JP4421441B2 - Printing apparatus and adjustment method thereof - Google Patents

Description

  The present invention relates to an ink jet printing apparatus, and more particularly, to measures for improving image quality suitable for an apparatus in which a plurality of head units are integrally provided in one print head.

  Conventionally, an image is formed by ejecting ink droplets while reciprocating the print head in the main scanning direction, and transporting print paper that receives the ink droplets in a sub-scanning direction perpendicular to the main scanning direction ( Ink-jet printing apparatuses that perform printing are well known. In such a printing apparatus, generally, it is required to increase the printing speed while improving the quality (image quality) of a printed image, and various ideas have been made for that purpose.

  For example, Patent Document 1 discloses that ink droplets are ejected in the forward path and the backward path of a print head that reciprocally scans the print paper in the width direction, thereby speeding up printing, and the ink droplets ejected in the forward path and the backward path. A technique for adjusting the ejection timing of ink droplets so as to prevent the ink droplets ejected in step 1 from shifting on the print paper is disclosed.

Specifically, in the document described in the above document, in a printing apparatus having two print modes for forming an image with dots having different sizes, the pattern in which the ink position shift is most conspicuous for each print mode is described. A test image is printed, the positional deviation of the dots is detected visually, and the ejection timing of the ink in the forward path and the backward path is adjusted accordingly.
JP 2003-112414 A

  By the way, in the known ink jet printing apparatus as described above, generally, the image quality and the printing speed can be improved by providing a large number of ink ejection nozzles in the print head. If the nozzles are provided, the manufacturing cost is remarkably increased. In order to avoid this, it has been proposed to configure one print head using a plurality of general-purpose head units.

  However, when such a plurality of head units are used, there is a problem that the quality of the printed image is deteriorated due to the difference in characteristics of the head units. In other words, each general-purpose head unit has individual variations, and when this is incorporated into a printing apparatus, the voltage supplied to each head unit also varies, so one print head discharges from each head unit. The sizes of the ink droplets to be produced are different from each other, and the size of the dots formed on the print paper also varies.

  In this case, the density of a portion drawn with larger dots in one image becomes higher, and on the contrary, the density of a portion drawn with smaller dots becomes lower. In addition, in the case of color printing, since the viscosity and density differ for each color ink, the variation in the size of the ink droplets differs for each color as described above, and not only the shading unevenness but also the hue change occurs. It will be.

  In order to prevent such deterioration of the image quality, a test pattern (image) is printed for each printing device as in the conventional example (Patent Document 1), and this is visually inspected. Alternatively, it is conceivable to measure the image density using a flatbed scanner or the like, and adjust the supply voltage to each head unit based on this.

  However, in general, visual inspection has a problem that it is difficult to stably ensure the required accuracy. On the other hand, a method using a separate device such as a scanner requires such a device and its installation environment, and is operable. In addition to being bad, both are very time-consuming and are not practical.

  The present invention has been made in view of such a point, and an object of the present invention is to discharge a plurality of inks of a print head, such as an ink jet printing apparatus in which one print head is configured by a plurality of head units. When the nozzles are divided into a plurality of nozzle groups, the method of detecting the ink discharge characteristics for each nozzle group (head unit) is devised to accurately vary the ink discharge variation between the nozzle groups. The purpose is to enable easy correction.

  In order to achieve the above object, according to the present invention, an adjustment image printed by each nozzle group of a print head is used as a gradation pattern in which a density deviation appears as a position deviation, and the density deviation is easily detected by a sensor. In addition, it is possible to detect accurately, and thereby to automatically detect deviations in ink ejection characteristics between the nozzle groups.

  More specifically, according to the first aspect of the present invention, an ink droplet is ejected by the ejection nozzle while at least scanning a print head provided with a plurality of ink ejection nozzles in the main scanning direction to form an image on the print member. The present invention is intended for an ink jet printing apparatus that performs printing.

When the plurality of ink discharge nozzles of the print head are divided into a plurality of nozzle groups each including at least one discharge nozzle, the optical density of the image printed on the print member is detected. Based on sensor and preset adjustment image data, the adjustment image creating means for printing the adjustment image by each nozzle group on the print member, and the density deviation between the adjustment images Characteristic difference detection means for detecting a deviation of the ink discharge amount characteristic between the nozzle groups corresponding to each adjustment image based on the density deviation obtained from a signal from the sensor;
The image data for adjustment includes a reference density pattern having a predetermined reference density, and a gradation pattern in which the density gradually changes in one direction and the density at a set position thereof is the reference density. Shall be
The adjustment image creating means causes the reference density pattern to be printed by any one of the plurality of nozzle groups and the gradation pattern to be printed by each nozzle group other than the reference nozzle group. Shall be
The characteristic difference detecting means identifies a position where the density matches the reference density in each printed gradation pattern, and detects a density deviation based on a deviation of the density matching position from the set position. .

  With the above-described configuration, when adjusting the ink ejection states of the plurality of nozzle groups of the print head so as to be substantially the same, the operation of the printing apparatus is first controlled by the adjustment image creating means, and the preset adjustment is performed. Based on the image data, a reference density pattern and a gradation pattern, which are adjustment images, are printed by the reference nozzle group of the print head and the other nozzle groups, respectively.

  Then, the printed reference density pattern and the density of each gradation pattern are detected by a sensor, and based on the signal from this sensor, the characteristic difference detection means determines the position where the density matches the reference density in each gradation pattern. Identified. Further, based on the deviation of the density matching position from the set position, the density deviation of each gradation pattern with respect to the reference density pattern is obtained, and based on this density deviation, the reference nozzle group of the nozzle group corresponding to each gradation pattern The deviation of the ink discharge amount characteristic with respect to is quantitatively determined.

  That is, by using the gradation pattern adjustment image as described above, the overall degree of shading of this image can be converted into a shift in the density matching position with the reference density. Based on the deviation amount of the density coincidence position, the density deviation of the adjustment image can be quantitatively obtained, and based on this, the deviation of the ink discharge amount characteristic of each nozzle group can be automatically detected.

  If the deviation of the ink discharge amount characteristic of each nozzle group with respect to the reference nozzle group is automatically detected, it is only necessary to correct the ink droplet discharge state by each nozzle group according to this deviation. Therefore, it is possible to eliminate the unevenness of the image and the change of the hue easily with almost no variation in the recording density of the discharged ink on the print member.

  The fact that the variation in the ink ejection characteristics between the nozzle groups can be detected and corrected is that, as described above, a plurality of head units each having a plurality of ink ejection nozzles are integrally provided in the print head, This is particularly effective when the ink discharge nozzles of each head unit constitute a nozzle group (invention of claim 8). Hereinafter, this case will be described in detail.

  That is, the ink droplet ejection state by each head unit is corrected so that the deviation becomes smaller in accordance with the deviation of the ink ejection amount characteristic of each head unit (nozzle group) detected by the characteristic difference detection means. It is preferable to include an ink discharge state correcting means for performing the invention (the invention of claim 2). In this way, the ink ejection state is automatically corrected according to the difference in ink ejection characteristics of each head unit automatically obtained as described above, so that the variation in the ink ejection amount of each head unit can be reduced. It can be corrected more easily.

  Further, the correction of the ink droplet discharge state in the head unit (nozzle group) by the ink discharge state correcting means is, for example, so that the size of the image dots formed on the print member changes. The size of the ink droplets ejected from the ink ejection nozzles may be adjusted (the invention of claim 5), or the head may be changed so that the number of image dots formed per unit area on the print member changes. The number of ink droplets ejected per unit time from the ink ejection nozzle of the unit may be adjusted (invention of claim 6).

  That is, for example, if the ink droplet discharge characteristic is such that the size of the ink droplets discharged from one of the head units is smaller than the reference unit and the image density is relatively low, the ink from this head unit The density of the image can be increased by performing correction control so as to increase the size of the droplets or by increasing the number of ink droplets ejected per hour to increase the recording density per unit area on the print member. On the contrary, if the head unit has the characteristic of increasing the image density, the ink droplets may be reduced or the number of ink droplets may be reduced.

  In the printing apparatus configured as described above, when each head unit (nozzle group) has a plurality of nozzle groups for each color that eject ink droplets of different colors, the adjustment image creation The means preferably prints the adjustment image for each of the colors (invention of claim 3). Further, in the case where each of the head units can eject ink droplets of different sizes from the ink ejection nozzles to form a plurality of types of image dots of different sizes on the print member, It is preferable that the adjustment image creating means prints an adjustment image for each type of the image dot (invention of claim 4).

  In this way, not only the ink ejection characteristics of the head unit can be adjusted as a whole, but also finer adjustments can be made for each of the colors and for the types of image dots of different sizes. The quality can be further improved.

  Preferably, the sensor for detecting the density of the image is arranged in the print head of the printing apparatus, and the gradation pattern of the adjustment image has a density that gradually changes in the main scanning direction of the print head. (Invention of claim 7) This makes it possible to detect the density coincidence position with the reference density pattern by scanning the gradation pattern once with the print head using a mechanism for printing an image on the print member by the print head. Become.

  Next, according to the ninth aspect of the present invention, an ink droplet is ejected by the ejection nozzle while scanning a print head provided with a plurality of ink ejection nozzles at least in the main scanning direction, and an image is formed on the print member. In the case where the plurality of ink ejection nozzles of the print head are divided into a plurality of nozzle groups each composed of at least one ejection nozzle, the adjustment method of the ink jet printing apparatus configured to print Preparation of adjustment image data including a reference density pattern having a predetermined reference density and a gradation pattern in which the density gradually changes in one direction and the density at the set position is the reference density. .

Based on the image data for adjustment, the reference density pattern is printed on the print member by any one of the plurality of nozzle groups, and each nozzle group other than the reference nozzle group is printed. An adjustment image creating step of printing the gradation pattern to create an adjustment image;
The reference density pattern of the image for adjustment and the density of each gradation pattern are detected by a sensor, and based on the signal from the sensor, the position where the density matches the reference density in each gradation pattern is specified. A density deviation detecting step for obtaining a density deviation of each gradation pattern with respect to a reference density pattern based on a deviation of the density matching position from the set position;
A characteristic difference detecting step for obtaining a deviation of ink discharge amount characteristics from a reference nozzle group of each nozzle group corresponding to each gradation pattern of the image for adjustment based on the density deviation obtained in the density deviation detecting step;
An ink discharge state correction step of correcting the ink droplet discharge state by each nozzle group so that the deviation is reduced in accordance with the deviation of the ink discharge amount characteristic obtained in the characteristic difference detection step. .

  According to the adjustment method, as in the first and second aspects of the invention, using the adjustment image in which the density deviation of the image appears as a positional deviation, the density deviation can be easily and accurately detected by the sensor. Since it can be detected, the deviation of the ink discharge amount characteristic of each head unit (nozzle group) can be automatically detected, and the variation of the ink discharge amount can be corrected accurately and easily.

  As described above, according to the printing apparatus and the adjustment method thereof according to the present invention, the ink discharge nozzles of the print head are divided into a plurality of nozzle groups, for example, as one print head is configured by a plurality of head units. In the divided inkjet printing apparatus, an adjustment image having a predetermined gradation pattern is created for each nozzle group, the density deviation is detected, and the ink ejection characteristic deviation of each nozzle group is automatically obtained. Therefore, by correcting the ink discharge state according to this characteristic deviation, it is possible to easily and accurately eliminate variations in the ink discharge amount among a plurality of nozzle groups. Can be improved. At this time, since there is no variation in detection accuracy as in visual inspection, the required accuracy can be secured stably.

Furthermore, if the ink ejection characteristic deviation is obtained for each color and each dot size of each nozzle group and the ink ejection state is corrected, the print quality can be further improved by fine adjustment.

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

[overall structure]
As shown in FIG. 1, an ink jet printing apparatus according to an embodiment of the present invention includes a reception block A that performs image data acquisition and order information acquisition to perform necessary correction processing, and communication from the reception block A. And a print block B that prints image data transmitted via the cable 1 on the print paper P based on the order information.

[Reception block]
The reception block A is provided at an intermediate position in the vertical direction of the frame 5, a reception device 6 provided at the top of the wagon frame 5, a liquid crystal display 8 whose display screen is constituted by the touch panel 7, and the frame 5. And a flatbed scanner FS. On the front surface of the accepting device 6, a semiconductor drive 9 for reading out image data stored in a recording medium Ms composed of a flash memory, and image data stored in a disk-type recording medium Md such as a CD-R or DVD. And a disk drive 10 for reading the data.

  The flat bed scanner FS includes a main body 11 having a scanning table 13 made of transparent glass and a scanning head 14 disposed on the lower side of the scanning table 13, and a platen cover 12 attached to the main body 11 so as to be freely opened and closed. And. The scanning head 14 includes a plurality of photoelectric conversion elements (for example, a CCD or the like) disposed in the main scanning direction and a light source, and is placed on the scanning table 13 by moving in the sub scanning direction orthogonal to the main scanning direction. The image of the scanned object is captured as image data that is color-separated into three primary colors of R (red), G (green), and B (blue).

[Print Block]
As shown in FIG. 1 and FIG. 2, the print block B is arranged on the casing 15, two magazine housing portions Ba and Ba arranged at the lower part of the casing 15, and arranged at the upper part of the casing 15 and printed. A printing unit Bb that records image data on the paper P and an ink storage unit Bc disposed on the side of the housing 15 are provided. On the upper surface of the housing 15, a sorting unit 17 that receives the small-size print paper P that is fed by the lateral feed belt 16 and a rack plate 18 that receives the large-size print paper P are disposed.

  The magazine accommodating portion Ba includes a drawer 20 that slides as the front wall body 15A slides, and is configured to accommodate the roll-shaped print paper P held by the paper magazine 21 in the drawer 20. . The width of the print paper P stored in the lower magazine storage portion Ba is larger than that of the print paper P stored in the upper magazine storage portion Ba (see FIG. 2).

  The print unit Bb includes a print head H that is provided in the wall body 15B and that prints an image by spraying minute ink droplets onto the print paper P. Although the structure of the print head H will be described later, each of the sprayed ink droplets forms minute image dots on the print paper P, and an image is formed as a set of the dots.

  The ink reservoir Bc includes seven ink cartridges 23,... That are detachably accommodated in the wall 15C and have different hues. These ink cartridges 23,... Can be replaced with new ink cartridges 23 by being inserted and removed. Each of these ink cartridges 23,... Has yellow (Y), magenta (M), cyan (C), black (K), red (R), violet (V), and clear (CL: transparent ink) ink. Is enclosed. The wall body 15C is configured to be swingable and openable about an axis extending in the vertical direction.

[Paper transport mechanism]
As shown in FIG. 3, the paper transport mechanism includes a supply unit U1, a print unit U2, a loop forming unit U3, a cutter unit U4, a reversing unit U5, and a discharge unit U6. In the paper transport mechanism, when image data is printed on the print paper P, the print unit P1 stores the print paper P stored in one of the two magazine storage units Ba and Ba by the printing unit. Then, image data is printed by the print head H while the supplied print paper P is conveyed by the print unit U2, and then the printed print paper P is transferred from the loop forming unit U3 to the cutter unit U4. After being cut into print sizes, the paper is fed to the lateral feed belt 16 or the rack plate 18 by the reversing unit U5 and the discharge unit U6.

  More specifically, the supply unit U1 is a support roller 25 that applies a rotational force to the print paper P accommodated in the paper magazine 21, and a pressure-bonding type for transporting the print paper P from the paper magazine 21 to the print unit U2. A supply roller 26 and a guide member (not shown) for guiding the print paper P conveyed by the supply roller 26 are provided. The support roller 25 and the supply roller 26 are driven by an electric motor for supply and conveyance.

  The print unit U2 includes a guide rail 28 that guides the print head H in the main scanning direction, a drive belt 30 that is wound around a pulley 29 and moves the printer head H back and forth along the guide rail 28, and printer paper P. A paper holding unit D that sucks and holds the head H at a position where printing can be performed, and pressure-type print transport rollers 31 and 31 disposed on the upstream side and the downstream side of the paper holding unit D are provided. Yes. The paper holding unit D includes a guide plate 32 having a plurality of holes formed in the thickness direction, and a fan that is provided in the housing 33 and applies negative pressure to the print paper P through the holes of the guide plate 32. 34.

  When the print unit U2 (print unit Bb) performs printing on the print paper P, the print unit P2 prints an image at a predetermined interval in the width direction of the print paper P, and prints the adjacent images. A cutting mark is formed in the area between.

  As shown in FIG. 3, the loop forming unit U <b> 3 includes a guide plate 36 disposed on the downstream side of the downstream print transport roller 31 and a pressure-bonding mold for transporting the print paper P guided by the guide plate 36. Intermediate roller 37. The guide plate 36 is configured to be switchable between a horizontal posture (dotted line in FIG. 3) extending substantially in the horizontal direction and an open posture (solid line in FIG. 3) extending in the vertical direction. In the loop forming unit U3, when printing a long print paper P, the front end portion of the print paper P is transferred to the intermediate roller 37 through the horizontal guide plate 36 and then printed by the intermediate roller 37. The conveyance of the paper P is stopped, and then the guide plate 36 is switched from the horizontal posture to the open posture, and the print paper P is suspended to form a loop.

  The cutter unit U4 includes a fixed blade 39, a movable blade 40, a cut position sensor 41 having a reflective sensor, and a pressure-feeding type feeding roller 42 for feeding out the print paper P. When the print paper P is cut by the cutter unit U4, adjacent to the width direction of the print paper P based on the cut mark formed in the print unit U2 as described above based on the detection result of the cut position sensor 41. By taking an area between the images so that the interval is slightly wider than the interval between the images, the marginless print can be cut without leaving a margin around the image.

  As shown in FIG. 3, the reversing unit U5 includes a pressure-reversal reversing roller 43 that crimps the printer paper P, a transport drive mechanism (not shown) that rotates the reversing roller 43 forward and backward, and a pair of reversing rollers 43. A reversing mechanism that rotates the roller 43 around the axis of the roller by 90 degrees. Then, in the reversing unit U5, the print paper P fed from the front end side by the cutter unit U4 is conveyed by the reversing roller 43 so that the rear end portion reaches the position of the reversing roller 43, and is indicated by an arrow in FIG. In this way, the reversing unit U5 is rotated 90 degrees around the axis, and then the reversing roller 43 is rotated in the reverse direction to feed the print paper P from the rear end to the discharge unit U6.

  The discharge unit U6 includes a plurality of pressure-bonding type discharge rollers 44 for conveying the print paper P, and the print paper P conveyed by the carry-out rollers 44,. A path switching mechanism (not shown) for sending out to one side is provided.

[Print head]
As shown in FIGS. 3 and 4, the print head H is provided with three head units 51 each having a plurality of ink discharge nozzles arranged on the bottom side thereof. For convenience, among the head units 51 provided in three stages, the one located on the downstream side (the front side in the transport direction of the print paper P), that is, the upper stage in the drawing is referred to as the first head unit 51a, and the middle one is referred to as the second head unit 51b. Further, the one located upstream (the rear side in the conveyance direction of the print paper P), that is, the lower stage is referred to as a third head unit 51c.

  In the present embodiment, all the head units 51 have the same specifications. As shown in FIG. 4, each head unit 51 has yellow (Y), magenta (M), cyan (C), and black (K). , Red (R), violet (V), and clear (CL), each of which is composed of seven nozzle arrays 54 (nozzle groups) that respectively eject ink droplets. In each nozzle array 54, ink ejection nozzles are arranged in a row in the sub-scanning direction orthogonal to the main scanning direction that is the scanning direction of the print head H. Thus, each head unit 51 is configured to be able to form a color image by itself.

  Further, the head unit 51 is configured such that the size of the ink droplets ejected from the ink ejection nozzles is changed by changing the supplied voltage. Thus, ink droplets of different sizes, large, medium, and small, are ejected. The ink droplets ejected in this manner and sprayed onto the print paper P form three types of image dots, large, medium and small, corresponding to the size.

  Further, at the front side of the print head H in the transport direction of the print paper P, reflected light of light emitted from the light source toward the image of the print paper P is received, and the optical density of the image is determined based on the received light amount. A reflective sensor S for detection is attached. This sensor S, along with the print head H, reciprocates in the main scanning direction to detect the density of check patterns CP1 to CP3 (adjustment images) printed on the print paper P, as will be described later.

[Control system]
The control system of the printing apparatus is configured as shown in FIG. That is, the receiving device 6 of the receiving block A transmits and receives information between a microprocessor (hereinafter referred to as a CPU) and the CPU via a data bus. The touch panel 7, the display 8, the semiconductor drive 9, and the disk drive 10 A semiconductor memory RAM / ROM, a hard disk HD, and a communication interface 61. The receiving device 6 further includes an operation system 62, an image processing system 63, and a printer driver 64, which are software for realizing the processing of the CPU. The accepting device 6 constitutes an input / output system for transmitting / receiving information to / from the flatbed scanner FS, and further constitutes a signal system for transmitting / receiving information to / from the print block via the communication interface 61. Yes.

  The print block B transmits / receives information to / from a microprocessor (hereinafter referred to as “CPU”) and the CPU via a data bus. The transport control unit 66, the head control unit 67, the semiconductor memory RAM / ROM, the reflection A mold sensor S, a cut position sensor 41, an attachment / detachment sensor 65 for determining whether or not the ink cartridge 23 is present in the ink reservoir Bc, and a communication interface 68 are provided. The print block B further includes a print control unit 69, an adjustment image creation unit 71, a characteristic difference detection unit 72, and a print control correction unit 73 (ink discharge state correction unit) that are made of software for realizing the processing of the CPU. ing.

  The transport control unit 66 is for controlling each of the units U1, U2, U3, U4, U5, U6 of the paper transport mechanism. The head controller 67 controls the operation of the print head H. The print control unit 69 controls the printing of an image on the print paper P in cooperation with the head control unit 67 based on the image data sent from the receiving block A. It is assigned which part of the first to third head units 51a to 51c is to form an image.

  The adjustment image creation unit 71, the characteristic difference detection unit 72, and the print control correction unit 73 are for correcting the ink ejection state described in detail below. The adjustment image creation unit 71 is set in advance. Based on the adjusted image data, check patterns CP1 to CP3 are printed by the first to third head units 51a to 51c, respectively. The characteristic difference detection unit 72 detects the density difference between the check patterns CP1 to CP3 by the reflective sensor S, and based on the detected density difference, the ink between the first to third head units 51a to 51c. A variation in droplet size, that is, a deviation in ink ejection characteristics is obtained. Then, the print control correction unit 73 corrects the ink ejection states (for example, the ejection amounts) of the first and second head units 51a and 51b so as to be aligned with the third head unit 51c so that the deviation becomes small.

[Correction of ink ejection state]
Next, the correction of the ink ejection state will be specifically described with reference to FIGS. FIG. 6 shows check patterns CP1 to CP3 for each of the head units 51a to 51c printed on the print paper P. In this embodiment, each of the check patterns CP1 to CP3 depends on the hue of the ink and the dot size. It consists of 18 divided areas.

  Specifically, each check pattern CP1 to CP3 has a rectangular shape that is long in the width direction (left and right direction in the figure) of the print paper P, and is divided into six equal parts in the longitudinal direction (up and down direction in the figure) of the print paper P. Thus, it is divided into six belt-like regions painted on each color of yellow (Y), magenta (M), cyan (C), black (K), red (R), and violet (V). Since clear (CL) is not checked, no area is provided.

  Further, each of the six belt-like regions is divided into three equal parts in the paper width direction, and an area drawn by large dots (-L: the left area in the figure) and an area drawn by small dots (-S: figure The right area) and an area (-M) drawn by medium dots are formed, and 18 areas having different hues or dot sizes are formed.

  In the check patterns CP1 and CP2 corresponding to the first and second head units 51a and 51b, the areas are respectively in the paper width direction (print head main scanning direction) from the left side to the right side of the drawing. As shown in FIG. 7, the density at the left end of the darkest figure becomes a certain set value (30% in the example in the figure), while the right end of the thinnest figure, as shown in FIG. The density of the part becomes another set value (10% in the example in the figure), and in the meantime, as shown by the solid line graph in FIG.

  This gradation pattern is obtained by, for example, gradually changing the ink droplet ejection amount, that is, the number of ink droplets ejected by the head units 51a to 51c per unit scanning distance (per unit time). The image density is changed by gradually changing the number of image dots formed in the paper width direction, thereby changing the ink recording density.

  On the other hand, in the check pattern CP3 corresponding to the third head unit 51c, the density of each area is substantially constant, and the density is set in the two gradation patterns of the corresponding areas of the check patterns CP1 and CP2. The median value (20% in the example in the figure) is set. This substantially constant density value serves as a reference when correcting variations in the size of the ink droplets of the first and second head units 51a and 51b. In this sense, the check pattern CP3 is a reference density pattern.

  In the data used as the basis of the adjustment image, the density at the center reference position (x = 0: setting position) of the gradation pattern is the reference density. If the relationship between the supplied voltage and the size of the ejected ink droplet is the same as that of the third head unit 51c, when the two check patterns CP1 and CP3 corresponding to them are compared, the center of the printed gradation pattern As shown schematically in FIG. 7, the solid line graph representing the change in density of the gradation pattern intersects with a one-dot chain line representing the reference density at the reference position. Become.

  On the other hand, for example, if the first head unit 51a has a characteristic that the size of the ink droplet is smaller than that of the third head unit 51c, the entire gradation pattern becomes lighter and the reference density pattern becomes smaller. There is a concentration deviation between them. That is, as shown by the broken line in FIG. 7, the gradation pattern graph is shifted upward by the amount of the density deviation, and the broken line graph and the one-dot chain line of the reference density intersect in proportion to the density deviation. The position (density matching position) to be shifted is shifted to the minus side (left side in the figure) from the reference position.

  Accordingly, the areas corresponding to each other of the check patterns CP1 and CP3 printed on the print paper P are scanned by the reflective sensor S, and the density of the check pattern CP3 matches the reference density value in the gradation pattern of the area of the check pattern CP1. If the position x in the paper width direction is detected, the magnitude of the density deviation between the two patterns CP1 and CP3 can be accurately obtained from the deviation amount Δx of the detected position x (density matching position) from the reference position. The magnitude of the density deviation represents the variation in the size of the ink droplets ejected from the first head unit 51a.

  More specifically, in the example shown by the broken line in FIG. 7, the detected density matching position x = −x1, and the magnitude of the positional deviation amount Δx at this time is an absolute value | −x1 | = x1. At this time, the density reduction rate (density deviation) is − (x1 / x0) × 10%, and this is the variation in the size of the ink droplet (the variation in the weight of the ink droplet. Say). Thus, by obtaining the density deviation converted into the position deviation, the density deviation can be detected more accurately than simply comparing the densities of the two images. It is possible to accurately determine the weight variation of the ink droplets due to the characteristic difference.

  Thus, if the ink droplet weight variation, that is, the rate of decrease in the ink droplet weight in the above example is quantitatively determined, the supply voltage to the first head unit 51a is corrected accordingly, or Increasing and correcting the ink droplet ejection amount by the first head unit 51a increases the recording density of the ink on the print paper P, thereby reducing the image density due to variations in the characteristics of the head unit. Can be largely canceled.

  Hereinafter, a procedure for correcting the ejection state of the ink droplets by the first and second head units 51a and 51b of the print head H according to the ink weight difference (ink ejection characteristic difference) from the third head unit 51c will be described. This will be described with reference to the flowchart of FIG.

  First, if a magazine is selected in step S1 after the start, sensitivity calibration of the reflective sensor S is executed (step S2). If the sensitivity calibration of the sensor S is completed normally (YES in step S3), the check patterns CP1 to CP3 are printed on the print paper P, respectively, and the check patterns CP1 to CP3 printed by the reflective sensor S are displayed. Each is scanned (step S4).

  That is, the areas for each color and each dot size in the check patterns CP1 to CP3 are scanned by the reflection type sensor S. In this embodiment, the density of the gradation pattern is set in each area of the check patterns CP1 and CP2. Since the print head H changes in the main scanning direction, the density of this pattern is detected by the print head H in one scan, and the time required for detection is very short.

  Further, the scanning by the reflective sensor S can be executed simultaneously with the scanning of the print head H for printing the check patterns CP1 to CP3. In this way, it is possible to detect the densities of the check patterns CP1 to CP3 almost simultaneously with the end of printing. However, the print paper P may be rewound after all the check patterns CP1 to CP3 have been printed once, and then scanned while the print paper P is conveyed again.

  Subsequent to step S4, in step S5, for each of the first and second head units 51a and 51b, for each area, that is, yellow (Y), magenta (M), cyan (C), and black (K). , Red (R) and violet (V), and for each of the large, medium, and small dot sizes, the position x in the paper width direction where the density matches the reference density is specified. Based on the deviation Δx of the coincidence position x from the reference position, the ink droplet size variation (ink weight difference) for each color and each dot size is obtained as described above.

  In the subsequent step S6, a correction value for the ink ejection amount is set in accordance with the ink weight difference for each color and each dot size in each of the first and second head units 51a and 51b, and this is set as a print control unit 69. Are registered for each color and each dot size in the control map for printing the image data, and then the control is terminated (END). In this way, among the seven types of ink used for printing, for each of the six colors excluding clear (CR), and for each of the large, medium, and small dot sizes, the ink between the head units 51a to 51c is finely divided. By detecting the variation in the weight of the droplets and correcting the ink ejection state so as to reduce this, the quality of the printed image can be made extremely high.

  In step S4 of the flow shown in FIG. 8, the procedure for printing the check patterns CP1 to CP3 on the print paper P by the first to third head units 51a to 51c, respectively, is performed by the adjustment image creation unit 71. This is an image creation process.

  Further, in the step S4, the check patterns CP1 to CP3 are respectively scanned by the reflective sensor S, and in the subsequent step S5, the deviation amount Δx (corresponding to the density deviation) of the density matching position x of the corresponding area is obtained. This is a density deviation detection step executed by the characteristic difference detection unit 72, and the procedure for obtaining the ink weight difference (deviation of the ejection amount characteristic) between the head units 51a to 51c from the deviation amount Δx in the same step S5 is also the characteristic difference. This is a characteristic difference detection step executed by the detection unit 72.

  Further, the procedure for correcting the ink ejection amounts by the first and second head units 51a and 51b in step S6 of the flow is an ink discharge state correction process executed by the print control correction unit 73.

  Therefore, according to the printing apparatus of this embodiment, in the ink jet printing apparatus in which one print head H is configured by the plurality of head units 51a to 51c, when correcting the ink discharge variation between the head units 51a to 51c. By simply performing a predetermined operation, preset check patterns CP1 to CP3 are printed on the print paper P by the individual head units 51a to 51c, and the density deviation between them is detected by the sensor S integrated with the print head H. The ink is automatically detected, and the ink ejection amount by the first and second head units 51a and 51b is automatically corrected accordingly.

  That is, since the check patterns CP1 and CP2 are gradation patterns in which the density deviation appears as a position deviation, the density deviation can be accurately detected by the sensor S. Therefore, the head units 51a and 51b are based on the density deviation. The ink ejection characteristics of the head units 51a to 51c can be accurately corrected.

  In this way, the ink discharge characteristics of the plurality of head units 51a to 51c incorporated in one print head H can be made substantially coincident, and there is no ink discharge variation between them, thereby improving the print quality.

  In addition, since the printing of the check patterns CP1 to CP3, the detection of ink ejection variation between the head units 51a to 51c based on the density detection, and the correction of the ink ejection amount according to this are performed fully automatically. In addition, since it takes no effort and is extremely easy, and there is no variation in detection accuracy as in visual inspection, the required accuracy can be stably secured.

  In addition, in this embodiment, the ink ejection characteristics of the first and second head units 51a and 51b are not adjusted as a whole, but are finely adjusted for each color and each dot size. It can be very high.

  In addition, the structure of this invention is not limited to the structure of the said embodiment, It can implement with other various forms, without deviating from the mind or main characteristics. That is, for example, in the above-described embodiment, the gradation patterns of the check patterns CP1 and CP2 that are adjustment images change in density in the width direction of the print paper P. However, the present invention is not limited to this.

  In the above embodiment, the density deviation is obtained and corrected for each large, medium, and small dot size for each color of the ink. However, the present invention is not limited to this. The density deviation may be detected and corrected for each color without considering the size, or the average correction may be performed for the entire head unit 51.

  In the above-described embodiment, the reflective sensor S is provided in the print head H. However, this may be provided separately from the print head H, and the sensor is not limited to the reflective type.

  In the above-described embodiment, the print block B includes the print control correction unit 73 made of software, and the ink ejection amount by the head units 51a and 51b is automatically corrected according to the density deviation. Not limited to this, the supply voltage (or current, etc.) to the head unit H may be corrected to adjust the size of the ink droplet, or the head unit may heat the ink to eject it. If there is, the heating amount may be corrected.

  Alternatively, the print control correction unit 73 is not provided, and for example, the operator may manually correct the ink discharge state of the head units 51a and 51b in accordance with the displayed density deviation.

  Furthermore, in the embodiment, the print head H is provided with the three head units 51a to 51c. However, the number is not limited to three, and may be two or four or more. H may be constituted by one head unit 51. That is, even when there is one head unit 51, the ink discharge nozzles are divided into a plurality of nozzle groups each composed of at least one discharge nozzle, and an ink discharge operation is performed for each nozzle group to form an image. This is because, in such a situation of use, it is effective to improve the image quality to eliminate variations in ink ejection for each nozzle group.

1 is a perspective view illustrating an entire print system. It is a perspective view of a print block. It is a figure which shows the conveyance system of the print paper of a print block. It is a bottom view of the print unit. 2 is a block diagram illustrating a control system of the print system. FIG. It is a top view of the printed paper with which the check pattern was created. It is explanatory drawing of a gradation pattern. 5 is a flowchart according to ink ejection characteristic correction processing.

Explanation of symbols

51 Head unit (nozzle group)
54 Nozzle array (nozzle group)
71 Adjustment image creation unit (adjustment image creation means)
72 Characteristic difference detection unit (characteristic difference detection means)
73 Print control correction unit (ink discharge state correction means)
H Print head P Print paper (printing material)
S Reflective sensor (sensor)
CP1 to CP3 check pattern (adjustment image)

Claims (9)

An ink jet printing apparatus that prints an image on a print member by ejecting ink droplets from the print head provided with a plurality of ink ejection nozzles at least in the main scanning direction and ejecting ink droplets from the ejection nozzles. And
A plurality of ink discharge nozzles of the print head are divided into a plurality of nozzle groups each consisting of at least one discharge nozzle;
A sensor for detecting an optical density of an image printed on the print member;
An adjustment image creating means for printing an adjustment image by each nozzle group on the print member based on preset adjustment image data;
A characteristic difference for obtaining a density deviation between the adjustment images based on a signal from the sensor, and detecting a deviation in ink discharge amount characteristics between the nozzle groups corresponding to the adjustment images based on the density deviation. Detecting means,
The adjustment image data includes a reference density pattern having a predetermined reference density and a gradation pattern in which the density gradually changes in one direction and the density at a set position thereof is the reference density. And
The adjustment image creating means causes the reference density pattern to be printed by any one of the plurality of nozzle groups and causes the gradation pattern to be printed by each nozzle group other than the reference nozzle group. Is,
The characteristic difference detecting means specifies a position where the reference density and the density match in each printed gradation pattern, and obtains a density deviation based on a deviation of the density matching position from the set position. A printing apparatus characterized by the above. The printing apparatus according to claim 1,
Ink ejection state for correcting the ejection state of the ink droplets by each nozzle group so that the deviation is reduced according to the deviation of the ink ejection amount characteristic of each nozzle group with respect to the reference nozzle group detected by the characteristic difference detection unit A printing apparatus, further comprising a correction unit. The printing apparatus according to claim 1 or 2,
Each nozzle group has a plurality of nozzle groups for each color that eject ink droplets of different colors,
The adjustment image creating means prints the adjustment image for each of the colors. The printing apparatus according to any one of claims 1 to 3,
Each nozzle group can eject ink droplets of different sizes from the ink ejection nozzles to form a plurality of types of image dots of different sizes on the print member,
The adjustment image creating means prints an adjustment image for each type of the image dots. In the printing apparatus according to any one of claims 2 to 4,
The ink discharge state correction means adjusts the size of the ink droplets discharged from the ink discharge nozzles of the nozzle group so that the size of the image dots formed on the print member changes. Printing device. In the printing apparatus according to any one of claims 2 to 4,
The ink discharge state correcting means adjusts the number of ink droplets discharged per time from the ink discharge nozzles of the nozzle group so that the number of image dots formed per unit area on the print member changes. A printing apparatus characterized by being. In the printing apparatus as described in any one of Claims 1-6,
A sensor for detecting the density of the image is arranged on the print head,
The printing apparatus according to claim 1, wherein the gradation pattern of the adjustment image has a density that gradually changes in a main scanning direction of the print head. In the printing apparatus as described in any one of Claims 1-7,
The print head includes a plurality of head units each having a plurality of ink discharge nozzles, and the ink discharge nozzles of each head unit constitute a nozzle group. apparatus. Adjustment of an ink jet printing apparatus in which a print head provided with a plurality of ink ejection nozzles is scanned at least in the main scanning direction, and ink droplets are ejected by the ejection nozzles to print an image on a print member. A method,
A plurality of ink discharge nozzles of the print head are divided into a plurality of nozzle groups each consisting of at least one discharge nozzle;
Preparation of adjustment image data comprising a reference density pattern having a predetermined reference density and a gradation pattern in which the density gradually changes in one direction and the density at the set position is the reference density. ,
Based on the image data for adjustment, the reference density pattern is printed on the print member by any one reference nozzle group of the plurality of nozzle groups, and each nozzle group other than the reference nozzle group respectively prints the reference density pattern. An adjustment image creating step of creating the adjustment image by printing the gradation pattern;
The reference density pattern of the adjustment image and the density of each gradation pattern are detected by a sensor, and based on the signal from this sensor, the position where the reference density and the density match in each gradation pattern is specified. A density deviation detecting step for obtaining a density deviation of each gradation pattern with respect to a reference density pattern based on a deviation of the density matching position from the set position;
A characteristic difference detecting step for obtaining a deviation of ink discharge amount characteristics from a reference nozzle group of each nozzle group corresponding to each gradation pattern of the image for adjustment based on the density deviation obtained in the density deviation detecting step;
An ink discharge state correction step of correcting the discharge state of the ink droplets by each nozzle group so that the deviation is reduced according to the deviation of the ink discharge amount characteristic obtained in the characteristic difference detection step;
A method for adjusting a printing apparatus, comprising:

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