JP2009241444A - Liquid droplet ejecting apparatus and image forming method - Google Patents

Abstract

A liquid capable of suppressing the occurrence of density unevenness in the sub-scanning direction of a formed image caused by tilting of the head posture when the matrix type recording head moves in the main scanning direction without complicating the configuration. A droplet discharge device and an image forming method are obtained.
A nozzle group in which nozzles are arranged at a predetermined angle with respect to the main scanning direction has nozzles adjacent to the sub-scanning direction having substantially the same interval in the sub-scanning direction and nozzles belonging to each nozzle group. The recording head 50 arranged in the sub-scanning direction forms dots on the recording paper 14 so that the positions in the sub-scanning direction are substantially the same, and the carriage belt 54 mainly moves the recording head 50 in the forward movement and the backward movement. The belt 32 is reciprocated in the main scanning direction while being tilted in the opposite direction with respect to the axis orthogonal to the scanning direction, and the belt 32 moves in the dot forming area with respect to the sub-scanning direction between the forward movement and the backward movement of the recording head 50. The recording paper 14 is conveyed by a distance obtained by multiplying the width by a predetermined integer less than the number of nozzle groups.
[Selection] Figure 2

Description

  The present invention relates to a droplet discharge device that discharges droplets from nozzles while reciprocating a recording head having a plurality of nozzles, and an image forming method using the recording head.

  In recent years, a recording head that forms dots forming an image on each recording medium by ejecting each droplet is reciprocated in the main scanning direction to eject the droplets, and at least one of the recording head and the recording medium is Liquid droplet ejection apparatuses that form images by moving relatively in the sub-scanning direction orthogonal to the main scanning direction have become widespread.

  On the other hand, as a recording head, a recording head (matrix type recording head) in which a plurality of nozzles are two-dimensionally arranged in order to arrange a large number of nozzles at a high density within a limited nozzle surface area is well known. In image formation using a matrix type recording head, it is possible to discharge liquid droplets with a high-density array of nozzles, so that high speed and high image quality can be realized. For example, in the case of image formation using a high-density, multi-nozzle matrix type recording head as shown in FIG. Image quality can be improved.

  On the other hand, however, the liquid droplet ejection apparatus using the matrix type recording head has a problem that uneven density in the sub-scanning direction is likely to occur in the formed image.

  In order to solve this problem, Japanese Patent Application Laid-Open No. H10-228667 discloses a spatial frequency of density unevenness in the sub-scanning direction by mixing dots having a large diameter and dots having a small diameter and forming these dots at regular intervals. A technique for increasing the density and reducing the visibility of density unevenness is disclosed.

  Japanese Patent Application Laid-Open No. 2004-228688 discloses a nozzle in which the recording head is composed of a nozzle row having an angle φ with respect to the main scanning direction and a nozzle row having an angle −φ with respect to the main scanning direction and intersecting the nozzle row. Occurs in an image that is formed by arranging each nozzle in an X shape so that adjacent nozzles belong to different nozzle rows when the nozzle group is projected so as to be aligned in the main scanning direction. A technique for reducing the visibility of uneven density is disclosed.

Further, in Patent Document 3, in a recording head having a plurality of nozzles arranged in a staggered manner along the sub-scanning direction, adjacent recording heads formed by the same nozzles in the forward and backward paths in the main scanning direction. A technique for preventing a stripe pattern generated in the sub-scanning direction by recording an image with two rasters as one unit is disclosed.
JP 2004-90504 A JP 2007-29786 A JP 2002-103579 A

  However, in the technique disclosed in Patent Document 1, a plurality of nozzle groups in which a plurality of nozzles are arranged on a straight line inclined at a predetermined angle with respect to the moving direction includes sub-scans of nozzles adjacent in the sub-scanning direction. In the recording heads arranged in the sub-scanning direction so that the intervals with respect to the direction are substantially the same and the positions of the nozzles belonging to each nozzle group in the sub-scanning direction are substantially the same, By tilting due to the inertial force accompanying movement, the density of dots formed by adjacent nozzles between nozzle groups adjacent in the sub-scanning direction differs from the density of dots formed by nozzles belonging to each nozzle group Thus, there is a problem that density unevenness in the sub-scanning direction that occurs can not be suppressed. In addition, the technique disclosed in Patent Document 2 has a problem in that the arrangement of nozzles is complicated, and restrictions such as the design of a flow path for supplying ink liquid to the nozzles increase. Furthermore, the technique disclosed in Patent Document 3 has a problem in that it may not be applicable to a recording head having a high nozzle array density.

  In addition, image formation using a matrix type recording head has a problem that density unevenness in the sub-scanning direction is likely to occur due to a deviation of the head posture. For example, as shown in FIG. 3, if the matrix type recording head is mounted accurately at a predetermined angle with respect to the main scanning direction, the adjacent dot intervals in the sub-scanning direction are all arranged at equal intervals. When even a slight angle error occurs, a difference occurs between the sub-scanning direction adjacent dot interval a in the nozzle array and the sub-scanning direction adjacent dot interval b of the folded portion of the nozzle array, and the density is high at the interval of the folding pitch P of the nozzle row. A portion or a thin portion appears, and density unevenness in the sub-scanning direction is visually recognized.

  Patent Documents 1 to 3 do not disclose a method for effectively reducing the density unevenness generated at the folded position of the nozzle row.

  The present invention has been made to solve the above problems. When a matrix type recording head in which a plurality of nozzles are two-dimensionally arranged is used, the matrix type recording head is mainly used without complicating the configuration. It is an object of the present invention to provide a droplet discharge device and an image forming method capable of suppressing the occurrence of density unevenness in the sub-scanning direction of a formed image caused by tilting the head posture when moving in the scanning direction.

  In order to achieve the above object, according to the first aspect of the present invention, a plurality of nozzles for forming dots constituting an image on a recording medium by ejecting droplets are inclined at a predetermined angle with respect to the main scanning direction. In the plurality of sets of nozzle groups arranged on the straight line, the intervals between the nozzles adjacent to each other in the sub-scanning direction are substantially the same, and the positions of the nozzles belonging to each nozzle group are substantially the same. As described above, the recording head arranged in the sub-scanning direction and the moving means for reciprocating the recording head in the main scanning direction while inclining in the opposite direction with respect to the axis orthogonal to the main scanning direction in the forward movement and the backward movement Between the forward movement and the backward movement of the recording head by the moving means, the width in the sub-scanning direction of the dot formation region by the set of nozzle groups is a predetermined integer multiple less than the number of the nozzle groups. Each distance, and a, conveying means for relatively transporting the at least one of the recording head and the recording medium in a sub-scanning direction.

  According to the droplet discharge device of the first aspect, a plurality of sets of nozzles in which a plurality of nozzles are arranged on a straight line inclined at a predetermined angle with respect to the main scanning direction includes nozzles adjacent to each other in the sub-scanning direction. While reciprocally moving in the main scanning direction by a recording head arranged in the sub-scanning direction so that the intervals in the sub-scanning direction are substantially the same and the positions of the nozzles belonging to each nozzle group are substantially the same in the sub-scanning direction. The droplets are ejected, and at least one of the recording head and the recording medium is relatively transported in the sub-scanning direction between forward printing and backward printing, thereby forming dots constituting the image on the recording medium.

  Here, “substantially identical” means that they are the same in design but are the same with allowance for deviations due to manufacturing errors.

  Here, in the present invention, the recording head is reciprocated in the main scanning direction while being inclined in the reverse direction with respect to the axis orthogonal to the main scanning direction in the forward movement and the backward movement, and the recording head is moved forward by the conveying means. Between the movement and the backward movement, at least one of the recording head and the recording medium in the sub-scanning direction by a distance obtained by multiplying the width in the sub-scanning direction of the dot formation region by a set of nozzle groups by a predetermined integer less than the number of nozzle groups. Are conveyed relatively.

  As a result, the density unevenness of the return pitch of the nozzle rows generated in the image formed by the forward movement and the image formed by the backward movement is leveled, so that the matrix type recording head can be used without complicating the configuration. It is possible to suppress the occurrence of density unevenness in the sub-scanning direction of the formed image caused by the tilt of the head posture when moving in the main scanning direction.

  According to the present invention, as in the invention described in claim 2, the moving means applies a force in a direction in which the recording head is moved with respect to one end of the recording head, so that the recording head is moved forward. It is also possible to reciprocate in the main scanning direction while inclining in the opposite direction with respect to the axis orthogonal to the main scanning direction in the movement and the backward movement. Thus, the recording head can be more reliably tilted in the reverse direction with respect to the axis orthogonal to the main scanning direction in the forward movement and the backward movement by a simple method.

  Further, in the invention described in claim 1 or 2, as in the invention described in claim 3, the moving means is configured to move relative to an axis orthogonal to the main scanning direction in the forward movement and the backward movement of the recording head. The recording head may be reciprocated in the main scanning direction in a state in which the angle of inclination is substantially symmetric with respect to the axis during forward movement and backward movement. As a result, the density distribution state in the sub-scanning direction of the dots in the dot formation region (the state of the adjacent dot interval in the sub-scanning direction) can be substantially reversed between the forward movement and the backward movement of the recording head, and more reliably. In addition, it is possible to suppress density unevenness of the folding pitch of the nozzle row.

  Here, “substantially symmetrical” means that it is symmetrical in terms of design, but is symmetrical with allowance for deviation due to manufacturing error or the like.

  On the other hand, in order to achieve the above object, the image forming method according to claim 4 is characterized in that a plurality of nozzles for forming dots constituting an image on a recording medium by ejecting liquid droplets are formed in the main scanning direction. A plurality of sets of nozzle groups arranged on a straight line inclined at a predetermined angle have substantially the same spacing in the sub-scanning direction between adjacent nozzles in the sub-scanning direction, and the positions of the nozzles belonging to each nozzle group in the sub-scanning direction are the same. The recording heads arranged in the sub-scanning direction so as to be substantially the same are reciprocated in the main scanning direction while being inclined in the reverse direction with respect to the axis orthogonal to the main scanning direction in the forward movement and the backward movement, Between the forward movement and the backward movement of the recording head, the width in the sub-scanning direction of the dot formation region by one set of the nozzle groups is a distance obtained by multiplying the width in the sub-scanning direction by a predetermined integer less than the number of the nozzle groups. At least one of the heads and the recording medium relatively transported.

  Therefore, according to the image forming method of the fourth aspect, since it operates in the same manner as the invention according to the first aspect, the matrix type can be obtained without complicating the configuration as in the case of the first aspect. It is possible to suppress the occurrence of density unevenness in the sub-scanning direction of the formed image caused by the tilt of the head posture when the recording head moves in the main scanning direction.

  As described above, according to the present invention, the density unevenness in the sub-scanning direction of the formed image caused by the inclination of the head posture when the matrix type recording head moves in the main scanning direction without complicating the configuration. It has an excellent effect that generation can be suppressed.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Here, a case where the present invention is applied to an ink jet recording apparatus will be described.

  FIG. 1 shows an overall configuration of an inkjet recording apparatus 10 according to the present embodiment.

  As shown in FIG. 1, an inkjet recording apparatus 10 includes an image forming unit 12 including a recording head including a plurality of nozzles that form dots on a recording paper 14 by ejecting ink droplets. A paper supply unit 16 for supplying the recording paper 14, a decurling unit 18 for removing curl of the recording paper 14, and a surface on which ink droplets are ejected from the recording head provided in the image forming unit 12 , Referred to as an “ink ejection surface”), and a belt conveyance unit 20 that conveys the recording paper 14 while maintaining the flatness of the recording paper 14, and discharges the recording paper 14 on which an image is formed. A paper discharge unit 22.

  In the inkjet recording apparatus 10 according to the present embodiment, a magazine for rolled paper (continuous paper) is applied as the paper supply unit 16. However, the present invention is not limited to this, and a plurality of magazines having different paper width, paper quality, and the like are used. You may apply. Further, instead of the roll paper magazine or in combination with this, a cassette in which cut sheets are stacked and loaded may be applied.

  In the case where a plurality of types of recording paper 14 can be used, an information recording body such as a barcode or a wireless tag that records the type information of the recording paper 14 is attached to the magazine, and the information on the information recording body is stored in a predetermined manner. It is preferable that the type of the recording paper 14 to be used is automatically determined by reading with the reading device, and ink ejection control is performed so as to realize appropriate ink ejection according to the type.

  The recording paper 14 delivered from the paper supply unit 16 retains curl due to having been loaded in the magazine. In order to remove this curl, heat is applied to the recording paper 14 by the heating drum 24 in the direction opposite to the curl direction of the magazine in the decurling unit 18. At this time, it is more preferable to control the heating temperature so that the surface on which the image is formed on the recording paper 14 (hereinafter referred to as “image forming surface”) is weakly curled outward.

  In the case of an apparatus configuration using roll paper, a cutter 26 is provided as shown in FIG. 1, and the roll paper is cut into a desired size by the cutter 26. Note that the cutter 26 is not necessary when cut paper is used.

  After the decurling process, the recording paper 14 cut by the cutter 26 is sent to the belt conveyance unit 20.

  The belt conveyance unit 20 is configured to have a structure in which an endless belt 32 is wound between rollers 28 and 30. When the power of a motor (not shown) is transmitted to at least one of the rollers 28 and 30 around which the belt 32 is wound, the belt 32 is driven in the clockwise direction in FIG. 14 is conveyed from left to right in FIG.

  The belt 32 has a width that is wider than the width of the recording paper 14, and a plurality of suction holes (not shown) are formed on the belt surface. As shown in the figure, an adsorption chamber 34 is provided inside the belt 32 spanned between the rollers 28 and 30 at a position facing the ink discharge surface, and the air in the adsorption chamber 34 is provided. Is sucked by the fan 36 to obtain a negative pressure, whereby the recording paper 14 is adsorbed and held on the belt 32. In the inkjet recording apparatus 10 according to the present embodiment, the suction suction method using the suction chamber 34 is applied as a method for holding the recording paper 14 on the belt 32. However, the invention is not limited thereto, and the recording paper 14 is not limited thereto. An electrostatic attraction method in which the belt 32 is electrostatically attracted to the belt 32 may be applied.

  A heating fan 38 is provided upstream of the image forming unit 12 in the conveyance direction of the recording paper 14 by the belt conveyance unit 20. The heating fan 38 blows heated air on the recording paper 14 before image formation to heat the recording paper 14. By heating the recording paper 14 immediately before image formation, it becomes easy to dry after ink droplets have landed on the recording paper 14.

  A post-drying unit 40 including a heating fan that blows hot air is provided at the subsequent stage of the image forming unit 12, and the post-drying unit 40 dries the image forming surface of the recording paper 14 on which the image is formed. The recording paper 14 on which the image is formed is discharged from the paper discharge unit 22.

  In addition, since ink droplets ejected from the image forming unit 12 may adhere to the belt 32, the belt cleaning unit 42 is provided outside the region of the belt 32 that transports the recording paper 14. Note that the ink jet recording apparatus 10 according to the present embodiment uses a brush / roll as the belt cleaning unit 42, but is not limited thereto, a water absorbing roll, an air blow for blowing clean air, or a combination thereof. May be applied.

  On the other hand, FIG. 2 shows a top view of the image forming unit 12 provided in the ink jet recording apparatus 10 according to the present embodiment and the periphery thereof.

  As shown in the figure, the image forming unit 12 uses a yellow (Y) ink liquid to form an image on the recording paper 14 and a magenta (M) ink liquid to form an image on the recording paper 14. , A recording head 50C that forms an image on the recording paper 14 using cyan (C) ink liquid, and a recording head that forms an image on the recording paper 14 using black (K) ink liquid The recording heads 50 </ b> Y, 50 </ b> M, 50 </ b> C, and 50 </ b> K are mounted on the carriage 51. Each of the recording heads 50Y, 50M, 50C, and 50K includes an ink tank filled with a corresponding color ink liquid. In the following description, when distinguishing corresponding colors, description is given with any one of Y, M, C, K corresponding to the end of the code, and when not distinguishing corresponding colors, Y, M, C, and K are omitted.

  The carriage 51 has an insertion hole in the vicinity of the upper end in FIG. 2, and a guide rail 52 arranged in parallel to the main scanning direction is inserted through the insertion hole. As a result, the carriage 51 can slide along the guide rail 52. The insertion hole is provided with a so-called play by making the inner diameter slightly larger than the outer diameter of the guide rail 52.

  Further, the carriage 51 includes a belt connecting portion 53 at the upper end of FIG. 2, and the belt connecting portion 53 is connected to a carriage belt 54 disposed in parallel to the main scanning direction. The carriage 51 is reciprocated in the main scanning direction along the guide rail 52 by applying a force in accordance with the direction of rotation as the carriage belt 54 rotates.

  The ink jet recording apparatus 10 according to the present embodiment includes the belt connecting portion 53 at one end portion of the carriage 51 (in this embodiment, the right end portion in FIG. 2 on the end surface on the side where the guide rail 52 is inserted). Thus, the carriage 51 is easily reciprocated in the main scanning direction while being inclined in the reverse direction with respect to the axis orthogonal to the main scanning direction in the forward movement and the backward movement.

  The carriage belt 54 is wound around the main pulley 55A and the driven pulley 55B. The main driving pulley 55A is mechanically connected to the rotation shaft of the carriage motor 56, and forward rotation (in the direction of arrow A shown in FIG. 2) and reverse rotation (arrow shown in FIG. 2) of the rotation shaft of the carriage motor 56. Rotate forward and backward according to (B direction). For this reason, the carriage belt 54 rotates in accordance with the forward rotation and the reverse rotation of the rotation shaft of the carriage motor 56, whereby the carriage 51 reciprocates along the guide rail 52 in the main scanning direction.

  The ink jet recording apparatus 10 according to the present embodiment rotates the rotation shaft of the carriage motor 56 in the forward direction, thereby moving the carriage 51 in the main scanning direction and rotating the rotation shaft of the carriage motor 56 in the reverse direction. The carriage 51 is moved backward in the main scanning direction.

  Next, the structure of the recording head 50 will be described.

  FIG. 3 is a perspective plan view showing a structural example of the recording head 50. FIG. 4 shows an enlarged view of the nozzle portion of the recording head 50.

  In order to increase the pitch of the dots constituting the image formed on the recording paper 14, it is necessary to increase the pitch of the plurality of nozzles provided in the recording head 50. Therefore, as shown in FIG. 3, the recording head 50 has a structure in which a plurality of ink chamber units 62 including nozzles 60 and pressure chambers 61 corresponding to the nozzles 60 are arranged two-dimensionally (matrix type). Have.

  Note that the recording head 50 provided in the ink jet recording apparatus 10 according to the present embodiment is a straight line in which a plurality of (seven in the present embodiment) nozzles 60 are inclined at a predetermined angle with respect to the main scanning direction. The nozzle groups 60A of a plurality of sets (three sets in the present embodiment) arranged in the same interval in the sub-scanning direction of the nozzles 60 adjacent in the sub-scanning direction are substantially the same, and the nozzles 60 belonging to each nozzle group 60A Are arranged in the sub-scanning direction so that their positions in the sub-scanning direction are substantially the same. Accordingly, the dot pitch is increased by achieving a higher density of substantial nozzle intervals (hereinafter referred to as “projection nozzle pitch”) projected so as to be aligned in the sub-scanning direction. . In the following, the width of the dot formation region in the sub-scanning direction by the set of nozzle groups 60A is referred to as a folding pitch P.

  Further, the pressure chamber 61 provided corresponding to each nozzle 60 has a square planar shape (see FIGS. 3 and 4), and both on the diagonal line (A-A line in FIG. 4). A nozzle 60 is provided at one of the corners, and a supply ink inlet (hereinafter referred to as “supply port”) 63 is provided at the other.

  In the inkjet recording apparatus 10 according to the present embodiment, a square is applied as the planar shape of the pressure chamber 61. However, the present invention is not limited to this, and other quadrangles such as a rhombus and a rectangle, a pentagon, a hexagon, and other various shapes. Other planar shapes such as a square, a circle, and an ellipse may be applied.

  FIG. 5 is a cutaway side view of the ink chamber unit 62 taken along line AA in FIG.

  As shown in the figure, each pressure chamber 61 communicates with a common channel 64 through a supply port 63. The common flow path 64 communicates with an ink tank provided in each recording head 50, and ink supplied from the ink tank is distributed and supplied to each pressure chamber 61 via the common flow path 64.

  An actuator 67 having an individual electrode 66 is joined to a pressure plate (vibrating plate also serving as a common electrode) 65 constituting a part of the pressure chamber 61 (the top surface in FIG. 5). By applying a driving voltage between the individual electrode 66 and the common electrode, the actuator 67 is deformed and the volume of the pressure chamber 61 is changed, and the ink droplet is ejected from the nozzle 60 due to the pressure change accompanying this. Then, when the displacement of the actuator 67 returns to the original state after discharging the ink droplets, new ink is refilled into the pressure chamber 61 from the common flow path 64 through the supply port 63. In the inkjet recording apparatus 10 according to the present embodiment, a piezoelectric element using a piezoelectric material such as lead zirconate titanate or barium titanate is applied as the actuator 67.

  On the other hand, FIG. 6 is a block diagram showing an electrical configuration of the inkjet recording apparatus 10. As shown in the figure, the inkjet recording apparatus 10 includes a system controller 80, a print controller 81, a communication interface 82, an image memory 84, a ROM (Read Only Memory) 85, a motor driver 86, a heater driver 88, a motor driver 92, And a recording head driver 93.

  The system controller 80 includes a CPU (Central Processing Unit) and its peripheral circuits, and functions as a control device that controls the entire inkjet recording apparatus 10 according to a predetermined program, and also functions as an arithmetic device that performs various calculations. That is, the system controller 80 controls the print control unit 81, the communication interface 82, the image memory 84, the ROM 85, the motor driver 86, and the heater driver 88, and performs communication control with the host device 89, the image memory 84, and In addition to performing read / write control of the ROM 85, a control signal for controlling the motor 90 and the heater 91 of the transport system is generated. The print control unit 81 transmits various data such as image data stored in the image memory 84 when performing control to form an image on the recording paper 14.

  The communication interface 82 is an interface unit with a host device 89 that is used by a user to instruct the inkjet recording apparatus 10 to form an image, and is equipped with a buffer memory for speeding up communication. Yes. In addition, although the inkjet recording apparatus 10 according to the present embodiment uses USB (Universal Serial Bus) as the communication interface 82, the present invention is not limited to this, and IEEE (Institute of Electrical and Electronics Engineers) 1394, Ethernet ( (Registered trademark), a serial interface such as a wireless network, or a parallel interface such as Centronics may be applied.

  The image memory 84 is a storage unit that stores image data and the like transmitted from the host device 89 via the communication interface 82, and various data are read and written through the system controller 80. The image memory 84 is used as a temporary storage area for various data, and is also used as a program development area and a calculation work area for the CPU. In the inkjet recording apparatus 10 according to the present embodiment, a memory made of a semiconductor element is applied as the image memory 84. However, the present invention is not limited to this, and a magnetic medium such as a hard disk may be applied.

  The ROM 85 stores programs executed by the CPU of the system controller 80 and various data necessary for control. The inkjet recording apparatus 10 according to the present embodiment uses a non-rewritable storage means as the ROM 85, but is not limited to this, and a rewritable storage such as an EEPROM (Electrically Erasable Programmable Read Only Memory). Means may be applied.

  The motor driver 86 is a drive circuit that drives the conveyance motor 90 in accordance with an instruction from the system controller 80, and the heater driver 88 is a driver that drives the heater 91 such as the post-drying unit 40 in accordance with an instruction from the system controller 80. is there.

  The print controller 81 performs various processes and corrections for generating ink discharge control data (hereinafter referred to as “ink discharge data”) from the image data transmitted from the system controller 80 in accordance with the control of the system controller 80. In addition to functioning as a signal processing means for performing the above processes, the recording head 50 is controlled via the recording head driver 93 and the carriage motor 56 is controlled via a motor driver 92 which is a drive circuit for driving the carriage motor 56.

  The recording head driver 93 is a drive circuit for driving the recording head 50 in accordance with an instruction from the print control unit 81, and discharges ink droplets from the nozzles 60 based on ink discharge data transmitted from the print control unit 81. Drive voltage is generated and output to the recording head 50.

  Here, with reference to FIG. 7, the density distribution in the sub-scanning direction of dots formed by the inkjet recording apparatus 10 according to the present embodiment will be described.

  As described above, the ink jet recording apparatus 10 according to the present embodiment tilts the carriage 51 in the main scanning direction while tilting the carriage 51 in the reverse direction with respect to the axis orthogonal to the main scanning direction in the forward movement and the backward movement during image formation. Move back and forth.

Therefore, as shown in FIG. 7A, when the recording head 50 provided in the carriage 51 moves forward in the main scanning direction, the recording head 50 is located on the upstream side in the sub scanning direction compared to the downstream side in the sub scanning direction. It is so delayed, to move while inclining at an angle theta _1.

  Therefore, among the plurality of nozzles 60 constituting the nozzle group 60A, the projection nozzles in the sub-scanning direction of the adjacent nozzles 60A and 60β between the nozzle groups 60A adjacent in the sub-scanning direction (hereinafter referred to as “adjacent nozzles”). While the pitch (hereinafter referred to as “projected adjacent nozzle pitch”) is shorter than that when the recording head 50 is not inclined, nozzles other than the adjacent nozzles 60α and 60β (hereinafter referred to as “intermediate nozzle”). ) In the sub-scanning direction (hereinafter referred to as “projection intermediate nozzle pitch”) is longer than that in the case where the recording head 50 is not inclined. Thereby, the density of the dots in the sub-scanning direction formed by the adjacent nozzles 60α and 60β becomes dense, while the density of the dots in the sub-scanning direction formed by the intermediate nozzle becomes sparse.

On the other hand, as shown in FIG. 7B, when the recording head 50 provided in the carriage 51 moves backward in the main scanning direction, the recording head 50 is located on the downstream side in the sub scanning direction compared to the upstream side in the sub scanning direction. It is so delayed, to move while inclining at an angle theta _2.

  For this reason, the projected adjacent nozzle pitch is longer than that when the recording head 50 is not inclined, while the projected intermediate nozzle pitch is shorter than when the recording head 50 is not inclined. Thereby, the density in the sub-scanning direction of the dots formed by the adjacent nozzles 60α and 60β becomes sparse, while the density in the sub-scanning direction of the dots formed by the intermediate nozzles becomes dense.

  As described above, the carriage 51 is reciprocated in the main scanning direction while being inclined in the reverse direction with respect to the axis orthogonal to the main scanning direction in the forward movement and the backward movement, so that the sub-scanning of dots formed by the recording head 50 is performed. The density of the direction is different between forward movement and backward movement.

Further, in the ink jet recording apparatus 10 according to the present embodiment, the main scanning of the carriage 51 is performed in a state where the angles θ ₁ and θ ₂ are substantially symmetric with respect to the axis orthogonal to the main scanning direction in the forward movement and the backward movement. The movement speed of the carriage belt 54 and the assembly of the insertion hole through which the guide rail 52 of the carriage 51 is inserted are adjusted so that the carriage 51 can be reciprocated in the direction.

  The ink jet recording apparatus 10 according to the present embodiment adjusts the distance that the recording paper 14 is conveyed in the sub-scanning direction between the forward movement and the backward movement of the carriage 51, thereby forming dots formed by the forward movement. The dots formed by the backward movement are overlapped, and the density distribution of the dots in the sub-scanning direction on the recording paper 14 is leveled.

  Next, with reference to FIG. 8, the operation of the ink jet recording apparatus 10 according to the present embodiment will be described. This figure is a flowchart showing the flow of processing of an image forming program executed by the CPU of the system controller 80 when an image indicated by image data is formed. The program is stored in advance in a storage area of the ROM 85. ing.

  First, in step 100 of the figure, the motor driver 86 is controlled so that the recording paper 14 is conveyed to the position where the carriage 51 is disposed. Thus, the motor driver 86 drives the motor 90 to cause the belt conveyance unit 20 to convey the recording paper 14 to a position where the carriage 51 is disposed. Note that the curl of the recording paper 14 is removed by the decurling unit 18 during the conveyance process, and the recording paper 14 is cut into a desired size by the cutter 26.

  In the next step 102, the print controller 81 is controlled so that ink droplets are ejected from the recording head 50 using the ink ejection data while the carriage 51 is moved in the main scanning direction. As a result, the print control unit 81 causes the carriage 51 to move forward in the main scanning direction by rotating the rotation shaft of the carriage motor 56 forward via the motor driver 92, and the nozzles of the recording head 50 based on the ink ejection data. Ink droplets are ejected from 60.

  In the next step 104, the motor driver 86 is controlled so that the recording paper 14 is conveyed in the sub-scanning direction.

  In the inkjet recording apparatus 10 according to the present embodiment, a predetermined integer less than the number of nozzle groups 60A included in one recording head 50 is m (2 in the present embodiment), and the folding pitch is set as described above. As P, the recording paper 14 is conveyed in the sub-scanning direction by a distance N calculated by the following equation (1).

N = m × P (1)
Note that the inkjet recording apparatus 10 according to the present embodiment calculates the distance N in advance and stores it in the image memory 84 in advance.

  The motor driver 86 conveys the recording paper 14 by the distance N by the belt conveyance unit 20 by rotating the motor 90 by the number of rotations corresponding to the distance N.

  In the next step 106, the print control unit 81 is controlled so that ink droplets are ejected from the recording head 50 using the ink ejection data while the carriage 51 is moved backward in the main scanning direction. As a result, the print control unit 81 reversely rotates the rotation shaft of the carriage motor 56 via the motor driver 92 to move the carriage 51 in the backward direction in the main scanning direction, and the nozzles of the recording head 50 based on the ink ejection data. Ink droplets are ejected from 60.

  In the process in step 104, the recording paper 14 is transported in the sub-scanning direction by the distance N, so that the dots formed while moving the carriage 51 in the backward path and the dots formed while moving the carriage 51 in the forward path are turned back. Since they are superimposed at every pitch P, the density distribution in the sub-scanning direction of the dots formed on the recording paper 14 is leveled.

  In the next step 108, it is determined whether or not the formation of the image indicated by the image data corresponding to one sheet of recording paper 14 has been completed. After the motor driver 86 is controlled so as to convey in the sub-scanning direction by the distance N, the process returns to step 102. If the determination is affirmative, the process proceeds to step 112.

  In step 112, it is determined whether or not the formation of the image indicated by all the image data stored in the image memory 84 has been completed. If the determination is negative, the process returns to step 100 and indicated by the remaining image data. If the determination is affirmative, the process proceeds to step 114.

  In step 114, the motor driver 86 is controlled to discharge the recording paper 14 on which the image is formed. Thus, the motor driver 86 drives the motor 90 to convey the recording paper 14 to the paper discharge unit 22 by the belt conveyance unit 20.

  As described above in detail, in the present embodiment, a plurality of nozzle groups in which a plurality of nozzles are arranged on a straight line inclined at a predetermined angle with respect to the main scanning direction are arranged in the nozzles adjacent to each other in the sub-scanning direction. By ejecting liquid droplets by a recording head arranged in the sub-scanning direction so that the intervals in the sub-scanning direction are substantially the same and the positions of the nozzles belonging to each nozzle group are substantially the same in the sub-scanning direction, images are ejected. Are formed on the recording medium, and the recording head is reciprocated in the main scanning direction while being inclined in the reverse direction with respect to the axis perpendicular to the main scanning direction in the forward movement and the backward movement by the moving unit. Between the forward movement and the backward movement of the recording head by the conveying means, the distance in the sub-scanning direction of the dot formation area by one set of nozzle groups is not a distance that is a predetermined integer multiple less than the number of nozzle groups. Since at least one of the recording head and the recording medium is relatively conveyed in the sub-scanning direction, the head posture is inclined when the matrix-type recording head moves in the main scanning direction without complicating the configuration. Generation of density unevenness in the sub-scanning direction of the formed image can be suppressed.

  In this embodiment, the moving means applies a force in the direction of moving the recording head relative to one end of the recording head, so that the recording head is moved to an axis orthogonal to the main scanning direction in the forward movement and the backward movement. In contrast, since the recording head is reciprocated in the main scanning direction while being inclined in the reverse direction, the recording head can be more reliably inclined in the reverse direction with respect to the axis perpendicular to the main scanning direction in the forward movement and the backward movement by a simple method. Can do.

  Further, in this embodiment, the angle at which the moving unit is inclined with respect to the axis orthogonal to the main scanning direction in the forward movement and the backward movement of the recording head is substantially symmetrical with respect to the axis in the forward movement and the backward movement. In this state, the recording head is reciprocated in the main scanning direction, so that the density distribution state of dots in the dot formation area can be made almost opposite between the forward movement and the backward movement of the recording head. The density unevenness of the folded pitch can be suppressed.

  As mentioned above, although this invention was demonstrated using the said embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. Various modifications or improvements can be added to the above-described embodiment without departing from the gist of the invention, and embodiments to which such modifications or improvements are added are also included in the technical scope of the present invention.

  Further, the above embodiments do not limit the invention according to the claims (claims), and all the combinations of features described in the embodiments are essential for the solution means of the invention. Not exclusively. The embodiments described above include inventions at various stages, and various inventions can be extracted by combinations of a plurality of disclosed constituent elements. Even if some constituent elements are deleted from all the constituent elements shown in the above embodiment, as long as an effect is obtained, a configuration in which these some constituent elements are deleted can be extracted as an invention.

  For example, in the above-described embodiment, the case where the ink liquid ejected by the recording head 50 is four colors Y, M, C, and K has been described, but the present invention is not limited to this, A form in which the combination of the number of colors is changed, or a form in which a special color ink liquid such as a light ink liquid or a light ink liquid such as a light cyan liquid or a light magenta liquid is added may be used. In this case as well, the same effects as in the above embodiment can be obtained.

  In the above embodiment, the case where ink droplets are ejected using a piezoelectric element has been described as a method of ejecting ink droplets from the recording head 50, but the present invention is not limited to this. Other forms such as a thermal jet method in which ink liquid is heated by a heating element such as a heater to generate bubbles and ink droplets are ejected by the pressure may be used. In this case as well, the same effects as in the above embodiment can be obtained.

  Moreover, although the case where the belt connection part 53 is provided in the right end part of the end surface by which the guide rail 52 of the carriage 51 is inserted was demonstrated in the said embodiment, this invention is not limited to this, It is good also as a form provided in the left end part of the said surface, the center part, or the left end part of FIG. 9 left end part, the right end part, or center part of the end surface by which the guide rail 52 of the carriage 51 is not penetrated as shown in FIG. In this case as well, the same effects as in the above embodiment can be obtained.

  In the above-described embodiment, the case where the carriage 51 and the recording paper 14 are relatively moved by moving only the recording paper 14 in the sub-scanning direction has been described. However, the present invention is not limited to this. Instead, the recording paper 14 is fixed, and the carriage 51 is moved in the sub-scanning direction so that the carriage 51 and the recording paper 14 are moved relatively, or the carriage 51 is moved together with the recording paper 14 in the sub-scanning direction. It is good also as a form made to do. In this case as well, the same effects as in the above embodiment can be obtained.

  In the above embodiment, the recording head 50 includes a plurality of nozzle groups 60A in which the plurality of nozzles 60 are arranged on a straight line inclined from the downstream side in the sub scanning direction to the upstream side in the sub scanning direction. As described above, the present invention is not limited to this, and the recording head 50 includes a plurality of sets of nozzles 60 in which a plurality of nozzles 60 are arranged on a straight line inclined from the upstream side in the sub-scanning direction to the downstream side in the sub-scanning direction. It is good also as a form provided with the group 60A. In this case as well, the same effects as in the above embodiment can be obtained.

  Furthermore, although the case where one guide rail 52 is inserted through the carriage 51 has been described in the above embodiment, the present invention is not limited to this, and the two guide rails 52 are inserted through the carriage 51. It is good also as a form. In this case as well, the same effects as in the above embodiment can be obtained.

  In addition, the configuration of the ink jet recording apparatus 10 described in the above embodiment (see FIGS. 1 to 6) is merely an example, and unnecessary portions may be deleted or new portions may be deleted without departing from the gist of the present invention. Needless to say, you can add.

  The processing flow of the image forming program described in the above embodiment (see FIG. 8) is also an example, and unnecessary steps are deleted or new steps are added without departing from the gist of the present invention. Needless to say, the processing order can be changed.

1 is a cutaway side view showing a configuration of an ink jet recording apparatus according to an embodiment. FIG. 3 is a top view of the image forming unit and its periphery according to the embodiment. 2 is a perspective plan view showing the structure of the recording head according to the embodiment. FIG. It is an enlarged view of a plane perspective view of a nozzle portion of a recording head according to an embodiment. FIG. 4 is a cutaway side view of an ink chamber unit of the recording head according to the embodiment. 1 is a block diagram illustrating a configuration of a main part of an electric system of an ink jet recording apparatus according to an embodiment. FIG. 6 is a diagram for explaining a tilt state of a recording head and a density distribution in a sub-scanning direction of dots to be formed according to an embodiment. 4 is a flowchart illustrating a flow of processing of an image forming program according to an embodiment. FIG. 6 is a top view of an image forming unit and its periphery according to another embodiment.

Explanation of symbols

10 Inkjet recording device 14 Recording paper (recording medium)
32 belt (conveying means)
50 Recording head 54 Carriage belt (moving means)
60 nozzles 60A nozzle group

Claims (4)

A plurality of nozzle groups in which a plurality of nozzles that form dots on the recording medium by ejecting liquid droplets on a recording medium are arranged on a straight line inclined at a predetermined angle with respect to the main scanning direction include a sub-scanning direction. Recording heads arranged in the sub-scanning direction so that the intervals in the sub-scanning direction of the nozzles adjacent to each other are substantially the same, and the positions of the nozzles belonging to each nozzle group are substantially the same,
Moving means for reciprocating in the main scanning direction while inclining the recording head in the reverse direction with respect to an axis orthogonal to the main scanning direction in forward movement and backward movement;
Between the forward movement and the backward movement of the recording head by the moving means, the width in the sub-scanning direction of the dot formation region by the set of nozzle groups is subtracted by a predetermined integer multiple less than the number of nozzle groups. Conveying means for relatively conveying at least one of the recording head and the recording medium in a scanning direction;
A droplet discharge device comprising:   The moving means applies a force in a direction in which the recording head is moved with respect to one end portion of the recording head, so that the recording head is reversely moved with respect to an axis orthogonal to the main scanning direction in the forward movement and the backward movement. The liquid droplet ejection apparatus according to claim 1, wherein the liquid droplet ejection apparatus is reciprocated in the main scanning direction while being inclined toward the main scanning direction.   The moving means is configured so that an angle inclined with respect to an axis orthogonal to the main scanning direction in the forward movement and the backward movement of the recording head is substantially symmetrical with respect to the axis in the forward movement and the backward movement. The liquid droplet ejection apparatus according to claim 1, wherein the liquid crystal is reciprocated in the main scanning direction. A plurality of nozzle groups in which a plurality of nozzles that form dots on the recording medium by ejecting liquid droplets on a recording medium are arranged on a straight line inclined at a predetermined angle with respect to the main scanning direction include a sub-scanning direction. The recording heads arranged in the sub-scanning direction are moved forward so that the intervals in the sub-scanning direction of the nozzles adjacent to each other are substantially the same, and the positions of the nozzles belonging to each nozzle group are substantially the same in the sub-scanning direction. Reciprocating in the main scanning direction while inclining in the reverse direction with respect to the axis orthogonal to the main scanning direction in the backward movement,
Between the forward movement and the backward movement of the recording head, the width in the sub-scanning direction of the dot formation region by a set of the nozzle groups is multiplied by a predetermined integer less than the number of the nozzle groups in the sub-scanning direction. Relatively transporting at least one of the recording head and the recording medium;
Image forming method.

Images