WO2018225489A1 - Image forming apparatus and method for controlling same - Google Patents

Abstract

The present invention addresses the problem of providing an image forming apparatus and a method for controlling the same that appropriately perform ejection droplet amount adjustment and ejection direction measurement for a plurality of liquid ejection heads arranged along a conveyance direction of a recording medium. The above problem is solved by the image forming apparatus provided with a chart forming control unit that causes a conveyance unit to convey a recording medium at a second conveyance speed slower than a first conveyance speed during image formation and causes a liquid to be ejected from a plurality of ejection elements of one liquid ejection head to form a chart on the recording medium, wherein Vh ≤ D × f/1000 is satisfied when a diameter of dots formed on the recording medium by the liquid ejected from the ejection elements is D[μm], an ejection frequency of the liquid of the ejection elements at the time of forming the chart is f[kHz], and the second conveyance speed is Vh[m/s].

Description

Image forming apparatus and control method thereof

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 discharge heads are arranged along a recording medium conveyance direction and a control method thereof.

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

In Patent Document 1, by ejecting ink from nozzles of four nozzle arrays that eject ink of the same color arranged along the transport direction, the transport speed is four times faster than when recording with one nozzle array. An ink jet printer capable of printing by conveying a recording medium is disclosed.

JP 2014-024209 A

Generally, inkjet heads have variations in the amount of ejected droplets due to manufacturing variations. In order to correct this variation, it is necessary to perform a correction operation for adjusting to an appropriate ejection droplet amount. In addition, it is necessary to check whether or not each ejection element is in a normal ejection state.

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

The present invention has been made in view of such circumstances, and an image forming apparatus that appropriately performs discharge droplet amount adjustment and discharge direction measurement for a plurality of liquid discharge heads arranged along the conveyance direction of the recording medium, and the image forming apparatus An object is to provide a control method.

In order to achieve the above object, one aspect of an image forming apparatus includes a conveyance unit that conveys a recording medium along a conveyance direction and a plurality of ejection elements that eject liquid, and is arranged side by side along the conveyance direction. A plurality of liquid ejection heads, a liquid supply unit that supplies the same liquid to each of the plurality of liquid ejection heads, and a conveyance unit that conveys the recording medium at a first conveyance speed, and a plurality of ejections from the plurality of liquid ejection heads An image formation control unit that discharges liquid from the element to form an image on a recording medium, and a conveyance unit conveys the recording medium at a second conveyance speed that is lower than the first conveyance speed, and a plurality of liquid ejection heads A chart formation control unit that discharges liquid from the discharge elements to form a chart on the recording medium, and sets the diameter of dots formed on the recording medium by the liquid discharged from the discharge elements to D [ m], the ejection frequency of the liquid discharge device for forming the chart f [kHz], the second conveying speed and Vh [m / s], satisfies the Vh ≦ D × f / 1000.

According to this aspect, the recording medium is transported by the transport unit at the second transport speed that is slower than the first transport speed at the time of image formation, and the liquid is ejected from the plurality of ejecting elements of one liquid ejecting head. 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 elements is D [μm], and the liquid discharge frequency of the discharge elements when forming the chart is Assuming that f [kHz] and the second transport speed are Vh [m / s], Vh ≦ D × f / 1000 is satisfied. Therefore, by adjusting the discharge droplet amount and measuring the discharge direction appropriately by reading the chart. be able to.

It is preferable that Vh ≦ Vm / N is satisfied when the first transport speed is Vm [m / s] and the number of liquid ejection heads is an integer N of 2 or more. Thereby, the discharge droplet amount adjustment and the discharge direction measurement can be appropriately performed.

When the first transport speed is Vm [m / s] and the number of liquid ejection heads is an integer N of 2 or more, Vm / N <Vh may be satisfied. Thereby, the discharge droplet amount adjustment and the discharge direction measurement can be appropriately performed.

An inline scanner that reads an image and a chart formed on a recording medium on the downstream side of a plurality of liquid ejection heads in the conveying direction is provided, and the reading frequency of the inline scanner and chart formation when reading the image formed by the image formation control unit It is preferable that the reading frequency of the inline scanner when reading the chart formed by the control unit is equal. As a result, the number of times of reading by the in-line scanner increases, so that noise in reading can be reduced.

A pretreatment liquid application unit that applies a pretreatment liquid to the recording medium upstream of the plurality of liquid ejection heads in the transport direction is provided, and the image formation control unit applies a first recording medium that has an uncoated ink absorbing layer to the surface. The pretreatment liquid is applied by the pretreatment liquid application section, and the chart formation control section uses the second recording medium having the surface coated with the ink absorption layer, and the pretreatment liquid application section applies the pretreatment liquid. Is preferably stopped. Thereby, the fluctuation | variation of the coating amount of the pretreatment liquid accompanying the fluctuation | variation of a conveyance speed can be excluded.

It is preferable that a pretreatment liquid application unit that applies a pretreatment liquid to the recording medium is provided upstream of the plurality of liquid ejection heads in the transport direction, and the pretreatment liquid application unit includes an inkjet head that discharges the pretreatment liquid. . Thereby, even if a conveyance speed fluctuates, the application quantity of a pretreatment liquid can be made into an appropriate quantity.

The distance between the liquid ejection head and the recording medium when the chart is formed on the recording medium by the chart formation control unit is larger than the distance between the liquid ejection head and the recording medium when the image formation control unit forms an image on the recording medium. It is preferable that this is smaller. When the chart is formed, the conveyance 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 the damage caused by contact is small. For this reason, the distance between the liquid ejection head and the recording medium can be reduced, and noise in the chart can be reduced by reducing the distance.

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

The liquid discharge head can form a plurality of dots having different diameters, and the diameter of the smallest dot among the plurality of dots having different diameters is preferably D [μm]. Thereby, a chart can be appropriately formed in the smallest dot.

The chart preferably includes density patches formed for each liquid ejection head. By reading this chart, it is possible to appropriately adjust the ejection droplet amount.

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

The liquid discharge head is preferably arranged with a plurality of head modules arranged in a first direction intersecting the transport direction. The present embodiment is applicable to a liquid discharge head in which a plurality of head modules are arranged side by side.

In order to achieve the above object, one aspect of a method for controlling an image forming apparatus includes a transport unit that transports a recording medium along a transport direction and a plurality of ejection elements that eject liquid, respectively, along the transport direction. A control method for an image forming apparatus comprising: 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. An image forming control process for forming an image on a recording medium by ejecting liquid from a plurality of ejection elements of a plurality of liquid ejection heads and conveying the recording medium at a speed lower than the first conveyance speed by a conveyance unit; A chart forming control step of forming a chart on a recording medium by transporting at two transport speeds and ejecting liquid from a plurality of ejection elements of one liquid ejection head, and ejecting from the ejection elements The diameter of the dots formed on the recording medium by the liquid to be formed is D [μm], the liquid discharge frequency 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 transported by the transport unit at the second transport speed that is slower than the first transport speed at the time of image formation, and the liquid is ejected from the plurality of ejecting elements of one liquid ejecting head. 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 elements is D [μm], and the liquid discharge frequency of the discharge elements when forming the chart is Assuming that f [kHz] and the second transport speed are Vh [m / s], Vh ≦ D × f / 1000 is satisfied. Therefore, by adjusting the discharge droplet amount and measuring the discharge direction appropriately by reading the chart. be able to.

According to the present invention, it is possible to appropriately perform discharge droplet amount adjustment and discharge direction measurement for a plurality of liquid discharge heads arranged along the conveyance direction of the recording medium.

Perspective view of inkjet head Enlarged view of inkjet head viewed from nozzle side Plan view showing an example of the nozzle surface of the head module Sectional drawing which shows the structural example of the droplet discharge element for 1 nozzle of a head module Top view of single bar inkjet printer Side view of inkjet printer The figure which shows an example of the chart for density adjustment printed on paper with an inkjet printer Top view of dual-bar inkjet printer Side view of inkjet printer 100 Block diagram showing system configuration of inkjet printer The figure which shows an example of the chart for density adjustment printed on paper with an inkjet printer The figure which shows an example of the chart for density adjustment printed on paper with an inkjet printer The figure which shows an example of the chart for discharge direction measurement printed on a paper by an inkjet printer The figure for demonstrating the landing position shift of the ink droplet discharged from the nozzle Enlarged view of one line constituting the chart for measuring the discharge direction An example of a read image obtained by reading 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 droplet discharged from the nozzle forms on paper, and the distance between dots Graph showing the relationship between the ink dot diameter and the density of the density patch when the density patch is printed Diagram showing an example configuration of an inkjet printer The figure which shows distance TD between the nozzle surface of an inkjet head, and the outer peripheral surface of a drawing drum. Block diagram showing system configuration of inkjet printer

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

<Configuration example of inkjet head>
A configuration example of the inkjet head used in the present embodiment will be described. FIG. 1 is a perspective view of an inkjet head 10 used in this embodiment. The inkjet head 10 is formed by connecting a plurality of (n integers greater than or equal to 2) head modules 12-i (i = 1, 2,... N) in the X direction (an example of a first direction intersecting the transport direction). 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 the common direction. The structures of the head modules 12-i are 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 the head module holding member 22 from both sides in the Y direction, and both ends in the X direction are supported by the head protection member 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 surface on the long side along the v direction having an inclination of angle γ with respect to the X direction, and a short side on the short side along the w direction having an inclination of angle α with respect to the Y direction. It is a parallelogram planar view shape which has an end surface. The nozzles 28 are two-dimensionally arranged on the nozzle surface 20 of the head module 12-i. The projection nozzle row LN projected in the X direction is equivalent to a single nozzle row in which the nozzles 28 are arranged at equal intervals at a nozzle density that achieves the recording resolution.

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

The full-line bar head applied to the single-pass method is not limited to the case where the entire surface of the recording medium is set as the printing range, but when a part of the recording medium is a printing area (for example, around the recording medium). In the case of providing a blank portion, etc.), it is sufficient that the nozzle rows necessary for printing are 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.

<Internal structure example of head module>
The head module 12-i includes an ejection energy generation element (for example, a piezoelectric element or a heating element) that generates ejection energy necessary for ink ejection corresponding to each nozzle 28. The head module 12-i ejects ink droplets (an example of a liquid) on demand according to the drive signal and the ejection control signal supplied via the flexible substrate 18.

FIG. 4 is a cross-sectional view showing an example of the internal structure of a droplet discharge element for one nozzle of the head module 12-i. The head module 12-i has a nozzle plate 30 on which nozzles 28 serving as ink droplet ejection ports are formed, and a pressure chamber 32, a supply port 34, a common channel 36, and the like corresponding to the nozzles 28. And a flow path plate 38.

The flow path plate 38 constitutes a side wall portion of the pressure chamber 32 and a flow path forming a supply port 34 as a narrowed portion (most narrowed portion) of an individual supply path that guides 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 a single substrate, or may have a structure in which a plurality of substrates are stacked. The nozzle plate 30 and the flow path plate 38 can be processed into a required shape using a semiconductor manufacturing technique using silicon as a material.

A plurality of pressure chambers 32 are connected to the common flow path 36 via 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 constituting a part of the pressure chamber 32 (the top surface in FIG. 4) is provided with a piezoelectric element 44 having an individual electrode 42 for each pressure chamber 32. The diaphragm 40 of this example is made of silicon with a conductive layer functioning 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 disposed 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. Moreover, you may comprise the diaphragm which serves as a common electrode with metals (electroconductive material), such as stainless steel.

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

The head module 12-i selects a driving voltage to be applied to the individual electrode 42, so that a small droplet having a relatively small amount of ink from each nozzle 28, a medium droplet having a relatively large amount of ink than a small droplet, and One of the three types of ink droplets, a large droplet having a relatively large ink amount than the middle droplet, can be ejected. Accordingly, an ink dot having a diameter of 30 [μm] for a small ink droplet, an ink dot having a diameter of 40 [μm] for a medium ink droplet, and an ink having a diameter of 50 [μm] for a large ink droplet. Dots are formed on the recording medium. As described above, 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 discharge element as a recording element unit for recording one pixel. The head module 12-i includes a plurality of ink chamber units 50 corresponding to the two-dimensional nozzle array described with reference to FIG.

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

The inkjet printer 200 includes a platen 102, ink tanks 106K, 106C, 106M, and 106Y, and inkjet heads 204K, 204C, 204M, and 204Y.

The platen 102 places the paper 1 as a recording medium and conveys it in the Y direction.

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

The inkjet head 10 described above is applied to each of the inkjet heads 204K, 204C, 204M, and 204Y. The inkjet heads 204K, 204C, 204M, and 204Y are sequentially arranged with a certain interval in the Y direction. The inkjet heads 204K, 204C, 204M, and 204Y are arranged with the nozzle surface 20 facing the platen 102.

During normal image printing, a control unit (not shown) that supervises the recording control of the inkjet printer 200 controls the platen 102 to convey the paper 1 at the conveyance speed Vs [m / s]. Further, 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 respectively discharged from the nozzles 28 at an ejection frequency f [kHz]. Depending on the image data, small, medium, or large ink droplets are ejected. As a result, an image is printed on the recording surface of the sheet 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, the 17 head modules 12-i constituting the inkjet heads 204K, 204C, 204M, and 204Y have variations in the amount of ink ejected from the nozzles 28 due to variations in 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 nozzles 28.

In order to adjust the ink droplet amount, a control unit (not shown) of the ink jet printing machine 200 transports the paper 1 at the same transport speed Vs as the transport speed during normal image printing, and the ink jet heads 204K, 204C, 204M, and 204Y. As a result, a small ink droplet is ejected at an ejection frequency f [kHz] to print a density adjustment chart on the 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 illustrating an example of a density adjustment chart printed on the paper 1 by the inkjet printer 200. Concentration adjustment chart group _{C 1,} each head module of the ink jet head 204K 12-i (i = 1,2 , ... n) density patch 210K-i printed respectively by (i = 1,2, ... n) , Density patches 210Y-i (i = 1, 2,... N) printed by the respective head modules 12-i of the inkjet head 204Y and density patches 210M- printed by the respective head modules 12-i of the inkjet head 204M. i (i = 1, 2,... n) and density patches 210C-i (i = 1, 2,... n) respectively printed by the head modules 12-i of the inkjet head 204C.

Each density patch 210K-i, 210C-i, 210M-i, and 210Y-i has a conveyance speed Vs [m / s] of the paper 1, an ejection frequency f [kHz] of the nozzle 28, and a small ink drop. 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 or the like (not shown), 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 adjusted appropriately. The same applies to the inkjet heads 204C, 204M, and 204Y.

<Dual bar inkjet printer>
FIG. 8 is a top view of a dual bar type inkjet printer 100 (an example of an image forming apparatus) in which the number of inkjet heads (bar heads) that eject the same color ink is two, and FIG. 9 is an inkjet printer. FIG.

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

The platen 102 (an example of a conveyance unit) places the paper 1 as a recording medium and conveys it in the Y direction (an example of the conveyance direction).

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

The inkjet head 10 described above is applied to each of the inkjet heads 104Ka, 104Kb, 104Ca, 104Cb, 104Ma, 104Mb, 104Ya, and 104Yb.

The inkjet heads 104Ka, 104Kb, 104Ca, 104Cb, 104Ma, 104Mb, 104Ya, and 104Yb are sequentially arranged at a certain interval in the Y direction. The inkjet heads 104Ka, 104Kb, 104Ca, 104Cb, 104Ma, 104Mb, 104Ya, and 104Yb are disposed with the nozzle surface 20 facing 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 position in the X direction. To do.

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

The storage unit 108 stores image data and chart data to be printed by the inkjet printer 100.

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 an 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 and causes the sheet 1 to be conveyed at the conveyance speed Vd (an example of the first conveyance speed). Further, the inkjet heads 104Ka, 104Kb, 104Ca, 104Cb, 104Ma, 104Mb, 104Ya, and 104Yb are controlled, and black ink droplets are respectively ejected from the nozzles 28 of the inkjet heads 104Ka and 104Kb, and the nozzles 28 of the inkjet heads 104Ca and 104Cb are respectively. Image data of cyan ink droplets, magenta ink droplets from the nozzles 28 of the inkjet heads 104Ma and 104Mb, respectively, and yellow ink droplets of the nozzles 28 of the inkjet heads 104Ya and 104Yb, respectively, at an ejection frequency f [kHz]. In response to this, small, medium, or large ink droplets are ejected (an example of an image formation control process).

Thus, in the ink jet printer 100, the amount of ink droplets discharged per unit time is double that of the ink jet printer 200. Therefore, the inkjet printer 100 can ideally print at twice the printing speed of the inkjet printer 200.

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

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

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

FIG. 11 is a density adjustment chart printed on the paper 1 by the ink jet printer 100. The ink jet heads 104Ka, 104Kb, 104Ca, Vd and the discharge frequency are the same f [kHz] as in normal image printing. 10 is a diagram illustrating an example of a density adjustment chart including density patches formed for each of 104Cb, 104Ma, 104Mb, 104Ya, and 104Yb (an example of each liquid ejection head). FIG. Concentration adjustment chart group _{C 2,} each head module of the ink jet head 104Ka 12-i (i = 1,2 , ... n) the density patch 210 kA-i printed respectively by (i = 1,2, ... n) , Density patches 210Kb-i (i = 1, 2,... N) respectively printed by the head modules 12-i (i = 1, 2,... N) of the inkjet head 104Kb, and each head module 12- of the inkjet head 104Ya. .., density patches 210Ya-i (i = 1, 2,... n) respectively printed by i (i = 1, 2,... n), and each head module 12-i (i = 1, 2,... n) of the inkjet head 104Yb. n) printed by the density patches 210Yb-i (i = 1, 2,... n) respectively, and the head modules 12-i (i = 1, 2,... n) of the inkjet head 104Ma. Density patches 210Ma-i (i = 1, 2,... N) respectively printed and density patches 210Mb-i respectively printed by the head modules 12-i (i = 1, 2,... N) of the inkjet head 104Mb. (I = 1, 2,... N), density patches 210Ca-i (i = 1, 2,... N) respectively printed by the head modules 12-i (i = 1, 2,... N) of the inkjet head 104Ca. ), And density patches 210Cb-i (i = 1, 2,... N) respectively printed by the head modules 12-i (i = 1, 2,... N) of the inkjet head 104Cb.

When density patches are printed for each inkjet head 104Ka, 104Kb, 104Ca, 104Cb, 104Ma, 104Mb, 104Ya, and 104Yb with the conveyance speed set to Vd and the discharge frequency set to the same f [kHz] as during normal image printing, the conveyance speed Vd is single. Since it is faster than the conveyance speed Vs of the bar-type ink jet printer 200, the density of the density patch is insufficient, and an appropriate density area is not obtained. As a result of the density gradation of the density patch being narrowed, it becomes vulnerable to noise and density measurement accuracy is reduced.

Therefore, in the inkjet printer 100 having two inkjet heads that discharge the same color ink, the conveyance speed Vh during printing of the density adjustment chart is set to the conveyance speed Vd during normal image printing.
Vh ≦ Vd / 2 (Formula 3)
And

The chart formation control unit 112 controls the platen 102 and transports the paper 1 at a transport speed Vh that satisfies Equation 3. Further, the ink-jet heads 104Ka, 104Kb, 104Ca, 104Cb, 104Ma, 104Mb, 104Ya, and 104Yb eject small droplets of ink at a discharge frequency f [kHz] to print a density adjustment chart on the paper 1 (chart formation). An example of a control process).

FIG. 12 is a density adjustment chart printed on the paper 1 by the ink jet printer 100. The ink jet heads 104Ka, 104Kb, 104Ca, 104Cb, 104Ma, 104Mb, the transport speed is Vh, and the discharge frequency is f [kHz]. FIG. 10 is a diagram illustrating an example of a density adjustment chart group including density patches formed for each of 104Ya and 104Yb (an example of each liquid ejection head).

Similarly to the density adjustment chart group C ₂ , the density adjustment chart group C ₃ is a density patch 210 Ka-i printed by each head module 12-i (i = 1, 2,... N) of the inkjet head 104 Ka. (I = 1, 2,... N) (an example of a chart), density patches 210Kb-i (i = 1) respectively printed by the head modules 12-i (i = 1, 2,... N) of the inkjet head 104Kb. , 2,... N), density patches 210Ya-i (i = 1, 2,... N) respectively printed by the head modules 12-i (i = 1, 2,... N) of the inkjet head 104Ya, inkjet heads A density patch 210Yb-i (i = 1, 2,... N) printed by each head module 12-i (i = 1, 2,... N) of 104Yb, an inkjet head 104M. Density patches 210Ma-i (i = 1, 2,... n) respectively printed by the head modules 12-i (i = 1, 2,... n) of a, and the head modules 12-i (i.e., inkjet heads 104Mb). density patches 210Mb-i (i = 1, 2,... n) respectively printed by i = 1, 2,... n), and each head module 12-i (i = 1, 2,... n) of the inkjet head 104Ca. Density patches 210Ca-i (i = 1, 2,... N) respectively printed by, and density patches 210Cb respectively printed by the head modules 12-i (i = 1, 2,... N) of the inkjet head 104Cb. -I (i = 1, 2,... 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 It 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 each nozzle 28 of the inkjet heads 104Ka, 104Kb, 104Ca, 104Cb, 104Ma, 104Mb, 104Ya, and 104Yb (ink droplet ink amount per ejection by the nozzle 28) is appropriately adjusted. can do.

When there are N inkjet heads that discharge the same color ink, the conveyance speed Vh at the time of printing the density adjustment chart is set to the conveyance speed Vm at the time of normal image printing.
Vh ≦ Vm / N (Formula 4)
And it is sufficient.

<Measurement of discharge direction in single bar method>
FIG. 13 is a diagram illustrating an example of a discharge direction measurement chart printed on the paper 1 by the inkjet printer 200. Discharge direction measurement chart C ₄ is composed of a pattern by a line segment (line), a so-called 1-one n-off type test chart image for nozzle check. 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 supervises the recording control of the inkjet printer 200 controls the platen 102 and transports the paper 1 at the transport 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 every seven, and sequentially discharges them in units of groups. Thus, one line LD along the Y direction is formed by one nozzle 28, and a line LD of all nozzles is formed.

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

Ideally, the ink droplets ejected from the nozzle 28 fly in parallel with the Z direction and land on the paper 1. Accordingly, the normal X position of the nozzle 28 and the X dot 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 position, respectively. It has become.

On the other hand, the X direction position of the nozzle 28-2 and the X direction position of the ink dot ID-2 are shifted by ΔX. This deviation is called a landing position deviation, and ΔX is called a 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 by connecting the ink dots ID formed by landing the small ink droplets ejected from the nozzles 28 on the paper 1 in the Y direction.

The landing position deviation amount ΔX for each nozzle 28 can be measured by reading the ejection direction measurement chart C ₄ printed in this way with a scanner.

In FIG. 16, the scanner scans 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. It is an example of a read image. Here, since the landing position deviation of the landing position deviation amount ΔX has occurred in the ink droplets constituting the line LD-2, the interval between the line LD-1 and the line LD-2, and the line LD-2 and the line LD. The interval from −3 is not equal.

By measuring this landing position deviation amount ΔX, it is possible to inspect the presence or absence of a non-ejection state nozzle and the presence or absence of a nozzle with a defective ejection 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 ejection direction measurement chart C ₄ includes a line pattern formed respectively for each of the plurality of nozzles 28 (an example of each ejecting element).

FIG. 17 is a diagram showing an example of a line LD printed on the paper 1 by one nozzle 28 (see FIG. 3) with the ejection frequency set to f [kHz] at the conveyance speed Vd at the conveyance speed Vd. It 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 and transports the paper 1 at a transport speed Vh that satisfies 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} .

As in the case of the ink jet printing machine 200, the chart formation control unit 112 divides the nozzles 28 (see FIG. 3) constituting the projection nozzle row LN of each ink jet head into eight groups every seven, and sequentially in groups. To discharge. Thus, one line LD along the Y direction is formed by one nozzle 28, and a line LD of all nozzles is formed.

Incidentally, if the ink jet head for ejecting the same color ink is the N, the conveying speed at the time of printing of the ejection direction measurement chart C _4, it may be the conveyance speed Vh satisfying the equation 4.

<Conveying speed for connecting ink droplets>
FIG. 18 is a diagram for explaining the diameters of ink dots and the inter-dot distances formed on the paper 1 by the ink droplets ejected from the nozzles 28. If multiple dots of different diameters can be formed, consider the smallest dot. In the example shown in FIG. 18, each ink dot ID is formed by a small droplet ejected from one nozzle 28 landing on the paper 1. When the diameter of the ink dot ID is D [μm] and the distance in the Y direction between the two ink dot IDs (inter-dot distance) is L [μm],
D ≧ L (Formula 5)
By satisfying the above, the ink dot IDs are connected in the Y direction.

Here, when printing in the discharge direction measurement chart _{C 4,} the conveying speed of the sheet 1 (an example of a second conveying speed) Vh [m / s], the ejection frequency of the nozzle 28 f [kHz], and to,
L = 1000 × Vh / f (Formula 6)
It can be expressed as.

From Equation 5 and Equation 6, the following Equation 7 can be derived.

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

For example, if the ejection frequency f = 50 [kHz] and the ink dot ID diameter D = 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. Thereby, the amount of landing position deviation can be measured with high accuracy.

In the inkjet printer 100, in order to achieve an image resolution of 1200 [dpi] when the discharge frequency is f = 50 [kHz], the conveyance speed of the paper 1 during normal image printing is about 2 [m / s] or higher. . 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. In addition, dpi (dot per inch) is a unit representing the number of dots per [inch]. One [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 conveyance speed Vh may be determined as in the following Expression 8.

Vd / 2 <Vh (Formula 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 (Formula 9)
The line LD may be formed using ink droplets having a size other than 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 ink dot ID diameter (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 steeply. 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 a gap. Thereby, when the density is low, it is easily affected by 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 depending on the diameter D [μm] of the ink dot ID satisfying Expression 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 inkjet printer>
Another aspect of the ink jet printer will be described. FIG. 20 is a diagram illustrating a configuration example of the inkjet printer 300. The inkjet printer 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 that is conveyed in the conveyance direction by the drawing drum 370. This is a dual bar ink jet printer.

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

[Paper Feeder]
A sheet 1 that is a sheet is stacked on the sheet feeding unit 312. The sheets 1 are fed one by one from the sheet feeding tray 350 of the sheet feeding unit 312 to the pretreatment liquid application unit 314. A sheet (cut paper) is used as the paper 1, but a configuration in which a continuous paper (roll paper) is cut to a required size and fed is also possible.

[Pretreatment liquid application part]
The pretreatment liquid application unit 314 is disposed upstream of the drawing unit 316 in the conveyance direction of the paper 1. The pretreatment liquid application unit 314 is a mechanism that applies the pretreatment liquid to the recording surface of the paper 1. The pretreatment liquid contains a color material aggregating agent that aggregates the color material (pigment in this example) in the ink applied by the drawing unit 316, and the ink comes into contact with the pretreatment liquid and the ink. Separation of the colorant and the 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 includes a claw-shaped holding means (gripper) 355 on its outer peripheral surface, and the paper 1 is sandwiched between the claw of the holding means 355 and the peripheral surface of the pretreatment liquid drum 354. The tip can be held. 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. The pretreatment liquid application unit 356 can employ various methods such as a spray method in addition to an application method using a roller.

The sheet 1 to which the pretreatment liquid is applied is transferred from the pretreatment liquid drum 354 to the drawing drum 370 of the drawing unit 316 via the intermediate conveyance unit 326.

[Drawing part]
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 a transport unit) includes a claw-shaped holding unit (gripper) 371 on the outer peripheral surface thereof. Suction holes are provided on the outer peripheral surface of the drawing drum 370, and the sheet 1 is sucked and held on the outer peripheral surface of the drum by negative pressure suction.

The inkjet head 10 described above is applied to each of the inkjet heads 372Ka, 372Kb, 372Ca, 372Cb, 372Ma, 372Mb, 372Ya, and 372Yb. Each of the inkjet heads 372Ka, 372Kb, 372Ca, 372Cb, 372Ma, 372Mb, 372Ya, and 372Yb has a length corresponding to the maximum width of the image forming area on the sheet 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.

Black ink is supplied from the ink tank to the inkjet heads 372Ka and 372Kb. The inkjet heads 372Ca and 372Cb are supplied with cyan ink from an ink tank. Magenta ink is supplied from the ink tank to the inkjet heads 372Ma and 372Mb. The inkjet heads 372Ya and 372Yb are supplied with yellow ink 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 conveyance direction of the paper 1 (the rotation direction of the drawing drum 370).

FIG. 21 is a diagram illustrating 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 printer 300 can change the distance TD by changing the positions of the inkjet heads 372Ka, 372Kb, 372Ca, 372Cb, 372Ma, 372Mb, 372Ya, and 372Yb by a motor 496 (see FIG. 22).

The drawing drum 370 conveys the sheet 1 at a constant speed, and the movement of the sheet 1 and the inkjet heads 372Ka, 372Kb, 372Ca, 372Cb, 372Ma, 372Mb, 372Ya, and 372Yb is relatively performed in this conveying direction. The image can be recorded in the image forming area of the paper 1 by performing only once (that is, by one sub-scan).

Here, the inkjet printing machine 300 using four colors of ink of black, cyan, magenta, and yellow is illustrated, but the combination of the ink color and the number of colors is not limited to this embodiment, and the arrangement order of each color head There is no particular limitation.

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

(Dry part)
The drying unit 318 is a mechanism for drying moisture contained in the solvent separated by the color material aggregation action, and includes a drying drum 376 and a solvent drying device 378. Similarly to the pretreatment liquid drum 354, the drying drum 376 includes a claw-shaped holding means (gripper) 377 on the outer peripheral surface thereof. The solvent drying device 378 includes a plurality of halogen heaters 380 and a hot air jet nozzle 382. The sheet 1 that has been dried by the drying unit 318 is transferred from the drying drum 376 to the fixing drum 384 of the fixing unit 320 via the intermediate conveyance unit 330.

[Fixing part]
The fixing unit 320 is disposed downstream of the drawing unit 316 in the conveyance direction of the paper 1. The fixing unit 320 includes a fixing drum 384, a halogen heater 386, a fixing roller 388, and an inline scanner 390. Like the pretreatment liquid drum 354, the fixing drum 384 includes a claw-shaped holding means (gripper) 385 on the outer peripheral surface thereof.

Line scanner 390 reads the paper 1 to the printed image and chart (the density patch of density adjustment chart group C _3, including a discharge direction measurement chart C ₄₎ at a fixed reading frequency (sampling frequency), the image In this case, a CCD (Charge Coupled Device) line sensor or the like is applied.

[Paper output section]
The paper discharge unit 322 includes a discharge tray 392, and a transfer drum 394, a conveyance belt 396, and a stretching roller 398 are provided between the discharge tray 392 and the fixing drum 384 of the fixing unit 320 so as to be in contact therewith. Is provided. The sheet 1 is sent to the transport belt 396 by the transfer drum 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 printed paper 1 is held at the leading end of the paper by a gripper (not shown) that is stretched between the endless transport belt 396, and the transport belt 396 rotates. It is carried above the discharge tray 392.

Although not shown in FIG. 20, the ink jet printing machine 300 of the present example includes means for supplying a pretreatment liquid to the pretreatment liquid application unit 314, and each ink jet head 372 Ka, 372 Kb, 372 Ca. , 372Cb, 372Ma, 372Mb, 372Ya, and 372Yb cleaning (nozzle surface wiping, purging, nozzle suction, etc.), a head maintenance unit, a position detection sensor for detecting the position of the sheet 1 on the sheet conveyance path, and the temperature of each part of the apparatus A temperature sensor or the like is detected.

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

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

The communication interface 470 is an interface unit that receives image data sent from the host computer 550 that is a host controller. A serial interface or a parallel interface can be applied to the communication interface 470. In this part, a buffer memory (not shown) for speeding up communication may be mounted.

The image data sent from the host computer 550 is taken into the ink jet printer 300 via the communication interface 470 and temporarily stored in the memory 490.

The memory 490 is a storage unit that temporarily stores an image input via the communication interface 470, and data is read and written through the system controller 472. The memory 490 is not limited to a memory made of a semiconductor element, and a magnetic medium such as a hard disk may be used.

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

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

The motor driver 480 is a driver that drives the motor 496 in accordance with an instruction from the system controller 472. In FIG. 22, various motors arranged in each unit in the apparatus are represented by reference numeral 496. The motor 496 includes a feed drum 352, a pretreatment liquid drum 354, a drawing drum 370, a drying drum 376, a fixing drum 384, a transfer drum 394, and other motors that drive rotation of the drawing drum 370. A motor for changing 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 inkjet head 450; A motor or the like of a retraction mechanism that moves the inkjet head 450 to a maintenance area outside the drawing drum 370 is included.

The heater driver 482 is a driver that drives the heater 498 in accordance with an instruction from the system controller 472. In FIG. 22, various heaters arranged in each unit in the apparatus are represented by reference numeral 498.

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

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

The print control unit 474 includes an image buffer memory (not shown), and image data, parameters, and other data are temporarily stored in the image buffer memory when the print control unit 474 processes image data. Also possible is an aspect in which the print control unit 474 and the system controller 472 are integrated to form a single processor.

The head driver 478 outputs a drive signal for driving the ejection energy generating element corresponding to each nozzle of the inkjet head 450 based on the print data provided from the print control unit 474. The head driver 478 may include a feedback control system for keeping the head driving condition 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 nozzle. An image is formed on the recording surface of the paper 1 by controlling ink ejection from the ink jet head 450 while transporting the paper 1 at the transport speed.

The pretreatment liquid application controller 484 controls the operation of the pretreatment liquid application unit 356 (see FIG. 20) in accordance with an 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 an instruction from the system controller 472.

The fixing controller 488 controls the operation of the fixing pressure unit 499 including the halogen heater 386 and the fixing roller 388 (see FIG. 20) of the fixing unit 320 in accordance with an instruction from the system controller 472.

The in-line scanner 390 reads an image printed on the paper 1 and performs necessary signal processing and the like to detect a printing situation (whether ejection is performed, droplet ejection variation, optical density, etc.), and the detection result is a 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 droplet ejection timing of the inkjet head 450 is synchronized with the detection signal of the encoder 494. Thereby, the landing position can be determined with high accuracy.

The print controller 474 performs various corrections (non-discharge correction and density correction) on the inkjet head 450 based on information obtained from the in-line scanner 390, and cleaning operations (nozzles such as preliminary discharge, suction, and wiping as necessary) Control to implement recovery operation).

[Image printing and chart printing (control method of image forming apparatus)]
The inkjet printer 300 conveys the image by conveying the paper 1 at the conveyance speed Vd and printing the image with a high-definition printing mode (an example of the normal printing mode) and conveying the paper 1 at a conveyance speed faster than the conveyance speed Vd. A high-speed printing mode for printing, and a chart printing mode for printing a chart for adjusting the droplet amount 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 the printing speed is given priority over the printing quality. In the high-speed printing mode, printing is performed at a conveyance speed in which ink dot IDs formed by small ink droplets ejected from one nozzle 28 (see FIG. 3) are connected in the Y direction (see FIG. 14).

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

When printing a normal image in the high-definition printing mode, first, the system controller 472 (an example of an image formation control unit) controls the motor 496 to control 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 sheet 1 (an example of the first recording medium) with the ink absorption layer uncoated on the surface by the sheet feeding unit 312, and feeds the sheet feeding cylinder 352, the pretreatment liquid drum 354, the drawing drum 370, and the drying. The drum 376, the fixing drum 384, and the transfer drum 394 are controlled to convey the sheet 1 at the conveyance 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 causes the drawing drum 370 to convey the paper 1 at the conveyance speed Vd, and based on the image data in the memory 490, the inkjet head 450 (each inkjet head 372Ka, 372Kb, 372Ca, 372Cb, 372Ma, 372Mb, 372Ya). , 372Yb), and ejects small, medium, or large ink droplets according to the image data at an ejection frequency f [kHz], and prints an image on the paper 1 (an example of an image formation control process). .

Furthermore, the system controller 472 controls the inline scanner 390 and reads the image on the recording surface of the paper 1 conveyed by the fixing drum 384 at the conveyance speed Vd 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 inline 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, A distance TD between the nozzle surface 20 of 372 Kb, 372 Ca, 372 Cb, 372 Ma, 372 Mb, 372 Ya, and 372 Yb and the outer peripheral surface 370 A of the drawing drum 370 is TD 2 [mm]. Here, TD2 is a value smaller than TD1.

When printing a density adjustment chart group _{C 3} and discharge direction measurement chart _{C 4,} since slower transport speed than when printing images, the ink jet head 372Ka, 372Kb, 372Ca, 372Cb, 372Ma, 372Mb, 372Ya, In addition, the risk of contact between 372Yb and the paper 1 is low, and the damage caused by contact is small. Therefore, when printing the density adjustment chart group C ₃ and the ejection direction measurement chart C ₄ , the distance TD can be made smaller than when printing an image, and the density adjustment can be performed by reducing 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 sheet 1 has a recording surface (front surface) coated with an ink absorbing layer (ink receiving layer) (an example of a second recording medium). The ink absorption 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 conveyance speed Vh. The conveyance speed Vh is a speed slower than the conveyance speed Vd and satisfies Expression 4 or Expression 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. In this way, by not using the paper 1 whose surface is coated with the ink absorbing layer and not applying the pretreatment liquid, it is possible to eliminate fluctuations in the application amount of the pretreatment liquid accompanying fluctuations in the conveyance speed.

Note that the paper 1 that does not have the ink absorbing layer may be used, and the pretreatment liquid may be applied by the inkjet head in the pretreatment liquid application unit 356. By applying the pretreatment liquid with the ink jet head, the application amount of the pretreatment liquid can be easily adjusted, and the pretreatment liquid can be applied in an appropriate amount even if the conveyance speed fluctuates.

Further, the system controller 472 causes the drawing drum 370 to convey the paper 1 at the conveyance speed Vh, 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 in [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.

Thus, the reading frequency fr [kHz] of the inline scanner 390 at the time of chart formation at the conveyance speed Vh is equal to that at the time of normal image formation at the conveyance speed Vd. As a result, the number of readings by the inline scanner 390 during chart formation is greater than the number of readings during 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 the image formation control unit 110, the chart formation control unit 112, the system controller 472, the print control unit 474, and the 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 a CPU (Central Processing Unit), FPGA (Field Programmable Gate Array), which is a general-purpose processor that functions as various processing units by executing software (programs). Includes a dedicated electrical circuit that is a processor having a circuit configuration specifically designed to execute a specific process such as a programmable logic device (PLD) or ASIC (Application Specific Integrated Circuit) It is.

One processing unit may be configured by one of these various processors, or may be configured by two or more processors of the same type or different types (for example, a plurality of FPGAs or a combination of CPUs and FPGAs). May be. Further, the plurality of processing units may be configured by one processor. As an example of configuring a plurality of processing units with one processor, first, as represented by a computer such as a server and a client, one processor is configured with a combination of one or more CPUs and software. There is a form in which the processor functions as a plurality of processing units. Second, as represented by a system-on-chip (SoC) or the like, a form using a processor that realizes the functions of the entire system including a plurality of processing units with a single IC (integrated circuit) chip. is there. As described above, various processing units are configured 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 embodiment. The configurations and the like in the embodiments can be appropriately combined between the embodiments without departing from the gist 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 channel 38 channel plate 40 diaphragm 42 individual electrode 44 piezoelectric element 46 common electrode 50 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 1 06M 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 204M Inkjet head 204Y Inkjet head 210C-i Density patch 210Ca-i Density patch 210Cb-i Density patch 210K-i density patch 210Ka-i density patch 210Kb-i density patch 210M-i density patch 210Ma-i density patch 210Mb-i density patch 210Y-i density patch 210Ya-i density patch 210Yb-i density patch 300 inkjet printer 312 Paper feed unit 314 Pretreatment liquid application unit 316 Drawing unit 318 Drying unit 320 Fixing unit 322 Paper discharge unit 326 Intermediate transport unit 328 Intermediate transport Feed unit 330 Intermediate transport unit 350 Paper feed tray 352 Paper feed drum 354 Pretreatment liquid drum 355 Holding means 356 Pretreatment liquid application 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 Inkjet head 374 Roller 376 Drying drum 377 Holding means 378 Solvent drying device 380 Halogen heater 382 Hot air ejection nozzle 384 Fixing drum 385 Holding means 386 Halogen heater 388 Fixing roller 390 Inline scanner 392 Discharge tray 394 Transfer drum 396 Conveyor belt 398 Tension roller 450 Inkjet head 470 communications interface 472 system controller 474 print controller 478 a head driver 480 a motor driver 482 heater driver 484 pre-treatment liquid deposition control unit 486 drying control unit 488 fixing control unit 490 memory 492 ROM
494 Encoder 496 Motor 498 Heater 499 Fixing pressure unit 550 Host computer C ₁ Density adjustment chart C ₂ Density adjustment chart C ₃ Density adjustment chart C ₄ Ejection direction measurement chart ID-1 Ink dot ID-2 Ink dot ID -3 Ink dots LD Line LD-1 Line LD-2 Line LD-3 Line LN Projection nozzle row

Claims (13)

1. A transport unit for transporting 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;
   A liquid supply unit for supplying the same liquid to each of the plurality of liquid ejection heads;
   An image formation control unit that forms the image on the recording medium by causing the recording unit to convey the recording medium at a first conveying speed and ejecting the liquid from the plurality of ejection elements of the plurality of liquid ejection heads; ,
   The recording medium is transported at a second transport speed that is slower than the first transport speed by the transport unit, and the liquid is ejected from the plurality of ejecting elements of one liquid ejecting head, and the recording medium is charted. A chart formation control unit for forming
   With
   The diameter of dots formed on the recording medium by the liquid ejected from the ejection element is D [μm], the ejection frequency of the liquid of the ejection element when forming the chart is f [kHz], and the second When the transport speed is Vh [m / s]
   Vh ≦ D × f / 1000
   An image forming apparatus satisfying the requirements.
2. When the first transport speed is Vm [m / s] and the number of the liquid discharge heads is an integer N of 2 or more,
   Vh ≦ Vm / N
   The image forming apparatus according to claim 1, wherein:
3. When the first transport speed is Vm [m / s] and the number of the liquid discharge heads is an integer N of 2 or more,
   Vm / N <Vh
   The image forming apparatus according to claim 1, wherein:
4. An inline scanner that reads an image and a chart formed on the recording medium on the downstream side of the plurality of liquid ejection heads in the transport direction;
   The reading frequency of the inline scanner when reading an image formed by the image formation control unit is equal to the reading frequency of the inline scanner when reading a chart formed by the chart formation control unit. The image forming apparatus according to claim 1.
5. A pretreatment liquid application unit for applying a pretreatment liquid to the recording medium upstream of the plurality of liquid ejection heads in the transport direction;
   The image formation control unit uses a first recording medium having an ink absorption layer uncoated on the surface, and applies the pretreatment liquid by the pretreatment liquid application unit,
   5. The chart forming control unit uses a second recording medium having an ink absorbing layer coated on a surface thereof, and stops application of the pretreatment liquid by the pretreatment liquid application unit. The image forming apparatus described in 1.
6. A pretreatment liquid application unit for applying a pretreatment liquid to the recording medium upstream of the plurality of liquid ejection heads in the transport direction;
   The image forming apparatus according to claim 1, wherein the pretreatment liquid application unit includes an inkjet head that discharges the pretreatment liquid.
7. The liquid ejection head when a chart is formed on the recording medium by the chart formation control unit rather than the distance between the liquid ejection 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 claim 1, wherein a distance between the recording medium and the recording medium is smaller.
8. The image forming control unit includes a normal printing mode in which the recording unit conveys the recording medium at the first conveyance speed, and high-speed printing in which the conveyance unit conveys the recording medium at a speed higher than the first conveyance speed. The image forming apparatus according to claim 1, having a mode.
9. The liquid discharge head can form a plurality of dots having different diameters,
   9. The image forming apparatus according to claim 1, wherein a diameter of a smallest dot among the plurality of dots having different diameters is D [μm].
10. 10. The image forming apparatus according to claim 1, wherein the chart includes a density patch formed for each of the liquid ejection heads.
11. The image forming apparatus according to claim 1, wherein the chart includes a line pattern formed for each of the ejection elements.
12. 12. The image forming apparatus according to claim 1, wherein the liquid ejection head includes a plurality of head modules arranged in a first direction intersecting the transport direction.
13. A plurality of liquid ejection heads each having a conveyance unit that conveys a recording medium along a conveyance direction, a plurality of ejection elements that eject liquid, and arranged side by side along the conveyance direction; and the plurality of liquid ejection heads A liquid supply unit that supplies the same liquid to each of the image forming apparatuses,
    An image formation control step of forming an image on the recording medium by causing the recording unit to convey the recording medium at a first conveying speed and ejecting the liquid from the plurality of ejection elements of the plurality of liquid ejection heads; ,
    The recording medium is transported at a second transport speed that is slower than the first transport speed by the transport unit, and the liquid is ejected from the plurality of ejecting elements of one liquid ejecting head, and the recording medium is charted. A chart formation control step for forming
    With
    The diameter of dots formed on the recording medium by the liquid ejected from the ejection element is D [μm], the ejection frequency of the liquid of the ejection element when forming the chart is f [kHz], and the second When the transport speed is Vh [m / s]
    Vh ≦ D × f / 1000
    An image forming apparatus control method that satisfies the above.

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