Patent Publication Number: US-8979230-B2

Title: Drive device, liquid jet head, liquid jet recording apparatus, and drive method

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a drive device for driving a liquid jet head which ejects liquid from nozzle holes to record images and characters on a recording medium, and to a liquid jet head, a liquid jet recording apparatus, and a drive method for the liquid jet head. 
     2. Description of the Related Art 
     Generally, a liquid jet head, to which ink (liquid) is supplied from an ink tank, includes a head chip. Ink is ejected from nozzle holes of the head chip onto a recording medium to perform recording. In some liquid droplet ejection type (ink jet type) liquid jet heads (ink jet heads) described above, there is one in which ejection of liquid droplets is performed by driving a piezoelectric actuator provided in the head chip by a head drive portion. 
     For example,  FIG. 9  is a block diagram illustrating a configuration example of a drive portion of a liquid jet head chip which is built into the liquid jet head. 
     In the example illustrated in  FIG. 9 , a liquid jet head chip  73  includes 512 nozzles NZ 1  to NZ 512  (collectively referred to as “nozzle NZ”). A pressure generating element PZT corresponding to each nozzle NZ in the liquid jet head chip  73  is driven by a drive portion  100  mounted on a control circuit board  80 . The drive portion  100  includes four driver ICs  101  to  104  as a drive device for the liquid jet head chip  73 , and each of the driver ICs (IC 1  to IC 4 )  101  to  104  is configured to drive the pressure generating elements PZT corresponding to the respective 128 nozzles NZ. Further, each of the driver ICs (IC 1  to IC 4 )  101  to  104  inputs, via a connector  100 A, image data for printing and various clock signals (shift CLK, pixel CLK, and the like) to be used for printing operation. 
     Further,  FIG. 10  illustrates a configuration example of the drive device for the pressure generating element PZT, and is a block diagram illustrating, for example, a configuration example of the driver IC illustrated in  FIG. 9 . As illustrated in  FIG. 10 , the drive device (driver IC)  101  includes a selector  111 , a setting value storage element  112 , a waveform generating circuit  113 , a shift register  121 , a latch circuit (latch)  122 , a waveform selecting circuit (waveform selection)  123 , and a level converting circuit (level conversion)  124 . Note that, details of the respective components are described in the section of embodiments below. 
     The drive device  101  illustrated in  FIG. 10  drives, based on drive signals OUT 1  to OUTn output from the level converting circuit  124 , the pressure generating elements PZT corresponding to the respective n nozzles NZ in the liquid jet head chip  73  (see FIG.  9 ). 
     By the way, the drive waveform from the head drive portion, for driving the pressure generating element PZT (piezoelectric actuator), influences the liquid droplet ejection characteristics. For example, the pressure generating element PZT has a very fast response speed with respect to the drive signals OUT 1  to OUTn. Therefore, when the pressure generating element PZT is driven by a square wave having a crest value Vp as shown in  FIG. 11A , a rapid pressure change occurs inside the nozzle. Therefore, the meniscus motion cannot be controlled with high accuracy, and satellites or mist may be generated. Further, the side wall of the pressure generating element PZT rapidly deforms, and hence cavitation may be generated. 
     In view of this, as illustrated in  FIG. 10  described above, a fixed resistor R is inserted between the level converting circuit  124  and a drive power supply Vd (for example, DC 30 V power supply). In this case, the pressure generating element PZT becomes a capacitive load (capacitor load), and a first order delay circuit is formed between the fixed resistor R and the electrostatic capacitance of the pressure generating element PZT. 
     Therefore, with the first order delay circuit formed of the fixed resistor R and the electrostatic capacitance of the pressure generating element PZT, as shown in  FIG. 11B , the drive voltage for the pressure generating element PZT gently rises up to the voltage Vp while drawing a curved line. Therefore, the drive voltage waveform for the pressure generating element PZT does not rapidly increase, but gently rises from a time t 1  to a time t 2 . Therefore, the deformation of the pressure generating element PZT also becomes gentle, and hence no rapid pressure change occurs inside the nozzle NZ. Thus, generation of cavitation and mist can be prevented. 
     Further, as for a drive method for the piezoelectric actuator, there is disclosed a technology of controlling the rising and falling shape of the drive waveform to control the liquid droplet ejection characteristics (for example, see Japanese Patent Application Laid-open Nos. 2007-098795 and 2003-276188). 
     However, Japanese Patent Application Laid-open No. 2007-098795 discloses a technology of providing, as the power supply for supplying power for driving the piezoelectric actuator, a plurality of power supply voltage sources having different output voltages, and selecting the power supply voltages output from the respective power supply voltage sources by a plurality of transistors. When the head drive portion is configured as described above, a plurality of power supply voltage sources need to be prepared, which complicates the circuit and increases the manufacturing cost. 
     Further, Japanese Patent Application Laid-open No. 2003-276188 discloses a technology in which a plurality of charge resistors having different resistance values are provided for limiting a current value (charge current) for driving the piezoelectric actuator and supplying power for driving the piezoelectric actuator. A plurality of transistors are provided correspondingly to those charge resistors, and a charge resistor which causes a desired current value to flow is selected by the transistors. When the head drive portion is configured as described above, not merely that the circuit configuration is complicated, but also the heat lost increases in the drive circuit forming the head drive portion, and hence the amount of heat generation increases in the head drive portion. Further, a step of trimming the charge resistors or the like is required at the time of manufacture, and hence the manufacturing cost increases. 
     SUMMARY OF THE INVENTION 
     The present invention has been made to solve the above-mentioned problems, and therefore has an object to provide a drive device for driving a liquid jet head, which is capable of controlling the shape of a drive waveform for driving the liquid jet head and reducing the amount of heat generation in a head drive portion, and to provide a liquid jet head, a liquid jet recording apparatus, and a drive method for the liquid jet head. 
     [1] The present invention has been made to solve the above-mentioned problems, and, according to an exemplary embodiment of the present invention, there is provided a drive device for driving a liquid jet head including: a nozzle provided with a nozzle opening; a pressure generating chamber communicated to the nozzle opening; and a pressure generating element for generating pressure fluctuations inside the pressure generating chamber in response to input of a drive waveform, the liquid jet head ejecting an ink droplet from the nozzle opening by the pressure fluctuations, the drive device including a drive portion for driving, as a load, the pressure generating element provided correspondingly to the nozzle, and controlling a state of driving the load, in which the drive portion includes: a first drive section for causing a first current to flow to drive the load; and a second drive section for causing a second current smaller than the first current to flow to drive the load, in which the state of driving the load includes a first state and a second state, and in which the second drive section causes the second current in a direction in which the load is switched from the first state to the second state to flow from a timing that is faster by a predetermined time determined in advance with respect to a timing at which the first drive section causes the first current for switching the state of driving the load from the first state to the second state to flow. 
     As described above, the second current in the direction in which the load is switched from the first state to the second state is caused to flow from a timing that is faster by the predetermined time determined in advance with respect to the timing at which the first drive section causes the first current for switching the state of driving the load from the first state to the second state to flow. Thus, it is possible to control the shape of the drive waveform for driving the liquid jet head. Further, the second drive portion causes the second current smaller than the first current to flow to drive the load. Thus, it is possible to reduce the loss at the drive portion and reduce the amount of heat generation in the head drive portion. 
     [2] Further, according to the present invention, the second drive section causes the second current for charging the load to flow from a timing that is faster by a predetermined time determined in advance with respect to a timing at which the first drive section causes the first current for charging the load to flow. 
     As described above, at the timing at which the load is charged, the second drive portion causes a charge current (second current) smaller than the first current to flow to drive the load. Thus, it is possible to control the shape of the drive waveform and reduce the amount of heat generation in the head drive portion. 
     [3] Further, according to the present invention, the second drive section causes the second current for discharging the load to flow from a timing that is faster by a predetermined time determined in advance with respect to a timing at which the first drive section causes the first current for discharging charges accumulated in the load to flow. 
     As described above, at the timing at which the load is discharged, the second drive portion causes a discharge current (second current) smaller than the first current to flow to drive the load. Thus, it is possible to control the shape of the drive waveform and reduce the amount of heat generation in the head drive portion. 
     [4] Further, according to the present invention, the second drive section limits the second current to such a current value that a change rate of a voltage of the load, which changes by causing the second current to flow, is smaller than a change rate of the voltage of the load, which changes by causing the first current to flow. 
     [5] Further, according to the present invention, the second drive section includes a pre-charge section which causes the second current for charging the load to flow from a timing that is faster by a predetermined time determined in advance with respect to a timing at which the first drive section causes the first current for charging the load to flow. 
     [6] Further, according to the present invention, the second drive section includes a pre-discharge section which causes the second current for discharging the load to flow from a timing that is faster by a predetermined time determined in advance with respect to a timing at which the first drive section causes the first current for discharging charges accumulated in the load to flow. 
     [7] Further, according to the present invention, the second drive section includes a current limiting section for limiting the second current for charging the load and the second current for discharging the load. 
     [8] Further, according to the present invention, the current limiting section has an impedance for limiting the second current, the impedance being set to a value larger than an internal resistance value of the pressure generating element. 
     [9] Further, according to the present invention, a timing at which the second drive section starts charging of the load is synchronized with a timing at which the first drive section switches the state of driving the load from a drive state in which charges accumulated in the load are discharged to a drive state in which a current for discharging the charges of the load is interrupted. 
     [10] Further, according to the present invention, a timing at which the second drive section starts discharging of charges accumulated in the load is synchronized with a timing at which the first drive section switches the state of driving the load from a drive state in which the load is charged to a drive state in which a current for charging the load is interrupted. 
     [11] Further, according to the present invention, the first drive section and the second drive section are supplied with power for driving the load from the same voltage power supply. 
     [12] Further, according to the present invention, the drive device further includes an adjustment portion for generating a first control signal for controlling the first drive section so as to drive the load and cause the first current for switching the state of driving the load from the first state to the second state to flow, and a second control signal for controlling the first drive section so as to cause the second current in the direction in which the load is switched from the first state to the second state to flow at the predetermined time before the first drive section causes the first current to flow. 
     [13] Further, according to another exemplary embodiment of the present invention, there is provided a liquid jet head, to be driven by the drive device according to the above-mentioned exemplary embodiment. 
     [14] Further, according to another exemplary embodiment of the present invention, there is provided a liquid jet recording apparatus, including the liquid jet head according to the above-mentioned another exemplary embodiment. 
     [15] Further, according to another exemplary embodiment of the present invention, there is provided a drive method for driving a liquid jet head including: a nozzle provided with a nozzle opening; a pressure generating chamber communicated to the nozzle opening; and a pressure generating element for generating pressure fluctuations inside the pressure generating chamber in response to input of a drive waveform, the liquid jet head ejecting an ink droplet from the nozzle opening by the pressure fluctuations, the method including driving, as a load, the pressure generating element provided correspondingly to the nozzle, and controlling a state of driving the load, in which the driving and controlling includes: causing, by a first drive section, a first current to flow to drive the load; and causing, by a second drive section, a second current smaller than the first current to flow to drive the load, in which the state of driving the load includes a first state and a second state, and in which the method further includes causing, by the second drive section, the second current in a direction in which the load is switched from the first state to the second state to flow at a predetermined time before the first drive section drives the load and causes the first current for switching the state of driving the load from the first state to the second state to flow. 
     According to the present invention, it is possible to control the shape of the drive waveforms for driving the liquid jet head and reduce the amount of heat generation in the head drive portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG. 1  is a perspective view of a liquid jet recording apparatus having a liquid jet head mounted thereon, the liquid jet head including a drive device of the present invention; 
         FIG. 2  is a partially cutout perspective view of the liquid jet head; 
         FIG. 3  is a block diagram illustrating a configuration of a drive device according to a first embodiment of the present invention; 
         FIG. 4  is a diagram illustrating a configuration of a level converting circuit in the first embodiment of the present invention; 
         FIG. 5  is a diagram illustrating drive waveforms generated in a conventional technology; 
         FIG. 6  is a diagram illustrating drive waveforms generated by a drive portion in the first embodiment; 
         FIG. 7  is a diagram illustrating drive waveforms generated by a drive portion according to a second embodiment of the present invention; 
         FIG. 8  is a block diagram illustrating a configuration of a drive device according to a third embodiment of the present invention; 
         FIG. 9  is a block diagram illustrating a configuration example of the drive portion of a liquid jet head chip; 
         FIG. 10  is a diagram illustrating a configuration example of the drive device for a pressure generating element PZT; and 
         FIGS. 11A and 11B  are graphs showing examples of drive waveforms for the pressure generating element PZT. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     (First Embodiment) 
     (Configuration of Liquid Jet Recording Apparatus) 
       FIG. 1  illustrates an example of a liquid jet recording apparatus having a liquid jet head mounted thereon, the liquid jet head including a drive device of the present invention, and is a perspective view of a liquid jet recording apparatus  1 . 
     The liquid jet recording apparatus  1  includes a pair of transfer means  2  and  3  for transferring a recording medium S such as paper, a liquid jet head  4  for jetting an ink droplet onto the recording medium S, liquid supply means  5  for supplying the liquid to the liquid jet head  4 , and scan means  6  for causing the liquid jet head  4  to scan the recording medium S in a direction (sub scan direction) substantially orthogonal to a transfer direction (main scan direction) of the recording medium S. 
     In the following, description is made under the assumption that the sub scan direction is an X direction, the main scan direction is a Y direction, and a direction orthogonal to both of the X direction and the Y direction is a Z direction. 
     The pair of transfer means  2  and  3  include grid rollers  20  and  30  provided so as to extend in the sub scan direction, pinch rollers  21  and  31  extending in parallel with the grid rollers  20  and  30 , respectively, and although not shown in detail, a drive mechanism, such as a motor, for rotating the grid rollers  20  and  30  around the axis. 
     The liquid supply means  5  includes a liquid container  50  for storing ink, and a liquid supply tube  51  connecting the liquid container  50  and the liquid jet head  4 . A plurality of the liquid containers  50  are provided. Specifically, ink tanks  50 Y,  50 M,  50 C, and  50 B storing four types of inks of yellow, magenta, cyan, and black, respectively, are arranged. Each of the ink tanks  50 Y,  50 M,  50 C, and  50 B includes a pump motor M capable of causing ink to move under pressure toward the corresponding liquid jet head  4  through the liquid supply tube  51 . The liquid supply tube  51  includes a flexible hose having flexibility, which is capable of responding to the movement of the liquid jet head  4  (carriage unit  62 ). 
     The scan means  6  includes a pair of guide rails  60  and  61  which are provided so as to extend in the sub scan direction, the carriage unit  62  which is slidable along the pair of guide rails  60  and  61 , and a drive mechanism  63  for causing the carriage unit  62  to move in the sub scan direction. The drive mechanism  63  includes a pair of pulleys  64  and  65  provided between the pair of guide rails  60  and  61 , an endless belt  66  wound around the pair of pulleys  64  and  65 , and a drive motor  67  for rotary-driving one pulley  64 . 
     The pulley  64  is disposed between one end portions of the pair of guide rails  60  and  61 , and the pulley  65  is disposed between the other end portions of the pair of guide rails  60  and  61 , and the pair of pulleys  64  and  65  are arranged with a gap provided therebetween in the sub scan direction. The endless belt  66  is disposed between the pair of guide rails  60  and  61 . The carriage unit  62  is coupled to this endless belt  66 . A plurality of the liquid jet heads  4  are mounted on a base end portion  62   a  of the carriage unit  62 . Specifically, liquid jet heads  40 Y,  40 M,  40 C, and  40 B corresponding to the four types of inks of yellow, magenta, cyan, and black, respectively, are mounted on the carriage unit  62  while being arranged in the sub scan direction. 
     (Liquid Jet Head) 
       FIG. 2  is a partially cutout perspective view of the liquid jet head  4 . 
     As illustrated in  FIG. 2 , the liquid jet head  4  includes, on base members  41  and  42 , a jetting portion  70  for jetting ink onto the recording medium S (see  FIG. 1 ), a control circuit board  80  electrically connected to the jetting portion  70 , and a pressure damper  90  interposed between the jetting portion  70  and the liquid supply tube  51 , via connection portions  93  and  94 , respectively. The pressure damper  90  is provided for causing the ink to flow from the liquid supply tube  51  to the jetting portion  70  while damping the pressure fluctuations in the ink. 
     The jetting portion  70  includes a flow path substrate  71  which is connected to the pressure damper  90  via a connection portion  72 , a liquid jet head chip  73  for jetting ink as liquid droplets onto the recording medium S through application of a voltage, and flexible wiring  74  which is electrically connected to the liquid jet head chip  73  and the control circuit board  80 , for transmitting a drive signal to the liquid jet head chip  73 . The control circuit board  80  includes a drive portion  100  for generating a drive pulse for the liquid jet head chip  73  based on signals such as pixel data from a main body control portion (not shown) of the liquid jet recording apparatus  1 . 
     The liquid jet head chip  73  includes a substantially rectangular piezoelectric actuator whose longitudinal direction is in the Z direction of  FIG. 2 , and a plurality of nozzles formed of a plurality of nozzle openings arrayed in the Y direction of  FIG. 2 . The piezoelectric actuator is made of, for example, lead zirconate titanate (PZT) as a pressure generating element. Further, the piezoelectric actuator includes a pressure generating chamber communicated to each nozzle opening, and a drive electrode portion extending in a plate-like manner. 
     The drive electrode portion is electrically connected to the control circuit board  80  via the flexible wiring  74 , and thus the drive signal is input from the control circuit board  80  to the liquid jet head chip  73 . With the input of the drive signal, pressure fluctuations are generated in the pressure generating chamber, and the ink droplet is ejected from the nozzle opening by the pressure fluctuations. 
     Further, on a front end surface of the piezoelectric actuator (end surface on the lower side in the Z direction of  FIG. 2 ), a nozzle plate made of polyimide and the like is provided. One main surface of the nozzle plate is a bonding surface with respect to the piezoelectric actuator, and the other main surface thereof is coated with a water-repellent film having a water-repellent property or a hydrophilic property for preventing adhesion of ink and the like. 
     Further, as described above, the nozzle plate has a plurality of nozzle holes (nozzle openings) formed in its longitudinal direction at predetermined intervals (intervals equivalent to the pitches of the pressure generating chambers). The nozzle hole is formed in the nozzle plate formed of a polyimide film and the like by using, for example, an excimer laser device. Those nozzle holes are arranged so as to match with the pressure generating chambers, respectively. 
     With such a configuration, a predetermined amount of ink is supplied from a storage chamber in the pressure damper  90  (see  FIG. 2 ) via the connection portions  72  and  94  to the flow path substrate  71 . Further, the flow path substrate  71  is communicated to the pressure generating chambers of the liquid jet head chip  73 , and thus the ink can be provided across the pressure generating chambers from the connection portions  72  and  94 . That is, the pressure generating chamber functions as an ink chamber into which ink is filled, whereas the flow path substrate  71  functions as a common ink chamber for communicating the respective pressure generating chambers. 
     (Configuration of Drive Device of First Embodiment) 
       FIG. 3  is a block diagram illustrating the configuration of the drive device according to the first embodiment of the present invention. The drive device illustrated in  FIG. 3  is a device built into the liquid jet head  4  included in the liquid jet recording apparatus  1  illustrated in  FIG. 1 , specifically, a drive device  110  to be mounted as a driver IC on the control circuit board  80  of the liquid jet head  4  illustrated in  FIG. 2 . With this drive device  110 , the above-mentioned piezoelectric actuator inside the liquid jet head chip  73  is driven. 
     Note that, in this embodiment, a part of the piezoelectric actuator corresponding to respective components of the piezoelectric actuator (drive electrode portion corresponding to each nozzle NZ and drive portion corresponding to the drive electrode portion), which are driven so as to eject an ink droplet correspondingly to each nozzle, is referred to as a pressure generating element PZT to distinguish from the integrally-formed piezoelectric actuator. Further, the phrase “drive the nozzle” more precisely means that the pressure generating element PZT corresponding to the nozzle is driven. 
     The drive device  110  illustrated in  FIG. 3  includes a selector  111 , a setting value storage element  112 , a waveform generating circuit  113 , a shift register  121 , a latch circuit (latch)  122 , a waveform selecting circuit (waveform selection)  123 , and a level converting circuit (level conversion)  124 . 
     The selector  111  inputs image data (or setting data), data IN as an image data acquisition signal, and shift CLK as a clock signal for performing data shift (data transfer) in the shift register  121 . The selector  111  acquires image data in synchronization with the data IN signal, and based on the acquired image data, generates and outputs a signal D. 
     The signal D output from the selector  111  is output toward the shift register  121  and the setting value storage element  112 . Further, the selector  111  outputs the shift CLK toward the shift register  121  and the setting value storage element  112 . 
     The shift register  121  holds the signal D input from the selector  111  while sequentially shifting (transferring) the signal D in a period synchronized with the shift CLK. Then, after all of pieces of data to be printed (n pieces of data to be printed by the liquid jet head chip  73 ) are input to the shift register  121 , in response to pixel CLK, the n pieces of image data (more precisely, signal D) held in the shift register  121  are latched by the latch circuit  122 . Further, the shift register  121  outputs the 2-bit data held thereby to data OUT as an output signal while sequentially shifting (transferring) the data in a period synchronized with the shift CLK. 
     The setting value storage element  112  inputs the above-mentioned signal D and shift CLK from the selector  111 . 
     The setting value storage element  112  holds information on a “pre-charging start time” and information on a “pre-discharging start time” for each of the nozzles. The information on the “pre-charging start time” and the information on the “pre-discharging start time” for each of the nozzles are converted by the waveform generating circuit  113  so as to be referred to as information on the waveform generation in the level converting circuit  124 . 
     Further, the setting value storage element  112  generates a signal indicating a waveform setting value (for example, waveform height and waveform output period) which corresponds to the contents indicated by the above-mentioned signal D. This signal indicating the waveform setting value is output toward the waveform generating circuit  113 . 
     The waveform generating circuit  113  refers to the information on the “pre-charging start time” and the information on the “pre-discharging start time” for each of the nozzles, which are held in the setting value storage element  112 , converts the pieces of information to waveform shaping information for the level converting circuit  124 , and outputs the waveform shaping information to the level converting circuit  124 . 
     Further, the waveform generating circuit  113  generates a waveform signal Wave based on the signal indicating the waveform setting value input from the setting value storage element  112 , and outputs the waveform signal Wave to the waveform selecting circuit  123 . 
     Specifically, the waveform generating circuit  113  generates the waveform signal Wave including waveform signals Wave 0 , Wave 1 , Wave 2 , and Wave 3  based on the signal indicating the waveform setting value input from the setting value storage element  112 , and outputs the waveform signals to the waveform selecting circuit  123 . 
     For example, the waveform signal Wave 0  is a waveform signal to be applied to the pressure generating element PZT for preventing ink fixation. Further, the waveform signal Wave 1  is a waveform signal of a pulse P 1  for ejecting one ink droplet from the nozzle, the waveform signal Wave 2  is a waveform signal corresponding to the pulse P 1  and a pulse P 2  used when two ink droplets are ejected from the nozzle, and the waveform signal Wave 3  is a waveform signal corresponding to the pulse P 1 , the pulse P 2 , and a pulse P 3  used when three ink droplets are ejected from the nozzle. 
     The waveform selecting circuit  123  selects, in accordance with the signal indicating printing data (printing data indicated by the above-mentioned signal D) for each of the nozzles, which is input from the latch circuit  122 , one of the waveform signals Wave 0  to Wave 3  output from the waveform generating circuit  113 , and outputs the selected waveform signal toward the level converting circuit  124 . 
     The waveform selecting circuit  123  selects, based on the signal (2-bit data) input from the latch circuit  122 , one of the waveform signals Wave 0  to Wave 3  output from the waveform generating circuit  113  correspondingly to each nozzle NZ, and outputs the selected waveform signal toward the level converting circuit  124 . 
     The level converting circuit  124  converts, at a timing at which the image is printed, the voltage levels of the waveform signals Wave 0  to Wave 3  set for each of the pressure generating elements PZT, which are input from the waveform selecting circuit  123 , by a power supply voltage Vd, and outputs the converted signals as drive signals OUT 1  to OUTn. The pressure generating elements PZT are driven by the drive signals OUT 1  to OUTn output from the level converting circuit  124 , respectively. 
     With reference to  FIG. 4 , details of the level converting circuit are described.  FIG. 4  is a diagram illustrating the configuration of the level converting circuit in this embodiment. 
     In  FIG. 4 , the pressure generating element PZT provided correspondingly to each nozzle is represented by a load L. The pressure generating element PZT is modeled as a series circuit of an electrostatic capacitance C and an internal impedance r. 
     The level converting circuit  124  illustrated in  FIG. 4  includes a drive portion  500  corresponding to each nozzle, and an adjustment portion  550 . The drive portion  500  drives the pressure generating element PZT provided correspondingly to the nozzle as the load L, and controls the drive state of the load L. 
     The drive portion  500  includes a drive section  510  (first drive section) and a drive section  520  (second drive section). The drive section  510  causes a first current (I 1  or I 1 ′) to flow to drive the load L. The drive section  520  causes a second current (I 2  or I 2 ′) which is smaller than the first current (I 1  or I 1 ′) to flow to drive the load L. 
     The adjustment portion  550  generates control signals for controlling the drive states of the drive section  510  and the drive section  520  of the drive portion  500 , and supplies the control signals to the drive section  510  and the drive section  520 , respectively. 
     Such a drive portion  500  generates a desired drive waveform for driving the load L by combining different drive sections  510  and  520  having different characteristics in current supply ability. 
     In the following, respective components included in the drive portion  500  are described in order. In the following description, the state of driving the load L by the drive portion  500  includes a state with voltage application and a state without voltage application. When it is not clearly specified, there are cases where one of the state with voltage application and the state without voltage application is referred to as a first state, and the other thereof is referred to as a second state. 
     The drive section  510  controls the first current (I 1  or I 1 ′) to be caused to flow to/from the load L in accordance with the control signal from the adjustment portion  550 . The drive section  510  includes a main charge section  511  and a main discharge section  512 . The main charge section  511  includes a switch for interrupting a charge current (first current (I 1 )) to be caused to flow to the load L. The main discharge section  512  includes a switch for interrupting a discharge current (first current (I 1 ′)) to be caused to flow from the load L. The switch included in each of the main charge section  511  and the main discharge section  512  is formed of a semiconductor circuit element such as an FET and a transistor. The drive section  510  mainly supplies power for driving the load L. The drive signal waveform (voltage waveform) to be output to the load L by the drive section  510  is formed so that the voltage change rate at the rising timing and the falling timing of the waveform is large. As described above, by supplying the drive signal waveform that steeply changes to the load L by the drive section  510 , the state of the pressure generating element PZT is steeply changed to eject the ink droplets. 
     The connection in the drive section  510  is organized. The main charge section  511  includes a power supply terminal, an output terminal, and a control signal input terminal. The power supply terminal of the main charge section  511  is connected to the power supply Vd, and the output terminal thereof is connected to the load L. The main discharge section  512  includes a ground terminal, an output terminal, and a control signal input terminal. The ground terminal of the main discharge section  512  is grounded (G), and the output terminal thereof is connected to the load L. 
     The drive section  520  controls the second current (I 2  or I 2 ′) to be caused to flow to/from the load L in accordance with the control signal from the adjustment portion  550 . The drive section  520  includes a pre-charge section  521 , a pre-discharge section  522 , and a current limiting section  5230 . The pre-charge section  521  includes a switch for interrupting a charge current (second current (I 2 )) to be caused to flow to the load L. The pre-discharge section  522  includes a switch for interrupting a discharge current (second current (I 2 ′)) to be caused to flow from the load L. The switch included in each of the pre-charge section  521  and the pre-discharge section  522  is formed of a semiconductor circuit element such as an FET and a transistor. The current limiting section  5230  limits the current values of the charge current (second current (I 2 )) and the discharge current (second current (I 2 ′)) to be caused to flow to/from the load L. For example, the current limiting section  5230  is a resistor, and its impedance is determined in advance in accordance with the charge current (second current (I 2 )) and the discharge current (second current (I 2 ′)) to be caused to flow to/from the load L and the power supply voltage Vd. For example, the impedance of the current limiting section  5230  for limiting the charge current (second current (I 2 )) and the discharge current (second current (I 2 ′)) is set to a value larger than the internal impedance r of the pressure generating element PZT illustrated as the load L. 
     In contrast to the above-mentioned drive section  510 , the drive section  520  supplies auxiliary power for adjusting the state of the load L. The drive signal waveform (voltage waveform) to be output to the load L by the drive section  520  is formed so that the voltage change rate at a rising timing and a falling timing of the waveform is small. Therefore, liquid droplets are not directly ejected by the power supplied from the drive section  520 . 
     The connection in the drive section  520  is organized. The pre-charge section  521  includes a power supply terminal, an output terminal, and a control signal input terminal. The power supply terminal of the pre-charge section  521  is connected to the power supply Vd, and the output terminal thereof is connected to one end of the current limiting section  5230 . The pre-discharge section  522  includes a ground terminal, an output terminal, and a control signal input terminal. The ground terminal of the pre-discharge section  522  is grounded (G), and the output terminal thereof is connected to the one end of the current limiting section  5230 . The other end of the current limiting section  5230  is connected to a node that connects the main charge section  511 , the main discharge section  512 , and the load L. 
     Next, the adjustment portion  550  is described. The adjustment portion  550  generates the control signals for driving the drive section  510  and the drive section  520  configured as described above as follows. 
     The adjustment portion  550  generates the control signals for controlling the drive portion  500 . The adjustment portion  550  is supplied with setting information in accordance with the characteristics of each nozzle. The setting information to be supplied is information based on the information on the “pre-charging start time” and the information on the “pre-discharging start time” for each nozzle. The setting information may be, as information for instructing pre-charging start and pre-discharging start for each nozzle, information for continuously instructing time or information for instructing time by some representative values. The adjustment portion  550  adjusts, in accordance with the set information, the timing for changing the following signals. 
     The adjustment portion  550  generates a control signal CONT_C 1  (first control signal), a control signal CONT_D 1  (first control signal), a control signal CONT_C 2  (second control signal), and a control signal CONT_D 2  (second control signal). The above-mentioned control signal CONT_C 1  (first control signal), control signal CONT_D 1  (first control signal), control signal CONT_C 2  (second control signal), and control signal CONT_D 2  (second control signal) are control signals for controlling the above-mentioned main charge section  511 , main discharge section  512 , pre-charge section  521 , and pre-discharge section  522 , respectively, and are control signals to be supplied to the control signal input terminals of the respective sections from the adjustment portion  550  to control the supply of the current to be caused to flow to the load L. 
     With reference to  FIGS. 5 and 6 , the drive waveforms generated by the drive portion  500  are described. 
       FIG. 5  is a diagram illustrating the drive waveforms generated by the conventional technology. There is exemplified a configuration illustrated in  FIG. 5 , which is illustrated as an example of the conventional technology. For example, in the configuration of  FIG. 4 , there is presumed a drive portion not including the drive section  520  but including only the drive section  510 . 
     In  FIG. 5 , a waveform P 1  represents a drive waveform for charging the load, a waveform N 1  represents a drive waveform for discharging the load, and a waveform Q represents a waveform indicating a voltage to be applied to the load. 
     In the waveform P 1  and the waveform N 1 , the state represented by “ON” represents a state in which a current to be caused to flow to the load is caused to flow, and the state represented by “OFF” represents a state in which a current to be caused to flow to the load is interrupted. In this case, it is assumed a case where the waveform for charging the load is output in a period from a time t 2  to a time t 4 . In a case where such a drive method as described above is performed, the waveform Q obtained as an output becomes a square waveform in which its crest value is limited by the power supply voltage (V). As described above, for example, when the charge/discharge of the load is controlled only by the drive section  510  of  FIG. 4 , it is only possible to obtain a square wave in which its crest value depends on the power supply voltage, and the fluctuations of the characteristics of the nozzles cannot be absorbed. 
       FIG. 6  is a diagram illustrating the drive waveforms generated by the drive portion of this embodiment. 
     The drive waveforms illustrated in  FIG. 6  are waveforms obtained by the configuration of  FIG. 4  illustrated as this embodiment. 
     In  FIG. 6 , a waveform P 1  represents a drive waveform for charging the load L by the main charge section  511 , a waveform P 2  represents a drive waveform for charging the load L by the pre-charge section  521 , a waveform N 1  represents a drive waveform for discharging the load L by the main discharge section  512 , a waveform N 2  represents a drive waveform for discharging the load L by the pre-discharge section  522 , and a waveform Q represents a waveform indicating a voltage to be applied to the load L. 
     In the waveform P 1 , the waveform P 2 , the waveform N 1 , and the waveform N 2 , the state represented by “ON” represents a state in which a current to be caused to flow to the load L is caused to flow by each section, and the state represented by “OFF” represents a state in which a current to be caused to flow to the load L is interrupted by each section. In this case, it is assumed a case where the waveform which maintains a state in which the load L is charged is output in a period from a time t 1  to the time t 4 . Note that, a period until the time t 1  and a period after the time t 4  are in states in which the voltage is not applied to the load L. 
     The state before the time t 1  is an initial state in which the discharge by the previously-generated drive waveform is completed, and as illustrated in order by the waveform P 1 , the waveform P 2 , the waveform N 1 , and the waveform N 2 , the main charge section  511 , the pre-charge section  521 , and the pre-discharge section  522  are in the “OFF” state in which the current is interrupted, and main discharge section  512  is in the “ON” state in which the current is caused to flow for discharge. 
     At the time t 1 , the states of the pre-charge section  521  and the main discharge section  512  are inverted, and thus only the pre-charge section  521  (waveform P 2 ) is set in the “ON” state, and the other sections are set in the “OFF” state. In short, the load L is set to a “pre-charging” state. As illustrated in the waveform Q, by maintaining this state, the load L (electrostatic capacitance C) is gradually charged in accordance with the elapse of time, and the voltage of the load L is charged up to a voltage ?V 1  when a time ?t 1  has elapsed (time t 2 ). 
     At the time t 2 , the states of the main charge section  511  and the pre-charge section  521  are inverted, and thus the main charge section  511  (waveform P 1 ) is set to the “ON” state, and the other sections are set to the “OFF” state. In short, the load L is set to a “main charging” state. 
     The voltage of the load L has been already charged up to the voltage ΔV 1  by the “pre-charging” until reaching the time t 2 . When the charging by the main charge section  511  (waveform P 1 ) is started, the voltage of the load L is charged instantaneously from the voltage ΔV 1  to the voltage V. By transiting the state as described above, a change of (V−ΔV 1 ) is generated in the voltage of the load L. 
     At the time t 3 , the states of the main charge section  511  and the pre-discharge section  522  are inverted, and thus only the pre-discharge section  522  (waveform N 2 ) is set to the “ON” state, and the other sections are set to the “OFF” state. In short, the load L is set to a “pre-discharging” state. As illustrated in the waveform Q, by maintaining this state, the load L (electrostatic capacitance C) is gradually discharged in accordance with the elapse of time, and after the elapse of a time Δt 2 , the voltage reduces by a voltage ΔV 2 . Thus, the load is in a state in which a voltage (V−ΔV 2 ) is charged (time t 4 ). 
     At the time t 4 , the states of the main discharge section  512  and the pre-discharge section  522  are inverted, and thus the main discharge section  512  (waveform N 1 ) is set to the “ON” state, and the other sections are set to the “OFF” state. In short, the load L is set to a “main discharging” state. 
     The voltage of the load L has already been in a state in which the voltage (V−ΔV 2 ) is charged by the “pre-charging” until reaching the time t 4 . When the discharging by the main discharge section  512  (waveform N 1 ) is started, through instantaneous discharging, the voltage of the load L changes from the voltage Δ(V−ΔV 2 ) to a reference potential. By transiting the state as described above, a voltage change of (V−ΔV/ 2 ) is generated in the voltage of the load L. 
     The adjustment portion  550  controls the drive portion  500  as described above, and thus the drive waveform illustrated as the waveform Q can be output from the drive portion  500 . 
     The voltage change generated at the time t 2  appears as a voltage change of a potential difference of (V−ΔV 1 ). The voltage change generated at the time t 4  appears as a voltage change of a potential difference of (V−ΔV 2 ). As described above, by adjusting the voltages ΔV 1  and ΔV 2 , the voltage width to be instantaneously-changed in the voltage to be applied to the pressure generating element PZT can be adjusted. The characteristics of the pressure generating element PZT for ejecting liquid droplets depend on the voltage width to be instantaneously-changed in the voltage to be applied to the pressure generating element PZT. Therefore, in accordance with the liquid droplet ejection characteristics of each nozzle, the voltages ΔV 1  and ΔV 2  are adjusted. In this manner, the fluctuations in liquid droplet ejection characteristics of the nozzles can be absorbed. 
     As described above, the pre-charge section  521  starts charging of the load L from the time t 1  that is faster by Δt 1  (predetermined time) determined in advance with respect to the time t 2 , and the pre-discharge section  522  starts discharging of the charges accumulated in the load L from the time t 3  that is faster by Δt 2  (predetermined time) determined in advance with respect to the time t 4 . In this manner, the fluctuations in liquid droplet ejection characteristics of the nozzles are absorbed. 
     Note that, at the time t 2 , the states of the main charge section  511  and the pre-charge section  521  are inverted, but there is a case where, when the timing to set the main charge section  511  (waveform P 1 ) to the “ON” state is delayed from the timing to set the pre-charge section  521  to the “OFF” state, unnecessary pressure fluctuations are generated in the pressure generation chamber. In this embodiment, adjustment is made so that, after the main charge section  511  (waveform P 1 ) is set to the “ON” state, the pre-charge section  521  is set to the “OFF” state, to thereby prevent the unnecessary pressure fluctuations from being generated in the pressure generation chamber. 
     Note that, the adjustment of the timings at the time t 2  can be made as follows. After the elapse of a predetermined time after the main charge section  511  (waveform P 1 ) is set to the “ON” state, the pre-charge section  521  is set to the “OFF” state. 
     Note that, at the time t 4 , the states of the main discharge section  512  and the pre-discharge section  522  are inverted, but there is a case where, when the timing to set the main discharge section  512  (waveform N 1 ) to the “ON” state is delayed from the timing to set the pre-discharge section  522  to the “OFF” state, unnecessary pressure fluctuations are generated in the pressure generation chamber. In this embodiment, adjustment is made so that, after the main discharge section  512  (waveform N 1 ) is set to the “ON” state, the pre-discharge section  522  is set to the “OFF” state, to thereby prevent the unnecessary pressure fluctuations from being generated in the pressure generation chamber. 
     Note that, the adjustment of the timings at the time t 4  can be made as follows. After the elapse of a predetermined time after the main discharge section  512  (waveform N 1 ) is set to the “ON” state, the pre-discharge section  522  is set to the “OFF” state. 
     As described above, by adjusting the timings at the times t 2  and t 4 , it is possible to prevent the unnecessary pressure fluctuations from being generated in the pressure generation chamber. Note that, the management of the timing to change each signal cannot be performed only by the four timings of the times t 1 , t 2 , t 3 , and t 4 , and, in order to manage the timings delayed from the times t 2  and t 4 , management of six timings is necessary for each nozzle. 
     (Second Embodiment) 
     With reference to  FIG. 7 , the drive waveforms generated by the drive portion are described.  FIG. 7  is a diagram illustrating drive waveforms generated by the drive portion of this embodiment. The drive waveforms illustrated in  FIG. 7  are waveforms obtained by the configuration of  FIG. 4  illustrated as this embodiment. 
     The drive method illustrated in  FIG. 7  is a drive method that performs transition of the states of the pre-charge section  521  (waveform P 2 ) and the pre-discharge section  522  (waveform N 2 ) at different timings from those in the above-mentioned drive method illustrated in  FIG. 6 . 
     In the above-mentioned drive method illustrated in  FIG. 6 , the adjustment of the timings at the times t 2  and t 4  needs to be cared, but, in the drive method described in this embodiment, such an adjustment is unnecessary. 
     In  FIG. 7 , similarly to  FIG. 6  described above, a waveform P 1  represents a drive waveform for charging the load L by the main charge section  511 , a waveform P 2  represents a drive waveform for charging the load L by the pre-charge section  521 , a waveform N 1  represents a drive waveform for discharging the load L by the main discharge section  512 , a waveform N 2  represents a drive waveform for discharging the load L by the pre-discharge section  522 , and a waveform Q represents a waveform indicating a voltage to be applied to the load L. 
     In the waveform P 1 , the waveform P 2 , the waveform N 1 , and the waveform N 2 , the state represented by “ON” represents a state in which a current to be caused to flow to the load L is caused to flow by each section, and the state represented by “OFF” represents a state in which a current to be caused to flow to the load L is interrupted by each section. In this case, it is assumed a case where the waveform which maintains a state in which the load L is charged is output in the period from the time t 1  to the time t 4 . 
     The state before the time t 1  is an initial state in which the discharge by the previously-generated drive waveform is completed, and as illustrated in order by the waveform P 1 , the waveform P 2 , the waveform N 1 , and the waveform N 2 , the main charge section  511  and the pre-charge section  521  are in the “OFF” state in which the current is interrupted, and the main discharge section  512  and the pre-discharge section  522  are in the “ON” state in which the current is caused to flow for discharge. 
     At the time t 1 , the states of the pre-charge section  521 , the main discharge section  512 , and the pre-discharge section  522  are inverted, and thus only the pre-charge section  521  (waveform P 2 ) is set in the “ON” state, and the other sections are set in the “OFF” state. In short, the load L is set to a “pre-charging” state. As illustrated in the waveform Q, by maintain this state, the load L (electrostatic capacitance C) is gradually charged in accordance with the elapse of time, and the voltage of the load L is charged up to the voltage ΔV 1  when the time Δt 1  has elapsed (time t 2 ). 
     At the time t 2 , the state of the main charge section  511  is inverted, and thus the main charge section  511  (waveform P 1 ) and the pre-charge section  521  (waveform P 2 ) are set to the “ON” state, and the other sections are set to the “OFF” state. In short, the load L is set to a “main charging” state. 
     The voltage of the load L has been already charged up to the voltage ΔV 1  by the “pre-charging” until reaching the time t 2 . When the charging by the main charge section  511  (waveform P 1 ) is started, the voltage of the load L is charged instantaneously from the voltage ΔV 1  to the voltage V. By transiting the state as described above, a change of (V−ΔV 1 ) is generated in the voltage of the load L. 
     At the time t 3 , the states of the main charge section  511 , the pre-charge section  521 , and the pre-discharge section  522  are inverted, and thus only the pre-discharge section  522  (waveform N 2 ) is set to the “ON” state, and the other sections are set to the “OFF” state. In short, the load L is set to a “pre-discharging” state. As illustrated in the waveform Q, by maintaining this state, the load L (electrostatic capacitance C) is gradually discharged in accordance with the elapse of time, and after the elapse of the time Δt 2 , the voltage reduces by the voltage ΔV 2 . Thus, the load is in a state in which the voltage (V−ΔV 2 ) is charged (time t 4 ). 
     At the time t 4 , the state of the main discharge section  512  is inverted, and thus the main discharge section  512  (waveform N 1 ) and the pre-discharge section  522  (waveform N 2 ) are set to the “ON” state, and the other sections are set to the “OFF” state. In short, the load L is set to a “main charging” state. 
     The voltage of the load L has already been in a state in which the voltage (V−ΔV 2 ) is charged by the “pre-charging” until reaching the time t 4 . When the discharging by the main discharge section  512  (waveform N 1 ) is started, through instantaneous discharging, the voltage of the load L changes from the voltage Δ(V−ΔV 2 ) to a reference potential. By transiting the state as described above, a voltage change of (V−ΔV 2 ) is generated in the voltage of the load L. 
     The adjustment portion  550  controls the drive portion  500  as described above, and thus the drive waveform illustrated as the waveform Q can be output from the drive portion  500 . 
     The voltage change generated at the time t 2  appears as a voltage change of a potential difference of (V−ΔV 1 ). The voltage change generated at the time t 4  appears as a voltage change of a potential difference of (V−ΔV 2 ). As described above, by adjusting the voltages ΔV 1  and ΔV 2 , the voltage width to be instantaneously-changed in the voltage to be applied to the pressure generating element PZT can be adjusted. The characteristics of the pressure generating element PZT for ejecting liquid droplets depend on the voltage width to be instantaneously-changed in the voltage to be applied to the pressure generating element PZT. Therefore, in accordance with the liquid droplet ejection characteristics of each nozzle, the voltages ΔV 1  and ΔV 2  are adjusted. In this manner, the fluctuations in liquid droplet ejection characteristics of the nozzles can be absorbed. 
     (Third Embodiment) 
     With reference to  FIG. 8 , details of the level converting circuit are described.  FIG. 8  is a diagram illustrating a configuration of the level converting circuit in this embodiment. 
     A level converting circuit  124 A illustrated in  FIG. 8  differs from the above-mentioned level converting circuit  124  illustrated in  FIG. 4  in that the drive section  520  (second drive section) is replaced by a drive section  520 A (second drive section). 
     The drive section  520 A controls the second current (I 2  or I 2 ′) to be caused to flow to/from the load L in accordance with the control signal from the adjustment portion  550 . The drive section  520 A includes a pre-charge section  521 A and a pre-discharge section  522 A. The pre-charge section  521 A includes a switch  5211  for interrupting the charge current (second current (I 2 )) to be caused to flow to the load L, and a current limiting section  5231 . The pre-discharge section  522 A includes a switch  5221  for interrupting the discharge current (second current (I 2 ′)) to be caused to flow from the load L, and a current limiting section  5232 . 
     The connection in the drive section  520 A is organized. The pre-charge section  521 A includes a power supply terminal, an output terminal, and a control signal input terminal. The power supply terminal of the pre-charge section  521 A is connected to the power supply Vd, and the output terminal thereof is connected to the main charge section  511 , the main discharge section  512 , and the load L. 
     The pre-discharge section  522 A includes a ground terminal, an output terminal, and a control signal input terminal. The ground terminal of the pre-discharge section  522 A is grounded (G), and the output terminal thereof is connected to a node connecting the main charge section  511 , the main discharge section  512 , and the load L. 
     The configuration of the drive section  520 A is different from the above-mentioned drive section  520  in detail, but the drive section  520 A can function similarly to the drive section  520 . 
     As described above, the current limiting section can be separated for charging and discharging. By separating the current limiting section for charging and discharging, it becomes easy to set the currents during charging and discharging independently. 
     The embodiments of the present invention have been described above, but the drive device  110  of the present invention is not limited to the illustrated example described above, and it is needless to say that various modifications can be made thereto without departing from the gist of the present invention. 
     For example, the drive methods described in the first and second embodiments can be combined to each other so that the drive method for the drive waveform rise employs the drive method of the first embodiment, and the drive method for the drive waveform fall employs the drive method of the second embodiment. 
     Further, for example, in the pre-charge section  521 A described in the third embodiment, the switch  5211  for interrupting the charge current (second current (I 2 )) to be caused to flow to the load L is connected in series to the current limiting section  5231 . The connection order of the switch  5211  and the current limiting section  5231  can be inverted from that illustrated in  FIG. 8 . 
     Further, in the pre-discharge section  522 A, the switch  5221  for interrupting the discharge current (second current (I 2 ′)) to be caused to flow from the load L is connected in series to the current limiting section  5232 . The connection order of the switch  5221  and the current limiting section  5232  can be inverted from that illustrated in  FIG. 8 . 
     Note that, any one of the current limiting section  5231  and the current limiting section  5232  may be configured as a constant current circuit.