JP4737625B2 - Image forming apparatus and image forming method - Google Patents

Description

  The present invention relates to an image forming apparatus and an image forming method, and more particularly to image formation for recording a desired image on a recording medium while ejecting ink from the recording head while scanning the recording head relative to the recording medium. The present invention relates to an apparatus and an image forming method.

  2. Description of the Related Art In recent years, ink jet image formation for recording a desired image on a recording medium by ejecting ink droplets from a large number of nozzles provided in the recording head (hereinafter simply referred to as “head”) toward the recording medium. Devices (inkjet recording devices) are widely used. For example, recording is performed for each recording band while repeatedly scanning a plurality of heads mounted on the carriage (integrated with the carriage) in a direction (main scanning direction) orthogonal to the recording medium conveyance direction (sub-scanning direction). There is something.

  In such an image forming apparatus, due to a slight error of the paper feed mechanism and various other factors, the density of the connection area between the recording bands recorded by the preceding and following scans is increased compared to other normal areas, and density unevenness is increased. May become visible. For this reason, techniques for preventing density unevenness in the connection region have been proposed.

For example, in Patent Document 1, as shown in the upper part of FIG. 14, the paper feed amount for one scan is set to the reference paper feed so that the first and second recording band ends recorded by the preceding and following scans overlap. The amount is set to be smaller than the amount, and in this state, the droplets are thinned out from the joint area. That is, droplet ejection control is performed so that the head droplet ejection rate for the joint region is smaller than the head droplet ejection rate for the normal region, thereby preventing an increase in density in the joint region.
JP 2004-168003 A

  Here, the droplet ejection control method (conventional droplet ejection control method) described in Patent Document 1 will be described in more detail. The left and right figures in the lower part of FIG. 14 are enlarged images of 40 pixels (8 pixels in the vertical direction × 5 pixels in the horizontal direction) between the first and second recording bands. In these drawings, the pixels indicated by reference numerals “1A” and “1B” are ejected during the previous scanning (when the first recording band is formed), and the reference numerals are applied during the subsequent scanning (when the second recording band is formed). This indicates that the pixels indicated by “2A” and “2B” are ejected. Note that the pixels indicated by reference numerals “1A” and “2A” are pixels corresponding to the normal area, and the reference signs “1B” and “2B” are pixels corresponding to the connection area.

  When the recorded image has a high density, as shown in the left figure, when the printing rate of the joint area is 100% (same as the normal area) (that is, when droplet ejection is performed with a head ejection rate of 50% with respect to the joint area). ) In some cases, the density of the connection area is higher than that of the normal area. This is because 100% of the normal area is recorded in one scan, whereas 50% of the connected area is recorded in the previous scan, and after the ink color material is fixed, the remaining 50% is recorded in the subsequent scan. Since the color material of the ink that was subsequently ejected is easily fixed around the color material of the ink that was previously ejected, the color material of the ink is likely to remain on the surface side of the recording medium as a whole. It is estimated that the density of the connection area is higher than that of the normal area. For this reason, when the connecting area has a high density, as shown in the right figure, droplet ejection is performed with the head droplet ejection rate being lowered for the joining area so that the printing rate of the joining area is smaller than 100%. . However, if the printing rate of the joining area is lowered in this way, a lot of white background (undropped pixels) is generated in the joining area, which may lead to a reduction in printing quality.

  The present invention has been made in view of such circumstances, and provides an image forming apparatus and an image forming method capable of realizing good print quality without density unevenness while suppressing generation of a white background in a connection area. With the goal.

In order to achieve the object, the invention according to claim 1 is characterized in that the ink ejecting means scans an ink ejecting means capable of ejecting at least two types of inks having different densities relative to a recording medium, and An image forming apparatus that performs recording on a recording medium by ejecting ink, and includes a region in the vicinity of an end portion that touches or overlaps another recording band among recording bands recorded on the recording medium by scanning of the ink ejection unit. In addition, the area other than the joining area is set as a normal area, the dark ink drop rate for the normal area is P (A), the light ink drop rate is P (a), and the dark ink drop rate for the continuous area is Provided is an image forming apparatus provided with droplet ejection control means for performing droplet ejection control so that the following equation is satisfied when P (B) and the droplet ejection rate of light ink are P (b): .
P (B) = k × P (A)
P (b) = k ′ × P (a)
k ≦ 1 <k ′

According to the present invention, not only thin ink droplets are thinned out more than light ink droplets, but also light ink droplets are ejected onto portions (pixels) where dark ink droplets are thinned out. As a result, it is possible to prevent a reduction in the printing rate of the connection area. As a result, it is possible to prevent an increase in density while suppressing the occurrence of white background in the connection area, and to realize good print quality without density unevenness.
The “droplet ejection rate (number of head droplets)” refers to the number of droplets deposited per unit area on which a head droplets a specific region.

According to a second aspect of the present invention, an ink ejection unit capable of ejecting at least two types of inks having different densities is scanned relative to the recording medium, and ink is ejected from the ink ejection unit onto the recording medium. An image forming apparatus for performing recording, wherein among the recording bands recorded on the recording medium by scanning of the ink ejection means, a connection region is provided in the vicinity of an end contacting or overlapping with another recording band, and a region other than the connection region is a normal region. P (A) is the dark ink drop rate for the normal region, P (a) is the light ink drop rate for the normal region, P (B) is the dark ink drop rate for the connected region, and Provided is an image forming apparatus provided with droplet ejection control means for performing droplet ejection control so as to satisfy the following formula when the droplet ejection rate is P (b).
P (B) = k × P (A)
P (b)> 0
P (a) = 0
k ≦ 1

According to the present invention, even in the case where image recording is performed only with dark ink, the printing rate of the connection area is obtained by ejecting light ink onto a portion (pixel) where ink droplets are thinned out. Can be prevented. As a result, it is possible to prevent an increase in density while suppressing the occurrence of white background in the connection area, and to realize good print quality without density unevenness.

A third aspect of the present invention is the image forming apparatus according to the first or second aspect , wherein the droplet ejection control means performs the droplet ejection control according to an image density.

In order to achieve the above object, according to a fourth aspect of the present invention, there is provided an ink ejection unit that scans an ink ejection unit capable of ejecting at least two types of inks having different densities relative to a recording medium. An image forming method for performing recording on a recording medium by ejecting more ink, wherein among the recording bands recorded on the recording medium by scanning of the ink ejecting means, the vicinity of an end portion that contacts or overlaps with another recording band is connected. A region other than the region and the joining region is set as a normal region, a dark ink droplet ejection rate for the normal region is P (A), a light ink droplet deposition rate is P (a), and the dark ink droplet ejection rate for the joint region is An image forming method is characterized in that droplet ejection control is performed so that the following equation is satisfied, where P (B) is the droplet ejection rate of the light ink and P (b).
P (B) = k × P (A)
P (b) = k ′ × P (a)
k ≦ 1 <k ′

The invention described in 請 Motomeko 5, while relatively scanned with respect to concentrations of at least two different ink recording medium an ink ejecting means capable of ejecting a recording medium by ejecting ink from said ink discharge means An image forming method for performing recording on the recording medium, wherein, among the recording bands recorded on the recording medium by scanning of the ink ejection means, the vicinity of the end portion in contact with or overlapping with the other recording bands is connected, and the areas other than the connecting areas are usually set. The area is defined as P (A), the ink drop rate for the normal area is P (A), the ink drop rate for the light ink is P (a), the ink drop rate for the dark ink is P (B), and the light ink An image forming method is characterized in that the droplet ejection control is performed so that the following equation is satisfied when the droplet ejection rate is P (b).
P (B) = k × P (A)
P (b)> 0
P (a) = 0
k ≦ 1

A sixth aspect of the present invention is the image forming method according to the fourth or fifth aspect, wherein the droplet ejection control is performed according to the image density.

  According to the present invention, it is possible to prevent an increase in density while suppressing the occurrence of a white background in a connection area, and to realize good print quality without density unevenness.

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

(First embodiment)
FIG. 1 is an overall configuration diagram of an inkjet recording apparatus 10 according to the first embodiment. The inkjet recording apparatus 10 supplies a printing unit 12 having a plurality of heads provided for each ink color, an ink storage / loading unit 14 for storing ink to be supplied to each head, and a recording paper 16. The sheet feeding unit 18, the decurling unit 20 for removing the curl of the recording paper 16, and the nozzle surface (ink ejection surface) of the printing unit 12 are arranged to face the recording sheet 16 while maintaining the flatness. A suction belt conveyance unit 22 that conveys the paper 16, a print detection unit 24 that reads a printing result by the printing unit 12, and a paper discharge unit 26 that discharges printed recording paper (printed matter) to the outside. Yes.

  In FIG. 1, a magazine for rolled paper (continuous paper) is shown as an example of the paper supply unit 18, but a plurality of magazines having different paper widths, paper quality, and the like may be provided side by side. Further, instead of the roll paper magazine or in combination therewith, the paper may be supplied by a cassette in which cut papers are stacked and loaded.

  In the case of an apparatus configuration using roll paper, a cutter 28 is provided as shown in FIG. 1, and the roll paper is cut into a desired size by the cutter 28. The cutter 28 includes a fixed blade 28A having a length equal to or greater than the conveyance path width of the recording paper 16, and a round blade 28B that moves along the fixed blade 28A. The fixed blade 28A is provided on the back side of the print. The round blade 28B is arranged on the print surface side with the conveyance path interposed therebetween. Note that the cutter 28 is not necessary when cut paper is used.

  When multiple types of recording paper are used, an information recording body such as a barcode or wireless tag that records paper type information is attached to the magazine, and the information on the information recording body is read by a predetermined reader. Therefore, it is preferable to automatically determine the type of paper to be used and perform ink ejection control so as to realize appropriate ink ejection according to the type of paper.

  The recording paper 16 delivered from the paper supply unit 18 retains curl due to having been loaded in the magazine. In order to remove this curl, heat is applied to the recording paper 16 by the heating drum 30 in the direction opposite to the curl direction of the magazine in the decurling unit 20. At this time, it is more preferable to control the heating temperature so that the printed surface is slightly curled outward.

  After the decurling process, the cut recording paper 16 is sent to the suction belt conveyance unit 22. The suction belt conveyance unit 22 has a structure in which an endless belt 33 is wound between rollers 31 and 32, and at least a portion facing the nozzle surface of the printing unit 12 and the sensor surface of the printing detection unit 24 is flat. It is configured to make.

  The belt 33 has a width that is greater than the width of the recording paper 16, and a plurality of suction holes (not shown) are formed on the belt surface. As shown in FIG. 1, an adsorption chamber 34 is provided at a position facing the nozzle surface of the print unit 12 and the sensor surface of the print detection unit 24 inside the belt 33 spanned between the rollers 31 and 32. Then, the suction chamber 34 is sucked by the fan 35 to be a negative pressure, whereby the recording paper 16 on the belt 33 is sucked and held.

  The power of a motor (not shown) is transmitted to at least one of the rollers 31 and 32 around which the belt 33 is wound, so that the belt 33 is driven in the clockwise direction in FIG. The recording paper 16 is conveyed in the sub-scanning direction (paper conveying direction) in FIG.

  Since ink adheres to the belt 33 when a borderless print or the like is printed, the belt cleaning unit 36 is provided at a predetermined position outside the belt 33 (an appropriate position other than the print area). Although details of the configuration of the belt cleaning unit 36 are not shown, for example, there are a method of niping a brush roll, a water absorbing roll, etc., an air blowing method of spraying clean air, or a combination thereof. In the case where the cleaning roll is nipped, the cleaning effect is great if the belt linear velocity and the roller linear velocity are changed.

  Although a mode using a roller / nip transport mechanism instead of the suction belt transport unit 22 is also conceivable, when the print area is transported by a roller / nip, the roller comes into contact with the print surface of the paper immediately after printing, so that the image blurs. There is a problem that it is easy. Therefore, as in this example, suction belt conveyance that does not contact the image surface in the printing region is preferable.

  A heating fan 40 is provided on the upstream side of the printing unit 12 on the paper conveyance path formed by the suction belt conveyance unit 22. The heating fan 40 heats the recording paper 16 by blowing heated air onto the recording paper 16 before printing. Heating the recording paper 16 immediately before printing makes it easier for the ink to dry after landing.

  The ink storage / loading unit 14 has a tank that stores ink of a color corresponding to each head of the printing unit 12, and each tank communicates with each head through a pipe line (not shown). Further, the ink storage / loading unit 14 includes notifying means (display means, warning sound generating means, etc.) for notifying when the ink remaining amount is low, and has a mechanism for preventing erroneous loading between colors. is doing.

  The print detection unit 24 includes an image sensor (line sensor or the like) for imaging the droplet ejection result of the print unit 12, and means for checking nozzle clogging and other ejection defects from the droplet ejection image read by the image sensor. Function as.

  The print detection unit 24 of this example is composed of a line sensor having a light receiving element array that is wider than the image recording width of the recording paper 16. The line sensor includes an R sensor row in which photoelectric conversion elements (pixels) provided with red (R) color filters are arranged in a line, a G sensor row provided with green (G) color filters, The color separation line CCD sensor includes a B sensor array provided with a blue (B) color filter. Instead of the line sensor, an area sensor in which the light receiving elements are two-dimensionally arranged can be used.

  The print detection unit 24 reads the test pattern printed by each color head and detects the ejection of each head. The ejection determination includes the presence / absence of ejection, measurement of dot size, measurement of dot landing position, and the like.

  A post-drying unit 42 is provided following the print detection unit 24. The post-drying unit 42 is means for drying the printed image surface, and for example, a heating fan is used. Since it is preferable to avoid contact with the printing surface until the ink after printing is dried, a method of blowing hot air is preferred.

  When printing on porous paper with dye-based ink, the weather resistance of the image is improved by preventing contact with ozone or other things that cause dye molecules to break by blocking the paper holes by pressurization. There is an effect to.

  A heating / pressurizing unit 44 is provided following the post-drying unit 42. The heating / pressurizing unit 44 is a means for controlling the glossiness of the image surface, and pressurizes with a pressure roller 45 having a predetermined uneven surface shape while heating the image surface to transfer the uneven shape to the image surface. To do.

  The printed matter generated in this manner is outputted from the paper output unit 26. It is preferable that the original image to be printed (printed target image) and the test print are discharged separately. The ink jet recording apparatus 10 is provided with sorting means (not shown) for switching the paper discharge path in order to select the print product of the main image and the print product of the test print and send them to the discharge units 26A and 26B. ing. Note that when the main image and the test print are simultaneously formed in parallel on a large sheet, the test print portion is separated by a cutter (second cutter) 48. The cutter 48 is provided immediately before the paper discharge unit 26, and cuts the main image and the test print unit when the test print is performed on the image margin. The structure of the cutter 48 is the same as that of the first cutter 28 described above, and includes a fixed blade 48A and a round blade 48B.

  Although not shown, the paper output unit 26A for the target prints is provided with a sorter for collecting prints according to print orders.

  FIG. 2 is a plan view of a main part around the printing unit 12 of the inkjet recording apparatus 10. The printing unit 12 is provided with a carriage 62 that can reciprocate along a guide rail 60 that extends in the paper width direction (main scanning direction) of the recording paper 16. In addition to the heads 50K, 50C, 50M, and 50Y corresponding to the standard colors (KCMY) of black (K), cyan (C), magenta (M), and yellow (Y), the carriage 62 is further provided with light black ( LK), light cyan (LC), light magenta (LM), and light yellow (LY) heads 50LK, 50LC, 50LM, and 50LY corresponding to light ink (light ink) with a lighter density than standard colors (KCMY) Has been. The combination of the ink color and the number of colors is not limited to this embodiment.

  While each head 50 is integrally scanned with the carriage 62 in the main scanning direction, the corresponding color ink is ejected from each head 50 to record a recording band having a predetermined width in the sub-scanning direction, and then the recording paper 16 Are transported in the sub-scanning direction, and a desired image is recorded on the recording paper 16 by repeating these operations.

  FIG. 3 is a plan view showing the nozzle surface of the head 50. As shown in the figure, nozzles 51 for ejecting ink are arranged in a staggered pattern along the sub-scanning direction on the nozzle surface of the head 50, and the projection nozzle rows projected along the sub-scanning direction are even. It is comprised so that it may become a nozzle pitch. In this embodiment, the nozzle pitch is 1200 npi (nozzle / inch). In addition, although the case where the number of nozzles is 32 is shown in order to simplify the description, more nozzles are actually provided.

  4A and 4B are configuration diagrams showing the internal structure of the head 50. FIG. 4A is a plan perspective view showing a part thereof, and FIG. 4B is a cross-sectional view taken along line 4b-4b in FIG. The head 50 of this example is provided with individual flow paths 52 corresponding to the respective nozzles 51. Each individual channel 52 communicates with a common channel 55. A heating element 58 is provided on one wall surface of the individual flow path 52 as an ejection unit for ejecting ink droplets from the nozzle 51. In this example, the heating element 58 is disposed on the wall surface facing the nozzle 51. The common flow channel 55 stores ink supplied from the ink storage / loading unit 14 of FIG. 1, and ink is distributed and supplied from the common flow channel 55 to each individual flow channel 52.

  With this configuration, when a predetermined drive signal is supplied to the heating element 58, bubbles grow in the individual flow path 52 due to heat generated by the heating element 58, and ink droplets are ejected from the nozzles 51 by the pressure generated by the bubbles. . After the ink is ejected, the ink is supplied again from the common channel 55 to the individual channel 52.

  FIG. 5 is a principal block diagram showing the system configuration of the inkjet recording apparatus 10. The inkjet recording apparatus 10 includes a communication interface 70, a system controller 72, an image memory 74, a motor driver 76, a heater driver 78, a print control unit 80, an image buffer memory 82, a head driver 84, and the like.

  The communication interface 70 is an interface unit that receives image data sent from the host computer 86. A serial interface or a parallel interface can be applied to the communication interface 70. In this part, a buffer memory (not shown) for speeding up communication may be mounted.

  Image data sent from the host computer 86 is taken into the inkjet recording apparatus 10 via the communication interface 70 and temporarily stored in the image memory 74. The image memory 74 is a storage unit that temporarily stores an image input via the communication interface 70, and data is read and written through the system controller 72. The image memory 74 is not limited to a memory made of a semiconductor element, and a magnetic medium such as a hard disk may be used.

  The system controller 72 is a control unit that controls each unit such as the communication interface 70, the image memory 74, the motor driver 76, and the heater driver 78. The system controller 72 includes a central processing unit (CPU) and its peripheral circuits, and performs communication control with the host computer 86, read / write control of the image memory 74, and the like, as well as a transport system motor 88 and heater 89. A control signal for controlling is generated.

  The motor driver 76 is a driver (drive circuit) that drives the motor 88 in accordance with an instruction from the system controller 72. The heater driver 78 is a driver that drives the heaters 89 of the post-drying unit 42 and other units in accordance with instructions from the system controller 72.

  The print control unit 80 has a signal processing function for performing various processing and correction processing for generating a print control signal from the image data in the image memory 74 according to the control of the system controller 72, and the generated print A control unit that supplies a control signal (dot data) to the head driver 84. Necessary signal processing is performed in the print controller 80, and the ejection amount and ejection timing of the ink droplets of the head 50 are controlled via the head driver 84 based on the image data. Thereby, a desired dot size and dot arrangement are realized. In particular, the print control unit 80 performs droplet ejection control based on the droplet ejection control method according to the present invention described later.

  The print control unit 80 includes an image buffer memory 82, and image data, parameters, and other data are temporarily stored in the image buffer memory 82 when image data is processed in the print control unit 80. In FIG. 5, the image buffer memory 82 is shown in a form associated with the print control unit 80, but it can also be used as the image memory 74. Also possible is an aspect in which the print controller 80 and the system controller 72 are integrated and configured with one processor.

  The head driver 84 generates a drive signal for driving the heating elements 58 (see FIG. 4) of the heads 50 of the respective colors based on the print data given from the print control unit 80, and the generated driving signal is generated in the heating elements 58. Supply. The head driver 84 may include a feedback control system for keeping the driving condition of the head 50 constant.

  As described above, the print detection unit 24 reads the test pattern recorded by the head 50, performs necessary signal processing, etc., and determines the ink ejection status (e.g. ejection status, dot size, dot landing position, etc.) of the head 50. Detection is performed (that is, variation in each nozzle 51 is detected), and the detection result is provided to the print control unit 80. The print controller 80 performs various corrections on the head 50 based on information obtained from the print detector 24 as necessary.

  Next, the droplet ejection control method according to the first embodiment of the present invention will be described with reference to FIG. In this embodiment, as shown in the upper part of the figure, the paper feed amount for one scan is set to be smaller than the reference paper feed amount, and the first and second recording band end portions recorded by the preceding and following scans. This is the same as the conventional droplet ejection control method in that the overlapping region exists. In the present embodiment, this overlapping area is handled as a connecting area.

  In the conventional droplet ejection control method, as described above, droplet ejection control is performed in this state so that the head droplet ejection rate for the joint region is smaller than the head droplet ejection rate for the normal region. That is, when the head droplet ejection rate for the normal region is P (A) and the head droplet ejection rate for the joint region is P (B), this droplet ejection control satisfies the following equation.

P (B) = k × P (A) (where k <1) (1)
It should be noted that the head droplet ejection rate P (B) for the joint region is the average value of the head droplet ejection rate in the preceding and following scans.

  As described above, in the conventional droplet ejection control method, the density increase in the joint region is prevented by thinning out the droplets for the joint region by a predetermined amount. However, when the recorded image has a high density, as shown in the right diagram in the lower part of FIG. 14, many white backgrounds (undropped pixels) are generated in the connection area due to a decrease in the printing rate of the connection area. There is.

  On the other hand, in the present invention, ink (lighter ink) having a lower density than the ink (dark ink) ejected onto other pixels with respect to the white background (non-droplet pixel) generated in the joining region by the conventional droplet ejection control method. Ink ejection control is performed such that ink) is ejected. That is, when recording an image using dark ink, not only thin ink droplets are thinned out in the connection area, but also light ink droplets are ejected onto portions (pixels) where the dark ink droplets are thinned out. That is, as shown in the lower part of FIG. 6, dark ink is ejected onto the pixels indicated by reference numerals “1A” and “1B” during the previous scanning (when the first recording band is formed), and the reference numeral “1b”. ”Is applied to the pixels in the connection area indicated by“ ”, and the dark ink is applied to the pixels indicated by reference numerals“ 2A ”and“ 2B ”during the subsequent scanning (when the second recording band is formed). Drip.

  Here, the head droplet ejection rate of the dark ink for the normal region is P (A), the head droplet ejection rate of the dark ink for the joint region is P (B), and the head droplet ejection rate of the light ink for the normal region is P (a). ), Where P (b) is the head droplet ejection rate of the light ink with respect to the joint region, the droplet ejection control method according to the first embodiment of the present invention satisfies Equation (1) and the following two equations.

P (b)> 0 (2)
P (a) = 0 (3)
It should be noted that the head drop rate P (B) and P (b) of the dark ink and the light ink with respect to the joint area are the average values of the head drop rates in the preceding and following scans, respectively.

  In this embodiment, the light ink is ejected onto the joint area at the time of the previous scan, but the present invention is not limited to this, and the ink may be ejected at the time of the subsequent scan, or may be ejected at the time of the previous and subsequent scans. May be. Further, FIG. 6 shows the case where the light ink is ejected to a part of the undropped pixels in the joint area, but the light ink may be ejected to all the undropped pixels. .

  In the present embodiment, the connecting area is the overlapping area of the end portions of the first and second recording bands. However, the present invention is not limited to this, and an adjacent area near the overlapping area may also be included. In other words, the head droplet ejection rate for the joint region including the adjacent region may be set to be lower than the head droplet ejection rate for the normal region.

  The combination of dark and light inks may be, for example, a combination of color inks having the same color and different densities such as magenta (M) and light magenta (LM), or different colors such as cyan (C) and light yellow (LY). A combination of color inks having different densities may be used. However, the former combination is preferable because the visibility of a white background can be more effectively reduced.

  According to the first embodiment, when recording an image using dark ink, not only thin ink droplets are thinned out to the joint area, but also a portion (pixel) where the dark ink droplets are thinned out. By ejecting the light ink, it is possible to prevent a reduction in the printing rate of the joint area. As a result, it is possible to prevent an increase in density while suppressing the occurrence of white background in the connection area, and to realize good print quality without density unevenness.

  It is preferable to change the head drop rate of the dark ink and the light ink with respect to the connection region in accordance with the density of the recorded image. That is, as the density of the recorded image increases, the head drop rate of the dark ink for the joint area is reduced, while the head drop rate of the light ink for the joint area is increased. Thereby, the visibility of density unevenness in the connection region can be more effectively reduced.

(Second Embodiment)
Next, a second embodiment according to the present invention will be described. In the following description, description of parts common to the first embodiment described above will be omitted, and description will be made focusing on characteristic parts of the present embodiment.

  In the second embodiment, the paper feed amount for one scan is set to be smaller than the reference paper feed amount so that the first and second recording band ends recorded by the preceding and following scans overlap. The point is the same as in the first embodiment.

  Hereinafter, the droplet ejection control method according to the second embodiment of the present invention will be described in detail using the four droplet ejection control examples 1 to 4 shown in FIG. Here, in order to simplify the description, a case will be described in which dark and light inks are respectively ejected at a ratio of 50% and a solid image is recorded at a printing rate of 100%.

  In droplet ejection control examples 1 and 2 shown in FIGS. 2A and 2B, the same concept as the conventional droplet ejection control method is applied. The droplet ejection control example 2 is a case where the recorded image has a higher density than the droplet ejection control example 1, and the head droplet ejection rate for the joint area is lowered. As shown in these drawings, in the droplet ejection control examples 1 and 2, the droplet ejection of the dark ink and the light ink is uniformly thinned out in the connection region. For this reason, as in the droplet ejection control example 2, a lot of white backgrounds may be generated in the joining region.

  Here, as described above, the head ejection rate of the dark ink for the normal region is P (A), the head ejection rate of the dark ink for the connection region is P (B), and the head ejection rate of the light ink for the normal region is Assuming P (a) and P (b) as the head ejection rate of the light ink with respect to the joint region, in the droplet ejection control examples 1 and 2, the following two equations satisfy the condition k = k ′ ≦ 1. ing.

P (B) = k × P (A) (4)
P (b) = k ′ × P (a) (5)
It should be noted that the head droplet ejection rates P (B) and P (b) for the joint area are the average values of the head droplet ejection rates in the preceding and following scans.

  On the other hand, the droplet ejection control example 3 shown in FIG. 7C applies the droplet ejection control method according to the present invention. In the droplet ejection control example 3, the coefficient k ′ representing the ratio between the head droplet ejection rate P (a) of the light ink relative to the normal region and the head droplet ejection rate P (b) of the light ink relative to the connection region is 1 or less, and The droplet ejection control is performed so that the coefficient k ′ is larger than the coefficient k representing the ratio of the dark ink head droplet ejection rate P (A) to the normal region and the dark ink head droplet ejection rate P (B) to the connection region. It is what I did. That is, droplet ejection control is performed so as to satisfy the condition of k <k ′ ≦ 1 in the equations (4) and (5). In other words, a lot of dark ink droplets are thinned out compared to light ink droplets in the joint region, and more pixels are ejected with light ink in the joint region than in droplet ejection control example 2. The white background (undropped pixels) is low.

  A droplet ejection control example 4 shown in FIG. 7D also applies the droplet ejection control method according to the present invention. In the droplet ejection control example 4, the coefficient k ′ representing the ratio between the head droplet ejection rate P (a) of the light ink relative to the normal region and the head droplet ejection rate P (b) of the light ink relative to the connection region is greater than 1, and The droplet ejection control is performed so that the coefficient k representing the ratio of the head ejection rate P (A) of the dark ink to the normal region and the head ejection rate P (B) of the dark ink to the connection region is 1 or less. is there. That is, droplet ejection control is performed so as to satisfy the condition of k ≦ 1 <k ′ in equations (4) and (5). In the droplet ejection control example 4, in addition to thinning out the dark ink droplets more than the light ink droplets in the joint area, the ink droplets are further thinned out in the joint area (pixels). Thus, light ink is ejected, and the ratio of the light ink in the connecting region is further increased. For this reason, the difference in the amount of water between the normal region and the connecting region is reduced, the difference in the amount of swelling due to the water is small, the occurrence of undulation of minute paper is suppressed, and the transportability is improved.

  Even in the case where an image is recorded using dark and light inks in this way, as shown in droplet ejection control examples 3 and 4, by thickening the ink droplets of dark ink more than the light ink droplets in the joint area, More specifically, in the equations (4) and (5), by performing droplet ejection control so as to satisfy the condition of k <k ′ ≦ 1 or k ≦ 1 <k ′, A reduction in printing rate can be prevented. As a result, it is possible to prevent an increase in density while suppressing the occurrence of white background in the connection area, and to realize good print quality without density unevenness.

  The coefficients k and k ′ representing the ratio of the respective droplet ejection rates are preferably changed according to the density of the recorded image, as shown as an example in FIGS. 8 (a) and 8 (b).

(Third embodiment)
Next, a third embodiment according to the present invention will be described. In the following description, description of parts common to the above-described embodiments will be omitted, and description will be made focusing on characteristic parts of the present embodiment.

  In the third embodiment, as shown in FIG. 9, the first and second recording band ends recorded by the preceding and following scans do not overlap. Even in such a case, the density in the vicinity of the end of the recording band may increase and density unevenness may be visually recognized. However, by applying the present invention, the density unevenness can be eliminated. Here, one raster at the rear end of the first recording band and one raster at the front end of the second recording band are collectively defined as a connection area. Note that the number of rasters constituting the connection area is not limited to one raster of each recording band.

  Hereinafter, the droplet ejection control method according to the third embodiment of the present invention will be described in detail using the four droplet ejection control examples 5 to 8 shown in FIG.

  The droplet ejection control examples 5 and 6 shown in (a) and (b) of the same figure apply the same concept as the conventional droplet ejection control method, and the droplet ejection control example 6 is applied to the droplet ejection control example 5. In comparison, the head droplet ejection rate with respect to the joint area is lowered. The droplet ejection control examples 5 and 6 correspond to the droplet ejection control examples 1 and 2 (see FIGS. 7A and 7B), respectively, and in the above-described equations (4) and (5), k = k The condition '≦ 1 is satisfied. That is, in the droplet ejection control examples 5 and 6, the droplets of the dark and light inks are uniformly thinned out in the joint region. For this reason, as in the droplet ejection control example 6, a lot of white background may occur in the joining region.

  On the other hand, droplet ejection control examples 7 and 8 shown in FIGS. 10C and 10D apply the droplet ejection control method of the present invention. The droplet ejection control examples 7 and 8 correspond to the droplet ejection control examples 3 and 4 (see FIGS. 7C and 7D), respectively. In the equations (4) and (5), the droplet ejection control example 7 is The condition k <k ′ ≦ 1 is satisfied, and the droplet ejection control example 8 satisfies the condition k ≦ 1 <k ′.

  In this way, even when the first and second recording band ends recorded by the preceding and following scans do not overlap, droplet ejection as in the droplet ejection control examples 7 and 8 is performed in the joint area corresponding to the vicinity of these recording band ends. By performing the control, it is possible to prevent a reduction in the printing rate of the connection area. As a result, it is possible to prevent an increase in density while suppressing the occurrence of white background in the connection area, and to realize good print quality without density unevenness.

  The droplet ejection control method according to the present embodiment can also be applied to the case where recording is performed by a multi-pass method as shown in FIG. The figure shows a case where a recording band corresponding to four rasters is recorded by four scans as an example. Also in this case, droplet ejection control examples 7 and 8 (FIG. 10 (c), ((c), (c), (2) in FIG. 10) are performed by connecting a total of two rasters including the raster recorded by the first scan and the raster recorded by the fourth scan. By performing the same droplet ejection control as in d), it is possible to prevent an increase in density in the joint area. Of course, the number of rasters constituting the connection area is not particularly limited.

  The present invention can also be applied to a case where a line head having a nozzle array over a length corresponding to the paper width is configured by connecting a plurality of short heads. FIG. 12 shows a line head 150 including a short first head 150A and a second head 150B as an example. In this case, since the heads 150A and 150B are arranged so as to be shifted in the sub-scanning direction, as shown in FIG. 13, the droplet ejection time difference becomes large between the boundaries of the first head recording area and the second head recording area. A phenomenon occurs in which the density near the boundary increases. Therefore, by applying the droplet ejection control method according to the present embodiment using several lines near the boundary as a connection region, it is possible to prevent an increase in density of the connection region.

  The image forming apparatus and the image forming method of the present invention have been described in detail above. However, the present invention is not limited to the above examples, and various improvements and modifications are made without departing from the gist of the present invention. Of course it is also good.

Overall configuration diagram of inkjet recording apparatus FIG. 1 is a plan view of the main part around the printing unit in FIG. Plan view showing the nozzle surface of the head Configuration diagram showing the internal structure of the head Main block diagram showing the system configuration of the inkjet recording apparatus Explanatory drawing of the droplet ejection control method concerning a 1st embodiment Explanatory drawing of the droplet ejection control method which concerns on 2nd Embodiment Explanatory drawing showing an example of the relationship between the density of the recorded image and the coefficients k and k ' Explanatory drawing which showed the relationship between the recording bands in 3rd Embodiment. Explanatory drawing of the droplet ejection control method which concerns on 3rd Embodiment Explanatory drawing showing the connecting area when recording by the multi-pass method Configuration diagram of a line head consisting of multiple short heads Explanatory drawing showing the connecting area for the line head Explanatory drawing of conventional droplet ejection control method

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Inkjet recording device, 12 ... Printing part, 16 ... Recording paper, 50 ... Head, 51 ... Nozzle, 80 ... Print control part

Claims (6)

An image forming apparatus that performs recording on a recording medium by ejecting ink from the ink ejecting means while scanning an ink ejecting means capable of ejecting at least two types of inks having different densities relative to the recording medium. ,
Of the recording bands recorded on the recording medium by the scanning of the ink discharge means, the vicinity of the edge that contacts or overlaps the other recording band is defined as a joining area, and the area other than the joining area is designated as a normal area, and dark ink is applied to the normal area. The drop rate is P (A), the light ink drop rate is P (a), the dark ink drop rate for the joint area is P (B), and the light ink drop rate is P (b). An image forming apparatus comprising: a droplet ejection control unit that performs droplet ejection control so as to satisfy the following expression.
P (B) = k × P (A)
P (b) = k ′ × P (a)
k ≦ 1 <k ′ An image forming apparatus that performs recording on a recording medium by ejecting ink from the ink ejecting means while scanning an ink ejecting means capable of ejecting at least two types of inks having different densities relative to the recording medium. ,
Of the recording bands recorded on the recording medium by the scanning of the ink discharge means, the vicinity of the edge that contacts or overlaps the other recording band is defined as a joining area, and the area other than the joining area is designated as a normal area, and dark ink is applied to the normal area. The drop rate is P (A), the light ink drop rate is P (a), the dark ink drop rate for the joint area is P (B), and the light ink drop rate is P (b). An image forming apparatus comprising: a droplet ejection control unit that performs droplet ejection control so as to satisfy the following expression.
P (B) = k × P (A)
P (b)> 0
P (a) = 0
k ≦ 1 The droplet ejection control means, the image forming apparatus according to claim 1 or claim 2, characterized in that said ejection control in accordance with the image density. An image forming method for recording on a recording medium by ejecting ink from the ink ejecting means while scanning an ink ejecting means capable of ejecting at least two types of inks having different densities relative to the recording medium. ,
Of the recording bands recorded on the recording medium by the scanning of the ink discharge means, the vicinity of the edge that contacts or overlaps the other recording band is defined as a joining area, and the area other than the joining area is designated as a normal area, and dark ink is applied to the normal area. The drop rate is P (A), the light ink drop rate is P (a), the dark ink drop rate for the joint area is P (B), and the light ink drop rate is P (b). An image forming method characterized by performing droplet ejection control so as to satisfy the following formula.
P (B) = k × P (A)
P (b) = k ′ × P (a)
k ≦ 1 <k ′ An image forming method for recording on a recording medium by ejecting ink from the ink ejecting means while scanning an ink ejecting means capable of ejecting at least two types of inks having different densities relative to the recording medium. ,
Of the recording bands recorded on the recording medium by the scanning of the ink discharge means, the vicinity of the edge that contacts or overlaps the other recording band is defined as a joining area, and the area other than the joining area is designated as a normal area, and dark ink is applied to the normal area. The drop rate is P (A), the light ink drop rate is P (a), the dark ink drop rate for the joint area is P (B), and the light ink drop rate is P (b). An image forming method characterized by performing droplet ejection control so as to satisfy the following formula.
P (B) = k × P (A)
P (b)> 0
P (a) = 0
k ≦ 1 6. The image forming method according to claim 4, wherein the droplet ejection control is performed according to an image density.

Images