JP2013199026A - Liquid droplet ejection apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid droplet ejection apparatus having high ejection stability, which decreases power consumption by changing a fine driving frequency with a circuit configuration of low cost without increasing the number of gray-scale signals.SOLUTION: A liquid droplet ejection apparatus includes a bias signal circuit for applying a bias voltage to an electrode on the other side of a piezoelectric actuator, wherein a fine drive wave pattern is provided to the side of a bias voltage circuit. The bias signal circuit changes the bias voltage at a timing for applying a drive wave voltage to the piezoelectric actuator that is not allowed to eject a liquid droplet within one printing cycle.

Description

  The present invention relates to a droplet discharge device, and more particularly to control of the frequency of fine driving performed to prevent drying or the like of a droplet discharge head.

<Liquid ejection device>
As an image forming apparatus such as a printer, a facsimile, a copying machine, a plotter, or a complex machine of these, for example, a liquid ejection recording type image forming using a recording head composed of a liquid droplet ejection head (liquid ejection head) that ejects ink droplets. As an apparatus, an ink jet recording apparatus or the like is known. This liquid discharge recording type image forming apparatus means that ink droplets from an inkjet head are transported on paper (not limited to paper, including OHP, and can be attached to ink droplets and other liquids). Yes, it is also ejected onto a recording medium or a recording medium, recording paper, recording paper, etc.) to form an image (recording, printing, printing, and printing are also used synonymously). A serial type image forming apparatus that forms an image by ejecting droplets while the inkjet head moves in the main scanning direction, and a line type head that forms images by ejecting droplets without moving the inkjet head There are line type image forming apparatuses using

  In the present application, the “image forming apparatus” of the liquid discharge recording method is an apparatus that forms an image by discharging liquid onto a medium such as paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, ceramics, or the like. In addition, “image formation” means not only giving an image having a meaning such as a character or a figure to a medium but also giving an image having no meaning such as a pattern to the medium (simply It also means that a droplet is landed on a medium). “Ink” is not limited to ink, but is used as a general term for all liquids capable of image formation, such as recording liquid, fixing processing liquid, and liquid. DNA samples, resists, pattern materials, resins and the like are also included. In addition, the “image” is not limited to a planar one, but includes an image given to a three-dimensionally formed image, and an image formed by three-dimensionally modeling a solid itself.

<Piezo method>
An inkjet head in an inkjet recording apparatus used as an image forming apparatus (image recording apparatus) such as a printer, a facsimile machine, a copying apparatus, or a plotter has a nozzle that ejects ink droplets and an ejection chamber (pressure chamber, pressurization) that communicates with the nozzle. A liquid chamber, a liquid chamber, an ink chamber, an ink flow path, etc.) and an actuator means (energy generating means) that generates energy for pressurizing the ink in the discharge chamber to drive the actuator means. Thus, the ink in the ejection chamber is pressurized and ink droplets are ejected from the nozzles, and an ink-on-demand system that ejects ink droplets only when recording is necessary is the mainstream.

  Ink-on-demand ink jet heads are roughly classified into several types depending on the type of actuator means for ejecting ink droplets (recording liquid).

  For example, as described in Patent Document 1 (Japanese Patent Laid-Open No. 10-100401), a part of the wall of the liquid chamber is a thin diaphragm, and a piezoelectric element as an electromechanical conversion element is arranged correspondingly. A piezoelectric element that changes the pressure in the liquid chamber by deforming the diaphragm due to the deformation of the piezoelectric element that occurs when a voltage is applied, and discharges ink droplets. A heating element is placed inside the liquid chamber. In general, a bubble jet (registered trademark) system in which bubbles are generated by heating a heating element by energization and ink droplets are ejected by the pressure of the bubbles is well known.

  In addition, as described in, for example, Patent Document 2 (Japanese Patent Laid-Open No. 2-289351), a diaphragm that forms the wall surface of the liquid chamber, and a liquid chamber outside the liquid chamber that is disposed to face the diaphragm. An individual electrode is provided, and the diaphragm is deformed by an electrostatic force generated by applying an electric field between the diaphragm and the electrode, and ink droplets are ejected from the nozzle by changing the pressure / volume in the liquid chamber. An electrostatic type has also been proposed.

  In addition, a piezoelectric type that uses a longitudinal vibration mode piezoelectric actuator that extends and contracts in the axial direction of the piezoelectric element and a flexural vibration mode piezoelectric actuator that has been put into practical use.

  The former can change the volume of the pressure generation chamber by bringing an ink jet type surface that discharges the end of the piezoelectric element into contact with the diaphragm, so that a head suitable for high-density printing can be manufactured. Difficult process of cutting elements into a comb-teeth shape according to the arrangement pitch of nozzle openings, and the work of positioning and fixing the cut piezoelectric elements in the pressure generating chamber, which complicates the manufacturing process There is.

  On the other hand, the latter can flexibly vibrate, although a piezoelectric element can be built on the diaphragm by a relatively simple process of sticking a green sheet of piezoelectric material according to the shape of the pressure generation chamber and firing it. There is a problem that a certain amount of area is required for the use of, and high-density arrangement is difficult.

  In order to eliminate the disadvantages of the latter recording head, a uniform piezoelectric material layer is formed by a film forming technique over the entire surface of the diaphragm, as seen in Patent Document 3 (Japanese Patent Laid-Open No. 05-286131). In this proposal, a piezoelectric element is formed by cutting the piezoelectric material layer into a shape corresponding to the pressure generating chamber by lithography and forming an independent element for each pressure generating chamber. This eliminates the need to affix the piezoelectric element to the diaphragm, so that not only can the piezoelectric element be created by a precise and simple technique called lithography, but also the thickness of the piezoelectric element can be reduced. There is an advantage that high-speed driving is possible.

<Butterfly characteristics>
By the way, in the configuration in which the piezoelectric material layer is directly formed on the diaphragm (herein referred to as a thin film piezo), the piezoelectric material layer is thin and the electric field strength at the time of driving is strong. Is known (see FIG. 21). This occurs because the polarization is reversed by the electric field during driving. Here, FIG. 21 is a graph showing the characteristic of the displacement amount (deflection amount) with respect to the applied voltage of the piezoelectric element.

  As a method of applying a voltage to a piezoelectric actuator, generally, a common electrode is grounded to Gnd, and a driving waveform for controlling the movement of the piezoelectric actuator is applied to the individual electrode side (see FIG. 22).

  In the case of a thin-film piezo, as seen in the butterfly characteristics of FIG. 21, when the electric field strength increases, the displacement tends to saturate (this also has the effect of strong electric field strength). There is a method of using a reverse voltage portion where the butterfly characteristic does not invert without exceeding. Since the slope of the butterfly characteristic is larger in that direction, a large displacement can be obtained with respect to the applied voltage.

  Regarding the ejection characteristics of droplets of ink or the like, Patent Document 4 (Japanese Patent Laid-Open No. 2006-321200) describes that there is a characteristic variation with respect to the bias voltage (see paragraph 0004). In order to cope with this, it is described that a bias voltage value with the same displacement amount of the piezoelectric pair element is detected and ranked according to the detected value (see paragraph 0044).

  In Patent Document 4, in order to use the voltage region, a bias voltage is applied to the common electrode side. Thereby, when viewed from the piezoelectric material layer, a reverse voltage is applied.

  FIG. 23A shows the bias voltage V0 and the drive voltage V1, and FIG. 23B shows the voltage ΔV = V1-V0 applied to the piezoelectric layer. In FIG. 23, since the voltage ΔV applied to the piezoelectric layer is simply ΔV = V1−V0, by applying a bias voltage V0 to the common electrode side, the voltage ΔV of the piezoelectric layer illustrated in FIG. Indicates that a voltage range with good displacement efficiency including a reverse polarity near ΔV = 0 can be used.

  Further, in Patent Document 5, for the purpose of preventing the drop velocity from being lowered due to the drive history (although the purpose is different), a switch circuit is provided on both electrodes of the piezoelectric actuator, and an electric field is applied in the polarization direction. A first mode in which the piezoelectric element is driven to discharge liquid from the nozzle, and an electric field is applied to the piezoelectric element in a direction opposite to the polarization direction of the piezoelectric body to drive the piezoelectric element to discharge liquid from the nozzle. The second mode can be switched. (FIG. 6 is a diagram of butterfly characteristics, but the butterfly characteristics are symmetric.) However, the circuit configuration is complicated and the cost is high.

<Fine drive to stabilize discharge>
By the way, in the case of a thin film piezo droplet ejection head, it is necessary to stabilize the ejection, particularly the ejection of the first droplet, by vibrating the meniscus with respect to the non-ejection channel (herein referred to as fine driving). is there.

  FIG. 24 is a block diagram of a driver IC (Integrated Circuit) circuit, and FIG. 25 is a diagram for explaining the operation thereof. Within the printing cycle, application of a part of the drive waveform to the piezoelectric layer by the driver IC is controlled to eject droplets having different sizes. The common electrode side is grounded to Gnd.

  In this example, 2-bit gradation signals (image data) are transferred in parallel, and the time axis data is converted into gradations (large droplets, medium droplets, small droplets) in each channel state by a shift register and a latch circuit. Droplet, non-ejection). Each channel applies a part of the drive waveform voltage to the piezoelectric element by turning on and off the switch in the driver IC based on the control signal of the gradation.

In the example of FIG. 8, the switching operation is performed as follows with respect to the switching timings T1, T2, T3, and T4 (the circled numbers in the figure are substituted with the numbers in parentheses in the following table).
T1 T2 T3 T4
Large droplet (1, 1) ON ON OFF ON (1), (2), (3), (4) Discharge medium droplet (1, 0) OFF OFF OFF ON (3), (4) Discharge small droplet (0 , 1) OFF ON OF OFF (2) Discharge Non-discharge (0, 0) OFF OFF ON OFF

  At this time, since the non-ejection (0, 0) is always ON for the period T3, the non-ejection channel is always finely driven.

  As described above, if there is no fine driving, the ink in the nozzles increases in viscosity, causing problems in stable ejection such as ejection bending and dot position deviation due to reduced speed. However, it is not preferable from the viewpoint of power consumption that the fine driving is continuously applied to the channel that does not discharge. In the case of business documents, since the number of channels to be discharged is about 10% or less, the remaining 90% of fine driving has a surprisingly large proportion of power consumption during printing.

  That is, it is preferable to apply the fine driving with the minimum frequency. However, as in this example, the number of gradations may be a constraint.

  If a 3-bit gradation signal is simply used, it is easy to separate fine driving and non-ejection into 5 gradations, but the number of data to be handled increases, and data processing on the recording apparatus main body side becomes easier. Due to the large scale, the problem of processing speed and the logic part of the driver IC become large, which causes the problem of the cost of the driver IC.

  Although a method of changing ON / OFF of the non-ejection (0, 0) of the control signal for each printing cycle is also conceivable, as shown in this example, the ejection operation is performed after through-up to an intermediate potential (reference potential). In such a case, it is necessary to turn on the driver IC at an intermediate potential once in a printing cycle even in the case of non-ejection (0, 0). This is to prevent the electric charge charged in the piezoelectric layer from leaking and the reference potential from dropping, and when the reference potential drops, the potential jumps at the next connection and the piezoelectric layer moves. The meniscus is broken and the ejection operation of the head becomes unstable.

  Although it may be possible to set a fine driving time and a charging time separately, the driving frequency has increased recently, and the extra time becomes a restriction on the driving frequency (printing cycle) of the head, thus reducing the printing productivity. It becomes a factor.

  In addition, it is possible to select a waveform with a fine drive part of the drive waveform itself and a waveform with no fine drive for each print cycle. However, since the entire waveform needs to be replaced, it is performed at a short time interval as per the print cycle. For this reason, a load is applied to the waveform generation circuit side, which leads to an increase in cost.

  The present invention has been made in view of the above-described circumstances, and has an ejection stability that reduces power consumption by changing the fine driving frequency with a low-cost circuit configuration without increasing the number of gradation signals. An object is to provide a high droplet discharge device.

  To achieve the above object, the present invention provides a plurality of nozzle openings, a flow path forming substrate having a pressurized liquid chamber communicating with each nozzle opening, a piezoelectric actuator formed on the flow path forming substrate, A droplet discharge head provided with a driver IC for switching voltage application of the piezoelectric actuator, drive waveform generating means for applying a drive waveform voltage to the droplet discharge head, and a bias voltage applied to an electrode on the opposite side of the piezoelectric actuator A bias signal circuit that changes the bias voltage at a timing when a drive waveform voltage is applied to the piezoelectric actuator that does not eject droplets within one printing cycle. A droplet discharge device is provided.

  According to the present invention, it is possible to provide a droplet ejection apparatus with high ejection stability that reduces power consumption by changing the fine driving frequency with a low-cost circuit configuration without increasing the number of gradation signals. .

1 is a perspective explanatory view showing an example of an ink jet recording apparatus equipped with a droplet discharge device according to an embodiment of the present invention. It is side surface explanatory drawing of the mechanism part of the inkjet recording device of FIG. It is sectional drawing which shows the structure of the inkjet head (droplet discharge head or thin film head) of FIG. FIG. 4 is an explanatory diagram (No. 1) of a method of creating the droplet discharge head of FIG. FIG. 4 is an explanatory diagram (part 2) of a method of creating the droplet discharge head of FIG. FIG. 4 is an explanatory diagram (No. 3) of a method of creating the droplet discharge head of FIG. FIG. 4 is an explanatory diagram (part 4) of a method of creating the droplet discharge head of FIG. FIG. 5 is an explanatory diagram (No. 5) of a method of creating the droplet discharge head of FIG. FIG. 6 is an explanatory diagram (No. 6) of a method of creating the droplet discharge head of FIG. FIG. 7 is an explanatory diagram (No. 7) of a method of creating the droplet discharge head of FIG. FIG. 8 is an explanatory diagram (No. 8) of a method of creating the droplet discharge head of FIG. FIG. 9 is an explanatory diagram (No. 9) of the method for producing the droplet discharge head of FIG. FIG. 10 is an explanatory diagram (No. 10) of a method of creating the droplet discharge head of FIG. FIG. 11 is an explanatory diagram (No. 11) of a method of creating the droplet discharge head of FIG. It is a figure which shows the structure of the driver IC of Example 1 of this invention. FIG. 16 is a diagram for explaining the operation of the driver IC of FIG. 15. It is a figure for demonstrating the voltage concerning a piezoelectric layer in FIG. It is a figure for demonstrating operation | movement of the driver IC in Example 2 of this invention. It is a setting table of the fine drive frequency in Example 3 of this invention. It is a setting table of the fine drive frequency in Example 4 of this invention. It is a figure for demonstrating a butterfly characteristic. It is a figure which shows the method of applying a voltage to a piezoelectric actuator. It is a figure for demonstrating the voltage concerning a piezoelectric layer in FIG. It is a figure which shows the structure of the driver IC for performing the fine drive performed in order to stabilize droplet discharge. FIG. 25 is a diagram for explaining the operation of the driver IC in FIG. 24.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

<Inkjet recording apparatus>
First, an example of an ink jet recording apparatus equipped with an ink jet head according to this embodiment will be described with reference to FIGS. 1 is an explanatory perspective view of the recording apparatus, and FIG. 2 is an explanatory side view of a mechanism portion of the recording apparatus.

  This ink jet recording apparatus includes a carriage movable in the main scanning direction inside the recording apparatus main body 81, a recording head composed of an ink jet head embodying the present invention mounted on the carriage, an ink cartridge for supplying ink to the recording head, and the like. A sheet feeding cassette (or a sheet feeding tray) 84 on which a large number of sheets 83 can be stacked from the front side is detachably attached to the lower part of the apparatus main body 81. The manual feed tray 85 for manually feeding the paper 83 can be opened, the paper 83 fed from the paper feed cassette 84 or the manual feed tray 85 is taken in, and the printing mechanism 82 After recording a required image, the image is discharged to a paper discharge tray 86 mounted on the rear side.

  The printing mechanism 82 holds a carriage 93 slidably in the main scanning direction by a main guide rod 91 and a sub guide rod 92 which are guide members horizontally mounted on left and right side plates (not shown). A head 94 composed of an inkjet head that ejects ink droplets of each color (Y), cyan (C), magenta (M), and black (Bk) is placed in a direction that intersects a plurality of ink ejection ports (nozzles) with the main scanning direction. They are arranged and mounted with the ink droplet ejection direction facing downward. In addition, each ink cartridge 95 for supplying ink of each color to the head 94 is replaceably mounted on the carriage 93.

  The ink cartridge 95 has an air port that communicates with the atmosphere upward, a supply port that supplies ink to the inkjet head below, and a porous body filled with ink inside, and the capillary force of the porous body. Thus, the ink supplied to the inkjet head is maintained at a slight negative pressure. Further, although the heads 94 of the respective colors are used here as the recording heads, a single head having nozzles that eject ink droplets of the respective colors may be used.

  Here, the carriage 93 is slidably fitted to the main guide rod 91 on the rear side (downstream side in the paper conveyance direction), and is slidably mounted on the sub guide rod 92 on the front side (upstream side in the paper conveyance direction). doing. In order to move and scan the carriage 93 in the main scanning direction, a timing belt 100 is stretched between a driving pulley 98 and a driven pulley 99 that are rotationally driven by a main scanning motor 97, and the timing belt 100 is moved to the carriage 93. The carriage 93 is driven to reciprocate by forward and reverse rotation of the main scanning motor 97.

  On the other hand, in order to convey the paper 83 set in the paper feed cassette 84 to the lower side of the head 94, the paper feed roller 101 and the friction pad 102 for separating and feeding the paper 83 from the paper feed cassette 84 and the paper 83 are guided. A guide member 103, a transport roller 104 that reverses and transports the fed paper 83, a transport roller 105 that is pressed against the peripheral surface of the transport roller 104, and a leading end that defines a feed angle of the paper 83 from the transport roller 104 A roller 106 is provided. The transport roller 104 is rotationally driven by a sub-scanning motor 107 through a gear train.

  A printing receiving member 109 is provided as a paper guide member that guides the paper 83 sent from the transport roller 104 below the recording head 94 in accordance with the movement range of the carriage 93 in the main scanning direction. A conveyance roller 111 and a spur 112 that are rotationally driven to send the paper 83 in the paper discharge direction are provided on the downstream side of the printing receiving member 109 in the paper conveyance direction, and the paper 83 is further delivered to the paper discharge tray 86. A roller 113 and a spur 114, and guide members 115 and 116 that form a paper discharge path are disposed.

  At the time of recording, the recording head 94 is driven according to the image signal while moving the carriage 93, thereby ejecting ink onto the stopped sheet 83 to record one line. Record the line. Upon receiving a recording end signal or a signal that the trailing edge of the paper 83 has reached the recording area, the recording operation is terminated and the paper 83 is discharged.

  Further, a recovery device 117 for recovering defective ejection of the head 94 is disposed at a position outside the recording area on the right end side in the movement direction of the carriage 93. The recovery device 117 includes a cap unit, a suction unit, and a cleaning unit. The carriage 93 is moved to the recovery device 117 side during printing standby and the head 94 is capped by the capping means, 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, the ink viscosity of all the ejection ports is made constant and stable ejection performance is maintained.

  When a discharge failure occurs, the discharge port (nozzle) of the head 94 is sealed with a capping unit, and bubbles and the like are sucked out from the discharge port with the suction unit through the tube. Is removed by the cleaning means to recover the ejection failure. Further, the sucked ink is discharged to a waste ink reservoir (not shown) installed at the lower part of the main body and absorbed and held by an ink absorber inside the waste ink reservoir.

<Droplet ejection head (inkjet head)>
FIG. 3 shows sectional views from three directions of the droplet discharge head according to the embodiment of the present invention. The droplet discharge head shown in FIG. 3 is called an inkjet head in FIGS. 1 and 2, and shows an example of a side shooter system that discharges ink droplets from nozzles provided on the surface of the substrate. Show.

  As shown in FIG. 3, the inkjet head of this embodiment includes a nozzle substrate 141 having nozzles for ejecting ink, a pressurized liquid chamber 138, a fluid resistance portion 139, a groove portion serving as an ink flow path, and a piezoelectric layer on the vibration plate 121. A three-layer structure in which a liquid chamber substrate 120 formed with an actuator portion such as 123 and a protective substrate (subframe) 137 provided with a piezoelectric element protection space 134 are stacked.

  The liquid chamber substrate 120 is an SOI substrate in which silicon is bonded to a silicon substrate via a silicon oxide film. The diaphragm in the present embodiment applies a pyro-oxidation method to the surface of the Si layer of the SOI substrate, forms a silicon oxide film, a platinum film serving as the lower electrode 122, a piezoelectric layer (PZT) 123, an upper electrode 124, An actuator having a multi-layer structure of platinum film is formed in a region facing the pressurized liquid chamber 128 formed by etching silicon.

  Further, an interlayer insulating film 125 disposed between the upper and lower electrodes (lower electrode 122 and upper electrode 124) and the wiring material (leading wiring 130), and a passivation film (passivation layer 131) for protecting the material of the leading wiring 130. Are arranged so as to cover the upper surface and side surfaces of the actuator (piezoelectric layer (PZT) 123).

  In the nozzle substrate 141, nozzle holes 142 are formed on a SUS substrate having a thickness of 30 to 50 microns by pressing and polishing. Each nozzle hole 142 is provided so as to communicate with the pressurized liquid chamber 138 of the liquid chamber substrate 120.

  The protective substrate 137 increases the rigidity of the groove portion serving as the ink flow path as the common liquid chamber 136, the space for preventing the piezoelectric element from being protected and displaced, and the flow path partition wall 144, and the column 143 to support the entire liquid chamber. Forming.

  Next, a manufacturing method and configuration of the droplet discharge head shown in FIG.

  A manufacturing method of this embodiment will be described with reference to FIGS. In this embodiment, an actuator is created by depositing a diaphragm material and a piezoelectric element material on a silicon substrate.

  First, an SOI substrate in which 0.2 μm of silicon oxide film and 2.0 μm of silicon are bonded to the surface of a 400 μm thick silicon substrate is used. A silicon oxide film of 0.3 μm is formed on the surface of the SOI substrate by a pyro oxidation method (FIG. 4), and this is used as a diaphragm layer 121. The silicon substrate having a thickness of 400 μm becomes the liquid chamber substrate 120.

  Thereafter, a platinum (Pt) layer to be the lower electrode (common electrode) 122 of the piezoelectric element is deposited and patterned by sputtering (FIG. 5). Further, the piezoelectric layer 123 is formed to a thickness of 2 μm by the sol-gel method, and further, a platinum (Pt) layer that becomes the upper electrode (individual electrode) 124 is formed to a thickness of 0.1 μm (FIG. 6). Thereafter, the upper electrode and the piezoelectric layer are patterned by a lithoetch method (FIG. 6).

  Next, an interlayer insulating film 125 is formed to 0.3 μm by plasma CVD, and a via hole 126 for making wiring contact is formed by lithoetch (FIG. 7). The interlayer insulating film 125 patterns a conductive portion (via hole 126) between the lead wiring 130 and the upper electrode 124 to be formed next, a conductive portion 128 to the bypass wiring, and a through portion 129 to be an ink supply hole ( FIG. 7).

  Further, an extraction electrode (extraction wiring 130) is formed of an aluminum material (FIG. 8). Since the extraction electrode receives stress due to vibration of the diaphragm due to driving of the piezoelectric body, a soft aluminum material is used and is thickly stacked so as not to be disconnected by vibration.

  Next, 2 μm of silicon nitride film is formed by plasma CVD as a passivation film (passivation layer 131) for protecting the aluminum wiring and patterned (FIG. 9). Thereafter, a portion to be an ink supply port of the vibration plate 121 is etched in advance (FIG. 10).

  Further, gold is laminated by a plating method, and the pad portion 132 of the individual electrode and the bypass wiring 133 are simultaneously formed (FIG. 11). By forming the pad portion 132 with gold, electrical connection with a driver IC (not shown) is connected by low-temperature wire bonding. Gold has a low resistance value, and has a great effect of reducing the common electrode resistance value as a bypass wiring. The pad portion 132 and the formation process can be separated and copper, aluminum, or the like can be used as a bypass wiring material. In that case, a protective layer that protects the bypass wiring 133 from corrosion may be required.

  Thereafter, a protective substrate 137 in which a pillar 143 is separately formed on a glass substrate by blasting is bonded to the liquid chamber substrate 120 (FIG. 12), and the surface opposite to the protective substrate bonding surface of the liquid chamber substrate 120 is polished to a desired thickness. (FIG. 13).

  The protective substrate 137 may be a silicon substrate obtained by processing a recess by a lithoetch method, or a silicon substrate processed by wet etching using an alkaline etching solution such as TMAH or KOH. Also, a molded part such as a resin mold or a metal injection mold may be used.

  In addition, when the driver circuit is integrally formed on the actuator substrate, an oxide film formed by a pyro-oxidation method is formed by a LOCOS oxidation method, and a driver circuit is formed on the same substrate by selecting an oxide film formation region. You can also

  Thereafter, recesses to be the pressure liquid chamber 138, the fluid resistance portion 139, and the supply portion 140 are formed on the opposite surface of the silicon substrate by ICP dry etching (FIG. 13).

  Finally, a nozzle substrate 141, in which nozzle holes 142 are formed on a 30 to 50 micron thick SUS substrate by pressing and polishing, is bonded to the surface of the liquid chamber substrate 120 where the channel partition wall 144 is formed, and the upper electrode 124 of the piezoelectric element is bonded. Further, the droplet discharge head is completed by connecting the aluminum wiring portion connected to the lower electrode 122 to the drive circuit (FIG. 14).

<Example 1>
FIGS. 15 and 16 are a block diagram of the driver IC circuit of this embodiment and a diagram for explaining the operation, and correspond to FIGS. 24 and 25 of the conventional example. Within the printing cycle, application of a part of the drive waveform to the piezoelectric layer is controlled by the driver IC, and droplets having different sizes are ejected.

  FIG. 17 shows the voltage ΔV = V1−V0 applied to the piezoelectric layer from the drive waveform V1 applied to the individual electrodes and the bias waveform V0 applied to the common electrode based on FIG.

  In the example shown in FIG. 17, 2-bit gradation signals (image data) are transferred in parallel, and the time axis data is converted into gradations in each channel (large droplets, medium drops) using a shift register and a latch circuit. Droplet, droplet, non-ejection). Each channel applies a part of the drive waveform voltage to the piezoelectric element by turning on and off the switch in the driver IC based on the control signal of the gradation.

In the example of FIG. 16, the switching operation is performed as follows with respect to the switching timings T1, T2, T3, and T4 (circled numbers in the figure are substituted with numbers in parentheses in the following table).
T1 T2 T3 T4
Large droplet (1, 1) ON ON OFF ON (1), (2), (3), (4) Discharge medium droplet (1, 0) OFF OFF OFF ON (3), (4) Discharge small droplet (0 , 1) OFF ON OFF OFF (2) Discharge Non-discharge (0, 0) OFF OFF ON OFF

  At this time, a voltage based on the bias voltage V0 is applied to the common electrode side, but a waveform that changes the voltage value is output in the period T3 instead of a constant voltage.

  FIG. 16 shows two printing cycles. In the first printing cycle A, the fine driving waveform is output as the bias voltage, and in the second printing cycle B, the fine driving waveform is output. It has not been. This is more easily realized than switching the presence / absence of fine driving in the driving waveform because the bias voltage waveform is not switched but only the bias voltage circuit selects whether or not to output the bias voltage fine driving waveform. .

  When a fine drive waveform is output (print cycle A) or not (print cycle B) every cycle, the frequency of occurrence of fine drive is 50%.

  In addition, since the channel in which the gradation signal is non-ejection (0, 0) is ON during the period T3, the individual electrode has a fine driving waveform (first cycle) or an intermediate potential (second cycle). A voltage is applied and charging is performed. As a result, a decrease in the reference potential due to the charge leakage of the piezoelectric layer can be prevented.

  In the case of a thin film piezo, since the piezoelectric layer is thin, the electric field strength at the time of driving shows the butterfly characteristic shown in FIG. 21, so that when a voltage is applied, the pressurized liquid chamber 138 is displaced in the contraction direction regardless of the polarity. That is, in order to realize so-called striking in which the pressurized liquid chamber 138 is once expanded and then contracted to discharge droplets, it is necessary to charge the piezoelectric layer to an intermediate potential (reference potential) and maintain it. This is very important for driving a piezo droplet discharge head.

  For the channels ejected by large droplets, medium droplets, and small droplets, since the bias voltage V0 is applied to the common electrode, the voltage ΔV = V1−V0 applied to the piezoelectric layer as shown in FIG. The piezoelectric layer is displaced in the voltage range with good displacement efficiency near 0 V described in 21.

  In other words, by using an efficient voltage range, the maximum voltage amplitude can be suppressed and the power supply voltage specification of the driver IC can be suppressed low. A power supply with high withstand voltage and good voltage accuracy leads to an increase in cost.

  In the present embodiment, by providing the fine drive waveform on the bias voltage circuit side, the frequency with which the fine drive waveform is applied can be changed with a simple configuration without increasing the number of gradation signals. In other words, two-bit pseudo five gradations (large droplet, medium droplet, small droplet, fine drive, and charge without fine drive) are realized. Thereby, it is easy to adjust the frequency of applying fine driving, and it is possible to avoid excessive fine driving and suppress power consumption.

  In addition, applying a bias voltage to the common electrode side is possible when using a piezoelectric layer that has a displacement-voltage that exhibits a butterfly characteristic and becomes saturated when the voltage is increased. This is effective in using a voltage range with good displacement efficiency including a reverse electric field in the vicinity of 0V. Note that applying a bias voltage to the electrode (common electrode) opposite to the electrode (individual electrode) to which the drive waveform is applied can be realized by a unipolar power source.

  Note that the method of cutting out the drive waveform and the waveform of the control vibration is not limited to this. In this embodiment, pseudo 5 gradations are created with 2 bits, but pseudo 3 gradations (discharge, fine driving, and charging without fine driving) can be made with 1 bit. The number of gradation signals is not limited to 2 bits, such as pseudo 9 gradations (3 bits, 8 gradations + 1 gradation).

<Example 2>
FIG. 18 shows another embodiment of the present invention, and the bias voltage waveform is different from that of the first embodiment.

  Various waveforms can be selected as the voltage output as the bias voltage waveform. In the first embodiment, the bias signal circuit and the amplifier circuit are required to output the bias voltage waveform. However, in the case of the fine driving waveform as in the present embodiment, discharging from the bias voltage (potential) is charged. Thus, a fine driving waveform can be generated.

  As described above, the technical features of the first and second embodiments are not based on the circuit configuration of the bias voltage waveform, but are characterized in that the bias voltage waveform is generated in the common electrode side wiring at a specific frequency.

<Example 3>
Next, in this embodiment, a table (FIG. 19) relating to the in-machine temperature and in-machine humidity of the droplet discharge device is created for the frequency with which the fine drive waveform is generated in the bias voltage, and the fine drive waveform is generated based on the table. Let As the temperature detection means and humidity detection means in the machine, those well known to those skilled in the art can be used.

  The optimal fine drive waveform application frequency varies depending on the type of ink used, and the probability of the table varies depending on the ink. As shown in FIG. 19, 100% indicates that a fine drive waveform is generated in the bias voltage every time during the printing cycle. 90% means that if it is generated nine times, the DC voltage of V0 is maintained once without generating a fine driving waveform. 80% is generated 4 times in 5 times. 70% means that it is randomly generated 7 times in 10 times.

  Since the ink in the nozzle is more likely to dry and thicken as the humidity is lower, the frequency of occurrence of fine driving is increased on the low humidity side. On the low temperature side, since the viscosity of the whole ink is increased, the fine driving frequency is increased.

  As described above, the minimum necessary fine driving can be applied by changing the frequency of occurrence of the fine driving waveform to be applied to the bias voltage based on the table of the in-machine temperature, the in-machine humidity, and the fine driving occurrence probability prepared in advance. As a result, it is possible to provide a highly reliable liquid droplet ejection device at low cost while preventing jet bending and ejection failure due to ink thickening of the nozzle, maintaining image quality.

<Example 4>
FIG. 20 is a setting table for applying a control method for determining a repetitive pattern with respect to the frequency of occurrence of the fine drive waveform in FIG. In FIG. 20, “1” and “0” indicate fine driving generation patterns with a printing cycle of 10 cycles.
1: Output fine drive waveform to bias voltage 0: Do not output fine drive waveform to bias voltage (DC output)

  According to the present embodiment, control is facilitated by determining a fine drive waveform generation pattern in advance. The generation pattern is preferably set so that the fine drive generation interval is as uniform as possible with respect to the printing cycle. When set in this way, the nozzle state for each printing cycle can be made uniform. For example, when the occurrence probability is 30%, (1001001000) is preferable to (11100000000).

<Example 5>
In the case of an inexpensive personal printer, a humidity sensor may not be provided. This embodiment is characterized in that the fine drive occurrence frequency is extracted from the table of FIG. 19 only with respect to the temperature, and the fine drive waveform is applied at the maximum frequency of each temperature. Thereby, even in a droplet discharge device that does not have a humidity sensor, power consumption can be reduced.

<Effect>
The effect by embodiment mentioned above is described. According to the embodiment, by providing the fine drive waveform on the bias voltage circuit side, the frequency with which the fine drive waveform is applied can be changed with a simple configuration without increasing the number of gradation signals. This makes it easy to adjust the frequency of applying fine driving, prevent image deterioration due to nozzle drying, maintain image quality, and avoid excessive fine driving to reduce power consumption.

  In addition, applying a bias voltage to the common electrode side is possible when using a piezoelectric layer that exhibits a butterfly characteristic when the displacement-voltage is high, such as a thin-film piezo, and that appears to be saturated when the voltage is increased. This is effective in using a voltage range with good displacement efficiency including a reverse electric field in the vicinity of 0 V, and can be realized with a unipolar power source, and is low in cost.

  The present invention can be used for an inkjet printer, a digital printing apparatus using an MFP, a printer used in an office or a personal computer, an MFP, and the like. As an application field, it can also be used for three-dimensional molding technology using inkjet technology. The present invention is not construed as being limited to the above-described embodiments.

120 Liquid chamber substrate 121 Diaphragm 122 Lower electrode (common electrode)
123 Piezoelectric layer (PZT)
124 Upper electrode (individual electrode)
DESCRIPTION OF SYMBOLS 125 Interlayer insulation film 126 Via hole 127 Opening part 128 Conduction part to bypass wiring 129 Through part 130 Lead-out wiring 131 Passivation layer 132 Pad part of individual electrode 133 Bypass wiring 134 Piezoelectric element protection space 135 Space for wiring 136 Common liquid chamber 137 Protective substrate (Sub-frame)
138 Pressurized liquid chamber 139 Fluid resistance part 140 Supply part 141 Nozzle substrate 142 Nozzle hole 143 Column 144 Flow path partition

Japanese Patent Laid-Open No. 10-100401 Japanese Patent Laid-Open No. 02-289351 JP 05-286131 A JP 2006-321200 A JP 2010-105300 A

Claims (4)

A plurality of nozzle openings;
A flow path forming substrate having a pressurized liquid chamber communicating with each nozzle opening;
A piezoelectric actuator formed on the flow path forming substrate;
A droplet discharge head provided with a driver IC for switching voltage application of the piezoelectric actuator;
Drive waveform generating means for applying a drive waveform voltage to the droplet discharge head;
A bias signal circuit for applying a bias voltage to the opposite electrode of the piezoelectric actuator;
With
The liquid droplet ejection apparatus, wherein the bias signal circuit changes a bias voltage at a timing of applying a drive waveform voltage to the piezoelectric actuator that does not eject liquid droplets within one printing cycle. Having temperature detection means,
2. The liquid droplet ejection apparatus according to claim 1, wherein the bias signal circuit changes the frequency of changing the voltage of the bias signal circuit within one printing cycle based on a table prepared in advance from the detected temperature. Having humidity detection means,
3. The droplet discharge device according to claim 2, wherein the bias signal circuit changes the frequency of changing the voltage of the bias signal circuit within one printing cycle based on a table prepared in advance from the detected temperature and humidity. .   4. The droplet discharge device according to claim 2, wherein the frequency of changing the voltage of the bias signal circuit is changed according to a table of repetitive patterns.

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