Abstract:
In a method for independently wiping a first and a second printhead of an inkjet printing device, a first and a second wiping assembly separated from each other are provided in the printing device. When the first wiping assembly wipes the first printhead, the second wiping assembly is separated from the second printhead so that the second wiping assembly does not simultaneously wipe the second printhead. When the second wiping assembly wipes the second printhead, however, the first wiping assembly is separated from the first printhead so that the first wiping assembly does not simultaneously wipe the first printhead.

Description:
BACKGROUND  
         [0001]    This invention relates generally to inkjet printing mechanisms, and in particular to techniques for maintaining inkjet printheads at its optimal conditions.  
           [0002]    Inkjet printing mechanisms use pens which shoot drops of liquid colorant, referred to generally herein as “ink,” onto a media sheet. Each pen has a printhead formed with very small nozzles through which the ink drops are fired. To print an image, each printhead is propelled back and forth across the media sheet, shooting drops of ink in a desired pattern as it moves. The particular ink ejection mechanism within the printhead may take on a variety of different forms known to those skilled in the art, such as those using piezoelectric or thermal printhead technology.  
           [0003]    To clean and protect the printhead, typically a conventional “wiper assembly” mechanism is mounted within the housing of the printing mechanism so the printheads can be moved to a wiping region over the assembly for maintenance, specifically for wiping off ink residue as well as any paper dust or other debris that has collected on the printheads. Normally, a printhead needs wiping after a certain amount of printing operations or a certain period of idleness.  
           [0004]    For a printing mechanism having more than one printhead, conventionally, all the printheads move to the wiping region together. Several flexible wiper-blades in close proximity to each other are provided in the conventional wiper assembly to wipe all the printheads simultaneously.  
           [0005]    However, different printheads may have different needs for maintenance due to different characteristics and usage during printing operations. The fact that one printhead needs wiping normally does not justify the wiping of the other printheads. If all the printheads are wiped at the same time whenever one of them needs wiping, the printheads may be exposed to excessive amount of wiping. Potentially, such excessive wiping of the printheads may deteriorate the health of the printheads.  
           [0006]    Furthermore, it is also observed that the conventional wiper assembly may cause an unwanted increase in the width of the printing mechanism. Such an unwanted increase in width may be undesirable, especially for printing mechanisms having very limited space.  
           [0007]    Take a printer with two printheads for example. As shown in FIG. 3A, the conventional wiper assembly is conventionally positioned at one side, for example the right side, of the printer out of the printing area  106  within which ink drops are projected from at least one of the printheads onto a media sheet for imprinting images. During wiping operations, both printheads have to travel out of the printing area to be above the wiper assembly for wiping. On the other hand, during printing operations, only the right pen  305  needs to travel out of the printing area to allow the left pen  303  to shoot ink drops onto the right edge of the media sheet. Thus, in the design as shown in FIG. 3A, the pintheads travel a longer distance to the right during wiping operations than during the printing operations. Such a longer distance may unnecessarily increase the width of the printing mechanism.  
           [0008]    Therefore, there is a need for an improved printhead wiping mechanism which optimizes the amount of wiping for different printheads. There is a further need for an improved wiping mechanism that does not cause the unwanted increase in width of the printing mechanism.  
         SUMMARY  
         [0009]    According to an aspect of the present invention, in a method for independently wiping a first and a second printhead of an inkjet printing device, a first and a second wiping assembly separated from each other are provided in the printing device. When the first wiping assembly wipes the first printhead, the second wiping assembly is separated from the second printhead so that the second wiping assembly does not simultaneously wipe the second printhead. When the second wiping assembly wipes the second printhead, however, the first wiping assembly is separated from the first printhead so that the first wiping assembly does not simultaneously wipe the first printhead.  
           [0010]    According to a second aspect of the present invention, a method for wiping a first and a second printhead of an inkjet printing mechanism is provided. The printheads are movable along a scanning axis in the printing mechanism. In addition, a first and a second wiping assembly are respectively provided at a first and a second wiping region. These regions are separated by a substantial distance from each other along the scanning axis. During wiping operations, both printheads are moved together to, for example, the first wiping region where the first wiping assembly is located, and the first wiping assembly subsequently wipes the first printhead, without the second printhead being simultaneously wiped by the second wiping assembly.  
           [0011]    According to a further aspect of the invention, an inkjet printing mechanism includes a chassis, a first and a second printhead, and a carriage supported by the chassis for transporting both printheads along a scanning axis. The printing mechanism includes a first wiping assembly located at a first wiping region for wiping the first printhead when the carriage moves to the first wiping region. The printing mechanism further includes a second wiping assembly located at a second wiping region for wiping the second printhead when the carriage moves to the second wiping region. According to the invention, the first and second wiping regions are separated by a substantial distance from each other along the scanning axis. Therefore, the two printheads are wiped independently by the two wiping assemblies respectively.  
           [0012]    The printing mechanism generally has a printing area extending along the scanning axis, within which area ink drops are projected from at least one of the printheads onto a media sheet for imprinting images on it. Preferably, the first and second wiping assemblies are located at the opposite ends out of the printing area. The printing mechanism also has a sweeping area extending along the scanning axis, within which area the printheads travel during printing operations. Ideally, the wiping assemblies are located within the sweeping area for minimizing a width of the printing mechanism.  
           [0013]    Other aspects and advantages of the invention will become apparent from the following detailed description in conjunction with the accompanying drawings; the description illustrates by way of example the principles of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a fragmented, partially schematic, perspective view of an exemplary embodiment of the present invention of an inkjet printing mechanism;  
         [0015]    [0015]FIG. 2 is a perspective view illustrating an exemplary embodiment of the present invention of a wiper mechanism that can be used in the printing mechanism of FIG. 1;  
         [0016]    [0016]FIG. 3A is a top plan view illustrating the position of a conventional wiper assembly relative to a printing area in a conventional printing mechanism; and  
         [0017]    [0017]FIG. 3B is a top plan view illustrating the positions of the wiper assemblies of FIG. 2 relative to the printing area. 
     
    
     DETAILED DESCRIPTION  
       [0018]    For convenience, the concepts of the present invention are illustrated in the environment of an inkjet printer  100 , while it is understood that the present invention as illustrated by the exemplary embodiment can also be used in other inkjet printing mechanisms such as facsimile machines and copiers.  
         [0019]    The typical inkjet printer includes a chassis  102  surrounded by a housing or casing enclosure  104 .  
         [0020]    The printer  100  also has a printer controller, illustrated schematically as a microprocessor  120 , that receives instructions from a host device, typically a computer, such as a personal computer (not shown), and manages different operations of different components of the printer  100 .  
         [0021]    A carriage guide rod  116  is supported by the chassis  102  to slidably support an inkjet carriage  107  for travel back and forth along a scanning axis  118  defined by the guide rod  116  across a printing area  106  within which images are imprinted onto media sheets. A conventional carriage propulsion system may be used to drive the carriage  107 , including a position feedback system, which communicates carriage position signals to the controller  120 . For instance, a carriage drive gear and DC motor assembly (not shown) may be coupled to drive an endless belt (not shown) secured in a conventional manner to the carriage  107 , with the motor operating in response to control signals received from the printer controller  120 . To provide carriage positional feedback information to the printer controller  120 , an optical encoder reader (not shown) may be mounted to the carriage  107  to read an encoder strip (not shown) extending along the path of carriage travel.  
         [0022]    In the printing area  106 , the media sheet receives ink from an inkjet cartridge, such as a black ink cartridge  108  and/or a color ink cartridge  110 . The cartridges  108 ,  110  are also often called “pens” by those in the art and are typically contained in the carriage  107 . The illustrated color pen  110  is a tri-color pen, although in some embodiments, a set of discrete monochrome pens may be used. Furthermore, for the purpose of this description, the color pen  110  is defined to be located on the right side of the black pen  108  as shown in FIG. 1.  
         [0023]    The illustrated pens  108 ,  110  each include a reservoir for storing a supply of ink. The pens  108 ,  110  also have printheads  112 ,  114  respectively, each of which has an orifice plate with a plurality of nozzles formed therethrough in a manner well known to those skilled in the art. Ink drops are ejected from the nozzles to the media sheet during printing operations. The illustrated printheads  112 ,  114  are thermal inkjet printheads, although other types of printheads may be used, such as piezoelectric printheads.  
         [0024]    Other components are arranged within the casing  104  for handling media sheets and imprinting images on the media sheets. A detailed description of the various printer components and their function is not provided herein, since they are generally understood by those with ordinary skill in the art.  
         [0025]    The carriage  107  can be propelled along the guide rod  116  into a left and a right wiping region, as indicated generally by arrows  122  and  124 , located within the interior of the casing  104  for independently wiping the printheads of the black pen  108  and the color pen  110  respectively. The wiping regions  122 ,  124  are separated by a substantial distance from each other since they are located on the two opposite sides of the printer respectively.  
         [0026]    In FIG. 2, a left and a right wiping assembly  200 ,  202  are respectively positioned at the left and right wiping regions  122 ,  124  for independent wiping of the printheads  112 ,  114  of the black and color pens  108 ,  110  respectively. The wiping assemblies  200 ,  202  are positioned at the opposite ends out of the printing area  106  along the scanning axis  118  (see FIG. 1), and within the printing area ink drops are ejected from the printheads onto a media sheet during printing operations.  
         [0027]    When the printhead  114  of the color pen  110  needs wiping, supported by the carriage  107  as shown in FIG. 1, both pens move to the right wiping region  124 , where the color pen  110  is positioned above the right wiping assembly  202 . Subsequently, driven by a motor  214  through a gear train  212 , the right wiping assembly  202  moves back and forth substantially perpendicularly to the scanning axis  118  (see FIG. 1) and wipes the printhead  114  of the color pen  110  accordingly. Note that when the pens  108 ,  110  stay in the right wiping region  124 , the left wiping assembly  200  is not in contact with the printhead  112  of the black pen  108 , since it is separated from the right wiping region  124  by the printing area  106 .  
         [0028]    When the printhead  108  of the black pen  108  needs wiping, however, both pens move to the left wiping region  122  instead. At this time, the left wiping assembly  200  wipes the printhead  108  of the black pen  112 , with the right wiping assembly  202  not in contact with the printhead  114  of the color pen  110 .  
         [0029]    A servicing algorithm executed by the controller  120  (see FIG. 1) determines which printhead needs wiping, to which wiping region the carriage moves, and what amount of wiping is needed. A detailed description of such a mechanism is not provided herein, since it is generally understood by those with ordinary skill in the art. For instance, U.S. Pat. No, 6,126,265, assigned to the present assignee, Hewlett-Packard Company, discloses a service station control procedure and is herein incorporated by reference.  
         [0030]    In this way, independent wiping of individual printhead is achieved.  
         [0031]    In FIG. 2, a right wiper gear  206  and a left wiper gear  208  are respectively mounted on two sides of a rotatable wiper shaft  210  for respectively driving the left and right wiping assemblies. The wiper shaft  210  is rotated during wiping operations by the motor  214  through the gear train  212  and a gear  222 . The gear  222  is mounted on one side of the wiper shaft  210  to engage with the gear train  212  and receive the driving forces from the motor  214 . Additionally, each wiping assembly  200 ,  202  has a flexible wiper blade  218  mounted on a platform (not shown), which is slidable along a guide track  216  mounted to the chassis  102 . Each platform is connected to a tooth rack  220 , which is engaged with one of the wiper gears  206 ,  208  through the engagement between the teeth of the gear and the rack. In this way, when the wiper shaft  210  is rotated, both wiper blades  218  are moved back and forth substantially perpendicularly to the scanning axis  118  (see FIG. 1) so that one of the printheads, which is in contact with one of the wiper blades  218 , can be wiped.  
         [0032]    As shown in FIG. 3B, the printing area  106  extends along the scanning axis  118 , and within the printing area ink drops are ejected from printheads onto a media sheet during printing operations. In addition, the left pen, i.e., the black pen  108  in the exemplary embodiment, needs to travel out of the left edge  224  of the printing area  106  to allow the color pen  110  to print onto the left of the media sheet. Similarly, the right pen, namely the color pen  110 , needs to travel out of the right edge  226  of the printing area  106 . A sweeping area (not shown) is defined by the furthest positions along the scanning axis  118  that the pens can travel during printing operations. Such a sweeping area affects the width of the printer along the scanning axis  118 .  
         [0033]    [0033]FIG. 3A is a simplified top plan view of an inkjet printer  300  that has a left pen  303  and a right pen  305  and uses a conventional wiping assembly  301  located at a wiping region  307  on the right side of the printer. Conventionally, such a wiping assembly is positioned out of the printing area  106 , and both pens  303 ,  305  need to move out of the printing area and to be stationed above the wiping assembly  301  for wiping. Therefore, in FIG. 3A, the width of the printer  300  along the scanning axis  118  is approximately the width of the sweeping area (not shown) plus the width of the right pen  305 .  
         [0034]    In the printer  100  of the present application of FIG. 3B, the wiping assemblies  200 ,  202  are located out of the printing area  106  but each in close proximity to the left and right edges of the printing area respectively so that the wiping assemblies are within the sweeping area (not shown). Furthermore, the left and right wiping assemblies  200 ,  202  are aligned with the left and right pens  108 ,  110  respectively, when during the printing operations the pens travel to the left and right edges of the sweeping area (not shown). By limiting the width of the wiping assemblies to be not more than the width of the pens, the width of the printer can be limited to approximately the width of the sweeping area (not shown). Compared to the conventional printer of FIG. 3A with a conventional wiping assembly positioned in a conventional wiping region, the width of the exemplary printer of the present application as shown in FIG. 3B is reduced by approximately the width of one pen.