A codable optical image measuring device and calibration method

Abstract

The present invention provides a codable optical image measurement device and calibration method, comprising a camera, an imaging system, a light source, a measuring stage, and a calibration plate. The calibration plate is a light-emitting array device that can illuminate light points row by row and / or column by column. The present invention replaces the traditional calibration plate with a light-emitting array device, which has high positioning accuracy and low production cost. In addition, the present invention also provides a calibration method that repeatedly scans and generates a calibration curve by illuminating the light-emitting array device with light points row by row and / or column by column. This is equivalent to the traditional method using a more detailed calibration pattern to improve calibration accuracy, while avoiding the problem of difficulty in grid image recognition when using fine pattern calibration in the traditional method, which easily leads to calibration failure.

Description

Technical Field

[0001] The present invention relates to the field of optical measurement technology, and in particular to a codable optical image measuring device and a calibration method. Background Art

[0002] Optical image measuring instruments utilize the principles of optical imaging to image the object being measured onto a camera's target surface. This image is then captured by a computer and converted into a digital image. Image processing techniques can be used to automatically or manually measure the object's two-dimensional profile. As a non-contact calibration method, optical image measuring instruments are gaining increasing recognition as an alternative to traditional measurement methods for thin-walled parts and surface contour measurements.

[0003] High-precision measurements typically require the use of a bilateral telecentric imaging lens and parallel light sources for illumination. This increases system complexity and cost; even with these methods, the object being measured can still be distorted due to numerous factors, such as machining and installation deviations.

[0004] The conventional method is to calibrate the imager using a standard calibration plate. Patterns are pre-prepared on the calibration plate. Common patterns include a checkerboard pattern with alternating black and white (OpenCV calibration plate) and a matrix of black disks (Halcon calibration plate). After the calibration plate is captured by the imager, image processing techniques are used to obtain the various parameters of the calibration plate image. Since the actual physical parameters of the calibration plate are already determined, the correspondence between the image pixels in the imager and the actual physical location dimensions can be calculated. This is the calibration process. The calibration process generates a series of calibration data and saves it in the computer. When measuring other objects, the measured image is restored to its actual physical dimensions based on the calibration data. This process is called the correction process. Based on the corrected image, combined with image processing techniques, high-precision dimensional measurement results can be obtained.

[0005] The calibration plate has high requirements for manufacturing accuracy and temperature stability of the material, making the processing complicated, time-consuming and costly. To achieve high calibration accuracy, a denser pattern is desired. However, in addition to increasing the production cost, a denser pattern can also easily lead to image recognition errors during the calibration process, resulting in greater errors. In addition, if the calibration plate is not properly maintained in the future and becomes contaminated or damaged, it will also affect the calibration accuracy. Summary of the Invention

[0006] Purpose of the invention: The purpose of the present invention is to provide a codable optical image measuring device and calibration method with high positioning accuracy and low production cost to address the shortcomings of the existing technology.

[0007] Technical solution: The present invention describes a codable optical image measuring device, comprising a camera, an imaging system, a light source, a measuring stage and a calibration plate. The calibration plate is a light-emitting array device that can illuminate light points row by row and / or column by column.

[0008] Furthermore, the light emitting array device is a passively luminous LCD liquid crystal screen.

[0009] Furthermore, the light emitting array device is an actively luminous OLED display screen.

[0010] The present invention also provides a calibration method for a codable optical image measuring device, comprising the following steps:

[0011] Step 1: The light emitting array device starts illuminating a row along the X-axis direction, and the actual Y-axis position of the light emitting point is recorded as y;

[0012] Step 2: The camera collects image signals and extracts the center line of the bright stripes in the collected image through image processing, and obtains the position of each point on the center line in the image (1, Iy i1 ),(2,Iy i2 ),...,(n,Iy in ), where n represents the number of camera image columns, i.e. the number of pixels in the X direction; i represents the index of the number of cycle lighting times.

[0013] Step 3: Turn off the currently lit array device;

[0014] Step 4: To achieve high calibration accuracy, repeat steps 1 to 3 row by row to complete the calibration in the X-axis direction; to achieve fast calibration, repeat steps 1 to 3 at fixed intervals;

[0015] Step 5: Through steps 1 to 4, a series of X-axis calibration positions and calibration curves are obtained. The X-axis calibration position is represented by a vector

[0016] (y1 y2...ym)

[0017] y1~ym are the actual physical y-axis coordinate positions corresponding to each row when the light-emitting array device is turned on each time;

[0018] The X-axis calibration curve is represented by a matrix:

[0019]

[0020] The first row in the X calibration curve matrix corresponds to the actual Y position y1, the second row corresponds to y2, and so on;

[0021] Step 6: The light-emitting array device starts a column of illumination in the Y-axis direction, and the actual X-axis position of the light-emitting point is recorded as x;

[0022] Step 7: The camera collects image signals and extracts the center line of the bright stripes in the collected image through image processing to obtain the position of each point on the center line in the image.

[0023] (Ix 1j ,1),(Ix 2j ,2),...,(Ix mj ,m);

[0024] j represents the index of the number of cycle lighting times, from 1 to n; m represents the number of pixels in the Y direction, that is, the number of camera image rows;

[0025] Step 8: Turn off the currently lit array device;

[0026] Step 9: To achieve high calibration accuracy, repeat steps 6 to 8 column by column to complete the Y-axis calibration. To achieve fast calibration, you can also repeat steps 6 to 8 at fixed intervals.

[0027] Step 10: Through steps 6 to 9, a series of Y-axis calibration positions and calibration curves are obtained. The Y-axis calibration position is represented by a vector

[0028] (x1x2...xn)

[0029] x1~xn are the actual physical x-axis coordinate positions corresponding to each column when the light-emitting array device is turned on each time;

[0030] The Y-axis calibration curve is represented by a matrix:

[0031]

[0032] The first column in the Y calibration curve matrix corresponds to the actual X position x1, the second column corresponds to x2, and so on;

[0033] Step 11: A set of calibration grids is formed by the X-axis calibration curve and the Y-axis calibration curve. The calibration parameters are combined with the X-axis calibration position and the Y-axis calibration position to form calibration parameters. The calibration parameters are saved to complete the calibration process.

[0034] Step 12: Place the object under test and illuminate it with a light source or by lighting up all the light-emitting devices according to the characteristics of the object under test;

[0035] Step 13: Acquire an image of the object to be measured and extract the outline of the object to be measured through an image processing algorithm;

[0036] Step 14: For each point P on the outline of the object, obtain its coordinate position (u, v) in the image, and determine the position (i, j) of point P in the calibration grid based on the calibration curve of the X axis and the calibration curve of the Y axis, so that Ix i,v ≤u≤Ix i+1,v , Iyu,j ≤v≤Iy u,j+1 ; Combined with the X-axis calibration position (x i ,x i+1 ) and Y-axis calibration position (y j ,y j+1 ), the actual physical coordinate information of point P is obtained through calculation as (x p ,y p );

[0037] Step 15: Correct the image contour of the object being measured, and measure the relevant geometric features based on the corrected image contour.

[0038] Furthermore, in step 14, x p , and y p The calculation formula is as follows:

[0039]

[0040] Where, △x1=u-Ix i,v , △x2=Ix i+1,v -u, △y1=v-Iy u,j , △y2=Iy u,j+1 -u.

[0041] Furthermore, in step 12, when the object to be measured is opaque, an upper light source is used for illumination;

[0042] When the object to be measured has a hollow structure or is made of transparent material, all the light-emitting array devices are selected to light up for illumination, without the need to light up an additional light source.

[0043] Furthermore, the image processing algorithm in step 13 is an edge extraction algorithm.

[0044] Beneficial effects: Compared with the prior art, the advantages of the present invention are:

[0045] (1) The light-emitting device can use a mature LCD screen or OLED screen, which has low production cost;

[0046] (2) The light-emitting points of the light-emitting devices of the LCD screen are processed by semiconductor technology, and their positioning accuracy is much higher than the measurement accuracy of the optical imager, meeting the requirements of the calibration block;

[0047] (3) Since the calibration has the characteristics of coded luminescence, different calibration patterns and scales can be edited, and they can be displayed and collected one by one, so that very fine patterns can be formed, which improves the reliability of the image calibration processing algorithm and achieves higher calibration accuracy;

[0048] (4) The finer the pattern, the higher the calibration accuracy. However, in traditional methods, too dense calibration lines will lead to calibration errors or even failure, so they cannot be too dense. The present invention will not cause interference errors between calibration lines because it lights up row by row or column by column.

[0049] (5) The present invention improves the calibration accuracy of the system, so a conventional imaging system can be used, which reduces the requirements for the parallelism of the illumination light source and significantly reduces the cost of the measuring instrument system. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 It is a structural schematic diagram of the present invention;

[0051] Figure 2 is the calibration curve along the X axis;

[0052] Figure 3 It is the X and Y axis calibration grid curve;

[0053] Figure 4 It is the contour information of the image collected by the object being measured;

[0054] Figure 5 It is a schematic diagram of the contour correction of the object being measured;

[0055] Figure 6 It is the contour image of the object after correction;

[0056] Figure 7 It is a calibration grid curve based on a circular calibration pattern. DETAILED DESCRIPTION

[0057] The technical solution of the present invention is described in detail below with reference to the accompanying drawings, but the protection scope of the present invention is not limited to the embodiments.

[0058] Example 1

[0059] like Figure 1 The illustrated codable optical image measuring device includes a camera 1, an imaging system 2, a light source 3, a measuring stage 4, and a calibration plate. The calibration plate is a light emitting array device 5 that can illuminate light points row by row and / or column by column.

[0060] The light emitting array device 5 may be a passively emitting LCD screen or an actively emitting OLED display screen, as long as the light points can be lit row by row and / or column by column.

[0061] The measuring stage 4 is located above the light-emitting array device, and the center is made of a transparent material, preferably tempered glass, which has a protective effect on the LCD screen. The stage can be just a piece of tempered glass, and can be integrated with the light-emitting array device. The light source is used to achieve uniform illumination of the object to be measured during the measurement process, and is preferably an LED ring cold light source to avoid deformation of the object to be measured due to heat during the measurement process. There is no need to light the light source during the calibration process, or when measuring the contour of the object to be measured with a hollow structure, it is only necessary to use the entire array during the lighting period without lighting the light source. The imaging system realizes imaging the object to be measured on the stage to the camera, which can be a lens with a bilateral telecentric optical path or an ordinary imaging lens. The camera collects the image of the object to be measured and sends it to the computer for subsequent processing.

[0062] Example 2

[0063] A calibration method for a codable optical image measuring device comprises the following steps:

[0064] Step 1: The light emitting array device starts illuminating a row along the X-axis direction, and the actual Y-axis position of the light emitting point is recorded as y;

[0065] Step 2: The camera collects image signals and extracts the center line of the bright stripes in the collected image through image processing, and obtains the position of each point on the center line in the image (1, Iy i1 ),(2,Iy i2 ),...,(n,Iy in ), where n represents the number of camera image columns, i.e., the number of pixels in the X direction; i represents the index of the number of cycle lighting times;

[0066] Step 3: Turn off the currently lit array device;

[0067] Step 4: To achieve high calibration accuracy, repeat steps 1 to 3 row by row to complete the calibration in the X-axis direction; to achieve fast calibration, repeat steps 1 to 3 at fixed intervals;

[0068] Step 5: Through steps 1 to 4, a series of X-axis calibration positions and calibration curves are obtained. The X-axis calibration position is represented by a vector

[0069] (y1 y2...ym)

[0070] y1~ym are the actual physical y-axis coordinate positions corresponding to each row when the light-emitting array device is turned on each time;

[0071] The X-axis calibration curve is represented by a matrix:

[0072]

[0073] The first row in the X calibration curve matrix corresponds to the actual Y position y1, the second row corresponds to y2, and so on;

[0074] Step 6: The light-emitting array device starts a column of illumination in the Y-axis direction, and the actual X-axis position of the light-emitting point is recorded as x;

[0075] Step 7: The camera collects image signals and extracts the center line of the bright stripes in the collected image through image processing to obtain the position of each point on the center line in the image.

[0076] (Ix 1j ,1),(Ix 2j ,2),...,(Ix mj ,m);

[0077] j represents the index of the number of cycle lighting times, from 1 to n; m represents the number of pixels in the Y direction, that is, the number of camera image rows;

[0078] Step 8: Turn off the currently lit array device;

[0079] Step 9: To achieve high calibration accuracy, repeat steps 6 to 8 column by column to complete the Y-axis calibration. To achieve fast calibration, you can also repeat steps 6 to 8 at fixed intervals.

[0080] Step 10: Through steps 6 to 9, a series of Y-axis calibration positions and calibration curves are obtained. The Y-axis calibration position is represented by a vector

[0081] (x1x2...xn)

[0082] x1~xn are the actual physical x-axis coordinate positions corresponding to each column when the light-emitting array device is turned on each time;

[0083] The Y-axis calibration curve is represented by a matrix:

[0084]

[0085] The first column in the Y calibration curve matrix corresponds to the actual X position x1, the second column corresponds to x2, and so on;

[0086] Step 11: A set of calibration grids is formed by the X-axis calibration curve and the Y-axis calibration curve. The calibration parameters are combined with the X-axis calibration position and the Y-axis calibration position to form calibration parameters. The calibration parameters are saved to complete the calibration process.

[0087] Step 12: Place the object under test and illuminate it with a light source or by lighting all the light-emitting devices according to the characteristics of the object under test; in step 12, if the object under test is opaque, illuminate it with an upper light source;

[0088] When the object to be measured has a hollow structure or is made of transparent material, all the light-emitting array devices are selected to light up for illumination, without the need to light up an additional light source.

[0089] Step 13: Acquire an image of the object to be measured, and extract the outline of the object to be measured using an image processing algorithm; the image processing algorithm in step 13 is an edge extraction algorithm.

[0090] Step 14: For each point P on the outline of the object, obtain its coordinate position (u, v) in the image, and determine the position (i, j) of point P in the calibration grid based on the calibration curve of the X axis and the calibration curve of the Y axis, so that Ix i,v ≤u≤Ix i+1,v , Iy u,j ≤v≤Iy u,j+1 ; Combined with the X-axis calibration position (x i ,x i+1 ) and Y-axis calibration position (y j ,y j+1 ), the actual physical coordinate information of point P is obtained through calculation as (x p ,y p );

[0091] In step 14, x p , and y p The calculation formula is as follows:

[0092]

[0093] Where, △x1=u-Ix i,v , △x2=Ix i+1,v -u, △y1=v-Iy u,j , △y2=Iy u,j+1 -u.

[0094] Step 15: Correct the image contour of the object being measured, and measure the relevant geometric features based on the corrected image contour.

[0095] Example 3

[0096] The difference between this embodiment and embodiment 2 is that the light emitting array device adopts a method of generating a circular pattern, such as Figure 7 As shown:

[0097] Step 1: Light up the center of the circle

[0098] (x1,y1),(x2,y1),...,(x n ,y1),(x1,y2),(x2,y2),...(x n ,y2),...,( x1 ,y m),(x2,y m ),...,(x n ,y m ) circular pattern;

[0099] Step 2: Each time a pattern is lit, an image is collected, and the circle contour information is extracted using an image processing algorithm. The circle center coordinates with sub-pixel accuracy are obtained using a circle fitting or ellipse fitting algorithm.

[0100] Step 3: All the circle center coordinates are combined with the actual position information to form calibration parameters and saved in the computer;

[0101] Step 4: The contour information of the object being measured can be corrected according to the calibration parameters.

[0102] As described above, although the present invention has been shown and described with reference to specific preferred embodiments, it should not be construed as limiting the present invention itself. Various changes may be made to it in form and detail without departing from the spirit and scope of the present invention as defined in the appended claims.

Claims

1. A calibration method for a codable optical image measuring device, the codable optical image measuring device comprising a camera (1), an imaging system (2), a light source (3), a measuring stage (4), and a calibration plate, wherein the calibration plate is a light emitting array device (5) capable of lighting light points row by row and / or column by column, characterized in that The steps include: Step 1: The light emitting array device starts illuminating a row along the X-axis direction, and the actual Y-axis position of the light emitting point is recorded as y; Step 2: The camera collects image signals and extracts the center line of the bright stripes in the collected image through image processing, and obtains the position of each point on the center line in the image (1, Iy i1 ),(2,Iy i2 ),...,(n,Iy in ), where n represents the number of camera image columns, i.e., the number of pixels in the X direction; i represents the index of the number of cycle lighting times; Step 3: Turn off the currently lit array device; Step 4: To achieve high calibration accuracy, repeat steps 1 to 3 row by row to complete the calibration in the X-axis direction; to achieve fast calibration, repeat steps 1 to 3 at fixed intervals; Step 5: Through steps 1 to 4, a series of X-axis calibration positions and calibration curves are obtained. The X-axis calibration position is represented by a vector (y1 y2 ... ym) y1~ym are the actual physical y-axis coordinate positions corresponding to each row when the light-emitting array device is turned on each time; The X-axis calibration curve is represented by a matrix: The first row in the X calibration curve matrix corresponds to the actual Y position y1, the second row corresponds to y2, and so on; Step 6: The light-emitting array device starts a column of illumination in the Y-axis direction, and the actual X-axis position of the light-emitting point is recorded as x; Step 7: The camera collects image signals and extracts the center line of the bright stripes in the collected image through image processing, and obtains the position of each point on the center line in the image (Ix 1j ,1),(Ix 2j ,2),...,(Ix mj ,m); j represents the index of the number of cycle lighting times, from 1 to n; m represents the number of pixels in the Y direction, that is, the number of camera image rows; Step 8: Turn off the currently lit array device; Step 9: To achieve high calibration accuracy, repeat steps 6 to 8 column by column to complete the Y-axis calibration. To achieve fast calibration, you can also repeat steps 6 to 8 at fixed intervals. Step 10: Through steps 6 to 9, a series of Y-axis calibration positions and calibration curves are obtained. The Y-axis calibration position is represented by a vector (x1 x2 ... xn) x1~xn are the actual physical x-axis coordinate positions corresponding to each column when the light-emitting array device is turned on each time; The Y-axis calibration curve is represented by a matrix: The first column in the Y calibration curve matrix corresponds to the actual X position x1, the second column corresponds to x2, and so on; Step 11: A set of calibration grids is formed by the X-axis calibration curve and the Y-axis calibration curve. The calibration parameters are combined with the X-axis calibration position and the Y-axis calibration position to form calibration parameters. The calibration parameters are saved to complete the calibration process. Step 12: Place the object under test and illuminate it with a light source or by lighting up all the light-emitting devices according to the characteristics of the object under test; Step 13: Acquire an image of the object to be measured and extract the outline of the object to be measured through an image processing algorithm; Step 14: For each point P on the outline of the object, obtain its coordinate position (u, v) in the image, and determine the position (i, j) of point P in the calibration grid based on the calibration curve of the X axis and the calibration curve of the Y axis, so that Ix i,v ≤u≤Ix i+1,v , Iy u,j ≤v≤Iy u,j+1 ; Combined with the X-axis calibration position (x i ,x i+1 ) and Y-axis calibration position (y j ,y j+1 ), the actual physical coordinate information of point P is obtained through calculation as (x p ,y p ); Step 15: Correct the image contour of the object being measured, and measure the relevant geometric features based on the corrected image contour.

2. The calibration method of a codable optical image measuring device according to claim 1, wherein: In step 14, x p , and y p The calculation formula is as follows: Among them, △x1=u-Ix i,v , △x2=Ix i+1,v -u, △y1=v-Iy u,j ,△y2=Iy u,j+1 -u.

3. The calibration method of a codable optical image measuring device according to claim 1, wherein: In step 12, when the object to be measured is opaque, an upper light source is used for illumination; When the object to be measured has a hollow structure or is made of transparent material, all the light-emitting array devices are selected to light up for illumination, without the need to light up an additional light source.

4. The calibration method of a codable optical image measuring device according to claim 1, wherein: The image processing algorithm in step 13 is an edge extraction algorithm.

5. The calibration method of a codable optical image measuring device according to claim 1, wherein: The light emitting array device (5) is a passively luminous LCD liquid crystal screen.

6. The calibration method of a codable optical image measuring device according to claim 1, wherein: The light-emitting array device (5) is an actively luminous OLED display screen.

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