JP2007118278A - Driving method for inkjet head, inkjet head, and inkjet recording device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet head and an inkjet type recording device which can increase the hitting position accuracy of ink droplets by eliminating a discharge speed difference in respective ink droplets when a gradation expression is performed by changing an ink capacity gradually in a plurality of steps. <P>SOLUTION: The signal waveform of a final driving pulse and the signal waveform of an initial driving pulse which is operated more than one time prior to the final driving pulse from among discharging pulse signals which are applied a plurality of times for changing the ink droplet capacity and discharging ink droplets in steps are made different. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ink jet head driving method and an ink jet recording apparatus for ejecting ink droplets to record an image on a recording medium.

2. Description of the Related Art Conventionally, an ink jet recording apparatus that records characters and images on a recording medium using an ink jet head having a plurality of nozzles that eject ink is known. FIG. 8 is a schematic front view of such an ink jet head, FIG. 9 is a schematic cross-sectional view, and FIG. 3 is an exploded view of the vicinity of a drive unit that generates pressure necessary for ejection and a nozzle unit that finally ejects ink.
As shown in FIG. 3, the piezoelectric ceramic plate 1 is provided with a plurality of grooves 5, and the grooves 5 are separated by side walls 7.

One end in the longitudinal direction of each groove 5 extends to one end face of the piezoelectric ceramic plate 1, and the other end does not extend to the other end face, and the depth gradually decreases.
In addition, an electrode 4 and an electrode 9 for applying a driving electric field are formed on the opening side surface of both side walls 7 in each groove 5 over the longitudinal direction.

  Further, a head chip 26 is formed by bonding the ink chamber plate 2 to the opening side of the groove 5 of the piezoelectric ceramic plate 1. The nozzle plate 3 is joined to the end face where the groove 5 of the joined body of the piezoelectric ceramic plate 1 and the ink chamber plate 2 is opened, and the nozzle hole 11 is located at a position facing each groove 5 of the nozzle plate 3. Is formed. The nozzle plate 3 and the head chip 26 are fixed by the head cap 12, and the electrode 4 formed on the head chip 26 and the drive circuit board 14 are connected by a flexible board 19.

  Further, an ink flow path 21 for supplying ink is fixed on the ink chamber plate 2, and an ink introduction port 41 for introducing ink is formed at the center of the flow path 21. Is connected to a pressure relaxation unit 20 for absorbing pressure fluctuations during printing.

Next, a method of driving the ink jet head configured as described above will be described with reference to FIGS. FIG. 2 is a diagram showing a discharge signal waveform of a conventional inkjet head, and FIG. 4 is a cross-sectional view showing an electrode wiring state of the inkjet head. FIG. 2A is a diagram showing an ejection signal waveform when ejecting a conventional ink volume of one drop, and FIG. 2B is a diagram showing an ejection signal waveform when ejecting an ink capacity of two conventional drops. FIG. 2C is a diagram showing ejection signal waveforms when ejecting a conventional three-drop ink capacity, FIG. 4A is a cross-sectional view when not driven, and FIG. 4B is a cross-sectional view when driving. FIG. Reference numeral 6 denotes a polarization direction. When an electric field is applied to the electrode 4 and the electrode 9 sandwiching the side wall 7, each side wall 7 is deformed in a desired direction. As shown in FIG. 4A, in this ink jet head, every other electrode 4 formed in the groove 5 is a common electrode having a ground potential, and an electrode 9 sandwiching the electrode 4 gives an output signal from the outside. Electrode structure. When a positive electric field pulse indicated by the ejection signal waveform of one drop of ink capacity shown in FIG. 2A is applied to the electrode 9, the side walls 7 are deformed as shown in FIG. . This deformation is deformed for a time t1 during which the positive electric field is applied, and when the potential becomes zero after t1, the state returns to the state of FIG. In addition, t1 is set to the time when the most efficient discharge speed becomes fast, as can be seen from the graph showing the relationship between the electric field application time and the discharge speed in FIG. This deformation causes a change in pressure in the ink filled in the groove 5, and the ink jets one drop from the nozzle hole 11. Further, by applying this positive electric field a plurality of times, gradation expression can be made by changing the ejection volume of the ink flying from the nozzle hole 11. For example, in order to eject two drops of ink from the nozzle hole 11, the positive electric field pulse t2 is operated at an interval of t4 before the positive electric field pulse t1, as shown in FIG. Similarly, in the case of ejecting three drops of ink, the positive electric field pulse t3 is operated before the positive electric field pulses t1 and t2, as shown in FIG. As a result, a volume of ink corresponding to three drops can be ejected from the nozzle hole 11. In this case, the positive electric field pulse application time and the pulse interval time are set to t1 = t2 = t3 = t4 = t5. By making all the rest periods between the positive electric field pulse application time and the pulse application the same, ink can be efficiently ejected.
Japanese Patent Laid-Open No. 2002-19103

  However, in the case of the conventional inkjet driving method using the driving waveforms shown in FIGS. 2A, 2B, and 2C, as shown in FIG. There is a problem that a difference occurs in the ejection speed of each of the two drops and the three drops. The reason why the discharge speed when the ink capacity is 2 drops and 3 drops is faster than when one drop is discharged is that the influence of the pressure change generated by driving at t3 and t2 remains, and the aftermath of the vibration is added to increase the discharge speed. Is due to The difference in the ejection speed generated here appears as a difference in the landing position of ink droplets when printed by an ink jet printer, and there is a problem that the image quality of the printed matter is deteriorated.

  In view of such circumstances, the present invention provides an ink jet head and an ink jet recording apparatus that eliminate the speed difference between one drop, two drops, and three drops when expressing gradation and improve the landing position system of ink drops. This is the issue.

  The present invention that solves the above-described problems includes a plurality of side walls configured by actuators that deform in response to an applied voltage, a plurality of grooves that are communicated with the nozzles and arranged in parallel between the side walls, and each of the grooves. An ink flow path for supplying ink, and a drive pulse that is input to an electrode provided on the side wall to cause the actuator to deform and cause ink to fly from the nozzle, and a pause time during which the actuator is not operated are set. In the method of driving an ink-jet head that changes the ink droplet volume that reaches the recording medium at a time by changing the number of times continuously given at intervals of pause time, the last of the plurality of driving pulses. The signal waveform of the last drive pulse given is different from the signal waveform of the initial drive pulse given at least once before the last drive pulse. In the driving method of an inkjet head that.

  As described above, according to the present invention, the ink droplet ejection speed difference is eliminated by ejecting the ink volume corresponding to a plurality of droplets, such as one droplet, two droplets, and three droplets when expressing gradation. It is possible to provide an ink jet head and an ink jet recording apparatus that improve the positional accuracy and have excellent image quality.

Hereinafter, the present invention will be described in detail based on embodiments of the present invention.
FIG. 8 is a front view of the entire inkjet head of the present embodiment, FIG. 9 is a schematic sectional view of the inkjet head of the present embodiment, and FIG. 3 is an exploded view showing the periphery of the discharge pressure generating portion of the inkjet head of the present embodiment. is there.

  As shown in the figure, the inkjet head of the present embodiment includes a head chip 26, a flow path 21 provided on one side of the head chip, a circuit board 14 on which a drive circuit for driving the head chip 26, and the like are mounted. The pressure relief unit 20 for relieving the pressure change in the head chip 26 is included, and each of these members is fixed to the base 13.

Next, details of the periphery of the head chip 26 that is a pressure generation source for ejection will be described. The piezoelectric ceramic plate 1 constituting the piezoelectric ceramic plate head chip 26 is provided with a plurality of grooves 5 communicating with the nozzle holes 11, and the grooves 5 are separated by side walls 7.
One end of each groove 5 in the longitudinal direction extends to one end face of the piezoelectric ceramic plate 1, and the other end does not extend to the other end face, and the depth gradually decreases.
On the side walls 7 on both sides in the width direction of each groove 5, electrodes 4 for applying a driving electric field are formed on the opening side of the groove 5 in the longitudinal direction.

  Each groove 5 formed in the piezoelectric ceramic plate 1 is formed by, for example, a disk-shaped die cutter, and a portion where the depth gradually decreases is formed by the shape of the die cutter. Moreover, the electrode 4 formed in each groove | channel 5 is formed by vapor deposition from the well-known diagonal direction, for example. One end of the flexible board 19 is joined to the electrode 4 provided on the opening side of the side wall 7 on both sides of the groove 5, and the other end side of the flexible board 19 is connected to a drive circuit (not shown) on the circuit board 14. By joining, the electrode 4 is electrically connected to the drive circuit. Further, the ink chamber plate 2 is joined to the opening side of the groove 5 of the piezoelectric ceramic plate 1.

  The ink chamber plate 2 can be formed of a ceramic plate, a metal plate, or the like, but considering the deformation after joining with the piezoelectric ceramic plate 1, it is preferable to use a ceramic plate having an approximate thermal expansion coefficient.

  Further, a nozzle plate 3 is joined to an end face where the groove 5 of the joined body of the piezoelectric ceramic plate 1 and the ink chamber plate 2 is opened, and the nozzle plate 3 has a nozzle at a position facing each groove 5. A hole 11 is formed.

  In this embodiment, the nozzle plate 3 is larger than the area of the end surface where the groove 5 of the joined body of the piezoelectric ceramic plate 1 and the ink chamber plate 2 is opened. The nozzle plate 3 is formed by forming nozzle holes 11 in a polyimide film or the like using, for example, an excimer laser device. Although not shown, a water repellent film having water repellency is provided on the surface of the nozzle plate 3 facing the substrate to prevent ink adhesion.

  Further, a head cap 12 that supports the nozzle plate 3 is joined to the outer peripheral surface on the end face side where the grooves 5 of the joined body of the piezoelectric ceramic plate 1 and the ink chamber plate 2 are opened. The head cap 12 is joined to the outside of the joined body end face of the nozzle plate 3 to stably hold the nozzle plate 3.

  In the ink jet head of this embodiment, an ink flow path 21 for supplying ink is fixed on the ink chamber plate 2, and an ink introduction port 41 for introducing ink is formed at the center of the flow path 21. The ink inlet 41 is connected to a pressure relaxation unit 20 for absorbing pressure fluctuation during printing. For example, in a mechanism in which ink from an ink tank (not shown) is filled into the pressure relaxation unit 20 at the time of initial filling or the like, and further, ink is introduced into the flow path 21 and finally the groove 5 is filled with ink. is there.

  Next, an electrode wiring method and a driving method according to this embodiment will be described with reference to FIGS. FIG. 1 is a view showing ejection signal waveforms of the ink jet head of this embodiment, and FIG. 4 is a cross-sectional view showing an electrode wiring state of the ink jet head. FIG. 1A is a diagram showing an ejection signal waveform when ejecting one drop of ink capacity according to this embodiment, and FIG. 1B is an ejection signal waveform when ejecting two drops of ink capacity according to this embodiment. FIG. 1C is a diagram showing the ejection signal waveform when ejecting the ink droplet of three drops according to the present embodiment, FIG. 4A is a cross-sectional view when not driven, and FIG. These are sectional views at the time of driving. Reference numeral 6 denotes a polarization direction. When an electric field is applied to the electrode 4 and the electrode 9 sandwiching the side wall 7, each side wall 7 is configured to be deformed in a desired direction, and constitutes an actuator. As shown in FIG. 4A, in this ink jet head, every other electrode 4 formed in the groove 5 is a common electrode of ground potential, and an electrode 9 sandwiching the electrode 4 gives an output signal from the outside. Electrode structure. When the positive electric field pulse V shown in FIG. 1A is applied to the electrode 9, the side walls 7 are deformed as shown in FIG. 4B due to the potential difference with the electrode 4. This deformation is deformed for the time T1 during which the positive electric field is applied, and when the potential after T1 becomes zero, the state returns to the state of FIG. Note that T1 is set to a time during which the most efficient discharge speed is increased, as can be seen from the relationship between the electric field application time and the discharge speed in FIG. The positive electric field pulse T1 that achieves this efficient ejection speed is called the final drive pulse. The deformation of the side wall 7 causes a change in pressure in the ink filled in the groove 5, and the ink is ejected from the nozzle hole 11 by one drop. Further, in order to change the ejection volume of the ink flying from the nozzle hole 11 in order to express gradation, a positive electric field pulse T2 shorter than T1 is provided at an interval T4 before the final drive pulse T1 shown in FIG. Apply. As a result, two drops of ink fly from the nozzle hole 11. Similarly, a positive drive pulse T3 that is shorter than the final drive pulse T1 and has the same application time as T2 is operated at intervals of T5 before the positive electric field pulses T1 and T2 shown in FIG. Then, a volume of ink corresponding to three drops can be ejected from the nozzle hole 11. Here, positive drive pulses T2 and T3 shorter than the final drive pulse T1 are referred to as initial drive pulses. The initial drive pulse has a shorter application time than the final drive pulse, but can eject the same volume of ink droplets. Since the ink droplets ejected at T2 and T3 are ejected continuously in a short time, they coalesce during the flight between the nozzle hole 11 and the recording medium and become large ink droplets on the recording medium. Landing is enabled to enable gradation expression (ink droplet volume varying means). In the present embodiment, the pulse voltage V is common, and T1 / 2 = T2 = T3. As a result, the initial drive pulses T2 and T3 have a lower discharge speed than the case of driving with the final drive pulse T1, as can be seen from the graph showing the relationship between the electric field application time and the discharge speed in FIG. The effect of the ink does not remain in the next ejection, and the after-effect of the vibration is not added, so that the ink droplet ejection speed does not increase. As a result, as shown in FIG. 6, even when the volume of the ink droplet was changed, the difference between the electric field applied voltage and the ejection speed could be made substantially the same.

  Further, the pause time T4 between the initial drive pulse and the final drive pulse and the pause time T5 between the initial drive pulses are ejection at T4 = T5 = T1 + (T1-T2) = 3 × T2 = 3 × T3. I do. This means that the amount of time (T1-T2) in which the time of the initial drive pulse is shorter than the final drive pulse is added to the pause time as a new pause time. (Conventionally, the pause time and the drive pulse application time are the time T1 at which ink can be ejected most efficiently in the same manner.) This makes it possible to eject ink continuously and efficiently as in the past. Specifically, since T1 is 12 μsec, ejection was performed at T2 and T3 at 6 μsec, T4 and T5 at 18 μsec.

  By continuously performing ejection as shown in FIGS. 1A, 1B, and 1C in any combination based on print data, ink droplets having different capacities are ejected on the recording medium. Any gradation expression can be performed.

  As another embodiment of the present invention, as shown in FIG. 1D, the application time T2 ′ or T3 ′ of the initial drive pulse can be made longer than the final drive pulse T1. In this case, the pulse voltage V is common and T2 ′ = T3 ′ = T1 × (3/2). As shown in FIG. 5, a slow discharge speed can also be realized by making the initial drive pulses T2 ′ and T3 ′ longer than the final drive pulse T1. Further, in the present embodiment, the pause time T4 ′ between the initial drive pulse and the final drive pulse and the pause time T5 ′ between the initial drive pulses are T4 ′ = T5 ′ = T1 + (T1−T2 ′). = T1-T1 / 2 = T1 / 2. Since the initial drive pulse is longer than the final drive pulse T1, the pause time is shortened. As a result, ink can be discharged efficiently as in the conventional case.

  As described above, in the ink jet head of the present embodiment, the ejection speeds at the time of ink drops of 2 drops and 3 drops are equal as compared with the case of ejecting 1 drop. It is possible to provide printed matter with excellent image quality.

  In the present embodiment, the ejection of the ink volume of 1 drop, 2 drops, and 3 drops has been described, but there is no particular limitation on the upper limit of the ink drop amount. In addition, although the rectangular wave with the electric field application time T1, T2, and T3 is used with the signal application voltage V used in the present embodiment, the waveform and the signal application voltage with a smooth rise are gradually increased in the electric field application time. It may be changed, and is not particularly limited to a waveform.

  Further, in the ink jet head used in this embodiment, every other electrode 4 formed in the groove 5 is a common electrode having a ground potential, and the electrode 9 is formed so as to sandwich it. However, there is no problem even when the sidewalls 7 are driven every other line by the wiring method as shown in the figure showing another electrode wiring state in FIG.

The figure which shows the discharge signal waveform which concerns on the inkjet head of embodiment of this invention. The figure which shows the discharge signal waveform of the conventional inkjet head The exploded view which shows the discharge pressure generation part periphery which concerns on embodiment of this invention Sectional drawing which shows the electrode wiring state of the inkjet head which concerns on embodiment of this invention The figure which shows the relationship between the electric field application time of the inkjet head which concerns on embodiment of this invention, and discharge speed. The figure which shows the relationship between the electric field applied voltage and discharge speed of the inkjet head which concerns on embodiment of this invention. The figure which shows the relationship between the electric field applied voltage and discharge speed of the conventional inkjet head 1 is a front view of an entire inkjet head according to an embodiment of the present invention. 1 is a schematic cross-sectional view of an entire sub inkjet head according to an embodiment of the present invention. Sectional drawing which shows the electrode wiring state of the inkjet head which concerns on embodiment of this invention The figure which shows the relationship between the electric field application time and discharge speed of the conventional inkjet head

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Piezoelectric ceramic plate 2 Ink chamber plate 3 Nozzle plate 4 Electrode 5 Groove 6 Polarization direction 7 Side wall 11 Nozzle hole 12 Head cap 13 Base 20 Pressure relaxation unit 21 Flow path 26 Head chip

Claims (11)

A plurality of side walls composed of actuators that deform in response to an applied voltage;
A plurality of grooves communicating with the nozzle and arranged in parallel between the side walls;
An ink flow path for supplying ink to each of the grooves,
A drive pulse that is input to the electrode provided on the side wall to cause the actuator to deform and eject ink from the nozzle and a pause time during which the actuator is not actuated are set, and the drive pulse is continued at the pause time interval. In the method of driving an ink jet head that changes the ink droplet volume that reaches the recording medium at a time by changing the number of times,
Of the plurality of driving pulses, the signal waveform of the final driving pulse given last is different from the signal waveform of the initial driving pulse given one or more times before the final driving pulse. Method.   2. The ink jet head driving method according to claim 1, wherein the signal waveform of the final drive pulse is longer than the signal waveform of the initial drive pulse.   2. The ink jet head driving method according to claim 1, wherein the signal waveform of the final drive pulse is shorter than the signal waveform of the initial drive pulse.   3. The ink jet head driving method according to claim 1, wherein the pause time is increased by a time difference between signal application times of the signal waveform of the final drive pulse and the signal waveform of the initial drive pulse.   4. The ink jet head driving method according to claim 1, wherein the pause time is shortened by a time difference between signal application times of the signal waveform of the final drive pulse and the signal waveform of the initial drive pulse.   6. The ink jet head driving method according to claim 1, wherein a signal waveform of the final driving pulse is equal to a driving pulse for causing one drop of ink to fly.   6. The inkjet head according to claim 1, wherein a signal waveform of the final drive pulse that causes an appropriate amount of ink of n−1 drops to fly is equal to a signal waveform of the final drive pulse that causes an appropriate amount of ink of n drops to fly. Driving method.   3. The ink jet head driving method according to claim 2, wherein a signal application time of the signal waveform of the initial drive pulse is half of a signal application time of the signal waveform of the final drive pulse.   4. The ink jet head driving method according to claim 3, wherein the signal application time of the signal waveform of the initial drive pulse is 1.5 times the signal application time of the signal waveform of the final drive pulse. A plurality of side walls composed of actuators that deform in response to an applied voltage;
A plurality of grooves arranged in parallel between the side walls in communication with the nozzle;
An ink flow path for supplying ink to each of the grooves;
A drive pulse that is input to the electrode provided on the side wall to cause the actuator to be deformed to eject ink from the nozzle and a pause time during which the actuator is not actuated are set, and the drive pulse is continued at the pause time interval. In an ink jet head provided with an ink droplet capacity varying means that changes the ink droplet capacity reaching the recording medium at a time by changing the number of times,
An inkjet head characterized in that a signal waveform of a final drive pulse given last among the plurality of drive pulses is different from a signal waveform of an initial drive pulse given at least once before the final drive pulse. An inkjet head according to claim 10;
An ink jet recording apparatus comprising: an ink supply unit that supplies ink to the ink jet head; and a recording medium transport unit that transports a recording medium on which ink is ejected from the ink jet head.

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