Abstract:
In a method for independently wiping a first and a second printhead of an inkjet printing mechanism, a first and a second wiping assembly separated from each other are provided in the printing mechanism. Furthermore, the wiping of the first printhead by the first wiper and the wiping of the second printhead by the second wiper are separately controlled.

Description:
This invention relates generally to inkjet printing mechanisms, and in particular to techniques for maintaining inkjet printheads at its optimal conditions. 
     Inkjet printing mechanisms such as thermal inkjet printers and piezoelectric printers 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. 
     To clean and protect the printhead, typically a conventional “wiping 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. 
     For a printing mechanism having more than one printhead, all the printheads move to the wiping region together. Conventionally, several flexible wiper-blades in close proximity to each other are provided in the conventional wiper assembly to wipe all the printheads simultaneously. 
     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. 
     Therefore, there is a need for an improved printhead wiping mechanism which optimizes the amount of wiping for different printheads. 
     SUMMARY 
     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 mechanism. Furthermore, the wiping of the first printhead by the first wiper and the wiping of the second printhead by the second wiper are separately controlled. 
     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. A first and a second wiper are movable to a wiping region in the printing mechanism and correspond to the first and second printheads respectively. Furthermore, each wiper is individually adjustable. During wiping operations, both printheads are moved to the wiping region facing the wipers. In addition, a character of the first wiper, that is, its position relative to its corresponding printhead, is adjusted prior to wiping of any printheads. Subsequently, both wipers are driven along a wiping axis such that the second printhead is wiped by the second wiper, with the first printhead not being simultaneously wiped by the first wiper due to this adjustment prior to the wiping operation. 
     According to a further aspect of the invention, an inkjet printing mechanism includes a chassis, a pair of printheads, a pair of wipers movable to a wiping region for wiping the printheads, and a carriage that transports both printheads to the wiping region facing the wipers. Each wiper corresponding to one of the printheads respectively, and each wiper is individually adjustable such that each printhead can be independently wiped with the other printhead not being simultaneously wiped by its corresponding wiper. 
     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 
     FIG. 1 is a fragmented, partially schematic, perspective view of an inkjet printing mechanism having an exemplary embodiment of the present invention; 
     FIG. 2 is a fragmented perspective view partially illustrating a service station of FIG. 1, in which an exemplary embodiment of the present invention of a wiping mechanism is embedded; 
     FIG. 3 is a perspective view of the wiping mechanism in FIG. 2; 
     FIG. 4 is a cross section view along A-A′ of the wiping mechanism in FIG. 3; 
     FIG. 5A is a cross section view along D-D′ of a left cam in FIG. 4; and 
     FIG. 5B is a cross section view along E-E′ of a right cam in FIG.  4 . 
    
    
     DETAILED DESCRIPTION 
     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 printing mechanisms using ink printing technologies such as facsimile machines and copiers. 
     The typical inkjet printer includes a chassis  102  surrounded by a housing or casing enclosure  104 . 
     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 . 
     A carriage guide rod  116  is supported by the chassis  102  to support an inkjet carriage  107  for reciprocating sliding motion along a scanning axis  118 . The scanning axis  118  is defined by the guide rod  116  extending 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. 
     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 tricolor 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 left side of the black pen  108  as shown in FIG.  1 . 
     Each of the illustrated pens  108 ,  110  includes a reservoir for storing a supply of ink. The pens  108 ,  110  also have a printhead  112 ,  114 ; each printhead  11 ,  114  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, such as piezoelectric printheads, may be used. Preferably, the outer surface of the printheads  112 ,  114  lies in a common printhead plane, which may serve as a reference place. 
     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. 
     The carriage  107  is propelled along the guide rod  116  into a servicing region  122  located within the interior of the casing  104 . The servicing region houses a service station  124 , which provides various conventional printhead servicing functions. Only wiping of the printheads is discussed in the current application. A detailed description of other functions is not provided herein, since it is generally understood by those with ordinary skill in the art. 
     In FIG. 2, an exemplary wiping mechanism  202  in the service station  124  is provided; the wiping mechanism  202  includes a left and a right wiper  204 ,  206  adjacent to each other. The left and right wipers are positioned in the service station  124  so that they are to be in contact with the printheads of the color pen  110  and the black pen  108  respectively when the carriage has moved to the servicing region  122  for servicing (see FIG.  1 ). Wiping of the printheads is accomplished by back-and-forth movements of the wipers in the service station  124  in the direction along a wiper axis  208  such that a wiper end  318 ,  320  describes a plane which is parallel to the printhead plane. 
     Furthermore, each wiper is adjustable in the vertical, or Z direction, which is perpendicular to the printhead plane as shown by the XYZ coordination axis  126  in FIGS. 1 and 2. In this way, each wiper can be individually spaced from its respective printhead in the Z direction. As a result, independent wiping of each printhead can be achieved. Specifically, for example, when only the color pen printhead  114  in the carriage  107  as shown in FIG. 1 needs wiping, both pens move to the servicing region  122 . Simultaneously, the controller  120  as shown in FIG. 1 controls to space, or position, the right wiper  206  from the black pen printhead  112  in the vertical, or Z direction. Due to such a spacing, during subsequent back-and-forth movements of the wipers along the wiper axis  208 , the right wiper  206  is not in contact with the black pen printhead  112 . As a result, the black pen printhead  112  is not wiped during this wiping routine. 
     The controller  120  of FIG. 1 records the status of each wiper and therefore is capable of determining which wiper needs adjusting in the Z direction. For example, consider that only the color pen printhead  114  (see FIG. 1) is wiped in the preceding wiping, or servicing, routine. In a succeeding servicing routine, if both printheads need wiping, the controller  120  controls driving the right wiper  206  towards the printhead plane in the Z direction so that the right wiper  206  can engage with the black pen printhead  112  during the succeeding servicing routine. Meanwhile, the left wiper remains in a position to be in contact with the color pen printhead  114 . However, if only the black pen printhead  112  needs wiping during the succeeding servicing routine, in addition to the adjustment of the right wiper, the controller  120  also needs to position or space the left wiper  204  from the color pen printhead  114  in the vertical or Z direction, 
     Different mechanisms can be used to adjust the spacing or position of the wipers in the Z direction. Shown in FIGS. 3 and 4 is one exemplary adjusting mechanism  300  used in the exemplary embodiment of the wiping mechanism  202  in FIG.  2 . 
     In FIGS. 3 and 4, each wiper  204 ,  206  has a flexible wiper blade  308 ,  312  for wiping printheads. Each wiper blade rests atop a left and a right platform  310 ,  314 , respectively, and both platforms are movable in the Z direction. By adjusting the relative position of each platform in Z direction, each wiper can be adjusted in the Z direction to engage or to not engage with their respective printhead during a wiping operation. 
     The adjusting mechanism  300  of the wiping mechanism  202  includes a left and a right cam  304 ,  306  that are mounted to and rotate together with a cam shaft  302 . The shaft  302  is rotatably mounted to the service station frame  124  (see FIG. 2) of the service station. Each cam is positioned below and designed to be in contact with one of the platforms for adjusting the wipers  204 ,  206  in the Z direction. A spring (not shown) with two ends attached to one of the platforms and passing through the cam shaft  302  can be used for biasing the cam shaft towards the platforms. In this way, each cam can be held tightly in contact with its respective platform at a respective contacting point  322 ,  324 . 
     Since the cam shaft  302  is mounted to the service station frame, the spacing in the Z direction between the shaft  302  and the printhead plane is fixed. Furthermore, the length of the wiper blades and the thickness of the platform in the Z direction are also fixed. Thus, the spacing in the Z direction between the wiping end  318 ,  320  of each wiper blade and its respective printhead is determined by the distance between the axis  326  about which the cam shaft  302  rotates and the respective cam-platform contacting point  322 ,  324 . By adjusting the spacing between the axis and the respective contacting point, each wiper position is adjusted in the Z direction. 
     In the exemplary embodiment, desired adjustments of the spacing between the axis and the contacting points are achieved by the design of the profile of the cam and the rotation of the cam shaft. For a printer having two pens and two respective wipers like the exemplary embodiment, the cam shaft is designed to rotate among three positions. Accordingly, each cam provides three points along its profile for contacting its respective platform. Since both cams are mounted to the cam shaft, each cam alternatively contacts its respective platform at one of these three points when the cam shaft rotates among the three positions. By pre-selecting the distance, or spacing, between each point and the center of the cam, desired adjustments of the wiper position in the Z direction are achieved. 
     Both cams have a common profile, but they are mounted to the cam shaft with different orientations. A cross section view of the profile of the left cam along line D—D′ (see FIG. 4) is shown in FIG. 5 a ; a cross section view of the profile of the left cam along line E—E′ (see FIG. 4) is shown in FIG. 5 b . Each cam has a center O, O′ through which the axis  326  (see FIG. 4) of the cam shaft passes, and provides contacting points along its profile. 
     Take the left cam for example. The left cam provides three points along its profile, namely, A, B and C. The spacing between point A and the center O is the same as the spacing between point B and center O, but larger than the spacing between point C and center O. When the left cam is in contact with the left platform at point A or B, the left wiper is in a position to engage the color pen printhead  114  during wiping operations. However, if the left cam is in contact with the left platform at its point C, due to the relatively short spacing between point C and its center O, the left platform is spaced relatively far away from the printhead in the Z direction. Consequently, a gap (not shown) in the Z direction is created between the left wiper and the color pen printhead  114 , and this left pen will not be wiped during the succeeding wiping operation. 
     Similarly, the right cam provides three contacting points A′ B′ and C′. The spacing between these points and its center O′ is about the same as the spacing between the contacting points A, B and C of the left cam and its center O. Adjusting of the right cam in the Z direction is similarly achieved by selecting at which point the right cam contacts the right platform. 
     Both cams rotate together with the cam shaft. In addition, the cams are oriented so that the right cam contacts the right wiper at point A′ when the left cam contacts the left wiper at point B, at point B′ when the left cam contacts the left wiper at point C, and at point C′ when the left cam contacts the left wiper at point A. 
     If the printer decides that only one of the printheads, for example, the color pen printhead needs wiping during a wiping operation, the controller controls to rotate the cam shaft to the extent such that the left cam comes into contact with the left platform at point A. As previously discussed, the right cam will be in contact with the right platform at point C′ at the same time. Therefore, during wiping operations, the left wiper engages the color pen printhead, while the right wiper does not engage the black pen printhead. In this way, independent wiping of the color pen printhead is achieved. This situation is illustrated in FIG.  4 . 
     In the case when only the black pen printhead needs wiping, the controller controls rotating the cam shaft so that the left cam comes into contact with the left platform at point C. At this time, the right cam will be in contact with the right platform at point B′, and independent wiping of the black pen printhead is achieved. 
     If both printheads need wiping, the controller controls rotating the cam shaft so that the left cam comes into contact with the left platform at point B. This time, the right cam is in contact with the right platform at point A′. Both printheads will be wiped during the subsequent wiping operation. 
     If neither printhead needs wiping, no movement of the carriage is required. 
     Rotation of the cam shaft and the cams can be accomplished wtih a DC motor (not shown) coupled to the cam shaft. By controlling the DC motor, the cam shaft and the cams can be rotated to the desired positions. Other mechanisms, for example, a mechanism to transfer the linear movements of the carriage along the scanning axis  118  into the rotation of the cam shaft about its axis  326 , can also be used as an alternative to the use of additional electrical components. 
     Alternatives can be made to the above exemplary embodiments. For example, instead of the cams and cam shaft, a pair of motors each coupled to one of the platforms can be used for adjusting the wipers in the Z direction to the desired positions. 
     In addition, each printhead defines a printhead plane; these planes are parallel to each other but may be offset in the Z direction. In that case, the profiles of the respective cams may need to be adjusted accordingly. 
     Furthermore, only a two-pen printer is discussed in the exemplary embodiment. It is understood that the claimed invention is also suitable for other inkjet printing mechanisms having more than two pens, though certain further modifications may be needed. For example, more cams may be needed for the increase of printheads if a similar adjusting mechanism is used. Also, the cam profile combination needs to be redesigned.