Abstract:
A valve for a printing apparatus that uses liquid ink includes a valve seat, a valve stop and a valve member interposed between the valve seat and the valve stop.

Description:
BACKGROUND 
     Ink jet printers create an image on a surface by ejecting ink through orifices in a print head face plate onto a substrate. The print head face plate communicates with a print head reservoir, which communicates with an ink source. Solid ink printers melt solid ink and deliver the melted ink to the print head reservoir. 
     When the solid ink printer is turned off, the ink that remains in the print head reservoir can freeze. When the ink thaws in the print head reservoir, air that was once in solution in the ink can come out of solution to form air bubbles or air pockets in the print head reservoir. Air pockets can impede the filtering of the ink as it travels toward the orifices in the print head face plate. Air pockets can also impair the print quality of the printer when an air bubble, as opposed to ink, is delivered through the orifice resulting in an unintended blank spot on the print media. Accordingly, it is desirable to purge periodically the cavities and channels in the print head reservoir to increase print quality. 
     It is known to purge air out of solid ink print heads using a vacuum system, but a vacuum system is costly, time consuming and less efficient than a system that uses positive pressure. Furthermore, it is desirable to wipe the jets during purging, which is not possible when using a vacuum system. Accordingly, a positive pressure purge system is desirable. In a positive pressure purge system it is desirable to provide a valve to allow purging air out of the orifices and to inhibit forcing ink back out of the cavity where the ink is loaded into the print head. 
     BRIEF DESCRIPTION 
     A valve for a printing apparatus that uses liquid ink includes a valve seat, a valve stop and a valve member interposed between the valve seat and the valve stop. The valve stop is positioned downstream from the valve seat and includes a contact surface that retains the valve member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front perspective view of a portion of a print head reservoir for an ink jet printer. 
         FIG. 2  is a front perspective view of a rear plate of the print head reservoir of  FIG. 1 . 
         FIG. 3  is a view of a side cross-section of the print head reservoir of  FIG. 1 . 
         FIG. 4  is a rear perspective view of a middle plate of the print head reservoir of  FIG. 1 . 
         FIG. 5  is a close up view of an inlet of the middle plate of  FIG. 4 . 
         FIG. 6  is close up view of a lower cross section of the print head reservoir as shown in  FIG. 3  showing the valve in an open position. 
         FIG. 7  is a close up view of a lower cross section of the print head reservoir as shown in  FIG. 3  showing the valve in a closed position. 
         FIG. 8  is a close up perspective view of a valve seat of the print head reservoir of  FIG. 1 . 
         FIG. 9  is a close up perspective view similar to  FIG. 8  showing the valve in a closed position. 
         FIG. 10  is a perspective view of an ink jet printer that can contain the print head reservoir of  FIG. 1 . 
         FIG. 11  is a side cross-sectional view of the ink jet printer of  FIG. 10 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 10 and 11 , a print head A for an ink jet printer B generally delivers liquid ink to a jet stack C that transfers the ink onto a drum D. The print media, which can include paper, travels around the drum and picks up the ink deposited on the drum. Air can get into the pathway of the ink as it travels through the print head. To remove the air from the pathway, the print head is purged, which will be described in more detail below. 
     With reference to  FIG. 1 , a print head reservoir  10  includes a first or front plate  12 , a second or middle plate  14  and a third or rear plate  16 . The print head reservoir  10  is a portion of the print head and is situated inside the ink jet printer such that the bottom of each plate is substantially horizontal and the reservoir can rotate about a pair of journals  18  (only one visible in  FIG. 1 ). The terms “front,” “middle,” and “rear” are used for ease of understanding to describe the components of the reservoir as they are shown in the figures; the terms are not used to limit the position of components in relation to one another. 
     Generally, the ink travels from the rear plate  16  towards the front plate  12 . With reference to  FIG. 2 , the rear plate includes a front side  20  that is adjacent the middle plate  14  when the reservoir is assembled and a rear side  22  opposite the front side. A plurality of bucket walls  24  extend from the rear side  22  to define a plurality of ink buckets  26 . In the embodiment depicted, four ink buckets are shown and each bucket receives a different color ink, particularly yellow, cyan, magenta and black; however, a fewer or greater number of ink buckets can be provided and the ink buckets can receive different colors of ink. The ink buckets  26  usually receive ink that has been melted and dripped into the buckets; however, liquid ink that has not been melted can also be delivered to the ink buckets. 
     With reference to  FIG. 3 , each ink bucket  26  communicates with a passage  28  which communicates with a rear plate outlet  32 . A filter  34  is disposed in each ink bucket on a shoulder  36  that projects inwardly from the bucket wall  24  into the ink bucket  26 . The filter  34  removes impurities in the ink before the ink travels into the passage  28  and towards the rear plate outlet  32 . The rear plate outlet  32  communicates with a middle plate inlet  40  through a valve member  42 . The valve member  42  comprises a component of a one-way check valve that allows ink to pass from the rear plate outlet  32  into the middle plate inlet  40 . The valve member  42  precludes ink from passing from the middle plate inlet  40  back into the rear plate outlet  32  during purging of the ink path downstream of the valve. The valve member  42  opens and closes in response to a pressure differential between the rear plate outlet  32  and the middle plate inlet  40 . Further description of the valve will be provided after further description of the path of the ink through the print head reservoir. 
     Referring to  FIG. 4 , the middle plate  14  includes a front side  44  and a rear side  46 . The front side  44  of the middle plate abuts the front plate  12  and the rear side  46  of the middle plate abuts the front side  20  of the rear plate  16 . The middle plate inlet  40  includes three lobed depressions situated 120 degrees apart from one another formed in the rear side  46  of the middle plate  16 . Two lobes  52  depend generally downward and the third lobe  50  extends upward to communicate with an ink chamber  56 . Ink flows from the ink bucket  26  into the middle plate inlet  40  and into the ink chamber  56  through the upward lobe  50 . The ink chamber  56  is defined as a depression in both the rear side  46  of the middle plate  14  and the front side  20  of the rear plate  16 , as seen in  FIG. 3 . 
     Ink exits the ink chamber  56  through openings  58  ( FIG. 5 ) in the downward lobes  52 . Each downward depending lobe  52  includes an opening  58  that communicates with a passage  64  (only one shown in phantom in  FIG. 3 ) which communicates with a middle plate outlet  68  on the front side  44  of the middle plate  14 . In the embodiment depicted, eight middle plate outlets  68  are provided at the bottom of the front side  44  of the middle plate, two for each color of ink. A greater or fewer number of middle plate outlets can be provided. Ink exits the middle plate outlets  68  and enters an upstream filter cavity  74  defined between the front side  44  of the middle plate  14  and the filter  76 . 
     Since the size of the orifices in the jet stack is so small, the ink is filtered prior to delivery to the ink stack. A vertical filter  76  is sandwiched between and situated substantially parallel to the front plate  12  and the middle plate  14 . Ink flows through the filter  76  from the upstream filter cavity  74  into a downstream filter cavity  86 . 
     The front plate  12  includes a front side  90  and a rear side  92  which is adjacent the filter  76 . The downstream filter cavity  86  is defined between the filter  76  and the rear side  92  of the front plate  12 . The front plate  12  includes a plurality of openings  94  (only one shown in  FIG. 3 ) on the rear side  92  that communicate through passages with a plurality of front plate outlets  96  on the front side  90  of the front plate. Ink flows through the filter  76  and into the openings  94 . 
     Ink flows from the ink buckets  26  towards the front side  90  of the front plate  12  and then on to a jet stack, which is not shown. More description of the front plate is provided in co-pending patent application entitled “Purgeable Print Head Reservoir,” which is assigned to the assignee of this application, filed on the same date as this application, and is incorporated by reference herein. Ink that flows through the print head reservoir can freeze when the printer is turned off. Air bubbles can form in the filter cavities  74  and  86  from freeze-thaw cycles when air comes out of the ink solution or from improper ink filling. Trapped air on the upstream side of the filter, i.e. in the upstream ink cavity  74 , reduces the effective size of the filter  76 . Trapped air on the downstream side, i.e. in the downstream filter cavity  86 , can dump bubbles into the flow path during printing which can require additional purges of the ink flow path. Purge vents (not shown) are provided to bleed any trapped air in the filter cavities  74  and  86 . These vents are more particularly described in co-pending patent application entitled “Print Head Reservoir Having Purge Vents,” which is assigned to the assignee of this application, filed on the same date as this application, and is incorporated by reference herein. Air can also form in channels leading from the upstream ink cavity  86  toward the ink stack. If these channels are not purged, air instead of ink can be delivered to the ink drum which can affect the print quality. Also, air bubbles can block the orifices in the ink stack. 
     To purge the filter cavities  74  and  86  and the channels leading to the print stack, pressure is introduced into the print head reservoir. With reference back to  FIG. 2 , a fitting  120  attaches to the rear side  22  of the rear plate  16 . The fitting  120  connects to an air pressure source (not shown). In an alternative embodiment, fluid pressure can be applied elsewhere on the print head and a fluid other than air, such as ink, can be used to apply the fluid pressure to purge the print head reservoir. The fitting communicates with a rear plate passage  122  which communicates with a middle plate passage  124  ( FIG. 4 ). The middle plate passage  124  communicates with a four air plenums  126 , one for each color. Each of the plenums  126  includes an opening  128  that leads a respective ink chamber  56 . The upper opening aligned with and across from the opening  128  can be covered. 
     During a purge cycle, air passes through the fitting  120  into the plenums  126  via the passages  122  and  124 . From the plenums  126  air travels through the openings  128  into the ink cavities  56 . The air pressure in the ink cavities results in a greater pressure on the downstream side of the valve member  42  ( FIG. 3 ), thus closing the valve. The air pressure forces ink through the middle plate outlets  68  forcing any air pockets found in the filter cavities  74  and  86  out the vents. The air pressure forces air out of the channels leading to the jet stack. After the ink is forced out of the jet stack, the jet stack can be wiped clean. 
     With reference to  FIGS. 6 and 7 , the valve member  42  is situated between the middle plate  14  and the rear plate  16 . More particularly, the valve is positioned between a valve seat  150  ( FIG. 6 ), which defines the rear plate outlet  32 , and a valve stop  152  ( FIG. 7 ), which defines the middle plate inlet  40 . The valve seat  150  is substantially vertical and flat, and the valve stop  152  is disposed at an angle to the valve seat  150 . In one embodiment, the angle between the valve seat  150  and the valve stop  152  is five degrees; however, in an alternative embodiment the angle can change. 
     The valve member  42  can be a flat full hard stainless steel disc made from a precision stamping die. Such a configuration results in little or no burrs around the periphery of the valve member, which could affect the valve member&#39;s ability to close the rear plate outlet  42  during purging. Nevertheless, the valve member can be made from other materials. The valve member  42  can be made from any material that will provide an adequate seal and be able to maintain the seal in the ink environment while not contaminating the ink. Furthermore, the valve member  42  can take other configurations such a ball. 
     With reference to  FIG. 8 , the valve seat  150  is sunk into the rear plate  16  so that a ledge  154  surrounds the outer periphery of the valve seat. The valve member  42  freely rests on the ledge  154  so the entire valve member  42  can move laterally between the valve seat  150  and the valve stop  152 . As more clearly seen when comparing  FIG. 6  to  FIG. 7 , the valve member both rotates slightly and moves laterally in the exemplary embodiment. The ledge  154  extends underneath the valve seat  150  to define a valve moat  156 . The filter  34  disposed in the ink bucket  26  ( FIG. 3 ) removes much of the impurities in the ink before they can reach the valve seat  150 . The valve moat  156  precludes small particles in the ink from building up around the periphery of the valve member  42  and on the valve seat  150 . The valve moat  156  also accommodates any burrs that exist on the periphery of the valve member  42  so that the valve member  42  can tightly seat against the valve seat  150 . 
     A relief passage  158  is provided adjacent the rear plate outlet  32  to reduce the flow resistance through the rear plate outlet when the valve member is in an open position. With reference to  FIG. 9 , the relief passage is situated above the valve member  42 . The relief passage  158  is defined by an upper portion of the ledge  152 . The relief passage aligns with the ink cavity  56  to promote upward flow of the ink over the valve member  42  into the ink cavity, as seen in  FIGS. 6 and 7 . 
     The middle plate  14  and the rear plate  16  can be glued together. A glue stop channel  162  can be provided around the periphery of the ledge  152  to catch any glue attempting to migrate towards the valve seat  150 . 
     The valve stop  152  retains the valve member  42  when in the open position. With reference to  FIG. 5 , the valve stop  152  includes a contact surface  164  that defines the lobed depressions  50  and  52 . The contact surface  164  retains the valve member  42 , and the depressions  50  and  52  provide adequate flow and surface area of the valve member exposed to the pressure that is applied during purging. 
     Since the valve member  42  is disposed substantially vertically between valve seat  150  and the valve stop  152 , the instability of the valve member position allows the valve to open at very low pressures. For example, in the exemplary embodiment, the valve can open at pressures below 0.1 inches of water. The head pressure of the ink stored in the ink bucket  26  provides the adequate pressure to open the valve. Nevertheless, the valve can be disposed at other orientations than vertical, such as horizontal or some angle between vertical and horizontal. In such a configuration, the orientation of the valve seat and valve stop may change. 
     The valve is kept from rotating too much by the valve stop  152  so that the valve can close at low pressures. In the exemplary embodiment, the valve can close at purge pressures below 5 inches of water. The exposed surface area of the valve member  42  because of the depressions  50  and  52 , allows a low purge pressure to close the valve. The seal between the valve seat  150  and the valve member  42  need not be air tight, the seal need only prevent ink from ejecting out of the ink bucket  26  during a purge. 
     The exemplary embodiment has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. For example, the valve system was described with particularity to an ink jet printer; however, the valve system is amenable to other environments where a valve needs to open and close in response to small pressure differentials. It is intended that the exemplary embodiment be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.