JP3909443B6 - Inkjet printhead module having a common ink supply - Google Patents

Description

The present invention generally relates to ink jet printers. In particular, the present invention relates to an apparatus for applying liquid ink to a series of drop-on-demand ink jet print orifices with appropriate static pressure.
As is well known, an ink jet printing apparatus utilizes a print head that ejects ink drops from one or more orifices onto a target surface. In impulse type drop-on-demand printing, the ejection of ink from the orifice is controlled by creating a pressure pulse in an ink chamber in the printhead. Referring to the prior art FIG. 1, a typical print head 2 comprises a row of offices 3, and the orifices have ink drops 4 that form the desired image on the target surface as the target surface moves relative to the print head. Individually controlled to release. The orifices are supplied with ink from individual chambers 5 in each print head in communication with the inlet 6. Ink is supplied from the reservoir 7 through the ink supply line 9 to each inlet 6 by capillary action.
It is important that a suitable static pressure, typically a small negative static pressure, be achieved at each inkjet orifice to avoid ink drooling. The static pressure in a print head is largely due to the static pressure at the print head inlet, because the capillary force in a given print head cancels out any changes in the pressure head in the print head orifice. Is a function of Thus, the static pressure at the inlet affects the pressure at the inkjet orifice immediately adjacent to the inlet. The optimum static pressure is determined by the physical properties of the ink, such as viscosity and surface tension, wettability and the substrate material used to construct the orifice.
Secondary, the optimum static pressure of the ink is a negative pressure of 1 to 3 inches of water. As can be seen in FIG. 1 and as known from hydraulic theory, the static pressure at the inlet is a function of the height (H) difference between the inlet and the ink level of the reservoir. In particular, the static pressure at each orifice is a function of the height difference between each orifice and the ink level in the reservoir.
In commercial ink jet printing applications, it would be advantageous to provide a printing device with a large print area so that a large image can be made on the target surface without having to pass the target surface through the print head many times. This is accomplished by stacking or “stitching” multiple printheads vertically. However, vertically stacked printhead structures present special challenges associated with static pressure control, and their commercial advantages have been limited so far by increasing the cost or complexity of ink storage and supply. It was done. It is not possible to supply all printheads in a stacked structure from a common reservoir, since a uniform static pressure cannot be achieved. As can be seen in FIG. 1, printheads located above the reservoir fluid level are subject to negative static pressure, while printheads located below the reservoir are subject to positive static pressure. Moreover, as shown in FIG. 2, although it is possible to provide a separate level-controlled reservoir in the printhead, the cost of such an arrangement is prohibitive. In addition, the space limitations and tight spacing between the printheads makes it physically impossible to mount the reservoir and level control device in this configuration.
Prior art dispensing devices are not readily applicable to stacked printhead structures due to the complexity and cost associated with manufacturing and maintenance. Thus, it is desirable to have an inkjet fluid dispensing device that can be easily and inexpensively configured and provides adequate and reliable control of the static pressure of ink supplied to each printhead in a stacked configuration.
According to the present invention, there is provided an apparatus for supplying ink to a composite printhead having at least two sets of orifices vertically arranged vertically,
For each of the sets of orifices, each having a liquid compartment through which liquid is circulated to the orifices, each compartment having an excess liquid flowing out of the compartment beyond its edge. Configured to maintain a level of liquid in the compartment at a desired fill height, wherein the compartments are positioned relative to each other to allow liquid to flow from the compartment to the next lower compartment. receiving the outflow of ink from compartments lowermost compartment, it has a reservoir for supplying liquid to the uppermost compartment of the compartment to further, desired fill height of each compartment, each set An apparatus is provided that defines a static height difference that is at a height with respect to the inlet to the orifice of the fluid, thereby creating a pressure acting on the liquid in the inlet .
In a preferred embodiment of the invention, several printheads each have a set of orifices for printing or marking on a substrate. Each print head is fed via a separate feed line from one of the compartments of the multi-compartment reservoir. The partitioned ink reservoir utilizes a weir device that maintains a predetermined optimum static pressure in each compartment. The supply pressure to each print head is controlled by the relative height of the fluid column in each compartment relative to the inlet height close to a set of orifices. The height of the fluid may be controlled by the height of the weir associated with that compartment or the level of fluid by such a weir.
The present invention provides significant advantages over other inkjet fluid dispensing devices. Since the weir device automatically maintains the desired level of ink in each compartment, there is no need for a separate level detector for each compartment, thereby reducing parts and cost.
The present invention will now be described by way of example with reference to the accompanying drawings.
FIG. 1 is a diagram of a prior art printhead and ink dispensing apparatus as described above.
FIG. 2 illustrates the challenges associated with an independent level controller for a stacked printhead structure.
FIG. 3 is a preferred embodiment of the present invention.
FIG. 4 is a diagram of the features of the vacuum chamber of the present invention.
Referring to FIG. 3, a fluidic device embodying the present invention has a composite printhead 12 that includes a plurality of inkjet printheads 12A-12D. The composite print head 12 is stationary and is arranged to print an image on a target surface (not shown) that moves relative to the composite print head. As a variation, the composite print head 12 may be movable relative to the target surface, or both the composite print head 12 and the target surface may be movable relative to each other.
Although shown schematically as four spaced printheads 12A-12D, the composite printhead 12 is preferably mounted integrally to distribute ink evenly as it is ejected from the printhead. It will be appreciated that any number of printheads may be used to create the desired width of the area to be printed, having two or four separate internal printheads or manifolds.
Preferably, each print head 12A-12D has a set of ejection nozzles or orifices 14, which are supplied with fluid by a common chamber or manifold 16 within each print head 12A-12D. There are twelve sets of orifices as shown, but there can be more or less, and it is within the skill of the art to select the number of orifices and the pattern of these orifices. . The manifold 16 is supplied with fluid via an associated inlet 18 and a supply line 19 to which the print heads 12A-12D are attached. Although it is desirable to have a separate printhead for each set of orifices, a single printhead may have two or more sets of orifices with associated inlets. Also, although several sets of orifices are shown in a single row, there may be multiple sets of orifices in the set or other configurations, as those skilled in the art can understand. is there.
In order to supply ink from supply line 19 to printheads 12A-12D, each printhead 12A-12D includes an associated compartment 20A-20D that uses a weir 22A-22D to maintain a constant fluid level of ink. Each weir 22 has an opening, drain or drain to allow ink flow from one compartment to the next lower compartment, or in the case of the lower compartment 20D, to return to the reservoir 24. Has other outlets. Pump 26 provides a low volume flow of ink from reservoir 24 via return line 27 to uppermost reservoir 20A. A detection device 28 is also provided to ensure that an appropriate ink holding amount is supplied to the reservoir 24 from the main storage container. In order to ensure that the proper amount of ink is supplied to the compartment, a device is provided to control the flow rate of the fluid in the return line 27. For example, bubbles or other control devices may be utilized, or the pump may be configured to pump ink at a desired constant flow rate from the supply line.
As will be appreciated, the ink level in each compartment 20 remains constant, and therefore at each printhead inlet determined by the supply line height H above the ink level in the associated compartment. The static pressure is the same for each print head. The entire set of orifices for each print head 12, preferably for each print head 12, is positioned above the ink level in the associated compartment 20 to create a negative pressure in the supply line 19, which negative pressure is In combination with the capillary force of the supply line, an appropriate pressure is created at the inlet 18 immediately adjacent to the orifice 14.
In order to reduce the vapor pressure of the gas and reduce dissolved air in the ink, a degassing device such as a membrane above the reservoir or a partial vacuum above the ink in each container is provided. Alternatively, all of the containers 20A-20D, as shown in FIG. 4, it may be in a single vacuum chamber 30. As shown, container 20 is stacked within chamber 30 and has a single port 32 for creating a low negative pressure that reduces dissolved air in the ink. As shown, containers 20 are also stacked so that outflow from adjacent containers is in the opposite direction, thereby bringing the containers closer to a vertical arrangement and conserving space. A controller 34 is provided to allow an appropriate amount of fluid to be supplied from reservoir 24 to containers 20A-20D.
Also, an adjustment mechanism may be provided to adjust the height of the print heads 12A-12D and thus the set of orifices 14 relative to the level of ink in the compartments 20A-20D. This type of adjustment mechanism is known in the art and may be configured to adjust the composite print head 12 as a unit. The adjustment mechanism may also be configured to exclusively adjust the height of the printheads 12A-12D, provided that the printheads are not joined together.
Similarly, a moving mechanism may be provided that adjusts the height of the compartments 20A-20D and thus the height of the ink in each compartment relative to the height of the printheads 12A-12D and their associated sets of orifices 14. Good. If the compartments 20 are joined together as a staggered unit, the moving mechanism may be configured to adjust the height of the entire assembly. As a modification, the moving mechanism may be configured to independently adjust the height of the compartment. This individual adjustment may be made by a moving mechanism such as the device disclosed in US patent application Ser. No. 08 / 728,866 filed Oct. 10, 1996.
It will be appreciated that one or more return lines may be used to supply each container individually rather than supplying the top container 20A. Various other devices such as valves, siphons, or the like may also be utilized to control ink ejection from each container.
Although the invention has been shown in schematic form, it is within the purview of those skilled in the art to enclose the weir with individual cartridges or as part of a single elongated container, thereby obtaining a compact ink device for an ink jet printer. is there. It is within the scope of the present invention to monitor the flow of ink supplied by the pump and the flow to each printhead so that each weir is fully maintained to ensure adequate static pressure for multiple printheads. .
Thus, there is provided an inkjet fluid dispensing apparatus that can be easily and inexpensively configured and that provides adequate and reliable control of the static pressure of ink supplied to each printhead in a stacked array.

Claims (12)

An apparatus for supplying ink to a composite printhead (12) having at least two sets of orifices (14) arranged vertically above and below,
For each of the sets of orifices (14), having liquid compartments (20A-20D) for fluid to flow through the orifices, each compartment having excess liquid from the compartments; By flowing out of the edge, the liquid level in the compartment is configured to maintain a desired fill height, the compartment (20A-D) being liquid from the compartment to the next lower compartment. A reservoir (24) positioned relative to each other for receiving the ink flow from the lowermost compartment of the ink compartment and supplying liquid to the uppermost compartment of the compartment; And the desired fill height of each compartment (20A-D) is at a certain height with respect to the inlet (18) to the respective set of orifices, thereby pressure acting on the liquid in the inlet (18) Cause static Determines the difference in height, the difference in static height defined for each compartment (20A-D) are the same, and the compartments (20A-D) is configured to contain the liquid in the same volume, it Thus, the negative pressure acting on the liquid in the inlet (18) to each set of orifices (14) is the same . The desired fill height of each compartment (20A-D) is at a lower height than the inlet (18) to its respective orifice (14) to define the upper static height difference. The apparatus according to claim 1, wherein a negative pressure acting on the liquid in (18) is generated. The desired fill height of the compartments (20A-D) is lower than the lowest orifice of each set of orifices, thereby maintaining a desired negative pressure at each orifice in the set of orifices. The apparatus according to 1 or 2. 4. A device according to any one of the preceding claims, further comprising a single supply line (27) for supplying liquid from a reservoir (24) to the uppermost compartment (20A). Each compartment (20A-D) maintains the desired fill height and directs liquid to the next lower compartment, or in the case of the lower compartment, to the reservoir (24). The device according to any one of claims 1 to 4, wherein an outflow opening (22A-D) adapted to discharge liquid from the compartment is formed. The outflow of liquid from the compartment is directed in the opposite direction to the flow of liquid from the next lower compartment, thereby allowing an upper and lower stacked arrangement of compartments (20A-D) and reservoir (24). The apparatus according to any one of claims 1 to 5. 7. A device according to any one of the preceding claims, further comprising control means configured to supply an appropriate amount of liquid from the reservoir (24) to the compartment (20A-20D). 8. A device according to any one of the preceding claims, further comprising a pump (26) for supplying liquid from the reservoir (24) to the first compartment (20A). The apparatus according to any one of claims 1 to 8, further comprising a device for generating a partial vacuum above the liquid in each compartment to reduce the vapor pressure of the gas in the compartment. The apparatus according to any one of claims 1 to 9, further comprising an adjusting mechanism for adjusting the height of the compartment (20A-D) to further control the height of the liquid in the compartment. . 11. Apparatus according to any one of the preceding claims, wherein each set of orifices (14) is formed in a respective print head of a composite print head. Each compartment (20A-D) has a weir (22A-D) that maintains the level of liquid in the compartment at the desired fill height and allows excess liquid to flow out of the compartment beyond its edges. 12. The apparatus according to any one of claims 1 to 11.

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