Patent Publication Number: US-11020969-B2

Title: Liquid ejection head

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2019-069614 filed on Apr. 1, 2019, the content of which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     Aspects described herein relate to a liquid ejection head including a plurality of pressure chambers, and a first common channel and a second common channel, which each communicate with the pressure chambers. 
     BACKGROUND 
     A known liquid ejection head includes a plurality of pressure chambers, a supply channel (a first common channel) communicating with the pressure chambers, and a circulating channel (a second common channel) communicating with the pressure chambers. The supply channel and the circulating channel are located on the same side of each pressure chamber, and the circulating channel and each pressure chamber define the supply channel therebetween. The supply channel and the circulating channel define a thin film portion therebetween. 
     SUMMARY 
     The above liquid ejection head includes the thin film portion between the supply channel and the circulating channel (of which only a portion facing the supply channel). In this case, the size of the thin film portion (a damper film) in contrast with that of the circulating channel may be too small to attain a sufficient damping effect on the circulating channel (a second common channel). 
     According to one or more aspects of the disclosure, a liquid ejection head includes a plurality of pressure chambers arranged in a first direction, a plurality of first communicating portions each communicating with a corresponding one of the pressure chambers, a first common channel, a plurality of second communicating portions each communicating with a corresponding one of the pressure chambers, a second common channel, and a damper film. The first common channel extends in the first direction and communicates with each of the first communicating portions. The first common channel includes a particular portion located to one side of each of the pressure chambers in a second direction orthogonal to the first direction. The second common channel extends in the first direction and communicates with each of the second communicating portions. The second common channel includes a first portion and a second portion. The first portion is located to the one side of each of the pressure chambers in the second direction. The first portion and each of the pressure chambers sandwich the particular portion of the first common channel therebetween in the second direction. The second portion connects the first portion and the second communicating portions. The second portion extends from the first portion in the second direction toward the pressure chambers and is located to a side of the first common channel opposite in a third direction to the pressure chambers. The third direction is orthogonal to both the first direction and the second direction. The damper film is located to a side of the second portion of the second common channel opposite in the third direction to the first common channel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view of a printer including a plurality of heads according to a first embodiment of the disclosure. 
         FIG. 2  is a plan view of a head. 
         FIG. 3  is a sectional view of the head taken along a line III-III of  FIG. 2 . 
         FIG. 4  is a block diagram illustrating an electrical system of the printer. 
         FIG. 5  is a sectional view of a head according to a second embodiment, corresponding to  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
     First Embodiment 
     Referring to  FIG. 1 , an overall structure of a printer  100  including heads  1  according to a first embodiment of the disclosure will be described. 
     The printer  100  includes a head unit  1   x  with four heads  1 , a platen  3 , a conveyor  4 , and a controller  5 . 
     The platen  3  receives a sheet  9  on its upper surface. 
     The conveyor  4  includes two roller pairs  4   a ,  4   b  which are disposed opposite to each other with the platen  3  therebetween in a conveyance direction. When a motor  4   m  ( FIG. 4 ) is driven under control by the controller  5 , the roller pairs  4   a ,  4   b  rotate while nipping the sheet  9  therebetween to convey the sheet  9  in the conveyance direction. 
     The head unit  1   x  is elongated in a sheet width direction orthogonal to both of the conveyance direction and a vertical direction. The head unit  1   x  is a line-head unit having stationary heads to eject ink toward the sheet  9  from nozzles  21  ( FIGS. 2 and 3 ) in form of ink droplets. The four heads  1  are elongated in the sheet width direction and disposed in two rows in a staggered configuration in the sheet width direction. 
     The controller  5  includes ROM (read only memory), RAM (random access memory), and ASIC (application specific integrated circuit). The ASIC performs recording processing in accordance with programs stored in the ROM. In the recording processing, the controller  5  controls a driver IC  1   d  ( FIG. 4 ) of each head  1  and a motor  4   m  ( FIG. 4 ) with a recording command (including image data) input from an external device, for example, a PC, to record an image on the sheet  9 . 
     Referring to  FIGS. 2 and 3 , a structure of a head  1  will be described. 
     As illustrated in  FIG. 3 , a head  1  includes a channel substrate  11 , an actuator substrate  12 , and a protective substrate  13 . 
     As illustrated in  FIG. 2 , the channel substrate  11  includes a plurality of pressure chambers  20 , a plurality of nozzles  21 , supply channels  30 A,  30 B, and return channels  40 A,  40 B. 
     The pressure chambers  20  are arranged in two staggered rows in the sheet width direction (hereinafter referred to as a first direction), constituting a first pressure chamber group  20 A and a second pressure chamber group  20 B. The first pressure chamber group  20 A and the second pressure chamber group  20 B are arranged alongside in a direction parallel to the conveyance direction (hereinafter referred to as a second direction), and each include pressure chambers  20  spaced at regular intervals in the first direction. Each pressure chamber  20  has a rectangular shape elongated in the second direction on a plane orthogonal to the vertical direction (hereinafter referred to as a third direction). The third direction is orthogonal to both of the first direction and the third direction. 
     Each of the pressure chambers  20  is connected, at its one end in the second direction, to a corresponding one of narrowed portions  23 . As illustrated in  FIG. 2 , the narrowed portions  23  are smaller in width (a dimension in the first direction) than the pressure chambers  20  and extend in the second direction. As illustrated in  FIG. 3 , the narrowed portions  23  are equal in depth (a dimension in the third direction) to the pressure chambers  20 . 
     Each of the narrowed portions  23  is connected, at its lower end (or an end on one side in the third direction), to a corresponding one of supply communicating portions  24 . As illustrated in  FIG. 2 , the supply communicating portions  24  are circular channels each having a diameter larger than a width (a dimension in the first direction) of a corresponding one of the narrowed portions  23 . The supply communicating portions  24  extends in the third direction. As illustrated in  FIG. 3 , the supply communicating portions  24  are located below the narrowed portions  23  and the pressure chambers  20  (or located to one side of each of the narrowed portions and the pressure chambers in the third direction, or located adjacent to each of the narrowed portions in the third direction). The supply communicating portions  24  communicate with the narrowed portions  23  which communicate with the pressure chambers  20 . 
     As illustrated in  FIG. 2 , each of the narrowed portions  23  has a first end  23   a  and a second end  23   b  in the send direction. Each of the narrowed portions  23  communicates with a corresponding one of the supply communicating portions  24  at the first end  23   a , and a corresponding one of the pressure chambers  20  at the second end  23   b . The first end  23   a  of each narrowed portion  23  in the second direction overlaps a corresponding supply communicating portion  24  in the third direction. 
     A narrowed portion  23  and a supply communicating portion  24  are provided for each pressure chamber  20 . 
     Narrowed portions  23  and supply communicating portions  24  provided for the first pressure chamber group  20 A are located opposite to the second pressure chamber group  20 B relative to the first pressure chamber group  20 A in the second direction. Narrowed portions  23  and supply communicating portions  24  provided for the second pressure chamber group  20 B are located opposite to the first pressure chamber group  20 A relative to the second pressure chamber group  20 B in the second direction. In the second direction, the first pressure chamber group  20 A and the second pressure chamber group  20 B are located between a row of the narrowed portions  23  and the supply communicating portions  24  provided for the first pressure chamber group  20 A and a row of the narrowed portions  23  and the supply communicating portions  24  provided for the second pressure chamber group  20 B. 
     The supply channel  30 A and the return channel  40 A are provided for the first pressure chamber group  20 A, and the supply channel  30 B and the return channel  40 B are provided for the second pressure chamber group  20 B. In other words, the supply channel  30 A and the return channel  40 A communicate with pressure chambers  20  in the first pressure chamber group  20 A, and the supply channel  30 B and the return channel  40 B communicate with pressure chambers  20  in the second pressure chamber group  20 B. The supply channels  30 A,  30 B and the return channels  40 A,  40 B extend in the first direction and have the same length in the first direction. 
     The supply channel  30 A and the return channel  40 A are located opposite to the second pressure chamber group  20 B relative to the first pressure chamber group  20 A in the second direction. The supply channel  30 B and the return channel  40 B are located opposite to the first pressure chamber group  20 A relative to the second pressure chamber group  20 B in the second direction. In the second direction, the first pressure chamber group  20 A and the second pressure chamber group  20 B are located between the supply channel  30 A and the supply channel  30 B. 
     Each of the supply channels  30 A,  30 B includes a first supply portion  31  and a second supply portion  32 . The first supply portion  31  and the second supply portion  32  are channels extending in the first direction and have the same length in the first direction. 
     As illustrated in  FIG. 3 , the first supply portion  31  has a greater depth (a dimension in the third direction) than the second supply portion  32 . 
     The second supply portion  32  extends from a lower end portion of the first supply portion  31  (or an end portion of the first supply portion on one side in the third direction, opposite to the pressure chambers) toward the pressure chambers  20  in the second direction and connects the first supply portion  31  and the supply communicating portions  24 . The supply communicating portions  24  are located above the second supply portion  32  (or located to the other side of the second supply portion in the third direction or adjacent to the second supply portion in the third direction). The second supply portion  32  communicates with the supply communicating portions  24  which communicate with the pressure chambers  20 . 
     The supply communicating portions  24  are an example of first communicating portions, and the supply channels  30 A,  30 B are an example of a first common channel. 
     An upper end of the first supply portion  31  of the supply channel  30 A and an upper end of the first supply portion  31  of the supply channel  30 B are merged into a merging channel  33 . The merging channel  33  extends in the second direction above the first pressure chamber group  20 A and the second pressure chamber group  20 B. As illustrated in  FIG. 2 , the merging channel  33  is located in a center of the channel substrate  11  in the first direction. 
     An upper surface of the merging channel  33  has an opening  33   x . The opening  33   x  is located in a center of the merging channel  33  in the second direction and between the first pressure chamber group  20 A and the second pressure chamber group  20 B. 
     The opening  33   x  communicates with a sub tank (omitted from the drawings). The sub tank communicates with a main tank to store ink supplied from the main tank. When a circulating pump  7   p  ( FIG. 4 ) is driven under control by the controller  5 , ink in the sub tank is allowed to enter the merging channel  33  from the opening  33   x.    
     As illustrated in  FIGS. 2 and 3 , ink entering the merging channel  33  from the opening  33   x  moves to both ends of the merging channel  33  in the second direction. Ink then enters the first supply portions  31  of the supply channels  30 A,  30 B from respective supply openings  30   x  provided at upper ends of the first supply portions  31  (or ends of the first supply portions, which are opposite in the third direction to a damper chamber). Ink entering the first supply portions  31  moves toward both ends of the respective first supply portions  31  in the first direction as illustrated in  FIG. 2  and downward (or toward one side in the third direction), and enters the second supply portions  32  as illustrated in  FIG. 3 . Ink entering the second supply portions  32  passes through the supply communicating portions  24  and the narrowed portions  23 , which are provided for their respective pressure chambers  20 , and then enters each of the pressure chambers  20 . 
     Each of the pressure chambers  20  is connected to a corresponding one of connection channels  22  at an end of each of the pressure chambers  20  in the second direction, which is opposite to a corresponding one of the narrowed portions  23 . The connection channels  22  extend downward (or toward one side in the third direction) from the pressure chambers  20  and connect the pressure chambers  20  and nozzles  21 . The nozzles  21  are located directly below the connection channels  22 . The pressure chambers  20  communicate with the connection channels  22  which communicate with the nozzles  21 . 
     Each of the connection channels  22  is connected, at its lower end portion (or an end portion on one side in the third direction), to a corresponding one of return communicating portions  25 . The return communicating portions  25 , although omitted from  FIG. 2 , are narrow channels each having substantially the same width (a dimension in the first direction) as that of a corresponding narrowed portion  23 , and extend in the second direction. 
     A connection channel  22 , a nozzle  21 , and a return communicating portion  25  are provided for each pressure chamber  20 . 
     Connection channels  22  and nozzles  21  provided for the first pressure chamber group  20 A are located on the same side of the first pressure chamber group  20 A, which is adjacent to the second pressure chamber group  20 B in the second direction. Connection channels  22  and nozzles  21  provided for the second pressure chamber group  20 B are located on the same side of the second pressure chamber group  20 B, which is adjacent to the first pressure chamber group  20 A in the second direction. 
     Return communicating portions  25  provided for the first pressure chamber group  20 A extend in a direction away from the second pressure chamber group  20 B relative to the second direction. Return communicating portions  25  provided for the second pressure chamber group  20 B extend in a direction away from the first pressure chamber group  20 A relative to the second direction. 
     Each of the return channels  40 A,  40 B includes a first return portion  41  and a second return portion  42 . The first return portion  41  and the second return portion  42  are channels extending in the first direction and have the same length in the first direction. 
     As illustrated in  FIG. 3 , the first return portion  41  has a greater depth (a dimension in the third direction) than the second return portion  42 . 
     The first return portion  41  has a width W 2  (a dimension in the second direction) greater than a width W 1  of the first supply portion  31 . In other words, the width W 1  of the first supply portion  31  is smaller than the width W 2  of the first return portion  41 . 
     The second return portion  42  extends from a lower end portion of the first return portion  41  (or an end portion of the first return portion on one side in the third direction, opposite to the pressure chambers) toward the pressure chambers  20  in the second direction and connects the first return portion  41  and the return communicating portion  25 . The second return portion  42  communicates with the return communicating portions  25  which communicate with the respective pressure chambers  20 . 
     The return communicating portions  25  are an example of second communicating portions, the return channels  40 A,  40 B are an example of a second common channel, the first return portion  41  is an example of a first portion, and the second return portion  42  is an example of a second portion. 
     An upper surface of the first return portion  41  has a return opening  40   x . The return opening  40   x  is located in a center of the first return portion  41  in the first direction and at the same position as the opening  33   x  in the first direction. The return opening  40   x  communicates with a sub tank (omitted from the drawings), as with the opening  33   x.    
     As illustrated in  FIG. 3 , ink entering each pressure chamber  20  moves downward through its associated connection channel  22 . Some of ink is ejected in form of ink droplets from an associated nozzle  21 , and the rest of ink passes through an associated return communicating portion  25  and enters an associated second return portion  42 . Ink entering the second return portion  42  moves in the second direction and enters the lower end of the first return portion  41 . Ink entering the lower end of the first return portion  41  moves upward (or toward the other side in the third direction) as illustrated in  FIG. 3  and then toward the center of the first return portion  41  in the first direction as illustrated in  FIG. 2 , and thus flows out from the return opening  40   x . Ink flowing out from the return opening  40   x  is returned to the sub tank. 
     Ink is thus circulated between the sub tank and the channel substrate  11 . The circulation of ink reduces air bubbles formed in the channel substrate  11  and prevents the viscosity of ink from increasing. For ink having settling ingredients (e.g., pigments) which settle down and form a sediment, the circulation of ink stirs the settling ingredients, thus preventing the settling ingredients from settling down. 
     The first supply portion  31  and the first return portion  41  provided for each of the first pressure chamber group  20 A and the second pressure chamber group  20 B are located on one side of the pressure chambers  20  included in a corresponding one of the first pressure chamber group  20 A and the second pressure chamber group  20 B in the second direction. In this embodiment, the first supply portion  31  and the first return portion  41  provided for the first pressure chamber group  20 A are located opposite to the second pressure chamber group  20 B relative to the first pressure chamber group  20 A in the second direction. The first supply portion  31  and the first return portion  41  provided for the second pressure chamber group  20 B are located opposite to the first pressure chamber group  20 A relative to the second pressure chamber group  20 B in the second direction. 
     Regarding each of the first pressure chamber group  20 A and the second pressure chamber group  20 B, the first supply portion  31  is located between the first return portion  41  and each of the pressure chambers  20  in the second direction. 
     Regarding each of the first pressure chamber group  20 A and the second pressure chamber group  20 B, the second return portion  42  is located below a corresponding supply channel  30 A,  30 B (or located to one side of the supply channel  30 A,  30 B in the third direction, opposite to the pressure chambers) as illustrated in  FIG. 3 . A damper film  51  is located to a lower side of the second return portion  42  (or located to a side of the second return portion  42  on one side in the third direction, opposite to the supply channel  30 A,  30 B). The damper film  51  is provided for each of the pressure chamber groups  20 A,  20 B. A damper film  51  provided for the first pressure chamber group  20 A is an example of a first damper film, and a damper film  51  provided for the second pressure chamber group  20 B is an example of a second damper film. 
     Regarding each of the pressure chamber groups  20 A,  20 B, a covering member  60  covers a corresponding damper film  51  from below (or a side of the damper film  51  opposite in the third direction to the second return portion  42 ). The covering member  60  and the damper film  51  define a damper chamber  50  therebetween. 
     The damper chamber  50  has a cross section orthogonal to the third direction, and the second return portion  42  has a cross section orthogonal to the third direction. The cross section of the damper chamber  50  is greater than the cross section of the second return portion  42 . The cross section of the second return portion  42  overlaps and includes the cross section of the damper chamber  50 . Specifically, in both of the first direction and the second direction, each damper chamber  50  is greater than the return channel  40 A,  40 B, and protrudes toward an exterior of the channel substrate  11  relative to the return channel  40 A,  40 B (by about 100 μm, for example). 
     The damper chamber  50  may communicate with air at its both ends in the first direction and have a pressure equal to the atmospheric pressure. In this case, as the damper chamber  50  is not an enclosed space, the damper film  51  is likely to bend, thereby enhancing a damping effect. Alternatively, the damper chamber  50  may have a pressure lower than the pressure in the second return portion  42 . In this case, by Le Chatelier&#39;s principle, foreign matter (e.g., air bubbles) in the damper chamber  50  may be prevented from passing through the damper film  51  and entering the second return portion  42 . 
     The channel substrate  11  is made of 10 plates  11   a - 11   j  stacked in the third direction. 
     Of the plates  11   a - 11   j , a lowermost plate  11   j  is a nozzle plate having a plurality of through holes functioning as nozzles  21 . The plate  11   j  has a nozzle surface  21   x  with a plurality of nozzles  21 . All the nozzles  21  in the plate  11   j  communicate with the pressure chambers  20  of both the first pressure chamber group  20 A and the second pressure chamber group  20 B. 
     In the second direction, the plate  11   j  is disposed between the covering member  60  provided for the first pressure chamber group  20 A and the covering member  60  provided for the second pressure chamber group  20 B. The nozzle surface  21   x  of the plate  11   j  is located above a lower surface of each covering member  60  (or located to the other side in the third direction relative to a surface of the covering member on one side in the third direction, or located closer to the pressure chambers than the covering member in the third direction). 
     A plate  11   i  bonded on an upper surface of the plate  11   j  is thinner than the plate  11   j . The plate  11   i  has through holes defining lower ends of the first return portions  41  and the second return portions  42 . The plate  11   i  has a lower surface (or a first surface in the third direction) and an upper surface (or a second surface in the third direction). The lower surface supports the plate  11   j , the damper films  51  and the covering members  60 . The upper surface defines the return communicating portions  25 . 
     The plate  11   i  is an example of a blocking plate, and a portion of the plate  11   i  between the plate  11   j  and each of the covering members  60  is an example of a blocking portion  11   ix . The blocking portion  11   ix  is located below the return communicating portions  25  (or located to one side of each of the return communicating portions in the third direction, opposite to the pressure chambers) and blocks a gap between the plate  11   j  and each of the covering members  60 . 
     A further damper film  52  is located above the merging channel  33  (or located to the other side of the merging channel in the third direction, or to a side of the merging channel  33  opposite in the third direction to the supply channel  30 A,  30 B). The damper film  52  is bonded to an upper surface of an uppermost plate  11   a , covering all over the merging channel  33 . A lower surface of the damper film  52  defines the merging channel  33 . 
     The opening  33   x  is formed in the damper film  52 . A tube connected to a sub tank is attached to the opening  33   x  in the damper film  52 . 
     The damper films  51 ,  52  may be made of a material such as resin (e.g., polyimide) and metal (e.g., stainless steel, SUS). The damper films  51 ,  52  may be made of the same material or different materials. 
     The pressure chambers  20  and the narrowed portions  23  are defined by through holes in a plate  11   c . The plate  11   c  has through holes defining the first supply portions  31  of the supply channels  30 A,  30 B, and the first return portions  41  of the return channels  40 A,  40 B, in addition to the through holes defining the pressure chambers  20  and the narrowed portions  23 . 
     The actuator substrate  12  includes a vibrating plate  12   a , a common electrode  12   b , a plurality of piezoelectric members  12   c , and a plurality of individual electrodes  12   d , which are stacked one another in this order from below. 
     The vibrating plate  12   a  and the common electrode  12   b  are located at an upper surface of the plate  11   c  and between through holes defining the first supply portions  31  of the supply channels  30 A,  30 B, and cover all the pressure chambers  20  and the narrowed portions  23  formed in the plate  11   c . A piezoelectric member  12   c  and an individual electrode  12   d  are provided for each pressure chamber  20  and overlap each pressure chamber  20  in the third direction. 
     The common electrode  12   b  and the individual electrodes  12   d  are electrically connected to a driver IC  1   d  ( FIG. 4 ). The driver IC  1   d  maintains the potential of the common electrode  12   b  at a ground potential, while changing the potential of each of the individual electrodes  12   d . Specifically, the driver IC  1   d  generates drive signals based on control signals from the controller  5  and transmits the drive signals to the individual electrodes  12   d . The potential of each of the individual electrodes  12   d  thus changes between a specified drive potential and a ground potential. At this time, an individual electrode  12   d  whose potential is changed to a drive potential causes a corresponding piezoelectric member  12   c  to become deformed, and thus a portion of the actuator substrate  12  that is sandwiched between the individual electrode  12   d  and the vibrating plate  12   a  and that overlaps the deformed piezoelectric member  12   c  in the third direction (that is, an actuator  12   x ) protrudes toward a corresponding pressure chamber  20 . The capacity of the pressure chamber  20  is thus changed and ink in the pressure chamber  20  is pressurized and ejected, in form of ink droplets, from the nozzle  21  communicating with the pressure chamber  20 . 
     The protective substrate  13  is bonded to an upper surface of the vibrating plate  12   a . Side surfaces of the protective substrate  13  define respective side surfaces of the first supply portions  31  of the supply channels  30 A,  30 B. An upper surface of the protective substrate  13  defines a lower surface of the merging channel  33 . 
     A lower surface of the protective substrate  13  has two recesses  13   x . The two recesses  13   x  extend in the first direction, one overlapping the pressure chambers  20  included in the first pressure chamber group  20 A in the third direction, the other overlapping the pressure chambers  20  included in the second pressure chamber group  20 B in the third direction. Each of the recesses  13   x  stores a plurality of actuators  12   x  for each of the first and second pressure chamber groups  20 A,  20 B. 
     As described above, according to this embodiment, the first supply portion  31  and the first return portion  41  in each of the first pressure chamber group  20 A and the second pressure chamber group  20 B are located on one side of the pressure chambers  20  included in a corresponding one of the first pressure chamber group  20 A and the second pressure chamber group  20 B in the second direction, and the first supply portion  31  is located between the first return portion  41  and each of the pressure chambers  20  in the second direction. Regarding each of the first pressure chamber group  20 A and the second pressure chamber group  20 B, the second return portion  42  extends from the first return portion  41  toward the pressure chambers  20  (toward the other side in the second direction) and is located below a corresponding supply channel  30 A,  30 B (or located to one side of the supply channel  30 A,  30 B in the third direction, opposite to the pressure chambers). In the embodiment, the damper film  51  is located to a lower side of the second return portion  42  (or located to a side of the second portion on one side in the third direction, opposite to the first common channel). In other words, the damper film  51  is not provided between the supply channel  30 A,  30 B and the return channel  40 A,  40 B. The second return portion  42  is a channel elongated in the second direction, which extends from the first return portion  41  in the second direction. Providing the damper film  51  in the second return portion  42  creates a space for increasing the size of the damper film  51  relative to the return channel  40 A,  40 B. 
     The supply channel  30 A and the return channel  40 A are provided for the first pressure chamber group  20 A, and the supply channel  30 B and the return channel  40 B are provided for the second pressure chamber group  20 B ( FIG. 3 ). The disclosure is applicable to a structure having two pressure chamber groups  20 A,  20 B to achieve high resolution. 
     The damper films  51  are spaced from each other and each provided for a corresponding one of the pressure chamber groups  20 A,  20 B ( FIG. 3 ). If one damper film  51  is provided for both of the first pressure chamber group  20 A and the second pressure chamber group  20 B, the damper film  51  should be devoid of a hole for surrounding the plate  11   j . This case may involve an oversize damper film  51 , which may increase material costs, require elaborate positioning, and reduce manufacturing yield. This embodiment, however, may prevent such problems as one damper film  51  is provided for each of the pressure chamber groups  20 A,  20 B. 
     The further damper film  52  is located above the merging channel  33  (or located to a side of a merging channel opposite in the third direction to a first common channel) ( FIG. 3 ). According to this embodiment, the size of the damper film  52  is large enough to cover the merging channel  33  that extends in the second direction and is elongated in the second direction. 
     The compliance of a common channel including the supply channel  30 A,  30 B and the return channel  40 A,  40 B is about 20 times larger than that of each actuator  12   x  in general. The compliance of the supply channel  30 A,  30 B and the compliance of the return channel  40 A,  40 B may be determined according to the ratio of fluid flow between the supply channel  30 A,  30 B and the return channel  40 A,  40 B to adjust the sizes of the damper films  51 ,  52 . When the damper film  51  is smaller in size than the damper film  52 , the Young&#39;s modulus of the damper film  51  may be lower than that of the damper film  52  to facilitate bending of the damper film  51 . To lower the Young&#39;s modulus of the damper film  51 , the damper film  51  may be made thinner than the damper film  52 . Alternatively, the damper film  51  may be made of resin (e.g., polyimide) while the damper film  52  may be made of metal (e.g., stainless steel, SUS). 
     The width W 1  of the first supply portion  31  is smaller than the width W 2  of the first return portion  41  ( FIG. 3 ). As the first supply portion  31  is merged into the merging channel  33 , a pressure loss between the first supply portion  31  and the merging channel  33  is low. Thus, there is no need to increase the width W 1  of the first supply portion  31  to as large as that of the first return portion  41 . According to this embodiment, narrowing the width W 1  of the first supply portion  31  contributes to reducing the size of the head  1  in the second direction. 
     The covering member  60  covers a corresponding damper film  51  from below (or a side of the damper film  51  opposite in the third direction to the second return portion  42 ), and the covering member  60  and the corresponding damper film  51  define the damper chamber  50  therebetween. In this case, the damper film  51  is not exposed. If a damper film  51  is exposed, the damper film  51  may become prone to breakage by contact with a sheet  9 . This embodiment, however, may prevent breakage of the damper film  51 , as the damper film  51  is not exposed. 
     The cross section, orthogonal to the third direction, of the second return portion  42  is greater than the cross section, orthogonal to the third direction, of the damper chamber  50  in the third direction. The cross section of the damper chamber  50  overlaps and includes the cross section of the second return portion  42  ( FIG. 3 ). According to this embodiment, the damper chamber  50  which is larger in size than the second return portion  42  enhances a damping effect. Even if there is a misalignment between the bonded plates  11   a - 11   j  in the third direction, the damper chamber  50  may reliably overlap the second return portion  42  in the third direction, thus ensuring a damping effect. 
     The nozzle surface  21   x  of the plate  11   j  is located above a lower surface of each covering member  60  (or located to the other side in the third direction relative to a surface of the covering member on one side in the third direction, or located closer to the pressure chambers than the covering member in the third direction) ( FIG. 3 ). According to this embodiment, the nozzle surface  21   x  is recessed as protection against damage by contact with a sheet  9 . 
     Each of the return communicating portions  25  is connected to a lower end portion (or one end portion in the third direction) of a corresponding one of the connection channels  22 . According to this embodiment, the return communicating portions  25  are located in close vicinity to the nozzle surface  21   x , which effectively may reduce the viscosity of ink circulating in the nozzles  21  and discharge air bubbles out of the nozzles  21 . 
     The blocking portion  11   ix  is located below the return communicating portions  25  (or located to one side of each of the return communicating portions in the third direction, opposite to the pressure chambers) and blocks the gap between the plate  11   j  and each of the covering members  60  ( FIG. 3 ). According to this embodiment, the blocking portion  11   ix  may prevent ink leakage from the return communicating portions  25  and enables locating of the return communicating portions  25  in close vicinity to the nozzle surface  21   x.    
     The blocking portion  11   ix  is included in the plate  11   i  of which lower surface (or a first surface in the third direction) supports the plate  11   j , the damper films  51  and the covering members  60 , and of which upper surface (or a second surface in the third direction) defining the return communicating portions  25  ( FIG. 3 ). According to this embodiment, ink leakage can be prevented relatively simply by providing the plate  11   j.    
     The plate  11   i  is thinner than the plate  11   j  ( FIG. 3 ). According to this embodiment, the return communicating portions  25  can be located in close vicinity to the nozzle surface  21   x.    
     Second Embodiment 
     Referring to  FIG. 5 , a head  201  according to a second embodiment of the disclosure will be described. In the second embodiment, elements illustrated and described in the first embodiment are designated by the same reference numerals, and thus the description thereof will be omitted. 
     The first embodiment shows that the blocking portion  11   ix  of the plate  11   i  blocks the gap between the plate  11   j  and each of the covering members  60 . In the second embodiment, an adhesive  70  blocks the gap between the plate  11   j  and each of the covering members  60 . In the second embodiment, the adhesive  70  is an example of a blocking portion. 
     In the second embodiment, a channel substrate  211  is similar to the channel substrate  11  of the first embodiment devoid of the plate  11   i . The channel substrate  211  is made of nine plates  11   a - 11   h ,  11   j  stacked in the third direction. The plate  11   j  and the covering members  60  are bonded to a lower surface of the plate  11   h . The damper films  51  are fixed to the respective covering members  60 . The adhesive  70  is applied to between the plate  11   j  and each of the covering members  60 . Upper surfaces of the plate  11   j , the adhesive  70 , and an end (closer to the nozzles  21  in the second direction) of each covering member  60  define the return communicating portions  25 . The adhesive  70  is preferably ink resistant. Examples of the adhesive  70  may include polyurethane-based adhesives and epoxy-based adhesives. 
     As described above, the second embodiment may have the following effects in addition to the effects obtained from the similar structure to that described in the first embodiment. 
     The second embodiment prevents ink leakage without having to use the plate  11   i . This eliminates material cost and assembly time taken for the plate  11   i . Omission of the plate  11   i  contributes to reducing the size of the head  201  in the third direction. 
     Alternative Embodiments 
     The above embodiments are merely examples. Various changes, arrangements and modifications may be applied therein without departing from the spirit and scope of the disclosure. 
     The second direction is not limited to being orthogonal to the first direction, but may cross the first direction. 
     The further damper film  52  may not be located above the merging channel  33  in the third direction. 
     The merging channel  33  may be omitted. Alternatively, in the above embodiments, a tube connected to a sub tank may be attached to the supply opening  30   x  of each supply channel  30 A,  30 B. In this case, a sub tank may be provided for each pressure chamber group  20 A,  20 B. A sub tank connected to a tube in the supply opening  30   x  of the supply channel  30 A and a sub tank connected to a tube in the supply opening  30   x  of the supply channel  30 B may each store a different type (e.g., color) of liquid. 
     The protective substrate  13  may be omitted. In this case, the merging channel  33  may be defined by a member different from the protective substrate  13 . Alternatively, the merging channel  33  and the protective substrate  13  may be omitted. In this case, the upper surface of the first common channel may be level with the upper surfaces of the pressure chambers  20 . 
     The width of the first return portion  41  (as an example of a dimension in the second direction of the first portion) may be smaller than or equal to the width of the first supply portion  31  of the supply channel  30 A,  30 B (as an example of a dimension of a further portion of the first common channel extending from the merging channel in the third direction toward the second portion). 
     The supply opening  30   x  and the return opening  40   x  are provided at the upper surfaces of the supply channel  30 A,  30 B (as an example of the first common channel) and the return channel  40 A,  40 B (as an example of the second common channel), but are not limited to this structure. The supply opening and the return opening may be provided at lower surfaces or side surfaces of the supply channel  30 A,  30 B and the return channel  40 A,  40 B. 
     The above embodiments show but not limited to the supply channel  30 A,  30 B being a first common channel, and the return channel  40   a ,  40 B being a second common channel. In some embodiments, the first common channel may be a return channel and the second common channel may be a supply channel. Alternatively, both of the first common channel and the second common channel may be supply channels. In other words, the disclosure does not limit the flow direction of liquid in the first common channel and the second common channel. 
     The above embodiments show, but not limited to, each pressure chamber group  20 A,  20 B including a single row of pressure chambers  20 . Each pressure chamber group  20 A,  20 B may include a plurality of rows of pressure chambers  20 . In this case, a first common channel and a second common channel may be provided for each row of the pressure chambers  20 . 
     The above embodiments show but not limited to that the supply channel  30 A (as an example of a first common channel) and the return channel  40 A (as an example of a second common channel), which are provided for the first pressure chamber group  20 A, are located opposite to the second pressure chamber group  20 B relative to the first pressure chamber group  20 A in the second direction, and the supply channel  30 B (as an example of a first common channel) and the return channel  40 B (as an example of a second common channel), which are provided for the second pressure chamber group  20 B, are located opposite to the first pressure chamber group  20 A relative to the second pressure chamber group  20 B in the second direction. For example, the first common channel and the second common channel, which are provided for the first pressure chamber group, and those which provided for the second pressure chamber group may be located on the same side of each of the first pressure chamber group and the second pressure chamber group in the second direction, such that the first pressure chamber group and the second pressure chamber group sandwich therebetween those which provided for the first pressure chamber group or the second pressure chamber group. 
     Each head  1 ,  201  may include a single pressure chamber group, and a first common channel and a second common channel which each communicate with the single pressure chamber group. 
     The narrowed portions  23  may be omitted by narrowing the widths of the supply communicating portions  24 . 
     The cross section, orthogonal to the third direction, of the damper chamber  50  may coincide with the cross section, orthogonal to the third direction, of the second return portion  42  (as an example of a second portion). Alternatively, the cross section of the damper chamber  50  may be smaller than the cross section of the second return portion  42 . 
     In some embodiments, a covering member  60  may be provided at or for each head  1 ,  201 . Alternatively, a covering member  60  may be provided for a plurality of heads  1 ,  201 . (For example, a covering member may cover the head unit  1   x  illustrated in  FIG. 2  except for areas with nozzles  21 .) In some embodiments, the covering members  60  may be omitted. In this case, damper chambers  50  are also omitted. The nozzle surface  21   x , which may be recessed relative to the damper film  51  (or located above the lower surface of the damper film  51 ), may be prevented from suffering damage by contact with a sheet. 
     The nozzle surface  21   x  is not limited to being located above the lower surface of each of the covering member  60  and the damper film  51 . The nozzle surface may be level with or below the lower surface. 
     The damper film  51  is not limited to being provided for each pressure chamber group. The damper film  51  may be provided in common for the first pressure chamber group  20 A and the second pressure chamber group  20 B. 
     The return communicating portions  25  (as an example of second communicating portions) are each not limited to being connected to a lower portion of the connection channel  22  (or one end portion of the connection channel in the third direction). The return communicating portions  25  may be each connected to a middle portion or an upper portion of the connection channel  22  (or the other end portion thereof in the third direction). 
     In the above embodiments, a single nozzle  21  communicates with a single pressure chamber  20 . However, two or more nozzles  21  may communicate with a single pressure chamber  20 . Alternatively, a single nozzle  21  may be provided for two or more pressure chambers  20 . 
     The heads  1 ,  201  are not limited to line heads. The heads may be serial heads (which eject liquid droplets to a target object from nozzles while moving in a scanning direction parallel to the sheet width direction). 
     The target object is not limited to a sheet of paper, but may be, for example, a cloth, a substrate, and other materials. 
     A liquid to be ejected from nozzles in form of droplets is not limited to ink, but may be any liquids, for example, a process liquid for condensation or precipitation of an ink component. 
     The disclosure may be applied to not only printers but also other apparatus such as a facsimile, a copier, and a multifunction apparatus. The disclosure may be applied to various liquid ejection devices intended for, not only image recording on sheets, but also conductive pattern forming to form conductive patterns on substrates by ejecting a conductive liquid thereon.