Patent Publication Number: US-9884496-B1

Title: System for detecting contamination on decurler rollers in aqueous ink printers

Description:
TECHNICAL FIELD 
     This disclosure relates generally to inkjet printers that eject aqueous ink directly onto media and, more particularly, to maintaining a decurler within such a printer. 
     BACKGROUND 
     In general, inkjet printers include at least one printhead having a plurality of inkjets that eject drops 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 is 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 pull sheets from a media supply and propel them through the printer to an output tray. 
     In inkjet printers that eject ink directly onto sheets, media deformation occurs more frequently in sheet printers than continuous web printers since a web is generally taut as it passes through the printer. Sheets, however, can absorb moisture from the inks ejected onto the sheets and this moisture can cause curling or other deformations in the media sheets. These deformations are particularly troublesome in inkjet printers that employ water-based or solvent-based inks in which pigments or other colorants are suspended or are in solution with water or another solvent. The water and solvents in the inks can change the physical properties of the sheets in ways that degrade the quality of the images produced on the media sheets. In these aqueous ink printers, an unacceptable level of curl can be induced on the printed sheet by the image, particularly when a solid stripe of ink is printed on the leading edge of a sheet. To address the curl in a sheet, a device known as a decurler is used to induce curl in the sheet in the opposite direction to counteract the curl induced by the printed image on the sheet. This function is important, particularly when the printed sheet is delivered to an in-line stacker, which can only handle sheets having curl no greater than a predetermined radius. 
     A decurler in an aqueous inkjet printer has an indent roller and an elastomeric roller. An actuator operatively connected to the elastomeric roller pushes the roller into the indent roller as the rotation of the two rollers passes a sheet between them. This action induces curl into the sheet in the opposite direction of the curl induced by the ink image on the sheet to reduce the curl in the sheet to a level that enables the stacker to handle the sheet. Because the indent roller contacts the ink on the freshly printed side of the media, some of the ink can adhere to the roller. The ink adhering to the indent shaft can build to levels that adversely impact the ability of the decurler to induce opposite curl in the media sheets and may wrinkle the sheet in the decurler. Generally, wrinkled sheets are not acceptable to printer users. The appearance of wrinkled sheets in the output tray requires printer down time for maintenance of the decurler to remove the ink from the indent roller and the discarding of the wrinkled sheets. Detection of ink adherence to the indent roller would enable maintenance to be performed on the indent roller before the printed sheets begin to wrinkle and be discarded. 
     SUMMARY 
     A decurler for use in an aqueous ink printer enables adhering ink on an indent roller in the decurler to be detected before enough ink has accumulated to cause wrinkling. The decurler includes an indent roller having a first end and a second end, an elastomeric roller having a first end and a second end, the elastomeric roller and indent roller being parallel to one another and the elastomeric roller being configured to move to form a nip with the indent roller selectively to enable media sheets to pass through the nip and induce a curl in the media sheets that is opposite to a curl induced in the media sheets by aqueous ink ejected onto the media sheets prior to entry into the nip between the indent roller and the elastomeric roller, a reflective sensor having a light emitter that is oriented to direct light onto a surface of the indent roller of the decurler and a light receiver that is oriented to receive specular reflections of the light directed onto the surface of the indent roller and to generate an electrical signal indicative of an amount of specular light reflection received by the light receiver from the surface of the indent roller, and a controller operatively connected to the reflective sensor to receive the electrical signal generated by the light receiver of the reflective sensor. The controller is configured to compare a magnitude of the electrical signal to a predetermined threshold and store an indication for maintenance of the indent roller in a memory in response to the magnitude of the electrical signal being less than the predetermined threshold. 
     A printer that enables adhering ink on an indent roller in a decurler within the printer to be detected before enough ink has accumulated to cause wrinkling. The printer includes a media feeding system configured to remove media sheets from a media sheet receptacle, a media transport system configured to move media sheets through the aqueous inkjet printer, at least one printhead configured to eject drops of aqueous ink onto media sheets as the media transport system moves the media sheets past the at least one printhead, a decurler having an indent roller and an elastomeric roller, the elastomeric roller being configured to move and form a nip with the indent roller in the decurler to enable media sheets to pass through the nip and induce a curl in the media sheets that is opposite to a curl induced in the media sheets by aqueous ink ejected by the at least one printhead onto the media sheets prior to entry into the decurler, a reflective sensor having a light emitter that is oriented to direct light onto a surface of the indent roller of the decurler and a light receiver that is oriented to receive specular reflections of the light directed onto the surface of the indent roller and to generate an electrical signal indicative of an amount of specular light reflection received by the light receiver from the surface of the indent roller, and a controller operatively connected to the reflective sensor to receive the electrical signal generated by the light receiver of the reflective sensor. The controller is configured to compare a magnitude of the electrical signal to a predetermined threshold and store an indication for maintenance of the indent roller in a memory in response to the magnitude of the electrical signal being less than the predetermined threshold. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing aspects and other features of an apparatus that detects ink accumulation on an indent roller in a decurler are explained in the following description, taken in connection with the accompanying drawings. 
         FIG. 1  is diagram of an inkjet printer that compensates for media wrinkle prior to the media reaching a stacker apparatus. 
         FIGS. 2A and 2B  are frontal views of a decurler and an ink contamination detector. 
         FIG. 3  is a view of the indent roller of the decurler shown in  FIG. 2A  and  FIG. 2B  through a frame. 
     
    
    
     DETAILED DESCRIPTION 
     For a general understanding of the environment for the indent roller ink contamination detector as well as the details for the detector, reference is made to the drawings. In the drawings, like reference numerals designate like elements. As used in this document, 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 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 identified in this document 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 solvent in the ink. The term ‘sheet’ in this document refers to any relatively flexible planar member made of paper, plastic, media, or other printable substrate, whether precut or initially web fed. 
     The term “printhead” as used in this document refers to a component in the printer that is configured with inkjet ejectors to eject liquid ink drops onto a surface of a sheet. A typical printhead includes a plurality of inkjet ejectors that eject ink drops of one or more ink colors onto the sheet 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. A sheet 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 sheet. As used in this document, the term “aqueous ink” includes liquid inks in which colorant is in a solution, suspension or dispersion within a liquid that includes water and perhaps one or more liquid solvents. The terms “liquid solvent” or more simply “solvent” are used broadly to include liquids that dissolve colorants into a solution or that hold particles of colorant in a suspension or dispersion without dissolving the colorant. 
       FIG. 1  shows a configuration of an inkjet printer  100  that includes a controller  104 , one or more actuators  108 , a printhead assembly  112 , a transport system  120 , and a media feeding system  124 . The controller  104  is operatively connected to the actuators  108 , the printhead assembly  112 , and the media feeding system  124 . The controller  104  is configured to receive image data from an image data source and generate firing signals for the operation of the printheads in the printhead assembly  112  for the formation of ink images on media sheets as the sheets pass the printheads. The media sheets are stored in the media feeding system  124  and the controller operates the media feeding system to retrieve media sheets from a storage receptacle for the sheets and feed the sheets into the transport system  120 . The controller operates the actuators  108  to drive rollers within the transport system  120  to move the media sheets along a path in the transport system that moves the sheets past printhead assembly  112 . After printing, the sheets pass through decurler  130 , which induces a curl into the sheets that is opposite to the curl induced in the sheets by the absorption of water. A second decurler  140  is optionally provided for further leveling of the sheets. When the sheets reach position  136 , they are either ejected from the transport system into a conventional stacker  150  for retrieval or they are diverted to the lower path of the transport system. The lower path is configured for flipping the sheets over so the unprinted side of the sheets can be returned to the path that carries the sheets past the printhead assembly  112  for printing. If both sides of a sheet are printed, then when the sheets reach position  136  they are directed into stacker  150  for retrieval. 
     Decurler  130  includes an ink contamination sensor  134  that generates a signal indicative of the presence of ink or other adherents to the surface of the indent roller in the decurler  130 . The structure of the sensor  134  is described in more detail below. Although not shown, if the optional decurler  140  is provided, it can also be configured with an ink contamination sensor  134  that generates a signal indicative of the surface of the indent roller in the decurler  140 . The sensor  134  may not be necessary, however, for decurler  140  since the recently deposited ink on the media sheets is more likely to adhere to the indent roller of decurler  130  rather than the indent roller of the decurler  140 . 
     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 printhead controller in the printhead assembly  112  for the generation of firing signals or the controller  104  can generate the firing signals and download them to the 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 sheets through the printer  100  and the operation of the inkjet ejectors in the printheads of the printhead assembly  112 . 
     Turning to  FIGS. 2A-2B , an indent roller  12  is mounted on a shaft  30  and is rotatable around a longitudinal axis of the shaft. As shown, the shaft  30  alone performs as an axle for the indent roller  12 , but embodiments are not so limited and the shaft  30  may be mounted about a separate axle. The shaft  30  may be driven by an independent motor (not shown). An opposing elastomeric roller  16  is mounted on a shaft  18  and is likewise rotatable with the axle  18  around a longitudinal axis of the shaft  18 . Elastomeric roller  16  and shaft  18  are further optionally driven by an actuator  108 , such as a motor, instead of or in addition to a rotational force driving the shaft  30  of the indent roller  12 . Likewise, shaft  30  may be driven by a separate motor instead of or in addition to the rotational force driving the shaft  18  of roller  16 . Elongated slots or holes with bearings are provided in frame  50  to accommodate the ends of shafts  30 ,  18 , and  22 . For example, the ends of shaft  18  require a slot to accommodate the translation of the shaft and the elastomeric roller  16 , as described in more detail below, while the ends of shaft  30  fit within bearings mounted in circular holes in the frame  50 . Similarly, shaft  22  fits within a bearing mounted in a circular hole in frame  50  to enable actuator  108  to rotate the shaft and the cams mounted to the shaft. 
     The shaft  18  is mounted to translate in a direction transverse to the longitudinal axis of the shaft  30  to bring a surface  34  the elastomeric roller  16  into engagement with the indent roller  12 . In one embodiment, one or more cams  20 A,  20 B may be mounted on a shaft  22  and may rotate with the shaft  22 . The shaft  22  is in turn driven by an actuator  108 , which can be a stepper motor as shown in the figure, to position and hold the cams  20 A,  20 B, which act on the shaft  18  through cam followers  26 A,  26 B, which are mounted about the shaft  18  as collars on the shaft  18 . Alternatively or additionally, the actuator  108  may comprise a servo motor, a hybrid motor, or a fluid-powered motor. Optionally the cams may be moved linearly rather than or in addition to being moved rotationally. Within the range of the transverse motion of the elastomeric roller  16 , space  28 , as shown in  FIG. 2A , admits a media sheet. The elastomeric roller  16  is moved to close space  28  so the indent roller  12  presses against a surface of and indents the body of the elastomeric roller  16  to induce opposite curl in the media sheet moved through the nip formed by the two rollers. 
     In more detail, the sensor  134  of  FIGS. 2A and 2B  includes a reflective sensor  204  that has been mounted on a shaft  208  for bi-directional translation along the shaft. An actuator  108  is operatively connected to the sensor  204  to urge the sensor along the shaft bidirectionally. The controller  104  is operatively connected to the sensor  204  to receive the signal generated from the sensor. The controller  104  is configured to analyze the signal generated by the sensor  134  to detect ink contamination on the indent roller of the decurler. The reflective sensor includes a light emitter that directs light at the indent roller and a light receiver that generates a signal indicative of the light reflected from the roller surface into the receiver of the sensor. The sensor should be positioned to achieve an optimal focal length from the roller surface to the sensor. The sensor  204  can be configured in a number of ways. In the embodiment shown in  FIG. 2A  and  FIG. 2B , the sensor  204  has a predetermined number of light sources and receivers that is less than the number required to extend the length of the indent roller. That is, the length of the sensor  204  is less than the length of the roller  12 . Therefore, the sensor  204  is mounted to shaft  208  so it can move from one end of the shaft to the other to illuminate and receive light reflected from the surface of the roller  12 . In this embodiment, the controller  104  synchronizes sensor position with a corresponding position on the indent roller. Alternatively, the number of light sources and receivers can be increased to a number that when positioned together in a linear array they extend the entire length of the indent roller. In this embodiment, the controller  104  correlates a position index for each receiver with a position on the indent roller. In this embodiment, the sensor can include a lens that extends the length of the indent roller and the lens focuses light to a linear array of receivers, such as a CCD array, in the sensor  204 . 
     In both embodiments, a light-emitting element emits light toward the surface of the indent roller and a light-receiving element receives the reflected light from the surface of the roller. The receiver generates an electrical signal having a magnitude that corresponds to the amount of light received. Thus, the electrical signal has a greater magnitude when the light is reflected from a relatively bare indent roller. When the light strikes ink on the indent roller it is absorbed or scattered and does not reflect into the receiver. Consequently, the electrical signal has a lower magnitude. The controller  104  compares the signals received from the sensor  204  to a predetermined threshold to determine whether the signals indicate a level of ink has adhered to the indent roller that requires maintenance. These indications of maintenance are stored in a memory operatively connected to the controller and once the number of indications exceeds a predetermined threshold, the controller generates a signal for activating a contamination indicator  54 . The number of indications can be the number of receivers in the sensor  204  generating a signal indicative of maintenance, the number of positions at which the sensor  204  generates a signal indicative of maintenance as it moves along the shaft  208 , or the number of times that the sensor  204  generates the signal indicative of maintenance. The activation of the contamination indicator  54  includes activating an annunciator, an indicator light, or a text message on a user display, which informs an operator of the system that maintenance is required in the decurler. 
     A view of frame  50  from the perspective of the sensor  204  is shown in  FIG. 3 . The frame  50  has an upper planar member  60  that has an array of elongated openings  64  that extend linearly across the member. The planar member  60  is parallel to the indent roller  12 . The controller  104  operates the actuator  108  to move the sensor  204  along the shaft  208  so the light emitters in the sensor  204  can direct light through the holes  64  and onto the indent roller  12 . The specular light reflected by the surface of the roller  12  returns through the hole through which the light was emitted and is received by a receiver in the sensor. The receiver generates a signal indicative of the amount of specular light received and the controller compares that signal to a predetermined threshold to determine whether contamination of that portion of the indent roller has reached a level indicative of maintenance. Additionally, the controller  104  operates the actuator  108  to move the sensor  204  back and forth along the shaft  208  to ensure that the sensor directs light onto each sector of the indent roller over the course of several traversals of the shaft so contamination on each portion of the circumference of the indent roller  12  can be detected. 
     Prior to commencing operation of the sensor for indent roller purposes, the controller  104  operates the actuator  108  to move the sensor along shaft  208  while the sensor is operating to detect the signal magnitude differences between reflections received from the indent roller and those received from the solid portions of the frame between the openings  64 . The controller  104  uses these signals to identify the positions along the shaft  208  that are over the frame  50 . This positional data is stored and used during the monitoring of the indent roller  12  so the controller can ignore the signals corresponding to the solid portions of the frame for purposes of detecting contamination of the indent roller  12 . The configuration of holes in the frame favors the use of a sensor that moves bidirectionally along a shaft because a continuous linear array of light emitters and receivers for the sensor  204  in this embodiment would mean some of the emitters and receivers would always be opposite solid portions of the frame. Thus, the moving sensor is more efficient and cost effective. 
     It will be appreciated that variations of the above-disclosed apparatus and other features, and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art, which are also intended to be encompassed by the following claims.