Abstract:
A printhead module includes a substrate and a head mount. The substrate includes a bottom surface having a plurality of nozzles formed therein and a top surface on a side of the substrate opposite the bottom surface. The substrate includes a plurality of actuators. Each actuator of the plurality of actuators is configured to cause a fluid to be ejected from a nozzle of the plurality of nozzles. The head mount is secured to the substrate and extends over the top surface of the substrate. The head mount includes a first side surface extending upwardly from the bottom surface and a groove formed in the first side surface. The groove is sized and shaped to cause fluid on the first side surface to be drawn by capillary action into the groove.

Description:
PRIORITY CLAIM 
     This application claims the benefit of U.S. Provisional Patent Application No. 61/641,687, filed May 2, 2012. The entire contents of the foregoing are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     This disclosure relates to a print head module having a groove for waste fluid. 
     BACKGROUND 
     A fluid ejection system, for example, an ink jet printer, typically includes an ink path from an ink supply to an ink nozzle assembly that includes nozzles from which ink drops are ejected. Ink is just one example of a fluid that can be ejected from a jet printer. Ink drop ejection can be controlled by pressurizing ink in the ink path with an actuator, for example, a piezoelectric deflector, a thermal bubble jet generator, or an electrostatically deflected element. Atypical printhead module has a line or an array of nozzles with a corresponding array of ink paths and associated actuators, and drop ejection from each nozzle can be independently controlled. In a so-called “drop-on-demand” printhead module, each actuator is fired to selectively eject a drop at a specific location on a medium. The printhead module and the medium can be moving relative one another during a printing operation. 
     In some systems, multiple printhead modules can be positioned in a row across the medium and perpendicular to the direction of travel of the medium in order to provide single-pass printing on the medium. In addition, multiple printhead modules can be positioned along the direction of travel of the medium to increase overall rate of printing output or to print multiple colors of ink onto the medium. 
     SUMMARY 
     During operation or maintenance of the fluid ejection system, ejected fluid can become trapped and accumulate in a gap between adjacent printhead modules. Without being limited to any particular theory, fluid can leak from the nozzles in the printhead, or fluid ejected from the printhead can be reflected back onto the printhead. The presence of such fluid is generally undesirable. For example, the fluid can drip, leaving undesired large spots of ink on the medium. In addition, the fluid can dry, creating debris or particulates. A technique to address these problems is to provide the print head module with a groove that can carry away waste fluid, e.g., by capillary action. 
     In one aspect, a printhead module includes a substrate and a head mount. The substrate includes a bottom surface having a plurality of nozzles formed therein and a top surface on a side of the substrate opposite the bottom surface. The substrate includes a plurality of actuators. Each actuator of the plurality of actuators is configured to cause a fluid to be ejected from a nozzle of the plurality of nozzles. The head mount is secured to the substrate and extends over the top surface of the substrate. The head mount includes a first side surface extending upwardly from the bottom surface and a groove formed in the first side surface. The groove is sized and shaped to cause fluid on the first side surface to be drawn by capillary action into the groove. 
     Implementations of this aspect may include one or more of the following features. For example, the head mount may include a second side surface extending upwardly from the bottom surface. The second surface may be at a non-zero angle to the first side surface and may be connected to the first side surface at a first corner. The groove may extend around the corner onto the second side surface. The head mount may include an upper surface substantially parallel to the bottom surface. The first side surface may extend from the upper surface to the bottom surface. The groove may have a first end on the second side surface. The groove may extend along an entire length of the first side surface. The head mount may include a third side surface extending upwardly from the bottom surface. The third side surface may be at a non-zero angle to the first side surface and may be connected to the first side surface at a second corner at a far end of the first side surface from the first corner. The groove may extend around the second corner onto the third side surface. The groove may have a second end on the third side surface. The second side surface may be parallel to the third side surface. The printhead module may further include an absorbent material in contact with a portion of the groove on the second side surface. The printhead module may further include an absorbent material in contact with a portion of the groove. The first side surface may include a first outer surface, a second outer surface above and recessed relative to the first outer surface, and a ledge surface connecting the first outer surface to the second outer surface. The ledge surface may have a width between 0.1 and 1 mm. The ledge surface may have a width of about 0.25 mm. A first edge between the second outer surface and the ledge surface may have a first radius of curvature. A second edge between the ledge surface and the first outer surface may have a second radius of curvature greater than the first radius of curvature. A first edge between the second outer surface and the ledge surface may have a first radius of curvature less than 0.1 mm. A second edge between the ledge surface and first outer surface may have a second radius of curvature greater than 0.5 mm. The head mount may have substantially the same coefficient of thermal expansion as the substrate. 
     In another aspect, a printhead assembly includes a plurality of printhead modules arranged in a row. Each printhead module of the plurality of printhead modules includes a substrate and a head mount. The substrate includes a bottom surface having a plurality of nozzles formed therein and a top surface on a side of the substrate opposite the bottom surface. The substrate includes a plurality of actuators, each actuator of the plurality of actuators configured to cause a fluid to be ejected from a nozzle of the plurality of nozzles. The head mount is secured to the substrate and extends over the top surface of the substrate. Adjacent printhead modules of the plurality of the printhead modules are separated by a gap. Each head mount from the adjacent printhead modules includes a side surface extending upwardly from the bottom surface and facing the gap. The side surface of each head mount includes a groove sized and shaped to cause fluid in the gap to be drawn by capillary action into the groove. 
     Implementations of this aspect may include one or more of the following features. For example, a width of the gap may be 0.3 mm or less. Side surfaces of adjacent printhead modules may be substantially parallel. Each head mount from the adjacent printhead modules may include a second side surface extending upwardly from the bottom surface. The second side surface may be at a non-zero angle to the first side surface and may be connected to the first side surface at a first corner. The groove may extend around the corner onto the second side surface. Second side surfaces of adjacent printhead modules may be substantially coplanar. The printhead assembly may further include an absorbent material in contact or configured to move into contact with a portion of the groove on the second side surface of each head mount of the adjacent printhead modules. The absorbent material may include a laterally extending main portion that contacts the portion of the groove on the second side surface of each head mount portion, and a tapered portion projecting downwardly from the laterally extending main portion. The printhead assembly may further include a motor coupled to the absorbent material and a controller configured to cause the motor to move the absorbent material into contact with the portion of the groove on the second side surface of each head mount. 
     The details of one or more implementations are set forth in the accompanying drawings and the description below. Other aspects, features and advantages will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of a printhead module. 
         FIG. 2A  is a close-up perspective view of multiple printhead modules from  FIG. 1  arranged side by side. 
         FIG. 2B  is a close-up perspective view of the printhead module. 
         FIG. 2C  is a partial cross-sectional view of  FIG. 2B . 
         FIGS. 3A and 3B  are cross-sectional views of grooves between the printhead modules. 
         FIG. 4A  is a side view of an implementation of the printhead module having a fluid wicking bar. 
         FIG. 4B  is a top view of another implementation of the printhead module having the fluid wicking bar. 
     
    
    
     Like reference symbols in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a printhead module  10  includes a head mount  12  and a flexible circuit  14  that carries various electrical signals to a substrate  18 . The print module  10  also includes a housing  16  that is coupled to an upper surface of the head mount  12  and the substrate  18 , e.g., a microfabricated die, that is coupled to a lower portion of the head mount  12 . The substrate  18  includes a plurality of nozzles  42  (see  FIG. 2C ) on a bottom surface and a plurality of actuators  40  (see  FIG. 2C ) configured to cause drops of fluid, such as ink, to be ejected from the plurality of nozzles. During operation, in order to create a desired image, drops are selectively ejected from the plurality of nozzles while the printhead module  10  moves relative to a medium to be imprinted, e.g., paper. As discussed in detail below, one or more waste fluid grooves  20   a, b  can be formed in a side surface of the head mount  12  to draw in fluid by capillary action. 
     As shown in  FIG. 2A , a plurality of printhead modules  10  can be mounted side by side on a bar (not shown). In some implementations, the printhead modules  10  can be arranged in a row perpendicular to the direction of motion of the medium. During a maintenance process or, in some cases, during normal printing operation, fluid can enter a gap  22  between adjacent printhead modules  10  and become trapped. For example, wiping the bottom surface of the substrate  18  with a blade during the maintenance process can direct excess fluid into the gap  22  where the fluid is subsequently trapped, e.g., due to capillary forces. Such trapped fluid can be difficult to remove due to the typically small size of the gap  22  and can cause damage to the module  10 , for example, if the trapped fluid contacts application-specific integrated circuits (ASICs) or electrical traces of the module  10 . In some cases, the trapped fluid can unexpectedly escape the gap and drip onto the printing medium. 
     Referring to  FIGS. 2A-2C , the head mount  12  includes an upper surface  46  that is substantially parallel to the bottom surface of the substrate  18 , a first side surface  24 , a fourth side surface  26  that is on an opposite side of the head mount  12  from the first side surface  24  and generally parallel to the first side surface  24 , and a second side surface that provides a front surface  28 . The side surfaces  24 ,  26  are connected, respectively, to opposite ends of the front surface  28  at corners  30   a, b . The side surfaces  24 ,  26  are oriented at non-zero angles of, for example, 80 degrees and 110 degrees, respectively, relative to the front surface  28 . In some cases, the side surfaces  24 ,  26  are oriented 90 degrees relative to the front surface  28 . Additionally, the head mount  12  can include a third side surface that provides a back surface  29  that is on an opposite side of the head mount  12  from the front surface  28  and is generally parallel to the front surface  28 . The side surfaces  24 ,  26  are connected, respectively, to opposite ends of the back surface  29  at corners  32   a, b . The side surfaces  24 ,  26 , front surface  28 , and back surface are connected to and oriented substantially perpendicularly to the upper surface  46 . 
     As mentioned above, a groove  20   a  can be formed in the side surface  24  of the head mount  12 . Similarly, a second groove  20   b  can be formed in the side surface  26 . In some cases, one or both of the grooves  20   a, b  can extend along an entire length of side surfaces  24 ,  26 , respectively. Additionally, the groove  20   a  can extend around the corners  30   a ,  32   a  onto the front and back surfaces  28 ,  29 , respectively, terminating at groove ends  34   a ,  36   a  (see  FIG. 4B ). Similarly, the groove  20   b  can extend around the corners  30   b ,  32   b , onto the front and back surfaces  28 ,  29 , respectively, terminating at groove ends  34   b ,  36   b  (see  FIG. 4B ). Various methods may be used to form the grooves  20   a, b  in the head mount  12  including, but not limited to, machining, molding, or die casting. In some cases, the grooves  20   a, b  can be formed by attaching additional materials around the head mount  12 . As discussed further below, the head mount  12  can be made from a wide range of suitable materials, for example, moldable ceramic. 
     Referring particularly to  FIG. 2C , the substrate  18  is secured to the lower portion of the head mount  12  such that the head mount  12  extends over a top surface  38  of the substrate  18 . The top surface  38  of the substrate  18  includes the plurality of actuators  40  that can force fluid to be ejected from the plurality of nozzles  42  that are positioned at the bottom surface  44  of the substrate  18 . The substrate  18  can be secured and positioned relative to the head mount  12  such that the side surface  24 ,  26  extend from the upper surface  46  of the head mount  12  to the bottom surface  44  of the substrate  18 . Additionally, the substrate  18  can be oriented relative to the head mount  12  such that the bottom surface  44  of the substrate  18  is generally parallel to the upper surface  46  of the head mount  12 . 
     Referring again to  FIG. 2A  and further to  FIGS. 3A and 3B , the gap  22  is formed between side surfaces  24 ,  26  of adjacent head mounts  12 . In some cases, a width, W G , of the gap  22  can be less than 0.3 mm ( FIG. 3A ). 
     As shown in the close-up views of the gap region in  FIGS. 3A and 3B , grooves  20   a, b  are formed, respectively, in the side surfaces  24 ,  26 . The side surface  24 ,  26  having the groove  20   a, b  consequently has a lower outer surface  50  and an upper outer surface  52  that is recessed relative to the lower outer surface  50 . A ledge surface  54  is positioned between and oriented generally perpendicular to the lower and upper outer surfaces  50 ,  52 . The ledge surface  54  connects to the upper outer surface  52  at an inner edge  56  and connects to the lower outer surface  50  at an outer edge  58 . The portion of the groove  20   a, b  that extends to the front and/or back surfaces of the head mount  12  can be configured as described above with respect to the side surface  24 ,  26 . 
     Various dimensions associated with the groove  20   a, b  can be selected to aid in wicking accumulated fluid out of the gap  22  and into the inner edge  56 . In particular, the ledge surface  54  can have a width, W L , of between 0.1 and 1 mm, for example 0.25 mm. A radius of curvature, R 2 , of the outer edge  58  is greater than a radius of curvature, R 1 , of the inner edge  56 . For example, R 1  can be less than 0.1 mm, and R 2  can be greater than 0.5 mm. Dimensions of R 1  and R 2  can be selected such that the accumulated fluid in gap  22  flows along the outer edge  58  and subsequently becomes trapped in the inner edge  56 , where a relative sharpness of a corner region at the inner edge  56  can help the fluid to form a meniscus in the region. In some cases, the inner edge  56  can form a sharp corner that forms an acute, right, or obtuse angle. 
     Referring particularly to  FIG. 3B , a flow of accumulated fluid from the gap  22  into grooves  20   a, b  is illustrated. Within the gap  22 , accumulated fluid can form a meniscus  60  and travel upward, as indicated by arrow A, due to capillary forces. Upon coming in contact with the outer edge  58 , the fluid subsequently flows along the outer edge  58 , along the ledge surface  54 , and into the inner edge  56 , as indicated by arrows B and C. The fluid can flow into one or both of the opposing grooves  20   a, b  and form a meniscus  62  as shown and as discussed above. Wicking away of fluid from the gap  22  into the grooves  20   a, b  as described above can prevent accumulation of fluid in the gap  22 . In some cases, fluid can enter the grooves  20   a, b  when the gap  22  as described above is not present, for example, when there is only one printhead module  10 . 
     Referring also to  FIG. 2B , due to capillary forces, fluid that becomes trapped in the groove  20   a, b  can travel along a length of the groove  20   a, b  toward the groove ends  34   a, b  located on the front surface  28  and/or toward the groove ends  36   a, b  located on the back surface  29 . Fluid that accumulates at the groove ends  34 ,  36  can then be removed away from the head mount  12  as described below. 
     In some implementations, as illustrated in  FIG. 4A , a fluid wicking bar  70  can be placed against the front surface  28  of the head mount  12  to contact the groove ends  34   a, b  ( FIG. 4B ). The fluid wicking bar  70  has a main portion  71  that extends laterally across the front surface  28 . When multiple head mounts  12  are placed side by side, as shown in  FIG. 4A , such that their front surfaces  28  are substantially coplanar, the fluid wicking bar  70  can be positioned to simultaneously come in contact with the groove ends  34   a, b  on each head mount  12 . Once the fluid wicking bar  70  comes in contact with fluid that has accumulated in the groove ends  34   a, b , the fluid wicking bar  70  can wick away the fluid along a length of the main portion  71  toward a drainage end  72 . 
     All or portions of the fluid wicking bar  70  can be made from an absorbent material that is configured and adapted to transport fluid away from the head mount  12  and toward the drainage end  72 . For example, the fluid wicking bar  70  can be made from felt, cotton, or the like. Additionally, the drainage end can have a tapered portion  74  that projects downwardly from an end of the main portion  71 . In operation, the downward orientation and configuration of the tapered portion  74  can create a pressure gradient that drives fluid away from the main portion  71  and toward a drainage tip  75 . Alternatively, or additionally, the fluid wicking bar  70  can include channels through which fluid can flow. In some cases, a vacuum can be created in the fluid wicking bar  70  to remove fluid away from the front surface  28  and may or may not include the drainage end  72 . 
     Referring to  FIG. 4B , in an alternative implementation, a motor  78  and a motor controller  80  are configured and adapted to move the fluid wicking bar  70  in and out of contact with the front surface  28  of the head mount  12 . For example, the motor  78  can be coupled to the fluid wicking bar  70  via a linkage  82  to move the fluid wicking bar  70  in a direction indicated by arrow D. When the fluid wicking bar  70  is not in contact with the portion of the groove  20   a, b  on the front surface  28 , fluid from the gap  22  ( FIG. 4A ) can continue to accumulate, for example, at the groove ends  34   a, b . When the fluid wicking bar  70  is moved by the motor  78  to come in contact with the accumulated fluid at the groove ends  34   a, b  the accumulated fluid can be wicked away toward the drainage portion  72  as discussed above. In some cases, the fluid wicking bar  70  can additionally or alternatively be positioned against the back surface  29  of the head mount  12  to remove fluid from the portion of the groove  20   a, b  on the back surface  29 . 
     In some implementations, as mentioned above and referring again to  FIG. 2C , the head mount  12  can be made from a variety of suitable materials including, but not limited to, moldable ceramic. To reduce warping and stress at bond joints between the head mount  12  and the substrate  18 , a material used in the head mount  12  can have a coefficient of thermal expansion (CTE) that is similar to the CTE of the substrate  18 , which can be made from, for example, silicon. Additionally, the material of head mount  12  can have a homogeneous CTE such that the head mount  12  expands and contracts uniformly in all directions. 
     A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made. For example, the configuration and dimensions of the groove  20   a, b  can vary along a length of the groove  20   a, b . As another example, each head mount  12  can have an integrated element for removing fluid accumulated at the end portions of the groove  20   a, b . The groove need not extend around the corners. There can be only a single groove on the side surface. Accordingly, other implementations are within the scope of the following claims.