In some inkjet printers, a stationary, substrate wide print bar is used to print on paper or other print substrate moved past the print bar. Substrate wide print bars usually include multi-part flow structures with complex pathways through which ink flows from the ink supplies to the printheads on the print bar. Such pathways often necessarily include horizontal sections where it is more difficult to remove air bubbles that can impede the flow of ink.
The same part numbers are used to designate the same or similar parts throughout the figures.
Due to geometric constraints and other design criteria, it is often necessary to include horizontal sections in the conduits that carry ink to the printheads in a page wide inkjet print bar. While these ink flow conduits are intended to be completely filled with ink, air or other gas may enter the conduits, for example during fabrication (the conduits start out full of air) and printing. It is particularly difficult to purge gas from horizontal conduits.
A new fluid flow structure has been developed to help purge gas from horizontal ink flow conduits in an inkjet print bar assembly. The new structure utilizes capillary channels within a conduit to encourage gas bubbles to move out of the conduit without obstructing the flow of ink through the conduit. Although examples of the new flow structure are described with reference to ink flow paths in an inkjet print bar assembly, the new flow structure is not limited to ink flow, print bars, or inkjet printers, but may be implemented in other liquid flow paths and/or in other types of liquid handling devices. Accordingly, the examples shown in the figures and described herein illustrate but do not limit the invention, which is defined in the Claims following this Description.
As used in this document: “capillary channel” means an open channel that allows or induces capillary action; “upstream” and “downstream” refer to the desired direction of the flow of ink or other liquid; and “horizontal”, “vertical” and other terms of orientation refer to the orientation of a part for its intended use even if the part is oriented differently for other than its intended use, for example during manufacturing and shipping. A “printhead” as used in this document refers to that part of an inkjet printer or other inkjet type dispenser that expels ink or other liquid, for example as drops or streams.
Each printhead receives ink through a complex ink flow path from ink supplies 20 into and through flow regulators 16 and print bar 12. The ink flow path includes one example a new fluid flow structure 24 that conveys ink from ink supplies 20 to flow regulators 16. Flow structure 24 includes a set of four conduits 26A-26D that carry ink from ink supplies 20 toward flow regulators 16. For example, conduits 26A-26D might carry ink from corresponding cyan, magenta, yellow and black (CMYK) ink supplies 20. More or fewer conduits for more or fewer inks are possible and implementation of the new flow structure is not limited to ink flow between the ink supplies and the flow regulators but may be used in other parts of the ink flow path.
Each conduit 26A-26D includes an upstream vertical section 28, a horizontal section 30, and a downstream vertical section 32. While each conduit 26A-26D is divided into sections 28-32, each section 28-32 could itself be characterized as a discrete conduit rather than a section of a single conduit. Also, a typically short upstream vertical section 28 functions as an ink inlet 28 to horizontal conduit 30. Similarly, a typically short downstream vertical section 32 functions as an ink outlet 32 from horizontal conduit 30.
As described in detail below, each conduit 26A-26D includes multiple parallel capillary channels 34 that extend continuously from an ink reservoir at inlet 28 to ink outlet 32. In addition, horizontal conduit 30 expands in size from outlet 32 to inlet 28 to urge gas bubbles upstream toward the ink reservoir. Ink in the reservoir above horizontal conduit 30 creates a pressure head that urges capillary ink flow along channels 34 in the desired direction—from inlet 28 toward outlet 32. Capillary flow along channels 34 helps moves ink through a horizontal or even a slightly inclined conduit 30 and into the volume behind any large gas bubbles present in conduit 30. As the volume of ink grows behind a bubble, it urges the bubble upstream toward the ink reservoir, supplementing the effect of the expanding conduit 30 (which also encourages bubbles to move to the ink reservoir).
Referring to
Capillary channels 34 extend parallel to one another along the length of horizontal conduit 30 on ceiling 46 and floor 48 with a constant cross sectional area. Accordingly, due to the converging sidewalls 50, 52, ridges 54 between channels 34 are tapered from a wider part at the upstream end of horizontal conduit 30 to a narrower part at the downstream end of horizontal conduit 30. While tapered channels or other suitable configurations are possible for channels 34, constant area, parallel channels 34 are less difficult to design manufacture than tapered channels while still providing adequate flow. Tapered capillary channels, which can induce flow in the direction of taper without a pressure head, might still be desirable in some applications such as when there is no pressure head. It may be possible in some applications to include only floor channels or only ceiling channels. Sidewall channels could also be used in some applications, although difficulties making sidewall channels using plastic molding and other inexpensive manufacturing operations may limit their use. Also, as best seen in
As best seen in
One challenge configuring fluid flow structures in a printer is addressing angular deviations from the horizontal plane. Although the desired orientation of the printer during use has a nominal horizontal plane, there may be some small angular deviation from the desired orientation during actual use, for example of the printer is placed on a surface that is not perfectly horizontal. The printer may be tilted at a “bad” angle in which ink must “flow” uphill and bubbles “float” downhill or at a “good” angle in which ink flows downhill and bubbles float uphill. The pressure head of ink in reservoir 44 and the capillary forces generated along channels 34 allow ink to flow horizontally or even slightly uphill through conduit 30 and, as noted above, this flow helps move gas bubbles horizontally and even slightly downhill toward reservoir 44.
Smaller capillary channels tend to generate higher capillary forces that can push the liquid up a steeper incline, but at a lower flow rate. On the other hand, if the capillary channels are too large, the capillary forces may be insufficient to push the liquid up the incline. Accordingly, the sizing of the capillary channels will vary depending on the particular application, including the number of channels, the degree of incline and the desired flow rate. For a substrate wide inkjet printer such as printer 10 shown in
Conduit 30 need not be perfectly horizontal, even when the parts are in the intended orientation. Conduit 30 may be declined slightly to aid the flow of ink without increasing the risk of trapping gas bubbles or possibly even inclined slightly to aid the movement of gas bubbles without impeding the flow of ink. Although the tolerable slope will vary depending on the particular application, a flow structure 24 such as the shown
As noted above, the examples shown and described do not limit the invention. Other examples may be made without departing from the scope of the invention, which is defined in the following claims.
Number | Name | Date | Kind |
---|---|---|---|
4771295 | Baker et al. | Sep 1988 | A |
5969739 | Altendorf et al. | Oct 1999 | A |
6007193 | Kashimura et al. | Dec 1999 | A |
6513920 | Deshmukh et al. | Feb 2003 | B1 |
6572214 | Otis et al. | Jun 2003 | B2 |
6682186 | Smith et al. | Jan 2004 | B2 |
7399074 | Aldrich et al. | Jul 2008 | B2 |
7419253 | Olsen et al. | Sep 2008 | B2 |
7575309 | Childs et al. | Aug 2009 | B2 |
7748822 | Scardovi et al. | Jul 2010 | B2 |
8172376 | Nathan et al. | May 2012 | B2 |
20060232649 | Wu et al. | Oct 2006 | A1 |
20120154491 | Price et al. | Jun 2012 | A1 |
Number | Date | Country |
---|---|---|
19540472 | May 1996 | DE |