Patent Publication Number: US-10780691-B2

Title: Drive waveform generating device, liquid discharge apparatus, and head driving method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application is based on and claims priority pursuant to 35 U.S.C. § 119(a) to Japanese Patent Application No. 2018-050913, filed on Mar. 19, 2018, in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein. 
     BACKGROUND 
     Technical Field 
     The present disclosure relates to a drive waveform generating device, a liquid discharge apparatus, and a head driving method. 
     Discussion of the Background Art 
     In an apparatus using a liquid discharge head, to prevent increases in viscosity of liquid, micro vibration driving (also referred to as micro vibration, non-discharge driving, or preliminary discharge) is performed to shake the meniscus of a nozzle to such an extent that no droplet is discharged. 
     A pulse for discharging a liquid is called “discharge pulse”. Conventionally used is a discharge pulse including a raising waveform element that rises in two stages. A second stage includes a voltage holding waveform element and a raising waveform element, which are used as a micro vibrating pulse. 
     SUMMARY 
     According to an aspect of this disclosure, a drive waveform generating device includes circuitry configured to generate a drive waveform to be applied to a pressure generation element of a liquid discharge head. The drive waveform including a first waveform and a second waveform continuous in time series with the first waveform. The first waveform includes a falling element to lower a potential from an intermediate potential to a lower potential lower than the intermediate potential, a raising element to raise the potential from the lower potential to a higher potential higher than the intermediate potential, and a potential holding element to hold the higher potential. The second waveform includes a raising element to raise the potential from the intermediate potential to a raised potential higher than the intermediate potential, a potential holding element to hold the raised potential, and a falling element to lower the potential from the raised potential to the intermediate potential. 
     According to another aspect of this disclosure, a liquid discharge apparatus includes a liquid discharge head and drive waveform generating device described above. The liquid discharge head includes a nozzle configured to discharge liquid and the pressure generation element configured to generate a pressure to discharge liquid from the nozzle. 
     Yet another aspect concerns a method for applying a drive waveform to a pressure generation element of a liquid discharge head to drive the liquid discharge head. The method includes generating the drive waveform to be applied to the pressure generation element. The drive waveform includes the first waveform described above and a second waveform. The second waveform is discontinuous with the potential holding element of the first waveform. The second waveform includes a raising element to raise the potential from the intermediate potential to a raised potential higher than the intermediate potential, a potential holding element to hold the raised potential, and a falling element to lower the potential from the raised potential to the intermediate potential. The method further includes performing discharge driving to drive the liquid discharge head to discharge liquid. The discharge driving includes inputting the first waveform to the pressure generation element; interrupting an input of the first waveform to the pressure generation element while the higher potential is held in the first waveform, and inputting the second waveform to the pressure generation element while the raised potential is held in the second waveform. The method further includes performing non-discharge driving to drive the liquid discharge head not to discharge the liquid. The non-discharge driving includes inputting the second waveform to the pressure generation element. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the disclosure and many of the attendant advantages and features thereof can be readily obtained and understood from the following detailed description with reference to the accompanying drawings, wherein: 
         FIG. 1  is a plan view of a mechanism as an example of a liquid discharge apparatus according to an embodiment of the present disclosure; 
         FIG. 2  is a side view of a main part of the mechanism; 
         FIG. 3  is a cross-sectional view of an example of a liquid discharge head in a direction orthogonal to a nozzle arrangement direction (liquid chamber longitudinal direction); 
         FIG. 4  is a cross-sectional view of the example of the liquid discharge head in the nozzle arrangement direction (liquid chamber short direction); 
         FIG. 5  is a block diagram of a control device of the apparatus; 
         FIG. 6  is a block diagram of an example of a portion related to head drive control; 
         FIGS. 7A to 7C  are views for explaining a common drive waveform, a mask signal, a non-discharge drive waveform, and a discharge drive waveform in a first embodiment of the present disclosure; 
         FIGS. 8A to 8C  are views for explaining a common drive waveform, a selection signal (mask signal), a non-discharge drive waveform, and a discharge drive waveform in a second embodiment of the present disclosure; 
         FIGS. 9A to 9C  are views for explaining a common drive waveform, a selection signal (mask signal), a non-discharge drive waveform, and a discharge drive waveform in a third embodiment of the present disclosure; 
         FIGS. 10A to 10C  are views for explaining a common drive waveform, a selection signal (mask signal), a non-discharge drive waveform, and a discharge drive waveform in a fourth embodiment of the present disclosure; 
         FIGS. 11A to 11C  are views for explaining a common drive waveform, a selection signal (mask signal), a non-discharge drive waveform, and a discharge drive waveform in a fifth embodiment of the present disclosure; 
         FIGS. 12A to 12C  are views for explaining a common drive waveform, a selection signal (mask signal), a non-discharge drive waveform, and a discharge drive waveform in a sixth embodiment of the present disclosure; and 
         FIGS. 13A to 13C  are views for explaining a common drive waveform, a selection signal (mask signal), a non-discharge drive waveform, and a discharge drive waveform in a seventh embodiment of the present disclosure. 
     
    
    
     The accompanying drawings are intended to depict embodiments of the present invention and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. 
     DETAILED DESCRIPTION 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. 
     In describing embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that have a similar function, operate in a similar manner, and achieve a similar result. 
     Hereinafter, embodiments of the present disclosure will be described with reference to the attached drawings. First, an example of a liquid discharge apparatus according to an embodiment of the present disclosure will be described with reference to  FIG. 1 .  FIG. 1  is a schematic view of the apparatus. 
     The liquid discharge apparatus includes a full line type head, and has an apparatus main body  1  and an exit unit  2  for earning drying time. The exit unit  2  is on the size of the apparatus main body  1 . 
     In this apparatus, a continuous sheet is used as a medium  10  to which a liquid is to be attached. The medium  10  is unwound from a root winding roller  11 , conveyed by conveying rollers  12  to  18 , and wound by a winding roller  21 . Note that an apparatus to which aspects of the present disclosure are applied may use a sheet-shaped medium. 
     The medium  10  is conveyed on a conveying guide member  19  facing a liquid discharge unit  5  between the conveying rollers  13  and  14 , and an image is formed by a liquid discharged from the liquid discharge unit  5 . 
     Here, the liquid discharge unit  5  has, for example, full line type head units  51 D,  51 C,  51 M, and  51 Y for four colors (hereinafter, referred to as “head units  51 ” unless these units are distinguished from each other depending on a color) arranged from an upstream side in a medium conveying direction. The head units  51  discharge liquids of black (D), cyan (C), magenta (M), and yellow (Y) and apply the liquids onto the medium  10  which is conveyed, respectively. Note that the types and the number of colors are not limited thereto. 
     For example, as illustrated in  FIG. 2 , the head unit  51  is formed by arranging a plurality of liquid discharge heads  100  (also simply referred to as “heads”)  100  in a staggered pattern on a base member  52  to form a head array. However, the aspects of the present disclosure are not limited thereto. The head unit  51  includes a liquid discharge head and a head tank for supplying a liquid to the liquid discharge head. However, the aspects of the present disclosure are not limited thereto, and the head unit  51  may include the liquid discharge head alone. 
     Next, an example of one liquid discharge head constituting the head unit will be described with reference to  FIGS. 3 and 4 .  FIG. 3  is a cross-sectional view of the head in a direction orthogonal to a nozzle arrangement direction (liquid chamber longitudinal direction), and  FIG. 4  is a cross-sectional view of the head in the nozzle arrangement direction (liquid chamber short direction). 
     In the liquid discharging head, a nozzle plate  101 , a channel plate  102 , and a diaphragm member  103  are jointed to each other. This liquid discharge head includes a piezoelectric actuator  111  for displacing the diaphragm member  103  and a frame member  120  as a common channel member. 
     As a result, individual chambers  106  (also referred to as pressure chambers or pressurizing chambers) communicating with a plurality of nozzles  104  for discharging liquid droplets, a liquid supply path  107  for supplying a liquid to the individual chambers  106 , serving also as a fluid restrictor, and a liquid introduction unit  108  communicating with the liquid supply path  107  are formed. Adjacent individual chambers  106  are partitioned by a partition wall  106 A in the nozzle arrangement direction. 
     A liquid is supplied from the common liquid chamber  110  as a common channel of the frame member  120  to the plurality of individual chambers  106  via a filter  109  formed in the diaphragm member  103 , the liquid introduction unit  108 , and the liquid supply path  107 . 
     The piezoelectric actuator  111  is disposed on the opposite side to the individual chamber  106  across a deformable vibration region  130  forming a wall surface of the individual chamber  106  of the diaphragm member  103 . 
     The piezoelectric actuator  111  includes a plurality of laminated piezoelectric members  112  bonded onto a base member  113 . In each of the piezoelectric members  112 , a piezoelectric element (piezoelectric pillar)  112 A serving as a pillar-shaped pressure generation element for applying a drive waveform and a support  112 B are formed in a comb shape at predetermined intervals by groove processing using half cut dicing. 
     The piezoelectric element  112 A is bonded to an island-shaped protrusion  103   a  formed in the vibration region  130  of the diaphragm member  103 . The support  112 B is bonded to the protrusion  103   b  of the diaphragm member  103 . 
     The piezoelectric member  112  is formed by alternately laminating piezoelectric layers and internal electrodes. Each of the internal electrodes is drawn out to an end surface to provide an external electrode. To the external electrode of the piezoelectric element  112 A, a flexible printed circuit (FPC)  115  as a flexible wiring board having flexibility is connected for applying a drive waveform. 
     The frame member  120  includes a common liquid chamber  110  to which a liquid is supplied from a head tank or a liquid cartridge. 
     In a liquid discharge head having such a configuration, for example, by lowering a voltage applied to the piezoelectric element  112 A from an intermediate potential Ve, the piezoelectric element  112 A contracts, and the vibration region  130  of the diaphragm member  103  goes down to expand the volume of the individual chamber  106 . As a result, liquid flows into the individual chamber  106 . 
     Thereafter, the voltage applied to the piezoelectric element  112 A is increased to expand the piezoelectric element  112 A in a lamination direction, and the vibration region  130  of the diaphragm member  103  is deformed toward the nozzle  104  to contract the volume of the individual chamber  106 . As a result, a liquid in the individual chamber  106  is pressurized, and the liquid is discharged (jetted) from the nozzle  104 . 
     By returning the voltage applied to the piezoelectric element  112 A to a reference potential, the vibration region  130  of the diaphragm member  103  is restored to an initial position, and the individual chamber  106  expands to generate a negative pressure. Therefore, the liquid flows from the common liquid chamber  110  into the individual chamber  106  via the liquid supply path  107 . Therefore, vibration of a meniscus surface of the nozzle  104  is attenuated and stabilized, and then the process proceeds to operation for next discharge. 
     Next, an outline of a control device of this apparatus will be described with reference to  FIG. 5 . Note that  FIG. 5  is a block diagram of the control device. 
     The control device includes a main controller  501  (a system controller) constructed of a microcomputer including a central processing unit (CPU)  511  for controlling the entire apparatus, a read-only memory (ROM)  512 , a random-access memory (RAM)  513 , input/output (I/O), and the like, an image memory, a communication interface, and the like. 
     The main controller  501  sends print data to a print controller  502  in order to form an image on a medium based on image data transferred from an external information processing apparatus (host side) or the like and various kinds of command information. 
     The print controller  502  transfers the image data received from the main controller  501  as serial data, and outputs a transfer clock, a latch signal, a control signal, and the like necessary for transfer and transfer confirmation of the image data to a head driver  503 . 
     The print controller  502  includes a drive waveform generator including a digital/analog (D/A) converter for performing D/A conversion of pattern data of a common drive waveform stored in an internal ROM, a voltage amplifier, a current amplifier, and the like, and outputs a common drive waveform constructed of one or more drive pulses (drive signals) to the head driver  503 . 
     The head driver  503  selects a drive pulse constituting a common drive waveform based on image data corresponding to one head unit  51  serially input, and applies the drive pulse to the piezoelectric element  112 A as a pressure generation element (unit) to discharge a liquid. At this time, by selecting a part or all of the pulses constituting the common drive waveform or all or a part of waveform elements forming the pulses, dots having different sizes such as large droplets, medium droplets, or small droplets can be given separately. 
     The main controller  501  controls driving of each of rollers  510  such as the root winding roller  11 , the conveying rollers  12  to  18 , and the winding roller  21  via a motor driver  504 . 
     To the main controller  501 , a detection signal is input from a sensor group  506  including various sensors, and input/output of various kinds of information and exchange of display information are performed between the main controller  501  and an operation unit  507 . 
     Next, an example of a portion related to head drive control will be described with reference to the block view of  FIG. 6 . 
     The print controller  502  includes a drive waveform generator  701  as a drive waveform generating device according to an embodiment of the present disclosure. The print controller  502  further includes a data transferrer  702  for outputting 2-bit image data (gradation signal 0 or 1) corresponding to a print image and a mask signal (selection signal) MN for selecting a clock signal, a latch signal, or a drive pulse (or a waveform element) constituting a common drive waveform. 
     Here, from the drive waveform generator  701 , a drive waveform Vcom including one or more drive pulses (drive signals) for discharging a liquid is generated and output within one print cycle (one drive cycle). 
     Note that the mask signal MN is a signal for instructing opening/closing of an analog switch AS which is a switching unit of the head driver  503  for each droplet. A state transition to an H level (ON) occurs with a drive pulse (or waveform element) to be selected in accordance with the print cycle (drive cycle) of the common drive waveform Vcom, and a state transition to an L level (OFF) occurs when selection is not made. 
     The head driver  503  includes a shift register  711 , a latch circuit  712 , a decoder  713 , a level shifter  714 , and an analog switch array  715 . 
     The shift register  711  inputs a transfer clock (shift clock) and serial image data (gradation data: 2 bits/1 channel (1 nozzle)) from the data transferrer  702 . The latch circuit  712  latches each register value of the shift register  711  with a latch signal. 
     The decoder  713  decodes gradation data and a selection signal and outputs the result. The level shifter  714  performs level conversion of a logic level voltage signal of the decoder  713  to a level at which the analog switch AS of the analog switch array  715  can operate. 
     The analog switch AS of the analog switch array  715  is turned on/off (opened/closed) by output of the decoder  713  applied via the level shifter  714 . 
     The analog switch AS of the analog switch array  715  is connected to an individual electrode of the piezoelectric element  112 A, and the common drive waveform Vcom from the drive waveform generator  701  is input thereto. Therefore, the analog switch AS is turned on according to a result of decoding the serially transferred image data (gradation data) and the selection signal MN by the decoder  713 . As a result, a required drive pulse (or a waveform element) constituting the common drive waveform Vcom passes (is selected) and applied to an individual electrode of the piezoelectric element  112 A. 
     Next, a drive waveform in a first embodiment of the present disclosure will be described with reference to  FIGS. 7A to 7C .  FIGS. 7A to 7C  are views for explaining a common drive waveform, a mask signal, a non-discharge drive waveform, and a discharge drive waveform in the first embodiment. 
     Note that the “common drive waveform” is a waveform generated by D/A conversion or the like of drive waveform data, the non-discharge drive waveform is a micro-vibration drive waveform to perform drive to such a degree that no liquid is discharged, and the discharge drive waveform is a waveform to discharge a liquid. The “intermediate potential” is “the first voltage in time series in the drive waveform of one cycle”. 
     First, as illustrated in  FIG. 7A , the common drive waveform Vcom includes a discharge pulse Pa as a drive pulse which is a first waveform and continuous in time series and a non-discharge pulse Pb (micro vibrating pulse) as a drive pulse which is a second waveform. 
     The discharge pulse Pa as the first waveform is a waveform in which the potential falls from an intermediate potential V 0 , then rises to a potential V 1  higher than the intermediate potential, and is held at the potential V 1 . 
     This discharge pulse P 1  includes a falling waveform element a, a holding waveform element b, a raising waveform element c, and a holding waveform element d. The falling waveform element a is a waveform element for expanding the individual chamber  106  and is also referred to as a drawing-in waveform element or an expansion waveform element. The raising waveform element c is a waveform element for contracting the individual chamber  106  and is also referred to as a contraction waveform element or a push-in waveform element. 
     The falling waveform element a lowers the potential from the intermediate potential V 0  to a potential V 2  lower than the intermediate potential V 0  (V 2 &lt;V 0 ) to expand the individual chamber  106 . The holding waveform element b holds the falling potential V 2  by the falling waveform element a for a certain period of time. The raising waveform element c raises the potential from the potential V 2  held by the holding waveform element b to the potential V 1  higher than the intermediate potential V 0  to contract the individual chamber  106  to discharge a liquid. 
     The non-discharge pulse Pb as the second waveform is a waveform which is discontinuous with a waveform element holding the potential of the discharge pulse Pa as the first waveform and in which the potential rises from the intermediate potential V 0  to the potential V 1  higher than the intermediate potential V 0 , is held at the potential V 1  for a predetermined time, and then falls to the intermediate potential V 0 . Although the non-discharge pulse Pb is discontinuous with the waveform element of the discharge pulse Pa, for example, the duration between the time points t 2  and t 3  is short so that the non-discharge pulse Pb is continuous in time series with the discharge pulse Pa. 
     The non-discharge pulse P 2  includes a holding waveform element e holding the intermediate potential V 0 , a raising waveform element f that raises the potential from the intermediate potential V 0  held by the holding waveform element e to the potential V 1 , a holding waveform element g holding the potential V 1 , and a raising waveform element h that lowers the potential from the potential V 1  held by the holding waveform element g to the intermediate potential V 0 . At this time, the piezoelectric element  112 A is driven by the non-discharge pulse Pb to such a degree that a meniscus sways, and no liquid is discharged (micro vibration driving or non-discharge driving). 
     Next, as illustrated in  FIG. 7B , a mask signal (selection signal) MN 0  is a signal to be turned on at the time point t 3  and kept on to the time point t 5 . Therefore, when the mask signal MN 0  is applied, the waveform element of the non-discharge pulse Pb is selected, and the other waveform elements are masked. 
     As a result, as illustrated in  FIG. 7C , the non-discharge pulse P 2  is applied to the piezoelectric element  112 A as a non-discharge drive waveform (micro-vibration drive waveform). The non-discharge drive waveform contracts the individual chamber  106  to perform micro vibration driving. 
     As illustrated in  FIG. 7B , a mask signal MN 1  is a signal to be turned on from the time point t 1  to the time point t 2 , to be turned off from the time point t 2  to the time point t 4 , to be turned on again at the time point t 4 , and to be turned off at the time point t 5 . 
     As a result, as illustrated in  FIG. 7C , a discharge drive waveform constructed of the waveform elements of the discharge pulse Pa and the non-discharge pulse Pb are applied to a piezoelectric element  112 A. 
     That is, the falling waveform element a, the holding waveform element b, and the raising waveform element c of the discharge pulse Pa are applied, and a liquid is thereby discharged (discharge driving). The holding waveform element d of the discharge pulse Pa is applied to the piezoelectric element  112 A, and then a drive waveform applied to the piezoelectric element  112 A is interrupted. The piezoelectric element  112 A holds the potential V 1  when the drive waveform is interrupted. 
     Thereafter, the holding waveform element g of the non-discharge pulse Pb is selected, and the non-discharge pulse Pb is applied to the piezoelectric element  112 A until the time point t 5 . Therefore, the potential V 1  is again applied to the piezoelectric element  112 A. 
     Here, the holding waveform element d holding the potential V 1  of the discharge pulse Pa is for performing damping after discharge of a liquid by the raising waveform element c or shortening satellite droplets. Even when application of the holding waveform element d is interrupted, the potential V 1  is held, and the potential V 1  is applied again by the holding waveform element g of the non-discharge pulse Pb. Therefore, the potential V 1  can be held for a predetermined time, enabling damping after discharge of liquid or shortening of satellite droplets. 
     That is, in the present embodiment, the non-discharge pulse Pb is embedded in the waveform element for damping of the discharge pulse Pa or shortening of satellite droplets. At this time, time during which the drive waveform is interrupted by a damping waveform element is short, an influence of free discharge of a piezoelectric element can be relaxed, and stable drive can be performed. It is not necessary to increase the length of a waveform because of micro vibration driving. Therefore, high frequency drive can be achieved. 
     Next, a drive waveform in a second embodiment of the present disclosure will be described with reference to  FIGS. 8A to 8C .  FIGS. 8A to 8C  are views for explaining a common drive waveform, a selection signal (mask signal), a non-discharge drive waveform, and a discharge drive waveform in the second embodiment. 
     In the present embodiment, a waveform element c that raises the potential from the falling potential V 2  of the discharge pulse Pa to the raised potential V 1  includes a first raising waveform element c 1  that raises the potential from the potential V 2  to a potential V 3  higher than the intermediate potential V 0  and lower than the potential V 1  (V 0 &lt;V 3 &lt;V 1 ) to discharge a liquid, a holding waveform element c 2  holding the potential V 3 , and a second raising waveform element c 3  that raises the potential from the potential V 3  to the potential V 1 . Thus, with the waveform element c, the potential changes and rises stepwise. The potential V 1  that has risen with the second raising waveform element c 3  is held by a holding waveform element d. 
     At this time, a liquid is discharged by the first raising waveform element c 1 , and the potential is held by the holding waveform element i for a predetermined time. Thereafter, the individual chamber  106  is contracted again by the second raising waveform element c 3 . In this manner, extrusion is performed in two stages after discharging a liquid, which facilitates damping or enables satellite shortening as compared with the drive waveform of the first embodiment. As in the first embodiment, by commonly using a damping waveform element for micro vibration driving from the middle, it is not necessary to increase the length of a waveform for micro vibration driving, and high frequency drive can be achieved. 
     Next, a drive waveform in a third embodiment of the present disclosure will be described with reference to  FIGS. 9A to 9C .  FIGS. 9A to 9C  are views for explaining a common drive waveform, a selection signal (mask signal), a non-discharge drive waveform, and a discharge drive waveform in the third embodiment. 
     In the present embodiment, the raised potential of the first raising waveform element c 1  of the discharge pulse Pa of the second embodiment is set to a potential V 4  lower than the intermediate potential V 0  (V 4 &lt;V 0 ). 
     Such setting enables a reduction in droplet size at the same discharge speed as compared with the second embodiment. 
     Next, a drive waveform in a fourth embodiment of the present disclosure will be described with reference to  FIGS. 10A to 10C .  FIGS. 10A to 10C  are views for explaining a common drive waveform, a selection signal (mask signal), a non-discharge drive waveform, and a discharge drive waveform in the fourth embodiment. 
     The common drive waveform Vcom according to the present embodiment includes, before the discharge pulse Pa, a discharge pulse Pc as a third waveform. In the discharge pulse Pc, the potential falls from the intermediate potential V 0  to the potential V 2  with a falling waveform element a, the potential is kept at the potential V 2  with a holding waveform element b, and then the potential rises to the intermediate potential V 0  with a raising waveform element c. The discharge pulse Pc is a waveform for discharging a liquid. 
     Meanwhile, as mask signals MN, together with a mask signal MN 0  for selecting the non-discharge pulse Pb and a mask signal MN 1  for selecting the discharge pulse Pa and the non-discharge pulse Pb, a mask signal MN 2  for selecting both the discharge pulses Pc and Pa and the non-discharge pulse Pb is set. 
     By selecting the discharge pulses Pc and Pa, two droplets are discharged, and the amount of liquid adhering can be increased to increase image density. Discharging one droplet with the discharge pulse Pa is advantageous in smoothing image graininess and a gradation change in image density. 
     Next, a drive waveform in a fifth embodiment of the present disclosure will be described with reference to  FIGS. 11A to 11C   FIGS. 11A to 11C  are views for explaining a common drive waveform, a selection signal (mask signal), a non-discharge drive waveform, and a discharge drive waveform in the fifth embodiment. 
     The common drive waveform Vcom according to the present embodiment includes, after the non-discharge pulse Pb, a discharge pulse Pc as a third waveform. In the discharge pulse Pc, the potential falls from the intermediate potential V 0  to the potential V 2  with a falling waveform element a, the potential is kept at the potential V 2  with a holding waveform element b, and then the potential rises to the intermediate potential V 0  with a raising waveform element c. The discharge pulse Pc is a waveform for discharging a liquid. 
     Meanwhile, as mask signals MN, together with a mask signal MN 0  for selecting the non-discharge pulse Pb and a mask signal MN 1  for selecting the discharge pulse Pa and the non-discharge pulse Pb, a mask signal MN 2  for selecting both the discharge pulses Pc and Pa and the non-discharge pulse Pb is set. 
     By selecting the discharge pulses Pc and Pa, two droplets are discharged, and the amount of liquid adhering can be increased to increase image density. By discharging one droplet by the discharge pulse Pa, it is possible to smooth image graininess and a gradation change in image density. 
     Next, a sixth embodiment of the present disclosure will be described with reference to  FIGS. 12A to 12C .  FIGS. 12A to 12C  are views for explaining a common drive waveform, a selection signal (mask signal), a non-discharge drive waveform, and a discharge drive waveform in the sixth embodiment. 
     In addition to the discharge pulse Pa and the non-discharge pulse Pb, the common drive waveform Vcom according to the present embodiment includes a discharge pulse Pd and a non-discharge pulse Pe. 
     The discharge pulse Pd as a first waveform is a waveform in which the potential falls from the intermediate potential V 0 , then rises to a potential V 5  higher than the intermediate potential, and is held at the potential V 5 . 
     The discharge pulse Pd includes the falling waveform element a, the holding waveform element b, the raising waveform element c, and the holding waveform element d. The falling waveform element a expands the individual chamber  106 . 
     The falling waveform element a lowers the potential from the intermediate potential V 0  to a potential V 2  lower than the intermediate potential V 0  (V 2 &lt;V 0 ) to expand the individual chamber  106 . The holding waveform element b holds the falling potential V 2  by the falling waveform element a for a certain period of time. The raising waveform element c raises the potential from the potential V 2  held by the holding waveform element b to the potential V 5  higher than the intermediate potential V 0  to contract the individual chamber  106  to discharge a liquid. 
     The non-discharge pulse Pe is a waveform which is discontinuous with the holding waveform element d holding the potential of the discharge pulse Pd and in which the potential rises from the intermediate potential V 0  to the potential V 5  higher than the intermediate potential V 0 , is held at the potential V 5 , and then falls to the intermediate potential V 0 . 
     The non-discharge pulse Pe includes a holding waveform element e holding the intermediate potential V 0 , a raising waveform element f that raises the potential from the intermediate potential V 0  held by the holding waveform element e to the potential V 5 , a holding waveform element g holding the potential V 5 , and a raising waveform element h that lowers the potential from the potential V 5  held by the holding waveform element g to the intermediate potential V 0 . At this time, the piezoelectric element  112 A is driven by the non-discharge pulse Pb to such a degree that a meniscus sways, and no liquid is discharged (micro vibration driving). 
     Next, a mask signal MN 0  is similar to the mask signal MN 0  of the first embodiment. A mask signal MN 1  is turned on from the time point t 3  to the time point t 5 , and is turned on from the time point t 6  to the time point t 8 . By applying the mask signal MN 1 , the non-discharge pulses Pb and Pe are selected. 
     A mask signal MN 2  is turned on from the time point t 1  to the time point t 2 , turned off from the time point t 2  to the time point t 4 , turned on from the time point t 4  to the time point t 6 , and turned off from the time point t 6  to the time point t 8 . 
     By applying the mask signal MN 2 , as in the first embodiment, after the halfway of the holding waveform element d of the discharge pulse Pa is applied, the drive waveform to the piezoelectric element  112 A is interrupted, and the non-discharge pulse Pb is selected from the middle of the holding waveform element g of the non-discharge pulses Pb to the time point t 5 . Similarly, after the halfway of the holding waveform element d of the discharge pulse Pd is applied, the drive waveform to the piezoelectric element  112 A is interrupted, and the non-discharge pulse Pe is selected from the middle of the holding waveform element g of the non-discharge pulses Pe to the time point t 9 . 
     As described above, the present embodiment enables selective use of micro vibration driving by one non-discharge pulse Pb and micro vibration driving by two non-discharge pulses Pb and Pd (two second waveforms). As a result, these can be selectively used, for example, in a case where standing time is different or in a case where the pigment size in a liquid is different. 
     Next, a seventh embodiment of the present disclosure will be described with reference to  FIGS. 13A to 13C .  FIGS. 13A to 13C  are views for explaining a common drive waveform, a selection signal (mask signal), a non-discharge drive waveform, and a discharge drive waveform in the seventh embodiment. 
     In the present embodiment, a raising waveform element of the discharge pulse Pa includes a first raising waveform element c 1  in which the potential rises from the potential V 2  to a potential V 6  (V 6 &lt;V 0 ), a second raising waveform element c 2  in which the potential rises from the potential V 6  to a potential V 7  (V 1 &gt;V 7 &gt;V 0 ) at an inclination (potential change rate) different from that of the first raising waveform element c 1 , and a third raising waveform element c 3  in which the potential rises from the potential V 7  to the potential V 1 . 
     As described above, the potential change rate per unit time is different in continuous raising waveform element s. By further performing contraction (extrusion) with a plurality of raising waveform element s, meniscus vibration caused by extrusion can be smaller than the waveform of the third embodiment, and discharge stability can be improved even with a liquid having a low viscosity. 
     In the present application, a liquid to be discharged may be any liquid as long as having a viscosity and surface tension that can be discharged from a head, and is not particularly limited, but preferably has a viscosity of 30 mPa·s or less at ordinary temperature and normal pressure or by heating or cooling. More specifically, the liquid to be discharged is a solution, a suspension liquid, an emulsion, or the like containing a solvent such as water or an organic solvent, a colorant such as a dye or a pigment, a function-imparting material such as a polymerizable compound, a resin, or a surfactant, a biocompatible material such as deoxyribonucleic acid (DNA), amino acid, protein, or calcium, or an edible material such as a natural pigment, which can be used, for example, for an inkjet ink, a surface treatment liquid, a liquid for forming a constituent element of an electronic element or a light emitting element or an electronic circuit resist pattern, a three-dimensional modeling material liquid, or the like. 
     Examples of an energy generation source for discharging a liquid include those using a piezoelectric actuator (a laminated type piezoelectric element and a thin film type piezoelectric element), a thermal actuator using an electrothermal transducer such as a heating resistor, and an electrostatic actuator including a diaphragm and a counter electrode. 
     The “liquid discharge apparatus” includes not only an apparatus capable of discharging a liquid onto a liquid-attachable object but also an apparatus for discharging a liquid toward a gas or a liquid. 
     The “liquid discharge apparatus” may also include a unit related to feeding, conveying, or sheet ejection of a liquid-attachable object, a pretreatment device, a post-treatment device, and the like. 
     Examples of the “liquid discharge apparatus” include an image forming apparatus for discharging an ink to form an image on a sheet and a stereoscopic modeling apparatus (three-dimensional modeling apparatus) for discharging a modeling liquid onto a powder layer obtained by forming a powder into a layer shape in order to model a stereoscopic modeled object (three-dimensional modeled object). 
     The “liquid discharge apparatus” is not limited to an apparatus in which a significant image such as a letter or a graphic is visualized by a discharged liquid. Examples of the “liquid discharge apparatus” include an apparatus for forming a pattern or the like having no meaning by itself and an apparatus for modeling a three-dimensional image. 
     The “liquid-attachable object” means an object to which a liquid can be attached at least temporarily, and means an object causing adhesion by attachment, an object causing permeation by attachment, or the like. Specific examples of the “liquid-attachable object” include a recording medium such as a sheet, recording paper, a recording sheet, a film, or a cloth, an electronic component such as an electronic substrate or a piezoelectric element, and a medium such as a powder layer (powdery layer), an organ model, or an inspection cell. Unless particularly limited, the “liquid-attachable object” includes everything to which a liquid is attached. 
     A material of the “liquid-attachable object” may be any material as long as a liquid can be attached to the object even temporarily, such as paper, yarn, fiber, cloth, leather, metal, plastic, glass, wood, or ceramics. 
     The “liquid discharge apparatus” includes an apparatus in which a liquid discharge head and a liquid-attachable object move relatively to each other, but is not limited thereto. Specific examples thereof include a serial type apparatus for moving a liquid discharge head and a line type apparatus for not moving a liquid discharge head. 
     Examples of the “liquid discharge apparatus” further include a treatment liquid application apparatus for discharging a treatment liquid onto a sheet in order to apply the treatment liquid to a surface of the sheet, for example, in order to modify the surface of the sheet, and a spraying granulation apparatus for spraying a composition liquid in which a raw material is dispersed in a solution via a nozzle to granulate fine particles of the raw material. 
     In the terms of the present application, image formation, recording, letter printing, photograph printing, printing, modeling, and the like are all synonymous. 
     The above-described embodiments are illustrative and do not limit the present invention. Thus, numerous additional modifications and variations are possible in light of the above teachings. For example, elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of the present invention. 
     Any one of the above-described operations may be performed in various other ways, for example, in an order different from the one described above. 
     Each of the functions of the described embodiments may be implemented by one or more processing circuits or circuitry. Processing circuitry includes a programmed processor, as a processor includes circuitry. A processing circuit also includes devices such as an application specific integrated circuit (ASIC), digital signal processor (DSP), field programmable gate array (FPGA), and conventional circuit components arranged to perform the recited functions.