Overprinting error detection method for digital ink-jet printer and related device

Abstract

The invention relates to an overprinting error detection method for a digital ink-jet printer and a related device, and the method comprises the steps: controlling a nozzle system of the digital ink-jet printer, and spraying a preset test pattern on a printing stock driven by a main shaft; in the process of spraying the test pattern, a position coding signal of rotation of the main shaft is obtained through an encoder linked with the main shaft, and the position coding signal comprises a pulse signal count value and a period count value; through an image acquisition device, acquiring an actual printing image of the printed material which is painted with the test pattern; and analyzing the position coding signal and the actual printing image to obtain error characteristics, and classifying the error into one of a plurality of preset error types based on the error characteristics. The method has the advantages that the printing errors caused by different roots are accurately found out, later maintenance or compensation is facilitated, and the error checking difficulty and the checking time are reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of digital inkjet printing, and in particular to a method for detecting overprint error of a digital inkjet printer and related device. BACKGROUND

[0002] In the field of digital inkjet printing, in order to achieve high-precision color overprint and exquisite image details, the printing machine must accurately position and control the movement position of the printing substrate in the paper running direction (i.e. the longitudinal axis). At present, the commonly used technical solution in the industry is to install a rotary encoder or a proximity sensor on the main drive shaft or the driven shaft to generate high-speed pulse signals, and the control system counts these pulses to monitor the movement speed and position of the paper.

[0003] However, in actual operation, due to changes in the mechanical state of the equipment, signal transmission interference, or physical interaction between the printing substrate and the transmission mechanism, etc., there is often a deviation between the theoretical position represented by the pulse count value and the actual physical position of the paper. When dealing with such deviations, the existing technology usually only focuses on the final overprint error result, for example, by measuring a total deviation value through image recognition, etc., and then making a unified compensation through software algorithms in order to correct the deviation in subsequent printing.

[0004] This processing method has a problem, which is that it cannot distinguish and identify the source of the deviation. In fact, the final observed printing error can be caused by completely different causes, for example, it can be caused by mechanical sliding due to insufficient tension of the printing substrate, it can be caused by periodic eccentricity due to wear or improper installation of the main drive shaft, or it can be caused by loss of pulse signal counting due to bus congestion. The existing technology does not distinguish these different sources of error and blindly compensates by software adaptation. This general processing method cannot fundamentally solve the problem, resulting in frequent printing quality accidents after the working condition of the equipment changes, and maintenance and debugging personnel also spend a lot of time troubleshooting because they cannot locate the root cause of the fault, affecting the stability and efficiency of production. SUMMARY

[0005] In order to accurately find out the printing errors caused by different sources and facilitate later maintenance or compensation, reduce error troubleshooting difficulty and troubleshooting time, the present application provides a method for detecting overprint error of a digital inkjet printer and related device.

[0006] In the first aspect, the present application provides a method for detecting overprint error of a digital inkjet printer, which adopts the following technical solution: A method for detecting overprint error of a digital inkjet printer, comprising: S1. Control a printhead system of a digital inkjet printer to print a preset test pattern on a substrate driven by a spindle; S2. During the printing of the test pattern, acquire a position encoding signal of the spindle rotation through an encoder linked with the spindle, wherein the position encoding signal comprises a pulse signal count value and a period count value; S3. Acquire an actual printed image of the test pattern printed on the substrate through an image acquisition device; S4. Analyze the position encoding signal and the actual printed image to obtain an error feature, and classify the error into one of a plurality of preset error types based on the error feature.

[0007] By using the above technical solution, the position encoding signal representing the mechanical instruction and the actual printed image representing the physical result are acquired, thereby establishing two independent data dimensions for error analysis. Then, the deviation between the two data dimensions is quantified and analyzed to associate the external manifestation of the printing error with the internal fault nature of the equipment, such as mechanical sliding, spindle eccentricity, or signal loss. Finally, the general printing quality problem displayed externally is converted into a diagnosable and specific equipment state diagnosis conclusion, so that subsequent targeted calibration or repair measures can be taken instead of general error compensation.

[0008] Optionally, the encoder is installed on the spindle, and the number of encoder pulses corresponding to one rotation of the spindle is predefined; the encoder is defined with a reference point at a certain position of the spindle, and the encoder generates a zero calibration signal when the spindle rotates to the reference point, clears the count and increases the period count.

[0009] Optionally, the S1 comprises the following sub-steps: S11. Read a pre-established mapping relationship between a digital model of the test pattern and the position encoding signal; S12. Control the spindle to rotate, and trigger the printhead system to print the test pattern on the substrate according to the real-time acquired position encoding signal and the mapping relationship.

[0010] By using the above technical solution, the digital model of the test pattern is accurately bound with the physical position signal generated by the encoder. During the printing execution stage, the system triggers the printhead operation according to the real-time acquired position encoding signal and the mapping relationship, so that the printing process of the test pattern is highly accurately synchronized with the actual rotation state of the spindle. Finally, the pattern formed on the substrate can accurately reproduce the theoretical printing result of the control system based on the position encoding signal. In the case that the printing process itself is correct, the test pattern and the encoder signal can be compared to diagnose the error at the physical level.

[0011] Optionally, the preset error types include: a paper slip error type, the paper slip error being 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; a spindle eccentricity error type, the spindle eccentricity error being obtained by identifying the periodic geometric deformation of the test pattern in the actual printed image within a single rotation period of the spindle; a pulse count loss error type, the pulse count loss error being obtained by comparing the difference between the actual pulse signal count value and the theoretical pulse signal count value corresponding to the displacement of the substrate calculated based on the actual printed image within a rotation period defined by the periodic reference information.

[0012] By using the above technical solution, the error sources are accurately distinguished by inducing error types for errors of different physical causes. For example, the paper slip error is determined by comparing the deviation between the positions of the substrate in two different reference systems. The identification of the spindle eccentricity error does not depend on the direct position comparison with the encoder signal, but by analyzing the geometric features of the printed image itself, the regular deformation with the same period of the spindle rotation is separated, so as to directly point to the mechanical defects of the rotating part. The judgment of the pulse count loss error is to compare the actual count value of the encoder output with the theoretical count value based on the physical displacement in an independent rotation period, i.e. one week in which the count is reset every time the spindle rotates one week, to verify whether the signal acquisition and transmission correspond to the paper movement accurately. Here, exclusive judgment criteria are set for each error type to ensure the uniqueness and accuracy of the diagnosis results.

[0013] Optionally, the test pattern is a stripe with a preset interval; and the S4 includes the following sub-steps: determining whether the actual position of the stripe calculated based on the actual printed image leads the theoretical position of the stripe calculated based on the pulse signal count value, if yes, the error type is determined as the pulse count loss error; if no, determining whether the change of the relative deviation of the stripe position has periodicity, if no, the error type is the paper slip error, if yes, the error type is: determining whether the change of the stripe on the actual printed image relative to the test pattern is the interval gradual change or the inclination gradual change, if the change is the interval gradual change, the error type is the spindle eccentricity error of the spindle with consistent eccentricity on the left and right sides, if the change is the inclination gradual change, the error type is the spindle eccentricity error of the spindle with inconsistent eccentricity on the left and right sides.

[0014] By adopting the technical scheme, a hierarchical judgment logic is realized. The logic first uses the leading or lagging relationship between the actual position and the theoretical position of the stripe as a first layer filter for distinguishing the signal level error and the mechanical level error, and can efficiently separate the signal transmission problem of pulse count loss in advance.

[0015] For the lagging deviation belonging to the mechanical level, the periodicity analysis of the deviation change trend is used as a second layer judgment standard to distinguish the non-systematic accidental failure (such as paper sliding) and the systematic periodic failure caused by the rotating part defect.

[0016] For the systematic periodic error, the scheme analyzes the geometric deformation mode of the printed stripe to perform fault subdivision, so as to distinguish whether the whole eccentricity of the main shaft causes the periodic change of the speed or the inconsistent eccentricity of the two sides causes the medium lateral swing. Through the series of hierarchical judgments, the scheme decomposes the complex mixed error possibility into a clear and unique diagnosis path, and finally realizes the accurate locking of the specific fault mode.

[0017] Optionally, the method further comprises the following steps: S5. Displaying the classified type of the printing error and the quantitative analysis data thereof to the user terminal, and providing a plurality of processing options for the identified error for the user to select.

[0018] Optionally, the processing options at least include: performing software adaptation compensation, adjusting the operation parameters of the printer, or replacing the related hardware components.

[0019] In a second aspect, the present application provides a computer device, which adopts the following technical scheme: A computer device comprises: one or more processors; a memory; one or more application programs, wherein the one or more application programs are stored in the memory and configured to be executed by the one or more processors, and the one or more programs are configured to: execute the above-mentioned registration error detection method for a digital inkjet printer.

[0020] In a third aspect, the present application provides a computer readable storage medium, which adopts the following technical scheme: A computer readable storage medium stores a computer program capable of being loaded and executed by a processor to execute the above-mentioned method.

[0021] The storage medium stores at least one instruction, at least one program, a code set or an instruction set, and the at least one instruction, the at least one program, the code set or the instruction set are loaded and executed by the processor to realize: The overprint error detection method for a digital inkjet printer as described above.

[0022] In summary, the present application includes at least one of the following beneficial technical effects: 1. The general printing quality problem is converted into accurate diagnosis of the physical state of the equipment. By establishing the correlation analysis of the position encoding signal and the actual printed image, and using hierarchical judgment logic to reason the deviation of the two, the errors caused by different physical sources such as mechanical sliding, component eccentricity or signal loss can be accurately distinguished.

[0023] 2. The efficiency and fundamentality of equipment calibration and maintenance are improved. Based on the accurate fault tracing diagnosis, targeted solutions are provided for the operators, such as adjusting mechanical parameters or replacing specific components, avoiding the defects of traditional methods that rely only on general software compensation and cannot fundamentally solve the problem, leading to repeated faults.

[0024] 3. The long-term positioning accuracy and system reliability of the printing process are enhanced. By using an independent period analysis mechanism based on periodic reference signals, the cross-period accumulation of signal counting errors is effectively suppressed, ensuring that the positioning reference of the system does not drift even in long-time continuous operation, thereby ensuring the stability of production. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 An application environment schematic diagram of the overprint error detection method for a digital inkjet printer in an embodiment of the present application is shown.

[0026] Figure 2 A flowchart of the overprint error detection method for a digital inkjet printer in an embodiment of the present application is shown.

[0027] Figure 3 A flowchart of the S1 sub-step in an embodiment of the present application is shown.

[0028] Figure 4 An actual printed image corresponding to the consistent eccentric error of the main shaft is shown.

[0029] Figure 5 A schematic diagram of the consistent eccentricity of the main shaft on both sides in an embodiment of the present application is shown.

[0030] Figure 6 A schematic diagram of the inconsistent eccentricity of the main shaft on both sides in an embodiment of the present application is shown.

[0031] Figure 7 An actual printed image corresponding to the inconsistent eccentric error of the main shaft is shown.

[0032] Figure 8A flow chart illustrating the S4 sub-step in one embodiment of the present application is shown.

[0033] Figure 9 A schematic diagram of a computer device in one embodiment of the present application is shown.

[0034] BRIEF DESCRIPTION OF DRAWINGS 1. drive system; 2. nozzle system; 3. main shaft; 4. roll-shaped printing substrate; 5. recycling roll. DETAILED DESCRIPTION

[0035] The present application is further described in the detailed description that follows, in reference to the drawings wherein like numerals represent like elements throughout the several views. It should be understood that the specific embodiments described herein are merely exemplary in nature intended to provide an overall understanding of the application and are not intended to limit the scope of the application.

[0036] In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present application. As part of the present disclosure, some of the drawings can represent structural and electrical devices in block diagram form in order to avoid obscuring the present principles disclosed. Some features of actual implementations can not be described in detail in order to avoid unnecessarily obscuring the present principles. Also, the language used in the present disclosure has been principally selected for readability and instructional purposes and can not have been selected to delineate or circumscribe the subject matter of this application, resort to the claims being necessary to determine such subject matter. Reference in the specification to "one implementation" or "an implementation" means that a particular feature, structure, or characteristic described is included in at least one implementation and multiple references to "one implementation" or "an implementation" do not necessarily all refer to the same implementation.

[0037] Unless specifically stated otherwise, the terms "a," "an" and "the" are not intended to refer to singular entities but include the general class of which a specific example can be used for illustration. The use of the terms "a" or "an" can mean any number of including "one," "one or more," "at least one," and "one or more than one." The term "or" means any one of the alternatives, as well as any combination of the alternatives, including all of the alternatives, unless the alternatives are expressly indicated to be mutually exclusive. The phrase "at least one of" followed by a list of items means individual items in the list or any combination of the items in the list, unless expressly indicated to the contrary. The phrase "at least one of" followed by a list of items means individual items in the list or any combination of the items in the list, unless expressly indicated to the contrary.

[0038] The embodiments of the present application provide a digital inkjet printer, to realize its functions, and execute the error detection method to be described later, refer to Figure 1 The digital inkjet printer can include functional modules such as a drive system 1, a nozzle system 2, a control system, and a power supply system.

[0039] The transmission system 1 is responsible for the accurate conveying of the print substrate. Specifically, the transmission system 1 includes a main shaft 3 for driving the movement of the print substrate. In one embodiment, a roll-shaped print substrate 4 (e.g. a paper roll) is installed on a feed roll, and the rotation of the main shaft 3 provides a pulling force for the print substrate to move smoothly through the working plane. In some applications, a take-up roll can also be provided for rewinding the printed print substrate. In order to accurately obtain the movement state of the main shaft, the transmission system further includes an encoder coupled to the main shaft, configured to obtain a position encoding signal of the rotation of the main shaft.

[0040] The printhead system 2 is the core execution mechanism for realizing pattern spraying. In one embodiment, the printhead system 2 can be fixedly installed above the working plane, and its overall height can be adjusted according to the thickness of the print substrate. During printing, the printhead system 2 remains stationary, and the movement of the print substrate in the longitudinal axis realizes the line-by-line spraying of the pattern.

[0041] The control system is responsible for coordinating the work of each module and executing the core error detection algorithm. In addition, the digital inkjet printer also includes an image acquisition device configured to obtain the actual printed image of the sprayed pattern on the print 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 spraying effect. The control system interacts with the encoder in the transmission system, the printhead system, and the image acquisition device for data and instruction exchange.

[0042] The power supply system provides the electrical energy required for the operation of the above-mentioned transmission system, printhead system, control system, etc. It can use standard power supply modules in the prior art, which will not be described here.

[0043] After the above-mentioned digital inkjet printer is installed, debugged, and loaded with a print substrate 4 (e.g. a paper roll), its working process can be entered. Before formal production printing, parameter debugging and test printing are usually performed to verify and ensure the printing quality of the printer.

[0044] In some application scenarios such as color printing, the printhead system can include multiple groups of printheads for spraying different colors of ink. For ease of understanding, it can be simplified as a head printhead group and a tail printhead group arranged in the movement direction of the print substrate. When the head printhead group completes the printing of the pattern of the first color, the print substrate is accurately conveyed by a predetermined distance to the position of the tail printhead group. Subsequently, the tail printhead group performs overprinting of the second color based on the pattern of the first color, thereby completing the entire color printing process.

[0045] It is noted that the positioning technology of other digital inkjet printers on the market is usually based on a high-speed pulse counting mode, i.e. a pulse signal is generated by a rotary encoder or a proximity sensor linked with the main shaft to monitor the movement speed and position of the substrate. However, in this mode, the signal may be lost in the process of transmission or counting, thereby introducing positioning accuracy problems. A significant defect of these digital inkjet printers in dealing with these positioning deviations is that they cannot effectively distinguish the physical source of the error. For example, in the commonly used scheme of using cross-shaped marks for overprint error detection, the system can only identify the final, superimposed deviation result, such as the overall offset of one color relative to another color. However, this scheme cannot tell the operator whether this deviation is caused by mechanical sliding between the substrate and the transmission mechanism, periodic eccentricity of the main drive shaft, or other electrical reasons. Since the root cause of the error cannot be identified, the prior art can only take a unified software adaptation approach for compensation, which is a temporary solution and cannot fundamentally solve the problem, leading to repeated printing quality problems.

[0046] In addition, another defect thereof is that it is difficult to solve the problem of long-term accumulation of errors. The above-mentioned cross-shaped detection method is essentially a post-compensation mechanism. Although it can discover and correct the error at the current time, it does not provide an effective solution to the positioning error caused by pulse signal loss and other reasons that accumulates over time. Such accumulated error will cause the printing position to gradually drift in a long printing task, seriously affecting the printing quality of large-format or long-image prints.

[0047] Therefore, the embodiment of the present application discloses an overprint error detection method for a digital inkjet printer, referring to Figure 2 , comprising S1-S4.

[0048] S1. Control the printhead system of the digital inkjet printer to print a preset test pattern on the substrate driven by the main shaft.

[0049] It is noted that in order to solve the defects existing in the prior art, the embodiment of the present application makes corresponding design on the hardware configuration. In an optional embodiment, the encoder is installed on the main shaft, and the number of encoder pulses corresponding to one revolution of the main shaft is predefined. However, the key difference of the present embodiment is that the encoder is defined with a reference point at a certain position of the main shaft, and the encoder generates a zero calibration signal when the main shaft rotates to the reference point, which is used to clear the pulse count and increase the period count. That is, by decomposing the continuous rotary motion into independent data segments in units of turns at the data level, the problem of long-term accumulation of errors is fundamentally solved.

[0050] For example, the encoder can be rigidly connected to the end of the main shaft. This direct coupling avoids the delay or gap error that can be introduced by intermediate transmission elements such as belts or gears, thereby ensuring that the position encoding signal accurately reflects the actual angular position of the main shaft, and thereby supporting the speed variation of the print substrate during acceleration and deceleration without affecting the positioning accuracy of the print. Specifically, the encoder can be a high-resolution model, for example, it can output 65535 pulse signals during one revolution of the main shaft. At the same time, when the main shaft passes through the preset reference point, the encoder will output a Z signal as the zero calibration signal. After receiving the Z signal, the control system will clear the pulse count of the current cycle and start a new count, while the cycle count value is incremented by one. In addition, to further ensure the reliability of signal transmission, the encoder and the control system can be connected through a high-speed optical communication channel with strong anti-interference capability to avoid pulse signal loss due to bus congestion or electrical noise.

[0051] In addition, it should be noted that the print substrate is a medium on which ink is sprayed. Its specific material can vary depending on the application scenario, for example, it can be various types of paper, plastic film, textile fabric, etc. For the convenience of subsequent description, the embodiments of the present application will take paper as a representative example of the print substrate, but this is not a limitation on the scope of protection of the present application.

[0052] The preset test pattern is a reference pattern for subsequent image analysis, which is sprayed by the printhead system. In an optional embodiment, the test pattern is a stripe with a preset pitch. The stripe pattern, especially the equidistant stripes perpendicular to the movement direction of the print substrate, is selected because of its simple geometric characteristics, which facilitates the subsequent image acquisition device to accurately identify the position, pitch and inclination angle of each stripe. It should be understood that the form of the test pattern is not limited to this, any pattern containing geometric features that can be used for accurate measurement of relative position relationship (such as grid, dot matrix or specific mark) can be applied to the present application as long as it can reflect the front and back pitch changes of the print position in the paper movement direction. For the convenience of explaining the error classification logic of the present application, the following will take the equidistant vertical stripe as a specific example of the test pattern to be described in detail.

[0053] Specifically, in an embodiment, referring to Figure 3 S1 includes the following sub-steps S11-S12.

[0054] S11. Read the pre-established mapping relationship between the digital model of the test pattern and the position encoding signal.

[0055] S12. Control the rotation of the main shaft, and trigger the printhead system to spray the test pattern on the print substrate according to the real-time acquired position encoding signal and the mapping relationship.

[0056] The digital model refers to the digital representation of the test pattern in an ideal coordinate system. Taking the example of the equally-spaced vertical stripes as the test pattern, the digital model can be represented as a list of preset longitudinal coordinate values, where each coordinate value represents the exact theoretical position at which a stripe should be printed. The "mapping relationship" is the rule or data table that links these theoretical coordinate values with the position encoding signal output by the encoder (i.e. the combination of pulse count and period count). For example, if the spindle rotation advances the substrate by 100mm per revolution, and the encoder outputs 65535 pulses per revolution, and the test pattern requires a vertical stripe to be printed every 1mm. The mapping relationship can be established as: when period count = 0, pulse count ≈ 655, corresponding to the printing position of the first stripe; when period count = 0, pulse count ≈ 1311, corresponding to the printing position of the second stripe, and so on. When the pulse count exceeds 65535 with the spindle rotation, the period count value becomes 1, and the pulse count value starts from 0 again, and the mapping relationship continues to correspond to the subsequent printing positions.

[0057] When performing 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 certain target value preset in the mapping relationship, the control system immediately issues a trigger instruction to the printhead system, completing a spray-drawing action. The high-resolution encoder provides sufficient dense trigger points, ensuring the fineness of positioning.

[0058] At the same time as performing the above S1, the method also simultaneously performs S2: in the process of spray-drawing the test pattern, acquiring the position encoding signal of the spindle rotation through the encoder linked with the spindle, wherein the position encoding signal contains pulse count and period count.

[0059] Here, digital information representing the mechanical motion state of the spindle is collected in real time and continuously, which reflects the theoretical position that the substrate should reach without any physical deviation (such as sliding or eccentricity). This signal is decomposed into pulse count and period count, the former representing the angular position of the spindle in the current rotation period, and the latter recording the number of complete rotation cycles completed by the spindle.

[0060] Continuing the example above, the control system begins to perform the data acquisition task of S2 when the spindle is started. Initially, the position encoder signal can be represented as period count = 0, pulse count = 0. As the spindle rotates, the pulse count continuously increases from 0 until it reaches its maximum value for one revolution. When the spindle completes the first revolution and passes the reference point, the Z signal of the encoder is triggered. Upon receiving the signal, the control system immediately updates the position encoder signal as period count = 1, pulse count = 0. Thereafter, the spindle enters the second revolution period, and the pulse count again starts from 0.

[0061] S3. Acquire, by an image acquisition device, an actual printed image of the test pattern that has been printed on the substrate.

[0062] As mentioned above, 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, with its field of view covering the entire width of the test pattern in the lateral direction of the substrate. Meanwhile, a stable and uniform light source should be provided for the shooting area to eliminate the interference of environmental light changes on image quality and ensure the repeatable identification of image features.

[0063] Before performing formal error detection, the image acquisition device needs to be calibrated to establish the conversion relationship between image pixel coordinates and physical space coordinates. The calibration process can include: First, a calibration pattern with precisely known dimensions is printed on the substrate. Then, the image acquisition device is controlled to capture the calibration pattern, and an image processing algorithm is used to analyze the pixel size and distortion of the calibration pattern in the image. Through this process, the conversion coefficient from pixels to physical distance can be calculated, and a parameter model for correcting lens distortion can be generated.

[0064] Continuing the example above, suppose the conversion coefficient obtained through calibration is 0.005 mm / pixel. When performing S3, the camera captures the printed vertical stripe pattern with a theoretical spacing of 1 mm. The image processing module in the control system first calls the distortion correction parameters to correct the original image captured. Subsequently, the module identifies the center position of each stripe in the image through edge detection, center line extraction, and other algorithms, and records its pixel coordinates in the direction of substrate movement. Finally, the system applies the calibrated conversion coefficient to convert these pixel coordinates into physical positions. For example, a list of actual physical position data for a set of stripes is calculated.

[0065] S4. Analyze the position encoder signal and the actual printed image to obtain error features, and classify the error into one of the multiple pre-set error types based on the error features.

[0066] The preset error types include a paper slip error type, a spindle eccentricity error type, and a pulse count loss error type.

[0067] The paper slip error is obtained by comparing the difference between the actual position of the printing substrate calculated based on the actual printing image and the theoretical position calculated based on the pulse signal count value. Here, the paper slip error is a common mechanical error. Its physical cause is that the friction between the printing substrate and the spindle or other transmission rollers is insufficient, so that the actual advancing distance of the printing substrate is less than the theoretical value although the spindle has rotated by a certain angle. This is manifested as that the theoretical position represented by the encoder count value is ahead of the actual position calculated by the printing image.

[0068] Referring to Figure 4 , the spindle eccentricity error is obtained by identifying the periodic geometric deformation of the test pattern in the actual printing image within a single rotation period of the spindle. Here, the spindle eccentricity error is caused by the mechanical manufacturing or installation defects of the spindle itself, so that the rotation center and the geometric center thereof are not coincident. The characteristic of this error is that the total travel within a single rotation period is consistent with the theoretical value, but the instantaneous speed within the period is uneven. This error can be further divided into two types: one is consistent eccentricity on both sides of the spindle (see Figure 5 ), which causes the effective rotation radius of the spindle to periodically change, thereby causing the paper feeding speed of the printing substrate to be uneven, and finally resulting in the regular change in the spacing of the equidistant pattern on the printing image; the other is inconsistent eccentricity on both sides of the spindle (see Figure 6 ), which causes the printing substrate to regularly swing in the horizontal direction, and finally results in the periodic change in the inclination angle of the vertical stripes on the printing image, see Figure 7 , Figure 7 , the paper feeding direction is from bottom to top, and it can be seen from the figure that the expected straight edge is tilted left and right in the paper feeding direction. The pulse count loss error is obtained by comparing the difference between the actual obtained pulse signal count value and the theoretical pulse signal count value corresponding to the displacement of the printing substrate calculated based on the actual printing image within a rotation period defined by the periodic reference information. Here, the pulse count loss error belongs to the error in the electrical or signal transmission layer. Its cause is usually that some of the pulses normally emitted by the encoder are not successfully received and counted by the control system due to signal interference or control system bus blocking during high-speed transmission. Its physical manifestation is that the actual position of the printing substrate has reached or exceeded a certain point, but the pulse count value recorded by the control system is less than the theoretical value.

[0069] Specifically, referring to Figure 8 , the S4 includes the following sub-steps: determining whether the actual stripe position of the actual printed image is ahead of the theoretical stripe position calculated based on the pulse signal count value, and if so, determining that the error type is a pulse count loss error type; if not, determining whether the change in the relative deviation of the stripe position has periodicity, and if not, determining that the error type is a paper slip error type, and if so: determining whether the change in the actual stripe position of the actual printed image relative to the change in the stripe position of the test pattern is a change in pitch or a change in inclination, and if the change is a change in pitch, determining that the error type is a spindle eccentricity error type of consistent eccentricity of the left and right sides of the spindle, and if the change is a change in inclination, determining that the error type is a spindle eccentricity error type of inconsistent eccentricity of the left and right sides of the spindle.

[0070] For example, assume that the position encoding signal obtained by S2 is converted to a list of theoretical stripe positions [1.00 mm, 2.00 mm, 3.00 mm,...]. At the same time, S3 obtains a list of actual stripe positions through image analysis. The control system will compare and analyze these two lists.

[0071] First, the system compares the actual position and the theoretical position of each corresponding stripe. If it is found that the actual position is consistently ahead of the theoretical position, for example, the actual position list is [1.05 mm, 2.06 mm, 3.07 mm,...], which indicates that the physical displacement of the substrate exceeds the displacement recorded by the encoder, which is consistent with the characteristics of pulse count loss. Therefore, the system directly determines that the error type is a pulse count loss error type.

[0072] If the system finds that the actual position is consistently behind the theoretical position, it enters the second layer of judgment. At this time, the system will calculate and analyze the relative deviation sequence of the stripe position, i.e., the theoretical position-actual position. If the change in the deviation sequence does not have periodicity, for example, the deviation value monotonically increases over time, such as [0.05 mm, 0.12 mm, 0.20 mm,...], which is consistent with the characteristics of cumulative slip caused by mechanical slip. Therefore, the system determines that the error type is a paper slip error type.

[0073] If the system finds that the sequence of relative deviations exhibits periodic fluctuations synchronized with the rotation period of the main shaft, it can be determined that the error is caused by the main shaft eccentricity. At this time, the third layer of judgment is entered to subdivide the eccentricity type. The system will perform a more in-depth geometric analysis on the actual printed image obtained in S3. If the analysis finds that the spacing between the printed stripes exhibits periodic changes in density, for example, the spacing is 0.99 mm, 1.01 mm, 0.99 mm,..., which is consistent with the speed change characteristics caused by the overall eccentricity of the main shaft, the system determines that the main shaft eccentricity error type is the consistent eccentricity of the left and right sides of the main shaft. If the analysis finds that the inclination angle of the printed stripes exhibits periodic changes, which is consistent with the characteristics of the medium transverse displacement caused by the main shaft swing, the system determines that the main shaft eccentricity error type is the inconsistent eccentricity of the left and right sides of the main shaft.

[0074] In optional embodiments, the method for detecting the overlay error of a digital inkjet printer described in the embodiments of the present application can further include the following steps: S5. Display the classified types of printing errors and their quantitative analysis data to the user terminal, and provide multiple processing options for the identified errors for the user to choose. The processing options at least include: software adaptation compensation, adjustment of printer operating parameters, or replacement of related hardware components.

[0075] For example, after the analysis is completed, the control system displays a diagnostic report on the user terminal. For example, the report can show: the main shaft consistent eccentricity error is detected, the maximum deviation is 0.02 mm, and the period is synchronized with the rotation of the main shaft. Then the system lists the processing options for the user to make a decision.

[0076] If the user chooses to perform software adaptation compensation, the system will start the corresponding algorithm according to the error type. For example, for the main shaft eccentricity error, the system can generate a dynamic compensation mapping table synchronized with the main shaft Z signal according to the measured periodic deviation data, and advance or delay the inkjet trigger time of each position by microseconds during printing to offset the impact caused by uneven speed. For paper slip error, the system can calculate a dynamic slip coefficient and compensate all subsequent printing positions by advancing the trigger point as a whole. For the randomly occurring pulse count loss error, the system can dynamically fine-tune the trigger delay of the subsequent printing points after detecting the leading deviation to smooth the impact of the sudden error.

[0077] As an example, the compensation algorithm for the main shaft eccentricity error can be divided into the following stages: First is the error characteristic modeling stage. In the analysis process of S4, the system has obtained a series of deviation values between the theoretical position and the actual position of the printed stripes. Continuing the example above, the system can obtain a set of data pairs, that is, at each theoretical pulse count value position p 理论, there is a corresponding position error Ay. The system first converts the physical unit error Ay into a pulse unit error Ap 偏差 . Then, the system constructs a series of (p 理论 , Ap 偏差 ) data pairs into an error lookup table, with the total number of pulses in one revolution of the spindle as the period. The error lookup table describes the amount of advance or lag of the printing position at different angles of the spindle rotation (represented by the pulse count value within a single revolution). Linear or higher order interpolation can be performed between the discrete data points in the lookup table to cover all positions.

[0078] Second, the compensation lookup table generation phase. Based on the error lookup table described above, the system generates a compensation lookup table. For any pulse position p in the lookup table, the compensation value Ap 补偿 (p) = -Ap 偏差 (p). For example, if the error lookup table shows that there is an error of -5 pulses (lag) at pulse position 10000, then the compensation value recorded at the corresponding position in the compensation lookup table is +5 pulses (advance). The compensation lookup table is stored in the memory of the control system, and the Z signal of the encoder is used as the starting point of its period (i.e. pulse position 0 point).

[0079] Finally, the real-time compensation execution phase. When performing formal pattern printing, the compensation algorithm is activated. For any line of the image to be printed, the control system first calculates its corresponding theoretical inkjet trigger position p 目标 , which is a specific period count value and pulse signal count value, according to its position in the digital image. During the rotation of the spindle and the advancement of the substrate, the control system monitors the current position encoding signal p 当前 in real time. At the same time, it looks up or interpolates the real-time compensation value Ap 补偿 in the compensation lookup table using the current pulse signal count value as the index. Then, the system calculates the dynamically adjusted actual trigger position p 触发 = p 目标 + Ap 补偿 . The control system will continue to monitor p 当前 until the condition p 当前 = p 触发 is met, and then immediately issue an inkjet command to the printhead system.

[0080] If the user chooses to adjust the press operating parameters, the system can provide specific guidance. For example, after diagnosing a paper slip error, the terminal can prompt the user to "please check and appropriately increase the substrate tension to XX Newton" or "please check the platen air pressure". The operator can then adjust the tension control system or the air system of the press to physically increase the friction between the substrate and the drive roller, thus solving the slip problem.

[0081] If the user chooses to replace the relevant hardware components, this option usually corresponds to a determined physical damage. For example, after diagnosing a severe spindle eccentricity error, the terminal can suggest "please check or replace the spindle bearing". The maintenance personnel can then overhaul the spindle and replace the worn-out bearing. Similarly, if the pulse count loss error occurs frequently and communication interference is ruled out, the terminal can suggest "please replace the encoder" to solve the possible hardware failure of the encoder itself.

[0082] It should be understood that the size of the serial number of each step in the above embodiment does not mean the order of execution, and the execution order of each process should be determined according to its function and internal logic, and should not constitute any limitation on the implementation process of the embodiment of the present application.

[0083] In an embodiment, a computer device is provided, which can be a server, and its internal structure diagram can be shown in FIG. 9. The computer device includes a processor, a memory, a network interface and a database connected through a system bus. The processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, a computer program and a database. The internal memory provides an environment for the operating system and the computer program in the non-volatile storage medium to run. The database of the computer device is used for data related to the registration error detection method for digital inkjet printers. The network interface of the computer device is used for communication connection with the external terminal through the network. The computer program is executed by the processor to implement a registration error detection method for digital inkjet printers.

[0084] In an embodiment, a computer device is provided, which includes a memory, a processor and a computer program stored in the memory and executable on the processor. The processor implements the registration error detection method for digital inkjet printers of the above-mentioned embodiments when executing the computer program, for example Figure 2 S1 to S4, or S1 to S5 shown in FIG. 9.

[0085] In an embodiment, a computer readable storage medium is provided, which stores a computer program. The computer program is executed by the processor to implement the registration error detection method for digital inkjet printers of the above-mentioned embodiments, for example Figure 2 S1 to S4, or S1 to S5 shown in FIG. 9.

[0086] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer readable storage medium. When the computer program is executed, it can include the processes of the above-mentioned embodiment methods. Any reference to memory, storage, database or other medium used in the embodiments of the present 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. As an illustration but not limitation, RAM is available in various forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDR SDRAM), enhanced SDRAM (ESDRAM), synchronous link (Synchlink) DRAM (SLDRAM), memory bus (Rambus) direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM), etc.

[0087] Those skilled in the art can clearly understand that, for the convenience and brevity of description, only the above-mentioned division of functional units and modules is exemplified, and in actual application, the above-mentioned functions can be completed by different functional units and modules according to needs, that is, the internal structure of the device is divided into different functional units or modules to complete all or part of the above-described functions.

[0088] The above embodiments are only used to illustrate the technical solutions of the present application, but not limit it; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be included in the protection scope of the present application.

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 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; 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.

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 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.

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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