Patent Publication Number: US-8123319-B2

Title: High speed high resolution fluid ejection

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to fluid droplet ejection. 
     BACKGROUND 
     In some implementations of a fluid droplet ejection device, a substrate, such as a silicon substrate, includes a fluid pumping chamber and a nozzle formed therein. Fluid droplets can be ejected from the nozzle onto a medium, such as in a printing operation. The nozzle is fluidly connected to the fluid pumping chamber. The fluid pumping chamber can be actuated by a transducer, such as a thermal or piezoelectric actuator, and when actuated, the fluid pumping chamber can cause ejection of a fluid droplet through the nozzle. The medium can be moved relative to the fluid ejection device. The ejection of a fluid droplet from a nozzle can be timed with the movement of the medium to place a fluid droplet at a desired location on the medium. Fluid ejection devices typically include multiple nozzles, and it is usually desirable to eject fluid droplets of uniform size and speed, and in the same direction, to provide uniform deposition of fluid droplets on the medium. 
     SUMMARY 
     In general, in one aspect, a fluid ejection system includes a fluid reservoir, a support to move a media in a first direction, a first plurality of independently controllable fluid ejector units, a second plurality of independently controllable fluid ejector units, and a controller electronically coupled to the first plurality of actuators and the second plurality of actuators. The first plurality of independently controllable fluid ejector units includes a first plurality of nozzles and a first plurality of actuators and is coupled to draw a liquid from the fluid reservoir. The second plurality of independently controllable fluid ejector units includes a second plurality of nozzles and a second plurality of actuators and is coupled to draw the same liquid from the fluid reservoir. The controller is configured to cause the first plurality of nozzles and the second plurality of nozzles to eject droplets of the liquid while the media is moving to form a line of pixels on the media in a single pass, pixels in the line of pixels uniformly spaced at a pixel pitch p. The first plurality of nozzles and the second plurality of nozzles are arranged in a plurality of nozzle pairs, each nozzle pair of the plurality of nozzle pairs including a first nozzle from the first plurality of nozzles and an associated second nozzle from the second plurality of nozzles, the first nozzle and associated second nozzle of each nozzle pair spaced apart in a second direction perpendicular to the first direction by greater than zero and less than the pixel pitch p and spaced apart in the first direction, and wherein the controller is configured such that the first nozzle and the second nozzle of each nozzle pair deposit droplets at the same pixel in the line of pixels. 
     In general, in one aspect, a fluid ejection system includes a fluid reservoir, a support to move a media in a first direction, a first plurality of independently controllable fluid ejector units, a second plurality of independently controllable fluid ejector units, and a controller electronically coupled to the first plurality of actuators and the second plurality of actuators. The first plurality of independently controllable fluid ejector units includes a first plurality of nozzles and a first plurality of actuators and is coupled to draw a liquid from the fluid reservoir. The second plurality of independently controllable fluid ejector units includes a second plurality of nozzles and a second plurality of actuators and is coupled to draw the same liquid from the fluid reservoir. The controller is configured to cause the first plurality of nozzles and the second plurality of nozzles to eject droplets of the liquid while the media is moving to form a line of pixels on the media in a single pass at a speed of greater than 3 m/s, pixels in the line of pixels uniformly spaced at a pixel pitch p. The first plurality of nozzles and the second plurality of nozzles are arranged in a plurality of nozzle pairs, each nozzle pair of the plurality of nozzle pairs including a first nozzle from the first plurality of nozzles and an associated second nozzle from the second plurality of nozzles, the first nozzle and associated second nozzle of each nozzle pair spaced apart in a second direction perpendicular to the first direction by less than the pixel pitch p and spaced apart in the first direction, and wherein the controller is configured such that the first nozzle and the second nozzle of each nozzle pair deposit droplets at the same pixel in the line of pixels. 
     These and other embodiments can optionally include one or more of the following features. The first plurality of nozzles and the second plurality of nozzles can have n rows of nozzles per pixel in the second direction, and a spacing between the nozzles in the second direction can be greater than zero and less than p/n. 
     The first plurality of independently controllable fluid ejector units and the second plurality of independently controllable fluid ejector units can be part of the same fluid ejection module. The first and second plurality of nozzles can be arranged in a matrix. The first plurality of independently controllable fluid ejector units can be part of a first fluid ejection module, and the second plurality of independently controllable fluid ejector units is part of a second fluid ejection module. The nozzles of the first plurality of nozzles can be arranged in a first matrix, and the nozzles of the second plurality of nozzles can be arranged in a second matrix. 
     Subpixel droplets can be ejected from the first and second plurality of nozzles. Each plurality of nozzles can eject only one droplet of fluid at each pixel. The first and second plurality of nozzles can be configured such that a line of pixels having a density of greater than 300 dpi is formed when the first and the second nozzle of each nozzle pair deposit droplets at the same pixel in the line of pixels. The density can be approximately 1200 dpi. The first and second plurality of nozzles can be configured to eject liquid having a droplet size of between about 0.1 pL and 30 pL. The line of pixels is formed on the media at a speed greater than 3 m/s. The speed can be approximately 4 m/s. 
     Certain implementations may have one or more of the following advantages. Having pairs of nozzles spaced apart in a direction perpendicular to the print direction by less than the pixel pitch and spaced apart in the print direction, but controlled to deposit fluid droplets at the same pixel, can increase the print speed, improve print quality, and allow for a decreased fluid ejection module size. 
     The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages will become apparent from the description, the drawings, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an exemplary fluid ejection module. 
         FIG. 2A  shows a cross section of an exemplary fluid ejection module. 
         FIG. 2B  is a schematic cross sectional view of an exemplary fluid ejection module. 
         FIG. 3  is a schematic bottom view of a nozzle layer of a fluid ejection module. 
         FIG. 4  shows an exemplary fluid ejection system having multiple fluid ejection modules. 
         FIG. 5  illustrates a relationship of a fluid ejection system having multiple aligned nozzles per pixel to locations of droplets deposited on the print media. 
         FIG. 6  illustrates a relationship of a fluid ejection system having multiple offset nozzles per pixel to locations of droplets deposited on the print media. 
         FIG. 7  is a schematic illustration of a printing system. 
     
    
    
     Like reference numbers and designations in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     During fluid droplet ejection, such as digital ink jet printing, it is desirable to print at speeds of 3-5 m/s while avoiding banding and other errors in the printed images. By aligning nozzles such that multiple nozzles drop fluid at each pixel, high quality images at high printing speeds can be achieved. 
     Referring to  FIG. 1 , a fluid ejection system  199  includes a fluid ejector  100  surrounded by a fluid ejector casing  105 . A mounting component  110  is attached to the casing  105  to secure the fluid ejector  100  to a print frame  140  to hold the fluid ejector over the print medium. The fluid ejector  100  further includes tubing  170 ,  180  to carry fluid from a fluid reservoir (not shown). 
     The fluid ejector  100  also includes a fluid ejection module, e.g., a parallelogram-shaped printhead module, which can be a die fabricated using semiconductor processing techniques, attached to the bottom of the casing  105 . The fluid ejection module includes a substrate  190 , which can be made of a semiconductor material, e.g. single crystal silicon, with a plurality of fluid flow paths  192  (see  FIG. 2B ), and a plurality of actuators  401  (see  FIG. 2B ) to individually control ejection of fluid from nozzles  180  of the fluid flow paths. 
     The fluid ejector  100  is attached to print frame  140  through a mounting component  110  having a mounting surface  120 . A connector  130  is positioned on the mounting surface  120 , between the fluid ejector  100  and the print frame  140  and can be detachably connected to the print frame  140 , for example with screws  135 , so as to allow relatively easy removal without causing damage to the print frame  140 . 
     Referring to  FIGS. 2A and 2B , the fluid ejector  100  can include an upper supply chamber  410 , a supply filter  415 , and a lower supply chamber  420 . Fluid for ejection can leave the fluid reservoir, enter the upper supply chamber  410 , pass through the supply filter  415  into the lower supply chamber  420 , through an interposer  430 , and into the substrate  190 . 
     The substrate  190  can include a fluid flow path  192  or multiple fluid flow paths  192  and one or more nozzles  180  formed in a nozzle layer  195  (only one fluid flow path  192  and associated nozzle  180  is shown in  FIG. 2B ). When actuators  401  on the substrate  190  are actuated, pumping chambers  174  in the fluid flow paths  192  can contract, forcing fluid to be ejected as droplets from the nozzles  180 . Integrated circuit elements  104  on the substrate  190  provide electrical signals for control of ejection of fluid from the nozzles  180 . 
     The fluid ejector  100  can further include a lower return chamber  450 , a return filter  455 , and an upper return chamber  460 . Fluid that is not ejected through the nozzles  180  can exit the substrate  190  through return passages  184 , pass through the interposer  430  into the lower return chamber  450 , pass through the return filter  455  into the upper return chamber  460 , and return to the fluid reservoir. 
     As shown in  FIG. 3 , the nozzle layer  195  on the bottom surface of the substrate  190  includes multiple nozzles  180 . The nozzles  180  can be considered part of the fluid paths  192  and can extend through the nozzle layer  195 , terminating in an opening in a bottom surface of the nozzle layer  195 . The nozzle layer  195  can be a layer that is secured to the substrate  190 . Alternatively, the nozzle layer  195  can be a unitary part of the substrate  190 , e.g., a result of etching of the flow path body. The nozzles  180  can be in a regular array, e.g., nozzle layer  195  can include multiple columns and row of nozzles  180 , although in some implementations the printhead module might include only a single row of nozzles. When the fluid ejector  100  is secured to the print frame  140 , the rows of nozzles can be perpendicular or nearly perpendicular to the direction of travel of the print media. 
     In some implementations, as shown in  FIG. 4 , a fluid ejection system  101  can multiple fluid ejectors  100  mounted to the print frame  140 , e.g., side-by-side (perpendicular to the direction of travel of the print media) to extend across the width of the print media. Each fluid ejector  100  includes a mounting component  110 . Connectors  130  are positioned between each mounting component  110  and the print frame  140 , which as shown includes an optional upper portion  141 . The tubing  170  supply fluid to each fluid ejector  100 , and the tubing  180  provide a fluid return path for each fluid ejector  100 . Each fluid ejector  100  on a common print frame  140  can be connected through tubing  170  and  180  to a common fluid reservoir, i.e., each fluid ejector  100  (and the nozzles thereof) can eject the same fluid, e.g. color of ink. In addition, fluid ejector  100  on different print frames  140  in the same printer can be connected through tubing  170  and  180  to a common fluid reservoir, i.e., fluid ejectors  100  (and nozzles thereof) located at different positions along the direction of travel of the print media can eject the same fluid, e.g. color of ink. 
     Referring to  FIGS. 5 and 6 , a fluid ejection system  102  can include a multiple sets  181  of nozzles  180 . The nozzles  180  of each of the sets  181  can be spaced apart from one another in the print direction (the direction of travel of the print media, shown by the arrow in  FIG. 5 ). Although spaced apart, the nozzles can be in proximity in the print direction, e.g. approximately 100-1,000 μm apart if in the same module and approximately 10 mm apart if in separate modules, to minimize issues with web weave, as discussed further below. The nozzles of a particular set can be controlled to fire droplets to form a line of adjacent pixels on the print media perpendicular to the print direction. The nozzles of a particular set are all formed in the same fluid ejection module. The different sets  181  of nozzles  180  may all be part of the same fluid ejection module, or at least some of the sets may be part of separate fluid ejection modules, e.g., every set of nozzles can be formed on a different fluid ejection module. 
     As shown in  FIG. 7 , a controller  702  can be electronically coupled to the fluid ejector  100  through a circuit board  704 . The circuit board  704  can be electronically connected with the integrated circuit elements  104  of the substrate  190  to control ejection of fluid from the fluid ejector  100  The controller  702  can cause the nozzles  180  of the sets  181  of nozzles to eject droplets of liquid while a media is moving to form a line of pixels  502  on the media in a single pass, for example along axis  5  in  FIGS. 5 and 6 . For example, the controller  702  can send image data to the fluid ejector  100  in queues, each queue representing the desired printing order for a set of nozzles. The pixels can be uniformly spaced at a pixel pitch p, for example of between 20 and 250 μm. Although only three pixels  502  are outlined in dotted lines in  FIGS. 5 and 6 , each build-up of fluid droplets shown has a corresponding pixel. 
     Referring to  FIG. 5 , for each set, the nozzles  180  of the set  181  can be aligned on an axis perpendicular or nearly perpendicular to the print direction. For example, the set of nozzles including nozzles  11 ,  12 ,  13 ,  14 , and  15  is aligned along axis  1  in the direction perpendicular or nearly perpendicular to the print direction. Although the nozzles of each set are shown in  FIG. 5  as aligned, the sets  181  of nozzles  180  need not be aligned in the direction perpendicular to the print direction. Rather, the nozzles in the set can be offset along the print direction, but by application of appropriate delays by the controller  702 , the set of nozzles can be caused to eject droplets to form a line of adjacent pixels on the print media along a line perpendicular to the print direction. For example, the controller might put print data in a queue, each queue including a delay such that two sets of nozzles not aligned in the direction perpendicular to the print direction still print a line of pixels perpendicular to the print direction. 
     In addition, nozzles from multiple sets can form groups, with each group having one nozzle from each set, and with the nozzles  180  of each of the groups aligned along an axis parallel to the print direction. For example, in  FIG. 5 , the group of nozzles including nozzles  15 ,  25 ,  35 , and  45  are aligned along axis  5  in the print direction. 
     During fluid droplet ejection, the controller can cause the nozzles  180  of each group to deposit droplets at the same pixel  502 . The droplets of fluid can be 0.1 pL-30 pL in size, such as 0.1 pL-2.0 pL, and can be subpixel droplets, i.e. smaller than would be required to fully fill the pixel  502  if additional droplets were not added by other nozzles. For example, as shown in  FIG. 5 , nozzle  11  might eject a droplet  11   a  of fluid at pixel location  502   a . Nozzle  21  might then eject a droplet of fluid directly over droplet  11   a  at the same pixel location  502   a , causing the accumulated fluid on the print media at pixel location  502   a  to spread over region  21   a . Nozzle  31  might also eject a droplet of fluid at pixel location  502   a , causing the accumulated fluid on the print media at pixel location  502   a  to spread over region  31   a , and so on. The result would be a pixel  502   a  fully covered in fluid from the various droplets. The same process would occur for every pixel  502  along the media. Although not shown, an additional set of nozzles could be included for redundancy. 
     A fluid ejection system can thus include first and second sets of nozzles at least partially overlapping in a direction perpendicular to the direction of travel of the print media so that some of the nozzles in the first set align with some of the nozzles in the second set to form one or more pairs of aligned nozzles. The fluid ejection system can further include a mechanism to enable, in at least one pair of the aligned nozzle, one nozzle to eject a first ink drop that has a size smaller than a size of an ink drop the nozzle would otherwise be required to eject to form a desired pixel on the substrate and the other nozzle to eject a second ink drop that has a size sufficient to form the desired pixel in combinations with the first ink drop. Each nozzle in the first set can align with a corresponding nozzle in the second set. 
     Referring to  FIG. 6 , in other implementations, the nozzles can be misaligned, i.e. not perfectly aligned along an axis. Thus, the nozzles  180  of each set  181  can be offset from one another in a direction perpendicular to the print direction. For example, in  FIG. 6 , the set of nozzles including nozzles  11 ,  12 ,  13 ,  14 , and  15  are each offset from axis  1 . Again, although shown in  FIG. 6  as approximately aligned, the  181  sets of nozzles  180  need not be aligned, as the ejection of fluid droplets along a line perpendicular to the print direction can be caused by delays set by the controller  702 . 
     Nozzles from multiple sets can form groups, with each group having one nozzles from each set, and with the nozzles  180  of each of the groups approximately aligned along an axis parallel to the print direction. The nozzles  180  of each group can be offset from one another in the direction parallel to the print direction. For example, in  FIG. 6 , the group of nozzles including nozzles  15 ,  25 ,  35 , and  45  are each offset from axis  5 . Any pair of nozzles from the same group of nozzles, but different sets of nozzles, can be offset by a same amount. Further, the offset for nozzles in a particular group can form a repetitive pattern. 
     As in the embodiment of  FIG. 5 , during fluid droplet ejection, the controller can cause the nozzles  180  of each of the sets  181  that are approximately aligned along the direction parallel to the print direction to deposit droplets at the same pixel  502 . Again, the droplets of fluid can be subpixel droplets, i.e. smaller than would usually be required to fill the pixel  502 . Unlike the embodiment of  FIG. 5 , however, the droplets of fluid ejected from nozzles approximately aligned along the print direction are not concentric within a pixel  502 . Rather, the droplets each land in a slightly different spot within a pixel  502 . For example, as shown in  FIG. 6 , nozzle  11  might eject a droplet  11   a  of fluid at in the upper left-hand corner of pixel location  502   b . Nozzle  21  might then eject a droplet of fluid  21   a  in the upper right hand corner of pixel location  502   b . Although droplets  11   a  and  21   a  overlap, they are not concentric with one another. Likewise, nozzle  31  might eject a droplet of fluid  31   a  in the lower right hand corner, and nozzle  41  might eject a droplet of fluid  41   a  in the lower left hand corner. The result would be a pixel  502   b  fully covered in fluid from the various drops. The same process would occur for every pixel  502  along the media. Although not shown, an additional set of nozzles could be included for redundancy. 
     There can be n columns of nozzles per pixel, the columns parallel to the print direction, and nozzles within a set can be separated with a uniform pitch p. For example, in  FIG. 6 , there are two columns of nozzles per pixel; for pixel  502   b , nozzles  11  and  41  form one column, and nozzles  21  and  31  the other column. The spacing between nozzles that are approximately aligned in the print direction, i.e., in different sets but in the same group, e.g. along axis  5  in the embodiment of  FIG. 6 , can be greater than zero, e.g., greater than k*p/(n−1) where k is about 0.1-1.0, for example 0.5, but less than p/n in the direction perpendicular to the print direction. Thus, in  FIG. 6 , the distance between nozzles  11  and  21  in the direction perpendicular to the print direction is greater than zero, but less than p/2. Although the nozzles  180  of  FIG. 6  are shown as arranged in a regular pattern, a more stochastic pattern could be used. Further, the nozzles  180  in each group can be arranged in a matrix having interlacing. An exemplary interlacing arrangement is described in U.S. application No. 61/055,936, titled NOZZLE LAYOUT FOR FLUID DROPLET EJECTING, all of which is incorporated herein by reference. 
     Although four sets  181  of nozzles  180  are shown in  FIGS. 5 and 6 , the fluid ejection system  102  can include fewer or greater numbers of sets. For example, there may only be two sets  181  of nozzles  180 . As such, only two nozzles, i.e. one pair of nozzles, would eject fluid at each pixel  502 . Further, although the sets  181  of nozzles  180  are shown in  FIGS. 5 and 6  as including only a single row nozzles along the direction perpendicular to the print direction, the nozzles  180  of each set  181  may be arranged in a matrix. 
     An alignment mechanism can be used to obtain the desired relative position for nozzles that are in different fluid, i.e. to adjust those nozzles spaced apart in the print direction or perpendicular to the print direction. 
     By having multiple nozzles per scan line, i.e. multiple droplets of fluid ejected at each pixel, higher speed, e.g. 3-5 m/s or higher, fluid droplet ejection can be achieved than in conventional single pass printing because smaller droplets can be ejected at a higher frequency. For example, a conventional interleaved single pass fluid ejection system might include a single nozzle to eject a droplet of 2 pL at each pixel at 1200 dpi at an operating frequency of 100 kHZ for a maximum printing speed of 2.1 m/s. The system described herein, however, could include four nozzles ejecting 0.5 pL droplets of fluid at a single pixel at 1200 dpi and an operating frequency of 200 kHZ for a maximum printing speed of 4.2 m/s. Although the example described herein suggests a dpi of 1200, the system could be used for a dpi anywhere from 300 to 2400. Further, speeds higher than 3-5 m/s are possible by reducing the droplet size to get higher operating frequencies and utilizing more jets per scan line. 
     In conventional single pass printing, where a single jet fires continuously to produce a line of ink on the page, errors can occur in the resulting image, such as banding and edge raggedness, due to misalignment of the jets, nozzle straightness errors, jet velocity, and web weave errors. Further, in a system using an interleaved approach to obtain higher speeds, i.e. a system in which two sets of nozzles are aligned in the print direction, and each row prints every other line of pixels, banding can occur in the process direction due to misalignment of the first set of nozzles in relation to the second set of nozzles. 
     Advantageously, with a fluid ejection system as described herein, wherein multiple nozzles drop fluid at the same pixel location, the print quality can be increased. Because each nozzle ejects fluid at each pixel, banding will not occur in the processing direction. Further, in the system described herein, print quality can be increased by electronically adjusting drops a pixel at a time in the process direction simply by adjusting the firing pulse used. For example, in a 1200 dpi printer, the drops can be electrically adjusted in about 20 micron increments to compensate for fixed errors such as stand off and jet velocity offset. Moreover, printing quality can be improved if all of the jets that address a particular line of pixels can be located in a single print-head close together to improve mechanical alignment and minimize jet-to-jet velocity variations. Finally, by using the fluid ejection system described herein, the drop size can be modulated 4:1 at each location, thereby allowing for an improved grayscale system wherein between 0 and 4 drops could be ejected at each pixel. 
     Misaligning the nozzles such that each nozzle drops fluid at a separate location within a single pixel can further improve the quality of the resulting image. During conventional fluid droplet ejection, the surface energy of the droplets can cause the drops to fail spread out over the entire pixel area. By offsetting multiple droplets at the same pixel, the ink can spread out better throughout the pixel, resulting in a larger spot than if the drops all landed on top of one another. For example, in the 1200 dpi example given above, the drops would be spread out 10-20 microns. The result is improved dot gain linearity and a reduced amount of ink needed for solid coverage. 
     Moreover, redundancy can be provided more efficiently, as adding one additional jet to a four-jet line, for example, would increase the jet count by only 25%. As long as no more than one jet is out in each group, normal output could be reached. Further, even if two jets were out in one group, acceptable printing could still be produced if all five jets were working in one or both of the neighboring lines. 
     The controller can cause each nozzle in a group to eject the same volume of fluid. Even when less than all of the a pixel is desired to be covered, e.g., for printing of a grayscale pixel, the volume of fluid ejected by each nozzle of the group can be reduced (compared to a pixel at full intensity) with each nozzle in the group ejecting a droplet of the same volume. 
     Finally, although the system described herein requires additional circuitry and data throughput, the fluid ejection system can advantageously be made smaller than an interleaved fluid ejection system. For example, four 0.5 pL gets could ideally fit in the same area as one 2.0 pL jet, while the interleaved approach would require two 2.0 pL jets. 
     Particular embodiments have been described. Other embodiments are within the scope of the following claims.