Abstract:
An apparatus and method for transporting substrate of media including a nip assembly having a drive wheel operably connected to a drive mechanism for rotating the drive wheel and an idler wheel disposed adjacent the drive wheel. The drive wheel and idler wheel forming a nip therebetween. The drive wheel and idler wheel being displaced from each other forming a nip gap, wherein the nip gap is present absent the presence of the substrate media in the nip.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure generally relates to document processing devices and methods for operating such devices. More specifically, the present disclosure relates to a substrate media transport system with spaced nip to mitigate nip entrance disturbances that affect registration of a substrate media. 
       BACKGROUND 
       [0002]    In document processing devices, accurate and reliable registration of the substrate media as it is transferred in a process direction is desirable. Even a slight skew or misalignment of the substrate media through an image transfer zone can lead to image and/or color registration errors. Such registration errors can occur as the substrate media passes through the nips. 
         [0003]    Document processing devices typically include one or more sets of nip assemblies used to transport substrate media, such as sheets of paper, through the device. A nip assembly provides a force to the sheet as it passes through the nip assembly to propel it through the document processing device. A nip assembly typically includes a drive wheel and an idler wheel in rolling contact with the drive wheel to form the nip therebetween. One or more sets of drive wheels and idler wheels may be longitudinally aligned in order to form a nip. The driving wheel and the idler wheel may be urged together by a biasing device which in turn creates the nip force. The nip force is required such that the wheels properly engage the sheet as it passes through the nip. This nip force must be significant enough in order to eliminate slipping between the drive wheel and the sheet. 
         [0004]    When a sheet being transported through the document processing device first engages the nip, the drive wheel and idler wheel are in rolling engagement with each other. As the sheet engages the wheels, at least one of the idler and drive wheels typically moves against the nip force in order to permit the sheet to enter the nip. The entering of the sheet into the nip results in nip disturbances which negatively affect sheet registration. When a sheet enters a nip, the sheet must perform work in displacing the wheel an amount equal to its thickness multiplied by the nip force. This work needs to be performed in the time it takes the sheet to fully enter the nip. The work required to move the wheel originates from a decrease in kinetic energy, i.e., speed, of the rotating nip assembly components. The controls used to regulate the nip velocity typically cannot effectively mitigate the nip disturbances. Registration of the sheets, therefore, is compromised. 
         [0005]    Accordingly it would be desirable to provide a substrate media transport system having nips that reduce the disturbance caused by substrate media nips. 
       SUMMARY 
       [0006]    Before the present systems, devices and methods are described, it is to be understood that this disclosure is not limited to the particular systems, devices and methods described, as these may vary. It is also to be understood that the terminology used in the description is for the purposes of describing the particular versions or embodiments only, and is not intended to limit the scope. 
         [0007]    According to aspects described herein, there is disclosed an apparatus for transporting substrate media including a nip assembly having a drive wheel operably connected to a drive mechanism for rotating the drive wheel and an idler wheel disposed adjacent the drive wheel. The drive wheel and idler wheel forming a nip therebetween. The drive wheel and idler wheel being displaced from each other forming a nip gap, wherein the nip gap is present absent the presence of the substrate media in the nip. 
         [0008]    According to further aspects described herein, there is disclosed an apparatus for mitigating nip entry disturbances including a nip assembly for transporting substrate media having a thickness therethrough. The nip assembly includes a drive wheel operably connected to a drive mechanism for rotating the drive wheel and including an idler wheel disposed adjacent the drive wheel. The drive wheel and idler wheel defining a nip therebetween. The drive wheel and idler wheel being displaced from each other forming a nip gap. The nip gap increasing in size upon entry of substrate media into the nip. A nip gap adjuster is operably connected to the nip assembly. The nip gap adjuster causing relative movement between the idler wheel and the drive wheel to adjust the size of the nip gap in response to the thickness of the substrate of media. 
         [0009]    According to still further aspects described herein, there is disclosed a method of mitigating nip entrance disturbances including: 
         [0010]    positioning an idler wheel adjacent to a drive wheel forming a nip, the drive wheel and idler wheel cooperating to transport substrate media through the nip; and 
         [0011]    forming a space between the idler wheel and the drive wheel to form a nip gap in the absence of substrate of media. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a top perspective schematic view of a sheet transport system according to an embodiment. 
           [0013]      FIG. 2  is a side elevational schematic view of the sheet transport system of  FIG. 1 . 
           [0014]      FIG. 3  is a side elevational view of a sheet transport system of  FIG. 1  depicting an adjustable nip gap. 
           [0015]      FIG. 4  is a schematic of a nip gap control system. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    The following terms shall have, for the purposes of this application, the respective meanings set forth below. 
         [0017]    A “document processing device” refers to a device that performs an operation in the course of producing, replicating, or transforming a document from one format to another format, such as from an electronic format to a physical format or vice versa. Document processing devices may include, without limitation, printers (using any printing technology, such as xerography, ink-jet, or offset); document scanners or specialized readers such as check readers; mail handling machines; fabric or wallpaper printers; or any device in which an image of any kind is created on and/or read from a moving substrate. 
         [0018]    A “substrate of media” refers to, for example, paper, transparencies, parchment, film, fabric, plastic, or other substrates on which information can be reproduced, preferably in the form of a sheet or web. 
         [0019]    A “nip” refers to a location in a document processing device at which a sheet is propelled in a process direction. A nip may be formed between an idler wheel and a drive wheel. 
         [0020]    A “nip assembly” refers to components, for example and without limitation, a drive wheel and an idler wheel which form a nip. 
         [0021]    A “drive wheel” refers to a nip assembly component that is designed to propel a sheet in contact with the nip. A drive wheel may comprise a compliant material, such as rubber, neoprene or the like. A drive wheel may be directly driven via a stepper motor, a DC motor or the like. Alternately, a drive wheel may be driven using a gear train, belt transmission or the like. 
         [0022]    An “idler wheel” refers to a nip assembly component that is designed to provide a normal force against a sheet in order to enable the sheet to be propelled by the drive wheel. An idler wheel may comprise a non-compliant material, such as plastic. 
         [0023]    A “nip gap” refers to a space disposed between the drive wheel and idler wheel of the nip assembly. 
         [0024]    A “nip gap adjuster” refers to a device in communication with a nip for changing the size of the nip gap. 
         [0025]    With reference to  FIGS. 1-3 , a substrate media transport system  10  conveys substrate of media such as sheet of media  12  along a processing path  14 . The substrate media transport system may include one or more nip assemblies  16  longitudinally aligned transverse to the process direction  14 . Each nip assembly  16  may include an idler wheel  18  and a drive wheel  20  which form a nip  21  therebetween. The idler wheel  18  provides a normal force against a sheet  12  that is being transported by the substrate media transport system  10  in order to enable the sheet to be propelled by the rotating drive wheel  20 . The idler wheel  18  may have an outer surface  22  including a noncompliant material, such as hard plastic. The idler wheel  18  may rotate around a shaft  24 . The idler wheel may be rotatably secured to one end of a pivot arm  26 . Pivot arm  26  is pivotably secured to a pivot shaft  28  such that the idler wheel may pivot toward and away from the drive wheel  20 . The pivot arm  26  may be attached to a biasing device  30 , such as a torsion spring. The biasing device  30  tends to urge the idler wheel  18  toward the drive wheel  20  and provides the normal force, represented by arrow  31  in  FIG. 2 , for the idler wheel  18 . Other methods of applying a normal force for the idler wheel  18  may be used and are within the scope of this disclosure. 
         [0026]    The drive wheel  20  may include an outer surface  32  having a compliant material such as rubber, neoprene or the like. The compliant material helps to grip the sheet  12  and permit the drive wheel  20  to move the sheet through the nip  21 . The drive wheel  20  rotates about a drive shaft  34  and may be directly driven by a drive motor  36 , such as a stepper motor, a DC motor or the like. A transmission device  38  may extend between the drive motor  36  and the drive wheel  20  for imparting motion to the drive wheel  20 . The transmission device  38  may include a timing belt, gear trains or other transmission means known to those of ordinary skill in the art. The drive wheels  20  of each of the nip assemblies  16  may move in a coordinated manner to propel the sheets  12  through the nips  21  in a controlled manner. 
         [0027]    For each nip assembly  16 , the idler wheels  18  and drive wheels  20  are separated by a nip gap  40 . The nip gap size may be the sheet thickness minus a fixed value or a percentage of the sheet thickness. For example if a sheet is 20 milli-inches, the nip gap may be 16 milli-inches. The nip gap  40  is present even when there is no sheet within the nip  21 . Upon receiving a sheet, the nip gap  40  may be sized such that it is less than the thickness of the sheet  12  being transported through the nips  21 . Accordingly, when a sheet enters the nip  21 , the drive wheel  20  will engage the sheet  12  and the sheet will separate the idler wheel from the drive wheel increasing the size of the nip gap  40 . Movement of the idler wheel  18  acts against the force of the biasing device  30  resulting in a normal force being imparted by the idler wheel  18  as the sheet extends therethrough. This normal force helps to maintain the sheet in rolling contact with the drive wheel  20  to prevent slippage. 
         [0028]    By selectively setting an initial nip gap  40  based on the sheet thickness, the sheet  12  entering the nips  21  does not have to lift the idler wheel the entire thickness of the sheet as would be the case if the idler wheel  18  were in rolling engagement with the drive wheel  20 . Since the distance the sheet has to move the idler is substantially less, the amount of work required to lift the idler wheel  18  is also significantly less. By reducing the amount of work needed to be performed by the sheets, nip velocity disturbance is reduced and the sheets may maintain proper registration. In addition, reducing the work needed to be performed by the sheet decreases sheet damage and wear on the components. 
         [0029]    When the nip assemblies  16  are intended to propel the sheets therethrough, the nip gap  40  may also be set such that it is smaller than the thickness of the sheet thereby the nip assemblies  16  still act upon the sheet, and the nip force is sufficient to propel the sheets through the nips  21 . Typically, a nip force of 1 to 3 pounds may be used to propel a sheet through the nips, although other nip forces may be used. Accordingly, the nip gap  40  will be sized based on the sheet thickness. Alternatively, the nip gap  40  may be increased in size such that no nip force is applied to the sheets in which case the nip assembly  16  is in an open state. In the nip open state, a sheet may pass through the nip  21  without being influenced by the nip assembly  16 . 
         [0030]    The nip gap  40  may be adjustable in order to accommodate sheets having various thicknesses. Accordingly, the substrate media transport system  10  may include a gap adjustor  50 . The gap adjustor  50  may operate to move the drive wheel and/or the idler wheel. For purposes of explanation, the gap adjustor  50  is shown operably connected to, and moves, the idler wheel  18  relative to the drive wheel  20 . However, it is to be understood that it is within the contemplation of the present disclosure that the gap adjuster  50  may be operably connected to the drive wheel  20  to move the drive wheel  20  relative to the idler wheel  18 . In one embodiment, the gap adjustor  50  may include a mechanical actuator such as a cam  52  secured to a cam shaft  54 . The cam shaft  54  may be operably connected to a cam drive  53 , such as a motor, a stepper motor or other device well known in the art, so that the position of the cam  52  may be adjusted. A cam follower  56  may be attached to the pivot arm  26  at the end opposite that of the idler wheel  18 . The pivot arm  26  may be biased to move the idler wheel  18  toward the drive wheel  20 , and the action of the cam drives the pivot arm  26  against the bias to move the idler wheel  18  away from the drive wheel. The cam  52  may be configured such that as the cam  52  is rotated the follower  56  moves, thereby moving the idler wheel  18  closer to or further from the drive wheel  20 . This results in a change in the size of the nip gap  40 . The cam  52  may be configured such that rotation of the cam in one direction moves the idler wheel  18  from the drive wheel  20 , and when the cam is rotated in the opposite direction the idler wheel  18  moves closer to the drive wheel  20 . It is to be understood that the idler wheel may be mounted to other mechanical actuators, such as electric, pneumatic, or electropneumatic actuators, which remove the idler wheel and adjust the nip gap. 
         [0031]    The gap adjuster  50  may also be able to adjust the nip gap  40  such that it is larger than the thickness of the sheets being transported. In this case, the nip assembly  16  would be in the open state allowing sheets to freely pass therethrough. 
         [0032]    With reference to  FIGS. 1 and 4 , the nip gap  40  is adjustable and the size of the gap is a function of the thickness of the sheets of media passing through the nips  21 . The nip gap is set such that the work performed by the sheets is reduced to mitigate nip disturbances, yet the nip assemblies still provide suffice nip force to propel the sheets through the nip assemblies without slippage. The nip gap  40  may be set in response to a signal generated by a thickness device  58 . Device  58  may include one or more sensors  60  which determine the thickness of the sheets. Alternatively, the thickness device  58  may be an input device  64  on which an operator can enter the thickness of the media. Signals from either the sensors  60  and/or user input device  64  may be communicated to a controller  62 . The controller may be in the form of a processor, micro processor, or the like. The controller  62  may be operably connected to the gap adjustor  50  and, in particular, the cam drive  53  to control the operation of the cam drive to adjust the size of the nip gap  40 . A gap sensor  66  may be disposed adjacent to the nip assemblies  16  in order to sense the size of the nip gap  40 . The gap sensor  66  may be in operative communication with the controller  62  in order to and provide feedback to the controller to permit precise control of the nip gap  40 . Once the media thickness is determined and communicated to the controller  62 , the controller may generate and send a signal to the gap adjustor  50  causing the nip gap  40  to be set to the appropriate size in response to the media thickness. 
         [0033]    It will be appreciated that various of 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.