JP2009226694A - Liquid discharge apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently discharge, during flushing, a degraded liquid that flows back into a descender hole either during wiping or prior to wiping after purging. <P>SOLUTION: The lower end opening 155 of the descender hole 152 has a larger opening size than an inlet 153 of a nozzle hole 151. Eight grooves 161 that are elongate in the thickness direction of a descender plate 129 are formed on the interior wall surface 157 of the descender hole 152. Thus, the area of contact between the metallic descender plate 129 of high heat conductivity and ink is greater than the case if the eight grooves 161 are not formed on the descender hole 152. The ink in the descender 152, the viscosity of which ink decreases as it is heated by a heater during wiping after purging, is efficiently discharged during flushing. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a liquid ejection apparatus including a liquid ejection head having a nozzle plate in which nozzle holes are formed and a descender plate in which descender holes communicating with the nozzle holes are formed.

  Patent Document 1 describes a printer including an inkjet head having a flow path unit formed by laminating a plurality of plates. The outermost layer of the plurality of plates constituting the flow path unit is a nozzle plate in which nozzle holes having ejection ports for ejecting ink are formed. Adjacent to the nozzle plate is a manifold plate in which through holes serving as descender holes communicating with the nozzle plate are formed.

Japanese Unexamined Patent Publication No. 2008-18862 (FIGS. 4 and 5)

  In the inkjet head described in Patent Document 1, from the viewpoint of stabilizing the discharge performance, the diameter of the opening (lower end opening) facing the nozzle plate of the through hole formed in the manifold plate is the opening facing the manifold plate of the nozzle hole. It is larger than the diameter of (upper end opening). Furthermore, the through-hole formed in the manifold plate has a cylindrical shape. Therefore, ink tends to stay in a region near the lower end of the through hole and close to the wall surface that defines the through hole.

  On the other hand, in a liquid discharge apparatus such as an ink jet printer, an operation called wiping is performed in which a discharge surface on which discharge ports are formed is wiped with a wiper. The wiping is mainly performed following an operation called “purging” in which the ink in the head is forcibly discharged by using a pressure application device such as a pump arranged outside the head. During this wiping or before wiping after purging, the ink adhering to the ejection surface (for example, discharged from the ejection port during purging) may flow back into the nozzle hole. The ink adhering to the ejection surface may be deteriorated due to contamination with foreign matters such as paper dust or color mixing (mixing of two or more different types of ink). In order to prevent the quality from being deteriorated, it is necessary to perform an ink ejection operation in a nozzle hole, which is called flushing, using an actuator of the head after wiping.

  However, when the ink flowing back into the nozzle hole reaches the through hole formed in the manifold plate, it is necessary to perform flushing for a long time in order to discharge the ink in the through hole from the discharge port. In the ink jet head of Patent Document 1, ink tends to stay in a region near the lower end of the through hole and near the corner connecting the wall surface defining the through hole and the upper surface of the nozzle plate. Because it is scarce. When the flushing is performed for a long time as described above, a large amount of wasted ink that is not used for printing is consumed. As a countermeasure, it is conceivable to reduce the amount of ink staying at the lower end of the through hole by making the diameter of the lower end opening of the through hole as close as possible to the diameter of the upper end opening of the nozzle hole. If the displacement between the two plates during manufacturing is large, the lower end of the wall surface of the through hole may be closer to the central axis of the nozzle hole than the upper end of the wall surface of the nozzle hole, and the discharge performance may become unstable. is there. Therefore, there must be a certain difference between these two opening diameters, and as a result, long-time flushing is unavoidable.

  An object of the present invention is to provide a liquid ejecting apparatus that can efficiently discharge a deteriorated liquid that has flowed back into a descender hole during wiping or before wiping after purging.

  The liquid discharge apparatus of the present invention is a flow in which a nozzle plate having a discharge surface in which a discharge port which is one of the nozzle holes is formed and a descender plate in which a descender hole communicating with the nozzle hole is formed are stacked. A wiper movement including a liquid discharge head including a path unit and an actuator for applying discharge energy to the liquid in the flow path unit, and a wiper for wiping the discharge surface, and relatively moving the wiper along the discharge surface A mechanism, a heating means for heating the flow path unit, and heating of the flow path unit by the heating means after wiping of the discharge surface by the wiper, after which the actuator moves the liquid in the flow path unit Controlling the wiper moving mechanism, the heating means, and the actuator so as to apply discharge energy to And a control unit. The diameter of the opening of the descender hole facing the nozzle plate is larger than the diameter of the other opening of the nozzle hole, the nozzle plate and the descender plate are made of metal, and the inner wall surface of the descender hole has Unevenness is formed.

  According to the present invention, since the irregularities are formed on the inner wall surface of the descender hole, the contact area between the metal having a high thermal conductivity and the liquid is increased. Therefore, the temperature of the liquid in the descender hole increases and the viscosity decreases, and the deteriorated liquid in the descender hole can be efficiently discharged during flushing.

  It is preferable that a plurality of grooves extending in the thickness direction of the descender plate are formed on the inner wall surface of the descender hole. As a result, the deteriorated liquid can be discharged more efficiently.

  It is preferable that the inner wall surface of the descender hole has a taper shape with a larger amount of inward protrusion as it approaches the nozzle plate between the adjacent grooves. As a result, the deteriorated liquid can be discharged more efficiently.

  It is preferable that the inner wall surface of the descender hole has a tapered shape in which the amount of protrusion toward the inside increases as the nozzle plate approaches the nozzle plate. As a result, the deteriorated liquid can be discharged more efficiently.

  It is preferable that the heating unit is fixed to the wiper moving mechanism so as to relatively move along the discharge surface together with the wiper. Thereby, the mechanism required for heating can be simplified.

  The liquid discharge apparatus of the present invention preferably further comprises a purge means for forcibly discharging the liquid in the flow path unit. At this time, the control means forcibly discharges the liquid in the flow path unit by the purge means, and then the heating means heats the flow path unit after the wiper wipes the discharge surface, Thereafter, the wiper moving mechanism, the heating unit, the actuator, and the purge unit are controlled so that the actuator applies discharge energy to the liquid in the flow path unit. This makes it possible to discharge the deteriorated liquid during wiping after purging.

  According to the present invention, since the irregularities are formed on the inner wall surface of the descender hole, the contact area between the metal having a high thermal conductivity and the liquid is increased. Therefore, the temperature of the liquid in the descender hole increases and the viscosity decreases, and the deteriorated liquid in the descender hole can be efficiently discharged during flushing.

  A preferred embodiment of the present invention will be described below with reference to the drawings.

<Schematic configuration of inkjet printer>
FIG. 1 shows an inkjet printer 1 which is a liquid ejection apparatus according to an embodiment of the present invention. An ink jet printer 1 shown in FIG. 1 is a color ink jet printer having four ink jet heads 2 that respectively eject magenta, cyan, yellow, and black inks. The ink jet printer 1 is provided with a paper feed mechanism 11 on the left side in FIG. 1 and a paper discharge tray 12 on the right side in FIG.

  Inside the inkjet printer 1, a paper transport path is formed through which a paper as a recording medium is transported from the paper feed mechanism 11 toward the paper discharge tray 12. The paper feed mechanism 11 is provided with a pickup roller 22. When the pickup roller 22 is rotated by driving a motor 42 (see FIG. 9), the uppermost sheet in the sheet tray 21 is fed out and sent from the left to the right in FIG. A paper transport mechanism is disposed at an intermediate portion of the paper transport path. The paper transport mechanism includes two belt rollers 6 and 7 and an endless transport belt 8 wound around the rollers 6 and 7. The belt roller 6 on the right side in FIG. 1 is a driving roller that receives a driving force from a transport motor 41 (see FIG. 9) and rotates clockwise in FIG.

  A pressing roller 5 that presses the paper against the outer peripheral surface 8a of the adhesive conveying belt 8 is disposed immediately downstream of the paper feeding mechanism 11 and at a position facing the belt roller 7 with the conveying belt 8 interposed therebetween. . The sheet pressed against the outer peripheral surface 8a is transported along the transport direction B while being held by the outer peripheral surface 8a. A substantially rectangular parallelepiped platen 9 is disposed in a region surrounded by the conveyor belt 8. A weakly adhesive silicon resin layer is formed on the outer peripheral surface 8 a of the conveyor belt 8.

  A peeling plate 13 is provided immediately downstream of the conveying belt 8 along the sheet conveying path. The peeling plate 13 is configured to peel the paper held on the outer peripheral surface 8 a of the transport belt 8 from the outer peripheral surface 8 a and send it to the right paper discharge tray 12.

  A pump 17 is connected to each ink supply pipe 16 of the four inkjet heads 2. The ink supply pipe 16 is connected to an ink tank (not shown) further upstream of the pump 17. These pumps 17 are used to initially introduce ink into the head 2 and to forcibly discharge ink in the head by performing a purge operation.

  The operation of each unit of the inkjet printer 1 is controlled by the control unit 18. Details of the control unit 18 will be described later.

  FIG. 2 is a partial plan view of the ink jet printer 1. 3 is a cross-sectional view taken along line III-III depicted in FIG. As shown in FIG. 2, each of the four inkjet heads 2 extends in the main scanning direction (the direction perpendicular to the sub-scanning direction and perpendicular to the paper surface of FIG. 1), and the sub-scanning direction (conveyance) (Direction along direction B). That is, the ink jet printer 1 is a line printer. As shown in FIGS. 1 and 3, the inkjet head 2 has a head body 3 at the lower end thereof. In the head main body 3, four actuator units 121 (see FIG. 4) for applying pressure to ink in the pressure chamber are bonded to a flow path unit 109 (see FIG. 4) in which a plurality of individual ink flow paths including pressure chambers are formed. It has an elongated rectangular parallelepiped shape in the main scanning direction. On the bottom surface of the head body 3, that is, the discharge surface 3a, a large number of small-diameter discharge ports 108 (see FIG. 6) that are one end of the nozzles are formed.

  As shown in FIGS. 1 and 3, a reservoir unit 10 that temporarily stores ink is fixed to the upper surface of the head body 3. The reservoir unit 10 is longer than the head body 3 and protrudes from both longitudinal sides of the head body 3. In the protruding portion, the reservoir unit 10 is fixed to the frame 4 having a rectangular opening so that the discharge surface 3a is exposed downward from the opening. More specifically, a pair of flanges 4a that support the reservoir unit 10 from the lower side protrude from the opposite sides of the frame 4 toward the inside of the opening. The flange 4 a and both ends of the reservoir unit 10 in the longitudinal direction are fixed with screws 50. The discharge surface 3 a is almost the same height as the bottom surface of the frame 4.

  The head body 3 is parallel to the ejection surface 3a and the portion of the conveyor belt 8 supported by the platen 9 so as to face each other, and a slight gap is formed between the ejection surface 3a and the conveyor belt 8. Is arranged. The gap constitutes a part of the paper transport path. When the paper that is conveyed while being held on the outer peripheral surface 8a of the conveyance belt 8 sequentially passes immediately below the four head bodies 3, ink of each color is ejected toward the upper surface of the paper, that is, the printing surface. Thus, a desired color image is formed on the paper.

<Elevating mechanism>
As shown in FIGS. 2 and 3, the frame 4 is supported by a pair of lifting mechanisms 51 provided in the printer 1 so as to be movable in the vertical direction. The pair of lifting mechanisms 51 are arranged so as to sandwich the four inkjet heads 2 in the sub-scanning direction. Each lifting mechanism 51 includes a motor 52 as a drive source for moving the frame 4 in the vertical direction, a pinion gear 53 fixed to the shaft of the motor 52, a rack gear 54 that meshes with the pinion gear 53, and a rack gear between the pinion gears 53. 54 and a guide 56 arranged at a position sandwiching 54. As will be described later, the elevating mechanism 51 is driven based on the control of the control unit 18.

  Motors 52 included in the elevating mechanism 51 are respectively fixed to a pair of main body frames 1 a of the inkjet printer 1. The pair of body frames 1a are arranged to face each other in the sub-scanning direction. The rack gear 54 extends in the vertical direction, and the lower end thereof is fixed to the side surface of the frame 4. The side surface of the rack gear 54 opposite to the pinion gear 53 is slidably in contact with the guide 56. The guide 56 is fixed to the main body frame 1a.

  When the two motors 52 are synchronized and the pinion gear 53 is rotated in the forward / reverse direction, the rack gear 54 moves upward or downward. As the rack gear 54 moves, the frame 4 moves up and down with the four inkjet heads 2 in the vertical direction.

  A pair of guide units 59 are disposed on both sides of the frame 4 along the sub-scanning direction. Each guide unit 59 includes a bar 58 and a pair of guides 57 sandwiching the bar 58. As shown in FIG. 3, the pair of guides 57 extend in the vertical direction and are respectively fixed to the pair of main body frames 1 b of the inkjet printer 1. The pair of main body frames 1b are arranged to face each other in the main scanning direction. The bar 58 extends in the vertical direction similarly to the guide 57 and is fixed to the side surface of the side of the frame 4 facing the main body frame 1b. The bar 58 is slidably in contact with each of the pair of guides 57.

  The guide unit 59 prevents the ejection surface 3a of the inkjet head 2 from being inclined with respect to the portion of the conveyor belt 8 supported by the platen 9 when the frame 4 is vertically moved by the lifting mechanism 51. That is, even when the frame 4 and the inkjet head 2 are moved up and down in the vertical direction by the lifting mechanism 51, the discharge surface 3 a is always parallel to the upper surface of the platen 9. As a result, the accuracy of ink landing on the paper is improved during printing.

  Normally, the frame 4 is moved in the direction of arrow C in FIG. 3 by the elevating mechanism 51, and the printing positions (positions shown in FIG. 3) where the four inkjet heads 2 eject ink onto the paper for printing on the paper. ). The frame is used only during maintenance of the inkjet head 2 (when purging forcibly ejecting ink from the inkjet head 2, wiping off ink adhering to the ejection surface 3a, and covering the ejection surface 3a with a cap). 4 is moved in the direction of arrow C in FIG. 3 by the elevating mechanism 51, and the four inkjet heads 2 are arranged at the upper retracted position above the printing position.

<Configuration of maintenance unit>
A maintenance unit 70 for performing maintenance on the inkjet head 2 will be described. As shown in these drawings, the maintenance unit 70 is disposed on the left side of the inkjet head 2. The maintenance unit 70 has two trays 71 and 75 that can move horizontally. Among these, the tray 71 has a substantially square box shape opened upward, and includes the tray 75. The tray 71 and the tray 75 are engaged with a later-described concave portion 74b and a convex portion 83a, and when the engagement is released, the two are connected and the two are released. Can be switched.

  When the maintenance unit 70 moves horizontally to the right, the frame 4 has moved to the upper retracted position in advance, and a space for the maintenance unit 70 is secured between the four ejection surfaces 3a and the conveyor belt 8. Yes. In this state, the maintenance unit 70 moves horizontally in the direction of arrow D in FIG. When the side surface farther from the inkjet head 2 is opened and the engagement between the concave portion 74b and the convex portion 83a is released (for example, during the purge operation), the tray 71 leaves the tray 75 to be included, Only 71 moves horizontally to the right.

  A waste ink receiving tray 77 is disposed immediately below the maintenance unit 70. The waste ink receiving tray 77 has a size including the tray 71 in a plan view, and even when the tray 71 moves to the right end in FIG. 2, the edge of the tray 71 opposite to the inkjet head 2 overlaps. have. An ink discharge hole 77 a is formed at the end of the waste ink receiving tray 77 that is closer to the inkjet head 2. The ink discharge hole 77a distributes the ink that has flowed onto the waste ink receiving tray 77 to a waste ink reservoir (not shown).

  In the tray 75, four caps 76 having a rectangular planar shape are provided side by side corresponding to each inkjet head 2. Each cap 76 has a longitudinal direction parallel to the longitudinal direction of the inkjet head 2 and is arranged at the same pitch as the inkjet head 2 in the sub-scanning direction.

  The cap 76 includes a plate-like member 76b having a rectangular planar shape that is substantially the same size as the ejection surface 3a, and an annular protrusion 76a that protrudes upward from the peripheral edge of the plate-like member 76b. The annular protrusion 76a is made of an elastic material such as rubber, and has a size and a shape facing the peripheral edge of the discharge surface 3a. The cap 76 forms a sealed space when the annular protrusion 76a and the peripheral edge of the discharge surface 3a come into contact with each other. Thus, the cap 76 can cover the ejection surface 3a. Each cap 76 is biased upward while being supported on the bottom surface of the tray 75 by two springs (not shown).

  A holding plate 74 having a U-shaped planar shape is disposed in the tray 71 at a position closer to the inkjet head 2 than the tray 75. An elongated groove 74a is formed on the upper surface of the portion of the holding plate 74 that extends in the sub-scanning direction. An elongated rectangular parallelepiped base 78 is disposed in the groove 74a. A wiper blade 72 is fixed on the base 78. On the other hand, concave portions 74b are formed on the upper surfaces of the two portions extending in the main scanning direction of the holding plate 74, respectively.

  The wiper blade 72 is made of an elastic material such as rubber. The wiper blade 72 is formed slightly longer than the width of the entire four inkjet heads 2 arranged in parallel, and is fixed to the base 78 so that the longitudinal direction thereof is along the sub-scanning direction.

  A long and elongated heater 43 having the same length as that of the wiper blade 72 is disposed in the groove 74a and to the left of the base 78 in FIG. The heater 43 is energized in response to an energization command from the control unit 18 to heat the flow path unit 109 of the head body 3 so as to face the ejection surface 3a during wiping.

  Arms 83 are provided in the vicinity of the left and right sides of the tray 75, respectively. The arm 83 extends in the main scanning direction and is rotatable at the center thereof. A convex portion 83 a that protrudes downward is formed at the end of the arm 83 that is closer to the inkjet head 2. Arms 84 are respectively disposed at positions corresponding to the two arms 83 above the maintenance unit 70. The arm 84 is rotatably supported and is driven by a motor 44 (see FIG. 9). When the arm 84 rotates counterclockwise in FIG. 3 and moves away from the other end 83b of the arm 83, the convex portion 83a engages with the concave portion 74b due to the weight of the arm 83. On the other hand, when the arm 84 rotates clockwise, one end of the arm 84 comes into contact with the end portion 83b. When these arms 84 are further rotated clockwise, the arm 83 is rotated counterclockwise, and the engagement between the convex portion 83a and the concave portion 74b is released. In this way, the tray 71 and the tray 75 are in a state where the tray 71 and the tray 75 are connected and the connection between the two is released depending on whether or not the concave portion 74b and the convex portion 83a are engaged. The state can be switched.

  When the maintenance of the inkjet head 2 is not performed, the maintenance unit 70 is stationary at a “side retracted position” that does not face the inkjet head 2 as shown in FIGS. 2 and 3. When maintenance is performed, the maintenance unit 70 moves horizontally from the side retracted position to the right toward the “maintenance position” facing the ejection surface 3 a of the inkjet head 2. At this time, since the frame 4 is disposed at the upper retracted position, the tips of the wiper blade 72 and the cap 76 do not contact the discharge surface 3a.

  Note that during the purge operation during the maintenance, only the tray 71 is left, and the tray 71 is moved from the side evacuation position to the maintenance position to receive the discharged ink. When covering the discharge surface 3a with the cap 76, the tray 71 and the tray 75 are connected by the engagement of the concave portion 74b and the convex portion 83a and moved from the side retreat position to the maintenance position, and the cap 76 and the discharge surface 3a face each other. To do.

  Each tray 71, 75 is slidably supported by a pair of guide shafts 96a, 96b extending in the main scanning direction. Two bearing members 97 a and 97 b are attached to the tray 71. The bearing members 97 a and 97 b protrude from the left and right side surfaces of the holding plate 74. Two bearing members 98 a and 98 b are attached to the tray 75. The bearing members 98 a and 98 b protrude from the left and right side surfaces of the tray 75. Further, both ends of the pair of guide shafts 96a and 96b are fixed to the main body frames 1b and 1d, and are disposed parallel to each other between the frames 1b and 1d.

  Here, a horizontal movement mechanism 91 that moves the trays 71 and 75 in the horizontal direction (arrow D direction) along the guide shafts 96a and 96b will be described. As shown in FIG. 2, the horizontal movement mechanism 91 includes a motor 92, a motor pulley 93, an idle pulley 94, a timing belt 95, guide shafts 96a and 96b, and the like.

  The motor 92 is fixed to the surface 1c formed at the end of the main body frame 1b extending in parallel with the sub-scanning direction. The motor pulley 93 is connected to the motor 92 and rotates as the motor 92 is driven. The idle pulley 94 is rotatably supported by the leftmost main body frame 1d in FIG. The timing belt 95 is disposed in parallel with the guide shaft 96 a and is wound so as to be bridged between the motor pulley 93 and the idle pulley 94. The timing belt 95 is fixed to a bearing member 97a protruding from the holding plate 74.

  When the motor 92 is driven, the timing belt 95 travels as the motor pulley 93 rotates in the forward or reverse direction. As the timing belt 95 travels, the tray 71 connected to the timing belt 95 via the bearing 97a moves along the horizontal direction. When the concave portion 74b and the convex portion 83a of the holding plate 74 are engaged, the tray 71 and the tray 75 move together. On the other hand, when the convex portion 83a is not engaged with the concave portion 74b, only the tray 71 moves.

<Configuration of head body>
Next, the head body 3 will be described. As shown in FIG. 4, the head main body 3 includes a flow path unit 109 and four actuator units 121 fixed to the upper surface 109 a of the flow path unit 109.

  The flow path unit 109 has a rectangular parallelepiped shape. A total of ten ink supply ports 105 b are opened on the upper surface 109 a of the flow path unit 109. As shown in FIGS. 4 and 5, a manifold channel 105 communicating with the ink supply port 105 b and a sub-manifold channel 105 a that is a common ink chamber branched from the manifold channel 105 are formed in the channel unit 109. Has been. In FIG. 5, the pressure chamber 110, the aperture 112, and the discharge port 108 below the actuator unit 121 and to be drawn with broken lines are drawn with solid lines. As shown in FIGS. 5 and 6, a discharge surface 3 a in which a plurality of discharge ports 108 are two-dimensionally arranged in a matrix is formed on the lower surface of the flow path unit 109. The pressure chambers 110 are also two-dimensionally arranged in a matrix in the same manner as the discharge ports 108 on the fixed surface of the actuator unit 121 in the flow path unit 109.

  In the present embodiment, 16 rows of pressure chambers 110 along the longitudinal direction of the flow path unit 109 are arranged in parallel with each other in the width direction with respect to one actuator unit 121 at 16 rows. With respect to one actuator unit 121, the number of pressure chambers 110 included in each pressure chamber row is arranged so as to gradually decrease from the long side toward the short side corresponding to the outer shape of the trapezoidal actuator unit 121. Has been. The discharge ports 108 are also arranged in the same manner.

  As shown in FIG. 6, the flow path unit 109 includes a cavity plate 122, a base plate 123, an aperture plate 124, a supply plate 125, manifold plates 126, 127, and 128, a descender plate 129, and a nozzle plate 130 in order from the top. 9 metal plates, specifically, stainless steel plates. These plates 122 to 130 have a rectangular planar shape that is long in the main scanning direction. By laminating these plates 122 to 130 while aligning each other, the manifold unit 105, the sub-manifold channel 105a, and the outlet of the sub-manifold channel 105a are discharged into the channel unit 109 through the pressure chamber 110. A plurality of individual ink flow paths 132 reaching the outlet 108 are formed.

  The ink flow in the flow path unit 109 will be described. The ink supplied from the reservoir unit 10 into the flow path unit 109 via the ink supply port 105b flows from the manifold flow path 105 into the sub manifold flow path 105a. The ink in the sub-manifold channel 105a flows into each individual ink channel 132 and reaches the ejection port 108 via the aperture 112 and the pressure chamber 110 functioning as a throttle.

  Next, the actuator unit 121 will be described. As shown in FIG. 4, each of the four actuator units 121 has a trapezoidal planar shape, and is arranged in a staggered manner in the main scanning direction so as to avoid the ink supply ports 105b. Furthermore, the parallel opposing sides of each actuator unit 121 are along the longitudinal direction of the flow path unit 109, and the oblique sides of the adjacent actuator units 121 overlap each other in the main scanning direction of the flow path unit 109.

  As shown in FIG. 7A, the actuator unit 121 is composed of three piezoelectric layers 141 to 143 made of a lead zirconate titanate (PZT) ceramic material having ferroelectricity. An individual electrode 135 is formed at a position facing the pressure chamber 110 on the upper surface of the uppermost piezoelectric layer 141. A common electrode 134 is interposed between the uppermost piezoelectric layer 141 and the lower piezoelectric layer 142 over the entire surface of the sheet.

  As shown in FIG. 7B, the individual electrode 135 has a substantially rhombic planar shape similar to the pressure chamber 110. In plan view, most of the individual electrodes 135 are in the region of the pressure chamber 110. One of the acute corners of the substantially rhomboid individual electrode 135 extends outside the pressure chamber 110, and a circular individual land 136 that is electrically connected to the individual electrode 135 and thicker than the individual electrode 135 is provided at the tip thereof. ing.

  The common electrode 134 is connected to the ground so that the reference potential is equally applied in the region corresponding to all the pressure chambers 110. On the other hand, the plurality of individual electrodes 135 are individually electrically connected to the control unit 18 via wires connected to the individual lands 136. Therefore, the control unit 18 can activate only the drive signal supplied to one or more desired individual electrodes 135. That is, in the actuator unit 121, each of a plurality of portions overlapping with the plurality of individual electrodes 135 in a plan view functions as an individual actuator. That is, in the actuator unit 121, a plurality of actuators having the same number as the pressure chambers 110 are constructed.

  Here, a driving method of the actuator unit 121 will be described. The piezoelectric layer 141 is polarized in the thickness direction. On the other hand, the piezoelectric layers 142 and 143 are inactive layers that do not spontaneously deform. The piezoelectric layers 141 to 143 are fixed to the upper surface of the cavity plate 122 that partitions the pressure chamber 110. Therefore, when an electric field is applied in the polarization direction to the piezoelectric layer 141 by setting the individual electrode 135 to a potential different from that of the common electrode 134, the electric field application portion in the piezoelectric layer 141 functions as an active portion that is distorted by the piezoelectric effect. When the electric field and the direction of polarization are the same, the active portion expands in the thickness direction and contracts in the surface direction. Here, when there is a difference in the amount of strain in the plane direction between the electric field application portion of the piezoelectric layer 141 and the piezoelectric layers 142 and 143 below the portion, the entire piezoelectric layers 141 to 143 are convex toward the pressure chamber 110. The unimorph is deformed as follows. As a result, pressure, that is, ejection energy is applied to the ink in the pressure chamber 110, and a pressure wave is generated in the pressure chamber 110. Then, the generated pressure wave propagates from the pressure chamber 110 to the ejection port 108, whereby ink droplets are ejected from the ejection port 108.

  In the present embodiment, a predetermined positive potential is applied to the individual electrode 135 in advance, and a ground potential is once applied to the individual electrode 135 every time there is a discharge request, and then the predetermined positive potential is again applied at a predetermined timing. A pulse to be applied to the electrode 135 is output from the control unit 18. In this case, at the timing when the individual electrode 135 becomes the ground potential, the pressure of the ink in the pressure chamber 110 drops and the ink is sucked from the sub manifold channel 105 a into the individual ink channel 132. Thereafter, the ink pressure in the pressure chamber 110 rises at the timing when the individual electrode 135 is set to a predetermined potential again, and ink droplets are ejected from the ejection port 108. That is, a rectangular wave pulse is applied to the individual electrode 135. This pulse width is equal to AL (Acoustic Length), which is the length of time during which the pressure wave propagates from the outlet of the sub-manifold channel 105a to the tip of the discharge port 108 in the pressure chamber 110. By doing so, the pressure chamber of the positive pressure and the positive pressure newly applied from the actuator unit 121 and the positive pressure wave that has been reversed in phase by reflection at the boundary end of the individual ink channel 132 with the sub-manifold channel 105 a Since they are stacked in 110, a large pressure can be applied to the ink in the pressure chamber 110.

<Details of nozzle hole and descender hole>
FIG. 8A is an enlarged plan view of the vicinity of the ejection port 108 of the individual ink flow path 132. 8B is a cross-sectional view taken along line BB in FIG. 8A, and FIG. 8C is a cross-sectional view taken along line CC in FIG. 8A. As shown in these drawings, the nozzle holes 151 formed in the nozzle plate 130 are formed in a circular discharge port 108 formed in the discharge surface 3a of the nozzle plate 130 and a connection surface 130a which is the opposite surface of the discharge surface 3a. It is a through-hole formed between the formed circular inlet 153. The nozzle hole 151 includes a cylindrical portion 151a having the discharge port 108 at one end and continuing to the discharge surface 3a, and a truncated cone portion 151b having the inflow port 153 at one end and continuing to the connection surface 130a. The top of the truncated cone portion 151b has the same diameter as the cylindrical portion 151a. The nozzle hole 151 is formed by a pressing process divided into two times, a pressing process for providing the truncated cone part 151b and a pressing process for providing the cylindrical part 151a.

  On the descender plate 129 having a thickness of about 50 μm, a descender hole 152 having a diameter of about 180 μm, which is a through-hole penetrating in the thickness direction, is formed. The descender hole 152 is formed between a circular lower end opening 155 formed in the lower surface 129a of the descender plate 129 and a circular upper end opening 156 formed in the upper surface 129b opposite to the lower surface 129a. The opening diameter of the lower end opening 155 of the descender hole 152 is larger than the opening diameter of the inlet 153 of the nozzle hole 151. Therefore, the connecting surface 130a of the nozzle plate 130 is exposed in an annular shape from the descender hole 152. The nozzle hole 151 and the descender hole 152 share the central axis X.

  As illustrated in FIGS. 8A and 8B, the inner wall surface 157 of the descender hole 152 has a tapered shape in which the protruding amount toward the inner side, that is, the direction toward the central axis X increases as the nozzle plate 130 is approached. It has become. The inner wall surface 157 has eight grooves 161 that are elongated in the thickness direction of the descender plate 129. The eight grooves 161 are formed in the inner wall surface 157 at an equal angle of 45 ° with respect to the central axis X. As illustrated in FIG. 8C, the inner wall surface 157 has a tapered shape in which the protruding amount toward the inside increases as the nozzle plate 130 is approached in each groove 161. 8B and 8C, the upper end of the tapered surface of the inner wall surface 157 is at the upper end of the descender hole 152 outside the groove 161, and the center of the descender hole 152 in the thickness direction is within the groove 161. It is in. The distance from the central axis X of the lower end of the tapered surface of the inner wall surface 157 is not different between the inside and outside of the groove 161.

  As can be seen from the above description, in this embodiment, the eight elongated grooves 161 are formed in the thickness direction, so that irregularities are formed in the descender hole 152 along the circumferential direction. As a result, the contact area between the metallic descender plate 129 having high thermal conductivity and the ink is larger than that in the case where the eight grooves 161 are not formed in the descender hole 152. Further, since the inner wall surface 157 of the descender hole 152 has a tapered shape, the ink in the descender hole 152 can be easily discharged toward the nozzle hole 151. Furthermore, since the inner wall surface 157 has a tapered shape in the eight grooves 161, the ink in the descender hole 152 can be more easily discharged toward the nozzle hole 151.

<Control system>
Returning to FIG. 1, the controller 18 will be described. The controller 18 includes a plurality of hardware such as a CPU (Central Processing Unit), a RAM (Random Access Memory), and a ROM (Read Only Member). Various software for controlling the inkjet printer 1 is stored in the ROM. As the software and hardware in the control unit 18 cooperate, the control unit 18 includes a conveyance control unit 31, a discharge control unit 32, a heater control unit 33, maintenance, as shown in FIG. Functional units of the control unit 34 and the purge control unit 35 are constructed. In the present specification, the description will be made assuming that the control unit 18 includes driver circuits of various devices.

  The conveyance control unit 31 controls the motor 42 so that the pickup roller 22 is rotated by driving the motor 42 so that the uppermost sheet in the sheet tray 21 is sent out onto the conveyance belt 8. The motor 41 is controlled so that the belt roller 6 is rotated and the sheet is conveyed while being held on the outer peripheral surface 8 a of the conveying belt 8.

  The ejection control unit 32 is linked with the conveyance of the paper by the conveyance control unit 31 so that the four inkjet heads 2 are ejected from the four inkjet heads 2 based on the print data received from the external host computer. To control. Specifically, a pulse signal is supplied to the individual electrode 135 of the actuator unit. Further, the ejection control unit 32 controls the four inkjet heads 2 so that the flushing operation is performed. In this embodiment, the flushing operation means that ink droplets are ejected from all the ejection ports 108 almost simultaneously by giving ejection pulses to all the individual electrodes 135 of the actuator unit. The ink droplets ejected at the time of flushing land on the paper or a specific area of the belt. The amount of ink ejected during flushing is less than during the purge operation.

  The heater control unit 33 controls energization to the heater 43. This control is performed in conjunction with the purge operation and wiping operation control by the maintenance control unit 34.

  The maintenance control unit 34 controls the two motors 52 in the elevating mechanism 51, the motor 44 for driving the arm 84 related to the connecting operation of the tray 71 and the tray 75, and the motor 92 for horizontally moving the tray 71. Thus, the operations of the lifting mechanism 51 and the maintenance unit 70 are controlled.

  Specifically, the maintenance control unit 34 moves the tray 71 to the maintenance position after the purge so that the tray 71 moves horizontally from the side retracted position to the maintenance position at the time of initial ink introduction to the head 2 and at the time of purging. The motors 44 and 92 are controlled so as to move horizontally from the side to the side retracted position. In addition, the maintenance control unit 34 receives the print data from the host computer so that the trays 71 and 75 move horizontally from the side retracted position to the maintenance position during capping. The motors 44 and 92 of the maintenance unit 70 are controlled so as to move horizontally to the retreat position.

  Further, the maintenance control unit 34 raises and lowers the lifting mechanism 51 so that the frame 4 is positioned at the upper retracted position when the ink is initially introduced into the head 2 and when the head 2 is maintained, and so that the frame 4 is positioned at the printing position during printing. The two motors 52 are controlled.

  The purge controller 35 controls the four pumps 17 so that the ink in the ink tank is forcibly sent to the head main body 3 at the time of initial ink introduction into the head 2 and at the time of purging.

<Printer operation>
Next, the maintenance operation of the inkjet printer 1 according to the present embodiment will be described with reference to the flowchart shown in FIG. This flowchart shows an operation when an interrupt command for performing a maintenance operation is generated for the inkjet printer 1 in operation. The interrupt command is generated, for example, when a user's manual operation for purging is performed and when a predetermined number of prints are completed since the previous purge.

  First, in step S1, the frame 4 is moved to the upper retracted position based on the control of the maintenance control unit 34. Specifically, the two motors 52 are driven to rotate the pinion gears 53 in the forward direction (clockwise direction in FIG. 3). Then, the rack gear 54 moves upward as the pinion gear 53 rotates. The frame 4 fixed to the rack gear 54 moves upward together with the four inkjet heads 2. Then, when the frame 4 reaches the upper retracted position, the rotation of the drive motor 52 is stopped. Thus, a space in which the maintenance unit 70 can be disposed is formed between the ejection surface 3a and the conveyor belt 8. Thus, when the frame 4 is in the upward retracted position, even if the maintenance unit 70 moves to the maintenance position, the ejection surface 3a of the inkjet head 2 and the bottom surface of the frame 4 are in contact with the tips of the wiper blade 72 and the annular protrusion 76a. do not do.

  Thereafter, only the tray 71 is moved from the side retracted position to the maintenance position. Specifically, the motor 44 is driven to bring the arm 84 into contact with the end 83b of the arm 83 to separate the convex portion 83a from the concave portion 74b, and the engagement between the concave portion 74b and the convex portion 83a is released. That is, the connection between the tray 71 and the tray 75 is released. In this state, the timing belt 95 is caused to travel by driving the motor 92 of the horizontal movement mechanism 91 so as to move the tray 71 to the maintenance position. Then, when the tray 71 reaches the maintenance position, the driving of the motor 92 is stopped. The relationship between the head main body 3 and the tray 71 at this time is shown in FIG. FIG. 11A is a side view when the frame 4 is in the upward retracted position from the printing position and the tray 71 of the maintenance unit 70 is in the maintenance position.

  Thereafter, based on the control of the purge control unit 35, the pump 17 is used to forcibly send the ink in the ink tank to the head body 3 and perform the purge operation for forcibly discharging the ink in the head body 3. The ink discharged in the purge operation flows down from the waste ink receiving tray 77 to the waste ink reservoir. Some ink remains on the ejection surface 3a. The purge operation eliminates the clogging of the ink flow path and the increased viscosity of the ink in the ink flow path that have caused the ejection failure.

  In step S <b> 2, the heater control unit 33 starts energizing the heater 43.

  In step S <b> 3, the inkjet head 2 is moved slightly downward from the upper retracted position by the lifting mechanism 51 based on the control of the maintenance control unit 34. At this time, the height of the inkjet head 2 is set such that the upper end of the wiper blade 72 is higher than the lower surfaces of the ejection surface 3 a and the frame 4 when it is assumed that the wiper blade 72 is not elastically deformed. Actually, since the wiper blade 72 is elastically deformed, the vicinity of the upper end of the wiper blade 72 is deformed along the discharge surface 3a. Then, the tray 71 is moved to the left by the horizontal movement mechanism 91 (that is, the tray 71 is moved from the maintenance position to the side retreat position).

  By this wiping operation, the wiper blade 72 moves in the wiping direction from right to left in FIG. 11B, and the wiping operation of the discharge surface 3a by the wiper blade 72 is performed. At this time, the portion in contact with the discharge surface 3a near the upper end of the wiper blade 72 wipes the ink adhering to the discharge surface 3a by purging. By executing the series of maintenance operations described above, the ejection failure can be recovered to a normal state. However, the ink adhering to the ejection surface 3 a may flow back into the nozzle hole 151 and the descender hole 152 at the time of wiping or before wiping after purging.

  During the wiping operation, the heated heater 43 during energization passes in the vicinity of the discharge surface 3a, so that the flow path unit 109 of the head body 3, particularly the nozzle plate 130 and the descender plate 129 near the discharge surface 3a are effectively heated. Is done. As described above, in the present embodiment, since the eight grooves 161 form irregularities in the descender hole 152, the contact area between the metallic descender plate 129 having high thermal conductivity and the ink is increased. . For this reason, it is possible to significantly increase the temperature of ink that tends to stay in a region near the lower end of the descender hole 152 and close to the inner wall surface 157 of the descender hole 152, and the viscosity of the ink in this region can be significantly reduced. .

  In step S <b> 4, the heater control unit 33 ends energization of the heater 43.

  In step S <b> 5, a flushing operation is performed based on the control of the discharge controller 32. At the time of flushing, the deteriorated ink in the descender hole 152 having a lowered viscosity is efficiently discharged.

  Next, based on the control of the maintenance control unit 34, the lifting mechanism 51 returns the frame 4 to the printing position. Alternatively, the elevating mechanism 51 raises the inkjet head 2 to the upper retracted position, the trays 71 and 75 move to the maintenance position, and the cap 76 covers the ejection surface 3a. After the above operation is completed, the state before the maintenance operation starts is restored.

  According to the present embodiment described above, unevenness is formed on the inner wall surface 157 of the descender hole 152, so that the contact area between the metal having high thermal conductivity and the ink is increased. Therefore, when the flow path unit 109 is heated using the heater 43, the temperature of the ink in the descender hole 152 increases and the viscosity decreases, and the deteriorated ink in the descender hole 152 can be efficiently discharged during flushing. Become. In particular, since the unevenness is formed in the circumferential direction as in the present embodiment, more efficient ink discharge is possible.

  Further, since the eight grooves 161 are formed in the inner wall surface 157 of the descender hole 152, the deteriorated ink can be discharged more efficiently.

  Furthermore, since the inner wall surface 157 of the descender hole 152 has a tapered shape with a larger amount of inward protrusion as it approaches the nozzle plate 130 between the adjacent grooves 161, the ink that has deteriorated more efficiently is discharged. Is possible.

  In addition, since the inner wall surface 157 of the descender hole 152 has a tapered shape in which the protruding amount toward the inner side becomes larger toward the nozzle plate 130 in the groove 161, it is possible to discharge the deteriorated ink more efficiently. .

  Moreover, since the heater is fixed to the tray 71 of the maintenance unit 70 which is a wiper moving mechanism so as to move relative to the wiper blade 72 along the discharge surface 3a, the mechanism required for heating is simplified.

  Further, since the operations are performed in the order of purge, wiping, and flushing, the deteriorated ink ejected by the purge and attached to the ejection surface 3a can be heated simultaneously with wiping and discharged at the time of flushing. Therefore, a series of operations can be performed in a short time.

  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 to the above-described embodiments as long as they are described in the claims. It is possible to apply. For example, in the above-described embodiment, the heater 43 as the heating unit is fixed to the tray 71. However, the heater may be disposed in a place other than the tray 71 as long as the flow path unit 109 can be heated. Further, heating means other than the heater 43 (for example, a halogen lamp) may be used.

  Rather than simultaneously wiping the discharge surface 3a by the wiper blade 72 and heating the flow path unit 109 by the heater 43, the flow path unit 109 is heated by the heater 43 after the discharge surface 3a is wiped by the wiper blade 72. You may go. As a result, the heating means is not soiled by ink, and the residual ink on the ejection surface is dried and thickened before being wiped by the wiper, so that it becomes difficult to wipe. A wiper other than the wiper blade 72 may be used.

  Although the groove 161 extending in the thickness direction of the descender plate 129 is formed in the above-described embodiment, the present invention is limited to the groove 161 having such a shape formed on the inner wall surface 157 of the descender hole 152. However, if the inner wall surface 157 of the descender hole 152 is uneven, the same effects as those of the above-described embodiment can be obtained.

  The inner wall surface 157 of the descender hole 152 does not have to have a tapered shape in which the protruding amount toward the inside increases as the nozzle plate 130 is approached between the adjacent grooves 161 and / or in the groove 161.

  In the present invention, the heater 43 as the heating means is not necessarily fixed to the tray 71 so as to move relative to the wiper blade 72 along the discharge surface 3a. For example, a heater may be fixed to the platen 9. However, it is preferable from the viewpoint of the heating efficiency of the flow path unit 109 that it is fixed to the tray 71 whose distance from the discharge surface 3 a is closer than the platen 9. From the viewpoint of improving the heating efficiency, a water repellent film made of a nickel film containing a fluorine-based resin is preferably formed on the heated surface (discharge surface) of the nozzle plate. The water repellent film is, for example, a gray to black film formed by an electrolytic plating method, and easily absorbs heat rays (including infrared rays) for heating. Of course, even when water repellency is not required, a film that absorbs heat rays is preferably formed on the ejection surface.

  In the embodiment described above, wiping and heating of the flow path unit 109 using a heater are performed after purging, but it is not always necessary to perform purging. That is, flushing may be performed after wiping the discharge surface 3a and heating with the heater irrespective of the purge. In addition, the pump may be connected between the head and the ink tank to push out the ink in the head, but may be connected to a cap that covers the ejection surface of the head to suck out the ink in the head.

  The inkjet printer according to the above-described embodiment is provided with a lifting mechanism that lifts and lowers the head. However, the conveyance belt may be lifted and lowered without raising and lowering the head. The present invention can be applied to a serial printer in addition to a line printer. Further, the present invention is not limited to the ink jet printer and can be widely applied to a liquid ejecting apparatus.

1 is a side view of an ink jet printer that is a liquid ejection apparatus according to an embodiment of the present invention. FIG. 2 is a partial plan view of the ink jet printer depicted in FIG. 1. FIG. 3 is a sectional view taken along line III-III depicted in FIG. 2. FIG. 2 is a plan view of an inkjet head included in the inkjet printer depicted in FIG. 1. FIG. 4 is an enlarged view of a region indicated by a one-dot chain line in FIG. 3. It is sectional drawing in the VI-VI line of FIG. It is the fragmentary sectional view and the fragmentary top view of the actuator unit which are included in the ink jet head. FIG. 6 is an enlarged plan view and a cross-sectional view of the vicinity of an ejection port of an individual ink channel. It is a functional block diagram of the inkjet printer shown in FIG. 2 is a flowchart showing a maintenance operation of the ink jet printer depicted in FIG. 1. FIG. 3 is a side view for explaining a maintenance operation in the ink jet printer depicted in FIG. 1.

Explanation of symbols

1 Inkjet printer (liquid ejection device)
2 Inkjet head (liquid discharge head)
3 Head body 3a Discharge surface 4 Frame 8 Conveying belt 10 Reservoir unit 16 Ink supply pipe 17 Pump (purge means)
18 Control unit (control means)
31 Transport control unit 32 Discharge control unit 33 Heater control unit 34 Maintenance control unit 35 Purge control unit 43 Heater (heating means)
44 Motor 51 Lifting mechanism 52 Motor 70 Maintenance unit (wiper moving mechanism)
71, 75 Tray 72 Wiper blade 74 Holding plate 76 Cap 77 Waste ink receiving tray 78 Base 83, 84 Arm 92 Motor 96a, 96b Guide shaft 108 Discharge port 109 Flow path unit 110 Pressure chamber 121 Actuator unit 129 Decender plate 129a Lower surface 129b Upper surface 130 Nozzle plate 130a Connection surface 132 Individual ink flow path 134 Common electrode 135 Individual electrode 141-143 Piezoelectric layer 151 Nozzle hole 151a Cylindrical portion 151b Frustum portion 152 Decender hole 153 Inlet 155 Lower end opening 156 Upper end opening 157 Inner wall surface 161 Groove

Claims (6)

A flow path unit in which a nozzle plate having a discharge surface in which a discharge opening which is one of the nozzle holes is formed, and a descender plate in which a descender hole communicating with the nozzle hole is formed, and the flow path A liquid discharge head including an actuator that applies discharge energy to the liquid in the unit;
A wiper moving mechanism including a wiper for wiping the discharge surface, and relatively moving the wiper along the discharge surface;
Heating means for heating the flow path unit;
The wiper moving mechanism, so that the flow path unit is heated by the heating means after wiping the discharge surface by the wiper, and then the actuator applies discharge energy to the liquid in the flow path unit, Control means for controlling the heating means and the actuator,
The diameter of the opening of the descender hole facing the nozzle plate is larger than the diameter of the other opening of the nozzle hole,
The nozzle plate and the descender plate are made of metal,
An unevenness is formed on the inner wall surface of the descender hole.   The liquid ejection apparatus according to claim 1, wherein a plurality of grooves extending in a thickness direction of the descender plate are formed on an inner wall surface of the descender hole.   3. The liquid ejection device according to claim 2, wherein an inner wall surface of the descender hole has a taper shape in which a protruding amount toward an inner side becomes larger toward the nozzle plate between the adjacent grooves. .   4. The liquid ejection device according to claim 3, wherein an inner wall surface of the descender hole has a tapered shape in which the amount of protrusion toward the inside increases toward the nozzle plate in the groove. 5.   5. The liquid ejection apparatus according to claim 1, wherein the heating unit is fixed to the wiper moving mechanism so as to move relative to the wiper along with the wiper. A purge means for forcibly discharging the liquid in the flow path unit;
The control means forcibly discharges the liquid in the flow path unit by the purge means, and then the heating means heats the flow path unit after the discharge surface is wiped by the wiper. 6. The wiper moving mechanism, the heating unit, the actuator, and the purge unit are controlled so that the actuator applies discharge energy to the liquid in the flow path unit. The liquid ejection device according to item.

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