Abstract:
A curved wiper blade system is provided for an inkjet printing mechanism to remove ink residue from an inkjet printhead installed in the printing mechanism, here, ill as an inkjet printer. A pair of wiper blades each curve inwardly toward each other, and maintain this curvature during bi-directional wiping strokes. This configuration allows one wiper blade to receive an ink solvent from an applicator and apply the solvent to the ink-ejecting nozzles of the printhead when moving in one wiping direction. When wiping in the opposite direction, one wiper blade also removes ink residue from an interconnect portion of the printhead, as well as from the ink-ejecting orifice plate portion of the printhead.

Description:
This is a continuation of application Ser. No. 10/015,818 filed on Oct. 30, 2001, now U.S. Pat. No. 6,655,781, which is hereby incorporated by reference herein. 
    
    
     INTRODUCTION 
     The present invention relates generally to inkjet printing mechanisms, and more particularly to a curved wiper blade system for removing ink residue from an inkjet printhead in an inkjet printing mechanism. 
     Inkjet printing mechanisms use pens which shoot drops of liquid colorant, referred to generally herein as “ink,” onto a page. Each pen has a printhead formed with very small nozzles through which the ink drops are fired. To paint an image, the printhead is propelled back and forth across the page, shooting drops of ink in a desired pattern as it moves. The particular ink ejection mechanism within the printhead may take on a variety of different forms known to those skilled in the art, such as those using piezo-electric or thermal printhead technology. For instance, two earlier thermal ink ejection mechanisms are shown in U.S. Pat. Nos. 5,278,584 and 4,683,481, both assigned to the present assignee, Hewlett-Packard Company. In a thermal system, a barrier layer containing ink channels and vaporization chambers is located between a nozzle orifice plate and a substrate layer. This substrate layer typically contains linear arrays of heater elements, such as resins, which are energized to heat ink within the vaporization chambers. Upon heating, an ink droplet is ejected from a nozzle associated with the energized resistor. By selectively energizing the resistors as the printhead moves across the page, the ink is expelled in a pattern on the print media to form a desired image (e.g., picture, chart or text). 
     To clean and protect the printhead, typically a “service station” mechanism is mounted within the printer chassis so the printhead can be moved over the station for maintenance. For storage, or during non-printing periods, the service stations usually include a capping system which hermetically seals the printhead nozzles from contacts and drying. To facilitate priming, some printers have priming caps that are connected to a pumping unit to draw a vacuum on the printhead. During operation, partial occlusions or clogs in the printhead are periodically cleared by firing a number of drops of ink through each of the nozzles in a clearing or purging process known as “spitting.” The waste ink is collected at a spitting reservoir portion of the service station, known as a “spittoon.” After spitting, uncapping, or occasionally during printing, most service stations have a flexible wiper, or a more rigid spring-loaded wiper, that wipes the printhead sure to remove ink residue, as well as any paper dust or other debris that has collected on the printhead. 
     To improve the clarity and contrast of the printed image, recent research has focused on improving the ink itself. To provide quicker, more waterfast printing with darker blacks and more vivid colors, pigment based inks have been developed. These pigment based inks have a higher solids content than the earlier dye-based inks, which results in a higher optical density for the new inks. Both types of ink dry quickly, which allows inkjet printing mechanisms to use plain paper. 
     One way to improve nozzle wiping efficiency is through the use of fluid assisted wiping, where the service station stores a supply of a non-volatile ink solvent fluid, such as glycerol or polyethylene glycol (“PEG”), with the wiper occasionally picking up some of the cleaning fluid and transferring it to the printhead nozzle plate. One inlet printer having such a solvent application system is the Hewlett-Packard Company&#39;s model 2000C Professional Series Inkjet Printer. This wiper fluid also acts as a lubricant to minimize nozzle bore deformation that may occur due to the wiping action. Unfortunately, while the earlier wiper designs allowed for an easy pick and dispense of the fluid onto the nozzle plate, they were not well suited for removing the resulting waste ink and fluid mixture from the nozzle plate. 
     For ire, FIG. 8 shows a side elevational view of such an earlier wiper system during a wiping stroke, with FIG. 9 being side elevational of a later stage of the wiping stroke, while FIG. 10 shows an enlarged view of an intermediate stage of the wiping stroke. In FIG. 8, we see an inkjet cartridge C having a printhead P which is being wiped by a dual bladed wiper system W, which has a first wiper blade B 1  and a second wiper blade B 2 . The wiper system W is constructed as described in U.S. Pat. No. 5,614,930, currently assign to the present assignee, the Hewlett-Packard Company. Each of the wiper blades B 1  and B 2  have wiper tips with an arcuate exterior wiping edge and an angular interior wiping edge as described in U.S. Pat. No. 5,614,930. 
     When wiping in a direction D, the rounded exterior wiping edge of the first wiper blade B 1  is used to wick or draw ink from the nozzles through capillary action. This wicked ink is then moved by blade B 1  along succeeding nozzles to dissolve ink residue accumulated on the nozzle plate. The angular interior wiping edge of the second wiper blade B 2  then scrapes away the extracted ink and dissolved ink residue, along with any other debris from the nozzle plate P. Unfortunately in some cases, after much use, the second wiper blade B 2  was not able to efficiently remove the ink residue from the nozzle plate, and instead, merely spread the dirty fluid mixture over the nozzle plate. In extreme cases, the accumulated dirty fluid/ink mixture could migrate to the sides of the nozzle plate, or to the back of the nozzle area where the printhead receives electrical signals from an electrical interconnect I, corroding the electrical traces on the interconnect or causing electrical shorts between the interconnect traces. 
     FIG. 10 illustrates another problem associated with the earlier wiper blade designs. The action of FIG. 10 occurs between that shown in FIGS. 8 and 9. In FIG. 8 we see the second wiper blade B 2  has just come into contact with the interconnect I. In this flat-to-flat contact position, wiper blade B 2  has no ability to wipe ink, ink residue, or any combination thereof from the interconnect I. Quite to the contrary, as shown in FIG. 10, any ink solvent and/or ink residue remaining on the interior surface of the wiper blade B 2  is actually clean from the wiper blade by the corner between the orifice plate P and the interconnect I, leaving an undesirable deposit of solvent and residue are along interconnect I. Eventually, a leading amount of fluid may accumulate along the lower portion of the interconnect I, leading to additional electrical trace corrosion and/or electrical ink shorts caused by ink bridging between the electrical traces. 
    
    
     DRAWING FIGURES 
     FIG. 1 is a perspective view of one form of an inkjet printing mechanism, here shown as an inkjet printer, having a service station with one form of a curved wiper blade system of the present invention. 
     FIG. 2 is an enlarged perspective view of the service station of FIG.  1 . 
     FIG. 3 is an enlarge side elevational view of one inkjet cartridge and the service station of FIG. 1, shown prior to the beginning of a wiping stoke. 
     FIG. 4 is an en side elevational view of a first stage of a wiping stroke using the service station of FIG.  1 . 
     FIG. 5 is an enlarged side elevational view of a second stage of a wiping stroke using the service station of FIG.  1 . 
     FIG. 6 is an enlarged side elevational view of an intermediate stage of a wiping stroke using the service station of FIG.  1 . 
     FIG. 7 is an enlarged side elevational view of an alternate embodiment of a curved wiper blade system which may be used in the service station of FIG.  1 . 
     FIG. 8 is an enlarged side elevational view of a prior art dual blade wiping system shown during an initial phase of a wiping stoke. 
     FIG. 9 is an enlarged side elevational view of the prior art wiping system of FIG. 8, shown during a later stage of the wiping stroke. 
     FIG. 10 is an enlarged, side elevational, detailed view of the prior at wiping system of FIG. 8, shown during an intermediate portion of the wiping stroke. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 illustrates an embodiment of an inkjet printing mechanism, here shown as an inkjet printer  20 , constructed in accordance with the present invention, which may be used for printing for business reports, correspondence, desktop publishing, and the like, in an industrial, office, home or other environment. A variety of inkjet printing mechanisms are commercially available. For instance, some of the printing mechanisms that may embody the present invention include plotters, portable printing units, copiers, cameras, video printers, and facsimile machines, to name a few. For convenience the concepts of the present invention are illustrated in the environment of an in printer  20 . 
     While it is apparent that the printer components may vary from model to model, the typical inkjet printer  20  includes a chassis  22  surrounded by a housing or casing enclosure  24 , typically of a plastic material. Sheets of print media are fed though a printzone  25  by a print media handling system  26 . The print media may be any type of suitable sheet material, such as paper, card-stock, transparencies, mylar, and the like, but for convenience, the illustrated embodiment is described using paper as the print medium. The print media handling  26  has a feed tray  28  for storing sheets of paper before printing. A series of conventional motor-driven paper drive rollers (not shown) may be used to move the print media from tray  28  into the printzone  25  for printing. After printing, the shin then land on output tray portion  30 . The media handling system  26  may include a series of adjustment mechanisms for accommodating different sizes of print media, including letter, legal, A-4, envelopes, etc., such as a sliding length and width adjustment levers  32  and  33  for the input tray, and a sliding length adjustment lever  34  for the output tray. 
     The printer also has a printer controller, illustrated schematically as a microprocessor  35 , that receives instructions from a host device, typically a computer, such as a personal computer (not shown). Indeed, many of the printer controller functions may be performed by the host computer, by the electronics on board the printer, or by interactions therebetween. As used herein, the term “printer controller  35 ” encompasses these functions, whether performed by the host computer, the printer, an intermediary device therebetween, or by a combined interaction of such elements. The printer controller  35  may also operate in response to user input provided through a key pad (not shown) located on the exterior of the casing  24 . A monitor coupled to the computer host may be used to display visual information to an operator, such as the printer status or a particular program being run on the host computer. Personal computers, their input devices, such as a keyboad and/or a mouse device, and monitors are all well known to those skilled in the art. 
     A carriage guide rod  36  is mounted to the chassis  22  to define a scanning axis  38 . The guide rod  36  slideably supports a reciprocating inkjet carriage  40 , which travels back and forth across the printzone  25  and into a servicing region  42 . Housed within the servicing region  42  is a service station  44 , which will be discussed in greater detail below with respect to the present invention. The illustrated carriage  40  carries four inkjet cartridges or pens  50 ,  51 ,  52 , and  53  over the printzone  25  for printing, and into the servicing region  42  for printhead servicing. Each of the pens  50 ,  51 ,  52 , and  53  have an inkjet printhead  54 ,  55 ,  56 , and  58 , respectively, which selectively eject droplets of ink in response to firing signals received from the controller  35 . 
     One suitable type of carriage support System is shown in U.S. Pat. No. 5,366,305, assigned to Hewlett-Packard Company, the assignee of the present invention. A conventional carriage propulsion system may be used to drive carriage  40 , including a position feedback system, which communicates carriage position signals to the controller  35 . For instance, a carriage drive gear and DC motor assembly may be coupled to drive an endless belt secured in a conventional manner to the pen carriage  40 , with the motor operating in response to control signals received from the printer controller  35 . To provide carriage positional feedback information to printer controller  35 , an optical encoder reader may be mounted to carriage  40  to read an encoder strip extending along the of carriage travel. 
     In the printzone  25 , the media sheet receives ink from the inkjet carriages  50 ,  51 ,  52  and  53 , such as the yellow ink cartridge  50 , the ink magenta cartridge  51 , the yellow ink cartridge  52 , and/or the cyan ink cartridge  53 . The cartridges  50 - 53  are also often called “pens” by those in the art. While the color pens  50 ,  51  and  53  may contain pigment based inks, for the purposes of illustration, the color pens arc described as containing debased inks. The black ink pen  52  is illustrated herein as containing a pigment-based ink. It is apparent that other types of inks may also be used in pens  50 - 53 , such as thermoplastic, wax or paraffin based inks, as well as hybrid or composite inks having both dye and pigment characteristics. The illustrated pens  5053  each include reservoirs for storing a supply of ink. 
     The printheads  54 - 58  each have an orifice plate with a plurality of nozzles formed therethrough in a manner known to those skilled in the art. The illustrated printheads  54 - 58  are thermal inkjet heads, although other types of printheads may be used, such as piezoelectric printheads. Indeed, the printheads  54 - 58  typically include a substrate layer having a plurality of resistors which are associated with the nozzles. Upon energizing a selected resistor, a bubble of gas is formed to eject a droplet of ink from the nozzle and onto media in the printzone  25 . The printhead resistors are selectively energized in response to enabling or firing command control signals, which may be delivered by a conventional multi-conductor strip (not shown) from the controller  35  to the printhead carriage  40 , and through conventional interconnects between the carriage and pens  50 - 53  to the printheads  54 - 58 . 
     FIG. 2 shows service station  44  as having one form of a curved wiper blade system  60 , constructed in accordance with the preset invention The illustrated service station  44  has a base portion  62  and a bonnet portion  64 , with a moveable pallet  65  sandwiched therebetween. The pallet is driven forwards and backwards parallel to the Y-axis by a motor  66  and a gear assembly, for instance such as a rack and pinion gear assembly discussed further below with respect to FIG. 3 which may be constructed as described in U.S. Pat. Nos. 5,980,018 and 6,132,026, currently assigned to the present assignee, the Hewlett-Packard Company. The pallet  65  may carry other printhead servicing components, such as primers or caps, for instance, such as cap  67  shown schematically in dashed lines in FIG.  3 . The caps are moved into position under their associated printheads and elevated to cap each of the printheads  54 - 58 . The interior of the service station base  62  forms a spittoon  68 , which is exposed to receive ink purged or spit from the printheads  54 - 58  when the pallet  65  is moved partially or totally under bonnet  64 . 
     The curved blade wiper system  60  has four sets of wiper blades  70 ,  71 ,  72  and  73 , which each wipe printheads  54 ,  55 ,  56  and  58 , respectively. To assist in the wiping, one portion of the bonnet  64  houses an ink solvent reservoir  74 , which may be filled with any type of suitable ink solvent, but in the illustrated embodiment it is preferably filled with a polyethyl glycol (“PEG”) solvent. The service station  44  has four solvent applicators  75 ,  76 ,  77 , and  78  which are in fluid communication with the solvent reservoir  74 , to extract solvent therefrom and have it available along their outer surfaces for application to the wiper blades. 
     Each of the wiper blade sets  70 ,  71 ,  72 , and  73  has a first blade  80  and a second wiper blade  82 . The wide wiper/narrow wiper combination was first introduced in the Hewlett-Packard Company&#39;s model 2000C Professional Series Color Inkjet Printer using upright wiper blades having a tip configuration, such as those disclosed in U.S. Pat. No. 5,614,930, assigned to the Hewlett-Packard Company. In the illustrate embodiment, the first wiper blade  80  is wider in width than the second wiper blade  82 , allowing the wide wiper blade  80  to clean the entire orifice plate surface, while the narrow wiper blade  82  concentrates along the linear any of nozzles, which we centrally located in the orifice plate. FIG. 3 shows the yellow wide wiper blade  80  in dashed lines contain the solvent applicator  75  in operation, which preferably occurs when the carriage  40  has the pens  50 - 53  removed from the servicing area  42  and over the printzone  25 . FIG. 3 shows the yellow wiper blade set  70  in solid line after it has received the solvent from applicator  75 , aid in an initial position before the beginning of a wiping routine, as representative of each of the wiper blade sets  70 - 73 . 
     FIG. 3 shows the yellow wiper blade set  70 , poised ready for wiping the yellow printhead  54 . The wide wiper blade  80  has a base  84 , while the narrow blade  82  has a base  86 . Please note that while these principles are illustrated using a wide/narrow wiper blade set, these principles apply equally if both blades are of the same width, which may be preferable in some implementations. The blade bases  84  and  86  are separated by a base spacing, indicated as dimension  88  in FIG.  3 . Distal firm the base, the wide blade  80  has a tip  90  and the narrow blade  82  has a tip  92 , with the tips  90  and  92  being separated by a tip spacing, indicated as dimension  94  in FIG.  3 . The inwardly curved nature of each of the wiper blades  80 ,  82  yields a base spacing dimension  88  which is wider than the tip spacing  94 , yielding a unique configuration when compared to the earlier upright parallel wiper blades, such as those disclosed in U.S. Pat. No. 5,614,930, mentioned above, and which was first commercially available in the Hewlett-Packard Company&#39;s Model 850C and 855C Color Inkjet Printer. 
     As mentioned above, FIG. 3 shows that a conventional gear assembly may be used to couple the motor  66  to a rack and pinion gear assembly  95 , with the pallet  65  carrying the rack portion of assembly  95 . Together, the motor  66  and the gear assembly  95  cooperate to drive the pet  65  in a forward direction  96  and a rearward direction  98 . A front portion  64 ′ of the service station bonnet may include a wiper scraper blade, which removes ink residue from the wiper blades  80 ,  82  as they enter and exit from a storage position underneath the front bonnet portion  64 ′, for instance as described in U.S. Pat. Nos. 5,980,018 and 6,132,026, mentioned above. 
     From the ink solvent pick position shown in dashed lines in FIG. 3, motor  66  drives the pallet  65  in the forward direction  96  until reaching the initial wiping position shown solid lines in FIG.  3 . From the position in FIG. 3, the motor drives the wipers in the rot direction  98 , as shown in FIG. 4 to allow the wide wiper blade  80  to apply ink solvent  74 ′ to the surface of printhead  54 . A mixture of ink residue and solvent  74 ′ is then formed on the orifice plate after the passage of the wide wiper blade  80 . This mixture of ink solvent and ink residue  74 ″ is then removed immediately by blade  82  from the portion of the orifice plate where the linear nozzle arrays reside, as shown in FIG.  4 . After passing over the entire printhead  54 , the pallet  65  reverses direction and begins moving in the forward direction  96 , as shown in FIG.  5 . 
     In FIG. 5 we see the narrow wiper  82  is configured to wick ink from the nozzles and drag it along the linear nozzle array, in the same manner as described in U.S. Pat. No. 5,614,930 previously mentioned. However, in the second portion of the wiping stroke, the wide wiper blade  80  vigorously attack ink solvent and residue or other debris  74 ″ along the orifice plate in a scraping or bulldozing action, removing the mixture  74 ″ from both the outer regions of the orifice plate and along the linear nozzle arrays. This scraping angle of attack A, shown in FIG. 5, of the trailing blade, and shown as A′ in FIG. 4 for the narrow blade  82 , is an acute angle, as opposed to an obtuse angle T shown in FIG. 9 between the leading surface of the trailing blade B 2  and the surface of printhead P which bas just been wiped. The acute angle of attack A, A′ of the trailing blade is believed to better clean and remove ink residue from the printhead orifice plate than the earlier use of an obtuse angle of attack T. 
     FIG. 6 illustrates an interconnect wiping stage, which occurs between the wiping stages shown in FIGS. 4 and 5. In FIG. 6, we see an interconnect portion  99  of the yellow cartridge  50  being wiped by wiping tip  90  of the wide wiper blade  80 . The interconnect portion  99  carries signals between the controller  35  and the printhead  54 , such as the firing signals to resistors which cause ink to be ejected from the nozzles, and temperature sensing signals which sense the printhead temperature and provide feedback to controller  35 . Other signals may also be communicated by the interconnect portion  99 , such as various printhead identification signals to let controller  35  know whether and when a new pen  50 - 53  has been inserted in carriage  40 . The electrical interface pads between the pens  50 - 53  and the carriage  40  are located above the interconnect trace portion  99  shown in FIG.  6 . Maintaining pen cleanliness in the interconnect portion  99  is important for many reasons, including those discussed in the Introduction section above. In FIG. 6, we see the inwardly curving tip  90  of the wide wiper blade  80  vigorously attacking and removing ink residue from the interconnect  99 . In comparing the angle of attack of blade tip  90  with that of blade B 2  shown in FIG. 10, we see wiper tip  90  actively removing ink residue R from the interconnect I, as opposed to the prior art blade B 2  which actually deposit residue along the interconnect I of FIG.  10 . 
     FIG. 7 illustrates an alternative embodiment of another curved blade wiper system  100 , constructed in accordance with the present invention, which may be substituted for one or all of the blade systems  70 - 73  shown in FIGS. 1-6. First and second wiper blades  102 ,  104  have bases  105 ,  106 , respectively, extending upwardly from the pallet  65 . The blade bases  105  and  106  are separated by a base spacing labeled as dimension  108  in FIG.  7 . The distal end of the wiper blades  102 ,  104  each terminate in an inwardly hooked wiping tip  110 ,  112 , respectively. The inwardly hooked wiper tips  110  and  112  are separated by a spacing distance labeled as dimension  114  in FIG. 7, with the tip spacing distance  114  being less that the base spacing distance  108 . The inwardly hooked wiping tips  110 ,  112  function as described above with rod to FIGS. 4-6 for the wiper blade sets  70 - 73 , including cleaning of the interconnect portion  99  as shown in FIG.  6 . The inwardly hooked wiping tips  110 ,  112  when in a trailing position also attack the printhead at an acute angle, similar to angles A′ and A shown in FIGS. 4 and 5, rather than the obtuse angle T of FIG.  9 . 
     The wiper blade sets  70 - 73  and  100  may also be distinguished by their cross-sectional profiles, where each blade  102 ,  104  has a concave interior surface  116 , and a convex exterior surface  118 , whereas for blade set  70 - 73 , they each share an interior concave surface  116 ′ and an exterior convex surface  118 ′ (FIG.  3 ). These concave interior surfaces  116 ,  116 ′ and convex exterior surfaces  118 ,  118 ′ are quite different from the planar parallel surfaces of the prior art blades B 1 , B 2  of FIGS. 8-10. Indeed, another way of distinguishing the curved wiper blades  70 - 73  and  100  from the prior art wiper sets W of FIGS. 8-10 is by the trailing blade having an obtuse angle of attack, which is 180° minus angle A or A′, versus the prior art bailing blade B 2  having an acute angle of attack, which is equal to 180° minus the angle T of FIG.  9 . 
     The ability of wipers  70 - 73 ,  100  to effectively remove fluid and ink residue from the interconnect portion  99  of the pens  50 - 53  reduces the occurrence of fluid-induced printhead failures, such as electrical shorts and electrical trace corrosion in the interconnected region  99  which were discussed above in the introduction section. Furthermore, the curved wiper blade system  60 ,  100  may be implemented using current solvent application techniques, such as shown in FIGS. 2 and 3. Moreover, the exact shape and configuration of wipers  70 - 73  and  100  may be varied to better control the wiping force through curvature changes, dimensional changes and/or material changes, such as durometer changes, to balance between excessive wiping force which causes nozzle bore deformation, and insufficient wiping force which leads to inefficient cleaning of the nozzle plate, resulting in nozzle plugs and misdirected ink drops from partially plugged nozzles. The curved wiping tips prevent the wipers from hydroplaning over waste fluid on the nozzle plate, and allow removed residue  74 ″ (FIG. 5) to flow downwardly along the trailing blade interior  116 , as indicated by arrow  120  in FIG. 5, and eventually fall into soon  68 . Either wiper design  70 - 73 ,  100  may be molded with pass core techniques or through using extrusion techniques. Finally, the illustrated embodiments described above with respect to FIGS. 1-7 illustrate the principles and concepts of the invention as set forth in the claims below, and a variety of modifications and variations may be employed in various implementations, while still falling within the scope of the claims below.