A method for diagnosing a fault of a printing device in a printing production line

Abstract

This invention relates to the field of image processing technology, specifically to a fault diagnosis method for printing equipment in a printing production line. The method involves image analysis of the printed material after each monochrome printing stage, including the following steps: Step 1: Analyze the image based on a standard printing pattern, dividing it into multiple colored and colorless regions; Step 2: At the start of printing, periodically acquire images. The time interval between image acquisitions is denoted as the acquisition interval, and the total acquisition time is the cycle acquisition period. The image acquisition process within the first cycle acquisition period is denoted as the initial acquisition; Step 3: Based on the multiple images acquired during the initial acquisition process, fuse them to obtain a complete image of the paper and determine the beginning and end points of the complete paper image; Step 4: Compare and analyze the surface image of the currently printed paper with the colored regions in the standard printing pattern one by one. When differences exist, a stop detection signal is generated.

Description

Technical Field

[0001] This invention relates to the field of image processing technology, and more specifically to a fault diagnosis method for printing equipment in a printing production line. Background Technology

[0002] An offset printing press is a type of planographic printing press. During printing, the image is first transferred from the printing plate to a rubber roller, and then transferred from the rubber roller to the paper. Offset printing presses can be classified according to their paper feeding method (sheet-fed offset presses and web offset presses), the number of colors printed in a single pass (single-color, two-color, four-color, and multi-color presses), and the maximum paper size they can handle (small offset presses, six-open, four-open, half-open, and full-sheet presses).

[0003] Printing production lines typically consist of multiple monochrome printing units. Paper passes through each unit sequentially, with each unit adding one color to achieve multicolor printing. In existing offset printing presses, printing quality inspection is usually performed after printing is complete. While this allows for the inspection of the overall printed product and the detection of printing quality issues, the fact that this inspection step is located at the very end of the printing process results in untimely output of inspection results and low efficiency in troubleshooting printing faults, thus presenting certain shortcomings. Summary of the Invention

[0004] In view of the above-mentioned shortcomings of the prior art, the present invention provides a fault diagnosis method for printing equipment in a printing production line, which can effectively solve the problem of lag in the detection of printing quality defects in the prior art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a fault diagnosis method for printing equipment in a printing production line, which involves image analysis of the printed matter after each monochrome printing stage, including the following steps: Step 1: Analyze the image based on the standard printed pattern, dividing it into multiple colored and colorless areas; Step 2: At the start of printing, periodic image acquisition is performed using an image acquisition device located at the exit of the monochrome printing component. The time interval between image acquisitions is called the acquisition interval. The acquisition interval depends on the image features of the standard printing pattern and the circumferential rotational linear speed of the printing plate cylinder. The total duration of multiple image acquisitions is equal to the preset cycle acquisition period. The image acquisition process within the first cycle acquisition period is called the initial acquisition. Step 3: Based on the fusion of images acquired multiple times during the initial acquisition process, a complete image of the paper is obtained, and the beginning and end points of the complete image of the paper are determined; Step 4: Based on the acquisition time of the first image of the complete paper image in Step 3 and the cyclic acquisition cycle, determine the current image set. The current image set corresponds to the surface image of the current printed paper. Merge the images in the current image set and compare them one by one with the colored areas in the standard printing pattern. When there are differences, generate a stop detection signal.

[0006] Furthermore, the process of dividing colored regions is as follows: A positioning coordinate system is constructed using any feature point at the bottom of the standard printed pattern as the origin of the coordinate system. Based on the positioning coordinate system, the two-dimensional plane is divided into multiple rectangular unit recognition areas. The two adjacent sides of the unit recognition area are parallel to the vertical axis and horizontal axis of the positioning coordinate system, respectively. The unit identification area containing the standard printed pattern is designated as the colored area, and the unit identification area not containing the standard printed pattern is designated as the colorless area. The size of the unit identification area is adjusted so that the number of colored areas equals the preset quantity value.

[0007] Furthermore, the vertical axis of the positioning coordinate system corresponds to the circumferential direction of the printing cylinder, and the horizontal axis corresponds to the axial direction of the printing cylinder; There are multiple preset feature conditions. A feature point is a point that satisfies one and only one feature condition.

[0008] Furthermore, the process for determining the data collection interval is as follows: The circumferential rotational linear velocity of the printing cylinder is calculated by obtaining its diameter and rotational speed. A pre-set overlap threshold is used, derived from feature analysis of a standard printed pattern image. The maximum paper width D in the acquired image is obtained and substituted into the formula. The calculation is performed to obtain the acquisition interval t, where RV represents the overlap threshold and v represents the circumferential rotational linear velocity of the printing plate cylinder.

[0009] Furthermore, the overlap threshold acquisition process is as follows: S1: Draw multiple straight lines parallel to the horizontal axis of the positioning coordinate system and denote them as analysis lines. Denote the analysis lines that do not intersect with the standard printed pattern as target lines. S2: When the number of target lines is greater than or equal to 2, the target lines are divided based on their x-coordinates, and then divided into different interval regions. The target lines within each interval region are closely arranged, with no gaps between any two adjacent target lines, and no standard printed patterns are present within the interval regions. Obtain the ordinate of each target line within the interval region, and calculate the range of the ordinates of each target line as the interval width. The interval width represents the maximum interval distance of the standard printed pattern along the longitudinal axis. When the number of target lines is less than 2, set the interval width to 0; S3: There is a preset acquisition interval threshold. When the acquisition interval between two adjacent images is greater than or equal to the acquisition interval threshold, there is no overlapping area in the two images. The acquisition interval threshold is calculated by multiplying it by the circumferential rotational linear velocity of the printing plate cylinder to obtain the upper limit of overlap. The dimension of the upper limit of overlap is made consistent with the interval width and recorded as the width threshold. S4: Obtain the number of intersections between each analysis line and the standard printed pattern and record it as the overlap degree. Construct a line graph showing the change of the overlap degree with the vertical axis of the analysis line. Analyze and calculate the target width value based on the line graph. The target width value enables any two adjacent images to be merged and stitched together to form one image. S5: Perform a dimension conversion on the target width value to obtain the overlap threshold.

[0010] Furthermore, the process for obtaining the target width value is as follows: Multiple cut-off intervals with different widths are constructed. The width of each cut-off interval is greater than the interval width but less than a width threshold. The cut-off intervals are used to randomly cut off the changing lines in the changing line graph. The area of ​​the closed shape enclosed by the changing line graph and the horizontal axis of the coordinate is calculated within each cut-off interval. The minimum value of the closed shape area obtained from multiple cut-offs is divided by the width of the cut-off interval to obtain the pattern distribution index of each cut-off interval. All cut-off intervals with a pattern distribution index greater than or equal to a preset pattern distribution threshold are selected and recorded as target cut-off intervals. The target cut-off interval with the smallest width is selected and its corresponding width value is recorded as the target width value.

[0011] Furthermore, the process of obtaining the cyclic acquisition cycle is as follows: The cyclic acquisition cycle is equal to the sum of the fixed cycle and the compensation cycle. The fixed cycle represents the paper output cycle, and the compensation cycle represents the compensation duration of the dynamic compensation system.

[0012] Furthermore, the process of acquiring a complete image of the paper is as follows: Images acquired during the initial acquisition process are designated as target images. Multiple target images constitute a target image set, which is then labeled according to the order of acquisition time. Let i be the target image index, i = 1, 2, ..., j, and j represent the total number of target images. The construction of j groups of adjacent images is denoted as... When i=j, adjacent images are combined as follows: ; Overlap analysis is performed on two target images in adjacent image combinations, dividing adjacent image combinations into adjacent combinations and isolated combinations. Based on the overlapping area of ​​the target images in the adjacent combination, the two target images are spliced ​​together to obtain a complete paper image. The beginning and end of the complete paper image are determined based on the target images in the isolated combination.

[0013] Furthermore, the overlap analysis process is as follows: In a combination of adjacent image sets, the adjacent sides of two target images are overlapped, with the overlap width equal to the overlap threshold. The overlapping portion is denoted as the overlap region. The overlap degree of the standard printed pattern within the overlap region of the two target images is calculated using the following formula: , where S represents the area of ​​the overlapping part, and S1 and S2 represent the areas of the standard printed patterns of the two target images within the overlapping area, respectively; When the overlap is greater than the preset overlap threshold, adjacent image combinations are recorded as adjacent combinations; when the overlap is less than or equal to the preset overlap threshold, adjacent image combinations are recorded as isolated combinations.

[0014] Furthermore, the image acquisition time is obtained, and the target image containing the beginning of the complete image of the paper is recorded as the anchor point image. Based on the cyclic acquisition cycle, the anchor point image and all images acquired after it are divided into multiple single image sets and a current image set. A single image set satisfies the following condition: Condition 1: A single image set contains multiple consecutively acquired images; Condition 2: The first element of the first single image set is the anchor point image; Condition 3: The acquisition period for a single image set is equal to the cyclic acquisition period; Condition 4: The number of elements in a single image set is greater than the number of elements in the current image set; Multiple images in the current image set are acquired and fused to form an analysis image. The points corresponding to the feature points in the analysis image are determined and recorded as analysis anchor points. An analysis coordinate system is constructed with the analysis anchor points as the origin. The analysis image is divided into analysis regions corresponding to the colored regions. The analysis regions are compared with the corresponding images in the colored regions in groups. When there is a difference between any group of analysis regions and the images in the colored regions, a shutdown detection signal is generated.

[0015] The technical solution provided by this invention has the following advantages compared with the known prior art: This invention improves efficiency in image fusion analysis by increasing the shooting interval, thereby reducing the number of shots required and the number of photos stored in the system, while ensuring that multiple images can be pieced together to form a complete pattern on the paper. Furthermore, by comparing patterns in the analysis area and the colored area, it can quickly screen out anomalies in the printed pattern and thus determine printing defects in the paper. Compared to terminal detection in existing technologies, this allows for more timely shutdown and maintenance, avoiding paper waste. Moreover, since anomaly detection is performed only on images within the colored area, the comparison area is smaller and the efficiency is higher compared to comparing the entire sheet of paper. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0017] Figure 1 This is the overall flowchart of the present invention. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0019] The present invention will be further described below with reference to embodiments.

[0020] See Figure 1 A fault diagnosis method for printing equipment in a printing production line, which divides the printing process into multiple monochrome printing stages, each monochrome printing stage corresponding to one monochrome printing, and performs image analysis on the printed matter after each monochrome printing stage, includes at least the following steps: Step 1: Analyze the image based on the standard printed pattern, dividing it into multiple colored and colorless areas. The specific process is as follows: A standard printing pattern is drawn in a two-dimensional plane, and a Cartesian coordinate system, denoted as the positioning coordinate system, is drawn on the two-dimensional plane. The vertical axis of the positioning coordinate system corresponds to the circumferential direction of the printing cylinder, and the horizontal axis corresponds to the axial direction of the printing cylinder. That is to say, in the actual printing process, the standard printing pattern will be printed onto the paper gradually along the vertical axis, while the pattern on the horizontal axis will be printed onto the paper simultaneously. The origin of the positioning coordinate system is any feature point at the bottom of the standard printing pattern. A feature point on the standard printing pattern refers to a point in the standard printing pattern that satisfies any feature condition. A unique and clear coordinate system can be constructed for the standard printing pattern through the feature point. The feature condition includes, but is not limited to, being located at the bottom left or bottom right of the standard printing pattern.

[0021] The two-dimensional plane is divided into multiple rectangular unit recognition regions based on the positioning coordinate system. The two adjacent sides of each unit recognition region are parallel to the vertical and horizontal axes of the positioning coordinate system, respectively. The size of each unit recognition region depends on the number of unit recognition regions containing the standard printed pattern within the region. The specific division process is as follows: The unit identification areas containing standard printed patterns within the region are designated as colored areas, and the unit identification areas without standard printed patterns within the region are designated as colorless areas. The size of the unit identification areas is adjusted so that the number of colored areas equals a preset quantity value (the value of the quantity value is specifically set by the staff during implementation; in one specific embodiment, it is set to 10). By adjusting the size of the unit identification areas, the number of colored areas is fixed, thus ensuring that the number of comparisons required for different standard printed patterns is uniform when performing one-by-one comparison analysis on the colored areas. This step uniformly limits the total time of comparison analysis, thereby ensuring the stability of the output time of each comparison result and ensuring that the comparison analysis process proceeds in an orderly manner without being affected by changes in the standard printed patterns.

[0022] Furthermore, the center coordinates of each colored region are obtained, and each colored region is assigned a region number. The superscript and subscript of the region number correspond to the x-coordinate and y-coordinate of its center coordinates, respectively.

[0023] Step 2: At the start of printing, periodic image acquisition is performed using an image acquisition device located at the exit of the monochrome printing component. The time interval between image acquisitions is called the acquisition interval. The acquisition interval depends on the image characteristics of the standard printing pattern and the circumferential rotational linear speed of the printing plate cylinder. The total duration of multiple image acquisitions is equal to the preset cycle acquisition period. The image acquisition process within the first cycle acquisition period is called the initial acquisition.

[0024] The process for determining the data collection interval is as follows: The circumferential rotational linear velocity of the printing plate cylinder is calculated by obtaining its diameter and rotational speed. A pre-set overlap threshold is used, obtained based on feature analysis of a standard printed pattern image. The maximum paper width D (along the paper transport direction) in the acquired image is obtained and substituted into the formula. The calculation is performed to obtain the acquisition interval t, where RV represents the overlap threshold and v represents the circumferential rotational linear velocity of the printing cylinder. Image acquisition at this acquisition interval can ensure that images acquired in two adjacent acquisitions can be combined for analysis without losing local details of the overall paper pattern due to segmented acquisition.

[0025] More specifically, the process for obtaining the overlap threshold is as follows: S1: Draw multiple straight lines parallel to the horizontal axis of the positioning coordinate system (the straight lines are closely connected, and the minimum unit length of the positioning coordinate system is 1 pixel, so the difference in the vertical coordinates of two adjacent straight lines is equal to 1 pixel) and denote them as analysis lines. Denote the analysis lines that do not intersect with the standard printed pattern as target lines. S2: When the number of target lines is greater than or equal to 2, the multiple target lines are divided based on their x-coordinates, and then divided into different interval regions, where: Multiple target lines within each interval region are closely arranged, with no gap between any two adjacent target lines (i.e., the difference in the x-coordinate of adjacent target lines is equal to 1 pixel), and no standard printed pattern exists within the interval region. Obtain the ordinate of each target line within the interval region, and calculate the range of the ordinates of each target line as the interval width. The interval width represents the maximum interval distance of the standard printed pattern along the longitudinal axis (when the standard printed pattern consists of multiple independent patterns). When the number of target lines is less than 2, set the interval width to 0.

[0026] It is worth noting that when the width of the overlapping area of ​​two images is less than the gap width, there may be a situation where the standard printed patterns in the two images do not overlap.

[0027] S3: There is a preset acquisition interval threshold. When the acquisition interval between two adjacent images is greater than or equal to the acquisition interval threshold, there is no overlapping area in the two images. The acquisition interval threshold is calculated by multiplying it by the circumferential rotational linear velocity of the printing plate cylinder to obtain the upper limit of overlap. The dimension of the upper limit of overlap is converted into unit pixels and recorded as the width threshold (keeping consistent with the interval width). It should be noted that the initial dimension of the overlap upper limit is millimeters, and the overlap upper limit is obtained by converting it to the unit pixel dimension through the ratio of the number of unit pixels corresponding to the actual length.

[0028] S4: Obtain the number of intersections between each analysis line and the standard printed pattern and record it as the overlap degree. Construct a line graph showing the change of overlap degree with the vertical axis of the analysis line. Construct multiple interception intervals with different widths (intervals are distinguished by their width values). The width of the interception interval must be greater than the interval width and less than the width threshold. Randomly intercept the changing lines in the changing line graph using the interception interval (along the horizontal axis of the changing line graph). Calculate the area of ​​the closed shape enclosed by the changing line graph and the horizontal axis within the interception interval during each interception process. Divide the minimum value of the closed shape area obtained from multiple interceptions by the width of the interception interval to obtain the pattern distribution index of each interception interval. Select all interception intervals with a pattern distribution index greater than or equal to the preset pattern distribution threshold and record them as target interception intervals. Select the target interception interval with the smallest width and record the corresponding width value as the target width value. The pattern distribution threshold is set by the staff during the implementation process. When the pattern distribution index is greater than or equal to the preset pattern distribution threshold, the area of ​​the standard printed pattern within the range obtained by arbitrarily cutting the standard printed pattern with the intercept interval can be used as the overlapping part for splicing and combining two sets of images. In a specific embodiment, the resolution of the acquired image is 2448*2048, and the value of the pattern distribution threshold is 612.

[0029] S5: Convert the dimensions of the target width value to millimeters and record it as the overlap threshold.

[0030] It should be noted that using the target width value as the overlap threshold can maximize the shooting interval while ensuring that the overlapping parts of two adjacent images can be used for image fusion analysis. This reduces the number of images required to obtain the overall paper pattern (the overall paper pattern can be obtained by fusing multiple consecutively acquired images within a cyclic acquisition cycle), reduces the total amount of data processing, and improves data processing efficiency. Furthermore, this data is calculated based on the shape characteristics of the standard printed pattern itself and can be applied to different standard printed patterns (different standard printed patterns require different minimum width values ​​for fusion, and relatively dispersed patterns usually require a larger overlap range for fusion).

[0031] The process of obtaining the cyclic acquisition cycle is as follows: The cyclic acquisition cycle is equal to the sum of the fixed cycle and the compensation cycle. The fixed cycle represents the paper output cycle (i.e., the time interval between the output of the printed paper by the monochrome printing component; under normal circumstances, offset printing maintains a fixed rate for paper printing). The compensation cycle represents the compensation time of the dynamic compensation system (i.e., the duration of the closed-loop registration control to overcome paper offset). Multiple images with an acquisition interval equal to one cyclic acquisition cycle are denoted as synchronous images.

[0032] It is worth noting that, macroscopically, the opening and closing sequence of the gripper and the phase of the roller do follow a strict periodic pattern, meaning that the paper feeding has a periodic pattern. However, at the microscopic level, the movement trajectory of each sheet of paper is unique. Therefore, it is necessary to compensate for the registration deviation of the preceding color group in real time. In the existing technology, a CCD camera is used to scan the printed cross marks to measure the offset data, and the offset is overcome by axial and axial motor compensation. Therefore, the time required for this adjustment process (i.e., the compensation period) is a measurable value. In this way, the cycle acquisition period can be calculated so that the image acquisition time can correspond to the paper shooting angle (generally, when the interval between two shots is equal to the cycle acquisition period, the angle of the paper image captured remains consistent).

[0033] Step 3: Based on the images acquired multiple times during the initial acquisition process, a complete image of the paper is obtained through fusion, and the beginning and end points of the complete image of the paper are determined, where: Images acquired during the initial acquisition process are designated as target images. Multiple target images constitute a target image set, which is then labeled according to the order of acquisition time. Let i be the target image index, i = 1, 2, ..., j, and j represent the total number of target images. The construction of j groups of adjacent images is denoted as... When i=j, adjacent images are combined as follows: The method performs overlap analysis on two target images in adjacent image combinations, classifying adjacent image combinations into adjacent combinations and isolated combinations. Based on the overlapping area of ​​the target images in adjacent combinations, the two target images are spliced ​​together. Based on the target images in isolated combinations, the beginning and end of the complete paper image are determined. By distinguishing between adjacent combinations and isolated combinations, it is determined whether two images can be spliced ​​together, and then multiple images are combined into a complete paper image and the beginning and end are determined.

[0034] It should be noted that when paper is transported between different monochrome printing components, the transport path is from the paper feed cylinder to the paper transfer cylinder and then to the impression cylinder. The paper transfer cylinder mainly relies on the toothed chain for transport. In order to ensure that the paper can be transported stably, at least a part of the paper is clamped and fixed by the transport mechanism. Therefore, it is not possible to directly obtain the surface image of the entire sheet of paper during the paper transport stage. It is necessary to perform fusion analysis to obtain the overall image.

[0035] Specifically, the overlap analysis process is as follows: In a combination of adjacent image sets, the adjacent sides of two target images are overlapped, with the overlap width equal to the overlap threshold. The overlapping portion is denoted as the overlap region. The overlap degree of the standard printed pattern within the overlap region of the two target images is calculated using the following formula: Where S represents the area of ​​the overlapping part, and S1 and S2 represent the standard printed pattern areas of the two target images located in the overlapping area, respectively. When the overlap is greater than the preset overlap threshold (99% in a specific embodiment), the adjacent image combination is recorded as an adjacent combination. When the overlap is less than or equal to the preset overlap threshold, the adjacent image combination is recorded as an isolated combination.

[0036] Step 4: Based on the acquisition time of the first image of the complete paper image in Step 3, determine the current image set. The current image set corresponds to the surface image of the current printed paper. Merge the images in the current image set and compare them one by one with the colored areas in the standard printing pattern to determine whether the pattern of the printed product matches the standard printing pattern. If there is a difference, generate a stop detection signal.

[0037] Specifically, all images captured during the printing process are acquired and their corresponding acquisition times are extracted. The target image containing the beginning of the complete paper image is designated as the anchor point image. Based on the cyclic acquisition cycle, the anchor point image and all images acquired afterward are divided into multiple single image sets and a current image set. A single image set satisfies the following conditions: Condition 1: A single image set contains multiple consecutively acquired images; Condition 2: The first element of the first single image set is the anchor point image; Condition 3: The acquisition period for a single image set is equal to the cyclic acquisition period; Condition 4: The number of elements in a single image set is greater than the number of elements in the current image set (the current image set can be an empty set); It should be noted that each image set, as well as all images captured within the current image set, corresponds to the same printed product.

[0038] Furthermore, multiple images within the current image set are fused to form an analysis image. The points corresponding to the feature points in the analysis image are determined and recorded as analysis anchor points. An analysis coordinate system is constructed using the analysis anchor points as the origin. Based on the analysis coordinate system, analysis regions corresponding to the colored regions in the positioning coordinate system are divided in the analysis image. The analysis regions are compared with the corresponding colored regions in groups. When there is a difference between any group of analysis regions and the images in the colored regions (meaning that the printed pattern in that region is different from the standard printed pattern), a stop detection signal is generated.

[0039] It should be noted that the "fusion" mentioned in this embodiment refers to combining two or more images into one image. The combination mainly relies on the overlapping parts between these images. Fusion technology is a conventional image processing method in the prior art, and will not be described in detail here.

[0040] By comparing and analyzing patterns within the colored and non-colored areas, abnormalities in the printed patterns can be quickly identified, leading to printing defects on the paper. This allows for more timely machine shutdown and maintenance, preventing paper waste. Because the abnormality detection only targets images within the colored areas, the comparison area is smaller and more efficient compared to comparing the entire sheet of paper.

[0041] A computer device includes a memory and a processor, the memory storing a computer program, and the processor executing the computer program to implement the steps in the above method.

[0042] A computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps in the above method.

[0043] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the protection scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for fault diagnosis of printing equipment in a printing production line, wherein image analysis is performed on the printed matter after each monochrome printing stage, characterized in that, Includes the following steps: Step 1: Analyze the image based on the standard printed pattern, dividing it into multiple colored and colorless areas; The process of dividing colored regions is as follows: A positioning coordinate system is constructed using any feature point at the bottom of the standard printed pattern as the origin of the coordinate system. Based on the positioning coordinate system, the two-dimensional plane is divided into multiple rectangular unit recognition areas. The two adjacent sides of the unit recognition area are parallel to the vertical axis and horizontal axis of the positioning coordinate system, respectively. The unit identification area containing the standard printed pattern is recorded as the colored area, and the unit identification area not containing the standard printed pattern is recorded as the colorless area. The size of the unit identification area is adjusted so that the number of colored areas is equal to the preset quantity value. Step 2: At the start of printing, periodic image acquisition is performed using an image acquisition device located at the exit of the monochrome printing component. The time interval between image acquisitions is called the acquisition interval. The acquisition interval depends on the image features of the standard printing pattern and the circumferential rotational linear speed of the printing plate cylinder. The total duration of multiple image acquisitions is equal to the preset cycle acquisition period. The image acquisition process within the first cycle acquisition period is called the initial acquisition. The process for determining the data collection interval is as follows: The circumferential rotational velocity of the printing cylinder is calculated by obtaining its diameter and rotational speed. A pre-set overlap threshold is used, derived from feature analysis of a standard printed pattern image. The maximum paper width D in the acquired image is obtained and substituted into the formula. The calculation is performed to obtain the acquisition interval t, where RV represents the overlap threshold and v represents the circumferential rotational linear velocity of the printing plate cylinder; Step 3: Based on the fusion of images acquired multiple times during the initial acquisition process, a complete image of the paper is obtained, and the beginning and end points of the complete image of the paper are determined; The process of acquiring a complete image of the paper is as follows: Images acquired during the initial acquisition process are designated as target images. Multiple target images constitute a target image set, which is then labeled according to the order of acquisition time. Let i be the target image index, i = 1, 2, ..., j, and j represent the total number of target images. The construction of j groups of adjacent images is denoted as... When i=j, adjacent images are combined as follows: ; Overlap analysis is performed on two target images in adjacent image combinations, and adjacent image combinations are divided into adjacent combinations and isolated combinations. Based on the overlapping area of ​​the target images in the adjacent combination, the two target images are spliced ​​together to obtain a complete paper image. The beginning and end of the complete paper image are determined based on the target images in the isolated combination. Step 4: Based on the acquisition time of the first image of the complete paper image in Step 3 and the cyclic acquisition cycle, determine the current image set. The current image set corresponds to the surface image of the current printed paper. Merge the images in the current image set and compare them one by one with the colored areas in the standard printing pattern. When there are differences, generate a stop detection signal.

2. The fault diagnosis method for printing equipment in a printing production line according to claim 1, characterized in that, The vertical axis of the positioning coordinate system corresponds to the circumferential direction of the printing cylinder, and the horizontal axis corresponds to the axial direction of the printing cylinder. There are multiple preset feature conditions. A feature point is a point that satisfies one and only one feature condition.

3. The fault diagnosis method for printing equipment in a printing production line according to claim 2, characterized in that, The process of obtaining the overlap threshold is as follows: S1: Draw multiple straight lines parallel to the horizontal axis of the positioning coordinate system and denote them as analysis lines. Denote the analysis lines that do not intersect with the standard printed pattern as target lines. S2: When the number of target lines is greater than or equal to 2, the target lines are divided based on their x-coordinates, and then divided into different interval regions. The target lines within each interval region are closely arranged, with no gaps between any two adjacent target lines, and no standard printed patterns are present within the interval regions. Obtain the ordinate of each target line within the interval region, and calculate the range of the ordinates of each target line as the interval width. The interval width represents the maximum interval distance of the standard printed pattern along the longitudinal axis. When the number of target lines is less than 2, set the interval width to 0; S3: There is a preset acquisition interval threshold. When the acquisition interval between two adjacent images is greater than or equal to the acquisition interval threshold, there is no overlapping area in the two images. The acquisition interval threshold is calculated by multiplying it by the circumferential rotational linear velocity of the printing plate cylinder to obtain the upper limit of overlap. The dimension of the upper limit of overlap is made consistent with the interval width and recorded as the width threshold. S4: Obtain the number of intersections between each analysis line and the standard printed pattern and record it as the overlap degree. Construct a line graph showing the change of the overlap degree with the vertical axis of the analysis line. Analyze and calculate the target width value based on the line graph. The target width value enables any two adjacent images to be merged and stitched together to form one image. S5: Perform a dimension conversion on the target width value to obtain the overlap threshold.

4. The fault diagnosis method for printing equipment in a printing production line according to claim 3, characterized in that, The process of obtaining the target width value is as follows: Multiple cut-off intervals with different widths are constructed. The width of each cut-off interval is greater than the interval width but less than a width threshold. The cut-off intervals are used to randomly cut off the changing lines in the changing line graph. The area of ​​the closed shape enclosed by the changing line graph and the horizontal axis of the coordinate is calculated within each cut-off interval. The minimum value of the closed shape area obtained from multiple cut-offs is divided by the width of the cut-off interval to obtain the pattern distribution index of each cut-off interval. All cut-off intervals with a pattern distribution index greater than or equal to a preset pattern distribution threshold are selected and recorded as target cut-off intervals. The target cut-off interval with the smallest width is selected and its corresponding width value is recorded as the target width value.

5. The fault diagnosis method for printing equipment in a printing production line according to claim 1, characterized in that, The process of obtaining the cyclic acquisition cycle is as follows: The cyclic acquisition cycle is equal to the sum of the fixed cycle and the compensation cycle. The fixed cycle represents the paper output cycle, and the compensation cycle represents the compensation duration of the dynamic compensation system.

6. The fault diagnosis method for printing equipment in a printing production line according to claim 1, characterized in that, The overlap analysis process is as follows: In a combination of adjacent image sets, the adjacent sides of two target images are overlapped, with the overlap width equal to the overlap threshold. The overlapping portion is denoted as the overlap region. The overlap degree of the standard printed pattern within the overlap region of the two target images is calculated using the following formula: , where S represents the area of ​​the overlapping part, and S1 and S2 represent the areas of the standard printed patterns of the two target images within the overlapping area, respectively; When the overlap is greater than the preset overlap threshold, adjacent image combinations are recorded as adjacent combinations; when the overlap is less than or equal to the preset overlap threshold, adjacent image combinations are recorded as isolated combinations.

7. The fault diagnosis method for printing equipment in a printing production line according to claim 1, characterized in that, The image acquisition time is obtained, and the target image containing the beginning of the complete image of the paper is recorded as the anchor point image. Based on the cyclic acquisition cycle, the anchor point image and all images acquired after it are divided into multiple single image sets and a current image set. A single image set satisfies the following condition: Condition 1: A single image set contains multiple consecutively acquired images; Condition 2: The first element of the first single image set is the anchor point image; Condition 3: The acquisition period for a single image set is equal to the cyclic acquisition period; Condition 4: The number of elements in a single image set is greater than the number of elements in the current image set; Multiple images in the current image set are acquired and fused to form an analysis image. The points corresponding to the feature points in the analysis image are determined and recorded as analysis anchor points. An analysis coordinate system is constructed with the analysis anchor points as the origin. The analysis image is divided into analysis regions corresponding to the colored regions. The analysis regions are compared with the corresponding images in the colored regions in groups. When there is a difference between any group of analysis regions and the images in the colored regions, a shutdown detection signal is generated.

Images