JP2015089645A - Ink jet head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink jet head capable of stably and highly accurately discharging a sufficiently large quantity of ink.SOLUTION: An ink jet head includes: a plurality of nozzles provided on one surface; each of a plurality of pressure chambers provided corresponding to each of the nozzles and filled with ink; a plurality of piezoelectric members corresponding to the pressure chambers; and a drive signal generation section for applying a drive waveform including a first waveform expanding the pressure chambers for a half time of a natural oscillation period in the pressure chambers, a second waveform repeating contraction and expansion of the pressure chambers for a half or less of time of the natural oscillation period in the pressure chambers to follow the first waveform and a third waveform contracting the pressure chambers in the pressure chambers to follow the second waveform to the piezoelectric members by adjusting the contraction and expansion time of the second waveform and the contraction time of the third waveform so that flow velocity of ink discharged from the surfaces of the nozzles may be zero.

Description

  Embodiments described herein relate generally to an inkjet head.

  An ink jet head used in an ink jet printer or the like has a plurality of pressure chambers for containing ink, and nozzles for ejecting ink droplets corresponding to the pressure chambers. There are provided a plurality of nozzle plates, and a plurality of piezoelectric actuators provided corresponding to the pressure chambers and applying vibrations to the pressure chambers via a vibration plate.

  In this type of ink jet head, when a piezoelectric actuator is driven, vibration is applied to a pressure chamber corresponding to the actuator. Due to this pressure vibration, the volume in the pressure chamber changes, and ink droplets are ejected from the nozzles corresponding to the pressure chamber. The ink droplets land on a recording medium such as recording paper and form dots on the recording medium. By continuously forming such dots, the inkjet head forms characters, images, and the like based on the image data on the recording medium.

  In an inkjet head, it is preferable to stably eject ink droplets from the viewpoint of printing accuracy and the like. Therefore, there is known a 111-waveform driving method in which a voltage of −V, 0, + V is applied for 3 AL time in units of a predetermined cycle (AL).

  In this method, ink droplets can be stably ejected. However, in this method, the adjacent voltage difference is V, so that a sufficient discharge amount cannot be obtained. Therefore, a 120-wave drive method has been considered in which −V is applied to the first AL time, + V is applied to the next 2 AL time, and 0 is applied to the next AL time. In this case, since the voltage difference between the first AL time and the second AL time is 2 V, sufficient ink discharge can be performed.

  However, when + V is applied during the second AL time, ink ejection becomes unstable.

Japanese Patent Laid-Open No. 2002-19103 JP 2000-15802 A

  An object of the present invention is to provide an ink jet head capable of stably discharging a sufficiently large amount of ink with high accuracy.

  An inkjet head according to an embodiment includes a plurality of nozzles provided on one surface, a plurality of pressure chambers provided corresponding to each of these nozzles and filled with ink, and a plurality of piezoelectrics corresponding to these pressure chambers. A member, a first waveform that expands the pressure chamber for a time that is half of the natural vibration period in the pressure chamber, a time that is less than a half of the natural vibration period in the pressure chamber following the first waveform, A second waveform that repeats contraction and expansion, a drive waveform composed of a third waveform that contracts the pressure chamber in the pressure chamber following the second waveform, and a flow velocity of ink ejected from the surface of the nozzle is zero. And a drive signal generator for adjusting the contraction and expansion time of the second waveform and the third contraction time so as to be applied to the piezoelectric member.

It is a perspective view of the ink jet head of one embodiment. It is a block diagram which shows the principal part of an inkjet head in cross section. It is sectional drawing of the inkjet head seen from the direction of arrow AA in FIG. It is a schematic diagram for demonstrating operation | movement of an inkjet head. It is an example of the drive waveform applied to the piezoelectric member of an example of a conventional inkjet head. FIG. 6 is a characteristic diagram showing an example of ink pressure and ink flow velocity when the drive waveform shown in FIG. 5 is applied. It is an example of the drive waveform applied to the piezoelectric member of the inkjet head of one Embodiment. FIG. 8 is a characteristic diagram showing an example of ink pressure and ink flow velocity when the drive waveform shown in FIG. 7 is applied. It is a figure which shows the pitch error characteristic when the drive waveform of FIG. 5 is applied. It is a figure which shows the pitch error characteristic when the drive waveform shown in FIG. 7 is applied.

  Hereinafter, embodiments will be described with reference to the drawings. FIG. 1 is a perspective view of an ink jet head 1 according to an embodiment, FIG. 2 is a structural view showing a main part of the ink jet head in cross section, and FIG. 3 is a cross sectional view of the ink jet head viewed from the direction of arrow AA in FIG. It is.

  The inkjet head 1 includes a driving device 2, a head substrate 3, and a manifold 4. The manifold 4 includes an ink supply pipe 5 and a discharge pipe 6. The ink jet head ejects ink supplied from the ink supply means via the supply pipe 5 from each nozzle 13a in accordance with a drive signal from the drive device. Of the ink supplied from the supply pipe 5 into the manifold 4, the ink that has not been discharged from the nozzles 13 a is discharged from the discharge pipe 6 to the ink supply means.

  The head substrate 3 includes a nozzle plate 13. The nozzle plate 13 is formed with a plurality of nozzles 13a for ejecting ink droplets. Each nozzle 13 a is aligned in a plurality of rows (two rows in FIG. 1) in the longitudinal direction of the nozzle plate 13.

  The head substrate 3 is provided with a plurality of pressure chambers 11 corresponding to each of the nozzles 13a. Each pressure chamber 11 is partitioned by a partition wall 12, and each stores ink.

  The nozzle plate 13 is bonded to the bottom surface side of each pressure chamber 11. Each nozzle 13a has a tapered shape from the back surface side which is the pressure chamber 11 side toward the front surface side which is the ink discharge side.

  A diaphragm 14 is bonded to the top surface side of each pressure chamber 11. One end of a plurality of piezoelectric members 15 is connected to the upper surface side of the diaphragm 14 corresponding to each pressure chamber 11. The other end of each piezoelectric member 15 is held by a holding member 16. Each piezoelectric member 15 has a plurality of alternately laminated piezoelectric layers 15a and electrode layers 15b. A pair of electrodes 17 are arranged so as to sandwich each electrode layer 15b. Both electrodes 17 are electrically connected to the driving device 2.

  The head substrate 3 includes a common pressure chamber. Ink is injected into the common pressure chamber 18 via the supply pipe 5. The common pressure chamber 18 communicates with each pressure chamber 11, and the injected ink is filled in each pressure chamber 11 and the nozzle 13 a corresponding to the pressure chamber 11. By filling the pressure chamber 11 and the nozzle 13a with ink, an ink meniscus is formed in the nozzle 13a.

  In the inkjet head 1 having such a configuration, when a drive signal is applied to the piezoelectric member 15 via the electrode 17, the piezoelectric member 15 expands or contracts. As the piezoelectric member 15 expands or contracts, the vibration plate 14 is deformed to apply vibration to the pressure chamber 11. Due to this vibration, the volume of the pressure chamber 11 is changed to generate a pressure wave in the pressure chamber 11, and an ink droplet is ejected from the nozzle 13a.

  The diaphragm 14 and the piezoelectric member 15 form an actuator for applying vibration to the pressure chamber 11. The ink jet head 1 includes as many actuators as the number of nozzles 13a.

  Next, the drive device 2 will be described. The drive device 2 includes a communication unit 21, a calculation unit 22, and a drive signal generation unit 23. The communication unit 21 receives gradation data of an image to be printed from a host computer for controlling an inkjet printer, for example. The calculation unit 22 calculates the number of drive pulses based on the gradation data.

  A drive signal generator 23 serving as a drive signal generator selectively supplies a drive signal having the number of pulses calculated by the calculator 22 to each actuator. When the voltage of the drive signal is applied to the actuator, ink droplets having the number of drops corresponding to the number of pulses are ejected from the nozzle 13a of the pressure chamber 11 corresponding to the actuator.

  FIG. 5 shows an example of the waveform of the drive signal applied to each of the adjacent actuators in one embodiment. Details will be described later.

  This drive signal is completed in four times the AL time, and thereafter it is repeated. Here, the AL time is half the natural vibration period of the ink in the pressure chamber 11.

  FIG. 4 schematically shows the voltage application to the electrodes of each pressure chamber and the state of the pressure chamber in each state ST1, ST2, ST3. These drawings are for easy understanding, and the structural positional relationship and the like do not exactly match those shown in FIGS.

  In FIG. 4, the description will be made by paying attention to the ink ejected from the nozzle 33 a included in the nozzle plate 33.

  A pressure chamber 31a provided in the piezoelectric member 35 is directly connected to the nozzle 33a, and a terminal 37a is connected to an electrode of the pressure chamber. Next to the side, pressure chambers 31b, 31c, 31d and 31e having the same structure are provided. Although the pressure chambers are shown here independently, they are actually in communication. Terminals 37b, 37c, 37d, and 37e are connected to the electrodes of these pressure chambers.

  These terminals are applied with a positive voltage + V or grounded (GND). In the state ST1, the positive voltage + V is uniformly applied to each terminal. In the state ST2, the terminal 37a corresponding to the pressure chamber 31a is grounded, and the positive voltage + V is still applied to the other terminals. In the state ST3, a positive voltage is applied only to the electrode 37a, and the other electrodes are grounded. That is, the electrode 37a is relatively zero in the state ST1, meaning that a negative voltage is applied in the state ST2, and a positive voltage + V is applied in the state ST3.

  An example of a driving waveform in the conventional case is shown in FIG. 5, and an example of a driving waveform of one embodiment of the present invention is shown in FIG.

  The drive waveform in the example shown in FIG. 5 in the conventional case is a so-called 120 waveform. At time t1, the state ST1 is shifted to the state ST2, and only the electrode 37a is grounded. At time t2 after AL time, a positive voltage + V is applied to the electrode 37a, and the other electrodes are grounded. At time t3 after 2AL hours, the state returns to the state ST1, and this state continues for the AL time. Thus, 4AL is one cycle.

  FIG. 6 shows an example of characteristics of the ink pressure and the ink flow velocity when the driving waveform shown in FIG. 5 is applied to the pressure chamber, and is superimposed on the driving waveform. In FIG. 6, the horizontal axis represents time (μsec), and the vertical axis represents the normalized output magnitude. A characteristic line 61 is a driving waveform, a characteristic line 62 indicates the pressure applied to the ink, and a characteristic line 63 indicates the ink flow velocity at that time. How to see this characteristic will be described later in comparison with FIG. 8 showing the characteristic of the present embodiment.

  On the other hand, as shown in FIG. 7, the drive waveform in the present embodiment moves from state ST1 to state ST2 at time t1. In this state ST2, the terminal 37a is grounded, and the positive voltage + V is still applied to the other electrodes as before.

  In this state ST2, the electrode connected to the terminal 37a becomes zero potential, and the corresponding pressure chamber 31a expands and a negative pressure is applied. On the other hand, the side facing the pressure chamber 31a of the adjacent pressure chambers 31b and 31d is recessed due to this influence.

  Next, at time t2 after the AL time, the inkjet head 1 moves from the state ST2 to the state ST3, the positive voltage + V is applied to the terminal 37a, and the other electrodes are set to the ground potential (see FIG. 4). Here, the time from time t1 to time t2 is referred to as a first AL time.

  In the state ST3, a positive voltage + V is applied to the electrode connected to the terminal 37a. Then, the corresponding pressure chamber 31a is recessed, and ink droplets are ejected from the nozzle 33a. At this time, the pressure chamber 31a side of the adjacent pressure chambers 31b and 31d protrudes.

  The process until the state ST3 is the same as the conventional case shown in FIG.

  However, in this embodiment, at time t3 when a time equal to or less than AL / 2 (this time is T1) has elapsed, the state returns to the state ST1, and the positive voltage + V is applied to each terminal. In this state, each pressure chamber returns to a normal state.

  Then, at the time t4 when the next time of AL / 2 or less (this time is T2) has elapsed, the state ST3 is entered again. That is, a positive voltage + V is applied to the electrode 37a, and the pressure chamber 31a corresponding to the nozzle 33a is recessed. At this time, the pressure chamber 31a side of the adjacent pressure chambers 31b and 31d protrudes. This time T1 and time T2 are referred to herein as second AL time. That is, time T1 + time T2 is equal to or shorter than AL time.

  At the next time t5 when the AL time has elapsed from t4, the state returns to the state ST1 again. This time is referred to herein as the third AL time. Thus, the time from time t1 to time t2 and from time t4 to time t5 is AL, but the time from time t2 to time t4 is less than or equal to the AL time. The time from time t2 to time t3 is T1, and the time from time t3 to time t4 is T2 (T1 + T2 ≦ AL).

  Here, how to set the times T1 and T2 will be described.

  In FIG. 6 showing the characteristics of the conventional example, the horizontal axis represents time, and the vertical axis represents normalized pressure and flow velocity. A characteristic line 61 indicates a driving waveform, a characteristic line 62 indicates a pressure applied to the ink at that time, and a characteristic line 63 indicates a flow rate of the ejected ink.

  In FIG. 6, when the point P61 of the characteristic line 62 is seen, when the drive waveform returns from the state ST3 to the state ST1, the ink pressure is suddenly set to zero, but cannot be reduced to zero due to the rapid fluctuation. Then, as indicated by the point P62 and the like, the pressure fluctuation remains thereafter. For this reason, the ink flow velocity cannot be made zero at the point P65 or the like of the characteristic line 63, and fluctuations remain as indicated by the point P66.

  On the other hand, when the drive waveform shown in FIG. 7 of this embodiment is used, the ink pressure and the ink flow rate are as shown in FIG. Also in this figure, the horizontal axis represents time, and the vertical axis represents normalized pressure and flow velocity. A characteristic line 81 shows the driving waveform of this embodiment, a characteristic line 82 shows the pressure applied to the ink at that time, and a characteristic line 83 shows the flow velocity of the ink to be ejected.

  In this case, unlike the drive waveform shown in FIG. 7, the state is changed from state ST3 to state TS1 as shown at time t3. Therefore, a sudden change at the time of transition from the previous state ST2 to the state ST3 is alleviated. Therefore, as indicated by a point P81 on the ink pressure characteristic line 82 in FIG. 8, it is possible to suppress the pressure when returning from the state ST3 to the state ST1. That is, the pressure fluctuation can be zero. Therefore, the characteristic line 83 indicating the ink flow rate can be set to zero as indicated by a point P85 at time t5.

  These ink pressures and ink flow rates can be adjusted by adjusting the time T1 from time t2 to time t3 and the time T2 from time t3 to time t4, as indicated by an arrow 71. That is, the times T1 and T2 can be adjusted so that the ink flow velocity at time t5 becomes zero.

  Transition from state ST2 to state ST3, then transition from state ST3 to state ST1, time T1 from time t2 to time t3, transition from state ST3 to state ST1, and then transition from state ST1 to state ST3 The time T2 from the time t3 to the time t4 is normally AL / 2 or less. Therefore, T1 + T2 becomes AL time or less.

  The drive waveform applied to the piezoelectric member is as follows from the viewpoint of expansion and contraction of the pressure chamber. In FIG. 7, the pressure chamber 31a is expanded between the time t1 and the time t2, and the waveform in this state is referred to as a first waveform. Next, between time t2 and time t4, the pressure chamber 31a is repeatedly contracted and expanded, and the waveform applied to the piezoelectric member at this time is referred to as a second waveform. The pressure chamber is contracted again between time t4 and time t5, and the drive waveform at this time is referred to as a third waveform.

  In the drive signal generator, the first waveform for expanding the pressure chamber for half the time of the natural vibration period in the pressure chamber, and the pressure chamber is contracted for a time equal to or less than half of the natural vibration period in the pressure chamber following the first waveform. And a second waveform that repeats expansion, and a drive waveform consisting of a third waveform that contracts the pressure chamber for a time that is half the natural vibration period in the pressure chamber following the second waveform, is applied to the piezoelectric member. The second time is adjusted so that the flow rate of the ink ejected from the nozzle surface becomes zero.

  It is preferable that the first waveform and the second waveform are applied to the piezoelectric member at a timing at which the pressure chamber continuously changes from the expanded state to the contracted state.

  The second waveform is repeatedly applied to the piezoelectric member, and after the second waveform is applied, the flow rate of the ink ejected from the nozzle surface oscillates and becomes the second time at the second time. It is preferred that the second waveform is applied.

  Furthermore, it is preferable that the third waveform is applied to the piezoelectric member so as to suppress vibration of the nozzle surface after ejection after the input of the last second waveform.

  FIG. 9 and FIG. 10 show examples of pitch error characteristics when the ink chamber is driven with the conventional waveform shown in FIG. 5 and when the ink chamber is driven with the waveform shown in FIG.

  In these drawings, the horizontal axis represents the number of each nozzle, and the vertical axis represents the pitch error (μm) of the nozzle droplets discharged from each nozzle when a plurality of nozzles are arranged in a line at a theoretical value of 169 μm. ).

  As apparent from FIGS. 9 and 10, the pitch error in FIG. 10 is small. In comparison with the standard deviation, it was 1.22 μm in the case of FIG. 9 and 0.6 μm in the case of FIG. As described above, it can be understood that the use of the drive waveform of the present embodiment (FIG. 7) reduces the pitch error, that is, can stably and accurately eject ink droplets while suppressing fluctuations in the flow velocity of the ink droplets.

  In the present embodiment, the piezoelectric member 15 is directly connected to the pressure chamber 11, but the present invention is not limited to this, and the piezoelectric member may have a structure corresponding to the pressure chamber via a diaphragm.

  According to the embodiment, an inkjet head capable of stably discharging a sufficiently large amount of ink with high accuracy can be obtained.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 1 .... Inkjet head 2 ... Driving device 3 ... Head substrate 11 ... Pressure chamber 12 ... Partition 13 ... Nozzle plate 13a, 33a ... Nozzle 14 ··· Vibration plate 15 ··· Piezoelectric member 15a ··· Piezoelectric layer 15b ··· Electrode layer 17, 37a to 37e ··· Electrode 18 ··· Common pressure chamber 23 ··· Drive signal generator 31a to 31e ... Pressure chamber 81, 82, 83 ... Characteristic line

Claims (4)

A plurality of nozzles provided on one side;
A plurality of pressure chambers each provided corresponding to each of these nozzles and filled with ink;
A plurality of piezoelectric members corresponding to these pressure chambers;
A first waveform that expands the pressure chamber for a half time of the natural vibration period in the pressure chamber, and a contraction and expansion of the pressure chamber for a time that is less than half of the natural vibration period in the pressure chamber following the first waveform. The second waveform that repeats the above, the drive waveform consisting of the third waveform that contracts the pressure chamber in the pressure chamber following the second waveform, so that the flow velocity of the ink ejected from the nozzle surface becomes zero. Adjusting the contraction and expansion time and the third contraction time of the second waveform, and applying the drive signal generator to the piezoelectric member;
An inkjet head characterized by comprising:   The inkjet according to claim 1, wherein the first waveform and the second waveform are applied to the piezoelectric member at a timing at which the pressure chamber continuously changes from an expanded state to a contracted state. head.   The second waveform is repeatedly applied to the piezoelectric member, and after the second waveform is applied, the flow rate of the ink ejected from the nozzle surface oscillates and becomes the second time when it becomes zero. The ink jet head according to claim 1, wherein the second waveform is applied.   The inkjet head according to claim 3, wherein the third waveform is applied to the piezoelectric member so as to suppress vibration of the surface of the nozzle after ejection after the input of the last second waveform.

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