A digital inkjet nozzle splicing misalignment, nozzle state and color consistency detection and compensation method

Abstract

The present application relates to a kind of digital ink-jet head splicing misregistration, nozzle state and color consistency detection and compensation method, in the edge of printing medium width, pure color reference bar is arranged, and in the non-text area of page, interlaced test pattern is formed;After synchronously collecting print image, the center line of reference bar is extracted to calculate splicing offset and drive head physical correction, the fault state of corresponding nozzle is judged by establishing coordinate reference through positioning long line, color consistency analysis is completed by combining light source compensation and gamut mapping;Finally, ink-jet control compensation parameter is generated and fed back to ink-jet control system, and closed-loop feedback regulation is realized.The present application can realize splicing high-precision detection, nozzle fault accurate diagnosis and color quality control synchronously without interrupting normal production, response speed is fast, and it is suitable for online quality control of high-speed digital ink-jet printing.

Description

Technical Field

[0001] This invention belongs to the field of digital inkjet printing quality inspection and control technology, specifically involving inkjet printhead splicing misalignment detection, nozzle working status monitoring, and automatic color consistency compensation technology. Background Technology

[0002] In the field of digital inkjet printing, with the increasing demand for high-precision, large-format printing, printhead arrays composed of multiple nozzles arranged and spliced ​​together have been widely used. During high-speed continuous printing, ensuring the geometric splicing accuracy, ink ejection status, and color consistency of the printing medium are core technical requirements for digital inkjet printing equipment. Currently, the industry mostly uses manual sampling and visual inspection combined with offline image comparison to detect splicing misalignment, nozzle defects, and color differences; some online detection solutions use general image comparison algorithms to perform overall matching of the acquired printed images to identify defects.

[0003] However, in actual inkjet printing production, the existing technology has the following main shortcomings: First, it is difficult to perform real-time online positioning and dynamic compensation for printhead physical misalignment during high-speed printing. The seams between multiple printheads are susceptible to lateral, longitudinal, or angular offsets caused by mechanical vibration, thermal deformation, equipment malfunctions, and other factors. Existing detection methods mostly rely on manual visual inspection or offline shutdown inspection, which is inefficient, subjective, and has a high rate of missed detections. Furthermore, existing general image comparison algorithms are easily affected by paper texture and ambient lighting fluctuations, making it difficult to achieve sub-pixel-level precise seam positioning and efficiently extract offsets during printing to drive the fine-tuning mechanism for real-time physical correction.

[0004] Secondly, it is difficult to achieve precise real-time diagnosis of specific nozzles and other faults without affecting normal production. During the printing process, dust and ink particles adhering to the printhead surface or localized nozzle blockage and poor ink flow can easily lead to fixed vertical white streaks, missing single colors, or color deviations in the printed products. If a dedicated stoppage is made to proof and print a full-page test image for full nozzle inspection, it will interrupt the production process and waste ink and paper. On the other hand, if the inspection is performed directly on the graphic area of ​​the final product, the algorithm will find it difficult to accurately locate the physical sequence number of the faulty nozzle when some lines are missing due to the complexity of the graphic texture and the lack of a fixed layout benchmark.

[0005] Third, color consistency detection lacks stability and cannot form a highly responsive online closed-loop feedback. Existing color detection algorithms are poorly adaptable to fluctuations in light source stability and color differences between different printheads, resulting in a high false detection rate. Furthermore, existing detection systems are cumbersome in their processes from image acquisition and feature segmentation to anomaly detection, with long response times. The detection results are mostly used only for defect alarms and cannot be directly converted into dynamic adjustment commands for printhead parameters, making it difficult to meet the millisecond-level closed-loop adjustment requirements in high-speed printing scenarios.

[0006] In summary, existing technologies lack a comprehensive detection solution that can efficiently achieve precise positioning of printhead splicing misalignment, accurate diagnosis of nozzle faults, and real-time compensation for color consistency without interrupting normal production and while controlling media loss. Therefore, providing a high-precision, high-response method for detecting and compensating for digital inkjet printhead splicing misalignment, nozzle status, and color consistency is a technical problem urgently needing to be solved by those skilled in the art. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for detecting and compensating for misalignment, nozzle status, and color consistency in digital inkjet printhead splicing. This method achieves sub-pixel-level precise positioning and real-time dynamic compensation of multi-printhead splicing seam offset. It enables accurate fault diagnosis and sequence location at the single nozzle level without interrupting normal production and while controlling ink and paper media loss. Simultaneously, it improves the environmental adaptability and response speed of color consistency detection and constructs a millisecond-level closed-loop feedback mechanism from detection results to printhead parameter adjustment to meet the online quality control requirements of high-speed digital inkjet printing.

[0008] To achieve the above objectives, the present invention provides a method for detecting and compensating for misalignment, nozzle status, and color consistency of digital inkjet printheads, comprising the following steps: During the printing process, a solid-color reference strip extending along the paper feed direction is formed at the edge of the printing medium, and staggered test patterns corresponding to the nozzle arrangement are formed in the non-graphic areas of different pages of the printing medium. A printed image containing the solid color reference bar and the interlaced test pattern is acquired by an image acquisition device synchronized with the printing process. The centerline of the solid color reference strip is extracted, and the extracted centerline is compared with the preset ideal position to calculate the nozzle splicing offset. A compensation command is generated, and the nozzle control unit compensates according to the compensation command. Identify the long spatial positioning lines in the interlaced test pattern to establish a physical coordinate reference. Combine the missing or distorted state of the test lines to map and determine the fault status of the nozzle corresponding to the physical sequence number. Extract the color features of the printed image and perform color consistency analysis; Based on the printhead splicing offset, the nozzle fault status, and the color consistency analysis results, inkjet control compensation parameters are dynamically generated and fed back to the inkjet control system to achieve closed-loop feedback adjustment.

[0009] Furthermore, the width of the solid color reference strip is on the order of millimeters and extends across the entire printing area along the paper feed direction; the process of extracting the center line of the solid color reference strip includes: Edge distortion correction, HSV spatial adaptive thresholding, and multi-scale feature extraction are sequentially performed on the image region containing the solid color reference bar to obtain a binarized solid color bar image. A subpixel-level extraction algorithm is used to extract the subpixel-level positions of the reference bar edges and the center line of the splicing seam in the binarized solid color bar image.

[0010] Furthermore, the nozzle splicing offset includes lateral offset, longitudinal offset, and angular rotation angle.

[0011] Furthermore, the staggered test pattern is set in the non-product graphic area of ​​the paper head, the length direction of each test line is consistent with the paper feeding direction, and each test line is formed by a single nozzle printing.

[0012] Furthermore, the staggered test pattern is divided into upper and lower test lines in the non-image area of ​​a single printed page along the vertical direction of the paper feed, and is staggered in time according to the nozzle number group between consecutive printed pages. All nozzles are divided into several groups along the arrangement direction. Test lines corresponding to different groups are printed page by page in a continuous printing process. One round of testing coverage of all nozzles is completed by printing multiple pages in a continuous process.

[0013] Furthermore, all nozzles are divided into M groups according to their sequence numbers along the arrangement direction. The nozzle with the sequence number MN+i corresponds to the i-th group, where M is a positive integer greater than or equal to 2, i = 1, 2, ..., M, and N is an integer greater than or equal to 0. In the non-image and text areas of the continuously printed page, two different groups of nozzles are selected on each page to print the upper and lower test lines respectively, and the nozzle groups involved in the printing are switched page by page. Through continuous printing of multiple pages, a round of detection coverage of all nozzles is completed.

[0014] Furthermore, all nozzles are divided into four groups according to their sequence numbers along the arrangement direction. The nozzles with sequence numbers of 4N+1 are in the first group, the nozzles with sequence numbers of 4N+2 are in the second group, the nozzles with sequence numbers of 4N+3 are in the third group, and the nozzles with sequence numbers of 4N+4 are in the fourth group, where N is an integer greater than or equal to 0. In the non-image / text area of ​​the current page, the upper row of test lines is printed by the first group of nozzles, and the lower row of test lines is printed by the third group of nozzles. In the non-image / text area of ​​the next page, the upper row of test lines is printed by the second group of nozzles, and the lower row of test lines is printed by the fourth group of nozzles. The detection coverage of all nozzles is completed by printing on two consecutive pages.

[0015] Furthermore, the interlaced test pattern consists of multiple short lines extending along the paper feed direction and long lines periodically distributed at preset nozzle intervals, wherein the length of the long lines is greater than the length of the short lines. The process of identifying the spatial positioning long line is as follows: the position of the long line in the image is identified as the absolute physical coordinate anchor point in space, and the physical nozzle number corresponding to each long line and short line is calculated according to the preset nozzle physical layout data.

[0016] Furthermore, when a partial long line is detected to be missing, the pixel coordinates of the remaining long lines in the image are obtained, and combined with the preset nozzle physical arrangement data, the local resolution ratio is calculated. Based on the local resolution ratio and the coordinates of the remaining long lines, coordinate interpolation and fitting are performed to calculate the spatial physical coordinates of the missing long lines and adjacent short lines, thereby determining the physical sequence number of the faulty nozzle corresponding to the missing test line.

[0017] Furthermore, the process of mapping and determining the fault status of the nozzle corresponding to the physical sequence number specifically includes: If the test line at the preset coordinate position in the physical coordinate reference is missing, it is determined that the nozzle with the corresponding physical number is blocked. If the test line at the preset coordinate position in the physical coordinate reference is laterally offset or distorted in shape, it is determined that the nozzle with the corresponding physical number is in a state of spraying at an angle or poor ink output.

[0018] Furthermore, the process of performing color consistency analysis specifically includes: Before extracting color features, the acquired inkjet images are subjected to light source stability compensation processing. By using a cross-device color difference transfer learning algorithm, the color features of the acquired image are mapped to the target color gamut space, and the color difference value is calculated.

[0019] Furthermore, the inkjet control compensation parameters include at least one of the following: splicing position adjustment parameters, printhead drive voltage parameters, inkjet pulse width parameters, and adjacent nozzle overlap compensation parameters.

[0020] Furthermore, the total response time from image acquisition to the generation of inkjet control compensation parameters does not exceed 200ms, and the execution time for printhead physical displacement correction does not exceed 150ms.

[0021] Compared with existing technologies, the digital inkjet printhead splicing misalignment, nozzle status and color consistency detection and compensation method of the present invention can simultaneously realize printhead splicing accuracy calibration, nozzle fault online diagnosis and printing color quality control without interrupting the normal production process, and build a complete online detection and automatic compensation closed loop, effectively improving the operating efficiency and finished product quality stability of high-speed digital inkjet production.

[0022] First, by placing solid-color reference strips extending along the paper feed direction at the edge of the printing medium, and combining edge distortion correction, HSV spatial adaptive threshold segmentation, and multi-scale feature extraction processing, a sub-pixel-level extraction algorithm is used to obtain the precise position of the reference strip edge and the center line of the splicing seam. This allows for the stable calculation of the printhead's lateral offset, longitudinal offset, and angular rotation angle, effectively reducing the interference of paper texture and ambient light fluctuations on the detection results. The detected offset is directly converted into a displacement compensation command, driving the printhead fine-tuning mechanism to perform physical displacement correction, achieving real-time detection and dynamic correction of splicing deviation. This solves the technical defects of traditional manual detection, such as low efficiency, insufficient accuracy, and inability to dynamically adjust online.

[0023] Secondly, the system employs staggered test patterns placed in non-product graphic areas on the paper surface for nozzle status detection. This does not occupy the effective printing area and eliminates the need to stop printing dedicated test pages, thus avoiding production interruptions and additional losses of ink and paper media. Through a grouped, time-segmented, staggered printing design, different groups of nozzle test lines are covered page by page between consecutive printing pages. Only a small number of pages are needed to complete a round of detection coverage for all nozzles, achieving online polling monitoring of all nozzles while strictly controlling media loss. Furthermore, by using a graphic structure combining long and short lines, and establishing a positioning benchmark with longer positioning lines as spatial physical coordinate anchors, combined with coordinate interpolation and fitting algorithms, the system can accurately calculate the physical nozzle number corresponding to each test line even in scenarios where some long lines are missing due to nozzle malfunction or unstable paper feeding. It can also distinguish between various fault states such as nozzle blockage, spray skew, and poor ink flow, achieving precise fault diagnosis at the single nozzle level. This solves the pain point of traditional detection solutions, which struggle to accurately locate faulty nozzle numbers when some lines are missing.

[0024] Third, the color consistency analysis stage incorporates light source stability compensation processing. First, the acquired images are corrected for illumination non-uniformity. Then, a cross-device color difference transfer learning algorithm is used to map color features to the target color gamut space to calculate color difference values. This effectively eliminates detection errors caused by ambient light fluctuations and individual color differences between different printheads, improving the accuracy and stability of color difference determination. The overall solution integrates printhead splicing offset, nozzle fault status, and color consistency detection results into a unified compensation and control system. It dynamically generates multi-dimensional inkjet control compensation parameters, such as splicing position adjustment, printhead drive parameter adjustment, and supplementary spray compensation, and feeds them back to the inkjet control system, achieving integrated closed-loop adjustment of geometric accuracy and color quality. The entire process from image acquisition to compensation parameter generation can achieve millisecond-level response, fully adapting to the online control requirements of high-speed digital inkjet production, and significantly improving the automation and execution efficiency of quality control. Attached Figure Description

[0025] Figure 1This is a schematic diagram of the overall process of the method for detecting and compensating for misalignment of digital inkjet printhead splicing, nozzle status, and color consistency in an embodiment of the present invention. Figure 2 This is a schematic diagram illustrating the layout of the solid color reference strip and the principle of nozzle splicing misalignment detection in an embodiment of the present invention. Figure 3 This is a schematic diagram of the pagination layout structure of the interlaced test graphics on a continuously printed page in an embodiment of the present invention. Detailed Implementation

[0026] like Figure 1 As shown, this embodiment provides a method for detecting and compensating for misalignment, nozzle status, and color consistency in digital inkjet printhead splicing, including the following steps: During the printing process, a solid-color reference strip extending along the paper feed direction is formed at the edge of the printing medium, and staggered test patterns corresponding to the nozzle arrangement are formed in the non-graphic areas of different pages of the printing medium. This design, by setting up dedicated inspection marks in non-production graphic areas, does not require occupying effective printing area or interrupting the normal production process for separate sampling. The inspection marks can be generated synchronously during continuous production, taking into account both production continuity and inspection timeliness.

[0027] The printing image, which includes the solid color reference bar and the interlaced test pattern, is acquired by an image acquisition device synchronized with the printing process. The synchronous acquisition method ensures that the detection image and the printing position are strictly corresponding, avoiding feature positioning deviations caused by paper feeding errors, and providing a reliable image basis for subsequent high-precision offset calculation and fault location.

[0028] The centerline of the solid color reference strip is extracted, and the extracted centerline is compared with the preset ideal position to calculate the printhead splicing offset. A compensation command is generated, and the printhead control unit performs compensation according to the compensation command. This process realizes a complete link from image feature extraction to physical mechanism correction, which can dynamically correct splicing deviations during the printing process, avoid batch print scrapping caused by deviation accumulation, and effectively improve the geometric accuracy and stability of large-format splicing printing.

[0029] The spatial positioning long lines in the interlaced test pattern are identified to establish physical coordinate references. Combined with the missing or distorted state of the test lines, the fault status of the corresponding physical sequence number of the nozzle is determined. The positioning method of using long lines as physical coordinate anchor points can directly establish the mapping relationship between pixel coordinates and physical nozzle sequence numbers, eliminating the dependence on complete test patterns. It can still complete accurate diagnosis in scenarios where some nozzle faults cause missing lines, greatly improving the reliability and engineering practicality of the detection solution.

[0030] The color features of the printed image are extracted and color consistency analysis is performed. The independent color feature extraction and analysis process can share the same set of acquired images with splicing and nozzle detection without the need for additional image acquisition hardware, thus achieving multi-dimensional quality control without increasing system costs.

[0031] Based on the printhead splicing offset, the nozzle fault status, and the color consistency analysis results, inkjet control compensation parameters are dynamically generated and fed back to the inkjet control system to achieve closed-loop feedback adjustment. By unifying the three types of detection results into the compensation control system, coordinated adjustment of geometric accuracy, nozzle status, and color quality can be achieved, avoiding quality fluctuations in other dimensions caused by single-dimensional compensation, and constructing an integrated quality closed-loop management mechanism.

[0032] As one implementation method, the width of the solid color reference strip in this embodiment is on the order of millimeters and extends across the entire printing area along the paper feed direction. The millimeter-wide reference strip ensures sufficient feature recognition area without excessively occupying the edge space of the printing area. The process of extracting the center line of the solid color reference strip includes: Edge distortion correction, HSV spatial adaptive thresholding, and multi-scale feature extraction are sequentially performed on the image region containing the solid color reference bar to obtain a binarized solid color bar image. A subpixel-level extraction algorithm is used to extract the subpixel-level positions of the reference bar edges and the center line of the splicing seam in the binarized solid color bar image.

[0033] Multi-scale feature extraction can capture the contour features of the reference strip at different resolution levels, effectively resisting interference factors such as paper fiber texture and slight stains. Combined with sub-pixel level extraction algorithms, the detection accuracy of splicing offset can be improved to the sub-pixel level, which is far higher than the accuracy level of traditional pixel level detection.

[0034] As one implementation method, the nozzle splicing offset in this embodiment includes lateral offset, longitudinal offset, and angular rotation angle. These three types of offsets comprehensively cover all possible pose deviation scenarios that may occur during nozzle splicing, ensuring that the fine-tuning mechanism can perform precise correction for the actual deviation type and avoiding the problem that single-dimensional correction cannot eliminate compound deviations.

[0035] In one implementation, the staggered test pattern described in this embodiment is set in the non-product graphic area of ​​the paper tip. The length direction of each test line is consistent with the paper feed direction, and each test line is formed by a single nozzle printing. The design of the test lines extending along the paper feed direction is adapted to the scanning imaging characteristics of the line scan camera, which can ensure that the imaging of a single test line is complete and uniform during continuous scanning. The one-to-one mapping relationship between a single nozzle and a single test line provides a physical basis for subsequent accurate location of the faulty nozzle number.

[0036] In one implementation, all nozzles are divided into M groups according to their numbers along the arrangement direction. The nozzle with the number MN+i corresponds to the i-th group, where M is a positive integer greater than or equal to 2, i = 1, 2, ..., M, and N is an integer greater than or equal to 0. In the non-image and text areas of the continuously printed page, two different groups of nozzles are selected on each page to print the upper and lower test lines respectively, and the nozzle groups involved in the printing are switched page by page. Through continuous printing of multiple pages, a round of detection coverage of all nozzles is completed.

[0037] Furthermore, as a specific implementation of the above-described embodiment, in this embodiment, the staggered test pattern is divided into upper and lower test lines in the non-image area of ​​a single printing page along the vertical direction of the paper feed, and is staggered in time according to the nozzle sequence group between consecutive printing pages. All nozzles are divided into several groups along the arrangement direction. Test lines corresponding to different groups are printed page by page in a continuous printing process. One round of testing coverage of all nozzles is completed by printing multiple pages in a continuous process.

[0038] The segmented, staggered printing design allows for full nozzle coverage across multiple consecutive pages, while only printing a portion of the nozzle test lines on each page. This effectively reduces the space occupied by the test pattern on a single page and the amount of ink consumed, minimizing media and ink loss during testing while ensuring full nozzle detection coverage.

[0039] In one implementation, all nozzles are divided into four groups according to their numbers along the arrangement direction. The nozzles with the number 4N+1 are in the first group, the nozzles with the number 4N+2 are in the second group, the nozzles with the number 4N+3 are in the third group, and the nozzles with the number 4N+4 are in the fourth group, where N is an integer greater than or equal to 0. In the non-image / text area of ​​the current page, the upper row of test lines is printed by the first group of nozzles, and the lower row of test lines is printed by the third group of nozzles. In the non-image / text area of ​​the next page, the upper row of test lines is printed by the second group of nozzles, and the lower row of test lines is printed by the fourth group of nozzles. The detection coverage of all nozzles is completed by printing on two consecutive pages.

[0040] The four-group, two-page polling layout ensures that each page has two rows of test lines for comparison, improving detection reliability. It also requires only two pages to complete one round of testing for all nozzles, resulting in a short testing cycle and fast response speed. It can quickly detect nozzle faults and trigger compensation, avoiding the generation of a large number of defective products.

[0041] In one implementation, the staggered test pattern in this embodiment consists of multiple short lines extending along the paper feed direction and long lines periodically distributed at preset nozzle intervals, wherein the length of the long lines is greater than the length of the short lines. The process of identifying the spatial positioning long line is as follows: the position of the long line in the image is identified as the absolute physical coordinate anchor point in space, and the physical nozzle number corresponding to each long line and short line is calculated according to the preset nozzle physical layout data.

[0042] The periodically distributed long lines can form multiple coordinate anchor points along the entire nozzle arrangement direction, uniformly dividing the detection area and avoiding the remote positioning error caused by a single anchor point; using the physical nozzle arrangement data as the basis for calculation can ensure the accuracy of the mapping from pixel coordinates to physical nozzle numbers and eliminate the systematic deviation caused by imaging scaling.

[0043] As one implementation method, in this embodiment, when a partial long line is detected to be missing, the pixel coordinates of the remaining long lines in the image are obtained, and the local resolution ratio is calculated in combination with the preset nozzle physical arrangement data. Based on the local resolution ratio and the coordinates of the remaining long lines, coordinate interpolation and fitting are performed to calculate the spatial physical coordinates of the missing long lines and adjacent short lines, thereby determining the physical sequence number of the faulty nozzle corresponding to the missing test line.

[0044] This interpolation fitting mechanism can still reconstruct the local coordinate system by retaining effective anchor points even in extreme scenarios where multiple long positioning lines are simultaneously missing due to nozzle blockage. This ensures the accuracy of determining the fault nozzle number and completely solves the technical pain point of traditional solutions where the lack of positioning markers makes accurate diagnosis impossible.

[0045] As one implementation method, the process of mapping and determining the fault status of the nozzle corresponding to the physical serial number in this embodiment specifically includes: If the test line at the preset coordinate position in the physical coordinate reference is missing, it is determined that the nozzle with the corresponding physical number is blocked. If the test line at the preset coordinate position in the physical coordinate reference is laterally offset or distorted in shape, it is determined that the nozzle with the corresponding physical number is in a state of spraying at an angle or poor ink output.

[0046] Multi-dimensional fault status determination can distinguish between different fault levels, such as complete blockage and partial ink output abnormality, which makes it easier for the control system to trigger different compensation or maintenance strategies. For example, in the case of blockage, an automatic cleaning process can be triggered, and in the case of poor ink output, the drive parameters can be adjusted for compensation, thereby improving the accuracy and adaptability of fault handling.

[0047] As one implementation method, the process of performing color consistency analysis in this embodiment specifically includes: Before extracting color features, the acquired inkjet images are subjected to light source stability compensation processing. By using a cross-device color difference transfer learning algorithm, the color features of the acquired image are mapped to the target color gamut space, and the color difference value is calculated.

[0048] Light source stability compensation can eliminate the impact of uneven light intensity and color temperature fluctuations on color detection results in the on-site production environment; cross-device color difference transfer learning algorithm can adapt to the color differences between different printheads, eliminating the need to calibrate thresholds for individual devices, thus improving the device adaptability and on-site deployment efficiency of the detection solution.

[0049] As one implementation method, the inkjet control compensation parameters in this embodiment include at least one of the following: splicing position adjustment parameters, printhead drive voltage parameters, inkjet pulse width parameters, and adjacent nozzle overlap compensation parameters.

[0050] The multi-dimensional compensation parameters cover three types of adjustment methods: mechanical position adjustment, electrical drive parameter adjustment, and printing strategy compensation. It can match the optimal compensation scheme for different types of quality problems and realize closed-loop correction from hardware to software.

[0051] As one implementation method, in this embodiment, the total response time from image acquisition to the generation of inkjet control compensation parameters does not exceed 200ms, and the execution time for printhead physical displacement correction does not exceed 150ms.

[0052] With millisecond-level detection and correction response speed, it can adapt to the production rhythm of high-speed digital inkjet printing, ensuring that the correction is completed before the printed deviation accumulates to the non-conforming threshold, effectively reducing the scrap rate and meeting the online management and control needs of high-speed mass production scenarios.

[0053] The following is in conjunction with the appendix Figure 2 Appendix Figure 3 The specific implementation process of this method will be further explained in detail: Reference Figure 2 As shown, this embodiment achieves accurate detection and dynamic compensation for printhead misalignment by arranging solid color strips with known geometric references along the edge of the printing medium.

[0054] During the printing process, at least one pre-set solid-color reference strip is formed along the paper feed direction at the edge of the printing medium. This reference strip is approximately 1 mm wide and runs through the entire printing surface along the paper feed direction. It is used to characterize the seams between multiple printheads and the reference position of the printhead array. A high-precision linear scan camera, triggered synchronously with the paper feed, acquires the printing image of the reference solid-color strip area.

[0055] The acquired images are sequentially processed with edge distortion correction and HSV spatial adaptive thresholding. Then, sub-pixel level extraction is performed on the edges of the reference strip and the center line of the splicing seam to obtain the actual position of the strip center line in the current image. The extracted current center line position is compared with the ideal reference position preset by the system to calculate the lateral offset, longitudinal offset, and angular offset of the nozzle splicing seam and nozzle row.

[0056] Based on the calculated splicing offset, a displacement compensation command is dynamically generated and output to the inkjet control system. The corresponding motion control parameters and splicing alignment parameters are output to drive the printhead fine-tuning mechanism to perform physical displacement correction. In this embodiment, the execution time of printhead physical displacement correction does not exceed 150ms, which can quickly eliminate splicing deviation during continuous printing.

[0057] Reference Figure 3 As shown, this embodiment utilizes the inkjet lines on each sheet of paper during the printing process to detect nozzle blockage. It can identify faults such as missing prints and skewed prints caused by nozzle blockage in real time during the printing process, without needing to stop the machine for separate proofing.

[0058] To conserve ink and paper while maintaining the resolution of the imaging system, the inkjet lines on the paper head are designed with a grouped, time-segmented, and staggered approach. They are positioned within the non-product graphic area of ​​the paper head, without occupying the effective printing area. The test pattern consists of multiple short lines, with the length of the lines following the paper feed direction. Each line is printed individually from a single nozzle, and the printing system controls the corresponding nozzle to print the test pattern. The algorithm evaluates the working status of each nozzle by recognizing and assessing these line images.

[0059] Specifically, in the paper header area of ​​the m-th page of the printing medium, the upper row of test lines is printed by nozzles with serial numbers satisfying 4N+1, and the lower row of test lines is printed by nozzles with serial numbers satisfying 4N+3; in the paper header area of ​​the (m+1)-th page of the printing medium, the upper row of test lines is printed by nozzles with serial numbers satisfying 4N+2, and the lower row of test lines is printed by nozzles with serial numbers satisfying 4N+4, where N is an integer greater than or equal to 0, and m is a positive integer. One round of detection coverage for all nozzles can be completed by printing two consecutive pages, ensuring detection response speed while controlling detection loss.

[0060] The long lines in the test pattern can be used to locate the nozzle number. When there is no nozzle blockage, the nozzle can be located quickly and easily. Even if some long lines are missing, because multiple long lines are designed in the entire horizontal area, the algorithm can calculate the nozzle number corresponding to each long and short line in the test pattern based on the nozzle layout data and the preset design position of the long lines, and then determine the specific situation of nozzle blockage based on the missing test lines.

[0061] The specific judgment logic is as follows: if the test line at the preset coordinate position is completely missing, the corresponding nozzle is determined to be blocked; if the test line at the preset coordinate position shows lateral displacement or shape distortion, the corresponding nozzle is determined to be spraying at an angle or experiencing ink flow problems. The determined nozzle fault status is synchronously fed back to the inkjet control system, which can trigger targeted compensation and maintenance actions such as automatic cleaning, drive parameter adjustment, or overlapping re-spraying of adjacent nozzles.

[0062] In this embodiment, the splicing misalignment detection, nozzle fault diagnosis and color consistency analysis share the same set of image data acquired by the line scan camera. The color detection process introduces light source stability compensation and cross-device color difference transfer learning algorithms to ensure detection accuracy. The total response time from image acquisition to the generation of all inkjet control compensation parameters does not exceed 200ms, which can meet the millisecond-level closed-loop control requirements of high-speed digital inkjet production.

[0063] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. It should be noted that any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for detecting and compensating for misalignment, nozzle status, and color consistency in digital inkjet printhead splicing, characterized in that, Includes the following steps: During the printing process, a solid-color reference strip extending along the paper feed direction is formed at the edge of the printing medium, and staggered test patterns corresponding to the nozzle arrangement are formed in the non-graphic areas of different pages of the printing medium. A printed image containing the solid color reference bar and the interlaced test pattern is acquired by an image acquisition device synchronized with the printing process. The centerline of the solid color reference strip is extracted, and the extracted centerline is compared with the preset ideal position to calculate the nozzle splicing offset. A compensation command is generated, and the nozzle control unit compensates according to the compensation command. Identify the long spatial positioning lines in the interlaced test pattern to establish a physical coordinate reference. Combine the missing or distorted state of the test lines to map and determine the fault status of the nozzle corresponding to the physical sequence number. Extract the color features of the printed image and perform color consistency analysis; Based on the printhead splicing offset, the nozzle fault status, and the color consistency analysis results, inkjet control compensation parameters are dynamically generated and fed back to the inkjet control system to achieve closed-loop feedback adjustment.

2. The detection and compensation method according to claim 1, characterized in that, The width of the solid color reference strip is in the millimeter range and runs through the entire printing area along the paper feed direction; The process of extracting the center line of the solid color reference bar includes: Edge distortion correction, HSV spatial adaptive thresholding, and multi-scale feature extraction are sequentially performed on the image region containing the solid color reference bar to obtain a binarized solid color bar image. A subpixel-level extraction algorithm is used to extract the subpixel-level positions of the reference bar edges and the center line of the splicing seam in the binarized solid color bar image.

3. The detection and compensation method according to claim 1, characterized in that, The nozzle splicing offset includes lateral offset, longitudinal offset, and angular rotation angle.

4. The detection and compensation method according to claim 1, characterized in that, The staggered test pattern is set in the non-product graphic area of ​​the paper end, the length direction of each test line is consistent with the paper feed direction, and each test line is formed by a single nozzle printing.

5. The detection and compensation method according to claim 4, characterized in that, The staggered test pattern is divided into upper and lower test lines in the non-image area of ​​a single printed page along the vertical direction of the paper feed, and is staggered in time according to the nozzle number group between consecutive printed pages. All nozzles are divided into several groups along the arrangement direction. Test lines corresponding to different groups are printed page by page in a continuous printing process. One round of testing coverage of all nozzles is completed by printing multiple pages in a continuous process.

6. The detection and compensation method according to claim 5, characterized in that, All nozzles are divided into M groups according to their numbers along the arrangement direction. The nozzle with the number MN+i corresponds to the i-th group, where M is a positive integer greater than or equal to 2, i = 1, 2, ..., M, and N is an integer greater than or equal to 0. In the non-image and text areas of the continuously printed page, two different groups of nozzles are selected on each page to print the upper and lower test lines respectively, and the nozzle groups involved in the printing are switched page by page. Through continuous printing of multiple pages, a round of detection coverage of all nozzles is completed.

7. The detection and compensation method according to claim 4, characterized in that, The interlaced test pattern consists of multiple short lines extending along the paper feed direction and long lines periodically distributed at preset nozzle intervals, wherein the length of the long lines is greater than the length of the short lines. The process of identifying the spatial positioning long line is as follows: the position of the long line in the image is identified as the absolute physical coordinate anchor point in space, and the physical nozzle number corresponding to each long line and short line is calculated according to the preset nozzle physical layout data.

8. The detection and compensation method according to claim 7, characterized in that, When a partial long line is detected to be missing, the pixel coordinates of the remaining long lines in the image are obtained, and the local resolution ratio is calculated by combining the preset nozzle physical layout data. Based on the local resolution ratio and the coordinates of the remaining long lines, coordinate interpolation and fitting are performed to calculate the spatial physical coordinates of the missing long lines and adjacent short lines, thereby determining the physical sequence number of the faulty nozzle corresponding to the missing test line.

9. The detection and compensation method according to claim 7, characterized in that, The process of mapping and determining the fault status of the nozzle corresponding to the physical serial number specifically includes: If the test line at the preset coordinate position in the physical coordinate reference is missing, it is determined that the nozzle with the corresponding physical number is blocked. If the test line at the preset coordinate position in the physical coordinate reference is laterally offset or distorted in shape, it is determined that the nozzle with the corresponding physical number is in a state of spraying at an angle or poor ink output.

10. The detection and compensation method according to claim 1, characterized in that, The process of performing color consistency analysis specifically includes: Before extracting color features, the acquired inkjet images are subjected to light source stability compensation processing. By using a cross-device color difference transfer learning algorithm, the color features of the acquired image are mapped to the target color gamut space, and the color difference value is calculated.

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