Patent Publication Number: US-8113634-B2

Title: Recording head and manufacturing method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from Japanese Patent Application No. 2008-182466 filed on Jul. 14, 2008, the entire subject matter of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     Apparatuses, devices, and methods consistent with the present invention relate to recording heads and, more particularly, to recording heads having a stacked configuration. 
     BACKGROUND 
     A known inkjet head has a flow path unit formed with an ink flow path including a common ink chamber and a plurality of individual ink flow paths from the exit of the common ink chamber to a nozzle. The flow path unit has a stack structure wherein a plurality of plates are stacked on each other. Through holes formed in the plates are connected to each other, whereby an internal ink flow path is formed. An art of forming positioning holes in plates and inserting the positioning holes into positioning pins, thereby positioning the plates is known. However, in such an inkjet head, the ink flow path formed in the flow path unit is made increasingly smaller and smaller due to the demands of higher density of the nozzle and miniaturization of the inkjet head. Thus, with the dimensions of the ink flow path becoming more and more fine, the plates need to be positioned with even higher accuracy so that the through holes formed in the plates are joined precisely in a manufacturing process of the flow path unit. 
     SUMMARY 
     In the above-described inkjet head, the positioning accuracy of each plate depends on the tolerance of the inner diameter of the positioning hole formed in the plate and therefore it is difficult to position each plate with accuracy of the tolerance or less. 
     Therefore, illustrative aspects of the invention provide a recording head and a manufacturing method of the recording head for enabling adjacent plates to be positioned with high accuracy. 
     According to one illustrative aspect of the invention, there is provided a recording head comprising: a stacked body comprising: a liquid flow path; a plurality of plates stacked on each other; and a communicating hole piercing the stacked body, wherein each of the plurality of plates comprises a cross-sectional portion of the liquid flow path, such that when the plurality of plates are stacked on one another and the liquid flow path is formed, alternate ones of the plurality of plates comprise a reference hole, remaining ones of the plurality of plates comprise a positioning hole, a diameter of each of the references holes are the same, the diameter being larger than a diameter of each of the positioning holes, and the diameters of the positioning holes are successively smaller in order from one side to another side of the stacked body, and when the plates are stacked, the reference holes and the positioning holes of the plates alternate to communicate with each other to form the communicating hole. 
     According to another illustrative aspect of the invention, there is provided a recording head comprising: a stacked body comprising: a liquid flow path; a plurality of plates stacked on each other; and two communicating holes piercing the stacked body, wherein each of the plurality of plates comprises: a cross-sectional portion of the liquid flow path, such that when the plurality of plates are stacked on one another and the liquid flow path is formed; a positioning hole; and a reference hole, a diameter of the reference hole being larger than a diameter of the positioning hole, wherein locations of the positioning hole and the reference hole of a plate of the plurality of plates correspond to locations of the reference hole and the positioning hole, respectively, of a plate adjacent to the one plate such that, when the plates are stacked, the positioning holes and the reference holes of adjacent plates alternate to communicate with each other so as to form the two communicating holes, the diameters of the positioning holes of the plurality of plates being successively smaller in order from one side to another side of the stacked body relative to a stack direction of the plurality of plates. 
     According to still another illustrative aspect of the invention, there is provided a method for manufacturing the recording head according to the another aspect, the method comprising: a placing step comprising placing a new plate of the plurality of plates; a positioning step comprising: applying light through each of the two communicating holes from one side of the stacked body; picking up the light from the other side of the stacked body to form images of the two communicating holes; and performing relative positioning between the new plate and a plate placed immediately before the new plate based on the images; and a stacking step comprising stacking the new plate on the plate placed immediately before. 
     According to the illustrative aspects of the invention, in the placing step, the positioning hole involved in the new placed plate is accommodated in the reference hole and the positioning hole involved in the different plate placed just before that plate and the reference hole involved in the new placed plate accommodates the positioning hole involved in the different plate placed just before that plate. Thus, in the positioning step, when an image of the new placed plate is picked up while light in the direction from the one end to the opposite end is applied to the stacked body, the position of the positioning hole of the new placed plate and the position of the positioning hole of the plate placed just before that plate can be provided at the same time, as the image pickup result. Since relative positioning between the new placed plate and the plate placed just before that plate is performed based on the image pickup result, the adjacent plates can be positioned with high accuracy. Accordingly, the liquid flow path can be formed with high accuracy. 
     According to the illustrative aspects of the invention, in the positioning step, when an image of the new placed plate is picked up while light in the direction from the one end to the opposite end is applied to the stacked body, the position of the positioning hole of the new placed plate and the position of the positioning hole of the plate placed just before that plate can be provided at the same time, as the image pickup result. Since relative positioning between the new placed plate and the plate placed just before that plate is performed based on the image pickup result, the adjacent plates can be positioned with high accuracy. Accordingly, the liquid flow path can be formed with high accuracy. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic side view of an inkjet printer according to an exemplary embodiment of the invention; 
         FIG. 2  is a plan view of a head main body shown in  FIG. 1 ; 
         FIG. 3  is an enlarged view of the area surrounded by alternate long and short dash line shown in  FIG. 2 ; 
         FIG. 4  is a sectional view taken on line IV-IV shown in  FIG. 3 ; 
         FIG. 5  is a sectional view of a flow path unit close to one end portion thereof shown in  FIG. 2 ; 
         FIG. 6  is a block diagram showing a manufacturing process of the flow path unit shown in  FIG. 2 ; 
         FIG. 7  is a schematic top view of an assembling apparatus used for manufacturing the flow path unit shown in  FIG. 2 ; 
         FIG. 8  is a schematic side view of the assembling apparatus shown in  FIG. 7 ; 
         FIGS. 9A and 9B  are diagrams showing side and bottom views, respectively, of the flow path unit during the manufacturing process of  FIG. 6 ; 
         FIGS. 10A and 10B  are additional diagrams showing side and bottom views, respectively, of the flow path unit during a later stage of the manufacturing process than those of  FIGS. 9A and 9B ; and 
         FIGS. 11A and 11B  are yet another set of additional diagrams showing side and bottom views, respectively, of the flow path unit during a later stage of the manufacturing process than those of  FIGS. 10A and 10B . 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary embodiments of the invention will now be described with reference to the drawings. 
       FIG. 1  is a schematic side view of an inkjet printer  101  according to an exemplary embodiment of the invention.  FIG. 2  is a plan view of a head main body shown in  FIG. 1 . The inkjet printer  101  is a color inkjet printer having four inkjet heads  1  (one example of a recording head) as shown in  FIG. 1 . The inkjet printer  101  includes a feeder unit  11  at the left of  FIG. 1  and a sheet discharge part  12  at the right of  FIG. 1 . 
     The inkjet printer  101  includes a sheet conveying path for conveying a sheet P from the feeder unit  11  to the sheet discharge part  12 . A pair of conveying rollers  5   a  and  5   b  for conveying the sheet sandwiched therebetween is placed downstream just from the feeder unit  11  in a sheet conveying direction. The pair of conveying rollers  5   a  and  5   b  conveys the sheet P from the feeder unit  11  to the right in the figure. A conveying mechanism  13  is provided in an intermediate portion of the sheet conveying path. The conveying mechanism  13  includes two belt rollers  6  and  7 , an endless conveying belt  8  wound so as to be stretched between the belt rollers  6  and  7 , and a platen  15  placed in an area surrounded by the conveying belt  8 . The platen  15  supports the conveying belt  8  so that the conveying belt  8  does not bend downward at positions opposed to the inkjet heads  1 . A nip roller  4  is placed at a position opposed to the belt roller  7 . The nip roller  4  presses the sheet P conveyed by the conveying rollers  5   a  and  5   b  from the feeder unit  11  against an outer peripheral surface  8   a  of the conveying belt  8 . 
     A conveying motor (not shown) rotates the belt roller  6 , whereby the conveying belt  8  runs. Accordingly, the conveying belt  8  conveys the sheet P pressed against the outer peripheral surface  8   a  by the nip roller  4  to the sheet discharge part  12  while holding the sheet P in an adhesive manner. The conveying belt  8  is formed on the surface with a weakly adhesive silicon resin layer. 
     A peeling plate  14  is provided downstream from the conveying belt  8  in the sheet conveying direction. The peeling plate  14  is adapted to peel the sheet P adhering to the outer peripheral surface  8   a  of the conveying belt  8  from the outer peripheral surface  8   a  and guide the sheet P to the sheet discharge part  12  at the right from the left in the figure. 
     The four inkjet heads  1  are fixed along the conveying direction of the sheet P and correspond to four color inks (cyan (C), magenta (M), yellow (Y), and black (K)). In other words, the feeder unit  11  is a line printer. Each of the four inkjet heads  1  has a head main body  2  at the bottom (i.e., facing the conveying belt  8 . As shown in  FIG. 2 , the head main body  2  has an elongated rectangular parallelepiped shape extending in a main scanning direction of a direction orthogonal to the sheet conveying direction. The bottom face of the head main body  2  is an ink ejection face  2   a  opposed to the outer peripheral surface  8   a  of the conveying belt  8 . When the sheet P conveyed on the conveying belt  8  passes through the side just below the four head main bodies  2  in order, color ink droplets are ejected from the ink ejection face  2   a  to the top face of the sheet P, namely, a print face. Accordingly, any desired color image can be formed in a print area of the sheet P. 
     Next, the head main body  2  will be explained with reference to  FIGS. 2 to 5 .  FIG. 2  is a plan view of the head main body  2 .  FIG. 3  is an enlarged view of the area surrounded by the alternate long and short dash line in  FIG. 2 . Note that in  FIG. 3 , for convenience of the description, pressure chambers  110 , apertures  112 , and ejection ports  108  in a lower portion of an actuator unit  21  that would usually be drawn by dashed lines are drawn by solid lines.  FIG. 4  is a fragmentary sectional view taken on line IV-IV shown in  FIG. 3 .  FIG. 5  is a sectional view of the proximity of one end portion relative to the length direction of a flow path unit  9  (one example of a stacked body). 
     As shown in  FIG. 2 , the head main body  2  has four actuator units  21  fixed to a top face  9   a  of the flow path unit  9 . As shown in  FIG. 3 , an ink flow path including the pressure chambers  110 , etc., is formed in the flow path unit  9 . The actuator unit  21  includes a plurality of actuators corresponding to the pressure chambers  110  and has a function of selectively giving ejection energy to ink in the pressure chamber  110  as the actuator unit is driven by a driver IC (not shown). 
     As shown in  FIG. 2 , the flow path unit  9  has a rectangular parallelepiped shape. Ten ink supply ports  105   b  to which ink is supplied are opened in the top face  9   a  of the flow path unit  9 . A pair of communicating holes  20   a  and  20   b  piercing the flow path unit  9  is formed in the proximity of each end portion relative to the length direction of the flow path unit  9 . As shown in  FIG. 5 , the communicating holes  20   a  and  20   b  are formed of positioning holes  18   a  to  18   i  and reference holes  19   a  to  19   i  used when plates  122  to  130  forming the flow path unit  9  are stacked. As shown in  FIGS. 2 and 3 , the flow path unit  9  is internally formed with two manifold flow paths  105  communicating with five ink supply ports  105   b  arranged in the length direction (main scanning direction) of the flow path unit  9  in the proximity of the end portion relative to the short length direction (sub scanning direction) of the flow path unit  9 . Each of the manifold flow paths  105  has a plurality of submanifold flow paths  105   a  branching so as to be in parallel and extend in the main scanning direction. The flow path unit  9  is formed on a lower face with the ink ejection face  2   a  where a large number of ejection ports  108  are placed like a matrix (see  FIGS. 3 and 4 ). 
     As shown in  FIGS. 4 and 5 , the flow path unit  9  is made up of nine plates  122  to  130  (one example of a plurality of plates) made of a metal material of stainless steel, etc. Each of the plates  122  to  130  has a rectangular plane long in the main scanning direction. 
     The plates  122  to  130  are stacked on each other and aligned, whereby the through holes formed in the plates  122  to  130  are joined. When the plates  122  to  130  are aligned and stacked together, the two manifold flow paths  105  and a large number of individual ink flow paths  132 , each running from the exit of the submanifold flow path  105   a  involved in each manifold flow path  105  via the pressure chamber  110  to the ejection port  108 , are formed in the flow path unit  9 . The manifold flow paths  105 , the submanifold flow paths  105   a  and the individual ink flow paths  132  are one example of a liquid flow path. 
     A set made up of positioning holes  18   a  to  18   i  and reference holes  19   a  to  19   i  each having a circular opening is formed in the proximity of each end portion relative to the length direction of the plates  122  to  130 . The plates  122  to  130  are stacked on each other while they are aligned, whereby the positioning holes  18   a  to  18   i  and the reference holes  19   a  to  19   i  formed in the plates  122  to  130  are placed alternately and concentrically so as to communicate with each other to form communicating holes  20   a  and  20   b . Specifically, the positioning hole  18   a , the reference hole  19   b , the positioning hole  18   c , the reference hole  19   d , the positioning hole  18   e , the reference hole  19   f , the positioning hole  18   g , the reference hole  19   h , and the positioning hole  18   i  are placed alternately and concentrically in order from the plate  130  side (from the lower side in  FIG. 5 ) so as to communicate with each other to form the communicating hole  20   a . Similarly, the reference hole  19   a , the positioning hole  18   b , the reference hole  19   c , the positioning hole  18   d , the reference hole  19   e , the positioning hole  18   f , the reference hole  19   g , the positioning hole  18   h , and the reference hole  19   i  are placed alternately and concentrically in order from the plate  130  side (from the lower side in  FIG. 5 ) so as to communicate with each other to form the communicating hole  20   b.    
     In each of the communicating holes  20   a  and  20   b , the positioning holes  18   a  to  18   i  have opening areas progressively smaller in order from the lower end face of the flow path unit  9  (ink ejection face  2   a ) to the upper end face (the end face opposite to the ink ejection face  2   a , the top face of the plate  122 ). All reference holes  19   a  to  19   i  have the same size opening and the same shape. The opening area of each of the reference holes  19   a  to  19   i  is larger than the opening area of each of the positioning holes  18   a  to  18   i . Thus, in the plan view concerning each of the communicating holes  20   a  and  20   b , an outline of the positioning holes  18   a  to  18   i  are accommodated in the reference holes  19   a  to  19   i , and successive ones of the positioning holes  18   a  to  18   i  are accommodated in each other (see  FIGS. 11A and 11B ). 
     In the exemplary embodiment, the positioning holes  18   a  to  18   i  and the reference holes  19   a  to  19   i  are positioned on the center line extending in the length direction in the center of the short length direction of the plates  122  to  130 , as shown in  FIGS. 2 and 5 . The positioning holes  18   a  to  18   i  and the reference holes  19   a  to  19   i  forming a set are placed at symmetrical positions with respect to the center of placement of all through holes (all partial flow paths) in both end portions in the length direction in the plates  122  to  130 . All through holes are also placed symmetrically with respect to the center of placement thereof. Since the center of placement is positioned on the center line, when the plates  122  to  130  are stacked, the directions of the plates  122  to  130  need not be aligned. 
     An ink flow in the flow path unit  9  will be explained with reference to  FIGS. 2 to 4 . Ink supplied to the flow path unit  9  through the ink supply port  105   b  flows into the submanifold flow path  105   a  in the manifold flow path  105 . The ink in the submanifold flow path  105   a  is distributed to each of the individual ink flow paths  132  and arrives at the ejection port  108  through the aperture  112  functioning as a diaphragm and the pressure chamber  110 . The actuator unit  21  gives ejection energy to the ink in the pressure chamber  110 , whereby an ink droplet is ejected from the ejection port  108 . 
     Next, a manufacturing process of the flow path unit  9 , of a manufacturing method of the inkjet head  1  will be explained with reference to  FIGS. 6 to 11 .  FIG. 6  is a block diagram to show the manufacturing process of the flow path unit  9 .  FIG. 7  is a schematic top view of an assembling apparatus  80  used for manufacturing the flow path unit  9 .  FIG. 8  is a schematic side view of the assembling apparatus  80 .  FIGS. 9 to 11  are situation drawings to show the manufacturing process of the flow path unit  9 .  FIGS. 9A ,  10 A, and  11 A are sectional views of the plates  122  to  130  in a plate positioning step.  FIGS. 9B ,  10 B, and  11 B are top views of the plates  122  to  130  viewed from a camera  95 . Herein, an image of sets of the positioning holes picked up by cameras  95  are drawn by solid lines.  FIGS. 9 to 11  show only the set of positioning holes  18   a  to  18   i  and reference holes  19   a  to  19   i  formed in the proximity of one end portion of each of the plates  122  to  130 , which is similar to the set of positioning holes  18   a  to  18   i  and reference holes  19   a  to  19   i  formed in the proximity of the opposite one end portion. 
     As shown in  FIG. 6 , the assembling step of the flow path unit  9  includes a plate placing step, a plate positioning step, and a plate stacking step performed by the assembling apparatus  80 . 
     First, the assembling apparatus  80  will be explained. As shown in  FIGS. 7 and 8 , the assembling apparatus  80  includes a plate conveying mechanism  81 , a stage  91 , two cameras  95 , and two lighting fixtures  96 . The plate conveying mechanism  81  conveys the plates  122  to  130  one at a time onto the stage  91 . The stage  91  can move the plates  122  to  130  stacked in order on the top face in an X direction (right-left direction in  FIG. 7 ), a Y direction (up and down direction in  FIG. 7 ), a Z direction (up and down direction in  FIG. 8 ), and a θ direction (rotating direction of the plane in  FIG. 7 ). The two cameras  95  pick up an image by looking downward from above the stage  91 . The two lighting fixtures  96  are opposed to the cameras  95  and apply light upward from below from the inside of the stage  91 . In  FIG. 7 , for convenience of the description, the cameras  95 , which would usually be drawn by solid lines, are drawn using dashed lines. 
     The plate conveying mechanism  81  has a linear actuator  82  extending in the Y direction, an arm  83  extending in the X direction and capable of being moved in the Y direction by the linear actuator  82 , and an adsorption pad  84  fixed to the lower end face of the arm  83  for adsorbing and holding the plates  122  to  130 . The plate conveying mechanism  81  holds the plates  122  to  130  on the adsorption pad  84  and then moves the arm  83  so as to place the plates  122  to  130  held on the adsorption pad  84  at the stack position above the stage  91 . 
     After each of the plates  122  to  130  held on the adsorption pad  84  is placed at the stack position, the stage  91  moves upward (Z direction), whereby the next one of the plates  122  to  130  in order is stacked on the plate previously stacked on the stage  91 . 
     Each of the arm  83  and the adsorption pad  84  is formed with two through holes  85  opposed to the sets made up of the positioning holes  18   a  to  18   i  and the reference holes  19   a  to  19   i  involved in the plates  122  to  130  held on the adsorption pad  84 . On the other hand, the stage  91  is formed with two through holes  92  for allowing light applied from the lighting fixtures  96  to arrive at the cameras  95 . When each of the plates  122  to  130  are placed at the stack position by the plate conveying mechanism  81 , the two through holes  92  are opposed to the two through holes  85 . At this time, the light applied from each lighting fixture  96  passes through the through hole  92  and the through hole  85  and arrives at the corresponding camera  95 . Accordingly, the cameras  95  can pick up an image of the sets made up of the positioning holes  18   a  to  18   i  and the reference holes  19   a  to  19   i  of the plates  122  to  130  held on the adsorption pad  84 . 
     Referring again to  FIG. 6 , in the plate placing step, the plate conveying mechanism  81  places the plates  122  to  130  at the stack position one at a time in the stack order starting at the plate  130  (in the order starting at the plate close to the ink ejection face  2   a ). The plate  130  first placed at the stack position is placed directly on the stage  91  as the stage  91  moves upward along the Z direction. 
     In the plate positioning step, each time one plate of the plates  122  to  129  (i.e., the second plate or later) is placed at the stack position in the plate placing step, the cameras  95  pick up an image of the sets made up of the positioning holes  18   a  to  18   i  and the reference holes  19   a  to  19   i  of the plate  122  to  129  newly placed at the stack position. 
     For example, a case where the plate  129  is newly placed at the stack position in the plate positioning step after the plate  130  has been placed on the stage  91  as shown in  FIGS. 9A and 9B  will be explained. In this case, the opening area of the reference hole  19   b  is larger than the opening area of the positioning hole  18   a , and the opening area of the reference hole  19   a  is larger than the opening area of the positioning hole  18   b . Thus, in the plan view shown in  FIG. 9B , the reference hole  19   b  of the plate  129  accommodates the positioning hole  18   a  of the plate  130 , and the positioning hole  18   b  of the plate  129  is accommodated in the reference hole  19   a  of the plate  130 . 
     Thus, in the plate positioning step, only light passing through the positioning holes  18   a  and  18   b , of light applied from the lighting fixtures  96  arrives at the cameras  95 . Accordingly, the cameras  95  can pack up an image of the two positioning holes  18   a  and  18   b  at the same time. Since the cameras  95  pick up an image of transmitted light, a binarization processing is performed for the picked-up image, whereby the position and the shape of each of the positioning holes  18   a  and  18   b  can be precisely provided. Relative positioning between the plates  129  and  130  is performed by finely adjusting the position of the stage  91  in the X direction, the Y direction, and the θ direction so that the centers of the positioning holes  18   a  and  18   b  in each set are placed in a predetermined positional relationship in the picked-up image. Accordingly, the reference hole  19   b  and the positioning hole  18   a  are placed concentrically and the positioning hole  18   b  and the reference hole  19   a  are placed concentrically. 
     A case where the plate  128  is newly placed at the stack position in the plate positioning step after the plate  129  has been placed on the plate  130  as shown in  FIGS. 10A and 10B  will be explained. In this case, the opening area of the reference holes  19   a  and  19   c  is larger than the opening area of the positioning hole  18   b , and the opening area of the reference hole  19   b  is larger than the opening area of the positioning holes  18   a  and  18   c . Thus, in the plan view shown in  FIG. 10B , the reference holes  19   a  and  19   c  of the plates  128  and  130  accommodate the positioning hole  18   b  of the plate  129 , and the positioning hole  18   c  of the plate  128  is accommodated in the positioning hole  18   a  of the plate  130  and the reference hole  19   b  of the plate  129 . 
     Thus, in the plate positioning step, only light passing through the positioning holes  18   b  and  18   c , of light applied from the lighting fixtures  96  arrives at the cameras  95 . Accordingly, the cameras  95  can pack up an image of the two positioning holes  18   b  and  18   c  at the same time. Relative positioning between the plates  128  and  129  is performed by finely adjusting the position of the stage  91  in the X direction, the Y direction, and the θ direction so that the centers of the positioning holes  18   b  and  18   c  in each set are placed in a predetermined positional relationship in the picked-up image. Accordingly, the positioning hole  18   c , the reference hole  19   b , and the positioning hole  18   a  are placed concentrically and the reference hole  19   c , the positioning hole  18   b , and the reference hole  19   a  are placed concentrically. 
     Subsequently, a case where the last plate  122  is newly placed at the stack position in the plate positioning step after the plates  123  to  130  have been placed as shown in  FIGS. 11A and 11B  will be explained. In this case, the opening area of the reference holes  19   a  to  19   i  is larger than the opening area of the positioning holes  18   a  to  18   i . The opening areas of the positioning holes  18   a ,  18   c ,  18   e ,  18   g , and  18   i  are larger in order toward the ink ejection face  2   a . The opening areas of the positioning holes  18   b ,  18   d ,  18   f , and  18   h  are larger in order toward the ink ejection face  2   a . Thus, in the plan view shown in  FIG. 11B , the reference holes  19   a ,  19   c ,  19   e ,  19   g , and  19   i  and the positioning holes  18   b ,  18   d , and  18   f  accommodate the positioning hole  18   h , and the positioning hole  18   i  is accommodated in the positioning holes  18   a ,  18   c ,  18   e , and  18   g  and the reference holes  19   b ,  19   d ,  19   f , and  19   h . Accordingly, only light passing through the positioning holes  18   h  and  18   i , of light applied from the lighting fixtures  96  arrives at the cameras  95 . Accordingly, the cameras  95  can pack up an image of the two positioning holes  18   h  and  18   i  at the same time. 
     Relative positioning between the plates  122  and  123  is performed by finely adjusting the position of the stage  91  in the X direction, the Y direction, and the θ direction so that the centers of the positioning holes  18   h  and  18   i  in each set are placed in a predetermined positional relationship in the picked-up image. Accordingly, the positioning holes  18   a ,  18   c ,  18   e ,  18   g , and  18   i  and the reference holes  19   b ,  19   d ,  19   f , and  19   h  are placed concentrically and the positioning holes  18   b ,  18   d ,  18   f , and  18   h  and the reference holes  19   a ,  19   c ,  19   e , and  19   g  are placed concentrically. 
     In the plate stacking step, each newly placed plate  122  to  129  positioned in the plate positioning step and the plate of the plates  123  to  130  that is placed just before the newly placed plate are stacked by moving the stage  91  upward along the Z direction. 
     The plate placing step, the plate positioning step, and the plate stacking step described above are performed for the plates  122  to  130  (the plate  130  is only placed on the stage  91  in the plate placing step) in the stack order starting at the plate  130 . After the plate  122  is stacked on the plate  123 , the nine plates  122  to  130  are metal-joined. The flow path unit  9  is now complete. 
     According to the exemplary embodiment described above, relative positioning between two adjacent plates of the plates  122  to  130  is performed based on the center positions of the positioning holes formed in the newly placed plate, provided by picking up an image of the plate newly placed at the stack position while applying upward light of the lighting fixtures  96  to the plates which have already been placed on the stage  91  from below the ink ejection face  2   a . Thus, the adjacent plates of the plates  122  to  130  can be positioned with high accuracy. Accordingly, the ink flow path can be formed with high accuracy. 
     Since the set of positioning holes  18   a  to  18   i  and reference holes  19   a  to  19   i  is formed in the proximity of each end portion relative to the length direction of the plates  122  to  130 , the adjacent plates  122  to  130  are positioned at two distant points. Accordingly, the positioning accuracy of the plates  122  to  130  can be enhanced and the angle in the plane of the plates  122  to  130  can also be positioned with high accuracy. 
     Further, the reference holes  19   a  to  19   i  have the same size and the same shape, so that the cost of forming the reference holes  19   a  to  19   i  in the plates  122  to  130  can be reduced. 
     Although the exemplary embodiments of the invention have been described, the invention is not limited thereto. For example, in the above-described exemplary embodiments, a set of positioning holes  18   a  to  18   i  and reference holes  19   a  to  19   i  is formed in the proximity of each end portion relative to the length direction of the plates  122  to  130 . Alternatively, the set of positioning holes and reference holes may be formed at any other location on each plate such as the center of each plate. Additionally, three or more sets of positioning holes and reference holes may be formed in each plate or only one set may be formed. However, if only one set of positioning holes and reference holes is used, the angle in the plane of each plate cannot be determined. Thus, in such a case, it is advantageous for the plates to be stacked using an assembling apparatus for mechanically determining the angle of the plate. 
     Further, in the above-described exemplary embodiments, the reference holes  19   a  to  19   i  have the same size and the same shape. Alternatively, either the size or the shape of each reference hole may vary from one plate to another as long as the positioning hole positioned downstream relative to the light applying direction can be accommodated in the plan view. 
     In the above-described exemplary embodiments, the positioning holes  18   a  to  18   i  and reference holes  19   a  to  19   i  have each a circular opening. Alternatively, one or more of the positioning holes and reference holes may have an opening of any other shape such as a rectangle. 
     In the above-described exemplary embodiments, in the communicating holes  20   a  and  20   b , the positioning holes  18   a  to  18   h  and the reference holes  19   a  to  19   i  are placed concentrically. Alternatively, each plate may be precisely positioned by placing at least one of the positioning holes and the reference holes at a nonconcentric position. 
     In the above-described exemplary embodiments, metal joining is adopted for joining after stacking. Alternatively, an adhesive may be used to join the plates together. In this case, an adhesive applying step of applying an adhesive to the joint face of the plates to be stacked is provided before the plate placing step shown in  FIG. 6 . 
     In the adhesive applying step, a heat-hardening adhesive is applied to each joint face according to a transfer process. For example, a heat-hardening adhesive is applied onto a lumiler sheet like a film (adhesive support). An adhesive layer is formed in a predetermined thickness with a squeegee. The adhesive applying mechanism may be installed adjacent to the stage  91 . In this case, the arm  83  is moved to above the lumiler sheet together with the plates  122  to  129 . The joint face of the plates  122  to  129  (transfer face to which the adhesive is transferred) and the adhesive layer are opposed to each other with a predetermined gap. A transfer roller is placed below the lumiler sheet. Further, the transfer roller is moved upward, the lumiler sheet is sandwiched between the transfer roller and the plate  122  to  129 , and the transfer roller is moved in parallel along the joint face. Accordingly, the adhesive layer having a given thickness is transferred to the whole joint face of the plates  122  to  129 . The plate  130  first placed on the stage  91  is placed directly on the stage  91  without undergoing the applying step. 
     In addition to the described applying step, the plate placing step, the plate positioning step, and the plate stacking step described above are performed for the plates  122  to  129  in order and a precursor of the flow path unit  9 . Further, the precursor is pressurized while the precursor is heated at an adhesive hardening temperature or more, whereby the flow path unit  9  is provided. 
     According to another aspect of the invention, in the recording head, wherein each of the plurality of plates comprises a plurality of hole sets, each hole set comprising the positioning hole and the reference hole. 
     According thereto, each of the plates is positioned at two or more points. Therefore, the positioning accuracy can be enhanced and the angle in the plane of the plate can also be positioned with high accuracy. 
     According to still another aspect of the invention, in the recording head, wherein one hole set of the plurality of hole sets is positioned at one end of the recording head in a length direction thereof, and another hole set of the plurality of hole sets is positioned at the other end of the recording head in the length direction. 
     According thereto, the plates are positioned at two distant points. Therefore, each of the plates can be positioned still more precisely. 
     According to still another aspect of the invention, in the recording head, wherein the reference holes have substantially the same size and the same opening shape. 
     According thereto, the cost of forming the reference holes in the plates can be reduced. 
     According to still another aspect of the invention, in the method for manufacturing the recording head, wherein the relative positioning between the new plate and the plate placed immediately before the new plate is performed based on a positional relationship between the positioning hole of the new plate and the positioning hole of the plate placed immediately before the new plate. 
     According to still another aspect of the invention, in the method for manufacturing the recording head, wherein the relative positioning between the new plate and the plate placed immediately before the new plate is performed by aligning the center of the positioning hole of the new plate with the center of reference hole of the plate placed immediately before the new plate, and aligning the center of the reference hole of the new plate with the center of the positioning hole of the plate placed immediately before the new plate. 
     According to still another aspect of the invention, in the method for manufacturing the recording head, wherein, in the placing step, the plurality of plates are placed such that, in a plan view, the positioning hole of the new plate is accommodated in one or more reference holes and one or more positioning holes of one or more plates placed before the new plate, and the reference hole of the new plate accommodates the positioning hole of the plate placed immediately before the new plate.