Patent Publication Number: US-8123338-B2

Title: Liquid droplet jet head, liquid droplet discharging apparatus, and image forming apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a liquid-droplet jet head having plural nozzles discharging liquid droplets, a liquid discharging apparatus including the liquid-droplet jet head, and an image forming apparatus including the liquid discharging apparatus. 
     2. Description of the Related Art 
     Image forming apparatuses operate by discharging liquid droplets onto recording sheets such as paper to form images on the recording sheets. Such an image forming apparatus generally includes a liquid-droplet jet head having plural nozzles communicated with pressure liquid chambers, and pressure converters (actuators) provided to the corresponding pressure liquid chambers. 
       FIG. 1  is a view illustrating one example of a liquid-droplet jet head according to a related art. 
     A liquid-droplet jet head  10  includes a vibration board  3  partially forming a wall surface (hereinafter also called as “first surface of the vibration board”) of a pressurized chamber  2  communicated with a nozzle  1 , and an actuator  5  provided on a supporting substrate  4 . In the liquid-droplet jet head  10 , the vibration board  3  and the actuator  5  are connected via a connecting unit  6 . The vibration board  3  is elastically deformed with displacement of the actuator  5 . A second surface of the vibration board  3  (i.e., the other side of the wall surface of the pressurized chamber  2 ) is less rigid than other surfaces forming the pressure liquid chamber  2  to efficiently change the capacity of the pressure liquid chamber  2  by displacing the actuator  5 . 
     The pressure liquid chamber  2  is connected to a common liquid chamber  9  via a fluid resistor  7  and a communicating unit  8 . The common liquid chamber  9  is also connected to an unshown ink tank. The actuator  5  is deformed based on the voltage applied by an unshown driving circuit, and the vibration board  3  is deformed based on the deformation of the actuator  5  so as to increase or decrease the capacity of the pressure liquid chamber  2 . Increasing the capacity of the pressure liquid chamber  2  results in a decrease in internal pressure of the pressure liquid chamber  2 , thereby supplying ink to the pressure liquid chamber  2  from the common liquid chamber  9  via the communicating unit  8  and the fluid resistor  7 . In contrast, decreasing the capacity of the pressure liquid chamber  2  by driving the actuator  5  results in an increase in the internal pressure of the pressurized chamber  2 , thereby discharging the ink from the nozzle  1 . The discharged ink forms scattered liquid droplets (i.e., ink droplets), and the scattered liquid droplets are adhered to an unshown recording medium (e.g., paper), thereby forming an image on the recording medium. 
       FIG. 2  is a cross sectional view of the liquid-droplet jet head  10  taken along the line A-A of  FIG. 1 . The actuator  5  includes driving actuators  5 a arranged at positions to face the corresponding pressure liquid chambers  2 , and supporting actuators  5 b arranged at positions to face corresponding partitions  11  which partitions adjacently arranged pressure liquid chambers  2 . The aforementioned structure of the liquid-droplet jet head  10  is hereinafter called a “bi-pitch structure”. In the liquid-droplet jet head  10  having this bi-pitch structure, voltage is applied to the driving actuators  5   a  to deform the vibration board  3 , whereas no voltage is applied to the supporting actuators  5   b . The supporting actuators  5   b  are utilized for fixating the pressure liquid chambers  12  to the supporting substrate  4 . 
     It is preferable that the nozzles  1  be arranged as densely as possible in the liquid-droplet jet head  10  so as to carry out processing with increased speed and provide higher quality of images. However, since the liquid droplet jet head  10  having the bi-pitch structure includes both the driving actuators  5   a  and the supporting actuators  5   b , the number of the actuators  5  to be arranged is twice as many as the number of the nozzles  1  in total. Accordingly, it is generally difficult to manufacture such a liquid droplet jet head  10 . 
     Then, it is suggested that the liquid droplet jet head  10  include the actuator  5  consisting only of the driving actuator  5   a  as shown in  FIG. 3 . Such a structure is hereinafter called a “normal-pitch structure”.  FIG. 3  is a view illustrating another example of the liquid-droplet jet head  10  according to the related art. 
     The liquid droplet jet head  10  having the normal-pitch structure only includes half the number of actuators  5  as compared to that of the liquid-droplet jet head  10  having the bi-pitch structure, and hence is suitable for manufacturing an increased number of nozzles. 
     However, since the liquid droplet jet head  10  having the normal-pitch structure includes no supporting actuators  5   b , the pressure liquid chambers  12  are not sufficiently supported. Thus, the pressure liquid chambers  12  and nozzle plates  13  are pushed up by thrust force of the driving actuators  5   a , thereby generating a crosstalk. The more the number of bits generated by driving the driving actuators  5   a  there is, the more thrust force may be generated by the driving actuators  5   a , thereby increasing an adverse effect of the crosstalk on the characteristics of the jets. Thus, the characteristics of the jets vary with the increase or decrease in the number of bits generated by driving the actuators  5   a.    
     In order to suppress such a crosstalk in the liquid droplet jet head  10  having the normal-pitch structure, Japanese Patent No. 3381678 and Japanese Patent No. 3248486 disclose technologies in which an inactive region of a piezoelectric element is polarized such that both ends of the inactive region are utilized as supporting pillars, thereby leaving the both ends of the inactive region electrically floating. 
     However, in the disclosed technologies of both Japanese Patent No. 3381678 and Japanese Patent No. 3248486, since the piezoelectric element needs to have a deep groove in order to form the supporting pillars, the supporting pillars may each have a shape with an extremely high aspect ratio. Accordingly, the supporting pillars of the piezoelectric element may develop fractures during the manufacturing process. Further, with such technologies, since some of the internal electrodes are cut off, arrangement of the electrodes in the inactive regions of the piezoelectric element may become complicated. 
     SUMMARY OF THE INVENTION 
     Accordingly, embodiments of the present invention may provide a novel and useful liquid-droplet jet head having plural nozzles discharging liquid droplets, liquid discharging apparatus having the liquid-droplet jet head, and image forming apparatus having the liquid discharging apparatus solving one or more of the problems discussed above. More specifically, the embodiments of the present invention attempt to provide the liquid-droplet jet head having the normal-pitch structure, a liquid discharging apparatus having the liquid-droplet jet head, and an image forming apparatus having the liquid discharging apparatus that can suppress crosstalk generation at low cost. 
     According to an embodiment of the invention, a liquid droplet jet head includes a pressure liquid chamber substrate including a plurality of nozzles discharging liquid droplets and a plurality of pressure liquid chambers communicated with the nozzles, a vibration board configured to partially form wall surfaces of the pressure liquid chambers, and a first pressure converter configured to vibrate the vibration board to change pressure in the pressure liquid chambers to discharge the liquid droplets from the nozzles, and including a piezoelectric element having an active region and a first inactive region and electrodes disposed to apply an electric force to the active region and not to apply an electric force to the first inactive region, and a groove separating the active region from the first inactive region formed not so deep as to reach one of the electrodes in a portion in the first inactive region facing the vibration board. In the liquid droplet jet head, the pressure liquid chamber substrate is supported by the first inactive region of the piezoelectric element. 
     According to an embodiment of the invention, a liquid droplet discharging apparatus includes the aforementioned liquid droplet jet head. 
     According to an embodiment of the invention, An image forming apparatus includes the aforementioned liquid droplet discharging apparatus configured to discharge liquid droplets to adhere the liquid droplets on a recording medium. 
     Additional objects and advantages of the embodiments will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view illustrating one example of a liquid-droplet jet head according to a related art. 
         FIG. 2  is a cross sectional view of the liquid-droplet jet head according to the related art taken along the line A-A of  FIG. 1 . 
         FIG. 3  is a view illustrating another example of the liquid-droplet jet head according to the related art. 
         FIG. 4  is an exploded perspective view illustrating a liquid-droplet jet head according to a first embodiment. 
         FIG. 5  is a cross sectional view of the liquid-droplet jet head according to the first embodiment taken along the line A-A. 
         FIG. 6  is a detailed view of an actuator in the liquid-droplet jet head according to the first embodiment. 
         FIG. 7  is a graph illustrating an outcome of a numerical simulation analysis conducted on the liquid-droplet jet head according to the first embodiment. 
         FIG. 8  is a detail view of an actuator in a liquid-droplet jet head according to a second embodiment. 
         FIG. 9  is a graph illustrating an outcome of a numerical simulation analysis conducted on the liquid-droplet jet head according to the second embodiment. 
         FIG. 10  is a view illustrating a liquid-droplet jet head according to a third embodiment. 
         FIG. 11  is a view illustrating a liquid-droplet jet head according to a fourth embodiment. 
         FIG. 12  is a graph illustrating an outcome of a numerical simulation analysis conducted on the liquid-droplet jet head according to the fourth embodiment. 
         FIG. 13  is a view illustrating a modified liquid-droplet jet head obtained by applying the liquid-droplet jet head according to the fourth embodiment to the liquid-droplet jet head according to the second embodiment. 
         FIG. 14  is a view illustrating an image forming apparatus including a liquid discharging apparatus having one of the liquid-droplet jet heads according to the first to fourth embodiments. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERED EMBODIMENTS 
     A description is given below, with reference to the  FIGS. 4 through 14  of embodiments of the present invention. 
     A liquid-droplet jet head according to the embodiments of the invention generally includes a pressure converter having a piezoelectric element, and electrodes disposed to form an active region in which an electric field is generated and applied to the piezoelectric element and inactive regions in which no electric field is applied to the piezoelectric element, with the piezoelectric element and the electrodes arranged in a layered manner. The pressure converter further includes a groove formed in one of the inactive regions of the piezoelectric element facing the vibration board such that the groove is not brought into contact with the electrodes so as to separate the active region from the inactive region. 
     First Embodiment 
     A liquid-droplet jet head  100  according to a first embodiment of the invention is described with reference to accompanying drawings.  FIG. 4  is an exploded perspective view illustrating the liquid-droplet jet head  100  according to a first embodiment. 
     The liquid-droplet jet head  100  includes a nozzle plate  120  having plural nozzles  110 , a pressure liquid chamber substrate  140  having plural pressure liquid chambers  130 , a vibration board  150 , actuators  160 , a supporting substrate  170 , FPC cables  180 , and driver ICs  190 . 
     The plural nozzles  110  provided in the nozzle plate  120  are configured to communicate with the corresponding pressure liquid chambers  130 . The pressure liquid chambers  130  are connected to common liquid chambers  230  (see  FIG. 5 ) via fluid resistors  135  (see  FIG. 6 ) and communicating units  220  (see  FIGS. 5 and 6 ). The vibration board  150  is connected with the actuators  160  as pressure converters. The actuators  160  are electrically coupled with the FPC cables  180  connected to the driver ICs  190 . 
     The driver ICs  190  generate a driving signal to drive the actuators  160  based on an image forming signal (not shown). The driving signal is supplied to the actuators  160  via the FPC cables  180 . The actuators  160  expand and contract based on the supplied driving signal. The expansion or contraction of the actuators  160  is transmitted to the vibration board  150  as displacement. Internal pressure of the pressure liquid chambers  130  is controlled based on the displacement transmitted to the vibration board  150  so as to discharge ink-droplets (liquid droplets) from the nozzles  110 . The actuators  160  are connected with the supporting substrate  170 . The supporting substrate  170  is connected to frames  240  (see  FIGS. 5 and 6 ). 
     The liquid-droplet jet head  100  is attached to a main body of an image forming apparatus such that the frames  240  (see  FIG. 5 ) connected to the supporting substrate  170  are connected with an unshown carriage. The FPC cables  180  are connected with unshown electric circuits so as to supply ink from an unshown ink cartridge to the pressure liquid chambers  130 . An example of the image forming apparatus having the liquid-droplet jet head  100  according to the first embodiment is described later. 
       FIG. 5  is a cross sectional view of the liquid-droplet jet head  100  according to the first embodiment taken along the line A-A. 
     In the liquid-droplet jet head  100  of the first embodiment, two pressure liquid chambers  130  are partitioned by a partition  210 , so that the two pressure liquid chambers  130  are adjacently arranged to sandwich the partition  210 . The pressure liquid chambers  130  communicates with the common liquid chambers  230  via the communicating units  220 . The actuators  160  are electrically coupled with the FPC cables  180  connected to the driver ICs  190 . The pressure liquid chamber substrate  140  and the supporting substrate  170  are connected with the frames  240 . 
     In an example in  FIG. 5 , the frames  240  are formed of two separate components; however, the frames  240  may be formed of one component (i.e., one frame). Further, two actuators  160  are formed on one supporting substrate  170 ; however, the substrate  170  may be divided into two (i.e., two substrates). In the liquid-droplet jet head  100  of the first embodiment, the two pressure liquid chambers  130  are adjacently arranged in two rows in a longitudinal direction X-Y of the pressure liquid chamber, however, only one pressure liquid chamber  130  may be arranged in one row in the longitudinal direction X-Y of the pressure liquid chamber. 
       FIG. 6  is a detail view of an actuator  160  in the liquid-droplet jet head  100  according to the first embodiment. 
     In the liquid-droplet jet head  100  according to the first embodiment, the actuator  160  is connected to the vibration board  150  via the connecting unit  165 , and includes a layered type piezoelectric element. The FPC cables  180  are individually connected to one side of the actuator  160  close to the common liquid chamber  230  and to the other side of the actuators  160 . Hereinafter, the FPC cable  180  connected to the common liquid chamber  230  side of the actuator  160  is called an “external electrode  180   a ”, and the FPC cable  180  connected to the other side of the actuator  160  is called an “external electrode  180   b”.    
     The actuator  160  is configured to include the piezoelectric element, and internal electrodes alternately connected to one of the external electrodes  180   a  and  180   b , with the piezoelectric element and the internal electrodes arranged in a layered manner. The actuator  160  includes an active region  251  in which the internal electrodes  250  connected to the external electrode  180   a  are overlapped with the other internal electrodes  250  connected to the external electrode  180   b , and inactive regions  252 ,  253  in which those connected to the external electrode  180   a  are not overlapped with those connected to the external electrode  180   b.    
     In the actuator  160 , when voltage is applied to the external electrodes  180   a ,  180   b , the active region  251  is deformed due to the applied electric field. Since the inactive regions  252 ,  253  include the electrodes  250  connected to either one of the external electrode  180   a  and the external electrode  180   b , no electric field is applied to the inactive regions  252 ,  253 , thereby no deformation is caused in the inactive regions  252 ,  253 . Accordingly, the inactive regions  252 ,  253  are utilized as supporting pillars for the pressure liquid chamber substrate  140 . 
     In the actuator  160  of the first embodiment, it is preferable that a length L in the longitudinal direction X-Y of the pressure liquid chamber of the active region  251  be ranged from 1000 to 2000 μm, and lengths L 1 ,  12  in the longitudinal direction X-Y of the pressure liquid chamber of the inactive regions  252 ,  253  be ranged from 400 to 800 μm. Note that lengths of either active or inactive regions are not limited to the aforementioned lengths. Further, the lengths L 1 , L 2  in the longitudinal direction X-Y of the pressure liquid chamber of the inactive regions  252 ,  253  may either be the same or different. 
     The inactive regions  252 ,  253  individually include grooves  260 . The groove  260  is provided so as to separate the inactive region  252  from the inactive region  253 . According to the actuator  160  in the first embodiment, it is preferable that the width W of the groove  260  (see  FIG. 6 ) be ranged from 20 to 50 μm in view of manufacturing process. Further, it is preferable that the grooves  260  be formed at positions closer to the active region  251  to increase the displacement of the active region  251 . However, if the grooves  260  are formed too close to the active region  251 , the grooves  260  may cut off some of the internal electrodes  250  in the active region  251 . Thus, it is preferable that the grooves  260  each be formed at a position 50 to 100 μm distant from an end of the active region  251 . 
     The grooves  260  are formed so as not to reach some of the internal electrodes  250  located closest to the vibration board  150 , thereby preventing the grooves  260  from cutting off some of the internal electrodes  250 . Thus, it is preferable that the depth D of each of the grooves  260  be ranged from 10 to 100 μm. If the depth D of the groove  260  exceeds 100 μm, it maybe difficult to process (form) the groove  260 . Note that the width W, position, depth D of the groove  260  may not have to be within the aforementioned range. 
     According to the first embodiment, the connecting units  165  connecting the actuator  160  and vibration board  150  are not formed in regions  261 ,  262  in which the grooves  260  are formed. Accordingly, the actuator  160  in the first embodiment is connected with the vibration board  150  via the connecting units  165  intermittently formed in the active region  251 , and the inactive regions  252 ,  253 . As illustrated in  FIG. 6 , one of the connecting units  165  are formed in the active region  251  such that the connecting unit  165  does not interfere with the regions  261 ,  262 . Further, other connecting units  165  are formed so as not to interfere with the regions  261 ,  262  in the inactive regions  252 ,  253 . 
     According to the first embodiment, the actuator  160  is connected with the vibration board  150  via the connecting units  165 . However, the actuator  160  may directly be connected to the vibration board  150  without connecting via the connecting units  165 . 
     As described above, according to the first embodiment, the supporting pillars supporting the pressure liquid chamber substrate  140  may be formed without forming deep grooves  260  in the actuator  160 . Further, since the grooves  260  are formed without cutting off any of the internal electrodes  250  in the actuator  160 , the internal electrodes  250  in the inactive regions  252 ,  253  can be easily arranged. Thus, according to the first embodiment, the crosstalk generated in the liquid-droplet jet head  100  having the normal-pitch structure can be suppressed at low cost. 
       FIG. 7  is a graph illustrating an outcome of a numerical simulation analysis conducted on the liquid-droplet jet head  100  according to the first embodiment. The numerical simulation analysis is a quantitative evaluation system in which the crosstalk suppression effects are quantitatively evaluated by varying the depth of the groove  260 . In numerical simulation analysis, the length L of the active region is 1400 μm, the lengths L 1 , L 2  of the inactive regions  252 ,  253  are each 500 μm, and the height H of the actuator  160  is 800 μm. In this analysis, the suppression of the crosstalk is evaluated using the following crosstalk suppression index.
 
Crosstalk suppression index=Generated pressure of the pressure liquid chamber 130/Displacement amount of the pressure liquid chamber substrate 140
 
     When the pressure of the liquid chamber  130  rises, the pressure liquid chamber substrate  140  is pushed up, thereby increasing a displacement amount of the pressure liquid chamber substrate  140 . This is a cause of the crosstalk. In order to suppress the crosstalk generation, it is preferable that the displacement amount of the pressure liquid chamber substrate  140  be kept as small as possible while maintaining discharge efficiency by a high pressure of the liquid chamber  130 . Accordingly, the higher the value that the crosstalk suppression index is, the better the characteristics of the jets in the liquid-droplet jet head  100  may be. 
     As is clear from  FIG. 7 , in the liquid-droplet jet head  100  according to the first embodiment, even if a small depth of the groove  260  is formed in the actuator  160 , the value of the crosstalk suppression index is increased, thereby exhibiting the effect of suppressing the crosstalk, in comparison to the related art liquid-droplet jet head where no groove is formed. In  FIG. 7 , the value of the crosstalk suppression index increases with an increase of the depth D of the groove  260  until the depth D of the groove  260  reaches approximately 100 μm. However, the value of the crosstalk suppression index decreases after the depth D of the groove  260  exceeds approximately 100 μm. Accordingly, it is preferable that the depth D of the groove  260  be approximately 100 μm or less. However, if the depth D of the groove  260  is continuously increased, the value of the crosstalk suppression index starts increasing again after the depth D of the groove  260  reaches approximately 350 μm. Then, when the depth D of the groove  260  reaches approximately 500 μm, the value of the crosstalk suppression index exceeds the value obtained when the groove  260  is formed only in a surface of the actuator  160 . However, in such a case where the depth D of the groove  260  is approximately 500 μm, the groove  260  cuts off some of the internal electrodes  250 , thereby making it complicated to arrange the internal electrodes. In order to avoid such complicated arrangement of the internal electrodes, it is preferable to form the groove  260  only in the surface of the actuator  160 . As is clear from  FIG. 7 , crosstalk suppression effects may sufficiently be obtained by forming the groove  260  only in the surface of the actuator  160 . 
     Second Embodiment 
     A liquid-droplet jet head  100 A according to a second embodiment of the invention is described with reference to accompanying drawings. The liquid-droplet jet head  100 A according to the second embodiment differs in the actuator  160  in which the groove is formed only in one inactive region in the liquid-droplet jet head according to the first embodiment. Accordingly, in the second embodiment, only the difference between the first and second embodiments is described. Identical components in the second embodiment that fulfill the same function as those of the first embodiment are denoted by the same reference numerals and are not described again. 
       FIG. 8  is a detailed view of an actuator  160 A in the liquid-droplet jet head  100 A according to the second embodiment. 
     The actuator  160 A in the liquid-droplet jet head  100 A according to the second embodiment includes inactive regions  252 A,  253 B adjacently formed at both sides of an active region  251 A. The actuator  160 A of the second embodiment is formed such that a length L 1  of the inactive region  252 A in the longitudinal direction X-Y of the pressure liquid chamber is longer than a length L 2  of the inactive region  253 A. 
     In the actuator  160 A according to the second embodiment, a groove  260 A is formed in the inactive region  252 A alone. With this configuration, the length of the piezoelectric element in the longitudinal direction X-Y of the pressurized chamber may be decreased, thereby facilitating decreasing the size of the liquid-droplet jet head  100 A. 
     Further, since the length L 2  of the inactive region  253 A is shorter than the length L 1  of the inactive region  252 A, a size of the active region  251 A is less restricted by the inactive regions  252 A,  253 A in the actuator  160 A of the second embodiment than that of the active region  251  restricted by the inactive regions  252 ,  253  in the actuator  160  of the first embodiment. As a result, a displacement amount of the piezoelectric element in the actuator  160 A of the second embodiment is larger than that of the piezoelectric element in the actuator  160  of the first embodiment. Accordingly, efficiency of the jets in the liquid-droplet jet head  101 A can be improved. 
     Note that in the second embodiment, the length L 1  of the inactive region  252 A is longer than the length L 2  of the inactive region  253 A. However, the relationship between the lengths L 1  and L 2  is not limited thereto. For example, the length L 2  of the inactive region  253 A may he longer than the length L 1  of the inactive region  252 A. In such a case, the groove  260 A is formed in the inactive region  253 A alone. That is, the groove  260 A is formed in one of the inactive regions  252 A and  253 A that is longer in length than the other in the longitudinal direction X-Y of the pressure liquid chamber. 
       FIG. 9  is a graph illustrating an outcome of a numerical simulation analysis conducted on the liquid-droplet jet head  100 A according to the second embodiment. The details of the evaluation are the same as those in the first embodiment. In the numerical simulation analysis conducted on the liquid-droplet jet head  100 A according to the second embodiment, the length L of the active region  251 A is 1400 μm, the length L 1  of the inactive region  252 A is 500 μm, and the length L 2  of the inactive region  253 A is 150 μm. 
     As is clear from  FIG. 9 , the crosstalk can be suppressed best by forming the groove  260 A having the depth D of 100 μm or less. 
     Third Embodiment 
     A liquid-droplet jet head  100 B according to a third embodiment of the invention is described with reference to accompanying drawings. The liquid-droplet jet head  100 B according to the third embodiment of the invention includes a combination of the actuators in the liquid-droplet jet head according to in the second embodiment. Accordingly, identical components in the third embodiment that fulfill the same function as those of the second embodiment are denoted by the same reference numerals and are not described again. 
       FIG. 10  is a view illustrating the liquid-droplet jet head  100 B according to the third embodiment. 
     The liquid-droplet jet head  100 B according to the third embodiment of the invention includes nozzles  110  arranged in plural rows (e.g., two rows in  FIG. 10 ) in the longitudinal direction X-Y of the pressure liquid chamber, and the pressure liquid chambers  130  communicated with the nozzles  110 . In the liquid-droplet jet head  100 B according to the third embodiment, actuators  160 Al,  160 A 2  are formed corresponding to the adjacently arranged pressure liquid chambers  130 , and grooves  260 A 1 ,  260 A 2  are respectively formed in inactive regions  252 A 1 ,  252 A 2  located at sides where the actuators  160 A 1  and  160 A 2  mutually face. 
     The liquid-droplet jet head  100 B according to the third embodiment includes the actuator  160 A 1  that changes the internal pressure of the pressure liquid chamber  130 A, and the actuator  160 A 2  that changes the internal pressure of the pressure liquid chamber  130 B. 
     The actuator  160 A 1  according to the third embodiment includes the inactive regions  252 A 1 ,  253 A 1  adjacently formed at both sides of an active region  251 A 1 . In the actuator  160 A 1  according to the third embodiment, a length L 1  of the inactive region  252 A 1  in the longitudinal direction X-Y of the pressure liquid chamber is longer than a length L 2  of the inactive region  253 A 1  in the longitudinal direction X-Y of the pressure liquid chamber. Accordingly, the groove  260 A 1  is formed in the inactive region  252 A 1 . 
     The actuator  160 A 2  according to the third embodiment includes the inactive regions  252 A 2 ,  253 A 2  adjacently formed at both sides of an active region  251 A 2 . In the actuator  160 A 2  according to the third embodiment, a length L 3  of the inactive region  252 A 2  in the longitudinal direction X-Y of the pressure liquid chamber is longer than a length L 4  of the inactive region  253 A 2  in the longitudinal direction X-Y of the pressure liquid chamber. Accordingly, the groove  260 A 2  is formed in the inactive region  252 A 2 . 
     Accordingly, in the actuator  160 A 2  of the third embodiment, the grooves  260 A 1 ,  260 A 2  are formed in inactive regions  252 A 1 ,  252 A 2  located at the sides where the actuators  160 A 1  and  160 A 2  mutually face. The pressure liquid chamber substrate  140  located at the sides where the actuators  160 A 1  and  160 A 2  mutually face may be most susceptible to deformation. 
     As described above, in the liquid-droplet jet head according to the third embodiment of the invention, the crosstalk can be efficiently suppressed by providing the inactive regions  252 A 1 ,  253 A 2  at the sides where the actuators  160 A 1  and  160 A 2  mutually face. 
     Fourth Embodiment 
     A liquid-droplet jet head according to a fourth embodiment of the invention is described with reference to accompanying drawings. The liquid-droplet jet head  100 C according to the fourth embodiment differs in the connecting unit that is formed in an entire region between the actuator  160  and the vibration board  150  from the liquid-droplet jet head  100  according to the first embodiment. Accordingly, in the fourth embodiment, only the difference between the first and fourth embodiments is described. Identical components in the fourth embodiment that fulfill the same function as those of the first embodiment are denoted by the same reference numerals and are not described again. 
       FIG. 11  is a view illustrating the liquid-droplet jet head  100 C according to the fourth embodiment. 
     The liquid-droplet jet head  100 C according to the fourth embodiment includes a connecting unit  165 A that is continuously formed in an entire region between the actuator  160  and the vibration board  150  in the longitudinal direction X-Y of the pressure liquid chamber. With this configuration, even if the positions of the grooves  260  are shifted in a horizontal direction, the characteristics of the jets may not vary to a large extent. 
     As shown in  FIG. 6 , the connecting units  165  are not provided above the grooves  260  in the liquid-droplet jet head  100  according to the first embodiment. If positions of the grooves  260  are shifted when attaching the actuator  160  to the liquid-droplet jet head  100 , positions of the connecting units  165  and the grooves  260  may overlap. In the liquid-droplet jet head  100  according to the first embodiment, if the positions of the connecting units  165  and the grooves  260  overlap, a connected condition made by the connecting units  165  between the actuator  160  and the vibration board  150  changes. As a result, the jet characteristics of the liquid-droplet jet head  100  may vary. 
     Accordingly, in the liquid-droplet jet head  100 C according to the fourth embodiment, the connecting unit  165 A is continuously formed in the entire region between the actuator  160  and the vibration board  150 . 
     With this configuration, even if the positions of the grooves  260  are shifted when attaching the actuator  160  to the liquid-droplet jet head  100 C, the connected condition made by the connecting unit  165 A between the actuator  160  and the vibration board  150  remains unchanged. As a result, fluctuation in the jet characteristics of the jets in the liquid-droplet jet head  100  may be reduced. 
     Note that in  FIG. 11 , a length of a layer of the vibration board  150  is longer than a length of the connecting unit  165 A in the horizontal direction (i.e., longitudinal direction X-Y of the pressure liquid chamber). However, the actual vibration board  150  can be formed only under the pressure liquid chamber  130 . Accordingly, the length of the actual vibration board  150  in the horizontal direction is longer than that of the connecting unit  165 A in the horizontal direction. 
       FIG. 12  is a graph illustrating an outcome of a numerical simulation analysis conducted on the liquid-droplet jet head  100 C according to the fourth embodiment. The details of the evaluation are the same as the first embodiment shown in  FIG. 7 . In the liquid-droplet jet head  100 C according to the fourth embodiment, a length L of the active region  251  is 1400 μm, and lengths L 1 , L 2  of the inactive regions  252 ,  253  are each 500 μm. As is clear from  FIG. 12 , the crosstalk suppression effects can be obtained with this configuration of the liquid-droplet jet head  100 C according to the fourth embodiment. 
     Note that the fourth embodiment may also be applied to the liquid-droplet jet head  101 A according to the second embodiment.  FIG. 13  is a view illustrating a liquid-droplet jet head  100 D obtained by applying the liquid-droplet jet head  100 C according to the fourth embodiment to the liquid-droplet jet head  101 A according to the second embodiment (modification of the fourth embodiment). The liquid-droplet jet head  100 D includes the connecting unit  165 A continuously formed in an entire region between the actuator  160 A and the vibration board  150 . 
     An image forming apparatus including a liquid discharging apparatus having one of the aforementioned liquid-droplet jet heads  100 ,  100 A,  100 B,  100 C, and  100 D according to corresponding first to fourth embodiments may realize excellent characteristics of the jets and higher processing speeds of the jets.  FIG. 14  is a view illustrating an image forming apparatus including a liquid discharging apparatus having one of the liquid-droplet jet heads according to the first to fourth embodiments. 
     An image forming apparatus  300  includes a liquid discharging apparatus  310  that is movable in a major scanning direction of the liquid discharging apparatus  310 . The liquid discharging apparatus  310  includes a printing mechanical unit  340  including a carriage  320 , the liquid-droplet jet head  100  attached to the carriage  320 , and an ink cartridge  330  supplying ink to the liquid-droplet jet head  100 . The image forming apparatus  300  obtains a sheet of paper from a paper-feeding cassette or a manual bypass tray, allows the printing mechanical unit  340  to print or record a desired image on the sheet, and discharges the sheet of paper on which the image is formed onto a discharging plate. 
     Note that the liquid-droplet jet head  100  according to the first embodiment is used as an example of the liquid-droplet jet head attached to the image forming apparatus  300  illustrated in  FIG. 14 ; however, any one of the liquid-droplet jet heads  100 A to  100 D according to the corresponding first to fourth embodiments may be used. 
     With this configuration, the image forming apparatus  300  may realize less variability in printing characteristics and excellent image formation with high accuracy. 
     According to the liquid-droplet jet heads each having the normal-pitch structure according to the first to fourth embodiments, the crosstalk can be suppressed at low cost. 
     The liquid-droplet jet head, the liquid discharging apparatus and the image forming apparatus are described according to the first to fourth embodiments of the invention; however, the elements described in the embodiments are not limited thereto. Various changes and alterations may be made to those elements based on the applications of the embodiments without departing from the scope of the invention. 
     All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority or inferiority of the invention. Although the embodiment of the present invention has been described in detail, it should be understood that various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention. 
     This patent application is based on Japanese Priority Patent Application No. 2008-237128 filed on Sep. 16, 2008, the entire contents of which are hereby incorporated herein by reference.