Abstract:
Printing systems and method of printing on substrates are provided. A method of printing one or more images using a printhead, the method including moving a substrate on a transporter, providing a printhead configured to print a plurality of print lines in a direction, rotating an image to an image angle relative to the direction of the print lines, and printing the image rotated to an angle onto the substrate.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This claims priority to U.S. Application Ser. No. 60/729,940, filed on Oct. 25, 2005. 
     
    
     TECHNICAL FIELD  
       [0002]     In general, this disclosure related to printing systems and methods of printing on substrates.  
       BACKGROUND  
       [0003]     Droplet ejection devices are used for depositing droplets on a substrate. Ink jet printers are a type of droplet ejection device. Ink jet printers typically include an ink supply to nozzle path. The nozzle path terminates in a nozzle opening from which ink drops are ejected. Ink drop ejection is controlled by pressurizing ink in the ink path with an actuator, which may be, for example, a piezoelectric deflector, a thermal bubble jet generator, or an electro statically deflected element. A typical printhead has an array of ink paths with corresponding nozzle openings and associated actuators, such that drop ejection from each nozzle opening can be independently controlled. In a drop-on-demand printhead, each actuator is fired to selectively eject a drop at a specific pixel location of an image as the printhead and a printing substrate are moved relative to one another. In high performance printheads, the nozzle openings typically have a diameter of 50 microns or less, e.g., around 35 microns, are separated at a pitch of 100-300 nozzle/inch, have a resolution of 100 to 3000 dpi or more, and provide drop sizes of about 1 to 70 picoliters or less. Drop ejection frequency can be 10 kHz or more.  
         [0004]     Printing accuracy is influenced by a number of factors, including the size and velocity uniformity of drops ejected by the nozzles in the head and among multiple heads in a printer. The drop size and drop velocity uniformity are in turn influenced by factors such as the dimensional uniformity of the ink paths, acoustic interference effects, contamination in the ink flow paths, and the actuation uniformity of the actuators.  
       SUMMARY  
       [0005]     Generally, the invention relates to printing systems and methods of printing on substrates, In an aspect, a method of printing one or more images using a printhead, the method includes moving a substrate on a transporter, providing a printhead configured to print a plurality of print lines in a direction, rotating an image to an image angle (i.e., about 45 degrees) relative to the direction of the print lines,and printing the image rotated to an image angle onto the substrate.  
         [0006]     Implementations may include one or more of the following features. The method can include moving the transporter to a transporter angle (i.e., about 45 degrees) relative to the printhead, the transporter angle substantially equals the image angle.  
         [0007]     In another aspect, a method of printing one or more images on a substrate using a printhead, the method includes moving a substrate on a transporter in a direction, rotating at least two orifices on a printhead to an orifice angle (i.e., about 45 degrees) relative to the transporter, the printhead configured to print a plurality of print lines in a direction substantially parallel to the direction of the transporter, rotating an image to an image angel relative to the print lines, and printing the image rotated to an image angle.  
         [0008]     Implementations can include one or more of the following features. The method can include orifices that are parallel it a side of the printhead, or orifices that are rotated to the orifice angle relative to a side of the printhead.  
         [0009]     In an aspect, a printing system includes a printhead configured to print a plurality of print lines in a direction, a transporter for moving a substrate relative to the printhead, and an image rotated to an image angle (i.e., about 45 degrees) relative to the direction of the print lines, the printhead prints the image onto the substrate.  
         [0010]     Implementations can include one or more of the following features. The printing system can include the transporter being rotated to a transporter angle relative to printhead and the transporter angle substantially equals the image angle. The printing system can include and image database for storing images, a digital imager for processing the image, or a computer network through which the image travels to the printhead. The system can also include an ink reservoir or a control unit to control functions. of the printhead, The printhead can include at least two orifices rotated to an orifice angle relative to the transporter. The orifices can be parallel to a side of the printhead or rotated to the orifice angle relative to a side of the printhead.  
         [0011]     These printing systems and methods of printing create less noticeable jet-out artifacts. A jet-out artifact is a black space left through an image when a jet becomes inoperative and stops depositing ink. Also, when printing rotated images, if either the transporter or the orifices are rotated, the substrates may be printed closer together. Furthermore, printing rotated images increases jet sustainability. Since more jets are used to print rotated images than are used to print parallel or perpendicular images, it is less likely that jets will dry out or clog. If a jet dries out or clogs, a jet-out artifact may be left on the image. 
     
    
     DESCRIPTION OF DRAWINGS  
       [0012]      FIG. 1  is a block diagram of a printing system  
         [0013]      FIG. 2   a  is a top view of an image on a substrate.  
         [0014]      FIG. 2   b  is top view of a rotated image of  FIG. 2   a  rotated on a substrate.  
         [0015]      FIG. 3   a  is a top view of the image of  FIG. 2   a  with a jet-out artifact.  
         [0016]      FIG. 3   b  is a top view of the rotated image of  FIG. 3   a  with a jet-out artifact.  
         [0017]      FIG. 4  is a block diagram of a printing system with a printhead, a rotated image, and a rotated transporter.  
         [0018]      FIGS. 5   a  &amp; b are bottom views of a printhead with orifices parallel to a side of the printhead.  
         [0019]      FIGS. 6   a  &amp; b are bottom views of a printhead with orifices aligned at an angle relative to a side of the printhead.  
         [0020]      FIG. 7  is a block diagram of a printing system with a printhead similar to  FIG. 5   b  printing a rotated image on a substrate traveling along the transporter.  
         [0021]      FIG. 8  is a block diagram of a printing system with a printhead similar to  FIG. 6   b  printing a rotated image on a substrate traveling along the transporter. 
     
    
     DETAILED DESCRIPTION  
       [0022]     Referring to  FIG. 1 , a printing system  10  includes an imaging system  12  for printing one or more images  14  on a substrate  16 . The imaging system  12  includes a digital imager  18  for processing images  14  stored in a image database  20  and provided to the digital imager  18  via a local area network  22 . In other implementations, the images  14  can be delivered from the database via wide area network (e.g., Internet). The imaging system  12  converts an image  14  into a format compatible with a printhead  24 . In this embodiment, the image database may include a library of images  14  stored on a server  26 . Other servers  27  may be connected to the network  22  for storing and sending images  14 .  
         [0023]     More specifically, and discussed in greater detail below, digital imager  18  processes the images  14  by electronically rotating the image  14  relative to the print lines before sending the image  14  to a printhead  24 . The printhead  24  prints the image  14  onto a substrate  16  traveling on the transporter  28 , which in this embodiment includes a conveyor belt that moves along rollers  30 . Additionally, the printing system  10  includes an ink reservoir  32  to store one or more inks, and in this embodiment, includes a control unit  34  for performing different functions, such as monitoring the ink level, managing data transfers, sensing a jet-out, or controlling the temperature of the ink.  
         [0024]     The printing system  10  may print one image  14  on one substrate  16 , or multiple images on one substrate  16 . In a preferred embodiment, the printing system  10  prints one or more images  14  on multiple substrates  16  traveling along the transporter  28 .  
         [0025]     By rotating an image to be printed on a substrate, jet-out artifacts are less noticeable. If a jet dries out or clogs, a jet-out artifacts may be left on the image. A jet-out artifact is a blank space left through an image when a jet becomes inoperative an stops depositing ink (see  FIGS. 3   a  and  3   b  below). For higher print resolution, an array of printhead orifices may be rotated (see  FIGS. 6   a  and  6   b  below).  
         [0026]     Referring to  FIG. 2   a,  an image  104  is printed in a substrate  108 , in this embodiment, and alphanumeric image (“ABC”) with the print lines  112  perpendicular to the image  104 . In other embodiments, the print lines  112  parallel to the image  104 .  
         [0027]     Referring to  FIG. 2   b,  an image  104  is rotated to an image angle θ  116  relative to the print lines  112 . The image  104  is neither perpendicular nor parallel to the print lines  112 . The image angle  116  may be between 0 and 90 degrees, preferably between 5 and 35 degrees or 55 and 85, more preferably between 35 and 55 degrees, 90 and 180 degrees, preferably between 95 and 125 degrees or 145 and 175, more preferably between 125, and 145 degrees; 180 and 270 degrees, preferably between 185 and 215 degrees or 235 and 265, more preferably between 215 and 235 degrees; or 270 and 360 degrees, preferably between 275 and 305 degrees or 325 and 355, more preferably between 305 and 325 degrees. In this embodiment, the image angle  116  is about 35 degrees relative to the print lines  112 .  
         [0028]     As shown in  FIGS. 3   a  and  3   b,  when the image  104  is rotated to an angle, such that the image  104  is neither parallel nor perpendicular to the print lines (not shown), a jet-out artifact  120  is less noticeable to the human eye. For example,  FIG. 3   a  shows an image  104  on a substrate  108 , where the image  104  is perpendicular to the print lines (not shown). In  FIG. 3   a,  a jet-out artifact  120  is more noticeable to the human eye because the jet-out may leave white space through the entire length of the image  104 . Moreover, the human eye is more sensitive to horizontal and vertical lines, thus a horizontal or vertical jet-out artifact  120  is more noticeable.  
         [0029]     In addition to less noticeable jet-out artifacts, printing rotated images increases jet sustainability. Since more jets are used to print rotated images than are used to print parallel or perpendicular images, it is less likely that jets will dry out or clog. For example, if rows of text are printed and the rows are parallel to the print lines, the jets corresponding to the spaces between the rows of text will not be used, On the other hand, if the rows of text are rotated to angle relative to the print lines, most, if not all, of the jets will be used because the spaces between the rows are no longer parallel to the print lines.  
         [0030]     Conversely, in  FIG. 3   b,  when the image  104  is rotated to an angle relative to the print lines (not shown), a jet-out artifact  120  is less noticeable. The jet-out artifact  120  may leave white space only through a portion of the image  104  on the substrate  108  rather than the entire length of the image  104 . Also, the human eye is less sensitive to angled lines, and may not perceive the jet-out artifact  120 . Thus, in one embodiment, the image is an image rotated such that it is neither parallel nor perpendicular relative to the print lines.  
         [0031]      FIG. 4  depicts a printing system  200  including a printhead  204 , transporter  208  rotated to a transporter angle α  212 , and a substrate  216  with and image  220  rotated to an angle θ  224 . As shown in  FIG. 4 , for substrates  216  with an orientation (i.e., business cards), the transporter  208  may be rotated such that the rotated image  220  aligns with the orientation of the substrate  216 . In one embodiment, the transporter angle  212  substantially equals the image angle  224 . In one embodiment, the transporter angle  212  and image angle  224  are about 45 degrees. For other applications, the transporter angle  212  may by different from the image angle  224 . In some embodiments, the transporter angle  212  and image angle are between 0 and 90 degrees, preferably between 5 and 35 degrees or 55 and 85, more preferably between 35 and 55 degrees; 90 and 180 degrees, preferably between 95 and 125 degrees or 145 and 175, more preferably between 125 and 145 degrees; 180 and 270 degrees, preferaly between 185 and 215 degrees or 235 and 265, more preferably between 215 and 235 degrees; or 270 and 360 degrees, preferably between 275 and 305 degrees or 325 and 355, more preferably between 305 and 325 degrees.  
         [0032]     In  FIG. 5   a,  an embodiment of a printhead  300  has a single row of orifices  304  aligned parallel to a side of the printhead  300 . In another embodiment, as depicted in  FIG. 5   b,  a printhead  300  may have multiple rows of orifices  304  parallel to a side of the printhead  300 .  
         [0033]     Referring to  FIGS. 6   a  and  6   b,  to achieve higher print resolution, a printing system  200  may have orifices on a printhead  204  rotated to an orifice angle.  FIGS. 6   a  and  6   b  show printheads  300  with orifices  304  that are aligned at an orifice angle φ  304  relative to a side of the printhead  300 . In  FIG. 6   a,  a printhead  300 , while  FIG. 5   b  depicts a printhead  300  with multiple rows of rotated orifices  304 .  
         [0034]      FIG. 7  shows a printing system  400  with a printhead  404 , a transporter  408 , and substrates  412  traveling along the transporter  408 . The printhead  404  with parallel orifices as shown in  FIG. 5   b  is rotated to an angle, such that the orifices are at an orifice angle β  416 .  
         [0035]     Similarly, the printing system  500  in  FIG. 8  shows a printhead  504 , a transporter  508 , and substrates  512  traveling along the transporter  508 .  FIG. 8  uses the printhead  504  of  FIG. 6   b,  in which the orifices are rotated to an angle φ on the printhead  504  and an image  516  is rotated. In one embodiment, the printhead  504  is placed perpendicular to the transporter  508 . In another embodiment, the printhead  504  may be rotated relative to the transporter  508 , such that both the printhead  504  and the orifices are rotated.  
         [0036]     In some embodiments of  FIG. 7  or  8 , the orifice angle and image angle are between 0 and 90 degrees, preferably between 5 and 35 degrees or 55 and 85, more preferably between 35 and 55 degrees; 90 and 180 degrees; preferably between 95 and 125 degrees or 145 and 175, more preferably between 125 and 145 degrees; 180 and 270 degrees, preferably between 185 and 215 degrees, or 235 and 265, more preferably between 215 and 235 , degrees; 270 and 360 degrees, preferably between 275 and 305 degrees or 325 and 355, more preferably between 305 and 325 degrees.  
         [0037]     In some embodiments of  FIG. 7  or  8 , the printing system may print rotated images on a paper web that are cut out of the paper web, such as business cards or wrappers. Similarly, in other embodiments, the printing system may print rotated images on one or more sheets of food products, like confectionery or dough, which are subsequently cut into smaller pieces.  
         [0038]     Other embodiments are within the scope of the claims. For example, although printing system is shown having one imaging system, in other applications, a number of imaging systems associated with the same or different transporter may by connected to the computer network.  
         [0039]     The printing systems may be used to print on substrates of any shape, such as round, rectangular, planar, or nonplanar. Some types of substrates may include food products, such as confectionery, gum, cookies, crackers, yogurt, ice cream, and pastries. Other substrates may include paper products, such as envelopes, stationery, business cards, as well as foil wrappers, candy wrappers, food packaging, textiles, plastic products, or round shaped objects, like golf balls. Also, the substrate may be a paper web. The images printed on the substrates may be text, graphic, or any combination thereof.  
         [0040]     Other embodiments may use other printing systems, such as rotary printing, drum printing, thermal bubble jet printing, continuous ink jet, laser printing, and helical printing.  
         [0041]     Referring to  FIG. 7 , the printing system  400  may include a sensor (not shown) that detects the edge of a substrate  412 , at which time the sensor signals the printhead  404  to start printing. If substrates  412  are being printed close together, the printhead  404  may abruptly stop printing on a first substrate when the sensor detects the second substrate, leaving an incomplete image on the first substrate. In such circumstances, software can be used to overlay consecutive images to move the images closer together. The printhead can then continue printing the first substrate after the sensor signals the printhead to start printing the second substrate.  
         [0042]     Before the images are rotated, they have a rectangular orientation. The images are then rotated and have a skewed rectangular orientation. To make the images rectangular for bitmap rasterization, the skewed regions are filled with zeros. These skewed regions cause the consecutive images to be further apart and make it difficult to print on substrates close together on a conveyor. To move the images closer together, the images are overlaid and combined by “or” logic function. For example, image  2  overlays image  1  and covers a few pixels of image  1 . The “or” logic function ensures that the pixels in image  1  that are overlaid by image  2  will still be printed. The images can also be slanted after they are rotated, which permits the images to be overlaid even closer together.