JP5262215B2 - Inkjet recording device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet recording device capable of preventing ink from spreading on a recording medium. <P>SOLUTION: In accordance with each printing period, either of four ink amounts is allocated to each discharging port. When the amount of ink allocated to the discharging port is "medium" or "small", ink droplets having landing areas 231 and 241, respectively, are landed on the paper ((b) and (c)). When the amount of ink allocated to the discharging port is "large", three ink droplets having landing areas 221, 222 and 223 are successively landed on the paper (a). <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to an ink jet recording apparatus having an ink jet head provided with a plurality of ejection openings.

  Japanese Patent Application Laid-Open No. 2004-228561 describes a technique for continuously ejecting two or three ink droplets having the same amount of ink corresponding to the gradation value with respect to one pixel during main scanning. Has been. Since the landing areas of two or three ink droplets on the paper partially overlap, flat dots are formed on the paper.

JP 2004-034720 A (FIG. 6)

  According to the technique described in Patent Document 1, since a plurality of ink droplets having the same amount of ink land on the paper almost simultaneously, the ink tends to spread on the paper and the sharpness of the image edge is lost. .

  An object of the present invention is to provide an ink jet recording apparatus capable of making it difficult for ink to bleed on a recording medium.

An inkjet recording apparatus according to the present invention includes a transport mechanism that transports a recording medium, and a plurality of spacings in an orthogonal direction that is orthogonal to a transport direction of the recording medium by the transport mechanism being a predetermined interval corresponding to the print resolution in the orthogonal direction. An ink jet head provided with an ejection port, a storage means for storing image data, and a recording medium by the transport mechanism for a unit distance corresponding to the print resolution in the transport direction based on the image data stored in the storage means For each printing cycle, which is the time required for the ink to be transported, and an allocating unit that allocates an ink amount to each ejection port of the inkjet head, and the ink amount allocated by the allocating unit is less than a predetermined value, As an ink droplet, the amount of ink allocated by the allocation unit is ejected from the ejection port. The inkjet head is controlled to land on a recording medium, and when the amount of ink allocated by the allocation unit is equal to or greater than the predetermined value, ink is ejected from the ejection port to land second. And an ejection control unit that controls the inkjet head so that three ink droplets larger than the first and third ink droplets land on the recording medium sequentially along the transport direction. The ejection control means includes a first ink amount that is less than the predetermined value, a second ink amount that is less than the predetermined value and greater than the first ink amount, and a third ink that is greater than or equal to the predetermined value. Three discharge waveforms related to the amount are stored, and a pulse train signal obtained by amplifying the three discharge waveforms is supplied to the ink jet head according to the ink amount assigned by the assigning unit, and the first ink amount is related to the ink amount. The ejection waveform is a waveform including only one predetermined pulse for ejecting one or more ink droplets, and the ejection waveform related to the second ink amount includes a plurality of the ejection waveforms arranged via a first separation time. The ejection waveform related to the third ink amount is a waveform composed of a predetermined pulse, and the ejection waveform related to the third ink amount includes a pulse group composed of a plurality of the predetermined pulses arranged via the first separation time and the first separation time. A waveform composed of the predetermined pulse arranged before the pulse group through a wider second separation time and the predetermined pulse arranged after the pulse group through the second separation time; The first separation time is an interval at which a plurality of ink droplets ejected by the plurality of predetermined pulses are combined to form one ink droplet before or simultaneously with the landing on the recording medium. The two separation times include a single ink droplet ejected by the predetermined pulse disposed before and after the pulse group and a plurality of ink droplets ejected by the plurality of predetermined pulses included in the pulse group. The interval at which the recording medium is not merged before or simultaneously with the landing.

  When an ink droplet of a predetermined value or more is assigned, three ink droplets are ejected from the ejection port so that the second ink droplet that is landed is larger than the first and third landed ink droplets. The first ink droplet that lands is smaller than the ink droplet that lands second (small amount of ink), so the first ink droplet that lands on a small volume dries quickly with almost no bleeding on the recording medium. To do. In addition, the first ink droplet that lands quickly is prevented from spreading in the direction of the first ink droplet that lands on the recording medium. As a result, an image having a sharp edge with little blur is obtained. On the recording medium, the first and third landing ink droplets are smaller than the second landing ink droplet, and the second landing ink droplet is sandwiched between the ink droplets. The shape of the dots to be symmetric can be made symmetric, and the print image quality can be improved. In addition, since the flushing effect of the ink in the vicinity of the ejection port is obtained by the ejection operation of the first landing ink droplet, the ejection characteristics of the second and third landing ink droplets are excellent, and printing is performed. The image quality is improved. Further, since the landing areas of the three ink droplets are shifted from each other in the transport direction, it is possible to suppress the ink from penetrating deeply into the recording medium and causing cockling (blurring of the recording medium).

  The predetermined value is preferably a value having the diameter of the ink droplet as the predetermined interval when it is assumed that the ink ejected from the ejection port forms one ink droplet within the printing cycle. This further reduces ink bleeding on the recording medium.

  It is preferable that the total ink amount of the first to third landing ink droplets is equal to or larger than the ink amount allocated to the ejection port by the allocation unit. As a result, it is possible to suppress image quality deterioration due to a decrease in the ink amount.

  In addition, it is more preferable that the total ink amount of the first to third ink droplets to be landed is the same as the ink amount allocated to the ejection port by the allocation unit. As a result, it is possible to suppress deterioration of image quality due to a decrease in the amount of ink while further reducing ink bleeding on the recording medium.

  More preferably, the diameter of the first landed ink droplet is the same as the diameter of the third landed ink droplet. This further reduces ink bleeding on the recording medium.

  The landing area of the first landing ink droplet on the recording medium partially overlaps the landing area of the second landing ink droplet on the recording medium, and the recording medium of the second landing ink droplet It is preferable that the landing area of the ink partially overlaps the landing area of the third ink droplet landing on the recording medium. This further reduces ink bleeding on the recording medium without reducing the print density.

  When an ink droplet of a predetermined value or more is assigned, three ink droplets are ejected from the ejection port so that the second ink droplet that is landed is larger than the first and third landed ink droplets. The first ink droplet that lands is smaller than the ink droplet that lands second (small amount of ink), so the first ink droplet that lands on a small volume dries quickly with almost no bleeding on the recording medium. To do. In addition, the first ink droplet that lands quickly is prevented from spreading in the direction of the first ink droplet that lands on the recording medium. As a result, an image having a sharp edge with little blur is obtained. On the recording medium, the first and third landing ink droplets are smaller than the second landing ink droplet, and the second landing ink droplet is sandwiched between the ink droplets. The shape of the dots to be symmetric can be made symmetric, and the print image quality can be improved. In addition, since the flushing effect of the ink in the vicinity of the ejection port is obtained by the ejection operation of the first landing ink droplet, the ejection characteristics of the second and third landing ink droplets are excellent, and printing is performed. The image quality is improved. Further, since the landing areas of the three ink droplets are shifted from each other in the transport direction, it is possible to suppress the ink from penetrating deeply into the recording medium and causing cockling (blurring of the recording medium).

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

  FIG. 1 shows an ink jet printer 1 which is an ink jet recording apparatus according to the present embodiment. This inkjet printer 1 has four inkjet heads 12K, 12M, 12C, and 12Y having the same structure. The four inkjet heads 12K, 12M, 12C, and 12Y respectively eject four different colored inks (black, magenta, cyan, and yellow).

  The ink jet printer 1 has a paper feed tray 21 on the left side in the figure and a paper discharge tray 22 on the right side in the figure. Inside the ink jet printer 1, a conveyance path is formed through which the paper P as a recording medium is conveyed from the paper feed tray 21 toward the paper discharge tray 22. A pair of feed rollers 25 a and 25 b that convey the paper while pinching it are arranged immediately downstream of the paper feed tray 21. The pair of feed rollers 25a and 25b feed the paper P from the paper feed tray 21 to the right in the drawing. The feed roller 25a is rotationally driven by a motor 36 (see FIG. 7).

  In an intermediate portion of the conveyance path, two belt rollers 26 and 27, an endless conveyance belt 28 wound around the rollers 26 and 27, and a region surrounded by the conveyance belt 28 There is provided a belt conveyance mechanism 23 including a platen 29 disposed at a position facing the four inkjet heads 12K, 12M, 12C, and 12Y with the conveyance belt 28 interposed therebetween. The platen 29 supports the conveyance belt 28 so that the conveyance belt 28 does not bend downward in a region facing the four inkjet heads 12K, 12M, 12C, and 12Y.

  A nip roller 24 is disposed on the belt roller 27. The nip roller 24 presses the paper P fed from the paper feed tray 21 by the feed rollers 25 a and 25 b against the outer peripheral surface of the transport belt 28. A weak adhesive silicon resin layer is formed on the outer peripheral surface.

  When the motor 35 (see FIG. 7) rotates the belt roller 26 as a driving roller, the transport belt 28 rotates. As a result, the transport belt 28 transports the paper P pressed against the outer peripheral surface by the nip roller 24 toward the paper discharge tray 22 while being adhesively held. A peeling plate 30 is provided immediately downstream of the conveying belt 28 along the conveying path. The peeling plate 30 peels the paper P adhered to the outer peripheral surface of the conveyance belt 28 from the outer peripheral surface.

  The four inkjet heads 12K, 12M, 12C, and 12Y are arranged along the transport direction of the paper P, and are fixed at positions facing the platen 29. That is, the ink jet printer 1 is a line printer. The four inkjet heads 12K, 12M, 12C, and 12Y have a rectangular parallelepiped shape that is long in the direction orthogonal to the paper surface of FIG. 1, that is, in the main scanning direction. The bottom surface of each inkjet head is an ejection surface that is opposed to the upper conveyance surface 28a of the outer circumferential surface of the conveyance belt 28 and that has a plurality of ejection ports 108 (see FIG. 5).

  As will be described later, in each head, the plurality of ejection ports 108 are two-dimensionally arranged. The pitch of the ejection ports 108 in the main scanning direction on the ejection surface is an interval corresponding to the printing resolution in the main scanning direction (600 dpi in the present embodiment). Each of the four inkjet heads 12K, 12M, 12C, and 12Y is provided with four actuator units 121 (see FIG. 3) including a plurality of actuators. The plurality of actuators have a one-to-one correspondence with the plurality of ejection ports, and ink is ejected from the ejection ports corresponding to the actuators activated in each printing cycle. Which actuator is activated in each printing cycle depends on drive data supplied to the head. Here, the printing cycle means the time required for the paper P to be conveyed by a unit distance corresponding to the printing resolution in the sub-scanning direction.

  When the paper P transported by the transport belt 28 sequentially passes under the four heads, ink droplets of each color are directed from the plurality of ejection openings formed on the ejection surface toward the upper surface of the paper P, that is, the printing surface. Discharged. A color image of a desired pattern is formed on the paper P with colored ink ejected from the four inkjet heads 12K, 12M, 12C, and 12Y.

  A paper sensor 31 that is a reflective optical sensor is disposed between the inkjet head 12K located at the most upstream of the four heads and the nip roller 24. The paper sensor 31 outputs a detection signal when the leading edge of the paper transported along the transport path reaches directly below the paper sensor 31.

  Next, the inkjet head 12K will be described in detail with reference to FIG. The remaining three inkjet heads 12M, 12C, and 12Y have the same structure as the inkjet head 12K. As shown in FIG. 2, the inkjet head 12K includes a head body 2 including a flow path unit 9 and an actuator unit 121, a reservoir unit 71 that is disposed on the upper surface of the head body 2, and supplies ink to the head body 2. A COF (Chip On Film) 50, which is a flat flexible substrate on which a driver IC 52 for generating a pulse train signal (see FIGS. 8A to 8C) that is a drive signal for driving the actuator unit 121 is mounted. , The side cover 53 and the head cover 55 for covering the control unit 54 electrically connected to the COF 50, the actuator unit 121, the reservoir unit 71, the COF 50, and the control board 54 and preventing ink mist from entering from the outside. have.

  The reservoir unit 71 is formed by stacking four plates 91 to 94, and an ink inflow channel, an ink reservoir 61, and ten ink outflow channels 62 (not shown) communicate with each other. Is formed. In FIG. 2, only one ink outflow channel 62 appears. The ink stored in the ink reservoir 61 passes through the ink outflow channel 62 and is supplied to the channel unit 9 via the ink supply port 105b (see FIG. 3). Further, the plate 94 is formed with a plurality of convex portions 94 a including the ink outflow channel 62. Since a plurality of convex portions 94 a are formed on the plate 94, a gap is provided between the plate 94 and the flow path unit 9. In this gap, four actuator units 121 are arranged (in FIG. 2, only one of the four actuators is shown).

  In the COF 50, a plurality of wirings (not shown) are formed. One end of these wirings is electrically connected to an individual electrode 135 and a common electrode 134, which will be described later, at a joint surface that is the upper surface of the actuator unit 121. The COF 50 extends upward between the side cover 53 and the reservoir unit 71. The other end of the wiring formed in the COF 50 is connected to an electrical component on the control board 54 via a connector 54a. The control board 54 outputs a control signal from a host control device (not shown) to the driver IC 52.

  The control board 54 controls driving of the actuator unit 121 via the driver IC 52. The driver IC 52 generates a drive signal that drives the actuator unit 121.

  Next, the head body 2 will be described. As shown in FIG. 3, the head body 2 includes a flow path unit 9 and four actuator units 121 fixed to the upper surface 9 a of the flow path unit 9.

  The flow path unit 9 has a rectangular parallelepiped shape that has substantially the same planar shape as the plate 94 of the reservoir unit 71. A total of ten ink supply ports 105 b are opened on the upper surface 9 a of the flow path unit 9 corresponding to the ink outflow flow paths 62 of the reservoir unit 71. As shown in FIGS. 3 and 4, 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 inside the channel unit 9. Has been. In FIG. 4, 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. 4 and 5, a discharge surface 2 a in which a plurality of discharge ports 108 are arranged in a matrix is formed on the lower surface of the flow path unit 9. A plurality of pressure chambers 110 are also arranged in a matrix on the fixed surface of the actuator unit 121 in the flow path unit 9, similar to the discharge ports 108.

  In the present embodiment, 16 rows of the pressure chambers 110 along the longitudinal direction of the flow path unit 9 are arranged in parallel with each other in the width direction with respect to one actuator unit 121 at 16 rows. For one actuator unit 121, the number of pressure chambers 110 included in each pressure chamber row gradually decreases from the long side toward the short side corresponding to the external shape (trapezoidal shape) of the actuator unit 121. Has been placed. The discharge ports 108 are also arranged in the same manner.

  As shown in FIG. 5, the flow path unit 9 includes a cavity plate 122, a base plate 123, an aperture plate 124, a supply plate 125, manifold plates 126, 127, and 128, a cover plate 129, and a nozzle plate 130 in order from the top. It consists of nine metal 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 9 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 9 will be described. The ink supplied from the reservoir unit 71 into the flow path unit 9 via the ink supply port 105b is branched from the manifold flow path 105 to 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. 3, 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 9, and the oblique sides of the adjacent actuator units 121 overlap each other in the main scanning direction of the flow path unit 9.

  As shown in FIG. 6A, the actuator unit 121 includes 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 surface of the uppermost piezoelectric layer 141 (joint surface of the actuator unit 121). A common electrode 134 formed on the entire surface of the sheet is interposed between the uppermost piezoelectric layer 141 and the lower piezoelectric layer 142.

  As shown in FIG. 6B, 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 any one of the plurality of terminals of the driver IC 52 via the individual lands 136 and the internal wiring of the COF 50. Therefore, the driver IC 52 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 (see FIGS. 8A to 8C) is output from the driver IC 52. 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 wave of the positive pressure that has been phase-inverted and returned from the outlet of the sub-manifold flow path 105a due to reflection and the positive pressure newly applied from the actuator unit 121 are superimposed in the pressure chamber 110, so that the pressure A large pressure can be applied to the ink in the chamber 110.

  Returning to FIG. 1, the inkjet printer 1 includes a control unit 32. The control unit 32 controls the operation of each unit of the inkjet printer 1. The control unit 32 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 the hardware in the control unit 32 cooperate, the control unit 32 includes a storage unit 41, an allocation unit 42, a transport control unit 44, and a discharge unit, as shown in FIG. The functional part of the control part 45 is constructed. In the present embodiment, it is assumed that the control unit 32 includes both the electronic components on the control board 54 and the driver IC 52.

  The storage unit 41 stores image data (for example, bitmap format, jpeg format) indicating a color image to be printed on the paper P by four inkjet heads 12K, 12M, 12C, and 12Y sent from a host computer (not shown). To do.

  The allocating unit 42 allocates ink amounts to the respective ejection openings 108 of the four inkjet heads 12K, 12M, 12C, and 12Y for each printing cycle based on the image data stored in the storage unit 41. Here, “assigning an ink amount to the ejection port 108” is synonymous with assigning an ink amount to the pressure chamber 110 and the individual electrode 135 corresponding to the ejection port 108. In the present embodiment, the amount of ink allocated by the allocation unit 42 is any one of four types: “large” (16 pl), “medium” (8 pl), “small” (4 pl), and none (0 pl). . Then, (“large” ink amount) = (“medium” ink amount) + (“small” ink amount × 2). Information on the allocated ink amount is applied to the individual electrode 135 as a drive pulse from the driver IC 52. By applying a drive pulse (pulse train signal) to the individual electrode 135, the actuator undergoes unimorph deformation so that a predetermined amount of ink droplets are ejected. The allocation unit 42 may be built in the host computer. In this case, the ink jet recording apparatus of the present invention corresponds to an apparatus including the host computer and the ink jet printer 1.

  The conveyance control unit 44 controls a motor 35 that is a drive source of the belt roller 26 and a motor 36 that is a drive source of the feed roller 25a.

  The discharge control unit 45 is synchronized with the control of the motor 35 by the conveyance control unit 44, and the detection signal of the leading edge of the paper P from the paper sensor 31, the determination result in the determination unit 43, and the storage unit 41 Based on the image data, the four inkjet heads 12K, 12M, 12C, and 12Y are controlled. Then, a desired color image is formed on the paper P using colored ink.

  In the present embodiment, when the ink amount allocated by the allocating unit 42 is less than a predetermined value, the ejection control unit 45 ejects ink of the ink amount allocated by the allocating unit 42 from the ejection port 108. Each inkjet head is controlled to land on the paper P as one ink droplet. In this case, only one ink droplet having the allocated ink amount may be ejected from the ejection port, and one ink droplet may land on the paper P as it is, or the total ink amount becomes the allocated ink amount. A plurality of ink droplets may be ejected from the ejection port, and one ink droplet formed by combining them before or at the time of landing may land on the paper P.

  In the present embodiment, the predetermined value means that the diameter of the ink droplet is printed in the main scanning direction when it is assumed that the ink ejected from one ejection port 108 in the printing cycle forms one ink droplet. This is a value corresponding to the distance (42 μm) corresponding to the resolution (600 dpi). The diameter of the ink droplet is calculated assuming that the ink droplet is a sphere. In the present embodiment, the predetermined value is an amount smaller than “large” (16 pl) and larger than “medium” (8 pl). Therefore, the case where the allocated ink amount is less than the predetermined value means that the allocated ink amount is one of “medium”, “small”, and none.

  Then, when the ink amount allocated by the allocating unit 42 is equal to or greater than the predetermined value (that is, the ink amount “large”), the ejection control unit 45 ejects ink from the ejection port 108, thereby Each ink jet head is controlled such that three ink droplets that are larger than the first and third ink droplets land on the paper P sequentially in the transport direction. In this case, only three ink droplets having the allocated ink amount may be ejected from the ejection port, and the three ink droplets may land on the paper P as they are, or the total ink amount becomes the allocated ink amount. Four or more ink droplets may be ejected from the ejection port, and three ink droplets formed by combining them before landing or at the same time may land on the paper P.

  Here, the ejection control unit 45 performs control so that the total ink amount of the first to third ink droplets is the same as the ink amount allocated to the ejection port 108 by the allocation unit 42. In addition, the ejection control unit 45 performs control so that the diameter of the ink droplet that lands first is the same as the diameter of the ink droplet that lands third. Further, the ejection control unit 45 partially overlaps the landing area 221 of the first ink droplet landing on the paper P with the landing area 222 of the second ink droplet landing on the paper P, and landed second. Control is performed so that the landing area 222 of the ink droplets on the paper P partially overlaps the landing area 223 of the ink droplets that land on the paper P (see FIG. 9A).

  Specifically, when the assigned ink amount is equal to or greater than the predetermined value, the ejection control unit 45 causes both the first and third ink droplets to land to be “small” and land second. The control is performed so that the ink droplet becomes the “medium” amount of ink. The discharge control unit 45 stores three types of discharge waveforms as shown in FIGS. The ejection control unit 45 outputs a pulse train signal obtained by amplifying any ejection waveform corresponding to the drive data to a predetermined positive potential to each individual electrode 135 for each printing cycle.

  FIG. 8A shows an ejection waveform 201 when the allocated ink amount is “large”. The ejection waveform 201 includes four pulses having a width equal to AL. The first pulse ejects one ink drop of “small” ink quantity, and the second and third pulses eject one ink drop of “medium” ink quantity (each pulse produces one or more ink drops). In the fourth pulse, one ink droplet having a small ink amount is ejected. As in the first pulse and the fourth pulse, one ink droplet having an ink amount “small” is ejected. Only one ink droplet having an ink amount “small” is ejected from an ejection port, and one ink droplet is ejected as it is. When ink droplets land and when a plurality of ink droplets are ejected, one ink droplet of “small” ink amount formed by combining the plurality of ink droplets before landing or at the same time of landing landed on the paper P Means either. Which of these two cases is used depends on the characteristics of the ink, the flow path configuration of the head, and the like.

  The second and third pulses are separated by a time equal to AL. Thus, one or more ink droplets are ejected for each pulse, and the plurality of ink droplets are combined before landing or simultaneously with landing to form one ink droplet of “medium” ink amount. In contrast, the separation time between the first pulse and the second pulse and the separation time between the third pulse and the fourth pulse are considerably longer than AL. As a result, the first ink droplet that lands on the ink amount “small” and the second ink droplet that lands on the medium amount “middle” do not merge before landing or at the same time as the landing, and each landed area. 221 and 222 (see FIG. 9A) partially overlap each other, and the ink droplet that lands on the second ink amount “medium” and the ink droplet that lands on the third ink amount “small”. The landing areas 222 and 223 (see FIG. 9A) are partially overlapped with each other before landing or simultaneously with landing.

  FIG. 9A illustrates a case where a plurality of ink droplets ejected corresponding to the ejection waveform 201 from the three ejection ports 108 adjacent in the main scanning direction are landed when the allocated ink amount is “large”. FIG. 6 is a schematic diagram depicting a state and spreading of ink on paper P. In FIG. 9A, reference numeral 221 indicates the landing area of the first ink droplet that lands (corresponding to the size of the ink droplet at the time of landing that does not consider the spreading of the ink on the paper P). Reference numeral 222 indicates the landing area of the ink droplet that lands second, and reference numeral 223 indicates the landing area of the ink droplet that lands third. Landing areas adjacent in the main scanning direction are separated from each other by a distance corresponding to the printing resolution in the main scanning direction. The landed ink spreads on the paper P in a range indicated by reference numeral 226. This range is formed by connecting the landing areas 222 adjacent to each other in the main scanning direction.

  As shown in FIG. 9A, when the allocated ink amount is “large”, the landing area of the second ink droplet is larger than that of the first and third ink droplets. This means that the ink droplet itself is larger than the first and third landed ink droplets. In the present embodiment, the first ink droplet that lands first is smaller than the ink droplet that lands second (the amount of ink is small). Dry quickly without bleeding. In addition, the first ink droplet that lands on the paper P is prevented from spreading the second and third landed ink droplets. Furthermore, the third ink drop is not as sharp as the first ink drop due to the drying effect of the part that does not overlap with the second ink drop, but the image has a sharp edge shape. Contributes to forming. As a result, an image having a sharp edge with little blur is obtained.

  On the paper P, the first and third landed ink droplets smaller than the second landed ink droplet sandwich the second landed ink droplet, so the dots formed by the three ink droplets Can be made symmetrical, and the printing image quality can be improved.

  In addition, since the flushing effect of the ink in the vicinity of the ejection port is obtained by the ejection operation of the first landing ink droplet, the ejection characteristics of the second and third landing ink droplets are excellent, and printing is performed. The image quality is improved.

  In addition, since the landing areas 221, 222, and 223 of the three ink droplets are shifted from each other in the transport direction, it is possible to suppress ink from penetrating deeply into the paper P and causing cockling (bluring of the paper P).

  FIG. 8B shows an ejection waveform 202 when the allocated ink amount is “medium”. The ejection waveform 202 includes two pulses having a width equal to AL (each ejecting one or more ink droplets). These two pulses cause one ink droplet of “medium” ink amount to be ejected. These two pulses are separated by a time equal to AL. Thus, one or more ink droplets are ejected for each pulse, and the plurality of ink droplets are combined before landing or simultaneously with landing to form one ink droplet of “medium” ink amount.

  FIG. 9B illustrates a case where three ink droplets ejected corresponding to the ejection waveform 202 from the three ejection ports 108 adjacent in the main scanning direction are landed when the allocated ink amount is “medium”. FIG. 6 is a schematic diagram depicting a state and spreading of ink on paper P. In FIG. 9B, reference numeral 231 indicates a landing area of one ink droplet having a medium amount of ink to be landed, which is the same size as the landing area indicated by reference numeral 222. The landed ink spreads on the paper P in a range indicated by reference numeral 236. This range is formed by connecting the landing areas 231 adjacent to each other in the main scanning direction.

  FIG. 8C shows an ejection waveform 203 when the allocated ink amount is “small”. The ejection waveform 203 includes one pulse whose width is equal to AL. This pulse ejects one ink droplet having the ink amount “small” (meaning the same as described in the first pulse when the ink amount is “large”).

  FIG. 9C shows a case where three ink droplets ejected corresponding to the ejection waveform 203 from the three ejection ports 108 adjacent in the main scanning direction when the assigned ink amount is “small”. FIG. 6 is a schematic diagram depicting a state and spreading of ink on paper P. In FIG. 9C, reference numeral 241 indicates a landing area of one ink droplet having a landing ink amount “small”, which is the same size as the landing areas indicated by reference numerals 221 and 223. The landed ink spreads on the paper P in a range indicated by reference numeral 246 (separated from each other in the main scanning direction).

  Next, the printing operation of the inkjet printer 1 according to the present embodiment will be described with reference to the flowchart of FIG. In step S1, the control unit 32 repeatedly determines whether a print command from the host has been received. When a print command is received (S1: YES), the print command received in step S2 is stored in the storage unit 41. The print command includes image data to be printed, the number of prints, layout information, and the like.

  In step S <b> 3, the conveyance control unit 44 starts the rotation of the motor 36. As a result, the feed roller 25a rotates and the conveyance of the paper P starts.

  Subsequently, in step S4, the allocating unit 42 applies the above-described four types to the respective ejection ports of the four inkjet heads 12K, 12M, 12C, and 12Y based on the image data stored in the storage unit 41 for one printing cycle. Assign one of the ink amounts. In the first printing cycle in which ink is ejected from the inkjet head 12K only after the leading edge of the paper P reaches the lower side of the inkjet head 12K, the ink amount is assigned only to the most upstream ejection port array in the inkjet head 12K.

  In step S <b> 5, the control unit 32 determines whether or not the next ink ejection is the second or later printing cycle. If it is the first printing cycle (S5: NO), the process proceeds to step S6. In step S <b> 6, the control unit 32 repeatedly determines whether or not the detection signal for the leading edge of the paper P output from the paper sensor 31 has been received. When the detection signal is received (S6: YES), the process proceeds to step S7 and waits until a predetermined time elapses. This predetermined time is equal to the quotient obtained by dividing the distance along the transport direction from the paper sensor 31 to the inkjet head 12K by the transport speed of the paper P by the transport belt 28.

  If it is determined in step S5 that the print cycle is the second or later (S5: YES), the process proceeds to step S8 and waits until one print cycle has elapsed since the previous ink ejection operation. Then, the process proceeds to step S9 as soon as one printing cycle elapses.

  In step S9, based on the control of the ejection control unit 45, ink ejection for one printing cycle is performed from the four inkjet heads 12K, 12M, 12C, and 12Y. After completion of step S9, the process proceeds to step S10. In step S10, the control unit 32 determines whether or not ink ejection has been completed for all lines in the main scanning direction where printing is to be performed. When the non-ejection line remains (S10: NO), the process returns to step S4, and the ink amount for ink ejection in the next printing cycle is assigned. If no undischarged line remains (S10: YES), the printing process is terminated.

  According to the present embodiment described above, when the allocated ink amount is “large”, the ink droplet that lands first, which has a small volume, dries quickly on the paper P with almost no bleeding. In addition, the first ink droplet that lands on the paper P is prevented from spreading the second and third landed ink droplets. As a result, an image having a sharp edge with little blur is obtained. In addition, the shape of the dots formed by the three ink droplets can be made symmetric, and the print image quality can be improved. In addition, since the flushing effect of the ink in the vicinity of the ejection port is obtained by the ejection operation of the first landing ink droplet, the ejection characteristics of the second and third landing ink droplets are excellent, and printing is performed. The image quality is improved. In addition, cockling can be suppressed.

  Further, when it is assumed that the predetermined value of the assigned ink amount, which is a control threshold value in the ejection control unit 45, is that ink ejected from the ejection port 108 within one printing cycle forms one ink droplet. Since the diameter of the ink droplet is a value that is the pitch of the ejection ports 108 in the main scanning direction, the ink bleeding on the paper P is further reduced.

  When the allocated ink amount is “large”, the total ink amount of the first to third ink droplets to be landed is the same as the ink amount allocated to the ejection port by the allocating unit 42. In addition, it is possible to suppress deterioration of image quality due to a decrease in the amount of ink while further reducing ink bleeding. Even if the total ink amount of the first to third ink droplets is equal to or larger than the ink amount assigned to the ejection port by the assigning unit 42, the effect of suppressing ink bleeding on the paper P is slightly reduced. Image quality deterioration due to a decrease in the ink amount can be suppressed.

  In addition, since the diameter of the ink droplet that lands first is the same as the diameter of the ink droplet that lands third, the ink bleeding on the paper P is further reduced.

  Further, the landing area of the first ink droplet landing on the paper P partially overlaps the landing area of the second ink droplet landing on the paper P, and the second landing ink droplet on the paper P. The ink landing area partially overlaps the landing area of the third ink droplet landing on the paper P, so that the ink bleeding on the paper P is further reduced without lowering the print density.

  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 amount of ink allocated by the allocation unit 42 is four types, but this may be three types or five or more types. Further, the predetermined value of the allocated ink amount, which is a control threshold value in the discharge control unit 45, sets the diameter of the ink droplet to a value different from the predetermined interval that is the pitch in the main scanning direction of the plurality of discharge ports. It may be a thing. This predetermined value may be variable according to the operation by the user. In this case, the user can change the predetermined value depending on, for example, the type of paper to be used.

  The total ink amount of the first to third ink droplets may be less than the ink amount assigned to the ejection port by the assigning unit. Further, the diameter of the ink droplet that lands first may be different from the diameter of the ink droplet that lands third. Furthermore, the first and second ink droplets do not need to overlap, and the second and third ink droplets do not need to overlap. .

  Furthermore, if the allocated amount of ink droplets is greater than or equal to a predetermined value within one printing cycle, three ink droplets land on the paper P sequentially. On the other hand, when the allocated amount is less than the predetermined value, one dot is formed by one ink droplet. However, when this allocated amount is less than a predetermined value, the same drive pulse as when the allocated amount is equal to or larger than the predetermined value may be applied. In this case, from the viewpoint of preventing the ink from thickening at the discharge outlet to be discharged and forming dots of a predetermined size with certainty, the drive pulses corresponding to the first and third landing ink droplets are actually A pulse that does not cause ink ejection may be used, and a pulse that actually ejects only the second ink droplet may be used. The meniscus near the ejection port vibrates by the first pulse, and the ink near the ejection port is agitated. In this case, from the viewpoint that unnecessary residual vibration is not left in the ink at the ejection port, a driving pulse having no third pulse may be used.

  In addition, the structure of the head is not limited to that described with reference to FIGS. 2 to 6, and any head may be used.

1 is a side view of an ink jet printer which is an ink jet recording apparatus according to an embodiment of the present invention. FIG. 2 is a longitudinal sectional view of the inkjet head depicted in FIG. 1. FIG. 2 is a plan view of the ink jet head 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 VV line | wire of FIG. It is the fragmentary sectional view and fragmentary top view of the actuator unit which are included in the ink jet head. It is a functional block diagram of the inkjet printer shown in FIG. FIG. 8 is a schematic diagram of three types of discharge waveforms stored in the discharge control unit shown in FIG. 7. FIG. 9 is a schematic diagram depicting the appearance of ejected ink droplets and the spread of ink on paper P for each of the three types of ejection waveforms shown in FIG. 8. 2 is a flowchart showing a printing operation of the ink jet printer shown in FIG. 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inkjet printer 12K, 12M, 12C, 12Y Inkjet head 23 Belt conveyance mechanism 25a, 25b Feed roller 28 Conveyor belt 31 Paper sensor 32 Control part 41 Storage part 42 Assignment part 44 Conveyance control part 45 Discharge control part 108 Discharge port 110 Pressure chamber 135 Individual electrode 221, 222, 223 Landing area 226, 236, 246 Range where landed ink spreads on paper P 231 Landing area 241 Landing area

Claims (6)

A transport mechanism for transporting the recording medium;
An inkjet head provided with a plurality of ejection openings whose interval in the orthogonal direction orthogonal to the conveyance direction of the recording medium by the conveyance mechanism is a predetermined interval corresponding to the print resolution in the orthogonal direction;
Storage means for storing image data;
Based on the image data stored in the storage means, for each printing cycle, which is the time required for the recording medium to be conveyed by the conveyance mechanism by a unit distance corresponding to the printing resolution in the conveyance direction, An assigning means for assigning an ink amount to each ejection port;
When the ink amount allocated by the allocating unit is less than a predetermined value, the ink amount allocated by the allocating unit is landed on the recording medium as one ink droplet ejected from the ejection port. When the ink amount assigned by the assigning unit is equal to or greater than the predetermined value by controlling the ink-jet head, the ink droplets ejected from the ejection ports cause the first and third ink droplets to land. Discharge control means for controlling the inkjet head so that three ink droplets larger than the ink droplets that land on the recording medium sequentially land on the recording medium along the transport direction ;
The ejection control means sets a first ink amount that is less than the predetermined value, a second ink amount that is less than the predetermined value and greater than the first ink amount, and a third ink amount that is greater than or equal to the predetermined value. The three ejection waveforms are stored, and a pulse train signal obtained by amplifying the three ejection waveforms is supplied to the inkjet head according to the ink amount allocated by the allocation unit,
The ejection waveform relating to the first ink amount is a waveform including only one predetermined pulse for ejecting one or more ink droplets;
The ejection waveform relating to the second ink amount is a waveform composed of a plurality of the predetermined pulses arranged via a first separation time,
The ejection waveform relating to the third ink amount includes the pulse group composed of a plurality of the predetermined pulses arranged via the first separation time and the second separation time wider than the first separation time. A waveform composed of the predetermined pulse arranged before the pulse group and the predetermined pulse arranged after the pulse group via the second separation time;
The first separation time is an interval at which a plurality of ink droplets ejected by the plurality of predetermined pulses are combined to form one ink droplet before or simultaneously with the landing on the recording medium. The two separation times include a single ink droplet ejected by the predetermined pulse disposed before and after the pulse group and a plurality of ink droplets ejected by the plurality of predetermined pulses included in the pulse group. An ink jet recording apparatus having an interval at which the recording medium does not merge before landing on the recording medium or at the same time as landing .   The predetermined value is a value having a diameter of the ink droplet as the predetermined interval when it is assumed that the ink ejected from the ejection port forms one ink droplet within the printing cycle. The ink jet recording apparatus according to claim 1.   3. The ink jet recording apparatus according to claim 1, wherein a total ink amount of the first to third ink droplets is equal to or larger than an ink amount assigned to the ejection port by the assigning unit.   4. The ink jet recording apparatus according to claim 3, wherein the total ink amount of the first to third ink droplets is the same as the ink amount assigned to the ejection port by the assigning unit.   5. The ink jet recording apparatus according to claim 1, wherein a diameter of the first ink droplet that is landed is the same as a diameter of the third ink droplet that is landed.   The landing area of the first landing ink droplet on the recording medium partially overlaps the landing area of the second landing ink droplet on the recording medium, and the recording medium of the second landing ink droplet 6. The ink jet recording apparatus according to claim 1, wherein a landing area of the ink droplet partially overlaps a landing area of the third ink droplet landed on the recording medium.

Images