JP2011156795A - Printer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide printer which optimizes a conveyance speed while suppressing bleeding among inks. <P>SOLUTION: The printer is equipped with: a conveyance mechanism for conveying a medium in a conveyance direction; a plurality of heads arranged side by side in the conveyance direction, and discharging respective color inks to the medium; a reading section for reading an image printed on the medium by the plurality of heads; a comparing section for comparing the reading result of an image when the medium is conveyed at the reference speed in which, by the time when ink discharged from a certain head lands on the medium, ink discharged from other head on the upstream side of the certain head in the conveyance direction is dried, with that of an image when the medium is conveyed at a first conveyance speed lower than the reference speed. When the comparison result of the comparing section exceeds an allowance, the next printing is made at a second conveyance speed lower than the first conveyance speed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a printing apparatus.

As an ink jet printer that prints an image using ink, a plurality of heads provided with a plurality of nozzles arranged in the paper width direction are provided in the transport direction, and ink drops are respectively ejected from the plurality of heads while transporting a medium (for example, paper). There is a printer (so-called line printer) that prints an image by discharging.

JP 2007-68202 A

In the printer as described above, the printing speed can be increased by increasing the conveyance speed. However, if the transport speed is increased too much, there is a problem that bleeding (hereinafter also referred to as bleed) may occur between the inks ejected from the heads arranged in the transport direction.
Therefore, an object of the present invention is to optimize the conveyance speed while suppressing bleeding between inks.

The main invention for achieving the above object is a transport mechanism for transporting a medium in the transport direction, and a plurality of heads arranged side by side in the transport direction, each of which includes a plurality of inks that discharge ink of each color onto the medium. A head, a reading unit that reads an image printed on the medium by the plurality of heads, and an upstream side in the transport direction from the certain head until ink ejected from the certain head lands on the medium. Reading result of the image when the medium is transported at a reference speed at which ink discharged from another head is dried, and reading of the image when the medium is transported at a first transport speed that is faster than the reference speed A comparison unit that compares the result, and when the comparison result of the comparison unit exceeds an allowable value, the next printing is performed at a second conveyance speed that is slower than the first conveyance speed. A printing apparatus.
Other features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

1 is a block diagram illustrating a configuration of a printing system. FIG. 2 is a schematic view around a printing area of a printer. FIG. 8 is an explanatory diagram of processing by a printer driver. It is a flowchart about the optimization of the conveyance speed of 1st Embodiment. It is explanatory drawing about the comparison of a scanning image. It is a figure which shows the change of a conveyance speed. It is a figure which shows the relationship between the conveyance speed and difference in the modification 1 of 1st Embodiment. It is a figure which shows the correspondence of the magnitude | size of a difference and step size in the modification 2 of 1st Embodiment. It is a figure which shows the printing image of the modification 3 of 1st Embodiment. It is a figure which shows a bleed evaluation pattern. It is the schematic of the printing area periphery of the printer of 2nd Embodiment. FIG. 6 is a schematic view around a printing area after moving a head. It is explanatory drawing of the modification of 2nd Embodiment. FIG. 14A is a diagram illustrating an image printed on the paper S in the third embodiment. FIG. 14B is a diagram illustrating a correspondence relationship between each area in FIG. 14A and the ejection duty of ink from each head of the printer 1. 15A to 15D are diagrams illustrating the positional relationship between the arrangement of each head of the printer 1 and the head that ejects ink. It is explanatory drawing of the modification 1 of 3rd Embodiment. It is explanatory drawing of each area | region of the image printed in the modification 2 of 3rd Embodiment. It is a figure which shows the relationship between the duty of discharge of each ink and fixing time in the modification 2 of 3rd Embodiment. 19A to 19E are explanatory diagrams of a method for calculating the conveyance speed according to the second modification of the third embodiment. It is a perspective view of the printer (serial printer) of the modification 4 of 3rd Embodiment. It is explanatory drawing of the modification 4 of 3rd Embodiment.

  At least the following matters will become clear from the description of the present specification and the accompanying drawings.

A transport mechanism for transporting the medium in the transport direction; a plurality of heads arranged side by side in the transport direction; each of the plurality of heads ejecting ink of each color onto the medium; and the plurality of heads to the medium. The ink discharged from the reading unit that reads the printed image and the other head upstream in the transport direction from the certain head is dried before the ink discharged from the certain head reaches the medium. A comparison unit that compares the reading result of the image when the medium is conveyed at a reference speed with the reading result of the image when the medium is conveyed at a first conveyance speed that is faster than the reference speed. When the comparison result of the comparison unit exceeds an allowable value, the printing apparatus is characterized in that the next printing is performed at a second conveyance speed that is slower than the first conveyance speed.
According to such a printing apparatus, it is possible to optimize the conveyance speed while suppressing bleeding between inks.

In addition, a transport mechanism that transports the medium in the transport direction, a plurality of heads arranged side by side in the transport direction, each of the plurality of heads that discharge ink of each color onto the medium, and the plurality of heads A reading unit that reads an image printed on a medium, and ink ejected from another head upstream in the transport direction from the certain head until ink ejected from the certain head lands on the medium. A comparison unit that compares the reading result of the image when the medium is conveyed at a reference speed for drying with the reading result of the image when the medium is conveyed at a first conveyance speed that is faster than the reference speed; When the comparison result of the comparison unit does not exceed an allowable value, the printing apparatus is characterized in that the next printing is performed at a second transport speed that is faster than the first transport speed.
According to such a printing apparatus, it is possible to optimize the conveyance speed while suppressing bleeding between inks.

In this printing apparatus, it is preferable that the magnitude of the second transport speed is determined according to the comparison result of the comparison unit.
According to such a printing apparatus, the number of times of printing at a low conveyance speed can be reduced, and an optimum conveyance speed can be determined earlier.

In this printing apparatus, the reading unit reads a part of an image printed on a medium, and the comparison unit reads a part of the image when the medium is conveyed at the reference speed. It is desirable to compare the reading results of a part of the image when the medium is transported at the first transport speed.
According to such a printing apparatus, the time required for reading can be shortened.

The printing apparatus includes a calculation unit that determines a discharge amount of ink discharged from each head when the image is printed, and the discharge amount calculated by the calculation unit before printing on the medium. Based on the above, it is desirable to change the position of each head in the transport direction for discharging the ink.
According to such a printing apparatus, it is possible to further increase the conveyance speed while suppressing bleeding between inks.

In this printing apparatus, each of the plurality of heads may be moved in the transport direction based on the ejection amount obtained by the calculation unit.
According to such a printing apparatus, the ink ejection position from each head can be reliably changed.

In such a printing apparatus, each head includes a plurality of nozzle rows in which a plurality of nozzle rows arranged in a direction intersecting the transport direction has a plurality of nozzle rows arranged in the transport direction, The nozzle rows used in each head may be changed based on the obtained ejection amount.
According to such a printing apparatus, the ink ejection position (position in the transport direction) can be changed without providing a mechanism for moving the head in the transport direction.

In this printing apparatus, the calculation unit calculates the ink discharge amount of each head for each of a plurality of regions of the medium, and sets the ink of each head according to the ink discharge amount of each of the plurality of regions. It is desirable to change the position in the transport direction for discharging.
According to such a printing apparatus, the conveyance speed can be further increased, and the conveyance speed can be optimized while suppressing bleeding.

  In the following embodiments, an ink jet printer (hereinafter also referred to as printer 1) will be described as an example.

=== Configuration of Printing System ===
FIG. 1 is a block diagram illustrating a configuration of the printing system 100.
As shown in FIG. 1, the printing system 100 according to the present embodiment is a system that includes a printer 1, a computer 110, and a scanner 120.

  The printer 1 is a liquid ejecting apparatus that ejects ink as a liquid onto a medium to form an image on the medium. In the present embodiment, the printer 1 is a color ink jet printer. The printer 1 can print images on a plurality of types of media such as paper, cloth, and film sheets. In this embodiment, printing is performed on the paper S as a medium.

  The computer 110 is communicably connected to the printer 1 via the interface 111, and outputs print data corresponding to the image to the printer 1 in order to cause the printer 1 to print an image. The computer 110 includes a CPU 112 for executing various programs installed in the computer 110, and a memory 113 for storing the various programs. Among the programs installed in the computer 110, there are a printer driver for converting image data output from the application program into print data, and a scanner 120 connected to the computer 110 via the interface 111 so as to be communicable. There is a scanner driver to control. In the present embodiment, the computer 110 corresponds to a comparison unit.

  The scanner 120 irradiates light on the paper S conveyed to a document table (not shown), detects the reflected light by a sensor (for example, a CCD sensor) (not shown) provided in the reading carriage 121, and the image of the paper S Is a device for acquiring color information of the image.

  The scanner 120 reads an image by moving, for example, a line sensor (for example, a CCD sensor) along the main scanning direction in the sub-scanning direction. This line sensor includes, for example, a sensor that detects red (R) light, a sensor that detects green (G) light, and a sensor that detects blue (B) light. Then, the scanner 120 irradiates the paper S with light, and detects (color separation) the reflected light with each sensor, whereby three color information (red (R), green (G), and blue (B)) ( Reading gradation value).

  The scanner 120 includes a controller 125 having an interface 122, a CPU 123, and a memory 124, and transmits data indicating image color information to the scanner driver of the computer 110 via the interface 122.

  Note that “printing apparatus” means the printer 1 in a narrow sense, but means a system of the printer 1, the computer 110, and the scanner 120 in a broad sense.

<Configuration of Printer 1>
Next, the configuration of the printer 1 will be described with reference to FIGS. 1 and 2. FIG. 2 is a schematic view around the print area of the printer 1.

  As shown in FIG. 1, the printer 1 includes a head unit 20, a transport unit 30, a detector group 40, and a controller 50. When the printer 1 receives print data from the computer 110, the controller 50 controls each unit (head unit 20, transport unit 30) based on the print data to print an image on a print medium. The situation in the printer 1 is monitored by the detector group 40, and the detector group 40 outputs a signal corresponding to the detection result to the controller 50.

  The head unit 20 is for ejecting ink onto the paper S. The head unit 20 forms dots on the paper S by ejecting ink onto the paper S being conveyed, and prints an image on the paper S. The printer 1 of this embodiment is a line printer, and the head unit 20 can form dots for the paper width at a time.

  As shown in FIG. 2, the head unit 20 of the present embodiment discharges a black ink head K that discharges black ink, a cyan ink head C that discharges cyan ink, a magenta ink head M that discharges magenta ink, and a yellow ink. A yellow ink head Y.

  These heads are arranged at equal intervals (for example, 10 inch intervals) in the order of the black ink head K, cyan ink head C, magenta ink head M, and yellow ink head Y from the upstream side in the transport direction.

  Each head is provided with a nozzle row in which a plurality of nozzles for discharging each ink are arranged in the paper width direction. A row of dots arranged in the direction in which the head and the paper move relative to each other is referred to as a “raster line”. In the case of a line printer as in this embodiment, “raster line” means a row of dots arranged in the paper transport direction. On the other hand, in the case of a serial printer that prints using a head mounted on a carriage, “raster line” means a row of dots arranged in the carriage movement direction. A printed image is formed by arranging a large number of raster lines in a direction perpendicular to the moving direction.

  The transport unit 30 is for transporting a medium (for example, paper S) in the transport direction. The transport unit 30 includes an upstream roller 32 </ b> A and a downstream roller 32 </ b> B, and a belt 34. When a conveyance motor (not shown) rotates, the upstream roller 32A and the downstream roller 32B rotate, and the belt 34 rotates. The fed paper S is conveyed by the belt 34 to a printable area (area facing the head). When the belt 34 transports the paper S, the paper S moves in the transport direction with respect to the head unit 20. The paper S being conveyed is electrostatically attracted or vacuum attracted to the belt 34. The paper S that has passed through the printable area is discharged by the belt 34 and then conveyed to the scanner 120 by a belt (not shown).

  The controller 50 is a control unit for controlling the printer. As shown in FIG. 1, the controller 50 includes an interface unit 51, a CPU 52, a memory 53, and a unit control circuit 54. The interface unit 51 transmits and receives data between the computer 110 that is an external device and the printer 1. The CPU 52 is an arithmetic processing unit for controlling the entire printer. The memory 53 is for securing an area for storing a program of the CPU 52, a work area, and the like, and includes storage elements such as a RAM and an EEPROM. The CPU 52 controls each unit via the unit control circuit 54 in accordance with a program stored in the memory 53.

<About print processing>
In such a printer 1, when the controller 50 receives print data, the controller 50 first rotates a paper feed roller (not shown) by the transport unit 30 and sends the paper S to be printed onto the belt 34. The paper S is conveyed on the belt 34 without stopping at a constant speed, and passes under each head of the head unit 20. And while the paper S passes under the head unit 20, ink is intermittently ejected from the nozzles of each head. That is, the dot formation process and the paper S transport process are performed simultaneously. As a result, a dot row composed of a plurality of dots along the transport direction and the paper width direction is formed on the paper S, and an image is printed.

<Outline of processing by printer driver>
As described above, the printing process is started when print data is transmitted from the computer 110 connected to the printer 1. The print data is generated by processing by the printer driver. Hereinafter, processing by the printer driver will be described with reference to FIG. FIG. 3 is an explanatory diagram of processing by the printer driver.

The printer driver receives image data from the application program, converts it into print data in a format that can be interpreted by the printer 1, and outputs the print data to the printer. When converting image data from an application program into print data, the printer driver performs resolution conversion processing, color conversion processing, halftone processing, rasterization processing, command addition processing, and the like.
The resolution conversion process is a process for converting image data (text data, image data, etc.) output from an application program into a resolution (print resolution) for printing on paper. For example, when the print resolution is specified as 720 × 720 dpi, the vector format image data received from the application program is converted into bitmap format image data with a resolution of 720 × 720 dpi. Note that each pixel data of the image data after the resolution conversion process is multi-gradation (for example, 256 gradations) RGB data represented by an RGB color space.

  The color conversion process is a process for converting RGB data into data in the CMYK color space. The image data in the CMYK color space is data corresponding to the ink color of the printer. In other words, the printer driver generates CMYK plane image data based on the RGB data.

  This color conversion processing is performed based on a table (color conversion lookup table LUT) in which gradation values of RGB data and gradation values of CMYK data are associated with each other. Note that the pixel data after the color conversion processing is CMYK data of 256 gradations represented by a CMYK color space.

  The halftone process is a process for converting high gradation number data into gradation number data that can be formed by a printer. By this halftone processing, data indicating 256 gradations is converted into 1-bit data indicating 2 gradations or 2-bit data indicating 4 gradations. In the image data after halftone processing, 1-bit or 2-bit pixel data corresponds to each pixel, and this pixel data indicates the dot formation status (the presence / absence of dots, the size of dots) in each pixel. Become data. For example, in the case of 2 bits (4 gradations), no dot corresponding to the dot gradation value [00], formation of a small dot corresponding to the dot gradation value [01], and medium corresponding to the dot gradation value [10] It is converted into four stages like dot formation and large dot formation corresponding to the dot gradation value [11]. Thereafter, the dot generation rate is determined for each dot size, and pixel data is created so that the printer 1 forms the dots in a dispersed manner by using a dither method, γ correction, error diffusion method, or the like. .

  The rasterizing process rearranges the pixel data arranged in a matrix for each pixel data in the order of data to be transferred to the printer 1. For example, the pixel data is rearranged according to the arrangement order of the nozzles of each head.

  The command addition process is a process for adding command data corresponding to the printing method to the rasterized data. The command data includes, for example, conveyance data indicating the medium conveyance speed.

  The print data generated through these processes is transmitted to the printer 1 by the printer driver.

<Breaking between inks>
In the printer 1 as described above, the printing speed can be increased by increasing the transport speed of the paper S. However, if the transport speed is increased too much, bleeding (hereinafter also referred to as bleed) occurs between the inks ejected from the heads arranged in the transport direction, which may cause deterioration in image quality.

  For example, when printing a blue image on the paper S, cyan ink and magenta ink are used. First, when the paper S being transported in the transport direction passes under the cyan ink head C, cyan ink is ejected from the cyan ink head C. Then, when the paper S landed with cyan ink passes under the magenta ink head M, the magenta ink is ejected from the magenta ink head M. At this time, if the transport speed is too high, the magenta ink lands on the paper S before the cyan ink dries, and bleeding occurs between the cyan ink and the magenta ink.

  The relationship between the ejection amount of each ink and the drying time differs depending on the type of paper S. For this reason, in order to prevent bleeding from occurring regardless of the type of paper S or ink, even in the worst conditions (when using paper that is difficult to dry ink and when the amount of ink discharged is large) It was necessary to reduce the conveyance speed to such a speed that the ink dried between the heads, and the conveyance speed could not be increased to an optimum speed. Alternatively, it was necessary to print a test pattern separately for evaluation, which was troublesome.

  Therefore, in this embodiment, the conveyance speed is optimized while suppressing bleeding. In the following embodiment, the same image (or part of the same image) is printed on a plurality of sheets of paper S.

=== First Embodiment ===
FIG. 4 is a flowchart for optimizing the conveyance speed according to the first embodiment.
First, with respect to the first paper S, when ink ejected from each head lands on the paper S, the ink ejected from the head upstream in the transport direction is surely dried. Printing is performed at a conveyance speed (hereinafter also referred to as a reference speed, for example, 25 cps) (S101). The computer 110 scans the image printed at the reference speed with the scanner 120, and stores the scanned image (hereinafter also referred to as a reference image) in the memory 113 (S102).
Printing is performed on the next paper S at a conveyance speed higher than the reference speed (for example, at 50 cps) (S103). After the printing, the printed image is scanned by the scanner 120 in the same manner as the first paper S (S104).
Then, the computer 110 compares the scanned image obtained by this scanning with the reference image stored in the memory 113 (S105).

FIG. 5 is an explanatory diagram for comparison of scanned images.
Image 1 in the figure is a scanned image (reference image) of an image printed at a reference speed. In this case, since the drying speed is sufficient due to the low conveyance speed, bleeding does not occur between different ink colors. Image 2 is a scanned image of an image printed with the conveyance speed higher than the reference speed. Here, the image is printed in two different colors (in the figure, white and black).
With respect to the image 1 and the image 2, when the difference (tone value difference) is obtained for each pixel, an image (difference image) on the right side of the figure is obtained. If no bleed occurs in the image 2, no difference in gradation values appears in each pixel of the difference image (the gradation values are almost the same). However, in the difference image of FIG. 5, the color (tone value) at the color boundary portion in the images 1 and 2 is different from the other portions. That is, it can be seen that bleeding occurs in the image 2 at this portion.

In this way, the computer 110 obtains, for each pixel, the difference between the results read by the scanner 120 for two images printed at different conveyance speeds. Then, the peak value (maximum value) of the difference is calculated.
Subsequently, the computer 110 determines whether or not the calculated peak value of the difference exceeds a threshold value (S106). If the peak value of the difference does not exceed the threshold value (YES in S106), the process returns to step S103, and the next printing is performed by further increasing the conveyance speed.
Thereafter, the same operation is repeated, and if the peak value exceeds the threshold value in step S106 (NO in S106), the next printing is performed at a lower transport speed than the current transport speed (S107). Return to S104.

FIG. 6 is a diagram illustrating an example of a change in the conveyance speed. In the present embodiment, the conveyance speed is changed by a constant change amount (hereinafter also referred to as a step size). In addition, the horizontal axis of a figure is a conveyance speed and a vertical axis | shaft is a peak value of a difference. Moreover, the dotted line of a figure is a threshold value.
As shown in the figure, since the peak value of the difference when the conveyance speed is 50 cps does not exceed the threshold value, the next paper S is further increased by 25 cps and printed at a conveyance speed of 75 cps. Also in this case, the peak value of the difference does not exceed the threshold value. Therefore, the next paper S is printed at a transport speed of 100 cps with the transport speed further increased by 25 cps.
When printing is performed at a transport speed of 100 cps, the peak value of the difference exceeds the threshold as shown in the figure. That is, there is a high possibility that bleeding has occurred in the printed image. Therefore, printing is performed on the next sheet S at a lower transport speed (75 cps).

  Note that it is preferable to prepare different threshold values depending on the type of paper S to be printed. For example, since plain paper has a large variation from paper to paper, the threshold value is increased. In the case of ink-jet dedicated paper, since the ink absorption layer is small and the variation from paper to paper is small, the threshold value may be reduced.

  Further, in the present embodiment, it is evaluated whether or not the maximum value of the difference for each pixel of the two images exceeds the threshold value, but the evaluation may be performed by a method other than this. For example, you may evaluate by the number of the pixels from which the magnitude | size of the difference of two images becomes more than fixed value. That is, it is only necessary to be able to evaluate whether or not the comparison result of two images is within an allowable range (within an allowable value).

  As described above, in this embodiment, the conveyance speed can be optimized while suppressing bleed regardless of the combination of the type of paper S and the ink and without performing the evaluation using the test pattern. . Further, according to the present embodiment, the conveyance speed can be automatically optimized.

(Modification 1 of the first embodiment)
FIG. 7 is a diagram illustrating an example of a relationship between the conveyance speed and the difference in the first modification of the first embodiment. In the figure, the horizontal axis represents the conveyance speed, and the vertical axis represents the peak value of the difference. Moreover, the dotted line of a figure is a threshold value.
In the first embodiment, the step size of the conveyance speed is constant (25 cps), but in the first modification, the step size is initially large and the step size is gradually reduced. That is, the conveyance speed is changed stepwise.

Specifically, first, printing is performed at a slow conveyance speed (a reference speed of 25 cps) at which bleeding does not occur reliably, and the scanned image (reference image) is stored in the memory 113 of the computer 110.
On the next paper S, printing is carried out at a conveyance speed of 70 cps (up 45 cps). From FIG. 7, the peak value of the difference does not exceed the threshold value also in this case. Therefore, printing is performed on the next paper S at a transport speed of 100 cps (increase by 30 cps).
However, when printing at 100 cps, the peak value of the difference exceeds the threshold as shown in FIG.
Therefore, printing is performed on the next sheet S at a conveyance speed of 85 cps (down 15 cps). Then, the peak value of the difference becomes smaller than the threshold value. Therefore, the next paper S is printed with a transport speed of 93 cps (up 8 cps).
When the conveyance speed can be changed in multiple stages, the optimum printing speed can be reached earlier by changing the conveyance speed stepwise as in this embodiment.

(Modification 2 of the first embodiment)
In the first modification described above, the step size is gradually reduced. However, in this second modification, the relationship between the difference size and the step width is determined in advance, and the step width is changed according to the difference size. Like to do.
FIG. 8 is a diagram illustrating an example of a correspondence relationship between the difference magnitude and the step size in the second modification of the first embodiment. The horizontal axis in the figure indicates the magnitude of the difference (corresponding to the vertical axis in FIGS. 6 and 7), and the vertical axis indicates the step size. The dotted line in the figure indicates a threshold value (corresponding to the threshold value in FIGS. 6 and 7). In the second modification, data indicating the relationship of FIG. 8 is stored in advance in the memory 113 of the computer 110, for example.

In the second modification, the computer 110 obtains an image difference in the same manner as in the above-described embodiment, and then determines the next conveyance speed with reference to the data in FIG.
For example, when the difference value is considerably smaller than the threshold value, the increment of the conveyance speed is increased. That is, the next printing is performed with a large increase in the conveyance speed (increase the step size). If the difference value is close to the threshold value, the next printing is performed by slightly increasing the conveyance speed (decreasing the step size). When the difference value is equal to the threshold value, the step size is set to zero. That is, the next printing is performed without changing the conveyance speed.
When the difference exceeds the threshold value, the step size becomes a negative value. In this case, the next printing is performed at a reduced conveyance speed.
Thereby, the number of times of printing at a low transport speed can be reduced, and an optimal transport speed can be determined earlier.

(Modification 3 of the first embodiment)
In the above-described embodiment, the entire image printed on the paper S is scanned by the scanner 120. However, in this case, the scan time becomes long, and the scanned image data becomes large.
Therefore, in the third modification, the presence / absence of bleed is determined by scanning a part of the image, not the entire image.

FIG. 9 is a diagram illustrating an example of a print image according to the third modification of the first embodiment. In FIG. 9, area 1 is printed in cyan, area 2 is printed in blue (mixed color of cyan and magenta), and area 3 is printed in green (mixed color of cyan and yellow).
In this case, scanning time can be shortened by scanning a portion where bleeding is likely to occur (for example, a portion surrounded by a dotted line in the figure) rather than scanning the entire image. Further, at this time, the bleed can be effectively suppressed by selecting a portion where the bleed is likely to occur in the image.
The scan time can be shortened by scanning a part of the image instead of scanning the entire image in this way. Therefore, the next printing can be performed earlier, and the optimum conveyance speed can be determined earlier. In addition, the capacity for storing the scanned image in the memory 113 of the computer 110 can be reduced.

Alternatively, a bleed evaluation pattern as shown in FIG. 10 may be printed on the edge of the paper S, for example, and only this evaluation pattern may be scanned by the scanner 120. FIG. 10 shows an example of a bleed evaluation pattern.
In the bleed evaluation pattern shown in FIG. 10, a plurality of ruled lines having different thicknesses are printed in the vertical direction, the horizontal direction, and the diagonal direction. The ruled lines and portions other than the ruled lines are printed in different colors. For example, ruled lines are printed in green (mixed color of cyan and yellow), and other than ruled lines are printed in yellow (solid printing). By printing such a pattern on a part of the paper S, bleed of yellow and cyan can be efficiently evaluated. Similarly, patterns of other colors (for example, cyan and magenta, magenta and yellow) may be created.
As described above, in the third modification, a part of the image is scanned instead of scanning the entire image. By doing so, the optimum transport speed can be determined more quickly.

=== Second Embodiment ===
In the above-described embodiment, the intervals in the transport direction of the heads are the same. In the present embodiment, the position of each head in the transport direction is changed according to the image to be printed.

  FIG. 11 is a schematic view around the print area of the printer 1 of the second embodiment. In the second embodiment, the cyan ink head C, the magenta ink head M, and the yellow ink head Y that discharge ink of each color can be independently moved upstream or downstream in the transport direction. ing. The printer 1 changes the position of each head in the transport direction according to the print data received from the computer 110. In other words, the position at which ink is ejected from each head (position in the transport direction) is changed.

  The controller 50 (corresponding to the calculation unit) of the printer 1 of the second embodiment calculates the ejection duty of each color ink after the halftone process from the print data received from the computer 110. Note that the duty is a ratio of the ink ejection amount when a large dot is formed on all pixels of the paper S as 100%.

For example, when printing an image in which red (mixed color of magenta and yellow) is not used on the paper S, the interval between the magenta ink head M and the yellow ink head Y may be close.
Therefore, in this case, the controller 50 of the printer 1 moves the cyan ink head C that discharges cyan ink to the upstream side in the transport direction as shown in FIG. 12 based on the print data of the image, and the yellow that discharges yellow ink. The ink head Y is moved upstream in the transport direction. By doing so, the distance between the cyan ink head C and the magenta ink head M and the distance between the cyan ink head C and the yellow ink head Y can be made larger than those in FIG. 11, and bleeding between the cyan ink and magenta ink can be achieved. And bleeding between cyan ink and yellow ink can be made difficult to occur. Further, the interval between the yellow ink head Y and the paper discharge can also be made larger than that in FIG. As a result, ink can be prevented from adhering even when the discharged paper S overlaps.

As described above, the bleed can be made difficult to occur by changing the ejection position of the ink from each head according to the print data. As a result, it is possible to further increase the transport speed than the fastest transport speed when the heads are equally spaced (FIG. 11). In this embodiment, since each head is moved in the transport direction according to the print data, the ink ejection position can be changed reliably.
Then, when actually printing an image on a plurality of papers S, after changing the position of each head in this way, the same processing as in the first embodiment is performed. That is, at first, printing is performed on the paper S at a slow conveyance speed that does not cause bleeding, and the scanned image (reference image) is stored. Then, the next printing is performed by increasing the conveying speed, and the difference between the scanned image (the scanned image of the image printed by increasing the conveying speed) and the reference image is obtained. The conveyance speed is changed according to the comparison between the difference value and the threshold value.
Thereby, the conveyance speed can be further increased, and the conveyance speed can be optimized while suppressing bleeding.

(Modification of the second embodiment)
In the second embodiment described above, the head is moved in the transport direction. In this modification, each head is provided with a plurality of nozzle arrays arranged in the transport direction, and is used in each head according to the duty of the image. Change the nozzle row.

FIG. 13 is an explanatory diagram of a modification of the second embodiment. In this modification, as shown in the figure, the cyan ink head C has six nozzle rows in which a plurality of nozzles for ejecting ink are arranged in the paper width direction (c1 to c6 in order from the upstream side). Is provided.
Similarly, the magenta ink head M is also provided with six nozzle rows (m1 to m6) arranged in the carrying direction, and the yellow ink head Y has six nozzle rows (y1 to y6) in the carrying direction. It is provided side by side.
Then, the controller 50 of the printer 1 selects a nozzle row that ejects ink from among the plurality of nozzle rows of each head according to the duty based on the print data.

For example, when printing an image in which red (mixed color of magenta and yellow) is not used on the paper S, the controller 50 selects a nozzle row (for example, nozzle row c1) on the upstream side in the transport direction in the cyan ink head C. The magenta ink head M selects the nozzle row (for example, nozzle row m6) on the downstream side in the transport direction, and the yellow ink head Y selects the nozzle row on the upstream side in the transport direction (for example, nozzle row y1). By doing this, it is possible to change the position (position in the transport direction) at which ink is ejected from each head without moving each head in the transport direction.
When actually printing an image on a plurality of sheets S, after changing the nozzle rows used in each head, the same processing as in the first embodiment is performed. That is, at first, printing is performed on the paper S at a slow conveyance speed that does not cause bleeding, and the scanned image (reference image) is stored. Then, the next printing is performed by increasing the conveying speed, and the difference between the scanned image (the scanned image of the image printed by increasing the conveying speed) and the reference image is obtained. The conveyance speed is changed according to the comparison between the difference value and the threshold value.
Thereby, since the conveyance speed can be further increased, the conveyance speed can be optimized while suppressing bleeding.

  In this modification, the ink ejection position (position in the transport direction) can be changed without providing a mechanism for moving the head in the transport direction. Also in this case, the conveyance speed can be optimized while suppressing bleeding.

=== Third Embodiment ===
In the third embodiment, the conveyance speed is optimized in accordance with the ink ejection duty for each area of the paper S.
FIG. 14A is a diagram illustrating an example of an image printed on the paper S in the third embodiment. FIG. 14B is a diagram illustrating a correspondence relationship between each region in FIG. 14A and the ejection duty of ink from each head of the printer 1.

  For example, area 1 is printed in cyan. As shown in FIG. 14B, in this region 1, only cyan ink is ejected with a duty of 60%. Area 2 is printed in blue. In this area 2, as shown in FIG. 14B, cyan ink and magenta ink are each ejected with a duty of 60%. Area 3 is printed in green. In this area 3, as shown in FIG. 14B, cyan ink and yellow ink are each ejected with a duty of 60%.

15A to 15D are diagrams showing the positional relationship between the arrangement of the heads of the printer 1 and the heads that eject ink. In the figure, the head for ejecting ink is indicated by oblique lines.
As shown in FIG. 15A, in this embodiment, a black ink head K, a cyan ink head C, a magenta ink head M, and a yellow ink head Y are arranged at intervals of 10 inches. If the paper S is transported at a transport speed of 100 cps, the time required for the paper S to pass between adjacent heads is 10 (inch) / 100 (cps) = 1 (sec).

Here, in region 1 in FIG. 14A, an image is formed with cyan ink. If only this area 1 is printed, ink is ejected from the cyan ink head C at a duty of 60% as shown in FIG. 15B. After ink is ejected from the cyan ink head C, the paper S is transported in the transport direction for 30 inches until paper discharge.
In this case, if the time required for fixing (drying) ink with a duty of 60% is 3 seconds, 30 inches may be transported in 3 seconds. That is, it can be conveyed at 30 (inch) / 3 (sec) = 100 (cps).

  14A, an image is formed with cyan ink and magenta ink. If only this area 2 is printed, ink is ejected from the cyan ink head C and the magenta ink head M at a duty of 60% as shown in FIG. 15C. In this case, the cyan ink needs to be fixed (dried) before the magenta ink lands on the paper S. That is, 10 inches between the cyan ink head C and the magenta ink head M must be transported over at least 3 seconds (time required for fixing ink with a duty of 60%). Therefore, the fastest conveyance speed during this period is 10 (inch) / 3 (sec) = 33.3 (cps). Further, it is necessary to transport 20 inches from the discharge of magenta ink to the discharge of paper over at least 3 seconds. Therefore, the fastest conveyance speed during this period is 20 (inch) / 3 (sec) = 66.6 (cps).

14A, an image is formed with cyan ink and yellow ink. If only this area 3 is printed, ink is ejected from the cyan ink head C and the yellow ink head Y at a duty of 60% as shown in FIG. 15D. In this case, the cyan ink needs to be fixed (dried) before the yellow ink lands on the paper S. That is, 20 inches between the cyan ink head C and the yellow ink head Y must be conveyed for at least 3 seconds. Therefore, the fastest conveyance speed during this period is 20 (inch) / 3 (sec) = 66.6 (cps). Further, it is necessary to carry 10 inches from discharging yellow ink to discharging it over at least 3 seconds. Accordingly, the fastest conveyance speed during this period is 10 (inch) / 3 (sec) = 33.3 (cps).
In order to print the three areas 1 to 3 so that no bleed occurs, it is only necessary to transport at the lowest transport speed (33.3 cps) among the transport speeds obtained above.

It is assumed that ink is ejected from the head adjacent in the transport direction (for example, cyan ink head C and magenta ink to head M) to the same area of paper S, and the upstream head (in this case, cyan ink head). It is assumed that the ink ejection duty from the printer C) is 100% and that fixing takes 6 seconds. In this case, it is necessary to transport 10 inches between the cyan ink head C and the magenta ink head M in 6 seconds. In this case, the conveyance speed is 10 (inch) / 3 (sec) = 16.6 (cps).
In this embodiment, the conveyance speed is determined according to the ink ejection duty to each area of the print image. For example, when printing is performed with each ink ejection duty of 60%, the above-described conveyance speed is used. The conveyance speed (33.3 cps) can be more suitable than (16.6 cps).

Also in the present embodiment, when an image is actually printed on a plurality of sheets S, the same processing as in the first embodiment is performed. That is, first, printing is performed on the paper S at a low conveyance speed and the scan image (reference image) is stored, and the next paper S is printed at an increased conveyance speed and the difference between the scan image and the reference image is stored. And the conveyance speed is increased in accordance with the comparison with the threshold value.
Thereby, the conveyance speed can be further increased, and the conveyance speed can be optimized while suppressing bleeding.

(Modification 1 of 3rd Embodiment)
In Modification 1 of the third embodiment, the position of the head (position in the transport direction) is changed as in the second embodiment. In Modification 1, it is assumed that the same image as in FIG. 14A is printed, and the ink ejection duty to each region is the same as in FIG. 14B. Further, it is assumed that the fixing time of the ink having a duty of 60% is 3 seconds as in the third embodiment.

  FIG. 16 is an explanatory diagram of Modification 1 of the third embodiment. In this way, by moving the cyan ink head C and the yellow ink head Y to the upstream side in the transport direction, the period from the discharge of cyan to the discharge is 37.5 inches. Therefore, when printing only in cyan as in region 1 in FIG. 14A, the transport speed until paper discharge is 37.5 (inch) / 3 (sec) = 125 (cps).

  The interval between the cyan ink head C and the magenta ink head M is 17.5 inches, and the distance from the magenta ink head M to the paper discharge is 20 inches. Therefore, when printing in blue as in region 2 in FIG. 14A, 17.5 inches between the cyan ink head C and the magenta ink head M must be transported over at least 3 seconds. Therefore, the fastest transport speed in this region is 17.5 (inch) / 3 (sec) = 58.3 (cps). Further, it is necessary to transport 20 inches from the discharge of magenta ink to the discharge of paper over 3 seconds. Accordingly, the fastest conveyance speed during this period is 20 (inch) / 3 (sec) = 66.6 (cps).

  The interval between the cyan ink head C and the yellow ink head Y is 20 inches, and the distance from the yellow ink head Y to the paper discharge is 17.5 inches. Therefore, when printing in green as in region 3 in FIG. 14A, 20 inches between the cyan ink head C and the yellow ink head Y must be transported over 3 seconds. Therefore, the fastest conveyance speed in this region is 20 (inch) / 3 (sec) = 66.6 (cps). Further, 17.5 inches from the discharge of yellow ink to the discharge of paper must be transported over 3 seconds. Therefore, the fastest conveyance speed during this period is 17.5 (inch) / 3 (sec) = 58.3 (cps).

  Therefore, when the image of FIG. 14A is printed, the controller 50 performs the above calculation and selects the lowest transport speed from the determined transport speeds. In this case, it becomes 58.3 (cps). This is faster than 33.3 (cps) obtained in the third embodiment. In this way, it is possible to increase the transport speed by moving the head. Instead of moving the heads, a plurality of nozzle rows are provided in each head in the transport direction as in the modified example of the second embodiment, and the nozzle rows used in each head are selected when printing. You may do it.

(Modification 2 of 3rd Embodiment)
In the second modification of the third embodiment, the calculation method for obtaining the conveyance speed from the duty of each ink is different from that of the above-described embodiment. FIG. 17 is an explanatory diagram of each area of an image to be printed in the second modification of the third embodiment. FIG. 18 shows the relationship between the ejection duty of each ink and the fixing time in the second modification of the third embodiment. FIG. Moreover, FIG. 19A-FIG. 19E is explanatory drawing of the calculation method of the conveyance speed of the modification 2 of 3rd Embodiment. In FIG. 18, the horizontal axis represents the ink ejection duty, and the vertical axis represents the fixing (drying) time of each ink on the paper S. As shown in the figure, the time required for fixing varies depending on the ink color even at the same duty.

  In the second modification of the third embodiment, as shown in FIG. 17, the paper S is divided into a plurality of regions in a lattice shape. In the present embodiment, an optimum transport speed is obtained from five regions of regions 1 to 5 along the transport direction among the plurality of regions.

  First, the controller 50 calculates the ink ejection duty to each region from image print data (data after halftone processing) (FIG. 19A). For example, in region 1, only cyan ink is ejected with a duty of 60%. In area 4, cyan ink is ejected at a duty of 60%, magenta ink is ejected at a duty of 40%, and yellow ink is ejected at a duty of 20%.

  Next, the fixing time of each ink in each region is calculated from the relationship between the ink duty and the fixing time shown in FIG. 18 (FIG. 19B). For example, in region 1, since cyan ink is ejected at a duty of 60%, a fixing time of 3 seconds is required from FIG. 18 until the next head (magenta ink head M). In area 2, since cyan ink and magenta ink are each discharged at a duty of 60%, a fixing time of 3 seconds from the cyan ink head C to the magenta ink head M, and from the magenta ink head M to the yellow ink head Y A fixing time of 4 seconds is required.

  If there is a head that does not eject ink in each region of FIG. 19B, the fixing time by the head upstream in the transport direction from that head is equally divided (FIG. 19C). For example, in region 1, the duty of the magenta ink head M and the yellow ink head Y is 0% from FIG. 19A. In this case, the time (3 seconds) required for fixing the cyan ink (duty 60%) discharged from the cyan ink head C on the upstream side in the transport direction is divided equally (1 second each) between the heads. In region 2, the duty of the yellow ink head Y is 0%. In this case, as shown in FIG. 19C, the time (4 seconds) required for fixing the magenta ink (duty 60%) ejected from the magenta ink head Y on the upstream side in the transport direction of the yellow ink head Y is equally divided ( 2).

  After performing the process of equally dividing the fixing time, the maximum time of the fixing times calculated for each head is obtained in all areas (FIG. 19D).

  Then, the minimum necessary conveyance speed between the heads is obtained from the relationship between the distance between the heads and the maximum fixing time (FIG. 19E), and the lowest conveyance speed is obtained among the obtained conveyance speeds. In FIG. 19E, the cyan ink head C to the magenta ink head M can be conveyed at 33.3 cps. Further, it can be transported at 25 cps from the yellow ink head Y to the paper discharge. Of these, the minimum speed is 25 cps. Note that “MAX” in the figure is a transport speed when fixing takes 6 seconds when the ejection duty of ink of a certain color is 100%. In this case, the maximum value of the conveyance speed is 10 (inch) / 6 (sec) = 16.66 ·· (cps). Thus, in this embodiment, the conveyance speed can be made larger (25 cps) than this conveyance speed, and the conveyance speed can be improved while suppressing bleeding.

(Modification 3 of 3rd Embodiment)
In the third modification, the position of the head is moved according to the print data of each area. The process until the maximum time of each ink is obtained is the same as that of the above-described modification 2 (FIG. 19D). In this case, the total of the maximum time is 11 seconds (= 1 + 3 + 3 + 4), and the total length of 40 inches is transported in 11 seconds. Therefore, the conveyance speed is 40 (inch) / 11 (sec) = 36.4 (cps). Since the required time is known between the heads, the distance between the heads can be determined from this transport speed.

  For example, since the maximum time between the black ink head K and the cyan ink head C is 1 second, the head interval may be set to 36.4 (cps) × 1 (sec) = 3.6 (inch). For example, since the maximum time between the cyan ink head C and the magenta ink head M is 3 seconds, the head interval may be set to 36.4 (cps) × 3 (sec) = 10.9 (inch). Thus, the optimum head interval can be set from the print data of each region.

  In this embodiment, the position of the head is moved. However, as in the modified example of the second embodiment, a plurality of nozzle rows arranged in the transport direction are provided in each head, and each head is set based on the print data. The nozzle array used in each head may be changed.

(Modification 4 of 3rd Embodiment)
In the above-described embodiment, the line printer is used. However, in Modification 4 of the third embodiment, the transport operation for transporting the medium in the transport direction and the head is moved in the direction (moving direction) intersecting the transport direction. A printer (so-called serial printer) is used that prints an image on a medium by repeatedly performing a dot forming operation (hereinafter also referred to as a pass) for discharging ink while forming dots.

FIG. 20 is a perspective view of a printer (serial printer) of Modification 4 of the third embodiment.
The carriage 11 can reciprocate in the moving direction and is driven by a carriage motor (not shown). The carriage 11 also detachably holds an ink cartridge that stores ink.
The head unit 20 ′ has a plurality of heads that eject ink, and is provided on the carriage 11. The head unit 20 ′ of the fourth modification includes a plurality of heads arranged in the movement direction for each ink color, and each head has a nozzle row in which a plurality of nozzles are arranged in the transport direction. Yes.
For this reason, when the carriage 11 moves in the movement direction, the head unit 20 'also moves in the movement direction. Then, while the head unit 20 ′ is moving in the moving direction, ink is intermittently ejected from the nozzle row of each head, thereby forming a dot line (raster line) along the moving direction on the medium.

FIG. 21 is a diagram for explaining an operation in the fourth modification of the third embodiment.
In this modified example 4, first, in each pass, the ejection duty of each ink to each region (region 1 to region 5) along the moving direction by the head unit 20 ′ is obtained. Similarly to the above-described embodiment, the pass speed is changed according to the ejection duty of ink from the heads of the respective colors. In the above-described embodiment, the conveyance time is optimized, but in the fourth modification, the movement time of the head unit 20 ′ in the movement direction is optimized. The optimization method is the same as in the case of a line printer (when the conveyance time is optimized). Thereby, the pass time can be shortened and the printing speed can be improved.
Similarly to the above-described embodiment, the position of the head of each color (in this case, the position in the movement direction) and the position of the nozzle row that ejects ink (position in the movement direction) are changed according to the ink ejection duty. May be.

=== Other Embodiments ===
Although a printer or the like as one embodiment has been described, the above embodiment is for facilitating the understanding of the present invention, and is not intended to limit the present invention. The present invention can be changed and improved without departing from the gist thereof, and it is needless to say that the present invention includes equivalents thereof. In particular, the embodiments described below are also included in the present invention.

<About liquid ejection device>
In the above-described embodiment, an ink jet printer is described as an example of the liquid ejecting apparatus. However, the liquid ejecting apparatus is not limited to the ink jet printer, and ejects fluids other than ink (liquid, liquid material in which functional material particles are dispersed, fluid such as gel). It can also be embodied in a liquid ejection device. For example, color filter manufacturing apparatus, dyeing apparatus, fine processing apparatus, semiconductor manufacturing apparatus, surface processing apparatus, three-dimensional modeling machine, gas vaporizer, organic EL manufacturing apparatus (especially polymer EL manufacturing apparatus), display manufacturing apparatus, film formation You may apply the technique similar to the above-mentioned embodiment to the various apparatuses which applied inkjet technology, such as an apparatus and a DNA chip manufacturing apparatus. These methods and manufacturing methods are also within the scope of application.

<About ink>
Since the above-described embodiment is an embodiment of a printer, ink is ejected from the nozzles, but this ink may be water-based or oil-based. Further, the liquid ejected from the nozzle is not limited to ink. For example, liquids (including water) including metal materials, organic materials (especially polymer materials), magnetic materials, conductive materials, wiring materials, film-forming materials, electronic inks, processing liquids, gene solutions, etc. are ejected from nozzles. May be.

<Ink ejection method>
The ink ejection method for ejecting ink from the nozzles of the printer 1 may be a piezo method in which the ink chamber is expanded or contracted by driving a piezo element, or bubbles are generated in the nozzle using a heating element. Further, a thermal method in which ink is ejected by the bubbles may be used.

<About the scanner>
In the above-described embodiment, the scanner 120 has R, G, and B sensors (for example, a CCD), and reads the reflected light of the light irradiated on the document with each sensor, thereby obtaining R, G, and B color information. Although the sensor-type thing to acquire is used, it is not limited to this. For example, the fluorescent lamps for R, G, and B colors are sequentially blinked, the reflected light is read by a monochrome image sensor, and the R, G, and B color information is acquired, or between the light source and the sensor. An R, G, and B color filter may be provided, and a filter switching type that acquires R, G, and B color information by sequentially switching the color filters may be used.
Further, a sensor may be provided on the downstream side of the transport direction from the head, and the image may be read by the sensor while transporting the printed paper S in the transport direction.

1 printer, 20 head units,
30 transport unit, 32A upstream roller,
32B downstream roller, 34 belt,
40 detector groups, 50 controllers,
51 interface, 52 CPU,
53 memory, 54 unit control circuit,
100 printing systems, 110 computers,
111 interface, 112 CPU, 113 memory,
120 scanner, 121 reading carriage,
122 interface, 123 CPU,
124 memory, 125 controller

Claims (8)

A transport mechanism for transporting the medium in the transport direction;
A plurality of heads arranged side by side in the transport direction, each of which ejects ink of each color onto the medium;
A reading unit that reads an image printed on the medium by the plurality of heads;
When the medium is transported at a reference speed at which the ink ejected from another head upstream of the certain head in the transport direction dries before the ink ejected from the certain head reaches the medium. A comparison unit that compares the reading result of the image with the reading result of the image when the medium is transported at a first transport speed faster than the reference speed;
With
When the comparison result of the comparison unit exceeds an allowable value, the printing apparatus performs the next printing at a second transport speed that is slower than the first transport speed. A transport mechanism for transporting the medium in the transport direction;
A plurality of heads arranged side by side in the transport direction, each of which ejects ink of each color onto the medium;
A reading unit that reads an image printed on the medium by the plurality of heads;
When the medium is transported at a reference speed at which the ink ejected from another head upstream of the certain head in the transport direction dries before the ink ejected from the certain head reaches the medium. A comparison unit that compares the reading result of the image with the reading result of the image when the medium is transported at a first transport speed faster than the reference speed;
With
When the comparison result of the comparison unit does not exceed an allowable value, the printing apparatus performs the next printing at a second conveyance speed that is faster than the first conveyance speed. The printing apparatus according to claim 1 or 2,
The magnitude of the second transport speed is determined according to the comparison result of the comparison unit.
A printing apparatus characterized by that. The printing apparatus according to any one of claims 1 to 3,
The reading unit reads a part of an image printed on a medium,
The comparison unit compares a reading result of a part of the image when the medium is transported at the reference speed and a reading result of the part of the image when the medium is transported at the first transport speed. ,
A printing apparatus characterized by that. The printing apparatus according to any one of claims 1 to 4,
A calculation unit that obtains an ejection amount of ink ejected from each head when the image is printed;
Before performing printing on the medium, the printing apparatus is characterized in that the position in the transport direction for ejecting ink of each head is changed based on the ejection amount obtained by the calculation unit. The printing apparatus according to claim 5,
The plurality of heads are moved in the transport direction, respectively, based on the discharge amount obtained by the calculation unit.
A printing apparatus characterized by that. The printing apparatus according to claim 5,
Each head has a plurality of nozzle rows in which a plurality of nozzle rows arranged in a direction crossing the transport direction are arranged in the transport direction,
Based on the ejection amount obtained by the calculation unit, each nozzle row used in each head is changed,
A printing apparatus characterized by that. The printing apparatus according to any one of claims 5 to 7,
The calculation unit calculates an ink ejection amount of each head for each of a plurality of regions of the medium,
Changing the position in the transport direction for discharging the ink of each head according to the amount of ink discharged for each of the plurality of regions;
A printing apparatus characterized by that.