A three-point auxiliary positioning method and device for invisible pulse laser processing focus

Abstract

The present invention discloses a three-point auxiliary positioning method and device for invisible pulse laser processing focus. By setting a coaxial pinhole device and combining multiple image algorithms with translation stage feedback, real-time focus tracking is achieved, positioning accuracy is improved, and anti-interference ability is enhanced. There is no need for repeated calibration after the first calibration, which improves processing efficiency. The equilateral triangle structure is used to suppress single-point errors, and the processing defocus amount and whether the vertical processing requirements are met can be quickly determined. The overall cost is reduced and the operational safety is improved. The positioning of the pulse focus is mainly determined by the image acquisition algorithm, and its focus calibration is replaced by three visible light indicator lasers. There is no need to use expensive photoelectric detection equipment. In addition, the entire calibration process is mainly completed by a computer or other controller, avoiding the harm of invisible pulses to operators.

Description

Technical Field

[0001] The present invention relates to the technical field of precision laser processing, and in particular to a three-point auxiliary positioning method and device for an invisible pulse laser processing focus. Background Art

[0002] As an important branch of the advanced manufacturing field, invisible pulse laser processing technology has been widely used in scenarios such as precision instrument manufacturing, microelectronic device processing, and micro-nanostructure preparation. Among them, femtosecond laser processing technology, due to its unique ultrashort pulse characteristics (typical pulse width 1 to 1000fs), shows significant advantages of low thermal damage and universal processing capabilities. Its physical mechanism stems from the non-thermodynamically dominant characteristics of the interaction between ultrafast lasers and matter: during the action of femtosecond pulses, energy is instantaneously deposited on the surface of the material through the multi-photon absorption mechanism, while the electron-phonon coupling process requires a time delay of several picoseconds to tens of picoseconds, and the heat diffusion and material melting process occur on a time scale of tens to hundreds of picoseconds, resulting in the completion of the material ablation process before the thermodynamic response occurs. This transient energy deposition characteristic enables femtosecond lasers to break through the limitations of traditional heat conduction and effectively suppress the expansion of the heat-affected zone. It is defined as a "cold processing" technology, which is particularly suitable for high-precision processing of heat-sensitive materials. Furthermore, femtosecond lasers, with their extremely high peak power density (up to 10 12 ~10 15 W / cm 2 ) and nonlinear absorption characteristics, can achieve sub-diffraction limit processing accuracy, and its action area is strictly localized within the spot size range. For example, ultraviolet femtosecond lasers can break through the processing limits of the visible light band in the processing of metal and metal oxide thin films and obtain nanoscale characteristic structures. During the processing process, the defocus distance between the laser focus and the workpiece surface is the core parameter that determines the processing quality. It is necessary to accurately calibrate the focus position and optimize the defocus distance to achieve the best processing effect. However, due to the lack of intuitive optical signal feedback, the focus position of invisible pulsed lasers (such as ultraviolet or near-infrared bands) cannot be directly observed by conventional CCD imaging, and the focus detection method based on optical imaging is difficult to apply directly. Traditional laser focus calibration methods, including CNC positioning dotting method and burning method, mainly rely on manual methods to determine the focus position by identifying the change trend of the small hole diameter or the size of the "spark" formed by laser ablation during the interaction between the laser and the whiteboard. These solutions require debugging personnel to make judgments based on experience, which is extremely inaccurate. The calibration process cannot quantify data and it is difficult to ensure repeatability. There are also safety risks. Therefore, it is necessary to develop new high-precision, non-contact focus calibration technology to adapt to its processing characteristics.

[0003] Patent CN117309328A discloses a method for determining the focal point and optimal light output position by installing a photoelectric sensor to measure the reflected light intensity of a laser beam. This method converts the photoelectric signal into a light intensity curve, integrates the curve, and then integrates the integrals of multiple consecutive intensity curves into a curve for trend analysis. The laser used in this method has its own visible light guide light. The Z-axis origin of the focal point is determined by directly observing the smallest and brightest point of the guide light spot. However, this method suffers from insufficient positioning accuracy and is unsuitable for invisible lasers without guide light.

[0004] Current methods for locating the laser processing focus typically rely on collecting and detecting reflected photon signals or plasma generated during the interaction between the laser beam and the material being processed. These signals are then processed using equipment equipped with photoelectric detection and conversion capabilities to determine the position of the laser focus spot on the material being processed. These methods rely on the strength of the reflected signal and the sensitivity of the associated detection equipment, making them susceptible to ambient stray light and laser intensity. Furthermore, most observations are made using a guide beam in the visible light band, making them unsuitable for invisible lasers that lack a guide beam. Summary of the Invention

[0005] In order to solve the problems existing in the above-mentioned background technology, the present invention provides a three-point auxiliary positioning method and device for invisible pulse laser processing focus, which realizes high-precision positioning of invisible pulse laser focus without guide light, and does not require repeated calibration after the first calibration. It has the advantages of high precision, high efficiency and low cost, and is suitable for the field of high-end precision manufacturing.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A first aspect of the present invention provides a three-point auxiliary positioning method for an invisible pulse laser processing focus, comprising the following steps:

[0008] S1. Horizontal position positioning:

[0009] The visible processing bright spot produced by the interaction between the pulsed laser and the sample surface is captured by a coaxial CCD camera. The geometric center of the processing bright spot area is extracted using grayscale processing and binarization algorithms, and the relative coordinate values of the laser beam focus in the X and Y directions are calculated.

[0010] S2, Z-axis position positioning:

[0011] Perform local acquisition of the center of the processing bright spot area, determine the optimal focal plane in combination with the image clarity algorithm, and obtain the spatial coordinates (X, Y, Z) of the laser beam focus;

[0012] S3. Indicator laser settings:

[0013] Three visible light indicator lasers are installed in an equilateral triangle layout. Through observation and adjustment, the three indicator light beams emitted by the three visible light indicator lasers are overlapped and pointed to the focal position. The overlapping and visible indicator light spots emitted by the three visible light indicator lasers replace the position of the laser beam focal point for processing guidance;

[0014] S4. Defocus detection and correction:

[0015] If the processing surface deviates from the focal plane, the triangle formed by the indicator light spots in the image captured by the CCD camera will be deformed compared to the set equilateral triangle. The distance values between the indicator light spots in the image captured by the CCD camera are calculated. According to the calculated value, the position of the processing surface is readjusted so that the pulsed laser is perpendicular to the processing plane, and the defocus amount is calculated.

[0016] Specifically, step S4 completes the setting of the indicator light with overlapping light spots at a specific position and the calculation of the laser defocus amount. The visible light indicator laser is located in the visible light band. After obtaining the accurate spatial coordinates (X, Y, Z) of the pulse focus, the multiple indicator light beams are overlapped and pointed to the focal position through observation and adjustment. At this time, the invisible focus is replaced by the visible light spot, and the function of not needing to repeat the calibration after the first calibration is realized during the repeated processing process. Based on the characteristic of excellent collimation of the laser, when there is a distance difference between the processing plane and the focal plane, a specific shape determined by the installation position will be projected on the processing plane. By calculating the distance between each indicator laser point, the Z-direction distance difference between the planes, that is, the defocus amount, can be obtained. Moreover, the parallelism between the processing surface and the focal plane can also be judged according to the deformation of the graphic formed by the indicator laser points. It can be used to judge whether the pulse laser is perpendicular to the processing surface when processing complex curved surface materials.

[0017] Furthermore, in step S1, the CCD camera is synchronously triggered to capture images during pulse laser operation and transmit them to the controller, the captured color image is converted into a grayscale image using a conversion formula, and then a threshold range is set for region segmentation, and finally the relative coordinates of the geometric center of the processing bright spot in the CCD camera field of view are calculated to complete the calibration of the horizontal position of the focus, and the CCD camera field of view coordinates are mapped to the coordinates of the actual processing surface.

[0018] Furthermore, the following formula is used to calculate the relative coordinates of the geometric center of the processing bright spot in the field of view of the CCD camera:

[0019] ;

[0020] ;

[0021] in, The geometric center of the laser beam focus in the image collected by the CCD camera after focusing. are the row and column values of the processed bright spots in the captured image, Indicates the grayscale value of the corresponding coordinate point.

[0022] Preferably, in order to reduce errors, the above-mentioned dotting process can be repeated for multiple positioning calibrations.

[0023] Furthermore, in step S2, a local image acquisition range of 300×300 is first divided with the processing bright spot area as the center, and then the galvanometer system and the field lens are moved upward until the field of view of the CCD camera is blurred, and the distance between the field lens and the processing plane at this time is recorded as f 1, and then control the galvanometer system and the field mirror to move downward with a moving interval of 1 μm, which is recorded as f 1-n, where n=1, 2, 3..., the value of n is determined by the number of moves, and the movement is stopped when blur-clear-blur changes appear in the CCD camera field of view. At the same time, the image information during the movement is saved for subsequent image clarity evaluation and processing, and the image clarity evaluation value is given. The image clarity evaluation value corresponding to the maximum image clarity evaluation value is selected. f The 1-n value is used as the Z coordinate value of the laser beam focus.

[0024] Furthermore, an auxiliary lighting source is arranged around the field lens, and the reflected light on the focal plane passes through the focusing lens coaxially and is then controlled by a pinhole device to enter the CCD camera. The pinhole device is located at the focus of the focusing lens.

[0025] Furthermore, methods for evaluating image clarity include Laplace gradient method, Sobel gradient method or sum of absolute grayscale variance method.

[0026] Furthermore, in step S3, with the laser emission point of the galvanometer system as the center, an equilateral triangle formed by the three visible light indicator lasers is inscribed in a circle with a radius of m. In the initial state, the emission ports of the three visible light indicator lasers and the field lens emission surface are in the same direction and parallel, and an electric reflector is installed under each visible light indicator laser to adjust the direction of the indicator light it emits.

[0027] Furthermore, the direction of the indicator light emitted by each visible light indicator laser is coarsely and finely adjusted respectively by the electric reflector; during the coarse adjustment process, the initial installation deflection angle of each electric reflector is first determined. θ , and make corresponding adjustments, and then adjust the mirror normals of each electric reflector around the spatial Z-axis to intersect with the laser emission optical axis; during the fine-tuning process, according to the spatial coordinates (X, Y, Z) of the laser beam focus obtained in steps S1 and S2, fine-tune the deflection and pitch angles of the electric reflector, so that the indicator light spots emitted by the three visible light indicator lasers overlap at the geometric center of the laser beam focus.

[0028] Furthermore, in step S4, the laser defocus amount d f It is calculated using the following formula:

[0029] ;

[0030] in, is the angle between the indicator light emitted by the visible light indicator laser and the Z-axis direction of the space, is the distance between each indicator light spot obtained in the image collected by the CCD camera, f is the distance from the field lens exit surface to the processing focus, N is the installation distance from the visible light indicator laser to the electric reflector, and m is the horizontal distance from the indicator light emitted by the visible light indicator laser to the laser exit optical axis.

[0031] The second aspect of the present invention provides a three-point auxiliary positioning device for invisible pulse laser processing focus, which is used to implement the above-mentioned three-point auxiliary positioning method, including a laser, a beam expander group, an optical path steering module, a galvanometer system, a field lens, a processing platform, a displacement stage, a focusing lens and a CCD camera; the pulsed laser beam emitted by the laser is collimated by the beam expander group, enters the galvanometer system by the optical path steering module, and is then focused by the field lens on the processing platform, and the distance between the field lens exit surface and the processing platform is adjusted by the displacement stage so that the reflected light on the focal plane can coaxially pass through the focusing lens and enter the image acquisition field of the CCD camera; the distance between the field lens exit surface and the processing platform is adjusted by the displacement stage so that the reflected light on the focal plane can coaxially pass through the focusing lens and enter the image acquisition field of the CCD camera.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) The present invention utilizes the characteristic that the relative position of the light spot in the image captured by the coaxial CCD camera remains unchanged without using a guide light, and combines image algorithms such as grayscale processing and binarization with a local autofocus algorithm to quickly and accurately obtain the spatial position coordinates of the invisible pulse focus;

[0034] (2) A coaxial pinhole device is set between the CCD camera and the focusing lens. By controlling the size of the pinhole aperture, the light signal at the focus is collected, which plays a role in blocking the non-focal plane reflected light and reducing the interference of ambient stray light, thereby enhancing the image resolution and signal-to-noise ratio and improving the focus positioning accuracy;

[0035] (3) Based on the three points determining a plane in the case of non-collinearity, a visible light indicator laser is set around the galvanometer system or field mirror in an equilateral triangle structure, and the invisible pulse focus determined by the position is replaced by a visible indicator light spot, thereby achieving the processing requirement of not needing to repeat calibration after the first calibration. Moreover, by calculating the relative coordinate position of each indicator light spot obtained in the image captured by the CCD camera, when the indicator light spots no longer overlap, the defocus amount of the processing surface at this time can be quickly determined by the distance between the two points. In addition, if the distance between each indicator light spot in the image captured by the CCD camera no longer satisfies the specific relationship of the equilateral triangle, it can be determined that the emitted laser is not processing vertically at this time, and it needs to be adjusted and corrected by controlling the displacement stage;

[0036] (4) In the present invention, by setting up a coaxial pinhole device and combining multiple image algorithms with translation stage feedback, real-time focus tracking is achieved, positioning accuracy is improved, and anti-interference ability is enhanced. After the first calibration, there is no need for repeated calibration, which improves processing efficiency. The equilateral triangle structure is used to suppress single-point errors, and the processing defocus amount and whether the vertical processing requirements are met can be quickly determined. The overall cost is reduced and the operation safety is improved. The positioning of the pulse focus is mainly determined by the image acquisition algorithm. Its focus calibration is replaced by three visible light indicator lasers, and there is no need to use expensive photoelectric detection equipment. In addition, the entire calibration process is mainly completed by a computer or other controller, avoiding the harm of invisible pulses to operators. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0038] Figure 1 Schematic diagram of the structure of the three-point auxiliary positioning device for invisible pulse laser processing focus in Example 1;

[0039] Figure 2 This is a flow chart of the three-point auxiliary positioning method for invisible pulse laser processing focus in Example 2;

[0040] Figure 3 Schematic diagram of the position of the visible light indicator laser installed in an equilateral triangle structure in Example 2;

[0041] Figure 4 This is a schematic diagram of adjusting the visible light indicator laser to point to the focal position at the initial moment in Example 2;

[0042] Figure 5 Schematic diagram of determining the defocus amount of the processing plane and whether vertical processing is performed in Example 2;

[0043] Among them, the specific drawings are marked as follows:

[0044] Laser 1, beam expander group 2, first reflector 3, second reflector 4, galvanometer system 5, field lens 6, annular shadowless lighting source 7, processing platform 8, focusing lens 9, pinhole device 10, CCD camera 11, first visible light indicator laser 12, second visible light indicator laser 13, third visible light indicator laser 14, first electric reflector 15, second electric reflector 16, third electric reflector 17, translation stage 18, controller 19. DETAILED DESCRIPTION

[0045] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0046] Example 1

[0047] This embodiment discloses a three-point auxiliary positioning device for invisible pulse laser processing focus, such as Figure 1 As shown, it includes a laser 1 module consisting of a laser 1 and a beam expander group 2, an optical path steering module consisting of a first reflector 3 and a second reflector 4, a processing module consisting of a galvanometer system 5, a field lens 6, and a processing platform 8, an image acquisition module consisting of a focusing lens 9, a pinhole device 10, a CCD camera 11, and an annular shadowless lighting source 7, an auxiliary lighting source (annular shadowless lighting source 7) is arranged around the field lens 6, an indicator light module consisting of a first visible light indicator laser 12, a second visible light indicator laser 13, a third visible light indicator laser 14, a first electric reflector 15, a second electric reflector 16, and a third electric reflector 17, and a motion control module consisting of a translation stage 18 and a controller 19.

[0048] The laser 1 can be an ultrafast laser 1 such as infrared or ultraviolet. The pulsed laser beam emitted by the laser 1 is collimated by the beam expander group 2, enters the galvanometer system 5 through the optical path steering module, and is then focused by the field lens 6 on the processing platform 8. The distance between the output surface of the field lens 6 and the processing platform 8 is adjusted by the displacement stage 18 so that the reflected light on the focal plane can coaxially pass through the focusing lens 9 and enter the image acquisition field of the CCD camera 11.

[0049] Each optical device is placed along the optical axis, and the light path steering module is adjusted so that the outgoing light of the laser 1 enters the galvanometer system 5 at the geometric center and is emitted by the field lens 6. According to the known working focal length of the field lens 6, the distance between the exit surface of the field lens 6 and the processing platform 8 is adjusted so that the reflected light on the focal plane can pass through the focusing lens 9 coaxially and then be controlled by the pinhole device 10 to enter the image acquisition field of view of the CCD camera 11. The pinhole device 10 is located at the focal point of the focusing lens 9 and is optically conjugate with the center of the focal plane of the processing laser. In theory, only the signal light returning from the focus can be converged and fully pass through the pinhole and be collected by the photodetector. Therefore, the feedback light signal at the focus is the strongest. By adjusting the aperture size of the pinhole device 10, the amount of luminous flux and the ability to block stray light from the off-focus surface are determined, thereby improving the system's recognition accuracy and anti-interference ability.

[0050] Specifically, the actual physical aperture of the coaxially arranged pinhole device 10 needs to match the pixel size and system magnification of the CCD camera 11. Due to the diffraction limit and processing constraints, the equivalent aperture of the pinhole device 10 is typically approximately 1 to 3 times the focal plane spot diameter (e.g., the Airy disk diameter under uniform light intensity distribution). In this case, the aperture of the pinhole device 10 is approximately tens of microns. However, in actual industrial processing, it is necessary to balance the signal-to-noise ratio and signal light flux requirements. Therefore, the aperture of the pinhole device 10 is generally selected in the submillimeter range. In addition, the aperture size of the pinhole device 10 is directly related to the laser wavelength. The longer the wavelength, the larger the focused spot diameter, and the larger the aperture needs to be. For example, infrared light requires a larger pinhole device 10 aperture than ultraviolet light.

[0051] Example 2

[0052] This embodiment discloses a three-point auxiliary positioning method for invisible pulse laser processing focus, such as Figure 2 As shown, the following steps are included:

[0053] S1. Horizontal position positioning:

[0054] Because the image acquisition module and laser processing module are coaxially positioned, and the effective Z-axis processing distance of the galvanometer system 5 is controlled by the translation stage 18, the relative position of the laser beam within the field of view of the CCD camera 11 remains unchanged when the coaxial CCD camera 11 is used to capture images at the processing focal plane. Furthermore, in actual processing, it has been found that although the invisible pulsed laser spot cannot be directly observed, the laser ablation process is visible when a single laser pulse interacts with the sample surface. This is manifested as a distinct bright spot in the CCD camera 11's field of view. This bright spot represents the area where the pulsed laser interacts with the sample surface.

[0055] Therefore, the visible processing bright spot generated by the interaction between the pulsed laser and the sample surface is captured by the coaxial CCD camera 11, and the geometric center of the processing bright spot area is extracted using grayscale processing and binarization algorithms, and the relative coordinate values of the laser beam focus in the X and Y directions are calculated.

[0056] Specifically, the CCD camera 11 is synchronously triggered to capture images during pulse laser operation and transmit them to the controller 19. The optional image resolution is 1024×1280 pixels and the grayscale range is 0 to 255. Then, a conversion formula is used to convert the captured color image into a grayscale image to improve the processing speed. The threshold range is then set for regional segmentation to improve the recognition accuracy of position judgment. Finally, the relative coordinates of the geometric center of the processing bright spot in the field of view of the CCD camera 11 are calculated according to the formula to complete the calibration of the horizontal position of the focus, and the field coordinates of the CCD camera 11 are mapped to the coordinates of the actual processing surface.

[0057] The formula for calculating the relative coordinates of the geometric center of the processing bright spot in the field of view of the CCD camera 11 is as follows:

[0058] ;

[0059] ;

[0060] in, The focus of the laser beam after focusing is the geometric center of the image collected by the CCD camera 11. are the row and column values of the processed bright spots in the captured image, Indicates the grayscale value of the corresponding coordinate point.

[0061] To simplify subsequent processing and reduce computational complexity, a grayscale processing algorithm is used to convert the color image into a grayscale image. For each pixel in the image, a weighted average method is typically used to convert the RGB value into a grayscale value, such as Gray = 0.299R + 0.587G + 0.114B. Binarization is then performed, the goal of which is to segment the bright spot area through strong contrast so that it can be more clearly identified. This is achieved by setting a judgment threshold, which can be manually set based on experience or by using an adaptive threshold method, such as the Otsu algorithm, to adapt to different lighting conditions. All pixels with grayscale values greater than or equal to the threshold are set to white (255), and the rest are set to black (0). At this point, the bright spot area may be several connected white pixel blocks, so a scanning-based connected component marking algorithm is also required to determine which pixels belong to the same area.

[0062] In order to reduce errors, the above-mentioned marking process can be repeated for multiple positioning calibrations.

[0063] S2, Z-axis positioning:

[0064] The position of the laser beam focus after being focused by the field lens 6 in the image captured by the CCD camera 11 can be determined by step S1, which is equivalent to solving the problem of the coordinate positioning of the focus in the X and Y directions of the focal plane. However, the spatial Z coordinate of the focus cannot be determined, that is, the distance from the light-emitting surface of the field lens 6 to the focus. f .

[0065] The Z-focus accuracy of the pulsed laser determines the quality of subsequent laser processing. Although the spot size is invisible, the image of the sample surface can still be captured by the CCD camera 11 with the help of an auxiliary light source (annular shadowless illumination source 7). Therefore, focus determination can be made by evaluating image clarity. However, unlike commonly used autofocus algorithms that capture images from the entire sample surface, the present invention uses a localized capture method based on the center of the processing bright spot area, as determined by the previous positioning algorithm, to minimize deviations in the Z-focus position.

[0066] The specific implementation process is:

[0067] First, a local image acquisition range of 300×300 is divided with the processing bright spot area as the center. Then, the galvanometer system 5 and the field lens 6 are moved upward until the field of view of the CCD camera 11 is blurred, and the distance between the field lens 6 and the processing plane at this time is recorded as f 1. Since the Rayleigh length of the pulsed laser is in the micrometer range, the galvanometer system 5 and the field lens 6 are controlled to move downward at a moving interval of 1 μm, which is recorded as f 1-n, where n=1, 2, 3..., the value of n is determined by the number of moves, and the movement is stopped until a change from blur to clear to blur appears in the field of view of the CCD camera 11. At the same time, the image information during the movement is saved for subsequent image clarity evaluation processing, and an image clarity evaluation value is given. The image clarity evaluation value corresponding to the maximum image clarity evaluation value is selected. f The 1-n value is used as the Z coordinate value of the laser beam focus.

[0068] Specifically, methods for evaluating image clarity include Laplace gradient method, Sobel gradient method or sum of absolute grayscale variance method.

[0069] Furthermore, to enhance the recognition and extraction of surface feature information from processed images, the present invention incorporates a pinhole device 10 between the coaxial CCD camera 11 and the focusing lens 9. The pinhole aperture of the pinhole device 10 extracts the reflected light signal at the focal plane, blocking stray light from off-focus areas and improving anti-interference capabilities. Furthermore, the field lens 6 undergoes achromatic processing, effectively reducing the focus deviation between the visible light band and invisible light, further enhancing positioning accuracy. In specific embodiments, the galvanometer mirror and field lens 6 of the processing module can be replaced with a processing objective lens.

[0070] After steps S1 and S2, the spatial coordinates (X, Y, Z) of the laser beam focus are obtained.

[0071] S3, indicating laser 1 settings:

[0072] A visible light indicator laser 1 is installed at a specific location and superimposed with a pointing laser focus. Replacing the invisible laser focus with a visible light indicator of similar spot size eliminates the need for repeated calibration during subsequent repetitive processing. Based on the principle that three non-collinear points define a plane, an equilateral triangle configuration is chosen as the installation location for the visible light indicator laser 1.

[0073] like Figure 3 As shown, with the laser emission point of the galvanometer system 5 as the center, an equilateral triangle formed by three visible light indicator lasers 1 is inscribed in a circle with a radius of m, and they are marked as the first visible light indicator laser 12, the second visible light indicator laser 13, and the third visible light indicator laser 14. At this time, the visible light indicator laser 1 emits vertically and the emission port is flush with the emission surface of the field lens 6. In order to deflect each indicator light to the pulse focus position, a first electric reflector 15, a second electric reflector 16, and a third electric reflector 17 are installed behind the first visible light indicator laser 12, the second visible light indicator laser 13, and the third visible light indicator laser 14, respectively, and perform coarse and fine adjustments.

[0074] First, make a rough adjustment. Figure 4 In the front view of the indicator light installation shown, the initial installation deflection angle of each electric reflector is determined according to the following formula :

[0075] ;

[0076] ;

[0077] in, is the angle between the indicator light emitted by the visible light indicator laser 1 and the Z-axis direction of the space, f is the distance from the exit surface of the field lens 6 to the processing focus, N is the installation distance from the visible light indicator laser 1 to the electric reflector, and m is the horizontal distance from the indicator light emitted by the visible light indicator laser 1 to the laser exit optical axis.

[0078] After obtaining the initial deflection angle of the electric reflector Then, the mirror normals of each electric reflector are adjusted around the Z direction to intersect with the laser emission optical axis.

[0079] Finally, fine-tuning is performed. Based on the spatial coordinates (X, Y, Z) of the laser beam focus obtained in steps S1 and S2, controller 19 fine-tunes the deflection and pitch angles of the motorized reflector to ensure that the indicator spot overlaps the geometric center of the laser beam focus. The motorized reflector used is a Picomotor-8807 model, with an angular resolution of 0.7µrad, which is ideal for precise optical alignment.

[0080] S4. Defocus detection and correction:

[0081] Determine whether the processing surface and the focal plane are out of focus and deflected. In the subsequent processing, a visible indicator light spot is used to replace the position of the laser processing focus for processing guidance. Taking advantage of the excellent collimation of the laser beam, when the focal plane where the focus is located is deflected or not coplanar with the processing surface, the indicator light will project a specific shape determined by the installation position on the processing surface, such as Figure 5 When the processing surface is deflected relative to the focal plane, the triangle formed by the projected light spot can be observed to be deformed compared to the set equilateral triangle in the acquisition field of view of the CCD camera 11. The distance between each point can be calculated using the relative coordinates. Based on the calculated value, the processing surface position is readjusted so that the pulsed laser is perpendicular to the processing plane.

[0082] For laser defocus d f After adjusting the focal plane and the processing plane to keep them parallel, the following formula is used to calculate:

[0083] ;

[0084] in, is the angle between the indicator light emitted by the visible light indicator laser 1 and the Z-axis direction of the space, is the distance between each indicator light spot obtained from the image collected by the CCD camera 11, f is the distance from the exit surface of the field lens 6 to the processing focus, N is the installation distance from the visible light indicator laser 1 to the electric reflector, and m is the horizontal distance from the indicator light emitted by the visible light indicator laser 1 to the laser exit optical axis.

[0085] As can be seen from the above formula, the laser defocus amount at this time is only related to the side length of the projected triangle, the installation position of the visible light indicator laser 1, and the Z-direction distance of the pulsed laser focus. Compared with the traditional use of distance sensors and other equipment to measure defocus values, the present invention converts the slightly changing defocus amount into a relatively large spatial dimension value, making the measurement more accurate, simpler to implement, and relatively lower in cost. After completing the focus calibration of the processing plane, further processing can be started; otherwise, the above debugging steps need to be repeated in sequence to recalibrate the focus.

[0086] The present invention realizes real-time focus tracking, improves positioning accuracy, and enhances anti-interference capability by providing a coaxial pinhole device 10 and combining multiple image algorithms with feedback from the translation stage 18. There is no need for repeated calibration after the initial calibration, which improves processing efficiency. The equilateral triangle structure is used to suppress single-point errors, and the processing defocus amount and whether the vertical processing requirements are met can be quickly determined. Overall costs are reduced, and operational safety is improved. The positioning of the pulse focus is mainly determined by the image acquisition algorithm, and its focus calibration is replaced by three visible light indicator lasers, eliminating the need for the use of expensive photoelectric detection equipment. In addition, the entire calibration process is mainly completed by a computer or other controller, avoiding the harm of invisible pulses to operators.

[0087] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A three-point auxiliary positioning method for invisible pulse laser processing focus, characterized in that: The following steps are involved: S1. Horizontal position positioning: The visible processing bright spot produced by the interaction between the pulsed laser and the sample surface is captured by a coaxial CCD camera. The geometric center of the processing bright spot area is extracted using grayscale processing and binarization algorithms, and the relative coordinate values of the laser beam focus in the X and Y directions are calculated. S2, Z-axis positioning: Perform local acquisition of the center of the processing bright spot area, determine the optimal focal plane in combination with the image clarity algorithm, and obtain the spatial coordinates (X, Y, Z) of the laser beam focus; S3. Indicator laser settings: Three visible light indicator lasers are installed in an equilateral triangle layout. Through observation and adjustment, the three indicator light beams emitted by the three visible light indicator lasers are overlapped and pointed to the focal position. The overlapping and visible indicator light spots emitted by the three visible light indicator lasers replace the position of the laser beam focal point for processing guidance; S4. Defocus detection and correction: If the processing surface deviates from the focal plane, the triangle formed by the indicator light spots in the image captured by the CCD camera will be deformed compared to the set equilateral triangle. The distance values between the indicator light spots in the image captured by the CCD camera are calculated. According to the calculated value, the position of the processing surface is readjusted so that the pulsed laser is perpendicular to the processing plane, and the defocus amount is calculated.

2. The three-point auxiliary positioning method for invisible pulse laser processing focus according to claim 1, characterized in that: In step S1, the CCD camera is synchronously triggered to capture an image during the pulse laser operation and transmit it to the controller. The captured color image is converted into a grayscale image using a conversion formula, and then a threshold range is set for region segmentation. Finally, the relative coordinates of the geometric center of the processing bright spot in the CCD camera field of view are calculated to complete the calibration of the focus horizontal position, and the CCD camera field of view coordinates are mapped to the coordinates of the actual processing surface.

3. The three-point auxiliary positioning method for invisible pulse laser processing focus according to claim 2, characterized in that: The following formula is used to calculate the relative coordinates of the geometric center of the processing bright spot in the CCD camera field of view: ； ； in, The geometric center of the laser beam focus in the image collected by the CCD camera after focusing. are the row and column values of the processed bright spots in the captured image, Indicates the grayscale value of the corresponding coordinate point.

4. The three-point auxiliary positioning method for invisible pulse laser processing focus according to claim 1, characterized in that: In step S2, a local image acquisition range of 300×300 is first divided with the processing bright spot area as the center, and then the galvanometer system and the field lens are moved upward until the field of view of the CCD camera is blurred, and the distance between the field lens and the processing plane at this time is recorded as f 1, and then control the galvanometer system and the field mirror to move downward with a moving interval of 1 μm, which is recorded as f 1-n, where n=1, 2, 3..., the value of n is determined by the number of moves, and the movement is stopped when blur-clear-blur changes appear in the CCD camera field of view. At the same time, the image information during the movement is saved for subsequent image clarity evaluation and processing, and the image clarity evaluation value is given. The image clarity evaluation value corresponding to the maximum image clarity evaluation value is selected. f The 1-n value is used as the Z coordinate value of the laser beam focus.

5. The three-point auxiliary positioning method for invisible pulse laser processing focus according to claim 4, characterized in that: An auxiliary lighting source is set around the field lens. The reflected light on the focal plane passes through the focusing lens coaxially and is then controlled by a pinhole device to enter the CCD camera. The pinhole device is located at the focus of the focusing lens.

6. The three-point auxiliary positioning method for invisible pulse laser processing focus according to claim 4, characterized in that: Methods for evaluating image clarity include the Laplace gradient method, the Sobel gradient method, or the sum of absolute grayscale variance method.

7. The three-point auxiliary positioning method for invisible pulse laser processing focus according to claim 1, characterized in that: In step S3, an equilateral triangle formed by the three visible light indicator lasers is inscribed in a circle with a radius of m, with the laser emission point of the galvanometer system as the center. In the initial state, the emission ports of the three visible light indicator lasers and the field lens emission surface are in the same direction and parallel, and an electric reflector is installed under each visible light indicator laser to adjust the direction of the indicator light it emits.

8. The three-point auxiliary positioning method for invisible pulse laser processing focus according to claim 7, characterized in that: The direction of the indicator light emitted by each visible light indicator laser is coarsely and finely adjusted by the electric reflector. During the coarse adjustment process, the initial installation deflection angle of each electric reflector is first determined. θ , and make corresponding adjustments, and then adjust the mirror normals of each electric reflector around the spatial Z-axis to intersect with the laser emission optical axis; during the fine-tuning process, according to the spatial coordinates (X, Y, Z) of the laser beam focus obtained in steps S1 and S2, fine-tune the deflection and pitch angles of the electric reflector, so that the indicator light spots emitted by the three visible light indicator lasers overlap at the geometric center of the laser beam focus.

9. The three-point auxiliary positioning method for invisible pulse laser processing focus according to claim 1, characterized in that: In step S4, the laser defocus amount d f It is calculated using the following formula: ； in, is the angle between the indicator light emitted by the visible light indicator laser and the Z-axis direction of the space, is the distance between each indicator light spot obtained in the image collected by the CCD camera, f is the distance from the field lens exit surface to the processing focus, N is the installation distance from the visible light indicator laser to the electric reflector, and m is the horizontal distance from the indicator light emitted by the visible light indicator laser to the laser exit optical axis.

10. A three-point auxiliary positioning device for invisible pulse laser processing focus, used to implement the three-point auxiliary positioning method according to any one of claims 1 to 9, characterized in that: Including laser, beam expander, optical path steering module, galvanometer system, field lens, processing platform, translation stage, focusing lens and CCD camera; The pulsed laser beam emitted by the laser is collimated by the beam expander group, enters the galvanometer system through the optical path steering module, and is then focused by the field lens on the processing platform. The distance between the field lens exit surface and the processing platform is adjusted by the translation stage so that the reflected light on the focal plane can coaxially pass through the focusing lens and enter the image acquisition field of the CCD camera.

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