Tandem printing module with a gap bar for optimizing air flow

Abstract

The printing unit includes a unit chassis having a pair of side bars interconnected by a pair of end bars, first and second printing modules attached to the unit chassis, the first and second printing modules each having a respective printing head and associated printing zone, an aerosol extractor for providing an air flow through the printing zone, and a gap bar disposed in the space between the printing heads. The gap bar is configured to regulate the air flow through the printing zone.

Description

[Technical Field]

[0001] The present invention relates to a high speed printing unit, which has been developed primarily to minimize the width of the print zone and optimize print quality in full color digital inkjet printing machines with multiple redundancies for each ink color. [Background technology]

[0002] Inkjet printers employing Memjet® Page Wide technology are commercially available for a variety of printing applications, including desktop printers, digital inkjet presses, and wide-format printers. Memjet® printers typically contain one or more user-replaceable fixed inkjet printheads, typically at least 200 mm long. For example, a desktop label printer contains a single user-replaceable full-color printhead, a high-speed inkjet press contains multiple user-replaceable monochrome printheads aligned along the media feed direction, and a wide-format printer contains multiple user-replaceable printheads in an interleaved arrangement spanning the wide-format media feed path.

[0003] Analog printing presses are traditionally used for relatively long print runs where the cost of producing specialized printing plates is economically feasible. Industrial printing systems are increasingly using single-pass digital inkjet printing for relatively short print runs. Digital inkjet printing avoids the high setup costs of producing printing plates and allows each print job to be tailored to a specific customer. It is desirable for the web-feed systems of existing analog printing systems to be adaptable to allow for the use of "drop-in" inkjet modules, for example, in place of offset printing stations. Therefore, it is desirable to minimize the space occupied by the inkjet modules in the media feed direction while still allowing for high-speed, full-color printing with optimal print quality.

[0004] The Memjet® printing technology uses rows of print chips butted end-to-end to form a page-wide printhead, which is well-suited to reducing the overall span of the print zone along the media feed direction. Each print chip has five rows of nozzles and can be used for five-fold redundant printing in a monochrome printhead.

[0005] US10,857,821 (the content of which is incorporated herein by reference) describes a printing system having a configurable array of printing modules, each printing module having a respective monochrome printhead configured for single-pass printing. By arranging four printing modules along a media path, full-color (CMYK) printing with five-fold redundancy in each color plane can be performed. The system described in US10,857,821 provides flexibility to OEMs in the design of inkjet printers and enables high-quality and high-speed printing using five-fold redundancy, but the printing modules need to be aligned and spaced along the media feed path for full-color printing. For this reason, the media supply system is subject to requirements for aligning all colors, resulting in relatively high setup costs for OEMs. Nevertheless, those costs are still significantly lower compared to alternative page-wide printing systems that use overlapping print chips or very large print chips to achieve single-pass printing.

[0006] US10,293,609 (the content of which is incorporated herein by reference) describes a full-color page-wide printhead having two rows of butted print chips that receive ink from a common manifold. This printhead has two-fold redundancy for each ink color provided by four active nozzle rows in each row of the print chips.

[0007] It is desirable to provide a low-cost printing unit that has multiple redundancies for each ink color and minimizes the span of the printing zone along the media feed direction for printing in four colors (CMYK). Further, it is desirable to provide a printing unit that can access the print head for replacement, simplifies the alignment and setup procedures of the print head, and enables printing with various print head-to-paper spacings (PPS) while optimizing print quality.

Summary of the Invention

[0008] In a first aspect, a printing unit is provided, the printing unit comprising a unit chassis having a pair of side bars interconnected by a pair of end bars, a first printing module attached to the unit chassis, the first printing module including respective first print heads having associated first printing zones, a second printing module attached to the unit chassis downstream of the first printing module with respect to the media feed direction, the second printing module including respective second print heads having associated second printing zones, an aerosol extractor disposed downstream of the second print head, the aerosol extractor having one or more suction nozzles configured to provide an air flow through at least one of the first and second printing zones, a gap bar disposed in the space between the first and second print heads, the gap bar extending between the side bars parallel to the first and second print heads, wherein the gap bar is configured to regulate an air flow through at least one of the first and second printing zones.

[0009] Preferably, the gap bar has a lower surface that extends across the space between the first and second print heads, and the lower surface has a length dimension at least the same as that of the first and second print heads.

[0010] Preferably, the lower surface is disposed at the same height as the first and second print heads with respect to the media path.

[0011] Preferably, the lower surface is configured to provide a uniform air flow from the first printing zone to the second printing zone.

[0012] Preferably, the lower surface is defined by a planar polymer plate.

[0013] Preferably, the gap bar includes a support bar to which the polymer plate is attached.

[0014] Preferably, the gap bar includes a support bar to which a film is attached to the lower surface, and the film has first and second wings that extend upstream and downstream from the support bar with respect to the media feed direction, respectively.

[0015] Preferably, the film is elastically deformable, and when the first print head is lowered toward the first wing, the first wing bends downward so as to move away from the support bar, and when the second print head is lowered toward the second wing, the second wing bends downward so as to move away from the support bar.

[0016] Preferably, the film is attached along the longitudinal middle portion of the support bar, and at the printing position, the film is configured to have a concave profile between the first and second print heads.

[0017] Preferably, by the engagement of each printing module with the respective wing, a seal is at least partially formed therebetween, thereby minimizing the air flow through the space between the print heads.

[0018] Preferably, the first and second printing modules are each height-adjustable with respect to the media surface in order to print at various heights with respect to the media surface.

[0019] Preferably, the aerosol extractor is cantilevered with a free end including a suction nozzle, the suction nozzle being movable towards and away from the media surface.

[0020] Preferably, the suction nozzle is height adjustable relative to the media surface by pivoting movement of the aerosol extractor.

[0021] Preferably, the aerosol extractor is resiliently biased away from the media path.

[0022] Preferably, a downstream portion of the second printing module is configured for abutting engagement with an engagement surface of the aerosol extractor, whereby the height of the suction nozzle can be adjusted.

[0023] Preferably, when the second print module is lowered towards the media surface, the second print module simultaneously engages the second wing and the engagement surface of the aerosol extractor.

[0024] Preferably, at least the second printing module comprises a nest, the second printing head being telescopically fixed to the nest, the nest having respective upstream and downstream abutment portions for abutting engagement with the engagement surfaces of the second wing and the aerosol extractor, respectively.

[0025] Preferably, the printing unit further comprises first and second inkjet modules pivotally mounted to the unit chassis, the first and second inkjet modules comprising first and second printing modules, respectively, and the first and second printing modules being slidably movable relative to the first and second inkjet modules, respectively.

[0026] Preferably, in the clamshell closed configuration the printing units are configured for printing, and in the clamshell open configuration the front of each inkjet module is accessible for printhead replacement.

[0027] Preferably, the upper surface of the gap bar is configured to complementarily engage the first and second inkjet modules in the clamshell closed configuration.

[0028] In a second aspect, there is provided a printing unit, the printing unit comprising: a height adjustable print module including a print head for printing on a media surface; a resilient flap positioned to engage a portion of the print module; The print module moves toward the media surface into a printing position, thereby at least partially forming a seal between the print module and the flap for printing.

[0029] The printing unit according to the second aspect advantageously optimizes airflow through the print zone associated with the print head by sealing the roof of the print zone to minimize airflow through gaps around the longitudinal side regions of the print head. By sealing the print zone in this manner and smoothing the airflow, print quality is improved.

[0030] Preferably, the flap comprises an elastically deformable film.

[0031] Preferably, a film is attached to the underside of the support bar, the film extending from the support bar towards the print head.

[0032] Preferably, in the printing position, the film is deformed by engagement with a portion of the printing module to define a concave surface relative to the media surface.

[0033] Preferably, the print position of the print module is adjustable for different jobs, thereby allowing the height of the print head relative to the media surface to be varied.

[0034] Preferably, the film is located upstream of the printing module relative to the media feed direction, and an upstream portion of the printing module is configured to engage the film.

[0035] Preferably, a cantilevered aerosol extractor is positioned downstream of the printing module, the aerosol extractor having a free end including a plurality of suction nozzles, the suction nozzles being movable towards and away from the media surface.

[0036] Preferably, the suction nozzles are oriented to provide an air flow along the media feed direction.

[0037] Preferably, the lower surface of the film is configured to provide uniform air flow along the media feed direction.

[0038] Preferably, the suction nozzle is height adjustable relative to the media path by means of a pivoting movement of the aerosol extractor.

[0039] Preferably, the aerosol extractor is resiliently biased away from the media path.

[0040] Preferably, the downstream portion of the printing module is configured for abutting engagement with an engagement surface of the aerosol extractor, whereby the height of the suction nozzle can be adjusted.

[0041] Preferably, as the print module is lowered towards the media surface, the print module simultaneously engages the film and the engagement surface of the aerosol extractor.

[0042] Preferably, the printing module comprises a nest, the printing head being telescopically fixed to the nest, the nest having respective upstream and downstream abutment portions for abutting and engaging with the engagement surfaces of the film and the aerosol extractor, respectively.

[0043] It will of course be understood that the preferred embodiments described above in relation to the first and second aspects are equally applicable to either the first or second aspects, where relevant.

[0044] As used herein, the term "inkjet module" is meant to mean an assembly of components, including an inkjet printhead, such as an elongated printhead configured for single-pass printing (known in the art as a "page-wide" or "linehead" printhead). The inkjet module typically includes one or more components among maintenance components such as cappers and / or wipers, a mechanism for moving the printhead and / or maintenance components, ink delivery components such as one or more pumps, one or more valves, one or more ink connectors, and an electronic circuit for supplying power and / or data to the printhead, in order to provide a fully integrated inkjet system.

[0045] As used herein, the term "ink" is meant to mean any printing fluid that can be printed from an inkjet printhead. The ink may or may not contain a colorant. That is, the term "ink" may include conventional dye-based or pigment-based inks, infrared inks, fixatives (e.g., precoats and finishers), 3D printing fluids, solar inks, biological fluids, and sensing fluids, among others.

[0046] As used herein, the term "attached" includes both direct attachment and indirect attachment via intervening components.

Brief Description of the Drawings

[0047] Hereinafter, specific embodiments of the present invention will be described by way of example only with reference to the accompanying drawings.

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DETAILED DESCRIPTION OF THE INVENTION

[0048] Printing unit Referring to Figure 1, a print unit 200 mounted on a support chassis 202 is shown. This print unit is configured to feed media through the print unit along the media feed direction M. The print unit 200 shown separately in Figure 2 includes a unit chassis 204 and a pair of opposing upstream and downstream inkjet modules 1A, 1B mounted tandemly on the unit chassis in the forward and reverse directions. Each individual inkjet module 1 will be described in detail below.

[0049] Each inkjet module 1 includes a module chassis 10 rotatably attached to a chassis side bar 205 of a unit chassis 204 about a respective pair of module pivots 206 disposed on both sides of the module chassis. For this reason, each inkjet module 1 is rotatable about a pivot axis perpendicular to the media feed direction M. The upstream and downstream inkjet modules 1A, 1B of the printing unit 200 are rotatably movable so as to approach and separate from each other such that the printing unit can be configured into a clam shell closed configuration (FIGS. 1 and 2) for printing and a clam shell open configuration (FIGS. 4 and 5) for print head replacement and / or maintenance. Each module chassis 10 has an open respective front face, and access to the internal components of each individual inkjet module 1 in the clam shell open configuration is facilitated by the opposing relationship of the inkjet modules of the printing unit (i.e., one inkjet module is rotated 180 degrees with respect to the other inkjet module). A gas strut 208 interconnects each module chassis 10 and the chassis side bar 205, providing a damped over-center rotation mechanism for each inkjet module 1.

[0050] In the embodiments shown in FIGS. 1 to 5, the upstream and downstream inkjet modules 1A, 1B are independently rotatable, and one or both of the inkjet modules can be rotated. However, those skilled in the art will understand that other rotation mechanisms can be employed to mechanically couple the pair of module chassis 10 such that the inkjet modules always rotate to the clam shell open position together. Those rotation mechanisms and other rotation mechanisms will be readily understood by those skilled in the art.

[0051] Each individual inkjet module 1 is a fully integrated unit including a respective printhead 3 and a capper and wiper for maintaining the printhead. Each printhead 3 is of the type described in US 10,293,609, the contents of which are incorporated herein by reference, and includes two rows of print chips 5 mounted on the unit surface of the respective ink manifold. The print chips 5 of each row include a plurality of print chips arranged end-to-end along the length of the respective printhead 3. Each inkjet module 1 prints two colors of ink from the two rows of print chips 5 of the respective printhead 3, and further, the printheads 3 of a pair of inkjet modules 1 mounted in tandem on the unit chassis 204 are generally aligned with respect to the media feed direction M such that the printing unit 200 is configured for redundant full color printing of four inks (CMYK). Redundancy for each color channel is provided by a plurality of aligned nozzle rows (e.g., 3, 4 or 5 nozzle rows) in each printhead 3 that are generally aligned along the media feed direction M and print the same color ink. This allows each set of aligned nozzles to print at the same pixel location during a single pass printing from the fixed printhead 3, thereby providing redundancy in each colour.

[0052] The module chassis 10 of each inkjet module 1 has an elongated base plate 12 with a back wall 14 and a pair of opposite end walls 16 extending upwardly from the base plate. Each base plate is C-shaped in plan view with a pair of lateral arms 18 extending parallel to the media feed direction from opposite ends of a longitudinal base member 20 extending perpendicular to the media feed direction. Each base plate 12 thus defines an open longitudinal slot 22 for receiving a respective printhead 3. In Figure 2 the printhead 3 is raised above the base plate 12 for capping and / or wiping, and in Figure 6 the printhead is lowered through the slot 22 for printing.

[0053] The inkjet modules 1A, 1B on the opposite upstream and downstream sides of the printing unit 200, facing forward and backward, respectively, have opposing C-shaped base plates 12 with a pair of open longitudinal slots 22 disposed proximal to the pair of longitudinal base members 20. As a result, the print heads 3 received through the respective slots 22 are positioned relatively close together, thereby minimizing the total span of the print zone (indicated by the double arrow Z in FIG. 3 ) along the media feed direction M. For example, the print zone Z including both print heads 3 is less than 20 cm, less than 150 cm, or less than 125 cm in the printing unit 200.

[0054] As shown in Figures 3-5, the base plate 12 also serves as a reference plate for each inkjet module 1 through reference engagement with a chassis reference block 210 that projects inwardly from each chassis side bar 205. Each chassis reference block 210 serves as a common reference for the lateral arms 18 on either side of a pair of base plates 12. The chassis reference block 210 provides a z reference for each inkjet module 1, as well as x and y reference functions for global reference of the inkjet modules along the x and y axes. Fine adjustment of the relative skew of the printheads 3 about the theta z-axis is provided by the printhead nest, as described in further detail below.

[0055] 6, the printing unit 200 is shown in the printing position with both printheads 3 protruding through their respective slots 22 in the base plate 12. The aerosol extractor 212 is mounted to the rear end bar 207 of the unit chassis 204 and extends below the base plate 12 of the downstream inkjet module 1B towards the downstream printhead in the media feed direction M. The aerosol extractor 212 is pivotally mounted to the rear end bar 207 via a spring-loaded pivot mount 214 such that it is cantilevered with its free end adjacent the downstream printhead 3.

[0056] The aerosol extractor 212 includes a duct arm 216 that extends from a vacuum port 218 at one end and is connected at the other end to a suction manifold 220. The duct arm 216 and the suction manifold 220 have an overall low height profile with a planar underside that extends parallel to the plane of the base plate 12. In the rest position, the aerosol extractor 212 is pressed against the base plate 12 of the downstream inkjet module 1 and extends parallel to the media feed path so as to minimize the space occupied between the base plate and, for example, a platen for supporting the print medium.

[0057] The suction manifold 220 is of the same length as the slots 22 and has a number of suction nozzles 222 for extracting aerosol from the vicinity of the print zone. The suction nozzles 222 are configured to direct the airflow through the print zone along substantially the same direction as the media feed direction M. Thus, the aerosol extractor 212 not only serves to remove the ink mist, but also helps to stabilize the vortex associated with the flow of droplets in the print zone during printing. The base plate 12 of the upstream inkjet module 1A promotes a uniform airflow through the print zone that is optimal for stabilizing the vortex associated with the flow of droplets ejected from the print heads 3. The airflow provided by the aerosol extractor 212 can be further optimized, for example, by optional gap bars with respective plates arranged between the print heads 3 to provide a more uniform airflow between the print heads and through the print zone (see Figs. 25-27).

[0058] The printing unit 200 is configured to print on a printing medium at various projection distances (known in the art as the print head - paper spacing or PPS) by adjusting the height of the print head 3 using the lift mechanism within each inkjet module 1. Adjusting the height of the print head 3 typically disrupts the optimized air flow through the printing zone. However, in the printing unit 200, the cantilevered aerosol extractor 212 allows the height of the suction nozzle proximate to the downstream print head to be adjusted. In particular, as shown in FIG. 7, the tip tab portion 224 connected to the suction manifold 220 is arranged to abut and engage with the print head nest 102 that supports the downstream print head 3. Thus, when the downstream print head 3 is lowered, the print head nest 102 and the tab portion 224 abut and engage, causing the suction manifold 220 to pivot against the biasing of the pivot mount 218, thereby lowering the height of the suction nozzle 222 corresponding to the height of the print head 3. When the print head 3 rises, the suction manifold 220 rises with the print head due to the biasing of the pivot mount 218. Thereby, the printing unit 200 is suitable for variable PPS printing with optimized aerosol extraction and air flow through the printing zone.

[0059] Ink priming In one embodiment, the print head 3 can be plumed so that each column of print chips 5 (where individual print chips 6 have multiple aligned nozzle rows for redundant printing) receives only one color of ink. In the four columns of print chips 5 spanning two print heads 3, full - color (CMYK) redundant printing can be achieved using all the nozzle rows of each print chip. In this way, the printing unit 200 can mimic a conventional inkjet printer (e.g., FujiFilm JPress 750S) with a monochrome inkjet printing bar, despite having a much narrower printing zone (and lower cost) than conventional systems.

[0060] However, in order to maximize print quality, in alternative embodiments shown in FIGS. 8 and 9, the printing unit 200 can utilize a unique architecture in which each print head 3 has two columns of print chips 5 with 180-degree rotational symmetry. As described in US10,293,609, the first and second columns of print chips 5A, 5B of each print head 3 include four color channels, and two colors of ink are supplied to each individual print chip 6 within a column. Thus, the two print heads 3 of the printing unit 200 can be considered to have eight color channels (two color channels for each column of print chips 5) for printing four different inks (CMYK).

[0061] A fundamental problem pervasive in page-wide printing systems having multiple print chips is the degradation of print quality in the joint regions between the print chips 6. Inevitably, page-wide print heads require some form of correction to print across the chip joint regions, for example, using electronic stitching techniques, mechanical positioning of the chips, a dedicated chip design that enables chip butting, or combinations thereof. In the Memjet® print head 3 having butting chips 6, the physical proximity of adjacent chips and the unique chip architecture having "drop nozzle rows" (see, e.g., US7,290,852, the content of which is incorporated herein by reference) generally minimize print quality issues. The nozzle firing of the drop nozzle rows is delayed or advanced with respect to the main nozzle row depending on the orientation of the print chips 6 to provide a seamless joint between adjacent print chips. Nevertheless, as described in WO2022 / 053258, in the Memjet® print head, print artifacts can still be present as a result of the drop nozzle rows, particularly in certain printing modes.

[0062] The printing unit 200 having two color channels available for each ink color enables the pluming of the print head 3 so as to hide the printing artifacts resulting from the joint area between adjacent printing chips 6. Basically, each color of ink is assigned to the first color channel of the printing chips 6 in the first forward column 5A and to the second color channel of the printing chips 6 in the second reverse column 5B (i.e., the direction rotated 180 degrees with respect to the printing chips in the first column 5A). In this way, the compensation set (e.g., the drop nozzle row) of the nozzles 8A of the printing chips 5A in the first column is offset from the compensation set of the nozzles 8B of the printing chips 5B in the second column. For this reason, the printing artifacts resulting from the drop nozzle row 8A of the printing chips 5A in the first column are minimized by the corresponding (i.e., aligned) nozzles from the main nozzle area 7B of the printing chips 5B in the second column. Similarly, the printing artifacts resulting from the drop nozzle row 8B of the printing chips 5B in the second column are minimized by the corresponding (i.e., aligned) nozzles from the main nozzle area 7A in the printing chips 5A in the first column.

[0063] In the print head 3 shown in FIG. 9, the printing chips 5A in the first column have two cyan (C) nozzle rows (each nozzle row having "odd" and "even" sub-rows) and two yellow (Y) nozzle rows. As described in US10,293,609, the middle nozzle row (N) is not used to provide separation between the color channels and minimize ink mixing on the nozzle plate. Similarly, the printing chips 5B in the second column have two cyan (C) nozzle rows and two yellow (Y) nozzle rows. For each color (e.g., cyan), there are four nozzles aligned along the media feed direction, providing four-fold redundancy. However, as shown in FIG. 9, only two cyan dots are generated from the drop nozzle row 8A of the printing chips 5A in the first column, and the other two cyan dots are generated from the main nozzle row 7B of the printing chips 5B in the second column. Similarly, the aligned yellow (Y) dots are generated from the drop nozzle row 8A of the printing chips 5A in the first column and the main nozzle row 7B of the printing chips 5B in the second column.

[0064] It will thus be appreciated that the 180 degree rotational symmetry of the first and second rows of print chips 5A, 5B of the same print head 3 can hide or at least minimize printing artifacts resulting from the drop nozzle row 8. This complementary arrangement of the first and second rows of print chips 5A, 5B in each print head 3, combined with a proper ink priming order, advantageously maximizes print quality in a printing unit 200 having two print heads. Each print head 3 receives two colors of ink, but both inks are supplied to both rows of print chips 5 of the respective print head.

[0065] Inkjet module For completeness, the individual inkjet modules 1 used in tandem in the printing system 200 will now be described with reference to Figures 10 to 24.

[0066] As shown in FIG. 10, the inkjet module 1 includes a chassis 10 having an elongated base plate 12 with a rear wall 14 and a pair of end walls 16 extending upwardly from the base plate. In addition to providing structural rigidity to the chassis 10, the rear wall 14 also serves as a support for mounting various fluid components (e.g., pinch valves 15 and pump 17) and electronic components (e.g., module controller PCB 19) on both its front and rear sides. Openings in the rear wall 14 allow for fluid connections from the rear of the inkjet module 1 without requiring access from above. Openings may also be provided to allow in situ access to the screw adjusters of any of the printhead nests 102 of the printing unit 200 using a suitable tool (not shown), as described in more detail below.

[0067] The base plate 12 is generally C-shaped in plan view and has a pair of lateral arms 18 extending from both ends of the longitudinal base member 20 along the nominal x-axis of the inkjet module 1. The open longitudinal slot 22 defined between the lateral arms 18 extends parallel to the longitudinal axis along the nominal y-axis of the inkjet module 1 and is configured to receive the elongated print head 3. For this reason, the print head 3 is asymmetrically arranged towards its front side within the inkjet module 1 so that the print heads are arranged in close proximity within the print unit 200. The print head 3 can be lowered through the slot 22 for printing or raised above the base plate 12 for maintenance (e.g., capping and / or wiping).

[0068] A pair of struts 24 extend upward from the lateral arms 18 of the base plate 12 at both ends of the open longitudinal slot 22. The lower end of each strut 24 is fixed to the base plate 12 and the upper end of each is fixed to the respective end wall 16. A pair of brackets 26 are slidably engaged with the struts 24 via respective sleeve bushes 28 inserted into each bracket. Each sleeve bush 28 is slidable relative to the respective strut 24, thereby enabling the vertical linear movement of the bracket 26 in a direction approaching and separating from the base plate 12 along the nominal z-axis of the inkjet module 1. The flange portion 25 at the lower end of each sleeve bush 28 is fixed to each bracket 26 and aligned with respect to the respective bracket relative to the base plate 12 in the lowered position of the print head (Figure 10).

[0069] The elongated printhead carrier 30 is fixedly supported between brackets 26 and is slidable linearly together with the brackets. The printhead carrier 30 includes spaced-apart front and rear carrier plates 32 which interconnect the brackets 26 and define therebetween a cavity 34 for housing electronic components for supplying power and data to the printhead 3. Braces 38 connect the upper portions of the carrier plates 32 to each other and a pair of carrier reference blocks 40 connect the lower portions of the carrier plates to each other. The carrier reference blocks 40 are disposed at opposite longitudinal ends of the printhead carrier 30 toward respective brackets 26. The braced printhead carrier 30, in combination with the sleeve bush 28, the support posts 24 and the chassis 10, provides a robust support structure for the printhead 3. The printhead 3 is itself fixed within a complementary nest 102 to form a printhead nest assembly 100 which is attached to the carrier reference blocks 40 via screws 42 which engage the nests.

[0070] The printing head 3 is linearly slidable relative to the base plate 12 in a direction approaching and separating between a printing position (FIG. 10) and a maintenance position (FIG. 12) by a lift mechanism operably connected to each bracket 26. Also, the height of the printing head 3 with respect to the printing medium can be adjusted at the printing position by the lift mechanism. As best shown in FIG. 15, the lift mechanism includes a pair of lead screws 44 rotatably attached to the base plate 12 and extending upward in parallel with the support posts 24. Each lead screw 44 has a respective lead nut 46 fixedly connected to a respective bracket via a lead nut connector 48. The lead screws 44 are rotatable by an interconnected pulley belt assembly 50 operably connected to a common lift motor 52. For this reason, the printing head 3 can be raised and lowered by the operation of the lift motor 52, and the lift motor simultaneously rotates the lead screws 44 via the pulley belt assembly 50, thereby raising or lowering the print head carrier 30 connected to the lead nut 46 via the bracket 26.

[0071] As best shown in FIG. 12, the inkjet module 1 includes a wiper carriage 54 having a microfiber wiping web 56 stopped at one end of the longitudinal slot 22. In the raised position of the printing head, the wiper carriage 54 is movable longitudinally along the length of the printing head 3 by a wiper movement mechanism 57 attached to the longitudinal wiper support 55 to wipe ink and debris from the printing head surface. In the lowered position of the printing head (FIG. 10), one of the brackets 26 having a bracket roof 27 and a bracket side wall 29 shields the wiper carriage 54. For this reason, the bracket roof 27 and the bracket side wall 29 provide at least some protection from ink mist and / or debris that could contaminate the wiper carriage 54 through the open front face of the inkjet module 1 during printing.

[0072] The inkjet module 1 further includes a capping assembly 60, which is stopped toward the rear wall 14 and can linearly slide in a direction approaching and separating from the print head 3 along the lateral capper rail 62 by a rack and pinion mechanism 64. The capping assembly 60 includes a capper base 66 slidably engaged with the capper rail 62, an outer peripheral print head capper 68 attached to the capper base, and cam guides 70 fixedly attached to the capper base at both ends of the print head capper. In the stopped (cover) position shown in FIG. 12, the print head capper 68 is covered by a cap cover 72 rotatably attached to the rear wall 14 of the chassis 10. The cap cover 72 is in the form of a rigid plate, seals against the outer peripheral seal 69 of the print head capper, and always maintains a high-humidity environment inside the print head capper when the print head capper is not being used for capping the print head 3. The wiper movement mechanism 57 is attached to the wiper support 55, and this wiper support is fixedly attached to the rear wall 14 directly above the cap cover 72.

[0073] To cap the print head, the capping assembly 60 moves laterally away from the cap cover 72 to align with the print head 3, and the print head is gently lowered onto the print head capper 68 to the capping position using a lift mechanism. When the print head is raised, the rear cam surface 73 of the cam guide 70 engages with the engagement nodes 77 of the respective rocker arms 74 at each end of the cap cover by a lateral movement returning toward the rear wall 14 of the capping assembly 60. The rocker arms 74 are rotatably attached to the rear wall 14, and the engagement with the cam guide 70 enables the cap cover 72 to rotate upward, thereby enabling the capping assembly 60 to slide under and cross under the cap cover. When the capping assembly 60 reaches its most rearward stop position, the cap cover 72 rotates downward by the profiles of the cam guide 70 and the rocker arms 74 to return to the cover position where the print head capper 68 is covered by the cap cover.

[0074] Figure 17A shows the state in which when the capping assembly 60 approaches the rear wall 14, the rear cam surface 73 of the cam guide 70 engages with the engagement node 77 of the rocker arm 74. Figure 17B shows the state in which when the capping assembly moves toward its cover position, the rocker arm 73 rotates upward. Figure 17C shows the capping assembly 60 at its most rearward stop position in a state where the rocker arm 74 rotates back to the horizontal plane and the print head capper 68 is covered by the cap cover 72. For capping the print head, the capping assembly 60 slides from its stop position shown in Figure 17C toward the print head 3. To rotate the rocker arm upward and enable the sliding movement of the capping assembly toward the print head 3, the front cam surface 75 of the cam guide 70 engages with the engagement node 77 of the rocker arm 74.

[0075] As described above, referring to FIGS. 12 and 13, the print head carrier 30 defines a cavity 34 between its front and rear plates 32. The cavity 34 houses a supply module 80 including front and rear PCBs 82 for supplying power and / or data to the print head 3. A cooling fan 84 is disposed between the PCBs 82 to cool the electronic components with cool air taken into the cavity 34 from above the print head carrier 30. The brace 38 defining the roof portion of the print head carrier 30 has an open truss structure, thereby enabling the circulation of cool air through the cavity 34 and between the PCBs 82. The supply module 80 further includes an ink coupling 86 for engaging with complementary ink ports 88 at both ends of the print head 3. The supply module 80 forms an ink connection and an electrical connection with the print head 3 when attaching the print head (fixed to its print head nest assembly 100) to the print head carrier 30, as will be described in more detail below.

[0076] Figures 18 and 19 show the print head nest assembly 100 separately. As shown in Figure 18, the nest is in a closed position where the print head 3 is nested and fixed within the nest 102 and surrounded on all sides by the nest. In Figure 19, the nest 102 is in its open position and the print head 3 can be removed from the nest, but only if the print head nest assembly 100 has been completely removed from the print head carrier 30. That is, before fixing the nest 102 to the print head carrier 30 and attaching the print head (e.g., a replacement print head) to the inkjet module 1, it is necessary to integrate the print head 3 with the nest 102 to form the print head nest assembly 100, thereby forming a print module 81 that includes the print head carrier 30, the supply module 80, the nest 102, and the print head 3, which are fixed to each other.

[0077] The nest 102 is configured to be removably fixed to the print head carrier 30 via a pair of screws 42 that extend vertically across the height of the print head carrier 30. Each screw 42 has a screw lever 43 accessible to the user from above the print head carrier 30 at one end, and the screw tips project through the concave openings 41 of the respective carrier reference blocks 40 (Figure 14). On the upper surface of the nest 102, there are a pair of reference pins 104 configured to engage complementarily with the concave openings 41 of the carrier reference blocks 40. To attach the print head nest assembly 100, each screw 42 is screwed into the threaded nut insert 106 of the nest 102 through the hollow bore 105 of the respective reference pin 104. For this reason, the print head nest assembly 100 can be firmly fixed to the print head carrier 30 in a state where the alignment is accurately controlled by the complementary reference engagement between the reference pins 104 and the concave openings 41 of the respective carrier reference blocks 40. The nest 102 enables the use of relatively large reference pins 104 separate from the print head 3 for high-precision and repeatable alignment between the print head carrier 30 and the print head nest assembly 100.

[0078] By screwing the print head nest assembly 100 to the print head carrier 30 via the carrier reference block 40, an ink connection and an electrical connection are simultaneously formed between the print head 3 and the supply module 80. The ink ports 88 at both ends of the print head 3 are lifted to engage with the ink connectors 86 of the supply module 80. Similarly, the electrical contacts 109 extending along both longitudinal sides of the print head 3 are in electrical contact with the complementary PCB contacts 89 of the respective PCBs 82 of the supply module 80. The spring-biased PCB mounting plate 90 of the supply module 80 allows the PCBs 82 to be bent laterally away from each other while the print head 3 is lifted between the PCBs during the mounting of the print head nest assembly 100. The spring bias provides a reliable electrical connection, and the required insertion force (for both the ink connection and the electrical connection) is provided by the screw fastener 42 that can be easily operated by the user using the screw lever 43. Thus, this arrangement obviates the need for the movable supply assembly and the two-stage ink and electrical connections described in US10,967,638.

[0079] The print head nest assembly 100 can be fixed to the print head carrier 30 either in the position where the print head is lowered (Figure 10) or in the position where the print head is raised (Figure 12), depending on the configuration that is more accessible in a particular module setup of the inkjet module 1. As shown in Figure 14, the print head nest assembly 100 is removed in the position where the print head is lowered.

[0080] 19 and 22, the nest 102 can be configured in an open position for removal and insertion of a print head. The nest 102 includes first and second longitudinal side bars 110, 112 extending parallel to opposite longitudinal sides of the print head 3, and a pair of short transverse end bars 114 interconnecting the ends of the longitudinal side bars to define a rectangular nest cavity 115. The first longitudinal side bar 110 and end bars 114 are fixed, but the second longitudinal side bar 112 is movable toward and away from the first longitudinal side bar between an open position and a closed position.

[0081] Each end bar 114 has a dowel pin 116 that is inserted into a movable second longitudinal side bar 112. Sliding movement of the second longitudinal side bar 112 relative to the fixed dowel pin 116 causes linear movement of the second longitudinal side bar toward or away from the first longitudinal side bar 110.

[0082] Movement of the second longitudinal side bar 112 is effected by a locking mechanism, which configures the nest 102 in either a closed or an open position. The locking mechanism includes a pair of nest levers 120, each pivotally mounted to a respective end bar 114 and having a pivot axis perpendicular to the horizontal plane of the nest (i.e., parallel to the direction of drop ejection from the printhead 3). Each nest lever 120 defines a cam slot 122 at each end of the second longitudinal side bar 112 that engages a respective follower pin 124 extending parallel to the pivot axis. Pivotal movement of each nest bar 120 away from its respective end bar 114 causes the cam engagement between the cam slot 122 and the follower pin 124 to linearly move the second longitudinal side bar 112 away from the first longitudinal side bar 110, thereby opening the nest 102. Conversely, pivotal movement of each nest bar 120 toward its respective end bar 114 causes the second longitudinal side bar 112 to move linearly toward the first longitudinal side bar 110, thereby locking the nest 102 in a closed position. Each nest lever 120 has a finger grip portion 126 at the end opposite the pivot axis for user actuation of the locking mechanism.

[0083] In its closed position, the nest 102 is configured to form an ink mist seal around the printhead 3. The ink mist seal prevents ingress of ink mist into the supply module 80, thereby protecting sensitive electronics on the PCB 82 from contamination by ink mist generated during printing. The ink mist seal includes a pair of opposing first and second longitudinal lips 130 that project inwardly toward the printhead from respective first and second longitudinal sidebars 110, 112. Each lip 130 engages a longitudinal edge region 132 of the printhead 3 to form a portion of the ink mist seal.

[0084] To insert a print head 3 into the nest 102, the nest is first configured in an open position, as shown in FIG. 22. The print head is then guided laterally into the nest cavity 115, which opens at an oblique angle (FIG. 21) toward the first longitudinal side bar 110. The first longitudinal flange 134 on one side of the print head 3 is then initially held angled below and overlapping the longitudinal lip 130 of the first longitudinal side bar 110, after which the print head is rotated about its longitudinal axis to lie in a plane parallel to the plane of the nest. Print head datums 136 on both ends of the print head 3 then engage complementary nest datums 138 (FIG. 23), providing accurate and repeatable positioning of the print head within the nest.

[0085] Thereafter, with the printhead 3 properly positioned within the open nest (FIG. 19), the nest lever 120 is pivoted inwardly to close the second longitudinal sidebar 112 and lock the nest 102 in its closed position, thereby forming the locked printhead nest assembly 100 (FIG. 18). As the nest 102 closes, the longitudinal lip 130 of the second longitudinal sidebar 112 is moved towards the printhead 3 such that each longitudinal flange 134 of the printhead is positioned under and overlaps its respective longitudinal lip to complete the ink mist seal.

[0086] The completed printhead nest assembly 100 is then secured to the printhead carrier 30 using the threaded fasteners 42 as described above. Removal of the printhead is accomplished in reverse: the printhead nest assembly 100 is removed from the printhead carrier 30, the nest is opened using the nest lever 120, and the printhead 3 is removed at an angle from the open nest 102.

[0087] Skew adjustment of the print head in the printing unit 200 In the printing unit 200, the alignment of the printing heads 3 on the upstream and downstream sides is important to ensure optimal print quality. In each inkjet module 1 of the printing unit 200 and both between a pair of inkjet modules, the stable positioning of the printing head 3 is provided by the above-described reference arrangement configuration. However, in a printing system including a plurality of printing heads, especially when the printing heads are replaceable, a small misalignment between the printing heads is somewhat inevitable. If the alignment of the printing heads along the x-axis, y-axis, and z-axis is not optimal, it can usually be electronically corrected as needed using information obtained from a test pattern during system setup.

[0088] However, since it is more difficult to electronically correct the skew misalignment between the printing heads, usually, the print quality is optimized by mechanically minimizing such skew misalignment. The skew misalignment refers to a relative rotational misalignment of one printing head with respect to the other around the z-axis based on the nominal coordinate system shown in FIGS. 5 and 10. Naturally, it is ideal for both printing heads to be parallel.

[0089] FIG. 24 shows a modified print head nest assembly 150 including a modified print head nest 152 and a print head 3, which is suitable for correcting the skew deviation between a pair of print heads within the print unit 200. In the modified print head nest 152, a cantilever spring 154 is formed at one end of the print head nest by a micromachined slot 156 defined in the first (fixed) longitudinal side bar 110. A screw adjuster 158 received through the screw opening of the first longitudinal side bar 110 engages with the cantilever spring 154 to move the cantilever spring 154 closer to or farther from the print head 3. Since the print head 3 is aligned with respect to the cantilever spring 154, when the screw adjuster 158 is screwed along the x-axis, the movement of the cantilever spring 154 can impart a slight rotational movement to one end of the print head 3. Therefore, fine skew adjustment for the print head 3 can be performed in situ using the screw adjuster 158.

[0090] Typically, in the print unit 200, the print head 3 of one inkjet module is taken as the reference print head, and the skew of the other print head is adjusted with respect to the reference print head. Therefore, only one of the print head nests needs to have the cantilever spring 154 and the screw adjuster 158, but in practice, it is convenient for both print head nests to be identical.

[0091] As described above, preferably, the screw adjuster 158 can be accessed when the print module 200 is set up for use. For this reason, the rear wall 14 of each module chassis 10 typically has an appropriate window that allows external access to the screw adjuster 158 (either in the raised position or the lowered position of the print head) when the print unit 200 is in the clam shell closed position shown in FIG. 1.

[0092] Optimization of the air flow through the printing zone Optimizing the airflow through the printing zone during high-speed printing is known to improve print quality, particularly for high PPS printing, i.e., printing with a printhead-to-substrate spacing (PPS) exceeding approximately 1 mm (e.g., 1 - 10 mm or 1 - 5 mm). For example, US6,997,538 (assigned to Hewlett-Packard Development Company, L.P.) describes an inkjet printer having means for generating an airflow through the printing zone in the direction of media movement. The airflow is generated using an upstream blower, a downstream suction, or a combination thereof. Subsequent research by the present applicant has confirmed the importance of controlling the airflow through one or more printing zones as a means of optimizing print quality. A uniform airflow creates a pressure gradient across the printing zone, and this pressure gradient tends to stabilize the vortices associated with the flow of ejected ink droplets. These vortices are generated by the interaction of the ink droplet flow with the quiescent flow induced by the moving print media. In the absence of a forced airflow through the printing zone that creates a pressure gradient, the vortices tend to drift, resulting in a distinctive print artifact known as the "washboard" or "wood grain" effect.

[0093] Referring to FIGS. 25 - 27, there is shown an improved printing system 300 that is similar to the printing system 200 described above in connection with FIGS. 1 - 6, but having a gap bar 302 disposed in the space between the upstream and downstream printheads 3A, 3B of the upstream and downstream inkjet modules 1A, 1B, respectively. Where relevant, like reference numerals are used to denote like features in the printing system 200 and the modified printing system 300.

[0094] The gap bar 302 extends between the side bars 205 on both sides of the unit chassis 204, that is, parallel to the longitudinal axes of the end bar 207 and the upstream and downstream print heads 3A, 3B. The gap bar 302 includes a polymer plate 304 attached to the lower surface of a metal support bar 306, and the polymer plate defines a planar lower surface that is substantially at the same height as the lower surfaces of the print heads 3A, 3B relative to the print medium 301. In some embodiments, the gap bar 302 and / or the polymer plate 304 may be height adjustable to match the relative height of the polymer plate and the print heads 3A, 3B.

[0095] The polymer plate 304 has a width dimension that extends across substantially the entire space between the upstream and downstream print heads 3A, 3B (e.g., at least 70%, at least 80% or at least 90% of the space between the print heads), and a length dimension that is at least the same as that of the print heads. By thus filling the space between the print heads, a relatively uniform air flow is provided from the upstream printing zone 305, through the downstream printing zone 307, and towards the suction nozzle 222 of the aerosol extractor 212 (Figure 27). This optimized air flow advantageously stabilizes the vortices associated with the flow of ejected ink droplets from the print heads 3A, 3B, thereby minimizing misplacement of errant satellite droplets and optimizing print quality. In the absence of the gap bar 302, the uniformity of the air flow is reduced and the suction nozzle 222 has a minimal impact on the upstream printing zone 305 and instead primarily draws air from the space between and around the print heads.

[0096] Furthermore, the polymer plate 304 advantageously minimizes the condensation of ink mist onto the gap bar 302. For example, condensate on a metal surface may undesirably drip onto the print medium and smear the printed image.

[0097] As best shown in FIG. 26, the upper surface of the support bar 306 has a pair of concave portions 308 configured to receive complementary portions of the upstream and downstream inkjet modules 1A, 1B. Specifically, the bracket sidewalls 29 of each inkjet module are received in their respective concave portions 308 when the printing unit 300 is in its clam shell closed position.

[0098] It will be appreciated that the gap bar 302 may be useful for aligning each inkjet module with respect to the unit chassis 204. However, in the embodiments shown in FIGS. 25-27, the alignment of each inkjet module 1 is achieved by engagement of respective magnet references 310 fixed to each module chassis 10 with complementary chassis reference blocks in the form of electromagnets 312. Thus, reliable alignment of each inkjet module 1 with respect to the unit chassis 204 is achieved via magnetic attraction force, as described in US11,376,869, the content of which is incorporated herein by reference. Release of the inkjet module 1 from each printing position can be controlled by the electromagnet 312.

[0099] Referring to FIGS. 28 to 30, a modified example of the gap bar 302 is shown in which an elastically deformable polymer film 320 is attached to the lower surface of the support bar 306 instead of the polymer plate 304. The film 320 has a first wing 322A and a second wing 322B that extend upstream and downstream, respectively, from the longitudinal edges of the support bar 306 with respect to the media feed direction. As shown in FIGS. 28 and 29, in its undeformed configuration, the film 320 is generally planar having a plane that extends parallel to the print media 301. However, when the printing modules (each having a respective nest 102) move downward toward the print media 301, the upstream and downstream wings 322A, 322B of the film 320 bend downward toward the print media due to engagement with the respective nests of the upstream and downstream inkjet modules 1A, 1B (FIG. 30). Thereby, each of the upstream and downstream wings 322A, 322B functions as an elastic flap that can bend toward the print media 301 by engagement with the respective nest 102.

[0100] Since the film 320 is attached along the longitudinal middle portion of the support bar 306 via the retainer pin 324, the film 30 takes a concave profile between the upstream and downstream print heads 3A, 3B at the printing position shown in FIG. 30. Engagement between the nest 102 and the respective wings 322A, 332B forms a partial seal therebetween sufficient to minimize the airflow through the space between the upstream and downstream print heads 3A, 3B. For this reason, the film 320 provides a more effective seal across the space between the upstream and downstream print heads 3A, 3B than the arrangement shown in FIGS. 25 to 27. This is because the polymer plate 304 can only extend partially across this space depending on the height of one or more of the print heads relative to the print media 301. The film 320 can accommodate a range of different print head heights while maintaining an effective seal and optimizing the airflow through the printing zone.

[0101] From the foregoing and FIG. 30, it will be further appreciated that the nest 102 corresponding to the downstream print head 3B engages simultaneously with both the downstream wing 322B and the tab portion 224 (see FIG. 7) of the aerosol extractor 212. This dual function of the nest 102 is particularly advantageous for optimizing the air flow through one or more printing zones by controlling both the height of the suction nozzle 222 commensurate with the height of the print head 3B and the configuration of the film 320.

[0102] Of course, it is to be understood that the present invention has been described for purposes of illustration only and that details may be changed within the scope of the invention as defined in the appended claims.

Claims

1. A printing unit, comprising: A unit chassis having a pair of side bars interconnected by a pair of end bars; A first printing module attached to the unit chassis, the first printing module including respective first printing heads having associated first printing zones; A second printing module attached to the unit chassis downstream of the first printing module in the media feed direction, the second printing module including respective second printing heads having associated second printing zones; An aerosol extractor disposed downstream of the second printing heads, the aerosol extractor having one or more suction nozzles configured to provide an air flow through at least one of the first and second printing zones; A gap bar disposed in the space between the first and second printing heads, the gap bar extending between the side bars parallel to the first and second printing heads; The printing unit, wherein the gap bar is configured to regulate an air flow through at least one of the first and second printing zones.

2. The printing unit according to claim 1, wherein: The gap bar has a lower surface extending across the space between the first and second printing heads, the lower surface having a length dimension at least the same as that of the first and second printing heads.

3. The printing unit according to claim 2, wherein: The lower surface is disposed at the same height as the first and second printing heads with respect to the media path.

4. The printing unit according to claim 2, wherein: The lower surface is configured to provide a uniform air flow from the first printing zone to the second printing zone.

5. The printing unit according to claim 2, wherein: The lower surface is defined by a planar polymer plate.

6. The printing unit according to claim 5, wherein: The gap bar includes a support bar to which the polymer plate is attached.

7. The printing unit according to claim 1, wherein: The gap bar includes a support bar to which a film is attached to the lower surface, and the film has first and second wings extending upstream and downstream from the support bar with respect to the medium feeding direction, respectively. A printing unit characterized by this.

8. In the printing unit according to claim 7, The film is elastically deformable, and when the first printing head is lowered toward the first wing, the first wing bends downward so as to move away from the support bar, and when the second printing head is lowered toward the second wing, the second wing bends downward so as to move away from the support bar. A printing unit characterized by this.

9. In the printing unit according to claim 8, The film is attached along the longitudinal middle portion of the support bar, and at the printing position, the film is configured to have a concave profile between the first and second printing heads. A printing unit characterized by this.

10. In the printing unit according to claim 8, By the engagement of each printing module with its respective wing, a seal is formed at least partially therebetween, thereby minimizing the air flow through the space between the printing heads. A printing unit characterized by this.

11. In the printing unit according to claim 8, The first and second printing modules are each height-adjustable with respect to the medium surface in order to print at various heights with respect to the medium surface. A printing unit characterized by this.

12. In the printing unit according to claim 8, The aerosol extractor is a cantilever type having a free end including the suction nozzle, and the suction nozzle is movable toward and away from the medium surface. A printing unit characterized by this.

13. In the printing unit according to claim 12, The suction nozzle is height-adjustable with respect to the medium surface by the rotational movement of the aerosol extractor. A printing unit characterized by this.

14. In the printing unit according to claim 13, The aerosol extractor is elastically biased to move away from the medium path. A printing unit characterized by this.

15. In the printing unit according to claim 14, The downstream portion of the second printing module is configured to engage with the engagement surface of the aerosol extractor in abutment therewith, whereby the height of the suction nozzle can be adjusted. A printing unit characterized by this.

16. In the printing unit according to claim 15, When the second printing module is lowered toward the medium surface, the second printing module simultaneously engages with the second wing and the engagement surface of the aerosol extractor. A printing unit characterized by this.

17. In the printing unit according to claim 16, At least the second printing module is provided with a nest, the second print head is fixedly nested therein, and the nest has respective upstream and downstream abutting portions for engaging in abutment with the second wing and the engagement surface of the aerosol extractor, respectively. A printing unit characterized by this.

18. In the printing unit according to claim 11, The unit chassis further includes first and second inkjet modules rotatably attached thereto, the first and second inkjet modules each include the first and second printing modules, and the first and second printing modules are each slidable relative to the first and second inkjet modules. A printing unit characterized by this.

19. In the printing unit according to claim 18, In the clam shell closed configuration, the printing unit is configured for printing, and in the clam shell open configuration, the front surfaces of the respective inkjet modules are accessible for print head replacement. A printing unit characterized by this.

20. In the printing unit according to claim 19, The upper surface of the gap bar is configured to engage complementarily with the first and second inkjet modules in the clam shell closed configuration. A printing unit characterized by this.

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