JP2007185879A - Inkjet head and inkjet recording apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable to suppress increase in viscosity of ink and to eliminate foreign substances in all the ink delivering holes of an inkjet head. <P>SOLUTION: A vibrator 110a and a vibration absorbing element 120a are respectively equipped on an ink delivering face 30a of the inkjet head 2a and on the opposite side of the vibrator 110a in placing a plurality of nozzles 8 between them in relation to the travelling direction of a travelling wave generated. As the surroundings of the nozzles 8 are agitated by the travelling wave, and the travelling wave is absorbed by the vibration absorbing element 120a, generation of nodes of a standing wave caused by overlapping the travelling wave and a reflected wave can be prevented from occurring, so that an effect to suppress the increase in viscosity of the ink and an effect to eliminate the foreign substances can be obtained in all the nozzles 8. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ink jet printer that forms an image by ejecting ink from nozzles.

  The ink jet head has a large number of nozzles that are ink ejection holes and an ink flow path that communicates with each nozzle. The ink flow path includes a pressure chamber that generates pressure for ejecting ink. An image can be formed on the printing medium by ejecting a desired amount of ink from the nozzles onto the printing medium.

  In such an ink jet head, an ink having a high drying property is used so that the droplet discharge frequency of the ink jet head is increased in order to increase the output speed, and the ink discharged to the recording medium dries instantaneously. Has been developed. However, when the drying property of the ink becomes high, the ink is dried and thickened, and the nozzles are clogged. As a result, the ejection of the ink is disturbed, or the ejection failure becomes impossible. Such an ejection failure can occur in the same manner regardless of the drying property of the ink if the output pause time is increased in the ink jet printer.

  As a countermeasure against this nozzle clogging, a purge operation is performed in which a cap is brought into close contact with the ink discharge surface of the printer head to discharge the gas inside the cover, and the ink and foreign matters in the nozzle are sucked and removed accordingly. ing. However, it is difficult to reliably remove the thickened ink and foreign matter in the nozzle by such a method.

  Further, the nozzle cleaner disclosed in Patent Document 1 cleans the nozzle surface with a wiper blade and removes the adhering ink by a recovery mechanism. However, even with this technique, the ink and foreign matter in the nozzle cannot be reliably removed. Furthermore, since the nozzle has been refined in recent years, the technique of Patent Document 1 may damage the nozzle.

  In addition, in the ink jet printer head disclosed in Patent Document 2, an ultrasonic transducer and a pressure detector are attached in each ink flow path that communicates with each nozzle, and the pressure detector is the nozzle eye. When clogging is detected, only the detected nozzle is ejected while the ultrasonic vibrator is excited to agitate the thickened ink in the nozzle and remove foreign matter. With this structure, the ink viscosity in the vicinity of the ejection port is lowered, and the ejection port from which ink is not ejected can be recovered.

JP 2001-205816 A JP 2003-145882 A

  However, in the technique of Patent Document 2, a traveling wave generated by excitation by an ultrasonic transducer and a reflected wave thereof are overlapped to generate a stationary wave, and the thickened ink is agitated and discharged by vibration at the node. There is a possibility that foreign matter adhering to the outlet is not removed at all, and the respective effects of lowering the ink viscosity near the ejection port and recovering the ejection port from which ink is not ejected may not be obtained. In this case, the quality of the formed image is deteriorated, and a large amount of ink is consumed when the thickened ink and the foreign matter are removed by ejecting the ink from the ink ejection holes at the time of purging.

  The object of the present invention is to reduce the ink viscosity in the vicinity of the ejection port by stirring the thickened ink in the vicinity of the ejection port, and in the ejection port from which ink is not ejected by removing foreign matter attached to the ejection port. It is an object of the present invention to provide an ink jet head and an ink jet recording apparatus which can be recovered and can improve the quality of a formed image and reduce the amount of waste ink during purging.

Means for Solving the Problems and Effects of the Invention

  In order to achieve the above object, an ink jet head according to the present invention includes a plurality of ejection ports formed on an ink ejection surface and a plurality of individual ink channels formed in communication with the ejection ports. A unit, a vibrator that is disposed in the flow path unit, generates a traveling wave that travels along the ink discharge surface using the flow path unit as a medium, and the flow path unit that is disposed in the flow path unit. A vibration absorber that absorbs the traveling wave formed on the opposite side of the vibrator with respect to the traveling direction of the wave is provided.

  According to the present invention, since the flow path unit vibrates in the vicinity of the ink discharge port, the thickened ink near the discharge port of the individual ink flow path is agitated. For this reason, the ink viscosity in the vicinity of the ejection port is lowered. Further, by removing the foreign matter attached to the ejection port, it is possible to recover the ejection port from which ink is not ejected. As a result, it is possible to improve the quality of the formed image and reduce the amount of waste ink during purging.

  Further, since the vibration is absorbed by the vibration absorber, a reflected wave that travels on the ink ejection surface in the direction opposite to the traveling wave is not generated. For this reason, the traveling wave and the reflected wave do not overlap to generate a standing wave, so that no stationary wave node where the above-described effect cannot be obtained does not occur. Therefore, the above effects can be obtained at all the discharge ports.

  Preferably, the flow path unit is formed by stacking a plurality of plates including a nozzle plate having the ink discharge surface, and the vibrator and the vibration absorber are disposed on the ink discharge surface. According to this, since the amplitude of the nozzle plate is increased, a larger ink thickening suppressing effect and a foreign matter removing effect can be obtained.

  It is preferable that the vibrator and the vibration absorber include a piezoelectric body and a pair of electrodes that sandwich the piezoelectric body. According to this, the structure of the vibrator and the vibration absorber can be simplified.

  The vibrator and the vibration absorber include three or more electrodes and two or more piezoelectric bodies arranged between the adjacent electrodes, and every other electrode is electrically connected to each other. May be. According to this, since the amplitude of the traveling wave generated becomes larger, a larger ink thickening suppressing effect and a foreign matter removing effect can be obtained, and efficient traveling wave absorption can be achieved.

  The plurality of electrodes are preferably opposed to each other in a direction connecting the vibrator and the vibration absorber. According to this, a traveling wave can be reliably advanced in a desired direction.

  It is desirable that the inkjet head further includes a resistor connected to the plurality of electrodes of the vibration absorber. According to this, the electric power generated by the vibration absorber can be consumed.

  It is preferable that the vibrator generates ultrasonic vibration. According to this, since the frequency is large, a larger ink thickening suppressing effect and a foreign matter removing effect can be obtained.

  An ink jet recording apparatus of the present invention includes the above ink jet head and vibration control means for generating a command for causing the vibrator to generate a traveling wave. According to this, the timing which generates a traveling wave can be adjusted.

  The vibration control means may generate the command intermittently. According to this, the adverse effect of vibration on printing can be reduced.

  The vibration control means may continuously generate the command. Even during printing, an ink thickening suppressing effect and a foreign matter removing effect can be obtained.

  In another aspect, an ink jet recording apparatus of the present invention includes the above-described ink jet head and resistors connected to the plurality of electrodes of the vibration absorber. According to this, the electric power generated by the vibration absorber can be consumed.

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

  First, an inkjet printer according to a first embodiment of the present invention will be described with reference to FIG. A printer 1 shown in FIG. 1 is a line head type color ink jet printer having four fixed ink jet heads 2a, 2b, 2c, and 2d that are elongated in a direction orthogonal to the paper surface of FIG. The printer 1 is provided with a paper feeder 14 at the bottom in the figure, a paper receiver 16 at the top in the figure, and a transport unit 20 at the center in the figure. Further, the printer 1 is provided with a control device 100 for controlling these operations.

  The paper feeding device 14 is a paper storage unit 15 that can store a plurality of stacked rectangular printing papers P, and a feeding unit that feeds the uppermost printing paper P in the paper storage unit 15 toward the transport unit 20 one by one. And a paper roller 45. The paper storage unit 15 stores the printing paper P so that it is fed in a direction parallel to the long side. Two pairs of feed rollers 18a, 18b, 19a, and 19b are disposed between the paper storage unit 15 and the transport unit 20 along the transport path. The printing paper P discharged from the paper feeding device 14 is fed to the upper side in FIG. 1 by the feed rollers 18a and 18b with one short side as a leading end, and then left toward the transport unit 20 by the feed rollers 19a and 19b. Sent to the direction.

  The rotation axis of the paper feed roller 45 is arranged such that an axis and a line extending in the transport direction from a point where the axis intersects the inner wall of the paper storage unit 15 are at an acute angle. Specifically, the paper feed roller 45 is inclined by 3 ° so as to be closer to the transport unit as it is farther from the inner wall. Therefore, the printing paper P picked up by the paper feed roller 45 is slightly inclined from the inner wall of the paper container 15 so that one long side of the printing paper P is forcibly brought close to the inner wall of the paper container 15. Proceed in the direction The inner wall of the paper storage unit 15 is parallel to the direction in which the printing paper P is transported by the transport unit 20. Then, before one short side of the printing paper P reaches the feed rollers 18 a and 18 b, one long side of the printing paper P contacts the inner wall of the paper storage unit 15. Thereafter, the printing paper P is directed toward the feed rollers 18a and 18b along the inner side wall of the paper storage unit 15 while one long side of the printing paper P and the inner side wall of the paper storage unit 15 are in contact with each other. proceed. As described above, the simple configuration in which the paper feed roller 45 is inclined with respect to the inner wall of the paper storage unit 15 can correct the skew of the print paper P while ensuring the continuous supply of the print paper P. It has become. Then, the printing paper P sandwiched by the feed rollers 18a and 18b is sent out toward the transport unit 20 through the feed rollers 19a and 19b.

  The transport unit 20 includes an endless transport belt 11 and two belt rollers 6 and 7 around which the transport belt 11 is wound. The length of the conveyor belt 11 is adjusted so that a predetermined tension is generated in the conveyor belt 11 wound between the two belt rollers 6 and 7. By being wound around the two belt rollers 6 and 7, the transport belt 11 is formed with two parallel planes each including a common tangent of the belt rollers 6 and 7. Of these two planes, the one facing the inkjet head 2 becomes the transport surface 27 of the printing paper P. The printing paper P sent out from the paper feeding device 14 is conveyed on the conveying surface 27 while being printed on the upper surface (printing surface) by the ink jet heads 2 a to 2 d and reaches the paper receiving unit 16. In the paper receiving unit 16, a plurality of printed printing papers P are placed so as to overlap each other.

  Each of the four inkjet heads 2a to 2d has head bodies 13a, 13b, 13c, and 13d at the lower ends thereof. As will be described later, the head main bodies 13 a to 13 d include a flow path unit 4 (see FIG. 4) in which a large number of individual ink flow paths 32 including the pressure chambers 10 communicating with the nozzles 8 are formed, and a large number of pressure chambers 10. The actuator unit 21 that can apply pressure to the ink in the desired pressure chamber 10 is bonded together.

  The head main bodies 13a to 13d have a rectangular parallelepiped shape elongated in a direction orthogonal to the paper surface of FIG. The four head bodies 13a to 13d are arranged close to each other along the left-right direction on the paper surface of FIG. A large number of nozzles 8 having minute diameters are provided on the bottom surfaces (ink ejection surfaces) of the four head bodies 13a to 13d (see FIG. 3). The ink color ejected from the nozzle 8 is one of magenta (M), yellow (Y), cyan (C), and black (K), and is ejected from a large number of nozzles 8 belonging to one head body. The ink color is the same. In addition, inks of different colors selected from four colors of magenta, yellow, cyan, and black are ejected from a large number of ink ejection ports belonging to the four head bodies 13a to 13d.

  A slight gap is formed between the bottom surfaces of the head main bodies 13 a to 13 d and the transport surface 27 of the transport belt 11. The printing paper P is conveyed from right to left in FIG. 1 along a conveyance path that passes through the gap. When the printing paper P sequentially passes below the four head bodies 13a to 13d, ink is ejected from the nozzles 8 according to the image data toward the upper surface of the printing paper P, so that the desired printing paper P is formed on the printing paper P. A color image is formed.

  The outer peripheral surface 11a of the conveyor belt 11 is treated with adhesive silicon rubber. Accordingly, the transport unit 20 is configured such that one of the belt rollers 6 rotates counterclockwise in the figure (in the direction of arrow A in FIG. 1), so that the printing paper P is transported by the feed rollers 18a, 18b, 19a, and 19b. Can be conveyed toward the paper receiver 16 while being held on the outer peripheral surface 11a of the conveyor belt 11 by its adhesive force.

  The two belt rollers 6 and 7 are in contact with the inner peripheral surface 11 b of the transport belt 11. Of the two belt rollers 6 and 7 of the transport unit 20, the belt roller 6 located on the downstream side of the transport path is connected to the transport motor 74. The transport motor 74 is rotationally driven based on the control of the control device 100. The other belt roller 7 is a driven roller that rotates by the rotational force applied from the conveyor belt 11 as the belt roller 6 rotates.

  Near the belt roller 7, a nip roller 38 and a nip receiving roller 39 are arranged so as to sandwich the conveyance belt 11. The nip roller 38 and the nip receiving roller 39 have a rotatable cylindrical body having a length substantially equal to the axial length of the belt roller 7. The nip roller 38 is biased downward by a spring (not shown) so that the printing paper P supplied to the transport unit 20 can be pressed against the transport surface 27. Since the nip roller 38 and the nip receiving roller 39 sandwich the printing paper P together with the conveyance belt 11, the printing paper P is reliably adhered to the conveyance surface 27.

  A peeling plate 40 is provided on the left side of the transport unit 20 in FIG. The release plate 40 peels the cut sheet adhered to the conveyance surface 27 of the conveyance belt 11 from the conveyance surface 27 by the right end of the separation plate 40 entering between the printing paper P and the conveyance belt 11.

  Two pairs of feed rollers 21 a, 21 b, 22 a, and 22 b are disposed between the transport unit 20 and the paper receiver 16. The printing paper P discharged from the transport unit 20 is sent to the upper side in FIG. 1 by the feed rollers 21a and 21b with one short side as the leading edge, and is sent to the paper receiver 16 by the feed rollers 22a and 22b.

  As shown in FIG. 1, a paper surface sensor 33, which is an optical sensor composed of a light emitting element and a light receiving element, is disposed between the nip roller 38 and the inkjet heads 2a to 2d located on the most upstream side. The paper surface sensor 33 emits light from the light emitting element toward the detection position on the transport path, and receives the reflected light by the light receiving element. The output signal level from the paper surface sensor 33 reflects the difference in the intensity of reflected light depending on the presence or absence of the printing paper P on the detection position. That is, the leading edge of the printing paper P has reached the detection position at the time when the output signal level suddenly increases. Since the output signal from the paper surface sensor 33 indicates that the leading edge of the printing paper P has reached the detection position, the printing signal is supplied to the inkjet heads 2a to 2d accordingly.

  Next, the details of the head bodies 13a to 13d will be described with reference to FIGS. FIG. 2 is a plan view of 13a as an example of the head body shown in FIG. Although not shown here, the head main bodies 13b to 13d have the same structure as the head main body 13a. FIG. 3 is an enlarged plan view of a block surrounded by an alternate long and short dash line in FIG. As shown in FIGS. 2 and 3, the head main body 13 a has a flow path unit 4 in which a large number of pressure chambers 10 and nozzles 8 constituting the pressure chamber group 9 are formed. A plurality of trapezoidal actuator units 21 arranged in a staggered manner and arranged in two rows are bonded to the upper surface of the flow path unit 4. More specifically, each actuator unit 21 is arranged such that its parallel opposing sides (upper side and lower side) are along the longitudinal direction of the flow path unit 4. Further, the oblique sides of the adjacent actuator units 21 overlap in the width direction of the flow path unit 4.

  The lower surface of the flow path unit 4 facing the adhesion area of the actuator unit 21 is an ink ejection area. As shown in FIG. 3, a large number of nozzles 8 are arranged in a matrix on the surface of the ink ejection region. The pressure chambers 10 communicated with one nozzle 8 are also arranged in a matrix, and a plurality of pressure chambers 10 existing on the lower surface of the flow path unit 4 facing the adhesion region of one actuator unit 21 are provided with one pressure. The chamber group 9 is comprised. In the present embodiment, 16 rows of pressure chambers 10 arranged in the longitudinal direction of the flow path unit 4 at equal intervals are arranged in parallel to each other in the lateral direction. As a whole, it is possible to form an image with a resolution of 600 dpi.

  Each nozzle 8 is a tapered nozzle, and communicates with a sub-manifold channel 5 a that is a branch channel of the manifold channel 5 through a pressure chamber 10 having a substantially rhombic shape in plan view and an aperture 12. ing. In the flow path unit 4, a plurality of individual ink flow paths from the outlet of the sub manifold flow path 5 a to the corresponding nozzle 8 through the pressure chamber 10 are formed in this way. The opening 5b of the manifold channel 5 provided on the upper surface of the channel unit 4 is joined to an ink outflow channel (not shown). Ink is supplied to the flow path unit 4 from an ink tank (not shown) via the ink outflow flow path. 2 and 3, for the sake of easy understanding, the pressure chamber 10 (pressure chamber group 9), the opening 5b, and the aperture 12 which are to be drawn by broken lines below the actuator unit 21 are drawn by solid lines. Yes.

  Next, the cross-sectional structure of the head main body 13a will be described in detail with reference to FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. As shown in FIG. 4, the head body 13 a is obtained by bonding the flow path unit 4 and the actuator unit 21 (see FIG. 2). The flow path unit 4 has a laminated structure in which the cavity plate 22, the base plate 23, the aperture plate 24, the supply plate 25, the manifold plates 26, 27, and 28, the cover plate 29, and the nozzle plate 30 are laminated from the top. ing.

  The cavity plate 22 is a metal plate in which a large number of approximately rhombic holes that serve as the pressure chambers 10 are formed. The base plate 23 is a metal plate in which a number of communication holes for communicating each pressure chamber 10 and the corresponding aperture 12 and a number of communication holes for communicating each pressure chamber 10 and the corresponding nozzle 8 are formed. It is. The aperture plate 24 is a metal plate in which a large number of communication holes for communicating the holes to be the respective apertures 12 and the respective pressure chambers 10 with the nozzles 8 corresponding thereto are formed. The supply plate 25 is a metal plate in which a large number of communication holes for communicating each aperture 12 and the sub-manifold channel 5a and a large number of communication holes for communicating each pressure chamber 10 and the corresponding nozzle 8 are formed. is there. The manifold plates 26, 27, and 28 are metal plates in which a hole serving as the sub-manifold channel 5 a and a large number of communication holes for communicating each pressure chamber 10 with the nozzle 8 corresponding thereto are formed. The cover plate 29 is a metal plate in which a large number of communication holes for communicating each pressure chamber 10 and the corresponding nozzle 8 are formed. The nozzle plate 30 is a metal plate on which many nozzles 8 are formed. These nine metal plates are stacked in alignment with each other so that the individual ink flow paths 32 are formed.

  Next, the configuration of the actuator unit 21 will be described with reference to FIG. FIG. 5A is a partial enlarged cross-sectional view of the actuator unit 21 and the pressure chamber 10, and FIG. 5B is a plan view showing the shape of individual electrodes formed on the surface of the actuator unit 21.

  As shown in FIG. 5A, the actuator unit 21 has a laminated structure in which four piezoelectric sheets 41, 42, 43, and 44 are laminated. These piezoelectric sheets 41 to 44 are formed to have the same thickness of about 15 μm. Each of the piezoelectric sheets 41 to 44 is a continuous layered flat plate (continuous flat plate layer) so as to be disposed across a plurality of pressure chambers 10 formed in one ink discharge region in the head main body 13a. Yes. The piezoelectric sheets 41 to 44 are made of a lead zirconate titanate (PZT) ceramic material having ferroelectricity.

  On the uppermost piezoelectric sheet 41, individual electrodes 35 facing each pressure chamber 10 are formed. Between the uppermost piezoelectric sheet 41 and the lower piezoelectric sheet 42, a common electrode 34 having a thickness of about 2 μm formed on the entire surface of the sheet is interposed. Note that no electrode is disposed between the piezoelectric sheet 42 and the piezoelectric sheet 43. Both the individual electrode 35 and the common electrode 34 are made of, for example, a metal material such as Ag—Pd.

  The individual electrode 35 has a thickness of about 1 μm and a substantially rhombic planar shape that is substantially similar to the pressure chamber 10 shown in FIG. 3 as shown in FIG. 5B. One of the acute angle portions of the approximately rhombic individual electrode 35 is extended, and a circular land portion 36 having a diameter of approximately 160 μm and electrically connected to the individual electrode 35 is provided at the tip thereof. The land portion 36 is made of, for example, gold containing glass frit, and is bonded on the surface of the extended portion of the individual electrode 35 as shown in FIG.

  The common electrode 34 is grounded. As a result, the common electrode 34 is kept at the same ground potential in the regions corresponding to all the pressure chambers 10. The individual electrode 35 is electrically connected to a driver IC (not shown) which is a part of the control device 100 for each individual electrode 35 so that the potential can be selectively controlled corresponding to each pressure chamber 10. It is connected to the. In this embodiment, although not shown, surface electrodes are formed at the four corners of the actuator unit 21, and the common electrode 34 is electrically connected to each surface electrode through a through hole formed through the piezoelectric sheet 41. ing. That is, the common electrode 34 is installed via the surface electrode.

  Next, a method for driving the actuator unit 21 will be described. The polarization direction of the piezoelectric sheet 41 in the actuator unit 21 is the thickness direction. In other words, the actuator unit 21 includes the upper piezoelectric element 41 (that is, away from the pressure chamber 10) as a layer in which the active portion exists and the lower piezoelectric element (that is, close to the pressure chamber 10). It has a so-called unimorph type configuration in which 42 to 44 are inactive portions. Accordingly, when the individual electrode 35 has a predetermined positive or negative potential with respect to the common electrode, for example, if the electric field and the polarization are in the same direction, the electric field application portion sandwiched between the electrodes in the piezoelectric sheet 41 acts as an active portion, Shrink in the direction perpendicular to the polarization direction due to the piezoelectric transverse effect. On the other hand, since the piezoelectric sheets 42 to 44 are not affected by the electric field, they do not spontaneously shrink. Therefore, a difference in distortion in a direction perpendicular to the polarization direction occurs between the upper piezoelectric sheet 41 and the lower piezoelectric sheets 42 to 44, and the entire piezoelectric sheets 41 to 44 are convex on the inactive side. (Unimorph deformation). At this time, as shown in FIG. 5A, the lower surfaces of the piezoelectric sheets 41 to 44 are fixed to the upper surface of the cavity plate 22 that defines the pressure chambers. Deforms so that it is convex to the side. Further, the volume of the pressure chamber 10 decreases, the ink pressure increases, and ink is ejected from the nozzle 8. Thereafter, when the individual electrode 35 is returned to the same potential as that of the common electrode 34, the piezoelectric sheets 41 to 44 return to the original shape and the volume of the pressure chamber 10 returns to the original volume, so that ink is sucked from the manifold channel 5 side. .

  In an actual driving procedure, the individual electrode 35 is set to a potential higher than the common electrode 34 (hereinafter referred to as a high potential) in advance, and the individual electrode 35 is temporarily set to the same potential as the common electrode 34 (hereinafter referred to as a low potential) every time there is a discharge request. After that, the potential is set to a high potential again at a predetermined timing. Thereby, at the timing when the individual electrode 35 becomes a low potential, the piezoelectric sheets 41 to 44 return to the original shape, and the volume of the pressure chamber 10 increases compared to the initial state (a state where the potentials of both electrodes are different). At this time, a negative pressure is applied to the pressure chamber 10 and ink is sucked into the pressure chamber 10 from the manifold channel 5 side. Thereafter, when the individual electrode 35 is again set to a high potential at a predetermined timing, the piezoelectric sheets 41 to 44 are deformed so as to protrude toward the pressure chamber 10, and the pressure in the pressure chamber 10 becomes positive due to the volume reduction of the pressure chamber 10. The pressure on the ink rises and ink drops are ejected. That is, in order to eject ink droplets, a pulse based on a high potential is supplied to the individual electrode 35. This pulse width is ideally AL (Acoustic Length), which is the length of time during which the pressure wave propagates one way from the manifold channel 5 to the nozzle 8 in the pressure chamber 10. In the present embodiment in which the pressure chamber 10 is disposed in the approximate center of the individual ink flow path 32, when the pressure chamber 10 is reversed from the negative pressure state to the positive pressure state, the pressures of the two are combined, and the ink is applied with a stronger pressure. Drops can be ejected.

  In gradation printing, gradation expression is performed by the number of ink droplets ejected from the nozzle 8, that is, the ink amount (volume) adjusted by the number of ink ejections. For this reason, the number of ink ejections corresponding to the designated gradation expression is continuously performed from the nozzle 8 corresponding to the designated dot area. In general, when ink is ejected continuously, it is preferable to set the interval between pulses supplied to eject ink droplets to AL. As a result, the period of the residual pressure wave of the pressure generated when ejecting the previously ejected ink droplets coincides with the period of the pressure wave of the pressure generated when ejecting the ink droplets ejected later, and these are superimposed. Thus, the pressure can be amplified to eject ink droplets.

  Next, with reference to FIG. 6, the structure of a vibrator for generating ultrasonic vibration and a vibration absorber for absorbing the generated ultrasonic vibration will be described. FIG. 6A is a bottom view showing a state in which the inkjet heads 2a to 2d are provided side by side. FIG. 6B is a side view of the nozzle plate 30 portion of the inkjet head 2a.

  The ink jet heads 2a to 2d are elongated rectangular shapes having a longitudinal direction perpendicular to the paper transport direction as shown in FIG. 6A, which is a view of the ink jet heads 2a to 2d as viewed from the ink ejection surface (bottom surface) side. The nozzle plate 30 attached to the nozzle plate is formed with a large number of minute diameter nozzles 8 for discharging ink downward. These nozzles 8 are arranged in a matrix like the pressure chambers 10.

  As shown in FIGS. 6A and 6B, for each of the inkjet heads 2a to 2d, an ultrasonic vibration is generated in the vicinity of one end of the ink discharge surface 30a of the nozzle plate 30 in the longitudinal direction. The vibrators 110a to 110d are provided with vibration absorbers 120a to 120d for absorbing ultrasonic vibrations near the other end. The vibrators 110a to 110d and the vibration absorbers 120a to 120d are a nozzle plate. 30 are arranged so as to face each other across the nozzles 8 formed in large numbers.

  FIG. 7A and FIG. 7B are equivalent circuit diagrams of the vibrator 110a, the vibration absorber 120a, and their surroundings installed on the nozzle plate 30 of the inkjet head 2a, respectively. 110b to 110d and 120b to 120d have the same structure.

  First, the structure of the vibrator 110a will be described with reference to FIG. Two electrodes 113a and 113b are provided near one end in the longitudinal direction of the ink ejection surface 30a of the nozzle plate 30, and three electrodes 111a to 111c and 112a to 112c are provided from each of them. Are branched, and each of the electrodes 113a and 113b forms a comb-like electrode. The electrodes 111a to 111c and the electrodes 112a to 112c are arranged so as to face each other in the longitudinal direction of the nozzle plate 30 without directly contacting each other. More specifically, they are arranged in the order of 111a, 112a, 111b, 112b, 111c, and 112c from the end.

  These adjacent electrodes are disposed on the piezoelectric body 114. Specifically, the electrodes 111a, 112a to 111c, 112c are arranged at regular intervals on the piezoelectric body 114 indicated by oblique lines in the drawing. If the electrode interval is d and the drive frequency is f, a surface wave with a velocity v = 2 df is generated. Piezoelectric ceramics are used as the material of the piezoelectric body. Here, portions of the piezoelectric body 114 sandwiched between the electrodes are referred to as piezoelectric body portions 114a to 114e. These correspond to the portions surrounded by the electrodes and broken lines in FIG.

  The AC power supplies 150 a and 150 b are located outside the head main body 13 a and inside the control device 100. Further, an AC voltage having the same period and a phase difference of 90 degrees is applied to the electrodes 113a and 113b from the AC power sources 150a and 150b through the lead wires. The AC power supplies 150a and 150b are grounded to obtain a stable potential reference (160a and 160b).

  Next, the structure of the vibration absorber 120a will be described with reference to FIG. Two electrodes 123a and 123b are provided in the vicinity of the other end of the ink ejection surface 30a of the nozzle plate 30 with respect to the vibrator 110a in the longitudinal direction, and three electrodes 121a to 121c and 122a to 122c are respectively provided from these electrodes. Each electrode is branched, and each of the electrodes 123a and 123b forms a comb-like electrode. The electrodes 121a to 121c and the electrodes 122a to 122c are arranged so as to face each other in the longitudinal direction of the nozzle plate 30 without being in direct contact with each other. More specifically, they are arranged in the order of 121a, 122a, 121b, 122b, 121c, 122c from the end.

  These adjacent electrodes are disposed on the piezoelectric body 124. Specifically, the electrodes 121a, 122a to 121c, 122c are arranged at regular intervals on the piezoelectric body 124 indicated by hatching in the drawing. Here, portions of the piezoelectric body 124 sandwiched between the electrodes are referred to as piezoelectric body portions 124a to 124e. These correspond to the portions surrounded by the electrodes and broken lines in FIG.

  The electrodes 123a and 123b are electrically connected via a resistor 125. The resistor 125 is located on the head main body 13a in this embodiment. However, it is not limited to this form, and may be located outside the head body 13a (this embodiment will be described later as a second embodiment). The surface wave (mechanical energy) propagating from the vibrator 110a is converted again into electric energy by the vibration absorber 120a and further consumed by the resistor 125.

  Next, the operation of the head main body 13a configured as described above will be described.

  When a voltage is applied to the electrodes 113a and 113b of the vibrator 110a by the AC power sources 150a and 150b in the control device 100, the inverse piezoelectric effect is applied to the piezoelectric portions 114a to 114e sandwiched between the electrodes 111a to 111c and 112a to 112c. Occurs. Specifically, the piezoelectric portion 114a to which an electric field is applied by the electrodes 111a and 112a, the piezoelectric portion 114b to which an electric field is applied by 112a and 111b, and the piezoelectric portion 114c to which an electric field is applied similarly. , 114d, 114e, distortion in the longitudinal direction of the nozzle plate 30 occurs, and vibrations correlated with the frequencies of the AC power supplies 150a and 150b are excited. In the present embodiment, ultrasonic vibrations are generated by the vibrator 110a by using 150a and 150b as high-frequency AC power supplies.

  In addition, since the vibrator 110a is disposed on the ink ejection surface 30a of the nozzle plate 30 that is an elastic member, the excited ultrasonic vibration is transmitted from the vibrator 110a on the ink ejection surface 30a.

  As described above, the distortion of the piezoelectric portions 114 a to 114 e occurs in the longitudinal direction of the nozzle plate 30. Therefore, the traveling direction of the traveling wave of the excited ultrasonic vibration is the direction of the other end with respect to the vibrator 110a side in the longitudinal direction of the nozzle plate 30 (the direction of arrow A in FIGS. 6A and 7A). Therefore, the traveling wave of the ultrasonic vibration is transmitted to the nozzles 8 formed in large numbers on the nozzle plate 30.

  The operation obtained from the above will be described below with reference to FIG. FIG. 8 is an enlarged cross-sectional view of a portion surrounded by an alternate long and short dash line in FIG. The ultrasonic vibrations that are excited and transmitted as traveling waves on the nozzle plate 30 reach the respective nozzles 8 as shown in FIG. 8 and apply a stirring force to the ink 130 in the direction of arrow C. Therefore, a slight vibration is generated in the ink meniscus in the vicinity of the nozzle 8 to suppress ink thickening. Further, since it has a foreign matter removing effect on the foreign matter adhering to the nozzle 8, it is possible to recover the nozzle 8 in a state where ink is not ejected. As a result, it is possible to improve the quality of the formed image and reduce the amount of waste ink during ink purging.

  Further, since the vibrator 110a is installed on the ejection surface 30a of the nozzle plate 30, the amplitude of the traveling wave transmitted on the nozzle plate 30a is increased, and a larger ink thickening suppressing effect and a foreign matter removing effect can be obtained. Furthermore, since the vibrator 110a generates ultrasonic vibrations, a larger ink thickening suppression effect and foreign matter removal effect can be obtained due to the large vibration frequency.

  On the other hand, with respect to the vibration absorber 120a, a positive piezoelectric effect is produced by applying strain deformation to the piezoelectric portions 124a to 124e sandwiched between the electrodes 121a to 121c and 122a to 122c. Specifically, the traveling wave of the ultrasonic vibration generated by the vibrator 110a as described above is transmitted on the nozzle plate 30 and reaches the vibration absorber 120a (FIGS. 6A and 7B). Arrow B), an electromotive force is generated by distortion deformation in the piezoelectric body portions 124a to 124e due to the transmitted ultrasonic vibration. The electromotive force is applied between the electrodes 121a and 122a for the piezoelectric portion 124a, between the electrodes 122a and 121b for the piezoelectric portion 124b, and similarly for each of the electrodes 121b, 121c, and 122b for the piezoelectric portions 124c to 124e. , 122c is transmitted as a potential difference. That is, the surface wave (mechanical energy) propagating from the vibrator 110a is converted into electric energy again by the vibration absorber 120a, and is consumed by the electric resistor 125 through the electrodes 123a and 123b. As a result, since the traveling wave generated by the vibrator 110a can be absorbed by the vibration absorber 120a, the generation of the reflected wave traveling on the ejection surface 30a in the direction opposite to the traveling wave can be prevented. If traveling waves and reflected waves overlap to generate a standing wave, the ink thickening suppressing effect and the foreign matter removing effect cannot be obtained at the node of the generated standing wave, but due to the action of the vibration absorber 120a as described above, An ink thickening suppressing effect and a foreign matter removing effect can be obtained at all the ejection openings.

  The vibrator 110a and the vibration absorber 120a include a piezoelectric body and six electrodes that sandwich the piezoelectric body portion therebetween. The piezoelectric ceramic used as the material of the piezoelectric body has high electromechanical conversion efficiency and can make a relatively free shape, so that the structure of the vibrator 110a and the vibration absorber 120a can be simplified. It is. Further, since the six electrodes face each other in the longitudinal direction of the nozzle plate 30, the traveling wave generated by the vibrator 110a reliably vibrates in the vicinity of many nozzles 8 on the ink discharge surface 30a. It can be advanced in the direction.

  Further, with respect to each of the vibrator 110a and the vibration absorber 120a, a plurality (five) of piezoelectric body portions are disposed between adjacent electrodes of a pair of comb-like electrodes disposed to face each other. The amplitude of the ultrasonic vibration generated in the vibrator 110a can be made larger than in the case where there is only one piezoelectric body portion, and a larger ink thickening suppressing effect and foreign matter removing effect can be obtained. In addition, the traveling wave of the generated ultrasonic vibration can be efficiently absorbed by the vibration absorber 120a.

  Further, since the electrodes of the vibration absorber 120a and the resistor 125 placed on the ejection surface 30a of the nozzle plate 30 are electrically connected, the power generated in the piezoelectric portions 124a to 124e is consumed. Can do.

  In the present embodiment, ultrasonic vibrations are generated by the vibrator 110a by using 150a and 150b as high-frequency AC power supplies. Here, since the vibrator 110a is disposed on the ink ejection surface 30a of the nozzle plate 30 which is an elastic member, the excited ultrasonic vibration is transmitted from the vibrator 110a on the ink ejection surface 30a.

  Further, as described above, distortion deformation of the piezoelectric portions 114 a to 114 e occurs in the longitudinal direction of the nozzle plate 30. Therefore, the traveling direction of the traveling wave of the excited ultrasonic vibration is the direction of the other end facing the one end on the vibrator 110a side in the longitudinal direction of the nozzle plate 30 (the direction of arrow A in FIGS. 6A and 7A). Therefore, the traveling wave of ultrasonic vibration is transmitted to the nozzles 8 formed on the nozzle plate 30 in large numbers.

  In the resistor 125, electric power generated by the positive piezoelectric effect of the vibration absorber 120a is consumed and heat is generated. Therefore, the printer 1 has a cooling mechanism such as a cooling fan and a heat release mechanism such as an exhaust port around the resistor 125 in order to eliminate the adverse effect on the head main body 13a and other devices due to the generated heat. desirable.

  Furthermore, the control device 100 of the printer 1 includes AC power supplies 150a and 150b inside, and generates a command for generating a traveling wave for the vibrator 110a. With such a configuration, the timing at which the vibrator 110a generates a traveling wave can be adjusted.

  The control device 100 does not operate during the printing of the vibrator 110a, for example, the AC power supplies 150a and 150b are operated only when a printing operation such as a printing paper replenishing operation is not performed. Give an order. A time chart showing this operation is shown in FIG. 9A shows the printing timing of the printer 1, and FIG. 9B shows the vibration timing of the vibrator 110a instructed to intermittently vibrate by the control device 100 as described above. The horizontal axis in FIG. 9 represents the time common to FIG. 9, and S is the time required for the printer 1 to perform a printing operation on one sheet of printing paper. As can be seen from FIGS. 9A and 9B, the vibrator 100 does not operate while the printer 1 is printing, and operates when it is not printing. With such a configuration, the vibrator 110a does not generate vibration during printing, so that the adverse effect of vibration on the printing can be reduced.

  The control device 100 is not limited to the above-described configuration in which a traveling wave generation command is intermittently generated for the vibrator 110a. By changing the setting of the control device 100, the vibrator 110a is changed. It is also possible to generate a traveling wave generation command continuously. A time chart for such a configuration is shown in FIG. With such a configuration, the vibrator 110a generates a traveling wave even during printing, so that an ink thickening suppressing effect and a foreign matter removing effect can be obtained even during printing.

  Next, based on FIG. 10, an ink jet printer according to a second embodiment of the present invention will be described. FIG. 10 shows an equivalent circuit diagram of the vibration absorber in the ink jet head main body 313a according to the present embodiment, in which a resistor connected to the vibration absorber is arranged outside the ink jet head main body. In the present embodiment, the same parts (200, 220a, 221a to 221c, 222a to 222c, 223a, 223b, 224, 224a to 224e, 230, 230a, 313a) as the constituent members of the first embodiment described above. 325), the reference numerals (100, 120a, 121a to 121c, 122a to 122c, 123a, 123b, 124, 124a to 124e, 30, 30a, 13a, and 125) of the first embodiment are sequentially matched. The description of the similar part may be omitted.

  In the inkjet head main body 313a according to the second embodiment, the resistor 325 electrically connected to the vibration absorber 220a is provided inside the control device 200, which is outside the head main body 313a. In this way, each electrode of the vibration absorber 220a and the resistor 325 installed inside the control device 200 are electrically connected, thereby consuming electric power generated in the piezoelectric portions 224a to 224e. Can do. Further, unlike the first embodiment, the resistor 325 is installed outside the head main body 313a, so that the structure of the head main body 313a can be simplified and an excessive temperature rise of the head main body is caused. It is possible to suppress the change in ink ejection characteristics.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various design changes can be made as long as they are described in the claims.

  For example, in the above-described embodiment, the application to the line head type ink jet printer of the present invention has been described, but the present invention can be similarly applied to a serial head type printer.

  Further, in the above-described embodiment, for the vibrator and the vibration absorber, a total of six piezoelectric parts and two electrodes are arranged so as to face each other and three branches from each electrode so as to sandwich the piezoelectric substance. However, the structure of the piezoelectric portion and the electrode sandwiching the piezoelectric portion is not limited to this, and the number of piezoelectric portions may be any number, and according to the present invention, An appropriate number of electrodes may be arranged within the range in which the above effect can be obtained.

  Furthermore, the above-described vibrator 110a may be provided with a reflector on the opposite side of the vibrator 110a from the vibration absorber 120a. Thereby, the propagation direction of the surface wave generated by the vibrator 110a can be restricted to the vibration absorber 120a side. The reflector is configured by a reflective electrode formed on the same piezoelectric body as that of the vibrator 110a. The reflective electrode includes an electrode group arranged in parallel with the electrodes 111a and 112a for the vibrator 110a and a short-circuit electrode for connecting all the electrodes.

  In the above embodiment, the vibrator and the vibration absorber are installed on the ink discharge surface of the nozzle plate (the lower surface of the flow path unit). However, the present invention is not limited to this, and the range of the configuration that can obtain the effects of the present invention. For example, it may be installed inside or on the upper surface of the flow path unit.

  Further, the timing of intermittent vibration shown in FIG. 10B is not limited to such timing, and may be less frequent. For example, it may vibrate only before printing or only at the time of purging.

  Further, only one of the AC power supplies 150a and 150b may be installed.

  In the above embodiment, one vibrator and one vibration absorber are arranged in the vicinity of both ends in the longitudinal direction for each head. However, the present invention is not limited to this, and there may be two or more each. The arrangement is not limited to the vicinity of both ends in the longitudinal direction as long as the nozzles face each other across the nozzle.

1 is a schematic configuration diagram of a printer according to a first embodiment of the present invention. The top view of the main body of the head shown in FIG. The enlarged view of the area | region enclosed with the dashed-dotted line drawn in FIG. Sectional drawing along the IV-IV line of FIG. (A) is a partial expanded sectional view of the actuator unit 21 and the pressure chamber 10. FIG. 4B is a plan view showing the shape of individual electrodes formed on the surface of the actuator unit 21. (A) is a bottom view of the head shown in FIG. (B) is a side view of the nozzle plate portion of the head shown in FIG. FIG. 2 is an equivalent circuit diagram of the vibrator according to the first embodiment of the present invention and its periphery. The vibration absorber which concerns on 1st embodiment of this invention, and its equivalent circuit schematic. The enlarged view of the area | region enclosed with the dashed-dotted line drawn in FIG. 4 showing the stirring state of the ink in the nozzle part by this invention. (A) is a time chart showing the printing timing of the printer. (B) is a time chart showing the vibration timing of the vibrator that vibrates intermittently. (C) is a time chart showing the vibration timing of a vibrator that vibrates continuously. The vibration absorber which concerns on 2nd embodiment of this invention, and its equivalent circuit schematic.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Printer 4 Flow path unit 5 Manifold flow path 5a Sub manifold flow path 8 Nozzle 10 Pressure chamber 13, 313a Head main body 21 Actuator unit 30, 230 Nozzle plate 30a, 230a Ink discharge surface 100, 200 Control device 110a Vibrator 120a, 220a Vibration absorbers 111a to 111c, 112a to 112c, 121a to 121c, 122a to 122c, 221a to 221c, 222a to 222c, 113a, 113b, 123a, 123b, 223a, 223b Electrodes 114, 124, 224 Piezoelectric bodies 114a to 114e, 124a to 124e, 224a to 224e Piezoelectric portion 125, 325 Resistors 150a, 150b AC power supply

Claims (11)

A flow path unit having a plurality of discharge openings formed on the ink discharge surface, and a plurality of individual ink flow paths formed in communication with the discharge openings, respectively.
A vibrator that is disposed in the flow path unit and generates a traveling wave that travels along the ink discharge surface using the flow path unit as a medium;
A vibration absorber that is disposed in the flow path unit and absorbs the traveling wave formed on the opposite side of the vibrator with respect to the traveling direction of the traveling wave across the plurality of discharge ports. An inkjet head characterized by that. The flow path unit is a laminate of a plurality of plates including a nozzle plate having the ink ejection surface,
The inkjet head according to claim 1, wherein the vibrator and the vibration absorber are disposed on the ink ejection surface.   The inkjet head according to claim 1, wherein the vibrator and the vibration absorber include a piezoelectric body and a pair of electrodes that sandwich the piezoelectric body.   The vibrator and the vibration absorber include three or more electrodes and two or more piezoelectric bodies arranged between the adjacent electrodes, and every other electrode is electrically connected to each other. The inkjet head according to claim 1, wherein the inkjet head is provided.   The inkjet head according to claim 3 or 4, wherein the plurality of electrodes are opposed to each other in a direction connecting the vibrator and the vibration absorber.   The inkjet head according to claim 3, further comprising a resistor connected to the plurality of electrodes of the vibration absorber.   The inkjet head according to claim 1, wherein the vibrator generates ultrasonic vibration. The inkjet head according to any one of claims 1 to 7,
An ink jet recording apparatus comprising: vibration control means for generating a command for causing the vibrator to generate a traveling wave.   The ink jet recording apparatus according to claim 8, wherein the vibration control unit intermittently generates the command.   The inkjet head recording apparatus according to claim 8, wherein the vibration control unit continuously generates the command. The inkjet head according to any one of claims 3 to 5,
An ink jet recording apparatus comprising: a resistance connected to the plurality of electrodes of the vibration absorber.

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