Ellipsoidal reflector surface shape detection method based on zero compensation method

Abstract

The invention discloses a flat ellipsoid reflector surface shape detection method based on a zero compensation method, and belongs to the field of optical detection. The implementation method comprises the following steps of: placing a flat plate with holes in front of a flat ellipsoidal mirror, wherein the distance between the flat plate with holes and the ellipsoidal mirror is the length of a short axis of a generatrix of the ellipsoidal mirror; the perforated flat plate is provided with three equidistant holes in the same horizontal plane, the distance between the first hole site and the second hole site is equal to the distance between two focuses of the ellipsoidal mirror, and the third hole site is located at the midpoint of a connecting line of the first hole site and the second hole site; the short axis direction of the flat ellipsoidal mirror and the spatial positions of two focuses are determined based on the auxiliary optical flat plate, the spherical wave focus emitted by the interferometer is made to coincide with one focus of the ellipsoid to be measured, and the sphere center of the standard spherical mirror is made to coincide with the other focus of the ellipsoidal mirror. The light emitted by the interferometer is reflected by the ellipsoidal mirror, then is converged to another focus, is reflected by the spherical mirror and then is returned along the same path, so that zero position detection is formed, and formed interference fringes are processed to obtain the surface shape error of the ellipsoidal mirror to be detected.

Description

Technical Field

[0001] The invention relates to a surface shape detection method of an ellipsoidal reflector based on a zero position compensation method, and belongs to the technical field of optical detection. Background Art

[0002] The surface shapes of optical components can be mainly divided into three categories: plane, spherical, and aspherical. Aspherical surfaces can be further divided into secondary aspherical surfaces and higher-order aspherical surfaces. Secondary aspherical surfaces include hyperboloids, paraboloids, and ellipsoids. Using aspherical mirrors in optical systems can effectively reduce spherical aberration and reduce the number of optical components used. The surface shape accuracy of optical components directly affects the performance of the optical system.

[0003] The surface shape detection methods in optical detection can be mainly divided into three categories: profile method, geometric method and interference method. The profile method uses a detection head to scan the surface to be measured to obtain surface shape data. This method has wide applicability and can measure almost any surface shape of optical parts. It is simple to operate, but the measurement efficiency is low. The geometric method mainly obtains the surface shape of the measured surface by detecting the slope of the surface shape of the measured surface. It has a simple structure and mainly includes the knife edge method, Ronchi method, fringe reflection method and Hartmann method. However, due to factors such as the asphericity cannot be too large, the manufacturing accuracy of the lens array, and strong subjectivity, the application of this method is greatly limited. The interference method obtains the surface shape error information of the measured surface by analyzing the interference fringes generated by the wavefront reflected by the measured surface and the reference wavefront. It has the advantages of high accuracy, fast speed, high sensitivity, good stability, and good repeatability. The zero compensation method is a commonly used detection method in the interference method.

[0004] The ellipsoidal reflector is a body of revolution formed by a partial ellipse rotating around the long axis. The more common ellipsoidal reflectors on the market are those formed by rotating the elliptical curve at the long axis end. This type of reflector has a rotationally symmetrical surface shape, with two foci coinciding with the optical axis. The positions of the optical axis and the foci are easy to determine, and the surface shape detection method is relatively mature. However, for the oblate ellipsoidal reflector formed by rotating the curve near the short axis end, the positions of the two foci and the direction of the optical axis are difficult to determine. This type of oblate ellipsoidal reflector lacks an effective high-precision surface shape detection method. Summary of the invention

[0005] In order to solve the problem that there is a lack of corresponding high-precision surface detection method for oblate ellipsoidal reflectors, the purpose of the present invention is to provide a surface detection method and device for an oblate ellipsoidal reflector based on a zero-position compensation method, which determines the short-axis direction of the oblate ellipsoidal mirror and the spatial positions of the two foci based on an auxiliary optical plate, so that the focus of the spherical wave emitted by the interferometer coincides with one focus of the ellipsoidal surface to be measured, and the center of the standard spherical mirror coincides with the other focus of the ellipsoidal mirror. The light emitted by the interferometer converges to the other focus after being reflected by the ellipsoidal mirror, and can return to the original path after being reflected by the spherical mirror, thereby forming a zero-position detection, and processing the formed interference fringes to obtain the surface error information of the ellipsoidal mirror to be measured.

[0006] The purpose of the present invention is achieved through the following technical solutions.

[0007] The present invention discloses a method for detecting the surface shape of an ellipsoidal reflector based on a zero compensation method, comprising the following steps:

[0008] Step 1: Place a plate with holes in front of the oblate ellipsoidal mirror, the distance between the plate with holes and the ellipsoidal mirror is the short axis length of the generatrix of the ellipsoidal mirror; the plate with holes has three equidistant holes in the same horizontal plane, the distance between the first hole and the second hole is the distance between the two foci of the ellipsoidal mirror, and the third hole is located at the midpoint of the line connecting the first hole and the second hole; the window glass is fixed at the middle hole.

[0009] Step 2: Adjust the installation position of the perforated plate: When the laser enters from the window glass, the window glass surface will reflect part of the light back. Adjust the pitch angle and azimuth angle of the perforated plate until the reflected light returns along the original path. At this time, the normal of the plane of the perforated plate is parallel to the optical axis.

[0010] Preferably, a beam of He-Ne laser is incident on the window glass, and the surface of the window glass will reflect part of the light back.

[0011] Step 3: Adjust the installation posture of the oblate ellipsoid mirror: let the laser beam through the window glass hit the geometric center point of the oblate ellipsoid mirror, adjust the pitch angle and azimuth angle of the oblate ellipsoid mirror until the reflected light of the oblate ellipsoid mirror returns along the original path. At this time, the normal at the center of the ellipsoid mirror is parallel to the optical axis.

[0012] Step 4: Align the focus of the spherical wave emitted by the interferometer with the first hole position of the holed plate.

[0013] Step 5: Align the center of the standard spherical mirror with the second hole position of the holed plate; the relative aperture of the standard spherical mirror is larger than that of the oblate ellipsoidal mirror.

[0014] Preferably, a standard spherical mirror with a relative aperture larger than the mirror to be tested is selected, and the center of the standard spherical mirror is made to coincide with the second hole position of the plate with holes.

[0015] Step 6: Start surface measurement. The measuring beam emitted by the interferometer is focused on the first hole position and then incident on the oblate ellipsoidal mirror. The measuring light is reflected and converged at the second hole position. It is then reflected by the standard spherical mirror and returns along the original path. The measuring beam carrying the surface error information returns to the interferometer to interfere with the reference light to generate interference fringes. The interference fringe image is processed by the interferometer to obtain the surface error of the ellipsoidal mirror to be measured.

[0016] The present invention also discloses a surface shape detection device of an ellipsoidal reflector based on a zero position compensation method, which is used to implement a surface shape detection method of an ellipsoidal reflector based on a zero position compensation method. A surface shape detection device of an ellipsoidal reflector based on a zero position compensation method comprises a window glass, a plate with a hole, a standard spherical mirror and an interferometer. The plate with a hole comprises a first hole position, a second hole position and a third hole position; the distance between the first hole position and the second hole position is the distance between the two foci of the ellipsoidal mirror, and the third hole position is located at the midpoint of the line connecting the first hole position and the second hole position. The plate with a hole is placed in front of the standard spherical mirror, and the distance between the plate with a hole and the standard spherical mirror is the minor axis length of the generatrix of the ellipsoidal mirror.

[0017] Beneficial Effects

[0018] 1. The present invention discloses a surface shape detection method of an ellipsoidal reflector based on a zero-position compensation method. The method determines the short-axis direction of the oblate ellipsoidal mirror and the spatial positions of the two foci based on an auxiliary optical plate, so that the focus of the spherical wave emitted by the interferometer coincides with one focus of the ellipsoidal surface to be measured, and the center of the standard spherical mirror coincides with the other focus of the ellipsoidal mirror. The light emitted by the interferometer converges to the other focus after being reflected by the ellipsoidal mirror, and can return to the original path after being reflected by the spherical mirror, thereby forming a surface shape zero-position detection. The present invention can realize reliable and high-precision oblate ellipsoidal mirror surface shape detection through an interferometer and auxiliary components.

[0019] 2. The present invention discloses a method for detecting the surface shape of an ellipsoidal reflector based on a zero compensation method. The indicating laser is incident on the center of the mirror to be measured through a window glass. The direction of the short axis of the oblate ellipsoidal mirror can be determined by adjusting the reflected light to return along the original path. Then, the spatial positions of the two foci can be determined according to the generatrix equation. The first hole position and the second hole position of the plate with holes are adjusted to coincide with the two foci respectively. The present invention can determine the direction of the short axis of the oblate ellipsoidal mirror to be measured and the spatial position of the foci, making it easier to build the detection optical path.

[0020] 3. The present invention discloses a surface shape detection method of an ellipsoidal reflector based on a zero-position compensation method. The auxiliary optical elements used in the detection are a holed flat plate and a standard spherical mirror. The manufacturing cost is low and the detection optical path is easy to adjust. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1Schematic diagram of the detection principle of the present invention, 1-ellipsoidal reflector to be measured, 2-interferometer, 3-standard spherical mirror, 4-plate with holes, 5-window glass, f is the distance from the focus to the center of the mirror, c is the distance between the two focal points;

[0022] Figure 2 Front view of the plate with holes, 6-first hole position, 7-second hole position, 8-third hole position, the distance between the first hole position and the second hole position is the distance between the two foci of the ellipsoidal mirror, and the third hole position is located at the midpoint of the line connecting the first hole position and the second hole position;

[0023] Figure 3 Schematic diagram of the window glass fixing position;

[0024] Figure 4 Schematic diagram of the optical path of the 430mm×420mm aperture ellipsoidal reflector. DETAILED DESCRIPTION

[0025] In order to better illustrate the purpose and advantages of the present invention, the invention is further described below with reference to the accompanying drawings and examples.

[0026] Example 1

[0027] The present invention is used to detect the surface accuracy of an ellipsoidal reflector with an aperture of 430mm×420mm. The detection optical path is shown in FIG. Figure 4 This embodiment discloses a method for detecting the surface shape of an ellipsoidal reflector based on a zero compensation method. The object to be detected is an ellipsoidal reflector 1 to be detected. The specific implementation steps are as follows:

[0028] Step 1: Prepare a square plate with holes 4, the size of which is 500mm×500mm, and the hole positions are distributed as follows: Figure 2 As shown, the size of the first hole 1 and the second hole 2 is Φ2mm, the size of the third hole 3 is Φ3mm, and the window glass 5 with a size of 10mm×10mm is fixed at the third hole 3, and the fixing position is as shown in FIG. Figure 3 As shown;

[0029] Step 2: Use a height gauge to make the hole center line of the hole plate 4 and the long axis of the oblate ellipsoidal mirror be in the same horizontal plane;

[0030] Step 2: Use a beam of He-Ne laser to irradiate the window glass 5. The surface of the window glass 5 will reflect part of the light back. Adjust the pitch angle and azimuth angle of the plate with holes 4 until the reflected light returns along the original path. At this time, it means that the normal line of the plane of the plate with holes 4 is parallel to the optical axis.

[0031] Step 3: Make a mark at the center of the ellipsoidal mirror to be tested, so that the laser beam passing through the window glass 5 hits the center point of the ellipsoidal mirror to form reflected light, and adjust the pitch angle and azimuth angle of the ellipsoidal mirror until the reflected light of the ellipsoidal mirror returns along the original path. At this time, it means that the normal line at the center of the ellipsoidal mirror is parallel to the optical axis, that is, the optical axis coincides with the short axis of the ellipsoidal surface;

[0032] Step 4: Remove the He-Ne laser, turn on the interferometer 2 and make the focus of the emitted spherical wave coincide with the hole position 1 of the hole plate 4;

[0033] Step 5: Select a standard spherical mirror 3 with a diameter of Φ250 and a radius of 1600, and adjust the position of the standard spherical mirror 3 so that its center coincides with the hole on the right side of the hole-carrying plate 4;

[0034] Step 6: Start surface shape measurement. The measuring light beam emitted by the interferometer 2 is focused on the first hole position 6, and then incident on the oblate ellipsoidal mirror. The measuring light is reflected and converged at the second hole position 7, and then reflected by the standard spherical mirror 3 and returned along the original path. The measuring light beam carrying the surface shape error information returns to the interferometer 2 to interfere with the reference light to generate interference fringes. The interference fringe image is processed by the interferometer 2 to obtain the surface shape error of the ellipsoidal mirror to be measured.

[0035] This embodiment also discloses a surface shape detection device of an ellipsoidal reflector based on a zero position compensation method, which is used to implement a surface shape detection method of an ellipsoidal reflector based on a zero position compensation method. A surface shape detection device of an ellipsoidal reflector based on a zero position compensation method comprises a window glass 5, a plate with holes 4, a standard spherical mirror 3 and an interferometer 2. The plate with holes 4 comprises a first hole position 6, a second hole position 7 and a third hole position 8; the distance between the first hole position 6 and the second hole position 7 is the distance between the two foci of the ellipsoidal mirror, and the third hole position 8 is located at the midpoint of the line connecting the first hole position 6 and the second hole position 7. The plate with holes 4 is placed in front of the oblate ellipsoidal mirror 3, and the distance between the plate with holes 4 and the oblate ellipsoidal mirror 3 is the short axis length of the generatrix of the oblate ellipsoidal mirror 3.

[0036] The specific description above further illustrates the purpose, technical solutions and beneficial effects of the invention in detail. It should be understood that the above is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for detecting the surface shape of an ellipsoidal reflector based on a zero compensation method, characterized in that: The following steps are included: Step 1: Place a plate with holes in front of the oblate ellipsoid mirror, the distance between the plate with holes and the ellipsoid mirror is the length of the minor axis of the generatrix of the ellipsoid mirror; the plate with holes has three equidistant holes in the same horizontal plane, the distance between the first hole and the second hole is the distance between the two foci of the ellipsoid mirror, and the third hole is located at the midpoint of the line connecting the first hole and the second hole; the window glass is fixed at the middle hole; Step 2: Adjust the installation position of the plate with holes: When the laser enters from the window glass, the surface of the window glass will reflect part of the light back. Adjust the pitch angle and azimuth angle of the plate with holes until the reflected light returns along the original path. At this time, the normal line of the plane of the plate with holes is parallel to the optical axis. Step 3: Adjust the installation posture of the oblate ellipsoid mirror: let the laser beam through the window glass hit the geometric center of the oblate ellipsoid mirror, adjust the pitch angle and azimuth angle of the oblate ellipsoid mirror until the reflected light of the oblate ellipsoid mirror returns along the original path, which means that the normal line at the center of the ellipsoid mirror is parallel to the optical axis; Step 4: Align the focus of the spherical wave emitted by the interferometer with the first hole position of the plate with holes; Step 5: Align the center of the standard spherical mirror with the second hole position of the hole-carrying plate; the relative aperture of the standard spherical mirror is larger than that of the oblate ellipsoidal mirror; Step 6: Start surface measurement. The measuring beam emitted by the interferometer is focused on the first hole position and then incident on the oblate ellipsoidal mirror. The measuring light is reflected and converged at the second hole position. It is then reflected by the standard spherical mirror and returns along the original path. The measuring beam carrying the surface error information returns to the interferometer to interfere with the reference light to generate interference fringes. The interference fringe image is processed by the interferometer to obtain the surface error of the ellipsoidal mirror to be measured.

2. The method for detecting the surface shape of an ellipsoidal reflector based on a zero compensation method as claimed in claim 1, characterized in that: In step 2, a beam of He-Ne laser is directed toward the window glass, and the surface of the window glass will reflect part of the light back.

3. The method for detecting the surface shape of an ellipsoidal reflector based on a zero compensation method as claimed in claim 1, characterized in that: In step five, a standard spherical mirror with a relative diameter larger than the mirror to be tested is selected, and the center of the standard spherical mirror is aligned with the second hole position of the holed plate.

4. A surface shape detection device of an ellipsoidal reflector based on a zero position compensation method, used to implement a surface shape detection method of an ellipsoidal reflector based on a zero position compensation method as claimed in claim 1, 2 or 3, characterized in that: It includes window glass, a plate with holes, a standard spherical mirror and an interferometer. The plate with holes includes a first hole position, a second hole position and a third hole position; the distance between the first hole position and the second hole position is the distance between the two foci of the ellipsoid mirror, and the third hole position is located at the midpoint of the line connecting the first hole position and the second hole position. The plate with holes is placed in front of the standard spherical mirror, and the distance between the plate with holes and the standard spherical mirror is the short axis length of the generatrix of the ellipsoid mirror.

5. The surface shape detection device of an ellipsoidal reflector based on a zero compensation method as claimed in claim 4, characterized in that: The ellipsoidal mirror is an oblate ellipsoidal mirror.

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