JP2014195924A - Ink jet head array and ink jet image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink jet array and an image forming apparatus of which the maintenance work such as replacement of ink jet head units of the image forming apparatus having a line-head type ink jet array in which a plurality of ink jet head units are arranged in a direction perpendicular to a conveyance direction of a recording medium can be simply performed in short time.SOLUTION: In an ink jet head array in which a plurality of ink jet head units 9 having nozzle arrays perforated at predetermined intervals in a predetermined arrangement direction are arranged and loaded on a support member, the plurality of ink jet head units are arranged so that at least parts of the nozzle arrays of the adjacent ink jet head units overlap with each other by being viewed along a conveyance direction of a recording medium, and only parallelism between mutual nozzle arrays of the plurality of ink jet head units is made mechanically adjustable.

Description

  The present invention relates to an image forming apparatus for forming an image by an ink jet system, and in particular, a plurality of ink jet head units each having an ink discharge nozzle array narrowed in one direction are arranged in a direction perpendicular to the conveyance direction of a recording medium. The present invention relates to an image forming apparatus having a line head type inkjet head array.

  Inkjet image forming apparatuses are roughly classified into two types, a so-called carriage type and a line head type, depending on the arrangement method of the inkjet head.

  In the carriage type, the ink jet head is provided on a carriage that moves in a direction orthogonal to the conveyance direction of the recording medium, and the ink ejected from the ink jet head while relatively moving both the ink jet head and the recording medium. In this method, an image is formed on a recording medium. Since a small ink-jet head is provided on the carriage, the device size can be made relatively small, so that it can be used for a small printer for general home use, or conversely, if a carriage mechanism is configured, a so-called large format, wide recording medium Therefore, in addition to the production of drawings and posters, it is often used for industrial and industrial purposes such as dyeing of fabrics and design coating of interior wall materials for buildings.

  On the other hand, the line head type is an ink jet head having an ink discharge nozzle row that is narrowed in one direction on the nozzle surface, and many are fixedly arranged so that the nozzle row is in a direction perpendicular to the conveyance direction of the recording medium. In this method, an image is formed on a recording medium by simultaneously ejecting ink from a plurality of ink ejection nozzles while conveying the recording medium. Since there is no need to move the carriage, it has a feature that image formation at a relatively high speed is possible.

  In a line head type ink jet image forming apparatus, there may be a case where only one ink jet head having a discharge width equal to or larger than the width of a recording medium on which image formation is performed, but in many cases, it is narrower than the width of the recording medium. In general, a plurality of inkjet head units having a discharge width are arranged adjacent to each other in the width direction (referred to as an inkjet head array). For example, if it is assumed that the recording medium passes through A3 (297 mm) and the print density is 800 dots per 25.4 mm (so-called 800 dpi), the ink jet head has 297 / 25.4 × 800 = approximately 9354 ink ejection holes. It is necessary to stenosis at 32μm (25.4mm / 800) intervals. In such a case, in addition to the problem that the inkjet head becomes expensive due to the manufacturing yield problem, there are cases where an undesirable problem occurs in terms of maintenance and replacement of the inkjet head. As is well known, when a line-type ink jet head cannot eject even one ink ejection hole, so-called white streaks in the transport direction on the recorded image and image formation defects often occur on white spots. Many of the recording media are paper-based, and paper dust generated from the recording medium adheres to the nozzle surface, contact with the nozzle surface due to poor handling of the inkjet head or recording medium, contamination of foreign matter into the ink, etc. Head ejection failure or the like due to the above is known as a problem that occurs relatively frequently. If even one of these defective nozzles occurs, it is often necessary to replace the inkjet head itself, but a plurality of inkjet head units having an ejection width narrower than the width of the recording medium are arranged adjacent to each other in the width direction. With this configuration, it is only necessary to replace the relatively inexpensive inkjet head unit at the location where the ejection failure has occurred, and it is not necessary to replace the entire expensive inkjet head every time the ejection failure occurs. This is because it is often advantageous.

  When a plurality of inkjet head units having a discharge width narrower than the width of the recording medium are arranged adjacent to each other in the width direction of the recording medium, the individual inkjet head units are arranged adjacent to each other as shown in FIGS. In general, the inkjet head units to be moved are shifted by a predetermined distance d in the conveyance direction of the recording medium and arranged in a so-called zigzag or staircase pattern. This is because the discharge width of the individual inkjet head unit is not smaller than the entire width of the unit itself, and there is no gap in the width direction. This is because it is necessary to shift the direction by a minimum amount.

  Of course, in the case of such a staggered or stepped arrangement, for example, in order to form a horizontal line perpendicular to the transport direction on the recording medium, the time difference Δt determined from the transport speed v of the recording medium and the predetermined distance d is used. (= D / v) is provided so that ink is ejected from the adjacent inkjet head unit so that a continuous straight line is formed on the recording medium.

  In the following description, the recording medium surface is the xy plane, the recording medium transport direction is the y axis, the direction perpendicular to it (the recording medium width direction), the x axis, and the direction orthogonal to xy (between the recording medium and the head). Z-axis in the distance direction). When a plurality of inkjet head units having a discharge width narrower than the width of the recording medium are arranged adjacent to each other in the width direction of the recording medium, in addition to adjusting the relative position between the individual inkjet head units and the recording medium, It is also necessary to adjust the relative position between the head units.

  In each ink jet head unit, it is necessary that at least the nozzle surface is parallel to the recording medium surface (position adjustment in the z-axis direction). This is because of the support member on which the ink jet head unit is mounted and the recording medium. It is often ensured with mechanical and structural accuracy between the transport surfaces. Of course, this adjustment mechanism may be provided.

  Further, in the xy plane direction, first, it is necessary to adjust the position of the rotation direction in the xy plane so that both ejection nozzle arrays are parallel to the x axis between adjacent inkjet head units. In addition, position adjustment in the x-axis direction is performed so that one discharge width and the other discharge width are continuous in the x-axis direction without gaps and without overlapping, and further, both discharge nozzle arrays Position adjustment in the y-axis direction is also necessary so that the distance in the y-axis direction is exactly the predetermined distance d described above.

  In the prior art, an adjustment mechanism capable of adjusting the three degrees of freedom in the rotation direction, the x-axis direction, and the y-axis direction is provided for each individual inkjet head unit to actually form an image on a recording medium. I went and checked the image and adjusted the 3 degrees of freedom by trial and error.

JP 2004-322606 A Japanese Patent No. 4774894 Japanese Patent No. 3848026

  In such a conventional technique, first, an adjustment mechanism with three degrees of freedom is required for each individual inkjet head unit, and the support member, the attachment, fixing mechanism, and the adjustment mechanism for the inkjet head unit are complicated and expensive. There was a problem of becoming something. Also, in actual adjustment work, for example, in the adjustment in the x-axis direction, the actual image formation result is observed with a microscope or the like to check whether there are so-called white spots or overlap between the adjacent inkjet head units. It was necessary to perform complicated and time-consuming adjustment work such as performing position adjustment by trial and error while checking.

  This complicated adjustment work also becomes a problem when an image forming apparatus such as a printer having an inkjet head unit is manufactured and shipped in a factory, but moreover, maintenance work such as replacement of a head unit by a user of the printer or the like. However, there has been a problem that the user's printer is stopped for a long time.

  Accordingly, in view of the above problems, image formation having a line head type ink jet array in which a plurality of ink jet head units each having an ink ejection nozzle array narrowed in one direction is arranged in a direction perpendicular to the recording medium conveyance direction. An object of the present invention is to provide an inkjet array and an image forming apparatus that can perform maintenance work such as replacement of an inkjet head unit of the apparatus in a short time.

  In order to solve the above problems, in the present invention, an ink jet head array in which a plurality of ink jet head units each having a nozzle array narrowed at a predetermined interval in a predetermined arrangement direction are arranged and mounted on a support member. The plurality of inkjet head units are disposed so that at least a part of the nozzle rows of the adjacent inkjet head units overlap each other when viewed in the transport direction of the recording medium, and There is provided an inkjet head array characterized in that only the parallelism between the nozzle rows of the inkjet head unit can be mechanically adjusted.

  In a preferred aspect of the present invention, each of the plurality of inkjet head units has a positioning member for positioning the plurality of inkjet head units on the support member for each of the plurality of inkjet head units. A mechanism for engaging the contact member provided on the member to position the inkjet head unit on the support member, and a mechanism for parallelism between the nozzle rows of the plurality of inkjet head units; An ink jet head array is provided in which the adjustment is performed by adjusting the relative position between the nozzle row and the contact surface.

  In a further preferred aspect of the present invention, in the overlap portion, the nozzle row of each of the adjacent inkjet head units is continuous with the non-overlap portion, and a discharge region for discharging ink and an ink discharge. The interval between the one ejection area and the other ejection area as viewed in the predetermined arrangement direction is 0.5 to 1.0 times the print resolution in the width direction of the inkjet head unit. An inkjet head array is provided.

  In a further preferred aspect of the present invention, the plurality of inkjet head units are disposed and mounted on the support member at different positions as viewed in the conveyance direction of the recording medium, and the plurality of inkjet heads An inkjet head array is provided in which correction of ejection timing of ink droplets from a unit is set for each of the plurality of inkjet head units.

  In another aspect of the present invention, an inkjet image forming apparatus having the above-described inkjet head array is provided.

According to the present invention, there is provided an image forming apparatus having a line head type ink jet array in which a plurality of ink jet head units each having an ink discharge nozzle array narrowed in one direction are arranged in a direction perpendicular to the conveyance direction of a recording medium. Maintenance work such as replacement of the inkjet head unit can be performed easily and in a short time.

1 is a diagram illustrating a schematic configuration of a continuous paper inkjet printer according to an embodiment of the present invention. It is a figure which shows a conveyance unit. It is a perspective view of an inkjet head array. It is a top view of an inkjet head array. It is a three-sided view of an inkjet head unit. It is a figure which shows an inkjet head array unit and a discharge surface. It is a figure of a base plate. It is a figure which shows the positioning mechanism of an inkjet head array unit. It is a figure which shows the positioning mechanism of an inkjet head array unit. It is a figure which shows the position preparation of an inkjet head array unit. It is a figure which contrasts the nozzle row of an inkjet head array unit, and a printing result. It is a figure which contrasts the nozzle row of an inkjet head array unit, and a printing result. It is a figure which contrasts the vertical shift of an inkjet head array unit, and a printing result.

  Hereinafter, a continuous paper inkjet printer 1 as an inkjet image forming apparatus according to an embodiment of the present invention will be described in detail with reference to FIG.

  The continuous paper inkjet printer 1 is an image forming apparatus that forms an image on a continuous paper recording medium MRC having feed holes at both ends in the width direction by an inkjet method. As the continuous paper recording medium MRC, so-called Z paper in which creases are alternately provided at predetermined intervals in the longitudinal direction (conveyance direction) is mainly used. Of course, other than this, an image can be formed on a so-called roll paper wound in a roll form.

  An upper casing 1a is placed on the lower casing 1b, and a pin tractor 3 serving as a main conveying means in the upper casing 1a, an inkjet head array 4 having an inkjet head unit 9, and a platen 5 facing the inkjet head unit 9 are conveyed. A transport unit 6 having a transport table 10 as means, a curing device 7 and the like are arranged.

  The continuous paper recording medium MRC is introduced from the right inlet 1c of the continuous paper inkjet printer 1 and discharged from the left outlet 1d as shown in the figure. In FIG. 1, a stacker 8 is attached to the left side of the ink jet printer 1 and refolds the continuous paper recording medium MRC discharged from the discharge port 1d. The stacker 8 can be attached to and detached from the continuous paper inkjet printer 1, and the continuous paper inkjet printer 1 can of course print without the stacker 8.

  The pin tractor 3 as the main transport means is driven by a drive motor (not shown) and transports the continuous paper recording medium MRC. The conveyance speed of the continuous paper recording medium MRC is set to 423.33 mm / s. This transport speed is 1 line (6 / 25.4mm), which corresponds to a printing speed of 6000 lines per minute. In addition, the continuous paper recording medium MRC can cope with a minimum width of 177.8 mm (7 inches) to a maximum width of 508 mm (20 inches).

  When the continuous paper recording medium MRC is transported, the pin tractor 3 is transported while the transport pins 3a (pin members) are engaged with the feed holes of the continuous paper recording medium MRC, that is, while restraining the continuous paper recording medium MRC. Therefore, the conveyance speed of the continuous paper recording medium MRC, timing control such as start / stop / acceleration / deceleration, etc. are all performed by the pin pin tractor 3.

  An inkjet head array 4 having an inkjet head unit 9 is located behind the pin tractor 3 when viewed in the transport direction of the continuous paper recording medium MRC. The inkjet head unit 9 allows an inkjet image to be recorded on the continuous paper recording medium MRC. Formation is made.

  The ink jet head unit 9 is an ink jet head unit having a recording density of 600 dots per 25.4 mm (so-called 800 DPI). The ink used is an ultraviolet curable ink (active light curable ink) and has an absorption peak at a wavelength of 385 nm.

  The platen 5 is at a position facing the inkjet head array 4 with the continuous paper recording medium MRC interposed therebetween, and is a member that constitutes a transport surface of the continuous paper recording medium MRC at that portion. The platen 5 body is formed by SUS cutting. The back surface of the continuous paper recording medium MRC is appropriately pressed against the platen 5 by the tension applied to the continuous paper recording medium MRC by a conveyance table 10 and the like which will be described later, and the continuous paper recording medium MRC is stably conveyed with appropriate tension. The The interval between the transport surface of the continuous paper recording medium MRC and the ink discharge surface of the inkjet head unit 9 can be set to an arbitrary value between 1 and 3 mm by an interval setting means (not shown).

  Within the transport unit 6, there is a transport table 10 which is one of the platen 5 and transport means. The conveyance table 10 is a conveyance means having a negative pressure adsorption type conveyance belt 12 as shown in FIG. 2, and has a function of cooperating with the scaflora pair 11 to apply an appropriate tension to the continuous paper recording medium MRC. It has two functions of holding and transporting the continuous paper recording medium MRC when the inkjet image is cured by the curing means 7. In FIG. 2, the platen 5 and others are not shown because they are complicated.

  The conveyance table 10 is configured such that the inside of the housing 13 formed of a sheet metal member is made negative pressure by a negative pressure generating means such as a blower (not shown), and a plurality of suction ports 14 (partially suction conveyance belts) narrowed in the conveyance surface. 12 is removed and the recording medium MRC is adsorbed. A drive roller 17 and a driven roller 15 are arranged on both sides of the housing 13 when viewed in the conveyance direction of the recording medium MRC, and the four suction conveyance belts 12 are wound around the rollers 13 so as to enclose the housing 13. It is disguised. The suction conveyance belt 12 is also provided with an opening 16 that cooperates with the suction port 14, and the suction conveyance belt 12 conveys the continuous paper recording medium MRC while adsorbing it while sliding with the housing 13 by the driving roller 14.

  A pair of scat flora 11 is also a conveying means, which is composed of a scaflora 11a and a driven roller 11b. The scaflora is made of SUS with a diameter of 40 mm, and the driven roller is a 20 mm diameter with a surface made of polyacetal. Follows with pressure contact.

  Both the scaflora pair 11 and the drive roller 17 of the transport table 10 are commonly driven by a motor (not shown), and the transport speed is set to a speed that is 2% faster than the transport speed of the tractor unit 3. The conveyance belt 12 of the conveyance table 10 and the back surface of the continuous paper recording medium MRC are adsorbed moderately by the negative pressure, and the continuous paper recording medium MRC is conveyed in a state where both of them can slide due to this speed difference. Similarly, the Scarofora pair 11 holds and conveys the continuous paper recording medium MRC with an appropriate pressure contact force capable of sliding relative to the recording medium, and both provide an appropriate tension to the continuous paper recording medium MRC. Is done.

  The conveyance table 10 can be rotated clockwise around the drive roller 17 as a rotation axis. By performing the rotation operation, the interval between the curing device 7 and the conveyance table 10 is increased. It is made easy to handle paper jams at that location.

  The shape of the conveyance path of the entire continuous paper recording medium MRC in the ink jet printer 1 is a convex shape with the platen 5 as the apex. Therefore, the continuous paper recording medium MRC is applied to the platen 5 with an appropriate pressure by the tension. Therefore, the continuous paper recording medium MRC can be stably conveyed on the platen 5 and conveyed on the platen.

  A curing device 9 is disposed above the transport table 10 with the continuous paper recording medium MRC interposed therebetween. The curing device 9 cures an inkjet image formed by ultraviolet curable ink formed on the continuous paper recording medium MRC, and has a UV-LED (ultraviolet light emitting LED) having an emission wavelength of 385 nm as an ultraviolet light source.

  In addition to the UV-LED, the curing device may be an ultraviolet light source such as a metal halide lamp. In the ink jet printer of this embodiment, a combination of an ultraviolet curable ink and an ultraviolet curable apparatus is used, but a thermosetting apparatus comprising a heat drying type, thermosetting aqueous or oil-based ink, and various heat sources. The present invention can also be implemented in a combination of heat drying apparatuses.

  Next, the details of the structure of the inkjet head array 4 and the inkjet head unit 9 and their surroundings and the adjustment method will be described with reference to FIG.

  As shown in FIGS. 3 and 4, the inkjet head array 4 has a structure in which up to five inkjet head units 9 shown in FIG. 5 can be mounted on a base plate 30 as a support member. The base plate 30 is a 14 mm thick stainless steel material having the shape shown in FIG. 7 and is mounted so that each inkjet head unit 9 covers the rectangular openings 31 arranged in a staggered manner, and the nozzles exposed from the rectangular openings 31 Ink droplets are ejected from the surface onto the recording medium MRC through the rectangular opening 31.

  As shown in FIG. 8, a set of positioning pins A32 and positioning pins B33, which are contact members, are provided for each inkjet head unit 9 at both ends of each rectangular opening 31 of the base plate 30. In the present embodiment, as will be described later, the position of each inkjet head unit 9 is not adjusted with respect to the base plate 30. Therefore, it is necessary to process the positioning pin A32 and the positioning pin B33 with the necessary and sufficient accuracy of the shape accuracy, the dimensional accuracy between the positioning pins, and the shape accuracy. That is, the positioning pin A32 and the positioning pin B33 are made of 5 mm diameter SUS having a tolerance of +0.005 to +0.01, and are press-fitted and fixed to the base plate 30. The positioning accuracy of each positioning pin A32 and positioning pin B33 in the x-axis direction and y-axis direction Is processed to an accuracy of 0.005 mm, and the parallelism of the imaginary line segment passing through the centers of the positioning pin A32 and the positioning pin B33 is ± 0.005 mm.

  The inkjet head unit 9 has the structure shown in FIG. 5 and has a width direction printing resolution of 600 dots per 25.4 mm (so-called 600 DPI). The ink nozzle surface is shown in FIG. The inkjet head unit 9 has a printing resolution of 600 dpi, that is, 42.3 μm in the width direction, but the ink discharge nozzles are narrowed at a pitch of 635 μm in the width direction (predetermined arrangement direction), and the pitch is 42.3 in the width direction. The nozzle row 35 shifted by μm is provided in parallel with 16 rows, thereby realizing the above-mentioned width direction printing resolution of 42.3 μm (= 635/15). Of course, the present invention is also applicable to the case where there are a plurality of nozzle rows that are narrowed at a predetermined interval in a predetermined arrangement direction.

  As shown in FIGS. 8 and 9, each inkjet head unit 9 has a V-shaped plate 40 and an L-shaped plate 41 as positioning members at both ends in the width direction. The V-shaped notch surfaces 40a and 40b of the V-shaped plate 40 and the L-shaped notched surface 41a of the L-shaped plate 41 are contact surfaces. The V-shaped plate 40 and the L-shaped plate 41 are adjusted and fixed to the inkjet head unit base plate 9a with two hexagonal bolts 42. A line segment that connects the center of a virtual circle with a diameter of 5 mm that contacts the V-shaped notch surfaces 40a and 40b, the center of the virtual circle with a diameter of 5 mm that contacts the L-shaped notch surface 41a, and the nozzle row 35 of the nozzle surface Only the parallelism is adjusted to 0.005 mm (see FIG. 10B), and is fixed to the inkjet head unit base plate 9a with hexagonal bolts. The adjustment of only the parallelism between the contact surfaces 40a, 40b, 41a and the nozzle row 35 can be performed by various known methods as disclosed in Patent Document 1. The adjustment allowance is provided in the V-shaped plate 40 and the L-shaped plate 41, and a slight allowance is provided in the through hole (not shown) of the hexagon bolt 42 that fastens each to the inkjet head unit base plate 9a. Is enough.

  A method of mounting each inkjet head unit 9 on the base plate 30 will be described with reference to FIGS. FIG. 8 is an enlarged perspective view of the vicinity of the L-shaped plate 41 as a positioning member, and FIG. 9 is an enlarged perspective view of the vicinity of the V-shaped plate 40 as a positioning member. For simplicity, only one inkjet head unit 9 is mounted, and members not directly related to the positioning mechanism or operation are omitted. The V-shaped notch surfaces 41a and 41b of the V-shaped plate 40 are brought into contact with positioning pins A32 provided on one side of each opening 31 of the base plate 30, and then the L-shaped notched surface 41a of the other L-shaped plate 41 is Then, the inkjet head unit 9 is positioned on the base plate 30 in contact with the positioning pins B33. In this state, the inkjet head unit 9 is fixed on the base plate 30 by the fixing screws 44. On the base plate 30, positioning pins B33, a plunger A38, and a plunger B39 are arranged so as to surround the protruding portion of the L-shaped plate 41 from three directions. The plunger A38 urges the ink jet head unit 9 in the direction of arrow A (that is, the width direction) in the drawing, and presses the V-shaped notch surfaces 40a and 40b of the other V-shaped plate 40 against the positioning pin A32. As a result, the inkjet head unit 9 is positioned in the x-axis direction. On the other hand, the plunger B39 urges the ink jet head unit 9 in the direction of arrow B in the drawing to press the L-shaped notch surface 41a of the L-shaped plate 41 against the positioning pin B33. Thereby, positioning in the rotational direction in the xy plane of the inkjet head unit 9 is performed. At the same time, the ink jet head unit 9 is positioned in the y-axis direction together.

  As schematically shown in FIG. 10, each contact surface of the V-shaped plate 40 and the L-shaped plate 41 attached to each inkjet head unit 9 (precisely, the center of a virtual circle with a diameter of 5 mm that contacts each contact surface) ) And the nozzle array 35 have been adjusted to 0.005 mm (FIG. 10A), and the parallelism between the positioning pins A32 and B33 of the base plate 30 is also processed to 0.005 mm (FIG. 10 ( b)). Therefore, just by mounting each inkjet head unit 9 on the base plate 30, at least the parallelism between the nozzle rows 35 of each inkjet head unit 9 is adjusted to within 0.01 mm.

  Next, adjustment in the x-axis direction will be described with reference to FIG. In FIG. 11, it is assumed that there is no displacement in the y-axis direction of each inkjet head unit 9 described later.

  First, with respect to the x-axis direction, as described above, in each inkjet head unit 9, the nozzle row 35 includes the center of a virtual circle having a diameter of 5 mm that contacts the V-shaped notch surfaces 40a and 40b and the L-shaped notch surface 41a. Only the parallelism with the imaginary line segment connecting the centers of the imaginary circles with a diameter of 5 mm abutting on the nozzle is adjusted to have a predetermined value (FIG. 10 (a)), and the effective discharge width of the nozzle row 35 in the x-axis direction. The position of each of the contact surfaces (positioning pins) is not positioned. Therefore, in a state where each inkjet head unit 9 is mounted on the base plate 30, the nozzle row 35 within the effective discharge width of each inkjet head unit 9 is shown in any of FIGS. 11 (a), 12 (a), and 13 (a). It becomes a state as shown in the above. That is, the nozzle rows 35 within the effective ejection width overlap when viewed from the conveyance direction of the recording medium MRC, but their mutual positions are not defined at all.

  Assume that the nozzle holes of adjacent ink jet head units 9 are aligned in the x-axis direction as shown in FIG. Assuming that the nozzle row 35 of the overlap portion 50 of both ink jet head units 9 is divided into two, a discharge region 53 continuous with the non-overlap portion 51 and a non-discharge region 54 located outside thereof, both ink jet head units. The interval between the nine ejection regions 53 can be exactly matched with the width direction printing resolution of the inkjet head unit 9. In this case, printing can be performed without any problem in printing.

  Next, consider a case where the positions of the nozzle holes of adjacent ink jet head units 9 are shifted as shown in FIG. At this time, the interval between the ejection regions 53 of both the inkjet head units 9 can be set to an arbitrary value of 0 or more according to the amount of deviation.

  When the present inventors compared the interval between the two ejection regions 53 and the print result, the interval between the two ejection regions 53 is 0.5 times the print resolution in the width direction of the inkjet head unit 9 (FIG. 12 (a)). It was found that printing with practically no problem was possible at a magnification of 1.0 (the state shown in FIG. 11). If the interval between the ejection areas 53 is smaller than 0.5 times the print resolution in the width direction of the inkjet head unit 9, the ink droplets ejected from both ejection areas 53 are too close, and the print density is high in a halftone image or the like. There may be streaky printing unevenness (state shown in FIG. 12B). On the other hand, when it is larger than 1.0 times, for example, 1.5 times as shown in FIG. 12C, conversely, white streaky printing may be lost in the solid image (FIG. 12D).

  The interval between the two ejection regions 53 can be set in the range of 0.5 to 1.0 regardless of the amount of deviation by setting the boundary position between the ejection region 53 and the non-ejection region 54 of the two inkjet head units 9. In addition, dividing the nozzle row 35 of the overlap portion 50 into the discharge region 53 and the non-discharge region 54 can be achieved by individually controlling the drive of each nozzle of the overlap portion 50, or by image data, for example, in bitmap units. It can be done by means such as shifting.

  Next, with regard to the adjustment in the y-axis direction, the y-axis direction is the same as the x-axis direction. Since only the parallelism with the imaginary line segment connecting the centers of the imaginary circles having a diameter of 5 mm that abuts the surface 41a is adjusted to a predetermined value, the nozzle rows 35 of the individual inkjet head units 9 are arranged in the y-axis direction. (Y-axis direction) No distance is specified. Accordingly, if, for example, a dot row extending in the width direction of the continuous paper recording medium MRC is formed in this state, each ink jet head unit 9 is drawn in a staircase pattern shifted in the y-axis direction as shown in FIG. It becomes. In FIG. 13, there is no deviation in the x-axis direction of the nozzles of each inkjet head unit 9.

  This adjustment is sufficient by setting the time difference Δt described in the prior art for each inkjet head unit 9. For reference, as shown in FIG. 13, the discharge area 53 and the non-discharge area 54 of the overlap portion 50 can have only one nozzle on either inkjet head unit side. Alternatively, it is possible to eliminate the non-ejection area on the one ink jet head unit side and use all the nozzles on the other ink jet head unit side as ejection areas.

  In summary, when mounting the inkjet head unit 9 on the base plate 30, the inkjet head unit 9 in which the parallelism between the nozzle array 35 and the contact surface of the positioning member is adjusted in advance is prepared, and the parallelism is within the specified range. The ink jet head array 4 in which the parallelism (only) of the nozzle row 35 is within the specified range can be realized on the base plate 30 by abutting against the positioning member of the base plate 30 that has been processed into the shape.

  After this, it is necessary to adjust the print position in the x-axis and y-axis directions. However, both of these are not mechanical adjustments, and control of the individual nozzles of the overlap portions 50 and 51 is controlled. It can be controlled and adjusted electrically and softly, such as shifting in units of bitmaps, or adjusting the time difference Δt (= d / v) determined from the recording medium conveyance speed v and the predetermined distance d. .

  This eliminates the need for complicated and expensive three-degree-of-freedom adjustment mechanisms and fixing mechanisms. The feature is that the adjustment work of the adjustment mechanism and the fixing mechanism due to complicated and time-consuming trial and error is not required.

  Furthermore, in the maintenance work such as replacement of the inkjet head unit 9 by the user, it is possible to avoid the occurrence of a problem that the user's printer is stopped for a long time.

  An image forming apparatus for forming an image by an ink jet method, in particular, a line head type in which a plurality of ink jet head units each having an ink ejection nozzle array narrowed in one direction are arranged in a direction perpendicular to the conveyance direction of a recording medium. The present invention is applied to an image forming apparatus having an inkjet head array.

DESCRIPTION OF SYMBOLS 1 Continuous paper inkjet printer 1a Upper housing | casing 1b Lower housing | casing 1c Inlet 1d Outlet 3 Pin tractor 4 Inkjet head array 5 Platen 6 Transfer unit 7 Curing device 8 Stacker 9 Inkjet head unit 9a Inkjet head unit base board 10 Conveying table 11 Scarflora pair 11a Scaflora 11b Follower roller 12 Adsorption conveyance belt 13 Case 14 Suction port 15 Follower roller 16 Opening 17 Drive roller 30 Base plate 31 Rectangular opening 32 Positioning pin A
33 Positioning pin B
35 Nozzle array 38 Plunger A
39 Plunger B
40 V-shaped plate 40a V-shaped notched surface 40b V-shaped notched surface 41 L-shaped plate 41a L-shaped notched surface 42 Hexagon bolt 44 Fixing screw 50 Overlap portion 51 Overlap portion 52 Non-overlap portion 53 Discharge area 53 Non Discharge area

Claims (5)

In an inkjet head array in which a plurality of inkjet head units having nozzle rows narrowed at predetermined intervals in a predetermined arrangement direction are mounted on a support member, at least one of the nozzle rows of the adjacent inkjet head units. The plurality of inkjet head units are arranged so that the portions overlap each other when viewed in the conveyance direction of the recording medium, and only the parallelism between the nozzle rows of the plurality of inkjet head units is a mechanism An ink jet head array characterized in that it can be adjusted in an automatic manner. Each of the plurality of inkjet head units has a positioning member that positions itself on the support member for each of the plurality of inkjet head units, and the positioning member is associated with a contact member provided on the support member. A contact surface for positioning the ink jet head unit on the support member, and mechanical adjustment of parallelism between the nozzle rows of the plurality of ink jet head units. The inkjet head array according to claim 1, wherein the adjustment is performed in adjustment of a relative position between the contact surfaces. In the overlap portion, the nozzle row of each of the adjacent inkjet head units is divided into two, a discharge region that discharges ink continuously and a non-discharge region that does not discharge ink. The distance between the ejection region and the other ejection region in the predetermined arrangement direction is 0.5 to 1.0 times the print resolution in the width direction of the inkjet head unit. The inkjet head array as described. The plurality of inkjet head units are arranged and mounted on the support member at different positions when viewed in the conveyance direction of the recording medium, and correct the ejection timing of ink droplets from the plurality of inkjet head units. 4. The inkjet head array according to claim 1, wherein the inkjet head array is set for each of the plurality of inkjet head units. An inkjet image forming apparatus comprising the inkjet head array according to claim 1.

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