective of the invention is in order to solve the high-acruracy survey problem of small value aperture, overlength focal length lenses, and propose a kind of confocal combination ultra-long focal length measuring method and device.

The objective of the invention is to be achieved through the following technical solutions.

A kind of confocal combination ultra-long focal length measuring method of the present invention may further comprise the steps:

(a) directional light sees through beam splitting system 2, be focused at focal position a7 through reference lens 5, light is again by after catoptron 8 reflections, enter confocal fixed-focus system 10 by beam splitting system 2 reflections, catoptron 8 is moved in optical axis direction scanning, and confocal fixed-focus system 10 is determined with reference to lens 5 corresponding focal position a7 by the maximum point of probe response signal;

(b) measured lens 3 is inserted beam splitting system 2 and with reference between the lens 5, and coaxial with reference lens 5, utilize confocal fixed-focus system 10 once more, determine because of inserting the new focal position b9 that measured lens 4 causes by the maximum point of probe response signal;

(c) distance, delta 6 between measurement focal position a7 and the focal position b9;

(d) measure measured lens 3 and spacing d with reference to lens 5 ₀4;

(e) calculate measured lens 3 and principal plane spacing d by following formula with reference to lens 5:

$d=d_0+\frac{r_{12}{b}_1}{n_1(r_{12}-r_{11})+(n_1-1)b_1}-\frac{r_{21}{b}_2}{n_2(r_{22}-r_{21})+(n_2-1)b_2}$

Known parameters comprises the thickness b of measured lens 3 ₁, refractive index n ₁, radius-of-curvature r ₁₁, r ₁₂, with reference to the focal distance f of lens 5 ₂', thickness b ₂, refractive index n ₂, radius-of-curvature r ₂₁, r ₂₂

(f) calculate the focal length value of measured lens 3 by following formula:

${\mathrm{<figure-callout\; id="1"\; label="f"\; filenames="H2008102269676E00011.png"\; state="\{\{state\}\}">f</figure-callout>}}_1\&prime;=\frac{1-\frac{\mathrm{<figure-callout\; id="2"\; label="d\; f"\; filenames="H2008102269676E00011.png,H2008102269676E00012.png"\; state="\{\{state\}\}">d</figure-callout>}}{f_{}}+\frac{\mathrm{<figure-callout\; id="2"\; label="d\; f"\; filenames="H2008102269676E00011.png,H2008102269676E00012.png"\; state="\{\{state\}\}">d</figure-callout>}}{f_{}}}{\frac{1}{{\mathrm{<figure-callout\; id="2"\; label="f"\; filenames="H2008102269676E00011.png,H2008102269676E00012.png"\; state="\{\{state\}\}">f</figure-callout>}}_2\&prime;-\mathrm{\&Delta;}}-\frac{1}{{\mathrm{<figure-callout\; id="2"\; label="f"\; filenames="H2008102269676E00011.png,H2008102269676E00012.png"\; state="\{\{state\}\}">f</figure-callout>}}_2\&prime;}}.$

Measuring method of the present invention can also be compressed optical system 1 and confocal fixed-focus system 10 cooperatings by depth of focus, and use pupil filtering technique compresses is with reference to lens 5 and measured lens 3 and with reference to the depth of focus after lens 5 combinations, raising focuses sensitivity.

Measured lens of the present invention can place with reference to before the lens 5, also can place with reference to behind the lens 5.

The present invention also provides a kind of confocal compound lens ultra-long focal length measuring device, comprises beam splitting system 2, with reference to lens 5, catoptron 8, confocal fixed-focus system 10; Wherein beam splitting system 2, be successively placed on light source 12 emergent ray directions with reference to lens 5 and catoptron 8, confocal fixed-focus system 10 is placed on beam splitting system 2 reflection directions, catoptron 8 with beam splitting system 2 with beam reflection to confocal fixed-focus system 10, and cooperate confocal fixed-focus system 10 to realize focusing of focal position a7 and focal position b9.

Can also comprise depth of focus compression optical system 1, be used to reduce with reference to lens 5 and measured lens 3 with reference to the depth of focus after lens 5 combinations.

Can also comprise modulating control system 11, be used to control light source 12 and modulate and filtering, suppress the influence of environmental interference measuring accuracy with confocal fixed-focus system 10.

The present invention contrasts prior art and has following remarkable advantage:

1. the characteristic of the corresponding microcobjective focus in target location realizes accurately focusing when proposing to utilize confocal response curve to reach maximum value first, proposes the confocal principle that focuses, and the micro confocal system principle is expanded to the ultra-long focal length measuring field.

2. merge confocal principle and the compound lens method of focusing,, reduce the influence of environment focusing measuring accuracy to reduce to measure optical path length.

3. confocal focus principle with the light intensity response curve as focusing criterion, this patent proposes in the ultra-long focal length measuring process, cooperate the confocal principle that focuses to carry out intensity modulation and filtering, environmental interference such as deaeration disturbance are to the influence of measuring accuracy, compare with image, interference fringe to have better high stability as the focal-length measurement method that focuses criterion.

4. adopt the pupil filtering technology to match, in ultra-long focal length measuring, reduce the lens depth of focus, strengthen focusing sensitivity with confocal technology.

Description of drawings

Fig. 1 is the synoptic diagram of measuring method of the present invention;

Fig. 2 is the synoptic diagram of measurement mechanism of the present invention;

Fig. 3 is the synoptic diagram of the embodiment of the invention;

Fig. 4 is the ccd detector response curve of the embodiment of the invention;

Wherein: 1-depth of focus compression optical system, 2-beam splitting system, 3-measured lens, 4-spacing d ₀, 5-is with reference to lens, 6-distance, delta, 7-focal position a, 8-catoptron, 9-focal position b, the confocal fixed-focus system of 10-, 11-modulating control system, 12-light source, 13-polarization spectroscope, 14-1/4 wave plate, 15-translation stage a, 16-gauge block, 17-connecting rod, 18-translation stage b, 19-CCD detector, 20-pin hole, 21-condenser.

Embodiment

The invention will be further described below in conjunction with drawings and Examples.

Basic thought of the present invention is to utilize the confocal principle that focuses to realize that high precision focuses under big depth of focus situation, merges the compound lens method simultaneously and reduces to measure optical path length, further reduces the influence of environment to measuring accuracy.

Embodiment

As shown in Figure 3, a kind of confocal combination ultra-long focal length measuring method, its measuring process is:

At first, open light source 12, penetrate directional light and see through the beam splitting system that constitutes by polarization spectroscope 13 and quarter wave plate 14, through focal length is that the reference lens 5 of 3000mm are focused at focal position a7, light enters confocal fixed-focus system again by after catoptron 8 reflections by quarter wave plate 14 and polarization spectroscope 13 reflections; Condenser 21 in the confocal fixed-focus system is with convergence of rays, and converging ray passes pin hole 20 illumination ccd detectors 19; Catoptron 8 is moved in the scanning of reference lens 5 optical axis directions along translation stage a15, and confocal fixed-focus system determines that by the maximum point of surveying ccd detector 19 response signals response signal as shown in Figure 4 with reference to the corresponding focal position a7 of lens.

Then, measured lens 3 inserted quarter wave plate 14 and with reference between the lens 5, and it is coaxial with reference lens 5, utilize confocal fixed-focus system once more, catoptron 8 is moved in the scanning of reference lens 5 optical axis directions along translation stage a15, determine because of inserting the new focal position b9 that measured lens 4 causes by the maximum point of probe response signal;

Then, the grating measuring length mechanism among the translation stage a15 drives catoptron 8 and moves at reference lens 5 optical axis directions, and in the process that catoptron 8 moves, translation stage a15 uses the distance, delta 6 between measurement focal position a7 of grating measuring length mechanism and the focal position b9;

Then, gauge block 16 is inserted light path, make its two side plane with vertical with reference to lens 5 optical axises, translation stage b18 drives gauge block 16 by connecting rod 17 and moves axially, and touches respectively with reference to lens 5 and measured lens 3.The distance that gauge block 16 moves in the touching lens surface process adds the thickness of gauge block 16, calculates measured lens 3 and surface spacing d with reference to lens 5 ₀4;

Then, calculate measured lens 3 and principal plane spacing d by following formula with reference to lens 5:

$d=d_0+\frac{r_{12}{b}_1}{n_1(r_{12}-r_{11})+(n_1-1)b_1}-\frac{r_{21}{b}_2}{n_2(r_{22}-r_{21})+(n_2-1)b_2}---\left(1\right)$

Known parameters comprises the thickness b of measured lens 3 in the formula ₁, refractive index n ₁, radius-of-curvature r ₁₁, r ₁₂, with reference to the focal distance f of lens 5 ₂', thickness b ₂, refractive index n ₂, radius-of-curvature r ₂₁, r ₂₂

At last, calculate the focal length value of measured lens 3 by following formula:

${\mathrm{<figure-callout\; id="1"\; label="f"\; filenames="H2008102269676E00011.png"\; state="\{\{state\}\}">f</figure-callout>}}_1\&prime;=\frac{1-\frac{\mathrm{<figure-callout\; id="2"\; label="d\; f"\; filenames="H2008102269676E00011.png,H2008102269676E00012.png"\; state="\{\{state\}\}">d</figure-callout>}}{f_{}}+\frac{\mathrm{<figure-callout\; id="2"\; label="d\; f"\; filenames="H2008102269676E00011.png,H2008102269676E00012.png"\; state="\{\{state\}\}">d</figure-callout>}}{f_{}}}{\frac{1}{{\mathrm{<figure-callout\; id="2"\; label="f"\; filenames="H2008102269676E00011.png,H2008102269676E00012.png"\; state="\{\{state\}\}">f</figure-callout>}}_2\&prime;-\mathrm{\&Delta;}}-\frac{1}{{\mathrm{<figure-callout\; id="2"\; label="f"\; filenames="H2008102269676E00011.png,H2008102269676E00012.png"\; state="\{\{state\}\}">f</figure-callout>}}_2\&prime;}}---\left(2\right)$

Also compress optical system 1 and confocal fixed-focus system 10 cooperatings by depth of focus among this embodiment, use pupil filtering technique compresses is with reference to lens 5 and measured lens 3 and with reference to the depth of focus after lens 5 combinations, raising focuses sensitivity.

As shown in Figure 3, a kind of confocal compound lens ultra-long focal length measuring device, comprise light source 12, be successively placed on the polarization spectroscope 13, quarter wave plate 14 of light source 12 outgoing parallel rays directions, with reference to lens 5 and catoptron 8, also comprise the confocal fixed-focus system that is placed on polarization spectroscope 13 reflection directions, wherein catoptron 8, polarization spectroscope 13, quarter wave plate 14 with beam reflection to confocal fixed-focus system, light passes through condenser 21, pin hole a20 successively in the confocal fixed-focus system, and illumination ccd detector 19; Catoptron 8 places on the translation stage a15, and cooperates confocal fixed-focus system to realize focusing of focal position a7 and focal position b9.

Gauge block 16 is connected with translation stage b18 by connecting rod 17, is used to measure measured lens 3 and with reference to the surface spacing d of lens 5 ₀4;

This device comprises that depth of focus compression optical system 1 is iris filter, be used to reduce with reference to lens 5 and measured lens 3 with reference to the depth of focus after lens 5 combinations.

This device comprises modulating control system 11, is used to control light source 12 and modulates and filtering with confocal fixed-focus system 10, suppresses the influence of environmental interference to measuring accuracy.

As spacing d ₀=500mm, with reference to the focal distance f of lens 8 ₂'=3000mm, tested focal distance f ₁During ≈ 30000mm, its focometry error is ± 4.2mm that the relative measurement error is:

$\mathrm{\&delta;f}=\frac{\mathrm{\&delta;}{f}_1}{{\mathrm{<figure-callout\; id="1"\; label="f"\; filenames="H2008102269676E00011.png"\; state="\{\{state\}\}">f</figure-callout>}}_1}=\&PlusMinus;\frac{4.2}{30000}\&times;100\%\&ap;\&PlusMinus;0.014\%$

This embodiment has realized the high-acruracy survey of overlength focal length having realized confocal combination ultra-long focal length measuring method and device by a series of measure, compares with the routine measurement method, has higher measuring accuracy.

Below in conjunction with the accompanying drawings the specific embodiment of the present invention is described; but these explanations can not be understood that to have limited scope of the present invention; protection scope of the present invention is limited by the claims of enclosing, and any change on claim of the present invention basis all is protection scope of the present invention.

Claims (5)

1. confocal compound lens ultra-long focal length measuring method is characterized in that:

1) directional light sees through beam splitting system (2), be focused at focal position a (7) through reference lens (5), light is again by after catoptron (8) reflection, enter confocal fixed-focus system (10) by beam splitting system (2) reflection, catoptron (8) is moved in optical axis direction scanning, and confocal fixed-focus system (10) is determined with reference to the corresponding focal position a (7) of lens (5) by the maximum point of probe response signal;

2) measured lens (3) is inserted beam splitting system (2) and with reference between the lens (5), and it is coaxial with reference lens (5), utilize confocal fixed-focus system (10) once more, determine because of inserting the new focal position b (9) that measured lens (3) causes by the maximum point of probe response signal;

3) distance, delta (6) between measurement focal position a (7) and the focal position b (9);

4) measure measured lens (3) and spacing d with reference to lens (5) ₀(4);

5) calculate measured lens (3) and principal plane spacing d by following formula with reference to lens (5):

$d=d_0+\frac{r_{12}{b}_1}{n_1(r_{12}-r_{11})+(n_1-1)b_1}-\frac{r_{21}{b}_2}{n_2(r_{22}-r_{21})+(n_2-1)b_2}$

6) known parameters comprises the thickness b of measured lens (3) ₁, refractive index n ₁, radius-of-curvature r ₁₁, r ₁₂, with reference to the focal distance f of lens (5) ₂', thickness b ₂, refractive index n ₂, radius-of-curvature r ₂₁, r ₂₂Calculate the focal length value of measured lens (3) by following formula:

${f_1}^{\&prime;}=\frac{1-\frac{d}{{f_2}^{\&prime;}}+\frac{d}{{f_2}^{\&prime;}-\mathrm{\&Delta;}}}{\frac{1}{{f_2}^{\&prime;}-\mathrm{\&Delta;}}-\frac{1}{{f_2}^{\&prime;}}}.$

2. confocal compound lens ultra-long focal length measuring method according to claim 1, it is characterized in that: by depth of focus compression optical system (1) and confocal fixed-focus system (10) cooperating, use pupil filtering technique compresses is with reference to lens (5) and measured lens (3) and with reference to the depth of focus after lens (5) combination, raising focuses sensitivity.

3. use method according to claim 1 to carry out the confocal compound lens ultra-long focal length measuring device of ultra-long focal length measuring, comprise light source (12), it is characterized in that: also comprise beam splitting system (2), with reference to lens (5), catoptron (8), confocal fixed-focus system (10); Wherein beam splitting system (2), be successively placed on light source (12) emergent ray direction with reference to lens (5) and catoptron (8), confocal fixed-focus system (10) is placed on beam splitting system (2) reflection direction, catoptron (8) and beam splitting system (2) to confocal fixed-focus system (10), and cooperate confocal fixed-focus system (10) to realize focusing of focal position a (7) and focal position b (9) beam reflection.

4. according to right 3 described confocal compound lens ultra-long focal length measuring devices, it is characterized in that: comprise depth of focus compression optical system (1), be used to reduce with reference to lens (5) and measured lens (3) with reference to the depth of focus after lens (5) combination.

5. according to right 3 described confocal compound lens ultra-long focal length measuring devices, it is characterized in that: comprise modulating control system (11), be used to control light source (12) and modulate and filtering, suppress the influence of environmental interference measuring accuracy with confocal fixed-focus system (10).

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