JP6761545B2 - Image forming apparatus and its control method - Google Patents

Description

The present invention relates to an image forming apparatus and a control method thereof, and more particularly to an image forming apparatus in which a plurality of liquid ejection heads are arranged along a conveying direction of a recording medium and a control method thereof.

In an inkjet printing machine, in order to improve the printing speed, a configuration is known in which a plurality of inkjet heads capable of ejecting ink of the same color are arranged along the paper transport direction to improve the transport speed of the recording medium.

In Patent Document 1, by ejecting ink from the nozzles of four nozzle rows that eject the same color ink arranged along the conveying direction, the conveying speed is four times faster than the case of recording with one nozzle row. An inkjet printer capable of transporting a recording medium for printing is disclosed.

Japanese Unexamined Patent Publication No. 2014-024209

In general, an inkjet head has a variation in the amount of discharged droplets due to a variation in manufacturing. In order to correct this variation, a correction work for adjusting the amount of discharged droplets is required. In addition, it is also necessary to confirm whether or not the discharge element is in the normal discharge state for each discharge element.

Patent Document 1 discloses a method of detecting a defective ejection element by analyzing an analysis pattern recorded for each nozzle row. However, at the time of high-speed transfer utilizing the four nozzle trains, there is a problem that the analysis pattern cannot be properly formed and the analysis accuracy cannot be ensured.

The present invention has been made in view of such circumstances, and is an image forming apparatus for appropriately adjusting the amount of discharged droplets and measuring the discharge direction of a plurality of liquid discharge heads arranged along the transport direction of the recording medium. The purpose is to provide a control method.

In order to achieve the above object, one aspect of the image forming apparatus includes a transport unit that transports the recording medium along the transport direction and a plurality of discharge elements that discharge the liquid, and arranges them side by side along the transport direction. The recording medium is conveyed at the first transfer speed by the plurality of liquid discharge heads, the liquid supply unit that supplies the same liquid to the plurality of liquid discharge heads, and the transfer unit, and a plurality of discharges of the plurality of liquid discharge heads. A plurality of image formation control units that discharge liquid from an element to form an image on a recording medium, and a transport unit that transports the recording medium at a second transport speed slower than the first transport speed, and one liquid discharge head. A chart formation control unit that discharges liquid from the discharge element to form a chart on the recording medium is provided, and the diameter of dots formed on the recording medium by the liquid discharged from the discharge element is D [μm], and the chart. If the discharge frequency of the liquid of the discharge element is f [kHz] and the second transport speed is Vh [m / s], Vh ≦ D × f / 1000 is satisfied.

According to this aspect, the recording medium is conveyed by the transfer unit at a second transfer speed slower than the first transfer speed at the time of image formation, and liquid is discharged from a plurality of discharge elements of one liquid discharge head for recording. A chart formation control unit for forming a chart on the medium is provided, the diameter of dots formed on the recording medium by the liquid discharged from the discharge element is D [μm], and the discharge frequency of the liquid of the discharge element when forming the chart is set. Assuming that f [kHz] and the second transport speed are Vh [m / s], Vh ≦ D × f / 1000 is satisfied. Therefore, the discharge amount is adjusted and the discharge direction is appropriately measured by reading the chart. be able to.

When the first transfer speed is Vm [m / s] and the number of liquid discharge heads is an integer N of 2 or more, it is preferable that Vh ≦ Vm / N is satisfied. As a result, the discharge droplet amount can be adjusted and the discharge direction measurement can be appropriately performed.

Assuming that the first transfer speed is Vm [m / s] and the number of liquid discharge heads is an integer N of 2 or more, Vm / N <Vh may be satisfied. As a result, the discharge droplet amount can be adjusted and the discharge direction measurement can be appropriately performed.

An in-line scanner for reading images and charts formed on a recording medium is provided downstream of a plurality of liquid discharge heads in the transport direction, and the reading frequency and chart formation of the in-line scanner when reading the images formed by the image formation control unit. It is preferable that the reading frequency of the in-line scanner when reading the chart formed by the control unit is equal. As a result, the number of readings by the in-line scanner is increased, so that noise in reading can be reduced.

A pretreatment liquid application unit for applying the pretreatment liquid to the recording medium is provided on the upstream side of the plurality of liquid discharge heads in the transport direction, and the image formation control unit uses the first recording medium whose surface is not coated with the ink absorbing layer. The pretreatment liquid is applied by the pretreatment liquid coating unit, and the chart formation control unit uses a second recording medium whose surface is coated with an ink absorbing layer, and the pretreatment liquid is applied by the pretreatment liquid coating unit. It is preferable to stop. As a result, it is possible to eliminate fluctuations in the coating amount of the pretreatment liquid due to fluctuations in the transport speed.

It is preferable that the pretreatment liquid coating unit for applying the pretreatment liquid to the recording medium is provided on the upstream side of the plurality of liquid discharge heads in the transport direction, and the pretreatment liquid application unit has an inkjet head for discharging the pretreatment liquid. .. As a result, even if the transport speed fluctuates, the amount of the pretreatment liquid applied can be adjusted to an appropriate amount.

The distance between the liquid discharge head and the recording medium when the chart formation control unit forms a chart on the recording medium is rather than the distance between the liquid discharge head and the recording medium when the image formation control unit forms an image on the recording medium. It is preferable that the size is smaller. When the chart is formed, the transport speed is slower than when the image is formed, so that the risk of contact between the liquid ejection head and the recording medium is low, and there is little damage when the chart is formed. Therefore, the distance between the liquid discharge head and the recording medium can be reduced, and the noise of the chart can be reduced by reducing the distance.

The image formation control unit may have a normal printing mode in which the recording medium is conveyed by the conveying unit at the first conveying speed, and a high-speed printing mode in which the recording medium is conveyed by the conveying unit at a speed higher than the first conveying speed. preferable. In this case, the second transport speed is slower than the first transport speed in the normal print mode. Thereby, the chart can be appropriately formed in one liquid discharge head.

The liquid discharge head can form a plurality of dots having different diameters, and it is preferable that the diameter of the smallest dot among the plurality of dots having different diameters is D [μm]. This allows the chart to be properly formed at the smallest dots.

The chart preferably includes a concentration patch formed for each liquid discharge head. By reading this chart, the amount of discharged droplets can be adjusted appropriately.

The chart preferably includes a line pattern formed for each discharge element. By reading this chart, the discharge direction can be measured appropriately.

It is preferable that the liquid discharge heads are arranged side by side in the first direction in which a plurality of head modules intersect in the transport direction. This embodiment is applicable to a liquid discharge head in which a plurality of head modules are arranged side by side.

One aspect of the control method of the image forming apparatus for achieving the above object is to have a transport unit that transports the recording medium along the transport direction and a plurality of discharge elements that discharge the liquid, respectively, along the transport direction. It is a control method of an image forming apparatus including a plurality of liquid discharge heads arranged side by side and a liquid supply unit that supplies the same liquid to each of the plurality of liquid discharge heads, and the recording medium is first conveyed by the transfer unit. An image formation control step of transporting at a high speed and discharging liquid from a plurality of discharge elements of a plurality of liquid discharge heads to form an image on a recording medium, and a transfer unit slowing the recording medium to a speed lower than the first transport speed. It is provided with a chart formation control step of transporting at two transport speeds and discharging liquid from a plurality of discharge elements of one liquid discharge head to form a chart on a recording medium, and recording by the liquid discharged from the discharge element. Assuming that the diameter of the dots formed on the medium is D [μm], the discharge frequency of the liquid of the discharge element when forming the chart is f [kHz], and the second transport speed is Vh [m / s], Vh ≦ D × f / 1000 is satisfied.

According to this aspect, the recording medium is conveyed by the transfer unit at a second transfer speed slower than the first transfer speed at the time of image formation, and liquid is discharged from a plurality of discharge elements of one liquid discharge head for recording. A chart formation control unit for forming a chart on the medium is provided, the diameter of dots formed on the recording medium by the liquid discharged from the discharge element is D [μm], and the discharge frequency of the liquid of the discharge element when forming the chart is set. Assuming that f [kHz] and the second transport speed are Vh [m / s], Vh ≦ D × f / 1000 is satisfied. Therefore, the discharge amount is adjusted and the discharge direction is appropriately measured by reading the chart. be able to.

According to the present invention, it is possible to appropriately adjust the discharge droplet amount and measure the discharge direction of a plurality of liquid discharge heads arranged along the transport direction of the recording medium.

Perspective view of the inkjet head Enlarged view of the inkjet head as seen from the nozzle surface side Top view showing an example of the nozzle surface of the head module Cross-sectional view showing a structural example of a droplet ejection element for one nozzle of a head module Top view of a single bar type inkjet printing machine Side view of the inkjet printing machine The figure which shows an example of the density adjustment chart group printed on the paper by an inkjet printing machine. Top view of dual bar type inkjet printing machine Side view of the inkjet printing machine 100 Block diagram showing the system configuration of an inkjet printing machine The figure which shows an example of the density adjustment chart group printed on the paper by an inkjet printing machine. The figure which shows an example of the density adjustment chart group printed on the paper by an inkjet printing machine. A diagram showing an example of a chart for measuring the ejection direction printed on paper by an inkjet printing machine. The figure for demonstrating the landing position deviation of the ink droplet ejected from a nozzle Enlarged view of one line constituting the discharge direction measurement chart group An example of a scanned image obtained by scanning three lines printed by three nozzles with a scanner. The figure which shows an example of the line printed on the paper by one nozzle The figure for demonstrating the diameter of the ink dot which the ink drop ejected from a nozzle forms on a paper, and the distance between dots. A graph showing the relationship between the diameter of the ink dots and the density of the density patch when the density patch is printed. The figure which shows the configuration example of the inkjet printing machine The figure which shows the distance TD between the nozzle surface of an inkjet head and the outer peripheral surface of a drawing drum. Block diagram showing the system configuration of an inkjet printing machine

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

<Configuration example of inkjet head>
An example of the configuration of the inkjet head used in this embodiment will be described. FIG. 1 is a perspective view of the inkjet head 10 used in the present embodiment. The inkjet head 10 connects a plurality of head modules 12-i (i = 1, 2, ... n) of a plurality of head modules (n integers of 2 or more) in the X direction (an example of a first direction intersecting the transport direction). It is composed. Here, an example in which 17 (n = 17) head modules 12-i are arranged is shown. The frame 16 functions as a frame for fixing the plurality of head modules 12-i. Each head module 12-i is fixed to the frame 16 with the nozzle surface 20 facing a common direction. The structure of each head module 12-i is common.

A flexible substrate 18 is connected to each head module 12-i. A drive signal, a discharge control signal, and the like are supplied to each head module 12-i via the flexible substrate 18.

FIG. 2 is an enlarged view of the inkjet head 10 as viewed from the nozzle surface 20 side. Each head module 12-i is supported by head module holding members 22 from both sides in the Y direction, and both ends in the X direction are supported by head protection members 24.

FIG. 3 is a plan view showing an example of the nozzle surface 20 of the head module 12-i. The head module 12-i has an end face on the long side along the v direction having an inclination of an angle γ with respect to the X direction and a short side along the w direction having an inclination of an angle α with respect to the Y direction. It is a parallelogram with an end face in a plan view. Nozzles 28 are two-dimensionally arranged on the nozzle surface 20 of the head module 12-i. The projected nozzle row LN projected in the X direction is equivalent to a row of nozzle rows in which nozzles 28 are arranged at equal intervals at a nozzle density that achieves recording resolution.

By connecting a plurality of head modules 12-i in the X direction (see FIG. 2), the inkjet head 10 is formed with a nozzle array that covers the entire printing range of the recording medium. The inkjet head 10 is a full-line type bar head capable of printing at a recording resolution in a single transfer of a recording medium.

The full-line type bar head applied to the single-pass method is not limited to the case where the entire surface of the recording medium is the print range, but also when a part of the recording medium is a print area (for example, around the recording medium). In the case of providing a margin portion, etc.), it is sufficient that the nozzle row required for printing is formed.

The number of nozzles of the head module 12-i, the nozzle density, and the arrangement form of the nozzles are not particularly limited.

<Example of internal structure of head module>
The head module 12-i includes an ejection energy generating element (for example, a piezoelectric element or a heat generating element) that generates ejection energy required for ink ejection corresponding to each nozzle 28. The head module 12-i discharges ink droplets (an example of a liquid) on demand according to a drive signal and a discharge control signal supplied via the flexible substrate 18.

FIG. 4 is a cross-sectional view showing an example of the internal structure of the droplet ejection element for one nozzle of the head module 12-i. In the head module 12-i, a nozzle plate 30 in which a nozzle 28 which is an ink droplet ejection port is formed, and a flow path such as a pressure chamber 32, a supply port 34, and a common flow path 36 corresponding to the nozzle 28 are formed. Includes a flow path plate 38.

The flow path plate 38 constitutes a side wall portion of the pressure chamber 32, and also forms a supply port 34 as a throttle portion (maximum narrowed portion) of an individual supply path for guiding ink from the common flow path 36 to the pressure chamber 32. It is a forming member. The flow path plate 38 may be composed of one substrate, or may have a structure in which a plurality of substrates are laminated. The nozzle plate 30 and the flow path plate 38 can be processed into a required shape by using silicon as a material and using semiconductor manufacturing technology.

A plurality of pressure chambers 32 are connected to the common flow path 36 via their respective supply ports 34. Ink is supplied to the common flow path 36 from the outside of the head module 12-i.

The diaphragm 40 forming a part of the surface (top surface in FIG. 4) of the pressure chamber 32 is provided with a piezoelectric element 44 provided with an individual electrode 42 for each pressure chamber 32. The diaphragm 40 of this example is made of silicon with a conductive layer that functions as a common electrode 46 corresponding to the lower electrode of the piezoelectric element 44, and also serves as a common electrode of the piezoelectric element 44 arranged corresponding to each pressure chamber 32. .. It is also possible to form the diaphragm with a non-conductive material such as resin. In this case, a common electrode layer made of a conductive material such as metal is formed on the surface of the diaphragm member. Further, a diaphragm that also serves as a common electrode may be formed of a metal (conductive material) such as stainless steel.

By applying a driving voltage to the individual electrodes 42, the piezoelectric element 44 is deformed to change the volume of the pressure chamber 32, and the pressure change accompanying this causes ink to be ejected from the nozzle 28. After ejecting the ink, new ink is refilled in the pressure chamber 32 from the common flow path 36 through the supply port 34.

By selecting the drive voltage applied to the individual electrodes 42, the head module 12-i has a small drop having a relatively small amount of ink from each nozzle 28, a medium drop having a relatively large amount of ink than the small drop, and a medium drop. It is possible to eject one of three types of ink droplets, a large droplet having a relatively larger amount of ink than a medium droplet. As a result, ink dots having a diameter of 30 [μm] for small ink droplets, ink dots having a diameter of 40 [μm] for medium ink droplets, and ink having a diameter of 50 [μm] for large ink droplets. Dots are formed on the recording medium. In this way, the head module 12-i can form a plurality of ink dots having different diameters on the recording medium.

The ink chamber unit 50 including the nozzle 28, the pressure chamber 32, the supply port 34, and the piezoelectric element 44 is a droplet ejection element as a recording element unit responsible for recording one pixel. The head module 12-i includes a plurality of ink chamber units 50 corresponding to the two-dimensional nozzle arrangement described with reference to FIG.

<Single bar type inkjet printing machine>
FIG. 5 is a top view of the single bar type inkjet printing machine 200 in which the number of inkjet heads (bar heads) for ejecting the same color ink is one, and FIG. 6 is a side view of the inkjet printing machine 200.

The inkjet printing machine 200 includes a platen 102, ink tanks 106K, 106C, 106M, and 106Y, and an inkjet head 204K, 204C, 204M, and 204Y.

On the platen 102, the paper 1 which is a recording medium is placed and conveyed in the Y direction.

The ink tanks 106K, 106C, 106M, and 106Y (an example of the liquid supply unit) store inks of black (K), cyan (C), magenta (M), and yellow (Y), respectively. The ink tanks 106K, 106C, 106M, and 106Y supply each color ink to the inkjet heads 204K, 204C, 204M, and 204Y, respectively.

The above-mentioned inkjet head 10 is applied to the inkjet heads 204K, 204C, 204M, and 204Y, respectively. The inkjet heads 204K, 204C, 204M, and 204Y are arranged in order at regular intervals in the Y direction. The inkjet heads 204K, 204C, 204M, and 204Y are arranged so that the nozzle surface 20 faces the platen 102.

At the time of normal image printing, a control unit (not shown) that controls the recording control of the inkjet printing machine 200 controls the platen 102 and conveys the paper 1 at a conveying speed Vs [m / s]. In addition, the inkjet heads 204K, 204C, 204M, and 204Y are controlled, and black ink droplets, cyan ink droplets, magenta ink droplets, and yellow ink droplets are ejected from each nozzle 28 at an ejection frequency f [kHz]. Small, medium, or large ink droplets are ejected according to the image data. As a result, the image is printed on the recording surface of the paper 1 conveyed by the platen 102. The ejection frequency is the number of ink droplets ejected by one nozzle 28 per unit time.

<Drop volume adjustment in single bar method>
In the unadjusted state of the 17 head modules 12-i constituting the inkjet heads 204K, 204C, 204M, and 204Y, the amount of ink ejected from the nozzle 28 varies due to variations during manufacturing. As a result, the printed image has a density variation in the X direction. Therefore, in order to obtain a high-quality image, it is necessary to appropriately adjust the amount of ink ejected from the nozzle 28.

In order to adjust the amount of ink droplets, the control unit (not shown) of the inkjet printing machine 200 conveys the paper 1 at the same conveying speed Vs as the conveying speed at the time of normal image printing, and the inkjet heads 204K, 204C, 204M, and 204Y. A small ink droplet is ejected at an ejection frequency f [kHz] to print a density adjustment chart on paper 1. By reading the density of this density adjustment chart, it is possible to detect variations and appropriately adjust the amount of ink ejected from each nozzle 28 so that the density becomes an appropriate value.

FIG. 7 is a diagram showing an example of a density adjustment chart printed on paper 1 by the inkjet printing machine 200. The density adjustment chart group C ₁ is a density patch 210K-i (i = 1,2, ... n) printed by each head module 12-i (i = 1,2, ... n) of the inkjet head 204K. Density patch 210Y-i (i = 1,2, ... n) printed by each head module 12-i of the inkjet head 204Y, density patch 210M- printed by each head module 12-i of the inkjet head 204M, respectively. It has i (i = 1,2, ... n) and density patches 210C-i (i = 1,2, ... n) printed by each head module 12-i of the inkjet head 204C.

In each density patch 210K-i, 210C-i, 210M-i, and 210Y-i, the transport speed Vs [m / s] of the paper 1, the ejection frequency f [kHz] of the nozzle 28, and the small ink droplets are present. Printing is performed at a dot recording rate determined by the diameter D [μm] of dots formed on the paper 1.

The density of the density patch 210K-i is read by a scanner (not shown) or the like, and the read density data is analyzed to adjust the drive voltage applied to the piezoelectric element 44 of each head module 12-i of the inkjet head 204K. Thereby, the amount of ink ejected from the nozzle 28 of each head module 12-i of the inkjet head 204K can be appropriately adjusted. The same applies to the inkjet heads 204C, 204M, and 204Y.

<Dual bar type inkjet printing machine>
FIG. 8 is a top view of a dual bar type inkjet printing machine 100 (an example of an image forming apparatus) in which the number of inkjet heads (bar heads) for ejecting the same color ink is two, and FIG. 9 is a top view of the inkjet printing machine. It is a side view of 100.

The inkjet printing machine 100 includes a platen 102, an inkjet head 104Ka, 104Kb, 104Ca, 104Cb, 104Ma, 104Mb, 104Ya, 104Yb, an ink tank 106K, 106C, 106M, and 106Y (an example of a liquid ejection head).

On the platen 102 (an example of a transport unit), paper 1 which is a recording medium is placed and transported in the Y direction (an example of a transport direction).

The ink tanks 106K, 106C, 106M, and 106Y store inks of black (K), cyan (C), magenta (M), and yellow (Y), respectively. The ink tank 106K supplies each color ink to the inkjet heads 104Ka and 104Kb, the ink tank 106C supplies the inkjet heads 104Ca and 104Cb, the ink tank 106M supplies the inkjet heads 104Ma and 104Mb, and the ink tank 106Y supplies the inkjet heads 104Ya and 104Yb.

The above-mentioned inkjet head 10 is applied to the inkjet heads 104Ka, 104Kb, 104Ca, 104Cb, 104Ma, 104Mb, 104Ya, and 104Yb, respectively.

The inkjet heads 104Ka, 104Kb, 104Ca, 104Cb, 104Ma, 104Mb, 104Ya, and 104Yb are sequentially arranged at regular intervals in the Y direction. Further, the inkjet heads 104Ka, 104Kb, 104Ca, 104Cb, 104Ma, 104Mb, 104Ya, and 104Yb are arranged so that the nozzle surface 20 faces the platen 102. The inkjet heads 104Ka, 104Kb, 104Ca, 104Cb, 104Ma, 104Mb, 104Ya, and 104Yb are arranged at the same position in the X direction, and the nozzles 28 arranged on the respective nozzle surfaces 20 have the same positions in the X direction. To do.

FIG. 10 is a block diagram showing a system configuration of the inkjet printing machine 100. As shown in FIG. 10, the inkjet printing machine 100 includes the platen 102, the inkjet heads 104Ka, 104Kb, 104Ca, 104Cb, 104Ma, 104Mb, 104Ya, 104Yb, the ink tanks 106K, 106C, 106M, 106Y, and the like. It includes a storage unit 108, an image formation control unit 110, and a chart formation control unit 112.

Image data and chart data printed by the inkjet printing machine 100 are stored in the storage unit 108.

The image formation control unit 110 controls the platen 102 and the inkjet heads 104Ka, 104Kb, 104Ca, 104Cb, 104Ma, 104Mb, 104Ya, 104Yb based on the image data stored in the storage unit 108, and prints the image on the paper 1. To do.

The chart formation control unit 112 controls the platen 102 and the inkjet heads 104Ka, 104Kb, 104Ca, 104Cb, 104Ma, 104Mb, 104Ya, 104Yb based on the chart data stored in the storage unit 108, and prints an image on the paper 1. To do.

Here, the image formation control unit 110 controls the platen 102 to convey the paper 1 at a transfer speed Vd (an example of a first transfer speed). Further, the inkjet heads 104Ka, 104Kb, 104Ca, 104Cb, 104Ma, 104Mb, 104Ya, and 104Yb are controlled, and black ink drops from the nozzles 28 of the inkjet heads 104Ka and 104Kb, and black ink droplets from the nozzles 28 of the inkjet heads 104Ca and 104Cb, respectively. Image data of cyan ink droplets, magenta ink droplets from the nozzles 28 of the inkjet heads 104Ma and 104Mb, and yellow ink droplets from the nozzles 28 of the inkjet heads 104Ya and 104Yb, respectively, at an ejection frequency of f [kHz]. Small, medium, or large ink droplets are ejected according to the above (an example of the image formation control step).

As described above, in the inkjet printing machine 100, the amount of ink droplets ejected per unit time is twice that in the case of the inkjet printing machine 200. Therefore, the inkjet printing machine 100 can ideally print at twice the printing speed of the inkjet printing machine 200.

That is, the transport speed Vd of the dual bar type inkjet printing machine 100 can be expressed by the following formula 1 with respect to the transport speed Vs of the single bar type inkjet printing machine 200.

Vd = 2 × Vs… (Equation 1)
Similarly, by increasing the number of inkjet heads (bar heads) that eject the same color ink to three or four, it is possible to ideally improve the printing speed by three times or four times. The transport speed Vm (an example of the first transport speed) of a multi-bar type inkjet printing machine having N inkjet heads for ejecting ink of the same color can be expressed by the following formula 2.

Vm = N × Vs… (Equation 2)
<Drop volume adjustment in dual bar method>
Similar to the inkjet printing machine 200, the inkjet printing machine 100 has a nozzle 28 in a state where the head modules 12-i constituting the inkjet heads 104Ka, 104Kb, 104Ca, 104Cb, 104Ma, 104Mb, 104Ya, and 104Yb are not adjusted. The amount of ink ejected from the printer varies. Therefore, in order to obtain a high-quality image, it is necessary to appropriately adjust the amount of ink ejected from the nozzle 28.

Here, in the inkjet printer 100, when printing the density adjustment chart group _{C 1} shown in FIG. 7, for example be read density of the density patch 210K-i, the adjustment of the head module 12-i of the ink jet head 104Ka It is difficult to individually know the adjustment amount of the head module 12-i of the inkjet head 104Kb and the adjustment amount of the head module 12-i. Therefore, in the case of the inkjet printing machine 100, it is necessary to print the density patch on each of the inkjet heads 104Ka, 104Kb, 104Ca, 104Cb, 104Ma, 104Mb, 104Ya, and 104Yb.

FIG. 11 is a density adjustment chart printed on paper 1 by the inkjet printing machine 100, wherein the transport speed is Vd and the ejection frequency is f [kHz] which is the same as that at the time of normal image printing, and the inkjet heads 104Ka, 104Kb, 104Ca. It is a figure which shows an example of the density | concentration adjustment chart which includes the density | concentration patch formed for every 104Cb, 104Ma, 104Mb, 104Ya, and 104Yb (an example for every liquid discharge head). The density adjustment chart group C ₂ is a density patch 210Ka-i (i = 1,2, ... n) printed by each head module 12-i (i = 1,2, ... n) of the inkjet head 104Ka, respectively. Density patch 210Kb-i (i = 1,2, ... n) printed by each head module 12-i (i = 1,2, ... n) of the inkjet head 104Kb, each head module 12- of the inkjet head 104Ya. The density patches 210Ya-i (i = 1,2, ... n) printed by i (i = 1,2, ... n) and the head modules 12-i (i = 1,2, ... n) of the inkjet head 104Yb, respectively. The density patch 210Ybi (i = 1,2, ... n) printed by n) and the density patch printed by each head module 12-i (i = 1,2, ... n) of the inkjet head 104Ma. Density patch 210Mb-i (i = 1,2) printed by each head module 12-i (i = 1,2, ... n) of 210Ma-i (i = 1,2, ... n) and the inkjet head 104Mb. , ... n), the density patch 210Ca-i (i = 1,2, ... n) printed by each head module 12-i (i = 1,2, ... n) of the inkjet head 104Ca, and the inkjet head 104Cb. It has a density patch 210Cb-i (i = 1,2, ... n) printed by each head module 12-i (i = 1,2, ... n) of the above.

When the density patch is printed for each of the inkjet heads 104Ka, 104Kb, 104Ca, 104Cb, 104Ma, 104Mb, 104Ya, and 104Yb with the transport speed set to Vd and the ejection frequency set to the same f [kHz] as in normal image printing, the transport speed Vd is single. Since the transfer speed is faster than the transfer speed Vs of the bar-type inkjet printing machine 200, the density of the density patch is insufficient and the density range is not appropriate. As a result of narrowing the density gradation of the density patch, it becomes vulnerable to noise and the density measurement accuracy is lowered.

Therefore, in the inkjet printing machine 100 in which the number of inkjet heads that eject the same color ink is two, the transport speed Vh at the time of printing the density adjustment chart is set with respect to the transport speed Vd at the time of normal image printing.
Vh ≤ Vd / 2 ... (Equation 3)
And.

The chart formation control unit 112 controls the platen 102 to convey the paper 1 at a transfer speed Vh satisfying the equation 3. Further, the inkjet heads 104Ka, 104Kb, 104Ca, 104Cb, 104Ma, 104Mb, 104Ya, and 104Yb eject small ink droplets at an ejection frequency f [kHz] to print a density adjustment chart on paper 1 (chart formation). An example of a control process).

FIG. 12 is a density adjustment chart printed on paper 1 by the inkjet printing machine 100, wherein the transport speed is Vh and the ejection frequency is f [kHz], and the inkjet heads 104Ka, 104Kb, 104Ca, 104Cb, 104Ma, 104Mb, It is a figure which shows an example of the density | concentration adjustment chart group which includes the density | concentration patch formed for every 104Ya and 104Yb (an example for every liquid discharge head).

Concentration adjustment chart group _{C 3,} similar to the density adjustment chart group _{C 2,} the head modules 12-i of the ink jet head 104Ka (i = 1,2, ... n ) are respectively printed by the density patch 210 kA-i (I = 1,2, ... n) (an example of a chart), density patch 210Kb-i (i = 1) printed by each head module 12-i (i = 1,2, ... n) of the inkjet head 104Kb. , 2, ... n), density patch 210Ya-i (i = 1,2, ... n) printed by each head module 12-i (i = 1,2, ... n) of the inkjet head 104Ya, an inkjet head. The density patch 210Yb-i (i = 1,2, ... n) printed by each head module 12-i (i = 1,2, ... n) of 104Yb, and each head module 12-i (i = 1,2, ... n) of the inkjet head 104Ma. Density patches 210Ma-i (i = 1,2, ... n) printed by i = 1,2, ... n), head modules 12-i (i = 1,2, ... n) of the inkjet head 104Mb, respectively. Density patch 210Mb-i (i = 1,2, ... n) printed by, and density patch 210Ca- printed by each head module 12-i (i = 1,2, ... n) of the inkjet head 104Ca. Density patch 210Cb-i (i = 1,2, ... n) printed by each head module 12-i (i = 1,2, ... n) of i (i = 1,2, ... n) and the inkjet head 104Cb, respectively. ... n).

As shown in FIG. 12, each density patch 210K-i of the density adjustment chart group _{C 3,} the 210C-i, 210M-i, and 210Y-i concentration is the concentration adjustment chart group _{C 1} shown in FIG. 7 This is the same as the density of each density patch 210K-i, 210C-i, 210M-i, and 210Y-i.

Thus reading the density adjustment chart group _{C 3} printed, read and analyze the density data, an ink jet head 104Ka, 104Kb, 104Ca, 104Cb, 104Ma, 104Mb, 104Ya, and piezoelectric head modules 12-i of 104Yb The drive voltage applied to the element 44 is adjusted. As a result, the amount of ink ejected from the nozzles 28 of the inkjet heads 104Ka, 104Kb, 104Ca, 104Cb, 104Ma, 104Mb, 104Ya, and 104Yb (the amount of ink droplets per ejection by the nozzle 28) is appropriately adjusted. can do.

When there are N inkjet heads that eject ink of the same color, the transport speed Vh at the time of printing the density adjustment chart is set with respect to the transport speed Vm at the time of normal image printing.
Vh ≤ Vm / N ... (Equation 4)
And it is sufficient.

<Measurement of discharge direction in single bar method>
FIG. 13 is a diagram showing an example of a chart for measuring the ejection direction printed on the paper 1 by the inkjet printing machine 200. The discharge direction measurement chart C ₄ is a so-called 1-on-n-off type nozzle check test chart image composed of a pattern of line segments (lines). In the example shown in FIG. 13 shows a 1 on 7 off type discharge direction measurement chart C ₄ of.

A control unit (not shown) that controls the recording control of the inkjet printing machine 200 controls the platen 102 and conveys the paper 1 at the conveying speed Vs. Further, the printing ink jet head 204K, 204C, 204M, and ejects ink droplets of the droplet at ejection frequency f [kHz] by 204Y in the sheet 1 the discharge direction measurement chart _{C 4.}

Here, the control unit divides the nozzles 28 (see FIG. 3) constituting the projection nozzle row LN of each inkjet head into eight groups of every seven, and ejects them in order in group units. As a result, one nozzle 28 forms one line LD along the Y direction, and line LDs for all nozzles are formed.

FIG. 14 is a diagram for explaining the landing position deviation of the ink droplets ejected from the nozzle. Here, the ink formed by landing the ink droplets of the small droplets ejected from the three nozzles 28-1, 28-2, and 28-3 arranged on the nozzle surface 20 of the inkjet head 10 on the paper 1. Dots ID-1, ID-2, and ID-3 are shown.

Ideally, the ink droplets ejected from the nozzle 28 fly parallel to the Z direction and land on the paper 1. Therefore, the normal X-direction position of the nozzle 28 and the X-direction position of the ink dot ID ejected and landed from the nozzle 28 are the same position. As shown in FIG. 14, the X-direction position of the nozzle 28-1 and the X-direction position of the ink dot ID-1, and the X-direction position of the nozzle 28-3 and the X-direction position of the ink dot ID-3 are the same positions. It has become.

On the other hand, the position of the nozzle 28-2 in the X direction and the position of the ink dot ID-2 in the X direction are deviated by ΔX. This deviation is called the landing position deviation, and ΔX is called the landing position deviation amount.

Figure 15 is an enlarged view of one line LD constituting the discharge direction measurement chart C _4. As shown in FIG. 15, the line LD is configured such that ink dot IDs formed by landing small ink droplets ejected from a nozzle 28 on paper 1 are connected in the Y direction.

By reading this manner printed ejection direction measurement chart C ₄ in the scanner, it is possible to measure the deposition position displacement amount ΔX of each nozzle 28.

FIG. 16 is a scanner reading the three lines LD-1, LD-2, and LD-3 printed by the three nozzles 28-1, 28-2, and 28-3 shown in FIG. 14, respectively. This is an example of a scanned image. Here, since the landing position shift of the landing position shift amount ΔX occurs in the ink droplets constituting the line LD-2, the distance between the line LD-1 and the line LD-2 and the distance between the line LD-2 and the line LD-2 are generated. The interval with -3 is not equal.

By measuring the landing position deviation amount ΔX, it is possible to inspect the presence or absence of a nozzle in a non-discharged state and the presence or absence of a nozzle having a defective discharge direction.

<Measurement of discharge direction in dual bar method>
Inkjet printer 100, similar to the droplet amount adjustment, the inkjet head 104Ka also discharge direction measurement, 104Kb, 104Ca, 104Cb, 104Ma , 104Mb, 104Ya, and the segment of the ejection direction measurement chart _{C 4} in each 104Yb Need to print. That is, the discharge direction measurement chart C ₄ includes a line pattern formed for each of the plurality of nozzles 28 (an example for each discharge element).

FIG. 17 is a diagram showing an example of a line LD printed on paper 1 by one nozzle 28 (see FIG. 3) in an inkjet printing machine 100 with a discharge frequency of f [kHz], which is the same as that at the time of normal image printing, at a transport speed Vd. Is. As shown in FIG. 17, the ink dot IDs constituting the line LD are not connected in the Y direction. When reading the ejection direction measurement chart C ₄ having such a line LD in the scanner, or the concentration becomes insufficient line LD, to or longer recognize the line LD as a line segment, easily out parsing errors Become.

Therefore, when printing the ejection direction measurement chart C ₄ in the ink-jet printer 100, by slowing down the conveying speed for printing the appropriate line LD of ink dots ID led in the Y direction as shown in FIG. 15 ..

For example, with respect to the conveying speed Vd of the normal image printing, the conveying speed at the time of printing of the ejection direction measurement chart C _4, and the conveying speed Vh satisfying the formula 3.

The chart formation control unit 112 (see FIG. 10) controls the platen 102 to convey the paper 1 at a transfer speed Vh satisfying the equation 3. Further, the printing ink jet head 104Ka, 104Kb, 104Ca, 104Cb, 104Ma, 104Mb, 104Ya, and ejects ink droplets of the droplet at ejection frequency f [kHz] by 104Yb the paper 1 a discharging direction measurement chart _{C 4} ..

Similar to the case of the inkjet printing machine 200, the chart formation control unit 112 divides the nozzles 28 (see FIG. 3) constituting the projection nozzle row LN of each inkjet head into eight groups of seven, and orders them in group units. To discharge. As a result, one nozzle 28 forms one line LD along the Y direction, and line LDs for all nozzles are formed.

When there are N inkjet heads for ejecting the same color ink, the conveying speed at the time of printing of the ejection direction measurement chart C ₄ may be set to the conveying speed Vh satisfying the formula 4.

<Transport speed for connecting ink droplets>
FIG. 18 is a diagram for explaining the diameter of the ink dots formed on the paper 1 by the ink droplets ejected from the nozzle 28 and the distance between the dots. If it is possible to form dots of different diameters, consider the smallest dot. In the example shown in FIG. 18, each ink dot ID is formed by landing small droplets ejected from one nozzle 28 on the paper 1. Assuming that the diameter of the ink dot ID is D [μm] and the distance between the two ink dot IDs in the Y direction (distance between dots) is L [μm],
D ≧ L ... (Equation 5)
By satisfying, the ink dot IDs are connected in the Y direction.

Here, assuming that the transport speed of the paper 1 (an example of the second transport speed) at the time of printing the discharge direction measurement chart C ₄ is Vh [m / s] and the discharge frequency of the nozzle 28 is f [kHz].
L = 1000 × Vh / f ... (Equation 6)
It can be expressed as.

The following equation 7 can be derived from equations 5 and 6.

Vh ≦ D × f / 1000… (Equation 7)
That is, the chart formation control unit 112 (see FIG. 10) determines the diameter D [μm] of the ink dot ID satisfying the equation 7, the transport speed Vh [m / s] of the paper 1, and the ejection frequency f [kHz] of the nozzle 28. it may be printed ejection direction measurement chart C _4.

For example, assuming that the ejection frequency f = 50 [kHz] and the diameter D of the ink dot ID is 30 [μm], the ink dot ID is Y if the transport speed Vh of the paper 1 is 1.5 [m / s] or less. Connect in the direction. As a result, the amount of landing position deviation can be measured with high accuracy.

In order to realize an image resolution of 1200 [dpi] in the case of the ejection frequency f = 50 [kHz] in the inkjet printing machine 100, the transport speed of the paper 1 at the time of normal image printing is about 2 [m / s] or more. .. When printing of the ejection direction measurement chart C _4, by the conveying speed to satisfy the Vh ≦ 1.5 [m / s] of the transport speed, it is possible to connect the ink dots ID in the Y direction. Note that dpi (dot per inch) is a unit representing the number of dots per [inch]. 1 [inch] is about 25.4 [mm].

Incidentally, when the conveyance speed Vh is too slow, undesirable because it takes too much time to print discharge direction measurement chart C _4. Therefore, the transport speed Vh may be determined as in the following equation 8.

Vd / 2 <Vh ... (Equation 8)
Further, if the ink jet head for ejecting the same color ink is N the conveyance speed Vh at the time of printing of the ejection direction measurement chart C _4, using the conveying speed Vm of the normal image printing, expressed by the following equation 9 be able to.

Vm / N <Vh ... (Equation 9)
The line LD may be formed by using ink droplets having a size other than the small droplets.

Here has been described the ejection direction measurement chart C _4, it is the same for each concentration patch of density adjustment chart group C _3.

FIG. 19 is a graph showing the relationship between the diameter of the ink dot ID (dot diameter) and the density of the density patch when the density patch is printed. As shown in FIG. 19, when the dot diameter is such that adjacent ink dot IDs are connected in the Y direction, the density rises sharply. This is because the ink dot IDs are connected to each other so that the ink can easily fill the recording surface of the paper 1 without any gaps. As a result, when the density is low, it is easily affected by the measurement noise, but when the density is high, the measurement is stable.

Therefore, also the density patch density adjustment chart group C _3, it is preferable that the ink dots ID adjacent to each other in Y direction leads to the Y direction. That is, the chart formation control unit 112 (see FIG. 10) determines the density according to the diameter D [μm] of the ink dot ID satisfying Equation 7, the transport speed Vh [μm] of the paper 1, and the ejection frequency f [kHz] of the nozzle 28. each concentration patch of the adjustment chart group C ₃ may be printed.

<Other aspects of an inkjet printing machine>
Another aspect of the inkjet printing machine will be described. FIG. 20 is a diagram showing a configuration example of the inkjet printing machine 300. The inkjet printing machine 300 forms a desired color image by ejecting ink from the inkjet heads 372Ka, 372Kb, 372Ca, 372Cb, 372Ma, 372Mb, 372Ya, and 372Yb onto the paper 1 conveyed in the conveying direction by the drawing drum 370. This is a dual-bar type inkjet printer.

As shown in FIG. 20, the inkjet printing machine 300 mainly includes a paper feeding unit 312, a pretreatment liquid application unit 314, a drawing unit 316, a drying unit 318, a fixing unit 320, and a paper ejection unit 322. ..

[Paper feed section]
Paper 1, which is a sheet of paper, is laminated on the paper feed unit 312. Paper 1 is fed one by one from the paper feed tray 350 of the paper feed unit 312 to the pretreatment liquid application unit 314. Although sheet paper (cut paper) is used as the paper 1, it is also possible to cut the continuous paper (roll paper) into a required size and feed the paper.

[Pretreatment liquid application part]
The pretreatment liquid application unit 314 is arranged on the upstream side of the drawing unit 316 in the transport direction of the paper 1. The pretreatment liquid application unit 314 is a mechanism for applying the pretreatment liquid to the recording surface of the paper 1. The pretreatment liquid contains a color material coagulant that agglomerates the color material (pigment in this example) in the ink applied by the drawing unit 316, and the ink is released by contact between the pretreatment liquid and the ink. Separation of color material and solvent is promoted.

The pretreatment liquid application unit 314 includes a paper feed cylinder 352, a pretreatment liquid drum 354, and a pretreatment liquid application unit 356. The pretreatment liquid drum 354 is provided with a claw-shaped holding means (gripper) 355 on the outer peripheral surface thereof, and the paper 1 is sandwiched between the claws of the holding means 355 and the peripheral surface of the pretreatment liquid drum 354. It is designed to hold the tip. The pretreatment liquid application unit 356 applies the pretreatment liquid to the recording surface of the paper 1 conveyed by the pretreatment liquid drum 354. In addition to the roller coating method, various methods such as a spray method can be applied to the pretreatment liquid coating unit 356.

The paper 1 to which the pretreatment liquid is applied is delivered from the pretreatment liquid drum 354 to the drawing drum 370 of the drawing unit 316 via the intermediate transport unit 326.

[Drawing section]
The drawing unit 316 includes a drawing drum 370, a paper holding roller 374, and an inkjet head 372Ka, 372Kb, 372Ca, 372Cb, 372Ma, 372Mb, 372Ya, and 372Yb. Similar to the pretreatment liquid drum 354, the drawing drum 370 (an example of the transport unit) is provided with a claw-shaped holding means (gripper) 371 on the outer peripheral surface thereof. A suction hole is provided on the outer peripheral surface of the drawing drum 370, and the paper 1 is sucked and held on the outer peripheral surface of the drum by negative pressure suction.

The above-mentioned inkjet head 10 is applied to the inkjet heads 372Ka, 372Kb, 372Ca, 372Cb, 372Ma, 372Mb, 372Ya, and 372Yb, respectively. The inkjet heads 372Ka, 372Kb, 372Ca, 372Cb, 372Ma, 372Mb, 372Ya, and 372Yb each have a length corresponding to the maximum width of the image forming region on the paper 1.

The drawing unit 316 includes an ink tank (not shown) that supplies ink to each of the inkjet heads 372Ka, 372Kb, 372Ca, 372Cb, 372Ma, 372Mb, 372Ya, and 372Yb, respectively.

Black ink is supplied to the inkjet heads 372Ka and 372Kb from the ink tank. Cyan ink is supplied to the inkjet heads 372Ca and 372Cb from the ink tank. Magenta ink is supplied to the inkjet heads 372Ma and 372Mb from the ink tank. Yellow ink is supplied to the inkjet heads 372Ya and 372Yb from the ink tank.

The inkjet heads 372Ka, 372Kb, 372Ca, 372Cb, 372Ma, 372Mb, 372Ya, and 372Yb are installed so as to extend in a direction orthogonal to the transport direction of the paper 1 (rotation direction of the drawing drum 370).

FIG. 21 is a diagram showing a distance TD between the nozzle surface 20 of the inkjet heads 372Ka, 372Kb, 372Ca, 372Cb, 372Ma, 372Mb, 372Ya, and 372Yb and the outer peripheral surface 370A of the drawing drum 370. The inkjet printing machine 300 can change this distance TD by changing the positions of the inkjet heads 372Ka, 372Kb, 372Ca, 372Cb, 372Ma, 372Mb, 372Ya, and 372Yb by the motor 496 (see FIG. 22).

The operation of transporting the paper 1 at a constant speed by the drawing drum 370 and relatively moving the paper 1 and the respective inkjet heads 372Ka, 372Kb, 372Ca, 372Cb, 372Ma, 372Mb, 372Ya, and 372Yb in this transport direction is 1 An image can be recorded in the image forming region of the paper 1 only by performing it once (that is, by one sub-scanning).

Here, an inkjet printing machine 300 using four colors of inks of black, cyan, magenta, and yellow is illustrated, but the combination of ink colors and the number of colors is not limited to this embodiment, and the arrangement order of each color head is not limited to this embodiment. Is not particularly limited.

Returning to the description of FIG. 20, the paper 1 on which the image is formed by the drawing unit 316 is delivered from the drawing drum 370 to the drying drum 376 of the drying unit 318 via the intermediate transport unit 328.

[Dry part]
The drying unit 318 is a mechanism for drying the water contained in the solvent separated by the color material aggregating action, and includes a drying drum 376 and a solvent drying device 378. Similar to the pretreatment liquid drum 354, the drying drum 376 is provided with a claw-shaped holding means (gripper) 377 on its outer peripheral surface. The solvent drying device 378 is composed of a plurality of halogen heaters 380 and a warm air ejection nozzle 382. The paper 1 that has been dried by the drying section 318 is delivered from the drying drum 376 to the fixing drum 384 of the fixing section 320 via the intermediate transport section 330.

[Fixing part]
The fixing portion 320 is arranged on the downstream side of the drawing portion 316 in the transport direction of the paper 1. The fixing unit 320 includes a fixing drum 384, a halogen heater 386, a fixing roller 388, and an in-line scanner 390. Similar to the pretreatment liquid drum 354, the fixing drum 384 is provided with a claw-shaped holding means (gripper) 385 on the outer peripheral surface thereof.

The in-line scanner 390 reads an image and a chart (including each density patch of the density adjustment chart group C ₃ and a discharge direction measurement chart C ₄ ) printed on the paper 1 at a constant reading frequency (sampling frequency) and images. A CCD (Charge Coupled Device) line sensor or the like is applied as a means for detecting the density of the image, defects in the image, or the like.

[Paper ejection section]
The paper discharge unit 322 includes a discharge tray 392, and a transfer cylinder 394, a transport belt 396, and a tension roller 398 are placed between the discharge tray 392 and the fixing drum 384 of the fixing unit 320 so as to face each other. It is provided. The paper 1 is sent to the transport belt 396 by the delivery cylinder 394 and discharged to the discharge tray 392. Although the details of the paper transport mechanism by the transport belt 396 are not shown, the paper 1 after printing is held by a gripper (not shown) hung between the endless transport belts 396, and the rotation of the transport belt 396 causes the paper 1 to be held. It is carried above the discharge tray 392.

Further, although not shown in FIG. 20, the inkjet printing machine 300 of this example is provided with means for supplying the pretreatment liquid to the pretreatment liquid application unit 314, and each of the inkjet heads 372Ka, 372Kb, and 372Ca. , 372Cb, 372Ma, 372Mb, 372Ya, and 372Yb cleaning (nozzle surface wiping, purging, nozzle suction, etc.), head maintenance unit, position detection sensor that detects the position of paper 1 on the paper transport path, temperature of each part of the device It is equipped with a temperature sensor and the like to detect.

[Control system]
FIG. 22 is a block diagram showing a system configuration of the inkjet printing machine 300. The inkjet printing machine 300 includes an inkjet head 450, a communication interface 470, a system controller 472, a print control unit 474, a head driver 478, a motor driver 480, a heater driver 482, a pretreatment liquid application control unit 484, a drying control unit 486, and fixing control. A unit 488, a memory 490, a ROM (Read Only Memory) 492, an encoder 494, and the like are provided.

Here, the inkjet heads 372Ka, 372Kb, 372Ca, 372Cb, 372Ma, 372Mb, 372Ya, and 372Yb are referred to as the inkjet head 450.

The communication interface 470 is an interface unit that receives image data sent from the host computer 550, which is a higher-level control device. A serial interface or a parallel interface can be applied to the communication interface 470. A buffer memory (not shown) for speeding up communication may be mounted on this portion.

The image data transmitted from the host computer 550 is taken into the inkjet printing machine 300 via the communication interface 470 and temporarily stored in the memory 490.

The memory 490 is a storage means for temporarily storing an image input via the communication interface 470, and data is read / written through the system controller 472. The memory 490 is not limited to a memory composed of semiconductor elements, and a magnetic medium such as a hard disk may be used.

The system controller 472 is composed of a central processing unit (CPU) and peripheral circuits thereof, and functions as a control device that controls the entire inkjet printing machine 300 according to a predetermined program, and also performs various calculations. Functions as a device.

The ROM 492 stores a program executed by the CPU of the system controller 472 and various data necessary for control. The ROM 492 may be a non-rewritable storage means or a rewritable storage means. The memory 490 is used as a temporary storage area for image data, and is also used as a program expansion area and a CPU calculation work area.

The motor driver 480 is a driver that drives the motor 496 according to an instruction from the system controller 472. In FIG. 22, various motors arranged in each part of the apparatus are represented by reference numerals 496. The motor 496 is negative from the suction holes of the drawing drum 370, the motor that drives the rotation of the paper feed cylinder 352, the pretreatment liquid drum 354, the drawing drum 370, the drying drum 376, the fixing drum 384, the transfer cylinder 394, and the like. A motor that changes the distance TD (see FIG. 21) between the nozzle surface 20 of the inkjet head 450 and the outer peripheral surface of the drawing drum 370 by changing the position of the drive motor of the pump for pressure suction and the inkjet head 450. It includes a motor for a retracting mechanism that moves the inkjet head 450 to a maintenance area outside the drawing drum 370.

The heater driver 482 is a driver that drives the heater 498 according to the instruction from the system controller 472. In FIG. 22, various heaters arranged in each part of the apparatus are represented by reference numerals 498.

The print control unit 474 has a signal processing function that performs various processing, correction, and the like for generating a signal for print control from the image data in the memory 490 according to the control of the system controller 472, and the generated print data. This is a control unit that supplies (dot data) to the head driver 478.

The print control unit 474 performs the required signal processing, and based on the obtained dot data, the ink droplet ejection amount and the ejection timing of the inkjet head 450 are controlled via the head driver 478.

The print control unit 474 is provided with an image buffer memory (not shown), and data such as image data and parameters are temporarily stored in the image buffer memory during image data processing by the print control unit 474. Further, it is also possible to integrate the print control unit 474 and the system controller 472 to form one processor.

The head driver 478 outputs a drive signal for driving the discharge energy generating element corresponding to each nozzle of the inkjet head 450 based on the print data given from the print control unit 474. The head driver 478 may include a feedback control system for keeping the driving condition of the head constant.

When the drive signal output from the head driver 478 is applied to the inkjet head 450, ink droplets are ejected from the corresponding nozzles. An image is formed on the recording surface of the paper 1 by controlling the ink ejection from the inkjet head 450 while transporting the paper 1 at the transport speed.

The pretreatment liquid application control unit 484 controls the operation of the pretreatment liquid application unit 356 (see FIG. 20) according to the instruction from the system controller 472. The drying control unit 486 controls the operation of the solvent drying device 378 (see FIG. 20) according to the instruction from the system controller 472.

The fixing control unit 488 controls the operation of the fixing pressurizing unit 499 including the halogen heater 386 of the fixing unit 320 and the fixing roller 388 (see FIG. 20) according to the instruction from the system controller 472.

The in-line scanner 390 reads the image printed on the paper 1, performs necessary signal processing, etc., detects the printing status (presence / absence of ejection, variation in droplets, optical density, etc.), and outputs the detection result to the system controller 472. And the print control unit 474.

The encoder 494 is provided on the drawing drum 370 (see FIG. 20). A discharge trigger signal (pixel trigger) is issued based on the detection signal of the encoder 494. The dropping timing of the inkjet head 450 is synchronized with the detection signal of the encoder 494. As a result, the landing position can be determined with high accuracy.

The print control unit 474 performs various corrections (emission correction and density correction) on the inkjet head 450 based on the information obtained from the in-line scanner 390, and also performs preliminary ejection, suction, wiping, and other cleaning operations (nozzles) as necessary. Controls to perform recovery operation).

[Image printing and chart printing (control method of image forming device)]
The inkjet printing machine 300 has a high-definition printing mode (an example of a normal printing mode) in which the paper 1 is conveyed at a conveying speed Vd to print an image, and a paper 1 is conveyed at a conveying speed faster than the conveying speed Vd to transfer an image. It has a high-speed printing mode for printing and a chart printing mode for printing a chart for adjusting the amount of drops and measuring the ejection direction for each of the inkjet heads 372Ka, 372Kb, 372Ca, 372Cb, 372Ma, 372Mb, 372Ya, and 372Yb. The high-speed printing mode is a mode in which printing speed is prioritized over printing quality. In the high-speed printing mode, the ink dot IDs formed by the small ink droplets ejected from one nozzle 28 (see FIG. 3) are connected in the Y direction (see FIG. 14), and printing is performed at a transport speed.

The user of the inkjet printing machine 300 can determine the printing mode of the inkjet printing machine 300 by operating an operation unit (not shown) of the inkjet printing machine 300.

When printing a normal image in the high-definition print mode, first, the system controller 472 (an example of the image formation control unit) controls the motor 496, and the inkjet heads 372Ka, 372Kb, 372Ca, 372Cb, 372Ma, 372Mb, 372Ya, The distance TD between the nozzle surface 20 of 372Yb and the outer peripheral surface 370A of the drawing drum 370 is TD1 [mm].

The system controller 472 feeds the paper 1 (an example of the first recording medium) whose surface is not coated with the ink absorbing layer by the paper feed unit 312, and feeds the paper feed cylinder 352, the pretreatment liquid drum 354, the drawing drum 370, and the drying. The drum 376, the fixing drum 384, and the transfer cylinder 394 are controlled to transport the paper 1 at the transport speed Vd.

The system controller 472 applies the pretreatment liquid to the recording surface of the paper 1 by the pretreatment liquid application unit 356. Further, the system controller 472 conveys the paper 1 at the conveying speed Vd by the drawing drum 370, and based on the image data in the memory 490, the inkjet head 450 (each inkjet head 372Ka, 372Kb, 372Ca, 372Cb, 372Ma, 372Mb, 372Ya). , And 372Yb) at an ejection frequency of f [kHz], ejects small, medium, or large ink droplets according to the image data, and prints an image on paper 1 (an example of an image formation control step). ..

Further, the system controller 472 controls the in-line scanner 390 and reads the image of the recording surface of the paper 1 conveyed at the transfer speed Vd by the fixing drum 384 at the reading frequency fr [kHz]. The system controller 472 determines the quality of the image printed on the paper 1 based on the read data of the in-line scanner 390.

On the other hand, when printing the density adjustment chart group C ₃ or ejection direction measurement chart C ₄ in the chart printing mode, the system controller 472 (an example of a chart formation control unit) controls the motor 496, the ink jet head 372Ka, The distance TD between the nozzle surface 20 of 372Kb, 372Ca, 372Cb, 372Ma, 372Mb, 372Ya, and 372Yb and the outer peripheral surface 370A of the drawing drum 370 is TD2 [mm]. Here, TD2 is a value smaller than TD1.

When printing the density adjustment chart group C ₃ and the ejection direction measurement chart C ₄ , the transfer speed is slower than when printing an image, so that the inkjet heads 372Ka, 372Kb, 372Ca, 372Cb, 372Ma, 372Mb, 372Ya, The risk of contact between 372Yb and the paper 1 is low, and there is little damage when contacting the paper 1. Therefore, when printing the density adjustment chart group C ₃ and discharge direction measurement chart C _4, the concentration adjustment by the image it is possible to reduce the distance TD than when printing a and to reduce the distance TD noise use charts group C ₃ and discharge direction measurement chart C ₄ can be reduced.

Next, the system controller 472 feeds the paper 1 by the paper feed unit 312. The recording surface (surface) of this paper 1 is coated with an ink absorbing layer (ink receiving layer) (an example of a second recording medium). The ink absorbing layer is a layer for preventing bleeding due to ink by absorbing ink and accelerating drying.

The system controller 472 controls the paper feed cylinder 352, the pretreatment liquid drum 354, the drawing drum 370, the drying drum 376, the fixing drum 384, and the transfer cylinder 394 to convey the paper 1 at the transfer speed Vh. The transport speed Vh is a speed slower than the transport speed Vd, and satisfies the formula 4 or 7.

Here, the system controller 472 does not apply the pretreatment liquid to the recording surface of the paper 1. That is, the system controller 472 stops the application of the pretreatment liquid by the pretreatment liquid application unit 356. As described above, by not applying the pretreatment liquid using the paper 1 having the ink absorbing layer coated on the surface, it is possible to eliminate the fluctuation of the coating amount of the pretreatment liquid due to the fluctuation of the transport speed.

The paper 1 having no ink absorbing layer may be used, and the pretreatment liquid may be applied to the pretreatment liquid application unit 356 by an inkjet head. By applying the pretreatment liquid with the inkjet head, it becomes easy to adjust the application amount of the pretreatment liquid, and even if the transport speed fluctuates, an appropriate amount of the pretreatment liquid can be applied.

Further, the system controller 472 conveys the paper 1 at the conveying speed Vh by the drawing drum 370, and based on the data of the density adjustment chart group C ₃ or the ejection direction measurement chart C ₄ in the memory 490, the inkjet head 450 (each). inkjet head 372Ka, 372Kb, 372Ca, 372Cb, 372Ma, 372Mb, 372Ya, and 372Yb) by ejecting ink droplets of the droplet at ejection frequency f [kHz], the concentration control chart group _{C 3} or ejection direction measured sheet 1 print use chart C ₄ (an example of a chart formation control step).

Further, the system controller 472 controls the line scanner 390, a recording surface density adjustment chart group C ₃ or read the ejection direction measurement chart C ₄ frequency fr of the sheet 1 transported at the transportation speed Vh by the fixing drum 384 Read at [kHz]. The system controller 472 analyzes the read data of the density adjustment chart group _{C 3,} the ink jet heads 372Ka, 372Kb, 372Ca, 372Cb, 372Ma, 372Mb, corresponding to 372Ya, and 372Yb nozzle 28 (see FIG. 3) adjusting each driving voltage applied to the piezoelectric element 44, or by analyzing the read data in the ejection direction measurement chart C _4, for measuring the landing position shift amount ΔX of each nozzle 28.

As described above, the reading frequency fr [kHz] of the in-line scanner 390 at the time of forming the chart of the transport speed Vh is equal to the time of forming the normal image at the transport speed Vd. As a result, the number of readings by the in-line scanner 390 at the time of chart formation is larger than the number of readings at the time of image formation. Therefore, it is possible to reduce the noise in the read density adjustment chart group C ₃ and discharge direction measurement chart C _4.

<Others>
In the embodiments described so far, for example, a processing unit (processing) that executes various processes such as an image formation control unit 110, a chart formation control unit 112, a system controller 472, a print control unit 474, and a pretreatment liquid application control unit 484. The hardware structure of unit) is various processors as shown below. For various processors, the circuit configuration can be changed after manufacturing the CPU (Central Processing Unit), FPGA (Field Programmable Gate Array), etc., which are general-purpose processors that execute software (programs) and function as various processing units. Includes a dedicated electric circuit, which is a processor having a circuit configuration specially designed for executing a specific process such as a programmable logic device (PLD), an ASIC (Application Specific Integrated Circuit), etc. Is done.

One processing unit may be composed of one of these various processors, or may be composed of two or more processors of the same type or different types (for example, a plurality of FPGAs or a combination of a CPU and an FPGA). You may. Further, a plurality of processing units may be configured by one processor. As an example of configuring a plurality of processing units with one processor, first, one processor is configured by a combination of one or more CPUs and software, as represented by a computer such as a server and a client. There is a form in which the processor functions as a plurality of processing units. Secondly, as typified by System On Chip (SoC), there is a form in which a processor that realizes the functions of the entire system including a plurality of processing units with one IC (Integrated Circuit) chip is used. is there. As described above, the various processing units are configured by using one or more various processors as a hardware structure.

Further, the hardware structure of these various processors is, more specifically, an electric circuit (circuitry) in which circuit elements such as semiconductor elements are combined.

The technical scope of the present invention is not limited to the scope described in the above embodiments. The configurations and the like in each embodiment can be appropriately combined between the respective embodiments without departing from the spirit of the present invention.

1 Paper 10 Inkjet head 12-i Head module 16 Frame 18 Flexible substrate 20 Nozzle surface 22 Head module holding member 24 Head protection member 28 Nozzle 28-1 Nozzle 28-2 Nozzle 28-3 Nozzle 30 Nozzle plate 32 Pressure chamber 34 Supply port 36 Common flow path 38 Flow path plate 40 Vibrating plate 42 Individual electrode 44 piezoelectric element 46 Common electrode 50 Ink chamber unit 100 Ink chamber unit 100 Inkjet printer 102 Platen 104Ca Inkjet head 104Cb Inkjet head 104Ka Inkjet head 104Kb Inkjet head 104Ma Inkjet head 104Mb Inkjet head 104Ya Inkjet Head 104Yb Inkjet head 106C Ink tank 106K Ink tank 106M Ink tank 106Y Ink tank 108 Storage unit 110 Image formation control unit 112 Chart formation control unit 200 Inkjet printer 204C Inkjet head 204K Inkjet head 204K Inkjet head 204M Inkjet head 204Y Inkjet head 210C-i Density patch 210Ca-i Concentration Patch 210Cb-i Concentration Patch 210K-i Concentration Patch 210Ka-i Concentration Patch 210Kb-i Concentration Patch 210M-i Concentration Patch 210Ma-i Concentration Patch 210Mb-i Concentration Patch 210Y-i Concentration Patch 210Ya-i Concentration Patch 210Ybi Concentration patch 300 Inkjet printer 312 Feeding unit 314 Pretreatment liquid application unit 316 Drawing unit 318 Drying unit 320 Fixing unit 322 Paper ejection unit 326 Intermediate transport unit 328 Intermediate transport unit 330 Intermediate transport unit 350 Feed tray 352 Supply Paper cylinder 354 Pretreatment liquid drum 355 Holding means 356 Pretreatment liquid coating part 370 Drawing drum 370A Outer peripheral surface 371 Holding means 372Ca Inkjet head 372Cb Inkjet head 372Ka Inkjet head 372Kb Inkjet head 372Ma Inkjet head 372Mb Inkjet head 372Ya Inkjet head 372Yb Roller 376 Drying drum 377 Holding means 378 Solvent drying device 380 Halogen heater 382 Warm air ejection nozzle 384 Fixing drum 385 Holding means 386 Halo Gen heater 388 Fixing roller 390 In-line scanner 392 Discharge tray 394 Delivery cylinder 396 Conveyance belt 398 Stretching roller 450 Inkjet head 470 Communication interface 472 System controller 474 Print control unit 478 Head driver 480 Motor driver 482 Heater driver 484 Pretreatment liquid application control unit 486 Drying control unit 488 Fixing control unit 490 Memory 492 ROM
494 Encoder 496 Motor 498 Heater 499 Fixing pressurizing unit 550 Host computer C ₁ Concentration adjustment chart C ₂ Concentration adjustment chart C ₃ Concentration adjustment chart C ₄ Discharge direction measurement chart ID-1 Ink dot ID-2 Ink dot ID -3 Ink dot LD line LD-1 line LD-2 line LD-3 line LN Projection nozzle row

Claims (13)

A transport unit that transports the recording medium along the transport direction,
A plurality of liquid discharge heads each having a plurality of discharge elements for discharging liquid and arranged side by side along the transport direction, and a plurality of liquid discharge heads.
A liquid supply unit that supplies the same liquid to each of the plurality of liquid discharge heads,
An image forming control unit that transports the recording medium at the first transport speed by the transport unit, and discharges the liquid from the plurality of discharge elements of the plurality of liquid discharge heads to form an image on the recording medium. ,
The recording medium is transported by the transport unit at a second transport speed slower than the first transport speed, and the liquid is discharged from the plurality of discharge elements of one liquid discharge head, and charted on the recording medium. Chart formation control unit that forms
With
The diameter of dots formed on the recording medium by the liquid discharged from the discharge element is D [μm], the discharge frequency of the liquid of the discharge element when forming the chart is f [kHz], and the second. Assuming that the transport speed is Vh [m / s],
Vh ≤ D × f / 1000
An image forming apparatus that satisfies. Assuming that the first transport speed is Vm [m / s] and the number of liquid discharge heads is an integer N of 2 or more,
Vh ≤ Vm / N
The image forming apparatus according to claim 1. Assuming that the first transport speed is Vm [m / s] and the number of liquid discharge heads is an integer N of 2 or more,
Vm / N <Vh
The image forming apparatus according to claim 1. An in-line scanner for reading images and charts formed on the recording medium is provided downstream of the plurality of liquid discharge heads in the transport direction.
The reading frequency of the in-line scanner when reading an image formed by the image formation control unit and the reading frequency of the in-line scanner when reading a chart formed by the chart formation control unit are equal to each of claims 1 to 3. The image forming apparatus according to any one item. A pretreatment liquid application unit for applying the pretreatment liquid to the recording medium is provided on the upstream side of the plurality of liquid discharge heads in the transport direction.
The image formation control unit uses a first recording medium whose surface is not coated with an ink absorbing layer, and the pretreatment liquid is applied by the pretreatment liquid application unit.
The chart formation control unit uses a second recording medium whose surface is coated with an ink absorbing layer, and any one of claims 1 to 4 for stopping the application of the pretreatment liquid by the pretreatment liquid application unit. The image forming apparatus according to. A pretreatment liquid application unit for applying the pretreatment liquid to the recording medium is provided on the upstream side of the plurality of liquid discharge heads in the transport direction.
The image forming apparatus according to any one of claims 1 to 4, wherein the pretreatment liquid application unit has an inkjet head for discharging the pretreatment liquid. The liquid discharge head when a chart is formed on the recording medium by the chart formation control unit rather than the distance between the liquid discharge head and the recording medium when an image is formed on the recording medium by the image formation control unit. The image forming apparatus according to any one of claims 1 to 6, wherein the distance between the image and the recording medium is smaller. The image formation control unit has a normal printing mode in which the recording medium is conveyed by the conveying unit at the first conveying speed, and high-speed printing in which the recording medium is conveyed by the conveying unit at a speed higher than the first conveying speed. The image forming apparatus according to any one of claims 1 to 7, further comprising a mode. The liquid discharge head can form a plurality of dots having different diameters.
The image forming apparatus according to any one of claims 1 to 8, wherein the diameter of the smallest dot among the plurality of dots having different diameters is D [μm]. The image forming apparatus according to any one of claims 1 to 9, wherein the chart includes a density patch formed for each liquid discharge head. The image forming apparatus according to any one of claims 1 to 10, wherein the chart includes a line pattern formed for each of the discharging elements. The image forming apparatus according to any one of claims 1 to 11, wherein the liquid discharge head is arranged side by side in a first direction in which a plurality of head modules intersect in the transport direction. A plurality of liquid discharge heads having a transport unit for transporting a recording medium along the transport direction, a plurality of discharge elements for discharging liquids, and arranged side by side along the transport direction, and the plurality of liquid discharge heads. A control method for an image forming apparatus including a liquid supply unit that supplies the same liquid to each of the media.
An image formation control step of transporting the recording medium at the first transport speed by the transport unit and discharging the liquid from the plurality of discharge elements of the plurality of liquid discharge heads to form an image on the recording medium. ,
The recording medium is transported by the transport unit at a second transport speed slower than the first transport speed, and the liquid is discharged from the plurality of discharge elements of one liquid discharge head, and charted on the recording medium. And the chart formation control process to form
With
The diameter of dots formed on the recording medium by the liquid discharged from the discharge element is D [μm], the discharge frequency of the liquid of the discharge element when forming the chart is f [kHz], and the second. Assuming that the transport speed is Vh [m / s],
Vh ≤ D × f / 1000
A method of controlling an image forming apparatus that satisfies the above conditions.