JP2008132657A - Method for driving piezoelectric element, driving circuit for piezoelectric element, apparatus for driving liquid droplet delivering head, and liquid droplet delivering apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for driving a piezoelectric element capable of preventing occurrence of erroneous delivery caused by a sudden change of the electric potential between electrodes of the piezoelectric element during charging and discharging electricity, a driving circuit for the piezoelectric element, and an apparatus for driving a liquid droplet delivering head. <P>SOLUTION: The piezoelectric element 30 is gradually charged by loading intermittently an electric voltage to the electrode 30A of the piezoelectric element 30 by repeating on-off of p-MOS 68 being a switch element during charging electricity. In addition, the electrostatic capacity of the piezoelectric element 30 is gradually discharged by intermittently grounding the electrode 30A of the piezoelectric element 30 by repeating on-off of n-MOS 70 being a switch element during discharging electricity. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a piezoelectric element driving method, a piezoelectric element driving circuit, a droplet discharge head driving device, and a droplet discharging device, and more particularly, a droplet that discharges a droplet by applying a driving voltage to the piezoelectric element. The present invention relates to a piezoelectric element drive method, a piezoelectric element drive circuit, a droplet discharge head drive device, and a droplet discharge device including the droplet discharge head for driving the discharge head.

  In an ink jet printer using a piezoelectric element such as a piezo element that changes its volume when a voltage is applied, a driving voltage is applied to the piezoelectric element provided in the recording head to change the internal pressure of the pressure chamber filled with ink, Ink droplets are ejected from the tip of a nozzle communicated with the nozzle. However, the piezoelectric element provided in the recording head has a capacitance similar to that of the capacitor, and there is a problem in that erroneous discharge is caused when the potential between the electrodes of the piezoelectric element changes rapidly.

  For example, when the interelectrode potential at the bias level is used as the reference potential, the piezoelectric element to which the drive voltage is not applied for a long time spontaneously discharges and the interelectrode potential decreases. If a driving voltage is suddenly applied to such a piezoelectric element, there is a risk of causing erroneous ejection.

  For this reason, various methods have been proposed for maintaining the interelectrode potential of the piezoelectric element at the bias level during operation of the ink jet printer. For example, waveform data including data for applying a drive voltage at regular intervals is used (Patent Document 1), and a constant bias voltage is applied when print data is not transmitted (Patent Document 2). A bias power supply circuit for applying a bias voltage to the electrode is provided (Patent Document 3), a bypass path for applying a voltage to the piezoelectric element is provided regardless of whether it is driven, and discharge is performed by applying a voltage through the bypass path. For example, the potential of the piezoelectric element that is raised is replenished (Patent Document 4).

JP 2001-010035 A JP 2002-144558 A JP 2002-264325 A Japanese Patent Laid-Open No. 2003-039668

  However, in the conventional method, since the degree of decrease in the interelectrode potential due to natural discharge is unknown, there is a problem that the interelectrode potential changes abruptly when a drive voltage is applied, and it is not always possible to prevent erroneous ejection. In addition, when the piezoelectric element is charged to the bias level in the initial operation, or when the piezoelectric element is discharged to the ground level in the end operation, the potential between the electrodes of the piezoelectric element may change abruptly. There is a problem that the conventional method cannot cope with such a case. In addition, the methods disclosed in Patent Documents 2 to 4 require an attached circuit such as a driver circuit dedicated to charging / discharging, resulting in an increase in cost.

  An object of the present invention is to provide a piezoelectric element driving method, a piezoelectric element driving circuit, a droplet discharge head driving apparatus, and a liquid that can prevent erroneous ejection due to a sudden change in the interelectrode potential of the piezoelectric element during charging and discharging. To provide a droplet discharge device.

  In order to achieve the above object, the invention described in claim 1 is a piezoelectric device for driving the piezoelectric element of a droplet discharge head that applies a driving voltage to the piezoelectric element and discharges a droplet from a nozzle corresponding to the piezoelectric element. A method of driving an element, wherein one electrode of the piezoelectric element is connected to a power source of a reference voltage level in a plurality of times and charged to a reference voltage level, and one electrode of the piezoelectric element is grounded a plurality of times. It is characterized in that it is divided and connected to discharge to the ground level.

  According to a second aspect of the present invention, in the first aspect of the present invention, one electrode of the piezoelectric element is intermittently connected to a power source of a reference voltage level to charge to the reference voltage level, and One electrode is intermittently connected to the ground and discharged to the ground level.

  According to a third aspect of the present invention, there is provided a driving circuit for a piezoelectric element that drives the piezoelectric element of a droplet discharge head that applies a driving voltage to the piezoelectric element and discharges a droplet from a nozzle corresponding to the piezoelectric element. , One electrode of the piezoelectric element is connected to a power supply of a reference voltage level in a plurality of times and charged to a reference voltage level, and one electrode of the piezoelectric element is connected to the ground in a plurality of times to connect to the ground. It is characterized by discharging to a level.

  According to a fourth aspect of the present invention, in the third aspect of the present invention, the piezoelectric element of the droplet discharge head that drives the piezoelectric element to discharge a droplet from a nozzle corresponding to the piezoelectric element by driving the piezoelectric element is driven. A drive circuit for the piezoelectric element that switches on and off intermittently, a charging waveform signal for charging one electrode of the piezoelectric element to a reference voltage level, or one electrode of the piezoelectric element that switches intermittently on and off A signal selection means for selecting a discharge waveform signal for discharging the signal to the ground level, and the charging waveform signal selected by the signal selection means are input, and one electrode of the piezoelectric element is connected when the input signal is on. A first switch element that is connected to a power source at a reference voltage level and disconnects the electrode from the power source when the input signal is off, and is selected by the signal selection means A second switching element that receives the discharge waveform signal and connects one electrode of the piezoelectric element to the ground when the input signal is on and disconnects the electrode from the ground when the input signal is off; It is characterized by having.

  The invention according to claim 5 is the invention according to claim 4, wherein the charge waveform signal and the discharge waveform signal are on / off signals in which the time T1 is turned on and the time T2 is turned off alternately. It is said.

  According to a sixth aspect of the present invention, in the fifth aspect of the present invention, at the time T1 when the charge waveform signal or the discharge waveform signal is turned on, one electrode of the piezoelectric element is connected to the power source or the ground. The amount of change in the interelectrode potential of the piezoelectric element when it is connected to is set so as to be in a range where no droplet is ejected from the nozzle corresponding to the piezoelectric element.

  The invention according to claim 7 is the invention according to claim 5, wherein the time T2 when the charge waveform signal or the discharge waveform signal is turned off is not an integral multiple of the natural period TC of the meniscus vibration. It is characterized by being set.

  The invention according to claim 8 is the invention according to claim 5, wherein the time T2 when the charge waveform signal or the discharge waveform signal is turned off is set to be 0.5TC or an odd multiple thereof. It is characterized by that.

  The invention described in claim 9 is a driving device for a droplet discharge head that applies a driving voltage to a piezoelectric element and discharges a droplet from a nozzle corresponding to the piezoelectric element, and the driving applied to the piezoelectric element Signal storage means storing a plurality of drive waveform signals representing voltage waveforms, a charge waveform signal for charging one electrode of the piezoelectric element to a reference voltage level, and discharging one electrode of the piezoelectric element to the ground level A signal generation means for generating a discharge waveform signal for performing, a drive waveform signal stored in the signal storage means, a charge waveform signal generated by the signal generation means and a signal supply means for supplying a charge waveform signal, and printing A predetermined waveform signal is selected from the drive waveform signal, the charging waveform signal, and the charging waveform signal supplied by the signal supply means based on the data, and the selected wave And a drive circuit that drives the piezoelectric element by applying a driving voltage to the piezoelectric element based on a signal, and when the charging waveform signal is selected, one electrode of the piezoelectric element has a reference voltage level. Connect to the power supply in multiple times to charge to the reference voltage level, and when the discharge waveform signal is selected, connect one electrode of the piezoelectric element to the ground in multiple times to the ground level It is characterized by discharging.

  A tenth aspect of the present invention is the invention according to the ninth aspect, wherein the drive circuit is intermittently switched on and off, and a charging waveform signal for charging one electrode of the piezoelectric element to a reference voltage level, or ON / OFF is switched on and off intermittently, a signal selection means for selecting a discharge waveform signal for discharging one electrode of the piezoelectric element to the ground level, and the charging waveform signal selected by the signal selection means are input, and an input signal A first switch element that connects one electrode of the piezoelectric element to a power source at a reference voltage level when the signal is on, and disconnects the electrode from the power source when the input signal is off; When the selected discharge waveform signal is input and the input signal is on, one electrode of the piezoelectric element is connected to the ground, and the input signal is off It is characterized by comprising a second switch element for cutting the electrode from the ground.

  According to an eleventh aspect of the present invention, in the invention according to the ninth or tenth aspect, the signal supply means includes a drive waveform signal stored in the signal storage means, a charging waveform signal generated by the signal generation means, and A charge waveform signal is supplied in parallel to the drive circuit.

  A twelfth aspect of the invention is the invention according to any one of the ninth to eleventh aspects, wherein the signal generating means counts at a time T1 and stops functioning at a time T2. A second counter that counts at time T2 and stops functioning at time T1, and outputs an ON signal while the first counter is counting and outputs an OFF signal when the function of the first counter is stopped Thus, the charging waveform signal or the discharging waveform signal in which the time T1 is turned on and the time T2 is alternately switched is generated.

  According to a thirteenth aspect of the present invention, a droplet discharge head that discharges droplets from a nozzle corresponding to the piezoelectric element by applying a driving voltage to the piezoelectric element, and the droplet discharge head is driven. The apparatus for driving a droplet discharge head according to any one of the above, and a transport unit that transports a recording medium to face the droplet discharge head.

  According to the first aspect of the present invention, it is possible to prevent erroneous ejection due to a rapid change in the interelectrode potential of the piezoelectric element during charging and discharging.

  According to invention of Claim 2, a piezoelectric element can be charged or discharged in steps.

  According to the third aspect of the present invention, it is possible to prevent erroneous ejection due to a sudden change in the interelectrode potential of the piezoelectric element during charging and discharging.

  According to the fourth aspect of the present invention, since a constant voltage can be applied multiple times simply by switching the switch element in accordance with the charge waveform signal or the discharge waveform signal, the piezoelectric element can be charged or discharged in a short time. can do.

  According to the fifth aspect of the present invention, one electrode of the piezoelectric element can be intermittently connected to the power source at the reference voltage level for charging at time T1, and the connection can be disconnected at time T2. Alternatively, one electrode of the piezoelectric element can be intermittently connected to the ground at time T1 and discharged, and the connection can be disconnected at time T2.

  According to the sixth aspect of the present invention, it is possible to reliably prevent erroneous ejection due to a rapid change in the interelectrode potential of the piezoelectric element during charging and discharging.

  According to the seventh aspect of the present invention, it is possible to prevent erroneous ejection due to abnormal meniscus vibration during charging and discharging.

  According to the eighth aspect of the present invention, it is possible to reliably prevent erroneous ejection due to abnormal meniscus vibration during charging and discharging.

  According to the ninth aspect of the invention, since the piezoelectric element can be driven and charged or discharged based on the charging waveform signal or the charging waveform signal, a dedicated accessory circuit such as a driver circuit dedicated to charging and discharging is provided. There is no need to provide it, and it is possible to prevent erroneous ejection due to a rapid change in the interelectrode potential of the piezoelectric element during charge and discharge at low cost.

  According to the tenth aspect of the present invention, the piezoelectric element can be charged or discharged in stages only by switching the switch element in accordance with the charge waveform signal or the discharge waveform signal.

  According to the eleventh aspect, similarly to the drive waveform signal, the charge waveform signal or the charge waveform signal can be selected based on the print data, and the piezoelectric element is driven based on the selected signal. Charging or discharging can be performed.

  According to the twelfth aspect of the present invention, it is possible to easily generate a charge waveform signal or a discharge waveform signal in which the time T1 is turned on and the time T2 is turned off alternately.

  According to the invention described in claim 13, since the piezoelectric element can be driven and charged or discharged based on the charging waveform signal or the charging waveform signal, a dedicated accessory circuit such as a driver circuit dedicated to charging and discharging is provided. There is no need to provide it, and it is possible to prevent erroneous ejection due to a rapid change in the interelectrode potential of the piezoelectric element during charge and discharge at low cost.

  Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings.

(Schematic configuration of inkjet recording apparatus)
FIG. 1 is a schematic diagram showing a main configuration of an ink jet recording apparatus 10 according to an embodiment of the present invention. Here, the illustration of the recording paper conveyance system is omitted. As shown in FIG. 1, the inkjet recording apparatus 10 includes a controller 12 that controls the operation of the entire inkjet recording apparatus 10 and an inkjet recording head 14 that ejects ink droplets based on the supplied print data.

  The ink jet recording head 14 includes a plurality of ejector groups 34 configured by two-dimensionally arranging a plurality of ejectors 32, and a plurality of drive ICs (Integrated Circuits) 16 provided corresponding to the plurality of ejector groups 34, respectively. It is equipped with. Each of the plurality of ejectors 32 ejects ink droplets by deformation of a piezoelectric element (for example, a piezo element) 30 provided individually. Each of the plurality of piezoelectric elements 30 included in the ejector group 34 is driven by a drive voltage applied from the corresponding drive IC 16.

  Each of the plurality of drive ICs 16 is connected to the controller 12. The operation control of the drive IC 16 is performed by the clock signal, print data, latch signal, drive waveform signal, and charge / discharge initial value data input from the controller 12. The drive waveform signal is a pair of signals representing the waveform of the drive voltage applied to the piezoelectric element 30. The shape (for example, large droplet, medium droplet, small droplet) of the ink droplet ejected from the ejector 32 and the ejection timing are controlled according to the waveform of the drive voltage. In the present embodiment, 14 types of drive waveform signals are prepared, including non-injection drive waveform signals. The charge / discharge initial value data will be described later.

  FIG. 2 is a plan view showing a schematic configuration of the inkjet recording head 14. The ink jet recording head 14 according to the present embodiment can be a long recording head having a width substantially equal to the width of the recording paper, as will be described below. That is, the ink jet recording apparatus 10 can be configured as a so-called FWA (Full Width Array) type ink jet recording apparatus that performs recording while transporting the recording paper while the ink jet recording head 14 is fixed.

  As shown in FIG. 2, the inkjet recording head 14 includes a plurality of substantially parallelogram-shaped head units 15. The plurality of head units 15 are arranged along the longitudinal direction of the inkjet recording head 14. Each of the head units 15 is provided with a pair of trapezoidal ejector groups 34 so as to face each other. As a result, the ejector groups 34A1, 34B1, 34A2, 34B2,... Are arranged so that the print areas of the adjacent ejector groups partially overlap with the longitudinal direction of the inkjet recording head 14.

  The ejector groups 34A1, 34B1, 34A2, 34B2,... Are provided with drive ICs 16A1, 16B1, 16A2, 16B2,. Each of the ejector groups 34 and the corresponding drive IC 16 is electrically connected by a connection line 18. In the following description, when it is not particularly necessary to distinguish between the ejector groups 34A1, 34B1, 34A2, 34B2,... Collectively referred to as “driving IC 16”.

  FIG. 3 is a cross-sectional view showing the internal structure of the ejector 32. The ejector 32 includes an ink storage chamber 20 that stores ink, an ink pressure chamber 24 that communicates with the ink storage chamber 20 via the ink supply path 22, a vibration plate 26 that forms part of the wall surface of the ink pressure chamber 24, and vibrations. A piezoelectric element 30 bonded to the plate 26 and a nozzle 28 communicating with the ink pressure chamber 24 are included.

  The ink pressure chamber 24 is filled with ink supplied from the ink storage chamber 20 via the ink supply path 22. When a driving voltage is applied to the piezoelectric element 30, the piezoelectric element 30 is deformed to vibrate the diaphragm 26, and the vibration of the diaphragm 26 propagates in the ink pressure chamber 24 as a pressure wave. As a result, the ink in the ink pressure chamber 24 is ejected as ink droplets from the nozzle 28 communicating with the ink pressure chamber 24.

(Schematic configuration of drive IC)
FIG. 4 is a block diagram showing a schematic configuration of the drive IC 16. The ejector group 34 has a plurality includes a piezoelectric element ₃₀ 1 to 30 _n of (here, n) of each of the piezoelectric elements ₃₀ 1 to 30 _n are driven by the drive IC 16. The number of piezoelectric elements 30 included in the ejector group 34 can be, for example, 128, 256, and 512. The drive IC 16 is provided with _n drive voltage generators 40 ₁ to 40 _n that generate drive voltages to be applied to the piezoelectric elements, corresponding to the _n piezoelectric elements 30 ₁ to 30 _n , respectively. In the following description, the piezoelectric elements 30 ₁ to 30 _n are collectively referred to as “piezoelectric elements 30”, and the drive voltage generation units 40 ₁ to 40 _n are referred to as “drive voltage generation unit 40” unless it is particularly necessary to distinguish between them. Collectively.

  The drive voltage generator 40 includes a selector 42 that selects a drive waveform signal based on print data, a decoder 44 that decodes the selected drive waveform signal, a level shifter 46 that boosts the decoded signal to a predetermined voltage level, and a decode A driver circuit 48 that generates a driving voltage based on the signal and applies it to the piezoelectric element 30 is provided.

The drive IC 16 includes a plurality of waveform data storage memories 52 _{1 to} 52 ₁₄ each storing a plurality of types (14 types in this case) of drive waveform signals input from the controller 12, and the stored drive A waveform data input circuit 50 that reads and outputs a waveform signal, and a charge / discharge waveform data generation circuit 54 that generates a charge waveform signal or a discharge waveform signal from initial value data input from the controller 12 are provided.

In addition, the drive waveform signal read from the waveform data storage memories 52 _{1 to} 52 ₁₄ and the charge waveform signal or the discharge waveform signal generated by the charge / discharge waveform data generation circuit 54 are transferred to the drive IC ₁₆ to generate a drive voltage. A plurality of shift register trains 56 _{1 to} 56 ₁₆ are provided to be supplied to each of the units 40 ₁ to 40 _n . Here, 16 shift register trains are provided corresponding to 14 types of drive waveform signals and 2 types of charge / discharge waveform signals. Each of the shift register trains 56 _{1 to} 56 ₁₆ is configured by connecting n shift registers 58 corresponding to each of the drive voltage generation units 40 ₁ to 40 _n in series.

In addition, the drive IC 16 is provided with a data transfer input unit 60 that supplies print data to each of the drive voltage generation units 40 ₁ to 40 _n . The data transfer input unit 60 transfers a plurality of (here, n) shift registers 62 that transfer print data input from the controller 12 and supply the print data to each of the drive voltage generation units 40 ₁ to 40 _n , and each shift A plurality (n in this case) of latches 64 that are connected to the output terminal of the register 62 and hold the print data output from the shift register 62 based on the input of the latch signal are provided. The n shift registers 62 are connected in series. N latches 64 are also connected in series.

(Schematic operation of drive IC)
Next, the operation of the drive IC 16 will be described. The print data and latch signal output from the controller 12 are input to the data transfer input unit 60. The print data is a selection signal for selecting one type of waveform signal (a pair of signals) from the drive waveform signal and the charge / discharge waveform signal, and is 4-bit serial data. The print data is continuously input by the number of piezoelectric elements 30 included in the ejector group 34, converted into 4-bit parallel data by a plurality of shift registers 62 connected in series, and output to the corresponding latch 64. The

  The output terminal of the latch 64 is connected to the select terminal of the selector 42 of the corresponding drive voltage generator 40. The print data transferred in synchronization with the clock signal by the shift register array composed of a plurality of shift registers 62 is held in the latch 64 based on the input of the latch signal and is input to the corresponding selector 42.

The drive waveform signal stored in each of the waveform data storage memories 52 _{1 to} 52 ₁₄ of the waveform data input circuit 50 and the charge / discharge waveform signal generated by the charge / discharge waveform data generation circuit 54 are synchronized with the clock signal. Are read out and output to the corresponding shift register trains 56 _{1 to} 56 ₁₆ . The output terminals of the n shift registers 58 constituting each of the shift register trains 56 _{1 to} 56 ₁₆ are connected to the input terminal of the selector 42 of the corresponding drive voltage generation unit 40. The drive waveform signal and the charge / discharge waveform signal are transferred in synchronization with the clock signal by each of the shift register trains 56 _{1 to} 56 ₁₆ and input to the corresponding selector 42. As a result, 16 types of waveform signals are input to the selector 42.

  The output terminal of the selector 42 is connected to the input terminal of the decoder 44, and the output terminal of the decoder 44 is connected to the input terminal of the level shifter 46. The selector 42 selects one type of waveform signal from the 16 types of waveform signals based on the print data input from the select terminal, and outputs the selected waveform signal to the decoder 44.

  For example, a waveform signal for non-ejection is selected when the print data is “0000”, a charge waveform signal is selected when the print data is “1110”, and a discharge waveform signal is selected when the print data is “1111”. Can be set to select. The decoder 44 decodes the input waveform signal based on a truth table, which will be described later, and outputs the decoded signal to the level shifter 46. The level shifter 46 boosts the decoded signal to a predetermined voltage level.

The output terminal of the level shifter 46 is connected to the input terminal of the driver circuit 48. The signal boosted by the level shifter 46 is output to the driver circuit 48. The driver circuit 48 generates a drive voltage whose voltage level changes based on the input signal, and applies the generated drive voltage to the piezoelectric element 30. Thereby, each of the piezoelectric elements 30 ₁ to 30 _n is independently driven by the driving IC 16.

(Driver circuit for drive voltage generator)
FIG. 5 is a circuit diagram showing the configuration of the driver circuit 48 in the drive voltage generator 40. A portion surrounded by a dotted line is a driver circuit 48. The driver circuit 48 includes a p-channel MOSFET (hereinafter referred to as “p-MOS”) 66, a p-MOS 68, and an n-channel MOSFET (hereinafter referred to as “n-MOS”) 70.

  A voltage of a predetermined level (HV2 [V]) is supplied to the source of the p-MOS 66 from a constant voltage power supply (not shown). A voltage of a predetermined level (HV1 [V]) is supplied to the source of the p-MOS 68 from a constant voltage power supply (not shown). HV2 is at a higher level than HV1. For example, HV1 can be set to 15 [V] and HV2 can be set to 20 [V]. The source of the n-MOS 70 is grounded to a ground level (GND; 0 [V]). Each drain of the p-MOS 66, the p-MOS 68, and the n-MOS 70 is connected to one electrode 30A of the piezoelectric element 30. The other electrode 30B of the piezoelectric element 30 is grounded.

As described above, the selector 42 selects one type of waveform signal based on the print data, and outputs a pair of signals V ₁ and V ₂ . FIG. 6 is a truth table of the decoder. As shown in FIG. 6, when the signals V ₁ and V ₂ are input to the decoder 44, the signal voltage levels “H (high level), L (low level)” are replaced with “1, 0”. Based on the truth table, the signals V ₁ and V ₂ are decoded, and the decoded signals D ₁ , D ₂ and D ₃ are output. That is, a waveform signal whose voltage level changes to three values of GND, HV1, and HV2 is generated. The signals D ₁ , D ₂ , D ₃ do not simultaneously become H level (= 1).

The gate of the p-MOS66 is connected to the decoder 44 via the level shifter 46 _1. The signal D ₁ is boosted by the level shifter 46 ₁ and logically inverted and input to the gate of the p-MOS 66. The gate of the p-MOS68 is connected to the decoder 44 via the level shifter 46 _2. The gate of the p-MOS68, signal _{D 2} is boosted by the level shifter 46 _2, it is input are logically inverted. The gate of the n-MOS70 is connected to the decoder 44 via the level shifter 46 _3. The gate of the n-MOS70, signal _{D 3} is input is boosted by the level shifter 46 _3.

The signal D _{1 at} H level (= 1) is logically inverted by the level shifter 46 ₁ to become L level (= 0). When an L level (= 0) signal is input to the gate of the p-MOS 66, the p-MOS 66 is turned on, and the output voltage level of the driver circuit 48 becomes HV2 [V]. As a result, a drive voltage of HV2 [V] is applied to the electrode 30A of the piezoelectric element 30.

Similarly, the signal _{D 2} of the H level (= 1) is a logic inverted by L level (= 0) in the level shifter 46 _2. When an L level (= 0) signal is input to the gate of the p-MOS 68, the p-MOS 68 is turned on, and the output voltage level of the driver circuit 48 becomes HV1 [V]. As a result, a drive voltage of HV1 [V] is applied to the electrode 30A of the piezoelectric element 30.

Further, when an H level (= 1) signal D ₃ is input to the gate of the n-MOS 70, the n-MOS 70 is turned on, and the output voltage level of the driver circuit 48 becomes GND (= 0 [V]). . That is, the electrode 30A of the piezoelectric element 30 is grounded. When the signals D ₁ , D ₂ , D ₃ are simultaneously at the L level (= 0), the output voltage level of the driver circuit 48 is open. That is, the drive voltage is not applied to the electrode 30A of the piezoelectric element 30.

As described above, each of the p-MOS 66, the p-MOS 68, and the n-MOS 70 functions as a switch element that switches connection with the power supply or GND in accordance with the signals D ₁ , D ₂ , and D ₃ . Incidentally, each of the p-MOS66, p-MOS68, n-MOS70, and a level shifter ₄₆ 1-46 ₃ is driven from a constant pressure source (not shown) predetermined level (VDD [V]) a voltage is supplied Yes.

(Charge / discharge waveform data generation circuit)
FIG. 7 is a block diagram showing a configuration of the charge / discharge waveform data generation circuit 54. The charge / discharge waveform data generation circuit 54 counts a first counter 72 that counts a period during which an H level signal is output (ON time T1), and a second counter that counts a period during which an L level signal is output (OFF time T2). 74. The first counter 72 and the second counter 74 are in an active state alternately. While one counter is active, the other counter is disabled.

  The charge / discharge waveform data generation circuit 54 outputs an H level signal while the first counter 72 is active, and outputs an L level signal when the first counter 72 stops functioning. As a result, a waveform signal whose voltage level changes to a binary value (H level, L level) is generated, and a charge waveform signal or a discharge waveform signal is output from the charge / discharge waveform data generation circuit 54.

  Hereinafter, a case will be described in which a voltage of HV1 [V] level is supplied from the power source to charge the piezoelectric element 30 to a reference potential of HV1 [V] level.

  As can be seen from the truth table (FIG. 6), when the signal V1 is L level (= 0) and the signal V2 is H level (= 1), a voltage of HV1 [V] is applied to the electrode 30A of the piezoelectric element 30. Is done. When the signal V1 is at the H level (= 1) and the signal V2 is at the L level (= 0), the electrode 30A of the piezoelectric element 30 is grounded. Therefore, as the charging waveform signal, a signal V1 having a voltage level of L level and a signal V2 whose voltage level changes to a binary value are generated. Further, as the discharge waveform signal, a signal V1 whose voltage level changes to binary and a signal V2 whose voltage level is L level are generated.

FIG. 8 is a timing chart showing the operation of the charge / discharge waveform data generation circuit.
Initial value data for the on time T1 is input to the first counter 72 and the second counter 74 is turned off at a predetermined timing, such as when the cycle clock signal representing the print data output cycle (print cycle) becomes H level. When the initial value data for T2 is input, first, the first counter 72 is activated.

  The first counter 72 starts counting from the input initial value. The first counter 72 counts in synchronization with the clock signal (CLK), and an H level signal is output (COUT) while the first counter 72 is active. When the count reaches the preset set value, the carry-out signal (CO1) of the first counter 72 is set to H level, and the function of the first counter 72 is stopped. At the same time, a carry-out signal (CO1) is input to the second counter 74, and the second counter 74 is activated.

  The second counter 74 starts counting from the input initial value. The second counter 74 counts in synchronization with the clock signal (CLK), and an L level signal is output (COUT) while the first counter 72 is stopped. When the count reaches the preset set value, the carry-out signal (CO2) of the second counter 74 is set to H level, and the function of the second counter 74 is stopped. At the same time, a carry-out signal (CO2) is input to the first counter 72 to make the first counter 72 active again. When the first counter 72 becomes active, the first counter 72 resets the count value to the initial value, and starts counting from the initial value.

  By alternately making the first counter 72 and the second counter 74 active for a predetermined period such as until the cycle clock signal becomes L level, the output of the H level signal of the on time T1 and the off time T2 The output of the L level signal is repeated, and a waveform signal whose voltage level changes to binary (H level, L level) is generated.

  The initial value data input to the charge / discharge waveform data generation circuit 54 can be, for example, 16-bit data. In this initial value data, the on-time T1 is defined by the first 8 bits and the off-time T2 is defined by the latter 8 bits. When the initial value data is “10000000000000010”, the on-time T1 corresponds to 128 clocks and the off-time T2 corresponds to 2 clocks. When the clock cycle is 10 MHz, the on time T1 and the off time T2 can be set in the range of 0 to 25.5 μs.

  As described above, when the signal V2 of the charging waveform signal is at the H level (on period T1), the voltage HV1 [V] is applied to the electrode 30A of the piezoelectric element 30, and the signal V2 of the charging waveform signal is In the case of L level (period of off time T2), it is opened. In this way, by repeatedly turning on and off the p-MOS 68 that is the switch element and intermittently applying a voltage to the electrode 30A of the piezoelectric element 30, the piezoelectric element 30 can be charged in stages, and the electrode of the piezoelectric element 30 can be charged. It is possible to prevent erroneous ejection due to a sudden change in the inter-potential.

  When the discharge waveform signal V1 is at the H level (on time T1), the electrode 30A of the piezoelectric element 30 is grounded, and when the discharge waveform signal V1 is at the L level (off time T2). Period) is open. Thus, by repeatedly turning on and off the n-MOS 70 that is a switch element and grounding the electrode 30A of the piezoelectric element 30 intermittently, the capacitance of the piezoelectric element 30 can be discharged stepwise, and the piezoelectric element 30 Incorrect ejection due to a rapid change in the interelectrode potential can be prevented.

  The on-time T1 is set so that the amount of change in the interelectrode potential generated when a voltage is applied to the electrode 30A of the piezoelectric element 30 is at least smaller than HV1 [V] so as not to cause erroneous ejection of the corresponding ejector 32. To do. When the capacitance of the piezoelectric element 30 is C and the resistance of the p-MOS 68 is R, the time required for the interelectrode potential of the piezoelectric element 30 to be equal to HV1 [V] is a time constant τ (= RC seconds). Will change accordingly. When the time constant τ is small, the rise of the potential between the electrodes is accelerated, so it is preferable to shorten the on-time T1. For example, the on-time T1 is preferably in the range of 0.2 to 0.5 μs with respect to the time constant τ = 1 μs.

  The off time T2 is set so as not to be an integral multiple of the natural period TC of the meniscus vibration. The off time T2 is theoretically preferably 0.5TC or an odd multiple thereof, that is, 0.5TC, 1.5TC, 2.5TC, 3.5TC, but in reality, the entire waveform is practical. Considering the length, it may be about 0.5TC or 1.5TC. The meniscus at the nozzle vibrates at a predetermined period according to the acoustic vibration due to the application of the drive voltage. When the off time T2 is an integral multiple of the natural period TC of the meniscus vibration, abnormal vibration occurs in the meniscus, causing erroneous ejection. Since the natural period TC of the meniscus vibration is about 12 μs, the off time T2 is preferably 6 μs or 18 μs.

  Since the amount of change in the potential between the electrodes that causes erroneous ejection of the ejector 32 varies depending on various factors such as the environmental temperature at the time of charging and discharging and the ink color, initial value data for defining the on time T1 and the off time T2 is used. You may set according to discharge conditions. For example, initial value data is stored in a memory (not shown) of the controller 12 in a table in association with discharge conditions such as environmental temperature and ink color, and the initial value data is stored in accordance with the discharge conditions during charging and discharging. You can choose.

(Charge / discharge operation)
FIG. 9 is a timing chart showing changes in the interelectrode potential of the piezoelectric element 30 when charging is performed in the initial operation. The charge waveform signal includes a signal V1 having a voltage level of L level (= 0) and a signal V2 having a voltage level that changes to a binary value. The on time T1 when the signal V2 becomes H level (= 1) is 0.2 μs, and the off time T2 when the signal V2 becomes L level (= 0) is 6 μs. Such a charging waveform signal is generated by setting the clock cycle to 10 MHz and setting the 16-bit initial value data input to the above-described charging / discharging waveform data generation circuit 54 to “000000000111100”.

  Simultaneously with the rise of the cycle clock signal at time t0, the signal V2 of the charging waveform signal becomes H level (= 1), the p-MOS 68 is turned on, and HV1 [V is applied to the electrode 30A of the piezoelectric element 30 at the ground level. ] Voltage is applied. At time t1 after 0.2 μs has elapsed from time t0, the charge waveform signal V2 becomes L level (= 0), the p-MOS 68 is turned off, and the electrode 30A of the piezoelectric element 30 is opened. By applying a voltage between time t0 and time t1, the interelectrode potential of the piezoelectric element 30 rises from GND to about ¼ of HV1 [V].

  At time t2 after 6 μs has elapsed from time t1, the signal V2 of the charging waveform signal becomes H level (= 1), and a voltage of HV1 [V] is applied to the electrode 30A of the piezoelectric element 30. At time t3 after 0.2 μs has elapsed from time t2, the charge waveform signal V2 becomes L level (= 0), and the electrode 30A of the piezoelectric element 30 is opened. As a voltage is applied between time t2 and time t3, the interelectrode potential of the piezoelectric element 30 rises to about ½ of HV1 [V].

  At time t4 after 6 μs has elapsed from time t3, the signal V2 of the charging waveform signal becomes H level (= 1), and a voltage of HV1 [V] is applied to the electrode 30A of the piezoelectric element 30. At time t5 after 0.2 μs has elapsed from time t4, the signal V2 of the charging waveform signal becomes L level (= 0), and the electrode 30A of the piezoelectric element 30 is opened. By applying a voltage between time t4 and time t5, the interelectrode potential of the piezoelectric element 30 rises to about 3/4 of HV1 [V].

  At time t6 after 6 μs has elapsed from time t5, the signal V2 of the charging waveform signal becomes H level (= 1), and a voltage of HV1 [V] is applied to the electrode 30A of the piezoelectric element 30. At time t7 after 0.2 μs has elapsed from time t6, the signal V2 of the charging waveform signal becomes L level (= 0), and the electrode 30A of the piezoelectric element 30 is opened. Since the voltage is applied between time t6 and time t7, the interelectrode potential of the piezoelectric element 30 rises to HV1 [V].

  Similarly, the voltage HV1 [V] is intermittently applied to the electrode 30A of the piezoelectric element 30 from the time t0 to the falling edge of the cycle clock signal at time t8 after 55.6 μs. In this example, the voltage of HV1 [V] is applied for 0.2 μs at a time to increase the interelectrode potential of the piezoelectric element 30 from GND to the reference potential HV1 [V] by applying the voltage four times. .

  FIG. 10 is a timing chart showing changes in the interelectrode potential of the piezoelectric element 30 when discharging is performed in the end operation. The discharge waveform signal includes a signal V1 whose voltage level changes to a binary value and a signal V2 whose voltage level is L level (= 0). The on time T1 when the signal V1 becomes H level (= 1) is 0.2 μs, and the off time T2 when the signal V1 becomes L level (= 0) is 6 μs. Such a discharge waveform signal is generated by setting the clock cycle to 10 MHz and setting the 16-bit initial value data input to the above-described charge / discharge waveform data generation circuit 54 to “000000000111100”.

  Simultaneously with the rise of the cycle clock signal at time t0, the signal V1 of the discharge waveform signal becomes H level (= 1), the n-MOS 70 is turned on, and the electrode of the piezoelectric element 30 at the voltage level of HV1 [V]. 30A is grounded. At time t1 after 0.2 μs has elapsed from time t0, the signal V1 of the discharge waveform signal becomes L level (= 0), the n-MOS 70 is turned off, and the electrode 30A of the piezoelectric element 30 is opened. Since the electrode 30A is grounded from time t0 to time t1, the piezoelectric element 30 is discharged, and the interelectrode potential of the piezoelectric element 30 is reduced from HV1 [V] to about ¾ of HV1 [V].

  At time t2 after 6 μs has elapsed from time t1, the signal V1 of the discharge waveform signal becomes H level (= 1), and the electrode 30A of the piezoelectric element 30 is grounded. At time t3 after 0.2 μs has elapsed from time t2, the signal V1 of the discharge waveform signal becomes L level (= 0), and the electrode 30A of the piezoelectric element 30 is opened. Since the electrode 30A is grounded from time t2 to time t3, the piezoelectric element 30 is discharged, and the interelectrode potential of the piezoelectric element 30 is reduced to about ½ of HV1 [V].

  At time t4 after 6 μs has elapsed from time t3, the signal V1 of the discharge waveform signal becomes H level (= 1), and the electrode 30A of the piezoelectric element 30 is grounded. At time t5 after 0.2 μs has elapsed from time t4, the signal V1 of the discharge waveform signal becomes L level (= 0), and the electrode 30A of the piezoelectric element 30 is opened. Since the electrode 30A is grounded from the time t4 to the time t5, the piezoelectric element 30 is discharged, and the interelectrode potential of the piezoelectric element 30 is reduced to about ¼ of HV1 [V].

  At time t6 after 6 μs has elapsed from time t5, the signal V1 of the discharge waveform signal becomes H level (= 1), and the electrode 30A of the piezoelectric element 30 is grounded. At time t7 after 0.2 μs has elapsed from time t6, the signal V1 of the discharge waveform signal becomes L level (= 0), and the electrode 30A of the piezoelectric element 30 is opened. Since the electrode 30A is grounded from time t6 to time t7, the piezoelectric element 30 is discharged, and the potential between the electrodes of the piezoelectric element 30 is reduced to the ground level.

  Similarly, the electrode 30A of the piezoelectric element 30 is intermittently grounded until the cycle clock signal falls at time t8, which is 55.6 μs after time t0. In this example, by grounding for 0.2 μs each time, the interelectrode potential of the piezoelectric element 30 is lowered from the reference potential HV1 [V] to GND by four times of grounding.

  FIG. 11 is a timing chart showing a state in which the inter-electrode potential of the piezoelectric element 30 that has decreased due to natural discharge is charged. When the waveform signal for non-injection is selected continuously, or when the drive voltage is not applied for a long time, the piezoelectric element 30 spontaneously discharges and the interelectrode potential decreases. When such a piezoelectric element 30 exists in the ejector group 34, the charging operation is performed in the next printing cycle. The charging operation is the same as when charging is performed in the initial operation. As the charging waveform signal, the waveform signal shown in FIG. 9 (the ON time T1 of the signal V2 is 0.2 μs and the OFF time T2 is 6 μs) is used.

  A print cycle is started simultaneously with the rise of the cycle clock signal at time t0, and a drive voltage is applied to each piezoelectric element 30 of the ejector group 34 based on print data. While the printing cycle is repeated a plurality of times, it is detected whether or not there is a piezoelectric element 30 in which the waveform signal for non-ejection is continuously selected. For example, when there is a piezoelectric element 30 in which the waveform signal for non-injection is continuously selected four times or more, the normal printing cycle is terminated by the falling of the cycle clock signal at time t1, and the charging printing cycle is started. Transition.

  Simultaneously with the rise of the cycle clock signal at time t2, the charge waveform signal V2 becomes H level (= 1), the p-MOS 68 is turned on, and the voltage HV1 [V] is applied to the electrode 30A of the piezoelectric element 30. Applied. At time t3 after 0.2 μs has elapsed from time t2, the charge waveform signal V2 becomes L level (= 0), the p-MOS 68 is turned off, and the electrode 30A of the piezoelectric element 30 is opened. As a voltage is applied between time t2 and time t3, the interelectrode potential of the piezoelectric element 30 that has been reduced to about ½ of HV1 [V] rises to the vicinity of HV1 [V].

  At time t4 after 6 μs has elapsed from time t3, the signal V2 of the charging waveform signal becomes H level (= 1), and a voltage of HV1 [V] is applied to the electrode 30A of the piezoelectric element 30. At time t5 after 0.2 μs has elapsed from time t4, the signal V2 of the charging waveform signal becomes L level (= 0), and the electrode 30A of the piezoelectric element 30 is opened. By applying a voltage between time t4 and time t5, the interelectrode potential of the piezoelectric element 30 rises to HV1 [V].

  Similarly, the voltage HV1 [V] is intermittently applied to the electrode 30A of the piezoelectric element 30 until the cycle clock signal falls at time t6. In this example, by applying a voltage of HV1 [V] for 0.2 μs at a time, the interelectrode potential of the piezoelectric element 30 is recovered to the reference potential HV1 [V] by applying the voltage twice.

  As described above, in the present embodiment, the piezoelectric element 30 is charged stepwise by repeatedly applying the voltage to the electrode 30A of the piezoelectric element 30 by repeatedly turning on and off the p-MOS 68 as the switching element during charging. Thus, erroneous ejection due to a rapid change in the interelectrode potential of the piezoelectric element 30 can be prevented. Further, by repeatedly turning on and off the n-MOS 70 that is a switch element during discharge and intermittently grounding the electrode 30A of the piezoelectric element 30, the capacitance of the piezoelectric element 30 can be discharged stepwise. It is possible to prevent erroneous ejection due to a rapid change in the 30 interelectrode potential.

  In the above embodiment, the case of ejecting ink droplets has been described as an example. However, the present invention is not limited to this, and the ejected droplets are used for promoting solidification of the ink droplets. It may be a droplet of a treatment liquid. In addition, the present invention can also be applied to the application of the alignment film forming material of the liquid crystal display element, the application of the flux, the application of the adhesive, and the like by the inkjet method.

  In the above embodiment, an example in which the charge / discharge waveform data generation circuit provided in the drive IC generates the charge / discharge waveform signal has been described. However, the waveform signal including the charge waveform signal and the discharge waveform signal is preliminarily stored as waveform data. It can also be stored in the built-in memory of the input circuit 50.

  In the above embodiment, the ink jet recording apparatus has been described with a drawing omitting the recording paper conveyance system. However, for example, the present invention can be applied to a full color ink jet recording apparatus as shown in FIG. As shown in the figure, the ink jet recording apparatus 110 includes a paper feed tray 120, a paper discharge tray 122, and a plurality of rollers 124.

  Recording paper is stored in the paper feed tray 120. During image formation, the recording paper in the paper feed tray 120 is taken out one by one by a roller 124, and the inside of the ink jet recording apparatus 110 is moved to a predetermined transport path F. An image is recorded by an inkjet recording head 118 (described later) while being conveyed along, and is discharged onto a discharge tray 122.

  In the recording paper conveyance path F, an endless belt 114 and an adsorber 116 that are stretched around a conveyance roll 112 that rotates in the direction of arrow E are disposed. The adsorber 116 presses the recording paper conveyed on the conveyance path F against the endless belt 114 and applies electric charges to the recording paper so that the endless belt 114 adsorbs the recording paper.

  Further, in the recording paper conveyance path F, four color inks of yellow (Y), magenta (M), cyan (C), and black (K) are disposed at positions facing the recording paper attracted by the endless belt 114. Are provided with four recording heads 118Y, 118M, 118C, and 118K. The recording heads 118Y, 118M, 118C, and 118K for the respective colors have a FWA (Full Width Array) in which head units each having a plurality of discharge nozzles are arranged over the entire width direction of the endless belt 114 and are configured by a large number of discharge nozzles. ) Type.

  In the following description, the members provided for each color are indicated by adding alphabets (Y / M / C / K) indicating the respective colors to the end of the reference numerals, but will be described without particularly distinguishing the colors. In this case, the explanation will be made by omitting the alphabet at the end of the code.

  Further, as shown in the figure, the ink jet recording apparatus 110 according to the present embodiment is configured to include a conveyance path R for reversing the front and back. In duplex printing, after forming an image on one side, the recording paper is conveyed along the conveyance path R so that the back side of the surface on which the image is formed faces the recording heads 118Y, 118M, 118C, and 118K. Inversion can be performed. Here, the recording heads 118Y, 118M, 118C, and 118K are configured to be able to move away from the endless belt 114 by a drive mechanism (not shown).

  Furthermore, maintenance devices 128A and 128B are provided on the upstream side and the downstream side of the conveyance path F of the recording heads 118Y, 118M, 118C, and 118K, respectively. The maintenance device 128A includes maintenance units 130K and 130C for black and cyan, and the maintenance device 128B includes maintenance units 130M and 130Y for magenta and yellow. Each maintenance device 128A, 128B is configured to be movable in a direction approaching each other by a drive mechanism (not shown).

1 is a schematic diagram illustrating a main configuration of an ink jet recording apparatus according to an embodiment of the present invention. It is a top view which shows schematic structure of an inkjet recording head. It is sectional drawing which shows the internal structure of an ejector. It is a block diagram which shows schematic structure of drive IC. It is a circuit diagram which shows the structure of the driver circuit in a drive voltage generation part. It is a truth table of a decoder. It is a block diagram which shows the structure of a charging / discharging waveform data generation circuit. It is a timing chart which shows operation | movement of a charging / discharging waveform data generation circuit. It is a timing chart which shows the mode of the change of the electric potential between electrodes of a piezoelectric element in the case of charging in an initial operation. It is a timing chart which shows the mode of the change of the electric potential between electrodes of a piezoelectric element in the case of discharging in an end operation. It is a timing chart which shows a mode that the electric potential between electrodes of the piezoelectric element reduced by natural discharge is charged. 1 is a schematic diagram illustrating a configuration of an ink jet recording apparatus to which the present invention is applicable.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Inkjet recording device 12 Controller 14 Inkjet recording head 15 Head unit 16 Drive IC
18 Connection line 20 Ink storage chamber 22 Ink supply path 24 Ink pressure chamber 26 Diaphragm 28 Nozzle 30 Piezoelectric element 30A Electrode 30B Electrode 32 Ejector 34 Ejector group 40 Drive voltage generator 42 Selector 44 Decoder 46 Level shifter 48 Driver circuit 50 Waveform data input Circuit 52 Waveform data storage memory 54 Charge / discharge waveform data generation circuit 56 Shift register train 58 Shift register 60 Data transfer input unit 62 Shift register 64 Latch 72 Counter 74 Counter 110 Inkjet recording device 112 Transport roll 114 Endless belt 116 Adsorber 118 Inkjet recording Head 120 Paper feed tray 122 Paper discharge tray 124 Roller 128A Maintenance device 128B Maintenance device 128A Each maintenance device 130K Maintenance unit Tsu door 130M maintenance unit

Claims (13)

A driving method of a piezoelectric element for driving the piezoelectric element of a droplet discharge head for applying a driving voltage to the piezoelectric element and discharging a droplet from a nozzle corresponding to the piezoelectric element,
One electrode of the piezoelectric element is connected to a power supply of a reference voltage level in multiple times and charged to the reference voltage level, and one electrode of the piezoelectric element is connected to ground in multiple times and connected to the ground level. A method for driving a piezoelectric element, characterized by discharging to a maximum.   One electrode of the piezoelectric element is intermittently connected to a power supply at a reference voltage level to charge to the reference voltage level, and one electrode of the piezoelectric element is intermittently connected to ground to be discharged to the ground level. The method for driving a piezoelectric element according to claim 1. A drive circuit for a piezoelectric element that drives the piezoelectric element of a droplet discharge head that applies a drive voltage to the piezoelectric element and discharges a droplet from a nozzle corresponding to the piezoelectric element,
One electrode of the piezoelectric element is connected to a power supply of a reference voltage level in multiple times and charged to the reference voltage level, and one electrode of the piezoelectric element is connected to ground in multiple times and connected to the ground level. A drive circuit for a piezoelectric element, wherein A drive circuit for a piezoelectric element that drives the piezoelectric element of a droplet discharge head that applies a drive voltage to the piezoelectric element and discharges a droplet from a nozzle corresponding to the piezoelectric element,
A charge waveform signal for intermittently switching on / off to charge one electrode of the piezoelectric element to a reference voltage level, or a discharge waveform for intermittently switching on / off to discharge one electrode of the piezoelectric element to the ground level Signal selection means for selecting a signal;
When the charging waveform signal selected by the signal selection means is input and the input signal is on, one electrode of the piezoelectric element is connected to a power source of a reference voltage level, and when the input signal is off, the electrode A first switching element for disconnecting from the power source;
When the discharge waveform signal selected by the signal selection means is input and the input signal is on, one electrode of the piezoelectric element is connected to the ground, and when the input signal is off, the electrode is connected from the ground. A second switch element to be disconnected;
A drive circuit for a piezoelectric element, comprising:   5. The piezoelectric element driving circuit according to claim 4, wherein the charging waveform signal and the discharging waveform signal are on / off signals that alternately switch on at time T <b> 1 and off at time T <b> 2.   The time T1 when the charge waveform signal or the discharge waveform signal is turned on is the amount of change in the interelectrode potential of the piezoelectric element when one electrode of the piezoelectric element is connected to the power source or the ground. 6. The drive circuit for a piezoelectric element according to claim 5, wherein the drive circuit is set so that a droplet is not ejected from a nozzle corresponding to the piezoelectric element.   The piezoelectric element drive according to claim 5, wherein the time T2 when the charge waveform signal or the discharge waveform signal is turned off is set so as not to be an integral multiple of a natural period TC of meniscus vibration. circuit. 6. The piezoelectric element drive circuit according to claim 5, wherein the time T2 when the charge waveform signal or the discharge waveform signal is turned off is set to 0.5TC or an odd multiple thereof. A droplet discharge head driving device that applies a driving voltage to a piezoelectric element and discharges a droplet from a nozzle corresponding to the piezoelectric element.
Signal storage means for storing a plurality of drive waveform signals representing waveforms of drive voltages applied to the piezoelectric elements;
A signal generation means for generating a charge waveform signal for charging one electrode of the piezoelectric element to a reference voltage level and a discharge waveform signal for discharging one electrode of the piezoelectric element to a ground level;
A signal supply means for supplying a drive waveform signal stored in the signal storage means, a charge waveform signal generated by the signal generation means, and a charge waveform signal;
A predetermined waveform signal is selected from the drive waveform signal, the charging waveform signal, and the charging waveform signal supplied by the signal supply unit based on print data, and the piezoelectric element is applied to the piezoelectric element based on the selected waveform signal. A driving circuit for driving the piezoelectric element by applying a driving voltage;
With
When the charging waveform signal is selected, one electrode of the piezoelectric element is connected to a power source of a reference voltage level divided into a plurality of times and charged to the reference voltage level, and the discharge waveform signal is selected In addition, the droplet discharge head driving apparatus is characterized in that one electrode of the piezoelectric element is connected to the ground in a plurality of times and discharged to the ground level.   The driving circuit is intermittently switched on and off, and a charging waveform signal for charging one electrode of the piezoelectric element to a reference voltage level, or intermittently switched on and off and discharges one electrode of the piezoelectric element to a ground level. A signal selection means for selecting a discharge waveform signal for performing the operation, and the charging waveform signal selected by the signal selection means is input, and when the input signal is on, one electrode of the piezoelectric element is connected to a power supply at a reference voltage level. And when the input signal is OFF, the first switch element that disconnects the electrode from the power source and the discharge waveform signal selected by the signal selection means are input, and the input signal is ON A second switch element for connecting one electrode of the piezoelectric element to the ground and disconnecting the electrode from the ground when an input signal is off; Drive device of a liquid droplet discharge head according to claim 9, further comprising a.   The said signal supply means supplies the drive waveform signal memorize | stored in the said signal memory | storage means, the charge waveform signal produced | generated by the said signal generation means, and a charge waveform signal to the said drive circuit in parallel. Drive device for droplet discharge head.   The signal generating means includes a first counter that counts at time T1 and stops functioning at time T2, and a second counter that counts at time T2 and stops functioning at time T1. The charging waveform signal or the discharging waveform signal in which the time T1 is turned on and the time T2 is turned off alternately by outputting an on signal during the counting of the first counter and outputting an off signal while the function of the first counter is stopped. The droplet discharge head driving device according to claim 9, wherein the droplet discharge head driving device is generated. A droplet discharge head for applying a driving voltage to the piezoelectric element and discharging a droplet from a nozzle corresponding to the piezoelectric element;
The droplet discharge head drive device according to any one of claims 9 to 12, which drives the droplet discharge head;
Conveying means for conveying a recording medium to face the droplet discharge head;
A droplet discharge apparatus comprising:

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