A method for calibrating a differential plate thickness gauge

Abstract

The application discloses a kind of for differential medium plate thickness gauge calibration method, comprising: top area array camera is calibrated step;Bottom area array camera is calibrated step;Wherein, top area array camera is calibrated step and bottom area array camera is calibrated step all include calculating multiple height values on laser line step, and filtering, calculating mean and average step, bring following beneficial effects: by calculating multiple height values on laser line, then by filtering, calculating mean, average etc., obtain better thickness value of precision.

Description

Technical Field

[0001] This invention belongs to the field of camera calibration technology, specifically relating to a calibration method for a differential medium-thickness plate thickness measuring device. Background Technology

[0002] To measure the thickness of medium-thick plates in practical applications, existing technologies typically combine laser triangulation with differential measurement. This involves illuminating the target with a laser beam at a specific angle. The laser beam is reflected and scattered on the target surface, and a lens at another angle focuses the reflected laser light into an image, which is then projected onto a CCD position sensor. When the object moves along the laser direction, the laser spot on the position sensor moves accordingly, with the displacement corresponding to the object's movement distance. Therefore, an algorithm can be designed to calculate the distance between the object and a baseline from the laser spot displacement. Displacement sensors are installed on the upper and lower surfaces of the object. Differential measurement effectively eliminates measurement errors caused by plate vibration. The installation method is tailored to the width requirements of the plates on the production line, using the roller conveyor surface as a measurement reference plane to measure the thickness in real time. However, a point laser rangefinder is a special type of laser rangefinder. It calculates the distance between the object and the sensor by emitting a small laser point and detecting the reflected light. Point laser rangefinders are commonly used in machine vision, 3D scanning, and security monitoring. However, point laser rangefinders can only measure the distance to a specific point. In harsh industrial environments, the results are easily affected by noise on the surface of the object being measured, impacting measurement accuracy. Summary of the Invention

[0003] To address the aforementioned problems, the present invention provides a calibration method for a differential medium-thickness plate thickness measuring device. This calibration method for a differential medium-thickness plate thickness measuring device is characterized by comprising:

[0004] Calibrate the top area array camera;

[0005] Calibrate the bottom area array camera;

[0006] The calibration steps for the top area array camera and the bottom area array camera both include steps for calculating multiple height values ​​on the laser line of the line structured light source, filtering, and calculating the median and average values.

[0007] As an improvement, the top area scan camera and the bottom area scan camera are respectively calibrated in their respective world coordinate systems, and the measurement height planes of the top line structured light and the bottom line structured light are aligned.

[0008] As a further improvement, both the calibration step for the top area array camera and the calibration step for the bottom area array camera include an intrinsic parameter calibration step, which includes:

[0009] Several top intrinsic parameter calibration images and several bottom intrinsic parameter calibration images are obtained by taking pictures of calibration boards at different placement positions using the top area array camera and the bottom area array camera respectively; intrinsic parameters are calculated for the several top intrinsic parameter calibration images and the several bottom intrinsic parameter calibration images respectively to obtain the intrinsic parameters of the top area array camera and the intrinsic parameters of the bottom area array camera.

[0010] As a further improvement, both the calibration step for the top area array camera and the calibration step for the bottom area array camera include the steps of establishing a world coordinate system and a temporary coordinate system. The steps of establishing a world coordinate system and a temporary coordinate system include:

[0011] Select any of the top intrinsic parameter calibration images and any of the bottom intrinsic parameter calibration images respectively, and establish a top world coordinate system and a bottom world coordinate system based on the position of the calibration plate of the selected top intrinsic parameter calibration image and any of the bottom intrinsic parameter calibration images respectively;

[0012] Based on the position of the calibration plate when establishing the top world coordinate system and the bottom world coordinate system, the calibration plate is moved so that there is a height difference between the positions of the calibration plate before and after the movement, and the top temporary coordinate system and the bottom temporary coordinate system are established respectively.

[0013] As a further improvement, both the calibration step for the top area array camera and the calibration step for the bottom area array camera include an external parameter calibration step, which includes:

[0014] The extrinsic parameters of the top area array camera and the extrinsic parameters of the bottom area array camera are calculated based on the top world coordinate system and the top temporary coordinate system, the bottom world coordinate system and the bottom temporary coordinate system, respectively.

[0015] As a further improvement, both the calibration step for the top area array camera and the calibration step for the bottom area array camera include the steps of capturing images in the world coordinate system and in the temporary coordinate system. The steps of capturing images in the world coordinate system and in the temporary coordinate system include:

[0016] Line structured light is irradiated onto the front and back of the calibration plate by the top and bottom line structured light sources, respectively, and the top and bottom area array cameras are used to capture images to obtain top world coordinate system images and bottom world coordinate system images.

[0017] Line structured light is irradiated onto the front and back of the calibration plate by the top and bottom line structured light sources, respectively, and images of the top temporary coordinate system and the bottom temporary coordinate system are obtained by the top area array camera and the bottom area array camera.

[0018] As a further improvement, both the calibration step for the top area array camera and the calibration step for the bottom area array camera include a fitting step, which includes:

[0019] By fitting the spatial point coordinates of the top world coordinate system image and the spatial point coordinates of the top temporary coordinate system image, and the spatial point coordinates of the bottom world coordinate system image and the spatial point coordinates of the bottom temporary coordinate system image, the top laser line plane and the bottom laser line plane are obtained respectively.

[0020] As a further improvement, both the calibration steps for the top area array camera and the calibration steps for the bottom area array camera include a motion direction parameter calibration step. The motion direction parameter calibration step includes: making the calibration plate move in the same way as the object being measured; taking pictures of the calibration plate at different times using the top area array camera and the bottom area array camera to obtain several top motion direction parameter calibration images and several bottom motion direction parameter calibration images; calculating the motion direction parameters of the several top motion direction parameter calibration images and the several bottom motion direction parameter calibration images respectively to obtain the motion direction parameters of the object being measured.

[0021] As a further improvement, the steps for calculating multiple height values ​​on the laser line of the structured light are configured as follows:

[0022] Each column of the laser line in the linear structured light source takes a height value;

[0023] The filtering step is configured as follows: mean filtering, taking an average value for every 5 height values.

[0024] As a further improvement, the step of calculating the median and average value is configured as follows: there are two laser lines on the laser line plane, the upper laser line consists of m points and the lower laser line consists of n points. The n points of the lower laser line segment are fitted with a straight line. The distances from the m points of the upper laser line to the straight line are calculated, and the median and average value are calculated from the n distances.

[0025] This invention provides a calibration method for a differential medium-thickness plate thickness measuring device, which has the following advantages: the thickness of the steel plate is measured by combining line structured light with an area array camera. By calculating multiple height values ​​on the laser line, and then by filtering, calculating the median and average values, a more accurate thickness value is obtained. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of a calibration method for a differential medium-thickness plate thickness measuring device according to the present invention. Detailed Implementation

[0027] The patent, CN114820817A, entitled "Invention Patent on Calibration Method and 3D Reconstruction Method Based on High-Precision Line Laser 3D Camera," describes a method that involves placing a calibration plate on a working plane according to preset rules and photographing the calibration plate to obtain several first calibration plate images; converting these first calibration plate images into corresponding grayscale images; numbering the circular markers on the calibration plate in the grayscale images; calculating the camera's internal parameters based on the circular markers and their numbers; establishing a reference world coordinate system and a temporary coordinate system for the calibration plate; and calculating the camera's external parameters based on the reference world coordinate system and the temporary coordinate system; and fitting a light plane based on laser lines illuminating different planes and calculating the pose transformation matrix of the light plane relative to the origin of the reference world coordinate system. However, this method cannot be used for the calibration of differential medium-thickness plate thickness measurement devices.

[0028] To address the aforementioned technical problems, this invention provides a calibration method for a differential medium-thickness plate thickness measuring device. It should be noted that the differential medium-thickness plate thickness measuring device includes a top thickness measuring device and a bottom thickness measuring device. The top thickness measuring device includes a top area array camera and a top line structured light source, and the bottom thickness measuring device includes a bottom area array camera and a bottom line structured light source. During the calibration process, the area array camera and the line structured light source are fixedly placed, and their relative positions remain unchanged. The method includes:

[0029] Calibrate the top area array camera;

[0030] Calibrate the bottom area array camera;

[0031] The calibration steps for both the top and bottom area array cameras include steps for calculating multiple height values ​​on the laser line of the structured light source, filtering, and calculating the median and average values.

[0032] According to some embodiments of the present invention, a calibration method for a differential medium-thickness plate thickness measuring device is provided, wherein the top area array camera and the bottom area array camera are respectively calibrated in their respective world coordinate systems, and the measurement height planes of the top line structured light and the bottom line structured light are aligned.

[0033] A calibration method for a differential medium-thickness plate thickness measuring device according to some embodiments of the present invention includes an intrinsic parameter calibration step in both the calibration steps for the top area array camera and the calibration steps for the bottom area array camera. The intrinsic parameter calibration step includes:

[0034] Several top intrinsic parameter calibration images and several bottom intrinsic parameter calibration images are obtained by taking pictures of calibration boards at different placement positions using a top area array camera and a bottom area array camera. Intrinsic parameters are calculated from the several top intrinsic parameter calibration images and several bottom intrinsic parameter calibration images to obtain the intrinsic parameters of the top area array camera and the bottom area array camera.

[0035] A calibration method for a differential medium-thickness plate thickness measuring device according to some embodiments of the present invention includes a calibration step for both the top area array camera and the bottom area array camera, which involves establishing a world coordinate system and a temporary coordinate system. The steps for establishing the world coordinate system and the temporary coordinate system include:

[0036] Select any top intrinsic parameter calibration image and any bottom intrinsic parameter calibration image respectively, and establish a top world coordinate system and a bottom world coordinate system based on the position of the calibration plate of the selected top intrinsic parameter calibration image and any bottom intrinsic parameter calibration image respectively;

[0037] Based on the position of the calibration plate when establishing the top world coordinate system and the bottom world coordinate system, the calibration plate is moved to create a height difference between the positions of the calibration plate before and after the movement, and a top temporary coordinate system and a bottom temporary coordinate system are established respectively.

[0038] A calibration method for a differential medium-thickness plate thickness measuring device according to some embodiments of the present invention includes an external parameter calibration step in both the calibration steps for the top area array camera and the calibration steps for the bottom area array camera. The external parameter calibration step includes:

[0039] The extrinsic parameters of the top area array camera and the bottom area array camera are calculated based on the top world coordinate system and the top temporary coordinate system, and the bottom world coordinate system and the bottom temporary coordinate system, respectively.

[0040] A calibration method for a differential medium-thickness plate thickness measuring device according to some embodiments of the present invention includes a calibration step for both the top area array camera and the bottom area array camera, which involves capturing images in a world coordinate system and a temporary coordinate system. The steps for capturing images in the world coordinate system and the temporary coordinate system include:

[0041] Line structured light is irradiated onto the front and back of the calibration plate by the top and bottom line structured light sources, respectively, and the top and bottom area array cameras are used to capture images to obtain the top world coordinate system image and the bottom world coordinate system image.

[0042] Line structured light is irradiated onto the front and back of the calibration plate by top and bottom line structured light sources, respectively. The top and bottom area array cameras are used to capture images, resulting in top temporary coordinate system images and bottom temporary coordinate system images.

[0043] A calibration method for a differential medium-thickness plate thickness measuring device according to some embodiments of the present invention includes a fitting step in both the calibration steps for the top area array camera and the calibration steps for the bottom area array camera. The fitting step includes:

[0044] By fitting the spatial point coordinates of the top world coordinate system image and the top temporary coordinate system image, as well as the spatial point coordinates of the bottom world coordinate system image and the bottom temporary coordinate system image, the top laser line plane and the bottom laser line plane are obtained respectively.

[0045] A calibration method for a differential medium-thickness plate thickness measuring device according to some embodiments of the present invention includes a motion direction parameter calibration step in both the calibration steps for the top area array camera and the calibration steps for the bottom area array camera. The motion direction parameter calibration step includes: making the calibration plate move in the same way as the object being measured; taking pictures of the calibration plate at different times using the top and bottom area array cameras to obtain several top motion direction parameter calibration images and several bottom motion direction parameter calibration images; calculating the motion direction parameters of the several top motion direction parameter calibration images and several bottom motion direction parameter calibration images respectively to obtain the motion direction parameters of the object being measured.

[0046] A calibration method for a differential medium-thickness plate thickness measuring device according to some embodiments of the present invention is configured such that the step of calculating multiple height values ​​on the laser line of the line structured light is as follows:

[0047] Each column of the laser line in the line structured light source is assigned a height value;

[0048] The filtering step is configured as follows: mean filtering, taking the average value for every 5 height values.

[0049] A calibration method for a differential medium-thickness plate thickness measuring device according to some embodiments of the present invention is configured as follows: there are two laser lines on the laser line plane, the upper laser line consists of m points and the lower laser line consists of n points. The n points of the lower laser line segment are fitted to a straight line. The distances from the m points of the upper laser line to the straight line are calculated. The median and average values ​​are calculated from the n distances.

[0050] It should be noted that the present invention is implemented through the following algorithm. Based on the transformation relationship between the pinhole camera model and the spatial coordinate system, the relationship between the image coordinate system and the world coordinate system can be obtained as shown in equation (1):

[0051]

[0052] Where (u,v) are the image coordinates, (x) w ,y w ,z wLet be the world coordinate system, K be the camera's intrinsic parameter matrix, T be the extrinsic parameter matrix, and M be the projection matrix. f c It is the effective focal length of the camera, S x ,S y These are the physical dimensions of each pixel's length and width, respectively. Since the image coordinate system (u, v) cannot be known, the three-dimensional spatial coordinates (x, y) cannot be calculated. w ,y w ,z w Therefore, the equation for the light plane is added:

[0053] ax w +by w +cz w +d=0 (2)

[0054] Combining equations (1) and (2), we obtain the mapping between image coordinates and world coordinates:

[0055]

[0056] Solving for:

[0057]

[0058] Thus, the line structured light measurement model is established. After determining the light plane structure parameters, the spatial three-dimensional coordinates of any point in the image coordinate system can be solved by equation (4).

[0059] The following embodiments further illustrate the content of the present invention, but should not be construed as limiting the present invention. Any modifications or substitutions made to the methods, steps, or conditions of the present invention without departing from the spirit and essence of the invention are within the scope of the present invention.

[0060] Although the present invention has been described in detail above with general descriptions, specific embodiments, and experiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A calibration method for a differential medium-thickness plate thickness measuring device, characterized in that, include: Calibrate the top area array camera; Calibrate the bottom area array camera; The calibration steps for the top area array camera and the bottom area array camera both include steps for calculating multiple height values ​​on the laser line of the line structured light source, filtering, and calculating the median and average values. The multiple height value steps on the laser line of the computational line structured light are configured as follows: Each column of the laser line in the linear structured light source takes a height value; The filtering step is configured as follows: mean filtering, taking an average value for every 5 height values; The steps for calculating the median and average value are configured as follows: There are two laser lines on the laser line plane, the upper laser line consists of m points and the lower laser line consists of n points. The n points of the lower laser line segment are fitted with a straight line. The distances from the m points of the upper laser line to the straight line are calculated, and the median and average value are calculated from the n distances.

2. The calibration method for a differential medium-thickness plate thickness measuring device according to claim 1, characterized in that, The top area array camera and the bottom area array camera are respectively calibrated in their respective world coordinate systems, and the two laser lines of the top line structured light source and the bottom line structured light source are coplanar.

3. The calibration method for a differential medium-thickness plate thickness measuring device according to claim 1, characterized in that, Both the calibration steps for the top area array camera and the calibration steps for the bottom area array camera include an intrinsic parameter calibration step, which includes: Several top intrinsic parameter calibration images and several bottom intrinsic parameter calibration images are obtained by taking pictures of calibration boards at different placement positions using the top area array camera and the bottom area array camera respectively; intrinsic parameters are calculated for the several top intrinsic parameter calibration images and the several bottom intrinsic parameter calibration images respectively to obtain the intrinsic parameters of the top area array camera and the intrinsic parameters of the bottom area array camera.

4. The calibration method for a differential medium-thickness plate thickness measuring device according to claim 3, characterized in that, Both the calibration steps for the top area array camera and the calibration steps for the bottom area array camera include establishing a world coordinate system and a temporary coordinate system. The steps for establishing the world coordinate system and the temporary coordinate system include: Select any of the top intrinsic parameter calibration images and any of the bottom intrinsic parameter calibration images respectively, and establish a top world coordinate system and a bottom world coordinate system based on the position of the calibration plate of the selected top intrinsic parameter calibration image and any of the bottom intrinsic parameter calibration images respectively; Based on the position of the calibration plate when establishing the top world coordinate system and the bottom world coordinate system, the calibration plate is moved so that there is a height difference between the positions of the calibration plate before and after the movement, and the top temporary coordinate system and the bottom temporary coordinate system are established respectively.

5. A calibration method for a differential medium-thickness plate thickness measuring device according to claim 4, characterized in that, Both the calibration steps for the top area array camera and the calibration steps for the bottom area array camera include an external parameter calibration step, which includes: The extrinsic parameters of the top area array camera and the extrinsic parameters of the bottom area array camera are calculated based on the top world coordinate system and the top temporary coordinate system, the bottom world coordinate system and the bottom temporary coordinate system, respectively.

6. The calibration method for a differential medium-thickness plate thickness measuring device according to claim 3, characterized in that, Both the calibration steps for the top area array camera and the calibration steps for the bottom area array camera include the steps of capturing images in the world coordinate system and in the temporary coordinate system. The steps of capturing images in the world coordinate system and in the temporary coordinate system include: Line structured light is irradiated onto the front and back of the calibration plate by the top and bottom line structured light sources, respectively, and the top and bottom area array cameras are used to capture images to obtain top world coordinate system images and bottom world coordinate system images. Line structured light is irradiated onto the front and back of the calibration plate by the top and bottom line structured light sources, respectively, and images of the top temporary coordinate system and the bottom temporary coordinate system are obtained by the top area array camera and the bottom area array camera.

7. A calibration method for a differential medium-thickness plate thickness measuring device according to claim 6, characterized in that, Both the calibration step for the top area array camera and the calibration step for the bottom area array camera include a fitting step, which includes: By fitting the spatial point coordinates of the top world coordinate system image and the spatial point coordinates of the top temporary coordinate system image, and the spatial point coordinates of the bottom world coordinate system image and the spatial point coordinates of the bottom temporary coordinate system image, the top laser line plane and the bottom laser line plane are obtained respectively.

8. The calibration method for a differential medium-thickness plate thickness measuring device as described in claim 1, characterized in that, Both the calibration steps for the top area array camera and the calibration steps for the bottom area array camera include a motion direction parameter calibration step. The motion direction parameter calibration step includes: making the calibration plate move in the same way as the object being measured; taking pictures of the calibration plate at different times using the top area array camera and the bottom area array camera to obtain several top motion direction parameter calibration images and several bottom motion direction parameter calibration images; calculating the motion direction parameters of the several top motion direction parameter calibration images and the several bottom motion direction parameter calibration images respectively to obtain the motion direction parameters of the object being measured.

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