Device and method for detecting the front and back surfaces of an interferometric ultra-small curvature plano-convex or plano-concave lens

Abstract

The application discloses a detection device and method for positive and reverse surfaces of an interference type ultra-small curvature plano-convex lens or plano-concave lens. The detection method comprises the following steps: obtaining an interference image of a surface of a sample to be detected; and determining whether the surface is a curved surface or a flat surface according to the shape of the interference image. The detection method is simple, easy to operate, high in efficiency and 100% in accuracy. The detection device for positive and reverse surfaces of the interference type ultra-small curvature plano-convex lens or plano-concave lens is simple in structure and convenient to use. After the optical system with the specific structure is used, the interference image of the surface of the lens can be obtained by using a plane array camera, and whether the surface is a curved surface or a flat surface can be determined according to the shape of the obtained interference image. Further, after the interference image is sequentially subjected to Fourier transform and automatic threshold value calculation related to a mode, the difference between the calculation results of the curved surface and the flat surface can be used to realize automatic reading of the curved surface and the flat surface.

Description

Technical Field

[0001] This invention relates to a device and method for detecting the front and back surfaces of an interference-type plano-convex lens or plano-concave lens with ultra-small curvature, belonging to the technical field of determining the front and back surfaces of plano-convex lenses or plano-concave lenses. Background Technology

[0002] In production practice, there are plano-convex or plano-concave lenses with extremely small curvature (i.e., extremely large radius of curvature). Due to their very small curvature, the front and back of the lens are indistinguishable to the naked eye, causing significant challenges in product manufacturing. Even when attempting to differentiate them by measuring the sag, the sag is often smaller than the error introduced by height measurement, making it practically impossible to distinguish the upper and lower surfaces of a plano-convex or plano-concave lens. For example, if the difference between the center and edge thickness of a customer's plano-convex lens is only 3.5µm, quickly measuring the center thickness and then moving to the edge to measure the edge thickness on the production line requires a flatness of <+ / -1µm on the moving platform (a very high requirement, almost the limit of current industrial technology). Considering the measurement accuracy of the ranging tool (or height measuring tool) itself (<+ / -1µm), plus the measurement error caused by vibrations in the actual production environment, it is difficult to distinguish the front and back of a plano-convex lens by measuring the height difference between the center and edge. However, distinguishing the front and back of a plano-convex lens is essential in production, making it a thorny problem. Through communication with clients and research conducted before R&D, it was found that there is currently no reliable technical solution. Summary of the Invention

[0003] This invention provides a device and method for detecting the front and back surfaces of an interference-type plano-convex lens or plano-concave lens with ultra-small curvature, which can quickly and accurately identify the front and back surfaces of an ultra-small curvature plano-convex lens or plano-concave lens.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0005] A method for detecting the front and back surfaces of an interference-type ultra-small curvature plano-convex or plano-concave lens is provided, which acquires an interference image of the surface of the sample being tested and determines whether the curved surface is facing upwards or the flat surface is facing upwards based on the shape of the interference image.

[0006] This application considers plano-convex or plano-concave lenses whose front and back sides cannot be distinguished by the naked eye as having ultra-small curvature.

[0007] During testing, the sample to be tested is placed on a platform with the sample surface facing upwards.

[0008] The method for determining whether the curved surface or the plane is facing upwards based on the shape of the interference pattern is as follows: if only a circular interferogram is obtained, the curved surface of the sample is facing upwards; if both straight fringes and a circular interferogram are obtained simultaneously, the plane of the sample is facing upwards. This method is applicable to both plano-convex and plano-concave lenses.

[0009] To achieve automatic interpretation, an interferometric image is obtained using an area array camera. After automatic thresholding using Fourier transform and mode correlation, the image is automatically interpreted based on the difference between the curved-up and planar-up calculations. For example, one of the most significant differences between curved-up and planar-up interferograms is that the curved-up interferogram, after calculation, yields a single light spot; while the planar-up interferogram, after calculation, yields three or more light spots, with at least a pair of substantially symmetrical smaller light spots on either side of the larger light spot. The computer can distinguish between curved and planar surfaces by automatically reading the number of calculated light spots.

[0010] A detection device for the front and back surfaces of an interference-type ultra-small curvature plano-convex or plano-concave lens includes a light source, a collimating mirror, a beam splitter, a reflecting mirror, a beam reducer, and a surface array camera.

[0011] The light source, collimating lens, beam splitter, and reflector are arranged in order from left to right, with the reflecting surface of the reflector facing the beam splitter; the area array camera, beam reducer, and beam splitter are arranged in order from top to bottom.

[0012] The measurement of the center and edge of the plano-convex or plano-concave lens in this application is completed in one step, and there is no flatness error due to the translation stage moving from the center to the edge.

[0013] The top, bottom, left, and right positions in this application are based on the relative positions shown in the attached drawings.

[0014] As one preferred implementation, the beam splitter is a cubic beam splitter composed of two 45° right-angled triangular prisms joined together; the optical axis of the collimating lens forms a 45° angle with the joint of the beam splitter, and the optical axis of the collimating lens is perpendicular to the reflecting surface of the reflecting mirror; the optical axis of the beam constrictor forms a 45° angle with the joint of the beam splitter. Of course, the beam splitter is not limited to a cubic beam splitter, but can also be a monolithic 45° beam splitter, etc.

[0015] The aforementioned detection device for the front and back surfaces of an interference-type ultra-small curvature plano-convex lens or plano-concave lens also includes a computer, with an area array camera connected to the computer.

[0016] To ensure accuracy in the detection, a laser light source is used.

[0017] As one specific implementation, the laser source has a wavelength of 650nm. Of course, this application is not limited to 650nm lasers, and lasers of other wavelengths can also be selected as needed.

[0018] The detection method using the aforementioned interferometric ultra-small curvature plano-convex or plano-concave lens front and back detection device includes the following steps:

[0019] 1) Place the sample to be tested on the platform directly below the beam splitter;

[0020] 2) The light emitted by the light source is collimated by the collimating lens and then split into a first ray and a second ray by the beam splitter. The first ray hits the reflecting mirror and is reflected back. It is then reflected upward by the beam splitter and, after passing through the beam reducer, hits the area array camera as a reference light.

[0021] 3) The second ray strikes the surface of the sample under test downwards and is reflected upwards. It passes through the beam splitter and then through the beam reducer before striking the area array camera as the test light.

[0022] 4) The test light and reference light form an interference image on the area array camera. The shape of the interference image determines whether the curved surface is facing upwards or the plane is facing upwards.

[0023] In step 4) above, if only a circular interferogram is obtained, the curved surface of the sample being tested should face upwards; if both straight fringes and a circular interferogram are obtained simultaneously, the plane of the sample being tested should face upwards.

[0024] To achieve automated detection, in step 4), an interference image is formed on the area scan camera and transmitted to the computer. The computer first performs a Fourier transform on the obtained interference image, and then performs automatic threshold calculation for mode correlation. Based on the difference between the calculation results for curved surface upward and planar surface upward, automatic interpretation of curved surface upward and planar surface upward is achieved. This realizes fully automated detection and saves manual labor.

[0025] The above method uses the Fast Fourier Transform (FFT) algorithm to obtain the spatial spectrum of the interferogram, and then uses the mode correlation automatic thresholding method to obtain the final pattern. The final pattern obtained with the curved surface facing up and the flat surface facing down is completely different. Based on the difference between the two, the front and back of the plano-convex or plano-concave lens can be automatically identified, thereby realizing automated detection and production.

[0026] The automatic threshold calculation methods for Fourier transform and mode correlation in this application directly adopt existing mature algorithms. Combined with existing technologies, they can realize automatic calculation and interpretation by computers. The improvement of this application does not lie in the automatic threshold calculation methods for Fourier transform and mode correlation themselves, but in applying the automatic threshold calculation methods for Fourier transform and mode correlation to realize the automatic interpretation of curved and flat surfaces in this application.

[0027] Any techniques not mentioned in this invention are based on existing technologies.

[0028] The present invention provides a method for detecting the front and back surfaces of an interference-type ultra-small curvature plano-convex or plano-concave lens, which is simple, easy to operate, highly efficient, and 100% accurate. The present invention also provides a device for detecting the front and back surfaces of an interference-type ultra-small curvature plano-convex or plano-concave lens, which is simple in structure and easy to use. After passing through the optical system of the specific structure described in this application, an interference image of the lens surface can be obtained using a planar array camera. The shape of the obtained interference image can accurately determine whether the surface is curved upwards or flat upwards. Furthermore, after the interference image is sequentially processed through Fourier transform and mode-correlation automatic threshold calculation, the difference between the calculation results for curved upwards and flat upwards can be used to automatically determine whether the surface is curved upwards or flat upwards. Attached Figure Description

[0029] Figure 1 This is a diagram showing the elevation of the sag.

[0030] Figure 2 This is a schematic diagram of the detection optical path of the detection device for the front and back surfaces of the interference-type ultra-small curvature plano-convex lens or plano-concave lens of the present invention;

[0031] Figure 3 This is a measured interference image of the plano-convex lens with its convex surface facing upwards, as shown in the embodiment.

[0032] Figure 4 The interference image obtained by the plano-convex lens with the convex surface facing upwards is a calculated pattern obtained by sequentially performing Fourier transform and automatic threshold calculation based on mode correlation.

[0033] Figure 5 The image shows the measured interference pattern when the plane of the plano-convex lens is facing upwards (the left image shows a small tilt angle, the middle image shows a large tilt angle, and the right image shows the middle image with the tilt direction changed).

[0034] Figure 6 The diagrams shown in the example are the calculation patterns obtained by sequentially performing Fourier transform and mode-dependent automatic threshold calculation on the interference image obtained with the plane of the plano-convex lens facing upwards (the diagrams from top to bottom correspond to the following patterns). Figure 5 (Image from left to right);

[0035] In the figure, 1 is the light source, 2 is the collimating mirror, 3 is the beam splitter, 4 is the reflecting mirror, 5 is the beam reducer, 6 is the area array camera, 7 is the sample being tested, and 8 is the sag. Detailed Implementation

[0036] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0037] Example 1

[0038] like Figure 2As shown, a detection device for the front and back surfaces of an interference-type ultra-small curvature plano-convex lens or plano-concave lens includes a light source, a collimating lens, a beam splitter, a reflecting mirror, a beam reducer, and a surface array camera.

[0039] The light source, collimating lens, beam splitter, and reflector are arranged sequentially from left to right, with the reflecting surface of the reflector facing the beam splitter. The light source is located on the optical axis of the collimating lens, and the optical axis of the collimating lens is perpendicular to the reflecting surface of the reflector. The area array camera, beam reducer, and beam splitter are arranged sequentially from top to bottom. The beam splitter is a cubic beam splitter composed of two 45° right-angled triangular prisms. The optical axis of the collimating lens forms a 45° angle with the junction of the collimating lens and the beam splitter (the beam splitting point), and the optical axis of the collimating lens is perpendicular to the reflecting surface of the reflector. The optical axis of the beam reducer also forms a 45° angle with the junction of the collimating lens and the beam splitter. The light source is a 650nm laser. The vertical and horizontal positions are based on the relative positions shown in the attached diagram.

[0040] Taking a plano-convex lens as an example, the difference between the center thickness and the edge thickness of the plano-convex lens product is only 3.5µm. The inspection using the aforementioned interference-type ultra-small curvature plano-convex or plano-concave lens front and back inspection device includes the following steps:

[0041] 1) such as Figure 2 As shown, the sample to be tested is placed on a platform directly below the beam splitter;

[0042] 2) The light emitted by the light source is collimated by the collimating lens and then split into the first ray and the second ray by the beam splitter. The first ray hits the reflecting mirror and is reflected back. It is then reflected upward by the beam splitter and, after passing through the beam reducer, hits the area array camera as a reference light (solid line part).

[0043] 3) The second ray hits the surface of the sample under test downwards and is reflected upwards. It passes through the beam splitter and then through the beam reducer before hitting the area array camera as the test light (dashed line part).

[0044] 4) The test light and reference light form an interference image on the area array camera. The shape of the interference image determines whether the curved surface is facing upwards or the flat surface is facing upwards. Figure 3 As shown, if the convex surface faces upwards, the resulting interference pattern is simply a circular interferogram, as... Figure 5 As shown, if the plane faces upward, the resulting interference pattern includes straight fringes and circular interferograms. This allows for quick identification of whether the convex surface or the plane is facing upward by visually observing the interference pattern. If the plane faces upward and the curved surface faces downward, the horizontal state of the sample is difficult to guarantee, and a certain degree of tilt may occur. Figure 5 As shown, the larger the tilt angle, the greater the density of straight fringes; the smaller the tilt angle, the lower the density of straight fringes. If the tilt direction is changed, the interference pattern still includes straight fringes and circular interferograms, but the position of the circular interferogram relative to the straight fringes will change.

[0045] Meanwhile, taking a plano-concave lens as an example, the detection steps are the same as above. If the concave surface faces upward, the obtained interference image is only a circular interferogram. If the flat surface faces upward, the obtained interference image includes straight fringes and a circular interferogram, which is consistent with the judgment method for a plano-convex lens.

[0046] The above measurements of the center and edge of a plano-convex or plano-concave lens are completed in one step, eliminating the flatness error inherent in the translation stage that moves from the center to the edge. The inventors simultaneously tested a series of lenses with different sagittal heights, including lenses whose front and back sides are distinguishable to the naked eye, achieving 100% accuracy in all cases.

[0047] Example 2

[0048] Based on Example 1, the following improvements were made: the detection device for the front and back surfaces of an interferometric ultra-small curvature plano-convex or plano-concave lens further includes a computer, with an area array camera connected to the computer. During detection, in step 4), an interferometric image is formed on the area array camera and transmitted to the computer. The computer first performs a Fourier transform on the obtained interferometric image, and then performs automatic threshold calculation for mode correlation. Figure 4 The computational pattern is obtained by sequentially performing Fourier transform and mode-correlation automatic thresholding on the interference image obtained by a plano-convex lens with the convex surface facing upwards. Figure 6 The interference pattern obtained by a plano-convex lens with its flat surface facing upwards is calculated using Fourier transform and mode-dependent automatic thresholding. The two patterns are significantly different. One of the most significant differences between the curved-up and flat-up patterns is that the interference pattern obtained with the curved surface facing upwards results in a single light spot, while the interference pattern obtained with the flat surface facing upwards results in three or more light spots. At least one pair of substantially symmetrical small light spots flank a large light spot. The computer can distinguish between curved and flat surfaces by automatically reading the number of calculated light spots. The inventors verified that the results for a plano-concave lens with its concave surface facing upwards and downwards are consistent with those for a plano-convex lens. The calculated patterns of the interference images obtained by the Fourier transform and mode-dependent automatic thresholding for concave-up and concave-down lenses are significantly different. Based on the difference in the calculated results for curved-up and flat-up lenses, the computer can automatically interpret the results. The inventors simultaneously tested a series of lenses with different sagittas, achieving 100% accuracy. This achieves fully automated testing without human intervention, saving labor and reducing quality instability caused by manual testing.

Claims

1. A method for detecting the front and back surfaces of an interference-type plano-convex or plano-concave lens with ultra-small curvature, characterized in that: Obtain the interference image of the surface of the sample under test, and determine whether the curved surface is facing upwards or the flat surface is facing upwards based on the shape of the interference image; An interferometric device for detecting the front and back surfaces of a plano-convex or plano-concave lens with ultra-small curvature, comprising a light source, collimating lens, beam splitter, reflecting mirror, beam reducer, area array camera, and computer; The light source, collimating lens, beam splitter, and reflector are arranged from left to right, with the reflecting surface of the reflector facing the beam splitter; the area scan camera, beam reducer, and beam splitter are arranged from top to bottom; the area scan camera is connected to the computer. The method for detecting the front and back surfaces of an interference-type plano-convex or plano-concave lens with ultra-small curvature includes the following steps: 1) Place the sample to be tested on the platform directly below the beam splitter; 2) The light emitted by the light source is collimated by the collimating lens and then split into a first ray and a second ray by the beam splitter. The first ray hits the reflecting mirror and is reflected back. It is then reflected upward by the beam splitter and, after passing through the beam reducer, hits the area array camera as a reference light. 3) The second ray strikes the surface of the sample under test downwards and is reflected upwards. It passes through the beam splitter and then through the beam reducer before striking the area array camera as the test light. 4) The test light and reference light form an interference image on the area array camera; In step 4), an interference image is formed on the area array camera and transmitted to the computer. The computer first performs a Fourier transform on the obtained interference image, and then performs automatic threshold calculation for mode correlation. Based on the difference between the calculation results for curved surface upward and planar surface upward, the computer can automatically distinguish between curved surface upward and planar surface upward. The interference pattern obtained with curved surface upward is calculated to obtain one spot; while the interference pattern obtained with planar surface upward is calculated to obtain more than three spots. There is at least one pair of basically symmetrical small spots on both sides of a large spot. The computer can distinguish between curved surface and planar surface by automatically reading the number of calculated spots.

2. The method for detecting the front and back surfaces of an interference-type ultra-small curvature plano-convex lens or plano-concave lens as described in claim 1, characterized in that: The beam splitter is a cubic beam splitter composed of two 45° right-angled triangular prisms; the optical axis of the collimating lens forms a 45° angle with the joint of the beam splitter, and the optical axis of the collimating lens is perpendicular to the reflecting surface of the reflecting mirror; the optical axis of the beam reducer forms a 45° angle with the joint of the beam splitter.

3. The method for detecting the front and back surfaces of an interference-type ultra-small curvature plano-convex lens or plano-concave lens as described in claim 1 or 2, characterized in that: The light source is located on the optical axis of the collimating mirror; the optical axis of the collimating mirror is perpendicular to the reflecting surface of the mirror; the light source is a laser source.

4. The method for detecting the front and back surfaces of an interference-type ultra-small curvature plano-convex lens or plano-concave lens as described in claim 3, characterized in that: The wavelength of the laser source is 650nm.

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