Ridge angle in-situ detection method based on laser tracker

Abstract

The application discloses a kind of Ritchey angle in situ detection method based on laser tracker, and main steps are as follows: (1) set up large aperture plane mirror Ritchey-Common test optical path;(2) collimation method calibrates system main optical axis;(3) calibrates laser interferometer focal point position with target ball and records with tracker;(4) hand-held target ball carries out feature point sampling to the mirror surface and its outer contour of the mirror to be measured and modeling;(5) fit out mirror surface center point of the mirror to be measured, connect the focal point of the interferometer positioned with mirror surface center point as main optical axis, calculate the angle between main optical axis and plane mirror normal, i.e.Ritchey angle.The method of the application can more accurately and objectively measure Ritchey angle, has small dependence on artificial, hardware or software algorithm, can be applied to plane mirror of various shapes, improves positioning precision, and reduces random error.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of optical detection, and particularly relates to a large-aperture plane mirror surface shape detection method and device, which measures and calibrates the Ritchey angle in the Ritchey-Common detection light path of the large-aperture plane mirror by using a laser tracker. BACKGROUND

[0002] The Ritchey-Common method is a commonly used large-aperture plane mirror detection method. Since the plane mirror itself has no light converging function, the Ritchey-Common method needs to use another large-aperture standard spherical mirror to cooperate to realize the detection of the measured mirror. When the Ritchey-Common method is used to detect a large-aperture plane mirror, the measured plane mirror is placed in the light path at an angle, and the angle between the normal of the mirror surface and the main optical axis of the light path is called the Ritchey angle. The accuracy of the Ritchey angle measurement will directly affect the accuracy of the Ritchey-Common method in recovering the surface shape of the measured plane mirror.

[0003] At present, there are two commonly used methods for measuring the Ritchey angle: 1. measuring the distance between the three points of the focal point of the measurement system, the intersection point of the optical axis and the plane mirror, and the intersection point of the optical axis and the spherical reference mirror, and then calculating the Ritchey angle by the cosine formula; 2. using the edge detection method in image processing technology to analyze the pixel ratio of the major and minor axes of the wave aberration image, and then inversely solving the Ritchey angle by the conversion formula from the pupil surface coordinates to the plane mirror coordinates. However, in practice, it is quite difficult to accurately measure the distance between the three points by the traditional distance measuring method, and the measurement process is easily disturbed by human subjective factors; secondly, the edge detection algorithm is also difficult to obtain an accurate Ritchey angle because of low contrast of the interference pattern, deformation or insufficient sharpness of the interference fringes, and other factors that make it difficult to identify the boundary.

[0004] The Ritchey angle is the spatial angle between the main light of the interferometer and the normal of the measured plane mirror, and its measurement is essentially a geometric angle calculation problem. Laser trackers have a very high advantage in large-scale space coordinate measurement, and their distance measurement can reach micron accuracy. Laser trackers have been widely used in the field of precision optical detection, but they have not been applied in the surface shape detection of large-aperture plane mirrors. Laser trackers can meet the requirements of precise measurement of spatial geometric parameters, and their application in Ritchey-Common detection can effectively solve the problem of inaccurate measurement of the Ritchey angle. SUMMARY

[0005] In view of the above shortcomings of the prior art, the present application provides a Ritchey angle in-situ measurement method based on a laser tracker, which can accurately establish a complete geometric model of the Ritchey-Common detection light path in space, accurately give the positions and attitudes of the focal point of the interferometer, the plane mirror and the spherical mirror in space, and finally achieve the purpose of accurately measuring the Ritchey angle intelligently, objectively and digitally.

[0006] To achieve the above object, the present application provides the following technical solutions:

[0007] The Ritchey angle in-situ detection method based on a laser tracker comprises the following steps:

[0008] Step 1: build a Ritchey-Cornu detection light path of a large-aperture plane mirror;

[0009] According to the curvature radius of a standard spherical mirror, the position of the plane mirror to be measured and the position of the laser interferometer, the position of the laser interferometer is adjusted so that the collimated laser emitted thereby is accurately irradiated on the center of the plane mirror to be measured; the pitch angle and the yaw angle of the plane mirror to be measured are adjusted so that the reflected laser is accurately incident to the exit of the laser interferometer and clear interference fringes are obtained on the screen of the laser interferometer;

[0010] Step 2: place the measuring head of the laser tracker at the central normal of the plane mirror to be measured, place the target ball near the focal point of the lens of the laser interferometer, build a collimation light path, and interference patterns appear on the screen of the laser interferometer to obtain the defocus amount of the target ball at this time; the position of the target ball at this time is recorded by the laser tracker, and the accurate spatial coordinates of the focal point of the interferometer are input in combination with the defocus amount;

[0011] Step 3: sample the feature points of the mirror surface and the outer contour of the plane mirror to be measured by closely attaching the target ball to the mirror surface and the outer contour of the plane mirror to be measured, and record the spatial coordinate positions of the target ball by using the laser tracker;

[0012] Step 4: the coordinates obtained in step 3 are used to model the mirror surface and the outer contour of the plane mirror to be measured in the software of the laser tracker, so as to obtain a complete spatial geometric model of the plane mirror; the center point of the outer contour model of the plane mirror to be measured is fitted, and the center point is projected onto the mirror surface model of the plane mirror to be measured to obtain the center point of the mirror surface of the plane mirror to be measured;

[0013] Step 5: the line connecting the focal point of the laser interferometer and the center point of the plane mirror to be measured is the reference optical axis of the Ritchey-Cornu detection light path; the included angle between the reference optical axis and the normal of the mirror surface of the plane mirror to be measured is calculated, and the Ritchey angle to be measured is obtained.

[0014] Further, in step 2, the defocus amount of the target ball ② at this time is obtained by selecting Mask graph measurement.

[0015] Further, in step 2, the geometric defocus amount of the target ball ② is calculated by the formula: wherein S4 is the Zernike defocus term parameter measured by the laser interferometer, f is the focal length of the selected interferometer lens, and R is the radius of the selected interference region.

[0016] Compared with the prior art, the advantages of the present application are:

[0017] The method for measuring the Ritchey angle can more accurately and objectively measure the Ritchey angle, has small dependence on artificial, hardware or software algorithm, and ensures the accuracy of the Ritchey-Cornu method for measuring a large-diameter plane mirror surface shape. The application has strong adaptability and can be applied to plane mirrors of various shapes. The application adopts a theoretical calculation method to obtain the spatial position of the interferometer focus, improves positioning accuracy, and reduces random errors by sampling and modeling the to-be-measured plane mirror through multiple points. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a measurement flowchart of the Ritchey angle in-situ detection method based on a laser tracker;

[0019] Figure 2 is a schematic diagram of a Ritchey-Cornu detection light path and a laser tracker position;

[0020] Figure 3 is a schematic diagram of a target ball positioning interferometer focus;

[0021] Figure 4 is a schematic diagram of a target ball sampling a feature point of a to-be-measured plane mirror;

[0022] Figure 5 is a "cross" sampling schematic diagram.

[0023] Markings in the figure: 1-laser tracker, 2-target ball, 3-laser interferometer, 4-to-be-measured plane mirror, 5-standard spherical mirror. DETAILED DESCRIPTION

[0024] The application will be further described in detail below with reference to the drawings.

[0025] The Ritchey angle in-situ detection method based on a laser tracker uses devices and elements including a laser tracker 1, a target ball 2, an interferometer 3, a to-be-measured plane mirror 4 and a standard spherical mirror 5 to measure the Ritchey angle in the Ritchey-Cornu detection light path of a large-diameter plane mirror, and the Ritchey angle in the Ritchey-Cornu detection light path can be accurately and objectively measured.

[0026] In this embodiment, a 2m-diameter to-be-measured plane mirror main mirror is taken as an example for illustration. The measurement flowchart of the Ritchey angle in-situ detection method based on a laser tracker is as shown in Figure 1 and specifically includes the following steps:

[0027] Step 1: as shown in Figure 2As shown, the large-aperture plane mirror Ritchey-Common detection light path is built. According to the radius of curvature of the standard spherical mirror 5, the plane mirror 4 to be measured and the laser interferometer 3 are placed at appropriate positions to ensure that the focal point of the interferometer 3 coincides with the center of the radius of curvature of the standard spherical mirror 5. The position of the laser interferometer 3 is adjusted so that the collimated laser emitted thereby accurately irradiates the center of the plane mirror to be measured; the pitch angle and the yaw angle of the plane mirror 4 to be measured are adjusted so that the reflected laser accurately enters the exit of the laser interferometer 3 and clear interference fringes are obtained on the screen.

[0028] Step 2: The laser tracker probe is placed at or as close as possible to the normal line at the center of the plane mirror 4 to be measured, as shown in Figure 3 The target ball 2 is placed near the focal point of the laser interferometer 3, the autocollimation light path is built, and the interference pattern appears on the screen of the laser interferometer main machine. The defocus amount of the target ball 2 at this time is obtained by selecting the Mask diagram measurement. The geometric defocus amount of the target ball 2 is calculated by the formula: The geometric defocus amount of the target ball 2 is calculated by the formula: S4 is the Zernike defocus term parameter measured by the laser interferometer, f is the focal length of the selected interferometer lens, and R is the radius of the selected interference area. The position of the target ball at this time is recorded by the laser tracker 1, and the precise spatial coordinates of the focal point of the interferometer are input in combination with the defocus amount.

[0029] Step 3: as shown in Figure 4 The target ball is closely attached to the mirror surface and the outer contour of the plane mirror 4 to be measured to sample the feature points, and the spatial position of the target ball is recorded by the laser tracker 1. As shown in Figure 5 The mirror surface of the plane mirror 4 to be measured adopts the "herringbone" sampling mode; the outer contour adopts the generatrix sampling mode, and n target ball 2 spatial coordinates are obtained:

[0030] (x1,y1,z1)……(x n ,y n ,z n ).

[0031] Step 4: The coordinates obtained in step 3 are used to model the mirror surface and the outer contour of the plane mirror 4 to be measured in the laser tracker software, and a complete spatial geometric model of the plane mirror is obtained. The center point of the outer contour model of the plane mirror 4 to be measured is fitted, and the mirror center point of the plane mirror 4 to be measured is obtained by projecting it onto the mirror surface model.

[0032] Step 5: the line connecting the focal point of the laser interferometer 3 obtained in step 2 and the center point of the plane mirror 4 to be measured is the reference optical axis of the Ritchey-Common detection light path. The included angle between the reference optical axis and the normal of the mirror center of the plane mirror 4 to be measured is calculated, which is the measured Ritchey angle.

[0033] The contents not described in detail in the specification of the present application belong to the known technology of the person skilled in the art.

[0034] In summary, the present application is a kind of Ritchey angle in situ detection method based on laser tracker, and the main steps include: (1) set up large aperture plane mirror Ritchey-Common test optical path;(2) collimation method calibrates system main optical axis;(3) calibrate laser interferometer focal position with target ball and record with tracker;(4) hand-held target ball to the mirror surface and its outer contour of the plane mirror to be measured for feature point sampling and modeling;(5) fit out the plane mirror mirror center point, connect the located interferometer focal point and the plane mirror mirror center point as main optical axis, calculate the included angle between main optical axis and plane mirror normal, that is, Ritchey angle.The present application is a kind of large aperture optical system reference optical axis establishment method based on laser tracker-interferometer combined measurement, which can realize the fast and accurate establishment of optical system such as telescope during the adjustment stage to provide accurate and reliable adjustment reference for subsequent adjustment process.

[0035] The above only describes preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement and improvement within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A Ritchie angle in-situ detection method based on a laser tracker, characterized in that, Comprising the following steps: Step 1: build a large aperture plane mirror Ritchey-Common detection light path; According to the curvature radius of the standard spherical mirror, the position of the plane mirror to be measured and the position of the laser interferometer; adjust the position of the laser interferometer so that the collimated laser emitted thereby accurately irradiates the center of the plane mirror to be measured; adjust the pitch angle and yaw angle of the plane mirror to be measured so that the reflected laser accurately enters the exit port of the laser interferometer and obtains clear interference fringes on the screen of the laser interferometer; Step 2: The host of the laser tracker is placed at the center normal of the plane mirror to be measured, the target ball is placed near the focal point of the laser interferometer lens, the self-collimation light path is built, the interference pattern appears on the screen of the laser interferometer, and the defocus amount of the target ball at this time is obtained; the position of the target ball at this time is recorded by the laser tracker, and the precise spatial coordinates of the focal point of the interferometer are input combined with the defocus amount; the defocus amount of the target ball at this time is obtained by selecting the Mask diagram measurement; the geometric defocus amount of the target ball is calculated by the formula: , wherein S4 is the Zernike defocus term parameter measured by the laser interferometer, f is the focal length of the selected interferometer lens, and R is the radius of the selected Mask diagram; Step 3: sample the feature points of the target ball closely attached to the mirror surface and the outer contour of the plane mirror to be measured, and record the spatial coordinate positions of the target ball using a laser tracker; Step 4: based on the coordinates obtained in step 3, model the mirror surface and the outer contour of the plane mirror to be measured in the laser tracker software to obtain a complete spatial geometric model of the plane mirror; fit the center point of the outer contour model of the plane mirror to be measured, project it onto the mirror surface model of the plane mirror to be measured, and obtain the center point of the mirror surface of the plane mirror to be measured; Step 5: the line connecting the focal point of the laser interferometer and the center point of the plane mirror to be measured is the reference optical axis of the Ritchey-Common detection light path; Calculate the included angle between the reference optical axis and the normal of the mirror surface of the plane mirror to be measured, which is the measured Ritchey angle.

Images