Laminated piezoelectric element, liquid droplet ejection head using same, and image forming apparatus comprising same

The laminated piezoelectric element comprises a plurality of layers including first electrodes, piezoelectric material bodies, and second electrodes, wherein: the layers are laminated in order of the first electrode, the piezoelectric material body, the second electrode, and the piezoelectric material body; a plurality of active parts of the laminated piezoelectric element, where the piezoelectric material bodies are capable of actively expanding and contracting when a voltage is applied to the first electrode and the second electrode that are mutually opposing across the piezoelectric material body, are two-dimensionally arranged in a row direction and a column direction; and the first electrodes are common to the plurality of active parts in the row direction and the second electrodes are common to the plurality of active parts in the column direction.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a laminated piezoelectric element, a liquid droplet ejection head using the laminated piezoelectric element, and an image forming apparatus having the liquid droplet ejection head.

2. Description of the Related Art

One conventionally known image forming apparatus which forms images on a recording medium is an inkjet recording apparatus, which forms an image by ejecting ink in the from of liquid droplets from nozzles (liquid droplet ejection ports) toward the recording medium.

It has been sought to form high-resolution, high-quality images, such as photographic prints, with the inkjet recording apparatuses. For this purpose, it is effective to reduce the size of the ink droplets ejected from the nozzles by reducing the nozzle size as well as to arrange the nozzles at higher density.

However, about reducing the nozzle pitch and arranging the nozzles at high density in one row, there are manufacturing restrictions, and the like. If the nozzles are to be arranged at high density without restricting the real nozzle pitch, then it is effective to arrange the nozzles in the form of a matrix (two-dimensional matrix).

On the other hand, in order to eject ink of high viscosity, it is necessary to increase the generated pressure for ejecting the ink. For example, it has been considered that the generated pressure can be increased by layering together a plurality of piezoelectric elements in a piezoelectric system, in which a diaphragm that forms a portion of a pressure chamber is deformed by means of the deformation of a piezoelectric element, thereby changing (reducing) the volume of the pressure chamber, applying a pressure to the ink inside the pressure chamber, and thereby causing the ink to be ejected from a nozzle in the form of a droplet.

For example, Japanese Patent Application Publication No. 8-11304 discloses an inkjet head using a laminated piezoelectric element of this kind, in which a laminated piezoelectric element formed of piezoelectric members and intermediate electrodes of conductive material layered together alternately and burned is cut by slicing to leave a base portion (common seating) without electrodes, thus forming grooves which mechanically separate the individual piezoelectric elements. The laminated electrodes are formed to connect a pair of opposing electrodes through the respective side faces of each of the individual piezoelectric elements, in such a manner that the electrodes can be wired to the uppermost surface.

However, in Japanese Patent Application Publication No. 8-11304, it is necessary to form the electrodes on the side faces of the grooves after forming the laminated piezoelectric elements and then applying grooves to the laminated piezoelectric elements. Therefore, if the grooves are very fine due to high-density arrangement of the nozzles, and/or if a large force is required when it is to eject high-viscosity ink, for instance, then the total number of piezoelectric elements will be very large, the thickness of the piezoelectric elements will also be large, and the grooves will be deep. Consequently, the bottom portion of the grooves becomes obscured, and it becomes difficult or impossible to form electrodes on the side faces of the grooves.

Japanese Patent Application Publication No. 3-261560, for example, discloses a flat surface printer based on a bubble jet system in which the ink is heated, thus generating air bubbles, and ink is ejected by the expansive energy created as these air bubbles grow, the nozzles of the head being arranged in the form of a matrix. In this printer, a plurality of segment lines and common lines are arranged in a matrix fashion, and nozzles, ink flow channels for supplying ink to these nozzles, and heat generating resistances are arranged in the vicinity of the points of intersections between the segment lines and the common lines.

However, Japanese Patent Application Publication No. 3-261560 is limited to the bubble jet type inkjet printer, which is inadequate for ejecting ink of high viscosity. Furthermore, it is hard to form an image of high quality since the tonal gradation of the recorded image is difficult to be controlled.

SUMMARY OF THE INVENTION

The present invention has been contrived in view of the foregoing circumstances, and it is an object of the invention to provide a laminated piezoelectric element, a liquid droplet ejection head using the laminated piezoelectric element, and an image forming apparatus comprising the liquid droplet ejection head, whereby the number of wires can be reduced and a high-density nozzle arrangement can be achieved by enabling electrodes to be wired through the side surfaces of the laminated piezoelectric elements, in such a manner that cross-talk can be prevented, tonal gradation can be controlled, and high-quality image formation can be achieved.

In order to attain the aforementioned object, the present invention is directed to a laminated piezoelectric element, comprising a plurality of layers including first electrodes, piezoelectric material bodies, and second electrodes, wherein: the layers are laminated in order of the first electrode, the piezoelectric material body, the second electrode, and the piezoelectric material body; a plurality of active parts of the laminated piezoelectric element, where the piezoelectric material bodies are capable of actively expanding and contracting when a voltage is applied to the first electrode and the second electrode that are mutually opposing across the piezoelectric material body, are two-dimensionally arranged in a row direction and a column direction; and the first electrodes are common to the plurality of active parts in the row direction and the second electrodes are common to the plurality of active parts in the column direction.

Preferably, the first electrodes and the second electrodes are connected to wiring through end faces of the laminated piezoelectric element.

According to the present invention, the electrode wiring can be connected readily, and high-density arrangement of nozzles can be achieved. In addition to that, the number of control circuits and drivers can be reduced, and handling during head manufacture can be facilitated.

Preferably, at least a portion of inactive parts that are not activated by application of voltage to the first electrode and the second electrode is formed into one of a recessed shape and a perforated shape.

Preferably, electrode pairs formed by the first electrodes and the second electrodes arranged in a two-dimensional arrangement are divided into a plurality of regions that are drivable independently from each other. Preferably, the plurality of regions are obtained by dividing into four regions by means of a line parallel to the row direction and a line parallel to the column direction, the two lines passing through an substantial central portion of the two-dimensional arrangement.

According to the present invention, it is possible to increase the number of active parts that can be simultaneously driven.

Preferably, the first electrodes are common to every other of the active parts and the second electrodes are common to every other of the active parts. Preferably, two of the first electrodes that are arranged adjacently in the row direction are arranged in a staggered fashion and connected so as to be simultaneously driven.

According to the present invention, it is possible to prevent cross-talk and droplets-interference between mutually adjacent active parts.

Preferably, electrode pairs formed by the first electrodes and the second electrodes are not only arranged two-dimensionally in the row direction and the column direction but also superimposed to each other in a lamination direction that is perpendicular to the row direction and the column direction, in such a manner that each of the layers is independently drivable.

According to the present invention, it is possible to control tonal gradation by varying the amount of drive displacement without altering the voltage, and it is also possible to alter the drive timing.

In order to attain the aforementioned object, the present invention is also directed to a liquid droplet ejection head, comprising a drive actuator including the above-described laminated piezoelectric element. According to the present invention, the electrode wiring can be connected readily, high-density arrangement of the nozzles can be achieved, high-viscosity ink can be ejected, and the tonal gradation can be controlled. Moreover, it is possible to prevent cross-talk and droplets-interference.

In order to attain the aforementioned object, the present invention is also directed to an image forming apparatus, comprising the above-described liquid droplet ejection head. According to the present invention, it is possible to form an image of high quality.

As described above, according to the laminated piezoelectric element according to the present invention, the liquid droplet ejection head using the laminated piezoelectric element, and the image forming apparatus comprising the liquid droplet ejection head, the electrode wiring can be connected readily, the nozzles can be arranged at high density, the number of the control circuits and the drivers can be reduced, and the handling during head manufacture is facilitated.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1is a general compositional drawing showing an overview of one embodiment of an inkjet recording apparatus as an image forming apparatus having a liquid droplet ejection head which uses the laminated piezoelectric element according to the present invention.

As shown inFIG. 1, the inkjet recording apparatus10comprises: a printing unit having a plurality of print heads (inkjet recording heads)12K,12C,12M, and12Y for ink colors of black (K), cyan (C), magenta (M), and yellow (Y), respectively; an ink storing and loading unit14for storing inks of black (K), cyan (C), magenta (M), and yellow (Y) to be supplied to the print heads12K,12C,12M, and12Y; a paper supply unit18for supplying recording paper16; a decurling unit20for removing curl in the recording paper16supplied from the paper supply unit18; a suction belt conveyance unit22disposed facing the nozzle face (ink-droplet ejection face) of the print unit12, for conveying the recording paper16while keeping the recording paper16flat; a print determination unit24for reading the printed result produced by the printing unit12; and a paper output unit26for outputting image-printed recording paper (printed matter) to the exterior.

InFIG. 1, a magazine for rolled paper (continuous paper) is shown as an example of the paper supply unit18; however, more magazines with paper differences such as paper width and quality may be jointly provided. Moreover, papers may be supplied with cassettes that contain cut papers loaded in layers and that are used jointly or in lieu of the magazine for rolled paper.

In the case of a configuration in which roll paper is used, a cutter28is provided as shown inFIG. 1, and the roll paper is cut to a desired size by the cutter28. The cutter28has a stationary blade28A, whose length is not less than the width of the conveyor pathway of the recording paper16, and a round blade28B, which moves along the stationary blade28A. The stationary blade28A is disposed on the reverse side of the printed surface of the recording paper16, and the round blade28B is disposed on the printed surface side across the conveyance path. When cut paper is used, the cutter28is not required.

In the case of a configuration in which a plurality of types of recording paper can be used, it is preferable that an information recording medium, such as a bar code and a wireless tag, containing information about the type of paper is attached to the magazine, the type of paper to be used is automatically determined by reading the information contained in the information recording medium with a specific reading device, and ink-droplet ejection is controlled so that the ink-droplets are ejected in an appropriate manner in accordance with the type of paper.

The recording paper16delivered from the paper supply unit18retains curl due to having been loaded in the magazine. In order to remove the curl, heat is applied to the recording paper16in the decurling unit20by a heating drum30in the direction opposite from the curl direction in the magazine. The heating temperature at this time is preferably controlled so that the recording paper16has a curl in which the surface on which the print is to be made is slightly round outward.

The decurled and cut recording paper16is delivered to the suction belt conveyance unit22. The suction belt conveyance unit22has a configuration in which an endless belt33is set around rollers31and32so that the portion of the endless belt33facing at least the nozzle face of the printing unit12and the sensor face of the print determination unit24forms a horizontal plane (flat plane).

The belt33has a width that is greater than the width of the recording paper16, and a plurality of suction apertures (not shown) are formed on the belt surface. A suction chamber34is disposed in a position facing the sensor surface of the print determination unit24and the nozzle surface of the printing unit12on the interior side of the belt33, which is set around the rollers31and32, as shown inFIG. 1. The suction chamber34provides suction with a fan35to generate a negative pressure, and the recording paper16is held on the belt33by suction.

The belt33is driven in the clockwise direction inFIG. 1by the motive force of a motor (not shown) being transmitted to at least one of the rollers31and32, which the belt33is set around, and the recording paper16held on the belt33is conveyed from left to right inFIG. 1.

Since ink adheres to the belt33when a marginless print job or the like is performed, a belt-cleaning unit36is disposed in a predetermined position (a suitable position outside the printing area) on the exterior side of the belt33. Although the details of the configuration of the belt-cleaning unit36are not shown, examples thereof include a configuration in which the belt33is nipped with cleaning rollers such as a brush roller and a water absorbent roller, an air blow configuration in which clean air is blown onto the belt33, or a combination of these. In the case of the configuration in which the belt33is nipped with the cleaning rollers, it is preferable to make the line velocity of the cleaning rollers different than that of the belt33to improve the cleaning effect.

The inkjet recording apparatus10can comprise a roller nip conveyance mechanism, in which the recording paper16is pinched and conveyed with nip rollers, instead of the suction belt conveyance unit22. However, there is a drawback in the roller nip conveyance mechanism that the print tends to be smeared when the printing area is conveyed by the roller nip action because the nip roller makes contact with the printed surface of the paper immediately after printing. Therefore, the suction belt conveyance in which nothing comes into contact with the image surface in the printing area is preferable.

A heating fan40is disposed on the upstream side of the printing unit12in the conveyance pathway formed by the suction belt conveyance unit22. The heating fan40blows heated air onto the recording paper16to heat the recording paper16immediately before printing so that the ink deposited on the recording paper16dries more easily.

The print unit12is a so-called “full line head” in which a line head having a length corresponding to the maximum width of paper is arranged in a direction (main scanning direction) perpendicular to the paper conveyance direction (sub-scanning direction) (seeFIG. 2). As shown inFIG. 2, each of the print heads12K,12C,12M and12Y is constituted by a line head in which a plurality of ink ejection ports (nozzles) are arranged along a length exceeding at least one side of the maximum size recording paper16that can be used with the inkjet recording apparatus10.

The print heads12K,12C,12M,12Y corresponding to respective ink colors are disposed in the order, black (K), cyan (C), magenta (M) and yellow (Y), from the upstream side (left-hand side inFIG. 1) in the feed direction of the recording paper16(the paper conveyance direction). A color print can be formed on the recording paper16by ejecting the inks from the print heads12K,12C,12M, and12Y, respectively, onto the recording paper16while conveying the recording paper16.

The print unit12, in which the full-line heads covering the entire width of the paper are thus provided for the respective ink colors, can record an image over the entire surface of the recording paper16by performing the action of moving the recording paper16and the print unit12relatively to each other in the paper conveyance direction (sub-scanning direction) just once (in other words, by means of a single sub-scan). Higher-speed printing is thereby made possible and productivity can be improved in comparison with a shuttle type head in which a recording head moves reciprocally in the direction (main scanning direction) perpendicular to the paper conveyance direction (sub-scanning direction).

The terms main scanning direction and sub-scanning direction are used in the following senses. In a full-line head comprising a row of nozzles that have a length corresponding to the entire width of the recording paper, the “main scanning” is defined as printing one line (a line formed of a row of dots, or a line formed of a plurality of rows of dots) in the breadthways direction of the recording paper (the direction perpendicular to the conveyance direction of the recording paper) by driving the nozzles in one of the following ways: (1) simultaneously driving all the nozzles; (2) driving the nozzles sequentially from one side toward the other side; and (3) dividing the nozzles into blocks and driving the blocks of the nozzles sequentially from one side toward the other side. The direction indicated by one line recorded by a main scanning action (the lengthwise direction of the band-shaped region thus recorded) is called the “main scanning direction”.

On the other hand, “sub-scanning” is defined as to repeatedly perform printing of one line (a line formed of a row of dots, or a line formed of a plurality of rows of dots) formed by the main scanning, while moving the full-line head and the recording paper relatively to each other. The direction in which sub-scanning is performed is called the sub-scanning direction. Consequently, the conveyance direction of the recording paper is the sub-scanning direction and the direction perpendicular to the sub-scanning direction is called the main scanning direction.

Although the configuration with the KCMY four standard colors is described in the present embodiment, combinations of the ink colors and the number of colors are not limited to those. Light and/or dark inks can be added as required. For example, a configuration is possible in which inkjet heads for ejecting light-colored inks such as light cyan and light magenta are added. Furthermore, there are no particular restrictions of the sequence in which the print heads of respective colors are arranged.

As shown inFIG. 1, the ink storing and loading unit14has tanks for storing inks of the colors corresponding to the respective print heads12K,12C,12M and12Y, and each tank is connected to a respective print head12K,12C,12M,12Y, via a tube channel (not shown). Moreover, the ink storing and loading unit14also comprises notifying means (display means, alarm generating means, or the like) for generating a notification if the remaining amount of ink has become low. Furthermore, the ink storing and loading unit14also comprises a mechanism for preventing incorrect loading of the wrong colored ink.

The print determination unit24has an image sensor (line sensor or the like) for capturing an image of the ink-droplet deposition result of the printing unit12, and functions as a device to check for ejection defects such as clogs of the nozzles in the printing unit12from the ink-droplet deposition results evaluated by the image sensor.

The print determination unit24of the present embodiment is configured with at least a line sensor having rows of photoelectric conversion elements with a width that is greater than the ink-droplet ejection width (image recording width) of the print heads12K,12C,12M, and12Y. This line sensor has a color separation line CCD sensor including a red (R) sensor row composed of photoelectric conversion elements (pixels) arranged in a line provided with an R filter, a green (G) sensor row with a G filter, and a blue (B) sensor row with a B filter. Instead of a line sensor, it is possible to use an area sensor composed of photoelectric conversion elements which are arranged two-dimensionally.

The print determination unit24reads a test pattern image printed by the print heads12K,12C,12M, and12Y for the respective colors, and the ejection from each head is determined. The ejection determination includes the presence of the ejection, measurement of the dot size, and measurement of the dot deposition position.

A post-drying unit42is disposed following the print determination unit24. The post-drying unit42is a device to dry the printed image surface, and includes a heating fan, for example. It is preferable to avoid contact with the printed surface until the printed ink dries, and a device that blows heated air onto the printed surface is preferable.

In cases in which printing is performed with dye-based ink on porous paper, blocking the pores of the paper by the application of pressure prevents the ink from coming contact with ozone and other substance that cause dye molecules to break down, and has the effect of increasing the durability of the print.

A heating/pressurizing unit44is disposed following the post-drying unit42. The heating/pressurizing unit44is a device to control the glossiness of the image surface, and the image surface is pressed with a pressure roller45having a predetermined uneven surface shape while the image surface is heated, and the uneven shape is transferred to the image surface.

The printed matter generated in this manner is outputted from the paper output unit26. The target print (i.e., the result of printing the target image) and the test print are preferably outputted separately. In the inkjet recording apparatus10, a sorting device (not shown) is provided for switching the outputting pathways in order to sort the printed matter with the target print and the printed matter with the test print, and to send them to paper output units26A and26B, respectively. When the target print and the test print are simultaneously formed in parallel on the same large sheet of paper, the test print portion is cut and separated by a cutter (second cutter)48. The cutter48is disposed directly in front of the paper output unit26, and is used for cutting the test print portion from the target print portion when a test print has been performed in the blank portion of the target print. The structure of the cutter48is the same as the first cutter28described above, and has a stationary blade48A and a round blade48B.

Although not shown in the drawings, the paper output unit26A for the target prints is provided with a sorter for collecting prints according to print orders.

Next, the structure of a print head (liquid droplet ejection head) will be described. The print heads12K,12C,12M and12Y provided for the respective ink colors have the same structure, and a reference numeral50is hereinafter designated to any of the heads.FIG. 3shows a plan perspective view of the print head50.

As shown inFIG. 3, the print head50according to the present embodiment achieves a high density arrangement of nozzles51by using a two-dimensional staggered matrix array of pressure chamber units54. Each of the pressure chamber units54comprises a nozzle51for ejecting ink as ink droplets, a pressure chamber52for applying pressure to the ink in order to eject ink, and an ink supply port53for supplying ink to the pressure chamber52from a common flow channel (not shown).

As shown inFIG. 3, each pressure chamber52has a substantially square shape when viewed from above, and a nozzle51is formed at one end of a diagonal of the square, while an ink supply port53is provided at the other end thereof.

As shown inFIG. 4, each pressure chamber unit54is formed by a pressure chamber52which is connected to the nozzle51that can eject ink, a common flow channel55for supplying ink via a supply port53is connected to the pressure chamber52, and one surface of the pressure chamber52(the ceiling-surface inFIG. 4) is formed by a diaphragm56. A laminated piezoelectric element58which deforms the diaphragm56by applying pressure to the diaphragm56is bonded to the upper part of the diaphragm.

As will hereinafter be described in detail, the laminated piezoelectric element58includes electrode layers and piezoelectric element layers that are layered alternately. Each of the laminated piezoelectric elements58comprises a piezoelectric element which is layered between two electrodes (a common electrode and an individual electrode (described in more detail below)), and the piezoelectric element (and consequently, the whole of the laminated piezoelectric element58) is deformed by applying a drive voltage between these electrodes, thereby pushing the diaphragm56, reducing the volume of the pressure chamber52, and causing ink to be ejected from the nozzle51. When the laminated piezoelectric element58returns to its original position, the volume of the pressure chamber52returns to its original size, and new ink is supplied into the pressure chamber52from the common supply channel55and via the supply port53.

FIG. 5is a perspective plan view showing another example of the structure of a print head. As shown inFIG. 5, one long full line head may be constituted by combining a plurality of short heads50′ arranged in a two-dimensional staggered array, in such a manner that the combined length of this plurality of short heads50′ corresponds to the full width of the print medium.

FIG. 6is a schematic drawing showing the configuration of the ink supply system in the inkjet recording apparatus10. The ink tank60is a base tank that supplies ink to the print head50and is set in the ink storing and loading unit14described with reference toFIG. 1. The aspects of the ink tank60include a refillable type and a cartridge type: when the remaining amount of ink is low, the ink tank60of the refillable type is filled with ink through a filling port (not shown) and the ink tank60of the cartridge type is replaced with a new one. In order to change the ink type in accordance with the intended application, the cartridge type is suitable, and it is preferable to represent the ink type information with a bar code or the like on the cartridge, and to perform ejection control in accordance with the ink type. The ink tank60inFIG. 6is equivalent to the ink storing and loading unit14inFIG. 1described above.

As shown inFIG. 6, a filter62for eliminating foreign material and air bubbles is provided at an intermediate position of the tubing which connects the ink tank60with the print head50. Desirably, the filter mesh size is the same as the nozzle diameter in the print head50, or smaller than the nozzle diameter (generally, about 20 μm).

Although not shown inFIG. 6, it is preferable to provide a sub-tank integrally to the print head50or nearby the print head50. The sub-tank has a damper function for preventing variation in the internal pressure of the head and a function for improving refilling of the print head.

The inkjet recording apparatus10is also provided with a cap64as a device to prevent the nozzles from drying out or to prevent an increase in the ink viscosity in the vicinity of the nozzles, and a cleaning blade66as a device to clean the nozzle face50A.

A maintenance unit including the cap64and the cleaning blade66can be relatively moved with respect to the print head50by a movement mechanism (not shown), and is moved from a predetermined holding position to a maintenance position below the print head50as required.

The cap64is displaced upwards and downwards relatively with respect to the print head50by an elevator mechanism (not shown). When the power of the inkjet recording apparatus10is switched OFF or when in a print standby state, the elevator mechanism raises the cap64to a predetermined elevated position so as to come into close contact with the print head50, and the nozzle region of the nozzle face50A is thereby covered by the cap64.

The cleaning blade66is composed of rubber or another elastic member, and can slide on the ink discharge surface (nozzle surface50A) of the print head50by means of a blade movement mechanism (not shown). If there are ink droplets or foreign matter adhering to the nozzle surface50A, then the nozzle surface50A is wiped by causing the cleaning blade66to slide over the nozzle surface50A, thereby cleaning the nozzle surface50A.

During printing or during standby, if the use frequency of a particular nozzle51has declined and the ink viscosity in the vicinity of the nozzle51has increased, then a preliminary ejection is performed toward the cap64, in order to remove the ink that has degraded as a result of increasing in viscosity.

Also, when bubbles have become intermixed in the ink inside the print head50(inside the pressure chamber52), the cap64is placed on the print head50, the ink inside the pressure chamber52(the ink in which bubbles have become intermixed) is removed by suction with a suction pump67, and the suction-removed ink is sent to a collection tank68. This suction action entails the suctioning of degraded ink whose viscosity has increased (hardened) also when initially loaded into the head, or when service has started after a long period of being stopped.

In other words, when a state in which ink is not ejected from the print head50continues for a certain amount of time or longer, the ink solvent in the vicinity of the nozzles51evaporates and the ink viscosity increases. In such a state, ink can no longer be ejected from the nozzles51even if the actuators (laminated piezoelectric elements58) for ejection driving are operated. Therefore, the laminated piezoelectric element58is operated toward an ink receptacle, before reaching such a state (while the ink viscosity is within a range that allows ejection by the operation of the laminated piezoelectric elements58), and a “preliminary ejection” is performed which causes the ink in the vicinity of the nozzles whose viscosity has increased to be ejected. Furthermore, after cleaning away soiling on the surface of the nozzle surface50A by means of a wiper, such as a cleaning blade66, provided as a cleaning device on the nozzle surface50A, a preliminary ejection is also carried out in order to prevent infiltration of foreign substances inside the nozzles51due to the rubbing action of the wiper. The preliminary ejection is also referred to as “dummy ejection”, “purge”, “liquid ejection”, and so on.

When bubbles have become intermixed in the nozzle51or the pressure chamber52, or when the ink viscosity inside the nozzle51has increased over a certain level, ink can no longer be ejected by the preliminary discharge, and a suctioning action is carried out as follows.

More specifically, when bubbles have become intermixed in the ink inside the nozzle51and the pressure chamber52, or when the ink viscosity in the nozzle51increases to a certain level or more, ink can no longer be ejected from the nozzles51even if the laminated piezoelectric element58is operated. In a case of this kind, a cap64is placed on the nozzle surface50A of the print head50, and the ink containing air bubbles or the ink of increased viscosity inside the pressure chambers52is suctioned by a pump67.

This suction action is performed with respect to all the ink in the pressure chamber52, and therefore the amount of ink consumption is considerable. Consequently, it is desirable that a preliminary ejection is carried out, whenever possible, while the increase in viscosity is still minor. The cap64described inFIG. 6functions as a suctioning device and it may also function as an ink receptacle for the preliminary ejection.

Moreover, desirably, the inside of the cap64is divided by means of partitions into a plurality of areas corresponding to the nozzle rows, thereby achieving a composition in which suction can be performed selectively in each of the demarcated areas, by means of a selector, or the like.

FIG. 7is a principal block diagram showing the system configuration of the inkjet recording apparatus10. The inkjet recording apparatus10comprises a communication interface70, a system controller72, an image memory74, a motor driver76, a heater driver78, a print controller80, an image buffer memory82, a head driver84, and the like.

The communication interface70is an interface unit for receiving image data sent from a host computer86. A serial interface such as USB, IEEE1394, Ethernet, wireless network, or a parallel interface such as a Centronics interface may be used as the communication interface70. A buffer memory (not shown) may be mounted in this portion in order to increase the communication speed. The image data sent from the host computer86is received by the inkjet recording apparatus10through the communication interface70, and is temporarily stored in the image memory74. The image memory74is a storage device for temporarily storing images inputted through the communication interface70, and data is written and read to and from the image memory74through the system controller72. The image memory74is not limited to a memory composed of semiconductor elements, and a hard disk drive or another magnetic medium may be used.

The system controller72is a control unit for controlling the various sections, such as the communications interface70, the image memory74, the motor driver76, the heater driver78, and the like. The system controller72comprises a central processing unit (CPU) and peripheral circuits thereof, and the like. In addition to controlling communications with the host computer86and controlling reading and writing from and to the image memory74, or the like, the system controller72also generates a control signal for controlling the motor88of the conveyance system and the heater89.

The motor driver (drive circuit)76drives the motor88in accordance with commands from the system controller72. The heater driver (drive circuit)78drives the heater89of the post-drying unit42or the like in accordance with commands from the system controller72.

The print controller80has a signal processing function for performing various tasks, compensations, and other types of processing for generating print control signals from the image data stored in the image memory74in accordance with commands from the system controller72so as to supply the generated print control signal (print data) to the head driver84. Prescribed signal processing is carried out in the print controller80, and the ejection amount and the ejection timing of the ink droplets from the respective print heads50are controlled via the head driver84, on the basis of the print data. By this means, prescribed dot size and dot positions can be achieved.

The print controller80is provided with the image buffer memory82; and image data, parameters, and other data are temporarily stored in the image buffer memory82when image data is processed in the print controller80. The aspect shown inFIG. 7is one in which the image buffer memory82accompanies the print controller80; however, the image memory74may also serve as the image buffer memory82. Also possible is an aspect in which the print controller80and the system controller72are integrated to form a single processor.

The head driver84drives the actuators58of the print heads50of the respective colors on the basis of print data supplied by the print controller80. The head driver84can be provided with a feedback control system for maintaining constant drive conditions for the print heads.

The print determination unit24is a block that includes the line sensor (not shown) as described above with reference toFIG. 1, reads the image printed on the recording paper16, determines the print conditions (presence of the ejection, variation in the dot formation, and the like) by performing desired signal processing, or the like, and provides the determination results of the print conditions to the print controller80.

According to requirements, the print controller80makes various corrections with respect to the print head50on the basis of information obtained from the print determination unit24.

Below, the composition of the laminated piezoelectric element according to an embodiment of the present invention will be described.

FIG. 8is a plan view showing a first embodiment of the laminated piezoelectric element according to the present invention. As shown inFIG. 8, the laminated piezoelectric element58according to the present embodiment is formed by combining a plurality of band-shaped row electrodes (first electrodes)90(row X, . . . , row Xm) and a plurality of band-shaped column electrodes (second electrodes)92(column Y1, . . . , column Yn) in a lattice configuration. The thin film-shaped piezoelectric body94is sandwiched between the plurality of band-shaped row electrodes (first electrodes)90(row X1, . . . , row Xm) and the plurality of band-shaped column electrodes (second electrodes)92(column Y1, . . . , column Yn).

Here, the “lattice configuration” is not necessarily a lattice in which the row electrodes90and the column electrodes92are orthogonal, and it may also indicate a state where the column electrodes92are arranged so as to intersect obliquely with the row electrodes90at an angle slightly less than 90°, as shown inFIG. 8.

As shown inFIG. 3, the intersection points96of the respective row electrodes90and the respective column electrodes92correspond to the positions of the pressure chambers52arranged in a staggered two-dimensional matrix in the print head50. When a voltage is applied to both the row electrode90and the column electrode92passing through an intersection point96, then the portion of the piezoelectric body94sandwiched between the row electrode90and the column electrode92is deformed and the ink inside the pressure chamber52is ejected from the nozzle51communicating with that pressure chamber52. In this manner, the portion of the intersection point96between the row electrode90and the column electrode92forms an active part which drives in ejecting the ink.

In this case, the row electrode90and the column electrode92between which the piezoelectric body94is sandwiched on the intersection point96form an electrode pair for activating the active part. As shown inFIG. 8, each of the row electrodes90(row X1, . . . , row Xm) is common to the plurality of active parts in the row direction, and at the same time, each of the column electrodes92(column Y1, . . . , column Yn) is common to the plurality of active parts in the column direction.

FIG. 9Ais an oblique perspective view showing a partial enlarged view of the laminated piezoelectric element58inFIG. 8.FIG. 9Ashows a portion of the row electrodes90(X1, X2, X3) and the column electrodes92(Y1, Y2, Y3) shown at the bottom left-hand part ofFIG. 8. As shown inFIG. 9A, a plurality of row electrodes90and column electrodes92are layered respectively (in three layers in the embodiment shown inFIG. 9A). Furthermore, although omitted fromFIG. 9A, thin-film piezoelectric bodies94(seeFIG. 8orFIG. 10) forming the active part are sandwiched respectively between the electrode pairs formed by the row electrodes90and the column electrodes92.

Moreover, as shown inFIG. 9A, the row electrodes90(X1, X2, X3) layered in a plurality of layers are electrically connected to each other at an end section90aformed at the side face of the laminated piezoelectric element58, in such a manner that wiring can be connected to the row electrodes90through this end section90a(from the side face of the laminated piezoelectric element58). Furthermore, the same applies to the column electrodes92, in other words, the column electrodes92(Y1, Y2, Y3) are electrically connected to each other at the end section92aformed at the other side face of the laminated piezoelectric element58, in such a manner that wiring can be connected to the column electrodes92through this end section92a.

FIG. 10shows a cross-sectional view along line10-10of the intersection point96between the row electrodes90and the column electrodes92inFIG. 9A. As shown inFIG. 10, at the intersection point96between the row electrodes90and the column electrodes92in the laminated piezoelectric element58, the row electrodes90and the column electrodes92are layered alternately via piezoelectric bodies94, and there are piezoelectric bodies94between the row electrodes90and the column electrodes92.

Of the row electrodes90and the column electrodes92, one set of electrodes are common electrodes and the other set of electrodes are individual electrodes. For example, when a voltage is applied to the row electrode Xi, and the column electrode Yj is selected and a voltage is applied to the column electrode Yj, then ink is ejected from the pressure chamber52located at the position (i, j) of these two electrodes (the ith electrode from the bottom and the jth electrode from the left inFIG. 8orFIG. 3). In this way, it is possible to freely drive any of the active parts which are arranged in the two-dimensional matrix array.

Furthermore, it is possible to simultaneously drive each of the columns Y1, . . . , Yn of the column electrodes92with respect to the row X1of the row electrodes90. Hence, the voltage is switched on to the row electrodes90of row X1(rows X2, . . . Xm being switched off), and by selecting the column electrodes92corresponding to a nozzle from which ink is to be ejected with respect to this row (X1), from among those of the rows Y1, . . . , Yn, then ink is ejected from the specific nozzle located on row X1.

Next, the voltage is switched on to the row electrodes90of row X2(the voltage is switched off to all of the row electrodes90other than those of row X2), and by selecting a column electrode92corresponding to a nozzle from which ink is to be ejected with respect to this row (X2), from among those of the rows Y1, . . . , Yn, then ink is ejected from the specific nozzle located on row X2.

Thereafter, ink is ejected sequentially from the nozzles in rows X3to Xm, and when ink ejection has finished, the recording paper16is conveyed and ink ejection is driven again in a similar manner, starting again from row X1. Hence, the drive frequency is slower compared to a simple system in which each nozzle is provided with an individual electrode; however, a benefit is obtained in that the number of driving operations is reduced accordingly.

By driving the row electrodes90and the column electrodes92arranged in m rows and n columns in this way, ink is ejected from the nozzles51corresponding to the m×n pressure chambers52, and hence an image is formed. In this case, since it is possible to connect respective wires through both the end portions90aand92a, the number of wires connected to the row electrodes90and the column electrodes92is the total, m+n, of m electrodes from the row electrodes90and n electrodes from the column electrodes92. Therefore, it is possible to drive each of m×n individual electrodes (piezoelectric active parts) by means of the m+n wires. In this way, in the present embodiment, it is possible to reduce the number of wires connected to from the electrodes.

In the m+n driving method, it is possible to achieve a composition in which each pressure chamber is provided with a plurality of actuators, by separately connecting wires to the respective electrodes (row electrodes90and column electrodes92) in the direction of lamination of the piezoelectric body. Furthermore, in this case, it is possible to control the ejection pressure generated in any one pressure chamber by independently driving the plurality of actuators laminated with respect to that pressure chamber, by means of the separately wired electrodes. Thus, the size of the ejected droplet of ink can be controlled, thereby making it possible to control the tonal gradation.

Moreover, it is also possible to use a portion of the plurality of actuators corresponding to one pressure chamber as an actuator for driving refill.

The laminated piezoelectric elements58may be formed into one general integrated composition in which piezoelectric bodies94, row electrodes90and column electrodes92are layered in the sequential order as described above. Alternatively, a composition may be adopted in which a part or all of the unnecessary portions (inactive parts)100, in which no row electrodes90and no column electrodes92are located and which are not used in driving, such as the region indicated by the thick frame lines in the corner section of the laminated piezoelectric element58inFIG. 9A, are removed by sandbrasting or the like. In this case, these unnecessary portions (inactive parts)100can be formed into a recessed shape or a perforated shape in such a manner that each of the active parts is able to be independently driven, and hence the displacement efficiency of the laminated piezoelectric elements58is improved.

For example, it is also possible to remove the unnecessary portions such as the corner section of the laminated piezoelectric element58indicated by reference numeral100inFIG. 9B, where no row electrodes90and no column electrodes92are present, as shown inFIG. 9C. In this case, as shown inFIG. 9C, piezoelectric bodies94are laminated in between the respective layers formed by the plurality of laminated electrodes90and92. In the embodiment shown inFIGS. 9B and 9C, the unnecessary portions100, where none of the row electrodes90(X1, X2, X3) and the column electrodes92(Y1, Y2, Y3) are located, are removed completely from top to bottom, thereby forming a perforated shape. It is also possible to form the unnecessary portions100into a recessed shape in which the base region of the unnecessary portion is left, rather than completely removing it.

By adopting this composition, it is possible to prevent cross-talk between mutually adjacent active parts and/or interference between liquid droplets.

In the laminated piezoelectric element according to the first embodiment in which so-called active parts corresponding to pressure chambers are arranged in the two-dimensional matrix array, it is possible to wire the electrodes through the side faces, and therefore the electrode wiring can be connected readily, the number of the control circuits and the drivers can be reduced, and consequently, handling is improved.

It is possible to simultaneously drive the nozzles arranged on the same row electrode by arranging the electrodes in this fashion (seeFIG. 8); however, if the patterns of the selected column electrodes are not the same between the adjacent row electrodes, then it may not be possible to simultaneously drive the adjacent row electrodes.

The laminated piezoelectric element according to a second embodiment which is described below serves to deal with this problem.FIG. 11shows a laminated piezoelectric element according to the second embodiment.

FIG. 11is a plan view that is similar toFIG. 8shown above. As shown inFIG. 11, in the laminated piezoelectric element158of the second embodiment, the row electrodes and the column electrodes are respectively divided into two parts at the central regions of the laminated piezoelectric element158, by means of a straight line parallel to the row direction and a straight line parallel to the column direction, as indicated by the dotted lines. In this case, by forming the row electrodes190-1and190-2and the column electrodes192-1and192-2, the laminated piezoelectric element158is split into four blocks including an upper left block, an upper right block, a lower left block, and a lower right block. By dividing the electrodes in this fashion and connecting electrode wires through the end portions on either side of the blocks, the electrodes of the respective blocks can be independently driven, and hence it is possible to independently drive the nozzles corresponding to the electrodes of these respective different blocks.

As a result, it is possible to increase the number of electrodes that can be simultaneously driven, in other words, the number of nozzles which can be simultaneously driven, and hence printing can be performed at higher speed. The number of the divided regions of the electrodes which can each be independently driven in this way is not limited to four as shown inFIG. 11, and the number of nozzles which can be simultaneously driven can be increased by dividing the electrodes into any desired number of regions.

Next, the laminated piezoelectric element according to a third embodiment will be described.

FIG. 12is an oblique perspective view showing the schematic composition of the laminated piezoelectric element according to the third embodiment.FIG. 12shows the arrangement of the electrodes in particular, and the piezoelectric bodies sandwiched between these electrodes are omitted from the drawings.

As shown inFIG. 12, the laminated piezoelectric element258according to the present embodiment has two or more types of pattern electrodes in the lamination direction, as well as in the row direction and in the column direction. Of the row electrodes290arranged in the row direction, row X11, for example, comprises the electrodes that are provided with two parallel electrodes X11aand X11b(row electrodes) and form the electrode pairs activating the active parts together with column electrodes (described hereinafter). Electrodes X11-1, X11-3, and so on, forming the electrode pairs corresponding to the active parts, are arranged on the electrode X11b, and electrodes X11-2, and so on, similarly forming the electrode pairs corresponding to the active parts, are arranged on the electrode X11a. The electrodes (e.g., electrodes X11-1and X11-3) formed on the electrode X11band the electrodes (e.g., electrodes X11-2) formed on the electrode X11aare arranged alternately in a direction along the electrodes X11bor X11a, and they are arranged on every other of the active part.

Furthermore, the same applies to the column direction; namely, of the column electrodes292, column Y11, for example, comprises the electrodes Y11-1, Y11-2, and so on, that are formed on two parallel electrodes Y11aand Y11b(column electrodes) and form the electrode pairs corresponding to the active parts

Regarding the laminated structure of the row electrodes290and column electrodes292inFIG. 12, the upper four layers in the laminated structure are shown inFIGS. 13A to 13D, which show the layers separately.

FIG. 13Ashows the row electrodes290-1, which form the electrodes in the uppermost layer inFIG. 12. For example, electrodes X11-2and so on are arranged on the electrode X11a.FIG. 13Bshows the row electrodes290-2, which form the electrodes in the second layer from the top inFIG. 12. For example, electrodes X11-1, X11-3and so on are arranged on the electrode X11b.

FIG. 13Cshows the column electrodes292-1, which form the electrodes in the next layer below the layer shown inFIG. 13B. For example, electrodes Y11-2and so on are formed on the electrode Y11b. Furthermore,FIG. 13Dshows the column electrodes292-2, which form the electrodes in the further layer below the layer shown inFIG. 13C. For example, electrodes Y11-1and so on are formed on the electrode Y11a.

In this way, the row electrodes290-1,290-2and so on, and the column electrodes292-1,292-2and so on, are layered via piezoelectric bodies (not shown) which are placed between the row electrodes and the column electrodes, and hence the laminated piezoelectric element258is formed as shown inFIG. 12. As shown inFIG. 12, the electrode pair is formed by arranging the electrode Y11-1formed on the column electrode Y11below the electrode X11-1formed on the row electrode X11, and similarly, another row electrode and another column electrode forming another electrode pair are arranged below this.

Moreover, the electrode pair is formed by arranging the electrode Y12-1formed on the column electrode Y12below the electrode X11-2formed on the row electrode X11, and furthermore, the electrode pair is formed by arranging the electrode Y11-2formed on the column electrode Y11below the electrode X12-1formed on the row electrode X12. In all of these cases, further another row electrode and another column electrode forming another electrode pair are arranged below this.

FIG. 14is a plan view showing a typical arrangement of the row electrodes290and the column electrodes292. Electrodes X-12and X-14are formed on the electrode Xa forming a row electrode290, and similarly, electrodes X-11and X-13are formed on the electrode Xb. Moreover, the electrodes (X-12, X-14, and so on) formed on the electrode Xa, and the electrodes (X-11, X-13, and so on) formed on the electrode Xb are arranged alternately in a direction along the electrodes Xa or Xb, and they are arranged on every other of the active part.

Furthermore, the same applies to the column electrode292, in which the electrodes Y-11and Y-13formed on the electrode Ya, and the electrodes Y-12and Y-14formed on the electrode Yb are arranged alternately in a direction along the electrodes Ya or Yb, and are arranged on every other of the active part. The electrode Y-12formed on the electrode Yb is disposed below the electrode X-11of the row electrodes290, and hence the electrode Y-12is not shown inFIG. 14.

WhileFIG. 14is a plan view,FIG. 15shows a partial cross-sectional view along the row electrode X11inFIG. 12, for example. As shown inFIG. 15, the row electrodes and the column electrodes are layered alternately, having a piezoelectric body94sandwiched between them.

FIGS. 13A to 13Dshow the lamination structure of the respective electrodes, butFIGS. 16A to 16Dshow how these lamination structures are actually formed. In the actual manufacture of the laminated piezoelectric element, green-sheets formed with respective electrode patterns and thin film piezoelectric bodies are taken and alternately layered in order.FIGS. 16A to 16Dindicate the order of this lamination, in which the row electrodes290-1, row electrodes290-2, column electrodes292-1and column electrodes292-2are layered in sequence.

The two row electrodes290-1and290-2and the two column electrodes292-1and292-2layered together form one set of four laminated layers, and furthermore, two of these sets are layered together. The row electrodes in the first set are referred to as a Row Electrode1, the column electrodes in the first set are referred to as a Column Electrode1, the row electrodes in the second set are referred to as a Row Electrode2, and the column electrodes in the second set are referred to as a Column Electrode2. In this way, the electrodes in the lamination direction (T direction) can be used as well as the electrodes in the row direction and the column direction, and thus the piezoelectric element can be driven in an arrangement which prevents cross-talk or liquid-droplets-interference caused, for instance, by mixing between liquid droplets deposited in adjacent positions on the recording paper16.

FIG. 17shows one embodiment of this kind of a driving method.

For example, inFIG. 12, if the electrodes X11aand X12aare connected to each other in such a manner that the electrodes X12-1, X11-2, X12-3, and the like, formed on the electrodes X11aand X12acan be simultaneously driven, then the electrodes on the jagged line indicated by the broken line A inFIG. 17can be simultaneously driven.

Furthermore, inFIG. 12, if the electrodes X11band X12bare connected to each other in such a manner that the electrodes X11-1, X12-2, X11-3, and the like, formed on the electrodes X11band X12bcan be simultaneously driven, then the electrodes on the jagged line indicated by the solid line B inFIG. 17can be simultaneously driven.

By devising the electrode connections (electrode wiring) in this way, it is possible to ensure that the electrodes which are mutually adjacent in the same row direction do not simultaneously drive the piezoelectric element, and hence cross-talk and droplet interference can be prevented.

Next, a method for driving electrodes in the T direction (the lamination direction or an oblique direction), which is a third direction in addition to the row direction and column direction described above, is explained below with reference to the drawings.

FIG. 18is a plan view of a laminated piezoelectric element258, showing a situation where the active parts of a laminated piezoelectric element formed by layering electrode layers via piezoelectric bodies over respective pressure chambers are arranged in the row direction and the column direction.

FIG. 19is a cross-sectional view along line19-19inFIG. 18. In the embodiment shown inFIG. 19, two sets (a first set and a second set) of electrode layers, each having four layers comprising two layers of row electrodes290and two layers of column electrodes292, are laminated in the T direction.

By layering the electrodes in this manner and devising the wiring in such a manner that the electrodes can be independently driven in the T direction (lamination direction) as well as the row direction and the column direction, it is possible to prevent cross-talk and interference between the liquid droplets. Furthermore, if a plurality of sets of electrodes are layered in the lamination direction in such a manner that these sets can be independently driven, then it is also possible to use one of these sets of electrodes as sensors for determining the pressure of the ink inside the pressure chambers to evaluate the ejection state.

While two sets of the electrode layers are arranged in the lamination direction (T direction) inFIG. 19, it is also possible to laminate a third set, a fourth set, or further layers of electrodes. By laminating a plurality of electrode layers in the T direction in this way and independently driving each of these layers, it becomes possible to control the generated pressure in a plurality of stages, and hence the tonal gradation can be controlled readily. Furthermore, it is also possible to constitute actuators for driving refill.

According to the embodiments described above, the electrodes are arranged in the row direction and the column direction, and the wiring is derived from the side faces of the laminated piezoelectric element. Hence, it is possible to increase the number of rows and columns of electrodes. Moreover, since the matrix structure is adopted for the laminated structure, it is possible to generate greater pressure in comparison with a conventional single-plate piezoelectric element, and therefore, even ink of high viscosity can be ejected.

Moreover, by increasing the number of layers, a larger pressure can be generated by means of a low voltage. Furthermore, the device is easier to handle than a single plate structure when a single long head corresponding to a matrix arrangement is made.

Furthermore, since the matrix-drive is adopted by using the wiring arranged in the row direction and the column direction, the number of wires is reduced and the number of drivers can be reduced in comparison with the conventional art where one driver is required for each nozzle.

The laminated piezoelectric element according to the present invention, the liquid droplet ejection head using the laminated piezoelectric element, and the image forming apparatus using the liquid droplet ejection head have been described in detail above. It should be understood, however, that there is no intention to limit the scope of the invention to the specific forms disclosed, but on the contrary, the invention is to cover all modifications, alternate constructions and equivalents falling within the spirit and scope of the invention as expressed in the appended claims.