WO2017220030A1

WO2017220030A1 - Method for calibrating beam spot

Info

Publication number: WO2017220030A1
Application number: PCT/CN2017/089866
Authority: WO
Inventors: 郭超; 马旭龙; 向虎
Original assignee: 天津清研智束科技有限公司
Priority date: 2016-06-24
Filing date: 2017-06-23
Publication date: 2017-12-28
Also published as: CN106204535A; RU2722267C1; CN106204535B

Abstract

A method for calibrating a beam spot comprises: calibrating a position of a beam spot in an image to a preset coordinate, such that the beam spot is in a preset state, and storing a circularity of the beam spot in the preset state in the image; without changing astigmatism of the beam spot, changing a focus value of the beam spot at least once; and generating a functional relation between a position parameter of the beam spot and the focus value, and adjusting the position parameter of the beam spot according to a current focus value and the functional relation.

Description

Beam spot calibration method

Technical field

The present disclosure relates to a calibration method, for example, to a calibration method of a beam spot.

Background technique

Calibration, also known as calibration, correction. Even if the size, shape and position of the beam spot reaches a preset state, the state is recorded in the system.

In the field of high energy beam processing such as additive manufacturing (eg, 3D (Dimension) printing), the size, shape and position of the beam spot of the high energy beam may affect the quality of the processing process. For example, the size of the beam spot should be kept to a minimum to make the energy more concentrated; the beam spot size is too large, which may result in energy inconsistency, resulting in processing defects. The shape of the beam spot should be kept round, and the distortion of the beam spot may result in a decrease in processing accuracy. The position of the beam spot should be accurate, and the beam spot with a deviation in position may cause the processing precision to decrease. Therefore, the beam spot can be calibrated before high energy beam processing.

One of the calibration methods for beam spot in the related art is manual calibration, that is, manually adjusting the size, shape and position of the beam spot to a preset state. Manual calibration methods can be performed with standard parts, such as marking points on standard parts, and the position of the points is precisely positioned. Adjust the beam spot to coincide with the marked point, adjust the beam spot to make it the smallest size and the roundest shape. The number of marked points can be greater than one, and the marked points can be distributed in an array. Manual calibration methods rely on human experience, lack of reliability and time-consuming and laborious.

The calibration method for the beam spot can also be an automatic calibration, that is, relying on a computer and a sensor to adjust the size, shape and position of the beam spot to a preset state. In the related art, a visual sensing method can be used to capture an image by an imaging device to extract beam spot size, shape, and position information. However, in the calibration method, the positional information of the beam spot is difficult to extract due to the distortion of the captured image, the positional relationship of the imaging device with respect to the plane of the beam spot, and the influence of the focus on the position of the beam spot cannot be eliminated, and the position information of the beam spot is difficult to extract, and cannot be quickly Complete the calibration.

Summary of the invention

A calibration method for beam spot to solve the problem of insufficient reliability of the calibration method in the related art and The position information of the beam spot is difficult to extract, and the problem of calibration cannot be completed quickly.

A method for calibrating a beam spot, comprising:

Adjusting the position of the beam spot in the image to a preset coordinate, so that the beam spot is in a preset state, and recording the circularity of the beam spot in the image when the beam spot is in a preset state;

Changing the focus value of the beam spot at least once while maintaining the beam astigmatism unchanged;

A functional relationship between the positional parameters of the beam spot and the focus value is generated to adjust the positional parameters of the beam spot based on the current focus value and the functional relationship.

Optionally, the placing the beam spot in a preset state includes:

Adjusting a focus value of the beam spot such that the beam spot size reaches a preset minimum value;

Adjusting the astigmatism of the beam spot such that the beam circularity is at a predetermined circularity;

Adjusting the positional parameter of the beam spot such that the distance between the center of the beam spot and the center of the preset coordinates is less than a preset value.

Optionally, if the beam astigmatism is kept unchanged, changing the focus value of the beam spot at least once includes:

Maintaining the astigmatism of the beam spot unchanged, such that the absolute value of the difference between the circularity of the current beam spot in the image and the circularity of the beam spot in the image in the preset state is less than a preset value;

The focus value of the beam spot is changed for the first time such that the position of the focus focus after the beam spot change is higher or lower than the position of the focus focus when the beam spot is in a preset state.

Optionally, the method further includes:

After the first change of the focus value of the beam spot such that the position of the focus focus after the beam spot is changed is higher than the position of the focus focus when the beam spot is in a preset state, the second change is performed. Determining a focus value of the beam spot such that a position of the focus focus after the beam spot is changed is lower than a position of the focus focus when the beam spot is in a preset state; or

After the first change of the focus value of the beam spot such that the position of the focus focus after the beam spot is changed is lower than the position of the focus focus when the beam spot is in a preset state, the second change is performed. Determining the focus value of the beam spot such that the position of the focus focus after the beam spot is changed is higher than when the beam spot is in a preset state The focus of the focus position.

Optionally, the function relationship between the generated beam spot position parameter and the focus value includes:

Recording the focus value of the beam spot and the position parameter when in the preset state;

Recording the focus value of the beam spot after the change of the focus value, changing the position parameter until the beam spot moves to the preset coordinate, and recording the new position parameter;

A function relationship between the beam spot position parameter and the focus value is generated according to the focus value of the beam spot in the preset state and the position parameter, and the focus value of the beam spot after the focus value is changed and the new position parameter.

Optionally, the function relationship between the position parameter of the beam spot and the focus value is

as well as

Or (X,Y)=f(F), where:

X is the coordinate control parameter of the beam spot position in the X direction, Y is the coordinate control parameter of the beam spot position in the Y direction, F is the focus value, k is the coefficient, b is a constant, (X, Y) =f(F) represents a function relationship between the coordinates of the X and Y directions and the focus value F.

Optionally, before the adjusting the beam spot to the preset coordinates, the method further includes:

Setting at least one marker point on the standard board;

Taking an image of the standard panel by an imaging device;

Corresponding preset coordinates are generated according to each of the marker points in the image.

Optionally, the imaging device is a charge coupled device CCD camera, a complementary metal oxide semiconductor CMOS camera, an infrared camera, a near infrared camera or a far infrared camera.

Optionally, the method further includes:

When the preset coordinates are greater than or equal to two, the beam spot corresponding to the first preset coordinate is calibrated;

After the beam spot calibration corresponding to the first preset coordinate is finished, the beam spot corresponding to the next preset coordinate is calibrated until the beam spot corresponding to all the preset coordinates is calibrated.

Optionally, the method further includes:

When the preset coordinates are greater than or equal to two, adjust the position of each beam spot in the image to the preset coordinates corresponding to the beam spot, and make each beam spot in a preset state, and record each beam spot. Presupposed The circularity of the beam spot in the image;

Changing the focus value of the beam spot at least once after all beam spots are adjusted to the corresponding preset coordinates and are in a preset state, while keeping each beam spot astigmatism unchanged;

A functional relationship between the positional parameters of each beam spot and the focus value of the beam spot is generated to adjust the positional parameter of each beam spot based on the current focus value of each beam spot and a functional relationship corresponding to the beam spot. In the above technical solution, the beam bundle can be realized by setting the beam spot in a preset state and generating a functional relationship between the beam spot position parameter and the focus value, and according to the function relationship and the circularity when the beam spot is in a preset state. The calibration of the spot position, and can calibrate the influence of the focus on the position of the beam spot, and the calibration of the beam spot can be unaffected by the image distortion, without solving the complex pose relationship between the imaging device and the plane of the beam spot. The method is fast, convenient and reliable.

DRAWINGS

1 is a schematic structural view of a calibration system in an embodiment;

2 is a flow chart showing a method of calibrating a beam spot of a high energy beam in an embodiment;

3 is a schematic structural view of a middle standard plate member in an embodiment;

4 is a schematic diagram of an image of a standard panel photographed by an imaging device in an embodiment;

5 is a positional relationship between a beam spot and a preset coordinate when the beam spot is not adjusted in an embodiment;

6 is a positional relationship between a beam spot and a preset coordinate when the beam spot is adjusted to a preset coordinate in an embodiment;

7 is a positional relationship between a beam spot and a preset coordinate when the beam spot focus value is changed for the first time in an embodiment;

Figure 8 is a diagram showing the positional relationship between the beam spot and the preset coordinates when the beam spot focus value is changed for the second time in an embodiment.

In the picture:

1, ray generating device; 2, working plane; 3, imaging device; 4, computer; 5, beam; 6, standard plate; 7, marking points; 8, coordinates; 9, beam spots.

detailed description

The following technical solutions are described below with reference to the accompanying drawings and specific embodiments. The technical features in the following embodiments and the embodiments may be arbitrarily combined with each other without conflict.

The embodiment provides a calibration method for a beam spot of a high energy beam, which can calibrate the position of a beam spot of a high energy beam in the field of high energy beam processing such as additive manufacturing, and the method can be completed by a calibration system, such as As shown in FIG. 1, the calibration system may include a radiation generating device 1, a working plane 2, an imaging device 3, and a computer 4, wherein the radiation generating device 1 may generate a beam 5, which may be a laser or an electron beam, the present embodiment For example, the beam 5 is an electron beam, and the radiation generating device 1 may have an accelerating voltage of 60 kV and a power of 0 to 10 kW, and the electron beam may be used in a high vacuum environment formed by a pump or a valve. The work plane 2 is the plane on which the workpiece to be machined is placed.

Optionally, the beam 5 is formed on the working plane 2, the imaging device 3 can take a beam spot on the working plane 2, and acquire an image, and the computer 4 receives the image captured by the imaging device 3 and processes the image. The computer 4 can also control the radiation generating device 1 to adjust the size, shape and position of the beam spot on the working plane 2 to achieve calibration of the beam spot position.

In this embodiment, the imaging device 3 may be a Charged Coupled Device (CCD) camera, a Complementary Metal Oxide Semiconductor (CMOS) camera, an infrared camera, a near infrared camera, or a far infrared camera. Among them, the near-infrared camera is a camera that uses near-infrared imaging, and the far-infrared camera is a camera that uses far-infrared imaging. The wavelength of near-infrared rays can be between (0.75-1) and (2.5-3) μm; the wavelength of far infrared rays It can be located between (25-40) and 1000 μm.

In this embodiment, the calibration system described above can be used on an additive manufacturing apparatus to calibrate the beam spot of the high energy beam during the additive manufacturing process. The computer 4 can perform the following calibration method.

As shown in FIG. 2, the calibration method of the beam spot of the high energy beam of the present embodiment may include the following steps.

In step 100, the position of the beam spot in the image is adjusted to a preset coordinate, so that the beam spot is in a preset state, and the circularity of the beam spot in the image when the beam spot is in the preset state is recorded.

The shape of the beam spot in the image may be circular and elliptical. The calculation formula of the circularity may be e=L1/L2, L1 is the short axis length of the graphic, L2 is the long axis length of the graphic, and / is the division operator. .

In this embodiment, the preset coordinates may be preset before being calibrated, and the method for acquiring the preset coordinates is as follows.

Referring to FIG. 3, a standard plate member 6 is provided, which is in the form of a flat plate in the standard plate member 6. At least one marker point 7 is disposed, and the marker point 7 may be arranged in an array, for example, may be a circular array, or an N×N array setting (for example, 5×5, or 7×7, etc.), where N is A positive integer. The above marking point 7 may be a hole, a laser marking pattern, a painting or a polishing point, and the marking point 7 may be strongly contrasted with other parts of the standard panel 6, and is easily identifiable. The shape of the marker point 7 may be a regular pattern such as a circle, a square or a regular polygon. Since the setting of the marker point 7 is performed on the standard panel 6, the relative position of the marker point 7 on the standard panel 6 is precise and unique.

The standard plate member 6 is placed on the working plane 2 of the calibration device, and the upper surface of the standard plate member 6 is photographed by the imaging device 3. When the imaging device 3 is photographed, the image captured by the imaging device 3 is distorted, and the captured image is as As shown in FIG. 4, the photographed standard panel 6 and the marker point 7 thereon are different from the shape of the standard panel 6 and the marker point 7, and the coordinates 8 of the marker point 7 in the image are calculated by the computer 4, in which the image is The coordinate 8 may be the above-mentioned preset coordinates. Since the marker point 7 is set to at least one, the number of preset coordinates is at least one.

In this embodiment, the preset coordinates may be stored in the computer 4, the relative pose between the imaging device 3 and the work plane 2 is unchanged, and the preset coordinates may not be updated.

In the image captured by the imaging device 3, the marker point 7 and the beam spot are both in the form of pixels, and the coordinates of the marker point 7 or the beam spot can be represented by the coordinates of the marker point 7 or the center of the beam spot. The coordinates are in pixels and the resolution can be less than 1 pixel.

After the preset coordinates are set, the image of the beam spot under the focus value is captured by the imaging device 3, and the positional relationship between the beam spot 9 and the preset coordinates is as shown in FIG. 5, where × in the figure Expressed as a preset coordinate, the beam spot size, shape, and position are in a random state, and the size, shape, and position of the beam spot 9 are calculated by the computer 4.

The focus value is a parameter that characterizes the focus state of the high energy beam. When the high energy beam is an electron beam, the focus value may be the current value in the focus coil.

The beam spot shown in FIG. 5 is adjusted to be placed at a preset coordinate and is in a preset state (as shown in FIG. 6 ). In this embodiment, the step of causing the beam spot to be in a preset state may include:

Adjusting the astigmatism of the beam spot such that the beam circularity is at a preset circularity;

Adjusting the positional parameter of the beam spot such that the distance between the center of the beam spot and the center of the preset coordinates is less than a preset value. The preset value depends on the shooting range and resolution of the imaging device 3 and the calculation method of the computer 4. In the embodiment, the resolution of the imaging device 3 exceeds 20 million pixels, and the preset value can be selected. It is 0.2mm, 0.1mm or 0.05mm. After the beam spot is adjusted to the preset state, the astigmatism, the focus value, and the position parameter of the beam spot when the beam spot is in the preset state are recorded by the computer 4, and in this embodiment, when the beam spot is in the preset state, the beam spot is The position parameter may refer to the preset coordinates described above, and the position parameter of the beam spot may be a coordinate control parameter in the X and Y directions on the captured image.

In 110, the focus value of the beam spot is changed at least once while keeping the beam astigmatism constant.

In the case that the astigmatism of the beam spot is unchanged in the maintaining step 100, the absolute value of the difference between the circularity of the current beam spot in the image and the circularity of the beam spot in the image in the preset state may be made smaller than the preset value. The value changes the focus value of the beam spot. At this time, since the focus value of the beam spot changes, not only the size of the beam spot is changed, but also the position parameter of the beam spot changes accordingly.

In this embodiment, the focus value of the beam spot can be changed once, and at this time, the focus value of the beam spot is changed, and the position of the focus focus after the beam spot change can be made higher or lower than the focus focus of the beam spot when the beam spot is in the preset state. Location, as shown in Figure 7.

It is also possible to change the focus value of the beam spot as many times as necessary to improve the accuracy of the calibration. In this embodiment, the focus value of the beam spot can be changed twice, and the focus value of the beam spot is changed for the first time, so that the position of the focus focus after the beam spot is changed is higher than the focus focus when the beam spot is in the preset state. The position (as shown in Fig. 7) changes the focus value of the beam spot a second time, and the changed focus focus is lower than the focus focus when the beam spot is in the preset state (as shown in Fig. 8). In this embodiment, the focus focus may be the center of the beam spot in the image.

In step 120, a functional relationship between the positional parameters of the beam spot and the focus value is generated to adjust the positional parameters of the beam spot based on the current focus value and the functional relationship.

Optionally, when the adjustment beam spot is in a preset state, the focus value and the position parameter of the beam spot in the preset state are recorded;

After changing the focus value of the beam spot, recording the focus value of the beam spot after the focus value is changed, and changing the position parameter until the beam spot moves to the preset coordinates, and recording the new position parameter;

Optionally, if only the focus value of the beam spot is changed once, the focus value and the position parameter of the beam spot in the preset state, and the focus value of the beam spot after the focus value is changed, and the new position parameter are generated to generate a beam. A functional relationship between the spot position parameter and the focus value.

Optionally, if the focus value of the beam spot is changed twice, after the first focus value of the beam spot is changed for the first time, the first focus value of the beam spot after the first focus value change is recorded, and the position parameter is changed. Until the spot Moving to the preset coordinates, recording the first position parameter of the beam spot, after changing the first focus value of the beam spot for the second time, recording the second focus value of the beam spot after the second focus value change, and changing the position The parameter is moved until the beam spot moves to the preset coordinates, and the second position parameter of the beam spot is recorded,

According to the focus value of the beam spot in the preset state and the position parameter, the first focus value and the first position parameter of the beam spot after the first change of the focus value, and the beam spot after the second change of the focus value The second focus value and the second position parameter generate a functional relationship between the beam spot position parameter and the focus value. The number of times the focus value is changed can also be greater than 2 times, and the more the number of times, the more accurate the functional relationship between the beam spot position parameter and the focus value.

In this embodiment, the position parameter may be represented in a coordinate form in the image, and the position parameter may include parameters in two directions of X and Y, and the function relationship may be a function relationship between the focus value F and the X direction coordinate and focus. The functional relationship formed between the value F and the Y direction coordinate, that is, the function relationship can be

as well as

Where X is the coordinate control parameter of the beam spot position in the X direction, Y is the coordinate control parameter of the beam spot position in the Y direction, F is the focus value, k is the coefficient, and b is a constant. The above functional relationship may also be a function relationship between the coordinates of the X and Y directions and the focus value F, that is, the function relationship may be (X, Y)=f(F), where X is the beam spot position. The coordinate control parameter in the X direction, Y is the coordinate control parameter of the beam spot position in the Y direction, and F is the focus value.

In this embodiment, after the function relationship is generated, the position parameter of the beam spot of a focus value used in the manufacturing process may be determined according to the function relationship, that is, the current coordinate control parameter of the beam spot can be calculated according to the function relationship. Under the control of the coordinate control parameters, the error between the coordinates of the beam spot on the working plane and the given coordinates is small, which can improve the precision of the beam spot processing.

In the present embodiment, in the above calibration method, when the radiation beam 5 emitted by the radiation emitting device 1 is an electron beam, the focus value of the beam spot can be adjusted by changing the current in the focus coil, and the current adjustment in the astigmatism coil can be changed. The beam spot shape adjusts the position of the beam spot by changing the current in the deflection yoke.

In this embodiment, the preset coordinates may be one, and calibration of a beam spot may be completed. The preset coordinates can also be multiple, and the calibration method of the beam spot can be divided into two types.

In the first calibration method, the beam spot corresponding to the first preset coordinate may be calibrated, that is, the operation in step 100-step 120 is performed on the beam spot corresponding to the first preset coordinate;

After the beam spot calibration corresponding to the first preset coordinate is finished, the beam spot corresponding to the next preset coordinate is calibrated, and the beam spot corresponding to the preset coordinate is also subjected to the operations in step 100-step 120;

By analogy, all the calibration of the beam spot is completed.

In the second calibration method, the operation in step 100 can be performed on all the beam spots, that is, the position of each beam spot in the image is adjusted to the preset coordinates corresponding to the beam spot, and each beam spot is pre- Set the state, record the circularity of the beam spot in the image when each beam spot is in a preset state;

After all beam spots are adjusted to the corresponding preset coordinates and are in a preset state, the focus value of each beam spot is changed, and the focus value of each beam spot is changed while keeping each beam spot astigmatism unchanged. Change at least once; and

Generating a functional relationship between the positional parameters of each beam spot and the focus value of the beam spot, that is, each beam spot corresponds to a functional relationship, according to a current focus value of each beam spot and a function corresponding to the beam spot The relationship adjusts the positional parameters of each beam spot. The above calibration method may be performed by the above computer 4, which may include a processor and a storage medium; wherein the storage medium stores executable instructions that are executed by the processor to cause the processor to perform the above Calibration method. The storage medium may be a non-transitory storage medium, including: a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk, and the like. The medium of the program code may also be a transient storage medium.

Industrial applicability

A beam spot calibration method, the calibration of the beam spot is not affected by image distortion, and there is no need to solve the pose relationship between the imaging device and the plane of the beam spot.

Claims

A method for calibrating a beam spot, comprising:

Adjusting the position of the beam spot in the image to a preset coordinate, so that the beam spot is in a preset state, and recording the circularity of the beam spot in the image when the beam spot is in a preset state;

Changing the focus value of the beam spot at least once while maintaining the beam astigmatism unchanged;

A functional relationship between the positional parameters of the beam spot and the focus value is generated to adjust the positional parameters of the beam spot based on the current focus value and the functional relationship.
The method of claim 1 wherein said placing the beam spot in a preset state comprises:

Adjusting a focus value of the beam spot such that the beam spot size reaches a preset minimum value;

Adjusting the astigmatism of the beam spot such that the beam circularity is at a predetermined circularity;

Adjusting the positional parameter of the beam spot such that the distance between the center of the beam spot and the center of the preset coordinates is less than a preset value.
The method according to claim 2, wherein said changing the focus value of said beam spot at least once without maintaining said beam spot astigmatism comprises:

Maintaining the astigmatism of the beam spot unchanged, such that the absolute value of the difference between the circularity of the current beam spot in the image and the circularity of the beam spot in the image in the preset state is less than a preset value;

The focus value of the beam spot is changed for the first time such that the position of the focus focus after the beam spot change is higher or lower than the position of the focus focus when the beam spot is in a preset state.
The method of claim 3 further comprising:

After the first change of the focus value of the beam spot such that the position of the focus focus after the beam spot is changed is higher than the position of the focus focus when the beam spot is in a preset state, the second change is performed. Determining the focus value of the beam spot such that the position of the focus focus after the beam spot is changed is lower than when the beam spot is in a preset state The focus of the focus; or

After the first change of the focus value of the beam spot such that the position of the focus focus after the beam spot is changed is lower than the position of the focus focus when the beam spot is in a preset state, the second change is performed. The focus value of the beam spot is such that the position of the focus focus after the beam spot is changed is higher than the position of the focus focus when the beam spot is in the preset state.
The method of claim 3 wherein said generating a functional relationship between the beam spot position parameter and the focus value comprises:

Recording the focus value of the beam spot and the position parameter when in the preset state;

Recording the focus value of the beam spot after the change of the focus value, changing the position parameter until the beam spot moves to the preset coordinate, and recording the new position parameter;

A function relationship between the beam spot position parameter and the focus value is generated according to the focus value of the beam spot in the preset state and the position parameter, and the focus value of the beam spot after the focus value is changed and the new position parameter.
The method of claim 4 wherein said generating a functional relationship between the beam spot position parameter and the focus value comprises:

Recording the focus value of the beam spot and the position parameter when in the preset state;

Recording the focus value of the beam spot after the change of the focus value, changing the position parameter until the beam spot moves to the preset coordinate, and recording the new position parameter;

A function relationship between the beam spot position parameter and the focus value is generated according to the focus value of the beam spot in the preset state and the position parameter, and the focus value of the beam spot after the focus value is changed and the new position parameter.
The method of claim 5 wherein the functional relationship between the positional parameters of the beam spot and the focus value is
as well as
Or (X,Y)=f(F), where:

X is the coordinate control parameter of the beam spot position in the X direction, and Y is the beam spot position on the Y side. The upward coordinate control parameter, F is the focus value, k is the coefficient, b is the constant, and (X, Y)=f(F) represents the relationship between the coordinates of the X and Y directions and the focus value F.
The method of claim 6 wherein the functional relationship between the positional parameters of the beam spot and the focus value is
as well as
Or (X,Y)=f(F), where:

X is the coordinate control parameter of the beam spot position in the X direction, Y is the coordinate control parameter of the beam spot position in the Y direction, F is the focus value, k is the coefficient, b is a constant, (X, Y) =f(F) represents a function relationship between the coordinates of the X and Y directions and the focus value F.
The method according to any one of claims 1-8, before the adjusting the beam spot to the preset coordinates, the method further comprises:

Setting at least one marker point on the standard board;

Taking an image of the standard panel by an imaging device;

Corresponding preset coordinates are generated according to each of the marker points in the image.
The method of claim 9, wherein the imaging device is a charge coupled device CCD camera, a complementary metal oxide semiconductor CMOS camera, an infrared camera, a near infrared camera, or a far infrared camera.
The method of claim 10 further comprising:

When the preset coordinates are greater than or equal to two, the beam spot corresponding to the first preset coordinate is calibrated;

After the beam spot calibration corresponding to the first preset coordinate is finished, the beam spot corresponding to the next preset coordinate is calibrated until the beam spot corresponding to all the preset coordinates is calibrated.
The method of claim 10 further comprising:

Adjusting the position of each beam spot in the image to the beam when the preset coordinates are greater than or equal to two The preset coordinates corresponding to the spots, and each beam spot is in a preset state, and the circularity of the beam spot in the image when each beam spot is in a preset state is recorded;

Changing the focus value of the beam spot at least once after all beam spots are adjusted to the corresponding preset coordinates and are in a preset state, while keeping each beam spot astigmatism unchanged;

A functional relationship between the positional parameters of each beam spot and the focus value of the beam spot is generated to adjust the positional parameter of each beam spot based on the current focus value of each beam spot and a functional relationship corresponding to the beam spot.