Patent Publication Number: US-9427956-B2

Title: Drive method and drive apparatus for ink jet head

Description:
FIELD 
     Embodiments described herein relate to a drive method and a drive apparatus for the ink jet head used in an ink jet printer and the like. 
     BACKGROUND 
     An ink jet head comprises a plurality of pressure chambers for accommodating ink, a plurality of piezoelectric actuators arranged corresponding to each of the pressure chambers and a nozzle plate arranged on one end of each of the pressure chambers. A plurality of nozzles, which are connected with the pressure chambers, respectively, are formed on the nozzle plates to eject ink drops. Each piezoelectric plate vibrates a corresponding pressure chamber across a vibration plate. 
     A drive apparatus for such an ink jet head applies a drive pulse signal to piezoelectric actuators. Vibration is generated in pressure chambers according to the drive pulse signal when the internal volume of the pressure chambers is changed to eject ink drops from nozzles connected with the pressure chambers. 
     However, the vibration generated in the pressure chambers remains in the pressure chambers after the ink drops are ejected out, which hinders the stable ejection of following ink drops. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an oblique view of an ink jet head; 
         FIG. 2  is a configuration diagram illustrating main components of an ink jet head with a cross-section surface; 
         FIG. 3  is a cross-sectional view illustrating an ink jet head observed from the direction of the arrow A-A shown in  FIG. 2 ; 
         FIG. 4  is a block diagram illustrating the configuration of a drive signal generation section; 
         FIG. 5  is a timing chart illustrating an example of the waveform of a drive pulse signal output from a drive signal generation section; 
         FIG. 6  is a diagram illustrating a DRP waveform; 
         FIG. 7  is a diagram illustrating an equivalent circuit equivalent to the pressure chamber of an ink jet head; 
         FIG. 8  is a timing chart illustrating the drive pulse waveform of a DRP waveform, and the waveforms of the pressure and the flow velocity in the pressure chamber; 
         FIG. 9  is a timing chart illustrating the DRP waveform shown in  FIG. 8  when a damping pulse is not turned off; 
         FIG. 10  is a timing chart illustrating the DRP waveform shown in  FIG. 9  when the on-timing of a damping pulse is delayed; 
         FIG. 11  is a timing chart illustrating the DRP waveform shown in  FIG. 10  when a damping pulse is turned off; 
         FIG. 12  is a timing chart illustrating the DRP waveform shown in  FIG. 8  when the on-timing of a damping pulse is ahead of time and a damping pulse is not turned off; 
         FIG. 13  is a timing chart illustrating the DRP waveform shown in  FIG. 12  when a damping pulse is turned off; 
         FIG. 14  is a diagram illustrating a DRCRP waveform; 
         FIG. 15  is a timing chart illustrating the drive pulse waveform of a DRCRP waveform when a damping pulse is omitted, and the waveforms of the pressure and the flow velocity in the pressure chamber; 
         FIG. 16  is a timing chart illustrating the drive pulse waveform of a DRCRP waveform when a damping pulse is turned on, and the waveforms of the pressure and the flow velocity in the pressure chamber; and 
         FIG. 17  is a timing chart illustrating the drive pulse waveform of a DRCRP waveform shown in  FIG. 15  when a damping pulse is turned off, and the waveforms of the pressure and the flow velocity in the pressure chamber. 
     
    
    
     DETAILED DESCRIPTION 
     In an embodiment, a drive method for an ink jet head comprises: as a drive pulse, applying a first pulse for increasing and then restoring the volume of a pressure chamber and giving pressure vibration to the chamber in which ink are accommodated and then a second pulse for reducing and then restoring the volume of the pressure chamber to an actuator arranged corresponding to the pressure chamber. 
     In the drive method, 
     the second pulse is turned on at first point of time causing the pressure vibration amplitude at second point of time to be the same with that of generated by the first pulse when the first pulse is turned on, 
     The second point of time is the time when flow velocity of the ink nearby the nozzle inside the pressure chamber becomes 0 after the first point of time, 
     and the second pulse is turned off at the second point of time. 
     Embodiments of the drive method and the drive apparatus for an ink jet head provided herein are described below with reference to the accompanying drawings. First, the ink jet head  1  used in the embodiment is described with reference to  FIG. 1 - FIG. 3 . 
       FIG. 1  is an oblique view illustrating the ink jet head  1 ,  FIG. 2  is a configuration diagram illustrating main components of the ink jet head  1  with a cross-section surface, and  FIG. 3  is a cross-sectional view illustrating the ink jet head  1  observed from the direction of the arrow A-A shown in  FIG. 2 . 
     The ink jet head  1  comprises a drive device  2 , a head substrate  3  and a manifold  4 . The manifold  4  is equipped with an ink feed tube  5  and an ink discharging tube  6 . The ink jet head  1  ejects the ink fed from an ink feeding unit (not shown) through the feed tube  5  out from each nozzle  13   a  according to a drive signal from the drive device  2 . The part of the ink fed into the manifold  4  from the feed tube  5  which is not ejected out from each nozzle  13   a  is discharged from the discharging tube  6  to the ink feeder. 
     A plurality of parallel pressure chambers  11  are arranged in the head substrate  3  corresponding to the nozzles  13   a , respectively. The bottom side (the bottom side in  FIG. 2 , the top side in  FIG. 1 ) of each pressure chamber  11  is adhered with a nozzle plate  13  on which a plurality of nozzles  13   a  are bored. The pressure chambers  11  are separated from each other by partition walls  12  to accommodate ink separately. The nozzles  13   a  are bored on the nozzle plate  13  in columns (two columns in  FIG. 1 ) along the longitudinal direction of the nozzle plate  13 . From the inner side, that is, the side of the pressure chambers  11  to the surface (surface=bottom side in  FIG. 2 , and surface=top side in  FIG. 1 ) serving as an ink ejecting side, each nozzle  13   a  is formed in a tapered shape. 
     In the ink jet head  1 , a vibration plate  14  is adhered to the top face side of each pressure chamber  11 , with whose top side stuck fast to one end of a plurality of piezoelectric members  15  arranged corresponding to the pressure chambers  11 , respectively. The ink jet head  1  holds the other end of each piezoelectric member  15  with a holding member  16 . Each piezoelectric member  15  is formed by laminating a plurality of piezoelectric layers  15   a  and electrode layers  15   b  alternatively. In the ink jet head  1 , a pair of electrodes  17  are arranged in such a manner that each electrode layer  15   b  is sandwiched between the electrodes. The two electrodes  17  are electrically connected with the drive device  2 . 
     A common liquid chamber  18  is formed in the head substrate  3  of the ink jet head  1 . Ink is injected into the common liquid chamber  18  through the feed tube  5 . The common liquid chamber  18  is connected with each pressure chamber  11  so that the injected ink is filled into each pressure chamber  11  and the nozzle  13   a  corresponding to the pressure chamber  11 . By filling the pressure chambers  11  and the nozzles  13   a  with ink, an ink meniscus is formed in the nozzles  13   a.    
     In the ink jet head  1  with a related structure, if a drive signal is applied from the drive device  2  to the piezoelectric member  15  through the electrodes  17 , then the piezoelectric member  15  expands or contracts. With the expansion or contraction of the piezoelectric member  15 , the vibration plate  14  is deformed such that vibration is given to the pressure chamber  11 . Because of the vibration, the volume of the pressure chamber  11  changes, generating a pressure wave in the pressure chamber  11  to eject ink drops from the nozzle  13   a . Here, the vibration plate  14  and the piezoelectric member  15  serve as an actuator which vibrates the pressure chamber  11 . That is, as many actuators are arranged on the ink jet head  1  as the nozzles  13   a.    
     Next, the drive device  2  is described. The drive device  2  comprises: a communication section  21 , an operation section  22  and a drive signal generation section  23 . The communication section  21  receives gradation data of an image to be printed from a host computer for controlling, for example, an ink jet printer. The operation section  22  calculates the number of drive pulse trains for each nozzle  13   a  based on the gradation data. The drive signal generation section  23  supplies a drive pulse signal to a piezoelectric member  15  corresponding to a nozzle  13   a , the drive pulse signal having as many drive pulse trains as the number calculated by the operation section  22  for each nozzle  13   a.    
     By applying the pulse voltage of the drive pulse signal to the piezoelectric member  15 , ink drops, the number of which is equivalent to that of pulse trains, are ejected out from the nozzle  13   a  of the pressure chamber  11  corresponding to the piezoelectric member  15 . An ink jet recorder consisting of the ink jet head  1  and the drive device  2  converts the number of the ink drops into a pixel unit and adjusts the concentration of pixels to implement gradation printing to print an image, that is, the ink jet recorder prints in a multi-drop manner. 
       FIG. 4  is a block diagram illustrating the configuration of the drive signal generation section  23 . The drive signal generation section  23  comprises a reference drive waveform generation portion  231  and passing range selection circuits  232 - 1  to  232 - n  for the nozzles  13   a . The reference drive waveform generation portion  231  generates a drive pulse signal for the continuous ejecting, from the nozzles  13   a , of the number of ink drops needed for the formation of pixels of a maximum gradation value G. In the embodiment, the drive pulse signal is referred to as a reference pulse signal. Each of the passing range selection circuits  232 - 1  to  232 - n  replaces the reference pulse signal with a drive pulse signal indicating a drop number 0-K selected by a selection signal and output the drive pulse signal. 
       FIG. 5  shows an example of waveforms of drive pulse signals PA 4 , PA 3 , PA 2  and PA 1  output from the passing range selection circuits  232 - 1  to  232 - n  when the maximum gradation value G is ‘4’. The drive pulse signal PA 4  consists of the DRP waveform in the time range t 0 -t 1 , the DRP waveform in the time range t 1 -t 2 , the DRP waveform in the time range t 2 -t 3  and the DRCRP waveform in the time range t 3 -t 4 . DRP waveform and DRCRP waveform are drive pulse trains, respectively. The drive pulse signal PA 4  consisting of four drive pulse trains is the same as the reference pulse signal generated by the reference drive waveform generation portion  231 . 
     When a selection signal indicating the selection on four drops is input to the passing range selection circuits  232 - 1  to  232 - n , the passing range selection circuits  232 - 1  to  232 - n  select the time range t 0 -t 4  of the reference pulse signal as a whole passing range, as a result, the drive pulse signal PA 4  is output. When the drive pulse signal PA 4  is applied to the piezoelectric member  15 , four drops of ink are ejected out from the nozzle  13   a  corresponding to the piezoelectric member  15 . 
     The drive pulse signal PA 3  is a signal obtained by removing the DRP waveform in the time range t 0 -t 1  from the drive pulse signal (reference pulse signal) PA 4 . When a selection signal indicating the selection on three drops is input to the passing range selection circuits  232 - 1  to  232 - n , the passing range selection circuits  232 - 1  to  232 - n  select the time range t 1 -t 4  of the reference pulse signal as a passing range, as a result, the drive pulse signal PA 3  is output. When the drive pulse signal PA 3  is applied to the piezoelectric member  15 , three drops of ink are ejected out from the nozzle  13   a  corresponding to the piezoelectric member  15 . 
     The drive pulse signal PA 2  is a signal obtained by removing the two DRP waveforms in the time range t 0 -t 2  from the drive pulse signal (reference pulse signal) PA 4 . When a selection signal indicating the selection on two drops is input to the passing range selection circuits  232 - 1  to  232 - n , the passing range selection circuits  232 - 1  to  232 - n  select the time range t 2 -t 4  of the reference pulse signal as a passing interval, as a result, the drive pulse signal PA 2  is output. When the drive pulse signal PA 2  is applied to the piezoelectric member  15 , two drops of ink are ejected out from the nozzle  13   a  corresponding to the piezoelectric member  15 . 
     The drive pulse signal PA 1  is a signal obtained by removing the three DRP waveforms in the time range t 0 -t 3  from the drive pulse signal (reference pulse signal) PA 4 . When a selection signal indicating the selection on one drop is input to the passing range selection circuits  232 - 1  to  232 - n , the passing range selection circuits  232 - 1  to  232 - n  select the interval t 3 -t 4  of the reference pulse signal as a passing interval, as a result, the drive pulse signal PA 1  is output. When the drive pulse signal PA 1  is applied to the piezoelectric member  15 , one drop of ink is ejected out from the nozzle  13   a  corresponding to the piezoelectric member  15 . 
       FIG. 6  is a diagram illustrating a DRP waveform. As shown in  FIG. 6 , a DRP waveform includes an ejection pulse SP serving as a first pulse and a damping pulse DP serving as a second pulse. The ejection pulse SP is the pulse of a voltage −V 1  changed to be lower than a reference voltage Vm, and the pulse width of the ejection pulse SP is set to Ts; the damping pulse DP, which is the pulse of a voltage changed to be higher than the reference voltage Vm and the pulse width of which is set to Td, is generated Tw 1  later than the rising of the ejection pulse SP. The reference voltage Vm refers to the voltage applied to the piezoelectric member  15  corresponding to the nozzle  13   a  in a normal state in which no ink drop is ejected. 
     When applying the ejection pulse SP (negative voltage pulse-on), the voltage applied to the piezoelectric member  15  is changed from Vm to −V 1 . At the point of time t 11  the ejection pulse SP falls, the piezoelectric member  15  contracts with respect to the normal state; with the contraction, the vibration plate  14  stuck fast to the piezoelectric member  15  is deformed, increasing the volume of the pressure chamber  11 . As the volume of the pressure chamber  11  is increased, a negative pressure is generated instantly in the pressure chamber  11 . 
     The expansion of the pressure chamber  11  lasts after the time Ts elapsed. The pulse width Ts of the ejection pulse SP is set to ½ of the natural vibration period of the pressure chamber  11 . In this embodiment, the natural vibration period is 4.6 μs, and the pulse width Ts is 2.3 μm. During Ts, ink flows from the common liquid chamber  18  into the pressure chamber  11 . Further, the meniscus on the front end of the nozzle  13   a  backs to the side of the pressure chamber  11 . The pressure in the pressure chamber  11  changes from a negative pressure to a positive pressure. 
     When rising the ejection pulse SP (negative voltage pulse-off), the voltage applied to the piezoelectric member  15  is changed back to Vm from −V 1 . At the point of time t 12  the ejection pulse SP rises, the piezoelectric member  15  recovers to normal. With the recovery, the internal volume of the pressure chamber  11  returns to normal. At this time, a positive pressure is generated instantly in the pressure chamber  11 , and with the pressure, the meniscus in the nozzle  13   a  advances. 
     The meniscus advances till ½ of the natural vibration period elapses (e.g. 2.3 μs) from the moment the ejection pulse SP rises, meanwhile, the pressure in the pressure chamber  11  changes again from a positive pressure to a negative pressure. Then, ink drops are separated from the ink inside the nozzle and ejected out. Then, applying the damping pulse DP (positive voltage pulse-on), the voltage applied to the piezoelectric member  15  is changed from Vm to V 1  at the point of time t 13 , the volume of the piezoelectric member  15  increases. With the expansion, the vibration plate  14  stuck fast to the piezoelectric member  15  is deformed to make the pressure chamber  11  contract. A positive pressure is generated instantly in the pressure chamber  11  as the volume of the pressure chamber  11  contracts. 
     The pressure chamber  11  contracts for a time of the pulse width Td (e.g. 0.9 us) of the damping pulse DP. Then, at the point of time t 14  the voltage applied to the piezoelectric member  15  is changed back to Vm from V 1  because of the falling of the damping pulse DP (positive voltage pulse-off), the piezoelectric member  15  recovers to normal. The turn-off of the positive voltage pulse makes the charging state of the piezoelectric member charged to V 1  return back to Vm. With the recovery, the positive pressure in the pressure chamber  11  drops back to 0. Then, the residual vibration in the pressure chamber  11  is eliminated. 
     Next, the output timing of the damping pulse DP is described using the equivalent circuit  30  shown in  FIG. 7 . 
     The equivalent circuit  30  is a circuit formed by connecting a series circuit (hereinafter referred to as an LCR circuit  32 ) consisting of a resistor R, a capacitor C and an inductor L with a voltage source  31 . The resistance of the resistor R is 0.18Ω, the capacitance of the capacitor C is 0.69 uF, and the inductance of the inductor L is 0.736 uH. The equivalent circuit  30  represents the pressure chamber  11  of the ink jet head  1 . The voltage generated at two terminals of the voltage source  31  is equivalent to the displacement of the actuator and can be deemed as a drive voltage applied to the actuator. The voltage generated at two terminals of the inductor L is equivalent to the pressure on the periphery of the nozzle  13   a  in the pressure chamber  11 . On the periphery of the nozzle  13   a  in the pressure chamber  11 , the circuit current is equivalent to the velocity of the ink flowing towards the nozzle. In the equivalent circuit  30 , the voltage source  31  is connected with a voltmeter V in parallel; an ammeter (current meter) S is connected between the voltage source  31  and the resistor R, and the inductor L is connected with a voltmeter P in parallel. The flow velocity of the ink from the common liquid chamber  18  to the inlet of the pressure chamber  11  is reverse to that of the ink on the periphery of the nozzle  13   a . For example, at the time t 11  shown in  FIG. 6 , the pressure chamber  11  expands, the ink on the periphery of the nozzle  13   a  backs to the side of the pressure chamber  11  while an ink flow flowing from the common liquid chamber  18  to the pressure chamber  11  appears. The flow of the ink in this direction is equivalent to a value changing the value of the ammeter S to be negative. 
     A pulse signal  41  having the DRP waveform shown in  FIG. 8  is applied from the voltage source  31  to the LCR circuit  32 . In the pulse signal  41 , the pulse width Ts of the ejection pulse SP is 2.3 μs, the pulse width of the damping pulse DP is 0.9 us, and the interval Tw 1  between the ejection pulse SP and the damping pulse DP is 3.0 us. The waveform  42  shown in  FIG. 8  represents the change of the voltage generated at two terminals of the inductor L when the pulse signal  41  is applied to the LCR circuit  32 , that is, a pressure change; and the waveform  43  shown in  FIG. 8  represents the circuit current change, that is, the flow velocity change. 
     At the point of time the 6.2 μs elapses from the point of time the ejection pulse SP falls (just before the damping pulse DP falls), the voltage (pressure) generated at two terminals of the inductor L becomes V 1 . The circuit current (flow velocity) becomes 0. The voltage (pressure) V 1  is reverse in polarity to but equal in amplitude to the voltage (pressure) generated at two terminals of the inductor L at the point of time the ejection pulse SP falls. In this case, the voltage (pressure) generated at two terminals of the inductor L becomes 0 if the damping pulse DP falls at this point. In addition, the circuit current (flow velocity) becomes 0 as well. That is, the residual vibration of the pressure chamber  11  is eliminated. 
     The damping pulse DP should be raised at the time causing vibration of the voltage (pressure) generated at two terminals of the inductor L becomes V 1  when the circuit current (flow velocity) becomes 0, which indeed eliminates the residual vibration of the pressure chamber  11 . In other words, the residual vibration of the pressure chamber  11  cannot be eliminated if there is no point of time at which the voltage (pressure) generated at two terminals of the inductor L becomes V 1  and the circuit current (flow velocity) becomes 0. 
     The amplitude of the voltage (pressure) generated at two terminals of the inductor L is changed by adjusting the time at which the damping pulse DP rises. In the case of the equivalent circuit  30 , as shown in  FIG. 9 , if the damping pulse DP rises after 5.3 μs elapses from the point of time the ejection pulse SP falls, then, the voltage (pressure) generated at two terminals of the inductor L becomes V 1  after 6.2 μs elapses, moreover, the circuit current (flow velocity) becomes 0. At this time, if the damping pulse DP falls (refer to  FIG. 8 ), the residual vibration of the pressure chamber  11  is eliminated, as shown in  FIG. 8 . 
       FIG. 10  shows the rise of the damping pulse DP after more than 5.3 μs elapses from the point of time the ejection pulse SP falls. At this time, the voltage (pressure) generated at two terminals of the inductor L is greater than V 1  at the point of time after 6.24 μs when the circuit current (flow velocity) becomes 0 elapses. Thus, as shown in  FIG. 11 , at the point of time the circuit current (flow velocity) becomes 0, the residual vibration of the pressure chamber  11  is still remained even if the damping pulse DP falls. 
       FIG. 12  shows the rise of the damping pulse DP after less than 5.3 μs elapses from the point of time the ejection pulse SP falls. At this time, the voltage (pressure) generated at two terminals of the inductor L is smaller than V 1  at the point of time after 6.17 μs when the circuit current (flow velocity) becomes 0 elapses. Thus, as shown in  FIG. 13 , at the point of time the circuit current (flow velocity) becomes 0, the residual vibration of the pressure chamber  13  is still remained even if the damping pulse DP falls. 
     The damping pulse DP is contained in the drive pulse signal to eliminate the residual vibration of the pressure chamber  11 . As described above with reference to  FIG. 10 - FIG. 13 , the residual vibration cannot be eliminated when the output timing of the damping pulse DP is deviated. 
     Thus, as to the damping pulse DP in a DRP waveform, as shown in  FIG. 9 , the damping pulse DP rises (positive voltage pulse-on) at the point of time the voltage (pressure) generated at two terminals of the inductor L becomes V 1  and the circuit current (flow velocity) becomes 0 after the rise of the damping pulse DP. Then, as shown in  FIG. 8 , the damping pulse DP falls (positive voltage pulse-off) at the point of time the voltage (pressure) generated at two terminals of the inductor L becomes V 1  and the circuit current (flow velocity) becomes 0. The reference drive waveform generation portion  231  generates a reference pulse signal having such a DRP waveform. 
       FIG. 14  is a diagram illustrating a DRCRP waveform. As shown in  FIG. 14 , in a DRCRP waveform, there is a satellite canceling pulse CP serving as a third pulse between the ejection pulse SP and the damping pulse DP of a DRP waveform. The satellite canceling pulse CP is a pulse of the voltage V 1  changed to be higher than the reference voltage Vm, and the pulse width of the satellite canceling pulse CP is set to Tc. The satellite canceling pulse CP is generated after Tw 2  elapses from the rise of the ejection pulse SP. The damping pulse DP is generated after Tw 3  elapses from the falling of the satellite canceling pulse CP. 
     The ‘satellite’ of the satellite canceling pulse CP refers to a satellite drop. An ink drop is usually ejected out from the nozzle  13   a , leaving a trail. Then, when the ink drop is separated from the ink in the nozzle  13   a , the trail part, that is, the called liquid column becomes a spherical satellite drop and flies following the main ink drop. The satellite drop flying at a lower speed is separated from the main liquid drop and impacts on a recording medium. Consequentially, printing quality is degraded due to the density unevenness and ghost caused by the satellite drop. The satellite canceling pulse CP is used to prevent the generation of a satellite drop. 
     During the period from t 21  at which the ejection pulse SP drops to t 22  at which the ejection pulse SP rises, the DRCRP waveform functions as a DRP waveform, that is, at the point of time t 22  the voltage applied to the piezoelectric member  15  is changed back to Vm from −V 1 , the meniscus in the nozzle  13   a  starts to advance. 
     The meniscus advances till ½ of the natural vibration period elapses (e.g. 2.3 μs) from the point of time the ejection pulse SP rises, then, the ink liquid column is to be separated from the nozzle  13   a  after the time Tw 2  (e.g. 3.25 us) elapses. At this time, the satellite canceling pulse CP rises (positive voltage pulse-on). The volume of the piezoelectric member  15  increases at the point of time t 23  the voltage applied to the piezoelectric member  15  is changed from Vm to V 1  due to the rise of the satellite canceling pulse CP. With the expansion, the vibration plate  14  stuck fast to the piezoelectric member  15  is deformed to make the pressure chamber  11  contract. A positive pressure is generated instantly in the pressure chamber  11  as the pressure chamber  11  contracts. With the pressure, the ink liquid column is pushed out from the pressure chamber  11 . As a result, the liquid column and the ink drop are separated from the ink in the nozzle together and ejected out from the nozzle  13   a . Thus, no satellite drop is generated. 
     The pressure chamber  11  keeps in a contracted state for a time equivalent to the pulse width Tc (e.g. 1.85 us) of the satellite canceling pulse CP. Tc is the time needed for the separation of the liquid column from the ink in the nozzle  13   a  and the following ejection of the whole separated liquid column out from the nozzle  13   a . Then, the piezoelectric member  15  recovers to normal at the point of time t 24  the voltage applied to the piezoelectric member  15  is changed back to Vm from V 1  due to the falling of the satellite canceling pulse CP (positive voltage pulse-off). With the recovery, the internal volume of the pressure chamber  11  returns to normal and is kept in the normal state for Tw 3  (e.g. 1.3 us). Then, the volume of the piezoelectric member  15  increases again at the point of time t 25  the voltage applied to the piezoelectric member  15  is changed from Vm to V 1  due to the rise of the damping pulse DP. With the expansion, the vibration plate  14  stuck fast to the piezoelectric member  15  is deformed to make the pressure chamber  11  contract. As the pressure chamber contracts, a positive pressure is generated instantly in the pressure chamber  11 . 
     The pressure chamber  11  is kept in the contracted state for a time equivalent to the pulse width Td (e.g. 0.95 us) of the damping pulse DP, then, the piezoelectric member  15  recovers to normal again at the point of time t 26  the voltage applied to the piezoelectric member  15  is changed back to Vm from V 1  due to the falling of the damping pulse DP. With the recovery, the positive pressure in the pressure chamber  11  is changed to 0. Then, the residual vibration in the pressure chamber  11  is eliminated. 
     Next, the output timing of the satellite canceling pulse CP is described with reference to the equivalent circuit  30  shown in  FIG. 7 . 
     A pulse signal  51  having the DRC waveform shown in  FIG. 15  is applied from the voltage source  31  to the LCR circuit  30 . Additionally, the DRC waveform is a waveform obtained by removing the damping pulse DP serving as the second pulse from a DRCRP waveform. In the pulse signal  51 , the pulse width Ts of the ejection pulse SP is 2.3 μs, the pulse width of the satellite canceling pulse CP is 1.85 us, and the interval Tw 1  between the ejection pulse SP and the satellite canceling pulse CP is 3.25 us. The waveform  52  shown in  FIG. 15  represents the change of the voltage generated at two terminals of the inductor L when the pulse signal  51  is applied to the LCR circuit  32 , that is, a pressure change; and the waveform  53  shown in  FIG. 15  represents the circuit current, that is, the flow velocity change. 
     At the point of time 5.55 μs elapses from the moment the ejection pulse SP falls, the ink drop is to be separated from the nozzle  13   a . At this time, the voltage (pressure) generated at two terminals of the inductor L is approximate to ‘0’. Here, the satellite canceling pulse CP rises, which reduces the volume of the pressure chamber  11  to push out the ink liquid column. Then, at the point of time 7.4 μs elapses from the moment the ejection pulse SP falls, the liquid column is ejected out from the nozzle  13   a . At this time, the voltage (pressure) generated at two terminals of the inductor L is approximate to ‘0’ again. Here, if the satellite canceling pulse falls, then the internal volume of the pressure chamber  11  returns to normal, the pressure in the pressure chamber  11  drops sharply, making the ink which is not ejected out but left nearby the nozzle return back into the pressure chamber. In this way, the liquid column is separated from the ink in the nozzle, thereby inhibiting the generation of a satellite drop. 
     However, as shown in  FIG. 15 , the vibration of the pressure chamber in the DRC waveform cannot be eliminated. Thus, if a DRC waveform is continuously supplied to eject ink, the ejection becomes unstable. So, as shown in  FIG. 16 , after the satellite canceling pulse CP falls, a damping pulse DP is supplied to eliminate pressure vibration. The damping pulse DP rises at the time causing pressure vibration of the voltage (pressure) generated at two terminals of the inductor L becomes V 1  when the circuit current (flow velocity) becomes 0, and then falls when the voltage (pressure) generated at two terminals of the inductor L becomes V 1  and circuit current (flow velocity) becomes 0, as shown in  FIG. 17 . By applying a drive pulse signal having such a DRCRP waveform to the ink jet head  1 , the generation of a satellite drop is prevented while the residual vibration of the pressure chamber  11  is eliminated. 
     Though DRCRP waveform eliminates both the satellite drop and the residual vibration as mentioned above, it takes longer time for one drive pulse train of the waveform compared with the DRC or DRP waveform. 
     Especially in a case where a multi-drop manner which includes multiple pulse trains of waveforms for sub drops in a dot, using DRCRP waveform for every sub drop takes longer waveform time and degrades the print speed. But in this case, DRCRP waveform is necessary only at the last waveform for the last sub drop in the multiple drops with the following reason. 
     It&#39;s because, in the case of the multi-drop manner, generated satellites at any time prior to the last ink sub drop will be gathered with the following liquid drop and never reaches on the printing medium alone, which causes no deterioration of the print quality. 
     In this embodiment, as shown in  FIG. 5 , a DRCRP waveform is used only when the last sub drop is ejected, and before this, DRP waveform is used. Thus, this embodiment achieves high-speed printing while eliminating problems caused by the satellite drop and the residual vibration. 
     Further, in this embodiment, as shown in  FIG. 5 , each waveforms for sub drops are filled with backward (later time) justified manner, which means the timing of the waveform for the last drop is common regardless of the gradation (the number of drops). The time of the DRCRP waveform in the time range t 3 -t 4  of the drive pulse signal is common in each actuator as a base timing. Then, DRP waveforms are added prior to the DRCRP waveform if the number of ink drops is more than 1. 
     Because of using the backward justified manner for placing each waveform for each sub drop, the waveform PA 4  including 3 DRP waveforms prior to 1 DRCRP waveform can be used as a reference drive waveform. 
     Thus, the reference drive waveform generation portion  231  of the drive signal generation section  23  shown in  FIG. 4  generates the waveform of PA 4  as a reference drive waveform which is common to each actuator, simplifying the structure of the drive signal generation section  23 . 
     Further, the present invention is not limited to the embodiments above. 
     For example, the aforementioned embodiments are described as a drive apparatus and a drive method for the ink jet head  1  having the structure shown in  FIG. 1 - FIG. 3 , however, the embodiments may be applied to an ink jet head with another structure, for example, the embodiments may be applied to an ink jet head for driving each nozzle in a time division manner. 
     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.