Patent Publication Number: US-6983692-B2

Title: Printing apparatus with a drum and screen

Description:
BACKGROUND 
   There are many types of printing mechanisms. One type of printing mechanism includes a drum for handling media. Positioned near the drum are one or more printheads that place ink on the media as the media is moved through a print zone. The media is held on the drum using a vacuum that holds the print medium onto the drum. In operation, a sheet is fed to the rotating drum by a sheet feeder, and the vacuum captures it and rolls it on to the drum. As the drum and media rotate, the media passes one or more printheads that print on the paper with as many revolutions as is necessary. After the leading edge of the media passes the printhead, or last printhead, on its last pass, an ejector is used to remove the media from the drum. As soon as the trailing edge of the media has passed the sheet feeder, the next sheet of media is fed on to the drum. Difficulties exist in separating the media from the drum after placing the ink on the media. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a simplified front view of a printing apparatus according to one embodiment of the invention. 
       FIG. 2  is a schematic view of a printing apparatus that includes the printer controller and a host computer according to an embodiment of the invention. 
       FIG. 3  is a schematic view of a print drum and the paper path of the printing apparatus according to an embodiment of the invention. 
       FIG. 4  is an exploded perspective view of the print drum and the screen according to an embodiment of the invention. 
       FIG. 5  is an assembled view of the print drum and the screen and a nozzle for directing air or another gas toward the ejection channels of the print drum according to an embodiment of the invention. 
       FIG. 6  is a cross sectional schematic diagram illustrating a pick-off shovel for removing paper from the surface of a drum according to an embodiment of the invention. 
       FIG. 7  is a schematic diagram illustrating a plurality of pick-offs positioned near the surface of a screen of a drum according to an embodiment of the invention. 
   

   DETAILED DESCRIPTION 
   In the following detailed description of the embodiments, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustrating specific embodiments in which the invention may be practiced. The embodiments illustrated are described in sufficient detail to enable those skilled in the art to practice the teachings disclosed herein. Other embodiments may be utilized and derived therefrom, such that structural and logical substitutions and changes may be made without departing from the scope of present inventions. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of various embodiments of the invention is defined only by the appended claims, along with the full range of equivalents to which such claims are entitled. 
     FIG. 1  shows one embodiment of a printing device according to one embodiment of this invention.  FIG. 1  includes a printing apparatus  110 , that includes a chassis  112  and a print media handling system  120  for supplying a print media. The print media handling system  120  includes at least one media input tray  122 , a media output tray  124  and a media or paper path  126 . The media or paper path  126  includes a series of rollers  130  that position the paper to receive ink from an ink source  140 . In addition to the rollers  130 , the media or paper path includes a print drum  310 . The print drum  310  moves the media into a print zone  128 . The ink source  140  is positioned near the print drum  310  in the print zone  128 . In this embodiment, the ink source  140  includes a plurality of ink jets  220  positioned around a portion of the print drum  310 . It should be understood that the ink source  140  is not limited to a plurality of ink jets and could be any other source of ink or fluid, such as toner cartridge or other source of ink or fluid. Furthermore, the print media used includes any type of suitable sheet material, such as paper, photo-quality paper, card-stock, transparencies, mylar, foils, and any other similar print media. The printing apparatus also includes a control panel  150 . The control panel includes a display  152  and a keypad  154  for inputting commands to the printing apparatus  110 . Parameters related to a print job are displayed on the display  152 . Selections are made at the keypad  154 . After a selection is made, the result is displayed on the display  152 . The location and configuration of the control panel may vary. 
     FIG. 2  is a schematic view of a printing apparatus  200  that includes the printing apparatus  110  with a printer controller  242 , according to an embodiment of the invention. A host computer  270  is attached to the printing apparatus  110 . The controller  242  generally receives instructions from the host computer  270 , such as a personal computer. A monitor or display  272  coupled to the host computer  242  is used to display visual information to an operator, such as the printer status or a particular program being run on the host computer  270 . Screens on the monitor or display  272  are one form of user interface to the printing apparatus  110 . 
   The controller  242  controls many aspects of the printing apparatus  10 . A memory  240  is attached to the controller  242 . The host computer  270  is also attached to the controller  242 . A display  272  is also attached to the host computer  270 . The display  272  is associated with the host computer  270  and displays screens associated with the type of hardware and software associated with the host computer  270 . The display  272  is different from the display  152  of the display panel  150  of the printing apparatus  10 . The display  152  of the display panel  150  generally displays messages related to the printing apparatus  110 . 
   The controller  242  is communicatively coupled to a host computer  270 . The host computer  270  is shown connected to a display device  272 . The host computer  270  can be a variety of information sources such as a personal computer, work station, or server, to name a few, that provide image information to the controller  242  by way of a data link  274 . The data link  274  may be any one of a variety of data links such as an electrical link, radio frequency link, or an infrared link. The data link transfers information between the host computer  270  and the printing apparatus  10 . The controller  242  controls the transfer of information between the host computer  270  and a plurality of printheads  230 ,  231 ,  232  and  233  in the print zone  128  of the printing apparatus. The controller, in some embodiments of the invention, can monitor ink type and ink color in a plurality of reservoirs  220 ,  221 ,  222 , and  223 . The controller  242  also controls many other aspects of the printing apparatus  110 , such as the speed of rotation of the print drum  310 . A media  350  is shown as temporarily attached to the print drum  310 . 
     FIG. 3  is a schematic view of a print drum  310 , and a portion of the paper path  126  according to an embodiment of this invention. As shown in  FIG. 3 , there is a plurality of printheads located near the outer peripheral surface of the print drum  310 . The printheads include printheads  230 ,  231 ,  232 , and  233  as well as other printheads. All the printheads, which place the ink onto a medium, or paper, form the ink source  140 . All the printheads are located within the print zone  128 . The portion of the paper path  126  includes a media feeder  326 , which loads media onto the print drum  310  along the paper load area, depicted by the reference numeral  320  on the area of the drum downstream from the media feeder  326 . The print drum  310  rotates in a direction depicted by arrow  312 . 
   The print drum  310  and the printing apparatus include several sensors. First of all, there is a top of form (“TOF”) sensor  340  which is a senses when the incoming media enters the print zone. The signal from the TOF sensor  340  feeds a signal back to the controller  242  (shown in FIG.  2 ). The TOF sensor is located upstream of the print zone  128 . There is also a media load sensor  342 . The media load sensor shows that there is paper or a medium  350  on the outer surface of the print drum  310  downstream from the print zone  128 . The media load sensor  342  indicates that a media is on the outer peripheral surface of the print drum  310 . 
   Located adjacent the media load sensor  342  is a media pick-off sensor  344 . The media pick-off sensor  344  senses the presence of the paper. In some instances, the paper or media  320  stays on the print drum for a single pass. In other instances, the paper or media stays on the print drum  310  for multiple passes. The media pick-off sensor  344  senses the presence of the paper or media  320  for a single pass or a multiple pass. The media pick off sensor inputs this information to the controller  242  (shown in FIG.  2 ). The controller  242  enables a media pick-off when the media is to be picked off, or removed, from the surface, or outer peripheral surface of the print drum  310 . The controller  242  (shown in  FIG. 2 ) moves the media pick-off  360  into position to remove the media from the print drum  310 , and specifically from the surface of the print drum  310  (shown in FIGS.  2  and  3 ). 
   If the media pick-off  360  is not enabled, the media  350  stays attached to the drum for one or more additional rotations. In other words, media  350  can be on or remain on the surface of the drum  310  in the event multiple passes are needed in order to accomplish a particular print job. The print drum also includes a source of vacuum  365 . The vacuum  365  produces a vacuum at the peripheral surface of the drum  310 . Also located within the print drum  310  is a source of radiant heat  370 . The source of heat  370  is used to dry or partially dry any ink that is laid down or placed on the media  350  which is located on the outer peripheral surface of the print drum  310 . In this particular embodiment, the media pick-off  360  includes an air jet, or a device which produces a stream of high-pressure, high-volume air which can be directed at the surface of the print drum  310 . 
     FIG. 4  shows an exploded view of the print drum  310 . The print drum  310  includes a vacuum drum portion  410 , and a screen portion  430 . The screen portion  430  is dimensioned to fit over an outside or peripheral surface  411  of the drum  410 . The drum includes a series of channels, such as channel  412  and channel  413 , which are circular channels which pass over the outer or peripheral surface of the drum  410 . The drum also includes longitudinal channels, such as  414  and  415 . The drum  410  includes openings which occur at the intersections of the circular channels  412 ,  413  and the longitudinal channels  414 ,  415 . The openings pass through the drum to the vacuum source  365  (as shown in FIG.  3 ). The channels, such as  412 ,  413 ,  414 ,  415 , and the openings, such as opening  490 , at the intersections of the various channels, form passageways that distribute the vacuum over the peripheral or outer surface  411  of the drum  410 . The vacuum  365 , and especially the channels  412 ,  413 ,  414 ,  415  and openings  490  distribute the vacuum over the surface of the drum so that media, or paper, such as  350  shown in  FIG. 3 , are temporarily attached to the drum by the vacuum during the print job. The vacuum source  365  acting throughout the channels such as  412 ,  413 ,  414 ,  415  and openings can be maintained so that the media  350  (shown in FIG.  3 ), stays on print drum  310  for single or multiple passes through the print zone  128  (shown in FIGS.  2  and  3 ). 
   The screen or cover  430  which covers the outer peripheral surface  411  of the drum  410  serves to distribute heat from the radiant heat source  370 . The screen  430  is made of a heat-conducting material so that heat from the heat source  370  is distributed substantially evenly over the outside surface of the drum which corresponds to the peripheral surface  431  of the screen  430 . The screen  430  or covering, as shown in  FIG. 4 , includes a plurality of apertures, such as  432 ,  433  that are placed over the entire peripheral surface  431  of the covering or screen  430 . Each dot shown on the screen  430  represents an aperture. The apertures  432 ,  433  are sufficient to allow the vacuum from the channels  412 ,  413 ,  414 ,  415  to act through the apertures  432 ,  433 . The vacuum can then be transferred through the screen or through the covering  430  so that paper or medium  350  (shown in  FIGS. 2 and 3 ) remains on the surface  431  of the screen or covering  430 . The screen or covering  430 , according to some embodiments, has a sufficient amount of material so that the channels, such as  412 ,  413 ,  414 ,  415  are spanned and heat is distributed substantially evenly over the surface  431  of the screen or covering  430 . In some embodiments, the openings  432 ,  433  in the screen are small enough so that a substantial amount of material spans the channels  412 ,  413 ,  414 ,  415  associated with the air passageways to prevent uneven heating along the peripheral surface  411  of the print drum  310  between the solid portions and the channels  412 ,  413 ,  414 ,  415 . The apertures  432 ,  433  in the screen  430  are also sufficient to allow the pick-off device  360  (shown in  FIG. 3 ) to direct a stream of air toward the surface  431  of the cover or screen  430  and allow air to pass to the surface  411  of the outer drum  410 . It should be noted that the screen or cover  430  is made of a material which is thermally compatible with the drum  410 . In some embodiments, the screen  430  is made of a material having a coefficient of thermal expansion which is substantially similar to the coefficient of thermal expansion associated with the vacuum drum portion  410  so that thermal mismatches will be either reduced or will not occur. In some embodiments, the screen material has a coefficient of thermal expansion within the range of 1.0 to 30.0 micrometers/meter/degree Centigrade. In some other embodiments, the screen material has a coefficient of thermal expansion within the range of ten percent less than a coefficient of thermal expansion of the drum material and ten percent greater than the coefficient of thermal expansion of the drum material. In some embodiments, the cover or screen  430  may be made of the same material as the vacuum drum portion  410 . Therefore, the screen  430  and the vacuum drum portion  410  would have the same coefficient of thermal expansion. 
     FIG. 5  shows print drum  500  according to another embodiment of this invention. In this particular embodiment, the print drum includes a vacuum drum portion  410  which has a screen  530  thereon. The vacuum drum portion  410  and the screen  530  are made of materials which have substantially the same coefficient of thermal expansion. This prevents thermal mismatches from occurring when the source of heat or radiant energy within the drum  370  (shown in  FIG. 3 ) heats the vacuum drum portion  410  and the screen  530 . The screen includes a series of apertures  532 ,  533  that extend through an outer surface  531  of the screen  530 . The apertures  532 ,  533  in the screen  530  are 0.3 mm in diameter, in one embodiment, although the size and shape of the openings may vary. The apertures, such as apertures  532 ,  533 , may be evenly distributed over the screen  530  in the embodiment shown in FIG.  5 . The amount of material that remains as part of the cover or screen is sufficient to span the channels  412 ,  413 ,  414 ,  415  (shown in  FIG. 4 ) of the vacuum drum portion  410  and to allow heat to be distributed evenly over the surface  531  of the screen  530 . In other words, there is an amount of material  530  on the screen or covering that allows the screen  530  to span the channels  412 ,  413 ,  414 ,  415  (shown in  FIG. 4 ) and yet allow an even thermal distribution of the radiant heat coming from the radiant heat source  370  from within the drum  410 . The openings in the screen  530  also allow for an airstream type pick-off to force air to the surface  411  (shown in  FIG. 4 ) of the vacuum drum portion  410  to effectuate a removal of print medium  350  (shown in  FIGS. 2 and 3 ) from the surface of the screen  531 . 
   It should be noted that in some embodiments of the invention, the channel pattern forms a grid over the surface  411  of the print drum  410 . Although the width, shape, and depth of the channels may vary, in an example embodiment, the channels have a width of approximately 1 millimeter. As a result, the openings in the barrel through which the vacuum is drawn which occur at the intersections of channels  412 ,  413  and grooves  414 ,  415  are also on 20-25 millimeter centers. The material which forms the screen  430 ,  530 , in some embodiments, is 0.3 mm thick. One type of material is called Invar which is available from Belt Technologies, Inc. at Agawam, Mass. At temperatures typical of some of the example embodiments, Invar has a low, almost negligible, coefficient of thermal expansion. 
     FIG. 7  is a schematic diagram illustrating a plurality of media ejectors or pick-offs  600  positioned near the surface  631  of a screen  630  of a drum  610  according to an embodiment of the invention. Each of the media ejectors or pick-offs  600  is positioned near a circumferential channel  612  of the drum  610  Channels  612  are in communication with a vacuum chamber  660  via passages  690 . Each of the media ejectors or pick-offs  600  is in fluid communication with a source of pressurized gas  780 , such as air. Any type of pressurized gas may be used, although the example set forth here discusses the use of air.  FIG. 7  is illustrated without media on the surface  631  of the screen  630  of the drum, for the sake of clarity.  FIG. 6  is a cross sectional schematic drawing detailing a single pick-off or media ejector  600  for removing media  350  from the surface  631  of a screen  630  on the drum  610 . Now looking at both  FIGS. 6 and 7 , the media ejection and pick-offs for removal of media  350  from the surface  631  of the screen  630  of the drum will be discussed. The media ejector or pick-off  600  includes a shovel portion  602  and an air tube or conduit  604 . The pick-off  600  includes an internal cavity to allow an air tube  604  to pass down the length of the media ejector or pick-off  600  and through the shovel portion  602 . The air tube or conduit  604 , therefore, terminates near an end  606  of the pick-off  600  which is near the surface  631  of the screen  630  on the print drum  610 . The end  606  of the pick-off or media ejector is typically positioned so that the air tube or conduit  604  passing down its length of the pick-off or media ejector  600  directs a stream of air through apertures  632 ,  633  in the screen  630  and into a channel  612  on the drum  610 . The pick-off or media ejector  600  is actually positioned near the cover layer  630  and paper is removed from the drum  610  by blowing air into the circumferential channel  612  on the drum  610 . The air is directed through the apertures  632 ,  633  in the screen  630 . The end  606  of the air tube  604  does not extend into the screen  630 . Therefore, the screen also prevents the shovel portion  602  of the media-ejector or pick-off  600  from reaching below a lower surface of the paper  350  held onto the cover  630  of the drum  610 . 
   The air from the air tube or conduit  604  enters the channel  612  through the apertures  632 ,  633 . Raising the pressure along the channel  612  lifts the paper off the cover  630  upstream from the air tube or conduit  604  of the pick-off  600 . The pressurization along the channel  612  by the air passing through the air tube or conduit  604  results in an increase in the air pressure within the channel  612  that causes separation of the media  350  from the cover  630  upstream from the shovel portion  602 . After the leading edge of the media  350  separates from the cover  630 , the shovel portion  602  slides below the media  350  so it can then be completely separated from the screen  630  on the drum  610 . In one embodiment, the channel  612  corresponds to one of the air passageways that transmit a vacuum from the drum  610  to the media (see discussion in FIG.  4 ). In one embodiment, the source of vacuum is disabled before the media  350  is to be removed from the surface  631  of the screen  630 . In still other embodiments, there are a plurality of pick-offs or media ejectors  600  that pressurize a plurality of circumferential channels, such as channel  612 , in the drum  610  to remove the media  350  from the screen  630 . In some embodiments, a plurality of media ejection channels separate from the air passageways are pressurized to remove the media  350 . 
   Use of some embodiments of the present invention may result in fewer paper crashes using the pick-off or media ejector  600  which includes the shovel portion  602  and the air tubes or conduits  604 . Some embodiments may allow for separation of a wider range of paper or media weights and may do so in a more gentle, less abrasive way. As a result of using some embodiments of the present system and method for removing paper from the paper or media  350  from the screen  630  on the drum  610 , the integrity of the media is maintained which is especially important for duplex printing. In addition, pressurizing the media from below through a plurality of channels such as  612 , avoids touching the freshly printed or inked surface of the media  350 . Thus, using embodiments of this system may result in fewer ink smears on the printed surface of the print medium or paper  350 . 
   In conclusion, some embodiments of a printing apparatus include a print drum having a peripheral surface. The peripheral surface of the print drum has air passageway openings therein. A screen is placed over the peripheral surface of the print drum, the screen having openings therein that are smaller than the air passageway openings of the peripheral surface of the print drum. The printing apparatus also includes a heat source for heating the peripheral surface of the print drum and the screen. At least a portion of the heat source is located inside the print drum. The printing apparatus also includes a vacuum source. The vacuum source is in fluid communication with the air passageway openings on the peripheral surface of the print drum. At least a portion of the vacuum source is inside the print drum. 
   In some embodiments, the air passageway openings in the print drum include vacuum channels located between the air passageway openings on the peripheral surface of the print drum. The heat source heats the peripheral surface of the print drum and the screen, the screen covering the peripheral surface of the drum and passing over the air passageways and the vacuum channels. In some embodiments, the screen is made of a first material and the peripheral surface of the print drum is made of a second material, and the first material and the second material have a similar coefficient of thermal expansion. 
   In other embodiments, the screen and the peripheral surface of the print drum are made of a material having the same coefficient of thermal expansion. The peripheral surface of the printing apparatus includes a media ejection channel separate from the air passageway openings in the peripheral surface of the print drum, and also includes a source of pressurized gas in fluid communication with the at media ejection channel. In some embodiments the media ejection channel and the source of pressurized gas are adapted to produce a force on media greater than the force produced by the vacuum source in fluid communication with the air passageway openings on the peripheral surface of the print drum. The source of pressurized gas includes a pressure nozzle directed at the media ejection channel. The pressure nozzle is positioned near the screen so that pressurized gas from the pressure nozzle is directed through the screen and into the media ejection channel. 
   A method for printing on media held to a print drum by a vacuum includes placing a screen over the print drum, holding a print medium onto the print drum with a vacuum, depositing ink on the print medium, and heating the print drum and the screen. The method also includes removing the print media from the print drum. In some embodiments, pressurizing a media ejection channel on the surface of the print drum is part of removing the print media from the print drum. Pressurizing the media ejection channel includes directing a stream of gas into the media ejection channel and through the screen over the print drum. The stream of gas is directed toward the area of the print drum near a leading edge of the media. 
   A printing apparatus includes a print drum having a plurality of openings therein, an apparatus for holding media onto the print drum, an apparatus for heating the print drum, and an apparatus for preventing defects on the media due to differences in a heat transfer rate of a surface of the print drum and a heat transfer rate of the plurality openings in the print drum. In one embodiment, the apparatus for substantially lessening a set of defects on the media due to differences in a heat transfer rate of a surface of the print drum and a heat transfer rate of the plurality openings in the print drum includes a screen placed on the surface of the print drum, the screen spanning the plurality of openings in the print drum. The printing apparatus also includes an apparatus for removing media from the print drum. In some embodiments, the apparatus for removing media from the print drum includes at least one media ejection channel on a surface of the print drum. The at least one media ejection channel is separate from the plurality of openings in the print drum. The apparatus for removing media from the print drum includes a nozzle for directing pressurized gas at a surface of the print drum forward of a leading edge of the media on the print drum. The apparatus for holding media onto the print drum includes a source of low pressure in fluid communication with the plurality of openings in the print drum and the apparatus for removing media from the print drum, in some embodiments, includes a device for disconnecting the source of low pressure from the plurality of openings in the print drum. 
   A printing apparatus has a paper path that includes a source of paper, a print drum having an outside surface having vacuum openings therein for temporarily holding paper onto the print drum as the paper is moved through a print zone. The print drum includes a device to substantially lessens defects resulting from the difference between the vacuum openings and the surface of the print drum. The paper path also includes a mechanism for moving paper from the source of paper to the print drum, and a device for removing paper from the print drum. The printing apparatus also includes a source of ink positioned to deposit ink on the paper when the paper is positioned in the print zone. The printing also includes a housing. The paper path and the source of ink are located substantially within the housing. The printing apparatus also includes a heat source for heating the print drum. 
   A printing apparatus includes a print drum having a peripheral surface, and a nozzle positioned near the peripheral surface of the print drum. The nozzle directs a stream of gas toward the print drum and adapted to remove a media carried by the print drum. The print drum is substantially cylindrically-shaped and includes an axis. The stream of gas makes an angle traversing a radial line through the axis of the print drum. 
   Although specific embodiments have been illustrated and described herein, those of ordinary skill in the art will appreciate that any arrangement calculated to achieve the same purpose can be substituted for the specific embodiments shown. This disclosure is intended to cover any and all adaptations or variations of various embodiments of the invention. It is to be understood that the above description has been made in an illustrative fashion, and not a restrictive one. Combinations of the above embodiments, and other embodiments not specifically described herein will be apparent to those of skill in the art upon reviewing the above description. The scope of various embodiments of the invention includes any other applications in which the above structures and methods are used. Therefore, the scope of various embodiments of the invention should be determined with reference to the appended claims, along with the full range of equivalents to which such claims are entitled. 
   In the foregoing Detailed Description, various features are grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments of the invention require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separate embodiment.