Patent Application
20160089880
The device disclosed in this document relates to inkjet printers that eject ink directly onto media and, more particularly, to inkjet printers that eject aqueous ink.
In general, inkjet printing machines or printers include at least one printhead that ejects drops or jets of liquid ink onto a recording or image forming surface. In some inkjet printers, the printhead ejects ink directly onto the surface of media as the media passes the printhead. The media can be in the form of a continuous web or in the form of sheets. In continuous web printers, the media are pulled from a supply roll by actuator-driven rollers. As the web moves through the printer it passes around rollers to which tension is applied to keep the web taut as it passes through the printer to a take-up roll. In sheet printers, actuator-driven rollers are positioned against one another to form nips and these nips urge the sheets through the printer.
Image quality in an inkjet printer relies on the flatness of the media/substrate that receives the ink drops ejected by the inkjets in a printhead during the printing process. Currently, inkjet systems rely on mechanical devices to hold the media/substrate flat to ensure a uniform dot placement. In these systems, the printhead must rely on the paper handling capability of the mechanical system to maintain media/substrate flatness. In a continuous web printing system, movable rollers are operated to maintain tension in the web to help maintain flatness in the web as it passes the printheads in the printer. In cut sheet systems, vacuum platens or similar structures hold a sheet flat as the sheet passes one or more printheads. Despite these systems, the media/substrate presents, at least on occasion, an uneven surface profile to the printheads. For example, even if the substrate is held flat by tension or a vacuum, textured media presents uneven surfaces for printing. Unfortunately, these changes in the profile of the media/substrate from the side view lead to a sloped surface that affects dot to dot placement which is directly proportional to that slope.
For example,
A printer that compensates for slope in media being printed has been developed. The printer includes a transport path configured to convey media through the printer in a process direction, at least one printhead positioned opposite the transport path, the at least one printhead being configured to eject drops of ink onto the media conveyed by the transport path past the at least one printhead in the process direction, a sensor positioned adjacent the transport path, the sensor being configured to generate a signal indicating a slope in the media being conveyed by the transport path before the media passes the at least one printhead, and a controller operatively connected to the at least one printhead and the sensor, the controller being configured to operate the at least one printhead to vary a volume of ink ejected by at least one inkjet in the at least one printhead with reference to the signal indicating the slope of the media.
A method of operating a printer helps compensate for slope in media being printed. The method includes conveying media along a transport path through the printer in a process direction, ejecting drops of ink from at least one printhead onto the media conveyed by the transport path past the at least one printhead in the process direction, generating a signal with a sensor that indicates a slope in the media being conveyed by the transport path before the media passes the at least one printhead, and operating with a controller the at least one printhead to vary a volume of ink ejected by at least one inkjet in the at least one printhead with reference to the signal from the sensor indicating the slope of the media.
The foregoing aspects and other features of a printer that compensates for slope in media being printed are explained in the following description, taken in connection with the accompanying drawings.
For a general understanding of the environment for the device disclosed herein as well as the details for the device, reference is made to the drawings. In the drawings, like reference numerals designate like elements. As used herein, the terms “printer,” “printing device,” or “imaging device” generally refer to a device that produces an image on print media with liquid ink and may encompass any such apparatus, such as a digital copier, bookmaking machine, facsimile machine, multi-function machine, or the like, which generates printed images for any purpose. Image data generally include information in electronic form that a controller renders and uses to operate the inkjet ejectors in printheads in the printer to compensate for moisture in ink and to form an ink image on media sheets. These data can include text, graphics, pictures, and the like. The operation of producing images with colorants on print media, for example, graphics, text, photographs, and the like, is generally referred to herein as printing or marking. Aqueous inkjet printers are printers that use inks having a high percentage of water relative to the amount of colorant and/or solvent in the ink.
The term “printhead” as used herein refers to a component in the printer that is configured with inkjet ejectors to eject water-containing drops or ink drops onto an image receiving surface. A typical printhead includes a plurality of inkjet ejectors that eject ink drops of one or more ink colors onto the image receiving surface in response to firing signals that operate actuators in the inkjet ejectors. The inkjets are arranged in an array of one or more rows and columns. In some embodiments, the inkjets are arranged in staggered diagonal rows across a face of the printhead. Various printer embodiments include one or more printheads that form ink images on an image receiving surface. Some printer embodiments include a plurality of printheads arranged in a print zone. An image receiving surface, such as an intermediate imaging surface, moves past the printheads in a process direction through the print zone. The inkjets in the printheads eject ink drops in rows in a cross-process direction, which is perpendicular to the process direction across the image receiving surface. As used in this document, the term “aqueous ink” includes liquid inks in which colorant is in a solution, suspension or dispersion with a liquid solvent that includes water and/or one or more liquid solvents. The terms “liquid solvent” or more simply “solvent” are used broadly to include compounds that may dissolve colorants into a solution, or that may be a liquid that holds particles of colorant in a suspension or dispersion without dissolving the colorant.
As used herein, the term “process direction” refers to movement along the path in the transport subsystem that moves the sheets past the media slope detecting subsystem 116 and the printhead assembly 112 and “cross-process direction” refers to a direction orthogonal to the process direction axis in the plane of the path past those two subsystems. To operate the inkjet ejectors in the printheads of the printhead assembly 112, the controller 104 receives a file of image data of an image to be produced on the media sheet. This image can include text alone, graphics alone, or a combination of text and graphics. These image data can be provided by a scanner or by an application program in a known manner. The controller 104 generates color separations and renders the color separations to produce halftone data. These halftone data can be provided to a processor in the printhead assembly 112 for the generation of firing signals or the controller can generate the firing signals and download them to a printhead controller in the assembly 112. The printhead assembly then operates the inkjet ejectors in the printheads of the printhead assembly 112 to eject ink drops onto the media sheet as the sheet passes the printheads to form an ink image on the sheet. Additionally, the controller 104 generates signals to operate one or more of the actuators 108 to coordinate the movement of media sheet and the operation of the inkjet ejectors in the printheads of the printhead assembly 112.
To explain the principles for addressing slope in media sheets with the media slope detecting subsystem 116, reference is made to
In one embodiment of the media slope detecting subsystem 116, a light source directs light across the surface of the media as the media passes the subsystem 116. Subsystem 116 also includes a light receiver positioned on a side of the media that is opposite the side on which the light source is positioned. Thus, the amount of light incident on the light receiver corresponds to the path across the media sheet. If the media slopes in the process direction, the raised portion diminishes the amount of light received at the receiver and the amplitude of the signal generated by the receiver is correspondingly reduced. Using empirical data, the amount of light received at the receiver can be correlated to media slopes and these data can be stored in a memory operatively connected to the controller 104 to enable the controller to compare the signals generated by the light receiver to these data and determine a slope of the media. In response to the media exceeding a minimal threshold, the controller modulates the driving signals to the inkjets in the printhead ejecting ink into the slope areas to increase the volume of the ink drops ejected into those areas. The amount of the volumetric increase in the ink drop volumes corresponding to the angle of the slope detected by subsystem 116. Printheads that can be operated to eject variable volumes of ink drops include the 300 dpi KJ4B printheads made by FUJIFILM Dimatix, Inc. of Santa Clara, Calif. and the 600 dpi printheads made by Kyocera of Kyoto, Japan. Alternatively, the media detecting system can include a mechanical arm that extends across the media sheet passing along the transport path that is raised by a slope surface as it contacts the arm. A transducer operatively connected to the arm generates an electrical signal corresponding to the distance the arm is raised and the controller can compare this signal to the data stored in a memory connected to the controller to determine an amount of slope in the media.
A method of operating a printer that mitigates banding effects in ink images arising from a lack of flatness in media sheets is shown in
At the beginning of a media sheet printing operation, the controller 104 receives a data file of image data for the image (block 404). The controller 104 generates color separation data and renders the data to produce halftone data that are used to operate the inkjets in the printheads (block 408). Printing the image corresponding to the rendered data then commences (block 412). As the media passes by the media slope detection subsystem 116, the controller receives a signal indicative of the slope of the media and compares the signal to a minimal slope threshold (block 420). If the controller determines an increase in ink drop volume is needed to compensate for the slope, the ink drop volume is adjusted (block 424). The controller then modifies the firing signal to the inkjets ejecting ink into the positively sloped and negatively sloped areas, while leaving the firing signals for the relatively flat areas alone (block 428). As the inkjets eject the higher volume ink drops in the sloped areas, the gaps between adjacent rows of ink drops is reduced and image quality is maintained.
An alternative embodiment of the method for compensating for media slope in media is shown in
It will be appreciated that variants of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems, applications or methods. Various presently unforeseen or unanticipated alternatives, modifications, variations or improvements may be subsequently made by those skilled in the art that are also intended to be encompassed by the following claims.
