JP2008012917A - Liquid discharge head and imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid discharge head which can improve the controllability of a discharge direction and a discharge volume and avoid the viscous heat generation by the long-time oscillation of a capillary wave, and an imaging device using this liquid discharge head. <P>SOLUTION: This liquid discharge head comprises the following components: a surface elastic wave propagator (16) with a nozzle hole (12), a surface elastic wave generation means for generating a surface elastic wave (30), (e.g. an interdigital converter made up of a comb-type crossed digital electrode), arranged around the nozzle hole (12) on the surface elastic wave propagator (16), and a guide member (18) which is arranged in the center part of the nozzle hole (12), has a tapered conical surface shape projecting in the discharge direction from the discharge surface (22) of the nozzle hole (12), propagates the capillary wave (32) excited to the surface of the liquid (34) inside a nozzle by the surface elastic wave (30), along the curved liquid surface (24), while forming the curved liquid surface (24) along the conical surface by the surface tension of the liquid (34)inside the nozzle hole (12) and finally, ejects the liquid (34) from the apex (18B) of the conical surface. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a liquid discharge head and an image forming apparatus, and more particularly to a liquid discharge head that generates surface droplets from a liquid surface using surface acoustic waves and an image forming apparatus using the liquid discharge head.

2. Description of the Related Art Conventionally, an inkjet head that ejects ink by emitting surface acoustic waves (SAW) into the ink has been proposed (Patent Documents 1 and 2). In such a conventional surface acoustic wave head, when a surface acoustic wave (SAW, Rayleigh wave) is excited on a solid surface and leaked into the liquid, the angle is relative to the normal of the incident axis (Rayleigh angle). ) The liquid droplets are ejected from the vicinity of the three-phase interface by longitudinal waves radiated in the direction, or surface tension waves (capillary waves) are indirectly excited in the liquid by the longitudinal wave radiation, and this is amplified to a certain amplitude. When it reaches, a droplet group is ejected by using a mechanism (so-called capillary mist) that makes particles from the wave front.
JP 2000-62161 A JP-A-9-267473

  However, in the former case (when a group of fine droplets is ejected from the vicinity of the three-phase interface), there are problems that it is difficult to control the ejection direction and the particle diameter varies. On the other hand, the latter case (in the case of capillary mist formation) is not suitable for a high-viscosity liquid because it uses a mechanism that amplifies the capillary wave on the liquid surface by parameter resonance. In addition, if energy that satisfies the resonance condition is continuously applied for a certain period of time, there is a principle restriction that a phase transition due to viscous heat generation occurs before the particle size increases and particles are formed.

  The present invention has been made in view of such circumstances, and a liquid discharge head capable of improving controllability of the discharge direction and discharge amount and avoiding viscous heat generation due to long-time oscillation of capillary waves, and An object of the present invention is to provide an image forming apparatus used.

  In order to achieve the above object, a liquid ejection head according to the present invention includes a surface acoustic wave propagating body through which surface acoustic waves propagate, a nozzle hole formed in the surface acoustic wave propagating body, and the surface acoustic wave propagating body. A surface acoustic wave generating means disposed around the nozzle hole and generating a surface acoustic wave by exciting the surface acoustic wave propagating body; a liquid supply means for supplying a liquid to the nozzle hole; and the nozzle hole And has a tapered conical surface shape protruding from the discharge surface of the nozzle hole in the discharge direction, and follows the conical surface by the surface tension of the liquid inside the nozzle hole. A guide member for propagating a capillary wave excited on the liquid surface in the nozzle by the surface acoustic wave along the curved liquid surface and flying the liquid from the apex portion of the cone surface while forming a curved liquid surface. With And wherein the door.

  According to the present invention, the surface acoustic wave (SAW) generated by the surface acoustic wave generating means propagates on the surface acoustic wave propagating body toward the nozzle hole, and is radiated from the edge surface of the nozzle hole into the liquid in the nozzle. The The leaky SAW excites capillary waves (surface tension waves) on the liquid surface in the nozzle, and the capillary waves propagate on the liquid surface toward the center of the nozzle. In the present invention, since the guide member having a conical surface shape protruding from the nozzle hole is arranged at the center of the nozzle, the liquid surface (curved liquid) curved in accordance with the conical surface shape of the guide member in the nozzle due to the surface tension of the liquid. Surface) is formed. Therefore, the capillary wave indirectly excited by the leakage SAW propagates on the curved liquid surface and is focused on the apex portion of the guide member. In this way, the liquid concentrated on the apex portion of the guide member is separated from the liquid surface into particles and discharged as droplets.

  As described above, the curved liquid surface is formed by the surface tension of the liquid according to the conical surface of the guide member, so that the capillary wave easily propagates in the direction of the longitudinal wave radiation angle (Rayleigh angle) due to the leaky (Rayleigh) wave. Further, since the apex portion of the guide member becomes a boundary (triple point) of three layers of solid (guide member), liquid, and gas (air) (because the boundary of the three layers becomes a singular point at the tip of the guide member), conventional Compared with this configuration (configuration without the guide member), the controllability of the discharge direction and the discharge amount is improved.

  Furthermore, according to the present invention, since the conventional particle formation mechanism by the amplification of capillary waves is not used, it is possible to accumulate the viscosity of the high-viscosity liquid by long-time oscillation and avoid the phase transition due to this.

  A second aspect of the present invention is an aspect of the liquid ejection head according to the first aspect, wherein the surface acoustic wave generating means is a comb-shaped interdigitated electrode (IDT).

  As the surface acoustic wave generating means, for example, there is an embodiment in which comb-shaped electrodes (comb-shaped electrodes) are provided on a surface acoustic wave propagating body made of a piezoelectric material so as to intersect with each other alternately.

  A third aspect of the present invention is an aspect of the liquid ejection head according to the first or second aspect, wherein the liquid supply means is provided on the opposite side of the surface of the surface acoustic wave propagating body on which the surface acoustic wave propagates. A liquid reservoir.

  According to this aspect, the liquid reservoir is arranged on the back surface side (the side opposite to the ejection surface) of the surface acoustic wave propagating body, and the liquid is supplied from the liquid reservoir to the nozzle.

  A fourth aspect of the present invention is an aspect of the liquid ejection head according to any one of the first to third aspects, wherein the surface elastic propagation body includes a plurality of polarized piezoelectric bodies around the nozzle hole. It is characterized in that the cut substrate is laminated in a mosaic shape.

  For example, when using a material with strong anisotropy regarding the propagation speed of surface acoustic waves, the direction of good propagation speed is made to coincide with the direction toward the center of the nozzle hole, and the piezoelectric material is polarized around the nozzle hole. A board | substrate is arrange | positioned in mosaic shape and these are bonded together and a surface elastic propagation body is formed.

  A fifth aspect of the present invention is an aspect of the liquid ejection head according to the fourth aspect of the present invention, wherein the piezoelectric cut substrate has a partial arc-shaped interdigitated electrode (IDT) as the surface acoustic wave generating means. It is formed.

  According to this aspect, the rotationally symmetric electrode arrangement is realized around the nozzle hole by the comb-shaped interdigitated electrodes (IDT) of the plurality of piezoelectric cut substrates combined in a mosaic pattern around the nozzle hole. Can do.

  A sixth aspect of the present invention is an aspect of the liquid ejection head according to any one of the first to fifth aspects, wherein the guide member is made of a hydrophilic material.

  It is preferable that the surface of the guide member has hydrophilicity from the viewpoint of wetting and spreading the liquid on the conical surface of the guide member and forming a curved liquid surface protruding from the nozzle hole.

The invention according to claim 7 provides an image forming apparatus that achieves the object. That is, an image forming apparatus according to a seventh aspect includes the liquid ejection head according to any one of the first to sixth aspects, wherein the liquid droplets ejected from the apex portions of the guide members of the nozzle holes are formed on the recording medium. An image is formed on the screen.

  The driving of the surface acoustic wave generating means is controlled based on the input image data, and a droplet is ejected from the apex of the guide member. The ejected droplets adhere to the recording medium and dots are formed. A desired image (dot arrangement) can be recorded on the recording medium by controlling the ejection timing and the ejection amount of the droplets according to the image data.

  As a configuration example of the liquid discharge head, a full-line discharge head having a nozzle row in which a plurality of nozzles are arranged over a length corresponding to the entire width of the recording medium can be used.

  In this case, a combination of a plurality of relatively short ejection head modules having nozzle rows that are less than the length corresponding to the full width of the recording medium, and connecting them together, has a length corresponding to the full width of the ejection medium. There is an aspect that constitutes a discharge intersection row.

  The full-line type liquid discharge head is usually arranged along a direction perpendicular to the relative feeding direction (relative conveyance direction) of the recording medium, but with respect to the direction perpendicular to the conveyance direction. There may be a mode in which the liquid discharge head is disposed along an oblique direction with an angle.

  The “recording medium” is a medium that receives the adhesion of the liquid ejected from the nozzles. In the image forming apparatus, a medium such as recording paper or an intermediate transfer medium corresponds to this. That is, the “recording medium” can be called a printing medium, an image forming medium, a recording medium, an image receiving medium, an ejected medium, and the like, a continuous sheet, a cut sheet, a seal sheet, a resin sheet such as an OHP sheet, Various media are included regardless of the material and shape, such as a printed board on which a film, cloth, wiring pattern, or the like is formed, an intermediate transfer medium, and the like.

  The transporting means for moving the recording medium and the liquid discharge head relative to each other includes a mode for transporting the recording medium to the stopped (fixed) head, a mode for moving the head relative to the stopped recording medium, or a head And a mode in which both the recording medium and the recording medium are moved.

  According to the present invention, capillary waves are propagated along the shape of the conical surface of the guide member, and the liquid is granulated from the apex portion of the conical surface of the guide member, so that the controllability of the discharge direction and the discharge amount is improved. In addition, according to the particle formation mechanism of the present invention, it is possible to avoid the problem of viscous heat generation of a conventional high viscosity liquid and the problem of phase transition caused thereby.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a perspective view showing a configuration of a liquid discharge head according to an embodiment of the present invention. In the illustrated liquid discharge head 10, reference numeral 12 is a nozzle hole, 14 is an ink pool (corresponding to “liquid reservoir”), 16 is a surface acoustic wave generating substrate (corresponding to “surface acoustic wave propagating body”), and 18 is inside the nozzle. It is a guide member which prescribes | regulates the shape of the liquid level. In the figure, a droplet discharge element for one channel corresponding to one nozzle hole 12 is drawn, but when applied to an inkjet head (also referred to as “print head” or “recording head”), A plurality of channels are arranged in one dimension (row shape) or two dimensions (plane shape).

Nozzle holes 12 are formed in the surface acoustic wave generating substrate 16, and an ink pool 14 is formed in a space between the surface acoustic wave generating substrate 16 and the ink pool substrate 20 disposed so as to be opposed thereto. The ink pool 14 is filled with ink liquid.

  The guide member 18 is a columnar member having a tip portion 18 </ b> A having a conical shape, and is erected on the ink pool substrate 20 in a state where the center axis thereof coincides with the center of the nozzle hole 12. The front end portion 18A of the guide member 18 protrudes in the ink discharge direction (upward in the figure) from the discharge surface (nozzle surface) 22 of the nozzle hole 12, and the front end portion 18A is caused by the surface tension of the ink liquid. A liquid surface 24 is formed that is curved along a conical inclined surface (a tapered conical surface whose cross-sectional area gradually decreases toward the tip).

  Thus, from the viewpoint of forming the ink liquid surface along the shape of the tip end portion 18A of the guide member 18 protruding from the nozzle hole 12, the guide member 18 is preferably made of a hydrophilic material (such as a porous material). .

The surface acoustic wave generating substrate 16 is made of a piezoelectric material. As shown in FIG. 2, an arc-like comb-shaped interdigital electrode 26 that functions as an interdigital transducer (IDT) is provided around the nozzle hole 12. Is provided. As the substrate material, for example, a piezoelectric material such as Li ₂ NbO ₃ , Li ₂ TaO ₇ , Li ₂ B ₄ O ₇ , ZnO, or AlN is used. Also included are those obtained by depositing these piezoelectric materials on heat-resistant hard glass such as Pyrex glass (trade name) or sapphire.

  The surface acoustic wave generating substrate 16 of this example is a polarized cut substrate 16-1, 16-2, 16-3, 16-4 in which the periphery of the nozzle hole 12 is divided into four (divided by equal angular distribution of 90 degrees). It consists of the structure which stuck together in mosaic. On the surfaces of the cut substrates 16-1, 16-2, 16-3, 16-4, comb-shaped interdigitated electrodes 26 each having a partial arc (substantially 1/4 arc) are formed.

  The comb-shaped interdigitated electrodes 26 are provided in a state where the patterns of the comb-shaped first electrode 26-1 and the pattern of the second electrode 26-2 are alternately meshed with each other. The method for forming the comb electrode pattern on the substrate is not particularly limited, and a known electrode forming method such as a deposition method, an etching method, an ion implantation method, or a thermal diffusion method can be used. Alternatively, an electrode pattern may be formed by forming a groove on the substrate surface and filling (or adhering) a conductive material into the groove.

  As shown in the example of FIG. 2, the configuration in which the polarized cut substrates are bonded in a mosaic shape can use a material having strong anisotropy with respect to the propagation speed, and the direction in which propagation is easy is centered on the nozzle hole 12. This is beneficial in that the cut substrates can be combined to face.

  2 illustrates the configuration in which the periphery of the nozzle is divided into four parts, the number of divisions is not limited to the illustrated example. In addition, a mode in which the surface acoustic wave generating substrate is configured using a single piezoelectric element plate or a continuous piezoelectric material thin film is also possible. In this case, it is necessary to polarize according to the IDT shape.

  When an electric signal (driving signal) having an appropriate frequency and voltage is applied between the first electrode 26-1 and the second electrode 26-2 of the comb-shaped interdigitated electrode 26 shown in FIG. A surface acoustic wave (reference numeral 30 in FIG. 1) is excited on the surface of the generation substrate 16.

  The excited surface acoustic wave 30 propagates on the surface of the surface acoustic wave generating substrate 16 toward the center of the nozzle hole 12, reaches the opening edge of the nozzle hole 12, and is in contact with the opening edge. Radiated into the liquid. Due to this leakage SAW, a surface tension wave (capillary wave) 32 is generated on the liquid surface in the nozzle hole 12 (see FIG. 1). The annular capillary wave 32 indirectly excited in this way propagates (moves) toward the center of the nozzle hole 12, and along the curved liquid surface 24 according to the shape of the distal end portion 18 </ b> A of the guide member 18, the guide member 18. The liquid droplets 34 are separated (granulated) and discharged from the vertex 18B. In addition, a mode in which water repellent treatment is performed only in the vicinity of the top of the guide member 18 so that the discharged liquid is easily made into particles is also preferable.

  FIG. 3 is a diagram showing the propagation state of the surface tension wave excited in the nozzle by the surface acoustic wave and the discharge process. (A) of the figure shows the steady state before discharge driving. As shown in the figure, the guide member 18 is subjected to water repellent treatment only at the apex of the conical tip 18A and its vicinity range (only the apex vicinity range 36 indicated by the dotted line in the figure). The position of the conical bottom surface 18 </ b> C is located on the back side (downward in the drawing) of the nozzle with respect to the ejection surface 22 of the nozzle hole 12, and the inside of the nozzle hole 12 is conical due to the surface tension of the ink liquid 40. A curved liquid surface 24 reflecting the shape of the surface is formed.

  A burst signal for ejection driving is applied between the electrode pairs of the comb-shaped interdigitated electrodes 26 described in FIG. 2, and surface acoustic waves are emitted from the edge of the nozzle hole 12 into the ink liquid 40, whereby FIG. As shown in (b), the capillary wave 32 is excited on the liquid surface in the nozzle. The capillary wave 32 propagates on the curved liquid surface along the conical surface of the guide member 18 toward the center of the nozzle hole 12 (FIGS. 3C to 3D), and eventually reaches the apex portion 18B of the guide member 18. The concentrated ink separates (particulates) from the protruding end 18B of the guide member 18 and flies as droplets (FIGS. 3E to 3G).

  According to the droplet discharge head 10 according to the present embodiment, the capillary wave 32 propagates along the conical shape of the guide member 18, and the droplets 34 are discharged from the apex portion 18 </ b> B of the guide member 18. Controllability of the discharge direction and the volume (discharge amount) per drop (one particle) is improved. In addition, according to the particle formation mechanism according to the present invention, it is possible to avoid the problem of viscous heat generation of the conventional high viscosity liquid and the problem of phase transition caused thereby.

[Discussion of discharge volume]
Here, the volume of the liquid droplets ejected from the liquid ejection head 10 having the above configuration is estimated. In the torus shown in FIG. 4, when the radius of the cross section is r and the radius of the center line is R, the cross-sectional area A = πr ² and the circumference L = 2πR of the center line, so the volume V of the torus is V = A × L = 2π ² r ² R
It is. Assume that the nozzle diameter is D≈2 (R + r), the wavelength λ of the capillary wave generated by the leaky SAW is λ≈4r, and the amplitude thereof is about r. Since a solitary wave due to surface tension is generated by half-wave input of SAW, the volume V _d at the time of discharge is considered to be about V / 2.
V _d = (1/64) π ² λ ² (2D−λ)
It becomes. For example, when D = 20 [μm] and λ = 10 [μm], V _d ≈0.46 [pl] is calculated.

[Discussion of discharge speed]
Assuming that ejection is performed at the propagation speed of capillary waves, the ejection speed is given by U _d = √ (2πγ / (ρλ)). Where γ is the surface tension, ρ is the density, and λ is the wavelength of the capillary wave. For example, when “water” is used as the discharge liquid and γ = 70 [mN / m], ρ = 1000 [kg / m ³ ], and λ = 10 [μm], the discharge speed is U _d ≈6. It is calculated as 63 [m / s].

  Since the initial velocity required for landing at a gap length of 1.5 [mm] is about 5.36 [m / s] with respect to the discharge volume in this case, the landing conditions are satisfied. In order to reduce drift due to disturbance, a mode in which flight assist is added, such as applying an electric field to the flying space of the droplet and accelerating the charged ink droplet by the electric field, is preferable.

[Configuration example of image forming apparatus]
Next, an example of an image forming apparatus in which the liquid discharge head 10 described above is applied to a print head will be described.

  FIG. 5 is an overall configuration diagram of an ink jet recording apparatus showing an embodiment of an image forming apparatus according to the present invention. As shown in the drawing, the ink jet recording apparatus 110 includes a plurality of recording heads (hereinafter referred to as “inks”) corresponding to black (K), cyan (C), magenta (M), and yellow (Y) inks. A printing unit 112 having 112K, 112C, 112M, 112Y), an ink storage / loading unit 114 for storing ink to be supplied to each of the heads 112K, 112C, 112M, 112Y, and a recording medium A paper feeding unit 118 that supplies the recording paper 116, a decurling unit 120 that removes curling of the recording paper 116, and a nozzle surface (ink ejection surface) of the printing unit 112 are disposed to face the recording paper 116. A media conveyance unit 122 that conveys the recording paper 116 while maintaining the property, a print detection unit 124 that reads a printing result by the printing unit 112, and a recorded Rokushi the (printed matter) and a paper output unit 126 for discharging to the outside.

  The ink storage / loading unit 114 includes ink tanks that store inks of colors corresponding to the heads 112K, 112C, 112M, and 112Y, and the tanks are connected to the heads 112K, 112C, 112M, and 112Y via a required pipe line. Communicated with. Further, the ink storage / loading unit 114 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.

  In FIG. 5, a magazine for rolled paper (continuous paper) is shown as an example of the paper supply unit 118, 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 (media) can be used, an information recording body such as a barcode or a wireless tag that records media type information is attached to a magazine, and information on the information recording body is read by a predetermined reader. It is preferable to automatically determine the type of recording medium to be used (media type) and to perform ink ejection control so as to realize appropriate ink ejection according to the media type.

  The recording paper 116 delivered from the paper supply unit 118 retains curl due to having been loaded in the magazine. In order to remove this curl, the decurling unit 120 applies heat to the recording paper 116 by the heating drum 130 in the direction opposite to the curl direction of the magazine. 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 using roll paper, a cutter (first cutter) 128 is provided as shown in FIG. 5, and the roll paper is cut into a desired size by the cutter 128. Note that the cutter 128 is not necessary when cut paper is used.

  After the decurling process, the cut recording paper 116 is nipped and transported onto the platen 132 by the transport roller pair 131. A conveying roller pair 133 is also arranged at the subsequent stage of the platen 132 (downstream of the printing unit 112), and the recording sheet 116 is set in a predetermined manner in conjunction with the preceding conveying roller pair 131 and the succeeding conveying roller pair 133. Transport at a speed of.

  The platen 132 functions as a member (recording medium holding means) that holds (supports) the recording paper 116 while maintaining the planarity of the recording paper 116, and also functions as a back electrode for forming an electric field for flight assist. It is. The platen 132 in FIG. 5 has a width that is wider than the width of the recording paper 116, and is configured such that at least the portions facing the nozzle surface of the print unit 112 and the sensor surface of the print detection unit 124 form a horizontal plane (flat surface). Has been.

  A heating fan 140 is provided on the upstream side of the printing unit 112 in the conveyance path of the recording paper 116. The heating fan 140 heats the recording paper 116 by blowing heated air onto the recording paper 116 before printing. Heating the recording paper 116 immediately before printing makes it easier for the ink to dry after landing.

  Each of the heads 112K, 112C, 112M, and 112Y of the printing unit 112 has a length corresponding to the maximum paper width of the recording paper 116 targeted by the inkjet recording device 110, and the nozzle surface has a recording paper of the maximum size. This is a full-line type head in which a plurality of nozzles for ejecting ink are arranged over a length exceeding at least one side (full width of the drawable range) (see FIG. 6).

  The heads 112K, 112C, 112M, and 112Y are arranged in the order of black (K), cyan (C), magenta (M), and yellow (Y) from the upstream side along the feeding direction of the recording paper 116. 112K, 112C, 112M, and 112Y are fixedly installed so as to extend along a direction substantially orthogonal to the conveyance direction of the recording paper 116.

  A color image can be formed on the recording paper 116 by discharging different colors of ink from the heads 112K, 112C, 112M, and 112Y while the recording paper 116 is being conveyed by the media conveying unit 122.

  As described above, according to the configuration in which the full-line heads 112K, 112C, 112M, and 112Y having nozzle rows that cover the entire width of the paper are provided for each color, the recording paper 116 and the printing unit in the paper feeding direction (sub-scanning direction). An image can be recorded on the entire surface of the recording paper 116 by performing the operation of relatively moving the 112 once (that is, by one sub-scan). Accordingly, printing can be performed at a higher speed than a shuttle (serial) type head in which the recording head reciprocates in a direction orthogonal to the paper conveyance 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, dark ink, and special color ink are used as necessary. May be added. For example, it is possible to add a head for ejecting light-colored ink such as light cyan and light magenta. Also, the arrangement order of the color heads is not particularly limited.

  The print detection unit 124 shown in FIG. 5 includes an image sensor (line sensor or area sensor) for imaging the droplet ejection result of the printing unit 112. From the droplet ejection image read by the image sensor, nozzle clogging or It functions as a means for checking ejection defects such as landing position deviation. Test patterns or practical images printed by the heads 112K, 112C, 112M, and 112Y of the respective colors are read by the print detection unit 124, and ejection determination of each head is performed. 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 142 is provided following the print detection unit 124. The post-drying unit 142 is means for drying the printed image surface, and for example, a heating fan is used.

A heating / pressurizing unit 144 is provided following the post-drying unit 142. Heating / pressurizing unit 14
Reference numeral 4 denotes a means for controlling the glossiness of the image surface. The image surface is heated by a pressure roller 145 having a predetermined uneven surface shape, and the uneven shape is transferred to the image surface.

  The printed matter generated in this manner is outputted from the paper output unit 126. The ink jet recording apparatus 110 is provided with a sorting means (not shown) that switches the paper discharge path in order to select the prints of the main image and the prints of the test print and send them to the discharge units 126A and 126B. 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 the cutter (second cutter) 148. Although not shown in FIG. 5, the paper output unit 126A for the target prints is provided with a sorter for collecting prints according to print orders.

  FIG. 7 is a plan view of the ejection surface of the head. Since the structures of the respective heads 112K, 112C, 112M, and 112Y for each color described with reference to FIG. 5 are common, the heads are represented by the reference numeral 150 in the following.

  In order to increase the dot pitch printed on the recording paper 116, it is necessary to increase the nozzle pitch in the head 150. As shown in FIG. 7, the head 150 of this example has a structure in which nozzle holes 12 that are ink ejection ports are arranged in a matrix (two-dimensionally). High density of substantial nozzle intervals (projection nozzle pitch) projected so as to be aligned along the direction orthogonal to the feed direction (main scanning direction) is achieved.

  As shown in FIG. 8, comb-shaped interdigitated electrodes 26 corresponding to the respective nozzle holes 12 are arranged on the surface acoustic wave generating substrate 16 corresponding to the nozzle arrangement shown in FIG. The wiring form of the comb-shaped interdigitated electrodes 26 arranged around each nozzle hole 12 is not clearly shown in FIG. 8, but one electrode (for example, the comb-shaped interdigitated electrode 26 corresponding to each nozzle hole 12 (for example, The first electrode 26-1) is connected to a common ground (GND) line, and the other electrode (second electrode 26-2) is connected to a signal line (data line) of a data signal corresponding to the nozzle position. Has been.

  In carrying out the present invention, the nozzle arrangement structure is not limited to the example shown in FIG. For example, the configuration illustrated in FIG. 7 (with one long head) as a form of a full-line type head having a nozzle row extending in a direction corresponding to the entire width of the recording paper 116 in a direction substantially orthogonal to the feeding direction of the recording paper 116. As shown in FIG. 9, recording is performed by arranging short head blocks 150 ′ in which a plurality of nozzle holes 12 are two-dimensionally arranged and connected in a staggered manner, instead of a mode of forming a necessary nozzle row). You may comprise the line head which has a nozzle row of the length corresponding to the full width of the paper 116. FIG.

[Explanation of control system]
FIG. 10 is a block diagram illustrating a system configuration example of the inkjet recording apparatus 110. As illustrated in FIG. 10, the inkjet recording apparatus 110 includes a communication interface 170, a system controller 172, an image memory 174, a ROM 175, a motor driver 176, a heater driver 178, a print control unit 180, an image buffer memory 182, and a power supply control unit 183. , A head driver 184, an acceleration power source 185 for flight assist, and the like.

  The communication interface 170 is an interface unit (image input means) that receives image data sent from the host computer 186. As the communication interface 170, 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.

  Image data sent from the host computer 186 is taken into the inkjet recording apparatus 110 via the communication interface 170 and temporarily stored in the image memory 174. The image memory 174 is a storage unit that stores an image input via the communication interface 170, and data is read and written through the system controller 172. The image memory 174 is not limited to a memory composed of semiconductor elements, and a magnetic medium such as a hard disk may be used.

  The system controller 172 includes a central processing unit (CPU) and its peripheral circuits, and functions as a control device that controls the entire inkjet recording apparatus 110 according to a predetermined program, and also functions as an arithmetic device that performs various calculations. . That is, the system controller 172 controls the communication interface 170, the image memory 174, the motor driver 176, the heater driver 178, and the like, and performs communication control with the host computer 186, read / write control of the image memory 174 and ROM 175, and the like. At the same time, a control signal for controlling the motor 188 and the heater 189 of the transport system is generated. The transport motor 188 is, for example, a motor that applies power to the drive rollers of the transport roller pairs 131 and 133 described in FIG. Further, the heater 189 in FIG. 10 is a heating unit used for the heating drum 130, the heating fan 140, the post-drying unit 142, or the like described in FIG.

  The ROM 175 stores programs executed by the CPU of the system controller 172 and various data necessary for control. The ROM 175 may be a non-rewritable storage unit or a rewritable storage unit such as an EEPROM. The image memory 174 is used as a temporary storage area for image data, and is also used as a program development area and a calculation work area for the CPU.

  The motor driver 176 is a driver (driving circuit) that drives the conveyance motor 188 in accordance with an instruction from the system controller 172. The heater driver 178 is a driver that drives the heater 189 in accordance with an instruction from the system controller 172.

  The print control unit 180 functions as a signal processing unit that generates dot data of each color ink based on the input image. That is, the print control unit 180 performs various processes such as processing and correction for generating an ink droplet control signal from the image data in the image memory 174 according to the control of the system controller 172, and generates the generated print data ( The control unit supplies dot data to the head driver 184.

  The print control unit 180 includes an image buffer memory 182, and image data, parameters, and other data are temporarily stored in the image buffer memory 182 during image processing in the print control unit 180. In FIG. 10, the image buffer memory 182 is shown in a mode accompanying the print control unit 180, but it can also be used as the image memory 174. Also possible is an aspect in which the print controller 180 and the system controller 172 are integrated and configured with one processor.

  The power supply control unit 183 includes a control circuit that controls ON / OFF of the acceleration power supply 185 and the output voltage value. The power supply control unit 183 controls the output of the acceleration power supply 185 in accordance with a command from the print control unit 180.

  An outline of the flow of processing from image input to print output is as follows. Image data to be printed is input from the outside via the communication interface 170 and stored in the image memory 174. At this stage, for example, RGB image data is stored in the image memory 174.

  In the ink jet recording apparatus 110, a pseudo continuous tone image is formed by changing the droplet ejection density and dot size of fine dots with ink (coloring material) to the human eye. It is necessary to convert to a dot pattern that reproduces the gradation (shading of the image) as faithfully as possible. Therefore, the original image (RGB) data stored in the image memory 174 is sent to the print control unit 180 via the system controller 172, and the print control unit 180 uses a dither method, an error diffusion method, or the like. Conversion into dot data for each ink color by the conversion process.

  That is, the print control unit 180 performs a process of converting the input RGB image data into dot data of four colors K, C, M, and Y. Thus, the dot data generated by the print control unit 180 is stored in the image buffer memory 182.

  The head driver 184 drives the IDT 26 corresponding to each nozzle hole 12 of the head 150 based on the ink dot data (that is, the ink dot data stored in the image buffer memory 182) given from the print control unit 180. A drive signal for output is output. That is, the combination of the print control unit 180 and the head driver 184 functions as an ejection drive control unit. The head driver 184 may include a feedback control system for keeping the head driving condition constant.

  The drive signal output from the head driver 184 is applied to the head 150, and the capillary wave is excited in the corresponding nozzle hole 12, so that ink droplets are ejected from the nozzle hole 12 as described in FIG. An image is formed on the recording paper 116 by controlling ink ejection from the head 150 in synchronization with the conveyance speed of the recording paper 116.

  As described above, the ejection amount and ejection timing of the droplets from the head 150 are controlled based on the dot data generated through the required signal processing in the print control unit 180. Thereby, a desired dot size and dot arrangement are realized.

  As described with reference to FIG. 5, the print detection unit 124 is a block including an image sensor. The print detection unit 124 reads an image printed on the recording paper 116, performs necessary signal processing, and the like to perform a print status (whether ejection is performed, droplet ejection, and the like). Variation, optical density, etc.) and the detection result is provided to the print controller 180. It should be noted that other discharge detection means (corresponding to discharge abnormality detection means) may be provided instead of or in combination with the print detection unit 124.

  The print control unit 180 performs various corrections for the head 150 (correction of the discharge amount, correction of the discharge position, etc.) based on information obtained from the print detection unit 124 or other discharge detection means (not shown) as necessary. Control is performed to perform cleaning operations (nozzle recovery operations) such as preliminary discharge (sometimes referred to as “purge”, “empty discharge”, “spitting”), nozzle suction, and wiping as necessary.

  In addition, the ink jet recording apparatus 110 of this example includes a media type information acquisition unit 190 that acquires information about the type of recording medium (media type) used, and information about the type of ink used (ink type information). An ink type information acquisition unit 192 to be acquired, and information obtained from these units is sent to the system controller 172.

  The media type information acquisition unit 190 is a means for detecting the type (paper type) and size of the recording medium. For example, a means for reading information such as a barcode attached to the magazine of the paper feeding unit 118 described in FIG. 5, a sensor (paper width detection sensor, detecting the thickness of the paper) disposed at an appropriate location in the paper conveyance path. For example, a sensor for detecting the reflectance of the paper), and an appropriate combination thereof is also possible. Further, in place of or in combination with these automatic detection means, it is possible to specify information such as paper type and size by input from a predetermined user interface.

  As a means for acquiring ink type information, for example, the ink physical property information is read from the shape of the cartridge of the ink tank (a specific shape that can identify the ink type) or a barcode or IC chip incorporated in the cartridge. Means can be used. In addition, the operator may input necessary information using a user interface.

  The system controller 172 and the print control unit 180 specify the combination of the recording medium and the ink type based on the information obtained from the media type information acquisition unit 190 and the ink type information acquisition unit 192, and utilize the information in the ROM 175. Thus, ejection control suitable for the combination of the corresponding recording medium and ink is performed.

  In the above embodiment, a page-wide line head has been described. However, the application of the present invention is not limited to a line head printer, and multi-pass scanning by a shuttle (serial) scanning method or overlap scanning by a short head is performed. It can also be applied to a printer.

[Modification]
In the above-described embodiment, the aspect in which the conical guide member is provided in the circular nozzle has been described. However, the present invention is not limited to this aspect. For example, as shown in FIG. 11, a mode in which a quadrangular pyramid-shaped guide 216 is provided at the center of a rectangular nozzle hole 212 is also possible. In this case, IDTs 226 composed of comb-shaped electrodes 226-1 and 226-2 are provided corresponding to the four sides of the nozzle hole 212, respectively.

  In addition, the shape of the nozzle hole and the cone shape of the guide member disposed at the center thereof are preferably those having as little anisotropy as possible with respect to the center axis. A mode in which a regular n-pyramidal guide member is provided for an n-shaped nozzle hole (n is an integer of 3 or more), and an IDT is disposed corresponding to each side of the nozzle hole is preferable.

  In the above-described embodiment of the present invention, the ink jet recording apparatus 110 that forms a color image on the recording paper 116 by ejecting ink droplets on the recording paper 116 has been described. However, the scope of the present invention is applied to the ink jet recording apparatus. Without being limited thereto, the present invention can be widely applied to liquid ejection devices that eject water, chemicals, processing liquids, and other liquids from nozzle holes provided in the head.

The perspective view which shows the structure of the liquid discharge head which concerns on embodiment of this invention. The top view which shows the example of the interdigital converter (IDT) formed on a surface acoustic wave generation board | substrate Diagram showing the propagation of surface tension waves excited in the nozzle by surface acoustic waves and the discharge process Diagram of torus used to estimate discharge volume 1 is an overall configuration diagram of an ink jet recording apparatus showing an embodiment of an image forming apparatus according to the present invention. FIG. 5 is a plan view of the main part around the printing unit of the ink jet recording apparatus shown in FIG. Top view of the ejection surface of the head The top view which shows the example of the interdigital converter (IDT) formed on a surface acoustic wave generation board | substrate Plan view showing another configuration example of a full-line head Main block diagram showing the system configuration of the inkjet recording apparatus of this example The principal part perspective view which shows other embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Liquid discharge head, 12 ... Nozzle hole, 14 ... Ink pool, 16 ... Surface acoustic wave generation board, 16-1, 16-2, 16-3, 16-4 ... Cut board, 18 ... Guide member, 18B ... Apex part, 20 ... ink pool substrate, 22 ... discharge surface, 24 ... curved liquid surface, 26 ... comb-shaped interdigital electrode, 30 ... surface acoustic wave, 32 ... capillary wave, 34 ... droplet, 110 ... ink jet recording apparatus, 112: Printing section, 112K, 112C, 112M, 112Y, 150 ... Head, 116: Recording paper

Claims (7)

A surface acoustic wave propagating body through which surface acoustic waves propagate;
A nozzle hole formed in the surface acoustic wave propagating body;
A surface acoustic wave generating means disposed around the nozzle hole on the surface acoustic wave propagating body and generating the surface acoustic wave by exciting the surface acoustic wave propagating body;
Liquid supply means for supplying a liquid to the nozzle hole;
The tapered hole is disposed at the center of the nozzle hole and protrudes in the discharge direction from the discharge surface of the nozzle hole, and the cone is formed inside the nozzle hole by the surface tension of the liquid. A capillary wave excited on the liquid surface in the nozzle by the surface acoustic wave is propagated along the curved liquid surface while forming a curved liquid surface according to the surface, and the liquid is caused to fly from the apex of the cone surface. A guide member;
A liquid discharge head comprising:   2. The liquid discharge head according to claim 1, wherein the surface acoustic wave generating means is a comb-shaped interdigitated electrode (IDT).   3. The liquid discharge head according to claim 1, wherein the liquid supply unit is a liquid reservoir provided on an opposite side of a surface of the surface acoustic wave propagating body on which the surface acoustic wave propagates.   4. The surface elastic propagating body is configured by attaching a plurality of polarized piezoelectric cut substrates around the nozzle holes in a mosaic pattern. Liquid discharge head.   5. The liquid discharge head according to claim 4, wherein said piezoelectric cut substrate is formed with a partial arc-shaped interdigitated electrode (IDT) as said surface acoustic wave generating means.   The liquid ejection head according to claim 1, wherein the guide member is made of a hydrophilic material.   An image forming apparatus comprising: the liquid discharge head according to claim 1, wherein an image is formed on a recording medium by droplets discharged from an apex portion of the guide member in the nozzle hole. apparatus.

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