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

Method for Measuring Center Thickness of Reflective Confocal Lens

technical field

The invention belongs to the technical field of optical precision measurement and can be used for non-contact high-precision measurement of lens center thickness. the

technical background

In an optical system, a lens is one of the most basic and important components, and its optical performance will directly affect the overall performance of the system. Therefore, in order to ensure that the overall performance of the optical system meets the requirements, strict tolerance requirements will be imposed on the parameters of each lens used. Among all the parameters of the lens, the central thickness of the lens is one of the most basic and important parameters, and its processing accuracy will directly affect the comprehensive performance of the lens such as focal length and aberration, and then affect the performance of the entire optical system. And with the emergence of cutting-edge projects such as lithography machines and nuclear fusion optical systems, they put forward stricter requirements for all optical parameters including the center thickness of the lens. In order to ensure that the processed optical lens meets the design tolerance requirements, it is necessary to have a high-precision optical inspection instrument to detect its parameters item by item, thereby eliminating its processing deviation. Therefore, non-contact measurement of optical high-precision lens center thickness is of great significance to the processing and testing of high-precision lenses. the

At present, lens center thickness measurement technology can be divided into contact measurement and non-contact measurement. the

Contact measurement, usually with a hand-held dial gauge or micrometer. During measurement, the accuracy of the position of the center point of the lens will directly affect the measurement accuracy, so the inspector must move the measured lens back and forth during measurement to find the highest point (convex mirror) or the lowest point (concave mirror), so the measurement speed is slow and the error Large, and the high-transmission optical material currently used is soft, and the probe moves on the lens surface during measurement, which is easy to scratch the lens surface. the

Domestic scholars have also carried out relevant research on the problems existing in contact measurement. In the article "Grating Digital Display Lens Thickness Measuring Instrument" published in "Practical Testing Technology" in 1999, the author designed a lens center thickness measuring instrument that uses a grating sensor as a precision length measuring device. According to different types of optical According to the requirements of lens and measurement accuracy, different forms of probes and measuring seats can be used for measurement, and the measurement accuracy can be increased to 1 μm. The Chinese patent "Apparatus for Measuring the Center Thickness of Optical Lens" (patent number: 200620125116.9) adopts the method of placing the measured lens jig on the upper part of the measuring column, which avoids the damage to the lens caused by the probe moving back and forth on the lens surface when looking for the apex of the lens surface. damage. the

Non-contact measurement often includes image measurement method, coplanar capacitance method, white light confocal method and interferometry. the

In the article "Research on On-line Measurement of Assembly Gap Based on Image Measurement Technology" published in "Sensor Technology" in 2005, an online measurement scheme based on image measurement technology was introduced. Submit it to the image measurement software for processing and analysis, and the measurement software will give the results. This method can also be applied to the measurement of the center thickness of the lens, but due to the influence of the camera imaging system, CCD resolution, image clarity and calibration coefficient accuracy, the measurement error is within 15 μm. the

In the article "Automatic Detector of Optical Lens Center Thickness" published in "Journal of Instrumentation" in 1994, the thickness of the center of the lens was measured by the coplanar capacitance method. It adopts the method of relative measurement, that is, first adjust the capacitive probe to a certain fixed distance from the reference plane according to the requirements; then place the measured lens on the reference plane, and there is an air gap between the measured lens and the probe. Different lens thicknesses correspond to different air gaps and different probe capacitances; finally, by measuring the voltage signal corresponding to the capacitance change through the circuit, the relative change of the measured lens thickness can be found. The sorting accuracy of this method is less than 5 μm . However, this method needs to know the relationship curve between the signal voltage of the measured lens material and the air gap before the measurement. In engineering practice, the coplanar capacitance probe must be accurately tested to obtain reliable data as the detection basis. the

In the article "Noncontact measurement of central lens thickness" published in "GLASS SCIENCE AND TECHNOLOGY" in 2005, the white light confocal method was used to measure the thickness of the lens center. This method first uses the probe formed by axial chromatic aberration after white light passes through the lens to locate the surface apex of the tested lens, and then calculates the thickness of the lens through the spectral information reflected by the apex of the upper and lower surfaces of the tested lens. The feature of this method is that it can realize real-time measurement, but white light is incoherent light, the fixed focus sensitivity and resolution are low, and the working distance is limited (30μm-25mm). In particular, it is difficult to accurately know the refractive index of the measured lens at different wavelengths. Generally, it is obtained by interpolating after measuring the refractive index at a specific wavelength. This parameter has a great influence on the measurement results, so this method is practical. It is difficult to achieve high-precision measurement in the application. the

The Chinese patent "Optical Measuring Instrument for the Thickness of Optical Elements" (Patent No.: 87200715) uses a double interference system to measure the thickness of the lens center in a non-contact manner. The instrument is composed of two Michelson interference systems. It locates the two surfaces of the tested lens according to the white light interference fringes, and compares the tested lens with the standard block to obtain the central thickness of the tested lens. It can realize non-contact measurement of cemented lens, optical components opaque to visible light, optical components of unknown materials, etc. However, the structure of this instrument is relatively complicated, and components need to be replaced during the measurement process. Its measurement accuracy not only depends on the positioning accuracy of multiple surfaces, but also depends on the accuracy of the known thickness of the standard block. A standard block with a similar thickness to the measured lens. the

The Chinese patent "A Measuring Device for Micro Optical Interval" (Patent No.: 93238743.8) uses polarized light interferometry to measure the thickness of the sample. The two wave fronts formed by the reflection of the incident white light on the upper and lower surfaces of the sample pass through the polarizer, birefringent prism, and analyzer to form interference fringes on the photodetector array, and the thickness of the sample can be obtained from the distance between the interference fringes. At the same time, a column lens is added between the analyzer and the photodetector array to enlarge the interference pattern along the fringe spacing direction, which reduces the requirements for the photodetector array, and the measurement accuracy is 1-5%, but this method is currently only Used to measure the thickness of glass plates. the

In recent years, confocal technology in the field of microscopic imaging at home and abroad has developed rapidly. Compared with traditional measurement methods, it has good tomographic ability, high axial positioning and aiming accuracy, and strong environmental anti-interference ability; Compared with confocal technology, confocal technology has a simple optical path and is easy to implement. the

The inventor also proposed to use confocal technology to measure the center thickness of the lens, and applied for a patent "Measurement method and device for the center thickness of confocal lens" (patent number: 201010128449.8). However, in this patent, the lens under test is placed in the converging beam, and the lens under test needs to be adjusted four-dimensionally during the measurement, so that its optical axis is completely consistent with the optical axis of the converging beam, and the assembly and adjustment process is complicated. This patent proposes to use the measured lens as an objective lens at the same time. When measuring, the measured lens is placed in the parallel beam emitted from the collimator lens. Since the optical axis of the parallel beam has only two dimensions, pitch and yaw, it only needs Two-dimensional adjustment of the tested lens, the lateral offset of the tested lens will not affect the measurement, which greatly reduces the difficulty of installing and adjusting the tested lens, and reduces the measurement error item caused by the installation and adjustment error , which helps to further improve the measurement accuracy of the center thickness of the measured lens. the

Contents of the invention

The purpose of the present invention is to reduce the difficulty of installation and adjustment in the method of measuring the center thickness of the confocal lens, further improve the measurement accuracy of the center thickness of the measured lens, and propose a method for measuring the center thickness of the reflective confocal lens. the

The purpose of the present invention is achieved through the following technical solutions. the

A method for measuring the central thickness of a reflective confocal lens of the present invention comprises the following steps:

(a) Turn on the point light source, the light emitted by it passes through the beam splitter, collimating lens and the measured lens, and is reflected by the plane mirror to form a measuring beam. The measuring beam is irradiated on the front or rear surface of the tested lens, and the measured lens The front surface or the back surface reflects the measurement beam, and the reflected light returns along the original optical path, and is reflected by the beam splitter into the confocal measurement system;

(b) Adjust the lens under test so that it has the same optical axis as the collimator lens. The collimator lens collimates the light generated by the point light source into parallel light and irradiates it on the lens under test. Adjust the plane reflector so that it is aligned with the collimator lens. Common optical axis;

(c) Move the plane reflector along the optical axis so that the focal point of the measuring beam is close to the rear surface of the lens under test, scan the plane reflector near this position, and measure the confocal response curve by the confocal measurement system. The maximum point of the response curve is used to determine that the focal point of the measuring beam coincides with the rear surface of the measured lens, and record the position z ₁ of the plane mirror at this time;

(d) Continue to move the plane mirror along the optical axis to the direction of the lens under test, so that the focal point of the measurement beam is close to the front surface of the lens under test, scan the plane mirror near this position, and measure the confocal value by the confocal measurement system Response curve, through the maximum point of the confocal response curve to determine that the focus of the measurement beam coincides with the front surface of the measured lens, record the position z ₂ of the plane mirror at this time;

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

$\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="r"\; filenames="HDA00001749077800011.png"\; state="\{\{state\}\}">r</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\frac{\mathrm{<span\; class="notranslate">\; sin</span>}{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; arcsin</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="r"\; filenames="HDA00001749077800011.png"\; state="\{\{state\}\}">r</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; sin</span>}{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; arcsin</span>}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="r"\; filenames="HDA00001749077800011.png"\; state="\{\{state\}\}">r</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; sin</span>}{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>}<span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>$

Calculate the center thickness d of the tested lens. the

The method for measuring the central thickness of the reflective confocal lens of the present invention can also use the annular pupil to block the paraxial light to form a hollow measuring light cone, thereby reducing the influence of aberrations on the measurement results. the

The reflective confocal lens central thickness measurement method of the present invention can also modulate the light intensity of the light emitted by the point light source, and the modulated confocal response signal can be obtained by detecting the light intensity sensor in the confocal measurement system. After the modulated signal is demodulated, the confocal response curve is obtained, thereby improving the system's focus sensitivity. the

Beneficial effect:

Compared with the prior art, the present invention has the following innovations:

1. For the first time, it is proposed to use the light beam emitted by the tested lens itself combined with confocal technology to conduct high-precision fixed-focus aiming at the apex of the front and rear surfaces of the tested lens, and then measure its central thickness;

2. Introduce the annular pupil in the optical path to block the paraxial light, form a hollow measuring light cone, and reduce the influence of aberrations on the measurement results;

3. Using the good tomographic ability of the confocal system, the precise positioning of the lens surface is realized. the

Compared with the prior art, the present invention has the following significant advantages:

1. Compared with other methods of measuring the thickness of the lens center, the measurement accuracy of this method is significantly improved due to the use of confocal fixed-focus technology;

2. Compared with the patent "Confocal Lens Center Thickness Measurement Method and Device" (Patent No.: 201010000555.8), in the present invention, the measured lens is also used as the objective lens, which greatly reduces the complexity of the device At the same time, the installation and adjustment dimension of the tested lens is reduced from four dimensions to two dimensions, which reduces the difficulty of the installation and adjustment of the tested mirror;

3. Compared with the already applied patent "Confocal Lens Center Thickness Measurement Method and Device" (Patent No.: 201010000555.8), the present invention reduces the measurement error term caused by the installation and adjustment error, and further improves the measured lens Measurement accuracy of center thickness. the

Description of drawings

Fig. 1 is the schematic diagram of reflective confocal lens central thickness measuring method of the present invention;

Fig. 2 is the schematic diagram of embodiment of reflective confocal lens central thickness measurement of the present invention;

Fig. 3 is the confocal response curve obtained by confocal measurement system detection of the present invention;

Among them: 1-point light source, 2-beam splitter, 3-collimator lens, 4-annular pupil, 5-lens under test, 6-measurement beam, 7-plane mirror, 8-confocal measurement system, 9- Pinhole, 10-light intensity sensor, 11-microscopic objective lens, 12-CCD detector, 13-point light source generator, 14-optical fiber, 15-laser, 16-image acquisition card, 17-master computer, 18- Electromechanical control device, 19-linear translation guide rail, 20-two-dimensional adjustment frame. the

Detailed ways

The present invention will be further described below in conjunction with drawings and embodiments. the

In the present invention, the light beam emitted by the measured lens itself is reflected by a plane mirror to form a measuring light beam, and combined with the confocal fixed-focus technology, the apexes of the front and rear surfaces of the tested lens are aimed at the vertices of the measured lens with high precision, and then the measured lens is measured. center thickness. At the same time, the present invention also introduces an annular pupil into the measurement light path to block the paraxial light rays and form a hollow measurement light cone, which reduces the influence of aberrations on the measurement results. the

Example 1

As shown in accompanying drawing 1 and accompanying drawing 2, the measuring method of reflective confocal lens center thickness, its measuring steps are:

(a) Start the measurement software in the main control computer 17, and input relevant parameters, which mainly include the radius of curvature r ₂ =100.7134mm of the rear surface of the measured lens 5, the refractive index of air n ₀ =1, and the refractive index n of the measured lens 5 =1.5143 and the numerical aperture angle α ₀ of the measuring beam 6 =5.8°.

(b) Turn on the laser 15 , the light emitted by the laser 15 is transmitted through the optical fiber 14 to form the point light source 1 . The light emitted by the point light source 1 passes through the beam splitter 2 and the collimator lens 3 to form a parallel beam;

(c) Place the plane mirror 7 on the two-dimensional adjustment frame 20, adjust the plane mirror 7 by the two-dimensional adjustment frame 20, so that its surface is perpendicular to the optical axis of the parallel beam;

(d) Place the measured lens 5 between the collimator lens 3 and the plane mirror 7 , and adjust the measured lens 5 so that it has the same optical axis as the collimator lens 3 . Parallel light is irradiated on the measured lens 5, and the light converged by the measured lens 5 is reflected by the plane mirror 7 to form a measuring beam 6 and irradiates the surface of the measured lens 5;

(e) The measurement software in the main control computer 17 controls the axial translation of the linear translation guide rail 19 through the electromechanical control device 18, and then drives the plane mirror 7 to move along the optical axis. The focal point of the measuring beam 6 is brought close to the rear surface of the lens 5 under test. The plane mirror 7 is scanned near this position, and the measurement software collects the focal spot data through the image acquisition card 16 and processes the confocal response curve as shown in FIG. 3 . Determine that the focal point of the measurement beam 6 coincides with the rear surface of the measured lens 5 by the maximum point of the confocal response curve, and record the position z ₁ of the plane mirror 7 at this time = 0.0056mm;

(f) Move the plane mirror 7 along the optical axis to the measured lens 5, so that the focus of the measuring beam 6 is close to the front surface of the measured lens 5, scan the plane mirror 7 near this position, and the measurement software passes through the image again The acquisition card 16 acquires focal spot data and processes the confocal response curve as shown in FIG. 3 . Determine that the focal point of the measurement beam 6 coincides with the front surface of the measured lens 5 by the maximum point of the confocal response curve, and record the position z ₂ of the plane mirror 7 at this time = 1.3438mm;

(g) According to known parameters: the radius of curvature r ₂ of the rear surface of the measured lens 5 = 100.7134 mm, the refractive index of air n ₀ = 1, the refractive index of the measured lens 5 n = 1.5143, and the numerical aperture angle α ₀ of the measuring beam 6 =5.8°, and the amount of movement l=|z ₂ -z ₁ |=2.6764mm of the planar reflector 7 positioned twice, which is brought into the following formula:

$\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="r"\; filenames="HDA00001749077800011.png"\; state="\{\{state\}\}">r</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\frac{\mathrm{<span\; class="notranslate">\; sin</span>}{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; arcsin</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="r"\; filenames="HDA00001749077800011.png"\; state="\{\{state\}\}">r</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; sin</span>}{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; arcsin</span>}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="r"\; filenames="HDA00001749077800011.png"\; state="\{\{state\}\}">r</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; sin</span>}{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>}<span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>$

It can be obtained that the central thickness of the measured lens 5 is d=8.0380mm. the

As shown in FIG. 1 , the confocal measurement system 8 in the reflective confocal lens center thickness measurement method includes a pinhole 9 and a light intensity sensor 10 . The light reflected by the beam splitter 2 enters the confocal measurement system 8 and irradiates the light intensity sensor 10 through the pinhole 9 . In actual system design, the confocal measurement system 8 shown in Figure 2 is usually used to reduce the difficulty of system installation and adjustment. The confocal measurement system 8 includes a microscope objective lens 11 and a CCD detector 12 . Wherein the object plane of the microscope objective lens 11 is located at the focal plane of the reflected light beam, and the CCD detector 12 is placed on its image plane. The light reflected by the beam splitter 2 enters the confocal measurement system 8 and is imaged on the CCD detector 12 through the microscope objective lens 11 . the

Example 2

The difference from Embodiment 1 is that the annular pupil 4 is added to block the paraxial light in the method of measuring the central thickness of the reflective confocal lens, and then the measurement of the central thickness of the measured lens 5 is completed. Due to the addition of the annular pupil 4, the measurement beam 6 forms a hollow measurement light cone, which will effectively reduce the influence of aberrations on the measurement results. the

This embodiment realizes the non-contact and high-precision measurement of the center thickness of the measured lens through a series of measures. It has the advantages of no damage to the measured lens, high measurement accuracy, and convenient installation and adjustment. the

The specific embodiment of the present invention has been described above in conjunction with the accompanying drawings, but these descriptions can not be interpreted as limiting the scope of the present invention, the scope of protection of the present invention is defined by the appended claims, any claims on the basis of the present invention All modifications are within the protection scope of the present invention. the

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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