JP2022090827A - Inkjet printer head gap adjustment unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress deterioration of image quality and deterioration of paper transportability.
SOLUTION: In an inkjet printer 1 that prints an image on a sheet P being transferred on a transfer belt 21 with ink ejected from an inkjet head 23 to 26 above the transfer belt 21, the sheet P is orthogonal to the transfer direction A. The first adjusting unit 28 that individually adjusts the vertical distance between the inkjet heads 23 to 26 and the transport belt 21 according to the position of the paper in the width direction B, and the inkjet head 1 according to the position in the transport direction A. On the transport belt 21 passing directly under the inkjet head 1 by at least one of the second adjusting section 29, the first adjusting section 28 and the second adjusting section 29, which individually adjusts the vertical distance from the transport belt 21. A control unit 4 for controlling the head gap between the paper P and the inkjet heads 23 to 26 so that the end portion of the paper P in the width direction B or the transport direction A is larger than the central portion by a predetermined amount is provided.
[Selection diagram] Fig. 1

Description

The present invention relates to a head gap adjusting unit for an inkjet printer.

In an inkjet printer, ink droplets ejected from an inkjet head are landed on a paper being transported on a transport belt to form an image on the paper. If the head gap, which is the distance between the inkjet head and the paper, is large, the ink droplets are likely to flow due to the paper transport airflow generated in the head gap. When the ink droplets are flown, the landing position of the ink droplets shifts, causing uneven density, uneven wind print, and the like on the image on the paper, which causes deterioration of the image quality.

Further, when the head gap is large, the image quality is significantly deteriorated by the satellite dependent on the main droplet of the ink droplet in flight. Further, the minute satellite becomes an ink mist floating in the head gap, and when the ink mist adheres to the paper, the image on the paper becomes dirty and the image quality is deteriorated.

As a method of avoiding deterioration of the image quality of the image on the paper, it is conceivable to reduce the head gap. The head gap can be reduced by using, for example, the techniques described in Patent Documents 1 and 2. In the technique of Patent Document 1, the conveyor belt is pushed up from the back side to the inkjet head side to reduce the head gap. In the technique of Patent Document 2, the carriage unit of the inkjet head is lowered to the side to reduce the head gap.

Japanese Unexamined Patent Publication No. 8-156353 Japanese Unexamined Patent Publication No. 2017-128130

Reducing the head gap increases the likelihood that the paper will come into contact with the inkjet head or peripheral components. When the paper comes into contact with the inkjet head or peripheral parts, the paper transport is hindered and the paper transportability is deteriorated, or stains on the inkjet head or peripheral parts adhere to the paper and the image quality is deteriorated.

In particular, the edges of the paper are prone to curl or broken ears due to moisture or the like. Further, when the paper is adsorbed to the transport belt by negative pressure and transported, the end portion of the paper is easily peeled off from the transport belt due to insufficient suction force. Therefore, if the head gap is made small, the edges of the paper are particularly likely to come into contact with the inkjet head.

The techniques of Patent Documents 1 and 2 merely make the head gap adjustable, suppress the deterioration of the image quality of the image formed on the paper, and the edge of the paper comes into contact with the inkjet head. Therefore, it does not realize both the suppression of the deterioration of the paper transportability and the suppression.

An object of the present invention is to provide a head gap adjusting unit for an inkjet printer that can solve the above problems and realize both suppression of deterioration of image quality and suppression of deterioration of paper transportability.

In order to achieve the above object, the head gap adjusting unit of the inkjet printer according to one aspect of the present invention is provided.
In an inkjet printer that prints an image on paper being conveyed on a conveyor belt with ink ejected from an inkjet head above the conveyor belt.
A first adjusting unit that individually adjusts the vertical spacing between the inkjet head and the transport belt according to the position in the width direction of the paper that is orthogonal to the transport direction of the paper.
A second adjusting unit that individually adjusts the vertical distance between the inkjet head and the transport belt according to the position in the transport direction.
The head gap between the paper and the inkjet head on the transport belt passing directly under the inkjet head is set by at least one of the first adjusting section and the second adjusting section in the width direction or the transport direction. A control unit that controls the edge of the paper so that it is larger than the central portion by a predetermined amount.
To prepare for.

According to the present invention, it is possible to achieve both suppression of deterioration in image quality and suppression of deterioration in paper transportability.

FIG. 1 is an explanatory diagram showing a schematic configuration of an inkjet printer including a head gap adjusting unit according to an embodiment of the present invention. FIG. 2 is a block diagram showing a configuration of a control system in the inkjet printer of FIG. FIG. 3 is an explanatory view of the printed portion of FIG. 1 as viewed from above. FIG. 4A is an explanatory view of the belt height adjusting portion of the conveyor belt of FIG. 1 as viewed from above. FIG. 4B is an explanatory view of the belt height adjusting portion of the conveyor belt of FIG. 1 as viewed from the left-right direction. FIG. 5A is an explanatory diagram showing a case where the belt height adjusting portion of FIG. 4B is configured by using an eccentric roller. FIG. 5B is an explanatory diagram showing a case where the belt height adjusting portion of FIG. 4B is configured by using a polygonal roller. FIG. 5C is an explanatory diagram showing a case where the belt height adjusting portion of FIG. 4B is configured by using the rack and pinion mechanism. FIG. 6A is an explanatory view seen from the left-right direction when the head height adjusting portion of the inkjet head portion of FIG. 1 is configured by using an eccentric roller. FIG. 6B is an explanatory view seen from the left-right direction when the head height adjusting portion of the inkjet head portion of FIG. 1 is configured by using a gear and a ball screw. FIG. 7 is a plan view of the paper of FIG. 1 in which curls or broken ears have occurred at the edges. FIG. 8 is an explanatory view showing a head gap at the center portion and the end portion in the width direction adjusted by the control performed by the control unit of FIG. 2 when transporting paper having curls or broken ears at the edges in the width direction. Is. FIG. 9A is an explanatory diagram showing a state in which the head height adjusting unit of FIG. 1 moves the head block of each row of each line head to a position at the time of printing. FIG. 9B is an explanatory diagram showing a state in which the head height adjusting unit of FIG. 1 moves the head block of each row of each line head to a position during the standby period. FIG. 9C is an explanatory diagram showing a state in which the head block of the row in which the tip of the paper passes directly below is moved from the position during the standby period to the position at the time of printing by the head height adjusting unit of FIG. FIG. 9D shows a state in which the head block of the row in which the tip of the paper passes directly under the paper is moved from the position during the standby period to the position at the time of printing when the paper is further advanced. It is explanatory drawing which shows.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The same or equivalent parts and components are designated by the same or equivalent reference numerals throughout the drawings. However, it should be noted that the drawings are schematic and may differ from the actual ones. In addition, it goes without saying that the drawings include parts having different dimensional relationships and ratios from each other.

Further, the embodiments shown below exemplify an apparatus or the like for embodying the technical idea of the present invention, and the technical idea of the present invention describes the arrangement of each component and the like as follows. It is not specific to. The technical idea of the present invention can be modified in various ways within the scope of claims.

FIG. 1 is an explanatory diagram showing a schematic configuration of an inkjet printer including a head gap adjusting unit according to an embodiment of the present invention, and FIG. 2 is a block diagram showing a configuration of a control system of the inkjet printer shown in FIG.

In the following description, the front side direction of the paper surface of FIG. 1 in which the user is located is the front side, and the back side direction of the paper surface is the rear side. Further, when viewed from the user, the vertical and horizontal directions are defined as the vertical and horizontal directions. The path shown by the thick line in FIG. 1 is the transfer path R to which the paper P, which is the printing medium, is conveyed. In the following description, upstream and downstream mean upstream and downstream of the transport direction A of the paper P in the transport path R.

As shown in FIG. 1, the inkjet printer 1 includes a paper feeding unit 2 and a printing unit 3. Further, as shown in FIG. 2, the inkjet printer 1 further includes a control unit 4 that controls the operations of the paper feed unit 2 and the print unit 3.

The paper feed unit 2 feeds the paper P to the print unit 3. As shown in FIG. 1, the paper feed unit 2 includes a paper feed table 11, a paper feed roller 12, an intermediate transfer roller 15, and a resist roller 17. Further, as shown in FIG. 2, the paper feed unit 2 further includes a paper feed motor 14, an intermediate transfer motor 16, and a resist motor 18.

The paper feed tray 11 shown in FIG. 1 is loaded with the paper P used for printing, and the paper feed roller 12 is arranged on the upper side thereof. The paper feed roller 12 is rotated by the paper feed motor 14 of FIG. 2 to feed the paper P of the paper feed table 11 to the transport path R one by one.

A pair of intermediate transport rollers 15 shown in FIG. 1 are arranged on the transport path R. Both intermediate transport rollers 15 nip the paper P fed to the transport path R by the paper feed roller 12 and feed it to the downstream side of the transport path R. As a result, the paper P is conveyed in the transfer direction A in the transfer path R. One of the intermediate transfer rollers 15 is rotated by the intermediate transfer motor 16 of FIG.

In this embodiment, in order to facilitate the explanation, as shown in FIG. 1, the case where the paper feed unit 2 has a set of a paper feed table 11, a paper feed roller 12, and an intermediate transfer roller 15. explain. However, the present invention is also applicable when the paper feed unit 2 has a plurality of sets of a paper feed table 11, a paper feed roller 12, and an intermediate transfer roller 15.

A pair of resist rollers 17 are arranged on the transport path R on the downstream side of the intermediate transport roller 15. The resist roller 17 temporarily stops the tip of the paper P conveyed by the intermediate transfer roller 15 to correct the skew, and then nips the tip of the paper P and feeds it to the printing unit 3. The resist motor 18 of FIG. 2 drives the resist roller 17 of FIG.

The printing unit 3 prints on the paper P while conveying the paper P fed by the paper feeding unit 2 on the transport path R on the downstream side of the resist roller 17. In the present embodiment, the printing unit 3 includes a transport belt 21 and an inkjet head unit 22.

The transport belt 21 can be configured by using an endless belt spanned between a pair of guide rollers. The transport belt 21 sucks and holds the paper P conveyed by the resist roller 17 on the belt and conveys it. When the roller on which the belt of the conveyor belt 21 is hung is driven by a motor (not shown), the belt is rotated and the paper P on the belt is conveyed in the transport direction A.

The inkjet head portion 22 is arranged above the conveyor belt 21. As shown in FIG. 3, the inkjet head unit 22 has four color-coded line heads 23 to 26 arranged at intervals in the transport direction A of the paper P on the transport belt 21. Each line head 23 to 26 is held in the head holder 27. The line heads 23 to 26 are arranged in the order of K (black), C (cyan), M (magenta), and Y (yellow) from the upstream side of the paper P in the transport direction A.

The line heads 23 to 26 of each color have a plurality of head blocks 23a to 26a. In the present embodiment, the line heads 23 to 26 of each color have six head blocks 23a to 26a, respectively. The six head blocks 23a to 26a of each color are arranged in two columns in the transport direction A of the paper P and three rows in the width direction B (front-back direction) of the paper P orthogonal to the transport direction A. They are arranged in a staggered pattern at intervals in the width direction B. A plurality of nozzles (not shown) are arranged at equal intervals in the width direction B on the nozzle surface (not shown) facing the transport belt 21 of the head blocks 23a to 26a of each color.

The inkjet head unit 22 prints an image on the paper P conveyed by the conveyor belt 21 by ejecting ink from the nozzles of the head blocks 23a to 26a, respectively, in a pattern corresponding to the image to be printed on the paper P. ..

As shown in FIG. 1, the transport belt 21 has a belt height adjusting portion 28 as a first adjusting portion. The inkjet head unit 22 has a head height adjusting unit 29 as a second adjusting unit.

As shown in FIG. 4A, the belt height adjusting portion 28 of the conveyor belt 21 has a plurality of height adjusting mechanisms 28a arranged at intervals in the width direction B of the paper P. As shown in FIG. 4B, each height adjusting mechanism 28a is arranged on the back side of a portion of the transport belt 21 facing the inkjet head portion 22. Each height adjusting mechanism 28a always comes into contact with the conveyor belt 21 from the back side of the belt due to the tension of the conveyor belt 21. As shown in FIG. 4A, each height adjusting mechanism 28a contacts a portion of the paper P over the entire length in the transport direction A between the guide rollers of the transport belt 21.

As shown in FIG. 5A, each height adjusting mechanism 28a can be configured by using, for example, an eccentric roller 30. The eccentric roller 30 rotates around a rotation shaft 30a penetrating a portion eccentric from the center of a circular cross section.

The rotating shaft 30a of the eccentric roller 30 is rotated by the belt height adjusting motor 31 of FIG. The belt height adjusting motor 31 is provided corresponding to the rotating shaft 30a of each eccentric roller 30. Each eccentric roller 30 can be individually rotated by the corresponding belt height adjusting motor 31.

By rotating the eccentric roller 30 of FIG. 5A, the vertical distance between the transport belt 21 and the inkjet head portion 22 at the position where the eccentric roller 30 comes into contact from the back side of the belt can be adjusted.

As shown in FIG. 5B, each height adjusting mechanism 28a can also be configured by using a polygonal roller 32 instead of the eccentric roller 30. FIG. 5B shows a case where the cross section of the polygonal roller 32 is an equilateral triangle.

The polygonal roller 32 rotates around a rotation shaft 32a penetrating a portion deviated from the center of gravity of the cross section of an equilateral triangle. The distance between each vertex of the polygonal roller 32 and the rotation axis 32a is different. Each polygonal roller 32 can be individually rotated by the corresponding belt height adjusting motor 31 of FIG.

By rotating the polygonal roller 32 of FIG. 5B, the vertical distance between the transport belt 21 and the inkjet head portion 22 at the position where the polygonal roller 32 comes into contact from the back side of the belt can be adjusted.

As shown in FIG. 5C, each height adjusting mechanism 28a can also be configured by using a rack and pinion mechanism 33 instead of the eccentric roller 30. FIG. 5C shows a case where the rack and pinion mechanism 33 has a pinion gear 33a, a rack 33b, and an adjusting member 33c.

The rack 33b moves up and down by the rotation of the pinion gear 33a. The adjusting member 33c is attached to the upper end of the rack 33b. The adjusting member 33c has a certain dimension in the front and back directions of the paper surface of FIG. 5C, that is, in the transport direction A of the paper P. The adjusting member 33c comes into contact with a portion of the transport belt 21 between the guide rollers over almost the entire length. FIG. 5C shows a case where the tip of the adjusting member 33c in contact with the transport belt 21 has an arcuate cross section.

The pinion gear 33a of each rack and pinion mechanism 33 can be individually rotated by the corresponding belt height adjusting motor 31 of FIG.

By rotating the pinion gear 33a of FIG. 5C, the vertical distance between the conveyor belt 21 and the inkjet head portion 22 at the position where the adjusting member 33c comes into contact from the back side of the belt can be adjusted.

As described above, in the belt height adjusting portion 28 of FIG. 1, each height adjusting mechanism 28a is vertically spaced between the conveying belt 21 and the inkjet head portion 22 according to the position of the conveying belt 21 in the width direction B of the paper P. Can be adjusted individually.

The head height adjusting unit 29 of the inkjet head unit 22 shown in FIG. 1 is provided for each head block 23a to 26a of each row of the line heads 23 to 26 of each color shown in FIG. As shown in FIG. 6A, each head height adjusting unit 29 has a head mounting plate 34 and an elevating mechanism 35 for the head mounting plate 34.

Head blocks 23a to 26a in the same row of the line heads 23 to 26 are attached to the head mounting plate 34. Both ends of the head mounting plate 34 in the width direction B of the paper P are held by the head holder 27 of FIG. FIG. 6A shows a case where the elevating mechanism 35 is configured by using the cushioning spring 36 and the pressing roller 37.

The cushioning spring 36 is arranged between the end of the head mounting plate 34 and the head holder 27. The head mounting plate 34 is urged upwardly away from the head holder 27 by the elastic force of the cushioning spring 36.

The pressing roller 37 rotates around a rotation shaft 37a eccentric from the center of gravity. The pressing roller 37 can be configured as, for example, the eccentric roller 30 of FIG. 5A or the polygonal roller 32 of FIG. 5B. The pressing roller 37 always comes into contact with the head mounting plate 34 due to the elastic force of the cushioning spring 36. FIG. 6A shows a case where the pressing roller 37 is composed of a columnar eccentric roller.

The rotation shaft 37a of the holding roller 37 of FIG. 6A is rotated by the head height adjusting motor 38 of FIG. The head height adjusting motor 38 is provided corresponding to the head height adjusting portion 29 in each row. The holding rollers 37 in each row can be individually rotated by the corresponding head height adjusting motor 38.

By rotating the pressing roller 37 of FIG. 5A, the vertical distance between the head blocks 23a to 26a attached to the head mounting plate 34 with which the pressing roller 37 contacts and the transport belt 21 can be adjusted.

As shown in FIG. 6B, the elevating mechanism 35 can also be configured by using the ball screw mechanism 39 instead of the cushioning spring 36 and the pressing roller 37.

The ball screw mechanism 39 includes a ball screw shaft 39a attached to the head holder 27 and extending in the vertical direction, a ball screw nut 39b screwed to the ball screw shaft 39a, and a gear 39c formed on the peripheral surface of the ball screw nut 39b. It has an input gear 39d meshed with the screw. The ball screw nut 39b supports both ends of the head mounting plate 34 in the width direction B of the paper P.

The input gear 39d is rotated by the head height adjusting motor 38 of FIG. The head height adjusting motor 38 is provided corresponding to the input gear 39d of the ball screw mechanism 39 in each row. The input gears 39d in each row can be individually rotated by the corresponding head height adjusting motor 38.

When the input gear 39d rotates the ball screw nut 39b, the ball screw nut 39b moves up and down along the ball screw shaft 39a, and the head mounting plate 34 supported by the ball screw nut 39b moves up and down. By raising and lowering the head mounting plate 34, the vertical distance between the head blocks 23a to 26a mounted on the head mounting plate 34 and the transport belt 21 can be adjusted.

As described above, in the head height adjusting unit 29 of FIG. 1, the transport belt 21 and the head block of each row are arranged according to the positions of the head blocks 23a to 26a of each row in the transport direction A of the paper P by the elevating mechanism 35. The vertical spacing from 23a to 26a can be adjusted individually.

The control unit 4 controls the operation of each unit of the inkjet printer 1. The control unit 4 includes a CPU, RAM, ROM, and the like.

Specifically, the control unit 4 feeds the paper P to the printing unit 3 by the feeding unit 2, and while the paper P is conveyed by the conveying belt 21 in the printing unit 3, the ink is ejected by the inkjet head unit 22. Controls to print on paper P.

By the way, regarding the image quality of the image printed on the paper P by the printing unit 3, the reason that the head gap between the paper P on the transport belt 21 and the head blocks 23a to 26a is made smaller reduces the deviation of the ink landing position. Will be higher.

However, as shown in FIG. 7, for example, when the peripheral portion Pe of the paper P is curled or the ear is broken due to moisture or the like, the direction of the curl or the ear break is upward on the head block 23a to 26a side. The peripheral portion Pe of the paper P easily comes into contact with the head blocks 23a to 26a. When the paper P comes into contact with the head blocks 23a to 26a, the transport of the paper P may be hindered, or stains on the head blocks 23a to 26a may adhere to the paper P to deteriorate the image quality.

Even in the type of transport belt 21 that sucks the paper P by negative pressure, if the peripheral portion Pe of the paper P has curls or broken ears, the paper P cannot sufficiently adhere to the transport belt 21, and the transport belt 21 has insufficient suction force. There is a possibility that the paper P may come off from the head block 23a to 26a and come into contact with the head blocks 23a to 26a.

Therefore, in the present embodiment, the control unit 4 operates at least one of the belt height adjusting unit 28 and the head height adjusting unit 29 to adjust the distance between the conveyor belt 21 and the line heads 23 to 26. conduct. This control can be performed when the paper P being conveyed by the transfer belt 21 of FIG. 1 passes below the line heads 23 to 26. The control unit 4 detects the passage of the paper P by a sensor (not shown) at a predetermined position on the transport path R, for example, at a timing for adjusting the distance between the transport belt 21 and the line heads 23 to 26. It can be decided based on the timing.

Hereinafter, the content of the interval adjustment control between the conveyor belt 21 and the line heads 23 to 26 performed by the control unit 4 is performed by operating the belt height adjusting unit 28 and operating the head height adjusting unit 29. It will be explained separately.

The pattern including the position and shape of curls or broken ears generated on the peripheral portion Pe of the paper P fed to the printing unit 3 by the paper feeding unit 2 of the inkjet printer 1 is known in advance for each size of the paper P. Suppose there is. Among the peripheral portions Pe of the paper P, the pattern of curl or ear breakage generated at the end of the paper P in the transport direction A can be known for each dimension of the paper P in the transport direction A, for example. The pattern of curl or ear breakage generated at the end of the peripheral portion Pe of the paper P in the width direction B of the paper P can be known, for example, for each dimension of the paper P in the width direction B.

First, the interval adjustment control between the conveyor belt 21 and the line heads 23 to 26 performed by the control unit 4 by operating the belt height adjustment unit 28 will be described. In this interval control, the control unit 4 adjusts the position of the transfer belt 21 in the vertical direction to adjust the interval between the transfer belt 21 and the line heads 23 to 26.

From the image data and print setting data of the print job input to the control unit 4, the control unit 4 determines the size of the paper P used for printing and the size of the margin of the paper P generated around the print image. The width direction B of is specified. Then, the control unit 4 sets the distance between the transport belt 21 and the line heads 23 to 26 at the center and both ends of the width direction B of the paper P from the specified dimensions.

However, if there is no margin around the printed image in the width direction B of the paper P, the control unit 4 may cancel the interval adjustment by the belt height adjusting unit 28 and do not perform the operation. Further, even when the area of the conveyor belt 21 corresponding to the range in which the image of the paper P is printed overlaps with the range in which the vertical position is adjusted by the belt height adjusting unit 28 of the conveyor belt 21, the control unit 4 controls the belt. The interval adjustment by the height adjusting unit 28 may be canceled and not performed.

Cancellation of these spacing adjustments prevents the head gap in the range in which the image of the paper P is printed from fluctuating between the central portion and the end portion in the width direction B due to the adjustment of the vertical position of the transport belt 21. It is effective in preventing the quality of the printed image from being deteriorated due to the variation.

By the way, the distance between the transport belt 21 and the line heads 23 to 26 at the center and both ends of the paper P in the width direction B is based on the pattern of curl or ear breakage generated at the ends of the paper P in the width direction B. Can be set. The pattern of curl or ear breakage that occurs at the end of the paper P in the width direction B is known for each dimension of the paper P in the width direction B.

Therefore, if the dimension of the paper P in the width direction B is specified, the pattern of curl or ear bending generated at the end portion of the paper P in the width direction B is specified, and based on this, the center of the paper P in the width direction B is specified. The distance between the transport belt 21 and the line heads 23 to 26 at the portions and both ends can be specified.

Therefore, for example, in a memory (not shown) of the control unit 4, the dimensions of the paper P in the width direction B, the distance between the transport belt 21 and the line heads 23 to 26 at the center and both ends of the width direction B of the paper P Store the table associated with. Then, the control unit 4 refers to the table of the memory, and from the specified dimensions, the transfer belt 21 and the line heads 23 to 26 at the center portion and both end portions of the width direction B of the paper P, respectively. You can set the interval.

If upward curl or ear breakage occurs at both ends of the paper P in the width direction B, increase the distance between the transport belt 21 and each line head 23 to 26 by a predetermined amount with respect to the central portion. .. For example, when the distance between the central portions is the default of 1.5 mm, the distance between both ends can be set to 2.0 mm by increasing the predetermined amount of 0.5 mm. This numerical value is merely an example, and the distance between the transport belt 21 and the line heads 23 to 26 at the central portion and both ends in the width direction B can be set to an arbitrary value depending on the circumstances to be considered.

The control unit 4 adjusts the height of each belt height adjusting unit 28 so that the distance between the transport belt 21 and the line heads 23 to 26 at the center and both ends of the width direction B of the paper P becomes a set size. The belt height adjusting motor 31 corresponding to the mechanism 28a is operated.

As a result, as shown in FIG. 8, even if upward curl or ear breakage occurs at the end of the paper P on the transport belt 21 in the width direction B, between the paper P and the line heads 23 to 26. In addition, it is possible to secure a head gap having a size such that the paper P does not come into contact with the line heads 23 to 26. Note that FIG. 8 shows a case where the eccentric roller 30 of FIG. 5A is used for the height adjusting mechanism 28a.

The spacing adjustment control between the conveyor belt 21 and the line heads 23 to 26 performed by the control unit 4 by operating the belt height adjusting unit 28 is the height of the central portion of the conveyor belt 21 in the width direction B of the paper P described above. It does not have to be the content to raise the height of both ends without changing. For example, increase the height of the central portion in the width direction B to decrease the height of both ends, increase the height of the central portion to keep the height of both ends unchanged, and increase the height of the central portion to decrease the height of both ends. It suffices if the relative height between the central part and both ends can be adjusted, such as raising the height a little smaller than the central part or lowering the height of both ends without changing the height of the central part.

Further, if the image quality of the printed image is deteriorated due to the variation in the head gap in the width direction B of the paper P due to the vertical position adjustment of the transport belt 21, ink droplets are ejected from the nozzles of the line heads 23 to 26. The speed, discharge timing, etc. may be adjusted.

Next, the interval adjustment control between the transfer belt 21 and the line heads 23 to 26 performed by the control unit 4 by operating the head height adjustment unit 29 will be described. In this interval control, the control unit 4 adjusts the positions of the head blocks 23a to 26a in each row of the line heads 23 to 26 in the vertical direction to adjust the interval between the conveyor belt 21 and the line heads 23 to 26.

From the image data and print setting data of the print job input to the control unit 4, the control unit 4 determines the size of the paper P used for printing and the size of the margin of the paper P generated around the print image. The transport direction A of the above is specified. Then, the control unit 4 waits for the portion of the paper P on the transport belt 21 where the curl or the ear is broken passes directly under the head blocks 23a to 26a of each row of the line heads 23 to 26 from the specified dimensions. The spacing between the transport belt 21 and the head blocks 23a to 26a of each row during the period is set.

However, if there is no margin around the printed image in the transport direction A of the paper P, the control unit 4 may cancel the interval adjustment by the head height adjusting unit 29 so as not to perform the interval adjustment. Further, even when the area of the transport belt 21 corresponding to the range in which the image of the paper P is printed overlaps with the range in which the vertical position is adjusted by the head height adjusting unit 29, the control unit 4 is the head height adjusting unit. The interval adjustment by 29 may be canceled and not performed.

Cancellation of these spacing adjustments prevents the head gap in the range in which the image of the paper P is printed from fluctuating between the central portion and the end portion of the transport direction A by adjusting the vertical positions of the head blocks 23a to 26a, and the head. It is effective in preventing the quality of the printed image from being deteriorated due to the variation in the gap.

By the way, the distance between the transport belt 21 and the head blocks 23a to 26a of each row during the waiting period can be set based on the pattern of curl or ear breakage generated at the end of the paper P in the transport direction A. The pattern of curl or ear breakage that occurs at the end of the paper P in the transport direction A is known for each dimension of the paper P in the transport direction A.

Therefore, if the dimensions of the paper P in the transport direction A are specified, the pattern of curl or ear breakage generated at the end of the paper P in the transport direction A is specified, and based on this, the transport belt 21 and the transport belt 21 during the waiting period The distance between the head blocks 23a to 26a in each row can be specified.

Therefore, for example, in a memory (not shown) of the control unit 4, a table in which the dimensions of the paper P in the transport direction A and the spacing between the transport belt 21 and the head blocks 23a to 26a of each row during the standby period are associated with each other is provided. Remember it. Then, the control unit 4 can set the interval between the transfer belt 21 and the head blocks 23a to 26a of each row during the standby period from the specified dimensions by referring to the table of the memory.

If an upward curl or ear break occurs at the tip of the paper P in the transport direction A, the transport belt 21 and the head block 23a of each row are in the waiting period until the tip of the paper P passes directly underneath. The interval from to 26a is increased by a predetermined amount with respect to the interval at the time of printing shown in FIG. 9A. In FIG. 9A, the illustration of one of the two rows of head blocks 25a and both rows of the two rows of head blocks 26a is omitted. The illustration of the head blocks 25a and 26a in these rows is also omitted in FIGS. 9B to 9D which will be referred to hereafter.

For example, when the printing interval is 1.5 mm, the interval during the waiting period can be increased by 0.5 mm as a predetermined amount to 2.0 mm. This numerical value is only an example, and the distance between the transport belt 21 and the line heads 23 to 26 at the time of printing and during the standby period can be an arbitrary value depending on the circumstances to be considered.

When an upward curl or ear break occurs at the tip of the paper P in the transport direction A, the control unit 4 sets the distance between the transport belt 21 and the head blocks 23a to 26a of each row to be the distance between the paper P on the transport belt 21. The head height adjustment motor 38 corresponding to the elevating mechanism 35 of the head mounting plate 34 of each head height adjusting unit 29 is operated so as to have a set size during the waiting period in which the paper passes directly underneath.

The control unit 4 sets the waiting period of the head blocks 23a to 26a in each row, for example, the dimensions of the paper P in the transport direction A, the known transport speed of the paper P, and the arrangement of the head blocks 23a to 26a in each row. From, it can be specified respectively.

As a result, even if an upward curl or ear break occurs at the tip of the paper P on the transport belt 21 in the transport direction A, between the head blocks 23a to 26a of each row and the paper P during the waiting period, A head gap of the required size can be secured. In this head gap, as shown in FIG. 9B, the paper P can be prevented from contacting the head blocks 23a to 26a of the line heads 23 to 26.

When the tip of the paper P on which the upward curl or the ear is broken passes directly under the paper P, the control unit 4 adjusts the distance between the head blocks 23a to 26a of the row whose waiting period has expired and the transport belt 21 by adjusting the head height. The interval at the time of printing is sequentially changed by 29. The head blocks 23a to 26a of each row after being changed to the printing interval are arranged at positions closer to the transport belt 21 than during the waiting period, for example, as shown in FIGS. 9C and 9D.

As a result, at the time of printing, the head gap between the head blocks 23a to 26a of each row and the paper P can be reduced to a closeness that can suppress the deterioration of the print quality due to the deviation of the landing position of the ink.

It should be noted that the ear folds of the paper P generally occur at the four corners of the paper P. The paper P in which the ear is broken at some of the four corners can be specified by the control unit 4 from the dimensions of the paper P in the transport direction A and the width direction B. Then, when ear breakage occurs at any of the four corners of the paper P, the control unit 4 operates both the belt height adjusting unit 28 and the head height adjusting unit 29 to operate the conveyor belt 21 and the line head 23. It is possible to perform interval adjustment control between ~ 26.

In the above example, when ear breaks occur at the four corners of the paper P, the head gap is increased by 0.5 mm at both ends from the central portion in the width direction B by the belt height adjusting portion 28, and the head height is increased. The adjustment unit 29 further increases by 0.5 mm during the waiting period. Therefore, even if the four corners of the paper P are closer to the line heads 23 to 26 than when the four corners of the paper P are curled upward due to the broken ears, the space between the paper P on the transport belt 21 and the line heads 23 to 26 is sufficient. A large head gap can be secured.

According to the inkjet printer 1 of the present embodiment described above, the distance between the paper P on the transport belt 21 passing directly under the line heads 23 to 26 and the line heads 23 to 26 is set by the belt height adjusting unit 28. And the head height adjusting unit 29 is adjusted by at least one of them. For this reason, the curl or the broken ear portion of the paper P comes into contact with the line heads 23 to 26 in the head gap when the paper P passes directly under the line heads 23 to 26, which hinders transportation or stains the printed image. It is possible to control the deterioration of the print quality due to the increase of the head gap while suppressing the deterioration of the image quality.

It should be noted that the present invention is not limited to the above embodiment, and at the implementation stage, the components can be modified and embodied within a range that does not deviate from the gist thereof. In addition, various inventions can be formed by an appropriate combination of the plurality of components disclosed in the above-described embodiment. For example, some components may be removed from all the components shown in the embodiments.

[Additional Notes]
The embodiments described above disclose the inventions of the following aspects.

That is, as an invention of one aspect,
In an inkjet printer that prints an image on paper being conveyed on a conveyor belt with ink ejected from an inkjet head above the conveyor belt.
A first adjusting unit that individually adjusts the vertical spacing between the inkjet head and the transport belt according to the position in the width direction of the paper that is orthogonal to the transport direction of the paper.
A second adjusting unit that individually adjusts the vertical distance between the inkjet head and the transport belt according to the position in the transport direction.
The head gap between the paper and the inkjet head on the transport belt passing directly under the inkjet head is set by at least one of the first adjusting section and the second adjusting section in the width direction or the transport direction. A control unit that controls the edge of the paper so that it is larger than the central portion by a predetermined amount.
Disclosed is a headgap adjusting unit for an inkjet printer comprising.

According to the invention according to the above aspect, it is possible to realize both the suppression of the deterioration of the image quality and the suppression of the deterioration of the paper transportability.

1 Inkjet printer 2 Paper feed unit 3 Printing unit 4 Control unit 11 Paper feed stand 12 Paper feed roller 14 Paper feed motor 15 Intermediate transfer roller 16 Intermediate transfer motor 17 Resist roller 18 Resist motor 21 Transfer belt 22 Inkjet head section 23 to 26 lines Head (inkjet head)
23a-26a Head block 27 Head holder 28 Belt height adjustment part (1st adjustment part)
28a Height adjustment mechanism 29 Head height adjustment part (second adjustment part)
30 Eccentric roller 30a Rotating shaft 31 Belt height adjustment motor 32 Polygonal roller 32a Rotating shaft 33 Rack pinion mechanism 33a Pinion gear 33b Rack 33c Adjusting member 34 Head mounting plate 35 Elevating mechanism 36 Cushioning spring 37 Holding roller 37a Rotating shaft 38 Head height Adjustment motor 39 Ball screw mechanism 39a Ball screw shaft 39b Ball screw nut 39c Gear 39d Input gear A Transport direction B Width direction P Paper R Transport path

Claims (1)

In an inkjet printer that prints an image on paper being conveyed on a conveyor belt with ink ejected from an inkjet head above the conveyor belt.
A first adjusting unit that individually adjusts the vertical spacing between the inkjet head and the transport belt according to the position in the width direction of the paper that is orthogonal to the transport direction of the paper.
A second adjusting unit that individually adjusts the vertical distance between the inkjet head and the transport belt according to the position in the transport direction.
The head gap between the paper and the inkjet head on the transport belt passing directly under the inkjet head is set by at least one of the first adjusting section and the second adjusting section in the width direction or the transport direction. A control unit that controls the edge of the paper so that it is larger than the central portion by a predetermined amount.
Inkjet printer head gap adjustment unit.

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