Automatic tool setting process planning method for repairing surface global micro-defects of large aperture KDP crystal element based on node progressive

Abstract

The application discloses an automatic tool setting process planning method based on node progressive large-diameter KDP crystal element surface global micro-defect repair, relates to the technical field of optical engineering, and aims at solving the problems of low accuracy of existing automatic tool setting method in tool setting stage division, lack of safety criterion and low efficiency of automatic tool setting process. The application adopts a three-point calibration method outside the crystal aperture, establishes a fitting plane equation of the crystal surface to be repaired, divides the coarse tool setting stage and the fine tool setting stage by considering the influence of gravity deformation, determines the feed parameters and the in-feed tool feeding strategy of the coarse tool setting stage, corrects the distance of the tool tip to the crystal surface to be repaired in the movement process through the auxiliary distance measurement of the repair microscope system, adds the safety criterion, determines the feed parameters and the feed strategy of the fine tool setting stage, compares and processes the images collected by the scanning microscope before and after each feed, and takes the appearance of the tool setting pit in the field of view as the tool setting success sign.

Description

Technical Field

[0001] This invention relates to the field of optical engineering technology, and more specifically, to an automated tool setting process planning method for global micro-defect repair on the surface of large-aperture KDP crystal elements based on node progressive methods. Background Technology

[0002] To address energy scarcity and environmental pollution, countries worldwide are committed to developing new clean energy sources. Compared to relying on fossil fuels accumulated over centuries, developing new clean energy sources offers a fundamental solution to the global energy shortage crisis. After years of exploration, laser-driven inertial confinement fusion has gained significant attention due to its abundant, clean, and efficient energy production, leading to increased investment in related research. The development of laser fusion devices is crucial for achieving controlled laser fusion energy, with the National Ignition Facility in the United States being a prime example. This device boasts the world's highest energy output and is equipped with nearly 40,000 high-precision, high-quality optical components, of which approximately 8,000 are large-aperture. KDP crystal elements, due to their unique optical properties, are an indispensable core component in current laser fusion devices, with enormous demand. However, during the processing of KDP crystal elements, various factors such as processing vibration, process parameters, and material properties easily introduce micron-level defects into the surface. If these defects are not addressed, they will expand rapidly under subsequent intense laser irradiation, eventually rendering the entire optical element unusable. Therefore, it is particularly important to intensify research on global micro-defect repair technology for large-aperture KDP crystal elements.

[0003] Currently, the main method for repairing micro-defects on the surface of large-diameter KDP crystal components is micromechanical repair using high-speed micro-milling with ball end mills. This method can restore the laser damage threshold of the repaired component to over 85% of the level of a defect-free surface. In this repair process, the automatic tool setting process of the ball end mill is crucial to ensuring the efficiency of repairing micro-defects across the entire surface of large-diameter KDP crystal components. Existing tool setting methods are mainly based on the "reflection method," where the feed rate varies according to the distance between the tool and the tool setting surface, feeding the tool at different speeds until the tool setting completion marker (the appearance of tiny chips) is detected, completing the tool setting. The entire process takes 140 seconds. This automatic tool setting process is inaccurate in distinguishing between different feed parameters. If a deviation is too large in any step of the feed process and is not corrected, it will jeopardize the safety of subsequent tool setting steps. Furthermore, this automatic tool setting method also suffers from low accuracy in dividing the automatic tool setting stages, a lack of safety criteria, and low efficiency. Summary of the Invention

[0004] The technical problem to be solved by this invention is:

[0005] Existing tool setting process planning methods suffer from problems such as low accuracy in dividing the tool setting stage, lack of safety criteria leading to inaccurate identification of feed processes with different feed parameters, and low efficiency of automatic tool setting processes.

[0006] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0007] This invention provides an automated tool setting process planning method for global micro-defect repair on the surface of large-aperture KDP crystal devices based on node-progressive methods, comprising the following steps:

[0008] Step 1. Install the large-aperture KDP crystal, assemble and adjust the restoration microscope system and scanning microscope system, and automatically return each axis of the crystal restoration machine tool system to zero;

[0009] Step 2. Using a scanning microscope system to calibrate the crystal aperture at three points, establish a fitting plane equation for the surface of the crystal to be repaired. Based on the fitting plane equation and considering the influence of gravitational deformation on the tool setting position, determine the coordinates of the key points that divide the coarse tool setting stage and the fine tool setting stage.

[0010] Step 3. Determine the feed parameters for the rough tool setting stage. The rough tool setting stage adopts a node-based progressive feed strategy. The distance between the tool and the crystal surface to be repaired is calculated using the "reflection method" through the repair microscope system. Different feed parameters are used when the tool is between different nodes to achieve rapid feed tool setting.

[0011] Step 4. During the rough tool setting stage, the distance between the tool tip and the surface to be repaired of the crystal is corrected by using the distance measurement assisted by the repair microscope system. A safety criterion is added to achieve safe feed under different feed parameters.

[0012] Step 5. Determine the feed parameters for the fine tool setting stage, adopt a constant step feed strategy, compare and process the images acquired by the scanning microscope before and after each feed, and use the appearance of tool setting pits in the field of view as a sign of successful tool setting.

[0013] Furthermore, the crystal repair machine tool described in step 1 includes a scanning microscope system for rapidly searching for and acquiring real-time image information of the crystal tool surface during the repair process, a defect repair system for removing defects through three-axis linkage machining, and a repair microscope system for acquiring tool setting image information and calculating the distance between the tool and the crystal tool surface. The tool setting process is the process of feeding the tool upward to the lower surface of the crystal.

[0014] Furthermore, the scanning microscope used in the crystal restoration machine is a JAI BM-500GE CCD with a resolution of 2456×2058, a maximum frame rate of 15fps, and a pixel size of 3.45μm×3.45μm; the restoration microscope uses a MV-VD200SC industrial CCD with a resolution of 1600×1200 and a maximum frame rate of 12fps, and its driver provides a WDMIAT3.0 interface. Language standard library functions.

[0015] Furthermore, in step 2, the gravitational deformation of the crystal element is obtained using the finite element simulation method.

[0016] Furthermore, step 3, the rough setting stage, is divided into four processes, and the specific process planning for the rough setting process is as follows:

[0017] 3-1 Select 500μm as the safety plane. Based on the node-based progressive tooling strategy, when the distance between the tool and the surface to be repaired is greater than 500μm, move to 500μm at a feed rate of 500μm / s.

[0018] 3-2 When the distance between the tool and the surface to be repaired is less than 500μm, the tool enters the field of view, and the feed rate is adjusted to 100μm / s;

[0019] 3-3 When the distance between the tool and the surface to be repaired is less than 100μm, adjust the feed rate to 10μm / s;

[0020] 3-4 When the distance between the tool and the surface to be repaired is less than 50μm, adjust the feed rate to 5μm / s until the distance reaches 25μm.

[0021] Furthermore, in step 4, the distance d between the tool tip and the surface to be repaired of the crystal is calculated using the "reflection method" through a repair microscope system, and the tool position is corrected based on the value of d.

[0022] (1) When d≥500μm, the absolute motion reaches z-100μm;

[0023] (2) When d < 500 μm, the distance moved relative to the current position is d - 100 μm;

[0024] Meanwhile, to ensure the safety of the feed process during the roughing stage, the smaller value between the corrected motion amount and the original motion amount is always taken during the motion.

[0025] Furthermore, two safety criteria are added for the precision tool setting stage to address potential situations:

[0026] (1) The tool movement stop condition of the tool setting pit was not triggered, resulting in severe overcutting on the surface of the crystal to be repaired;

[0027] (2) The feed distance during the fine tool setting stage exceeds the expected distance and is beyond the predicted surface range;

[0028] To avoid the above two situations compromising the safety of the precision tool setting stage, two additional safety criteria are introduced:

[0029] (1) When a high grayscale area of ​​2800~3200 pixels, preferably greater than 30000 pixels, appears in the field of view of the scanning microscope system, it is considered that the pit stopping condition has not been triggered and a serious overcut phenomenon has occurred on the surface of the crystal to be repaired, while a large amount of chips are generated.

[0030] (2) When the feed distance during the fine tool setting stage is 40~60μm, preferably more than 50μm, it exceeds the predicted range of the crystal's lower surface to be repaired.

[0031] Furthermore, in step 5, when the image acquired by the scanning microscope changes, the image processing method of "subtraction and circle taking" is used to process the image. First, the images before and after each tool feed are subtracted and binarized. Then, the high grayscale areas of the crystal surface pits generated by the tool setting are subjected to dilation and erosion morphological processing to reduce noise and enhance features. Finally, the FindContours function is used to find the outer contour of the image and calculate the minimum circumcircle of the tool setting contour. When the pixel radius of the minimum circumcircle of the tool setting pit reaches the preset threshold, it is used as a sign of successful tool setting.

[0032] Furthermore, the method for determining the minimum circumcircle pixel radius threshold of the tool setting pit in step 5 is as follows: based on the magnification of the scanning microscope's zoom ring, calculate the theoretical size parameter c of the representative length of a single pixel. When the automatic tool setting depth of the micro-defects on the surface of the crystal element is 0.5μm, calculate the radius of the corresponding tool setting pit based on the diameter of the ball end mill, and further calculate its corresponding pixel radius, which is the pixel radius threshold of the minimum circumcircle of the tool setting pit.

[0033] Compared with the prior art, the beneficial effects of the present invention are:

[0034] This invention presents an automated tool setting process planning method for the repair of micro-defects on the surface of large-aperture KDP crystal elements based on a node-progressive approach. It fits the equation of the crystal's repair plane using a three-point calibration method outside the aperture of a scanning microscope system, comprehensively considering the influence of crystal tilt and gravitational deformation on the tool setting position, and determines the division into coarse and fine tool setting stages. The automated tool setting process is planned based on the distance from the tool tip to the crystal surface to be repaired obtained using the "reflection method" on the repair microscope system. Considering the efficiency of the automated tool setting process, the feed parameters for each tool setting stage are designed. To ensure the safety of the coarse tool setting stage, a safety judgment of the tool's distance to the crystal surface to be repaired is added at each stage to ensure the safety of subsequent feeds. Simultaneously, to ensure the safety of the fine tool setting stage, two safety judgment conditions are added: consideration of the grayscale area in the field of view and the tool movement distance, to ensure the safety of the second stage of tool setting. Attached Figure Description

[0035] Figure 1 This is a flowchart illustrating the automatic tool setting process planning and defect repair process for the global micro-defect repair of the surface of a large-diameter KDP crystal element in an embodiment of the present invention.

[0036] Figure 2 This is a device for rapid searching and micro-milling repair of micro-defects on the surface of large-diameter KDP crystals, as described in this embodiment of the invention.

[0037] Figure 3 This is a schematic diagram of the automatic tool setting and rough tool setting stage in an embodiment of the present invention;

[0038] Figure 4 This is a diagram of the crystal surface height calculation module in an embodiment of the present invention;

[0039] Figure 5 This is a gravity deformation cloud diagram in an embodiment of the present invention;

[0040] Figure 6 This is a diagram illustrating the process of identifying knife dents in an embodiment of the present invention.

[0041] Figure 7 This is a frequency distribution diagram of automatic tool setting time in an embodiment of the present invention. Detailed Implementation

[0042] In the description of this invention, it should be noted that the terms "first," "second," and "third" mentioned in the embodiments of this invention are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first," "second," and "third" may explicitly or implicitly include one or more of that feature.

[0043] 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.

[0044] Specific Implementation Method 1: This invention provides an automated tool setting process planning method for the repair of global micro-defects on the surface of large-aperture KDP crystal elements based on a node-progressive approach, such as... Figure 1 As shown, it includes the following steps:

[0045] Step 1. Install the large-aperture KDP crystal, assemble and adjust the restoration microscope system and scanning microscope system, and automatically return each axis of the crystal restoration machine tool system to zero;

[0046] Step 2. Using a scanning microscope system to calibrate the crystal aperture at three points, establish a fitting plane equation for the surface of the crystal to be repaired. Based on the fitting plane equation and considering the influence of gravitational deformation on the tool setting position, determine the coordinates of the key points that divide the coarse tool setting stage and the fine tool setting stage.

[0047] Step 3. Determine the feed parameters for the rough tool setting stage. The rough tool setting stage adopts a node-based progressive feed strategy. The distance between the tool and the crystal surface to be repaired is calculated using the "reflection method" through the repair microscope system. Different feed parameters are used when the tool is between different nodes to achieve rapid feed tool setting.

[0048] Step 4. During the rough tool setting stage, the distance between the tool tip and the surface to be repaired of the crystal is corrected by using the distance measurement assisted by the repair microscope system. A safety criterion is added to achieve safe feed under different feed parameters.

[0049] Step 5. Determine the feed parameters for the fine tool setting stage, adopt a constant step feed strategy, compare and process the images acquired by the scanning microscope before and after each feed, and use the appearance of tool setting pits in the field of view as a sign of successful tool setting.

[0050] like Figure 2 As shown, the crystal repair machine tool mentioned in step 1 is a self-developed large-diameter KDP crystal surface micro-defect rapid search and micro-milling repair device (application number: 201310744691.1). The repair machine tool includes a scanning microscope system (X1, Y1, Z1 axes) for rapid search of crystal surface defect points and acquisition of real-time image information of the crystal tool surface during the repair process; a defect repair system (X2, Y2, Z2 axes) for three-axis linkage machining removal of defect points; and a repair microscope system (X3, Y3, Z3 axes) for acquisition of tool setting image information and calculation of the distance between the tool and the crystal tool surface. During the repair process, the tool axis is designed to be at a 45° angle with the horizontal plane, and the tool setting microscope optical axis is at a 15° angle with the horizontal plane. The tool setting process is the process of the tool being fed upward to the lower surface of the crystal.

[0051] The repair machine uses a JAI BM-500GE CCD scanning microscope with a resolution of 2456×2058, a maximum frame rate of 15fps, and a pixel size of 3.45μm×3.45μm. The scanning microscope has a zoom ring (0.58X~7X) and allows manual adjustment of the zoom ring to change the microscope's magnification. The repair microscope used is a Vision Imaging MV-VD200SC industrial CCD with a resolution of 1600×1200 and a maximum frame rate of 12fps. Its driver program provides a WDMIAT 3.0 interface. The language's standard library functions encapsulate 37 classes, 17 global functions, 4 structure types, and 25 variable types, enabling real-time image acquisition, simple image processing, video stream processing, and other functions.

[0052] In step 2, the finite element simulation method is used to obtain the gravitational deformation of the crystal element.

[0053] In step 2, since it is not possible to guarantee that the surface of the crystal to be repaired is completely parallel to the scanning motion plane when installing the large-diameter KDP crystal on the repair machine tool, the tilting problem caused by installation factors will impair the safety of the precision tool setting process in automatic tool setting. The three-point calibration method is to collect the coordinates of three points outside the aperture of the scanning microscope system to determine the fitting plane equation of the crystal to be repaired, eliminate the influence of the tilt during crystal installation, obtain the gravitational deformation of the crystal element through finite element simulation, and thus determine the position parameters of the key points in the automatic tool setting stage when repairing different defect points. Based on this plane fitting equation, the distance between the tool and the surface to be repaired during defect repair at different locations can be estimated.

[0054] like Figure 3 As shown, step 3, the rough tool setting stage, is divided into four processes. The specific process planning for the rough tool setting process is as follows:

[0055] 3-1 Select 500μm as the safety plane. Based on the node-based progressive tooling strategy, when the distance between the tool and the surface to be repaired is greater than 500μm, move to 500μm at a feed rate of 500μm / s.

[0056] 3-2 When the distance between the tool and the surface to be repaired is less than 500μm, the tool enters the field of view, and the feed rate is adjusted to 100μm / s;

[0057] 3-3 When the distance between the tool and the surface to be repaired is less than 100μm, adjust the feed rate to 10μm / s;

[0058] 3-4 When the distance between the tool and the surface to be repaired is less than 50μm, adjust the feed rate to 5μm / s until the distance reaches 25μm.

[0059] In step 4, the distance d between the tool tip and the surface to be repaired on the crystal is calculated using the "reflection method" through a restoration microscope system. The tool position is then corrected based on the value of d.

[0060] (1) When d≥500μm, the absolute motion reaches z-100μm;

[0061] (2) When d < 500 μm, the distance moved relative to the current position is d - 100 μm;

[0062] Meanwhile, to ensure the safety of the feed process during the roughing stage, the smaller value between the corrected motion amount and the original motion amount is always taken during the motion.

[0063] The corrected movement has two standards: one is based on the calculated height of the lower surface, and the other is based on the distance measured by the restoration microscope system. Since the distance measured by the restoration microscope system is generally greater than the actual distance, it is generally determined that the movement should be based on the height z calibrated on the surface to be repaired of the crystal. The restoration microscope system assists in distance measurement, ensuring the safety of the roughing stage.

[0064] In step 5, the precision tool setting adopts a constant step feed strategy. First, the scanning microscope system image corresponding to the current position is acquired and fed by 1μm. The image is acquired again, and the two images are processed to identify whether the tool setting pit appears. If the tool setting pit appears, the automatic tool setting is considered to be completed. If the tool setting pit does not appear, the above steps are repeated until the tool setting pit appears and the tool setting is completed.

[0065] Two safety criteria are added for the precision tool setting stage to address potential situations:

[0066] (1) The tool movement stop condition of the tool setting pit was not triggered, resulting in severe overcutting on the surface of the crystal to be repaired;

[0067] (2) The feed distance during the fine tool setting stage exceeds the expected distance and is beyond the predicted surface range;

[0068] To avoid the above two situations compromising the safety of the precision tool setting stage, two additional safety criteria are introduced:

[0069] (1) When a high grayscale area of ​​2800~3200 pixels, preferably greater than 30000 pixels, appears in the field of view of the scanning microscope system, it is considered that the pit stopping condition has not been triggered and a serious overcut phenomenon has occurred on the surface of the crystal to be repaired, while a large amount of chips are generated.

[0070] (2) When the feed distance during the fine tool setting stage is 40~60μm, preferably more than 50μm, it exceeds the predicted range of the crystal's lower surface to be repaired.

[0071] In step 5, when the image acquired by the scanning microscope changes, the image processing method of "subtraction and circle taking" is used to process the image. First, the images before and after each tool feed are subtracted and binarized. Then, the high grayscale areas of the crystal surface pits generated by the tool setting are subjected to dilation and erosion morphological processing to reduce noise and enhance features. Finally, the FindContours function is used to find the outer contour of the image and calculate the minimum circumcircle of the tool setting contour. When the pixel radius of the minimum circumcircle of the tool setting pit reaches the preset threshold, it is used as a sign of successful tool setting.

[0072] The method for determining the minimum outer circle pixel radius threshold of the tool setting pit in step 5 is as follows: Based on the magnification of the scanning microscope's zoom ring, calculate the theoretical size parameter c of the representative length of a single pixel. When the automatic tool setting depth of the micro-defects on the crystal element surface is 0.5μm, calculate the radius of the corresponding tool setting pit based on the diameter of the ball end mill, and further calculate its corresponding pixel radius, which is the pixel radius threshold of the minimum outer circle of the tool setting pit.

[0073] Since the automatic tool setting process planning method for repairing micro-defects on the surface of large-diameter KDP crystal elements based on node-progressive design involves multiple process flows, in order to ensure the feasibility of the scheme and the defect detection effect, when testing the automatic tool setting process method according to the above steps, it is necessary to specifically implement the division of key point positions in the tool setting stage, consider the influence of crystal tilt during installation, crystal gravity deformation, and the determination of tool setting success markers and the identification of tool setting pits on the surface to be repaired.

[0074] 1) Tilting angle during crystal mounting

[0075] When a large-diameter KDP crystal is mounted on the fixture of a repair machine, it cannot be guaranteed that the surface of the crystal to be repaired is perfectly parallel to the scanning motion plane. Therefore, the tilt of the plane present during installation needs to be considered, which can be determined by establishing a square equation. This invention uses a three-point calibration method outside the aperture to fit the plane equation of the lower surface of the crystal to be repaired. Three points are selected outside the aperture of the crystal element, and the three external calibration points are recorded: , , The plane equation can be obtained by the following formula, where A, B, C, and D are the coefficients of the equation.

[0076]

[0077] Figure 4The calibration module for the crystal surface to be repaired, through manual tool setting at three points outside the aperture, can obtain the x and y values ​​of the current scanning motion system and the z value of the repair motion system. After calibration, the plane fitting equation of the crystal surface to be repaired is calculated. In the repair process of large-diameter KDP crystals, when a defect is in the repair state, the height value of the crystal surface corresponding to the current defect position coordinates can be calculated.

[0078] 2) Crystal deformation due to gravity

[0079] Commonly used large-diameter KDP crystals are mainly classified into three types based on their crystal planes: (001), Type I, and Type II. When considering gravitational deformation in simulation, material parameters, namely Poisson's ratio and elastic modulus, need to be input. Due to the anisotropy of KDP crystals, obtaining the elastic modulus is difficult. To meet the simulation requirements and obtain the material parameters, the stiffness matrix method is used. The stiffness matrix of the (001) crystal type is shown in Table 1, which represents the stiffness matrix of the (001) plane of the KDP crystal. Simultaneously, different crystals exhibit geometric angle differences. By transforming the stiffness matrix, the stiffness matrices of Type I and Type II crystal types can be obtained. Finite element simulation is performed in Workbench, yielding the results as shown below. Figure 5 The gravity deformation cloud diagram shown.

[0080] Table 1

[0081]

[0082] According to the obtained gravity deformation cloud map, the anisotropy of the crystal has a relatively small influence on the gravity deformation of the crystal. The maximum deformation of (001), Type I and Type II crystal types are 1.77μm, 6.34μm and 2.53μm, respectively.

[0083] Based on existing automatic tool setting data, it can be concluded that the installation tilt difference between tool setting heights at different positions can reach 700μm. After fitting the data to a plane (goodness of fit R...), 2 =0.9989, then the fit is considered valid), the distance from the height of different tool setting positions to the fitting plane. With a diameter of only 14μm, it can effectively predict the tool setting height, according to Figure 5 Figure b) shows the maximum deformation caused by gravitational deformation of the crystal. The value is 6.34 μm. During the actual repair process, the workpiece platform moves horizontally on the machine tool. When the crystal is in different positions, the height of the same point on the crystal is not the same. Therefore, for the i-th defect point, the maximum distance difference between different tool setting positions and the fitted plane equation is... μm. Therefore, when the distance between the tool and the crystal surface to be repaired is 25 μm. Entering the precision tool setting stage at this time can improve tool setting efficiency and ensure the safety of the automatic tool setting stage.

[0084] 3) Determining the sign of successful tool setting

[0085] The zoom ring magnification range of a scanning microscope is 0.58~7X. To ensure accurate acquisition of the pixel radius corresponding to the tool-setting indentation in the image during automatic tool setting, a zoom ring magnification of 7X is selected for the automatic tool setting process. When the zoom ring magnification of the scanning microscope is 7X, pixel calibration yields an average pixel calibration value of 0.335 μm / pixel. Compared to the theoretical pixel calibration value of 0.328 μm / pixel, the calibration error is 0.2%, indicating that the error caused by pixel calibration is negligible. Furthermore, when processing images of the surface to be repaired, the radius of the tool setting pit obtained through image processing is generally smaller than the actual tool setting contour. This phenomenon is mainly due to the reduction in grayscale at the edge of the tool setting pit, which is filtered out. The maximum error of this process is 3.8 μm. After averaging, the error of the tool setting pit contour radius is approximately 2.11 μm. Subsequently, when measuring the depth of the tool setting pit, due to the unavoidable vibration of the tool during the tool setting process, the depth of the tool setting pit measured by the white light interferometer will be greater than the pit depth obtained from image processing, and its maximum error is 0.309 μm. Averaging the error results, the error of the tool setting pit depth is approximately 0.126 μm.

[0086] Based on the above error analysis of the radius and depth of the tool setting recess outline, the depth of the tool setting recess calculated using the radius of the circumcircle of the recess outline is compared with the actual depth of the tool setting recess measured by the white light morphology profile interferometer. The maximum error is 0.512 μm, and the average error is 0.178 μm after averaging the data. Considering the radius of curvature of the sphere, as the depth of the tool setting recess increases, the radius change of the recess becomes smaller, and the impact of the error on the result becomes greater. Therefore, the presence of a tool setting recess in the scanning microscope, with a pixel radius of 50 pixels for the circumcircle of the recess outline, can be effectively used as a marker that tool setting is complete.

[0087] 4) Development of an algorithm for identifying tool-setting pits on the surface to be repaired

[0088] Using the tool setting pit in the scanning microscope field of view as an indicator of successful tool setting, it is essential to accurately identify the tool setting pit from the scanning microscope field of view. Global micro-defect detection on the surface of KDP crystal components is a dark-field detection method, with low background grayscale and high grayscale of the tool setting pit. However, the reflection from the high-speed rotating micro-milling cutter irradiates the tool setting pit, creating a larger area of ​​high grayscale value near the pit, thus interfering with accurate pit identification. To address these issues, an OpenCV-based "subtraction and circle extraction" image processing algorithm was developed. The specific calculation process is as follows:

[0089] Step 1: During the fine tool setting stage, acquire an image of the tool setting surface after each feed motion. Images before and after the feed are shown below. Figure 6 Figure a) and Figure 6 As shown in Figure b), by subtracting and binarizing the two images, a clear image of the tool setting pit outline, unaffected by tool marks or other unrepaired damage points, can be obtained, as shown in Figure b). Figure 6 As shown in Figure c);

[0090] Step 2: Perform dilation and erosion morphological processing on the high-grayscale image of the tool-setting pit area, such as... Figure 6 As shown in Figure e), this achieves the purpose of eliminating noise and enhancing object features;

[0091] Step 3: Use the FindContours function to find the outer contour of the image, such as... Figure 6 As shown in Figure f), the minimum circumcircle of the profile is calculated, as follows: Figure 6 As shown in Figure g), the largest circumcircle is identified as the contour of the tool setting pit. When the pixel radius is greater than 50 pixels, the tool setting movement stops, and the current tool setting depth is calculated based on the number of pixel radii.

[0092] The above steps, using the process flow of this invention, realize the automatic tool setting function for the full-area micro-defect repair of large-aperture precision optical crystal surfaces based on dual-microscope collaboration. Experimental verification, using a white-light topography interferometer to measure the depth of the automatic tool setting pits, yielded results as shown... Figure 7 The diagram shows the frequency distribution of automatic tool cutting depth.

[0093] It can be seen that the maximum cutting depth does not exceed 2.5 μm, and the average cutting depth is 1.4 μm. Based on the above analysis, the error between the cutting pit depth calculated by scanning electron microscopy and the actual cutting pit depth does not exceed 0.512 μm. Adding a retraction motion after cutting to bring the tool back to the calculated element surface ensures that the actual distance between the tool and the element surface does not exceed 0.5 μm, meaning the cutting accuracy is better than 0.5 μm. This achieves the accuracy of automatic cutting for repairing micro-defects on the surface of large-diameter crystal elements while significantly improving the precision of automatic cutting.

[0094] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and all such changes and modifications will fall within the scope of protection of the present invention.

Claims

1. An automatic tool alignment process planning method for repairing the surface of a large-aperture KDP crystal element based on node progressive global micro-defects, characterized in that, The method comprises the following steps: Step 1. Install a large-diameter KDP crystal, assemble and adjust a repair microscope system and a scanning microscope system, and automatically return each axis of a crystal repair machine tool system to zero; Step 2. A three-point calibration method of the scanning microscope system is used to calibrate the crystal, a fitting plane equation of a crystal surface to be repaired is established, based on the fitting plane equation and considering the influence of gravity deformation on a tool setting position, key point position coordinates of a coarse tool setting stage and a fine tool setting stage are determined; Step 3. Coarse tool setting stage feeding parameters are determined, the coarse tool setting stage adopts a node type progressive feeding strategy, a tool distance from the crystal surface to be repaired is calculated by using the repair microscope system and an "inverted image method", when the tool is between different nodes, different feeding parameters are used to realize rapid feeding tool setting; Step 4. In the coarse tool setting stage, the tool distance from the crystal surface to be repaired is corrected by using the repair microscope system to assist in distance measurement, safety criteria are added, and thus safety feeding under different feeding parameters is realized; Step 5. Fine tool setting stage feeding parameters are determined, a constant step feeding strategy is adopted, images collected by the scanning microscope before and after each feeding are compared and processed, and a tool setting pit appearing in a field of view is taken as a tool setting success sign; In step 3, the coarse tool setting stage is divided into four processes, and the coarse tool setting process planning is specifically as follows: 3-1. 500 μm is selected as a safety plane, based on the node type progressive feeding strategy, when the tool distance from the surface to be repaired is greater than 500 μm, the tool is moved to the position of 500 μm at a feeding speed of 500 μm / s; 3-2. When the tool distance from the surface to be repaired is less than 500 μm, the tool enters the field of view, and the feeding speed is adjusted to 100 μm / s; 3-3. When the tool distance from the surface to be repaired is less than 100 μm, the feeding speed is adjusted to 10 μm / s; 3-4. When the tool distance from the surface to be repaired is less than 50 μm, the feeding speed is adjusted to 5 μm / s, and the distance is adjusted to 25 μm.

2. The automatic tool alignment process planning method for global micro-defect repair of large aperture KDP crystal element surface based on node progressive, according to claim 1, characterized in that, In step 1, the crystal repair machine tool comprises a scanning microscope system for quickly searching and collecting real-time image information of a crystal tool setting surface in a repair machining process, a defect repair system for three-axis linkage machining removal of a defect point, and a repair microscope system for collecting tool setting image information and calculating a tool distance from a crystal tool setting surface, and a tool setting process is a process of feeding the tool upward to the lower surface of the crystal.

3. The automatic tool alignment process planning method for global micro-defect repair of large aperture KDP crystal element surface based on node progressive, according to claim 2, characterized in that, The scanning microscope used in the crystal repairing machine tool is BM-500GE type CCD of JAI, the resolution is 2456x2058, the maximum frame speed can reach 15 fps, and the pixel size is 3.45μm x 3.45μm; the repairing microscope used in the view image MV-VD200SC type industrial CCD, the resolution is 1600x1200, the maximum frame speed can reach 12 fps, and its driver program can provide the interface of WDMIAT3.0 language standard library functions.

4. The automatic tool alignment process planning method for global micro-defect repair of large aperture KDP crystal element surface based on node progressive, according to claim 1, characterized in that, In step 2, a finite element simulation method is used to obtain gravity deformation of the crystal element.

5. The automatic tool alignment process planning method for global micro-defect repair of large aperture KDP crystal element surface based on node progressive, according to claim 1, characterized in that, Two safety criteria are added for the fine tool setting stage, and the possible situations are as follows: (1) The tool movement stop condition of the tool setting pit is not triggered, and serious overcutting occurs on the crystal surface to be repaired; (2) The feeding distance of the fine tool setting stage exceeds the expected distance, and the surface prediction range is exceeded; In order to avoid damage to the safety of the fine tool setting stage caused by the above two situations, two safety criteria are added as follows: (1) When a high gray area of 2800-3200 pixels appears in the field of view of the scanning microscope system, it is considered that the pit stop condition is not triggered and serious overcutting occurs on the crystal surface to be repaired, and a large amount of cutting chips are generated; (2) When the feed distance is 40~60μm in the fine tool setting stage, it is beyond the predicted range of the lower surface of the crystal to be repaired.

6. The automatic tool alignment process planning method for global micro-defect repair of large aperture KDP crystal element surface based on node progressive, according to claim 1, characterized in that, In step 5, when the image collected by the scanning microscope changes, the image processing method of "difference taking circle" is used to process the image. First, the image before and after each tool setting feed is subtracted and binarized. Then, the high gray area of the crystal surface pit area generated by tool setting is subjected to morphological processing of expansion and corrosion to reduce noise and enhance features. Finally, the FindContours function is used to find the external contour of the image, and the minimum circumscribed circle of the tool setting contour is calculated. When the pixel radius of the minimum circumscribed circle of the tool setting pit reaches the preset threshold value, it is regarded as the tool setting success mark.

7. The automatic tool alignment process planning method for global micro-defect repair of large aperture KDP crystal element surface based on node progressive, according to claim 6, characterized in that, In step 5, the determination method of the pixel radius threshold of the minimum circumscribed circle of the tool setting pit is as follows: according to the zoom ring multiple of the scanning microscope, the theoretical size parameter c of the representative length of a single pixel is calculated. When the automatic tool setting depth of the surface micro-defects of the crystal element is 0.5μm, the corresponding tool setting pit radius is calculated according to the diameter of the ball head micro-milling cutter, and the corresponding pixel radius is further calculated, which is the pixel radius threshold of the minimum circumscribed circle of the tool setting pit.

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