Abstract:
A service station system for cleaning printheads, particularly inkjet printheads is provided. The service station includes a body having a seal attached thereto and at least one pressure operated sprayer attached to the body within an area demarcated by the seal. Each sprayer includes a bent cap, which enables spraying a cleaning agent at a predetermined spray angle. The sprayers are positioned so that substantially all of the nozzle plate will be wetted by the cleaning agent when the seal, the body and the nozzle plate are positioned to form an enclosed volume. The service station also includes a pressure release valve to keep the pressure within the enclosed volume at atmospheric level during spraying.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to a system for cleaning printheads and more particularly to a service station and method for cleaning inkjet printheads. 
     BACKGROUND OF THE INVENTION 
     Inkjet printheads are widely used and well known in the art. One type of inkjet printhead is based on drop-on-demand systems that use either piezoelectric or thermal printhead technologies. 
     In high-resolution drop-on-demand inkjet printing, very small ink droplets are ejected through tiny apertures in a nozzle plate. Contaminants, such as dust particles and paper fibers, tend to accumulate in the vicinity of these apertures, interfering with the ejection of the ink droplets. In addition, modem ink formulations contain, among other components, pigments, resins, and fast drying accelerators When the printer is not in use, these components, particularly pigments, have a tendency to dry out, blocking the nozzle apertures of the printhead. In addition, they can become so hard that they scratch the face of the nozzle plate, degrading inkjet accuracy. 
     In order to avoid accumulation of ink residues, dust and print fibers when the printhead is not in use, service stations are installed in printing machines. These stations periodically clean the nozzle plate of the printheads, removing contaminants and residues. 
     Many types of service stations are known in the art. Usually, during periods of non-use, the service stations cap the system, sealing the nozzles from contamination and drying. Some capping systems also facilitate priming of the printhead by drawing a vacuum on the printhead. During maintenance, many service stations cause ejection of a number of ink drops through each of the nozzle apertures of the printhead. The droplet ejection process is known as spitting and the ejected ink is collected in a spittoon that is part of the service station. 
     Most service stations use an elastomeric wiper that wipes the nozzle plate and removes ink residues, paper dust and other debris that have collected during use. An example of such a service station is disclosed in PCT Patent Publication WO 9615908. In &#39;908, the cleaning and sealing station has among other features, a wiper, a sealing cap, and a suction element for withdrawing excess ink. 
     Other approaches or refinements to maintaining a clean nozzle surface on inkjet printheads are discussed in U.S. Pat. Nos. 6,786,830 and 5,815,176. The former teaches a station which uses a wiper with an adaptive wiping speed while the latter describes the use of a multi-finned wiping system. 
     SUMMARY OF THE INVENTION 
     The present invention describes a method for cleaning the nozzle plate of printheads by using at least one sprayer to spray a liquid cleaning agent onto a nozzle plate prior to wiping. The sprayed agent improves the efficiency of cleaning in several ways. It thins any liquid ink left on the nozzle plate and dissolves solid pigment residue stuck to the plate. It decreases the drying rate of fast drying inks and acts as a lubricant for the wiper, generally preventing scratches. 
     The present invention teaches a service station system for cleaning a printhead that includes a translational means for bringing the service station into proximity with the printhead. It also includes a cleaning agent means for distributing a cleaning agent over a printing face of the printhead when the service station is in proximity with the printhead. Finally, the system includes a wiper for wiping the cleaning agent off the printing face. 
     The translational means can either translate the service station with respect to the printhead or vice versa. Similarly, the translational means can translate the printhead with respect to the wiper or vice versa. 
     In an embodiment of the present invention, the cleaning agent means for distributing a cleaning agent is at least one sprayer. 
     In one embodiment the service station system can be used with an inkjet printhead. 
     The service station system uses cleaning agents, where the agents remove at least one of the following materials from a group consisting of ink, ink components, dust particles, and paper fibers. 
     The present invention also teaches a method for cleaning a printhead including the step of distributing a cleaning agent over a printing face of the printhead. 
     In one embodiment the present invention teaches a method for cleaning a printhead where the method includes spraying a printing face of a printhead with a cleaning agent. 
     In another embodiment, the invention teaches a method which includes the steps of bringing a service station into proximity with a printhead, spraying a printing face of a printhead with a cleaning agent; and lowering the service station to a level where a wiper of the service station wipes the printing face. 
     In yet another embodiment, the method for cleaning a printhead further includes the steps of pressing the service station to the printhead and effecting a vacuum. The vacuum causes ink to be discharged from nozzles in the printhead. Finally the method may also include the step of suctioning off the ink that has been discharged. The steps of pressing and suctioning are effected generally prior to the spraying step. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be understood and appreciated more fully from the following description taken in conjunction with the drawings in which: 
     FIGS. 1A,  1 B,  1 C,  1 D and  1 E are schematic isometric illustrations of a service station and its associated printhead in five different operational states; 
     FIG. 2 is a front view illustration of the service station and printhead of FIG. 1A; 
     FIG. 3 is a side view illustration of the service station and printhead of FIG. 1A; 
     FIG. 4 is a sectional illustration through a typical sprayer forming part of the service station in FIG. 1A; and 
     FIG. 5 is a block diagram illustration of the sequence of operations performed by the service station of the present invention. 
     Similar parts in different figures are given identical numbers throughout. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention describes a service station system meant to clean and maintain the nozzle plate of a printhead, preferably an inkjet printhead. It is intended to prevent blockages of, and scratches to, the nozzles which result from dried ink and other contaminants such as dust and paper fibers. 
     The present invention describes a method for cleaning the nozzle plate of printheads by using at least one sprayer to spray a liquid cleaning agent onto a nozzle plate prior to wiping. The sprayed agent improves the efficiency of cleaning in several ways. It thins any liquid ink left on the nozzle plate and dissolves solid pigment residue stuck to the plate. It decreases the drying rate of fast drying inks and acts as a lubricant for the wiper, generally preventing scratches. 
     Reference is now made to FIGS. 1A,  1 B,  1 C,  1 D and  1 E, where different stages of the operating cycle of a service station  36  of the present invention are shown. 
     Service station  36  comprises three sprayers  74 A,  74 B, and  74 C, a lower frame  60 , an upper frame  56 , a base  38 , a sponge-covered spittoon  60 , an elastomeric lip seal  58 , a wiper  78 , a drainage basin  80  and pressure release inlets  66 . In a working printing machine there will generally be a plurality of service stations  36  lined up in an array, one per printhead  32 . 
     FIG. 1A shows printhead  32  and its underside, nozzle plate  34  before service station  36  is brought into proximity with printhead  32 . Service station  36  is in its standby position directly beneath printhead  32 . Printhead  32  is shown on its side to better view nozzle plate  34 . Generally, nozzle plate  34  is parallel to the plane of spittoon  60  with its long axis  33  also parallel to the long axis  61  of spittoon  60 . Service station  36  is raised from its standby position (arrow  140 ) into a position proximate to nozzle plate  34  before any cleaning of nozzle plate  34  occurs. 
     Printhead  32  must be brought from its print position to a position essentially above, and aligned with, service station  36  before the latter is raised. Once station  36  is raised, nozzle plate  34  is joined to lip seal  58  of station  36 . As shown in FIG. 1B, the three sprayers  74 A,  74 B and  74 C then spray nozzle plate  34  with a cleaning agent. Sprayers  74 A,  74 B and  74 C are placed as close as possible to the walls of upper frame  56  to maximize the area of nozzle plate  34  which is wetted. As can be seen in FIG. 18, the spray from the two external sprayers  74 A and  74 C overlap slightly at central sprayer  748 . Sprayer  74 B is located along the opposite wall of frame  56 . Sprayers  74 A,  74 B, and  74 C spray in a lateral direction with a slight upward angle. 
     Sprayers  74 A,  74 B, and  74 C are located in upper frame  56  and are positioned in such a way that the sprayed cleaning agent from each sprayer wets a different sector of nozzle plate  34 . Accurate placement of sprayers  74  ensures that essentially the entire area of nozzle plate  34  is wetted. A typical spraying angle α (best seen in FIGS. 1B and 1C) of 160° can be used. This angle wets an approximate maximum area of nozzle plate  34 . The number of sprayers  74  can be more or less than three, depending on their type, dimensions, placement, the amount of cleaning agent sprayed, the area to be wiped, etc. 
     FIG. 1C shows spraying from sprayer  74 B, the latter located at the opposite wall of frame  56  The three sprayers  74 A,  74 B and  74 C are synchronized so that they do not operate simultaneously. In that way, the spray from sprayers positioned along opposite walls of service station  36  do not interfere with each other. 
     After nozzle plate  34  has been wetted with the cleaning agent, service station  36  is lowered slightly to its wiping position (not shown). As shown in FIG. 1D, service station  36  is then moved laterally (arrow  150 ), perpendicular to the long axis  33  of printhead  32 . This movement causes wiper  78  to be dragged along the face of nozzle plate  34 , removing the cleaning agent and any dissolved ink, ink pigments and solid contaminants. The removed material drops into drainage basin  80 . 
     Once the wiping operation is complete, service station  36  is moved downward, as indicated by the arrow  160  in FIG. 1E returning station  36  to its standby position shown in FIG.  1 A. 
     Reference is now made to FIGS. 2 and 3, where front and side views of service station  36  and printhead  32  are illustrated, and additional features of the system can be seen. Specifically, FIG. 2 contains the following features previously encountered: printhead  32 , nozzle plate  34 , wiper  78 , sponge-covered spittoon  60 , sprayer  74 , lip seal  58 , pressure release inlets  66 , base  38 , lower frame  50  and upper frame  56 . Features which appear here for the first time are springs  52 , connecting pins  54 , drainage outlets  62 , drainage valves  64 , a pressure release valve  68 , which opens and closes a path between the seal and atmosphere, a vacuum valve  65 , a sprayer valve  76 , a surplus tank  114 , a cleaning agent tank  112 , a vacuum source  110 , a pressure source  113 , rods  46 , a controller  8 , and an XY motion mechanism  108 . Because of the view, only one of the three sprayers ( 74 A,  74 B,  74 C) is shown. As shown in FIG. 2, sprayer  74  sits above the sponge in spittoon  60 , drainage outlets  62  usually sit below it and pressure release inlets  66  are generally approximately co-terminus with the top of the sponge. 
     FIG. 3 show s the following additional parts of the service station  36 : bushings  44 , a drainage basin  80  for wiper  78 , a drainage basin outlet  84  and a drainage basin valve  86 . FIG. 3 also illustrates the two directions in which service station  36  moves at the command of XY motion mechanism  108 , the latter being controlled by controller  8 . 
     Referring to FIGS. 2 and 3, additional details of the operation of service station  36  will now be explained. Aspects of raising and lowering, sealing and “purging” the service station will be discussed. 
     Upper frame  56 , lower frame  50  and base  38  assume three different positions during the operating cycle of the service station system. Moving from the position in which base  38  and frames  50  and  56  are in their lowest position to their highest position, these are: 
     a) a standby position (shown in FIG.  1 A); 
     b) a wiping position (shown in FIG.  1 D and FIG.  3 ); and 
     c) a sealing position in which elastomeric lip seal  58  is pressed tightly against printhead  32  (shown in FIG.  2 ). 
     Frames  50  and  56  are moved to their different positions by XY motion mechanism  108 , which is controlled by controller  8  shown in FIG.  2 . As indicated in FIG. 3, frames  50  and  56  and base  38  are movable horizontally in direction  42 , on bushings  44  which slide on rods  46  (the latter are best seen in FIG.  2 ). XY motion mechanism  108  also translates frames  50  and  56  in the vertical direction  40 . 
     Lower frame  50 , which includes vertical pins  62  and compression springs  54 , is assembled on base  38 . Upper frame  56  is slideable on pins  52  and rests on springs  54 . Lip seal  58 , typically made from an elastomeric material, sits on the periphery of upper frame  56 . When frames  50  and  56  are raised, lip seal  58  encloses a volume formed by nozzle plate  34 , upper frame  56  and spittoon  60 . As contact is made between nozzle plate  34  and lip seal  58 , upper frame  56  is pushed down on pins  52 . A counteracting force exerted by springs  54  is created which generates a tight seal between lip seal  58  and nozzle plate  34 . 
     While in this sealing position, nozzle plate  34  is close to, but does not touch, sprayers  74 A,  74 B and  74 C, or spittoon  60 . Pressure release inlets  66  are connected via a tube  89  through electrically operated pressure release valves  68  to the atmosphere. These valves are opened to prevent the formation of an overpressure in the enclosed volume created by lip seal  58 . Controller  8  controls pressure release valves  68  during the sealing step just described. 
     After this tight seal is formed, vacuum source  110  through vacuum valve  65 , tubes  88 , electrically operated drainage valves  64  and drainage outlets  62  creates a vacuum. The vacuum draws ink through the nozzle apertures of nozzle plate  34  This process is known as purging. The ejected ink is received in the sponge-covered spittoon  60  and withdrawn through the drainage inlets  62  via drainage valves  64  to surplus tank  114 . Controller  8  controls vacuum valve  65  and drainage valves  64 . 
     After the printhead has been purged, a cleaning liquid agent from cleaning agent tank  112  is supplied under pressure from pressure source  113  via sprayer valve  76  to sprayers  74 A,  74 B and  74 C The spraying operation, the sprayers, and their placement have already been described above. 
     The wiping action is performed by lowering base  38  and frames  50  and  56  (direction  40  in FIG. 3) to the wiping level and moving base  38  and frames  50  and  56  horizontally (direction  42  in FIG.  3 ), such that wiper  78  moves across nozzle plate  34 . Ink residue and cleaning agents collected in drainage basin  80  are drained via drainage basin outlet  84 , drainage tube  88 , and drainage basin valve  86  to surplus tank  114 . 
     Reference is now made to FIG. 4, where a sectional view of sprayer  74  is shown. The sprayer  74  contains a bent cap  120 , which directs the cleaning agent being sprayed into a given spray angle. The formulation of the cleaning agent is matched to the ink formulation used. For some ink formulations, plain water is an adequate cleaning agent, while for others anti-foaming agents and/or other additives are required. 
     Controller  8 , through its electronic control of sprayer valve  76 , controls the quantity of cleaning agent sprayed. Controller  8  also controls, among other things, the spray pressure and the duration of spraying. Typical values of these parameters are a spray pressure of about 3 atmospheres for a duration of about 0.1 sec. 
     Reference is now made to FIG. 5 where a block diagram of the operating cycle of service station  36  is shown and which outlines the operational steps of the system. Electronic controller  8  of FIG. 2, which typically is an integral part of the printing machine controller, controls the various steps in the cycle. 
     As shown in FIG. 5, a typical service cycle commences by moving printhead  32  from the printing area in a horizontal direction to a position directly above service station  36 . Frames  50  and  56  and base  38  remain at their standby level while printhead  32  is moved (step  10 ) into its service position. 
     Frames  50  and  56  and base  38  are then raised in direction  40  of FIG. 3 to their sealing level (FIG.  1 A), while pressure release valve  68  remains open. At the sealing level, lip seal  58  is pressed tightly (step  12 ) against printhead  32 . Keeping pressure release valve  68  open during step  12  prevents a buildup of pressure in the enclosed volume formed between lip seal  58 , nozzle plate  34  and spittoon  60 . 
     Pressure release valve  68  is closed (step  14 ) while drainage valves  64  and sprayer valve  76  remain in their closed position. After drainage valves  64  and vacuum valve  65  are opened (step  16 ), a vacuum is applied through drainage outlets  62  to nozzle plate  34  and the above-mentioned enclosed volume. The vacuum causes ink to flow, the “purging” step, from the nozzles of nozzle plate  34  into sponge-covered spittoon  60 . This brings fresh ink to nozzle plate  34  of printhead  32  and helps to dislodge any solidified ink residues. After drainage valves  64  and vacuum valve  65  are closed (step  17 ), pressure release valves  68  are opened (step  18 ). Nozzle plate  34  is then disconnected (step  19 ) from sealing lip  58  of service station  36 , and station  36  is moved downward. 
     In step  20 , sprayer valve  76  is opened and a cleaning agent from cleaning agent tank  112  is sprayed under pressure supplied by pressure source  113  through sprayers  74  onto nozzle plate  34 . Frames  50  and  56  and base  38  of service station  36  are then lowered in direction  40  of FIG. 3 to their wiping position (step  22 ), followed by opening drainage valves  64  and vacuum valve  65  which drain spittoon  60  via drainage inlets  62  (step  24 ). 
     Frames  56  and  58  and base  38  are moved (step  26 ) in the horizontal direction  42  as shown in FIG. 3, causing wiper  78  to wipe any ink residue from nozzle plate  34 . The wiped ink residue is then drained (step  28 ) from drainage basin  80  through drainage basin outlet  84 , drainage tube  88 , drainage basin valve  86  to surplus tank  114 . Steps  26  and  28  occur essentially simultaneously. 
     Printhead  32  is then moved (step  29 ) to the printing area. Frames  50  and  56  and base  38  of service station  36  are then lowered (step  30 ) in direction  40  of FIG. 3 to their standby position completing the operating cycle. 
     While in the above embodiment, wiper  78  moves across the face of stationary nozzle plate  34 , in another embodiment, wiper  78  is held stationary and printhead  32  moves across wiper  78 . Similarly, in the above embodiment, service station  36  is moved up to the level of nozzle plate  34  on printhead  32  and later lowered; in another embodiment service station  36  is held stationary while printhead  32  is lowered and later raised. 
     It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather the scope of the present invention is defined only by the claims that follow: