Inkjet printer having an aerodynamic element for reducing turbulences

An inkjet printer having at least one print head in which an aerodynamic element is placed before (e.g. in a transport direction) a recording medium (e.g. in the form of a sheet or page or plate) to reduce or avoid turbulences that may arise due to the relative motion between print head(s) and recording medium at an edge of the recording medium.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application claims priority to German Patent Application No. 102017127841.9, filed Nov. 24, 2017, which is incorporated herein by reference in its entirety.

BACKGROUND

The disclosure relates to an inkjet printer with which a recording medium in the form of a sheet or page or plate may be printed to. In particular, the disclosure relates to the transport of a recording medium in the form of a sheet or page or plate through the print group of an inkjet printer.

An inkjet printer typically includes a print group having one or more print bars for different inks. A print bar may thereby have one or more print heads with respectively one or more nozzles. For printing to a recording medium, the recording medium and a print head may be moved relative to one another in order to print the image dots of different lines of a print image bit by bit onto the recording medium.

Given the use of recording media in the form of sheets or pages or plates, inaccuracies in the positioning of dots of a print image on the recording medium may occur due to the relative movement between a recording medium and a print head. This applies in particular given recording media in the form of plates, such as corrugated board, that may have a thickness of up to, for example, 1 cm.

US2003/0043252A1 describes a printer that has a roller with a rocker for transport of a page. US 2010/0225719A1 describes a transport unit for an inkjet printer. US2002/0018097A1 describes a transport belt for a printer. DE102007014876A1 describes a transport system for CDs.

DETAILED DESCRIPTION

An object of the present disclosure includes increasing the positioning accuracy of dots in the printing to a recording medium in the form of a sheet or page or plate in an inkjet printer.

According to one aspect of the disclosure, an inkjet printer is described for printing to a recording medium in the form of a sheet or page or plate. In an exemplary embodiment, the printer includes at least one print head having one or more nozzles arranged in a nozzle plate. The printer can also include at least one movement means that is configured to move the print head and a recording medium in the form of a sheet or page or plate relative to one another in a transport direction in order to print dots of a print image onto the recording medium. In an exemplary embodiment, the movement means is designed to move the print head and the recording medium such that, as of an intake edge of the recording medium, the recording medium is arranged at least partially below the nozzle plate, wherein a clearance below the nozzle plate as of the intake edge corresponds to a reference clearance. In an exemplary embodiment, the movement means has an aerodynamic element that is designed to approximate the clearance below the nozzle plate to the reference clearance in a region that extends in the transport direction before the intake edge, starting from said intake edge, in particular to match the reference clearance.

According to a further aspect of the disclosure, an inkjet printer is described for printing to a recording medium in the form of a sheet or page or plate. The printer can include at least one print head having one or more nozzles arranged in a nozzle plate. Moreover, the printer includes at least one movement means that is configured to move the print head and a recording medium in the form of a sheet or page or plate relative to one another in a transport direction in order to print dots of a print image onto the recording medium. In an exemplary embodiment, the movement means may be configured such that an air flow produced by the relative motion between print head and recording medium is essentially free of eddies and/or turbulence in a clearance below the nozzle plate at an intake edge of the recording medium as of which the nozzle plate is positioned at least partially over the recording medium. Alternatively or additionally, the movement means may be designed such that the clearance below the nozzle plate remains essentially invariant in size at the intake edge. This may be achieved via use of a correspondingly designed aerodynamic element, for example.

FIG. 1ashows a printer100according to an exemplary embodiment. The printer100can be configured to print to a recording medium120in the form of a sheet or page or plate. The recording medium120may be produced from paper, paperboard, cardboard, metal, plastic, textiles, a combination thereof, and/or other materials that are suitable and can be printed to. The recording medium120is directed by a conveyor or other movement means130, along the transport direction1(represented by an arrow) through the print group140of the printer100. Successive recording media120thereby typically exhibit a defined distance123from one another (which is referred to as a conveying distance in this document). In an exemplary embodiment, the conveyor130includes, for example, a conveyor belt on which a recording medium120is placed.

In an exemplary embodiment, the print group140of the printer100includes two print bars102, where each print bar102may be used for printing with ink of a defined color (for example, black, cyan, magenta and/or yellow, and possibly Magnetic Ink Character Recognition (MICR) ink). Different print bars102may be used for printing with respective different inks. Furthermore, the print group140may include at least one fixer170that is configured to fix a print image printed onto the recording medium120. A fixer170may possibly be arranged after each print bar102in order to at least partially fix the print image applied by the respective print bar102.

A print bar102may include one or more print heads103that are possibly arranged next to one another in multiple rows in order to print the dots of different columns31,32of a print image onto the recording medium120. In the example depicted inFIG. 1a, a print bar102includes five print heads103, wherein each print head103prints the dots of one group of columns31,32of a print image onto the recording medium120.

In the embodiment depicted inFIG. 1a, each print head103of the print group140includes multiple nozzles21,22, wherein each nozzle21,22is configured to fire or push ink droplets onto the recording medium120. For example, a print head103of the print group140may include multiple thousands of effectively used nozzles21,22that are arranged along multiple rows transversal to the transport direction1of the recording medium120. The nozzles21,22in the individual rows may be arranged offset from one another. Dots of a line of a print image may be printed onto the recording medium120, transversal to the transport direction1(meaning along the width of the recording medium120), by means of the nozzles21,22of a print head103of the print group140.

In an exemplary embodiment, the printer100also includes a controller101(for example, an activation hardware) that is configured to activate the actuators of the individual nozzles21,22of the individual print heads103of the print group140in order to apply the print image onto the recording medium120depending on print data. In an exemplary embodiment, the controller101includes processor circuitry that is configured to activate the actuators and/or perform one or more other functions (e.g. control the overall operation of) the printer100.

The print group140of the printer100thus includes at least one print bar102having K nozzles21,22that may be activated with a specific line clock in order to print a line (transversal to the transport direction1of the recording medium120) with K pixels or K columns31,32of a print image onto the recording medium120. The nozzles21,22may be distributed among one or more print heads103. In the depicted example, the one or more print heads103are installed immobile or fixed in the printer100, and the recording medium120is directed past the stationary nozzles21,22with a defined transport velocity. Alternatively or additionally, the one or more print heads103may be moved across the recording medium120(for example transversal to the transport direction1of the recording medium120).

FIG. 1bshows a recording medium120that is directed past a print head103in the transport direction1by a conveyor130(for example on a conveyor belt). On the side facing toward the recording medium120, the print head103has a nozzle plate104on which are arranged the outputs of the one or more nozzles21,22of the print head103. Furthermore,FIG. 1billustrates the conveying distance123between two recording media120in direct succession.

As is clear fromFIG. 1b, upon transport of individual recording media120in the form of sheets or pages or plates, the clearance124below the nozzle plate104—meaning the distance between the nozzle plate104of a print head103and a solid medium situated thereunder (for example the conveyor belt or the recording medium120)—is not constant. Rather, the clearance124changes regularly by the magnitude of the thickness of the recording medium120. A recording medium120directed through the clearance124thus generates an eddy-like and/or turbulent and/or non-laminar air flow122that may have a disturbing influence on the positioning of the ink droplets. In particular, given a relatively thick recording medium120(for example given corrugated board), an eddy-like and/or turbulent air flow122may be generated at the intake edge121of the recording medium120, due to which ink droplets exiting at the nozzle plate104may be deflected. Such a (typically uncontrolled) deflection of the ink droplets may then lead to an inaccurate positioning of the corresponding dots on the recording medium120.

The extent of eddies or turbulence in an air flow122typically increases with the thickness of the recording medium120. In particular, significant air vortices may be generated at the intake edge121of a recording medium120if the thickness of the recording medium120is within the order of magnitude of the printing gap between the nozzle plate104and the recording medium120, or is greater than this. The printing gap corresponds to the clearance of nozzle plate104and top side of the recording medium120. The printing gap is typically constant (in order to enable a high print quality). The printing gap may, for example, have a reference gap measurement in the range of 1 mm. The thickness of the recording medium120be in the range from 1 mm to 9 mm (in particular given corrugated board).

In the present disclosure, an inkjet printer100is described for printing to a recording medium120in the form of a sheet or page or plate, in which inkjet printer100incorrect dot positionings on a recording medium120(in particular at the intake edge121of the recording medium120) may be reduced and/or avoided, and/or given which the air flow above the recording medium120in the form of a sheet or page or plate may be kept as laminar as possible.

In an exemplary embodiment, the printer100includes at least one print head103having one or more nozzles21,22arranged on a nozzle plate104. The outputs of the one or more nozzles21,22are thereby typically arranged at the nozzle plate104of the print head103. The one or more nozzles21,22may be activated depending on print data in order to print dots of a print image that is to be printed onto the recording medium120via the ejection of ink droplets.

In an exemplary embodiment, the printer100also includes at least one movement means130(also referred to as a conveyor in this document) that is configured to move the print head103and a recording medium120in the form of a sheet or page or plate in a transport direction1relative to one another in order to print dots of a print image onto the recording medium120. In particular, the recording medium120may be directed past the (stationary) print head104by the movement means130in order to print the dots of different lines of a print image bit by bit onto the recording medium120. If applicable, each nozzle21,22may thereby be associated with precisely one column31,32of a print image.

The movement means130may be configured to sequentially direct different recording media120in the form of a sheet or page or plate past the print head103in order to print to the different recording media120. Alternatively or additionally, the print head103may be sequentially directed past different recording media120in the form of a sheet or page or plate. Recording media120that are directly adjacent may thereby have a defined conveying distance123from one another. The different recording media120may possibly have different sizes and/or thicknesses.

The movement means130is designed to move the print head103and a recording medium120relative to one another such that the recording medium120is arranged at least partially below the nozzle plate104as of an intake edge121of said recording medium120. In other words, the print head103and the recording medium120may meet one another for the first time at the intake edge121of the recording medium120(after traversing the conveying distance123between a previously printed recording medium120and the recording medium120to be printed). The printing of a print image onto the recording medium120may thus begin at the intake edge121of the recording medium120and then continue sequentially up to an opposite discharge edge of the recording medium120.

As is depicted inFIG. 1b, a turbulent air flow122may form at the intake edge121of the recording medium120. The turbulent air flow may in particular form as a result of a clearance124below the nozzle plate104. The clearance124below the nozzle plate104may correspond to a defined (constant) reference clearance (for example in the range of 1 mm) (what is known as the printing gap) as of the intake edge121. On the other hand, the recording medium120has a defined thickness (for example in the range of 1 mm to 9 mm) so that the clearance124below the nozzle plate104is typically greater than the reference clearance by the thickness of the recording medium120in a region directly before the intake edge121. Such a variation of the clearance124may lead to turbulences, and thus to incorrect dot positionings.

In one or more exemplary embodiments, with reference toFIGS. 2a, 2b, and3, the movement means130may include an aerodynamic element205,305(also referred to as an aerodynamic component in this document) that is designed to converge the clearance124below the nozzle plate104to the reference clearance—in particular to match the reference clearance—starting from the intake edge121in the transport direction1before said intake edge121. For example, the aerodynamic element105,305may include a ramp that continuously reduces the clearance124below the nozzle plate104while approaching the intake edge121. Alternatively or additionally, the aerodynamic element205,305may have a flat surface, at least in regions, that travels parallel to the surface of the recording medium120(said surface facing toward the nozzle plate104) and that is preferably at the same height as the surface of the recording medium120. In particular, the surface of the aerodynamic element205,305, which surface faces toward the nozzle plate104, may be at the same height as the surface of the recording medium120at the intake edge121.

An inkjet printer100having at least one print head103is thus described in which an aerodynamic element205,305is placed before (in the transport direction1) a recording medium120in the form of a sheet or page or plate in order to reduce or avoid turbulences that may arise at the intake edge121of the recording medium120due to the relative motion between print head103and recording medium120. The print quality of the printer100may thus be increased (in particular upon printing to relatively thick recording media120).

FIGS. 2aand 2bshow an example of a carrier200that may be moved by the movement means or the conveyor130of a printer100in order to direct a recording medium120past a print head130. The movement means may, for example, have one or more conveyor rails in order to move a carrier200. The carrier200depicted inFIGS. 2aand 2bis designed as a sled for accommodation of a recording medium120.

In the example depicted inFIG. 2a, the floor of the carrier200has bores/holes204so that suction forces211(in particular a negative pressure) with which the recording medium120is held in the carrier200are produced by a portion of the air current122that travels below the carrier200. The bores204may thereby travel at an angle (counter to the transport direction1) in order to increase the suction forces211or the negative pressure. Moreover, a negative pressure may be actively generated via suitable means in order to keep the recording medium120firmly in the carrier200.

A carrier200is preferably shaped such that the top edge or top side of the recording medium120is on a plane with a high point of the carrier200. The high point, situated at the intake edge121of the recording medium120, thus represents an aerodynamic element205. Via the high point, it may be achieved that the relative air flow122above the recording medium120and the carrier200does not swirl and remains laminar to the greatest possible extent. The aerodynamic element205may be shaped such that possible turbulences in the air flow122that arise on a front side of the aerodynamic element205are directed to the underside of the recording medium120, and therefore do not negatively affect the printing process.

FIG. 2bshows a shortened variant of a carrier200(in particular of a sled). In this instance, only a forward part of the recording medium120is directed by the carrier200. Recording media120with different lengths may be directed in the transport direction1with the carrier200depicted inFIG. 2b.

The movement means130of a printer100may thus include a carrier200that is configured to accommodate the recording medium120at least in regions of the carrier200. In an exemplary embodiment, the carrier200includes a lowered region203to accommodate the recording medium120. Furthermore, the carrier200may have the aerodynamic element205in a front region201that is arranged before (with regard to the transport direction1) the lowered region203. Via the use of such a carrier200, recording media120may be reliably directed through the print group140of a printer100, as free of turbulence as is possible. In an exemplary embodiment, the carrier200is a sled. In another embodiment, the carrier200is a tray or other supporting means, support, or support member.

In an exemplary embodiment, the top side of the aerodynamic element205, which top side faces toward the nozzle plate104, is level with the top side of the recording medium120if the recording medium120is arranged in the lowered region203of the carrier200. The top side of the aerodynamic element205may thereby travel over a defined minimum distance at the same level as the top side of the recording medium120. The minimum distance is thereby sufficiently large in order to ensure that turbulences of the air flow122that arise at a front side (in relation to the transport direction1) of the aerodynamic element205have significantly decayed at the intake edge121of the recording medium120. In an exemplary embodiment, for this purpose, the minimum distance is dependent on the velocity of the relative motion between the print head103and the recording medium120. For example, the minimum distance may be extended with increasing velocity.

In an exemplary embodiment, alternatively or additionally, the aerodynamic element205of the carrier200is configured such that possible turbulences of the air flow122that are generated on the front side of the aerodynamic element205are directed toward the underside of the carrier200and/or of the recording medium.

In an exemplary embodiment, the lowered region203of the carrier200forms a trough to accommodate the recording medium120. A reliable transport of a recording medium120may thus be produced. Alternatively, the lowered region203of the carrier200may be designed to accommodate only a partial region of the recording medium120, starting from the intake edge121. Recording media with different lengths may thus be flexibly printed to within a printer100.

In an exemplary embodiment, the carrier200includes an additional aerodynamic element in a rear region202arranged after (with regard to the transport direction1) the lowered region203. An aerodynamic element may thus also be provided at the discharge edge of a recording medium120. Turbulences of the air flow122may thus be further reduced.

In an exemplary embodiment, the movement means130(e.g. carrier200) includes a floor that is configured to at least partially bear/support the recording medium120. In an exemplary embodiment, the aerodynamic element205is configured such that the air flow122produced by the relative motion between the print head103and the recording medium120travels at least in part below the floor of the carrier200. In an exemplary embodiment, the floor is configured such that a suction force211on the recording medium120toward the floor is produced due to the air flow122traveling below the floor (for example, the floor may have bores204that are configured to generate the suction force211). Advantageously, the recording medium120is reliably directed past a print head103. In particular, the undulation of a recording medium120upon printing a print image may be reduced via the suction force211. The print quality of a printer100may thus be further reduced. If applicable, the suction force211may be actively increased (for example by means of a negative pressure pump) in order to further reduce the undulation of a recording medium120.

In an exemplary embodiment, as shown with reference toFIG. 3, the movement means130is configured as a conveyor belt. The conveyor belt or transport belt shown inFIG. 3has a fill template to receive recording media120. The gaps between the recording media120in the form of a sheet or page or plate are thereby filled by an aerodynamic element305. In an exemplary embodiment, the aerodynamic element305is a block with the thickness of the recording medium120, so that the clearance124below the nozzle plate104always remains constant at the reference clearance. A laminar, eddy-free air flow122may thus be particularly reliably generated. In an alternative embodiment, the block has a thickness that is greater than the recording medium120.

In an exemplary embodiment, the movement means130includes a conveyor belt that is designed to carry one or more recording media120and direct them past a print head103. The aerodynamic element305may then be arranged on the conveyor belt. In particular, as depicted inFIG. 3, the conveyor belt may have a plurality of aerodynamic elements305that are arranged spaced apart from one another on the conveyor belt, such that a fill template is formed for receiving at least one recording medium120(in particular for receiving a corresponding plurality of recording media120). The fill template may be designed such that the clearance124below the nozzle plate104remains essentially constant in the printing operation. A reliable and precise dot positioning may thus be produced.

In an exemplary embodiment, the aerodynamic element205,305is arranged in a region between two successive recording media120. In an exemplary embodiment, the aerodynamic element205,305thereby has a flat surface on the top side facing toward the nozzle plate104. The printer100may be configured to print a regeneration print image and/or test print image (for example refresh lines) for regeneration and/or monitoring of the one or more nozzles21,22onto the surface of the aerodynamic element205,305, using the print head103. On the other hand, print data-dependent or user data-dependent print images may be printed onto the recording media120. The aerodynamic elements205,305that are arranged between the recording media120may thus be used to implement regeneration and/or test measures for the print head103. The spoilage generated by the printer100may thus be reduced or avoided. Furthermore, the excising of regeneration and/or test print images may thus be avoided.

Refresh lines and/or control elements, for example an NFD (Nozzle Failure Detection) chart, may be printed on the front sled web (fromFIGS. 2aand 2b) and/or onto the fill template (fromFIG. 3), for example. These may be detected by a sensor350of the printer100. The sensor350may, for example, include an inline scanner and/or an image camera. The sensor data of the sensor350may be evaluated in order to increase the reliability and/or the print quality of the printer100. If applicable, multiple layers of print images may thereby be printed onto the surface of an aerodynamic element205,305. The detected sensor data may be stored in a memory to document the print quality. A storage of physical test print images may thus be avoided.

In an exemplary embodiment, the surface of the aerodynamic element205,305(for example a coating on the surface of the aerodynamic element205,305) is configured such that the surface exhibits a behavior with regard to a flow of ink that is identical, or at least similar, to that of a recording medium120. On the other hand, the surface of the aerodynamic element205,305may have an adhesion for ink that is reduced or increased relative to the recording medium120.

In an exemplary embodiment, as illustrated inFIG. 3, the printer100includes a cleaner310that is configured to clean an aerodynamic element205,305. For this purpose, the cleaner310may have a wiper311. Given use of a conveyor belt, the cleaning of an aerodynamic element205,305may take place at every revolution of the conveyor belt. A repeated printing to the aerodynamic element205,305may be enabled via the regular cleaning of the surface of an aerodynamic element205,305.

In this document, an inkjet printer100for printing to a recording medium120in the form of a sheet or page or plate is thus described. The printer100includes at least one print head103having one or more nozzles21,22arranged on a nozzle plate. Moreover, the printer100includes at least one movement means130that is configured to move the print head103and a recording medium120in the form of a sheet or page or plate relative to one another in a transport direction1in order to print dots of a print image onto the recording medium120(possibly line by line).

In an exemplary embodiment, the movement means130is configured such that the air flow122produced in the clearance124below the nozzle plate104due to the relative motion between print head103and recording medium120is essentially free of eddies and/or turbulence at the intake edge121of the recording medium120. In an exemplary embodiment, alternatively or additionally, the movement means103is configured such that the clearance124below the nozzle plate104remains essentially unchanged in size at the intake edge121.

Suction holes may be arranged in the conveyor130(in particular in a conveyor belt) for the recording medium120, in which suction holes a negative pressure is developed in order to pull the recording medium120onto the conveyor belt (and thus to reliably move said recording medium120through the printer100). These suction holes are for the most part not covered in the gaps between two recording media120. Due to the negative pressure, air is then drawn downward through the suction holes so that an additional air current arises (that may travel in and/or counter to the transport direction1). This air current may have a negative effect on the droplet positioning, in particular at the intake edge121of a recording medium120. In particular, turbulences may be produced at the intake edge121of a recording medium120due to this air current. The negative effects of such an air current are reduced by the measures described in this document (in particular given use of a carrier200) or completely remedied (in particular given use of a fill template).

CONCLUSION

For the purposes of this discussion, the term “processor circuitry” shall be understood to be circuit(s), processor(s), logic, or a combination thereof. A circuit includes an analog circuit, a digital circuit, state machine logic, other structural electronic hardware, or a combination thereof. A processor includes a microprocessor, a digital signal processor (DSP), central processing unit (CPU), application-specific instruction set processor (ASIP), graphics and/or image processor, multi-core processor, or other hardware processor. The processor may be “hard-coded” with instructions to perform corresponding function(s) according to aspects described herein. Alternatively, the processor may access an internal and/or external memory to retrieve instructions stored in the memory, which when executed by the processor, perform the corresponding function(s) associated with the processor, and/or one or more functions and/or operations related to the operation of a component having the processor included therein.

REFERENCE LIST