Patent Publication Number: US-9889645-B2

Title: Inkjet head and ink jet printing apparatus using the head

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2014-251293, filed Dec. 11, 2014, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to an inkjet head and a printing apparatus. 
     BACKGROUND 
     A printing apparatus ejects ink once or a plurality of times on paper based on printing data to form images. An inkjet head ejects a given amount of ink every time. Thus, conventionally, there is a problem that the inkjet head cannot finely adjust the amount of ink to be ejected on the paper. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating an example of constitution of a printing apparatus according to an embodiment; 
         FIG. 2  is a cross-sectional view schematically illustrating an ejection section according to the embodiment; 
         FIG. 3  is a cross-sectional view illustrating a case in which the ejection section is in a PULL state according to the embodiment; 
         FIG. 4  is a cross-sectional view illustrating a case in which the ejection section is in a cancel state according to the embodiment; 
         FIG. 5  is a block diagram illustrating an example of constitution of a driving circuit according to the embodiment; 
         FIG. 6  is a diagram illustrating an example of constitution of a timer set according to the embodiment; 
         FIG. 7  is an example of a timer set selection table that is stored in a timer set-drop application register according to the embodiment; 
         FIG. 8  is a block diagram illustrating an example of constitution of printing data according to the embodiment; 
         FIG. 9  is a block diagram illustrating another example of the constitution of the printing data according to the embodiment; 
         FIG. 10  is a block diagram illustrating an example of constitution of waveform frame/waveform distribution control section according to the embodiment; 
         FIG. 11  is a diagram schematically illustrating an example of constitution of an HV switch section and the ejection section according to the embodiment; 
         FIG. 12  is a timing chart illustrating the voltage that is applied to an actuator of the ejection section according to the embodiment; 
         FIG. 13  is another timing illustrating the voltage that is applied to the actuator of the ejection section according to the embodiment; 
         FIG. 14  is still another timing chart illustrating the voltage that is applied to the actuator of the ejection section according to the embodiment; 
         FIG. 15  is a timing chart illustrating the voltages corresponding to multiple ink drops that are applied to the actuator of the ejection section according to the embodiment; 
         FIG. 16  is a timing chart illustrating the amount of ink ejected by the ejection section according to the embodiment; and 
         FIG. 17  is a timing chart illustrating the timings at which the ejection section ejects ink drops according to the embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In accordance with an embodiment, an inkjet head comprises an ejection section and a driving section. The ejection section ejects ink according to the operations of an actuator. In order to make the ejection section eject different amount of ink for different drops, the driving section applies voltage to the actuator of the ejection section such that the ejection section ejects ink continuously based on the printing data indicating the times the ejection section ejects ink and a position flag designating a drop frame number where ink starting to be ejected. 
     Hereinafter, the present embodiment is described with reference to the accompanying drawings. 
     Though in the present embodiment the inkjet head is a share mode or a shared-wall system, the inkjet head is not limited to a specific system. 
       FIG. 1  is a block diagram illustrating an example of constitution of a printing apparatus according to the embodiment. 
     In the constitution example shown in  FIG. 1 , a printing apparatus  1  comprises a CPU  11 , a ROM  12 , a RAM  13 , a communication I/F  14 , a head controller  15 , motor drivers  16  and  17 , an inkjet head  18 , a conveyance motor  19  and a carriage motor  20 . 
     The CPU  11  controls the whole printing apparatus  1 . The CPU  11  is a processor which executes programs to realize various processing. The CPU  11  connects with all sections inside the printing apparatus  1  through a system bus and the like. According to an operation instruction from an external device, the CPU  11  outputs the operation instruction to each section of the printing apparatus  1 , and then informs the external device of various information acquired from each section of the printing apparatus  1 . 
     The ROM  12  is a non-volatile memory which stores programs and control data in a non-rewritable manner. The RAM  13  is a volatile memory. The RAM  13  is a working memory, or a buffer memory. The CPU  11  executes the programs stored in the ROM  12  to realize various processing while using the RAM  13 . Further, the printing apparatus  1  may include a non-volatile rewritable memory. 
     The communication I/F  14  is an interface used to communicate with the external device. For example, the communication I/F  14  receives a print data corresponding to a print request from the external device. As long as the communication I/F  14  is an interface used to carry out data transmission/reception with the external device, no limitation is given to its form. For example, the communication I/F  14  may be connected to the external device locally, or may be a network interface used to communicate with the external device via a network. 
     The head controller  15  drives the inkjet head  18  based on signals from the CPU  11 . The head controller  15  is electrically connected to a driving circuit  22  of the inkjet head  18 . The CPU  11  transmits the print data and control signals to the driving circuit  22  through the head controller  15 . The control signals may be a shift clock signal, a latch pulse signal, a timing pulse signal and the like. The head controller  15  may also supply electric power, a clock signal and a reset signal to the driving circuit  22 . 
     The motor driver  16  drives the conveyance motor  19  based on the instructions from the CPU  11 . The motor driver  17  drives the carriage motor  20  based on the instructions from the CPU  11 . 
     The conveyance motor  19  drives a roller for conveying a printing medium used in the printing process by the printing apparatus  1  based on the instructions from the motor driver  16 . For example, the conveyance motor  19  drives a pickup roller, a conveyance roller and the like. The CPU  11  controls the conveyance motor  19  through the motor driver  16  to send the printing medium to positions where the inkjet head  18  ejects ink. 
     The carriage motor  20  drives a roller which is connected with a carriage comprising the inkjet head  18  based on the instructions from the motor driver  17 . The CPU  11  controls the carriage motor  20  through the motor driver  17  to arrange the inkjet head  18  to predetermined positions. 
     The inkjet head  18  ejects ink on the printing medium based on the instructions from the head controller  15 . That is, the CPU  11  enables the inkjet head  18  to eject ink with the head controller  15 . The inkjet head  18  comprises an ejection section  21  and the driving circuit  22 . 
     The ejection section  21  ejects ink on the printing medium based on the signals from the driving circuit  22 . The ejection section  21  fills a pressure chamber with ink using the voltage applied by the driving circuit  22 , and ejects the filled ink on the printing medium. 
     The conveyance motor may convey the printing medium at a constant speed at a right angle to the direction of nozzle row of the inkjet head, and drive a fixed inkjet head to carry out printing processing, or may convey the carriage motor at a constant speed at a right angle to the direction of nozzle row of the inkjet head to carry out printing processing in a state in which the printing medium is still. It may also be constituted in such a manner that in a state in which both the conveyance motor and the carriage motor are stopped, the inkjet head is driven to make the ink adhere to the printing medium, and then either the conveyance motor or the carriage motor moves a little to print at other position. The conveyance motor and the carriage motor may either have one integrated axis orthogonal to each other, or have two axes orthogonal to each other respectively. 
     For example, the printing medium is a paper, and it is not limited to a specific medium. The printing apparatus may print on a three-dimensional structure directly, may be an apparatus which forms the three-dimensional structure directly though the printing, or may be a printing apparatus which may dispense ink to the fine dispensing grooves of the printing medium. Further, the printing apparatus  1  may also not comprise the motor driver  16 , the motor driver  17 , the conveyance motor  19 , and the carriage motor  20 . In this case, the printing apparatus may print an image on a fixed printing medium or on a printing medium conveyed by other apparatus. 
       FIG. 2  is a cross-sectional view schematically illustrating the ejection section  21 . 
     As shown in  FIG. 2 , the ejection section  21  comprises a first piezoelectric member  31 , second piezoelectric members  32   a  and  32   b , electrodes  33   a ˜ 33   c , leads  34   a ˜ 34   c  and a top plate  35 . 
     The ejection section  21  has a constitution in which the first piezoelectric member  31  is joined to a top surface of a base plate (not shown), and the second piezoelectric member  32  is joined to the first piezoelectric member  31 . The first piezoelectric member  31  and the second piezoelectric member  32  are polarized in the opposite directions along the thickness direction of plate to be joined with each other. The ejection section  21  is provided with many long grooves from one end towards the other end of each of the joined first piezoelectric member  31  and the second piezoelectric member  32 . The grooves are arranged in parallel to each other and at given intervals. 
     The first piezoelectric member  31  and the second piezoelectric member  32   a  constitute an actuator  37   a . Similarly, the first piezoelectric member  31  and the second piezoelectric member  32   b  constitute an actuator  37   b . A voltage is applied from the driving circuit  22  to the actuators  37   a  and  37   b  through the electrode  33 . By applying the voltage, the actuators  37   a  and  37   b  change the volume of the pressure chamber  36   a.    
     The electrodes  33   a ˜ 33   c  are arranged on the side wall and bottom of each groove in the ejection section  21 . The leads  34   a ˜ 34   c  which direct from the inside to the outside of each grove and extend from the electrodes  33   a ˜ 33   c  are arranged in the ejection section  21 . 
     The top plate  35  is arranged above the grooves in the ejection section  21 . The top plate  35  and the electrode  33   a  constitute a pressure chamber  36   a  inside. Similarly, the top plate  35  and the electrode  33   b  constitute a pressure chamber  36   b  inside. The top plate  35  and the electrode  33   c  constitute a pressure chamber  36   c  inside. 
     In order to fill ink, the pressure chamber  36  is connected with a supply port which receives the supply of ink from an ink tank (not shown). Further, the pressure chamber  36  is connected with an ejection port for ejecting ink. 
     The electrode  33   a  and the electrode  33   b  apply a voltage to the actuator  37   a . That is, a difference of voltages between the voltage applied by the electrode  33   a  and the voltage applied by the electrode  33   b  is applied to the actuator  37   a . Similarly, the electrode  33   a  and the electrode  33   c  apply a voltage to the actuator  37   b.    
     In the example shown in  FIG. 2 , the channels for ejecting ink are applied with reference numerals No.  0 ˜ No.  2 , and the ejection section  21  may be provided with much more channels. 
     The ejection section  21  drives two actuators  37  and three electrodes  33  to eject (drop) the ink from nozzles arranged in one pressure chamber  36  on the printing medium. 
     For example, in a case of ejecting ink from the No.  1  channel, the ejection section  21  drives the actuators  37   a  and  37   b  to eject the ink from the nozzles arranged in a pressure chamber  36   a  to the printing medium. When one channel is ejecting ink, the adjacent channels to the one channel cannot eject ink at the same time. 
     For example, in a case of ejecting ink from the No.  1  channel, the ejection section  21  cannot eject ink from the No.  0  channel and the No.  2  channel. 
     The ejection operation is carried out three times by shifting channels one by one, and in this way, the ejection section  21  can eject ink from any one of all the channels. 
     The ejection section  21  can continuously eject ink from the channels for a plurality of times. For example, based on an instruction from the driving circuit  22 , the ejection section  21  ejects ink to a thick-print part for a plurality of times and ejects ink once or a few times to a thin-print part. The ejection section  21  can control the number of times of ejecting ink to adjust the shade of color. It is assumed herein that the ejection section  21  can continuously eject ink from the channels for seven times. Further, the number of the times that the ejection section  21  can continuously eject ink is not limited to a specific number of times. 
       FIG. 3  is a cross-sectional view schematically illustrating the ejection section  21  that is in a state (PULL state) in which the ink is filled. 
     In the example shown in  FIG. 3 , the channel capable of ejecting ink is the No.  1  channel. 
     In order to fill ink, the driving circuit  22  applies a voltage to the actuators  37   a  and  37   b  through the electrodes  33   a ˜ 33   c  to drive the actuators. As a result, the actuators  37   a  and  37   b  deform as shown in  FIG. 3 . 
     As shown in  FIG. 3 , the actuator  37   a  bends towards the inside of the pressure chamber  36   b  of the No.  0  channel serving as the adjacent channel. Similarly, the actuator  37   b  bends towards the inside of the pressure chamber  36   c  of the No.  2  channel serving as the adjacent channel. 
     As a result, the volume of the pressure chamber  36   a  increases when compared to the release state (the state shown in  FIG. 2 ), and the ink is filled from the ink supply port to the inside of pressure chamber  36   a.    
     When returning from the PULL state to the release state, the volume of the pressure chamber  36   a  returns to its initial state. In this way, the ejection section  21  ejects ink from an ejection port corresponding to the No.  1  channel on the printing medium. 
       FIG. 4  is a cross-sectional view schematically illustrating the ejection section  21  that is in a cancel state. 
     After an appropriate time elapses since the ejection operation is completed, the ejection section  21  sets the actuators to the cancel state for canceling the vibration generated in the actuators  37  due to the ejection operation. 
     In order to enable the actuators to be in the cancel state, the driving circuit  22  applies a voltage to the actuators  37   a  and  37   b  through the electrodes  33   a ˜ 33   c  to drive the actuators. Consequently, the actuators  37   a  and  37   b  deform as shown in  FIG. 4 . 
     During the period the voltage is applied to the actuators  37   a  and  37   b , the actuator  37   a  bends towards the inside of the pressure chamber  36   a  as shown in  FIG. 4 . Similarly, the actuator  37   b  bends towards the inside of pressure chamber  36   a . That is, the volume of the pressure chamber  36   a  decreases when compared to the release state (the state shown in  FIG. 2 ). After the cancel state is kept for a while and an appropriate time elapses, the voltage applied to the actuators  37   a  and  37   b  is returned to zero. As a result, the actuators  37   a  and  37   b  return to the state shown in  FIG. 2 . In this way, the ejection section  21  can suppress the vibration and the like generated in the actuators  37  while ejecting ink. 
     Next, the driving circuit  22  (driving section) is described. 
     The driving circuit  22  drives the ejection section  21  to eject ink based on an instruction from the head controller  15 . By applying a voltage to the electrodes  33  of the ejection section  21 , the driving circuit  22  drives and deforms the actuators  37  of the ejection section  21 . By driving the actuators  37 , the driving circuit  22  enables the ink to be filled in the ejection section  21  and to be ejected on the printing medium. The driving circuit  22  is electrically connected with the electrode  33  of each channel of the ejection section  21 . For example, the driving circuit  22  is constituted by IC. 
     In the present embodiment, the driving circuit  22  applies a voltage to the actuators  37  of the channels, resulting to eject different amount of ink for different drops. 
       FIG. 5  is a block diagram illustrating an example of constitution of the driving circuit  22 . 
     As shown in  FIG. 5 , the driving circuit  22  comprises an ACT register  41 , an INA register  42 , a NEG register  43 , a NEGINA register  44 , a timer set register  45 , a timer set-drop application register  46 , a waveform generation section  47 , a waveform frame/waveform distribution control section  48 , a division order designation register  49 , an HV switch section  50 , a drop sequence generation section  60  and the like. 
     The ACT register  41  stores information (pattern) for ejecting ink indicating the voltage levels of waveform segments which is applied to the electrodes of the channels that is capable of ejecting ink (target electrodes, No.  1  channel in  FIG. 2 ). That is, the ACT register  41  determines the voltage levels of the waveform of the ACT voltage. The ACT register  41  stores voltage information indicating a voltage applied during each period of the waveform segments in an associated manner. For example, the ACT register  41  stores “+”, “VSS” or “−” as the voltage information corresponding to the period of the waveform segments of ACT voltage. Herein, the “+” represents that +VAA voltage is applied to the target electrodes. The “VSS” represents that a voltage of 0V is applied to the target electrodes. The “−” represents −VAA voltage is applied to the target electrodes. 
     For example, the ACT register  41  stores “VSS, −, −, +” as the voltage information. In this example, it indicates that the ACT register  41  stores the voltage of 0V applied to the target electrodes in the first period of the ACT voltage, stores −VAA applied to the target electrodes in the second and third periods, and stores +VAA applied to the target electrodes in the fourth period. No limitation is given to the form of the pattern stored in the ACT register  41 . 
     The number of elements stored in the ACT register  41  is determined according to the number of waveform elements of the ACT voltage. Further, the ACT register  41  may be a fixed register where the patterns are written when manufacturing, or a rewritable register. If the ACT register  41  is a rewritable register, the values of the timer set register  45  may be stored through an initial setting from the CPU  11 , or may be stored or changed by the CPU  11  at any timing. 
     The INA register  42  stores a pattern for ejecting ink indicating the voltage levels of waveform segments that is applied to the electrodes of the channels adjacent to the channel capable of ejecting ink (adjacent electrodes, the No.  0  channel, and the No.  2  channel shown in  FIG. 2 ). That is, the INA register  42  determines the voltage levels of the waveform of the INA voltage. 
     The NEG register  43  stores a pattern of a voltage (NEG voltage) that is applied to the target electrodes in a case of not ejecting ink from the channel that is capable of ejecting ink. 
     The NEGINA register  44  stores a pattern of a voltage (NEGINA voltage) that is applied to the adjacent electrodes in a case of not ejecting ink from the channel that is capable of ejecting ink. Alternatively, the INA register  42  may be substituted for the NEGINA register  44 . 
     The constitutions of the INA register  42 , the NEG register  43  and the NEGINA register  44  are identical to the constitution of the ACT register  41 , and therefore the detailed descriptions thereof are not provided. 
     As stated above, each register described above stores the voltage pattern applied to the electrodes of the actuators. 
     On the other hand, the timer set register  45  stores a series of time intervals (timer set) of each period of the pattern of voltage. The timer set is constituted by time information indicating time interval of each period. The number of time information stored in the timer set may be identical to or different from the number of segments of the voltage pattern. The timer set register  45  may further store an ending time tdp at which the generation of voltage waveform by the waveform generation section  47  should be ended. 
     The timer set register  45  may be stored in advance as a non-rewritable and fixed register in the driving circuit  22 . Alternatively, the timer set register  45  may be a rewritable register in the driving circuit  22 . When the timer set register  45  is a rewritable register, the values of the timer set register  45  may be stored through an initial setting from the CPU  11 , or may be stored or changed by the CPU  11  at any timing. 
     In the example shown in  FIG. 5 , the timer set register  45  has plural timer sets. The timer set register  45  consists of a timer set Ta register  45   a , a timer set Tb register  45   b , a timer set Tc register  45   c  and a timer set Td register  45   d.    
     The timer set Ta register  45   a  stores a timer set Ta. 
     The timer set Tb register  45   b  stores a timer set Tb which is different from the timer set Ta. The timer set Tc register  45   c  stores a timer set Tc which is different from both the timer set Ta and the timer set Tb. The timer set Td register  45   d  stores a timer set Td which is different from each of the timer sets Ta˜Tc. 
       FIG. 6  is a diagram illustrating an example of constitution of the timer sets Ta˜Td. 
     In one embodiment, each timer set stores t 0 ˜t 10  as the time information as shown in  FIG. 6( a ) . The time information of a timer set indicates time intervals of the waveform segments. Further, the order of the time information corresponds to the order of the waveform segments. 
     For example, the timer set Ta register  45   a  stores “t 0   a , t 1   a , t 2   a , t 3   a  . . . ” as the timer set Ta. For example, the timer set Ta register  45   a  indicates that the first period is “t 0   a”.    
     In another embodiment, as shown in  FIG. 6( b ) , each timer set stores the time information indicating time intervals and the ending time tdp at which the generation of voltage waveform by the waveform generation section  47  is ended. The time information “t 0   a , t 1   a , t 2   a , t 3   a  . . . , t 9   a ” is identical to the time information shown in  FIG. 6( a ) . 
     The ending time tdp may be longer than or shorter than a sum of the time intervals indicated by corresponding time information. In a case in which the ending time tdp is longer than the sum of time intervals, the waveform generation section  47  applies a voltage of 0V to both the electrode of the target channel and the electrodes of the adjacent channels after the time interval indicated by the final time information elapses. 
     Each timer set of Ta˜Td may store the different ending time tdp respectively, or store the identical ending time tdp. 
     In a case in which the timer set stores the ending time tdp, the waveform generation section  47  ends the generation of waveform for an ejection operation of one ink droplet at the ending time tdp. This is an end of a drop frame. Then the waveform generation section  47  starts generation of waveform for next drop frame, for an ejection operation of next ink droplet if it exists. Here, “drop frame” is a time frame prepared for one ink droplet to be ejected. 
     Further, the timer set register  45  may store not only the timer set including the ending time tdp but also the time set not including the ending time tdp. 
     The timer set-drop application register  46  sends a selection signal for designating a timer set to be selected by a selector  47   a  to the selector  47   a . The selection signal indicates the timer set selected by the selector  47   a . That is, the selector  47   a  selects a timer set based on the selection signal sent by the timer set-drop application register  46 . 
     The timer set-drop application register  46  sends a selection signal every time the waveform generation section  47  generates a waveform, that is, the timer set-drop application register  46  sends a selection signal on each drop frame. Alternative structure is that the timer set-drop application register  46  sends all of the selection signals corresponding to every drop frames to the selector  47   a  simultaneously, and the selector  47   a  selects the selection signal on each drop frame in order. 
       FIG. 7  is an example of a timer set selection table stored in the timer set-drop application register  46 . The timer set selection table stores the drop frame number and the timer set in an associated manner. 
     The timer set-drop application register  46  sends the selection signal to the selector  47   a  based on the timer set selection table. That is, the timer set-drop application register  46  sends a selection signal for selecting a timer set corresponding to the drop frame number to the selector  47   a.    
     For example, the timer set-drop application register  46  sends a selection signal used for selecting the timer set Ta as the timer set of the first drop frame of ink to the selector  47   a.    
     Every time just after the waveform generation section  47  generates a waveform corresponding to one drop of ink, the timer set-drop application register  46  sends a selection signal corresponding to the next drop of ink to the selector  47   a . In the alternative structure mentioned above, the timer set-drop application register  46  sends the selection signals corresponding to all drops of ink to the selector  47   a , before the waveform generation section  47  generates the waveform corresponding to the drops of ink. 
     The waveform generation section  47  generates a waveform of voltage applied to the ejection section  21  based on the selection signal sent by each of the ACT register  41 , the INA register  42 , the NEG register  43 , the NEGINA register  44 , the timer set Ta register  45   a , the timer set Tb register  45   b , the timer set Tc register  45   c , the timer set Td register  45   d  and the timer set-drop application register  46 . The waveform generation section  47  generates a waveform of voltage by combining the pattern with the timer set. 
     For example, in a case of generating the waveform of ACT voltage, the waveform generation section  47  combines a pattern stored in the ACT register  41  with a timer set (for example, the timer set Ta) to generate the waveform of ACT voltage. In this case, the waveform generation section  47  sets the time of the first period of the voltage waveform to “t 0   a ” based on the timer set Ta. Further, the waveform generation section  47  sets the voltage in the first period of the ACT voltage to be “VSS” based on the information stored in the ACT register  41 . The waveform generation section  47  carries out the same operations in all periods to generate the waveform of the ACT voltage. 
     As shown in  FIG. 5 , the waveform generation section  47  is provided with the selector  47   a  and a timer  47   b.    
     The selector  47   a  selects a timer set from a plurality of timer sets (the timer sets Ta, Tb, Tc and Td in  FIG. 5 ) which is used to generate a voltage waveform. The selector  47   a  selects a timer set for each drop frame. For example, the selector  47   a  selects the timer set Ta for the first and the second drop frame, and selects the timer set Tb for the third and the fourth drop frame. The selector  47   a  selects the timer sets for the purpose of that the volume of the ejected ink becomes a predetermined volume. For example, the selector  47   a  selects the timer sets Ta for the drop volume of 5.5 pl ejected at first and the second drop frame, and selects the timer sets Tb for the drop volume of 6 pl ejected at third and the fourth drop frame. 
     The selector  47   a  sends the selected timer sets to the timer  47   b.    
     The timer  47   b  sets the length of each period of each voltage segment based on the timer sets selected by the selector  47   a . The timer  47   b  informs whole of the waveform generation section  47  about the end of the segment using a signal at the end of each period. 
     Further, in a case in which the timer set selected by the selector  47   a  stores an ending time tdp, the timer  47   b  sets the ending time tdp. In this case, for example, the timer  47   b  measures the time after the ejection operation is started. When the measured time reaches the ending time tdp, the timer  47   b  issues a signal to inform whole of the waveform generation section  47  that the ending time elapses. 
     The waveform generation section  47  generates a voltage waveform based on the length of each period set by the timer  47   b  and the voltage pattern, and sends the generated waveform to the waveform frame/waveform distribution control section  48 . 
     For generating a waveform of the ACT voltage, the waveform generation section  47  acquires information indicating the voltage of the first period from the ACT register  41 . Then, the waveform generation section  47  sends an instruction to apply the voltage indicated by the acquired information to the waveform frame/waveform distribution control section  48 . When the timer  47   b  informs the ending of the first period, the waveform generation section  47  acquires information indicating the voltage of the second period. Then, the waveform generation section  47  sends an instruction to apply the voltage indicated by the acquired information to the waveform frame/waveform distribution control section  48 . The waveform generation section  47  carries out the same operations for all periods to generate the waveform of the ACT voltage. 
     Through the operations similar to that described above, the waveform generation section  47  generates a waveform of the INA voltage, a waveform of the NEG voltage and a waveform of the NEGINA voltage. 
     For the same drop frame, the waveform generation section  47  applies a same timer set for any one of voltage waveforms. For example, for the first drop frame, the waveform generation section  47  applies the timer set Ta including t 0   a , t 1   a , t 2   a , . . . for any one of the voltage waveforms. Further, for the second drop frame, the waveform generation section  47  applies the timer set Tb for any one of the voltage waveforms. 
     The waveform frame/waveform distribution control section  48  generates a switch control signal used to apply a voltage to the electrodes of each channel. The waveform frame/waveform distribution control section  48  generates a switch control signal for applying the ACT voltage or the NEG voltage as the switch control signal of a group (target division) of channels capable of ejecting ink simultaneously. Further, the waveform frame/waveform distribution control section  48  generates a switch control signal for applying the INA voltage or the NEGINA voltage as the switch control signal of a group (adjacent division) of channels adjacent to the channels capable of ejecting ink. 
     The division order designation register  49  stores an order for setting the group capable of ejecting ink. 
     The waveform frame/waveform distribution control section  48  and the division order designation register  49  are described in detail later. 
     The HV switch section  50  applies a voltage to the actuators  37  of each channel based on the switch control signal from the waveform frame/waveform distribution control section  48 . 
     The HV switch section  50  is described in detail later. 
     The drop sequence generation section  60  generates a drop sequence based on the printing data and the position flag sent by the CPU  11  through the head controller  15 . 
     The printing data designates the times of ejecting ink for each channel. For example, the printing data may be represented by code data (e.g. the coded data representing the number of drops). Further, the printing data may indicate the times of ejecting ink by the channels with a sequence of 1/0 signals (binary signal). 
     The position flag designates a timing at which a channel starts to eject ink. The position flag designates a drop frame number of which the drop starting to be ejected. For example, in a case in which the position flag indicates “4”, the channel starts to eject ink from the fourth drop frame. 
     The drop sequence indicates the times and the timing of ejecting ink from the channel with 1/0 signals (binary signal) “1” represents ejection of ink, and “0” represents no ejection of ink. The drop sequence stores the 1/0 signals of the number which is as same as the number of times the channel can eject ink droplet continuously. 
     The drop sequence generation section  60  generates a drop sequence in such a manner that the channel starts to eject ink droplet from the drop frame number indicated by the position flag and continue to eject ink droplets of the number which is indicated by the printing data. 
     The drop sequence generation section  60  sends the generated drop sequence to the waveform frame/waveform distribution control section  48 . 
       FIG. 8  is an example of the constitutions of the printing data, the drop sequence and the number of drop. 
     It is assumed herein that the position flag is indicated by “4”. Further, in the drop sequence, “1” indicates the ejection of ink, and “0” indicates no ejection of ink. 
     Furthermore, it is also assumed that each channel can eject ink 7 times continuously. Thus, the printing data is constituted by 3-bit code data. 
     As shown in  FIG. 8 , the drop sequence is constituted in such a manner that the channel starts to eject ink from the fourth drop frame. For example, the drop sequence corresponding to the printing data “010” is constituted in such a manner that the channel ejects ink twice from the fourth drop frame. 
       FIG. 9  is an example of the constitutions of the position flag and the drop sequence. 
     It is assumed that the printing data is “011”. That is, the number of drop is 3. 
     As shown in  FIG. 9 , the drop sequence is constituted in such a manner that the channel starts to eject ink from the drop frame number indicated by the position flag. For example, the drop sequence corresponding to the position flag “2” is constituted in such a manner that the channel ejects ink three times from the second drop. 
     As stated above, instead of generating the drop sequence through the printing data and the position flag, the drop sequence can be supplied directly from the head controller  15  to the driving circuit  22  without equipping with the drop sequence generation section. 
       FIG. 10  is a block diagram illustrating an example of the constitution of the waveform frame/waveform distribution control section  48 . 
     As shown in  FIG. 10 , the waveform frame/waveform distribution control section  48  comprises a data transmission and latch control section  51 , an adjacent waveform control section  52 , a target waveform control section  53  and a division control section  54 . 
     The data transmission and latch control section  51  acquires the drop sequence. 
     The data transmission and latch control section  51  transmits the timings when the channels eject ink to the adjacent waveform control section  52  and the target waveform control section  53  based on the drop sequence. 
     Based on the timings when the channels eject ink, the adjacent waveform control section  52  sets a waveform of the voltage applied to the electrodes  33  of the channels (adjacent channels) adjacent to the channel (target channel) capable of ejecting ink. For example, the adjacent waveform control section  52  sets an INA voltage waveform or a NEGINA voltage waveform as the waveform of voltage which is applied to the adjacent channels. In a case in which the target channel ejects ink, the adjacent waveform control section  52  sets the INA voltage waveform as the waveform of voltage which is applied to the adjacent channels adjacent to the target channel. Further, in a case in which the target channel doesn&#39;t eject ink, the adjacent waveform control section  52  sets the NEGINA voltage waveform as the waveform of voltage which is applied to the adjacent channels adjacent to the target channel. 
     Based on the timings when the channels eject ink, the target waveform control section  53  sets a waveform of the voltage applied to the electrodes  33  of the channel capable of ejecting ink. For example, the target waveform control section  53  sets an ACT voltage waveform or a NEG voltage waveform as the waveform of voltage which is applied to the target channel. In a case in which the target channel ejects ink, the target waveform control section  53  sets the ACT voltage waveform as the waveform of voltage which is applied to the target channel. In a case in which the target channel doesn&#39;t eject ink, the target waveform control section  53  sets the NEG voltage waveform as the waveform of voltage which is applied to the target channel. 
     The division control section  54  sets a target channel group (target division) and an adjacent channel group (adjacent division) based on the division order stored in the division order designation register  49 . The division control section  54  sends a switch control signal based on the waveform set by the target waveform control section  53  to the HV switch section  50  as a switch control signal corresponding to the channel of the target division. Further, the division control section  54  sends a switch control signal based on the waveform set by the adjacent waveform control section  52  to the HV switch section  50  as a switch control signal corresponding to the channel of the adjacent division. 
     The division order designation register  49  stores the order for setting the group of channels capable of ejecting ink. For example, the division order designation register  49  may store information indicating that, first a group of channels having No. 3n+1 (n represents natural number including 0) is set as the target division, next a group of channels having No. 3n+2 is set as the target division, and finally a group of channels having No. 3n+3 is set as the target division. 
     In this example, the division control section  54  firstly sets the group of channels having No. 3n+1 (first division) as the target division. At this time, the division control section  54  sets the group of channels having No. 3n+2 and the group of channels having No. 3n+3 as the adjacent division. 
     After the ejection operation of the target division is ended, the division control section  54  sets the group of channels having No. 3n+2 (second division) as the target division. At this time, the division control section  54  sets the group of channels having No. 3n+1 and the group of channels having No. 3n+3 as the adjacent division. 
     After the ejection operation of the target division is ended, the division control section  54  sets the group of channels having No. 3n+3 (third division) as the target division. At this time, the division control section  54  sets the group of channels having No. 3n+1 and the group of channels having No. 3n+2 as the adjacent division. 
     With the operations described above, the division control section  54  can control to eject ink from all channels. 
       FIG. 11  is a block diagram illustrating an example of constitution of the HV switch section  50  (voltage applying section). 
     As shown in  FIG. 11 , the HV switch section  50  comprises a +VAA switch  61 , a −VAA switch  62  and a VSS switch  63 . 
     The +VAA switch  61  is a switch connecting the +VAA as a positive voltage supply with the electrodes  33  of a channel. 
     The −VAA switch  62  is a switch connecting the −VAA as a negative voltage supply with the electrodes  33  of a channel. 
     The VSS switch  63  is a switch connecting the VSS (ground) with the electrodes  33  of a channel. 
     The three switches operate exclusively. That is, if one of the three switches is connected with the electrodes  33 , the left two switches never connect with the electrodes  33 . 
     For example, the +VAA switch  61 , the −VAA switch  62  and the VSS switch  63  are constituted with an MOS transistor and the like. 
     In the present embodiment, the range of the +VAA is +7V˜+18V. Further, the range of the −VAA is −7V˜−18V. Neither the +VAA nor the −VAA is limited to a specific voltage. 
     Herein, the HV switch section  50  comprises the +VAA switch  61   b , the −VAA switch  62   b  and the VSS switch  63   b  as the switches corresponding to the No.  0  channel. Further, the HV switch section  50  comprises the +VAA switch  61   a , the −VAA switch  62   a  and the VSS switch  63   a  as the switches corresponding to the No.  1  channel. The HV switch section  50  also comprises the +VAA switch  61   c , the −VAA switch  62   c  and the VSS switch  63   c  as the switches corresponding to the No.  2  channel. 
     For example, when receiving a signal connecting with the “+VAA” as a switch control signal on the No.  1  channel, the HV switch section  50  turns off the −VAA switch  62   a  and the VSS switch  63   a , and turns on the +VAA switch  61   a . Through this operation, the HV switch section  50  applies +VAA to the electrodes  33  of the No.  1  channel. 
     Next, the voltage applied to the actuators  37  is described. 
       FIG. 12  is a timing chart indicating the voltage applied to the actuators  37 , the ACT voltage and the INA voltage. 
     The timing chart shown in  FIG. 12  represents each voltage when the target channel ejects one ink droplet at one drop frame. 
     An actuator voltage represents a voltage applied to the actuators  37  of the target channel. In the example shown in FIG.  2 , when the target channel is the No.  1  channel, the actuator voltage is the voltage applied to the actuator  37   a  and the actuator  37   b . A polarity of the voltage applied to the actuators  37  is defined to be positive if the voltage of electrode  33  of the target channel is positive relative to the opposite side of the actuator  37 , and defined to be negative if the voltage of electrode  33  of the target channel is negative relative of the opposite side of the actuator  37 . 
     As shown in  FIG. 12 , first, a negative voltage is applied to the actuator  37   a  and the actuator  37   b . When the negative voltage is applied, the actuator  37   a  and the actuator  37   b  become the PULL state shown in  FIG. 3 . At this time, the pressure chamber  36   a  attracts ink from the ink tank. 
     Then a voltage of 0V is applied to the actuator  37   a  and the actuator  37   b . When the voltage of 0V is applied, the actuator  37   a  and the actuator  37   b  become the release state shown in  FIG. 2 . At this time, the ink is ejected from the pressure chamber  36   a  on the printing medium. 
     Then a positive voltage is applied to the actuator  37   a  and the actuator  37   b . At this time, the actuator  37   a  and the actuator  37   b  become the cancel state shown in  FIG. 4 . Then, a voltage of 0V is applied to the actuator  37   a  and the actuator  37   b . At this time, the ejection operation of one ink droplet is ended. 
     The ACT voltage applied to the electrode  33   a  is generated with the pattern of the ACT voltage and the timer set. In the example in  FIG. 12 , the pattern of ACT voltage in the first period is “VSS”. Further, the timer set indicates that the first period has a time length of “t 0 ”. Thus, the first period of the ACT voltage is the t 0  time, and the ACT voltage in the first period is “0”. 
     Similarly, the pattern of ACT voltage in the second period is “−”. Further, the timer set indicates that the second period has a time length of “t 1 ”. Thus, the second period of the ACT voltage is the t 1  time, and the ACT voltage during the second period is “−VAA”. 
     Similarly, in each period of the ACT voltage segment, the length and the voltage thereof are determined. 
     The INA voltage is also generated similarly. The voltage applied to the actuators  37  is the difference of voltage between the ACT voltage and the INA voltage. 
     If the polarization direction of a first piezoelectric member  31  and second piezoelectric members  32   a  is opposite to this embodiment, the polarity of the voltage applied to the electrodes  33  should be the opposite polarity. 
       FIG. 13  is another timing chart illustrating the voltage applied to the actuators  37 , the ACT voltage and the INA voltage. 
     In the example shown in  FIG. 13 , the timer set doesn&#39;t contain t 10  but contains the ending time tdp. Further, sum of the time from t 0  to t 9  stored in the timer set is shorter than the ending time tdp. 
     As shown in  FIG. 13 , the “VSS” state in the 11th period of the ACT voltage lasts until the ending time tdp. Similarly, the “VSS” state in the 11th period of the INA voltage lasts until the ending time tdp. 
       FIG. 14  is another timing chart illustrating the voltage applied to the actuators  37 , the ACT voltage and the INA voltage. 
     In the example shown in  FIG. 14 , the timer set doesn&#39;t contain t 10  but contains the ending time tdp. Further, sum of the time from t 0  to t 9  stored in the timer set is longer than the ending time tdp. 
     As shown in  FIG. 14 , the driving circuit  22  generates the ACT voltage and the INA voltage until the ending time tdp, and won&#39;t generate a new ACT voltage and a new INA voltage after the ending time tdp. When the ending time tdp elapses, the driving circuit  22  ends the ejection operation of one drop of ink. 
     In this way, by setting the ending time tdp, it is possible to select to execute all the voltage patterns in each register in which the voltage patterns of the ACT voltage and the INA voltage are stored, or to execute part of voltage patterns. That is, as shown in  FIG. 13 , all the voltage patterns are executed and the ejection operation is carried out if the ending time tdp is set to be longer than the time t 0 ˜t 9 , and then the actuators  37  become the cancel state; as shown in  FIG. 14 , if the ending time tdp is set to be shorter than the time t 0 ˜t 9  and execution of voltage patterns is stayed en route, only the ejection operation is executed and the cancel pulse for setting the actuators to the state shown in  FIG. 4  is not provided. 
     Thus altering the value of the ending time tdp on each drop frame, it is possible to generate waveform for each ink droplet selecting whether or not there is a cancel pulse according to the drop number, while sharing the voltage pattern stored in ACT register  41  and INA register  42 . 
     For example, it is also possible to generate waveform in a manner that the cancel pulse is omitted for the first ink droplet as the vibration of the ink pressure in the pressure chamber is relatively small because of the influence of the ink thixotropic properties and the hysteresis of the actuator, and the cancel pulse is added for the later droplets. In this way, the time required to eject the first droplet can be saved, and it is possible to print with high speed correspondingly. 
       FIG. 15  is a timing chart illustrating the voltage applied to one actuator  37 , the ACT voltage and the INA voltage in the ejection operation of seven drops of ink. 
     Herein, the timer set-drop application register  46  stores the timer set Ta as the timer set of the first drop, stores the timer set Tb as the timer set of the second drop, stores the timer set Tc as the timer set of the third drop to sixth drop, and stores the timer set Td as the timer set of the seventh drop. 
     Next, an operation example of the inkjet head  18  is described. Herein, the operation example of the inkjet head  18  is described according to the timing chart shown in  FIG. 15 . 
     First, the CPU  11  starts printing based on an instruction from an external device. If the printing is started, the CPU  11  conveys a paper to positions where the inkjet head  18  ejects ink with the conveyance motor  19 . 
     Then, the selector  47   a  of the waveform generation section  47  selects the timer set Ta as the timer set of the first drop according to the selection signal sent by the timer set-drop application register  46 . If the selector  47   a  selects the timer set Ta, the timer  47   b  sets the length of each period of the waveform segment according to the timer set Ta. According to the length of each period set by the timer  47   b , the waveform generation section  47  generates the waveforms of the ACT voltage, the INA voltage, the NEG voltage and the NEGINA voltage. The waveform generation section  47  sends the information indicating the generated waveforms of the voltages to the waveform frame/waveform distribution control section  48 . 
     The target waveform control section  53  of the waveform frame/waveform distribution control section  48  sets the ACT voltage waveform and the NEG voltage waveform based on the information indicating the ACT voltage waveform and the NEG voltage waveform. The adjacent waveform control section  52  of the waveform frame/waveform distribution control section  48  sets the INA voltage waveform and the NEGINA voltage waveform based on the information indicating the INA voltage waveform and the NEGINA voltage waveform. 
     Further, the drop sequence generation section  60  receives the printing data and the position flag from the CPU  11 . If receiving the printing data and the position flag, the drop sequence generation section  60  generates a drop sequence based on the printing data and the position flag. After the drop sequence is generated, the drop sequence generation section  60  sends the generated drop sequence to the data transmission and latch control section  51 . 
     The data transmission and latch control section  51  receives the drop sequence from the drop sequence generation section  60 . 
     The division control section  54  sends a switch control signal based on the ACT voltage waveform and the NEG voltage waveform which are set by the target waveform control section  53  and the drop sequence, as a switch control signal corresponding to the channels of the target division to the HV switch section  50 . Further, the division control section  54  sends a switch control signal based on the INA voltage waveform and the NEGINA voltage waveform which are set by the adjacent waveform control section  52  and the drop sequence, as a switch control signal corresponding to the channels of the adjacent division to the HV switch section  50 . 
     The HV switch section  50  receives the switch control signal corresponding to each channel from the division control section  54 . Upon receiving the switch control signal corresponding to each channel, the HV switch section  50  applies a voltage to the actuators  37  of each channel according to the switch control signal corresponding to each channel. 
     With the operations described above, the target channel can eject ink from the pressure chamber  36  on the printing medium. In the example shown in  FIG. 15 , after the ejection operation of the first drop frame is ended, the selector  47   a  selects the timer set Tb as the timer set of the second drop frame according to the information stored in the timer set-drop application register  46 . Then the inkjet head  18  carries out same operations as described above but using time periods of timer set Tb. 
     After the ejection operations of two drops are ended, the selector  47   a  selects the timer set Tc as the timer set of the third drop according to the information stored in the timer set-drop application register  46 . Then the inkjet head  18  carries out same operations as described above for all the drops. 
     If the same operations are carried out on all drops, the inkjet head  18  ends the ejection operations of the target division. After the ejection operations of the target division are ended, the inkjet head  18  changes the setting of the target division to carry out the same operations. After the inkjet head  18  ends the ejection operations of all channels, the CPU  11  enables the paper to move through the conveyance motor  19  in such a manner that the inkjet head  18  can eject ink to the next printing position. Every time the CPU  11  controls to move the paper, the inkjet head  18  carries out the ejection operation similarly. When the inkjet head  18  ends the ejection operations at all printing positions, the CPU  11  ends the printing. 
     It can be set freely that which one of the timer sets Ta˜Td is used for which one drop according to the information stored in the timer set-drop application register  46 . 
     Further, the CPU  11  moves the inkjet head  18  with the carriage motor  20 . 
     The driving circuit  22  may select the initial timer set during the movement of the paper. 
     Next, the volume of ink ejected by the channels is described. 
     The channels eject ink of different volume according to the drop frame number. The volume of ejected ink for each droplet is adjusted by the content of each timer set stored in the timer set register  45 , the ending time stored in the timer set-drop application register  46  and the timer set selected by the selector  47   a . The timer set and the ending time are determined in such a manner that a channel ejects a given amount of ink for a predetermined drop number. Further, the selector  47   a  selects a timer set in such a manner that a channel ejects a given amount of ink for a predetermined drop frame number. 
     The ink volume to be ejected at each drop frame may increase with the drop frame number, and may decrease with the drop frame number. The constitution of the volume to be ejected at each drop frame is not limited to a specific constitution. 
     For example, the adjustment of volume may be realized by increasing and decreasing the time t 2  in the timer set in  FIG. 12 . The time t 1 , t 2  and t 3  in  FIG. 12  determine the time for increasing the volume of the pressure chamber like shown in  FIG. 3  and filling the pressure chamber with ink from the ink supply port. The maximum time capable of being used to fill ink is ½ of the natural vibration period of ink in the pressure chamber. The ½ of the natural vibration period of ink in the pressure chamber is set as a reference, and if the time used to increase the volume of the pressure chamber is reduced to be shorter than the reference, the filling amount of ink to the pressure chamber before the ejection operation is reduced, and thus the ejection amount also reduces. If the time adjustment can be carried out with the time t 2 , it is possible to adjust the ejection volume. By setting different values of the time t 2  for different timer sets, it is possible to change the timer set to eject different volume of ink. 
       FIG. 16  is a timing chart illustrating the drop frame number and the ejection volume. 
     In  FIG. 16 , the timer set Ta is used for the first drop frame and the second drop frame, the timer set Tb is used for the third drop frame and the fourth drop frame, and the timer Tc is used for the fifth drop frame, and the drop frames after the fifth drop. That is, when considering the first drop frame and the second drop frame, the third drop frame and the fourth drop frame, the fifth drop frame and the drop frames after the fifth drop frame as three groups, the ejection volumes at drop frames in the same group are identical to each other, and the ejection volumes at drop frames in different groups are different from each other. Though only the first drop frame˜the seventh drop frame are shown in  FIG. 16 , the eighth drop frame and the drop frame after the eighth drop frame may be added similar to the fifth drop frame to the seventh drop frame. 
     The setting time t 2  of the timer set Tc is adjusted in such a manner that the time used to fill the pressure chamber with ink becomes ½ of the natural vibration period of ink in the pressure chamber, and the ejection amount per droplet of ink is 6.5 pl in the driving waveform using the timer set. 
     In order to eject ink of 6 pl (pico liter) in the timer set Tb and to eject ink of 5.5 pl in the timer set Ta, the setting time t 2  in each of the timer set Tb and the timer set Ta is set to be shorter than the setting time t 2  in the timer set Tc and the driving waveform is adjusted. 
     That is, as shown in  FIG. 16 , the volumes of ink ejected by the channel at timings of the first drop frame and the second drop frame are respectively 5.5 pl (pico liter). Further, the volumes of ink ejected by the channel at timings of the third drop frame and the fourth drop frame are respectively 6 pl. The volumes of ink ejected by the channel at timings of the fifth drop frame to the seventh drop frame are respectively 6.5 pl. 
     Herein, it is assumed that the channel ejects ink three times. 
     As shown in  FIG. 16 , if a channel ejects ink three times from the first drop frame, the channel can eject 17 pl of ink in total on the printing medium. Further, if a channel ejects ink three times from the second drop frame, the channel can eject 17.5 pl of ink in total on the printing medium. Similarly, if a channel ejects ink three times from the third drop frame, the channel can eject 18.5 pl of ink in total on the printing medium. If a channel ejects ink three times from the fourth drop frame, the channel can eject 19 pl of ink in total on the printing medium. If a channel ejects ink three times from the fifth drop frame, the channel can eject 19.5 pl of ink in total on the printing medium. 
     The number of drop frames may be increased to maintain the capable number of drops to be ejected even in a case in which the drop frame number starting to be ejected is shifted back. For example, in a case of starting to eject ink from the fourth drop frame, the number of drop frames may be increased up to 10 (add 3 frames), for 7 drops capable of being ejected. 
     Next, an example carrying out a volume fine adjustment in a case of ejecting ink 7 times continuously by a plurality of channels is described with reference to  FIG. 17 . In this example, it is assumed that the setting of each timer set is the same as that shown in  FIG. 16 , and the number of drop frames is 10. 
       FIG. 17  is a timing chart illustrating the timings when the channels eject ink. 
       FIG. 17  illustrates the ejection operations of each channel of the first division, the ejection operations of each channel of the second division and the ejection operations of each channel of the third division respectively. 
     In  FIG. 17 , “A” represents that the corresponding channel ejects ink. That is, “A” represents that an ACT voltage is applied to the channel. “B” represents that the corresponding channel doesn&#39;t eject ink. That is, “B” represents that an INA voltage, a NEG voltage or a NEGINA voltage is applied to the channel. No driving waveform is applied to the part marked with “Z”, that is, the three transistors connected with the electrodes of the channel in  FIG. 11  are turned off. 
     As shown in  FIG. 17 , when a given period elapses after the ejection operations of a given division are ended, the ejection operations of the next division are started. 
     In this example, when ejecting ink 7 times continuously, only the ejection amount of ink ejected from the fourth channel of the first division, that is, from the #4 nozzle is adjusted to be finely increased when compared with that from other nozzles. 
     The fourth channel of the first division starts to eject ink from the fourth drop frame. In order to eject ink 7 times in the fourth channel, the driving circuit  22  increases the number of the drop frame which is the times frame capable of ejecting ink to 10, to eject ink droplets at the fourth drop frame to the tenth drop frame. In this way, the fourth channel can drop ink 7 times. At that time, the driving circuit  22  also increases the times frame in the adjacent channels (that is, the third channel and the fifth channel). That is, an INA voltage is applied to the adjacent channels from the eighth drop to the tenth drop. 
     As the timer sets are set as described in  FIG. 16 , total ejection amount of the general 7 drops (other than the drops from the #4 nozzle) is 5.5+5.5+6+6+6.5+6.5+6.5=42.5 pL. 
     On the other hand, as the timer sets which are shifted back for 3 drop frames are used when ink is ejected from the #4 nozzle, the total ejection amount of the 7 drops from the #4 nozzle is 6+6.5+6.5+6.5+6.5+6.5+6.5=45 pL. 
     That is, by shifting the drop frame number starting to be ejected back with 3, the ejection amount can be increased by 2.5 pL. Similarly, if the drop number starting to be ejected is shifted back with 2, the total ejection amount becomes 6+6+6.5+6.5+6.5+6.5+6.5=44.5 pL; and if the drop number starting to be ejected is shifted back with 1, the total ejection amount becomes 5.5+6+6+6.5+6.5+6.5+6.5=43.5 pL. As a result, the 7 drops of total ejection amount can be respectively increased by 2 pL, 1 pL when compared to the general 42.5 pL. 
     In a printing with a multi-drop system in which one dot is formed through a plurality of droplets by times of operations of the general actuator, ejection volume of one droplet by once in the plurality of times of operations is the minimum adjustment step of the ejection amount. That is, for example, if the ejection amount of one drop is 6 pL, the ejection volume cannot be finely adjusted by an amount below 6 pL. On the contrary, the 2.5 PL, 2 pL and 1 pL in the present embodiment are about below half of 6 pL serving as the adjustment step in a case of increasing/decreasing the ejection amount per drop unit, and thus it is possible to finely adjust the ejection amount. 
     Though it is exemplified in this example that the ejection volume of the #4 nozzle is finely increased, it is possible to finely increase or decrease the ejection volume of any one of nozzles at any timing similarly, as the setting values described above can be changed freely. 
     Since the timer sets can be set freely, the adjustment width of the fine adjustment and the position where the adjustment enters may be selected freely. 
     The spot positions of the ink on a print media are shifted slightly in a direction that the inkjet head and the printing medium are moved relatively, i.e., in the direction orthogonal to the direction of nozzle row through the fine adjustment. For example, in the example shown in  FIG. 17 , when three-drop frames are shifted, the shift amount of the spot positions is maximum 3/30=10% of the image resolution degree on the printing medium. If a printing application for printing on a general paper medium is carried out, the ink spots which are very close to each other on the paper gather together by the surface tension thereof and the ink permeates and spreads on the paper slightly. Thus such a slight change of the spot positions can be hardly detected on the printing object. So, it is possible to shift the drop frame number starting to be ejected to perform a fine adjustment of ejection volume. On the contrary, if such a slight change of printing positions can be detected, the appearance of the printing object may be regulated by utilizing the slight change of printing positions in a positive manner and combining the volume fine adjustment with a position fine adjustment. 
     Further, if the printing medium is not normal paper but the one which has fine dispensing grooves to which ink is dispensed, even if there is a slight shift of printing positions in a direction that the inkjet head and the printing medium are moved relatively, i.e., the direction orthogonal to the direction of nozzles row, the shift of printing positions is permissible, since the ink is dispensed to the same dispensing groove. Further, in a case of ejecting ink in a static state by fixing the relative position of the printing medium and the inkjet head one by one, a slight shift of timings for adjusting volumes is permissible. 
     The inkjet head with the constitution above can adjust the drop frame number starting to be ejected for each drop. Thus, the inkjet head can effectively adjust the amount of ink to be ejected on the printing medium. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the invention. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the invention. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the invention.