Patent Publication Number: US-8992004-B2

Title: Flow optimization for compact turnbar reversers

Description:
TECHNICAL FIELD 
     This disclosure relates generally to a printing system and methods for transporting a continuous web of recording media for duplex printing in the printing system. The disclosure includes a turnbar reverser to enable duplex printing on both sides of the continuous web of imaging material. 
     BACKGROUND 
     In general, inkjet printing machines or printers include at least one printhead unit that ejects drops of liquid ink onto recording media or an imaging member for later transfer to media. Different types of ink can be used in inkjet printers. In one type of inkjet printer, phase change inks are used. Phase change inks remain in the solid phase at ambient temperature, but transition to a liquid phase at an elevated temperature. The printhead unit ejects molten ink supplied to the unit onto media or an imaging member. Such printheads can generate temperatures of approximately 110 to 120 degrees Celsius. Once the ejected ink is on media, the ink droplets solidify. The printhead unit ejects ink from a plurality of inkjet nozzles, also known as ejectors. 
     The media used in both direct and offset (transfix) printers can be in web form. In a web printer, a continuous supply of media, typically provided in a media roller, is entrained onto rollers that are driven by motors. The motors and rollers pull the web from the supply roller through the printer to a take-up roller. The rollers are arranged along a linear media path, and the media web moves through the printer along the media path. As the media web passes through a print zone opposite the printhead or heads of the printer, the printheads eject ink onto the web. Along the feed path, tension bars or other rollers remove slack from the web so the web remains taut without breaking. 
     Existing web printing systems use a registration control method to control the timing of the ink ejections onto the web as the web passes the printheads. One known registration control method that can be used to operate the printheads is the single reflex method. In the single reflex method, the rotation of a single roller at or near a printhead is monitored by an encoder. The encoder can be a mechanical or electronic device that measures the angular velocity of the roller and generates a signal corresponding to the angular velocity of the roller. The angular velocity signal is processed by a controller executing programmed instructions for implementing the single reflex method to calculate the linear velocity of the web. The controller can adjust the linear web velocity calculation by using tension measurement signals generated by one or more load cells that measure the tension on the web near the roller. The controller implementing the single reflex method is configured with input/output circuitry, memory, programmed instructions, and other electronic components to calculate the linear web velocity and to generate the firing signals for the printheads in the marking stations. 
     Another existing registration control method that can be used to operate the printheads in a web printing system is the double reflex method. In the double reflex method, each encoder in a pair of encoders monitors one of two different rollers. One roller is positioned on the media path prior to the web reaching the printheads and the other roller is positioned on the media path after the media web passes the printheads. The angular velocity signals generated by the two encoders for the two rollers are processed by a controller executing programmed instructions for implementing the double reflex method to calculate the linear velocity of the web at each roller and then to interpolate the linear velocity of the web at each of the printheads. These additional calculations enable better timing of the firing signals for the printheads in the marking stations and, consequently, improved registration of the images printed by the marking stations in the printing system. Ejection of ink from the inkjet nozzles can be adjusted based on the calculations. A double reflex printing system is disclosed in issued U.S. Pat. No. 7,665,817. 
     Some continuous feed inkjet printers form printed images on only a first side of the continuous web, a process referred to as a simplex printing operation. Simplex continuous feed inkjet printers have printhead assemblies with printheads that are configured to eject ink across a printing zone on the continuous web that is less than the width of the web. The printing zone is typically centered on the web with appropriate margins on each side of the printing zone. During a simplex printing operation, the continuous web makes only one pass through the printer. Specifically, a rewinder pulls the continuous web through the printer along the web path only once during a simplex printing operation. 
     Some continuous feed inkjet printers are configured to form printed images on a first and a second side of the continuous web, which is known as a duplex printing operation. In a duplex printing operation, the continuous web makes two passes through the printer, and is referred to as a half-width dual-pass duplex printing operation. In particular, the continuous web is routed from a web supply through the printer to receive ink on the first side. After the continuous web exits the printer, the continuous web is inverted by an inverting system and is then routed again through the printer to receive ink on the second side. One type of duplex continuous feed printer includes an external continuous web inverting system. In another type of duplex continuous feed printer, the web inverting system is incorporated as part of the printer itself. As used herein, the term “inverting”, “inverter”, or “inversion” refers to manipulation of the web to turn the web from a first side to a second side to enable an unprinted side of the web to be presented to a printhead assembly for printing. 
     In duplex printing on a continuous web, an image on one side is registered with an image on the other side to insure that portions of an image are not lost when the continuous web is cut into sheets or that an image on a first side is not misaligned with an image on a second side. To insure that proper registration is achieved, the speed of the transport rollers is controlled according to a variety of factors including web and environmental humidity, temperature, atmospheric pressure. For instance if the web either stretches, shrinks, or otherwise becomes distorted during transport through the printer or during imaging, poor quality images can occur. Likewise, the amount of ink deposited on the continuous web can affect the material properties of the web and result in misregistration of images as well. Consequently, improvements to a printing system and to printing images by taking into account the types of media, the amount of ink being deposited on the continuous web, and conditions occurring in the printer are desirable. 
     SUMMARY 
     An inversion apparatus configured to invert a continuous web of recording media moving along a path in an imaging system wherein the inversion apparatus includes an input configured to receive the continuous web of recording media, an output, displaced from the input, the output configured to convey the continuous web of recording media after being inverted and a blower configured to provide a flow of forced air. A turnbar is configured to convey the continuous web of recording media between the input and the output and to enable inversion of the continuous web of recording media. The turnbar includes an exterior surface defining a first region having a plurality of apertures operatively connected to the blower and configured to direct the forced air from the exterior surface of the turnbar and a second region through which the forced air is not directed from the exterior surface. 
     A method of forming a duplex image on a continuous web of recording media having a first side and a second side with the continuous web moving along a transport path through a printer wherein a web inverter includes a turnbar having a surface defining a plurality of apertures, and a blower is operatively connected to the plurality of apertures to provide forced air to the apertures. The method includes imaging the first side of the continuous web of recording media during a first pass through the printer, directing the second side of the continuous web toward the plurality of apertures, directing air through the plurality of apertures to provide an air gap between the second side of the continuous web of recording media and the surface of the turnbar, wherein the directed air is confined to a predetermined region of the surface of the turnbar, the predetermined region extending over a first portion of the surface of the turnbar but not over a second portion of the surface of the turnbar, and imaging the second side of the continuous web of recording media during a second pass through the printer. 
     In another embodiment, an inversion apparatus is configured to invert a continuous web of recording media moving along a path in an imaging system. The inversion apparatus includes an input configured to receive the continuous web of recording media and an output, displaced from the input, wherein the output is configured to convey the continuous web of recording media after being inverted. A turnbar is configured to convey the continuous web of recording media between the input and the output and to enable inversion of the continuous web of recording media. The turnbar includes an exterior surface defining an air foil region having a plurality of apertures configured to provide an air gap between the surface of the turnbar and the recording media and a second region substantially devoid of apertures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is perspective view of an inversion apparatus including a blower. 
         FIG. 2  is perspective view of a web path for a continuous web of print media moving through an inversion apparatus. 
         FIG. 3  is a top view of a turnbar having a plurality of apertures disposed on a surface thereof to provide an air cushion between a continuous web of print media having a first width and the surface of the turnbar. 
         FIG. 4  is a front view of the turn bar of  FIG. 3  having a plurality of apertures disposed on the surface thereof to provide an air cushion between a continuous web of print media having the first width where a portion of the surface is non-apertured. 
         FIG. 5  is a top view of a turnbar having a plurality of apertures disposed on a surface thereof to provide an air cushion between a continuous web of print media, having a second width, and the surface of the turnbar. 
         FIG. 6  is a front view of the turn bar of  FIG. 5  having a plurality of apertures disposed on a surface thereof to provide an air cushion between a continuous web of print media having the second width where a portion of the surface is non-apertured. 
         FIG. 7  is a graphical representation of a gap clearance between a surface of a turnbar and the continuous web of print media. 
         FIG. 8  is a graphical representation of velocity and tension versus time. 
         FIG. 9  is a schematic view of a prior art inkjet imaging system that ejects ink onto a continuous web of media as the media moves past the printheads in the system. 
     
    
    
     DETAILED DESCRIPTION 
     For a general understanding of the environment for the system and method disclosed herein as well as the details for the system and method, the drawings are referenced throughout this document. In the drawings, like reference numerals designate like elements. As used herein the term “printer” or “printing system” refers to any device or system that is configured to eject a marking agent upon an image receiving member and includes photocopiers, facsimile machines, multifunction devices, as well as direct and indirect inkjet printers and any imaging device that is configured to form images on a print medium. As used herein, the term “process direction” refers to a direction of travel of an image receiving member, such as an imaging drum or print medium, and the term “cross-process direction” is a direction that is perpendicular to the process direction along the surface of the image receiving member. As used herein, the terms “web,” “media web,” and “continuous web of recording media” refer to an elongated print medium that is longer than the length of a media path that the web moves through a printer during the printing process. Examples of media webs include rollers of paper or polymeric materials used in printing. The media web has two sides having surfaces that can each receive images during printing. The printed surface of the media web is made up of a grid-like pattern of potential drop locations, sometimes referred to as pixels. 
     As used herein, the term “capstan roller” refers to a cylindrical member configured to have continuous contact with the media web moving over a curved portion of the member, and to rotate in accordance with a linear motion of the continuous media web. As used herein, the term “angular velocity” refers to the angular movement of a rotating member for a given time period, sometimes measured in rotations per second or rotations per minute. The term “linear velocity” refers to the velocity of a member, such as a media web, moving in a straight line. When used with reference to a rotating member, the linear velocity represents the tangential velocity at the circumference of the rotating member. The linear velocity v for circular members can be represented as: v=2πrω where r is the radius of the member and ω is the rotational or angular velocity of the member. 
       FIG. 9  depicts a prior art inkjet printer  100  having elements pertinent to the present disclosure. In the embodiment shown, the printer  100  implements a solid (phase change) ink print process for printing onto a continuous media web. Although a method and system for duplex printing of a continuous web of recording media are described below with reference to the printer  100  depicted in  FIG. 9 , the subject method and apparatus disclosed herein can be used in any printer, such as a cartridge inkjet printer, which uses serially arranged printheads to eject ink onto a continuous web image substrate. 
       FIG. 9  depicts a continuous web printer system  100  that includes twenty print modules  80 - 99 , a controller  128 , a memory  129 , guide roller  115 , guide rollers  116 , pre-heater roller  118 , apex roller  120 , leveler roller  122 , tension sensors  152 A- 152 B,  154 A- 154 B, and  156 A- 156 B, and velocity sensors, such as encoders  160 ,  162 , and  164 . The print modules  80 - 99  are positioned sequentially along a media path P and form a print zone from a first print module  80  to a last print module  99  for forming images on a print medium  114  as the print medium  114  travels past the print modules. Each print module  80 - 83  provides a magenta ink. Each print module  84 - 87  provides cyan ink. Each print module  88 - 91  provides yellow ink. Each print module  92 - 95  provides black ink. Each print module  96 - 99  provides a clear ink as a finish coat. In all other respects, the print modules  80 - 99  are substantially identical. 
     The media web travels through the media path P guided by rollers  115  and  116 , pre-heater roller  118 , apex roller  120 , and leveler roller  122 . A heated plate  119  is provided along the path adjacent roller  115 . In  FIG. 9 , the apex roller  120  is an “idler” roller, meaning that the roller rotates in response to engaging the moving media web  114 , but is otherwise uncoupled from any motors or other drive mechanisms in the printing system  100 . The pre-heater roller  118 , apex roller  120 , and leveler roller  122  are each examples of a capstan roller that engages the media web  114  on a portion of its surface. A brush cleaner  124  and a contact roller  126  are located at one end of the media path P. A heater  130  and a spreader  132  are located at the opposite end  136  of the media path P. 
     A web inverter  168  is configured to direct the media web  114  from the end  136  of media path P to the beginning  134  of the media path through an inverter path P′. The web inverter  168  flips the media web and the inverter path P′ returns the flipped web to the inlet  134  to enable single-engine (“Mobius”) duplex printing where the print modules  80 - 99  form one or more ink images on a second side (second side ink image) of the media web after forming one or more images on the first side (first side ink image). In this operating mode, a first section of the media web moves through the media path P in tandem with a second section of the media web, with the first section receiving ink images on the first side of the media web and the second section receiving ink images on the second side. This configuration can be referred to as a “mobius” configuration. Each of the print modules  80 - 99  is configured to eject ink drops onto both sections of the media web. Each of the rollers  115 ,  116 ,  118 ,  120 , and  122  also engage both the first and second sections of the media web. After the second side of the media web  114  is imaged, the media web  114  passes the end of the media path  136 . Registration of a second side ink image to a first side ink image forms a duplex image. In another embodiment, one print module is configured to span the width of the recording media, such that two print modules located side by side are used to eject ink on the first and second sections of the web. 
     Each of the print modules  80 - 99  of  FIG. 9  includes an array of printheads that are arranged across the width of both the first section of web media and second section of web media. Ink ejectors in each printhead in the array of printheads are configured to eject ink drops onto predetermined locations of both the first and second sections of media web  114 . 
     Operation and control of the various subsystems, components and functions of printing system  100  are performed with the aid of a controller  128  and memory  129 . In particular, controller  128  monitors the velocity and tension of the media web  114  and determines timing of ink drop ejection from the print modules  80 - 99 . The controller  128  can be implemented with general or specialized programmable processors that execute programmed instructions. Controller  128  is operatively connected to memory  129  to enable the controller  128  to read instructions and to read and write data required to perform the programmed functions in memory  129 . Memory  129  can also hold one or more values that identify tension levels for operating the printing system with at least one type of print medium used for the media web  114 . These components can be provided on a printed circuit card or provided as a circuit in an application specific integrated circuit (ASIC). Each of the circuits can be implemented with a separate processor or multiple circuits can be implemented on the same processor. Alternatively, the circuits can be implemented with discrete components or circuits provided in VLSI circuits. Also, the circuits described herein can be implemented with a combination of processors, ASICs, discrete components, or VLSI circuits. 
     Encoders  160 ,  162 , and  164  are operatively connected to preheater roller  118 , apex roller  120 , and leveler roller  122 , respectively. Each of the encoders  160 ,  162 , and  164  are velocity sensors that generate an angular velocity signal corresponding to an angular velocity of a respective one of the rollers  120 ,  118 , and  122 . Typical embodiments of encoders  160 ,  162 , and  164  include Hall effect sensors configured to generate signals in response to the movement of magnets operatively connected to the rollers and optical wheel encoders that generate signals in response to a periodic interruption to a light beam as a corresponding roller rotates. Controller  128  is operatively connected to the encoders  160 ,  162 , and  164  to receive the angular velocity signals. Controller  128  can include hardware circuits, software routines, or both, configured to identify a linear velocity of each of the rollers  120 ,  118 , and  122  using the generated signals and a known radius for each roller. 
     Tension sensors  152 A- 152 B,  154 A- 154 B, and  156 A- 156 B are operatively connected to a guide roller  117 , apex roller  120 , and post-leveler roller  123 , respectively. The guide roller  117  is positioned on the media path P prior to the preheater roller  118 . The post-leveler roller  123  is positioned on the media path P after the leveler roller  122 . Each tension sensor generates a signal corresponding to the tension force applied to the media web at the position of the corresponding roller. Each tension sensor can be a load cell configured to generate a signal that corresponds to the mechanical tension force between the media web  114  and the corresponding roller. 
     In  FIG. 9  where two sections of the media web  114  engage each roller in tandem, each of the tension sensors are paired to identify the tension on each section of the media web  114 . In embodiments where one surface of the media web engages each roller, a single tension sensor can be used instead. Tension sensors  152 A- 152 B generate signals corresponding to the tension on the media web  114  as the media web  114  enters the print zone passing print modules  80 - 99 . The print zone is also known as the ink application zone or the “jetting zone.” Tension sensors  154 A- 154 B generate signals corresponding to the tension of the media web around apex roller  120  at an intermediate position in the print zone. Tension sensors  156 A- 156 B generate signals corresponding to the tension of the media web around leveler roller as the media web  114  exits the print zone. The tension sensors  152 A- 152 B,  154 A- 154 B, and  156 A- 156 B are operatively connected to the controller  128  to enable the controller  128  to receive the generated signals and to monitor the tension between apex roller  118  and the media web  114  during operation. 
       FIG. 1  is an elevational perspective view of one embodiment of an inversion apparatus  200  to invert the web to enable printing of the web on the unprinted side.  FIG. 2  illustrates a flow path of the continuous web of recording media and is discussed in combination with  FIG. 1 , where a portion of the inversion apparatus is not shown to more clearly illustrate the paper path and transport direction.  FIG. 2  also illustrates a transport direction  202  toward the print modules, away from the print modules, to the inversion apparatus  200 , and back to the print modules for printing on the second side of the web. The letter P is used to illustrate the first side of the web being printed on during a first pass of the web through a printer. The letters NP are used to illustrate the second side of the web which is not printed on during a first pass of the web through a printer, but which is transported toward the print modules for printing on the NP side, or second side, at location  203 . The inversion apparatus  200  of  FIG. 1  replaces the web inverter  168  illustrated in  FIG. 9 .  FIG. 9  illustrates a media path P and an inverter path P′ wherein the web moves into one side (the left illustrated side) of the web inverter  168  and out another side (the right illustrated side) of the web inverter. In the inversion apparatus  200  of  FIG. 1 , the web reverses direction within the inversion apparatus  200 . Consequently, the arrow  202 A corresponds to the inverter path P′ located on the right side of the web inverter  168  as illustrated in  FIG. 9 . 
     The inversion apparatus  200 , or turnbar assembly, includes an input  204 , an output  206 , a turnbar mechanism  208  (not shown in  FIG. 2 ), an idler roller device  210  (not shown in  FIG. 2 ), a displacement guide assembly  211 , and a blower  212 . In this embodiment, the inversion apparatus  200  includes the input  204  generally shown as being located on the right side of the inversion apparatus  200  as illustrated in  FIG. 1 . At the input  204 , an input roller  214  receives and supports the web media after one side of the media has been imaged by the print modules at a location  205  shown in  FIG. 2 . The roller  214  is supported by a frame not shown. 
     A first turnbar  220  is generally diagonally supported with respect to the paper path  202  by a first portion of a frame  222 . A second turnbar  224  is also generally diagonally supported in a direction substantially perpendicular to the support location of roller  220  by the frame  222 . Turnbar  224  directs the unprinted side of the web back to the printing system for completion of a duplex image. The first turnbar  220  is located beneath the second turnbar  222  as illustrated and receives the media web after passing up from the bottom of the machine at location  207  from the supply side first pass. Once the web enters the turnbar assembly  200 , the web is transported in a direction  230  across the top surface of the turnbar  220  and wraps around the turnbar  220  where the web is directed toward a first idler roller  232 . The web is then directed towards a second idler roller  234  and moves in a direction  236  towards the second turnbar  224 . The web wraps around the second turnbar  224  and is directed toward the output  206  and through the displacement guide assembly  211  where the web is directed to the location  203  for printing on the second side of the web. The displacement guide assembly  211  adjusts the lateral position of the web for printing on the second side of the web. A lateral edge sensor (not shown) keeps the exit position of the web to within approximately plus or minus 0.1 millimeter (mm) for transport to the print modules  80 - 99 . 
     As illustrated in  FIG. 2 , the non-printed side of the continuous web of recording media is located adjacent to the external surfaces of the turnbars. Such placement of the web substantially reduces or prevents image drag out and scratching of images which could occur should the imaged side of the web face the turnbar surfaces during inversion from one side of the web to the other. 
     The first idler roller  232  and the second idler roller  234  can include a surface formed of a composite material placed on a metal roller or it can be a metal anodized roller. The composite material can either have a smooth surface or can be a treaded surface. In addition, one or both of the first idler roller  232  and the second idler roller  234  can be adjustably mounted in the inversion apparatus  200  to provide for registration adjustment of a first side image to a second side image. 
     The blower  212  of  FIG. 1  includes first and second blower outputs each respectively operatively connected to one of the turnbars  220  and  224 . Each of the turnbars  220  and  224  include internal cavities which receive forced air from the blower  212 . A plurality of apertures formed in the surface of a turnbar, as discussed below with reference to  FIGS. 3-6 , directs the forced air from the internal cavity to the surface of the turnbar where the forced air escapes. As the continuous web of print media moves across the turnbars, a cushion of air, or an air foil, is formed between the surface of the turnbar and the surface of the web facing the turnbar surface. Two blowers can be used in place of a single blower having two outputs. 
     The air directed through the apertures of the turnbar provides a lifting pressure to separate the web from the surface of the turnbar during movement of the web. The lifting force provided by the turnbar apertures depends on the air pressure provided by the blower, the area outer perimeter of the turnbar in contact with the paper, and the number and location of apertures formed in the surface of the turnbar through which the forced air escapes. The outer diameter of the turnbar determines the contact pressure of the paper to the surface given by tension/radius (T/R) psi. As the turnbar radius increases the T/R pressure will drop and the blower pressure can be reduced to provide the force to provide a stable gap. However; when increasing the diameter of the turnbar, which reduces the T/R pressure thereby providing more lift with a smaller blower pressure, more air flow is required due to a larger perimeter loss area. In one embodiment as illustrated in  FIG. 1 , the first turnbar  220  and the second turnbar  224  each include a diameter of approximately 3.5 inches. 
     In one embodiment of a known inversion apparatus, a turnbar assembly is used to flip the image between print engines or between stations on a flexo machine, a printing machine which utilizes a flexible relief plate, wherein the first side of the web being imaged first comes into contact with the turnbars when transported through an inversion apparatus. In most systems whether they flip on the image or non-image side the tensions are low &lt;0.1 pli and the turnbar diameters are four inches in diameter. At these low tensions, the turnbar blower is relatively small in pressure and volume delivery. However, when the turnbar is inserted in a high tension control loop having a range of 2 to 5 pli, in one embodiment, the need for a larger turnbar diameter and higher blower flow rates is desirable. If the web drags on the surface of the turnbar, the tension loop is disturbed and excites the printing machine to a web drive resonance of twenty-two (22) hertz which causes misregistration of images. In a printer with 3.5 inch diameter turnbar, the T/R pressure is nominally 1 pound per square inch (psi) surface pressure. The most difficult region to float the web at high tensions is at the turnbar tangents 
     The arrangement of holes around the entrance and exit web to turnbar tangents is critical. See  FIGS. 3 and 5 . The first row of lift holes are placed outside an incoming tangent line in a direction opposite the direction of travel of the web before the incoming tangent line and the row of exit holes are located after the outgoing tangent line. In one embodiment, the first row of holes is 10 degrees before the incoming tangent line and the row of exit holes is 10 degrees after the outgoing tangent line, so that the included angle between the rows of holes is 200 degrees included. 
     The placement of the holes includes at least three features: 1) the eddy currents generated by Bernoulli laws are reduced which eliminates the tendency to pull the web to the turnbar instead of lifting it away from the tangent entrance if the holes were located directly on center; 2) the second effect is to reduce the acoustic noise from the excitation of both web (drum skin) and air through the gap, for instance in one example with the holes placed directly on the tangent acoustic noise is greater than 95 decibels (db) and with the holes rotated 10 degrees past tangent the sound level is reduced 10 db; and 3) the optimized hole pattern assists the ensures that the web at high tension floats the web over the entire wrap of and without touching the turnbar using a given supply pressure and flow rate from a reasonably sized commercial blower. In one embodiment, a Bush 310D blower is used and which is available from Busch USA, Virginia Beach, Va. The operating points used in this embodiment for the blower are approximately 1 to 1.25 psi pressure at flows of 170 to 180 cfm. 
     In the present disclosure, printing at higher speeds is achieved by establishing a relationship between the T/R pressure, aperture size of a turnbar, patterns of the apertures disposed on the turnbar surface, flow rate and blower pressure to provide a uniform float height or air cushion along incoming contact points of the web with the turnbar, including nips and paper edges. 
     The third important aspect of the described embodiments is to provide higher web tensions to control the different web tensions provided in the spreader nip at 6000 lb. pressure. In one embodiment, the spreader nip provides a differential strain in the paper due to paper thickness/ink coverage/layer thickness/coefficient of friction between ink drum and rubber spreader roll. The selected blower with the optimized hole pattern also allows for web tensions of up to 5.5 pli which allows for higher overall web tensions in the machine. This keeps side 1 to side 2 tension with high area coverage images to maintain a 4 to 5 kg differential. It is essential for web tracking that the side 1 tension not drop below a minimum threshold. In addition, by transporting the paper through the inversion apparatus on the non-image side to ensure no image drag out, the image streaking resulting from an image facing a surface of the turnbar is eliminated. By selecting transport speed, turnbar diameter, aperture size, and aperture pattern, a commercially available blower of reasonable size supplies a sufficient amount of airflow to provide an acceptable air cushion at both turnbars with one blower. 
       FIG. 3  illustrates a top view of one of the turnbars, such as turnbar  220 , with a 9.5 inch wide imaging web media, such as paper, wrapped 180 degrees about an exterior surface  300  of the turnbar. While the turnbar  220  is illustrated, in one embodiment the other turnbar  224  is similarly configured. The exterior surface  300  includes an air foil region having a plurality of apertures  302  which extend from an interior cavity of the turnbar  220 , through a sidewall of the turnbar  220 , and through the surface  300  to provide airflow from the interior to the exterior of the turnbar. The plurality of apertures  302  are arranged on the surface of the turnbar in a region of apertures  302  organized in a predetermined pattern  304 . The predetermined pattern  304  includes a plurality of rows  306  extending along a longitudinal axis  308  of the turnbar  220 . The predetermined pattern  304  is also organized to include a plurality of columns  310  disposed along a circumference of the turnbar  220 , in which the columns  310  can be viewed as being either perpendicular to the longitudinal direction  308  or as being arranged diagonally as a helix about the circumference of the turnbar  220 . A region of a non-apertured surface  312  is disposed outside the pattern  304 . 
     The density of the apertures within the predetermined pattern  304 , in part, determines the amount of an air foil or a float provided between the surface of the turnbar at the region  304  and the continuous web. If the continuous web of print media does not float above the surface of the turnbar  220 , but instead contacts the surface  300 , a tangent line is defined on the turnbar  220  along a leading edge and a trailing edge of the web. For instance, a tangent line  314  is defined on a leading edge of the turnbar  220  when no air cushion is provided. The trailing edge tangent line when no air cushion is provided is not shown. The predetermined pattern  304  is defined to include at least one row of apertures located before the tangent line  314  and at least one row of apertures located after the trailing edge tangent line. In the illustrated embodiments, a row of apertures is provided at the leading edge and trailing edge tangent lines. A row of apertures need not be provided at both the leading edge and trailing edge tangent lines. In other embodiments, one or both of the rows of apertures include a size different than the remaining apertures in the pattern  304 . In still another embodiment, the number of apertures of the leading and trailing edge rows are different than the rows of apertures in the remaining pattern  304 . 
     As the continuous web moves across the surface  300  of the turnbar  220 , a row of apertures  316  outside the tangent lines  314  provides a float or air cushion in an area of the turnbar surface where the pressure under the web returns to atmosphere. The row  316  is spaced from the tangent line  314  by a distance of approximately the same distance existing between adjacent rows in the pattern  304  when the rows are evenly spaced. By placing at least one row of apertures before the leading edge tangent line and at least one row of apertures after the trailing edge tangent line, contact pressure between the web at the tangents is reduced or prevented. In one embodiment, the first and last row of holes are biased approximately ten (10) degrees before the incoming web tangent line and ten (10) degrees after the tangent line at the web exit. By locating the first and last row of apertures outside the tangent lines, eddy current cancelation is provided to aid in floating the web at the tangents. In another embodiment, the first and last rows of apertures are placed at the tangent lines, but include apertures of a different size that the remaining apertures of the pattern. 
     The first and last rows of apertures and the first and last columns of apertures define a perimeter where the first and last columns substantially coincide with the outer edges of the continuous web of recording media of the largest size of media being imaged. In the embodiment of  FIG. 3 , the width of the media is 9.5 inches. The first and last columns generally coincide with the outer edges of the width of the recording media. In one embodiment, the apertures within the perimeter defined by the pattern  304  are spaced evenly along the rows and along the columns such that no portion of the pattern within the perimeter is missing apertures. 
       FIG. 4  illustrates a front view another embodiment of a pattern of apertures  320  which in different embodiments are located on one or both of the turnbars  220  and or  224 . The pattern of apertures  320  which defines the air foil region includes a non-apertured portion  322  located within a perimeter border of apertures including one or more rows of apertures and one or more columns of apertures. As described above, the perimeter of apertures includes first and last rows and first and last columns, where the first and last rows are located outside the tangent lines. In this embodiment, the non-apertured portion  322  is generally centrally located within the perimeter border of apertures. The perimeter of border apertures includes a plurality of columns of apertures  324  and a plurality of columns of apertures  326 . At least one first and one last row of apertures is included in the pattern of apertures  320 . The missing holes in the front view are not needed because the entrained air at the non-apertured surface between the apertures floats the web. The gap increases in this area. As can be seen in  FIG. 4 , three columns of apertures  324  are located on a left side of the portion  322  and four columns of apertures  326  are located on a right side of the portion  324 . In this embodiment, the apertures which in one embodiment are located between the left side and right of the apertured surface at the non-apertured portion  322  are not required to assist in floating the web around the body of the turnbar  320 . By reducing the number or apertures, the total amount of air flow generated by the blower  212  can be reduced. 
       FIG. 5  shows a seven inch wide continuous web  400  moving across the surface of the turnbar  220  of  FIGS. 3  and/or  4  exposing four columns of apertures thus allowing more air to escape to atmosphere. One column of apertures  402  is exposed on the left side and three columns of apertures  404  is exposed on the right side. The floatation holes under the 7 inch web with air loss from the uncovered holes is sufficient pressure to counteract a T/R pressure of 1 psi to 1.25 psi. Also, the flotation holes must be small enough to maintain the internal plenum pressure with a chosen blower size. 
       FIG. 6  is the front view of the seven inch wide continuous web  400  on the turnbar  220  of  FIG. 5 . As can be seen, the non-apertured portion  322  is generally located within the edges of the perimeter of the apertured portion of the turnbar. 
     As described above, the Busch Model 0310D is used in one embodiment. While this particular blower has been chosen as being appropriately sized for this particular application, other types and sizes of blower are selected to provide the air flow for different embodiments. Since the described printer moves the continuous web of material at high speeds which require increased tensions of the transported web, the higher tensions provide high T/R pressures in one embodiment of about 0.7 psi that makes the generation of an air flow gap difficult to achieve. Therefore, the aperture size, the aperture distribution and the aperture quantity are determined to coordinate the amount of lift with the rate of air flow. In addition, the first and last row of apertures when moved away from and outside the contact area defined by the tangent contact points provides Bernoulli and eddy current cancelation at the leading edge and trailing edge where the pressure transitions to atmosphere. The leading and trailing rows outside the potential contact area defined by the tangents increases the float at the tangential contact points to reduce or prevent drag. 
       FIG. 7  is a graphical representation of a gap clearance between a surface of a turnbar and the continuous web of print media. In  FIG. 7 , a gap float height with the Busch 0310 blower for the 7 inch embodiment is shown in the case where three columns of holes are left exposed on a left side and a right side of the web. The exposure of three columns of apertures deflates the web in the wrap when the pressure drops below 1.1 psi. Since the printers are located in all elevations and climates, the blower size is increased where necessary to provide a desired float. For instance, in a location providing power at fifty (50) hertz and at an elevation of six-thousand (6000) feet, the size of the blower is increased to a blower of the 0310 size, available from Busch, to ensure that the web when printing to seven inch wide media with 4 or 5 columns of apertures exposed is elevated from the surface of the turnbar. 
       FIG. 8  is a graphical representation of velocity and tension versus time. In  FIG. 8  the velocity and tension graphs demonstrating that the web does not drag and excite the twenty-two hertz transfer function resonance frequency of the web/drive system. The lower traces on the graph are the tension zones and are shown to be stable during the ramp up of the web. 
     The disclosed embodiments substantially prevent the web from touching the turnbars at increased rates of transport speeds. 
     In one embodiment, the turnbar includes a non-uniform hole pattern for highly tensioned webs on a small radius to provide sufficient lift gap with an appropriately sized blower. One blower handles two turn bars. The first and last rows of holes are leading and lagging the tangents to reduce the acoustic noise approximately 15 db lower than a printer having a known web drum skin resonance. Flotation of the web at the tangents reduces or eliminates web drag and turnbar wear. 
     It will be appreciated that variants of the above-disclosed and other features and functions, or alternatives thereof, can be desirably combined into many other different systems, applications or methods. Various presently unforeseen or unanticipated alternatives, modifications, variations or improvements can be subsequently made by those skilled in the art that are also intended to be encompassed by the following claims.