Patent Publication Number: US-6905189-B1

Title: Wet capping tray for ink jet printheads

Description:
RELATED APPLICATION 
   This application claims the benefit of U.S. Provisional Application No. 60/381,124, filed May 16, 2002, the entire teachings of which are incorporated herein by reference. 

   BACKGROUND 
   In certain large-scale printing systems, printheads are used to eject ink onto a substrate to create the desired image, for example, on substrates such as museum displays, billboards, sails, bus boards, and banners. In some of these printing systems, the printheads receive ink from an ink supply or reservoir and use a so-called drop on demand ink jet process. With this type of process, ink is ejected from one or more nozzles of the printheads when a piezoelectric crystal in the printhead is actuated. The piezoelectric crystal generates a pulse in the ink so that the ink expels through the nozzle as a droplet. To create the image, a carriage which holds one or more printheads scans or traverses across the substrate while the printheads deposit ink as the substrate moves. 
   Regardless of the particular type of printing system in which the ink jet printheads are used; the printheads commonly have a series of manifolds and channels that transport the ink to the nozzles. As such, a particular concern for these printheads when the printing system is not in operation is that the ink in the manifolds and channels can harden. That is, water-based inks, as well as solvent-based inks can dry out, or the ink can polymerize if the ink happens to be UV curable. Thus, when the printheads are not in use, it is desirable to somehow seal the printheads to prevent exposing the ink in the printheads to air and/or to UV radiation. 
   Some have proposed sealing the nozzles of the printheads with a plastic sheet, while others have proposed placing a wet pad soaked with a flushing solvent, such as a solution made of water and glycol ether, against the nozzles when the printheads are not being used. These printhead capping processes are somewhat effective for short periods of time, say, for example, up to one day. However, the performance of these processes has been less than desirable for longer periods of time, for example, three to four days, since it is difficult to keep the printheads completely sealed for these longer periods. 
   Others have proposed introducing a model solution, such as polypropylene glycol, into the printheads to seal them when the printing system is not in operation. Typically, such solutions are used for shipping or storing the printheads for long periods of time, for example, weeks or months. However, it takes hours and sometimes days to flush the model solution out of the printheads before using them in a printing operation, which may be impractical if the printing system is only inoperative for a few days. 
   SUMMARY 
   For solvent-based inks, if the ink happens to dry out in a printhead, the ink can typically be redissolved so that the printhead can be recovered. However, for waterbased inks, once the ink drys out and hardens, or for UV-curable inks, once the ink polymerizes, it becomes very difficult to salvage the printheads. 
   As for capping processes which use wet pads to seal the printheads, particularly for water-based inks, the pads are typically made of textile fibers which can break off and enter the nozzles and plug them up. Furthermore, these stray fibers can serve as initiation sites for the ink to dry out and harden. 
   Therefore a need exists for a method and apparatus which is able to seal the printheads of a printing system to prevent exposing the ink in the printheads to air and/or UV radiation when the printing system is not in operation. Furthermore, the sealing process must occur rather quickly, especially if the ink is water-based or UV curable. 
   The present invention relates to an apparatus and method of sealing printheads efficiently and quickly with a wet capping station, in particular, a wet capping tray, when the printheads are not being used, for example, during the time period between printing operations. 
   In one aspect of the invention, a printing system includes a printhead containing ink, and a tray cooperatively associated with the printhead and containing a solution in which the printhead is immersed to seal the printhead to prevent the ink from clogging the printhead when the printing system is not in operation. The solution can be any suitable solution that is compatible with the printhead and the ink, and the solution may be provided to the tray from any convenient source. 
   Embodiments of this aspect can include one or more of the following features. The solution can be a waste solution made of a single colored ink emitted from a single printhead. There can be a plurality of printheads immersed in the waste solution. Thus, the waste solution can be a single colored ink emitted from one or more of the plurality of printheads, or the waste solution can be made from different colored inks emitted from the plurality of printheads. Additionally or alternatively, the waste solution can be made of a flushing solvent used to clean and purge the printheads. 
   To effectively seal the printheads in a short period of time, the wet capping station in some embodiments includes an actuator that moves the tray towards the printheads to immerse them in the waste solution. 
   The tray can have a basin that contains the waste solution. The tray can include a valve in fluid communication with the basin, in which case the valve is partially or fully opened to allow a desired amount of the waste solution to drain from the basin, and is closed to prevent the waste solution from draining from the basin. The valve can be adjustable to allow the waste solution to drain from the basin at a desired flow rate. 
   In particular embodiments, the tray has a first pair of oppositely opposed sidewalls that are substantially parallel to each other, a second pair of oppositely opposed sidewalls that are also substantially parallel to each other, and a base. The first pair of sidewalls, the second pair sidewalls, and the base define a basin in which the waste solution is contained. 
   In some embodiments, each of the sidewalls of the first pair of sidewalls is provided with one or more slots which engage with a respective head of a screw that is used to secure the printhead to a carriage. The slot can have a semi-circular shape with an opening that faces the basin. 
   In other embodiments, each of the sidewalls of the first pair of sidewalls is provided with at least one hole that engages with the head of a respective screw. 
   In another aspect of the invention, a method of immersing one or more printheads in a waste solution includes emitting ink from one or more printheads into a tray, so that the emitted ink in the tray is a waste solution, and immersing the one or more printheads in the waste solution. 
   Embodiments of this aspect of the invention can include one or more of the following features. Prior to immersing the printheads, a flushing solution is emitted from one or more printheads into the tray. Thus, the waste solution is made of the ink, as well as the flushing solution. The ink can be emitted from one or more printheads. The waste solution can contain different colored inks emitted from a plurality of printheads. The method can include moving the tray with the waste solution towards the printheads to immerse the printheads in the waste solution. In particular embodiments, the waste solution is periodically drained from the tray. 
   Some of the embodiments may include one or more of the following advantages. The cleaning station provides a relative quick way of sealing the printheads, particularly when the printing system is not in operation over period of days. The cleaning station provides a simple quick, process of immersing the printheads in the waste solution and then extracting the printheads for subsequent printing operations with a simple mechanism. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. 
       FIG. 1  is a partial view of a printing system with a cleaning station. 
       FIG. 2A  is a side view of the cleaning station of  FIG. 1  with a wet capping tray shown with a carriage and printhead in accordance with the invention. 
       FIG. 2B  is an end view of the carriage and printhead of FIG.  2 A. 
       FIG. 3A  is a top view of the wet capping tray of FIG.  2 A. 
       FIG. 3B  is a bottom view of the printhead of FIG.  2 A. 
       FIG. 4  is a top view of an alternative embodiment of a wet capping tray. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   A description of preferred embodiments of the invention follows. These embodiments are provided by way of example and not as limitations of the invention. 
   Referring to  FIG. 1 , there is shown a partial view of a printing system  10  with a cleaning/purging station  12 . The printing system  10  includes a carriage  14  that moves back and forth along a rail  16  mounted to a base  18 . As the carriage  14  traverses along the rail  16 , one or more printheads of a set of printheads  17  deposit ink onto a substrate that moves beneath the carriage  14 . The operation and features of a printing system like the one shown in  FIG. 1  is described in greater detail in U.S. patent application Ser. No. 09/834,999, filed Apr. 13, 2001, the entire contents of which are incorporated herein by reference. 
   A particular feature of the printing system  10  is the cleaning/purging station  12  positioned beneath the carriage  14 , and hence the set of printheads  17 , when the carriage  14  is in a rest position, which may occur between printing operations. Typically, during these down periods, an operator interacts with a controller  5  of the printing system through, for example, a minicomputer  6  to instruct the printing system  10  to pump a flushing solvent through the printheads  17 . The flushing solution is used to clean and purge the printheads, and is collected in a trough  20  as it ejects from the nozzles. From the trough  20 , the cleaning solution flows through a tube  21  connected to the bottom of the trough to a waste container  22  typically located within the base  18 . Moreover, for example, after a rest period and prior to the start of a new print operation, the printheads under the direction of the controller  5  may eject ink to prime the printheads. This waste ink is also collected in the trough  20  from where it drains through the tube  21  to the waste container  22 . 
   As shown in  FIG. 1 , the trough  20  is mounted to a pair of legs  24  that arc connected to a pair of actuators  26  positioned within the base  18 . The actuators in one embodiment are air cylinders which raise and lower the legs  24 , and hence the trough  20 , and to position the trough  20  a desired distance from the set of printheads  17  by filling and removing air from the air cylinders. 
   Referring now to  FIG. 2A , there is shown a close-up side view of the cleaning/purging station  12  and the printheads  17 , of which only a first printhead  17 - 1  is illustrated because of the orientation of the printheads. As shown in  FIGS. 2A and 2B , the printhead  17 - 1  is mounted to a bezel  28  which is attached to the carriage  16  with a pair of screws  29 . 
   When configured for sealing the printheads  17 , the cleaning/purging station  12  includes a plate  32  placed on top of the trough  20 , and a tray  30  mounted on top of the plate  32 . The tray  30  has a recessed region  31  in which the plate  32  is positioned in a manner to prevent the tray  30  from moving and/or sliding off the plate  32 , and hence the trough  20 . The tray  30  also includes a basin  34  defined by a pair spaced apart sidewalls with ledges  35  ( FIG. 3 ) that are substantially parallel to each other, and another pair of spaced apart side walls  36  orthogonal to the ledges  35  and substantially parallel to each other. 
   Attached to the side of the tray  30  is a valve  43  connected to a hole  40  of the tray  30 , which opens to the basin  34  and to a drain tube  42 . Accordingly, when an operator opens the valve  43 , for example, with a knob  44 , fluid contained in the basin  34  flows through the hole  40  and out through the drain tube  42 . Furthermore, the operator can adjust the knob  44  to control the flow rate of the liquid from the basin  34 . 
   The plate  32  is typically about 0.25 inch thick, about 26 inches long, and about 5 inches wide, and is made from a metal or plastic, or any other suitable stiff material. The tray  30  is typically made of a plastic or metal, depending on the compatibility with the ink, and is about 26 inches long and about 6 inches wide, and the basin is about 0.5 inch deep. In some embodiments, the tube  21  is made of a metal, and the tube  42  is a flexible hose made of a material that is compatible with the ink. 
   To seal the printheads  17  after a printing operation, an operator places the plate  32  on top of the trough  20 , and the tray  30  on top of the plate  32 . Then, under the direction of a controller  5 , the carriage  14  moves along the rail  16  and positions the printheads  17  above the tray  30 . 
   Subsequently, the controller  5  directs the printheads  17  to eject ink through their respected nozzles, such that the ink is collected in the basin  34  of the tray  30  as a waste solution. Moreover, in some circumstances a flushing solvent is pumped through the printheads  17  to clean and purge them. The ink and/or flushing solvent accumulates in the basin  34  to a depth of about 2 to 3 mm. 
   Next, the controller  5  activates the actuators  26  to move the trough  20  and hence the tray  30  towards the printheads  17 . Note that along each ledge  35  there is a series of slots  38  ( FIG. 3A ) with openings  39  that face the basin  34 . Typically, the number of slots  38  along each ledge  35  is equal to the number of printheads  17 , so that as the tray  30  moves towards the printheads, each head of the screws  29  fits within a respective slot  38 . Movement of the tray  30  stops when the face of the bezel  28  rests on top of the ledges  35 . The slots  38  stabilize the tray  30  and prevent excess movement between the tray  30  and the printheads  17 . In some embodiments, the printheads  17  are immersed in the waste solution of ink and/or flushing solvent to a depth of about 3 to 5 mm. That is, when printheads are immersed in the solution, the level of the waste solution rises to about 4 to 6 mm with the printheads about 1 mm off the bottom of the basin  34 . It typically takes about five seconds from the moment the printheads  17  are positioned above the tray  30  to when they are immersed in the waste solution. 
   Once immersed in the waste solution, the printheads remain wet and sealed even if some of the waste solution evaporates over a period of a few days to prevent ink in the printheads from drying out and clogging the channels, manifolds, and nozzles of the printheads. Furthermore, when the printheads  17  are sealed with the liquid waste solution, the printheads do not rest on top of some fibrous materials as in certain prior art cleaning stations. Thus, there are no fibers that flow into the nozzles of the printheads  17  which can also clog the nozzles. 
   After the down time or rest period and at the start of the next printing operation, the operator interacts with the controller  5  to direct the actuators  26  to lower the trough  20 , and hence the tray  30 , away from the printheads  17 . Subsequently, to prime the printheads  17  for the next printing operation, the printheads eject ink to clean out any of the waste solution that may have be drawn into the nozzles, channels, and manifolds of the printheads  17 , for example, by capillary action. 
   Next, the operator turns opens the valve  43  with the knob  44  to drain the waste solution from the basin  34 . The waste solution flows through the drain tube  42  which typically extends to the waste container  22  that is used to collect waste ink from the trough  20  through the tube  21 . The waste container  22  is able to hold about four gallons of waste solution. Periodically, the operator removes the waste container  22  and empties it, or replaces it with a new waste container. 
   As discussed above, the head of the screws  29  fit within the slots  38  of the tray to hold the printheads  17  in place when the printheads are immersed in the waste solution. There are, however, other embodiments of the invention which fulfill the purpose of the slots  38 . 
   For example, as illustrated in  FIG. 4 , there is shown an alternative embodiment of a wet capping tray  100 . Note that certain features of the tray  100  are identical to those of the tray  30 , and therefore are identified by like numerals. However, rather than having slots  38  which have openings  39  that face towards the basin  34 , as the tray  30 , the tray  100  of  FIG. 4  has a series of holes  102  in which the head of the screws  29  fit. As such, the series of holes  102  do not open up to the basin  34  so that the head of the screws  29  are not exposed to the waste solution when the printheads  17  are immersed in the solution. Hence, the screws  29  do not get any waste solution on them, which makes any required cleanup easier. 
   As with the tray  30 , the tray  100  has a recessed region  31  in which the plate  32 , placed on top of the trough  20 , is positioned when the cleaning/wet capping station is used to seal the printheads  17 . The tray  100  is used in much the same way as the tray  30  described above. Thus, in operation, as the actuators  26  move the tray  100  towards the printheads  17 , the bead of the screws  29  fit inside the holes  102  of the tray  100  while the printheads  17  are immersed in the waste solution. Again, the actuators  26 , under the direction of the controller  5 , terminate the upward movement of the tray  100  when the bezel  28  makes contact with the ledges  35 . 
   While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims. For example, the waste solution can also be any suitable liquid that is compatible with both the ink and the printheads, such as, for example, water, and/or model fluid.