JP2007090647A - Liquid delivery head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid delivery head which enables the power consumption and heat generation to be inhibited in a head with the structure wherein delivery elements are arranged with high density. <P>SOLUTION: A printhead 50, which is equipped with a piezoelectric actuator 58 including a piezoelectric element for utilizing the displacement of a d<SB>33</SB>mode and makes ink droplets having the volume of 1 pl to 2 pl discharged from a nozzle 51 having the diameter of 20 μm to 30 μm by carrying out a resonance driving of the piezoelectric actuator 58 with a resonance frequency of 250 kHz to 750 kHz, has the shape such that the thickness t of the piezoelectric actuator 58 is 1.8 mm or more and 5.5 mm or less. With the printhead 50 having such a structure, the power consumption and heat generation of the piezoelectric actuator 58 is inhibited. The piezoelectric actuator 58 is equipped with an individual electrode 57 on the first surface and a common electrode 62 on the second surface. A piezoelectric activity part corresponding to each pressure chamber 52 is partitioned by the first trench 60 provided on the first surface. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a liquid discharge head, and more particularly to a structure of a liquid discharge head used in a liquid discharge apparatus such as an ink jet recording apparatus.

  An ink jet recording apparatus is often used as an apparatus for outputting a desired image or document on a recording medium. An ink jet recording apparatus forms a desired image on a recording medium by ejecting ink droplets from nozzles provided in a head. In a head used in an ink jet recording apparatus, a large number of miniaturized nozzles are arranged at a high density in order to achieve high quality recording images and high recording speed. In addition, in an inkjet recording apparatus having a full-line head in which nozzles are arranged over a length corresponding to the entire width of the recording medium, an image is formed on the entire area of the recording medium by scanning the recording medium once with respect to the head. Single pass printing is possible, and single pass printing with a full-line head can improve productivity.

  The invention described in Patent Document 1 has a structure in which an overhang portion is formed on the side wall of the pressure chamber directly below the land as a means for suppressing deformation of the land portion formed on the piezoelectric sheet of the actuator unit of the inkjet head. In addition, it is configured to suppress crosstalk, which becomes a problem when the nozzles are arranged at high density.

  The inventions described in Patent Documents 2 and 3 are based on the piezoelectric effect and thin film method associated with the increase in density in a structure in which a common liquid chamber is provided in a direction facing the nozzle across the piezoelectric body in order to increase the density. The wiring is devised to obtain a thin electrode.

  In the invention described in Patent Document 4, a piezoelectric precursor film is patterned on a lower electrode in a predetermined shape, and the piezoelectric precursor film thus formed is crystallized to obtain a piezoelectric thin film. Even so, high insulation and sufficient piezoelectric characteristics are obtained.

The invention described in Patent Document 5 discloses a technique for preventing a decrease in ink discharge performance while narrowing the width of an actuator in an inkjet head.
JP 2005-59328 A JP 2004-154987 A Japanese Patent No. 2004-1366 Japanese Patent No. 2004-47814 Japanese Patent No. 2004-188900

  However, a line-type head in which nozzles are arranged at high density includes a large number of drive elements, and power consumption and heat generation during printing are problematic. In particular, in a head using a piezoelectric element as a driving element, when a piezoelectric element having a large capacitance is driven at a high voltage, both power consumption and heat generation tend to increase. When the nozzles are arranged at high density with a limited head area, the size of each piezoelectric element is reduced, so that each piezoelectric element is thinned to obtain energy necessary for ejection. Thus, when the thickness of the piezoelectric element is reduced, the capacitance of the piezoelectric element is increased. When the piezoelectric element is thinned, heat generation and power consumption are disadvantageous. An increase in the amount of heat generated by the head can adversely affect the ink contained in the head and cause deterioration in ejection performance. Further, the increase in power consumption increases the size of the power supply device that supplies power to the head, which may lead to an increase in size and cost of the head and device.

  In the inventions described in Patent Documents 1 to 5, techniques for solving problems such as crosstalk and insulation performance in a high-density head are disclosed, but techniques for suppressing power consumption and heat generation are not disclosed. .

  SUMMARY An advantage of some aspects of the invention is that it provides a liquid discharge head in which power consumption and heat generation are suppressed in a head having a structure in which discharge elements are arranged at high density.

  In order to achieve the above object, a liquid discharge head according to the present invention includes a nozzle that discharges droplets, a pressure chamber provided corresponding to the nozzle, a pressure plate joined to the pressure chamber, and the pressurizing plate. It includes a single-layer piezoelectric element that is bonded to the pressure plate and deforms in a direction substantially parallel to the direction of the applied electric field, and is resonance-driven at a predetermined resonance frequency and has a minimum size formed on at least a recording medium by one drive. And a piezoelectric actuator that discharges droplets of a volume that becomes dots, wherein the piezoelectric actuator has a structure in which the thickness of the piezoelectric element is 1.8 mm or more and 5.5 mm or less.

According to the present invention, in a liquid discharge head that discharges a droplet of a volume that becomes a minimum-sized dot by one discharge, an electric field in a direction substantially parallel to the polarization direction is applied, and an extension displacement in the same direction as the electric field is applied. piezoelectric actuator comprising a single layer piezoelectric element is resonance driving by employing an d ₃₃ mode of the displacement, since its thickness is configured to be 1.8mm or more 5.5mm or less, the drive other than the d ₃₃ mode Compared to the above, power consumption can be suppressed, and further, the temperature rise of the piezoelectric actuator can be suppressed.

  In the resonance driving, there is a driving method of the piezoelectric actuator in which a transient phenomenon generated in the pressure chamber or the liquid at the time of discharge is suppressed by operating the piezoelectric actuator at a resonance frequency between the pressure chamber and the piezoelectric actuator. When this resonance frequency is increased, liquid discharge with a high discharge frequency can be realized.

  PZT (lead zirconate titanate) is preferably used for the piezoelectric actuator (piezoelectric element).

  The liquid ejection head includes a line type head having an ejection hole array having a length corresponding to the entire width of the recording medium (image forming width of the recording medium), and an ejection hole having a length less than the entire width of the recording medium. There is a serial type head that scans a short head provided with a row in the width direction of a recording medium.

  The line type liquid discharge head has a length corresponding to the full width of the recording medium by arranging short heads having short discharge hole arrays that are less than the length corresponding to the full width of the recording medium in a staggered arrangement. It is good.

  In order to achieve the above object, a liquid discharge head according to a second aspect of the present invention includes a nozzle that discharges liquid droplets, a pressure chamber provided corresponding to the nozzle, and a pressure chamber. A pressure plate, and a two-layer piezoelectric element that is bonded to the pressure plate and deforms in a direction substantially parallel to the direction of the applied electric field, is resonantly driven at a predetermined resonance frequency, and is at least a recording medium by one drive. A piezoelectric actuator that discharges droplets of a volume that is a minimum-sized dot formed on the piezoelectric actuator, and the piezoelectric actuator has a thickness of 2.2 mm or more and 5.5 mm or less per layer of the piezoelectric element It is characterized by having.

  When a piezoelectric actuator that uses multiple piezoelectric elements and electrodes stacked alternately is used, the amount of displacement can be increased compared to a single-layer piezoelectric element when the same drive voltage is applied. is there.

  In order to achieve the above object, a liquid discharge head according to a third aspect of the invention includes a nozzle that discharges liquid droplets, a pressure chamber provided corresponding to the nozzle, and a pressure chamber. A pressure plate, and a three-layer piezoelectric element that is bonded to the pressure plate and deforms in a direction substantially parallel to the direction of the applied electric field, is driven to resonate at a predetermined resonance frequency, and is at least a recording medium by one drive. And a piezoelectric actuator that discharges droplets of a volume that is a minimum-sized dot formed on the piezoelectric actuator, and the piezoelectric actuator has a structure in which the thickness of each layer of the piezoelectric element is 3.3 mm or more and 5.5 mm or less It is characterized by having.

  By applying a laminated piezoelectric element in which three layers of piezoelectric elements are laminated to the piezoelectric actuator, a larger displacement can be obtained with the same drive voltage than when a single-layer or two-layer piezoelectric element is applied. In other words, the same amount of displacement can be obtained with a lower driving voltage compared to a single-layer or two-layer piezoelectric element.

  Although an embodiment using a piezoelectric actuator having four or more layers of piezoelectric elements is possible, since the amount of heat generated by the piezoelectric actuator as a whole increases as the number of stacked piezoelectric elements increases, a balance between the required amount of displacement and the amount of heat generated is required. The number of stacked piezoelectric elements should be determined in consideration of the above.

  A fourth aspect of the invention relates to an aspect of the liquid ejection head according to the first, second, or third aspect, wherein the piezoelectric actuator is opposite to the first surface and the first surface that are joined to the pressure plate. An electrode for applying a driving voltage is provided on the second surface on the side.

  When a driving voltage is applied to the electrode formed on the first surface and the electrode formed on the second surface, the piezoelectric actuator is deformed in a predetermined direction to cause a volume change in the pressure chamber. Liquid is ejected from the nozzle.

In the aspect using the multilayer piezoelectric element according to claim 2 and claim 3, electrodes are also formed between the layers. The electrodes formed between the respective layers are appropriately connected to either one of the electrodes formed on the first surface and the second surface.
A fifth aspect of the present invention relates to an aspect of the liquid ejection head according to the fourth aspect of the present invention, and includes a plurality of the nozzles and the pressure chambers, and the piezoelectric actuator includes the first surface on the first surface. A first groove is formed to be divided into regions corresponding to the plurality of pressure chambers, and individual electrodes corresponding to the pressure chambers are provided in the region divided by the first grooves.

  Since the piezoelectric element having a size corresponding to a plurality of pressure chambers is provided with an individual electrode corresponding to each pressure chamber, the piezoelectric activity in which the region where the individual electrode is formed is deformed by applying a driving voltage. Part.

  The invention described in claim 6 relates to an aspect of the liquid discharge head according to claim 4 or 5, wherein the piezoelectric actuator includes a common electrode common to the plurality of pressure chambers on the second surface. It is characterized by.

In embodiments where the piezoelectric element using displacement in the d ₃₃ mode piezoelectric actuator is applied, fixing means for fixing the second surface of the piezoelectric actuator is provided on a surface of the second.

  A seventh aspect of the invention relates to an aspect of the liquid discharge head according to the fourth, fifth, or sixth aspect, wherein the piezoelectric actuator includes a second groove on the second surface. .

  According to the seventh aspect of the invention, by providing the second groove on the second surface, the substantial surface area of the second surface is increased, and the heat dissipation effect of the piezoelectric actuator is expected to be improved.

  In the aspect in which the second groove having the shape and structure corresponding to the first groove formed on the first surface is provided, the shape (structure) of the first surface and the shape (structure) of the second surface are substantially the same. Since the piezoelectric actuators are the same and have a target structure, warpage and deformation due to a heating process in head manufacture can be suppressed.

  An eighth aspect of the present invention relates to one aspect of the liquid ejection head according to any one of the fourth to seventh aspects, wherein the piezoelectric actuator includes a heat radiating member on the second surface. Features.

  According to the invention described in claim 8, by providing the heat radiating member, it is possible to further prevent the temperature rise due to heat generation.

  A ninth aspect of the present invention relates to an aspect of the liquid ejection head according to any one of the first to eighth aspects, wherein the resonance frequency includes a frequency of 250 kHz to 750 kHz. .

  According to the ninth aspect of the invention, by setting the resonance frequency used for driving the piezoelectric actuator to be 250 kHz or more and 750 kHz or less, a droplet having a discharge volume of 1 pl to 2 pl is discharged from a nozzle having a diameter of 20 μm to 30 μm. Can do.

According to the present invention, in a liquid discharge head that discharges a droplet of a volume that becomes a minimum-sized dot by one discharge, an electric field in a direction substantially parallel to the polarization direction is applied, and an extension displacement in the same direction as the electric field is applied. of a piezoelectric actuator including a single layer piezoelectric element is resonance driving by utilizing the d ₃₃ mode of the displacement is configured such that a thickness of 1.8mm or more 5.5mm or less, the temperature rise of the piezoelectric actuator It becomes possible to suppress.

  In the embodiment using the two-layer piezoelectric element, the thickness of each layer is configured to be 2.2 mm or more and 5.5 mm or less. In the embodiment using the three-layer piezoelectric element, the thickness of each layer is 3.3 mm or more and 5.5 mm. It is comprised so that it may become the following.

[Overall configuration of inkjet recording apparatus]
FIG. 1 is an overall configuration diagram of an ink jet recording apparatus according to an embodiment of the present invention. As shown in the figure, the inkjet recording apparatus 10 includes a print unit 12 having a plurality of print heads 12K, 12C, 12M, and 12Y provided for each ink color, and each print head 12K, 12C, 12M, An ink storage / loading unit 14 for storing ink to be supplied to 12Y, a paper feeding unit 18 for supplying a recording medium (recording paper) 16, a decurling unit 20 for removing curl of the recording medium 16, and the printing A suction belt conveyance unit 22 that is arranged to face the nozzle surface (ink ejection surface) of the unit 12 and conveys the recording medium 16 while maintaining the flatness of the recording medium 16, and a print detection that reads a printing result by the printing unit 12 And a paper discharge unit 26 for discharging the printed recording medium 16 (printed material) to the outside.

  In FIG. 1, a magazine for rolled paper (continuous paper) is shown as an example of the paper supply unit 18, but a plurality of magazines having different paper widths, paper quality, and the like may be provided side by side. Further, instead of the roll paper magazine or in combination therewith, the paper may be supplied by a cassette in which cut papers are stacked and loaded.

  When a plurality of types of recording media can be used, an information recording body such as a barcode or wireless tag that records the medium type information is attached to the magazine, and the information on the information recording body is read by a predetermined reader. Thus, it is preferable to automatically determine the type of recording medium to be used and perform ink ejection control (droplet ejection control) so as to realize appropriate ink ejection according to the type of recording medium.

  The recording medium 16 delivered from the paper supply unit 18 retains curl due to having been loaded in the magazine. In order to remove this curl, heat is applied to the recording medium 16 by the heating drum 30 in the direction opposite to the curl direction of the magazine in the decurling unit 20. At this time, it is more preferable to control the heating temperature so that the printed surface is slightly curled outward.

  In the case of an apparatus configuration that uses roll paper, a cutter (first cutter) 28 is provided as shown in FIG. 1, and the roll paper is cut into a desired size by the cutter 28. The cutter 28 includes a fixed blade 28A having a length equal to or greater than the conveyance path width of the recording medium 16, and a round blade 28B that moves along the fixed blade 28A. The fixed blade 28A is provided on the back side of the print. The round blade 28B is disposed on the printing surface side with the conveyance path interposed therebetween. Note that the cutter 28 is not necessary when cut paper is used.

  After the decurling process, the cut recording medium 16 is sent to the suction belt conveyance unit 22. The suction belt conveyance unit 22 has a structure in which an endless belt 33 is wound between rollers 31 and 32, and at least portions facing the nozzle surface of the printing unit 12 and the sensor surface of the printing detection unit 24 are horizontal ( Flat surface).

  The belt 33 has a width that is greater than the width of the recording medium 16, and a plurality of suction holes (not shown) are formed on the belt surface. As shown in FIG. 1, a suction chamber 34 is provided at a position facing the nozzle surface of the print unit 12 and the sensor surface of the print detection unit 24 inside the belt 33 spanned between the rollers 31 and 32. Then, the suction chamber 34 is sucked by the fan 35 to make a negative pressure, whereby the recording medium 16 on the belt 33 is sucked and held.

  When the power of a motor (not shown in FIG. 1, not shown in FIG. 8) is transmitted to at least one of the rollers 31 and 32 around which the belt 33 is wound, the belt 33 rotates in the clockwise direction in FIG. , And the recording medium 16 held on the belt 33 is conveyed from left to right in FIG.

  Since ink adheres to the belt 33 when a borderless print or the like is printed, the belt cleaning unit 36 is provided at a predetermined position outside the belt 33 (an appropriate position other than the print area). Although details of the configuration of the belt cleaning unit 36 are not shown, for example, there are a method of niping a brush roll, a water absorbing roll, etc., an air blow method of blowing clean air, or a combination thereof. In the case where the cleaning roll is nipped, the cleaning effect is great if the belt linear velocity and the roller linear velocity are changed.

  Although an embodiment using a roller / nip conveyance mechanism instead of the suction belt conveyance unit 22 is also conceivable, if the roller / nip conveyance is performed in the printing area, the roller contacts the printing surface of the recording medium 16 immediately after printing, so that the image is printed. There is a problem of easy bleeding. Therefore, as in this example, suction belt conveyance that does not bring the image surface into contact with each other in the print region is preferable.

  A heating fan 40 is provided on the upstream side of the printing unit 12 on the recording medium conveyance path formed by the suction belt conveyance unit 22. The heating fan 40 heats the recording medium 16 by blowing heated air onto the recording medium 16 before printing. By heating the recording medium 16 immediately before printing, the ink becomes easy to dry after landing.

  The printing unit 12 is a so-called full line type head in which a line type head having a length corresponding to the maximum paper width is arranged in a direction (main scanning direction) orthogonal to the recording medium conveyance direction (see FIG. 2). Although a detailed structural example will be described later (FIGS. 3 to 5), each of the print heads 12K, 12C, 12M, and 12Y is a recording medium of the maximum size targeted by the inkjet recording apparatus 10 as shown in FIG. The line head includes a plurality of ink discharge ports (nozzles) arranged over a length exceeding at least one side of 16.

  A print head corresponding to each color ink in the order of black (K), cyan (C), magenta (M), and yellow (Y) from the upstream side along the feeding direction of the recording medium 16 (hereinafter referred to as the recording medium conveyance direction). 12K, 12C, 12M, and 12Y are arranged. A color image can be formed on the recording medium 16 by ejecting the color inks from the print heads 12K, 12C, 12M, and 12Y while conveying the recording medium 16, respectively.

  Thus, according to the printing unit 12 in which the full line head that covers the entire area of the paper width is provided for each ink color, the operation of relatively moving the recording medium 16 and the printing unit 12 in the sub-scanning direction is performed once. An image can be recorded on the entire surface of the recording medium 16 only by performing it (that is, by one sub-scan). Thereby, it is possible to perform high-speed printing as compared with a shuttle type head in which the print head reciprocates in the main scanning direction, and productivity can be improved.

  In this example, the configuration of KCMY standard colors (four colors) is illustrated, but the combination of ink colors and the number of colors is not limited to this embodiment, and light ink and dark ink are added as necessary. May be. For example, it is possible to add a print head that discharges light ink such as light cyan and light magenta.

  As shown in FIG. 1, the ink storage / loading unit 14 has tanks that store inks of colors corresponding to the print heads 12K, 12C, 12M, and 12Y, and each tank is connected via a conduit (not shown). The print heads 12K, 12C, 12M, and 12Y communicate with each other. Further, the ink storage / loading unit 14 includes notifying means (display means, warning sound generating means) for notifying when the ink remaining amount is low, and has a mechanism for preventing erroneous loading between colors. ing.

  The print detection unit 24 includes an image sensor for imaging the droplet ejection result of the print unit 12, and functions as a means for checking nozzle clogging and other ejection defects from the droplet ejection image read by the image sensor.

  The print detection unit 24 of this example is composed of a line sensor having a light receiving element array that is wider than at least the ink ejection width (image recording width) by the print heads 12K, 12C, 12M, and 12Y. The line sensor includes an R sensor row in which photoelectric conversion elements (pixels) provided with red (R) color filters are arranged in a line, a G sensor row provided with green (G) color filters, The color separation line CCD sensor is composed of a B sensor array provided with a blue (B) color filter. Instead of the line sensor, an area sensor in which the light receiving elements are two-dimensionally arranged can be used.

  The print detection unit 24 reads the test pattern printed by the print heads 12K, 12C, 12M, and 12Y for each color, and detects the ejection of each print head. The ejection determination includes the presence / absence of ejection, measurement of dot size, measurement of dot landing position, and the like.

  A post-drying unit 42 is provided following the print detection unit 24. The post-drying unit 42 is means for drying the printed image forming surface, and for example, a heating fan is used. Since it is preferable to avoid contact with the printing surface until the ink after printing is dried, a method of blowing hot air is preferred.

  When printing on porous paper with dye-based ink, the weather resistance of the image is improved by preventing contact with ozone or other things that cause dye molecules to break by pressurizing the paper holes with pressure. There is an effect to.

  A heating / pressurizing unit 44 is provided following the post-drying unit 42. The heating / pressurizing unit 44 is a means for controlling the glossiness of the image surface, and pressurizes with a pressure roller 45 having a predetermined surface uneven shape while heating the image surface, thereby forming an uneven shape on the image forming surface. Transcript.

  The printed matter generated in this manner is outputted from the paper output unit 26. It is preferable that the original image to be printed (printed target image) and the test print are discharged separately. The ink jet recording apparatus 10 is provided with a sorting means (not shown) that switches the paper discharge path so as to select the print product of the main image and the print product of the test print and send them to the discharge units 26A and 26B. Yes. Note that when the main image and the test print are simultaneously formed in parallel on a large sheet, the test print portion is separated by a cutter (second cutter) 48. The cutter 48 is provided immediately before the paper discharge unit 26, and cuts the main image and the test print unit when the test print is performed on the image margin. The structure of the cutter 48 is the same as that of the first cutter 28 described above, and includes a fixed blade 48A and a round blade 48B.

  Although not shown in FIG. 1, the paper output unit 26A for the target prints is provided with a sorter for collecting prints according to print orders.

[Description of print head structure]
Next, the structure of the print head will be described. Since the structures of the print heads 12K, 12C, 12M, and 12Y provided for the respective ink colors are common, the print heads are represented by reference numeral 50 in the following.

  3 is a perspective perspective view showing a schematic configuration of the print head 50, FIG. 4 is a view of the print head 50 as viewed from the upper surface side, and FIG. 5 is a cross-sectional view showing the three-dimensional structure of the print head 50 (FIG. 3). FIG. 6 is a view of the print head 50 as seen from the nozzle forming surface.

  As shown in FIG. 3, the print head 50 includes a plurality of ejection elements including nozzles 51 that eject ink and pressure chambers 52 that accommodate ink ejected from the nozzles 51 along the longitudinal direction of the head. Have a structure arranged in one row.

  Further, a supply port 54 is provided on the opposite side of the surface of each pressure chamber 52 where the nozzle 51 is formed (the surface facing the nozzle forming surface) (see FIGS. 4 and 5), and ink is supplied from the nozzle 51. When ejected, ink is supplied to the pressure chamber 52 from the common liquid chamber 55 (see FIG. 5) communicating with each pressure chamber 52 via the supply port 54 (see FIGS. 4 and 5).

  A piezoelectric actuator 58 having individual electrodes 57 provided corresponding to each pressure chamber 52 is joined to a pressure plate 56 that forms the lower surface of the pressure chamber 52 orthogonal to the surface on which the nozzle 51 is formed ( (See FIG. 5).

The piezoelectric actuator 58 shown in the present embodiment, a piezoelectric element driven by a driving method which uses the displacement of d ₃₃ mode is applied. Further, the piezoelectric actuator 58 has a first surface (indicated by reference numeral 100 in FIG. 9) having a size corresponding to the plurality of pressure chambers 52, and the first surface is attached to each pressure. A first groove 60 that is divided into a region (size) corresponding to the chamber 52 is provided, and an individual electrode 57 is provided in the region divided by the first groove 60.

  The region where the individual electrode 57 is formed functions as a piezoelectric active portion (indicated by reference numeral 104 in FIG. 9) that applies ejection force to the ink in the pressure chamber 52. The piezoelectric active part is joined to a pressure plate 56 constituting the bottom surface of the pressure chamber 52, and the pressure plate 56 is deformed to cause a volume change in the pressure chamber 52, thereby ejecting ink droplets from the nozzle 51.

  A common electrode 62 is formed on a second surface (indicated by reference numeral 102 in FIG. 9) opposite to the first surface of the piezoelectric actuator 58, and the second surface of the piezoelectric actuator 58 is formed on the second surface side. A fixing member (not shown) that fixes (restrains) the surface side is joined. When a predetermined drive voltage (drive signal) is applied to the individual electrode 57 and the common electrode 62, the piezoelectric actuator 58 is displaced in the extending direction toward the individual electrode 57, and the pressure plate 56 is pushed toward the pressure chamber 52. Ink in the pressure chamber 52 is ejected. The detailed structure of the piezoelectric actuator 58 will be described later.

  In the print head 50 shown in this example, the nozzle 51 is formed on one wall surface (nozzle formation surface 51A) constituting the pressure chamber 52, and the surface (in FIG. 6, the pressure chamber 52 of the pressure chamber 52 is substantially orthogonal to the nozzle formation surface 51A). The lower surface is a pressure plate 56. The piezoelectric actuator 58 is deformed in the vertical direction in FIG. 6, and ink is ejected from the nozzle 51 when the pressure plate 56 is deformed in the upward direction in FIG. 6 so as to reduce the volume of the pressure chamber 52. That is, the print head 50 is configured such that the ink ejection direction is substantially orthogonal to the deformation direction of the piezoelectric actuator 58.

  The print head 50 defines a minimum ink droplet amount that can be ejected when the piezoelectric actuator 58 is operated once. That is, when the piezoelectric actuator 58 is operated once by a predetermined driving voltage (minimum constituent unit of the driving signal), the size (diameter) of the nozzle 51 and the piezoelectricity so that 1 pl to 2 pl of ink droplets are ejected from the nozzle 51. The pressure generated by the actuator 58 is defined. The minimum amount of ink droplets (1 pl to 2 pl ink droplets) forms a minimum size dot on the recording medium.

  Note that, as in the print head 50 ′ shown in FIG. 7, a mode in which ink is ejected in a direction substantially parallel to the deformation direction of the piezoelectric actuator 58 is also possible. The print head 50 ′ shown in FIG. 7 has a nozzle 51 formed on the surface facing the pressure plate 56. When the piezoelectric actuator 58 is deformed upward in FIG. 7, ink is ejected upward in FIG. .

[Explanation of control system]
FIG. 8 is a principal block diagram showing the system configuration of the inkjet recording apparatus 10. The inkjet recording apparatus 10 includes a communication interface 70, a system controller 72, a memory 74, a motor driver 76, a heater driver 78, a print control unit 80, an image buffer memory 82, a head driver 84, and the like.

  The communication interface 70 is an interface unit that receives image data sent from the host computer 86. As the communication interface 70, a serial interface such as USB (Universal Serial Bus), IEEE 1394, Ethernet (registered trademark), a wireless network, or a parallel interface such as Centronics can be applied. In this part, a buffer memory (not shown) for speeding up communication may be mounted. The image data sent from the host computer 86 is taken into the inkjet recording apparatus 10 via the communication interface 70 and temporarily stored in the memory 74. The memory 74 is a storage unit that temporarily stores an image input via the communication interface 70, and data is read and written through the system controller 72. The memory 74 is not limited to a memory made of a semiconductor element, and a magnetic medium such as a hard disk may be used.

  The system controller 72 is a control unit that controls the communication interface 70, the memory 74, the motor driver 76, the heater driver 78, and the like. The system controller 72 includes a central processing unit (CPU) and its peripheral circuits, and performs communication control with the host computer 86, read / write control of the memory 74, and the like, and controls the motor 88 and heater 89 of the transport system. A control signal to be controlled is generated.

  The motor driver 76 is a driver (drive circuit) that drives the motor 88 in accordance with an instruction from the system controller 72. The heater driver 78 is a driver that drives the heater 89 such as the post-drying unit 42 in accordance with an instruction from the system controller 72.

  The print control unit 80 has a signal processing function for performing various processing and correction processing for generating a print control signal from image data in the memory 74 in accordance with the control of the system controller 72, and the generated print control. A control unit that supplies a signal (print data) to the head driver 84. Necessary signal processing is performed in the print controller 80, and the ejection amount and ejection timing (droplet ejection control) of the ink droplets of the print head 50 are performed via the head driver 84 based on the image data. Thereby, a desired dot size and dot arrangement are realized.

  The print control unit 80 includes an image buffer memory 82, and image data, parameters, and other data are temporarily stored in the image buffer memory 82 when image data is processed in the print control unit 80. In FIG. 8, the image buffer memory 82 is shown in a form associated with the print control unit 80, but it can also be used as the memory 74. Also possible is an aspect in which the print controller 80 and the system controller 72 are integrated and configured with a single processor.

  The head driver 84 drives the actuators of the print heads 12K, 12C, 12M, and 12Y for each color based on the print data given from the print control unit 80. The head driver 84 may include a feedback control system for keeping the head driving conditions constant.

Various control programs are stored in the program storage unit 90, and the control programs are read and executed in accordance with instructions from the system controller 72. The program storage unit 90 may use a semiconductor memory such as a ROM or an EEPROM, or may use a magnetic disk or the like. An external interface may be provided and a memory card or PC card may be used. Of course, you may provide several recording media among these recording media. In addition,
The program storage unit 90 may also be used as a recording unit (not shown) for operating parameters and the like.

  As described in FIG. 1, the print detection unit 24 is a block including a line sensor, reads an image printed on the recording medium 16, performs necessary signal processing, etc. And the detection result is provided to the print control unit 80.

  The print control unit 80 performs various corrections on the print head 50 based on information obtained from the print detection unit 24 as necessary.

[Description of Piezoelectric Actuator, First Embodiment]
Next, the piezoelectric actuator 58 applied to the print head 50 according to the present invention will be described in detail. FIG. 9A is a cross-sectional view showing the structure of the piezoelectric actuator 58. As described above, the piezoelectric actuator 58 is joined to the pressure plate 56 (see FIG. 3), and the first surface 100 having a size corresponding to the plurality of pressure chambers 52 and the common electrode 62 are formed. And a second surface 102 opposite to the surface, and a first groove 60 formed in the first surface 100 defines a section of the piezoelectric active portion 104 corresponding to each pressure chamber 52 (see FIG. 7). It has been decided.

  A mode in which the size of the piezoelectric active portion 104 is substantially the same as the bottom surface of the pressure chamber 52 is preferable. Of course, the size of the piezoelectric active portion 104 may be smaller or larger than the size of the bottom surface of the pressure chamber 52.

The piezoelectric actuator 58 shown in the present embodiment is applied is a piezoelectric element utilizing a displacement of d ₃₃ mode. That is, in the piezoelectric element using the d ₃₃ mode displacement, one end in a direction substantially parallel to the polarization direction is fixed (constrained) (in this example, the common electrode side is fixed), and substantially parallel to the polarization direction. A direction electric field is applied to cause an elongation displacement in a direction substantially parallel to the polarization direction. A volume change occurs in the pressure chamber 52 by deforming (moving) the pressure plate 56 constituting one wall surface of the pressure chamber 52 joined to the end opposite to the end fixed by the extension displacement, An amount of ink corresponding to the volume change is ejected from the nozzle 51.

  Further, as shown in FIG. 9B, a laminated piezoelectric element in which a plurality of piezoelectric layers 110 and electrodes 112 are alternately laminated on the piezoelectric actuator 58 may be applied. In the multilayer piezoelectric element, the same drive voltage is applied to each piezoelectric layer 110, and a displacement amount obtained by adding the displacement amounts of the respective layers can be obtained. FIG. 9B is an enlarged view of the piezoelectric active portion 104 when the piezoelectric active portion 104 shown in FIG. 9A has a laminated structure.

  As a driving method of the piezoelectric actuator 58, a driving method using the resonance of the pressure chamber 52, in which the piezoelectric actuator 58 is driven at a frequency n times (where n is a natural number) the resonance frequency of the pressure chamber 52, is applied. In the drive system using such resonance, the resonance frequency of the piezoelectric actuator 58 needs to be a constant value.

In the case of d ₃₃ drive, the amount of displacement is constant regardless of the thickness (indicated by the symbol t in FIG. 9A), and by reducing the electric field (voltage) applied to the piezoelectric actuator 58, the consumption of the piezoelectric actuator 58 is reduced. While suppressing electric power, the emitted-heat amount proportional to the square of an electric field can be suppressed. The piezoelectric actuator 58 shown in this example has a thickness t (mm) defined from the viewpoint of heat generation and resonance frequency.

Here, the resonance frequency f (Hz) of the piezoelectric element is defined by the thickness t (mm) of the piezoelectric actuator 58, the compliance S33E (m ² / N) of the piezoelectric actuator 58, and the density ρ (kg / m ³ ) of the piezoelectric actuator 58. It is calculated | required by following Formula [Equation 1] using.

[Equation 1]
f = 1 / (2 × (S33E) ^1/2 × ρ)
Further, the heat generation ΔT (° C.) per unit time of the piezoelectric actuator 58 is the drive frequency (resonance frequency) f, the dielectric constant ε ₀ (= 8.85 × 10 ⁻¹² F / m) in vacuum, Using the relative dielectric constant ε1, the electric field E (V / m) applied to the piezoelectric actuator 58, the driving time s (sec) of the piezoelectric actuator 58, the specific heat c (J / kg · K), and the dielectric loss tan δ of the piezoelectric actuator 58, It is obtained by the following equation [Equation 2].

[Equation 2]
ΔT = (π × f × ε ₀ × ε ₁ × tan δ × E ² × s) / (ρ × c)
The thickness t of the piezoelectric actuator 58 is included in the electric field E (voltage per unit thickness).

  FIG. 10 shows the relationship between the heat generation ΔT and the resonance frequency f (kHz) obtained from the above [Equation 1] and [Equation 2], and the thickness t (m) of the piezoelectric actuator 58.

  According to FIG. 10, the thickness t of the piezoelectric actuator 58 at which the resonance frequency f (illustrated by a plot of ◆) is 250 kHz to 750 kHz satisfies the following equation [Formula 3].

[Equation 3]
5.5 (mm) ≧ t ≧ 1.8 (mm)
Further, the thickness t (illustrated by a plot of ■) of the piezoelectric actuator 58 at which the heat generation ΔT generated in the piezoelectric actuator 58 when continuously driven for 1 hour is 1 ° C. or less (specified by image design) is the case where a single-layer piezoelectric element is used Satisfies the following equation [Equation 4].

[Equation 4]
t ≧ 1.0 (mm)
That is, when a single-layer piezoelectric element is used for the piezoelectric actuator 58, the thickness t of the piezoelectric actuator 58 is defined from the condition of the resonance frequency f. When a multilayer piezoelectric element is used for the piezoelectric actuator 58, the amount of heat generated is four times that of a single-layer piezoelectric element when a two-layer piezoelectric element is used, and a single-layer piezoelectric element is used when a three-layer piezoelectric element is used. Since the heat generation amount is nine times that of the case, it is necessary to increase the thickness t of the piezoelectric actuator 58. Note that the thickness t of the piezoelectric actuator 58 in the case of using the laminated piezoelectric element is a total thickness obtained by adding the thicknesses of the respective layers.

  According to FIG. 10, when two layers of piezoelectric elements are used (shown by a plot), the thickness t per layer of the piezoelectric actuator 58 satisfies the following equation [Equation 5].

[Equation 5]
2.2 (mm) ≦ t ≦ 5.5 (mm)
In addition, when three layers of piezoelectric elements are used (illustrated by x plots), the thickness t per layer of the piezoelectric actuator 58 satisfies the following equation [Formula 6].

[Equation 6]
3.3 (mm) ≦ t ≦ 5.5 (mm)
However, the upper limit (5.5 mm) of the thickness t of the piezoelectric actuator 58 (thickness per layer in the case of using the multilayer piezoelectric element) is defined by the condition of the resonance frequency f.

  Here, the relationship between the resonance frequency f and the ink discharge amount (pl) will be described. FIG. 11 shows the relationship between the resonance frequency f and the ink discharge amount (pl). In FIG. 11, the ■ plot indicates the actual amount of ink ejected from the nozzle 51 when a driving voltage (driving voltage of the minimum structural unit) for ejecting 1 pl to 2 pl of ink is applied when the diameter of the nozzle 51 is 25 μm. Is shown. (3) Based on the plot, the relationship between the resonance frequency f and the ink discharge amount when the diameter of the nozzle 51 is 20 μm is obtained as a substantially straight line indicated by reference numeral 200. That is, when the nozzle 51 has a diameter of 20 μm, an ink droplet having a resonance frequency f of about 250 kHz and a volume of 2 pl or less is ejected.

  The ♦ plot shows the actual amount of ink ejected from the nozzle 51 when the drive voltage of the minimum structural unit is applied when the diameter of the nozzle 51 is 30 μm. ◆ Based on the plot, the relationship between the resonance frequency f and the ink discharge amount when the diameter of the nozzle 51 is 30 μm is obtained as a substantially straight line indicated by reference numeral 202. If the nozzle 51 has a diameter of 30 μm, an ink droplet having a volume of 2 pl can be ejected even when the resonance frequency f is 1 MHz. In this case, it is necessary to generate a high pressure from the piezoelectric actuator 58. Note that when ink droplets having the same volume are ejected, a higher generated pressure is required as the diameter of the nozzle 51 increases.

  A substantially straight line 204 shown in FIG. 11 indicates the resonance frequency f and ink when the nozzle 51 diameter is 25 μm, which is predicted based on the nozzle 51 diameter of 20 μ (reference numeral 200) and 30 μm (reference numeral 202). This is the relationship with the droplet discharge amount.

  When the diameter of the nozzle 51 is 25 μm, an ink droplet having a volume of approximately 1 pl can be ejected when the resonance frequency f is 750 kHz, which is considered to be a substantial limit point.

  That is, when the diameter of the nozzle 51 is 20 μm to 30 μm, the resonance frequency for ejecting ink droplets having a volume of 1 pl to 2 pl is 250 kHz to 750 kHz.

  In the print head 50 configured as described above, a piezoelectric element that is driven by a resonance driving method using a d33 mode displacement is applied to the piezoelectric actuator 58 that applies an ejection force to the ink in the pressure chamber 52. Since the thickness t of 58 is configured so as to satisfy the condition of 1.8 mm ≦ t ≦ 5.5 mm, the ink droplet alone ejected from the nozzle 51 at a time in the resonance drive with the resonance frequency f of 250 kHz to 750 kHz. Thus, ink droplets having a volume of 1 pl to 2 pl capable of forming dots on the recording medium are ejected, and heat generation of the piezoelectric actuator 58 can be suppressed to 1 ° C. or lower.

  When a multilayer piezoelectric element is applied to the piezoelectric actuator 58, when a two-layered piezoelectric element is used, the thickness t per layer satisfies the condition of 2.2 mm ≦ t ≦ 5.5. When a piezoelectric element having a structure is used, the thickness t per layer is configured to satisfy the condition of 3.3 mm ≦ t ≦ 5.5.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. FIG. 12 is a cross-sectional view (corresponding to FIG. 9A) showing a three-dimensional structure of a piezoelectric actuator 58 ′ applied to the print head according to the present embodiment. FIG. 13 is an enlarged view illustrating a part of FIG. In FIG. 12 and FIG. 13, the same or similar parts as in FIG. 9A are denoted by the same reference numerals, and the description thereof is omitted.

  As shown in FIG. 12, the piezoelectric actuator 58 ′ has a first surface on the second surface 102 opposite to the first surface 100 in which the first groove 60 divided into sizes corresponding to the pressure chambers is formed. A second groove 300 having the same shape and structure as the groove 60 is provided. That is, in the piezoelectric actuator 58, the first surface 100 and the second surface 102 are symmetrical.

  In this way, by making the piezoelectric actuator 58 ′ symmetrical, the piezoelectric actuator 58 ′ does not warp even if there is a heating process in the manufacturing process, and the piezoelectric actuator 58 ′ and the print head using the piezoelectric actuator 58 ′ are used. The shape of is stable.

  Further, the surface area of the second surface 102 is increased by the second groove 300 formed in the second surface 102, and a high heat dissipation effect can be obtained. In this example, the second groove 300 has a shape and structure corresponding to the first groove 60 formed in the first surface 100. However, the second groove 300 is the first groove. An aspect having a shape and structure different from 60 is also possible.

  Further, by joining a heat radiating plate (a metal plate, a ceramic plate, etc.) 302 having a shape fitted to the second surface 102 to the second surface 102, a higher heat radiating effect can be obtained. In the aspect in which the second surface 102 is provided with a metal (for example, SUS) heat dissipation plate 302, the common electrode 62 separated by the second groove 300 is electrically connected to the heat dissipation plate 302, so that the second surface has the second surface 102. In the embodiment in which the two grooves 300 are provided, the common electrode 62 corresponding to each piezoelectric active portion 104 can be made conductive by a simple method (see FIG. 13).

  In the above embodiment, the print head 50 having the nozzle row in which the nozzles 51 are arranged in the longitudinal direction is shown. However, the present invention is also applicable to a matrix type head in which the nozzles 51 are two-dimensionally arranged. is there.

  In the above embodiment, a page-wide full-line head having a nozzle row having a length corresponding to the entire width of the recording medium has been described. However, the scope of application of the present invention is not limited to this, and a short recording head is reciprocally moved. The present invention can also be applied to a shuttle head that records an image while the image is recorded.

  The liquid ejection head according to the present invention forms an image (three-dimensional shape) with a liquid other than ink, such as a resist, in addition to an ink jet recording apparatus that ejects ink onto a recording medium to form a desired image on the recording medium. The present invention can also be widely applied to image forming apparatuses, liquid discharge apparatuses such as dispensers that discharge chemicals, water, and the like from nozzles (discharge holes).

1 is an overall configuration diagram of an ink jet recording apparatus equipped with a print head according to the present invention. FIG. 1 is a plan view of a main part around a printing unit of the ink jet recording apparatus shown in FIG. FIG. 3 is a perspective view showing a structure example of a print head according to the present invention. The figure explaining operation | movement of the liquid discharge head which concerns on this invention Sectional drawing which shows the three-dimensional structure of the print head shown in FIG. Plan view of the print head shown in FIG. The figure explaining the other aspect of the print head shown in FIG. Main part block diagram which shows the system configuration | structure of the inkjet recording device which concerns on this embodiment. The figure explaining the piezoelectric actuator used for the print head concerning a 1st embodiment of the present invention. The figure explaining the relationship between the thickness of the piezoelectric actuator shown in FIG. 9, and the resonance frequency The figure explaining the relationship between the resonant frequency of the piezoelectric actuator shown in FIG. 9, and the discharge amount of an ink droplet The figure explaining the piezoelectric actuator used for the print head which concerns on 2nd Embodiment of this invention. An enlarged view of a part of the piezoelectric actuator shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 50 ... Print head, 51 ... Nozzle, 52 ... Pressure chamber, 56 ... Pressure plate, 57 ... Individual electrode, 58, 58 '... Piezoelectric actuator, 60 ... 1st groove | channel, 62 ... Common electrode, 300 ... 2nd groove | channel 302 ... Metal plate (heat sink)

Claims (9)

A nozzle for discharging droplets;
A pressure chamber provided corresponding to the nozzle;
A pressure plate joined to the pressure chamber;
A minimum of a piezoelectric element that is bonded to the pressure plate and that is deformed in a direction substantially parallel to the direction of the applied electric field, is resonantly driven at a predetermined resonance frequency, and is formed on at least a recording medium by one drive. A piezoelectric actuator that ejects droplets of a volume that is a size dot; and
With
The piezoelectric actuator has a structure in which a thickness of the piezoelectric element is 1.8 mm or more and 5.5 mm or less. A nozzle for discharging droplets;
A pressure chamber provided corresponding to the nozzle;
A pressure plate joined to the pressure chamber;
A minimum of a piezoelectric element that is bonded to the pressure plate and that is deformed in a direction substantially parallel to the direction of the applied electric field and that is resonantly driven at a predetermined resonance frequency and is formed on at least a recording medium by a single drive. A piezoelectric actuator that ejects droplets of a volume that is a size dot; and
With
The piezoelectric actuator has a structure in which a thickness per layer of the piezoelectric element is 2.2 mm or more and 5.5 mm or less. A nozzle for discharging droplets;
A pressure chamber provided corresponding to the nozzle;
A pressure plate joined to the pressure chamber;
A minimum of a piezoelectric element that is bonded to the pressure plate and that is deformed in a direction substantially parallel to the direction of an applied electric field and that is resonantly driven at a predetermined resonance frequency and formed on at least a recording medium by a single drive. A piezoelectric actuator that ejects droplets of a volume that is a size dot; and
With
The piezoelectric actuator has a structure in which a thickness per layer of the piezoelectric element is 3.3 mm or more and 5.5 mm or less.   The piezoelectric actuator includes an electrode for applying a driving voltage to a first surface bonded to the pressure plate and a second surface opposite to the first surface. Or the liquid discharge head of 3. A plurality of nozzles and pressure chambers;
In the piezoelectric actuator, a first groove that divides the first surface into regions corresponding to the plurality of pressure chambers is formed on the first surface, and each of the regions is divided by the first groove. The liquid discharge head according to claim 4, further comprising an individual electrode corresponding to the pressure chamber.   6. The liquid discharge head according to claim 4, wherein the piezoelectric actuator includes a common electrode common to the plurality of pressure chambers on the second surface.   The liquid ejection head according to claim 4, wherein the piezoelectric actuator includes a second groove on the second surface.   The liquid ejection head according to claim 4, wherein the piezoelectric actuator includes a heat radiating member on the second surface. The liquid ejection head according to claim 1, wherein the resonance frequency includes a frequency of 250 kHz or more and 750 kHz or less.

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