Patent Application
20080117253
Inkjet printing mechanisms use cartridges, often called “pens,” which eject drops of ink onto a page. Each pen has a print head formed with very small nozzles through which the ink drops are fired. Drum-type ink jet printing systems generally include one or more print heads disposed over a rotating cylindrical drum. The print media is carried by the rotating drum past the print heads, which eject drops of ink in a desired pattern upon the media.
In order to maintain good image quality, proper maintenance of the condition of the print heads is desirable. An improperly maintained print head can become clogged and/or become the source of dot placement errors that reduce print quality. To that end, inkjet printing devices also typically include a print head service station, generally located outside the print zone, to allow cleaning and protection of the print heads. Print head service stations usually include a waste ink collector, called a “spittoon”, into which a number of drops of ink are periodically ejected, or “spit”, from each nozzle to flush out drying ink. If spitting is not performed, the first few drops ejected from each nozzle can have poor trajectory or be of low optical density, resulting in visible image or print quality defects.
In many printing systems, the print head assembly moves from the print zone to the service station for print head servicing during non-printing periods and during the shutdown process. However, speed is a desirable printing consideration. Moving the print heads from the print zone (above the drum) to a service station that is off the drum, and then back again is a relatively slow process, which increases downtime and reduces throughput of the printing system. Additionally, moving the print heads to a service station outside the print zone can introduce print head position errors, which can harm print quality.
Various features and advantages of the invention will be apparent from the detailed description which follows, taken in conjunction with the accompanying drawings, which together illustrate, by way of example, features of the invention, and wherein:
Reference will now be made to exemplary embodiments illustrated in the drawings, and specific language will be used herein to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Alterations and further modifications of the inventive features illustrated herein, and additional applications of the principles of the invention as illustrated herein, which would occur to one skilled in the relevant art and having possession of this disclosure, are to be considered within the scope of the invention.
The present disclosure relates generally to servicing of ink jet nozzles in drum-type ink jet printers. These types of printers are often considered “high end” printers, and can be configured to print about 30 pages per minute or more. Drum-type printers can make up the heart of an office printer or copier machine, or they can be photographic quality printers, for example. As shown in
As noted above, in order to maintain good image quality, it is desirable that the print heads be ready to print at all times, for which periodic (e.g. between successive pages) decap spitting into some sort of waste ink collector is desirable to flush out drying ink from the nozzles. If decap spitting is not performed, the first few drops ejected from each nozzle can have poor trajectory or be of low optical density, resulting in visible image or print quality defects. One approach to this issue has been to provide “spit strips” at the top of each page of print media. Before printing an image on the page, all ink nozzles fire upon this spit strip so as to keep the nozzles ready. Unfortunately, since spit strips are visible on the printed page, they are generally undesirable to users. Another approach has been to eliminate spitting altogether, which, unfortunately, does not address the issue, but merely ignores it.
With drum-type printers, it is generally considered impractical to interrupt printing by moving the print heads to a position off the drum to perform the decap spitting. As is apparent from the embodiment of
Advantageously, the inventors have developed a drum-mounted roller spittoon system that allows decap spitting as often as desired without the need to move the print heads out of the print zone. Embodiments of a drum-type printer 10 having a drum-mounted roller spittoon system in accordance with the present disclosure are shown in
Various views of one embodiment of a roller spittoon cartridge are shown in
The roller spittoon cartridge 18 also includes an ink collecting structure, located adjacent to the roller 30 and opposite the opening 26. The ink collecting structure can take a variety of forms. In the embodiment shown in
Below the scraper 34 is a capillary absorber 42. The capillary absorber can be a piece of felt material such as polyester, or a piece of foam or cellulose type material. Bits of dried or partially dried ink 44 that have been scraped from the roller will naturally fall upon and be captured by the capillary absorber. Liquid ink residue, on the other hand, is drawn downward (in the direction of arrows 46) by capillary action to the main waste ink absorber/reservoir 48 that is located below the capillary absorber. The main waste ink absorber can be a piece of felt material, such as polyester, or a piece of foam or cellulose type material. The absorber can fill the entire lower space of the roller spittoon cartridge, or this space can include an empty space (not shown) below the absorber. Whether there is an open reservoir space, or the absorber/reservoir space is occupied by the absorber material, this region acts as a reservoir for liquid ink, represented by liquid surface 49. The liquid ink is prevented from spillage when the drum rotates by virtue of the absorbent material.
During normal operation of the printer, the roller 30 remains stationary as the roller spittoon cartridge 18 passes each print head 12 in succession. Each print head can spit waste ink onto the exposed surface of the roller as the roller spittoon cartridge passes. The roller rotates when it periodically engages with a roller drive mechanism 50, as shown in
The planet gear 56 is in mechanical engagement with the drive gear 54. When the drive arm 58 is rotated away from the drum, as shown in
The drive arm 58 and drive gear 54 can be actuated by a motor 59 that, when operated in one direction moves the swing arm toward the drum 14 and the roller spittoon cartridge 18 to engage the roller gear 52 for scraping of the roller, and when operated in the opposite direction retracts the drive arm from that position, thus disengaging from the roller gear. In the position shown in
It will be apparent that other types of selective mechanical drive and engagement mechanisms could also be employed to selectively engage the roller with a drive mechanism. For example, a releasable clutch mechanism could be used to selectively interconnect the roller with a drive motor. Other alternatives are also possible. For example, a portion of a ring gear could be affixed adjacent to the drum and positioned to engage the roller gear 52 during each rotation of the drum 14.
When the roller 30 is engaged with the drive mechanism 50 and rotates as described above, waste ink material will be scraped from the roller and transferred to the ink collecting structure. The frequency of advancing of the roller can vary. For example, advancing the roller to clean it can be performed with each revolution of the drum. Alternatively, roller cleaning can happen less often, even if spitting occurs more frequently. For example, engagement of the roller for cleaning can be performed at the end of each print job, rather than with each revolution of the drum. In some circumstances, the inventors anticipate rotating the roller after every 30 to 50 printed pages. When the roller remains stationary for multiple spit passes, this can cause the waste ink 38 to build up on the roller. Such accumulation over time is not a concern so long as the build up of waste ink is not so thick as to contact the print heads on subsequent revolutions of the drum, and is not so thick as to contact the edges of the opening 26 in the top of the roller spittoon cartridge when the roller is advanced. It will be apparent that such build up of waste ink will occur faster with more viscous inks, and scraping and removing more viscous inks from the roller is likely to involve more force.
Advantageously, the roller spittoon cartridge 18 is removable from the printing drum 14. As shown in
Given the easy removability of the roller spittoon cartridge 18, once sufficient ink has been collected in the spittoon cartridge, it can be easily removed from the drum and replaced with a clean spittoon cartridge. Spittoon systems associated with ink jet printing systems frequently employ a drop counter that counts drops that are spit into a spittoon system. Such drop counters can be associated with each print head in the present system, and can count drops of ink spit onto the roller. When a preset spit threshold is reached, the printing system can provide a message or indication to a user, informing the user that the spittoon is full and prompting the user to replace it. It will be apparent that if too much waste ink is transferred to the ink collecting structure, ink spillage or other undesirable consequences are possible. To prevent this, the spit threshold can be set to a level that allows additional operation of the printing device before ink spillage or other undesirable situations arise, providing a comfortable window for printer maintenance activities.
As shown in
The inventors have thus developed a removable drum-mounted roller spittoon cartridge that is compatible with a wide variety of types of inks. With each rotation of the drum (or less frequently, if desired), the pens can spit onto the roller surface. Advantageously, the spit roller can be as wide as the drum, or as wide as the print media (paper), so that the print heads can spit whenever the spittoon passes, regardless of their printing position. The roller spittoon includes a roller gear, a scraper, and an absorber/reservoir. The roller gear is periodically rotated by an external drive system, causing the spit roller to rotate against a scraper within the roller spittoon cartridge, to remove ink from the surface of the roller, and transfer liquid ink residue to the absorber/reservoir. Once sufficient ink has been collected in the spittoon cartridge, it can be removed from the drum and replaced with a clean spittoon cartridge
It is to be understood that the above-referenced arrangements are illustrative of the application of the principles of the present invention. It will be apparent to those of ordinary skill in the art that numerous modifications can be made without departing from the principles and concepts of the invention as set forth in the claims.
