JP6299424B2 - Liquid ejection head unit and image forming apparatus - Google Patents

Description

  The present invention relates to a liquid discharge head unit and an image forming apparatus.

  As an image forming apparatus, for example, a liquid discharge recording type image forming apparatus using a liquid discharge head (droplet discharge head) for discharging droplets as a recording head, for example, an ink jet recording apparatus is known. Further, as an image forming apparatus, there is a line type image forming apparatus that uses a line type head that forms an image by ejecting liquid droplets without moving a recording head.

  A full line type head having a nozzle row length equivalent to the paper width used in the line type image forming apparatus or a long head having a nozzle row length equivalent to half the paper width (both of them are simply referred to as “long head Is known as a multi-array head in which a plurality of short heads (head chips) are arranged side by side in the paper width direction (Patent Document 1).

JP 2012-139980 A

  By the way, when a driving waveform is given to each pressure generating means (driving element) corresponding to a plurality of nozzles of the head chip, a plurality of switching means corresponding to the plurality of pressure generating means correspond to the arrangement direction of the switching means. A configuration in which one-sided supply for supplying a drive waveform from one side is known.

  At this time, the rounding of the drive waveform becomes larger as the pressure generating means is given via the switching means located farther from the drive waveform supply side. Therefore, the nozzle corresponding to the pressure generating means to which the driving waveform is given via the switching means on the side close to the driving waveform supply side, and the pressure to which the driving waveform is given via the switching means far from the driving waveform supply side The nozzle corresponding to the generating means has different droplet discharge characteristics.

  As a result, when a long head (which is referred to as a “liquid ejection head unit”) is configured by arranging a plurality of head chips as described above, the droplet ejection characteristics differ at the joints between adjacent head chips in the arrangement direction. There is a problem that the image quality at the joint portion is deteriorated.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to reduce deterioration in image quality at a joint portion of a head chip.

In order to solve the above problems, a liquid discharge head unit according to the present invention includes:
A liquid discharge head unit in which a plurality of nozzles for discharging droplets are arranged and a plurality of head chips having a plurality of pressure generating means corresponding to each nozzle are arranged in the longitudinal direction,
The row of the pressure generating means of the head chip has a side closer to and a side farther from the power supply portion of the drive waveform applied to the pressure generating means,
In the two head chips adjacent in the head chip arrangement direction, the sides close to the power supply part of the drive waveform or the sides far from the power supply part of the drive waveform overlap in the head chip arrangement direction. Configuration.

  According to the present invention, it is possible to reduce image quality deterioration at the joint portion of the head chip.

FIG. 2 is a schematic plan view illustrating the liquid discharge head unit according to the first embodiment of the invention. FIG. 6 is an explanatory cross-sectional view along a direction (liquid chamber longitudinal direction) orthogonal to the nozzle arrangement direction of an example of a head chip. It is sectional explanatory drawing which follows the nozzle arrangement direction (liquid chamber short direction) of the head chip. It is a block circuit diagram for explanation of a head drive control device that drives a liquid discharge head unit. It is explanatory drawing which shows an example of a drive waveform. It is explanatory drawing which shows the example which the rounded drive waveform produced. It is explanatory drawing with which it uses for description of the relationship between the nozzle position with respect to the electric power feeding side of a head chip, and droplet speed. FIG. 6 is an explanatory plan view of a liquid discharge head unit for explaining the arrangement of head chips in the same embodiment and an explanatory diagram for explaining a change in droplet velocity Vj in the head unit. It is a plane explanatory view of a liquid discharge head unit for explaining the arrangement of head chips in a comparative example, and an explanatory view for explaining a change in droplet velocity Vj in the head unit. FIG. 6 is a schematic plan explanatory view of a liquid discharge head unit according to a second embodiment of the present invention. It is typical explanatory drawing with which it uses for description of the example of electric power feeding to the head chip in each embodiment. 1 is a schematic explanatory diagram of an example of an image forming apparatus according to the present invention. It is explanatory drawing of an example of the recording head unit of the apparatus.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. A liquid discharge head unit according to a first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic plan view of the liquid discharge head unit.

  In the liquid discharge head unit 100, a plurality of head chips 101 are arranged on a base member 102 in a staggered manner along the longitudinal direction, here, the nozzle arrangement direction.

  Here, an example of the head chip 101 will be described with reference to FIGS. 2 is a cross-sectional explanatory view along a direction (liquid chamber longitudinal direction) orthogonal to the nozzle arrangement direction of the head chip, and FIG. 3 is a cross-sectional explanatory view along the nozzle arrangement direction (liquid chamber short direction) of the head chip. .

  The head chip 101 includes, for example, a flow path plate 1 composed of two SUS substrates 1A and 1B, a vibration plate member 2 bonded to one surface of the flow path plate 1, and a nozzle bonded to the other surface of the flow path plate 1. And a plate 3.

  As a result, a plurality of nozzles 4 for discharging liquid droplets (liquid droplets) also serve as a plurality of individual liquid chambers 6 serving as individual flow paths that communicate with each other through a passage 5 and a supply path for supplying liquid to the individual liquid chambers 6. A fluid introducing portion 8 that communicates with the individual liquid chamber 6 via the fluid resistance portion 7 and the fluid resistance portion 7 is formed.

  Then, the liquid is supplied from the common liquid chamber 10 formed in the frame member 17 to the liquid introducing portion 8 through the supply port 9 formed in the diaphragm member 2.

  The diaphragm member 2 has each vibration region (diaphragm portion) 2a that forms the wall surface corresponding to each individual liquid chamber 6, and has an island-like convexity on the outer side of the vibration region 2a (on the side opposite to the liquid chamber 6). A portion 2b is provided. Then, the upper end surface (joint surface) of the piezoelectric column 12A of the laminated piezoelectric member 12 as pressure generating means (drive element, actuator means) for deforming the vibration region 2a is joined to the island-shaped convex portion 2b of the diaphragm member 2. ing. Further, the opposite surface of the multilayer piezoelectric member 12 is bonded to the base member 13.

  Here, the piezoelectric member 12 is obtained by alternately stacking piezoelectric layers 21 and internal electrodes 22A and 22B. The internal electrodes 22A and 22B are respectively drawn out to end faces, that is, side faces substantially perpendicular to the diaphragm member 2 of the piezoelectric member 12, and connected to end face electrodes (external electrodes) 23 and 24 formed on the side faces. When a voltage is applied between the external electrodes 23 and 24, displacement in the stacking direction occurs. Here, the external electrode 23 is used as an individual external electrode (individual electrode), and the external electrode 24 is used as a common external electrode (common electrode).

  This piezoelectric member 12 is processed into a groove 31 (FIG. 3) by half-cut dicing, and a required number of columnar piezoelectric elements (piezoelectric columns) 12A and 12B are comb-shaped at a predetermined interval with respect to one piezoelectric member 12. Is formed. The piezoelectric columns 12A and 12B of the piezoelectric member 12 are the same, but a piezoelectric column that is driven by giving a driving waveform is a driving column 12A, and a piezoelectric column that is used as a simple column without giving a driving waveform is a non-driving column. It is distinguished as 12B. Further, the non-driving column 12B at the end of the piezoelectric member 12 is a non-driving column 12Ba formed wide to take out the common electrode to the outside, and the internal electrodes 23 and 24 are both formed to both end surfaces.

  The piezoelectric member 12 is connected to an FPC 15 as a flexible wiring board (signal transmission means) for transmitting a drive signal applied to the drive column 12A.

  The FPC 15 includes an individual electrode wiring that is a wiring for transmitting a driving signal, which is connected to the individual external electrode 23 of the driving column 12A, and a common electrode 24 of the plurality of driving columns 12A taken out to the non-driving piezoelectric column 12Ba at the end. And a common electrode wiring connected to the connected common extraction electrode.

  The FPC 15 includes a driving IC (driver IC) 16 that outputs a driving signal to the driving column 12A according to image data.

  In the nozzle plate 3, nozzles 4 having a diameter of 10 to 35 μm are formed corresponding to the individual liquid chambers 6 and bonded to the flow path plate 1 with an adhesive. A liquid repellent layer is provided on the droplet discharge side surface (surface in the discharge direction: discharge surface or the surface opposite to the liquid chamber 6 side) of the nozzle plate 3.

  Further, a frame member 17 formed by injection molding with, for example, epoxy resin or polyphenylene sulfite is joined to the outer peripheral side of the piezoelectric actuator constituted by the piezoelectric member 12, the base member 13, the FPC 15, and the like.

  The frame member 17 is formed with the common liquid chamber 10 described above. Further, a supply port 19 for supplying liquid from the outside to the common liquid chamber 10 is formed in the frame member 17, and the supply port 19 is further connected to a liquid supply source such as a sub tank or an ink cartridge (not shown).

  In the head chip 101 configured as described above, for example, when the voltage applied to the drive column 12A of the piezoelectric member 12 is lowered from the reference potential, the drive column 12A contracts, and the vibration region 2a of the diaphragm member 2 is deformed and individually separated. The volume of the liquid chamber 6 expands. As a result, the liquid (ink) flows into the individual liquid chamber 6.

  Thereafter, the voltage applied to the drive column 12A of the piezoelectric member 12 is increased to extend the drive column 12A in the stacking direction, and the vibration region 2a of the diaphragm member 2 is deformed in the nozzle 4 direction to contract the volume of the individual liquid chamber 6. . As a result, the ink in the individual liquid chamber 6 is pressurized and droplets are ejected from the nozzle 4.

  Then, by returning the voltage applied to the drive column 12A of the piezoelectric member 12 to the reference potential, the vibration region 2a of the diaphragm member 2 is restored to the initial position, and the individual liquid chamber 6 expands to generate a negative pressure. At this time, ink is filled from the common liquid chamber 10 into the individual liquid chamber 6. Therefore, after the vibration of the meniscus surface of the nozzle 4 is attenuated and stabilized, the operation proceeds to the next droplet discharge.

  Next, a head drive control device for driving the liquid discharge head unit will be described with reference to FIG. FIG. 4 is a block circuit diagram for explaining a head drive control device according to one head chip.

  As described above, the driving column 12A (herein referred to as “piezoelectric element PZT”), which is a pressure generating unit, is disposed in one head chip 101 corresponding to each nozzle 4.

  On the other hand, the drive waveform generation circuit 601 generates and outputs a drive waveform as shown in FIG. 5, for example. The drive waveform generated by the drive waveform generation unit 601 is supplied to the drive IC 16 of the head chip 101 via the wiring means such as the FPC 15 and via the switch means SW configured by analog switches included in the drive IC 16. It is given to each piezoelectric element PZT.

  The waveform selection control circuit 602 outputs a signal for controlling ON / OFF of the switch means SW according to the image data. As a result, a drive waveform (drive signal) is input to the piezoelectric element PZT in which the switch means SW is turned on.

  Here, the drive waveform (drive signal) is supplied (powered) to the row of the plurality of switch means SW of the drive IC 16 from one side (one end side of the row). Thereby, the row of the plurality of piezoelectric elements PZT arranged in the nozzle arrangement direction has an end side (feeding power) close to the feeding part of the driving waveform (specifically, the driving waveform input part 162 of the driving IC 16 is used as the feeding part). Part end) and a far end (end opposite to the power feeding part).

  Specifically, for example, as shown in FIG. 11, the drive signal generated by the control device 300 is supplied to the piezoelectric elements PZT corresponding to the nozzle rows via the FPC 15. The FPC 15 is connected to only one side of the nozzle row, and the current of the drive signal is transmitted from the control device 300 through the FPC 15 via the drive signal wiring 301, the drive IC 16, the individual wiring 302, the piezoelectric element PZT, and the common electrode wiring 303. Through the control device 300.

  Returning to FIG. 4, the supply circuit that supplies the drive waveform supplied from the drive waveform generation circuit 601 to each switch means SW of the drive IC 16 includes the drive signal wiring, the combined resistance component R of the drive IC internal wiring, An RC low-pass filter (LPF) circuit composed of the resistance component R1 of the common electrode wiring and the capacitance component C of the piezoelectric element PZT in which the switch means SW is in the ON state.

  When the drive waveform passes through this LPF, the high frequency component of the drive waveform is cut. Therefore, the number of LPF stages through which the drive waveform passes increases as the distance from the power supply unit side of the drive waveform increases, and the drive waveform is rounded as shown in FIG. In particular, as the number of piezoelectric elements PZT that are driven simultaneously increases, the number of LPFs increases and the amount of rounding of the drive waveform also increases.

  The drop velocity Vj decreases due to the rounding of the drive waveform. Therefore, as shown in FIG. 7, the droplet velocity Vj decreases as the distance from the nozzle close to the power supply unit side of the drive waveform increases toward the nozzle (on the opposite side to the power supply unit side).

  Therefore, the arrangement of the head chip and the droplet velocity in this embodiment will be described with reference to FIG. FIG. 8 is a schematic plan view of a liquid discharge head unit used for the description and an explanatory view for explaining a change in droplet velocity Vj in the head unit.

  In the liquid ejection head unit 100 of the present embodiment, as shown in FIG. 8A, in the head chip arrangement direction, two adjacent head chips 101 are close to the power feeding unit side end of the driving waveform. It is set as the structure where the parts or the edge part on the opposite side to the electric power feeding part side far from the electric power feeding part side of a drive waveform overlaps in the head chip arrangement direction, and is arrange | positioned adjacently.

  As a result, as shown in FIG. 8B, in the head chip arrangement direction, the droplet speed Vj of the two adjacent head chips 101 changes in the opposite direction. Accordingly, for example, if the amount of change in the droplet velocity Vj of each head chip 101 is substantially the same, the droplet velocity Vj in the liquid ejection head unit 100 as a whole has one maximum variation in the droplet velocity Vj of each head chip 101. The amount falls within the amount of change in the drop velocity Vj of the head chip 101.

  Further, since the drop velocity Vj at the joint portion between the adjacent head chips 101 and 101 becomes substantially the same, the streak due to the difference in the drop velocity Vj becomes inconspicuous, and the deterioration of the image quality at the joint portion can be reduced. Can be improved.

  Here, a liquid discharge head unit of a comparative example will be described with reference to FIG. FIG. 9 is a schematic plan view of a liquid discharge head unit provided for the explanation and an explanatory view for explaining a change in droplet velocity Vj in the head unit.

  In this comparative example, as shown in FIG. 9 (a), the plurality of head chips 101 are all arranged with the feeding waveform side end of the drive waveform on the same side.

  In this configuration, in the head chips 101 that are adjacent in the head chip arrangement direction, the power supply side end of one head chip 101 and the power supply side opposite to the power supply side of the other head chip 101 are adjacent to each other. .

  Therefore, as shown in FIG. 9B, for example, the feeding portion side end where the drop velocity Vj is fast, the feeding portion where the drop velocity Vj is slow and the opposite end are adjacent to each other at the joint portion. The change in the drop velocity Vj at this time becomes large.

  For this reason, streaks due to the difference in droplet velocity occur at the joints between the head chips 101 and 101, and the image quality deteriorates.

  Next, a liquid discharge head unit according to a second embodiment of the invention will be described with reference to FIG. FIG. 10 is a schematic plan view of the liquid discharge head unit.

  In the present embodiment, the plurality of head chips 101 are arranged with the nozzle arrangement direction inclined with respect to the head chip arrangement direction.

  Thus, by arranging the head chip 101 obliquely, the nozzle interval can be made wider than the dot interval necessary for printing, and the manufacture of the head chip is facilitated.

  In each of the above-described embodiments, it is preferable that the plurality of head chips 101 measure the drop amount of the drop velocity Vj in advance through experiments or the like, and combine those having characteristics close to each other.

  Next, an example of the image forming apparatus according to the present invention will be described with reference to FIGS. FIG. 12 is an explanatory view of the image forming apparatus, and FIG. 13 is a plan view of a recording head unit of the apparatus.

  This image forming apparatus is a line type image forming apparatus. A sheet 400 as a recording medium stacked on the sheet feeding tray 401 is conveyed by a sheet feeding roller 402 along a conveyance path illustrated by a broken line. The sheet 400 conveyed to the conveyance path is conveyed to the belt conveyance unit 404 via a pair of timing adjustment and skew correction rollers (so-called registration rollers) 403.

  The belt conveyance unit 404 includes a conveyance roller 405 driven at a predetermined timing, a tension roller 406, and an endless conveyance belt 407 wound around these rollers 405 and 406.

  In order to hold the sheet 400 with the transport belt 407 of the belt transport unit 404, means by electrostatic suction, suction by air suction, or other known means can be used.

  The paper 400 is conveyed by the belt conveyance unit 404 so as to face the recording head unit 200, and the recording head unit 200 is driven according to the image data to eject droplets, thereby forming an image.

  The recording head unit 200 includes a plurality of liquid ejection head units 100 according to the first embodiment. As shown in FIG. 13, yellow (Y), magenta (M), cyan (C), and black (K). Liquid head units 211Y, 211M, 211C, and 211K for discharging the ink droplets.

  Then, the sheet 400 on which an image is formed by the recording head unit 200 is conveyed to the decurler unit 409 and decurled (curl correction).

  When the paper 400 that has passed through the decurler unit 409 is discharged as it is, it is transported by the separation claw 410 through the transport path 411 to the paper discharge roller 412 and discharged.

  In the case of reverse paper discharge or reverse side printing (double-sided printing), the separation claw 410 is switched counterclockwise from the illustrated position, passes through the conveyance path 413, passes through the guide member 414, and is sent to the hitting roller 415. . The sheet 400 sent to the hitting roller 415 is conveyed in the reverse direction by the hitting roller 415 whose rotation direction has been switched.

  In the case of reverse paper discharge as it is, the paper passes through the second separation claw 416, passes through the conveyance path 417, is sent to the paper discharge roller 412 and is discharged.

  In the case of printing on the reverse side, the sheet 400 conveyed in the reverse direction by the tapping roller 415 passes between the second separation claw 416 and the double-side reversing roller 418 which are switched counterclockwise from the illustrated position, and is conveyed in the conveying path 419. Is sent to the registration roller pair 403.

  A maintenance / recovery unit 408 is provided to maintain and recover the performance of the recording head unit 200. The maintenance / recovery unit 408 wipes off the ink remaining on the head when the ink is sucked into the cap 420 that caps the nozzle surface of each head chip of the recording head unit 200, a suction pump (not shown) connected to the cap 420, and the cap 420. A wiper 421 is provided.

  Here, when performing the maintenance / recovery operation, the recording head unit 200 moves up, and the maintenance / recovery unit 408 moves to below the recording heads of the recording head unit 200 to perform the maintenance / recovery operation. Further, the cap 420 of the maintenance / recovery unit 408 also serves as a moisture retention cap that maintains the humidity of each head chip of the recording head unit 200 during standby, and the recording head unit 200 rises during non-printing to maintain / recovery unit 408. Moves below the recording head unit 200 to perform moisture retention capping.

  As described above, by including the liquid discharge head unit according to the present invention, it is possible to suppress a decrease in image quality in the head chip arrangement direction and form a high-quality image.

DESCRIPTION OF SYMBOLS 1 Flow path plate 2 Vibrating plate member 3 Nozzle plate 4 Nozzle 6 Individual liquid chamber 10 Common liquid chamber 12 Piezoelectric member 12A Drive column (piezoelectric element PZT; pressure generating means)
15 FPC
16 Drive IC
DESCRIPTION OF SYMBOLS 100 Liquid discharge head unit 101 Head chip 200 Recording head unit 211Y, 211M, 211C, 211K Liquid discharge head unit 400 Paper (recording medium)
404 Belt transport unit 601 Drive waveform generation circuit

Claims (3)

A liquid discharge head unit in which a plurality of nozzles for discharging droplets are arranged and a plurality of head chips having a plurality of pressure generating means corresponding to each nozzle are arranged in the longitudinal direction,
The row of the pressure generating means of the head chip has a side closer to and a side farther from the power supply portion of the drive waveform applied to the pressure generating means,
In the two head chips adjacent in the head chip arrangement direction, the sides close to the power supply part of the drive waveform or the sides far from the power supply part of the drive waveform overlap in the head chip arrangement direction. A liquid discharge head unit characterized by being arranged.   The liquid ejection head unit according to claim 1, wherein the plurality of head chips are arranged with a nozzle arrangement direction inclined with respect to a head chip arrangement direction.   An image forming apparatus comprising the liquid discharge head unit according to claim 1.

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