JP2013014121A - Inkjet recording apparatus - Google Patents

Abstract

An inkjet recording apparatus capable of improving image quality by suppressing variation in ejection performance is provided.
A pressure is applied to each pressurized liquid chamber 1-1-1 by driving a piezoelectric element 1-4 provided in each of a plurality of pressurized liquid chambers 1-1-1 communicating with a nozzle hole 2-1. In the ink jet recording apparatus 50 having the ink jet recording head 53 that discharges ink droplets from the nozzle holes 2-1 by the generated pressure, each piezoelectric element 1-4 is repeatedly driven from a reference potential. The piezoelectric element 1-4 is driven by switching at least a part of the waveform, and has a counting means for counting the number of times of driving each piezoelectric element 1-4. The driving of each piezoelectric element 1-4 after the drive waveform has been slewed up to the reference potential The number of times is counted by the counting means, and the driving state of each piezoelectric element 1-4 is classified into any one of the predetermined forms according to the counting result, and the drive waveform is slewed down based on the form. To change the timing.
[Selection] Figure 17

Description

  The present invention relates to an inkjet recording apparatus such as an inkjet printer and a digital printing apparatus using an MFP.

  The ink jet recording apparatus has many advantages, such as extremely low noise during recording, high speed printing, and use of inexpensive plain paper with a high degree of ink freedom. Among these, the so-called ink-on-demand method, in which ink droplets are ejected only when recording is necessary, has become the mainstream at present because it does not require collection of ink droplets that are not necessary for recording.

  An inkjet head, which is a droplet discharge head used in an image recording apparatus such as a printer, a facsimile machine, or a copying apparatus, or an ink jet recording apparatus used as an image forming apparatus, includes a nozzle that discharges ink droplets and a discharge that communicates with the nozzle. Chamber (also referred to as a pressurized liquid chamber, a pressure chamber, an ink flow path, etc.) and a pressure generating means for generating a pressure for pressurizing the ink in the discharge chamber, and the discharge chamber is configured by the pressure generated by the pressure generating means. Ink droplets are ejected from the nozzles by pressurizing the ink.

  As such a droplet discharge head, a piezoelectric type that discharges ink droplets by deforming and displacing a diaphragm forming the wall surface of the discharge chamber using an electromechanical transducer element such as a piezoelectric element as a pressure generating means And a bubble type (thermal type) in which bubbles are generated by boiling an ink film and an ink droplet is ejected by using an electrothermal conversion element such as a heating resistor arranged in a discharge chamber. Piezoelectric types include a longitudinal vibration type using deformation in the D33 direction, a transverse vibration (vent mode) type using deformation in the D31 direction, and a shear mode type using shear deformation. Among them, an actuator configuration in which a pressurizing chamber and a piezo element are directly formed on a low-cost Si substrate has been devised due to recent advances in semiconductor processes and micromachining techniques, and a patterning technique has been established. This eliminates the need to attach the piezoelectric element to the diaphragm, and not only can the piezoelectric element be created by a precise and simple technique called a lithography method, but also the piezoelectric element can be reduced in thickness and driven at high speed. There is an advantage that it becomes possible.

  In “Patent Document 1”, the residual polarization of the piezoelectric element is maintained by holding the piezoelectric element in a state in which the electrical connection state between both electrodes constituting the piezoelectric element is controlled during a period when the printing operation is not performed. An ink jet recording apparatus that suppresses relaxation is disclosed. Thereby, since the ink ejection characteristics are maintained within a predetermined range, the print quality can be stabilized. Further, in “Patent Document 2”, a high-potential period in which a driving waveform applied to a piezoelectric body during a liquid discharge operation applies a voltage indicating an electric field strength exceeding the coercive electric field of the piezoelectric body, A liquid ejecting apparatus including a reverse potential period in which a voltage having a reverse potential is applied is disclosed. Thereby, the progress of remanent polarization is suppressed and the ink ejection characteristics are stabilized.

  “Patent Document 3” includes a discharge number measuring unit that measures the number of times a droplet is discharged and voltage correction information that corrects the voltage of a drive signal in accordance with the number of discharges. A liquid ejecting apparatus having a voltage correcting unit that corrects the weight of the droplet by correcting the voltage of the drive signal based on the voltage correction table is disclosed. As a result, the ink ejection characteristics are stabilized by correcting the voltage according to the number of ejections. Further, “Patent Document 4” discloses a function for generating a waveform to be through-up or through-down when a plurality of types of drive waveforms are switched and used in an image forming apparatus.

In an ink jet recording head having a piezoelectric element made of a thin film as described above, when ink droplets are ejected from the nozzle openings by continuously driving the piezoelectric element, the ink ejection characteristics gradually deteriorate. is there.
FIG. 22 shows that when continuous discharge (2500 drops) at 25 kHz was performed for 100 ms, and recovery times (applied voltage was slewed down to Gnd) of 0 ms (continuous), 100 μs, 1 ms, and 100 ms, respectively, This is an observation of how the drop velocity Vj changes. When continuous discharge is performed, the thin film piezo is polarized and the displacement of the diaphragm is reduced, so that the droplet velocity Vj gradually decreases. When the recovery time is given, the polarization is relaxed during that time, so that the displacement of the diaphragm and the droplet velocity Vj are also recovered. Therefore, the drop in the droplet velocity Vj is reduced by the length of the recovery time. This result indicates that the piezoelectric element is affected by the discharge history, and discharge variation occurs. For this reason, when the printing operation is continuously performed, the size of the ejected ink droplets varies, and there is a problem that the printing quality is not stable. In the case of a piezo obtained by firing a bulk instead of a thin film piezo, there is residual polarization due to voltage application. However, since the thin film piezo is driven with a thin electric field strength, the influence of the residual polarization becomes remarkably significant.

The technique disclosed in the above-mentioned “Patent Document 1” does not solve the problem that the ejection history (driving history) of a plurality of piezoelectric elements causes a difference in the ink ejection characteristics in the head. In the technique disclosed in “Patent Document 2”, a voltage having a reverse polarity must be generated as a drive voltage, so that the withstand voltage of the driver IC is increased and a power supply voltage for the reverse polarity needs to be prepared. This will increase costs. In the technique disclosed in “Patent Document 3”, voltage correction is correction for the entire head, and it does not solve the problem of causing a difference in ink ejection characteristics in the head. The technique disclosed in “Patent Document 4” does not solve the problem with respect to the temporal change in ink ejection characteristics.
SUMMARY OF THE INVENTION An object of the present invention is to provide an ink jet recording apparatus which can solve the above-described problems and can improve the image quality by suppressing variations in ejection performance.

  According to the first aspect of the present invention, pressure is generated in each of the pressurizing fluid chambers by driving piezoelectric elements respectively provided in the plurality of pressurizing fluid chambers communicating with the nozzle holes, and each of the pressurizing fluid chambers is generated by the generated pressure. In an ink jet recording apparatus having an ink jet recording head for ejecting ink droplets from nozzle holes, each piezoelectric element is driven by switching at least a part of a driving waveform repeatedly output from a reference potential, and each piezoelectric element Counting means for counting the number of times of driving of each piezoelectric element after the drive waveform has been slewed up to the reference potential, and counting the number of times the piezoelectric element is driven. The drive state is classified into one of predetermined forms, and the timing of through-down of the drive waveform is changed based on the form. And wherein the Rukoto.

  According to a second aspect of the present invention, in the ink jet recording apparatus according to the first aspect, each of the piezoelectric elements is a thin film piezo in which a piezoelectric material layer is formed on a vibration plate constituting at least one surface of the pressurized liquid chamber. It is characterized by.

  According to a third aspect of the present invention, in the ink jet recording apparatus according to the first or second aspect, the image forming apparatus is a serial type that performs image formation while scanning the ink jet recording head. It is performed every time.

  According to a fourth aspect of the present invention, in the ink jet recording apparatus according to any one of the first to third aspects, at least a part of the piezoelectric element when the drive waveform is slewed down according to the counting result. This driving state is characterized in that it is once through up and then through down.

  According to a fifth aspect of the present invention, in the ink jet recording apparatus according to the fourth aspect, the through-up is further performed up to the maximum value of the drive waveform.

  According to a sixth aspect of the present invention, in the ink jet recording apparatus according to any one of the first to fifth aspects, the counting means is a means for classifying whether or not the piezoelectric element is driven.

  According to the present invention, it is possible to reduce the discharge variation in the discharge history affected by the remanent polarization, thereby stabilizing the image quality formed.

1 is a schematic perspective view of an ink jet recording apparatus to which an embodiment of the present invention can be applied. 1 is a schematic side view of an ink jet recording apparatus to which an embodiment of the present invention can be applied. FIG. 2 is a cross-sectional view of a recording head used in an embodiment of the present invention. It is the schematic explaining the manufacturing process of the recording head used for one Embodiment of this invention. It is the schematic explaining the manufacturing process of the recording head used for one Embodiment of this invention. It is the schematic explaining the manufacturing process of the recording head used for one Embodiment of this invention. It is the schematic explaining the manufacturing process of the recording head used for one Embodiment of this invention. It is the schematic explaining the manufacturing process of the recording head used for one Embodiment of this invention. It is the schematic explaining the manufacturing process of the recording head used for one Embodiment of this invention. It is the schematic explaining the manufacturing process of the recording head used for one Embodiment of this invention. It is the schematic explaining the manufacturing process of the recording head used for one Embodiment of this invention. It is the schematic explaining the manufacturing process of the recording head used for one Embodiment of this invention. It is the schematic explaining the manufacturing process of the recording head used for one Embodiment of this invention. It is the schematic explaining the manufacturing process of the recording head used for one Embodiment of this invention. It is a control block diagram used for one embodiment of the present invention. FIG. 3 is a schematic diagram illustrating a drive waveform of a recording head used in an embodiment of the present invention. FIG. 3 is a schematic diagram illustrating a drive waveform of a recording head used in the first embodiment of the present invention. It is the schematic explaining the drive waveform of the recording head used for the 2nd Embodiment of this invention. FIG. 10 is a schematic diagram illustrating a drive waveform of a recording head used in a third embodiment of the present invention. It is the schematic explaining the drive waveform of the recording head used for the 4th Embodiment of this invention. It is the schematic explaining the drive waveform of the recording head used for the 5th Embodiment of this invention. It is a diagram which shows the result of having observed how the droplet velocity Vj changes, when each predetermined recovery time is provided after performing continuous discharge.

  FIG. 1 is a schematic perspective view of an inkjet recording apparatus equipped with an inkjet recording head to which an embodiment of the present invention can be applied, and FIG. 2 is a schematic side view thereof. The ink jet recording apparatus 50 includes a carriage 52 that can move in the main scanning direction, a recording head 53 that is an ink jet recording head that implements the present invention and is mounted on the carriage 52, and an ink cartridge that supplies ink to the recording head 53. A printing mechanism 55 composed of 54 and the like is housed inside the apparatus main body 51, and a paper feed cassette (a paper feed tray) on which a large number of sheets 56 can be stacked from the front side in the lower part of the apparatus main body 51. ) 57 is detachably attached. Further, a manual feed tray 58 used for manually feeding the paper 56 is provided on the front side of the apparatus main body 51 on the left side in FIG. The manual feed tray 58 is provided so as to be displaceable between a position in close contact with the apparatus main body 51 as shown in FIG. 2 when not in use and a position in which the paper 56 is tilted so that the paper 56 can be placed when in use. ing. The ink jet recording apparatus 50 takes in the paper 56 sent from the paper feed cassette 57 or the manual feed tray 58, records a desired image on the I 56 by the printing mechanism 55, and then uses the paper 56 after the image recording on the apparatus main body 51. The paper is discharged to a paper discharge tray 59 provided on the rear side.

  The printing mechanism 55 holds a carriage 52 movably by a main guide rod 60 and a sub guide rod 61 that are stretched between left and right side plates (not shown). The carriage 52 is provided with yellow (Y) and cyan (C). , Magenta (M) and black (Bk) recording heads 53 that eject ink droplets of each color are arranged so that a plurality of ink ejection ports (nozzles) intersect the main scanning direction, and then the ink liquid It is mounted so that the droplet discharge direction is downward. Further, ink cartridges 54 corresponding to the respective colors for supplying the respective color inks to the recording head 53 are mounted on the carriage 52 in a replaceable manner. The ink cartridge 54 has an air port that communicates with the atmosphere above, a supply port that supplies ink to the recording head 53 below, and a porous body filled with ink inside. Due to this phenomenon, the ink supplied to the recording head 53 is maintained at a slight negative pressure. Here, the recording head 53 is provided for each color, but a configuration using a single recording head having nozzles capable of ejecting ink droplets of each color may be used.

  The carriage 52 is slidably supported by the main guide rod 60 on the rear side, which is the downstream side in the paper conveyance direction, and the front side, which is the upstream side in the paper conveyance direction, is placed on the sub guide rod 61. Yes. In order to move and scan the carriage 52 in the main scanning direction, a timing belt 65 fixed to the carriage 52 is stretched between a driving pulley 63 and a driven pulley 64 that are rotationally driven by a main scanning motor 62. With this configuration, the carriage 52 is reciprocated as the main scanning motor 62 rotates forward and backward.

  On the other hand, in order to convey the paper 56 stacked on the paper feed cassette 57 to the lower side of the recording head 53, the paper 56 is guided from the paper feed roller 57 and the friction pad 67 for separating and feeding the paper 56 from the paper feed cassette 57. The guide member 68, a conveyance roller 69 that reverses and conveys the fed paper 56, a conveyance roller 70 that is pressed against the peripheral surface of the conveyance roller 69, and a feeding angle of the paper 56 from the conveyance roller 69 are defined. A tip roller 71 is provided. The conveyance roller 69 is rotationally driven by a sub-scanning motor 72 via a gear train.

  Corresponding to the range of movement of the carriage 52 in the main scanning direction, there is provided a printing receiving member 73 which is a paper guide member for guiding the paper 56 fed from the transport roller 69 on the lower side of the recording head 53. On the downstream side of the paper conveyance direction, a conveyance roller 74 and a spur 75 that are rotationally driven to send the paper 56 in the paper discharge direction, a paper discharge roller 76 and a spur 77 that send the paper 56 to the paper discharge tray 59, each roller 74, Guide members 78 and 79 are provided between 76 and form a paper discharge path.

  With the above-described configuration, the ink jet recording apparatus 50 performs recording for one line by ejecting ink onto the stopped paper 56 by driving the recording head 53 according to the image signal while moving the carriage 52 during recording. After the paper 56 is conveyed by a predetermined amount, the next line is recorded. The ink jet recording apparatus 50 receives the recording end signal or the signal that the rear end of the paper 56 has reached the recording area, and thereby ends the recording operation and discharges the paper 56 to the paper discharge tray 59.

  A recovery device 80 having a cap unit, a suction unit, and a cleaning unit for recovering defective ejection of the recording head 53 is provided at a position outside the recording area on the right end side in the movement direction of the carriage 52. The carriage 52 is moved to the recovery device 80 side during printing standby, and the recording head 53 is capped by the cap unit, and the ejection port portion is kept in a wet state to prevent ejection failure due to ink drying. Further, by ejecting ink that is not related to recording during recording or the like (empty ejection), the ink viscosity at all ejection ports is made constant, and stable ejection performance is maintained. When ejection failure occurs, the ejection port (nozzle) of the recording head 53 is sealed by the cap unit, and bubbles and the like are sucked out together with the ink from the ejection port by the suction unit through the tube. Etc. are removed by the cleaning means, thereby recovering the ejection failure. The sucked ink is discharged into a waste ink reservoir (not shown) provided at the lower part of the main body, and is absorbed and held by an ink absorber provided inside the waste ink reservoir.

  Next, the configuration of the above-described recording head 53 used in an embodiment of the present invention will be described with reference to FIG. 3 which is a sectional view from three directions. The recording head 53 is a droplet discharge head using an actuator, and employs a side shooter method in which ink droplets are discharged from nozzle holes provided on one surface of a substrate. The recording head 53 includes a nozzle substrate 2 having a nozzle hole 2-1 for ejecting ink droplets, a pressurized liquid chamber 1-1-1, a fluid resistance unit 1-1-2, a groove serving as an ink flow path, and vibration. Three substrates of a liquid chamber substrate 1 having an actuator such as a plate 1-2, an interlayer insulating film 1-6 that is a piezoelectric layer, and a protective substrate (subframe) 3 having a piezoelectric element protection space 3-1. It has a stacked structure.

  The liquid chamber substrate 1 which is the first substrate uses an SOI substrate in which silicon is bonded to a silicon substrate via a silicon oxide film. The diaphragm 1-2 is formed by applying a pyro-oxidation method to the silicon layer surface of the SOI substrate, forming a silicon oxide film thereon, a platinum film 1-3 serving as a lower electrode, and a piezoelectric material (PZT) constituting a piezoelectric element. 1-4) An actuator having a multilayer structure of a platinum film 1-5 serving as an upper electrode is formed in a region facing the pressurized liquid chamber 1-1-1 formed by etching silicon. Further, an interlayer insulating film 1-6 protects the wiring material 1-7 so as to cover the upper surface and side surfaces of the actuator between the films 1-3, 1-5 as the electrodes and the wiring material 1-7. A passivation film 1-8 is provided for the purpose.

  The nozzle substrate 2 as the second substrate is provided with a nozzle hole 2-1 by pressing and polishing a stainless substrate having a thickness of 30 to 50 μm. The nozzle hole 2-1 is arranged so as to communicate with 1-1. The protective substrate 3 as the third substrate includes, as the common liquid chamber 3-3, a groove portion serving as an ink flow path, a piezoelectric element protection space 3-1 for preventing protection and displacement of the piezoelectric element, and a flow path. It has a column 3-2 for increasing the rigidity of the partition wall 1-1-5 and supporting the entire liquid chamber.

Next, a method for manufacturing the recording head 53 shown in this embodiment will be described.
In this embodiment, an actuator is created by depositing a diaphragm material and a piezoelectric element material on the liquid chamber substrate 1 which is a silicon substrate. First, an SOI substrate in which a silicon oxide film of 0.2 μm and silicon of 2.0 μm are bonded to the surface of a <100> silicon substrate having a thickness of 400 μm is used, and a silicon oxide film is formed on this surface by a pyro oxidation method. 3 μm is formed, and this is used as a diaphragm 1-2 as shown in FIG. Thereafter, as shown in FIG. 5, a platinum film (layer) 1-3 serving as a lower electrode of the piezoelectric element is formed by patterning with a sputtering method of 0.2 μm, and further a piezoelectric material 1-4 is formed with a thickness of 2 μm by a sol-gel method. Further, a platinum film (layer) 1-5 serving as an upper electrode is formed to a thickness of 0.1 μm. Here, although the piezoelectric material 1-4 is formed to a thickness of 2 μm, the drop in the droplet velocity Vj due to driving is confirmed even if the thickness of the piezoelectric material 1-4 is changed in the range of 1 to 3 μm. Since the driving conditions change when the thickness of the piezoelectric material 1-4 is changed, the driving conditions in which the droplet velocity Vj is Vj = 7 m / s at a position 1 mm away from the nozzle hole 2-1 with respect to each thickness. It is the result when aligned.

  Thereafter, as shown in FIG. 6, the platinum film 1-5 and the piezoelectric material 1-4 are patterned by a lithoetch method. Next, an interlayer insulating film 1-6 is formed to a thickness of 0.3 μm by a plasma CVD method, and a via hole for making a wiring contact is formed by a lithoetch method. As shown in FIG. 7, the interlayer insulating film 1-6 includes a conductive portion 1-6-2 between the wiring material 1-7 to be formed next and the platinum film 1-5, and a conductive portion 1 to the bypass wiring 1-10. -6-3 and penetrating portions 1-6-4 serving as ink supply holes are patterned, respectively, and lead-out electrodes are formed of a wiring material 1-7 made of an aluminum material as shown in FIG. Since this lead electrode receives stress due to vibration of the diaphragm 1-2 driven by the piezoelectric material 1-4, the lead electrode is thickly stacked by using a soft aluminum material so as not to be disconnected by vibration.

  Next, as shown in FIG. 9, as a passivation film 1-8 for protecting the aluminum wiring, a silicon nitride film by plasma CVD is formed to a thickness of 2 μm and patterned. Then, as shown in FIG. 10, the part used as the through-hole 1-2-1 of the diaphragm 1-2 is etched previously. Further, as shown in FIG. 11, gold is laminated by a plating method, and pad portions 1-9 of individual electrodes and bypass wiring 1-10 are formed simultaneously. By forming the pad portion 1-9 with gold, it is possible to connect an electrical connection with a driver IC (not shown) by low-temperature wire bonding, and since the resistance value of gold is low, the bypass wiring 1-10 is used. There is an advantage that the effect of reducing the common electrode resistance value is great. Note that the pad portion 1-9 is separated from the forming step, and copper, aluminum, or the like can be used as the material of the bypass wiring 1-10. In this case, a protective layer for protecting the bypass wiring 1-10 from corrosion may be necessary.

  Thereafter, as shown in FIG. 12, the protection substrate 3 in which the pillar 3-2 is separately formed on a glass substrate by a blasting method is joined to the liquid chamber substrate 1, and the surface of the liquid chamber substrate 1 to which the protection substrate 3 is joined Polishes the opposite side to the desired thickness. The protective substrate 3 may be a silicon substrate formed with a recess by a litho-etch method, a <110> silicon substrate processed by wet etching using an alkaline etching solution such as TMAH, KOH, etc., and a resin mold, a metal injection mold, etc. The molded part may be used. Further, when the driver circuit is integrally formed on the liquid chamber substrate 1 which is an actuator substrate, an oxide film formed by a pyro oxidation method is formed by a LOCOS oxidation method, and a drive circuit is selected by selecting a region where the oxide film is formed. It is also possible to form on the same substrate.

  Thereafter, as shown in FIG. 13, concave portions that become the pressurized liquid chamber 1-1-1, the fluid resistance unit 1-1-2, and the supply unit 1-1-3 are formed on the polishing surface of the liquid chamber substrate 1 by ICP dry etching. Form. Finally, as shown in FIG. 14, the nozzle substrate 2 in which the nozzle holes 2-1 are formed on the stainless steel substrate having a thickness of 30 to 50 μm separately by pressing and polishing is used as the flow path partition 1-of the liquid chamber substrate 1. The recording head 53, which is a droplet discharge head, is completed by pressure bonding to the 1-5 forming surface and connecting the aluminum wiring portion connected to each platinum film 1-3.1-5 of the piezoelectric element to the drive circuit. .

  FIG. 15 is a block diagram of a drive circuit that drives the recording head 53. In this embodiment, a 2-bit gradation signal (image data) is serially transferred from the main body to the recording head 53, and each bit is converted from serial to parallel by two shift registers. Then, the data is latched at the beginning of the printing cycle, and one of the control signals MN0 to MN3 is selected based on the gradation data. On / off of the analog switch within the printing cycle is selected based on the control signals MN0 to MN3.

  By adopting such a circuit configuration, data transfer is required only once in one printing cycle, and on / off switching is based on control signals MN0 to MN3 input from the outside, so that switching time can be easily changed. is there. However, the circuit configuration for switching the analog switch within one printing cycle based on the gradation signal is not limited to this. In the present invention, the circuit configuration is not limited as long as desired on / off switching is possible. As the drive voltage waveform, the waveform stored in the ROM is output from the D / A circuit of the recording apparatus main body, and is supplied to the recording head 53 via the voltage power amplifier circuit of the operational amplifier and the transistor.

  Next, the drive waveform of the recording head 53 will be described with reference to FIG. As shown in FIG. 16, the recording head 53 switches the common drive waveform based on the image data in accordance with the movement of the carriage 52, thereby applying a voltage to each piezoelectric element corresponding to each nozzle to cause lateral vibration. The piezoelectric material 1-4, which is a piezoelectric element that deforms in the mode, contracts, and the entire diaphragm 1-2 that is in close contact with the piezoelectric material 1-2 is deformed so as to be convex toward the pressurized liquid chamber 1-1-1. To do. The pressure in the pressurizing liquid chamber 1-1-1 is controlled by the volume change of the pressurizing liquid chamber 1-1-1, and ink droplets are ejected from the nozzle holes 2-1 toward the paper 56. Ink can be continuously ejected from the nozzle holes 2-1 by repeating the continuous application of the drive waveform in accordance with the pressure fluctuation period in the pressurized liquid chamber 1-1-1.

  In driving the piezoelectric material 1-4, so-called striking is often performed in which the pressure in the pressurized liquid chamber 1-1-1 is once lowered and then the pressure is increased again to perform discharge. This is because continuous discharge is easy to perform, but the drive waveform at this time is raised to the reference potential (through-up) and the waveform when discharged from there is repeated. In the case of the serial type ink jet recording apparatus 50 in which the recording head 53 is mounted on the carriage 52 and forms an image while scanning the carriage 52 as in the present invention, each piezoelectric element is in the acceleration section of the carriage 52 or before the acceleration section. A through-up voltage is applied to the piezoelectric element to raise the potential of each piezoelectric element to a reference potential. At the end of printing, the potential of each piezoelectric element is through-down from the reference potential, but there is also a method of through-down every time when the carriage 52 is turned back.

  In the first embodiment of the present invention, there is a counting unit that counts the number of ejections that is the number of times each piezoelectric element is driven, and the drive-like body of the recording head 53 is set to a small, medium, or large number of ejections according to the number of ejections. According to this classification, the through-down timing is changed as shown in FIG. 17, and this through-down is performed for each scan of the carriage 52 (each return). Since the counting by the counting means is performed from through-up until the start of through-down, in this embodiment, the number of ejections of each nozzle is counted for each scan (the scan is different from the forward pass and the return pass). In the ink jet recording apparatus 50, the image data is directly counted from the image data.

  In the case of the thin film piezo as in the present embodiment, since the polarization is advanced only by holding the piezoelectric element at the reference potential, it is desirable to provide a recovery time as frequently as possible. For this reason, the drive waveform is slewed up and down for each scan. In addition, the correction for making the polarization state uniform can be carried out in detail by counting each scan, and the discharge variation in the discharge history affected by the residual polarization can be reduced. Image quality can be stabilized.

  Further, in the thin film piezoelectric ink jet recording head, since the piezoelectric material 1-4 is thin (2 μm in this embodiment), the electric field strength is high, and the polarization is inevitably advanced. If the voltage application is stopped, the polarization is recovered, but due to the time delay, the discharge volume Mj and the discharge speed Vj change depending on the discharge history. In the present invention, by changing the timing of through-down according to the discharge history (the number of discharges), the polarization is aligned and the occurrence of discharge variation of each nozzle is suppressed. Specifically, as shown in FIG. 17, for the piezoelectric elements classified into three stages (low discharge number, medium and large) according to the number of discharges, the drive waveform is switched in the same manner as the discharge operation, thereby controlling the through-down timing. Is changing. Here, in order to make the voltage application uniform, a group of piezoelectric elements with a small number of ejections is set to have a long time until through-down, and a group of piezoelectric elements with a large number of ejections is set to have a short time to through-down. Since the drive waveform is common, the time for returning the drive waveform from the through-down state to the reference potential to the reference potential is all off so that the drive waveform is not applied to the piezoelectric element. In the present embodiment, the number of ejections in the driving state is classified into three stages, but the classification may be other than three stages.

  Next, a second embodiment of the present invention will be described with reference to FIG. In the second embodiment, the voltage applied to the piezoelectric element is slewed up with a slope of the voltage that is not discharged once during the slewing down. With this configuration, remanent polarization can be advanced in a short time, so that the polarization state of each piezoelectric element can be made uniform. In this embodiment, as shown in FIG. 18, the voltage holding time after through-up is changed according to each classification for piezoelectric elements classified into three stages (low discharge number, medium, large) according to the discharge number. ing. Here, by increasing the voltage holding time in order from the group of piezoelectric elements with the smallest number of ejections, it is possible to align the polarization state of each piezoelectric element and suppress the ejection variation of each nozzle. Since the drive waveform is common, the time for returning the drive waveform from the through-down state to the maximum voltage potential is all off so that the drive waveform is not applied to the piezoelectric element. In the present embodiment, the number of ejections in the driving state is classified into three stages, but the classification may be other than three stages.

  Next, a third embodiment of the present invention will be described with reference to FIG. In the third embodiment, the voltage is slewed up to the maximum voltage of the ejection waveform with a slope of the voltage that is not ejected once at the time of through-down. With this configuration, a state closer to the voltage application by ejection can be created, so that the polarization state of each piezoelectric element can be made uniform. In the present embodiment, as shown in FIG. 19, for the piezoelectric elements classified into three stages (low discharge number, medium and large) according to the number of discharges, the holding time at the maximum voltage is changed according to each classification. Yes. Here, a group of piezoelectric elements with a small number of ejections can further reduce the ejection variation of each nozzle by aligning the polarization state of each piezoelectric element by making a through-down after extending the holding time at the maximum voltage. . Since the drive waveform is common, the time for returning the drive waveform from the through-down state to the maximum voltage potential is all off so that the drive waveform is not applied to the piezoelectric element. In the present embodiment, the number of ejections in the driving state is classified into three stages, but the classification may be other than three stages.

  Next, a fourth embodiment of the present invention will be described with reference to FIG. In the fourth embodiment, the voltage is raised to the maximum voltage of the ejection waveform with a slope of the voltage that is not ejected once during the through-down. With this configuration, a state closer to the voltage application by ejection can be created, so that the polarization state of each piezoelectric element can be made uniform. In the present embodiment, as shown in FIG. 20, it is classified into three stages (low discharge number, medium and large) according to the discharge number. Here, a group of piezoelectric elements with a large number of ejections is slewed down from the reference potential after the end of the printing section, and a group of piezoelectric elements with a middle number of ejections is slewed up once from the reference potential to the maximum voltage of the ejection waveform. To go down. In addition, a group of piezoelectric elements with a small number of ejections is once slewed up from the reference potential to the maximum voltage of the ejection waveform, and then slewed down after the application time of the maximum voltage is maintained longer than that of the middle group. With this configuration, it is possible to align the polarization states of the piezoelectric elements and suppress the discharge variation of the nozzles. As in the present embodiment, a method may be used in which the case of once through up to the maximum voltage and the case of immediate through down are selectively used. Since the drive waveform is common, the time for returning the drive waveform from the through-down state to the reference potential to the reference potential is all off so that the drive waveform is not applied to the piezoelectric element. In the present embodiment, the number of ejections in the driving state is classified into three stages, but the classification may be other than three stages.

  Next, a fifth embodiment of the present invention will be described with reference to FIG. In the fifth embodiment, the number of discharges is classified into two types, 0 times and 1 or more times, that is, according to whether or not the discharge is performed after the drive voltage is slewed up and then slewed down. Yes. With this configuration, counting including classification only needs to set a flag for each piezoelectric element, and a counter for counting is unnecessary, so that ejection variation due to ejection history can be corrected with simple means. Since there are two types of classification in this embodiment, there are also two types of slowdown. Since the drive waveform is common, the time for returning the drive waveform from the through-down state to the reference potential to the reference potential is all off so that the drive waveform is not applied to the piezoelectric element.

1-1-1 Pressurized liquid chamber 1-2 Diaphragm 1-4 Piezoelectric material (piezoelectric element)
2-1. Nozzle hole 50 Inkjet recording device 53 Inkjet recording head (recording head)

JP 2003-266682 A JP 2006-231928 A JP 2009-66948 A JP 2009-29038 A

Claims (6)

Pressure is generated in each of the pressurizing liquid chambers by driving the piezoelectric elements provided in the plurality of pressurizing liquid chambers communicating with the nozzle holes, and ink droplets are ejected from the respective nozzle holes by the generated pressure. In an ink jet recording apparatus having an ink jet recording head,
Each piezoelectric element is driven by switching at least a part of a driving waveform repeatedly output from a reference potential, and has counting means for counting the number of driving times of each piezoelectric element, and the driving waveform is set to the reference potential. The number of driving times of each piezoelectric element after the through-up is counted by the counting means, and the driving state of each piezoelectric element is classified into any one of the predetermined forms according to the counting result, An inkjet recording apparatus characterized in that the timing of through-down of the drive waveform is changed on the basis thereof. The inkjet recording apparatus according to claim 1, wherein
Each of the piezoelectric elements is a thin film piezo in which a piezoelectric material layer is formed on a vibration plate constituting at least one surface of the pressurized liquid chamber. The inkjet recording apparatus according to claim 1 or 2,
2. An ink jet recording apparatus according to claim 1, wherein the ink jet recording head is a serial type that forms an image while scanning the ink jet recording head, and the drive waveform is slewed up and down every scanning. The inkjet recording apparatus according to any one of claims 1 to 3,
2. An ink jet recording apparatus according to claim 1, wherein when the drive waveform is through-down according to the counting result, at least a part of the drive state of the piezoelectric element is once through up and then down. The inkjet recording apparatus according to claim 4.
The through-up is performed up to the maximum value of the drive waveform. In the ink jet recording apparatus according to any one of claims 1 to 5,
The ink jet recording apparatus according to claim 1, wherein the counting means is means for classifying whether or not the piezoelectric elements are driven.

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