Abstract:
A stripper blade has been developed for high throughput inkjet printers. The stripper blade includes a metallic blade body having a first thickness that extends to a leading edge having a second thickness that is less than about 25% of the first thickness, and at least one beveled surface leading from the metallic blade body to the leading edge to form a stripping edge that facilitates separation of media from a drum.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates generally to printers having a drum and, more particularly, to the components for facilitating removal of media from an offset imaging member after the media has passed through a transfix nip. 
       BACKGROUND 
       [0002]    In known printing systems having a drum, the print process includes an imaging phase, a transfix phase, and an overhead phase. In ink printing systems, the imaging phase is the portion of the print process in which the ink is expelled from the print head in an image pattern onto a transfer imaging surface or drum or other intermediate imaging member. The transfix phase is the portion of the print process in which the ink image is transferred from the drum to the recording medium. The image transfer typically occurs by bringing a transfix roller into contact with the imaging member to form a nip. The surface that is initially imaged may be referred to as a drum or receiving member and may be in the form of a drum, platen, band or the like. These surfaces may be referred to, for convenience, as an imaging drum, imaging member, or more simply, as a drum. The drum typically has a very thin release film on its surface that historically has been referred to as an intermediate transfer layer. This intermediate transfer layer receives the image and permits a more complete transfer of the image to media. A recording medium arrives at the nip as the drum rotates the image through the nip. The pressure in the nip helps transfer the image formed of malleable inks from the drum to the recording medium. As part of the overhead phase, the trailing edge of the recording medium passes out of the nip and the transfix roller is released from contacting the drum. The removal of the transfix member helps release the media from the drum. In some intermediate imaging printers, a stripper blade may be moved into position to intervene between the leading edge of a media leaving the transfix nip and the drum to facilitate separation of the media from the drum. 
         [0003]    Inkjet printers that use drums, sometimes called offset printers, have been developed with higher throughput rates. Some of these printers have drum that have larger circumferences than previously known printers. The curvature of a larger drum and the speed of the drum in higher throughput printers reduce the window of time available for moving the stripper blade into position for separation of the media from the drum. As this window of time decreases, the time for the ink on the media to cool after passing through the transfix nip also decreases. Consequently, some portion of the malleable ink may transfer to the stripper blade. Accumulation of this ink on the stripper blade may interfere with the effectiveness of the stripper blade to lift media from the drum. The use of wider media also presents greater challenges in constructing a blade that is sufficiently straight and rigid to establish full strip edge contact across the length. Additionally, at higher rotational speeds the contact between a stripper blade and the drum has resulted in a greater likelihood of damage to the drum&#39;s surface. A system that separates media from a drum while preserving the quality of the ink image on each media sheet as well as the surface of the drum benefits the field of offset printing. 
       SUMMARY 
       [0004]    A stripper blade has been developed for high throughput inkjet printers. The stripper blade includes a metallic blade body having a first thickness that extends to a leading edge having a second thickness that is less than about 25% of the first thickness, and at least one beveled surface leading from the metallic blade body to the leading edge to form a stripping edge that facilitates separation of media from a drum. 
         [0005]    A printer uses the stripper blade described above to facilitate the separation of media from the intermediate imaging member after the media exits a nip formed between the intermediate imaging member and a transfix roller. The printer includes a drum rotating past at least one printhead to receive ink ejected from the at least one printhead, a transfix roller configured to engage the drum selectively to form a nip through which media is transported to receive ink from the drum, and a stripper blade having metallic blade body with a first thickness that extends to a leading edge having a second thickness that is less than about 25% of the first thickness, at least one beveled surface leading from the metallic blade body to the leading edge, and the stripper blade being configured to engage the drum with the leading edge at a position near the nip formed between the transfix roller and the drum to facilitate separation of the media exiting the nip from the drum. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The foregoing aspects and other features of an ink printer implementing a stripper blade system are explained in the following description, taken in connection with the accompanying drawings, wherein: 
           [0007]      FIG. 1A  is a cross-sectional view of a metallic stripper blade. 
           [0008]      FIG. 1B  is a cross-sectional view depicting the leading edge of the stripper blade of  FIG. 1A . 
           [0009]      FIG. 1C  is a perspective view depicting the metallic stripper blade of  FIG. 1A . 
           [0010]      FIG. 1D  is a perspective view depicting an alternative stripper blade. 
           [0011]      FIG. 2 . is a side view of a stripper blade stripping a media sheet from a drum. 
           [0012]      FIG. 3  is a side view of a prior art ink printer. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    Referring to  FIG. 3 , there is shown a side view of a prior art ink printer  10  that may be modified to include a stripper blade system that reduces undesirable ink transfer during the printing process. The reader should understand that the embodiment of the print process discussed below may be implemented in many alternate forms and variations. In addition, any suitable size, shape or type of elements or materials may be used. 
         [0014]    As shown in  FIG. 3 , the ink printer  10  may include an ink loader  40 , an electronics module  44 , a paper/media tray  48 , a print head  50 , a drum  52 , a drum maintenance subsystem  54 , a transfix subsystem  58 , a wiper subassembly  60 , a paper/media preheater  64 , a duplex print path  68 , and an ink waste tray  70 . In brief, solid ink sticks are loaded into ink loader  40  through which they travel to a melt plate (not shown). At the melt plate, the ink stick is melted and the liquid ink is diverted to a reservoir in the print head  50 . The ink is ejected by piezoelectric elements to form an image on the drum  52  as the member rotates. Member  52  is called a drum because an ink image is formed on the rotating member and then transferred to media with the transfix subsystem. 
         [0015]    A drum heater is controlled by a controller to maintain the drum within an optimal temperature range for generating an ink image and transferring it to a sheet of recording media. A sheet of recording media is removed from the paper/media tray  48  and directed into the paper pre-heater  64  so the sheet of recording media is heated to a more optimal temperature for receiving the ink image. The sheet of recording media is synchronized so its movement between the transfix roller in the transfer subsystem  58  and the intermediate image member or drum  52  is coordinated for the transfer of the image from the imaging member to the sheet of recording media. 
         [0016]    The operations of the ink printer  10  are controlled by the electronics module  44 . The electronics module  44  includes a power supply  80 , a main board  84  with a controller, memory, and interface components (not shown), a hard drive  88 , a power control board  90 , and a configuration card  94 . The power supply  80  generates various power levels for the various components and subsystems of the ink printer  10 . The power control board  90  regulates these power levels. The configuration card contains data in nonvolatile memory that defines the various operating parameters and configurations for the components and subsystems of the ink printer  10 . The hard drive stores data used for operating the ink printer and software modules that may be loaded and executed in the memory on the main card  84 . The main board  84  includes the controller that operates the ink printer  10  is configured in accordance with an operating program executing in the memory of the main board  84 . The controller receives signals from the various components and subsystems of the ink printer  10  through interface components on the main board  84 . The controller also generates control signals that are delivered to the components and subsystems through the interface components. These control signals, for example, drive the piezoelectric elements to expel ink from the print heads to form the image on the imaging member  52  as the member rotates past the print head. The printer depicted in  FIG. 3  is merely exemplary of a printer suitable for adaptation with a stripper blade system, and the stripper blade system described herein may be used in a variety of printers with alternative components and configurations. 
         [0017]    The actuator  128  and transfix roller actuator  156  are both configured to operate in response to signals received from a controller (not shown). The controller may be a general purpose microprocessor that executes programmed instructions that are stored in a memory. The controller also includes the interface and input/output (I/O) components for receiving status signals from the printer and supplying control signals to the printer components. Alternatively, the controller may be a dedicated processor on a substrate with the necessary memory, interface, and I/O components also provided on the substrate. Such devices are sometimes known as application specific integrated circuits (ASIC). The controller may also be implemented with appropriately configured discrete electronic components or primarily as a computer program or as a combination of appropriately configured hardware and software components. 
         [0018]    A cross sectional view of a stripper blade that may be used to strip media away from an imaging member is depicted in  FIG. 1A . The stripper blade  100  has a body portion  112  with a substantially uniform thickness. In the embodiment of  FIG. 1A  the central portion  112  is approximately 0.4 mm thick. The stripper blade  100  has two beveled edges  106  and  108  that extend from the body portion  112  to an edge  104 . In the example of  FIG. 1A , edge  104  is approximately 0.02 mm thick, and the beveled edges  106  and  108  are each beveled at a 7° angle from horizontal. The upper and lower beveled edges  106  and  108  each have a length of approximately 1.63 mm. The upper beveled edge  106  comes into contact with the drum when the stripper blade  100  is placed in contact with the drum. One embodiment of a stripper blade implementation has been described, however, the blade may be configured with a one sided bevel or compound bevels on one or both sides and any bevel may be any angle. Drum width and diameter as well as other influences, such as media type, speed, ink formulation and the like may influence optimal blade geometry. In the implementation described, the beveled blade edge converges to a sharp edge with thickness of 0.03 mm or less, including a razor sharp thickness that is essentially zero. Anti-friction coating or plating may add to this thickness. The stripper blade  100  is composed of a metal or metallic alloy, such as steel, tempered steel, or stainless steel. 
         [0019]    A detailed view of the leading edge of stripper blade  100  is depicted in  FIG. 1B . An optional low-friction coating  116  covers the lower beveled edge  108 . The low friction coating  116  lubricates the area of contact between the stripper blade  100  and a media sheet that is being separated from the drum, facilitating a smooth separation of the media sheet. The low friction coating  116  also resists the transfer of ink from the media sheet to the stripper blade  100 . The low friction coating  116  is typically composed of a polymer, such as polysaccharide, polytetrafluoroethylene, or silicone. The coating may be applied to the surface of beveled edge  108 , or bonded into the beveled edge  108  using an oxidation infusion process known to the art. In an alternative blade arrangement where the upper beveled edge  106  contacts media sheets instead of the lower beveled edge  116 , the low friction coating  116  would instead be applied to the upper beveled edge  106 . 
         [0020]    A surface of the stripper blade from  FIG. 1A  is depicted in  FIG. 1C . In  FIG. 1C , the stripper blade  100  has a leading edge  104  that may have a width of approximately 320 mm, which is approximately equal to the width of drums in many tabloid size inkjet printers. Alternative widths are envisioned depending upon the width of the drum and the print media handled by a printer using stripper blade  100 . The beveled edges  108  and  106  form sloped surfaces with surface  120 A depicted in  FIG. 1C . The surface  120 A is covered by the low friction coating material discussed above. The body portion  112  of the stripper blade  100  extends from the beveled edges  106  and  108 , and in the embodiment of  FIG. 1C , the surface  120 B of the central portion  112  is also covered with the low-friction coating material. The low-friction coating material covers both surfaces  120 A and  120 B to facilitate separation of a media sheet over the entire surface of the stripper blade  100 . The leading or stripper edge that is functional for stripping media bearing a transfixed image from the surface initially imaged is at least as long as the largest media size to be accommodated, plus appropriate system tolerances. End treatment beyond this stripping edge may be modified to prevent the ends of the sharp stripping edge from scaring or digging into the drum, image or media. This end treatment includes rounding, chamfering, or forming the ends of the stripping edge so the ends do not substantially contact the drum. Consequently, the sharp stripping edge that facilitates the separation of the media from the drum may be all or a substantial portion of the blade length. Blade length as used in this document refers to the distance between the ends of the stripper blade at the stripping edge. 
         [0021]    An alternative embodiment of a stripper blade is depicted in  FIG. 1D . The stripper blade  150  in  FIG. 1D  has a curved leading edge  124 . The curved leading edge  124  curves or bows downwardly, allowing the outboard blade ends  128 A and  128 B to engage a drum before the central portion of leading edge  124 . This configuration allows for a more uniform distribution of pressure between the stripper blade  150  and a drum than the embodiments have a straight leading edge. When the stripping edge of the blade  150  is held flat, as with force against a drum, a blade fabricated with the intentional bow forms a straight stripping edge. 
         [0022]    A stripper blade stripping a media sheet from a drum is depicted in  FIG. 2 . The drum, depicted in  FIG. 2  as a rotating drum  208 , rotates in direction  216  carrying media sheet  212 . Stripper blade  204  engages the surface of drum  208 , and the media sheet  212  separates from the drum  208  as it moves over the stripper blade  204 , beginning at the blade-drum intersection  216 . The stripper blade  204  is arranged with the beveled leading edge  206  opposing the rotational direction  216  of drum  208 . The beveled leading edge  206  begins to lift the media sheet  212  from the drum  208 , and the media sheet continues lifting away from the drum  208  as it passes over stripper blade  204 . A low-friction coating may be applied to the surface of stripper blade  204  that contacts the media sheet  212 , reducing the likelihood of the media sheet  212  stubbing on contact with the stripper blade  204 . 
         [0023]    In operation, ink is ejected from at least one print head onto the surface of the drum, forming a latent image. The transfix roller is moved into a transfix nip position with the drum, and the drum rotates, carrying a media sheet through the transfix nip to transfer the latent image from the drum to the media sheet. The stripper blade is placed against the surface of the drum at a position ahead of the leading edge of the media sheet after the leading edge of the media sheet emerges from the transfix nip. At least a portion of the media sheet surface that was in contact with the drum contacts the stripper blade as the media sheet separates from the drum. The portion of the media sheet contacting the stripper blade contacts the stripper blade&#39;s low-friction coating. The stripper blade is removed from contact with the drum after the media sheet has separated from the drum. The transfix roller is removed from the transfix nip after the media sheet has passed through the transfix nip. The process recited above may be repeated for multiple media sheets in a printer and may vary to some extent as to phasing or timing of the process. 
         [0024]    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.