CN114909994B - Calibration method of image measuring instrument - Google Patents
Calibration method of image measuring instrument Download PDFInfo
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- CN114909994B CN114909994B CN202210468834.XA CN202210468834A CN114909994B CN 114909994 B CN114909994 B CN 114909994B CN 202210468834 A CN202210468834 A CN 202210468834A CN 114909994 B CN114909994 B CN 114909994B
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- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
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Abstract
The present disclosure provides a calibration method of an image measuring instrument, which is a method for calibrating based on a calibration sheet, wherein the calibration sheet is provided with a center mark and a plurality of calibration patterns having a fixed position relation with the center mark, the image measuring instrument comprises a first lens and a second lens, the multiplying power of the first lens is not more than that of the second lens, and the calibration method comprises: the first lens is used as a working lens, the calibration sheet is fixed on the objective table, the objective table is moved so that the center mark is positioned in the field of view of the first lens, the second lens is used as the working lens of the image measuring instrument, the second lens is adjusted to focus the center mark, the movement scheme of the objective table is obtained based on the fixed position relation, the calibration item is selected, the objective table is moved based on the movement scheme until one target calibration pattern is positioned in the field of view of the working lens, and the first lens and the second lens are calibrated. According to the method and the device, the lens can be conveniently calibrated, and the measurement error of the image measuring instrument is reduced.
Description
Technical Field
The invention relates to the intelligent manufacturing equipment industry, in particular to a calibration method of an image measuring instrument.
Background
As a common precision instrument for two-dimensional plane measurement, unlike conventional contact measurement, an image measuring instrument picks up an image of an article by a CCD, and then reads information from an image obtained by the CCD by a computer to obtain dimensional data (e.g., workpiece parameters) of the article. During such non-contact measurements, the sharpness of the camera (lens) visualization is often closely related to the accuracy of the instrument measurement.
When a lens is used to photograph a workpiece, if the focal length of the camera is not clear or the photographing angle is deviated (for example, upward photographing or downward photographing), a large deviation is introduced in the measured data. In addition, some random errors must be introduced into the instrument during the manufacturing and assembly process, so that the lens needs to be calibrated in multiple ways before measurement to ensure the accuracy of the camera (lens) measurement.
In the prior art, when calibrating the lens of the image measuring instrument, the most adopted correction module is used for carrying out single calibration on the lens, and when the calibrated project is replaced, the next correction module is needed to be selected for calibrating the lens, so that great inconvenience is brought to operation under the condition that the correction module needs to be replaced frequently, automatic calibration is not facilitated, excessive replacement time is spent, and the calibration efficiency of calibration is reduced.
Disclosure of Invention
The present disclosure has been made in view of the above-described conventional art, and an object thereof is to provide a calibration method capable of performing a plurality of calibration of a lens and further capable of reducing a measurement error of an image measuring instrument.
To this end, the present disclosure provides a calibration method of an image measuring apparatus, which is a method for performing calibration based on a calibration sheet, the calibration sheet having a center mark and a plurality of calibration patterns having a fixed positional relationship with the center mark, the image measuring apparatus including a first lens and a second lens, a magnification of the first lens being not greater than a magnification of the second lens, the calibration method including: the first lens is used as a working lens of the image measuring instrument, the calibration sheet is fixed on a stage of the image measuring instrument, the stage is moved so that the center mark is located in the central area of the field of view of the first lens, the working lens is switched so that the second lens is used as the working lens of the image measuring instrument, the position of the second lens is adjusted so as to focus the center mark, a movement scheme of the stage is obtained based on the fixed position relation between the center mark and each calibration pattern, at least one calibration item is selected, the stage is moved based on the movement scheme until one target calibration pattern is located in the field of view of the working lens, and the first lens and the second lens are calibrated, wherein the target calibration pattern is a calibration pattern matched with one calibration item in the at least one calibration item.
In this case, the lens of the image measuring instrument is calibrated by the calibration method, and the calibration of the calibration item is completed by moving the objective table, so that errors generated during the lens measurement can be reduced, and the measurement accuracy of the lens can be improved during the workpiece measurement. In addition, the calibration of a plurality of parameters of the lens is completed through one calibration piece, so that the calibration efficiency can be improved.
In addition, in the calibration method according to the present disclosure, optionally, after the first lens and the second lens are calibrated, the stage is moved based on the movement scheme until the next target calibration pattern is in the field of view of the working lens, and the first lens and the second lens are calibrated. Therefore, the first lens and the second lens can be accurately calibrated based on the movement scheme.
In addition, in the calibration method related to the present disclosure, optionally, calibrating the first lens and the second lens includes: and switching the working lens to enable the first lens to serve as the working lens of the image measuring instrument, calibrating the first lens by utilizing the target calibration pattern, switching the working lens to enable the second lens to serve as the working lens of the image measuring instrument, and calibrating the second lens by utilizing the target calibration pattern.
In addition, in the calibration method according to the present disclosure, optionally, after the calibration sheet is fixed on the stage, the brightness of the calibration sheet is adjusted until the brightness of the calibration sheet meets a preset requirement. Thereby, calibration can be performed under appropriate brightness adjustment.
In addition, in the calibration method according to the present disclosure, optionally, the calibration sheet is polished by a light source provided on the stage, and light from the light source passes through the calibration sheet from the bottom of the stage and enters the working lens, and the brightness of the calibration sheet is adjusted by adjusting the brightness of the light source.
In addition, in the calibration method according to the present disclosure, optionally, when focusing the center mark, an image is acquired through the second lens, a variance of a gray value of the image is calculated, and whether the second lens completes focusing is determined based on the variance of the gray value.
Additionally, in the calibration method according to the present disclosure, optionally, the calibration items include at least a common Jiao Jiaozhun and pixel calibration, the common Jiao Jiaozhun being performed before the pixel calibration.
In addition, in the calibration method according to the present disclosure, optionally, in performing the pixel calibration, a calibration pattern of the pixel calibration is selected according to a lens magnification, and a calibration pattern matching the pixel calibration includes concentric circles and checkerboards. In this case, after the in-focus calibration is completed, the calibration can be performed by switching the lenses of different magnifications. Thereby, the efficiency of calibration can be improved.
In addition, in the calibration method related to the present disclosure, optionally, the calibration item includes a camera angle calibration, which is performed after the pixel calibration.
In addition, in the calibration method according to the present disclosure, optionally, when the camera angle is calibrated, the stage is moved along a first direction, a change in the position of the center mark is recorded, and whether the camera angle needs to be calibrated is determined based on the movement direction of the center mark and the first direction. Thus, it can be relatively quickly determined whether the camera angle needs to be calibrated.
Therefore, the calibration method can conveniently calibrate the lens in multiple items, and further reduce the measurement error of the image measuring instrument.
Drawings
Embodiments of the present disclosure will now be explained in further detail by way of example only with reference to the accompanying drawings, in which:
fig. 1 is a schematic view illustrating a scenario of image meter calibration according to an embodiment of the present disclosure.
Fig. 2 is a schematic diagram showing a calibration sheet according to an embodiment of the present disclosure.
Fig. 3 is a flow chart illustrating image gauge calibration according to an embodiment of the present disclosure.
Fig. 4A is a calibration pattern illustrating in-focus calibration according to an embodiment of the present disclosure.
Fig. 4B is an enlarged view showing a partial region of a calibration pattern of in-focus calibration according to an embodiment of the present disclosure.
Fig. 5 is a schematic diagram illustrating the principle of pixel calibration according to an embodiment of the present disclosure.
Fig. 6 is a schematic diagram illustrating pixel calibration according to an embodiment of the present disclosure.
Fig. 7 is a schematic diagram illustrating concentric calibration in accordance with embodiments of the present disclosure.
Fig. 8A is a first state diagram illustrating camera angle calibration according to an embodiment of the present disclosure.
Fig. 8B is a second state diagram illustrating camera angle calibration according to an embodiment of the present disclosure.
Detailed Description
All references cited in this disclosure are incorporated by reference in their entirety as if fully set forth. Unless defined otherwise, technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. A general guide for many of the terms used in the present application is provided to those skilled in the art. Those skilled in the art will recognize many methods and materials similar or equivalent to those described in the present disclosure that can be used in the practice of the present disclosure. Indeed, the present disclosure is in no way limited to the described methods and materials.
The present disclosure relates to a calibration method for an image measuring instrument, which can be used for calibrating a lens used for shooting and measuring by the image measuring instrument. The calibration method for an image measuring instrument according to the present disclosure may also be simply referred to as a calibration method. In some examples, the calibration method of the image measuring instrument related to the present disclosure may be used to detect a measurement error of a lens.
In some examples, the calibration methods of the present disclosure may be applied in industrial production, e.g., the calibration methods of the present disclosure may be introduced into a pipeline where calibration of an image gauge is achieved. In some examples, the calibration methods related to the present disclosure may also be applied to calibration of image gauges in a laboratory. In some examples, the steps in the calibration method may be implemented by automation. In some examples, steps in the calibration method may be implemented manually.
The present disclosure also relates to a calibration patch for an image measurement instrument. In some examples, calibration of the image gauge may be achieved using a calibration patch. In some examples, the calibration tile may include a plurality of calibration images that match different calibration items. In this case, a plurality of calibration items can be performed with one calibration patch, while the calibration accuracy of each calibration item can be improved with the relative relationship between the calibration images.
The present disclosure also relates to a calibration system for an image measurement instrument, which can calibrate the image measurement instrument by using the calibration method related to the present disclosure. In some examples, the calibration system may be coupled to an image gauge and receive images captured by the image gauge. In some examples, the calibration system may analyze and obtain calibration data from images captured by the image gauge. In some examples, the calibration system may include a calculation module that may calculate measured data or calibration data after the image is captured by the image gauge, and a display module that may display the data calculated by the calculation module, in some examples, the display module may have a calibration interface, and the calibration data may be displayed on the calibration interface. In some examples, the image measurements referred to in this disclosure may be connected to a computer and then automatically calibrated in a one-touch manner.
The calibration method for an image measuring instrument according to the present disclosure is described below with reference to the accompanying drawings.
The calibration method for calibrating the image measuring instrument can calibrate the lens through the calibration sheet, after the corresponding calibration project is completed, the position of the calibration sheet is moved, and different calibration projects can be carried out by aligning the lens to different calibration patterns. After the calibration of the lens matched with the patterns is completed on the basis of the patterns on the calibration piece, deviation data of matched calibration items can be obtained, and errors of the lens in shooting and measuring the relevant size of the workpiece can be calculated clearly. In addition, as the image measuring instrument is provided with a plurality of lenses with different multiplying powers, the lenses with different multiplying powers of the image measuring instrument can be calibrated in different projects through the calibration sheet, so that the calibration of at least one lens can be completed more comprehensively. Moreover, by integrating various calibration patterns on one calibration sheet, all calibration related to the calibration patterns can be completed at one time, automatically and conveniently by the calibration method related to the present disclosure.
The calibration sheet can also be used for pipeline calibration, and through the calibration method, the operation of calibration can be completed by one-click after the display module selects calibration, so that the calibration of an instrument is completed.
In some examples, the calibration tile may also be referred to as a standard tile, a calibration tile, or a calibration tile. In some examples, the calibration tile may be used to correct parameters of a high-precision instrument. In this embodiment, the calibration sheet may be used to calibrate and correct an image measuring apparatus, and particularly, a lens for photographing and measuring by the image measuring apparatus. In some examples, the calibration methods related to the present disclosure may also be applied to other precision instruments that take measurements by taking images through a lens (optical lens).
Fig. 1 is a schematic view illustrating a scenario in which an image measuring instrument 1 according to an embodiment of the present disclosure is calibrated. Fig. 2 is a schematic diagram showing a calibration sheet 2 according to an embodiment of the present disclosure.
In some examples, the image measuring instrument 1 may include a stage 10 and a lens. In some examples, stage 10 may be mobile. In addition, the subject table 10 can be used to carry items such as certain precision devices. The lens may face the stage 10 and photograph an object placed on the stage 10.
In some examples, as shown in fig. 1, when the stage 10 places the calibration sheet 2, the calibration sheet 2 (described later) may be photographed through a lens of the image measuring instrument 1.
In the present embodiment, the calibration sheet 2 may be provided with a center mark and a plurality of calibration patterns (see fig. 2). As shown in fig. 2, the calibration sheet 2 may be provided with a plurality of calibration patterns other than the calibration patterns having the center marks, checkerboard, concentric circles, center marks, a square frame, and the like.
In some examples, a calibration pattern may be used to calibrate the lens, particularly the lens of the image gauge 1, and different calibration patterns may be used to calibrate different items. That is, different calibration patterns and different calibration items may be matched to each other. Specifically, the calibration sheet 2 may be provided with a calibration area for calibrating the lens. For example, on the calibration area, the photographing focal length of the lens, pixels, and camera angle may be calibrated (described in detail later) and the obtained deviation may be calculated.
In other examples, the calibration tile 2 may also be provided with a verification area having a verification pattern. In some examples, after the completion of the calibration project for the shots, the calculated deviation data may be compensated for in data by software, and after the compensation, the shots may be checked again by a check area to determine whether each shot is valid to complete the calibration. Thereby, accuracy of lens calibration can be ensured.
In some examples, each pattern of the plurality of calibration patterns and the center mark may have a fixed positional relationship. That is, the center mark may be used for positioning, and once the position of the center mark is determined, the position of the other calibration pattern may be determined by a fixed positional relationship. In this case, after the corresponding calibration item is completed on one calibration pattern, the calibration pattern required for the next calibration item can be quickly located based on the positional relationship between the other calibration patterns and the center mark. This makes it possible to accurately calibrate a plurality of items on the same calibration sheet 2.
Preferably, the center mark may be a calibration pattern with a "cross" mark. In this case, a rectangular coordinate system can be established with the center of the pattern as the origin, and the positions of other calibration patterns on the calibration sheet 2 can be found in the rectangular coordinate system according to the center origin.
Fig. 3 is a schematic flow chart illustrating calibration of the image measuring instrument 1 according to the embodiment of the present disclosure.
In some examples, as shown in fig. 3, the measurement method of the image measuring instrument 1 may include: the calibration sheet 2 is moved to the field of view of the working lens (step S100), the focus center mark is focused by the working lens (step S200), the calibration item is selected and calibrated (step S300), and the working lens is switched to be calibrated again (step S400).
In some examples, the image gauge 1 may have a plurality of measured lenses, and the magnification of the lenses may be different. In general, the higher the lens magnification, the better the imaging quality and the higher the sharpness. In this case, when it is necessary to measure different sizes of workpieces or different parameters of the workpieces by the image measuring instrument 1, a lens matching with the size data (magnification and) may be selected for photographing measurement. Thereby, the accuracy of the dimension measurement can be improved.
In general, when using the image measuring apparatus 1 to measure a workpiece, lenses with different magnifications are often switched to match different size data, and due to errors in manufacturing or assembling processes, calibration data of an original lens may not be suitable for the switched lenses after the magnifications of the lenses are switched, and deviation generated when the lenses are switched can be reduced after the lenses of the image measuring apparatus 1 are calibrated by the calibration sheet 2.
In the present embodiment, the image measuring apparatus 1 includes a first lens and a second lens, and the magnification of the first lens and the magnification of the second lens may be different. Specifically, the magnification of the first lens may be not larger than the magnification of the second lens. That is, the first lens may be a low-magnification lens with respect to the second lens, and the second lens may be a high-magnification lens. In some examples, both the first lens and the second lens may be working lenses, which may represent lenses being used when the image measuring instrument 1 is working. In some examples, the magnification of the first lens and the magnification of the second lens may also be the same.
In step S100, the first lens may be used as a working lens of the image measuring apparatus 1, and the calibration sheet 2 may be fixed to the stage 10 of the image measuring apparatus 1. Since the stage 10 is movable, after the calibration sheet 2 is fixed to the stage 10, the stage 10 can be moved so that the working lens (i.e., the first lens) is aligned with the calibration sheet 2. In some examples, alignment may refer to the calibration tile 2 entering the field of view of the working lens. In some examples, alignment may also refer to the calibration tile 2 entering the central region of the field of view of the working lens. Since the low magnification lens can have a larger field of view, the center mark of the calibration piece 2 can be found for positioning relatively quickly under the low magnification lens.
In some examples, the center mark may be located in the center region of the first lens when movement of the stage 10 is started. In this case, if it is necessary to switch a lens of a large magnification as the working lens, the center mark is located at the center of the field of view, so that the possibility that the mark slips out of the shooting range of the lens can be reduced.
Preferably, in step S100, after the calibration sheet 2 is fixed on the stage 10, the brightness of the light irradiated on the calibration sheet 2 may be adjusted so that the working lens is in a brighter photographing environment. Thus, the brightness of the image obtained by the working lens photographing can be ensured. The image quality is improved.
In some examples, the stage 10 may be provided with a light source that can shine the calibration sheet 2, and the light of the light source can be transmitted through the calibration sheet 2 through the bottom of the stage 10 and then enter the working lens, and the brightness of the calibration sheet 2 can be adjusted by adjusting the brightness of the light source. In some examples, the brightness of the calibration sheet 2 may be adjusted to a predetermined brightness. In some examples, the predetermined brightness may be a brightness that causes the working lens to capture an image for a predetermined time without overexposure. In some examples, the predetermined brightness may also be a human defined brightness. Therefore, the definition and brightness of the shot image can be effectively ensured. In some examples, step S200 may be performed after dimming is completed.
In step S200, after determining that the center mark is located in the center area of the field of view of the working lens, the working lens may be switched such that the second lens functions as the working lens of the image measuring instrument 1. That is, the magnification of the working lens is switched from low magnification to high magnification. In some examples, the second lens may be the highest magnification lens used by the image gauge 1.
In some examples, after switching the working lens to the second lens, the second lens may be adjusted to be in focus with the center mark.
In some examples, the calibration sheet 2 may be photographed by a second lens and the image observed to determine whether the lens is in focus. In some examples, it may be determined whether focusing is completed based on the gray value variance of the image captured by the second lens (i.e., the lens is in focus with the image captured by the calibration sheet 2). In general, the larger the gray value variance of an image, the stronger the contrast of the image. In this case, the larger the gray value variance of the image, the clearer the focusing is considered, the higher the image quality photographed by the working lens will be, and the more accurate the measurement data acquired by the image will be.
In some examples, when the gray value variance is greater than a preset value, the working lens may be considered to complete focusing.
The present disclosure also relates to a calibration system for an image measurement apparatus 1, which can calibrate the image measurement apparatus 1 by using the calibration method according to the present disclosure. In some examples, the calibration system may be coupled to the image gauge 1 and receive images captured by the image gauge 1.
In some examples, the calibration system may analyze and obtain calibration data from images captured by the image gauge 1. In some examples, the calibration system may include a calculation module that may calculate measured data or calibration data after the image is captured by the image measuring instrument, and a display module that may display the data calculated by the calculation module.
In some examples, the display module may have a calibration interface, and the calibration data may be displayed on the calibration interface. In some examples, the operation may also be selected at the calibration page to manipulate the image gauge 1. In some examples, the calibration item may be selected on a calibration page.
In step S300, after focusing is completed using the working lens, the calibration page may be entered and the image measuring instrument 1 is operated to start calibrating the working lens. A calibration item is selected and calibration is performed.
In some examples, the calibration item may be selected and checked by a computer. Since the calibration items and the calibration patterns on the calibration sheet 2 belong to a one-to-one correspondence, and the positional relationship of the respective calibration patterns and the center marks is fixed. In this case, after completing the calibration items on one calibration pattern, the calibration pattern required for the next calibration item can be found accurately according to the positional relationship between the respective calibration patterns. The movement scheme of the stage 10 at the time of calibration is determined based on the positional relationship between the calibration patterns. In some examples, the above-described movement scheme may be stored on a computer.
In some examples, at least one calibration item needs to be selected when the calibration item is selected. In some examples, one of the selected calibration items may be selected and execution of the calibration item may begin. Specifically, a movement scheme may be obtained based on the calibration item, and the stage 10 is moved based on the movement scheme until the target calibration pattern is in the field of view of the working lens, and the first lens and the second lens are calibrated.
In some examples, after calibration of the working lens is completed by one target calibration pattern, the stage 10 may be moved until the working lens is aligned with the next target calibration for calibration.
In other examples, it is also possible to switch between the lenses of the image measuring apparatus 1 and then calibrate the switched working lenses one by one.
In some examples, the calibration pattern used in performing the calibration may be referred to as a target calibration pattern. And the target calibration pattern is matched to one of the at least one calibration item.
In some examples, a method of calibrating a working lens may include: the working lens is switched to make the first lens as the working lens of the image measuring instrument 1, the first lens is calibrated by utilizing the target calibration pattern, the working lens is switched to make the second lens as the working lens of the image measuring instrument 1, and then the second lens is calibrated by utilizing the target calibration pattern.
In step S400, the switching working lens is calibrated again. In some examples, switching the working shots to calibrate means that after switching one of all shots as the working shot completes a first calibration item, switching another non-calibrated shot of all shots one by one as the working shot performs a second calibration item until all shots (shots of different magnifications) complete all calibration items selected. The calibration item may be the calibration item selected in S300. Thereby, multiple parameters of the lens on the device can be automatically calibrated at one time.
In some examples, the deviation data for shots under different calibration items may be correspondingly calculated after each calibration item is completed. By the calibration method, after correction and compensation are performed on deviation data of the lens by software, the lens can be checked again by the calibration piece 2 to judge whether the lens meets the standard or not. Thereby, the accuracy of the lens measurement can be further ensured, and the accuracy of the workpiece size measurement by the image measuring instrument 1 can be further ensured.
Fig. 4A is a calibration pattern illustrating in-focus calibration according to an embodiment of the present disclosure. Fig. 4B is an enlarged view showing a partial region of a calibration pattern of in-focus calibration according to an embodiment of the present disclosure. Fig. 5 is a schematic diagram illustrating the principle of pixel calibration according to an embodiment of the present disclosure. Fig. 6 is a schematic diagram illustrating pixel calibration according to an embodiment of the present disclosure. Fig. 7 is a schematic diagram illustrating concentric calibration in accordance with embodiments of the present disclosure.
In some examples, the calibration items may include at least the same Jiao Jiaozhun and pixel calibration. As Jiao Jiaozhun, the lenses with different magnifications are calibrated so that the focal points of the respective lenses are located at the same position. In other words, when the image measuring instrument 1 is used for measurement, the focus positions of the lenses of different magnification can be ensured to be at the same position even after the working lenses are switched. In this case, after calibration of each lens in the first calibration item is completed and calibration of other items is performed through a fixed positional relationship between different patterns, focusing on the working lens to determine the positions of the calibration patterns under different magnifications may not be repeated when performing the second calibration item. Thereby, the efficiency of calibration can be improved.
In some examples, fig. 4A may be used to represent a calibration pattern with a center mark photographed by a working lens when the same Jiao Jiaozhun is performed, and fig. 4B may be represented as an enlarged view of a partial area of the calibration pattern in fig. 4A. Specifically, when the magnification of the working lens is changed from low to high, the calibration pattern in the field of view of the working lens is also enlarged, and the calibration pattern in the center 1 region in the field of view of the working lens may be changed from fig. 4A to fig. 4B.
In some examples, the focus of a lens shot may change with changes in lens magnification, so after switching the magnification of the working lens, in-focus calibration is typically required to bring the working lens focus into focus and take the shot. This can reduce errors caused by focusing discomfort after lens switching.
In some examples, the focus position under the first lens may be used as a reference focus position, and when switching from a low-magnification lens to a high-magnification lens one by one, the shift amount of the focus of the different lenses may be determined by observing the focus positions under the lenses of the respective magnifications. In some examples, the offset of focus may be the reference focus position minus the current focus position (i.e., the focus position switched to the other working lens).
In some examples, pixel calibration may mean calibrating the pixel size at each magnification and correcting for small magnification lens distortion. In some examples, when an image is captured by a lens, if the lens is distorted or deformed, the image captured by the lens is easily distorted and image information is lost. Specifically, when the lens is used for shooting an image, uneven distribution of boundary pixels and central pixels of the image easily causes large errors in data (especially size) during measurement, and consistency or uniformity of the lens boundary is maintained as much as possible through pixel calibration, so that consistency of the image can be improved.
In this embodiment, the distortion condition or the field of view of the lens can be calibrated by squares of different sizes and circles of different radius sizes.
(checkerboard calibration)
In some examples, the checkerboard calibration pattern may appear as a combination of squares, each of uniform size and alternating black and white, which may all be squares of 0.25mm size. In this case, the calibration pattern is photographed through a lens, and if the lens is distorted, the square on the photographed picture may not be in the form of a square having the same size in a strict sense. Thereby, calibration can be facilitated.
In some examples, as the lens magnification changes, the field of view of the lens also changes. Specifically, the higher the magnification of the lens, the smaller the field of view, and when photographing with a low magnification lens, even a slight distortion of the lens may cause a significant measurement error in the image photographed by the lens. In this case, the distortion of the lens can be calibrated by a specific uniform size square black-and-white checkerboard.
In some examples, the uniformity of the field of view of the low magnification lens may be determined based on the checkerboard shown in fig. 6. In the case of determining the position of the center mark, the pixel distortion condition of the lens can be calculated by a checkerboard calibration method. In some examples, a black-and-white checkerboard is photographed by a working lens, corner points of the checkerboard are extracted, a plurality of parameters of the checkerboard under ideal conditions (namely, under the condition that the lens does not generate distortion) are estimated, and then distortion parameters under radial distortion of the checkerboard in an image are calculated based on a least square method, so that the working lens can be corrected or calibrated based on the distortion parameters.
(Concentric circle calibration)
In some examples, when the image gauge 1 uses a high magnification lens for measurement, the field of view of the lens is small, and the field of view may be uneven. In this case, the lens is subjected to pixel calibration through concentric circle patterns with different radius sizes, and the uniformity of pixels in the field of view of the lens can be rapidly judged by extracting the graphic boundaries of the concentric circles.
In some examples, the size of individual pixels in an image is determined when the pixels of the image are uniform. In some examples, the size of a pixel may be determined by a horizontal pixel and a vertical pixel, and thus, uniformity of the pixel size may be comprehensively determined based on a deviation of the size of the horizontal pixel and the size of the vertical pixel.
In some examples, a principle sketch of pixel calibration may represent how the calculation of pixels is performed based on the calibration pattern, thereby obtaining a pixel deviation of the shot picture. In some examples, the size X of the horizontal pixels may be r×2/(X2-X1), and the size Y of the vertical pixels may be r×2/(Y2-Y1). In some examples, R is determined by extracting the boundaries of circles of different radius sizes, and the size of the pixel can be calculated by extracting the position coordinates (i.e., X1, X2, Y1, Y2) of the pixel points of the circle boundaries (see fig. 5).
In some examples, the calibration pattern of concentric circles may be formed by a combination of a common center of a plurality of circles of different radius sizes.
In some examples, the radius size of the circle may be selected between 0.2-3 mm, e.g., the radius of the circle may be 0.2mm, 0.5mm, 0.6mm, 1mm, 1.1mm, 1.5mm, 1.6mm, 2.5mm, or 3mm. In some examples, the circle that is calibrated may be determined by extracting the inner or outer boundary of the circle.
In some examples, the calibration pattern may be calibrated by selecting pixels of the lens magnification. The pattern matching the pixel alignment may include concentric circles and a checkerboard (see fig. 2). In some examples, the magnification of the lens of the image gauge 1 may be between 0.58X and 7.5X, for example, the magnification of the lens of the image gauge 1 may be 0.58X, 1.0X, 1.5X, 2.0X, 2.5X, 3.0X, 3.5X, 4.0X, 4.5X, 5.0X, 5.5X, 6.0X, 6.5X, 7.0X, or 7.5X.
In some examples, a 7.5X-2.5X lens may be moved to a concentric circle pattern for calibration and a 2.0X-0.58X lens may be moved to a checkerboard pattern for calibration. In addition, when the concentric circle pattern is used for pixel calibration, concentric circles with different sizes can be selected as reference circles according to the multiplying power of the lens. For example, a 2.5X lens may be calibrated with a 0.4mm concentric circle, while a 3.5X-7.5X magnification lens may be calibrated with a 0.4mm concentric circle.
In some examples, the same Jiao Jiaozhun is performed prior to pixel calibration. In this case, after the in-focus calibration is completed, the calibration can be performed by only switching lenses with different multiplying powers, so that the influence of unclear focusing on errors caused by subsequent calibration is reduced. Thereby, the efficiency of calibration can be improved.
In some examples, the calibration items of the lens may also include concentric calibrations. In some examples, the items of concentric calibration may be performed on calibration patterns having concentric circles of different radii. (see FIG. 7)
In some examples, since the concentric circle pattern and the center mark have a fixed position relationship, when the concentric calibration is performed, a rectangular coordinate system can be established by the center mark, so that the circle center position of each radius circle can be conveniently determined, the abscissa and the ordinate of the reference circle center can be determined, the circles with the corresponding radius can be determined under the lenses with different multiplying powers, and the lenses with each multiplying power can be accurately calibrated. Therefore, when concentric calibration is carried out, the reference circle can be extracted under the lenses with different multiplying powers, the circle center coordinates are recorded, the position of the circle center is recorded, and then the measured circle center position under the lenses with different multiplying powers and the circle center offset of the reference circle are calculated.
In some examples, a circle with phi 0.4mm under a 0.58X lens can be used as a reference circle, the coordinates of the center of the reference circle are used as reference coordinates, the coordinates of the center of the reference circle (i.e. the circle with phi 0.4 mm) can be measured by switching lenses with different multiplying powers, and the offset of the center of the circle under different multiplying powers can be obtained according to the deviation between the measured center of the circle coordinate and the center of the reference circle under different multiplying powers.
Fig. 8A is a first state diagram illustrating camera angle calibration according to an embodiment of the present disclosure. Fig. 8B is a second state diagram illustrating camera angle calibration according to an embodiment of the present disclosure.
In some examples, the calibration items may also include camera angle calibration. When photographing an object placed on the stage 10 using a lens, it is often necessary to ensure that the photographing surface of the lens and the plane in which the calibration sheet 2 is located are parallel to ensure that the inclination of the photographed image of the lens is 0.
In some examples, the camera angle calibration may be performed after the pixel calibration. In some examples, when the pixel and the camera angle are not calibrated, a larger error is caused to the measurement result, and when the pixel is not calibrated, it cannot be judged that the pixel is not calibrated and/or the camera angle is not calibrated, and at the same time, an additional error is introduced to the calibration of the camera angle, so that the measurement accuracy is reduced.
In some examples, when the factors affecting the measurement result of the lens are not determined, if the field of view of the lens is ensured to be uniform (pixel calibration is completed), the influence of the pixel calibration on the measurement result can be removed, and further the influence of the improper shooting angle of the camera on the data can be calculated. Therefore, whether the camera angle needs to be calibrated or not can be effectively judged, and the calibration efficiency of the image measuring instrument is improved.
In some examples, the stage 10 may be moved in a first direction while the camera angle is being made, and the change in position of the center is recorded and a determination is made as to whether the camera angle needs to be calibrated based on the direction of movement of the center mark and the first direction. Preferably, when the center mark is a "cross" mark, the "cross" mark may be a mark formed extending in four directions from the geometric center of the mark. In some examples, two of the four directions that are perpendicular to each other may correspond to the direction in which the transverse axis of the rectangular coordinate system points and the direction in which the longitudinal axis points, respectively, described above.
In some examples, the first direction may be one of four directions, in which case the stage 10 may be moved along the first direction to determine whether the camera angle needs to be calibrated while the calibration sheet 2 is fixed to the stage 10.
In some examples, when the camera angle calibration is performed, the stage 10 is moved to make the center mark in the field of view of the working lens, and the state of the center mark is recorded, at this time, the center mark in the field of view of the working lens may be in the state as shown in fig. 8A, the working lens is kept still, the stage 10 is moved to move the calibration piece along the first direction, and if the camera angle of the working lens is in the preset state, the connecting line between the center mark in the field of view and the geometric center of the center mark initially extends along the first direction.
In some examples, if the center mark within the center field of view of the working lens changes from the position of the dashed line to the position of the solid line in fig. 8B within the field of view of the lens as the stage 10 moves in the first direction, this indicates that the camera angle of the working lens needs to be calibrated. As shown in fig. 8B, when the position of the center mark generates an offset dx along the first direction, if the position of the center mark generates an offset dy along the second direction, the magnitude of the camera angle may be close to dx/dy.
In some examples, calibration tile 2 may have multiple verification patterns. In some examples, each verification pattern may also have a fixed positional relationship with the center mark. In this case, the movement scheme of the stage 10 at the time of verification can be determined based on the positional relationship between the center mark and each verification pattern.
In some examples, the calibration pattern may also be used for verification. For example, the concentric circle pattern can also be used for checking the errors of the under-lens measurement standard circles with different multiplying powers after calibration and compensation. In addition, the concentric circle patterns can verify the deviation between the circle centers under the lenses with different multiplying powers after compensation.
In some examples, after completing each calibration item, the image measuring instrument 1 may be compensated based on the deviation calculated at the time of calibration and then the lens may be checked again. Thereby, the accuracy of measuring each parameter by the lens can be improved.
In some examples, the display module may also be provided with a verification page, and different verification items may be selected for verification on the verification page, and in some examples, the verification items may also be matched with different verification patterns. In some examples, after calibration is completed, at least one calibration item may be selected to calibrate the working lens, e.g., the first lens and the second lens may be calibrated based on a movement scheme to move the stage 10 until the target calibration pattern is within the field of view of the working lens. In some examples, the target verification pattern may be a verification pattern that matches one of the at least one verification item.
In some examples, the verification pattern may also include a pattern of circles, rings, rectangular grids, or square boxes, etc., having a particular size. After the measurement data of the lens are compensated by software, the check pattern is measured and compared with the size of the pattern (the distance from the center of the adjacent pattern and the boundary of the pattern to the frame), and whether the calibration of each item of the lens meets the preset requirement can be conveniently judged.
In some examples, the rectangular grid may include a plurality of grid patterns having different sizes through which the full field of view uniformity of different magnification shots may be verified. The loop frame can verify the calibration effect of the camera angles of different lenses.
In some examples, the invention to which the present disclosure relates is described in its entirety, with the understanding that the above description is not intended to be limiting of the present disclosure. The calibration sheet 2 is positioned by the low-magnification lens of the image measuring instrument 1 so as to be in the field of view of the lens, then the high-magnification lens is switched to focus, the low-magnification lens is switched back after focusing is finished, a calibration item is selected, a plurality of lenses are calibrated, data deviation is obtained after calibration is finished, and the lenses are compensated for accuracy inspection based on the deviation. Under the condition, parameter calibration and precision inspection after calibration of the lens are completed on the same calibration piece 2, and the calibration piece 2 does not need to be replaced for a plurality of times, so that the calibration efficiency can be effectively improved. And based on a plurality of calibration items, the measurement accuracy of the image measuring instrument 1 can be improved.
In some examples, when calibrating the lenses of the image measuring apparatus 1, calibration of a plurality of lenses can be automatically completed only by starting calibration with one key. Therefore, high automation of calibration can be realized, and the calibration efficiency is improved.
Various embodiments of the present disclosure are described above in the detailed description. While the description directly describes the above embodiments, it should be understood that modifications and/or variations to the specific embodiments shown and described herein will occur to those skilled in the art. Any such modifications or variations that fall within the scope of this specification are intended to be included therein. Unless specifically indicated otherwise, the inventors intend that words and phrases in the specification and claims be given the ordinary and accustomed meaning of a person of ordinary skill.
The foregoing description of various embodiments of the present disclosure, as known to the inventors at the time of filing the present application, has been presented and is intended for the purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise form disclosed, and many modifications and variations are possible in light of the above teaching. The described embodiments are provided to explain the principles of the present disclosure and its practical application and to enable others skilled in the art to utilize the present disclosure in various embodiments and with various modifications as are suited to the particular use contemplated. Therefore, it is intended that the disclosure not be limited to the particular embodiments disclosed for carrying out this disclosure.
While particular embodiments of the present disclosure have been shown and described, it will be obvious to those skilled in the art that, based upon the teachings of this disclosure, changes and modifications may be made without departing from this disclosure and its broader aspects and, therefore, the appended claims are to encompass within their scope all such changes and modifications as are within the true spirit and scope of this disclosure. It will be understood by those within the art that, in general, terms used in this disclosure are generally intended to be "open" terms (e.g., the term "comprising" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "comprising" should be interpreted as "including but not limited to," etc.).
Claims (10)
1. The calibration method of the image measuring instrument is a method for calibrating based on a calibration sheet, the calibration sheet is provided with a center mark and a plurality of calibration patterns with fixed position relation with the center mark, the image measuring instrument comprises a first lens and a second lens, and the multiplying power of the first lens is not larger than that of the second lens, and the calibration method is characterized by comprising the following steps: the first lens is used as a working lens of the image measuring instrument, the calibration sheet is fixed on a stage of the image measuring instrument, the stage is moved so that the center mark is located in the central area of the field of view of the first lens, the working lens is switched so that the second lens is used as the working lens of the image measuring instrument, the position of the second lens is adjusted so as to focus the center mark, a movement scheme of the stage is obtained based on the fixed position relation between the center mark and each calibration pattern, at least one calibration item is selected, the stage is moved until one target calibration pattern is located in the field of view of the working lens based on the movement scheme, the first lens and the second lens are calibrated, the target calibration pattern is a calibration pattern matched with one calibration item in the at least one calibration item, the calibration item at least comprises a same focus calibration enabling focuses of the first lens and the second lens to be located at the same position, and the same Jiao Jiaozhun is the first calibration item.
2. The calibration method according to claim 1, characterized in that:
after the first lens and the second lens are calibrated, the objective table is moved based on the movement scheme until the next target calibration pattern is in the field of view of the working lens, and the first lens and the second lens are calibrated.
3. The calibration method according to claim 1, characterized in that:
calibrating the first lens and the second lens includes:
and switching the working lens to enable the first lens to serve as the working lens of the image measuring instrument, calibrating the first lens by utilizing the target calibration pattern, switching the working lens to enable the second lens to serve as the working lens of the image measuring instrument, and calibrating the second lens by utilizing the target calibration pattern.
4. The calibration method according to claim 1, characterized in that:
and after the calibration sheet is fixed on the objective table, adjusting the brightness of the calibration sheet until the brightness of the calibration sheet meets the preset requirement.
5. The method of calibrating according to claim 4, wherein:
the light source arranged on the object stage is utilized to polish the calibration sheet, the light of the light source penetrates through the calibration sheet from the bottom of the object stage and enters the working lens, and the brightness of the calibration sheet is adjusted by adjusting the brightness of the light source.
6. The calibration method according to claim 1, characterized in that:
and when focusing the center mark, acquiring an image through the second lens, calculating the variance of the gray value of the image, and judging whether the second lens finishes focusing or not based on the variance of the gray value.
7. The calibration method according to claim 1, characterized in that:
the calibration items include at least a pixel calibration, which is performed after the in-focus calibration.
8. The method of calibrating according to claim 7, wherein:
when the pixel calibration is performed, the calibration pattern of the pixel calibration is selected according to the lens magnification, and the calibration pattern matched with the pixel calibration comprises concentric circles and checkerboard.
9. The method of calibrating according to claim 8, wherein:
the calibration item includes a camera angle calibration, which is performed after the pixel calibration.
10. The method of calibrating according to claim 9, wherein:
when the camera angle is calibrated, the object stage is moved along a first direction, the position change of the center mark is recorded, and whether the camera angle needs to be calibrated or not is judged based on the movement direction of the center mark and the first direction.
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