A high-speed autofocus method and system based on the parallel differential confocal principle

Abstract

A high-speed autofocus method and system based on the parallel differential confocal principle is disclosed. A spatial light modulator is placed at the field stop of the illumination optical path to digitally modulate the light emitted from the illumination path, forming multiple light spots or stripes. These spots or stripes are then illuminated onto the surface of the object under test after passing through a collimating lens group, a first beam splitter, and an objective lens. The light reflected from the object surface is then sent to a pre-focus detection unit and a post-focus detection unit via the beam splitter, forming pre-focus and post-focus images, respectively. A microprocessor calculates the defocus compensation amount from the images acquired by the pre-focus and post-focus detection units and controls the focusing motor driving the objective lens to reduce the absolute value of the defocus to a set value based on the defocus compensation amount. This invention has advantages such as a large focusing range, fast focusing speed, high focusing accuracy, and wide applicability.

Description

Technical Field

[0001] This invention relates to the field of autofocus, and in particular to a high-speed autofocus method and system based on the principle of parallel differential confocal focusing. Background Technology

[0002] Optical microscopes, due to their ability to magnify images of tiny objects, are widely used in fields such as biological research, materials science, medical diagnostics, and industrial product inspection. A crucial step in applying optical microscopes is focusing to obtain a clear image of the sample. Currently, focusing methods for optical microscopes are divided into manual focusing and automatic focusing. Manual focusing, due to its low efficiency and high operator skill requirements, is no longer suitable for some scenarios, such as the inspection of large-size industrial samples. To address the shortcomings of manual focusing, traditional automatic focusing methods based on various principles have emerged, such as laser triangulation, infrared ranging, ultrasonic ranging, and image processing-based automatic focusing methods. These traditional automatic focusing methods have improved the efficiency of optical microscopes to some extent. However, with the continuous development of science and technology, higher demands have arisen in related fields, such as high-precision and high-efficiency inspection of large samples, and the desire for inspection methods applicable to more sample types to reduce costs. Current traditional automatic focusing methods, due to their inherent limitations, may have drawbacks including, but not limited to, a small focusing range, limited applicable sample types, and low focusing accuracy. Summary of the Invention

[0003] The main objective of this invention is to overcome the aforementioned deficiencies in the prior art and propose a high-speed autofocus method and system based on the principle of parallel differential confocal focusing, which has the advantages of large range, high precision, and high efficiency.

[0004] The present invention adopts the following technical solution:

[0005] A high-speed autofocus method based on the principle of parallel differential confocal focusing is characterized by: placing a spatial light modulator at the field stop of the illumination optical path to digitally modulate the light emitted from the illumination optical path to form multiple light spots and stripes. These light spots and stripes are then illuminated onto the surface of the object under test after passing through a collimating lens group, a first beam splitter, and an objective lens. After being reflected by the surface of the object under test, the light is then transmitted through the beam splitter to the pre-focus detection unit and the post-focus detection unit, respectively, and converted into pre-focus and post-focus images by photoelectric conversion. A microprocessor calculates the pre-focus and post-focus images acquired by the pre-focus and post-focus detection units to obtain three parameters: the sharpness parameter Q1 of the pre-focus image, the sharpness parameter Q2 of the post-focus image, and the brightness difference δI between the pre-focus and post-focus images. Based on a pre-calibrated function relationship Z(Q1,Q2,δI) for defocus compensation, the defocus compensation amount Z is obtained. The motor is then controlled to drive the objective lens to move along the axial direction based on the defocus compensation amount Z, reducing the absolute value of the defocus amount Z' to within a pre-set threshold range T.

[0006] The steps for calculating the coarse defocus compensation Z1(Q1,Q2) and the fine defocus compensation Z1(δI) are set up as follows: First, the coarse defocus compensation Z1(Q1,Q2) is calculated. If the coarse defocus compensation |Z1(Q1,Q2)| is one or more times larger than the depth of field Δd of the imaging system, then the defocus compensation Z = Z1(Q1,Q2). If |Z1(Q1,Q2)| is located near the depth of field Δd of the imaging system, then the fine defocus compensation Z1(δI) is calculated and set as the defocus compensation amount.

[0007] Z = Z1(δI); After determining the defocus compensation amount Z, control the motor to drive the objective lens to move a distance of Z, and reduce the defocus amount Z' to 0 or within a preset threshold range T.

[0008] The steps for calculating the coarse defocus compensation amount are as follows:

[0009] C1 analyzes the focus sharpness parameter Q1 of the striped line structured light or dot matrix structured light in the image information from the focus front detection unit;

[0010] C2 analyzes the focus sharpness parameter Q2 of the striped line structured light or dot matrix structured light in the image information from the back focus detection unit;

[0011] C3 analyzes the focus sharpness parameter Q1 and the focus sharpness parameter Q2, obtains the absolute value of the defocus compensation amount |Z| based on the pre-calibrated relationship between the focus sharpness parameter and the defocus compensation amount, and determines the defocus direction based on the positive or negative value of the defocus compensation amount;

[0012] C4 controls the movement of the motor driving the objective lens based on the calculated defocus compensation amount and defocus direction, thereby reducing the defocus amount Z'.

[0013] Repeat steps C1-C4 until the absolute value of the defocus amount Z' is reduced to within the preset threshold range T.

[0014] The analysis of the focus sharpness parameter Q1 of the striped line structured light or dot matrix structured light in the image information from the focus front detection unit specifically includes:

[0015] Calculate the gradient of the edge portion in the image information to obtain the gradient matrix G, and calculate the weighted average of the gradient matrix G as the focus sharpness parameter Q1;

[0016] Alternatively, the average grayscale value of the image information can be calculated as the focus sharpness parameter Q1;

[0017] Alternatively, the spot diameter or line width in the image information can be obtained as the focus sharpness parameter Q1.

[0018] The analysis of the focus sharpness parameter Q2 of the striped line structured light or dot matrix structured light in the image information from the back focus detection unit specifically includes:

[0019] Calculate the gradient of the edge portion in the image information to obtain the gradient matrix G, and calculate the weighted average of the gradient matrix G as the focus sharpness parameter Q2;

[0020] Alternatively, the average grayscale value of the image information can be calculated as the focus sharpness parameter Q2;

[0021] Alternatively, the spot diameter or line width in the image information can be obtained as the focus sharpness parameter Q2.

[0022] It also includes a pre-calibration step:

[0023] By setting the step and scanning range, the image information from the front focus detection unit and the image information from the back focus detection unit are scanned and acquired in the axial position, and the focus sharpness parameter Q1 / focus sharpness parameter Q2 value is calculated to obtain the relationship between the defocus compensation amount and Q1 / Q2 Z=Z1(Q1,Q2), where Z is the defocus compensation amount;

[0024] By setting the step and scanning range, the image information from the front focus detection unit and the image information from the back focus detection unit are scanned and acquired at the axial position. The gray value I corresponding to the image information is calculated, and I(z) curves are established respectively to obtain the curve I_pre(z) corresponding to the image information of the front focus detection unit and the curve I_post(z) corresponding to the image information of the back focus detection unit. The relationship z1(δI) between the differential signal and the defocus compensation amount is established, where δI=I_pre(z)-I_post(z).

[0025] The steps for calculating the fine-tuned defocus compensation amount specifically include:

[0026] The confocal differential signal I(z) = I is obtained by subtracting the intensity of the lattice structured light in the image information of the pre-focus detection unit and the image information of the post-focus detection unit. c_Pre (z)-I c_Post (z), I c_Pre (z) represents the spot intensity of the dot matrix structured light of the image information from the focal front detection unit, I c_Post (z) represents the intensity of the dot matrix structured light of the image information of the back-focus detection unit;

[0027] Based on the linear component I in the pre-calibrated axial differential confocal signal D =I pre -Ipost The relationship between z1(δI) and the defocus compensation amount is used to determine the defocus compensation amount.

[0028] A high-speed autofocus system based on the principle of parallel differential confocal focusing includes an objective lens, a collimating lens group, a beam splitting module, a pre-focus detection module, a post-focus detection module, and a microprocessor. Employing the aforementioned high-speed autofocus method based on the principle of parallel differential confocal focusing, it further includes a spatial light modulator. The spatial light modulator is placed at the field stop of the illumination optical path to modulate the light emitted from the illumination optical path, forming multiple light spots and stripes. These light spots and stripes are then irradiated onto the surface of the object under test after passing through the collimating lens group, beam splitting module, and objective lens. After being reflected by the surface of the object under test, the light is then dispersed by the beam splitting module to reach the pre-focus detection unit and the post-focus detection unit, respectively. The microprocessor acquires the image information collected by the pre-focus detection unit and the post-focus detection unit, calculates the defocus compensation amount, and controls the objective lens to reduce the absolute value of the defocus amount to a set value based on the defocus compensation amount.

[0029] The front focus detection module is located M in front of the focal point; the back focus detection module is located N behind the focal point; the front focus detection module and the back focus detection module are equidistant from the focal plane and opposite in direction; the reference planes of the front focus detection module and the back focus detection module are conjugate to the effective surface of the spatial light modulator and the focal plane of the microscopic imaging system.

[0030] The spatial light modulator is a digital micromirror reflective spatial light modulator, or a transmissive field aperture with fixed holes and line openings, or a digitally dynamically adjustable liquid crystal transmissive spatial light modulator.

[0031] As can be seen from the above description of the present invention, compared with the prior art, the present invention has the following beneficial effects:

[0032] 1. In this invention, a spatial light modulator is placed at the field stop of the illumination light path to digitally modulate the light emitted from the illumination light path to form multiple light spots or stripes. After being reflected by the surface of the object under test, the light is split and reaches the front focus detection unit and the back focus detection unit respectively. The microprocessor acquires the image information collected by the front focus detection unit and the back focus detection unit respectively, calculates the defocus compensation amount, and controls the objective lens to reduce the absolute value of the defocus amount to the set value according to the defocus compensation amount. It has the advantages of large range, high precision, and high efficiency.

[0033] 2. In this invention, autofocus is divided into a coarse adjustment stage and a fine adjustment stage. The coarse adjustment stage uses structured light for focusing, resulting in a wider focusing range; the fine adjustment stage is based on the differential confocal principle, which has higher accuracy and efficiency compared to other focusing methods.

[0034] 3. In this invention, the invention can be attached to any optical microscope for autofocus and shares the objective lens with any optical microscope, without the need to attach a separate objective lens to the autofocus device.

[0035] 4. This invention uses a high-speed embedded microprocessor for data analysis and processing, which further improves focusing efficiency. Compared with traditional autofocus methods, it can be applied to autofocus of more types of samples and has a wider range of application scenarios. Attached Figure Description

[0036] Figure 1 This is a system composition diagram (DLP) of the present invention;

[0037] Figure 2 This is a system composition diagram (dot matrix aperture) of the present invention;

[0038] Figure 3 A schematic diagram of a spatial light modulator;

[0039] Figure 4 For curve I c_pre Curve I c_post Curve I D The calibration relationship between z and z;

[0040] Among them: 20, objective lens; 21, motor; 30, collimating lens group; 40, beam splitting module; 41, first beam splitting lens; 42, second beam splitting lens; 43, first focusing lens; 44, second focusing lens; 50, pre-focus detection module; 60, post-focus detection module; 70, microprocessor; 80, spatial light modulator.

[0041] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Detailed Implementation

[0042] The present invention will be further described below through specific embodiments.

[0043] In this invention, the terms "first," "second," and "third," etc., are used only to distinguish similar objects and are not necessarily used to describe a specific order or sequence, nor should they be construed as indicating or implying relative importance. The use of terms such as "upper," "lower," "left," "right," "front," and "rear" to indicate orientation or positional relationships is based on the orientation or positional relationships shown in the accompanying drawings and is only for the convenience of describing the invention, not to indicate or imply that the device referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation on the scope of protection of this invention. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0044] Furthermore, in the description of this application, unless otherwise stated, "multiple" means two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0045] A high-speed autofocus method based on the parallel differential confocal principle is proposed. A spatial light modulator is placed at the field stop of the illumination path to digitally modulate the light emitted from the illumination path, forming multiple light spots and stripes. These light spots and stripes are then illuminated onto the surface of the object under test after passing through a collimating lens group, a first beam splitter, and an objective lens. The light reflected from the object surface is then transmitted through the beam splitter to the pre-focus and post-focus detection units, respectively, and converted into pre-focus and post-focus images via photoelectric conversion. A microprocessor calculates the pre-focus and post-focus images acquired by the pre-focus and post-focus detection units to obtain three parameters: the pre-focus image sharpness parameter Q1, the post-focus image sharpness parameter Q2, and the pre-focus and post-focus image brightness difference δI. Based on a pre-calibrated function relationship Z(Q1,Q2,δI) for defocus compensation, the defocus compensation amount Z is obtained. The motor driving the objective lens along the axial direction is then controlled according to the defocus compensation amount to reduce the absolute value of the defocus amount Z' to within a pre-set threshold range T. The method of this invention obtains a defocus compensation amount by detecting the defocus amount, controls the motor to operate based on the defocus compensation amount, drives the motor to move the objective lens, and reduces the defocus amount Z' to a set value, for example, to 1 / 3 of the objective lens depth of field. Focusing is performed by cyclically executing the defocus amount detection and combining it with the defocus compensation amount.

[0046] The calculation of the defocus compensation amount specifically includes the steps of calculating the coarse defocus compensation amount Z1(Q1,Q2) and the fine defocus compensation amount Z1(δI). The process is set up so that the coarse defocus compensation amount Z1(Q1,Q2) is calculated first. If the coarse defocus compensation amount |Z1(Q1,Q2)| is one or more times larger than the depth of field Δd of the imaging system, then the defocus compensation amount Z = Z1(Q1,Q2). If |Z1(Q1,Q2)| is within a comparable range to the depth of field Δd of the imaging system, then the step of calculating the fine defocus compensation amount Z1(δI) is performed, and the defocus compensation amount Z = Z1(δI) is set. After determining the defocus compensation amount Z, the motor drives the objective lens to move a distance of Z, reducing the defocus amount Z' to 0 or within a pre-set threshold range T.

[0047] Further steps for calculating the coarse defocus compensation amount are as follows:

[0048] C1 analyzes the focus sharpness parameter Q1 of the striped line structured light or dot matrix structured light in the image information from the focus front detection unit;

[0049] C2 analysis is performed on the focus sharpness parameter Q2 of the striped line structured light or dot matrix structured light in the image information from the back focus detection unit;

[0050] C3 analyzes the focus sharpness parameter Q1 and focus sharpness parameter Q2, obtains the absolute value of the defocus compensation amount |Z| based on the pre-calibrated relationship between the focus sharpness parameter and the defocus compensation amount, and determines the defocus direction based on the positive or negative value of the defocus compensation amount;

[0051] C4 controls the movement of the motor driving the objective lens based on the calculated defocus compensation amount and defocus direction, thereby reducing the defocus amount Z'.

[0052] Repeat steps C1-C4 until the absolute value of the defocus amount |Z| shrinks to within the preset threshold range T.

[0053] Specifically, in step C2, the focus sharpness parameter Q1 of the striped structured light or dot matrix structured light in the image information from the focus front detection unit can be obtained by calculating the edge gradient, intensity, or spot diameter / line width, specifically including the following:

[0054] Calculate the gradient of the edge portion in the image information to obtain the gradient matrix G, and calculate the weighted average of the gradient matrix G as the focus sharpness parameter Q1; or, calculate the average gray level of the image information as the focus sharpness parameter Q1; or, obtain the spot diameter or line width in the image information as the focus sharpness parameter Q1.

[0055] Similarly, the focus sharpness parameter Q2 of the striped line structured light or dot matrix structured light in the image information from the back focus detection unit can be obtained by calculating the edge gradient, intensity, or spot diameter / line width, specifically including the following:

[0056] Calculate the gradient of the edge portion in the image information to obtain the gradient matrix G, and calculate the weighted average of the gradient matrix G as the focus sharpness parameter Q2; or, calculate the average gray level of the image information as the focus sharpness parameter Q2; or, obtain the spot diameter or line width in the image information as the focus sharpness parameter Q2.

[0057] The invention also includes a pre-calibration step: by setting the step size and scanning range, image information from the pre-focus detection unit and the post-focus detection unit are scanned and acquired in the axial position, and the focus sharpness parameter Q1 / focus sharpness parameter Q2 is calculated to obtain the relationship Z = Z1(Q1,Q2) between the defocus compensation amount and Q1 / Q2, where Z is the defocus compensation amount. This step is a pre-calibration step for the relationship between image sharpness Q1 / Q2 and defocus compensation amount Z used for coarse measurement of defocus amount over a large range.

[0058] The detailed measurement of defocus compensation amount in this invention specifically includes:

[0059] The confocal differential signal I(z) = I is obtained by subtracting the spot intensity of the lattice structured light from the image information of the pre-focus detection unit and the image information of the post-focus detection unit. c_Pre (z)-I c_Post (z), I c_Pre (z) represents the spot intensity of the structured light of the dot matrix of the image information of the focal front detection unit, I c_Post (z) represents the spot intensity of the structured light in the image information of the back-focus detection unit; based on the linear component I in the pre-calibrated axial differential confocal signal... D =I pre -I post The relationship between the defocus compensation amount z1(δI) and the defocus compensation amount is used to determine the defocus compensation amount.

[0060] Figure 3 middle, I c_Pre (z) and I c_Post (z) represents the relationship between the image grayscale and defocus compensation amount obtained by the front-focus detection unit and the back-focus detection unit, respectively. D(z) The curve to be obtained. The boxed area is I. D(z) The linear region. Image grayscale I obtained at any defocus position z by the front-focus and back-focus detection units. pre and I post By subtracting the difference, we can obtain the corresponding I. D , the I D in I D(z) The horizontal axis corresponding to the curve is the defocus compensation amount Z. If Z < 0, the defocus compensation direction is towards the back of focus; if Z > 0, the direction is opposite.

[0061] Furthermore, it also includes a pre-calibration step: by setting the step size and scanning range, image information from the pre-focus detection unit and the post-focus detection unit are scanned and acquired at the axial position. The grayscale value I corresponding to the image information is calculated, and I(z) curves are established respectively to obtain the curve I_pre(z) corresponding to the image information of the pre-focus detection unit and the curve I_post(z) corresponding to the image information of the post-focus detection unit. The relationship z1(δI) between the differential signal and the defocus compensation amount is established, where δI = I_pre(z) - I_post(z). This step is for the differential signal I used for high-precision fine measurement. D =I pre -I post A pre-calibration step regarding the relationship between the defocus compensation amount and the target focus. In this invention, the two pre-calibration steps described above can be combined.

[0062] This invention divides autofocus into a coarse adjustment stage and a fine adjustment stage. The coarse adjustment stage uses structured light for focusing, resulting in a wider focusing range; the fine adjustment stage is based on the differential confocal principle, which offers higher accuracy and efficiency compared to other focusing methods.

[0063] Based on this, see Figure 1 The present invention also explores a high-speed autofocus device based on the principle of parallel differential confocal focusing, including an objective lens 20, a collimating lens group 30, a beam splitting module 40, a pre-focus detection module 50, a post-focus detection module 60, and a microprocessor 70. It also includes a spatial light modulator 80, which is placed at the field stop of the illumination light path to digitally modulate the light emitted from the illumination light path to form multiple light spots or stripes. After passing through the collimating lens group 30, the beam splitting module 40, and the objective lens 20, the light is irradiated onto the surface of the object under test. After being reflected by the surface of the object under test, the light is then sent to the pre-focus detection unit and the post-focus detection unit by the beam splitting module 40, respectively. The microprocessor acquires the image information collected by the pre-focus detection unit and the post-focus detection unit, calculates the defocus compensation amount, and controls the objective lens 20 to reduce the absolute value of the defocus amount to a set value according to the defocus compensation amount.

[0064] The spatial light modulator 80 can modulate a single beam of light into an arbitrary pattern structure containing both line and dot features. The spatial light modulator 80 can be a digital micromirror (DMD) reflective spatial light modulator, a transmissive field aperture with fixed holes and line openings, or a digitally dynamically adjustable liquid crystal (LCD) transmissive spatial light modulator, etc.

[0065] The beam splitting module 40 includes a first beam splitting lens 41, a second beam splitting lens 42, a first focusing lens 43, and a second focusing lens 44. The first focusing lens 43 is located between the second beam splitting lens 42 and the post-focus detection module 60, and the second focusing lens 44 is located between the second beam splitting lens 42 and the pre-focus detection module 50. The first beam splitting lens 41 and the second beam splitting lens 42 can be dichroic mirrors, semi-transparent mirrors, or a combination of polarizers and polarizing beam splitters.

[0066] Furthermore, the front focus detection module 50 is located M in front of the focal point of the light beam; the back focus detection module 60 is located N behind the focal point of the light beam; the front focus detection module 50 and the back focus detection module 60 are equidistant from the focal plane and are in opposite directions; the reference planes of the front focus detection module 50 and the back focus detection module 60 are conjugate with the effective surface of the spatial light modulator 80 and the focal plane of the microscopic imaging system.

[0067] The microprocessor uses an embedded microprocessor. It performs high-speed calculations on the acquired image information to obtain the defocus compensation amount, and controls motor 21 to reduce the absolute value of the defocus amount to a set value based on this compensation amount. For practical applications of this invention, see [link to relevant documentation]. Figure 1Spatial light modulators 80, etc., can be replaced by digital projectors (DLP) with infrared or ultraviolet bands. See [link to relevant documentation]. Figure 2 Spatial light modulators 80, etc., can be implemented using dot matrix apertures.

[0068] The system of the present invention uses the above-mentioned high-speed autofocus method based on the parallel differential confocal principle to achieve focusing. It has the advantages of large focusing range, fast focusing speed, high focusing accuracy, wide application range, and can be used as a standalone device in optical microscopes without adding an additional objective lens 20.

[0069] The above are merely specific embodiments of the present invention, but the design concept of the present invention is not limited thereto. Any non-substantial modifications made to the present invention using this concept shall be considered as infringing upon the protection scope of the present invention.

Claims

1. A high-speed autofocus method based on the principle of parallel differential confocal focusing, characterized in that: A spatial light modulator is placed at the field stop of the illumination light path to digitally modulate the light emitted from the illumination light path, forming multiple light spots and stripes. After passing through a collimating lens group, a first beam splitter, and an objective lens, the light is irradiated onto the surface of the object under test. After being reflected by the surface of the object under test, the light reaches the front-focus detection unit and the back-focus detection unit respectively through the beam splitter and is converted into front-focus images and back-focus images by photoelectric conversion. The microprocessor calculates the front-focus image sharpness parameter Q1, the back-focus image sharpness parameter Q2, and the brightness difference δI between the front-focus and back-focus images respectively. According to the pre-calibrated function relationship Z(Q1,Q2,δI) of the defocus compensation amount, the defocus compensation amount Z is obtained. Based on the defocus compensation amount Z, the motor drives the objective lens to move along the axis to reduce the absolute value of the defocus amount Z' to within the pre-set threshold range T. The calculation of the defocus compensation amount specifically includes the steps of calculating the coarse defocus compensation amount Z1(Q1,Q2) and the fine defocus compensation amount Z1(δI). The calculation is configured such that the coarse defocus compensation amount Z1(Q1,Q2) is calculated first. If the coarse defocus compensation amount |Z1(Q1,Q2)| is one or more times larger than the depth of field Δd of the imaging system, then the defocus compensation amount Z = Z1(Q1,Q2). If |Z1(Q1,Q2)| is located near the depth of field Δd of the imaging system, then the fine defocus compensation amount Z1(δI) is calculated, and the defocus compensation amount Z = Z1(δI). After determining the defocus compensation amount Z, the motor drives the objective lens to move a distance of Z, reducing the defocus amount Z' to 0 or within a pre-set threshold range T. The steps for calculating the coarse defocus compensation amount are as follows: Step C1: Analyze the focus sharpness parameter Q1 of the striped line structured light or dot matrix structured light in the image information from the focus front detection unit; Step C2: Analyze the focus sharpness parameter Q2 of the striped line structured light or dot matrix structured light in the image information from the back focus detection unit; Step C3: Analyze the focus sharpness parameter Q1 and the focus sharpness parameter Q2, obtain the absolute value of the defocus compensation amount |Z| according to the pre-calibrated relationship between the focus sharpness parameter and the defocus compensation amount, and determine the defocus direction according to the positive or negative value of the defocus compensation amount; Step C4: Based on the calculated defocus compensation amount and defocus direction, control the movement of the motor driving the objective lens to reduce the defocus amount Z'. Repeat steps C1-C4 until the absolute value of the defocus amount Z' is reduced to within the preset threshold range T; It also includes a pre-calibration step: By setting the step and scanning range, the image information from the front focus detection unit and the image information from the back focus detection unit are scanned and acquired in the axial position, and the focus sharpness parameter Q1 / focus sharpness parameter Q2 value is calculated to obtain the relationship between the defocus compensation amount and Q1 / Q2 Z=Z1(Q1,Q2), where Z is the defocus compensation amount; By setting the step and scanning range, the image information from the front focus detection unit and the image information from the back focus detection unit are scanned and acquired at the axial position. The gray value I corresponding to the image information is calculated, and I(z) curves are established respectively to obtain the curve I_pre(z) corresponding to the image information of the front focus detection unit and the curve I_post(z) corresponding to the image information of the back focus detection unit. The relationship Z1(δI) between the differential signal and the defocus compensation amount is established, where δI=I_pre(z)-I_post(z).

2. The high-speed autofocus method based on the parallel differential confocal principle as described in claim 1, characterized in that: The analysis of the focus sharpness parameter Q1 of the striped line structured light or dot matrix structured light in the image information from the focus front detection unit specifically includes: Calculate the gradient of the edge portion in the image information to obtain the gradient matrix G, and calculate the weighted average of the gradient matrix G as the focus sharpness parameter Q1; Alternatively, the average grayscale value of the image information can be calculated as the focus sharpness parameter Q1; Alternatively, the spot diameter or line width in the image information can be obtained as the focus sharpness parameter Q1.

3. The high-speed autofocus method based on the parallel differential confocal principle as described in claim 1, characterized in that: The analysis of the focus sharpness parameter Q2 of the striped line structured light or dot matrix structured light in the image information from the back focus detection unit specifically includes: Calculate the gradient of the edge portion in the image information to obtain the gradient matrix G, and calculate the weighted average of the gradient matrix G as the focus sharpness parameter Q2; Alternatively, the average grayscale value of the image information can be calculated as the focus sharpness parameter Q2; Alternatively, the spot diameter or line width in the image information can be obtained as the focus sharpness parameter Q2.

4. The high-speed autofocus method based on the parallel differential confocal principle as described in claim 1, characterized in that: The steps for calculating the fine-tuned defocus compensation amount specifically include: The confocal differential signal I(z) = I is obtained by subtracting the intensity of the lattice structured light in the image information of the pre-focus detection unit and the image information of the post-focus detection unit. c_Pre (z)-I c_Post (z), I c_Pre (z) represents the spot intensity of the dot matrix structured light of the image information from the focal front detection unit, I c_Post (z) represents the intensity of the dot matrix structured light of the image information of the back-focus detection unit; Based on the linear component I in the pre-calibrated axial differential confocal signal D =I pre -I post The relationship between the defocus compensation amount and Z1(δI) is used to determine the defocus compensation amount.

5. A high-speed autofocus system based on the principle of parallel differential confocal focusing, comprising an objective lens, a collimating lens group, a beam splitting module, a pre-focus detection module, a post-focus detection module, and a microprocessor, characterized in that: The high-speed autofocus method based on the parallel differential confocal principle according to any one of claims 1 to 4 further includes a spatial light modulator. The spatial light modulator is placed at the field stop of the illumination optical path to modulate the light emitted from the illumination optical path to form multiple light spots and stripes. After passing through the collimating lens group, the beam splitting module and the objective lens, the light is irradiated onto the surface of the object under test. After being reflected by the surface of the object under test, the light is split by the beam splitting module and reaches the pre-focus detection unit and the post-focus detection unit respectively. The microprocessor acquires the image information collected by the pre-focus detection unit and the post-focus detection unit respectively, calculates the defocus compensation amount, and controls the objective lens to reduce the absolute value of the defocus amount to a set value according to the defocus compensation amount.

6. A high-speed autofocus system based on the parallel differential confocal principle as described in claim 5, characterized in that: The front focus detection module is located M in front of the focal point; the back focus detection module is located N behind the focal point; the front focus detection module and the back focus detection module are equidistant from the focal plane and opposite in direction; the reference planes of the front focus detection module and the back focus detection module are conjugate to the effective surface of the spatial light modulator and the focal plane of the microscopic imaging system.

7. A high-speed autofocus system based on the parallel differential confocal principle as described in claim 5, characterized in that: The spatial light modulator is a digital micromirror reflective spatial light modulator, or a transmissive field aperture with fixed holes and line openings, or a digitally dynamically adjustable liquid crystal transmissive spatial light modulator.

Images