Patent Document

BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a recording head capable of recording high quality images rapidly and reliably, and to an inkjet recording device equipped with the recording head. 
   2. Description of Related Art 
   In order to record high-quality images rapidly and reliably using an on-demand inkjet recording device having a plurality of densely integrated nozzles, it is particularly necessary to increase the ink droplet ejection rate and to achieve stable ink ejection at a high frequency. 
   One structure of nozzles configured of push-type piezoelectric elements is disclosed in Japanese unexamined patent application publication No. HEI-6-270403. In this push-type piezoelectric element system, vertical vibrations of a pole-shaped piezoelectric element push a diaphragm that constitutes one surface of an ink pressure chamber, decreasing the volume in the pressure chamber and causing an ink droplet to be ejected from the nozzle hole. Pole-shaped piezoelectric elements of a number equal to the number of nozzle holes are arranged in a row. One end of the pole-shaped piezoelectric element opposite another side that contacts the diaphragm is fixed to a support base. The support base is affixed to a head housing. 
   However, when piezoelectric elements are driven in a recording head having this construction, vertical vibrations from the piezoelectric element are transferred not only to the diaphragm, but also to the support base, the head housing, and the like, making ink droplet ejection unstable. Vibrations from the piezoelectric element also affect nozzles adjacent to the nozzle corresponding to the piezoelectric element, generating what is called cross talk, which produces fluctuations in the ink droplet ejection characteristics. 
   In order to avoid this problem, Japanese unexamined patent application publication No. 2002-361868 discloses an inkjet recording device in which the piezoelectric element support base is configured of a stiff member capable of absorbing vibrations from the piezoelectric element. 
   Another inkjet recording device disclosed in Japanese unexamined patent application publication No. HEI-9-99554 supplies a piezoelectric element with a voltage considering the effects of vibrations on neighboring piezoelectric elements to alleviate mutual interference between nozzle units. 
   However, when using one of the methods described in Japanese unexamined patent application publications Nos. 2002-361868 and HEI-9-99554, abnormal vibrations were generated in a specific frequency range in parts or all of the print head when ejecting ink droplets. These abnormal vibrations generate ink mist or cause the ink ejection direction to deviate from the desired direction. These abnormal vibrations also cause ink to protrude from the nozzle hole and wet the region around the hole. This can result in ejection failures or, when ink droplets are ejected, irregular ejection characteristics due to cross talk. 
   This is particularly problematic when lengthening the head to integrate a plurality of nozzles therein, as in a push-type on-demand recording head, or when lowering the resonance frequency of such components as the piezoelectric element support base and increasing the excitation force in order to eject ink with a high viscosity. 
   Further, conventional recording head driving devices are provided with control elements, such as switching elements, and a flexible cable connecting each control element to a piezoelectric element, in order to selectively apply a drive pulse to piezoelectric elements corresponding to each nozzle. Accordingly, a recording head having a plurality of densely integrated nozzles requires a larger number of control elements and wires in the flexible cable, thereby increasing costs and leading to problems in mounting. 
   SUMMARY OF THE INVENTION 
   In view of the above-described drawbacks, it is an objective of the present invention to provide a recording head and an inkjet recording device equipped with the recording head that are capable of consistently ejecting ink droplets with stability, without producing abnormal vibrations in components of the recording head. 
   It is another object of the present invention to provide a recording head and an inkjet recording device that are inexpensive to produce and easy to mount, by reducing the number of switching elements required for selectively driving the piezoelectric elements. 
   In order to attain the above and other objects, the present invention provides an ink jet recording head unit including a plurality of nozzle elements, a plurality of piezoelectric elements and a driving unit. 
   The plurality of nozzle elements ejects ink droplets. Each nozzle element has an ink pressure chamber filling ink therein, an orifice leaded to the ink pressure chamber, and a diaphragm formed as a part of the ink pressure chamber and having a first surface opposed to the ink pressure chamber, and a second surface opposite to the first surface. 
   The plurality of piezoelectric elements is provided in one-to-one correspondence with the plurality of nozzle elements. Each piezoelectric element is fixed to the second surface of each diaphragm and has a positive pole and a negative pole. Each piezoelectric element expands and contracts to vary volume of the ink pressure chamber when a voltage potential difference between the positive pole and the negative pole is varied. Each nozzle element ejects an ink droplet from the corresponding orifice when the volume of the corresponding ink pressure chamber decreases. 
   The driving unit controls expansion and contraction of each piezoelectric element. The plurality of nozzle elements includes a first nozzle element and a second nozzle element adjacent to the first nozzle element. A first piezoelectric element and a second piezoelectric element correspond to the first nozzle element and the second nozzle element respectively. The driving unit controls the first piezoelectric element and the second piezoelectric element to expand and contract in a complementary manner. 
   Another aspect of this invention provides an ink jet recording device including an ink jet recording head having a plurality of nozzle elements and a plurality of piezoelectric elements, and a driving unit. 
   The plurality of nozzle elements ejects ink droplets. Each nozzle element has an ink pressure chamber filling ink therein, an orifice leaded to the ink pressure chamber, and a diaphragm formed as a part of the ink pressure chamber and having a first surface opposed to the ink pressure chamber, and a second surface opposite to the first surface. 
   The plurality of piezoelectric elements is provided in one-to-one correspondence with the plurality of nozzle elements. Each piezoelectric element is fixed to the second surface of each diaphragm and having a positive pole and a negative pole. Each piezoelectric element expands and contracts to vary volume of the ink pressure chamber when a voltage potential difference between the positive pole and the negative pole is varied. Each nozzle element ejects an ink droplet from the corresponding orifice when the volume of the corresponding ink pressure chamber decreases. 
   The driving unit controls expansion and contraction of each piezoelectric element. The plurality of nozzle elements includes a first nozzle element and a second nozzle element adjacent to the first nozzle element. A first piezoelectric element and a second piezoelectric element correspond to the first nozzle element and the second nozzle element respectively. The driving unit controls the first piezoelectric element and the second piezoelectric element to expand and contract in a complementary manner. 
   Another aspect of this invention provides an ink jet recording device including an ink jet recording head having a plurality of nozzle elements and a plurality of piezoelectric elements, and a driving unit having a drive signal generating unit, a switching element and a switching element driving unit. 
   The plurality of nozzle elements ejects ink droplets. Each nozzle element has an ink pressure chamber filling ink therein, an orifice leaded to the ink pressure chamber, and a diaphragm formed as a part of the ink pressure chamber and having a first surface opposed to the ink pressure chamber, and a second surface opposite to the first surface. 
   The plurality of piezoelectric elements is provided in one-to-one correspondence with the plurality of nozzle elements. Each piezoelectric element is fixed to the second surface of each diaphragm and having a positive pole, a negative pole, a common electrode to which a drive signal is applied and an individual electrode. Each piezoelectric element expands and contracts to vary volume of the ink pressure chamber when a voltage potential difference between the positive pole and the negative pole is varied. Each nozzle element ejects an ink droplet from the corresponding orifice when the volume of the corresponding ink pressure chamber decreases. 
   The driving unit controls expansion and contraction of each piezoelectric element. The drive signal generating unit generates the drive signals. The switching element is capable of performing on/off switching actions. The switching element has a first terminal to which a predetermined voltage is applied and a second terminal connected to the individual electrodes of both of the first piezoelectric element and the second piezoelectric element commonly so that each piezoelectric element expands and contracts when the switching element is closed. The switching element driving unit controls the on/off actions of the switching element. 
   The plurality of nozzle elements includes a first nozzle element and a second nozzle element adjacent to the first nozzle element. A first piezoelectric element and a second piezoelectric element correspond to the first nozzle element and the second nozzle element respectively. The positive pole of the first piezoelectric element is connected to the common electrode of the first piezoelectric element and the negative pole of the first piezoelectric element is connected to the individual electrode of the first piezoelectric element, when the positive pole of the second piezoelectric element is connected to the individual electrode of the second piezoelectric element and the negative pole of the second piezoelectric element is connected to the common electrode of the second piezoelectric element. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the invention will become more apparent from reading the following description of the preferred embodiments taken in connection with the accompanying drawings in which: 
       FIG. 1  is a schematic diagram and a block diagram of an inkjet recording device according to a first embodiment of the present invention; 
       FIG. 2  is a perspective view of a recording head according to the first embodiment; 
       FIG. 3(   a ) is an explanatory diagram illustrating operations of the recording head according to the first embodiment; 
       FIG. 3(   b ) is an explanatory diagram illustrating operations of the recording head according to the first embodiment; 
       FIG. 3(   c ) is an explanatory diagram illustrating operations of the recording head according to the first embodiment; 
       FIG. 4  is a graph of signal waveforms for various components in the recording head, illustrating operations of the recording head according to the first embodiment; 
       FIG. 5  is a perspective view of a recording head according to a second embodiment of the present invention; 
       FIG. 6  is a perspective view of a recording head according to a third embodiment of the present invention; 
       FIG. 7  is a perspective view of a recording head according to a fourth embodiment of the present invention; and 
       FIG. 8  is an explanatory diagram illustrating a variation of the recording head according to the preferred embodiments. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   An inkjet recording device according to a first embodiment of the present invention will be described with reference to  FIGS. 1 through 4 .  FIG. 1  shows the structure of an inkjet recording device  1 . The inkjet recording device  1  includes a recording head  10  according to the preferred embodiment, and a recording head driving device  20 . 
   As shown in  FIG. 1 , the recording head  10  includes an ink channel unit  101 , a head housing  102  for retaining the ink channel unit  101 , and a piezoelectric element unit  103 . The piezoelectric element unit  103  further includes pole-shaped piezoelectric elements  110  and a piezoelectric element support base  113  having a squared U-shape. One end of each of the piezoelectric elements  110  is fixed to the piezoelectric element support base  113 , and the other end to the ink channel unit  101 . The ink channel unit  101  accommodates ink that is ejected as an ink droplet  30  onto a recording paper  40  when pressed by the piezoelectric element  110 . 
   Next, the recording head  10  will be described in greater detail with reference to  FIG. 2 .  FIG. 2  shows the overall structure of the recording head  10 . The recording head  10  in  FIG. 2  is oriented opposite the recording head  10  shown in  FIG. 1  in the vertical direction. The ink channel unit  101  includes an orifice plate  130 , an ink channel forming plate  142 , and a diaphragm forming plate  122 . The ink channel forming plate  142  is interposed between the orifice plate  130  and the diaphragm forming plate  122 , and is bonded to both of the orifice plate  130  and the diaphragm forming plate  122  by an adhesive, anodic bonding, or the like. Nozzle holes  131  are formed through the orifice plate  130  so as to form a row in which the nozzle holes  131  are separated at a prescribed pitch. The surface of the diaphragm forming plate  122  opposed to the orifice plate  130  is configured of a diaphragm  120 . 
   Interposing the ink channel forming plate  142  between the orifice plate  130  and diaphragm  120  forms ink pressure chambers  140  in fluid communication with an end of the nozzle holes  131 , ink channel inlets  145  for directing ink to the ink pressure chambers  140 , and a common ink chamber  150  for supplying ink to the ink channel inlets  145 . The surface of the diaphragm forming plate  122  on which the diaphragm  120  is formed configures one wall surface of the ink pressure chambers  140 , while the other surface is bonded by adhesive to an end of the piezoelectric elements  110  provided in the piezoelectric element unit  103 . 
   The piezoelectric elements  110  are fixed to the piezoelectric element support base  113  in a configuration similar to the teeth of a comb so as to correspond to the nozzle holes  131 . Each of the piezoelectric elements  110  is configured of a plurality of layered piezoelectric elements  111  and a plurality of layered electrodes  112 . The piezoelectric elements  111  and electrodes  112  are stacked alternately in the vertical direction of the drawing. A common electrode  1121  and an individual electrode  1122  are provided on opposite side surfaces of the piezoelectric elements  110 . The electrodes  112  are alternately connected to the common electrode  1121  and the individual electrode  1122 . 
   Further, a common electrode  1121 ′ and a plurality of individual electrodes  1122 ′ are formed on the piezoelectric element support base  113  and are connected to the common electrode  1121  and individual electrode  1122 , respectively. The individual electrodes  1122 ′ are also connected by pairs to flexible cable terminals  161  of a flexible cable  160 . The flexible cable  160  connects the piezoelectric elements  110  to a switching circuit  304  (see  FIGS. 1 and 3(   a )) described later for driving the piezoelectric elements  110 . 
   As shown in  FIG. 1 , two columnar support base fixing units  114  are provided on either end of the piezoelectric element support base  113  with respect to the row of piezoelectric elements  110 . The bottom surface of the support base fixing units  114  is fixed by adhesive or the like to the ink channel unit  101 . The ink channel unit  101  in turn is adhesively fixed to the head housing  102  on endpoints near the areas bonded to the support base fixing units  114 . Accordingly, the support base fixing units  114  are fixed relative to the head housing  102 . 
   With this construction, the ink pressure chambers  140  in fluid communication with the nozzle holes  131  and the piezoelectric elements  110  form n nozzle elements # 1 , # 2 , . . . , n in the recording head  10 . 
   In the preferred embodiment, adjacent piezoelectric elements  110  are polarized with reverse polarity, and the amount of polarization is set approximately equal. 
   Therefore, in the case of a first nozzle element # 1  and a second nozzle element # 2  (see  FIG. 3(   a )), the piezoelectric element  110  retains the polarization shown in  FIG. 3(   a ) that is substantially equivalent to, but directionally opposite of the polarization retained in the piezoelectric element  110  of second nozzle element # 2 . Hence, when a similar voltage is applied to both nozzle elements # 1  and # 2 , the piezoelectric elements  110  in nozzle elements # 1  and # 2  are displaced approximately the same amount, but in opposing directions from each other. The volume of the ink pressure chambers  140  changes due to the expansion and contraction of the piezoelectric elements  110 . 
   Next, the recording head driving device  20  will be described with reference to  FIGS. 1 and 3(   a ). As shown in  FIG. 1 , the recording head driving device  20  includes a recording data signal generating circuit  302 , a piezoelectric element drive data signal generating circuit  303 , the piezoelectric element drive switching circuit  304 , a timing signal generating circuit  301 , and a A&amp;B phase piezoelectric element driving pulse waveform generating circuit  305 . 
   The recording data signal generating circuit  302  generates a recording data signal based on input data for a recording signal received from a host device (such as a personal computer, not shown). The piezoelectric element drive data signal generating circuit  303  further includes an odd-numbered piezoelectric element drive data signal circuit  3031  for driving piezoelectric elements in odd-numbered nozzles, and an even-numbered piezoelectric element drive data signal circuit  3032  for driving piezoelectric elements in even-numbered nozzles. The piezoelectric element drive data signal generating circuit  303  generates each of the piezoelectric element drive data signals based on the recording data signal generated by the recording data signal generating circuit  302  and a timing signal generated by the timing signal generating circuit  301 . 
   The piezoelectric element drive switching circuit  304  includes a switching element drive circuit  3042 , and a plurality of switching elements  3041  (SW 1 , SW 2 , . . . ; see  FIG. 3(   a )). The switching element drive circuit  3042  actuates the switching elements  3041  based on the piezoelectric element drive data signal generated by the piezoelectric element drive data signal generating circuit  303 . One end of each switching elements  3041  is connected to two adjacent piezoelectric elements  110 , while the other end is grounded. 
   Specifically, as shown in  FIG. 3(   a ), a switching element SW 1  is connected commonly to the individual electrode  1122  of the piezoelectric elements  110  in both nozzle elements # 1  and # 2 . A switching element SW 2  is connected commonly to the individual electrode  1122  of the piezoelectric elements  110  in both a third nozzle element # 3  and a fourth nozzle element # 4 . In the same way, other switching elements are commonly connected to the individual electrode  1122  of two piezoelectric elements  110  belonging to a set of two adjacent nozzle elements. 
   The A&amp;B phase piezoelectric element driving pulse waveform generating circuit  305  generates a A-phase drive pulse and a B-phase drive pulse (see ( a ) in  FIG. 4 ) for driving the piezoelectric elements  110 . As shown in  FIG. 3(   a ), the A&amp;B phase piezoelectric element driving pulse waveform generating circuit  305  is commonly connected to common electrodes  1121  of the piezoelectric elements  110  via the piezoelectric element drive switching circuit  304  for all nozzle elements # 1 , # 2 , # 3 , . . . , #n. Hence, when the switching element SW 1  is turned on, for example, a A-phase drive pulse or a B-phase drive pulse is applied simultaneously to piezoelectric elements  110  in the two adjacent nozzle elements # 1  and # 2 . 
   Next, an ink ejection operation performed with the inkjet recording device  1  of the preferred embodiment will be described with reference to  FIGS. 3(   a ),  3 ( b ),  3 ( c ), and  4 .  FIGS. 3(   a )- 3 ( c ) are explanatory diagrams illustrating the operation of the recording head  10  according to the preferred embodiment.  FIG. 4  is a timing chart of the signal waveforms for each element during an operation of the recording head  10 , where (a) indicates an output waveform of the A&amp;B phase piezoelectric element driving pulse waveform generating circuit  305 , (b 1 ) indicates a drive pulse waveform supplied to the switching element SW 1 , and (b 2 ) indicates a drive pulse waveform supplied to the switching element SW 2 . 
   As shown in ( a ) of  FIG. 4 , the voltage of the A-phase drive pulse changes from 0 to −V during an interval T 1  and remains at −V for a prescribed time T 2 . Subsequently, the voltage of the A-phase drive pulse rises from −V to +V during an interval T 3  and remains at +V for a prescribed time T 4 , after which the voltage returns to 0 during an interval T 5 . The B-phase drive pulse acts opposite the A-phase drive pulse, rising from 0 to +V during the initial interval T 1  and remaining at +V for the prescribed time T 2 . Subsequently, the voltage changes from +V to −V during the interval T 3  and remains at −V for the prescribed time T 4  before returning to 0 during the interval T 5 . 
   The switching element SW 1  turns on when the drive pulse for the switching element SW 1  (b 1 ) is high, and turns off when the pulse is low. The switching element SW 2  turns on when the drive pulse for the switching element SW 2  (b 2 ) is high, and turns off when the pulse is low 
   As shown in  FIG. 4 , since the drive pulse for the switching element SW 1  (b 1 ) is high during a period T( 1 )-A, the switching element SW 1  is on during this period. Further, since the level of the drive pulse for the switching element SW 2  (b 2 ) is low during this period, the switching element SW 2  is off. In other words, as shown in  FIG. 3(   a ), the contact point for the switching element SW 1  is closed while the contact point for the switching element SW 2  is open. Accordingly, the individual electrodes  1122  of nozzle elements # 1  and # 2  are both grounded via the switching element SW 1 , while the individual electrodes  1122  for nozzle elements # 3  and # 4  are in a floating state. 
   Since the A&amp;B phase piezoelectric element driving pulse waveform generating circuit  305  is commonly connected to the common electrode  1121  of each piezoelectric element  110 , a potential difference is generated between the common electrode  1121  and individual electrode  1122  of the nozzle elements # 1  and # 2  during the period T( 1 )-A. This potential difference corresponds to the voltage variation in the A-phase drive pulse shown in ( a ) of  FIG. 4 . 
   Hence, throughout the period T( 1 )-A, the piezoelectric element  110  of nozzle element # 1  gradually contracts during the interval T 1 , maintains its contracted state during the interval T 2 , rapidly expands during the interval T 3 , maintains this expanded state in the interval T 4 , and gradually returns to its original state during the interval T 5 . In this way, the expansion and contraction of the piezoelectric element  110  changes the volume in the ink pressure chamber  140 . 
     FIG. 3(   a ) shows nozzle element # 1  in the state at time t 1  in  FIG. 4 , that is, when the piezoelectric element  110  has rapidly expanded. The expansion of the piezoelectric element  110  constricts the volume in the ink pressure chamber  140  so that the ink droplet  30  is ejected through the nozzle hole  131  of nozzle element # 1 . Since the polarization of the piezoelectric element  110  in the neighboring nozzle element # 2  is set to about the same magnitude but has an opposite direction as that in nozzle element # 1 , expansion and contraction of the piezoelectric element  110  and ink pressure chamber  140  in nozzle element # 2  is completely opposite that in nozzle element # 1 . Consequently, the volume of the ink pressure chamber  140  increases during the interval T 3 , and ink is supplied from the common ink chamber  150  to the ink pressure chamber  140  via the ink channel inlets  145 . 
   Since the polarization directions of the piezoelectric elements  110  in nozzle elements # 1  and # 2  are opposite one another, an ink droplet is ejected through the nozzle hole  131  of nozzle element # 1  and not through the nozzle hole  131  of nozzle element # 2  when the A-phase drive pulse shown in ( a ) of  FIG. 4  is applied. 
   Since switching element SW 2  is off for the piezoelectric elements  110  in nozzle elements # 3  and # 4 , a potential differential between the common electrode  1121  and individual electrode  1122  of the piezoelectric elements  110  does not change, even when the drive pulse voltage shown in ( a ) of  FIG. 4  is applied to the individual electrodes  1122  in these nozzle elements. Hence, the piezoelectric elements  110  in nozzle elements # 3  and # 4  do not expand and contract, but remain still. 
   Further, when ink is supplied from the common ink chamber  150  to the ink pressure chamber  140 , a force to draw ink in from the nozzle hole  131  also works. Hence, the meniscus formed in the nozzle hole  131  tends to be drawn toward the ink pressure chamber  140  and, in some cases, air bubbles can be sucked through the nozzle hole  131  into the ink pressure chamber  140 . In order to prevent this problem, the size of the ink channel inlet  145  (see  FIG. 2 ) should be fairly large, and the impedance of the ink channel inlet  145  should be set smaller than that of the nozzle hole  131 . 
   Next, since the drive pulse for switching element SW 1  (b 1 ) is low during the following interval T( 1 )-B, the switching element SW 1  is switched off. Further, since the drive pulse for the switching element SW 2  (b 2 ) is high, the switching element SW 2  is switched on. Accordingly, the contact point for switching element SW 1  is open, while the contact point for switching element SW 2  is closed, as shown in  FIG. 3(   b ). At this time, the individual electrode  1122  of the piezoelectric elements  110  in nozzle elements # 3  and # 4  are both grounded via switching element SW 2 . 
   Since the A&amp;B phase piezoelectric element driving pulse waveform generating circuit  305  is connected to the common electrode  1121  of each piezoelectric element  110 , a potential differential is generated between the common electrode  1121  and individual electrode  1122  of nozzle elements # 3  and # 4 . This potential difference corresponds to voltage changes in the B-phase drive pulse shown in ( a ) of  FIG. 4 . 
   Therefore, the piezoelectric element  110  of nozzle element # 4  expands at the time t 2 , constricting the volume in the ink pressure chamber  140  so that the ink droplet  30  is ejected. At the same time, the piezoelectric element  110  of nozzle element # 3  is set to approximately the same magnitude of polarization but an opposite direction of polarization to the piezoelectric element  110  in nozzle element # 4 . Accordingly, the volume in the ink pressure chamber  140  increases at t 2 , so that the ink pressure chamber  140  draws ink from the common ink chamber  150  and does not eject an ink droplet. Since the switching element SW 1  is off, the A&amp;B-phase piezoelectric element drive pulse voltages are not applied to the piezoelectric elements  110  in nozzle elements # 1  and # 2 . Therefore, the piezoelectric elements  110  in nozzle elements # 1  and # 2  remain still and do not expand or contract. 
   Next, both switching elements SW 1  and SW 2  are turned off during the period T( 2 )-A shown in  FIG. 4 . Hence, nozzle elements # 3  and # 4  are halted, while nozzle elements # 1  and # 2  continue to remain halted. 
   Since switching elements SW 1  and SW 2  are both on in the period T( 2 )-B, the B-phase drive pulse voltage is applied to nozzle elements # 1 -# 4 . At the time t 3 , the piezoelectric elements  110  of nozzle elements # 2  and # 4  expand, as shown in  FIG. 3(   c ), causing ink droplets to be ejected from nozzle elements # 2  and # 4 . 
   The following is a description of the operations for the four nozzle elements # 1 -# 4 , but a similar control process can be employed when the number of nozzle elements is increased. Specifically, the nozzle elements are driven by the A-phase drive pulse (or B-phase drive pulse) when wishing to eject ink from odd-numbered nozzle elements, while the B-phase drive pulse (or A-phase drive pulse) is used when wishing to eject ink droplets from even-numbered nozzle elements. It is not possible to eject ink droplets simultaneously from two adjacent nozzle elements (i.e. one odd-numbered and one even-numbered). However, in light of the time difference between the A-phase and B-phase drive pulses, it is possible to eject ink droplets from desired nozzle elements by offsetting recording data for odd-numbered nozzle elements from recording data for even-numbered nozzle elements. 
   The recording head  10  is suitable for a serial scanning inkjet recording device and a line scanning inkjet recording device. In a serial scanning inkjet recording device, the recording head  10  is disposed so that the surface of the orifice plate  130  confronts the recording paper. The recording head  10  ejects ink droplets based on the recording signal while being moved in a direction that transverses the conveying direction of the recording paper (main scan) to record one line of an image. Subsequently, the recording paper is conveyed a prescribed distance in the conveying direction (sub scan), and the recording head  10  repeats the main scan to record the next line of the image. The entire image is recorded by repeatedly performing the main scan and sub scan. 
   When employing the recording head  10  in a line scanning inkjet recording device, a plurality of recording heads are arranged in a row along the width of a continuous recording paper so as to oppose the surface of the recording paper across the entire width. The recording heads  10  eject ink droplets based on recording signals, while simultaneously the continuous recording paper is moved at a high speed in the longitudinal direction of the paper (main scan). Dot formation on the scan lines is controlled by controlling the main scan and the ejection of ink droplets to record an image on the recording paper. 
   As described above, adjacent nozzle elements in the recording head  10  according to the preferred embodiment have piezoelectric elements  110  with approximately the same magnitude of polarization but reverse polarities. Since the piezoelectric elements  110  are driven by drive pulse voltages having similar waveforms, vibrations in the diaphragms, excitation of the piezoelectric element support base, displacement of each element, and the like in the adjacent nozzle elements are in completely opposite directions to one another. 
   Accordingly, it is possible to suppress the excitation of other elements, that is, excitation of other nozzle elements or such common members as the piezoelectric element support base and the housing. In other words, this structure suppresses abnormal vibrations when driving the piezoelectric element, thereby avoiding abnormal vibrations in the meniscus formed in the nozzle holes. Since cross talk is reduced in this way, ink droplets can be ejected with greater stability. Hence, ink droplets can be reliably ejected from each nozzle with a uniform ejection rate and droplet weight. Therefore, the present invention can provide an inkjet recording device capable of reliably recording high-quality images at a high speed. 
   Since two adjacent nozzle elements are connected to a single switching element in the recording head  10  according to the preferred embodiment, the number of switching elements and the number of wires in a cable connecting the recording head to the recording head driving device can be half that required for conventional devices, thereby reducing the cost and size of the recording device. 
   Next, a recording head  12  according to a second embodiment of the present invention will be described with reference to  FIG. 5 , wherein like parts and components are designated with the same reference numerals to avoid duplicating description.  FIG. 5  shows the general structure of the recording head  12  according to the second embodiment. Unlike the recording head  10  in the first embodiment, pairs of the individual electrodes  1122  are connected on the surface of the piezoelectric element support base  113 . With this construction, the surface area of the individual electrodes  1122 ′ capable of being connected to the flexible cable terminals  161  is greater than that in the first embodiment, thereby facilitating connection of the individual electrodes  1122 ′ with the flexible cable terminals  161  of the flexible cable  160 . 
   Next, a recording head  13  according to a third embodiment of the present invention will be described with reference to  FIG. 6 , wherein like parts and components are designated with the same reference numerals to avoid duplicating description.  FIG. 6  shows the general structure of the recording head  13  according to the third embodiment. In the third embodiment, the ink channel inlet  145  grows gradually smaller in a direction from the common ink chamber  150  toward the ink pressure chamber  140 , giving the ink channel inlet  145  the characteristics of a fluid diode in the direction from the common ink chamber  150  to the ink pressure chamber  140 . 
   Since ink flows in the direction from the common ink chamber  150  to the ink pressure chamber  140 , this construction can restrain movement of the meniscus generated in the nozzle hole  131  toward the ink pressure chamber  140 . Hence, this construction can prevent air from being sucked through the nozzle hole  131  and can prevent a drop in frequency response in ink ejection. 
   In the third embodiment, an ink accumulating part  132  is also formed around each nozzle hole  131  as a recessed part. Since ink accumulated in the ink accumulating part  132  around the nozzle hole can flow into the ink pressure chamber  140 , this construction more effectively prevents the lo meniscus from being completely drawn into the ink pressure chamber  140  and, hence, prevents air bubbles from being drawn into the ink pressure chamber  140 . 
   Next, a recording head  14  according to a fourth embodiment of the present invention will be described with reference to  FIG. 7 , wherein like parts and components are designated with the same reference numerals to avoid duplicating description. 
     FIG. 7  shows the general structure of the recording head  14  according to the fourth embodiment. Unlike the recording head  10  in the first embodiment, the polarizations of all of the piezoelectric elements  110  have same direction, the common electrode  1121  of the nozzle element # 1  is connected to the individual electrode  1122  of the nozzle element # 2  via a wire A and the individual electrode  1122  of the nozzle element # 1  is connected to the common electrode  1121  of the nozzle element # 2  via a wire B. The wire A is connected to the A&amp;B phase piezoelectric element driving pulse waveform generating circuit  305  and the wire B is connected to the switching elements  3041  for each pair of nozzle elements. 
   With this construction, vibrations in the diaphragms, excitation of the piezoelectric element support base, displacement of each element, and the like in the adjacent nozzle elements are in completely opposite directions to one another. Accordingly, it is possible to suppress the excitation of other elements with the piezoelectric elements  110  whose polarizations have same direction. 
   While the invention has been described in detail with reference to specific embodiments thereof, it would be apparent to those skilled in the art that many modifications and variations may be made therein without departing from the spirit of the invention, the scope of which is defined by the attached claims. For example, a pair of the flexible cables  160  can be connected on the circuit board of the piezoelectric element drive switching circuit  304 , as shown in  FIG. 8 , for sharing a switching element with two adjacent nozzle elements. While the number of wires in the flexible cable  160  is the same as the conventional device in this case, the number of switching elements can be decreased by half. 
   In addition to an inkjet recording device for recording on a recording paper in ink, the recording head can also be applied to an industrial liquid dispenser, such as a marking device or a coating device for marking or coating products. Further, the piezoelectric elements used in the present invention are not limited to the pole-shaped elements described in the preferred embodiments.

Technology Category: 7