Patent Publication Number: US-2011064424-A1

Title: Dynamic media thickness, curl sensing system

Description:
BACKGROUND AND SUMMARY 
     Embodiments herein generally relate to printing methods and devices and more particularly relate to systems that accommodate media curling and different media thicknesses. 
     Printing systems such as electro-photographic, inkjet, and ultra-violet (UV) curable systems, have higher quality results if the thickness and curl of the media being used is known and adjusted for. Current systems rely on users to input the type of paper being used via the “user interface”. This approach only tells the printing apparatus the approximate weight of the paper and not its actual thickness and is subject to wrong input. Conventional decurling adjustments are also based on a combination of user inputs and some sensor data such as temperature, humidity, double sided printing mode, etc. Current systems do not measure actual curl, but estimate what the curl is likely to be based on setup parameters. In addition to an apparatus automatically picking a decurler setting or curler setting, some machines provide an additional manual adjustment that usually cannot be made on the fly. Complicating the problem for these systems is the uncertain nature of paper in its curl behavior. 
     For example, U.S. Pat. No. 5,519,481 (incorporated herein by reference) describes an adaptive decurler for selective decurling localized image areas, where a segmented decurling device forms a drive nip with an elastically deformable surfaced roll. A plurality of sensors are provided to determine the basis weight of the copy sheet, the density of the image being transferred to the copy sheet and fused thereon, the relative humidity of the machine environment, the process speed of the print engine, and any other relevant parameters. Signals indicative of these parameters are generated and sent to the machine controller which processes these signals to determine the degree of curl expected in a sheet. Based on the degree of curl for each sheet section corresponding to a decurler segment, the decurler segment is actuated to a setting which should provide the proper amount of mechanical decurling force. Each segment is activated only for the duration deemed necessary to decurl the imaged sheet portion corresponding thereto. 
     While conventional systems estimate sheet curl, the present embodiments comprise a method and a system of rollers, sensors, and processors used to determine actual paper curl and paper thickness. Once the actual paper curl and thickness is determined, such information is used for adjusting printing parameters. The system uses rollers to hold the paper precisely at a fixed distance while a displacement sensor measures edge curl followed by paper thickness. The resulting data is then processed to predict the overall curl of the paper. The system uses the thickness data to more accurately determine curl based on methodologies and/or look up tables. Also, the setup can involve a calibration mode to accurately measure paper thickness. 
     More specifically, embodiments herein provide an apparatus that has a media path that transports a media sheet; a first nip (comprising opposing rollers) that moves the media sheet in a processing direction; a second nip (also comprising opposing rollers) that is positioned within the media path to receive the media sheet from the first nip; and a third nip (again comprising opposing rollers) that is positioned within the media path to receive the media sheet from the second nip. A sensor is positioned between the second nip and the third nip. The sensor senses the position of the media sheet relative to the sensor. 
     A processor that is operatively connected to the sensor automatically calculates the amount of curl (up or down) the media sheet contains based on the difference between a predetermined position (determined using a calibration sheet) and the position of the leading edge of the media sheet (relative to the sensor) as the leading edge of the media sheet passes between the second nip and the third nip. 
     In addition, the processor can automatically calculate the thickness of the media sheet based on the difference between the predetermined position and the position of the media sheet (relative to the sensor) as the media sheet passes between the second nip and the third nip. 
     The opposing rollers within the first nip, the second nip, and the third nip each comprise a fixed-position roller and a floating roller. The floating roller is positioned to contact a first side (the top side) of the media sheet and the sensor is also positioned to sense the first side of the media sheet. The opposing rollers of the second nip rotate faster than the opposing rollers of the first nip, and the opposing rollers of the third nip rotate faster than the opposing rollers of the second nip to keep the media sheet taunt during the curl and thickness measurements. 
     The apparatus can also include a decurler positioned within the media path. The processor automatically alters settings of the decurler based on the actual amount of curl the media sheet contains. Further, the apparatus can contain a marking engine positioned within the media path. Again, the processor automatically alters settings of the marking engine based on the amount of curl the media sheet contains and the thickness of the media sheet. The marking engine can comprise any type of marking engine, such as an electro-photographic printing engine, an inkjet printing engine, an ultra-violet curable printing engine, etc. 
     Method embodiments are also described below. In such embodiments, the method moves the media sheet in the processing direction of the media path from the first nip to the second nip and moves the media sheet in the processing direction of the media path from the second nip to the third nip. The method senses, using the sensor positioned between the second nip and the third nip, the position of the media sheet relative to the sensor. The method automatically calculates the amount of curl the media sheet contains based on the difference between the predetermined position and the position of the leading edge of the media sheet (relative to the sensor) as the leading edge of the media sheet passes between the second nip and the third nip, using the processor. Further, the method automatically calculates the thickness of the media sheet based on the difference between the predetermined position and the position of the media sheet (relative to the sensor) as the media sheet passes between the second nip and the third nip, using the processor. 
     The method can also automatically alter the settings of the decurler positioned within the media path based on the amount of the curl the media sheet contains using the processor. Also, the method can automatically alter settings of the marking engine positioned within the media path based on the amount of curl the media sheet contains and the thickness of the media sheet using the processor. 
     These and other features are described in, or are apparent from, the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various exemplary embodiments of the systems and methods are described in detail below, with reference to the attached drawing figures, in which: 
         FIG. 1  is a side-view schematic diagram of a device according to embodiments herein; 
         FIG. 2  is a side-view schematic diagram of a device according to embodiments herein; 
         FIG. 3  is a schematic diagram illustrating hanging curl measurement; 
         FIG. 4  is a chart illustrating the relationship between displacement and curl radius according to embodiments herein; 
         FIG. 5  is a side-view schematic diagram of a device according to embodiments herein; and 
         FIG. 6  is a flowchart illustrating method embodiments herein. 
     
    
    
     DETAILED DESCRIPTION 
     As mentioned above, current systems rely on users to input the type of paper being used via the “user interface”. Conventional decurling adjustments are also based on a combination of user inputs and some sensor data such as temperature, humidity, double sided printing mode, etc. Current systems do not measure actual curl, but estimate what the curl is likely to be based on such setup parameters. 
     Therefore, the embodiments herein provide a media thickness curl sensing system that comprises a series of three nips used to control a sheet of paper in a precise way so that the curl and thickness attributes can be measured. At the heart of the system is a displacement sensor that is used to measure fly height and paper thickness. 
     More specifically, as shown in  FIG. 1 , one apparatus according to embodiments herein has a media path  116  that transports a media sheet  124 ; a first nip  102  (comprising opposing rollers  110 ,  112 ) that moves the media sheet  124  in a processing direction; a second nip  104  (also comprising opposing rollers  120 ,  122 ) that is positioned within the media path  116  to receive the media sheet  124  from the first nip  102 ; and a third nip  130  (again comprising opposing rollers) that is positioned within the media path  116  to receive the media sheet  124  from the second nip  104 . A sensor  108  is positioned between the second nip  104  and the third nip  130 . The sensor can be any type of readily available sensor, such as one that is light based (laser), sound based (sonar), air pressure based, etc. The sensor  108  senses the position of the media sheet  124  relative to the sensor  108 . 
     The apparatus can also include a decurler  136  positioned within the media path  116 . The processor  118  automatically alters settings of the decurler  136  based on the amount of curl the media sheet  124  contains. Further, the apparatus can contain a marking engine  138  positioned within the media path  116 . Again, the processor  118  automatically alters setting of the marking engine  138  based on the amount of curl the media sheet  124  contains. The marking engine  138  can comprise any type of marking engine  138 , such as an electro-photographic printing engine, an inkjet printing engine, an ultra-violet curable printing engine, etc. Note that some of the elements from  FIG. 1  are not included in  FIGS. 2 and 5  to avoid clutter in the drawings; however, such elements could be included in the structures shown in  FIGS. 2 and 5  and are intended to be understood as being included in such structures. Further, while the decurler  136  and the marking engine  138  are shown in certain positions relative to the sensor  108  and nips  102 ,  104 ,  106 , those ordinarily skilled in the art would understand that the relative positions of such items could be different and that more than one of each item could be included in embodiments herein. 
     Referring to  FIG. 2 , the media sheet  124  first enters nip  1  ( 102 ) then is driven to nip  2  ( 104 ) which is overdriven slightly faster than nip one  102 . Over-driving the media sheet  124  in combination with nip  2  ( 104 ) being a set of two like rolls (both soft or both hard) helps to eliminate any bias of nip  2  ( 104 ) from driving the media sheet  124  up or down. Restated, nip two ( 104 ) drives the media sheet  124  out of its nip in plane with the media plane  116  formed by nips one and two. The media sheet  124  is held very close to 90° from the centerline  116  of nip  2  ( 104 ) so that its entry angle does not influence its exit angle. As shown in  FIG. 2 , the media sheet  124  on exiting nip  2  ( 104 ) is free to curl up, curl down or exit straight out of the nip to be measured by the displacement sensor  108 . With embodiments herein, the media sheet  124  curl (fly height) is read very close to nip two  104  (e.g., 10 mm, 20 mm, 30 mm, etc., from the second nip  104 ). 
     The processor  118  (that is operatively connected to the sensor  108 ) automatically calculates the amount of curl the media sheet  124  contains based on the difference between a predetermined position (which could be the centerline of the media path  116 ) and the position of the leading edge of the media sheet  124  (relative to the sensor  108 ) as the leading edge of the media sheet  124  passes between the second nip  104  and the third nip  130 . The position of the leading edge of the media  124  is shown as item  144  in  FIG. 2 . Therefore, the processor  118  calculates the curl distance as the difference between  116  and  144 . From this distance the curl radius and sheet curl can be determined using lookup charts or methodologies, as discussed below. 
     By reading the media height a short distance from the second nip  104 , the effects of the media&#39;s beam strength are mitigated because a very short stub of media sheet  124  is less likely to bend under its own weight than if it is a longer unsupported piece. 
     The systems and methods disclosed herein determine overall or uniform curl on media as can be seen in the hanging radius curl method of determining curl, see  FIG. 3 . With this method, media is fit to the circumference or curvature of a circle (item  202 ) with its curl being defined as the radius or 1/radius using a predetermined lookup chart  200 . Because the curl is even, the angle formed by any line tangent to the media sheet  124  will be the same for any point about the curvature of the media sheet  124 . With this in mind, measuring the height of the media sheet  124  just as the media sheet  124  exits nip  2  ( 104 ) should be the same angle that would be seen further into the sheet if gravity were not a factor. So by measuring the height of the media sheet  124  immediately exiting nip  2  ( 104 ) the hanging radius curl can be determined. 
     There are other advantages of measuring the media sheet  124  close to the second nip  104 . For example, by doing so the media sheet  124  will have less distance to curl up or down and its displacement height will be less, so the displacement sensor  108  needed can be of a smaller displacement range (which lowers cost). Also, by measuring the media sheet  124  close to the second nip  104 , the media cannot curl up or down excessively thereby getting out of control and possibly folding over on itself when it enters any downstream baffles  114 . Note that baffles  114  have a wide opening that narrows as the baffle reaches the third nip  106  to allow curled sheets to be properly fed to the third nip  106 . 
       FIG. 4  is a chart showing curl data taken from a laser displacement sensor  108 . In the example in  FIG. 4 , a coated 120 gsm media was fed through a nip of two solid 20 mm diameter rolls and readings were taken 18 mm from the center of the second nip  104 . The data show is in pairs, that is, each sheet of media sheet  124  was fed twice, once in the up and once in the down curl position. The test shows that as the media sheet  124  curl decreases so does the tip fly height. Of note, is the fact that tip fly height and media sheet caliper thickness are very close together for less curled media sheet in the 400 mm radius curl area. The caliper thickness of the media sheet  124  was 0.10 mm. 
     Another aspect of embodiments herein is the ability to measure the media&#39;s thickness. The processor  118  can automatically calculate the thickness of the media sheet  124  based on the difference between the predetermined position  116  and the position of the media sheet  146  (relative to the sensor  108 ) as the media sheet  124  passes between the second nip  104  and the third nip  130 . Therefore, as shown in  FIG. 5 , if the “predetermined position” is established as the portion of of the media path  116  where the bottom of the media sheet lies, the media sheet thickness would be the difference between items  116  and  146 . If the “predetermined position” is the centerline of the media path  116 , the media sheet thickness would be twice the difference between items  116  and  146 . 
     The media thickness measurement is accomplished with the same displacement sensor  108 , but with the media sheet  124  stretched tight into nip  3  ( 106 ) as opposed to allowing the leading edge of the media to curl up or down, as was shown in  FIG. 2 . Again the downstream nip  106  is slightly over-driven to take up any slack and ensure that the media sheet  124  is flat between the second nip  104  and the third nip  106 . 
     For the accuracy of displacement sensor  108 , a calibration procedure can occur, whereby a known thickness media sheet  124  is run and measured for media thickness by the displacement sensor  108  as in  FIG. 5 . The resulting values would then be compared to known values and the sensor  108  would be calibrated to the known value. This process establishes the “predetermined position” that is mentioned above. 
     Within the nips  102 ,  104 ,  106 , the bottom three rollers  110 ,  120 ,  130  are fixed (these rollers can rotate, but their axles do not move relative to the media path  116 ). Therefore, the top rollers  112 ,  122 ,  132 , can rotate and move up and down relative to the media path  116  to accommodate different media thicknesses. This provides an unmovable reference plane (e.g.,  116 ) with respect to media sheet  124  to allow the media thickness and curl measurements to be consistent. Therefore, the opposing rollers within the first nip  102 , the second nip  104 , and the third nip  130  each comprise a fixed-position roller and a floating roller. The floating roller is positioned to contact a first side (the top side) of the media sheet  124  and the sensor  108  is also positioned to sense the first side of the media sheet  124 . The opposing rollers  120 ,  122  of the second nip  104  rotate faster than the opposing rollers  110 ,  112  of the first nip  102 , and the opposing rollers  130 ,  132  of the third nip  130  rotate faster than the opposing rollers of the second nip  104  to keep the media sheet  124  taunt during the curl and thickness measurements. 
     Method embodiments are also included herein as shown, for example, in  FIG. 6 . In such embodiments, as shown in item  600 , the method moves the media sheet  124  in the processing direction of the media path  116  from the first nip  102  to the second nip  104  and moves the media sheet  124  in the processing direction of the media path  116  from the second nip  104  to the third nip  130 . In item  602 , the method senses, using the sensor  108  positioned between the second nip  104  and the third nip  130 , the position of the media sheet  124  relative to the sensor  108 . In item  604 , the method automatically calculates the amount of curl the media sheet  124  contains based on the difference between the predetermined position and the position of the leading edge of the media sheet  124  (relative to the sensor  108 ) as the leading edge of the media sheet  124  passes between the second nip  104  and the third nip  130 , using the processor  118 . Further, the method automatically calculates the thickness of the media sheet  124  based on the difference between the predetermined position and the position of the media sheet  124  (relative to the sensor  108 ) as the media sheet  124  passes between the second nip  104  and the third nip  130 , using the processor  118  in item  606 . 
     In item  608 , the method can also automatically alter the settings of the decurler  136  positioned within the media path  116  based on the amount of the curl the media sheet  124  contains using the processor  118 . Also, the method can automatically alter settings of the marking engine  138  positioned within the media path  116  based on the amount of curl the media sheet  124  contains and the thickness of the media sheet  124  using the processor  118  in item  610 . 
     Thus, as show above, the embodiments herein use a displacement sensor to measure the amount of curl of media exiting from a controlled nip and can use the same displacement sensor to measure the media sheet thickness in a controlled nip for more accurate results. The embodiments herein use actual measured properties of media to determine curl which is dynamic and more accurate that projections based on environmental conditions and user input. Similarly, the embodiments herein use actual measured thickness to determine media weight which provides greater accuracy and less fallibility when compared to user input. 
     Many computerized devices are discussed above. Computerized devices that include chip-based central processing units (CPU&#39;s), input/output devices (including graphic user interfaces (GUI), memories, comparators, processors, etc. are well-known and readily available devices produced by manufacturers such as Dell Computers, Round Rock Tex., USA and Apple Computer Co., Cupertino Calif., USA. Such computerized devices commonly include input/output devices, power supplies, processors, electronic storage memories, wiring, etc., the details of which are omitted herefrom to allow the reader to focus on the salient aspects of the embodiments described herein. Similarly, scanners and other similar peripheral equipment are available from Xerox Corporation, Norwalk, Conn., USA and the details of such devices are not discussed herein for purposes of brevity and reader focus. 
     The terms printer or printing device as used herein encompasses any apparatus, such as a digital copier, bookmaking machine, facsimile machine, multi-function machine, etc., which performs a print outputting function for any purpose. The details of printers, printing engines, etc., are well-known by those ordinarily skilled in the art and are discussed in, for example, U.S. Pat. No. 6,032,004, the complete disclosure of which is fully incorporated herein by reference. The embodiments herein can encompass embodiments that print in color, monochrome, or handle color or monochrome image data. All foregoing embodiments are specifically applicable to electrostatographic and/or xerographic machines and/or processes. 
     It will be appreciated that the above-disclosed 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. The claims can encompass embodiments in hardware, software, and/or a combination thereof. Unless specifically defined in a specific claim itself, steps or components of the embodiments herein cannot be implied or imported from any above example as limitations to any particular order, number, position, size, shape, angle, color, or material.