JPH07132598A - Ink jet printer and its controlling method - Google Patents

Abstract

PURPOSE:To stabilize a concentration of a printing and raise a durability of an electrostatic actuator by controlling a charged electric charge quantity to an electrostatic actuator, and a time and a speed for charging and discharging. CONSTITUTION:An oxidizing treatment is applied to a face of a side opposing a separate electrode of an oscillating plate 5, and an oxidized membrane 5a is formed. This oxidized membrane 5a prevents a short of a circuit in the case wherein the oscillating plate contacts with an electrode with a protecting membrane 24 which is arranged at a side of the separate electrode. A positive hole 19 in a P type silicone migrates to a side of the oxidized membrane 5a through the oscillating plate 5, by an electric field having a direction from a common electrode 17 to the separate electrode 21. A negative electric charge of boron which is generated by a migration of this positive hole 19, is neutralized by a positive charge supplied from a substrate electrode 17, a first substrate is positively charged, and as no space electric charge layer is generated, it can be recognized as an electric conductor. Besides, a side of the separate electrode 21 is negatively charged and, as a result of this, an electrostatic power executes an action between the oscillating plate 5 and the separate electrode through an impressed voltage, and the oscillating plate 5 is made to bend to a direction of the separate electrode 21.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet printer and a control method thereof, and more particularly to an ink jet head driving device of an ink jet printer in which electrostatic force is applied to an ink jet head, and a control method thereof.

[0002]

2. Description of the Related Art Conventionally, as an ink jet head to which electrostatic force is applied, those disclosed in U.S. Pat. No. 4,520,375 and Japanese Unexamined Patent Publication No. 2-289351 related to the invention of Chlor are known. . The inkjet head according to the invention of Mr. Kroll uses an electrostatic actuator composed of a vibration plate forming a part of the ink discharge chamber and a counter plate facing the vibration plate and provided outside the ink discharge chamber. By applying a voltage that changes with time to the facing plate, ink droplets are ejected from the nozzles connected to the ejection chamber. In the inkjet head according to the latter patent application, the diaphragm is bent by applying a voltage to an electrostatic actuator provided adjacent to the ink ejection chamber, and the ink is sucked into the ink ejection chamber and then applied. The diaphragm is restored by cutting off the voltage, and ink droplets are ejected.

[0003]

First, the operating principle of the electrostatic actuator used in the ink jet head will be described in detail. The diaphragm is in a bent state by being attracted to the electrodes by the electrostatic force generated due to the voltage applied between the diaphragm and the opposite electrode, while the diaphragm generates a restoring force in the bent state. Therefore, when the voltage is applied to the electrostatic actuator, the deflection amount of the diaphragm, that is, the displacement amount of the antinode of the diaphragm (hereinafter, simply referred to as the displacement amount of the diaphragm or the displacement of the diaphragm) is the electrostatic force and the vibration. It is a value that balances with the restoring force of the plate. The restoring force P and displacement x of the diaphragm are given by the following: C is the compliance of the diaphragm.

[0004]

[Equation 1]

It is represented by In addition, the electrostatic force generated between the diaphragm and the electrode is expressed as follows: where the effective voltage is Va, the distance between the diaphragm and the electrode (hereinafter referred to as the electrical gap length) is δ, and the dielectric constant in the gap is ε.

[0006]

[Equation 2]

It is represented by From this equation (1) and equation (2), it is possible to obtain the position of the displacement balance of the diaphragm.

FIG. 34 shows characteristics obtained by the above equations (1) and (2) for the relationship between the displacement of the diaphragm and the restoring force of the diaphragm, and the relationship between the displacement of the diaphragm and the generated electrostatic force. It is a figure. The horizontal axis shows the vibration plate displacement amount x, and the vertical axis shows the pressure generated by the restoring force of the vibration plate and the pressure generated by the electrostatic force. Also, the parameters used in the calculation are the same as those used in the experiment, which are as follows.

C = 5 × 10 ^-18 [m ⁵ / N], δ = 0.25 [μm], ε = 8.85 [pF / m] The electrostatic force is calculated for each applied voltage. The curves are respectively shown. On the other hand, the relationship between the displacement of the diaphragm and the restoring force of the diaphragm is shown by a straight line, and the intersection on the left side of the intersection of this straight line and these curves is the amount of deflection (displacement) of the diaphragm at each applied voltage. Is shown. In addition, at an applied voltage (for example, 35 V) at which the restoring force of the diaphragm and the electrostatic force do not intersect, the electrostatic force always exceeds the restoring force of the diaphragm regardless of the displacement amount of the diaphragm, so the displacement is infinite. Become. In reality, since there are electrodes facing each other, the diaphragm is displaced up to the electrodes. When the electrostatic actuator as described above is applied to an inkjet head of an actual printer, there are the following problems with respect to its driving. In order to improve the printing speed of the printer, it is necessary to increase the frequency at which the inkjet head can continuously eject ink, that is, the response frequency of the inkjet head. Therefore, in order to obtain a high-speed response of the vibrating plate, a rapid pulse voltage is applied to inject a charge between the vibrating plate and the electrode, and the vibrating plate is rapidly attracted to the electrode to rapidly increase the volume of the ink ejection chamber. When increased to
Bubbles may enter from a nozzle communicating with the flow path, or gas such as nitrogen gas dissolved in the ink and existing may appear as bubbles due to rapid vibration of the ink generated in the ink ejection chamber. When air bubbles are present in the ink ejection chamber as described above, the electric charge stored between the diaphragm and the electrode is discharged, and even if the volume of the ink ejection chamber is returned to the standby state, the increase in pressure due to this is Is absorbed and ink is not ejected. Moreover, the secondary vibration of the diaphragm is generated by suddenly attracting the diaphragm to the electrode,
There is a problem that the vibrating plate violently collides with the electrode facing the vibrating plate and the head is destroyed.

Further, since the electrostatic actuator operates with a very small amount of electric charge, there is a possibility that it may malfunction due to external noise, inductive noise, or the like. Particularly in an on-demand type inkjet printer, only one of the adjacent electrostatic actuators may be driven, and the other electrostatic actuator may malfunction due to induction.
In addition, in this type of printer, the non-operation time from the ejection of ink to the ejection of the next ink may be considerably long, and malfunctions due to external noise during this period have been a problem.

As described above, there are many problems to be solved for practical use of the ink jet head using the electrostatic actuator, such as improvement of durability of the electrostatic actuator, stabilization of print density, prevention of malfunction, and the like. A method for solving these problems has not been proposed, and the development of the method has been long awaited.

[0012]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems by controlling the amount of charge charged to an electrostatic actuator, and the time and speed of charge and discharge, and first of all, to provide a stable ink. Stable high print quality due to ejection, secondly high reliability that does not cause damage such as damage even after long-term use, and thirdly high printing speed by improving the response of the inkjet head. Fourth, it is to realize an inkjet printer that can be efficiently driven with a low drive voltage.

The ink jet printer of the present invention includes a nozzle, an ink flow path communicating with the nozzle, a vibration plate provided in a part of the ink flow path, the vibration plate and the ink flow path facing the vibration plate. An ink jet head having an electrostatic actuator composed of an electrode provided outside, and
In an inkjet printer that applies a voltage to an electrostatic actuator to deform a vibration plate by an electrostatic force and ejects ink droplets from a nozzle to perform printing, a charging speed control unit that controls a charging speed of electric charges to the electrostatic actuator. , And a discharge means for discharging electric charge to the electrostatic actuator.

Further, the charging speed control means is characterized in that the charging speed in the vicinity of the electrodes of the diaphragm is controlled to be smaller than the discharging speed of electric charges for the electrostatic actuator.

Further, the charging speed control means is characterized in that it is configured to control the charging speed so that the pressure in the ink flow path is kept below 2 × 10 ⁵ Pascal.

In these ink jet printers, the charging speed control means includes a target value generating means for generating a target value of the electric charge for charging the electrostatic actuator, a target value of the electric charge and an amount of the electric charge charged in the electrostatic actuator. And a target charge charging circuit that charges the electrostatic actuator so that they are equal to each other.

In this ink jet printer, the target value generating means is configured to change the target value to be output according to the time elapsed from the charging start timing.

Further, these ink jet printers further include printer state detecting means for detecting the state of the ink jet printer, and charge condition storing means for storing charge / discharge conditions of the electrostatic actuator according to the state of the printer. The target value generating means is a variable target value generating means for generating a target value of the charging charge based on the charging / discharging condition from the charging condition storing means according to the detection value of the printer state detecting means.

Further, these ink jet printers are characterized by further comprising charge / discharge timing control means for controlling the timing of starting and stopping charging by the charging speed control means and the timing of starting discharge by the discharging means.

Further, in this ink jet printer, the charging / discharging timing control means is characterized in that a hold time during which charging / discharging is not performed is provided between the stop of charging and the start of discharging.

In these ink jet printers, the charging time constant determined by the charging resistance and the electrostatic capacity of the electrostatic actuator is set to be approximately one half or less of the charging time of the electrostatic actuator.

Further, a charge amount detecting means for detecting the charge amount charged in the electrostatic actuator and a comparing means for comparing the charge amount detected by the charge amount detecting means with a predetermined value are further provided. The discharge timing control means is configured to stop charging the electrostatic actuator based on the output of the comparison means.

Further, the printer further comprises a printer status detecting means for detecting the status of the ink jet printer, and a charging condition storing means for storing charging / discharging conditions of the electrostatic actuator according to the status of the printer. ,
The charging / discharging timing of the electrostatic actuator is controlled based on the charging / discharging condition from the charging condition storing unit according to the detection value of the printer state detecting unit.

According to another invention of the present application, in the above ink jet printer, charging means for charging the electrostatic actuator with electric charge, discharging means for discharging the electric charge, and timing for starting and stopping charging by the charging means. And a charging / discharging timing control means for controlling the timing of starting and stopping the discharging by the discharging means, and the charging / discharging timing control means is configured to stop the discharging immediately before the charging of the electrostatic actuator is started. It is characterized by

As a control method of such an ink jet printer, the present invention is a charging speed control means for controlling a charging speed of electric charges for an electrostatic actuator, a discharging means for discharging electric charges for an electrostatic actuator, and a charging speed control. A charging / discharging timing control means for controlling the timing of starting and stopping charging by the means and the timing of starting discharging by the discharging means, wherein the charging speed control means starts charging of the electrostatic actuator. And the second step of stopping the charging of the electrostatic actuator by the charging speed control means, the third step of keeping the charging speed control means and the discharging means inactive for a predetermined time, and the discharging means. And a fourth step of discharging the electrostatic actuator. .

Further, a first step of starting charging of the electrostatic actuator by the target value generating means and the target charge charging circuit, and a second step of determining the target value of the charging charge based on the state of the ink jet printer. A third step of outputting the target value of the charge to be charged from the target value generating means, a fourth step of stopping the charging operation by the target charge charging circuit, and a fifth step of discharging the electrostatic actuator by the discharging means. And having.

Further, the first step of starting charging of the electrostatic actuator by the charging means, the second step of stopping charging of the electrostatic actuator by the charging means, and the discharging of the electrostatic actuator by the discharging means. And a fourth step of stopping the discharge from the electrostatic actuator by the discharging means. The fourth step is the first step.
It is characterized in that it is performed immediately before the step of.

[0028]

Next, the operation of the present invention will be described. FIG. 35 is a characteristic diagram obtained by numerical calculation of the relationship between the displacement amount of the diaphragm and the electrostatic capacitance of the actuator. In the figure, the horizontal axis represents the displacement of the diaphragm and the vertical axis represents the capacitance. When the vibrating plate is displaced, the distance between the vibrating plate and the individual electrode is shortened, so that the electrostatic capacitance of the electrostatic actuator increases. The capacitance is about 200 [p in this case with respect to the displacement of the diaphragm.
It changes in the range of F] to 1000 [pF].

The ink jet head according to the present invention is
In order to obtain the ink ejection amount required for printing, the lower limit of the gap length between the diaphragm and the electrode is set to about 0.05 μm, and the upper limit is set to about 2.0 μm in consideration of the practical driving voltage. In order to set the driving voltage low, the gap length is
The closer to the lower limit, the better. However, in this case, as described above, the diaphragm and the electrode are likely to come into contact with each other, and a problem such as breakage of the head easily occurs.

In the method of driving the ink jet head according to the invention of the present application, since the energizing width or voltage of the electric pulse is set to such a degree that the diaphragm and the electrode do not come into contact with each other in the control means, the diaphragm and the electrode come into contact with each other. If the circuit is short-circuited and the head is destroyed, or if a protective film is formed on the diaphragm and the electrode, the diaphragm and the electrode come into contact with each other through the protective film, and an extremely large voltage is applied to the protective film, making it easier for the head to break. It does not cause problems peculiar to the inkjet head that uses electrostatic force, etc., and it can be driven with a low driving voltage even if the gap length between the diaphragm and the electrode is small, even if it is practically sufficient. is there.

According to another aspect of the present invention, the voltage between the diaphragm and the electrode is measured, or the electric current flowing through the diaphragm or the electrode is integrated to measure the charge accumulated between the diaphragm and the electrode. The measured value is compared with a preset value corresponding to the amount of electric charge that does not allow the electrode to contact the preset diaphragm, and when the measured value reaches the preset value, the applied voltage between the diaphragm and the electrode is adjusted. It is possible to prevent the contact of the electrode and the vibration plate by lowering or stopping them and prevent the above-mentioned destruction of the head.

Furthermore, another aspect of the method for driving an ink jet head of the present invention has the following steps. First, a charging circuit that charges the electrodes and the diaphragm is connected to the electrodes or the diaphragm, and ink is sucked by attracting the diaphragm to the electrodes, and the flexed diaphragm does not contact the electrodes, and the ink At a position where sufficient suction for ejection is possible, the connection with the charging circuit is cut off and the suction of ink is stopped. After holding this state for a certain period of time until the amplitude of the vibration of the ink system reaches its maximum, the discharge circuit that discharges the electric charge accumulated between the electrode and the diaphragm is activated to store the electric charge between the electrode and the diaphragm. The ink is pressurized by abruptly discharging the generated electric charge to eject ink droplets. The reason for performing such a process is that the vibration of the vibration plate and the vibration of the ink system are slightly delayed compared with the vibration of the vibration plate due to the flow path resistance determined by the viscosity of the ink and the shape of the flow path. This is because the displacement of the vibration plate is stopped until it does not come into contact with the electrodes, and then the ink is pressurized after waiting for the amplitude of the vibration of the ink system to become maximum, so that the ink can be ejected efficiently. You can

Furthermore, in another aspect of the method for driving an ink jet head of the present invention, the applied voltage is gradually increased,
After the diaphragm is attracted to the electrodes by electrostatic force to increase the volume of the flow path, the applied voltage is gradually decreased and the charge accumulated between the electrode and the vibration plate is discharged to put the volume of the flow path in the standby state. It is returned and driven so as to eject ink droplets from the nozzle. As a result, a voltage can be applied between the vibrating plate and the electrode so that the negative pressure applied to the ink generated in the flow path when the vibrating plate is attracted to the electrodes becomes 2 × 10 5 Pascal or less. Air is not drawn in from the nozzle, and nitrogen or the like dissolved in the ink does not appear as bubbles in the flow path, and stable ejection is always obtained. Further, since the vibrating plate and the electrode do not come into contact with each other due to the sudden attraction of the vibrating plate to the electrode, it is possible to prevent the head from being broken.

Further, if a charging circuit for charging electric charge and a discharging circuit for discharging the electric charge are provided between the electrode and the vibrating plate and the time constant of the charging circuit is set to 1/2 or less of the energization width of the electric pulse, the vibration is generated. About 90% of the capacity of the capacitor composed of the plate and the electrode is charged, the ink is sufficiently sucked for ejection, and the responsiveness of the head described above is not impaired.

According to another aspect of the present invention, when the electric charge applied between the electrode and the diaphragm is changed stepwise by applying the electric pulse, the diaphragm is gradually attracted to the electrode,
Similarly, the problems described above do not occur.

In addition to the above embodiment, the present invention further comprises a means for detecting the operating environment of the ink jet printer and a charging condition storing means for storing in advance charging / discharging conditions corresponding to the operating environment. Start timing,
Since it is possible to change the amount and change speed of the charged electric charge, the effects obtained in each embodiment can be stably maintained even when the power supply voltage of the inkjet printer, the environmental temperature, or the like changes.

Further, since the electrostatic actuator is held in the discharged state during the non-operation period from the discharge of the electrostatic actuator to the start of the next charging, the electrostatic actuator is not affected by external noise, inductive noise or the like. It is possible to prevent malfunction.

[0038]

【Example】

(Embodiment 1) FIG. 1 is an exploded perspective view of an ink jet head in one embodiment of the present invention, and is a partial cross-sectional view. This embodiment shows an example of an edge-eject type inkjet head that ejects ink droplets from nozzle holes provided at the end of the substrate. 2 is a sectional side view of the assembled inkjet head, and FIG. 3 is a view taken along the line AA of FIG. The ink jet head 10 of this embodiment is composed of three substrates 1 having the structures described in detail below.
It has a laminated structure in which two and three layers are stacked and joined.

The intermediate first substrate 1 is a silicon substrate, on the surface of which a plurality of nozzle grooves 11 are formed which are parallel to each other and form a plurality of nozzle holes 4, and which are formed at equal intervals. Discharge chamber 6 that communicates with the bottom wall as a vibration plate 5
, A thin groove 13 for forming an orifice 7 provided at the rear of the recess 12, and a common groove 13 for supplying ink to each ejection chamber 6. And a concave portion 14 which will form the ink cavity 8 of the above. Also, the lower part of the vibration plate 5 has a vibration chamber 9 when it is bonded to a second substrate 2 described later.
The concave portion 15 that constitutes the above is provided.

In this embodiment, the facing gap between the diaphragm 5 and the individual electrode arranged to face the diaphragm 5, that is, the length G of the gap portion 16 (see FIG. 3, electrical gap length) is equal to that of the concave portion 15. It is configured to be obtained as the difference between the depth and the thickness of the electrode. The vibrating chamber recess 15 functioning as a spacing maintaining means for defining the electric gap length is formed on the back surface side of the first substrate 1 in this embodiment, but as another example, the recess is formed. 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.

Further, as a technique for providing the common electrode 17 on the first substrate 1, in this embodiment, considering the magnitude of the work function of each of the first substrate 1 as a semiconductor and the metal material used as the electrode, As the common electrode material, titanium is used as the underlayer and platinum is used as the underlayer, or chromium is used as the underlayer and gold is used. Of course, other than this, well-known electrode forming technology can be applied.

Borosilicate glass such as Pyrex glass is used for the second substrate 2, and the vibration chamber 9 is formed by bonding the second substrate 2 to the lower surface of the first substrate 1. Gold is sputtered to a thickness of 0.1 μm on each portion of the second substrate 2 corresponding to the vibrating plate 5 to form a gold pattern having substantially the same shape as the vibrating plate 5 to form the individual electrode 21.
I am trying. The individual electrode 21 includes a lead portion 22 and a terminal portion 2.
Have 3. Further, except for the electrode terminal portion 23, a borosilicate glass sputtered film is coated on the entire surface by 0.2 μm to form an insulating layer 24, and a film is formed to prevent dielectric breakdown, short circuit or the like when the inkjet head is driven. There is.

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

Next, the first substrate 1 and the second substrate 2 are subjected to anodic bonding 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 2 are bonded together. Board 3
And are joined together to assemble the inkjet head as shown in FIG. The electrical gap length G formed between the diaphragm 5 after the anodic bonding and the individual electrode 21 formed on the second substrate 2 is the difference between the depth of the recess 15 and the thickness of the individual electrode 21, In this embodiment, the thickness is 0.5 μm. The mechanical gap length G1 formed by the diaphragm 5 and the insulating layer 24 covering the individual electrode 21 is 0.3 μm.

In order to drive the ink jet head having the above structure, the drive circuit 40 is connected to the common electrode 17 and the terminal portion 23 of the individual electrode 21 by the wiring 101. The ink 103 is supplied from an ink tank (not shown) through the ink supply port 31 to the ink cavity 8 and the ejection chamber 6.
Etc. are filled in the ink flow path. 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, whereby printing is performed on the recording paper 105.

Next, the operation of the electrostatic actuator according to this embodiment will be described. FIG. 4 is a partial detailed schematic diagram of the diaphragm and the individual electrodes in the present embodiment, and schematically shows the state of charges. Here, P-type silicon is used for the first substrate 1, that is, the diaphragm 5, and the common electrode 17 is used.
The figure shows the case where the electric potential of is higher than the electric potential of the individual electrode 21. The surface of the diaphragm 5 facing the individual electrodes is oxidized to form an oxide film 5a having a thickness of 0.1 to 0.2 μm. The oxide film 5a, together with the protective film 24 provided on the individual electrode side, prevents a short circuit of the circuit when the diaphragm and the electrode come into contact with each other. Boron (B) is diffused in the P-type silicon of this embodiment,
It is known to have holes equal in number to boron. The holes 19 in the P-type silicon move in the vibrating plate 5 due to the electric field from the common electrode 17 to the individual electrodes 21 and the oxide film 5a.
Move to the side. The negative charge of boron generated by the movement of the holes 19 is neutralized by the positive charge supplied from the substrate electrode 17, so that the first substrate 1 is positively charged and does not generate the space charge layer. It can be regarded as a conductor. Further, the individual electrode 21 side is negatively charged, and as a result, the applied voltage causes an electrostatic attraction between the diaphragm 5 and the individual electrode to bend the diaphragm 5 toward the individual electrode 21.

FIG. 33 shows the ink jet head 10 described above.
It is a schematic diagram of a printer to which is applied. 300 is recording paper 1
A platen 30 as a recording paper conveying means for conveying 05
Reference numeral 1 denotes an ink tank that stores ink inside, and an inkjet head 1 via an ink supply tube 306.
Ink is supplied to 0. The inkjet head 10 is mounted on a carriage 302, and is moved in a direction orthogonal to the direction in which the recording paper 105 is conveyed by a carriage driving unit 310 composed of a stepping motor. Then, in synchronization with this movement, ink is appropriately ejected from the nozzle row to print characters and figures on the recording paper 105. As will be described later, it is desirable that the drive circuit be arranged in the vicinity of the inkjet head, so it is mounted inside the inkjet head 10. In the same figure, an apparatus for preventing clogging of nozzles of an inkjet head, which is peculiar to a printer equipped with an on-demand inkjet head, is shown. In order to prevent the nozzles of the inkjet head 10 from being clogged, when the inkjet head is moved in front of the cap 304 and the ink ejection operation is performed several times to several tens of times, the pump 303 uses the cap 304 and the waste ink recovery tube. Ink is sucked through 308 and a waste ink reservoir 305
To collect.

FIG. 5 is a block diagram showing the configuration of the printer of the embodiment of the present invention. The print request device 61 is an external device such as a host computer when the printer is a terminal printer, and is a calculation processing unit or the like inside the device when the printer is incorporated in the device.

When the print control device 62 receives a print request from the print request device 61, it sends a drive signal to the recording paper conveying device 300 and the carriage drive device 310, and the ink jet head 10 is mounted at a predetermined position on the recording paper. Printing is performed while moving the carriage 302 and moving the carriage 302 in the printing direction. Inkjet head 1
An electrostatic actuator driving device 40 is connected to each of the electrostatic actuators 27 of 0. The print control device 62 sends a print start signal S1 to the electrostatic actuator drive device 40 of one or a plurality of electrostatic actuators 27 corresponding to the positions of the dots to be printed according to the print data, and in response thereto, electrostatic The actuator driving device drives the electrostatic actuator. In order to reduce the inductance of the wiring to the electrostatic actuator, the electrostatic actuator driving device 40 is preferably mounted on the carriage to minimize the wiring length of the wiring, but the present invention is not limited to this. Instead, the electrostatic actuator driving device may be arranged outside the carriage.

FIG. 6 is a block diagram of the electrostatic actuator driving device of this embodiment. The electrostatic actuator driving device comprises a timing pulse generating means 63, a charging circuit 64 and a discharging circuit 65. When the print start signal S1 is input to the timing pulse generating means 63, the timing pulse generating means 63 sends a charging pulse having a predetermined width to the charging circuit 64, and the charging circuit 64 supplies electric charges to the electrostatic actuator 27. After that, the timing pulse generating means 63 sends a discharge pulse having a predetermined width to the discharge circuit 65. The discharge circuit 65 discharges the electric charge stored in the electrostatic actuator 27. As a result, the electrostatic actuator 27 sucks and ejects ink. Hereinafter, the configuration and operation will be described in more detail using a specific circuit example.

FIG. 7 shows an example of the charging circuit 64 and the discharging circuit 65, and FIG. 8 shows the voltage waveform 53 between the input signals 51 and 52 to the charging and discharging circuit and the diaphragm 5-electrode 21.
And the vibration of the meniscus 102 of the ink 103 formed at the tip of the nozzle 4, and FIG. 9 shows the state of each stage around the ejection chamber 6 when the diaphragm 5 is driven.

Before time t0, that is, in the standby state, the transistor 42 is off and the transistor 45 is on, so that no voltage is applied between the vibrating plate 5 and the electrode 21, so that the vibrating plate 5 is not displaced and the discharge chamber 6 is not displaced. In this state, as shown in FIG. 9A, no pressure is applied to the ink 103.

At time t0, the transistor 42 is turned on at the rising of the charging signal 51, so that the vibration plate 5-
A voltage is applied between the electrodes 21, a current flows in the direction of arrow A, and the electric charge charged between the diaphragm 5 and the electrodes 21 causes
The vibrating plate 5 is attracted to the electrode 21 by the electrostatic attractive force acting between the vibrating plate 5 and the electrode 21, and the volume of the ejection chamber 6 increases as shown in FIG. It is attracted in the direction of the arrow. At this time, the diaphragm 5-electrode 2
The voltage 53 between 1 and 1 changes according to the time constant determined by the charging resistance 43 and the capacity of the head itself, as shown in C part of FIG. 8, and the meniscus 102 changes as shown in FIG.
It changes like the E part of.

At time t1, the charging signal 51 is turned off.
At the same time, the discharge signal 52 is turned on. At this time, the transistor 42 is turned off, so that the charging between the diaphragm 5 and the electrode 21 is stopped, while the transistor 45 is turned on, so that the charge accumulated between the diaphragm 5 and the electrode 21 is discharged through the discharge resistor 46. It is discharged in the direction of arrow B.

The relationship between the discharge resistor 46 and the charge resistor 43 is
Normally, the discharge resistor 46 is set to be considerably smaller than the charge resistor 43. However, the electrostatic force acting on the diaphragm increases in inverse proportion to the square of the distance between the diaphragm and the electrode as the diaphragm approaches the electrode. However, the pressure in the ejection chamber, which is involved in the suction and ejection of ink, is greatly affected. Therefore, these resistances do not necessarily have to satisfy the above relationship, and it is sufficient that the charge rate of the charges in the vicinity of the electrodes of the diaphragm is sufficiently smaller than the discharge rate of the charges.

In this embodiment, since the time constant at the time of discharging is smaller than the time constant at the time of charging, the battery is discharged in a short time as compared with the charging as shown in part D of FIG. At this time, the vibrating plate is released from the electrostatic attraction all at once, and as shown in FIG. 9 (c), the vibrating plate 5 returns to the standby position by the elastic force of the vibrating plate 5 itself, and suddenly presses the ejection chamber 6 to The pressure generated on the ink drops 10
4 is discharged from the nozzle 4. Further, at this time, the displacement 54 of the meniscus 102 changes as shown in the F portion of FIG. 8, and the ink is ejected when the ejection pressure exceeds the force of drawing back the ink into the nozzle 4 due to the viscosity and surface tension of the ink 103. Occurs, and after that, damping vibration occurs.

In FIG. 7, the discharge resistor 47 is a resistor having a sufficiently larger value than the charge resistor 43 and the discharge resistor 46, and has almost no effect on the charge / discharge when the head is driven, and when the power is turned on. , A resistor having a function of slowly discharging the electric charge initially accumulated between the diaphragm 5 and the electrode 21. This discharge resistor 47 can hold the initial charge of the electrostatic actuator at zero.

FIG. 10 shows a circuit example of the timing pulse generating means in this embodiment. When the print start signal S1 is input to the trigger input terminal of the known monostable multivibrator 81, a positive phase pulse having a time width determined by the constants of external resistors and capacitors is output as a charging signal. Further, in the present embodiment, since the discharge is started at the same time when the charging of the electrostatic actuator is stopped, the pulse having the opposite phase to the charge signal can be used as the discharge signal.

According to the experiment, the driving frequency is 3 V under the driving voltage of 30 V, the charging resistance of 50 Ω, the charging time of 15 μs, and the charging resistance of 5 KΩ and the charging time of 45 μsec.
Stable discharge could be confirmed at KHz.

At the time of t1, OF of the charging signal 51
When only F is performed and the discharge signal 52 is kept OFF, the displacement 54 of the meniscus 102 attenuates and vibrates as shown by the broken line in FIG. The period T of these damping vibrations is mainly determined by the shape of the flow path and the viscosity of the ink. In consideration of this phenomenon, ink is sucked up to 1/4 (time t2) of the cycle T of the damping vibration, preferably until a time slightly longer than 1/4, and the ink is sucked at the same timing as the suction end. When pressure is applied, the vibration energy of the ink system can be effectively used for ejecting the ink, the driving efficiency is highest, and the ink can be ejected with low power (Japanese Patent Publication No. 2-24).
218).

However, in the ink jet head using the electrostatic actuator, the driving voltage is set to a value large enough to bring the diaphragm into contact with the opposing electrodes in a steady state. It is necessary to stop, but at this point, the phase of vibration of the ink system is always behind the phase of the diaphragm, and it is difficult to drive such efficiently. Therefore, in order to realize this efficient driving method, it is necessary to further improve the timing pulse generating means.

FIG. 11 is a timing chart showing a driving method of the electrostatic actuator which is an improvement of this embodiment.
Reference numeral 1 is a print start signal. Further, S2 is a signal that schematically represents the states of the charge signal 51 and the discharge signal 52. The high level represents the charge signal, the low level represents the discharge signal, and the intermediate level represents the hold state. The circuit configuration of the electrostatic actuator driving device 40 is the same as that of the driving device described above except the timing pulse generating means 63.

At time t10, the print start signal S1 is sent from the print control device 62 to the timing pulse generating means of the electrostatic actuator driving device corresponding to the electrostatic actuator to be printed.
Sends a charging signal to the charging circuit 64. After a lapse of a predetermined time required for sucking the ink, at time t11, the timing pulse generating means 63 stops the charging signal, deactivates both the charging and discharging circuits, and puts the electrostatic actuator 27 in the hold state. After the elapse of the time to recover the phase delay of the ink system, at time t13, the timing pulse generation means 63 sends the discharge signal 52 to the discharge circuit 65 to start discharging the electric charge accumulated in the electrostatic actuator.

In this way, by using the driving method in which the charging state is held for a certain period after the end of charging and then discharging is started,
Ink can be ejected efficiently. because,
The vibration of the diaphragm 5 and the vibration of the ink system are slightly delayed from the phase of the vibration of the diaphragm 5 due to the flow path resistance determined by the viscosity of the ink and the shape of the flow path. When the displacement of the ink is stopped at a position where it does not come into contact with the electrode 21 and then the ink is pressurized while the amplitude of the vibration of the ink system is maximized, the vibration energy of the ink system can be effectively used for ink ejection. This is because.

FIG. 12 shows an example of the timing pulse generating means of this embodiment. When the print start signal S1 is input to the trigger input terminal of the well-known first monostable multivibrator 82, the charging pulse having the time width determined by the external resistor and the capacitor is output as the positive phase signal. At the same time, the print start signal S1 is similarly input to the well-known second monostable multivibrator 83, and the discharge signal having the time width determined by the external element is output from the negative-phase output terminal to the discharge circuit. In such a circuit configuration, the pulse width of the pulse generated by the first monostable multivibrator 82 is set shorter than that of the second monostable multivibrator 83 by the hold time.

FIG. 13 shows another example of the timing generating means of this embodiment, which is realized by using a microprocessor. In this example, it is configured so that whether or not the hold time is set can be selected. The operation of the timing pulse generating means of this example will be described below. When receiving a print start signal S1, a well-known microprocessor (not shown) sets the discharge signal to a non-operating state in ST1 and sets the charging signal 51 to an operating state in ST2 to start charging the electrostatic actuator 27. In ST3, the charging time (Tc) is set. Then, in ST4, the time-up of the timer is detected, and in ST5, the charging signal is set to the non-operating state and the charging is stopped. At this time ST
In step 6, it is determined from the specifications of the printer whether or not the hold state is provided. If the hold state is provided, the hold time (Th) is set in the timer, and ST8
The hold state is maintained until the time-up is detected at. After the time-up is detected or when the specification is such that the hold state is not provided, in ST9, the discharge signal 52 is set to the operating state and discharging is performed.

In the timing chart of the present embodiment shown in FIG. 11, as is clear from the signal S2 indicating the charge / discharge state, in the present embodiment, from the time of discharging until the start of the next charging, That is, the discharge state is maintained from t14 to t12. As a result, the impedance between the electrodes of the electrostatic actuator is kept low, and external noise,
It is possible to prevent malfunction due to the influence of induced noise or the like.

(Embodiment 2) In the above embodiment, the voltage of the power supply used for charging the electrostatic actuator is assumed not to change, but in an actual printer, the power supply voltage is initially set due to various factors. It also changes dynamically. In this case, it is necessary to change the charging condition as described below.

FIG. 14 is a simple model for obtaining the displacement of the diaphragm of the electrostatic actuator. Here, m is the sum of the inertance of the ink and the mass of the diaphragm, r is the flow path resistance of the ink, C0 is the compliance of the diaphragm, e is the dielectric constant, and Vh is applied between the diaphragm and the electrode. Voltage, G is the gap length between the diaphragm and the electrode, and x is the displacement of the diaphragm. Equation (3) is obtained by obtaining the equation of motion based on this model.

[0070]

[Equation 3]

Also,

[0072]

[Equation 4]

Here, Vs is the voltage of the power supply used for charging,
R is the resistance value of the charging resistor 43, and C is the electrostatic capacitance of the electrostatic actuator.

As is clear from the equations (3) and (4), the displacement amount x of the diaphragm 5 depends on the power supply voltage Vs, and therefore the contact time for the diaphragm 5 to contact the electrodes is also the power supply. It varies depending on the voltage Vs. FIG. 15 shows an example of the relationship between the power supply voltage and the contact time. In this example, the above constants are as follows.

M = 1.0 × 10 ⁸ [Kg / m ⁴ ] r = 1.5 × 10 ¹² [N · s / m ⁵ ] C 0 = 2.5 × 10 ^-18 [m ⁵ / N] R = 3.9 [KΩ] According to FIG. 15, the contact time changes at a rate of 2 us per 1 V in the vicinity of the normal drive voltage of 30 V. Therefore, in order to avoid this contact, the charging time depends on the power supply voltage. It is necessary to change the charging condition, for example, the charging resistance value or the charging time.

The present embodiment and the following embodiments are made in consideration of such a problem. FIG. 17 is a block diagram showing an ink jet head driving device according to the second embodiment of the present invention, and FIG. 16 is a timing chart showing an ink jet head driving method according to the present embodiment. When the print start signal S1 is sent to the generating means 63, the timing pulse generating means 63 sends the charging signal 51 to the charging circuit 6
4, and charging of the electrostatic actuator 27 is started. The comparison circuit 67 compares the voltage between the terminals of the electrostatic actuator 27 detected by the voltage detection circuit 66 with the voltage value corresponding to the predetermined charge q0, and the charge charged in the electrostatic actuator 27 is a predetermined amount q0. At time t21, the reset signal S4 is sent to the timing pulse generating means 63. As a result, the timing pulse generating means sets the charging signal 51 to the non-operating state and stops charging the electrostatic actuator. Subsequent operations are the same as those in the first embodiment described above.

FIG. 18 shows a circuit example of the voltage detection circuit 66 and the comparison circuit 67 of this embodiment. Electrostatic actuator 27
The voltage between the terminals is divided and then input to the comparator 85 via the voltage follower 84. Then, in the comparator 85, it is compared with the voltage value corresponding to the charge quantity q0. When the comparison result shows that the charging voltage has reached the predetermined value, the comparator 85 sends a low level reset signal to the timing pulse generating means. In the circuit example of the timing pulse generating means of FIGS. 10 and 12, the reset signal is input to the reset terminals of the monostable multivibrators 81 and 82, and the charging signal 51 is in the non-operating state. Further, in the example of the timing pulse generating means using the microprocessor of FIG. 13, the presence or absence of the reset signal is checked in ST4, and if there is the reset signal, the charging is immediately stopped.

As described above, the inter-terminal voltage and the displacement of the diaphragm have a one-to-one correspondence as shown in FIG. 34, and the displacement of the diaphragm can be uniquely derived from the inter-terminal voltage. Also,
The relationship between the inter-terminal voltage and the charge amount is uniquely determined from the displacement amount of the diaphragm as shown in FIG. Therefore, according to the above configuration, the charge pulse is not regulated by time but by the terminal voltage corresponding to the charge amount in a one-to-one manner, so that the displacement amount of the diaphragm 5 can always be accurately grasped, As a result, it is possible to reduce the influence of the variation in the value of the charging resistor 43 and the variation in the drive voltage value, so that more stable ink ejection can be obtained.

By providing a predetermined hold time before the discharge signal is activated, the ink can be ejected more efficiently as described above.

Further, as the means for measuring the amount of charge charged in the electrostatic actuator, it is possible to use means for detecting the integrated value of the charging current instead of the voltage across the terminals of the electrostatic actuator. FIG. 19 shows a block diagram of such a configuration. The timing pulse generating means 63 activates the charging signal 51 at time t20 and sends a reset signal to the current integrating circuit 68. This allows
The charging circuit 64 starts charging the electrostatic actuator,
The current integration circuit 68 starts integration of the charging current to the electrostatic actuator. The integrated value of the charging current, that is, the charge amount of charge is compared with a predetermined charge amount q0 in the comparison circuit 67 to generate a reset signal. Subsequent operations are the same as those in the above-described embodiment of voltage detection.

FIG. 20 shows a circuit example of the current integrating circuit 68. The voltage proportional to the current generated by the current detection resistor 87 provided in the charging path is converted into a current value by the operational amplifier 86 and the constant current driver 90, and the capacitor 88 is converted.
Will be charged. The capacitor 88 is discharged by turning on the discharge transistor 89 by the reset signal from the timing pulse generating means 63. The current proportional to the charging current integrated by the capacitor 88 is compared with a predetermined value by the comparison circuit 67 to generate a reset signal to the timing pulse generation circuit.

(Embodiment 3) In Embodiment 2, a voltage detection circuit or a current integration circuit and a comparison circuit for directly detecting the charged state of the electrostatic actuator 27 are provided for each electrostatic actuator. Becomes complicated.
In order to avoid this, in the present embodiment, an optimum charging time for a driving voltage such as a power supply voltage is set in advance, and the charging time is changed based on information from a means for measuring the driving voltage. Has been done.

FIG. 21 is a block diagram of the electrostatic actuator driving device of this embodiment. When the print start signal S1 is output from the print control device 62, the variable timing pulse generating means 73 fetches information about the printer status from the printer status detecting means 74 for detecting the printer status such as the power supply voltage, and based on this. The optimum charging time for the state of the printer is received from the charging condition storage means 75. Then, thereafter, charging and discharging of the electrostatic actuator are performed based on the charging time as described in the first embodiment. In addition, the charging condition storage means is not only for charging time,
It is also possible to output hold time information. Hereinafter, further details will be described based on actual circuit examples and the like.

FIG. 22 is a flow chart showing the operation procedure when the variable timing pulse generating means is realized by a microprocessor, and FIG. 23 is an example of a circuit for detecting the drive voltage of the electrostatic actuator as an example of the printer state detecting means. Is shown. Upon receiving the print start signal S1, the microprocessor stops discharging in ST31 and simultaneously starts charging in ST32. And
In ST33, the information and the status data regarding the status of the printer are received from the printer status detecting means 74. In this example, the state of the printer is the voltage of the driving power supply. S
At T34, a subroutine for determining the charging time is started. In this subroutine, in ST35, the state data is set to the pointer of the charging time table, and ST
At 36, the table is referenced. In ST37, the charging time data is fetched from the table and passed to the main routine. In the main routine, a series of processing such as timer setting is executed based on this charging time data. The subsequent operation is similar to that of the first embodiment.
When changing the hold time based on the status of the printer, a hold time table is prepared and the same process may be performed when setting the hold time, and the status data is transferred to the pointer of the hold time table. Just do it. In FIG. 23, the A / D converter 9
Reference numeral 9 is for converting the voltage of the driving power source into a digital value after voltage division, and the measuring point of the driving power source is preferably on a common wiring of a plurality of charging circuits 64.

(Embodiment 4) In Embodiments 1 to 3 described above, the value of the charging resistance is an important factor that influences the printing characteristics of the electrostatic actuator type ink jet head.
The reason for this and the method of setting the charging resistance value will be described below.

FIG. 24 is a graph showing changes in the charge amount between the electrode 21 and the diaphragm 5 during charging. In the charging circuit shown in FIG. 7, the charging resistor 43 that determines the time constant during charging
When the value of is small, the change in the charge amount changes as shown by the solid line 55,
When the value of the charging resistor 43 is large, the change in the charge amount changes as shown by the solid line 57.

When the change in the charge amount changes gently as indicated by the solid line 57, sufficient charge for ink suction cannot be obtained at time t41, and therefore the change in volume of the discharge chamber 6 is sufficient to discharge a sufficient amount of ink. In some cases, if the ink is ejected in this state, the print quality may be significantly deteriorated or the ink may not be ejected. Therefore, in order to obtain a sufficient charge, the charge pulse width must be extended until time t43, which impairs the responsiveness of the head and makes it impossible to obtain a desired printing speed. According to the values confirmed by the experiment and calculation, a sufficient amount of ink is sucked if about 90% of the electric charge q1 is charged with respect to the capacity of the capacitor composed of the diaphragm 5-electrode 21. Therefore, if the ratio of the time constant (RC) of the charging circuit consisting of the charging resistance and the electrostatic actuator capacitance and the charging time (T0) is obtained from the equation (5), the equation (6) is obtained, and the maximum charging resistance is obtained. The value is fixed.

[0088]

[Equation 5]

On the other hand, when the change in the amount of charge changes rapidly as shown by the line 91, the ink in the flow path is drawn rapidly to the vicinities of the vibrating plate, as shown in FIG. At this time, a pressure lower than atmospheric pressure (negative pressure) that attempts to suck ink
As a result, bubbles 106 enter from a nozzle communicating with the flow path, or a gas such as nitrogen existing in the ink dissolved in the flow path 106 becomes bubbles 106 due to the rapid vibration of the ink in the flow path and appears in the flow path. As described above, in such a state, the bubble 106 absorbs the pressure acting to push out the generated ink even if the electric charge stored between the diaphragm and the electrode is discharged to return the volume of the flow path to the standby state. As a result, the phenomenon that ink is not ejected occurs. Therefore, it is also necessary to specify the lower limit of the time constant of the charging circuit. According to the results confirmed by the experiment, even when the gas such as nitrogen contained in the ink is removed by the degassing process to make it difficult to foam, when the negative pressure of 2 × 10 5 Pascal or more is applied, the ink flow Bubbles are generated in the passage, making it impossible to eject ink.

The electrostatic actuator type ink jet head used in the experiment was carried out under the conditions that the head applied voltage was 30 V, the charging time T0 was 15 μsec, and the resistance 43 was 50 Ω. A discharge was obtained. At this time, the capacitance of the capacitor composed of the electrode 21 and the diaphragm 5 was measured to be about 270.
When the time constant is calculated at about pF, 0.0135 μse
It will be about c.

Therefore, in the method of driving the ink jet head of the present invention, the value of the charging resistor 43 is defined so that the upper limit of the time constant of the charging circuit is ½ or less of the charging pulse width, and the lower limit is the ink when sucking ink. Stable ink ejection can be obtained by limiting the negative pressure applied to the ink to 2 × 10 5 Pascal or less.

(Embodiment 5) FIG. 27 is a block diagram showing a method of driving an ink jet head according to a fifth embodiment of the present invention, and FIG. 26 is a timing chart showing a method of driving an ink jet head according to the fifth embodiment. And
This is an example applied to the serial type printer shown in FIG.

The configuration and operation of this embodiment will be described below with reference to FIGS. 27 and 26.

The feature of this embodiment is that the electrostatic actuator 27 is used.
The variable voltage charging circuit 71 is used as a charging circuit for charging the battery, and the variable voltage charging circuit is provided with the target value generating means 70 for outputting the target value of the charging voltage according to the elapsed time from the start of charging. is there. When the print control device 62 moves the carriage to a predetermined print position, the print start signal S1 is sent to one or a plurality of electrostatic actuator drive devices 40 corresponding to the dots to be printed at time t50.
Is sent. When the timing pulse generating means 63 in the electrostatic actuator driving device receives the print start signal S1, it sends an activation signal to the target value generating means 70.
As described above, the target value generating means generates a target voltage as shown in FIG. 26, for example, corresponding to the elapsed time from the time when the activation signal is received, and supplies it to the voltage variable charging circuit 71. In response to this, the voltage variable charging circuit 71 supplies the charging voltage according to the target value to the electrostatic actuator.

At time t51, when the activation signal from the timing pulse generating means 63 becomes inactive, the target value generating means 70 stops the generation of the target value and the voltage variable charging circuit 71 charges the electrostatic actuator. Stop. The subsequent discharge operation of the electrostatic actuator is the same as in the first embodiment described above.
And the same as 2.

FIG. 28 is a circuit example of the target value generating means 70 and the voltage variable charging circuit 71 of this embodiment. The activation signal from the timing pulse generating means 63 is connected to the reset input of the counter 91, and when the activation signal becomes the operating state, the counter 91 starts its operation. That is, the counting of the clock signal supplied from the transmitting circuit 94 is started. The count output of the counter 91 is a binary output and is input to the address input of the memory 92 in which the target value data is stored. Therefore, the address of the memory is updated every predetermined number of clocks from the transmission circuit 94, and the target value data stored at the address is supplied to the digital input of the D / A converter 93. And D /
The target value is output as a voltage from the A converter 93.
When the activation signal becomes inactive, the counter 91 is reset, and the target value data stored at address 00H of the memory 92 is input to the digital input of the D / A converter. Therefore, the charging of the electrostatic actuator can be stopped by storing the data for setting the charging voltage to 0 at the address.

The variable voltage charging circuit 71 is a constant voltage driver that attenuates the output voltage and feeds it back, and can obtain an output voltage proportional to the target value voltage from the D / A converter 93.

FIG. 29 shows another example of the target value generating means 70 of this embodiment, which is an example using a well-known microprocessor. At time t50, the print start signal S1 is output from the print control device 62, and the timing pulse generating means 63 is generated.
When the activation signal is output from the microprocessor,
At T21, the address pointer of the table storing the target value data is initialized. Then, in ST22, the address is updated, in ST23, the data stored in the address is read from the table and is output to the D / A converter. Next, at ST24, a predetermined time interval (Ti) suitable for updating the target value.
Is set to the timer, and in ST25, it waits until the time is up. When the time-up is detected, it is judged in ST26 whether or not the data in the target value table has ended. If not completed, the process loops to ST22 to output the next target value, and if completed, the charging voltage in ST27. The data that sets 0 is output and the generation of the target value is completed.

FIG. 30 shows a modified example of this embodiment. Instead of the target value of the charging voltage of the electrostatic actuator, the target value of the charge amount of charge is generated, and the difference between the target value and the integral value of the charging current is calculated. By supplying only the charging current, the charge amount of the electrostatic actuator corresponding to the elapsed time from the start of charging is controlled.

The target value generating means uses the circuit example or the control sequence of the microprocessor as it is. When the timing pulse generating means 63 sends the activation signal to the target value generating means, the target value generating means generates the target value of the charge amount corresponding to the elapsed time as described above. On the other hand, the current integration circuit 68 described in the second embodiment receives the activation signal from the timing pulse generation means 63 and starts integration of the charging current, and outputs the output from the current variable charging circuit 7.
It returns to the command value of 2 charging current. That is, the difference between the target value of the charge amount supplied from the target value generating means 70 and the charge amount charged in the electrostatic actuator fed back from the current integrating circuit 72 is the current command value of the current variable charging circuit. Has become. As a result, the electrostatic actuator 2
The amount of charge charged in 7 is controlled so that it is always equal to the target value from the target value generating means 70.

FIG. 31 shows a circuit example of the current variable charging circuit. The current command value obtained as the difference between the target value and the integrated current value by the differential amplifier 96 is attenuated and then level-shifted by the level converter 97, and the constant current driver 9
8 is input. Thereby, the charging current corresponding to the current command value is obtained.

In the above embodiment, the content of the memory 92 or the target value table storing the target value is set so that the negative pressure applied to the ink at the time of ink suction becomes 2 × 10 ⁵ Pascal or less and sufficient for ink ejection. It is set so that the amount of charge for ink suction is charged between the electrode 21 and the diaphragm 5.

By performing feedback control of the amount of charge charged between the electrode 21 and the diaphragm 5 in this manner, the amount of charge finally charged between the electrode 21 and the diaphragm 5 is adjusted.
Does not come into contact with the electrode 21 and is charged with an amount of electric charge that can be sufficiently sucked to eject ink, and always secure an appropriate gap,
It is possible to obtain stable ink ejection.

(Embodiment 6) Although the electromechanical characteristics of the electrostatic actuator and the characteristics such as the viscosity of the ink are constant in the above embodiments, in reality, variations in manufacturing lots, changes with time, Since there is a temperature change, when setting the charging time and the target value, these are taken into consideration and the setting is made closer to the safe side than the optimum value. As mentioned above,
In an electrostatic actuator type inkjet head, it is desirable to control the diaphragm and the electrode so that they are as close as possible to each other within a range where they do not come into contact with each other. This means that the distance at the time of the closest approach is set to be large, and drive efficiency and print quality are sacrificed. Further, even if the contact does not occur, the fact that the closest distance is not constant means that the printing quality such as the printing density is not stable, and improvement in practical use is desired.

In view of such a problem, in the present embodiment, as shown in FIG. 32, in addition to the configuration of the fifth embodiment, the printer state detecting means 74, the variable timing pulse generating means 73 and the charging condition storage described in the third embodiment are stored. With the means 75,
The target value generating means is variable target value generating means capable of changing the target value according to the state of the printer. As a result, it is possible to flexibly deal with a change in ink viscosity that cannot be dealt with only by changing the charging time.

An example of the variable target value generating means is shown in FIG.
In the example of the target value generating means using the microprocessor shown in FIG. 1, in the table address initialization processing of ST21, the status data from the printer status detecting means is fetched and the corresponding target value is prepared from a plurality of target value tables prepared in advance. Make sure you select a value table. Subsequent processing is the same as the flowchart shown in FIG. In addition to the specific example of detecting the printer state shown in FIG. 23, a well-known temperature detector such as a thermistor is arranged in the vicinity of the inkjet head in order to detect the temperature change of the viscosity of the ink, for example, and its output Means such as digitizing the voltage by an A / D converter and inputting it to a microprocessor can be used.

The detection of the printer status includes the detection of the printer setting status. That is, when the common inkjet head and the driving device are used in the printers having different specifications, the driving device controls the power supply voltage of the printer, the printing density,
It is possible to detect the specifications of the recording medium used and the like from the setting state of the DIP switch of the printer and select the driving conditions suitable for these.

As described above, the present invention has been made to solve the driving problem that must be solved when the electrostatic actuator is applied to the ink jet head of an actual printer. It has been possible to realize a practical inkjet head driving device using the above and an inkjet printer using the same.

[0109]

As described above, the ink jet printer of the present invention has the charging speed control means for controlling the charging speed of the electric charges for the electrostatic actuator and the discharging means for discharging the electric charges for the electrostatic actuator. It becomes possible to control the operating speed of the electrostatic actuator, and it is possible to stabilize the suction and ejection of ink by the inkjet head.

Further, since the charging speed control means is configured to control the charging speed in the vicinity of the electrodes of the diaphragm to be smaller than the discharging speed of the electric charges for the electrostatic actuator, the suction speed of the ink by the ink jet head is set to the ink level. It is possible to achieve a stable ink ejection by utilizing the difference in flow path impedance between the nozzle and the orifice.

Further, since the charging speed control means is constructed so as to control the charging speed so that the pressure in the ink flow path is kept below 2 × 10 ⁵ pascals, the charging speed control means in the ink flow path at the time of ink suction is controlled. Generation of bubbles and suction of air from the nozzle can be prevented, and stable ink ejection can be obtained.

In these ink jet printers, the charging speed control means includes a target value generating means for generating a target value of the electric charge for charging the electrostatic actuator, a target value of the electric charge and an amount of the electric charge charged in the electrostatic actuator. Since it is composed of a target charge charging circuit that charges the electrostatic actuators so as to be equal, the charge speed can be controlled more accurately by controlling the target value of the charge charge, and the above effect is further enhanced. Can be increased.

In this ink jet printer, the target value generating means is configured to change the target value to be output according to the elapsed time from the charge start timing, so that the target value of the charge charge can be changed from time to time. Therefore, the charging speed can be controlled to obtain the above-described effects.

Further, these ink jet printers further include printer state detection means for detecting the state of the ink jet printer, and charge condition storage means for storing charge / discharge conditions of the electrostatic actuator according to the state of the printer. Since the target value generating means is a variable target value generating means for generating the target value of the charging charge based on the charging / discharging condition from the charging condition storing means in accordance with the detection value of the printer state detecting means, the operating environment of the inkjet printer If the operating conditions such as the above are different, or if the conditions change during use, the optimum charging conditions corresponding to them can be set and the electrostatic actuator can be controlled based on that, and the above effects continue. Can be obtained stably.

Further, these ink jet printers further include charge / discharge timing control means for controlling the timing of starting and stopping charging by the charging speed control means and the timing of starting discharge by the discharging means, so these timings are controlled. As a result, it is possible to obtain the optimum drive timing of the inkjet head in consideration of the vibration of the ink and the displacement amount of the diaphragm.

Furthermore, in this ink jet printer, since the charge / discharge timing control means is configured to provide a hold time during which charging / discharging is not performed between charging stop and discharging, the ink with respect to the displacement of the diaphragm is set. It is possible to correct the phase delay of the vibration, and it is possible to effectively use the vibration energy of the ink for ejecting the ink.

In these ink jet printers, the charging time constant, which is determined by the charging resistance and the electrostatic capacity of the electrostatic actuator, is set to approximately one half or less of the charging time of the electrostatic actuator. It is possible to charge a sufficient amount of electric charge within a predetermined charging time in order to obtain the required amount of operation of the electrostatic actuator, and it is possible to fully exert the capacity of the electrostatic actuator.

Further, a charge amount detecting means for detecting the charge amount charged in the electrostatic actuator and a comparing means for comparing the charge amount detected by the charge amount detecting means with a predetermined value are further provided. Since the discharge timing control means is configured to stop charging the electrostatic actuator based on the output of the comparison means, it is possible to immediately stop charging when the charge amount reaches a predetermined value. By accurately controlling the displacement amount of the diaphragm and operating it in the range where it does not contact the counter electrode, it is possible to obtain an inkjet head with a long life and high reliability.

Further, it further comprises a printer status detecting means for detecting the status of the ink jet printer, and a charging condition storing means for storing charging / discharging conditions of the electrostatic actuator according to the status of the printer. ,
Since the charging / discharging timing of the electrostatic actuator is controlled based on the charging / discharging conditions from the charging condition storing means according to the detection value of the printer state detecting means, the operating conditions such as the operating environment of the printer vary. Even if it is changed, optimum inkjet print head drive conditions are generated, and by controlling the charge / discharge timing of the electrostatic actuator accordingly, the influence of the operating environment of the printer is eliminated, and it is more stable. It is possible to obtain various ink ejections.

According to another invention of the present application, in the above ink jet printer, charging means for charging the electrostatic actuator with electric charge, discharging means for discharging the electric charge, and timing for starting and stopping charging by the charging means. And a charging / discharging timing control means for controlling the timing of starting and stopping the discharging by the discharging means, and the charging / discharging timing control means is configured to stop the discharging immediately before the charging of the electrostatic actuator is started. Therefore, it is possible to prevent charges from being stored between the electrodes of the electrostatic actuator between the time of discharging and the start of the next charging, and it is possible to prevent malfunction of the electrostatic actuator due to external noise or inductive noise. .

Further, in the control method of the ink jet printer according to the present invention, the first step of starting the charging of the electrostatic actuator by the charging speed control means and the stopping of the charging of the electrostatic actuator by the charging speed control means. The vibrating plate has a second step, a third step of keeping the charging speed control means and the discharging means inactive for a predetermined time, and a fourth step of discharging the electrostatic actuator by the discharging means. 3rd phase delay of ink vibration to
In this step, the vibration energy of the ink can be effectively used for ejecting the ink.

In another aspect, the target value of the charging charge is determined based on the first step of starting the charging of the electrostatic actuator by the target value generating means and the target charge charging circuit and the state of the ink jet printer. The second step, the third step of outputting the target value of the charge to be charged from the target value generating means, the fourth step of stopping the charging operation by the target charge charging circuit, and the discharging of the electrostatic actuator by the discharging means. And the fifth step for performing the above, it is possible to determine the optimum target value for the state of the inkjet printer prior to the generation of the target value, and it is possible to always obtain stable ink ejection.

Furthermore, the first step of starting charging of the electrostatic actuator by the charging means, the second step of stopping charging of the electrostatic actuator by the charging means, and the discharging of the electrostatic actuator by the discharging means. And a fourth step of stopping the discharge from the electrostatic actuator by the discharging means. The fourth step is the first step.
Since it is performed immediately before the step of, the electrostatic actuator can be kept in the discharge state between the discharge of the electrostatic actuator and the start of the next charging, and the electrostatic actuator is in the non-operation state. However, it is possible to prevent malfunction due to the influence of external noise or inductive noise.

Further, according to the present invention, when the ink jet head which uses electrostatic force for ink ejection is driven, the gap between the electrode and the diaphragm when the diaphragm is bent most and approaches the electrode at the end of charging. Since it is always constant and a minute distance where the electrode and the diaphragm do not come into contact with each other can be secured, the fluctuation of the ink ejection amount and the speed is small, and the printing quality is improved. Further, it is possible to solve a problem peculiar to an inkjet head that uses electrostatic force, that is, the diaphragm and the electrode come into contact with each other to cause a short circuit, and the head is destroyed. Therefore, the durability and reliability of the head can be improved and the driving voltage can be reduced It also has the effect.

Further, according to the above-described method for driving an ink jet head of the present invention, a charging circuit for charging the electrodes and the diaphragm with electric charges is connected to the electrodes and the diaphragm, and the diaphragm is attracted to the electrodes to suck the ink. At the position where the flexed diaphragm does not come into contact with the electrodes and is capable of sucking a sufficient amount of ink for ejection, the connection with the charging circuit is cut off and ink suction is stopped. After holding this state for a certain period of time until the amplitude becomes maximum, connect a discharge circuit that discharges the electric charge stored in the electrode and the diaphragm to the electrode or the diaphragm, and store the electric charge stored between the electrode and the diaphragm. By virtue of the driving method that pressurizes ink and discharges ink droplets by abruptly discharging, it is prevented that the vibrating plate and the electrode come into contact with each other to cause a short circuit and the head is destroyed. Can be efficiently utilized in the ink discharge, there is an effect that it is possible to drive at a low voltage.

Furthermore, according to the above-described method for driving the ink jet head of the present invention, the charging pulse between the electrode and the diaphragm is raised with the inclination of a predetermined range, so that air bubbles are generated in the flow path and the ink is discharged. It is possible to obtain sufficient responsiveness to improve the printing speed of the printer without sacrificing the printing quality without causing the problem of being unable to eject the ink and sucking the ink enough to eject the ink. Produce an effect.

[Brief description of drawings]

FIG. 1 is an exploded perspective view of an inkjet head used in an inkjet printer according to the present invention.

FIG. 2 is a sectional side view of an inkjet head according to the inkjet printer of the present invention.

FIG. 3 is a view taken along the line AA of FIG.

FIG. 4 is a partial detailed schematic diagram of a diaphragm and an individual electrode according to the inkjet printer of the present invention.

FIG. 5 is a functional block diagram of an inkjet printer according to the present invention.

FIG. 6 is a block diagram of an electrostatic actuator driving device according to a first embodiment of the present invention.

FIG. 7 is a circuit diagram showing an example of a charging circuit and a discharging circuit of the electrostatic actuator driving device according to the first embodiment of the present invention.

FIG. 8 is a timing chart showing an input signal to the electrostatic actuator drive device according to the present invention, a voltage waveform of a diaphragm-electrode, and vibration of a meniscus of ink formed at a tip of a nozzle.

FIG. 9 is a cross-sectional side view of the inkjet head showing the operating principle of the first embodiment.

FIG. 10 is a circuit diagram showing a circuit example of timing pulse generating means of the electrostatic actuator driving device according to the present invention.

FIG. 11 is a timing chart showing an input signal to the electrostatic actuator driving device and a voltage waveform of a diaphragm-electrode according to the first embodiment of the present invention.

FIG. 12 is a circuit diagram showing a circuit example of a timing pulse generating means of the electrostatic actuator drive device according to the present invention.

FIG. 13 is a circuit diagram showing an example of a timing pulse generating means of the electrostatic actuator driving device according to the present invention.

FIG. 14 is a diagram showing a simple model for obtaining the displacement of the diaphragm of the electrostatic actuator.

FIG. 15 is a diagram showing a relationship between a drive voltage applied to an electrostatic actuator and a diaphragm-electrode contact time.

16 is a timing diagram showing an input signal to the electrostatic actuator driving device shown in FIGS. 17 and 19 and a voltage waveform of a diaphragm-electrode according to the present invention.

FIG. 17 is a block diagram of an electrostatic actuator driving device according to a third embodiment of the present invention.

FIG. 18 is a diagram showing a circuit example of a voltage detection circuit and a comparison circuit of the electrostatic actuator drive device according to the present invention.

FIG. 19 is a block diagram of another electrostatic actuator drive device according to the third embodiment of the present invention.

FIG. 20 is a diagram showing a circuit example of a current integration circuit and a comparison circuit of the electrostatic actuator drive device according to the present invention.

FIG. 21 is a block diagram of another electrostatic actuator driving device according to the fourth embodiment of the present invention.

FIG. 22 is a diagram showing an example of a variable timing pulse generating means and a charging condition storing means of the electrostatic actuator driving device according to the present invention.

FIG. 23 is a circuit diagram showing a circuit example of printer state detection means of the electrostatic actuator driving device according to the present invention.

FIG. 24 is a diagram showing changes in the charge amount between the electrode 21 and the diaphragm 5 when the inkjet head is charged, with respect to the charging resistance value of the inkjet printer of the present invention.

FIG. 25 is a sectional side view of an inkjet head in which bubbles are generated in a flow path.

FIG. 26 is a timing chart showing an input signal to the electrostatic actuator driving device and a diaphragm-electrode voltage waveform according to the fifth embodiment of the present invention.

FIG. 27 is a block diagram of an electrostatic actuator driving device according to a fifth embodiment of the present invention.

FIG. 28 is a circuit diagram showing a circuit example of a target value generating means and a voltage variable charging circuit of the electrostatic actuator driving device according to the present invention.

FIG. 29 is a diagram showing another example of the target value generating means of the electrostatic actuator driving device according to the present invention.

FIG. 30 is a block diagram of another electrostatic actuator drive device according to the fifth embodiment of the present invention.

FIG. 31 is a circuit diagram showing a circuit example of a variable current charging circuit of the electrostatic actuator driving device according to the present invention.

FIG. 32 is a block diagram of an electrostatic actuator driving device according to a sixth embodiment of the present invention.

FIG. 33 is a diagram showing an outline of the mechanism of the inkjet printer of the present invention.

FIG. 34 is a characteristic diagram showing the relationship between the displacement amount of the diaphragm and the electrostatic attraction force and the restoring force of the diaphragm.

FIG. 35 is a characteristic diagram showing the relationship between the displacement of the diaphragm and the electrostatic capacitance of the actuator.

[Explanation of symbols]

1 1st board 2 2nd board 3 3rd board 4 Nozzle hole 5 Vibrating plate 6 Discharge chamber 9 Vibrating chamber 10 Inkjet head 21 Individual electrode 24 Insulating film 27 Electrostatic actuator 40 Electrostatic actuator drive device 41 Inverter 42, 45 transistor 43 charge resistance 44 buffer 46, 47 discharge resistance 51 charge signal 52 discharge signal 53 electrode-vibration plate voltage (Vh) 61 print request device 62 print control device 63 timing pulse generating means 64 charge circuit 65 discharge circuit 66 voltage detection Circuits 67, 69 Comparison circuit 68 Current integration circuit 70 Target value generation means 71 Voltage variable charging circuit 72 Current variable charging circuit 73 Variable timing pulse generation means 74 Printer state detection means 75 Charge / discharge condition storage means 76 Variable target value generation means 81, 82,83 Monostable circle Vibrator 84, 86, 90, 95, 96, 97, 98 Operational amplifier 85 Comparator 87 Current detection resistor 88 Current integration capacitor 89 Discharge transistor 91 Counter 92 Memory 93 D / A converter 94 Oscillator 99 A / D converter 102 Meniscus 103 Ink 104 Ink droplet 105 Recording paper 302 Carriage 310 Carriage drive means

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Naoki Kobayashi 3-3-5 Yamato, Suwa-shi, Nagano Seiko Epson Co., Ltd. (72) Inventor Asahiro Oguchi 3-3-5 Yamato, Suwa-shi, Nagano Seiko Epson Within the corporation

Claims (15)

[Claims] 1. A nozzle, an ink flow path communicating with the nozzle, a vibrating plate provided in a part of the ink flow path, and the vibrating plate facing the vibrating plate and outside the ink flow path. An inkjet head having an electrostatic actuator composed of electrodes provided is provided, and a voltage is applied to the electrostatic actuator to deform the diaphragm by electrostatic force, and ink droplets are ejected from the nozzles to perform printing. An inkjet printer for performing the above-mentioned inkjet printer, comprising: a charging speed control unit that controls a charging speed of electric charges to the electrostatic actuator; and a discharging unit that discharges electric charges to the electrostatic actuator. 2. The ink jet printer according to claim 1, wherein the charging speed control means is configured to control the charging speed in the vicinity of the electrodes of the diaphragm to be smaller than a discharging speed of electric charges to the electrostatic actuator. Inkjet printer characterized by 3. The ink jet printer according to claim 1, wherein the charging speed control means is configured to control the charging speed so that the pressure in the ink flow path is maintained at 2 × 10 ⁵ Pascal or less. Inkjet printer characterized by. 4. The ink jet printer according to claim 1, wherein the charging speed control unit includes a target value generation unit that generates a target value of the electric charge with which the electrostatic actuator is charged, the target value of the electric charge, and the target value of the electric charge. An inkjet printer, comprising: a target charge charging circuit that charges the electrostatic actuator so that the amount of charge charged in the electrostatic actuator becomes equal. 5. The inkjet printer according to claim 4, wherein the target value generating means is configured to change the target value to be output according to the elapsed time from the charging start timing. Printer. 6. The ink jet printer according to claim 4 or 5, wherein a printer state detection unit that detects a state of the ink jet printer, and a charging condition that stores a charging / discharging condition of the electrostatic actuator according to the state of the printer. The target value generating means is configured to generate a target value of the charged electric charge based on the charging / discharging condition from the charging condition storing means according to the detection value of the printer state detecting means. An inkjet printer characterized by being used as a target value generating means. 7. The ink jet printer according to claim 1, further comprising a charging / discharging timing control unit that controls timing of starting and stopping charging by the charging speed control unit and timing of starting discharging by the discharging unit. Inkjet printer characterized by. 8. The ink jet printer according to claim 7, wherein the charging / discharging timing control means is configured to provide a hold time during which charging / discharging is not performed between charging stop and discharging. And inkjet printer. 9. The ink jet printer according to claim 7, wherein a charging time constant determined by the charging resistance and the electrostatic capacitance of the electrostatic actuator is approximately one half of the charging time of the electrostatic actuator. An inkjet printer characterized by the following. 10. The ink jet printer according to claim 7, wherein a charge amount detecting means for detecting the charge amount charged in the electrostatic actuator, a charge amount detected by the charge amount detecting means and a predetermined value. An ink jet printer, further comprising: a comparison unit that compares the charge and discharge timing control unit based on an output of the comparison unit. 11. The ink jet printer according to claim 7 or 8, wherein a printer state detection unit that detects a state of the ink jet printer, and a charging condition that stores a charging / discharging condition of the electrostatic actuator according to the state of the printer. The charging / discharging timing control means is further provided with a storage means for charging and discharging the electrostatic actuator based on the charging / discharging condition from the charging condition storing means according to the detection value of the printer state detecting means. An inkjet printer characterized in that it is configured to control timing. 12. A nozzle, an ink flow path communicating with the nozzle, a vibrating plate provided in a part of the ink flow path, and the vibrating plate facing the vibrating plate and outside the ink flow path. An inkjet head having an electrostatic actuator including an electrode provided, and a voltage is applied to the electrostatic actuator to deform the diaphragm by an electrostatic force,
In an inkjet printer that performs printing by ejecting ink droplets from the nozzles, a charging unit that charges the electrostatic actuator with electric charges, a discharging unit that discharges electric charges with respect to the electrostatic actuator, and a charging unit that performs charging by the charging unit. A charge / discharge timing control means for controlling the start and stop timings and the start and stop timings of the discharge by the discharge means, wherein the charge / discharge timing control means performs the discharge immediately before the start of charging the electrostatic actuator. An inkjet printer characterized in that it is configured to stop. 13. A nozzle, an ink flow path communicating with the nozzle, a vibration plate provided in a part of the ink flow path, the vibration plate and the vibration plate facing the vibration plate and outside the ink flow path. An inkjet head having an electrostatic actuator including an electrode provided, and a voltage is applied to the electrostatic actuator to deform the diaphragm by an electrostatic force,
An inkjet printer that ejects ink droplets from the nozzles to perform printing, comprising a charging speed control unit that controls a charging speed of electric charges for the electrostatic actuator, and a discharging unit that discharges electric charges for the electrostatic actuator. A method of controlling an inkjet printer, comprising: a charging / discharging timing control unit that controls the timing of starting and stopping charging by the charging speed control unit and the timing of starting discharging by the discharging unit. The first step of starting the charging, the second step of stopping the charging of the electrostatic actuator by the charging speed control means, the charging speed control means and the discharging means are inactive for a predetermined time. And the electrostatic actuation by the discharging means. And a fourth step of discharging the data. 14. A nozzle, an ink flow path communicating with the nozzle, a vibration plate provided in a part of the ink flow path, the vibration plate and the vibration plate facing the vibration plate and outside the ink flow path. An inkjet head having an electrostatic actuator including an electrode provided, and a voltage is applied to the electrostatic actuator to deform the diaphragm by an electrostatic force,
An ink jet printer for ejecting ink droplets from the nozzle to perform printing, comprising: target value generating means for generating a target value of electric charge for charging the electrostatic actuator; and a target value of the electric charge and charging of the electrostatic actuator. A target charge charging circuit that charges the electrostatic actuator so that the generated charge amount becomes equal, a discharging unit that discharges the electric charge to the electrostatic actuator, the target value generating unit, and the target charge. Charging / discharging timing control means for controlling the timing of starting and stopping charging by the charging circuit and the timing of starting discharging by the discharging means,
A method for controlling an inkjet printer, comprising: a printer status detecting unit that detects a status of the inkjet printer; and a charging condition storage unit that stores charging and discharging conditions of the electrostatic actuator according to the status of the inkjet printer. A first step of starting charging of the electrostatic actuator by the generating means and the target charge charging circuit; a second step of determining a target value of the charged charge based on the state of the inkjet printer; A third step of outputting the target value of the charged electric charge from the value generating means, a fourth step of stopping the charging operation by the target electric charge charging circuit, and a fifth step of discharging the electrostatic actuator by the discharging means. And a method of controlling an inkjet printer. 15. A nozzle, an ink flow path communicating with the nozzle, a vibrating plate provided in a part of the ink flow path, and the vibrating plate facing the vibrating plate and outside the ink flow path. An inkjet head having an electrostatic actuator including an electrode provided, and a voltage is applied to the electrostatic actuator to deform the diaphragm by an electrostatic force,
An inkjet printer that ejects ink droplets from the nozzle to perform printing, comprising: charging means for charging the electrostatic actuator with electric charge; discharging means for discharging electric charge with respect to the electrostatic actuator; and the charging means. A method of controlling an inkjet printer, comprising: a charging / discharging timing control means for controlling the timing of starting and stopping charging and the timing of starting and stopping discharging by the discharging means, wherein charging of the electrostatic actuator by the charging means is started. A second step of stopping the charging of the electrostatic actuator by the charging means, a third step of starting the discharging of the electrostatic actuator by the discharging means, and the discharging means. The fourth to stop the discharge from the electrostatic actuator by And a step, wherein the fourth step is performed immediately before the first step.