JP2006175760A - LIQUID DISCHARGE HEAD DRIVING DEVICE AND IMAGE FORMING DEVICE - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a large dot or a dot group corresponding to a large dot, when a drive pulse is applied a plurality of times, an insulating film on the electrode is damaged by long-term driving, and the function of the actuator cannot be maintained.
When three drive pulses are sequentially applied within one drive cycle, the drive pulse voltage has the same polarity as the drive pulse voltage and is greater than 0 in sections (time intervals) Td31 and Td32 between the drive pulses. A drive waveform for applying voltages Vp31d and Vp32d smaller than the pulse potential Vp is applied.
[Selection] Figure 3

Description

  The present invention relates to a liquid ejection head driving apparatus, a liquid ejection apparatus, and an image forming apparatus, and more particularly to a liquid ejection head, a liquid ejection apparatus, and an image forming apparatus that use an electrostatic actuator.

  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. In this way, the variable electrode (vibrating plate) is displaced by an electrostatic force, and pressure is generated in the liquid chamber by the mechanical restoring force of the vibrating plate, thereby including an electrostatic actuator that discharges droplets from the nozzle. Some have an electric liquid discharge head mounted as a recording head.

  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 dot number modulation method substitutes one dot with a plurality of dots, so that the dot shape becomes irregular and the image quality is not sufficient. In addition, although the density modulation method is technically difficult to achieve, it is necessary to assign a certain number of nozzles according to the increased number of ink colors, which increases the cost of the head or the nozzles of each color. As a result of reducing the number of assignments, it is inevitable that the printing speed will decrease. On the other hand, the dot diameter modulation method that separates droplets having different droplet volumes is a halftone recording method that is effective in achieving both image quality and printing speed without increasing the head cost.

Therefore, as a driving device that drives by a dot diameter modulation method using an electrostatic liquid discharge head, conventionally, as described in, for example, Patent Document 1, a plurality of pulsed driving voltages are applied, and a liquid is applied. It is known that the diaphragm is restored every time when the pressure fluctuation in the room becomes positive pressure, and a large droplet is ejected or ejected, and then combined into a large droplet during flight.
JP 2002-113863 A

  In the dot number modulation method or the dot diameter modulation method described above, a plurality of drive pulse applications are required to obtain a large dot or a dot group corresponding to a large dot. On the other hand, the electrostatic actuator is driven by applying a voltage between the electrodes. However, if it is driven for a long time, the insulating film provided on the electrode is damaged by the voltage application, and the function of the electrostatic actuator can be maintained. There is a problem of disappearing.

  Therefore, when the ratio of ejecting large dots to a normal size of dots ejected by applying one drive pulse is large, it is inevitable that the durability (number of times of printing) of the electrostatic actuator is reduced. However, ensuring durability is the most important item even in an electrostatic actuator, and it is difficult to put it to practical use as a liquid discharge head without it.

  As a countermeasure, in order to prevent damage to the electrostatic actuator due to the dielectric breakdown of the insulating film over time, the thickness of the insulating film can be increased or the applied voltage can be lowered. As a result, the applied voltage is increased or the insulating film is thinned. Furthermore, when an electrostatic actuator is used as actuator means of a liquid discharge head, there is a problem that a sufficient discharge force for discharging droplets is required, and the above measures may not satisfy the specifications.

  The present invention has been made in view of the above problems, and a liquid discharge head drive device that prevents damage to the insulating film of an electrostatic actuator and avoids a decrease in durability, and a droplet discharge device including the drive device. An object is to provide an image forming apparatus and an image forming apparatus.

  In order to solve the above-described problem, when a driving waveform including a plurality of driving pulses is applied in one driving cycle, the droplet ejection head driving device according to the present invention applies at least one section among the plurality of driving pulses. Is configured to include means for applying a drive waveform having the same polarity as the previous and subsequent drive pulses and a non-zero potential.

  The liquid ejection apparatus and the image forming apparatus according to the present invention are configured to include the liquid ejection head driving apparatus according to the present invention.

  According to the droplet discharge head drive device, liquid discharge device, and image forming apparatus according to the present invention, when a drive waveform including a plurality of drive pulses is applied within one drive cycle, at least one of the plurality of drive pulses is applied. In one section, a driving waveform having the same polarity as the preceding and following driving pulses and a non-zero potential is applied, so that damage to the insulating film of the electrostatic actuator is reduced, durability is improved, and reliability is improved.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. First, the configuration of an electrostatic liquid discharge head to which the present invention is applied will be described with reference to FIG. FIG. 1 is an explanatory cross-sectional view of the head in the lateral direction of the liquid chamber (nozzle arrangement direction).

  This liquid discharge head 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 composed of a conductive layer 5a and an insulating layer 5b as variable electrodes, and a support substrate 7 provided with a counter electrode 6 facing the diaphragm 5 as a variable electrode with a predetermined gap (gap) 10 therebetween. I have. An insulating film 6 b is formed on the surface of the counter electrode 6. Here, the diaphragm 5 and the counter electrode 6 which are variable electrodes constitute an electrostatic actuator.

  Note that the diaphragm 5 can be a variable electrode as a whole, or a multi-layer structure as described above, and a part of the diaphragm 5 can be a variable electrode. Further, the vibration plate 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 7 using sacrificial layer etching.

  In this liquid discharge head, an electrostatic force is generated between the diaphragm 5 and the counter electrode 6 by applying a predetermined drive pulse from the drive circuit V between the diaphragm 5 which is a variable electrode and the counter electrode 6. As a result, the diaphragm 5 is displaced until it comes into contact with the counter electrode 6 (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. 6, the recording liquid (hereinafter also referred to as “ink”) in the liquid chamber 6 is pressurized by the mechanical force of the vibration plate 5, and the droplet 8 (or droplet 8 a) is discharged from the nozzle 1. , 8b, 8c, etc.) are ejected and land on the recording medium 11.

Here, by applying three driving pulses (pulse voltage) within one printing cycle (within one driving cycle), three dots of a normal size or large dots corresponding to three drops are applied to the recording medium. A drive waveform (hereinafter referred to as “triple pulse”) to be attached will be described.
As shown in FIG. 2A, when three drive pulses are applied within one drive cycle, the application time of each drive pulse is Pw31, Pw32, Pw33, and the interval time between each pulse is Td31, Td32 And The voltage value at Pw ** is expressed as Vp **, and the voltage value at Td ** is expressed as Vp ** d.

  On the other hand, the pulse width of the single pulse in FIG. 2B is Pw11, and the voltage value at that time is Vp11.

  Here, in the triple pulse in FIG. 2A, if Vp31 = Vp32 = Vp33 = Vp, Pw31 = Pw32 = Pw33 = Pw, and the single pulse in FIG. 2B is Vp11 = Vp, Pw11 = Pw When the triple pulse is continuously applied to the electrostatic actuator, the function as the actuator is deteriorated three times faster than when the single pulse is continuously applied.

  That is, in a semiconductor, there is a phenomenon called dielectric breakdown over time with respect to an insulating layer provided between electrodes, and even if the insulating film is not damaged at all by a certain constant voltage Vs applied between the electrodes, this constant voltage Vs. If the voltage is applied for a long time, the insulating film is damaged.

  Considering this, the triple pulse is considered to be damaged earlier because the voltage application time (of the same voltage) is three times longer than that of the single pulse. However, when the durability test of the electrostatic actuator was conducted, the damage to the insulating film was accelerated by triple pulse driving not because the voltage application time was long but because the number of times the pulse voltage was turned on and off was large. Became clear. That is, although a single pulse as shown in FIG. 2C is used, a drive waveform whose pulse width is three times that of each pulse shown in FIG. 2A is used. It was confirmed to have the same degree of durability.

  From this, it is considered that the durability depending on the insulation film damage of the electrostatic actuator greatly depends not on the voltage application time but on the number of ON / OFF times when the voltage is applied and the transition voltage difference between the ON and OFF times. .

  Therefore, when a triple pulse is applied, for example, as shown in FIGS. 3A to 3C, in the time intervals Td31 and Td32 between pulses in at least one section between a plurality of drive pulses, the drive pulse voltage Vp The durability can be improved by applying a voltage Vpd having the same polarity and greater than 0 and smaller than the potential Vp.

  The drive waveform in FIG. 3A is a waveform in which voltages Vp31d and Vp32d having the same polarity as the drive pulse voltage Vp, greater than 0, and less than the voltage Vp are applied at any of the three drive pulse intervals Td31 and Td32. It is what.

  Further, the drive waveform of FIG. 3B is a voltage Vp31d having the same polarity as the drive pulse voltage Vp and greater than 0 and less than the voltage Vp at the interval Td31 among the intervals Td31 and Td32 of the three drive pulses. The voltage Vp32d is set to “0” at the interval Td32.

  Further, the drive waveform of FIG. 3C is a voltage Vp32d having the same polarity as the drive pulse voltage Vp and having a polarity greater than 0 and smaller than the voltage Vp at the interval Td32 among the intervals Td31 and Td32 of the three drive pulses. The voltage Vp31d is set to “0” at the interval Td31.

  That is, by applying such a drive waveform, the number of ON / OFF times at the time of voltage application does not change, but the transition voltage difference at ON / OFF can be reduced, thereby improving durability (number of times of printing). Can be prevented. Of course, it is not preferable that the droplet velocity Vj ejected at this time is different from the velocity in the case of single pulse driving, and thus the voltages Vp31d and Vp32d are limited to a certain value or less.

  As described above, for example, as shown in FIG. 4 (a), the effect of applying a drive waveform having the same polarity as the pulse voltage and a potential higher than 0 in at least one section between the plurality of drive pulses is one. It cannot be obtained by lowering the potential of the drive pulse (Vpd ′) or by putting clogging on the potential Vpd on all the drive pulses as shown in FIG.

  That is, in the drive waveform of FIG. 4A, the diaphragm cannot be sufficiently bent by the second drive pulse, and eventually the discharge efficiency is lowered. This occurs because the δ (displacement) -Vp (voltage value) characteristic (see FIG. 5) of the electrostatic actuator is non-linear.

  More specifically, the displacement amount δ in FIG. 5 is the displacement amount at the variable electrode short side center YA in FIG. When the diaphragm is displaced by 1/3 of the effective gap (eff-Gap) between the electrodes by applying the voltage Vc, the displacement increases discontinuously at a voltage equal to or higher than the voltage Vc. As a result of such non-linearity, the energy (restoring force) stored in the variable electrode of the electrostatic actuator becomes larger as the voltage value becomes higher if the potential difference is constant.

  Therefore, the potential Vpd ′ = voltage difference Vp−Vpd of the second drive pulse in FIG. 3A and the potential of the second pulse = voltage difference Vp−Vpd in FIG. However, since the energy (restoring force) stored in the variable electrode is smaller in the case of FIG. 4A, a sufficient ejection droplet velocity Vj cannot be obtained with the drive waveform of FIG. 4A.

  Further, it has been found that when droplet ejection is performed using the drive waveform shown in FIG. 4B, conditions for ejecting without reducing the droplet velocity cannot be obtained. In this case, although it is not a clear explanation, it is presumed that the discharge efficiency is eventually lowered by restricting the return of the variable electrode in all pulses.

  On the other hand, in consideration of the limitation of the driver IC standard, when the drive waveforms shown in FIGS. 3A to 3C are used, the voltage values of the three pulses are the same in order to increase the return force of the variable electrode. Then, the pulse voltages Vp31d and Vp32d may be changed.

Next, specific examples will be described.
[Example 1]
First, a manufacturing process of a prototype electrostatic actuator will be schematically described with reference to FIGS.
As shown in FIG. 7A, a thermal oxide film 30 is formed on a Si substrate (not shown), and a polysilicon (PolySi) 31 serving as a conductive layer of a counter electrode (fixed electrode) is laminated thereon with a thickness of 0.5 μm. To do. Next, as shown in FIG. 7B, as will be described later, both electrodes are in contact with each other only through a convex portion provided on the variable electrode side during driving, and correspond to the convex portion and the convex portion. A slit 32 is formed to electrically float the portion.

  Thereafter, as shown in FIG. 7C, an HTO 33 serving as an insulating film is laminated to a thickness of 0.2 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 to be laminated thereafter. Not shown.

  Next, as shown in FIG. 7D, after sacrificial layer 34 is laminated with a thickness of 0.4 μm in order to form a gap space (gap) between both electrodes, as shown in FIG. 7E. Thus, in order to form a convex portion that becomes a portion where the two electrodes are brought into contact with each other, the concave portion 35 is etched to a depth of 0.06 μm in a portion corresponding to the convex portion of the sacrificial layer 34.

  Thereafter, as shown in FIG. 8A, an HTO 35 serving as an insulating film is formed on the sacrificial layer 34 to a thickness of 0.2 μm. Again, since the thickness of the stacked HTO 35 is the same in the concave portion 35 as in the other portions, a step occurs in the concave portion 35, and a step remains in the laminated material layer. This step is illustrated. Absent.

  Next, as shown in FIG. 8 (b), polysilicon 37 serving as a conductive layer of the variable electrode is laminated with a thickness of 0.2 μm, and the protrusions are electrically floated as shown in FIG. 8 (c). A slit 38 is formed.

Further, as shown in FIG. 8 (d), Si ₃ N ₄ 38 having a tensile internal stress is 0.12 μm thick on the polysilicon 37, and an HTO 39 is formed thereon as shown in FIG. 9 (a). Sequentially stacked with a thickness of 6 μm. Again, there is a step in the material laminated on the slit 38, but this is not shown.

  Thereafter, as shown in FIG. 9B, the polysilicon 34 as the sacrificial layer is removed by ICP through a removal hole (not shown) for removing the sacrificial layer 34 to form a gap (gap space) 10. To do. At this time, a portion corresponding to the concave portion 35 described above is formed as the convex portion 41. Finally, as shown in FIG. 9C, an electrostatic actuator in which a resin polyimide layer 42 as a liquid contact layer is laminated to a thickness of 1 μm so that the variable electrode 5 and the counter electrode 6 face each other with a gap 3 therebetween. Although not shown in the drawings, a flow path plate and a nozzle plate are sequentially laminated to obtain a liquid discharge head in which a plurality of liquid discharge heads are integrated.

  Note that polysilicon is implanted into the polysilicon layers 31 and 37, which are conductive layers, in order to increase the conductivity. Further, the short side length of the variable electrode = 60 μm and the long side length of the variable electrode = 1200 μm.

  Then, using the above-described electrostatic actuator having the same parameters, a vibration durability test was performed in which the driving conditions were changed and the variable electrode was vibrated. To determine whether the actuator is durable or not, after performing a vibration durability test of the actuator, the variable electrode 1 is removed from the actuator, and the HTO (insulation) formed on the variable electrode (vibrating plate) 5 and the fixed electrode (counter electrode) 6 Evaluation was made based on the presence or absence of damage to the films 36 and 33.

  In addition, although the endurance test in the present embodiment was not performed while discharging droplets, the result of the endurance test in this embodiment is directly linked to the result of the endurance test performed while discharging droplets. . Therefore, the durability of the actuator in the droplet discharge head can also be determined directly from this embodiment.

  The drive waveform is a single pulse having the drive waveform (voltage between pulses is 0 V) in FIG. Table 1 shows driving conditions and durability test results. In addition, when the actuator is driven, the electric field is most applied to the oxide film (insulating film) in a state where the two electrodes are closest to each other, that is, in a state where the two electrodes are in contact with each other through the convex portion. Therefore, the contact time is shown in Table 1 together with the pulse width of the applied pulse voltage.

  From this result, the damage of the oxide film after the test is the largest in the sample of test B, and then the test A, the oxide film damage of tests C, D, and E is small, and the difference between them is difficult to judge. It was.

  From the comparison between these tests A and E, the comparison between tests B and E, and the comparison between tests D and E, the oxide film damage is not the total contact time (approximately the total voltage application time) but the number of applied pulses. It turns out that it depends greatly. Of course, it can be seen from the comparison of tests B and C that the magnitude of the drive voltage also affects the damage to the oxide film.

[Example 2]
The vibration durability test (test F) using the drive waveform of FIG. 2A and the vibration durability test G (test G) using the drive waveform of the present invention of FIG. Compared. Note that the drive frequency is 12.5 kHz (1 printing cycle 80 μs), both test F and G are Vp31 = Vp32 = Vp33 = 63 V, Pw31 = Pw32 = Pw33 = 6 μs, Td31 = Td32 = 10 μs, and Vp31d = Vp32d = 0 V in test F In Test G, Vp31d = Vp32d = 31.5V. Table 2 shows the conditions and results at this time.

  In test G, an extra voltage is applied between Td31 and Td32 with respect to test F, but damage to the oxide film (HTO) is clearly greater in test F, and is a driving waveform according to the present invention. The effect of the drive waveform shown in 3 (a) was confirmed.

Example 3
Using the same electrostatic actuator for the electrostatic ink jet head, the drive conditions were changed, and ink ejection was evaluated. Note that, here, the evaluation is performed under the condition that a plurality of droplets are ejected as one large droplet or one large droplet from the nozzle before reaching the recording medium by triple pulse driving, that is, under the condition of the dot diameter modulation method. The conclusion is the same for the conditions of the dot number modulation method.

  FIG. 10 shows the correlation among the ink droplet velocity (Vj), the ink droplet volume (Mj), and the driving voltage pulse width (Pw11) when the driving waveform (single pulse) in FIG. 2B is used. The drive voltage is Vp11 = 73V.

  In addition, when large droplets are formed using the normal torque pulse driving waveform of FIG. 2A, the correlation between the ink droplet velocity (Vj), the ink droplet volume (Mj), and the driving voltage pulse width (Pw33) is also shown. It is shown in FIG. Table 3 shows the drive waveform conditions at this time.

  What is important here is whether or not there is a condition capable of forming an equivalent drop velocity Vj with the same drive voltage with respect to the drop velocity Vj in the single pulse drive.

  Next, the ink droplet velocity (Vj), ink droplet volume (Mj), and drive voltage pulse width (Pw33) in the case where a large droplet is formed using the torpulle pulse driving waveform shown in FIG. The correlation is shown in FIG. Table 4 shows the drive waveform conditions at this time.

  Here, what is important is whether or not there is a condition capable of forming an equivalent drop velocity Vj with the same drive voltage with respect to the drop velocity Vj in the single pulse drive. As shown in Table 4, it is necessary to slightly change the setting as compared with the case of the drive waveform of FIG. 2A. However, even with the drive waveform of FIG. It can be seen that the droplet can be ejected.

Next, an example of the image forming apparatus according to the present invention on which the liquid ejection head driving device 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 which are horizontally mounted on left and right side plates (not shown), and a timing belt 105 is slid by a main scanning motor 104. 14 is moved and scanned in the direction indicated by the arrow (main scanning direction) in FIG.

  On this carriage 103, for example, four recording heads 107 each comprising a droplet discharge head according to the present invention for discharging yellow (Y), cyan (C), magenta (M), and black (Bk) ink droplets, respectively. Are arranged in a direction crossing the main scanning direction and the ink droplet discharge direction is directed downward.

  As described above, the electrostatic liquid discharge head is used as the liquid discharge head constituting the recording head 107. 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 that is a charging unit 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. 14, a slit disk 134 is attached to the shaft of the transport roller 127, and a sensor 135 that detects the slit of the slit disk 134 is provided. An encoder 136 is configured.

  The charging roller 126 is arranged so as to contact the surface layer of the conveyor belt 121 and rotate following the rotation of the conveyor belt 121, and applies 2.5N to both ends of the shaft as a pressing force.

  Further, as shown in FIG. 14, an encoder scale 142 having slits is provided on the front side of the carriage 103, and an encoder sensor composed of a transmissive 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, as shown in FIG. 14, a maintenance / recovery mechanism 191 for maintaining and recovering the state of the nozzles 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 positive voltage output and a negative output are alternately repeated from the high voltage power supply to the charging roller 126 by a control circuit (not shown), that is, an alternating voltage is applied, and a charging voltage pattern in which the conveying belt 121 alternates, that is, In the sub-scanning direction, which is the circumferential direction, plus and minus are alternately charged in a band shape with a predetermined width. 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 generates 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-scan motor 131 that drives the sub-scanning motor 131. Inputs detection signals from a scanning motor driving unit 213, an AC bias supply unit 214 that supplies an AC bias voltage to the charging roller 126, an environmental sensor 218 that detects environmental temperature and / or environmental humidity, and various sensors (not shown). I / O 216 and the like are 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 includes a D / A converter that performs D / A conversion on the drive pulse pattern data, and has a drive waveform composed of one drive pulse and a plurality of drive pulses that satisfy the above-described conditions. Output to the driver 208.

  The head driver 208 selectively records a drive pulse constituting a drive waveform supplied 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 being applied between the diaphragm of the head 7 and the counter electrode.

  This control unit constitutes a drive device according to the present invention in which a drive waveform is applied to a recording head, which is a liquid ejection head, by a drive waveform generation unit 207 and a head driver 208. Therefore, large droplets can be formed stably, gradation recording with high image quality is possible, and both printing speed and image quality can be achieved.

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 which shows the example from which the drive pulse which comprises the drive waveform which concerns on the comparative example used for the drive of the head differs. It is explanatory drawing which shows the example from which the drive waveform which consists of the triple pulse produced | generated and output with the drive device which concerns on this invention differs. It is explanatory drawing which shows the example from which the drive pulse which comprises the drive waveform which concerns on the other comparative example used for the drive of the head differs. It is explanatory drawing which shows the relationship between the applied voltage and the displacement characteristic (change of a space | gap) of a diaphragm. It is a typical explanatory view of an electrostatic actuator similarly. It is explanatory drawing with which it uses for description of the manufacturing process of an electrostatic actuator. FIG. 8 is also an explanatory diagram for explaining a process subsequent to the process of FIG. 7. FIG. 9 is also an explanatory diagram for explaining a process subsequent to the process of FIG. 8. It is explanatory drawing which shows an example of the measurement result of the drop velocity at the time of using the drive waveform of FIG.2 (b), drop discharge amount-pulse width. It is explanatory drawing which shows an example of the measurement result of drop velocity at the time of using the drive waveform of FIG.2 (c), drop discharge amount-pulse width. It is explanatory drawing which shows an example of the measurement result of the drop velocity at the time of using the drive waveform of Fig.2 (a), drop discharge amount-pulse width. 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 ... Vibration plate 6 ... Counter electrode 207 ... Drive waveform generation part 208 ... Driver

Claims (3)

  A nozzle that ejects a droplet of the recording liquid, a liquid chamber that communicates with the nozzle, a variable electrode that forms at least a part of a diaphragm that forms a wall surface of the liquid chamber, and a counter electrode that faces the variable electrode, And a driving device that drives a liquid discharge head that discharges liquid droplets from the nozzles by a mechanical force when a driving pulse is applied between the electrodes. When applying a driving waveform including a plurality of driving pulses, at least one section among the plurality of driving pulses is provided with means for applying a driving waveform having the same polarity as the preceding and following driving pulses and a non-zero potential. A drive device for a liquid discharge head.   A liquid droplet ejection apparatus equipped with a liquid ejection head for ejecting recording liquid droplets, comprising the liquid ejection head drive device according to claim 1. An image forming apparatus that mounts a liquid discharge head that discharges recording liquid droplets and forms an image on a recording medium, comprising the liquid discharge head drive device according to claim 1. Forming equipment.

Images