Patent Publication Number: US-7901035-B2

Title: Directed flow drip bib for printhead with three point contact

Description:
TECHNICAL FIELD 
     This disclosure relates generally to phase change ink jet imaging devices, and, in particular, to the printheads used in such imaging devices. 
     BACKGROUND 
     In general, ink jet printing machines or printers include at least one printhead that ejects drops or jets of liquid ink onto a recording or image forming media. A phase change ink jet printer employs phase change inks that are solid at ambient temperature, but transition to a liquid phase at an elevated temperature. The molten ink can then be ejected onto a printing media by a printhead directly onto an image receiving substrate, or indirectly onto an intermediate imaging member before the image is transferred to an image receiving substrate. Once the ejected ink is on the image receiving substrate, the ink droplets quickly solidify to form an image. 
     In various modes of operation, ink may be purged from the printheads to ensure proper operation of the printhead. During purging, ink is typically forced through the ink pathways, chambers, and out the ink jets of the printhead to help remove contaminants, such as air bubbles, dried ink, and debris from in and around the ink jets. The purged ink flows down and off the face of the printhead typically to a waste tray positioned below the printhead. Absent any additional structure, the ink can flow freely along the bottom edge of the printhead and drip from the printhead anywhere along that bottom edge. To help control this dripping flow of waste ink, a drip bib may be added near the bottom edge of the printhead. 
     Previously known drip bibs were formed by generally flat plates that were secured to printheads by fasteners, such as screws or bolts. When secured to the printhead, the upper edge of these previously known drip bibs were generally in contact with the printhead adjacent the lower edge of the ejecting face along the entire drip bib upper edge. Because the previously known drip bibs were secured to the printhead with a plurality of screws, the majority of the clamping force of the fasteners against the drip bib is exerted along the contact edge of the drip bibs in the areas that are closest to the screws with lesser force being applied to the contact edge as the distance from the fasteners along the contact edge increases. This variation in clamping force can cause deformation or distortion of the drip bib, and, consequently, a corresponding distortion of the printhead. Distortion or deformation of a printhead may cause some areas of the printhead to be closer or farther away from the imaging member than others during printing which, in turn, may adversely impact the print quality of images formed by the printhead. 
     SUMMARY 
     In order to alleviate the problems associated with uneven contact pressure across the contact edge of a drip bib, a drip bib has been developed that includes load points spaced across the contact edge to distribute the clamping force of the fasteners more evenly across the contact edge. In particular, a drip bib for use with a printhead of an imaging device includes a plate having an angled upper surface, a flat intermediate surface, and a lower edge. The intermediate surface includes a plurality of fastener openings. The lower edge includes a drip point projecting from the lower edge with remaining portions of the lower edge being upturned and angled downwardly from at least one end of the lower edge toward the drip point. The angled upper surface is angled in a first direction with respect to the intermediate portion and includes an upper edge. A plurality of protrusions protrudes from the angled upper surface in the first direction. The protrusions in the plurality of protrusions are spaced from each other and proximate the upper edge. 
     In another embodiment, a printhead assembly for use in an imaging device includes a printhead having an ejecting face. The printhead is configured to receive liquid ink from an ink source and to eject ink through the ejecting face onto an ink receiving surface. A drip bib is attached to the printhead by a plurality of fasteners. The drip bib has an outer surface that faces away from the printhead and an inner surface that faces toward the printhead. The drip bib includes a lower portion having a lower edge. The lower portion includes a drip point extending below the lower edge. The remaining portions of the lower edge are upturned and angled downwardly from at least one end of the lower edge toward the drip point. A substantially flat intermediate portion is positioned above the lower portion that includes a plurality of fastener openings through which the plurality of fasteners is inserted into the printhead. An upper edge is positioned above the intermediate portion and adjacent a lower edge of the ejecting face that includes a plurality of protrusions that protrude from the inner surface of the drip bib proximate the upper edge. 
     In yet another embodiment, an imaging device is provided that includes a first upper printhead and a second upper printhead laterally positioned across a width of an image receiving surface and having a first gap therebetween, the first and the second upper printheads each having an ejecting face through which ink is ejected toward the image receiving surface. The imaging device also includes a first lower printhead and a second lower printhead laterally spaced across the width of the image receiving surface and having a second gap therebetween, the first and the second upper printheads each having an ejecting face through which ink is ejected toward the image receiving surface. The first and the second lower printheads are positioned below the first and the second upper printheads and laterally offset from the upper printheads so that the first upper printhead overlaps a portion of both the first and the second lower printheads and the second upper printhead overlaps a portion of the second lower printhead extending laterally beyond the second lower printhead. A drip bib is attached to each of the first and second upper and lower printheads adjacent a lower edge of respective ejecting faces of the printheads. Each drip bib has a lower edge with a drip point that extends below the lower edge with remaining portions of the lower edge being upturned and angled downwardly from at least one end of the lower edge toward the drip point, the drip point of the first upper printhead being positioned along the lower edge above the second gap between the first and the second lower printheads. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing aspects and other features of the present disclosure are explained in the following description, taken in connection with the accompanying drawings, wherein: 
         FIG. 1  is a schematic diagram of an embodiment of an ink jet printing apparatus. 
         FIG. 2  is front elevational view of the printhead system of the imaging device of  FIG. 1 . 
         FIG. 3  is perspective view of a printhead of the printhead system showing an embodiment of a drip bib. 
         FIG. 4  is a side cross-sectional view of the drip bib of  FIG. 3  taken along line  4 - 4 . 
     
    
    
     DETAILED DESCRIPTION 
     For a general understanding of the present embodiments, reference is made to the drawings. In the drawings, like reference numerals have been used throughout to designate like elements. 
     As used herein, the terms “printer” or “imaging device” generally refer to a device for applying an image to print media and may encompass any apparatus, such as a digital copier, bookmaking machine, facsimile machine, multi-function machine, etc. which performs a print outputting function for any purpose. “Print media” can be a physical sheet of paper, plastic, or other suitable physical print media substrate for images, whether precut or web fed. The imaging device may include a variety of other components, such as finishers, paper feeders, and the like, and may be embodied as a copier, printer, or a multifunction machine. A “print job” or “document” is normally a set of related sheets, usually one or more collated copy sets copied from a set of original print job sheets or electronic document page images, from a particular user, or otherwise related. An image generally may include information in electronic form which is to be rendered on the print media by the marking engine and may include text, graphics, pictures, and the like. 
     Referring now to  FIG. 1 , an embodiment of an image producing machine, such as a high-speed phase change ink image producing machine or printer  10  of the present disclosure, is depicted. As illustrated, the machine  10  includes a frame  11  to which are mounted directly or indirectly all its operating subsystems and components, as described below. To start, the high-speed phase change ink image producing machine or printer  10  includes an imaging member  12  that is shown in the form of a drum, but can equally be in the form of a supported endless belt. The imaging member  12  has an imaging surface  14  that is movable in the direction  16 , and on which phase change ink images are formed. A heated transfix roller  19  rotatable in the direction  17  is loaded against the surface  14  of drum  12  to form a transfix nip  18 , within which ink images formed on the surface  14  are transfixed onto a heated copy sheet  49 . 
     The high-speed phase change ink image producing machine or printer  10  also includes a phase change ink delivery subsystem  20  that has at least one source  22  of one color phase change ink in solid form. Since the phase change ink image producing machine or printer  10  is a multicolor image producing machine, the ink delivery system  20  includes four (4) sources  22 ,  24 ,  26 ,  28 , representing four (4) different colors CYMK (cyan, yellow, magenta, black) of phase change inks. The phase change ink delivery system also includes a melting and control apparatus (not shown) for melting or phase changing the solid form of the phase change ink into a liquid form. The phase change ink delivery system is suitable for then supplying the liquid form to a printhead system  30  including at least one printhead assembly  32 . Since the phase change ink image producing machine or printer  10  is a high-speed, or high throughput, multicolor image producing machine, the printhead system  30  includes multicolor ink printhead assemblies and a plural number (e.g. four (4)) of separate printhead assemblies  32 ,  34 ,  36  and  38  as shown. 
     As further shown, the phase change ink image producing machine or printer  10  includes a substrate supply and handling system  40 . The substrate supply and handling system  40 , for example, may include sheet or substrate supply sources  42 ,  44 ,  46 ,  48 , of which supply source  48 , for example, is a high capacity paper supply or feeder for storing and supplying image receiving substrates in the form of cut sheets  49 , for example. The substrate supply and handling system  40  also includes a substrate or sheet heater or pre-heater assembly  52 . The phase change ink image producing machine or printer  10  as shown may also include an original document feeder  70  that has a document holding tray  72 , document sheet feeding and retrieval devices  74 , and a document exposure and scanning system  76 . 
     Operation and control of the various subsystems, components and functions of the machine or printer  10  are performed with the aid of a controller or electronic subsystem (ESS)  80 . The ESS or controller  80  for example is a self-contained, dedicated mini-computer having a central processor unit (CPU)  82 , electronic storage  84 , and a display or user interface (UI)  86 . The ESS or controller  80  for example includes sensor input and control means  88  as well as a pixel placement and control means  89 . In addition the CPU  82  reads, captures, prepares and manages the image data flow between image input sources such as the scanning system  76 , or an online or a work station connection  90 , and the printhead assemblies  32 ,  34 ,  36 ,  38 . As such, the ESS or controller  80  is the main multi-tasking processor for operating and controlling all of the other machine subsystems and functions, including the printhead cleaning apparatus and method discussed below. 
     In operation, image data for an image to be produced are sent to the controller  80  from either the scanning system  76  or via the online or work station connection  90  for processing and output to the printhead assemblies  32 ,  34 ,  36 ,  38 . Additionally, the controller determines and/or accepts related subsystem and component controls, for example, from operator inputs via the user interface  86 , and accordingly executes such controls. As a result, appropriate color solid forms of phase change ink are melted and delivered to the printhead assemblies. Additionally, pixel placement control is exercised relative to the imaging surface  14  thus forming desired images per such image data, and receiving substrates are supplied by any one of the sources  42 ,  44 ,  46 ,  48  and handled by means  50  in timed registration with image formation on the surface  14 . Finally, the image is transferred from the surface  14  and fixedly fused to the copy sheet within the transfix nip  18 . 
     Referring now to  FIG. 2 , the printer/copier  10  described in this example is a high-speed, or high throughput, multicolor image producing machine, having four printheads, including upper printheads  32  and  36 , and lower printheads  34  and  38 . Each printhead  32 ,  34 ,  36  and  38  has a corresponding front face  33 ,  35 ,  37  and  39  for ejecting ink onto the receiving surface  14  to form an image. While forming an image, a mode referred to herein as print mode, the upper printheads  32 ,  36  may be staggered with respect to the lower printheads  34 ,  38  in a direction transverse to the receiving surface path  16  ( FIG. 1 ) in order to cover different portions of the receiving surface  14 . The staggered arrangement enables the printheads to form an image across the full width of the substrate. In print mode the printhead front faces  33 ,  35 ,  37 ,  39  are disposed close to the imaging surface  14 , for example about 23 mils. 
     In various modes of operation, ink may be purged from the printheads to ensure proper operation of the printhead. When ink is purged through the printhead, the ink flows down and off the front face of the printhead. Commonly, during a cleaning cycle, a scraper or wiper blade (not shown) may also be drawn across the ink ejecting front face of the printhead to squeegee away any excess liquid phase ink that may collect there. The waste ink wiped-off or otherwise removed from the face of the printhead is typically allowed to drop directly from a lower edge  124  ( FIG. 3 ) of the front face of a printhead into a collection pan or waste ink container  54  ( FIG. 1 ) where it cools and re-solidifies. When the collection pan is full, it may be removed, manually emptied and then reinstalled in the printer. 
     Absent any additional structure, the ink can flow freely along the bottom edge of the printhead ejecting face and drip from the printhead anywhere along that bottom edge. Due to the staggered arrangement of the upper and lower printheads, however, purged ink that flows or drips from the bottom edge of the upper printheads may splash onto the lower printheads. Ink from the upper printheads splashing onto the lower printheads may cause a variety of problems, including: color mixing in the printhead aperture plate, contamination of the drum, inhibited range of motion of the motors or pivot points that control printhead movement, and contamination of other systems within the imaging device. 
     To help control this dripping flow of waste ink from the ejecting face of the printheads, a drip bib  100  may be added near the bottom edge of the ejecting faces of the printheads as depicted in  FIG. 2 .  FIGS. 3 and 4  show a more detailed view of an embodiment of a drip bib  100 . The drip bib  100  comprises a metal plate, such as stainless steel or aluminum, having a one-piece construction that may be manufactured using conventional sheet metal forming techniques. Other suitable material or combination of materials, however, may be utilized for the drip bib plate including other metals and/or rigid plastic materials. 
     The drip bib plate has an outer surface  104  that faces in generally the same direction as the ejecting face  33  of the printhead and comprises the surface to which the ink flows from the ejecting face. The drip bib plate  100  includes an upper surface  110 , an angled intermediate surface  114 , and an upturned lower edge  118 . When the drip bib  100  is secured to the jet stack (explained below), the upper surface  110  is below and generally parallel to the front face  33  of the printhead  32 , as depicted in  FIG. 4 . The upper surface  110  of the drip bib  100  includes an upper edge  120 , also referred to herein as a contact edge. The upper surface  110  of the drip bib is positioned with respect to the ejecting face  33  so that the contact edge  120  of the drip bib abuts the lower edge  124  of the ejecting face  33 . The angled intermediate surface  114  is below the upper surface and angled backwardly with respect to the upper surface in a direction J toward the printhead  32 , and, in particular, toward a recessed mounting surface  152 . The upper surface  110  guides the waste ink from the ejecting face  33  to the intermediate surface  114  which in turn guides the flow of the ink to channels formed by the upturned lower edges  118  of the drip bib. As waste ink flows down the drip bib, the waste ink remains in contact with the angled intermediate surface  114  of the drip bib due to the surface tension characteristics of the ink relative to the drip bib outer surface. 
     The lower edge  118  of the drip bib is curled or upturned at one or more locations along the lower edge to form one or more channels that are open across the top to collect the ink that flows down from the ejecting face  33  of the printhead. The upturned edges  118  are curled or rounded at the bottom although they may be angled to form a V-shaped or square-shaped bottom surface. The channels defined by the upturned lower edges  118  of the bib have a depth D from the top  128  of the upturned edge  118  to the bottom surface  130  of the channel and a width W from the inner surface  134  of the upturned edge  118  to the outer surface  138  of the upper edge. The depth D and the width W of the channels may be suitably sized to enable the channels  118  to have enough capacity to prevent ink that flows down from the ejecting face  33  from overflowing and escaping the channels prior to the ink reaching the drip point  140  on the lower edge. The upturned edges  118  that form the channels of the drip bib begin at one or both ends  144 ,  148  of the drip bib lower edge and are angled downwardly from the end(s)  144 ,  148  to force the flow of ink to a protruding tip  140 , referred to herein as a drip point, that channels the waste ink flow in a controlled and timely manner. 
     The drip point  140  is positioned along the lower edge at a gap  150  between the channels  118  formed by the upturned lower edges of the drip bib. The drip point  140  comprises a projection or extension that extends below the lower edge  118  and the channel(s) formed by the lower edge of the lower portion of the drip bib. The protruding tip of the drip point  140  concentrates the flow of ink from the channels, and allows the ink to collect at the tip and form a critical mass for drop formation and release which may be beneficial especially near the end of a purge cycle when the waste ink flow slows and eventually stops. The drip point may be any suitable configuration that enables ink to drip or flow in a controlled manner from the drip point. In the embodiment of  FIGS. 2-4 , the drip point  140  has a narrow, tapered shape with a rounded end. The drip point, however, may have any suitable shape including pointed or flat ends and straight, angled, or rounded edges. In addition, the drip point  140  is positioned at a predetermined location along the lower edge of the drip bib to enable the flow of waste ink to be directed in a manner that avoids, for example, splashing ink onto other printheads or systems within the imaging device. The drip point may be at any suitable location along the lower edge of the drip bib. For example, depending on printhead placement, waste ink tray position, and available space within the imaging device, the drip point may be positioned at any point along the lower edge from end to end. In alternative embodiments, more than one drip point may be utilized. 
     In the embodiment of  FIGS. 2-4 , the drip point is positioned at an intermediate location along the lower edge  118 . The gutters  118  formed by the upturned portions of the lower edge  118  are angled downwardly toward the drip point  140  to form the channels that channel ink toward the drip point  140 . As depicted in  FIGS. 3 and 4 , gutter-to-drip point transition surfaces  136  are included in the drip bib to control the flow of ink from the gutters to the drip point. The transition surfaces comprise angled surfaces that extend between the bottom surface of the gutters and the drip point. Transition surfaces may be formed in any suitable manner. For example, in one embodiment, transition surfaces may be formed integrally with drip bib by, for example, stretching or deforming the material that connects the lower edges  118  that form the gutters to the drip point  140  during the gutter formation process. 
     The drip point position, at least on the drip bibs of the upper printheads  32 ,  36 , enables the waste ink generated by the upper printheads  32 ,  36  to be directed through gaps between the lower printheads. For example, referring to  FIG. 2 , upper printhead  32  is positioned above the two lower printheads  34  and  38  such that the drip point  140  of the drip bib  100  of printhead  32  is located directly above a lateral gap  70  between the two lower printheads  34  and  38 . The waste ink from the printhead  32  is then directed in a stream from the drip point  140  of printhead  32  between the two lower printheads  34  and  38  into waste tray (not shown) so the waste ink does not drip or splash onto the lower printheads  34 , 38 . 
     To secure the drip bib  100  to the printhead jet stack, the drip bib includes fastener openings (not shown) that extend through the intermediate portion  114  of the drip bib and align with fastener openings (not shown) in the lower portion of the printhead jet stack when the drip bib  100  is properly placed on the jet stack. The drip bib  100  may be secured to the jet stack using fasteners  158 , such as threaded screws or through-bolts, which are inserted through the fastener openings in the drip bib and threaded into or otherwise secured to the fastener openings in the jet stack. In the embodiment of  FIGS. 2-4 , two fasteners  158  are used to secure the drip bib  100  to the jet stack although, in other embodiments, more or fewer (i.e., one) fasteners may be utilized. In the embodiment of  FIGS. 2-4 , the fastener openings are formed in recessed features  154  in the intermediate surface  114  that enable the fasteners to be inserted through the openings and received in the fastener holes in the jetstack in a direction (J) perpendicular to the front face  33  and upper surface  110  of the drip bib  100 . 
     As mentioned above, one issue faced in securing the drip bib to the printhead using fasteners is uneven contact pressure between the upper edge of the drip bib and the lower edge of the ejecting face caused by the clamping force of the fasteners which may cause a corresponding distortion or deformation of the printhead ejecting face. Accordingly, in order to prevent uneven contact pressure between the upper edge  120  of the drip bib and the lower edge  124  of the ejecting face, the upper edge  120  of the drip bib has been modified to include load points  160 . In the embodiment of  FIGS. 2-4 , the load points  160  comprise dimples or similar protruding structures that are located in the upper surface  110  of the drip bib adjacent or proximate the upper edge  120  and that protrude from the inner surface of the upper surface  110  of the drip bib in the direction J toward the printhead  32 . As used herein, the term dimple(s) refers to a protrusion that may be formed by pressing or stamping one side of the plate to cause plate material to protrude from the opposite side of the plate. Dimples may be formed using conventional sheet metal processing techniques. As an alternative to using dimples to form the load points, material may be added to drip bib to serve as the load points. For example, the load points may be formed by adding material, such as metal, rigid plastics or ceramics, to the upper portion of the drip bib at appropriate locations along the upper edge  120 . 
     When the drip bib is secured to the printhead by the fasteners  158 , the load points  160  are configured to control the contact between the upper edge  120  of the drip bib and the ejecting face for a uniform distribution of the clamping load of the fasteners  158  along the upper edge  120  of the drip bib. The load points  160  of the drip bib thus enable the drip bib to be secured to the printhead using fasteners without the clamping load of the fasteners deforming the drip bib  100  and/or ejecting face  33 . In the embodiment of  FIGS. 2-4 , three load points  160  are utilized in the drip bib  100  thereby spreading the clamping load of the fasteners onto three separate points proximate the upper edge  120  of the drip bib. The load points are substantially evenly distributed or spaced along the upper edge with a load point being positioned adjacent each end of the upper edge, and a load point in a central location along the upper edge that is between the two fasteners. Any suitable number and positioning of load points, however, may be utilized. 
     While the drip bib apparatus described above has been discussed with reference to a phase change ink printing device, it may be used with other imaging devices to control the flow of waste ink therein. It will be appreciated that various of the above-disclosed and other features, and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art, which are also intended to be encompassed by the following claims.