Error calibration method for measuring off-axis convex aspheric surface by using optical profile scanner

Abstract

The invention relates to an error calibration method for measuring an off-axis convex aspheric surface by using an optical contour scanner, which comprises the following steps of: (1) selecting a circular off-axis convex aspheric surface 1 as a measurement standard part, measuring the circular off-axis convex aspheric surface 1 by using an interferometer in cooperation with a Hindle ball, and storing a surface shape measurement result 1; (2) measuring the circular off-axis convex aspheric surface 1 by using an optical contour scanner, and storing a surface shape measurement result 2; (3) analyzing and processing the measurement result 1 and the measurement result 2 to obtain a surface shape measurement error; (4) calculating the change trend and the difference value of the normal angles on the optical surface specific ring belts of the off-axis convex aspheric surface 1 of the standard part and the off-axis convex aspheric surface 2 of the tested part, and the difference value of the sensor angle and the normal angle when the contourgraph is used for testing; (5) taking the normal angle difference value calculated in the previous step and the difference value between the sensor angle and the normal angle as error calibration parameters, and adjusting the surface shape reference measurement error according to the error calibration parameters to obtain an error calibration result '; and (6) measuring the surface shape of the off-axis convex aspheric surface 2 of the measured piece by using an optical contourgraph, and eliminating the measurement result to obtain the accurate surface shape of the convex aspheric surface 2.

Description

Technical Field

[0001] The invention belongs to the technical field of processing and testing of large-aperture optical elements of optical lenses in the field of remote sensing, and in particular relates to an error calibration method for measuring off-axis convex aspheric surfaces by using an optical profile scanner. Background Art

[0002] Large-aperture optical systems have the characteristics of high angular resolution and strong energy collection capabilities. They are widely used in astronomical observations and space-to-earth observations. As a key component of optical systems, large-aperture reflectors are one of the key technologies that countries have invested a lot of money, manpower and material resources in research and development. Large-aperture convex aspheric surfaces are often used as secondary mirrors in optical systems. The surface shape detection, especially the measurement of off-axis convex aspheric mirror shape, has always been a difficult point in optical detection. The classic test method is to use the Hindle sphere for aberration-free point measurement. However, the size of the Hindle sphere is often several times that of the mirror to be measured, and the high-precision large-aperture Hindle sphere greatly increases the manufacturing cost. Using a compensating lens or CGH to perform zero-position compensation interferometric measurement on a convex aspheric surface is also a conventional method for detecting convex aspheric surfaces, but the aperture of the measuring compensating lens and CGH needs to be larger than the aspheric element to be tested. There are currently many difficulties in the preparation of large-sized compensating lenses and CGHs, and the cost is also very high. In recent years, it has become increasingly common to use high-precision optical profile scanners to measure convex aspheric surfaces. However, the accuracy of this equipment in measuring off-axis convex aspheric surfaces is low and cannot meet the surface shape index requirements of optical components. Summary of the invention

[0003] The technical problem solved by the present invention is: to overcome the shortcomings of the existing measurement technology, to provide an error calibration method for measuring off-axis convex aspheric surfaces using an optical profile scanner, and to achieve high-precision, high-efficiency and low-cost measurement of off-axis convex aspheric surfaces.

[0004] The technical solution of the present invention is: an error calibration method for measuring an off-axis convex aspheric surface using an optical profile scanner, comprising:

[0005] (1) A circular off-axis convex aspheric surface 1 with a precision that meets the requirements is selected as a measurement standard, and the circular off-axis convex aspheric surface 1 is measured by using an interferometer in conjunction with a Hindle sphere, and the surface measurement result 1 is saved;

[0006] (2) measuring the circular off-axis convex aspheric surface 1 using an optical profile scanner, and saving the surface measurement result 2;

[0007] (3) Analyze and process measurement results 1 and 2 to obtain the surface shape measurement error △ of the profile scanner relative to the interferometer;

[0008] (4) Calculate the change trend and difference of the normal angle on the specific ring zone of the optical surface of the standard off-axis convex aspheric surface 1 and the off-axis convex aspheric surface 2 of the measured part, as well as the difference between the sensor angle and the normal angle during the profilometer test;

[0009] (5) The normal angle difference calculated in the previous step and the difference between the sensor angle and the normal angle are used as error calibration parameters. According to the error calibration data and the error calibration parameters of step (4), the surface reference measurement error △ calculated in step (3) is adjusted to obtain the error calibration result △′;

[0010] (6) The surface shape of the off-axis convex aspheric surface 2 of the measured object is measured using an optical profilometer. The measurement result is eliminated from the error calibration result △′ to obtain the accurate surface shape of the convex aspheric surface 2.

[0011] Preferably, the surface error obtained by performing surface shape detection of the circular off-axis convex aspheric surface 1 using an interferometer in conjunction with a Hindle sphere should be better than the surface shape index requirement of the off-axis convex aspheric surface 2 of the measured object.

[0012] Preferably, in step (2), the circular off-axis convex aspheric surface 1 is placed at the center of the optical profiler as a flat-back optical element with equal edge thickness for measurement.

[0013] Preferably, the centering error of the circular off-axis convex aspheric surface 1 placed on the optical profilometer is controlled within 0.05 mm, and the tilt error is controlled within 20".

[0014] Preferably, in step (4), 36k evenly distributed points are selected on the specific ring belt, and k is 1, 2, or 3.

[0015] Preferably, the specific annulus is selected from a 50% diameter annulus to a 70% diameter annulus.

[0016] Preferably, the error calibration result Δ′ is obtained by the following method:

[0017] Determine whether the error calibration parameters are all within 1°. If they are all within 1°, determine the error calibration result according to the aperture; otherwise, the processing is terminated, and other existing processing methods can be used to perform error calibration; the error calibration result determined according to the aperture is: determine the aperture of the off-axis convex aspheric surface 1 of the standard part and the off-axis convex aspheric surface 2 of the measured part. If they are the same aperture, △′=△, otherwise, the error calibration result is proportionally scaled according to the aperture.

[0018] Compared with the prior art, the beneficial effects of the present invention are: in view of the current difficulty in detecting off-axis convex aspheric optical components, an error calibration method for measuring off-axis convex aspheric surfaces using an optical profile scanner is studied, which can effectively improve the detection accuracy and efficiency of off-axis convex aspheric surfaces and achieve a comprehensive improvement in the preparation accuracy and production capacity of large-aperture optical components. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present invention. Moreover, the same reference symbols are used throughout the accompanying drawings to represent the same components. In the accompanying drawings:

[0020] Figure 1 The measuring optical path for measuring off-axis convex aspheric surfaces using an interferometer and a Hindle sphere;

[0021] Figure 2 Schematic diagram of a flat-back off-axis optical element with equal edge thickness

[0022] Figure 3 Schematic diagram of off-axis aspheric surface measurement by profile scanner;

[0023] Figure 4 Schematic diagram of the normal angle of the off-axis convex aspheric annulus;

[0024] Figure 5 It is the normal angle difference curve in the embodiment. DETAILED DESCRIPTION

[0025] The present invention will be further described below in conjunction with the embodiments.

[0026] Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present disclosure and to be able to fully convey the scope of the present disclosure to those skilled in the art. It should be noted that, in the absence of conflict, the embodiments of the present invention and the features described in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0027] An error calibration method for measuring an off-axis convex aspheric surface using an optical profile scanner, the method comprising the following steps:

[0028] (1) A circular high-precision off-axis convex aspheric surface 1 is selected as a measurement standard, and the convex aspheric surface 1 is measured using an interferometer and a high-precision Hindle ball, and the surface measurement result 1 is saved;

[0029] The off-axis convex aspheric surface 1 should be able to be tested using an interferometer with a high-precision Hindle sphere. The optical path is shown in the attached Figure 1The system error measured by this aberration-free point method is easy to separate and only includes the surface error of the Hindle sphere, which can achieve high measurement accuracy; the surface error of the off-axis convex aspheric surface 1 obtained should be better than the surface index requirement of the off-axis convex aspheric surface 2 of the measured object;

[0030] (2) measuring the circular off-axis convex aspheric surface 1 using an optical profile scanner, and saving the surface measurement result 2;

[0031] The circular off-axis convex aspheric surface 1 is a flat-back optical element with equal thickness at the edge, see the attached Figure 2 , put it in the center of the profilometer for measurement, and try to eliminate the centering and tilt errors. See the attached diagram Figure 3 ;

[0032] (3) Analyze and process measurement results 1 and 2 to obtain the surface shape measurement error △ of the profile scanner relative to the interferometer;

[0033] (4) calculating the change trend and difference of the normal angle on a specific ring zone of the optical surface of the standard off-axis convex aspheric surface 1 and the off-axis convex aspheric surface 2 of the measured object as error calibration parameters;

[0034] Generally, 50% diameter annulus and 70% diameter annulus are selected; off-axis convex aspheric surfaces used for space cameras are usually off-axis hyperbolas, so they have similar normal angle direction change trends, such as Figure 4 , 5 shown.

[0035] (5) adjusting the surface reference measurement error △ calculated in step (3) according to the sensor angle error calibration data of the profile scanner and the error calibration parameter of step (4), so as to obtain the error calibration result △′;

[0036] Calculate the difference in normal angles on specific rings of the optical surfaces of the standard off-axis convex aspheric surface 1 and the measured off-axis convex aspheric surface 2, with a variation range within 1°. Then calculate the difference between the sensor angle and the normal angle during the profiler test. According to the sensor angle error calibration data, the difference between the measured angle and the normal angle is within 1°, and the measurement data error can be ignored. The sensor angle error calibration data of the profile scanner represents the profile scanning error when the sensor angle deviates from the normal angle of the optical surface of the measured object. Combined with the error calibration parameters obtained in step (4), perform a transformation calculation on △ to obtain the error calibration result △′.

[0037] (6) Use a profilometer to measure the surface shape of the off-axis convex aspheric surface 2 of the measured object. The measurement result is eliminated from the error calibration result △′ to obtain the accurate surface shape of the convex aspheric surface 2.

[0038] Example

[0039] This embodiment provides an error calibration method for measuring an off-axis convex aspheric surface using an optical profile scanner, the method comprising the following steps:

[0040] (1) A circular high-precision off-axis convex aspheric surface 1 is selected as the measurement standard. The parameters of the high-precision convex aspheric surface selected in this project are as follows: R = 702mm, K = -1.01, off-axis amount is 148mm, and diameter D = Φ200mm; the parameters of the off-axis convex aspheric surface 2 of the measured object are: R = 480mm, K = -1.01, off-axis amount is 114.82mm, and diameter D = Φ150mm; the surface shape error of the off-axis convex aspheric surface 1 obtained should be better than the surface shape index requirements of the off-axis convex aspheric surface 2 of the measured object;

[0041] Use interferometer with high-precision Hindle sphere to perform aberration-free point measurement. See attached for the optical path. Figure 1 , Hindle spherical error is RMS = 0.01λ (λ = 632.8nm), the surface error measurement result of the off-axis convex aspheric surface 1 is 0.013λ, and the surface error requirement of the off-axis convex aspheric surface 2 of the measured object is 0.02λ;

[0042] (2) Use an optical profile scanner to measure the circular off-axis convex aspheric surface 1 and save the surface measurement results; the off-axis convex aspheric surface 1 should be placed at the center of the profiler as an optical element with basically equal thickness at the edge for measurement. See the attached schematic diagram. Figure 2 ; Try to eliminate the centering and tilt errors, the centering error is controlled within 0.05mm, and the tilt error is controlled within 20"; the contour scanning measurement result is the surface error RMS = 0.025λ;

[0043] (3) The interferometric measurement results and profile measurement results of the off-axis convex aspheric surface 1 are analyzed and processed, and the difference △ between the profiler and the interferometer is obtained as RMS = 0.018λ;

[0044] (4) Calculate the change trend and difference of the normal angle on the specific ring zone of the optical surface of the standard off-axis convex aspheric surface 1 and the off-axis convex aspheric surface 2 of the measured object as the error calibration parameter. In this project, the 65% diameter ring zone is selected to calculate the normal angle; the off-axis convex aspheric surfaces used for space cameras are usually off-axis hyperbolas, so they have similar normal angle direction change trends;

[0045] The following are the normal angles of the Φ150 mm diameter annulus of the off-axis convex aspheric surface 1, taking 36 points evenly distributed on the annulus.

[0046]

[0047]

[0048] The following is the normal angle of the 70% diameter annulus of the off-axis convex aspheric surface 2:

[0049]

[0050]

[0051] The normal angle difference is as follows Figure 4 shown.

[0052] (5) According to the sensor angle error calibration data of the profile scanner and the error calibration parameter of step (4), i.e., the normal angle difference, the surface reference measurement error △ calculated in step (3) is adjusted to obtain the error calibration result △′; according to the normal angle difference of the two aspherical annuli calculated in step (4), the difference is within the range of [1.9, 2.5], and the variation range is less than 0.6°, see Figure 5 . The difference between the sensor angle and the normal angle during the test can be calculated in the profilometer measurement software, which is less than 1°. According to the profilometer sensor angle error calibration data, the difference between the measured angle and the normal angle is within 1°, and the measurement data error can be ignored. According to the normal angle curve, it is believed that the normal angle change trends of the two aspherical surfaces on the taken rings are consistent, that is, the measurement error distribution is consistent, △ = △′ under the same caliber, and the error is proportionally scaled under different calibers. This project is suitable for the second case;

[0053] (6) The off-axis convex aspheric surface 2 to be measured is measured using a profile scanner, and the measurement error △′ is eliminated from the measurement result to obtain the accurate surface shape of the off-axis convex aspheric surface 2 to be measured.

[0054] Although the present invention has been disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the protection scope of the technical solution of the present invention.

Claims

1. An error calibration method for measuring off-axis convex aspheric surfaces using an optical profile scanner, characterized in that: include: (1) A circular off-axis convex aspheric surface 1 with a precision that meets the requirements is selected as a measurement standard, and the circular off-axis convex aspheric surface 1 is measured by using an interferometer in conjunction with a Hindle sphere, and the surface measurement result 1 is saved; (2) measuring the circular off-axis convex aspheric surface 1 using an optical profile scanner, and saving the surface measurement result 2; (3) Analyze and process measurement results 1 and 2 to obtain the surface shape measurement error △ of the profile scanner relative to the interferometer; (4) Calculate the change trend and difference of the normal angle on the specific ring zone of the optical surface of the standard off-axis convex aspheric surface 1 and the off-axis convex aspheric surface 2 of the measured part, as well as the difference between the sensor angle and the normal angle during the profilometer test; (5) The normal angle difference calculated in the previous step and the difference between the sensor angle and the normal angle are used as error calibration parameters. According to the error calibration data and the error calibration parameters of step (4), the surface reference measurement error △ calculated in step (3) is adjusted to obtain the error calibration result △′; (6) The surface shape of the off-axis convex aspheric surface 2 of the measured object is measured using an optical profilometer. The measurement result is eliminated from the error calibration result △′ to obtain the accurate surface shape of the convex aspheric surface 2.

2. The error calibration method according to claim 1, characterized in that: The surface error of the circular off-axis convex aspheric surface 1 obtained by surface shape detection using an interferometer in conjunction with a Hindle sphere should be better than the surface shape index requirement of the off-axis convex aspheric surface 2 of the measured object.

3. The error calibration method according to claim 1, characterized in that: In step (2), the circular off-axis convex aspheric surface 1 is placed at the center of the optical profiler as a flat-back optical element with equal edge thickness for measurement.

4. The error calibration method according to claim 3, characterized in that: The centering error of the circular off-axis convex aspheric surface 1 placed on the optical profiler is controlled within 0.05mm, and the tilt error is controlled within 20".

5. The error calibration method according to claim 1, characterized in that: In step (4), 36k points evenly distributed on the specific ring are selected, and k is 1, 2, or 3.

6. The error calibration method according to claim 1 or 5, characterized in that: The specific annulus is selected from a 50% diameter annulus to a 70% diameter annulus.

7. The error calibration method according to claim 1, characterized in that: The error calibration result △′ is obtained by the following method: Determine whether the error calibration parameters are all within 1°. If they are all within 1°, determine the error calibration result according to the aperture; otherwise, the processing is terminated; the error calibration result determined according to the aperture is: determine the aperture of the off-axis convex aspheric surface 1 of the standard part and the off-axis convex aspheric surface 2 of the measured part. If they are the same aperture, △′=△, otherwise, scale the error calibration result proportionally according to the aperture.

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