A method for detecting an abnormality of a circulation ink supply system of a digital printing machine

Abstract

The present application belongs to the technical field of fault prediction and health management, and particularly relates to a circulating ink supply system anomaly detection method for a digital printing machine. The method comprises: obtaining an initial color digital image to be printed and generating a static dot matrix, combining micro-scan cycle data and printing head instantaneous mechanical coordinates to extract the real-time dot area rate of each micro-printing partition; calculating the theoretical dynamic ink consumption volume flow based on the real-time dot area rate and piezoelectric nozzle parameters; obtaining the dynamic friction resistance pressure drop and the transient fluid inertia pressure drop by using the Hagen-Poiseuille circular tube laminar flow model and Newton's second law respectively, and superimposing to obtain the reference differential pressure; collecting the actual vacuum air pressure difference and calculating the real-time physical deviation, and determining the underlying physical failure based on the preset safety threshold and tolerance time window and executing physical anomaly shutdown intervention. The present application realizes dynamic prediction of the ink supply fluid state, eliminates detection hysteresis, and effectively avoids printing waste.

Description

Technical Field

[0001] This invention relates to the field of fault prediction and health management technology. More specifically, this invention relates to a method for detecting abnormalities in the circulating ink supply system of a digital printing press. Background Technology

[0002] In the printing industry, the stability and accuracy of ink supply are the core factors in ensuring the quality of printed products. By controlling the ink output of the ink supply system, the color consistency and clarity of printed images and text can be directly determined.

[0003] Chinese patent document CN106113936B discloses an intelligent ink supply device and method for printing presses. It utilizes a digital scanner to acquire a digital image of the original artwork, processes it through computer color separation to calculate the dot area ratio of each color zone, and determines the motor step rate based on the dot area ratio. This drives the ink knife to move closer to or further away from the ink fountain roller to adjust the ink supply gap. However, this patent primarily pre-sets the ink supply amount based on the original image before printing begins, failing to provide feedback on real-time changes during the printing process. This makes it difficult to dynamically adjust the ink supply when dealing with fluctuations in the printing environment or sudden physical anomalies within the ink supply path.

[0004] Chinese patent document CN119348296B, authorized by patent announcement number CN119348296B, provides an automatic differential pressure circulating ink supply system, method, and medium for UV digital printing presses. It involves capturing a surface image of the printed product and converting it into a pixel-grid image, then comparing the detected image with a standard printed image to determine if ink leakage or uneven color transitions exist. However, this patent relies heavily on post-printing image comparison, making it a post-processing detection method. Due to the physical and temporal delay between ink spraying onto the paper and image scanning, by the time the system detects a problem through the image, a large number of defective products have often already been generated on the production line, making it impossible to detect abnormalities in the system's internal operation before ink is sprayed.

[0005] In existing technologies, some solutions attempt to preset the ink supply volume by analyzing the original image, or to check the quality by scanning the printed product with a camera after printing. However, these methods mostly focus on the static processing of image data or the visual comparison of printing results, lacking the ability to monitor the internal fluid operation of the ink supply system in real time. Current visual inspection methods are often lagging, and problems can only be detected after visible defects appear on the printed product. This not only wastes paper and ink, but also fails to make timely predictions about minor fluctuations in the ink supply pipeline. In addition, relying solely on the grayscale differences of pixels for comparison is easily affected by changes in lighting or the surface texture of the substrate, resulting in an inaccurate judgment of the actual working condition of the ink supply system. Summary of the Invention

[0006] To address the inherent lag in existing printing ink supply detection technologies, which heavily rely on post-printing visual comparison and cannot dynamically predict the internal fluid physical state of the ink supply system before ink ejection, leading to extremely delayed fault detection and a large amount of printing waste, this invention provides an anomaly detection method for the circulating ink supply system of a digital printing press. The method includes: acquiring the initial color digital image to be printed and discretizing it to generate a static dot matrix; combining microscopic scanning cycle data and the instantaneous mechanical coordinates of the printhead to divide the microscopic printing areas to extract the real-time dot area ratio; and based on the real-time dot area ratio, the standard ink droplet volume of the piezoelectric printhead, and the... The system uses a fixed drive trigger frequency to obtain the theoretical dynamic ink consumption volumetric flow rate; it also obtains the dynamic frictional resistance pressure drop based on the Hagen-Poiseuille circular tube laminar flow model and the theoretical dynamic ink consumption volumetric flow rate; it obtains the transient fluid inertial pressure drop based on Newton's second law and the theoretical dynamic ink consumption volumetric flow rate; it superimposes the dynamic frictional resistance pressure drop and the transient fluid inertial pressure drop to obtain the reference pressure difference on the reference pressure difference fluctuation envelope; it collects the actual vacuum air pressure difference, obtains the real-time physical deviation based on the actual vacuum air pressure difference and the reference pressure difference, and determines the underlying physical fault and performs physical abnormal shutdown intervention based on the real-time physical deviation, the preset safety threshold, and the tolerance time window.

[0007] This invention is based on the theory of dynamic ink consumption volume flow rate calculated by digital image pre-feature calculation, and combined with the physical model to derive the reference pressure difference composed of the superposition of dual pressure drops. Finally, it is compared with the actual vacuum pressure difference to realize fault judgment and shutdown intervention. This process transforms the static visual printing requirements into dynamic fluid dynamics prediction, and realizes real-time dynamic prediction of the fluid physical operation state before the ink leaves the piezoelectric printhead. It overcomes the inherent detection lag defect of the existing technology that relies heavily on post-printing visual comparison. It can accurately identify and block the abnormal evolution of the circulating ink supply system into macroscopic printing defects, effectively avoiding the generation of a large number of printing wastes.

[0008] Preferably, the step of acquiring the initial color digital image to be printed and discretizing it to generate a static dot matrix, and then dividing the micro-printing partitions by combining the micro-scanning cycle data and the instantaneous mechanical coordinates of the print head to extract the real-time dot area ratio, includes: converting the initial color digital image from the red-green-blue color space to the cyan-magenta-yellow-black color space, separating the continuous tone image of the physical printing channel; processing the continuous tone image using a frequency modulation screening algorithm to generate a static dot matrix; projecting the instantaneous mechanical coordinates of the print head onto the static dot matrix to extract a local pixel sub-matrix; dividing the local pixel sub-matrix into micro-printing partitions by mesh cutting according to the physical nozzle array arrangement of the piezoelectric printhead; and statistically calculating the ratio of the number of pixels with a value of 1 in the micro-printing partitions to the total number of pixels to obtain the real-time dot area ratio.

[0009] This invention obtains the real-time dot area ratio of each micro-printing zone by performing color space conversion, halftone discretization, and grid cutting combined with the mechanical coordinates of the printhead on the initial color digital image. It constructs a rigorous geometric mapping from the digital two-dimensional pixel space to the physical three-dimensional real jetting space, transforming the macroscopic continuous color requirements into discrete micro-jetting load distributions. This provides a high-fidelity pre-distribution feature benchmark for the accurate calculation of subsequent ink consumption, ensuring the accuracy of the conversion from front-end visual requirements to back-end power source.

[0010] Preferably, the formula for calculating the theoretical dynamic ink consumption volumetric flow rate is: In the formula, For a moment Theoretical dynamic ink consumption volumetric flow rate; For a moment The total number of micro-printed partitions covered by the current scan line; This refers to the serial number of the micro-printed partition; For the first Each micro-printed partition at time Real-time branch area ratio; Standard ink droplet volume; This is the rated drive trigger frequency.

[0011] This invention obtains the theoretical dynamic ink consumption volumetric flow rate by multiplying the real-time dot area ratio, representing the spatial distribution ratio, with the inherent operating parameters of the piezoelectric printhead and then discretely accumulating the results within each micro-printing zone. This operation strictly follows the law of conservation of fluid mass and uses the spatial distribution area ratio to physically reduce the maximum limit jet flow rate of the device in the time dimension. This allows the control system to calculate the instantaneous fluid volumetric velocity that the ink supply pipeline terminal should reach before the actual jetting action occurs, providing reliable initial power source data for the dynamic simulation of the pressure drop in the underlying pipeline.

[0012] Preferably, the step of obtaining the dynamic frictional resistance pressure drop based on the Hagen-Poiseuille circular tube laminar flow model and theoretical dynamic ink consumption volumetric flow rate includes: obtaining the real-time system temperature. And the dynamic viscosity of the UV ink was obtained by mapping. Obtain the physical length and inner diameter of the ink supply pipeline; In the formula, For a moment Dynamic frictional resistance pressure drop; To keep pace with the real-time temperature of the system Dynamic viscosity of UV inks with varying mapping effects; The physical length of the ink supply line; Indicates time The theoretical dynamic ink consumption volumetric flow rate required at the ink supply pipeline terminal; This refers to the inner diameter of the ink supply pipeline.

[0013] This invention derives the dynamic frictional resistance pressure drop by introducing dynamic viscosity mapped to the real-time temperature of the system and the size parameters of the ink supply pipeline, combined with the Hagen-Poiseuille circular tube laminar flow model. This operation fully considers the microscopic influence of temperature fluctuations on the viscosity characteristics of ink, and truly restores the inherent viscous frictional loss of the tube wall that the fluid needs to overcome in order to maintain flow in the micro-tube under the current dynamic flow requirements, thereby ensuring the accuracy of the steady-state frictional resistance prediction benchmark under complex working environment temperatures.

[0014] Preferably, the step of obtaining the transient fluid inertial pressure drop based on Newton's second law and theoretical dynamic ink consumption volumetric flow rate includes: In the formula, For a moment Transient fluid inertial pressure drop; The fluid density of the ink; The equivalent inertial length of the pipeline impedance; Indicates time The theoretical dynamic ink consumption volumetric flow rate required at the ink supply pipeline terminal; Representative moment The theoretical dynamic ink consumption volumetric flow rate required at the ink supply pipeline terminal, with respect to time.

[0015] This invention combines the fluid density of ink, the equivalent inertial length of pipeline impedance, and the instantaneous derivative of theoretical flow rate to derive the transient fluid inertial pressure drop using Newton's second law. This operation determines, from the underlying mechanical mechanism, the additional mass inertial kinetic energy loss required for the ink column in the tube to generate acceleration when the equipment crosses image regions of different densities and causes sudden changes in flow rate. It reveals the physical origin of the sudden deep pressure pull in high-speed printing and eliminates the interference of normal instantaneous pressure fluctuations caused by drastic changes in legitimate colors during dynamic detection.

[0016] Preferably, the preliminary encapsulation method for the equivalent inertial length of the pipeline impedance is as follows: constructing a fluid reference operating environment without structural faults and performing a step response test; driving the piezoelectric printhead to instantaneously open to the rated maximum displacement to generate a theoretical dynamic ink consumption volume flow rate change rate; using a hardware pressure sensor to synchronously capture the transient pressure difference peak value generated at both ends of the ink supply pipeline; calculating the product of the theoretical dynamic ink consumption volume flow rate change rate and the fluid density of the ink; and using the ratio of the transient pressure difference peak value to the product as the equivalent inertial length of the pipeline impedance.

[0017] This invention performs a step response test on a piezoelectric printhead under a fault-free environment, and calculates the equivalent inertial length of the pipeline impedance by inversely using the captured transient pressure difference peak and the theoretical flow rate mutation rate. This calibration operation reduces the complex three-dimensional spatial resistance caused by the non-ideal geometry of the circulating ink supply system to fluid acceleration and encapsulates it into a global constant, thus offloading the calculus computational overhead of the underlying system during operation and ensuring the computational response agility of the detection method under high-speed pulse jet conditions.

[0018] Preferably, obtaining the real-time physical deviation based on the actual vacuum pressure difference and the reference pressure difference includes: performing a difference operation between the actual vacuum pressure difference and the reference pressure difference and taking the absolute value to obtain the real-time physical deviation.

[0019] Preferably, the determination of underlying physical faults based on real-time physical deviation, a preset safety threshold, and a tolerance time window includes: when the real-time physical deviation is determined to be greater than the safety threshold, controlling a hardware timer to start timing; if the real-time physical deviation falls back to or below the safety threshold during the timing process, resetting the hardware timer to zero; if the real-time physical deviation continues to be greater than the safety threshold and the duration recorded by the hardware timer is greater than the tolerance time window, then determining that there is an underlying physical fault in the circulating ink supply system.

[0020] Preferably, the physical abnormal shutdown intervention includes: issuing an interrupt command to cut off the drive power of the piezoelectric printhead; simultaneously shutting down the ink supply pump motor inside the circulating ink supply system; and issuing an alarm prompt message through the human-machine interface.

[0021] Preferably, the safety threshold is calibrated as follows: a microleakage induction valve is connected in parallel at the pipeline side of the circulating ink supply system; the leakage orifice diameter of the microleakage induction valve is slowly enlarged during the dynamic printing process, and the printing quality of the substrate surface is monitored using a high-speed camera; the value of the real-time physical deviation corresponding to the moment when physical ink leakage or broken line defects appear on the substrate surface is captured, and this value is established as the safety threshold.

[0022] The beneficial effects of this invention are as follows: This invention discretizes the initial color digital image to be printed to generate a static dot matrix. It then combines microscopic scanning cycle data with the instantaneous mechanical coordinates of the printhead to divide the image into microscopic printing zones to extract the real-time dot area ratio. Based on this real-time dot area ratio, the standard droplet volume of the piezoelectric printhead, and the rated drive trigger frequency, the theoretical dynamic ink consumption volumetric flow rate is pre-calculated. Furthermore, this invention obtains the dynamic frictional resistance pressure drop based on the Hagen-Poiseuille circular tube laminar flow model and the transient fluid inertial pressure drop based on Newton's second law. By superimposing the dual pressure drops representing fluid viscous friction and mass acceleration kinetic energy loss, a benchmark pressure difference that dynamically fluctuates with the image's ink consumption demand is constructed. Finally, by comparing the actual vacuum pressure difference to obtain real-time physical deviations, a preset safety threshold and tolerance time window are used to determine underlying physical faults and execute physical anomaly shutdown intervention.

[0023] The aforementioned specific technical features support and synergize with each other functionally, successfully transforming the traditional reactive detection method, which relies on visual comparison of printed materials after printing, into a pre-printing physical impedance prediction model based on fluid dynamics. This solution achieves mutual verification between pre-printing digital image features and fluid dynamics physical impedance, enabling accurate prediction and identification of fluid flow abnormalities within the circulating ink supply system before ink actually detaches from the piezoelectric printhead and causes macroscopic print defects such as broken lines or ink leakage. It then immediately halts the printing process, fundamentally eliminating the extremely delayed fault detection shortcomings of existing technologies and effectively preventing the generation of a large number of printed waste products. Attached Figure Description

[0024] Figure 1 This is a flowchart illustrating an abnormality detection method for the circulating ink supply system of a digital printing press according to the present invention; Figure 2 This is a diagram showing the calculation results of constructing a reference pressure difference fluctuation envelope by superimposing the dual pressure drops of the fluid; Figure 3 This is a comparison diagram showing the effects of monitoring actual air pressure deviation and triggering physical anomaly shutdown intervention. Detailed Implementation

[0025] Addressing the technical problem mentioned in the background section that existing printing ink supply detection technologies heavily rely on the inherent lag of post-printing visual comparison, failing to provide real-time dynamic prediction of the internal fluid physical state of the ink supply system before ink ejection, resulting in extremely delayed fault detection and a large amount of printing waste, this invention aims to establish an anomaly detection model that can predict the physical state before ink leaves the printhead, based on the mutual corroboration of digital image pre-features and fluid dynamic physical impedance. Firstly, at the data input end, the dot area ratio is extracted using the color separation and halftone data of the initial digital image to be printed. Combined with the inherent physical parameters of the piezoelectric printhead, the static visual printing requirements are converted into the theoretical dynamic ink consumption volumetric flow rate that the ink supply pipeline terminal should achieve, thus realizing pre-measurement of ink consumption. First, at the baseline construction end, instead of using a fixed static pressure threshold that is prone to false alarms or missed alarms, a baseline pressure difference fluctuation envelope that can follow the dynamic ink consumption volume flow rate mentioned above is reconstructed by strictly superimposing the dynamic frictional resistance pressure drop generated by the fluid overcoming the pipe wall and the transient fluid inertial pressure drop generated by the sudden change in flow velocity, based on the above-mentioned theory of dynamic ink consumption volume flow rate. Finally, at the anomaly judgment end, the actual vacuum pressure difference collected in real time at both ends of the dual negative pressure printhead is compared with the baseline pressure difference fluctuation envelope to calculate the physical deviation. Through the comprehensive judgment of this physical deviation and the preset safety threshold and tolerance time window, accurate identification and shutdown intervention are achieved before the pipeline anomaly is characterized as a macroscopic print defect, thereby eliminating detection lag and avoiding the generation of printing waste.

[0026] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0027] This invention discloses a method for detecting abnormalities in the circulating ink supply system of a digital printing press, referring to... Figure 1 This includes steps S1 to S3: S1. Extract the area ratio of the network points to calculate the theoretical dynamic consumption of volumetric flow rate.

[0028] It should be noted that the pixel color information of a digital image is not directly equivalent to the ink output of the printhead; it must undergo a conversion process from color signal to physical ink droplet ejection command. This invention aims to transform visual requirements into flow source dynamic parameters in real fluid dynamics by extracting the distribution characteristics of the image in the pre-printing stage.

[0029] Specifically, the initial color digital image to be printed is obtained from the front-end image processor of the digital printing press, and the micro-scanning cycle data that is strictly aligned with the mechanical scanning action of the print head in time is read simultaneously; the initial color digital image is converted from RGB color space to CMYK color space using the built-in ICC color feature description file, thereby separating the continuous tone images corresponding to the four physical printing channels of cyan, magenta, yellow, and black; for the continuous tone image of each physical printing channel, the Dither frequency modulation halftone algorithm is used for spatial discretization processing, mapping the continuous pixel gray values ​​to the numerical values ​​0 or 1, generating a complete static halftone matrix composed of binary pixels.

[0030] Subsequently, a fixed geometric conversion ratio was established between the physical printing area of ​​the substrate and the two-dimensional pixel space of the static dot matrix; the physical time window defined by the microscopic scanning cycle data of the print head was extracted. The instantaneous mechanical coordinates within the matrix are projected onto the entire static dot matrix to extract a local pixel sub-matrix equal to the current actual physical coverage area of ​​the printhead. Furthermore, based on the inherent physical nozzle array arrangement on the bottom surface of the printhead, the local pixel sub-matrix is ​​rigidly meshed in two-dimensional space, thereby precisely dividing the spatial positions of the actual physical independent nozzles. A micro-printed partition, It equals the total number of all individual nozzles.

[0031] Finally, regarding the time... The next The process involves traversing and counting the number of pixels with a value of 1 within the halftone matrix mapped to each micro-printed partition, and then calculating the physical ratio of this number to the total number of pixels within that micro-printed partition. This allows for the precise acquisition of the first... Each micro-printed partition at time Real-time branch area ratio .

[0032] Furthermore, based on the law of conservation of fluid mass, in order to map the acquired real-time dot area ratio into a specific fluid volume flow rate, the inherent physical parameters of the piezoelectric printhead are read from the underlying control system of the digital printing press, namely the standard ink droplet volume ejected by the piezoelectric printhead in a single physical extrusion action. and the rated drive trigger frequency of the piezoelectric nozzle .

[0033] In physical printing conditions, the rated drive trigger frequency The piezoelectric printhead determines the maximum number of physical ejections per unit time and the standard droplet volume. The droplet volume determined by a single injection, and their product, characterizes the limiting volumetric flow rate of a single micro-printed partition under full load; real-time dot area ratio. As a spatial distribution ratio parameter, it constrains the actual volumetric demand of this limiting volumetric flow rate within a specific partition; by using time... By discretely summing the actual volume requirements of all micro-printing zones, a theoretical dynamic ink consumption volume flow rate calculation formula is constructed:

[0034] In the formula, Indicates time The theoretical dynamic ink consumption volumetric flow rate required at the ink supply pipeline terminal; For the first Each micro-printed partition at time Real-time branch area ratio; Indicates the standard ink droplet volume; Indicates the rated drive trigger frequency; For a moment The total number of micro-printed partitions covered by the current scan line.

[0035] The above calculation process uses the spatial distribution area ratio to physically reduce the maximum jet flow rate of the device in the time dimension, and calculates the internal flow rate of the ink supply pipeline at time 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 ... The instantaneous fluid volume velocity that should be achieved provides accurate initial fluid dynamics input parameters for the subsequent calculation of dynamic frictional resistance and transient fluid inertial pressure drop in the ink supply pipeline.

[0036] S2. Construct the baseline pressure difference fluctuation envelope by superimposing the dual pressure drops of the fluid.

[0037] It should be noted that when ink flows in a micro-tube, it must not only overcome the frictional resistance of the tube wall, but also the mass inertia of the fluid column when the flow rate changes abruptly. Traditional static detection methods only consider the pressure under constant flow rate and ignore the physical resistance generated by the rapid acceleration of ink during high-density image printing. This invention restores the pressure fluctuation benchmark of the ink supply tube under real pulse load by mechanically superimposing static frictional resistance and dynamic inertial resistance.

[0038] Specifically, this step completes the benchmark construction through the following three physical derivation stages: Phase 1: Deriving the dynamic frictional resistance pressure drop based on pipe wall friction.

[0039] Based on the Hagen-Poiseuille circular tube laminar flow model, when the fluid flows at a constant velocity, the thrust at both ends of the tube remains in balance with the viscous friction within the fluid. By applying an area integral to the velocity distribution across the tube cross-section, the linear relationship between pressure difference and flow rate is determined. Considering the physical properties of UV ink varying with temperature, real-time readings from the tube temperature sensor are used as the system's real-time temperature readings. The dynamic viscosity of the UV ink is obtained by mapping. Combined with the physical length of the ink supply pipeline and inner diameter The dynamic frictional resistance pressure drop is calculated using the following formula:

[0040] In the formula, For a moment The dynamic frictional resistance pressure drop; To keep pace with the real-time temperature of the system Dynamic viscosity of UV inks with varying mapping effects; The physical length of the ink supply line; Indicates time The theoretical dynamic ink consumption volumetric flow rate required at the ink supply pipeline terminal; This refers to the inner diameter of the ink supply pipeline.

[0041] This reflects the inherent frictional losses that ink must overcome in order to pass through the pipeline under current flow requirements.

[0042] Second stage: Derive the transient inertial pressure drop based on fluid mass inertia.

[0043] Based on Newton's second law, that force equals mass multiplied by acceleration, when an image transitions from a white area to a dark area, the ink in the tube experiences instantaneous acceleration, driving a mass of... The liquid column generates acceleration The required instantaneous force is Mapping force to pressure difference, i.e. , The transient fluid inertial pressure drop to be solved is... Represents the cross-sectional area of ​​the ink supply pipeline, and , The inner diameter of the ink supply pipe; mass mapping is the product of volume and density, i.e. , The fluid density of the ink. The physical length of the ink supply pipe; acceleration is mapped to the rate of change of flow velocity, which is the derivative of flow velocity with respect to time, because volumetric flow rate equals cross-sectional area multiplied by flow velocity, i.e. Then the flow velocity can be deduced by reverse calculation. , flow rate Substituting into the formula for calculating acceleration, we get... Due to the cross-sectional area of ​​the ink supply pipeline It is fixed, the cross-sectional area Extracted from the formula for calculating acceleration, we obtain .

[0044] Furthermore, substituting into the formula that force equals mass multiplied by acceleration:

[0045] Perform algebraic simplification, simplify both sides of the equation to obtain the cross-sectional area. Then, the equivalent inertial length of the pipeline impedance is introduced. Equivalent replacement of the calculation formula The transient fluid inertial pressure drop was obtained. The calculation formula:

[0046] In the formula, For a moment Transient fluid inertial pressure drop; The fluid density of the ink; The equivalent inertial length of the pipeline impedance; Indicates time The theoretical dynamic ink consumption volumetric flow rate required at the ink supply pipeline terminal; Representative moment The theoretical dynamic ink consumption volumetric flow rate required at the ink supply pipeline terminal, with respect to time.

[0047] This reflects the additional kinetic energy loss of the fluid in response to sudden changes in image load, explaining the physical cause of the instantaneous deep pressure difference during high-concentration printing.

[0048] It should be added that this invention introduces the equivalent inertial length of the pipeline impedance. This design aims to encapsulate the complex, non-ideal geometries in ink supply pipelines, such as pipe bends, reducing joints, and filter resistance, to address the combined physical resistance to fluid acceleration. In engineering practice, it reduces the dimensionality of high-order three-dimensional flow field partial differential equations that would otherwise require solving to algebraic operations, thereby compressing the real-time computing power overhead of the digital printer's main control chip and ensuring millisecond-level response speed for anomaly detection algorithms under high-speed pulse jet conditions. The equivalent inertial length of the pipeline impedance... The initial packaging method is as follows: During the equipment factory calibration stage, a fluid reference operating environment without structural faults is constructed and a step response test is performed. The piezoelectric printhead is driven by the control system to open instantaneously to the rated maximum displacement, generating a controlled theoretical dynamic ink consumption volume flow rate change rate. The transient pressure difference peak generated at both ends of the ink supply pipeline is captured synchronously using a hardware pressure sensor. Combined with the known ink fluid density, the equivalent inertial length of the pipeline impedance is equal to the ratio of the transient pressure difference peak to the theoretical dynamic ink consumption volume flow rate change rate and the ink fluid density. The equivalent inertial constant of the current ink supply system is then calibrated in reverse and stored in the underlying system configuration file of the digital printer.

[0049] The third stage: synthesizing the reference pressure difference fluctuation envelope based on the principle of force superposition.

[0050] Based on the quasi-steady-state assumption, within microseconds, the total impedance experienced by the fluid is equal to the absolute sum of the two physical pressure drops mentioned above. Therefore, summing the two physical pressure drop results yields the reference pressure difference fluctuation envelope, where at time... reference pressure difference The formula for calculation is:

[0051] In the formula, For a moment The reference pressure difference; To keep pace with the real-time temperature of the system Dynamic viscosity of UV inks with varying mapping effects; The physical length of the ink supply line; Indicates time The theoretical dynamic ink consumption volumetric flow rate required at the ink supply pipeline terminal; The inner diameter of the ink supply pipe; The fluid density of the ink; The equivalent inertial length of the pipeline impedance; Representative moment The theoretical dynamic ink consumption volumetric flow rate required at the ink supply pipeline terminal, with respect to time.

[0052] This calculation establishes a dynamic safety range that fluctuates in real time according to the image color requirements, eliminating the pressure artifacts caused by normal printing load.

[0053] For example, Figure 2The calculation results of constructing a reference pressure difference fluctuation envelope for superimposed fluid pressure drops demonstrate the decoupling deduction process of the internal physical resistance of the ink supply pipeline under dynamic printing load in a digital printer. The figure includes the fluctuation curve corresponding to the dynamic frictional resistance pressure drop, the peak curve corresponding to the transient fluid inertial pressure drop, and the reference pressure difference fluctuation envelope synthesized by mechanically superimposing the two. It can be seen that the dynamic frictional resistance pressure drop exhibits a step-like fluctuation with the theoretical dynamic ink consumption volume flow rate, reflecting the inherent laminar flow loss of the pipeline; the peak curve corresponding to the transient fluid inertial pressure drop only produces positive or negative extreme surges at the moment of sudden change in flow rate, reflecting the additional kinetic energy loss required to overcome the fluid mass inertia; after superimposing the pressure drops of the above two different physical mechanisms, a reference pressure difference fluctuation envelope that can accurately encompass the transient fluid dynamics characteristics is constructed.

[0054] S3. Monitor actual air pressure deviation and trigger physical anomaly shutdown intervention.

[0055] It should be noted that the system has now obtained a baseline differential pressure fluctuation envelope that dynamically fluctuates in line with the current digital image ink consumption demand. This envelope pre-eliminates normal pressure drops caused by drastic changes in image color intensity. Based on this, any additional pressure fluctuations exceeding this baseline differential pressure fluctuation envelope have a unique physical structure indication, namely, an actual increase in friction inside the ink supply pipeline, such as micron-level filter blockage, or system airtightness damage, such as air leakage at pipeline joints. This enables anomaly detection based on underlying physical characteristics.

[0056] Specifically, by using hardware air pressure sensors installed at the ink inlet and ink outlet ends of the dual negative pressure printhead, the time is collected synchronously. Actual vacuum pressure difference The actual vacuum pressure difference Δ With the time of calculation output reference pressure difference Perform the difference operation and take the absolute value to obtain the time. Real-time physical deviation.

[0057] Furthermore, the real-time physical deviation is compared with a safety threshold pre-stored in the underlying control system: when the real-time physical deviation is determined to be greater than the safety threshold, the underlying control system starts a hardware timer to begin timing; if the real-time physical deviation falls back to or below the safety threshold during the timing process, the hardware timer is reset to zero; if the real-time physical deviation continues to be greater than the safety threshold, and the duration recorded by the hardware timer is greater than the set tolerance time window, it is determined that there is an underlying physical fault in the circulating ink supply system.

[0058] Upon detecting a fundamental physical fault, the underlying control system immediately issues an interrupt command to cut off the drive power to the piezoelectric printhead, thereby stopping ink ejection. Simultaneously, it shuts down the ink pump motor inside the circulating ink supply system and issues an alarm message through the device's human-machine interface.

[0059] To ensure the reliability of the judgment results, the judgment parameters involved in this embodiment are calibrated through the following physical experiments: 1. The tolerance time window is a time-determination parameter set to filter extremely short-frequency mechanical vibration noise and fluid turbulence interference. The initial calibration process of its value is as follows: build a fluid reference operating environment without physical structural faults, control the digital printing press to operate at full load and full speed, use an oscilloscope to dynamically acquire the normal background air pressure oscillation signal caused by the rotation of the mechanical pump in the fluid pipeline, record the maximum physical time span during which the normal background air pressure oscillation signal is continuously maintained, and use it as the final set value of the tolerance time window.

[0060] 2. The aforementioned safety threshold is a pressure difference limit parameter set to distinguish between normal manufacturing tolerances and abnormal physical structural changes. The preliminary calibration process for its value is as follows: a micro-leakage induction valve is connected in parallel at the side end of the circulating ink supply system pipeline. During the continuous dynamic printing process of the digital printer, the leakage orifice diameter of the valve is slowly enlarged, while a high-speed camera is used to monitor the printing quality of the substrate surface. The moment when the first microscopic physical ink leakage or broken line defect appears on the substrate surface is captured, and the corresponding real-time physical deviation value is extracted simultaneously. This value is established as the final determination basis for the safety threshold.

[0061] For example, Figure 3The comparison diagram, designed to monitor actual air pressure deviations and trigger physical anomaly shutdown interventions, illustrates the difference in detection effectiveness between the dynamic benchmark defense mechanism of this invention and the static judgment boundary of existing technologies when dealing with microscopic physical faults. The diagram includes the fluctuation curve corresponding to the actual vacuum air pressure difference, the constant threshold line corresponding to the static air pressure difference boundary of existing technologies, the safety zone constructed by extending the benchmark pressure difference fluctuation envelope outwards, and discrete action markers representing the accurate capture of underlying physical faults. Analysis shows that, in order to accommodate the normal transient fluid inertial pressure drop generated during large-block printing, existing technologies are forced to restrict the static air pressure difference boundary... The limit is set at an extremely high position; when the system subsequently experiences a real micron-level frictional increment fault, the abnormal rise in the actual vacuum pressure difference does not reach this excessively high static limit, resulting in missed detections in existing technologies; however, the safety zone constructed by this invention can closely follow the dynamic fluctuations of image color load. When the actual vacuum pressure difference deviates from this safety zone and continues to exceed the set tolerance time window, the system immediately outputs discrete action markers to trigger physical abnormal shutdown intervention, successfully and accurately intercepting weak abnormal signals before the macroscopic static limit is breached, thus solving the engineering problems of preventing false alarms and missed detections in the circulating ink supply system.

Claims

1. A method for detecting abnormalities in the circulating ink supply system of a digital printing press, characterized in that, include: The initial color digital image to be printed is acquired and discretized to generate a static dot matrix. The micro scanning cycle data and the instantaneous mechanical coordinates of the print head are combined to divide the micro printing partitions to extract the real-time dot area ratio. The theoretical dynamic ink consumption volume flow rate is obtained based on real-time dot area ratio, standard ink droplet volume of piezoelectric printhead and rated drive trigger frequency. Based on the Hagen-Poiseuille circular tube laminar flow model and theoretical dynamic ink consumption volume flow rate, dynamic frictional resistance pressure drop is obtained. Based on Newton's second law and theoretical dynamic ink consumption volume flow rate, transient fluid inertial pressure drop is obtained; The dynamic frictional resistance pressure drop is superimposed with the transient fluid inertial pressure drop to obtain the reference pressure difference on the reference pressure difference fluctuation envelope; The system collects the actual vacuum air pressure difference, obtains the real-time physical deviation based on the actual vacuum air pressure difference and the reference pressure difference, and determines the underlying physical fault and performs physical anomaly shutdown intervention based on the real-time physical deviation, the preset safety threshold and the tolerance time window.

2. The method for detecting abnormalities in the circulating ink supply system of a digital printing press according to claim 1, characterized in that, The process of acquiring the initial color digital image to be printed and discretizing it to generate a static dot matrix, and then combining the microscopic scanning cycle data and the instantaneous mechanical coordinates of the print head to divide the microscopic printing zones to extract the real-time dot area ratio, includes: The initial color digital image is converted from the red-green-blue color space to the cyan-magenta-yellow-black color space, and the continuous tone image of the physical printing channel is separated. The continuous tone image is processed by the frequency modulation halftone algorithm to generate a static halftone matrix. The instantaneous mechanical coordinates of the print head are projected onto the static halftone matrix to extract a local pixel sub-matrix. According to the physical nozzle array arrangement of the piezoelectric printhead, the local pixel sub-matrix is ​​divided into micro-printing zones by mesh cutting. The ratio of the number of pixels with a value of 1 in the micro-printing zone to the total number of pixels is counted and calculated to obtain the real-time halftone area ratio.

3. The method for detecting abnormalities in the circulating ink supply system of a digital printing press according to claim 1, characterized in that, The formula for calculating the theoretical dynamic ink consumption volumetric flow rate is: ； In the formula, For a moment Theoretical dynamic ink consumption volumetric flow rate; For a moment The total number of micro-printed partitions covered by the current scan line; This refers to the serial number of the micro-printing partition; For the first Each micro-printed partition at time Real-time branch area ratio; Standard ink droplet volume; This is the rated drive trigger frequency.

4. The method for detecting abnormalities in the circulating ink supply system of a digital printing press according to claim 1, characterized in that, The method for obtaining dynamic frictional resistance pressure drop based on the Hagen-Poiseuille circular tube laminar flow model and theoretical dynamic ink consumption volumetric flow rate includes: Obtain system real-time temperature And the dynamic viscosity of the UV ink was obtained by mapping. Obtain the physical length and inner diameter of the ink supply pipeline; ； In the formula, For a moment The dynamic frictional resistance pressure drop; To keep pace with the real-time temperature of the system Dynamic viscosity of UV inks with varying mapping effects; The physical length of the ink supply line; Indicates time The theoretical dynamic ink consumption volumetric flow rate required at the ink supply pipeline terminal; This refers to the inner diameter of the ink supply pipeline.

5. The method for detecting abnormalities in the circulating ink supply system of a digital printing press according to claim 1, characterized in that, The method for obtaining transient fluid inertial pressure drop based on Newton's second law and theoretical dynamic ink consumption volumetric flow rate includes: ； In the formula, For a moment Transient fluid inertial pressure drop; The fluid density of the ink; The equivalent inertial length of the pipeline impedance; Indicates time The theoretical dynamic ink consumption volumetric flow rate required at the ink supply pipeline terminal; Representative moment The theoretical dynamic ink consumption volumetric flow rate required at the ink supply pipeline terminal, with respect to time.

6. The method for detecting abnormalities in the circulating ink supply system of a digital printing press according to claim 5, characterized in that, The initial encapsulation method for the equivalent inertial length of the pipeline impedance is as follows: Construct a structure-free, fault-free fluid benchmark operating environment and perform step response tests; The piezoelectric printhead is driven to open instantaneously to its rated maximum displacement, generating a theoretical dynamic ink consumption volumetric flow rate mutation rate; The peak value of the transient pressure difference generated at both ends of the ink supply pipeline is captured synchronously using a hardware pressure sensor. Calculate the product of the theoretical dynamic ink consumption volume flow rate change rate and the fluid density of the ink; use the ratio of the transient pressure difference peak value to the product as the equivalent inertial length of the pipeline impedance.

7. The method for detecting abnormalities in the circulating ink supply system of a digital printing press according to claim 1, characterized in that, The method of obtaining real-time physical deviation based on actual vacuum pressure difference and reference pressure difference includes: The real-time physical deviation is obtained by subtracting the actual vacuum pressure difference from the reference pressure difference and taking the absolute value.

8. The method for detecting abnormalities in the circulating ink supply system of a digital printing press according to claim 1, characterized in that, The method for determining underlying physical faults based on real-time physical deviation, preset safety thresholds, and tolerance time windows includes: When the real-time physical deviation is determined to be greater than the safety threshold, the hardware timer is controlled to start counting. If the real-time physical deviation falls back to or below the safety threshold during the timing process, the hardware timer will be reset to zero. If the real-time physical deviation continues to exceed the safety threshold and the duration recorded by the hardware timer exceeds the tolerance time window, then the circulating ink supply system is determined to have an underlying physical fault.

9. The method for detecting abnormalities in the circulating ink supply system of a digital printing press according to claim 1, characterized in that, The execution of physical anomaly shutdown intervention includes: An interrupt command is issued to cut off the driving power supply of the piezoelectric nozzle; Simultaneously shut down the ink supply pump motor inside the circulating ink supply system; Alarm notifications are sent through the human-computer interaction interface.

10. The method for detecting abnormalities in the circulating ink supply system of a digital printing press according to claim 1, characterized in that, The calibration method for the security threshold is as follows: A micro-leakage induction valve is connected in parallel at the pipeline side of the circulating ink supply system; During the dynamic printing process, the leakage orifice diameter of the microleakage induction valve is slowly enlarged, and the printing quality of the substrate surface is monitored using a high-speed camera mechanism. The value of the real-time physical deviation corresponding to the instant when physical ink leakage or broken line defects appear on the surface of the printing substrate is captured, and this value is established as a safety threshold.

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