A printing method and device applied to irregular column outer facade multi-ink line and storage medium

Abstract

The application discloses a kind of applied irregular cylinder outer facade multiple ink line printing method, equipment and storage medium, the method is according to the physical spacing of multiple channel ink-jet head ink ejection hole, calibrates the position data of multiple corresponding ink line;Printing image is divided into different layers according to ink ejection hole;In the helical printing process of continuous rotation of cylinder, continuous movement of ink-jet head, through field programmable gate array FPGA control, when ink-jet head is accurately moved to each target ink line, nanosecond level delay triggers corresponding layer of jet printing, to realize the high-precision alignment of multiple ink lines in one forming;The method introduces curved surface adaptive path planning, ink drop volume real-time monitoring and correction, environmental humidity compensation mechanism, effectively overcome the influence brought by ink-jet head physical structure error, cylinder curvature change and environmental fluctuation, improve the printing quality, efficiency and consistency on irregular cylinder.

Description

Technical Field

[0001] This invention relates to the field of digital inkjet printing technology, specifically to a method, device, and storage medium for printing multiple ink lines on the exterior facade of an irregular column. Background Technology

[0002] In recent years, industrial-grade piezoelectric printheads, such as the Ricoh G5 / G6 series, have been tested for use in exterior decoration printing of cylindrical and conical consumables due to their high speed, high precision and multi-channel characteristics. However, when these printheads, which were originally optimized for planar printing, are used on irregular columns, they face inherent technical bottlenecks, resulting in poor printing results and restricting the industrial application of this technology.

[0003] The core problem stems from the dual contradiction between the physical structure of the printhead and the irregular cylindrical geometry. Firstly, taking the Ricoh G6 printhead as an example, its internal multiple ink discharge holes, such as the large fixed line spacing between channels 1 / 2 and 3 / 4, can be easily compensated for in planar printing through image data delay. However, in cylindrical printing, especially on non-standard cylinders such as cones, prisms, or curved surfaces with unevenness, this spacing leads to a fatal problem of inconsistent inkjet height. For example... Figure 1 As shown, in the ideal cylindrical arc surface model, the ink jet distances of the two channels are approximately equal only when the nozzle centerline X is aligned with the cylinder centerline. However, in actual continuous spiral printing, this is an instantaneous state that cannot be maintained. For irregular cylinders, the surface curvature changes continuously, which causes the normal distance between the ink outlets of different rows and the cylinder surface, i.e., the ink jet height, to be different most of the time. This results in significant differences in the trajectory, landing point, and shape of ink droplets, directly leading to image blurring, ghosting, and uneven color.

[0004] Secondly, existing technical solutions, such as Figure 1 As shown, a single ink line printing mode is usually adopted, which attempts to make a reference point of the printhead adapt to the entire changing curved surface. In order to accommodate the curvature change, this method often requires the frame to have extremely high installation and dynamic tracking accuracy, which becomes extremely demanding and difficult to achieve in the actual production environment, and cannot guarantee stable printing quality.

[0005] Therefore, there is an urgent need in this field for an innovative printing method and equipment that can fundamentally compensate for the errors caused by the inherent physical spacing of the printhead and the curvature of the irregular cylindrical surface, freeing it from dependence on extreme mechanical precision and achieving high-quality, stable printing on complex curved surfaces. Summary of the Invention

[0006] To overcome the problems of the prior art, this invention discloses a method for printing multiple ink lines on the exterior facade of an irregular column, comprising the following steps:

[0007] S1, parameter preset, based on the physical distance between each ink discharge hole of the multi-channel printhead, pre-store the motor step number from the first ink line, the second ink line and the center line aligned ink line to the printhead frame position of the motor origin sensor respectively;

[0008] The first ink line corresponds to the center of the first group of ink outlet holes of the multi-channel printhead, the second ink line corresponds to the center of the second group of ink outlet holes of the multi-channel printhead, and the center line alignment ink line corresponds to the geometric center line of two adjacent ink outlet holes, so as to complete the center line secondary printing without stopping during a single spiral continuous rotation.

[0009] S2, Image Layering, divides the image to be printed into a first layer, a second layer, and a center line layer;

[0010] The image data printed from the first set of ink outlets is divided into the first layer, the image data printed from the second set of ink outlets is divided into the second layer, and the WCV type data printed from two adjacent ink outlets is divided into the midline layer.

[0011] S3, collaborative printing, under the premise that the column consumable continues to rotate and the motor at the nozzle holder position does not stop, the field-programmable gate array (FPGA) is triggered sequentially according to the spiral rhythm:

[0012] When the multi-channel printhead moves to the first ink line alignment printing reference position, the first layer is printed.

[0013] When the multi-channel printhead moves to the centerline aligned ink line aligned printing reference position, the centerline layer is printed.

[0014] When the multi-channel printhead moves to the second ink line alignment printing reference position, the second layer is printed.

[0015] This allows WCV type data to be programmed into the corresponding layers in two steps and completes non-stop spiral printing.

[0016] Preferably, before the parameter preset step S1, step S0, adaptive surface planning, is also included:

[0017] Three-dimensional point cloud data of irregular cylinders are obtained by LiDAR scanning;

[0018] Based on point cloud data, a deep learning network is used to identify the macroscopic geometric type of a column.

[0019] For the identified non-standard cylinders, a variable-pitch spiral path or Bézier curve transition path that is parallel to the first and second ink lines and adapts to their local curvature is generated to replace the fixed phase difference path model applicable to standard cylinders.

[0020] Preferably, the inkjet dot position error includes:

[0021] The physical structure error of the multi-channel printhead caused by the fixed physical spacing between multiple sets of ink outlet holes;

[0022] Curvature error of irregular cylindrical surfaces caused by changes in the curvature of irregular cylindrical surfaces;

[0023] The number of steps preset in the S1 step parameter preset is used to comprehensively compensate for the physical structure error of the multi-channel printhead and the curvature error of the irregular cylindrical surface during the printing process.

[0024] Preferably, in the image layering step S2, the basis for dividing the image data is the mapping relationship between color data and the physical channels of the multi-channel nozzle;

[0025] During the printing process, the volume of ink droplets in each channel is monitored in real time by a quantum dot concentration sensor integrated into the outlet of the multi-channel printhead. When the ink volume deviation between different channels exceeds a preset threshold, the driving voltage of the piezoelectric ceramic micro-driving element corresponding to the nozzle or ink chamber integrated inside the multi-channel printhead is dynamically adjusted to achieve real-time synchronous correction of ink droplet volume.

[0026] Preferably, the first group of ink outlet holes are rows A and B, corresponding to channels 3 and 4, and the second group of ink outlet holes are rows C and D, corresponding to channels 1 and 2, and the center distance between rows B and C is 11mm.

[0027] The first ink line corresponds to the center of rows A and B, and the second ink line corresponds to the center of rows C and D;

[0028] The generation of variable pitch helical paths uses an 11mm center distance as a constraint condition for the density of path points.

[0029] Preferably, in step S3, during collaborative printing, while the column consumable is continuously rotating, the temperature field distribution of the UV-LED curing lamp is monitored in real time by an infrared thermal imager integrated on the side of the multi-channel nozzle.

[0030] When a localized high-temperature area is identified, the UV power output of the corresponding area is dynamically reduced simultaneously to compensate for thermal decay and ensure consistent curing.

[0031] Furthermore, the temperature and humidity data of the printing environment are collected in real time by a MEMS sensor array, and combined with a pre-stored ink viscosity-temperature and humidity relationship model, the step number is dynamically corrected to offset the inkjet dot position drift caused by environmental changes.

[0032] Preferably, the method for printing multiple ink lines on the exterior facade of an irregular column includes step S3a, calibration, before printing:

[0033] The nozzle mount is moved to trigger the motor origin sensor, and the position is established as the origin of the nozzle mount position motor count;

[0034] The calibration uses a set of calibration templates containing known curvature and standard thickness, and automatically fits the film thickness and curing degree calibration curve for the current ink-material combination using the measurement results of the confocal chromatograph sensor.

[0035] Preferably, in the collaborative printing of step S3, the timing of sending printing data to the multi-channel printhead is locked to the action of the printhead holder moving to the target ink line;

[0036] This locking mechanism is implemented by a field-programmable gate array (FPGA) to ensure that printing data is sent out within a nanosecond delay after the printhead is in place.

[0037] Preferably, an apparatus for printing on the exterior facade of an irregular column includes:

[0038] The printhead assembly includes at least one multi-channel printhead having multiple sets of ink outlets;

[0039] Sprayer mount, used to mount the sprayer assembly;

[0040] The moving mechanism, including a nozzle holder position motor and a motor origin sensor, is used to drive the nozzle holder to move continuously in a spiral direction parallel to the axis of the column consumable.

[0041] The control unit is electrically connected to the printhead assembly and the moving mechanism, and has pre-stored the position data of the first ink line, the second ink line, and the center line aligned ink line.

[0042] The control unit is configured to execute a multi-line printing method applied to the exterior facade of an irregular column.

[0043] Preferably, a computer-readable storage medium stores a computer program that, when executed by a processor, implements the steps of a multi-line printing method applied to the exterior facade of an irregular column.

[0044] The beneficial effects of this invention are as follows:

[0045] Through multi-line collaborative printing and composite error compensation mechanism, this invention accurately compensates for the inkjet dot position error caused by the fixed physical spacing of the printhead and the irregular curvature of the cylindrical surface, solving the problem of poor color registration. It can also obtain high-quality images with clear edges, uniform color and precise alignment between layers on complex curved surfaces such as cones and prisms, with better results than traditional single-line printing.

[0046] By reducing the stringent reliance on the precision of the mechanical system and compensating for the limitations of mechanical precision through control algorithms, the centerline secondary inkjet printing strategy, combined with nanosecond-level timing locking implemented by a field-programmable gate array (FPGA), enables the system to achieve accurate printing without relying on extremely high-precision mechanical alignment and installation adjustments. This also reduces the requirements for the precision of the frame processing and assembly, minimizes the risk of precision failure due to mechanical wear and vibration, and makes the equipment more stable and durable in the production environment.

[0047] Based on the collaborative printing process, the entire printing process is completed without stopping while the column rotates continuously and the nozzle frame moves continuously, avoiding the time spent on repeated start-stop and alignment in traditional step-by-step printing.

[0048] Through surface adaptive planning, real-time ink droplet volume correction, environmental temperature and humidity compensation, and quantitative calibration, this invention endows the printing system with intelligent perception and self-adjustment capabilities. The equipment can automatically adapt to different cylindrical shapes, environmental changes, and ink characteristics, dynamically optimize printing parameters, and ensure a high degree of consistency and reliability in the quality of products produced in different batches and under different environments.

[0049] The method and equipment of this invention are not only applicable to standard cylinders, but can also handle various non-standard cylinders, such as cones, polygonal prisms, and irregularly shaped cylinders, expanding the application boundaries of industrial inkjet printing technology in the field of curved surface decoration, and providing feasible technical solutions for personalized and small-batch customized production in more industries.

[0050] In summary, this invention uses a smart control algorithm that combines hardware and software to transform existing physical constraints into precisely controllable parameters, ensuring excellent printing quality while reducing manufacturing difficulty, equipment usage barriers, and maintenance costs. Attached Figure Description

[0051] Figure 1 This is a schematic diagram of printing on a curved surface using the existing G6 printhead.

[0052] Figure 2 This is a schematic diagram comparing the printing effects of Embodiment 1 of the present invention with those of the prior art;

[0053] Figure 3 This is a diagram showing the unfolded distribution of the multi-channel nozzle in Embodiment 1 of the present invention;

[0054] Figure 4 This is a schematic diagram showing the position of the ink line in Embodiment 1 of the present invention;

[0055] Figure 5 This is a flowchart illustrating the steps of a multi-line printing method for irregular column exteriors provided in Embodiment 1 of the present invention. Detailed Implementation

[0056] To further illustrate the technical means and effects adopted by the present invention to achieve its intended purpose, exemplary embodiments will be described in detail below, examples of which are illustrated in the accompanying drawings. In the following description relating to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of methods and systems consistent with some aspects of this application as detailed in the appended claims.

[0057] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The singular forms “a,” “the,” and “the” used in this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0058] The following detailed description of the specific implementation methods, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided in detail.

[0059] Example 1

[0060] Please see Figure 2 , 3 4. A method for printing multiple ink lines on the exterior facade of an irregular column, the method comprising the following steps:

[0061] S1, parameter preset, based on the physical distance between each ink discharge hole of the multi-channel printhead, pre-store the motor step number from the first ink line, the second ink line and the center line aligned ink line to the printhead frame position of the motor origin sensor respectively;

[0062] The first ink line corresponds to the center of the first group of ink outlet holes of the printhead, the second ink line corresponds to the center of the second group of ink outlet holes of the printhead, and the center line alignment ink line corresponds to the geometric center line of the two adjacent ink outlet holes, so as to complete the center line secondary printing without stopping during a single spiral continuous rotation.

[0063] S2, Image Layering, divides the image to be printed into a first layer, a second layer, and a center line layer;

[0064] The image data printed from the first set of ink outlets is divided into the first layer, the image data printed from the second set of ink outlets is divided into the second layer, and the WCV type data printed from two adjacent ink outlets is divided into the midline layer.

[0065] S3, collaborative printing, under the premise that the column consumable continues to rotate and the motor at the nozzle holder position does not stop, the field-programmable gate array (FPGA) is triggered sequentially according to the spiral rhythm:

[0066] The first layer is printed when the printhead moves to the first ink line alignment with the printing reference position.

[0067] When the printhead moves to the centerline aligned ink line aligned printing reference position, the centerline layer is printed;

[0068] When the printhead moves to the second ink line alignment printing reference position, the second layer is printed;

[0069] This allows WCV type data to be programmed into the corresponding layers in two steps and completes non-stop spiral printing.

[0070] Furthermore, before the parameter preset step S1, step S0, adaptive surface planning, is also included:

[0071] A high-precision LiDAR scanner is used to perform omnidirectional scanning of irregular columnar consumables. During scanning, the column can be fixed on a CNC rotating platform, and the LiDAR moves in a linear or arc trajectory to cover the entire exterior of the column. The scanning resolution is set to 0.1mm to 0.5mm to obtain dense three-dimensional point cloud data. Each point contains three-dimensional coordinates (X, Y, Z) and reflection intensity information. The point cloud data is transmitted to the control unit, such as an industrial PC, in real time, and noise is removed through filtering algorithms, such as statistical outlier removal.

[0072] After point cloud data preprocessing, it is input into a pre-trained deep learning network for geometric type recognition. The network structure adopts a variant based on PointNet++. The deep learning network can directly process point cloud data and extract global and local features. The training dataset contains labeled point clouds of various cylinder types, such as standard cylinders, cones, prisms, and twisted surfaces. The network output is the macroscopic geometric classification result of the cylinder, such as standard cylinders or non-standard cylinders and key parameters, such as local radius of curvature and tilt angle. For non-standard cylinders, the network will also segment regions with different geometric features, such as convex and concave features.

[0073] For the identified non-standard cylinders, the path generation module calculates the curvature distribution of each local region based on point cloud data. The path generation algorithm is constrained by the physical spacing of the ink nozzles, such as the center distance between rows B and C being 11mm, generating a printing path parallel to the first and second ink lines.

[0074] The variable pitch spiral path dynamically adjusts the pitch according to the local curvature. In areas with high curvature, such as sharp protrusions, a smaller pitch is used to increase the density of path points and ensure accurate ink droplet coverage.

[0075] In regions with low curvature, such as flat areas, a larger pitch is used to improve efficiency. Path point coordinates are calculated using interpolation algorithms, such as cubic spline interpolation, to ensure path continuity.

[0076] Bézier curve transition path: In areas of geometric abrupt change, such as edges or connections, quadratic or cubic Bézier curves are used to generate smooth transition paths to avoid printing defects caused by path jumps. The curve control points are jointly determined by the curvature derivative of the point cloud data and the nozzle movement direction.

[0077] The path data is ultimately converted into control commands for the nozzle mount position motor, replacing the fixed phase difference model of the standard cylinder, and realizing dynamic path planning that matches the local curvature.

[0078] Specifically, step S0 achieves high-precision modeling and printing path optimization of the irregular column exterior through lidar scanning, deep learning recognition, and adaptive path generation, effectively compensating for inkjet point position errors caused by the geometric irregularity of the column, and ensuring the alignment accuracy and image quality of multiple ink lines printed on complex curved surfaces.

[0079] Furthermore, the number of steps pre-stored in the S1 step parameter preset is used to compensate for the inkjet dot position error caused by the physical structure of the printhead itself and the irregular cylindrical curvature during the printing process.

[0080] Errors include printhead physical structure errors and irregular cylindrical surface ratio errors. Printhead physical structure errors are systematic errors. Taking the Ricoh G6 printhead as an example, the center distance between the ink outlets in row B and row C is a fixed value of 11mm. When the printhead frame moves, the first set of ink outlets A and B and the second set of ink outlets C and D cannot be aligned with the same theoretical printing baseline on the cylinder at the same time. If not compensated, the two ink lines will produce a fixed misalignment on the cylinder surface that is related to the pitch.

[0081] The curvature error of irregular cylindrical surfaces is a dynamic error. For non-standard cylinders, such as cones, polygonal prisms, or cylinders with concavities and convexities, the normal direction at any point on the surface is changing. Even if the printhead sprays ink at the same axial position, due to the change in the cylinder radius, the landing point of the ink droplet will drift radially and tangentially relative to the theoretical position of the cylinder surface. For example, at the small end of a cone, the arc length corresponding to the same angular displacement is shorter, which will cause the image to be compressed.

[0082] The pre-stored step count, i.e., the step count from the first ink line, the second ink line, the center-aligned ink line to the motor origin sensor, is a base value dynamically fine-tuned based on the surface adaptive planning results. The control unit, such as a field-programmable gate array (FPGA) or a high-performance motion control card, implements compensation according to the following process:

[0083] Based on the physical spacing of the printhead, such as 11mm and the standard cylindrical model, the basic step number corresponding to each ink line is calculated. For example, when printing a standard cylinder with a circumference of L, the basic value of the step number offset of the second ink line relative to the first ink line can be calculated as (11mm / L) * the total number of steps required for one revolution of the motor.

[0084] During the printing process, the control unit will call the variable pitch helical path or Bézier curve path data generated by the surface adaptive planning in step S0 in real time; the path data has encoded the local curvature information of each axial position of the cylinder;

[0085] When the printhead carriage moves to a certain axial position, the control unit will dynamically correct the basic step number based on the radius of curvature of the path position. For example, in the area where the radius of the column becomes smaller, in order to maintain tangential printing accuracy, it is necessary to fine-tune the ink jet trigger timing, which is equivalent to fine-tuning the step number, so that the ink droplets fall on the correct tangential position and prevent the image from being stretched or compressed.

[0086] All these compensation calculations are performed in a unified motion control coordinate system. The motor origin sensor provides an absolute physical position reference, and the pre-stored step number and real-time correction amount together ensure that the printhead triggers inkjet at the correct three-dimensional spatial position.

[0087] Specifically, by pre-storing and dynamically correcting the step number of the printhead position motor, a precise spatiotemporal mapping relationship is established. This mechanism incorporates the fixed physical spacing error of the printhead and the curvature error of the dynamically changing column into a unified compensation model. Thus, under the premise that these errors cannot be eliminated at the hardware level, through precise motion control and data processing, the precise alignment of multiple ink line printing points on the complex irregular cylindrical surface is finally achieved, ensuring the geometric fidelity of the overall printed image.

[0088] Furthermore, in the image layering step S2, the basis for dividing the image data is the mapping relationship between color data and the physical channels of the nozzle;

[0089] The control unit performs color separation and rasterization processing on the source image to be printed, such as CMYK mode;

[0090] The separated data is assigned to specific physical channels of the nozzle according to a pre-defined mapping table:

[0091] The cyan C data may be assigned to channels in rows A and B of the first set of ink outlets;

[0092] The magenta M data is assigned to the channels in rows C and D of the second set of ink outlets;

[0093] This mapping relationship ensures that each color component is printed by a designated, physically fixed ink outlet, which is the basis for achieving precise alignment of multiple ink outlet lines.

[0094] Real-time monitoring and correction of droplet volume solves the problem of inconsistent ink output caused by differences in nozzle status and ink viscosity in multi-channel printing.

[0095] Piezoelectric ceramics are miniature driving elements integrated inside each nozzle or ink chamber of a printhead. When a driving voltage is applied, the piezoelectric ceramic deforms, squeezing the ink chamber and thus precisely ejecting the ink.

[0096] Piezoelectric ceramics are the direct actuators of inkjet printing. The waveform of the driving voltage of the piezoelectric ceramic, such as voltage amplitude and pulse width, directly determines the ejection speed and volume of ink droplets.

[0097] A quantum dot concentration sensor is integrated near the printhead outlet. By emitting light of a specific wavelength to illuminate the ejected ink droplets, the spectral characteristics of the transmitted or reflected light are detected. Since the optical properties of quantum dot materials, such as fluorescence intensity, have a linear relationship with the concentration of dyes / pigments in the ink, and the concentration is directly related to the ink droplet volume under the premise of fixed ink formulation, the real-time ink droplet volume can be calculated indirectly and with high precision through spectral data.

[0098] During the printing process, the volume of ink droplets in each channel is monitored in real time by a quantum dot concentration sensor integrated into the outlet of the multi-channel printhead. When the ink volume deviation between different channels exceeds a preset threshold, the driving voltage of the piezoelectric ceramic micro-driving element corresponding to the nozzle or ink chamber integrated inside the multi-channel printhead is dynamically adjusted to achieve real-time synchronous correction of ink droplet volume.

[0099] Setting the preset threshold:

[0100] The preset threshold is typically set to ±1% to ±3% of the rated droplet volume;

[0101] The threshold is set primarily based on two factors:

[0102] The human eye's visual resolution limit; when the deviation exceeds this range, the printed color blocks will show density unevenness or color difference that is perceptible to the human eye, affecting image quality.

[0103] The curing process requires that inconsistent ink volume will lead to uneven film thickness after UV curing, affecting the gloss consistency and physical properties of the product surface.

[0104] The threshold is stored as a configurable parameter in the control unit and can be fine-tuned according to different ink types or print quality requirements;

[0105] The quantum dot sensor continuously monitors the droplet volume in each channel and transmits the data to the field programmable gate array (FPGA) in real time.

[0106] The field-programmable gate array (FPGA) compares real-time data with the rated droplet volume and calculates the deviation value.

[0107] If the ink volume deviation of a certain channel is detected to continuously exceed the preset threshold, such as if 5 ink droplets exceed the standard in a row, the correction mechanism will be triggered.

[0108] The programmable gate array (FPGA) dynamically adjusts the amplitude or pulse width of the driving voltage sent to the corresponding piezoelectric ceramic of the channel. If the ink droplet volume is too small, the driving voltage is appropriately increased to enhance the deformation amplitude of the piezoelectric ceramic, thereby squeezing out more ink.

[0109] This process is completed within milliseconds, forming a closed-loop control that ensures that the ink droplet volume in all channels remains consistent throughout the printing process.

[0110] By employing the above process, key data such as WCV type are encoded into the corresponding layers in two steps. This allows for precise overprinting within a single continuous spiral printing stroke, achieving the same result as traditional methods that require multiple stops for alignment, without needing to stop the printer. (Reference) Figure 1 This technology overcomes the problem of poor color registration at the edges of cylindrical surfaces far from the center caused by the single-layer printing of the center ink line in the existing technology a1, and achieves the effect of clear image edges generated by the precise superposition printing of dual ink lines in a2.

[0111] Specifically, by establishing a precise mapping relationship between color and physical channels, and combining real-time ink droplet volume monitoring based on quantum dot sensing with feedback control of piezoelectric ceramic driving voltage, the inherent problem of uneven ink output in multi-channel printing is effectively overcome. Scientific thresholds based on visual and process requirements are set, and piezoelectric ceramics are used as actuators to achieve nanosecond-level precise correction. Without interrupting printing, the color uniformity and curing consistency of the color image on the surface of irregular columns are guaranteed, thus improving the overall printing quality.

[0112] Furthermore, this embodiment uses a Ricoh G6 multi-channel piezoelectric printhead, and the ink outlet array of the Ricoh G6 multi-channel piezoelectric printhead is divided into four rows: A, B, C, and D.

[0113] The first set of ink outlet holes is specifically designated as row A and row B, which together correspond to channel 3 and channel 4 in the control unit. The first ink line is precisely defined to be aligned with the center line of the physical array formed by the ink outlet holes of row A and row B.

[0114] The second set of ink outlet holes is specifically designated as rows C and D, which together correspond to channels 1 and 2 in the control unit. The second ink line is precisely defined to be aligned with the center line of the physical array formed by the ink outlet holes of rows C and D.

[0115] The physical distance between the center of ink discharge hole B and the center of ink discharge hole C is 11mm. This fixed distance is the main source of error in the physical structure of the printhead and is also the core basis for subsequent motion compensation and path planning.

[0116] When performing adaptive surface planning, when generating variable pitch spiral paths or Bézier curve transition paths, a center distance of 11 mm must be used as the key path point density constraint condition.

[0117] The original basis for setting the center distance of 11mm: The value of 11mm is quoted from the official technical documents or design specifications of Ricoh G6 series printheads, which clearly specifies the precise physical layout between the rows of nozzles inside the printhead.

[0118] This distance is a fixed physical parameter determined by the precision manufacturing process inside the nozzle, such as silicon wafer etching and bonding. For all nozzles of the same model, this is a non-adjustable system constant.

[0119] The overall principle of path planning is to ensure that the spiral path formed by the rotation of the column during the movement of the printhead frame by an axial distance of 11mm can accurately match the circumference change under the current local curvature, so that the patterns printed by the first set of ink outlets and the second set of ink outlets can be seamlessly aligned on the curved surface.

[0120] In the path point density calculation, in areas with large cylindrical curvature, such as small radii, the arc length of the cylindrical surface corresponding to a unit axial distance is short. To prevent image stretching, the algorithm will automatically densify the path points in areas with large cylindrical curvature based on an 11mm constraint, that is, reduce the pitch, so that the printhead triggers more rotational synchronous printing within a displacement of 11mm, ensuring the restoration of image details.

[0121] In areas with low column curvature, the density of path points will be appropriately increased and the pitch will be increased. Throughout the path generation process, the 11mm center distance serves as the basic benchmark, dynamically adjusting the distribution of path points to directly compensate for the inherent printing misalignment caused by this fixed spacing.

[0122] Specifically, by using the Ricoh G6 printhead, the first and second sets of ink outlets and ink lines are clearly associated with the specific physical parameters of the printhead. The inherent and critical 11mm physical spacing of the printhead is used as an unchangeable hard constraint in the surface adaptive planning algorithm. The variable pitch characteristic of the path directly serves to compensate for the performance differences of this spacing on different curvature cylinders, which is reflected in the optimized design in the application scenario.

[0123] Furthermore, in step S3 of collaborative printing, a real-time monitoring and feedback control closed loop is added, along with temperature management during the curing process and compensation for inkjet dot drift caused by the environment, to ensure the stability of the final print quality under complex environments. The specific implementation method is as follows:

[0124] UV curing consistency control, based on dynamic power adjustment of thermal imaging, solves the problem of insufficient or over-curing caused by thermal decay or unevenness of UV-LED curing lamps due to long-term operation.

[0125] A miniature infrared thermal imager is integrated on the side of the multi-channel printhead. It scans the temperature field of the light spot projected by the UV-LED curing lamp onto the freshly printed wet ink film in real time at a rate of several to tens of frames per second. The temperature field distribution indirectly reflects the distribution of UV light intensity.

[0126] Local high temperature areas are identified. The field programmable gate array (FPGA) receives thermal imaging data and uses image processing algorithms to identify local high temperature areas in the temperature field in real time, that is, areas that exceed the preset average temperature threshold. This area indicates that the output power of the UV lamp beads is relatively high or the heat dissipation is poor, which may cause the ink to over-cur, yellow or become brittle.

[0127] Once a local high-temperature area is identified, the FPGA will immediately send a command to the UV-LED lamp driving system to synchronously and dynamically reduce the driving current of the corresponding LED beads, i.e., the power output. For example, for a UV lamp array with zone control, the power of the high-temperature zone can be directly reduced. This adjustment has a millisecond-level response, ensuring that the UV radiation energy received by the ink layer remains consistent throughout the printing process.

[0128] Through the feedback mechanism, the light decay and uneven light output of LED beads caused by heat are compensated, ensuring the uniformity and consistency of the curing effect and avoiding color difference and product life problems.

[0129] Temperature and humidity-based nozzle position correction addresses the problem that changes in ambient temperature and humidity cause variations in ink viscosity, which in turn lead to changes in ink droplet ejection speed and ultimately cause ink droplet position drift.

[0130] Inside the printing equipment, a microelectromechanical system (MEMS) sensor array is deployed near the printhead to collect temperature and relative humidity data of the printing environment in real time and at high frequency;

[0131] The printing device has a pre-stored ink viscosity-temperature and humidity relationship model fitted by a large amount of experimental data; the water viscosity-temperature and humidity relationship model is a mathematical function or lookup table that specifies the expected viscosity value of the specific ink currently in use under different temperature and humidity combinations.

[0132] The field-programmable gate array (FPGA) inputs the real-time collected temperature and humidity data into the water viscosity-temperature and humidity relationship model to calculate the ink viscosity under the current environment. Since changes in viscosity directly affect the flight speed of ink droplets, the speed usually decreases as the viscosity increases, resulting in a delay in the landing point. The FPGA then fine-tunes the number of motor steps for the printhead position corresponding to each ink line in step S1 based on the pre-stored viscosity-flight time-position offset correspondence. For example, when the ambient temperature rises, causing the viscosity to decrease and the ink droplet flight speed to increase, the printing device will trigger the inkjet command in advance, which is equivalent to increasing the number of steps, so that the ink droplets can still accurately hit the target position.

[0133] Specifically, the process status and external environment are perceived in real time by an infrared thermal imager and a MEMS sensor array, and the high-speed processing capability of the field-programmable gate array (FPGA) is used to dynamically and precisely adjust the output power of the UV-LED curing lamp and the positioning step number of the nozzle frame, thereby solving the problem of curing uniformity.

[0134] Furthermore, the method includes step S3a calibration before printing:

[0135] The nozzle mount is moved to trigger the motor origin sensor, which establishes the position as the origin of the nozzle mount position motor count;

[0136] When a specific mechanical structure on the nozzle frame, such as a baffle, triggers the motor origin sensor, which is usually a photoelectric sensor or a proximity switch, the motor origin sensor generates an electrical signal.

[0137] Upon receiving the signal, the field programmable gate array (FPGA) or motion control card immediately resets the encoder count value of the motor at the current printhead position to zero or sets it to a known reference value. The position of the printhead at any point in the entire printing stroke can be precisely quantized by the motor step count, providing a coordinate origin for the step count of each ink line pre-stored in step S1.

[0138] The calibration uses a set of calibration templates containing known curvatures to simulate irregular cylindrical surfaces and standard thicknesses. The material of the templates should be the same as or similar to the consumables in actual production. The film thickness and curing degree calibration curve under the current ink-material combination is automatically fitted by the measurement results of the confocal chromatograph sensor.

[0139] Using the ink-material combination currently intended for production, print a series of test blocks with different gray levels or inkjet frequencies on a calibration template.

[0140] A confocal chromatography sensor, a high-precision measuring device utilizing the principles of optical confocalization and color difference, scans the printed test pattern. This sensor can simultaneously measure two key physical quantities:

[0141] Film thickness is measured non-contactly by detecting changes in the focal point position to determine the thickness of the cured ink film.

[0142] Curing degree is indirectly evaluated by analyzing the spectral characteristics of reflected light to assess the degree of cross-linking and curing of UV inks. For example, the spectral characteristics of fully cured inks differ from those of incompletely cured inks.

[0143] Curve fitting and model establishment: The control unit receives the measurement data from the trigger motor origin sensor and correlates the measurement data with the corresponding inkjet parameters during printing, such as drive voltage, inkjet pulse width, and UV lamp power. Through mathematical algorithms, such as the least squares method, the relationship model between inkjet parameters, film thickness, and curing degree is automatically fitted, i.e., the film thickness and curing degree calibration curve.

[0144] The film thickness and curing degree calibration curve is stored in the printing equipment. During actual printing, the printing equipment can automatically look up the curve in reverse according to the target film thickness and curing degree requirements, so as to accurately set the optimal inkjet and curing parameters and ensure the quality stability of each batch of products.

[0145] Specifically, by combining mechanical origin calibration with quantitative quality calibration based on confocal chromatography sensing, a precise, data-driven preprocessing workflow is achieved, establishing an accurate spatial coordinate system. For specific ink and consumable combinations, an objective and quantifiable quality calibration model is established to replace the traditional trial-and-error adjustments that rely on operator experience, thereby improving the consistency, repeatability, and rapid adaptability of the printing process to different production tasks.

[0146] Furthermore, in the S3 step of collaborative printing, the timing of sending printing data to the multi-channel printhead is locked to the action of the printhead carriage moving to the target ink line;

[0147] The locking mechanism is implemented by a field-programmable gate array (FPGA) to ensure that printing data is sent out within a nanosecond delay after the printhead is in place;

[0148] The hardware core of the locking mechanism is a field-programmable gate array (FPGA). In this embodiment, the FPGA acts as a high-speed, hardware-based synchronous controller rather than a processor running general-purpose operating software. The parallel processing and hardware programmable characteristics are the basis for achieving nanosecond-level precise control.

[0149] Field-Programmable Gate Arrays (FPGAs) can internally build dedicated digital logic circuits, such as state machines, comparators, and precise delay units, to perform locking operations.

[0150] The specific process of the locking mechanism:

[0151] The field-programmable gate array (FPGA) receives and decodes high-frequency signals from the nozzle holder position motor encoder in real time, continuously and accurately calculating the current position of the nozzle holder, usually expressed in steps.

[0152] The field-programmable gate array (FPGA) compares the real-time position with the step number corresponding to the target ink line position, i.e., the first ink line, the center-aligned ink line, and the second ink line, which are pre-stored in step S1.

[0153] When the difference between the real-time position and a target position enters a very small preset window, the matching circuit inside the FPGA is activated and enters a pre-trigger state.

[0154] Within the same clock cycle of precisely matching the target position, the hardware logic of the FPGA automatically generates a printing trigger signal, which is then sent directly to the printhead driver via a hardware link. The entire process, from position matching to the issuance of the printing trigger signal, is completed within the FPGA using hardware logic. The delay is controlled at the nanosecond level and exhibits high determinism and repeatability, avoiding the uncertainty of software delays.

[0155] Specifically, the locking mechanism ensures that regardless of the curvature of the cylindrical surface or the change in the speed of the printhead movement, the inkjet action is always triggered the instant the printhead physically reaches the predetermined ink line. This is crucial for achieving precise alignment of multiple layers and multiple ink lines on irregular curved surfaces. Through nanosecond-level delay control, it ensures that each ink droplet can be precisely released at the predetermined three-dimensional spatial coordinates, solving the problem of timing drift of inkjet points under high-speed continuous motion.

[0156] Furthermore, an apparatus for printing on the exterior facade of an irregular column includes:

[0157] The printhead assembly includes at least one multi-channel printhead having multiple sets of ink outlets;

[0158] The printhead assembly includes at least one multi-channel printhead, such as the Ricoh G6 printhead, which has multiple sets of independent ink outlets A, B, C, and D inside the printhead. Each set can spray inks of the same or different properties, such as different colors or functional coatings.

[0159] The printhead assembly can also be integrated with a quantum dot concentration sensor for droplet monitoring and a confocal chromatography sensor for calibration;

[0160] A printhead mount is used to mount the printhead assembly, ensuring that the printhead mount is stable in attitude and distance relative to the column being printed.

[0161] The moving mechanism, including a nozzle holder position motor and a motor origin sensor, is used to drive the nozzle holder to move continuously in a spiral direction parallel to the axis of the column consumable.

[0162] The control unit is electrically connected to the printhead assembly and the moving mechanism, and has pre-stored the position data of the first ink line, the second ink line, and the center line aligned ink line.

[0163] The control unit is configured to perform a multi-line printing method applied to the exterior facade of an irregular column;

[0164] This method can be implemented using a computer-readable storage medium containing a computer program. When the computer program is executed by a processor, it is used to implement the above-described method for printing multiple ink lines on the exterior facade of an irregular column.

Claims

1. A method for printing multiple ink lines on the exterior facade of an irregular column, characterized in that, The method includes the following steps: S1, parameter preset, based on the physical distance between each ink discharge hole of the multi-channel printhead, pre-store the motor step number from the first ink line, the second ink line and the center line aligned ink line to the printhead frame position of the motor origin sensor respectively; The first ink line corresponds to the center of the first group of ink outlet holes of the multi-channel printhead, the second ink line corresponds to the center of the second group of ink outlet holes of the multi-channel printhead, and the centerline aligned ink line corresponds to the geometric centerline of two adjacent ink outlet holes, so as to complete the centerline secondary printing without stopping during a single spiral continuous rotation. S2, Image Layering, divides the image to be printed into a first layer, a second layer, and a center line layer; The image data printed from the first set of ink outlets is divided into the first layer, the image data printed from the second set of ink outlets is divided into the second layer, and the WCV type data printed from two adjacent ink outlets is divided into the midline layer. S3, collaborative printing, under the premise that the column consumable continues to rotate and the motor at the nozzle holder position does not stop, the field-programmable gate array (FPGA) is triggered sequentially according to the spiral rhythm: When the multi-channel printhead moves to the first ink line alignment printing reference position, the first layer is printed. When the multi-channel printhead moves to the centerline aligned ink line aligned printing reference position, the centerline layer is printed. When the multi-channel printhead moves to the second ink line alignment printing reference position, the second layer is printed. This allows WCV type data to be programmed into the corresponding layers in two steps and completes non-stop spiral printing; Inkjet dot position error includes: The physical structure error of the multi-channel printhead caused by the fixed physical spacing between multiple sets of ink outlet holes; Curvature error of irregular cylindrical surfaces caused by changes in the curvature of irregular cylindrical surfaces; The number of steps pre-stored in the S1 step parameter preset is used to comprehensively compensate for the physical structure error and irregular cylindrical surface curvature error of the multi-channel nozzle during the printing process.

2. The method for printing multiple ink lines on the exterior facade of an irregular column according to claim 1, characterized in that, Before the parameter preset step S1, step S0, adaptive surface planning, is also included: Three-dimensional point cloud data of irregular cylinders are obtained by LiDAR scanning; Based on the point cloud data, a deep learning network is used to identify the macroscopic geometric type of the column. For the identified non-standard cylinders, a variable-pitch spiral path or Bézier curve transition path that is parallel to the first and second ink lines and adapts to their local curvature is generated to replace the fixed phase difference path model applicable to standard cylinders.

3. The method for printing multiple ink lines on the exterior facade of an irregular column according to claim 1, characterized in that, In the image layering step S2, the basis for dividing the image data is the mapping relationship between color data and the physical channels of the multi-channel nozzle. During the printing process, the volume of ink droplets in each channel is monitored in real time by a quantum dot concentration sensor integrated into the outlet of the multi-channel printhead. When the ink volume deviation between different channels exceeds a preset threshold, the driving voltage of the piezoelectric ceramic micro-driving element corresponding to the nozzle or ink chamber integrated inside the multi-channel printhead is dynamically adjusted to achieve real-time synchronous correction of ink droplet volume.

4. The method for printing multiple ink lines on the exterior facade of an irregular column according to claim 2, characterized in that, The first group of ink outlet holes consists of rows A and B, corresponding to channels 3 and 4. The second group of ink outlet holes consists of rows C and D, corresponding to channels 1 and 2. The center distance between rows B and C is 11 mm. The first ink line corresponds to the center of rows A and B, and the second ink line corresponds to the center of rows C and D; The generation of the variable pitch helical path uses the center distance as a constraint condition for the path point density.

5. The method for printing multiple ink lines on the exterior facade of an irregular column according to claim 1, characterized in that, In the collaborative printing process described in step S3, while the cylindrical consumable material is continuously rotating, the temperature field distribution of the UV-LED curing lamp is monitored in real time by an infrared thermal imager integrated on the side of the multi-channel nozzle. When a local high-temperature area is identified, the UV power output of the corresponding area is dynamically reduced simultaneously to compensate for thermal decay and ensure consistent curing. Furthermore, the temperature and humidity data of the printing environment are collected in real time by a MEMS sensor array, and combined with a pre-stored ink viscosity-temperature and humidity relationship model, the step number is dynamically corrected to offset the inkjet dot position drift caused by environmental changes.

6. The method for printing multiple ink lines on the exterior facade of an irregular column according to claim 1, characterized in that, The method includes step S3a calibration before printing: The nozzle mount is moved to trigger the motor origin sensor, and the position is established as the origin of the nozzle mount position motor count; The calibration uses a set of calibration templates containing known curvature and standard thickness, and automatically fits the film thickness and curing degree calibration curve under the current ink-material combination using the measurement results of the confocal chromatograph sensor.

7. The method for printing multiple ink lines on the exterior facade of an irregular column according to claim 1, characterized in that, In the S3 step of collaborative printing, the timing of sending printing data to the multi-channel printhead is locked to the action of the printhead holder moving to the target ink line; This locking mechanism is implemented by a field-programmable gate array (FPGA) to ensure that printing data is sent out within a nanosecond delay after the printhead is in place.

8. A device for printing on the exterior facade of an irregular column, characterized in that, include: The printhead assembly includes at least one multi-channel printhead having multiple sets of ink outlets; Sprayer mount, used to mount the sprayer assembly; The moving mechanism, including a nozzle holder position motor and a motor origin sensor, is used to drive the nozzle holder to move continuously in a spiral direction parallel to the axis of the column consumable. The control unit is electrically connected to the printhead assembly and the moving mechanism, and has pre-stored the position data of the first ink line, the second ink line and the center line aligned ink line. The control unit is configured to perform the multi-line printing method for irregular columnar facades as described in any one of claims 1 to 7.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the steps of the method for printing multiple ink lines on the exterior facade of an irregular column as described in any one of claims 1 to 7.

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