Automatic focusing system

Abstract

The present invention discloses an automatic focusing system. In the automatic focusing system, an illumination system generates two illumination beams directed toward a characteristic signal generating system; the characteristic signal generating system includes two transparent gratings with regular periods; the two illumination beams pass through a transparent grating respectively to form two transparent grating image beams, which are directed toward a TIR prism. The two transparent grating image beams passing through the TIR prism are directed toward an objective lens at different angles. After passing through the objective lens, the two transparent grating image beams interfere on the object surface to form a moiré fringe image. An imaging system is used to capture the moiré fringe image. A processor is used to determine the defocus direction and defocus amount of the automatic focusing system based on the position of the moiré fringe image captured by the imaging system, and to determine the adjustment amount of the objective lens position based on the defocus direction and defocus amount. The technical solution of the present invention realizes rapid and accurate automatic focusing.

Description

Technical Field

[0001] The present invention relates to the field of optical technology, in particular to an automatic focusing system. Background Art

[0002] As modern industry's requirements for lens resolution develop towards micrometers, submicrometers, and nanometers, the depth of focus of lenses is getting smaller and smaller. Modern industry's requirements for production efficiency are also getting higher and higher, and automatic focusing systems that assist imaging have come into being.

[0003] Autofocus technologies are broadly divided into two categories: the first directly calculates the image contrast of the object being imaged and identifies the lens position with the highest contrast; the second requires a dedicated autofocus system. The first requires predicting the focus movement direction, which doesn't meet the efficiency requirements of modern industry, so the second focusing method is widely used.

[0004] The existing autofocus method makes judgments based on the different spot shapes of the semi-conical light beam on the focal plane, before and after focus. When focused out of focus (before focus), the laser spot appears as a semicircle on the left; when focused in focus (after focus), the laser spot appears as a semicircle on the right; at the focus, the laser beam theoretically converges to a point. This is true in theory, but in actual operation, when the lens gradually defocuses from the focal position, the shape of the laser beam changes slowly. Since the numerical aperture of the semi-conical beam only accounts for half of the numerical aperture of the microscope, that is, the focal depth of the focusing signal is greater than the focal depth of the objective lens, it cannot fully reflect the degree of defocus of the object.

[0005] The above content is only used to assist in understanding the technical solution of the present invention and does not constitute an admission that the above content is prior art. Summary of the Invention

[0006] The main purpose of the present invention is to provide an automatic focusing system, aiming to solve the technical problem of inaccurate focusing and imaging in the prior art.

[0007] To achieve the above-mentioned object, the automatic focusing system proposed in the present invention includes an illumination system, a characteristic signal generating system, a TIR prism, a reflector, an objective lens, an imaging system and a processor;

[0008] The lighting system generates two lighting beams directed toward the characteristic signal generating system;

[0009] The characteristic signal generating system includes two transparent gratings with regular periods;

[0010] The two illumination light beams respectively pass through one of the transparent gratings to form two transparent grating image light beams and are emitted to the TIR prism. The two transparent grating image light beams passing through the TIR prism are emitted to the objective lens at different angles. The two transparent grating image light beams interfere on the object plane after passing through the objective lens to form a moiré fringe image. The imaging system is used to capture the moiré fringe image. The processor is used to determine the defocus direction and defocus amount of the automatic focusing system according to the position of the moiré fringe image captured by the imaging system, and determine the adjustment amount of the objective lens position according to the defocus direction and defocus amount.

[0011] The automatic focusing system proposed in the technical solution of the present invention generates two illumination beams directed to the characteristic signal generating system through an illumination system, and the characteristic signal generating system includes two transparent gratings with a regular period, so that the two illumination beams pass through the transparent gratings to form two transparent grating image beams, which enter the objective lens at different angles through the action of TIR prisms and reflectors, and then generate interference on the object surface to form moiré fringes. Since moiré fringes have an amplifying effect on tiny relative displacements, the smaller the relative angle, the greater the moiré fringe displacement magnification. According to the different positions of the moiré fringes, the processor can more accurately give the defocus direction and defocus amount, thereby being more accurate during the focus adjustment process.

[0012] Optionally, the automatic focusing system further includes an execution system;

[0013] The processor generates an adjustment command according to the adjustment amount, and sends the adjustment command to the execution system;

[0014] The execution system adjusts the position of the objective lens according to the adjustment command.

[0015] Optionally, the lighting system includes an illumination light source, an illumination lens, a first reflector, a second reflector, and a third reflector;

[0016] After the light beam emitted by the illumination light source passes through the illumination lens, part of the light beam is reflected by the first reflector and the second reflector in sequence to form an illumination light beam directed toward one of the transparent gratings, while another part of the light beam is reflected by the third reflector to form another illumination light beam directed toward another transparent grating, wherein the aperture of each of the illumination light beams is less than or equal to half of the aperture of the objective lens.

[0017] Optionally, the automatic focusing system further includes a fourth reflecting mirror and a dichroic mirror, and the transparent grating image light beam is reflected by the fourth reflecting mirror and the dichroic mirror in sequence and then emitted to the objective lens.

[0018] Optionally, the dichroic mirror is a beam splitter with a splitting ratio of 50 / 50 or a dichroic mirror.

[0019] Optionally, the imaging system includes a first tube lens and a first camera, and the autofocus system further includes a first beam splitter. The two transparent grating image light beams passing through the TIR prism pass through the first beam splitter and the first tube lens in sequence and then are emitted to the fourth reflector, and the moiré fringe image generated on the object plane passes through the objective lens, the color separation mirror, the fourth reflector, and the first beam splitter and is incident on the photosensitive surface of the first camera.

[0020] Optionally, the automatic focusing system further includes an imaging light source, a second spectroscope, a second tube lens, and a second camera;

[0021] The light beam emitted by the imaging light source is reflected by the second beam splitter and directed toward the dichroic mirror. The dichroic mirror performs beam splitting on the illumination light beam and directs it toward the objective lens. The illumination light beam passing through the objective lens is projected onto the object surface for illuminating the object to be inspected on the object surface. The object to be inspected reflects the illumination light beam to form reflected light. The reflected light sequentially passes through the objective lens, the dichroic mirror, the second beam splitter, and the second tube lens, and finally converges to the second camera.

[0022] Optionally, the splitting ratio of the second beam splitter is 50 / 50. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0024] Figure 1 Schematic diagram of the structure of an automatic focusing system according to an embodiment of the present invention;

[0025] Figure 2 for Figure 1 Schematic diagram of an application scenario of the automatic focusing system;

[0026] Figure 3 for Figure 1 Schematic diagram of the automatic focusing system.

[0027] Description of Figure Numbers:

[0028]

[0029]

[0030] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION

[0031] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0032] It should be noted that all directional indications in the embodiments of the present invention (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the various components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0033] In addition, the descriptions of "first", "second", etc. in the present invention are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of such features. In addition, "and / or" in the full text includes three solutions. Taking A and / or B as an example, it includes technical solution A, technical solution B, and technical solution that satisfies both A and B. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in this field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0034] The present invention provides an automatic focusing system.

[0035] Please refer to Figures 1 to 3 In an embodiment of the present invention, the automatic focusing system proposed in the present invention includes an illumination system 110, a characteristic signal generating system (not shown), a TIR prism 130, an objective lens 160, an imaging system 140 and a processor (not shown).

[0036] The illumination system 110 generates two illumination beams directed toward a characteristic signal generation system, which includes two transparent gratings 120 with a regular period. The two illumination beams pass through a transparent grating 120, respectively, to form two transparent grating image beams that are directed toward a TIR prism 130. The two transparent grating image beams passing through the TIR prism 130 are directed toward an objective lens 160 at different angles. After passing through the objective lens 160, the two transparent grating image beams interfere on an object plane W to form a moiré fringe image. The imaging system 140 is configured to capture the moiré fringe image. The processor is configured to determine a defocus direction and defocus amount of the autofocus system based on a position of the moiré fringe image captured by the imaging system 140, and to determine an adjustment amount for the position of the objective lens 160 based on the defocus direction and defocus amount.

[0037] The automatic focusing system proposed in the technical solution of the present invention generates two illumination beams directed to the characteristic signal generating system through the illumination system 110, and the characteristic signal generating system includes two transparent gratings 120 with a regular period, so that the two illumination beams pass through the transparent grating 120 to form two transparent grating image beams, which enter the objective lens 160 at different angles through the action of the TIR prism 130, and then interfere with the object surface W to form moiré fringes. Since moiré fringes have an amplifying effect on tiny relative displacements, the smaller the relative angle, the greater the moiré fringe displacement magnification. According to the different positions of the moiré fringes, the processor can more accurately give the defocus direction and defocus amount, which is more accurate during the focus adjustment process.

[0038] In one embodiment, the automatic focusing system further includes an execution system; the processor generates an adjustment command based on the adjustment amount and sends the adjustment command to the execution system; the execution system adjusts the position of the objective lens 160 according to the adjustment command. The execution system has at least three adjustment dimensions, including x-direction rotation adjustment and y-direction rotation adjustment for automatic leveling; and z-direction movement adjustment for automatic focusing. It includes components such as a servo motor and a transmission mechanism, which can be designed with reference to existing structural designs and will not be described in detail here. Through the design of this execution system, the automatic focusing system of the present application can adapt to the automatic adjustment requirements used in industrial production.

[0039] In one embodiment, the illumination system 110 includes an illumination light source 111, an illumination lens 112, a first reflector 113, a second reflector 114, and a third reflector 115. After the light beam emitted by the illumination light source 111 passes through the illumination lens 112, part of the light beam is reflected by the first reflector 113 and the second reflector 114 in sequence to form an illumination light beam directed toward one transparent grating 120, while another part of the light beam is reflected by the third reflector 115 to form another illumination light beam directed toward another transparent grating 120. The aperture of each illumination light beam is less than or equal to half of the aperture of the objective lens 160. Please continue to refer to Figure 1 In the present application, the illumination lens 112 is a lens group consisting of at least two lenses, thereby improving the light output quality. The TIR prism 130 includes two triangular prisms to form a total reflection prism. The first reflector 113 and the third reflector 115 are respectively arranged on both sides of the optical axis of the illumination lens 112 and direct half of the light beam emitted by the illumination lens 112 to a triangular prism in the TIR prism 130 at different angles. Figure 1 It can be seen that a transparent grating 120 is arranged between the third reflector 115 and the triangular prism. Then, a transparent grating image beam formed after one illumination light beam passes through the transparent grating 120 is vertically incident through the right-angled surface of the triangular prism at a vertical angle. In this way, in principle, 100% of the transparent grating image beams can pass through. Another transparent grating 120 is arranged between the second reflector 114 and the other triangular prism. Another transparent grating image beam formed after another illumination light beam passes through the transparent grating 120 is incident through the inclined surface of the other triangular prism at an inclined angle. Then, the transparent grating image beam is totally reflected by the TIR prism 130. Through the above arrangement, the light loss of the illumination light source 111 during the formation of the two transparent grating image beams is relatively small. It can also be seen that the solution of the present application only requires one illumination light source 111 to be implemented, which can greatly simplify the structure of the entire autofocus system, reduce costs, and not place too high requirements on the illumination light source 111. This makes it easier to apply it to industrial production and more practical. Of course, without considering the factors of installation space and cost, the lighting system 110 of the present application can also adopt the form of two lighting light sources 111 and multiple lighting lenses 112 to form two lighting beams, and the present application does not impose any restrictions on this.

[0040] In one embodiment, the autofocus system further includes a fourth reflector 170 and a dichroic mirror 180. The transparent grating image light beam is sequentially reflected by the fourth reflector 170 and the dichroic mirror 180 and then directed toward the objective lens 160. Optionally, the dichroic mirror 180 is a beam splitter or a dichroic mirror with a 50 / 50 splitting ratio. The provision of the fourth reflector 170 and the dichroic mirror 180 in the present application can improve the space utilization of the entire autofocus system, making the overall structure more compact and thus more adaptable to the installation requirements of industrial production.

[0041] Furthermore, the imaging system 140 includes a first tube lens 142 and a first camera 141. The autofocus system also includes a first beam splitter 150. The two transparent grating image light beams emitted from the TIR prism 130 sequentially pass through the first beam splitter 150 and the first tube lens 142 before being emitted to the fourth reflector 170. The moiré fringe image generated on the object plane W passes through the objective lens 160, the dichroic mirror 180, the fourth reflector 170, and the first beam splitter 150 and is incident on the photosensitive surface of the first camera 141. The transparent grating 120 is located on the object plane W of the first tube lens 142. The structure of the first beam splitter 150 can be referred to that of the TIR prism 130 and will not be further described here. The autofocus system of the present application, through this optical path arrangement, has a more compact overall structure and better imaging effects.

[0042] Optionally, the automatic focusing system further includes an imaging light source (not shown), a second beam splitter 190 , a second tube lens 200 and a second camera 210 ;

[0043] The light beam emitted by the imaging light source is reflected by the second dichroic mirror 190 and directed to the dichroic mirror 180. The dichroic mirror 180 performs spectroscopic processing on the illumination light beam and directs it to the objective lens 160. The illumination light beam passing through the objective lens 160 is projected onto the object plane W for illuminating the object to be detected on the object plane W. The object to be detected reflects the illumination light beam to form reflected light. The reflected light passes through the objective lens 160, the dichroic mirror 180, the second dichroic mirror 190 and the second tube lens 200 in sequence, and finally converges to the photosensitive surface of the second camera 210. Optionally, the splitting ratio of the second dichroic mirror 190 is 50 / 50. That is, the automatic focusing system of the present application can also detect objects on the object plane W, making the entire system more powerful.

[0044] Please refer to Figure 2In combination with the above, the automatic focusing system of the present application uses the above structure. In an application scenario, when the object plane W is in focus, the formed moiré fringes are offset to the left in the image of the transparent grating 120. When the object plane W is out of focus, the formed moiré fringes are offset to the right in the image of the transparent grating 120. When the object plane W is in focus, the formed moiré fringes are located in the middle of the image of the transparent grating 120. In this way, the processor can very clearly determine the defocus direction of the object plane W.

[0045] Please refer to Figure 3 , the relationship between the moiré fringe spacing L and the transparent grating 120 grating pitch d is:

[0046] L=d / sin(θ), where θ is the angle between the two transparent grating 120 images.

[0047] When θ is small, the above formula can be simplified to:

[0048] L=d / θ where θ is expressed in radians.

[0049] When the grating moves relative to the grating by Δd, the moiré fringe moves by ΔL, and the moiré fringe movement magnification factor is K, then K:

[0050] K=ΔL / Δd=1 / θ. When θ=3°, K=19 times.

[0051] From the above, we can know that the relative movement of the images of the two transparent gratings 120 is amplified by the moiré fringes and imaged to the first camera 141 by the first tube lens 142, thereby ensuring more accurate focusing.

[0052] The above descriptions are merely optional embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made using the contents of the present description and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. An automatic focusing system, characterized in that: The automatic focusing system includes an illumination system, a characteristic signal generating system, a TIR prism, an objective lens, an imaging system and a processor; The lighting system generates two lighting beams directed toward the characteristic signal generating system; The characteristic signal generating system includes two transparent gratings with regular periods; The two illumination beams respectively pass through one of the transparent gratings to form two transparent grating image beams, which are emitted toward the TIR prism. The two transparent grating image beams passing through the TIR prism are emitted toward the objective lens at different angles. The two transparent grating image beams interfere on the object plane after passing through the objective lens to form a moiré fringe image. The imaging system is used to capture the moiré fringe image. The processor is used to determine the defocus direction and defocus amount of the autofocus system based on the position of the moiré fringe image captured by the imaging system, and determine the adjustment amount of the objective lens position based on the defocus direction and defocus amount. Wherein, the lighting system includes an illumination light source, an illumination lens, a first reflector, a second reflector and a third reflector; After the light beam emitted by the illumination light source passes through the illumination lens, part of the light beam is reflected by the first reflector and the second reflector in sequence to form an illumination light beam directed toward one of the transparent gratings, while another part of the light beam is reflected by the third reflector to form another illumination light beam directed toward another transparent grating, wherein the aperture of each of the illumination light beams is less than or equal to half of the aperture of the objective lens.

2. The automatic focusing system according to claim 1, wherein: The automatic focusing system also includes an execution system; The processor generates an adjustment command according to the adjustment amount, and sends the adjustment command to the execution system; The execution system adjusts the position of the objective lens according to the adjustment command.

3. The automatic focusing system according to claim 1, wherein: The automatic focusing system further comprises a fourth reflector and a dichroic mirror. The transparent grating image light beam is sequentially reflected by the fourth reflector and the dichroic mirror and then emitted to the objective lens.

4. The automatic focusing system according to claim 3, wherein: The dichroic mirror is a dichroic mirror with a splitting ratio of 50 / 50 or a dichroic mirror.

5. The automatic focusing system according to claim 3, wherein: The imaging system includes a first tube lens and a first camera, and the autofocus system also includes a first beam splitter. The two transparent grating image light beams passing through the TIR prism sequentially pass through the first beam splitter and the first tube lens and are then emitted to the fourth reflector, while the moiré fringe image generated on the object plane passes through the objective lens, the dichroic mirror, the fourth reflector, and the first beam splitter and is incident on the photosensitive surface of the first camera.

6. The automatic focusing system according to claim 3, wherein: The automatic focusing system further includes an imaging light source, a second spectroscope, a second tube lens, and a second camera; The light beam emitted by the imaging light source is reflected by the second beam splitter and directed toward the dichroic mirror. The dichroic mirror performs beam splitting on the illumination light beam and directs it toward the objective lens. The illumination light beam passing through the objective lens is projected onto the object surface for illuminating the object to be inspected on the object surface. The object to be inspected reflects the illumination light beam to form reflected light. The reflected light sequentially passes through the objective lens, the dichroic mirror, the second beam splitter, and the second tube lens, and finally converges to the second camera.

7. The automatic focusing system according to claim 6, wherein: The splitting ratio of the second beam splitter is 50 / 50.

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