JP2011000738A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve such the problem that when a plurality of piezoelectric actuators are driven in a time-sharing manner in a passive system, the piezoelectric actuator is also displaced with respect to a non-discharge nozzle and accordingly, discharge or drip of a liquid from a nozzle is caused.SOLUTION: Each of the piezoelectric actuators 7 for a liquid discharge head 1 is formed by layering a first electrode 11, a first piezoelectric layer 12, a second electrode 13, a second piezoelectric layer 14, and a third electrode 15 in this order on a diaphragm 6. The second electrode 13 is connected to all the actuators 7 in common, so that the same voltage is simultaneously applied to them. The first electrodes 11 are divided into first groups as scanning electrodes and the same voltage is simultaneously applied to each of these groups. The third electrodes 15 are divided into second groups as signal electrodes, and the same voltage is simultaneously applied to each of these groups. Only one actuator 7 is used in common to the group belonging to the first group and the group belonging to the third group.

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus including a liquid discharge head including a piezoelectric actuator.

  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 discharge recording type image forming using a recording head composed of a liquid discharge head (droplet discharge head) that discharges 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 are transported from a recording head (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). And a serial type image forming apparatus that forms an image by ejecting liquid droplets while the recording head moves in the main scanning direction, and a line type head that forms images by ejecting liquid droplets without moving the recording 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. “Piezoelectric element” and “piezoelectric layer” mean an electromechanical conversion element and an electromechanical conversion layer.

  Conventionally, as a liquid ejection head, a piezoelectric actuator is used as a pressure generating means (actuator means) for generating pressure to pressurize ink which is liquid in a liquid chamber, an electrostatic actuator, a thermal actuator, etc. It has been known. As a piezoelectric actuator, a unimorph type piezoelectric element in which a first electrode (lower electrode), a first piezoelectric layer, and a second electrode (upper electrode) are laminated on a diaphragm is arranged, and the first electrode and the second electrode are arranged on the diaphragm. There is one that causes expansion and contraction in the in-plane direction of the piezoelectric element by applying a driving voltage to bend the diaphragm in the out-of-plane direction.

  By the way, in an image forming apparatus (hereinafter, also referred to as “inkjet recording apparatus”), in order to form a high-quality image at high speed, the liquid discharge head constituting the recording head is highly integrated, and as a result, the number of nozzles is increased. Increase in nozzle density and nozzle density. In addition, the head tends to increase in size as represented by the line type head.

  In this case, since the actuator of the liquid ejection head is driven by applying a voltage, electrode wiring corresponding to the number of actuators is simply required. Therefore, the number of electrode wiring increases as the number of nozzles increases. As a result, unnecessary head enlargement and apparatus enlargement are caused, and the apparatus cost is increased.

  Therefore, as a method for reducing the number of electric wires, there is a method that applies time-division driving that has been adopted in the field of displays (a head using a thermal actuator: Patent Document 1). The time-division driving has m rows of scanning electrodes and n columns of signal electrodes, each is applied with a potential in a time-sharing manner, and elements arranged at the intersections thereof are selectively driven.

  As the time-division driving method, two driving methods of passive driving and active driving are known. The passive drive system has a configuration in which a potential applied to the scanning electrode is directly applied to one electrode of the actuator, and a potential applied to the signal electrode is applied to the other electrode of the actuator. On the other hand, the active drive system adopts a configuration in which a thin film active element such as a thin film transistor (TFT) or a thin film diode (TFD) is provided at the intersection of a scanning electrode and a signal electrode, and enables high-speed switching response.

  For the display field and the liquid discharge head using the above-described thermal actuator (electric-thermal conversion element), an active drive system is employed. However, regarding a liquid discharge head using a piezoelectric actuator composed of a thin film piezoelectric element, it is technically difficult to provide a thin film active element for each actuator. That is, because the method for manufacturing the thin film piezoelectric element and the method for manufacturing the semiconductor are different, or the film forming temperatures thereof are greatly different, it is difficult to manufacture both on one substrate. Therefore, when performing time-division driving for a liquid ejection head using a piezoelectric actuator of a thin film piezoelectric element, a passive driving method is employed (Patent Documents 2 to 4).

Japanese Patent Laid-Open No. 01-020152 Japanese Patent No. 4019197 Japanese Patent Application Laid-Open No. 06-127034 JP 07-137242 A

  However, when a plurality of piezoelectric actuators are driven in a time-sharing manner by the passive drive method, there is a problem that it is impossible to create a state in which no voltage is applied to all unselected actuators that are not desired to be driven. This point will be described with reference to FIGS.

  First, as shown in FIG. 13, the liquid discharge head forms a liquid chamber 502 in which a nozzle (not shown) communicates with a flow path plate 501, and a part of the wall surface of the liquid chamber 502 is formed with a vibration plate 503. A piezoelectric actuator 504 is disposed outside the diaphragm 503. The piezoelectric actuator 504 is configured by sequentially laminating a first electrode (lower electrode) 511, a piezoelectric layer 512, and a second electrode (upper electrode) 513 on a vibration plate 503.

  When a plurality of piezoelectric actuators are provided, for example, as shown in FIG. 14, the m first electrodes 511 are used as scanning electrodes, the j second electrodes 513 are used as signal electrodes, and scanning electrodes (first electrodes). Actuators 504 are configured by disposing piezoelectric layers 512 at the intersections of 511 and signal electrodes (second electrodes) 513. Here, for the sake of explanation, it is assumed that the actuators are arranged in a matrix. However, as shown in FIG. 15, the same problem described below also occurs when the actuators 504 are arranged in a line.

  Here, in order to perform passive driving, a method in which the potentials applied to the scanning electrode (first electrode) 511 and the signal electrode (second electrode) 513 are different in polarity can be considered. In this case, when only the actuator 504a in FIG. 14 is ON-driven (droplet is ejected), the potential E1 shown in FIG. 16 is applied to the scanning electrode 511 and the signal electrode 512 when the driving voltage is V0. The actuator 504a is driven ON. However, at this time, the potential E2 in FIG. 16 is applied to the actuator 504b, the potential E3 is applied to the actuator 504c, and the potential E4 is applied to the actuator 504d. That is, the voltage of the potential V0 / 3 is applied to the actuator 504b, and the voltage of the potential 2 × V0 / 3 is applied to the actuator 504c.

  As described above, when passive driving is performed using a piezoelectric actuator, a voltage equal to or greater than ½ of the driving voltage is applied to a non-selected actuator that does not desire ON driving. Since the piezoelectric element expands and contracts substantially linearly with respect to the driving voltage, the out-of-plane displacement of the diaphragm also has characteristics that are approximately linear with respect to the driving voltage, and therefore corresponds to a non-selected (no nozzle that does not eject droplets). ) The piezoelectric actuator also generates a driving force that is approximately ½ or more of that during ejection, and displaces the diaphragm by a ½ displacement amount at the time of selection.

  As a result, there is a risk of droplets being ejected due to the displacement of the vibration plate even for nozzles that are not ejected with droplets (non-ejection), and even if the droplets are not ejected, ink overflows to the nozzle surface due to the rise of the meniscus. There is a problem that stable droplet ejection cannot be performed.

  The present invention has been made in view of the above problems, and stably ejects droplets by preventing droplet ejection and overflow from a non-ejection nozzle when time-sharing driving a liquid ejection head having a piezoelectric actuator. Therefore, it is an object to be able to form a high quality image.

In order to solve the above problems, an image forming apparatus
A plurality of nozzles for discharging droplets, a plurality of liquid chambers communicating with the nozzles, a plurality of diaphragms forming a part of a wall surface of the liquid chambers, and a plurality of piezoelectric actuators for displacing the diaphragms A liquid ejection head having
The piezoelectric actuator of the liquid ejection head is configured by sequentially laminating a first electrode, a first piezoelectric layer, a second electrode, a second piezoelectric layer, and a third electrode on the diaphragm.
Of the first, second, and third electrodes of the plurality of piezoelectric actuators,
One electrode is applied with a common potential across all piezoelectric actuators,
The other one electrode is divided into a plurality of first groups, and a common potential is simultaneously applied to each group,
Furthermore, the other one electrode is divided into a plurality of second groups, and a common potential is simultaneously applied to each group,
The image forming apparatus according to claim 1, wherein only one piezoelectric actuator exists in common in the first group and the second group.

  Here, one electrode to which a common potential is applied to all the piezoelectric actuators can be configured as the second electrode.

  The electric field strength applied to the first piezoelectric layer may be greater than the electric field strength applied to the second piezoelectric layer.

  The second electrode can be connected to a ground potential.

  According to the image forming apparatus of the present invention, the piezoelectric actuator of the liquid ejection head is formed by sequentially laminating the first electrode, the first piezoelectric layer, the second electrode, the second piezoelectric layer, and the third electrode on the vibration plate. The first electrode, the second electrode, and the third electrode of the plurality of piezoelectric actuators are configured, one electrode is applied with a common potential in all the piezoelectric actuators, and the other one electrode is a plurality of first groups. A common potential is applied to each group simultaneously, and the other electrode is further divided into a plurality of second groups, and a common potential is applied to each group simultaneously. Since there is only one piezoelectric actuator that exists in common in the group, it is possible to prevent droplet discharge and overflow from the non-discharge nozzle when performing time-division driving, and stably perform droplet discharge. Capable of forming high-quality images Kill.

FIG. 3 is a cross-sectional explanatory diagram of the liquid discharge head in the short side direction of the liquid ejection head for explaining the first embodiment of the present invention. FIG. 6 is an explanatory plan view for explaining a first example of time-division driving for a plurality of piezoelectric actuators in the embodiment. It is explanatory drawing with which it uses for description of the applied voltage given to each electrode of a some piezoelectric actuator by simultaneous division drive. FIG. 6 is an explanatory plan view for explaining a second example of time-division driving for a plurality of piezoelectric actuators in the embodiment. It is explanatory drawing with which it uses for description of the applied voltage given to each electrode of a some piezoelectric actuator by simultaneous division drive. It is sectional explanatory drawing with which it uses for description of the manufacturing process of the piezoelectric actuator of the liquid discharge head in this invention. It is explanatory drawing with which it uses for description of the measurement result of the applied voltage with respect to the piezoelectric layer of a piezoelectric actuator of a comparative example and an Example, and a diaphragm displacement amount. It is explanatory drawing with which it uses for description of the measurement result of the other applied voltage with respect to the piezoelectric layer of the piezoelectric actuator of a comparative example and an Example, and a diaphragm displacement amount similarly. It is explanatory drawing with which it uses for description of the applied voltage in 2nd Embodiment of this invention. It is explanatory drawing with which it uses for description of the applied voltage given to each electrode of the piezoelectric actuator which comprises a liquid discharge head. 1 is an overall configuration diagram illustrating an example of an image forming apparatus according to the present invention. Similarly it is principal part plane explanatory drawing. It is principal part sectional explanatory drawing of the diaphragm short side direction used for description of the piezoelectric actuator in the conventional liquid discharge head. FIG. 6 is an explanatory plan view for explaining time-division driving for a plurality of piezoelectric actuators of the liquid ejection head. It is a plane explanatory view showing another example of actuator arrangement for explaining time-division driving for a plurality of piezoelectric actuators. It is explanatory drawing with which it uses for description of the applied voltage with respect to the piezoelectric actuator in simultaneous division drive.

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is an explanatory diagram for explaining the first embodiment of the present invention. FIG. 1 is a cross-sectional explanatory view of a portion corresponding to one nozzle of the liquid ejection head of the same embodiment in the diaphragm short side direction.
The liquid discharge head 1 constituting the recording head includes a nozzle plate 3 on which nozzles 2 for discharging liquid droplets are formed, a flow path plate 5 that forms a liquid chamber (pressure chamber) 4 with which the nozzles 2 communicate, and a liquid chamber 4. The diaphragm 6 that forms a part of the wall surface of the motor and the piezoelectric actuator 7 that displaces (deforms) the diaphragm 6 are provided.

  The piezoelectric actuator 7 includes a first electrode 11, a first piezoelectric layer (first piezoelectric material layer) 12, a second electrode 13, a second piezoelectric layer (second piezoelectric material layer) 14, and a third electrode on the diaphragm 6. 15 are sequentially laminated.

  The drive voltage application unit 20 applies drive voltages V1, V2, and V3 to the first electrode 11, the second electrode 13, and the third electrode 15 of the piezoelectric actuator 7 according to the print data.

  Here, the three electrodes 11, 13, and 15 are independent from each other, and when discharging droplets, both the first piezoelectric layer 12 and the second piezoelectric layer 14 extend (or contract together) in the in-plane direction. Voltage is applied to On the other hand, when not discharging, voltage is applied so that only one of the first piezoelectric layer 12 and the second piezoelectric layer 14 extends (or contracts), and the other piezoelectric layer is not expanded or contracted.

  First, when only the first piezoelectric layer 12 is expanded and contracted, a voltage is applied only to the first piezoelectric layer 12, but the diaphragm 6 and the second piezoelectric layer 14 that do not expand and contract exist on both sides thereof. The diaphragm 6 is not a unimorph type, and the in-plane expansion and contraction of the first piezoelectric layer is greatly limited. As a result, the out-of-plane displacement of the diaphragm 6 is also very small.

  Next, when only the second piezoelectric layer 14 is expanded and contracted, the piezoelectric actuator 7 and the diaphragm 6 are unimorph type, and the diaphragm 6 can be flexed efficiently. However, since the diaphragm 6 and the first piezoelectric layer 12 or the second piezoelectric layer 14 usually have the same thickness, when only the second piezoelectric layer 14 is expanded and contracted, the first piezoelectric layer 14 is also a part of the diaphragm. The configuration is as follows. At this time, the driving voltage for droplet discharge is set to V0, and the voltage V0 / 2 is applied to the second piezoelectric layer 14, and the voltage V0 / 2 is applied to the piezoelectric layer 512 having the configuration shown in FIG. In this case, assuming that the total piezoelectric layer thickness is the same in FIG. 21 and FIG. 1, the displacement amount is smaller in the former case.

  In other words, assuming that the driving voltage for droplet discharge is V0, even if the voltage V0 / 2 is applied, the displacement amount of the vibration plate 6 is ½ or less of the displacement amount during droplet discharge. In addition, problems such as liquid dripping due to the operation of the actuator 7 that does not discharge droplets are improved.

  Further, when it is desired to reduce the amount of displacement when only the second piezoelectric layer 14 is expanded and contracted, the expansion and contraction of the first piezoelectric layer 12 in the no-load state is larger than the expansion and contraction of the second piezoelectric layer 14 in the no-load state. Should be set to be larger. As described above, when a voltage is applied only to the first piezoelectric layer 12, the displacement of the diaphragm 6 is very small because the actuator is not a unimorph type. That is, the amount of displacement is smaller when a voltage having the same magnitude is applied only to the second piezoelectric layer 14 than when a voltage other than “0” is applied only to the second piezoelectric layer 14. Therefore, when both the first piezoelectric layer 12 and the second piezoelectric layer 14 are driven, a desired vibration plate displacement amount is obtained, and the first piezoelectric layer 12 and the second piezoelectric layer 14 are independent. When driven, the expansion and contraction of the first piezoelectric layer 12 in the no-load state is set to be larger than the expansion and contraction of the second piezoelectric layer 14 so that the obtained vibration plate displacement amount is approximately the same. It is good to leave.

  In this case, as a method of relatively increasing the expansion and contraction of the first piezoelectric layer 12, for example, the maximum voltage applied to the first piezoelectric layer 12 and the second piezoelectric layer 14 is the same, and the first piezoelectric layer 12 is moved to the second piezoelectric layer. It is formed thinner than the layer 14. Alternatively, the thickness of the first piezoelectric layer 12 and the second piezoelectric layer 14 are substantially the same, and the maximum voltage applied to the first piezoelectric layer 12 is increased, so that the electric field strength applied to the first piezoelectric layer 12 is increased. There is a configuration in which the electric field strength applied to 13 is relatively larger.

Next, a first example of a configuration in which the piezoelectric actuators of the liquid discharge head described above are arranged in a matrix and time-division driven will be described with reference to FIGS.
As shown in FIG. 2, the liquid ejection head 1 uses the first electrode 11 of each piezoelectric actuator 7 as a scanning electrode (hereinafter also referred to as “scanning electrode 11”) and the third electrode 15 as a signal electrode (hereinafter referred to as “scanning electrode 11”). The second electrode 13 is a common electrode, and the first and second piezoelectric layers 12 and 12 are respectively connected to the intersections of the scanning electrode 11 and the signal electrode 15 via the second electrode 13. 14 is provided, and the piezoelectric actuator 7 is arranged.

  Here, the second electrode 13, which is one electrode of all the actuators 7, is connected to a wiring at an end portion in the long side direction of the diaphragm, and is a common electrode to which a common potential is applied at the same time.

  The first electrode 11, which is another electrode, is divided into a plurality of first groups by the first grouping, and the first electrodes 11 divided into the plurality of first groups are end portions in the diaphragm long side direction for each group. The first electrode 11 is simultaneously applied with a common potential for each group. Here, the first electrode 11 is divided into m groups of i = 1 to i = m. For example, the first electrode 11 of the piezoelectric actuator 7 belonging to i = 1 is simultaneously applied with a common potential. In addition, a common potential is applied to each group i = 1 to i = m so that the first electrode 11 of the piezoelectric actuator 7 belonging to i = 2 is simultaneously applied with a common potential.

  Further, the third electrode 15 which is another electrode is divided into a plurality of second groups by the second grouping, and the third electrodes 15 divided into the plurality of second groups are arranged in the longitudinal direction of the diaphragm for each group. A common potential is applied to the third electrode 15 at the same time for each group. Here, the third electrode 15 is divided into n groups of j = 1 to j = n. For example, the third electrode 15 of the piezoelectric actuator 7 belonging to j = 1 is simultaneously applied with a common potential. In addition, a common potential is applied to each group j = 1 to j = n so that the third electrode 15 of the piezoelectric actuator 7 belonging to j = 2 is simultaneously applied with a common potential.

  At this time, among the plurality of piezoelectric actuators 7 belonging to a certain group of the first group, there is only one piezoelectric actuator 7 belonging to a certain group of the second group. For example, the piezoelectric actuator 7 belonging to the first group i = 3 and the third group j = 4 is only one of the piezoelectric actuators 7a.

  Here, the description will be made assuming that the maximum voltages applied to the first piezoelectric layer 12 and the second piezoelectric layer 14 of each actuator 7 are the same.

  First, when only the actuator 7a is driven (droplet is ejected), the potentials of the electrodes 11, 13, and 15 with respect to the first, second, and third electrodes 11, 13, and 15 of the actuator 7a are shown in FIG. It is assumed that droplets can be ejected by applying the voltages V1, V2, and V3 (the potential E1 is obtained) at the potential E1 shown. At this time, in order for both the first piezoelectric layer 12 and the second piezoelectric layer 14 to expand or contract, it is necessary that the orientation directions of both the piezoelectric layers 12 and 14 are reversed.

  There are three potentials applied to the other actuators 7b, 7c, and 7d. For example, the first, second, and third electrodes 11, 13, and 15 of the actuator 7b shown in FIG. Voltages V1, V2, and V3 to be E2 are applied, and voltages V1, V2, and V3 to be the potential E3 in FIG. 3 are similarly applied to the first, second, and third electrodes 11, 13, and 15 of the actuator 7c. Similarly, voltages V1, V2, and V3 that are the potential E4 of FIG. 3 are applied to the first, second, and third electrodes 11, 13, and 15 of the actuator 7d.

  In this case, since no voltage is applied to the first and second piezoelectric layers 12 and 14 of the actuator 7d, no droplets are ejected.

  In the actuator 7b, a voltage is applied only to the first piezoelectric layer 12, but since it does not have a monomorph structure as described above, a voltage equal to or higher than 1/2 (V / 02) of the drive voltage V0 for ejection is used. Even if it is applied, the amount of displacement of the diaphragm 6 is small and droplets cannot be ejected. Further, there is no problem that the ink overflows from the nozzle.

  In the actuator 7 c, a voltage is applied only to the second piezoelectric layer 14. As described above, since the first piezoelectric layer 12 is configured as a part of the diaphragm 6, the displacement of the diaphragm is small. Further, by setting the electric field strength applied to the first piezoelectric layer 12 to be larger than the electric field strength applied to the second piezoelectric layer 14, the displacement amount of the actuator 7c can be further reduced, In addition to not discharging droplets, there is no problem of overflowing liquid from the nozzle.

Next, a second example of the configuration in which the piezoelectric actuators of the liquid ejection head described above are arranged in a matrix and driven in a time-sharing manner will be described with reference to FIGS.
Here, the first electrode 11 which is one electrode of all the actuators 7 is connected to the wiring at the end portion in the long side direction of the diaphragm, and is a common electrode to which a common potential is applied at the same time.

  The second electrode 13, which is another electrode, is divided into a plurality of first groups by the first grouping, and the second electrodes 13 divided into the plurality of first groups are end portions in the diaphragm long side direction for each group. Are electrically connected to each other, and a common potential is simultaneously applied to the second electrode 13 for each group. Here, the second electrode 13 is divided into m groups of k = 1 to k = m. For example, the second electrode 13 of the piezoelectric actuator 7 belonging to k = 1 is simultaneously applied with a common potential. In addition, a common potential is applied to each of the groups k = 1 to k = m so that the second electrode 13 of the piezoelectric actuator 7 belonging to k = 2 is simultaneously applied with a common potential.

  Further, the third electrode 15 which is another electrode is divided into a plurality of second groups by the second grouping, and the third electrodes 15 divided into the plurality of second groups are arranged in the longitudinal direction of the diaphragm for each group. A common potential is applied to the third electrode 15 at the same time for each group. Here, the third electrode 15 is divided into n groups of j = 1 to j = n. For example, the third electrode 15 of the piezoelectric actuator 7 belonging to j = 1 is simultaneously applied with a common potential. In addition, a common potential is applied to each group j = 1 to j = n so that the third electrode 15 of the piezoelectric actuator 7 belonging to j = 2 is simultaneously applied with a common potential.

  At this time, among the plurality of piezoelectric actuators 7 belonging to a certain group of the first group, there is only one piezoelectric actuator 7 belonging to a certain group of the second group. For example, there is only one piezoelectric actuator 7a belonging to the first group k = 3 and the third group j = 4.

  Here, the description will be made assuming that the maximum voltages applied to the first piezoelectric layer 12 and the second piezoelectric layer 14 of each actuator 7 are the same.

  First, when only the actuator 7a is driven (droplet is discharged), the potentials of the electrodes 11, 13, and 15 with respect to the first, second, and third electrodes 11, 13, and 15 of the actuator 7a are shown in FIG. It is assumed that droplets can be ejected by applying the voltages V1, V2, and V3 (the potential E1 is obtained) at the potential E1 shown. At this time, in order for both the first piezoelectric layer 12 and the second piezoelectric layer 14 to expand or contract, it is necessary that the orientation directions of both the piezoelectric layers 12 and 14 are reversed.

  At this time, voltages V1, V2, and V3 that are the potential E2 of FIG. 5 are similarly applied to the first, second, and third electrodes 11, 13, and 15 of the actuator 7b, and the voltage is applied only to the first piezoelectric layer 12. 5 is applied to the first, second, and third electrodes 11, 13, and 15 of the actuator 7 c in the same manner, and the voltage is applied only to the second piezoelectric layer 14. Similarly, voltages V1, V2, and V3 that are the potential E3 of FIG. 5 are applied to the first, second, and third electrodes 11, 13, and 15 of the actuator 7d, and the first and second piezoelectric layers 12, Since no voltage is applied to 14, no droplets are ejected from the actuators 7b, 7c, 7d.

  However, in the second example, a voltage of −V0 / 2 is applied to the third electrode 15 of the actuator 7 that does not perform droplet discharge (the states of the potentials E2 and E4 in FIG. 5). Power efficiency is reduced.

Next, an example of a method for manufacturing a piezoelectric actuator will be described with reference to FIG. FIG. 6 is a sectional view in the short side direction of the diaphragm of one actuator.
Here, as shown in FIG. 6A, an SOI substrate 30 having a silicon oxide film 41 between single crystal silicon substrates 31 and 32 is used. Then, as shown in FIG. 6B, a resist film (not shown) is formed on the surface of the silicon substrate 31, and the silicon film 32 is wet-etched with KOH or the like using the oxide film 41 as a stop layer, and the digging portion is formed. Form. The digging portion becomes the liquid chamber 4 of the head, and the portion other than the digging becomes the liquid chamber interval wall. Further, the silicon substrate 31 becomes the diaphragm 6 (for example, a silicon substrate 31 having a thickness of 2 μm is used).

  Next, as shown in FIG. 6C, the resist on the vibration plate 6 made of the silicon substrate 31 is removed, and a 0.3 μm HTO (silicon oxide) film 42 is formed by CVD. Thereafter, as shown in FIG. 5D, the first electrode 11, the first piezoelectric layer 12, the second electrode 13, the second piezoelectric layer 14, and the third electrode 15 are sequentially stacked by CVD film formation and patterning. Thus, the piezoelectric actuator 7 is formed. The thickness of each electrode was 0.1 μm, the thickness of the piezoelectric layer was 1.5 μm, and the electrode material was platinum.

  Here, although FIG. 6 is a cross-sectional view in the short side direction of the diaphragm, it is not clear, but as described above, the second electrode 12 which is one electrode of all the actuators 7 is wired at the end part in the long side direction of the diaphragm. And a common electrode to which a common potential is applied at the same time. The first electrode 11 and the third electrode of each actuator 7 are grouped and divided into a plurality of first groups and second groups. The first electrode 11 and the third electrode 15 of each group are simultaneously provided for each group. A common potential is applied. In this case, only one piezoelectric actuator 7 exists in common in the first group and the second group.

Next, a comparison with a conventional piezoelectric actuator will be described.
Example 1
A piezoelectric actuator was manufactured in the manufacturing process of FIG.
(Comparative Example 1)
In the manufacturing process of FIG. 6 described above, as shown in FIG. 13, the piezoelectric actuator 504 without the second piezoelectric layer 13 and the third electrode 15 is used, and the thickness of the first piezoelectric layer 512 is 3 μm. Other than that, a similar configuration was produced.

  When 13V is applied to the first piezoelectric layer 12 of the piezoelectric actuator of Example 1 and 13V is applied to the second piezoelectric layer 14, vibration is applied to the case of applying 26V to the first piezoelectric layer 512 of the piezoelectric actuator of Comparative Example 1. The displacement at the center of the short side of the plate was measured with a laser Doppler vibrometer. As a result, as shown in FIG. 7, the displacement amount of the diaphragm is substantially the same.

  Further, when 13 V is applied only to the first piezoelectric layer 12 of the piezoelectric actuator of Example 1, and 13 V is applied only to the second piezoelectric layer 14, 16 V is applied to the first piezoelectric layer 512 of the piezoelectric actuator of Comparative Example 1. Similarly, in the case of application, the amount of displacement at the central portion in the short side direction of the diaphragm was measured with a laser Doppler vibrometer. The result is shown in FIG.

  As can be seen from FIG. 8, in the configuration of Example 1, a voltage of 13 V is applied only to the first piezoelectric layer 12 and the voltage applied to the second piezoelectric layer 14 is “0”. Alternatively, when a voltage of 13 V is applied only to the second piezoelectric layer 14 and the voltage applied to the first piezoelectric layer 12 is “0”, a voltage of 13 V is applied to the piezoelectric layer of Comparative Example 1. The amount of displacement of the diaphragm is smaller than when the voltage is applied.

  In the configuration of the first embodiment, the diaphragm displacement amount 0.2 μm when 13 V is applied only to the first piezoelectric layer 12 is more than the diaphragm displacement amount 0.6 μm when 13 V is applied to the second piezoelectric layer. Is also very small. For example, the voltage applied to the first piezoelectric layer 12 may be set larger than the voltage applied to the second piezoelectric layer 14 so that the difference between the displacement amounts becomes substantially equal.

  As described above, the piezoelectric actuator is configured by sequentially laminating the first electrode, the first piezoelectric layer, the second electrode, the second piezoelectric layer, and the third electrode on the diaphragm, and each of the first piezoelectric actuators. Of the electrodes, the second electrode, and the third electrode, one electrode is applied with a common potential to all the piezoelectric actuators, and the other electrode divided into a plurality of first groups is simultaneously applied to each group. A common potential is applied, and a further common electrode is applied to each of the other electrodes divided into a plurality of second groups at the same time for each group, and the group belonging to the first group and the group belonging to the second group are applied. By adopting a configuration with only one piezoelectric actuator in common, it is possible to prevent droplet discharge and overflow from the non-discharge nozzle when performing time-division driving, and stably perform droplet discharge. Shape high quality images It can be.

Next, the applied voltage in the second embodiment of the present invention will be described with reference to FIG.
Here again, the maximum voltage applied to the first piezoelectric layer 12 and the second piezoelectric layer 14 is assumed to be the same.
First, in the case where only the actuator 7a shown in FIG. 2 described above is driven (droplets are discharged) with the potential for discharging droplets as V0, the first, second, and third electrodes 11 of the actuator 7a, It is assumed that droplets can be ejected by applying voltages V1, V2, and V3 of the potential E1 shown in FIG. At this time, in order for both the first piezoelectric layer 12 and the second piezoelectric layer 14 to expand or contract, it is necessary that the orientation directions of both the piezoelectric layers 12 and 14 are reversed.

  The potential applied to the other actuator 7 has three states. For example, the first, second, and third electrodes 11, 13, and 15 of the actuator 7 b shown in FIG. 2 have a voltage V 1 that is the potential E 2 of FIG. V2 and V3 are applied, and voltages V1, V2, and V3 that are the potential E3 of FIG. 9 are applied to the first, second, and third electrodes 11, 13, and 15 of the actuator 7c, and the first and second electrodes of the actuator 7d are applied. 2. The voltages V1, V2, and V3 that are the potential E4 in FIG. 7 are applied to the third electrodes 11, 13, and 15, respectively.

  In this case as well, as described in the above-described embodiment, the deformation of the diaphragm 6 by the actuators 7b, 7c, and 7d does not lead to the discharge of liquid droplets, and there is a risk of liquid dripping from the nozzles. Disappear.

  Further, by always setting the second electrode 13 to the potential “0 V” (connecting the second electrode 13 to GND), it is not necessary to provide a circuit for generating a voltage to be applied to the second electrode 13, thereby reducing the cost. Can be lowered.

Next, examples and comparative examples of the liquid discharge head will be described.
A liquid discharge head was manufactured by bonding a nozzle plate having nozzles to the substrate 30 on which the diaphragm 6 of Example 1 described above was formed.

  Then, using this liquid discharge head, droplet discharge evaluation was performed. The applied voltage is shown in FIG. The voltage V0 = 26V for droplet discharge is set. A positive potential was applied to the first electrode 11 and a negative potential was applied to the third electrode 15. The rise time Tr and the fall time Tf of the pulse potential input to the first electrode 11 and the third electrode 15 are both Tr = Tf = 1.0 μs. The pulse width Pw was set to 1.5 μs. The maximum potential applied to the first electrode 11 was 29.5V, and the minimum potential applied to the third electrode 15 was −6.5V.

  When a drive waveform capable of obtaining the potential E1 of FIG. 10 was applied to the actuator 7, it was confirmed that a droplet having a volume of 5.1 pl was ejected at an average speed of 6 m / s in a flight of 1 mm. Further, the drive waveforms for obtaining the potentials E2 and E3 in FIG. 10 were applied to the 10 actuators 7 for 10 minutes at a frequency of 10 kHz, respectively, but this affects the ejection characteristics such that ink overflows from the nozzles. Such a failure could not be confirmed.

  On the other hand, when the drive waveform for obtaining the potential E4 in FIG. 10 was applied to the 10 actuators 7 at a frequency of 10 kHz for 10 minutes, the liquid slightly overflowed from the nozzles of the four actuators 7. It was confirmed. The overflow of these liquids from the nozzle is thought to affect the subsequent ejection characteristics.

Next, an example of the image forming apparatus according to the present invention including the liquid discharge head according to the present invention will be described with reference to FIGS. FIG. 11 is a schematic configuration diagram for explaining the overall configuration of the mechanism portion of the apparatus, and FIG. 12 is a plan view of a main portion of the mechanism portion.
This image forming apparatus is a serial type image forming apparatus, and a carriage 233 is slidably held in a main scanning direction by main and sub guide rods 231 and 232 which are guide members horizontally mounted on left and right side plates 201A and 201B. The main scanning motor that does not perform moving scanning in the direction indicated by the arrow (carriage main scanning direction) via the timing belt.

  The carriage 233 includes a plurality of recording heads 234 including the liquid discharge head unit according to the present invention for discharging ink droplets of each color of yellow (Y), cyan (C), magenta (M), and black (K). Nozzle rows consisting of these nozzles are arranged in the sub-scanning direction orthogonal to the main scanning direction, and are mounted with the ink droplet ejection direction facing downward.

  The recording head 234 is configured by attaching liquid ejection heads 234a and 234b each having two nozzle rows to one base member, and one nozzle row of one head 234a has a black (K) droplet, The other nozzle row ejects cyan (C) droplets, the other nozzle row of the other head 234b ejects magenta (M) droplets, and the other nozzle row ejects yellow (Y) droplets. . Note that, here, a two-head configuration is used to eject four color droplets, but a liquid ejection head for each color may be provided.

  The carriage 233 is equipped with sub tanks 235a and 235b (referred to as “sub tank 235” when not distinguished) for supplying ink of each color corresponding to the nozzle rows of the recording head 234. The sub tank 235 is supplied with ink of each color from the ink cartridge 210 of each color by the supply unit 224 via the supply tube 236 of each color.

  On the other hand, as a paper feeding unit for feeding the paper 242 stacked on the paper stacking unit (pressure plate) 241 of the paper feed tray 202, a half-moon roller (feeding) that separates and feeds the paper 242 one by one from the paper stacking unit 241. A separation pad 244 made of a material having a large coefficient of friction is provided opposite to the sheet roller 243 and the sheet feeding roller 243, and the separation pad 244 is urged toward the sheet feeding roller 243 side.

  In order to feed the sheet 242 fed from the sheet feeding unit to the lower side of the recording head 234, a guide member 245 for guiding the sheet 242, a counter roller 246, a conveyance guide member 247, and a tip pressure roller. And a conveying belt 251 which is a conveying means for electrostatically attracting the fed paper 242 and conveying it at a position facing the recording head 234.

  The conveyor belt 251 is an endless belt, and is configured to wrap around the conveyor roller 252 and the tension roller 253 so as to circulate in the belt conveyance direction (sub-scanning direction). In addition, a charging roller 256 that is a charging unit for charging the surface of the transport belt 251 is provided. The charging roller 256 is disposed so as to come into contact with the surface layer of the conveyor belt 251 and to rotate following the rotation of the conveyor belt 251. The transport belt 251 rotates in the belt transport direction when the transport roller 252 is rotationally driven through timing by a sub-scanning motor (not shown).

  Further, as a paper discharge unit for discharging the paper 242 recorded by the recording head 234, a separation claw 261 for separating the paper 242 from the transport belt 251, a paper discharge roller 262, and a paper discharge roller 263 are provided. A paper discharge tray 203 is provided below the paper discharge roller 262.

  A double-sided unit 271 is detachably attached to the back surface of the apparatus main body. The duplex unit 271 takes in the paper 242 returned by the reverse rotation of the transport belt 251, reverses it, and feeds it again between the counter roller 246 and the transport belt 251. The upper surface of the duplex unit 271 is a manual feed tray 272.

  Further, a maintenance / recovery mechanism 281 that is a head maintenance / recovery device according to the present invention includes a recovery means for maintaining and recovering the nozzle state of the recording head 234 in the non-printing area on one side of the carriage 233 in the scanning direction. Is arranged. The maintenance / recovery mechanism 281 includes cap members (hereinafter referred to as “caps”) 282a and 282b (hereinafter referred to as “caps 282” when not distinguished) for capping each nozzle surface of the recording head 234, and nozzle surfaces. A wiper blade 283 that is a blade member for wiping the ink, and an empty discharge receiver 284 that receives liquid droplets for discharging the liquid droplets that do not contribute to recording in order to discharge the thickened recording liquid. ing.

  Further, in the non-printing area on the other side in the scanning direction of the carriage 233, there is an empty space for receiving a liquid droplet when performing an empty discharge for discharging a liquid droplet that does not contribute to the recording in order to discharge the recording liquid thickened during the recording. A discharge receiver 288 is disposed, and the idle discharge receiver 288 is provided with an opening 289 along the nozzle row direction of the recording head 234 and the like.

  In this image forming apparatus configured as described above, the sheets 242 are separated and fed one by one from the sheet feed tray 202, and the sheet 242 fed substantially vertically upward is guided by the guide 245, and is conveyed to the conveyor belt 251 and the counter. It is sandwiched between the rollers 246 and conveyed, and further, the leading end is guided by the conveying guide 237 and pressed against the conveying belt 251 by the leading end pressing roller 249, and the conveying direction is changed by approximately 90 °.

  At this time, a positive output and a negative output are alternately applied to the charging roller 256, that is, an alternating voltage is applied, and a charging voltage pattern in which the conveying belt 251 alternates, that is, in the sub-scanning direction that is the circumferential direction. , Plus and minus are alternately charged in a band shape with a predetermined width. When the sheet 242 is fed onto the conveyance belt 251 charged alternately with plus and minus, the sheet 242 is attracted to the conveyance belt 251, and the sheet 242 is conveyed in the sub scanning direction by the circumferential movement of the conveyance belt 251.

  Therefore, by driving the recording head 234 according to the image signal while moving the carriage 233, ink droplets are ejected onto the stopped paper 242 to record one line, and after the paper 242 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 242 has reached the recording area, the recording operation is finished and the paper 242 is discharged onto the paper discharge tray 203.

  At this time, the liquid discharge head described above is used as the liquid discharge head constituting the recording head 234, and the drive voltage described in the above-described embodiments is applied to the piezoelectric actuator corresponding to each nozzle. Yes.

  As a result, the withstand voltage of the electronic component can be reduced, the cost can be reduced, and a high-quality image can be stably formed without causing problems such as dripping.

  In the above embodiment, the present invention has been described with reference to an example in which the present invention is applied to an image forming apparatus having a printer configuration. However, the present invention is not limited to this example. In addition, the present invention can also be applied to an image forming apparatus using a liquid other than the narrowly defined ink or a fixing processing liquid.

DESCRIPTION OF SYMBOLS 1 Liquid discharge head 2 Nozzle 3 Nozzle plate 4 Liquid chamber 5 Flow path plate 6 Vibrating plate 7 Piezoelectric actuator 11 1st electrode 12 1st piezoelectric layer 13 2nd electrode 14 2nd piezoelectric layer 15 3rd electrode 234 Carriage 235 Recording head ( Liquid discharge head)

Claims (4)

A plurality of nozzles for discharging droplets, a plurality of liquid chambers communicating with the nozzles, a plurality of diaphragms forming a part of a wall surface of the liquid chambers, and a plurality of piezoelectric actuators for displacing the diaphragms A liquid ejection head having
The piezoelectric actuator of the liquid discharge head is configured by sequentially laminating a first electrode, a first piezoelectric layer, a second electrode, a second piezoelectric layer, and a third electrode on the diaphragm.
Of the first, second, and third electrodes of the plurality of piezoelectric actuators,
One electrode is applied with a common potential across all piezoelectric actuators,
The other one electrode is divided into a plurality of first groups, and a common potential is simultaneously applied to each group,
Furthermore, the other one electrode is divided into a plurality of second groups, and a common potential is simultaneously applied to each group,
The image forming apparatus according to claim 1, wherein only one piezoelectric actuator exists in common in the first group and the second group.   The image forming apparatus according to claim 1, wherein one electrode to which a common potential is applied to all the piezoelectric actuators is the second electrode.   The image forming apparatus according to claim 1, wherein an electric field strength applied to the first piezoelectric layer is larger than an electric field strength applied to the second piezoelectric layer.   The image forming apparatus according to claim 1, wherein the second electrode is connected to a ground potential.

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