JP2017177431A - Ink jet printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a floating part of a recording medium from colliding against an ink jet head on a conveyor belt even when flotation of a printing medium such as a sheet is large as the printing medium floats, bends and so on.SOLUTION: An ink jet printer comprises: an ink jet head 31 which has a plurality of nozzle arrays arranged in parallel; a suction conveyance part 3 which is provided below the ink jet head 31, and sucks and conveys a printing medium such as a sheet with negative pressure; a sheet flotation sensor 29 which is provided upstream from the ink jet head 31, and detects the sheet floating at the suction conveyance part 3; a head gap adjustment unit 33 which adjusts a head gap; and a control part 5 which retracts the suction conveyance part 3 downward away from the ink jet head 31 by placing the head gap adjustment unit 33 in operation and also increases suction force for the sheet by increasing the negative pressure at the suction conveyance part 3 when the sheet flotation sensor 29 detects the sheet floating.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an ink jet printing apparatus that performs printing by ejecting ink to a print medium such as paper conveyed from the upstream side by an ink jet head having a plurality of nozzle arrays arranged in parallel, and in particular, during suction conveyance. The present invention relates to an ink jet printing apparatus that detects floating of the print medium and prevents the print medium from colliding with an ink jet head.

  In an inkjet printing apparatus, suction conveyance is performed below an inkjet head having a plurality of nozzle rows arranged in parallel, by sucking air and adsorbing and conveying a print medium such as paper by negative pressure.

  In suction conveyance, air is sucked from a plurality of air intake holes formed in the conveyance belt of the conveyance device and the print medium such as paper is sucked and conveyed by negative pressure. In the inkjet printing device, the paper is close to the inkjet head. Therefore, it is necessary to prevent the paper from colliding with the inkjet head.

  For this reason, when a sheet lift of a predetermined value or more occurs on a print medium such as a sheet, an ink jet printing apparatus that detects the lift and stops the conveyance of the print medium by suddenly stopping the upstream conveyance roller (for example, a patent) Reference 1) or an ink jet printing apparatus that prevents the paper from colliding with the ink jet head by increasing the suction force of the suction holes provided in the transport belt of the transport device when curling or the like occurs on the paper. For example, see Patent Document 2).

JP 2007-136726 A JP 2006-176265 A

  However, in the inkjet printing apparatus described in Patent Document 1 described above, when the floating of the sheet is detected, the trailing edge of the sheet is niped (clamped) by the upstream roller to suddenly stop the sheet. If it is short, or if floating is detected at the trailing edge of the paper, the upstream roller cannot nip the paper trailing edge, and the paper is sent to the suction conveyance section as it is. There was a problem of colliding with the inkjet head.

  Further, in the ink jet printing apparatus described in Patent Document 2 described above, when the floating of the paper is detected, the suction force at the time of paper suction and conveyance in the suction conveyance unit is increased to adsorb the paper. If the suction force is increased, the airflow around the head increases, the ink landing position shifts, the amount of mist generation increases, and stringing (satellite) flows laterally, which may reduce print quality. In other words, there is a problem that the paper cannot be brought into close contact with the conveyance belt, and the floating portion of the paper collides with the inkjet head.

  The present invention has been made in view of such a problem, and even when the print medium such as paper floats or bends and the print medium is largely lifted, collision between the recording medium and the inkjet head in the suction conveyance unit is achieved. An object of the present invention is to provide an ink jet printing apparatus that can prevent the above problem more reliably.

In order to achieve the above object, the first feature of the ink jet printing apparatus according to the present invention is as follows.
An inkjet head having a plurality of nozzle rows arranged in parallel;
A suction conveyance unit that is provided below the inkjet head and that adsorbs and conveys the print medium by negative pressure;
A float detecting means provided on the upstream side of the ink jet head and detecting the float of the print medium transported by the suction transport means;
A head gap adjusting means for adjusting a head gap which is a distance between a medium holding surface in the suction conveying means and an ink discharge surface of the inkjet head;
When the floating of the printing medium is detected by the floating detection means, the head gap adjusting means is operated to retract the suction conveyance means downward to move away from the inkjet head, and negative pressure in the suction conveyance means And a control means for increasing the suction force of the print medium.

The second feature of the ink jet printing apparatus according to the present invention is as follows.
The suction conveying means includes
A plurality of air intake holes, and a conveyance belt that adsorbs and conveys the print medium;
A pressure chamber provided below the conveyor belt, the volume of which can be changed by driving the movable side wall;
A suction fan that makes the pressure chamber negative and sucks the print medium by a plurality of suction holes of the conveyor belt,
The control means includes
When the floating of the printing medium is detected by the floating detection unit and the negative pressure in the suction conveyance unit is increased, the movable side wall of the pressure chamber is driven to reduce the volume of the pressure chamber. .

  According to the first feature of the ink jet printing apparatus of the present invention, the control means operates the head gap adjusting means to retract the suction conveyance means downward when the floating detection means detects the floating of the print medium. As a result, the suction force of the print medium is increased by moving away from the inkjet head and increasing the negative pressure in the suction conveyance means.

  For this reason, even when the print medium such as paper floats or bends and the print medium is largely lifted, it is possible to more reliably prevent the recording medium and the inkjet head from colliding with each other in the suction conveyance unit.

  In particular, in the present invention, when the floating of the printing medium is detected by the floating detection means, not only the negative pressure in the suction conveyance means is increased to increase the suction force of the print medium, but also the suction conveyance means is retracted downward. Therefore, it is possible to prevent the print medium from colliding with the inkjet head more reliably than simply increasing the negative pressure in the main suction conveyance stage.

  As a result, according to the first feature of the present invention, the conveyance speed of the paper PA can be improved, and the detection accuracy of the floating of the printing medium is improved by installing the floating detection means closer to the inkjet head. And since the frequency | count of an error reduces, a user's usability can be improved.

  Further, according to the second feature of the ink jet printing apparatus according to the present invention, the control means detects the float of the print medium by the float detection means, and when the negative pressure in the suction conveyance means is increased, the control chamber can move the pressure chamber. The side wall is driven to reduce the volume of the pressure chamber.

  For this reason, when the floating of the print medium is detected and the negative pressure in the suction conveying means is increased to increase the suction force of the print medium, the volume of the pressure chamber is reduced, so that the negative pressure is not changed without changing the volume of the pressure chamber. The suction force of the print medium can be increased more quickly than when increasing the negative pressure or increasing the negative pressure by closing the intake hole with a shutter or the like.

1 is a schematic configuration diagram of an inkjet printing apparatus according to an embodiment of the present invention. It is a block diagram which shows the structure of the control system of the inkjet printing apparatus of embodiment which concerns on this invention. It is sectional drawing of the inkjet head and conveyance belt in the inkjet printing apparatus of embodiment which concerns on this invention. It is a disassembled perspective view which shows in detail the structure of the printing part and suction conveyance part in the inkjet printing apparatus of embodiment which concerns on this invention. It is a flowchart which shows the operation | movement in the inkjet printing apparatus of embodiment which concerns on this invention. (A), (b) is a state in which the volume is maximized with the variable side wall of the pressure chamber in the ink jet printing apparatus according to the embodiment of the present invention, and the volume is minimized by raising the variable side wall vertically. It is sectional drawing which shows the state made into.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the embodiments described below are given as examples for embodying the technical idea of the present invention, and the technical idea of the present invention is to specify the arrangement and the like of each component as follows. Not. The technical idea of the present invention can be variously modified within the scope of the claims.

(Configuration of inkjet printing apparatus 1)
FIG. 1 is a schematic configuration diagram of an inkjet printing apparatus according to an embodiment of the present invention, FIG. 2 is a block diagram illustrating a configuration of a control system of the inkjet printing apparatus illustrated in FIG. 1, and FIG. It is a partial expanded sectional view.

  In the following description, the paper surface direction of FIG. Moreover, as shown in FIG. 1, when viewed from the user, the top, bottom, left, and right are defined as the top, bottom, left and right directions. Further, a path indicated by a broken line in FIG. 1 is a transport path R along which the paper PA, which is a print medium, is transported. In the following description, upstream and downstream mean upstream and downstream in the transport path R, respectively.

  As shown in FIGS. 1 and 2, the inkjet printing apparatus 1 includes a paper feeding unit 2, a suction conveyance unit 3, a printing unit 4, a control unit 5, a paper discharge unit 6, an operation panel unit 7, and the like. Prepare.

  The paper feeding unit 2 feeds paper PA, which is a printing medium. The sheet feeding unit 2 includes a sheet feeding table 11, a sheet feeding roller 12, and a registration roller 13.

  The paper feed tray 11 is loaded with paper PA used for printing.

  The paper feed roller 12 picks up the paper PA stacked on the paper feed tray 11 one by one and conveys the paper PA toward the registration roller 13. The paper feed roller 12 is disposed on the upper side of the paper feed tray 11. The paper feed roller 12 is rotationally driven by a motor (not shown).

  The registration roller 13 temporarily stops the paper PA conveyed by the paper feed roller 12 and then conveys the paper PA toward the suction conveyance unit 3. The registration roller 13 is disposed on the downstream side of the paper feed roller 12. The registration roller 13 is rotationally driven by a motor (not shown).

  The suction conveyance unit 3 functions as a suction conveyance unit of the present invention, and conveys the paper PA conveyed from the registration roller 13 toward the printing unit 4 and the paper discharge unit 6. The suction conveyance unit 3 includes a conveyance belt 21, a drive roller 22, driven rollers 23 to 25, a belt drive motor 26, a plastic template 27, a suction fan 28, a paper floating sensor 29, and a pressure chamber 30. Prepare.

  The conveyor belt 21 is an annular endless belt that is stretched around the driving roller 22 and the driven rollers 23 to 25. As shown in FIG. 3, the conveyance belt 21 is formed with a large number of intake holes 21 a that are through holes for attracting and holding the paper PA. The conveyance belt 21 sucks and holds the paper PA on the paper holding surface 21b by the negative pressure (suction force) generated in the suction hole 21a when the suction fan 28 is driven.

  The sheet holding surface 21 b is an upper surface of the conveyance belt 21 that is substantially horizontal between the driving roller 22 and the driven roller 23. The conveyor belt 21 rotates in the clockwise direction in FIG. Accordingly, the transport belt 21 moves endlessly, thereby transporting the paper PA sucked and held on the paper holding surface 21b in the right direction.

  The driving roller 22 and the driven rollers 23 to 25 are for the conveyance belt 21 to be stretched over. The driving roller 22 is driven to rotate by a belt driving motor 26 and rotates the conveyor belt 21. The driven rollers 23 to 25 are driven by the driving roller 22 via the conveyance belt 21. The driven roller 23 is substantially the same height as the drive roller 22 and is spaced from the drive roller 22 by a predetermined distance in the left-right direction. The driven rollers 24 and 25 are disposed at substantially the same height below the driving roller 22 and the driven roller 23 and spaced apart from each other by a predetermined distance in the left-right direction.

  The belt drive motor 26 drives the drive roller 22 to rotate.

  The plastic template 27 is disposed below the conveying belt 21 between the driving roller 22 and the driven roller 23, and supports the lower surface of the conveying belt 21 so as to be slidable. As shown in FIG. 3, the plastic template 27 penetrates from the upper surface to the lower surface at a portion through which the intake hole 21 a passes, and penetrates the lower surface of the plastic template 27 from a part of the bottom surface of the concave portion 27 a. A plurality of suction holes 27b.

  The suction fan 28 is disposed below the plastic template 27 and generates a downward airflow. Thus, the suction fan 28 sucks air through the pressure chamber 30, the suction hole 27 b of the plastic template 27, the recess 27 a, and the suction hole 21 a of the transport belt 21 to generate negative pressure, and holds the paper PA. Adsorbed on the surface 21b.

  The paper floating sensor 29 functions as a floating detection unit of the present invention, and is provided on the upstream side of the inkjet head 31 and the downstream side of the registration roller 13. The paper floating sensor 29 floats on the paper PA conveyed by the suction conveyance unit 3. Is detected. The sheet floating sensor 29 is configured by, for example, a reflective sensor or the like, and a plurality of sheet floating sensors 29 are arranged at predetermined intervals in the width direction of the sheet PA, and detect the amount of floating of the entire area of the sheet PA. When the sheet floating sensor 29 detects a floating amount of a predetermined threshold, for example, 0.3 mm or more, the control unit 5 determines that the abnormality is present, and operates as shown in FIG. To prevent collisions.

  The pressure chamber 30 is a space provided between the plastic template 27 and the suction fan 28 as described above, and drives the movable side walls 30a and 30b provided upstream and downstream by a drive unit (not shown), which will be described later. 6 (a), by tilting it to a horizontal state, or as shown in FIG. 6 (b), standing up in a vertical state to bring the tips of the movable side walls 30a, 30b into contact with the lower surface of the plastic template 27. The volume of the pressure chamber 30 is changed.

  The printing unit 4 performs printing on the paper PA conveyed by the suction conveyance unit 3. The printing unit 4 is provided on the upper side of the suction conveyance unit 3. The printing unit 4 is fixed in a housing (not shown) of the inkjet printing apparatus 1. The printing unit 4 includes cyan (C), magenta (M), yellow (Y), and black (K) inkjet heads 31C, 31K, 31M, and 31Y (hereinafter abbreviated as inkjet head 31; the same applies to FIG. 2). The head holder 32 and the head gap adjustment unit 33 are provided.

  The head holder 32 holds the head block 35 of the inkjet head 31 above the suction conveyance unit 3. The head holder 32 is formed in a hollow, substantially rectangular parallelepiped shape.

  The head gap adjusting unit 33 functions as the head gap adjusting means of the present invention. The head gap adjusting unit 33 sets the head gap H according to the thickness of the paper PA such as normal paper or cardboard, the type of the paper PA such as normal paper or envelope, and the like. adjust. As shown in FIG. 3, the head gap H is an interval between the paper holding surface 21 b of the conveyor belt 21 and the ejection surface 36 a of the inkjet head 31.

  The head gap adjustment unit 33 includes a head gap adjustment unit 40, a lift motor 41, an electromagnetic clutch 42, and a connection member 43.

  The head gap adjustment unit 40 moves the suction conveyance unit 3 up and down with respect to the inkjet head 31. Two head gap adjusters 40 are provided apart in the front-rear direction. The head gap adjusting unit 40 includes a pair of wire take-up reels 46 and 47, a shaft 48, and wires 49 and 50.

  The wire take-up reels 46 and 47 take up and feed out the wires 49 and 50, respectively. The wire take-up reels 46 and 47 are supported in the head holder 32 so as to be spaced apart from each other in the left-right direction.

  The shaft 48 connects a pair of wire take-up reels 46 and 47 to each other. The shaft 48 is made of a long member extending in the left-right direction, and one end is fixed to the pulley 46 and the other end is fixed to the pulley 47. As a result, the pair of wire take-up reels 46 and 47 are rotated in synchronization.

  The wires 49 and 50 suspend and support the suction conveyance unit 3. One ends of the wires 49 and 50 are connected to the suction conveyance unit 3, and the other ends are wound around the wire take-up reels 46 and 47. As the wires 49 and 50 are taken up and fed out by the rotation of the wire take-up reels 46 and 47, the suction conveyance unit 3 moves up and down, and the head gap H changes.

  The elevating motor 41 drives the wire take-up reels 46 and 47 to rotate.

  The connection member 43 is a member that connects the head holder 32 and the suction conveyance unit 3. The connecting member 43 is configured such that the length in the vertical direction can be adjusted according to the head gap H.

  The control unit 5 includes, for example, a CPU, a RAM, a ROM, a hard disk, and the like, and controls the operation of each unit of the inkjet printing apparatus 1. In particular, the control unit 5 functions as the control means of the present invention and operates as shown in FIG. 5 to be described later. When the floating of the printing medium such as the paper PA is detected by the paper floating sensor 29, the registration roller 13 and In addition to stopping the rotation of the conveyor belt 21 of the suction conveyance unit 3, the head gap adjustment unit 33 is operated to retract the suction conveyance unit 3 downward, thereby moving away from the inkjet head 31, and the negative in the suction conveyance unit 3. The pressure is increased to increase the adsorption force of the paper PA, or the movable side walls 30a and 30b of the pressure chamber 30 are driven to change the volume of the pressure chamber 30.

  The paper discharge unit 6 discharges the paper PA printed by the printing unit 4.

  The operation panel unit 7 includes an input unit such as a numeric keypad and a display unit. The operation panel unit 7 receives an input operation by a user, displays an input result, an operation state in the inkjet printing apparatus, and displays an error.

  FIG. 4 is an exploded perspective view showing in detail the structure of the printing unit 4 and the suction conveyance unit 3 in the ink jet printing apparatus according to the embodiment of the present invention.

  1, the suction conveyance unit 3 is suspended from the head holder 32 of the printing unit 4 by wires 49 and 50, and the wires 49 and 50 are rotated by rotation of the wire take-up reels 46 and 47. By being wound up or fed out, the suction conveyance unit 3 moves up and down, and the head gap H changes.

  Here, in the case of this embodiment, the electromagnetic clutch 42 is provided between the drive gear 41a rotated by the lifting motor 41 and the shaft 48 to which the wire take-up reels 46 and 47 are connected.

  The electromagnetic clutch 42 is turned on or off by a control signal from the control unit 5 to connect the lifting motor 41 and the shaft 48 or release the connection.

  That is, when the electromagnetic clutch 42 is turned on, the lifting motor 41 and the shaft 48 are connected, so that the shaft 48 is rotated by the rotation of the lifting motor 41 and the wire take-up reels 46 and 47 are also rotated. The head gap H between the inkjet head 31 and the suction conveyance unit 3 can be adjusted.

  On the other hand, when the electromagnetic clutch 42 is turned off, the connection between the lifting motor 41 and the shaft 48 is released, so that the suction conveyance unit 3 suspended by the wires 49 and 50 falls due to its own weight. Thereby, the suction conveyance unit 3 can be lowered more quickly than the wire take-up reels 46 and 47 are rotated by the rotation of the lifting motor 41.

(Operation of Inkjet Printing Apparatus 1)
Next, the operation of the inkjet printing apparatus 1 according to the embodiment of the present invention configured as described above will be described.

  FIG. 5 is a flowchart showing the operation of the inkjet printing apparatus 1 according to the embodiment of the present invention.

  In the inkjet printing apparatus 1, first, when printing is started, first, in the paper feed unit 2, the paper feed roller 12 rotates and picks up the paper PA stacked on the paper feed tray 11 one by one to register rollers 13. The registration roller 13 temporarily stops the paper PA and then sends it toward the suction conveyance unit 3 (step S101).

  In the suction conveyance unit 3, the paper PA conveyed from the registration roller 13 is placed on the conveyance belt 21 rotated by the driving roller 22 and the driven rollers 23 to 25 and conveyed toward the ink jet head 31 (step S103). .

  Specifically, in the suction transport unit 3, the suction fan 28 below the transport belt 21 and the plastic template 27 rotates, and the air from the plurality of suction holes 27 b provided in the plastic template 27 and the suction holes 21 a of the transport belt 21. , The pressure chamber 30 is set to a negative pressure, the paper PA is adsorbed on the upper surface of the transport belt 21, and the transport belt 21 is rotated and transported.

  During normal conveyance, if the suction force is increased around the ink jet head 31, the ink landing position may be shifted or the amount of mist generated may increase, resulting in a decrease in print quality. The duty ratio is suppressed to about 50 to 60%.

  When transporting the paper PA, the paper lift sensor 29 provided above the transport belt 21 and upstream of the ink jet head 31 detects the lift amount of the paper PA on the transport belt 21 (step S105), and the control unit 5 determines whether or not the floating amount of the paper PA from the paper floating sensor 29 exceeds a predetermined threshold (step S107).

  The purpose of detecting the floating amount of the paper PA is to avoid the paper PA floating on the conveyor belt 21 and the floating portion due to the folding of the paper PA from colliding with the inkjet head 31. The predetermined threshold value to be compared with the amount is less than the current value of the thickness of the paper PA from the interval between the upper surface of the transport belt 21 and the lower end of the inkjet head 31.

  If the amount of lift of the paper PA is not larger than the predetermined threshold, that is, not more than the predetermined threshold (step S107; YES), the paper PA placed on the transport belt 21 does not float or floats. Even if there is, the floating portion does not collide with the inkjet head 31.

  Therefore, in this case, the control unit 5 sends a print operation instruction to the printing unit 4 to discharge ink from the inkjet heads 31 of the respective colors onto the paper PA (step S109), and prints the printed paper PA. Paper is discharged from the paper discharge unit 6 (step S111), and it is determined whether or not all printing is completed (step S113).

  If the printing has not been completed (step S113; NO), the control unit 5 returns to the process of step S101 and performs the processes after step S101. On the other hand, if the printing has been completed (step S113; YES) ) End printing.

  On the other hand, when the floating amount of the paper PA is larger than the predetermined threshold (step S107; YES), since the floating portion of the paper PA is expected to be highly likely to collide with the inkjet head 31, the control unit 5 At the same time as the process of stopping the rotation of the registration roller 13 and the conveyance belt 21 of the suction conveyance unit 3 (step S115), the processes of steps S117, S119, and S121 described later are also performed simultaneously.

  That is, the control unit 5 turns off the electromagnetic clutch 42 and lowers the suction conveyance unit 3 (step S117) simultaneously with the process of stopping the rotation of the conveyance belt 21 of the registration roller 13 and the suction conveyance unit 3 (step S115). . Thereby, since the connection between the lifting motor 41 and the shaft 48 is released, the suction conveyance unit 3 is suddenly dropped by its own weight.

  Therefore, the suction conveyance unit 3 can be lowered more rapidly than when the suction conveyance unit 3 is lowered by rotating the wire take-up reels 46 and 47 by the rotation of the elevating motor 41. It can prevent more reliably that a part collides with the inkjet head 31. FIG.

  At the same time, the controller 5 simultaneously drives the movable side walls 30a and 30b of the pressure chamber 30 to stand up and reduces the volume of the pressure chamber 30 (step S119). Here, the movable side walls 30a and 30b can be driven by rotation of a cam or gear by a motor (not shown), a solenoid, or the like.

  6A is a cross-sectional view showing a state of the pressure chamber 30 in a state where the movable side walls 30a and 30b of the pressure chamber 30 are tilted sideways, and FIG. 6B shows the movable side walls 30a and 30b of the pressure chamber 30. It is sectional drawing which shows the state of the pressure chamber 30 made to stand upright.

  In the case of FIG. 6A, the volume of the pressure chamber 30 is maximum with the movable side walls 30 a and 30 b of the pressure chamber 30 lying down sideways, and the number of suction holes 27 b communicating with the pressure chamber 30 is also maximum. Become.

  Therefore, since the volume of the pressure chamber 30 is maximized, when the number of rotations of the suction fan 28 is the same, the pressure fluctuation is smaller than when the volume of the pressure chamber 30 is minimum as shown in FIG. The floating paper PA or the floating part of the paper cannot be picked up quickly.

  In addition, since the number of suction holes 27b communicating with the pressure chamber 30 is also the largest, when the paper size is A3 or the like, air is sucked from the suction holes 21a of the conveyance belt 21 on which the paper PA is not placed. Never do. However, when the paper size is reduced to A4, B5, or the like, in the state of FIG. 6A, air is also sucked from the suction holes 21a of the transport belt 21 around the paper PA, and the paper PA is sucked. Since the force is greatly reduced, the floating paper PA or the floating portion of the paper cannot be strongly adsorbed.

  On the other hand, in the case shown in FIG. 6B, the movable side walls 30a and 30b of the pressure chamber 30 stand vertically and the tips of the movable side walls 30a and 30b come into contact with the lower surface of the plastic template 27. The volume of the pressure chamber 30 is smaller than in the case shown in (a), and the number of suction holes 27b communicating with the pressure chamber 30 is also reduced.

  Here, the range of the suction hole 27 b that communicates with the pressure chamber 30 by the upright movable side walls 30 a and 30 b, that is, the suction hole 27 b that can suck air by the suction fan 28, is the smallest paper PA that can be transported by the suction transport unit 3. In order to eliminate leakage of air sucked from the surroundings, the size is set to be equal to or smaller than the minimum size of the paper PA that can be conveyed.

  For this reason, since the volume of the pressure chamber 30 is smaller than in the case of FIG. 6A, the fluctuation in pressure becomes large even when the number of rotations of the suction fan 28 is the same, and the sheet floats more than in the case of FIG. The adsorption power of PA can be increased quickly, and the quick response to the floating of the paper PA is improved.

  Further, in the case of FIG. 6B, the range of the suction hole 27b communicating with the pressure chamber 30 is less than or equal to the minimum size of the transportable paper PA by raising the movable side walls 30a and 30b. In addition, air does not leak from the air intake holes 21a around the paper PA, and the adsorption power of the paper PA increases, so that the floating of the paper PA can be strongly suppressed.

  Next, the control unit 5 sends a control signal to the suction fan 28 to increase the duty ratio of the suction fan 28 as compared with the normal conveyance state, thereby increasing the suction force by the suction fan 28 (step S121).

  For example, during normal conveyance, the duty ratio of the suction fan 28 is indicated at a low level of about 50%, and when the floating of the paper PA is detected, the duty ratio of the suction fan 28 is doubled to the MAX level of 100%. The suction force by the suction fan 28 is improved.

  As a result, when the floating of the paper PA is detected, the paper PA is strongly adsorbed and adsorbed to the suction hole 21a of the conveyance belt 21, so that the paper PA is suddenly stopped on the conveyance belt 21 of the suction conveyance unit 3. Thus, the collision between the floating portion of the paper PA and the inkjet head 31 on the transport belt 21 can be reliably prevented.

  Then, the control unit 5 displays an error on the operation panel unit 7 (step S123), and stops the above printing process.

  Thus, the user restarts the printing process shown in FIG. 5 again by, for example, opening the repair door of the inkjet printing apparatus 1 and removing the sheet PA that has floated above a predetermined threshold.

  Therefore, according to the ink jet printing apparatus 1 of the embodiment of the present invention, the control unit 5 operates the head gap adjustment unit 33 when the paper floating sensor 29 detects that the paper PA, which is a printing medium, is lifted. By retracting the suction conveyance unit 3 downward, the suction conveyance unit 3 is moved away from the inkjet head 31, and the negative pressure in the suction conveyance unit 3 is increased to increase the suction force of the paper PA.

  For this reason, even when the paper PA, which is a print medium, has a large float or the print medium has been deformed, it is possible to prevent a collision between the float portion of the paper PA and the inkjet head 31 on the transport belt 21.

  In particular, in the inkjet printing apparatus 1 according to the embodiment of the present invention, when the lift of the paper PA is detected by the paper lift sensor 29, only the suction pressure of the paper PA is increased by increasing the negative pressure in the suction conveyance unit 3. Instead, the suction conveyance unit 3 is retracted downward and away from the inkjet head 31.

  Therefore, it is possible to more reliably prevent the floating portion of the paper PA from colliding with the inkjet head 31 than when simply increasing the negative pressure in the suction conveyance unit 3 to prevent collision with the inkjet head 31. As a result, the conveyance speed of the paper PA can be improved, and the paper floating sensor 29 is installed closer to the ink jet head 31 to improve the detection accuracy of the paper PA and reduce the number of false detections and errors. Therefore, user convenience can be improved.

  In particular, in the ink jet printing apparatus 1 according to the embodiment of the present invention, when the suction conveyance unit 3 is retracted downward, the electromagnetic clutch 42 is turned off to turn the lifting motor 41, the wire take-up reels 46, 47, and the shaft 48. The connection between the two is released to a free state, and the suction conveyance unit 3 is lowered by the weight of the suction conveyance unit 3 to move away from the inkjet head 31.

  Therefore, the suction conveyance unit 3 can be lowered more quickly than when the wire take-up reels 46 and 47 are rotated by the rotation of the lifting motor 41 and the suction conveyance unit 3 is retracted downward. Can be prevented from colliding with the inkjet head 31.

  Further, in the inkjet printing apparatus 1 according to the embodiment of the present invention, when the floating of the paper PA is detected, the movable side walls 30a and 30b of the pressure chamber 30 are raised to reduce the volume of the pressure chamber 30.

  Therefore, when the floating of the paper PA is detected, the movable side walls 30a and 30b stand up and the volume of the pressure chamber 30 is reduced. Therefore, even when the paper PA transported by the suction transport unit 3 is small, the periphery of the paper PA The air leaks from the air intake holes 21a, and the paper PA is more strongly sucked, and the floating portion of the paper PA can be prevented from colliding with the inkjet head 31 more reliably.

  In particular, when the range of the suction hole 27b communicated with the pressure chamber 30 by the upright movable side walls 30a and 30b is equal to or smaller than the minimum size of the paper PA that can be transported by the suction transport unit 3, the lift of the paper PA is detected. Since there is no leakage of air sucked from the suction holes 27b, the paper PA can be sucked more strongly, and the paper PA can be prevented from colliding with the inkjet head 31 more reliably.

  Further, when the floating of the paper PA is detected and the negative pressure in the suction conveyance unit 3 is increased to increase the suction force of the paper PA, the volume of the pressure chamber 30 is reduced, so that suction is simply performed according to the size of the paper PA. The suction force of the paper PA can be increased more quickly than when the hole is closed by a shutter or the like, the quick response to the floating of the paper PA is improved, and the paper PA is prevented from colliding with the inkjet head 31 more reliably. it can.

  In the description of the above embodiment, when the lift amount of the paper PA exceeds a predetermined threshold by the paper lift sensor 29, the electromagnetic clutch 42 is turned off and the lifting motor 41 and the wire take-up reels 46 and 47 are provided. Although the description has been made such that the suction conveyance unit 3 is dropped while being separated from the shaft 48, the present invention is not limited to this.

  For example, a solenoid or the like is used in place of the electromagnetic clutch 42, and the shaft is pulled by pulling the support member (stopper) that supports the shaft 48 when the sheet floating sensor 29 has a floating amount of the sheet PA exceeding a predetermined threshold. 48, the suction conveyance unit 3 or the like may be dropped by their own weight, or when the sheet floating amount exceeds the predetermined threshold by the sheet floating sensor 29, the shaft 48 and the wire take-up reel 46, It is also possible to configure such that the pin or the like connected to 47 is pulled out by a solenoid or the like so that the wire take-up reels 46 and 47 are free to rotate, and the suction conveyance unit 3 or the like falls due to their own weight.

  Further, when the wire take-up reels 46 and 47 can be rotated at high speed by the rotation of the elevating motor 41, the wire take-up reels 46 and 47 are rotated and sucked and conveyed without using the electromagnetic clutch 42 or the solenoid. The part 3 may be dropped suddenly.

DESCRIPTION OF SYMBOLS 1 Inkjet printing apparatus 2 Paper feed part 3 Suction conveyance part (suction conveyance means)
4 Printing section 5 Control section (control means)
6 Paper discharge unit 7 Operation panel unit 21 Conveyor belt 21a Air intake hole 28 Suction fan 29 Paper float sensor (float detection means)
30 Pressure chambers 30a, 30b Movable side walls 31C, 31K, 31M, 31Y Inkjet head 33 Head gap adjustment unit (head gap adjustment means)
40 Head gap adjusting part 41 Lifting motor 42 Electromagnetic clutch 46, 47 Wire take-up reel 48 Shaft 49, 50 Wire PA Paper

Claims (2)

An inkjet head having a plurality of nozzle rows arranged in parallel;
A suction conveyance unit that is provided below the inkjet head and that adsorbs and conveys the print medium by negative pressure;
A float detecting means provided on the upstream side of the ink jet head for detecting the float of the print medium transported by the suction transport means;
A head gap adjusting means for adjusting a head gap which is a distance between a medium holding surface in the suction conveying means and an ink discharge surface of the inkjet head;
When the floating of the printing medium is detected by the floating detection means, the head gap adjusting means is operated to retract the suction conveyance means downward to move away from the inkjet head, and negative pressure in the suction conveyance means Control means for increasing the adsorption force of the printing medium by increasing
An ink jet printing apparatus comprising: The suction conveying means includes
A plurality of air intake holes, and a conveyance belt that adsorbs and conveys the print medium;
A pressure chamber provided below the conveyor belt, the volume of which can be changed by driving the movable side wall;
A suction fan that makes the pressure chamber negative and sucks the print medium by a plurality of suction holes of the conveyor belt,
The control means includes
When the floating of the printing medium is detected by the floating detection unit and the negative pressure in the suction conveyance unit is increased, the movable side wall of the pressure chamber is driven to reduce the volume of the pressure chamber. The inkjet printing apparatus according to claim 1.

Images