Patent Publication Number: US-6334661-B1

Title: System and method for inducing tensioning of a flexible nozzle member of an inkjet printer with an adhesive

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to inkjet and other types of printers and more particularly, to a printing system and method for inducing tensioning of a flexible nozzle member of a printhead portion of an inkjet printer with an adhesive. 
     BACKGROUND OF THE INVENTION 
     Inkjet printers are commonplace in the computer field. These printers are described by W. J. Lloyd and H. T. Taub in “Ink Jet Devices,” Chapter 13 of  Output Hardcopy Devices  (Ed. R. C. Durbeck and S. Sherr, San Diego: Academic Press, 1988) and U.S. Pat. Nos. 4,490,728 and 4,313,684. Inkjet printers produce high quality print, are compact and portable, and print quickly and quietly because only ink strikes a printing medium, such as paper. 
     An inkjet printer produces a printed image by printing a pattern of individual dots at particular locations of an array defined for the printing medium. The locations are conveniently visualized as being small dots in a rectilinear array. The locations are sometimes “dot locations”, “dot positions”, or pixels”. Thus, the printing operation can be viewed as the filling of a pattern of dot locations with dots of ink. 
     Inkjet printers print dots by ejecting very small drops of ink onto the print medium and typically include a movable carriage that supports one or more print cartridges each having a printhead with a nozzle member having ink ejecting nozzles. The carriage traverses over the surface of the print medium. An ink supply, such as an ink reservoir, supplies ink to the nozzles. The nozzles are controlled to eject drops of ink at appropriate times pursuant to command of a microcomputer or other controller. The timing of the application of the ink drops is intended to correspond to the pattern of pixels of the image being printed. 
     In general, the small drops of ink are ejected from the nozzles through orifices by rapidly heating a small volume of ink located in vaporization chambers with small electric heaters, such as small thin film resistors. The small thin film resistors are usually located adjacent the vaporization chambers. Heating the ink causes the ink to vaporize and be ejected from the orifices. Specifically, for one dot of ink, an electrical current from an external power supply is passed through a selected thin film resistor of a selected vaporization chamber. The resistor is then heated for superheating a thin layer of ink located within the selected vaporization chamber, causing explosive vaporization, and, consequently, a droplet of ink is ejected from the nozzle and onto a print media. One very important factor in assuring high print quality is the accuracy of the trajectory of the ejected droplet since this affects where it lands upon the print media. The accuracy of this trajectory is mostly dependent upon the particular geometry of the nozzle. 
     One challenge in controlling the nozzle geometry and hence trajectory of the droplets is to regulate bending and/or buckling of the nozzle member, otherwise known as “dimpling” of the nozzle member. Dimpling of the nozzle member causes the nozzles to be skewed, which leads to imprecise nozzle geometry. Dimpling tends to be induced during print cartridge manufacturing, which includes cartridge assembly processes such as adhesively bonding the printhead to the cartridge. More specifically, dimpling can be caused by inadvertent bending and/or buckling of the nozzle member due to structural thermal expansions and contractions occurring when the nozzle member is adhesively sealed to the print cartridge. For example, during the heat, cure and cool process when the nozzle member is adhered to the cartridge, the cartridge experiences thermal expansions and contractions. These thermal expansions and contractions cause the nozzle member to buckle, bend and deform, thereby skewing the nozzles. 
     Since dimpling of the nozzle member skews the nozzles, it tends to adversely affect nozzle geometry, thereby causing nozzle trajectory errors. A measure of this bending of the nozzle member is referred to as the “nozzle camber angle” (NCA), which is proportional to the bending of the nozzle member from an ideal flat state. Poor nozzle camber angles (NCAs) causes ink drop trajectory errors and uncontrolled ink drop directionality. In other words, when the printhead assembly is scanned across a recording medium, the NCA-induced ink drop trajectory errors will affect the location of printed dots and, thus, affect the quality of printing. Also, the bending of the nozzle member can restrict ink flow into nozzles, thus limiting the refill speed and hence the maximum droplet ejection frequency. This is turn limits printer speed. Therefore, what is needed is a nozzle member that has incurred limited bending or deformation during manufacturing of the print cartridge and to be as flat as possible. What is also needed is a printing system incorporating a device that reduces dimpling of a nozzle member during manufacture of a printhead portion of an inkjet printer. 
     SUMMARY OF THE INVENTION 
     To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention is embodied in a printing system and method for inducing tensioning of a flexible nozzle member of a printhead portion of an inkjet printer with an adhesive and novel arrangement. 
     The printing system of the present invention includes a printhead assembly and an ink supply for printing ink on print media. The printhead assembly includes a printhead body having ink channels and a nozzle member having plural nozzles coupled to respective ink channels. The nozzle member is preferably flexible and is securely coupled to the printhead body with an adhesive arrangement that induces tensioning of the nozzle member. The adhesive arrangement includes having an adhesive layer located between a top portion of the printhead body and the flexible nozzle member. The top portion has a mechanical structure suitable to induce tensioning of the flexible nozzle member during thermal expansion (heating and curing) of the adhesive when the adhesive layer is located between the mechanical structure and the nozzle member. Namely, the adhesive arrangement of the printing system of the present invention is capable of efficiently tensioning, and thus, flattening the flexible nozzle member during the adhesion process (which includes heating and curing the adhesive) of the nozzle member. As a result, trajectory errors of ejected ink droplets from the nozzles are reduced. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention can be further understood by reference to the following description and attached drawings that illustrate the preferred embodiment. Other features and advantages will be apparent from the following detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. 
     FlG.  1  shows a block diagram of an overall printing system incorporating the preset invention. 
     FIG. 2 is an exemplary printer that incorporates the invention and is shown for illustrative purposes only. 
     FIG. 3 shows for illustrative purposes only a perspective view of an exemplary print cartridge incorporating the present invention. 
     FIG. 4 is a schematic cross-sectional view taken through section line  4 — 4  of FIG. 3 showing the adhesive arrangement of the print cartridge of FIGS. 1 and 3. 
     FIG. 5 is a schematic cross-sectional view taken through section line  4 — 4  of FIG. 3 showing another adhesive arrangement of the print cartridge of FIGS. 1 and 3. 
     FIG. 6 is a schematic cross-sectional view taken through section line  4 — 4  of FIG. 3 showing another adhesive arrangement of the print cartridge of FIGS. 1 and 3. 
     FIG. 7 is a schematic cross-sectional view taken through section line  4 — 4  of FIG. 3 showing another adhesive arrangement of the print cartridge of FIGS.  1  and  3 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following description of the invention, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration a specific example in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention. 
     General Overview: 
     FIG. 1 shows a block diagram of an overall printing system incorporating the present invention. The printing system  100  of the present invention includes a printhead assembly  110 , an ink supply  112  and print media  114 . The printhead assembly  110  includes a printhead body  116 , a flexible nozzle member  118  with orifices or nozzles  120  fluidically coupled to associated ink channels  121 . The printhead body  116  is securely coupled to the nozzle member  118  with an adhesive arrangement  122  for inducing tensioning of the flexible nozzle member  118 . The induced tension helps create a flatter flexible nozzle member  118  during the adhesion process, which typically includes heating and curing the adhesive. As a result, trajectory errors of ejected ink droplets from the nozzles are reduced. 
     During a printing operation, ink is provided from the ink supply  112  to an interior portion (such as an ink reservoir) of the printhead body  116 . The interior portion of the printhead body  116  provides ink to the ink channels  121  for allowing ejection of ink through adjacent nozzles  120 . Namely, the printhead assembly  110  receives commands from a processor (not shown) to print ink and form a desired pattern for generating text and images on the print media  114 . Print quality of the desired pattern is dependent on accurate placement of the ink droplets on the print media  114 . 
     One way to increase print quality is to improve the accuracy and precision of ink droplet placement. This can be achieved by limiting the skew of the nozzles by minimizing nozzle camber angles (NCA). In one embodiment, the present invention is embodied in a printhead body  116  with an adhesive arrangement  122  defined by an adhesive layer being located between a top portion of the printhead body  116  and the flexible nozzle member  118 . The top portion is mechanically structured so that it induces tensioning of the flexible nozzle member during adhesion of the nozzle member  118  to the printhead body  116  when the adhesive layer is located between the mechanical structure and the nozzle member  118 . The mechanical structure can be any physical structure or geometrical arrangement that induces the above tensioning. Consequently, skewing of the nozzles is reduced and NCA is improved, and thus, trajectory errors for the ejected ink droplets from the nozzles  120  are reduced. 
     Exemplary Printing System: 
     FIG. 2 is an exemplary high-speed printer that incorporates the invention and is shown for illustrative purposes only. Generally, printer  200  includes a tray  222  for holding print media  114  (shown in FIG.  1 ). When a printing operation is initiated, print media  114 , such as a sheet of paper, is fed into printer  200  from tray  222  preferably using a sheet feeder  226 . The sheet then brought around in a U direction and travels in an opposite direction toward output tray  228 . Other paper paths, such as a straight paper path, can also be used. The sheet is stopped in a print zone  230 , and a scanning carriage  234 , supporting one or more print cartridges  236 , is then scanned across the sheet for printing a swath of ink thereon. After a single scan or multiple scans, the sheet is then incrementally shifted using, for example, a stepper motor and feed rollers to a next position within the print zone  230 . Carriage  234  again scans across the sheet for printing a next swath of ink. The process repeats until the entire sheet has been printed, at which point it is ejected into output tray  228 . 
     The present invention is equally applicable to alternative printing systems (not shown) such as those incorporating grit wheel or drum technology to support and move the print media  114  relative to the printhead assembly  110 . With a grit wheel design, a grit wheel and pinch roller move the media back and forth along one axis while a carriage carrying one or more printheads scans past the media along an orthogonal axis. With a drum printer design, the media is mounted to a rotating drum that is rotated along one axis while a carriage carrying one or more printheads scans past the media along an orthogonal axis. In either the drum or grit wheel designs, the scanning is typically not done in a back and forth manner as is the case for the system depicted in FIG.  2 . 
     The print cartridges  236  may be removeably mounted or permanently mounted to the scanning carriage  234 . Also, the print cartridges  236  can have self-contained ink reservoirs in the body of the printhead (shown in FIG. 3) as the ink supply  112  (shown in FIG.  1 ). The self-contained ink reservoirs can be refilled with ink for reusing the print cartridges  236 . Alternatively, the print cartridges  236  can be each fluidically coupled, via a flexible conduit  240 , to one of a plurality of fixed or removable ink containers  242  acting as the ink supply  112  (shown in FIG.  1 ). As a further alternative, ink supplies  112  can be one or more ink containers separate or separable from print cartridges  236  and removeably mountable to carriage  234 . 
     FIG. 3 shows for illustrative purposes only a perspective view of an exemplary printhead assembly  300  (an example of the printhead assembly  110  of FIG. 1) incorporating the present invention. A detailed description of the present invention follows with reference to a typical printhead assembly used with a typical printer, such as printer  200  of FIG.  2 . However, the present invention can be incorporated in any printhead and printer configuration. 
     Referring to FIGS. 1 and 2 along with FIG. 3, the printhead assembly  300  is comprised of a thermal head assembly  302  and a printhead body  304 . The thermal head assembly  302  can be a flexible material commonly referred to as a Tape Automated Bonding (TAB) assembly. The thermal head assembly  302  contains a flexible nozzle member  306  and interconnect contact pads  308  and is secured to the printhead assembly  300 . The thermal head assembly  302  can be secured to the print cartridge  300  with suitable adhesives. An integrated circuit chip (not shown) provides feedback to the printer  200  regarding certain parameters of printhead assembly  300 . The contact pads  308  align with and electrically contact electrodes (not shown) on carriage  234 . The nozzle member  306  preferably contains plural parallel rows of offset nozzles  310  through the thermal head assembly  306  created by, for example, laser ablation. It should be noted that other nozzle arrangements can be used, such as non-offset parallel rows of nozzles. 
     Component Details: 
     FIG. 4 is a cross-sectional schematic taken through section line  4 — 4  of FIG. 3 of the inkjet print cartridge  300  utilizing the present invention. A detailed description of the present invention follows with reference to a typical printhead used with print cartridge  300 . However, the present invention can be incorporated in any printhead configuration. Also, the elements of FIG. 4 are not to scale and are exaggerated for simplification. 
     Referring to FIGS. 1-3 along with FIG. 4, as discussed above, conductors (not shown) are formed on the back of thermal head assembly  302  and terminate in contact pads  308  for contacting electrodes on carriage  234 . The other ends of the conductors are bonded to the printhead  302  via terminals or electrodes (not shown) of a substrate  410 . The substrate  410  has ink ejection elements  416  formed thereon and electrically coupled to the conductors. The integrated circuit chip provides the ink ejection elements  416  with operational electrical signals. 
     An ink ejection or vaporization chamber  418  is adjacent each ink ejection element  416 , as shown in FIG. 4, so that each ink ejection element  416  is located generally behind a single orifice or nozzle  420  of the nozzle member  306 . The nozzles  420  are shown in FIG. 4 to be located near an edge of the substrate  410  for illustrative purposes only. The nozzles  420  can be located in other areas of the nozzle member  306 , such as centered between an edge of the substrate  410  and an interior side of the body  304 . Each ink ejection element  416  acts as ohmic heater when selectively energized by one or more pulses applied sequentially or simultaneously to one or more of the contact pads  308  via the integrated circuit. The ink ejection elements  416  may be heater resistors or piezoelectric elements. The orifices  420  may be of any size, number, and pattern, and the various figures are designed to simply and clearly show the features of the invention. The relative dimensions of the various features have been greatly adjusted for the sake of clarity. 
     The printhead body  304  is defined by a headland portion  426  located proximate to the back surface of the nozzle member  306  and includes an inner raised support  430 . An adhesive layer  432  is located between the back surface of the nozzle member  306  and a top surface  434  of the inner raised support  430  to securely affix the nozzle member  306  to the headland  426 . The inner raised support  430  preferably includes an overflow slot  436  for receiving excess adhesive (i.e., adhesive overflow during fabrication of the printhead). The adhesive layer  432  forms an adhesive seal between the nozzle member  306  of the thermal head assembly  302  and the headland  426 . Some adhesives that can be used include hot-melt, silicone, UV curable adhesive, and mixtures thereof. Further, a patterned adhesive film may be positioned on the headland  426 , as well as a dispensed bead of adhesive. 
     Referring to FIGS. 1-4, during a printing operation, ink stored in an ink reservoir  424  defined by the printhead body  304  generally flows around the edges of the substrate  410  and into the vaporization chambers  418 . Energization signals are sent to the ink ejection elements  416  and are produced from the electrical connection between the print cartridges  236  and the printer  200 . Upon energization of the ink ejection elements  416 , a thin layer of adjacent ink is superheated to provide explosive vaporization and, consequently, cause a droplet of ink to be ejected through the orifice or nozzle  420 . The vaporization chamber  418  is then refilled by capillary action. This process enables selective deposition of ink on print media  114  to thereby generate text and images. 
     During typical fabrication of the printhead assembly  300  and adhesion of the nozzle member  306  to the headland  426 , dimpling is usually formed in the nozzle member  306  and thermal head assembly  302 . Dimpling is caused by inadvertent bending or deformation of the flexible nozzle member  306  and thermal head assembly  302 . Bending and deformation can be caused by disproportionate thermal expansion and contraction of the headland  426  as compared to the thermal expansion and contraction of the flexible nozzle member  306 . In other words, since the flexible nozzle member  306  and the headland  426  are typically made of different materials, their respective coefficients of thermal expansion and contraction are different so they deform disproportionately. 
     Thermal expansion, bending or deformation of the flexible nozzle member  306  occurs when a dispersed (non-localized) heat source, such as hot air, is applied to the flexible nozzle member  306  to initiate curing of the adhesive  432 . Thermal contraction, bending or deformation of the flexible nozzle member  306  occurs when cooling is applied to the flexible nozzle member  306  to finalize curing of the adhesive and to seal the flexible nozzle member  306  to the headland  426 . This bending or deformation causes dimpling of the nozzle member  306 , which results in skewed nozzles  420 , thereby causing trajectory errors for the ejected ink droplets from the nozzles  420 . Consequently, when the printhead assembly  300  is scanned across the print media during printing, the ink trajectory errors will affect the location of the ejected ink and reduce the quality of printing. 
     In one embodiment, the headland  426  of the present invention includes an integrated heat transfer device  440  for reducing thermal expansion of the printhead body  304 . The integrated heat transfer device  440  can be any suitable device for reducing the thermal expansion of the headland  426  by reducing the temperature of the bulk volume of the headland  426  during exposure to heat, such as when the adhesive is heated to initiate curing. For example, as shown in FIG. 4, the heat transfer device  440  can be an aperture or cutaway portion of the headland  426 . The aperture or cutaway  440  reduces the cross sectional area of the headland  426 , thereby minimizing heat transfer from the curing adhesive  432  to the printhead body  304  and headland  426 . As a result, dimpling is reduced because thermal expansion of the headland  426  is reduced during exposure to heat when the nozzle member  306  is adhesively sealed to the headland  426 . 
     Specifically, this can be accomplished, for example, by having the integrated heat transfer device  440 , such an aperture or cutaway, located in close proximity to the bottom portion  450  of the inner raised support  430 . This reduces a cross sectional portion of the headland  426 , thereby reducing heat transfer to a top portion of the headland  426  and thus, limiting thermal expansion of the headland  426 . For instance, the aperture or cutaway  440  can be located near the overflow slot  436  and between the bottom portion  450 , as shown in FIG.  4 . 
     FIG. 5 is a schematic cross-sectional view taken through section line  4 — 4  of FIG. 3 showing another heat transfer device of the print cartridge of FIGS. 1 and 3 and a controlled heating process. In another embodiment, an integrated heat transfer device  445  is a cutaway of the bottom portion  450  of the inner raised support  430  to form a slotted portion  510  for reducing heat transfer to a top portion  452  of the headland  426 , as shown in FIG.  5 . 
     In another embodiment, the headland  426  of the present invention includes an adhesive arrangement  447  that induces tensioning of the flexible nozzle member  306  during the adhesion process. This induced tension helps create a flatter flexible nozzle member  306 . The adhesive arrangement  447  can be any suitable arrangement, such as an adhesive layer located on a sloped surface or strategic geometrical configuration, that induces tension in the flexible nozzle member  306  in order to flatten the flexible nozzle member  306  during the adhesion process. 
     For example, as shown in FIG. 4, the adhesive arrangement  447  can be defined by an adhesive bead or layer  432  formed between the flexible nozzle member  306  and a top sloped or angled surface  434 . During the adhesion process, the adhesive shrinks toward the center of the adhesive in directions defined by vector components  460 ,  462 . The components  460 ,  462  show the shrinkage direction of adhesive, and thus, the tension direction of the flexible nozzle member  306  induced by the adhesive arrangement  447 . As a result, dimpling is reduced because the flexible nozzle member  306  is tensioned, and thus, flattened, when it is adhesively sealed to the headland  426 . 
     FIG. 6 is a schematic cross-sectional view taken through section line  4 — 4  of FIG. 3 showing another adhesive arrangement of the printhead of FIGS. 1 and 3. In another embodiment, an adhesive arrangement  506  includes a top sloped or angled surface  508  and a z-stop  510  adjacent the overflow slot  436  and the top angled surface  508 , suitable to cause the adhesive to shrink in a direction that tensions the nozzle member, as shown in FIG.  5 . Similar to the embodiment of FIG. 4, the adhesive bead or layer  432  is formed between the flexible nozzle member  306  and the top angled surface  508  and shrinks in the same manner as depicted in FIG. 4 to thereby tension the flexible nozzle member  306 . The z-stop  510  is preferably a guide post for height referencing or keeping the nozzle member  306  at a desired height by allowing it to rest on top of the z-stop  510 . The z-stop  510  improves height control and uniformity, reduces the thickness of the adhesive  432  and allows for maximum spacing between the adhesive  432  and the substrate  410  for further increasing the flatness of the nozzle member  306 . 
     Further, a controlled process can be used to heat and cure the adhesive  432  for regulating the amount of heat applied to the printhead body  304  by localizing the application of the heat, as shown in FIG.  6 . Regulating the amount of heat applied to the printhead body  304  helps control the thermal expansion of the headland  426 . In particular, hot gimbaled rails  520  can be placed in direct contact with the nozzle member  306  at a contact area  522  to conductively heat and cure the adhesive  432 . The contact area  522  is preferably located directly above the adhesive  432  between the nozzle member  306  and the headland  426 . Since the rails  520  only contact the nozzle member  306 , heat can be applied to a regulated area, such as the contact area  522 , with controlled amounts of temperature. For instance, a minimum required amount of heat to cure the adhesive  432  can be applied to a controlled area  460  directly above the adhesive  432 . 
     In addition, an insulator device  530  can be used to insulate other areas from the heat. Namely, an insulated gimbal locating device  530  can be placed in direct contact with the nozzle member  306  at a contact area  532  to insulate certain areas. The contact area  532  is preferably located in direct contact with the headland  426  of the printhead body  304  to reduce the bulk temperature of the body  304  when the body is exposed to the heat. Since the insulated gimbal locating device  530  directly contacts a portion of the headland  426 , the temperature of the headland  426  near the contact area  532  can be regulated. As a result of this localized heating method, only a small portion of the headland  426  is heated, thereby efficiently controlling and reducing thermal expansion of the headland  426 , which reduces bending, deformation and dimpling of the thermal head assembly  302 . Consequently, trajectory errors of ejected ink droplets from the nozzles  420  are reduced. It should be noted that the above embodiments could also be performed in combination to further reduce thermal expansion of the printhead body. 
     In another embodiment, precise tensioning and shaping of the nozzle member  306  can be achieved during the adhesive process with the configuration  700  shown in FIG.  7 . FIG. 7 is a schematic cross-sectional view taken through section line  4 — 4  of FIG. 3 showing another adhesive arrangement of the print cartridge of FIGS. 1 and 3. Namely, the configuration  700  includes clamps  704  and temperature controlled cure horns  720  for tensioning the nozzle member during the adhesion process (only one clamp, one cure horn and one side of the nozzle member are shown in FIG. 7 for simplicity). 
     During the adhesion process, the clamps  704  are compressed onto each outer side  710  of the nozzle member  306  with a force P 2 . The temperature controlled cure horns  720  are compressed onto the nozzle member  306  over an area  722  proximate an adhesive layer  724  with force P 1 . The cure horns  720  apply heat to the area  722  proximate the adhesive layer  724  for curing the adhesive layer  724  while the nozzle member  306  is held in this controlled state. Force P 1  is set to provide the desired amount of nozzle member  306  tensioning and hold down force and P 2  is set at a sufficient level for securely holding the nozzle member  306  during the process. Due to possible inherent tension amplification effects, force P 2  may be higher than P 1 . 
     The compressive forces P 1  and P 2  causes the nozzle member  306  to be tensioned over a z-stop rail  510 , which forces the nozzle member  306  to conform to the profile of the rail  510  over the length of the nozzle member  306 . Also, this tension tends to remove excess flexible material of the nozzle member  306  over the vaporization channel  418  that would normally cause bending or buckling. As a result, the nozzle member  306  will tend to be as flat as the rail  510 , thereby minimizing the NCA variation. 
     The foregoing has described the principles, preferred embodiments and modes of operation of the present invention. However, the invention should not be construed as being limited to the particular embodiments discussed. As an example, the above-described inventions can be used in conjunction with inkjet printers that are not of the thermal type, as well as inkjet printers that are of the thermal type. Thus, the above-described embodiments should be regarded as illustrative rather than restrictive, and it should be appreciated that variations may be made in those embodiments by workers skilled in the art without departing from the scope of the present invention as defined by the following claims.