Patent Description:
The airflow in the print zone of a print apparatus may also be influential to image quality since the airflow may directly impact print fluid (for example ink) drop consistency. For good image quality it is desirable to have predictable and consistent drop behavior of both main and satellite ink drops. <CIT> discloses a vacuum platen mechanism and fluid droplet discharge device. <CIT> discloses an inkjet printer.

Various features of the present disclosure will be apparent from the detailed description which follows, taken in conjunction with the accompanying drawings, which together illustrate features of the present disclosure, and wherein:.

A print apparatus <NUM> in accordance with this disclosure is shown in cross-section in <FIG>. The print apparatus includes a print engine <NUM> for printing on print media <NUM> in a print zone <NUM>. A platen <NUM> is provided to support the print media <NUM>. The platen <NUM> opposes the print engine <NUM> and may extends in a generally parallel spaced apart plane to the head (or heads) of the print engine <NUM>. The platen <NUM> may, for example, include a conveyor belt <NUM> for advancing the print media <NUM>. Alternatively, it will be appreciated that rollers or other conveying means may be provided in association with the platen <NUM>. Whilst a single platen <NUM> and print zone are shown for simplicity in the figures, in some examples an array of such platens may be provided. For example, a plurality of apparatus according to the example may extend across a print apparatus to print across the full width of a print media.

It may be noted that arrow A in the figures shows the feed direction of the apparatus <NUM>. It will be appreciated that references herein to "forward" or "rearward" are intended with reference to the feed direction. In other words, "forward" may be understood to refer parts or surfaces closest to the input end of the apparatus and "rearward" may be understood to refer parts or surfaces closest to the output end of the apparatus.

The platen <NUM> may be provided with a vacuum system to maintain print media <NUM> alignment and/or flatness during printing. The vacuum system can include one or more vacuum cavities or chambers <NUM> within the body of the platen <NUM> which feed vacuum outlets <NUM> at the support surface <NUM> of the platen. The vacuum cavities or chambers may be connected to a vacuum pump (not shown) and can distribute vacuum flow across a plurality of outlets <NUM>. As seen in the cross-section of <FIG>, the outlets <NUM> may comprise recesses in the surface <NUM> of the platen <NUM>. Passageways <NUM> may extend from the vacuum cavities <NUM> to the lower surface of each recesses outlet <NUM> to feed the outlet with vacuum flow. It may be appreciated that the outlets <NUM> may be arranged in an array, for example a plurality of rows across the surface <NUM> of the platen <NUM>. The size, shape and configuration of the openings <NUM> may be optimized for any given print apparatus <NUM> to provide the desired effect on the print media.

The conveyor belt <NUM> may be air permeable to allow the pressure from the vacuum opening <NUM> to be applied to print media on top of the conveyor belt <NUM>. For example, the conveyor belt can be provided with a plurality of regularly spaced apertures <NUM> which may move across and into alignment with the plurality of vacuum openings <NUM> of the platen <NUM>. Thus, the apertures <NUM> may transfer vacuum pressure from the plurality of openings <NUM> to any print media <NUM> which is placed on the conveyor belt <NUM>. This may allow the vacuum to hold and flatten the print media <NUM> as it is advanced relative to the print engine <NUM>.

For image quality reasons it may be useful to provide an airflow system to produce a controlled airflow through the print zone <NUM>. The airflow system may, for example, be an airflow bar suction system <NUM>. The airflow bar <NUM> extends across the width of the print zone <NUM> at the outlet side of the print engine <NUM>. The airflow bar <NUM> provides a suction through the print zone in the media feed direction. The airflow bar <NUM> may be arranged to provide a generally homogenous air flow across the print zone <NUM>. For example, the airflow system may provide a laminar type flow in the print zone to improve consistency and predictability of print drops. For example, the provision of an airflow system may provide reduced intra-die uniformities in a print engine having multiple print dies and may eliminate defects due to airflow. For example, image quality may benefit from more consistent on media placement of main and satellite ink drops. Inconsistencies in the distance between ink drops (for example as a direct result of unsteady or fluctuating airflow in the print zone) may be perceived by the human eye as different color lightness in the resulting print.

A potential cause of variation in the airflow during printing may be due to interaction between the flow from the airflow system and the vacuum system. This will be explained further with reference to <FIG> and <FIG>. <FIG> illustrate the transition as the leading edge of print media <NUM> is introduced into the print zone <NUM>. The print media <NUM> is carried on the conveyor belt <NUM> and advances from the left-hand side of <FIG>. In the initial position of <FIG> the leading edge of the print media <NUM> has not entered the print zone and the media is forward of the print zone <NUM>. As such, the vacuum openings within and on the output side of the print zone <NUM> are uncovered. The uncovered vacuum openings cause a resulting flow through the print zone <NUM> as shown by the solid arrows in <FIG>. The airflow is in the same direction as the flow from the airflow bar <NUM>, as shown by the broken arrows in the figure.

As shown <FIG>, when the media <NUM> advances in the feed direction (indicated by arrow A) the portion of the vacuum outlets covered by the print media <NUM> increases. As a result, there is a decrease in the influence of the vacuum system on the print zone airflow as illustrated by the reduced size of the solid arrow in <FIG>. Thus, the airflow speed through the print zone <NUM> decreases as the leading edge of the print media <NUM> moves into and through the print zone <NUM>. As shown in <FIG>, once the leading edge has passed the print zone (and is sufficiently forward thereof) the vacuum no longer impacts the airflow in the print zone <NUM>.

The speed transition developed in the airflow through the print zone <NUM> as the leading edge of the print media <NUM> enters the print zone may cause color gradients in leading edge portions of the resulting print. When the print engine comprises a plurality of print dies the position of each die in the feed direction may be different (for example, the print engine may include a plurality of dies arranged in two or more rows extending perpendicular to the feed direction each row being spaced apart in the feed direction). As a result of these different positions the color gradient for each die may not be the same since the air speed effects at each location will be distinct. This may lead to variations across the print media which are more perceptible to the human eye.

The trailing edge transition is represented in <FIG>. As the print media <NUM> moves forward vacuum openings <NUM> rearward to the print zone <NUM> become uncovered. This may results in an airflow shown by the solid arrow which is counter to the flow, shown by the broken arrows, provided by the airflow bar <NUM>. The vacuum flow may for example cause the airflow in the print zone to become turbulent. Trailing edge disruptions may result in image defects referred to as "aeroworms" in the print. Aeroworms are wavy horizontal bands in the print which can in some cases give the image a woodgrain type appearance. <FIG> includes the conveyor belt <NUM> (shown as semi-transparent for clarity) whereas the conveyor is omitted from <FIG>. It can be seen in <FIG> that the conveyor belt <NUM> has a series of regularly spaced apertures <NUM> which may be arranged in rows across the width of the platen and can be spaced to be positioned over the vacuum outlets <NUM> of the platen. In the illustrated example, each widthwise row includes an aperture <NUM> aligned with every other outlet <NUM> and each row is offset from the previous row to expose a different line of outlets <NUM>. It will be appreciated that the layout of the apertures may be varied as part of the design process dependent upon various factors including, for example, the vacuum flow level or the size of the platen or type of print media.

The print zone <NUM> may overlie the platen <NUM> and conveyor belt <NUM>. In the disclosed example the print engine <NUM> is of a type having a fixed print head comprising a plurality of discreet and fixed positioned print dies. Such an arrangement may for example be used in a printer which is arranged to provide full width printing on the print media. The print dies are arranged in a forward row <NUM>, which is closest to the media input, and a rear row <NUM>, which is closest to the media output. Each row <NUM>, <NUM> is formed of an array of dies which are spaced across the width of the print zone. In the example of <FIG> and <FIG> the array of dies in the two rows <NUM>, <NUM> are laterally staggered but it will be appreciated that other configurations may be possible. The airflow bar of the airflow system <NUM> is positioned at the outlet side of the print zone <NUM>.

It may be noted that a central portion of the platen in <FIG> and <FIG> does not have passageways <NUM> connected to the vacuum system. This central portion is aligned with and extends at least partially through the print zone <NUM>. The central portion may still include surface recesses <NUM> but these are not vacuum outlets. The provision of recesses is useful even in the absence of vacuum outlets for example it may reducing or avoiding static electricity build up in the print media and may allow the print media to expand due to ink absorption without wrinkling of the media. As shown in <FIG>, the area of the platen without vacuum outlets provides a non-vacuum region <NUM> bounded by box marked on the figure. The non-vacuum region <NUM> may extend across the full width of the print zone <NUM> (and may therefore extend the full width of the print head).

The position of the non-vacuum region <NUM> relative to the print zone <NUM> and the print head dies <NUM> and <NUM> may be optimized and will be explained in further detail. The positioning of the non-vacuum region seeks to meet conflicting requirements of reducing interference between the vacuum flow and the flow through the print zone without compromising the flatness of the media leading or trailing edges provided by the vacuum system.

As shown in the example, the non-vacuum region <NUM> may start (in the feed direction) at the rearmost portion of the first row of die <NUM> and the non-vacuum region may end at the rearmost portion of the last row of die <NUM>. The region immediately ahead of the non-vacuum region <NUM> is marked by box <NUM>, this is the region which may be considered to immediately feed the print zone <NUM>. It may be noted that in the example the row of openings 52a in this region extend into the print region and overlap the forward row <NUM> of print dies. The region immediately behind the non-vacuum region <NUM> is marked by box <NUM>, this is the region which may be considered to be the immediately outlet from the print zone <NUM>. It may be noted that the row of openings 52b in the outlet region <NUM> may commence immediately to the rear of the print zone. The forward most edge of the vacuum outlets 52b may for example be aligned with rearmost edge of the rearward row of dies <NUM>.

As a result of the positioning of the non-vacuum region <NUM> in the example, the front row of die <NUM> may commence printing on a leading edge of print media as the media is covering the last vacuum outlets, row 52a, before the non-vacuum area. The length of the non-vacuum region <NUM> may be similar to the leading-edge color gradient and helps avoid issues with the front die. Whilst a similar approach could be applied for the rear row of dice <NUM> this is less effective as increasing the non-vacuum area further in the feed direction may affect the flatness of the print media. Therefore, as shown in the example of <FIG>, the row of vacuum outlets <NUM> may be positioned immediately to the rear of the rear row of dies <NUM>. As the leading edge of the print media is leaving the outlet side of the print zone the vacuum force may be applied to avoid media lifting.

To ensure that the print media <NUM> is always subject to some vacuum pressure even when passing through the non-vacuum area <NUM>, the vacuum outlet depressions both before 52a and after 52b may be provided with a pitch (in the feed direction) matching the pitch of the apertures <NUM> in the conveyor belt <NUM>. This may ensure that at least one of the apertures <NUM> of the belt are pressurized whether the leading edge, trailing edge or central portion of the print media is in the print zone.

Whilst the vacuum sinks 52b after the non-vacuum area <NUM> may generate image quality defects at the leading edge it should be noted that examples in accordance with this disclosure may ensure that such defects are consistent within each die of the print engine. It may be appreciated that by ensuring the vacuum along the print bar <NUM> is generally homogenous the defect within each die may be consistent and homogenous. Such defects may be corrected by calibration.

To address the trailing edge "aeroworm" image defects the example of the present disclosure reduces the flux generated by the uncovered platen in the Media Input area <NUM> forward of the print zone. The number of vacuum openings in the region may be reduced and the opening number and diameter may be optimized based upon the number of belt apertures to be fed by the vacuum openings. Optimization of the vacuum openings may also take into account that during usage, media fibers and aerosol particles may be drawn into the vacuum openings. This may create a mass of material that clogs the openings, most commonly this may occur in the print zone area. In the example of the present disclosure, the vacuum opening size may be increased in the areas most vulnerable to blockage. The opening size may be unmodified in the input area <NUM> where such blocking is expected to be less severe. Such modifications may both reduce flux in the airflow to reduce or avoid aeroworm defects and may also improving the service life of the platen.

Claim 1:
An apparatus comprising:
a print engine (<NUM>) in a print zone (<NUM>);
a platen (<NUM>) opposing the print engine to support print media (<NUM>), the platen including a plurality of openings (<NUM>) in communication with at least one vacuum source; wherein
the platen includes a non-vacuum region (<NUM>), comprising a surface devoid of openings in communication with the at least one vacuum source, the non-vacuum region underlying at least a portion of the print zone;
wherein the print engine comprises a print head having a length in a print feed direction and a width perpendicular to the print feed direction and wherein the non-vacuum region extends the full width of the print head; and
wherein the print engine comprises a print head having an array of print dies,
characterized in that the non-vacuum region extends from a rearward edge of a forward row of dies (<NUM>) to a rearward edge of a rearward row of dies (<NUM>).