BRIEF DESCRIPTION OF THE DRAWINGS
In the detailed description of the preferred embodiments of the invention presented below, reference is made to the accompanying drawings, in which:
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. 4A and 4B are schematic views of the difference in air stream through a non-HEPA filtration system and a HEPA filtration system, respectively;
FIGS. 5A 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; and
FIGS. 6A and 6B are graphs of concentrations of particles in a print head when media is at rest and moving, respectively.
DETAILED DESCRIPTION OF THE INVENTION
The present description will be directed in particular to elements forming part of, or cooperating more directly with, apparatus in accordance with the present invention. It is to be understood that elements not specifically shown or described may take various forms well known to those skilled in the art.
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. For example, 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. The same is true of 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). As in the prior art, the manifold 4 may include a replaceable filter.
The print head assembly of FIG. 2 is positioned similarly to the print head assembly shown in FIG. 1, as designated by the print media movement direction 7. 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.
A high efficiency particulate air (HEPA) filtration system 11 is positioned between air inlet opening 9 and manifold 4. Generally, 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 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. 3, 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. 4A 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. As can be seen from the schematic drawing, the presence of a non-HEPA filtration system 13 does little if anything to decrease turbulence 14, as shown in FIG. 4A. By contrast, in FIG. 4B, HEPA filtration system 11 reduces the turbulence and creates laminar output air stream 15.
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-radians) and more sensitive to air turbulence. 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.
Turbulence that could affect ink jet straightness can also be generated when air, moving at high velocity, turns around objects and interfaces, such as particles and debris that settle on surfaces. FIGS. 5A 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.
FIGS. 6A 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. FIG. 6A a reduction of foreign particles greater than 5 μm 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. FIG. 6B demonstrates similar data but for foreign particles of at least 0.5 μm 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.
The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.
PARTS LIST
1) print head interface controller enclosure
2) Air inlet fan
3) Air inlet filter
4) Manifold
5) Manifold filter
6) Print head
7) Print media movement direction
8) Air stream direction
9) Air inlet opening
10) Placement of print head
11) HEPA filtration system
12) Air fan
13) Non-HEPA filtration system
14) Input air
15) Output air
16) Foreign particle
17) Laminar air
18) Foreign particle induced turbulent stream
Patent Application
20070291097
