JPH07214776A - Printing apparatus and driving method thereof - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a simple ink jet printing apparatus in which the residual charge is eliminated when the power is turned on to obtain good printing quality. A driving device of an inkjet head that applies an electric pulse in a forward direction between a vibrating plate provided in an ink flow path communicating with a nozzle and an individual electrode to eject ink droplets from the nozzle Residual charge removing means that has a suppressing means for suppressing a change in potential and applies a reverse voltage having a polarity different from that of the forward electric pulse for a predetermined period between the vibrating plate and the individual electrode when the power supply is turned on. Have.

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 to solve the above problems, and an object thereof is to eliminate the adverse effect of the residual charges accumulated between the diaphragm and the electrode on the driving of the ink jet head, Provided are a method for driving an inkjet head and a device for stabilizing the relative displacement between a diaphragm and an individual electrode, and a printer for obtaining good printing quality. It is an object of the present invention to provide a printing apparatus that can easily execute a recovery unit that eliminates an adverse effect on the drive of an inkjet head due to residual charges accumulated in the printer when the power is turned on.

[0011]

A method of driving a printing apparatus according to the present invention comprises: a nozzle; an ink flow path communicating with the nozzle;
A vibration plate provided in a part of the flow path, and an actuator including an electrode provided to face the vibration plate,
Applying a forward electrical pulse to the actuator,
In a method of driving a printing apparatus that deforms the vibration plate by electrostatic force, ejects ink droplets from the nozzles, and performs recording, when the power supply for supplying voltage to the actuator is turned on, the forward electric pulse is applied. Applies a reverse voltage having different polarities to the actuator.

In the printing apparatus of 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 electrode provided opposite to the vibration plate. And an actuator formed by applying a forward electric pulse to the actuator, deforming the vibration plate by an electrostatic force, and ejecting ink droplets from the nozzle,
In a printing apparatus for recording, when a power supply for supplying a voltage to the actuator is turned on, the forward electric pulse has a residual charge removing unit that applies a reverse voltage having a polarity different from that of the forward electric pulse to the actuator. Characterize.

In a preferred mode of the residual charge removing means, in the printing apparatus of the present invention, when the vibrating plate is made of a P-type semiconductor substrate, the potential on the electrode side is kept constant for a predetermined period when the power is turned on. , A suppressing means for suppressing a change in the electric potential on the diaphragm side so as to be larger than the electric potential on the diaphragm side, while the diaphragm is made of an N-type semiconductor substrate, the power supply is turned on. There is a suppressing unit that suppresses a change in the potential on the diaphragm side so that the potential on the electrode side becomes smaller than the potential on the diaphragm side for a predetermined period during raising.

The suppressing means may be, for example, a capacitor connected to the diaphragm side or the electrode side, and is activated when the output voltage of the power source reaches a predetermined potential, for example, The switching circuit may include a Zener diode connected to the output of the power supply and a transistor that operates when the output voltage of the power supply reaches the Zener voltage of the Zener diode.

[0015]

In the present invention, by applying a forward electric pulse (hereinafter referred to as a print pulse) between the diaphragm of the ink jet head and the individual electrode (actuator),
An attractive force due to an electrostatic force acts between the diaphragm and the individual electrode arranged so as to face the diaphragm, and the electrostatic plate deforms the diaphragm. Then, by canceling the print pulse, ink droplets are ejected from the nozzle holes by the restoring force of the vibration plate.

However, even if the print pulse is released, the electric charge remains between the diaphragm and the individual electrodes, and the electric field generated 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, when the power source is turned on,
For example, a Zener diode connected to the output of the power supply and a switching circuit consisting of a transistor that operates when the output voltage of the power supply reaches the Zener voltage of the Zener diode suppresses the change in the potential on the diaphragm side, During the period, the voltage opposite to the polarity of the driving voltage of the print pulse is applied to the actuator, so that the residual charge accumulated in the previous printing operation disappears. (Hereinafter, this is referred to as a vibration plate recovery process.) Therefore, the relative displacement amount between the vibration plate and the individual electrode does not decrease.

[0018]

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 at equal intervals from one end 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. 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 together. 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, like 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 together. 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 electrode 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 in 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 polarization of the dielectric (insulating layer) inside the vibrating plate 5 and the individual electrode 21 of this embodiment, comparisons called ionic polarization and interface polarization other than atomic polarization and electronic polarization, which have a short relaxation time, are 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 view 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 droplets and the ink speed reduction 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.

A drive control circuit 213 for the ink jet head 10 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 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 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 refresh 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 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. 19 shows a configuration for performing a pseudo diaphragm recovery processing operation for each printing. 509 is a low output impedance voltage regulator,
A potential VHL lower than H is generated. Control pulse P1
When 0 is not applied, the transistor 500 turns off
Since it is in the state, as shown in FIG.
Since the potential of 1 becomes higher than that of the diaphragm 5, the reverse voltage is always applied. As a result, the dielectric polarization itself can be reduced to such an extent that there is no problem in practical use. In the case of implementing this configuration, the vibration plate is bent during the standby of the print pulse, but since the displacement amount is small, ink is not ejected.

In the circuit diagram shown above, the drive circuit on the side of the individual electrode 21 is simplified and shown, but the present invention can be implemented even if the circuit used in FIG. 9 is adopted.

An embodiment in which the diaphragm recovery processing operation is performed when the power is turned on will be described below with reference to FIGS.

FIG. 20 (a) shows a circuit diagram according to one aspect of this embodiment. In this embodiment, the diaphragm 5 is made of P-type semiconductor. With this configuration, as shown in FIG. 20B, the potential of the diaphragm 5 rises while being charged in the capacitor 503 through the resistor 508. By controlling the transistor 500 to be turned off when the power is turned on, the individual electrode 21
Becomes VH when the power is turned on. Therefore, the reverse voltage is applied to the head when the power is turned on, and if the residual charge from the previous drive remains on the diaphragm,
Immediately after the power is turned on, this residual charge can be completely removed without ejecting ink droplets from the nozzle.

When this control is performed, it is necessary to speed up the rise of VH when the power is turned on, as in the potential change of the individual electrode 21 shown in FIG. 20 (b). If VH rises slowly, the effect of the present invention cannot be expected. Therefore, it suffices to use a switching circuit that performs the same operation as the configuration shown in FIG. 21A and increase the rising speed of VH. 512 is a power supply, and the output VH0 is
The output terminal VH is connected to the power input terminal on the individual electrode side, and the output terminal VH is connected to the power input terminal on the common electrode side to supply power required for driving the printer. In general, since the power supply is provided with a large-capacity capacitor at the output, the output VHO immediately after rising changes with the curve shown in FIG. If the Zener voltage of the Zener diode 511 is VZ, the Zener diode 511 is in the OFF state until the output voltage of the power supply 512 rises to VZ, so the transistor 513 is also in the OFF state. Therefore, the power supply voltage is not supplied to the output VH. The output VH0 of the power supply 512 is the Zener voltage VZ of the Zener diode 511.
When it becomes higher, the Zener diode 511 is turned on, the potential at the point A is fixed to VZ, and a potential difference is generated between the point A and VHO. Further, the transistor 513 is turned off.
When VH0 rises to a voltage VS generated between point A and VH0, a potential difference sufficient to bring it to the N state, the transistor 5
13 is turned on and the voltage VH on the common electrode side is rapidly V
Rise to S.

Therefore, the potential of the individual electrode 21 and the potential of the diaphragm 5 in the circuit diagram shown in FIG.
This potential change is almost equal to the potential change shown in (b), and immediately after the power switch of the printer is turned on, this residual charge can be completely removed without ejecting ink droplets from the nozzle. In particular, when used in an application with a low printing frequency, this configuration can be implemented.

In the present embodiment, the case where the vibrating plate 5 is a P-type semiconductor has been described, but when an N-type semiconductor is used for the vibrating plate 5, the connection wiring needs to be opposite to that of the P-type semiconductor. There are as described above.

[0057]

As described above, according to the present invention, by applying a pulse voltage between the diaphragm and the individual electrode, electrostatic discharge is generated between the individual electrode and the diaphragm arranged opposite thereto. In a printing device that uses attractive force to eject ink, changes in the potential on the diaphragm side are suppressed when the power is turned on, and a voltage opposite to the polarity of the print pulse drive voltage is applied to the actuator for a predetermined period. Therefore, the residual charge accumulated in the previous printing operation disappears and the relative displacement amount between the diaphragm and the individual electrode does not decrease. Quality and reliability are obtained. In addition, since the residual charge is removed almost at the same time when the power is turned on with a simple circuit configuration, complicated control is not required.

[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 drive circuit diagram of an inkjet head and a potential change diagram of a vibrating plate and an individual electrode for reducing the residual charge to the extent that there is no problem in practical use.

FIG. 20 is a drive circuit diagram of an inkjet head for performing a recovery processing operation of a diaphragm when power is turned on and a potential change diagram of the diaphragm and individual electrodes.

21 is a power supply switching circuit diagram for operating the circuit shown in FIG. 20 and a timing chart showing a change in output voltage.

[Explanation of symbols]

 1, 1st substrate 2, 2nd substrate 3, 3rd substrate 4, nozzle hole 5, diaphragm 6, discharge chamber 10, inkjet head 17, common electrode 21, individual electrode 27, insulating layer 28, polarization 29 , Remanent polarization 102, drive circuit 212, diaphragm polarization recovery processing means

Claims (7)

[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, a forward electric pulse is applied to the actuator, the diaphragm is deformed by electrostatic force, ink droplets are ejected from the nozzles, and a voltage is applied to the actuator in a method of driving a printing apparatus. A method of driving a printing apparatus, comprising applying a reverse voltage having a polarity different from that of the forward electric pulse to the actuator when the power supply to be supplied is turned on. 2. 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. In the printing apparatus that applies a forward electric pulse to the actuator, deforms the diaphragm by electrostatic force, ejects ink droplets from the nozzle, and performs recording, a power supply that supplies voltage to the actuator. The printing apparatus further comprises residual charge removing means for applying a reverse voltage having a polarity different from that of the forward electric pulse to the actuator at the start-up. 3. When the diaphragm is made of a P-type semiconductor substrate, the potential on the electrode side is higher than the potential on the diaphragm side for a predetermined period when the power source is turned on. The printing apparatus according to claim 2, further comprising a suppressing unit that suppresses a change in potential on the diaphragm side. 4. When the diaphragm is made of an N-type semiconductor substrate, the potential on the electrode side is set to be smaller than the potential on the diaphragm side for a predetermined period when the power source is turned on. The printing apparatus according to claim 2, further comprising a suppressing unit that suppresses a change in potential on the diaphragm side. 5. The printing apparatus according to claim 3, wherein the suppressing unit is a capacitor connected to the diaphragm side. 6. The printing apparatus according to claim 3, wherein the suppressing unit is a switching circuit that operates when the output voltage of the power source reaches a predetermined potential. 7. The switching circuit comprises a Zener diode connected to the output of the power supply, and a transistor that operates when the output voltage of the power supply reaches the Zener voltage of the Zener diode. Item 6. The printing device according to item 6.