A curved high-definition CNC composite printing system and method

Abstract

The application discloses a curved-surface high-definition CNC composite printing system and method, and belongs to the technical field of curved-surface printing. The system comprises a CNC four-axis linkage work platform and a full-servo closed-loop overprinting control system; the four-axis linkage platform supports X, Y and Z linear and C-axis rotary linkage, and the closed-loop overprinting control system independently carries out position compensation on each product through visual detection, and the overprinting accuracy is less than or equal to ±0.05 mm. The system further comprises feeding, surface treatment, primer coating, special process, high-definition direct printing, LED UV curing, varnishing and discharging modules arranged along a conveying path in sequence. The primer coating module adopts a recyclable primer coating layer, and the deinking recovery rate is greater than or equal to 95% after the primer coating layer is soaked with an auxiliary agent and centrifuged. The application integrates primer coating, anti-counterfeiting, gold stamping, printing and varnishing into one, and completes all processes at one time, and is suitable for high-definition decorative printing of curved-surface containers such as bottles and cans.

Description

Technical Field

[0001] This invention relates to the field of curved surface printing technology, specifically to a CNC composite printing system and method for high-definition decorative printing on the surface of curved packaging containers such as bottles, cans, cups, and tubes. Background Technology

[0002] Curved surface printing is an important process in the packaging industry, widely used for decorative printing on the outer surfaces of curved packaging containers such as cosmetic bottles, pharmaceutical bottles, wine bottles, beverage bottles, and various food cans. Currently, the mainstream surface decoration processes for curved packaging containers on the market mainly include two categories: labeling processes (such as self-adhesive labels and shrink film labels) and direct printing processes.

[0003] In terms of labeling processes, traditional curved packaging containers often use plastic shrink film or self-adhesive labels for surface decoration. However, this process has significant technical drawbacks: First, the process is lengthy, requiring multiple transfers of the product, which not only increases the production cycle but also easily causes product damage during transfers; second, the labeling process requires the additional production of label materials, involving multiple stages such as label manufacturing, warehousing, and transportation, resulting in significant energy consumption; furthermore, shrink film labels are mostly made of plastic, which is difficult to degrade after disposal, placing a significant burden on the environment and failing to meet the current environmental protection requirements of green manufacturing.

[0004] In terms of direct printing processes, existing technologies offer various solutions for curved surface printing equipment. For example, Chinese patent CN101181837A discloses a "high-speed curved surface printing machine with automatic registration." This technology, based on existing curved surface printing machines, adds longitudinal and transverse registration drive devices and control devices for the registration drive devices to the printing roller assembly, thus improving the color registration problem in curved surface printing to some extent. However, this equipment still primarily relies on a single offset printing process and cannot flexibly combine multiple printing processes on the same machine. It struggles to meet the increasingly diverse needs of special processes such as anti-counterfeiting printing, variable code inkjet printing, and hot stamping, and also cannot achieve rapid and effective ink separation and material recycling during the packaging and recycling of printed materials.

[0005] For example, Chinese patent CN116787937A discloses a "cylindrical curved surface printing device," which achieves automatic centering and positioning of the cylinder to be printed through an adjustment mechanism. However, this device is also limited to a single digital inkjet printing process and has significant shortcomings in multi-process composite printing.

[0006] Regarding modular printing equipment, Chinese patent CN105109193A discloses a "multi-functional composite printing machine." This equipment can flexibly combine various printing methods and exchange different color group printing methods according to the diversity of products, and its technical solution realizes modular combination of printing functions to a certain extent. However, this equipment is mainly designed for paper-based flat printing and does not involve special fixtures and conveying systems for curved packaging containers, resulting in inherent deficiencies in curved surface adaptability. In addition, the module replacement of this equipment relies on manual operation, resulting in low production changeover efficiency, and it lacks automated mechanisms for curved surface registration detection and closed-loop compensation.

[0007] In terms of international technology, PCT patent WO2009112160A1 discloses a "modular linear printing machine for printing on hollow bodies using different printing methods." This equipment uses interchangeable printing modules and supports multiple processes such as screen printing, flexographic printing, and offset printing. The printing modules have independent drives and are connected to the main control system through interfaces. However, this equipment is mainly suitable for simple printing on cylindrical hollow bodies. It has limitations in terms of adaptability to printing on irregular curved surfaces (such as elliptical bottles, square-round bottles, and conical bottles) and multi-axis linkage positioning accuracy. Furthermore, its drying modules are mostly fixed in configuration and cannot be flexibly adjusted to meet the differentiated needs of different processes.

[0008] In addition, Chinese patent CN216610476U discloses a "new type of CNC printing machine for curved surface products". This machine discloses a technical solution for screen printing sheet-like curved surface products by using four-axis linkage of C-axis, X1-axis, Z-axis and X2-axis. However, this machine adopts an open-loop control method and does not involve full servo closed-loop overprint compensation based on visual feedback. It has limitations in overprint accuracy and is limited to the single process of screen printing.

[0009] In summary, existing curved surface printing technologies have the following unresolved technical problems: First, the process flow is fragmented, making it difficult to combine multiple processes. Existing equipment often only enables a single printing process (such as screen printing or offset printing). When multiple processes such as base coating, high-definition printing, anti-counterfeiting marking, hot stamping, and varnishing need to be performed on a single product, multiple machines are often required to complete the process step by step, resulting in frequent material transfers between processes and low production efficiency.

[0010] Secondly, the registration accuracy for curved surface printing is insufficient. For irregularly shaped curved surfaces (such as elliptical bottles, square-round bottles, and conical bottles), the existing equipment's conveying fixtures and positioning systems are mostly of general design, making it difficult to achieve high-precision multi-color registration and multi-layer printing, resulting in a high scrap rate of finished products. Existing four-axis linkage solutions mostly use open-loop or semi-closed-loop control, which cannot perform real-time detection and dynamic compensation for individual positional deviations of each product.

[0011] Third, energy-saving and environmental protection performance needs improvement. Existing equipment mostly uses traditional high-pressure mercury lamp UV curing systems, which consume a lot of energy and generate a large amount of heat, making it difficult to control the temperature of the production environment. At the same time, the printing ink adheres firmly to the substrate, making it difficult to achieve effective ink removal during product packaging recycling, thus restricting the recycling and reuse of packaging materials.

[0012] Fourth, regarding the problem of tracking complex curved surfaces in printing on irregular curved surfaces, existing solutions, such as using simple indexing positioning or multi-station turntables to replace continuous curved surface interpolation, although structurally simple, cannot fundamentally solve the problems of uniform ink layer transfer and constant pressure control on surfaces with varying curvature. This is not a simple choice between superior and inferior mechanical solutions, but a rigid technical requirement determined by the geometric characteristics of printing on irregular curved surfaces. Summary of the Invention

[0013] This invention aims to overcome the shortcomings of the prior art and provide a curved surface high-definition CNC composite printing system and method. It can complete multiple processes such as base coating, anti-counterfeiting printing, variable code printing, hot stamping, high-definition direct printing, and varnishing on the same machine in one go. It also features high-precision curved surface overprinting, clean energy curing, and environmentally friendly recyclability, which significantly improves the printing efficiency, product quality, and environmental performance of curved packaging containers.

[0014] To achieve the above objectives, the present invention provides a curved high-definition CNC composite printing system, the system comprising multiple functional modules arranged sequentially along the product conveying path, a CNC four-axis linkage work platform, a full servo closed-loop overprinting control system, and a clean energy curing system.

[0015] Specifically, the curved surface high-definition CNC composite printing system of the present invention includes the following functional modules: Module A, Feeding Module: Used to feed the curved packaging containers to be printed into the printing system one by one in an orderly manner.

[0016] Module B, Surface Treatment Module: Performs dust removal and tension adjustment on the product surface to ensure the printed surface is clean and has suitable wetting tension.

[0017] Module C, Primer Process Module: Apply an environmentally friendly and recyclable primer to the product surface. This primer improves the adhesion between the ink and the substrate, and can be completely deinked by soaking in a special additive during the recycling process, allowing the substrate material to be recycled.

[0018] Module D, Special Process Module: Used for special processes such as anti-counterfeiting printing, variable code inkjet printing, and hot stamping on the product surface.

[0019] E-module, high-definition direct printing module: It adopts fully servo automatic registration technology, combined with water-based inks and / or UV-curable inks and high-definition nano templates, to achieve high-resolution, high-color-fidelity decorative pattern printing on the product surface.

[0020] Module F, LED UV curing module: This module uses LED UV curing technology to quickly cure printed patterns. It is a clean energy curing system with low energy consumption, low heat generation, and is ready to use immediately.

[0021] G module, varnishing module: applies water-based or UV-cured varnish to the printed surface of the product to form a protective layer and improve the surface feel and gloss.

[0022] H module, output module: Outputs the finished printing products from the system for subsequent packaging or quality inspection.

[0023] Furthermore, the system of this invention also includes a CNC four-axis linkage work platform. This work platform serves as the core actuator of the system, supporting the linkage control of linear motion along the X, Y, and Z axes and the rotary axis (C-axis). The work platform is equipped with several workstations (e.g., 12 workstations, but not limited to this; it can be flexibly expanded to 6, 8, 12, 16, or more workstations according to actual production capacity requirements or product size). Each workstation is equipped with a fixture specifically designed for curved products. Through the CNC four-axis linkage numerical control system, precise position control and motion trajectory planning of the printing head relative to the curved surface of the product are achieved, thereby realizing all-round high-definition printing on irregular curved surfaces (including elliptical bottles, square-round bottles, conical bottles, etc.).

[0024] Compared to existing technologies that use simple mechanical indexing or multi-station intermittent turntables to approximate curved surface printing, this invention employs continuous four-axis interpolation linkage. The necessity of this approach lies in the fact that the tangent and normal vectors of irregular curved surfaces continuously change along the product contour. Only through real-time spatial linkage of the X, Y, Z, and C axes can a constant gap and normal pressure be maintained between the printing head and the curved surface in areas of varying curvature. This technical requirement cannot be solved by increasing the number of stations or improving indexing accuracy. Indexing methods are essentially discrete approximations; when the product cross-sectional curvature radius changes by more than 10%, the indexing method will cause printing pressure fluctuations exceeding 30%, and ink layer thickness deviations reaching ±15μm or more, failing to meet the quality requirements of high-definition printing (line count ≥175lpi). Therefore, the four-axis linkage solution of this invention is a necessary technical means to solve this type of technical problem, rather than a simple alternative.

[0025] The core difference between this invention and existing four-axis linkage solutions lies in the fact that existing solutions mostly employ open-loop or semi-closed-loop control methods, driving the printing head movement solely through a preset trajectory. This fails to provide real-time detection and dynamic compensation for individual positional deviations of each product. In contrast, this invention employs a full servo closed-loop overprinting control system. A vision positioning unit independently detects the position of each product and then uses feedforward compensation to superimpose the detected deviation values ​​into the CNC four-axis linkage motion control commands in real time, achieving independent dynamic correction for each product. This combination of "four-axis linkage + full servo closed-loop vision overprinting" technology enables the overprinting accuracy of this invention to reach ±0.05mm, significantly superior to the accuracy levels of existing open-loop or semi-closed-loop four-axis linkage solutions.

[0026] Furthermore, the system of the present invention also includes a temperature control module for precisely adjusting the temperature of the printing medium during high-precision printing. The temperature control module includes a quantitative ink cartridge and a high-precision ceramic roller; the ceramic roller has a built-in intelligent heat source, with a rare-earth thick film covering the entire surface of its inner core. Conductive ink integrated circuit heating chips are printed on the thick film, enabling digital intelligent control of the printing temperature through these heating chips.

[0027] In the temperature control module, the core control quantities involved in the PID closed-loop temperature control include the temperature deviation e(t) = T_set - T_actual (unit: °C), and the control output quantity calculated from it. Where u(t) is a dimensionless PWM duty cycle adjustment signal (range 0~1), and is related to the heating power of the ceramic roller surface. (Unit: W) shows a linear relationship. The physical meaning of each parameter is clear: K_p (proportional gain, unit: 1 / ℃) reflects the response amplitude of the instantaneous temperature deviation, and Ki (integral gain, unit: ...) shows a linear relationship. The differential gain (K_d, in s / ℃) is used to eliminate steady-state residual deviation, and the differential gain (K_d) is used to suppress temperature overshoot. After multiplication, all three dimensions are normalized to a dimensionless control signal, conforming to the physical dimension matching rule. The sampling period of the temperature sensor is set to ≤100ms to ensure real-time thermal inertia compensation. This parameter is selected based on the measured value of the thermal time constant of the ceramic roller (approximately 3.5s), determined according to control theory that the sampling period should be less than 1 / 30 of the thermal time constant.

[0028] The core difference between the recyclable primer coating of this invention and ordinary primer coatings in the prior art lies in the fact that: existing primer coatings usually aim for permanent adhesion, while the primer coating of this invention is modified with pH-sensitive monomers. Under normal use conditions (pH≈7), it has stable adhesion and weather resistance, with an adhesion strength (cross-cut test) ≤1 grade; however, under specific alkaline conditions (pH9.0~11.0), the pH-sensitive monomer (N,N-dimethylaminoethyl methacrylate) in the primer coating undergoes a hydrolysis reaction, causing the cross-linked network to break, thereby achieving precise separation of the ink layer from the substrate. This "controlled desorption" technical concept is the first of its kind proposed in the field of curved surface printed containers.

[0029] Compared with the prior art, the present invention has the following beneficial effects: First, multiple processes are completed in one go, significantly improving production efficiency. This invention integrates multiple processes such as base coating, anti-counterfeiting printing, variable code inkjet printing, hot stamping, high-definition direct printing, and varnishing onto a single machine. Products can complete all decoration processes in one go, eliminating the need for transfer between multiple machines, greatly shortening the production cycle, reducing product loss and energy consumption, while also having a small footprint and a high degree of automation.

[0030] Secondly, high-precision surface overprinting ensures high-definition printing quality. This invention employs a CNC four-axis linkage work platform and a full servo closed-loop overprinting control system, achieving precise positioning and motion trajectory control of the print head on complex curved surfaces. Compared to existing open-loop or semi-closed-loop four-axis linkage solutions, the closed-loop control method of "independent visual inspection for each product + feedforward compensation" significantly improves overprinting accuracy, especially suitable for multi-color overprinting and multi-layer overlay printing on irregular curved surfaces such as elliptical bottles, square and round bottles, and conical bottles, resulting in a substantial increase in yield.

[0031] Third, it is environmentally friendly and recyclable, achieving green manufacturing. This invention uses water-based inks and plant-based inks, supplemented with recyclable primer materials and special deinking agents. In the packaging product recycling process, after soaking in the agent, the ink and substrate can be quickly and completely separated under centrifugal separation conditions, achieving effective recycling and regeneration of materials. This technical solution fundamentally solves the industry problem of the difficulty in recycling and reusing printed curved packaging containers.

[0032] Fourth, it uses clean energy curing, which is energy-saving and environmentally friendly. This invention uses an LED UV curing device to replace the traditional high-pressure mercury lamp, which has the advantages of low energy consumption, low heat generation, instant use, and long service life. It improves the working environment of the production workshop while reducing production energy consumption.

[0033] Fifth, modular design allows for flexible adaptation to diverse production needs. The functional modules of this invention can be flexibly configured and quickly replaced according to actual production requirements. The same equipment can be used for order production of different products and different process combinations, significantly improving equipment utilization and flexible production capabilities. Attached Figure Description

[0034] Figure 1 This is a block diagram of the overall system structure of the present invention; Figure 2 This is a schematic diagram of the CNC four-axis linkage work platform structure of the present invention; Figure 3 This is a schematic diagram of the ceramic roller structure of the temperature control module of the present invention; Figure 4 This is a flowchart of the full servo closed-loop overlay control of the present invention; Figure 5 This is a flow chart of the recyclable base coating deinking and recycling process of the present invention; Figure 6 This is a schematic diagram of a specific embodiment of the system of the present invention; Figure 7 This is a schematic diagram of the curved surface-specific fixture structure of the system of the present invention; Figure 8 This is a hardware architecture diagram of the full servo closed-loop overlay control system of the present invention. Figure 9 This is a schematic diagram showing the integration of the temperature control module and the ink path system of the present invention. Detailed Implementation

[0035] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0036] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0037] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0038] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0039] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0040] It should be noted that when an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0041] Please refer to the following: Figures 1 to 9 The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. Example 1: Overall System Structure See Figure 1 and Figure 6This embodiment provides a curved high-definition CNC composite printing system, which includes multiple functional modules arranged sequentially along the product conveying path, a CNC four-axis linkage work platform, and an electrical control system.

[0042] Specifically, Figure 6 This is a schematic diagram of a specific embodiment of the system of the present invention. In this embodiment, the curved high-definition CNC composite printing system has a ring-shaped layout. Along the product conveying direction, the following modules are sequentially installed on the frame: feeding module A, surface treatment module B, primer coating module C, special process module D, high-definition direct printing module E, LED UV curing module F, varnishing module G, and unloading module H. The modules are detachably connected via standardized mechanical and electrical interfaces to form a complete automated printing production line. A protective cover (not shown) can be installed above the frame. A CNC numerical control operation panel (not shown) can be installed above the high-definition direct printing module E, allowing operators to set process parameters and select module configurations via a touchscreen.

[0043] Specifically, the multiple functional modules include: Module A, feeding module, Module B, surface treatment module, Module C, primer coating module, Module D, special process module, Module E, high-definition direct printing module, Module F, LED UV curing module, Module G, varnishing module, and Module H, discharging module. These modules are connected sequentially to form a complete automated printing production line.

[0044] The feeding module (Module A) includes a feeding conveyor belt and a product sorting mechanism, used to feed the curved packaging containers to be printed one by one into the printing system in an orderly manner. The feeding module can be directly connected to the upstream production container equipment to realize integrated operation from container production to high-definition printing; or it can be set up independently in a dedicated printing workshop as the feeding end of an offline printing system.

[0045] The surface treatment module (Module B) includes an electrostatic dust removal device and a corona treatment device. The electrostatic dust removal device removes dust particles from the product surface through high-voltage electrostatic action, ensuring a clean printing surface; the corona treatment device increases surface tension and improves the wettability and adhesion of ink to the substrate by applying corona discharge treatment to the product surface.

[0046] The primer coating process module (Module C) includes a primer coating application device and a primer recycling device. The primer coating application device is used to uniformly coat the product surface with an environmentally friendly and recyclable primer coating layer. The primer coating layer has a dual function: on the one hand, it acts as an adhesion promoting layer for ink printing, improving the bonding strength between subsequent printed layers and the substrate; on the other hand, it acts as a deinkable sacrificial layer, achieving effective separation of ink and substrate during the packaging and recycling process.

[0047] (a) Experimental verification data of recyclable primer coating The recyclable base coating is composed of a water-based peelable resin system, and the applicant has verified its technical feasibility through the following experiments: (1) Primer formulation range: Waterborne polyurethane acrylate copolymer emulsion (solid content 35%~45%) as the main resin, supplemented with 5%~10% pH-sensitive monomer (N,N-dimethylaminoethyl methacrylate), 0.5%~2% photoinitiator (2-hydroxy-2-methyl-1-phenylpropanone), and the remainder deionized water. This formulation, after UV curing ( The base coating forms a cross-linked network structure, with a pencil hardness ≥ HB and adhesion (cross-cut test) ≤ grade 1. After UV curing, the cross-linking density of the base coating is ≥ .

[0048] (2) Deinking performance test data: The above-mentioned base coating was applied to a PET substrate (50 μm thick), and then CMYK four-color ink layers were printed. After curing, deinking tests were conducted. The substrate was immersed in a sodium carbonate-sodium bicarbonate buffer solution at pH 10.0 at 45°C for 45 minutes. After centrifugation at 2500 r / min for 10 minutes, microscopic observation and infrared spectroscopy analysis were performed. The ink residue area on the substrate surface was ≤2%, and the deinking recovery rate, calculated from multiple experiments, was 96.2%~97.8% (n=30). The control group, without the base coating of this invention, had an ink residue area ≥85% under the same conditions, and effective deinking could not be achieved.

[0049] (3) Weather resistance verification: After the sample with the base coating of the present invention was coated and printed, the adhesion remained ≤1 level and the color difference value ΔE≤2 after 168 hours under the conditions of 40℃ and 85% humidity, proving that the stability of the base coating under normal use conditions meets the industrial requirements.

[0050] The primer recycling device includes a primer recycling tank, a filter, and a circulation pump, which is used to recycle excess primer liquid during the coating process, realize the recycling of primer materials, and reduce material waste.

[0051] The special process module (Module D) includes an anti-counterfeiting printing unit, a variable code inkjet printing unit, and a hot stamping unit. Some or all of these units can be selected based on product requirements. The anti-counterfeiting printing unit is used to print anti-counterfeiting patterns or microtext on the product surface; the variable code inkjet printing unit is used to print variable QR codes, barcodes, or production traceability codes; and the hot stamping unit is used to implement the hot stamping process, enhancing the product's decorative appeal and anti-counterfeiting performance.

[0052] See Figure 2 The high-definition direct printing module (E module) includes a CNC four-axis linkage work platform and a full servo closed-loop overprint control system.

[0053] The CNC four-axis linkage work platform includes an X-axis linear motion unit, a Y-axis linear motion unit, a Z-axis linear motion unit, and a C-axis rotary motion unit. The X, Y, and Z-axis linear motion units are driven by high-precision ball screws and servo motors, achieving a positioning accuracy of ±0.01mm. The C-axis rotary motion unit uses a direct-drive torque motor, which can drive the product fixture to rotate continuously or index and position around the product axis.

[0054] The work platform is equipped with several workstations (e.g., 12 workstations, but not limited to this; in actual industrial production, it can be flexibly expanded to 6, 8, 12, 16 or more workstations according to the user's production capacity plan or changes in product diameter, height and other dimensions to achieve the best production cycle matching), and each workstation is equipped with a special curved surface fixture that can be quickly replaced.

[0055] The CNC four-axis linkage work platform's CNC system incorporates a surface interpolation algorithm, which automatically generates the print head's motion trajectory based on the product's three-dimensional surface model. During printing, it achieves synchronous linkage of the X, Y, and Z axes with the C axis (i.e., four-axis linkage interpolation). This technical feature allows the print head to maintain constant printing pressure and a constant printing linear velocity relative to the product surface, thus achieving uniform and high-definition printing on irregularly shaped surfaces. For example, when printing the curved surface of an elliptical bottle, the CNC system adjusts the C-axis rotational angular velocity in real time according to the curvature changes of the elliptical cross-section, ensuring that the print head does not experience uneven ink distribution due to sudden changes in linear velocity in areas of high curvature. When printing the inclined surface of a conical bottle, the CNC system synchronously adjusts the Z-axis height and X-axis position, ensuring that the print head is always perpendicular to the product surface during printing.

[0056] The C-axis rotational motion of this invention, combined with the X, Y, and Z-axis linear motion, constitutes a complete four-axis linkage system capable of accurately fitting the spatial trajectories of common irregular curved surfaces such as cylinders, ellipses, and cones. See also... Figure 3 The high-definition direct printing module (E module) also includes a temperature control module, which includes a quantitative ink cartridge and a high-precision ceramic roller.

[0057] The quantitative ink cartridge is used to contain high-definition water-based ink and can precisely control the amount of ink supplied per unit time. The high-definition water-based ink adopts the technical solution disclosed in the inventor's Chinese invention patent CN109021688B, and has high color concentration, high dispersion stability and excellent printability.

[0058] The high-precision ceramic roller is positioned between the ink outlet of the quantitative ink cartridge and the print head, used to uniformly transfer ink to the print head. The roller shaft is hollow, with its inner core fully covered by a rare-earth thick film layer. A conductive ink integrated circuit heating chip (such as the conductive ink integrated circuit technology disclosed in the inventor's patent application CN108707370B) is installed on this rare-earth thick film layer via screen printing. The heating chip is connected to a temperature sensor and a PID temperature controller, forming a closed-loop temperature control circuit. This allows for precise control of the ceramic roller's surface temperature within a preset range (e.g., a set temperature of 25~60℃ with a control accuracy of ±0.5℃), thereby ensuring constant ink viscosity during the transfer process and guaranteeing the dimensional stability and color consistency of the printed pattern.

[0059] In the PID closed-loop control algorithm of the temperature control module, the temperature deviation e(t) has the dimension of °C, and the control output u(t) is a dimensionless PWM duty cycle signal (with a value range normalized to 0~1), and the heating power... In this context, P is measured in W, and P_max is the maximum power of the heater (in W), which is related to e(t) through PID coefficients. The dimensions of each coefficient are matched as follows: the proportional gain K_p is in 1 / ℃, and the integral gain Ki is in ℃. The differential gain K_d is expressed in s / ℃. The physical basis for the above normalization is that the duty cycle of the PWM drive signal is linearly proportional to the heating power (semiconductor switching devices operate in the linear amplification region), requiring no additional nonlinear mapping; the measured signal from the temperature sensor is converted into a digital quantity after sampling by a 24-bit ADC, and the sampled value is linearly mapped to the corresponding temperature value. The sampling period τ_s ≤ 100ms is selected based on the following: the measured value of the ceramic roller thermal time constant τ_th is 3.5s. According to the control theory requirement that the sampling frequency should be at least 10 times the system cutoff frequency, τ_s ≤ τ_th / 30 can ensure a system stability margin PM ≥ 45°. All the above formulas and parameters are calculated in real time in an industrial computer and output to the actuator. The applicant has verified the effectiveness of the above parameter selection through prototype testing.

[0060] See Figure 4 The fully servo closed-loop overprinting control system includes: a visual positioning unit, an overprinting deviation detection unit, and a deviation compensation control unit.

[0061] The visual positioning unit includes a high-resolution industrial camera and a light source system positioned upstream of each printing unit. When the product is transported to the printing station with the fixture, the visual positioning unit performs real-time image acquisition and coordinate extraction of the positioning marks (such as positioning crosshairs and product feature points) on the product, and calculates the actual spatial position of the product through image processing algorithms.

[0062] The overprinting deviation detection unit compares the actual product position data obtained by the visual positioning unit with the system's standard position data, and calculates the position deviation values ​​(ΔX, ΔY, ΔZ, ΔC) in the four directions of X, Y, Z, and C. Among them, ΔX, ΔY, and ΔZ are the linear deviations, and ΔC is the rotational deviation (angular error).

[0063] The deviation compensation control unit, based on the detected deviation value, corrects the print head's motion trajectory and the product's rotation parameters in real time within the CNC four-axis linkage motion control system. This ensures that the actual position of the printed pattern on the product surface matches the preset design position, achieving high-precision registration. The deviation compensation control unit independently detects and compensates for registration deviations for each product, unlike existing open-loop or semi-closed-loop registration methods based on mechanical adjustments. When the deviation exceeds a preset threshold, the deviation compensation control unit automatically marks the product as defective or triggers an alarm.

[0064] See Figure 1 The LED UV curing module (F module) includes multiple LED UV lamp bead arrays and a cooling system. The main emission wavelength of the LED UV lamp beads is 365~395nm, and the irradiance per unit area is not less than... This system enables UV-curable inks printed on curved product surfaces to fully cure within 1-2 seconds, achieving instant drying. The cooling system includes water-cooling or air-cooling devices to promptly dissipate heat from the LED UV lamp beads, ensuring that the lamp beads' operating temperature remains within a safe range.

[0065] The varnishing module (Module G) includes a varnish coating device and a varnish recovery device. The varnish coating device applies water-based or UV-cured varnish to the printed surface of the product, forming a protective layer of uniform thickness. This varnish protective layer is wear-resistant, scratch-resistant, and UV-resistant, and can achieve matte, glossy, or special tactile effects according to customer needs. The varnish recovery device recovers excess varnish from the coating process, enabling recycling.

[0066] The discharge module (H module) includes a product collection device and a product inspection device. The product inspection device performs online inspection of the printed quality of the finished product through optical or visual inspection. Qualified products enter the collection device, while unqualified products are rejected and sent to the waste bin.

[0067] The electrical control system adopts an industrial Ethernet bus architecture, using an industrial computer (based on x86 architecture) and a supercomputing board (high-throughput data processor) in conjunction with a numerical control (CNC) system to centrally control and coordinate the various functional modules. The industrial computer, acting as the host computer, is equipped with a visual human-machine interface (HMI) responsible for human-machine interaction, process parameter setting, module configuration management, and production data statistics. The supercomputing board, as a high-speed motion coprocessor, is responsible for high-frequency data acquisition and real-time motion control interpolation calculations, ensuring millisecond-level instantaneous response even in multi-axis linkage and high-frequency overprint compensation scenarios. Operators can conveniently set process parameters, select module configurations, and monitor equipment via a touchscreen.

[0068] Example 2: Printing Method This embodiment provides a method for printing curved containers using the above-mentioned high-definition CNC composite printing system for curved surfaces, including the following steps: Step S1: Product Feeding. The curved packaging containers to be printed are fed into the printing system one by one in an orderly manner through the conveyor belt and sorting mechanism of the feeding module.

[0069] Step S2: Surface Treatment. After the product enters the surface treatment module, surface dust is first removed by an electrostatic dust removal device, and then the product surface is subjected to corona discharge treatment by a corona treatment device to improve the surface wetting tension. The surface wetting tension of the treated product is not less than 38mN / m, ensuring that the ink has good wetting and spreading properties.

[0070] Step S3: Primer Coating. The product enters the primer coating module, where the primer coating device evenly coats the product surface with an environmentally friendly and recyclable primer coating. The thickness of the primer coating is controlled between 5 and 15 μm. After coating, the product can undergo preliminary drying in the primer drying area.

[0071] Step S4: Special Processing. The product enters the special processing module, where anti-counterfeiting printing, variable code printing, and / or hot stamping are selected according to order requirements. After special processing, the product surface is covered with anti-counterfeiting patterns, variable traceability codes, or hot stamping decorations.

[0072] Step S5: High-Definition Direct Printing. The product enters the high-definition direct printing module. The system calls the product's 3D surface model data, and the CNC four-axis linkage system generates the motion trajectory program for the printing head. The product is fixed by a fixture at one of several stations (e.g., 12 stations, but not limited to this). The vision positioning unit collects the actual position of the product, the registration deviation detection unit calculates the positional deviation, and the deviation compensation control unit makes real-time corrections. After precise alignment is achieved, the printing head moves relative to the product surface under four-axis linkage control, printing high-definition water-based ink onto the base coating layer of the product surface according to the design pattern. The printing process can be completed in one go or multi-layer overlay printing (such as multi-color overlay printing). During the printing process, the temperature control module maintains the surface temperature of the ceramic roller within a preset range to ensure stable ink viscosity and transfer volume.

[0073] Step S6: LED UV Curing. Immediately after high-definition printing, the product enters the LED UV curing module. Multiple LED UV lamp arrays irradiate the printed pattern, causing the photoinitiator in the ink to undergo a cross-linking reaction, and the ink is completely cured within 1-2 seconds.

[0074] Step S7: Varnish Coating. The cured product enters the varnish coating module, where the varnish coating device applies a water-based varnish or UV-cured varnish to the printed surface of the product as a protective layer. The coating amount is controlled at... If UV-curable varnish is used, it can be cured again using an LED UV curing device.

[0075] Step S8: Unloading and Inspection. Products that have completed all processes enter the unloading module, where online quality inspection is performed using optical or visual methods. Qualified products are collected and stored, while unqualified products are automatically rejected.

[0076] See Figure 5 The printing system of the present invention also includes a base coating recycling method for recycling packaging materials of printed products. The recycling method specifically includes: The printed products to be recycled are crushed into flakes or granules. The crushed material is put into a special auxiliary agent tank containing an environmentally friendly liquid auxiliary agent with a pH range of 9.0 to 11.0. The material is soaked at a temperature of 40 to 50°C for 30 to 60 minutes to cause the recyclable base coating to swell and peel off at the interface. The soaked material is processed by a high-speed centrifuge at a speed of 1500~3000 r / min for 5~15 minutes to achieve complete separation of the ink layer from the substrate material; The separated substrate materials are collected, cleaned, and dried before being used as recycled raw materials. Collect the separated ink residue and deinking aid for environmentally friendly treatment or resource recycling.

[0077] The feasibility of the aforementioned base coating recovery method has been verified by the applicant through the following experimental data: (1) Correspondence between deinking rate and soaking time (fixed pH=10.0, temperature 45℃): the deinking rate was 62.3% after soaking for 15 minutes; 91.5% after soaking for 30 minutes; 96.8% after soaking for 45 minutes; and 97.2% after soaking for 60 minutes. The results show that a soaking time of 30~60 minutes can achieve a satisfactory deinking effect (≥90%).

[0078] (2) Correspondence between deinking rate and centrifugal speed (fixed pH=10.0, temperature 45℃, soaking time 45 minutes): The deinking rate was 84.6% at 1000 r / min; 93.2% at 1500 r / min; 96.5% at 2000 r / min; and 97.8% at 3000 r / min. When the speed was further increased to 4000 r / min, the deinking rate only increased to 98.1%, but the substrate breakage rate increased from 0.3% to 2.7%. Considering all factors, 1500~3000 r / min is the optimal speed range.

[0079] (3) Substrate recycling rate: The intrinsic viscosity (IV value) of the PET substrate after the above recycling treatment is 95.2%~97.8% of the raw material, and the tensile strength retention rate is 94.5%~96.9%. After three recycling cycles, the IV value is still maintained at more than 91% of the initial value, which proves that the recycling method can still ensure the effective recycling of the substrate in multiple cycles.

[0080] Through the above-described recycling method, the printing system and method of the present invention realize the recycling of materials after printing on curved packaging containers, solving the technical problem that ink and substrate are difficult to separate and cannot be effectively recycled in traditional labeling and direct printing processes.

[0081] Performance indicators: Using the curved surface high-definition CNC composite printing system and method of this invention, a batch printing test was conducted on a round bottle with a diameter of 60mm and a height of 200mm as an example product, and the following technical indicators were obtained:

[0082] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0083] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A high-definition CNC composite printing system for curved surfaces, characterized in that, include: The CNC four-axis linkage work platform supports linear motion on the X, Y, and Z axes and rotary linkage on the C axis, and is used to drive the printing head to perform interpolation motion on the surface of irregular curved products. The full servo closed-loop overprinting control system includes a vision positioning unit, an overprinting deviation detection unit, and a deviation compensation control unit. The image acquisition frequency of the vision positioning unit is ≥50fps. The deviation compensation control unit superimposes the detected deviation values ​​in the X, Y, Z, and C directions into the CNC four-axis linkage motion control command through feedforward compensation to achieve dynamic real-time correction and an overprinting accuracy of ≤±0.05mm. The temperature control module is used to adjust the temperature of the ink transfer medium during the printing process to ensure that the ink viscosity remains constant. Multiple functional modules are arranged sequentially along the product conveying path. These modules include a feeding module, a surface treatment module, a primer coating module, a special process module, a high-definition direct printing module, an LED UV curing module, a varnishing module, and a discharge module. The CNC four-axis linkage work platform serves as the actuator for the high-definition direct printing module. At least some of the functional modules are detachably mounted on the system frame, and the modules are connected to each other through standardized mechanical and electrical interfaces.

2. The curved surface high-definition CNC composite printing system according to claim 1, characterized in that, The CNC four-axis linkage work platform has several workstations, each equipped with a special fixture for curved surfaces. The fixture is used to fix the product and ensure that the product's rotation axis coincides with the axis of the C-axis rotation unit. The CNC system of the CNC four-axis linkage work platform has a built-in curved surface interpolation algorithm, which can automatically generate the motion trajectory of the printing head based on the three-dimensional curved surface model of the product. The number of the several workstations is 6, 8, 12, 16, or other numbers expanded according to production capacity requirements.

3. The curved surface high-definition CNC composite printing system according to claim 1, characterized in that, In the full servo closed-loop overprinting control system, the visual positioning unit is used to acquire real-time images of positioning marks on the product and extract actual position data; the overprinting deviation detection unit is used to calculate the X, Y, Z, and C direction deviation values ​​between the actual position and the standard position; the response time of the deviation compensation control unit is ≤10ms.

4. The curved surface high-definition CNC composite printing system according to claim 1, characterized in that, The temperature control module includes a quantitative ink cartridge and a high-precision ceramic roller. The roller shaft of the ceramic roller has a hollow structure, and the entire surface of the inner shaft core is covered with a rare earth thick film layer. A conductive ink integrated circuit electrothermal chip is disposed on the rare earth thick film layer. The electrothermal chip is connected to a temperature sensor and a PID temperature controller to form a closed-loop temperature control circuit, which can control the surface temperature of the ceramic roller within a preset range. In the control algorithm of the closed-loop temperature control loop, the temperature deviation e(t) = T_set - T_actual, with the dimension of °C; the control output u(t) is a dimensionless PWM duty cycle signal, with the value normalized to the range of 0~1, and has a linear relationship with the heating power P = u(t)·P_max, where P_max is the maximum power of the heater, with the dimension of W; The dimension of the proportional gain K_p is 1 / ℃, and the dimension of the integral gain Ki is... The dimension of the differential gain K_d is s / ℃; the sampling period τ_s ≤ 100ms; The PID temperature controller calculates the PWM duty cycle signal u(t) based on the temperature deviation e(t), and controls the heating power in the following segmented manner: when |e(t)|≥5℃, u(t)=1; when |e(t)|<0.5℃, .

5. The curved surface high-definition CNC composite printing system according to claim 1, characterized in that, The primer coating process module includes a primer coating device and a primer recycling device, used to coat the product surface with an environmentally friendly and recyclable primer coating. The recyclable primer coating is composed of a water-based peelable resin system, which is based on a water-based polyurethane acrylate copolymer emulsion and contains the pH-sensitive monomer N,N-dimethylaminoethyl methacrylate. After soaking in a special additive at pH 9.0~11.0 for 30~60 minutes, combined with centrifugation, the ink layer can be completely separated from the substrate material, with an ink recovery rate of ≥95%. The deinking recovery rate of ≥95% was verified by the following experimental conditions: pH=10.0, temperature 45℃, soaking time 45 minutes, centrifugation speed 1500~3000r / min, centrifugation time 10 minutes, which was obtained by statistical analysis of 30 repeated experiments, and the intrinsic viscosity retention rate of the substrate was ≥95%.

6. The curved surface high-definition CNC composite printing system according to claim 1, characterized in that, The LED UV curing module includes multiple LED UV lamp bead arrays and a cooling system. The main emission wavelength of the LED UV lamp beads is 365~395nm, and the irradiation power per unit area is ≥8W / cm², which can completely cure the printing ink within 1~2 seconds.

7. The curved surface high-definition CNC composite printing system according to claim 1, characterized in that, The surface treatment module includes an electrostatic dust removal device and a corona treatment device, used to remove dust from the product surface and increase the surface wetting tension to ≥38mN / m.

8. A method for high-definition CNC composite printing of curved surfaces using the system described in any one of claims 1 to 7, characterized in that, Includes the following steps: S1: Feeding, which sends the curved packaging container to be printed into the printing system; S2: Surface treatment, including electrostatic dust removal and corona treatment; S3: Primer coating, applying a recyclable primer coating to the product surface; S4: Special process treatment, including anti-counterfeiting printing, variable code inkjet printing and / or hot stamping; S5: High-definition direct printing, through a CNC four-axis linkage and full servo closed-loop overprint control system, high-resolution pattern printing on curved products; S6: LED UV curing for rapid curing of printed patterns; S7: Apply varnish and coat a protective layer; S8: Material output and inspection, outputting finished products and conducting online inspection.

9. The method for high-definition CNC composite printing of curved surfaces according to claim 8, characterized in that, In step S5, the CNC four-axis linkage work platform automatically generates the printing head motion trajectory based on the product's three-dimensional curved surface model, realizing four-axis interpolation linkage of X, Y, Z and C axes, ensuring that the printing head always maintains a constant printing pressure and linear speed relative to the product surface.

10. The method for high-definition CNC composite printing of curved surfaces according to claim 8, characterized in that, It also includes a base coating recycling step: after the printed products to be recycled are crushed, they are soaked in an environmentally friendly liquid additive with pH 9.0~11.0 for 30~60 minutes, and then processed by a centrifuge with a speed of 1500~3000r / min for 5~15 minutes to separate the ink layer from the substrate and obtain a renewable substrate material. The environmentally friendly liquid additive is a sodium carbonate-sodium bicarbonate buffer solution with a pH of 9.0~11.0, and contains 0.5%~2% nonionic surfactant; the soaking is carried out at a temperature of 40~50℃; after centrifugation, the separated substrate material is further rinsed with clean water and dried with hot air at 80~100℃.

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