Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2001-11-02
2004-11-23
Feggins, K. (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06820970
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to the field of digitally controlled printing devices, and in particular to continuous ink jet printers in which a liquid ink stream breaks into drops, some of which are selectively collected by a catcher and prevented from reaching a recording surface while other drops are permitted to reach a recording surface.
BACKGROUND OF THE INVENTION
Traditionally, digitally controlled inkjet printing capability is accomplished by one of two technologies. Both technologies feed ink through channels formed in a printhead. Each channel includes at least one nozzle from which drops of ink are selectively extruded and deposited upon a recording surface.
The first technology, commonly referred to as “drop-on-demand” ink jet printing, provides ink drops for impact upon a recording surface using a pressurization actuator (thermal, piezoelectric, etc.). Selective activation of the actuator causes the formation and ejection of a flying ink drop that crosses the space between the printhead and the print media and strikes the print media. The formation of printed images is achieved by controlling the individual formation of ink drops, as is required to create the desired image. Typically, a slight negative pressure within each channel keeps the ink from inadvertently escaping through the nozzle, and also forms a slightly concave meniscus at the nozzle, thus helping to keep the nozzle clean.
Conventional “drop-on-demand” ink jet printers utilize a pressurization actuator to produce the ink jet drop at orifices of a print head. Typically, one of two types of actuators are used including heat actuators and piezoelectric actuators. With heat actuators, a heater, placed at a convenient location, heats the ink causing a quantity of ink to phase change into a gaseous steam bubble that raises the internal ink pressure sufficiently for an ink drop to be expelled. With piezoelectric actuators, an electric field is applied to a piezoelectric material possessing properties that create a mechanical stress in the material causing an ink drop to be expelled. The most commonly produced piezoelectric materials are ceramics, such as lead zirconate titanate, barium titanate, lead titanate, and lead metaniobate.
The second technology, commonly referred to as “continuous stream” or “continuous” ink jet printing, uses a pressurized ink source which produces a continuous stream of ink drops. Conventional continuous ink jet printers utilize electrostatic charging devices that are placed close to the point where a filament of working fluid breaks into individual ink drops. The ink drops are electrically charged and then directed to an appropriate location by deflection electrodes having a large potential difference. When no print is desired, the ink drops are deflected into an ink capturing mechanism (catcher, interceptor, gutter, etc.) and either recycled or disposed of. When print is desired, the ink drops are not deflected and allowed to strike a print media. Alternatively, deflected ink drops may be allowed to strike the print media, while non-deflected ink drops are collected in the ink capturing mechanism.
U.S. Pat. No. 4,460,903, which issued to Guenther et al. on Jul. 17, 1994, illustrates a catcher assembly that attempts to minimize splattering and misting. However, as the ink drops first strike and collect on a hard surface of the catcher, the potential for splattering and misting still exists. Additionally, this catcher assembly incorporates an oblique blade edge to initially capture the non-printed ink drops. The incoming non-printed ink drop velocity (typically approaching 10 m/s) is high enough to at least partially obstruct the preferred drop flow direction along the oblique blade edge causing at least a portion of the collected drop volume to flow in a direction opposite to the preferred deflection direction. As the drop volume flows up to the edge of the oblique blade, the effective position of the blade edge is altered increasing the uncertainty as to whether a non-printed ink drop will be captured. Additionally, ink drops that have built up on the blade edge of the catcher can be “flung” onto the receiving media by the movement of the printhead.
U.S. Pat. No. 3,373,437, which issued to Sweet et al. on Mar. 12, 1968, illustrates a catcher assembly that incorporates a planer porous cover member in an attempt to minimize splattering and misting. However, this type of catcher affects print quality in other ways. The need to create an electric charge on the catcher surface complicates the construction of the catcher and it requires more components. This complicated catcher structure requires large spatial volumes between the printhead and the media, increasing the ink drop trajectory distance. Increasing the distance of the drop trajectory decreases drop placement accuracy and affects the print image quality. There is a need to minimize the distance the drop must travel before striking the print media in order to insure high quality images.
The combination electrode and gutter disclosed by Sweet et al. creates a long interaction area in the ink drop trajectory plane. As such, the porous gutter is much longer in this plane than is required for the guttering function. This causes an undesirable extraneous air flow that can adversely affect drop placement accuracy. Additionally, as the Sweet gutter is planer in the ink drop trajectory plane, there is no collection area for ink drops removed from the ink drop path. As collected drops build up on the planer surface of the Sweet gutter, the potential for collected drops to interfere with non-collected drops increases. Additionally, the build up of collected drops creates a new interaction surface that is continually changing in height relative to the planer surface of the gutter effectively creating less of a definitive discrimination edge between printing and non-printing drops. This increases the potential for collecting printing drops while not collecting non-printing drops.
U.S. Pat. No. 4,667,207, which issued to Sutera et al. on May 19, 1987, discloses a gutter having an ink drop deflection surface positioned above a primary ink drop collection surface. Both surfaces are made from a non-porous material. The need to create an electric charge potential between the ink drops and the catcher surface complicates the construction of the catcher and it requires more components. This complicated catcher structure requires large spatial volumes between the printhead and the media, increasing the ink drop trajectory distance. Increasing the distance of the drop trajectory decreases drop placement accuracy and affects the print image quality. Additionally, there is no collection area for ink drops removed from the ink drop path in the catcher disclosed by Sutera et al. Collected drops build up on the planer and inclined surfaces of Sutera et al. gutter and move downward toward a vacuum channel positioned at the bottom edge of the catcher. At this point, ink begins to collect on the inclined surface of the catcher creating a region having a thick dome shaped ink surface. The potential for collected drops to interfere with non-collected drops in this region increases. Additionally, the build up of collected drops creates a new interaction surface that is continually changing in height relative to the surface of the gutter effectively creating less of a definitive discrimination edge between printing and non-printing drops. This increases the potential for collecting printing drops while not collecting non-printing drops.
Catcher assemblies, like the one disclosed by Sweet et al. and Sutera et al., also commonly apply a vacuum at one end of an ink removal channel to assist in removing ink build up on the catcher surface in order to minimize the amount of ink that can be flung onto the media. However, air turbulence created by the vacuum decreases drop placement accuracy and adversely affects the print quality image.
It can be seen that there is a need to provide a simply constructed catcher that reduces ink splatter
Feggins K.
Zimmerli William R.
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