Error calibration method for off-axis convex aspheric surface by optical profilometer

Abstract

The error calibration method of off-axis convex aspheric surface by optical profilometer, (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 an interferometer cooperating with a Hindle sphere, and saving a surface shape measurement result 1; (2) measuring the circular off-axis convex aspheric surface 1 by an optical profilometer, and saving 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 Δ; (4) calculating the variation trend, difference and the difference between the sensor angle and the normal angle of the optical surface specific ring of the off-axis convex aspheric surface 1 and the off-axis convex aspheric surface 2 to be measured when the profilometer is tested; (5) taking the normal angle difference and the difference between the sensor angle and the normal angle calculated in the previous step as error calibration parameters, adjusting the surface shape reference measurement error Δ according to the error calibration parameters, that is, obtaining an error calibration result Δ'; (6) measuring the surface shape of the off-axis convex aspheric surface 2 to be measured by the optical profilometer, eliminating the measurement result Δ', and obtaining the accurate surface shape of the convex aspheric surface 2.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of processing and testing technology of large-aperture optical elements of optical lens in remote sensing, and particularly relates to a method for measuring error calibration of off-axis convex aspheric surface by using an optical profile scanner. BACKGROUND

[0002] Large-aperture optical systems have the characteristics of high angular resolution and strong energy collection capability, and are widely used in astronomical observation and space-to-ground observation. As a key element of optical systems, large-aperture mirrors are one of the key technologies that countries invest a large amount of funds and manpower to research and develop. Large-aperture convex aspheric surfaces are often used as secondary mirrors of optical systems, and the surface shape detection, especially the measurement of off-axis convex aspheric surface, has always been a difficulty in optical detection. The classical testing method is to use Hindle ball for no-difference point measurement. However, the size of Hindle ball is often several times that of the mirror to be measured, and the high-precision large-aperture Hindle ball greatly increases the manufacturing cost. Using compensation lenses or CGH for zero compensation interferometric measurement of convex aspheric surfaces is also a conventional method for detecting convex aspheric surfaces, but the aperture of the compensation lens and CGH to be measured is larger than the convex aspheric element to be detected. At present, there are many difficulties in the preparation of large-size compensation lenses and CGH, and the cost is also very high. In recent years, it is more and more common to measure convex aspheric surfaces by using high-precision optical profile scanners, but the accuracy of measuring off-axis convex aspheric surfaces by using the device is low, and cannot meet the surface shape index requirements of optical elements. SUMMARY

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

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

[0005] (1) selecting a circular off-axis convex aspheric surface 1 with a required precision as a measurement standard part, measuring the circular off-axis convex aspheric surface 1 by using an interferometer with a Hindle ball, and saving the surface shape measurement result 1;

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

[0007] (3) analyzing and processing the measurement result 1 and the measurement result 2 to obtain the surface shape measurement error of the profile scanner relative to the interferometer;

[0008] (4) calculating the variation trend, difference of normal angle on specific zone of optical surface of the standard off-axis aspheric convex surface 1 and the measured off-axis aspheric convex surface 2, and the difference of sensor angle and normal angle during the test of the profilometer;

[0009] (5) taking the normal angle difference calculated in the last step and the difference of sensor angle and normal angle as error calibration parameters, adjusting the surface shape reference measurement error △ calculated in step (3) according to the error calibration data and the error calibration parameters in step (4), i.e. obtaining the error calibration result △';

[0010] (6) measuring the surface shape of the measured off-axis aspheric convex surface 2 with the optical profilometer, and eliminating the error calibration result △' from the measurement result, i.e. obtaining the accurate surface shape of the convex aspheric surface 2.

[0011] Preferably, the surface shape error of the circular off-axis aspheric convex surface 1 obtained by the interferometer cooperating with the Hindle sphere for surface shape detection should be better than the surface shape index requirement of the measured off-axis aspheric convex surface 2.

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

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

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

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

[0016] Preferably, the error calibration result △' is obtained by the following method:

[0017] determining whether all the error calibration parameters are within 1°, if all the error calibration parameters are within 1°, then the error calibration result is determined according to the aperture, if not, the process is terminated, and other existing error calibration methods can be selected to calibrate the error; the error calibration result determined according to the aperture is: determining the apertures of the standard off-axis aspheric convex surface 1 and the measured off-axis aspheric convex surface 2, if the apertures are the same, then △' = △, otherwise, the error calibration result is scaled according to the apertures.

[0018] Compared with the prior art, the present application has the beneficial effects that: in view of the difficulty in detecting the off-axis aspheric convex surface optical element, a kind of error calibration method for measuring the off-axis aspheric convex surface with the optical profilometer is researched, which can effectively improve the detection precision and efficiency of the off-axis aspheric convex surface, and realize the overall improvement of the preparation precision and capacity of large-aperture optical elements. BRIEF DESCRIPTION OF DRAWINGS

[0019] Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The accompanying drawings are included to provide a better understanding of the preferred embodiments, and are not intended to be limiting of the application. Moreover, in the drawings, like reference numerals denote same or similar components. In the drawings:

[0020] Figure 1 The measurement optical path for interferometer to measure off-axis convex aspheric surface with Hindle sphere;

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

[0022] Figure 3 Schematic diagram of profile scanner to measure off-axis aspheric surface

[0023] Figure 4 Schematic diagram of off-axis convex aspheric surface with ring zone normal angle

[0024] Figure 5 Normal angle difference curve in the embodiment DETAILED DESCRIPTION

[0025] The application will be further described below with reference to the embodiments.

[0026] Exemplary embodiments of the present disclosure will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the present disclosure are shown. This present disclosure may, however, be embodied in various forms without being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and fully convey the scope of the present disclosure to those skilled in the art. It will be apparent to those skilled in the art that the embodiments of the present disclosure and features thereof can be combined with each other without conflict. The present disclosure will be described in detail with reference to the accompanying drawings and embodiments.

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

[0028] (1) Select a circular high-precision off-axis convex aspheric surface 1 as a measurement standard, measure the convex aspheric surface 1 with an interferometer combined with a high-precision Hindle sphere, and save the surface shape measurement result 1;

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

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

[0031] The circular off-axis convex aspheric surface 1 is an edge-equal-thickness flat-back optical element, as shown in the attached Figure 2 , and is placed in the center of the profiler for measurement, and the centering and tilt errors are eliminated as much as possible, as shown in the attached Figure 3 ;

[0032] (3) analyzing and processing the measurement result 1 and the measurement result 2 to obtain the surface measurement error Δ of the profiler relative to the interferometer;

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

[0034] Generally, the 50% diameter zone and the 70% diameter zone are selected; the off-axis convex aspheric surface of the space camera is generally an off-axis hyperbola, and thus has a similar variation trend of the normal angle direction, as shown in Figure 4 , 5 .

[0035] (5) adjusting the surface reference measurement error Δ calculated in step (3) according to the sensor angle error calibration data of the profiler and the error calibration parameter in step (4), that is, obtaining the error calibration result Δ';

[0036] The difference of the normal angle on the specific zone of the optical surface of the standard off-axis convex aspheric surface 1 and the measured off-axis convex aspheric surface 2 is calculated, and the variation amplitude is within 1°. The difference between the sensor angle and the normal angle during the profiler test is calculated, the difference between the measurement angle and the normal angle is within 1° according to the sensor angle error calibration data, and the measurement data error can be ignored. The sensor angle error calibration data of the profiler represents the profile scanning error when the sensor angle deviates from the normal angle of the optical surface of the measured piece. Combined with the error calibration parameter obtained in step (4), the transformation calculation of Δ is performed to obtain the error calibration result Δ'.

[0037] (6) measuring the surface of the measured off-axis convex aspheric surface 2 by the profiler, and eliminating the error calibration result Δ' from the measurement result, that is, obtaining the accurate surface of the convex aspheric surface 2.

[0038] Embodiment

[0039] The embodiment provides a method for calibrating errors of off-axis convex aspheric surfaces by using an optical profilometer, and the method comprises the following steps:

[0040] (1) selecting a circular high-precision off-axis convex aspheric surface 1 as a measurement standard part, the parameters of the high-precision convex aspheric surface selected in the project are as follows: R=702 mm, K=-1.01, off-axis amount is 148 mm, and the aperture D=Φ200 mm; the parameters of the measured off-axis convex aspheric surface 2 are as follows: R=480 mm, K=-1.01, off-axis amount is 114.82 mm, and the aperture D=Φ150 mm; the off-axis convex aspheric surface 1 surface error obtained is better than the surface error of the measured off-axis convex aspheric surface 2;

[0041] The interferometer is used to measure the off-axis convex aspheric surface 1 by using the high-precision Hindle sphere without aberration point method, and the optical path is shown in the attached Figure 1 The Hindle sphere surface error is RMS=0.01λ (λ=632.8 nm), the off-axis convex aspheric surface 1 surface error measurement result is 0.013λ, and the surface error of the measured off-axis convex aspheric surface 2 is 0.02λ;

[0042] (2) the optical profilometer is used to measure the circular off-axis convex aspheric surface 1, and the surface measurement result is saved; the off-axis convex aspheric surface 1 should be placed in the center of the profilometer as an optical element with edge basic equal thickness, and the schematic diagram is shown in the attached Figure 2 ; the centering error is controlled to be within 0.05 mm, the tilt error is controlled to be within 20", and the profilometer scanning measurement result is that the surface error RMS=0.025λ;

[0043] (3) the interference measurement result and the profilometer measurement result of the off-axis convex aspheric surface 1 are analyzed and processed, and the measurement result difference Δ of the profilometer relative to the interferometer is RMS=0.018λ;

[0044] (4) the variation trend and the difference of the normal angle of the optical surface specific ring of the off-axis convex aspheric surface 1 and the off-axis convex aspheric surface 2 are calculated as error calibration parameters, and the normal angle of the 65% diameter ring is selected in the project; the off-axis convex aspheric surface used for a space camera is usually an off-axis hyperbola, and thus has a similar variation trend of the normal angle direction;

[0045] The following is the normal angle of the Φ150 mm diameter ring of the off-axis convex aspheric surface 1, and 36 points uniformly distributed on the ring are taken.

[0046]

[0047]

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

[0049]

[0050]

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

[0052] (5) According to the sensor angle error calibration data of the profilometer and the error calibration parameters of step (4), i.e. the normal angle difference value, the surface shape reference measurement error △ calculated in step (3) is adjusted, i.e. the error calibration result △' is obtained; according to the two aspheric annular zone normal angle difference values calculated in step (4), the variation range is less than 0.6° in the interval [1.9, 2.5], see Figure 5 . The difference between the sensor angle and the normal angle during the test can be calculated in the profilometer measurement software, and both are less than 1°. According to the profilometer sensor angle error calibration data, the measurement angle and the normal angle difference value are within 1°, and the measurement data error can be ignored. According to the normal angle curve, it is considered that the normal angle variation trends of the two aspheres on the annular zone are consistent, i.e. the measurement error distribution is consistent, △=△' under the same caliber, and the error is scaled proportionally under different calibers. The present project is applicable to the second case;

[0053] (6) The measured off-axis convex asphere 2 is measured by the profilometer, and the measurement result eliminates the measurement error △', to obtain the accurate surface shape of the measured off-axis convex asphere 2.

[0054] Although the present application has been disclosed with the above preferred embodiments, it is not intended to limit the present application, and any person skilled in the art can make possible changes and modifications to the technical solutions of the present application by using the disclosed methods and technical contents without departing from the spirit and scope of the present application. Therefore, any simple modification, equivalent change and modification made according to the technical essence of the present application to the above embodiments, which does not deviate from the technical solutions of the present application, belongs to the protection scope of the technical solutions of the present application.

Claims

1. A method for calibrating the errors of an off-axis convex aspheric surface measured with an optical profiler, characterized in that, The method comprises the following steps: (1) selecting a circular off-axis convex aspheric surface 1 with a required precision as a measurement standard, and measuring the circular off-axis convex aspheric surface 1 by using an interferometer and a Hindle sphere, and saving a surface shape measurement result 1; (2) measuring the circular off-axis convex aspheric surface 1 by using an optical profilometer, and saving 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 of the optical profilometer relative to the interferometer; (4) calculating a variation trend, a difference and a difference between a sensor angle and a normal angle of the optical profilometer during testing of an optical surface specific ring of the circular off-axis convex aspheric surface 1 and a measured off-axis convex aspheric surface 2; (5) taking the difference between the normal angles of the optical surface specific ring and the difference between the sensor angle and the normal angle of the optical profilometer during testing as error calibration parameters, adjusting the surface shape reference measurement error calculated in step (3) according to the error calibration data and the error calibration parameters in step (4), and obtaining an error calibration result; The error calibration result is obtained in the following manner: determining whether the error calibration parameters are all within 1°, if all the error calibration parameters are within 1°, determining the error calibration result according to an aperture, if the apertures of the circular off-axis convex aspheric surface 1 and the measured off-axis convex aspheric surface 2 are the same, then the error calibration result is equal to the error, otherwise, the error calibration result is scaled according to the apertures; (6) measuring the surface shape of the measured off-axis convex aspheric surface 2 by using the optical profilometer, eliminating the error calibration result from the measurement result, and obtaining an accurate surface shape of the measured off-axis convex aspheric surface 2.

2. The error calibration method of claim 1, wherein: The surface shape error of the circular off-axis convex aspheric surface 1 obtained by using the interferometer and the Hindle sphere should be better than a surface shape index requirement of the measured off-axis convex aspheric surface 2.

3. The error calibration method of claim 1, wherein: In step (2), the circular off-axis convex aspheric surface 1 is measured as an edge-thickness flat-back optical element in the center of the optical profilometer.

4. The error calibration method of claim 3, wherein: The centering error of the circular off-axis convex aspheric surface 1 in the optical profilometer is controlled within 0.05 mm, and the tilt error is controlled within 20".

5. The error calibration method of claim 1, wherein: In step (4), 36k points are selected on the specific ring, and k is 1, 2 or 3.

6. The error calibration method of claim 1 or 5, wherein: The specific ring is selected from a 50% diameter ring to a 70% diameter ring.

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