CN101526341A - Differential confocal curvature radius measurement method and device - Google Patents

Abstract

The invention belongs to the technical field of optical precision measurement, and relates to a method and device for measuring the radius of curvature of a differential confocal lens. The method first determines the position of the vertex and the center of the sphere of the measured lens through the principle of differential confocal fixed focus, and then measures the two focal points At the same time, the pupil filtering technology can also be used to improve the measurement sensitivity of the radius of curvature during the measurement process. The invention proposes for the first time to use the characteristics of the vertex and the center of the measured lens when the response curve of the differential confocal corresponds to the zero crossing point to realize precise focusing, and extends the principle of differential confocal microscopy to the field of curvature radius measurement, forming the principle of differential confocal fixed focus . The invention uses the principle of differential confocal fixed focus, has the advantages of high measurement accuracy and strong ability to resist environmental interference, and can be used for the detection of the curvature radius of the lens and the high-precision measurement of the curvature radius during the assembly process of the optical system.

Description

Differential confocal curvature radius measurement method and device

technical field

The invention belongs to the technical field of optical precision measurement and can be used for lens curvature radius detection and high-precision curvature radius measurement in the optical system assembly process.

technical background

In the field of optics, the measurement of the radius of curvature of a lens plays an important role. It is very difficult to precisely measure the radius of curvature of an optical spherical surface on a high-quality spherical sample. The precise measurement of the radius of curvature of an optical spherical surface is an important link in the process of optical measurement and optical cold processing. As an important parameter of an optical lens, the high-precision measurement of its radius of curvature has always been a difficult point in the field of optical measurement. The main factor is that the contact measurement method requires the surface to be tested to be polished, which will bring about the measurement caused by the wear or extrusion of the optical spherical surface. error; non-contact measurement method, although avoiding the wear of the optical spherical surface to be measured, the focus and alignment of the optical path need to be very accurate, which makes it difficult to adjust the optical path, and the optical path adjustment process is easy to lead to system errors; the spherical model method, the spherical diameter Most of the traditional measurement methods such as the instrument method and the autocollimation microscope method use the visual reading method, which is not highly automated and increases the random error of the measurement. It is difficult to achieve high-precision measurement of the radius of curvature.

For the measurement of the radius of curvature, domestic scholars have proposed new measurement methods, including "Research on the Measurement of Optical Spherical Radius Based on White Light Interference" published in Applied Optics in 2007. This type of technology mainly uses the Moiré grating displacement measurement system, Michelson The white light interference system realizes accurate measurement. The system adopts the optical non-destructive measurement method to avoid damage to the optical surface by contact measurement; the digital image processing technology can be used to directly process the image and calculate the measurement result according to the image measurement data, reducing The focus and alignment error of the visual optical measurement system is eliminated. Compared with the traditional method, the sensitivity is improved, and the measurement accuracy of hundreds of microns can be achieved. However, the measurement accuracy of the optical spherical automatic system for small curvature radius optical spherical There are many parameters.

Compared with the foreign curvature radius measurement technology, in the "Radius case study: Optical bench measurement and uncertainty including stage error motions" published in SPIE in 2005, a new coordinate model technology was used to measure the curvature radius, and it reached the micron level measurement accuracy. However, due to the use of interferometers, the measurement process is easily disturbed by environmental factors such as temperature, airflow, and vibration, which imposes strict requirements on the measurement environment.

The commonality of the above several non-contact measurement methods is that their evaluation scales are all based on the image information in the vertical axis direction. Since the change of axial magnification caused by the change of the object distance of the optical system is the square of the change of vertical magnification, if one kind of axial information can be selected as the evaluation scale, the sensitivity of curvature radius measurement can be further improved.

In recent years, the differential confocal (confocal) technology in the field of microscopic imaging at home and abroad has developed rapidly. This technology uses the axial light intensity response curve as the evaluation scale, and its sensitivity is higher than the evaluation method in the vertical direction. As data information, it has a higher ability to resist environmental interference than image processing methods. For example, the Chinese patent "Differential Confocal Scanning Detection Method with High Spatial Resolution" (Patent No.: 200410006359.6), which proposed a super-resolution differential confocal detection method, made the axial resolution of the system reach the nanometer level, and significantly improved However, the differential confocal technology is mainly applicable to the field of microscopic microscopic measurement, and the report that this technology is directly applied to the fixed focus, and then realizes the measurement of the radius of curvature has not been seen so far.

Contents of the invention

The purpose of the present invention is to solve the problem of high-precision measurement of the radius of curvature of the lens, and propose a method and device for measuring the radius of curvature of the differential confocal, using the point of focus corresponding to the apex of the measured lens and the center of the sphere when the response curve of the differential confocal is zero-crossing features for precise focusing.

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

The differential confocal radius of curvature measuring method of the present invention includes

(a) Adjust the optical system before the measurement, pass the parallel light through the spectroscopic system (2), converge at the focal point (4) through the lens (3), place the concave lens (7) to be measured near the focal point (4), and then the light is passed by After being reflected by the concave lens (7) to be measured, it is reflected by the spectroscopic system (2) and enters the differential confocal system (8);

(b) During measurement, scan and move the measured concave lens (7) in the direction of the optical axis, and the differential confocal system (8) determines the apex and focus of the measured concave lens (7) by detecting the absolute zero value of the differential response signal (4) coincide, the position of measured concave lens (7) is the first focus position (5) now;

(c) Scanning and moving the measured concave lens (7) along the optical axis direction, using the differential confocal system (8) again, when the focal point (4) coincides with the spherical center of the measured concave lens (7), detect The differential response signal is an absolute zero value, and the position of the measured concave lens (7) is the second focus position (6);

(d) measuring the distance between the first focus position (5) and the second focus position (6), which is the radius of curvature r of the measured lens;

According to the method for measuring the radius of curvature of the differential confocal lens, the concave lens can be replaced by a convex lens to form a method for measuring the radius of curvature of the differential confocal convex lens.

According to the method for measuring the radius of curvature of the differential confocal lens, the differential confocal system (8) can be replaced by the confocal system (9) to form a method for measuring the radius of curvature of the confocal lens.

The method of measuring the radius of curvature of the confocal lens is:

(a) Adjust the optical system before the measurement, pass the parallel light through the spectroscopic system (2), converge at the focal point (4) through the lens (3), place the measured lens near the focal point (4), and then pass the light through the measured lens (7) After reflection, it enters into the confocal system (9) through the spectroscopic system (2) reflection;

(b) During measurement, the lens under test (7) is scanned and moved in the direction of the optical axis, and the confocal system (9) determines that the apex of the lens under test coincides with the focal point (4) by detecting the maximum value point of the response signal. When the position of the measured lens (7) is the first focus position (5);

(c) Scan and move the tested lens (7) along the optical axis, and use the confocal system (9) again. When the focal point (4) coincides with the spherical center of the tested lens, the detected response signal is extremely Large value point, the position of the measured lens (7) is the second focus position (6) at this moment;

(d) measuring the distance between the first focus position (5) and the second focus position (6), which is the radius of curvature r of the measured lens;

The differential confocal (confocal) lens curvature radius measurement method can also work together with the differential confocal system (8) (confocal system (9)) through the focal depth compression optical system (1), using pupil filtering technology The focal depth of the measured lens (7) is compressed, and the fixed-focus sensitivity is improved.

The differential confocal lens curvature radius measurement device includes a light source (11), and also includes a spectroscopic system (2), a converging lens (3), and a differential confocal system (8); wherein the spectroscopic system (2), the converging lens (3 ) and the measured lens (7) are sequentially placed in the light source (11) outgoing light direction, the differential confocal system (8) is placed in the reflection direction of the spectroscopic system (2), the measured lens (7), the converging lens (3) and The beam splitting system (2) reflects the light beam to the differential confocal system (8), and cooperates with the differential confocal system (8) to realize the fixed focus of the first focus position (5) and the second focus position (6).

According to the differential confocal curvature radius measuring device, the differential confocal system (8) can be replaced by the confocal system (9).

The differential confocal (confocal) radius of curvature measurement device may further include a focal depth compression optical system (1) for reducing the focal depth of the measured lens (7).

The differential confocal (confocal) radius of curvature measurement device may also include a modulation control system (10) for controlling the light source (11) and the differential confocal system (8) (confocal system (9)) to perform modulation and Filtering to suppress the impact of environmental interference on measurement accuracy.

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

1. For the first time, it is proposed to use the zero-crossing point of the differential confocal response curve to determine the target position, to achieve two precise focusing, and to extend the principle of differential confocal microscopy to the field of curvature radius measurement.

2. For the first time, it is proposed to use the maximum point of the confocal response curve to determine the target position, to achieve two precise focusing, and to extend the principle of confocal microscopy to the field of curvature radius measurement.

3. In this measurement method, the differential confocal (confocal) principle uses the light intensity response curve as the focus criterion, and cooperates with the differential confocal (confocal) system for light intensity modulation and filtering to reduce air disturbances and other environments The impact of interference on measurement accuracy has higher stability than the curvature radius measurement method that uses images and interference fringes as the focus criterion.

4. Using pupil filtering technology and differential confocal (confocal) technology to reduce the focal depth of the lens in the measurement of the radius of curvature and enhance the sensitivity of fixed focus.

Description of drawings

Fig. 1 is the schematic diagram of the method for measuring the radius of curvature of a differential confocal concave lens of the present invention;

Fig. 2 is the schematic diagram of the method for measuring the radius of curvature of the differential confocal convex lens of the present invention;

Fig. 3 is the schematic diagram of confocal radius of curvature measuring method of the present invention;

Fig. 4 is the schematic diagram of differential confocal radius of curvature measuring device of the present invention;

Fig. 5 is the schematic diagram of confocal radius of curvature measuring device of the present invention;

6 is a schematic diagram of an embodiment of the differential confocal radius of curvature measurement of the present invention;

7 is a schematic diagram of an embodiment of the measurement of the confocal radius of curvature of the present invention;

Fig. 8 is a differential response curve diagram of an embodiment of differential confocal curvature radius measurement of the present invention;

Fig. 9 is a detector response curve diagram of an embodiment of confocal radius of curvature measurement in the present invention;

Among them: 1-focal depth compression optical system, 2-splitting system, 3-converging lens, 4-focus position, 5-first focus position, 6-second focus position, 7-lens under test, 8-differential common Focal system, 9-confocal system, 10-modulation control system, 11-light source, 12-polarization beam splitter, 13-1/4 wave plate, 14-translation stage, 15-mirror holder, 16-photoelectric sensor, 17- Pinhole, 18-lens, 19-photoelectric sensor, 20-pinhole, 21-lens, 22-beam splitter.

Detailed ways

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

The basic idea of the present invention is to use the principle of differential confocal (confocal) to perform precise focusing twice, realize high-precision curvature radius measurement, and reduce the influence of the environment on the measurement accuracy through light intensity modulation and filtering technology.

Embodiment one

In this embodiment, differential confocal curvature radius measurement is performed on a concave lens. As shown in Figure 6, it is a differential confocal radius of curvature measurement method, and its measurement steps are:

First, adjust the optical system before the measurement, turn on the light source 11, the emitted parallel light passes through the beam splitting system composed of the polarizing beam splitter 12 and the 1/4 wave plate 13, converges at the focal point 4 through the converging lens 3, and places the measured lens Near the focus position 4, after the light is reflected by the measured lens 7, it is reflected by the 1/4 wave plate 13 and the polarization beam splitter 12 and enters the beam splitter 22 of the differential confocal system; the beam splitter 22 divides the light into two paths, wherein One path of transmitted light passes through the lens 21 and the pinhole 20 to illuminate the photoelectric sensor 19, and the other path of reflected light passes through the lens 18 and the pinhole 17 to illuminate the photoelectric sensor 16;

During the measurement process, the measured lens 7 is moved along the translation stage 14 in the direction of the optical axis of the converging lens 3, and the differential confocal system 8 determines the absolute zero point value of the differential response signals of the photoelectric sensor 16 and the photoelectric sensor 19. The apex of the tested lens coincides with the focal point 4 , that is, this position is the first focal point position 5 . The response signal is shown in Figure 8, where I ₁ (z) and I ₂ (z) are the response signals of the two photoelectric sensors, and FES(z) is the differential response signal;

Then, using the differential confocal system 8 again, the measured lens 7 is scanned and moved along the translation stage 14 in the direction of the optical axis of the converging lens 3, and the second focus position 6 is determined by detecting the absolute zero point value of the differential response signal. When the focal point 4 coincides with the spherical center of the tested lens, the response signal is shown in Figure 8, where I ₁ (z) and I ₂ (z) are the response signals of the two photoelectric sensors, and FES(z) is the differential response signal ;

Then, the translation stage 14 uses a grating length measuring mechanism to measure the distance between the first focus position 5 and the second focus position 6, which is the value of the radius of curvature r of the measured lens;

In this embodiment, the depth of focus compression optical system 1 cooperates with the differential confocal system 8 to compress the depth of focus of the measured lens 7 by using pupil filtering technology to improve the focus sensitivity.

As shown in Figure 6, a differential confocal radius of curvature measurement device includes a light source 11, a polarizing beam splitter 12, a 1/4 wave plate 13, a converging lens 3 and a measured lens placed in the light source 11 in the direction of parallel light rays 7. It also includes a differential confocal system placed in the reflection direction of the polarizing beam splitter 12, wherein the measured lens 7, polarizing beam splitter 12, and 1/4 wave plate 13 reflect the light beam to the beam splitter 22 in the differential confocal system The beam splitter 22 divides the light into two paths, and the transmitted light passes through the lens 21, the pinhole 20 to illuminate the photoelectric sensor 19, and the reflected light passes through the lens 18, the pinhole 17 to illuminate the photoelectric sensor 16; the measured lens 7 is placed on the translation platform 14, and Cooperate with the differential confocal system to realize the positioning of the first focus position 5 and the second focus position 6 .

The device includes a focal depth compression optical system 1 for reducing the focal depth of the measured lens 7 .

The device includes a modulation control system 10, which is used to control the light source 11 and the differential confocal system 8 to perform modulation and filtering, so as to suppress the impact of environmental interference on the measurement accuracy.

Embodiment two

This embodiment is aimed at the measurement of the confocal curvature radius of the concave lens. According to the embodiment of the method for measuring the radius of curvature of the differential confocal, in the process of adjusting the optical path, the differential confocal system 8 in Embodiment 1 can be replaced by the confocal system 9, and the condenser lens 18 in the confocal system converges the light rays and converges them. The light passes through the pinhole 17 to illuminate the photoelectric sensor 16;

As shown in Figure 7, during the measurement process, the measured lens 7 is scanned and moved along the translation stage 14 in the direction of the optical axis of the converging lens 3, and the confocal system determines the measured lens by detecting the maximum point of the corresponding signal of the photoelectric sensor 16. The response signal of the first focus position 5 is shown in FIG. 9 .

Then, the grating length measuring mechanism in the translation stage drives the measured lens to move in the direction of the optical axis of the converging lens 3. During the moving process of the measured lens, the confocal system determines the maximum value point of the corresponding signal of the photoelectric sensor 16 to determine the measured lens. For the second focus position 6 of the lens, the translation stage uses a grating length measuring mechanism to measure the distance between the first focus position 5 and the second focus position 6, which is the radius of curvature r of the measured lens;

This embodiment realizes the high-precision measurement of the curvature radius through a series of measures, realizes the differential confocal (confocal) curvature radius measurement method and device, and has higher measurement accuracy than conventional measurement methods.

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 protection scope 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.

Claims (9)

1. The differential confocal radius of curvature measurement method is characterized in that: (a) Adjust the optical system before the measurement, pass the parallel light through the spectroscopic system (2), converge at the focal point (4) through the lens (3), place the concave lens (7) to be measured near the focal point (4), and then the light is passed by After being reflected by the concave lens (7) to be measured, it is reflected by the spectroscopic system (2) and enters the differential confocal system (8); (b) During measurement, the measured concave lens (7) is scanned and moved in the direction of the optical axis, and the differential confocal system (8) determines the phase between the vertex of the measured lens and the focal point (4) by detecting the absolute zero value of the differential response signal. Overlap, the position of measured concave lens (7) is the first focus position (5) now; (c) Scanning and moving the measured concave lens (7) along the optical axis direction, using the differential confocal system (8) again, when the focal point (4) coincides with the spherical center of the measured concave lens (7), detect The differential response signal is an absolute zero value, and the position of the measured concave lens (7) is the second focus position (6); (d) Measure the distance between the first focus position (5) and the second focus position (6), which is the radius of curvature r of the measured concave lens. 2. The method for measuring the radius of curvature of a differential confocal lens according to claim 1, wherein the concave lens is replaced by a convex lens to form a method for measuring the radius of curvature of a differential confocal convex lens. 3. The differential confocal radius of curvature measurement method according to claim 1, characterized in that: the differential confocal system (8) can be replaced by a confocal system (9) to form a confocal lens curvature radius measurement method. 4. according to claim 1 and 3 described confocal lens radius of curvature measuring methods, it is characterized in that: (a) Adjust the optical system before the measurement, pass the parallel light through the spectroscopic system (2), converge at the focal point (4) through the lens (3), place the measured lens near the focal point (4), and then pass the light through the measured lens (7) After reflection, it enters into the confocal system (9) through the spectroscopic system (2) reflection; (b) During measurement, the lens under test (7) is scanned and moved in the direction of the optical axis, and the confocal system (9) determines that the apex of the lens under test coincides with the focal point (4) by detecting the maximum value point of the response signal. When the position of the measured lens (7) is the first focus position (5); (c) Scan and move the tested lens (7) along the optical axis, and use the confocal system (9) again. When the focal point (4) coincides with the spherical center of the tested lens, the detected response signal is extremely Large value point, the position of the measured lens (7) is the second focus position (6) at this moment; (d) Measure the distance between the first focus position (5) and the second focus position (6), which is the radius of curvature r of the lens under test. 5. differential confocal (confocal) lens curvature radius measuring method according to claim 1, is characterized in that: also can compress optical system (1) and differential confocal system (8) (or common The focal system (9) works together to compress the depth of focus of the lens under test (7) by using pupil filtering technology to improve the sensitivity of fixed focus. 6. The differential confocal lens curvature radius measuring device comprises a light source (11), and is characterized in that: it also includes a beam splitting system (2), a converging lens (3), and a differential confocal lens (8); wherein the beam splitting system (2 ), the converging lens (3) and the measured lens (7) are sequentially placed in the light source (11) outgoing light direction, the differential confocal system (8) is placed in the reflection direction of the spectroscopic system (2), the measured lens (7), The converging lens (3) and the beam splitting system (2) reflect the beam to the differential confocal system (8), and cooperate with the differential confocal system (8) to realize the first focus position (5) and the second focus position (6) fixed focus. 7. The differential confocal curvature radius measurement device according to claim 6, characterized in that: the differential confocal system (8) can also be replaced by a confocal system (9). 8. The differential confocal (confocal) radius of curvature measuring device according to claim 6, characterized in that: it can also include a focal depth compression optical system (1) for reducing the focal depth of the measured lens (7). deep. 9. differential confocal (confocal) radius of curvature measurement device according to claim 6, is characterized in that: can also comprise modulation control system (10), is used for controlling light source (11) and differential confocal system ( 8) or confocal system (9) for modulation and filtering to suppress the impact of environmental interference on measurement accuracy.

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