CN102679895B - Method for measuring center thickness of reflective confocal lens - Google Patents

Abstract

The invention belongs to the technical field of optical precision measurement, and relates to a method for measuring the center thickness of a reflective confocal lens. The method comprises the steps of precisely positioning the vertex of the front surface of the lens and the vertex of the rear surface of the lens by using a confocal measurement method and a plane mirror, and obtaining the center thickness of the lens according to a ray tracing formula. High-precision fixed focus collimation of the vertex of the front surface and the vertex of the rear surface of the measured lens is realized by utilizing light rays emitted by the measured lens for the first time, and adopting the confocal technology, difficulty in adjustment of the measured lens is reduced to a great extent, and the method has the advantages of high measurement precision and environmental interference resistance, and can be used for precisely measuring center thicknesses of the lenses.

Description

Reflection-type confocal lens center thickness measuring method

Technical field

The invention belongs to technical field of optical precision measurement, the contactless high-precision that can be used for lens center thickness is measured.

Technical background

In optical system, lens are one of its most basic and important elements, and the height of its optical property will directly affect the overall performance of system.Therefore,, for the overall performance that guarantees optical system reaches requirement, will the parameter of each lens using be proposed to strict tolerance.In all parameters of lens, the center thickness of lens is one of the most basic and important parameters, and its machining precision will directly affect the combination property such as the focal length of lens, aberration, and then affect the performance of whole optical system.And along with the appearance of the most advanced and sophisticated engineerings such as litho machine, nuclear fusion optical system, it has proposed more strict requirement to all optical parametrics including lens center thickness.For guaranteeing that the optical lens of processing meets design tolerance requirement, just need to have high-precision optical detecting instrument to detect item by item its parameter, and then eliminate its machining deviation.So processing, the detection of high-accuracy optical lens center thickness non-cpntact measurement to high-precision lenses has great importance.

At present, lens center thickness measuring technique can be divided into two kinds of contact type measurement and non-contact measurements.

Contact type measurement is generally with hand-held clock gauge or miking.When measurement, the accuracy of some position, lens center will directly affect measuring accuracy, therefore checker's measured lens that will move around in the time measuring, find peak (convex lens) or minimum point (concave mirror), thereby measuring speed is slow, error is large, and the high transmission optical material using at present, material is softer, and when measurement, gauge head moves at lens surface, easily scratches lens surface.

The problem existing for contact type measurement, domestic scholars has also been carried out correlative study.In " the explicit lens thickness measuring instrument of raster count " literary composition of delivering in " practical measuring technology " for 1999, author designed a kind of utilize grating sensor as precision measurement of length device form lens center thickness measuring instrument, according to dissimilar optical lens and measuring accuracy requirement, can adopt multi-form gauge head and measuring seat combination to measure, measuring accuracy is brought up to 1 μ m.(the patent No.: 200620125116.9) that Chinese patent " is measured the device of optical lens center thickness ", adopted the method for placing measured lens smelting tool measuring column top, while having avoided finding lens surface summit, gauge head is in the lens surface damage that lens are caused that moves around.

Non-contact measurement often has image measurement method, coplanar capacitance method, the confocal method of white light and interferometric method.

In " the fit-up gap Research on on-line-measuring based on image measurement technology " literary composition of delivering in " sensor technology " for 2005, introduce a kind of on-line measurement scheme based on image measurement technology, the picture that gap is become in ccd video camera by optical system is delivered in image measurement software and processes and analyze, and provides result by Survey Software.This method also can be applied to the measurement of lens center thickness, but owing to being subject to the impact of camera imaging system, CCD resolving power, clear picture degree and calibration coefficient degree of accuracy etc., measuring error is in 15 μ m.

In " optical lens center thickness automatic tester " literary composition of delivering in " Chinese journal of scientific instrument " for 1994, utilize coplanar capacitance measurement lens center thickness.What it adopted is the method for relative measurement, first as requested electric capacity gauge head and reference field is adjusted to a certain fixed range; Then measured lens is placed on reference field, between measured lens and gauge head, has clearance, the clearance that different lens thicknesses is corresponding different and different gauge head electric capacity; Finally go out by circuit measuring the voltage signal changing corresponding to electric capacity, just can find out the relative variation of measured lens thickness, the sharpness of separation of the method is less than 5 μ m.But this method needs the signal voltage of known measured lens material and the relation curve of clearance before measuring, and in engineering reality, must accurately test coplanar electric capacity gauge head, to obtain authentic data as detecting foundation.

In " Noncontact measurement of central lens thickness " literary composition of delivering in " GLASS SCIENCE AND TECHNOLOGY " for 2005, adopt the confocal method of white light to measure lens center thickness.First this method utilizes the probe that axial chromatic aberration forms after white light scioptics to position measured lens surface vertices, then calculates the thickness of lens by the spectral information of measured lens upper and lower surface summit reflection.The feature of the method is to realize real-time measurement, but white light is incoherent light, focuses sensitivity and resolving power is lower, operating distance limited (30 μ m-25mm).Particularly be difficult to the refractive index of accurate known measured lens at different wave length place, general is all by the refractive index interpolation gained of mensuration certain wave strong point, this parameter is larger on the impact of measurement result, and institute is in this way difficult to realize high-acruracy survey in actual applications.

Chinese patent " optical gauge of optical element the thickness " (patent No.: 87200715), utilize two interference systems to carry out non-cpntact measurement to lens center thickness.This instrument is made up of two Michelson interference systems, according to white-light fringe, two of measured lens surfaces is positioned, and measured lens and calibrated bolck are compared to the center thickness in the hope of measured lens.Can be to balsaming lens, the opaque optical element of visible ray, the optical element of unknown material etc. is realized non-cpntact measurement.But the complicated structure of this instrument, in measuring process, need to change element, its measuring accuracy not only depends on the positioning precision on multiple surfaces, also depends on the precision of calibrated bolck known thickness, in order to improve measuring accuracy, need to choose the calibrated bolck close with measured lens thickness simultaneously.

Chinese patent " a kind of measurement mechanism of the micro-optical space " (patent No.: 93238743.8), adopt polarized light interference method to measure thickness of sample.Two wave fronts that incident white light reflects to form in sample upper and lower surface form interference fringe after polarizer, birefringent prism, analyzer on photodetector array, get final product to obtain thickness of sample by interference fringe spacing.Between analyzer and photodetector array, add post lens that interference pattern is amplified along fringe spacing direction simultaneously, reduce the requirement to photodetector array, measuring accuracy is 1-5%, but this method is at present only for measuring the thickness of glass plate.

In recent years, both at home and abroad the confocal technology in micro-imaging field develops rapidly, has good chromatography ability, higher axial location pointing accuracy, stronger environment interference compared with traditional measuring method; Compared with differential confocal technology, confocal technology light path is simple, is easy to realize.

The inventor also once proposed to utilize confocal technology to measure the center thickness of lens, and applied for a patent " confocal lens center thickness measuring method and device " (patent No.: 201010128449.8).But in this patent, measured lens is positioned in convergent beam, when measurement, need to carry out four-dimension adjustment to measured lens, its optical axis and convergent beam optical axis are adjusted in full accord, debug process complexity.This patent proposes that measured lens is also made to object lens simultaneously and uses, when measurement, measured lens is positioned over from the parallel beam of collimation lens outgoing, because the optical axis of parallel beam only has pitching, two dimensions of beat, therefore only need measured lens to carry out two dimension adjustment, the lateral excursion of measured lens can not impact measuring, reduce largely the resetting difficulty of measured lens, reduce the measuring error item bringing because debuging error, contributed to further to improve the measuring accuracy of measured lens center thickness.

Summary of the invention

The object of the invention is, in order to reduce the resetting difficulty in confocal lens center thickness measuring method, further to improve the measuring accuracy of measured lens center thickness, propose a kind of reflection-type confocal lens center thickness measuring method.

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

A kind of reflection-type confocal lens center thickness measuring method of the present invention, comprises the following steps:

(a) open pointolite, after light transmission spectroscope, collimation lens and measured lens that it sends, reflect to form measuring beam by plane mirror, measuring beam is radiated at measured lens front surface or rear surface, measuring beam is reflected in front surface or the rear surface of measured lens, the light reflecting returns along original optical path, and enters confocal measuring system by spectroscope reflection;

(b) adjust measured lens, make itself and collimation lens common optical axis, the optical alignment that collimation lens produces pointolite becomes directional light to be radiated on measured lens, and adjustment plane mirror, makes itself and collimation lens common optical axis;

(c) along optical axis direction plane of motion catoptron, focusing focus and the measured lens rear surface of measuring beam are approached, near plane of scanning motion catoptron this position, record confocal response curve by confocal measuring system, determine that by the maximum of points of confocal response curve the focus of measuring beam and measured lens rear surface coincide, record the now position z of plane mirror ₁;

(d) plane mirror is continued to move along optical axis direction measured lens direction, focusing focus and the measured lens front surface of measuring beam are approached, near plane of scanning motion catoptron this position, record confocal response curve by confocal measuring system, determine that by the maximum of points of confocal response curve the focus of measuring beam and measured lens front surface coincide, record the now position z of plane mirror ₂;

(e) according to known parameters: the numerical aperture angle α of measuring beam ₀, measured lens rear surface radius-of-curvature r ₂, air refraction n ₀, measured lens refractive index n and twice location plane mirror amount of movement l=|z ₂-z ₁|, can be by following formula:

$d={\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="HDA00001749077800011.png"\; state="\{\{state\}\}">r</figure-callout>}}_2+\frac{n_0}{n}\&CenterDot;\frac{\sin {\mathrm{\&alpha;}}_0}{\sin [{\mathrm{\&alpha;}}_0+\arcsin (\frac{2l-r_2}{{\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="HDA00001749077800011.png"\; state="\{\{state\}\}">r</figure-callout>}}_2}\&CenterDot;\sin {\mathrm{\&alpha;}}_0)-\arcsin (\frac{n_0}{n}\&CenterDot;\frac{2l-r_2}{{\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="HDA00001749077800011.png"\; state="\{\{state\}\}">r</figure-callout>}}_2}\&CenterDot;\sin {\mathrm{\&alpha;}}_0)]}\&CenterDot;(2l-r_2)$

Calculate the center thickness d of measured lens.

Reflection-type confocal lens center thickness measuring method of the present invention, can also utilize annular pupil to block paraxial rays, forms hollow measurement light cone, cuts down the impact of aberration on measurement result.

Reflection-type confocal lens center thickness measuring method of the present invention, the light that can also send pointolite carries out intensity modulation, surveyed the confocal response signal that obtains modulated system by the light intensity sensor in confocal measuring system, to after this modulation signal demodulation, obtain confocal response curve, thereby improve the sensitivity that focuses of system.

Beneficial effect:

The present invention contrasts prior art and has following innovative point:

1. propose first to utilize the light beam that measured lens self sends and in conjunction with confocal technology, high precision is carried out in measured lens front and rear surfaces summit to focus aiming, and then record its center thickness;

2. in light path, introduce annular pupil, block paraxial rays, form hollow measurement light cone, cut down the impact on measurement result of aberration;

3. the accurate location that utilizes chromatography ability that confocal system is good to realize lens surface.

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

1. measure the method for lens center thickness than other, the method is owing to adopting the confocal technology that focuses, and its measuring accuracy significantly improves;

2. than the patent of having applied for " confocal lens center thickness measuring method and the device " (patent No.: 201010000555.8), in the present invention, measured lens also makees object lens simultaneously and uses, reduce to a great extent the complexity of device, the dimension of debuging of measured lens is reduced to two dimension by the four-dimension simultaneously, has reduced the resetting difficulty of measured lens;

3. than the patent of having applied for " confocal lens center thickness measuring method and the device " (patent No.: 201010000555.8), the present invention has reduced the measuring error item bringing because debuging error, has further improved the measuring accuracy of measured lens center thickness.

Accompanying drawing explanation

Fig. 1 is the schematic diagram of reflection-type confocal lens center thickness measuring method of the present invention;

Fig. 2 is the schematic diagram that reflection-type confocal lens center thickness of the present invention is measured embodiment;

Fig. 3 is that the present invention is surveyed the confocal response curve obtaining by confocal measuring system;

Wherein: 1-pointolite, 2-spectroscope, 3-collimation lens, 4-annular pupil, 5-measured lens, 6-measuring beam, 7-plane mirror, 8-confocal measuring system, 9-pin hole, 10-light intensity sensor, 11-microcobjective, 12-CCD detector, 13-pointolite generating means, 14-optical fiber, 15-laser instrument, 16-image pick-up card, 17-main control computer, 18-electromechanical controlling device, 19-rectilinear translation guide rail, 20-two dimension adjustment rack.

Embodiment

Below in conjunction with drawings and Examples, the invention will be further described.

The present invention utilizes the light beam of measured lens self outgoing to form measuring beam by plane mirror reflection is rear, and in conjunction with the confocal technology that focuses, the high-precision aiming that focuses is carried out in the summit of measured lens front and rear surfaces, and then records the center thickness of measured lens.Meanwhile, the present invention also introduces annular pupil in optical path, blocks paraxial rays, forms hollow measurement light cone, has cut down the impact of aberration on measurement result.

Embodiment 1

As shown in Figures 1 and 2, reflection-type confocal lens center thickness measuring method, its measuring process is:

(a) start the Survey Software in main control computer 17, input correlation parameter, it mainly comprises the radius-of-curvature r of measured lens 5 rear surfaces ₂=100.7134mm, air refraction n ₀=1, the numerical aperture angle α of measured lens 5 refractive index n=1.5143 and measuring beam 6 ₀=5.8 °.

(b) open laser instrument 15, the light that laser instrument 15 sends forms pointolite 1 after optical fiber 14 transmission.The light that pointolite 1 sends forms parallel beam through spectroscope 2, collimation lens 3;

(c) plane mirror 7 is positioned on two-dimentional adjustment rack 20, adjusts plane mirror 7 by two-dimentional adjustment rack 20, make its surface perpendicular with parallel beam optical axis;

(d) measured lens 5 is positioned between collimation lens 3 and plane mirror 7, adjusts measured lens 5, make itself and collimation lens 3 common optical axis.Directional light is radiated on measured lens 5, and the light of being assembled by measured lens 5 forms measuring beam 6 and be radiated at the surface of measured lens 5 after plane mirror 7 reflects;

(e) Survey Software in main control computer 17 is controlled rectilinear translation guide rail 19 axial translations by electromechanical controlling device 18, and then drives plane mirror 7 to move along optical axis direction.The focusing focus of measuring beam 6 and the rear surface of measured lens 5 are approached.Near plane of scanning motion catoptron 7 this position, Survey Software is collected focus spot data and is processed out confocal response curve as shown in Figure 3 by image pick-up card 16.Determine that by the maximum of points of confocal response curve the focusing focus of measuring beam 6 and the rear surface of measured lens 5 coincide, and record the now position z of plane mirror 7 ₁=0.0056mm;

(f) plane mirror 7 is moved along optical axis direction measured lens 5 directions, focusing focus and measured lens 5 front surfaces of measuring beam 6 are approached, near plane of scanning motion catoptron 7 this position, Survey Software is again collected focus spot data and is processed out confocal response curve as shown in Figure 3 by image pick-up card 16.Determine that by the maximum of points of confocal response curve the focusing focus of measuring beam 6 and measured lens 5 front surfaces coincide, and record the now position z of plane mirror 7 ₂=1.3438mm;

(g) according to known parameters: the radius-of-curvature r of measured lens 5 rear surfaces ₂=100.7134mm, air refraction n ₀=1, the numerical aperture angle α of measured lens 5 refractive index n=1.5143, measuring beam 6 ₀=5.8 °, and the plane mirror 7 amount of movement l=|z of twice location ₂-z ₁|=2.6764mm, carries it into following formula:

$d={\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="HDA00001749077800011.png"\; state="\{\{state\}\}">r</figure-callout>}}_2+\frac{n_0}{n}\&CenterDot;\frac{\sin {\mathrm{\&alpha;}}_0}{\sin [{\mathrm{\&alpha;}}_0+\arcsin (\frac{2l-r_2}{{\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="HDA00001749077800011.png"\; state="\{\{state\}\}">r</figure-callout>}}_2}\&CenterDot;\sin {\mathrm{\&alpha;}}_0)-\arcsin (\frac{n_0}{n}\&CenterDot;\frac{2l-r_2}{{\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="HDA00001749077800011.png"\; state="\{\{state\}\}">r</figure-callout>}}_2}\&CenterDot;\sin {\mathrm{\&alpha;}}_0)]}\&CenterDot;(2l-r_2)$

The center thickness that can obtain measured lens 5 is d=8.0380mm.

As shown in Figure 1, the confocal measuring system 8 in this reflection-type confocal lens center thickness measuring method comprises pin hole 9 and light intensity sensor 10.The light being reflected by spectroscope 2 is radiated on light intensity sensor 10 by pin hole 9 after entering confocal measuring system 8.In actual system design, conventionally adopt confocal measuring system 8 as shown in Figure 2 to reduce system resetting difficulty.This confocal measuring system 8 comprises microcobjective 11 and ccd detector 12.Wherein the object plane of microcobjective 11 is positioned at the focusing surface of folded light beam, places ccd detector 12 at it as plane.The light being reflected by spectroscope 2 is imaged on ccd detector 12 by microcobjective 11 after entering confocal measuring system 8.

Embodiment 2

As different from Example 1, in reflection-type confocal lens center thickness measuring method, add annular pupil 4 to block paraxial rays, then complete the measurement to measured lens 5 center thicknesses.Owing to adding annular pupil 4, measuring beam 6 forms hollow measurement light cone, will effectively cut down the impact of aberration on measurement result.

This embodiment has realized noncontact, the high-acruracy survey to measured lens center thickness by a series of measure.Have high to measured lens not damaged, measuring accuracy, debug the advantages such as convenient.

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

Claims (3)

1. reflection-type confocal lens center thickness measuring method, is characterized in that:

(a) open pointolite, after light transmission spectroscope, collimation lens and measured lens that it sends, reflect to form measuring beam by plane mirror, measuring beam is radiated at measured lens front surface or rear surface, measuring beam is reflected in front surface or the rear surface of measured lens, the light reflecting returns along original optical path, and enters confocal measuring system by spectroscope reflection;

(b) adjust measured lens, make its with collimation lens common optical axis, collimation lens by pointolite produce optical alignment become directional light to be radiated on measured lens, adjust plane mirror, make its surface and parallel beam optical axis perpendicular;

(c) along optical axis direction plane of motion catoptron, focusing focus and the measured lens rear surface of measuring beam are approached, near plane of scanning motion catoptron this position, record confocal response curve by confocal measuring system, determine that by the maximum of points of confocal response curve the focus of measuring beam and measured lens rear surface coincide, record the now position z of plane mirror ₁;

(d) plane mirror is continued to move along optical axis direction measured lens direction, focusing focus and the measured lens front surface of measuring beam are approached, near plane of scanning motion catoptron this position, record confocal response curve by confocal measuring system, determine that by the maximum of points of confocal response curve the focus of measuring beam and measured lens front surface coincide, record the now position z of plane mirror ₂;

(e) according to known parameters: the numerical aperture angle α of measuring beam ₀, measured lens rear surface radius-of-curvature r ₂, air refraction n ₀, measured lens refractive index n and twice location plane mirror amount of movement l=|z ₂-z ₁|, can be by following formula:

$d=r_2+\frac{n_0}{n}\&CenterDot;\frac{\sin {\mathrm{\&alpha;}}_0}{\sin [{\mathrm{\&alpha;}}_0+\arcsin (\frac{2l-r_2}{r_2}\&CenterDot;{\sin \mathrm{\&alpha;}}_0)-\arcsin (\frac{n_0}{n}\&CenterDot;\frac{2l-r_2}{r_2}\&CenterDot;\sin {\mathrm{\&alpha;}}_0)]}\&CenterDot;(2l-r_2)$

Calculate the center thickness d of measured lens.

2. reflection-type confocal lens center thickness measuring method according to claim 1, is characterized in that: utilize annular pupil to block paraxial rays, form hollow measurement light cone, cut down the impact of aberration on measurement result.

3. reflection-type confocal lens center thickness measuring method according to claim 1 and 2, it is characterized in that: the light that pointolite is sent carries out intensity modulation, surveyed the confocal response signal that obtains modulated system by the light intensity sensor in confocal measuring system, to after this modulation signal demodulation, obtain confocal response curve, thereby improve the sensitivity that focuses of system.

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