Patent Publication Number: US-8113616-B2

Title: Liquid ejecting apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims priority from Japanese Patent Application No. 2008-239383, which was filed on Sep. 18, 2008, the disclosure of which is herein incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a liquid ejecting apparatus including a liquid ejecting head configured to eject liquid droplets. 
     2. Description of the Related Art 
     Patent Document 1 (US 2006/0221112 A1 corresponding to JP-A-2006-272909) discloses an ink-jet recording apparatus including an ink-jet head having a channel unit, and an actuator unit and a driver IC fixed on an upper surface of the channel unit. In this ink-jet recording apparatus, when a temperature sensor included in the driver IC detects a temperature lower than a predetermined temperature, the controller controls the driver IC to supply a non-ejection signal to the actuator unit. In this time, heat of the driver IC is transferred to the actuator unit via the channel unit. Thus, an environmental temperature of the actuator unit is risen by a multiplier effect of heat generated by the actuator unit and heat from the driver IC. As a result, there can be restrained a deterioration of a recording quality owing to a change of a displacement amount of an active portion of the actuator unit, which change is caused by the environmental temperature. 
     SUMMARY OF THE INVENTION 
     In the ink-jet recording apparatus described in the Patent Document 1, a control is performed in which mainly the environmental temperature of the actuator unit is kept at a value equal to or higher than a predetermined value, but a control is not performed in which the diver IC is driven to generate heat where a low-temperature ink is flowed into the ink-jet head. Thus, the low-temperature ink flowed into the head lowers an ink temperature in the head, thereby increasing an ink viscosity. This increase in the ink viscosity may pose a risk in which the ink cannot be ejected from nozzles or ejected with a relatively small amount because a resistance to a flow of the ink becomes relatively large. 
     On the other hand, where ejection energy applied to the ink is increased in order to eject the ink, whose viscosity is increased, from the nozzles with the same amount as at ordinary temperatures, electric power consumption upon the ink ejection becomes large. Further, it is possible to restrain the increase in the ink viscosity in the head by also providing a heater on the ink-jet head, but in this case, a manufacturing cost unfortunately increases. 
     This invention has been developed in view of the above-described situations, and it is an object of the present invention to provide a liquid ejecting apparatus which can heat a liquid in a liquid channel of a liquid ejecting head and a liquid to be flowed into the liquid channel by heat generated by a driver IC and thereby lower a liquid viscosity. 
     The object indicated above may be achieved according to the present invention which provides a liquid ejecting apparatus, comprising: A liquid ejecting apparatus, comprising: a liquid ejecting head including (a) a plurality of liquid-ejection openings from each of which a liquid droplet is ejected, (b) a liquid channel having a plurality of individual liquid channels each having one end as a corresponding one of the plurality of liquid-ejection openings, and (c) a plurality of actuators each of which applies, to a liquid in a corresponding one of the plurality of individual liquid channels, ejection energy that causes the liquid droplet to be ejected from a corresponding one of the plurality of liquid-ejection openings; an inflow liquid temperature sensor which detects a temperature of the liquid to be flowed into the liquid channel from an outside; a driver IC which is disposed so as to be thermally connected to the liquid ejecting head, which includes a signal producing circuit configured to produce (a) an ejection signal that causes the liquid droplet to be ejected from the liquid-ejection opening, (b) a non-ejection signal that causes the liquid droplet not to be ejected from the liquid-ejection opening and a liquid near the liquid-ejection opening not to be vibrated, and (c) a vibration signal that causes the liquid droplet not to be ejected from the liquid-ejection opening and the liquid near the liquid-ejection opening to be vibrated, and which supplies one of the produced signals to each of the plurality of actuators in each recording period; and a controller configured to control the driver IC, wherein the controller includes: a storing section configured to store drive data of the plurality of actuators that indicate an amount of the liquid droplets ejected from the plurality of liquid-ejection openings in each recording period; a first estimating section configured to estimate a first heat amount by which the liquid to be flowed into the liquid channel in a predetermined period including a plurality of the recording periods deprives the liquid ejecting head of heat on the basis of (a) an amount of the liquid to be flowed into the liquid channel by the ejection of the liquid droplets from the plurality of liquid-ejection openings on the basis of the stored drive data, (b) an internal channel liquid temperature as a temperature of the liquid in the liquid channel, and (c) an inflow liquid temperature detected by the inflow liquid temperature sensor; a second estimating section configured to estimate, on the basis of the stored drive data, a second heat amount generated by the driver IC in the predetermined period by supplying the ejection signal to the plurality of actuators by the signal producing circuit; and a signal-producing-circuit controlling section configured to cause the signal producing circuit to produce the ejection signal, the non-ejection signal, and the vibration signal in each recording period on the basis of the stored drive data such that one of the ejection signal, the non-ejection signal, and the vibration signal is supplied to each of the plurality of actuators, and wherein the signal-producing-circuit controlling section controls the signal producing circuit such that an increased heat amount exceeds a third heat amount obtained by subtracting the second heat amount from the first heat amount, the increased heat amount being as a heat amount of the driver IC which is increased by supplying, instead of the non-ejection signal supplied to each of at least one of the plurality of actuators, the vibration signal to each of at least one of the at least one actuator to which the non-ejection signal is supplied. 
     In the liquid ejecting apparatus as described above, since the signal-producing-circuit controlling section controls the signal producing circuit such that the driver IC generates the heat amount exceeding the third heat amount, the liquid in the liquid channel and the liquid flowed from the outside into the liquid channel are heated by the heat amount generated by the driver IC, thereby restraining an increase in thickening of a viscosity of the liquid. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The objects, features, advantages, and technical and industrial significance of the present invention will be better understood by reading the following detailed description of a preferred embodiment of the invention, when considered in connection with the accompanying drawings, in which: 
         FIG. 1  is a schematic view showing an internal structure of an ink-jet printer as an embodiment of the present invention; 
         FIG. 2  is a generally perspective view showing one of ink-jet heads and one of ink tanks shown in  FIG. 1 ; 
         FIG. 3  is a cross-sectional view of the ink-jet head shown in  FIG. 2 ; 
         FIG. 4  is a plan view of the ink-jet head shown in  FIG. 2 ; 
         FIG. 5  is a plan view of a head main body; 
         FIG. 6  is an enlarged view of an area enclosed with one-dot chain line in  FIG. 5 ; 
         FIG. 7  is a cross-sectional view of a channel unit and an actuator unit which constitute the head main body; 
         FIG. 8  is a partially cross-sectional view of the actuator unit; 
         FIG. 9  is a functional block diagram of a controller; and 
         FIG. 10  is a schematic view of unit waveforms outputted by an outputting circuit. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Hereinafter, there will be described a preferred embodiment of the present invention by reference to the drawings. 
     As shown in  FIG. 1 , an ink-jet printer  101  includes a body  101   a  having a rectangular parallelepiped shape, and an inside of the body  101   a  is separated into three spaces A, B, C in order from above. In the space A, there are disposed four ink-jet heads (i.e., liquid-droplets ejecting heads)  1  which respectively eject inks of four colors, namely, magenta, cyan, yellow, and black, and a sheet-feed mechanism  16 . A top portion of the body  101   a  which partly defines the space A is provided by a sheet-discharge portion  15 . In the space B is disposed a sheet-supply unit  101   b  attachable to and detachable from the body  101   a  while in the space C is disposed an ink-tank unit  101   c  attachable to and detachable from the body  101   a . Further, in the body  101   a , there is provided a controller  100  configured to control operations of the ink-jet heads  1  and the sheet-feed mechanism  16 . 
     In the ink-jet printer  101 , there is formed a sheet feeding path in which each sheet P is fed from the sheet-supply unit  101   b  toward the sheet-discharge portion  15  along boldface arrow in  FIG. 1 . The sheet-supply unit  101   b  includes a sheet-supply tray  11  and a sheet-supply roller  12 . The sheet-supply tray  11  has a box-like shape opening upward and accommodates a plurality of the sheets P in a state in which the sheets P are stacked on each other. The sheet-supply roller  12  supplies an uppermost one of the sheets P accommodated in the sheet-supply tray  11 . The supplied sheet P is fed to the sheet-feed mechanism  16  while being guided by guides  13   a ,  13   b  and nipped by and between a pair of feed rollers  14 . 
     As shown in  FIG. 1 , the sheet-feed mechanism  16  includes two belt rollers  6 ,  7 , a sheet-feed belt  8 , a tension roller  10 , and a platen  18 . The sheet-feed belt  8  is an endless belt wound around the rollers  6 ,  7  so as to bridge the rollers  6 ,  7 . The tension roller  10  applies tension to the sheet-feed belt  8  by being biased downward while contacting with an inner peripheral surface of the sheet-feed belt  8  at a lower portion thereof. The platen  18  is disposed in an area enclosed by the sheet-feed belt  8 . Further, the platen  18  supports the sheet-feed belt  8  at a position opposed to the ink-jet heads  1  such that the sheet-feed belt  8  is not bent or warped downward. The belt roller  7  is a drive roller which is rotated in a clockwise direction in  FIG. 1  by being given a drive force to a shaft of the belt roller  7  from a sheet-feed motor  19 . The belt roller  6  is a driven roller which is rotated in the clockwise direction in  FIG. 1  by rotation of the sheet-feed belt  8  which is caused by rotation of the belt roller  7 . 
     An outer peripheral surface  8   a  of the sheet-feed belt  8  is subjected to a silicone treatment to have a viscosity. At a position opposed to the belt roller  6  is disposed a nipping roller  4 . The nipping roller  4  presses, to the outer peripheral surface  8   a  of the sheet-feed belt  8 , each sheet P supplied by the sheet-supply unit  101   b . The sheet P pressed to the outer peripheral surface  8   a  is fed in a sheet feeding direction (i.e., a rightward direction in  FIG. 1  or a sub-scanning direction) while being held by and on the outer peripheral surface  8   a  owing to the viscosity thereof. It is noted that, in the present embodiment, the sub-scanning direction is a direction parallel to the sheet feeding direction in which each sheet P is fed by the sheet-feed mechanism  16  while a main scanning direction is a direction perpendicular to the sub-scanning direction and along a horizontal surface. 
     A peeling plate  5  is provided at a position opposed to the belt roller  7 . The peeling plate  5  peels each sheet P from the outer peripheral surface  8   a . The peeled sheet P is fed while being guided by guides  29   a ,  29   b  and being nipped between two pairs of feed rollers  28 . Then, the sheet P is discharged to the sheet-discharge portion  15  from an opening  30  formed in an upper portion of the body  101   a.    
     The four ink-jet heads  1  are respectively corresponded to the inks of four colors, namely, magenta, cyan, yellow, and black, and each of the ink-jet heads  1  has a generally rectangular parallelepiped shape extending in the main scanning direction. Further, the four ink-jet heads  1  are fixed so as to be arranged in the sheet feeding direction. That is, the ink-jet printer  101  is a printer of a line type. 
     A bottom surface of each of the ink-jet heads  1  is provided by an ink-ejection surface  2   a  in which a plurality of ink-ejection openings  108  (with reference to  FIGS. 6 and 7 ) are formed. Through the plurality of ink-ejection openings  108 , the ink is ejected. When each sheet P is fed through just below the four ink-jet heads  1 , the inks of the respective colors are sequentially ejected to an upper surface of the sheet P from the ink-ejection openings  108 . As a result, a desired color image is formed on the upper surface of the sheet P, i.e., a recording surface. 
     The ink-jet heads  1  are respectively connected to ink tanks (liquid storing portions)  17  in the ink-tank unit  101   c . That is, each of the inks of the four colors is stored in a corresponding one of the four ink tanks  17  and is supplied from the corresponding ink tank  17  via a corresponding one of tubes (i.e., connecting tubes)  3  (with reference to  FIG. 2 ) to an ink channel (a liquid channel) in the corresponding ink-jet head  1 . 
     There will be next explained the ink-jet heads  1  in detail with reference to  FIGS. 2-4 . As shown in  FIGS. 2 and 3 , each of the ink-jet heads  1  includes a head main body (a second channel member)  2  and a reservoir unit (a first channel member)  70  fixed to an upper surface of the head main body  2 . It is noted that the four ink-jet heads  1  have the same construction and thus there will be explained one of the ink-jet heads  1 . 
     As shown in  FIG. 3 , the reservoir unit  70  includes three metal plates  71 - 73  each of which has a rectangular planar shape and which are stacked on each other. Thus, the reservoir unit  70  has a generally rectangular parallelepiped shape in the main scanning direction. Further, in the reservoir unit  70 , there are formed an ink-inlet channel  71   a , a reservoir channel  74 , and eight ink-outlet channels  73   a  each of which partly constitutes the ink channel of the head  1  and which are communicated with each other. It is noted that  FIG. 3  shows only one of the ink-outlet channels  73   a.    
     To the ink-inlet channel  71   a  is connected the tube  3 , so that the ink is flowed into the ink-inlet channel  71   a  via the tube  3 . It is noted that a temperature sensor (an inflow liquid temperature sensor)  98  is provided on or fixed to a midway portion of the tube  3  (with reference to  FIGS. 2 and 9 ). The temperature sensor  98  is configured to detect a temperature of the ink existing on an outside of the ink-jet head  1  (i.e., the ink to be flowed into the ink-jet head  1 ) to transmit, to the controller  100 , a detected signal based on the detection by the temperature sensor  98 . In the present embodiment, the temperature sensor  98  is disposed near an outlet of the ink tank  17  so as to be allowed to measure a temperature of the tube  3 . 
     The reservoir channel  74  temporarily stores the ink supplied from the ink tank  17 . The reservoir channel  74  ( 74   a - 74   d ) extends as shown in  FIG. 4  in the main scanning direction or in a lengthwise direction thereof and has the largest capacity among the channels formed in the head  1 . 
     A lower surface of the plate  73  is provided by a surface having projections and depressions such that spaces are formed between the lower surface of the plate  73  and FPCs (Flexible Printed Circuits)  50  which will be described below. The plate  73  is fixed to a channel unit  9  (which will be described below) by projected potions of the lower surface of the plate  73 , and the reservoir channel  74  is communicated with ink-supply openings  105   b  (which will be described below) of the channel unit  9  by the ink-outlet channels  73   a  respectively formed in the projected portions. As a result, the ink supplied from the ink tanks  17  passes through the ink-inlet channel  71   a , the reservoir channel  74 , and the ink-outlet channels  73   a  in order and to be supplied from the ink-supply openings  105   b  to the channel unit  9 . 
     As shown in  FIG. 4 , to the reservoir unit  70 , there are fixed four heaters  97   a - 97   d  so as to be thermally connected to each other, more specifically, the heaters  97   b ,  97   d  are fixed to a side face  70   b  of the reservoir unit  70  while the heaters  97   a ,  97   c  are fixed to a side face  70   c  of the reservoir unit  70 . As shown in  FIG. 3 , these four heaters  97   a - 97   d  are disposed in correspondence with the ink-outlet channels  73   a . The heaters  97   a - 97   d  generate heat by being energized by a control of the controller  100 , and thereby individually heat the ink in respective partial channels  74   a - 74   d  which are formed by dividing the reservoir channel  74  in quarters in the main scanning direction. More specifically, the heaters  97   a - 97   d  mainly heat the ink near the ink-outlet channels  73   a  of the reservoir channel  74 . 
     Further, to the reservoir unit  70 , there are fixed four temperature sensors (first temperature sensors)  99   a - 99   d , more specifically, the temperature sensors  99   a ,  99   c  are fixed to the side face  70   b  while the temperature sensors  99   b ,  99   d  are fixed to the side face  70   c . These four temperature sensors  99   a - 99   d  are disposed at positions respectively opposed to the heaters  97   a - 97   d  in the sub-scanning direction, and configured to individually detect respective temperatures of the ink in the partial channels  74   a - 74   d  formed by dividing the reservoir channel  74  in quarters. This allows a temperature of the ink (i.e., ink temperature) in the reservoir channel  74  to be accurately detected. The four temperature sensors  99   a - 99   d  transmit, to the controller  100 , detected signals based on the detections by the respective temperature sensors  99   a - 99   d.    
     As shown in  FIG. 3 , the head main body  2  is constituted by the channel unit  9  and four actuator units  21  which are bonded to each other by adhesives, and has a generally rectangular parallelepiped shape in the main scanning direction or in a longitudinal direction thereof. To upper surfaces of the respective actuator units  21 , there are respectively fixed one ends of the FPCs  50 , the FPCs  50  are drawn to an outside from openings of the respective spaces formed by depressed portions of the lower surface of the plate  73 . As shown in  FIGS. 2 and 4 , on the four FPCs  50  are respectively mounted driver ICs  51   a - 51   d . Each of the driver ICs  51   a - 51   d  has an outputting circuit  52  configured to produce signals (specifically, an ejection signal, a non-ejection signal, a vibration signal which will be described below) for driving the actuator units  21  and to sequentially output the produced signals to individual electrodes  135  (with reference to  FIG. 8 ). The other ends of the respective FPCs  50  are electrically connected to the controller  100 , and the controller  100  controls drivings of the actuator units  21  via the respective driver ICs  51   a - 51   d.    
     As shown in  FIGS. 2-4 , the four driver ICs  51   a - 51   d  are fixed to an upper surface  70   a  of the reservoir unit  70  (with reference to  FIG. 3 ). More specifically, the four driver ICs  51   a - 51   d  are thermally coupled to the plate (i.e., a defining member)  71  partly defining the reservoir channel  74 . Further, the four driver ICs  51   a - 51   d  are arranged at a center of the upper surface  70   a  in the sub-scanning direction so as to be equally spaced from each other in the main scanning direction. Further, the four driver ICs  51   a - 51   d  are respectively opposed to the partial channels  74   a - 74   d  of the reservoir channel  74 . As shown in  FIG. 4 , the four driver ICs  51   a - 51   d  are disposed respectively adjacent to the temperature sensors  99   a - 99   d  and the heaters  97   a - 97   d  in correspondence with the respective partial channels  74   a - 74   d . In this construction, when the driver ICs  51   a - 51   d  are driven to generate heat by a control of the controller  100 , the generated heat mainly heats the ink in the respective partial channels  74   a - 74   d  via the plate  71 . In this time, as will be described below, the heat generated by the driver ICs  51   a - 51   d  also heats the channel unit  9  via the reservoir unit  70 . 
     There will be next explained the head main body  2  in more detail with reference to  FIGS. 5-8 . It is noted that, in  FIG. 6 , a pressure chamber  110 , an aperture  112 , and the ink-ejection opening  108  are indicated by solid lines for easier understanding purposes though these elements should be indicated by broken lines because these elements are located under the actuator unit  21  (i.e., in the channel unit  9 ). 
     As shown in  FIG. 5 , in the head main body  2 , the four actuator units  21  are fixed to an upper surface  9   a  of the channel unit  9 . As shown in  FIG. 7 , in the channel unit  9 , there are formed ink channels including a plurality of the pressure chambers  110  and so on. The actuator units  21  include a plurality of actuators corresponding to each of the pressure chambers  110  and each has a function to selectively apply ejection energy to the ink in the pressure chambers  110  by the supply of the ejection signal from the driver ICs  51 . 
     As shown in  FIG. 5 , the channel unit  9  has a rectangular parallelepiped shape extending in the main scanning direction. In the upper surface  9   a  of the channel unit  9 , the eight ink-supply openings  105   b  are opened in correspondence with the ink-outlet channels  73   a  of the reservoir unit  70 . These ink-supply openings  105   b  are disposed in the main scanning direction in a staggered configuration with each two of the ink-supply openings  105   b  being as a pair. As shown in  FIGS. 5 and 6 , in the channel unit  9 , there are formed four manifold channels  105  each of which is communicated with a corresponding one of pairs of the ink-supply openings  105   b.    
     The four manifold channels  105  are arranged in the main scanning direction so as to be respectively opposed to the partial channels  74   a - 74   d  in a vertical direction. To each of the manifold channels  105 , the ink is flowed mainly from a corresponding opposed one of the partial channels  74   a - 74   d . It is noted that the four manifold channels  105  are independent of each other in the channel unit  9 , but are communicated with each other in the reservoir unit  70 . 
     Further, each of the manifold channels  105  includes four sub-manifold channels  105   a  branched therefrom and extending in the main scanning direction so as to be parallel to each other. As shown in  FIGS. 5 and 6 , the four sub-manifold channels  105   a  are disposed respectively at positions in which an entirety of the four sub-manifold channels  105   a  is superposed on each of the actuator units  21  in the vertical direction. As thus described, the manifold channels  105  and the partial channels  74   a - 74   d  are disposed in correspondence with the actuator units  21 , and the temperature sensors  99   a - 99   d  and the heaters  97   a - 97   d  are disposed in correspondence with the partial channels  74   a - 74   d . That is, the manifold channels  105 , the partial channels  74   a - 74   d , the temperature sensors  99   a - 99   d , and the heaters  97   a - 97   d  are provided in correspondence with a placement of the actuator units  21 . 
     Further, the channel unit  9  has a smaller thermal capacity than the reservoir unit  70 , and is thermally coupled to the four driver ICs  51   a - 51   d  via the reservoir unit  70 . As a result, the heat from the driver ICs  51   a - 51   d  is diffused by the reservoir unit  70  having a relatively large thermal capacity, so that the channel unit  9  is uniformly heated from a surface thereof which is coupled to the reservoir unit  70 . Thus, the channel unit  9  is less affected by a thermal fluctuation based on a placement of the driver ICs  51   a - 51   d  and a difference of an amount of generated heat when compared with a case in which the driver ICs  51   a - 51   d  are directly fixed to or thermally coupled to the channel unit  9 . Further, the channel unit  9  is heated, whereby the ink in the ink channels in the channel unit  9  is also heated. 
     In the present embodiment, in the upper surface  9   a  of the channel unit  9 , a plurality of the pressure chambers  110  are arranged in matrix in the main scanning direction so as to be equally spaced from each other, thereby constituting sixteen rows of the pressure chambers  110 . These pressure-chamber rows are disposed in the sub-scanning direction so as to be parallel to each other. In correspondence with an outer shape (a trapezoid shape) of each of the actuator units  21 , the number of the pressure chambers  110  included in each of the pressure-chamber rows gradually decreases from a longer side toward a shorter side of the trapezoid shape of each of the actuator units  21 . The ink-ejection openings  108  are also disposed in a manner similar to this configuration in the lower surface (the ink-ejection surface  2   a ) of the channel unit  9 . 
     As shown in  FIG. 7 , the channel unit  9  is constituted by nine plates  122 - 130  each formed of a metal material such as stainless steel. Each of these plates  122 - 130  includes a planar surface having a rectangular shape extending in the main scanning direction. 
     Through holes formed through the respective plates  122 - 130  are communicated with each other by stacking the plates  122 - 130  on each other while positioning. As a result, in the channel unit  9 , there are formed a plurality of individual ink channels  132  partly constituting the ink channels of the head  1  and extending from the four manifold channels  105  (the sub-manifold channels  105   a ) and outlets of the respective sub-manifold channels  105   a  to the ink-ejection openings  108  via the pressure chambers  110 . 
     There will be next explained a flow of the ink in the channel unit  9 . The ink supplied from the reservoir unit  70  into the channel unit  9  via the ink-supply openings  105   b  is diverted into the sub-manifold channels  105   a  in each of the manifold channels  105 . The ink in the sub-manifold channels  105   a  is flowed into each of the individual ink channels  132  and reaches a corresponding one of the ink-ejection openings  108  via a corresponding one of a plurality of the apertures  112  each as functioning as a restrictor and a corresponding one of the pressure chambers  110 . 
     There will be next explained the actuator units  21 . As shown in  FIG. 5 , each of the actuator units  21  has a trapezoid planar shape. Further, each actuator unit  21  is formed of a ceramic material of lead zirconate titanate (PZT) having ferroelectricity, and as shown in  FIG. 8 , is constituted by three piezoelectric sheets  141 - 143 . On an upper surface of the piezoelectric sheet  141 , the plurality of individual electrodes  135  are formed so as to be respectively opposed to the pressure chambers  110 . Each of the individual electrodes  135  includes (a) an electrode portion disposed on an area of the upper surface which is opposed to a corresponding one of the pressure chambers  110  and (b) an extended portion drawn to an outside of the area opposed to the corresponding pressure chamber  110 . On the extended portion is formed a land  136 . Between the piezoelectric sheet  141  and the piezoelectric sheet  142 , there is provided a common electrode  134  formed so as to extend or cover an entirety of the piezoelectric sheet  142 . It is noted that on the upper surface of the piezoelectric sheet  141  is formed the land  136  for the common electrode in addition to the land  136  for the individual electrode, so that the common electrode  134  is electrically connected to the land  136  for the common electrode. 
     Via the land  136  and inner wiring of the FPCs  50 , the common electrode  134  is kept at a ground potential equally in areas thereof respectively corresponding to all the pressure chambers  110 . On the other hand, the individual electrodes  135  are electrically connected to the respective outputting circuits  52  of the respective driver ICs  51   a - 51   d , so that one of the ejection signal, the non-ejection signal, and the vibration signal from the driver ICs  51   a - 51   d  is selectively inputted to the individual electrodes  135 . As thus described, in each of the actuator units  21 , there are provided a plurality of the actuators corresponding to the number of the pressure chambers  110 , with the individual electrodes  135  and areas interposed between the individual electrodes  135  and the pressure chambers  110  as individual actuators. 
     Here, there will be explained a method for driving the actuator units  21  in order to eject ink droplets from the ink-ejection openings  108 . The piezoelectric sheet  141  is polarized across a thickness thereof (hereinafter, may be referred to as a “polarization direction”), and when an electric field is applied to the piezoelectric sheet  141  in the polarization direction in a state in which the individual electrodes  135  are given a potential different from that of the common electrode  134 , the piezoelectric sheet  141  functions as an active portion in which a portion of the piezoelectric sheet  141  to which the electric field is applied is deformed owing to piezoelectric effect. This active portion extends in its thickness direction and contracts or shrinks in its surface direction when directions of the electric field and the polarization are the same as each other. An amount of displacement of this extension and contraction is larger in the surface direction than in the thickness direction. On the other hand, the lower piezoelectric sheets  142 ,  143  nearer to the pressure chambers  110  are non-active layers which are not voluntarily displaced with respect to an external electric field. 
     As shown in  FIG. 8 , the piezoelectric sheet  143  is fixed to an upper surface of the cavity plate  122  partly defining the pressure chambers  110 , and thus when a difference in distortion is produced in a direction (a planar direction) perpendicular to the vertical direction between portions of the piezoelectric sheet  141  to which the electric field is applied and the underlying piezoelectric sheets  142 ,  143 , the piezoelectric sheets  141 - 143  are entirely deformed into a convex shape that protrudes toward the pressure chambers  110 , that is, a unimorph deformation occurs. As a result, a pressure (i.e., ink-ejection energy) is applied to the ink in the pressure chambers  110 , thereby producing a pressure wave in the pressure chambers  110 . Then, the produced pressure wave is propagated from the pressure chambers  110  to the ink-ejection openings  108 , whereby the ink droplets are ejected from the ink-ejection openings  108 . 
     In the present embodiment, the ejection signal including one or a plurality of a voltage pulse or pulses is outputted from the driver ICs  51   a - 51   d , and a positive predetermined potential is applied to the individual electrodes  135  in advance. Then, the ground potential is temporarily applied to the individual electrodes  135  each time when the ejection of the ink is required, and then the predetermined potential is applied again to the individual electrodes  135  at a predetermined timing. In this case, at the timing when the individual electrodes  135  become the ground potential, a negative pressure wave is produced in the pressure chambers  110 . The negative pressure wave is transmitted from each of the pressure chambers  110  toward opposite ends of a corresponding one of the individual ink channels  132 , then is reversed to positive at a position near the outlets of the sub-manifold channels  105   a , and then is returned to the pressure chambers  110  again. The timing at which the predetermined potential is applied to the individual electrodes  135  corresponds to a timing at which the reversed pressure wave is returned to the pressure chambers  110 . That is, the ink is sucked from the sub-manifold channels  105   a  by the negative pressure produced in the pressure chambers  110 . When the predetermined potential is applied to the individual electrodes  135  at the timing when the ink has reached the pressure chambers  110 , a pressure of the ink in the pressure chambers  110  rises, whereby the ink droplets are ejected from the ink-ejection openings  108 . 
     A width of each of the voltage pulse(s) applied to the individual electrodes  135  is a length of time AL (Acoustic Length) in which the pressure wave is propagated from the outlets of the sub-manifold channels  105   a  to the ink-ejection openings  108  via the ink as a medium as described below. The width of each of the voltage pulse(s) included in the ejection signal is set as thus described, whereby (a) the pressure wave made positive by being reversed at the opposite ends of each individual ink channel  132  and (b) the positive pressure wave produced at the timing when the predetermined potential is applied to the corresponding individual electrode  135  are superposed on each other in the corresponding pressure chamber  110 . Thus, the ink droplets can be ejected from the ink-ejection openings  108  in a state in which a height of the voltage pulse(s) is relatively low. 
     In order to drive the actuator units  21  such that the ink droplets are not ejected from the ink-ejection openings  108 , a vibration signal including a plurality of voltage pulses each of which has a lower height beyond a specific value than the voltage pulse(s) included in the ejection signal and/or a vibration signal including a plurality of voltage pulses each of which has a narrower or wider pulse width beyond a specific value than the length of time AL are or is applied to the individual electrodes  135 . In each case, since an amplitude of the pressure wave produced in the pressure chambers  110  does not become large beyond a threshold required for the ejection, the ink droplets are not ejected from the ink-ejection openings  108 , and fine vibrations are produced in a meniscus of the ink The ink near the ink-ejection openings  108  is agitated by the vibrations of the ink meniscus, thereby restraining thickening of the ink due to drying. Thus, an ink ejection failure is restrained. It is noted that, in the present embodiment, there is employed, as the vibration signal, the vibration signal including the plurality of voltage pulses each of which has the narrower pulse width beyond the specific value than the length of time AL. 
     There will be next explained the controller  100  in detail with reference to  FIG. 9 . The controller  100  includes a Central Processing Unit (CPU) as an arithmetic processing unit, a Read Only Memory (ROM) storing programs performed by the CPU and data used for the program, a Random Access Memory (RAM) for temporarily storing data when performing the program, and other logic circuits. These components are integrally functioned, whereby the controller  100  configures functioning sections which will be described below. It is noted that  FIG. 9  schematically shows only one of the four ink-jet heads  1 . 
     As shown in  FIG. 9 , the controller  100  includes a recording-data storing section  151 , a waveform storing section  152 , a signal-produce controller  153 , and a sheet-feed controller  154 . Further, the temperature sensors  98 ,  99   a - 99   d  and the heaters  97   a - 97   d  are connected to the controller  100 . 
     The recording-data storing section  151  is configured to store recording data transmitted from a host computer, not shown. The recording data includes image data relating to an image to be formed on the sheet P. The image data is a group of dot data indicating an amount of a liquid ejected from the ink-ejection openings  108 , to one of which each of dots of the image is corresponded. The image data has a type of drive data for driving the actuator units  21  by a recording controller  161  which will be described below. That is, the drive data indicate an amount of the ink ejected from each of the ink-ejection openings  108  in each of recording periods (recording cycles). Specifically, the drive data indicate that the amount of the ink ejected from each ink-ejection opening  108  in each recording period is one of four levels or settings (i.e., a small amount, a medium amount, a large amount, and no amount). Here, with reference to  FIG. 10 , the “small amount” corresponds to an ejection waveform W 1  described below, the “medium amount” corresponds to an ejection waveform W 2  described below, the “large amount” corresponds to an ejection waveform W 3  described below, and the “no amount” corresponds to a non-ejection waveform W 4  described below. 
     The waveform storing section  152  stores twelve unit waveforms and outputs the twelve unit waveforms to the respective outputting circuits  52  of the driver ICs  51   a - 51   d  in parallel. In the present embodiment, with reference to  FIG. 10 , the ejection waveforms W 1 , W 2 , W 3 , the non-ejection waveform W 4 , and the vibration waveforms S 1 , S 2  are prepared. Each of the ejection waveforms W 1 -W 3  is a unit waveform for producing the ejection signal which causes the ink to be ejected from the ink-ejection openings  108 . The non-ejection waveform W 4  is a unit waveform for producing the non-ejection signal which causes the ink not to be ejected from the ink-ejection openings  108  and also causes the ink near the ink-ejection openings  108  not to vibrate. Each of the vibration waveforms S 1 , S 2  is a unit waveform for producing the vibration signal for causing the ink not to be ejected from the ink-ejection openings  108  and the ink near the ink-ejection openings  108  to vibrate. 
     These six unit waveforms have the same length of time (one recording period), and are used when the one recording period is 50i sec (drive frequency: 20 kHz). It is noted that the one recording period corresponds to a time required that the sheet is fed by a predetermined distance (i.e., a minimum dot pitch) corresponding to a recording resolution in the sub-scanning direction. 
     Further, in the waveform storing section  152 , there are prepared ejection waveforms W 1 ′, W 2 ′, W 3 ′, a non-ejection waveform W 4 ′, and vibration waveforms S 1 ′, S 2 ′ used when the one recording period is 100i sec (drive frequency: 10 kHz). It is noted that since there is only a small difference between the waveforms W 1 , W 2 , W 3 , W 4 , S 1 , S 2  and the waveforms W 1 ′, W 2 ′, W 3 ′, W 4 ′, S 1 ′, S 2 ′, that is, a unit waveform of each of the waveforms W 1 ′, W 2 ′, W 3 ′, W 4 ′, S 1 ′, S 2 ′ has one recording period twice as long as that of a unit waveform of each of the waveforms W 1 , W 2 , W 3 , W 4 , S 1 , S 2  in the length of time by adding, to the unit waveform of each of the waveforms W 1 , W 2 , W 3 , W 4 , S 1 , S 2 , a high-level period whose length is the same as that of the one recording period of each of the waveforms W 1 , W 2 , W 3 , W 4 , S 1 , S 2 ,  FIG. 10  shows only one of the waveforms W 1 ′, W 2 ′, W 3 ′, W 4 ′, S 1 ′, S 2 ′ as an example. 
     The ejection signals, the non-ejection signal, and the vibration signals are ones made by amplifying the above-described twelve unit waveforms by the respective outputting circuits  52  of the driver ICs  51   a - 51   d . A low level potential of each signal is set to the ground potential, and a high level potential of each signal is set to a positive first predetermined potential (for example, 24V). This amplification is performed for each of the individual electrodes  135  in each of the recording periods, and one amplifying subject waveform is selected from the twelve unit waveforms on the basis of an ejection-selecting signal and a vibration-selecting signal as described below. It is noted that, in the present embodiment, in addition to the above-described vibration signal, there is also used, as the vibration signal, a vibration signal amplified by the respective outputting circuits  52  of the driver ICs  51   a - 51   d  such that a low level potential of each of the vibration waveforms S 2 , S 2 ′ is the ground potential while a high level potential thereof becomes a second predetermined potential (for example, 36V) higher than the first predetermined potential. 
     Here, there will be explained the unit waveform. As shown in  FIG. 10 , the ejection waveforms W 1 , W 2 , W 3  respectively include one, two, and three pulses. A width of each pulse included in the ejection waveforms W 1 -W 3  (a pulse transferred from the high level potential to the low level potential, and then returned to the high level potential) is equal to the AL. Thus, when the ejection signal is applied to the individual electrodes  135 , an amplitude of the pressure wave produced in the pressure chambers  110  becomes large beyond the threshold required for the ejection, whereby the ink is ejected from the ink-ejection openings  108 . In this time, each one of the pulse(s) included in the ejection waveforms W 1 -W 3  corresponds to one ink droplet ejected from one of the ink-ejection openings  108 . An amount of the ink ejected in one ejection is constant. Thus, an amount of the ink ejected by the ejection waveform W 2  is twice as large as an amount of the ink ejected by the ejection waveform W 1 , and an amount of the ink ejected by the ejection waveform W 3  is three times as large as an amount of the ink ejected by the amount of the ink ejected by the ejection waveform W 1 . Further, a distance between pulses of each of the ejection waveforms W 2 , W 3  is equal to the AL. Here, when the ejection signal is applied to each of the individual electrodes  135 , the ink droplets whose number is according to the ejection waveforms W 1 -W 3  are ejected from the corresponding ink-ejection openings  108 , whereby one dot is formed on the sheet in each of the ejection waveforms W 1 -W 3 . 
     The non-ejection waveform W 4  is always kept at the high level potential. Thus, even where the non-ejection signal produced on the basis of the non-ejection waveform W 4  is applied to the individual electrodes  135 , the ink is not ejected from the ink-ejection openings  108 , so that the fine vibration is not produced in the meniscus of the ink. 
     Further, the vibration waveforms S 1 , S 2  respectively include five and ten pulses. A width of each pulse included in the vibration waveforms S 1 , S 2  is about half of the AL and equal to or less than the above-described specific value. Thus, even where the vibration signal produced on the basis of the vibration waveforms S 1 , S 2  is applied to the individual electrodes  135 , the ink is not ejected though the ink meniscus formed in the ink-ejection openings  108  is vibrated. An amount of heat (i.e., a heat amount) generated when the vibration signal is applied to the individual electrodes  135  is in proportion to a number of the pulses included in the vibration signal. For example, a heat amount generated when the vibration signal produced on the basis of the vibration waveform S 1  is applied to the individual electrodes  135  is half of a heat amount generated when the vibration signal produced on the basis of the vibration waveform S 2  is applied. Further, the heat amount generated when the vibration signal is applied to the individual electrodes  135  is in proportion to a square of a pulse height included in the vibration signal. That is, the heat amount generated when the vibration signal amplified such that the high level potential of the vibration waveform S 2  becomes the first predetermined potential is applied to the individual electrodes  135  is 1/2.25 of the heat amount generated when the vibration signal amplified such that the high level potential of the vibration waveform S 2  becomes the second predetermined potential is applied. 
     The signal-produce controller  153  includes the recording controller  161 , a vibration controlling section  162 , and a changing section  165 . The recording controller  161  is configured to output the ejection-selecting signal to the outputting circuits  52  on the basis of the stored drive data. The ejection-selecting signal is outputted in each of the recording periods to command the waveform (W 1 -W 4 ) of the signal applied to each of the individual electrodes  135 . Each of the outputting circuits  52  selects one of the ejection waveforms W 1 -W 3  and the non-ejection waveform W 4  on the basis of the ejection-selecting signal and applies the selected waveform to each individual electrode  135  as the ejection signal and the non-ejection signal amplified such that the high level potential of the waveform becomes the first predetermined potential. 
     The vibration controlling section  162  is configured to output, upon turning on the printer  101  (Le., just after a start of an operation of the printer  101 ), the vibration-selecting signal to the outputting circuits  52  where an average ink temperature in the reservoir channel  74  (an average value in the four temperature sensors  99   a - 99   d ) which is an average temperature of the four temperatures respectively detected by the temperature sensors  99   a - 99   d  is lower than a predetermined temperature. In this time, the vibration-selecting signal functions as a signal commanding the vibration waveform S 2  where the average ink temperature is lower than a threshold temperature, and functions as a signal commanding the vibration waveform S 1  where the average ink temperature is equal to or more than the threshold temperature. Further, in this time, the number of the individual electrodes  135  to which the vibration signal is supplied is increased in accordance that the detected ink temperature becomes low. Each of the outputting circuit  52  selects one of the two vibration waveforms S 1 , S 2  on the basis of the vibration-selecting signal, and supplies the selected waveform to the corresponding individual electrodes  135  as a vibration signal amplified such that the high level potential thereof becomes the first predetermined potential. 
     As a result, when the printer  101  is turned on, and the ink temperature is lower than the predetermined temperature, the driver ICs  51   a - 51   d  generate heat to heat the reservoir unit  70  before the recording. Thus, the ink in the reservoir channel  74  is heated and the ink in the ink channels of the channel unit  9  is also heated via the reservoir unit  70 , whereby the ink ejection failure occurs less frequently. Further, depending upon the detected ink temperature, the one of the vibration waveforms S 1 , S 2  to be selected and the number of the individual electrodes  135  supplying the signal are changed, thereby restraining electric power consumption. 
     It is noted that the control of the vibration controlling section  162  in this time is performed for a predetermined length of time since the printer  101  is turned on such that the ink in the head becomes a temperature equal to or more than the predetermined temperature, but where the recording data is transmitted to the controller  100  before the predetermined length of time has passed, the vibration of the ink meniscus is forced to be finished. On the other hand, where the recording data is not transmitted to the controller  100  after the predetermined length of time has passed, the above-described control may be performed at regular intervals over a period until the recording data is transmitted. As a result, the ink ejection failure occurs much less frequently. 
     The vibration controlling section  162  includes a first estimating section  163  and a second estimating section  164 . The first estimating section  163  is configured to calculate in advance an amount of the ink ejected from the ink-ejection openings  108  in a predetermined period (i.e., a period from a start of recording on one sheet P to an end of the recording), i.e., an amount of the ink (an ink amount V) to be flowed into the ink channel of the head  1  (i.e., the reservoir channel  74 ) on the basis of the stored drive data. Further, the first estimating section  163  is configured to estimate in advance a heat amount Q 1  by which the ink to be flowed into the head  1  in the predetermined period deprives the head  1  of heat, on the basis of the calculated ink amount V, a temperature of the ink (i.e., an ink temperature T 2 ) to be flowed into the head  1  which temperature has been detected by the temperature sensor  98 , and an average ink temperature T 1  (i.e., an internal channel liquid temperature) in the reservoir channel  74  which has been detected by the temperature sensors  99   a - 99   d.    
     Specifically, a head temperature T 1 ′ after being changed by the flow of the ink into the reservoir channel  74  is obtained by the following expression (1). Expression (1) represents a balance of heat before and after the ink is flowed into. Further, a variation of a volume of the ink by the temperature is ignored here.
 
α T 2 V+αT 1 V 1+β T 1 V 2=α T 1′( V+V 1)+β T 1′ V 2  (1)
 
Here, “α” represents a specific heat capacity of the ink (cal/k·cm 3 ), “β” represents a specific heat capacity of the reservoir unit  70  (specifically, only solid portions thereof exclusive of channel portions thereof), “V 1 ” represents an amount of the ink in the reservoir unit  70  (exclusive of a discharged ink whose amount is the same as that of an inflow ink), and “V 2 ” represents a volume of the reservoir unit  70  (specifically, only the solid portions thereof exclusive of the channel portions thereof). Then, “Q 1 ” is calculated by substituting the calculated T 1 ′ into the following expression (2), whereby the heat amount Q 1  is assumed. Expression (2) represents the heat amount obtained by the inflow ink. This heat amount is equal to the heat amount by which the head  1  is deprived of heat.
 
 Q 1=α( T 1′− T 2)× V   (2)
 
     The second estimating section  164  is configured to assume in advance a total heat amount Q 2  of the heat generated by the driver ICs  51   a - 51   d  in the predetermined period, on the basis of the stored drive data by supplying the ejection signal to the individual electrodes  135 . 
     The vibration controlling section  162  outputs the vibration-selecting signal to the outputting circuits  52  where the average ink temperature in the reservoir channel  74  is lower than the predetermined temperature even in times other than a time just after the printer  101  is turned on. The vibration-selecting signal commands the vibration waveform (S 1  and S 2 ) and a value of the high level potential (the first predetermined potential and the second predetermined potential) depending upon the ink temperature. Each of the outputting circuit  52  to which the vibration-selecting signal is inputted in this time corresponds to at least one of the individual electrodes  135  to which the non-ejection signal is applied. At least one of the outputting circuits  52  selects one of the vibration waveforms S 1 , S 2  on the basis of the vibration-selecting signal and applies the selected vibration waveform to the individual electrodes  135  after amplifying such that the vibration waveform is at a commanded potential. To the individual electrodes  135  is applied the vibration signal instead of the non-ejection signal. 
     In this time, the vibration controlling section  162  outputs the vibration-selecting signal to the outputting circuits  52  in the predetermined period by supplying the vibration signal to ones of the individual electrodes  135  whose number is required for an entirety of the four driver ICs  51   a - 51   d  to generate an amount of heat larger than a heat amount Q 3  obtained by subtracting the heat amount Q 2  from the heat amount Q 1 . It is noted that, in the present embodiment, the heat amount at least larger than the heat amount Q 3  is a heat amount in which the ink in the head  1  and the ink flowed thereinto can be heated to a temperature equal to or more than the predetermined temperature. Further, an amount of heat released by the head  1  to ambient air and a component for mounting the head  1  is taken into consideration to obtain the heat amount Q 3 . 
     As thus described, where the average ink temperature is equal to or more than the predetermined temperature, the signal-produce controller  153  performs the control to command one of the ejection signal and the non-ejection signal which is to be supplied to each of the individual electrodes  135  in each recording period on the basis of the drive data. On the other hand, where the average ink temperature is lower than the predetermined temperature, the signal-produce controller  153  performs a control to command the ejection signal, the non-ejection signal, and the vibration signal to be supplied to each individual electrode  135  in each recording period on the basis of the drive data, while satisfying a condition that the vibration signal is supplied in at least one recording period to at least one of the individual electrodes  135  to which the non-ejection signal is supplied in at least one recording period in the predetermined period when the average ink temperature is equal to or more than the predetermined temperature. It is noted that the number of the individual electrodes  135  to which the vibration signal is supplied may be equal to or smaller than the number of the individual electrodes  135  to which the non-ejection signal is supplied. 
     Further, in this time, in accordance that a difference (i.e., a temperature difference) between the ink temperature T 1  and the ink temperature T 2  becomes large, the vibration controlling section  162  outputs, to the outputting circuits  52 , the vibration-selecting signal in which the total number of drivings of the individual electrodes  135  to which the vibration signal is supplied in each recording period is increased. Further, in this time, where the temperature difference between the ink temperature T 1  and the ink temperature T 2  is less than a first predetermined value, the vibration controlling section  162  causes the outputting circuits  52  to select the vibration waveform S 1 . On the other hand, where the temperature difference is equal to or more than the first predetermined value and less than a second predetermined value, the vibration controlling section  162  causes the outputting circuits  52  to select the vibration waveform S 2 . In both cases, the high level potential is the first predetermined potential. Further, where the temperature difference between the ink temperature T 1  and the ink temperature T 2  is equal to or more than the second predetermined value, the vibration controlling section  162  causes the outputting circuits  52  to select the vibration waveform S 2 . The high level potential in this case is the second predetermined potential. By these controls, in accordance that the temperature difference between the ink temperature T 1  and the ink temperature T 2  becomes large, the heat amount of the heat generated by the driver ICs  51   a - 51   d  is increased. Thus, the ink in the head  1  and the ink flowed thereinto can be effectively heated. 
     Further, in accordance that an amount (hereinafter may be referred to as an “inflow ink amount”) of the ink to be flowed into the head  1  in the predetermined period becomes large, the vibration controlling section  162  may output, to the outputting circuits  52 , the vibration-selecting signal in which the above-described total number of the drivings of the individual electrodes  135  is increased. 
     Further, the vibration controlling section  162  may perform a control based on the inflow ink amount. Where the inflow ink amount is smaller than a first predetermined amount, the vibration controlling section  162  causes the outputting circuits  52  to select the vibration waveform S 1 . On the other hand, where the inflow ink amount is equal to or more than the first predetermined amount and smaller than a second predetermined amount, the vibration controlling section  162  causes the outputting circuits  52  to select the vibration waveform S 2 . In both cases, the high level potential may be the first predetermined potential. Further, where the inflow ink amount is equal to or more than the second predetermined amount, the vibration controlling section  162  causes the outputting circuits  52  to select the vibration waveform S 2 . The high level potential in this case may be the second predetermined potential. By these controls, in accordance that the inflow ink amount becomes large, the heat amount of the heat generated by the driver ICs  51   a - 51   d  is increased. Thus, like the above-described controls, the ink in the head  1  and the ink flowed thereinto can be effectively heated. 
     Further, the vibration controlling section  162  may perform the control based on the inflow ink amount as just mentioned in addition to the above-described control based on the temperature difference. For example, an explanation will be given assuming that only the first predetermined value is set as the threshold value relating to the temperature difference. Where the temperature difference is less than the first predetermined value, a difference of a content of the control with respect to the inflow ink amount is as described above. Where the temperature difference is equal to or more than the first predetermined value and where the inflow ink amount is smaller than the first predetermined amount, the vibration controlling section  162  causes the outputting circuits  52  to select the vibration waveform S 2 . The high level potential in this case is the first predetermined potential. Where the inflow ink amount is equal to or more than the first predetermined amount and smaller than the second predetermined amount, the vibration controlling section  162  causes the outputting circuits  52  to select the vibration waveform S 2 , but makes the high level potential be the second predetermined potential. Further, where the inflow ink amount is equal to or more than the second predetermined amount, the vibration controlling section  162  causes the outputting circuits  52  to select a new vibration waveform though a setting of this new vibration waveform is required. The high level potential in this case is the second predetermined potential. In this case, the new vibration waveform includes more pulses than the vibration waveform S 2 . Alternately, though the vibration controlling section  162  causes the outputting circuits  52  to select the vibration waveform S 2 , the high level potential may be a potential greater than the second predetermined potential. 
     The content of the control of the vibration controlling section  162  with respect to each outputting circuit  52  is not limited to a combination of the above-described levels relating to the temperature difference and the inflow ink amount. That is, there may be set the number of the pulses included in the vibration waveform and a drive voltage (i.e., the value of the high level potential) in accordance with the number of the levels. 
     Further, in a non-recording period, in which the image is not recorded on the sheet P, in the predetermined period, the vibration controlling section  162  causes each outputting circuit  52  to select one of the vibration waveforms S 1 , S 2  and makes the high level potential be the first predetermined potential or the second predetermined potential with regard to the plurality of individual electrodes  135 . As a result, the driver ICs  51   a - 51   d  can be operated to generate the heat even in the non-recording period, so that the ink can be efficiently heated. Further, in this time, the signal may be applied in a state in which the vibration waveform is selected with respect to all the individual electrodes  135 . In both cases, the ink meniscus in the ink-ejection openings  108  is vibrated, thereby restraining the thickening of the ink caused in the non-recording period. 
     It is noted that, the predetermined period means the recording period in which the recording is performed on one sheet P and a continuous recording period in which the recording is continuously performed on the plurality of sheets. That is, the predetermined period includes a plurality of the recording periods. Further, the non-recording period can refer to a period in the predetermined period, in which the non-ejection signal is supplied to all the individual electrodes  135  to which the signal is supplied from the outputting circuit  52  of the driver IC  51   a . Furthermore, the non-recording period can also refer to a period in the predetermined period, in which the non-ejection signal is supplied to all the individual electrodes  135  to which the signal is supplied from each of the driver ICs  51   a - 51   d.    
     Further, in this time, the vibration controlling section  162  individually controls the heat amount of the heat generated by the driver ICs  51   a - 51   d  in accordance with the ink temperature detected by the four temperature sensors  99   a - 99   d . For example, where the ink temperature detected by the temperature sensor  99   a  among the four temperature sensors  99   a - 99   d  is the lowest, the vibration controlling section  162  increases, compared with the other driver ICs, an amount of heat generated by the driver IC  51   a  in the predetermined period with the one recording period being as a unit. For example, the vibration controlling section  162  outputs, to the outputting circuit  52  of the driver IC  51   a , the vibration-selecting signal such that the total number of the drivings of the individual electrodes  135  to which the vibration signal is supplied becomes the largest. In this time, as described above, in according to the combination of the temperature difference and the inflow ink amount, there may be changed the combination of the vibration signal (S 1  or S 2 ) to be selected and its high level potential value (the first predetermined potential or the second predetermined potential). 
     As a result, the ink having a relatively low temperature can be heated efficiently. Thus, it is made possible to eliminate waste driving of the driver ICs  51   b - 51   d  which heat the ink having a relatively high temperature. As a result, the driving of the driver ICs  51   a - 51   d  can be restrained to the minimum necessity, thereby reducing the electric power consumption. 
     Further, the manifold channels  105 , the partial channels  74   a - 74   d , the temperature sensors  99   a - 99   d , and the heaters  97   a - 97   d  are disposed in correspondence with the placement of the respective actuator units  21 . When the actuator units  21  are driven to eject the ink from the ink-ejection openings  108 , the ink is flowed into the respective manifold channels  105  mainly from the respective partial channels corresponding to the actuator units  21 . The ink in the partial channels is mainly heated by the heat generation of the respective driver ICs  51   a - 51   d . The temperature sensor  99  detects the temperature of the ink in the corresponding partial channels, and the vibration controlling section  162  individually controls the amount of the heat generated by the driver ICs  51   a - 51   d  in accordance with the detected ink temperature as described above. That is, the vibration controlling section  162  performs a control of the temperature of the ink in each of the manifold channels  105 . As a result, the temperature of the ink can be minutely controlled in each of the manifold channels  105  which corresponds to one of the actuator units  21 . 
     Further, the vibration controlling section  162  may apply the vibration signal instead of the non-ejection signal to one or ones of the individual electrodes  135  to which the non-ejection signal is supplied over a predetermined number of the recoding periods even where the average ink temperature in the reservoir channel  74  is equal to or more than the predetermined temperature. That is, the vibration controlling section  162  causes the outputting circuits  52  to select one of the vibration waveforms S 1 , S 2  instead of the non-ejection waveform W 4 . In this time, the high level potential is the first predetermined potential or the second predetermined potential in accordance with the combination of the temperature difference and the inflow ink amount. As a result, since the vibration signal is applied to the one or ones of the individual electrodes  135  while the non-ejection signal is continued to be applied to the individual electrode(s)  135 , the ink near the ink-ejection openings  108  is agitated, thereby restraining the ink ejection failure owing to the thickening of the ink. 
     Where there is assumed that the vibration signal is supplied to all the individual electrodes  135 , the changing section  165  judges, as a judging section, in advance whether the heat amount generated by the entirety of the driver ICs  51   a - 51   d  in the predetermined period exceeds the heat amount Q 3  or not. Where this heat amount exceeds the heat amount Q 3 , the changing section  165  does not perform a change. That is, each of the driver ICs  51   a - 51   d  is driven in accordance with a content of the command of the ejection-selecting signal outputted by the recording controller  161  and a content of the command of the vibration-selecting signal outputted by the vibration controlling section  162 . Detailed operations of these components are as described above. 
     On the other hand, where the heat amount generated by the entirety of the driver ICs  51   a - 51   d  does not exceed the heat amount Q 3 , the changing section  165  changes the content of the command of the ejection-selecting signal outputted by the recording controller  161  and the content of the command of the vibration-selecting signal outputted by the vibration controlling section  162 . Specifically, the ejection-selecting signal causes each outputting circuit  52  to select one of the ejection waveforms W 1 ′, W 2 ′, W 3 ′, and the non-ejection waveform W 4 ′ on the basis of the stored drive data. Further, the ejection-selecting signal causes each outputting circuit  52  to select one of the vibration waveforms S 1 ′, S 2 ′ on the basis of the stored drive data for at least one of the individual electrodes  135  to which the non-ejection signal W 4 ′ is supplied. It is noted that, whether the vibration waveform is amplified such that the high level potential is the first predetermined potential or the second predetermined potential is as in the case where the heat amount exceeds the heat amount Q 3 . 
     Further, the changing section  165  controls the sheet-feed controller  154  such that a velocity of the sheet-feed motor  19  from a first feeding velocity to a second feeding velocity which will be described below. That is, a printer operation in a case where the heat amount generated by the entirety of the driver ICs  51   a - 51   d  does not exceed the heat amount Q 3  is as in the case where the heat amount exceeds the heat amount Q 3  except where each recording period is doubled (to 100i sec). 
     It is noted that, in the present embodiment, only two types of the vibration waveforms whose recording periods are different from each other are prepared, but equal to or more than three types of the vibration waveforms may be prepared. In a case of this modification, the changing section may control the vibration controlling section such that each outputting circuit  52  selects a vibration waveform in which a time length of each recording period becomes longer or is lengthened in accordance that the temperature difference between the ink temperature T 1  and the ink temperature T 2  becomes large. Further, the changing section may control the vibration controlling section such that each outputting circuit  52  selects the vibration waveform in which the time length of each recording period becomes longer in accordance that the amount of the ink to be flowed into the head in the predetermined period becomes large. 
     As thus described, the changing section  165  performs the changing operation in which the time length of each recording period becomes longer, whereby the amount of the ink to be flowed into the head  1  in a unit time becomes small, and accordingly the heat generated by the driver ICs  51   a - 51   d  is more likely to be transferred to an entirety of the head  1  (mainly the reservoir unit  70 ). As a result, the ink in the ink channels of the head  1  and the ink flowed thereinto can be effectively heated. Further, the ink temperature in the head  1  can be reliably increased. 
     Further, where the heat amount generated by the entirety of the driver ICs  51   a - 51   d  does not exceed the heat amount Q 3 , the changing section  165  energizes the four heaters  97   a - 97   d  to compensate the heat amount given to the head  1 . As a result, a heat amount which is insufficient with only the heat generated by the driver ICs  51   a - 51   d  can be compensated with the heaters  97   a - 97   d . Thus, the temperature of the ink can be reliably controlled. 
     The sheet-feed controller  154  controls the sheet-feed motor  19  such that the sheet P is fed at a predetermined feeding velocity. It is noted that the predetermined feeding velocity includes two types, namely, the first feeding velocity used where the one recording period is 50i sec and the second feeding velocity used where the one recording period is 100i sec. The second feeding velocity is a velocity half of the first feeding velocity. The sheet-feed controller  154  normally controls the sheet-feed motor  19  such that the sheet P is fed at the first feeding velocity. However, by the changing operation of the changing section  165  described above, the sheet-feed controller  154  controls the sheet-feed motor  19  such that the sheet P is fed at the second feeding velocity. 
     As described above, according to the ink-jet printer  101  as the present embodiment, even where the ink in the ink channels in the head  1  and the ink flowed thereinto have a relatively low ink temperature and a relatively high ink viscosity, the signal-produce controller  153  controls the driver ICs  51   a - 51   d  to generate the heat whose amount is larger than the heat amount Q 3 . Thus, the ink in the ink channels and the ink flowed thereinto are heated to a temperature equal to or more than the predetermined temperature, thereby lowering the ink viscosity. Consequently, there is eliminated a need for increasing an ink ejection energy for ejecting, from the ink-ejection openings  108 , the ink droplets having the same amount as at ordinary temperatures, thereby maintaining electric power consumption for the ink ejection. Further, there is eliminated a need for providing heat sinks and the like for cooling the driver ICs  51   a - 51   d  having generated the heat, thereby simplifying the construction of the ink-jet heads  1 . Further, there is obviated unevenness of an appropriate amount of the ink according to the viscosity of the ink, thereby contributing to maintaining of an image quality. 
     While the preferred embodiment of the present invention has been described, it is to be understood that the present invention is not limited to the details of the illustrated embodiment, but may be embodied with various changes and modifications, which may occur to those skilled in the art, without departing from the spirit and scope of the present invention. For example, in the above-described embodiment, the heat amount exceeding or larger than the heat amount Q 3  may simply exceed the heat amount Q 3  and may also be an amount in which the ink in the head  1  and the ink flowed thereinto are heated to a temperature lower than the predetermined temperature. Further, the vibration signal may be supplied in the predetermined period to only one or ones of the individual electrodes  135  to which the non-ejection signal is supplied. That is, the vibration signal may not be supplied to the individual electrodes  135  upon turning on the printer  101 , in the non-recording period, and the like. 
     Further, in the above-described embodiment, any of a plurality of types of the vibration signals is supplied to the individual electrodes  135  instead of the non-ejection signal in each recording period on the basis of the drive data, but only one type of the vibration signal may be supplied to the individual electrodes  135 . That is, the vibration controlling section  162  may not output, to the outputting circuits  52 , the vibration-selecting signal for causing the outputting circuits  52  to select the vibration waveform S 2  having more pulses than the vibration waveform S  1 . Further, the vibration controlling section  162  may not increase the total number of the drivings of the individual electrodes  135  to which the vibration signal is supplied, in accordance that the temperature difference between the ink temperature T 1  and the ink temperature T 2  becomes large and in accordance that the amount of the ink to be flowed into the head becomes large. Further, the vibration controlling section  162  may not control the amount of the heat generated by the driver ICs  51   a - 51   d  depending upon the ink temperature detected by the four temperature sensors  99   a - 99   d . In these cases, the control is simplified. Furthermore, in the above-described embodiment, the temperature sensors  99   a - 99   d  are fixed to the side face  70   b  or the side face  70   c  of the reservoir unit  70 , but the present invention is not limited to this construction. For example, the temperature sensors  99   a - 99   d  may be disposed at positions distant from the reservoir unit  70  with a space interposed therebetween. Further, the temperature sensors  99   a - 99   d  may also be respectively disposed on the driver ICs  51   a - 51   d  directly fixed to the metal plate  71  of the reservoir unit  70 . Where the reservoir unit  70  and the metal plate  71  are thermally connected to each other, it is possible to detect the temperature of the ink in the reservoir channel  74  also on the driver ICs  51   a - 51   d . Further, the temperature of the ink in the reservoir channel  74  may be estimated using driver-IC temperature sensors respectively disposed on the diver ICs  51   a - 51   d  for detecting temperatures of the respective diver ICs  51   a - 51   d , and then perform the calculations and the controls in the above-described embodiment using the estimated temperature of the ink. In this case, there is eliminated a need for providing the temperature sensors  99   a - 99   d  on the reservoir unit  70 , thereby reducing the manufacturing cost. 
     Further, the changing section  165  may not be provided. Further, only one driver IC may be provided on each ink-jet head. Furthermore, the heaters  97   a - 97   d  may not be particularly provided because the heaters  97   a - 97   d  are supplementary components. In this case, there is eliminated a need for providing the heater for heating the ink in the ink channels of the head and the ink flowed thereinto, thereby reducing a manufacturing cost. 
     Further, the reservoir unit may not be provided. In this case, the temperature sensors  99   a - 99   d  and the driver ICs  51   a - 51   d  may be provided on the channel unit  9 . In this case, the temperature sensors  99   a - 99   d  and the driver ICs  51   a - 51   d  may be disposed in correspondence with the four manifold channels  105  instead of the partial channels  74   a - 74   d  described above. Further, only one temperature sensor which detects the ink temperature in the ink channel may be provided on the ink-jet heads  1 . 
     Further, in the above-described embodiment, from the viewpoint that the ink supplied to the channel unit  9  is effectively heated, the heaters  97   a - 97   d  are disposed so as to be opposed to the ink-outlet channels  73   a  of the reservoir unit  70 . However, from the viewpoint that the temperature of the ink supplied to the channel unit  9  is measured more accurately, the temperature sensors  99   a - 99   d  may be disposed so as to be opposed to the ink-outlet channels  73   a . That is, the heaters  97   a - 97   d  and the temperature sensors  99   a - 99   d  may have a reverse positional relationship to each other. 
     Further, the manifold channels  105  are separated from each other in correspondence with the placement of the actuator units  21 , but the present invention is not limited to this construction. For example, all the manifold channels may be communicated with each other in a longitudinal direction of the heads  1 . 
     Further, the above-described embodiment is one example in which the present invention is applied to an ink-jet printer including ink-jet heads configured to eject an ink from ink-ejection openings, but an object to which the present invention can be applied is not limited to the ink-jet printer of this type. For example, the present invention is applicable to various liquid ejecting apparatuses including liquid ejecting head which ejects conductive paste to form a wiring pattern on a circuit board, which ejects organic illuminant on a circuit board to form a high-definition display, or which ejects optical plastic on a circuit board to form a fine electronic device such as a light guide.