JP2008023873A - Actuator driver, liquid discharging apparatus, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an actuator driver which drives and controls an electrostatic actuator by suppressing the occurrence of residual charges without lowering a driving frequency, and also to provide a liquid discharging apparatus having the driver and an electrostatic liquid discharging head and an image forming apparatus. <P>SOLUTION: In the driver, drive waveforms include pulse patterns PP1 to PP3, and a first to sixth pulses P1 to P6 constituting the pulse patterns PP1 to PP3 are generated and outputted in one drive cycle. Each of the pulse patterns PP1, PP2, and PP3 includes a pulse(s) having a positive polarity potential and a pulse(s) having a negative polarity potential in such a manner that PP2 has the same number, and PP1 and PP3 have the number more by one, and the numbers of pulses included through all the pulse patterns PP1 to PP3 have the relation where the number (three) of pulses having the positive polarity potential and that (three) having the negative polarity potential are the same. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an actuator driving device, a liquid ejecting apparatus, and an image forming apparatus, and more particularly to an actuator driving device for an electrostatic actuator, a liquid ejecting apparatus including an electrostatic liquid ejecting head, and an image forming apparatus.

  For example, as an image forming apparatus such as a printer, a facsimile machine, a copying apparatus, a plotter, etc., a nozzle that discharges a recording liquid droplet and a liquid chamber (discharge chamber, pressure chamber, pressurizing chamber, ink flow path) communicating with the nozzle are used. And a variable electrode constituting at least a part of the diaphragm forming the wall surface of the liquid chamber, and a counter electrode facing the variable electrode, and a voltage is applied between the electrodes. As a recording head, an electrostatic liquid discharge head having an electrostatic actuator that displaces the variable electrode (vibrating plate) with electrostatic force and generates pressure in the liquid chamber by the mechanical restoring force of the vibrating plate There is something installed.

  In such a recording liquid discharge type image forming apparatus, gradation recording is indispensable for forming a high-quality image. Therefore, as a method for performing multi-value recording (halftone recording), a density has been conventionally used. A density modulation method that changes the density by using a plurality of inks of the same color of different colors, a dot number modulation method that modulates the dot size by forming a plurality of minute dots at substantially the same position, and a plurality of capacities ( The liquid discharge head is driven by a dot diameter modulation method that divides ink droplets (droplet volume) and modulates the size of the dots.

  Among these modulation methods, the density modulation method is technically difficult to achieve, but it is necessary to allocate a certain number of nozzles according to the increased number of ink colors, and the cost of the head increases accordingly. Alternatively, it is inevitable that the printing speed decreases as a result of reducing the number of assigned nozzles for each color. The dot number modulation method and the dot diameter modulation method are halftone recording methods effective for achieving both image quality and printing speed without increasing the head cost.

  Therefore, as described in Patent Document 1, conventionally, as a head drive device that performs drive control by a dot diameter modulation method using an electrostatic liquid discharge head, a plurality of pulsed drive voltages are applied, It is known that the diaphragm is restored every time when the pressure fluctuation in the liquid chamber becomes positive pressure, and a large droplet is ejected or ejected and then combined into a large droplet during flight.

As a method for forming a small droplet, as described in Patent Document 1, a liquid called a suppression pulse is added to a single pulse for ejecting a droplet, followed by a liquid ejected by a single pulse. There is known a method of ejecting a droplet of about 1/2 that is smaller than the droplet volume.
JP 2002-096466 A

  By the way, in the electrostatic actuator, when the driving method in which the variable electrode is brought into contact with the counter electrode side is employed, if a potential having the same polarity is continuously applied, a residual charge is generated in the insulating film formed on the electrode. As a result, in the case of the liquid discharge head, there arises a problem that the characteristics of the discharged droplets change with time.

Therefore, in Patent Document 2, if the pulse for ejecting a droplet is the first electric pulse, the polarity is opposite to that of the first electric pulse, and the voltage is higher than the voltage at which the diaphragm (variable electrode) contacts the facing surface. It is described that the residual electric charge is removed by applying a second electric pulse at a voltage of 1 and not discharging a droplet for each dot or line.
Japanese Patent No. 3252608

Patent Document 3 describes that two drops are used to form one dot, and the residual charge is suppressed by reversing the direction of the voltage applied when these two drops are formed. ing.
Japanese Patent No. 3536483

  As in the prior art described above, it is effective to apply pulse voltages having different polarities in order to remove residual charges.

  However, as described in Patent Document 2, applying a pulse voltage only to remove residual charges requires time for that purpose, leading to a reduction in driving frequency.

  In addition, as described in Patent Document 3, two drops are required to form one dot in order to suppress the generation of residual charges, resulting in a decrease in driving frequency, and a dot diameter modulation method is adopted. In this case, the number of pulses applied to form one dot is not always an even number, and there is a problem that it cannot be applied.

  Further, the countermeasures for residual charges as described above are considered to be absolutely necessary for electrostatic actuators that are very prone to generate residual charges. This is over-spec for the actuator, and as a result, the drive frequency of the actuator is lowered.

  The present invention has been made in view of the above problems, and an actuator driving device capable of driving and controlling an electrostatic actuator by suppressing the generation of residual charges without lowering the driving frequency, and the actuator driving device and the electrostatic type. It is an object of the present invention to provide a liquid discharge apparatus and an image forming apparatus including a liquid discharge head.

  In order to solve the above problems, an actuator driving apparatus according to the present invention is an actuator driving apparatus that generates and outputs a plurality of pulse patterns including one to a plurality of pulses within one driving cycle to drive an electrostatic actuator. Each pulse pattern includes pulses having the same number or one having one more potential than the other and having a positive potential and pulses having a negative potential, and the number of pulses included in all pulse patterns is positive. The number of pulses having a negative potential and the number of pulses having a negative potential are the same, or one is one more than the other.

  A liquid ejection apparatus according to the present invention includes an electrostatic liquid ejection head including an electrostatic actuator and an actuator driving apparatus according to the present invention.

  An image forming apparatus according to the present invention includes an electrostatic liquid discharge head including an electrostatic actuator and an actuator driving device according to the present invention.

  According to the actuator driving apparatus according to the present invention, for a plurality of pulse patterns including one to a plurality of pulses generated and output within one driving cycle, each pulse pattern has the same number or a relationship in which one is one more than the other. The number of pulses included in all pulse patterns includes the number of pulses having a positive potential and the number of pulses having a negative potential. Since the same or one has a relationship of one more than the other, generation of residual charges can be suppressed without lowering the driving frequency.

  According to the liquid ejection apparatus according to the present invention and the image forming apparatus according to the present invention, since the actuator driving apparatus according to the present invention is provided, it is possible to eject liquid droplets at a high driving frequency.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. First, an example of the configuration of a liquid discharge apparatus including an electrostatic liquid discharge head to which the present invention is applied will be described with reference to FIG.

  The liquid discharge head 10 forms a nozzle plate 2 on which nozzles 1 for discharging recording liquid droplets are formed, a flow path plate 4 that forms a liquid chamber 3 that communicates with the nozzles 1, and a wall surface of the liquid chamber 3. A diaphragm 5 that is a variable electrode, and a support substrate 8 that is provided with a counter electrode 7 that faces the diaphragm 5 that is a variable electrode with a predetermined gap 6 therebetween. Here, the diaphragm 5 which is a variable electrode and the counter electrode 7 constitute an electrostatic actuator.

  The entire diaphragm 5 can be a variable electrode, or a part of the diaphragm 5 can be a variable electrode. Further, the diaphragm 5 can be formed integrally with the flow path plate 4 by anisotropic etching of a silicon substrate, or can be formed integrally with the support substrate 8 using sacrificial layer etching.

  An electrostatic force is applied between the diaphragm 5 and the counter electrode 7 by applying a predetermined drive pulse from the actuator driving device 11 between the diaphragm 5 which is a variable electrode of the liquid discharge head 10 and the counter electrode 7. Is generated until the diaphragm 5 comes into contact with the counter electrode 7 (the state shown in the broken line), and the electrostatic force disappears when the drive pulse falls, so that the diaphragm 5 is liquidated by its own restoring force. Since the liquid is restored to the chamber 3 side, the recording liquid (hereinafter also referred to as “ink”) in the liquid chamber 3 is pressurized by the mechanical force of the vibration plate 5, and the liquid droplet 9 (or liquid droplet) is discharged from the nozzle 1. A plurality of continuous droplets such as 9a and 9b) are ejected and land on the recording medium P.

  Here, as shown in FIG. 2, the actuator driving apparatus 11 according to the present invention generates and outputs a drive waveform generation unit 12 that generates and outputs a plurality of pulse patterns including one to a plurality of pulses within one drive cycle, and a drive waveform generation. A selection unit 13 that selects a pulse included in a required pulse pattern from the drive waveform output from the unit 12 and applies the selected pulse to the electrostatic actuator 14 of the liquid ejection head 10 according to the selection signal. ing. One electrostatic actuator 14 is constituted by the diaphragm 5 and one counter electrode 7 facing the diaphragm 5, and the liquid ejection head 10 has a plurality of electrostatic actuators 14.

  The drive waveform generator 11 includes storage means such as a ROM for storing pulse pattern waveform data, D / A conversion means for D / A converting waveform data of a required pulse pattern read from the storage means, voltage It is composed of an amplifier, a current amplifier and the like. The selection unit 13 includes a shift register, a latch circuit, an analog switch, and the like that input image data for driving a required actuator of the liquid ejection head 10, and outputs a pulse output from the drive waveform generation unit 11 as an image. Select according to the data.

A first example of the drive waveform generated and output by the drive waveform generation unit 12 will be described with reference to FIG.
In this example, the driving waveform is used to divide droplets of three sizes, small droplets, medium droplets, and large droplets. This driving waveform includes a pulse pattern PP1 for forming a small droplet, a pulse pattern PP2 for forming a medium droplet, and a pulse pattern PP3 for forming a large droplet, and these pulse patterns PP1 to PP3 are configured. The first to sixth pulses P1 to P6 are generated and output within one driving cycle. Note that one driving cycle is one printing cycle, and one printing cycle is a time interval for each actuator to form each dot on the medium and is equal to a time obtained by reversing the driving frequency of the liquid ejection head. .

  Here, the pulse pattern PP1 for small droplets is composed of only the first pulse P1, the pulse pattern PP2 for medium droplets is composed of the second and third pulses P2, P3, and the pulse pattern PP3 for large droplets is the fourth to fourth pulses. It consists of 6 pulses P4 to P6. The first pulse P1 constituting the pulse pattern PP1 for small droplets is positive, the second pulse P2 constituting the pulse pattern PP2 for medium drops is positive, the third pulse P3 is negative, and the pulse pattern PP3 for large drops The fourth pulse P4 constituting the negative polarity is negative, the fifth pulse P5 is positive, and the sixth pulse P6 is negative.

  That is, each pulse pattern PP1, PP2, PP3 has the same number (in the case of PP2) or one pulse having a positive potential and one in the negative relationship (in the case of PP1, PP3). The number of pulses included in all pulse patterns PP1 to PP3 is the same as the number of pulses having a positive potential (three) and the number of pulses having a negative potential (three). It is.

  Then, one electrode of the liquid ejection head 10 (for example, the diaphragm 5 serving as a movable electrode) is set as a ground potential, and the other electrode (for example, the counter electrode 7) is set as an individual electrode, and the pulse pattern of the potential A shown in FIG. A required pulse pattern is selected from PP1 to PP3 and a pulse included in the pulse pattern is applied.

  In this case, in the pulse pattern PP2, since pulses P2 and P3 having different polarities are applied one by one, a total of two pulses are applied, even if the diaphragm 5 is in contact with the counter electrode 7 side, the residual charge in the insulating film 7A There is no occurrence.

  On the other hand, in the pulse patterns PP1 and PP3, the number of pulses of one polarity is one more, that is, the pulse pattern P1 has one positive pulse and the pulse pattern PP3 has one negative pulse. It has become.

  Therefore, for example, in a certain actuator (a part constituted by the diaphragm 5 and one counter electrode 7), if voltage application of the pulse pattern PP1 is continued, residual charges are generated. However, in the actuator, the voltage application of the pulse pattern PP1 cannot be semi-infinite.

  Therefore, if the actuator is difficult to generate a residual charge to some extent, the number of positive pulses and the number of negative pulses are the same for each pulse pattern, or there is only one more pulse of one polarity. When all pulses included in all pulse patterns are viewed, the number of positive pulses and the number of negative pulses are the same, or the number of pulses of one polarity is increased by one. In the short term, almost no residual charge is generated.

  On the other hand, it has been found that the residual charge generated in the actuator decreases very slowly if left without being driven. Accordingly, from a long-term viewpoint such as half year, one year, and two years including the time when the liquid discharge head is not used, if the residual charge generated by driving is small, it can be ignored.

  Therefore, when driving an actuator that hardly generates residual charges to some extent, the number of positive pulses and the number of negative pulses are the same for each pulse pattern, or the number of pulses of one polarity is only one, and When all pulses included in all pulse patterns are viewed, use drive waveforms that have the same number of positive pulses as the number of negative pulses or one more pulse of one polarity. Therefore, practically, the generation of the residual charge can be sufficiently suppressed, and the actuator can be driven while minimizing the influence of the residual charge without lowering the driving frequency.

  Here, the number of pulses is counted as a pulse having a voltage value equal to or higher than the minimum drive voltage value at which a droplet can be ejected, and is intended only for the oscillation of the liquid in the liquid chamber, for example. Pulses are not counted in the number of pulses.

Next, a second example of the drive waveform will be described with reference to FIG.
This example is a driving waveform using the suppression pulse described in Patent Document 1. This drive waveform includes a pulse pattern PP2 for forming a medium drop, a pulse pattern PP3 for forming a large drop, and a pulse pattern PP1 for forming a small drop. These pulse patterns PP1 to PP3. The first to fourth pulses P11 to P14 and the suppression pulse P15 constituting the same are generated and output within one driving cycle. Note that the sizes of “small droplet”, “medium droplet”, and “large droplet” in this example are relatively smaller than in the case of the driving waveform of the first example.

  Here, the medium droplet pulse pattern PP2 is composed of only the first pulse P11, and the large droplet pulse pattern PP3 is composed of the first, second, and third pulses P11, P12, and P13, and the small droplet pulse pattern PP1. Consists of a fourth pulse P14 and a suppression pulse P15. The first pulse P11 constituting the medium drop pulse pattern PP2 is positive, the first pulse P11 constituting the large drop pulse pattern PP3 is positive, and the second and third pulses P12 and P13 are negative. The fourth pulse P14 constituting the drop pulse pattern PP1 has a positive polarity, and the suppression pulse P15 has a negative polarity.

  In this case, each pulse pattern PP1, PP2, PP3 has the same number (in the case of PP1) or one more than the other (in the case of PP2, PP3) and a pulse having a positive potential and a negative potential. The number of pulses included in all the pulse patterns PP1 to PP3 is the same as the number of pulses having a positive potential (3) and the number of pulses having a negative potential (3). It is a relationship. As a supplementary explanation, the drive waveform includes five pulses of the first to fifth pulses P11 to P15. The pulse pattern PP1 has two pulses, the pulse pattern PP2 has one pulse, and the pulse pattern PP3 has three pulses. (Including one pulse of the pulse pattern PP2), the “number of pulses included in all pulse patterns” is a total of 6 pulses included in the three pulse patterns PP1 to PP3.

  Thus, again, each pulse pattern includes a pulse having a positive potential and a pulse having a negative potential in the same number or one more than the other, and all pulse patterns are included in all pulse patterns. The number of pulses included is the same as the number of pulses having a positive potential and the number of pulses having a negative potential, or one is one more than the other. Can be driven.

  When the suppression pulse is used, the post-pulse of the two pulses constituting the pulse pattern 1 to which the suppression pulse method is applied has a short pulse width (PW15 <PW14 in the example of FIG. 4). When the “number of pulses included in the pattern” is an odd number, it is preferable to increase the number of pulses having the same polarity as the subsequent pulse of the suppression pulse by one.

Next, a third example of the drive waveform will be described with reference to FIG.
This drive waveform is an example in the case where the potential applied to the common electrode is not the ground potential. A pulse of one potential (for example, potential A) is applied to the individual electrode of each actuator, and the reverse polarity is applied to the common electrode. A pulse of potential (potential B) is applied. Also here, an example using the suppression pulse method (pulse pattern PP1) is used. In the figure, the magnitudes of the potential A and the potential B are expressed in substantially the same way, but it is not always necessary.

  This drive waveform includes a pulse pattern PP2 for forming a medium droplet, a pulse pattern PP3 for forming a large droplet, and a pulse pattern PP1 for forming a small droplet. The first to third pulses P21A to P23A and the suppression pulse P24A constituting the pulse patterns PP1 to PP3 as the pulse of the potential A are used as the first to third pulses constituting the pulse patterns PP1 to PP3 as the pulse of the potential B. The pulses P21B to P23B and the suppression pulse P24B are generated and output within one driving cycle. Note that the sizes of “small droplet”, “medium droplet”, and “large droplet” in this example are also relatively smaller than in the case of the driving waveform of the first example.

  Here, the medium droplet pulse pattern PP2 is composed of first pulses P21A and P21B, and the large droplet pulse pattern PP3 is composed of first to third pulses P21A to P23A and P21B to P23B. Consists of a third pulse P23A, a suppression pulse P24A, a third pulse P23B, and a suppression pulse P24B.

  The first pulse P21A of the potential A constituting the medium droplet pulse pattern PP2 is positive, the first pulse P21B of the potential B is negative, and the first pulse P21A of the potential A constituting the large droplet pulse pattern PP3. Is positive, first pulse P21B at potential B is negative, second and third pulses P22A and P23A at potential A are negative, and second and third pulses P22B and P23B at potential B are positive and for droplets The third pulse P23A of potential A constituting the pulse pattern PP1 is negative, the third pulse P23B of potential B is positive, the suppression pulse P24A of potential A is positive, and the suppression pulse P24B of potential B is negative.

  In this case, each pulse pattern PP1, PP2, PP3 includes the same number of pulses having a positive potential and a pulse having a negative potential, and the number of pulses included in all the pulse patterns PP1 to PP3 is The number of pulses having a positive potential and the number of pulses having a negative potential have the same relationship. Therefore, it is possible to drive at a high driving frequency while suppressing residual charges.

  Note that the potential applied to the common electrode has such a magnitude that droplets cannot be ejected only by the voltage. Therefore, the liquid droplet is discharged only when a potential having a polarity opposite to that applied to the common electrode is also applied to the individual electrode. Here, even when a pulse voltage is not applied to the individual electrodes, four pulses are applied to the common electrode every printing cycle. When a pulse is not applied to the individual electrode and a pulse is applied to the common electrode, droplets are not ejected, but the liquid in the flow path system can be stirred so that the liquid viscosity in the vicinity of the nozzle does not increase, It is convenient as an actuator.

Next, a fourth example of the drive waveform will be described with reference to FIG.
This drive waveform is also an example in the case where the potential applied to the common electrode is not the ground potential, and a pulse of one potential (for example, potential A) is applied to the individual electrode of each actuator, and the reverse polarity is applied to the common electrode. A pulse of potential (potential B) is applied. Here, an example in which the suppression pulse method (pulse pattern PP1) is not used is shown. In the figure, the magnitudes of the potential A and the potential B are expressed in substantially the same way, but it is not always necessary.

  This drive waveform includes a pulse pattern PP1 for forming a small droplet, a pulse pattern PP2 for forming a medium droplet, and a pulse pattern PP3 for forming a large droplet. The first to fourth pulses P31A to P34A constituting the pulse patterns PP1 to PP3 as the pulses of the potential A, and the first to fourth pulses P31B to P34B constituting the pulse patterns PP1 to PP3 as the pulses of the potential B. Are generated and output within one driving cycle.

  Here, the droplet pattern PP1 is composed of first pulses P31A and P31B. The medium drop pulse pattern PP2 is composed of first pulses P31A and P31B and second pulses P32A and P32B, and the large drop pulse pattern PP3 is composed of first to fourth pulses P31A to P34A and P31B to P34B.

  The first pulse P31A having the potential A constituting the droplet pattern PP1 has a negative polarity, the first pulse P31B having the potential B has a positive polarity, and the first pulse P31A having the potential A constituting the pulse pattern PP2 for the medium droplet has a negative polarity. Positive polarity, first pulse P31B of potential B is negative polarity, second pulse P32A of potential A is negative polarity, second pulse P32B of potential B is positive polarity, and the pulse pattern PP3 for large droplets is the first pulse of potential A. One pulse P31A is positive, first pulse P31B at potential B is negative, second pulse P32A at potential A is negative, second pulse P32B at potential B is positive, and third pulse P33A at potential A is positive. The third pulse P33B at the potential B is negative, the fourth pulse P34A at the potential A is negative, and the fourth pulse P34B at the potential B is positive.

  In this case, each pulse pattern PP1, PP2, PP3 includes the same number of pulses having a positive potential and a pulse having a negative potential, and the number of pulses included in all the pulse patterns PP1 to PP3 is Since the number of pulses having a positive potential and the number of pulses having a negative potential are the same, it is possible to drive at a high driving frequency while suppressing residual charges.

  In each of the above examples, three examples of pulse patterns have been described. However, the present invention is not limited to this.

Next, specific examples will be described.
(Example 1)
An outline of a manufacturing process of the electrostatic actuator constituting the liquid ejection head used in Example 1 will be described with reference to FIGS. In this electrostatic actuator, a gap between the diaphragm and the counter electrode is formed by sacrificial layer etching.
First, as shown in FIG. 7A, a thermal oxide film 30 is formed on a silicon substrate (not shown), and polysilicon 31 serving as a counter electrode is laminated on the thermal oxide film 30 to a thickness of 0.5 μm. As shown in FIG. 7B, during driving, the variable electrode and the counter electrode are in contact with each other only via a convex portion provided on the variable electrode side (diaphragm side). A slit 32 is formed to electrically float the corresponding part.

  Thereafter, as shown in FIG. 7C, an HTO 33 serving as an insulating film is laminated with a thickness of 0.15 μm. At this time, since the thickness of the laminated HTO 33 is the same in the slit 32 portion as in the other portions, a step occurs in the slit 32 portion, and a step remains in the material layer laminated thereafter. Not shown.

  Next, as shown in FIG. 7D, after forming polysilicon as a sacrificial layer 34 with a thickness of 0.4 μm in order to form a gap (Gap) space between the opposing electrodes, the opposing electrodes are brought into contact with each other. In order to form a convex portion to be a portion to be formed, a digging portion 35 having a depth of 0.04 μm is formed by etching in a portion corresponding to the convex portion of the sacrificial layer 34 as shown in FIG.

  Thereafter, as shown in FIG. 7F, an HTO 41 serving as an insulating film is laminated with a thickness of 0.15 μm. Again, since the thickness of the stacked HTO 41 is the same as the other portions in the digging portion 35, a step is generated in the digging portion 35, and then a step remains in the laminated material layer. The step is not shown.

  Next, as shown in FIG. 7 (g), polysilicon 42 in which As serving as the conductive layer of the variable electrode is laminated on the HTO 41 with a thickness of 0.2 μm, and as shown in FIG. 8 (a), A slit 43 for electrically floating the convex portion is formed.

Then, as shown in FIG. 8B, Si ₃ N ₄ 44 having a tensile internal stress is formed on the polysilicon 42 to a thickness of 0.12 μm, and on this, HTO 45 is set to a thickness of 0.12 μm as shown in FIG. The layers are sequentially stacked with a thickness of 6 μm. Again, a step is produced in the material laminated on the slit 43, but this is not shown.

  After that, as shown in FIG. 8D, the polysilicon which is the sacrificial layer 34 is removed by ICP through a removal hole (not shown) for removing the sacrificial layer 34 to form a gap space 53. At this time, a convex portion 47 is also formed. Finally, as shown in FIG. 8E, a polyimide layer 46 that is a liquid contact layer is laminated with a thickness of 1 μm, and the electrostatic actuator in which the diaphragm 51 and the counter electrode 52 are opposed to each other through the gap 53 is completed. .

  Although not shown, a liquid discharge head is completed by laminating a flow path plate in which a liquid chamber is formed on the vibration plate 51 side of the electrostatic actuator and a nozzle plate in which a nozzle is formed.

  Note that polysilicon is implanted into the polysilicon 31 and 42 as the conductive layers in order to increase the conductivity. A water repellent material is applied in the gap space 53 in order to prevent the variable electrode (vibrating plate) 51 from sticking to the opposing surface.

(Example 2)
An outline of a manufacturing process of the electrostatic actuator constituting the liquid ejection head used in Example 2 will be described with reference to FIGS. In this electrostatic actuator, a gap between the diaphragm and the counter electrode is formed by sacrificial layer etching.
First, as shown in FIG. 9A, a thermal oxide film 30 is formed on a silicon substrate (not shown), and a polysilicon 31 serving as a counter electrode is laminated on the thermal oxide film 30 to a thickness of 0.5 μm. Thereafter, as shown in FIG. 9bc), an HTO 33 serving as an insulating film is laminated with a thickness of 0.15 μm.

  Next, as shown in FIG. 9C, in order to form a gap (Gap) space between the opposing electrodes, polysilicon as a sacrificial layer 34 is stacked with a thickness of 0.4 μm. Thereafter, as shown in FIG. 9D, an HTO 41 serving as an insulating film is laminated with a thickness of 0.15 μm.

Next, as shown in FIG. 9E, a polysilicon layer 42 having a thickness of 0.2 .mu.m is laminated on the HTO 41 with As implanted as a conductive layer of the variable electrode. Then, as shown in FIG. 10A, Si ₃ N ₄ 44 having a tensile internal stress is formed on the polysilicon 42 to a thickness of 0.12 μm, and on this, HTO 45 is set to a thickness of 0.12 μm as shown in FIG. The layers are sequentially stacked with a thickness of 6 μm.

  Thereafter, as shown in FIG. 10C, the polysilicon which is the sacrificial layer 34 is removed by ICP through a removal hole (not shown) for removing the sacrificial layer 34 to form a gap space 53. Finally, as shown in FIG. 10D, a polyimide layer 46 that is a liquid contact layer is laminated to a thickness of 1 μm, and the electrostatic actuator in which the diaphragm 51 and the counter electrode 52 face each other through the gap 53 is completed. .

  Although not shown, a liquid discharge head is completed by laminating a flow path plate in which a liquid chamber is formed on the vibration plate 51 side of the electrostatic actuator and a nozzle plate in which a nozzle is formed.

  Therefore, using the electrostatic actuators of Examples 1 and 2, it was evaluated how much residual charge was generated in the actuator when only one polarity pulse was applied. The results for Example 1 are shown in FIG. 11, and the results for Example 2 are shown in FIG.

  The driving conditions for the electrostatic actuator of Example 1 were as follows: driving voltage +67 V (positive polarity), driving frequency 61 kHz, pulse width 6 μs, driving time 23.7 hours, driving frequency 5.2E + 9 times. The driving conditions for the electrostatic actuator of Example 2 were as follows: driving voltage +67 V (positive polarity), driving frequency 61 kHz, pulse width 6 μs, driving time 5 minutes, driving frequency 3.6E + 7 times.

  Thus, in both Examples 1 and 2, a positive pulse voltage is applied at a frequency of 61 kHz. In this case, in the electrostatic actuator of Example 2, the voltage at which the variable electrode is brought into contact with the opposing surface is 61.4 V → 64.4 V and increased by 3.0 V with the number of driving times of 3.6E + 7. That is, a residual charge of 3.0V is generated. On the other hand, in the electrostatic actuator of Example 1, the voltage at which the variable electrode abuts against the opposing surface is 61.4V → 63.9V, increasing by 2.5V when the number of driving times is 5.2E + 9. . From this result, it can be seen that the configuration of the electrostatic actuator of Example 1 is a configuration in which residual charges are less likely to be generated than the configuration of the electrostatic actuator of Example 2.

  On the other hand, depending on the configuration of the actuator, when the drive voltage value is changed by 3 to 5 V, the speed of the ejected droplet changes by approximately 1 m / s. Therefore, in Example 2, when the continuous driving is performed for about 15 minutes (20 kHz) with only the voltage having the same polarity, the speed of the ejected droplet is reduced by 1 m / s. In an actual liquid ejecting apparatus, it is fully possible that a voltage having the same polarity is continuously applied to a certain actuator for a while. Therefore, in order to use an actuator having a configuration in which residual charge is likely to be generated as in the second embodiment, for example, the residual charge can be canceled for each printing (while one dot is formed) or each time the carriage is reciprocated once. It is necessary to do so.

  Next, the actuator having the configuration of the first embodiment will be considered. The driving frequency of current image forming apparatuses such as an ink jet printer is 30 kHz or less, and the total number of dots in a normal chart is at most on the order of 1E + 5 although it depends on the image. Therefore, in consideration of the above evaluation results, when the liquid ejection head including the actuator of Example 1 is mounted on the image forming apparatus, it is treated from the short-term viewpoint that the droplet ejection characteristics due to residual charges are not substantially changed. be able to.

  On the other hand, although it is not possible to indicate the degree as data, it has been found that the residual charge generated in the actuator decreases very slowly if left without being driven. Therefore, if the residual charge generated by the drive is very small like the actuator of the configuration of the first embodiment, this slight amount is seen from a long-term viewpoint such as half a year including the time when the image forming apparatus is not used. Residual charge can be ignored.

  In other words, by driving the electrostatic actuator that is unlikely to generate residual charges as in the configuration of the first embodiment by applying the driving waveform according to the present invention, the residual (which affects the droplet ejection characteristics) is substantially reduced. Generation of electric charges can be suppressed.

Next, an example of an image forming apparatus including the liquid ejection apparatus according to the present invention on which the head drive control device for the liquid ejection head according to the present invention is mounted will be described with reference to FIGS. FIG. 13 is an explanatory side view for explaining the overall configuration of the image forming apparatus according to the present invention, and FIG. 14 is an explanatory plan view of the main part of the apparatus.
In this image forming apparatus, a carriage 103 is slidably held in a main scanning direction by a guide rod 101 and a guide rail 102 that are horizontally mounted on left and right side plates (not shown). Moving and scanning is performed in the direction indicated by the arrow (main scanning direction) in FIG. 14 via a timing belt 105 stretched between 106 and a driven pulley 107.

  For example, four recording heads 107 each including a liquid discharge head that discharges yellow (Y), cyan (C), magenta (M), and black (Bk) ink droplets are provided on the carriage 103. The outlets are arranged in a direction crossing the main scanning direction, and the ink droplet ejection direction is directed downward. As the liquid discharge head constituting the recording head 107, the electrostatic liquid discharge head including the electrostatic actuator is used as described above. Note that the recording head can also be configured by one or a plurality of liquid ejection heads provided with a plurality of nozzle rows that eject different colors.

  The carriage 103 is equipped with a sub tank 108 for each color for supplying each color ink to the recording head 107. Ink is supplied to the sub tank 108 from a main tank (ink cartridge) (not shown) via an ink supply tube 109.

  On the other hand, as a paper feeding unit for feeding paper 112 stacked on a paper stacking unit (pressure plate) 111 such as a paper feeding cassette 110, a half-moon roller (separately feeding paper 112 one by one from the paper stacking unit 111) A separation pad 114 made of a material having a large friction coefficient is provided opposite to the sheet feeding roller 113 and the sheet feeding roller 113, and the separation pad 114 is urged toward the sheet feeding roller 113 side.

  As a transport unit for transporting the paper 112 fed from the paper feed unit below the recording head 107, a transport belt 121 for electrostatically attracting and transporting the paper 112, and a paper feed unit A counter roller 122 for transporting the paper 112 fed through the guide 115 while sandwiching it between the transport belt 121 and the paper 112 fed substantially vertically upward is changed by about 90 ° and copied on the transport belt 121. A conveying guide 123 for adjusting the pressure and a tip pressure roller 125 urged toward the conveying belt 121 by a pressing member 124. In addition, a charging roller 126 for charging the surface of the conveyance belt 121 is provided.

  Here, the conveyance belt 121 is an endless belt, is stretched between the conveyance roller 127 and the tension roller 128, and the conveyance roller 127 is rotated from the sub-scanning motor 131 via the timing belt 132 and the timing roller 133. By doing so, it is configured to circulate in the belt conveyance direction (sub-scanning direction) of FIG. A guide member 129 is disposed on the back side of the conveyance belt 121 in correspondence with the image forming area formed by the recording head 107.

  Further, as shown in FIG. 13, an encoder scale 142 having slits is provided on the front side of the carriage 103, and an encoder sensor comprising a transmission type photosensor that detects the slits of the encoder scale 142 on the front side of the carriage 103. The encoder 144 for detecting the position of the carriage 103 in the main scanning direction is configured by these.

  Further, as a paper discharge unit for discharging the paper 112 recorded by the recording head 107, a separation unit for separating the paper 112 from the conveying belt 121, a paper discharge roller 152 and a paper discharge roller 153, and paper discharge A paper discharge tray 154 for stocking the paper 112 to be printed.

  A double-sided paper feeding unit 161 is detachably attached to the back. The double-sided paper feeding unit 161 takes in the paper 112 returned by the reverse rotation of the transport belt 121, reverses it, and feeds it again between the counter roller 122 and the transport belt 121.

  Further, a maintenance / recovery mechanism 191 for maintaining and recovering the nozzle state of the recording head 107 is disposed in a non-printing area on one side of the carriage 103 in the scanning direction.

  The maintenance and recovery mechanism 191 includes caps 192a to 192d for capping each nozzle surface of the recording head 107 (referred to as “cap 192” when not distinguished) and a wiper that is a blade member for wiping the nozzle surface. A blade 193 and a blank discharge receptacle 194 for receiving droplets when performing blank discharge for discharging droplets that do not contribute to recording in order to discharge the thickened recording liquid are provided.

  In the image forming apparatus configured as described above, the sheets 112 are separated and fed one by one from the sheet feeding unit, and the sheet 112 fed substantially vertically upward is guided by the guide 115, and includes the conveyance belt 121 and the counter roller 122. The leading end is guided by the conveying guide 123 and pressed against the conveying belt 121 by the leading end pressure roller 125, and the conveying direction is changed by approximately 90 °.

  At this time, a charging voltage pattern in which a positive output and a negative output are alternately repeated from the AC bias supply unit of the control unit (not shown) to the charging roller 126, that is, an alternating voltage is applied, and the conveying belt 21 is alternating. That is, plus and minus are alternately charged in a band shape with a predetermined width in the sub-scanning direction which is the circumferential direction. When the paper 112 is fed onto the conveyance belt 121 charged alternately with plus and minus, the paper 112 is attracted to the conveyance belt 121 by electrostatic force, and the paper 112 is conveyed in the sub-scanning direction by the circular movement of the conveyance belt 121. Is done.

  Therefore, by driving the recording head 107 according to the image signal while moving the carriage 103, ink droplets are ejected onto the stopped paper 112 to record one line, and after the paper 112 is conveyed by a predetermined amount, Record the next line. Upon receiving a recording end signal or a signal that the trailing edge of the paper 112 has reached the recording area, the recording operation is finished, and the paper 112 is discharged onto the paper discharge tray 154.

  In the case of double-sided printing, when recording on the front surface (surface to be printed first) is completed, the recording belt 112 is fed into the double-sided paper feeding unit 161 by rotating the conveyor belt 121 in the reverse direction. The paper 112 is reversed (with the back surface being the printing surface), and is fed again between the counter roller 122 and the conveyor belt 121. The timing is controlled, and the sheet is conveyed onto the conveyor bell 121 as described above. After recording on the back side, the sheet is discharged to the discharge tray 154.

  Further, during printing (recording) standby, the carriage 103 is moved to the maintenance / recovery mechanism 191 side, the nozzle surface of the recording head 107 is capped by the cap 192, and the nozzles are kept in a wet state. To prevent. In addition, the recording liquid is sucked from the nozzle in a state where the recording head 107 is capped with the cap 192 (referred to as “nozzle suction” or “head suction”), and a recovery operation is performed to discharge the thickened recording liquid or bubbles. Wiping is performed by the wiper blade 193 in order to clean and remove ink adhering to the nozzle surface of the recording head 107 by this recovery operation. In addition, an idle ejection operation for ejecting ink not related to recording is performed before the start of recording or during recording. Thereby, the stable ejection performance of the recording head 107 is maintained.

Next, an outline of the control unit of the image forming apparatus will be described with reference to FIG. This figure is an overall block diagram of the control unit.
The control unit 200 includes a CPU 201 that controls the entire apparatus, a ROM 202 that stores programs executed by the CPU 201 and other fixed data, a RAM 203 that temporarily stores image data, and the like, while the apparatus is powered off. 1 includes a non-volatile memory (NVRAM) 204 for holding data, an image processing for performing various signal processing and rearrangement on image data, and an ASIC 205 for processing input / output signals for controlling the entire apparatus. Yes.

  The control unit 200 also has an I / F 206 for transmitting and receiving data and signals to and from the host, which is an image processing apparatus (or data processing apparatus) such as a personal computer, and a drive for driving the recording head 107. A drive waveform generation unit 207 that is a means for generating a waveform, a head driver 208 that drives and controls the recording head 107, a main scanning motor drive unit 211 that drives the main scanning motor 104, and a sub-scanning motor 131 are driven. Detection from a sub-scanning motor driving unit 213 for the purpose, an AC bias supply unit 214 for supplying an AC bias voltage to the charging roller 126, an environmental sensor 218 for detecting environmental temperature and / or environmental humidity, and various sensors (not shown). An I / O 216 for inputting a signal is provided.

  The control unit 200 is connected to an operation panel 217 for inputting and displaying information necessary for the apparatus.

  Here, the control unit 200 transmits print data (print data) including image data from the host side such as an image processing apparatus such as a personal computer, an image reading apparatus such as an image scanner, an imaging apparatus such as a digital camera, or the like. The data is received by the I / F 206 via the net.

  The CPU 201 reads and analyzes the print data in the reception buffer included in the I / F 206, performs necessary image processing, data rearrangement processing, and the like in the ASIC 205, and transfers the image data to the head driver 208. The dot pattern data for image output may be generated by storing font data in the ROM 202, for example, or the image data is developed into bitmap data by a host-side printer driver and transferred to this apparatus. You may do it.

  The drive waveform generation unit 207 is configured by a D / A converter that performs D / A conversion on the drive pulse pattern data, and the drive waveform including a plurality of pulse patterns including one to a plurality of pulses is supplied to the head driver 208. Output.

  The head driver 208 selectively selects a plurality of drive pulses constituting a drive waveform provided from the drive waveform generation unit 207 based on image data (dot pattern data) corresponding to one line of the recording head 107 input serially. The head is driven by applying between the diaphragm of the recording head 7 and the counter electrode.

  The CPU 291, the drive waveform generation unit 207, and the head driver 208 of the control unit 200 constitute an actuator driving device according to the present invention that drives a recording head that is a liquid ejection head.

  Therefore, as described above, the drive waveform generated by the drive waveform generation unit 207 has the same number of positive pulses and the number of negative pulses for each pulse pattern, or one more pulse of one polarity. If all of the pulses included in all pulse patterns are seen, the number of positive pulses and the number of negative pulses are the same, or the number of pulses of one polarity is one more drive By using the waveform, it is possible to practically sufficiently suppress the generation of the residual charge, and it is possible to drive the liquid discharge head while minimizing the influence of the residual charge without lowering the driving frequency.

FIG. 5 is a cross-sectional explanatory view along the lateral direction of the liquid chamber showing an example of an electrostatic liquid discharge head to which the present invention is applied. It is explanatory drawing with which it uses for description of the actuator drive device which concerns on this invention. It is explanatory drawing which shows the 1st example of a drive waveform. It is explanatory drawing which shows the 2nd example of a drive waveform. It is explanatory drawing which shows the 3rd example of a drive waveform. It is explanatory drawing which shows the 4th example of a drive waveform. It is sectional explanatory drawing which shows the electrostatic actuator of Example 1 with a manufacturing process. FIG. 8 is a cross-sectional explanatory view showing the process following FIG. 7. It is sectional explanatory drawing which shows the electrostatic actuator of Example 2 with a manufacturing process. FIG. 8 is a cross-sectional explanatory view showing the process following FIG. 7. It is explanatory drawing with which it uses for description of the drive result of the electrostatic actuator of Example 1. FIG. It is explanatory drawing with which it uses for description of the drive result of the electrostatic actuator of Example 2. FIG. 1 is an explanatory side view illustrating an overall configuration of an image forming apparatus according to the present invention. FIG. 2 is an explanatory plan view of a main part of the image forming apparatus. 2 is a block diagram illustrating an overview of a control unit of the image forming apparatus. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Nozzle 2 ... Nozzle plate 3 ... Liquid chamber 4 ... Flow path plate 5 ... Vibrating plate 6 ... Gap 7 ... Counter electrode 10 ... Actuator drive device 11 ... Drive waveform generation part 12 ... Selection part 207 ... Drive waveform generation part 208 ... driver

Claims (3)

In an actuator driving device for driving and generating an electrostatic actuator by generating and outputting a plurality of pulse patterns including one to a plurality of pulses within one driving cycle,
Each pulse pattern includes pulses having the same number or one having one more potential than the other and having a positive potential and pulses having a negative potential, and the number of pulses included in all pulse patterns is positive. An actuator driving device characterized in that the number of pulses having a negative potential and the number of pulses having a negative potential are the same or one is one more than the other.   The actuator driving device according to claim 1, wherein the electrostatic driving device is driven and controlled in a liquid discharging device including a liquid discharging head including an electrostatic actuator and an actuator driving device that drives and controls the electrostatic actuator. A liquid ejecting apparatus comprising the liquid ejecting apparatus. The image forming apparatus for forming an image by ejecting liquid droplets from a liquid ejection head including an electrostatic actuator includes the actuator driving device according to claim 1, wherein the electrostatic actuator is driven and controlled. An image forming apparatus.

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