Abstract:
In some examples, a printing system including a rotating platen having an axis of rotation and configured to support a substrate, and a printhead configured to eject drops in a direction parallel with the axis of rotation onto the substrate supported by the rotating platen.

Description:
CLAIM OF PRIORITY 
     This application is a continuation of and claims priority under 35 U.S.C. §120 to U.S. application Ser. No. 11/871,597, filed on Oct. 12, 2007, which claimed priority to U.S. Provisional Application No. 60/829,496, filed Oct. 13, 2006, the contents of both are hereby incorporated by reference. 
    
    
     BACKGROUND 
     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 a 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 typical 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 some 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. 
     SUMMARY 
     Generally, the invention relates to printing on moving surfaces. In an aspect, a printing system includes a platen that moves a substrate along a non-straight path (e.g., by the platen rotating about an axis of rotation) and configured to support a substrate, and a printhead configured to eject drops of an image on the substrate as it is moved along the non-straight path. 
     In another aspect, a printing system has a printhead for depositing droplets, a platen to support a substrate and rotate about an axis in a circular motion relative to the printhead, the printhead being positioned to deposit droplets in a direction parallel with the axis of rotation, and an imaging system to format image data to account for the circular motion of the substrate and to send instructions to the printhead to deposit droplets on the substrate based on the formatted image data. 
     Implementation may include one or more of the following features. The printhead can be an ink jet printhead. The printing system can have a plurality of printheads (e.g., four printheads, one for each ink color, cyan, magenta, yellow, and black). The system can include a printhead for depositing a coating on a surface of the substrate, or a curing station for curing the droplets on the substrate. The system can have a platen including a cavity for holding the substrate, a trigger that rises above a surface of the platen when the substrate is placed in the cavity. The system can include a key (e.g., barcode) on the platen and a reader that reads information (e.g., set-up parameters for the rotating platen) stored on the key, the reader sends the information to the imaging system. The platen can be made of a moldable material that conforms to a shape of the substrate, and the platen can support a plurality of substrates. The platen can be coupled to a conveyor that moves relative to the printhead. There can also be a plurality of platens coupled to the conveyor. 
     In an aspect, a method of printing includes rotating a substrate on a platen about an axis in a circular motion, formatting image data to account for the circular motion of the substrate, and using a printhead to deposit droplets in a direction parallel to the axis of rotation to print an image on the substrate based on the formatted image data. 
     Implementations can include one or more of the following features. Formatting the image data can include converting the image data into bitmap raster data, applying an arc process, applying a gradient mask process, or separating the image data into cyan, magenta, yellow, and black. The method can also include sending the formatted image data to the printhead, curing the droplets on the substrate, or sensing the substrate in the platen and causing the printhead to deposit droplets when the substrate is sensed. A key can store information about the platen, and the method can include reading the information on the key and sending the information to an imaging system. The method can also include storing image data in an imaging system. The image can be comprised of dots having a certain image resolution after one revolution, and the method can further include increasing the image resolution by moving the printhead relative to the platen and printing dots in a space between the dots after the first revolution. 
     Certain implementations may have one or more of the following advantages. Fewer printheads are needed to print higher resolution because the substrates can be rotated under the same printheads several times to increase the resolution. The platen can be used to print on a small number of substrates (e.g., customized products) or a less than full platen. The set-up time is minimal. The printing system can print on different substrates within the same platen. Rotating the substrates under the printheads can be faster than some conventional printing methods, especially for small items. 
     Further aspects, features, and advantages will become apparent from the following detailed description, the drawings, and the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  depicts a perspective view of a printing system with a rotating platen. 
         FIG. 2  depicts a top view of a printing system. 
         FIG. 3  depicts the printing system including a rotating platen with a key and a key reader. 
         FIG. 4  is a flowchart of the image data processing before printing. 
         FIG. 4A  depicts image data for printing on a substrate 
         FIG. 4B  depicts formatted image data after the arc process. 
         FIG. 4C  depicts the variation of image boldness when printing on a rotating platen. 
         FIG. 4D  depicts a random matrix of white dots for the gradient mask process. 
         FIG. 5  depicts a top view of a printing system with rotating platens on a conveyor. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a printing system  10  including two printheads  12  (e.g., ink jet printheads) for depositing fluids (e.g., cyan, magenta, yellow, and black ink) onto a substrate  14  supported by a rotating platen  16 . The platen in  FIG. 1  shows a rotating platen  16  with an axis of rotation X  18 . A substrate  14  is placed on the platen  16 , the platen rotates about the axis X  18 , and the printhead  12  prints on the substrate as the substrate passes under the printhead. The printhead prints images retrieved from an imaging system  20  e.g., a computer). The imaging system  20  can store, process, and send image data to the printhead  12 . Processing image data can include dividing and translating the image data, such as converting the image data into a format compatible with the printer. 
     Unlike single-pass or scan printing, which operates in a linear motion, the printing system in  FIG. 1  operates in a circular motion. The imaging system  20  uses software to format the image data to account for the circular movement of the substrate relative to the printhead. 
     Referring to  FIG. 1 , the platen  16  supports multiple substrates  14  to be printed. When the printhead  12  finishes printing on the substrates  14 , the platen  16  can be removed and replaced with the next platen. This can be a manual or automated process. 
       FIG. 2  shows a printing system  100  including a platen  102  made from a moldable material (e.g., thermoplastic material), such that the platen  102  conforms to the shape of the customized product and forms recessed cavities  104 . The platen  102  can then hold the exact number of products to be printed. The platen can also be molded to hold different types of products within the same platen, such as lighters and pens. 
     Referring to  FIG. 2 , the platen includes a trigger  110  that rises above the surface of the platen  102  when a product is placed in a cavity  104 . The printing system can have a trigger sensor  112  to detect a raised trigger and to communicate with the printhead  114  if there is a product in the cavity  104 . This enables users to print less than a full platen. 
     Referring to  FIG. 3 , the printing system  200  includes a platen  202  with a key  204  (e.g., bar code, RFID tag) and a reader  206  to read the key  204  on the platen  202 . The key  204  can provide information about the platen  202 , such as the type of products on the platen  202  and set-up parameters (e.g., automatic adjustment of printhead stand-off distance). The reader  206  communicates with the imaging system  208 , which instructs the printhead based on this information. 
     For example, a barcode on a platen can indicate that the platen holds coffee mugs. A barcode reader reads the barcode that the platen contains coffee mugs. The imaging system, in response, adjusts the printhead stand-off distance to a height that permits the mugs to pass under the printhead without damaging the head. The imaging system also processes the images to account for the circular motion of the mugs relative to the printhead. 
     Alternatively, a user can manually enter into the imaging system the type of products on the platen and select the images to be printed. The printhead can have a home position that is a predetermined vertical or horizontal distance from the platen. This enables users to easily transfer platens on and off the printing system. 
     While the platen in  FIG. 1  rotates about a stationary axis, a platen  402  could rotate about an axis that moves along a conveyor system  404 , as shown in the printing system  400  of  FIG. 5 . A rotating peg  406  could be used in place of a platen. Multiple rotating pegs connected to a conveyor system spin objects  408 , such as compact disc (CD) or digital video disc (DVD). The printhead  410  prints on the spinning compact discs as they travel linearly along the conveyor, similar to single pass printing. This can be faster than scanning printing, especially for small objects. The printhead can print a coating on the surface of the disc or print graphics on it. The printhead  410 , in  FIG. 5 , includes four colors, cyan  412 , magenta  414 , yellow  416 , and black  418 . 
     Referring to  FIG. 4 , the flowchart  300  shows how image data is processed so that the printhead can print data on a substrate supported by a rotating platen or peg. First, the image data is in a format stored by the imaging system  302  (e.g., graphic image format (gif), joint experts group (jpeg), PostScript, Printer Command Language (PCL), or other image data collection). Second, the imaging system uses software to convert the image data into a format compatible with the printhead  304 , such as bitmap raster data. The image data goes through an arc process  306  and gradient mask process  308  to compensate for the circular motion of the substrate and the image resolution variation of a substrate from the center to the edge of the platen. 
     The portion of the substrate closer to the edge of the platen moves faster than the portion of the substrate closer to the center. This causes errors in drop placement of the image data on a substrate. The drops placed near the center of the platen are closer together than the drops placed near the edge of the platen. To compensate for the circular motion, the image data  30  illustrated graphically in  FIG. 4A  (“ABC”) goes through an arc process that bends the image data  30  to compensate for the faster and slower portions of the substrate and correct the drop placement. 
       FIG. 4B  graphically shows formatted image data  40  after going through the arc process. The “A” is closer to the edge of the platen, therefore its size is reduced to compensate for the platen moving faster near the edge, which spaces the dots further apart. On the other hand, the “C” is enlarged because it is closer to the center, which is moving slower causing the dots to land closer together. 
     The gradient mask process compensates for the variation of image boldness, in which the portion  52  of the image furthest from the center is lighter than the portion  54  closest to the center of the platen, as seen in  FIG. 4C . The gradient mask process overlays a random matrix of white dots  60 , shown in  FIG. 4D , onto the image data with more white dots in the darker areas  62 . The number of white dots decreases from the darker areas  62  to the lighter areas  64  to provide uniformity in the image boldness from the center to the edge of the platen. 
     The image data can be separated into cyan, magenta, yellow, and black  310 , and sent to the printhead for printing  312 . The sequence of steps described is an example of how the image data can be processed. These steps can be rearranged, some steps can be combined into a single step, or some steps can be added or eliminated. 
     With respect to the printing systems in  FIGS. 1 ,  2  and  3 , the printheads used can include NOVA JA 256 or GALAXY JA 256, which are commercially available from FUJIFILM Dimatix, Inc. located in Lebanon, N.H. The printheads can print images with a resolution of about 400 dpi to about 1200 dpi. 
     In  FIGS. 1 ,  2  and  3 , the substrates can be cell phones, edible items, compact discs, DVDs, specialty advertising products, such as lighters, golf balls, medallions, pens, letter openers, and any other objects. The objects can be customized for business or for personal use. The printheads can deposit ink (e.g., ultraviolet, solvent, aqueous, or hot melt ink), coatings, edible substances, plastic, or any other materials. The platen can be any shape, such as a circular, rectangular, or triangular. The platen can be mounted horizontally, vertically, or any other desired orientation, and can rotate around a center axis or an off-centered axis. 
     The printing system in  FIGS. 1 and 2  shows two printheads, but the printing system can have any number of printheads or only one printhead. The printing system can include a printhead for depositing a coating on a substrate, such as a varnish top coat. The imaging system shown in  FIG. 1  can support text, line art, logotypes, and graphics. 
     The printing system of  FIGS. 1 ,  2  and  3  can also include a curing station, such as an ultraviolet curing station. The term “peg” is not limited to a particular shape or size. For example, the peg can be round or square. The peg can have more than one prong. While  FIGS. 1 ,  2  and  3  shows platens and pegs to support objects, other implementations can be used to support and rotate objects relative to a printhead. Alternatively, the platens or pegs in  FIGS. 1 ,  2  and  3  could be stationary while the printheads rotate relative to the substrates. 
     Referring to  FIG. 2 , the trigger can be a mechanical trigger (e.g., knob), optical trigger (e.g., laser beam), an electrical trigger, or any other type of trigger. 
     The printing system  100  of  FIG. 2  can print images having a certain image resolution that correlates with the nozzle pitch of the printheads  114 . The image resolution can be increased by increasing the number of dots per inch with each revolution of the platen. For example, when the substrates pass under the head one time, the heads print an image having 100 dpi. After the first revolution, the heads are then moved from the center  116  of the platen to the outside edge a short distance (e.g., one or more pixels). During a second revolution, the heads print dots in the space between the dots from the first revolution. The image resolution after two revolutions can therefore be increased to 200 dpi. By increasing the number of revolutions, the image resolution can correspondingly increase (e.g., to 300 dpi, 600 dpi, 1200 dpi, or greater). The heads can alternatively move from the outside edge toward the center of the platen. 
     This is similar to single pass printing, in which the nozzles from a plurality of printheads are interlaced to increase the resolution. In single pass printing, the number of heads must increase to increase the image resolution. However, with this printing system, the resolution can be increased without increasing the number of printheads, instead the resolution can increase by increasing the number of revolutions. 
     This process also applies to the printing system  400  of  FIG. 5 , which has rotating platens  402  on a moving conveyor  404 . 
     Other implementations and combinations of these implementations are within the scope of the following claims. The platen can move the substrate along paths that are other than circular, for example, any non-straight path.