Patent Application
20140240388
The invention relates to the field of printing systems, and in particular, to generating flush lines for printing systems.
Businesses or other entities having a need for volume printing typically purchase a production printer. A production printer is a high-speed printer used for volume printing (e.g., one hundred pages per minute or more). Production printers are typically continuous-forms printers that print on webs of print media that are stored on large rolls.
A production printer typically includes a localized print controller that controls the overall operation of the printing system, and a marking engine (sometimes referred to as an “imaging engine” or as a “print engine”). The marking engine includes one or more printhead assemblies, with each assembly including a printhead controller and a printhead (or array of printheads). An individual printhead includes multiple tiny nozzles (e.g., 360 nozzles per printhead depending on resolution) that are operable to discharge ink as controlled by the printhead controller. A printhead array is formed from multiple printheads that are spaced in series across the width of the print media.
When in operation, the web of print media is quickly passed underneath the printhead arrays while the nozzles of the printheads discharge ink at intervals to form pixels on the web. In order to ensure that ink does not partially dry within the printheads during printing (which would adversely affect print quality), flush lines are printed at page boundaries on the web. These flush lines are used to flush ink from the nozzles on a regular basis to ensure that the ink does not become overly viscous.
To reduce the visual footprint of individual flush lines, all of the nozzles located at a single horizontal position along a width of the web may be discharged at the same vertical location along the height of the web. This means that, at a single physical location, the web is saturated with a great deal of ink. For example, in cyan, magenta, yellow, and black (CMYK) printing systems, a C, M, Y, and K nozzle may each discharge a droplet at the same physical pel location on the page. This is repeated across the entire width of the page. These flush lines have a small overall size, but may oversaturate the web with ink, which can cause warping or distortion of the web, or even can smear or offset the ink to different portions of the printed page.
Embodiments described herein identify ink drying limits for printing systems that use dryers. The ink drying limits indicate the amount of ink density that the printing system can properly dry. Based on the ink drying limit for the system, embodiments herein can generate customized flush lines that do not exceed the ink drying limit, take up a small amount of visual space on the printed page, and also ensure that the nozzles for the printing system are flushed at the desired frequency.
One embodiment is a system that includes a flush line generator able to receive a print job, to determine a drying limit that defines a maximum areal density of ink for the print job that may be dried by a dryer, and to generate a flush line based on the drying limit that does not exceed the drying limit. The system further includes a marking engine able to mark the print job and the flush line onto a web of printable media upstream from the dryer.
Another embodiment is a method for generating flush lines. The method includes receiving a print job, and determining a drying limit that defines a maximum areal density of ink that may be dried by a dryer. The method also includes generating a flush line based on the drying limit that does not exceed the drying limit, and marking the print job and the flush line onto a web of printable media upstream from the dryer.
Another embodiment is a non-transitory computer readable medium embodying programmed instructions which, when executed by a processor, are able to perform a method. The method includes receiving a print job, and determining a drying limit that defines a maximum areal density of ink that may be dried by a dryer. The method also includes generating a flush line based on the drying limit that does not exceed the drying limit, and marking the print job and the flush line onto a web of printable media upstream from the dryer.
Other exemplary embodiments (e.g., methods and computer-readable media relating to the foregoing embodiments) may be described below.
Some embodiments of the present invention are now described, by way of example only, and with reference to the accompanying drawings. The same reference number represents the same element or the same type of element on all drawings.
The figures and the following description illustrate specific exemplary embodiments of the invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the invention and are included within the scope of the invention. Furthermore, any examples described herein are intended to aid in understanding the principles of the invention, and are to be construed as being without limitation to such specifically recited examples and conditions. As a result, the invention is not limited to the specific embodiments or examples described below, but by the claims and their equivalents.
In some existing printing systems, flush lines are generated without regard for the drying capabilities of the dryer that is being used. This means that the flush lines may be subject to smearing if the dryer is not sufficiently powerful. In other printing systems, each color is printed and dried separately, which requires a great deal more space at the print shop. In either case, the end result is undesirable.
Ink flushing controller 120 has been enhanced to address this problem by designing flush lines that do not exceed an ink drying limit defined for printing system 100. The ink drying limit indicates the maximum areal density of ink that may be dried by a dryer of printing system 100. Flushing controller 120 generates flush lines that will meet (but not exceed) this ink drying limit. Thus, the flush lines can be designed to ensure adequate drying at a downstream dryer, while still taking up a small amount of space on the printed page.
Ink flushing controller 120 may be implemented, for example, as custom circuitry, as a special or general purpose processor executing programmed instructions stored in an associated program memory, or some combination thereof. While ink flushing controller 120 is illustrated as an independent element in
Illustrative details of the operation of printing system 100 will be discussed with regard to
In step 202, printing system 100 receives a print job. The print job may comprise, for example, rasterized print data or a PDL version of the print data. If the print job includes PDL data, print controller 110 may rasterize the PDL print data to transform it into an appropriate format for marking engine 130.
In step 204, ink flushing controller 120 determines an ink drying limit for the print job. The ink drying limit defines a maximum areal density of ink that may be dried by a dryer of the printing system. This ink drying limit may be a function of ink used, web material used, temperature of the dryer, size of the dryer, speed of the web, power applied to the web, ambient humidity in the printing system, and many other factors. Thus, the ink drying limit may be constant for the printing system, or may vary depending on the settings for the print job. In one embodiment, ink flushing controller 120 is capable of determining the ink drying limit dynamically as a function of one or more of the above-listed variables.
Ink drying limits, which may also be known as “ink limits,” are often defined as a percentage that indicates the number of ink droplets that may be placed, on average, per physical pel location on the page. For example, an ink limit that allows a maximum of one drop of ink (of any color) per pel position on average may be described as a 100% ink limit, while an ink limit that allows up to three drops of ink per pel position on average may be described as a 300% ink limit. While the ink limit may be exceeded for individual pels, on an areal basis (e.g., across small areas even less than ten pels in size) the ink limit is not exceeded.
Defining an ink limit on an areal basis still allows for adequate drying within the printing system, because surrounding pel locations (below the ink limit) may absorb some of the ink placed onto neighbor pel locations (which may be above the limit). The web will therefore still adequately dry even when individual pels are above the limit, so long as, on very small scales, the ink density does not exceed the limit.
In step 206, ink flushing controller 120 generates a flush line based on the drying limit that does not exceed the drying limit. For example, the flush line may include staggered patterns of ink droplets. In these patterns, not every ink of the printing system has to be flushed onto the same pel position on the page. For example, a flush pattern may be generated based on the following rules: each nozzle (for each color) flushes the same number of drops for the total pattern, the ink drying limit may only be exceeded by up to one droplet (and in regions no larger than one single pel), colors are evenly distributed throughout the pattern to allow for a more uniform visual appearance, and the single pel locations that exceed the drying limit are evenly spaced through the pattern to allow for a more uniform visual appearance and to ensure that on an areal basis, the ink drying limit is not exceeded.
The flush line therefore may not be uniform in its coloration, but will be substantially uniform in the areal density of ink applied to the page. Furthermore, because the average ink density of the flush line is below the ink limit, the flush line will adequately dry when it passes through a dryer of the printing system. Typically, flush lines will be repeated regularly throughout the print job (e.g., once per page, once every set distance of linear feet of a web of print media, etc.).
The exact height of the flush line on the page (i.e., the thickness of the flush line) may vary depending on the amount of ink that should be flushed per page to keep ink from partially drying onto the nozzles of marking engine 130. Ink flushing controller 120 may determine the amount of ink to flush as a hard-coded value, or may determine the amount based on the ink type used for the print job.
In step 208, marking engine 130 marks the print job and the flush line onto a web of printable media. This creates a physical output for the print job, which may then be dried by a downstream dryer, cut, and stacked for final delivery to a customer.
Using method 200 described above, a print shop may flush ink in a printing system to ensure that print quality meets the desired standards of a customer. At the same time, method 200 can ensure that flush lines used for the print job are not so oversaturated with ink that they will fail to dry when passed through a dryer of the printing system.
In further embodiments, ink flushing controller 120 may dynamically generate flush patterns on the fly based on the ink drying limit. In still further embodiments, ink flushing controller 120 may include multiple pre-defined flush patterns, and may select a flush pattern based upon the determined ink limit for the print job.
In another further embodiment, ink flushing controller 120 flushes the largest available drop size of ink onto the page at a maximum flow rate. Flushing the largest available droplet of ink onto a physical pel location at once (instead of many smaller droplets of ink) increases the efficacy of the flushing process, because the higher energy imparted into the nozzle chambers by the droplets can surpass the surface tension requirements to eject partially dried ink out of the nozzles.
In a further embodiment, ink flushing controller 120 may be operated in a printing system that utilizes a radiant dryer. If the dryer uses radiant energy, then highly absorptive inks (e.g., black) will dry faster than less absorptive inks Thus, ink flushing controller 120 may intentionally flush more black ink onto the flush line than is normally used to keep the black nozzles clean, because this will enhance the absorptive properties of the flush line, causing it to dry more quickly. This may be particularly desirable for portions of the flush line that would normally include light (and therefore less absorptive) inks.
In the following examples, additional processes, systems, and methods are described in the context of a printing system that manages flush lines for a print job based upon an ink drying limit.
In this example, a continuous-forms inkjet printing system includes a radiant dryer. The radiant dryer operates at a fixed power level, generating a fixed amount of radiant heat. The inkjet printing system utilizes one type of ink, but in four colors: cyan, magenta, yellow, and black. The inkjet printing system also has a pre-defined ink drying limit of 125%, which means that, over an area of 16 pels (e.g., 4×4 pels). A print controller of the printing system receives a print job, and determines that the print job utilizes all four colors of the printing system. Therefore, the printing system generates a flush pattern that flushes all four colors of ink from the printing system. The flush pattern is designed so that, when measured by column or by row, or when measured in 4×4 sections of pels, the flush pattern meets the ink limit but does not exceed it. The flush pattern further ensures that each nozzle of each color flushes equal amounts of droplets. Here, the flush pattern used is flush pattern 400 of
Embodiments disclosed herein can take the form of software, hardware, firmware, or various combinations thereof. In one particular embodiment, software is used to direct a processing system of printing system 100 to perform the various operations disclosed herein.
Computer readable storage medium 712 can be an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor device. Examples of computer readable storage medium 712 include a solid state memory, a magnetic tape, a removable computer diskette, a random access memory (RAM), a read-only memory (ROM), a rigid magnetic disk, and an optical disk. Current examples of optical disks include compact disk-read only memory (CD-ROM), compact disk-read/write (CD-R/W), and DVD.
Processing system 700, being suitable for storing and/or executing the program code, includes at least one processor 702 coupled to program and data memory 704 through a system bus 750. Program and data memory 704 can include local memory employed during actual execution of the program code, bulk storage, and cache memories that provide temporary storage of at least some program code and/or data in order to reduce the number of times the code and/or data are retrieved from bulk storage during execution.
Input/output or I/O devices 706 (including but not limited to keyboards, displays, pointing devices, etc.) can be coupled either directly or through intervening I/O controllers. Network adapter interfaces 708 may also be integrated with the system to enable processing system 700 to become coupled to other data processing systems or storage devices through intervening private or public networks. Modems, cable modems, IBM Channel attachments, SCSI, Fibre Channel, and Ethernet cards are just a few of the currently available types of network or host interface adapters. Presentation device interface 710 may be integrated with the system to interface to one or more presentation devices, such as printing systems and displays for presentation of presentation data generated by processor 702.
Although specific embodiments were described herein, the scope of the invention is not limited to those specific embodiments. The scope of the invention is defined by the following claims and any equivalents thereof.
