Visual calibration ruler and method for calibration of reference ruler of measurement system

Abstract

The invention relates to the field of visual calibration, and discloses a visual calibration ruler and method for calibration of a reference ruler of a measurement system. According to the method and the device, manual misoperation is avoided through a two-dimensional code automatic analysis and posture verification mechanism, and meanwhile, image distortion possibly occurring in the calibration process can be accurately recognized. And a two-dimensional code and actual side length correlation design and a general algorithm are adopted, so that the calibration ruler is high in adaptability and can be easily integrated into various machine vision or industrial camera platform models. Manual intervention is not needed in the calibration process, calibration switching under different multiplying powers can be rapidly completed, the calibration efficiency is remarkably improved, nanoscale precision can be achieved through the photomask technology and the calibration ruler, the method can be suitable for automatic calibration in the chip industry, nanoscale precision can be achieved through the calibration ruler manufactured through the photomask technology, and the application range is further expanded. Image distortion occurring in the calibration process is accurately recognized; the universality is high, and meanwhile, various platform models can be easily adapted; and different multiplying power calibration can be rapidly switched.

Description

Technical Field

[0001] The present application belongs to the field of vision calibration technology, and specifically relates to a vision calibration ruler and method for calibrating a reference ruler of a measurement system. Background Art

[0002] Calibration of a measurement system's standard ruler refers to the process of calibrating and verifying measuring equipment in a measurement system using a standard measuring tool (i.e., a standard ruler) of known precise dimensions to ensure the accuracy and consistency of measurement results. Standard rulers are typically made of high-precision materials and certified by authoritative organizations. They have extremely small thermal expansion coefficients and extremely high geometric stability, and can maintain their dimensions under various environmental conditions. The calibration process typically involves placing the standard ruler in the measurement system, recording its measurements, and comparing them with the actual dimensions of the standard ruler to calculate the measurement system's error range and correction factor. Regular standard ruler calibration can promptly detect and correct deviations in measuring equipment, improve measurement accuracy, and is widely used in industrial manufacturing, scientific research, quality control, and other fields. Standard ruler calibration is an important means to ensure the reliability, traceability, and standardization of measurement systems.

[0003] However, the existing technology requires placing a calibration ruler within the field of view, manually inputting the calibration ruler reference length and unit, and calibrating the starting point of the calibration ruler. The ratio of the actual length of the calibration ruler to the imaged length is then calculated to obtain a measurement reference value (e.g., actual length of the calibration ruler / imaged length). Switching between magnifications requires recalibration, resulting in cumbersome steps that are difficult for users to understand and unable to confirm whether the operation is accurate or to obtain the correct results. This results in inconvenience during use and affects measurement efficiency. Summary of the Invention

[0004] The purpose of this application is to provide a visual calibration ruler and method for calibrating a reference ruler of a measurement system in order to solve the above-mentioned problems.

[0005] The technical solution adopted in this application is as follows: a visual calibration ruler and method for calibrating a reference ruler of a measurement system, comprising: a plurality of calibration QR code setting areas provided on the front of the calibration ruler body; a plurality of reference QR codes provided on the surface of the calibration QR code setting areas; a reference QR code side length provided below the reference QR codes; the reference QR code side length being a silk screen indicating the QR code side length;

[0006] The calibration ruler body material can be divided into transparent and non-transparent, transparent materials include but not limited to glass and film;

[0007] Non-transparent includes but is not limited to stainless steel;

[0008] The surface of the calibration QR code setting area is integrated with a specially designed square QR code;

[0009] The surface of the calibration QR code setting area is integrated with a specially designed square QR code;

[0010] The QR code content is strongly associated with the actual side length: The QR code content (such as "001JiangWenjie7912", "020JiangWenjie7912", etc.) directly or indirectly corresponds to the actual square side length (such as 0.1mm, 2.0mm, 40mm, etc.) of the calibration scale QR code through a preset index table.

[0011] Square structural features: The QR code is a standard square, and its four corners (marked as a, b, c, and d) serve as the positioning reference points of the vision system to calculate the imaging side length and verify the placement of the calibration ruler.

[0012] In a preferred embodiment, the calibration QR code setting area is further provided with a posture verification auxiliary structure;

[0013] The posture verification auxiliary structure verifies whether the placement of the calibration ruler in the field of view meets the requirements through the coordinate relationship of the three top corners of the QR code square: a, b, and c:

[0014] The length of the sides between the three points must satisfy the "equilateral triangle" condition: ab = ac;

[0015] The length of the side between the three points must satisfy the Pythagorean theorem: ab 2 +ac 2 =bc 2 ;

[0016] The error thresholds can be adjusted to: Δ1 = 0.1f, Δ2 = 0.2f to meet different printing accuracy requirements and ensure that the calibration ruler is perpendicular to the optical system.

[0017] In a preferred embodiment, the size of the calibration ruler body is selected according to the field of view of the vision system.

[0018] In a preferred embodiment, the side length specifications of the calibration ruler body include 0.1mm to 400mm, which is adapted to the needs of rapid calibration under different magnifications.

[0019] In a preferred embodiment, a visual calibration method for measuring system reference scale calibration includes the following steps:

[0020] S1: Select a calibration ruler of the corresponding size according to the current image field of view, and place the calibration ruler flat in the observation field of view, ensuring that it occupies more than 60% of the field of view.

[0021] S2: After the visual system detects the QR code on the calibration ruler, it parses the QR code content and obtains the coordinates of the four top corners of the QR code in the entire picture, marked as a, b, c, and d.

[0022] S3: Select any three points a, b, and c from the four corners of the QR code, and calculate the side lengths between these three points: ab represents the imaging side length between a and b, ac represents the imaging side length between a and c, and bc represents the imaging side length between b and c;

[0023] Verify whether the equilateral triangle conditions: ab equals ac; and the Pythagorean theorem: ab squared plus ac squared equals bc squared. If so, the calibration ruler is correctly placed and proceed to the next step. If not, adjust the calibration ruler so that it is perpendicular to the optical system and re-verify.

[0024] S4: According to the parsed QR code content, the actual square side length L of the calibration scale QR code is obtained through a preset index table (for example, the QR code content "020JiangWenjie7912" corresponds to an actual side length of 2.0 mm).

[0025] S5: Calculate the calibration reference value, that is, the ratio of the actual side length L to the side length of the QR code image: ￡ = L / ac, and complete the calibration of the measurement system reference ruler.

[0026] In a preferred embodiment, in step S1, the calibration ruler is selected and placed. First, the size of the calibration ruler needs to be determined based on the actual size of the image field of view of the current visual system. Specifically, the calibration ruler can be selected by measuring the horizontal or vertical length of the field of view, and a calibration ruler that matches the field of view can be selected. For example, when the field of view width is 50 mm, a 40 mm calibration ruler can be selected to ensure that the calibration ruler occupies more than 60% of the field of view area after placement to ensure that the QR code is clear enough in the image and covers the main observation area. When placing, the calibration ruler needs to be flat on the stage or measuring plane to avoid tilting, curling or hanging in the air, and ensure that the surface of the calibration ruler is perpendicular to the optical axis of the optical system to reduce imaging distortion caused by angular deviation.

[0027] In a preferred embodiment, in step S2, after the visual system is activated, the camera captures an image containing the calibration ruler. The image is then scanned using a built-in QR code recognition algorithm to detect and locate the QR code. The algorithm further extracts the pixel coordinates of the four corners of the QR code (labeled a, b, c, and d) within the image. Specifically, these coordinates are represented by the horizontal and vertical coordinates of each vertex, such as (a_x, a_y) for point a and (b_x, b_y) for point b. These coordinates serve as the basis for subsequent posture verification.

[0028] In a preferred embodiment, in step S3, during the calibration ruler posture verification process, any three points of the four corners of the QR code, such as a, b, and c, are selected, and the imaging side lengths between these three points are calculated: ab is the pixel distance between point a and point b, ac is the pixel distance between point a and point c, and bc is the pixel distance between point b and point c. The Euclidean distance formula is used for calculation, such as ab = √[(a_x - b_x) 2 +(a_y-b_y) 2 Then verify two key conditions: first, the difference between ab and ac must be less than 0.1. This threshold can be adjusted according to the printing accuracy of the QR code. For example, it can be set to 0.05 for high-precision printing to ensure that the lengths of the sides between the two points are basically equal, meeting the equilateral triangle condition; second, ab 2 +ac 2 With bc 2 The difference must be less than 0.2 and can be adjusted based on actual needs to verify the Pythagorean Theorem. If both conditions are met, the calibration ruler is correctly placed. If not, the user is prompted to adjust the calibration ruler until it meets the requirements.

[0029] In a preferred embodiment, in step S4, after confirming that the calibration ruler's posture is correct, the visual system matches the parsed QR code content, such as "020JiangWenjie7912," with a preset index table. The index table stores the correspondence between the QR code content and the actual square side length. For example, "001JiangWenjie7912" corresponds to 0.1mm, "020JiangWenjie7912" corresponds to 2.0mm, and "400JiangWenjie7912" corresponds to 400mm. By looking up the table, the system can directly obtain the actual square side length L of the calibration ruler's QR code.

[0030] In a preferred embodiment, in step S5, a calibration reference value, ￡, is calculated using the verified imaged side length, such as ac, as a benchmark. The calculation formula is ￡ = L / ac, where L is the actual side length and ac is the imaged side length between points a and c. This reference value serves as the measurement system's scale factor. Subsequent measurements of the object require only the imaged length in the image and multiplying it by ￡ to obtain the actual length. This completes the calibration of the measurement system's reference scale and allows for direct use in subsequent high-precision measurement tasks.

[0031] In summary, due to the adoption of the above technical solution, the beneficial effects of this application are:

[0032] In this application, manual misoperation is avoided through the automatic parsing of QR codes and the posture verification mechanism, while accurately identifying image distortions that may occur during the calibration process. The QR code and actual side length association design and general algorithm adopted make the calibration ruler highly adaptable and can be easily integrated into various machine vision or industrial camera platform models. The calibration process does not require manual intervention and can quickly complete calibration switching under different magnifications, significantly improving calibration efficiency. In addition, for scenarios with high precision requirements, the calibration ruler produced by the photomask process can achieve nanometer-level precision, further expanding the scope of application. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a schematic diagram of the structure of this application;

[0034] Figure 2 This is a schematic diagram of the process principle of this application.

[0035] Markings in the figure: 1. Calibration ruler body; 2. Frame; 3. Placement base; 4. Calibration QR code setting area. DETAILED DESCRIPTION

[0036] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0037] Example:

[0038] Reference Figure 1 ,

[0039] A visual calibration ruler and method for calibrating a reference ruler of a measurement system, comprising a calibration ruler body 1, a plurality of calibration QR code setting areas 2 being provided on the front of the calibration ruler body 1, a plurality of reference QR codes 3 being provided on the surface of the calibration QR code setting areas 2, a reference QR code side length 4 being provided below the reference QR codes 3, the reference QR code side length 4 being a silk screen indicating the QR code side length;

[0040] The material of the calibration ruler body 1 can be divided into transparent and non-transparent, and transparent materials include but are not limited to glass and film;

[0041] Non-transparent includes but is not limited to stainless steel;

[0042] The surface of the calibration QR code setting area 2 is integrated with a specially designed square QR code;

[0043] The surface of the calibration QR code setting area 2 is integrated with a specially designed square QR code;

[0044] The QR code content is strongly associated with the actual side length: The QR code content (such as "001JiangWenjie7912", "020JiangWenjie7912", etc.) directly or indirectly corresponds to the actual square side length (such as 0.1mm, 2.0mm, 40mm, etc.) of the calibration scale QR code through a preset index table.

[0045] Square structure features: The QR code is a standard square, and its four corners (marked as a, b, c, d) serve as the positioning reference points of the visual system, which are used to calculate the imaging side length and verify the placement of the calibration ruler. The calibration QR code setting area 2 is also equipped with a posture verification auxiliary structure;

[0046] The posture verification auxiliary structure verifies whether the placement of the calibration ruler in the field of view meets the requirements through the coordinate relationship of the three top corners of the QR code square: a, b, and c:

[0047] The length of the sides between the three points must satisfy the "equilateral triangle" condition: ab = ac;

[0048] The length of the side between the three points must satisfy the Pythagorean theorem: ab 2 +ac 2 =bc 2 ;

[0049] The error thresholds can be adjusted to: Δ1 = 0.1f, Δ2 = 0.2f to meet different printing accuracy requirements and ensure that the calibration ruler is perpendicular to the optical system.

[0050] The size of the calibration ruler body 1 is selected according to the field of view of the visual system.

[0051] The side length specifications of the calibration ruler body 1 include 0.1mm to 400mm, which is suitable for rapid calibration requirements under different magnifications.

[0052] The implementation principle of the embodiment of the visual calibration ruler and method for calibrating the reference ruler of the measurement system of the present application is as follows:

[0053] S1. Select a calibration ruler of the corresponding size according to the current image field of view and place it flat in the observation field of view, occupying more than 60% of the field of view;

[0054] S2: After the visual system detects the QR code, it analyzes the QR code content and the coordinates of the four corners a\b\c\d of the QR code in the entire image;

[0055] S3. Select any three points from a\b\c\d, such as a\b\c, and calculate the length between the three points. The three ab represent the length between a\b (i.e., the length of the QR code imaging side), ac represents the length between a\c (i.e., the length of the QR code imaging side), and bc represents the length between b\c (i.e., the length of the QR code imaging side). The three lengths conform to the following formula:

[0056] ab=ac, an equilateral triangle,

[0057] ab x ab+ac x ac=bc x bc, Pythagorean theorem.

[0058] If the formula is met, it means that the calibration ruler is placed as required and you can proceed to the next step of calibration; otherwise, you need to confirm whether the calibration ruler is perpendicular to the optical system;

[0059] S4. Based on the identified QR code content, the software can directly or indirectly index the side length L of the calibration scale QR code. For example, the index table is as follows:

[0060]

[0061]

[0062] S5. The calibration reference value is the ratio of L to ac (i.e., the side length of the QR code), such as ￡ = L / ac;

[0063] The calibration process algorithm is:

[0064]

[0065]

[0066]

[0067] From the above we can know:

[0068] In the present invention, the visual calibration ruler has significant advantages in terms of ease of operation and accuracy assurance. During traditional visual measurement calibration, it is necessary to manually input the actual length and unit of the calibration ruler, and manually operate the calibration starting point. The process is cumbersome and prone to deviations in the results due to human error. However, the calibration ruler is designed with a strong correlation between the QR code content and the actual side length. The visual system can directly parse the QR code information and automatically index to the corresponding side length without manual input; at the same time, the placement posture is verified by calculating the coordinate relationship of the three vertex angles of the QR code (such as an equilateral triangle and the Pythagorean theorem conditions), ensuring that the calibration ruler is perpendicular to the optical system, avoiding image distortion errors caused by skewed placement. This process simplifies the traditional multi-step manual operation into an automated process of "placement-identification-verification-calculation", greatly reducing the operating threshold, allowing non-professionals to quickly complete the calibration, while effectively improving the accuracy and reliability of the calibration results.

[0069] In the present invention, the calibration ruler has outstanding performance in adaptability and application expansion. It adopts a universal design, and the calibration algorithm of the QR code does not rely on specific encoding or decoding technology. It only needs to index the side length according to the QR code content to complete the calculation. Therefore, it can be easily integrated into machine vision systems or industrial cameras of different brands and models, and is compatible with multiple platform models. The calibration ruler supports multiple specifications of actual side lengths from 0.1mm to 400mm (such as 0.1mm, 2.0mm, 40mm, etc.). Users can select the corresponding size according to the size of the field of view (it must occupy more than 60% of the field of view) to meet the needs of fast calibration under different magnifications. There is no need to repeat manual calibration when switching magnifications, which significantly improves measurement efficiency. In addition, for high-precision scenarios (such as automated calibration in the chip industry), the calibration ruler is made using a photomask process, which can achieve nanometer-level precision, breaking through the accuracy bottleneck of traditional calibration rulers due to manufacturing process limitations, and providing more reliable technical support for the field of precision measurement.

[0070] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A visual calibration ruler for calibrating a reference ruler of a measurement system, comprising a calibration ruler body (1), characterized in that: The front of the calibration ruler body (1) is provided with a plurality of calibration two-dimensional code setting areas (2), the surface of the calibration two-dimensional code setting areas (2) is provided with a plurality of reference two-dimensional codes (3), and a reference two-dimensional code side length (4) is provided below the reference two-dimensional code (3), and the reference two-dimensional code side length (4) is a silk screen indicating the length of the two-dimensional code; The material of the calibration ruler body (1) can be divided into transparent and non-transparent, and transparent materials include but are not limited to glass and film; Non-transparent includes but is not limited to stainless steel; The surface of the calibration two-dimensional code setting area (2) is integrated with a specially designed square two-dimensional code; The QR code content is strongly associated with the actual side length: the QR code content directly or indirectly corresponds to the actual square side length of the calibration scale QR code through a preset index table; Square structural features: The QR code is a standard square, and its four corners, marked as a, b, c, and d, serve as the positioning reference points of the visual system to calculate the imaging side length and verify the placement of the calibration ruler.

2. A visual calibration ruler for calibrating a reference ruler of a measurement system according to claim 1, characterized in that: The calibration QR code setting area (2) is also provided with a posture verification auxiliary structure; The posture verification auxiliary structure verifies whether the placement of the calibration ruler in the field of view meets the requirements through the coordinate relationship of the three top corners of the QR code square: a, b, and c: The length of the sides between the three points must satisfy the "equilateral triangle" condition: ab = ac; The length of the side between the three points must satisfy the Pythagorean theorem: ab 2 +ac 2 =bc 2 ; The error thresholds can be adjusted to: Δ1 = 0.1f, Δ2 = 0.2f to meet different printing accuracy requirements and ensure that the calibration ruler is perpendicular to the optical system.

3. The visual calibration ruler for calibrating a reference ruler of a measurement system according to claim 1, characterized in that: The size of the calibration ruler body (1) is selected according to the visual field size of the visual system.

4. The visual calibration ruler for calibrating a reference ruler of a measurement system according to claim 1, wherein: The side length specifications of the calibration ruler body (1) include 0.1mm to 400mm, which is adapted to the needs of rapid calibration under different magnifications.

5. A visual calibration method for calibrating a reference ruler of a measurement system, characterized by: The method uses a visual calibration ruler for calibration of a measurement system reference ruler as claimed in any one of claims 1 to 4; The method comprises the following steps: S1: Select a calibration ruler of the corresponding size according to the current image field of view, and place the calibration ruler flat in the observation field of view, ensuring that it occupies more than 60% of the field of view; S2: After the visual system detects the QR code on the calibration ruler, it parses the QR code content and obtains the coordinates of the four corners of the QR code in the entire image, marked as a, b, c, and d; S3: Select any three points a, b, and c from the four corners of the QR code, and calculate the side lengths between these three points: ab represents the imaging side length between a and b, ac represents the imaging side length between a and c, and bc represents the imaging side length between b and c; Verify whether the equilateral triangle conditions: ab equals ac; and the Pythagorean theorem: ab squared plus ac squared equals bc squared. If so, the calibration ruler is correctly placed and proceed to the next step. If not, adjust the calibration ruler so that it is perpendicular to the optical system and re-verify. S4: According to the parsed QR code content, the actual square side length L of the calibration scale QR code is obtained through a preset index table; S5: Calculate the calibration reference value, that is, the ratio of the actual side length L to the side length of the QR code image: ￡ = L / ac, and complete the calibration of the measurement system reference ruler.

6. A visual calibration ruler for calibrating a reference ruler of a measurement system according to claim 5, characterized in that: In step S1, the calibration ruler is selected and placed. First, the size of the calibration ruler needs to be determined based on the actual size of the image field of view of the current visual system. Specifically, the horizontal or vertical length of the field of view can be measured to select a calibration ruler that matches the field of view. Ensure that the calibration ruler occupies more than 60% of the field of view area after placement to ensure that the QR code is clear enough in the image and covers the main observation area. When placing the calibration ruler, it is necessary to place it flat on the stage or measuring plane to avoid tilting, curling or hanging in the air, and ensure that the surface of the calibration ruler is perpendicular to the optical axis of the optical system to reduce imaging distortion caused by angular deviation.

7. The visual calibration ruler for calibrating a reference ruler of a measurement system according to claim 5, characterized in that: In step S2, after the visual system is started, the camera captures an image containing the calibration ruler, and the built-in QR code recognition algorithm is used to scan the image to detect and locate the position of the QR code. The algorithm further extracts the four vertex marks a, b, c, and d of the QR code, and the pixel coordinates in the image, which are specifically expressed as the horizontal and vertical coordinate values ​​of each vertex: the coordinates of point a are (a_x, a_y), and the coordinates of point b are (b_x, b_y). These coordinate values ​​will serve as the basic data for subsequent posture verification.

8. The visual calibration ruler for calibrating a reference ruler of a measurement system according to claim 5, characterized in that: In step S3, during the calibration ruler posture verification process, any three points a, b, and c are selected from the four corners of the QR code, and the imaging side lengths between these three points are calculated respectively: ab is the pixel distance between point a and point b, ac is the pixel distance between point a and point c, and bc is the pixel distance between point b and point c; the Euclidean distance formula is used for calculation: ab = √[(a_x - b_x)] 2 +(a_y-b_y) 2 ]; Then verify two key conditions: First, the difference between ab and ac must be less than 0.

1. The threshold can be adjusted according to the printing accuracy of the QR code. For high-precision printing, it can be set to 0.05 to ensure that the lengths of the sides between the two points are basically equal, meeting the equilateral triangle condition; second, ab 2 +ac 2 With bc 2 The difference must be less than 0.2, which can also be adjusted according to actual needs to verify the Pythagorean theorem conditions; if both conditions are met, it is determined that the calibration ruler is placed correctly; if not, the user is prompted to adjust the position of the calibration ruler until it meets the requirements.

9. The visual calibration ruler for calibrating a reference ruler of a measurement system according to claim 5, characterized in that: In step S4, after confirming that the calibration ruler posture is correct, the visual system matches the parsed QR code content with a preset index table; the index table stores the correspondence between the QR code content and the actual square side length, and the system can directly obtain the actual square side length L of the calibration ruler QR code by looking up the table.

10. The visual calibration ruler for calibrating a reference ruler of a measurement system according to claim 5, characterized in that: In step S5, the calibration reference value ￡ is calculated based on the verified imaging side length, using the calculation formula ￡ = L / ac, where L is the actual side length and ac is the imaging side length between points a and c. This reference value is the scale factor of the measurement system. When measuring the object to be measured subsequently, it is only necessary to obtain its imaging length in the image and multiply it by ￡ to obtain the actual length. At this point, the calibration of the measurement system's reference ruler is completed and can be directly used for subsequent high-precision measurement tasks.

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