A kind of calibration method and device of Z-axis height position compensation XY coordinate based on flat crystal

Abstract

The application discloses a kind of based on flat crystal Z-axis height position compensation XY coordinate's calibration device, for compensating the XY measurement deviation generated when different height products are measured visually.The device includes fixed platform, calibration reference, parallel crystal, camera assembly movable along Z-axis and control and calculation unit.Parallel crystal is placed on the static calibration reference, and the focusing imaging height of camera is equivalently raised using refraction image shift characteristics.Control and calculation unit calculates offset coefficient by comparing the actual measured Z-axis height difference before and after placing flat crystal and reference coordinate difference, to compensate and correct product coordinates in actual measurement.The application does not need to use high-precision step calibration block, fundamentally isolates physical placement error, low in cost, and can significantly improve the consistency of different height product geometric parameter measurement.

Description

Technical Field

[0001] This invention belongs to the field of industrial vision inspection and precision measurement technology, specifically relating to a calibration method and device for XY coordinates based on Z-axis height position compensation using a flat crystal. Background Technology

[0002] With the rapid development of industrial automation and precision manufacturing, vision measurement systems have been widely used in the inspection of geometric parameters such as dimensions, position, and concentricity. In actual production, it is often necessary to measure products of different heights within the same batch, or multiple feature surfaces with height differences on the same product. To ensure clear imaging, the camera's Z-axis usually needs to move up and down to focus on products of different heights.

[0003] Existing vision measurement systems generally suffer from measurement errors due to hardware mechanical structures when measuring objects of different heights. Z-axis non-perpendicularity error: Due to limitations in machining and assembly precision, the direction of the camera's movement along the Z-axis guide rail often cannot maintain absolute perpendicularity with the XY plane carrying the material. When the camera moves up and down along the Z-axis to focus, it will produce parasitic displacement in the XY plane, resulting in inconsistent measurement coordinates of the same product at different Z-axis heights.

[0004] Optical axis tilt error: Even if the Z-axis guide is perfectly perpendicular to the XY platform, if the optical center axis (optical axis) of the camera is not perpendicular to the XY plane, the center of the imaging plane will shift as the height of the object changes.

[0005] Currently, the closest existing technology in the industry is to use high-precision stepped blocks for calibration compensation. Specifically, this involves machining a physical calibration block with multiple steps of known precise height, and machining perfectly concentric circles or crosshairs on each step surface. The Z-axis offset compensation is calculated by measuring the coordinate differences of the marks on steps of different heights.

[0006] However, this existing technology, which relies on high-precision step blocks, has significant problems: Firstly, the machining of ultra-high precision (micron-level concentricity) three-dimensional stepped blocks is extremely difficult and the manufacturing cost is high; Secondly, during calibration, it is unavoidable to move or reposition the calibration block. This manual physical displacement error will directly mix into the calibration data, reducing the calibration accuracy. Third, because the stepped blocks need to be used repeatedly over a long period of time, the markings on their surface are easily worn, and the metal structure is easily affected by the temperature and humidity of the environment, causing thermal expansion and contraction deformation, which leads to the decay of calibration accuracy over time and high maintenance costs.

[0007] Therefore, how to provide a Z-axis height compensation calibration device that does not rely on expensive high-precision three-dimensional calibration blocks and can eliminate physical placement errors during the calibration process is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0008] In order to overcome the shortcomings and deficiencies of the existing technology, the purpose of this invention is to provide a calibration method and device for Z-axis height position compensation of XY coordinates based on optical flat crystal. The device utilizes the principle of optical flat crystal refraction to change the optical path, and replaces the mechanical step block by equivalently raising the imaging height, thereby completing high-precision offset compensation calibration without any movement of the physical position of the calibration object.

[0009] This invention is achieved through the following technical solution: In a first aspect, the present invention discloses a calibration method for XY coordinates based on Z-axis height position compensation using a flat crystal, which includes the following steps: S1. Fix the calibration reference on the platform, and move the camera without placing the parallel crystal. Axial focus is achieved, and the measurement coordinates of the calibration reference center are obtained. At the same time, record the camera's... Axis position ; S2. Place the parallel crystal on the calibration reference surface and move the camera again. Axial focus is clear, and measurement coordinates are obtained from the same calibration reference center. At the same time, record the camera's... Axis position ; S3. Actual measurement after focus is clear. Axis position difference, calculate equivalent height change ; S4. Calculate the offset coefficient caused by unit height change. , ; S5. When actually measuring a product of unknown height, the actual product in focus should be used as the reference. Axis position Its initial measurement coordinates After correction, the compensated coordinates are obtained. The compensation formula is:

[0010] .

[0011] In conjunction with the first aspect, further, in step S2, the parallel crystal includes at least two parallel crystals with different thicknesses; Parallel crystals of different thicknesses are placed individually on the calibration reference surface for calibration. The Z-axis position and coordinates when the focus is clear are recorded each time. Combined with the recorded data in step S1, multiple sets of offset coefficients are calculated. The average offset coefficient is obtained by averaging the multiple sets of offset coefficients. and ; In step S5, the average offset coefficient is... and Substitute into the compensation formula and replace the original and Perform coordinate compensation correction.

[0012] In conjunction with the first aspect, further, in step S1 or step S2, the process of obtaining the coordinates of the calibration reference center specifically includes: controlling the camera to acquire an image containing the calibration reference, extracting the pixel coordinates of the calibration reference center in the image, and converting them into corresponding physical millimeter coordinates.

[0013] In conjunction with the first aspect, furthermore, during the entire calibration process from step S1 to step S2, the calibration reference remains stationary relative to the platform.

[0014] In conjunction with the first aspect, further, in step S5, the actual measurement is based on the acquired compensated coordinates. and Calculate the product's concentricity, position, or geometric dimensional parameters.

[0015] Secondly, the present invention discloses a calibration device for Z-axis height position compensation XY coordinates based on a flat crystal, used to run the calibration method described above, comprising: A fixed platform is used to support the product under test or the calibration reference so that the physical position of the reference remains unchanged during the calibration process; The calibration reference is placed and fixed on the fixed platform; A parallel crystal, comprising at least one light-transmitting parallel plate having a known thickness and refractive index, configured to be placed on the calibration reference surface during the calibration phase; The motion module provides displacement travel along the Z-axis. A camera assembly, mounted on the motion module, is configured to move along the Z-axis for focusing and image acquisition; The control and calculation unit is communicatively connected to the motion module and the camera assembly, and is configured to perform Z-axis motion control, acquire Z-axis position, extract coordinates, calculate offset coefficients, and execute coordinate compensation formulas.

[0016] In conjunction with the second aspect, the camera assembly further includes an industrial camera and a telecentric lens; the device also includes a parallel backlight located below the fixed platform to provide collimated illumination.

[0017] In conjunction with the second aspect, the parallel crystal is further described as an optical-grade parallel flat crystal with a parallelism of better than 2 μm between its upper and lower surfaces; when the parallel crystal comprises multiple pieces, each piece of parallel crystal has a different thickness specification.

[0018] The beneficial effects of this invention are: The present invention provides a calibration device for Z-axis height position compensation of XY coordinates based on a flat crystal. By introducing a parallel crystal and placing it on the calibration reference, the device utilizes the refraction image shift effect generated by light passing through the parallel crystal to effectively raise the focusing imaging height of the camera.

[0019] During the calibration data acquisition process, the calibration reference is fixed on the platform and remains absolutely still, which fundamentally isolates the mechanical placement error introduced by repeated insertion and removal and movement of calibration blocks in traditional methods. At the same time, the device eliminates the need for high-precision three-dimensional stepped calibration blocks that are difficult to process and expensive. It only requires a conventional planar calibration plate combined with a parallel crystal to complete the calibration of system errors, effectively reducing equipment costs and long-term maintenance costs. Attached Figure Description

[0020] The present invention will be further described with reference to the accompanying drawings, but the embodiments in the drawings do not constitute any limitation on the present invention. For those skilled in the art, other drawings can be obtained based on the following drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the calibration device provided in an embodiment of the present invention.

[0022] Figure Labels Fixed platform--100, calibration reference--101, parallel crystal--102, motion module--103, camera assembly--104, parallel backlight--106. Detailed Implementation

[0023] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0024] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0025] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0026] like Figure 1 As shown, this embodiment discloses a calibration device for Z-axis height position compensation XY coordinates based on a flat crystal, which includes a fixed platform 100, a calibration reference 101, a parallel crystal 102, a motion module 103, a camera assembly 104, and a control and calculation unit.

[0027] The fixed platform 100 is used to support the product under test or the calibration reference 101, and the position of the product or the calibration reference 101 remains unchanged during the calibration process. The calibration reference 101 is fixedly set on the fixed platform 100 and is used to determine the center position during calibration. The parallel crystal 102 is at least one optically parallel flat plate with a known thickness and refractive index. During the calibration stage, it is placed on the surface of the calibration reference 101 to change the equivalent imaging height. Preferably, the parallel crystal 102 is an optically grade parallel flat crystal, and the parallelism of its upper and lower surfaces is better than that of the standard parallel crystal. The camera assembly 104 is mounted on a motion module 103 that can move along the Z-axis; the device also includes a parallel backlight 106 located below the fixed platform 100 for providing collimation illumination; the control and computing unit is configured to control Z-axis movement, acquire images, calculate measurement values, and establish calibration mapping.

[0028] Example 1 The hardware parameters provided in this embodiment are as follows: Camera assembly 104 uses a 5-megapixel industrial camera (pixel size...). Paired with a telecentric lens (magnification) Telecentricity The Z-axis travel of motion module 103 is 50mm, and the repeatability is... The parallel backlight 106 uses green light with a wavelength of 525nm. The calibration reference 101 uses a ceramic calibration plate. The parallel crystal 102 is made of K9 glass with a thickness of [missing information]. refractive index .

[0029] The following are the specific steps for calibration and compensation in this embodiment.

[0030] Step 1: Fix the ceramic calibration plate onto the fixed platform 100, and move the motion module 103 to adjust the Z-axis height until the camera assembly 104 is in focus. The control and calculation unit records the height at this point. The camera assembly 104 acquires images, extracts the center pixel coordinates of the calibration board, and converts them into corresponding millimeter coordinates. .

[0031] Step 2: Place the parallel crystal 102 directly on the calibration plate, move the Z-axis again until it is in focus, and record the height at this point. The camera component 104 acquires images, extracts the pixel coordinates of the same reference center, and converts them into corresponding millimeter coordinates. .

[0032] Step 3: Calculate the equivalent height change using the measured height difference after the image is in focus. .

[0033] Step 4: Calculate the offset coefficient as well as .

[0034] Step 5: Establish the compensation formula. When actually measuring products with unknown heights, establish the compensation formula based on the measured Z-axis height. Compensation will be provided. , .

[0035] Example 2 To further improve the consistency of compensation within different height ranges and reduce single calibration errors, this embodiment uses two parallel crystals of different thicknesses for calibration calculations.

[0036] Parallel crystal A: K9 glass, thickness t = 65.00 mm; Parallel crystal B: K9 glass, thickness t = 40.00 mm. Other hardware parameters are the same as in Example 1.

[0037] The following are the specific steps for calibration and compensation in this embodiment.

[0038] Crystal-free reference measurement: Obtaining the Z-axis position when in focus and the millimeter coordinates of the calibration plate center .

[0039] Crystal A Measurement: Place crystal A with a thickness of 40mm, refocus, and record the Z-axis position. and millimeter coordinates Calculate the first set of offset coefficients: , .

[0040] Measurement of Crystal B: Remove Crystal A and place Crystal B (65mm thick) on the calibration plate. Repeat the focusing and coordinate extraction steps described above to obtain the second set of offset coefficients. and .

[0041] Calculate the average coefficient: Take the mean of the two sets of coefficients to smooth out the error, that is... , .

[0042] In actual measurements, the mean coefficient is substituted into the coordinate compensation formula for correction.

[0043] Actual measurement verification: To verify the technical effectiveness of this solution, a true concentricity was used. The standard circular ring was tested, and measurements were taken at three heights: 0mm, 5mm, and 10mm. The concentricity results before and after compensation were compared.

[0044] Comparison of height measurement data: At a height of 0mm (reference), the camera's Z position is 50mm, and the true concentricity is... The concentricity measured before and after compensation was both ; At a height of 5mm, the camera's Z position is 47.84mm, and the true concentricity is 8μm. The concentricity measured before compensation was 11.8μm, and the concentricity measured after compensation decreased to 8.3μm.

[0045] At a height of 10mm, the camera's Z position is 43.52mm, and the true concentricity is 8μm. Before compensation, the concentricity was increased to 15.6μm, and after compensation, the concentricity was measured to be 8.1μm.

[0046] Analysis revealed that without compensation, the maximum measurement deviation reached +7.4 μm and the standard deviation was 3.7 μm as the product height increased. After calibration and compensation using the device of this invention, the maximum deviation at different heights was significantly reduced to +0.3 μm and the standard deviation to 0.1 μm, with a consistency improvement rate of approximately 96%. After compensation, the concentricity measurement results of products at different heights were highly consistent, effectively eliminating the measurement offset caused by height changes. In summary, the present invention provides a calibration device for Z-axis height position compensation of XY coordinates based on a flat crystal. By introducing a parallel crystal and placing it on the calibration reference, the device utilizes the refraction image shift effect generated by light passing through the parallel crystal to effectively raise the focusing imaging height of the camera.

[0047] During the calibration data acquisition process, the calibration reference is fixed on the platform and remains absolutely still, which fundamentally isolates the mechanical placement error introduced by repeated insertion and removal and movement of calibration blocks in traditional methods. At the same time, the device eliminates the need for high-precision three-dimensional stepped calibration blocks that are difficult to process and expensive. It only requires a conventional planar calibration plate combined with a parallel crystal to complete the calibration of system errors, effectively reducing equipment costs and long-term maintenance costs.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A calibration method for XY coordinates based on Z-axis height position compensation using a flat crystal, characterized in that, Includes the following steps: S1. Fix the calibration reference on the platform, and move the camera without placing the parallel crystal. Axial focus is achieved, and the measurement coordinates of the calibration reference center are obtained. At the same time, record the camera's... Axis position ; S2. Place the parallel crystal on the calibration reference surface and move the camera again. Axial focus is clear, and measurement coordinates are obtained from the same calibration reference center. At the same time, record the camera's... Axis position ; S3. Actual measurement after focus is clear. Axis position difference, calculate equivalent height change ; S4. Calculate the offset coefficient caused by unit height change. , ; S5. When actually measuring a product of unknown height, the actual product in focus should be used as the reference. Axis position Its initial measurement coordinates After correction, the compensated coordinates are obtained. The compensation formula is: 。 2. The calibration method according to claim 1, characterized in that, In step S2, the parallel crystal comprises at least two parallel crystals with different thicknesses; Parallel crystals of different thicknesses are placed individually on the calibration reference surface for calibration. The Z-axis position and coordinates when the focus is clear are recorded each time. Combined with the recorded data in step S1, multiple sets of offset coefficients are calculated. The average offset coefficient is obtained by averaging the multiple sets of offset coefficients. and ; In step S5, the average offset coefficient is... and Substitute into the compensation formula and replace the original and Perform coordinate compensation correction.

3. The calibration method according to claim 1 or 2, characterized in that, In step S1 or step S2, the process of obtaining the coordinates of the calibration reference center specifically includes: controlling the camera to acquire an image containing the calibration reference, extracting the pixel coordinates of the calibration reference center in the image, and converting them into the corresponding physical millimeter coordinates.

4. The calibration method according to claim 1, characterized in that, Throughout the calibration process from step S1 to step S2, the calibration reference remains stationary relative to the platform.

5. The calibration method according to claim 1, characterized in that, In step S5, the actual measurement is based on the acquired compensated coordinates. and Calculate the product's concentricity, position, or geometric dimensional parameters.

6. A calibration device for Z-axis height position compensation XY coordinates based on a flat crystal, used to run the calibration method as described in any one of claims 1-5, characterized in that, include: A fixed platform is used to support the product under test or the calibration reference so that the physical position of the reference remains unchanged during the calibration process; The calibration reference is placed and fixed on the fixed platform; A parallel crystal, comprising at least one light-transmitting parallel plate having a known thickness and refractive index, configured to be placed on the calibration reference surface during the calibration phase; The motion module provides displacement travel along the Z-axis. A camera assembly, mounted on the motion module, is configured to move along the Z-axis for focusing and image acquisition; The control and calculation unit is communicatively connected to the motion module and the camera assembly, and is configured to perform Z-axis motion control, acquire Z-axis position, extract coordinates, calculate offset coefficients, and execute coordinate compensation formulas.

7. The calibration device for Z-axis height position compensation XY coordinates based on flat crystal as described in claim 6, characterized in that: The camera assembly includes an industrial camera and a telecentric lens; the device also includes a parallel backlight located below the fixed platform to provide collimated illumination.

8. The calibration device for Z-axis height position compensation XY coordinates based on flat crystal as described in claim 6, characterized in that: The parallel crystal is an optical-grade parallel flat crystal with a parallelism of better than 2μm on its upper and lower surfaces; when the parallel crystal comprises multiple pieces, each piece of parallel crystal has a different thickness specification.

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