Automatic correction method based on defocusing amount in laser automatic focusing and focusing system

Abstract

The invention discloses an automatic correction method based on the defocusing amount in laser automatic focusing and a focusing system, and the automatic correction method based on the defocusing amount in laser automatic focusing comprises the steps: executing at least one compensation correction according to a defocusing amount calculation model; the single compensation correction comprises the following steps: acquiring a first defocusing amount according to a defocusing amount calculation model; controlling the objective lens to move once according to the first defocusing amount; according to a defocusing amount calculation model, obtaining a second defocusing amount after the objective lens is moved; acquiring a compensation coefficient according to the first defocusing amount and the second defocusing amount; correcting the defocusing amount calculation model according to the compensation coefficient; wherein when the compensation correction is executed for the first time, the used defocusing amount calculation model is a calibrated defocusing amount calculation model. The focusing speed can be increased, the focusing times can be reduced, and the method is suitable for accurate focusing of samples with different reflectivity.

Description

Technical Field

[0001] This application relates to the field of laser autofocus technology, and in particular to an automatic correction method and focusing system for defocusing in laser autofocus. Background Technology

[0002] In laser focusing, the calculation of defocus is affected by the sample characteristics and the intensity of its reflected light. When the brightness of the light spot received by the image sensor changes, the calculated defocus will change, causing the actual value to deviate from the originally calibrated defocus calculation model. To address this problem, existing laser autofocus systems typically employ the following approach: when changing samples with different reflectivities, the laser power is adjusted in real time to maintain a consistent light spot brightness received by the image sensor. Then, the defocus is calculated according to the calibrated defocus calculation model, and a motor is used to move the objective lens to complete focusing. However, this method has the following significant drawbacks: First, when the spot brightness does not meet the preset requirements, the system needs to perform at least one cycle of taking a picture, image processing, spot brightness judgment, adjusting laser power, taking a picture, image processing, spot brightness judgment, and calculating the defocus amount. The defocus amount calculation requires at least two complete picture taking and image processing steps, and the laser power also needs to be judged and adjusted to the set value during the process, which greatly increases the focusing time. Especially when the laser intensity is unstable, more pictures and image processing steps may be needed to obtain the defocus amount, further extending the focusing time. Second, when measuring special samples, the originally calibrated defocus amount calculation model is no longer applicable, causing the defocus amount calculation to always have deviations, making accurate focusing impossible. Finally, frequent adjustments to the output power of the laser diode can easily affect the working stability of the laser diode and shorten its lifespan. Summary of the Invention

[0003] This application aims to address at least one of the technical problems existing in the prior art. To this end, this application proposes an automatic correction method for defocusing in laser autofocus, which can improve focusing speed, reduce the number of focusing attempts, and is suitable for accurate focusing of samples with different reflectivities.

[0004] This application also proposes a focusing system.

[0005] The automatic correction method for defocusing in laser autofocus according to the first aspect of this application includes: Based on the defocus calculation model, at least one compensation correction is performed; each compensation correction includes: According to the defocusing amount calculation model, the first defocusing amount is obtained; Based on the first defocus amount, control the objective lens to move once; Based on the defocus calculation model, the second defocus amount after the objective lens is moved is obtained; The compensation coefficient is obtained based on the first defocus amount and the second defocus amount; The defocus calculation model is corrected based on the compensation coefficient. Specifically, when the compensation correction is performed for the first time, the defocus calculation model used is the calibrated defocus calculation model.

[0006] The automatic correction method for defocusing in laser autofocus according to the embodiments of this application has at least the following beneficial effects: First, this application obtains a compensation coefficient based on the defocus amount before and after a single objective lens movement, and uses this compensation coefficient to correct the defocus amount calculation model online. This achieves rapid compensation for model deviations caused by changes in sample reflectivity, ensuring that the final defocus amount matches the actual defocus distance. This significantly improves focusing speed, reduces the number of focusing attempts, and typically requires only one compensation correction step to meet focusing needs. Second, through the aforementioned compensation correction process, this application can update the defocus amount calculation model in real time to correct any inaccuracies caused by changes in sample reflectivity. This process does not rely on adjusting the spot brightness to a fixed range; therefore, even for special samples, the model can be automatically corrected using the obtained compensation coefficient, enabling accurate focusing on samples with different reflectivities. Third, since this application does not require real-time calculation and judgment of grayscale values, it reduces the requirements for image sensor frame rate and processor computing speed caused by real-time calculations. Fourth, the laser power in this application can be constant, and the laser emitting unit (e.g., laser diode) does not need to frequently adjust the power to adapt to different samples. This not only improves the stability of the laser output power, but also avoids the problem of accelerated aging of the laser emitting unit due to frequent power adjustment, and can extend the service life of the laser emitting unit.

[0007] According to some embodiments of this application, the defocus amount calculation model is a linear model based on spot morphology parameters, and the step of correcting the defocus amount calculation model according to the compensation coefficient includes: The compensation coefficient is multiplied by the slope of the currently used defocus calculation model to obtain the corrected defocus calculation model.

[0008] According to some embodiments of this application, the spot morphology parameter is one of the following: spot centroid value, spot radius value, spot diameter value, and spot area value.

[0009] According to some embodiments of this application, the spot morphology parameter is the spot centroid value, and the calibrated defocusing amount calculation model is expressed as: , In the formula, This is the defocus amount. This is the centroid value of the light spot. and These are calibration parameters.

[0010] According to some embodiments of this application, the spot centroid value Represented as: , In the formula, The first spot in the image line, number The grayscale value of the column pixels.

[0011] According to some embodiments of this application, the first In the compensation correction described below, the compensation coefficient The following formula is used for calculation: , In the formula, This refers to the first defocus amount in the compensation and correction described herein. This refers to the second defocus amount in the compensation correction described herein.

[0012] According to some embodiments of this application, the step of correcting the defocus calculation model based on the compensation coefficient includes: Set the threshold range; Determine whether the compensation coefficient is within the threshold range; The defocus calculation model is corrected only when the compensation coefficient is within the threshold range.

[0013] According to some embodiments of this application, performing at least one compensation correction is performed as performing multiple compensation corrections, and the threshold range is different in different orders of the compensation corrections.

[0014] According to some embodiments of this application, the threshold range gradually tightens as the order of the compensation correction increases.

[0015] A focusing system according to a second aspect embodiment of this application includes: Objective lens; A laser emitting unit is used to emit a laser beam that passes through the objective lens toward the sample under test; An image sensor is used to receive the light spot formed by the light reflected from the sample under test and passing through the objective lens again; Motion control unit, used to drive the objective lens movement; The processing unit is communicatively connected to the image sensor and the motion control unit, respectively, and is configured to execute the automatic correction method for defocusing in laser autofocus based on any of the above embodiments.

[0016] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0017] The present application will be further described below with reference to the accompanying drawings and embodiments, wherein: Figure 1 This is a flowchart illustrating an embodiment of the automatic correction method for defocusing in laser autofocus based on this application. Detailed Implementation

[0018] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0019] In the description of this application, it should be understood that the orientation descriptions, such as up, down, etc., are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0020] In the description of this application, "multiple" refers to two or more. The use of "first" and "second" is for the purpose of distinguishing technical features only and should not be construed as indicating or implying relative importance, or implicitly indicating the number of technical features indicated, or the order in which the technical features are indicated.

[0021] In the description of this application, unless otherwise expressly defined, terms such as "setup," "installation," and "connection" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this application in conjunction with the specific content of the technical solution.

[0022] An embodiment of this application provides an automatic correction method for defocus amount in laser autofocus, comprising: performing at least one compensation correction based on a defocus amount calculation model; a single compensation correction includes: The first defocus amount is obtained based on the defocus amount calculation model; Based on the first defocusing amount, control the objective lens to move once; Based on the defocus calculation model, obtain the second defocus amount after the objective lens is moved; The compensation coefficient is obtained based on the first defocus amount and the second defocus amount; The defocus calculation model is corrected based on the compensation coefficient; When performing compensation correction for the first time, the defocus calculation model used is the calibrated defocus calculation model. If compensation correction is performed multiple times, the steps for each subsequent correction will use the defocus calculation model corrected in the previous correction.

[0023] The automatic correction method for defocusing amount in laser autofocus based on the embodiments of this application has the following beneficial effects: First, this application obtains a compensation coefficient based on the defocus amount before and after a single objective lens movement, and uses the compensation coefficient to correct the defocus amount calculation model online. This achieves rapid compensation for model deviations caused by changes in sample reflectivity, ensuring that the final defocus amount is consistent with the actual defocus distance. This significantly improves focusing speed, reduces the number of focusing attempts, and typically only requires one compensation correction step to meet focusing needs.

[0024] Secondly, through the aforementioned compensation and correction process, this application can update the defocus calculation model that is out of focus due to changes in sample reflectivity in real time. This process does not rely on adjusting the spot brightness to a fixed range. Therefore, even for special samples, the model can be automatically corrected through the obtained compensation coefficient to achieve accurate focusing on samples with different reflectivities.

[0025] Third, since this application does not require real-time calculation and judgment of grayscale values, it can reduce the requirements for image sensor frame rate and processor computing speed caused by real-time calculation.

[0026] Fourth, the laser power in this application can be constant, and the laser emitting unit (e.g., laser diode) does not need to frequently adjust the power to adapt to different samples. This not only improves the stability of the laser output power, but also avoids the problem of accelerated aging of the laser emitting unit due to frequent power adjustment, and can extend the service life of the laser emitting unit.

[0027] In some embodiments of this application, the defocus amount calculation model is a linear model based on the spot morphology parameters, meaning that the defocus amount and the spot morphology parameters have a linear relationship. The step of correcting the defocus amount calculation model based on the compensation coefficient includes: multiplying the compensation coefficient as a factor by the slope of the currently used defocus amount calculation model, using this as the new slope, thereby obtaining the corrected defocus amount calculation model. In this embodiment, the slope of the defocus amount calculation model is the theoretical rate of change of the defocus amount. By correcting this rate of change, the theoretical value can be made closer to the true value, thereby improving focusing accuracy.

[0028] In some embodiments of this application, the spot morphology parameter is one of the following: spot centroid value, spot radius value, spot diameter value, and spot area value.

[0029] In some embodiments of this application, the spot morphology parameter is the spot centroid value, and the calibrated defocus calculation model is expressed as: , In the formula, This is the defocus amount. This is the centroid value of the light spot. and These are calibration parameters.

[0030] in, and Determined by calibration, The calibration process is as follows: using a smooth and flat surface as the sample to be tested, the centroid value is calculated from the light spot when the sample is clear. ; The calibration process is as follows: the objective lens is moved multiple times, each time a fixed distance is moved and a spot image is acquired. The centroid value of the spot at each position of the objective lens is calculated based on the spot, and a one-to-one correspondence is established with the objective lens movement distance. A fitting is then performed to obtain the result. .

[0031] In some embodiments of this application, the centroid value of the light spot Represented as: , In the formula, The first spot in the image line, number The grayscale value of the column pixels; This represents the sequence values ​​of pixel rows in the light spot image. =1, 2, ..., , This indicates the total number of rows in the light spot image; This represents the sequence value of the pixel column in the light spot image. =1, 2, ..., , This indicates the total number of columns in the light spot image.

[0032] In some embodiments of this application, the first In the subsequent compensation adjustment, the compensation coefficient The following formula is used for calculation: , In the formula, This is the first defocus amount in this compensation correction. This is the second defocus amount in this compensation correction. This is the actual distance the objective lens moved during this compensation correction.

[0033] Based on the above embodiments, it should be noted that in this application, the focusing requirement can usually be met by performing only one compensation correction step, that is, performing at least one compensation correction as described above means performing only one compensation correction; however, in special cases, multiple compensation corrections may be performed, that is, performing at least one compensation correction as described above means performing multiple compensation corrections.

[0034] Taking a single compensation adjustment as an example, only one compensation coefficient is obtained, which is... In this case, the corrected defocus calculation model is expressed as: Then, based on this model, the defocus amount is calculated, and the objective lens is moved to focus.

[0035] And by execution Taking the secondary compensation correction as an example, obtain The compensation coefficient is, that is , ... In this case, the final corrected defocus calculation model is expressed as: Then, based on this model, the defocus amount is calculated, and the objective lens is moved to focus.

[0036] In some embodiments of this application, the step of correcting the defocus calculation model according to the compensation coefficient includes: setting a threshold range; determining whether the compensation coefficient is within the threshold range; using the compensation coefficient to correct the defocus calculation model only when the compensation coefficient is within the threshold range; if it is not within the range, the compensation coefficient may be disabled or other preset processing strategies may be adopted.

[0037] In this embodiment, by setting a threshold range for enabling the compensation coefficient, and only performing the correction of the defocus calculation model when the compensation coefficient is within the threshold range, abnormal compensation coefficients caused by some accidental factors can be effectively filtered out, thereby improving the stability and reliability of the correction process.

[0038] In some embodiments of this application, performing at least one compensation correction is performed instead of performing multiple compensation corrections. The threshold range is different in different orders of compensation corrections. The threshold range gradually tightens as the order of compensation corrections increases, so that the slope of the defocus amount calculation model (i.e. the theoretical rate of change of defocus amount) slowly approaches the actual rate of change of defocus amount, reducing the noise impact caused by objective lens movement and centroid calculation.

[0039] For example, if only one compensation correction is performed, it can correspond to The threshold range is set to 0.9 to 1.1, meaning that when 0.9 < When <1.1, use The calibrated defocus calculation model is corrected. If multiple compensation corrections are performed, a threshold range for each compensation coefficient can be set, for example, 0.5 < <1.5, 0.8< <1.2、...0.9< <1.1.

[0040] It should be noted that when performing at least one compensation correction instead of multiple compensation corrections, the threshold range may not gradually tighten as the order of the compensation corrections increases.

[0041] The following is an execution Taking multiple (more than two) compensation corrections as an example, refer to... Figure 1 The present application describes an automatic correction method for defocusing in laser autofocus based on one specific embodiment, which includes the following steps: Perform the first compensation correction: Calculate the centroid value of the light spot based on the current position of the light spot. The defocus calculation model is used. Calculate the first defocus amount for this compensation correction. Based on the first defocusing amount, control the objective lens to perform its first movement; calculate the centroid value of the light spot based on the position of the light spot after the movement. The second defocus amount for this compensation correction is calculated using the calibrated defocus amount calculation model. The compensation coefficient is calculated based on the first and second defocus amounts corrected in this compensation. Determine the compensation coefficient Does it satisfy 0.5 < <1.5, if satisfied, then use The calibrated defocus calculation model is corrected to obtain the first corrected defocus calculation model. If the conditions are not met, the compensation coefficient will be triggered. If it does not take effect or other preset processing strategies are adopted; Perform a second compensation correction: calculate the centroid value of the light spot based on the current position of the light spot. The defocus calculation model was revised using the first revision. Calculate the first defocus amount for this compensation correction. Based on the first defocusing amount, control the objective lens to move a second time; calculate the centroid value of the light spot based on the position of the light spot after the movement. The second defocus amount for this compensation correction is calculated using the defocus amount calculation model of the first correction. The compensation coefficient is calculated based on the first and second defocus amounts corrected in this compensation. Determine the compensation coefficient Does it satisfy 0.8 < <1.2, if satisfied, then use The first revised defocus calculation model is then modified to obtain the second revised defocus calculation model. If the conditions are not met, the compensation coefficient will be triggered. If it does not take effect or other preset processing strategies are adopted; Following the steps of the second compensation correction, perform subsequent compensation corrections in sequence until the first correction is completed. The second compensation correction yields the final corrected defocus calculation model. ;No. During the secondary compensation adjustment process, the compensation coefficient The threshold range is 0.9 < <1.1; After performing the above compensation and correction steps, the defocus amount is calculated based on the final corrected defocus amount calculation model, and the objective lens is moved according to the defocus amount. Focusing is completed when the defocus amount is within the set tolerance.

[0042] This application also proposes a focusing system, including an objective lens, a laser emitting unit, an image sensor, a motion control unit, and a processing unit.

[0043] The system comprises a laser emitting unit (which can be a laser diode) for emitting a laser beam through the objective lens onto the sample under test; an image sensor for receiving the light spot formed by the light reflected from the sample and passing through the objective lens again; a motion control unit for driving the objective lens to move (which can be a motor); and a processing unit that is communicatively connected to both the image sensor and the motion control unit and configured to execute the aforementioned automatic correction method for defocusing in laser autofocus. Specifically, the processing unit acquires light spot image data from the image sensor; calculates the defocusing amount according to the currently used defocusing amount calculation model and generates corresponding control commands for the motion control unit; after the objective lens moves according to the control commands, the processing unit recalculates the defocusing amount and determines a compensation coefficient; and the processing unit corrects the defocusing amount calculation model based on the compensation coefficient for subsequent focusing control.

[0044] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine different embodiments or examples described in this specification.

[0045] The embodiments of this application have been described in detail above with reference to the accompanying drawings. However, this application is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of this application.

Claims

1. A method for automatically correcting defocus in laser autofocus, characterized in that, include: Based on the defocus calculation model, perform at least one compensation correction; A single compensation correction includes: According to the defocusing amount calculation model, the first defocusing amount is obtained; Based on the first defocus amount, control the objective lens to move once; Based on the defocus calculation model, the second defocus amount after the objective lens is moved is obtained; The compensation coefficient is obtained based on the first defocus amount and the second defocus amount; The defocus calculation model is corrected based on the compensation coefficient. Specifically, when the compensation correction is performed for the first time, the defocus calculation model used is the calibrated defocus calculation model.

2. The automatic correction method for defocusing amount in laser autofocus according to claim 1, characterized in that, The defocus calculation model is a linear model based on the spot shape parameters, and the correction of the defocus calculation model according to the compensation coefficient includes: The compensation coefficient is multiplied by the slope of the currently used defocus calculation model to obtain the corrected defocus calculation model.

3. The automatic correction method for defocusing amount in laser autofocus according to claim 2, characterized in that, The light spot morphology parameter is one of the following: light spot centroid value, light spot radius value, light spot diameter value, and light spot area value.

4. The automatic correction method for defocusing amount in laser autofocus according to claim 2, characterized in that, The light spot morphology parameter is the light spot centroid value, and the calibrated defocus calculation model is expressed as follows: ， In the formula, This is the defocus amount. This is the centroid value of the light spot. and These are calibration parameters.

5. The automatic correction method for defocusing amount in laser autofocus according to claim 4, characterized in that, The centroid value of the light spot Represented as: ， In the formula, The first spot in the image line, number The grayscale value of the column pixels.

6. The automatic correction method for defocusing amount in laser autofocus according to claim 1, characterized in that, No. In the compensation correction described below, the compensation coefficient The following formula is used for calculation: ， In the formula, This refers to the first defocus amount in the compensation and correction described herein. This refers to the second defocus amount in the compensation correction described herein.

7. The automatic correction method for defocusing amount in laser autofocus according to claim 1, characterized in that, The step of correcting the defocus calculation model based on the compensation coefficient includes: Set the threshold range; Determine whether the compensation coefficient is within the threshold range; The defocus calculation model is corrected only when the compensation coefficient is within the threshold range.

8. The automatic correction method for defocusing amount in laser autofocus according to claim 7, characterized in that, The execution of at least one compensation correction is performed as multiple compensation corrections, and the threshold range is different in different orders of the compensation corrections.

9. The automatic correction method for defocusing amount in laser autofocus according to claim 8, characterized in that, The threshold range gradually tightens as the compensation correction increases in sequence.

10. A focusing system, characterized in that, include: Objective lens; A laser emitting unit is used to emit a laser beam that passes through the objective lens toward the sample under test; An image sensor is used to receive the light spot formed by the light reflected from the sample under test and passing through the objective lens again; Motion control unit, used to drive the objective lens movement; The processing unit is communicatively connected to the image sensor and the motion control unit, respectively, and is configured to execute the automatic correction method for defocusing amount based on laser autofocus as described in any one of claims 1 to 9.

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