Abstract:
A hybrid printing assembly includes a first printing subassembly operable to produce a first pattern on a medium, and a second printing subassembly operable to generate a second pattern on the medium.

Description:
This application is a continuation of U.S. patent application Ser. No. 11/087,284, filed Mar. 22, 2005, (now U.S. Pat. No. 7,274,883), the entire contents of which are incorporated herein by reference. 

   BACKGROUND 
   Today, the two leading types of printers on the market are laser printers and inkjet printers. In general, laser printers utilize toner to produce images, while inkjet printers produce images by depositing ink. 
   Laser printers and inkjet printers have major differences in performance and price. In general, laser printers are significantly faster and have a greater printing duty cycle than inkjet printers. In addition, laser printers typically have significantly lower operating costs than inkjet printers. However, inkjet printers are capable of producing photo-quality images at higher resolutions than laser printers. And inkjet printers are typically significantly less expensive than color laser printers. 
   As a result, most of the printers on the market are monochrome laser printers and color inkjet printers. Office computer networks typically include a monochrome laser printer for large-volume and rapid printing, and typically use a color inkjet printer for the occasional color print job. However, this approach not only involves the expense of purchasing at least two separate printers, but also the expense of supporting and maintaining the at least two separate printers. There are few, if any, printers available that have the speed and duty cycle of a laser printer as well as the color and resolution of an inkjet printer at a reasonable price. 
     FIG. 1  is a diagram of a typical laser printer  10  including a movable photoreceptor  12 , typically a revolving drum or cylinder. This drum  12  is made out of a highly photoconductive material that is discharged by light photons. Initially, the photoreceptor drum  12  is given a total positive charge by a charging electrode  14 , typically a wire or roller having a current running through it. As the drum  12  revolves, the printer  10  uses a laser unit  16  (such as a laser diode) to shine a laser beam  18  across the surface of the drum  12  to discharge certain points. In this manner, the laser beam  18  “draws” the text and images to be printed as a pattern of electrical discharges (an electrostatic image) on the drum  12 . If the on-time or intensity of the laser beam  18  is modulated, resulting variations in charge on the drum  12  will ultimately be translated to proportionate amounts of toner deposited on a print medium  21  such as paper. 
   In scanning the laser beam  18  across the drum  12 , the laser unit  16  does not actually move the laser beam  18  itself but instead bounces the laser beam  18  off of a movable mirror  26 , such as a rotating mirror or an oscillating mirror. As the mirror  26  moves, it reflects the laser beam  18  through a series of lenses (not shown) and onto the drum  12 . These lenses change characteristics of the light beam  18  to compensate for image distortion that would otherwise be caused by the varying distance between the mirror  26  and points along the drum  12 . 
   After the laser beam  18  begins scanning the desired electrostatic pattern on the drum  12 , the printer  10  uses a toner roller  20  to coat the drum  12  with positively charged toner powder. Since the toner has a positive charge, it clings to the negative discharged areas of the drum  12  that have been scanned by the laser beam, but the toner does not cling to the positively charged “background” of the drum. With the toner pattern affixed to the drum  12 , the drum rolls over the sheet of paper  21  traveling below it. Before the paper  21  travels under the drum  12 , the paper is given a negative charge that is stronger than the negative charge of the electrostatic image on the drum  12  so that the paper pulls the toner powder away from the drum  12 . Finally, the printer  10  passes the paper  21  through a fuser  24 , which is typically a pair of heated rollers. As the paper  21  passes through the fuser  24 , the loose toner powder on the paper melts, fusing with the fibers in the paper and forming a permanent image on the paper. 
   After the toner on the drum  12  is transferred to the paper  21 , the drum surface rotates past a discharge lamp  22 , which generates a bright light that exposes the photoreceptor surface of the drum  12 , erasing the electrostatic image. The drum surface then passes the charging electrode  14 , which reapplies a positive charge to the surface of the drum  12  in anticipation of the laser beam  18  scanning the next portion of the image to be printed onto the drum. In this way, the scanning of the laser, the transfer of the toner, and the erasing of the photoreceptor surface is a continuous process that may be repeated before the printing of an entire image is complete. 
     FIG. 2  is a perspective view of portions of the laser printer  10  in  FIG. 1  better showing the scanning of the laser beam  18  in a horizontal direction across the drum  12  as indicated by an arrow  28 . Image processing circuitry (not shown) controls the laser unit  16  to modulate the laser beam  18  as the beam scans across the drum  12  in the horizontal direction  28  one line at a time. The image processing circuitry controls the laser unit  16  to turn ON and emit a pulse of light for every dot to be printed in a given horizontal line and to turn OFF where no dots are to be printed in the line. 
   Laser printers typically have several advantages when compared to other types of printers. For example, laser printers often produce documents with the highest text and line quality. This is because laser printers use toner, which sits crisply on top of the paper and does not spread like ink does as it is absorbed by the paper. Also, the cost of operating a laser printer is typically low; certain toner cartridges have average yields of over 40,000 pages. This allows laser printers to have a cost per page as low as one cent. In addition, laser printers are often designed to print pages at a high rate; current laser printers can print black-and-white documents at speeds of up to 85 pages per minute (ppm). 
   Laser printers do, however, have certain limitations. To print in color, laser printers typically have a separate toner cartridge for each of the primary colors. Consequently, instead of a single black toner cartridge, a color laser printer often has four toner cartridges (e.g., black, red, yellow, blue). In addition, the architecture of a color laser printer is often significantly more complex than the architecture of a black-and-white laser printer. For example, the four toner cartridges either share the same drum so that four passes of the paper are made over the same drum, or have their own respective drums so that the paper passes over four separate drums in series. As a result, the cost of a color laser printer is typically higher than the costs of other types of color printers. Also, because overlapping toner colors may reduce image resolution and quality, color laser printers often produce color images that are lower in resolution and quality than comparable color images produced by other types of color printers. 
     FIG. 3  is a perspective view of a typical inkjet printer  30  that emits droplets of ink (not shown) onto print media  32 , such as paper, to create images and text. The inkjet printer  30  includes a printhead (not shown) mounted within a carriage  34  that travels back and forth across the paper  32 . The printhead includes an array of tiny nozzles (not shown) that emit the droplets of ink. As the printhead moves across the paper  32 , a controller activates the printhead to emit droplets of ink at precise locations corresponding to a pattern of pixels of the image being printed. 
   Ink is typically provided to the printhead by an ink cartridge  36  that is attached to the carriage  34 . Depending on the design of the printer  30 , the ink cartridge  36  can come in various combinations ranging from a single cartridge for black ink to multiple cartridges each for an ink of a desired color. The ink cartridge  36  may even include the printhead itself. Alternatively, the ink cartridge  36  may be a stationary ink reservoir that is separate from the carriage  34  and connected to the printhead by a hose. 
   Different types of inkjet printers emit the droplets of ink in different ways. The two main inkjet technologies currently used by printer manufacturers are thermal bubble (also known as bubble jet) and piezoelectric. 
     FIG. 4A  is a cross-sectional view of a typical bubble jet printhead  40  used in a thermal inkjet printer. In the printhead  40 , a heating element  41  such as a resistor creates heat that vaporizes ink in a reservoir  42  to create a bubble. As the bubble expands, a tiny amount of the ink is emitted from a nozzle  43  onto the paper. When the bubble collapses, a vacuum is created that pulls more ink into the reservoir  42  from the ink cartridge  36  ( FIG. 3 ). 
     FIG. 4B  is a cross-sectional view of a typical piezoelectric printhead  45  used in a piezoelectric inkjet printer. In the printhead  45 , a transducer  46  such as a piezo crystal is located at the back of an ink reservoir  47 . The transducer  46  receives an electric signal that causes it to vibrate. When the transducer  46  vibrates inward toward the reservoir  47 , it forces a tiny amount of ink out of a nozzle  48  onto the paper. When the transducer  46  vibrates outward away from the reservoir  47 , it pulls more ink into the reservoir  47  from the ink cartridge  36 . 
   Color inkjet printers typically have several advantages when compared to other types of printers. For example, color inkjet printers are often capable of high resolutions. Current inkjet printheads can emit droplets of ink as small as 2 picoliters. This allows such printheads to produce images with resolutions exceeding 4800 dots per inch (dpi). In addition, color inkjet printers can have up to eight color ink cartridges, each having a different color of ink. This significantly broadens the range of colors produced by the printhead, and allows the printhead to produce photo-quality images that change tone gradually without discernable patterns or jumps in color. Also, the cost of color inkjet printers is significantly lower than the cost of other types of color printers. 
   SUMMARY 
   An embodiment of the present invention is a hybrid printer assembly including a laser printing subassembly operable to apply toner to a medium and an inkjet printing subassembly operable to apply ink to a medium. 
   Such a printer assembly is capable of providing the speed and duty cycle of a laser printer as well as the color and resolution of an inkjet printer. Each of the laser and inkjet subassemblies may be used to produce separate printouts, or the laser and inkjet subassemblies may produce different portions of the same printout. For example, the laser subassembly may be dedicated to producing the text portions of a printout, and the inkjet subassembly may be dedicated to producing the image portions of the printout. Alternatively, the laser subassembly may be dedicated to producing the black-and-white portions of the printout, and the inkjet subassembly may be dedicated to producing the color portions of the printout. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross-sectional view of a conventional laser printer. 
       FIG. 2  is a perspective view of various components of the conventional laser printer of  FIG. 1 . 
       FIG. 3  is a perspective view of a conventional inkjet printer. 
       FIG. 4A  is a cross-sectional view of a conventional bubble jet printhead used in a thermal inkjet printer. 
       FIG. 4B  is a cross-sectional view of a conventional piezoelectric printhead used in a piezoelectric inkjet printer. 
       FIG. 5  is a cross-sectional view of a hybrid printing assembly that includes both laser and inkjet printing subassemblies according to an embodiment of the present invention. 
       FIG. 6  is a flow chart of a procedure according to which the hybrid printing assembly of  FIG. 5  operates according to an embodiment of the present invention. 
       FIG. 7  is a block diagram of an electronic system that incorporates a printing device having the hybrid printing assembly of  FIG. 5  according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
     FIG. 5  is a diagram of a hybrid printing assembly  50  according to an embodiment of the present invention. The hybrid printing assembly  50  includes similar components found in the laser printer  10  of  FIG. 1  and the inkjet printer  30  of  FIG. 3 , and these components are numbered accordingly. 
   The photoreceptor  12 , charging electrode  14 , laser unit  16 , laser beam  18 , toner roller  20 , discharge lamp  22 , fuser  24  and mirror  26  are collectively referred to as a laser printing subassembly  51  of the hybrid printing assembly  50 . 
   An inkjet printing subassembly  52  of the hybrid printing assembly  50  includes a printhead  53  and a roller  54  in addition to the carriage  34  and the ink cartridge  36 . 
   In this example, the hybrid printing assembly  50  is oriented so that it applies toner to the print medium  21  before it deposits ink to the print medium. However, the orientation of the laser and inkjet subassemblies  51  and  52  may also be reversed so that ink is deposited before toner is applied. In addition, depending on the print job, the printer assembly  50  may use both or only one of the laser and inkjet subassemblies  51  and  52 . 
   Also, in this example, the hybrid printing assembly  50  is utilized so that the laser subassembly  51  produces a text portion of a printout, and the inkjet subassembly  52  produces an image portion of the printout. In this way, the laser subassembly  51  uses black toner to produce text having the quality of a laser printer, and the inkjet subassembly  52  uses black and color ink to produce images having the resolution (and color) of an inkjet printer. If the printout contains only text, then only the laser subassembly  51  is used. Similarly, if the printout contains only images, then only the inkjet subassembly  52  is used. In addition, if the printout is only in black-and-white but contains both text and images, then both of the laser and inkjet subassemblies  51  and  52  are used for the text and image portions, respectively. 
   Because print media such as paper  21  is fed to the laser and inkjet subassemblies  51  and  52  in a serial manner, the hybrid printing assembly  50  begins operation of the laser and inkjet subassemblies at separate times and utilizes a controller (not shown in  FIG. 5 ) to control the timing of the laser and inkjet subassemblies. The controller incorporates a time delay, which may be a predetermined line offset between the laser and inkjet subassemblies  51  and  52 . For example, a line printed by the laser subassembly  51  may arrive at the inkjet subassembly  52  ten lines later, in which case the line delay is ten lines. The controller may take into account that the photoreceptor drum  12  and/or roller  54  is rotated by a stepping motor (not shown) and calculate the line delay from the number of steps made by the stepping motor. The controller may also incorporate a counter (not shown) to keep track of the number of steps made by the stepping motor to determine when to start the inkjet subassembly  52 . For example, one or more small scanners (not shown) located, for example, in the inkjet printhead  53 , may be used to detect a first line of the printout and the controller may then use the counter to wait a certain number of steps before the inkjet subsassembly  52  starts printing at the desired line. One manner in which the scanners may detect a first line is by detecting a registration mark produced by the laser subassembly  51 . Such a registration mark is typically small enough so that it is unnoticed by the human eye, and thus does not form a visible artifact on the printed media. 
   The operation and additional features of the hybrid printing assembly  50  are discussed below in conjunction with  FIGS. 6 and 7 . 
     FIG. 6  is a flowchart of a method  60  by which the hybrid printing assembly  50  ( FIG. 5 ) prints on a print media such as paper  21  ( FIG. 5 ) according to an embodiment of the present invention. 
   Referring to  FIGS. 5 and 6 , at step  61 , the laser subassembly  51  and the inkjet subassembly  52  are calibrated so that the portions of the printout generated by the laser subassembly are aligned with the portions of the printout generated by the inkjet subassembly. This calibration may occur at startup of the printer, when a toner or ink cartridge is replaced, or at any other predetermined or user-specified time. For example, the printer may be instructed to print a test pattern that utilizes both the laser subassembly  51  and the inkjet subassembly  52 . More specifically, the laser subassembly  51  may be instructed to print a pattern of horizontal lines on the print medium  21 , and the inkjet subassembly  52  may be instructed to print a pattern of vertical lines on the print medium. If the patterns of horizontal and vertical lines are aligned within a measurable tolerance, then the laser and inkjet mechanisms are calibrated. If the patterns of horizontal and vertical lines are not aligned so that either the printer (using a built-in calibration scanner, which is not shown in the Figures) or the user measures a variation between the patterns, then the printer or the user can calibrate the inkjet subassembly  51  and/or the laser subassembly  52  so that the patterns are aligned within the measurable tolerance. This may be done in one location or in a number of locations across the print medium. 
   At step  62 , a print request is processed by a print driver software  73  (shown in  FIG. 7 ). For example, the print driver  73  may determine the text and image portions of the printout. In addition, the print driver  73  may determine the black-and-white and color portions of the printout. The manner in which the print driver  73  processes the print request and determines the different portions of the printout depends on the manner in which the laser and inkjet subassemblies  51  and  52  are utilized to produce the printout. 
   At step  63 , the data for each portion of the printout is spooled from the print driver  73  to a printer  76  (shown in  FIG. 7 ). For example, the printer  76  may have a single controller  77  (shown in  FIG. 7 ) for controlling both the laser and inkjet subassemblies  51  and  52 . The controller  77  may receive the data for the text and image portions of the printout; alternatively, the controller may receive the data for the black-and-white and color portions of the printout. 
   At step  64 , assuming the operation of the laser subassembly  51  begins before the operation of the inkjet subassembly  52 , toner is applied to the print medium  21 . For example, the toner may represent only the text portion of the printout. In this case, the laser subassembly  51  produces only the text portion of the printout—text within the images may be considered text, and thus be printed with the laser subassembly  51 , or may be considered part of the image, and thus be printed with the inkjet subassembly  52 —and the inkjet subassembly  52  produces the entire image portion of the printout, including the black and color portions of the images. Consequently, the inkjet subassembly  52  includes a black ink cartridge in addition to the color ink cartridges. Furthermore, the images of the printout typically have high consistency and resolution because there is no resolution mismatch between the black and color portions of the images. In addition, because only ink is used in the images, any contrast between ink and toner in the images is eliminated. Moreover, the absorption of the ink into the print medium  21  is not interfered with or hindered by any fused toner in the images. 
   At step  65 , the toner is fused to the print medium  21 . For example, the print medium  21  may pass through a fuser  24  shortly after the toner is applied. All of the toner portions of the printout may be fused to the print medium  21  before any ink is deposited to the print medium. Alternatively, even if all of the toner portions of the printout are not yet fused to the print medium  21 , ink may still be deposited to those portions of the print medium where toner has already been fused to the print medium. 
   At step  66 , the inkjet subassembly  52  begins printing at the correct time relative to the portions of the printout generated by the laser subassembly  51 . For example, the timing may be calculated after toner has been fused and before ink has been deposited. As discussed above, the controller  77  controls the timing of the laser and inkjet subassemblies  51  and  52 , and incorporates a time delay which may be a predetermined line offset between the laser and inkjet subassemblies. The controller  77  may calculate the line offset from a number of steps made by the stepping motor rotating the photoreceptor drum  12 , and keep count of the number of steps with a counter. Based on the number of steps made by the stepping motor, the controller  77  is able to determine when to start the inkjet subassembly  52 . For example, small scanners (not shown) may be included in the inkjet printhead  53  to detect a first line of the printout, and the controller  77  may use the counter to wait a certain number of steps after detecting the first line before the inkjet subassembly  52  begins printing at the desired line. One manner in which the small scanners in the inkjet subassembly  52  may detect a first line is by detecting a registration mark produced by the laser subassembly  51  as discussed above in conjunction with  FIG. 5 . In addition, the small scanners in the inkjet subassembly  52  may be utilized for registration to detect various other aspects of the toner portion of the printout so that the inkjet printhead  53  is aligned properly and begins depositing ink at the proper location. 
   At step  67 , ink is deposited by the inkjet subassembly  52  to the print medium  21 . For example, if the inkjet subassembly  52  includes black and color ink cartridges, then the inkjet printhead  53  deposits black ink as well as color ink in this step to produce the image portions of the printout. 
   Methods and printers according to embodiments of the present invention may include various modifications to the steps of method  60 , including changes to the sequence of the steps and additional steps. For example, the embodiment described in  FIG. 6  is a method where the laser and inkjet subassemblies  51  and  52  are calibrated at either startup of the printer, when a toner or ink cartridge is replaced, or at any other user-specified time. However, additional embodiments may use each print job for calibration so that the laser and inkjet subassemblies  51  and  52  are calibrated dynamically. For example, dynamic calibration may occur after each print job has been completed. In this case, a specific location of the completed printout may be analyzed to see if a toner mark produced by the laser subassembly  51  is aligned with an ink mark produced by the inkjet subassembly  52 . If the toner and ink marks are not aligned, the necessary calibration may take place in either the laser or inkjet subassemblies because the print job has already been completed. But it may be simpler and more cost effective for the calibration to take place in the inkjet subassembly  52  because the inkjet subassembly moves across the page while printing on the medium, so the position of the inkjet subassembly can be calibrated relatively easily. 
   Additional embodiments may also have separate controllers for each of the laser and inkjet subassemblies. In this case, the controller for the laser subassembly may receive the data for the text portions of the printout, and the controller for the inkjet subassembly may receive the data for the image portions of the printout. Or alternatively, the controller for the laser subassembly may receive the data for the black-and-white portions of the printout, and the controller for the inkjet subassembly may receive data for the color portions of the printout. 
   Furthermore, instead of the toner representing only the text portions of a printout, the toner may also represent all of the black-and-white portions of the printout. In this case, the laser subassembly produces not only the black text portion of the printout, but also the black portion of the images in the printout. This makes a black ink cartridge in the inkjet subassembly unnecessary because the inkjet subassembly produces only the color portions of the printout. 
   Additional embodiments may also deposit the ink prior to applying the toner. In this case, the printer may first deposit the ink, then align the laser assembly, and then apply and fuse the toner to complete the printout. 
   Furthermore, it is not necessary that both of the laser and inkjet subassemblies be used. Depending on the requirements of the printout, one of the laser and inkjet subassemblies may not be used. For example, if the printout only contains text or black-and-white portions, then the inkjet subassembly may not be used. Or alternatively, if the printout only contains image or color portions, then the laser subassembly may not be used. 
   It should be noted that the inkjet printhead may be any type of inkjet printhead, including thermal bubble and piezoelectric. In addition, the laser printing subassembly may be any type of laser subassembly, including those having rotating mirrors and oscillating mirrors. 
   It should also be noted that, although the beam utilized to discharge the photoconductive drum has been described as a laser beam, other beam-generating sources may be used as well if suitable in particular applications. Thus, the term laser beam is not limited to a beam of light generated by a laser, but instead should be construed broadly. 
   Consequently, a printer having the hybrid printing assembly  50  often provides several advantages over the prior art. For example, the printer provides the speed, cost per page, and text quality of a laser printer, as well as providing the image quality of an inkjet printer. Furthermore, the printer is typically less complex than a color laser printer, and less expensive than the combined cost of a laser printer and an inkjet printer. 
     FIG. 7  is a block diagram of an electronic system  70 , which includes a printing device  76  that incorporates the hybrid printing assembly  50  of  FIG. 5  according to an embodiment of the present invention. The printing device  76  may be a printer, copier, or any device that generates a printed media. In addition to the printing device  76 , the electronic system  70  includes a computer  72  connected to the printing device  76  by a network  74  and including the print driver  73 . The printing device  76  includes a controller  77  and a media source  78 . 
   The print driver  73  is a software program stored in the computer  72  for processing a print job and determining the various portions of the printout, including text, image, black-and-white, and color portions. After determining the portions of the printout, the print driver  73  spools the appropriate print data to the printing device  76  through the network  74 . 
   The network  74  may be any type of network connection between the computer  72  and the printing device  76 , including a wireless network connection. 
   The controller  77  receives the print data from the print driver  73 . Then the controller  77  determines which data to provide to the laser printing subassembly  51  and which data to provide to the inkjet printing subassembly  52 . For example, the controller  77  may provide data representing the text portions of the printout to the laser subassembly  51  and provide data representing the image portions of the printout to the inkjet subassembly  52 . Alternatively, the controller  77  may provide data representing the black-and-white portions of the printout to the laser subassembly  51  and provide data representing the color portions of the printout to the inkjet subassembly  52 . The controller  77  also controls the operation and timing of the laser subassembly  51  and the inkjet subassembly  52 . 
   The media source  78  provides the print media  21  to the hybrid printing assembly  50 . For example, the media source  78  may include one or more media trays or manual media feeds. 
   Alternative embodiments of the electronic system  70  are contemplated. For example, the print driver  73  may be located in the printing device  76 , and the controller  77  may be located in the computer  72 . 
   From the foregoing it will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention.