JPH07214775A - Printing apparatus and driving method thereof - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a driving method of an ink jet head and a driving apparatus therefor so as to obtain a good printing quality by eliminating residual polarization. [Configuration] A nozzle and an ink flow path communicating with the nozzle,
A vibrating plate provided in a part of the flow path and an electrode provided so as to face the vibrating plate are applied, and an electric pulse in a forward direction is applied between the vibrating plate and the electrode to apply an electrostatic force In the driving device of the inkjet head that deforms the ink droplets by ejecting ink droplets from the nozzle, an electric pulse in the direction opposite to the electric pulse in the forward direction and in which the diaphragm contacts the individual electrode is changed to the electric pulse in the forward direction. It has a residual charge removing means 212 of the vibration plate which is applied between the vibration plate and the electrode immediately before the application.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of driving an ink jet head using static electricity as an actuator and a device therefor, and more particularly to eliminating the influence of residual charge remaining on a diaphragm constituting the actuator.

[0002]

2. Description of the Related Art Ink jet printers have many advantages such as extremely low noise during recording, high-speed printing capability, and the availability of inexpensive plain paper with a high degree of freedom in ink. Of these, the so-called ink-on-demand method, which ejects ink droplets only when recording is necessary, is currently mainstream because it does not require the collection of ink droplets unnecessary for recording.

As a conventional ink-on-demand driving method, for example, there is a driving method disclosed in Japanese Patent Publication No. 2-24218. In this driving method, a piezoelectric element that changes the volume of the pressure chamber that generates the ink ejection pressure is provided, and an electric pulse in the same direction as the polarization voltage of the piezoelectric element is applied to the piezoelectric element in a standby state, The volume of the pressure chamber is reduced by charging, the piezoelectric element is gradually discharged during ink ejection to increase the volume of the pressure chamber, and then an electrical pulse is applied to the piezoelectric element again to rapidly move the piezoelectric element. Ink is ejected from the nozzle by charging and reducing the volume of the pressure chamber. In this driving method, in order to eject the ink droplets most efficiently at a low voltage, the voltage is applied to the piezoelectric element again in the vicinity of the maximum value of the damping vibration of the ink system that occurs when the ink is sucked into the pressure chamber. Rapidly reducing the volume of the pressure chamber.

On the other hand, an ink jet head which uses an electrostatic force to drive an actuator has, for example, USP 4,5.
The structure disclosed in 20,375 is known.

US Pat. No. 4,520,375 is composed of a capacitor, which is composed mainly of two capacitor plates facing each other with a gap mainly by an insulating means, and a reservoir for containing ink, and one of the capacitor plates is, for example, one of them. By forming a thin diaphragm made of silicon semiconductor and applying a time-varying voltage to the capacitor, mechanical vibration is generated in the diaphragm, and in response to the movement of the diaphragm, for example, ink such as ink. A liquid ejecting apparatus that ejects liquid from a nozzle is disclosed.

[0006]

The above-mentioned conventional method for driving an ink jet head is one of the most suitable methods for the ink-on-demand system using a piezoelectric element as an actuator.

However, in the case of driving an ink jet head using electrostatic force for driving the actuator shown in USP 4,520,375 by the ink-on-demand method, the above-mentioned driving method using a piezoelectric element is simply applied. However, the following problems occur and it is difficult to put them into practical use.

An ink jet head using static electricity as an actuator is different from one using a piezoelectric element, and after a pulse voltage is applied between the diaphragm and individual electrodes, electric charges remain in the dielectric between the diaphragm and the electrodes, The electric field generated by this residual charge reduces the relative displacement between the diaphragm and the individual electrodes. This reduction in the relative displacement amount causes ejection failure such as the ejection amount of ink droplets and the ink speed, which leads to deterioration of print quality such as print density and pixel shift, and deterioration of reliability such as pixel omission. There was a problem.

Further, the residual charge is, as will be described later,
Since the magnitude of the applied voltage varies depending on the history of the applied voltage in the past, the relative displacement amount between the diaphragm and the individual electrode is not fixed uniquely and becomes unstable. The ejection speed and the like became unstable, and in any case, it became a factor of lowering the reliability such as defective print quality such as print density and pixel shift and pixel omission.

The present invention has been made in order to solve the above problems, and its objects are the following three points.

A method and apparatus for driving an inkjet head, which eliminates the adverse effect of residual charges accumulated between the diaphragm and the electrodes on the driving of the inkjet head and stabilizes the relative displacement between the diaphragm and the individual electrodes. The present invention provides a printing apparatus and a driving method thereof, which provide good printing quality.

The recovery means that eliminates the adverse effect that the residual charges accumulated between the diaphragm and the electrode have on the drive of the inkjet head is reliably executed in a short time, and the execution of the recovery means consumes a lot of time. (EN) Provided is a printing device capable of printing at high speed without lowering the printing speed, and a driving method thereof.

By performing a recovery means for eliminating the adverse effect of the residual charges accumulated between the diaphragm and the electrode on the driving of the inkjet head, the inkjet head is broken or the life is shortened, and the reliability is lowered. To provide a printing device that does not cause problems related to printing.

[0014]

A printing apparatus according to the present invention includes a nozzle, an ink flow path communicating with the nozzle, a vibration plate provided in a part of the flow path, and a diaphragm facing the vibration plate. An actuator including an electrode provided and a driving unit that deforms the vibration plate and ejects ink droplets for recording from the nozzle, the driving unit, when recording, causes the actuator to First for flexing diaphragm
Voltage is applied to the actuator and the first voltage is applied to the actuator with a second voltage having a polarity different from that of the voltage applied to the electrode and the diaphragm being in contact with the electrode. And a residual charge removing means. An insulating layer is formed between the vibrating plate of the actuator and the electrode, and a preferable material of the vibrating plate is silicon, and the preferable insulating layer is a thermal oxide film of silicon, and the electrode The preferred material of is an ITO film.

In the method for driving a printing apparatus according to the present invention, the nozzle, the ink flow path communicating with the nozzle, the vibration plate provided in a part of the flow path, and the vibration plate provided opposite to the vibration plate. In a method of driving a printing apparatus that has an actuator including an electrode and deforms the diaphragm, ejects ink droplets from the nozzles, and performs recording, the diaphragm is deformed during normal recording. In order to stabilize the displacement amount of the diaphragm at a predetermined time by applying the first voltage, the polarity is different from that of the first voltage and is larger than the voltage value at which the diaphragm contacts the electrode. The second voltage is applied. The second voltage may be applied every time one dot or one line is printed, or may be applied when the recovery processing operation of the nozzle is performed.

[0016]

In the present invention, by applying an electric pulse in the forward direction between the diaphragm of the ink jet head and the individual electrode, an attractive force due to electrostatic force is exerted between the diaphragm and the individual electrode facing the diaphragm. Works, and this electrostatic force deforms the diaphragm. Next, by releasing the electric pulse, ink droplets are ejected from the nozzle holes by the restoring force of the vibration plate.

However, even if the electric pulse is released, the electric charge remains between the diaphragm and the individual electrodes, and the electric field created by the residual electric charge causes the diaphragm to bend without being completely restored. . Then, the relative displacement amount between the diaphragm and the individual electrode decreases, and the ejection amount and ejection speed of the ink droplets also decrease with the driving time, resulting in poor print quality such as print density and pixel shift, and defective pixels. Will occur. In the present invention, a voltage having a polarity different from that at the time of driving (hereinafter referred to as a refresh voltage) is applied, for example, after performing a one-line printing operation, and is accumulated by applying the driving voltage. The residual electric charge has disappeared. Therefore, the amount of relative displacement between the diaphragm and the individual electrode does not decrease.

Furthermore, if a refresh voltage having a magnitude higher than the voltage value at which the diaphragm contacts the individual electrodes (hereinafter referred to as a contact voltage) is applied, the residual charge accumulated on the diaphragm disappears in a short time. However, as a result, the flexure of the diaphragm due to the residual charges is eliminated in a short time, a lot of time is spent for applying the refresh voltage, and the printing speed is not reduced.

Further, in the printing apparatus of the present invention, an insulating layer made of a thermal oxide film of silicon, which is strong against electrical and mechanical stress, is formed between the silicon diaphragm and the individual electrodes, and the driving voltage is increased. Or, when a refresh voltage is applied to the actuator, the vibrating plate contacts the individual electrodes through the thermal oxide film, so the actuator is not destroyed by a short circuit, and the individual electrodes have excellent withstand voltage. Since it is formed of an ITO film, the problem that the head is destroyed is unlikely to occur even during long-term driving.

[0020]

FIG. 2 is an exploded perspective view of an ink jet head in one embodiment of the present invention. The present embodiment shows an example of an edge eject type in which ink droplets are ejected from nozzle holes provided at the end of the substrate, but a face image ejecting ink droplets from nozzle holes provided at the upper surface of the substrate is used. It may be a cut type. 3 is a cross-sectional side view of the entire assembled inkjet head, and FIG. 4 is A- of FIG.
It is a line A arrow line view. Inkjet head 1 of this embodiment
Reference numeral 0 has a laminated structure in which three substrates 1, 2 and 3 having the structure described in detail below are stacked and joined.

The intermediate first substrate 1 is a silicon substrate, and a plurality of nozzle grooves 1 are formed on the surface of the substrate 1 in parallel from one end at equal intervals so as to form a plurality of nozzle holes 4.
1 and a recess 12 communicating with each nozzle groove 11 and forming a discharge chamber 6 having a diaphragm 5 as a bottom wall;
2 is a narrow groove 13 for an ink inflow port, which will form an orifice 7 provided at the rear of the nozzle 2, and a recessed part, which will form a common ink cavity 8 for supplying ink to each ejection chamber 6. 14 and. Also, the diaphragm 5
A concave portion 15 which constitutes the vibration chamber 9 for mounting an electrode described later is provided in the lower part of the. In this embodiment, each of the orifices 7 has three parallel thin grooves 13 in order to mainly increase the flow path resistance and to maintain the normal operation of the inkjet head even if one of the narrow grooves is clogged. Is formed.

In the present embodiment, the gap between the diaphragm 5 and the electrode arranged opposite thereto, that is, the gap portion 1
A length G of 6 (see FIG. 3, hereinafter referred to as “gap length”).
So that there is a difference between the depth of the recess 15 and the thickness of the electrode,
The space holding means is composed of a vibration chamber recess 15 formed on the lower surface of the first substrate 1. As another example, the recess may be formed on the upper surface of the second substrate 2. Here, the depth of the recess 15 is set to 0.6 μm by etching. The pitch of the nozzle grooves 11 is 0.72 mm and the width thereof is 70 μm.

Regarding the provision of the common electrode 17 to the first substrate 1, it is important that the work function of the metal material of the semiconductor and the electrode is large or small. In this embodiment, titanium is used as the common electrode material. Although platinum is used as an attachment and gold is used as an underlay of chromium, the present invention is not limited to this embodiment, and another combination may be used depending on the characteristics of the semiconductor and the electrode material. The resistivity of the semiconductor material used in this example is 8 to 12 Ωcm.

Borosilicate glass is used for the lower second substrate 2 bonded to the lower surface of the first substrate 1, and the vibration chamber 9 is formed by bonding the second substrate 2 to each other. Gold is sputtered by 0.1 μm on each position corresponding to the vibration plate 5 on the substrate 2 to form a gold pattern in substantially the same shape as the vibration plate 5 to form the individual electrodes 21. Individual electrode 2
1 has a lead portion 22 and a terminal portion 23. Furthermore, except for the electrode terminal portion 23, the Pyrex sputtered film is 0.2
An insulating layer 24 is formed by coating with a thickness of μm to form a film for preventing dielectric breakdown and short circuit when the inkjet head is driven.

The upper third substrate 3 bonded to the upper surface of the first substrate 1 is made of borosilicate glass as with the second substrate 2. By joining the third substrate 3, the nozzle hole 4, the ejection chamber 6, the orifice 7, and the ink cavity 8 are formed. Further, the third substrate 3 is provided with an ink supply port 31 communicating with the ink cavity 8. The ink supply port 31 is connected to an ink tank (not shown) via a connection pipe 32 and a tube 33.

Next, the first substrate 1 and the second substrate 2 are anodically bonded at a temperature of 300 to 500 ° C. and a voltage of 500 to 800 V, and under the same conditions, the first substrate 1 and the third substrate 3 are joined. And the ink jet head is assembled as shown in FIG. After joining the anode, the gap length G formed between the diaphragm 5 and the individual electrode 21 on the second substrate 2 is equal to the recess 1
5 and the thickness of the individual electrode 21, which is 0.5 μm in this embodiment. The gap G1 between the diaphragm 5 and the insulating layer 24 on the individual electrode 21 is 0.3 μm.

After the ink jet head is assembled as described above, the common electrode 17 and the terminal portion 23 of the individual electrode 21 are formed.
A drive circuit 102 is connected between the wirings 101 to form an inkjet printer. Ink 103
Is supplied to the inside of the first substrate 1 from an ink tank (not shown) through the ink supply port 31, and fills the ink cavity 8, the ejection chamber 6, and the like. Then, as shown in FIG. 3, the ink in the ejection chamber 6 is ejected as ink droplets 104 from the nozzle holes 4 when the inkjet head 10 is driven, and is printed on the recording paper 105.

Next, the electrical connection of this embodiment constructed as described above will be explained.

In the so-called MIS structure, which is a structure composed of a metal-insulating layer-semiconductor layer, a space charge layer (depletion layer) may or may not have a large difference in current value depending on the polarity of the applied voltage. Also known as) phenomenon. When the semiconductor material of the substrate is P-type silicon, it can be regarded as a conductor when a positive voltage is applied to the substrate electrode side, but when a negative voltage is applied, it is not regarded as a conductor due to the existence of the space charge layer and the capacitance is I know I have it.

FIG. 5 is a partially enlarged detailed view of the vibrating plate and the individual electrodes in this embodiment, and schematically shows the state of electric charges. P-type silicon is used for the first substrate 1, the first substrate 1 (vibration plate 5) side, that is, the common electrode 17 is connected to the drive circuit 102 so that the positive polarity and the individual electrode 21 side have the negative polarity, Common electrode 17 and individual electrode 21
This is the case where a pulse voltage is applied by the drive circuit 102 to.

The P-type silicon is doped with boron,
It is known that the electrons have the same number of holes as the number of doped boron because the number of electrons is insufficient. P
The holes 19 in the shaped silicon are repelled toward the insulating layer 26 side by the positive charge of the common electrode 17. Due to the movement of the holes 19, the acceptor (ionized boron) becomes
Since charges are supplied from the substrate electrode 17, holes flow in the first substrate 1 and a space charge layer is not generated, which can be regarded as a conductor. Further, the individual electrode 21 side is charged with a negative electric charge, and as a result, the applied pulse voltage generates an attractive force due to static electricity sufficient to bend the diaphragm 5. Therefore, the diaphragm 5 is bent toward the individual electrode 21 side.

6 and 7 are schematic diagrams focusing on the residual charge of the dielectric between the diaphragm and the individual electrodes of FIG.
Similar to FIG. 5, FIG. 6 shows a state when a voltage is applied, and FIG. 7 shows a state when the electric field is removed. Next, generation of residual charges will be described with reference to FIGS. 6 and 7. 6 and 7, as described above, the diaphragm 5 is a semiconductor, the common electrode 17 is made of metal, and they are ohmic-connected.

The diaphragm 5 is covered with an insulating layer 26. The insulating layer 24 formed on the individual electrode 21 faces the insulating layer 26 via the gap 16, and the insulating layer 26, the gap 16 and the insulating layer 24 form the insulating layer 27 as a whole. . Therefore, here, it can be regarded as a model in which the dielectric is interposed in the parallel plate capacitor constituted by the diaphragm 5 and the individual electrode 21. The dielectric corresponds to the protective film insulating layers 24 and 26.
When a voltage is applied to the parallel plates, the dielectric material cancels the applied electric field as shown in FIG. 6 (in the direction opposite to the electric field).
Polarization 28 is generated. Most of the polarized light 28 disappears in a short time when the applied voltage is cut off and the electric charge stored in the capacitor is discharged through the resistor 46. The delay time from the discharge to the disappearance of the polarization is called the relaxation time, which greatly differs depending on the type of polarization.

In the case of the polarization of the dielectric (insulating layer) inside the vibrating plate 5 and the individual electrode 21 of this embodiment, a comparison called ion polarization or interface polarization other than atomic polarization or electronic polarization with a short relaxation time is made. It contains a polarization component with a long dynamic relaxation time. Ion polarization is generated by the movement of Na +, K +, B +, etc. inside the insulating layer along the applied electric field, and interface polarization causes contact between media having different dielectric constants when the dielectric has a heterogeneous structure. The polarization that occurs at the interface between the silicon oxide and the pure silicon. Therefore, in the dielectric 5 (24, 26) inside the vibrating plate 5 and the individual electrodes 21 of this embodiment, as shown in FIG. 7, a part of the polarization is completely generated by repeated application of an electric field or continuous application for a long time. The polarization remains for a long time without disappearing. As a result, the dielectric material has a residual polarization 29, and the residual electric field P created by the residual polarization between the diaphragm 5 and the electrode 21 causes a decrease in the relative displacement amount between the diaphragm 5 and the individual electrode 21.

FIG. 8 is a diagram showing the deflection of the diaphragm and the individual electrodes with time. FIG. 8A shows the diaphragm 5 and the individual electrode 21.
No voltage is applied between them, and the diaphragm 5 and the individual electrode 21 are parallel to each other as shown in the figure. Figure 8
(B) is a state when voltage is applied to the diaphragm 5 and the individual electrode 17, and the diaphragm 5 bends as shown in the figure. Here, the amount of the deflection is ΔV1. Next, FIG. 8C shows a state after the electric charge stored in the diaphragm 5 and the individual electrode 17 is discharged, and the diaphragm 5 is bent by the residual electric field generated by the residual charge even after the discharge, for example, The amount of deflection is ΔV2
And Therefore, it is understood that the relative displacement amount between the diaphragm 5 and the individual electrode 21 becomes ΔV1-ΔV2, and the relative displacement amount decreases.

The decrease in the relative displacement amount between the vibrating plate 5 and the individual electrode 21 causes the ejection failure such as the ejection amount of the ink droplet or the ink speed as described above, and the reliability of the ink jet printer. And the print quality will be adversely affected. Therefore, in the present embodiment, as described later, the electric field in the direction opposite to that of FIG. 6 is applied between the diaphragm 5 and the individual electrode 21 to eliminate the above-mentioned residual charges.

FIG. 1 is a conceptual diagram of an ink jet printer according to an embodiment of the present invention. In the figure, 202 is a drive motor that moves the inkjet head or a print medium such as paper, and 203 is a printer that mainly includes the inkjet head 10 and the drive motor 202. The printer 203 prints characters and images by ejecting ink from the inkjet head 10 to reach the print medium while moving the inkjet head 10 and the print medium by the drive motor 202. Reference numeral 204 denotes a time measuring means, which measures time. 20
Reference numeral 6 denotes a nozzle clogging recovery processing means for controlling the nozzle clogging recovery processing. 207 is an input means,
Reference numeral 0 denotes a print calculation control unit 210 that performs print control and receives various input signals from the input unit 207 and performs various calculation controls. The print calculation control means 210 outputs an initialization signal for activating the clock means 204, a print control signal for controlling the printer 203, and performs various controls.
A storage unit 211 stores various data used in the arithmetic processing of the print arithmetic control unit 210. Two
Reference numeral 12 denotes a residual charge removing means for the diaphragm, which outputs a diaphragm recovery processing control signal in order to perform recovery processing for the residual charge on the diaphragm as described later.

Reference numeral 213 is a drive control circuit for the ink jet head 10, which has the circuit configuration shown in FIG. A nozzle recovery process control signal, a print control signal, and a diaphragm recovery process control signal are input to the drive control circuit 213, and the drive of the inkjet head 10 is controlled based on these control signals. Reference numeral 214 denotes a drive control circuit for the drive motor 202, which receives a nozzle recovery process control signal, a print control signal, and a diaphragm recovery process control signal, and controls the drive of the drive motor 202 based on these control signals.

FIG. 9 is a diagram showing the configuration of the drive control circuit of the ink jet head 10. This drive control circuit 21
3 is a control circuit 215 and a drive circuit 10 as shown.
2a. The drive circuit 102a includes transistors 106 to 109 and amplifiers 110 to 113. The control circuit 215 receives the nozzle recovery processing control signal, the print control signal, and the diaphragm recovery processing control signal, outputs pulse voltages P1 to P4 to the amplifiers 110 to 113 as appropriate based on those control signals, and the amplifiers 110 to 1
The transistors 106 to 109 are driven by the output of 13, and as a result, the capacitor 114 formed by the diaphragm 5 and the individual electrode 21 is charged or discharged, whereby the ink droplet 104 is ejected from the nozzle hole 4. Is ejected. Here, the resistor 115 is a resistor that determines the discharge rate, and the resistor 116 is a resistor that determines the charge rate. The time constant of charging and discharging is determined by each resistance value and the capacitance of the capacitor 114.

FIG. 10 shows the ink jet head 10 described above.
FIG. 2 is a schematic diagram of a printer equipped with the. 300 is recording paper 1
A platen 301 for transporting 05 is an ink tank for storing ink therein, and supplies ink to the inkjet head 10 via an ink supply tube 306.
Reference numeral 302 denotes a carriage, which is the inkjet head 10.
Is moved in a direction orthogonal to the conveyance direction of the recording paper 105. Reference numeral 303 denotes a pump, which is the inkjet head 10.
In the case of defective ink ejection, etc., it has a function of sucking the ink through the cap 304 and the waste ink collection tube 308 and collecting it in the waste ink reservoir 305.

FIG. 11 is a flow chart showing the control method of the ink jet printer of the embodiment of FIG.
2 is a flowchart showing the subroutine.
In FIG. 12, (a) shows the subroutine for the nozzle recovery operation, and (b) shows the subroutine for the printing operation. First, in step S0, the print calculation control means 21
Based on the instruction of 0, the initialization of the printer mechanism unit and the like is executed. At this time, the timing means 204 is reset at the same time and the timing starts. In the next step S1, the nozzle recovery operation is performed immediately after the power is turned on. This nozzle recovery operation is performed by a series of processes shown in steps SS1 to SS3 of the nozzle recovery operation subroutine of FIG.

First, the ink jet head 10 is driven by driving the drive motor 202 in step SS1.
Mount the carriage 302 with the cap from the standby position to the cap 3
Move to position 04. Next, in step SS2, a nozzle recovery operation, that is, a refresh operation is performed. The refreshing of the nozzles is performed by driving the vibrating plate 5 corresponding to all the nozzles in order to discharge defective ink that causes defective ink ejection such as thickened ink in the nozzle portion of the inkjet head 10. That is, the ink is ejected from the nozzle of a predetermined number of times. Normally, 10 to 200 ejections are performed for each nozzle, and the thickened defective ink is ejected outside the nozzle. The number of refresh discharges is determined in advance by the set time of the timer means 204.
After the refreshing of the nozzles is completed, the carriage 302 is returned to the standby position again in step SS3, and a series of refresh operations is completed. When power is turned on,
Generally, there is a high possibility that the head will not be used for a long time, so 160 to 200 ink ejections are executed.

After the completion of the nozzle refreshing operation, the timer means 204 starts measuring a predetermined time. In step S2, the presence or absence of a timer-up signal is determined in order to determine whether or not the time counting means 204 has measured a predetermined time. Here, if the timer-up signal has been generated, the process proceeds to the nozzle recovery operation of step S8, and FIG.
The refresh operation shown in the nozzle recovery operation subroutine of (a) is performed, and the process proceeds to step S3. If the timer-up signal is not generated, the process directly proceeds to step S3. In step S3, it is determined whether to print. If printing is not performed, the process returns to step S2. In the case of printing, after resetting the clock means 204 in step S4, the printing operation is executed in step S5.

This printing operation is performed by a series of operations shown in steps SS10 to SS16 of the printing operation subroutine of FIG. The count value n is set to 1 in step SS10, and the carriage 302 is moved by one dot in step SS11. Then, in steps SS12 and SS13, the designated dot ink based on the print data is sucked and ejected. Then, in step SS14, refreshing (disappearance of residual charges) is performed only on the specific diaphragm 5 driven in steps SS12 and SS13. In the next step SS15, the count value n = n + 1 is incremented, and step SS
In 16, it is determined whether n is the final dot,
If it is not the final dot, the process returns to step SS11 and the above-described processing is repeated. If it is the final dot, the printing operation is ended, and in step S6, the carriage 3
02 is returned to the standby position again, and the paper is fed by a predetermined amount in step S7. Then, in step S9, it is determined whether or not the process is to be continued. If the process is to be continued, the process returns to step S2 to repeat the above process. When not continuing, all the processes are ended.

FIG. 13 is a timing chart showing the operation of the embodiment shown in FIGS. 1, 9 and 12. Here, in the standby state, since the capacitor 114 is held in the discharged state via the resistor R, the pulse voltage P4 is applied and the transistor 108 is turned on. First, in the section a, the pulse voltages P1 and P4 are supplied, the transistors 108 and 107 are turned on, a positive voltage is applied to the diaphragm 5, and a negative voltage is applied to the electrode 21. As a result, the capacitor 114 is charged with the electric charge in the forward direction, the vibrating plate 5 is bent to the individual electrode 21 side by the attraction force by the static electricity, the pressure of the ejection chamber 6 is reduced, and the ink 103 is ejected from the ink cavity 8. It is replenished into the discharge chamber 6 through the orifice 7.

After that, when the hold section of b is passed,
In the section c, the pulse voltages P2 and P4 are supplied, the transistors 106 and 108 are turned on, and the charges accumulated in the capacitor 104 are rapidly discharged. As a result, the attraction force due to static electricity that acts between the diaphragm 5 and the individual electrode 21 disappears, and the diaphragm 5 is restored due to its own rigidity. By restoring the diaphragm 5,
The pressure in the ejection chamber 6 rapidly rises, and the ink droplets 104 are ejected from the nozzle holes 4 toward the recording paper 105. After that, as shown in the section of d, the diaphragm 5 is refreshed. Here, the pulse voltages P2 and P3 are supplied, the transistors 106 and 109 are turned on, and a negative voltage is applied to the diaphragm 5 and a positive voltage is applied to the individual electrode 21. An electric charge is charged in the capacitor 114 formed by the diaphragm 5 and the individual electrode 21. But,
This is the reverse voltage in the normal printing operation, and the charging direction is opposite. As a result, the residual charges in FIG. 7 disappear. After that, when the electric charge is discharged again in the section e, the residual electric charge disappears and is not left, so that the diaphragm 5 is not bent as shown in FIG. 8C and is completely restored. Therefore, the ink ejection amount that is ejected again through the next sections a2, b2, and c2 substantially matches the ink ejection amount that was ejected last time. In the present embodiment, the ink droplets 104 are ejected while eliminating the residual charge generated between the vibrating plate 5 and the individual electrode 21 for each dot as described above.

Although the P-type semiconductor substrate is used as the substrate in this embodiment, when the N-type semiconductor substrate is used as the substrate, the connection wiring between the drive circuit 102a and the ink jet head 10 is made of P-type semiconductor. It should be the opposite of the case.

FIG. 14 is a flow chart showing another control method of the ink jet printer of the embodiment of FIG.
FIG. 15 is a flowchart showing the subroutine. In FIG. 15, (a) shows the subroutine for the nozzle recovery operation, and (b) shows the subroutine for the printing operation. In this embodiment, the vibrating plate recovery operation is performed row by row. Step S4 of FIG.
Step SS12 for refreshing the diaphragm is inserted between the step 5 and the step 5, and in this step, the diaphragm of the above-described embodiment is refreshed. Therefore, the print operation subroutine of FIG.
The second step SS12 is deleted, and the other processes are the same.

FIG. 16 is a timing chart showing the operation of the embodiment shown in FIGS. 14 and 15. In this embodiment, the pulse voltages P2 and P4 are supplied in the section a every time the carriage 302 returns, and the transistor 10 is supplied.
6, 109 are turned on, the diaphragm 5 and the individual electrode 2
A reverse voltage is applied to 1 to eliminate the above-mentioned residual charge.

FIG. 17 is a flow chart showing still another control method of the ink jet printer of the embodiment of FIG. 1, and FIG. 18 is a flow chart showing its subroutine. In FIG. 18, (a) shows a nozzle / vibration plate recovery operation subroutine, and (b) shows a printing operation subroutine. In this embodiment, when the head nozzle is recovered, the diaphragm is also recovered. Steps S1 and S8 of FIG. 11 correspond to steps S1a and S8a of FIG. 17, and in these steps S1a and S8a, not only the nozzle recovery operation but also the diaphragm recovery process is performed. Therefore, FIG.
In the nozzle / vibration plate recovery operation subroutine of (a),
After the carriage 302 is moved to the standby position in step SS1, the next step is step SS12.
At 5, the diaphragm 5 is refreshed. Therefore, step SS12 of FIG. 12 is deleted from the print operation subroutine of FIG. 18 (b).

According to the embodiment described above, for example, 1
It is possible to avoid the adverse effect of the residual charge by periodically removing the residual charge at every dot, every time one line is printed, or based on timing. Each of these aspects of the present embodiment may be used in combination. By removing residual charge in this manner, it is desirable to completely eliminate residual deflection of the diaphragm, but resetting the electrostatic actuator to a defined state allows complete retention of the diaphragm. Even if the bending is not removed, the residual bending is at least constant, and the relative displacement amount of the diaphragm is also constant. If the residual flexure is constant, there is an effect that the ink ejection amount and the ink ejection speed can be easily corrected by increasing the drive voltage according to the residual flexure.

FIG. 19A is a sectional view showing another mode of the head 10 shown in FIGS. 2, 3 and 4.
19B is a cross-sectional view of the main part A in FIG. The head 50 shown in FIGS. 19A and 19B is different from the head 10 shown in FIGS. 2, 3, and 4 in the following points in specifications.

First of all, the recess 15 provided in the intermediate first substrate 1 in FIG. 2 is abolished, and the lower second substrate joined to the lower surface of the first substrate 1 is etched to a depth. A recess 18 of 0.3 μm is formed, and ITO (indium oxide to which tin is added) is sputtered in the recess at a position corresponding to each diaphragm 5 by 0.1 μm so that the shape is almost the same as that of the diaphragm. An ITO pattern was formed to serve as an individual electrode 21.

Second, the insulating layer 24 formed on the second substrate 2 in FIG. 2 is abolished, and the common electrode 1 of the first substrate 1 is removed.
Thermal oxide film (S _i O ₂₎ to 0.1μm formed on the entire surface except for 7, which breakdown during inkjet head drive,
The insulating layer 51 is used to prevent a short circuit. Therefore, the gap distance G1 between the insulating layer 51 on the diaphragm 5 and the individual electrode 21 after anodic bonding is 0.2 μm.

The pitch of the nozzle grooves 11 is 0.07 m.
The width of the diaphragm 5 is 50 μm, and the thickness of the diaphragm 5 is 1 μm.
It was 8 μm. The thickness of the diaphragm 5 and the size of the gap G1 greatly contribute to the drive voltage, the ejection amount of the ink droplets, and the ejection speed. However, in the case of the inkjet head having the structure shown in this embodiment, the thickness of the diaphragm 5 is large. Is 12 to 24 μm,
It is practically preferable that the gap G1 is in the range of about 0.15 to 0.25 μm.

FIG. 20 is a graph showing the experimental results of measuring the ink ejection speed Vm of the ink droplet 104 ejected from one nozzle. The vertical axis of the graph indicates the ink ejection speed V
m is the m-axis, and the horizontal axis is the pulse width in the section a in which the reverse voltage (refresh voltage) is applied to the diaphragm 5 and the individual electrode 21. Here, using the drive circuit shown in FIG.
The head 50 shown in FIG. 9 is driven in the sequence shown in FIG. 16 to refresh voltage 20V, 25V, 30
Experiments were conducted for V and 35V, respectively.

FIG. 21 is a timing chart showing the driving conditions in the above-mentioned experiment and showing the change over time in the applied voltage of the electrode 21 to the diaphragm 5. The forward voltage for ejecting ink is 27 V, the forward energization width is 40 μsec, and the energization period is 333 μsec (3 kHz).
After the ink was ejected in pulses, a reverse voltage (refresh voltage) V was applied for a second, the voltage V and the pulse width a were changed, and the change in the ink ejection speed Vm was measured.

When the ink discharge speed Vm is low, the amount of ink discharged per one time also decreases in proportion to the ink discharge speed Vm. Therefore, the dot diameter on the recording paper becomes small and the density of the entire recorded image becomes insufficient. I get the impression that the so-called contrast is poor. In addition, the ink droplet 104 is
It does not fly as one spherical droplet, but a plurality of spherical droplets fly as if drawing a thread. For this reason, when the ink discharge speed Vm is low, liquid droplets (satellite) other than the liquid droplet at the leading end reach the recording paper with a delay, the dot shape formed on the recording paper is deformed, and the entire recorded image is blurred. It gives the impression of lacking sharpness. Also, head 1
When the scanning speed is increased to 0, this tendency becomes more remarkable. Therefore, in terms of improving the printing speed, the ink ejection speed Vm is also increased.
Is inconvenient, and it is desirable to obtain an ink ejection speed of 10 m / sec or more.

Reference numeral 404 represents the ink ejection speed Vm when the recovery operation of the diaphragm 5 is not performed. Even in this case, the ink ejection speed of 10 m / sec or more is initially obtained, but the ink ejection speed is gradually reduced each time the ink is ejected, and the ink ejection speed is about 5 at about 1 million ejections.
It drops to m / sec and stabilizes.

Reference numerals 403, 402, 401, and 400 are voltages for applying a reverse voltage (refresh voltage) of 20 V, 25 V, 30 V, and 35 V, respectively, to recover the diaphragm 5. At this time, when the ink discharge is driven, that is, when a forward voltage is applied between the vibrating plate 5 and the electrode 21, 23 V is applied.
The diaphragm 5 and the electrode 21 contacted each other to some extent (hereinafter, this voltage is referred to as a contact voltage). As shown in FIG. 20, the recovery operation of the diaphragm 5 was performed at a contact voltage of 23 V or higher, 402, 40.
1, 400 is uniform, 10 m when energization width a is 30 μsec.
While the ink ejection speed Vm of more than 1 second was realized,
In the case where the recovery operation of the vibrating plate 5 is performed at a contact voltage of 23 V or less, 402 is 10 m even when the energization width a is 10 seconds or more.
The ink ejection speed Vm of 1 / second cannot be realized. When the refresh voltage is 25 V or higher, for example, 30 V and 35
In the case of V, there is no great difference in the ink ejection speed with respect to the voltage difference, while in the case of 20V and 25V across the contact voltage, there is a large difference in the ink ejection speed even with the same voltage difference, and the refresh voltage is It can be seen that a large effect can be obtained at a contact voltage or higher.

From the above experimental results, a refresh voltage is applied to the vibrating plate 5 and the electrode 21 for a predetermined time at a voltage equal to or higher than the voltage at which the vibrating plate 5 contacts the electrode 21 at a predetermined period to recover the polarization of the vibrating plate. It has been found that the ink discharge speed of 10 m / sec can always be obtained stably if it is performed.

[0062]

As described above, according to the present invention, by applying a pulsed driving voltage between the diaphragm and the individual electrode, the gap between the individual electrode and the diaphragm arranged to face the individual electrode is applied. In a method for driving an inkjet head that discharges ink by applying electrostatic attraction to the electrode, refreshing in a direction opposite to the above pulse voltage and having a magnitude greater than a driving voltage (contact voltage) at which the diaphragm contacts the individual electrode By appropriately applying a voltage between the vibration plate and the individual electrodes, the relative displacement amount between the vibration plate and the individual electrodes does not decrease, and as a result, the cause of defective ejection of ink droplets is eliminated. Reliable.

By applying the refresh voltage for a short time, the amount of relative displacement between the vibrating plate and the individual electrodes, which is decreasing, can be recovered instantly and reliably, so that much time is not spent on the recovery means. A printing device capable of printing at high speed can be provided.

Further, in the printing apparatus of the present invention, since the insulating layer made of the thermal oxide film of silicon is formed between the diaphragm made of silicon and the individual electrodes formed of the ITO film, the diaphragm- By performing a recovery means that eliminates the adverse effect of the residual charge accumulated between the electrodes on the driving of the inkjet head, the inkjet head will not be broken or the life will be shortened, so that there will be no problems related to deterioration of reliability. A printing device can be provided.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of an inkjet printer according to an embodiment of the present invention.

FIG. 2 is an exploded perspective view of the inkjet head of the embodiment.

FIG. 3 is a cross-sectional side view of the inkjet head of the embodiment.

FIG. 4 is a view taken along the line AA of FIG.

FIG. 5 is a partial detailed schematic diagram of a diaphragm and individual electrodes of the above-described embodiment.

FIG. 6 is a schematic diagram focusing on polarization of the diaphragm and the individual electrodes of FIG.

FIG. 7 is a schematic diagram focusing on remanent polarization of the diaphragm and individual electrodes of FIG.

FIG. 8 is a schematic diagram showing the bending of the diaphragm in the above-described embodiment over time.

FIG. 9 is a diagram showing a configuration of a drive control circuit of the ink jet head of the embodiment.

FIG. 10 is a schematic diagram of a printer equipped with the jet head of the embodiment.

FIG. 11 is a flowchart showing a method of controlling the inkjet printer of the embodiment of FIG.

12 is a flowchart showing a subroutine of FIG.

13 is a timing chart showing the operation of the embodiment of FIG.

FIG. 14 is a flowchart showing another control method of the inkjet printer of the embodiment of FIG.

FIG. 15 is a flowchart showing a subroutine of FIG.

16 is a timing chart showing the operation of the embodiment of FIG.

FIG. 17 is a flowchart showing another control method of the inkjet printer of the embodiment of FIG.

FIG. 18 is a flowchart showing the subroutine of FIG.

FIG. 19 is a sectional side view showing another aspect of the inkjet head of the present invention.

20 is a graph showing the relationship between the voltage and pulse width of an electric pulse in the opposite direction and the ink ejection speed Vm, which was obtained by an experiment using the inkjet head shown in FIG.

FIG. 21 is a timing chart showing driving conditions in the experiment of FIG.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shuji Koeda 3-3-5 Yamato, Suwa City, Nagano Seiko Epson Co., Ltd. (72) Inventor Naoki Kobayashi 3-5-5 Yamato, Suwa City, Nagano Prefecture Seiko -In Epson Corporation

Claims (9)

[Claims] 1. An actuator comprising a nozzle, an ink flow path communicating with the nozzle, a vibration plate provided in a part of the flow path, and an electrode provided opposite to the vibration plate. Then, in the method of driving a printing apparatus that deforms the diaphragm and ejects ink droplets from the nozzles to perform recording, during normal recording, a first voltage that deforms the diaphragm is applied, and at a predetermined time. In order to stabilize the displacement amount of the diaphragm, a second voltage having a polarity different from that of the first voltage and having a magnitude equal to or larger than a voltage value at which the diaphragm contacts the electrode.
A method for driving a printing apparatus, characterized in that the voltage is applied. 2. The second voltage is set to 1 dot or 1
The driving method of the printing apparatus according to claim 1, wherein the voltage is applied each time line printing is performed. 3. The second voltage is applied when the recovery processing operation of the nozzle is performed.
A method for driving a printing apparatus described in claim 1. 4. An actuator comprising a nozzle, an ink flow path communicating with the nozzle, a vibration plate provided in a part of the flow path, and an electrode provided facing the vibration plate.
A driving unit configured to deform the diaphragm and eject ink droplets for recording from the nozzles, wherein the driving unit causes the actuator to bend the diaphragm during recording. A voltage applying unit that applies a voltage and the first voltage have different polarities, and a second voltage having a magnitude equal to or larger than a voltage value at which the diaphragm contacts the electrode is applied to the actuator. A printing apparatus comprising: a charge removing unit. 5. The printing apparatus according to claim 4, wherein the residual charge removing unit of the diaphragm applies the second voltage every time one dot or one line is printed. 6. The residual charge removing means of the vibration plate, when performing the recovery processing operation of the nozzle with the second voltage,
The printing apparatus according to claim 4, wherein the voltage is applied. 7. The printing apparatus according to claim 4, wherein an insulating layer is formed between the vibration plate of the actuator and the electrode. 8. The material of the diaphragm is silicon,
The printing apparatus according to claim 7, wherein the insulating layer is formed of a thermal oxide film of silicon. 9. The printing apparatus according to claim 7, wherein the electrode is made of an ITO film.