JPH07214780A - Printing apparatus and driving method thereof - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a driving method of an ink jet head and a driving apparatus therefor so as to obtain a good printing quality by eliminating residual polarization. A forward direction electric pulse is applied between a vibrating plate provided in an ink flow path communicating with a nozzle and an individual electrode to eject an ink droplet from the nozzle. It has diaphragm recovery processing means 212 for applying an electric pulse in the opposite direction to the electric pulse between the diaphragm and the electrodes. Further, the rear end portion of the electric pulse in the opposite direction is configured to have an inclination such that ink is not ejected. [Effect] Good print quality can be obtained by the recovery process of the diaphragm. In addition, since ink is not ejected by the recovery process, control can be simplified.

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 the purpose thereof is to provide the following two points.

A method and apparatus for driving an inkjet head, which eliminates the adverse effect of residual charges accumulated between the diaphragm and the electrodes on the driving of the inkjet head and stabilizes the relative displacement between the diaphragm and the individual electrodes. And to provide a printing apparatus that achieves good printing quality.

[0012] While the recovery means for eliminating the adverse effect of the residual charge accumulated between the diaphragm and the electrode on the drive of the inkjet head is being executed, the position of the inkjet head can be determined without ejecting ink droplets from the nozzle. Even so, it is possible to provide a printing device that can perform recovery processing reliably and can print at high speed.

[0013]

A printing apparatus according to the present invention includes a nozzle, an ink flow path communicating with the nozzle, a vibration plate provided in a part of the flow path, and a diaphragm facing the vibration plate. An actuator including an electrode provided and a driving unit that deforms the vibration plate and ejects ink droplets for recording from the nozzle, the driving unit, when recording, causes the actuator to First for flexing diaphragm
The voltage applying means for applying the electric pulse and the first electric pulse have different polarities, and the rear end of the pulse is
A residual electric charge removing means for applying to the actuator a second electric pulse having a predetermined inclination that suppresses the displacement speed of the diaphragm so that the ink droplets are not ejected from the nozzle. .

In the method for driving a printing apparatus according to the present invention, the nozzle, the ink flow path communicating with the nozzle, the vibration plate provided in a part of the flow path, and the vibration plate provided opposite to the vibration plate. In a method of driving a printing apparatus that has an actuator including an electrode and deforms the diaphragm, ejects ink droplets from the nozzles, and performs recording, the diaphragm is deformed during normal recording. A driving method of applying a first electric pulse and applying a second electric pulse having a polarity different from that of the first electric pulse in order to stabilize the displacement amount of the diaphragm at a predetermined time, The rear end portion of the second electric pulse has a predetermined inclination that suppresses the displacement speed of the vibration plate to the extent that ink droplets are not ejected from the nozzle.

In a preferred embodiment of the present invention, the second electric pulse is a reserve for recovering ink droplets ejected by the nozzle to recover from clogging every time one dot or one line is printed. Except when in the dispensing position,
It is applied appropriately.

[0016]

In the present invention, by applying an electric pulse in the forward direction (hereinafter referred to as a printing pulse) between the diaphragm of the ink jet head and the individual electrode, the diaphragm and the individual electrode arranged so as to face the diaphragm are separated. An attractive force due to an electrostatic force acts between them, and this electrostatic force 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, the print pulse is applied by applying an electric pulse (hereinafter referred to as a refresh pulse) having a polarity different from the drive voltage of the print pulse, for example, after performing a one-line print operation. The residual charges accumulated by the application are eliminated. (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.

Further, especially when the material of the diaphragm is a semiconductor having a low resistivity, the diaphragm is bent even when the refresh pulse is applied and the residual charges are extinguished, but the refresh pulse is a simple rectangular shape. Since it is not a wave but a trapezoidal wave or an integrated wave with a slope at the trailing edge of the pulse, the vibration plate gradually recovers, and its deformation speed is slow. It is not discharged from the nozzle.

Therefore, the recovery process of the diaphragm can be surely performed regardless of the position of the ink jet head. Accordingly, for example, in order to recover the clogging of the nozzle, it is not necessary to move the inkjet head to the preliminary ejection position where the ink droplets that do not contribute to recording are ejected, and the vibration plate recovery process can be performed. Therefore, it is possible to provide a printing apparatus capable of printing at high speed without spending a lot of time for recovery processing.

[0021]

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

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

In this embodiment, the distance between the diaphragm 5 and the electrodes 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 on the first substrate 1, it is important that the work function of the metal material of the semiconductor and the electrode is large or small. In this embodiment, titanium is used as the common electrode material. Although platinum is used as an attachment and gold is used as an underlay of chromium, the present invention is not limited to this embodiment, and another combination may be used depending on the characteristics of the semiconductor and the electrode material. The resistivity of the semiconductor material used in this example is 8 to 12 Ωcm.

Borosilicate glass is used for the lower second substrate 2 bonded to the lower surface of the first substrate 1, and the vibration chamber 9 is formed by bonding the second substrate 2 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 as with the second substrate 2. By joining the third substrate 3, the nozzle hole 4, the ejection chamber 6, the orifice 7, and the ink cavity 8 are formed. Further, the third substrate 3 is provided with an ink supply port 31 communicating with the ink cavity 8. The ink supply port 31 is connected to an ink tank (not shown) via a connection pipe 32 and a tube 33.

Next, the first substrate 1 and the second substrate 2 are anodically bonded by applying 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 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 the present 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.

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

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

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

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

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

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

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

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

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

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

In the above-described embodiment, the diaphragm 5 is bent by applying a reverse voltage (refresh voltage) in order to extinguish the residual charge, but the diaphragm 5 is also bent by the reverse voltage. Therefore, as in the example shown in FIG. 17, it is necessary to prevent ink droplets from being ejected except when the vibration plate recovery process is also performed during the head nozzle recovery operation. When a semiconductor having a relatively high resistivity is used for the vibrating plate 5, even if the magnitude of the reverse voltage is the same as the forward voltage, the amount of deflection is small, and there is no fear of ink droplet ejection. On the other hand, when a semiconductor having a relatively low resistivity is used for the vibration plate 5, if the magnitude of the reverse voltage is made equal to the forward voltage, the vibration plate is largely bent. It is necessary to devise to prevent the discharge of the liquid.

Hereinafter, the recovery process of the diaphragm in which ink droplets are not ejected will be described with reference to FIGS. 19 to 25.

FIG. 19 (a) shows a waveform between the common electrode and the individual electrode when a square-wave reverse pulse having no inclination is applied to the transition part. P10 is a print pulse, and P11 is a refresh pulse for performing the recovery processing operation of the diaphragm. As shown in the figure, by applying the refresh pulse P11 in the opposite direction to the print pulse P10, the residual charge disappears. If the time interval Ta between the print pulse P10 and the refresh pulse P11 is small, the ink ejection operation becomes unstable. Therefore, Ta is preferably set to 100 μsec or more, which allows stable ink ejection.

When the refresh pulse P11 is a square wave, ink may be ejected because the shape recovery speed of the diaphragm bent by the recovery processing operation of the diaphragm is fast. In particular, when the amount of impurities such as boron diffused in the semiconductor is large, the resistance value of the diaphragm decreases and this tendency becomes stronger. To prevent this, the refresh pulse P12 shown in FIG. 19B may be applied instead of P11. Since the refresh pulse P12 has an inclination at the rear end portion of the pulse, the flexed diaphragm gradually restores its original shape. In this way, since the shape recovery speed of the diaphragm is slow, it is possible to prevent ink droplets from being ejected from the nozzle due to the recovery processing of the diaphragm.
In the case of the present embodiment, the ink ejection prevention effect can be expected by setting the inclination time Tb at the rear end of the refresh pulse P12 to 150 μsec or more.

The two types of refresh pulses thus formed may be switched and applied to the ink jet head depending on the situation in which the vibrating plate recovery means is executed as described below. For example, when the diaphragm recovery operation SS12 is performed simultaneously with the head nozzle recovery operation SS2 based on the flowcharts shown in FIGS. 17 and 18A, the carriage 502 mounting the inkjet head 10 is at the position of the cap 504. Since there is no problem even if ink droplets are ejected from the nozzle, a square-wave refresh pulse P11 is applied as shown in FIG. 19A, and the residual charge is removed from the diaphragm as the nozzle is refreshed. On the other hand, based on the flowcharts shown in FIGS. 14, 15, and 16 or the timing chart, when the recovery operation of the diaphragm is performed for each row, a refresh pulse is applied and ink droplets are ejected from the nozzles. If this happens, the recording paper or printer may be stained with ink.
The refresh pulse P12 having a slope at the trailing end of the pulse as in (b) may be applied.

Details of the recovery processing operation of the diaphragm including the above-described ink ejection prevention means will be described with reference to FIGS. 20 and 21. Symbols H and L in the operation logic diagram of FIG. 20B indicate a state where H is applied with a pulse and a state where L is not applied. The present embodiment is an example in which the circuit configuration is simplified and an ink ejection prevention circuit is added during the recovery processing operation of the diaphragm.

During standby, the control pulse P11 is applied, the transistor 501 is turned on, and the diaphragm 5
Is short-circuited with the power supply VH (state A). At the time of printing, the printing pulse P10 is applied. While P10 is being applied, the transistor 500 is in the ON state, the individual electrode 21 is at 0 V, the shape of the diaphragm 5 is bent as in the state B, and ink is supplied to the ejection chamber. When the application of P10 is stopped, the vibration plate 5 and the individual electrode 21 have the same potential, the shape of the vibration plate 5 is restored as in the state A, and ink is ejected.

During the recovery processing operation of the diaphragm, the control pulse P11 is stopped and the control pulse P12 is applied to turn off the transistor 501 and turn on the transistor 502 (state C). In this state, the capacitor 50 having the capacitance value of C
The electric charge charged in No. 3 is discharged through the resistor 504 having the resistance value R1. C is set to such a value that the capacitance C0 of the capacitor constituted by the diaphragm 5 and the individual electrode 21 can be ignored. As a result, the potential of the diaphragm 5 decreases to 0V with a curve having a time constant C · R1 that is much larger than that when the printing pulse is applied. Since the control pulse P10 is not applied during the recovery processing operation of the diaphragm, the transistor 500 is turned off.
In the FF state, the voltage VH is applied to the individual electrode 21. As a result, a voltage opposite to that during normal printing is applied to the head, and the diaphragm recovery processing operation is performed.

After the reverse voltage is applied for a time sufficient to eliminate the residual charge, the application of the control pulse P12 is stopped, the transistor 502 is turned off, and the resistor 5 having the resistance value R2 is applied.
05, the resistance value R1 through the resistor 504 to the capacitor 503
At the same time, the electric charge stored in the diaphragm 5 is discharged. At that time, the terminal voltage of the capacitor 503 has a time constant C
・ It rises in the curve of (R1 + R2) and becomes the same potential as VH. Control pulse P11 after the diaphragm 5 rises to VH
Is applied to turn on the transistor 501 to enter the print standby state (state A). As a result, when controlling the ejection for printing, it is possible to eliminate the influence of the resistors 504 and 505 and perform low impedance control.

FIG. 21 shows a specific timing chart. The time when the control pulse P11 is not applied is when the recovery processing operation of the diaphragm is being performed. Time T to apply reverse voltage
The present invention was carried out by setting c to about 30 msec and the time Td for charging the capacitor 503 to about 10 msec. Tc and Td can be shortened as described with reference to FIG. 19 when the time for performing the recovery processing operation of the diaphragm cannot be taken long.

In this way, by applying an integral wave that changes the potential over a sufficient time to the diaphragm 5,
The deformation speed of the vibrating plate 5 is slowed down, and ink can be prevented from being ejected at the end of the vibrating plate recovery processing operation.

When the output impedance of the transistor 501 is sufficiently small, the capacitor 503 can be omitted. In that case, the potential change of the diaphragm 5 causes the capacitance C0 of the capacitor 114 and the charging / discharging resistors 504 and 505.
It becomes a time constant by combining with. In this embodiment, the capacitance of the capacitor 503 is set to 1 μF, but the capacitor 1
The capacitance of 14 is about 300 pF. Therefore, the resistance 5
04 and 505 are required to have a size of about several hundred kΩ.

A capacitor having a capacity large enough to supply all the current flowing through the common electrode during printing is used.
The present invention can be implemented with the configuration shown in FIG. During the recovery processing operation of the diaphragm, by applying the control pulse P12, the transistor 502 is turned on, the potential drops to 0 V on the curve of the time constant C · R1, and the voltage between the diaphragm 5 and the individual electrode 21 increases. Reverse voltage is applied. By stopping the application of the control pulse P12, the electric potential of the diaphragm 5 becomes a time constant C · (R
The potential rises to VH by the curve of 1 + R2), and the normal printing operation becomes possible. With this configuration, one recovery processing operation control signal for the diaphragm can be used. There are resistors R1 and R2 between the diaphragm 5 and VH, but using a capacitor 503 having a capacity large enough to supply all the current flowing to the common electrode during printing causes a problem in actual use. Absent.

FIG. 23 shows a timing chart when the circuit configuration of FIG. 22 is used. The time Te from the stop of application of the control pulse P12 to the first printing needs to be long enough for the potential of the diaphragm 5 to rise to a level that does not affect the printing operation.

FIG. 24 shows an embodiment using a D / A converter.
Shown in. As the D / A converter 506, one whose output increases when the input data is counted up and whose output decreases when the input data is counted down is used. D
The output of the / A converter 506 is supplied to the diaphragm 5 through the low output impedance amplifier 507. In the printing state, all the data are set to 1 and VH is output. During the recovery processing operation of the diaphragm, the input data of the D / A converter 506 is gradually counted down and the potential of the diaphragm 5 is set to 0V. After the completion of the recovery processing operation of the diaphragm, the input data is gradually counted up and the potential of the diaphragm 5 is returned to VH. With this configuration, when the count-up or count-down is performed at equal time intervals, the timing chart of FIG.
As shown in FIG. 5, when the diaphragm recovery process is performed, the diaphragm 5
Although a trapezoidal wave is applied to, the same effect as that of the above-described embodiment using the integral wave is recognized. The input / output logic of the D / A converter may be inverted depending on the system configuration. Also, the D / A converter is the actuator 1
The low output impedance amplifier 507 is not necessary when there is sufficient drive capability to drive 14.

The present invention has been described above based on the example in which the refresh pulse is applied to each line of printing to perform the recovery process of the diaphragm without ink droplet ejection.
The refresh pulse is not limited to each row, and for example, a refresh pulse is applied to the diaphragm that has performed the printing operation every time one dot is printed. Good.

[0069]

As described above, according to the present invention, by applying a pulsed driving voltage between the diaphragm and the individual electrode, the gap between the individual electrode and the diaphragm arranged to face the individual electrode is applied. In a method for driving an inkjet head that discharges ink by applying an electrostatic attraction force to the ink, ink droplets are not discharged from the nozzle at the displacement speed of the diaphragm in the direction opposite to the pulse voltage and at the trailing end of the pulse. By applying a refresh pulse with a gradient that suppresses the degree to the appropriate level between the vibrating plate and the individual electrode, the relative displacement amount between the vibrating plate and the individual electrode does not decrease, and as a result, the cause of ink droplet ejection failure Is eliminated, high print quality and reliability can be obtained.

During the execution of the 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, ink droplets are not ejected from the nozzle and the inkjet head is positioned at any position. However, since the recovery process can be performed reliably and the head does not have to be moved to the ink ejection position during the recovery process operation of the diaphragm, the recovery process of the diaphragm does not require many steps and control is performed. A printing device that can be simplified and that can print at high speed can be provided. Further, it is possible to prevent the printer and the recording paper from being contaminated by the ink.

[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 ink jet 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.

6 is a schematic diagram focusing on polarization of the diaphragm and 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 inkjet 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.

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

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

14 is a flowchart showing another control method of the inkjet printer of the embodiment of 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 diagram showing a refresh pulse application method used for a diaphragm recovery process.

20A and 20B are a drive circuit diagram and an operation logic diagram of an inkjet head to which an ink ejection prevention circuit is added during a recovery processing operation of a diaphragm.

FIG. 21 is a timing chart showing the operation of FIG. 20.

22A and 22B are a drive circuit diagram and an operation logic diagram of an ink jet head, which is a simplified circuit of the circuit shown in FIG.

23 is a timing chart showing the operation of the circuit shown in FIG.

FIG. 24 is a drive circuit diagram of an inkjet head in which a D / A converter generates a reverse voltage pulse to be applied to the diaphragm during the recovery processing operation of the diaphragm.

25 is a timing chart showing the operation of the circuit shown in FIG.

[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 (5)

[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 facing the vibration plate. Then, in a method for driving a printing apparatus that deforms the diaphragm and ejects ink droplets from the nozzles to perform recording, during normal recording, a first electric pulse that deforms the diaphragm is applied, Sometimes, in order to stabilize the displacement amount of the diaphragm, the first electric pulse is a driving method of applying a second electric pulse having a different polarity, and a rear end portion of the second electric pulse. However, the method for driving the printing apparatus has a predetermined inclination that suppresses the displacement speed of the diaphragm so that the ink droplets are not ejected from the nozzle. 2. The method for driving a printing apparatus according to claim 1, wherein the second electric pulse is applied every time one dot or one line is printed. 3. An actuator comprising a nozzle, an ink flow path communicating with the nozzle, a vibration plate provided in a part of the flow path, and an electrode provided facing the vibration plate.
A driving unit configured to deform the diaphragm and eject ink droplets for recording from the nozzles, wherein the driving unit causes the actuator to bend the diaphragm during recording. The voltage applying means for applying an electric pulse and the first electric pulse have different polarities, and the rear end portion of the pulse has a displacement rate of the vibration plate so that ink droplets are not ejected from the nozzle. A printing apparatus comprising: a residual electric charge removing unit that applies a second electric pulse having a predetermined gradient to be suppressed to the actuator. 4. The residual charge removing means for applying the second electric pulse except when the nozzle is at a preliminary ejection position for collecting ink droplets ejected to recover clogging. The printing apparatus according to claim 3, wherein the printing apparatus is a printing apparatus. 5. The printing apparatus according to claim 1, wherein the residual charge removing unit applies the second electric pulse every time one dot or one line is printed.