Patent Publication Number: US-7717545-B2

Title: Liquid ejecting head and liquid ejecting apparatus

Description:
BACKGROUND 
   1. Technical Field 
   The present invention relates to a liquid ejecting head, such as an ink jet recording head, and a liquid ejecting apparatus and more particularly to a liquid ejecting head that is provided with a flow passage unit, which forms a continuous liquid flow passage extending from a common liquid chamber through pressure chambers to nozzle openings, and that is able to discharge liquid from the nozzle openings as liquid droplets, and a liquid ejecting apparatus. 
   2. Related Art 
   A liquid ejecting head that discharges liquid droplets from nozzle openings by generating pressure variation in the liquid contained in pressure chambers, for example, includes an ink jet recording head used for an image recording apparatus, such as a printer, a color material ejecting head used for manufacturing a color filter for a liquid crystal display, or the like, an electrode material ejecting head used for forming an electrode for an organic electro luminescence (EL) display, a field emission display (FED), or the like, and a bio-organic material ejecting head used for manufacturing a biochip, or the like. 
   The above described liquid ejecting heads have various types; however, for example, the ink jet recording head (hereinafter, referred to as recording head) used in an ink jet recording apparatus (hereinafter, simply referred to as printer) includes a flow passage unit that is formed by laminating a nozzle substrate, a flow passage substrate, and a diaphragm. The nozzle substrate has a plurality of nozzle openings formed therein. The flow passage substrate forms a flow passage portion, such as a pressure chamber space portion and a channel portion, which defines a continuous ink flow passage extending from a common ink chamber through pressure chambers to the nozzle openings. The diaphragm has diaphragm portions that face the pressure chambers and elastically deform in accordance with the action of pressure generating devices (for example, piezoelectric vibrators) (which may be regarded as a sealing plate that seals the opening of the flow passage substrate). Then, the flow passage unit is fixed to a head case that accommodates a vibrator unit. In the above recording head, the diaphragm portions are elastically deformed by the action of the piezoelectric vibrators that constitute the flow passage unit to thereby vary the volume of the pressure chambers. Thus, pressure variation is generated in the ink contained in the pressure chambers to thereby discharge ink droplets from the nozzle openings. 
   The head case is made of a plastic material that is more advantageous in terms of ease of formation, flexibility of shape and weight than a metal material. However, because a plastic material is generally lower in rigidity than a metal material, the head case may be compressively deformed due to the stress generated when the diaphragm portions are elastically deformed by the action of the piezoelectric vibrators. Particularly, compression deformation tends to occur at an open peripheral portion corresponding to the diaphragm portions in the head case. Then, there is a possibility that desired discharge characteristics of ink droplets cannot be obtained because of the occurrence of crosstalk due to the above deformation of the head case or deformation of the flow passage unit. Then, a reinforcing plate is laminated between the flow passage substrate and nozzle substrate of the flow passage unit to thereby enhance the rigidity of the head case and, as a result, the discharge characteristics of ink droplets have been attempted to improve (which is, for example, described in JP-A-6-99578). 
   However, when the reinforcing plate is laminated between the flow passage substrate and nozzle substrate of the flow passage unit, a flow passage also extends through the reinforcing plate and, therefore, the length of the flow passage increases. Thus, a nozzle side resistance and/or an inertance increase, so there is a problem that it becomes unsuitable for ink discharge with high response frequency or the discharge characteristics of the nozzle opening is not uniform. 
   In addition, as the size of the recording head increases, in the head case, the opening portion of an accommodation chamber for accommodating the vibrator unit increases. Then, as the size of the opening portion increases, the rigidity entirely decreases. Particularly, the rigidity at the center of the opening portion in the longitudinal direction is weaker than the rigidity at each end portion of the opening portion in the longitudinal direction. Therefore, there occurs a difference in the amount of displacement, or the like, between the diaphragm portions arranged at each end portion of the opening portion and the diaphragm portions arranged at the center of the opening portion. Thus, there has been a problem that uneven discharge characteristics occur among the nozzle openings. 
   SUMMARY 
   An advantage of some aspects of the invention is that it provides a liquid ejecting head and a liquid ejecting apparatus that are able to enhance the rigidity of a flow passage unit and also possible to obtain the discharge with high response frequency and/or uniform discharge characteristics. 
   An aspect of the invention provides a liquid ejecting head. The liquid ejecting head includes a flow passage unit, a vibrator unit, a case, and a reinforcing plate. The flow passage unit includes a liquid flow passage and a diaphragm portion. The liquid flow passage at least includes a pressure chamber that communicates with a nozzle opening. The diaphragm portion is formed at a portion corresponding to the pressure chamber and varies a volume of the pressure chamber. The vibrator unit includes a piezoelectric vibrator that is bonded to the diaphragm portion and that displaces the diaphragm portion. The case has an accommodation chamber formed therein to accommodate the vibrator unit. The reinforcing plate has an insertion opening portion that is formed at a position corresponding to the diaphragm portion and through which a free end portion of the piezoelectric vibrator is insertable. The reinforcing plate is interposed between the case and the flow passage unit. 
   According to the above configuration, the reinforcing plate has the insertion opening portion that is formed at a position corresponding to the diaphragm portion and through which a free end portion of the piezoelectric vibrator is insertable, and the reinforcing plate is interposed between the case and the flow passage unit. Thus, it is possible to enhance the rigidity in such a manner that the piezoelectric vibrator is surrounded by the insertion opening portion of the reinforcing plate of the opening end of the case and, thereby, it is possible to obtain the discharge with high response frequency and/or uniform discharge characteristics. In addition, by interposing the reinforcing plate between the case and the flow passage unit, there is no change in the length of a flow passage to the piezoelectric vibrator and to the nozzle opening, and it is suitable for the discharge with high response frequency. 
   Note that the aspect of the invention may be configured so that the reinforcing plate has a higher Young&#39;s modulus than the case and, thereby, the reinforcing plate is advantageous in that it has a reinforcing property with a Young&#39;s modulus higher than that of the case. 
   In addition, the reinforcing plate may be formed of a silicon substrate and, thereby, it is possible to manufacture the reinforcing plate with high accuracy by performing etching on the silicon substrate. 
   The aspect of the invention may be configured so that each of the case, the reinforcing plate and the flow passage unit have at least two positioning holes, wherein positions of the corresponding positioning holes of the case, the reinforcing plate and the flow passage unit are overlapped one another. 
   According to the above configuration, because the positions of the corresponding positioning holes of the case, the reinforcing plate and the flow passage unit are overlapped one another, it is possible to assemble the case, the reinforcing plate and the flow passage unit in a state where they are positioned with high accuracy. 
   In addition, the aspect of the invention may be configured so that the thickness of the reinforcing plate is set smaller than the length of the free end portion of the piezoelectric vibrator. 
   According to the above configuration, only with the change in configuration of the case and without changing the configuration of the existing flow passage unit, it is possible to provide the reinforcing plate. 
   In addition, the aspect of the invention may be configured so that the flow passage unit includes a plurality of the diaphragm portions that are provided in a column in correspondence with a plurality of the pressure chambers, wherein the reinforcing plate includes a plurality of the insertion opening portions in correspondence with the diaphragm portions of the flow passage unit. 
   According to the above configuration, even when the flow passage unit includes a plurality of the diaphragm portions that are provided in a column in correspondence with a plurality of the pressure chambers, by forming a plurality of the insertion opening portions in the reinforcing plate in correspondence with the diaphragm portions of the flow passage unit, it is possible to enhance the rigidity. 
   Note that the aspect of the invention may be configured so that a crosspiece is formed between any adjacent insertion opening portions of the reinforcing plate. Thus, owing to the crosspiece, it is possible to further enhance the rigidity. 
   In addition, the aspect of the invention may be configured so that the reinforcing plate has a clearance step portion that is formed on a face of the reinforcing plate, which is bonded with the flow passage unit, in an area, in which the insertion opening portion is formed, on a side of a face of the reinforcing plate, which is bonded with the case. 
   According to the above configuration, by forming the clearance step portion on the side of the face of the reinforcing plate, which is bonded with the case, even when the diaphragm portion displaces, it is possible to prevent the diaphragm portion from interfering with the reinforcing plate. That is, it is possible to prevent the reinforcing plate from interfering with displacement of the diaphragm portion. In this manner, it is possible to suppress the influence on the discharge characteristics of ink droplets. 
   Note that the aspect of the invention may be configured so that the amount of setback of the clearance step portion of the reinforcing plate from a face bonded with the flow passage unit is set larger than the amount of displacement by which the diaphragm portion is displaced by the piezoelectric vibrator toward the case. According to the above configuration, it is possible to further reliably prevent the diaphragm portion from interfering with the reinforcing plate. 
   In addition, an aspect of the invention provides a liquid ejecting apparatus having any one of the above configured liquid ejecting heads. 
   According to the above configuration, because the rigidity of the case, to which the vibrator unit that constitutes the liquid ejecting head is fitted, may be enhanced, it is possible to suppress the compression deformation of the case or the compression deformation of the flow passage unit when the discharge operation is performed by the liquid ejecting head. Thus, it is possible to discharge a prescribed amount of liquid droplets from the nozzle opening at a prescribed speed. As a result, it is possible to make the liquid droplets be placed on a discharged object with further high accuracy. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
       FIG. 1  is a perspective view that illustrates the configuration of a printer. 
       FIG. 2  is a cross-sectional view of a relevant portion, illustrating the configuration of a recording head. 
       FIG. 3  is a longitudinal cross-sectional view of a relevant portion, illustrating the configuration of the recording head. 
       FIG. 4  is an exploded perspective view of a flow passage unit, a reinforcing plate and a case unit. 
       FIG. 5A  and  FIG. 5B  are views, each of which illustrates a reference hole. 
       FIG. 6  is a view that illustrates an alternative example embodiment of a reinforcing plate. 
   

   DESCRIPTION OF EXEMPLARY EMBODIMENTS 
   Hereinafter, embodiments according to the invention will be described with reference to the accompanying drawings. Note that, in the embodiments described below, various limitations are made as desirable specific embodiments of the aspects of the invention; however, the scope of the invention is not intended to be limited to these embodiments unless otherwise expressly stated in the description to the effect that the invention is limited. In addition, in the following description, an ink jet printer (hereinafter, simply referred to as printer) shown in  FIG. 1  is exemplified as a liquid ejecting apparatus according to the aspects of the invention. 
   The printer  1  has an installed recording head  2 , which is a kind of liquid ejecting head, and schematically includes a carriage  4 , a platen  5 , a carriage moving mechanism  7 , a paper feed mechanism  8 , and the like. An ink cartridge  3  is detachably mounted on the carriage  4 . The platen  5  is arranged below the recording head  2 . The carriage moving mechanism  7  moves the carriage  4 , on which the recording head  2  is mounted, in a paper width direction of a sheet of recording paper  6  (a kind of discharged object). The paper feed mechanism  8  transports the sheet of recording paper  6  in a paper feed direction which is a direction perpendicular to the paper width direction. Here, the paper width direction is a main scanning direction (head scanning direction), and the paper feed direction is a sub scanning direction (that is, a direction perpendicular to the head scanning direction). Note that the ink cartridge  3  may employ a type that is attached to the carriage  4  or may employ a type that is attached to the case of the printer  1  and supplies the recording head  2  through an ink supply tube. 
   The carriage  4  is mounted so that it is pivotally connected to a guide rod  9  that extends in the main scanning direction. The carriage  4  is configured to move in the main scanning direction along the guide rod  9  by the action of the carriage moving mechanism  7 . The position of the carriage  4  in the main scanning direction is detected by a linear encoder  10 , and a detection signal is transmitted to a control portion (not shown) as positional information. In this manner, the control portion is able to recognize a scanning position of the carriage  4  (recording head  2 ) on the basis of the positional information from the linear encoder  10  and to control a recording operation (discharging or ejecting operation), or the like, by the recording head  2 . 
   In addition, a home position, which is a scanning start point (rest position when no recording is performed) of the recording head  2 , is set within a movable range of the recording head  2  and outside the platen  5 . At this home position, a capping mechanism  11  is provided. The capping mechanism  11  seals the nozzle forming face of the recording head  2  by a cap member  11 ′ to thereby prevent vaporization of ink solvent from nozzle openings  19  (see  FIG. 2 ). In addition, the capping mechanism  11  is used for a cleaning operation in which a negative pressure is applied to a sealed nozzle face to thereby forcibly sucks and drains ink from the nozzle openings  19 . 
   In addition, at the home position, a wiping mechanism  12  that wipes the nozzle forming face of the recording head  2  is arranged. The wiping mechanism  12  is provided with a wiper blade  12 ′, which is, for example, formed of an elastic material, such as elastomer. The wiping mechanism  12  is configured so that, when the recording head  2  passes over the wiping mechanism  12 , the upper end portion of the wiper blade  12 ′ moves to a position (wiping position) at which the upper end portion of the wiper blade  12 ′ is able to contact the nozzle forming face of the recording head  2 . Then, when the recording head  2  moves in a state where the upper end portion of the wiper blade  12 ′ is in contact with the nozzle forming face of the recording head  2 , the nozzle forming face of the recording head  2  is wiped by the wiper blade  12 ′. In this manner, it is possible to remove, for example, redundant ink droplets adhered on the nozzle forming face after cleaning operation. 
     FIG. 2  is a cross-sectional view of a relevant portion, illustrating the configuration of the recording head  2 .  FIG. 3  is a longitudinal cross-sectional view of a relevant portion, illustrating the configuration of the recording head  2 .  FIG. 4  is an exploded perspective view of the flow passage unit  18  and the head case  24 . The recording head  2  according to the present embodiment schematically includes actuator units  16 , each of which has a plurality of piezoelectric vibrators  15 , a flow passage unit  18  that forms a continuous ink flow passage (a kind of liquid flow passage) that extends from a common ink chamber  20  (common liquid chamber) through ink supply ports  21  and pressure chambers  22  to nozzle openings  19 , a head case  24 , and the like. 
   The head case  24  is a hollow box-shaped casing, and has case flow passages  31 , which are formed therein, and accommodation chambers  32 . The case flow passages  31  each are a flow passage for introducing ink from the ink cartridge  3  toward the common ink chamber  20 . The accommodation chambers  32  each accommodate the actuator unit  16 . The head case  24  is formed of a plastic material, such as epoxy resin, which is a kind of thermosetting resin, and the flow passage unit  18  is fixed on the flow passage fitting face of the head case  24 . In addition, the head case  24  has two pin retaining portions  34  (which also serve as positioning holes) that are formed therein and that extend through in the height direction of the case, as shown in  FIG. 4  (in  FIG. 4 , only one of two pin retaining portions  34  is shown). These pin retaining portions  34  are space portions for respectively retaining case pins (not shown) and each are formed into a cylindrical shape of which an inner diameter is slightly larger than the diameter of the case pin. In the present embodiment, the two pin retaining portions  34  are respectively provided at positions corresponding to reference holes  52  (see  FIG. 4 ) formed in the flow passage substrate  40 . Then, each case pin is implanted into the pin retaining portion  34  and is retained in a state where the distal end portion protrudes from the flow passage fitting face. Positioning may be performed by matching the diameters of the case pins to the diameters of the inscribed circles of the corresponding reference holes  52 . Note that positioning of the flow passage unit  18  with the head case  24  will be described later. 
   Each of the above actuator units  16  includes piezoelectric vibrators  15 , a fixed plate  37  to which these piezoelectric vibrators  15  are bonded, flexible cables  38  for supplying driving signals from a wiring substrate to the piezoelectric vibrators  15 , and the like. Each piezoelectric vibrator  15  is connected to the fixed plate  37 , which is formed of a metal plate material, such as stainless steel, in a state of a so-called cantilever such that a free end portion of each piezoelectric vibrator  15  protrudes outside the distal end face of the fixed plate  37 . Note that the pressure generating device may employ an electrostatic actuator, a magnetostrictive element, or the like, other than the above piezoelectric vibrator. 
   The flow passage unit  18  is formed so that a lamination of flow passage unit components composed of a diaphragm  39 , a flow passage substrate  40  and a nozzle substrate  41  is bonded and integrated. The pressure chambers  22  of the flow passage unit  18  are formed as long narrow chambers extending in a direction perpendicular to a column array direction (nozzle array direction) of the nozzle openings  19 . In addition, the common ink chamber  20  is a chamber into which ink is introduced from the side of an ink introducing needle. Then, ink introduced into the common ink chamber  20  is separately supplied through the ink supply ports  21  to the pressure chambers  22 . 
   The nozzle substrate  41  that is arranged at the bottom of the flow passage unit  18  is a metal thin plate material in which the plurality of nozzle openings  19  are formed in a column in the sub scanning direction at a pitch corresponding to the density of dot formation. The nozzle substrate  41  of the present embodiment is formed of a stainless plate material, and a plurality of the columns (nozzle columns) of the nozzle openings  19  are provided and aligned along the scanning direction (main scanning direction) of the recording head  2 . Then, one nozzle column is, for example, formed of 180 nozzle openings  19 . 
   The flow passage substrate  40  in the present embodiment is a plate-like member in which a flow passage portion that forms ink flow passages, that is, specifically, an opening portion that serves as the common ink chamber  20 , channel portions that serve as ink supply ports  21  and pressure chamber space portions that serve as the pressure chambers  22  are defined. The flow passage substrate  40  is formed by performing anisotropic etching on a silicon wafer, which is a kind of crystalline base material. 
   The above diaphragm  39  is, as shown in  FIG. 2 , a double layer structure composite plate material in which an elastic film  39   b , such as a PPS resin, is laminated on a support plate  39   a  made of metal, such as stainless steel. In the diaphragm  39 , island portions  48  for bonding the distal ends of the free end portions of the piezoelectric vibrators  15  are formed at portions corresponding to the pressure chambers  22 , and the above portions function as diaphragm portions. That is, the diaphragm  39  is configured so that elastic films around the island portions  48  elastically deform in accordance with the action of the piezoelectric vibrators  15 . In addition, the diaphragm  39  seals the open portion of the common ink chamber  20  of the flow passage substrate  40  and also serves as a compliance portion  49  as well. A portion of the diaphragm  39  corresponding to the compliance portion  49  is only formed of the elastic film  39   b  by removing the support plate  39   a . Note that the diaphragm  39  may be regarded as a sealing plate that seals the opening face of the flow passage portion  43  formed in the flow passage substrate  40 . 
   Here, in each of the above flow passage substrate  40 , four reference holes  52  in total for specifying the relative position with the diaphragm  39 , the nozzle substrate  42  and the head case  24  are formed in a frame region, which is a region located outside the region in which the flow passage portion  43  is formed (flow passage portion forming region), as shown in  FIG. 4  (in  FIG. 4 , three of the four reference holes  52  are shown). Then, the two reference holes  52  located on one long side (left side) of the flow passage substrate  40  are reference holes that are used when the flow passage unit  18  and the head case  24  are positioned, while, on the other hand, the two reference holes  52  located on the other long side (right side) are reference holes that are used when the components of the flow passage unit  18  are positioned. In this manner, by using two reference holes, which are used as a reference when positioning, that are located on any one of the long sides and that are spaced apart in long distance from each other, it is attempted to improve the positioning accuracy. 
   On the other hand, as shown in  FIG. 4 , in the diaphragm  39  and the nozzle substrate  41 , four through holes  53  and four through holes  54  are respectively formed at positions corresponding to the reference holes  52  of the flow passage substrate  40 . Then, when these flow passage unit components are bonded, the components are sequentially laminated on a jig. 
   In the present embodiment, first, in a state where positioning pins provided for the jig are respectively inserted into the through holes  54  on the other long side, the nozzle substrate  41  is laminated on a flow passage unit mounting face of the jig. Subsequently, the positioning pins are respectively inserted into the reference holes  52  on the other long side, and, in a state where an adhesive is interposed in between, the flow passage substrate  40  is mounted on the nozzle substrate  41 . Then, the positioning pins are respectively inserted into the through holes  53  on the other side, and, in a state where an adhesive is interposed in between, the diaphragm  39  is mounted on the flow passage substrate  40 . 
   In this manner, the nozzle substrate  41 , the flow passage substrate  40  and the diaphragm  39  are bonded one another in a state where their relative positions are specified, so that the flow passage unit  18  is assembled. 
   In the recording head  2 , a reinforcing plate  60  is interposed between the head case  24  and the flow passage unit  18 . Thus, compression deformation of the head case  24  or deformation of the flow passage unit  18  because of the action of the piezoelectric vibrators  15  of each vibrator unit that is fixedly accommodated in the accommodation chamber  32  of the head case  24  is suppressed. The reinforcing plate  60  is a plate-like member having insertion opening portions  61  that are formed at positions corresponding to island portions  48  that serve as diaphragm portions. The free end portions of the piezoelectric vibrators  15  are insertable through the insertion opening portions  61 . In this reinforcing plate  60 , the plurality of insertion opening portions  61  are provided and arranged at positions corresponding to the island portions  48 , which serve as the diaphragm portions of the flow passage unit  18 . Then, a crosspiece  62  is formed between any adjacent insertion opening portions  61 , and reinforcement is achieved by partitioning the insertion opening portions  61  with the crosspieces  62 . The thickness of the reinforcing plate  60  is set smaller than the length of the free end portion of each piezoelectric vibrator  15 . Thus, in a state where the reinforcing plate  60  is interposed between the head case  24  and the flow passage unit  18 , it is possible to closely adhere and bond the distal ends of the free end portions of the piezoelectric vibrators  15  with the island portions  48  of the diaphragm  39 . That is, the flow passage unit  18  includes a plurality of the diaphragm portions that are provided in a column in correspondence with a plurality of the pressure chambers, and the reinforcing plate  60  includes a plurality of the insertion opening portions  61  in correspondence with the diaphragm portions of the flow passage unit  18 . In addition, communication flow passages  65  are formed in the reinforcing plate  60  in correspondence with the case flow passages  31 . 
   In order to enhance the flow passage fitting face of the flow passage unit  18  of the head case  24 , the reinforcing plate  60  is formed of a material having a higher Young&#39;s modulus than the head case  24  made of plastic. The reinforcing plate  60  of the present embodiment is formed so that the insertion opening portions  61 , through which the free end portions of the piezoelectric vibrators  15  are inserted, and the crosspieces  62  that partition the insertion opening portions  61  are made by performing anisotropic etching process on a silicon substrate (silicon wafer), which is a kind of crystalline base material. Note that, in place of the silicon substrate, the reinforcing plate  60  may be, for example, formed of another material, such as stainless steel (SUS). 
   In addition, in the reinforcing plate  60 , a clearance step portion  63  is formed on its flow passage fitting face fitted with the flow passage unit  18  in an area, in which the insertion opening portions  61  are formed, on the side of the head case  24 . The amount of setback of the clearance step portion  63  from the face bonded with the flow passage unit  18  is set larger than the amount of displacement by which the piezoelectric vibrators  15  are displaced toward the head case  24  of the island portions  48  to thereby prevent the piezoelectric vibrators  15  from interfering with the insertion opening portions  61  or the crosspieces  62 . 
   Furthermore, the reinforcing plate  60  has two reference holes  64 , as positioning holes for positioning between the head case  24  and the flow passage unit  18 , and, as shown in  FIG. 4 , the two reference holes  64  are formed on one long side (right side) at which the reference holes  64  may be overlapped in correspondence with the reference holes  52  of the flow passage substrate  40  of the flow passage unit  18 . 
   At least one of the two reference holes  64  is formed in a polygonal shape having equal length of sides such that, as shown in  FIG. 5A , the polygonal shape is formed of, on the surface (110) plane of the silicon wafer of the reinforcing plate  60 , a first (111) plane that is perpendicular to the surface (110) plane and a second (111) plane that obliquely intersects with the first (111) plane at an angle of 70.53 degrees and that is perpendicular to the surface of the silicon wafer. In the present embodiment, the reference holes  64  are formed in a rhombic shape having four sides of equal length. The dimension of each reference hole  64  is determined so that a perpendicular distance between the opposite sides is d 1 . In other words, the dimension of the hole is determined so that the diameter of an imaginary inscribed circle Cv that inscribes the reference hole  64  is d 1 . The diameter d 1  of the inscribed circle Cv is made equal to the diameter of the positioning pin of the assembling jig and the diameter of the case pin of the head case  24 . That is, each reference hole  64  is set to a dimension such that rattling does not occur with respect to the positioning pin and/or the case pin. 
   In addition, at least the other one of the two reference holes  64  may be different in shape from the above reference hole  64 , as shown in  FIG. 5B , or may have a polygonal shape having sides of different length. In the present embodiment, the other one of two reference holes  64  is formed in a parallelogram oblong hole, the short side of which is defined by a first (111) plane and the long side of which is defined by a second (111) plane. The dimension of the short side of the above reference hole  64  is made equal to the dimension of each side of the above described reference hole  64 . Specifically, the perpendicular distance between the opposite long sides is set to d 1 , while, on the other hand, the perpendicular distance between the opposite short sides is set to d 2  that is longer than d 1 . Thus, when at least one of the two reference holes  64  of the reinforcing plate  60  is formed in a rhombic shape having four sides of equal length, the remaining one may be a polygonal shape having sides of different length, for example, a parallelogram oblong hole having a short side of which the length is equal to that of the reference hole  64  having a rhombic shape and a long side of which the length is different from that of the reference hole  64  having a rhombic shape. Alternatively, the two reference holes  64  all may be a rhombic shape. 
   When the head case  24 , the reinforcing plate  60  and the flow passage unit  18  are positioned with one another, using the two reference holes  64 , arranged on the long side, of the reinforcing plate  60 , the reinforcing plate  60  is bonded to the assembled flow passage unit  18  in a state where they are positioned with high accuracy and, thereafter, the reinforcing plate  60  is bonded to the head case  24 . Thus, it is possible to perform assembling in a state where it is positioned with high accuracy. The components of the flow passage unit  18  are laminated on the jig, when an adhesive between the components is hardened, the flow passage unit  18  is positioned using the reference holes  64  and then bonded. Then, these flow passage unit  18  and the reinforcing plate  60  are removed from the jig. After that, in a state where the diaphragm side faces the head case  24 , the reinforcing plate  60  is bonded to the flow passage fitting face of the head case  24 . At this time, by inserting the case pins respectively into the reference holes  64  of the reinforcing plate  60 , the reinforcing plate  60  and the head case  24  are fixed in a state where their relative position is specified. 
   In a case where the reinforcing plate  60  and the flow passage unit  18  are positioned and when the reinforcing plate  60  and the head case  24  are positioned, when one of the two reference holes  64  is formed as a parallelogram hole, the oblong hole resulting from the long side allows a gap to be formed between the parallelogram hole and the case pin of the head case  24 . Thus, even when there is a small tolerance, it is possible to absorb the tolerance by this gap. In this manner, without forming a crazing or a crack in the reinforcing plate  60  and/or the flow passage substrate  40 , it is possible to perform assembling in a state where positioning is made with high accuracy. 
   Here, when, among the two reference holes  64 , one reference hole  64  is formed as an oblong hole, it is elongated obliquely (second (111) plane direction). Therefore, when the center of the oblong reference hole  64  is deviated from the central axis of the case pin while positioning, there is a possibility that the position of the reinforcing plate  60  and the flow passage unit  18  may be deviated in a rotating direction about the case pin with respect to the head case  24 . However, the positional accuracy required between the flow passage unit  18  and the head case  24  is not as high as the positional accuracy required between the flow passage unit components, so that the above deviation in position is allowable. In addition, because the layout is made in such a manner that the distance between the two reference holes becomes long as much as possible, it is possible to suppress the adverse effect due to a deviation in position to a minimum degree. 
   In the above configured recording head  2 , because the reinforcing plate  60  having the insertion opening portions  61 , through which the free end portions of the piezoelectric vibrators  15  are insertable, at positions corresponding to the island portions  48 , which serve as the diaphragm portions, is interposed between the head case  24  and the flow passage unit  18 , the free end portions of the piezoelectric vibrators  15  are surrounded by the insertion opening portions  61  of the reinforcing plate  60  of the opening end of the head case  24  and the crosspieces  62  that partition the insertion opening portions  61 . Thus, it is possible to enhance the rigidity of the head case  24  and flow passage unit  18 . In this manner, it is possible to prevent the compression deformation of the head case  24  or the flow passage unit  18  due to the action of the piezoelectric vibrators  15 , and it is possible to obtain the discharge with high response frequency and/or uniform discharge characteristics. That is, it is possible to uniform the discharge characteristics of the pressure chambers (nozzle openings). 
   Particularly, because the opening edge of the accommodation chamber  32  of the head case  24  may be reinforced, it effectively prevents deformation of the flow passage unit  18 , and, because it is possible to uniform the discharge characteristics of the pressure chambers, it is suitable for the case in which a large-sized head, such as a line head, in which the shape of the opening of the accommodation chamber  32  is further large. In addition, in the recording head  2 , because the reinforcing plate  60  is interposed between the head case  24  and the flow passage unit  18 , without increasing the thickness of the flow passage unit  18  and the length of a flow passage from the distal end of each piezoelectric vibrator  15  to the corresponding nozzle opening  19 , it is possible to obtain the characteristic that is also advantageous in terms of high frequency response, or the like. 
   Furthermore, in the recording head  2 , because the reinforcing plate  60  is formed of a material having a higher Young&#39;s modulus than the head case  24  made of plastic, it is possible to reinforce the flow passage fitting face of the head case  24 . Particularly, by forming the reinforcing plate  60  using a silicon substrate, it is possible to manufacture the insertion opening portions  61  and the crosspieces  62  for the piezoelectric vibrators  15  by etching with high accuracy and, therefore, it is possible to minimize a gap between the insertion opening portions  61  or the crosspieces  62  and the piezoelectric vibrators  15  to thereby improve the rigidity. Then, because the clearance step portion  63  is formed on the reinforcing plate  60  adjacent to the flow passage fitting face, the island portions  48 , when displaced by the piezoelectric vibrators  15 , do not interfere with the reinforcing plate  60 . Thus, it is possible to further reduce the gap between the insertion opening portions  61  or the crosspieces  62  and the piezoelectric vibrators  15  and, therefore, it is possible to further effectively prevent the compression deformation of the head case  24  or the reinforcing plate  60 . 
   In addition, in the recording head  2 , because two reference holes  64  are formed as positioning holes along the long side of the reinforcing plate  60 , it is possible to assemble the flow passage unit  18  with the positioning holes that are overlapped using these reference holes  64  as a reference and also possible to assemble the head case  24  with the overlapped positioning holes. Thus, it is possible to assemble the case, the reinforcing plate and the flow passage unit in a state where they are positioned with high accuracy. 
   Note that, in the above described embodiments, when the accuracy of positioning holes (the accuracy of position or shape) of the reinforcing plate  60  is sufficiently ensured, it is applicable that, as shown in  FIG. 6 , positioning holes  64   a ′,  64   b ′ are formed at positions corresponding to two reference holes  52  located on the other long side of the flow passage substrate  40  on the reinforcing plate  60 , and, using the positioning holes  64   a ′,  64   b ′, the flow passage unit  18  and the reinforcing plate  60  are integrated and, after that, using the reference holes  64 , the head case  24  and the reinforcing plate  60  are bonded. In this case, the dimension of these reference holes  64  are set larger than the reference holes  52  of the flow passage substrate  40 . In addition, one positioning hole  64   a ′ is formed in a rhombic shape having four sides of equal length, and the other positioning hole  64   b ′ is set in a parallelogram oblong hole. That is, the positioning hole  64   a ′ is formed in a shape shown in  FIG. 5A , and the positioning hole  64   b ′ is formed in a shape shown in  FIG. 5B . 
   In addition, because the printer  1  may be placed in a state where the rigidity of the head case  24 , to which the piezoelectric vibrators  15  that constitute the recording head  2  are attached, is enhanced, it is possible to suppress the compression deformation of the head case  24  when the recording head  2  performs a discharge operation and, thereby, it is possible to discharge a prescribed amount of liquid droplets from the nozzle openings  19  at a prescribed speed. As a result, it is possible to make the liquid droplets be placed on a discharged object with further high accuracy. 
   In addition, because the printer  1  has the mounted recording head  2  that is assembled in a state where the components are positioned with high accuracy, when the recording head  2  performs a discharge operation (recording operation), it is possible to discharge a prescribed amount of ink droplets from the nozzle openings  19  at a prescribed speed. As a result, it is possible to make the discharged ink droplets be placed on the sheet of recording paper  6  with further high accuracy. In this manner, it is possible to improve the quality of an recorded image. 
   Incidentally, the aspects of the invention are not limited to the above described embodiments, but they may be modified into various alternative embodiments on the basis of the scope of the appended claims. 
   For example, in the above described embodiments, the clearance step portion  63  is provided in the reinforcing plate  60 ; however, when the diaphragm portions (island portions  48 ) are less likely to interfere with the insertion opening portions  61  or the crosspieces  62 , it is not necessary to provide the clearance step portion  63 . 
   In addition, the aspects of the invention are not limited to the recording head of the printer, but they may also be applied to other liquid ejecting heads or liquid ejecting apparatuses. For example, the aspects of the invention may be applied to a display manufacturing device that manufactures a color filter of a liquid crystal display, or the like, an electrode manufacturing device that forms an electrode of an organic EL (Electro Luminescence) display, an FED (field emission display), or the like, and a chip manufacturing device that manufactures a biochip, or the like.