Abstract:
A cover is configured for use with a fluid jet device having a surface defining a plurality of orifices formed therein through which a fluid is jetted. The cover includes a cover element movable parallel to the surface between a covered position in which the cover element overlies the orifices and an uncovered position in which the cover is moved to expose the orifices. The cover includes a mounting portion configured to maintain the cover spaced from the surface to define a vapor space region. At least one hinge element operably mounts the cover to the fluid jet device. The hinge element includes a first leg mounted at a free end to a stationary portion of the fluid jet device and a second leg mounted at a free end to the cover portion. The first and second legs are connected to one another by a flexible region such that movement of the legs slides the cover between the covered and exposed positions. The vapor space region maintains a level of fluid vapor concentration around the orifices to reduce the rate of evaporation of the fluid.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to fluid jet devices. More particularly, the present invention is directed to a cover for fluid jet device heads to reduce the maintenance of the head and to improve the performance of certain jetted fluids. 
         [0002]    Fluid jet devices are in wide-spread use. One major application of fluid jet devices is in inkjet printheads. These print heads are in wide-scale use from large industrial/commercial settings to small individual and consumer products. 
         [0003]    Inkjet technology can be categorized as drop-on-demand and continuous jetting. In drop-on-demand printing, ink is jetted from the printhead (from a series of orifices in the head) onto a substrate. The ink is jetted or ejected as droplets in a discrete pattern to form a desired pattern, such as lettering, designs or bar codes, on the substrate. In continuous inkjet technology, ink droplets are continuously jetted and are directed, by use of a field, such as an electromagnetic field, along a specific trajectory, to a substrate (to print) or into a gutter to be discarded. 
         [0004]    Drop-on-demand technology can be further categorized as thermal inkjet technology, piezoelectric technology and valve-based technology. All of these technologies have certain advantages. For example, thermal technology provides high resolution with relatively low cost. Piezoelectric technology offers high jetting frequency, long lifetime, and the ability to jet a wide range of fluids. 
         [0005]    Drop-on-demand (DOD) printing, although widely used, does have its drawbacks. For example, it is difficult to use quick-drying inks with DOD printing. These inks begin to dry rapidly, and have been found to, at times, begin drying before being ejected from the printhead orifice. This can result in the printhead orifices becoming partially or fully clogged, which can ultimately result in equipment shut downs for maintenance, repair or replacement. 
         [0006]    Accordingly, there is a need for a device for a fluid jet device, such as a printhead, that enhances the performance of the fluid jetted from the device. Desirably, such an enhancement includes extending the life of the fluid and the usable life of the jetting device. More desirably, such a device is used in-line and has minimal or no adverse impact on the use of the jetting device. 
       SUMMARY OF THE INVENTION 
       [0007]    A cover for a fluid jet device having a surface defining at least one orifice formed therein through which a fluid is jetted includes a cover element movable parallel to the surface between a covered position in which the cover element overlies the at least one orifice and an uncovered position in which the cover is moved to expose the at least one orifice. The cover includes a mounting portion configured to maintain the cover spaced from the surface to define a vapor space region. A preferred jet device includes a plurality of orifices. 
         [0008]    At least one hinge element operably mounts the cover to the fluid jet device. The hinge element includes a first leg mounted at a free end to a stationary portion of the fluid jet device and a second leg mounted at a free end to the cover portion. The first and second legs are connected to one another by a flexible region such that movement of the legs slides the cover between the covered and exposed positions. The vapor space region maintains a level of fluid vapor concentration around the orifices to reduce the rate of evaporation of the fluid. 
         [0009]    In one embodiment, the cover includes at least two hinge elements spaced from one another at about opposite ends of the cover element. The hinge element first leg has an extension portion that extends beyond the hinge flexible region to define a engaging portion. The cover can include fingers that depend from and extend inwardly of the cover element to maintain the cover on the faceplate and permit sliding the cover above (and parallel to) the faceplate. 
         [0010]    A fluid jetting device especially for use with evaporative fluids includes a fluid jetting member having a faceplate defining a surface having a plurality of orifices therein through which the fluid is jetted and a movable cover for the fluid jetting member. 
         [0011]    A method for maintaining a fluid in a fluidic or semi-fluidic state at an orifice of a fluid jetting device includes the steps of providing a fluid jet device having a plurality of orifices through which the fluid is jetted, providing a movable cover overlying the orifices, moving the cover to expose the orifices when fluid is being jetted from the orifices and moving the cover over the orifices when fluid is not being jetted from the orifices. The step of moving the cover can be effected by the movement of an object over the fluid jetting device in proximity to the cover. 
         [0012]    These and other features and advantages of the present invention will be apparent from the following detailed description, in conjunction with the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The benefits and advantages of the present invention will become more readily apparent to those of ordinary skill in the relevant art after reviewing the following detailed description and accompanying drawings, wherein: 
           [0014]      FIG. 1  is an illustration of a printing system having an inkjet printhead having a cover embodying the principles of the present invention 
           [0015]      FIGS. 2A-C  are graphic side view illustrations of a printhead in which  FIG. 2A  shows a conventional printhead with an automatic maintenance system,  FIG. 2B  shows a printhead with an automatic maintenance system and with the cover of the present invention, and  FIG. 2C  is an alternate embodiment showing a wrap-around cover configuration; 
           [0016]      FIGS. 3A-H  show, in sequence, the movement of the cover and the interaction with an object moving over the printhead; 
           [0017]      FIG. 4  is a graphic side view of an alternate embodiment of the printhead. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    While the present invention is susceptible of embodiment in various forms, there is shown in the drawings and will hereinafter be described a presently preferred embodiment with the understanding that the present disclosure is to be considered an exemplification of the invention and is not intended to limit the invention to the specific embodiment illustrated. 
         [0019]    It should be understood that the title of this section of this specification, namely, “Detailed Description Of The Invention”, relates to a requirement of the United States Patent Office, and does not imply, nor should be inferred to limit the subject matter disclosed herein. 
         [0020]    Referring now to the figures and in particular to  FIG. 1 , there is shown, schematically, an ink jet printing system  10  having a printhead  12  with a cover device  14  embodying the principles of the present invention. The printing system  10  includes, generally, the printhead  12 , an ink supply  16  and a waste collection system  18 . Lines (fluid conduits)  20  and valves  22  interconnect the various equipment items. The system  10  can also include a priming system  24 , return lines  26  and a vacuum system  28  that draws and collects vapors from the waste collection system  18  for automatic maintenance functions. 
         [0021]    Generally, in operation, ink is drawn from the ink supply  16  by virtue of capillary action that is created at the printhead  12  when ink is jetted from the head  12 . Ink is carried by supply lines  20  from the supply  16  to the printhead  12 . 
         [0022]    Waste fluid from the printhead  12  is routed, by a waste collection line  30 , from the head  12  to the waste collection system  18 . The waste collection system  18  includes a vapor separator  32  and a waste chamber  34 . Air and vapor from the separator  32  is drawn off by a vacuum pump  36  (which creates a negative pressure in the waste collection line  30 ). Waste fluid can include ink that may be contaminated with dust, maintenance fluids or other non-desired materials. 
         [0023]    The printhead  12  can operate by thermal, piezo-electric, valve-based or other drive principles, all of which will be well understood by those skilled in the art. In any case, the printhead  12  has a face plate  40  that is mounted to the body  42  of the printhead  12 . A plurality of jetting orifices  44  are formed in the faceplate  40  through which the ink is jetted. As set forth above, the ink can be driven using any of a number of technologies. For purposes of explanation, openings  46  in the faceplate  40  on either side of the orifices  44  accommodate fasteners (not shown) that secure the plate  40  to the body  42  of the printhead  12 . 
         [0024]    As will be appreciated, the orifices  44  are small openings through which the ink is jetted or expelled. Accordingly, the orifices  44  can become easily clogged if debris or contaminants (such as dust) come to rest on the faceplate  40 . As such, waste fluid is drawn away from the plate  40  during maintenance operations. 
         [0025]    It will also be appreciated that the problem of the orifices  44  becoming clogged is exacerbated when quick drying inks are used. Typically, quick drying inks include a solvent or carrier that is relatively volatile. This results in the liquid portion of the ink quickly evaporating after the ink has been jetted onto the object O to be printed (e.g., substrate). This also, however, can result in the liquid portion of the ink evaporating as the ink resides at the orifices  44 . It will be appreciated that drying occurs over a continuum. That is, as the solvent or carrier begins to evaporate from the ink, the viscosity of the ink increases to a point at which the ink becomes semi-fluidic and then subsequently becomes “dry” or solid. The present cover  12  is intended to maintain the ink in a fluidic or semi-fluidic, functional state for extended periods. 
         [0026]    In order to overcome the quick evaporation of the liquid, the present cover  14  resides over the orifices  44  when the printhead  12  is not in the jetting mode and opens or uncovers the orifices  44  when the printhead  12  is in the jetting mode. It will be appreciated that the rate at which the carrier or solvent evaporates from around the orifices  44  is related to, among other factors, the concentration of the carrier or solvent in the localized atmosphere around the orifices  44 . If the atmosphere is “dry” or low in localized vapor concentration, the rate of evaporation increases. Conversely, when the localized atmosphere is high in carrier or solvent vapor concentration, the rate of evaporation decreases. 
         [0027]    Accordingly, the present cover  14  resides over the orifices  44  when the printhead  12  is idle or not jetting and provides a localized environment E that is higher in vapor concentration than that of the surrounding environment A. The cover  14  is positioned over the orifices  44 , but is not in contact with the faceplate  40  at the orifice edges  41 . Rather, the cover  14  defines a gap (as indicated at  48  in  FIG. 2B ) between the inner surface  50  of the cover  14  and the faceplate  40 . In that the cover  14  extends over all or substantially all of the orifices  44 , the gap  48  provides a common or communal, localized, substantially closed environment E in which the concentration of vapors is kept at a higher level than the surrounding atmosphere A. The higher vapor concentration results in a reduced evaporation rate, which correlates to a reduced drying time and accordingly, enhanced ink (fluid) performance. 
         [0028]    As seen in FIGS.  2 B and  3 A-H, the cover can be configured to slide parallel to the surface  52  of the face plate  40 , to expose or cover the orifices  44 . In a present configuration, the cover  14  is operably connected to the head  12 , for example to a portion of a maintenance module faceplate  40 , to move between the exposed and the covered positions. The maintenance module faceplate  40  can be, for example, such as that illustrated in Jackson, U.S. Pat. Nos. 6,406,125, 6,457,802 and 6,739,697, and/or Cahill, et al., U.S. Pat. Nos. 6,637,862, 6,935,721 and D477,358, all of which patents are commonly assigned with the present application and are incorporated herein by reference. 
         [0029]    The cover  14  can be mounted to the printhead  12  by one or more living hinges  54 . In a present embodiment, the hinges  54  also serve to provide an engaging region  56  for contact by the object O for movement of the cover  14 . The hinges  54  include first and second rigid legs  58 ,  60  joined to one another by a flexible hinge portion  62 . One of the legs  58  is mounted to the faceplate  40  (at about the leg free end  64 ) and the other leg  60  is mounted to the cover  14  (at about that leg&#39;s free end  66 ). The hinge element  62  is biased to draw the legs  58 ,  60  toward one another. Applying a force at about the hinge portion  62  urges the legs  58 ,  60  outward—that is to spread. 
         [0030]    To facilitate sliding movement of the cover  14 , the faceplate  40  can include overhanging portions or flanges  68  (or grooves in the side of the faceplate  40 ) and the cover  14  can include fingers  70  (that depend and extend inwardly of the cover body  72 ) that wrap around and over the flanges  68 . This provides a way in which the cover  14  can be mounted to the faceplate  40  so as to maintain the vapor space or gap  48  for maintaining the higher vapor concentration while at the same time assuring that the cover  14  remains movably mounted to and spaced from the plate  40 . As will be appreciated from the figures, the cover  12  does not extend beyond the faceplate  40  form factor—that is, it is within the outline of the faceplate and does not extend beyond the edge  43  of the plate  40 . 
         [0031]    As seen in  FIG. 2B , with the legs  58 ,  60  mounted to the faceplate  40  and the cover  14 , and the hinge  54  in a relaxed or contracted state, the cover  14  overlies the orifices  44 . The illustrated hinges  54  include an upwardly extending leg contact portion  74  that is an extension of the faceplate leg  58  beyond the hinge  62 . The contact portion  74  provides a better transition for the movement of the cover leg  60 . 
         [0032]    As seen in  FIGS. 3A-H , a box or other object O to be printed moves (as indicated by the arrow at  76 ) to the printhead  12 , in close proximity to (e.g., a short transverse distance from) the faceplate  40 . As the object O moves adjacent to the printhead  12  ( FIG. 3C ), the object O contacts the contact portion  74  of leg  58  and urges the hinge  62  toward the faceplate  40 . Because the location of the free end  64  of the faceplate leg  58  is fixed, the free end  66  of the cover leg  60  moves which, in turn, forces the cover leg  60  to spread and the orifice cover  14  to open. 
         [0033]    The contact portion  74  provides an accommodation for slight variations in the height or distance of the object O to be printed (e.g., the box) from the faceplate  40 . The contact portion  74  provides an extended distance range over which the object O (such as a box) can be spaced from the faceplate  40  and actuate the hinge  54  without overstressing the legs  58 ,  60 . It will be appreciated that if the object O were to contact too low on the leg  58 , the hinge  54  could be overstressed, or if the object O was too high (too far from the printhead  12 ), the cover  14  might not open. Accordingly, the extended contact portion  74  provides a greater tolerance for object O distance from the printhead  12 . In addition, the elongated contact surface  74  provides a smoother movement to the cover  14  as it opens. That is, the object O can “ramp up” the leg  58 / 74  to open the hinge  54  (and cover  14 ). 
         [0034]    Referring to  FIG. 3D , as the object O continues to move over the printhead  12  and urges the hinge  54  toward the printhead  12  (downward), the cover  14  continues to move until fully open ( FIG. 3E ). Once the object O passes over the cover  14  and the force (of the object O) on the hinge  54  is removed, the hinge  54  begins to return to the relaxed state and the cover  14  begins to close (( FIGS. 3F and 3G ), until the cover  14  is fully closed ( FIG. 3H ). It will be understood by those skilled in the art that this is only one way in which the cover  14  can be opened. It is anticipated that electro-mechanical devices, such as solenoids and the like can also be used to effect movement of the cover  14 . Such other arrangements and methods are within the scope and spirit of the present invention. 
         [0035]    It will also be appreciated that the cover  14  provides a number of other advantages and enhancements. First, because the cover  14  is used in an in-line sense, that is with the printhead  12  in operation, it is possible to provide a means for clean “spitting”. As will be understood, “spitting” or forced purging of the printhead  12  is occasionally carried out to clear the printhead  12 . As can be imagined, without a cover  14 , a forced purge could otherwise result in ink being ejected into areas in which it is undesirable. The cover  14  provides the ability to carry out this purge without unduly spreading ink into these areas. It is also possible to shut down equipment for short periods without the need for undue purging or other extended start-up procedures. 
         [0036]    It will be understood by those skilled in the art that the cover  14  provides a communal or common environment E for all of the orifices  44  that are “under cover”. It is the higher concentration of fluid vapors in the local environment E (relative to the surrounding atmosphere or environment A) that prevents evaporation of fluid at the orifices  44  and thus retards solidifying of the fluid. In that the cover  14  can be incorporated into the fluid jet maintenance module or faceplate  40 , which, in turn, is in flow communication with the waste collection system  18 , this provides an even greater volume for fluid/vapor interaction with the cover environment E (as through the collection line  30 ). It is also contemplated that the cover  12  can be configured to provide individual compartments for each of the orifices  44 . 
         [0037]    An alternate embodiment of the cover  114  is shown mounted to a printhead  112  in  FIG. 4  in which the cover  114  is actuated by electro-mechanical means, such as a solenoid  115 . The solenoid  115  can be mounted in a variety of locations and can actuated directly or indirectly (such as by a linkage, not shown). The solenoid can be actuated through the use of, for example, a proximity sensor  117  that is located near the printhead  112  that senses the presence of an object O moving toward the printhead  112  (as indicated by the arrow at  119 ). 
         [0038]    The present cover  14  provides a host of advantages over known printhead systems. First, it enhances the performance of the ink (fluid) jetted from the printhead  12  in that it retards drying and solidifying at the printhead orifices  44 . Such an enhancement also includes extending the life of the ink and reducing maintenance of printhead  12 . In addition, in that the cover is used in-line, it has minimal or no adverse impact on the use of the printhead  12 . 
         [0039]    All patents referred to herein, are hereby incorporated by reference, whether or not specifically done so within the text of this disclosure. 
         [0040]    In the disclosures, the words “a” or “an” are to be taken to include both the singular and the plural. Conversely, any reference to plural items shall, where appropriate, include the singular. 
         [0041]    From the foregoing it will be observed that numerous modifications and variations can be effectuated without departing from the true spirit and scope of the novel concepts of the present invention. It is to be understood that no limitation with respect to the specific embodiments illustrated is intended or should be inferred. The disclosure is intended to cover all such modifications as fall within the scope of the claims.