JP6597108B2 - Liquid ejection device - Google Patents

Description

  The present invention relates to a liquid ejecting apparatus that ejects liquid from a nozzle.

  In the ink jet head, there is a problem that a part of the ink ejected from the nozzles is scattered as mist and stains surrounding components. In this regard, Patent Document 1 discloses a configuration in which an electrode for mist collection is disposed on the bottom surface of a platen, and an electric field is generated between the head and the platen by applying a potential to the electrode. . Mist generated when ink is ejected from the nozzle is negatively charged and is attracted to the platen side by the electric field.

  On the other hand, in Patent Document 2, for the purpose of suppressing warping of the recording paper being transported, the corrugating mechanism disposed upstream in the transport direction is along the direction orthogonal to the transport direction with respect to the recording paper being transported. Wave shape is given. In addition, the recording paper is supported by a plurality of support portions (ribs and upper surfaces of portions where ribs are not formed) of the platen in a region facing the ink jet head.

JP 2008-62573 A JP 2013-212585 A

  In the apparatus of Patent Document 2, when applying the mist collecting technique as in Patent Document 1, it is conceivable to provide an electrode portion on each of a plurality of support portions and to apply a potential to each of the plurality of electrode portions. However, if the potentials applied to the plurality of electrode portions having different heights are all the same, the equipotential lines between the head and the platen become wavy according to the tip positions of the plurality of support portions. Then, the charged droplet receives a Coulomb force in a direction orthogonal to the equipotential line. For this reason, the flight direction of the liquid droplets ejected from the nozzles is deviated toward the peak portion of the paper closest to the head, and a deviation in the scanning direction occurs at the liquid droplet landing position.

  An object of the present invention is to provide a liquid ejecting apparatus that ejects liquid onto a wave-shaped sheet that can suppress the deviation of the landing positions of droplets.

  A liquid discharge apparatus according to a first aspect of the present invention includes a liquid discharge head that discharges liquid toward the sheet while moving in the scanning direction with respect to the sheet, and the liquid discharge head with respect to the liquid discharge head. A sheet conveying unit that conveys the sheet in a conveying direction that intersects with the sheet, a wave shape imparting unit that imparts a wave shape along the scanning direction to the sheet conveyed by the sheet conveying unit, and the liquid with respect to the sheet A first support portion disposed on the opposite side of the discharge head and corresponding to the corrugated portion of the corrugated sheet; and a height lower than that of the first support portion corresponding to the valley portion of the sheet. A sheet support including a plurality of support units arranged in the scanning direction, and an electric field generation unit that generates an electric field between the liquid ejection head and the sheet support, The generator is the front A first conductive portion provided in the first support portion; a second conductive portion provided in the second support portion and positioned at a position lower than the first conductive portion; the first conductive portion and the second conductive portion; A potential applying section that applies a potential to each of the sections, and the potential applying section applies a higher potential to the second conductive section than the first conductive section.

  The liquid ejection apparatus of the present invention includes a first conductive portion provided on a first support portion having a high height and a second conductive portion provided on a second support portion having a low height. In addition, a higher potential is applied to the second conductive portion at the lower position than the first conductive portion at the higher position. As a result, the equipotential line between the liquid ejection head and the sheet becomes flatter than when the first conductive portion and the second conductive portion are set to the same potential, and the deviation of the droplet landing position in the scanning direction is shifted. It is suppressed.

  The liquid ejection apparatus according to a second aspect is the liquid ejection apparatus according to the first aspect, wherein the potential applying unit has an equipotential line between the liquid ejection head and the sheet parallel to the scanning direction. Thus, different potentials are applied to the first conductive portion and the second conductive portion, respectively.

  According to the present invention, since the potential is applied to the first and second conductive portions so that the equipotential lines of the electric field between the head and the sheet are parallel to the head scanning direction, the liquid droplets ejected from the nozzles The Coulomb force acts in a direction perpendicular to the moving plane of the head. This reliably suppresses the deviation of the landing position of the droplet in the scanning direction.

A liquid ejection apparatus according to a third aspect is the liquid ejection apparatus according to the first aspect , wherein the sheet support has a plate-like base member made of an insulating material, and the base member includes A plurality of slits are formed at intervals in the scanning direction, and the plurality of support portions formed of a conductive material are inserted through the plurality of slits of the base member, respectively.

  The plurality of support portions are respectively inserted into the slits of the base member made of an insulating material, whereby the first support portion and the second support portion having different potentials can be insulated by the base member.

  The liquid ejection device according to a fourth aspect of the present invention is the liquid ejection device according to any one of the first to third aspects, wherein the support portions positioned at both ends of the plurality of support portions arranged in the scanning direction are It is a 2nd support part.

  In the present invention, both end portions of the sheet are valley portions, and the second support portions having low heights are respectively disposed on both end sides, so that both ends of the sheet in the scanning direction are pressed by the wave shape imparting portions. Thereby, it is possible to prevent the end portion of the sheet in the scanning direction from being turned up during conveyance of the sheet.

  The liquid ejection device according to a fifth aspect of the present invention is the liquid ejection device according to any one of the first to fourth aspects, wherein the second support part is located downstream of the first support part in the transport direction. It is long.

  Regardless of the position in the transport direction, the length of the first and second support portions (first and second conductive portions) in the transport direction is used from the viewpoint of making the equipotential lines between the liquid discharge head and the sheet support uniform. It is preferable to increase the length to some extent. However, if the high first support portion extends downstream in the conveyance direction, the liquid discharged outside the sheet adheres to the first support portion when performing borderless printing, and thereafter There is a possibility that the passing sheet may be soiled. Therefore, in the present invention, the second support portion having a height lower than that of the first support portion is extended downstream in the transport direction from the first support portion. Thereby, it is possible to prevent the liquid adhering to the second support part from contaminating the sheet passing thereafter while increasing the length of the second support part in the transport direction.

  The liquid ejection device according to a sixth aspect of the invention is the liquid ejection device according to the fifth aspect of the invention, wherein the portion of the second support portion that extends further downstream in the transport direction than the first support portion is The height is lower than the upstream part.

  Since the portion of the second support portion that extends downstream from the first support portion is lower than the portion that is upstream of the second support portion, the portion that extends downstream from the second support portion is the sheet. Hard to touch. Therefore, it can prevent more reliably that the liquid adhering to the 2nd support part stains the sheet | seat which passes after that.

A liquid ejection apparatus according to a seventh aspect is the liquid ejection apparatus according to any one of the first to sixth aspects, wherein the wave shape imparting section is disposed upstream of the second support section in the transport direction. ,
The height of the second support portion decreases toward the upstream side in the transport direction.

  According to the present invention, since the second support portion becomes lower toward the upstream side in the transport direction, the sheet pressed by the wave shape imparting portion on the upstream side in the transport direction smoothly rises on the second support portion.

  A liquid ejection apparatus according to an eighth invention is the liquid ejection apparatus according to any one of the first to seventh inventions, wherein the liquid ejection head is formed with a liquid flow path and at least partly formed of a metal material. A flow path member is provided, and a metal portion of the flow path member is maintained at a ground potential.

  According to the present invention, by maintaining the potential of the metal portion of the flow path member in contact with the liquid at the ground, charging of the droplets ejected from the nozzle can be suppressed.

  A liquid ejection apparatus according to a ninth aspect is the liquid ejection apparatus according to any one of the first to eighth aspects, wherein the potential applying unit is responsive to a wave shape applied to the sheet by the wave shape applying unit. The potential applied to the first conductive portion and the second conductive portion is changed.

  The wave shape of the sheet differs depending on conditions such as the type of the sheet and whether or not the sheet is held by the roller of the conveyance unit. If the wave shape is different, the electric field to be generated between the head and the sheet also changes. For example, when the height of the mountain and the depth of the valley change, the potential difference between the mountain position and the valley position also needs to be changed. In the present invention, since the potential applied to the first conductive portion and the second conductive portion is changed according to the wave shape of the sheet, the potential of the first and second conductive portions is set to an appropriate potential according to the wave shape of the sheet. It can be.

  The liquid ejection apparatus of the present invention includes a first conductive portion provided on a first support portion having a high height and a second conductive portion provided on a second support portion having a low height. In addition, a higher potential is applied to the second conductive portion at the lower position than the first conductive portion at the higher position. As a result, the equipotential line between the liquid ejection head and the sheet becomes flatter than when the first conductive portion and the second conductive portion are set to the same potential, and the deviation of the droplet landing position in the scanning direction is shifted. It is suppressed.

1 is a schematic configuration diagram of an inkjet printer according to an embodiment of the present invention. It is a schematic block diagram of a printing part. (A) is the IIIA-IIIA sectional view taken on the line of FIG. 2, (b) is the figure which looked at FIG. 2 from the direction of arrow IIIB. (A) is the IV-IV sectional view taken on the line of FIG. 2, (b) is the elements on larger scale of (a). (A) is the VA-VA sectional view taken on the line of FIG. 2, (b) is the VB-VB sectional view taken on the line of FIG. FIG. 3 is a plan view of the inkjet head of FIG. 2. It is the VII-VII sectional view taken on the line of FIG. It is a block diagram which shows the electric constitution of an inkjet printer. FIG. 5 is a view corresponding to FIG. 4A when all the ribs have the same potential. (A) is a figure which shows the state in which the recording paper is pressed only in the upstream part of a conveyance direction, (b) is a figure which shows the state in which the recording paper is pressed in the part of the both sides of a conveyance direction. And (c) is a diagram showing a state in which the recording sheet is pressed only in the downstream portion in the transport direction. FIG. 10 is a diagram illustrating a relationship between a position of a recording sheet and a potential of a rib according to a first modification. FIG. 4A is a diagram corresponding to FIG. 4A of the second modification, and FIG. 4B is a diagram corresponding to FIG. 4B of the second modification. FIG. 4A is a view corresponding to FIG. 4A of the third modification, and FIG. 4B is a view corresponding to FIG. 4B of the third modification.

  Hereinafter, a preferred first embodiment of the present invention will be described.

(Overall configuration of MFP)
The ink jet printer 1 according to the present embodiment (the “liquid ejecting apparatus” of the present invention) is a so-called composite that can perform image reading and the like in addition to printing on the recording paper P (the “sheet” of the present invention). Machine. As shown in FIG. 1, the inkjet printer 1 includes a printing unit 2 (see FIG. 2), a feeding unit 3, a discharge unit 4, a reading unit 5, an operation unit 6, a display unit 7, and the like. The operation of the ink jet printer 1 is controlled by the control device 50 (see FIG. 8).

  The printing unit 2 is provided inside the inkjet printer 1 and performs printing on the recording paper P. The printing unit 2 will be described in detail later. The feeding unit 3 is a part that feeds the recording paper P to the printing unit 2. The discharge unit 4 is a portion where the recording paper P on which printing has been performed is discharged. The reading unit 5 is a scanner or the like, and reads a document. The operation unit 6 includes buttons and the ink jet printer 1 performs a predetermined operation based on a user operation (including button selection). The display unit 7 is a liquid crystal display or the like, and displays information necessary when the ink jet printer 1 is used.

(Printing department)
Next, the printing unit 2 will be described. As shown in FIGS. 2 to 5, the printing unit 2 includes a carriage 11, an inkjet head 12 (“liquid ejection head” of the present invention), a conveyance roller 13, a plurality of corrugated plates 14, and a platen 15 (“sheet of the present invention”). Support ”), a plurality of discharge rollers 16, a plurality of corrugated spurs 17, an encoder 18, and the like. However, in FIG. 2, in order to make it easy to see the corrugated plate 14, ribs 20 a and 20 b to be described later, the carriage 11 is illustrated by a two-dot chain line and is actually hidden behind the carriage 11 and is not visible. The members arranged at are indicated by solid lines. In FIG. 2, illustration of a guide rail and the like for supporting the carriage 11 is omitted.

  The carriage 11 is supported so as to be movable along a guide rail (not shown). The carriage 11 is connected to a carriage motor 56 (see FIG. 8) via a belt (not shown). When the carriage motor 56 is driven, the carriage 11 reciprocates in the scanning direction. In the following description, the right and left sides in the scanning direction are defined as shown in FIGS.

  The inkjet head 12 is mounted on the carriage 11 and moves together with the carriage 11. Further, the inkjet head 12 ejects ink from a plurality of nozzles 35 formed on the ink ejection surface 12a which is the lower surface thereof.

  Here, the configuration of the inkjet head 12 will be described in detail. As shown in FIGS. 6 and 7, the inkjet head 12 includes a flow path unit 21 (an “flow path member” of the present invention) in which an ink flow path such as a nozzle 35 and a pressure chamber 30 described later is formed, and a pressure chamber. And a piezoelectric actuator 22 for applying pressure to the ink in the ink 30.

  As shown in FIG. 7, the flow path unit 21 is a stacked body in which four plates 26 to 29 are stacked. Of the four plates 26 to 29, the upper three plates 26 to 28 are made of a metal material such as stainless steel. The plate 29 is made of a synthetic resin material such as polyimide or a metal material similar to the plates 26 to 28. Further, the three plates 26 to 28 are grounded. If the plate 29 is made of a metal material, the plate 29 is also at the same potential as the plates 26 to 28. In the present embodiment, the plates 26 to 28 (the plates 26 to 29 when the plate 29 is made of a metal material) correspond to the metal portion of the present invention.

  A plurality of through holes are formed in the plate 26. The through hole has an oval shape in the opening, and its longitudinal direction is parallel to the scanning direction. Each through hole is sealed up and down by a plate 27 and a vibration plate 41 of the piezoelectric actuator 22 described later, thereby constituting a plurality of pressure chambers 30. The plurality of pressure chambers 30 are arranged in the transport direction to form a pressure chamber row 39. In the plate 26, such pressure chamber rows 39 are arranged in four rows in the scanning direction.

  A circular through hole 32 is formed in the plate 27 at a portion overlapping the right end portion in the scanning direction of each pressure chamber 30. The through-hole 32 functions as a throttle channel and communicates the pressure chamber 30 and a manifold channel 31 described later. In addition, a circular through hole 33 is formed in the plate 27 at a portion overlapping the left end portion in the scanning direction of each pressure chamber 30. The through hole 33 communicates the pressure chamber 30 with a nozzle 35 described later.

  The plate 28 is formed with four slit-shaped through holes and a plurality of circular through holes 34. Each of the four slit-shaped through holes is arranged corresponding to one pressure chamber row 39 and is long in the transport direction. The slit-like through hole extends over the entire length of the pressure chamber row 39 and overlaps with the substantially right half of each pressure chamber 30 in the scanning direction. Each slit-shaped through hole is sandwiched between the plate 27 and the plate 29 to form a manifold channel 31. Ink is supplied to each manifold channel 31 from an ink supply port 38 on the downstream side in the transport direction. Black, yellow, cyan, and magenta inks are supplied to each manifold channel 31 in order from the right side in the scanning direction. The circular through hole 34 is disposed so as to overlap the through hole 33, and communicates the pressure chamber 30 and a nozzle 35 described later via the through hole 33.

  In addition, nozzles 35 are formed in the plate 29 at portions that overlap the through holes 34. The nozzle 35 is tapered toward the lower side of the plate 29 and opens on the lower surface. This lower surface is the ink discharge surface 12a.

  In the flow path unit 21 having the above-described configuration, as many individual ink flow paths as the number of pressure chambers 30 are configured. The individual ink flow path reaches from the outlet of the manifold flow path 31 to the nozzle 35 via the pressure chamber 30. The ink flowing into the manifold channel 31 is distributed to the individual ink channels and reaches the nozzles 35.

  The piezoelectric actuator 22 includes a vibration plate 41, a piezoelectric layer 42, a common electrode 43, and a plurality of individual electrodes 44. The diaphragm 41 is made of a piezoelectric material mainly composed of lead zirconate titanate, and covers the plurality of pressure chambers 30 on the upper surface of the plate 28. The diaphragm 41 may be made of an insulating material other than the piezoelectric layer, such as a synthetic resin.

  The piezoelectric layer 42 is made of the same piezoelectric material as that of the vibration plate 41, and its upper surface continuously extends across the plurality of pressure chambers 30. The common electrode 43 extends substantially between the diaphragm 41 and the piezoelectric layer 42. The common electrode 43 is maintained at the ground potential.

  The plurality of individual electrodes 44 have a substantially oval shape that is slightly smaller than the pressure chamber 30. The individual electrode 44 is formed on the upper surface of the piezoelectric layer 42 and overlaps the central portion of the pressure chamber 30 in plan view. The individual electrode 44 has the right end in the scanning direction outside the pressure chamber 30. The right end is a connection terminal 44a. Although not shown, a wiring member is connected to the connection terminal 44a, and a drive signal is supplied from the driver IC.

  As described above, the piezoelectric actuator 22 has a sandwich structure in which the individual electrode 44 and the common electrode 43 sandwich the piezoelectric layer 42 for each pressure chamber 30. The piezoelectric layer 52 in this portion is an active portion, and expands and contracts spontaneously by an electric field. The piezoelectric layer 42 of the active part is polarized from the individual electrode 44 toward the common electrode 43.

  Here, a method for ejecting ink from the nozzle 35 will be described. In the state before driving (standby state), all the individual electrodes 44 are held at the ground potential. When ink is ejected from a certain nozzle 35, a drive signal is supplied, and the potential of the corresponding individual electrode 44 is switched from the ground potential to the drive potential. At this time, an electric field from the individual electrode 44 toward the common electrode 43 is generated in the active portion of the piezoelectric layer 42 and contracts in the surface direction. On the other hand, the vibration film 41 does not spontaneously expand and contract due to an electric field. Accordingly, a strain difference is generated between the piezoelectric layer 42 and the vibration film 41, and the piezoelectric layer 42 and the vibration plate 41 are deformed in a convex manner toward the pressure chamber 30 side. At this time, the ink in the pressure chamber 30 is pressurized and a part thereof is ejected from the nozzle 35. Thereafter, when the potential of the individual electrode 44 returns to the ground potential, the deformation of the piezoelectric layer 42 and the diaphragm 41 is released, and the volume of the pressure chamber 30 also returns to the volume before the drive potential is applied. At this time, ink is replenished from the manifold channel 31 to the pressure chamber 30, and preparations for the next ink discharge (application of drive potential) are completed.

  2 to 5, the transport roller 13 is disposed on the upstream side in the transport direction from the inkjet head 12. The transport roller 13 includes an upper roller 13a and a lower roller 13b, and sandwiches the recording paper P from the feeding unit 3 and transports it in the transport direction. The upper roller 13a is a drive roller connected to the transport motor 57 (see FIG. 8). The lower roller 13b is a driven roller that interlocks with the upper roller 13a.

  The plurality of corrugated plates 14 overlap with the conveying roller 13 from above and are arranged at substantially equal intervals in the scanning direction. The corrugated plate 14 presses the recording paper P from above on the downstream side of the transport roller 13 in the transport direction. On the downstream side in the transport direction, as shown in FIG. 5, the lower surface (pressing surface 14 a) of the corrugated plate 14 is positioned below the nip portion of the transport roller 13.

  The platen 15 is disposed to face the carriage 11 and supports the recording paper P at a position suitable for image formation with respect to the ink ejection surface 12a of the inkjet head 12. The platen 15 spreads on both sides in the transport direction with respect to the inkjet head 12, and faces the pressing surface 14 a of the corrugated plate 14 from below on the upstream side. In the scanning direction, the platen 15 straddles all the pressing surfaces 14a. When the recording paper P is discharged from the nip portion of the transport roller 13, it is pushed down to the platen 15 side by the pressing surface 12 a and transported to the downstream side of the carriage 11. An image is formed on the recording paper P in an area facing the inkjet head 12 (image forming area).

  The platen 15 includes a base member 19, a plurality of first ribs 20a ("first conductive portion" of the present invention, "first support portion") and a plurality of second ribs 20b ("second conductive portion" of the present invention), "Second support part"). In the present embodiment, a combination of the plurality of first ribs 20a and the plurality of second ribs 20b corresponds to the plurality of support portions of the present invention.

  The base member 19 is a plate-like member made of an insulating material such as synthetic resin. On the upper surface of the base member 19, a plurality of slits long in the transport direction are arranged at equal intervals in the scanning direction. As shown in FIG. 2, the plurality of slits are arranged in a staggered manner to form two slit rows. The slit row on the upstream side in the transport direction is constituted by the slit 19a, and the slit row on the downstream side is constituted by the slit 19b. At this time, the conveyance direction downstream half of the slit 19a and the conveyance direction upstream half of the slit 19b overlap in the scanning direction. One slit 19a is sandwiched at equal intervals between two corrugated plates 14 (mainly the pressing surface 14a) at the upstream half in the transport direction. One slit 19b is aligned with one corrugated plate 14 along the conveying direction. In the present embodiment, the carriage 11 reciprocates in the scanning direction while facing the overlapping region of the two slits 19a and 19b.

  The first rib 20 a is erected by being fitted to the slit 19 a, and the top of the first rib 20 a is substantially the same height as the nip portion of the transport roller 13. The first rib 20a is made of a conductive material, and a potential V1 (for example, 850 V) is applied from the potential applying circuit 58 (see FIG. 8).

  The second rib 20b is erected so as to fit into the slit 19b, and the top of the second rib 20b is between the pressing surface 14a and the nip portion of the conveying roller 13 in the vertical direction. The second rib 20b has a convex shape upward as a whole. At this time, the tip on the upstream side in the transport direction is lower than the pressing surface 14a. In the transport direction, the second rib 20b is also lower than the central portion at a portion downstream of the first rib 20a. The first rib 20b is also made of a conductive material, and a potential V2 (for example, 1000 V) is applied from the potential applying circuit 58. Since the base member 19 is made of an insulating material, the second rib 20b is insulated from the first rib 20a, and both can apply a potential independently.

  In the arrangement of the ribs 20a and 20b, second ribs 20b are arranged at both ends in the scanning direction. In the transport direction, the pressing surface 14a, the second rib 20b, and the corrugated spur 17 (described later) are arranged in this order from the upstream side, and all are lower than the first rib 20a in the vertical direction. Therefore, both ends of the recording paper P in the scanning direction do not float during the conveyance of the paper. In the present embodiment, the combination of the plurality of first ribs 20a, the plurality of second ribs 20b, and the potential applying circuit 58 that applies a potential to the ribs 20a and 20b is the electric field generating section of the present invention. It corresponds to.

  A discharge roller 16 and a corrugated spur 17 are disposed adjacent to the platen 15 on the downstream side in the transport direction of the carriage 11. The discharge roller 16 includes a plurality of roller sets, each of which includes an upper roller 16a and a lower roller 16b. One roller set is along the first rib 20a and the conveying direction. The lower roller 16b is a driving roller and receives a rotational force from the transport motor 57 (see FIG. 7). The upper roller 16a is a driven roller and interlocks with the lower roller 16b. As shown in FIG. 5A, the nip portion of the discharge roller 16 is slightly lower than the top portion of the first rib 20a. The recording paper P after image formation is sandwiched between the roller sets and conveyed to the discharge unit 4 side. Here, the upper roller 16a is a spur. The upper roller 16a comes into contact with the image forming surface, but the image quality is not impaired.

  The corrugated spur 17 is adjacent to the discharge roller 16 from the downstream side in the transport direction, and is aligned with the pressing surface 14a and the second rib 20b along the transport direction. As shown in FIG. 5B, the lower end of the corrugated spur 17 is on the downstream side in the transport direction from the nip portion of the discharge roller 16. In the vertical direction, it is lower than the nip portion and slightly above the pressing surface 14 a of the corrugated plate 14. The recording paper P is headed toward the discharge unit 4 while being weakly pushed down by the corrugated spur 17. At this time, the corrugated spur 17 contacts the image forming surface, but the quality of the image is not impaired.

  With the above configuration, the recording paper P is formed into a wave shape that repeats the peak portion Pm and the valley portion Pv in the scanning direction, and moves on the platen 15. In the image forming region and its vicinity, the top of the first rib 20a and the nip of the discharge roller 16 are high in the vertical direction, and the pressing surface 14a, the top of the second rib 20b, and the lower end of the corrugated spur 17 are low. Therefore, also in the mountain portion Pm, the mountain peak portion Pt faces the top of the first rib 20a, and in the valley portion Pv, the valley bottom portion Pb faces the head of the second rib 20b.

Here, in the arrangement of the pressing surface 14a, the top of the second rib 20b, and the lower end of the corrugated spur 17, the top of the second rib 20b is the highest in the vertical direction. Therefore, when the recording paper P is conveyed through the image forming area, the recording paper P is pushed down by the pressing surface 14a and the lower end of the corrugated spur 17 and is supported by the tops of the ribs 20a and 20b above them.
In the present embodiment, the combination of the corrugated plate 14 and the corrugated spur 17 corresponds to the “wave shape imparting portion” of the present invention.

  In the present embodiment, the height of the upstream portion of the second rib 20b decreases in the transport direction as it goes upstream. Accordingly, the portion of the recording paper P that is pressed by the corrugated plate 14 can be smoothly raised to the upper end of the second rib 20b.

  The encoder 18 is mounted on the carriage 11 and outputs a signal indicating the position of the carriage 11 (inkjet head 12) in the scanning direction to the control device 50.

(Control device)
Next, the control device 50 for controlling the operation of the inkjet printer 1 will be described. As shown in FIG. 8, the control device 50 includes a CPU (Central Processing Unit) 51, a ROM (Read Only Memory) 52, a RAM (Random Access Memory) 53, an EEPROM (Electrically Erasable Programmable Read Only Memory) 54, an ASIC (Application Specific Integrated Circuit) 55 and the like.

  The control device 50 controls operations of the carriage motor 56, the inkjet head 12, the transport motor 578, the potential application circuit 58, the reading unit 5, the display unit 7, and the like. In addition, a signal corresponding to an operation in the operation unit 6 and a signal from the encoder 18 are input to the control device 50.

  Here, although only one CPU 51 is illustrated in FIG. 8, the control device 50 may include only one CPU 51, and this one CPU 51 may perform processing in a batch. The plurality of CPUs 51 may share the processing. Further, in FIG. 8, only one ASIC 55 is illustrated, but the control device 50 may include only one ASIC 55, and the one ASIC 55 may perform processing in a lump. A plurality of ASICs 55 may be provided to perform processing.

(Operation when printing)
Next, the operation of the printing unit 2 during printing will be described. In the printing unit 2, the recording paper P is transported by a predetermined distance by the transport roller 13 and the discharge roller 16, and each time the recording paper P is transported by the predetermined distance, the carriage 11 is moved back and forth in the scanning direction, Ink is ejected from the nozzles 35 to perform printing on the recording paper P.

  At this time, since the recording paper P is formed in a wave shape as described above, the distance between the nozzle 35 and the recording paper P differs depending on the position of the inkjet head 12 (carriage 11) in the scanning direction. Therefore, when the carriage 11 moves at a constant speed, if the ink ejection cycle and the ejection speed are constant, the interval between the ink landing positions on the recording paper P varies. Specifically, in the section where the distance between the nozzle 35 and the recording paper P is gradually reduced (the section in which the inkjet head 12 moves from the valley bottom portion Pb toward the peak portion Pt), this interval is small. On the other hand, in the section where the distance between the nozzle 10 and the recording paper P is gradually increased (the section in which the inkjet head 12 moves from the peak portion Pt toward the valley bottom portion Pb), this interval is increased.

  Therefore, in the present embodiment, a delay time is added to the reference ejection cycle to obtain the ink ejection timing. The adjustment of the delay time is based on the output of the encoder 18. Specifically, in a section where the paper-nozzle distance is gradually reduced, the delay time is set to be gradually longer. Thereby, even if the recording paper P has a wave shape, ink can land in the scanning direction at intervals corresponding to the printing resolution. Here, if ink is ejected at the reference ejection cycle, an image with a desired resolution can be formed in the valley bottom portion Pb. In addition, the delay time can be determined based on, for example, a reading result when a predetermined test pattern printed by the printing unit 2 is read by the reading unit 5.

  Here, as described above, when ink is ejected from the nozzle 35, a part of the ejected ink may be mist. In this case, mist is collected corresponding to the potential distribution in the vicinity of the recording paper P. Generally, in the vicinity of the top of the sharp peak portion Pt, the potential gradient becomes large and a large amount of mist is collected, which may lead to deterioration in image quality. In particular, this tendency is strong at the charged peak portion Pt.

  Therefore, in the present embodiment, the potential distribution between the platen 15 and the inkjet head 12 is adjusted by applying potentials V1 and V2 to the ribs 20a and 20b, respectively. As a result, a coulomb force having a uniform direction is generated in the mist, and the mist is uniformly adhered and collected on the recording paper P.

  Here, unlike the present embodiment, as shown in FIG. 9, a case where all the ribs 20a and 20b are set to the same potential V0 is considered. In this case, since the distance between the first rib 20a and the second rib 20b is different from the inkjet head 12, the equipotential line R2 between the inkjet head 12 and the platen 15 when viewed from the transport direction is Due to the difference in height between the first rib 20a and the second rib 20b, the first rib 20a has a wave shape along the scanning direction. In this case, the direction of the electric field E2 generated between the first rib 20a and the second rib 20b is closer to the mountain portion Pm and away from the valley portion Pv as it goes downward. At this time, since the Coulomb force along the direction of the electric field E2 is also generated in the ink droplet, the ink droplet landing position is shifted in the scanning direction. Depending on the magnitude of the Coulomb force, the shift is recognized and the image quality is deteriorated.

  Therefore, in the present embodiment, as shown in FIGS. 4A and 4B, when the potential V2 of the second rib 20b is made higher than the potential V1 of the first rib 20a and viewed from the carrying direction. The equipotential line R1 between the inkjet head 12 and the platen 15 is set to be parallel to the scanning direction as much as possible. Therefore, the direction of the electric field E1 between the inkjet head 12 and the platen 15 is parallel to the vertical direction, and the Coulomb force generated in the ink droplet is parallel to the vertical direction. Thereby, the shift | offset | difference to the scanning direction of the landing position of an ink drop can be suppressed.

  Here, in order to make the equipotential line R1 uniform in the range facing the ink ejection surface 12a regardless of the position in the transport direction, the length in the transport direction of the first rib 20a and the second rib 20b. It is preferable to lengthen the length to some extent. On the other hand, when performing borderless printing, on the downstream side in the transport direction, ink is ejected from the nozzles 35 on the downstream side of this end in order to ensure that the ink reaches the end of the recording paper P. At this time, if the first rib 20a having a high height is long on the downstream side in the transport direction, the ink is liable to adhere to the first rib 20a, and the ink may re-adhere to the subsequent recording paper P.

  Therefore, in the present embodiment, in the range facing the ink discharge surface 12a, the downstream end of the first rib 20a in the transport direction is at the center in the transport direction, and the downstream end of the second rib 20b is downstream of this. On the side. As shown in FIG. 5B, the second rib 20b is formed such that the downstream portion is lower than the upstream portion in the transport direction overlapping the first rib 20a in the scanning direction via a step. In borderless printing, when the downstream end of the recording paper P is printed, the downstream portion of the second rib 20b is used. Therefore, ink adheres to the downstream portion of the downstream portion of the recording paper P from the downstream end thereof. However, since the downstream portion is connected in steps with the upstream portion, the recording paper P is conveyed without touching the ink adhering portion.

  Further, since the plates 26 to 28 made of the metal material of the inkjet head 12 are maintained at the ground potential, charging of the ink ejected from the nozzle 35 can be suppressed.

  Next, modified examples in which various changes are made to the present embodiment will be described.

  In the above-described embodiment, when printing is performed in the printing unit 2, the potential V1 is always applied to the first rib 20a and the potential V2 is always applied to the second rib 20b. Absent. For example, the potentials of the ribs 20a and 20b may be changed during printing depending on the position in the transport direction of the recording paper P.

  At the time of printing, three positional relationships shown in FIG. 10 occur among the recording paper P, the transport roller 13 and the discharge roller 16. First, FIG. 10A shows a state (state A) when the recording paper P enters the printing area (area facing the ink ejection surface 12a). The recording paper P is sandwiched between the conveyance rollers 13 and is pressed down by the pressing surface 14a. At this time, the leading edge of the recording paper P is free. FIG. 10B shows a state (state B) when the recording paper P straddles the print area. The recording paper P is sandwiched between the transport roller 13 and the discharge roller 16 and is pressed down by the pressing surface 14 a and the corrugated spur 17. FIG. 10C shows a state (state C) immediately before the recording paper P exits the print area. The recording paper P is held between the discharge rollers 16 and pushed down by the corrugated spur 17. At this time, the trailing edge of the recording paper P is free.

  Therefore, for example, the potentials of the ribs 20a and 20b may be changed depending on which of the above states A to C the recording paper P is in. Specifically, in the state B, the recording paper P is pressed on both sides in the conveyance direction of the inkjet head 12, whereas in the states A and C, the recording paper P is on one side in the conveyance direction of the inkjet head 12. Can only be held down. Therefore, in the states A and C, the portion of the recording paper P that is not pressed up rises, and the height difference between the peak portion Pm and the valley portion Pv becomes larger than that in the state B.

  Therefore, in the first modification, as shown in FIG. 11, when the recording paper P is in the position in the state A, the potential of the first rib 20a is V1a and the potential of the second rib 20b is V2a (> V1a). And When the recording paper P is in the position where the state B is in the state B, the potential of the first rib 20a is set to V1b, and the potential of the second rib 20b is set to V2b (> V1b). In addition, when the recording paper P is in a position where the state C is set, the potential of the first rib 20a is set to V1c. At this time, the potentials V1a, V2a, V1b, V2b, V1c, and V2c are set to satisfy the relationship of (V2b−V1b) <(V2c−V1c) <(V2a−V1a).

  As described above, by changing the potential of the ribs 20a and 20b depending on the position in the transport direction of the recording paper P, the equipotential line R1 is parallel to the scanning direction regardless of the position in the transport direction of the recording paper P. Can be.

  In the first modification, the potentials of the ribs 20a and 20b are changed depending on which of the three states A to C the recording paper P is in. However, the present invention is not limited to this. For example, in the first modification, the state B is further distinguished based on whether or not the recording paper P is pressed by the corrugated spur 17, and further distinguished based on whether or not the recording paper is sandwiched between the conveyance rollers 13. Then, the potentials of the ribs 20a and 20b may be changed depending on which of the four or more recording papers P is in the state.

  In the above-described embodiment, the potential V1 is applied to the first rib 20a and the potential V2 is applied to the second rib 20b during printing regardless of the type of the recording paper P. The potentials of the ribs 20a and 20b may be changed depending on the type. For example, the higher the rigidity of the recording paper P, the smaller the difference in height between the peak portion Pm and the valley portion Pv. For this reason, as the rigidity of the recording paper P is higher, the potential may be applied to the ribs 20a and 20b so that the difference between the potential of the first rib 20a and the potential of the second rib 20b becomes smaller.

  In the above-described embodiment, the height of the upstream portion of the second rib 20b decreases toward the upstream side in the transport direction. However, the present invention is not limited to this. The height of the upstream portion of the second rib 20b may be constant.

  In the above-described embodiment, the height of the portion of the second rib 20b located on the downstream side in the transport direction from the first rib 20a is lower than the portion on the upstream side. I can't. The height of the portion of the second rib 20b located on the downstream side in the transport direction from the first rib 20a may be the same height as the portion on the upstream side.

  In the above-described embodiment, the second rib 20b extends to the downstream side in the transport direction from the first rib 20a. However, the present invention is not limited to this. In the transport direction, the position of the downstream end of the first rib 20a and the position of the downstream end of the second rib 20b may be the same. Alternatively, the first rib 20a may extend further downstream than the second rib 20b in the transport direction.

  Further, in the above-described embodiment, the ribs located at both ends in the scanning direction among the plurality of ribs 20a and 20b are the second ribs 20b having a low height, but are not limited thereto. Of the plurality of ribs 20a and 20b, the rib located at the end on at least one side in the scanning direction may be the first rib 20a having a high height.

  In the above-described embodiment, the platen 15 has a configuration in which the first rib 20 a is fitted in each slit 19 a of the base member 19 and the second rib 20 b is fitted in each slit 19 b of the base member 19. However, it is not limited to this. In the second modification, as shown in FIGS. 12A and 12B, the platen 71 includes a base member 72, a plurality of first ribs 73a (a “first support portion” of the present invention), and a plurality of first members. The two ribs 73b (the “second support portion” of the present invention) are integrally formed by resin molding or the like. A first electrode 74a (the “first conductive portion” in the present invention) is disposed on the upper surface of each first rib 73a. A second electrode 74b (the “second conductive portion” of the present invention) is disposed on the upper surface of each second rib 73b. The potential V1 is applied to the first electrode 74a, and the potential V2 is applied to the second electrode 74b. In FIG. 12A, illustration of equipotential lines and electric fields between the inkjet head 12 and the platen 71 is omitted.

  In the above-described embodiment, the valley bottom portion Pb of the recording paper P is supported by the second rib 20b having a low height. However, the present invention is not limited to this. In the third modification, as shown in FIGS. 13A and 13B, the second rib 20 b is not provided and the valley bottom portion Pb of the recording paper P is supported by the upper surface of the base member 19. Further, an electrode 81 (the “second conductive portion” of the present invention) extending in the transport direction is provided on a portion of the upper surface of the base member 19 that supports the valley bottom portion Pb of the recording paper P. It is applied to the potential V2. In this case, the portion of the base member 19 that supports the valley bottom portion Pb of the recording paper P corresponds to the second support portion of the present invention. In FIG. 13A, illustration of equipotential lines and electric fields between the inkjet head 12 and the platen 71 is omitted.

  In the above-described embodiment, the metal portion of the flow path unit 21 is maintained at the ground potential. However, the present invention is not limited to this. The metal portion of the flow path unit 21 may not be maintained at the ground potential.

  In the above-described embodiment, the ribs 20a and 20b are given a potential such that the equipotential lines between the inkjet head 12 and the platen 15 viewed from the transport direction are parallel to the scanning direction. It is not limited to. If the potential of the second rib 20b is higher than the potential of the first rib 20a, the potential difference between the first rib 20a and the second rib 20b may be slightly larger than the potential difference in the above-described embodiment, It may be small. In this case, the equipotential lines are wavy along the scanning direction. However, compared to the case where the potential of the first rib 20a and the potential of the second rib 20b are the same, the equipotential lines are flat, and the shift of the ink droplet landing position in the scanning direction can be suppressed. it can.

  In the above description, the ink jet printer is a so-called multi-function device. However, the present invention is not limited to this. The ink jet printer may perform only printing on the recording paper P. Furthermore, the present invention can be applied to a liquid ejecting apparatus that ejects liquid other than ink.

DESCRIPTION OF SYMBOLS 1 Inkjet printer 12 Inkjet head 13 Conveyance roller 14 Corrugated plate 15 Platen 17 Discharge roller 19 Base member 19a, 19b Slit 20a 1st rib 20b 2nd rib 26-28 Plate 58 Potential application circuit 71 Platen 72 Base member 73a 1st rib 73b Second rib 74a First electrode 74b Second electrode

Claims (9)

A liquid discharge head that discharges liquid toward the sheet while moving in the scanning direction with respect to the sheet;
A sheet conveying unit that conveys the sheet in a conveying direction intersecting the scanning direction with respect to the liquid ejection head;
A wave shape imparting unit that imparts a wave shape along the scanning direction to the sheet conveyed by the sheet conveying unit;
A first support portion disposed on the opposite side of the sheet from the liquid discharge head and corresponding to a crest portion of the corrugated sheet, and the first support portion corresponding to a trough portion of the sheet A sheet support including a plurality of support portions arranged in the scanning direction, including a second support portion having a lower height than the second support portion;
An electric field generator for generating an electric field between the liquid discharge head and the sheet support,
The electric field generator is
A first conductive portion provided on the first support portion;
A second conductive portion provided on the second support portion and located at a position lower than the first conductive portion;
A potential applying unit that applies a potential to each of the first conductive unit and the second conductive unit;
The liquid ejection device, wherein the potential applying unit applies a higher potential to the second conductive unit than the first conductive unit.   The potential applying unit applies different potentials to the first conductive unit and the second conductive unit so that equipotential lines between the liquid ejection head and the sheet are parallel to the scanning direction. The liquid ejection apparatus according to claim 1, wherein The sheet support has a plate-like base member made of an insulating material,
A plurality of slits are formed in the base member at intervals in the scanning direction,
The liquid ejecting apparatus according to claim 1 , wherein the plurality of support portions made of a conductive material are inserted through the plurality of slits of the base member.   The liquid ejecting apparatus according to claim 1, wherein among the plurality of support portions arranged in the scanning direction, the support portions positioned at both ends are the second support portions.   The liquid ejecting apparatus according to claim 1, wherein the second support part extends longer than the first support part on the downstream side in the transport direction.   The portion of the second support portion that extends further downstream in the transport direction than the first support portion is lower in height than the upstream portion. 5. The liquid ejection device according to 5. The wave shape imparting section is disposed on the upstream side in the transport direction from the second support section ,
The liquid ejecting apparatus according to claim 1, wherein the second support portion has a height that decreases toward an upstream side in the transport direction. The liquid discharge head includes a flow path member in which a liquid flow path is formed and at least a part is formed of a metal material,
The liquid ejecting apparatus according to claim 1, wherein the metal portion of the flow path member is maintained at a ground potential.   The potential applying unit changes a potential applied to the first conductive unit and the second conductive unit in accordance with a waveform applied to the sheet by the waveform applying unit. The liquid discharge apparatus in any one of -8.

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