Abstract:
A printhead assembly including a printhead module and a mounting structure is described. The printhead module is mounted on a receiving surface of the mounting structure and includes a first edge and a second edge opposite the first edge. The first and second edges extend beyond edges of the receiving surface by a first distance in a first direction and are positioned between featured edges of the mounting structure in a second direction that is substantially perpendicular to the first direction. Each featured edge includes a first feature protruding from the featured edge by a second distance in the first direction, where the second distance is greater than the first distance. The first features extend beyond the first and second edges of the printhead module. Each featured edge includes a recessed second feature configured to receive a first feature of a neighboring mounting structure.

Description:
TECHNICAL FIELD 
     The following description relates to a fluid ejection system for printing. 
     BACKGROUND 
     A fluid ejection system, for example, an ink jet printer, typically includes an ink path from an ink supply to a printhead module 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. A typical 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 one example, a printhead module can include a silicon printhead module and a piezoelectric actuator. The printhead module can be made of silicon etched to define pumping chambers. Nozzles can be defined by a separate substrate (i.e., a nozzle layer) that is attached to the printhead module. The piezoelectric actuator can have a layer of piezoelectric material that changes geometry, or flexes, in response to an applied voltage. Flexing of the piezoelectric layer causes a membrane to flex, where the membrane forms a wall of the pumping chamber. Flexing the membrane thereby pressurizes ink in a pumping chamber located along the ink path and ejects an ink drop from a nozzle at a nozzle velocity. The piezoelectric actuator is bonded to the membrane. 
     SUMMARY 
     This invention relates to printing from a fluid ejection system. In general, in one aspect, the invention features a printhead assembly including a printhead module and a mounting structure. The printhead module is mounted on a receiving surface of the mounting structure and includes a first edge and a second edge opposite the first edge where the first and second edges extend beyond edges of the receiving surface by a first distance in a first direction. The first and second edges are positioned between featured edges of the mounting structure in a second direction that is substantially perpendicular to the first direction. The mounting structure includes the receiving surface for mounting the printhead module and the featured edges positioned on either side of the mounting surface in the second direction. Each featured edge includes a first feature protruding from the featured edge by a second distance in the first direction, where the second distance is greater than the first distance, such that the first features extend beyond the first and second edges of the printhead module. Each featured edge further includes a second feature that is recessed from the featured edge and configured to receive a first feature of a neighboring mounting structure. 
     Implementations of the printhead assembly can include one or more of the following features. Each first feature can be configured as a nub and each second feature can be configured as a dimple. In some implementations, each nub protrudes from a featured edge of the mounting structure along an axis that is substantially perpendicular to the featured edge from which the nub protrudes. Each dimple can have a depth extending along an axis that is substantially perpendicular to a featured edge of the mounting structure from which the dimple is recessed. The first features and the second features can be arranged symmetrically or asymmetrically about a central longitudinal axis of the receiving surface. 
     The printhead module can have a substantially rectangular shape. In other implementations, the printhead module has a non-rectangular parallelogram shape and the first and second edges extend beyond the edges of the receiving surface at an angle, where the first distance is the greatest distance by which the first and second edges extend beyond the edges of the receiving surface. 
     The dimensions of the first features and the second features can be such that first features of the mounting structure are received into second features of a second mounting structure when the two mounting structures are positioned adjacent one another, without interfering with the position of the printhead module mounted in the mounting structure relative to a second printhead module mounted in the second mounting structure. In some implementations, the depth of a first feature of the mounting structure is less than a sum of the depth of a second feature of the second mounting structure positioned to receive said first feature, a gap between the printhead module and the second printhead module, the first distance by which the printhead module extends beyond the edge of the mounting structure, and a distance by which the second printhead module extends beyond the edge of the second mounting structure. 
     The mounting structure can include a central portion including the receiving surface on a face of the central portion, and winged portions. The winged portions can flank two opposing sides of the central portion and extend beyond a width of the central portion, where the featured edges are edges on the winged portions. The winged portions can be configured to attach the mounting structure to a fluid ejection system. 
     Implementations of the invention can realize one or more of the following advantages. Providing features along the edge of the mounting structure that extend beyond the exposed edges of the printhead module mounted therein can protect the exposed edges from damage. For example, during an assembly process where the printhead module already mounted within the mounting structure, handling of the printhead module/mounting structure assembly can result in stresses being placed on the exposed edges of the printhead module. However, by providing the features along the edge of the mounting structure, e.g., nubs, the features can absorb the stresses rather than the exposed edges of the printhead module, reducing the risk of damage to the printhead module. In an implementation where the first features are positioned asymmetrically about the central longitudinal axis of the receiving surface for the printhead module (i.e., as a mirror image about the central longitudinal axis, see for example  FIG. 4C ), the mounting structure cannot be inadvertently mounted backwards (i.e., rotated by 180°) onto the frame of a fluid ejection system if being mounted adjacent another mounting structure. That is, when the first features are asymmetrically positioned, they will only mate with second features of an adjacent mounting structure mounted onto the frame when the mounting structure is in one orientation. 
     The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1A  shows a perspective view of a printhead module mounted in a mounting structure. 
         FIG. 1B  shows the mounting structure of  FIG. 1A . 
         FIG. 2  shows a partial plan view of two adjacent printhead modules mounted in adjacent mounting structures. 
         FIG. 3A  shows a partial view of the printhead module and mounting structure of  FIG. 1  resting on a surface. 
         FIG. 3B  shows a printhead module mounted in a mounting structure according to the invention described herein. 
         FIG. 4A  shows a perspective view of the printhead module mounted in the mounting structure shown in  FIG. 3B . 
         FIG. 4B  shows the mounting structure of  FIG. 4A . 
         FIG. 4C  shows an alternative configuration of mounting structure. 
         FIG. 5  shows an enlarged partial view of two adjacent printhead modules mounted in adjacent mounting structures. 
         FIG. 6  shows a plan view of an alternative printhead module mounted in a mounting structure. 
         FIGS. 7A and 7B  show a cross-sectional view of an example printhead module. 
     
    
    
     Like reference symbols in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
       FIG. 1A  shows a simplified representation of a printhead module  106  mounted in a mounting structure  102 . The printhead module is typically formed of silicon and is relatively thin, for example, having a thickness in the range of approximately 0.3 to 2.0 millimeters. The exposed planar face shown in  FIG. 1A  of the printhead module  106  is the nozzle face and includes an array of nozzles (not shown) from which a printing fluid can be ejected. The printing fluid can be ink, but also can be other liquids, for example, electroluminescent material used in the manufacture of liquid crystal displays or liquid metals used in circuit board fabrication, or biological fluid. 
       FIG. 1B  shows the mounting structure with the printhead module  106  removed. In this implementation, the mounting structure includes a central portion  105  flanked on two opposing sides by winged portions  104 . A receiving surface  107  for the printhead module  106  is included on an end of the central portion  105 . Other configurations of mounting structure are possible, and the one shown is but one example. 
     The printhead module  106  is mounted on the receiving surface  107  in the mounting structure  102  between the two opposing winged portions  104 . In the mounting structure configuration shown, the winged portions  104  are configured with apertures  108 , such that the wing portions can be attached to a fluid ejection system where the mounting structure is supported by a frame attached to the winged portions  104  by connecting members passing through the apertures. It should be understood that the mounting structure can be attached to the fluid ejection system in other manners, for example, by an adhesive, and including apertures in the wing portions is optional. Typically, two or more printhead modules and mounting structures are mounted to such a frame. The nozzles included in each printhead module are aligned relative to one another when mounting to the frame, so as to provide a larger array of nozzles with consistent spacing between neighboring nozzles. To provide for some manipulation of the printhead module  106  when mounting the mounting structure  102  into a fluid ejection system, the exposed edges  110  and  112  of the printhead module  106  extend past the edges of the winged portions  104 . 
       FIG. 2  shows two printhead modules mounted in adjacent mounting structures and positioned adjacent one another, for example, as they may be positioned when mounted within the frame of a fluid ejection system. Although exaggerated for illustrative purposes, there is typically a gap “G” between the edges of the adjacent printhead modules and a larger gap “H” between the edges of the corresponding mounting structures. The gap “H” allows the relative positions of the printhead modules to be adjusted in one or more directions, for example, in the x direction or y direction, and/or rotationally in the z direction. The relative positions of the printhead modules, and accordingly the nozzles included therein, can thereby be adjusted to provide for precise nozzle alignment as between neighboring printhead modules before attaching the corresponding mounting structures to the frame of the fluid ejection system. 
     A difficulty with the mounting structure  102  shown in  FIG. 1B  is illustrated in  FIG. 3A . Because the edges  110  and  112  of the printhead module  106  extend past the winged portions  104  of the mounting structure, they are vulnerable to damage during assembly of the printhead module into a fluid ejection system.  FIG. 3A  shows a view of the configuration shown in  FIG. 1A  resting on end against a surface  112 , which could occur during the assembly process. The entire weight (or a substantial portion thereof) of the printhead module/mounting structure assembly can end up on the exposed edge  110  of the printhead module. Because the printhead module  106  is formed from a relatively thin layer of silicon, the exposed edge  110  is prone to damage. The printhead module  106  can be an expensive element in the assembly and if damaged, may be rendered completely unusable. Accordingly, preventing damage to the printhead module  106  and the exposed edges  110  and  112  is important to avoid unnecessary manufacturing expenses and delays. 
       FIG. 3B  shows a partial view of a printhead module  306  mounted within a mounting assembly including winged portions  304 . The winged portions  304  each include on their edges adjacent the exposed edges of the printhead module (e.g., edge  310 ) features that extend beyond the exposed edges of the printhead module. In the implementation shown, the features are nubs  303  that extend past the exposed edge  310  of the printhead module  306 . As such, when the printhead module/mounting structure assembly is resting against a surface  112 , as shown, the weight of the assembly is on the nubs  303  rather than the exposed edge  310  of the printhead module  306 . The edge  310  is less likely to come into contact with other surfaces and less vulnerable to damage. Dimples  305  are also provided along the edges of the winged portions  304  for allow a recess for the nubs  303  to position in when multiple mounting structures are arranged adjacent one another in a fluid ejection system, as is described further below. 
       FIG. 4A  shows a perspective view of the printhead module  306  mounted in the mounting structure  302 .  FIG. 4B  shows the mounting structure  302  with the printhead module  306  removed. In this implementation, the mounting structure  302  includes the winged portions  304  attached to a central portion  309 , the entire length of which is not shown. A receiving surface  307  for the printhead module  306  is provided on an end of the central portion  309  between the winged portions  304 . Apertures  308  are included in the winged portions  304  to attach the mounting structure  302  to a frame of a fluid ejection system. Such apertures  308  are optional, and other techniques can be used to attached the mounting structure to a fluid ejection system, e.g., adhesive. 
     The mounting structure can have other configurations, as long as the edges of the mounting structure (referred to herein as the “featured edges”) adjacent the exposed edges  310 ,  312  of the printhead module  306  include features that extend beyond the exposed edges  310 ,  312 , so as to provide protection from damage. That is, the mounting structure may not necessarily be configured to include winged portions  304  extending from a central portion  309 , or may have a differently shaped cross-section than shown. However, whatever the configuration of the mounting structure  302 , the printhead module  306  is positioned within the mounting structure such that the featured edges of the mounting structure are provided on either side of the exposed edges of the printhead module, and the featured edges include features as described above. 
     Referring again to  FIGS. 4A and 4B , in the implementation shown, the nubs  303  and dimples  305  extend the entire thickness of the winged portions  304 . However, in other implementations, the nubs  303  and dimples  305  extend only partially the thickness of the winged portions  304 . In the implementation shown, there is one nub and one dimple on each edge of the winged portion  304  and they are arranged symmetrically about a central longitudinal axis of the receiving surface  307 . In some implementations, the nubs and dimples can be arranged asymmetrically about the central longitudinal axis as shown in  FIG. 4C , i.e., as a mirror image about the central longitudinal axis. An advantage of this configuration, is that the mounting structure has a “right” and “wrong” way of being mounted onto the frame of a fluid ejection system, in order that the nubs of the mounting structure mate with the dimples of a neighboring mounting structure. That is, the mounting structure cannot be inadvertently mounted backwards (i.e., rotated by 180°) onto the frame, which can be important in implementations where the printhead module has a “right” and “wrong” orientation. 
     In some implementations, additional nubs and dimples can be included. It should also be understood that in other implementations, the features extending beyond the exposed edges of the printhead module can have a configuration other than a nub, for example, can have squared corners, or otherwise. 
     The nubs  303  and dimples  305  included in the winged portions  304  of the mounting structure  302  are configured so as not to interfere with the relative positioning of neighboring printhead modules  306 . That is, the nubs  303  and dimples  305  are positioned and dimensioned to allow for a nub  303  to nest within a corresponding dimple of an adjacent mounting structure, without dictating or interfering with the relative position of the printhead modules mounted within the two mounting structures. 
       FIG. 5  shows an enlarged view of a portion of a first mounting structure having a winged portion  304  positioned adjacent to a second mounting structure having a winged portion  314 . For illustrative purposes, the two mounting structures are affixed into a frame of a fluid ejection system and the relative positioning of the printhead modules  306  and  320  mounted therein has been determined so as to align the nozzles of the printhead modules  306  and  320  relative to each other. The nub  303  has a depth “B” and is nested within a dimple  316  of depth “D” formed in the second mounting structure. 
     The outer surface of the nub  303  does not need to contact the inner surface of the corresponding dimple  316  when the first and second mounting structures are attached to the frame of the fluid ejection system. As is shown in  FIG. 5 , a gap  318  (which is exaggerated for illustrative purposes) can exist between the surfaces of the nub  303  and dimple  316 . If the surfaces of the nub  303  and the dimple  316  do come into contact, this contact can dictate the final position of the first and second mounting structures, and therefore the relative position of the printhead modules  306  and  320  mounted therein. Preferably, the relative position of the printhead modules  306  and  320  is determined by alignment of the nozzles included in each printhead module, rather than the nubs and dimples of the mounting structures. Accordingly, the nubs and dimples can be configured and dimensioned to satisfy the relationship below, so as to prevent their interfering with the positioning of the printhead modules:
 
 X   1   +G+X   2   +D&gt;B  
 
     Where: 
     X 1 =the distance by which the exposed edge  310  of the printhead module  306  extends past the edge of the winged portion  304 ; 
     G=the gap between the printhead modules  306  and  320 ; 
     X 2 =the distance by which the exposed edge  322  of the printhead module  320  extends past the edge of the winged portion  314 ; 
     D=the depth of the dimple  316 ; and 
     B=the depth of the nub  303 . 
     Additionally, X 1 +X 2 &lt;B. The gap “G” between the printhead modules  306  and  320  can be determined by nozzle alignment between the two printhead modules  306 ,  320 , and therefore can vary from instance to instance. However, a range that the gap “G” may fall within can be estimated and the minimum value in the range can be used in the above relationship to determine a value for the depth B of the nub or the depth D of the dimple. 
     In the implementation shown in  FIGS. 3B ,  4 A and  5 , the printhead module  306  is configured having a rectangular shape. In other implementations, the printhead module can be configured with a different shape. In  FIG. 6 , an example is shown where the printhead module  330  is a non-rectangular parallelogram mounted within a mounting structure having a generally rectangular cross-section (other than the nubs and dimples included on the edges of the winged portions  304 ). In other implementations, the mounting structure can have a cross-section shaped other than as a rectangle. 
     Referring to  FIG. 6 , the exposed edges  332  and  334  of the printhead module  330  are angled relative to the featured edges of the winged portions  304  of the mounting structure. However, the nubs  303  still extend past the outermost corners of the edges  332  and  334 , and thereby provide protection for these vulnerable edges, e.g., during the assembly process. In some implementations, a printhead module  330  having a non-rectangular parallelogram configuration as shown has an array of nozzles formed therein that are aligned parallel to the edges  332  and  334 , and the printhead module  330  moves in the y direction relative to a substrate being printed on, i.e., moves in a direction parallel to the featured edges of the winged portions. Other implementations are possible, and this is but one example. 
     Referring to  FIGS. 7A and 7B , for illustrative purposes, an example printhead module  700  is shown. A cross-sectional view of a portion of the printhead module  700  is shown and  FIG. 7A  shows the upper section in an exploded view. The printhead module  700  is but one example of a printhead module that can be mounted within a mounting structure as described above and is not a limiting example; other configurations can be used. 
     In the example shown, the printhead module  700  includes a substrate  708  in which a plurality of fluid flow paths are formed (only one flow path is shown). The printhead module  700  also includes a plurality of actuators to cause fluid (e.g., ink) to be selectively ejected from the flow paths. Thus, each flow path with its associated actuator provides an individually controllable MEMS fluid ejector. 
     In this implementation of a printhead module, an inlet fluidically connects a fluid supply (not shown) to a substrate  708 . The inlet is fluidically connected to an inlet passage  110  through a channel (not shown). The inlet passage  710  is fluidically connected to a pumping chamber  712 . The pumping chamber  712  is fluidly connected to a descender  716  terminating in a nozzle  718 . The nozzle  718  can be defined by a nozzle layer  720  attached to the substrate  708 . 
     The membrane  704  is formed on top of the substrate  708  in close proximity to the pumping chamber  712 , e.g. a lower surface of the membrane  104  can define an upper boundary of the pumping chamber  712 . The actuator  702  is disposed on top of the membrane  704 , and an adhesive  703  is between the actuator  702  and the membrane  704 . In the example shown, the actuator  702  is a piezoelectric actuator and includes a piezoelectric layer  731  positioned between a drive electrode  730  and a ground electrode  732 . A voltage differential is applied across the drive and ground electrodes  730 ,  732  to activate the piezoelectric layer  731 , causing a deflection of the piezoelectric layer  731  and the member  704 . In other implementations, a different configuration of actuator can be used, for example, a thermal actuator. 
     It should be understood that in other implementations, the membrane  704  can be excluded, and the piezoelectric layer  731  itself can form a boundary of the pumping chamber  712 . In implementations where the printing fluid can corrode the piezoelectric material, the surface forming the boundary of the pumping chamber can be protected by a protective layer, for example, a polyimide layer such as Upilex® or Kapton®. 
     In operation, fluid flows through the inlet into the substrate  708  and through the inlet passage  710 . Fluid flows up the inlet passage  710  and into the pumping chamber  712 . When the actuator  702  above the pumping chamber  712  is actuated, the actuator  702  deflects the membrane  704  into the pumping chamber  712 . The resulting change in volume of the pumping chamber  712  forces fluid out of the pumping chamber  712  and into the descender  716 . Fluid then passes through the nozzle  718 , provided that the actuator  702  has applied sufficient pressure to force a droplet  719  of fluid through the nozzle  718 . The droplet  719  of fluid is ejected and can then be deposited on a substrate. 
     The use of terminology such as “front” and “back” and “top” and “bottom” throughout the specification and claims is for illustrative purposes only, to distinguish between various components of the printhead module and other elements described herein. The use of “front” and “back” and “top” and “bottom” does not imply a particular orientation of the printhead module. Similarly, the use of horizontal and vertical to describe elements throughout the specification is in relation to the implementation described. In other implementations, the same or similar elements can be orientated other than horizontally or vertically as the case may be. 
     A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.