Abstract:
Among other things, for jetting ink droplets on a substrate during relative motion of an apparatus and the substrate along a process direction, a first and second jetting assemblies at least partially overlap in a direction perpendicular to the process direction so that some jets in the first jetting assembly align with some jets in the second jetting assembly along the process direction to form one or more pairs of aligned jets. A mechanism enables, in at least one pair of the aligned jets, one jet to jet a first ink drop that has a size smaller than a size of an ink drop the jet would otherwise be required to jet to form a desired pixel and the other jet to jet a second ink drop that has a size sufficient to form the desired pixel in combination with the first ink drop.

Description:
TECHNICAL FIELD 
       [0001]    This description relates to ink jetting. 
       BACKGROUND 
       [0002]    Ink jetting can be done using an ink jetting printhead that includes jetting assemblies. Ink is introduced into the ink jetting printhead and when activated, the jetting assemblies jet ink and form images on a substrate. 
       SUMMARY 
       [0003]    In one aspect, for jetting ink droplets on a substrate during relative motion of an apparatus and the substrate along a process direction, the apparatus includes first and second jetting assemblies each including an array of jets. The first and second jetting assemblies at least partially overlap in a direction perpendicular to the process direction so that some of the jets in the first jetting assembly align with some of the jets in the second jetting assembly along the process direction to form one or more pairs of aligned jets. The apparatus also includes a mechanism to enable, in at least one pair of the aligned jets, one jet to jet a first ink drop that has a size smaller than a size of an ink drop the jet would otherwise be required to jet to form a desired pixel on the substrate and the other jet to jet a second ink drop that has a size sufficient to form the desired pixel in combination with the first ink drop. 
         [0004]    In another aspect, forming ink droplets on a substrate during relative motion of an ink jetting device and the substrate along a process direction, a method includes (a) causing a first jetting assembly of the ink jetting device to jet a first ink drop that has a size smaller than a size of an ink drop jet would otherwise be required to jet to form a desired pixel on the substrate; and (b) causing a second jetting assembly of the ink jetting device to jet a second ink drop that has a size sufficient to form the desired pixel in combination with the first ink drop. 
         [0005]    Implementations may include one or more of the following features. The first and second jetting assemblies each comprises more than 100 jets. One or more jets in the first jetting assembly each aligns with a corresponding jet in the second jetting assembly along the process direction. Each jet in the first jetting assembly aligns with a corresponding jet in the second jetting assembly. Each jet in the first and second jetting assemblies is capable of jetting ink drops with more than one size. Each jet in the first and second jetting assemblies is capable of jetting ink drops with three different sizes. Each jet in the first and second jetting assemblies is capable of jetting ink drops with a drop size of 30 nano-grams, 50 nano-grams, or 80 nano-grams. The first ink drop and the second ink drop having a total drop size of about 50 nano-grams. The aligned jets in the first and second jetting assemblies are about 50 mm from each other along the process direction. The apparatus also includes first and second jetting assembly arrays each comprising one or more jetting assemblies, along the direction perpendicular to the process direction, the first array of jetting assemblies aligning with the first jetting assembly and the second array of jetting assemblies aligning with the second jetting assembly. Each jetting assembly in the first jetting assembly array overlaps at least partially with at least one of the jetting assemblies in the second jetting assembly array along the direction perpendicular to the process direction. Each jetting assembly in the first jetting assembly array overlaps at least partially with two jetting assemblies in the second jetting assembly array along the direction perpendicular to the process direction. Each jetting assembly includes more than one jet each aligning with a corresponding jet in a corresponding overlapping jetting assembly. The first and second arrays of jetting assemblies have a width of about 25 mm to about 1 m along the direction perpendicular to the process direction. 
         [0006]    Implementations may also include one or more of the following features. The step (a) includes jetting a first ink drop having a drop size half of the size of the drop that is required to print the desired pixel on the substrate. The step (a) includes jetting a first ink drop having a drop size a third of the size of the drop that is required to print the desired pixel on the substrate. The first ink drop and the second ink drop to have a total drop size of about 50 nano-grams. 
         [0007]    These and other aspects and features can be expressed as methods, apparatus, systems, means for performing a function, and in other ways. 
         [0008]    Other features and advantages will be apparent from the following detailed description, and from the claims. 
     
    
     
       DESCRIPTION 
         [0009]      FIGS. 1A ,  1 B and  1 C are exploded perspective views of ink jetting printheads and a portion of an ink jetting printhead. 
           [0010]      FIGS. 2 and 3  are schematic top views of ink jet printers. 
           [0011]      FIGS. 2A ,  2 B, and  2 C are portions of a printed image schematically segmented in pixels. 
       
    
    
       [0012]    Referring to  FIG. 1A , ink jetting can be done using an ink jetting printhead  2  that includes assemblies  6  and  8  assembled onto a body  4  made, for example, of silicon or carbon. Ink is introduced into the ink jetting printhead  2  through the ink inlets  12  and  14  of the body  4 . The ink jetting printhead  2  also includes electronic components  10  that activate the assemblies  6  and  8  to jet ink and form images  17  on a substrate  16 . 
         [0013]    Referring to  FIG. 1B , the body  4  includes a cavity  16  connected to the ink inlets  12  and  14  to form ink fill passage when the assemblies  6  and  8  (not shown) are assembled onto a surface  18  and its opposite surface  48  ( FIG. 1C ) of the body  4 , respectively. On each of the surfaces  18  and  48 , each opening in a row of openings  33  or  35  ( FIG. 1C ) is connected to an ink jetting passage  38  and an opening  39  in the body  4  ( FIG. 1C ). The jetting assemblies  6  and  8  (not shown) each includes a cavity plate  20  having a cavity  22  with dimensions and location matching the dimensions and location of cavity  16  projected in the surface  18  and an array of cavities  24  having top ends  32  open to the cavity  16  and jetting ends  36 . 
         [0014]    The front and back surfaces of the cavity plate  20  are covered by a dimensionally matching polymer film  26  and a stiffener plate  28 , respectively, and ink pumping chambers are formed by the cavities  24 . Similar to the cavity  22  on the cavity plate  20 , the stiffener plate  28  also includes a cavity  30  so that when assembled and in use, ink is filled from the ink passage formed by the cavity  16  through the top ends  32  into the pumping chambers formed by the cavities  24 . The stiffener plate  28  also includes a row of openings  31 . When assembled, the dimensions and relative location of the openings  31  match those of the jetting ends  36  on the cavity plate and those of the openings  33  on the surface  18  of the body  4  so that when ink is pumped in the pumping chamber and reaches the jetting ends  36 , it passes the openings  31  in the stiffener plate  28  and the corresponding openings  33  on the body  4  and flows into the ink jetting passages  40  in the body  4 , where it is jetted from the openings  39  ( FIG. 1C ). 
         [0015]    Referring to  FIG. 1C , each of the ink jetting passages  38  corresponds to one pumping chamber in the assembly  6  or  8  ( FIGS. 1A and 1B ) and includes a horizontal portion  40  connected to an opening  33  or  35  and a vertical portion  42  connected to an opening  39  on the bottom  46  of the body  4 . The openings  33  and  35  are staggered along a long dimension  1  of the body  5  and when projected onto one of the surfaces  18  and  48 , the projection forms a row of equally distanced openings. The openings  39  are also equally distanced from each other and can be aligned in one (not shown) or two rows parallel to the long dimension  1  of the body  4 . In the example shown in the figure, the openings  39  in different rows are staggered along the long dimension  1  of the body  4 . One of the two rows of the openings  39  is connected to openings  35  in the back surface  48  of the body and the other row is connected to openings  33  in the front surface  18  of the body through the ink jetting passages  38 . 
         [0016]    In some embodiments, an orifice plate (not shown) containing orifices can be attached to the bottom  46  of the body  4 . Each orifice in contact with the bottom  46  of the body  4  aligns with an opening  39  and the orifices can be arranged, for example, in one or two rows corresponding to the number of rows in which the openings  39  are arranged. The orifices are connected to channels that are built within the orifice plate, which have another end connected to openings aligned in a single row in another surface of the orifice plate. Ink is jetted out to the substrate beneath the orifice plate through the single row of openings. Each pumping chamber, its corresponding ink jetting passage  38 , opening  39  and orifice together form an ink jet  44  (not shown). 
         [0017]    Referring back to  FIG. 1B , a piezoelectric element  34  having, for example, a thickness of about 200 microns, is attached to the outer surface of the polymer film  26  and covers the pumping chambers. The piezoelectric element  34  includes electrodes (not shown) that are electrically connected to the electronic components  10  on a flex board  9  that is assembled onto the body  4 . When in use, the electronic components  10  send signals, for example, voltage pulses, to selected electrodes and activate the portions of the piezoelectric element  34  that correspond to the selected electrodes to change shape and apply to pressures to the corresponding pumping chambers to jet ink. 
         [0018]    The resolution at which the printhead  2  prints depends, for example, on the size and density of the pumping chambers in the jetting assemblies  6  and  8 . In the example shown in the figures, the jetting assemblies  6  and  8  each has more than 50, 64, 100, 128, 256, 500, or 512 elongated parallel pumping chambers each having a length of about 5 mm, width of about 200 microns. The maximum width the printhead  2  can print is about 20 mm to about 100 mm. Information about the ink jetting printhead is also provided in U.S. Ser. No. ______, filed ______ (Attorney Docket No. 09991-259001). 
         [0019]    Referring to  FIG. 2 , one or more printheads  2  (two of the printheads  2  are named as  2   a  and  2   b;  the total number of printheads  2  and the number of jets in each printhead  2  shown are schematic) of  FIG. 1A  capable of printing, for example, at the same maximum resolution, can be incorporated into what is called a single-pass ink jet printer  45 . During printing, the printer  45  is kept still and based on the information about an image  43  obtained before printing and instantaneous information about motion of the substrate sent from a detector  52 , a controller  50  sends signals to the electronic components  10  ( FIGS. 1A and 1B ) of each printhead  2  to activate the relevant pumping chambers to jet ink at proper locations of a substrate  41  that is passing beneath the printer  45  and moving along a process direction y. 
         [0020]    The multiple printheads  2  are staggered in associated rows, for example, rows  47  and  49 , with their long dimensions  1  aligned across the substrate  41 , for example, perpendicular to the process direction y to cover the substrate width W 1C  ranging from less than 25 mm to 1 meter or more. Each printhead  2  in one of the rows  47  and  49  overlaps with at least one, for example, two, printhead  2  in the other row in stitching zones  48 . Each stitching zone  48  includes about 1 to about 4 jets  44 , or even more, for example, 16 jets  44  of each printhead  2 , in which each jet  44  of one printhead  2 , for example, jet  44   a,  aligns with a corresponding jet  44  of an overlapping printhead  2 , for example, jet  44   b,  along the process direction y. 
         [0021]    In some embodiments, each pixel, for example, pixel  54  of the image  43  is printed by a single jet  44  of the printheads  2  that is capable of jetting ink drops with one desired uniform size. For example, one type of printhead  2  is capable of jetting ink drops each having a mass of about 30 nano-grams, another type of printhead  2  capable of jetting ink drops each having a mass of about 50 nano-grams, or still another type of printhead  2  capable of jetting ink drops each having a mass of about 80 nano-grams. In particular, ink is jetted only from one of the overlapping jets, for example, either jet  44   a  or jet  44   b,  to print each pixel of the image  43  that is on the part of the substrate  40  passing beneath the stitching zones  48  along the process direction y. The selection of which one of the two aligned jets  44  can be random or regular, for example, taking turns, configured, for example, by the controller  50 . 
         [0022]    Referring to  FIGS. 2A and 2B , a portion  51  of the image  43  is printed on the substrate  41  using the two overlapping printheads  2  (printhead  2   a  with jets labeled as a in the row  47  and printhead  2   b  with jets labeled as b in the row  49 ). Each pixel of the portion  51  is enlarged and represented by a square  53 . In the example shown in the figures, two columns of the pixels fall into the stitching zone  48 , each printed by a one of the aligned jets  44 ( a  or  b ) taking turns ( FIG. 2A ), or randomly ( FIG. 2B ). Out of the stitching zone  48 , each of the pixels is printed by one available jet a or b. 
         [0023]    Printing with ink drops from one of the two aligned jets in each of the stitching zones  48  smoothes the seam between portions of images printed by different printheads across the substrate  41  and reduces or masks the undesired low quality printing, for example, streaks or image artifacts, caused by the possible misalignment of the printheads  2  in neighboring arrays both along and perpendicular to the process direction y, by the possible differences in properties between different printheads, which ideally would be identical, or by crooked or missing jets on one or more printheads. 
         [0024]    Referring to  FIG. 2C , when printing the portion  51  of the image  43  ( FIG. 2 ), some of the pixels, for example, pixels printed by the jets  44  in the stitching zones  48 , each can also be printed cooperatively by both of the aligned jets  44  along the process direction y. In some embodiments, the controller  50  is configured to allow the electronic components  10  of each printhead  2  to send voltage pulses having selected multiple waveforms at controlled frequencies to activate the pumping chambers and jet ink drops that have different properties, e.g., sizes, from each jet  44 . For example, each jet  44  of the printhead  2  is capable of jetting an ink drop having a mass that is, for example, ½, ⅓, or ¼ of the mass of the ink drop that a jet, capable of jetting ink drops with only one desired uniform size, of a printhead having the same physical properties, such as dimensions and densities of the pumping chambers. For example, such jet  44  can jet ink drops having a drop size of about 10 nano-grams to about 30 nano-grams, about 50 nano-grams, or about 80 nano-grams. In some embodiments, the smallest ink drop that the jet  44  is capable of jetting has a size that is about, for example, 10%, 20%, 25%, or 30%, and/or up to about, for example, 50%, 60%, 70%, 80%, or 90% of the size of the largest ink drop the jet  44  is capable of jetting. Information about printheads with jets capable of jetting ink drops having different properties is also provided in U.S. Ser. No. 10/800,467, filed Mar. 15, 2004 (Attorney Docket No. 09991-123001) and U.S. Ser. No. 11/652,325, filed Jan. 11, 2007 (Attorney Docket No. 09991-252001), which are incorporated here by references. 
         [0025]    In the example shown in the figures, the two aligned jets  44 , in particular, a and b of printhead  2   a  and  2   b  of  FIG. 2  jet ink drops to cooperatively print one pixel prints a fraction of the pixel. For example, one of the overlapping jets  44 , e.g., jet  44   a  jets ink drops having a drop size that is, e.g., half, a third, a fourth, a fifth, or other fraction of the size of an ink drop that is required to print a desired pixel. The controller  50  is configured, based on the transport speed of the substrate  41  and the relative distance p between the aligned jets  44  along the process direction y, to activate the other one of the overlapping jets  44 , e.g., jet  44   b,  at a proper time to jet ink drops that each compensates the size of the corresponding one of the ink drops that is already jetted to complementarily print the complete desired pixel on the substrate. The jets  44  that are not in the stitching zones  48 , although also capable of printing fractions of a pixel, jet ink drops to print full pixels of the image  43  on the substrate  41 . The use of both aligned jets in the stitching zones  48  obscures the quality difference of the portions of image  43  printed from different printheads  22  across the substrate  41  near the seams and enhances the overall quality of the image  43 . Also, jetting ink from both aligned jets  44  in the stitching zones  48  reduces the possible poor image quality caused by malfunctioning, for example, crooked or weak, jets of one of the overlapping printheads  2  in the stitching zones  48 . 
         [0026]    Referring to  FIG. 3 , in a printhead arrangement shown in a printer  58 , the printheads  2 , for example, six printheads  2  named as printheads  2   c - 2   h,  each including jets  44  (the total number of jets  44  shown is schematic) that are capable of jetting ink drops with one or more properties, e.g., sizes, as described above, can be arranged in two associated rows  54  and  56  in a single-pass ink jet printer  58 . Each jet  44  of at least one printhead  2  aligns with a corresponding jet of overlapping printheads  2  along the process direction y. In the example shown in the figure, except the printheads  2   c  and  2   h,  which are arranged nearby the two long ends  64  and  66  of the printer  58 , respectively, each of the printheads  2   b - 2   e  includes two stitching zones  68  and  70  that are similar to the stitching zone  48  of  FIG. 2 . 
         [0027]    Each of the stitching zones  68  and  70  contains jets  44  from overlapping printheads aligned in the process direction y. One of the stitching zones  68  and  70  can include a number of, for example, 0, 1, 2, and up to about half of the total number of jets  44 , each aligned with a corresponding jet of one overlapping printhead and the other one of the stitching zones  68  and  70  of the same printhead includes the rest of the jets  44  aligned with corresponding jets of another overlapping printhead. 
         [0028]    The printheads  2   c  and  2   h  each contains a dangling zone  72 , in which the jets  44  do not have corresponding aligned jets in the process direction y. The total number of jets  44  in each dangling zone  72  is dependent on the total number of aligned jets in each stitching zones  70 . In some embodiments, when the stitching zone  70  contains zero aligned jets  44 , each printhead in the row  54  fully overlaps with a corresponding printhead in the row  56  and dangling zone  72  does not exist. 
         [0029]    In some implementations, more or less than six printheads  2   a - 2   f  can be used in the way described above, depending on the width W 3  of a substrate  60  the printer  58  is required to cover to print an image  44  on the substrate  60 . The printer  58  can be configured so that when each jet  44  is capable of jetting ink drops with only one desired uniform property, each pixel, e.g., pixel  64 ,  66 ,  68 , or  70 , of the image  62  is printed with ink jetted from only one of the two aligned jets  44  along the process direction y. When each jet  44  is capable of jetting ink drops with two or more properties, each pixel of the image  62  is printed cooperatively with ink jetted from both aligned jets  44  along the process direction y. The extensive overlapping of printheads in the printer  58  allows a large number of jets  44  in the printer to have an aligned corresponding jet along the process direction y to further reduce the possible poor image quality caused by malfunctioning, for example, crooked or weak, jets of one of the printheads and blur the quality difference of portions of the image  62  printed from different printheads. 
         [0030]    Other embodiments are also within the scope of the following claims. 
         [0031]    For example, the printers  45  and  48  each can include more coupled printhead rows like printhead rows  47  and  49  and printhead rows  54  and  56 , stacked along the process direction y. Each pair of rows can print a different color than the other pairs. In each of the printers  45  and  48 , each printhead  2  can have its long dimensions  1  form an angle different than 90 degrees with the process direction y. Printheads other than that described in  FIG. 1A  can be used, for example, printheads that are made of sintered carbon or silicon and described in U.S. Pat. No. 5,265,315 and U.S. Ser. No. ______ filed ______ (Attorney Docket No. 09991-259001), which are incorporated here by reference. 
         [0032]    When there is little or no jetting in the printer  45  or  48 , ink recirculation can be done by letting ink flow slowly in one of the two ink inlets  12  and  14  of each printhead  2  through the ink passage  16  and out the other one of the ink inlets  12  and  14 . 
         [0033]    It should be understood that reference to ink as the printing fluid was for illustrative purposes only, and referring to components within the jetting assemblies described above with the adjective “ink” was also illustrative. The jetting assemblies can be used to dispense or deposit various printing fluids other than ink onto a substrate. The fluids can include non-image forming fluids. For example, three-dimensional model pastes can be selectively deposited to build models. Biological samples can be deposited on an analysis array.