Method for detecting overprint errors for digital inkjet printers and related devices

Abstract

The application relates to a method for detecting overprint error of a digital inkjet printer and a related device, the method comprising controlling a nozzle system of the digital inkjet printer to print a preset test pattern on a substrate driven by a spindle; during the printing of the test pattern, a position encoding signal of the spindle rotation is acquired through an encoder linked with the spindle, wherein the position encoding signal comprises a pulse signal count value and a period count value; an actual printed image of the test pattern printed on the substrate is acquired through an image acquisition device; the position encoding signal and the actual printed image are analyzed to obtain error characteristics, and the error is classified into one of a plurality of preset error types based on the error characteristics. The application has the advantages of accurately finding out printing errors caused by different sources, facilitating later maintenance or compensation, and reducing error checking difficulty and checking time.

Description

Technical Field

[0001] This application relates to the field of digital inkjet printing, and in particular to a method and related apparatus for detecting misregistration in a digital inkjet printer. Background Technology

[0002] In the field of digital inkjet printing, to achieve high-precision color registration and exquisite image details, the printing press must accurately position and control the movement of the substrate in the paper feed direction (i.e., the longitudinal axis). Currently, the commonly used technical solution in the industry is to install rotary encoders or proximity sensors on the main drive shaft or driven shaft to generate high-speed pulse signals. The control system counts these pulses to monitor the paper's movement speed and position.

[0003] However, in actual operation, due to various factors such as changes in the mechanical state of the equipment, signal transmission interference, or the physical interaction between the substrate and the transmission mechanism, a deviation often occurs between the theoretical position represented by the pulse count value and the actual physical position of the paper. Existing technologies, when dealing with such deviations, typically focus only on the final registration error result. For example, they measure an overall deviation value through image recognition and then use software algorithms for unified compensation, hoping to correct the deviation in subsequent printing.

[0004] This approach has a problem: it fails to distinguish and identify the source of the deviation. In fact, the ultimately observed printing error may stem from entirely different causes. For example, it could be mechanical slippage due to insufficient substrate tension, periodic eccentricity due to wear or improper installation of the main drive shaft, or loss of pulse signal counts due to electrical issues such as bus congestion. Current technology does not differentiate between these different sources of error, simply using software adaptation for compensation. This haphazard approach cannot fundamentally solve the problem, leading to frequent printing quality issues after changes in operating conditions. Maintenance and debugging personnel also spend considerable time troubleshooting because they cannot pinpoint the root cause of the fault, impacting production stability and efficiency. Summary of the Invention

[0005] In order to accurately identify printing errors caused by different root causes, and to facilitate later maintenance or compensation, thereby reducing the difficulty and time required for error troubleshooting, this application provides a method and related apparatus for detecting overprinting errors in digital inkjet printers.

[0006] Firstly, this application provides a method for detecting registration errors in a digital inkjet printer, which employs the following technical solution:

[0007] A method for detecting registration error in a digital inkjet printer, comprising:

[0008] S1. Control the printhead system of the digital inkjet printer to print a preset test pattern on the substrate driven by the spindle;

[0009] S2. During the process of printing the test pattern, the position encoding signal of the spindle rotation is obtained by the encoder linked to the spindle, wherein the position encoding signal includes a pulse signal count value and a period count value;

[0010] S3. Obtain the actual printed image of the test pattern printed on the substrate using an image acquisition device;

[0011] S4. Analyze the position encoding signal and the actual printed image to obtain error characteristics, and classify the error into one of a variety of preset error types based on the error characteristics.

[0012] By employing the aforementioned technical solution, position-encoded signals representing mechanical commands and actual printed images representing physical results are acquired, thus establishing two independent data dimensions for error analysis. Furthermore, by quantifying and analyzing the deviation between these two data dimensions, the external manifestations of printing errors are correlated with the underlying faults within the equipment, such as mechanical slippage, spindle eccentricity, or signal loss. Ultimately, the generalized printing quality issues displayed externally are transformed into categorized and specific equipment condition diagnostic conclusions, facilitating targeted calibration or repair measures rather than general error compensation.

[0013] Optionally, the encoder is mounted on the spindle, and the number of encoder pulses corresponding to one revolution of the spindle is predefined; the encoder has a reference point defined at a certain position on the spindle, and when the encoder spindle rotates to the reference point, a zeroing signal is generated to clear the count and increase the cycle count.

[0014] Optionally, S1 includes the following sub-steps:

[0015] S11. Read the pre-established mapping relationship between the digital model of the test pattern and the position-encoded signal;

[0016] S12. Control the spindle to rotate, and trigger the printhead system to print the test pattern on the substrate based on the real-time acquired position encoding signal and the mapping relationship.

[0017] By employing the above technical solution, the digital model of the test pattern is precisely bound to the physical position signal generated by the encoder. During the printing execution phase, the system triggers the printhead operation based on the real-time acquired position encoding signal and mapping relationship, enabling high-precision synchronization between the printing process of the test pattern and the actual rotation state of the spindle. The final pattern formed on the substrate accurately reproduces the theoretical printing result of the control system based on the position encoding signal. If the printing process itself is error-free, physical errors can be diagnosed by comparing the test pattern with the encoder signal.

[0018] Optionally, the preset error types include:

[0019] Paper slip error type: Paper slip error is obtained by comparing the difference between the actual position of the substrate calculated based on the actual printed image and the theoretical position calculated based on the pulse signal count value;

[0020] Spindle eccentricity error type: The spindle eccentricity error is obtained by identifying the periodic geometric deformation of the test pattern in the actual printed image within a single rotation cycle of the spindle.

[0021] The pulse count loss error type is obtained by comparing the difference between the actual pulse signal count value and the theoretical pulse signal count value corresponding to the substrate displacement calculated based on the actual printed image within the rotation period defined by the periodic reference information.

[0022] By employing the above technical solutions, and by categorizing errors of different physical causes, precise differentiation of error sources is achieved. For example, paper slippage error is determined by comparing the deviation of the substrate's position in two different reference frames. The identification of spindle eccentricity error does not rely on direct position comparison with encoder signals, but rather analyzes the geometric features of the printed image itself to separate the regular deformation that occurs within the same cycle as the spindle rotation, thus directly pointing the error to a mechanical defect in the rotating component. The judgment of pulse count loss error is performed within an independent rotation cycle—that is, within the cycle in which the count is reset for each rotation of the spindle—by comparing the actual count value output by the encoder with the theoretical count value calculated based on physical displacement, verifying whether the signal acquisition and transmission accurately correspond to the paper movement. Here, exclusive judgment criteria are set for each error type to ensure the uniqueness and accuracy of the diagnostic results.

[0023] Optionally, the test pattern is stripes with a preset spacing; step S4 includes the following sub-steps:

[0024] Determine whether the actual position of the stripes calculated from the actual printed image is ahead of the theoretical position of the stripes calculated based on the pulse signal count value. If it is ahead, it is determined to be a pulse count loss error type.

[0025] If it lags behind, determine whether the change in the relative deviation of the stripe position is periodic. If not, it is a paper slippage error; if so, then:

[0026] Determine whether the stripes on the actual printed image change in a gradual manner relative to the stripes on the test pattern, either in terms of spacing or tilt angle. If the change is in terms of spacing, it indicates a spindle eccentricity error where the left and right sides of the spindle are consistently eccentric; if the change is in terms of tilt angle, it indicates a spindle eccentricity error where the left and right sides of the spindle are inconsistently eccentric.

[0027] By adopting the above technical solution, a hierarchical judgment logic is realized. This logic first uses the leading or lagging relationship between the actual position and the theoretical position of the stripes as the first layer of filter to distinguish between signal level error and mechanical level error, which can efficiently separate the signal transmission problem of pulse count loss in advance.

[0028] For the lagging deviations at the mechanical level, the periodic analysis of the deviation change trend is used as a second-level judgment criterion to distinguish between non-systematic occasional failures (such as paper slippage) and systematic periodic failures caused by defects in rotating parts.

[0029] For systematic periodic errors, this solution analyzes the geometric deformation patterns of the printed stripes to perform fault subdivision, distinguishing between overall spindle eccentricity causing periodic speed changes and inconsistent eccentricity on both sides causing lateral oscillation of the medium. Through this series of hierarchical judgments, the solution deconstructs complex mixed error possibilities into a clear and unique diagnostic path, ultimately achieving precise identification of the specific fault mode.

[0030] Optionally, the following steps may also be included:

[0031] S5. Display the categorized types of printing errors and their quantitative analysis data to the user terminal, and provide the user with a variety of processing options for the identified errors.

[0032] Optionally, the processing options include at least: performing software adaptation compensation, adjusting printing press operating parameters, or replacing relevant hardware components.

[0033] Secondly, the computer device provided in this application adopts the following technical solution:

[0034] A computer device comprising:

[0035] One or more processors;

[0036] Memory;

[0037] One or more applications, wherein the one or more applications are stored in the memory and configured to be executed by the one or more processors, the one or more applications being configured to:

[0038] Perform the above-described method for detecting registration errors in digital inkjet printers.

[0039] Thirdly, this application provides a computer-readable storage medium that adopts the following technical solution:

[0040] A computer-readable storage medium storing a computer program that can be loaded by a processor and executed as described above.

[0041] The storage medium stores at least one instruction, at least one program, a code set, or an instruction set, wherein the at least one instruction, the at least one program, the code set, or the instruction set is loaded and executed by the processor to implement the following:

[0042] The above-mentioned method for detecting registration errors in digital inkjet printers.

[0043] In summary, this application includes at least one of the following beneficial technical effects:

[0044] 1. Transform general print quality issues into precise diagnoses of the equipment's physical condition. By establishing a correlation analysis between position encoding signals and actual printed images, and using hierarchical judgment logic to summarize the causes of deviations between the two, it is possible to accurately distinguish errors caused by different physical sources such as mechanical slippage, component eccentricity, or signal loss.

[0045] 2. Improved the efficiency and fundamental nature of equipment calibration and maintenance. Based on precise fault diagnosis, it provides operators with targeted solutions, such as adjusting mechanical parameters or replacing specific components, avoiding the shortcomings of traditional methods that rely solely on general software compensation, which cannot fundamentally solve problems and leads to recurring failures.

[0046] 3. Enhanced long-term positioning accuracy and system reliability in the printing process. By adopting an independent periodic analysis mechanism based on a periodic reference signal, the cross-cycle accumulation of signal counting errors is effectively suppressed, ensuring that the system's positioning reference will not drift even during long-term continuous operation, thereby guaranteeing production stability. Attached Figure Description

[0047] Figure 1 A schematic diagram illustrating the application environment of a method for detecting overprinting errors in a digital inkjet printer according to an embodiment of the present invention is shown.

[0048] Figure 2 A flowchart illustrating a method for detecting overprinting errors in a digital inkjet printer according to an embodiment of the present invention is shown.

[0049] Figure 3 A flowchart illustrating sub-step S1 in one embodiment of the present invention is shown.

[0050] Figure 4 Used to illustrate the actual printed image corresponding to the spindle consistency eccentricity error.

[0051] Figure 5 This is a schematic diagram illustrating the consistent eccentricity of the two sides of the main shaft in one embodiment of the present invention.

[0052] Figure 6 This is a schematic diagram illustrating the inconsistent eccentricity of the two sides of the spindle in one embodiment of the present invention.

[0053] Figure 7 This is used to illustrate the actual printed image corresponding to the spindle misalignment error.

[0054] Figure 8 A flowchart illustrating sub-step S4 in one embodiment of the present invention is shown.

[0055] Figure 9 A schematic diagram of a computer device according to an embodiment of the present invention is shown.

[0056] Explanation of reference numerals in the attached figures:

[0057] 1. Transmission system; 2. Printhead system; 3. Main shaft; 4. Roll-shaped printing substrate; 5. Recycle roll. Detailed Implementation

[0058] The present application will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the scope of the application.

[0059] In the following description, numerous specific details are set forth for purposes of explanation in order to provide a thorough understanding of the inventive concept. As part of this specification, some of the accompanying drawings of this disclosure are block diagrams illustrating structures and devices to avoid complicating the disclosed principles. For clarity, not all features of the actual embodiment need to be described. Furthermore, the language used in this disclosure has been primarily chosen for readability and instructional purposes and may not have been chosen to define or limit the subject matter of the invention, thus requiring the necessary claims to determine such inventive subject matter. References to “an embodiment” or “an embodiment” in this disclosure mean that a particular feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment, and multiple references to “an embodiment” or “an embodiment” should not be construed as necessarily referring to the same embodiment.

[0060] Unless explicitly defined, the terms “a,” “an,” and “the” are not intended to refer to a singular entity, but rather to include a general category whose specific examples can be used for illustration. Therefore, the use of the terms “a” or “an” can mean any number of at least one, including “a,” “one or more,” “at least one,” and “one or more.” The term “or” means any of the options and any combination of the options, including all options unless explicitly indicated that the options are mutually exclusive. The phrase “at least one of” when combined with a list of items refers to a single item in the list or any combination of items in the list. The phrase does not require all items listed unless explicitly defined as such.

[0061] This application provides a digital inkjet printer. To achieve its functions and execute the error detection method described below, refer to... Figure 1 The digital inkjet printer may include functional modules such as a transmission system 1, a printhead system 2, a control system, and a power supply system.

[0062] The transmission system 1 is fundamental for the precise transport of the printing substrate. Specifically, the transmission system 1 includes a main shaft 3 for driving the movement of the printing substrate. In one embodiment, the roll of printing substrate 4 (such as a paper roll) is mounted on an unwinding shaft, and the rotation of the main shaft 3 provides forward tension to the substrate, smoothly guiding it through the work surface. In some applications, a rewinding shaft can also be provided to rewind the printed substrate. To accurately obtain the motion state of the main shaft, the transmission system also includes an encoder linked to the main shaft, configured to acquire position encoded signals of the main shaft's rotation.

[0063] The printhead system 2 is the core actuator for printing patterns. In one embodiment, the printhead system 2 can be fixedly installed above the work surface, and its overall height can be adjusted according to the thickness of the substrate. During printing, the printhead system 2 remains in a fixed position, and the pattern is printed line by line by moving the substrate along the vertical axis.

[0064] The control system coordinates the work of each module and executes the core error detection algorithm. Additionally, the digital inkjet printer includes an image acquisition device configured to acquire the actual printed image of the pattern printed on the substrate. In one embodiment, the image acquisition device can be an industrial camera, installed downstream of the printhead system, to facilitate real-time or time-sharing monitoring of the printing effect. The control system interacts with the encoder, printhead system, and image acquisition device in the drive system, exchanging data and commands.

[0065] The power supply system provides the electrical energy required for the operation of the aforementioned transmission system, nozzle system, control system, etc. It can use standard power supply modules in the existing technology, which will not be described in detail here.

[0066] After the digital inkjet printer is installed, debugged, and loaded with substrate 4 (such as a paper roll), it can enter its workflow. Before formal production printing, parameter debugging and test printing are usually performed to verify and ensure the printer's print quality.

[0067] In applications such as color printing, a printhead system may include multiple printheads for printing different colors of ink. For ease of understanding, this can be simplified to a head printhead group and a tail printhead group positioned along the direction of substrate movement. After the head printhead group completes printing the first color pattern, the substrate is precisely transported a preset distance to the tail printhead group. Subsequently, the tail printhead group overprints the second color based on the first color pattern, thus completing the entire color printing process.

[0068] It is important to note that current positioning technologies in other digital inkjet printers on the market are typically based on high-speed pulse counting, which uses a rotary encoder or proximity sensor linked to the spindle to generate pulse signals to monitor the speed and position of the substrate. However, in this mode, signals may be lost during transmission or counting, introducing positioning accuracy issues. A significant drawback of these digital inkjet printers in handling these positioning deviations is their inability to effectively distinguish the physical source of the error. For example, in the common scheme of using crosshairs for overprinting error detection, the system can only identify the final, superimposed deviation result, such as the overall offset of one color relative to another. However, this scheme cannot inform the operator whether this deviation stems from mechanical slippage between the substrate and the transmission mechanism, periodic eccentricity of the main drive shaft, or other electrical causes. Due to the inability to identify the root cause of the error, existing technologies can only compensate using a uniform software adaptation method. This approach is merely a stopgap measure and cannot fundamentally solve the problem, leading to recurring print quality issues.

[0069] Another drawback is its inability to address the long-term accumulation of errors. The aforementioned crosshair detection methods are essentially post-processing compensation mechanisms. While they can detect and correct errors at the current moment, they do not provide an effective solution for positioning errors that accumulate over time due to factors such as pulse signal loss. This accumulated error leads to a gradually increasing drift in the printing position during long printing jobs, severely impacting the printing quality of large-format or long prints.

[0070] Therefore, this application discloses a method for detecting registration errors in digital inkjet printers, referring to... Figure 2 , including S1-S4.

[0071] S1. Control the printhead system of the digital inkjet printer to print a preset test pattern on the substrate driven by the spindle.

[0072] It should be noted that, to address the shortcomings of the prior art, the embodiments of this application have incorporated corresponding hardware configuration designs. In one optional embodiment, the encoder is mounted on the spindle, and the number of encoder pulses corresponding to one revolution of the spindle is predefined. However, the key difference in this embodiment lies in the fact that the encoder has a reference point defined at a certain position on the spindle. When the encoder spindle rotates to the reference point, a zero-calibration signal is generated. This zero-calibration signal is used to reset the pulse count and increment the cycle count. In other words, by deconstructing the continuous rotational motion into independent data segments in units of revolutions at the data level, the problem of long-term error accumulation is fundamentally solved.

[0073] For example, the encoder can be rigidly connected to the end of the spindle. This direct coupling avoids delays or backlash errors that may be introduced by intermediate transmission links such as belts or gears, ensuring that the position encoding signal accurately reflects the actual angular position of the spindle. This allows the encoder to support speed changes of the substrate during acceleration and deceleration without affecting the printing positioning accuracy. Specifically, the encoder can be a high-resolution model, for example, outputting 65,535 pulse signals per spindle revolution. Simultaneously, when the spindle passes a preset reference point, the encoder outputs a Z signal as the aforementioned zeroing signal. Upon receiving the Z signal, the control system resets the pulse count for the current cycle to zero and begins a new count, while simultaneously incrementing the cycle count. Furthermore, to further ensure the reliability of signal transmission, the encoder and control system can be connected via a high-speed optical communication channel with strong anti-interference capabilities to avoid pulse signal loss due to bus congestion or electrical noise.

[0074] Additionally, it should be noted that the substrate is the medium on which the ink is applied. The specific material can vary depending on the application scenario; for example, it can be various types of paper, plastic film, textile fabrics, etc. For ease of subsequent description, this application will use paper as a representative example of the substrate, but this is not intended to limit the scope of protection of this application.

[0075] The preset test pattern is a reference pattern used for subsequent image analysis to guide the printing of the printhead system. In an optional embodiment, the test pattern is stripes with a pre-defined spacing. Stripe patterns, especially equally spaced stripes perpendicular to the direction of substrate movement, are chosen because their geometric features are simple, facilitating accurate identification of the position, spacing, and tilt angle of each stripe by the subsequent image acquisition device. It should be understood that the form of the test pattern is not limited to this; any pattern containing geometric features (such as grids, dot matrices, or specific markings) that allow for precise measurement of relative positional relationships, as long as it reflects the change in the front-to-back spacing of the printing position in the paper feed direction, is applicable to this application. To facilitate the explanation of the error classification logic of this application, the following detailed description will use equally spaced vertical stripes as a specific example of a test pattern.

[0076] Specifically, in one embodiment, reference is made to... Figure 3 S1 includes the following sub-steps S11-S12.

[0077] S11. Read the pre-established mapping relationship between the digital model of the test pattern and the position-encoded signal.

[0078] S12. Control the spindle to rotate, and trigger the printhead system to print the test pattern on the substrate based on the real-time acquired position encoding signal and the mapping relationship.

[0079] A digital model refers to the digital representation of a test pattern in an ideal coordinate system. Continuing with the example of equally spaced vertical stripes as the test pattern, this digital model can be represented as a set of preset vertical coordinate values, where each coordinate value represents the precise theoretical position where a stripe should be printed. The "mapping relationship" is a rule or data table that associates and binds these theoretical coordinate values ​​with the position encoding signal output by the encoder (i.e., a combination of pulse count and period count). For example, if the spindle rotates one revolution, advancing the substrate by 100mm, and the encoder outputs 65535 pulses per revolution, and the test pattern requires printing a vertical stripe every 1mm, then the mapping relationship can be established as follows: when the period count = 0 and the pulse count ≈ 655, it corresponds to the printing position of the first stripe; when the period count = 0 and the pulse count ≈ 1311, it corresponds to the printing position of the second stripe, and so on. When the pulse count exceeds 65535 with the spindle rotation, the period count becomes 1, the pulse count restarts from 0, and the mapping relationship continues to correspond to subsequent printing positions.

[0080] During step S12, the control system monitors the position encoding signal stream from the encoder in real time. Once the currently acquired position encoding signal matches a preset target value in the mapping relationship, the control system immediately sends a trigger command to the printhead system to complete a printing operation. The high-resolution encoder provides a sufficiently dense set of trigger points, ensuring the precision of the positioning.

[0081] While performing S1, this method also performs S2: during the process of printing the test pattern, the position encoding signal of the spindle rotation is obtained by an encoder linked to the spindle, wherein the position encoding signal includes a pulse signal count value and a period count value.

[0082] Here, digital information representing the mechanical motion state of the spindle is acquired in real time and continuously, reflecting the theoretical position that the substrate should reach under the condition of no physical deviation (such as slippage or eccentricity). The signal is decomposed into two parts: pulse signal count value and period count value. The former represents the angular position of the spindle in the current rotation cycle, while the latter records the number of complete rotations that the spindle has completed.

[0083] Continuing the example above, the control system begins executing the data acquisition task S2 when the spindle starts rotating. Initially, the position encoding signal can be represented as a cycle count value = 0 and a pulse signal count value = 0. As the spindle rotates, the pulse signal count value continuously increases from 0 until it reaches its maximum value per revolution. When the spindle completes its first revolution and passes the reference point, the encoder's Z signal is triggered. Upon receiving this signal, the control system immediately updates the position encoding signal to a cycle count value = 1 and a pulse signal count value = 0. Afterward, the spindle enters its second rotation cycle, and the pulse signal count value again starts accumulating from 0.

[0084] S3. Obtain the actual printed image of the test pattern printed on the substrate using an image acquisition device.

[0085] As mentioned earlier, the image acquisition device is an industrial camera. To ensure image quality, the camera should be rigidly mounted at a fixed position downstream of the printhead system, and its field of view should completely cover the width of the test pattern in the transverse direction of the substrate. Simultaneously, a stable and uniform light source should be provided for the imaging area to eliminate the interference of ambient light variations on image quality and ensure the repeatable identification of image features.

[0086] Before conducting formal error detection, the image acquisition device needs to be calibrated to establish the transformation relationship between image pixel coordinates and physical space coordinates. The calibration process may include:

[0087] First, a calibration pattern with precisely known dimensions is printed on a substrate. Then, an image acquisition device is used to capture images of the calibration pattern, and image processing algorithms are used to analyze the pixel size and distortion of the calibration pattern in the image. Through this process, the conversion coefficient from pixel to physical distance can be calculated, and a parametric model for correcting lens distortion can be generated.

[0088] Continuing the example above, assume the calibration-derived conversion factor is 0.005 mm / pixel. During execution S3, the camera captures a printed pattern of vertical stripes with a theoretical spacing of 1 mm. The image processing module in the control system first corrects the original image using distortion correction parameters. Then, the module uses edge detection and centerline extraction algorithms to identify the center position of each stripe in the image and records its pixel coordinates in the direction of substrate movement. Finally, the system applies the calibrated conversion factor to convert these pixel coordinates into physical positions. For example, a list of actual physical positions of the stripes is calculated.

[0089] S4. Analyze the position encoding signal and the actual printed image to obtain error characteristics, and classify the error into one of a variety of preset error types based on the error characteristics.

[0090] The preset error types include paper sliding error type, spindle eccentricity error type, and pulse count loss error type.

[0091] Paper slippage error is obtained by comparing the difference between the actual position of the substrate calculated based on the actual printed image and the theoretical position calculated based on the pulse signal count value. Paper slippage error is a common mechanical error. Its physical cause lies in insufficient friction between the substrate and the spindle or other drive rollers, resulting in the substrate's actual forward distance being less than the theoretical value even though the spindle has rotated a specific angle. This manifests as the theoretical position represented by the encoder count value leading the actual position calculated from the printed image.

[0092] Reference Figure 4 Spindle eccentricity error is obtained by identifying the periodic geometric deformation of the test pattern in the actual printed image within a single spindle rotation cycle. Here, spindle eccentricity error originates from manufacturing or installation defects in the spindle itself, causing its rotation center to misalign with its geometric center. This error is characterized by a total travel within a single rotation cycle that matches the theoretical value, but the instantaneous speed within the cycle is uneven. This error can be further subdivided into two types: one is consistent eccentricity on both sides of the spindle (refer to...). Figure 5This can cause periodic changes in the effective rotation radius of the spindle, resulting in uneven paper feed speed on the substrate. Ultimately, this manifests as a regular variation in the spacing of lines in the printed image; another issue is inconsistent eccentricity on both sides of the spindle (see...). Figure 6 This causes the substrate to oscillate regularly along the horizontal axis, ultimately resulting in a periodic change in the tilt angle of the vertical stripes in the printed image. (Refer to...) Figure 7 , Figure 7 The paper feed direction is from bottom to top. As can be seen from the diagram, the expected straight edge tilts left and right in the paper feed direction. Pulse count loss error is obtained by comparing the actual acquired pulse signal count value with the theoretical pulse signal count value corresponding to the substrate displacement calculated based on the actual printed image within the rotation period defined by the periodic reference information. Here, pulse count loss error belongs to the electrical or signal transmission layer error. Its cause is usually due to interference during high-speed signal transmission or control system bus blockage, resulting in some pulse signals normally emitted by the encoder failing to be successfully received and counted by the main control system. Physically, the actual position of the substrate has reached or exceeded a certain point, but the pulse count value recorded by the control system is less than the theoretically expected value.

[0093] Specifically, refer to Figure 8 S4 includes the following sub-steps:

[0094] Determine whether the actual position of the stripes calculated from the actual printed image is ahead of the theoretical position of the stripes calculated based on the pulse signal count value. If it is ahead, it is determined to be a pulse count loss error type.

[0095] If it lags behind, determine whether the change in the relative deviation of the stripe position is periodic. If not, it is a paper slippage error; if so, then:

[0096] Determine whether the stripes on the actual printed image change in a gradual manner relative to the stripes on the test pattern, either in terms of spacing or tilt angle. If the change is in terms of spacing, it indicates a spindle eccentricity error where the left and right sides of the spindle are consistently eccentric; if the change is in terms of tilt angle, it indicates a spindle eccentricity error where the left and right sides of the spindle are inconsistently eccentric.

[0097] For example, suppose the theoretical fringe position list obtained after conversion from the position-encoded signal acquired by S2 is [1.00mm, 2.00mm, 3.00mm, ...]. Simultaneously, S3 obtains an actual fringe position list through image analysis. The control system will then compare and analyze these two lists.

[0098] First, the system compares the actual position of each stripe with its theoretical position. If the actual position consistently leads the theoretical position, for example, if the actual position list is [1.05mm, 2.06mm, 3.07mm, ...], this indicates that the physical displacement of the substrate exceeds the displacement recorded by the encoder, and its physical meaning matches the characteristics of pulse count loss. Therefore, the system directly determines the error type to be pulse count loss error.

[0099] If the system detects that the actual position consistently lags behind the theoretical position, it proceeds to the second level of judgment. At this point, the system calculates and analyzes the relative deviation sequence of the stripe positions, i.e., theoretical position - actual position. If the change in this deviation sequence is not periodic, for example, the deviation value increases monotonically with time, such as [0.05mm, 0.12mm, 0.20mm,...], this is consistent with the cumulative slippage characteristics caused by mechanical sliding. Therefore, the system determines the error type to be paper slippage error.

[0100] If the system detects that the relative deviation sequence exhibits periodic fluctuations synchronized with the spindle rotation cycle, it can determine that the error originates from spindle eccentricity. At this point, it proceeds to the third level of judgment to further refine the eccentricity type. The system performs a more in-depth geometric analysis of the actual printed image acquired in S3. If the analysis reveals that the spacing between the printed stripes exhibits periodic changes in density, for example, spacings of 0.99mm, 1.01mm, 0.99mm,..., which matches the speed variation characteristics caused by overall spindle eccentricity, the system classifies it as a spindle eccentricity error type where the left and right sides of the spindle are consistently eccentric. If the analysis reveals that the tilt angle of the printed stripes exhibits periodic changes, which matches the lateral displacement characteristics of the medium caused by spindle oscillation, the system classifies it as a spindle eccentricity error type where the left and right sides of the spindle are inconsistently eccentric.

[0101] In an optional embodiment, the method for detecting registration errors in a digital inkjet printer described in this application may further include the following steps:

[0102] S5. Display the categorized types of printing errors and their quantitative analysis data to the user terminal, and provide the user with a variety of processing options for the identified errors. These processing options include at least: software adaptation compensation, adjusting printing press operating parameters, or replacing relevant hardware components.

[0103] For example, once the analysis is complete, the control system will display a diagnostic report on the user terminal. The report might show: "Spindle misalignment error detected, maximum deviation 0.02mm, cycle synchronized with spindle rotation." The system will then list available processing options for the user to decide.

[0104] If the user chooses to perform software adaptation compensation, the system will activate the corresponding algorithm based on the error type. For example, for spindle eccentricity error, the system can generate a dynamic compensation mapping table synchronized with the spindle Z signal based on the measured periodic deviation data. During printing, the system can advance or delay the inkjet trigger time at each position by microseconds to counteract the effects caused by uneven speed. For paper slippage error, the system can calculate a dynamic slippage coefficient and use it to perform overall advance compensation for the trigger points of all subsequent printing positions. For randomly occurring pulse count loss error, the system can dynamically fine-tune the trigger delay of several subsequent printing points after detecting a leading deviation to smooth out the impact of this sudden error.

[0105] As an example, the compensation algorithm for spindle eccentricity error can be divided into the following stages:

[0106] The first stage is error characteristic modeling. During the S4 analysis, the system has obtained a series of deviation values ​​between the theoretical and actual positions of the printed stripes. Continuing from the previous example, the system can obtain a set of data pairs, i.e., at each theoretical pulse count position p... 理论 Each of these has a corresponding positional deviation Δy. The system first converts the deviation Δy in physical units into a deviation Δp in pulse units. 偏差 Subsequently, the system uses the total number of pulses per revolution of the spindle as the period, and outputs this series (p... 理论 ,Δp 偏差 The data pairs are constructed into an error lookup table. This lookup table describes the lead or lag in the print position at different angles of spindle rotation (represented by the pulse count value within a single revolution). To cover all positions, linear or higher-order interpolation can be performed between the discrete data points in the lookup table.

[0107] The next stage is the compensation mapping table generation phase. Based on the aforementioned error lookup table, the system generates a compensation lookup table. For any pulse position p in the lookup table, the compensation value Δp... 补偿 (p)=-Δp 偏差 (p). For example, if the error lookup table shows an error of -5 pulses (lag) at pulse position 10000, then the compensation lookup table records a compensation value of +5 pulses (advance) at the corresponding position. This compensation lookup table is stored in the control system's memory, with the encoder's Z signal as its cycle start point (i.e., pulse position 0).

[0108] Finally, there is the real-time compensation execution phase. This compensation algorithm is activated during the actual pattern printing. For any row of the image to be printed, the control system first calculates its corresponding theoretical inkjet trigger position p based on its position in the digital image. 目标This refers to a specific cycle count value and pulse signal count value. During the spindle rotation and the advance of the printing substrate, the control system monitors the current position encoding signal p in real time. 当前 Simultaneously, it uses the current pulse signal count as an index to look up or interpolate the compensation lookup table to calculate the real-time compensation value Δp to be applied. 补偿 Subsequently, the system calculates the actual trigger position p after dynamic adjustment. 触发 =p 目标 +Δp 补偿 The control system will continuously monitor p 当前 until p 当前 =p 触发 Only when the conditions are met will an inkjet command be immediately sent to the printhead system.

[0109] If the user chooses to adjust the printing press operating parameters, the system can provide specific guidance. For example, after diagnosing paper slippage error, the terminal can prompt the user to "check and appropriately increase the substrate tension to XX Newtons" or "check the pressure roller air pressure." The operator can then adjust the printing press's tension control system or pneumatic system accordingly, physically increasing the friction between the substrate and the drive rollers, thereby resolving the slippage problem.

[0110] If the user chooses to replace the relevant hardware component, this option typically corresponds to a confirmed physical failure. For example, after diagnosing a severe spindle eccentricity error, the terminal may suggest "Check or replace the spindle bearing." Maintenance personnel can then inspect the spindle and replace the worn bearing. Similarly, if pulse count loss errors occur frequently and communication interference has been ruled out, the terminal may suggest "Replace the encoder" to address a potential hardware fault in the encoder itself.

[0111] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0112] In one embodiment, a computer device is provided, which may be a server, and its internal structure diagram is shown in Figure 9. The computer device includes a processor, memory, a network interface, and a database connected via a system bus. The processor provides computing and control capabilities. The memory includes a non-volatile storage medium and internal memory. The non-volatile storage medium stores an operating system, computer programs, and a database. The internal memory provides an environment for the operation of the operating system and computer programs in the non-volatile storage medium. The database of the computer device contains data related to a method for detecting misregistration in a digital inkjet printer. The network interface of the computer device is used for communication with external terminals via a network connection. When the computer program is executed by the processor, it implements a method for detecting misregistration in a digital inkjet printer.

[0113] In one embodiment, a computer device is provided, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the registration error detection method for a digital inkjet printer described in the above embodiments, for example... Figure 2 S1 to S4, or S1 to S5, are shown.

[0114] In one embodiment, a computer-readable storage medium is provided, on which a computer program is stored. When executed by a processor, the computer program implements the registration error detection method for a digital inkjet printer described in the above embodiments, for example... Figure 2 S1 to S4, or S1 to S5, are shown.

[0115] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. This computer program can be stored in a non-volatile computer-readable storage medium. When executed, the computer program can include the processes of the embodiments of the above methods. Any references to memory, storage, databases, or other media used in the embodiments of this application can include non-volatile and / or volatile memory. Non-volatile memory can include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory. Volatile memory can include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in various forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), dual data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link DRAM (SLDRAM), RAMbus direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and RAMbus dynamic RAM (RDRAM), etc.

[0116] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is used as an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above.

[0117] 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 do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A method for detecting registration error in a digital inkjet printer, characterized in that, include: S1. Control the printhead system of the digital inkjet printer to print a preset test pattern on the substrate driven by the spindle; S2. During the process of spraying the test pattern, the position encoding signal of the spindle rotation is obtained by an encoder linked to the spindle, wherein the position encoding signal includes a period count value and a pulse signal count value corresponding to the period count value; S3. Obtain the actual printed image of the test pattern printed on the substrate using an image acquisition device; S4. Analyze the position encoding signal and the actual printed image to obtain error characteristics, and classify the error into one of a variety of preset error types based on the error characteristics. The variety of preset error types include paper sliding error type, spindle eccentricity error type and pulse count loss error type. The error characteristics obtained by analyzing the position encoding signal and the actual printed image include: By comparing the difference between the actual position of the substrate calculated based on the actual printed image and the theoretical position calculated based on the pulse signal count value, the paper slip error type is obtained; Identify the periodic geometric deformation of the test pattern in the actual printed image within a single rotation cycle of the spindle to obtain the spindle eccentricity error type; the periodic geometric deformation includes gradual changes in spacing or gradual changes in tilt angle; The pulse count loss error type is obtained by comparing the difference between the actual pulse signal count value and the theoretical pulse signal count value corresponding to the substrate displacement calculated based on the actual printed image within the rotation period defined by the periodic reference information.

2. The method for detecting registration error in a digital inkjet printer according to claim 1, characterized in that, The encoder is mounted on the spindle, and the number of encoder pulses corresponding to one revolution of the spindle is predefined; the encoder has a reference point defined at a certain position on the spindle, and when the encoder spindle rotates to the reference point, it generates a zeroing signal, clears the count, and increments the cycle count.

3. The method for detecting registration error in a digital inkjet printer according to claim 2, characterized in that, S1 includes the following sub-steps: S11. Read the pre-established mapping relationship between the digital model of the test pattern and the position-encoded signal; S12. Control the spindle to rotate, and trigger the printhead system to print the test pattern on the substrate based on the real-time acquired position encoding signal and the mapping relationship.

4. The method for detecting registration error in a digital inkjet printer according to claim 1, characterized in that, The preset error types include: Paper slip error type: Paper slip error is obtained by comparing the difference between the actual position of the substrate calculated based on the actual printed image and the theoretical position calculated based on the pulse signal count value; Spindle eccentricity error type: The spindle eccentricity error is obtained by identifying the periodic geometric deformation of the test pattern in the actual printed image within a single rotation cycle of the spindle. The pulse count loss error type is obtained by comparing the difference between the actual pulse signal count value and the theoretical pulse signal count value corresponding to the substrate displacement calculated based on the actual printed image within the rotation period defined by the periodic reference information.

5. The method for detecting registration error in a digital inkjet printer according to claim 4, characterized in that, The test pattern is a stripe with a preset spacing; step S4 includes the following sub-steps: Determine whether the actual position of the stripes calculated from the actual printed image is ahead of the theoretical position of the stripes calculated based on the pulse signal count value. If it is ahead, it is determined to be a pulse count loss error type. If it lags behind, determine whether the change in the relative deviation of the stripe position is periodic. If not, it is a paper slippage error; if so, then: Determine whether the stripes on the actual printed image change in a gradual manner relative to the stripes on the test pattern, either in terms of spacing or tilt angle. If the change is in terms of spacing, it indicates a spindle eccentricity error where the left and right sides of the spindle are consistently eccentric; if the change is in terms of tilt angle, it indicates a spindle eccentricity error where the left and right sides of the spindle are inconsistently eccentric.

6. The method for detecting registration error in a digital inkjet printer according to claim 1, characterized in that, It also includes the following steps: S5. Display the categorized error types and their quantitative analysis data to the user terminal, and provide the user with a variety of processing options for the identified errors.

7. The method for detecting registration error in a digital inkjet printer according to claim 6, characterized in that, The processing options include at least: performing software adaptation compensation, adjusting printing press operating parameters, or replacing relevant hardware components.

8. A computer device, characterized in that, It includes: One or more processors; Memory; One or more applications, wherein the one or more applications are stored in the memory and configured to be executed by the one or more processors, the one or more applications being configured to: perform the method for detecting misregistration for a digital inkjet printer according to any one of claims 1 to 7.

9. A computer-readable storage medium, characterized in that, The storage medium stores at least one instruction, at least one program, code set, or instruction set, wherein the at least one instruction, the at least one program, the code set, or the instruction set is loaded and executed by a processor to implement: the method for detecting overprinting errors for a digital inkjet printer as described in any one of claims 1 to 7.

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