Airflow management system for inkjet printers

Abstract

Satellite droplets may accumulate in undesirable locations on the substrate or on the nozzle plate surface of the print head. [Solution] A single vacuum source is used for multiple high-flow subsystems within an inkjet printer to control the dispersion of satellite droplets during ink ejection, ensuring that the substrate remains sufficiently flat during the printing process. This reduces costs and layout requirements, simplifies the control structure, and allows for the integration of a centralized liquid removal system with a single vacuum source. Consequently, the print quality, robustness, and versatility of the inkjet printer are improved.

Description

Technical Field

[0001] Various embodiments disclosed herein relate to an air flow management system in an inkjet printer.

Background Art

[0002] Inkjet printing is a non-contact process that ejects inkjet droplets from a print head. These droplets pass through a tiny gap between the print head and the printing medium and deposit on the receiving printing medium to form a desired image. There are various methods for droplet ejection. For example, a piezo print head generates droplet ejection by generating a pressure wave due to the deformation of a piezoelectric crystal. A thermal print head generates droplet ejection by locally evaporating a small amount of ink and releasing the liquid ink by that evaporation.

[0003] During the droplet ejection process, small secondary droplets may be generated. These are usually called satellite droplets. The formation of these droplets is related to the complex interaction between inertial forces and surface tension immediately after droplet ejection. Since these droplets are very small and are ejected at a low speed, the probability of depositing at the target position is extremely low. As a result, the droplets may deposit at an undesirable position on the printing medium or on the nozzle plate surface of the print head. As a result, the print quality and the robustness of the printer are degraded because additional cleaning procedures are required.

[0004] One common solution to this problem, which has been introduced in industrial printers, is to integrate a vacuum system near the print head. This vacuum system generates a gentle air flow in the gap between the print head and the printing medium, removes small satellite droplets present in this area, and prevents these droplets from depositing at undesirable positions. Such vacuum generation is usually performed using a blower or a compressed air-based vacuum system. Further, a liquid removal element may be provided to prevent the removed liquid from entering the vacuum generation system.

Summary of the Invention

[0005] Embodiments of the present invention control the dispersion of satellite droplets during ink ejection in printing by using a single vacuum source for multiple high-flow-rate subsystems within an inkjet printer. This reduces costs and layout requirements, simplifies the control structure, and integrates the vacuum source into a centralized liquid removal system. This improves the print quality, robustness, and versatility of the inkjet printer. [Brief explanation of the drawing]

[0006] [Figure 1] This is a front view of a single-pass printing press, showing a schematic diagram of the vacuum table and mist removal element according to an embodiment of the present invention. [Figure 2] This is a side view of a single-pass printing press, showing a schematic diagram of the vacuum table and mist removal element according to an embodiment of the present invention. [Figure 3] This is a block diagram showing the airflow path in a composite vacuum system according to an embodiment of the present invention. [Figure 4] This shows the suction element of a mist removal system equipped with a control valve according to an embodiment of the present invention. [Figure 5] An embodiment of the present invention shows a vacuum control system for maintaining a constant flow rate in a mist removal system while the downstream vacuum level is variable. [Figure 6] This is a block diagram of a computer system that can be used to implement some features of an embodiment. [Modes for carrying out the invention]

[0007] Conventional industrial printing presses may require multiple airflow sources to meet different requirements. These include airflow sources for vacuum table conveyor systems, mist removal systems, printhead cleaning systems, substrate cleaning systems, and substrate cooling systems. Typically, a separate airflow source is used for each of these subsystems, resulting in increased energy consumption, maintenance requirements, layout / packaging requirements, initial costs, and operating costs.

[0008] Embodiments of the present invention are applicable to a digital inkjet printer equipped with a vacuum conveyor system for transporting the workpiece and a vacuum system for removing satellite droplets generated by the printing process. These two subsystems have several things in common. Because it has relatively high conductance, it can generate relatively high flow even at low vacuum pressure levels. The mist removal system is positioned directly above the substrate, while the vacuum table system is positioned directly below the substrate, thus sharing similar areas within the printing press. Both methods generate multiple flows of ink droplets dispersed within a mainstream airflow.

[0009] Figure 1 is a front view of a single-pass printing press, illustrating a schematic diagram of a vacuum table and mist removal element according to an embodiment of the present invention. In Figure 1, a series of printing bars 10 are adjacent to a corresponding suction element 12 of the mist removal system. The workpiece 14 is transported by a vacuum table conveyor system 16, passing through the printing bars and the mist removal system suction element. Both the suction element and the vacuum table conveyor system can utilize a vacuum source during operation. The suction element of the mist removal system separates satellite droplets from the workpiece as ink is ejected from the printing bars and prevents these droplets from falling to undesirable locations.

[0010] The mist removal system may also use a separate blower or other vacuum generating mechanism to prevent satellite droplets from falling onto the surface of the printed material.

[0011] Figure 2 is a side view of a single-pass printing press and is a schematic diagram of the vacuum table and mist removal element according to an embodiment of the present invention. In Figure 2, the printing bar 10 is shown relative to the suction element 12 of the mist removal system. The connector tube 20 provides a vacuum source to the suction element of the mist removal system.

[0012] As shown in Figure 2, the workpiece 14 is transported by the vacuum table transport system 16, passing through the print bar and the suction element of the mist removal system. In the embodiment of the present invention, the vacuum source 24 to which the connector tube is connected is shared with the vacuum source of the vacuum table transport system.

[0013] In embodiments of the present invention, a single vacuum table source is used for both the mist removal system and the vacuum table transport system. This reduces costs and layout requirements, simplifies the control structure, and integrates it into a single centralized liquid removal system 22. In embodiments of the present invention, the centralized liquid removal system consists of a combination of coagulation elements, separation elements (e.g., cyclones), and filtration elements for removing ink from the airflow. These are the elements that constitute the liquid removal system for separating the liquid from the main airflow. This system prevents damage to the vacuum source by preventing ink from adhering to the vacuum source.

[0014] Figure 3 is a block diagram showing the airflow path in a combined vacuum system according to an embodiment of the present invention. In Figure 3, the airflow is supplied from the atmosphere 30 surrounding the printing press. The vacuum table system 31 and the mist removal system 32 receive operating vacuum from a common vacuum source 35. Examples of vacuum sources include centrifugal fans, axial fans, and venturi vacuum ejectors. In embodiments of the present invention, the mist removal system includes a steady-state vacuum actuator 33 that ensures the vacuum level remains constant regardless of the vacuum level of the vacuum source. A liquid removal system 34 positioned before the vacuum source sucks out any moisture from the system that may fall onto the liquid and the workpiece as they move along the surface of the vacuum table conveyor system, after being captured by the mist removal system. This system is open to the atmosphere 36. The airflow is typically discharged into the surrounding atmosphere after passing through all elements of the pneumatic system after the vacuum source.

[0015] One of the key aspects of properly operating this combined system is ensuring that the desired vacuum level is reliably maintained in each subsystem. Typically, the desired vacuum level for the vacuum table conveyor system is adjusted according to the requirements of the substrate. The more warped and stiffer the substrate, the higher the vacuum level required. On the other hand, the mist removal system requires a stable vacuum level to remove only the smallest satellite droplets without disturbing the main droplets. The desired vacuum level in each subsystem depends heavily on parameters such as the stiffness and warping of the substrate, the shape of the vacuum table conveyor and mist removal system, and the size of the droplets, but is usually in the range of 0.5 kPa to 8 kPa.

[0016] In conventional systems with only one vacuum source and no additional actuators, the increase in the vacuum level of the vacuum source necessary to ensure proper flatness of the workpiece passing through the vacuum conveyor system also increases the vacuum level of the mist removal system, making it impossible to stably control the vacuum level of the mist removal system. Embodiments of the present invention can integrate various methods for this purpose.

[0017] In the first method, the mist removal system is given sufficient conductance to achieve the desired flow with minimal vacuum power, and then a vacuum relief valve or vacuum regulator is installed at the outlet of the mist removal system to introduce the necessary air to the vacuum level of the high vacuum table.

[0018] In the second method, the vacuum level at the outlet of the mist removal system is controlled in a closed loop by changing the conductance of the valve. Under high vacuum output conditions, the valve is partially closed to prevent excessive flow rates, and under low vacuum output conditions, the valve is opened to ensure that the desired flow rate is achieved.

[0019] Figure 4 shows a suction element of a mist removal system with a control valve according to an embodiment of the present invention. In Figure 4, the suction element 40 receives a vacuum used to generate an upward airflow 42 that pulls satellite droplets ejected from the print bar away from the workpiece. The vacuum is controlled by a control valve 44, in this example, which is a butterfly valve operated to maintain the vacuum pressure at a desired level based on the vacuum pressure of the suction element detected by a pressure sensor in a pressure monitoring port 46.

[0020] FIG. 5 shows a vacuum control system for maintaining a constant flow rate in a mist removal system where the downstream vacuum level is variable according to an embodiment of the present invention. In FIG. 5, a vacuum set value 50 typically in the range of 0.5 kPa to 8 kPa is provided to the system. This vacuum set value is the desired vacuum level. This vacuum set value is adjusted to maintain an appropriate vacuum for operating the mist removal system by finding an optimal balance between satellite removal and vacuum error 52. The vacuum error is provided as an input to a controller 53 that sets a target angular position 54 of a control valve 44 (see FIG. 4). This target angular position is controlled by a valve position driver 55 such that the pressure measurement reaches the vacuum level set value. The valve position driver 55 is a general actuator. This can be, for example, an electric, pneumatic, or hydraulic type that changes the position of the valve according to a value specified by the controller. The valve angle can be measured using various devices such as an encoder, resolver, distance sensor, Hall sensor, etc. Computer Implementation

[0021] FIG. 6 is a block diagram of a computer system that can be used to implement some features of the embodiment. The computer system can be a server computer, client computer, personal computer (PC), user device, tablet PC, laptop computer, personal digital assistant (PDA), mobile phone, iPhone, iPad, Blackberry, processor, telephone, web appliance, network router, switch or bridge, console, handheld console, (handheld) game machine, music player, any portable device, mobile device, handheld device, wearable device, or any machine capable of executing a series of instructions (sequential instructions or other instructions) that specify the operations the machine should perform.

[0022] Computing system 300 may include one or more central processing units (“processors”) 305, memory 310, input / output devices 325 (e.g., keyboard and pointing device), touch devices, display devices, storage devices 320 (e.g., disk drive), and network adapters 330 (e.g., network interfaces connected to interconnect 315). Interconnect 315 is illustrated as an abstract concept representing one or more individual physical buses, point-to-point connections, or both, connected by appropriate bridges, adapters, or controllers. Thus, interconnect 315 may include, for example, a system bus, PCI (Peripheral Component Interconnect) bus or PCI-Express bus, HyperTransport or ISA (Industry Standard Architecture) bus, SCSI (Small Computer System Interface) bus, USB (Universal Serial Bus), I2C (12C) bus, or IEEE (Institute of Electrical and Electronics Engineers) standard 1394 bus (also called Firewire), etc.

[0023] Memory 310 and storage device 320 are computer-readable storage media that can store instructions implementing at least a portion of various embodiments. Further, data structures and message structures may be stored or transmitted via a data transmission medium, e.g., signals on a communication link. For example, various communication link methods such as the Internet, local area network, wide area network, or point-to-point dial-up connection are available. Thus, computer-readable media includes computer-readable storage media (e.g., non-transitory media) and computer-readable transmission media.

[0024] Instructions stored in memory 310 can be implemented as software and / or firmware to program the processor 305 to perform the operations described above. In some embodiments, such software or firmware is initially provided to the processing system 300 by downloading it from a remote system via the computing system 300 (e.g., network adapter 330).

[0025] The various embodiments described herein can be implemented, for example, by programmable circuits (e.g., one or more microprocessors) programmed with software and / or firmware, or by completely dedicated hardwired (non-programmable) circuits, or a combination of these forms. The dedicated hardwired circuits may take the form of, for example, one or more ASICs, PLDs, FPGAs, etc. The various embodiments described herein can be implemented, for example, by programmable circuits such as one or more microprocessors programmed with software and / or firmware, or by completely dedicated hardwired (non-programmable) circuits, or a combination of these forms. The dedicated hardwired circuits may take the form of, for example, one or more ASICs, PLDs, FPGAs, etc.

[0026] The language used herein has been selected primarily for readability and ease of explanation, and may not have been chosen to describe or limit the subject matter. Accordingly, the scope of the Art is intended to be limited not by this detailed description, but by the claims issued based thereon. Accordingly, the disclosure of various embodiments is intended to illustrate, not limit, the scope of the Art as described in the following claims.

Claims

1. A vacuum-driven conveyor system for transporting the workpiece through one or more print bars within the printing press during a printing sequence; and, A vacuum-operated mist removal system comprising at least one suction element for sucking satellite droplets from the substrate when ink is ejected from one or more print bars to prevent the satellite droplets from falling to undesirable locations during the printing sequence; and A common vacuum source connected to both the conveyor system and the mist removal system, A device equipped with the following features.

2. The mist removal system, A combination of coagulation elements, separation elements, and filtration elements, An element configured to prevent ink from reaching the vacuum source. The apparatus according to claim 1, further comprising the above.

4. The mist removal system, Actuator for ensuring a constant vacuum level, The apparatus according to claim 1, further comprising the above.

5. A liquid removal system positioned in front of the vacuum source, which sucks up the liquid captured by the mist removal system. The apparatus according to claim 1, further comprising the above.

6. The liquid removal system is positioned in front of the vacuum source and captures moisture that falls onto the conveyor system as the substrate moves along the surface of the conveyor system. The apparatus according to claim 4.

7. The mist removal system is open to the atmosphere after the vacuum source. The apparatus according to claim 1.

8. A vacuum control system configured to maintain a constant flow rate in the mist removal system regardless of the vacuum level in the conveyor system. The apparatus according to claim 1, further comprising the above.

9. An element for changing the vacuum level of the conveyor system according to the requirements of the substrate, wherein a higher vacuum level is applied to warped or hard substrates, and a stable vacuum level is maintained so that the mist removal system can remove satellite droplets without disturbing the print droplets. The apparatus according to claim 8, further comprising the above.

10. The vacuum liquid removal system has high conductance to provide the desired flow with the minimum vacuum output at the vacuum source. The apparatus according to claim 8.

11. A vacuum relief valve located at the outlet of the mist removal system, configured to introduce air when a high vacuum level exists in the conveyor system, The apparatus according to claim 10, further comprising the above.

12. The vacuum control system, valves; and, A closed-loop vacuum control located at the outlet of the mist removal system, wherein the closed-loop vacuum control is configured to change the conductance of the valve. Furthermore, it is equipped with, If the vacuum level downstream is high, the valve is partially closed to prevent excessive flow rate, and If the vacuum level downstream is low, the valve is opened to achieve the desired flow rate. The apparatus according to claim 8.

13. The at least one suction element, configured to receive a vacuum from the vacuum source and generate an upward airflow that separates satellite droplets ejected from one or more print bars from the workpiece, wherein the at least one suction element further comprises a pressure monitoring port, A sensor for detecting the vacuum pressure in the pressure monitoring port, and A control valve that can be operated to maintain a predetermined vacuum pressure in the suction element in response to the vacuum pressure in the suction element detected by the sensor in the pressure monitoring port, The apparatus according to claim 1, further comprising the above.

14. A vacuum control system that establishes a vacuum setpoint to maintain a constant flow rate in the mist removal system when the downstream vacuum level fluctuates: The vacuum control system, Pressure sensor; A controller configured to receive a vacuum error as input and provide an angular position signal as output; A control valve driver configured to receive the angular position signal and generate a corresponding valve drive signal; and A control valve configured to receive the valve drive signal and to set a desired angular position value to maintain the vacuum at the vacuum set point, The apparatus according to claim 1, further comprising the above.

15. A process of transporting a workpiece by passing it through one or more printing bars inside a printing press during a printing sequence using a vacuum-driven conveyor system; and A step of using a vacuum-driven mist removal system equipped with at least one suction element to suck satellite droplets from the substrate as ink is ejected from one or more print bars, thereby preventing the satellite droplets from falling to undesirable locations during the printing sequence; and The process involves connecting a common vacuum source to both the conveyor system and the mist removal system. A method that includes [a certain feature].

16. A step of sucking up the liquid captured by the mist removal system using a liquid removal system placed in front of the vacuum source, The method according to claim 15, further comprising the above.

17. A step of placing the liquid removal system in front of the vacuum source in order to capture moisture that falls onto the conveyor system as the substrate moves along the surface of the conveyor system, The method according to claim 16, further comprising the above.

18. A process of maintaining a constant flow rate in mist removal, regardless of the vacuum level in the conveyor system, using a vacuum control system. The method according to claim 15, further comprising the above.

19. A step of changing the vacuum level of the conveyor system according to the requirements of the substrate, wherein a higher vacuum level is applied to warped or hard substrates, and a stable vacuum level is maintained so that the mist removal system removes satellite droplets without disturbing the print droplets. The method according to claim 18, further comprising the above.

20. The vacuum liquid removal system has high conductance in order to provide the desired flow with the minimum vacuum output at the vacuum source. The method according to claim 18.

21. A step of introducing air into the conveyor system when a high vacuum level is present, using a vacuum relief valve located at the outlet of the mist removal system. The method according to claim 20, further comprising the above.

22. A step of changing the conductance of a valve located at the outlet of the mist removal system using closed-loop vacuum control; The step of partially closing the valve to prevent an excessive flow rate in the presence of a high vacuum or a high vacuum downstream; and, The process of opening the valve in order to achieve a desired flow rate when the vacuum level downstream is low. The method according to claim 18, further comprising the above.

23. A step of configuring at least one suction element to receive vacuum from the vacuum source and generate an upward airflow that separates satellite droplets ejected from one or more print bars from the workpiece, wherein the suction element further comprises a pressure monitoring port; A step of detecting the vacuum pressure at the pressure monitoring port using a sensor; and A step of operating a control valve to maintain a predetermined vacuum pressure in the suction element according to the vacuum pressure in the suction element detected by the sensor at the pressure monitoring port. The method according to claim 15, further comprising the above.

24. A step of establishing a vacuum setpoint using a vacuum control system in order to maintain a constant flow rate within the mist removal system when the vacuum level downstream fluctuates, Using this vacuum control system, Using a controller, receive the vacuum error as input and provide the angular position signal as output; Using a control valve driver, receive the angular position signal and generate a corresponding valve drive signal; and Using a control valve, receive the valve drive signal and set a desired angular position to maintain the vacuum at the set vacuum value. That is, The method according to claim 15.

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