Abstract:
A liquid ejecting head includes a plurality of nozzles each including an ejection outlet for ejecting a droplet, an ejection energy generating element, disposed at a position opposing the ejection outlet, for generating energy for ejecting a droplet, a pressure chamber provided with the ejection energy generating element and fluidly communicating with the ejection outlet, and a supply passage for supplying the liquid to the pressure chamber, wherein the nozzles include a first nozzle and a second nozzle which are connected with respective ones of the supply passages having lengths different from each other, wherein the first nozzle and the second nozzle are, disposed at one end portion with respect to a widthwise direction of an elongated supply chamber for supplying the liquid to the first nozzle, wherein the supply passage for the first nozzle extends in a direction perpendicular to a direction of liquid ejection from the ejection outlet and fluidly communicates with the supply chamber, and wherein the supply passage for the first nozzle extends in a direction parallel with the direction of liquid ejection.

Description:
FIELD OF THE INVENTION AND RELATED ART 
       [0001]    The present invention relates to a liquid jet head for jet liquid such as ink. 
         [0002]    In recent years, demand has been increasing for a recording apparatus which is significantly higher in speed, resolution, and image quality, and also, lower in noise than a conventional recording apparatus. One of the recording apparatuses which can satisfy such demand is an ink jet recording apparatus. An ink jet recording apparatus is structured to record an image on recording paper by jet droplets of ink (recording liquid) from its recording head so that the droplets of ink fly to the recording paper and adhere to the surface of the recording paper. 
         [0003]    Generally, an ink jet recording apparatus employs energy generating elements as the means for jet droplets of ink. Among various energy generating elements usable as the means for ejecting droplets of ink, an electrothermal transducer, such as a heater, and an electromechanical transducer, such as piezoelectric element, have been widely used. Both means can be controlled in their ink ejecting operation, by controlling the electric signals supplied thereto. The principle, on which the ink ejecting method which uses an electrothermal transducer is based, is as follows: As voltage is applied to an electrothermal transducer, the body of ink, which is in contact with the electrothermal transducer, instantaneously boils, that is, a bubble (bubbles) is generated (body of ink changes in phase), suddenly increasing the pressure in the adjacencies of the electrothermal transducer. As a result, an ink droplet (ink droplets) is jetted out of the ink ejecting head through a nearby opening of the head. The principle on which the ink ejecting method which uses an electromechanical transducer (piezoelectric element) is based, is as follows: As voltage is applied to a piezoelectric element, the element displaces, suddenly increasing the pressure in the adjacencies of the electromechanical transducer. As a result, and an ink droplet (droplets) is jetted out of a nearby opening the head by the pressure generated by the displacement of the element. 
         [0004]    The ink ejecting method which employs an electrothermal transducer as the ink ejecting energy generating element has merit in that it does not require a large amount of space, that it allows a recording head to be simple in structure, and also, that it makes easier to dispose a large number of ink ejecting nozzles in a small space. On the other hand, this ink ejecting method suffers from problems peculiar thereto. One of them is that the heat generated by an electrothermal transducer accumulates in a recording head, which results in the change in the volume of the ink droplet which an ink jet recording head jets. Another problem is that the electrothermal transducer is affected by the impact attributable to the collapsing of a bubble; the electrothermal transducer suffers from cavitation. Further, this ink ejecting method is problematic in that the air having dissolved into ink would reappear, as air bubbles, in the recording head, affecting thereby the ink jet recording head in terms of ink ejecting performance and image quality. 
         [0005]    There are various methods for solving the above-described problems. Some of them are disclosed in the following documents: 
         [0006]    Document 1: Japanese Laid-open Patent Application S54-161935 
         [0007]    Document 2: Japanese Laid-open Patent Application S61-185455 
         [0008]    Document 3: Japanese Laid-open Patent Application S61-249768 
         [0009]    Document 4: Japanese Laid-open Patent Application H04-10941 
         [0010]    They are related to a recording method based on ink jet, and an ink jet recording head. More specifically, the ink ejecting methods disclosed in the abovementioned Documents are characterized in that the ink jet head is structured so that the bubbles generated by driving an electrothermal transducer with a recording signal are allowed to escape into the atmosphere (ambient air). The Documents claim that the employment of the ink jet recording methods disclosed therein makes it possible to provide an ink jet recording head which is significantly more stable in ink droplet volume, significantly smaller in ink droplet volume, and significantly higher in the ink droplet ejecting speed than an ink jet recording head in accordance with the prior art. Further, they claim that they can prevent cavitation from occurring when the bubble collapses, and therefore, can improve an ink jet recording head in the length of its service life. Moreover, they claim that the employment of the ink jet recording methods disclosed therein can provide an ink jet recording head which is significantly higher in resolution than an ink jet recording apparatus in accordance with the prior art. 
         [0011]    The structure of the ink jet recording heads disclosed in the abovementioned Documents are characterized in that in order to allow the bubbles to escape into the atmosphere, the minimum distance between an electrothermal transducer for generating a bubble (bubbles), and the corresponding nozzle, through which ink is jetted out, is rendered significantly smaller than that in an ink jet recording head in accordance with the prior art. 
         [0012]      FIG. 12  shows one of the typical forms of the nozzle of an ink jet printing head in accordance with the conventional art.  FIG. 12(   a ) is a phantom plan view of the ink jet recording head in accordance with the prior art, as seen from the direction perpendicular to the substrate of the ink jet recording head, and  FIG. 12(   b ) is a sectional view of the ink jet recording head, at a plane F-F shown in  FIG. 12(   a ).  FIG. 12(   c ) is a sectional view of the ink jet recording head, at a plane G-G shown in  FIG. 12(   a ). 
         [0013]    To describe the structure of an ink jet recording head of the above described type, the ink jet recording head is made up of a substrate  102 , heaters  111 , an ink passage plate  103  (orifice plate). Each heater  111  is an electrothermal transducer for ejecting ink, and is on the substrate  102 . The ink passage plate  103  is joined with the substrate  102  to form ink passages. The ink passage plate  103  has: multiple passages, through which ink flows; a common ink chamber  116 , from which ink flows to each of the multiple ink passages; and multiple holes  114  (outward end portion of nozzle) ( FIG. 12 ), through which ink droplets are jetted out of the recording head. Each nozzle has: a bubble generation chamber  120 , in which a bubble is generated by the heater  111 ; and an ink passage  119  (dedicated ink passage) through which ink is delivered to the bubble generation chamber  120 . The heater  111  is on the bottom surface of the bubble generation chamber  120  (which is part of top surface of substrate  102 ). The substrate  102  has an ink supply chamber (common ink chamber), which is for supplying each of the dedicated ink passages  119  with ink from the back side of the substrate  102 , that is, the opposite side of the substrate  102  from the primary surface (top surface), that is, the side which is in contact with the ink passage plate  103 . Further, the ink passage plate  103  is provided with ink ejection outlets  114 , which oppose the heaters  111  on the substrate  102 , one for one. 
         [0014]    The operation of the recording head structured as described above is as follows: The ink supplied to the common ink chamber is supplied to the bubble generation chamber  120  through the dedicated ink passage  119  of each nozzle, and fills up the bubble generation chamber  120 . The ink in the bubble generation chamber  120  is jetted in the direction which is roughly perpendicular to the primary surface of the substrate  102 , by a bubble (bubbles) which generates as the ink is instantaneously boiled (film boiling) by the heater  111 . As the ink is jetted out of the ink ejection outlet  114 , it flies away in the form of an ink droplet. 
         [0015]    Currently, it is desired that when an ink jet printer is used to record on ordinary paper or the like, the printer records at a high speed, whereas when it is used to record on special purpose paper, such as glossy paper, it records at a high level of image quality. One of the methods for forming a high quality image at a high speed is to employ an ink jet recording head, which remains relatively large in ink droplet volume even when it is recording at a high speed. As the means for realizing a high speed printer, such as the one described above, there are a method which increases an ink jet printing head in the nozzle response speed, and a method which increases an ink jet head in nozzle count by disposing nozzles at higher density. 
         [0016]    One of the known methods for disposing multiple nozzles at a high density is to dispose the ink ejection outlets  114  in a zigzag pattern as shown in  FIG. 13 .  FIG. 13(   a ) is a phantom plan view of a part of the ink jet recording head, as seen from the direction perpendicular to the primary surface of the substrate, and  FIG. 13(   b ) s a plan view of the wiring of the ink jet recording head, which is on the substrate of the recording head. 
         [0017]    However, the method which disposes the ink ejection outlets  114  in the zigzag pattern as shown in  FIGS. 13(   a ) and  13 ( b ) is problematic in that in order to increase an ink jet recording head in ink ejection outlet density, the dedicated ink passage  119   b  of each of the second nozzles  115   b  has to be reduced in width. 
         [0018]    Reducing the dedicated ink passage  119   b  of the second nozzle  115   b  increases the dedicated ink passage  119   b  in viscous resistance D (value of which can be calculated using mathematical equation 1 given below). Thus, it reduces the nozzle  105   b  in response speed, making it difficult to increase the ink jet recording head in recording speed. 
         [0000]    
       
         
           
             D 
             = 
             
               η 
                
               
                 
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                   0 
                   1 
                 
                  
                 
                   
                     
                       G 
                        
                       
                         ( 
                         x 
                         ) 
                       
                     
                     
                       
                         S 
                          
                         
                           ( 
                           x 
                           ) 
                         
                       
                       2 
                     
                   
                    
                   
                       
                   
                    
                   
                      
                     x 
                   
                 
               
             
           
         
       
     
         [0019]    η: viscosity of liquid 
         [0020]    S(X): size of cross section of given point of dedicated ink passage  119   b    
         [0021]    G(X): shape factor of given point of dedicated ink passage  119   b    
         [0022]    l: length of dedicated ink passage  119   b    
         [0023]    One of the methods for increasing in size the cross section of the ink delivery passage  19   b  for the second nozzle  105   b  is to form the heater  111  and bubble generation chamber  112  of the first nozzle  105   a  so that the heater  111  is rectangular, as seen from the direction perpendicular to the primary surface of the substrate, and also, so that the bubble generation chamber  120  is rectangular in the vertical cross section. It is possible that the employment of this method will prevent the problem that increasing an ink jet recording head in nozzle density reduces the recording head in response speed. However, this solution has its own problem. That is, if the heater  111  is made rectangular, and the bubble generation chamber  120  of the second nozzle  105   b  is formed so that not only is its vertical cross section is rectangular, but also, it is extremely long and narrow, air bubbles are liable to collect in the bubble generation chamber  120 . As air bubbles collect in the bubble generation chamber  120 , they cause the ink jet recording head to erroneously jet ink. That is, they cause the ink jet recording head to change in the shape in which the ink jet recording head jets ink droplets, causing thereby such a problem as the increase in the number by which satellite ink droplets are produced. 
       SUMMARY OF THE INVENTION 
       [0024]    Thus, the primary object of the present invention is to solve the above described problems to make it possible to provide a high speed liquid ejecting head which is significantly higher in nozzle response, being therefore significantly higher in recording speed and image quality than a high speed liquid ejecting head in accordance with the prior art. 
         [0025]    According to an aspect of the present invention, there is provided a liquid ejecting head comprising a plurality of nozzles each including an ejection outlet for ejecting a droplet, an ejection energy generating element, disposed at a position opposing said ejection outlet, for generating energy for ejecting a droplet, a pressure chamber provided with said ejection energy generating element and fluidly communicating with said ejection outlet, and a supply passage for supplying the liquid to said pressure chamber, wherein said nozzles include a first nozzle and a second nozzle which are connected with respective ones of said supply passages having lengths different from each other, wherein said first nozzle and said second nozzle are, disposed at one end portion with respect to a widthwise direction of an elongated supply chamber for supplying the liquid to said first nozzle, wherein said supply passage for said first nozzle extends in a direction perpendicular to a direction of liquid ejection from said ejection outlet and fluidly communicates with said supply chamber, and wherein said supply passage for said first nozzle extends in a direction parallel with the direction of liquid ejection. 
         [0026]    According to the present invention, the first nozzle is in connection to the common ink supply chamber, and extends in the direction perpendicular to the liquid ejecting direction, whereas the second nozzle is extended in the direction parallel to the ink ejecting direction, making it possible to dispose multiple nozzles at a significantly higher level of density than the level of density at which nozzles are disposed in a comparable ink jet recording head in accordance with the prior art, without reducing the ink jet recording head in nozzle response. Therefore, the present invention can significantly increase an ink jet recording head (apparatus) in recording speed, compared to a comparable ink jet recording head in accordance with the prior art. 
         [0027]    These and other objects, features, and advantages of the present invention will become more apparent upon consideration of the following description of the preferred embodiments of the present invention, taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0028]      FIG. 1  is a perspective view of a typical ink jet printer in accordance with the present invention, showing the structure of the apparatus. 
           [0029]      FIG. 2  is a block diagram of the ink jet printer. 
           [0030]      FIG. 3  is a schematic drawing of a typical ink jet recording head in accordance with the present invention. 
           [0031]      FIG. 4  is a schematic drawing of the nozzle structure of the ink jet recording head in the first embodiment of the present invention. 
           [0032]      FIG. 5  is a schematic drawing of the wiring of the ink jet recording head in the first embodiment, which is on the substrate of the head. 
           [0033]      FIG. 6  is a phantom plan view of a part of the ink jet recording head in the second embodiment of the present invention, showing the nozzle structure thereof. 
           [0034]      FIG. 7  is a schematic drawing of a part of the ink jet recording head in the third embodiment of the present invention, showing the nozzle structure thereof. 
           [0035]      FIG. 8  is a schematic drawing of a part of the ink jet recording head in the fourth embodiment of the present invention, showing the nozzle structure thereof. 
           [0036]      FIG. 9  is a schematic drawing of a part of the ink jet recording head in the fifth embodiment of the present invention, showing the nozzle structure thereof. 
           [0037]      FIG. 10  is a phantom plan view of a part of the ink jet recording head in the sixth embodiment of the present invention, showing the nozzle structure thereof. 
           [0038]      FIG. 11  is a phantom plan view of a part of the ink jet recording head in the seventh embodiment of the present invention, showing the nozzle structure thereof. 
           [0039]      FIG. 12  is a schematic drawing of one of the nozzles of the typical ink jet recording head in accordance with the prior art which is comparable to the ink jet recording head in accordance with the present invention. 
           [0040]      FIG. 13  is a phantom plan view of a part of the typical ink jet recording head in accordance with the prior art, which is comparable to the ink jet recording head in accordance with the present invention, showing the multiple nozzles of the part. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0041]    Hereinafter, the preferred embodiments of the present invention will be described in detail with reference to the appended drawings. 
       &lt;Ink Jet Printer&gt; 
       [0042]      FIG. 1  is a perspective view of a typical ink jet printer in accordance with the present invention, and shows the structure of the apparatus. 
         [0043]    As will be evident from  FIG. 1 , an ink jet printer IJRA is provided with a carriage HC for moving the recording head IJH across the recording medium P, such as a piece of recording paper, in a manner to scan the surface of the recording medium P. The carriage HC has a pin (unshown) which fits in a spiral groove  5004  of a lead screw  5005  which is rotated forward or backward by the forward or backward rotation of the motor  5013 , through driving force transmission gears  5009 - 5011 . The carriage HC is movably supported by a guide rail  5003 . As a lead screw  5005  is rotationally driven, the carriage HC reciprocally moves in the direction indicated by an arrow mark a or the direction indicated by an arrow mark b. This carriage HC holds the ink jet cartridge IJC on its top surface. The ink jet cartridge IJC is an integral combination of the recording head IJH and ink container IT. 
         [0044]    The ink jet printer IJRA is also provided with a paper pressing plate  5002 , which presses the recording medium P upon a platen  5000 , across the entire range of the recording medium P in terms of the moving direction of the carriage HC. Further, the ink jet printer IJRA is provided with a pair of photo-couplers  5007  and  5008 , which are home position detecting devices and are used to detect the presence of the lever  5006   b  of the carriage HC to switch the direction in which the motor  5013  is to be rotated, or the like purposes. 
         [0045]    Further, the ink jet printer IJRA is provided with a recovery unit which restores the ink jet printer IJRA in ink ejecting performance by suctioning the ink in the ink jet recording head of the ink jet printer IJRA through the opening  5023  of a recording head capping member  5022 . The recovery unit has: the capping member  5022  for covering the ink ejecting side of the recording head IJH; a capping member supporting member  5016  for supporting the capping member  5022 ; and a suctioning device  5015  for reducing the internal pressure of the capping member  5022 . The recovery unit also has: a cleaning blade  5017  for wiping away the ink having adhered to the ink ejecting side of the recording head IJH; and a supporting member  5019  which supports the blade  5017  in such a manner that the blade  5017  can be moved forward or backward. The recovery unit is supported by a chassis  5018 . The blade  5017  for the recovery unit, and the structure for supporting the blade  5017 , do not need to be limited to those described above. Obviously, any of the known ink jet head cleaning blades is compatible with this embodiment of the present invention may be employed instead of the blade  5017 . The recovery unit is also provided with a lever  5021 , which is for starting the operation for suctioning the ink in the ink jet recording head to restore its performance. The lever  5021  is moved by the movement of a cam  5020  which is in engagement with the carriage HC. The movement of the lever  5021  is controlled the driving force transmitted from a motor to the lever  5021  through one of the known mechanical power transmitting mechanism, such as a clutch. 
         [0046]    The ink jet printer IJRA is structured so that the abovementioned capping operation, cleaning operation, and suction-based performance recovery operation of the recovery unit, are carried out by rotationally driving the lead screws  5005  while the carriage HC is in its home range (area in the adjacencies of home position), into which the carriage HC is moved by the lead screw  5005 , at the points which correspond to the abovementioned operations, respectively. Incidentally, the recovery unit structure does not need to be limited to the recovery unit structure described above; any recovery unit structure may be employed as long as the above-mentioned operations can be carried out with the known timing. 
       &lt;Control System&gt; 
       [0047]    Next, the structure of the control system for controlling the recording operation of the above described ink jet printer will be described. 
         [0048]      FIG. 2  is a block diagram of the control circuit of the ink jet printer IJRA, and shows the structure of the circuit. As will be evident from  FIG. 2 , the control circuit has: an interface  1700  through which recording signals are inputted; and a MPU  1701  (Micro Processing Unit) which functions as a logic circuit. The control circuit also has: a ROM  1702  in which the control programs which the MPU  1001  performs are stored; a DRAM  1703  in which various data (recording signals, recording data to be supplied to recording head IJH, and the like) are stored. Further, the control circuit has a gate array  1704  (G.A.) which controls the operation for outputting recording data to the recording head IJH. The gate array  1704  also controls the operation for transferring data among the interface  1700 , MPU  1701 , and RAM  1703 . 
         [0049]    The control circuit controls the driving of the recording head IJH through a head driver  1705  for driving the recording head IJH. It also controls the driving of a carrier motor  1701  for conveying the recording head IJH, and the driving of a conveyer motor  1709  for conveying the recording medium P, through motor drivers  1706  and  1707 , which drive the conveyer motor  1709  and carrier motor, respectively. 
         [0050]    Next, the operation of the above described control circuit will be described. As recording signals are inputted into the control circuit through the interface  1700 , they are converted into the recording data for a printer, between the gate array  1704  and MPU  1701 . Then, the motor drivers  1706  and  1707  are driven, and the recording head IJH is driven according to the recording data sent to the head drivers  1705 . As a result, an image is formed on the recording medium P. 
         [0051]    Next, the ink jet recording head IJH will be described. Of the aforementioned two types of an ink jet recording head, this ink jet recording head IJH is a recording head which has ink ejecting energy generating elements for generating the thermal energy for ejecting liquid ink from the ink jet recording head. This ink jet recording head IJH uses ink ejecting energy generating elements to generate thermal energy, and uses the thermal energy to change ink in phase. With the employment of this ink ejecting method, this ink jet recording IJH can achieve significantly higher level of image density and significantly higher level of precision, at which a text or image is recorded, than a comparable ink jet recording apparatus in accordance with the prior art. In particular, in this embodiment, electrothermal transducers are employed as the ink ejecting energy generating elements for generating thermal energy. That is, ink is jetted by utilizing the pressure which generates when a bubble generates as ink is instantaneously boiled (film boiling) by the heat generated by the electrothermal transducers. 
         [0052]    First the general structure of the ink jet recording head in this embodiment will be described. 
         [0053]      FIG. 3(   a ) is a schematic drawing of a typical ink jet recording head in accordance the present invention.  FIG. 3(   b ) is a sectional view of the ink jet recording apparatus, at a plane A-A shown in  FIG. 3(   a ). 
         [0054]    Referring to  FIGS. 3(   a ) and  3 ( b ), the ink jet recording head is provided with: a substrate  2 , on which heaters  11  (heat generating resistor), which are electrothermal transducers, have been formed; and an ink passage plate  3  (orifice plate), which is bonded to the substrate  2  to form ink passages. 
         [0055]    The substrate  2  may be formed of glass, ceramic, resin, metal, or the like, for example. However, generally, it is formed of Si. There are the heaters  11  and wiring electrodes (unshown), on the primary surface of the substrate  2 . The wiring electrodes are for applying voltage to the heaters  111 . The heaters  11  and wiring electrodes are directly formed on the primary surface of the substrate  2 . Each heater  11  is covered with dielectric film (unshown) for improving heat dispersion, and the dielectric film is covered with protective film (unshown) for protecting the heater  11  (dielectric film) from cavitation. Further, the ink passage plate  3  for forming the nozzles, etc., is formed of metal, polyimide, polysulfone, or epoxy resin, for example. 
         [0056]    Referring again to  FIGS. 3(   a ) and  3 ( b ), the ink jet recording head has: multiple heaters  11 ; multiple nozzles  5   a  having an ink ejection outlet  14   a  through which ink droplets are jetted; and multiple nozzle  5   b  having an ink ejection outlet  14   b  through which ink droplets are jetted. More specifically, there are two sets of nozzles  5   a , and two sets of nozzles  5   b . One set of nozzles  5   a  is on one side of the common ink supply chamber  16  and the other set of nozzles  5   a  is on the other side of the common ink supply chamber  16 . Further, one set of nozzles  15   b  is on one side of the common ink supply chamber  16 , and the other set is on the other side of the common ink supply chamber  16 . Further, the nozzles  5   a  and  5   b , which are on one side of the common ink supply chamber  16  in terms of the direction parallel to the shorter edges of the common ink supply chamber  16 , make up the first column  17  of nozzles, whereas the nozzles  5   a  and  5   b , which are on the other side of the common ink supply chamber  16  make up the second column  18  of nozzles. 
         [0057]      FIG. 4  is a schematic drawing of the ink jet recording head in the first embodiment, and shows the structure of the nozzles.  FIG. 4(   a ) is a phantom plan view of a part of the ink jet recording head, as seen from the direction perpendicular to the primary surface of the substrate  2 .  FIG. 4(   b ) is a sectional view of the ink jet recording head, at a plane B-B shown in  FIG. 4(   a ). 
         [0058]    Referring to  FIG. 4(   a ), each heater  11  is in the bubble generation chamber  20  (pressure chamber) formed by the substrate  2  and ink passage plate  3 . It is on the primary surface of the substrate  2 . The ink jet recording head has multiple separation walls which separate the adjacent two dedicated ink passages  19   a from each other. Each separation wall extends from the corresponding bubble generation chamber  20  to the adjacencies of the common ink supply chamber  16 . Referring to  FIG. 4(   b ), the top wall of the bubble generation chamber  20  is provided with the ink ejection outlet  14   a , which aligns with the heater  11  in terms of the direction perpendicular to the primary surface of the substrate  2 . 
         [0059]    The dedicated ink passage  19   a  is on the inward side of the bubble generation chamber  20  of the first nozzle  5   a , and is in connection to the first common ink channel  16   a . The lengthwise direction of the dedicated ink passage  19   a  of the first nozzle  5   a  is perpendicular to the direction in which ink is jetted from the ink ejection outlet  14   a . The dedicated ink passage  19   b , which is in connection to the second common ink channel  16   b , is on the outward side of the bubble generation chamber  20  of the second nozzle  5   b . The lengthwise direction of the dedicated ink passage  19   b a of the second nozzle  5   b  is parallel to the direction in which ink is jetted from the ink ejection outlet  14   b.    
         [0060]    In the case of the first nozzle  5   a , the ink supplied to the common ink supply chamber  16  from an ink container is supplied to the dedicated ink passage  19   a  through the first common ink channel  16   a  of the common ink supply chamber  16 . In the case of the second nozzle  5   b , ink is supplied from the ink container to the dedicated ink passage  19   b  through the second common ink channel  16   b , without going through the common ink supply chamber  16 . 
         [0061]    Structuring the ink jet recording head as described above makes it possible to leave satisfactorily large the width of the dedicated ink passage  19   a  of the first nozzle  5   a  and the width of the dedicated ink passage  19   b  of the second nozzle  5   b , while making significantly higher the density of the ink ejection outlet  14   a  of the first nozzle  5   a  and the density of the ink ejection outlet  14   b  of the second nozzle  5   b  than a comparable ink jet recording head in accordance with the prior art. In other words, it makes it possible to eliminate the problem that disposing ink ejection outlets (nozzles) at a high level of density increases the viscous resistance of each of the dedicated ink passages. Therefore, it makes it possible to provide an ink jet recording head which is high in nozzle response, being therefore capable of recording at a high speed. 
         [0062]    Incidentally, in this embodiment, the dedicated ink passage  19   b  for the second nozzle  5   b  is not in connection to the common ink supply chamber  16 . However, this structural arrangement is not intended to limit the present invention in scope. That is, the ink jet recording head may be structured so that the first and second nozzles  5   a  and  5   b  are both in connection to the common ink supply chamber  16 . 
         [0063]    Hereafter, the nozzles of the ink jet recording head, which are the essential portions of the recording head, will be described about their structure, with reference to some of the preferred embodiments of the present invention. 
       EMBODIMENT 1 
       [0064]      FIG. 5(   a ) is a schematic drawing of the wiring on the substrate  2  of ink jet recording head chip.  FIG. 5(   b ) is a schematic drawing of the wiring on the substrate  2 , which is different in position, in terms of the thickness direction of the substrate  2 , from the wiring shown in  FIG. 5(   a ) (wiring on back side of substrate  2  from wiring shown in  FIG. 5(   a )). The common wiring  25  shown in  FIG. 5(   a ) is in electrical connection to the dedicated wiring  26 , shown in  FIG. 5(   b ), which is different in position from the common wiring  25  in terms of the thickness direction of the substrate  2 , through the contact hole  27  (through hole) shown in  FIG. 5(   a ). 
         [0065]    In this embodiment, the first nozzle column  17  is on one side of the long and narrow common ink supply chamber  16 , in terms of the direction parallel to the shorter edges of the common ink supply chamber  16 , and the second nozzle column  18  is on the other side. Referring to  FIG. 4(   a ), the ink ejection outlets  14   a  and  14   b  of the nozzle column  17 , and the ink ejection outlets  14   a  and  14   b  of the nozzle column  18 , are arranged so that in terms of the direction parallel to the longer edges of the common ink supply chamber  16 , each ink ejection outlet  14   a  corresponds in position to the mid point between the two ink ejection outlets  14   b  adjacent to the hole  14   a ; they are arranged in a zigzag pattern. Further, the ink ejection outlets  14   a  and  14   b  of the nozzle column  17 , and the ink ejection outlets  14   a  and  14   b  of the second nozzle column  18 , are aligned so that the distance between the adjacent two ink ejection outlets  14   a , and the distance between the adjacent two ink ejection outlets  14   b , corresponds to a resolution of no less than 1,200 dpi (no less than 21.2 μm), and also, so that in terms of the direction perpendicular to the longer edges of the common ink supply chamber  16 , the distance between the adjacent ink ejection outlet  14   a  and  14   b  of the first nozzle column  17 , and the distance between the adjacent ink ejection outlet  14   a  and  14   b  of the second nozzle column  18 , also corresponds to a resolution of 1,200 dpi. That is, in terms of the direction parallel to the longer edges of the common ink storage chamber, an ink ejection outlet  14   a  is staggered in positioned from the corresponding ink ejection outlet  14   b.    
         [0066]    In this embodiment, the ink ejection outlet  14   a  of the first nozzle  5   a  is 12 μm in diameter. The heater  11  of the first nozzle  5   a  is square and is 22 μm in the length of each edge. Further, the bubble generation chamber  20  of the first nozzle  5   a  is a rectangular parallelepipedic space which is 26 μm, 26 μm, and 14 μm in length, width, and height, respectively. The dedicated ink passage  19   a  of the first nozzle  5   a  is a rectangular parallelepipedic space which is 21 μm, 10 μm, and 14 μm in length, width, and height, respectively. On the other hand, the ink ejection outlet  14   b  of the second nozzle  5   b  is 9 μm in diameter. The heater  11  of the second nozzle  5   b  is square and is 17 μm in the length of each edge. Further, the bubble generation chamber  20  of the second nozzle  5   b  is a rectangular parallelepipedic space which is 24 μm, 50 μm, and 14 μm in length, width, and height, respectively. The dedicated ink passage  19   b  of the second nozzle  5   b  is a rectangular parallelepipedic space which is 17 μm, 17 μm, and 320 μm in length, width, and height, respectively. 
         [0067]    The ink droplet jetted out of the first nozzle  5   a  is roughly 2.5 pl in volume V 1 , and roughly 14 m/sec in speed. The response frequency f 1  of the first nozzle  5   a  is roughly 25 kHz. “Response frequency” means the frequency value at which the amount of deviation from the referential frequency becomes roughly 70%. The ink droplet jetted out of the second nozzle  5   b  is roughly 1.5 pl in volume V 2 , and roughly 14 m/sec in speed. The response frequency f 2  of the second nozzle  5   b  is roughly 20 kHz. In this embodiment, therefore, the relationship between the volume V 1  of the ink droplet jetted out of the first nozzle  5   a  and the volume V 2  of the ink droplet jetted out of the second nozzle  5   b  satisfies an inequity of V 1 &gt;V 2 . Further, the response frequency fl of the first nozzle  5   a  and the response frequency f 2  of the second nozzle  5   b  satisfies an inequity of f 1 &gt;f 2 . 
         [0068]    In this embodiment, the wiring of the ink jet recording head is formed as shown in  FIGS. 5(   a ) and  5 ( b ), therefore, the wiring is roughly the same in size as that of a comparable ink jet recording head in accordance with the prior art, which is shown in  FIG. 13 . 
         [0069]    In the case of the nozzle structure shown in  FIG. 13(   a ), if an attempt is made to achieve the roughly the same level of performance as that of the ink jet recording head in this embodiment, the clearance T between the bubble generation chamber of the first nozzle  105   a  and the dedicated ink passage of the second nozzle  105   b  has to be no more than 4 μm. However, in consideration of the fastness of the bond between the ink passage plate (orifice plate) and substrate, it is very difficult to achieve the clearance T of no more than 4 μm. 
         [0070]    As described above, in the case of the ink jet recording head in this embodiment, the dedicated ink passage  19   a  of the first nozzle  5   a  is in contact with the common ink supply chamber  16 , and its lengthwise direction is perpendicular to the direction in which ink is jetted, whereas the lengthwise direction of the dedicated ink passage  19   b  of the second nozzle  5   b  is parallel to the direction in which ink jetted. This structural arrangement can eliminate the problem that arranging the first and second nozzles  5   a  and  5   b  at a high density requires the dedicated ink passage of the second nozzle  5   b  to be made narrower. Therefore, it makes it possible to provide an ink jet recording head which is no lower in nozzle response speed, while being significantly high in the density at which its nozzles  5   a  and  5   b  are disposed, and yet, is higher in recording speed than a comparative ink jet recording head in accordance with the prior art. 
         [0071]    Next, the other embodiments of the present invention will be described. For convenience, the portions of each of the ink jet recording head in the following embodiments of the present invention, which are the same as the counterparts of the ink jet recording head in the first embodiment, are given the same referential symbols as those given to the counterparts, one for one. 
       EMBODIMENT 2 
       [0072]      FIG. 6  is a phantom plan view of a part of the ink jet recording head in the second embodiment of the present invention, as seen from the direction perpendicular to the top surface of the ink passage plate  3 , and shows the nozzle structure of the recording head. Next, referring to  FIG. 6 , the specific differences of the ink jet recording head in this embodiment from the ink jet recording head in the first embodiment will be described. 
         [0073]    Referring to  FIG. 6 , in this embodiment, the centerline of the dedicated ink passage  19   a  of the first nozzle  5   a  is offset from the center of the primary surface of the heater  11 , in terms of the direction parallel to the nozzle columns. Positioning the dedicated ink passage  19   a  of the first nozzle  5   a  as shown in  FIG. 6  relative to the heater  11  causes ink to circularly flow about the axial line of the ink ejection outlet  14 , as disclosed in Japanese Laid-open Patent Application 2002-321369. That is, with the ink jet recording head structured as described above, even if a bubble generated by the heater  11  of the first nozzle  5   a  fails to come into contact with the ambient air, the circular flow of ink about the axial line of the ink ejection outlet  14   a  of the first nozzle  5   a  makes the ink jet recording head unstable in the point at which a bubble collapses, and therefore, the wiring is prevented from being broken by cavitation. The characteristics of the nozzles  5   a  and  5   b  in this embodiment are roughly the same as those in the first embodiment. 
       EMBODIMENT 3 
       [0074]      FIG. 7  shows the nozzle structure of the ink jet recording head in the third embodiment.  FIG. 7(   a ) is a phantom plan view of a part of the ink jet recording head, as seen from the direction perpendicular to the primary surface of the ink passage plate  3 .  FIG. 7(   b ) is a sectional view of the part of the ink jet recording head shown in  FIG. 7(   a ), at a plane C-C shown in  FIG. 7(   a ). Next, referring to  FIG. 7 , the specific differences of the ink jet recording head in this embodiment from the ink jet recording head in the first embodiment will be described. 
         [0075]    Referring to  FIG. 7 , the ink jet recording head in this embodiment is structured so that the positional relationship between the heater  11  of the second nozzle  5   b  and the first nozzle  5   a , positional relationship between ink ejection outlet  14   b  the second nozzle  5   b  and the first nozzle  5   a , and positional relationship between the dedicated ink passages  19   b  of the second nozzle  5   b  and the first nozzle  5   a , are reverse to those in the first embodiment. Positioning the heaters  11 , ink ejecting openings  14 , and dedicated ink passages  19  as described above makes it possible to increase the distance between the heater  11  of the first nozzle  5   a  and the heater  11  of the second nozzle  5   b . Thus, the wiring of the ink jet recording head in this embodiment is easier to form than that in the first embodiment. The characteristics of the nozzles  5   a  and  5   b  are roughly the same as those in the first embodiment. 
       EMBODIMENT 4 
       [0076]      FIG. 8  shows the nozzle structure of the ink jet recording head in the fourth embodiment.  FIG. 8(   a ) is a phantom plan view of a part of the ink jet recording head, as seen from the direction perpendicular to the primary surface of the ink passage plate  3 .  FIG. 8(   b ) is a sectional view of the part of the ink jet recording head shown in  FIG. 8(   a ), at a plane D-D in  FIG. 8(   a ). Next, referring to  FIG. 8 , the specific differences of the ink jet recording head in this embodiment from the ink jet recording head in the first embodiment will be described. 
         [0077]    Referring to  FIG. 8 , the ink jet recording head in this embodiment is structured so that in terms of the direction parallel to the direction in which ink is jetted, the ink ejection outlets  14   a  and  14   b  of the first and second ink ejecting portions  21  and  22 , respectively, of the ink jet recording head is made up of two portions, that is, the outward portion and inward portion, which are different in diameter. Structuring the ink jet recording head so that each of the ink ejection outlets of the first and second ink ejecting portions  21  and  22  of the ink jet recording head has two portions different in diameter reduces the nozzles in forward inertance, making it possible to reduce in size the heater  11  compared to the one in the first embodiment. In the case of the first and second nozzles  5   a  and  5   b  structured as shown in  FIG. 8 , the second portion, that is, the inward portion, of the ink ejection outlet  14   a  of the ink ejecting first portion  21  of the first nozzle  5   a , is 18 μm in diameter, and the second portion of the ink ejection outlet  14   b  of the ink ejecting second portion  22  of the second nozzle  5   b  is 15 μm in diameter. The heater  11  of the first nozzle  5   a  is square and 15 μm in the length of each edge, whereas the heater  11  of the second nozzle  5   b , which also is square, is 15 mm in the length of each edge. That is, the ink jet recording head in this embodiment is smaller in the size of the heater  11 . The characteristics of the nozzles  5   a  and  5   b  in this embodiment are virtually the same as those in the first embodiment. 
       EMBODIMENT 5 
       [0078]      FIG. 9  shows the nozzle structure of the ink jet recording head in the fifth embodiment.  FIG. 9(   a ) is a phantom plan view of a part of the ink jet recording head, as seen from the direction perpendicular to the primary surface of the ink passage plate  3 .  FIG. 9(   b ) is a sectional view of the part of the ink jet recording head shown in  FIG. 9(   a ), at a plane E-D shown in  FIG. 9(   a ). Next, referring to  FIG. 9 , the specific differences of the ink jet recording head in this embodiment from the ink jet recording head in the fourth embodiment will be described. 
         [0079]    Referring to  FIG. 9 , in this embodiment, the common ink channel  16   a  is formed by joining the ink passage plate  3  with the substrate  2  in which the common ink supply chamber  16  is formed by removing a part of the substrate  2  by anisotropic etching or the like method. Further, the bottom end of the common ink channel  16   b  is open at the slanted surface of the common ink supply chamber  16 , which is formed by the anisotropic etching or the like method. Therefore, the dedicated ink passage  19   b  of the second nozzle  5   b  is shorter than the thickness of the substrate  2 . 
         [0080]    Structuring an ink jet recording head so that its first and second common ink channel  16   a  and  16   b  are like those in this embodiment makes the second nozzle  5   b  faster in response speed than that of the second nozzle  5   b  in the fourth embodiment. 
       EMBODIMENT 6 
       [0081]      FIG. 10  is a phantom plan view of the ink jet recording head in the sixth embodiment, as seen from the direction perpendicular to the ink passage plate  3 . Next, referring to  FIG. 10 , the specific differences of this embodiment from the fourth embodiment will be described. 
         [0082]    Referring to  FIG. 10 , in this embodiment, each of the first nozzles  5   a  has a dedicated ink passage  19   a  which leads to the common ink channel  16   a , and a dedicated ink passage  19   b  which leads to the common ink channel  16   b , whereas each of the second nozzles  5   b  has two dedicated ink passages  19   b  which lead to the common ink channel  16   b.    
         [0083]    Providing each of the nozzles  5   a  and  5   b  with multiple (two in this embodiment) dedicated ink passages  19  improves the nozzles  5   a  and  5   b  in response speed, compared to the nozzles  5   a  and  5   b  in the fourth embodiment. 
       EMBODIMENT 7 
       [0084]      FIG. 11  is a phantom plan view of the ink jet recording head in the seventh embodiment, as seen from the direction perpendicular to the ink passage plate  3 . Next, referring to  FIG. 11 , the specific differences of this embodiment from the fourth embodiment will be described. 
         [0085]    Referring to  FIG. 11 , the ink jet recording head in this embodiment is provided with third nozzles  5   c  in addition to the first and second nozzles  5   a  and  5   b . The third nozzles  5   c  are different from the first and second nozzles  5   a  and  5   b  in the location of their ink ejection outlet, in terms of the direction parallel to the shorter edges of the top and bottom openings of the common ink supply chamber  16 . Like the dedicated ink passage  19   b  of each of the second nozzle  5   b , the dedicated ink passage  19   b  of each of the third nozzles  5   c  extends in the direction parallel to the direction in which ink is jetted. 
         [0086]    The employment of the nozzle structure in this embodiment makes it possible to form an ink jet recording head, a specific portion (or specific portions) of which is higher in nozzle density than the other portions. 
         [0087]    While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth, and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims. 
         [0088]    This application claims priority from Japanese Patent Application No. 225695/2007 filed Aug. 31, 2007 which is hereby incorporated by reference.