JP5782984B2 - Printing apparatus and printing method - Google Patents

Description

  The present invention relates to a printing apparatus and a printing method.

  2. Description of the Related Art There is known a printing apparatus that prints an image by ejecting a liquid such as ink from a head unit and landing droplets (dots) on a medium. As a printing apparatus, for example, there is a printing apparatus that ejects photocurable ink (for example, UV ink) that is cured by irradiation with light such as ultraviolet light (UV) or visible light. In such a printing apparatus, UV ink is ejected from a nozzle onto a medium, and then light is applied to UV ink dots formed on the medium. As a result, the UV ink dots are cured and fixed on the medium (for example, Patent Document 1).

JP 2000-158793 A

  In the method of Patent Document 1, the UV ink dots ejected onto the medium are cured by light, so that the occurrence of bleeding (bleeding) between the UV ink dots is suppressed, and an image with good image quality can be easily formed. However, this method still has a problem regarding the color difference of the image. For example, in a so-called line head type printing apparatus that ejects ink from a plurality of head portions arranged in the width direction of a medium, ink dots are applied to the medium due to the effects of misalignment of each head portion or meandering during medium conveyance. The landing position may be shifted. In this case, the printed image has a color difference depending on the location, and the image quality deteriorates. Further, such a problem is not limited to printing using UV ink, but also occurs in printing using normal ink (for example, general water-based ink that is fixed by penetrating into a medium). is there.

  An object of the present invention is to improve the image quality of a printed image in a line head type printing apparatus.

A main invention for achieving the above object includes a first head that ejects a first ink onto a medium conveyed in the conveyance direction, a first head aligned with the first head in the conveyance direction, and a second A second head for ejecting ink, and a head portion having a plurality of head sets in a direction intersecting the transport direction, and a band that is a region from which ink is ejected for each head set. A printing apparatus for printing an image by forming dots by ink and dots by the second ink, and a plurality of patches formed for each head set with dots having different dot diameters for each band Based on the result of measuring the color of the test pattern, a color difference representing a difference in hue between patches formed for each band with dots having the same dot diameter among the plurality of patches is obtained. The amounts of the first ink and the second ink ejected from the first head and the second head included in all the head groups are adjusted so that the dot diameter is determined by the color difference. The printing apparatus is characterized by the above.

  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 an overall configuration of a printer. FIG. 2 is a schematic side view illustrating a configuration of the printer 1. FIG. 3A is a diagram illustrating the arrangement of a plurality of short heads in the color ink heads 31 to 34 and the clear ink head 35 of the head unit 30. FIG. 3B is a diagram illustrating the state of the nozzle rows arranged on the lower surface of each head. It is a figure explaining the drive signal COM. It is a figure explaining the amplitude of a drive pulse. FIG. 6A is a diagram illustrating an image when UV ink dots have landed at an accurate position. FIG. 6B is a diagram for explaining an image when the UV ink dot does not land at an accurate position. FIG. 7A and FIG. 7B are diagrams for comparing the case where an image is printed by changing the dot diameter of ink dots. It is a figure showing the flow of the inspection process in 1st Embodiment. It is a figure showing an example of the test pattern printed in 1st Embodiment. It is a figure explaining concretely about the method of calculating color difference (DELTA) E1 of the _1st patch of each band. It is a figure showing the flow of the process performed by the printer driver in a printing process. It is a figure showing the flow of the inspection process in 2nd Embodiment. It is a figure showing an example of the data put together about color difference (DELTA) E and granularity (sigma) about the test pattern formed with four types of dot diameter of ad. It is a figure showing the flow for determining ink Duty in the inspection process of 3rd Embodiment. It is a figure showing an example of the test pattern printed on a certain band area | region in 3rd Embodiment. It is a figure showing an example of the graph showing the relationship between ink Duty and glossiness.

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

A first head that ejects a first ink onto a medium that is conveyed in the conveying direction; and a second head that is arranged in the conveying direction with the first head and ejects a second ink onto the medium. A plurality of head sets having a plurality of head sets in a direction intersecting the transport direction, and dots formed by the first ink and the second ink in a band which is a region where ink is ejected for each head set. A printing apparatus for printing an image by forming dots according to the above, and based on the result of colorimetric test patterns having a plurality of patches formed for each of the head groups with dots having different dot diameters for each band The color difference representing the difference in hue between the patches formed for each band with the same dot diameter among the plurality of patches is obtained, and the dot diameter determined by the color difference is obtained. Sea urchin, printing apparatus characterized by adjusting the amount of the first ink and the second ink to be ejected from the first head and the second head included in all of the head group.
According to such a printing apparatus, the image quality of an image to be printed can be improved in a line head type printing apparatus.

In such a printing apparatus, the color difference between adjacent bands was calculated from the values measured for each of the plurality of patches formed for each of the head groups with dots having the same dot diameter, and calculated. The first head and the second head included in all the head groups are selected such that the dot diameter is selected so that the color difference is less than or equal to a specified value or the minimum, and the selected dot diameter is obtained. It is desirable to adjust the amount of the first ink and the second ink ejected from the ink.
According to such a printing apparatus, it is possible to print an image with a good image quality with a small color difference by selecting the dot size when the color difference between the bands is equal to or less than the specified value or the minimum and printing the image.

In this printing apparatus, for the values measured for each of the plurality of patches formed for each head set with dots having the same dot diameter, the average value of the measured values and the respective colorimetric values The color difference is calculated based on the difference between the calculated value, the dot diameter is selected so that the calculated color difference is equal to or less than a specified value, and the selected dot diameter is all selected. It is desirable to adjust the amounts of the first ink and the second ink ejected from the first head and the second head included in the head set.
According to such a printing apparatus, it is possible to print an image with a good image quality with a small color difference by selecting the dot size when the color difference between the bands is equal to or less than the specified value or the minimum and printing the image.

In such a printing apparatus, based on the result of measuring the density of each patch with respect to the test pattern, the graininess of patches formed for each head set with dots having the same dot diameter among the plurality of patches The first degree ejected from the first head and the second head included in all the head groups is a dot diameter when the granularity is equal to or less than a predetermined threshold value. It is desirable to adjust the amount of ink and the second ink.
According to such a printing apparatus, it is possible to print a higher quality image by considering the graininess in addition to the color difference between the bands.

The printing apparatus includes a third head that is aligned with the first head in the transport direction and ejects a third ink to the medium, and the first ink is a color ink. When the ink is a clear ink, it is desirable to change the ejection amount per unit area of the third ink in accordance with the ejection amount per unit area of the first ink.
According to such a printing apparatus, an image having a desired glossiness can be printed by controlling the ejection amount of the clear ink in accordance with the ejection amount of the color ink for printing the image. Thereby, a higher quality image can be printed.

In this printing apparatus, it is preferable that the printing apparatus includes an irradiation unit that irradiates light, and the ink is ink that is cured by being irradiated with the light.
According to such a printing apparatus, since the curing of the dots can be controlled by controlling the UV irradiation, it is possible to suppress the bleeding between the dots and form an image with a good image quality. Also, printing can be performed on a medium that does not have an ink receiving layer and does not absorb ink.

  A first head that ejects the first ink onto the medium conveyed in the conveying direction; a second head that is arranged in the conveying direction with the first head and ejects the second ink onto the medium; From a head portion having a plurality of head sets having a plurality of head sets in a direction intersecting the transport direction, a band that is a region where ink is ejected for each head set, and dots formed by the first ink and the second set A printing method for printing an image by forming dots by ink, based on a result of colorimetry for a test pattern having a plurality of patches formed for each head set with dots having different dot diameters for each band Thus, among the plurality of patches, a color difference representing a difference in hue between patches formed for each band with dots having the same dot diameter is obtained, and the dot determined by the color difference is determined. The amount of the first ink and the second ink ejected from the first head and the second head included in all the head sets is adjusted so as to have a diameter. The printing method becomes clear.

=== Basic Configuration of Printing Apparatus ===
A line printer (printer 1) will be described as an example of a printing apparatus used in the present embodiment.

<Configuration of Printer 1>
The printer 1 is a printing apparatus that records an image by ejecting a liquid such as ink toward a medium such as paper, cloth, or film sheet. The printer 1 is an ink jet type printer, but the ink jet type printer may be an apparatus that employs any ejection method as long as it is a printing apparatus capable of printing by ejecting ink.

  The printer 1 prints an image on a medium by ejecting ink that is cured by irradiating light such as ultraviolet light (hereinafter, UV), for example, ultraviolet curable ink (hereinafter, UV ink). The UV ink is an ink containing an ultraviolet curable resin, and is cured by undergoing a photopolymerization reaction in the ultraviolet curable resin when irradiated with UV. In printing using UV ink, it is easy to control the degree of curing of the ink dots formed on the medium and the shape of the ink dots by controlling the UV irradiation amount and irradiation timing. Therefore, as described above, it is possible to form an image with a good image quality by suppressing the occurrence of bleeding that occurs between UV ink dots. Further, by forming dots by curing the UV ink, it is possible to perform printing even on a medium that does not have an ink receiving layer and does not absorb ink.

  Note that the printer 1 according to the present embodiment uses four color inks of black (K), cyan (C), magenta (M), and yellow (Y) as a UV ink, and a colorless and transparent clear ink (CL ) To record an image.

  FIG. 1 is a block diagram showing the overall structure of the printer 1. The printer 1 includes a transport unit 20, a head unit 30, an irradiation unit 40, a detector group 50, and a controller 60. The controller 60 is a control unit that controls each unit such as the head unit 30 and the irradiation unit 40 based on print data received from the computer 110 that is an external device. The situation in the printer 1 is monitored by the detector group 50, and the detector group 50 outputs the detection result to the controller 60. The controller 60 controls each unit based on the detection result output from the detector group 50.

<Computer 110>
The printer 1 is communicably connected to a computer 110 that is an external device. A printer driver is installed in the computer 110. The printer driver is a program for causing a display device to display a user interface and converting image data output from an application program into print data. This printer driver is recorded on a recording medium (computer-readable recording medium) such as a flexible disk FD or a CD-ROM. Also, the printer driver can be downloaded to the computer 110 via the Internet. In addition, this program is comprised from the code | cord | chord for implement | achieving various functions.

  The computer 110 outputs print data corresponding to the image to be printed to the printer 1 in order to cause the printer 1 to print an image. The print data is data in a format that can be interpreted by the printer 1 and includes various command data and pixel data. The command data is data for instructing the printer 1 to execute a specific operation. The command data includes, for example, command data for instructing medium supply, command data indicating the transport amount of the medium, and command data for instructing medium ejection. The pixel data is data related to pixels of an image to be printed.

  Here, a pixel is a unit element constituting an image, and an image is formed by arranging these pixels two-dimensionally. Pixel data in the print data is data (for example, gradation values) related to dots formed on a medium (for example, paper S). The pixel data is composed of, for example, 2-bit data for each pixel. The 2-bit pixel data is data that can express one pixel with four gradations.

<Transport unit 20>
FIG. 2 is a schematic side view showing the configuration of the printer 1 of the present embodiment.
The transport unit 20 is for transporting a medium in a predetermined direction (hereinafter referred to as a transport direction). The transport unit 20 includes a transport roller 23A on the upstream side in the transport direction, a transport roller 23B on the downstream side in the transport direction, and a belt 24 (FIG. 2). When a transport motor (not shown) rotates, the upstream transport roller 23A and the downstream transport roller 23B rotate, and the belt 24 rotates. The medium supplied by a medium supply roller (not shown) is transported to a printable area (area facing a head unit 30 described later) by the belt 24. The medium that has passed through the printable area is discharged to the outside by the belt 24. Note that the medium being conveyed is electrostatically attracted or vacuum attracted to the belt 24.

<Head unit 30>
The head unit 30 is for ejecting UV ink onto the medium. The head unit 30 forms ink dots by ejecting color (KCMY) and clear (CL) inks to the medium being conveyed, and prints an image on the medium. The printer 1 of the present embodiment is a line printer, and each head of the head unit 30 can form dots for the medium width at a time.

  In the printer 1 shown in FIG. 2, color ink heads 31 to 34 are provided in order from the upstream side in the transport direction. The color ink head includes a first color ink head 31 (hereinafter also referred to as the first head 31), a second color ink head 32 (hereinafter also referred to as the second head 32), and a third color ink head 33 (hereinafter referred to as the first head 31). And a fourth color ink head 34 (hereinafter also referred to as a fourth head 34). In the present embodiment, black ink (K) from the first head 31, cyan ink (C) from the second head 32, magenta ink (M) from the third head 33, and yellow ink (Y from the fourth head 34). ). However, it is arbitrary which color ink each of the color ink heads 31 to 34 ejects. For example, the first head 31 ejects yellow ink (Y) and the second head 32 ejects black ink (B). You may make it eject. However, in this embodiment, it is assumed that the same color ink is not ejected from different heads. For example, when the first head 31 ejects the black ink (B), the second head 32 to the second head 34 do not eject the black ink (B). In addition to the color ink heads 31 to 34, a color ink head that ejects ink of a color other than the above-described KCMY (for example, light cyan or metallic color) may be provided.

  On the downstream side of the color ink head 34 in the transport direction, a clear ink head 35 that ejects colorless and transparent clear (CL) UV ink is provided. Here, the clear (CL) ink is an ink generally referred to as “clear ink” which does not contain or contains a color material. Hereinafter, the clear ink head 35 is also referred to as a fifth head 35.

  Each head is composed of a plurality of short heads, and each short head is provided with a plurality of nozzles that are ejection ports for ejecting UV ink.

  FIG. 3A is a diagram illustrating the arrangement of a plurality of short heads in the color ink heads 31 to 34 and the clear ink head 35 of the head unit 30. FIG. 3B is a diagram for explaining a state of nozzle rows arranged on the lower surface of each short head. 3A and 3B are views of the nozzle virtually seen from above.

  In the first head 31, eight short heads 31 </ b> A to 31 </ b> H are arranged in a staggered pattern along the width direction of the medium that is a direction intersecting the medium conveyance direction. Similarly, in the second head 32, eight short heads 32A to 32H are arranged in a staggered pattern along the width direction. The same applies to the third head 33, the fourth head 34, and the fifth head 35 (FIG. 3A). In the example of FIG. 3A, each head is composed of eight short heads, but the number of short heads constituting each head may be more or less than eight.

  The eight short heads of each head are provided so that their positions are aligned in the width direction of the medium. That is, the nth short head 31n of the first head, the nth short head 32n of the second head, the nth short head 33n of the third head, the nth short head 34n of the fourth head, The nth short head 35n of the fifth head is provided at the same position in the width direction. These five short heads are defined as the nth “head set”. In FIG. 3A, eight head groups A to H are formed. Then, UV ink is ejected from each head set onto the medium to form dots, thereby forming an image in an area having a predetermined width in the medium width direction. This region is called a “band”. For example, the area corresponding to the head set A composed of 31A to 35A is the band A, and the KCMY color ink is ejected from the short heads 31A to 34A, respectively, and the clear ink is ejected from the short head 35A. An image is formed in the area. Similarly, an image is formed in the band B to band H by ejecting ink from the corresponding head group (B to H). In this way, an image to be printed (entire image) is formed by the bands A to H arranged in the medium width direction.

  A plurality of nozzle rows are formed in each short head (FIG. 3B). The nozzle row includes 180 nozzles that eject ink, and the nozzles are arranged at a constant nozzle pitch (for example, 360 dpi) from # 1 to # 180 along the width direction of the medium. In the case of FIG. 3B, two nozzle rows are arranged in parallel, and the nozzles of each nozzle row are provided at positions shifted by 720 dpi in the width direction of the medium. The number of nozzles in one row is not limited to 180. For example, 360 nozzles may be provided in one row, or 90 nozzles may be provided. Further, the number of nozzle rows provided in each short head is not limited to two rows.

  Each nozzle is provided with an ink chamber and a piezoelectric element (both not shown) which are piezoelectric elements. The piezo element is driven by a drive signal COM generated by the unit control circuit 64. Then, the ink chamber expands and contracts by driving the piezo element, and the ink filled in the ink chamber is ejected from the nozzle.

  In the printer 1, a plurality of types of ink droplets having different sizes (different ink amounts) can be ejected from each nozzle according to the magnitude of a pulse applied to the piezo element in accordance with the drive signal COM. For example, from each nozzle, there are three types of ink consisting of large ink droplets capable of forming large dots, medium ink droplets capable of forming medium dots, and small ink droplets capable of forming small dots. Can be ejected. Then, ink droplets are intermittently ejected from each nozzle to the medium being transported, whereby each nozzle forms a dot line (raster line) along the medium transport direction. The relationship between the drive signal COM and the size of dots formed by the drive signal will be described later.

<Irradiation unit 40>
The irradiation unit 40 irradiates UV toward the UV ink dots landed on the medium. The dots formed on the medium are cured by receiving UV irradiation from the irradiation unit 40. The irradiation unit 40 of this embodiment includes an irradiation unit 41.

  The irradiation unit 41 is provided on the downstream side in the transport direction of the clear ink head 35 (FIG. 2), and UV for curing the UV ink dots formed on the medium by the color ink heads 31 to 34 and the clear ink head 35. Irradiate. The length of the irradiation unit 41 in the medium width direction is equal to or greater than the medium width.

  In the present embodiment, the irradiation unit 41 includes a light emitting diode (LED) as a light source for UV irradiation. The LED can easily change the irradiation energy by controlling the magnitude of the input current. Moreover, you may use light sources other than LED, such as a metal halide lamp, as the irradiation part 41. FIG. The light source of the irradiation unit 41 is isolated from the clear ink head 35 (and the color ink heads 31 to 34) by being accommodated in the irradiation unit 41. This prevents the UV light emitted from the light source from leaking to the lower surface of the clear ink head 35, so that the UV ink is cured in the vicinity of the opening of each nozzle formed on the lower surface, so that the nozzles are clogged. Is suppressed from occurring.

  In FIG. 2, the irradiation unit 40 includes only one irradiation unit 41 on the most downstream side in the transport direction. However, the irradiation unit 40 may include one irradiation unit 41 downstream of each color ink head.

  Further, the irradiation unit 42 (not shown) is further provided on the most downstream side in the transport direction, and the UV ink dots are cured in two steps by irradiating UV from the irradiation unit 41 and the irradiation unit 42. May be. For example, UV is irradiated from the irradiation unit 41 with energy sufficient to cure (temporarily cure) the surface of the UV ink dots, and the entire UV ink dots are cured (completely cured) from the irradiation unit 42 at the final stage of medium conveyance. Irradiate with UV energy. As a result, the degree of cure of the UV ink dots is adjusted, and when the UV ink dots are ejected from each head, there is a problem that the landing positions of the dots are shifted due to the repelling of the UV ink dots having a high degree of cure. It can also be difficult.

<Detector group>
The detector group 50 includes a rotary encoder (not shown), a medium detection sensor (not shown), and the like. The rotary encoder detects the rotation amount of the upstream side conveyance roller 23A and the downstream side conveyance roller 23B. The transport amount of the medium can be detected based on the detection result of the rotary encoder. The medium detection sensor detects the position of the front end of the medium being supplied.

<Controller>
The controller 60 is a control unit (control unit) for controlling the printer. The controller 60 includes an interface unit 61, a CPU 62, a memory 63, and a unit control circuit 64.
The interface unit 61 transmits and receives data between the computer 110 that is an external device and the printer 1. The CPU 62 is an arithmetic processing device for performing overall control of the printer 1. The memory 63 is for securing an area for storing a program of the CPU 62, a work area, and the like, and is configured by a storage element such as a RAM or an EEPROM. Then, the CPU 62 controls each unit such as the transport unit 20 via the unit control circuit 64 in accordance with a program stored in the memory 63.

<Image printing operation>
An image printing operation by the printer 1 will be briefly described.
When the printer 1 receives print data from the computer 110, the controller 60 first rotates a medium supply roller (not shown) by the transport unit 20 and sends the medium to be printed onto the belt 24. The medium is conveyed on the belt 24 without stopping at a constant speed, and passes through the head unit 30 and the irradiation unit 40.

During this time, color ink (KCMY) is intermittently ejected from the nozzles of the color ink heads 31 to 34, thereby forming characters and images made up of color ink dots on the medium. Further, the clear ink (CL) is intermittently ejected from each nozzle of the clear ink head 35 to form clear ink dots at predetermined pixels. Then, the color ink dots and the clear ink dots are cured by irradiating UV from the irradiation unit 41 of the irradiation unit 40. Thus, an image is printed on the medium.
Finally, the controller 60 discharges the medium on which image printing has been completed.

=== Description of Drive Signal COM ===
FIG. 4 is a diagram for explaining the drive signal COM. As shown in the figure, the drive signal COM is generated using a period T with the rising timing of the latch signal LAT as a unit. The latch signal is a signal that serves as a mark for starting / ending other signals. The period T includes sections T1 to T4 divided by the rising timing of the latch signal LAT or the change signal CH. The sections T1 to T4 include drive pulses described later. A period T that is a repetition period corresponds to a period during which the nozzle moves by one pixel with respect to the medium. For example, when the print resolution is 720 dpi, the period T corresponds to a period during which the medium is conveyed 1/720 inch. The ink ejected from the nozzles is applied to the piezo elements by applying the drive pulses PS1 to PS4 in each section included in the period T based on the pixel data SI that is data representing the ink dots formed for each pixel. By adjusting the amount of the image, it is possible to express an image composed of a plurality of gradations.

The drive signal COM includes a first waveform section SS1 generated in the section T1 in the repetition period, a second waveform section SS2 generated in the section T2, a third waveform section SS3 generated in the section T3, and a section T4. And a fourth waveform section SS4 to be generated. Here, the first waveform section SS1 has a drive pulse PS1. The second waveform section SS2 has a drive pulse PS2, the third waveform section SS3 has a drive pulse PS3, and the fourth waveform section SS4 has a drive pulse PS4.

  Assuming that the pixel data SI is data represented by 2 bits, when the pixel data SI is [00], the first section signal SS1 of the drive signal COM is applied to the piezo element PZT, and the piezo element PZT is driven by the drive pulse PS1. Driven by. When the piezo element PZT is driven in accordance with the drive pulse PS1, pressure fluctuations such that ink is not ejected occur in the ink, and the ink meniscus (the free surface of the ink exposed at the nozzle portion) vibrates slightly.

  When the pixel data SI is [01], the third interval signal SS3 of the drive signal COM is applied to the piezo element PZT, and the piezo element PZT is driven by the drive pulse PS3. When the piezo element PZT is driven according to the drive pulse PS3, a small amount of ink is ejected, and a small dot is formed on the medium.

  When the pixel data SI is [10], the second interval signal SS2 of the drive signal COM is applied to the piezo element PZT, and the piezo element PZT is driven by the drive pulse PS2. When the piezo element PZT is driven according to the drive pulse PS2, a medium amount of ink is ejected, and a medium dot is formed on the medium.

  When the pixel data SI is [11], the second interval signal SS2 and the fourth interval signal SS4 of the drive signal COM are applied to the piezo element PZT, and the piezo element PZT is driven by the drive pulse PS2 and the drive pulse PS4. When the piezo element PZT is driven according to the drive pulse PS2 and the drive pulse PS4, a large dot is formed on the medium.

  Also, the size of each type of dot (the amount of ink ejected for each small, medium, and large dot) is defined by the amplitude of the drive pulse waveform. FIG. 5 is a diagram for explaining the amplitude of the drive pulse. FIG. 5 is an example in which the drive pulse PS2 for forming the above-described medium dots is enlarged. The amplitude of the drive pulse PS2 is expressed by a potential difference Vh between the maximum voltage Vmax and the minimum voltage Vmin, and the actual drive amount of the piezo element (the expansion / contraction amount of the ink chamber) is determined by the magnitude of Vh. That is, the amount of ink ejected from the nozzles is changed by changing the amplitude Vh of the pulse waveform. For example, when the amplitude of PS2 is Vh, a 3 pl ink droplet is ejected to form a 3 pl dot (medium dot). Further, when the amplitude of PS2 is changed to Vha represented by the broken line in FIG. 5 (Vha> Vh), 3.5 pl of ink is ejected, and medium dots that are slightly larger than when PS2 has an amplitude of Vh are formed. The Further, when the amplitude of PS2 is changed to Vhb represented by a one-dot chain line in FIG. 5 (Vh> Vhb), 2.5 pl of ink is ejected, and a medium dot slightly smaller than that when PS2 has an amplitude of Vh is formed. Is done.

  Thus, even when the same type of dots (medium dots in the above example) are formed, the size (dot diameter) of the dots to be formed can be adjusted by changing the amplitude of the drive pulse. Is possible. The same applies when forming small dots and large dots.

=== About the Printed Image ===
Next, an image printed by the printer 1 will be described. As described above, the printer 1 prints an image by forming UV ink dots in the bands A to H corresponding to the eight head groups A to H, respectively. At the time of printing, print data (pixel data) is generated from the original image data, and an image is formed by ejecting ink dots of a predetermined size into pixels specified by the print data (pixel data). . Therefore, if the ink dots are accurately formed at the positions (pixels) designated by the print data, an image with good image quality can be obtained. However, when the ink dots are formed at positions shifted from the positions (pixels) designated by the print data, the image quality of the formed image is deteriorated.

  FIG. 6A is a diagram illustrating an image when UV ink dots have landed at an accurate position. FIG. 6B is a diagram for explaining an image when the UV ink dot does not land at an accurate position. In both cases, an example of printing an image on the band A using the short head 31A (hereinafter also referred to as the first head 31A) and the short head 32A (hereinafter also referred to as the second head 32A) of the head set A is shown. Shows about. The white circles in the figure represent dots formed by the first head 31A, and the black circles represent dots formed by the second head 32A. In FIG. 6A and FIG. 6B, the number of dots to be formed and the size of the dots are schematically drawn for explanation, and the dots actually formed at the time of printing are different from these. is there.

  In FIG. 6A, when the positional relationship between the two short heads 31A and 31B is normal (there is no deviation in the width direction), and the medium is transported straight in the transport direction, that is, the factors that cause the dot landing positions to shift This shows how dots are formed when there are few dots. In this case, the ink dots ejected from both heads accurately land on the pixels designated by the print data. The position of each dot shown in FIG. 6A indicates an accurate landing point. As shown in the figure, when the positions in the width direction of the first head 31A and the second head 32A are aligned, in other words, when there is no misalignment of the head, dots (white circles) formed by the first head 31A and the second There is no deviation in the landing position in the width direction with the dot (black circle) formed by the head 32A.

  On the other hand, in FIG. 6B, of the two short heads, the position of the second head 32A is shifted in the medium width direction, in other words, the dot formed when the head is misaligned. It represents the situation. Dots (white circles) formed by the first head 31A that is not displaced are landed at the same position as in FIG. 6A. On the other hand, the dots (black circles) formed by the second head 32A in which misalignment occurs have landed at positions shifted in the medium width direction as compared with FIG. 6A. That is, the dots indicated by black circles are formed at positions shifted from the pixels specified by the print data. In addition to the influence of the head misalignment, such landing position deviation also occurs when the medium is meandered and conveyed.

  Comparing FIG. 6A and FIG. 6B, since the landing positions of dots (black circles) formed by the second head 32A in band A are different, both images appear to have different impressions. For example, in FIG. 6A and FIG. 6B, the difference in color of the image (color difference) increases. Since the landing positions of the ink dots are shifted, the center-to-center distance between the white circle and the black circle is changed, so that a difference is generated in the overlapping manner of the ink dots of the respective colors, thereby generating a color difference.

  6A and 6B has a difference in gloss (gloss difference). Since the landing positions of the ink dots are shifted, a region where dots are formed “dense” and a region where “sparse” is formed on the medium surface is generated. In the portion where the dots are formed “densely”, the image surface is also close to a flat shape, so that the light incident on the image surface (medium surface) is regularly reflected and the glossiness is increased. On the other hand, in the portion where the dots are formed "sparsely", the dots are dispersed and the image surface becomes rough, and the light incident on the image surface (medium surface) is scattered and reflected, resulting in a low glossiness. Therefore, the glossiness appears to change partially on the image surface.

  As described above, when a deviation occurs in the landing positions of the ink dots, the color difference or the gloss difference increases depending on the location, and the image quality deteriorates. That is, when the color difference or the gloss difference increases between the bands assigned to each head group, the image quality of the printed image deteriorates. Such a deviation in the landing position of the ink dots occurs for each manufactured printer due to an attachment error (alignment deviation) of the head unit 30 in the manufacturing stage of the printer 1, a conveyance characteristic of the conveyance unit 20, and the like. It is an inherent problem. Therefore, in order to print an image with good image quality, it is necessary to perform correction for each printer.

=== First Embodiment ===
In the first embodiment, in order to suppress the deterioration of the image quality of the print image as described above, the color difference for each band is corrected, and an image having a good image quality with little difference in hue over the entire image is printed. Specifically, the dot diameter of the dots formed on the medium is changed by adjusting the magnitude (see FIG. 5) of the pulse amplitude Vh of the drive signal COM. When the size of the dots changes, the ratio of dots formed in a predetermined area of the medium and the manner in which the dots overlap each other change, and the color difference between bands changes accordingly.

  FIG. 7A and FIG. 7B are diagrams for comparing cases in which images are printed by changing the dot diameter of ink dots. FIG. 7A shows an example when printing is performed with a certain predetermined dot diameter, and FIG. 7B shows an example when printing is performed with a larger dot diameter than FIG. 7A. In both figures, the figure shown on the left side shows a case where no deviation of the dot landing position occurs, and the figure shown on the right side shows a case where the deviation of the dot landing position occurs by a in the width direction. Also, the dots represented by the white circles in the figure and the dots represented by diagonal lines are dots ejected from different heads (short heads). Represents.

  In FIG. 7A, when there is no deviation in the landing position (left figure), overlap between dots is seen, but when there is a deviation in landing position (right figure), there is no overlap between dots. can not see. That is, in the example of FIG. 7A, a difference is easily caused in the overlapping of dots formed on the medium due to the deviation of the landing position. For example, in the diagram on the left side of FIG. 7A, compared with the diagram on the right side, a region where dots overlap with each other by the area of the blackened portion is larger. This means that the overlapping ratio of the KCMY color ink dots changes during actual printing, and the difference in color (color difference) of the formed image becomes conspicuous.

  On the other hand, in FIG. 7B, the dot formed on the medium is different when the landing position is not shifted (left figure) and when the landing position is shifted (right figure). There is little difference in how they overlap. For example, in the diagram on the left side and the diagram on the right side of FIG. 7B, the total area of the black portions of the dots is approximately the same, and therefore the ratio of overlapping dots on the medium is also approximately the same. At the time of actual printing, if the overlapping areas of ink dots of different colors are about the same, the colors expressed by these ink dots look similar. Therefore, the difference in color (color difference) of the printed image is less noticeable despite the positional deviation of the dots.

  As described above, even when the dot landing position is deviated, the influence on the color difference of the image varies depending on the change of the dot diameter. However, when printing is actually performed, the amount of ink ejected per predetermined area on the medium is partially different depending on the gradation value specified by the print data. I can't say it will be smaller.

  Therefore, in the present embodiment, the pulse amplitude Vh (drive signal COM) is adjusted so that the dot diameter formed during printing becomes an optimum size. As a result, even when a dot landing position is shifted due to misalignment or the like, an image with good image quality is printed so that the color difference between the bands is less noticeable.

<Overview of dot diameter adjustment>
An outline of an operation for performing printing so that the color difference generated between the bands is equal to or less than a certain value (specified value) or the color difference is minimized in printing using the printer 1 will be described.

  In this embodiment, an image is printed while adjusting the size of the dot diameter in two steps, an inspection step and a printing step. In the inspection process, the color difference actually generated for each band is measured by performing color measurement on the test pattern to be printed while changing the amplitude Vh of the pulse waveform (that is, changing the dot diameter) using the printer 1. Is calculated. In order to select the dot diameter when the calculated color difference between the bands is equal to or less than the predetermined value, or the dot diameter when the color difference is the smallest, and form the dot diameter on the storage medium such as the memory 63 of the printer 1. The waveform of the drive signal COM (the amplitude Vh of the pulse waveform) is stored. Subsequently, in the printing process, an image is actually printed by ejecting ink dots from all the heads so as to have the dot diameter stored in the inspection process. Details of each step will be described below.

<Inspection process>
In the inspection process, color measurement is performed by printing a test pattern composed of a plurality of patches, and a pulse amplitude Vh that defines the size (dot diameter) of the ink dots to be ejected from each head is determined based on the result. This Vh is commonly used for all the heads of the head unit 40 during printing. FIG. 8 shows a flow chart of the inspection process. The inspection process is performed by executing the processes of S101 to S105.

  First, a test pattern is printed (S101). The test pattern is formed by printing a plurality of patches for each of the eight bands A to H using KCMY color inks. The test pattern is printed on the same medium as that used for actual printing.

  FIG. 9 shows an example of a test pattern printed in this embodiment. As shown in the figure, the test pattern printed in the present embodiment has a plurality of rectangular patches for each band. For example, in FIG. 9, each of the bands A to H has four patches 1 to 4, and a total of 8 × 4 = 32 patches are formed. Hereinafter, the patch 1 in the band A is expressed as “patch A-1”. If codes (A-1, A-2,..., H-4) representing the patches are printed in the vicinity of each patch as shown in FIG. 9, the data is stored during the color measurement (S102) in the next process. Mistakes are less likely to occur. Also, the shape of the patch need not be rectangular.

  Each patch is printed with a predetermined tone value in a predetermined color by ejecting UV ink from each of the first to fourth heads. Here, for the sake of explanation, it is assumed that each patch is formed of only medium dots. For example, the patch A-1 is formed by medium dots of four color inks (KCMY). Then, by gradually changing the magnitude of the pulse amplitude Vh (see FIG. 5) of the drive signal COM, the dots belonging to the same band are formed so that the dot diameter of the medium dots gradually increases. That is, among patches 1 to 4, patch 1 forms the smallest medium dot by the pulse waveform of amplitude Vh1. Similarly, in the patch 2, medium dots are formed so that the dot diameter gradually increases with the pulse waveform with the amplitude Vh2 (Vh1 <Vh2) and with the patch 3 with the pulse waveform with the amplitude Vh3 (Vh2 <Vh3). In the patch 4, the largest medium dot is formed by the pulse waveform (Vh3 <Vh4) having the amplitude Vh4. For example, in band A, patch A-1 is formed with medium dots of 2.5 pl of ink, patch A-2 is formed of medium dots of 3.0 pl, and patch A-3 is formed of 3.5 pl. The patch A-4 is formed with medium dots of 4.0 pl. Here, it is assumed that a dot having a larger dot diameter is formed when the ink lands on the medium as the ink ejection amount is larger.

  All patches with the same number are formed by dots having the same dot diameter. For example, all the eight patches A1 to H1 included in the area surrounded by the broken line in FIG. 9 are formed by medium dots of 2.5 pl. In FIG. 9, four types with four types of dot diameters are used for each band. However, by adjusting the pulse amplitude Vh of the drive signal COM described above, five or more types of patches can be formed for each band while finely changing the dot diameter. it can. By increasing the types of patches (types of dot size) in each band, it is possible to further improve the accuracy of image correction.

Subsequently, color measurement is performed for each of the formed patches (S102). Patch colorimetry is performed using a colorimeter. The colorimeter is a spectrocolorimeter for measuring a colorimetric value in a predetermined range of an image and acquiring it as a colorimetric value in the predetermined range, and a general spectrophotometer can be used. The colorimetric values acquired for each patch are expressed as color component values in the L * a * b * color space, and the colorimetric values are temporarily stored in the memory 63 or the like. For example, the colorimetric value acquired from the patch A-1 is stored as (E _A1 ) = (L _A1 *, a _A1 *, b _A1 *). The colorimetric value may be measured as each color component of another color space (for example, XYZ color space or L * u * v * color space).

  Next, a color difference ΔE between patches formed with the same dot diameter is calculated (S103). As described above, since the hue changes in an image formed by a head set in which misalignment occurs, colorimetric values between bands depending on the state of the head set in which patches formed with the same dot diameter are formed. May be different. Therefore, the difference in colorimetric value between bands is calculated as a color difference. In this embodiment, the color difference ΔE is calculated by comparing the difference between the average value of the colorimetric values of a plurality of patches formed with the same dot diameter and the colorimetric value of each patch.

（式１）において、Ｌ_ｍｎ＊はパッチｍ−ｎから測定されたＬ＊値を表し、Ｌ_ｎave＊は８つのバンドの第ｎ番目のパッチのＬ＊値（Ｌ_Ａｎ＊，Ｌ_Ｂｎ＊，〜，Ｌ_Ｈｎ＊）の平均を表す。ａ_ｍｎ＊、ａ_ｎave＊、ｂ_ｍｎ＊、ｂ_ｎave＊についても同様である。
そして、バンドＡ〜Ｈのそれぞれ第ｎ番目のパッチについて求められたΔＥ_Ａｎ〜ΔＥ_Ｈｎのうちの最大値ΔＥ_ｎ（max）と、最小値ΔＥ_ｎ（min）との差が、第ｎ番目のパッチの色差ΔＥ_ｎとして算出される。 First, for the nth patch (patch mn) belonging to the band m, the average value of the colorimetric values of the patches (nth patch of each band) formed with the same dot diameter and the patch mn A difference ΔE _mn from the colorimetric value is obtained. ΔE _mn is calculated by the following (Equation 1).

In (Equation 1), L _mn * represents the L * value measured from the patch _mn , and L _nave * is the L * value (L _An *, L _Bn *, L) of the nth patch in the eight bands. ~, L _Hn *) average. The same applies to a _mn *, a _nave *, b _mn *, and b _nave *.
The difference between the maximum value ΔE _{n (max)} and the minimum value ΔE _{n (min) of} ΔE _An to ΔE _Hn obtained for each of the nth patches of the bands A to H is the nth It is calculated as the color difference ΔE _n of the patch.

FIG. 10 is a diagram specifically explaining a method for calculating the color difference ΔE ₁ of the first patch in each band. First, eight measurements obtained from patches (first patch of each band) A-1, B-1,..., H-1 formed with the same dot diameter belonging to the area surrounded by the broken line in FIG. Color value data (E _A1 ), (E _B1 ), ˜, (E _H1 ) are measured. (E _A1 ) to (E _H1 ) are data having variations as shown in FIG. Then, differences ΔE _{A1 to} ΔE _H1 between each colorimetric value data and the average value E _1ave of the eight data are calculated. As shown in (Expression 1), ΔE _mn is calculated as an absolute value. Next, a minimum value and a maximum value are obtained for the eight pieces of data ΔE _A1 to ΔE _H1 calculated. In the example of FIG. 10, the maximum value ΔE _{1 (max)} is ΔE _D1 , and the minimum value ΔE _{1 (min)} is ΔE _G1 . Then, the difference between the maximum value and the minimum value (ΔE _D1 −ΔE _G1 ) is calculated as the inter-band color difference ΔE ₁ in the first patch.

The color difference ΔE _n may be calculated as an average value of ΔE _An to ΔE _Hn . That is, it may be calculated as ΔE _n = (ΔE _An + ΔE _Bn + to + ΔE _Hn ) / 8.

The dot diameter when the color difference ΔE _n is equal to or smaller than a certain value (specified value) or when the color difference ΔE _n is the smallest is selected and determined as the dot diameter used during actual printing (S104). The determined dot diameter is stored in the memory 63 (S105). For example, in the case of FIG. 9, the color differences ΔE _{1 to} ΔE _{4 of the first to} fourth patches are calculated in the eight bands A to H, respectively. Among the four calculated color differences, ΔE is equal to or smaller than a predetermined value (for example, the color difference is 10) or the dot diameter (2.5 pl, 3.0 pl, 3.5 pl, 4. A medium dot of any size of 0 pl) is determined as a dot diameter (medium dot) used during actual printing. In other words, the pulse amplitude Vh that can form the optimum dot diameter is determined.

  Here, the color difference is conspicuous in an actual image when the color difference generated between adjacent bands (for example, between bands BC and between bands DE) is large. Therefore, a method using the color difference between adjacent bands as a reference for selecting the dot diameter may be used.

In this case, the color difference between adjacent bands is calculated for each of the eight bands A to H, and the dot diameter is selected so that the color difference between the adjacent bands is equal to or less than a specified value. Specifically, the color difference between adjacent bands A-B (| E _A1 -E _B1 |), the color difference between bands B-C (| E _B1 -E _C1 |), ..., the color difference between bands GH Seven color differences of (| E _G1 −E _H1 |) are calculated, and when the calculated color differences are each a predetermined value (for example, the color difference is 10) or less, or the average value of the color differences is the minimum or the predetermined value or less. The dot diameter at that time is selected as the dot diameter used during actual printing (S104) and stored in the memory 63 (S105).

  Then, by forming an image with dots having a dot diameter when the color difference ΔE between the bands is less than or equal to the specified value, the difference in hue between the bands is less noticeable, and the entire image is printed with good image quality. It becomes possible to do.

  In the above example, each patch is formed only with medium dots. However, when printing is performed using, for example, 2-bit pixel data during actual printing, small dots, medium dots, large dots, etc. An image is formed by a plurality of types of dots. Therefore, when a test pattern is formed, one patch is mixed with small dots, medium dots, and large dots. That is, in the step S101 described above, test patterns are formed for sets of small, medium, and large dots that are formed when the amplitude of the drive signal COM is Vh1 to Vh4. For example, the patch A-1 is composed of small dots, medium dots, and large dots formed in the region of the band A by the pulse waveform having the amplitude Vh1, and the patch B-2 is the band B by the pulse waveform having the amplitude Vh2. It is composed of small dots, medium dots, and large dots formed in this area.

  By performing the processing of S102 to S105 for such a test pattern, the size of each dot (pulse) when the color difference ΔE between the bands is less than or equal to the specified value or less in printing using a plurality of types of dots. A drive signal COM) having a waveform amplitude Vh is determined. When printing is actually performed, small, medium, and large dots are formed using the drive signal COM having the determined pulse amplitude Vh, so that the difference in hue between bands is less noticeable, and the entire image is displayed. It is possible to print with better image quality.

<Printing process>
In the printing process, an image is actually printed using the printer 1 under the user. At this time, printing is performed using a drive signal COM having an amplitude Vh of a pulse waveform that has a dot diameter determined in the inspection process.

  When the user of the printer 1 instructs printing of an image drawn on the application program, the printer driver of the computer 110 is activated. 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, and the like. FIG. 11 is a diagram illustrating a flow of processing performed by the printer driver in the printing process.

  First, a process (resolution conversion process) for converting image data (text data, image data, etc.) output from an application program into a resolution (print resolution) for printing on a medium is performed (S201). 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.

  Each pixel data of the image data after the resolution conversion process is RGB data of each gradation (for example, 256 gradations) represented by the RGB color space.

  Next, color conversion processing for converting RGB data into data in the CMYK color space is performed (S202). The image data in the CMYK color space is data corresponding to the ink color of the printer. 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.

  The pixel data after the color conversion processing is 8-bit CMYK data with 256 gradations represented by the CMYK color space.

  Next, halftone processing is performed to convert the high gradation number data into gradation number data that can be formed by the printer (S203). For example, data representing 256 gradations is converted into 1-bit data representing 2 gradations or 2-bit data representing 4 gradations by halftone processing. In the halftone process, a dither method, a γ correction, an error diffusion method, or the like is used. The data subjected to the halftone process has a resolution equivalent to the print resolution (for example, 720 × 720 dpi). The image data after halftone processing corresponds to 1-bit or 2-bit pixel data for each pixel, and this pixel data is data indicating the dot formation status (presence / absence of dot, dot size) in each pixel. Become.

  Thereafter, rasterization processing is performed in which the pixel data arranged in a matrix is rearranged for each pixel data in the order of data to be transferred to the printer 1 (S204). For example, the pixel data is rearranged according to the arrangement order of the nozzles in each nozzle row.

  Command addition processing for adding command data according to the printing method to the rasterized data is performed (S205). 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. Printing is actually performed by the printer 1. At the time of printing, each drive signal COM having a predetermined pulse amplitude Vh stored in the memory 63 is formed so as to form dots having a dot diameter that minimizes the color difference between bands determined in the inspection process. Applied to the piezo element of the nozzle. As a result, the diameters of the ink dots (small, medium, and large dots) ejected from all the heads (nozzles) are made uniform, and the color difference between the bands is inconspicuous.

  In the above example, the configuration in which various processes in the printing process are executed by the printer driver installed in the computer 110 has been described. However, the printer driver is installed in the controller 60 of the printer 1, and the printer 1 Processing may be performed.

<Summary of First Embodiment>
In the first embodiment, in the inspection process, based on the result of printing a test pattern having a plurality of patches formed for each head group with dots having different dot diameters for each band and measuring the color of the test pattern. Find the color difference between patches in each band. The color difference represents a difference in colorimetric values between patches formed for each band with dots having the same dot diameter among a plurality of patches. Then, the dot diameter when the color difference between the bands is less than or equal to the specified value or the minimum is selected as the dot diameter used for printing and stored in a memory or the like. Thereafter, in the printing process, ink is ejected from each of the head groups so as to achieve the determined dot diameter.
Thereby, in a line head type printing apparatus such as the printing apparatus 1, it is possible to print an image with good image quality in which the difference in hue between bands is not noticeable.

=== Second Embodiment ===
According to the method of the first embodiment, paying attention to the color difference between the bands, the color difference is reduced as much as possible by adjusting the drive signal COM so that the dot diameter becomes a predetermined size. Image quality can be improved. However, if the dot diameter is determined by paying attention only to the color difference between the bands, the graininess of the image may deteriorate even if the color difference can be made inconspicuous. The graininess represents the degree of roughness of the entire image. For example, if the ink dots (particles) formed on the medium are too large, the individual particles stand out and give the impression that the image is rough. Therefore, when printing is performed using the printing apparatus 1, even if the color difference between the bands is small, if the graininess is bad, the image quality of the printed image is deteriorated.
Therefore, in the second embodiment, an image with higher image quality is printed by considering the granularity of the image in addition to the color difference between the bands.

式２でＤｉは画像中の或る場所における濃度データ（第ｉ番目の濃度データ）を表し、ｎは濃度データの個数を表す。また、Ｄaveはｎ個の濃度データの平均値を表す。 <About graininess>
A concept for evaluating the degree of graininess is granularity. In this embodiment, “RMS granularity” is used to evaluate the granularity of an image.
The RMS granularity represents a variation in image density as a root-mean-square and is calculated by the following equation (2).

In Equation 2, Di represents density data (i-th density data) at a certain location in the image, and n represents the number of density data. Dave represents an average value of n density data.

<Inspection Process of Second Embodiment>
The second embodiment differs from the first embodiment in the processing until the determination of the pulse amplitude Vh for forming a dot having the optimum dot diameter in the inspection process. The configuration of the printing apparatus and the various processes in the printing process are the same as in the first embodiment.
FIG. 12 is a diagram showing a flow of the inspection process in the second embodiment. Steps S121 to S123 and S127 are the same as the corresponding steps (S101 to S103, S105) of the first embodiment, and steps S124 to S126 are different from those of the first embodiment. Hereinafter, different points will be described.

  In the inspection process of the second embodiment, after printing and measuring the test pattern to calculate the color difference ΔE (S121 to S123), the density of each patch of the test pattern is measured (S124). The test pattern used is the same as the test pattern described in the first embodiment (see FIG. 9). The density of the patch is measured using a microdensitometer. When measuring the density of each patch, it is considered that the density is basically constant no matter which part is measured within the same patch. However, in the present embodiment, since the density of a micro area on the order of micrometers is measured, it is difficult to accurately measure the density if dust or blur exists on the printing surface. Therefore, the density of a plurality of points is measured for each patch, and the average of data included in a predetermined density range is set as the density of the patch.

The measured density is stored in the memory 63. For example, the density (average density) measured from the patch A-1 is temporarily stored in the memory 63 as _DA1 . In this way, the density is measured for each of the 32 patches shown in FIG.

Subsequently, the RMS granularity σ is calculated for each dot diameter (pulse amplitude Vh) using the density value measured from each patch (S125). For example, from the eight density values D _{A1 to} D _H1 measured from the eight patches A-1 to H-1 surrounded by a broken line in FIG. 9, the first patch of each band (A to H). The granularity σ _{1 for} is calculated. In the calculation, the above formula 2 is used. In the case of FIG. 9, n = 8 in Equation 2, and D _Aave is an average value of D _{A1 to} D _H1 . This operation is performed for each dot diameter, and RMS granularities σ _{1 to} σ ₄ are obtained for four types of dot diameters (pulse amplitudes Vh1 to Vh4), respectively.

In the memory 63, a value σ _{S serving} as a reference for evaluating the graininess is registered as a threshold value. When the calculated RMS granularity (for example, σ _{1 to} σ ₄ ) is equal to or less than the threshold σ _S , it can be said that the granularity of the formed image is good, and a high-quality image can be printed. On the other hand, when the calculated RMS granularity is larger than the threshold σ _S, graininess of the formed image becomes conspicuous and the image quality is deteriorated. Thus, the granularity of the printed image can be determined by calculating and evaluating the RMS granularity for each dot diameter. It should be noted that the granularity reference value σ _S may be changed according to the user's preference and the purpose of the printed image.

Then, using both the color difference ΔE calculated in the first embodiment and the granularity σ described above, the dot diameter (pulse amplitude Vh) to be used in actual printing is determined (S126), and the memory 63 stores the dot diameter (pulse amplitude Vh). Saved (S127). In determining the dot diameter, the dot diameter is selected when the color difference ΔE is less than or equal to the specified value and the granularity σ is less than or equal to the predetermined reference value σ _S. FIG. 13 shows an example of data that summarizes the color difference ΔE and the granularity σ for the test patterns formed with the four types of dot diameters a to d. In the figure, the numerical value shown in the row of ΔE is the value of the color differences ΔE _{a to} ΔE _d calculated for each dot diameter in S123. In addition, the ◯ mark or X mark shown in the row of σ indicates the granularity based on the result of comparing the RMS granularity σ _{a to} σ _d calculated for each dot diameter in S125 with the reference threshold σ _S. Is good (σ ≦ σ _S ), and when the graininess is bad (σ _S <σ) is shown as x.

  In FIG. 13, focusing on the granularity σ, since the evaluation is x when the dot diameter is c, the dot diameter c is excluded from the candidate dot diameters used at the time of printing, and the dot diameters a, b, d Remains a candidate. Subsequently, paying attention to the color difference ΔE, the dot b which is the dot diameter when the value of ΔE is the smallest among the candidates is determined as the dot diameter at the time of printing. That is, an image is printed by ejecting UV ink from all the heads using a drive signal COM having a pulse amplitude Vh that forms dots having a dot diameter b.

  If attention is paid only to the color difference ΔE, the dot diameter c that minimizes the color difference is selected as the dot diameter used during printing. However, if printing is performed with the dot diameter c, an image with poor graininess is formed, and the image quality cannot be sufficiently improved. Therefore, as in this embodiment, by determining the optimum dot diameter in consideration of the color difference and the graininess at the same time, it is possible to print a high-quality image with a small color difference between bands and good graininess. Is possible.

In FIG. 12, the respective processes may be executed by switching the order of the process (S122 and S123) until the color difference ΔE is calculated and the process (S124 and S125) until the granularity σ is calculated. For example, the granularity σ is calculated first, and the granularity is evaluated, so that the color measurement is not performed on the patch formed with the dot diameter that is not adopted as a result of the evaluation. In this way, it is not necessary to perform useless color measurement work, so that the inspection process can be made more efficient.
Further, the granularity may be evaluated using an index other than the RMS granularity as the granularity evaluation index in the present embodiment.

<Summary of Second Embodiment>
In the second embodiment, the dot diameter is determined by considering the graininess in addition to the color difference, and printing is performed using the dot diameter.
Specifically, based on the result of measuring the density of each patch for the same test pattern as in the first embodiment, patches formed for each head group with dots having the same dot diameter among a plurality of patches The RMS granularity representing the graininess of is calculated. Then, the dot diameter when the RMS granularity is equal to or smaller than a predetermined threshold and the dot diameter when the color difference is equal to or smaller than the specified value or the minimum is adopted as the dot diameter during actual printing.
As a result, it is possible to form an image with a small color difference between bands and a good graininess, and to realize higher quality printing.

=== Third Embodiment ===
In the third embodiment, in addition to the above-described color difference and graininess, attention is also paid to a difference in glossiness between bands of a printed image. Specifically, after adjusting the dot diameter as in the above-described embodiments, the glossiness of the entire image can be reduced by changing the ejection amount (ink duty) per unit area of the color ink and the clear ink. adjust.

  Ink duty adjustment is performed by printing a test pattern composed of a plurality of patches in the inspection process, and adjusting the ejection amount of the clear ink relative to the ejection amount of the color ink based on the result of measuring the glossiness of each patch of the test pattern. This is done. FIG. 14 shows a flow for determining the ink duty in the inspection process of the third embodiment. This flow is performed independently of the flow for determining the dot diameter described in the inspection process of the first and second embodiments (FIGS. 8 and 12).

  First, a test pattern is printed (S131). Unlike the test pattern (FIG. 9) used in the first embodiment, the test pattern used in this embodiment is printed separately. FIG. 15 shows an example of a test pattern printed in a certain band area in the third embodiment. The test pattern ejects color ink and clear ink from the first to fourth heads (color ink heads) and the fifth head (clear ink head) for each head set (for each band) while changing the duty. Thus, it is formed by printing a plurality of patches. That is, as shown in FIG. 15, a test pattern composed of a plurality of patches each formed by dividing the color duty and the clear duty into a plurality of stages is formed for each head set (for each band). In the above-described example, the test pattern is formed by simultaneously ejecting the four color inks of KCMY and the clear ink. However, the test pattern may be formed for each color of KCMY. That is, a test pattern as shown in FIG. 15 may be formed separately for each color of KCMY. In that case, the ejection amount of the clear ink is individually adjusted with respect to the ejection amount of each color ink of KCMY in the printing process described later. For example, the duty of the clear ink (CL) is determined for the duty of the black ink (K), and the duty of the clear ink (CL) is separately determined for the duty of the cyan ink (C).

  A plurality of patches are formed as shown in the figure while changing the ejection amount per unit area of color ink (hereinafter also referred to as color duty) and the ejection amount per unit area of clear ink (hereinafter also referred to as clear duty). The In FIG. 15, the patch is formed while changing the color ink duty and the clear ink duty in five stages. However, as the change width of each ink duty is set narrower, more accurate data can be obtained. The arrangement and shape of each patch are not limited to the example shown in FIG.

  After the test pattern is printed, the glossiness of each patch is measured using a glossmeter (S132). The gloss meter emits light at a predetermined angle (incident angle) from the light source toward the measurement surface, and the light reflected from the measurement surface (reflected light) is detected by a light receiving unit installed in the regular reflection direction. It is an instrument capable of measuring glossiness. As the gloss meter, for example, a gloss meter GM-60 manufactured by Konica Minolta can be used. In addition, there is a method of measuring the light angle at 20 degrees, 45 degrees, 60 degrees, 75 degrees, and 85 degrees. In this embodiment, the measurement is performed with an incident angle / reflection angle of 20 degrees. Since the glossiness shows a value proportional to the size of the angle, it is possible to measure the glossiness at other angles by measuring the light at 20 degrees without measuring all the angles.

The gloss value acquired for each patch is temporarily stored in a storage unit such as the memory 63. For example, the glossiness value acquired from the patch A-1 is stored in the memory 63 as (G _A1 ).

Based on the measurement result of each patch, the relationship between the ink duty and the glossiness is obtained (S133). FIG. 16 is an example of a graph showing the relationship between ink duty and glossiness. The graph corresponding to FIG. 16 is created for each head set (for each band). In the figure, the vertical axis represents the clear duty, and the horizontal axis represents the color duty. The curves drawn like contour lines in the figure represent the magnitude of glossiness. For example, when the color ink is ejected so that the color duty becomes Dco (A1) when the image is printed, the clear duty is Dcl (A1) in order to print an image with a glossiness level of A. Alternatively, the clear ink may be ejected so as to be Dcl (A2). Conversely, when the clear duty is Dcl (A1), the color duty required to print an image with a glossiness level of A is Dco (A1) or Dco (A2).
The obtained relationship is stored in the memory 63 (S134).

  In the printing process, printing is performed while adjusting the clear duty for the color duty based on the relationship. Specifically, after color conversion processing and halftone processing in FIG. 11, KCMY data is created from RGB data, and the total amount of ejection per unit area of color ink (KCMY) is determined. According to the ink duty, the duty of the clear ink that gives a predetermined glossiness is determined for each head group, and the ink is actually ejected. As described above, by adjusting the clear duty with respect to the color duty for each head group, it is possible to print an image having a desired glossiness for each band. That is, it becomes possible to print a high-quality image in which the difference in glossiness between bands is less noticeable.

<Summary of Third Embodiment>
In the third embodiment, in addition to the difference in color and graininess of the printed image, the difference in gloss between the bands is taken into account, and the clear ink is selected according to the ejection amount (color duty) per unit area of the color ink. By changing the ejection amount (clear duty) per unit area, an image having a predetermined glossiness is formed for each head group (for each band). That is, the glossiness of the image is adjusted by adjusting the clear duty.
Since the degree of glossiness of the image can be freely controlled, the difference in gloss between the bands is less noticeable, and higher quality printing can be realized.

=== 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 printing devices>
In each of the above-described embodiments, a printer has been described as an example of a printing apparatus, but the present invention is not limited to this. For example, color filter manufacturing apparatus, dyeing apparatus, fine processing apparatus, semiconductor manufacturing apparatus, surface processing apparatus, three-dimensional molding machine, liquid vaporizer, organic EL manufacturing apparatus (especially polymer EL manufacturing apparatus), display manufacturing apparatus, film formation The same technology as that of the present embodiment may be applied to various printing apparatuses to which inkjet technology such as a device and a DNA chip manufacturing apparatus is applied.

<About nozzle row>
In the above-described embodiment, an example in which an image is formed using four colors of KCMY and clear ink has been described. However, the present invention is not limited to this. For example, an image may be recorded using inks of colors other than KCMY and CL, such as light cyan, light magenta, and white.
The order of arrangement of the nozzle rows in the head portion is also arbitrary. For example, the order of the nozzle rows for K and C may be switched, or the number of nozzle rows for K ink may be greater than the number of nozzle rows for other inks.

<About piezo elements>
In each of the above-described embodiments, the piezo element PZT is exemplified as the element that performs the operation for ejecting the liquid. However, other elements may be used. For example, a heating element or an electrostatic actuator may be used.

<Ink used>
In each of the above-described embodiments, the example in which the ink (for example, UV ink) that is cured by being irradiated with light such as UV has been described as the liquid (ink) used for printing, but the ink used for printing is It is not limited to such UV ink. For example, the present invention can also be applied to printing apparatuses using other inks such as a general water-based ink that is fixed by penetrating the medium and a solvent-based ink that is fixed by evaporating the solvent on the medium.

1 Printer 1,
20 transport unit, 23A upstream transport roller, 23B downstream transport roller,
24 belt,
30 head units, 31-34 color ink heads, 35 clear ink heads,
40 irradiation units, 41 irradiation units,
50 detector groups,
60 controller, 61 interface, 62 CPU, 63 memory,
64 unit control circuit,
110 computer

Claims (7)

A first head that ejects a first ink onto a medium that is conveyed in the conveying direction; and a second head that is arranged in the conveying direction with the first head and ejects a second ink onto the medium. A head unit having a plurality of head sets in a direction intersecting the transport direction,
A printing apparatus that prints an image by forming dots by the first ink and dots by the second ink in a band that is a region where ink is ejected for each head set;
Based on the result of colorimetric test pattern having a plurality of patches formed for each head set with dots having different dot diameters for each band,
Among the plurality of patches, a color difference representing a difference in hue between patches formed for each band with dots having the same dot diameter is obtained,
So that the dot diameter is determined by the color difference,
A printing apparatus that adjusts the amounts of the first ink and the second ink ejected from the first head and the second head included in all the head groups. The printing apparatus according to claim 1,
From the values measured for each of the plurality of patches formed for each head set with dots having the same dot diameter, the color difference between adjacent bands is calculated,
Select the dot diameter so that the calculated color difference is less than or equal to the specified value or minimum,
In order to achieve the selected dot diameter,
A printing apparatus that adjusts the amounts of the first ink and the second ink ejected from the first head and the second head included in all the head groups. The printing apparatus according to claim 1,
For the values measured for each of the plurality of patches formed for each head set with dots having the same dot diameter, the difference between the average value of the colorimetric values and the respective colorimetric values is calculated. Based on the color difference,
Select the dot diameter so that the calculated color difference is less than or equal to the specified value or minimum,
In order to achieve the selected dot diameter,
A printing apparatus that adjusts the amounts of the first ink and the second ink ejected from the first head and the second head included in all the head groups. The printing apparatus according to any one of claims 1 to 3,
Based on the result of measuring the density of each patch for the test pattern,
Obtain a granularity representing the granularity of patches formed for each head set with dots having the same dot diameter among the plurality of patches,
The dot diameter when the granularity is equal to or less than a predetermined threshold,
A printing apparatus that adjusts the amounts of the first ink and the second ink ejected from the first head and the second head included in all the head groups. The printing apparatus according to any one of claims 1 to 4,
A third head that is aligned with the first head in the transport direction and that ejects third ink to the medium;
When the first ink is a color ink and the third ink is a clear ink,
According to the ejection amount per unit area of the first ink,
A printing apparatus, wherein the ejection amount per unit area of the third ink is changed. The printing apparatus according to any one of claims 1 to 5,
It has an irradiating unit that emits light,
The printing apparatus according to claim 1, wherein the ink is an ink that is cured by being irradiated with the light. A first head that ejects a first ink onto a medium that is conveyed in the conveying direction; and a second head that is arranged in the conveying direction with the first head and ejects a second ink onto the medium. From the head portion having a plurality of head sets having a direction intersecting the transport direction,
A printing method for printing an image by forming dots by the first ink and dots by the second ink in a band which is a region where ink is ejected for each head set,
Based on the results of colorimetric measurements on test patterns having each band with a plurality of patches formed for each head set with dots having different dot diameters,
Among the plurality of patches, a color difference representing a difference in hue between patches formed for each band with dots having the same dot diameter is obtained,
So that the dot diameter is determined by the color difference,
A printing method comprising adjusting amounts of the first ink and the second ink ejected from the first head and the second head included in all the head groups.

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