Device and method for measuring scratch depth of optical element by using polarization imaging

Abstract

The invention relates to a device and method for measuring the scratch depth of an optical element through polarization imaging, and the device comprises an illumination module, a polarization module, an optical element bearing module, an imaging module, and an image collection module. The polarization module comprises a polarizer for polarizing a light path and a polarization analyzer for analyzing the polarization of the light path; the optical element bearing module is arranged between the polarizer and the analyzer; the imaging module is arranged on the polarization analyzer and is used for optical imaging; the image acquisition module acquires an image of the imaging module. The method for measuring the scratch depth of the optical element comprises six steps of opening a light source, polarizing, transmitting an element to be measured, analyzing polarization, calculating a polarized image and calculating the scratch depth. The time-sharing polarization imaging system is used for firstly measuring the phase delay amount caused by the scratch, then the scratch depth is measured in combination with the mathematical relationship between the scratch depth and the phase delay amount, the scratch depth can be automatically measured, the detection speed is high, the precision is high, and the scratch position and the scratch depth can be detected.

Description

Technical Field

[0001] This invention belongs to the field of optical component inspection, and particularly relates to a device and method for measuring the scratch depth of optical components using polarization imaging. Background Technology

[0002] Optical components are widely used in various fields and are an important part of optical systems. Due to limitations in modern manufacturing technology, optical components inevitably develop various defects such as scratches during actual production and processing. Scratch depth is an important indicator of the surface quality of optical components and plays a crucial guiding role in ensuring their quality, performance, and reliability. Therefore, the measurement of scratch depth of optical components is of great significance.

[0003] Currently, the main methods for measuring the scratch depth of optical components are visual inspection and contact measurement. Visual inspection uses a high-magnification optical microscope to observe the scratch and measures it by comparing the scratch with a standard sample or a reference scratch of known depth. Contact measurement, represented by a profilometer, measures the scratch depth through the interaction between a probe and the surface.

[0004] However, traditional visual methods use high-magnification optical microscopes to observe scratches and measure them by comparing the scratches with standard samples or reference scratches of known depth. However, their resolution is limited, and they cannot provide sufficient accuracy for shallow or minute scratches. Contact measurement methods, such as profilometers, measure scratch depth through the interaction between a probe and a surface. However, these methods are slow and can easily cause secondary damage to components. Summary of the Invention

[0005] The present invention addresses the problems existing in the prior art. Specifically, the technical problem to be solved by the present invention is to provide a device and method for measuring the scratch depth of optical elements using polarization imaging. The device and method are reasonably designed to achieve non-destructive and accurate measurement of the scratch depth of optical elements.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a device for measuring the scratch depth of an optical element using polarization imaging, comprising an illumination module, a polarization module, an optical element carrier module, an imaging module, and an image acquisition module. The illumination module is used to provide an imaging optical path from bottom to top. The polarization module includes a polarizer located above the illumination module for polarizing the optical path, and an analyzer located above the polarizer for analyzing the polarization of the optical path. The optical element carrier module is disposed between the polarizer and the analyzer. The imaging module is disposed above the analyzer and is used for optical imaging. The image acquisition module is disposed above the imaging module and is used to acquire images from the imaging module.

[0007] Furthermore, the polarizer and analyzer of the polarization module are both linear polarizers, and the extinction ratio of both the polarizer and analyzer is greater than 1000:1.

[0008] Furthermore, the polarization module also includes an electric rotary table, on which the analyzer is supported, and the electric rotary table drives the analyzer to rotate in an oriented manner.

[0009] Furthermore, it also includes a control module, the output of which is connected to the input of the electric rotary table carrying the analyzer, and is used to control the analyzer to achieve directional rotation.

[0010] Furthermore, the imaging module is a high-resolution telecentric lens; the image acquisition module includes a camera and a computer, and the high-resolution telecentric lens is threadedly connected to the camera; the camera uses a hard-triggered image acquisition method to automatically acquire polarization images in the corresponding direction after the analyzer is rotated to a specified position; the input terminal of the computer is connected to the output terminal of the camera, and the computer is used to display the polarization images acquired by the camera and to perform calculations and processing on the images.

[0011] Furthermore, the lighting module is a telecentric collimated LED white light source; it also includes an XYZ axis position adjustment module, and the optical element carrying module is positioned in the X, Y, and Z axis directions by the XYZ axis position adjustment module.

[0012] Furthermore, it also includes a support module, which includes a planar base and a vertical guide rail. The vertical guide rail is set on the planar base. The illumination module, polarization module, optical element carrier module and image acquisition module are each connected to the vertical guide rail via sliders. The imaging module is connected to the image acquisition module.

[0013] Another technical solution adopted in this invention is: a method for measuring the scratch depth of an optical element using polarization imaging, the method comprising the following steps: Step S1: Turn on the telecentric collimated LED white light source. The beam emitted by the light source will produce linearly polarized light after passing through the polarizer. Step S2: Place the optical element under test on the optical element carrier module, and use the XYZ axis position adjustment module to adjust the position of the optical element under test so that the center of the optical element under test is on the same optical axis as the center of the telecentric collimated LED white light source, polarizer, analyzer, and high-resolution telecentric lens, and complete the focusing of the surface of the optical element under test; after the linearly polarized light in step S1 is transmitted through the optical element under test, the polarization state of the transmitted light changes; Step S3: Start the electric rotary table. The electric rotary table starts to drive the analyzer to rotate. It stops every 45° and repeats this four times. The transmitted light passes through the above-mentioned analyzers with four different polarization directions to generate four beams of outgoing light. Step S4: After the four outgoing beams in step S3 are imaged by the high-resolution telecentric lens, the camera hardware triggers the acquisition of four polarization images, which are then displayed and saved in the computer in a timely manner, and the light intensity of these four outgoing beams is recorded. Step S5: Use a computer to calculate the phase delay of the four polarization images from step S4. Images; Step S6: Based on the phase delay amount With scratch depth The depth of the scratch is calculated using mathematical relationships. .

[0014] Furthermore, the light intensity emitted by the telecentric collimated LED white light source in step S1 can be expressed as I; the surface of the optical element under test in step 2 contains scratches, and the polarization information of the transmitted light includes the phase delay caused by the scratches. In step S3, the polarization direction of the analyzer makes angles of 0°, 45°, 90°, and 135° with the polarization direction of the polarizer, respectively; the light intensities of the four outgoing beams in step S4 can be represented as I1, I2, I3, and I4, respectively; the phase delay in step 5... The calculation formula is: .

[0015] Furthermore, the phase delay in step S6 With scratch depth The mathematical relationship is expressed as: The coefficients a and b are fitted using standard elements of the same material with known scratch depths.

[0016] Compared with the prior art, the present invention has the following advantages: The present invention utilizes a time-division polarization imaging system to first measure the magnitude of the phase delay caused by the scratch, and then combines the mathematical relationship between the scratch depth and the phase delay to measure the scratch depth. Moreover, during the measurement process, it is only necessary to manually place the component under test and then start the device to realize the automatic measurement of the scratch depth. It has a fast detection speed and high accuracy, and is a visual non-destructive testing method that can both detect the scratch position and measure the scratch depth. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of an embodiment of the present invention; Figure 2 This is a flowchart of an embodiment of the present invention; Figure 3 This is a schematic diagram of the optical path according to an embodiment of the present invention; Figure 4 It is a mathematical graph showing the relationship between phase delay and scratch depth.

[0018] In the picture: 1-Telecentric collimated LED white light source; 2-Polarizer; 3-Optical element carrier module; 4-Analyzer; 5-High resolution telecentric lens; 6-Camera; 7-Computer; 8-Control module; 9-Planar base; 10-Vertical guide rail; 11-Optical path; 12-Optical element under test. Detailed Implementation

[0019] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0020] In the description of this invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this invention, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0021] like Figures 1-2 As shown, this invention discloses a device for measuring the scratch depth of an optical element using polarization imaging. The device includes an illumination module, a polarization module, an optical element carrier module, an imaging module, and an image acquisition module. The illumination module provides an imaging optical path from bottom to top. The polarization module includes a polarizer 2 located above the illumination module and used to polarize the optical path, converting the natural light emitted by the illumination module into linearly polarized light. Above the polarizer 2 is an analyzer 4 used to analyze the polarization of the optical path. The optical element carrier module is positioned between the polarizer 2 and the analyzer 4, carrying the optical element under test, whose surface contains scratches. The imaging module is positioned above the analyzer 4 and used for optical imaging. The image acquisition module is positioned above the imaging module and used to acquire images from the imaging module.

[0022] In this embodiment, both the polarizer 2 and the analyzer 4 of the polarization module are linear polarizers. The polarizer 2 has a diameter of 50.8 mm and a thickness of 2.5 mm. Furthermore, the extinction ratio of both the polarizer 2 and the analyzer 4 is greater than 1000:1.

[0023] In this embodiment, the polarization module further includes an electric rotary table, on which the analyzer 4 is supported and rotated in an oriented manner. The electric rotary table embeds a stepper motor and a driver.

[0024] In this embodiment, a control module 8 is also included. The output of the control module 8 is connected to the input of the electric rotary table carrying the polarizer 4, and is used to control the polarizer 4 to achieve directional rotation. Specifically, the control module 8 contains a controller, a 24V DC power supply, and a relay. The output of the controller is connected to the input of the electric rotary table carrying the polarizer 4, and is used to control the polarizer 4 to achieve directional rotation. Furthermore, the controller's electrical control box has a "start" button on its surface.

[0025] In this embodiment, the imaging module is a high-resolution telecentric lens 5, used for optical imaging. It can eliminate the difference in magnification caused by the distance between objects within a certain object distance range, and the distortion is minimal.

[0026] In this embodiment, the image acquisition module includes a 20-megapixel monochrome industrial camera 6 and a computer 7. The high-resolution telecentric lens 5 is threadedly connected to the camera 6, and the input terminal of the computer 7 is connected to the output terminal of the camera 6. The camera 6 is used to automatically acquire polarization images in the corresponding direction after the analyzer 4 rotates to a designated position. The computer 7 is used to display the polarization images acquired by the camera 6 and to perform calculations and processing on the images. Furthermore, the camera 6 uses a hard-triggered image acquisition method to automatically acquire polarization images in the corresponding direction after the analyzer 4 rotates to a designated position.

[0027] In this embodiment, the lighting module is a telecentric collimated LED white light source 1 with an output spot diameter of 40mm, a rated voltage of 3V, a rated power of 10W, and adjustable light intensity.

[0028] In this embodiment, the optical element carrier module 3 is used to place the optical element under test, and its light-transmitting aperture is 30mm. It also includes an XYZ axis position adjustment module, which adjusts the position of the optical element carrier module 3 along the X, Y, and Z axes. Furthermore, the adjustment range of the X-axis for the XYZ axis position adjustment module is -10mm ≤ x ≤ 10mm, the adjustment range for the Y-axis is 0 ≤ y ≤ 10mm, and the adjustment range for the Z-axis is -20mm ≤ z ≤ 20mm.

[0029] In this embodiment, a support module is also included for supporting and fixing the other modules. The support module includes a planar base 9 and a vertical guide rail 10. The vertical guide rail 10, the control module 8, and the computer 7 are all mounted on the planar base 9. The illumination module, polarization module, optical element carrier module, and image acquisition module are each connected to the vertical guide rail 10 via sliders and are distributed sequentially along the light path direction output by the illumination module. The height position of each module can be adjusted by moving the sliders along the vertical guide rail 10. The imaging module is connected to the image acquisition module, and the height positions of the two are adjusted synchronously.

[0030] This invention discloses a method for measuring the scratch depth of an optical element using polarization imaging, implemented through the aforementioned device, such as... Figure 2 As shown, the method includes the following steps: Step S1: Turn on the telecentric collimated LED white light source 1, the intensity of the light beam emitted by it is I, and linearly polarized light is generated after passing through the polarizer 2; Step S2: Place the optical element under test 12 on the optical element carrier module 3, and use the XYZ axis position adjustment module to adjust the position of the optical element under test 12 so that the center of the optical element under test 12 is on the same optical axis as the center of the telecentric collimated LED white light source 1, polarizer 2, analyzer 4, and high-resolution telecentric lens 5, and complete the focusing of the surface of the optical element under test 12; the surface of the optical element under test 12 contains scratches, and after the linearly polarized light in step S1 is transmitted through the optical element under test, the polarization state of the transmitted light changes, and the polarization information of the transmitted light includes the phase delay caused by the scratches. ; Step S3: After confirming that the electric rotary table is in the initial position, start the electric rotary table. The electric rotary table starts to drive the analyzer 4 to rotate, pausing every 45°, and repeating this four times. The polarization direction of the analyzer 4 is at an angle of 0°, 45°, 90° and 135° with the polarization direction of the polarizer 2, respectively. The transmitted light generates 4 beams of outgoing light after passing through the above-mentioned analyzers 4 with 4 different polarization directions. Step S4: After the four outgoing beams in step S3 are imaged by the high-resolution telecentric lens 5, the camera 6 hardware triggers the acquisition of four polarization images, which are then displayed and saved in the computer 7 in a timely manner. The light intensities of these four outgoing beams are recorded as I1, I2, I3, and I4, respectively. Step S5: Use computer 7 to calculate the phase delay of the four polarization images from step S4. Image, phase delay The calculation formula is: ; Step S6: Based on the phase delay amount With scratch depth The depth of the scratch is calculated using mathematical relationships. Phase delay With scratch depth The mathematical relationship is expressed as: .

[0031] In this embodiment, the phase delay amount The calculation formula is explained as follows: Figure 3 Given the optical path diagram shown, and considering that the light intensity of the monochromatic light source S is I, its Stokes parameter can be expressed as:

[0032] Polarizer M1 is an ideal horizontal linear polarizer, and its Mueller matrix is:

[0033] The element under test, M2, is a defective optical element that can be considered to make an angle θ with the x-axis, with a phase delay of... The waveplate has the following Mueller matrix:

[0034] Rotate the analyzer (linear polarizer) to make angles of 0°, 45°, 90°, and 135° with the x-axis, respectively. Their Mueller matrices are as follows:

[0035]

[0036]

[0037]

[0038] The Stokes parameters of the emitted beam S' are as follows:

[0039]

[0040]

[0041]

[0042] The coefficient of the Stokes parameter of the emitted light is the light intensity detected by the camera, therefore:

[0043] The stress phase delay can be calculated from equation (12). The stress direction angle θ is:

[0044]

[0045] As can be seen from equations (13) and (14), the phase retardation of the optical element can be calculated simply by acquiring four images with different polarization directions and recording their respective light intensities. and the stress direction angle θ.

[0046] In this embodiment, the phase delay amount With scratch depth The coefficients a and b in the mathematical relationship are related to the material of the optical element being measured. These two coefficients differ for different materials. The coefficients a and b are fitted using a standard element of the same material with a known scratch depth. (Phase retardation) With scratch depth The following is an example of a method for fitting the coefficients a and b in the mathematical formula of an optical element made of a certain material.

[0047] Table 1 shows the reference values ​​for scratch depth of standard samples measured using a profilometer. .

[0048] Table 1 Reference values ​​for scratch depth

[0049] The phase delay at the location of each of the five scratch samples was detected using the method described in the patent. Five pixels were taken from the same scratch to measure the phase delay, and then the mean and standard deviation were calculated. The mean was used as the measured phase delay value for that scratch. The measured results are shown in Table 2.

[0050] Table 2. Measurement values ​​of scratch phase delay.

[0051] Use the scratch depth reference values ​​in Table 1 Using the average scratch phase delay in Table 2 as the x-axis, a coordinate graph was plotted with the average scratch phase delay as the y-axis, and the fitted straight line was calculated. Scratch depth reference value. Mean phase delay The relationship is basically linear, and the functional relationship of the fitted line is: That is, coefficient a = 0.05324, coefficient b = 0.22005, such as Figure 4 As shown. This allows us to obtain the phase retardation of the lens made of this material. With scratch depth The mathematical relationship.

[0052] The device of this invention includes a support module, an illumination module, a polarization module, an optical element carrier module, an image acquisition module, and a control module. The method for measuring the scratch depth of an optical element includes six steps: turning on a telecentric collimated LED white light source, polarization, transmitting the image to the element under test, polarization analysis, polarization image calculation, and scratch depth calculation. By employing a time-division polarization imaging system, the phase delay caused by the scratch is first measured, and then the corresponding mathematical relationship is used to measure the scratch depth. This ensures that no damage to the optical element under test is introduced during the measurement process, simplifying the experimental steps, reducing operational difficulty, and allowing for more direct data acquisition, thus improving measurement efficiency and accuracy. It achieves the goal of measuring both the scratch location and scratch depth.

[0053] The advantages of this invention are: by using a time-division polarization imaging system, the magnitude of the phase delay caused by the scratch is first measured, and then the scratch depth is measured by combining the mathematical relationship between the scratch depth and the phase delay; during the measurement process, the scratch depth can be automatically measured simply by manually placing the component under test and pressing the start button on the controller. It has a fast detection speed, high accuracy, and is a visual non-destructive testing method that can detect both the scratch location and the scratch depth.

[0054] If this invention discloses or relates to components or structural parts that are fixedly connected to each other, then, unless otherwise stated, a fixed connection can be understood as: a fixed connection that can be detached (e.g., using bolts or screws), or a fixed connection that cannot be detached (e.g., riveting, welding). Of course, a fixed connection can also be replaced by an integral structure (e.g., manufactured in one piece using a casting process) (except where it is obviously impossible to use an integral molding process).

[0055] In addition, unless otherwise stated, the terms used in any of the technical solutions disclosed in this invention to indicate positional relationships or shapes include states or shapes that are similar to, close to, or approximate with those states or shapes.

[0056] Any component provided by this invention can be assembled from multiple individual components or can be a single component manufactured by a one-piece molding process.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them; although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of the present invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the technical solutions claimed in the present invention.

Claims

1. A device for measuring the scratch depth of an optical element using polarization imaging, characterized in that: The system includes an illumination module, a polarization module, an optical element carrier module, an imaging module, and an image acquisition module. The illumination module provides an imaging optical path from bottom to top. The polarization module includes a polarizer (2) located above the illumination module for polarizing the optical path, and an analyzer (4) located above the polarizer (2) for analyzing the optical path. The optical element carrier module is located between the polarizer (2) and the analyzer (4). The imaging module is located above the analyzer and is used for optical imaging. The image acquisition module is located above the imaging module and is used to acquire images from the imaging module.

2. The apparatus for measuring the scratch depth of an optical element using polarization imaging according to claim 1, characterized in that: The polarizer (2) and analyzer (4) of the polarization module are both linear polarizers, and the extinction ratio of the polarizer (2) and analyzer (4) is greater than 1000:

1.

3. The apparatus for measuring the scratch depth of an optical element using polarization imaging according to claim 1 or 2, characterized in that: The polarization module also includes an electric rotary table, and the analyzer (4) is carried by the electric rotary table, which drives the analyzer (4) to rotate in an orientation.

4. The apparatus for measuring the scratch depth of an optical element using polarization imaging according to claim 3, characterized in that: It also includes a control module (8), the output of which is connected to the input of the electric rotary table carrying the analyzer (4), and is used to control the analyzer (4) to achieve directional rotation.

5. The apparatus for measuring the scratch depth of an optical element using polarization imaging according to claim 3, characterized in that: The imaging module is a telecentric lens (5); the image acquisition module includes a camera (6) and a computer (7), the telecentric lens (5) is threadedly connected to the camera (6); the camera (6) uses a hard-triggered image acquisition method to automatically acquire polarization images in the corresponding direction after the analyzer (4) is rotated to a specified position; the input end of the computer (7) is connected to the output end of the camera (6), and the computer (7) is used to display the polarization images acquired by the camera (6) and to perform calculations and processing on the images.

6. The apparatus for measuring the scratch depth of an optical element using polarization imaging according to claim 5, characterized in that: The lighting module is a telecentric collimated LED white light source (1); it also includes an XYZ axis position adjustment module, and the optical element carrying module (3) is adjusted in the X, Y and Z axis directions by the XYZ axis position adjustment module.

7. The apparatus for measuring the scratch depth of an optical element using polarization imaging according to claim 1, characterized in that: It also includes a support module, which includes a planar base (9) and a vertical guide rail (10). The vertical guide rail (10) is set on the planar base (9). The illumination module, polarization module, optical element carrier module and image acquisition module are each connected to the vertical guide rail (10) by a slider. The imaging module is connected to the image acquisition module.

8. A method for measuring the scratch depth of an optical element using polarization imaging, characterized in that: The method includes the apparatus for measuring the scratch depth of an optical element using polarization imaging as described in claim 6, wherein the method comprises the following steps: Step S1: Turn on the telecentric collimated LED white light source (1), and the beam emitted by it will generate linearly polarized light after passing through the polarizer (2); Step S2: Place the optical element under test (12) on the optical element carrier module (3), and use the XYZ axis position adjustment module to adjust the position of the optical element under test (12) so that the center of the optical element under test (12) is on the same optical axis as the center of the telecentric collimated LED white light source (1), polarizer (2), analyzer (4), and telecentric lens (5), and complete the focusing of the surface of the optical element under test (12); After the linearly polarized light in step S1 is transmitted through the optical element under test (12), the polarization state of the transmitted light changes; Step S3: Start the electric rotary table. The electric rotary table starts to drive the analyzer (4) to rotate. It stops every 45° and repeats this four times. The transmitted light passes through the above-mentioned analyzer (4) with four different polarization directions to generate four beams of outgoing light. Step S4: After the four outgoing beams in step S3 are imaged by the telecentric lens (5), the camera (6) hardware triggers the acquisition of four polarization images, which are then displayed and saved in the computer (7) in a timely manner, and the light intensity of these four outgoing beams is recorded. Step S5: Use computer (7) to calculate the phase delay of the four polarization images from step S4. Images; Step S6: Based on the phase delay amount With scratch depth The scratch depth is calculated using mathematical relationships. .

9. The method for measuring the scratch depth of an optical element using polarization imaging according to claim 8, characterized in that: The light intensity emitted by the telecentric collimated LED white light source (1) in step S1 is represented by I; the surface of the optical element (12) under test in step 2 contains scratches, and the polarization information of the transmitted light includes the phase delay caused by the scratches. In step S3, the polarization direction of the analyzer (4) makes angles of 0°, 45°, 90°, and 135° with the polarization direction of the polarizer (2), respectively; the light intensities of the four outgoing beams in step S4 are represented as I1, I2, I3, and I4, respectively; the phase delay in step 5... The calculation formula is: .

10. A method for measuring the scratch depth of an optical element using polarization imaging according to claim 8, characterized in that: Phase delay in step S6 With scratch depth The mathematical relationship is expressed as: The coefficients a and b are fitted using standard elements of the same material with known scratch depths.

Images