JP2016182730A - Image formation device and image formation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow an influence of deviation of impact positions of liquid with respect to ideal positions to be reduced.SOLUTION: An image formation device comprises: an input section inputting image data; a detection section detecting a position of a failure nozzle casing discharge failure in a head having a plurality of nozzles discharging liquid for forming dots; a determination section determining object pixels of which the failure nozzle takes charge on the basis of the image data and the position of the failure nozzle; and a generation section performing processing distributing an error caused by the object pixels to peripheral pixels of the object pixels by an error diffusion method and generating correction data obtained by correcting the image data. Conditions for forming the dots are defined as dot formation conditions. In an ideal state where the failure nozzle is dischargeable, a region where the object pixels and the dot formation condition are the same is defined as a first region and a region where the object pixels and the dot formation condition are different is defined as a second region. The generation section generates the correction data such that the error distributed to the first region is greater than the error distributed to the second region.SELECTED DRAWING: Figure 9

Description

  The present invention relates to an image forming technique for forming an image with a liquid discharged from a nozzle of a head.

  Conventionally, a printer that prints an image by landing ink ejected from a plurality of nozzles on a pixel is known. In such a printer, a process of assigning a nozzle that is responsible for ejecting ink to each of a plurality of pixels is executed, and each nozzle ejects ink to the assigned pixel. By the way, because of foreign matter clogging, some nozzles become non-ejection nozzles that cannot eject ink, and dots are not formed where ink from non-ejection nozzles should have landed, so-called missing dots occur. There is.

JP 2006-62088 A

  Therefore, in Patent Document 1, the influence of dot missing on image quality is mitigated by using an error diffusion method. Specifically, the amount of ink ejected from each nozzle in charge of the peripheral pixel is determined by treating dot missing as an error and diffusing the error to peripheral pixels located around the pixel in charge of the non-ejection nozzle. Processing such as increasing is executed. As a result, it is possible to expect a complementary effect that the amount of ink that lands on the periphery of the portion where the missing dot is generated increases and the influence of the missing dot is alleviated. However, for the following reasons, the technique of Patent Document 1 may not always obtain a sufficient complementing effect.

  In an image forming apparatus such as the printer described above, printing is generally performed on a print medium by ejecting liquid (ink) from a nozzle while moving the head in the main scanning direction with respect to the print medium such as paper. is there. At this time, control for discharging the liquid from the nozzle is performed at a timing corresponding to the relative positional relationship between the print medium and the head. Specifically, the nozzle is caused to discharge liquid at a position on the printing medium corresponding to the assigned pixel, that is, at a timing at which it is assumed that the nozzle faces the discharge target.

  However, at the assumed timing, the nozzle does not face the ejection target, and the liquid ejected from the nozzle may land at a position shifted from the ejection target. As described above, the deviation from the ideal position (ejection target) occurs, so that even when error diffusion is used, there is a possibility that complementation of missing dots may be insufficient.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a technique that can reduce the influence of the deviation of the landing position of the liquid from the ideal position.

  In order to achieve the above object, an image forming apparatus according to the present invention is a defect that causes ejection failure among an input unit that inputs image data and a head that has a plurality of nozzles that eject liquid to form dots. A detection unit that detects the position of the nozzle, a determination unit that determines a target pixel that the defective nozzle is in charge of based on the image data and the position of the defective nozzle, and an error that occurs with respect to the target pixel in the vicinity of the target pixel And a generation unit that generates correction data by correcting the image data by performing a process of allocating to the pixels. In an ideal state in which a defective nozzle can be ejected using a dot forming condition as a dot forming condition, the target pixel And the dot formation conditions are the first area and the different dot formation conditions are the second area, and the generator determines that the error allocated to the first area is the error allocated to the second area. It is characterized by generating the correction data to be increased.

  In order to achieve the above object, an image forming method according to the present invention includes a step of inputting image data and a defective nozzle that causes a discharge failure among a plurality of nozzles that discharge liquid for forming dots. Detecting the position of the target pixel, determining the target pixel assigned to the defective nozzle based on the image data and the position of the defective nozzle, and allocating the error generated for the target pixel to pixels around the target pixel by the error diffusion method And generating correction data obtained by correcting the image data. In the ideal state where the dot forming condition is the dot forming condition and the defective nozzle is capable of discharging, the target pixel and the dot forming condition Are the same as the first area and different ones are the second area, so that the error allocated to the first area is larger than the error allocated to the second area. It is characterized in that to generate the correction data.

  In the present invention (image forming apparatus and image forming method) configured as described above, the target pixel that is in charge of the defective nozzle is determined based on the result of detecting the position of the defective nozzle that causes ejection failure. Then, the error that is distributed to the first area where the target pixel and the dot formation condition are the same is made larger than the error that is distributed to the second area where the target pixel and the dot formation condition are different, and the error generated for the target pixel is distributed. Generate data. That is, the proportion allocated to the first area having the same dot formation condition as the target pixel increases, and the supplementary effect is enhanced. Thereby, the influence of the shift | offset | difference of the landing position of the liquid from an ideal position can be reduced.

  Various specific methods for performing the error diffusion method are conceivable. Therefore, the image forming apparatus may be configured such that the generation unit performs error diffusion using a preset complementary error diffusion matrix.

  The generation unit may configure the image forming apparatus so that no error is distributed to the second region. In such a configuration, no error is distributed to the second region where the target pixel and the dot formation conditions are different. Therefore, the influence of the deviation of the landing position of the liquid from the ideal position can be more reliably reduced.

  In addition, when it is determined that the ratio of the error diffused to the first region when the error is diffused to the pixels around the target pixel, the generation unit uses the normal error diffusion method. An image forming apparatus may be configured. In such a configuration, it is possible to deal with missing dots in more various modes by properly using the normal error diffusion matrix and the complementary error diffusion matrix.

  Various specific details of the dot formation conditions are conceivable. Therefore, the image forming apparatus may be configured such that the dot formation condition is determined by either the forward path or the backward path that is the direction in which the head is scanned. Further, the image forming apparatus may be configured such that a plurality of heads are provided as the first head and the second head, and the dot formation condition is determined by either the first head or the second head. Alternatively, the head is provided with a plurality of nozzle rows in which a plurality of nozzles are arranged as the first nozzle and the second nozzle, and the dot formation condition is determined by one of the first nozzle and the second nozzle. An image forming apparatus may be configured.

  Further, the image forming apparatus may be configured such that the total ratio of errors that the generation unit distributes to pixels around the target pixel is 1.

The perspective view which shows the printer concerning one Embodiment of the image formation apparatus of this invention. FIG. 2 is a perspective view schematically showing an internal mechanism of the printer shown in FIG. 1. FIG. 2 is a block diagram showing an electrical configuration of the printer shown in FIG. 1. FIG. 6 is a diagram schematically illustrating a scanning line for ejecting ink in the main scanning by the ejection head. The figure which shows typically the dot formation procedure in 1st Embodiment. The figure which shows an example of the flowchart which converts printing data into discharge data. The figure which shows the electrical structure which performs conversion to the discharge data of printing data. The schematic diagram for demonstrating the influence which a scanning direction has on a complementation effect. The figure which shows an example of the matrix of the error diffusion method used in 1st Embodiment. The figure which shows typically the dot formation procedure in 2nd Embodiment. The figure which shows an example of the matrix of the error diffusion method used by 2nd Embodiment. The figure which shows typically the dot formation procedure in 3rd Embodiment. The figure which shows an example of the matrix of the error diffusion method used in 3rd Embodiment. The figure which shows typically the dot formation procedure in 4th Embodiment. The figure which shows the dot formation procedure in 5th Embodiment, and the example of a matrix. The figure which shows typically the dot formation procedure in 6th Embodiment. The figure which shows typically the dot formation procedure in 7th Embodiment. The figure which shows typically the dot formation procedure in 8th Embodiment. The figure which shows typically the dot formation procedure in 9th Embodiment. The figure which shows typically the dot formation procedure in 10th Embodiment.

  FIG. 1 is a perspective view showing an appearance of a printer according to an embodiment of the image forming apparatus of the present invention. FIG. 2 is a perspective view schematically showing an internal mechanism of the printer shown in FIG. FIG. 3 is a block diagram showing an electrical configuration of the printer shown in FIG. The printer 1 receives print data from a host computer 100 that is an external device, and based on the print data, drops (hereinafter referred to as “ink droplets”) of an ink composition (hereinafter simply referred to as “ink”) on a print medium RM. Is discharged). As a result, an image (including information such as characters) corresponding to the print data is printed on the print medium RM. As the printing medium RM, for example, a large sheet such as JIS standard A1 size, a roll paper having the same sheet width as the same sheet, a resin film or the like can be used.

  As shown in FIG. 1, the printer 1 includes a housing 10 formed by combining three types of box members, that is, an upper box member 10 a, a lower box member 10 b, and a small box member 10 c, and a leg portion 12 that supports the housing 10. And have. The upper box member 10a and the lower box member 10b are stacked in the vertical direction. An operation panel 14 is provided on the front right side of the upper box member 10a. The operation panel 14 includes, for example, a liquid crystal display, an organic EL display, an LED lamp, and the like, and includes a display unit (not shown) for displaying various messages and an operation unit (not shown) including various switches. I have. A cartridge holder 16 for loading an ink cartridge 20 containing ink is provided on the front left side of the lower box member 10b.

  Although not shown in FIG. 1, a spindle is horizontally provided at the rear portion (back side in FIG. 1) of the lower box member 10 b, and a roll is attached to the spindle. The roll is obtained by winding a long print medium RM before printing, and the print medium RM can be drawn from the roll between the upper box member 10a and the lower box member 10b. Then, the transport unit 31 of the internal mechanism 30 sends the print medium RM pulled out from the roll to the front side, and the head unit 32 of the internal mechanism 30 prints an image on the print medium RM. The print medium RM printed in this way is further sent to the front side of the casing 10 (the front side in FIGS. 1 and 2) by the transport unit 31 and hangs downward due to its own weight.

  Next, the internal mechanism 30 will be described with reference to FIG. The internal mechanism 30 includes a scanning unit 33 that moves the head unit 32, a cap unit 34, a flushing unit 35, and the like in addition to the transport unit 31 and the head unit 32 described above.

  The transport unit 31 includes a transport motor (not shown), a transport drive roller 311, a transport driven roller (not illustrated), a suction platen 312, and the like. The transport driving roller 311 and the suction platen 312 are arranged in this order along the sub-scanning direction S that is the transport direction of the print medium RM. The transport driving roller 311 is accommodated in the upper box member 10a. On the other hand, the suction platen 312 is accommodated in the lower box member 10b. When the transport motor operates in response to a control command from the unit controller 42 (FIG. 3) of the controller 40 that controls the entire apparatus, the transport drive roller 311 that is rotationally driven by the transport motor presses the print medium RM. Rotate and feed onto the front suction platen 312.

  The suction platen 312 has a horizontal and flat surface, and supports the print medium RM fed from the transport driving roller 311 from below. The suction platen 312 has a large number of suction holes on the surface that communicate with a reduced pressure source such as a suction fan, and sucks the print medium RM. As a result, the suction platen 312 holds the print medium RM with the curl flat under the head unit 32. In addition, a smooth guide surface 312a is formed at the front end of the suction platen 312 and smoothly guides the print medium RM to be sent out downward.

  The head unit 32 has a discharge head H as shown in FIG. As will be described later, the ejection head H has a plurality of nozzles arranged in the sub-scanning direction S, and is moved by the scanning unit 33 in the main scanning direction M (FIG. 2) orthogonal to the sub-scanning direction S. Ink droplets are ejected intermittently from each nozzle in accordance with a drive command from the unit controller 42. Thereby, dot lines (raster lines) along the main scanning direction M are formed on the print medium RM.

  As shown in FIG. 2, the scanning unit 33 includes a guide rail 331, a carriage 332, a carriage motor 333, and the like. The guide rail 331 is provided in the upper box member 10a so as to extend horizontally in the longitudinal direction. The carriage 332 is supported by the guide rail 331 and can reciprocate (scan) horizontally in the main scanning direction M along the guide rail 331. The carriage 332 carries the head unit 32 and moves together with the head unit 32.

  A timing belt 335 hung on a pair of pulleys 334 is disposed behind the guide rail 331. One of the pulleys 334 is connected to a rotation shaft (not shown) of the carriage motor 333. Between the pulleys 334, the timing belt 335 can travel in parallel with the guide rail 331. A part of the timing belt 335 is coupled to the carriage 332. Therefore, the carriage 332 moves in the main scanning direction M when the carriage motor 333 is actuated in accordance with a control command from the unit controller 42.

  A linear scale 336 is arranged in parallel to the main scanning direction M. The linear scale 336 has a transparent main body and a light shielding band formed at a constant period along the main scanning direction M. Then, the unit controller 42 recognizes the amount of movement of the carriage 332 based on the result of the carriage detector 332a mounted on the carriage 332 detecting the light shielding member.

  On the outside of the suction platen 312 in the main scanning direction M, a flushing part 35 and a cap part 34 are arranged side by side in the main scanning direction M as maintenance units. The head motor 32 can be moved to the flushing part 35 or the cap part 34 by operating the carriage motor 333 in accordance with a control command from the unit control part 42. For example, the carriage 332 (head unit 32) is moved to the flushing section 35, and ink is ejected from a predetermined nozzle to perform flushing. On the other hand, the flushing part 35 absorbs the ejected ink. By such a flushing process, the thickened ink can be removed from the head unit 32. Further, the cap unit 34 hermetically seals the lower surface of the head unit 32 during the period when the printer 1 is at rest, and prevents the ink from being thickened or solidified in the head unit 32.

  Further, the printer 1 includes a residual vibration detection unit 36 that detects a discharge state of nozzles included in the discharge head H of the head unit 32. For example, as described in Japanese Patent Application Laid-Open No. 2004-276544, the residual vibration detection unit 36 applies vibration to the ink in the cavity of the ejection head H using a piezoelectric element, and detects the behavior of the ink with respect to the residual vibration. By doing so, the ejection state of the nozzle is determined. Then, the unit control unit 42 selects a non-ejecting nozzle that cannot eject ink due to a cause such as clogging of foreign matter (for example, solidified ink) based on the result of the residual vibration detection unit 36 determining the ejection state of each nozzle. Identify.

  In the printer 1 configured as described above, the controller 40 controls each unit of the printer 1 based on the print data received from the host computer 100, and prints an image corresponding to the print data on the print medium RM. The controller 40 includes a unit control unit 42, an interface unit 44, and a memory 46. The unit controller 42 is a computer configured with a CPU (Central Processing Unit) or the like. The interface unit 44 transmits and receives data between the host computer 100 which is an external device and the printer 1. The memory 46 includes storage elements such as a RAM (Random Access Memory) and an EEPROM (Electrically Erasable Programmable Read-Only Memory), and has an area for storing a program of the unit control unit 42, a work area, and the like. Further, the memory 46 stores a matrix 5 used in an error diffusion method described in detail later.

  Then, the unit control unit 42 executes the printing program stored in the memory 46 to appropriately execute main scanning and sub-scanning, and prints an image on the printing medium RM. Here, the main scanning is an operation of moving the ejection head 320 in the main scanning direction M relative to the print medium RM while ejecting ink from the nozzles of the ejection head 320. The sub-scan is an operation for moving the ejection head 320 in the sub-scanning direction S relative to the print medium RM. In the present embodiment, main scanning is performed by moving the ejection head 320 in the main scanning direction M integrally with the carriage 332, and sub-scanning is performed by conveying the print medium RM in the sub-scanning direction S. Incidentally, the main scanning is executed in each of the forward path and the backward path of the ejection head 320 that reciprocally moves in the main scanning direction M, and the sub-scanning print medium RM on one side (arrow side) in the sub-scanning direction S. It is executed by conveying.

  FIG. 4 is a diagram schematically illustrating scanning lines on which the ejection head ejects ink during main scanning. Here, the scanning line is an imaginary line serving as an ink discharge destination parallel to the main scanning direction M. As shown in FIG. 4, in the ejection head H, a nozzle row Nr is configured by a plurality of nozzles N arranged in a row at an equal pitch parallel to the sub-scanning direction S. In the main scanning, each of the plurality of nozzles N ejects ink while moving along the scanning line L to form dots along the scanning line L. Therefore, dots can be formed collectively along the plurality of scanning lines L by one main scanning. In addition, by executing sub-scanning and moving the ejection head H in the sub-scanning direction S relative to the print medium RM, the target range W for executing main scanning is appropriately changed in the sub-scanning direction S. Can do. Here, the scanning line L indicates a planar position where the nozzle N moves in the main scanning.

  The unit control unit 42 manages ink ejection from the nozzles N for each pixel P. Specifically, the unit controller 42 defines a nozzle N responsible for dot formation for each pixel P. Further, the unit control unit 42 defines which of the plurality of main scans to be repeatedly executed, each nozzle N is to perform ink ejection to the assigned pixel P in which main scan. Accordingly, each nozzle N executes the ejection of ink to the assigned pixel P in the main scan defined by the unit control unit 42. In such control, the unit controller 42 can execute, for example, the formation of dots along one scanning line L by two main scans of the forward path and the backward path.

  FIG. 5 is a diagram schematically showing a dot formation procedure in the first embodiment, and particularly shows an example of control for forming dots for one scanning line in two main scans. The unit control unit 42 controls the dot formation execution procedure for each of the plurality of pixels P constituting the scanning line L in a line in parallel with the main scanning direction M. Specifically, as shown in the column of “outward scan” in the drawing, in the forward scan (main scan) in which the ejection head H is moved to one side ((+ M) side) in the main scan direction M, one line is used. For each pixel P configured along the scanning line L, dots d1 are formed every other pixel P. As a result, in each scanning line L, the pixels P in which the dots d1 are formed and the pixels P in which the dots d1 are not formed are alternately arranged in the main scanning direction M.

  Subsequently, in the backward scanning (main scanning) in which the ejection head H is moved to the other side ((−M) side) in the main scanning direction M, as shown in the “return scanning” column of FIG. A dot d2 is formed for the pixel P in which d1 is not formed. That is, the formation of the dot d1 in the forward scanning and the formation of the dot d2 in the backward scanning are performed complementarily to form the dots d1 and d2 for all the pixels P along each scanning line L. . Accordingly, in each scanning line L, a raster line is formed by alternately arranging the pixel P in which the dot d1 is formed in the forward scanning and the pixel P in which the dot d2 is formed in the backward scanning in the main scanning direction M. The

  Incidentally, in the example of the figure, the forward scanning is executed so that the dot d1 is formed only in one pixel P of the two pixels P adjacent to the sub-scanning direction S and corresponding to the different scanning lines L. Thus, at the time when the forward scanning is completed, the pixels P in which the dots d1 are formed and the pixels P in which the dots d1 are not formed are alternately arranged in the sub-scanning direction S. Then, the backward scanning is executed so that the dot d2 is formed in the pixel P where the dot d1 is not formed. Therefore, at the time when the backward scanning is completed, the pixel P in which the dot d1 is formed by the forward scanning and the pixel P in which the dot d2 is formed by the backward scanning are alternately arranged in the sub scanning direction S.

  The unit control unit 42 converts the print data into ejection data indicating the presence or absence of dot formation for each pixel in order to cause each nozzle N to eject ink according to such a procedure. FIG. 6 is a diagram illustrating an example of a flowchart for converting print data into ejection data by an error diffusion method. FIG. 7 is a block diagram illustrating an example of an electrical configuration for executing an error diffusion method used for converting print data into ejection data. The flowchart in FIG. 6 is executed by the unit controller 42, and the electrical configuration in FIG. 7 is established in the unit controller 42 by the unit controller 42 executing a predetermined program.

  In step S101, the main scanning for dot formation and the dot formation procedure for defining the nozzle N for each pixel P are determined. With this procedure, it is defined for each pixel P which nozzle N is to perform dot formation on the pixel P in which main scan. Further, in step S102, the unit controller 42 specifies the position of the non-ejection nozzle N detected based on the determination result of the residual vibration detector 36. Then, after resetting the count value I for identifying the pixel P to zero (step S103), the count value I is incremented (step S104).

  In step S105, the binarization processing unit 421 binarizes the corrected gradation value V2 obtained by adding the diffusion error V6 to the gradation value V1 (input value) of the I-th pixel P defined in the print data Dp. The output value V3 is generated. Note that, at the stage of obtaining the output value V3 of the first (I = 1) pixel P, the diffusion error V6 is not generated, so the corrected gradation value V2 is equal to the gradation value V1.

  In step S106, the attribute of the I-th pixel P is determined by the pixel attribute determination unit 422. Specifically, the nozzle N responsible for dot formation on the I-th pixel P is specified based on the dot formation procedure determined in step S101, and whether or not the nozzle N is the non-ejection nozzle specified in step S102. Judging.

  When the nozzle N in charge of the I-th pixel P is a non-ejection nozzle N and the I-th pixel P is a non-ejection pixel (that is, a pixel in which dot missing occurs) (in the case of “YES” in step S107) Regardless of the value of the output value V3, no dot can be formed on the I-th pixel P. Therefore, the output value V3 is reset to zero (step S108), and the reset value (zero) is output as the final output value V4 (step S109). On the other hand, if the nozzle N in charge of the I-th pixel P is not the non-ejection nozzle N (“NO” in step S107), the output value V3 is output as it is as the final output value V4 (step S109). Thus, the final output value V4 indicating whether or not dots are formed on the I-th pixel P is obtained.

  In step S110, an error V5 (= V2−V4) between the final output value V4 and the corrected gradation value V2 is calculated. In step S111, the error V5 generated for the I-th pixel P is multiplied by the corresponding element of the matrix 5 to calculate a diffusion error V6 to be distributed to the peripheral pixels P of the I-th pixel P. If the count value I is equal to or less than the maximum count value Imax (“NO” in step S112), steps S104 to S111 are repeated. On the other hand, when the count value I exceeds the maximum count value Imax (“YES” in step S112), the flowchart of FIG. 6 ends.

  In this way, the ejection data Dd composed of the final output value V4 obtained for each pixel P is generated. Then, the unit controller 42 controls the ink ejection of the nozzles N based on the ejection data Dd, thereby forming dots in each pixel P as defined by the ejection data Dd.

  As described above, the unit control unit 42 executes a process (error diffusion process) for diffusing an error caused by missing dots to the peripheral pixels P located around the pixel P in charge of the non-ejection nozzle N. As a result, the amount of ink ejected from the nozzle N in charge of the peripheral pixel P is increased, so that the amount of ink that lands on the periphery of the portion where the missing dot is generated increases and the influence of missing dot is reduced. The effect can be expected. Here, the peripheral pixels in this embodiment will be described. First, a pixel in contact with the assigned pixel P is referred to as an “adjacent pixel”. When adjacent pixels are partitioned vertically and horizontally with the assigned pixel as the center, the adjacent pixel is a pixel in contact with the apex or the side of the assigned pixel, and corresponds to 8 pixels around the assigned pixel. Further, pixels other than the assigned pixel and the adjacent pixel are referred to as “peripheral pixels”. A pixel including an adjacent pixel and a peripheral pixel is a “peripheral pixel”.

  However, if the conditions for forming dots, that is, the dot formation conditions are different between the assigned pixel P of the non-ejection nozzle N and the peripheral pixels P, this complementary effect may not be sufficiently exhibited.

  Note that the non-ejection nozzle N cannot actually form dots. Therefore, when the non-ejection nozzle N assumes an ideal state in which dots can be formed, the conditions at which the non-ejection nozzle N forms dots according to the dot formation procedure are treated as the dot formation conditions of the non-ejection nozzle N. To do.

  FIG. 8 is a schematic diagram for explaining the influence of the scanning direction, which is an example of dot formation conditions, on the complementary effect. As described above, the formation of dots on the scanning line L is performed by ejecting ink from the nozzles N that move in the main scanning direction M. Specifically, the unit control unit 42 causes the nozzle N to eject ink at a timing when the nozzle N faces the ejection target Xt, thereby causing the ink to land on the ejection target Xt and forming dots on the ejection target Xt. To do. However, in the configuration in which ink is ejected from the nozzle N while moving the nozzle N in the main scanning direction M, the actual ink landing positions X1 and X2 may deviate from the ejection target Xt in the main scanning direction M.

  For example, FIG. 8 shows a case where the ink landing positions X1 and X2 are shifted by a distance ΔX upstream of the ejection target Xt in the traveling direction of the nozzle N. The position of the dot d1 formed by the ink ejected by the forward scanning is shifted upstream in the forward direction (+ M) with respect to the ejection target Xt. On the other hand, the position of the dot d2 formed by the ink ejected in the backward scanning is shifted to the upstream side in the backward direction (−M) with respect to the ejection target Xt. Here, since the forward direction (+ M) and the backward direction (−M) are opposite to each other, the dot d1 formed by the forward scan and the dot d2 formed by the backward scan are in the main scanning direction M. The distance is shifted by 2 × ΔX. Therefore, if the scanning direction (dot formation condition) when forming dots differs between the pixel in charge of the non-ejection nozzle N and the pixel to which the error is distributed, the landing position of the ink increased by the error distribution is Therefore, the distance of 2 × Δ is shifted in the main scanning direction M from the dot missing position. As a result, the complementary effect cannot be fully exhibited.

  On the other hand, in the first embodiment, the scanning direction in forming dots is made to coincide between the assigned pixel of the non-ejection nozzle N and the error distribution destination pixel. FIG. 9 is a diagram illustrating an example of an error diffusion matrix used in the first embodiment. FIG. 9A illustrates a dot formation procedure, and FIG. 9B illustrates a matrix configuration. The arrows shown in each pixel P in FIG. 9A indicate the main scanning direction in which dots are formed in the pixel P, and the numerical values shown in each pixel P in FIG. The ratio of the error V5 allocated to is shown. Note that in FIG. 9B, the pixel P for which no numerical value is described has no element (in other words, the element is zero).

  As described above with reference to FIG. 5, in the dot formation procedure shown in FIG. 9A, dots are formed by main scanning in different directions on each pixel P adjacent in a direction parallel to the main scanning direction M or the sub-scanning direction S. Is done. On the other hand, dots are formed by main scanning in the same direction in each pixel P adjacent in a direction inclined by 45 degrees with respect to the main scanning direction M. Therefore, the matrix 5 shown in FIG. 9B shows two pixels Pa among the four pixels Pa adjacent to the I-th pixel P (I) from the direction inclined 45 degrees with respect to the main scanning direction M. It has elements (5/8, 3/8). On the other hand, the matrix 5 has no elements for the four pixels Pb adjacent to the I-th pixel P (I) from the direction parallel to the main scanning direction M or the sub-scanning direction S. Each element of the matrix 5 is set so that the total value is 1.

  Here, the value “I” is the count value I introduced in the flowchart of FIG. In the example shown here, the count value I is assigned to increase from the top to the bottom in FIG. 9 and from the left to the right. The same applies to the value “I” shown below as appropriate.

  By performing the error diffusion method using the matrix 5, the error V5 generated for the I-th pixel P (I) is adjacent to the pixel P (I) from the direction inclined by 45 degrees with respect to the main scanning direction M. It is distributed only to the pixel Pa. That is, the error V5 is distributed only to the pixels Pa where dots are formed in the main scanning in the same direction as the main scanning for forming dots on the I-th pixel P (I).

  In the first embodiment configured as described above, the non-ejection pixel P assigned to the non-ejection nozzle N is determined based on the result of detecting the position of the non-ejection nozzle N that causes ejection failure (step S107). Then, an error (= 3/8 + 5/8) in which the main scanning direction in which dots are formed (dot forming conditions) is distributed to the same pixels Pa as the non-ejection pixels P is not ejected in the main scanning direction in which dots are formed. Discharge data Dd is generated in which an error V5 generated for the non-ejection pixel P is made larger than the error (= 0) that is allocated to the pixel Pb different from the pixel P. That is, the proportion of the main scanning direction in which dots are formed is distributed to the same pixels Pa as the non-ejection pixels P increases, and the complementary effect is enhanced. Thereby, it is possible to reduce the influence of the deviation of the ink landing position from the ejection target Xt.

  In particular, in the first embodiment, the error V5 is not distributed to the pixels Pb in which the main scanning direction in which dots are formed differs from the non-ejection pixels P. This makes it possible to more reliably reduce the influence of the deviation of the ink landing position from the ejection target Xt.

  By the way, the dot formation procedure is not limited to the content shown in FIG. 5, and various changes can be made. In addition, when the dot formation procedure is changed and the position of the pixel P that forms a dot is changed in each of the forward scan and the backward scan, the matrix 5 that defines the error distribution destination may be changed. Subsequently, a part of the modified example will be described. In addition, it cannot be overemphasized that the following modifications show the same effect by comprising the same structure as the above.

  FIG. 10 is a diagram schematically illustrating a dot formation procedure in the second embodiment. In the second embodiment, as in the first embodiment, in the forward scanning and the backward scanning, the dots d1 and d2 are arranged at intervals of one pixel P with respect to the pixels P configured along one scanning line L. Complementary formation. Accordingly, in each scanning line L, a raster line is formed by alternately arranging the pixel P in which the dot d1 is formed in the forward scanning and the pixel P in which the dot d2 is formed in the backward scanning in the main scanning direction M. The However, the second embodiment is different from the first embodiment in that the forward scanning and the backward scanning are performed so that the dots d1 and d2 formed in the main scanning in the same direction are arranged in a line parallel to the sub scanning direction S. Different.

  FIG. 11 is a diagram illustrating an example of an error diffusion matrix used in the second embodiment. The notation in FIG. 11 is the same as in FIG. As described above with reference to FIG. 10, in the dot formation procedure shown in FIG. 11A, dots are formed by main scanning in different directions on each pixel P adjacent in a direction parallel to the main scanning direction M. On the other hand, in each pixel P adjacent in a direction parallel to the sub-scanning direction S, dots are formed by main scanning in the same direction. Therefore, the matrix 5 shown in FIG. 11B includes elements (5/8, 3 /) for two pixels Pa among a plurality of pixels Pa arranged in parallel with the I-th pixel P (I) and the sub-scanning direction S. 8). Of these two pixels Pa, the element (5/8) included in the pixel Pa adjacent to the pixel P (I) is the element included in the pixel Pa separated by one pixel P from the pixel P (I). It is set larger than (3/8).

  FIG. 12 is a diagram schematically illustrating a dot formation procedure in the third embodiment. In the third embodiment, dots d1 and d2 are formed in each pixel P configured along one scanning line L by main scanning in the same direction. On the other hand, dots d1 and d2 are formed in each pixel P adjacent in the direction parallel to the sub-scanning direction S by main scanning in different directions. As a result, the scanning line L in which the dot d1 is formed in each pixel P by the forward scanning and the scanning line L in which the dot d2 is formed in each pixel P by the backward operation are alternately arranged in the sub scanning direction S.

  FIG. 13 is a diagram illustrating an example of an error diffusion matrix used in the third embodiment. The notation in FIG. 13 is the same as in FIG. As described above with reference to FIG. 12, in the dot formation procedure shown in FIG. 13A, dots are formed in the main scanning in different directions on the pixels P adjacent in the direction parallel to the sub-scanning direction S. On the other hand, in each pixel P adjacent in a direction parallel to the main scanning direction M, dots are formed by main scanning in the same direction. Therefore, the matrix 5 shown in FIG. 13B has elements (5/8, 3 /) for two pixels Pa among a plurality of pixels Pa arranged in parallel with the I-th pixel P (I) and the main scanning direction M. 8). Of these two pixels Pa, the element (5/8) included in the pixel Pa adjacent to the pixel P (I) is the element included in the pixel Pa separated by one pixel P from the pixel P (I). It is set larger than (3/8).

  FIG. 14 is a diagram schematically illustrating a dot formation procedure in the fourth embodiment. In the fourth embodiment, the forward scanning and the backward scanning are alternately repeated twice, thereby forming the dots d1 and d2 in a complementary manner in the pixels P constituting one scanning line L. Specifically, in the first forward scanning, dots d1 are formed every other pixel P in each of the main scanning direction M and the sub-scanning direction S. In the first backward scanning, a dot d2 is formed in the pixel P between the dots d1 formed in the first forward scanning in the sub-scanning direction S. In the second forward scanning, a dot d1 is formed in the pixel P between the dots d2 formed in the first backward scanning in the main scanning direction M. In the fourth backward scan, the dot d2 is formed in the pixel P between each dot d1 in the sub-scanning direction S in the second forward scan.

  In such a dot formation procedure, the arrangement of the finally formed dots d1 and d2 is the same as that in the first embodiment shown in FIG. Accordingly, the error distribution of the I-th pixel P (I) by the error diffusion method may be performed using the matrix 5 shown in FIG.

  Also in these second to fourth embodiments, the error in allocating the main scanning direction (dot forming condition) for forming dots to the same pixel Pa as the non-ejection pixel P is not the main scanning direction for forming dots. Discharge data Dd is generated in which the error V5 generated for the non-ejection pixel P is allocated to be larger than the error allocated to the pixel Pb different from the ejection pixel P. That is, the proportion of the main scanning direction in which dots are formed is distributed to the same pixels Pa as the non-ejection pixels P increases, and the complementary effect is enhanced. Thereby, it is possible to reduce the influence of the deviation of the ink landing position from the ejection target Xt.

  In particular, the error V5 is not distributed to the pixel Pb in which the main scanning direction in which dots are formed differs from the non-ejection pixel P. This makes it possible to more reliably reduce the influence of the deviation of the ink landing position from the ejection target Xt.

  By the way, the number of discharge heads H mounted on the head unit 32 is not limited to one, and two or more discharge heads H may be mounted on the head unit 32 in a row or in a staggered manner in the sub-scanning direction S. it can. However, in the configuration in which the plurality of ejection heads H are mounted on the head unit 32, the positional deviation in the main scanning direction M between the landing position of the ink ejected from the nozzle N and the ejection target Xt is different from that of the plurality of ejection heads H. Can vary between. As this cause, the attachment error to the head unit 32 differs depending on the ejection head H. Therefore, if the ejection head H (dot formation condition) for ejecting ink for forming dots differs between the pixel in charge of the non-ejection nozzle N and the pixel to which the error is distributed, the amount of ink increased due to the error distribution. There is a possibility that the landing position is shifted in the main scanning direction M from the dot missing position, and the complementary effect cannot be sufficiently exhibited. Therefore, the following configuration may be used.

  FIG. 15 is a diagram schematically showing a dot formation procedure and a matrix example in the fifth embodiment, and illustrates a case where two ejection heads H1 and H2 are arranged in the sub-scanning direction S and mounted on the head unit 32. To do. In the column of “dot formation procedure” in the figure, an arrow shown in each pixel P indicates a main scanning direction in which dots are formed on the pixel P, and symbols H1 and H2 shown in each pixel P are: The ejection heads H1 and H2 that form dots on the pixel P are shown. Further, the numerical value shown in each pixel P in the column of “first example” or “second example” in the figure indicates the ratio of the error V5 allocated to the pixel P. In addition, in these columns in FIG. 15, the pixel P in which a numerical value is not described has no element (in other words, the element is zero).

  As shown in the column “Dot Forming Procedure”, in the fifth embodiment, the main scanning direction in which dots are formed on each pixel P is the same as in the first embodiment shown in FIG. In each pixel P constituting one scanning line L, dots are formed by the same ejection head H (H1 / H2). On the other hand, in each pixel P adjacent in a direction parallel to the sub-scanning direction S, dots are formed by different ejection heads H1 and H2. As a result, the scanning lines L in which dots are formed in the respective pixels P by the ejection head H1 and the scanning lines L in which dots are formed in the respective pixels P by the ejection head H2 are alternately arranged in the sub-scanning direction S.

  For such a dot formation procedure, the error distribution of the I-th pixel P (I) by the error diffusion method is performed using the matrix 5 shown in the column of “first example” or “second example” in FIG. Use it. In any of these matrices 5, both the main scanning direction in which dots are formed and the ejection head H distribute the error V5 to the same peripheral pixel P as the I-th pixel P (I). On the other hand, the error V5 is not distributed to the pixel P in which at least one of the main scanning direction in which dots are formed and the ejection head H is different from the I-th pixel P (I).

  In the fifth embodiment, the main scanning direction in which dots are formed and the error in which the ejection heads H1 and H2 (dot formation conditions) are distributed to the same pixels Pa as the non-ejection pixels P are the main scanning directions in which the dots are formed. Alternatively, the ejection heads H1 and H2 generate an ejection data Dd in which an error V5 that occurs with respect to the non-ejection pixel P is allocated by making it larger than an error that is allocated to the pixel Pb different from the non-ejection pixel P. That is, the main scanning direction in which dots are formed and the ratio of the ejection heads H1 and H2 being distributed to the same pixels Pa as the non-ejection pixels P are increased, and the complementary effect is enhanced. Thereby, it is possible to reduce the influence of the deviation of the ink landing position from the ejection target Xt.

  In particular, the error V5 is not distributed to the main scanning direction in which dots are formed or to the pixels Pb whose ejection heads H1 and H2 are different from the non-ejection pixels P. This makes it possible to more reliably reduce the influence of the deviation of the ink landing position from the ejection target Xt.

  The dot formation procedure when the two ejection heads H1 and H2 are arranged in the sub-scanning direction S and mounted on the head unit 32 is not limited to the example in FIG. Therefore, for example, dots can be formed by the dot formation procedure shown in FIGS.

  FIG. 16 is a diagram schematically illustrating a dot formation procedure in the sixth embodiment. As shown in the figure, in the sixth embodiment, the main scanning direction in which dots are formed in each pixel P is the same as that in the first embodiment shown in FIG. In addition, with different ejection heads H1 and ejection heads H2, dots are formed complementary to each other for every pixel P with respect to the pixels P constituting one scanning line L. Thus, in each scanning line L, a raster line is formed by alternately arranging pixels P in which dots are formed by the ejection head H1 and pixels P in which dots are formed by the ejection head H2 in the main scanning direction M. The Further, the dots are formed so that the dots formed by the same ejection head H (H1 / H2) are arranged in a line parallel to the sub-scanning direction S.

  FIG. 17 is a diagram schematically showing a dot formation procedure in the seventh embodiment. As shown in the figure, in the seventh embodiment, the main scanning direction in which dots are formed in each pixel P is the same as that in the third embodiment shown in FIG. In addition, with the different ejection heads H <b> 1 and H <b> 2, dots are formed complementarily to every other pixel P with respect to the pixels P configured along one scanning line L. Thus, in each scanning line L, a raster line is formed by alternately arranging pixels P in which dots are formed by the ejection head H1 and pixels P in which dots are formed by the ejection head H2 in the main scanning direction M. The Further, the dots are formed such that the dots formed by the different ejection heads H1 and H2 are arranged in a line every other pixel P in parallel to the sub-scanning direction S.

  FIG. 18 is a diagram schematically illustrating a dot formation procedure in the eighth embodiment. As shown in the figure, in the eighth embodiment, the main scanning direction in which dots are formed in each pixel P is the same as that in the third embodiment shown in FIG. In addition, with the different ejection heads H <b> 1 and H <b> 2, dots are formed complementarily to every other pixel P with respect to the pixels P configured along one scanning line L. Thus, in each scanning line L, a raster line is formed by alternately arranging pixels P in which dots are formed by the ejection head H1 and pixels P in which dots are formed by the ejection head H2 in the main scanning direction M. The Further, the dots are formed so that the dots formed by the same ejection head H (H1 / H2) are arranged in a line parallel to the sub-scanning direction S.

  FIG. 19 is a diagram schematically illustrating a dot formation procedure in the ninth embodiment. As shown in the figure, in the ninth embodiment, the main scanning direction in which dots are formed in each pixel P is the same as in the second embodiment shown in FIG. In addition, with the different ejection heads H <b> 1 and H <b> 2, dots are formed complementarily to every other pixel P with respect to the pixels P configured along one scanning line L. Thus, in each scanning line L, a raster line is formed by alternately arranging pixels P in which dots are formed by the ejection head H1 and pixels P in which dots are formed by the ejection head H2 in the main scanning direction M. The Further, the dots are formed such that the dots formed by the different ejection heads H1 and H2 are arranged in a line every other pixel P in parallel to the sub-scanning direction S.

  FIG. 20 is a diagram schematically illustrating a dot formation procedure in the tenth embodiment. As shown in FIG. 10, in the tenth embodiment, the main scanning direction in which dots are formed in each pixel P is the same as in the second embodiment shown in FIG. In each pixel P configured along one scanning line L, dots are formed by the same ejection head H (H1 / H2). On the other hand, in each pixel P adjacent in a direction parallel to the sub-scanning direction S, dots are formed by different ejection heads H1 and H2. As a result, the scanning lines L in which dots are formed in the respective pixels P by the ejection head H1 and the scanning lines L in which dots are formed in the respective pixels P by the ejection head H2 are alternately arranged in the sub-scanning direction S.

  The matrix 5 exemplified in the “first example” or the “second example” in FIG. 15 can be applied to any of the dot formation procedures of the sixth to tenth embodiments. As a result, the error V5 is distributed to the peripheral pixel P that is the same as the I-th pixel P (I) in both the main scanning direction in which dots are formed and the ejection head H. On the other hand, the error V5 is not distributed to the pixel P in which at least one of the main scanning direction in which dots are formed and the ejection head H is different from the I-th pixel P (I). As a result, the same effect as that of the fifth embodiment can be obtained.

  As described above, in the above-described embodiment, the printer 1 corresponds to an example of the “image forming apparatus” of the present invention, the interface unit 44 corresponds to an example of the “input unit” of the present invention, and the ejection heads H, H1, and H2. Corresponds to an example of the “head” of the present invention, the nozzle N corresponds to an example of the “nozzle” of the present invention, the residual vibration detection unit 36 corresponds to an example of the “detection unit” of the present invention, and the unit control unit 42 corresponds to an example of each of the “determination unit” and “generation unit” of the present invention, the pixel P in charge of the non-ejection nozzle N corresponds to an example of the “target pixel” of the present invention, and the print data Dp corresponds to the present invention. The discharge data Dd corresponds to an example of the “correction data” of the present invention, the pixel Pa corresponds to an example of the “first region” of the present invention, and the pixel Pb corresponds to the present invention. Is equivalent to an example of the “second region” and the matrix 5 is Of corresponds to an example of "complementing error diffusion matrix", ink is equivalent to an example of "liquid" in the present invention.

  The present invention is not limited to the above-described embodiment, and various modifications can be made to the above-described one without departing from the spirit of the present invention. For example, in the above embodiment, the error diffusion method is executed using the matrix 5 stored in the memory 46 in advance. However, a coefficient for allocating the error V5 to the peripheral pixels P may be calculated based on the dot formation procedure when the error diffusion method is executed, and the error diffusion method may be executed using the calculated coefficient.

  Alternatively, the normal error diffusion matrix 5 may be stored in the memory 46 separately from the complementary error diffusion matrix 5 described above. The normal error diffusion matrix 5 is a matrix that distributes the error V5 to the I-th pixel P (I) without considering the dot formation conditions. The normal error diffusion matrix 5 has a configuration different from the complementary error diffusion matrix 5, and distributes the error V5 only to the pixel P adjacent to the I-th pixel P (I), for example.

  In such a configuration, the unit controller 42 simulates the case where the error V5 is distributed to the peripheral pixels P of the I-th pixel P (I) according to the normal error diffusion matrix 5. As a result of the simulation, it is determined that the ratio of the dot formation condition to be distributed to the same pixel Pa as the non-ejection pixel P is a predetermined value (for example, 50%, 60%, 70%, 80%, or 90%) or more. In such a case, the error diffusion method is executed so that the error V5 of each pixel P is distributed to the surrounding pixels P using the normal error diffusion matrix 5. On the other hand, as a result of the simulation, if it is determined that the ratio of the dot formation condition to be distributed to the same pixel Pa as the non-ejection pixel P is less than a predetermined value, the error of each pixel P is determined using the complementary error diffusion matrix 5. The error diffusion method is executed so that V5 is distributed to the peripheral pixels P. In such a configuration, it is possible to deal with missing dots in more various modes by properly using the normal error diffusion matrix 5 and the complementary error diffusion matrix 5.

  In the above description, the main scanning direction in which dots are formed and the case where the ejection head H is used as the dot formation conditions have been described. However, specific examples of the dot formation conditions are not limited to this. For example, the number of nozzle rows Nr provided in the ejection head H is not limited to one row, and two or more nozzle rows Nr can be arranged in the main scanning direction M. However, in the configuration in which the plurality of nozzle rows Nr are provided in the ejection head H, the positional deviation in the main scanning direction M between the landing position of the ink ejected from the nozzles N and the ejection target Xt is different from the plurality of nozzle rows Nr. Can vary between. As this cause, for example, a manufacturing error at the position of each nozzle row Nr can be cited. Therefore, if the nozzle row Nr (dot formation condition) for ejecting ink for forming dots differs between the pixel in charge of the non-ejection nozzle N and the pixel to which the error is distributed, the amount of ink increased due to the error distribution There is a possibility that the landing position is shifted in the main scanning direction M from the dot missing position, and the complementary effect cannot be sufficiently exhibited.

  Therefore, the error that the nozzle row Nr that forms dots (dot formation conditions) distributes to the same pixel Pa as the non-ejection pixel P, and the error that the nozzle row Nr that forms dots distributes to the pixel Pb different from the non-ejection pixel P The ejection data Dd to which the error V5 generated for the non-ejection pixel P is distributed is preferably generated. Thereby, it is possible to reduce the influence of the deviation of the ink landing position from the ejection target Xt.

  Further, it is not necessary to employ all the various dot forming conditions such as the main scanning direction in which dots are formed, the ejection head H, and the nozzle row Nr. Therefore, only the dot formation conditions that have a particularly great influence (for example, only the main scanning direction in which dots are formed) may be adopted to diffuse the error V5 generated for the non-ejection nozzle N to the peripheral pixels P.

  Further, the method for specifying the non-ejection nozzle is not limited to the method based on the residual vibration. That is, based on the result of printing the nozzle check pattern on the ejection head H, the operator can also confirm the non-ejection nozzles. In this case, the unit controller 42 may specify the non-ejection nozzle based on the content input by the operator using the input device of the host computer 100 or the like.

  In the above embodiment, the case where the present invention is applied to a so-called large format printer has been described as an example. However, the application target of the present invention is not limited to this, and the present invention can also be applied to, for example, a sheet-fed desktop printer.

  Various specific methods for ejecting ink from the nozzles N are also conceivable. Therefore, either a piezo-type or a thermal-type nozzle N can be used.

  Various types of ink are also conceivable, and either water-based ink or non-water-based ink may be used. Examples of non-aqueous inks include, for example, ultraviolet curable inks that are cured by irradiation with ultraviolet rays.

  DESCRIPTION OF SYMBOLS 1 ... Printer, 36 ... Residual vibration detection part, 42 ... Unit control part, 44 ... Interface part, 5 ... Matrix, H, H1, H2 ... Discharge head, N ... Nozzle, P, Pa, Pb ... Pixel, Dp ... Printing Data, Dd ... Discharge data

Claims (9)

An input unit for inputting image data;
Among the heads having a plurality of nozzles that discharge liquid for forming dots, a detection unit that detects the position of a defective nozzle that causes a discharge failure; and
A determination unit that determines a target pixel that the defective nozzle is in charge of based on the image data and the position of the defective nozzle;
A generation unit that generates correction data obtained by correcting the image data by performing a process of distributing an error that occurs with respect to the target pixel to pixels around the target pixel by an error diffusion method;
With
The conditions for forming the dots are the dot formation conditions,
In the ideal state in which the defective nozzle can discharge, the target pixel and the dot formation condition are the same as the first region, and the different one is the second region,
The image forming apparatus, wherein the generation unit generates the correction data so that an error allocated to the first area is larger than an error allocated to the second area.   The image forming apparatus according to claim 1, wherein the generation unit performs error diffusion using a preset error diffusion matrix.   The image forming apparatus according to claim 1, wherein the generation unit does not distribute an error to the second region.   The generation unit uses a normal error diffusion method when it is determined that the ratio of the error diffused to the first region is greater than or equal to a predetermined value when the error is diffused to the surrounding pixels of the target pixel. The image forming apparatus according to claim 1.   5. The image forming apparatus according to claim 1, wherein the dot forming condition is determined by one of a forward path and a backward path that are directions in which the head is scanned. 6. A plurality of the heads are provided as a first head and a second head,
The image forming apparatus according to claim 1, wherein the dot forming condition is determined by any one of the first head and the second head. The head is provided with a plurality of nozzle rows in which a plurality of the nozzles are arranged as a first nozzle and a second nozzle,
The image forming apparatus according to claim 1, wherein the dot formation condition is determined by any one of the first nozzle and the second nozzle.   8. The image forming apparatus according to claim 1, wherein a total ratio of errors that the generation unit distributes to pixels around the target pixel is one. Inputting image data;
A step of detecting a position of a defective nozzle that causes a discharge failure out of a head having a plurality of nozzles that discharge liquid for forming dots; and
Determining a target pixel that the defective nozzle is responsible for based on the image data and the position of the defective nozzle;
Performing a process of allocating an error occurring on the target pixel to pixels around the target pixel by an error diffusion method to generate correction data obtained by correcting the image data;
With
The conditions for forming the dots are the dot formation conditions,
In the ideal state in which the defective nozzle can discharge, the target pixel and the dot formation condition are the same as the first region, and the different one is the second region,
The image forming method, wherein the correction data is generated so that an error allocated to the first area is larger than an error allocated to the second area.

Images