Patent Publication Number: US-2023150260-A1

Title: Liquid ejection apparatus and control method of liquid ejection apparatus

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a liquid ejection apparatus that ejects a liquid from an ejection port and a control method of the same. 
     Description of the Related Art 
     Recent years, along with development in micromachine technology (MEMS technology), there has been proposed a liquid transportation device that transports liquid on the order of μms. 
     Japanese Patent Laid-Open No. 2003-286940 discloses a micropump that takes advantage of a flow channel resistance that is changed non-linearly with respect to a flow velocity and uses the action of fluid as a valve mechanism without using a mechanical valve structure. According to the micropump disclosed in Japanese Patent Laid-Open No. 2003-286940, it is possible to transport a liquid on the order of μms with a simple and small configuration including a few parts. Japanese Patent Laid-Open No. 2003-286940 discloses a driving method that allows the piezoelectric element to function as a pump by using a piezoelectric element in the form of membrane as a driving source and changing a voltage applied to the piezoelectric element asymmetrically against time. 
     In the liquid transportation device disclosed in Japanese Patent Laid-Open No. 2003-286940, the liquid is quantitatively transported by displacing the piezoelectric element and repeating an operation to rapidly expand (contract) the inner volume of a liquid transportation chamber and an operation to moderately contract (expand) the inner volume of the liquid transportation chamber. In a case where the liquid transportation device is used for a liquid transportation operation in a flow channel of a liquid ejection apparatus, a pressure variation that occurs due to the rapid change in the inner volume of the liquid transportation chamber may affect an ejection operation of a liquid droplet, and degradation in the ejection characteristics may be caused. 
     SUMMARY OF THE INVENTION 
     The present invention is made in view of the above-described problems, and an object thereof is to provide a liquid ejection apparatus that is capable of suppressing an effect on an ejection operation of a liquid even in a case where the ejection operation of the liquid from an ejection port and a liquid transportation operation to a flow channel communicating with the ejection port are performed in parallel. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS.  1 A and  1 B  are diagrams illustrating an ink jet printing apparatus in the present embodiment; 
         FIG.  2    is a perspective view of a printing head used in the present embodiment; 
         FIGS.  3 A and  3 B  are diagrams illustrating a flow channel configuration of one flow channel block in an element substrate; 
         FIGS.  4 A to  4 C  are schematic views describing a structure and operations of a liquid transportation mechanism; 
         FIGS.  5 A and  5 B  are diagrams illustrating a waveform of a driving voltage applied to a thin film piezoelectric element; 
         FIGS.  6 A and  6 B  illustrate waveforms of two types of driving voltages applied to the thin film piezoelectric element; 
         FIGS.  7 A to  7 C  are timing charts illustrating a driving sequence of ejection elements and pumps in a first embodiment; 
         FIGS.  8 A to  8 C  are timing charts illustrating a driving sequence of the ejection elements and the pumps in a second embodiment; 
         FIGS.  9 A to  9 C  are timing charts illustrating a driving sequence of the ejection elements and the pumps in a third embodiment; 
         FIGS.  10 A and  10 B  are diagrams illustrating waveforms of the two types of the driving voltages applied to a piezoelectric element of the liquid transportation mechanism; 
         FIGS.  11 A and  11 B  are diagrams illustrating flows of ink in two regions provided in the flow channel block; 
         FIGS.  12 A to  12 C  are timing charts illustrating a driving sequence of the ejection elements and the pumps in a fourth embodiment; 
         FIGS.  13 A to  13 C  are timing charts illustrating a driving sequence of the ejection elements and the pumps in a fifth embodiment; 
         FIGS.  14 A to  14 C  are timing charts illustrating an example of a driving sequence of the ejection elements and the pumps in a sixth embodiment; 
         FIGS.  15 A to  15 C  are timing charts illustrating another example of the driving sequences of the ejection elements and the pumps in the sixth embodiment; and 
         FIGS.  16 A to  16 C  are timing charts illustrating a driving sequence of ejection element and pumps in a seventh embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Embodiments of a liquid ejection apparatus according to the present invention are described below in detail with reference to the drawings. In the embodiments described below, as a liquid ejection apparatus ejecting a liquid, an ink jet printing apparatus in which a printing head ejecting ink is mounted is described as an example. The embodiments below are not intended to limit the present invention according to the scope of claims, and not all the combinations of the characteristics described in the present embodiments are necessarily required for the means for solving the problems of the present invention. 
     First Embodiment 
       FIGS.  1 A and  1 B  are diagrams illustrating an ink jet printing apparatus (hereinafter, simply referred to as a printing apparatus)  1  in the present embodiment.  FIG.  1 A  is a perspective view illustrating a basic configuration, and  FIG.  1 B  is a block diagram illustrating a schematic configuration of a control system of the printing apparatus  1 . The printing apparatus  1  in the present embodiment is a so-called full line type printing apparatus and includes a conveyance mechanism  20  that conveys a printing medium S in an X direction, a printing head  10  capable of ejecting ink (liquid) from multiple ejection ports, and the control system illustrated in  FIG.  1 B . The conveyance mechanism  20  of the present embodiment conveys the printing medium S in the X direction by using a conveyance belt  20 A that is moved by driving of a not-illustrated conveyance motor. 
     The printing head  10  is a full line type printing head extending in a Y direction crossing (in the present example, orthogonal to) the conveyance direction of the printing medium S (X direction). In the printing head  10 , the multiple ejection ports capable of ejecting the ink are arrayed along the Y direction. The ejection ports may also be referred to as nozzles. A later-described circulation flow channel is formed inside the printing head  10 . The ink is supplied to the circulation flow channel from an ink supply unit  105  (see  FIG.  2   ), and the ink is supplied to the ejection ports communicating with the circulation flow channel. Then, while the printing medium S is continuously conveyed, multiple ejection elements provided to face the corresponding multiple ejection ports of the printing head  10  are driven based on printing data, and the ink is ejected as a droplet from the ejection ports corresponding to the ejection elements. Thus, an image is printed on the printing medium S. 
     Next, the control system of the printing apparatus  1  is described with reference to  FIG.  1 B . As illustrated in  FIG.  1 B , a control unit  2  includes a CPU  21 , a ROM  22 , and a RAM  23 . The CPU  21  serves as a control unit that controls overall the printing apparatus  1  while using the RAM  23  as a working area in accordance with a program stored in the ROM  22 . For example, the CPU  21  performs predetermined image processing on image data, which is received from a host apparatus  30  connected externally, in accordance with the program and a parameter stored in the ROM  22 . The CPU  21  then outputs printing data to an ejection driving circuit  201   d  and the ejection driving circuit  201   d  generates ejection data to cause multiple ejection elements (ejection units)  201  of the printing head  10  to perform ejection at a predetermined frequency. According to the ejection data, ejection energy for the multiple ejection elements  201  to eject the ink is generated, and the ink is ejected from the ejection ports with the ejection energy. As the ejection element, an electrothermal conversion element (heater), a piezo element, and the like can be used. In a case where the electrothermal conversion element is used, film boiling occurs in the ink by heating the electrothermal conversion element, and the bubble generation energy in the film boiling is used as the ejection energy to eject the ink from the ejection port. During the ink ejection operation by the printing head  10 , a conveyance motor that moves the conveyance belt  20 A illustrated in  FIG.  1 A  is driven through a conveyance driving circuit  11   d , and the printing medium S is conveyed in the X direction at a speed corresponding to the above-described predetermined frequency. With this, an image corresponding to the image data received from the host apparatus  30  is printed on the printing medium S. 
     In the printing head  10 , a liquid transportation mechanism  208  that generates a pressure to flow the ink in the circulation flow channel is provided. The liquid transportation mechanism  208  is driven by a voltage applied from a liquid transportation driving circuit  208   d , and an operation of the liquid transportation driving circuit  208   d  is controlled by the CPU  21 . Details of the liquid transportation mechanism  208  and driving control thereof are described later. 
       FIG.  2    is a perspective view of the printing head used in the present embodiment. The printing head  10  includes multiple element substrates  114  in which the multiple ejection elements are arrayed in the Y direction. The multiple element substrates  114  are arrayed in the Y direction. Here is illustrated the full line type ink jet printing head  10  in which the element substrates  114  are arrayed in the Y direction for a distance corresponding to the width of A4 size. 
     Each of the element substrates  114  is connected to the same electric wiring substrate  102  through a flexible wiring substrate  101 . On the electric wiring substrate  102 , a power supply terminal  103  that accepts power and a signal input terminal  104  that receives an ejection signal are arranged. The power supplied to the power supply terminal  103  and the signal received by the signal input terminal  104  are supplied from the ejection driving circuit  201   d  and the liquid transportation driving circuit  208   d.    
     On the other hand, in the ink supply unit  105 , there is formed a flow channel to supply the individual element substrate  114  with the ink supplied from a not-illustrated ink tank and collect the ink that is not consumed for printing. 
       FIGS.  3 A and  3 B  are diagrams illustrating a flow channel configuration of one flow channel block  200  in the element substrate  114 . Multiple flow channel blocks  200  are formed in each element substrate  114 , and  FIG.  3 A  is a plan view in which one of the multiple flow channel blocks is viewed from an ejection port surface  211   a  side.  FIG.  3 B  is a cross-sectional view taken along the IIIB-IIIB line in  FIG.  3 A . 
     As illustrated in  FIG.  3 A , each flow channel block  200  includes eight ejection ports  202  arrayed in the Y direction, eight pressure chambers  203  communicating with the ejection ports  202 , respectively, two supply flow channels (first flow channels)  205 , and two collection flow channels (second flow channels)  206 . Each of the two supply flow channels  205  connected to a common liquid chamber (liquid supply unit)  218  supplies the four pressure chambers  203  with the ink commonly, and each of the two collection flow channels  206  collects the ink from the four pressure chambers  203  commonly. One liquid transportation mechanism  208 , which is described later, is provided for each flow channel block. 
     The combination of the ejection ports  202 , the pressure chambers  203 , the supply flow channels  205 , and the collection flow channels  206  provided in each flow channel block is not limited to the example illustrated in  FIG.  3 A . For example, each flow channel block may include the four ejection ports  202 , the four pressure chambers  203  communicating with the corresponding ejection ports  202 , the one supply flow channel  205 , and the one collection flow channel  206 . In this case, the one supply flow channel  205  connected to the common liquid chamber  218  supplies the four pressure chambers  203  with the ink commonly, and the one collection flow channel  206  collects the ink from the four pressure chambers  203  commonly. It is ideal for the liquid transportation mechanism (liquid transportation unit)  208  to perform control corresponding to each ejection port; for this reason, if it is possible to produce a small liquid transportation mechanism  208 , each flow channel block is desired to have a smaller configuration. In the present embodiment, a structure portion in which the ejection ports  202 , the ejection elements  201 , and the pressure chambers  203  are combined with each other is referred to as an ejection unit. 
     As illustrated in  FIG.  3 B , the element substrate  114  of the present embodiment includes a second substrate  213  (vibration plate), a middle layer  214 , a first substrate  212 , a functional layer  209 , a flow channel formation member  210 , and an ejection port formation member  211  that are laminated in this order in a +Z direction. On a surface of the functional layer  209 , the ejection elements  201  as the electrothermal conversion element are arranged, and in the ejection port formation member  211 , the ejection ports  202  are formed in positions corresponding to the ejection elements  201 . Between the multiple ejection elements  201  arrayed in the Y direction, the flow channel formation member  210  laid between the functional layer  209  and the ejection port formation member  211  is arranged as partitions and forms the pressure chambers  203  corresponding to the individual ejection elements  201  and ejection ports  202 . 
     The ink stored in each pressure chamber  203  forms a meniscus in the ejection port  202  in a stable state. Once a voltage pulse is applied to the ejection element  201  in accordance with the ejection signal, film boiling occurs in the ink that is put in contact with the ejection element  201 , and the ink is ejected as a droplet from the ejection port  202  in the +Z direction with the growth energy of the generated bubble. 
     The ink in the pressure chamber  203  consumed by the ejection operation is newly supplied by the capillary force of the pressure chamber  203  and the ejection port  202 , and a meniscus is formed again in the ejection port  202 . 
     As illustrated in  FIG.  3 B , in the element substrate  114  of the present embodiment, the circulation flow channel is formed with each of the second substrate  213 , the middle layer  214 , the first substrate  212 , the functional layer  209 , the flow channel formation member  210 , and the ejection port formation member  211  serving as a wall. The circulation flow channel can be sectioned into the supply flow channel  205 , the pressure chamber  203 , the collection flow channel  206 , a liquid transportation chamber  222 , and a connection flow channel  207 . 
     The pressure chamber  203  is provided for each ejection element  201 . The supply flow channel  205  and the collection flow channel  206  are provided for every four ejection elements  201  in the flow channel block  200 . The supply flow channel  205  supplies the four pressure chambers  203  with the ink commonly, and the collection flow channel  206  collects the ink from the four pressure chambers  203  commonly. 
     One liquid transportation chamber  222  and one connection flow channel  207  are provided for every four ejection elements. Accordingly, two liquid transportation chambers  222  and two connection flow channels  207  are provided in each flow channel block  200 . Each liquid transportation chamber  222  is arranged in a position overlapped with the four ejection elements  201  in an XY plane. In each liquid transportation chamber  222 , the liquid transportation mechanism  208  capable of changing the inner volume of each liquid transportation chamber  222  is arranged, and the liquid transportation mechanism  208  circulates the ink for the four pressure chambers  203  commonly. The connection flow channel  207  is arranged in the substantially center in the Y direction of a range in which the four pressure chambers  203  are formed and connects the liquid transportation chamber  222  with the supply flow channel  205 . The position of the supply flow channel connected with the connection flow channel  207  is a position upstream of a diverging point into the two supply flow channels  205 . 
     In the above configuration, with the liquid transportation mechanism  208  driven by applying a later-described voltage thereto, the circulation can be made in the circulation flow channel formed in each flow channel block  200  through a supply port  219  from the common liquid chamber  218 . That is, the ink can be flowed in the order of the supply flow channel  205 , the pressure chamber  203 , the collection flow channel  206 , the liquid transportation chamber  222 , and the connection flow channel  207  of each flow channel block  200 . This circulation of the ink (liquid) is referred to as a first circulation, and the flow of the circulated ink is referred to as a first circulation flow. On the other hand, the circulation in which the ink flows in the order of the supply flow channel  205 , the connection flow channel  207 , the liquid transportation chamber  222 , the collection flow channel  206 , the pressure chamber  203 , and the supply flow channel  205  is referred to as a second circulation, and the flow of the circulated ink is referred to as a second circulation flow. 
     The flowing direction of the ink can be switched by changing a voltage waveform applied to the liquid transportation mechanism  208 . The voltage waveform is described later. The circulation of the ink is stably performed regardless of whether there is the ejection operation or the frequency of the ejection operation, and it is possible to supply fresh ink constantly to the vicinity of the ejection port  202 . Although it is not illustrated, it is favorable to provide a filter for preventing entering of foreign matters or air bubbles in the middle of the supply flow channel  205  upstream of the pressure chamber  203 . As a filter, a columnar structure or the like can be employed. 
     The element substrate  114  can be manufactured as follows, for example. First, a structure is formed in advance in each of the first substrate  212  and the second substrate  213 . Thereafter, the first substrate  212  and the second substrate  213  are pasted together with the middle layer  214  arranged therebetween, the middle layer  214  including a groove that is formed in a position in which the connection flow channel  207  is formed later. With this, the element substrate  114  can be manufactured. 
     Here is described a specific dimension example of each ejection unit formed in the element substrate  114 . In the present embodiment, the individual ejection elements  201 , ejection ports  202 , and pressure chambers  203  are arrayed in the Y direction at a density of 600 npi (nozzles per inch). The size of the ejection element  201  is 20 μm×20 μm, the diameter of the ejection port  202  is 18 μm, and the thickness of the ejection port  202 , that is, the thickness of the ejection port formation member  211  is 5 μm. The size of the pressure chamber  203  is the length in the X direction (length) of 100 μm×the length in the Y direction (width) of 37 μm×the length in the Z direction (height) of 5 μm. The viscosity of the ink to be used is 2 cP, and the ink ejection amount from the individual ejection port is 2 pL. 
     In the present embodiment, the driving frequency of the individual ejection element  201  is 10 KHz. Such a driving frequency is set based on the time required to apply a voltage to the individual ejection element, the ink is actually ejected, new ink is refilled additionally, and the next ejection operation is available in the individual ejection element  201 . 
     On the other hand, in the element substrate  114  of the present embodiment, the size of the liquid transportation chamber  222  is designed appropriately in accordance with an area occupied by the flow channel block. For example, in a case of the flow channel block including the eight pressure chambers  203  (600 npi), the size of the liquid transportation chamber  222  is 250 μm in the X direction×290 μm in the Y direction×250 μm in the Z direction. In a case of the flow channel block including the four pressure chambers  203  (600 npi), the size of the liquid transportation chamber  222  is 250 m in the X direction×120 μm in the Y direction×250 μm in the Z direction. The size of the connection flow channel  207  is based on 25 μm in the X direction×25 μm in the Y direction×25 μm in the Z direction. Additionally, the flow channel width (cross-section area) is optimized such that the liquid transportation efficiency is maximized in view of a flow channel load ratio (the connection flow channel  207 , the supply flow channel  205 , the pressure chamber  203 , and the collection flow channel  206 ) with respect to the liquid transportation chamber  222 . 
     In the present embodiment, with the dimension relationship as described above, the flow channel resistance and the inertance of the connection flow channel  207  are lower than the flow channel resistance and the inertance of a flow channel as a combination of the supply flow channel  205 , the collection flow channel  206 , and the pressure chamber  203 . Here, “the flow channel resistance and the inertance of a flow channel as a combination of the supply flow channel  205 , the collection flow channel  206 , and the pressure chamber  203 ” indicates a total of a sum of the parallel flow channel resistances of the respective supply flow channel  205 , multiple pressure chamber  203 , and collection flow channel  206  and a sum of the series flow channel resistances thereof. The dimension values of the portions described above are merely an example and may be changed as needed in accordance with required specifications. 
       FIGS.  4 A to  4 C  are schematic views describing a structure and operations of the liquid transportation device including the liquid transportation mechanism  208 . The liquid transportation device (pump) includes the liquid transportation mechanism (liquid transportation unit)  208  and the liquid transportation chamber  222 . The liquid transportation mechanism  208  configured with a piezoelectric actuator which includes a thin film piezoelectric element (hereinafter, simply referred to as a piezoelectric element)  224 , two electrodes  223  sandwiching the thin film piezoelectric element  224  from the front and back surfaces, and a diaphragm  221 . The liquid transportation mechanism  208  is arranged on the second substrate  213  such that the diaphragm  221  is exposed to the liquid transportation chamber  222 . 
     The diaphragm  221  mainly includes a laminate including an inorganic material with a thickness of about few m and a piezoelectric element with a thickness of about 1 to 3 μm. With a voltage applied to the piezoelectric element  224  through the two electrodes  223 , the diaphragm  221  is bent with respect to the piezoelectric element  224 , and the inner volume of the liquid transportation chamber  222  is changed. That is, with a change in the voltage applied to the two electrodes, the diaphragm  221  can be displaced in the ±Z directions, and the inner volume of the liquid transportation chamber  222  can be changed. 
     It is possible to form the liquid transportation device (pump) including such a liquid transportation mechanism  208  by using general-purpose Micro Electro Mechanical Systems (MEMS) technology. For example, the liquid transportation device including the liquid transportation mechanism  208  can be formed by vacuum plasma etching, anisotropic etching using an alkaline solution, or a combination thereof performed on an Si substrate (silicon substrate). The liquid transportation device may be formed by forming a flow channel including the liquid transportation chamber  222  and the liquid transportation mechanism  208  separately on multiple Si substrates and thereafter bonding or adhering the flow channel and the liquid transportation mechanism  208  to paste them together. 
     A unimorph piezoelectric actuator is used for the liquid transportation mechanism  208 . The unimorph piezoelectric actuator is formed by forming the piezoelectric element  224  on one surface side of the second substrate (also called a vibration plate)  213 . A material of the vibration plate  213  is not particularly limited as long as the conditions such as required mechanical characteristics and endurance reliability are satisfied. For example, silicon nitride film, silicon, metal, heat-resistant glass, and the like can be used properly. 
     The piezoelectric element  224  can be film-formed by using a method such as vacuum sputtering film formation, sol-gel film formation, and CVD film formation and is fired after the film formation in many cases. The firing method is not particularly limited; however, for example, a lamp annealing heating method in which firing at about 650° C. at the maximum is performed under oxygen atmosphere can be employed. In view of consistency with a process flow, the piezoelectric element  224  may be directly film-formed on the vibration plate  213  and fired integrally or may be film-formed on a substrate different from the vibration plate  213  to be fired and then peeled and transferred onto the vibration plate  213 . Alternatively, the piezoelectric element  224  may be film-formed on a substrate different from the vibration plate  213  and then fired integrally after being peeled and transferred onto the vibration plate  213 . 
     For the electrodes  223 , it is preferable to select a Pt or Ir system if the firing process is included; however, if the firing process can be separated, an AL system is selectable. In the present embodiment, a piezoelectric material of PZT system is used for the piezoelectric element  224 , and for the electrodes  223 , a material that allows the piezoelectric element  224  to be displaced with a state of high linearity, that is, being highly responsive to the applied voltage is used. As the outermost layer exposed to the atmosphere, a protection film of SiN system is used, and the entire liquid transportation mechanism  208  may be sealed with the protection film. 
     Then, a relay board for transmitting a signal wiring to the liquid transportation device and the liquid transportation device are adhered to a not-illustrated holding frame body, and the liquid transportation device and the relay board are electrically implemented by wire bonding. Additionally, a manifold to be an inlet port and an outlet port of the ink is fixed with an adhesive agent so as to be connected to the supply flow channel (first flow channel)  205  and the collection flow channel (second flow channel)  206 . 
       FIGS.  4 B and  4 C  are diagrams illustrating a state of displacement of the piezoelectric element  224  in a case where the voltage is applied to the piezoelectric element  224  in the liquid transportation mechanism  208  formed as described above.  FIG.  4 B  illustrates a standby state where a constant bias voltage (hereinafter, also referred to as an initial voltage) is applied to the piezoelectric element  224 . In the standby state, the diaphragm  221  is in a state where the inner volume of the liquid transportation chamber  222  is contracted. On the other hand,  FIG.  4 C  illustrates a state where the inner volume of the liquid transportation chamber  222  is expanded from the standby state in a case where a transitional waveform of about 30 V is applied to the piezoelectric element  224  as the maximum voltage (hereinafter, also referred to as a reached voltage). The diaphragm  221  is displaced between the standby state illustrated in  FIG.  4 B  and the expansion state illustrated in  FIG.  4 C  in accordance with the amount of the voltage applied to the piezoelectric element  224 . 
       FIG.  5 A  is a diagram illustrating a waveform of a driving voltage applied to the piezoelectric element  224 . The waveform of the voltage (driving voltage) applied to the piezoelectric element  224  is a triangle wave  301  as illustrated in  FIG.  5 A . The triangle wave  301  includes a step-up waveform  302  that is changed from the initial voltage to the reached voltage and a step-down waveform  303  that is changed from the reached voltage to the initial voltage. The triangle wave  301  used in the present embodiment is a waveform in which a voltage change period (step-up period) t1 in the step-up waveform  302  and a voltage change period (step-down period) t2 in the step-down waveform  303  are different. That is, the triangle wave  301  used in the present embodiment is a triangle wave in which the step-up waveform  302  and the step-down waveform  303  are asymmetrically changed with respect to time. 
     In the present specification, an absolute value of a voltage change amount per unit time (voltage change rate) is referred to as a rate. Additionally, the rate in the step-up waveform  302  is referred to as a step-up rate, and the rate in the step-down waveform  303  is referred to as a step-down rate; the rates are defined as follows: 
       step-up rate=|(reached voltage−initial voltage)|/step-up period;
 
       step-down rate=|(reached voltage−initial voltage)|/step-down period.
 
     It is preferable to use an asymmetric triangle wave in order to maximize a difference between a rapid change and a moderate change in a deformation speed of the diaphragm  221 ; however, a trapezoidal waveform including a component of an asymmetric triangle wave that generates a rapid change and a moderate change may also be used. In the present specification, descriptions are given by using an asymmetric triangle wave. 
     In the triangle wave  301  exemplified in  FIG.  5 A , the step-up period t1 is set to be a period shorter than the step-down period t2; thus, the step-up rate in the step-up waveform  302  is greater than the step-down rate in the step-down waveform  303 . That is, the triangle wave  301  exemplified in  FIG.  5 A  is a waveform in which the voltage is changed rapidly in the step-up period and the voltage is changed moderately in the step-down period. 
     In a case where such a triangle wave  301  is applied to the piezoelectric element  224 , in the step-up period t1, the piezoelectric element  224  is displaced in a direction in which the liquid transportation chamber  222  is expanded rapidly by the step-up waveform  302  with the great rate. On the other hand, the step-down waveform  303  is a waveform in which the voltage drops moderately in the step-down period t2. With the step-down waveform  303  applied to the piezoelectric element  224 , the piezoelectric element  224  is displaced in a direction in which the liquid transportation chamber  222  is contracted moderately. As a result, in the liquid transportation chamber  222 , a flow in a direction illustrated in  FIG.  4 A  (hereinafter, this direction is referred to as a first direction S1) is generated, and a similar flow is accordingly generated in the pressure chamber  203  as well. 
     As the driving voltage of the piezoelectric element  224 , it is also possible to use a triangle wave in which the step-down period t2 is set to be a period shorter than the step-up period t1. In the triangle wave, the voltage drops rapidly in the step-down waveform  303 , and the voltage rises moderately in the step-up waveform  302 . In this case, with the step-up waveform  302  applied, the piezoelectric element  224  is displaced in a direction in which the liquid transportation chamber  222  is expanded moderately. With the step-down waveform  303  applied, the piezoelectric element  224  is displaced in a direction in which the liquid transportation chamber  222  is contracted rapidly. As a result, in the flow channel block  200 , a flow in an opposite direction of the first direction S1 (second direction S2) is generated. 
     As described above, the driving voltage of the piezoelectric element used in the present embodiment includes the step-up period and the step-down period, and those two voltage change periods are periods different from each other. That is, one is a period shorter than the other, and the piezoelectric element  224  is changed more rapidly by the voltage waveform that is changed in the short period (first period), and a more rapid flow of the ink is generated. 
     Here is simply described a mechanism of generating a constant flow by making a rapid inner volume change and a moderate inner volume change in the liquid transportation chamber  222 . In a case where the liquid transportation chamber  222  is expanded rapidly, a vortex is generated under a high flow velocity on a side of the connection flow channel  207  with a small area of flow channel cross-section, and the flow channel resistance is increased greatly. As a result, flow of the ink from the connection flow channel  207  into the liquid transportation chamber  222  is obstructed. In contrast, on a side of the connection flow channel  207  with a wide area of flow channel cross-section, a variation in the flow channel resistance due to a flow velocity is less, and the ink flows smoothly from the collection flow channel  206  into the liquid transportation chamber  222 . Thereafter, once the liquid transportation chamber  222  is contracted moderately, the ink in the liquid transportation chamber  222  flows to the connection flow channel  207  side at a low speed; thus, no vortex is generated and an increase in the flow channel resistance is suppressed, and therefore the ink in the liquid transportation chamber  222  flows moderately to the supply flow channel side through the connection flow channel  207 . Thus, with the rapid expansion and the moderate contraction of the liquid transportation chamber  222 , the flow in the first direction S1 from the collection flow channel  206  to the supply flow channel  205  through the liquid transportation chamber  222  and the connection flow channel  207  is generated, and the first circulation is performed. 
     In a case where the liquid transportation chamber  222  is contracted rapidly, a vortex is generated under a high flow velocity on the side of the connection flow channel  207  with a small area of flow channel cross-section, and the flow channel resistance is increased greatly. As a result, flowing out of the ink from the liquid transportation chamber  222  to the connection flow channel  207  is obstructed. In contrast, on the side of the connection flow channel  207  with a wide area of flow channel cross-section, the ink smoothly flows out from the liquid transportation chamber  222  to the collection flow channel. Thereafter, once the liquid transportation chamber  222  is expanded moderately, the ink flows from the connection flow channel  207  into the liquid transportation chamber  222  at a low speed. Accordingly, with the rapid contraction and the moderate expansion of the liquid transportation chamber  222 , the flow of the ink in the second direction S2 from the connection flow channel  207  to the collection flow channel  206  through the liquid transportation chamber  222  is generated, and the second circulation is performed. 
     In the printing head  10  used in the ink jet printing apparatus, the ink (liquid) may be deteriorated because of evaporation of volatile components in the ejection port in which the ejection operation is not performed for a while. If the degree of the evaporation is varied between multiple ejection ports depending on the ejection frequency, the ejection amount and the ejection direction are also varied, and unevenness in the density and a streak may be found in an image. For this reason, in the ink jet printing head  10 , it is necessary to flow the ink in the flow channel block  200  in order to constantly supply fresh ink to the vicinity of the ejection port. However, in a case where a great pressure variation during the flow of the ink is propagated to the ejection port, the ejection of the liquid droplet from the ejection port may be affected. Therefore, it is required to achieve both the appropriate ejection of the liquid droplet and liquid transportation operation. 
       FIG.  5 B  is a diagram illustrating an ejection signal  304  that prompts generation of the ejection energy to eject the liquid droplet in the ejection element  201 . In the present embodiment, in order to achieve both the appropriate ejection of the liquid droplet and liquid transportation operation, timings of the driving voltage inputted to the piezoelectric element  224  and the ejection signal are controlled. Specifically, the application timing of the driving voltage is controlled such that the period in which the rapid voltage change occurs within the triangle wave applied to the liquid transportation mechanism  208  (voltage application period) and the ejection signal  304  do not coincide with each other. For example, since the step-up rate is greater than the step-down rate in the driving voltage (triangle wave) illustrated in  FIG.  5 A , the application timing of the driving voltage is controlled such that the step-up period t1 with the great rate does not coincide with an ejection period t3 of the ink. With this, as described later, both the appropriate ejection of the liquid droplet and liquid transportation operation can be achieved. Details of the application timing of the driving voltage are described later. 
     Next, liquid transportation control in the printing head  10  of the present embodiment is described in more details.  FIGS.  6 A and  6 B  illustrate waveforms of two types of driving voltages applied to the piezoelectric element  224  of the liquid transportation mechanism  208 . Although it is not illustrated in  FIGS.  6 A and  6 B , usually, a transient waveform as illustrated in  FIG.  5 A  is applied in actuality in a state where a bias voltage (not illustrated) is applied. As a waveform of the driving voltage, it is necessary to apply a waveform in which the step-up period t1 and the step-down period t2 are different from each other. 
       FIG.  6 A  illustrates a case of repeatedly applying a driving voltage (first driving voltage) including the step-up waveform  302  with a high rate prompting the rapid expansion of the inner volume of the liquid transportation chamber  222  and the step-down waveform  303  with a low rate prompting the moderate contraction of the inner volume of the liquid transportation chamber  222 . With this driving voltage applied to the piezoelectric element  224 , a flow of the ink toward a first flow direction (S1 direction) is formed in the pressure chamber  203 . 
     On the other hand,  FIG.  6 B  illustrates a driving voltage (second driving voltage) including a step-up waveform  305  prompting the moderate expansion of the inner volume of the liquid transportation chamber  222  and a step-down waveform  306  prompting the rapid contraction. In a case where this driving voltage is applied to the piezoelectric element  224 , a flow of the ink toward a second direction (S2 direction), which is an opposite direction of the first direction, is formed in the pressure chamber  203 . 
     Thus, in the present embodiment, liquid transportation of a constant amount of the ink in the S1 direction or the S2 direction can be performed with cycles of the rapid inner volume change and the moderate inner volume change in the liquid transportation chamber  222  by using the fluid characteristics that the flow channel resistance is non-linearly changed in accordance with a pressure. This liquid transportation operation may be continuously repeated by continuously applying the driving voltage as illustrated in  FIGS.  6 A and  6 B  or may be intermittently performed by intermittent applying the driving voltage (not illustrated). 
     Thus, in the present embodiment, a function as the liquid transportation device (also called a pump) is achieved by the flow channel that includes the liquid transportation chamber  222  and the liquid transportation mechanism  208  as a driving source, in which the flow channel resistance is non-linearly changed by a flow velocity of the ink flowed by the liquid transportation mechanism  208 . A merit of the configuration of this pump may include improvement in the reliability obtained by not using a mechanical part to implement a valve function. However, a valve using the non-linearity of the flow channel resistance like the present embodiment has a lower performance as a check valve than a valve using a mechanical part, and thus the liquid transportation efficiency is low. For this reason, it is favorable to perform the circulation of the ink in the vicinity of the ejection port  202  in the ejection unit of the liquid droplet, and to this end, the liquid transportation chamber  222  needs to be arranged in a flow channel in the vicinity of the nozzle. In this case, once the rapid inner volume change occurs in the liquid transportation chamber  222 , a great pressure applied to the ink due to the rapid inner volume change is likely to be propagated to the ejection port  202 , and this may affect the ejection of the liquid droplet. If a rapid pressure variation occurs in the liquid transportation chamber  222  during the ejection operation of the liquid droplet, the ejection characteristics such as the ejection amount and the ejection direction of the liquid droplet are likely to be varied due to the effect of the pressure variation. 
     The liquid transportation chamber  222  communicates with the common liquid chamber  218 , and in a case where there are the multiple liquid transportation chambers  222 , the liquid transportation chambers  222  communicate with each other through the common liquid chamber  218 . Once the rapid inner volume variation occurs in the liquid transportation chamber  222 , a great pressure is propagated also to a common liquid chamber  218  side. Once the multiple liquid transportation mechanisms  208  are operated concurrently, pulsation close to the ejection cycle occurs in the common liquid chamber  218 , and a variation in the meniscus positions in the ejection ports  202  is caused. As a result, the ejection characteristics is likely to be varied. The preconditions for stable liquid transportation is that the pressure in the common liquid chamber  218  with respect to the liquid transportation chamber  222  is a constant open pressure. Accordingly, an increase and decrease in the pressure in the common liquid chamber  218  from the open pressure is unfavorable because the liquid transportation operation itself is affected. 
     Here, the voltage waveform that causes the rapid inner volume change in the liquid transportation chamber  222  is the step-up waveform  302  prompting the expansion operation of the liquid transportation chamber  222  in  FIG.  6 A  and is the step-down waveform  306  prompting the contraction operation in  FIG.  6 B . Once the rapid expansion operation is performed in the liquid transportation chamber  222 , a negative pressure is generated instantly in the vicinity of the liquid transportation chamber  222  in the common liquid chamber  218 . Once the rapid contraction operation is performed in the liquid transportation chamber  222 , a positive pressure is generated instantly in the vicinity of the liquid transportation chamber  222  in the common liquid chamber  218 . 
     In a case where the piezoelectric element  224  is used as the driving source of the liquid transportation mechanism  208 , a time corresponding to the rapid inner volume change in the liquid transportation chamber  222  (t1 in  FIG.  6 A , and t2 in  FIG.  6 B ) is about 2.5 to 10 μsec depending on the design dimension of the liquid transportation device (pump). 
     The voltage waveform that causes the moderate inner volume change in the liquid transportation chamber  222  is the step-down waveform  303  prompting the contraction operation of the liquid transportation chamber  222  in  FIG.  6 A  and is the step-up waveform  305  prompting the expansion operation in  FIG.  6 B . In a case where the piezoelectric element (piezoelectric element  224 ) is used as the driving source of the liquid transportation mechanism  208 , a time corresponding to the moderate operation (t2 in  FIG.  6 A , and t1 in  FIG.  6 B ) is about 30 to 100 μsec depending on the design dimension of the pump. 
     In the above configuration, in order to achieve both the appropriate ejection operation of the liquid droplet and liquid transportation operation by the liquid transportation mechanism  208 , satisfying the following conditions for the ejection operation of the liquid droplet and the liquid transportation operation is effective. 
     (1) The ejection operation timing of the liquid droplet and the rapid inner volume variation timing in the liquid transportation chamber  222  do not coincide with each other. 
     (2) The number of the liquid transportation mechanisms  208  driven concurrently is small. 
     (3) The liquid transportation operations in opposite phases are performed in the liquid transportation mechanisms  208  arranged adjacent to each other or in the vicinity to compensate the pressure generated in the common liquid chamber  218 . 
     In order to satisfy the above-described conditions, in the present embodiment, driving control of the ejection elements  201  that generate the ejection energy of the liquid droplet and the liquid transportation mechanisms  208  is performed according to the sequence below. 
       FIGS.  7 A to  7 C  are timing charts illustrating a driving sequence of the ejection elements  201  and the pumps. 
     First, driving timings of the multiple ejection elements  201  provided in the printing head  10  are described. As described above, in the printing head  10 , an ejection port row including the multiple ejection ports  202  is formed, and the multiple ejection elements  201  are arranged corresponding to the multiple ejection ports  202 . Hereinafter, a row including the multiple ejection elements  201  is referred to as an ejection element row. The ejection element row is divided into multiple groups for every predetermined number of the ejection elements in accordance with physical array positions. The inside of each group is divided into driving blocks driven for corresponding ejection elements in different timings, and block numbers are provided to the driving blocks, respectively. 
     Here is more specifically described the group and the driving block in the printing head  10  with reference to  FIG.  7 A . The ejection element row illustrated in  FIG.  7 A  is divided into N groups from a first group to a not-illustrated Nth group. Each group includes the eight ejection elements  201 . Thus, the ejection element row includes 8×N (not-illustrated) ejection elements  201 . The ejection elements of the ejection port row is provided with ejection element numbers of 1 to (8×N) according to the arrayed order. In  FIG.  7 A , for the sake of simplifying the descriptions, as the ejection element row, first to third groups are illustrated and first to twenty-fourth ejection elements are illustrated. The first group includes first ejection element to eighth ejection element, the second group includes ninth ejection element to sixteenth ejection element, and the third group includes seventeenth ejection element to twenty-fourth ejection element. 
     The ejection elements of each group are divided into eight blocks driven in different timings, and each ejection element belongs to any one of a zeroth block to a seventh block. That is, first, ninth, seventeenth, and not-illustrated twenty-fifth, thirty-third, forty-first . . . belong to the zeroth block, and second, tenth, eighteenth, and twenty-sixth, thirty fourth, four second . . . belong to the first block. The same applies to the second to seventh blocks, and those eight blocks are driven with time-division. 
     In the printing head  10  formed as above, all the ejection elements are driven in accordance with pulses (ejection timing signals)  501  to  508  illustrated in  FIG.  7 B  in the ascending order from the zeroth block to the seventh block. That is, the blocks are sequentially driven in eight different timings in a cycle T. With this, the liquid droplet (ink droplet) is ejected from the ejection port  202  corresponding to each ejection element  201  in a temporal relation illustrated in  FIG.  7 C . Thus, the multiple ejection elements  201  are driven with time-division. 
     Since it is possible to suppress the power consumption in the printing operation by dividing the number of the ejection elements driven concurrently, the time-division method is an effective method for downsizing an electric power source for driving the printing head and a member for the electric power source such as a connector and a cable. In a case of the printing head using a heater as the ejection element, reduction of a voltage variation and fine adjustment of a voltage value are required in order to perform stable ejection taking into consideration the characteristics of the heater, the ink, and the like. Thus, with the time-division driving, it is possible to reduce the capacity of the electric power source, and it is possible to satisfy the requirements relating to the electric power source. 
     As described above, in a case where the time-division driving is performed in eight different timings, for example, if the cycle T is 10 KHz (100 μsec), a timing difference between adjacent ejection signals is 12.5 μsec. Since the ejection signal is about 1 to 2 μsec, the following remaining period that is about 10 μsec is a blanking period. In the blanking period, no ejection signal is applied to each ejection element. As with the number of time-division, there are eight periods as the blanking period in which no ejection signal is applied in the cycle T. That is, in the cycle T illustrated in  FIG.  7 B , periods of  511 ,  512 ,  513 ,  514 ,  515 ,  516 ,  517 , and  518  are the blanking period (pause period). 
     Next, a driving timing of the pump that is the liquid transportation device performing the liquid transportation operation in the circulation flow channel is described. In the example illustrated in  FIG.  7 A , each group of the printing element row includes the eight ejection elements  201 . The four ejection elements  201  included in each group correspond to a pair of the supply flow channel  205  and the collection flow channel  206  as illustrated in  FIG.  3 A . Thus, one pump that is able to be driven independently is provided for every adjacent four ejection elements  201 , and two pumps are provided for each group. Accordingly, pumps (pump A to pump F) that are able to be driven independently are provided for the first to third groups illustrated in  FIG.  7 A . The pump A corresponds to the first to fourth ejection elements, the pump B corresponds to the fifth to eighth ejection elements, the pump C corresponds to the ninth to twelfth ejection elements, the pump D corresponds to the thirteenth to sixteenth ejection elements, the pump E corresponds to the seventeenth to twentieth driving elements, and the pump F corresponds to the twenty-first to twenty-fourth ejection elements. 
     In  FIG.  7 B,  509    indicates a driving timing to drive each pump to rapidly change the inner volume of the liquid transportation chamber  222 . The period in the driving timing  509  corresponds to the step-up period t1 in  FIG.  6 A  or the step-down period t2 in  FIG.  6 B . The CPU  21  in the control unit  2  controls driving of the liquid transportation mechanism  208  through the liquid transportation driving circuit  208   d  such that the driving timing  509  is within a range of the blanking period ( 511 ,  512 ,  513 ,  514 ,  515 ,  516 ,  517 , or  518 ). 
     In the example illustrated in  FIGS.  7 A to  7 C , the driving timing  509  of the pump A is set in the blanking period  511 . The driving timing  509  of the pump B is set in the blanking period  515 , the driving timing  509  of the pump C is set in the blanking period  513 , and the driving timing  509  of the pump D is set in the blanking period  517 , respectively. Additionally, the driving timing  509  of the pump E is set in the blanking period  511  as with the pump A. With this, an impact of the pulsation that occurs during the liquid transportation on the liquid ejection can be minimized. Moreover, a variation in the pressure that occurs in the common liquid chamber  218  can also be suppressed by distributing the driving timings of the pumps as illustrated in  FIG.  7 B . 
     A waveform conformable to the triangle wave illustrated in  FIG.  5 A  is used as the waveform of the driving voltage applied to the piezoelectric element  224  provided in the pump. For example, there is used a driving voltage with the maximum voltage of 30 V, the driving cycle of 50 μsec, the driving frequency of 20 KHz, the step-up period of 2.5 sec, and the step-down period of 47.5 μsec while the direction in which the inner volume of the liquid transportation chamber  222  is expanded is a positive direction of the voltage. 
     The above-described driving voltage was inputted to the liquid transportation mechanism of the pump, and a flow of the ink in the pressure chamber  203  was evaluated. As the evaluation method, commonly known Particle Tracking Velocimetry (PTV) was employed. With measurement of a flow velocity, it was confirmed that the ink is circulated at a favorable speed in the supply flow channel  205 , the pressure chamber  203 , the collection flow channel  206 , the liquid transportation chamber  222 , and the connection flow channel  207 , and fresh ink can be supplied stably to the vicinity of the ejection port  202 . In a state where the ink is circulated, the ejection operation of the liquid droplet (ink droplet) was started, and the situation of the ejection of the ink droplet was observed by a high-speed camera. The ejection situation of the liquid droplet was observed while changing the relationship between the driving timing of the ejection element to eject the liquid droplet and the timing of the rapid operation of the actuator. 
     With the driving timing  509  of the pump in which the inner volume of the liquid transportation chamber  222  is changed rapidly set to the blanking period including no ejection signal of the ejection element  201  as illustrated in  FIG.  7 B , it was confirmed that the ejection speed and the volume of the liquid droplet are stable. On the other hand, with the driving timing  509  of the pump in which the inner volume of the liquid transportation chamber  222  is changed rapidly set close to the timing of the ejection signal to coincide therewith, it was observed that the ejection speed of the liquid droplet is changed dramatically, and it was confirmed that the ejection characteristics become unstable. Additionally, with the ejection timing and the driving timing  509  pump set away from each other from the above state, it was confirmed that the liquid droplet is ejected stably. 
     In the above-described embodiment, the flow channel block  200  of the mode illustrated in  FIGS.  3 A and  3 B  is used; however, the configuration of the flow channel block is not limited to the mode illustrated in  FIGS.  3 A and  3 B . The numbers of the ejection elements  201  and the pressure chambers  203  that circulate the ink with one liquid transportation mechanism  208  are appropriately changeable depending on the required density and liquid transportation performance of the ejection elements. For example, a mode in which one pump is allocated for two ejection elements, a mode in which one pump is allocated for eight ejection elements, or another mode may be applicable. The numbers of the supply flow channels  205  and the collection flow channels  206  provided in each flow channel block may be three or more, or may be one. 
     In  FIGS.  3 A and  3 B , the element substrate  114  of a mode in which the ejection elements are arrayed in the Y direction in one row is described as an example; however, in the element substrate  114 , two or more rows of the ejection element rows as illustrated in  FIGS.  3 A and  3 B  may be arranged in the X direction. 
     In the above-described embodiment, a mode in which the electrothermal conversion element is used as the ejection element  201  and the ink is ejected by the growth energy of the bubble generated by making film boiling on the electrothermal conversion element is applied; however, it is not limited to such an ejection method. For example, various types of elements such as a piezoelectric actuator, a static actuator, a mechanical/impact driving type actuator, a voice coil actuator, and a magnetostriction driving type actuator can be employed as the ejection element. 
     In the above descriptions, a configuration to perform the liquid transportation operation in the long full line type printing head  10  in which the ejection elements and the ejection ports are arrayed in a range corresponding to the width of the printing medium is described as an example; however, it is not limited thereto. A configuration to perform the liquid transportation operation in the printing head  10  indicated in the above-described embodiment is also applicable to and effective for a relatively short serial type printing head in which the ejection ports and the ejection elements are arrayed along a conveyance direction of the printing medium. Note that, since the ink is likely to be evaporated and deteriorated in the long full line type printing head  10 , it is possible to enjoy more apparent effect by applying the configuration to perform the above-described liquid transportation operation to the full line type printing head. 
     Second Embodiment 
     Next, a second embodiment of the present invention is described. The configuration of  FIGS.  1 A to  6 B  is similarly included in the present embodiment as well, and different points from the first embodiment are mainly described below.  FIGS.  8 A to  8 C  are timing charts illustrating a driving sequence of the ejection elements and the pumps in the second embodiment. In the present embodiment, the pumps are driven such that the liquid transportation efficiency by the pump is enhanced about twice the liquid transportation efficiency of the first embodiment. 
     The liquid transportation performance of the pump is substantially proportional to the number of operations per unit time. For this reason, in the present embodiment, the ejection cycle T of the ejection elements  201  is 100 μsec, the driving cycle of the liquid transportation mechanism  208  is 50 μsec, and two cycles of the driving voltages are inputted to each pump during the cycle T of the ejection elements. With this, in the second embodiment, the driving voltages are inputted continuously, and accordingly, the liquid transportation operations are also performed continuously. On the other hand, in the above-described first embodiment, one cycle of the driving voltage is inputted during the ejection cycle T, and thus the pump is driven intermittently. 
     As with the first embodiment, the flow of the ink in the pressure chamber  203  was evaluated by the PTV in the present embodiment as well. As a result, it was confirmed that the flow velocity of the ink in the pressure chamber  203  is improved about twofold. Additionally, with the ejection of the ink and the liquid transportation operation performed concurrently based on the present sequence, it was confirmed that the ejection operation of the liquid droplet is performed stably. 
     Third Embodiment 
     Next, a third embodiment of the present invention is described.  FIGS.  9 A to  9 C  are timing charts illustrating a driving sequence of the ejection elements and the pumps in the third embodiment. In the present embodiment, the liquid transportation is performed while switching the direction in which the liquid transportation is performed at a predetermined timing. The driving timing  509  (vertical broken line) illustrated in  FIG.  9 B  indicates a timing of the liquid transportation of the ink in a forward direction (first direction), and a driving timing  510  (horizontal broken line) indicates a timing of the liquid transportation of the ink in an opposite direction of the forward direction (second direction). That is,  FIGS.  9 A to  9 C  illustrate a state where the flow direction of the ink is switched. 
     The liquid transportation direction of the ink can be switched by switching the voltage waveform of the driving voltage applied to the piezoelectric element  224  of the liquid transportation mechanism  208 . For example, a flow in the forward direction is generated in the pressure chamber  203  by applying the driving voltage illustrated in  FIG.  6 A  to the piezoelectric element  224  by a predetermined number of times. Thereafter, the driving voltage is switched to the driving voltage of the voltage waveform as illustrated in  FIG.  6 B  at a predetermined timing. With this, a flow in the opposite direction can be generated. This switching of the voltage is performed by the CPU  21  in the control unit  2  controlling the liquid transportation driving circuit  208   d . Switching of the flow direction of the ink as described above is highly effective to maintain the ejection performance of the printing head  10 . 
     That is, if a flow in a certain direction continues, a vortex is generated in the flow of the ink in a curved portion and the like in the flow channel, and the ink stagnates. Aggregates, air bubbles, and the like in the ink are likely to be accumulated in a portion with the stagnation, and if this state continues, the aggregates and air bubbles are increased, and the suppling capacity of the ink and the ejection performance of the liquid droplet may be reduced. To deal with this, in the present embodiment, control to switch the direction of the flow of the ink at a predetermined timing is performed. With this, even if there temporarily occur a vortex and stagnation in a curved portion and the like in the flow channel, the vortex and stagnation are moved and disappear by switching the flow of the ink. As a result, the aggregates and air bubbles do not stay in a fixed position and are discharged in accordance with the flow of the ink. Thus, it is possible to maintain the ejection performance in the printing head  10  for a longer period of time. 
     Fourth Embodiment 
     Next, a fourth embodiment of the present invention is described. In the present embodiment, driving of the pump is controlled such that flows of the ink generated by adjacent pumps have opposite phases to compensate the pulsation of the pressure generated in the common liquid chamber  218 . With this, it is possible to reduce a pressure variation in the pressure chamber  203  due to a pressure variation in the common liquid chamber  218 , and unevenness of the ejection performance in a macro perspective can be suppressed. 
       FIGS.  10 A and  10 B  are diagrams illustrating waveforms of the two types of the driving voltages applied to the piezoelectric element  224  of the liquid transportation mechanism  208  in the present embodiment. The driving voltage of the waveform illustrated in  FIG.  10 A  indicates a driving voltage for driving one of adjacent two pumps, and the driving voltage of the waveform illustrated in  FIG.  10 B  indicates a driving voltage for driving the other pump. In a case where the pumps are driven by the driving voltages, the directions of the flows of the ink are directions opposite of each other. In  FIGS.  10 A and  10 B , a pair of driving waveforms that are able to suppress the pulsation in the common liquid chamber  218  are illustrated with a thick solid line. 
     In  FIG.  10 A,  302    indicates a voltage waveform (step-up waveform) in the step-up period t1 prompting the rapid expansion operation of the liquid transportation chamber  222 . In a case where the pump is driven by the voltage waveform  302 , a strong negative pressure is generated in a local portion on the common liquid chamber  218  side. In  FIG.  10 B,  306    indicates a voltage waveform in the step-down period t2 prompting the rapid contraction operation of the liquid transportation chamber  222 . In a case where the pump is driven by the voltage waveform  306  (step-down waveform), a strong positive pressure is generated in a local portion on the common liquid chamber  218  side. 
       303  illustrated in  FIG.  10 A  indicates a voltage waveform (step-down waveform) in the step-down period t2 prompting the moderate contraction operation of the liquid transportation chamber  222 .  305  in  FIG.  10 B  indicates a voltage waveform (step-up waveform) in the step-up period t1 prompting the moderate expansion operation of the liquid transportation chamber  222 . Both the voltage waveforms  303  and  305  are voltage waveforms to change the liquid transportation chamber  222  moderately; thus, a pressure propagated to the common liquid chamber  218  with a change in the liquid transportation chamber  222  by those voltage waveforms is small, and an effect on the pressure in the common liquid chamber  218  can be ignored. 
     The spatial distance between the adjacent pumps is close; thus, the adjacent pumps are driven concurrently by the step-up waveform  302  and the step-down waveform  306  prompting the rapid change in the liquid transportation chamber  222 , respectively. In this case, the local pressures generated in the common liquid chamber  218  by the pumps have opposite directions, and thus, in a macro perspective, a pressure distribution in the common liquid chamber  218  can be compensated. As a result, the pulsation generated in the common liquid chamber  218  can be suppressed more than a case of driving the adjacent pumps only by the voltage waveforms of the same phases. As a result, the pressure variation provided to the ink near the ejection port  202  from the common liquid chamber  218  is reduced, and it is possible to stabilize the ejection characteristics. 
       FIGS.  11 A and  11 B  are diagrams illustrating flows of the ink in two regions  200   a  and  200   b  provided in one flow channel block  200 , while  FIG.  11 A  is a plan view, and  FIG.  11 B  is a cross-sectional view taken along the XIB-XIB line in  FIG.  11 A . The flow channel block  200  illustrated in  FIGS.  11 A and  11 B  has a configuration similar to that illustrated in  FIG.  3   . Each of the two regions  200   a  and  200   b  provided in the flow channel block is provided with the four pressure chambers  203 , one supply flow channel  205 , and one collection flow channel  206 . Additionally, each region is provided with one independent pump including the liquid transportation chamber  222  and the liquid transportation mechanism  208 . That is, one flow channel block  200  is provided with two adjacent pumps. The two pumps each serve to flow the ink to the four pressure chambers  203 . 
     One of the two pumps is driven by the driving voltage of the waveform illustrated in  FIG.  10 A , and the other pump is driven by the driving voltage of the waveform illustrated in  FIG.  10 B . With this, in the flow channels (the supply flow channel  205  and the collection flow channel  206 ) of the one region  200   a , a flow in the first direction S1 is generated, and in the flow channels (the supply flow channel  205  and the collection flow channel  206 ) of the other region  200   b , a flow in the second direction S2, which is an opposite direction of the first direction, is generated. As a result, the local pressures generated in the common liquid chamber  218  are compensated from each other, and occurrence of the pulsation is suppressed. 
       FIGS.  12 A to  12 C  are timing charts illustrating a driving sequence of the ejection elements and the pumps in a case where driving is performed such that flows of the adjacent pumps have opposite phases. The driving timing  509  (vertical broken line) illustrated in  FIG.  12 B  indicates a timing in which the pump is driven by the voltage waveform  302  in  FIG.  10 A , and the driving timing  510  (horizontal broken line) indicates a timing in which the pump is driven by the voltage waveform  306  illustrated in  FIG.  10 B . The driving timing  509  and the driving timing  510  are synchronized to each other. 
     Accordingly, the pumps adjacent to each other in the same group (same flow channel block) perform the rapid liquid transportation operations that generate the rapid inner volume change in the respective liquid transportation chambers  222  in the same driving timing in opposing directions. That is, the pump A and the pump B perform the rapid liquid transportation operation in each of the blanking periods  511  and  515  concurrently in opposing directions, and the pump C and the pump D perform the rapid liquid transportation operation in each of the blanking periods  513  and  517  concurrently in opposing directions. Additionally, the pump E and the pump F perform the rapid liquid transportation operation in each of the blanking period  511  and  515  concurrently in opposing directions. 
     In the present embodiment, the driving timings of the two pumps in the first group are synchronized but do not coincide with the driving timings of the pumps of the adjacent second group. However, the driving timings of the pumps in the third group in a position away from the first group are synchronized with the driving timings of the pumps in the first group. 
     With the pumps driven as described above and the ejection characteristics in each ejection unit measured, it was confirmed that a periodic swell, variation, and the like of the ejection characteristics are suppressed. In the present embodiment, the mode in which the two pumps are provided in each group is exemplified; however, the number of the pumps provided in each group is not limited thereto. Note that, in order to make the compensation by performing the rapid liquid transportation operations in the adjacent pumps in the same driving timing in opposing directions as described above, the number of the pumps provided in each group is preferably an even number. 
     Fifth Embodiment 
     Next, a fifth embodiment of the present invention is described.  FIGS.  13 A to  13 C  are timing charts illustrating a driving sequence of the pumps in the fifth embodiment. In the present embodiment, an example in which the pump is driven so as to reduce the liquid transportation amount in the above-described fourth embodiment by half. In the present embodiment, driving of the pump by the voltage waveform  302  illustrated in  FIG.  10 A  is performed in the driving timing  509 , and driving of the pump by the voltage waveform  306  illustrated in  FIG.  10 B  is performed in the driving timing  510 . Additionally, the driving timing of the pump by the voltage waveform  302  and the driving timing of the pump by the voltage waveform  306  are synchronized. The above points are similar to that in the fourth embodiment. 
     Note that, in the present embodiment, driving of the pump A is performed after driving of the first to fourth ejection elements ends and before the fifth to eighth ejection elements are driven. Driving of the pump B is performed after driving of the first to fourth ejection elements and before driving of the fifth to eighth ejection elements starts. Thus, in the present embodiment, the rapid liquid transportation operation by the pump is temporally away from the ejection operation of the liquid droplet, and therefore an effect on the ejection performance can be reduced. Additionally, since driving of the pumps is controlled such that the flows of the ink generated by the two pumps in the same group have opposite phases, pressures generated in the pressure chamber  203  can be compensated. With a reduction in the liquid transportation amount by the pump, an effect on the ejection operation due to driving of the pump can be suppressed. 
     Sixth Embodiment 
     Next, a sixth embodiment of the present invention is described. In the above-described embodiments, an example of performing the opposite phase operation to flow the ink in opposite directions in the two pumps corresponding to the same nozzle group is described. In contrast, in the present embodiment, the opposite phase operation to flow the ink in opposite directions is performed between the pumps in nozzle groups adjacent to each other. 
       FIGS.  14 A to  14 C  are timing charts illustrating a driving sequence of the pumps in the sixth embodiment. In the example illustrated in  FIGS.  14 A to  14 C , the opposite phase operation is performed by the pump B corresponding to the fifth to eighth ejection elements in the first group and the pump C corresponding to the ninth to twelfth ejection elements in the second group. Additionally, the opposite phase operation is performed by the pump D corresponding to the thirteenth to sixteenth ejection elements in the second group and the pump E corresponding to the seventeenth to twentieth ejection elements in the third group. In the present embodiment, since the opposite phase operation is also performed between the adjacent pumps, it is possible to suppress generation of the pulsation in the common liquid chamber  218 . 
     In the example illustrated in  FIGS.  15 A to  15 C , the opposite phase operation is performed by the pump A corresponding to the first to fourth ejection elements in the first group and the pump C corresponding to the ninth to twelfth ejection elements in the second group. Additionally, the opposite phase operation is performed by the pump D corresponding to the thirteenth to sixteenth ejection elements in the second group and the pump F corresponding to the twenty-first to twenty-fourth ejection elements in the third group. 
     In the present example, the opposite phase operation is performed between the pumps not adjacent to each other; however, it is possible to obtain an effect to suppress the pulsation in the common liquid chamber  218  in this case as well. Regarding routing of a driving wiring and the flow channel structure, it may be difficult to perform the opposite phase operation of pumps adjacent to each other, and the present example is effective in such a case. 
     Seventh Embodiment 
     Next, a seventh embodiment of the present invention is described.  FIGS.  16 A to  16 C  are timing charts illustrating a driving sequence of the pumps in the seventh embodiment. In the present embodiment, each flow channel block  200  includes the eight ejection elements  201  and pressure chambers  203  and also has a configuration to flow the ink commonly to the eight pressure chambers  203  by one pump. Each flow channel block  200  corresponds to one nozzle group. In  FIGS.  16 A to  16 C , only the first to third nozzle groups are illustrated as with the above-described embodiments. 
     The opposite phase operation between the adjacent pumps is performed in the present embodiment as well. That is, the opposite phase operation is performed between the pump A corresponding to all the ejection elements in the first group and the pump B corresponding to all the ejection elements in the second group. Additionally, the opposite phase operation is performed between the pump C corresponding to all the ejection elements in the third group and the pump D corresponding to all the ejection elements in the fourth group. 
     In the present embodiment, a case where the density of the ejection elements is 1200 npi is assumed. In a case where the ejection elements  201  have a high density of about 1200 npi, an area occupied by each flow channel block is small, and an area of about eight nozzles is required to form one pump. In such a case, it is possible to achieve both the ejection operation and the liquid transportation operation of the ink by employing the driving sequence as illustrated in  FIGS.  16 A to  16 C . 
     In the above embodiments, drying in the ejection unit is likely to progress near an end portion of the ejection port row; thus, the liquid transportation amount by the liquid transportation mechanism  208  may be increased to be relatively greater than that in a portion other than the end portion of the ejection port row (for example, central portion). This increase can be made by increasing an absolute value (rate) of the change amount in the voltage applied to the piezoelectric element of the liquid transportation mechanism  208 . 
     In a case of executing the printing operation, it is possible to grasp in advance the number of times of ejection of the liquid droplet, that is, the number of times of driving of the ejection element  201 , based on the printing data; for this reason, it is also possible to relatively increase the liquid transportation amount to the vicinity of the ejection unit in which the number of times of ejection is less. 
     Additionally, in a case where the ejection unit is positioned outside the printing medium in a serial type printing apparatus that performs printing by relatively moving the printing head  10  with respect to the printing medium, the liquid transportation amount may be increased more than a case where the ejection unit is positioned inside the printing medium. With this, thickening, drying, and the like of the ink caused by the ejection unit positioned outside the printing medium can be suppressed more effectively. 
     Preliminary ejection to perform ejection that does not contribute printing may be a situation where the ejection unit is positioned outside the printing medium. In the preliminary ejection, in general, more ink is ejected from the ejection port than that in the printing operation period. For this reason, in a preliminary ejection period, more ink needs to be supplied to the ejection port. Thus, in a case where the preliminary ejection is performed, the liquid transportation amount of the ink by the pump is favorably increased to be greater than that in the printing operation period. The liquid transportation amount is increased by increasing the driving amount of the pump. That is, the liquid transportation amount is increased by increasing the number of times of applying the driving voltage to the liquid transportation mechanism  208 . In the preliminary ejection, it is unnecessary to take into consideration a landing accuracy of the liquid droplet; for this reason, there is no problem even if a little variation occurs in the pressure near the ejection port due to the increase in the liquid transportation amount of the pump. 
     As described above, according to the printing apparatus of the embodiments, flowing and circulation of the ink in the printing head  10  can be performed while suppressing an effect on the ejection performance of the ink, and it is possible to maintain the ejection performance in the printing head  10  for a long period of time. The driving sequences of the liquid transportation devices described in the embodiments may be combined with each other. 
     OTHER EMBODIMENTS 
     In the above-described embodiments, the liquid transportation unit that changes the inner volume of the liquid transportation chamber  222  is formed of the liquid transportation mechanism  208  using the piezoelectric element (piezo) that responses substantially linearly to the voltage waveform of the applied driving voltage; however, it is not limited thereto. For example, it is also possible to arrange an energy generation unit such as an electrothermal conversion element (heater) in the liquid transportation chamber to use as the driving source of the liquid transportation. In a case where the electrothermal conversion element is used as the energy generation unit, an electrothermal converter is driven based on the driving signal inputted by the control unit, and heat energy is generated. With this heat energy, film boiling occurs in the liquid (ink), and the liquid in the liquid transportation chamber flows with the bubble generation energy in the film boiling. In this case, the relatively rapid pressure change during bubble generation and the relatively moderate pressure change during bubble disappearance are used to change the inner volume ratio occupied by the air bubbles in the liquid transportation chamber, and thus the liquid transportation operation based on the operations illustrated in  FIGS.  4 B and  4 C  can be performed. However, since the rapid pressure change occurs in the ink during bubble generation, the pressure change is likely to be propagated to the vicinity of the ejection port. Thus, in a case where the ejection timing of the liquid and the bubble generation in the liquid transportation operation temporarily coincide with each other, the amount and the direction of the ejected liquid droplet may be varied, and the ejection performance may be reduced. 
     Accordingly, in a case where the electrothermal conversion element is used, the input timing of the driving signal to control driving of the electrothermal conversion element is controlled by the control unit. That is, the input timing of the driving signal is controlled such that the timing of the bubble generation by the electrothermal conversion element does not coincide with the ejection timing of the liquid. As an example, the input timing of the driving signal may be controlled such that the ejection timing coincides with a bubble disappearance period. Since the pressure of the liquid is changed moderately during the bubble disappearance, if the bubble disappearance period coincides with the ejection timing, it is possible to suppress the reduction in the ejection performance. However, the input timing of the driving signal is not limited thereto. The input timing of the driving signal may be controlled arbitrarily as long as the ejection timing of the liquid and the bubble generation timing do not coincide with each other. As the driving voltage of the electrothermal conversion element, not the driving voltage of an analog waveform like the piezoelectric element but the driving voltage of a pulse waveform is used. Therefore, the driving timing of the electrothermal conversion element can be controlled by controlling the pulse width of the pulse waveform, a combination of multiple pulses, or the like. 
     According to the present invention, even in a case where an ejection operation of a liquid from an ejection port and a liquid transportation operation to a flow channel communicating with the ejection port are performed in parallel, it is possible to suppress an effect on the ejection operation of the liquid. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2021-186526 filed Nov. 16, 2021, which is hereby incorporated by reference wherein in its entirety.