Abstract:
A nozzle arrangement for ejecting ink includes a substrate defining an ink supply passage; a first endless wall extending from the substrate and bounding the ink supply passage; an elongate actuator anchored at a fixed end to the substrate, the actuator configured to bend towards and away from the substrate; and a cover terminating a free end of the actuator, the cover defining a second endless wall suspended from the cover within the confines of the first endless wall to define an ink chamber with the first endless wall. The bending of the actuator varies a volume of the ink chamber and effects ejection of ink through an ink ejection port. The first and second endless walls define a gap therebetween. The width of the gap is conducive to the formation of a fluidic seal effected via surface tension of the ink.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    The present application is a continuation of U.S. application Ser. No. 12/538,162 filed Aug. 10, 2009, which is a continuation of U.S. application Ser. No. 11/545,566 filed on Oct. 11, 2006, now issued with U.S. Pat. No. 7,581,819, which is a continuation of U.S. application Ser. No. 11/015,012 filed on Dec. 20, 2004, now issued as U.S. Pat. No. 7,134,741, which is a continuation of U.S. application Ser. No. 10/893,378 filed on Jul. 19, 2004, now issued as U.S. Pat. No. 6,994,425, which is a continuation of Ser. No. 10/303,347 filed on Nov. 23, 2002, now issued as U.S. Pat. No. 6,767,077, which is a continuation of Ser. No. 09/693,313 filed on Oct. 20, 2000, now issued as U.S. Pat. No. 6,505,916, the entire contents of which are herein incorporated by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    This invention relates to an ink jet printhead. More particularly, the invention relates to an ink jet printhead that includes tilt-compensating ink ejection ports. 
       BACKGROUND 
       [0003]    Ink jet printheads of the type manufactured using micro-electromechanical systems technology have been proposed in a construction using nozzle chambers formed in layers on the top of a substrate with nozzle chambers formed in the layers. Each chamber is provided with a movable paddle actuated by some form of actuator to force ink in a drop through the nozzle associated with the chamber upon receipt of an electrical signal to the actuator. Such a construction is typified by the disclosure in International Patent Application PCT/AU99/00894 to the Applicant. 
         [0004]    The present invention stems from the realisation that there are advantages to be gained by dispensing with the paddles and causing ink drops to be forced from the nozzle by decreasing the size of the nozzle chamber. It has been realised that this can be achieved by causing the actuator to move the nozzle itself downwardly in the chamber thus dispensing with the paddle, simplifying construction and providing an environment which is less prone to the leakage of ink from the nozzle chamber. 
         [0005]    Furthermore, Applicant has identified that it would be useful to incorporate a mechanism whereby ink ejection ports could be kept clear of obstructions, such as dried ink or paper dust. 
       SUMMARY 
       [0006]    According to an aspect of the present disclosure, a nozzle arrangement for ejecting ink comprises a substrate defining an ink supply passage; a first endless wall extending from the substrate and bounding the ink supply passage; an elongate actuator anchored at a fixed end to the substrate external to the confines of the first endless wall, the actuator configured to bend towards and away from the substrate on receipt of an electrical current; and a cover terminating a free end of the actuator, the cover defining a second endless wall suspended from the cover within the confines of the first endless wall to define an ink chamber with the first endless wall, the cover further defining an ink ejection port. The reciprocal bending of the actuator towards and away from the substrate varies a volume of the ink chamber and effects ejection of ink from the ink chamber through the ink ejection port. The first and second endless walls define a gap therebetween, a width of the gap being conducive to the formation of a fluidic seal effected via surface tension of the ink. Each of the first and second walls are hexagonal in shape. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    Notwithstanding any other forms that may fall within its scope, one preferred form of the invention will now be described by way of example only with reference to the accompanying drawings in which: 
           [0008]      FIG. 1  is a partially cutaway perspective view of a nozzle arrangement of a printhead of the invention, 
           [0009]      FIG. 2  is a similar view to  FIG. 1  showing the bend actuator of the nozzle arrangement bent causing a drop of ink to protrude from an ink ejection port of the nozzle arrangement. 
           [0010]      FIG. 3  is a similar view to  FIG. 1  showing the nozzle arrangement returned to a quiescent condition and the drop of ink ejected from the nozzle. 
           [0011]      FIG. 4  is a cross-sectional view through a mid line of the nozzle arrangement as shown in  FIG. 2 . 
           [0012]      FIG. 5  is a similar view to  FIG. 1  showing the use of a projection to clear the ink ejection port. 
           [0013]      FIG. 6  is a similar view to  FIG. 5  showing the bend actuator bent and a drop of ink protruding from the nozzle arrangement. 
           [0014]      FIG. 7  is a similar view to  FIG. 5  showing the bend actuator straightened and the drop of ink being ejected from the nozzle arrangement. 
           [0015]      FIG. 8  is a three dimensional view of the nozzle arrangement of  FIG. 1 . 
           [0016]      FIG. 9  is a similar view to  FIG. 8  with part of the nozzle arrangement removed to show an optional constriction in the nozzle chamber. 
           [0017]      FIG. 10  is a similar view to  FIG. 9  with upper layers removed, and 
           [0018]      FIG. 11  is a similar view to  FIG. 1  showing the bend actuator cut away, and the actuator anchor detached for clarity. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    It will be appreciated that a large number of similar nozzles are simultaneously manufactured using MEMS and CMOS technology as described in our co-pending patent applications referred to at the beginning of this specification. 
         [0020]    For the purposes of clarity, the construction of an individual ink jet nozzle arrangement will now be described. 
         [0021]    Whereas in conventional ink jet construction of the type described in our above referenced co-pending patent applications, ink is ejected from a nozzle chamber by the movement of a paddle within the chamber, according to the present invention the paddle is dispensed with and ink is ejected through an ink ejection port in a movable portion of a nozzle chamber defining structure, which is moved downwardly by a bend actuator, decreasing a volume of the nozzle chamber and causing ink to be ejected from the ink ejection port. 
         [0022]    Throughout this specification, the relative terms “upper” and “lower” and similar terms are used with reference to the accompanying drawings and are to be understood to be not in any way restrictive on the orientation of the nozzle arrangement in use. 
         [0023]    Referring now to  FIGS. 1 to 3  of the accompanying drawings, the nozzle arrangement is constructed on a substrate  1  by way of MEMS technology defining an ink supply conduit  2  opening through a hexagonal opening  3  (which could be of any other suitable configuration) into a nozzle chamber  4  defined by floor portion  5 , roof portion  6  and peripheral sidewalls  7  and  8  which overlap in a telescopic manner. The sidewalls  7 , depending downwardly from roof portion  6 , are sized to be able to move upwardly and downwardly within sidewalls  8  which depend upwardly from floor portion  5 . 
         [0024]    An ejection port is defined by rim  9  located in the roof portion  6  so as to define an opening for the ejection of ink from the nozzle chamber as will be described further below. 
         [0025]    The roof portion  6  and downwardly depending sidewalls  7  are supported by a bend actuator  10  typically made up of layers forming a heated cantilever which is constrained by a non-heated cantilever, so that heating of the heated cantilever causes a differential expansion between the heated cantilever and the non-heated cantilever causing the bend actuator  10  to bend as a result of thermal expansion of the heated cantilever. 
         [0026]    A proximal end  11  of the bend actuator  10  is fastened to the substrate  1 , and prevented from moving backwards by an anchor member  12  which will be described further below, and the distal end  13  is secured to, and supports, the roof portion  6  and sidewalls  7  of the nozzle arrangement. 
         [0027]    In use, ink is supplied to the nozzle chamber through conduit  2  and opening  3  in any suitable manner, but typically as described in our previously referenced co-pending patent applications. When it is desired to eject a drop of ink from the nozzle chamber, an electric current is supplied to the bend actuator  10  causing the actuator to bend to the position shown in  FIG. 2  and to move the roof portion  6  downwardly toward the floor portion  5 . This relative movement decreases the volume of the nozzle chamber, causing ink to bulge upwardly from the nozzle rim  9  as shown at  14  ( FIG. 2 ) where it forms a droplet by the surface tension in the ink. 
         [0028]    When the electric current is cut off, the actuator  10  reverts to the straight configuration as shown in  FIG. 3  moving the roof portion  6  of the nozzle chamber upwardly to the original location. The momentum of the partially formed ink droplet  14  causes the droplet to continue to move upwardly forming an ink drop  15  as shown in  FIG. 3  which is projected on to the adjacent paper surface or other article to be printed. 
         [0029]    In one form of the invention, the opening  3  in floor portion  5  is relatively large compared with the cross-section of the nozzle chamber and the ink droplet is caused to be ejected through the nozzle rim  9  upon downward movement of the roof portion  6  by viscous drag in the sidewalls of the aperture  2 , and in the supply conduits leading from the ink reservoir (not shown) to the opening  2 . This is a distinction from many previous forms of ink jet nozzles where the “back pressure” in the nozzle chamber which causes the ink to be ejected through the nozzle rim upon actuation, is caused by one or more baffles in the immediate location of the nozzle chamber. This type of construction can be used with a moving nozzle ink jet of the type described above, and will be further described below with specific reference to  FIGS. 9 and 10 , but in the form of invention shown in  FIGS. 1 to 3 , the back pressure is formed primarily by viscous drag and ink inertia in the supply conduit. 
         [0030]    In order to prevent ink leaking from the nozzle chamber during actuation i.e. during bending of the bend actuator  10 , a fluidic seal is formed between sidewalls  7  and  8  as will now be further described with specific reference to  FIGS. 3 and 4 . 
         [0031]    The ink is retained in the nozzle chamber during relative movement of the roof portion  6  and floor portion  5  by the geometric features of the sidewalls  7  and  8  which ensure that ink is retained within the nozzle chamber by surface tension. To this end, there is provided a very fine gap between downwardly depending sidewall  7  and the mutually facing surface  16  of the upwardly depending sidewall  8 . As can be clearly seen in  FIG. 4 , the ink (shown as a dark shaded area) is restrained within a small aperture between the downwardly depending sidewall  7  and inward faces  16  of the upwardly extending sidewall  8 . The small aperture is defined by the proximity of the two sidewalls, which ensures that the ink “self seals” across free opening  17  by surface tension. 
         [0032]    In order to make provision for any ink which may escape the surface tension restraint due to impurities or other factors which may break the surface tension, the upwardly depending sidewall  8  is provided in the form of an upwardly facing channel having not only the inner surface  16  but a spaced apart parallel outer surface  18  forming a U-shaped channel  19  between the two surfaces. Any ink drops escaping from the surface tension between the surfaces  7  and  16 , overflows into the U-shaped channel where it is retained rather than “wicking” across the surface of the nozzle strata. In this manner, a dual wall fluidic seal is formed which is effective in retaining the ink within the moving nozzle mechanism. 
         [0033]    As has been previously described in some of our co-pending applications, it is desirable in some situations to clear any impurities which may build up within the nozzle opening and ensure clean and clear ejection of a droplet from the nozzle under actuation. A configuration of the present invention using a projection in combination with a moving nozzle ink jet is shown in the accompanying  FIGS. 5 ,  6  and  7 . 
         [0034]      FIG. 5  is similar to  FIG. 1  with the addition of a bridge member or bridge  20  across the opening  3  in the floor of the nozzle chamber, on which is mounted an upwardly extending rod-like structure or rod  21  sized to protrude into and/or through the plane of the ink ejection port during actuation. 
         [0035]    As can be seen in  FIG. 6 , when the roof portion  6  is moved downwardly by bending of the bend actuator  10 , the rod  21  is caused to extend up through the ink ejection port defined by the nozzle rim  9  and partly into the bulging ink drop  14 . 
         [0036]    As the roof portion  6  returns to its original position upon straightening of the bend actuator  10  as shown in  FIG. 7  the ink droplet is formed and ejected as previously described and the poker  21  is effective in dislodging or breaking any dried ink which may form across the nozzle rim  9  and which would otherwise block the ink ejection port. 
         [0037]    It will be appreciated that as the bend actuator  10  is bent causing the roof portion to move downwardly to the position shown in  FIG. 2 , the roof portion tilts relative to the floor portion  5  causing the nozzle to move into an orientation which is not parallel to the surface to be printed, at the point of formation of the ink droplet. This orientation, if not corrected, would cause the ink droplet  15  to be ejected from the nozzle in a direction which is not quite perpendicular to the plane of the floor portion  5  and to the strata of nozzles in general. This would result in inaccuracies in printing, particularly as some nozzles may be oriented in one direction and other nozzles in a different, typically opposite, direction. 
         [0038]    The correction of this non-perpendicular movement can be achieved by providing the nozzle rim  9  with an asymmetrical shape as can be clearly seen in  FIG. 8 . The nozzle is typically wider and flatter across the end  22  which is closer to the bend actuator  10 , and is narrower and more pointed at end  23  which is further away from the bend actuator. This narrowing of the nozzle rim  9  at end  23  increases the force of the surface tension at the narrow part of the nozzle rim  9 , resulting in a net drop vector force indicated by arrow  24 A in the direction toward the bend actuator, as the drop is ejected from the nozzle. This net force propels the ink drop in a direction which is not perpendicular to the roof portion  6  and can therefore be tailored to compensate for the tilted orientation of the roof portion  6  at the point of ink drop ejection. 
         [0039]    By carefully tailoring the shape and characteristics of the nozzle rim  9 , it is possible to completely compensate for the tilting of the roof portion  6  during actuation and to propel the ink drop from the nozzle in a direction perpendicular to the floor portion  5 . 
         [0040]    Although, as described above, the backpressure to the ink held within the nozzle chamber may be provided by viscous drag in the supply conduits, it is also possible to provide a moving nozzle ink jet with backpressure by way of a significant constriction close to the nozzle. This constriction is typically provided in the substrate layers as can be clearly seen in  FIGS. 9 and 10 .  FIG. 9  shows the sidewall  8  from which depend inwardly one or more baffle members  24  resulting in an opening  25  of restricted cross-section immediately below the nozzle chamber. The formation of this opening can be seen in  FIG. 10  which has the upper layers (shown in  FIG. 9 ) removed for clarity. This form of the invention can permit the adjacent location of ancillary components such as power traces and signal traces which are desirable in some configurations and intended use of the moving nozzle ink jet. Although the use of a restricted baffle in this manner has these advantages, it also results in a longer refill time for the nozzle chamber which may unduly restrict the speed of operation of the printer in some uses. 
         [0041]    The bend actuator which is formed from a heated cantilever  28  positioned above a non-heated cantilever  29  joined at the distal end  13  needs to be securely anchored to prevent relative movement between the heated cantilever  28  and the non-heated cantilever  29  at the proximal end  11 , while making provision for the supply of electric current into the heated cantilever  28 .  FIG. 11  shows the anchor  12  which is provided in a U-shaped configuration having a base portion  30  and side portions  31  each having their lower ends formed into, or embedded in the substrate  26 . The formation of the bend actuator in a U-shape gives great rigidity to the end wall  30  preventing any bending or deformation of the end wall  30  relative to the substrate  26  on movement of the bend actuator. 
         [0042]    The non-heated cantilever  29  is provided with outwardly extending tabs  32  which are located within recesses  33  in the sidewall  31 , giving further rigidity, and preventing relative movement between the non-heated cantilever  29  and the heated cantilever  28  in the vicinity of the anchor  27 . 
         [0043]    In this manner, the proximal end of the bend actuator is securely and firmly anchored and any relative movement between the heated cantilever  28  and the non-heated cantilever  29  is prevented in the vicinity of the anchor. This results in enhanced efficiency of movement of the roof portion  6  of the nozzle arrangement.