A method and system for measuring effective jet length of a water guided laser and monitoring a nozzle

Abstract

This invention relates to the field of water-guided laser processing technology, specifically a method and system for measuring the effective jet length and monitoring nozzles in water-guided lasers. The main components of the method are: first, a stimulated Raman scattering optical isolation imaging system is constructed to acquire a grayscale image of the scattered red light from the jet; then, the jet contour features are extracted, the pixel length along the principal axis is calculated, and the actual physical length of the jet is obtained by combining equipment parameters; finally, the length is compared with a safety threshold to determine the status. This invention relies on a dual isolation mechanism of long-pass filters and Raman scattering to effectively avoid detection interference caused by metal reflection and water mist, accurately identify high-energy jet regions with cutting capabilities, and abandon traditional relative calculation methods. It can directly output millimeter-level measured lengths, enabling timely detection of sudden nozzle malfunctions and full-process quantitative tracking of wear levels, providing accurate data support for nozzle condition monitoring.

Description

Technical Field

[0001] This invention relates to the field of water-guided laser processing technology, specifically to a method and system for measuring the effective jet length of a water-guided laser and monitoring the nozzle. Background Technology

[0002] Water-guided laser processing technology utilizes the total internal reflection effect at the water-air interface to propagate laser light within a water jet, enabling long-distance energy transfer and thus cutting of workpieces. During processing, the stability and effective length of the water jet directly affect the processing quality and distance of the water-guided laser.

[0003] As the core component for forming high-speed water jets, the nozzle's outlet shape, surface finish, and geometric precision directly determine the velocity distribution and stability of the water jet.

[0004] However, during long-term operation or high-frequency processing, the nozzle is subjected to erosion from high-pressure water flow and laser ablation, leading to changes in nozzle diameter and increased inner wall roughness. This results in a shorter effective water jet length and unstable jet state, affecting the processing distance of the water-guided laser and the total internal reflection of the laser in water, thus reducing the processing efficiency of the water-guided laser. Therefore, timely detection and evaluation of wear on the water-guided laser nozzle is of great significance for ensuring stable equipment operation and improving processing quality and efficiency.

[0005] Chinese invention patent publication number "CN117324798A" discloses a method for detecting anomalies in water-guided laser nozzles, which provides a visual monitoring scheme based on a common industrial camera. This scheme uses a camera to capture real-time images of the processing waterline below the water-guided laser nozzle; the acquired images are cropped, filtered, and binarized to make the processing waterline white and the background black; in the anomaly detection phase, starting from the second frame, the sum of the absolute differences in pixel values ​​between adjacent frames is calculated; if the sum of these differences exceeds a set threshold, and the percentage of white waterline pixels in the current image is lower than another threshold, it is determined that there is no stable laser undergoing total internal reflection in the processing waterline, i.e., the nozzle is deemed abnormal, and finally, a shutdown warning signal is sent to the processing control system.

[0006] However, the aforementioned patents have the following drawbacks in practical engineering applications:

[0007] The physical boundaries are blurred, and the interference from scattering is severe. This method directly captures the intrinsic light of the laser (such as 532nm green light). In the fracture zone (water droplet splash zone) below the high-pressure water jet, the laser will also produce strong linear scattering. Ordinary cameras cannot distinguish between the "effective processing straight section where total internal reflection truly occurs" and the "ineffective water droplet splash zone" from a physical optics perspective, resulting in the extracted water line containing a large number of areas with no processing capability.

[0008] The algorithm has poor robustness. The frame difference method (evaluating the pixel difference between two consecutive frames) is easily affected by stray light in the processing environment, strong metallic reflection on the workpiece surface, and water mist generated during processing, causing drastic and disordered fluctuations in the pixel difference and leading to frequent false alarms in the system.

[0009] The lack of absolute physical range monitoring is a significant drawback. The frame difference method is essentially a qualitative detection of relative changes, capable of triggering alarms only when the nozzle experiences sudden damage, and cannot calculate the absolute physical dimension of the jet length. Therefore, it cannot quantitatively assess the gradual, minute wear of the nozzle during use, or the slow decline in processing capability. Summary of the Invention

[0010] Based on the above-mentioned technical problems, the purpose of this invention is to provide a method for measuring the effective length of a water-guided laser jet with strong anti-interference ability and high measurement accuracy. It aims to filter out invalid scattering and ambient light by utilizing stimulated Raman scattering effect at the optical hardware level, and establish a conversion model by combining visual parameters to accurately calculate the absolute physical length of the effective jet. This enables quantitative monitoring of nozzle wear status and actual processing capacity, overcoming the shortcomings of existing technologies that are easily affected by stray light interference and cannot provide absolute physical measurement data.

[0011] To achieve the above objectives, the present invention provides a method for measuring the effective jet length of a water-guided laser and monitoring the nozzle, comprising the following steps:

[0012] Step 1: Construct an optical isolation imaging system based on stimulated Raman scattering to continuously acquire the original grayscale image of the red light from the stimulated Raman scattering of the jet;

[0013] Step 2: Extract features from the jet contour in the original grayscale image and calculate the pixel length of the jet along the principal axis at the center of the image. ;

[0014] Step 3: Utilize the pixel length of the jet Based on the hardware configuration parameters of the optical isolation imaging system, the absolute physical length of the jet is calculated. ;

[0015] Step 4: Determine the absolute physical length of the jet. Compare with safety threshold :like If the current nozzle status is normal; The nozzle shows a stable and slight downward trend but remains near the threshold, indicating progressive wear and triggering a warning signal. If it is determined that the effective total reflection length in the current processing waterline is insufficient, or that the nozzle is severely worn or broken, a stop processing signal is immediately sent to the processing control system and an alarm is triggered.

[0016] Furthermore, step 2 includes:

[0017] Step 2.1: Perform Gaussian filtering noise reduction on the original grayscale image;

[0018] Step 2.2: Binarize the grayscale image using an adaptive local thresholding algorithm;

[0019] Step 2.3: Extract the jet profile based on connected component analysis and generate a jet mask map;

[0020] Step 2.4: Calculate the pixel length of the jet along the central main axis of the jet mask image. ;

[0021] Furthermore, step 2.4 includes:

[0022] Step 2.4.1: Determine the coarse positioning points at the uppermost and lower ends of the jet, respectively;

[0023] Step 2.4.2: Using the gray-scale centroid method, perform sub-pixel fine positioning of the coarse positioning points at the top and bottom ends of the jet to obtain the fine positioning center points at the top and bottom ends of the jet;

[0024] Step 2.4.3: Calculate the pixel length of the jet along the principal axis of the image center. .

[0025] Furthermore, step 2.4.1 includes:

[0026] Traverse the entire pixel area of ​​the jet mask image, scan the vertical pixel distribution column by column along the horizontal axis of the image. If there are multiple jet pixels in each column, take the minimum value of the vertical coordinate among the multiple jet pixels in that column as the uppermost point of the jet pixels in that column, and record the uppermost point of the jet pixels in each column to form the uppermost point set.

[0027] Take the maximum value of the y-coordinate among the multiple jet pixels in the column as the lowest point of the jet pixels in the column, record the lowest point of the jet pixels in each column, and form a set of lower points;

[0028] Select the point with the smallest ordinate from the set of upper endpoints as the coarse positioning point at the top.

[0029] If there are multiple points with the same minimum ordinate in the upper endpoint set, then the average of the corresponding x-coordinates of the multiple points with the same minimum ordinate is taken as the coarse positioning point at the top.

[0030] Select the point with the largest ordinate from the set of lower endpoints as the coarse positioning point at the bottom.

[0031] If there are multiple points with the same maximum ordinate in the lower endpoint set, then the average of the corresponding x-coordinates of the multiple points with the same maximum ordinate is taken as the coarse positioning point of the lowermost endpoint.

[0032] Furthermore, step 2.4.2 includes:

[0033] Using the coordinates of the coarse positioning points at the top and bottom as centers, local search windows are set up. The original grayscale image data corresponding to the jet pixels within the local search window are extracted. Then, the coordinates (Xc, Yc) of the fine positioning center points at the top and bottom ends within the local search window are calculated using the grayscale centroid method.

[0034] The coordinates (Xc, Yc) of the center point of the precision position satisfy the following formula;

[0035] , ;

[0036] Where: x and y are the horizontal and vertical coordinates of each pixel within the local search window, respectively;

[0037] I(x, y) is the pixel gray value of the original grayscale image of the pixel at the corresponding coordinate position (x, y);

[0038] Furthermore, in step 2.4.3, the pixel length Satisfy the following formula:

[0039] ;

[0040] in: These are the x and y coordinates of the topmost precise positioning center point in the image coordinate system;

[0041] These are the x and y coordinates of the bottommost precise positioning center point in the image coordinate system;

[0042] Furthermore, the hardware configuration parameters of the optical isolation imaging system in step 3 include: the focal length f of the industrial camera lens, the pixel size p of the image sensor, and the actual working distance d from the optical center of the lens to the water-guided laser processing waterline.

[0043] Pixel length With respect to the absolute physical length of the jet Satisfy the following formula:

[0044] .

[0045] On the other hand, based on the above method, the present invention also provides a system for measuring the effective jet length of a water-guided laser and monitoring the nozzle, including: an optical isolation imaging module, a jet contour feature extraction module, a jet length calculation module and a nozzle status early warning module;

[0046] The optical isolation imaging module is used to acquire images of stimulated Raman scattering of red light from the jet;

[0047] The jet contour feature extraction module is used to extract the precise positioning center coordinates of the uppermost and lowermost ends of the jet in the image and calculate the pixel length of the jet;

[0048] The jet length calculation module is used to calculate the absolute physical length of the jet based on the pixel length of the jet;

[0049] The nozzle status early warning module is used to determine the nozzle status and output an alarm signal by comparing the absolute physical length of the jet with a safety threshold.

[0050] Furthermore, the optical isolation imaging module is an industrial camera and a 600nm long-pass filter mounted on the lens of the industrial camera;

[0051] Furthermore, it also includes an interaction module, which is used to input the hardware configuration parameters of the optical isolation imaging module into the system, and to display the stimulated Raman scattering red light image of the acquired jet, the pixel length of the jet, the absolute physical length of the jet, and the nozzle status.

[0052] Compared with the prior art, the present invention has the following beneficial effects:

[0053] (1) Extremely high measurement accuracy under extreme conditions: The dual physical isolation mechanism of long-wave pass filter and Raman scattering completely solves the problem of visual misjudgment caused by metal reflection and water mist interference of workpiece. The extracted contour height is closely matched with the high-energy jet part with actual cutting capability.

[0054] (2) A leap from qualitative to quantitative measurement has been achieved: the relative measurement logic that relies on the summation of pixel changes between consecutive frames has been abandoned, and the system can directly output the physical length of the effective water line in millimeters. This not only captures sudden damage, but also quantitatively tracks the entire life cycle of nozzle wear, providing reliable data for monitoring nozzle status.

[0055] (3) Highly adaptable to engineering: When changing the camera model or the installation location in the industrial field, you only need to modify the focal length, pixel size and working distance parameters in the interactive interface, and the system can automatically calibrate the calculation model, eliminating the tedious and professional software recalibration process. Attached Figure Description

[0056] Figure 1 This is a flowchart of the present invention;

[0057] Figure 2 The original grayscale image of the stimulated Raman scattering red light from the jet with high signal-to-noise ratio;

[0058] Figure 3 The result is the binarized image obtained after binarizing the grayscale image.

[0059] Figure 4 The result diagram shows the marking of the fine positioning points at the top and bottom ends of the effective jet profile;

[0060] Figure 5 This is a schematic diagram of the interactive interface of the system of the present invention. Detailed Implementation

[0061] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0062] First, this invention provides a method for measuring the effective jet length of a water-guided laser and monitoring the nozzle. This invention is designed to address the characteristic that the 532nm high-power green light emitted during water-guided laser processing will produce stimulated Raman scattering in water. Specifically, in the water-guided laser jet, the 532nm high-energy green light in the water can only be excited to generate stimulated Raman scattering red light in the 630-650nm band when it has a certain energy density and undergoes stable total internal reflection. In the ineffective region where the jet breaks down and energy is dissipated, the energy density is insufficient to meet the excitation conditions for stimulated Raman scattering, and therefore, red light in this band will not be generated.

[0063] Therefore, the core idea of ​​this invention is to use the physical nonlinear optical properties of stimulated Raman scattering as a "natural filter" to build an optical isolation imaging module containing a 600nm long-pass filter to acquire a dedicated 630-650nm red light image of the effective jet segment of the water-guided laser. This completely cuts off the interference of splash scattering in the fracture zone and complex ambient light at the physical source, while preserving the image of the effective jet segment.

[0064] Then, the jet contour in the image is extracted through Gaussian filtering, adaptive local threshold binarization, and connected component analysis. Combined with column scanning for coarse localization and gray-scale centroid method for fine localization, the jet feature points A and B and the pixel length in the principal axis direction are obtained. Based on camera hardware parameters such as focal length, pixel size, and working distance, the pixel length is determined using optical geometric formulas. Converted to absolute physical length of the jet ;

[0065] Finally With preset safety threshold By comparing and combining the length change trend, the system can classify and determine the nozzle as normal, progressively worn, or severely damaged, and control the processing linkage (early warning or shutdown).

[0066] Its processing flow is as follows Figure 1 As shown, the specific steps include:

[0067] Step 1: Construct an optical isolation imaging system based on stimulated Raman scattering to continuously acquire the original grayscale image of the red light from the stimulated Raman scattering of the jet;

[0068] The optical isolation imaging module is an industrial camera and a 600nm long-pass filter set on the lens of the industrial camera;

[0069] Specifically, on the water-guided laser processing platform, an industrial camera and a 600nm long-pass filter set at the front of the industrial camera lens can be used to continuously acquire images of stimulated Raman scattering red light emitted from the water-guided laser jet section between 630-650nm, and obtain a high signal-to-noise ratio original grayscale image.

[0070] In this embodiment, a 600nm long-pass filter can be fixed to the front of the lens of an industrial camera using a dedicated filter holder. The industrial camera with the filter installed is then fixed to the side of the water-guided laser processing platform using an adjustment bracket, with the camera lens facing the direction of the water-guided laser jet transmission. This ensures that the lens optical axis is perpendicular to the jet transmission direction, avoiding interference from jet reflections. Then, the industrial camera is used to continuously acquire stimulated Raman scattering red light images of the jet, obtaining a high signal-to-noise ratio original grayscale image, such as... Figure 2 As shown.

[0071] Step 2: Extract features from the jet contour in the original grayscale image and calculate the pixel length of the jet along the main axis at the center of the image;

[0072] Step 2.1: Perform Gaussian filtering noise reduction on the original grayscale image;

[0073] Specifically, in this embodiment, a Gaussian convolution kernel is used to perform convolution processing on the original grayscale image, and a smooth grayscale image is obtained after filtering.

[0074] Step 2.2: Binarize the grayscale image using an adaptive local thresholding algorithm;

[0075] An adaptive local thresholding algorithm is used to binarize a smooth grayscale image, achieving precise pixel segmentation between the jet region and the background region; for example... Figure 3 As shown, after binarization, the jet region appears as a continuous white connected region, while the background and small noise areas appear as black. The jet region has a complete outline with no obvious breaks or noise misjudgments.

[0076] Step 2.3: Extract the jet profile based on connected component analysis and generate a jet mask map;

[0077] Specifically, connected component detection is performed on the binarized image to obtain parameters such as the number, area, and coordinates of all connected components. By setting a threshold for the area of ​​the smallest connected component, the connected component with the largest area is selected as the target region of the effective jet. Then, the pixels of the target region of the jet are set to 255 (white), and the pixels of the remaining regions are set to 0 (black) to generate a jet mask map, thus completing the accurate extraction of the jet contour.

[0078] Step 2.4: Calculate the pixel length of the jet along the main axis of the jet mask image center;

[0079] Step 2.4.1: Determine the coarse positioning points at the uppermost and lower ends of the jet, respectively;

[0080] Specifically, iterate through all pixels of the jet mask image, scan the vertical (Y-axis) pixel distribution column by column along the horizontal axis (X-axis) of the image. If there are multiple jet pixels in each column, take the minimum value of the vertical coordinate among the multiple jet pixels in that column as the uppermost point of the jet pixels in that column, and record the uppermost point of the jet pixels in each column to form a set of uppermost points.

[0081] Similarly, take the maximum value of the y-coordinate among the multiple jet pixels in the column as the lowest point of the jet pixels in the column, record the lowest point of the jet pixels in each column, and form a set of lower points;

[0082] The point with the smallest ordinate (i.e., the highest point in the image) in the upper endpoint set is selected as the coarse positioning point at the top. At the same time, if there are multiple points with the same smallest ordinate in the upper endpoint set, the average of the corresponding x-coordinates of the multiple points with the same smallest ordinate is taken as the coarse positioning point at the top.

[0083] The point with the largest ordinate (i.e., the lowest point in the image) in the lower endpoint set is selected as the coarse positioning point at the bottom. Similarly, if there are multiple points with the same largest ordinate in the lower endpoint set, the average of the corresponding x-coordinates of the multiple points with the same largest ordinate is taken as the coarse positioning point at the bottom.

[0084] Step 2.4.2: Using the gray-scale centroid method, perform sub-pixel fine positioning of the coarse positioning points at the top and bottom ends of the jet to obtain the fine positioning center points at the top and bottom ends of the jet;

[0085] Specifically, a local search window (or region of interest) is set with the coordinates of the topmost and bottommost coarse positioning points as the center. The original grayscale image data corresponding to the jet pixels within the local search window are extracted. Then, the coordinates of the topmost precise positioning center point A and the bottommost precise positioning center point B within the local search window are calculated using the grayscale centroid method.

[0086] In this embodiment, the coordinates of the topmost or bottommost coarse positioning point are set to (X0, Y0), and a rectangular local search window with a size of M×M is established with this coordinate as the center (for example, set to 5×5 or 10×10 pixels).

[0087] Then, the local search window set above is mapped back to the grayscale image after filtering and noise reduction, that is, the grayscale image is used instead of the binarized image to preserve the true energy distribution weight; the coordinates of all jet pixels within the local search window and their corresponding grayscale values ​​I(x, y) are extracted.

[0088] Using pixel grayscale values ​​as weights, the sub-pixel center coordinates within the local search window area are calculated using the grayscale centroid method, as shown in the following formula:

[0089] ;

[0090] Where: x and y are the horizontal and vertical coordinates of each pixel within the local search window, respectively;

[0091] I(x, y) is the pixel grayscale value at the corresponding coordinate position (x, y);

[0092] , For subpixel precision positioning of the center coordinates;

[0093] Using the above formula, this invention can break the integer limitation of physical pixel size and calculate sub-pixel level coordinates with decimal precision. By performing this operation on the top and bottom local search windows respectively, the coordinates of the precise positioning point A at the top of the jet can be obtained. , The coordinates of the precise positioning point B at the bottom () , );like Figure 4 Point A in the diagram represents the starting point of the effective jet length, and point B represents the ending point of the effective jet length.

[0094] 2.4.3 Calculate the pixel length of the jet along the principal axis of the image center. ;

[0095] Pixel length That is, the number of pixels occupied by the laser jet, and the specific calculation process is as follows:

[0096] Considering that the jet axis may be slightly tilted relative to the longitudinal direction of the image in the actual image, if only the difference between the ordinates of the two endpoints is used as the pixel length, the result is only the projection of the jet image length in the longitudinal direction, which may produce a cosine underestimation error caused by the inclination within the image.

[0097] Therefore, in order to obtain the true pixel length that perfectly matches the actual deflection axis of the jet, a two-dimensional Euclidean pixel distance spatial Euclidean distance model between two points is used for the solution.

[0098] The specific calculation formula is as follows: ;

[0099] in: These are the x and y coordinates of the precisely located center point A in the image coordinate system;

[0100] These are the x and y coordinates of the precise positioning center point B in the image coordinate system, respectively.

[0101] The effective sub-pixel length of the jet along the actual main axis direction after eliminating tilt error.

[0102] Step 3: Calculate the absolute physical length of the jet;

[0103] Obtain the hardware configuration parameters of the current optical isolation imaging system, including: the focal length f of the industrial camera lens, the pixel size p of the image sensor, and the actual working distance d from the optical center of the lens to the water-guided laser processing waterline.

[0104] Utilizing the proportional geometry of optical imaging, the pixel length Absolute physical length converted into a jet The formula for its calculation is:

[0105] ;

[0106] in, The absolute physical length of the jet.

[0107] Step 4: Set a safety threshold to quantify and determine the nozzle status.

[0108] The calculated real-time physical length Compared with the system's preset standard safety length threshold Compare:

[0109] (1) If The nozzle is now considered to be in normal condition.

[0110] (2) If The nozzle shows a stable and slight downward trend but remains near the threshold, indicating progressive wear and triggering a warning signal.

[0111] (3) If If the system determines that the effective total reflection length in the current processing waterline is insufficient, or that the nozzle is severely worn or broken, it will immediately send a stop processing signal and trigger an alarm to the processing control system.

[0112] Secondly, this invention also provides a water-guided laser effective jet length measurement and nozzle monitoring system based on the above method, comprising: an optical isolation imaging module, a jet profile feature extraction module, a jet length calculation module, and a nozzle status early warning module, wherein:

[0113] The optical isolation imaging module is used to acquire images of stimulated Raman scattering red light from the jet; in this embodiment, the optical isolation imaging module is an industrial camera and a 600nm long-pass filter mounted on the lens of the industrial camera.

[0114] The jet contour feature extraction module is used to extract the precise localization center coordinates of the uppermost and lowermost ends of the jet in the image and calculate the pixel length of the jet;

[0115] The jet length calculation module is used to calculate the absolute physical length of the jet, i.e., the actual length, based on the pixel length of the jet.

[0116] The nozzle status early warning module is used to determine the nozzle status and output an alarm signal by comparing the actual length of the jet with a safety threshold.

[0117] Furthermore, it also includes interactive modules, such as Figure 5 As shown, it is used to input the hardware configuration parameters of the optical isolation imaging module into the system, and to display the stimulated Raman scattering red light image of the acquired jet, the pixel length of the jet, the actual length of the jet, and the nozzle status.

[0118] Finally, the embodiments described above are merely some, not all, embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for measuring the effective jet length of a water-guided laser and monitoring the nozzle, characterized in that, Includes the following steps: Step 1: Construct an optical isolation imaging system based on stimulated Raman scattering to continuously acquire the original grayscale image of the red light from the stimulated Raman scattering of the jet; Step 2: Extract features from the jet contour in the original grayscale image and calculate the pixel length of the jet along the principal axis at the center of the image. ; Step 3: Utilize the pixel length of the jet Based on the hardware configuration parameters of the optical isolation imaging system, the absolute physical length of the jet is calculated. ; Step 4: Determine the absolute physical length of the jet. Compare with safety threshold :like If the current nozzle status is normal; The nozzle shows a stable and slight downward trend but remains near the threshold, indicating progressive wear and triggering a warning signal. like If the system determines that the effective total reflection length in the current processing waterline is insufficient, or that the nozzle is severely worn or broken, it will immediately send a stop processing signal and trigger an alarm to the processing control system.

2. The method for measuring the effective jet length of a water-guided laser and monitoring the nozzle according to claim 1, characterized in that, Step 2 includes: Step 2.1: Perform Gaussian filtering noise reduction on the original grayscale image; Step 2.2: Binarize the grayscale image using an adaptive local thresholding algorithm; Step 2.3: Extract the jet profile based on connected component analysis and generate a jet mask map; Step 2.4: Calculate the pixel length of the jet along the central main axis of the jet mask image. .

3. The method for measuring the effective jet length of a water-guided laser and monitoring the nozzle according to claim 2, characterized in that, Step 2.4 includes: Step 2.4.1: Determine the coarse positioning points at the uppermost and lower ends of the jet, respectively; Step 2.4.2: Using the gray-scale centroid method, perform sub-pixel fine positioning of the coarse positioning points at the top and bottom ends of the jet to obtain the fine positioning center points at the top and bottom ends of the jet; Step 2.4.3: Calculate the pixel length of the jet along the principal axis of the image center. .

4. The method for measuring the effective jet length of a water-guided laser and monitoring the nozzle according to claim 3, characterized in that, Step 2.4.1 includes: Traverse the entire pixel area of ​​the jet mask image, scan the vertical pixel distribution column by column along the horizontal axis of the image. If there are multiple jet pixels in each column, take the minimum value of the vertical coordinate among the multiple jet pixels in that column as the uppermost point of the jet pixels in that column, and record the uppermost point of the jet pixels in each column to form the uppermost point set. Take the maximum value of the y-coordinate among the multiple jet pixels in the column as the lowest point of the jet pixels in the column, record the lowest point of the jet pixels in each column, and form a set of lower points; Select the point with the smallest ordinate from the set of upper endpoints as the coarse positioning point at the top. If there are multiple points with the same minimum ordinate in the upper endpoint set, then the average of the corresponding x-coordinates of the multiple points with the same minimum ordinate is taken as the coarse positioning point at the top. Select the point with the largest ordinate from the set of lower endpoints as the coarse positioning point at the bottom. If there are multiple points with the same maximum ordinate in the lower endpoint set, then the average of the corresponding x-coordinates of the multiple points with the same maximum ordinate is taken as the coarse positioning point of the lowermost endpoint.

5. The method for measuring the effective jet length of a water-guided laser and monitoring the nozzle according to claim 3, characterized in that, Step 2.4.2 includes: Using the coordinates of the coarse positioning points at the top and bottom as centers, local search windows are set up. The original grayscale image data corresponding to the jet pixels within the local search window are extracted. Then, the coordinates of the fine positioning center points at the top and bottom ends within the local search window are calculated using the grayscale centroid method. , ); Among them, the coordinates of the center point of the sperm position ( , ) satisfies the following formula; ， ； Where: x and y are the horizontal and vertical coordinates of each pixel within the local search window, respectively; I(x, y) is the pixel grayscale value of the original grayscale image of the pixel at the corresponding coordinate position (x, y).

6. The method for measuring the effective jet length of a water-guided laser and monitoring the nozzle according to claim 3, characterized in that, In step 2.4.3, the pixel length Satisfy the following formula: ； in: These are the x and y coordinates of the topmost precise positioning center point in the image coordinate system; These are the x and y coordinates of the bottommost precise positioning center point in the image coordinate system.

7. The method for measuring the effective jet length of a water-guided laser and monitoring the nozzle according to claim 1, characterized in that, The hardware configuration parameters in step 3 include: the focal length f of the industrial camera lens, the pixel size p of the image sensor, and the actual working distance d from the optical center of the lens to the water-guided laser processing waterline. Pixel length With respect to the absolute physical length of the jet Satisfy the following formula: 。 8. A system for measuring the effective jet length of a water-guided laser and monitoring a nozzle as described in claim 1, characterized in that, include: Optical isolation imaging module, jet contour feature extraction module, jet length calculation module, and nozzle status early warning module; The optical isolation imaging module is used to acquire images of stimulated Raman scattering of red light from the jet; The jet contour feature extraction module is used to extract the precise positioning center coordinates of the uppermost and lowermost ends of the jet in the image and calculate the pixel length of the jet; The jet length calculation module is used to calculate the absolute physical length of the jet based on the pixel length of the jet; The nozzle status early warning module is used to determine the nozzle status and output an alarm signal by comparing the absolute physical length of the jet with a safety threshold.

9. The system according to claim 8, characterized in that, The optical isolation imaging module is an industrial camera and a 600nm long-pass filter mounted on the lens of the industrial camera.

10. The system according to claim 8, characterized in that, It also includes an interaction module, which is used to input the hardware configuration parameters of the optical isolation imaging module into the system and display the stimulated Raman scattering red light image of the acquired jet, the pixel length of the jet, the absolute physical length of the jet, and the nozzle status.

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