Abstract:
A nozzle arrangement includes a nozzle chamber having a roof defining an ink ejection port and a floor defining an ink supply inlet; a magnetic coil arrangement positioned around the ink supply inlet of the nozzle chamber; bridge members spanning over the magnetic coil arrangement, the bridge members supported on support posts protruding from the magnetic coil arrangement and having a resilient characteristic; and a paddle containing magnetic material and supported from the bridge members over the ink supply inlet, the paddle having a shape matching that of the ink supply inlet. The bridge members normally support the paddle in an open position spaced from the ink supply inlet. The magnetic coil arrangement is configured to attract the magnetic material of the paddle with a force exceeding the supporting tension of the resilient bridge members.

Description:
RELATED AND CROSS REFERENCED PATENT APPLICATIONS 
       [0001]    This application is a Continuation of U.S. application Ser. No. 13/037,145 filed Feb. 28, 2011, which is a Continuation of U.S. application Ser. No. 12/272,743 filed Nov. 17, 2008, now U.S. Pat. No. 7,922,293, which is a Continuation application of U.S. Ser. No. 12/050,938 filed on Mar. 18, 2008, now issued U.S. Pat. No. 7,465,030, which is a Continuation application of U.S. Ser. No. 11/754,367 filed on May 29, 2007, now U.S. Pat. No. 7,364,271, which is a Continuation application of U.S. Ser. No. 10/982,763 filed Nov. 8, 2004, now U.S. Pat. No. 7,240,992 which is a Continuation application of U.S. Ser. No. 09/864,379 filed May 25, 2001, now U.S. Pat. No. 6,814,429, which is a Continuation-In-Part of U.S. application Ser. No. 09/112,767, filed Jul. 10, 1998, now U.S. Pat. No. 6,416,167 all of which is herein incorporated by reference. 
         [0002]    U.S. Pat. Nos. 6,227,652 6,213,589 6,247,795 6,394,581 6,244,691 6,220,694 6,257,705 6,247,793 6,241,342 6,234,611 6,283,582 6,239,821 6,338,547 6,557,977 6,362,843 6,227,653 6,234,609 6,238,040 6,188,415 6,227,654 6,209,989 6,247,791 6,336,710 6,416,167 6,243,113 6,260,953 are hereby incorporated by reference. 
     
    
     TECHNICAL FIELD 
       [0003]    This invention relates to an ink jet printhead incorporating a back flow prevention mechanism. 
       BACKGROUND 
       [0004]    The Applicant has invented a printhead chip which is capable of printing text and images at a resolution of up to 1600 dpi. While developing this technology, the Applicant has filed many patent applications covering various inventions which have been conceived during this development. 
         [0005]    A large proportion of the inventions are in the field of micro electro-mechanical systems. These systems allow up to 84000 nozzle arrangements to be formed on a single printhead chip. As a result of various constraints arising from a necessity for the high density of nozzle arrangements, it has been necessary to design the systems in such a way that each nozzle arrangement, in most cases, includes one or more moving parts which serve to eject ink from each of the nozzle chambers defined by the nozzle arrangements. 
         [0006]    In most cases, these moving parts or components act on the ink within a nozzle chamber to eject that ink from the nozzle chamber. The Applicant has identified a particular difficulty to be overcome in the manufacture of such printheads. This has to do with the back flow of ink which is highly undesirable. The back flow of ink usually occurs after an ink drop has been ejected from a particular nozzle arrangement where a resulting break off of the drop and “suck back” of the ink into the nozzle chamber causes this back flow. Further, this back flow can also arise as a result of the operation of ink ejection mechanisms of such printheads. Many of the ink ejection mechanisms that the applicant has developed incorporate a reciprocal movement of one or more components. This reciprocal movement of the components can result in a back flow of ink as the components return to a start condition once a drop has been ejected. 
         [0007]    It will be appreciated that since the ink is physically ejected from each nozzle arrangement by the movement of the nozzle components it is extremely important that a consistent and correct amount of ink be supplied to each of the nozzle chambers. The back flow which can result in the absence of any mechanism to prevent it can disturb the fine balance required to achieve the accurate supply of ink to the various nozzle arrangements. 
         [0008]    Attempts have been made to address the problem of back flow in other forms of printheads such as thermal ink jet printheads. An example of such an attempt is indicated in  FIG. 1  of the drawings. Here, reference numeral  1  generally indicates part of a thermal ink jet printhead incorporating a back flow prevention mechanism. This printhead  1  includes an actuator in the form of a heater  2  which is positioned in a substrate  3  defining a floor  4  of a nozzle chamber  5 . An ink ejection port  6  is positioned above the heater  2 . The heater  2  heats ink  7  to an extent which is such that the ink  7  is ejected from the ejection port  6 . It will readily be appreciated that back flow of the ink in this case would inhibit the ejection of the ink  7  due to the loss of the required ejection pressure. Thus, a passive flap  8  is positioned in the chamber  5 . The flap  8  is configured to bend towards a roof  9  of the nozzle chamber  5  when acted upon by the ink  7 , thereby obstructing a possible back flow of ink. 
         [0009]    This form of back flow prevention device is not suitable for an ink jet printhead of the type described in this specification. The primary reason for this is that the operation of the device is dependent upon the heating of the ink. This form of printhead does not utilize the heating of ink to operate. Further, Applicant has found that it is highly advantageous to incorporate a back flow prevention device in an actuator mechanism so that a number of moving components can be kept to a minimum. 
         [0010]    The Applicant has conceived the present invention to at least reduce the level of back flow occurring once ink has been ejected from the nozzle chamber, while maintaining a suitably low level of energy consumption. 
       SUMMARY 
       [0011]    According to an aspect of the present disclosure, a nozzle arrangement comprises a nozzle chamber having a roof defining an ink ejection port and a floor defining an ink supply inlet; a magnetic coil arrangement positioned around the ink supply inlet of the nozzle chamber; bridge members spanning over the magnetic coil arrangement, the bridge members supported on support posts protruding from the magnetic coil arrangement and having a resilient characteristic; and a paddle containing magnetic material and supported from the bridge members over the ink supply inlet, the paddle having a shape matching that of the ink supply inlet. The bridge members normally support the paddle in an open position spaced from the ink supply inlet. The magnetic coil arrangement is configured to attract the magnetic material of the paddle with a force exceeding the supporting tension of the resilient bridge members. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    In the drawings: 
           [0013]      FIG. 1  shows a schematic view of a prior art apparatus that incorporates a back flow prevention mechanism; 
           [0014]      FIG. 2  shows a schematic side sectioned view of part of a first embodiment of an ink jet printhead, in accordance with the invention, showing a nozzle arrangement of the printhead; 
           [0015]      FIG. 3  shows a schematic side view of the printhead with a nozzle arrangement in a quiescent condition; 
           [0016]      FIG. 4  shows the nozzle arrangement of  FIG. 1  in the process of ejecting a drop of ink from a nozzle chamber of the nozzle arrangement; 
           [0017]      FIG. 5  shows the nozzle arrangement of  FIG. 1  immediately after the ink drop has been ejected; 
           [0018]      FIG. 6  shows a schematic side view of part of a second embodiment of a printhead, in accordance with the invention, showing a nozzle arrangement of the printhead; 
           [0019]      FIG. 7  shows a schematic, side sectioned view of part of a third embodiment of a printhead, in accordance with the invention, indicating cross sectional detail of a nozzle arrangement of that printhead; 
           [0020]      FIG. 8  shows a schematic, side sectioned view of part of a fourth embodiment of a printhead, in accordance with the invention; 
           [0021]      FIG. 9  shows a schematic, side sectioned view of part of a fifth embodiment of a printhead, in accordance with the invention, indicating cross sectional detail of a nozzle arrangement of that printhead; 
           [0022]      FIG. 10  shows a schematic, exploded view of a nozzle arrangement of  FIG. 9 ; 
           [0023]      FIG. 11  shows a schematic, exploded view of part of a sixth embodiment of a printhead, in accordance with the invention, indicating cross sectional detail of a nozzle arrangement of that printhead; 
           [0024]      FIG. 12  shows a schematic view of a nozzle arrangement of the printhead of  FIG. 11  in an operative condition; 
           [0025]      FIG. 13  shows a schematic, cross sectioned view of part of a seventh embodiment of a printhead, in accordance with the invention; 
           [0026]      FIG. 14  shows a schematic, cross sectioned view of part of an eighth embodiment of a printhead, in accordance with the invention, in a quiescent condition; 
           [0027]      FIG. 15  shows a schematic, cross sectioned view of the printhead of  FIG. 14 , in an active condition; and 
           [0028]      FIG. 16  shows another schematic, cross sectioned view of the printhead of  FIG. 14 . 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    The printhead shown in  FIG. 1  has already been described under the heading “Background to the Invention” above. 
         [0030]    In  FIGS. 2 to 5 , reference numeral  10  generally indicates part of a first embodiment of a printhead, in accordance with the invention, incorporating a plurality of nozzle arrangements  12 . 
         [0031]    The printhead  10  is manufactured using an integrated circuit fabrication technique. In particular, the printhead  10  is manufactured to define a micro electro-mechanical system. Details of the manufacturing process are set out in the cross-referenced applications and are therefore not described in any detail in this specification. Further, it is to be appreciated that, although the following description is directed to one or two nozzle arrangements  12 , the printhead  10  can incorporate up to 19 000 of the nozzle arrangements. This has been done for purposes of clarity and ease of description. 
         [0032]    The printhead  10  includes a wafer substrate  14 . A drive circuitry layer  16  is positioned on the wafer substrate  14  and incorporates drive circuitry for connection to the nozzle arrangements  12 . 
         [0033]    Each nozzle arrangement  12  includes two pairs of opposed side walls  18  and a roof wall  20  to define a nozzle chamber  22 . Each roof wall  20  has an ink ejection port  24  defined therein. 
         [0034]    An actuator  26  is positioned in each nozzle chamber  22 . Each actuator  26  includes an ink displacement member or paddle  28  which is displaceable, in the direction of an arrow  30 , towards the ink ejection port  24  to eject ink from the ink ejection port  24 . 
         [0035]    A passivation layer  32  is positioned on the drive circuitry layer  16 . 
         [0036]    A plurality of ink inlet channels  34  are defined through the wafer substrate  14 , the drive circuitry layer  16  and the passivation layer  32  so that an ink inlet channel  34  is in fluid communication with each nozzle chamber  22 , via an inlet  35 . 
         [0037]    Operation of the actuator  26  is schematically illustrated in  FIGS. 3 to 5 . 
         [0038]    A quiescent stage of the actuator  26  is shown in  FIG. 3 . In this stage, the ink inlet channels  34  and the nozzle chambers  22  are filled with ink  36  which also defines a meniscus  38  at the ink ejection port  24 . Upon actuation, the paddle  28  is driven towards the ink ejection port  24  as shown in  FIG. 3 . This results in the formation of a drop  40 . At this stage, the drop  40  is in fluid communication with the ink  36  within the nozzle chamber  28  and the ink inlet channel  34 . 
         [0039]    Eventually, as a result of the momentum of the ink  36 , the drop  40  is necked and separates from the ink  36  within the nozzle chamber  22  and ink inlet channel  34 . As can be seen in  FIG. 5 , a portion  41  of the ink that was ejected from the chamber  22  is drawn back into the chamber  22  as a result of surface tension effects. This has the tendency to set up a back flow of ink in the direction of an arrow  42 , which is highly undesirable, as set out above. As can clearly be seen from the drawings, the paddle  28  remains in a region between the ink inlet  35  and the ink ejection port  24 , thereby obstructing the back flow. 
         [0040]    As can be seen in  FIG. 3 , the paddle  28  is dimensioned to correspond generally with a cross sectional dimension of the nozzle chamber  22 . In particular, each paddle  28  is dimensioned so that, when the paddle  28  is at rest, the paddle  28  covers the ink inlet  35 . 
         [0041]    As a result of the fact that the paddle  28  covers the inlet  35  when at rest, the back flow of ink into the ink inlet channel  34  is inhibited by the paddle  28 . This results in the ink  36  within each of the ink inlet channels  34  remaining relatively quiescent subsequent to drop ejection. 
         [0042]    Furthermore, this allows the nozzle chamber  22  to re-fill in a stable manner. 
         [0043]    The actuator  26  includes an actuating mechanism  46  in the form of a heater element  48  embedded in a material having a coefficient of thermal expansion which is such that work can be performed as a result of expansion of the material. In this particular example, the material is of a polytetrafluoroethylene (PTFE). The heating element  48  is connected to drive circuitry within the drive circuitry layer  16  so that operation of the actuator  26  can be controlled with a suitable control system via the drive circuitry within the drive circuitry layer  16 . 
         [0044]    Details of the operation and structure of the actuator  26  are clearly set out in the above cross-referenced applications. Accordingly, these will not be described in any detail in this specification. 
         [0045]    In  FIG. 6 , reference numeral  50  generally indicates part of a second embodiment of a printhead, also in accordance with the invention, which incorporates a plurality of nozzle arrangements  52 , one of which is shown in  FIG. 6 . With reference to  FIGS. 1 to 4 , like reference numerals refer to like parts, unless otherwise specified. 
         [0046]    In the printhead  50 , each nozzle chamber  22  is formed in what is primarily an etching process in the wafer substrate  14 . A silicon nitride layer  54  is formed on the wafer substrate  14  to define the roof wall  20 . 
         [0047]    Details of the manufacture of the printhead  50  are clearly set out in the cross-referenced applications. It follows that these details will not be described in any detail in this specification. 
         [0048]    Instead of being thermally actuated, the actuator  26  includes a magnetic field generator in the form of a coil  56  which is formed on the drive circuitry layer  16 . The paddle  28  is of a material which is responsive to a magnetic field and which is displaceable on the application of a magnetic field of sufficient strength. 
         [0049]    The printhead  50  does not incorporate the separate ink inlet channels  34  extending through the wafer substrate  14 . However, each nozzle arrangement  52  includes an ink inlet opening  58  from which ink in a reservoir, indicated at  60 , can pass into the nozzle chamber  22 . 
         [0050]    It will readily be appreciated that the positioning of the paddle  28 , in this particular example, inhibits the back flow of ink through the opening  58  once an ink drop has been ejected from the nozzle arrangement  52 , in the manner described earlier. 
         [0051]    In  FIG. 7 , reference numeral  70  generally indicates part of a third embodiment of a printhead, also in accordance with the invention, incorporating a plurality of nozzle arrangements, one of which is shown at  72 . With reference to  FIGS. 2 to 6 , like reference numerals refer to like parts, unless otherwise specified. 
         [0052]    The nozzle arrangement  72 , for the purposes of this invention, is substantially the same as the nozzle arrangement  12 . The nozzle arrangement  72  has a different overall configuration to the nozzle arrangement  12 . However, the principle of operation is, again for the purposes of this invention, substantially the same. In particular, as can be seen in  FIG. 7 , the paddle  28  is restrained to move in a path that remains between the ink ejection port  24  and the inlet  35 . This is achieved primarily by having each ink inlet channel  34  and each respective ink ejection port  24  positioned on a common generally linear path with the paddle  28  in that path. 
         [0053]    Further, a side wall  74  of each nozzle arrangement  72  defines a guide formation  76 . The actuator  26  includes an actuator arm  78  mounted on a thermal actuator  80  to drive the actuator arm  78  towards and away from the substrate  14 . The actuator arm  78  has a complementary guide formation  82  which engages the guide formation  76 . The formations  76 ,  82  are shaped so that movement of the paddle  28  is constrained to a generally linear path between the ink inlet  35  and the ink ejection port  24 . 
         [0054]    In  FIG. 8 , reference numeral  90  generally indicates part of a fourth embodiment of a printhead, in accordance with the invention. With reference to  FIGS. 2 to 7 , like reference numerals refer to like parts, unless otherwise specified. 
         [0055]    In  FIGS. 9 and 10 , reference numeral  100  generally indicates part of a fifth embodiment of a printhead, in accordance with the invention. With reference to  FIGS. 2 to 8 , like reference numerals refer to like parts, unless otherwise specified. 
         [0056]    The printhead  100  includes a plurality of nozzle arrangements, one of which is indicated at  102 . The nozzle chamber  22  of each nozzle arrangement  102  is defined in the wafer substrate  14 . In particular, each nozzle chamber  22  is formed in an etching process carried out on the wafer substrate  14 . A passivation layer  104  is formed on the substrate  14 , to define the roof wall  20  and the ink ejection port  24  of each nozzle chamber  22 . 
         [0057]    The printhead  100  does not incorporate a plurality of inlet channels. Rather, the inlet  35  is in fluid communication with an ink reservoir  108 . 
         [0058]    In this example, the actuator  26  includes a magnetic field generator in the form of an electrical coil  106  positioned about the inlet  35  of the nozzle chamber  22 . The electrical coil  106  is coated with a passivation layer  110 . The electrical coil  106  is connected to the drive circuitry of the drive circuitry layer  16  so that, when required, the coil  106  can be activated to generate a magnetic field. 
         [0059]    The paddle  28  is dimensioned so that, when the paddle  28  is received in the inlet  35 , the paddle  28  serves to close the inlet  35 . The paddle  28  is movable between an open position in which the paddle  28  is spaced from the inlet  35  to permit the ingress of ink into the nozzle chamber  22  and a closed position in which the paddle  28  is received in the inlet  35  to close the inlet  35 . 
         [0060]    The paddle  28  is of a magnetic material  112  and is also coated with a passivation layer  114 . Thus, the paddle  28  can be displaced when the coil  106  is activated. It follows that, by energizing the coil  106  to a certain degree, the paddle  28  can be urged into the closed position while ejecting ink from the nozzle chamber  22 . It will therefore be appreciated that back flow is inhibited in this case since the inlet  35  is closed by the paddle  28  when the paddle  28  moves to eject ink from the ink ejection port  24 . 
         [0061]    Each nozzle arrangement  102  includes two pairs of opposed bridge members  116  which are mounted in a position spaced from the passivation layer  110  via two pairs of opposed support posts  118 . Each paddle member  28  is connected to the bridge members  116 . The bridge members  116  are configured so that each paddle member  28  is supported in the open position. The bridge members  116  are of a resilient material so that the paddle  28  acts against a tension in the bridge members  116  when it moves into the closed position. The bridge members  116  therefore serve to drive the paddle  28  back into the open position when the electrical coil  106  is de-activated. 
         [0062]    In  FIGS. 11 and 12 , reference numeral  120  generally indicates part of a sixth embodiment of a printhead, in accordance with the invention. With reference to  FIGS. 2 to 10 , like reference numerals refer to like parts, unless otherwise specified. 
         [0063]    In this embodiment, the actuator  26  includes an ink displacement member in the form of a segmented disc  122 . The segmented disc  122  is of a material having a coefficient of thermal expansion which is such that the material can expand to do work when heated to a sufficient extent. The disc  122  has a number of segments  123  which are circumferentially spaced. A wedge-shaped gap  124  is defined between consecutive segments  123 . A central portion  126  of the disc  122  is anchored to the drive circuitry layer  16 . 
         [0064]    In  FIG. 11 , the actuator  26  is in a rest position with the segments  123  generally parallel to the substrate  14 . In  FIG. 12 , the segments  123  of the actuator  26  are bent towards the ink ejection port  24  so that a portion of the ink  36  that is positioned between the disc  122  and the ink ejection port  24  is ejected from the ink ejection port  24 . The wedge shaped gaps  124  accommodate this movement so that buckling of the disc  122  is avoided. 
         [0065]    A heater element  128  is positioned in each segment  123 . In particular, each heater element  128  is positioned in a portion of each segment  123  distal with respect to the ink ejection port  24 . Resultant uneven heating of each segment  123  causes each segment  123  to be bent towards the ink ejection port  24 . 
         [0066]    As can be seen in  FIG. 11 , when the disc  122  is at rest, ink is permitted to flow into a region  130  between the disc  122  and the ink ejection port  24  via a space  132  defined between a periphery  134  of the disc  122  and the roof wall  20 . However, as can be seen in  FIG. 12 , this space  132  is effectively closed when the segments  123  are bent towards the ink ejection port  35 , as described above. This serves to inhibit the flow of ink through the space  132  away from the ink ejection port  35 , which, in this case, would constitute back flow. 
         [0067]    In  FIG. 13 , reference numeral  140  generally indicates part of a seventh embodiment of an ink jet printhead, in accordance with the invention. With reference to  FIGS. 2 to 12 , like reference numerals refer to like parts, unless otherwise specified. 
         [0068]    The ink jet printhead  140  includes a plurality of nozzle arrangements, one of which is indicated at  142 , arranged on the substrate  14 . The roof wall  20  of each nozzle arrangement defines a pair of ink ejection ports  144 ,  146 . A partition wall  148  extends from the roof wall  20  so that the nozzle chamber  22  is divided into a first part  22 . 1  and a second part  22 . 2 . The ink ejection port  144  is in fluid communication with the first part  22 . 1  and the ink ejection port  146  is in fluid communication with the second part  22 . 2 . The ink inlet  35  is in fluid communication with the first part  22 . 1 . 
         [0069]    The paddle  28  extends through one of the side walls  18  defining the nozzle chamber  22  and into the first part  22 . 1 . The paddle  28  is connected to an actuator arm  150  which, in turn, is connected to a double acting thermal actuator  152 . The thermal actuator  152  is fast with a support post  154 , which provides a connection for the actuator  152  to the drive circuitry of the drive circuitry layer  16 . The actuator  152  is configured so that, when activated, the actuator can drive the actuator arm  150  towards or away from the substrate  14 . 
         [0070]    The paddle  28  can thus be driven towards or away from the roof wall  20 . The parts  22 . 1  and  22 . 2  are in fluid communication so that, when the paddle  28  is driven towards the roof wall  20 , ink is ejected from the ejection port  144  and when the paddle  28  is driven away from the roof wall  20 , ink is ejected from the ejection port  146 . 
         [0071]    As can be seen in  FIG. 13 , the paddle  28  extends over the inlet  35 . Thus, when the paddle is driven towards and away from the roof wall  20 , back flow of ink from the part  22 . 1  is inhibited in a manner which has already been described. 
         [0072]    It will be appreciated that a flow path for ink to the second part  22 . 2  is defined between the paddle  28  and the substrate  14 . An obstructing formation  156  is defined on the paddle  28  to extend into the inlet channel  34 . The formation  156  is dimensioned and positioned on the paddle  28  so that, when the paddle  28  is driven away from and towards the roof wall  20 , the formation  156  remains in a position in which it obstructs the flow of ink back into the ink channel  34 . Thus, back flow from the part  22 . 2  is inhibited. 
         [0073]    In  FIGS. 14 to 16 , reference numeral  160  generally indicates part of a printhead, in accordance with the invention, that incorporates a nozzle arrangement  162 . With reference to  FIGS. 1 to 13 , like reference numerals refer to like parts, unless otherwise specified. 
         [0074]    The nozzle arrangement  162  includes a nozzle chamber  164  that is etched into the wafer substrate  14 . The nozzle chamber  164  has a substantially rectangular profile, with a pair of opposed major walls  166  and a pair of opposed minor walls  168 . The ink inlet channel  34  and the inlet  35  open into a floor  170  of the nozzle chamber  164  at a corner between one of the minor walls  168  and the floor  170 . 
         [0075]    A passivation layer  172  of a suitable material such as silicon nitride is positioned on the drive circuitry layer  16 . In this example, a portion  174  of the passivation layer  172  extends over the nozzle chamber  164  and defines an ink ejection port  176 . 
         [0076]    The actuator  26  includes a thermal ink displacement member  178  that extends from the portion  174  to span the nozzle chamber  164 . In particular, the ink displacement member  178  extends to a position adjacent one of the minor walls  168 , directly above the inlet  35 . The ink displacement member  178  includes a thermal actuator  180  which is configured to drive the ink displacement member  178  towards the inlet  35 . This serves to reduce a volume within the nozzle chamber, thereby ejecting ink from the port  176 . 
         [0077]    An obstruction member  182  depends from the displacement member  178 . The obstruction member  182  is dimensioned so that, as the ink displacement member  178  is driven into the nozzle chamber  164 , the obstruction member moves into a position in which ink is obstructed from flowing into the inlet channel  34 , which in this case would constitute back flow. 
         [0078]    Operation of the nozzle arrangement  162  is shown in  FIGS. 14 and 15 . 
         [0079]    Applicant submits that by incorporating a back flow prevention mechanism in the actuator  26 , the back flow of ink, during and subsequent to drop ejection, can be substantially prevented. As set out earlier, this has significant advantages in the field of micro electro-mechanical systems which are used for printing.