JP2020015177A - Ink jet printer - Google Patents

Abstract

To provide an ink jet printer which can reduce contamination of an inside of a device and a printed matter caused by ink mist.SOLUTION: A conveying part 3 conveys paper while sucking and holding by air suction. An ink jet head 36 discharges ink and prints on the paper conveyed by the conveying part 3. A box-like head holder 32 includes an opening part on which the ink jet head 36 is mounted through a clearance. A suction fan 49 generates cooling air which is exhausted from the head holder 32 and cools the ink jet head 36. A control part carries out drive adjustment control for decreasing a duty ratio of a drive signal of the suction fan 49 during a period when an inter-paper area passes below the ink jet head 36 than during a period when the paper passes below the ink jet head 36.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an inkjet printing apparatus that performs printing by discharging ink from an inkjet head.

  2. Description of the Related Art A line-type inkjet printing apparatus that discharges ink from a fixed inkjet head onto a sheet while transporting the sheet to perform printing is known. In a line-type inkjet printing apparatus, an air suction type transport mechanism is widely used to transport a sheet.

  In the air suction type transport mechanism, air is sucked through a number of suction holes provided in the transport belt by a fan, and the sheet is attracted and held on the transport belt by a suction force due to negative pressure generated in the suction holes. The sheet is transported by the transport belt moving while adsorbing and holding the sheet.

  In an ink jet printing apparatus, ink mist generated by ink ejection causes stains inside the apparatus and printed matter. However, in the ink jet printing apparatus using the air suction type transport mechanism as described above, the ink mist is sucked and collected together with air in a region between a plurality of continuously transported papers. The inside of the apparatus and the stains on the printed matter due to the above are reduced.

  In a line-type inkjet printing apparatus, as the printing speed increases, the driving frequency of the inkjet head increases, and the amount of heat generated by the inkjet head increases. Also, when an ink jet head having a large print resolution and piezo elements arranged at a high density is used, the amount of heat generated by the ink jet head increases. On the other hand, in order to use the head driver IC at a temperature lower than the rated temperature, it is necessary to cool the inkjet head to suppress the temperature rise.

  Therefore, cooling air is generated in the head holder by a fan to cool the inkjet head (see Patent Document 1).

JP-A-2006-150490

  In the inkjet printing apparatus that cools the inkjet head as described above, air may be sucked into the head holder via a gap between the opening of the head holder to which the inkjet head is attached and the inkjet head.

  The airflow caused by the air being sucked into the head holder is an airflow flowing in the upward direction, which is opposite to the airflow caused by the air suction type transport mechanism sucking the air. For this reason, when air is sucked into the head holder, the airflow caused by the air suction type transfer mechanism sucking air is weakened, and the transfer mechanism may not be able to sufficiently collect the ink mist. For this reason, the inside of the apparatus and the printed matter may be stained by the ink mist.

  The present invention has been made in view of the above, and an object of the present invention is to provide an ink jet printing apparatus that can reduce stains inside the apparatus and printed matter due to ink mist.

  In order to achieve the above object, an inkjet printing apparatus of the present invention includes a transport unit that transports a sheet while sucking and holding the sheet by air suction, an inkjet head that discharges ink onto the sheet transported by the transport unit, and performs printing. A box-shaped head holder having an opening to which the inkjet head is attached via a gap, a fan that generates cooling air that exhausts from the head holder and cools the inkjet head, and a control unit that controls the fan The control unit, during the period in which the sheet interval area, which is the area between the sheets conveyed in the conveyance unit, passes below the inkjet head, the period is longer than the period in which the sheet passes below the inkjet head. It is characterized in that drive adjustment control for reducing the drive rate of the fan is performed.

  ADVANTAGE OF THE INVENTION According to the inkjet printing apparatus of this invention, the inside of an apparatus and the smudge of a printed matter by an ink mist can be reduced.

FIG. 1 is a block diagram illustrating a configuration of an inkjet printing apparatus according to an embodiment. FIG. 2 is a schematic configuration diagram of a main part of the inkjet printing apparatus shown in FIG. 1. FIG. 2 is a plan view of a transport unit, a printing unit, and a cooling unit of the inkjet printing apparatus shown in FIG. FIG. 4 is a partially enlarged cross-sectional view of a printing unit and a conveyance unit along line AA in FIG. 3. It is a figure showing a duty ratio table. It is explanatory drawing of the cooling air in a head holder. FIG. 4 is an explanatory diagram of the behavior of an airflow and an ink mist near the inkjet head at the time of ink ejection. FIG. 4 is a diagram illustrating a state of an airflow at a position of an ink jet head on the forefront side when a sheet interval area passes below the head. FIG. 7 is a diagram illustrating a state of an airflow at the position of the rearmost inkjet head when a paper interval passes below the head. It is a flowchart of drive control of a suction fan. It is a flowchart of drive control of a suction fan.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The same or equivalent parts and components are denoted by the same or similar reference numerals throughout the drawings.

  The embodiments described below exemplify an apparatus or the like for embodying the technical idea of the present invention. The technical idea of the present invention is based on the material, shape, structure, arrangement, etc. of each component. Is not specified as: Various changes can be made to the technical idea of the present invention within the scope of the claims.

  FIG. 1 is a block diagram illustrating a configuration of an inkjet printing apparatus according to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram of a main part of the inkjet printing apparatus shown in FIG. FIG. 3 is a plan view of a transport unit, a printing unit, and a cooling unit of the inkjet printing apparatus shown in FIG. FIG. 4 is a partially enlarged cross-sectional view of the printing unit and the transport unit along the line AA in FIG. In the following description, the direction perpendicular to the plane of the paper of FIG. The upper, lower, left, and right sides of the paper surface in FIG.

  In FIG. 2, a path indicated by a thick line is a transport path R on which a sheet P as a print medium is transported. Upstream and downstream in the following description mean upstream and downstream in the transport route R.

  As shown in FIG. 1, an ink jet printing apparatus 1 according to the present embodiment includes a paper feed unit 2, a transport unit 3, a printing unit 4, a cooling unit 5, ink circulation mechanism units 6A to 6D, a head, A gap adjusting unit 7 and a control unit 8 are provided. It should be noted that the subscripts of the alphabets in the reference numerals of the ink circulation mechanism units 6A to 6D may be omitted and may be collectively described.

  The paper feed unit 2 feeds paper to the transport unit 3. As shown in FIGS. 1 and 2, the sheet feeding unit 2 includes a side sheet feeding table 11, a side sheet feeding roller 12, a side sheet feeding motor 13, three lower sheet feeding tables 14, and three pairs of lower sheets. The printer includes a paper feed roller 15, four pairs of lower paper feed / conveyance rollers 16, a lower paper feed motor 17, a vertical conveyance roller 18, a registration roller 19, and a registration motor 20.

  The side paper feed tray 11 is for loading paper P used for printing. The side paper feed table 11 is installed such that a part thereof is exposed outside a housing (not shown) of the inkjet printing apparatus 1.

  The side paper feed roller 12 takes out the paper P one by one from the side paper feed table 11 and conveys the paper P to the registration roller 19 along the conveyance path R.

  The side paper feed motor 13 drives the side paper feed roller 12 to rotate. The side paper feed motor 13 drives the vertical transport roller 18 to rotate. The side paper feed motor 13 is connected to the side paper feed roller 12 and the vertical transport roller 18 via a one-way clutch (not shown). As a result, the side paper feed roller 12 is driven to rotate by one side rotation of the side paper motor 13, and the vertical transport roller 18 is driven to rotate by the other side of the side paper motor 13. I have.

  The lower paper feed tray 14 is for loading paper P used for printing. The lower paper feed table 14 is disposed inside the housing (not shown) of the inkjet printing apparatus 1 and below the transport unit 3.

  The lower paper feed roller 15 takes out the paper P one by one from the lower paper feed table 14 and transports the paper P to the lower paper feed transport roller 16 along the transport path R.

  The lower paper feed roller 16 conveys the paper P taken out of the lower paper feed table 14 by the lower paper feed roller 15 toward the vertical paper feed roller 18.

  The lower feed motor 17 drives the lower feed roller 15 and the lower feed transport roller 16 to rotate. The lower feed motor 17 can be connected / disconnected to each lower feed roller 15 and each lower feed transport roller 16 via a clutch (not shown). The lower feed roller 15 and the lower feed transport roller 16 that are driven to rotate are switched by the clutch.

  The vertical transport roller 18 transports the paper P transported by the lower paper feed transport roller 16 to the registration roller 19.

  The registration roller 19 temporarily stops the sheet P conveyed by the side paper feed roller 12 or the vertical conveyance roller 18, corrects the skew, and then conveys the sheet P to the conveyance unit 3. The registration roller 19 is disposed near the downstream side of the junction of the portion extending from the side paper feed table 11 and the portion extending from the lower paper feed table 14 on the transport path R.

  The registration motor 20 drives the registration roller 19 to rotate.

  The transport unit 3 transports the paper P fed by the paper feed unit 2 while sucking and holding the paper P by air suction. As shown in FIGS. 1 and 2, the transport unit 3 includes a transport belt 21, a driving roller 22, driven rollers 23 to 25, a belt motor 26, a paper suction fan 27, and a paper sensor 28.

  The transport belt 21 transports the paper P while holding it by suction. The transport belt 21 is an annular belt that is stretched over a driving roller 22 and driven rollers 23 to 25. As shown in FIGS. 3 and 4, a plurality of suction holes 21 a, which are through holes for air suction, are formed in the transport belt 21. The transport belt 21 attracts and holds the paper P on the transport surface 21b by an attraction force generated in the suction holes 21a by driving the paper suction fan 27. The transport surface 21b is the upper surface of the transport belt 21 that is horizontal between the drive roller 22 and the driven roller 23. The transport belt 21 rotates the clockwise direction in FIG. 2 to transport the paper P held by suction to the right.

  The drive roller 22 rotates the transport belt 21 clockwise in FIG.

  The driven rollers 23 to 25 support the transport belt 21 together with the drive roller 22. The driven rollers 23 to 25 are driven and rotated by the transport belt 21. The driven roller 23 has the same height as the drive roller 22 and is disposed to the left of the drive roller 22. The driven rollers 24 and 25 are arranged at the same height below the driving roller 22 and the driven roller 23 and are separated from each other in the left-right direction.

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

  The paper suction fan 27 generates a downward airflow. As a result, the paper suction fan 27 sucks air through the suction holes 21a of the transport belt 21 to generate a negative pressure in the suction holes 21a, and causes the paper P to be sucked on the transport surface 21b. The paper suction fan 27 is arranged in a region surrounded by the annular conveyor belt 21.

  The sheet sensor 28 detects a sheet P conveyed on the conveyor belt 21 toward the line heads 31A and 31B described later. The paper sensor 28 is disposed above the transport belt 21 near the upstream side of the line head 31A.

  The printing unit 4 performs printing on the paper P transported by the transport unit 3. The printing section 4 is arranged above the transport section 3. As shown in FIGS. 1 to 3, the printing unit 4 includes line heads 31A and 31B and a head holder 32.

  The line heads 31 </ b> A and 31 </ b> B print by discharging ink onto the paper P. The line heads 31 </ b> A and 31 </ b> B are arranged side by side in the transport direction (left-right direction) of the sheet P. Each of the line heads 31A and 31B includes six ink jet heads 36 (ink jet heads 36A to 36F).

  In the line head 31, the six inkjet heads 36 are staggered. That is, the six inkjet heads 36 are arranged along the front-rear direction (main scanning direction), and are alternately arranged in the left-right direction (sub-scanning direction) every other one. Due to such an arrangement of the ink jet heads 36, four head rows 37A to 37D formed of three ink jet heads 36 arranged at equal intervals in the front-rear direction in the printing unit 4 and arranged in the left-right direction are formed. Have been.

The inkjet head 36 has an ink ejection surface 36a. The ink ejection surface 36a is the lower surface of the inkjet head 36, which faces the transport surface 21b of the transport belt 21 below. On the ink ejection surface 36a, two nozzle rows (both not shown) each including a plurality of nozzles arranged in the front-rear direction (main scanning direction) are formed. The ink jet head 36 can discharge inks of different colors from two nozzle rows.
The ink jet head 36 prints on the paper P by discharging ink supplied from the ink circulation mechanism 6 from the nozzles.

  Each inkjet head 36 is provided with a head temperature sensor 38. The head temperature sensor 38 detects the temperature of the inkjet head 36.

  The head holder 32 holds the inkjet head 36. The head holder 32 is formed of a box formed in a hollow rectangular parallelepiped shape. An attachment opening (corresponding to an opening) 32b for attaching the inkjet head 36 is formed in the bottom plate 32a of the head holder 32. The ink jet head 36 is inserted into the mounting opening 32b and fixed so that the ink ejection surface 36a projects from the bottom plate 32a toward the lower conveying surface 21b.

  The mounting opening 32b is formed of a through-hole larger than a cross section of the inkjet head 36 along a horizontal plane. Thereby, the mounting position and angle of the inkjet head 36 can be adjusted. Since the attachment opening 32b is formed in this manner, as shown in FIG. 4, the inkjet head 36 is attached to the attachment opening 32b via the gap 32c.

  The cooling unit 5 cools the inkjet head 36 with cooling air. The cooling unit 5 includes a blowing unit 41 and a suction unit 42.

  The blowing unit 41 sucks air into the head holder 32 and blows air to the inkjet head 36. The blowing section 41 is arranged on the front side of the head holder 32. The blowing section 41 includes a blowing chamber 46 and a blowing fan 47.

  The blowing chamber 46 distributes the wind from the blowing fan 47 to the head rows 37A to 37D. The blowing chamber 46 is formed in a hollow shape with a shape elongated in the left-right direction. The blowing chamber 46 has four blowing ports 46a to 46d.

  The blowing ports 46 a to 46 d are outlets of the air from the blowing chamber 46. The blowing ports 46 a to 46 d are opened in the head holder 32. The blowing ports 46a to 46d are arranged in parallel with each other in the left-right direction and on the extension lines of the head rows 37A to 37D, respectively.

  The blowing fan 47 blows air into the blowing chamber 46. Thereby, air is blown from the front side to the inkjet head 36 through the blowing ports 46 a to 46 d of the blowing chamber 46.

  The suction unit 42 sucks air from the head holder 32. The suction part 42 is arranged on the rear side of the head holder 32. The suction unit 42 includes a suction chamber 48 and a suction fan (corresponding to a fan) 49.

  The suction chamber 48 forms an air flow path between the head holder 32 and the suction fan 49. The suction chamber 48 is formed in a hollow shape with an elongated shape in the left-right direction. The suction chamber 48 has four suction ports 48a to 48d.

  The suction ports 48 a to 48 d are air inlets for the suction chamber 48. The suction ports 48 a to 48 d are opened in the head holder 32. The suction ports 48a to 48d are arranged side by side in the left-right direction and on extensions of the head rows 37A to 37D, respectively. That is, the suction ports 48a to 48d are arranged to face the blowing ports 46a to 46d with the head rows 37A to 37D interposed therebetween.

  The suction fan 49 sucks air from one end of the suction chamber 48. Thus, the air is exhausted from the head holder 32 through the suction ports 48a to 48d of the suction chamber 48.

  The ink circulating mechanisms 6A to 6D supply ink to the inkjet heads 36 of the line heads 31A and 31B while circulating the ink. The ink circulation mechanism units 6A and 6B supply the ink of each color ejected from the two nozzle rows of the inkjet head 36 in the line head 31A to the line head 31A. The ink circulation mechanisms 6C and 6D supply the ink of each color ejected from the two nozzle rows of the inkjet head 36 to the line head 31B in the line head 31B.

  The ink circulation mechanism 6 has an ink circulation path (not shown), and supplies ink to each inkjet head 36 of the line head 31 while circulating the ink along the ink circulation path. The ink circulation mechanism 6 includes an ink temperature sensor 51 that detects the temperature of the ink supplied to each inkjet head 36.

  The head gap adjusting unit 7 adjusts the head gap Hg by moving the transport unit 3 up and down. The head gap Hg is a distance between the transport surface 21b of the transport belt 21 and the ink ejection surface 36a of the inkjet head 36.

  The control unit 8 controls the operation of each unit of the inkjet printing device 1. The control unit 8 includes a CPU, a RAM, a ROM, a hard disk, and the like.

  Specifically, when performing the printing operation, the control unit 8 feeds the paper P by the paper feeding unit 2, discharges the ink from the inkjet head 36 while transporting the fed paper P by the transport unit 3. To print on the paper P. At the time of this printing operation, the control unit 8 drives the blowing fan 47 and the suction fan 49 to cool the inkjet head 36.

  After the number of prints from the first sheet of paper P to be printed in the series of printing operations reaches the specified number, the control unit 8 determines that the temperature of all the inkjet heads 36 is lower than the threshold value, and that the lower side (the inkjet heads 36) When the sheet interval Lg of the sheet interval area E passing through the lower portion of the suction fan 49 is larger than the specified interval, the period of time when the sheet interval P passes under the head is shorter than that of the sheet P passing under the head. Drive adjustment control for reducing the duty ratio (drive rate) of the drive signal is performed. When the sheet interval Lg is equal to or less than the specified interval, the control unit 8 performs control to reversely drive the suction fan 49 instead of the drive adjustment control.

  Here, the inter-sheet area E is an area between the sheets of the plurality of sheets P that are continuously conveyed by the conveyance unit 3 and printed by the inkjet head 36. That is, the inter-sheet area E is an area between the rear end of each sheet P continuously conveyed in the conveyance unit 3 and the front end of the next sheet P. The paper interval Lg is the length of the inter-sheet area E in the transport direction of the paper P, and is the distance between the rear end of the paper P in the transport unit 3 and the front end of the next paper P. The paper interval Lg is set according to the transport speed of the paper P in the transport unit 3. The transport speed of the paper P is determined according to the maximum number of drops per pixel, and the maximum number of drops per pixel is determined according to the type of paper. Therefore, the transport speed of the paper P is set according to the type of paper.

  Also, during a period in which the sheet interval area E passes under the head, the rear end of the sheet interval area E passes through the most downstream head row 37D from the time when the leading end of the sheet interval area E reaches the head row 37A at the most upstream. The period up to the point. The period during which the paper P passes under the head is a period from the time when the leading end of the paper P reaches the head row 37A at the most upstream to the time when the rear end of the paper P passes through the most downstream head row 37D.

  Further, the normal rotation drive of the suction fan 49 is a drive in the rotation direction for exhausting the air from the head holder 32. The reverse rotation drive of the suction fan 49 is a rotation in the direction opposite to the rotation direction in the normal rotation drive, in which air is blown to the inkjet head 36 in the head holder 32.

  The control unit 8 stores a duty ratio table 56 shown in FIG. The duty ratio table 56 is a table in which the paper interval Lg, the printing rate, the ink temperature, the head paper distance Hp, and the duty ratio of the drive signal of the suction fan 49 in the drive adjustment control are associated. Details of the duty ratio table 56 will be described later.

  Next, the operation of the inkjet printing apparatus 1 will be described.

  When a print job is input, the control unit 8 adjusts the head gap Hg. Specifically, first, the control unit 8 determines the type of paper used for printing based on the print setting information included in the print job. Then, the control unit 8 controls the head gap adjusting unit 7 so as to have a head gap Hg corresponding to the paper type.

  Next, the control unit 8 causes the driving of the driving roller 22 by the belt motor 26 to be started. Thereby, the circulation drive of the transport belt 21 is started. The control unit 8 drives the drive roller 22 so as to have a transport speed corresponding to the paper type.

  Further, the control section 8 starts driving the paper suction fan 27. As a result, air is sucked by the sheet suction fan 27 through the suction holes 21a of the conveyor belt 21, and suction force is generated in the suction holes 21a.

  In addition, the control unit 8 starts driving the blowing fan 47 and the suction fan 49. By driving the blowing fan 47, the air is sucked into the head holder 32 through the blowing ports 46 a to 46 d of the blowing chamber 46. When the suction fan 49 is driven, the air is exhausted from the head holder 32 through the suction ports 48a to 48d. Thereby, as shown in FIG. 6, the cooling air W flowing from the front side to the rear side is generated in the head holder 32.

  Next, the control unit 8 controls the paper feed unit 2 to feed the paper P to the transport unit 3 from either the side paper feed roller 12 or the lower paper feed table 14. When the number of prints in the print job is plural, the control unit 8 controls the registration roller to feed the paper P at a timing such that each paper P is transported at a paper interval Lg corresponding to the transport speed of the paper P in the transport unit 3. 19 is controlled.

  The paper P fed to the transport unit 3 is transported while being suction-held by the transport belt 21. When the number of prints is two or more, a plurality of sheets P are continuously conveyed at the sheet interval Lg. The control unit 8 controls each of the ink jet heads 36 so as to perform printing by discharging ink onto the paper P conveyed by the conveyance unit 3. The printed sheet P is discharged by a discharge unit (not shown).

  In the above-described printing operation, when the inkjet head 36 is driven, the inkjet head 36 generates heat. The temperature rise due to the heat generation causes a failure of the ink jet head 36 and the like. On the other hand, in the inkjet printing apparatus 1, the cooling air W suppresses the temperature rise of the inkjet head 36.

  Further, when the ink is ejected from the ink jet head 36, as shown in FIG. 7, the main droplet 61 of the ink flies and a minute ink mist 62 is generated. The ink mist 62 is caused to flow downstream by the transport airflow Fh. The transport airflow Fh is an airflow generated by the movement of the transport belt 21 and the paper P.

  As shown in FIG. 7, a part of the transport airflow Fh becomes a hoisted airflow Fm that is wound up by the inkjet head 36. A part of the ink mist 62 flows in the space between the inkjet heads 36 on the winding airflow Fm, and stays there.

  In the inter-sheet area E between the preceding sheet P and the succeeding sheet P to be conveyed, as shown in FIGS. 8 and 9, there is no sheet P on the suction hole 21a, and the suction hole 21a is exposed. ing. Therefore, a suction airflow Fk is generated. The suction airflow Fk is a downward airflow that flows from the space above the conveyance belt 21 to the inside of the conveyance unit 3 through the suction holes 21a by the driving of the paper suction fan 27.

  Here, in the area on the front side of the head holder 32, the air is exhausted from the head holder 32 through the gap 32 c between the mounting opening 32 b and the inkjet head 36 due to the influence of the air blown into the head holder 32 by the blowing fan 47. Thereby, as shown in FIG. 8, an outflow airflow Fs flowing out of the head holder 32 through the gap 32c is generated. Here, FIG. 8 shows a state of the airflow at the position of the foremost inkjet head 36A when the sheet interval area E passes below the head.

  The outflow airflow Fs is a downward airflow from the inside of the head holder 32 toward the space between the head holder 32 and the transport belt 21. For this reason, in the area on the front side of the head holder 32, when the inter-sheet area E passes below the head, the ink mist 62 staying in the space between the inkjet heads 36 and the ink mist 62 floating in the other space. Is flowed downward by the outflow airflow Fs and the suction airflow Fk, and is collected inside the transport unit 3 through the suction holes 21a.

  On the other hand, in the rear region of the head holder 32, air is sucked into the head holder 32 through the gap 32c due to the exhaust air from the head holder 32 by the suction fan 49. Thus, as shown in FIG. 9, an inflow airflow Fn flowing into the head holder 32 through the gap 32c is generated. Here, FIG. 9 shows the state of the airflow at the position of the rearmost inkjet head 36F when the inter-sheet area E passes below the head.

  The inflow airflow Fn is an upward airflow from the space between the head holder 32 and the transport belt 21 toward the inside of the head holder 32. For this reason, in the rear area in the head holder 32, even when the inter-sheet area E passes under the head, the inflow airflow Fn and the suction airflow Fk attract the ink mist 62 in directions opposite to each other. 3, the ink mist 62 is hardly collected.

  Therefore, in the inkjet printing apparatus 1, the drive adjustment control of the suction fan 49 for weakening the inflow airflow Fn and increasing the ink mist collected by the conveyance unit 3 by the suction airflow Fk is performed.

  The duty ratio in the drive adjustment control of the suction fan 49 is set to a value smaller than a set duty ratio which is a duty ratio set for cooling the inkjet head 36. Here, the smaller the duty ratio of the drive signal of the suction fan 49 is, the smaller the rotation speed of the suction fan 49 is, and the weaker the inflow airflow Fn is.

  The duty ratio of the drive signal in the drive adjustment control of the suction fan 49 is set according to factors related to the sheet interval Lg and the degree of ink mist generation, with reference to the duty ratio table 56 in FIG. In FIG. 5, the printing rate, the ink temperature, and the head paper distance Hp are factors relating to the degree of occurrence of ink mist.

  Here, the head paper distance Hp is the distance between the ink ejection surface 36a and the upper surface of the paper P on the transport surface 21b. In other words, the head-to-paper distance Hp is obtained by subtracting the thickness of the paper P from the head gap Hg. The head paper distance Hp changes depending on the paper type.

  As the sheet interval Lg is smaller, the area where the ink mist can be collected in the transport unit 3 by the suction airflow Fk is smaller. Therefore, under the same conditions of the printing rate, the ink temperature, and the head paper distance Hp, the duty ratio in the drive adjustment control of the suction fan 49 is set to be smaller as the paper interval Lg is smaller.

  If the paper interval Lg is the same, the duty ratio in the drive adjustment control of the suction fan 49 is set to be smaller as the degree of occurrence of ink mist is larger.

  The higher the printing rate, the greater the number of times the ink is ejected from the inkjet head 36, and therefore the degree of ink mist generation increases. Therefore, under the same conditions of the paper interval Lg, the ink temperature, and the head paper distance Hp, the duty ratio in the drive adjustment control of the suction fan 49 is set to be smaller as the printing rate is higher.

  Further, as the head-to-paper distance Hp is larger, minute ink droplets generated by ink ejection from the ink jet head 36 lose their propulsive force before landing on the paper P, and tend to become ink mist. Therefore, the greater the head paper distance Hp, the greater the degree of ink mist generation. Therefore, under the same conditions of the paper interval Lg, the printing rate, and the ink temperature, the duty ratio in the drive adjustment control of the suction fan 49 is set to be smaller as the head paper distance Hp is larger.

  Also, the lower the ink temperature, the higher the viscosity of the ink. The higher the viscosity of the ink, the longer the tail of the ink that is ejected from the nozzles of the inkjet head 36 and flies, and the easier it is to cut. Therefore, the lower the ink temperature, the greater the degree of ink mist generation. Therefore, under the same conditions of the paper interval Lg, the printing ratio, and the head paper distance Hp, the duty ratio in the drive adjustment control of the suction fan 49 is set to be smaller as the ink temperature is lower.

  As the duty ratio of the drive signal of the suction fan 49 decreases, the cooling efficiency of the inkjet head 36 decreases. For this reason, the duty ratio in the drive adjustment control is adjusted according to the sheet interval Lg and the degree of occurrence of ink mist as described above so that the duty ratio does not become smaller than necessary.

  Next, the drive control of the suction fan 49 including the above-described drive adjustment control will be described with reference to the flowcharts of FIGS.

  When receiving a print job and starting a printing operation, the control unit 8 starts driving the suction fan 49 in step S1 of FIG. The control unit 8 drives the suction fan 49 at a set duty ratio set for cooling the inkjet head 36.

  Next, in step S2, the control unit 8 determines whether the paper P has reached below the head. Here, when the leading end of the sheet P reaches the head row 37A at the uppermost stream, the control unit 8 determines that the sheet P has reached below the head. The control unit 8 can determine whether or not the leading edge of the sheet P has reached the head row 37A, which is the most upstream, based on the elapsed time from the timing when the leading edge of the sheet P is detected by the sheet sensor 28. If it is determined that the sheet P has not reached below the head (step S2: NO), the control unit 8 repeats step S2.

  If it is determined that the paper P has arrived under the head (step S2: YES), it is determined in step S3 whether the number of prints from the first paper P in the series of printing operations this time has reached a specified number. . Here, the number of prints corresponds to the number of sheets of paper P that has reached below the head.

  The specified number of sheets is set in advance as a number of sheets to be used as a condition for starting the drive adjustment control of the suction fan 49 in a series of printing operations. At a stage where the number of printed sheets is small, the ink mist is still small, and the necessity of the drive adjustment control of the suction fan 49 is small. Therefore, the specified number of sheets is provided as a condition for starting the drive adjustment control of the suction fan 49. I have. The specified number is a plurality.

  When it is determined that the number of prints from the first sheet P has reached the specified number (step S3: YES), in step S4, the last sheet to be printed in a series of printing operations is the sheet P that has reached the lower part of the head this time. It is determined whether it is P or not.

  If it is determined that the sheet is not the last sheet P (step S4: NO), the control unit 8 determines in step S5 whether the temperatures of all the ink jet heads 36 are lower than the threshold based on the detection values of the head temperature sensors 38. Determine whether or not.

  Here, the threshold value of the temperature of the inkjet head 36 is set in advance as a temperature of the inkjet head 36 which is a reference for determining whether to perform the drive adjustment control of the suction fan 49. When the drive adjustment control of the suction fan 49 is performed, the cooling efficiency of the inkjet head 36 by the cooling unit 5 is reduced. Therefore, when there is a high-temperature inkjet head 36, the drive adjustment control of the suction fan 49 is omitted. Are provided.

  When it is determined that the temperatures of all the ink jet heads 36 are lower than the threshold (step S5: YES), in step S6 of FIG. 11, the control unit 8 determines whether or not the inter-sheet area E has reached below the heads. I do.

  Here, when the leading end of the inter-sheet area E reaches the head row 37A at the uppermost stream, the control unit 8 determines that the inter-sheet area E has reached below the head. The control unit 8 determines, based on the elapsed time from the timing when the leading edge of the sheet P arrives at the head row 37A at the most upstream (the sheet P arrives below the head), the leading edge of the inter-sheet area E following the sheet P is the most upstream. Can be determined. When it is determined that the inter-sheet area E has not reached below the head (step S6: NO), the control unit 8 repeats step S6.

  If it is determined that the inter-sheet area E has reached below the head (step S6: YES), it is determined in step S7 whether the sheet interval Lg of the inter-sheet area E is larger than a specified interval.

  Here, the paper interval Lg is set according to the transport speed of the paper P in the transport unit 3 as described above. The specified interval is set in advance as a reference value of the sheet interval Lg for determining whether or not to perform the reverse rotation drive of the suction fan 49 instead of the drive adjustment control of the suction fan 49.

  When the suction fan 49 is driven to rotate in the reverse direction, air is blown into the head holder 32 from the suction ports 48a to 48d, so that an outflow airflow Fs is also generated in the rear area of the head holder 32, and Mist recovery efficiency is improved. However, when the suction fan 49 is driven to rotate in the reverse direction, the cooling efficiency of the inkjet head 36 decreases. Therefore, even if the inflow airflow Fn is weakened by the drive adjustment control of the suction fan 49, the reverse rotation drive of the suction fan 49 is performed only when the sheet interval Lg is small enough that the ink mist collection efficiency is not sufficient. The specified interval is set.

  When it is determined that the sheet interval Lg is larger than the specified interval (step SS7: YES), the control unit 8 starts the drive adjustment control of the suction fan 49 in step S8.

  Specifically, the control unit 8 acquires from the duty ratio table 56 a duty ratio corresponding to the paper interval Lg, the printing rate, the ink temperature, and the head paper distance Hp. For example, if the paper interval Lg is Lg1, the printing rate is R1 or more and less than R2, the ink temperature is less than T1, and the head paper distance Hp is less than Hp1, the control unit 8 sets the value of the duty ratio in the drive adjustment control of the suction fan 49. "Da211" is obtained.

  Then, the control unit 8 reduces the duty ratio of the drive signal of the suction fan 49 from the set duty ratio to the duty ratio acquired by referring to the duty ratio table 56. As a result, the inflow airflow Fn is weakened as compared with the case where the duty ratio is not reduced from the set duty ratio, and the efficiency of ink mist collection to the transport unit 3 is improved.

  Here, the control unit 8 uses the average print rate of all pages in the current print job as the print rate used when acquiring the duty ratio in the drive adjustment control of the suction fan 49. The control unit 8 uses the average value of the temperatures detected by the ink temperature sensors 51 of the ink circulation mechanism units 6A to 6D as the ink temperature used when acquiring the duty ratio in the drive adjustment control of the suction fan 49.

  Next, in step S9, the control unit 8 determines whether or not the sheet interval area E has passed under the head. Here, when the rear end of the inter-sheet area E passes through the head row 37D at the most downstream, the control unit 8 determines that the inter-sheet area E has passed below the head. The control unit 8 sets the rear end of the inter-sheet area E to the most downstream based on the elapsed time from the timing when the leading end of the inter-sheet area E reaches the head row 37A at the most upstream position (the inter-sheet area E reaches below the head). Can be determined. When it is determined that the sheet interval area E has not passed under the head (step S9: NO), the control unit 8 repeats step S9.

  When it is determined that the sheet interval area E has passed under the head (step S9: YES), the control unit 8 ends the drive adjustment control of the suction fan 49 in step S10. Specifically, the control unit 8 returns the duty ratio of the drive signal of the suction fan 49 from the duty ratio in the drive adjustment control to the set duty ratio. Thereafter, the process returns to step S4 in FIG.

  When the process returns from step S10 to step S4, in step S4, the control unit 8 controls the sheet P passing under the head when the inter-sheet area E for which the drive adjustment control of the suction fan 49 has passed under the head. Is the paper P that has reached below the head this time, and determines whether the paper P is the last paper P.

  If it is determined in step S7 of FIG. 11 that the sheet interval Lg is equal to or smaller than the specified interval (step S7: NO), in step S11, the control unit 8 starts the reverse rotation drive of the suction fan 49.

  Here, the duty ratio of the drive signal when the suction fan 49 is driven to rotate in the reverse direction may be a preset value, or may be set according to at least one of the factors relating to the sheet interval Lg and the degree of occurrence of ink mist. Good.

  Next, in step S12, the control unit 8 determines whether or not the sheet interval area E has passed under the head. When it is determined that the sheet interval area E has not passed under the head (step S9: NO), the control unit 8 repeats step S12.

  If it is determined that the sheet interval area E has passed under the head (step S12: YES), in step S13, the control unit 8 ends the reverse rotation drive of the suction fan 49 and returns to the normal rotation drive at the set duty ratio. Thereafter, the process returns to step S4 in FIG.

  When the process returns from step S13 to step S4, in step S4, the control unit 8 determines that the paper P passing under the head when the inter-sheet area E where the suction fan 49 has been driven to rotate in reverse passes under the head. Then, it is determined that the sheet P has reached the lower part of the head this time, and whether or not the sheet P is the last sheet P is determined.

  If it is determined in step S3 in FIG. 10 that the number of printed sheets has not reached the specified number (step S3: NO), in step S14, the control unit 8 determines that the sheet P that has reached below the head this time is the last sheet P Is determined. When determining that it is not the last sheet P (step S14: NO), the control unit 8 returns to step S2.

  If it is determined that the last sheet P is present (step S14: YES), the control unit 8 stops the suction fan 49 in step S15. Thus, the drive control of the suction fan 49 ends.

  If it is determined in step S4 that the sheet is the last sheet P (step S4: YES), the control unit 8 stops the suction fan 49 in step S15. Thus, the drive control of the suction fan 49 ends.

  If it is determined in step S5 that there is an inkjet head 36 whose temperature is equal to or higher than the threshold (step S5: NO), in step S16, the control unit 8 determines whether the next sheet P has reached below the head. . When determining that the next sheet P has not reached below the head (step S16: NO), the control unit 8 repeats step S16.

  If it is determined that the next sheet P has arrived under the head (step S16: YES), in step S17, the control unit 8 determines whether the sheet P is the last sheet P in a series of printing operations. I do. When determining that it is not the last sheet P (step S17: NO), the control unit 8 returns to step S5.

  When determining that it is the last sheet P (step S17: YES), the control unit 8 stops the suction fan 49 in step S15. Thus, the drive control of the suction fan 49 ends.

  As described above, in the inkjet printing apparatus 1, in the drive adjustment control of the suction fan 49, the control unit 8 controls the suction fan 49 so that the interval between the sheet intervals E passes below the head is shorter than the interval when the sheet P passes below the head. The duty ratio of the drive signal of the suction fan 49 is reduced. Accordingly, the inflow airflow Fn is weakened, and the efficiency of collecting the ink mist to the transport unit 3 by the suction airflow Fk is improved, so that the inside of the apparatus and the printed matter due to the ink mist can be reduced.

  If the degree of ink mist generation is the same, the controller 8 decreases the duty ratio of the drive signal of the suction fan 49 in the drive adjustment control as the sheet interval Lg decreases. Accordingly, it is possible to improve the efficiency of collecting the ink mist to the transport unit 3 while preventing the duty ratio from being reduced more than necessary and the cooling efficiency of the inkjet head 36 from being reduced.

  Further, the control unit 8 adjusts the duty ratio of the drive signal of the suction fan 49 in the drive adjustment control according to the factor relating to the degree of occurrence of ink mist. Thereby, while suppressing that the duty ratio becomes unnecessarily small and the cooling efficiency of the inkjet head 36 is reduced, the ink mist is efficiently collected in accordance with the degree of generation of the ink mist, and the inside of the apparatus and the The stain on the printed matter can be reduced.

  Further, the control unit 8 omits the drive adjustment control of the suction fan 49 until the number of printed sheets from the first sheet of the plurality of sheets P to be printed in the series of printing operations reaches the specified number. That is, when the number of prints from the first sheet P to be printed in the series of printing operations reaches the specified number, the control unit 8 performs drive adjustment control if the temperatures of all the inkjet heads 36 are lower than the threshold. . Thus, in a situation where the amount of ink mist is small and the necessity of the drive adjustment control of the suction fan 49 is small, the drive adjustment control is not performed, so that the complexity of the drive control of the suction fan 49 can be reduced.

  When the sheet interval Lg is equal to or less than the specified interval, the control unit 8 performs control to drive the suction fan 49 in the reverse direction instead of the drive adjustment control of the suction fan 49. Accordingly, the efficiency of collecting the ink mist can be further improved while suppressing the cooling efficiency of the inkjet head 36 from being reduced.

  In the above-described embodiment, when there is an inkjet head 36 whose temperature is equal to or higher than the threshold, the drive adjustment control of the suction fan 49 is not performed. Is not less than the threshold value, the drive adjustment control of the suction fan 49 may not be performed. Further, when there is a predetermined number or more of the inkjet heads 36 whose temperature is equal to or higher than the threshold value, the drive adjustment control of the suction fan 49 may not be performed.

  Further, drive adjustment control of the suction fan 49 may be performed irrespective of the temperature of the inkjet head 36. In this case, when the number of prints from the first sheet of paper P printed in a series of printing operations reaches the specified number, the drive adjustment control of the suction fan 49 may be started regardless of the temperature of the inkjet head 36.

  In the above-described embodiment, the drive adjustment control of the suction fan 49 is omitted until the number of prints from the first sheet P to be printed in the series of print operations reaches the specified number. Regardless of the number of sheets, drive adjustment control of the suction fan 49 may be performed.

  In the above-described embodiment, factors relating to the sheet interval Lg and the degree of ink mist generation are used as elements for setting the duty ratio of the drive signal in the drive adjustment control of the suction fan 49. Either may be omitted. Further, a duty ratio set in advance may be set without using any of these elements.

  In the above-described embodiment, the printing rate, the ink temperature, and the head-to-paper distance Hp are used as factors relating to the degree of occurrence of ink mist. However, any of these may be omitted, May be adopted.

  In the drive adjustment control of the suction fan 49, the duty ratio of the drive signal of the suction fan 49 may be adjusted so that the suction fan 49 is exhausted from the head holder 32 through the gaps 32c of all the mounting openings 32b. .

  Here, when the suction air flow rate (the number of rotations) of the suction fan 49 is sufficiently small, even at the mounting opening 32b closest to the suction section 42 due to the influence of the suction airflow Fk by the paper suction fan 27, the head holder is opened via the gap 32c. Exhaust from 32.

  Therefore, in the drive adjustment control of the suction fan 49, if the duty ratio of the drive signal of the suction fan 49 is adjusted so that the air is exhausted from the head holder 32 through the gap 32c in all the mounting openings 32b, the head holder 32 In the area on the rear side, the influence of the inflow airflow Fn can be avoided, and the ink mist can be efficiently collected in the transport unit 3 by the suction airflow Fk. Therefore, the efficiency of collecting the ink mist in the transport unit 3 can be further improved.

  In the case where the duty ratio of the drive signal of the suction fan 49 is adjusted so that the air is exhausted from the head holder 32 through the gaps 32c of all the mounting openings 32b as described above, the duty ratio depends on the factor relating to the degree of ink mist generation. The duty ratio may be adjusted by adjusting the duty ratio. Further, in a part of the combination of the conditions of each factor relating to the degree of occurrence of ink mist, the duty ratio of the drive signal of the suction fan 49 is set so that the air is exhausted from the head holder 32 through the gaps 32c of all the mounting openings 32b. It may be set.

  Further, when the length of the sheet P in the transport direction is shorter than the predetermined length, the sheet below the head is moved from when the first sheet interval area E reaches below the head to when the last sheet interval area E passes below the head. The suction fan 49 may be driven at a duty ratio lower than the set duty ratio, including the period during which P passes. Accordingly, it is possible to suppress the occurrence of a failure or the like in the suction fan 49 due to the frequency of switching the duty ratio of the drive signal of the suction fan 49 being too high.

  Further, in the above-described embodiment, a configuration having three line heads 31 is described, but the number of line heads is not limited to this. Further, in the above-described embodiment, an example has been described in which the plurality of inkjet heads 36 are arranged in a staggered manner to constitute the line head 31. However, the inkjet head is a single inkjet head that covers the print area in the main scanning direction. There may be.

  Further, in the above-described embodiment, the configuration in which the cooling air is generated by the blowing fan 47 and the suction fan 49 has been described. However, the configuration may be such that the cooling air is generated only by the suction fan exhausted from the head holder.

  The present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the components without departing from the spirit of the invention at the stage of implementation. Various inventions can be formed by appropriately combining a plurality of components disclosed in the above embodiments. For example, some components may be deleted from all the components described in the embodiments.

[Appendix]
This application discloses the following inventions.

(Appendix 1)
A transport unit that transports the paper while sucking and holding it by air suction,
An inkjet head that discharges and prints ink on paper conveyed by the conveyance unit,
A box-shaped head holder having an opening to which the inkjet head is attached via a gap,
A fan that generates cooling air that exhausts from the head holder and cools the inkjet head,
A control unit for controlling the fan,
The control unit is configured to drive the fan during a period in which a sheet interval area, which is an area between sheets conveyed by the conveyance unit, passes below the inkjet head, compared to a period in which a sheet passes below the inkjet head. An ink-jet printing apparatus for performing drive adjustment control for reducing the rate.

(Appendix 2)
2. The inkjet printing apparatus according to claim 1, wherein the control unit reduces the drive rate of the fan in the drive adjustment control as the sheet interval is smaller.

(Appendix 3)
Wherein the control unit starts the drive adjustment control when the number of printed sheets from the first sheet among a plurality of sheets printed in a series of printing operations reaches a specified number. An inkjet printing apparatus as described in the above.

(Appendix 4)
When the sheet interval is equal to or less than a predetermined interval, the control unit performs control to drive the fan in a rotation direction opposite to a rotation direction for exhausting from the head holder, instead of the drive adjustment control. 4. The inkjet printing apparatus according to any one of supplementary notes 1 to 3, wherein:

(Appendix 5)
Comprising a plurality of the inkjet heads,
The head holder has a plurality of openings to which a plurality of the inkjet heads are respectively attached,
The controller according to any one of claims 1 to 4, wherein in the drive adjustment control, the drive ratio of the fan is adjusted such that the drive rate is exhausted from the head holder through the gaps of all the openings. An inkjet printing apparatus according to any one of the above.

DESCRIPTION OF SYMBOLS 1 Ink-jet printing apparatus 2 Feeding part 3 Conveying part 4 Printing part 5 Cooling part 6, 6A-6D Ink circulation mechanism part 7 Head gap adjusting part 8 Control part 21 Conveying belt 21a Suction hole 21b Conveying surface 27 Paper suction fan 31, 31A , 31B Line head 36 Ink jet head 36a Ink ejection surface 41 Blowing unit 42 Suction unit 47 Blowing fan 49 Suction fan 56 Duty ratio table

Claims (5)

A transport unit that transports the paper while sucking and holding it by air suction,
An inkjet head that discharges and prints ink on paper conveyed by the conveyance unit,
A box-shaped head holder having an opening to which the inkjet head is attached via a gap,
A fan that generates cooling air that exhausts from the head holder and cools the inkjet head,
A control unit for controlling the fan,
The control unit is configured to drive the fan during a period in which a sheet interval area, which is an area between sheets conveyed by the conveyance unit, passes below the inkjet head, compared to a period in which a sheet passes below the inkjet head. An ink-jet printing apparatus for performing drive adjustment control for reducing the rate.   2. The ink jet printing apparatus according to claim 1, wherein the control unit reduces the drive rate of the fan in the drive adjustment control as the sheet interval is smaller.   3. The control unit according to claim 1, wherein the control unit starts the drive adjustment control when the number of printed sheets from a first sheet among a plurality of sheets printed in a series of printing operations reaches a specified number. 3. The inkjet printing apparatus according to claim 1.   When the sheet interval is equal to or less than a predetermined interval, the control unit performs control to drive the fan in a rotation direction opposite to a rotation direction for exhausting from the head holder, instead of the drive adjustment control. The inkjet printing apparatus according to any one of claims 1 to 3, wherein: Comprising a plurality of the inkjet heads,
The head holder has a plurality of openings to which a plurality of the inkjet heads are respectively attached,
5. The control unit according to claim 1, wherein the control unit adjusts a driving rate of the fan so that air is exhausted from the head holder through the gaps of all the openings in the drive adjustment control. 6. The inkjet printing apparatus according to claim 1.