JP3252627B2 - Printing apparatus and driving method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for driving an ink-jet head using static electricity for an actuator, and more particularly to eliminating the influence of residual charges 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, and the use of inexpensive plain paper with a high degree of freedom of ink. Among them, the so-called ink-on-demand method, which discharges ink droplets only when recording is necessary, is currently the mainstream because it does not require collection of ink droplets unnecessary for recording.

As a conventional ink-on-demand driving method, there is a driving method disclosed in Japanese Patent Publication No. 24218/1990. In this driving method, a piezoelectric element that changes the volume of a pressure chamber that generates 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, and the piezoelectric element is turned on. After charging, the volume of the pressure chamber is reduced, and at the time of ink jetting, the piezoelectric element is gradually discharged to increase the volume of the pressure chamber. The ink is ejected from the nozzles by charging and reducing the volume of the pressure chamber. In this driving method, in order to eject ink droplets most efficiently at a low voltage, a voltage is applied again to the piezoelectric element 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. The pressure chamber volume is rapidly decreasing.

On the other hand, an ink jet head using an electrostatic force for driving an actuator includes, for example, US Pat.
The structure disclosed in JP 20,375 is known.

[0005] US Pat. No. 4,520,375 discloses that a capacitor mainly comprises two capacitor plates opposed to each other at an interval by an insulating means and a reservoir for accommodating ink. By forming a thin diaphragm made of silicon semiconductor and applying a time-varying voltage to the capacitor, a mechanical vibration is generated in the diaphragm, and in response to the movement of the diaphragm, for example, ink such as ink is formed. A liquid ejecting apparatus that ejects liquid from a nozzle is disclosed.

[0006]

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

However, when an ink jet head using electrostatic force for driving an actuator disclosed in US Pat. No. 4,520,375 is driven by an ink-on-demand method, the above-described driving method using a piezoelectric element is simply applied. In this case, the following problems occurred, and it was difficult to put it to practical use.

In an ink jet head using static electricity for an actuator, unlike a device using a piezoelectric element, after a pulse voltage is applied between a diaphragm and an individual electrode, electric charges remain on a dielectric between the diaphragm and the electrode. The relative displacement between the diaphragm and the individual electrodes is reduced by the electric field generated by the residual charges. The decrease in the relative displacement amount causes a discharge failure such as a decrease in the discharge amount of the ink droplet or the ink speed, and causes a reduction in the reliability such as a print quality defect such as a print density or a pixel shift or a pixel omission. There was a problem.

Further, as will be described later, the residual charge
Due to the characteristic that the magnitude differs depending on the history of the applied voltage in the past, the relative displacement between the diaphragm and the individual electrode is undefined and unstable, and as a result, the ejection amount of the ink droplet and the Ejection speed and the like become unstable, and in any case, print quality is poor such as print density and pixel shift, and pixels are missing.

The present invention has been made to solve such a problem, and has the following three objects.

A method and apparatus for driving an ink-jet head that eliminates the adverse effect of residual charges accumulated between the diaphragm and the electrode on driving of the ink-jet head and stabilizes the relative displacement between the diaphragm and the individual electrodes. To provide a printing apparatus and a driving method for the same, which can obtain good printing quality.

The recovery means for eliminating the adverse effect of the residual charge accumulated between the diaphragm and the electrode on the driving of the ink jet head is reliably executed in a short time, and much time is consumed by the execution of the recovery means. To provide a printing device capable of printing at a high speed without lowering the printing speed, and a driving method thereof.

[0013] By performing recovery means for eliminating the adverse effect of the residual charge accumulated between the diaphragm and the electrode on the driving of the inkjet head, the reliability of the inkjet head is reduced, such as breakage of the inkjet head or shortening of its life. To provide a printing device that does not cause problems related to the printing.

[0014]

A printing apparatus according to the present invention comprises a nozzle, an ink flow path communicating with the nozzle, a vibrating plate provided in a part of the flow path, and a vibrating plate opposed to the vibrating plate. an actuator comprising a electrodes provided, electrostatic the diaphragm
Driving means for deforming by virtue of force to eject ink droplets for recording from the nozzles, wherein the driving means causes the actuator to statically move the diaphragm during recording.
Voltage applying means for applying a first voltage for bending by an electric force, and a second voltage having a polarity different from that of the first voltage and having a magnitude equal to or greater than a voltage value at which the diaphragm contacts the electrode. And a residual charge removing means for applying the voltage to the actuator. An insulating layer is formed between the vibration plate of the actuator and the electrode, and a preferable material of the vibration plate is silicon, and the preferable insulation layer is made of a thermal oxide film of silicon, and the electrode Is preferably an ITO film.

Further, in the method of driving a printing apparatus according to the present invention, there is provided a nozzle, an ink flow path communicating with the nozzle, a vibration plate provided in a part of the flow path, and a vibration plate provided facing the vibration plate. And an actuator composed of a plurality of electrodes, wherein the diaphragm is deformed by electrostatic force , and ink droplets are ejected from the nozzles to perform recording. A first voltage that deforms the diaphragm by an electrostatic force is applied, and at a predetermined time, in order to stabilize the amount of displacement of the diaphragm, the polarity is different from that of the first voltage, and the diaphragm contacts the electrode. A second voltage having a magnitude equal to or higher than the voltage value to be applied is applied. The second voltage may be applied every time one dot or one line is printed, or may be applied when performing the nozzle recovery processing operation.

[0016]

In the present invention, by applying a forward electric pulse between the diaphragm of the ink jet head and the individual electrodes, an attractive force is generated between the diaphragm and the individual electrodes arranged opposite thereto by electrostatic force. Works, and the diaphragm is deformed by the electrostatic force. Next, by releasing the electric pulse, ink droplets are ejected from the nozzle holes by the restoring force of the diaphragm.

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

Further, if a refresh voltage having a voltage higher than a voltage value at which the diaphragm comes into contact with the individual electrode (hereinafter referred to as a contact voltage) is applied, the residual charges stored in the diaphragm disappear in a short time. Accordingly, the deflection of the diaphragm due to the residual charge is eliminated in a short time, and much time is spent for applying the refresh voltage, and the printing speed does not decrease.

In the printing apparatus of the present invention, an insulating layer made of a thermal oxide film of silicon, which is resistant to electrical and mechanical stress, is formed between the silicon diaphragm and the individual electrodes. Alternatively, when a refresh voltage is applied to the actuator, the vibration plate contacts the individual electrode via the thermal oxide film, so that the actuator is not broken by a short circuit, and the individual electrode has excellent withstand voltage. Since the head is formed of a thin ITO film, a problem that the head is broken even during long-term driving hardly occurs.

[0020]

FIG. 2 is an exploded perspective view of an ink jet head according to an embodiment of the present invention. This embodiment shows an example of an edge eject type in which ink droplets are ejected from a nozzle hole provided at an end of a substrate. It may be an object type. FIG. 3 is a cross-sectional side view of the entire assembled inkjet head, and FIG.
It is an arrow A view. Inkjet head 1 of this embodiment
Reference numeral 0 denotes a laminated structure in which three substrates 1, 2, and 3 having a structure described in detail below are stacked and joined.

The intermediate first substrate 1 is a silicon substrate, and has a plurality of nozzle grooves 1 formed at equal intervals in parallel from one end on the surface of the substrate 1 so as to form a plurality of nozzle holes 4.
1 and a recess 12 communicating with each nozzle groove 11 to form a discharge chamber 6 having a diaphragm 5 as a bottom wall;
2, a narrow groove 13 for an ink inlet, which forms an orifice 7 provided in the rear part, and a concave portion, which forms a common ink cavity 8 for supplying ink to each discharge chamber 6. 14. Also, the diaphragm 5
Is provided with a concave portion 15 for forming a vibration chamber 9 for mounting an electrode to be described later. In the present embodiment, each orifice 7 has three parallel narrow grooves 13 mainly for increasing the flow path resistance and maintaining the normal operation of the ink jet head even if one of the narrow grooves is clogged. It is formed.

In the present embodiment, the gap between the diaphragm 5 and the electrode arranged opposite thereto, that is, the gap 1
6, a length G (see FIG. 3, hereinafter referred to as "gap length")
Is the difference between the depth of the recess 15 and the thickness of the electrode,
The spacing means is constituted by a recess 15 for the vibration chamber formed on the lower surface of the first substrate 1. Further, as another example, the concave portion may be formed on the upper surface of the second substrate 2. Here, the depth of the concave portion 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.

In addition, in providing the common electrode 17 to the first substrate 1, it is important that the work function of the semiconductor and the metal material as the electrode is large. In this embodiment, titanium is used as the common electrode material. Although platinum or chromium is used as an undercoat and gold is used as an undercoat, 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 embodiment is 8 to 12 Ωcm.

The lower second substrate 2 joined to the lower surface of the first substrate 1 is made of borosilicate glass. The vibration chamber 9 is formed by joining the second substrate 2, At each position corresponding to the vibration plate 5 on the second substrate 2, gold is sputtered at 0.1 μm, and a gold pattern is formed in substantially the same shape as the vibration plate 5 to form an individual electrode 21. Individual electrode 2
1 has a lead portion 22 and a terminal portion 23. Further, a Pyrex sputtered film is formed on the entire surface except for the electrode terminal portions 23 by 0.2.
The insulating layer 24 is formed by coating with a thickness of μm, and a film for preventing dielectric breakdown and short circuit when the inkjet head is driven is formed.

The upper third substrate 3 bonded to the upper surface of the first substrate 1 is made of borosilicate glass, like the second substrate 2. By joining the third substrate 3, the nozzle hole 4, the discharge chamber 6, the orifice 7, and the ink cavity 8 are formed. 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 the first substrate 1 and the third substrate 3 And an ink jet head is assembled as shown in FIG. The gap length G formed between the vibration plate 5 and the individual electrode 21 on the second substrate 2 after the bonding of the anode is equal to the concave length 1
5 and the thickness of the individual electrode 21, which is 0.5 μm in the present embodiment. The gap G1 between the diaphragm 5 and the insulating layer 24 on the individual electrode 21 is 0.3 μm.

After assembling the ink jet head as described above, the common electrode 17 and the terminal portions 23 of the individual electrodes 21 are formed.
A driving circuit 102 is connected between the wirings 101 by wirings 101 to form an ink jet printer. Ink 103
Is supplied from the ink tank (not shown) to the inside of the first substrate 1 through the ink supply port 31, and fills the ink cavity 8, the discharge 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 configured as described above will be described.

In a structure composed of a metal-insulating layer-semiconductor layer, that is, a so-called MIS structure, depending on the polarity of an applied voltage, there are cases where there is a large difference between current values and a case where there is no difference between the current value and the space charge layer (depletion layer). This effect is also known as a phenomenon. When the semiconductor as the substrate material is P-type silicon, when a positive voltage is applied to the substrate electrode side, it can be regarded as a conductor, but when a negative voltage is applied, the capacitance is not considered as a conductor due to the presence of the space charge layer. I know I have.

FIG. 5 is a partially enlarged detailed view of the diaphragm 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 and connected to the drive circuit 102 so that the first substrate 1 (diaphragm 5) side, that is, the common electrode 17 has a positive polarity and the individual electrode 21 side has a negative polarity, Common electrode 17 and individual electrode 21
Is a case in which a pulse voltage is applied by the drive circuit 102 to the pulse voltage.

P-type silicon is doped with boron,
It is known that electrons have holes equal to the doping amount, because electrons are deficient in the number of doped boron. P
The holes 19 in the shaped silicon are repelled toward the insulating layer 26 by the positive charge of the common electrode 17. Due to the movement of the holes 19, the acceptor (ionized boron) becomes
Since charge is supplied from the substrate electrode 17, holes flow in the first substrate 1 and can be regarded as a conductor without generating a space charge layer. In addition, the individual electrode 21 is charged with a negative charge, and as a result, the applied pulse voltage generates an attractive force due to static electricity sufficient to deflect the diaphragm 5. Therefore, the diaphragm 5 bends toward the individual electrode 21.

FIGS. 6 and 7 are schematic diagrams focusing on the residual charges of the dielectric between the diaphragm and the individual electrodes of FIG.
FIG. 6 shows a state when a voltage is applied similarly to FIG. 5, and FIG. 7 shows a state when the electric field is removed. Next, generation of a residual charge will be described with reference to FIGS. 6 and 7, as described above, the diaphragm 5 is a semiconductor, the common electrode 17 is formed 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 an insulating layer 27 as a whole. . Therefore, it can be considered here as a model in which a dielectric is interposed in a parallel plate capacitor constituted by the diaphragm 5 and the individual electrodes 21. The dielectric corresponds to the protective film insulating layers 24 and 26.
When a voltage is applied to the parallel flat plate, the direction of the dielectric is such that the applied electric field cancels out (as opposed to the electric field) as shown in FIG.
The polarization 28 is generated. Most of the polarization 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 varies greatly depending on the type of polarization.

In the case of the polarization of the dielectric (insulating layer) inside the vibration plate 5 and the individual electrode 21 of this embodiment, in addition to the atomic polarization and the electron polarization having a short relaxation time, a comparison called ionic polarization or interface polarization is made. It contains a polarization component having a long polarization relaxation time. Ionic polarization is caused by the movement of Na +, K +, B +, etc. in the insulating layer along the applied electric field. When the dielectric has a heterogeneous structure, media having different dielectric constants come into contact with each other. The polarization is generated at the interface between the silicon oxide and the pure silicon. For this reason, as shown in FIG. 7, a part of the polarization of the dielectric 5 (24, 26) inside the diaphragm 5 and the individual electrode 21 in this embodiment is completely reduced by repeated application of the electric field or continuous application for a long time. Polarization does not disappear for a long time. As a result, the dielectric has remanent polarization 29, and the residual electric field P generated by the polarization remaining between the diaphragm 5 and the electrode 21 causes a reduction in the relative displacement between the diaphragm 5 and the individual electrodes 21.

FIG. 8 is a diagram showing the deflection of the diaphragm and the individual electrodes over time. FIG. 8A shows the diaphragm 5 and the individual electrodes 21.
In this state, no voltage is applied therebetween, and the diaphragm 5 and the individual electrodes 21 are parallel to each other as shown in the figure. FIG.
(B) is a state when a voltage is applied to the diaphragm 5 and the individual electrodes 17, and the diaphragm 5 is bent as shown in the figure. Here, the amount of the bending is defined as ΔV1. Next, FIG. 8C shows a state after the electric charges stored in the diaphragm 5 and the individual electrodes 17 have been discharged. Even after the discharge, the diaphragm 5 is bent by the residual electric field generated by the residual charges. The amount of deflection is ΔV2
And Therefore, the relative displacement between the diaphragm 5 and the individual electrode 21 is ΔV1−ΔV2, and it can be seen that the relative displacement is reduced.

Such a decrease in the relative displacement between the vibration plate 5 and the individual electrode 21 causes a discharge failure such as a drop in the amount of ink droplets or a drop in the ink speed, as described above, and the reliability of the ink jet printer. And adversely affect print quality. Therefore, in the present embodiment, as described later, the above-described residual charges are eliminated by applying an electric field between the diaphragm 5 and the individual electrodes 21 in a direction opposite to that in FIG.

FIG. 1 is a conceptual diagram of an ink jet printer according to an embodiment of the present invention. In the figure, reference numeral 202 denotes a drive motor for moving an ink jet head or a print medium such as paper, and reference numeral 203 denotes a printer having the ink jet head 10 and the drive motor 202 as main components. 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 for measuring time. 20
Reference numeral 6 denotes nozzle clogging recovery processing means for controlling the nozzle clogging recovery processing. 207 is an input means;
Reference numeral 0 denotes a print operation control unit 210 that performs various types of operation control in response to print control and an input signal from the input unit 207. The print calculation control unit 210 outputs an initialization signal for activating the clock unit 204, a print control signal for controlling the printer 203, and performs various controls.
Reference numeral 211 denotes a storage unit that stores various types of data used when the print operation control unit 210 performs an operation process. 2
Numeral 12 denotes a diaphragm residual charge removing unit, which outputs a diaphragm recovery processing control signal in order to perform a recovery processing on the residual charge of the diaphragm as described later.

A drive control circuit 213 for the ink jet head 10 has the circuit configuration shown in FIG. The drive control circuit 213 receives a nozzle recovery processing control signal, a print control signal, and a diaphragm recovery processing control signal, and controls the driving of the inkjet head 10 based on these control signals. A drive control circuit 214 for the drive motor 202 receives a nozzle recovery processing control signal, a print control signal, and a diaphragm recovery processing control signal, and controls the drive of the drive motor 202 based on these control signals.

FIG. 9 is a diagram showing a configuration of a drive control circuit of the ink jet head 10. As shown in FIG. This drive control circuit 21
3, the control circuit 215 and the drive circuit 10
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, and outputs pulse voltages P1 to P4 to the amplifiers 110 to 113 as appropriate based on the control signals.
13, the transistors 106 to 109 are driven. As a result, the capacitor 114 formed by the diaphragm 5 and the individual electrode 21 is charged or discharged, so that the ink droplet 104 is discharged from the nozzle hole 4. Discharged. Here, the resistor 115 is a resistor that determines the discharging speed, and the resistor 116 is a resistor that determines the charging speed. The time constant of charging and discharging is determined by each resistance value and the capacity of the capacitor 114.

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

FIG. 11 is a flowchart showing a control method of the ink jet printer of the embodiment of FIG.
2 is a flowchart showing the subroutine.
In FIG. 12, (a) shows a subroutine of a nozzle recovery operation, and (b) shows a subroutine of a printing operation. First, in step S0, the print operation control unit 21
The initialization of the printer mechanism and the like is executed based on the instruction of 0. At this time, the resetting of the timer 204 is also performed at the same time, and the timer starts. In the next step S1, a nozzle recovery operation immediately after power-on is performed. 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, in step SS1, the drive motor 202 is driven to drive the ink jet head 10
When the carriage 302 with the
Move to position 04. Next, in step SS2, a nozzle recovery operation, that is, refresh is performed. This nozzle refresh is performed by driving the diaphragms 5 corresponding to all nozzles in order to discharge defective ink that causes ink discharge failure such as thickened ink in the nozzle portion of the inkjet head 10. Is ejected a predetermined number of times from the nozzles. Usually, 10 to 200 shots are ejected from each nozzle, and the thickened defective ink is discharged outside the nozzles. The number of times of this refresh ejection is determined in advance by the set time of the timer 204.
After the refresh of the nozzle is completed, the carriage 302 is returned to the standby position again in step SS3, and a series of refresh operations is completed. When turning on the power,
Generally, there is a high possibility that the head has not been used for a long time, so that 160 to 200 ink ejections are performed.

After the end of the nozzle refresh operation, the timer 204 starts measuring a predetermined time. In step S2, it is determined whether or not a timer up signal is present in order to determine whether or not the timer 204 measures 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 (a) is performed, and the process proceeds to the next step S3. If the timer-up signal has not been generated, the process proceeds directly to step S3. In this step S3, it is determined whether or not to perform printing. If printing is not performed, the process returns to step S2. When printing is performed, after the timer 204 is reset 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 subroutine of the printing operation in FIG. In step SS10, the count value n is set to 1, and in step SS11, the carriage 302 is moved by one dot. Then, in steps SS12 and SS13, the designated dot ink based on the print data is sucked and discharged. Then, in step SS14, refresh (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 is incremented as n = n + 1.
At 16 it is determined whether or not n is the last dot,
If it is not the last dot, the process returns to step SS11 and the above processing is repeated. If it is the last dot, the printing operation ends, 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, it is determined in step S9 whether or not to continue the processing. If the processing is to be continued, the process returns to step S2 and the above-described processing is repeated. If not to continue, all processing is terminated.

FIG. 13 is a timing chart showing the operation of the embodiment shown in FIGS. 1, 9 and 12. Here, in the standby state, in order to hold the capacitor 114 in the discharged state via the resistor R, it is assumed that 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 forward charges, the diaphragm 5 is bent toward the individual electrode 21 by the attraction force of static electricity, the pressure in the ejection chamber 6 is reduced, and the ink 103 is removed from the ink cavity 8. It is supplied into the discharge chamber 6 through the orifice 7.

Thereafter, when the hold section of b elapses,
In the section c, the pulse voltages P2 and P4 are supplied, the transistors 106 and 108 are turned on, and the charge accumulated in the capacitor 104 is rapidly discharged. As a result, the suction force due to the static electricity acting between the diaphragm 5 and the individual electrode 21 disappears, and the diaphragm 5 is restored by its own rigidity. Due to the restoration of the diaphragm 5,
The pressure in the discharge chamber 6 rapidly rises, and the ink droplets 104 are discharged from the nozzle holes 4 toward the recording paper 105. Thereafter, as shown in a section 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 electrodes 21. Electric charges are charged to the capacitor 114 formed by the diaphragm 5 and the individual electrodes 21. But,
This is a reverse voltage in a normal printing operation, and the charging direction is reversed. As a result, the residual charges in FIG. 7 disappear. Thereafter, in the section e, when the electric charge is discharged again, the residual electric charge disappears and remains, so that the diaphragm 5 is completely restored without being bent as shown in FIG. 8C. Therefore, the amount of ink ejected again through the next sections a2, b2, and c2 substantially matches the amount of ink ejected last time. In the present embodiment, the ink droplets 104 are ejected while eliminating the residual charge generated between the diaphragm 5 and the individual electrode 21 for each dot as described above.

In this embodiment, the P-type semiconductor substrate is used as the substrate. However, 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 a P-type semiconductor. It is necessary to reverse the case.

FIG. 14 is a flowchart 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 a subroutine of a nozzle recovery operation, and (b) shows a subroutine of a printing operation. In this embodiment, the recovery operation of the diaphragm is performed for each row. Step S4 in FIG.
A step SS12 for refreshing the diaphragm is inserted between step 5 and step 5, and in this step, the diaphragm of the above-described embodiment is refreshed. For this reason, the subroutine of the printing operation in FIG.
Step SS12 of Step 2 is deleted, and the other processes are the same.

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

FIG. 17 is a flowchart showing another control method of the ink jet printer of the embodiment of FIG. 1, and FIG. 18 is a flowchart showing a subroutine thereof. In FIG. 18, (a) shows a subroutine of a nozzle / diaphragm recovery operation, and (b) shows a subroutine of a printing operation. In this embodiment, the recovery operation of the diaphragm is also performed at the time of the recovery operation of the head nozzle. Steps S1 and S8 in FIG. 11 correspond to steps S1a and S8a in FIG. 17. In steps S1a and S8a, not only the nozzle recovery operation but also the diaphragm recovery processing is performed. Therefore, FIG.
In the subroutine of the nozzle / diaphragm recovery operation of (a),
After moving the carriage 302 to the standby position in step SS1, the next step, step SS12
, The diaphragm 5 is refreshed. Therefore, in the subroutine of the printing operation in FIG. 18B, step SS12 in FIG. 12 is deleted.

According to the embodiment described above, for example, 1
By removing the residual charge periodically every dot, every time one line is printed, or based on timing, adverse effects of the residual charge can be avoided. These aspects of the present embodiment may be used in combination. It is desirable that the residual deflection of the diaphragm be completely removed by removing the residual electric charges in this manner, but by resetting the electrostatic actuator to a predetermined state, the residual vibration of the diaphragm is completely eliminated. Even if the flexure is not removed, at least the residual flexure is constant, and the relative displacement of the diaphragm is also constant. If the residual deflection is constant, increasing the drive voltage in accordance with the residual deflection has an effect that the ink ejection amount and the ink ejection speed can be easily corrected.

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

First, the concave portion 15 provided in the intermediate first substrate 1 in FIG. 2 is eliminated, and the lower second substrate bonded to the lower surface of the first substrate 1 is etched to a depth. A recess 18 having a thickness of 0.3 μm is formed, and ITO (indium oxide to which tin is added) is sputtered in a thickness of 0.1 μm at each position corresponding to each diaphragm 5 in this recess to form the same shape as the diaphragm. An individual electrode 21 was formed by forming an ITO pattern.

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

The pitch of the nozzle grooves 11 is 0.07 m
m, the width is 50 μm, and the thickness of the diaphragm 5 is 1
8 μm. The thickness of the diaphragm 5 and the size of the gap G1 greatly contribute to the driving voltage, the ejection amount of ink droplets, and the ejection speed. 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 air gap G1 is in the range of about 0.15 to 0.25 μm.

FIG. 20 is a graph showing experimental results obtained by measuring the ink discharge speed Vm of the ink droplet 104 discharged from one nozzle. The vertical axis of the graph is the ink ejection speed V
m, and the horizontal axis represents the pulse width of the section a in which a reverse voltage (refresh voltage) is applied to the diaphragm 5 and the individual electrodes 21. Here, using the driving circuit shown in FIG.
9 is driven in the sequence shown in FIG. 16, and the refresh voltages 20 V, 25 V, 30
An experiment was performed for each of V and 35V.

FIG. 21 is a timing chart showing conditions at the time of driving in the above-described experiment, and showing a change with time of the voltage applied to the electrode 21 to the diaphragm 5. The forward voltage for ejecting ink is 27 V, the forward current width is 40 μsec, the energization cycle is 333 μsec (3 kHz), and one row is 660.
After the pulse ink ejection, a voltage (refresh voltage) V in the reverse direction was applied for a second, and the voltage V and the pulse width a were changed, and the change in the ink ejection speed Vm was measured.

When the ink ejection speed Vm is small, the amount of ink ejected at one time also decreases in proportion to the ink ejection speed Vm, so that the dot diameter on the recording paper becomes small and the density of the entire recorded image becomes insufficient. , So-called poor contrast. The ink droplet 104 is
Instead of flying as a single spherical droplet, a plurality of spherical droplets fly like a string. For this reason, if the ink ejection speed Vm is low, droplets (satellite) other than the droplet at the tip end arrive at the recording paper with a delay, the dot shape formed on the recording paper is deformed, and the entire recorded image is blurred. I get the impression of lack of sharpness. Also, head 1
When the scanning speed of 0 is increased, this tendency becomes more remarkable.
Is inconvenient, and it is desirable that an ink ejection speed of 10 m / sec or more can be obtained.

Reference numeral 404 denotes the ink ejection speed Vm when the recovery operation of the diaphragm 5 is not performed. In this case as well, an ink ejection speed of 10 m / sec or more can be obtained in the initial stage, but the ink speed gradually decreases every time ink is ejected.
m / sec and stabilizes.

Reference numerals 403, 402, 401, and 400 denote voltages obtained by applying reverse voltages (refresh voltages) of 20 V, 25 V, 30 V, and 35 V, respectively, to perform a recovery operation of the diaphragm 5. At this time, at the time of ink ejection driving, that is, when a forward voltage is applied between the diaphragm 5 and the electrode 21, 23 V
The diaphragm 5 and the electrode 21 were in contact with each other (this voltage is hereinafter referred to as a contact voltage). FIG. 20 shows that the recovery operation of the diaphragm 5 was performed at a contact voltage of 23 V or more, 402 and 40.
1, 400 are uniformly 10 m when the conduction width a is 30 μsec.
/ Sec or more ink discharge speed Vm
In the case 402 in which the recovery operation of the diaphragm 5 is performed at a contact voltage of 23 V or less, even if the energizing width a is 10 seconds or more, 10 m
/ M ink discharge speed Vm cannot be realized. When the refresh voltage is 25 V or more, for example, 30 V and 35 V
In the case of V, there is no significant difference in the ink discharge speed with respect to the voltage difference. On the other hand, in the case of 20 V and 25 V across the contact voltage, there is a large difference in the ink discharge speed obtained even with the same voltage difference. It can be seen that a great effect can be obtained at a contact voltage or higher.

From the above experimental results, a refresh voltage is applied to the diaphragm 5 and the electrode 21 for a predetermined time at a voltage higher than the voltage at which the diaphragm 5 contacts the electrode 21 at a predetermined cycle, and the polarization recovery processing of the diaphragm is performed. It has been found that if this is performed, an ink ejection speed of 10 m / sec can always be obtained stably.

[0062]

As described above, according to the present invention, by applying a pulse-like drive voltage between the diaphragm and the individual electrode, the gap between the individual electrode and the diaphragm arranged opposite to the individual electrode can be obtained. In the method of driving an ink-jet head in which ink is ejected by applying an electrostatic attractive force to the ink jet head, a refresh voltage in a direction opposite to the above-described pulse voltage and equal to or higher than a driving voltage (contact voltage) at which the diaphragm comes into contact with the individual electrode. By appropriately applying a voltage between the diaphragm and the individual electrodes, the relative displacement between the diaphragm and the individual electrodes does not decrease, and therefore, the cause of the ink droplet ejection failure is eliminated. Reliability is obtained.

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

In the printing apparatus of the present invention, an insulating layer made of a silicon thermal oxide film is formed between a silicon diaphragm and an individual electrode formed of an ITO film. By performing a recovery unit that eliminates the adverse effect of the residual charge accumulated between the electrodes on the driving of the inkjet head, the inkjet head is not broken or the lifetime is shortened. A printing device can be provided.

[Brief description of the drawings]

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

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

FIG. 3 is a sectional side view of the ink jet head of the embodiment.

FIG. 4 is a view taken in the direction of arrows AA in FIG. 3;

FIG. 5 is a partial detailed schematic view of the diaphragm and individual electrodes of the embodiment.

6 is a schematic diagram focusing on the polarization of the diaphragm and the individual electrodes of FIG. 5;

FIG. 7 is a schematic diagram focusing on the residual polarization of the diaphragm and the individual electrodes of FIG. 5;

FIG. 8 is a schematic diagram showing flexure of the diaphragm in the embodiment over time.

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

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

FIG. 11 is a flowchart showing a control method of the ink jet printer of the embodiment of FIG.

FIG. 12 is a flowchart showing a subroutine of FIG. 11;

FIG. 13 is a timing chart showing the operation of the embodiment in FIG. 11;

FIG. 14 is a flowchart illustrating another control method of the ink jet printer of the embodiment of FIG. 1;

FIG. 15 is a flowchart showing a subroutine of FIG. 14;

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

FIG. 17 is a flowchart illustrating another control method of the ink jet printer of the embodiment of FIG. 1;

FIG. 18 is a flowchart showing a subroutine of FIG. 17;

FIG. 19 is a sectional side view showing another embodiment of the ink jet head of the present invention.

20 is a graph showing a relationship between a voltage and a pulse width of an electric pulse in a reverse direction and an ink ejection speed Vm obtained by an experiment using the inkjet head shown in FIG. 19;

21 is a timing chart showing driving conditions in the experiment of FIG. 20.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shuji Oeda 3-3-5 Yamato, Suwa City, Nagano Prefecture Inside Seiko Epson Corporation (72) Inventor Naoki Kobayashi 3-3-5, Yamato Suwa City, Nagano Prefecture In Seiko Epson Corporation (56) References JP-A-4-344250 (JP, A) JP-A-2-162049 (JP, A) JP-A-3-159748 (JP, A) JP-A-4-344253 (JP, A) JP-A-5-50601 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B41J 2/01 B41J 2/045 B41J 2/055 B41J 2/06

Claims (9)

(57) [Claims] 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 to face the vibration plate. and, the vibration plate is deformed by electrostatic force, ejecting ink droplets from the nozzle, in the driving method of the printing apparatus for recording, during normal recording, the first voltage to the vibrating plate is deformed by electrostatic force In order to stabilize the amount of displacement of the diaphragm at a predetermined time, a second voltage having a different polarity from the first voltage and having a magnitude equal to or larger than a voltage value at which the diaphragm contacts the electrode is used. A method for driving a printing apparatus, comprising applying a voltage. 2. The method according to claim 1, wherein the second voltage is one dot or one dot.
2. The method according to claim 1, wherein the voltage is applied every time line printing is performed. 3. The method according to claim 1, wherein the second voltage is applied when performing a recovery operation of the nozzle.
The driving method of the printing apparatus according to the above. 4. An actuator including 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 to face the vibration plate,
Driving means for deforming the vibration plate by electrostatic force and discharging ink droplets for recording from the nozzles, wherein the driving means deflects the vibration plate to the actuator by electrostatic force during recording. Voltage applying means for applying a first voltage for applying, a second voltage having a different polarity from the first voltage and having a magnitude equal to or greater than a voltage value at which the diaphragm contacts the electrode, A printing apparatus comprising: a residual charge removing unit that applies a voltage to the actuator. 5. The printing apparatus according to claim 4, wherein the residual charge removing means of the diaphragm applies the second voltage every time one dot or one line is printed. 6. The method according to claim 6, wherein the residual charge removing unit of the diaphragm applies the second voltage to perform a recovery process operation of the nozzle.
5. 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 diaphragm 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 made of a thermal oxide film of silicon. 9. The printing apparatus according to claim 7, wherein said electrode is made of an ITO film.