Printing unit with rotating opposing inkjet module

Abstract

The printing unit includes a unit chassis and a pair of opposing inkjet modules mounted to the unit chassis, each having a respective printhead, each of the inkjet modules pivotally mounted to the unit chassis for pivotally moving the inkjet modules toward and away from each other.

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] Memjet® printing technology uses rows of print chips, arranged end-to-end, to create a page-wide printhead, making it well suited to reducing the overall span of the print zone along the media feed direction. Each print chip has five rows of nozzles, which can be used for 5x printing redundancy in a monochrome printhead.

[0005] US 10,857,821 (the contents of which are incorporated herein by reference) describes a printing system having a configurable array of printing modules, each having a respective monochrome printhead configured for single-pass printing. By arranging four printing modules along the media path, full-color (CMYK) printing can be performed with five-fold redundancy in each color plane. While the system described in US 10,857,821 enables high-quality, high-speed printing using five-fold redundancy in addition to providing OEMs with flexibility in inkjet printer design, the printing modules must be aligned and spaced along the media feed path for full-color printing. This places a demand on the media feed system to match all colors, resulting in relatively high setup costs for OEMs. However, these costs are still significantly lower than alternative page-wide printing systems that use overlapping or very large printing tips to achieve single-pass printing.

[0006] US 10,293,609 (the contents of which are 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, with two-fold redundancy for each ink color provided by four rows of active nozzles in each row of print chips.

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

[0008] In a first aspect, there is provided a printing unit, the printing unit comprising: A unit chassis; a pair of opposing inkjet modules mounted on the unit chassis, each inkjet module including a respective printhead; Each of the inkjet modules is pivotally mounted to the unit chassis for pivotally moving the inkjet modules towards and away from each other.

[0009] The printing unit according to the first aspect advantageously allows easy access to the printheads and maintenance system of a pair of closely spaced inkjet modules. Furthermore, the pivoting movement of the modules allows for more repeatable alignment of the printheads compared to, for example, systems that have a sliding drawer for accessing the printheads.

[0010] In a preferred embodiment, the opposing inkjet modules are generally aligned with respect to the media feed direction. In an alternative embodiment, the opposing inkjet modules are offset from one another in an overlapping arrangement. For example, two opposing inkjet modules may overlap partially across the media feed path. Alternatively, three inkjet modules may be arranged in an offset, overlapping arrangement, with one inkjet module facing the other two inkjet modules.

[0011] Preferably, in the clamshell closed configuration the printing units are configured for printing, and in the clamshell open configuration the respective front faces of each inkjet module are accessible for printhead replacement.

[0012] Preferably, a pair of inkjet modules are aligned in the printing position relative to opposite sides of a common chassis reference block.

[0013] Preferably, each inkjet module is independently rotatable relative to the unit chassis.

[0014] Preferably, the first inkjet module is mounted facing forward and the second inkjet module is mounted facing backward.

[0015] Preferably, each inkjet module includes a module chassis supporting a respective printhead, each module chassis including a base plate with a rear wall and end walls extending upwardly from the base plate.

[0016] Preferably, each base plate is C-shaped in plan view having a pair of lateral arms extending parallel to the media feed direction from opposite ends of a longitudinal base member extending perpendicular to the media feed direction, and each base plate defines an open longitudinal slot for receiving a respective printhead.

[0017] Preferably, the forward and reverse facing opposing ink jet modules have opposing C-shaped base plates with a pair of open longitudinal slots located proximally of the pair of longitudinal base members.

[0018] Preferably, each inkjet module includes a capper, and the pair of cappers are located distally of the pair of printheads.

[0019] Preferably, the unit chassis includes a rectangular frame having a pair of chassis side bars extending parallel to the media feed direction, and front and rear chassis end bars interconnecting the chassis side bars.

[0020] Preferably, the module chassis is pivotally mounted to the chassis side bars about a pivot axis perpendicular to the media feed direction.

[0021] Preferably, each chassis side bar has a chassis reference block positioned between the inkjet modules, and the base plates of each of the pair of inkjet modules are aligned relative to both sides of each chassis reference block in the clamshell closed configuration.

[0022] In a second aspect, there is provided a printing unit, the printing unit comprising: A unit chassis; first and second inkjet modules mounted on the unit chassis, each inkjet module including a respective printhead nest assembly, each printhead nest assembly including an interchangeable printhead nested within a respective nest, each nest enclosing a respective printhead around all sides; a nest of at least a second inkjet module; a cantilever spring engaging each print head, the cantilever spring being biased away from the print head; and a screw adjuster that abuts and engages with the cantilever spring to move the cantilever spring toward or away from the print head, such that the skew of the second print head of the second inkjet module relative to the first print head of the first inkjet module is mechanically adjustable by rotational movement of the screw adjuster.

[0023] Preferably, the printheads of the first and second inkjet modules are generally aligned with respect to the media advance direction.

[0024] Preferably, the nests of the first and second inkjet modules are the same.

[0025] Preferably, each printhead nest assembly is removable from its respective inkjet module.

[0026] Preferably, the screw adjusters are accessible when the printhead nest assemblies are secured to their respective inkjet modules.

[0027] Preferably, each nest is secured to a respective printhead carrier of a respective inkjet module.

[0028] Preferably, each nest is configurable into an open position and a closed position, and each nest allows the respective printhead to be removed from the nest only when it is in the open position and the printhead nest assembly is removed from the printhead carrier.

[0029] Preferably, each nest comprises a pair of longitudinal side bars extending parallel to opposite longitudinal sides of the printhead, and a pair of opposing end bars interconnecting the longitudinal side bars to define a nest cavity.

[0030] Preferably, the first longitudinal side bar is fixed and the second longitudinal side bar is relatively movable between an open position and a closed position.

[0031] Preferably, a cantilever spring is defined on one end of the first longitudinal side bar and a screw adjuster is received in a screw opening in the first longitudinal side bar.

[0032] Preferably, the printhead is aligned to the nest by complementary datum surfaces at opposite ends of the printhead and nest.

[0033] In a related third aspect, a printhead nest assembly is provided, the printhead nest assembly including interchangeable printheads nested and secured within a nest, the nest surrounding each printhead on all sides; Nest, a cantilever spring engaging each print head, the cantilever spring being biased away from the print head; and a screw adjuster that abuttingly engages the cantilever spring to move the cantilever spring toward or away from the print head.

[0034] Preferably, the nest is configurable into open and closed positions, and the nest only allows removal of each printhead from the nest in the open position.

[0035] Preferably, the nest comprises a pair of longitudinal side bars extending parallel to opposite longitudinal sides of the printhead, and a pair of opposing end bars interconnecting the longitudinal side bars to define a nest cavity.

[0036] Preferably, the first longitudinal side bar is fixed and the second longitudinal side bar is relatively movable between an open position and a closed position.

[0037] Preferably, a cantilever spring is defined on one end of the first longitudinal side bar and a screw adjuster is received in a screw opening in the first longitudinal side bar.

[0038] Preferably, the printhead is aligned to the nest by complementary datum surfaces at opposite ends of the printhead and nest.

[0039] It will of course be understood that the preferred embodiments described above in relation to the first, second and third aspects are equally applicable to any of the first, second and third aspects, where relevant.

[0040] As used herein, the term "inkjet module" is intended to mean an assembly of components that includes an inkjet printhead, such as an elongated printhead configured for single-pass printing (known in the art as a "pagewide" or "linehead" printhead). The inkjet module typically includes one or more of the following components to provide a fully integrated inkjet system: maintenance components such as a capper and / or wiper; mechanisms 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 electronic circuitry for providing power and / or data to the printhead.

[0041] As used herein, the term "ink" is intended to mean any printing fluid that can be printed from an inkjet printhead. Ink may or may not contain a colorant. That is, the term "ink" can include traditional dye-based or pigment-based inks, infrared inks, fixatives (e.g., precoats and finishers), 3D printing fluids, solar inks, biological fluids, and sensing fluids, etc.

[0042] As used herein, the term "mounted" includes both direct mounting and indirect mounting through intervening components. [Brief explanation of the drawings]

[0043] Specific embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Figure 1] FIG. 1 is a perspective view of a printing unit mounted on a support chassis. [Figure 2] FIG. 2 is a perspective view of a separate printing unit. [Figure 3] FIG. 3 is a bottom view of a portion of the printing unit. [Figure 4] FIG. 4 is a perspective view of the printing unit in the clamshell open position. [Figure 5] FIG. 5 is a top view of the printing unit in the clamshell open position. [Figure 6] FIG. 6 is a bottom perspective view of the printing unit. [Figure 7] FIG. 7 is an enlarged bottom perspective view of the suction manifold and print head. [Figure 8] FIG. 8 is a plan view of a portion of a print head. [Figure 9] FIG. 9 is an enlarged plan view of the chip bonding area of the printhead. [Figure 10] FIG. 10 is a top front perspective view of the inkjet module with the printhead in the lowered position. [Figure 11] 11 is a rear perspective view of the lower portion of the inkjet module shown in FIG. 1. FIG. [Figure 12] FIG. 12 is a top front perspective view of the inkjet module with the printhead in the raised position. [Figure 13] FIG. 13 is a perspective view of a portion of the inkjet module with the bracket shown transparent to allow the sleeve bushing to be seen. [Figure 14] FIG. 14 shows a portion of the printhead carrier with the printhead nest assembly removed. [Figure 15] FIG. 15 is a top perspective view of the inkjet module showing the lift mechanism. [Figure 16] FIG. 16 shows the inkjet module with the end wall removed to reveal the capping assembly and cap cover. [Figure 17] 17A-17C are side views showing the engagement between the cam guide of the capping assembly and the rocker arm of the cap cover. [Figure 18] FIG. 18 is a top perspective view of the printhead nest assembly in the closed position. [Figure 19] FIG. 19 is a top perspective view of the printhead nest assembly in the open position. [Figure 20] 20 is a bottom perspective view of the printhead nest assembly shown in FIG. 8. FIG. [Figure 21] FIG. 21 is a perspective view of the print head being inserted into the nest. [Figure 22] Figure 22 shows the nest in isolation in the open position. [Figure 23] FIG. 23 is a plan view of a portion of the nest. [Figure 24] FIG. 24 is a perspective view of a portion of a modified printhead nest assembly. [Figure 25] FIG. 25 is a bottom perspective view of a modified printing unit with gap bars. [Figure 26] FIG. 26 is a top perspective view of the modified print in a clamshell open configuration. [Figure 27] FIG. 27 is a side view showing the print zone of the modified printing unit. [Figure 28] FIG. 28 is a bottom perspective view of a modified printing unit having an alternative gap bar with a polymer film. [Figure 29] FIG. 29 is a side view of the modified printing unit shown in FIG. [Figure 30] FIG. 30 is a schematic side view of the modified printing unit shown in FIG. 28 in the printing position. DETAILED DESCRIPTION OF THE INVENTION

[0044] Printing Unit Referring to Figure 1, there is shown a printing unit 200 mounted on a support chassis 202 and configured to feed media through the printing unit along a media feed direction M. The printing unit 200, shown in isolation in Figure 2, comprises a unit chassis 204 and a pair of opposing upstream and downstream inkjet modules 1A, 1B mounted in tandem in forward and reverse orientations on the unit chassis. Each inkjet module 1 is described in more detail below.

[0045] Each inkjet module 1 includes a module chassis 10 pivotally mounted on chassis side bars 205 of a unit chassis 204 about a pair of module pivots 206 located on either side of the module chassis. Thus, each inkjet module 1 is pivotable about a pivot axis perpendicular to the media feed direction M. The inkjet modules 1A, 1B upstream and downstream of a printing unit 200 are pivotally movable toward and away from each other so that the printing unit can be configured into a clamshell-closed configuration (FIGS. 1 and 2) for printing and an open clamshell configuration (FIGS. 4 and 5) for printhead replacement and / or maintenance. Each module chassis 10 has an open front face, and the opposing relationship of the inkjet modules of the printing unit (i.e., one inkjet module rotated 180 degrees relative to the other) facilitates access to the internal components of each individual inkjet module 1 in the open clamshell configuration. Gas struts 208 interconnect each module chassis 10 with the chassis side bars 205 and provide a damped over-center pivot mechanism for each inkjet module 1 .

[0046] 1-5, the upstream and downstream inkjet modules 1A, 1B are independently rotatable, allowing one or both of the inkjet modules to rotate. However, those skilled in the art will appreciate that other rotation mechanisms can be employed to mechanically couple the pair of module chassis 10 together so that the inkjet modules always rotate together to the clamshell open position. These and other rotation mechanisms will be readily apparent to those skilled in the art.

[0047] 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 U.S. Pat. No. 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 a respective ink manifold. Each row of print chips 5 includes multiple 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 its respective printhead 3. Furthermore, 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 so that the printing unit 200 is configured for redundant full-color printing of four inks (CMYK). Redundancy for each color channel is provided by multiple aligned nozzle rows (e.g., three, four, or five 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 color.

[0048] The module chassis 10 of each inkjet module 1 has an elongated base plate 12 with a rear 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 shown raised above the base plate 12 for capping and / or wiping, while in Figure 6, the printhead is shown lowered through the slot 22 for printing.

[0049] 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.

[0050] As shown in FIGS. 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 protrudes inward 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 overall 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.

[0051] 6 shows the printing unit 200 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, thereby providing a cantilevered arrangement with its free end adjacent the downstream printhead 3.

[0052] 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 suction manifold 220 have an overall low profile with a planar underside that extends parallel to the plane of the base plate 12. In a rest position, the aerosol extractor 212 presses 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.

[0053] The suction manifold 220 is coextensive with the slot 22 and contains multiple suction nozzles 222 for extracting aerosol from the vicinity of the print zone. The suction nozzles 222 are configured to direct airflow through the print zone in a direction generally parallel to the media feed direction M. Thus, the aerosol extractor 212 not only removes ink mist but also helps stabilize vortices associated with the flow of droplets in the print zone during printing. The base plate 12 of the upstream inkjet module 1A promotes uniform airflow through the print zone, optimally stabilizing vortices 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 positioned between the print heads 3 to provide a more uniform airflow between the print heads and through the print zone (see Figures 25-27).

[0054] The printing unit 200 can be configured to print at various throw distances relative to the print media (known in the art as printhead-to-paper spacing, or PPS) by adjusting the height of the printheads 3 using a lift mechanism within each inkjet module 1. Adjusting the height of the printheads 3 typically disrupts the optimized airflow through the print zone. However, in the printing unit 200, the cantilevered aerosol extractor 212 allows for adjustment of the height of the suction nozzles adjacent to the downstream printheads. In particular, as shown in FIG. 7 , a leading tab portion 224 connected to the suction manifold 220 is positioned for abutting engagement with the printhead nest 102 that supports the downstream printhead 3. Thus, when the downstream printhead 3 is lowered, the abutting engagement between the printhead nest 102 and the tab portion 224 causes the suction manifold 220 to pivot against the bias of the pivot mount 218, thereby lowering the height of the suction nozzles 222 commensurate with the height of the printheads 3. When the print head 3 is raised, the suction manifold 220 rises with the print head due to the bias of the pivot mount 218. This makes the print unit 200 suitable for variable PPS printing with optimized aerosol extraction and airflow through the print zone.

[0055] Ink plumbing In one embodiment, the print heads 3 can be primed so that each row of print chips 5 (each print chip 6 has multiple aligned nozzle rows for redundant printing) receives only one color of ink. With four rows of print chips 5 across two print heads 3, full-color (CMYK) redundant printing can be achieved using all nozzle rows of each print chip. In this way, the printing unit 200 can mimic a conventional inkjet printer with a monochrome inkjet print bar (e.g., a FujiFilm JPress 750S), albeit with a much narrower print zone (and lower cost) than conventional systems.

[0056] However, to maximize print quality, the printing unit 200 can utilize a unique architecture in an alternative embodiment shown in Figures 8 and 9, in which each print head 3 has two rows of print chips 5 with 180-degree rotational symmetry. As described in US 10,293,609, the print chips 5A, 5B in the first and second rows of each print head 3 include four color channels, with each individual print chip 6 in a row being supplied with two colors of ink. Thus, the two print heads 3 of the printing unit 200 can be considered to have eight color channels (two color channels per row of print chips 5) for printing four different inks (CMYK).

[0057] A fundamental problem ubiquitous in page-wide printing systems with multiple print chips is print quality degradation in the junction areas between print chips 6. Inevitably, page-wide printheads require some form of compensation for printing across the junction areas, for example, using electronic stitching techniques, mechanical chip positioning, specialized chip designs that allow chip butting, or a combination thereof. In Memjet® printheads 3 with butted chips 6, print quality issues are typically minimized due to the physical proximity of adjacent chips and a unique chip architecture with “drop nozzle rows” (see, e.g., U.S. Pat. No. 7,290,852, the contents of which are incorporated herein by reference). The nozzle firing of the drop nozzle rows is delayed or advanced relative to the main nozzle row, depending on the orientation of the print chips 6, to provide a seamless junction between adjacent print chips. Nevertheless, as described in WO 2022 / 053258, print artifacts may still exist in Memjet® printheads as a result of the drop nozzle rows, particularly in certain print modes.

[0058] The printing unit 200, with two color channels available per ink color, allows the print head 3 to be primed in a way that hides printing artifacts resulting from the junction area between adjacent print chips 6. Essentially, each ink color is assigned to a first color channel of the print chips 6 of the first row 5A facing forward and a second color channel of the print chips 6 of the second row 5B facing backward (i.e., rotated 180 degrees relative to the print chips of the first row 5A). In this way, the compensation set (e.g., drop nozzle row) of nozzles 8A of the print chips 5A of the first row is offset from the compensation set of nozzles 8B of the print chips 5B of the second row. Therefore, printing artifacts resulting from the drop nozzle row 8A of the print chips 5A of the first row are minimized by the corresponding (i.e., aligned) nozzles from the main nozzle region 7B of the print chips 5B of the second row. Similarly, printing artifacts resulting from drop nozzle column 8B of second row print chips 5B are minimized by corresponding (ie, aligned) nozzles from main nozzle region 7A in first row print chips 5A.

[0059] In the print head 3 shown in FIG. 9, the first row of print chips 5A has two cyan (C) nozzle rows (each nozzle row has an "odd" and an "even" sub-row) and two yellow (Y) nozzle rows. As described in U.S. Pat. No. 10,293,609, the middle nozzle row (N) is unused to provide separation between color channels and minimize ink mixing on the nozzle plate. Similarly, the second row of print chips 5B has 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 originate from the drop nozzle row 8A of the first row of print chips 5A, while the other two cyan dots originate from the main nozzle row 7B of the second row of print chips 5B. Similarly, aligned yellow (Y) dots originate from drop nozzle row 8A of print chips 5A in the first row and main nozzle row 7B of print chips 5B in the second row.

[0060] It will thus be appreciated that the 180-degree rotational symmetry of the first and second rows of print chips 5A, 5B on the same print head 3 can hide or at least minimize printing artifacts resulting from the drop nozzle rows 8. This complementary arrangement of the first and second rows of print chips 5A, 5B on each print head 3, combined with proper ink plumbing ordering, advantageously maximizes print quality in a two-print head printing unit 200. Each print head 3 receives two colors of ink, but both inks are supplied to both rows of print chips 5 on each print head.

[0061] 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.

[0062] As shown in FIG. 10 , inkjet module 1 includes a chassis 10 having an elongated base plate 12 with a rear wall 14 and a pair of opposite end walls 16 extending upwardly from the base plate. In addition to providing structural rigidity to chassis 10, 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 rear wall 14 allow for fluid connections from the rear of inkjet module 1 without requiring access from above. Openings can also be provided to allow in-situ access to the screw adjusters of any of printhead nests 102 of printing units 200 using an appropriate tool (not shown), as described in more detail below.

[0063] The base plate 12 is generally C-shaped in plan view, with a pair of lateral arms 18 extending from opposite ends of a longitudinal base member 20 along the inkjet module 1's nominal x-axis. An open longitudinal slot 22 defined between the lateral arms 18 extends parallel to the inkjet module 1's longitudinal axis along the inkjet module 1's nominal y-axis and is configured to receive an elongated printhead 3. As such, the printhead 3 is positioned asymmetrically toward its front within the inkjet module 1, allowing the printheads to be closely spaced within the printing unit 200. The printhead 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).

[0064] A pair of posts 24 extend upwardly from the lateral arms 18 of the base plate 12 at either end of the open longitudinal slot 22. Each post 24 is fixed at its lower end to the base plate 12 and at its upper end to its respective end wall 16. A pair of brackets 26 slidably engage the posts 24 via respective sleeve bushings 28 inserted into each bracket. Each sleeve bushing 28 is slidable relative to its respective post 24, thereby allowing vertical translation of the brackets 26 toward and away from the base plate 12 along the nominal z-axis of the inkjet module 1. A flange portion 25 at the lower end of each sleeve bushing 28 is fixed to each bracket 26 and references the respective bracket to the base plate 12 in the printhead down position (FIG. 10).

[0065] An elongated printhead carrier 30 is fixedly supported between the brackets 26 and is linearly slidable therewith. The printhead carrier 30 includes spaced-apart front and rear carrier plates 32 that interconnect the brackets 26 and define a cavity 34 therebetween for housing electronic components that provide power and data to the printhead 3. A brace 38 interconnects the upper portions of the carrier plates 32, and a pair of carrier reference blocks 40 interconnect the lower portions of the carrier plates. The carrier reference blocks 40 are located at opposite longitudinal ends of the printhead carrier 30 toward their respective brackets 26. The braced printhead carrier 30, in combination with the sleeve bushings 28, support posts 24, and chassis 10, provide a rigid support structure for the printhead 3. The printhead 3 is itself secured within a complementary nest 102 to form a printhead nest assembly 100, which is attached to the carrier reference blocks 40 via threaded fasteners 42 that engage the nest.

[0066] The print head 3 can be linearly slidably moved toward and away from the base plate 12 between a printing position ( FIG. 10 ) and a maintenance position ( FIG. 12 ) by a lift mechanism operably coupled to each bracket 26. The lift mechanism also allows the height of the print head 3 to be adjusted relative to the print medium when in the printing position. As best shown in FIG. 15 , the lift mechanism includes a pair of lead screws 44 rotatably mounted to the base plate 12 and extending upwardly parallel to 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 interconnecting pulley belt assembly 50 operably connected to a common lift motor 52. Thus, the print head 3 can be raised and lowered by operation of the lift motor 52, which 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 nuts 46 via the brackets 26.

[0067] As best shown in FIG. 12 , inkjet module 1 includes wiper carriage 54 having a microfiber wiping web 56 suspended at one end of longitudinal slot 22. In the printhead-raised position, wiper carriage 54 is movable longitudinally along the length of printhead 3 by wiper-moving mechanism 57 attached to longitudinal wiper support 55 to wipe ink and debris from the printhead face. In the printhead-lowered position ( FIG. 10 ), one of brackets 26, including bracket roof 27 and bracket sidewall 29, shields wiper carriage 54. Thus, bracket roof 27 and bracket sidewall 29 provide at least some protection from ink mist and / or debris that may contaminate wiper carriage 54 through the open front of inkjet module 1 during printing.

[0068] Inkjet module 1 further includes a capping assembly 60 that is parked against rear wall 14 and linearly slidable along lateral capper rails 62 toward and away from printheads 3 by a rack-and-pinion mechanism 64. Capping assembly 60 includes a capper base 66 slidably engaged with capper rails 62, a peripheral printhead capper 68 mounted to the capper base, and cam guides 70 fixedly attached to the capper base at either end of the printhead capper. In the parked (covered) position shown in FIG. 12 , printhead capper 68 is covered by a cap cover 72 that is pivotally mounted to rear wall 14 of chassis 10. Cap cover 72 takes the form of a rigid plate that seals against a peripheral seal 69 of printhead capper 68 to maintain a humid environment within the printhead capper whenever the printhead capper is not being used to cap a printhead 3. The wiper movement mechanism 57 is attached to the wiper support 55, which is fixedly attached to the rear wall 14 directly above the cap cover 72.

[0069] To cap the printhead, the capping assembly 60 moves laterally away from the cap cover 72 to align with the printhead 3, and the printhead is gently lowered into the capping position onto the printhead capper 68 using the lift mechanism. With the printhead elevated, lateral movement of the capping assembly 60 back toward the rear wall 14 causes the rear cam surfaces 73 of the cam guide 70 to engage with engagement nodes 77 of respective rocker arms 74 at each end of the cap cover. The rocker arms 74 are pivotally mounted to the rear wall 14, and engagement with the cam guide 70 allows the cap cover 72 to pivot upward, thereby allowing the capping assembly 60 to slide across underneath. When the capping assembly 60 reaches its rearmost stop position, the cap cover 72 is pivoted downward by the profile of the cam guide 70 and rocker arms 74, returning to the cover position where the printhead capper 68 is covered by the cap cover.

[0070] FIG. 17A shows the rear cam surface 73 of the cam guide 70 engaging the engagement node 77 of the rocker arm 74 as the capping assembly 60 approaches the rear wall 14. FIG. 17B shows the rocker arm 73 pivoting upward as the capping assembly moves toward its cover position. FIG. 17C shows the capping assembly 60 in its rearmost park position with the rocker arm 74 pivoted back to a horizontal plane and the printhead capper 68 covered by the cap cover 72. To cap the printhead, the capping assembly 60 slides from its park position shown in FIG. 17C toward the printhead 3. The front cam surface 75 of the cam guide 70 engages the engagement node 77 of the rocker arm 74 to pivot the rocker arm upward and allow sliding movement of the capping assembly toward the printhead 3.

[0071] As noted above, and with reference to FIGS. 12 and 13 , the printhead 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 printhead 3. A cooling fan 84 is positioned between the PCBs 82 to cool the electronic components with cool air drawn into the cavity 34 from the top of the printhead carrier 30. The braces 38 defining the roof portion of the printhead carrier 30 have an open truss structure, allowing cool air to circulate through the cavity 34 and between the PCBs 82. The supply module 80 further includes ink couplings 86 for engaging complementary ink ports 88 at both ends of the printhead 3. The supply module 80 forms ink and electrical connections with the printhead 3 when the printhead (secured in its printhead nest assembly 100) is attached to the printhead carrier 30, as described in more detail below.

[0072] 18 and 19 show the printhead nest assembly 100 in isolation. As shown in FIG. 18, the nest is in a closed position with the printhead 3 nested and secured within the nest 102 and surrounded on all sides by the nest. In FIG. 19, the nest 102 is in its open position, and the printhead 3 can be removed from the nest, but only if the printhead nest assembly 100 is completely removed from the printhead carrier 30. That is, before the nest 102 can be secured to the printhead carrier 30 to install a printhead (e.g., a replacement printhead) in the inkjet module 1, the printhead 3 must be integrated with the nest 102 to form the printhead nest assembly 100, thereby forming a print module 81 including the printhead carrier 30, supply module 80, nest 102, and printhead 3 secured together.

[0073] The nest 102 is configured to be removably secured to the printhead carrier 30 via a pair of screw fasteners 42 that extend vertically across the height of the printhead carrier 30. Each screw fastener 42 has a screw lever 43 at one end that is user-accessible from above the printhead carrier 30, with a screw tip protruding through a recessed opening 41 in the respective carrier datum block 40 (FIG. 14). The top surface of the nest 102 has a pair of datum pins 104 configured to complementarily engage with the recessed openings 41 in the carrier datum blocks 40. To attach the printhead nest assembly 100, each screw fastener 42 threads through a hollow bore 105 in the respective datum pin 104 and into a threaded nut insert 106 in the nest 102. The printhead nest assembly 100 can thus be securely secured to the printhead carrier 30 with precisely controlled referencing provided by the complementary datum engagement between the datum pins 104 and the recessed openings 41 in each carrier datum block 40. The nest 102 allows for the use of relatively large reference pins 104 separate from the printhead 3 for highly accurate and repeatable reference between the printhead carrier 30 and the printhead nest assembly 100 .

[0074] Screwing the printhead nest assembly 100 onto the printhead carrier 30 via the carrier reference block 40 simultaneously forms ink and electrical connections between the printhead 3 and the supply module 80. Ink ports 88 on each end of the printhead 3 are raised to engage ink connectors 86 on the supply module 80. Similarly, electrical contacts 109 extending along each longitudinal side of the printhead 3 make electrical contact with complementary PCB contacts 89 on each PCB 82 of the supply module 80. The spring-loaded PCB mounting plate 90 of the supply module 80 allows the PCBs 82 to flex laterally away from each other while the printhead 3 is raised between them during installation of the printhead nest assembly 100. The spring load provides a reliable electrical connection, while the necessary insertion force (for both the ink and electrical connections) is provided by screw fasteners 42, which can be easily manipulated by the user using screw levers 43. This arrangement therefore eliminates the need for a movable supply assembly and two-stage ink and electrical connections as described in US Pat. No. 10,967,638.

[0075] The printhead nest assembly 100 can be secured to the printhead carrier 30 in either the printhead-down position (FIG. 10) or the printhead-up position (FIG. 12), depending on which configuration is more accessible for the particular module setup of the inkjet module 1. As shown in FIG. 14, the printhead nest assembly 100 has been removed in the printhead-down position.

[0076] 19 and 22, the nest 102 can be configured in an open position for print head removal and insertion. 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 lateral 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.

[0077] 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.

[0078] Movement of the second longitudinal side bar 112 is effected by a locking mechanism, which configures the nest 102 in either a closed or open position. The locking mechanism includes a pair of nest levers 120, each pivotally attached 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 with a respective follower pin 124 extending parallel to the pivot axis. Pivoting 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 linear movement of the second longitudinal side bar 112 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.

[0079] In its closed position, the nest 102 is configured to form an ink mist seal around the print head 3. The ink mist seal prevents ink mist from entering the supply module 80, thereby protecting the 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 print head from the respective first and second longitudinal side bars 110, 112. Each lip 130 engages a longitudinal edge region 132 of the print head 3 to form part of the ink mist seal.

[0080] 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.

[0081] Thereafter, with the printhead 3 properly positioned within the open nest (FIG. 19), the nest lever 120 is pivoted inward, closing the second longitudinal side bar 112 and locking 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 side bar 112 moves toward the printhead 3, positioning each longitudinal flange 134 of the printhead beneath and overlapping its respective longitudinal lip to complete the ink mist seal.

[0082] The completed printhead nest assembly 100 is then secured to the printhead carrier 30 using the screw fasteners 42 as described above. Removing 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.

[0083] Printhead skew adjustment in printing unit 200 Alignment of the upstream and downstream printheads 3 in the printing unit 200 is important to ensure optimal print quality. While the fiducial arrangements described above provide stable positioning of the printheads 3 both within each inkjet module 1 of the printing unit 200 and between pairs of inkjet modules, some small misalignment between printheads is unavoidable in printing systems including multiple printheads, especially when the printheads are interchangeable. If printhead alignment along the x-, y-, and z-axes is not optimal, it can usually be corrected electronically as needed using information obtained from test patterns during system setup.

[0084] However, skew between printheads is more difficult to correct electronically, so print quality is typically optimized by mechanically minimizing such skew. Skew refers to the relative rotational misalignment of one printhead relative to the other about the z-axis, based on the nominal coordinate system shown in Figures 5 and 10. Ideally, of course, both printheads would be parallel.

[0085] FIG. 24 shows a modified printhead nest assembly 150, including a modified printhead nest 152 and printhead 3, suitable for correcting skew misalignment between a pair of printheads in a printing unit 200. In the modified printhead nest 152, a cantilever spring 154 is formed at one end of the printhead nest by a micro-machined slot 156 defined in the first (fixed) longitudinal side bar 110. A screw adjuster 158, received through a screw opening in the first longitudinal side bar 110, abuts and engages the cantilever spring 154 to move the cantilever spring toward or away from the printhead 3. Because the printhead 3 is referenced to the cantilever spring 154, when the screw adjuster 158 is threaded along the x-axis, movement of the cantilever spring 154 can impart a slight rotational movement to one end of the printhead 3. Therefore, fine skew adjustments to the print head 3 can be made on the spot using the screw adjuster 158.

[0086] Typically, in a printing unit 200, the printhead 3 of one inkjet module is designated as the reference printhead, and the skew of the other printhead is adjusted relative to the reference printhead. For this reason, only one of the printhead nests needs to have the cantilever spring 154 and screw adjuster 158, although in practice it is convenient for both printhead nests to be identical.

[0087] As mentioned above, the screw adjusters 158 are preferably accessible when the printing modules 200 are set up for use. To this end, the rear wall 14 of each module chassis 10 typically has a suitable window that allows external access to the screw adjusters 158 (in either the printhead-up or printhead-down position) when the printing units 200 are in the clamshell closed position shown in FIG.

[0088] Optimizing airflow through the print zone Optimizing airflow through the print zone during high-speed printing is known to improve print quality, particularly for high PPS printing, i.e., printhead-to-paper spacing (PPS) greater than about 1 mm (e.g., 1-10 mm or 1-5 mm). For example, U.S. Pat. No. 6,997,538 (assigned to Hewlett-Packard Development Company, LP) describes an inkjet printer having a means for generating airflow through the print zone in the direction of media movement. The airflow is generated using an upstream blower, downstream suction, or a combination thereof. Subsequent research by the present applicant has confirmed the importance of controlling airflow through one or more print zones as a means of optimizing print quality. A uniform airflow creates a pressure gradient across the print zone, which tends to stabilize vortices associated with the stream of ejected ink drops. These vortices arise from the interaction of the ink drop stream with the Couette flow caused by the moving print media. Without a forced airflow through the print zone to create a pressure gradient, the vortices tend to drift, resulting in a distinctive printing artifact known as the "tiger stripe" or "wood grain" effect.

[0089] 25-27, there is shown a modified printing system 300 that is similar to the printing system 200 described above in relation to Figures 1-6, but that has a gap bar 302 positioned 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 indicate like features in printing system 200 and modified printing system 300.

[0090] The gap bar 302 extends between the side bars 205 on either side of the unit chassis 204, i.e., parallel to the end bars 207 and the longitudinal axes of the upstream and downstream print heads 3A, 3B. The gap bar 302 includes a polymer plate 304 attached to the underside of a metal support bar 306, the polymer plate defining a planar lower surface that is positioned substantially flush with the undersides 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 heights of the polymer plate and the print heads 3A, 3B.

[0091] The polymer plate 304 has a width dimension that spans 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 the print heads. Filling the space between the print heads in this manner provides a relatively uniform airflow from the upstream print zone 305, through the downstream print zone 307, and toward the suction nozzle 222 of the aerosol extractor 212 (FIG. 27). This optimized airflow advantageously stabilizes vortices associated with the stream of ejected ink drops ejected from the print heads 3A, 3B, thereby minimizing misplacement of stray satellite drops and optimizing print quality. Without the gap bar 302, the airflow would be less uniform, and the suction nozzle 222 would have minimal impact on the upstream print zone 305, instead primarily sucking air from and around the space between the print heads.

[0092] Additionally, the polymer plate 304 advantageously minimizes condensation of ink mist onto the gap bar 302. For example, condensation on a metal surface can undesirably drip onto the print media and smear the printed image.

[0093] 26, the upper surface of the support bar 306 has a pair of recessed 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 the respective recessed portions 308 when the printing unit 300 is in its clamshell closed position.

[0094] It will be appreciated that the gap bar 302 may be useful in referencing each inkjet module relative to the unit chassis 204. However, in the embodiment shown in Figures 25-27, referencing of each inkjet module 1 is achieved by a respective magnetic datum 310 fixed to each module chassis 10 engaging a complementary chassis datum block in the form of an electromagnet 312. Thus, positive referencing of each inkjet module 1 relative to the unit chassis 204 is achieved via magnetic attraction, as described in US 11,376,869, the contents of which are incorporated herein by reference. Release of the inkjet modules 1 from their respective printing positions may be controlled by the electromagnets 312.

[0095] 28-30, a variation of the gap bar 302 is shown in which an elastically deformable polymer film 320 is attached to the underside of the support bar 306 instead of the polymer plate 304. The film 320 has a first wing 322A and a second wing 322B extending upstream and downstream, respectively, from the longitudinal edge of the support bar 306 relative to the media feed direction. As shown in FIGS. 28 and 29, in its undeformed configuration, the film 320 is generally planar with its plane extending parallel to the print medium 301. However, as the print modules (with their respective nests 102) move downward toward the print medium 301, engagement with the respective nests of the upstream and downstream inkjet modules 1A, 1B causes the upstream and downstream wings 322A, 322B of the film 320 to bend downward toward the print medium (FIG. 30). This causes each of the upstream and downstream wings 322A, 322B to function as a resilient flap that can bend toward the print medium 301 through engagement with the respective nest 102.

[0096] Because the film 320 is attached along the longitudinal midsection of the support bar 306 via retainer pins 324, the film 320 assumes a concave profile between the upstream and downstream print heads 3A, 3B in the print position shown in FIG. 30 . Engagement between the nest 102 and the respective wings 322A, 332B forms a partial seal between the upstream and downstream print heads 3A, 3B sufficient to minimize airflow through the space between them. This allows the film 320 to provide a more effective seal across the space between the upstream and downstream print heads 3A, 3B than the arrangements shown in FIGS. 25-27 , because the polymer plate 304 can only partially extend across this space depending on one or more heights 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 airflow through the print zone.

[0097] From the foregoing and from Figure 30, it will be further appreciated that the nest 102 corresponding to the downstream print head 3B simultaneously engages both the downstream wing 322B as well as the tab portion 224 (see Figure 7) of the aerosol extractor 212. This dual function of the nest 102 is particularly advantageous for optimizing airflow through one or more print zones by controlling both the height of the suction nozzle 222 relative to the height of the print head 3B and the configuration of the film 320.

[0098] It will, of course, be understood that the invention has been described by way of example only and modifications of detail may be made within the scope of the invention as defined in the appended claims.

Claims

1. A printing unit comprising: A unit chassis; a pair of opposing inkjet modules mounted on the unit chassis, each inkjet module including a respective printhead; A printing unit, characterized in that each of the inkjet modules is pivotally mounted to the unit chassis for pivotally moving the inkjet modules towards and away from each other.

2. 2. The printing unit of claim 1, A printing unit, wherein in a clamshell closed configuration, the printing unit is configured for printing, and in a clamshell open configuration, a front face of each inkjet module is accessible for printhead replacement.

3. 2. The printing unit of claim 1, A printing unit characterized in that the pair of inkjet modules are aligned in a printing position with reference to both sides of a common chassis reference block.

4. 2. The printing unit of claim 1, A printing unit characterized in that each inkjet module is independently rotatable relative to the unit chassis.

5. 2. The printing unit of claim 1, A printing unit, characterized in that a first inkjet module is mounted facing forward and a second inkjet module is mounted facing backward.

6. 6. The printing unit according to claim 5, A printing unit characterized in that each inkjet module includes a module chassis supporting a respective printhead, each module chassis including a base plate with a rear wall and end walls extending upwardly from the base plate.

7. 7. The printing unit according to claim 6, A printing unit characterized in that each base plate is C-shaped in plan view having a pair of lateral arms extending parallel to the media feed direction from opposite ends of a longitudinal base member extending perpendicular to the media feed direction, and each base plate defines an open longitudinal slot for receiving a respective print head.

8. 8. The printing unit according to claim 7, A printing unit characterized in that the forward and reverse facing inkjet modules have opposing C-shaped base plates, and a pair of open longitudinal slots are located proximal to a pair of longitudinal base members.

9. 9. The printing unit according to claim 8, A printing unit characterized in that each inkjet module is provided with a capper, and the pair of cappers are disposed distally of the pair of print heads.

10. 7. The printing unit according to claim 6, A printing unit characterized in that the unit chassis includes a rectangular frame having a pair of chassis side bars extending parallel to the media feed direction and front and rear chassis end bars interconnecting the chassis side bars.

11. 11. The printing unit according to claim 10, The printing unit according to claim 1, wherein the module chassis is pivotally mounted to the chassis side bars about a pivot axis perpendicular to a media feed direction.

12. 12. The printing unit according to claim 11, a chassis side bar having a chassis reference block disposed between the inkjet modules, the base plates of each of the pair of inkjet modules being aligned relative to both sides of each chassis reference block in a clamshell closed configuration.

Images