Patent Publication Number: US-7914103-B2

Title: Liquid droplet jetting apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims priority from Japanese Patent Application No. 2008-082492, filed on Mar. 27, 2008, and Japanese Patent Application No. 2008-082491, filed on Mar. 27, 2008, the disclosure of which are incorporated herein by reference in their entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a liquid droplet jetting apparatus. 
     2. Description of the Related Art 
     In a liquid droplet jetting apparatus, such as an ink-jet printer, a pressure wave is generated by applying a voltage to a piezoelectric actuator, and a liquid such as an ink is made to be jetted from fine holes called nozzles. Therefore, a jetting performance is substantially affected by a variation and a change in a viscosity of ink. 
     It is possible to reduce a variation in a material and manufacturing by enhancing a production control, but at the time of use by a user, there occurs a variation and a change in the viscosity of ink due to a day-to-day change in temperature. 
     To cope with this change in the viscosity of ink, attempts have been made to detect a temperature around a recording head, and to keep constant a velocity of jetting of ink by changing a voltage to be applied to the piezoelectric actuator according to the temperature detected. 
     Even when the voltage to be applied is changed according to the temperature detected in such manner, since there is a variation in manufacturing of components of each recording head which cannot be ignored, various sorts of ranking of the voltage to be applied is necessary. Moreover, since a waveform control for jetting droplets of ink of various sizes is necessary, when the ranking of the voltage to be applied as described above is necessary in addition to the waveform control, checking of liquid droplet control in manufacturing of the recording head becomes extremely complex. 
     On the other hand, a head which is provided with a warm-up function to maintain the ink temperature to be not less than a certain fixed temperature all the time by heating the ink by providing a heater to the recording head has been known. However, this provision becomes expensive. Moreover, even when such heater is provided, it is difficult to provide such heater at a position where the heater makes a direct contact with the ink, and for increasing the temperature of ink, first of all, it is necessary to increase a temperature of a surrounding site, and it takes time for warming up. 
     Moreover, when a voltage is applied to a piezoelectric element, a deformation directly proportional to a strength of an electric field occurs (inverse piezoelectric effect), and causes heat generation by the piezoelectric element. Therefore, for heating the ink by using this, a method in which, a piezoelectric actuator (PZT) is driven prior to jetting of ink, and the temperature of ink is increased by the heat generation has been proposed (for example, refer to United States Patent Application Publication No. 2004/0135832 (corresponds to Japanese Patent Application Laid-open No. 2004-148784)). 
     In a liquid droplet jetting apparatus disclosed in United States Patent Application Publication No. 2004/0135832, since a pressure chamber is also deformed when the piezoelectric element is made to be deformed, when a voltage is let to be a drive voltage same as a voltage applied during a normal drive, ink droplets are jetted. Therefore, the drive voltage is controlled to be low at the time of increasing the ink temperature. 
     However, when the drive voltage is controlled to be low, an amount of deformation of the piezoelectric actuator is not much substantial, and a sufficient effect in heating the ink cannot be expected. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a liquid droplet jetting apparatus which is capable of heating a liquid efficiently without making the liquid jet in a case of heating the liquid by controlling a drive of a piezoelectric actuator for stabilizing a jetting performance of the liquid. 
     According to a first aspect of the present invention, there is provided a liquid droplet jetting apparatus which jets droplets of a liquid, including a liquid droplet jetting head having a cavity unit in which a pressure chamber extending in a predetermined direction and having a predetermined volume and a nozzle communicating with the pressure chamber are formed, and a piezoelectric actuator which is joined to the cavity unit to cover the pressure chamber, and which applies pressure to the liquid in the pressure chamber; and a controller which controls the piezoelectric actuator in a liquid droplet jetting mode of jetting the liquid droplets from the nozzle and in a warm-up mode of heating the liquid in the pressure chamber without jetting the liquid in the pressure chamber as the liquid droplets from the nozzle, and in the liquid droplet jetting mode, the controller controls the piezoelectric actuator to perform a liquid droplet jetting operation by which volume of the pressure chamber is decreased to a decreased volume smaller than the predetermined volume, and then the volume of the pressure chamber is increased to a increased volume greater than the predetermined volume, and the volume of the pressure chamber is again decreased to the decreased volume; and in the warm-up mode, the controller controls the piezoelectric actuator to perform at least one of a first warm-up operation to change the volume of the pressure chamber repeatedly between the predetermined volume and the increased volume, and a second warm-up operation to change the volume of the pressure chamber repeatedly between the predetermined volume and the decreased volume. 
     In the warm-up mode, since at least one of the first warm-up operation of changing the volume of the pressure chamber repeatedly to the reference state and the increased volume state alternately, and the second warm-up operation of changing the volume of the pressure chamber repeatedly to the predetermined volume and the decreased volume alternately is performed, it is possible to heat the liquid sufficiently without jetting the liquid inside the pressure chambers. Accordingly, it is possible to avoid an effect of a temperature of the liquid, and to stabilize the jetting performance. Particularly, since a volume change between the predetermined volume and the increased volume (first warm-up operation) and a volume change between the predetermined volume and the decreased volume (second warm-up state) have been used, it is possible to increase an amount of deformation of the piezoelectric actuator, and to heat the liquid, and the heating of the liquid is possible in a short time. Moreover, since the volume of the pressure chamber which stores the liquid and which is in contact with the liquid changes, an efficient heating of the liquid becomes possible. 
     In the liquid droplet jetting apparatus according to the present invention, the piezoelectric actuator may have a first deformable portion and a second deformable portion, and the first deformable portion and the second deformable portion may be deformed in different directions with each other, and the controller may control the piezoelectric actuator to deform the first deformable portion and the second deformable portion such that the volume of the pressure chamber is changed. In this case, the first deformable portion may correspond to a central portion of the pressure chamber, and the second deformable portion may correspond to outer peripheral portion, of the pressure chamber, outside the central portion. Moreover, the controller may control the piezoelectric actuator to perform the second warm-up operation by deforming the first deformable portion, and to perform the first warm-up operation by deforming the second deformable portion. 
     The liquid droplet jetting apparatus according to the present invention may further include a manifold extending in an orthogonal direction orthogonal to the predetermined direction and storing the liquid to be supplied to the pressure chamber, and the pressure chamber may be formed as a plurality of pressure chambers arranged in a row in the orthogonal direction and communicating with the manifold; the piezoelectric actuator may have a plurality of deformable portions which correspond to the pressure chambers respectively, and each of which is deformed to perform the liquid droplet jetting operation, and the first warm-up operation and the second warm-up operation; and in the warm-up mode, the controller may control the piezoelectric actuator such that when a deformable portion corresponding to one of two adjacent pressure chambers among the pressure chambers is deformed to perform one of the first warm-up operation and the second warm-up operation, a deformable portion, corresponding to the other pressure chamber of the two adjacent pressure chambers is not deformed and any of the first warm-up operation and the second warm-up operation is not performed. When an entire liquid channel through which the pressure chambers communicate with the manifold are taken into consideration, since the volume of some of the pressure chambers is to be changed only, as a whole, the change in the volume is small, and jetting of the liquid mistakenly is suppressed. 
     The liquid droplet jetting apparatus according to the present invention may further include a manifold extending in an orthogonal direction orthogonal to the predetermined direction and storing the liquid to be supplied to the pressure chamber, and the pressure chamber may be formed as a plurality of pressure chambers arranged in a row in the orthogonal direction and communicating with the manifold; the piezoelectric actuator may have a plurality of deformable portions which correspond to the pressure chambers respectively, and each of which is deformed to perform the liquid droplet jetting operation, and the first warm-up operation and the second warm-up operation; and in the warm-up mode, the controller may control the piezoelectric actuator such that when a deformable portion, corresponding to one of two adjacent pressure chambers among the pressure chambers is deformed to perform the first warm-up operation, a deformable portion, corresponding to the other pressure chamber of the two adjacent pressure chambers, is deformed to perform the second warm-up operation at a same cycle as a cycle of the first warm-up operation. When an entire liquid channel through which the pressure chambers communicate with the manifold are taken into consideration, since the volume of some of the pressure chambers is changed to be increased and the volume of the rest of the pressure chambers is changed to be decreased, the change in the volume of the some of the pressure chambers and the rest of the pressure chambers is counterbalanced, there is almost no change in the volume as a whole, and jetting of the liquid mistakenly is suppressed. 
     The liquid droplet jetting apparatus according to the present invention may further include a manifold extending in an orthogonal direction orthogonal to the predetermined direction and storing the liquid to be supplied to the pressure chamber, and the pressure chamber may be formed as a plurality of pressure chambers arranged in two rows in the orthogonal direction and communicating with the manifold, and the piezoelectric actuator may have a plurality of deformable portions which correspond to the pressure chambers respectively, and each of which is deformed to perform the liquid droplet jetting operation, and the first warm-up operation and the second warm-up operation; and in the warm-up mode, the controller may control the piezoelectric actuator such that when deformable portions corresponding to the pressure chambers forming one row of the two rows are deformed to perform one of the first warm-up operation and the second warm-up operation, deformable portions, corresponding to pressure chambers forming the other row of the two rows, are not deformed and any of the first warm-up operation and the second warm-up operation is not performed. When an entire liquid channel through which the pressure chambers communicate with the manifold are taken into consideration, since the volume of the pressure chambers only in one row is changed, the change in volume is small, and the liquid is suppressed from being jetted mistakenly. 
     The liquid droplet jetting apparatus according to the present invention may further include a manifold extending in an orthogonal direction orthogonal to the predetermined direction and storing the liquid to be supplied to the pressure chamber, and the pressure chamber may be formed as a plurality of pressure chambers arranged in two rows in the orthogonal direction and communicating with the manifold; the piezoelectric actuator may have a plurality of deformable portions which correspond to the pressure chambers respectively, and each of which is deformed to perform the liquid droplet jetting operation, and the first warm-up operation and the second warm-up operation; and in the warm-up mode, the controller may control the piezoelectric actuator such that when deformable portions corresponding to pressure chambers among the plurality of pressure chambers forming one row of the two rows, are deformed to perform the first warm-up operation, a deformable portions, corresponding to pressure chambers forming the other row of the two rows, are deformed to perform the second warm-up operation at a same cycle as a cycle of the first warm-up operation. When an entire liquid channel through which the pressure chambers communicate with the manifold are taken into consideration, since the volume of the pressure chambers in one row is changed to be increased and the volume of the pressure chambers in the other row is changed to be decreased, the change in the volume is counterbalanced for the two rows of pressure chambers, and there is almost no change in the volume as a whole, and the liquid is suppressed from being jetted mistakenly. 
     The liquid droplet jetting apparatus according to the present invention may further include an electric potential applying mechanism which applies an electric potential to the piezoelectric actuator, and the piezoelectric actuator may have at least two piezoelectric material layers, a first common electrode which is provided between the two piezoelectric material layers, a first individual electrode which is provided on a surface, of one of the piezoelectric material layers, opposite to a surface on which the first common electrode is provided, and a second common electrode which is provided on a surface, of the other of the piezoelectric material layers, opposite to a surface on which the first common electrode is provided; the first common electrode may have a portion facing a central portion, of the pressure chamber, in width direction of the pressure chamber, and the first individual electrode and the second common electrode may have portions which are formed to be longer than the first common electrode in the width direction of the pressure chamber respectively; and in the liquid droplet jetting mode, the controller may control the electric potential applying mechanism to apply to the first individual electrode an electric potential in order of ground electric potential, a positive electric potential, and the ground electric potential, in a state that the positive electric potential is applied to the first common electrode and the second common electrode is at the ground electric potential; and in the warm-up mode, the controller may control the electric potential applying mechanism to apply alternately the positive electric potential and the ground electric potential to the first common electrode in a state that the first individual electrode and the second common electrode are at the ground electric potential, or to apply alternately the positive electric potential and the ground electric potential substantially simultaneously to the first individual electrode and the first common electrode in a state that the second common electrode is at the ground electric potential. 
     Particularly, in the state of the individual electrode let to be at the ground electric potential, when the positive electric potential is applied and stopped applying repeatedly to the first common electrode, since the individual electrode is let to be at the same electric potential as the first common electrode, no electric field other than an electric field similar to as in the liquid droplet jetting mode is applied to the piezoelectric actuator, and there is no deterioration of the piezoelectric actuator. Moreover, when the positive electric potential is applied and stopped applying repeatedly, almost simultaneously to the first individual electrode and the first common electrode, since it is an application of the electric potential in which the displacement is suppressed, the deformation of the pressure chamber is extremely small, and there is no possibility that the liquid is jetted. 
     The liquid droplet jetting apparatus according to the present invention may further include an electric potential applying mechanism which applies an electric potential to the piezoelectric actuator, and the piezoelectric actuator may have at least one piezoelectric material layer, a second individual electrode and a third individual electrode which are provided on a side of one surface of the piezoelectric material layer, and a third common electrode which is provided on a side of the other surface of the piezoelectric material layer; the second individual electrode may have a portion facing a central portion of the pressure chamber in a width direction of the pressure chamber; the third individual electrode may be arranged on both sides of the second individual electrode in the width direction of the pressure chamber and the third common electrode may have a portion facing the second and the third individual electrode in the width direction of the pressure chamber; in the liquid droplet jetting mode, the controller may control the electric potential applying mechanism such that a ground electric potential is applied to the third individual electrode and the third common electrode and a positive electric potential is applied to the second individual electrode, and then the ground electric potential is applied to the second individual electrode and the third common electrode and the positive electric potential is applied to the third individual electrode, and then the ground electric potential is again applied to the third individual electrode and the third common electrode and a positive electric potential is again applied to the second individual electrode; and in the warm-up mode, the controller may control the electric potential applying mechanism to alternately apply the positive electric potential and the ground electric potential to one of the second individual electrode and the third individual electrode in a state that the third common electrode is at the ground electric potential. Even in this case, it is possible to realize the warm-up operation reasonably. 
     The liquid droplet jetting apparatus according to the present invention may further include an electric potential applying mechanism which applies an electric potential to the piezoelectric actuator, and the piezoelectric actuator may have at least one piezoelectric material layer, a fourth individual electrode and a fourth common electrode which are provided on a side of one surface of the piezoelectric material layer, and a fifth common electrode and a sixth common electrode which are provided on a side of the other surface of the piezoelectric material layer; the fourth individual electrode may have a portion facing a central portion, of the pressure chamber, in a width direction of the pressure chamber, and the fourth common electrode may be arranged on both sides of the fourth individual electrode in the width direction of the pressure chamber; and the fifth common electrode and the sixth common electrode may have portions facing the fourth individual electrode and the fourth common electrode, respectively, in the width direction of the pressure chamber; in the liquid droplet jetting mode, the controller may control the electric potential applying mechanism such that a ground electric potential is applied to the fourth individual electrode, the fifth common electrode, and the sixth common electrode and a positive electric potential is applied to the fourth common electrode, then the ground electric potential is applied to the sixth common electrode and a positive electric potential is applied to the fourth individual electrode, the fourth common electrode, and the fifth common electrode, and then the ground electric potential is applied again to the fourth individual electrode, the fifth common electrode, and the sixth common electrode and a positive electric potential is applied again to the fourth common electrode; and in the warm-up mode, the controller may control the electric potential applying mechanism such that application and non-application of the positive electric potential to the fourth common electrode is repeated in a state that the ground electric potential is applied to the fourth individual electrode, the fifth common electrode, and the sixth common electrode, or application and non-application of the positive electric potential to the fourth individual electrode, fourth common electrode, and the fifth common electrode is repeated in a state that the ground electric potential is applied to the sixth common electrode. 
     In the liquid droplet jetting apparatus according to the present invention, when a time during which a pressure wave is propagated one-way in a liquid channel, of the liquid droplet jetting head, including the pressure chambers is AL, the electric potential applying mechanism may switch between application of the electric potential and non-application of the electric potential at a timing of 2AL. In this case, since the timing of applying the positive electric potential and not applying the electric potential is let to be 2AL, the liquid droplets are not jetted. Only by letting the timing of applying and not applying the positive electric potential to be 2AL, it is possible to suppress further the jetting by lowering further the voltage applied. 
     In the liquid droplet jetting apparatus according to the present invention, the liquid droplet jetting head may have a temperature detector which detects a temperature corresponding to a temperature of the liquid in the pressure chamber, and the controller may select to perform the warm-up mode only when the temperature of the liquid is not more than a predetermined value. In this case, only when the temperature of the liquid in the pressure chamber is not higher than the set value, by putting a power supply ON, it is shifted to the warm-up mode prior to the liquid droplet jetting mode. The warm-up operation is carried out only when the heating is necessary for the liquid in the pressure chamber, and electric power is saved. 
     According to a second aspect of the present invention, there is provided a liquid droplet jetting apparatus which jets droplets of a liquid, including a liquid droplet jetting head having a cavity unit in which a pressure chamber extending in a predetermined direction and a nozzle communicating with the pressure chamber are formed, and a piezoelectric actuator which is joined to the cavity unit to cover the pressure chamber, which applies pressure to the liquid in the pressure chamber, and which has first active portion corresponding to a central portion of the pressure chamber, and a second active portion corresponding to outer peripheral portion, of the pressure chamber, outside the central portion; and a voltage applying mechanism which applies a voltage to the piezoelectric actuator in a liquid droplet jetting mode of jetting the liquid droplets from the nozzle and a warm-up mode of heating the liquid inside the pressure chamber without jetting the liquid as liquid droplets from the nozzle, and in the liquid droplet jetting mode, the voltage applying mechanism applies a voltage to the first active portion and does not apply the voltage to the second active portion to provide a first state in which the first active portion is deformed to project toward the pressure chamber, and then the voltage applying mechanism applies the voltage to the second active portion and does not apply the voltage to the first active portion to provide a second state in which the second active portion is deformed to project in a direction away from the pressure chamber, and then the first state is again provided; and in the warm-up mode, the voltage applying mechanism applies the voltage to both the first active portion and the second active portion to provide a third state in which the first active portion is deformed to project toward the pressure chamber and the second active portion is deformed to project in the direction away from the pressure chamber, and then the voltage applying mechanism does not apply any voltage to the first active portion and the second active portion to provide a fourth state in which both the first active portion and the second active portion are not deformed, such that the third state and the fourth state are repeated alternately. 
     In the warm-up mode, the piezoelectric actuator is driven such that the third state in which the first active portion is deformed to project toward the pressure chamber and the second active portion is deformed to project in a direction away from the pressure chamber by applying the voltage to both the first active portion and the second active portion, and the fourth state in which both the first active portion and the second active portion are not deformed as the voltage is not applied to both the first active portion and the second active portion, are repeated alternately. As a result, the piezoelectric actuator generates heat while letting in a state in which the change in the volume of the pressure chamber does not become substantial, and it is possible to heat without the liquid inside the pressure chamber being jetted, thereby stabilizing a liquid droplet jetting performance. Particularly, since the heat is generated by the piezoelectric actuator near the pressure chambers which accommodate the liquid and which are in contact with the liquid, it is possible to heat the ink efficiently. 
     In the liquid droplet jetting apparatus according to the present invention, in the warm-up mode, the voltage applying mechanism may apply, to the first active portion and the second active portion, another voltage greater than the voltage applied in the liquid droplet jetting mode, or may make a pulse width of the another voltage applied to the first active portion and the second active portion to be wider than a pulse width of the voltage applied in the liquid droplet jetting mode. In this case, in the warm-up mode, since it is possible to make substantial an amount of deformation of the first active portion and the second active portion (an amount of deformation of the piezoelectric actuator) than an amount of deformation of the first active portion and the second active portion in the liquid droplet jetting mode, it is possible to carry out efficiently the heating of the liquid in the pressure chamber. 
     In the liquid droplet jetting apparatus according to the present invention, the piezoelectric actuator may have at least one piezoelectric material layer, a first individual electrode and a second individual electrode which are provided on a side of one surface of the piezoelectric material layer, and a first common electrode which is provided on a side of the other surface of the piezoelectric material layer; the first individual electrode may have a portion corresponding to a central portion, of the pressure chamber, in a width direction of the pressure chamber, and the second individual electrode may have a portion corresponding to both side portions in the width direction of the pressure chamber, the first common electrode may have a portion corresponding to the first individual electrode and the second individual electrode in the width direction of the pressure chamber, a first active portion may be formed in a portion, of the piezoelectric material layer, sandwiched between the first individual electrode and the first common electrode, and a second active portion may be formed in a portion, of the piezoelectric material layer, sandwiched between the second individual electrode and the first common electrode; and in the liquid droplet jetting mode, the voltage applying mechanism may apply voltage to the piezoelectric actuator such that a ground electric potential is applied to the first common electrode and the second individual electrode and a positive electric potential is applied to the first individual electrode, and then the ground electric potential is applied to the first individual electrode and the first common electrode and a positive electric potential is applied to the second common electrode, and the ground electric potential is applied again to the first common electrode and the second individual electrode and the positive electric potential is applied again to the first individual electrode, and in the warm-up mode, the voltage applying mechanism may apply alternately the positive electric potential and the ground electric potential to the first individual electrode and the second individual electrode in a state that the ground electric potential is applied to the first common electrode. In this case, since in the warm-up mode, since the positive electric potential and the ground electric potential are applied to the first individual electrode and the second individual electrode in the state of the first common electrode let to be at the ground electric potential, the piezoelectric actuator is driven such that the change in the volume of the pressure chamber does not become substantial, and the liquid in the pressure chamber is heated by the heat generated by the piezoelectric actuator. 
     In the liquid droplet jetting apparatus according to the present invention, the piezoelectric actuator may have at least one piezoelectric material layer, a third individual electrode and a second common electrode which are provided on a side of one surface of the piezoelectric material layer, and a third common electrode and a fourth common electrode which are provided on a side of the other surface of the piezoelectric material layer; and the third individual electrode may have a portion corresponding to a central portion, of the pressure chamber, in a width direction of the pressure chamber; and the second common electrode may have a portion corresponding to both side portions in the width direction of the pressure chamber; and the third common electrode and the fourth common electrode may have portions corresponding to the second common electrode and the third individual electrode respectively, in the width direction of the pressure chamber; and a first active portion may be formed in a portion, of the piezoelectric material layer, sandwiched between the third individual electrode and the third common electrode; and a second active portion may be formed in a portion, of the piezoelectric material layer, sandwiched between the second common electrode and the fourth common electrode; and in the liquid droplet jetting mode, the voltage applying mechanism may apply voltage to the piezoelectric actuator such that a ground electric potential is applied to the fourth common electrode and a positive electric potential is applied to the third individual electrode, the second common electrode and the third common electrode, then the ground electric potential is applied to the third individual electrode, the third common electrode and the fourth common electrode and a positive electric potential is applied to the second common electrode, and the ground electric potential is applied again to the fourth common electrode and the positive electric potential is applied again to the third individual electrode, the second common electrode, and the third common electrode; and in the warm-up mode, the voltage applying mechanism may repeat application and non-application of the positive electric potential to the third individual electrode and the second common electrode in a state that the ground electric potential is applied to the third common electrode and the fourth common electrode. In this case, in the warm-up mode, since applying and not applying the positive electric potential to the third individual electrode and the second common electrode is repeated in the state of the third common electrode and the fourth common electrode let to be at the ground electric potential, the piezoelectric actuator is driven such that the change in the volume of the pressure chamber does not become substantial, and the liquid in the pressure chamber is heated by the heat generated by the piezoelectric actuator. 
     In the liquid droplet jetting apparatus according to the present invention, when a time during which a pressure wave is propagated one-way in a liquid channel, of the liquid droplet jetting head, including the pressure chambers is AL, the electric potential applying mechanism may switch between application of the electric potential and non-application of the electric potential at a timing of 2AL. 
     In the liquid droplet jetting apparatus according to the present invention, the liquid droplet jetting head may have a temperature detector which detects a temperature corresponding to a temperature of the liquid in the pressure chamber, and the voltage applying mechanism may select to perform the warm-up mode only when the temperature of the liquid is not more than a set value. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a schematic structural view showing a schematic structure of an ink-jet printer according to the present invention, and  FIG. 1B  is an explanatory diagram showing a relationship of a cavity unit, a piezoelectric actuator, and a flexible cable (COP) according to the present invention; 
         FIG. 2A  is a perspective view showing a state in which, the piezoelectric actuator is stuck to an upper side of the cavity unit, and  FIG. 2B  is an explanatory diagram of a plate assembly which is made by sticking a nozzle plate and a spacer plate; 
         FIG. 3A  is diagram showing a cavity plate disassembled to each plate which is a component of the cavity plate, with vibrations, and  FIG. 3B  is a diagram of a joined state; 
         FIG. 4A  is a diagram showing an arrangement at an upper-surface side of a piezoelectric material layer on an upper-surface side,  FIG. 4B  is a diagram showing an arrangement of an electrode on a lower-surface side of the piezoelectric material layer, and  FIG. 4C  is a cross-sectional view; 
         FIG. 5  is an explanatory diagram of an electrode arrangement when the electrode is seen in a plan view; 
         FIG. 6  is an explanatory diagram showing an example of dimensions of the electrode arrangement; 
         FIG. 7  is an explanatory diagram of polarization; 
         FIG. 8  is a block diagram showing an electrical control system of an ink-jet printer; 
         FIG. 9  is an explanatory diagram of an internal structure of a driving circuit; 
         FIG. 10A ,  FIG. 10B ,  FIG. 10C , and  FIG. 10D  are explanatory diagrams showing deformed states respectively; 
         FIG. 11A ,  FIG. 11B , and  FIG. 11C  are explanatory diagrams showing deformed states respectively; 
         FIG. 12A ,  FIG. 12B , and  FIG. 12C  are explanatory diagrams showing deformed states respectively; 
         FIG. 13A ,  FIG. 13B , and  FIG. 13C  are diagrams of a second embodiment, similar to  FIG. 4A ,  FIG. 4B , and  FIG. 4C ; 
         FIG. 14  is a diagram of the second embodiment, similar to  FIG. 5 ; 
         FIG. 15A ,  FIG. 15B ,  FIG. 15C , and  FIG. 15D  are explanatory diagrams of the second embodiment, showing deformed states respectively; 
         FIG. 16A ,  FIG. 16B , and  FIG. 16C  are diagrams of a third embodiment, similar to  FIG. 4A  to  FIG. 4C ; 
         FIG. 17  is a diagram of the third embodiment, similar to  FIG. 5 ; and 
         FIG. 18A ,  FIG. 18B ,  FIG. 18C  and  FIG. 18D  are explanatory diagrams of the third embodiment, showing deformed states respectively 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Exemplary embodiments of the present invention will be described below by referring to the accompanying diagrams. 
     To start with, a first embodiment of the present invention will be described below.  FIG. 1A  is a schematic structural view showing a schematic structure of an ink-jet printer according to the present invention, and  FIG. 1B  is an explanatory diagram showing a relation of a cavity unit, a piezoelectric actuator, and a flexible cable (COP) according to the present invention; 
     An ink-jet printer  1  according to the present invention, as shown in  FIG. 1A , is provided with an ink-jet printer head  3  (liquid droplet jetting head) for recording an image etc. on a recording paper P (recording medium), on a lower surface of a carriage  2  on which ink cartridges (not shown in the diagram) are mounted. The carriage  2  is supported by a guide plate (not shown in the diagram) and a carriage shaft  5  provided inside a printer frame  4 , and reciprocates in a direction (hereinafter called as “X-direction”) orthogonal to a direction of transporting of the recording paper P (hereinafter called as “Y-direction”). 
     The recording paper P which is transported in direction A from a paper feeding section which is not shown in the diagram is inserted between a platen roller (not shown in the diagram) and the printer head  3 , and is discharged by a discharge roller  6  upon a predetermined recording being carried out by an ink jetted from the printer head  3  toward the recording paper P. 
     Moreover, as shown in  FIG. 1B  and  FIG. 2 , the printer head  3  includes a cavity unit  11  and a piezoelectric actuator  12  in order from a lower side, and a flexible cable  13  (signal wire) which supplies a drive signal is provided to an upper surface side of the piezoelectric actuator  12 . 
     The cavity unit  11  includes a stacked body  14  formed by stacking a plurality of plates (plate materials) having an opening. At an upper side of the stacked body  14 , a vibration plate  15  is provided, and at a lower side thereof, a plate assembly  18  which is formed by stacking a nozzle plate  16  having nozzles  16   a  and a spacer plate  17  having through holes  7   a  corresponding to the nozzles  16   a , is stuck integrally. The piezoelectric actuator  12  is provided at an upper side of the vibration plate  15  (refer to  FIG. 1B ). Here, the vibration plate  15 , as it is shown in  FIG. 4C  which will be described later, is formed by a metal plate portion  15  which blocks a pressure chamber  40 , and an insulating layer  15   b  which is stacked on an upper side thereof. In other words, the insulating layer  15   b  and the piezoelectric actuator  12  are stacked on the upper side of the metal plate portion  15   a . A surface of the vibration plate  15  toward the piezoelectric actuator  12  (piezoelectric material layer  12 B) may be a surface having an insulating property, or a vibration plate which is entirely made of a synthetic resin may be used. 
     Moreover, as shown in  FIG. 2A , a filter  19  for trapping dust etc. in the ink is provided in an opening  11   a  of the cavity unit  11 . The nozzle plate  16  is a high-molecular synthetic resin (such as polyimide) plate in which the plurality of nozzles  16   a  which communicate with the plurality of pressure chambers  40  respectively formed in the cavity plate  14 A which will be described later (forming a stacked body  14 ) are formed. The nozzles  16   a  are formed in the high-molecular synthetic resin plate by an excimer laser machining. 
     The stacked body  14 , as shown in  FIG. 3 , includes the cavity plate  14 A, a base plate  14 B, an aperture plate  14 C, two manifold plates  14 D and  14 E, and a damper plate  14 F (plates  14 A to  14 F), which are stacked in this order. These six plates  14 A to  14 F are stacked upon positioning such that an ink channel is formed individually for each nozzle  16   a , and are fixed by metal diffusion joining. The vibration plate  15  is further stacked on the stacked body  14  and joined by the metal diffusion joining. A direction in which these six plates are stacked will be called as a “Z-direction” in the following description. 
     The ink channels formed in the cavity unit  11  are formed by openings in the plates  14 A to  14 F,  16 , and  17 , and the ink flowing through the ink channels is jetted from the nozzle  16   a  of the printer head  3 . 
     The cavity plate  14 A is a rectangular metal plate with a longer side of the rectangle in Y-direction, and a plurality of cavities which become the pressure chambers  40  are formed therein. The pressure chambers  40  (cavities) are formed as through holes in the cavity plate  14 A by an etching. The pressure chambers  40  form a plurality of pressure chamber rows, and each extending in Y-direction. Moreover, the pressure chamber rows are lined up in X-direction. The vibration plate  15  is stacked on an upper surface side of the cavity plate  14 A to cover the pressure chambers  40  (cavities). 
     The base plate  14 B is a metal plate in which a communicating hole  52   a  from manifold  50  (common ink chambers) to each pressure chamber  40 , and a communicating hole  51   a  from each pressure chamber  40  to each nozzle  16   a  are formed. The aperture plate  14 C is a metal plate in which, a communicating hole  52   b  which makes each pressure chamber  40  communicate with the manifold  50 , and a communicating hole  51   b  from each pressure chamber  40  to the nozzle  16   a  are formed as a recess channel on an upper surface side thereof. The manifold plates  14 D and  14 E are metal plates in which, communicating holes  52   c  and  52   d  from each pressure chamber  40  to each nozzle  16   a  are formed in addition to through holes  50   a  and  50   b  which form the manifold  50 . The damper plate  14 F is a metal plate in which, a communicating hole  52   e  which makes communicate each pressure chamber  40  and each nozzle  16   a , apart from a damper chamber  53  formed as a recess in a lower surface side thereof. 
     As shown in  FIG. 4C , the piezoelectric actuator  12  has two piezoelectric material layers  12 A and  12 B formed on the vibration plate  15 , and a first common electrode  12 C is formed between the piezoelectric material layers  12 A and  12 B. A first individual electrode  12 D is formed on a surface of one piezoelectric material layer  12 B, on an opposite side of a surface on which the first common electrode  12 C is formed, and a second common electrode  12 E is formed on a surface of the other piezoelectric material layer  12 A, on an opposite side of a surface on which the first common electrode  12 C is formed. When viewed in Z-direction, the first common electrode  12 C, as shown in  FIG. 4B  and  FIG. 5 , has a first portion  12 G extending in a longitudinal direction of the pressure chamber  40  (X-direction), corresponding to a central portion in a width direction of the pressure chamber (Y-direction) and a second portion  12 H extending in Y-direction which is connected to the first portion  12 G at one end side in X-direction. The first common electrode  12 C is formed to be comb-teeth shaped. 
     As shown in  FIG. 4A  and  FIG. 5 , the first individual electrode  12 D is formed corresponding to each pressure chamber  40 . A connecting terminal portion  12 K is formed on the first common electrode  12 C, on an opposite side (the other end side in X-direction) of the side on which the second portion  12 H is formed, in an area outside an area corresponding to the pressure chamber  40 . The second common electrode  12 E, as shown in  FIG. 4A  to  FIG. 4C , and  FIG. 5 , is formed to extend in Y-direction. Moreover, the first individual electrode  12 D and the second common electrode  12 E have a portion formed to be longer than the first common electrode  12 C, in Y-direction. 
     The piezoelectric material layers  12 A and  12 B are made of a ceramic material of lead zirconium titanate (PZT) which is a ferroelectric substance, and is polarized in Z-direction as it will be described later. The first individual electrode  12 D (including a connecting terminal portion  12 K of the first individual electrode  12 D) and the first common electrodes  12 C and the second common electrode  12 E are formed of a metallic material of Ag—Pd. The first individual electrode  12 D, the first common electrode  12 C, and the second common electrode  12 E are connected to a driving circuit  49  (an electric potential applying mechanism, a voltage applying mechanism) which will be described later, by a signal wire of the flexible cable  13  to which the drive signal is supplied, and a driving voltage is selectively supplied from the driving circuit  49  to each first individual electrode  12 D, and the first common electrodes  12 C and the second common electrodes  12 E. 
     As shown in  FIG. 6 , a length L 1  from a center to center in Y-direction of two column portions  40 A positioned at two sides in the direction of width (Y-direction) of each pressure chamber  40  is approximately 0.5 mm. Moreover, in Y-direction, a length L 2  of the first individual electrode  12 D is approximately 0.38 mm, and a length L 3  of the first common electrode  12 C is approximately 0.25 mm. A width L 4  of each pressure chamber  40  is approximately 0.4 mm, and a length L 5  in Y-direction of the column portions  40 A demarcating each pressure chamber  40  is approximately 0.1 mm. Each portion of the piezoelectric material layers  12 A and  12 B corresponding to both sides in the width direction of each pressure chamber  40  is sandwiched by the first individual electrode  12 D and the second common electrode  12 E. A length L 6  in Y-direction of these portions is approximately 0.065 mm. These portions, as shown in  FIG. 7 , are polarized in a direction same as a direction of a voltage applied when a positive electric potential is applied to the first individual electrode  12 D, and the second common electrode  14 E is let to be at the ground electric potential. Moreover, a portion of the piezoelectric material layer  12 B, corresponding to the central portion in the width direction of each pressure chamber  40 , and sandwiched between the first individual electrode  12 D and the first common electrode  12 C is polarized in a direction same as a direction of a voltage when the positive electric potential is applied to the first common electrode  12 C, and the first individual electrode  12 D is let to be at the ground electric potential. Furthermore, a portion of the piezoelectric material layer  12 A, corresponding to the central portion in the width direction of each pressure chamber  40 , and sandwiched between the first common electrode  12 C and the second common electrode  12 E, is polarized in a direction same as a direction of voltage applied when the positive electric potential is applied to the first common electrode  12 C and the second common electrode  12 E is let to be at the ground electric potential. 
     Next, an electrical structure of the ink-jet printer  1  will be described below by referring to  FIG. 8  and  FIG. 9 . As shown in  FIG. 8 , a control unit of the ink-jet printer  1  includes a CPU (central processing unit) (1-chip micro computer) which controls each section of the entire ink-jet printer  1 , a control circuit  22  which is a gate circuit LSI, a ROM  23  in which control programs and driving waveform data for jetting various inks are stored, and a RAM  24  which temporarily stores data. 
     The CPU  21 , is connected to an operation panel  25  for inputting various commands, a motor driver  27  which drives a carriage motor  26  which makes reciprocate the carriage  2 , and a motor driver  29  which drives a transporting motor  28  which drives a transporting unit. Furthermore, the CPU  21  is connected to (sensors such as) a paper sensor  30  which checks as to whether or not there is a recording paper P, an origin sensor  31  which checks that the printer head  3  is at an origin position, and an ink cartridge sensor  32  which detects a state of an ink cartridge (not shown in the diagram) being mounted correctly. 
     The CPU  21 , the ROM  23 , the RAM  24 , and the control circuit  22  are connected via an address bus  41  and a data bus  42 . Moreover, the CPU  21 , in accordance with a computer program stored in the ROM  23  in advance, generate a recording timing signal TS and a control signal RS, and transfers each of the TS and RS to the control circuit  22 . The control circuit  22  stores in an image memory  45 , recording data which is transferred from an external equipment (device) such as a personal computer  43  via an interface  44 . Further, the control circuit  22  generates a reception interrupt signal WS from the data which is transferred from the personal computer  43  via the interface  44 , and transfers a signal WS to the CPU  21 . The control circuit  22 , in accordance with the recording timing signal TS and the control signal RS, and based on the recording data stored in the image memory  45 , generates a recording-data signal DATA for forming the recording data on the recording paper P, a transfer clock TCK which is synchronized with the recording-data signal DATA, a strobe signal STB, and a drive signal ICK, and transfers each of the signals DATA, TCK, STB, ICK to the driving circuit  46 . 
       FIG. 9  is a diagram showing an internal structure of the driving circuit  46 . The driving circuit  46  includes a serial-parallel converter  51  which converts the recording-data signal DATA transferred serially in synchronization with the transfer clock signal TCK from a data transfer section (not shown in the diagram) of the control circuit  22 , to parallel data, a data latch  52  which latches the converted parallel data DATA based on the strobe signal STB, an AND gate  53  which selectively outputs the drive signal ICK based on the parallel data DATA, and a driver  54  which converts the drive signal which has been output to a predetermined voltage, and outputs as a drive pulse. The drive pulse output from the driver  54  is applied to the individual electrode  12 D, and the first common electrode  12 C and the second common electrode  12 E of the printer head  3 , and deforms the piezoelectric material layers  12 A and  12 B. The number of serial-parallel converters  51 , the data latches  52 , the AND gates  53 , and the drivers  54  is prepared in accordance with the number of nozzles of the printer head  3 . The drive signals ICK are stored in the ROM  23 , and are read selectively based on the computer program control. 
     Next, a driving operation at the time of driving the printer head  3  controlled by the control unit (control circuit  22 ) will be described below. 
     In an ink jetting mode in which the ink is jetted from the nozzle  16   a , in a state of the positive electric potential applied to the first common electrode  12 C all the time and the ground electric potential applied to the second common electrode  12 E all the time, an electric potential (to be) applied to the first individual electrode  12 D is changed. 
       FIG. 10A  shows a state in which an electric potential is not applied to any of the electrodes, or a state in which all the electrode are let to be at the ground electric potential. In this state, the piezoelectric material layers  12 A and  12 B are not deformed, and a volume of the pressure chamber  40  is not changed. A state in which the volume of the pressure chamber  40  is not changed, namely, the volume of the pressure chamber  40  is a predetermined volume is called as a “reference state” in the following description. Next, in a state in which the first individual electrode  12 D and the second common electrode  12 E are let to be at the ground electric potential, when a positive electric potential is applied to the first common electrode  12 C, a portion (a first active portion) of the piezoelectric material layer  12 B sandwiched between the first individual electrode  12 D and the first common electrode  12 C is contracted in a planar direction, and the vibration plate  15  undergoes a unimorph deformation to form a projection toward the pressure chamber  40 . In other words, a deformable portion (first deformable portion) S 1  of the piezoelectric actuator  12  corresponding to the central portion in the width direction of the pressure chamber  40  is deformed in a direction toward the pressure chamber  40 . Accordingly, the pressure chamber  40 , as shown in  FIG. 10B  changes to a state in which the volume is decreased to be less than the volume in the reference state (hereinafter called as a “decreased volume state”) shown in  FIG. 10B . The piezoelectric actuator  12  lets the pressure chamber  40  to be in the decreased volume state, and waits for a printing command. 
     Next, when the positive electric potential is applied to the first individual electrode  12 D while maintaining the first common electrode  12 C at the positive electric potential and the second common electrode  12 E at the ground electric potential, a portion of the piezoelectric material layer  12 B sandwiched between the first individual electrode  12 D and the first common electrode  12 C is not deformed. Whereas, a portion (second active portion) of the piezoelectric material layers  12 A and  12 B sandwiched between the first individual electrode  12 D and the second common electrode  12 E contract in a planar direction thereof. Accordingly, the vibration plate  15  undergoes the unimorph deformation to form a projection in a direction away from the pressure chamber  40 . In other words, a deformable portion (second deformable portion) S 2  of the piezoelectric actuator  12  corresponding to a portion on an outer peripheral side of the central portion in the width direction of the pressure chamber  40  is deformed in a direction away from the pressure chamber  40 . As a result, the pressure chamber  40  changes the state from a decreased volume state as shown in  FIG. 10B  to a state in which the volume of the pressure chamber  40  is increased to be greater than the volume in the reference state (hereinafter, called as an “increased volume state”) as shown in  FIG. 10C . Accordingly, a negative pressure wave is generated in the ink in the pressure chamber  40 . When the first individual electrode  12 D is let to be at the ground electric potential once again at a timing when the negative pressure wave is changed to positive upon elapsing of a time (AL) for one-way propagation, the pressure chamber  40  changes the state from the increased volume state shown in  FIG. 10C  to a decreased volume state shown in  FIG. 10D . As the state of the pressure chamber  40  is changed to the decreased volume state, a further positive pressure is superimposed on the ink having the pressure wave changed to positive, and the pressure on the ink becomes even higher and the ink is jetted from the nozzle  16   a . This is a so-called pulling ejection which is a method for driving the printer head  3 . 
     Although it is not shown in the diagram concretely, the printer head  3  is provided with a temperature detector which detects a temperature corresponding to a temperature of the ink in each pressure chamber  40 . A temperature signal from the temperature detector is input to the CPU  21 , and according to a judgment at the CPU  21 , only when the temperature of the ink is judged to be not higher than a set value, a warm-up mode which will be described below is selected. 
     For stabilizing the jetting performance irrespective of a use of environment of the ink-jet printer  1 , in the warm-up mode of heating the ink inside the pressure chamber  40  without jetting the ink from the nozzles  16   a , by applying the positive electric potential and the ground electric potential alternately to the first common electrode  12 C in a state of the first individual electrode  12 D and the second common electrode  12 E let to be at the ground electric potential, the piezoelectric material layers  12 A and  12 B, and the vibration plate  15  of piezoelectric actuator  12  are deformed. By driving the piezoelectric actuator  12  in such manner, and making the piezoelectric actuator  12  generate heat, the ink inside the pressure chamber  40  is heated (second warm-up operation). When the time for one-way propagation of the pressure wave inside the ink channels of the printer head  3  including the pressure chambers  40  is let to be AL, by the driving circuit  46  switching the timing of applying and not applying the positive electric potential to the first common electrode  12 C to 2AL, the jetting of liquid droplets from the nozzles  16   a  is prevented. 
     Concretely, by applying the positive electric potential to the first common electrode  12 C in a state of the first individual electrode  12 D and the second common electrode  12 E at the ground electric potential, the pressure chamber  40  is changed from a reference state shown in  FIG. 11A  to a decreased volume state sown in  FIG. 11B . Next, by letting the first common electrode to be at the ground electric potential, the pressure chamber  40  is made to regain the state from the decreased volume state shown in  FIG. 11B  to a reference state shown in  FIG. 11C , in other words, the state shown in  FIG. 11A . In other words, the second warm-up operation is performed by deforming only the deformable portion S 1  of the piezoelectric actuator  12  corresponding to the central portion of the pressure chamber  40  toward the pressure chamber  40 . Even when such change in the volume of the pressure chamber  40  is repeated, since a magnitude of the positive pressure applied is small as compared to the pressure applied in the ink jetting mode, the ink is not jetted from the nozzle  16   a . However, since an amount of deformation (amount of deformation in a direction toward the pressure chamber  40 ) of the piezoelectric actuator  12  is same as an amount of deformation in the ink jetting mode, the piezoelectric actuator  12  generates the heat sufficiently. Therefore, it is possible to heat sufficiently the ink inside the pressure chamber  40  by using this heat. 
     Moreover, even by applying alternately the positive electric potential and the ground electric potential to the first individual electrode  12 D and the first common electrode  12 C almost at the same time in a state of the second common electrode  12 E let to be at the ground electric potential, and by deforming the piezoelectric material layers  12 A and  12 B and the vibration plate  15  of the piezoelectric actuator  12 , it is possible to make the piezoelectric actuator  12  generate heat. Moreover, it is possible heat the ink inside the pressure chamber  40  by the heat generated by the piezoelectric actuator  12 . 
     Concretely, by applying the positive electric potential to the first individual electrode  12 D and the first common electrode  12 C almost at the same time in the state of the second common electrode  12 E let to be at the ground electric potential, the pressure chamber  40  is changed from a reference state shown in  FIG. 12A  to an increased volume state shown in  FIG. 12B . 
     Next, by letting the first individual electrode  12 D and the first common electrode  12 C to be at the ground electric potential, the pressure chamber  40  regains the state from the increased volume state shown in  FIG. 12B  to a reference state shown in  FIG. 12C , in other words, to the state shown in  FIG. 12A . In other words, the first warm-up operation is carried out by displacing only the deformable portion S 2  of the piezoelectric actuator  12 , corresponding to the outer peripheral portion of the central portion of the pressure chamber  40  in a direction away from the pressure chamber  40 . By repeatedly driving the piezoelectric actuator  12  in such manner, it is possible to make the piezoelectric actuator  12  generate heat, and to heat sufficiently the ink inside the pressure chamber  40  without jetting the ink from the nozzles  16   a.    
     In the first warm-up operation and the second warm-up operation, the piezoelectric actuator  12  is driven such that the pressure chamber  40  is deformed between the reference state and the increased volume state or the decreased volume state, and only a part of a deformation drive of the piezoelectric actuator  12  in the ink jetting mode is used. Therefore, although the piezoelectric actuator  12  is deformed, since the magnitude of the positive pressure applied to the ink is small as compared to the pressure applied in the ink jetting mode, the ink is not jetted from the nozzle  16   a . On the other hand, since the deformation for attaining the reference state is used for the increased volume state in which, the change in volume is maximum to an increased volume side of the pressure chamber  40  or for the decreased volume state in which the change is minimum to a decreased volume side of the pressure chamber  40 , it is possible to deform the piezoelectric actuator  12  substantially, and to heat the ink sufficiently. 
     Incidentally, as shown in  FIG. 3 , the ink to be supplied to the pressure chamber  40  is stored in the manifold  50  which extends in Y-direction. Moreover, the pressure chambers  40  communicating with the same manifold are arranged in one row or two rows in Y-direction. When the pressure chambers  40  are arranged in rows in such manner, when the driving of the piezoelectric actuator is controlled to change the volume of only some of the pressure chambers  40  based on the drive pulse from the driving circuit  46  (driver  54 ), the change in the volume for the overall ink channels is small, and it is possible to reduce a possibility of the ink being jetted mistakenly. 
     For example, when the pressure chambers  40  communicating with the same manifold are arranged in one row, an arrangement may be made such that in the warm-up mode, a portion of the piezoelectric actuator  12  facing one of the two adjacent pressure chambers  40  in the direction of row of pressure chambers  40  is made to carry out any one of the first warm-up operation and the second warm-up operation, and a portion of the piezoelectric actuator  12  facing the other pressure chamber  40  is not made to carry out any warm-up operation. Moreover, an arrangement may be made such that the portion of the piezoelectric actuator  12  facing one of the two adjacent pressure chambers  40  is made to carry out the first warm-up operation, and the portion of the piezoelectric actuator  12  facing the other pressure chambers  40  is made to carry out the second warm-up operation with the same cycle. In this case, when one of the pressure chambers is in the increased volume state, the other pressure chamber is in the decreased volume state, and the pressure change for the overall pressure chambers  40  is cancelled. 
     Moreover, when the plurality of pressure chambers  40  communicating with the same manifold are arranged in two rows, similarly, in the warm-up mode, for instance, the control may be carried out such that a portion of the piezoelectric actuator  12  facing the pressure chambers  40  belonging to one of the two rows is made to carry out one of the first warm-up operation and the second warm-up operation, and a portion of the piezoelectric actuator  12  facing the pressure chambers  40  belonging to the other row is made to carry out none of the first warm-up operation and the second warm-up operation. Moreover, the portion of the piezoelectric actuator  12  facing the pressure chambers  40  belonging to one of the two rows may be made to carry out the first warm-up operation, and the portion of the piezoelectric actuator  12  facing the pressure chambers  40  belonging to the other row may be made to carry out the second warm-up operation with the same cycle. 
     It is also possible to have a similar effect as in the warm-up mode in the first embodiment by arranging the individual electrodes and the common electrodes of the piezoelectric actuator as in a second embodiment and a third embodiment which will be described later, apart from the first embodiment. 
     Firstly, the second embodiment of the present invention will be described below. As shown in  FIG. 13C , a piezoelectric actuator  112  has a piezoelectric material layer  12 F polarized in a direction of thickness, which is formed on the vibration plate  15  (insulating layer  15   b ), and a second individual electrode  112 G and a third individual electrode  112 H are formed on an upper surface side (one surface side) of the piezoelectric material layer  12 F and a third common electrode  112 K is formed on a lower surface side (the other surface side) of the piezoelectric material layer  12 F. As shown in  FIG. 13A  and  FIG. 14 , when viewed in Z-direction, the second individual electrode  112 G has a portion  112 L extending in a longitudinal direction of the pressure chamber  40  (X-direction), corresponding to a central portion in the width direction of the pressure chamber  40  (Y-direction), and has a connecting terminal portion  112 K to be connected to a signal wire, on one side in the longitudinal direction of the pressure chamber  40 . The third individual electrode  112 H has a first portion  112 M which is arranged on both sides of the second individual electrode  112 G in the width direction of the pressure chamber  40 , and a second portion  112 N which connects them, on the other side in the longitudinal direction of the pressure chamber  40 . Moreover, the third common electrode  112 K is formed to extend in the width direction of the pressure chamber  40 . As shown in  FIG. 13C  and  FIG. 14 , the third common electrode  112 K has a portion corresponding to the second individual electrode  112 G and the third individual electrode  112 H in the width direction of the pressure chamber  40 . 
     Moreover, in the ink jetting mode, as shown in  FIG. 15A , from a state in which the second individual electrode  112 G, the third individual electrode  112 H, and the third common electrode  112 K are let to be at the ground electric potential, and when the positive electric potential is applied only to the second individual electrode  112 G, a portion of the piezoelectric material layer  12 F sandwiched between the second individual electrode  112 G and the third common electrode  112 K (a first active portion) contracts in a planar direction thereof, and as shown in  FIG. 15B , the vibration plate  15  undergoes the unimorph deformation to form a projection toward the pressure chamber  40  (a first state). In other words, a deformable portion (a first deformation portion) S 11  of the piezoelectric actuator  112  corresponding to the central portion in the width direction of the pressure chamber  40  is deformed in the direction toward the pressure chamber  40 . Accordingly, it is possible to make the pressure chamber  40  change the state from the reference state to the decreased volume state. Next, with the second individual electrode  112 G let to be at the ground electric potential, when the positive electric potential is applied to the third individual electrode  112 H, a portion of the piezoelectric material layer  12 F sandwiched between the third individual electrode  112 H and the third common electrode  112 K (a second active portion) contracts in a planar direction thereof, and as shown in  FIG. 15C , the vibration plate undergoes the unimorph deformation to form a projection in a direction away from the pressure chamber  40  (a second state). In other words, a deformable portion (second deformable portion) of the piezoelectric actuator  112  corresponding to an outer peripheral portion of a central portion in the width direction of the pressure chamber  40  is deformed in the direction away from the pressure chamber  40 . Accordingly, it is possible to make the pressure chamber  40  change the state from the decreased volume state to the increased volume state. Moreover, once again, by applying the positive electric potential to the second individual electrode  112 G and letting the third individual electrode  112 H to be at the ground electric potential, the state of the pressure changes  40  changes to a decreased volume state shown in  FIG. 15B . In other words, in a state of the third common electrode  112 K let to be at the ground electric potential, the positive electric potential is applied alternately to the second individual electrode  112 G and the third individual electrode  112 H, and when the positive electric potential is not being applied, the ground electric potential is applied. Accordingly, it is possible to make the pressure chamber  40  change the state repeatedly to the decreased volume state shown in  FIG. 15B  and an increased volume state shown in  FIG. 15C , and it is possible to jet the ink by the “pulling ejection” same as in the first embodiment. 
     In the warm-up mode, the piezoelectric actuator  112  is driven such that the positive electric potential and the ground electric potential are applied alternately to the second individual electrode  112 G in a state of the third individual electrode  112 H and the third common electrode  112 K let to be at the ground electric potential, and the state of the pressure chamber  40  is repeatedly changed to a reference state in  FIG. 15A  and the decreased volume state in  FIG. 15B  alternately. In other words, only the deformable portion S 11  of the piezoelectric actuator  112  corresponding to the central portion of the pressure chamber  40  is deformed toward the pressure chamber  40 . By such driving, the piezoelectric actuator  112  generates heat, and the ink inside the pressure chamber  40  is heated (second warm-up operation). 
     Moreover, the piezoelectric actuator  112  may be driven such that the positive electric potential and the ground electric potential are applied alternately to the third individual electrode  112 H in a state of the second individual electrode  112 G and the third common electrode  112 K let to be at the ground electric potential, and the state of the pressure chamber  40  is repeatedly changed to the reference state in  FIG. 15A  and the increased volume state in  FIG. 15C  alternately. In other words, only the deformable portion S 12  of the piezoelectric actuator  112  corresponding to the outer peripheral side of the central portion of the pressure chamber  40  may be deformed (first warm-up operation). 
     In the warm-up mode, the electric potential to be applied to the second individual electrode  112 G, the third individual electrode  112 H, and the third common electrode  112 K may be changed as follows. 
     By applying the positive electric potential and the ground electric potential alternately to the second individual electrode  112 G and the third individual electrode  112 H in a state of the third common electrode  112 K let to be at the ground electric potential, a deformation directly proportional to a strength of an electric field is occurred in the piezoelectric actuator  112  (inverse piezoelectric effect), and the piezoelectric actuator  112  generates heat, thereby heating the ink. It is possible to prevent the jetting of ink by letting a timing at which the positive electric potential is applied and not applied to the second individual electrode  112 G and the third individual electrode  112 H to be 2AL, when a time for one-way propagation of a pressure wave inside the liquid channels of the printer head  3  including the pressure chambers  40  is let to be AL. 
     To put elaborately, the positive electric potential is applied to the second individual electrode  112 G and the third individual electrode  112 H in the state of the third common electrode  112 K let to be at the ground electric potential. Accordingly, a voltage is applied to a portion of the piezoelectric material layer  12 F corresponding to the central portion of the pressure chamber  40  (first active portion) and a portion of the piezoelectric material layer  12 F corresponding to the outer peripheral portion of the pressure chamber  40  (second active portion). As a result, the portion of the piezoelectric material layer  12 F corresponding to the central portion of the pressure chamber  40  contracts, and the portion of the vibration plate  15  corresponding to the central portion of the pressure chamber  40  undergoes the unimorph deformation to form a projection in the direction toward the pressure chamber  40 , as well as the portion of the piezoelectric material layer  12 F corresponding to the outer peripheral portion of the pressure chamber contracts and a portion of the vibration plate  15  corresponding to the outer peripheral portion of the pressure chamber  40  undergoes the unimorph deformation to form a projection in a direction away from the pressure chamber  40 . This state is a state in  FIG. 15D  (third state). In the state in  FIG. 15D , since the deformation of the deformable portion (first deformable portion) S 11  of the piezoelectric actuator  112  corresponding to the central portion of the pressure chamber  40  and the deformation of the deformable portion (second deformable portion) S 12  of the piezoelectric actuator  112  corresponding to the outer peripheral portion of the pressure chamber  40  cancel with each other, the volume of the pressure chamber  40  almost does not change from the volume in the reference state shown in  FIG. 15A . 
     Next, by letting the second individual electrode  112 G and the third individual electrode  112 H to be at the ground electric potential in the state of the third common electrode  112 K let to be at the ground electric potential, both the portion of the piezoelectric material layer  12 F corresponding to the central portion of the pressure chamber  40  and the portion of the piezoelectric material layer  12 F corresponding to the outer peripheral portion of the pressure chamber  40  are not deformed (a fourth state), and the pressure chamber  40  assumes the reference state shown in  FIG. 15A . 
     When the piezoelectric actuator  112  is driven as described above, it is possible to heat the ink by making the piezoelectric actuator  112  generate heat. Moreover, since the volume of the pressure chamber  40  almost does not change by driving of the piezoelectric actuator  112 , there is no possibility of the ink being jetted mistakenly. Moreover, since the deformable portions of the piezoelectric actuator  112  are deformed as described above, the overall piezoelectric actuator  112  generates heat uniformly, and it is possible to heat the ink efficiently. 
     Furthermore, since there is no possibility of the ink being jetted mistakenly in the warm-up mode, it is possible to let the positive electric potential to be applied to the second individual electrode  112 G, the third individual electrode  112 H by a drive pulse which is output from the driving circuit  46  (driver  54 ) to be greater than the positive electric potential which is to be applied to the second individual electrode  112 G and the third individual electrode  112 H in the ink jetting mode. Consequently, since it is possible to make the voltage to be applied to the portion of the piezoelectric material layer  12 F corresponding to the central portion of the pressure chamber  40  and to the portion of the piezoelectric material layer  12 F corresponding to the outer peripheral portion of the pressure chamber  40  to be greater than the voltage to be applied in the ink jetting mode, it is possible improve further the efficiency of heating by increasing the amount of deformation of the piezoelectric actuator  112 . Moreover, it is also possible to improve further the efficiency of heating by increasing the amount of deformation of the piezoelectric actuator  112  not only by making high the positive electric potential to be applied to the second individual electrode  112 G and the third individual electrode  112 H, but also by making a pulse width of the voltage to be applied to the second individual electrode  112 G and the third individual electrode  112 H (in other words, a pulse width of the drive pulse) to be wider than a pulse width of the voltage to be applied in the ink jetting mode. 
     In the second embodiment and a modified embodiment thereof, the second individual electrode  112 G and the third individual electrode  112 H are formed on the upper surface side of the piezoelectric material layer  12 F, and the third common electrode  112 K is formed on the lower surface side of the piezoelectric material layer  12 F. However, the third common electrode  112 K may be formed on the upper surface side of the piezoelectric material layer  12 F and the second individual electrode  112 G and the third individual electrode  112 H may be formed on the lower surface side of the piezoelectric material layer  12 F. 
     Next, the third embodiment of the present invention will be described below. As shown in  FIG. 16C , a piezoelectric actuator  212  includes the piezoelectric material layer  12 F polarized in Z-direction which is formed on the vibration plate  15  (an insulating layer  15   b ), a plurality of fourth individual electrodes  212 M each extending in the longitudinal direction of each pressure chamber  40  (X-direction) and being formed to face a central portion of each pressure chamber  40  on an upper surface side of the piezoelectric material layer  12 F, and a fourth common electrode  212 N, a fifth common electrode  212 P, and a sixth common electrode  212 Q formed on an upper surface side and a lower surface side of the piezoelectric material layer  12 F. When viewed in Z-direction, as shown in  FIG. 16A  and  FIG. 17 , the fourth common electrode  212 N, has a plurality of first portions  212 S extending in the longitudinal direction of the pressure chamber  40 , facing the outer peripheral portion of the pressure chamber  40  which are arranged at both sides of the fourth individual electrode  212 M in the width direction of the pressure chamber  40 , and a second portion  212 T extending in the width direction of the pressure chamber  40 , which connects the first portions  212 S at one end side in the longitudinal direction of the pressure chamber  40 . 
     Moreover, as shown in  FIG. 16B  and  FIG. 17 , the fifth common electrode  212 P has a plurality of first portions  212 U extending in the longitudinal direction of the pressure chamber  40  (X-direction) which are formed corresponding to the central portion of the width direction of each pressure chamber  40  (Y-direction), and a second portion  212 V extending in the width direction of the pressure chamber  40 , which connects the first portions  212 U of the fifth common electrode  212 P mutually at one end side in the longitudinal direction of the pressure chamber  40 . The sixth common electrode  212 Q, in the width direction of the pressure chamber  40  (Y-direction), has a plurality of first portions  212 W extending in the longitudinal direction of the pressure chamber  40  (X-direction) which are arranged at both sides (two sides) of the first portion  212 U of the fifth common electrode  212 P, and a second portion  212 X extending in the width direction of the pressure chamber  40 , which connects the first portions  212 W of the sixth common electrode  212 Q at the other end side in the longitudinal direction of the pressure chamber  40 . Moreover, as shown in  FIG. 17 , when viewed in Z-direction, the sixth common electrode  212 Q is arranged corresponding to the fourth common electrode  212 N, and the fifth common electrode  212 P is arranged corresponding to the fourth individual electrode  212 M. Further, as shown in  FIG. 16B , the first portion  212 W of the sixth common electrode  212 Q is provided to be spreading over the two adjacent pressure chambers  40 . 
     In the ink jetting mode, from a state in which, the fourth individual electrode  212 M, the fifth common electrode  212 P, and the sixth common electrode  212 Q are let to be at the ground electric potential, the positive electric potential is applied to the fourth individual electrode  212 M, the fourth common electrode  212 N, and the sixth common electrode  212 Q. Accordingly, a portion of the piezoelectric material layer  12 F sandwiched between the fourth individual electrode  212 M and the fifth common electrode  212 P contracts, and the vibration plate  15  undergoes unimorph deformation to form a projection toward the pressure chamber  40  (first state). In other words, only a deformable portion (first deformable portion) S 21  of the piezoelectric actuator  212  corresponding to the central portion of the pressure chamber  40  is deformed in the direction toward the pressure chamber  40 . As a result, it is possible to change the state of the pressure chamber  40  from a reference state in  FIG. 18A  to a decreased volume state in  FIG. 18B . Next, the fourth individual electrode  212 M and the sixth common electrode  212 Q are let to be at the ground electric potential while maintaining the fifth common electrode  212 P at the ground electric potential and the fourth common electrode  212 N at the positive electric potential. Accordingly, a portion of the piezoelectric material layer  12 F sandwiched between the fourth common electrode  212 N and the sixth common electrode  212 Q contracts, and the vibration plate  15  undergoes the unimorph deformation to form a projection in the direction away from the pressure chamber  40  (second state). In other words, only a deformable portion (second deformable portion) S 22  of the piezoelectric actuator  212  corresponding to the outer peripheral portion of the central portion of the pressure chamber  40  is deformed in the direction away from the pressure chamber  40 . As a result, it is possible to change the state of the pressure chamber  40  to an increased volume state shown in  FIG. 18C . Moreover, by applying once again the positive electric potential to the fourth individual electrode  212 M and the sixth common electrode  212 Q, it is possible to change the state of the pressure chamber  40  to a decreased volume state shown in  FIG. 18B . In the manner described above, even in the third embodiment, it is possible to make jet the ink by the “pulling ejection” same as in the first embodiment. 
     In the warm-up mode, by driving the piezoelectric actuator  212  such that a reference state in  FIG. 18A  and the decreased volume state in  FIG. 18B  are repeated alternately, the heat is generated by the piezoelectric actuator  212  without the ink being jetted, and it is possible to heat the ink in the pressure chamber  40  (second warm-up operation). 
     Moreover, the piezoelectric actuator  212  may be driven such that the reference state in  FIG. 18A  and an increased volume state in  FIG. 18C  are repeated alternately (first warm-up operation). 
     In the warm-up mode, the electric potential to be applied to the fourth individual electrode  212 M, the fourth common electrode  212 N, the fifth common electrode  212 P, and the sixth common electrode  212 Q may be changed as follows. 
     By repeatedly applying and not applying the positive electric potential to the fourth individual electrode  212 M and the fourth common electrode  212 N in a state of the fifth common electrode  212 P and the sixth common electrode  212 Q let to be at the ground electric potential, the piezoelectric actuator  212  generates heat, and the ink is heated. Concretely, the positive electric potential is applied to the fourth individual electrode  212 M and the fourth common electrode  212 N in the state of the fifth common electrode  212 P and the sixth common electrode  212 Q let to be at the ground electric potential. Accordingly, a voltage is applied to a portion of the piezoelectric material layer  12 F corresponding to the central portion of the pressure chamber  40  and a portion of the piezoelectric material layer  12 F corresponding to an outer peripheral side portion of the central portion of the pressure chamber  40 . As a result, the portion of the piezoelectric material layer  12 F corresponding to the central portion of the pressure chamber  40  contracts, and the portion of the vibration plate  15  corresponding to the central portion of the pressure chamber  40  undergoes the unimorph deformation to form a projection toward the pressure chamber  40 , and also the portion of the piezoelectric material layer  12 F corresponding to the outer peripheral portion of the pressure chamber  40  contracts, and the portion of the vibration plate  15  corresponding to the outer peripheral portion of the pressure chamber  40  undergoes the unimorph deformation to form a projection in the direction away from the pressure chamber  40 . This state is a state in  FIG. 18D  (third state). In the state in  FIG. 18D , since a deformation of the deformable portion (the first deformable portion) S 21  of the piezoelectric actuator  212  corresponding to the central portion of the pressure chamber  40  and a deformation of the deformable portion (the second deformable portion) S 22  of the piezoelectric actuator  212  corresponding to the outer peripheral portion of the pressure chamber  40  are cancelled mutually, the volume of the pressure chamber  40  almost does not change from the reference volume in the state shown in  FIG. 18A . Next, by letting the fourth individual electrode  212 M and the fourth common electrode  212 N to be at the ground electric potential in the state of the fifth common electrode  212 P and the sixth common electrode  212 Q let to be at the ground electric potential, the pressure chamber  40  assumes the reference state shown in  FIG. 18A , without both the portion of the piezoelectric material layer  12 F corresponding to the central portion of the pressure chamber  40  and the portion corresponding to the outer peripheral portion of the pressure chamber  40  being deformed (fourth state). The piezoelectric actuator  212  generates heat by being driven in such manner, and it possible to heat the ink. Since the volume of the pressure chamber  40  almost does not change during the driving of the piezoelectric actuator  212 , there is no possibility that the ink is jetted mistakenly. 
     Even in this modified embodiment, since there is no possibility that the ink is jetted mistakenly, a positive electric potential to be applied to the fourth individual electrode  212 M and the fourth common electrode  212 N by a drive pulse which is output from the driving circuit  46  (driver  54 ) may be let to be higher than a positive electric potential to be applied to the fourth individual electrode  212 M and the fourth common electrode  212 N in the ink jetting mode, and a voltage to be applied to the piezoelectric actuator  212  may be let to be higher than a voltage to be applied in the ink jetting mode. Or, it is also possible to improve the efficiency of heating by making substantial an amount of deformation of the piezoelectric actuator  212  by making a pulse width of the voltage to be applied to the fourth individual electrode  212 M and the fourth common electrode  212 N (in other words, the pulse width of the drive pulse) to be wider than a pulse width of the voltage to be applied to the fourth individual electrode  212 M and the fourth common electrode  212 N in the ink jetting mode. 
     In the third embodiment and the modified embodiment thereof, the fourth individual electrode  212 M and the fourth common electrode  212 N are arranged on the upper surface side of the piezoelectric material layer  12 F, and the fifth common electrode  212 P and the sixth common electrode  212 Q are arranged on the lower surface side of the piezoelectric material layer  12 A. However, the fifth common electrode  212 P and the sixth common electrode  212 Q may be arranged on the upper surface side of the piezoelectric material layer  12 A, and the fourth individual electrode  212 M and the fourth common electrode  212 N may be arranged on the lower surface side of the piezoelectric material layer  12 A. 
     It is also possible to make the following changes in the embodiments described above. 
     In the embodiments described above, cases in which the liquid droplet jetting apparatus is an ink-jet printer have been described. However, the present invention is not restricted to the ink-jet printer, and is also applicable to other liquid droplet jetting apparatuses which apply a colored liquid as small droplets, or forms a wiring pattern by jetting an electroconductive liquid. 
     In the present invention, not only a recording paper but also various materials such as resins and cloth can also be used as a recording medium, and not only an ink but various liquids such as a colored liquid and a functional liquid can be used as a liquid to be jetted.