Abstract:
An apparatus and method 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 member disposed adjacent the drive wheel. The idler wheel and drive wheel forming a nip. The drive wheel and idler wheel are displaceable from each other to form a nip gap therebetween. A nip force generator is operably connected to the nip assembly. The nip force generator develops a first nip force upon entry of the substrate media into the nip and formation of the nip gap and develops a second nip force subsequent to the first nip force. The second nip force is greater than the first nip force.

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 reduced force 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 a nip 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. One or more sets of drive wheels and idler wheels may be longitudinally aligned in order to form the nip therebetween. 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, especially thick sheets, 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 of an amount equal to its thickness multiplied against 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 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 nip assemblies that reduce the disturbance caused by substrate media entering the nips. 
       SUMMARY 
       [0006]    There is provided 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 member disposed adjacent the drive wheel. The idler wheel and drive wheel forming a nip. The drive wheel and idler wheel are displaceable from each other to form a nip gap therebetween. A nip force generator is operably connected to the nip assembly. The nip force generator develops a first nip force upon entry of the substrate media into the nip and formation of the nip gap and develops a second nip force subsequent to the first nip force. The second nip force is greater than the first nip force. 
         [0007]    There is also provided an apparatus for mitigating nip disturbances caused by substrate media entering the nip including a nip assembly having a drive member operably connected to a drive mechanism for rotating the drive wheel. The nip assembling further including an idler member is disposed adjacent the drive wheel. The drive and idler wheels being movable relative to each other to form a nip gap therebetween. A first force generating device generates a first nip force which acts upon the nip assembly upon an initial separation of the drive member and the idler member. A second force generating device selectively generates a second nip force which acts upon the nip assembly in response to a predetermined condition, the second nip force being greater than the first nip force. 
         [0008]    There is still further provided a method of mitigating nip entrance disturbances including; 
         [0009]    transporting substrate media toward a nip formed between a drive wheel and an idler wheel, the drive wheel and idler wheel being displaceable from each other by action of the substrate media to form a nip gap; 
         [0010]    subjecting the substrate media to a first nip force upon entry of the substrate media into the nip and during displacement of the idler wheel from the drive wheel by the substrate media; and 
         [0011]    subjecting the substrate media to a second nip force subsequent to the first nip force, the second nip force being greater than the first nip force. 
     
    
     
       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  depicting a sheet about to enter the nip. 
           [0014]      FIG. 3  is a side elevational view of a sheet transport system of  FIG. 1  depicting a sheet after it has entered the nip. 
           [0015]      FIG. 4  is a side elevational schematic view of the sheet transport system of  FIG. 1  depicting a nip force generator. 
           [0016]      FIG. 5  is a side elevational schematic view of an alternative embodiment of the present disclosure. 
           [0017]      FIG. 6  is a schematic of a nip gap control system. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    The following terms shall have, for the purposes of this application, the respective meanings set forth below. 
         [0019]    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. 
         [0020]    A “substrate of media” refers to, for example, paper, transparencies, parchment, film, fabric, plastic, or other substrates on which information can be reproduced, for example, in the form of a sheet or web. 
         [0021]    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. 
         [0022]    A “nip assembly” refers to components, for example and without limitation, a drive wheel and an idler wheel which form a nip. 
         [0023]    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 include a wheel, roller or other rotable member. The drive wheel may have an outer surface including 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. 
         [0024]    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 include a wheel, roller or other rotatable member. The idler wheel may have an outer surface including a non-compliant material, such as plastic. 
         [0025]    A “nip force” refers to a force acting upon substrate media when transported through a nip. 
         [0026]    A “nip force generator” refers to a device, for example a mechanical, electro-mechanical, fluid power device, for exerting a nip force. 
         [0027]    A “nip gap” refers to a space formed between a drive wheel and idler wheel of a nip assembly. 
         [0028]    “Nip disturbances” refers to influences on nip components that affect desired operation of the nip assembly components. 
         [0029]    With reference to  FIGS. 1-4 , 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  and drive wheel  20  may be biased together creating a nip force shown by arrow  17 . The nip force  17  acts on 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 . 
         [0030]    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. 
         [0031]    When a sheet approaches the nip assembly  16 , the idler wheel  18  is in rolling engagement with the drive wheel  20  and the wheels are held together by the nip force  17 . In order for the nip assembly  16  to operate properly, the nip force may be high enough such that the sheet is propelled through the nip  21  without slippage. As the sheet engages the nip  21 , the idler and drive wheels  18 ,  20  are separated from each other by the sheet  12  forming a nip gap  40 . If the sheet  12  were to encounter a nip held together by a high nip force of the magnitude sufficient to prevent slippage, significant nip disturbances would be created detrimentally affecting registration and component wear. Thus, in accordance with the present disclosure, each nip  21  may be operated upon by a nip force generator  42  capable of producing a varying nip force. 
         [0032]    With reference to  FIG. 2 , the nip force generator  42  may develop a first nip force F 1  which acts upon the nip assembly  16 , and a sheet within the nip, when the sheet leading edge  12 A first enters the nips  21 . This first nip force F 1  may be relatively low. Since the sheet  12  is typically still being driven by an upstream transport system, the nip assembles  16  do not have to initially rely on a nip force to pull the sheet into the nips  16 . The relatively low nip force F 1  may act on the sheet when the sheet is separating the idler wheel  18  and drive wheel  20  as the leading edge  12 A enters the nips  16 . The low nip force F 1  limits the amount of work needed to be performed by the sheet entering the nips  16 , thereby reducing nip disturbances. 
         [0033]    With reference to  FIG. 3 , the nip force generator  42  may further produce a second nip force F 2  which acts upon the nip assemblies  16 , and a sheet within the nips, after the nip gap  40  has reached the thickness of the sheet passing through the nips  21 . The second nip force F 2  may be higher than first nip force F 1  and may have a value sufficient to permit the sheet to be propelled through the nips  21  without slipping. Since the idler wheel  18  and drive wheel  20  have been separated such that the sheet can pass therebetween, the sheet  12  need not work against the second nip force F 2 . 
         [0034]    Accordingly, the work performed by the sheet in forming the nip gap  40  is a function of the lower first nip force F 1 . Since the sheets entering the nips  16  only work against the lower nip force, nip entrance disturbances are greatly reduced. This helps to maintain proper registration of the sheets and also reduces damage to the sheets and the nip components. However, slippage of the sheets  12  passing through the nips  16  is also reduced since the second nip force F 2  is applied and acts on the sheets  12  as the sheets are propelled through the nips  16 . 
         [0035]    It is further contemplated that the nip force generator may be capable of generating more that just the first and second forces. Multiple nip forces could be provided to control the operation of the nip assemblies  16  and the transfer of sheets  12  through the nips  21 . 
         [0036]    The nip force generator  42  may act on the idler wheel  18  and/or the drive wheel  20  to create the desired nip force. For purposes of description, the force generating device  42  will be described as operating on the idler wheel  18 . With reference to  FIG. 4 , the idler wheel  18  may be rotatably connected to a ridged pivot arm  50  at a first end  51  thereof. A pivot arm second end  53  may be pivotally attached to a structure such as a shaft  52 . The pivot arm  50  may move such that the idler wheel  18  may be pivoted toward and away from the drive wheel  20 . The nip force generator  42  may include a first and second force generating device  54  and  56 , respectively, for urging the idler wheel  18  toward the drive wheel  20  with different degrees of force. In the alternative embodiment wherein the nip force generating device  42  is attached to the drive wheel  20 , the drive wheel may be attached to a pivot arm and the first and second force generating devices,  54 , and  56 , may urge the drive wheel  20  toward the idler wheel  18  with different degrees of force. 
         [0037]    The first force generating device  54  may provide the first nip force F 1  which holds the idler wheel  18  in rolling engagement with the drive wheel  20 . The first force generating device  54  may develop a relatively low force sufficient to maintain contact between the idler wheel  18  and the drive wheel  20 . For example F 1  may be approximately 0.1 to 0.5 pounds. When a sheet  12  first encounters the nip  16  and separates the idler wheel  18  from the drive wheel  20 , the sheet acts against the relatively low force, F 1 . The first force generating device  54  may include a spring  58  or other biasing device disposed between the pivot arm first end and a structure  60  such as a portion of a frame. As the sheet  12  enters the nip  16 , the idler wheel  18  is pivoted against the low force F 1 . The formed nip gap  40  is enlarged until it eventually reached a size equal to the thickness of the sheet. At this point, further movement of the idler wheel  18  against the first nip force F 1  ceases. 
         [0038]    When the nip gap  40  equal the thickness of the sheet  12 , the nip force generator  42  may engage the second force generating device  56  to develop the second nip force F 2 . The second force generating device  56  may be engaged in response to a signal generated when the idler wheel  18  has traveled a predetermined amount. Such a signal would be related to the nip gap size. Alternatively, engagement of the second force generating device  56  may be engaged after the sheet has reached a certain position or after a predetermined amount of time has elapsed after the sheet  12  has entered the nip  21 . The second nip force F 2 , may be sufficient to allow the nip assemblies  16  to drive the sheet there through without slippage. For example, the second nip force F 2  may be on the order of 1 to 3 pounds. However, other force values may be employed. The higher second nip force F 2  is not generated until the nip gap  40  has reached the thickness of the sheet  12 . 
         [0039]    The second force generating device  56  may include an actuator  62  that has first and second operating states. The actuator  62  may be selectively energized to change operating states to apply the second nip force F 2  at desired periods during the travel of the sheets through the nips  21 . The actuator  62  may include, for example, a linear drive such as a solenoid or pneumatic cylinder. The actuator  62  may be operably connected to the pivot arm  50  such that it urges the idler wheel  18  and drive wheel  20  together creating the second nip force F 2 . The actuator  62  may be connected to the pivot arm  50  by a second biasing device  64 . The second biasing device  64  may include a spring having one end attached to the actuator  62  and the other end connected to the pivot arm  50 . Energizing the actuator  62  causes the spring to be pulled, thereby urging the idler wheel  18  toward the drive wheel  20  and developing the second nip force F 2 . With the nips compressed onto the sheets by the second nip force F 2 , the nip may propel the sheet through the nips  21  without slippage. Accordingly, by selectively energizing the actuator  62 , the second nip force F 2  may be selectively engaged and disengaged. 
         [0040]    In alternative embodiment shown in  FIG. 5 , the nip force generator  66  may produce the first and second nip forces using a single actuator  68 . An actuator  68  capable of generating a variable output force, such as a fluid power or electric linear drive, may be secured to a first end  51  of the pivot arm  50 . Pivot arm  50  may be pivotally connected to a structure at a pivot arm second end  52 . As shown in  FIG. 5 , the drive wheel  20  may be pivotally attached to the pivot arm  50 . Alternatively, the idler wheel  18  may be pivotally secured to the pivot arm  50 . The actuator  68  may be controlled to assume a first operating state urging the drive wheel  20  into the idler wheel  18  thereby generating the first nip force F 1 . The relatively low first nip force F 1  may be generated when the sheet is entering the nips  21 . The actuator  68  may also be controlled to assume a second operating state to generate the second nip force F 2 , which is greater than the first nip force F 1 . The second nip force F 2  may be generated after the sheet has entered the nip and is of a value sufficient to permit the nip to drive the sheet  12  therethrough without slippage. 
         [0041]    In sheet transport system  10  having multiple nip assemblies  16  as shown in  FIG. 1 , each nip assembly  16  may have its own the nip force generator  42  having first and second force generating devices. Alternatively, the idler wheels may be coupled together (not shown) and a single the nip force generator  42  may act on all the nip assemblies  16 . 
         [0042]    With reference to  FIGS. 1 and 6 , the second nip force F 2  may be produced in response to one or more sensors  70  which determine the thickness of the sheets. Signals from the sensors  70  may be communicated to a controller  72 . The controller  72  may be operably connected to the nip force generator  42 . Alternatively, the sheet thickness may be entered by an operator via an input device  74 . A nip gap sensor  76  may sense the size of the nip gap  40 . When the nip gap  40  reaches the sheet thickness, the controller  72  may cause the nip force generator  42  to produce the second nip force F 2 . When a sheet has left the nips the controller  72  may cause the nip force generator  42  to de-energize the actuator such that only the first nip force F 1  acts on the nip assemblies  16 . The nip assemblies  16  are then ready to receive another sheet. 
         [0043]    Alternatively, the control of the nip force generator  42  may be responsive to a sheet position sensor  78 . When the sheet is about to enter the nip, the nip force generator  42  may generate the first nip force F 1 . When the position of the sheet is sensed indicating that the sheet has fully entered the nip  21 , the nip force generator  42  may berate the second nip force F 2 . 
         [0044]    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.