Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
  • B41J29/00—Details of, or accessories for, typewriters or selective printing mechanisms not otherwise provided for
  • B41J29/12—Guards, shields or dust excluders
  • B41J29/13—Cases or covers
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
  • B41J29/00—Details of, or accessories for, typewriters or selective printing mechanisms not otherwise provided for
  • B41J29/377—Cooling or ventilating arrangements

Definitions

• the present invention relates to the field of ink jet printers. More specifically, the invention relates to methods of providing laminar air within a printing region of such printers so that printed artifacts are reduced.
• InkJet printing systems are susceptible to turbulent air streams and paper dust, contamination that affect the proper functioning of the print head.
• Several methods of protecting the regions surrounding the print head from contamination have been established, such as by enclosing the print head and filling the enclosure with filtered air under positive pressure.
• FIG. 1 is an example of such a prior art system, wherein a print head assembly is provided with a print head interface controller enclosure 1 having an air inlet fan 2 adapted to force air into enclosure 1 through a replaceable air inlet filter 3.
• the filter reduces the amount of foreign debris from the internal components of the print head.
• the air stream through the print head assembly continues from air inlet fan 2, around a manifold 4, into a manifold filter 5, and into a print head 6.
• the direction of print media travel past the print head is illustrated in FIG. 1 by a dotted line arrow' 7, while air stream direction is depicted by a set of arrows 8.
• These objects and interfaces may be corners and edges of the print head structure or may even be dirt particles and debris that has settled on interior surfaces of enclosure 1.
• the objects and interfaces can trip the air boundary layer and decrease laminar airflow, thus increasing the variation in the speed and/or direction of the air stream. These air stream variations can be sufficient to change the speed and direction of ink droplets ejected from the print head.
• the air streams are necessary for cooling and contamination reduction, but the turbulence within the air stream needs to be controlled to inhibit print artifacts. Accordingly, it is an object of the present invention to reduce the turbulence of an air stream in a print head.
• the turbulence of the air moved through an inkjet print head enclosure can be reduced before reaching the printing region by positioning a HEPA filtration system between an air inlet opening in the enclosure and the printing region.
• a method for reducing artifacts in images produced by an inkjet print head.
• the method includes moving turbulent air through an air path from an air source toward the printing region and positioning a HEPA filtration system in the air path such that only laminar air flow is introduced to the printing region.
• FIG. 1 depicts a prior art print head interface controller with filtration system
• FIG. 2 depicts a print head interface controller according to the present invention
• FIG. 3 is a view similar to FIG. 2 showing the direction of air stream through the print head;
• FIGS. 4 A and 4B are schematic views of the difference in air stream through a non-HEPA filtration system and a HEPA filtration system, respectively;
• FIGS. 5 A and 5B are schematic views of the difference in air stream without particles in the air stream and with particles in the air stream, respectively.
• FIGS. 6A and 6B are graphs of concentrations of particles in a print head when media is at rest and moving, respectively.
• FIG. 2 illustrates a print head assembly according to a preferred embodiment of the present invention.
• Reference numerals that appear both in prior art FIG. 1 and in FIG. 2 refer to structure that is similar in function, but not necessarily identical in structure.
• reference numeral 1 identifies a print head interface controller enclosure 1 in FIG. 2 that has the same function as print head interface controller configuration 1 of FIG. 1, but clearly differs in configuration.
• manifold 4 which precedes the region 10 for placement of the print head (the print head has not been illustrated in FIG. 2 for clarity).
• the manifold 4 may include a replaceable filter.
• An air inlet opening 9 includes an air inlet fan and an air inlet filter (not individually shown), which draws air into print head interface controller enclosure 1 from the print head docking station.
• the air inlet filter associated with air inlet opening 9 may be replaceable.
• HEPA filtration system 11 A high efficiency particulate air (HEPA) filtration system 11 is positioned between air inlet opening 9 and manifold 4.
• HEPA filtration was developed by the Atomic Energy Commission during the Second World War to remove radioactive dust particles from the air in manufacturing plants.
• HEPA filters are conventionally made from very tiny glass fibers that are 007/013593
• HEPA filters are made into a tightly woven paper, but other constructions of HEPA filters are contemplated within the scope of the present invention. This creates a filter consisting of a multitude of very small sieves that can capture extremely small particles, including some biological agents. Once trapped, contaminates and particles are not able to stream back into circulation, due to the highly absorbent pores of the HEPA filter.
• HEPA filters are commonly used in hospital operating rooms, burn centers, laboratories and manufacturing facilities for products like computer chips, where particle and bacteria free air is mandatory . Beyond particulate filtration, HEPA filters are also capable of reducing air turbulence. That is, as air passes through the HEPA filter, a more laminar air flow results. As shown in FIG.
• the stream direction 8 of the air within the illustrated embodiment begins at air inlet opening 9, where air is introduced into print head interface controller enclosure 1 by a fan (not shown).
• the air moves through a HEPA filtration system 11.
• the moving air may then stream into manifold 4, into the print head (not shown), and through an exhaust opening (not shown).
• the air stream helps cool the print head, and air pressure is maintained positive relative to ambient to prevent dirt particles from entering the enclosure.
• the air inlet fan necessarily introduces air turbulence into the air stream through inlet opening 9.
• FIGS 4 A and 4B compare the amount of air turbulence 14 from an air fan 12 that is able to pass a non-HEPA filtration system 13 and a HEPA filtration system 11, respectively.
• the straightness requirement for the travel path of an ink droplet is dictated by the nominal resolution of the printer and is a function of the distance that ink droplets must travel between the nozzle and the print media.
• the space between the nozzle and the print media is referred to as the printing region.
• Target variation from a straight path in the printing region is preferably less than 3 milli-radians. As desired resolutions increase, the straightness requirement for the travel path of an ink droplet becomes more critical (even to less than 2 milli- 7 013593
• Air turbulence in the printing region causes unpredictable print misregistration.
• the air pressure within print head interface controller enclosure 1 is controlled, and air turbulence in the printing region is minimized by HEPA filtration system 11.
• the HEPA filtration system placement according to the present invention provides a laminar stream with minimal turbulence into the printing region.
• FIGS. 5 A and 5B demonstrate the difference between a laminar stream 17 and a foreign particle induced turbulent stream 18 when the air is disrupted by the presence of a foreign particle 16.
• Figures 6 A and 6B demonstrate the ability of the HEPA filtration system according to the preferred embodiment to remove foreign particles. Particle concentrations were measured during tests using an aerosol particle counter at the orifice plate, at the bottom of the print head, and in the room adjacent to the print head assembly.
• Figure 6A a reduction of foreign particles greater than 5 ⁇ m in diameter when a HEPA filtration system is employed according to the present invention. Even in the situation where the print media is in motion through the printer, the HEPA filtration system has effectively reduced the particle counts at both the orifice plate and the bottom of the print head.
• Figure 6B demonstrates similar data but for foreign particles of at least 0.5 ⁇ m in diameter. The reduction in foreign particle counts within the region of the orifice plate demonstrates the significance of the HEPA filtration system in effectively reducing this source of air turbulence. 007/013593

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• Ink Jet (AREA)
• Particle Formation And Scattering Control In Inkjet Printers (AREA)

Priority Applications (2)

Applications Claiming Priority (2)

Publications (2)

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Family Applications (1)

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• 2006
  • 2006-06-20 US US11/425,265 patent/US7458677B2/en not_active Expired - Fee Related
• 2007
  • 2007-06-08 JP JP2009516511A patent/JP2009541094A/ja active Pending
  • 2007-06-08 EP EP07809420A patent/EP2029369A2/en not_active Withdrawn
  • 2007-06-08 WO PCT/US2007/013593 patent/WO2007149244A2/en not_active Ceased

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