JP5469796B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus having an intermediate transfer medium, and more particularly to an image forming apparatus capable of printing in a short time without waste of paper and ink and without image quality defects.

  A conventional image forming apparatus has an ink jet printer head (liquid discharge head) in which a large number of liquid discharge nozzles are arranged, and the ink jet head and the recording medium are moved relative to each other while the ink jet head and the recording medium are moved relative to each other. Inkjet printers (inkjet recording apparatuses) that record images on a recording medium by discharging ink (liquid) are known.

  The ink jet head of such an ink jet printer is deformed by, for example, a pressure chamber to which ink is supplied from an ink tank through an ink supply path, a piezoelectric element driven by an electrical signal corresponding to image data, and driving of the piezoelectric element. A pressure generating unit including a diaphragm that forms a part of the pressure chamber, and a nozzle that communicates with the pressure chamber in which ink in the pressure chamber is ejected as droplets by reducing the volume of the pressure chamber due to deformation of the diaphragm Have. In the ink jet printer, one image is formed on the recording medium by combining dots formed by the ink ejected from the nozzles of the pressure generating unit.

  Thus, it is difficult to remove the ink adhering to the recording medium from the recording medium, and once recorded on the recording medium by the ink jet printer, it is difficult to correct even if there is a printing defect. In other words, the recording medium printed in a defective state has to be discarded, and it has been unfavorable from an economic point of view or environmental point of view.

  For this reason, several methods for reducing printing defects as much as possible have been proposed.

  For example, when the ink ejection port does not eject a desired amount of ink, it is detected whether the ink ejection port is faulty, and when the ink ejection port is faulty, the normal adjacent ink ejection port is There is a method for avoiding a printing defect by moving to a position corresponding to a failed ink ejection port and performing additional image formation (Patent Document 1).

In addition, there is a method in which a printing error of an image recorded on a printing medium is detected to identify an abnormal portion, and the printing head is moved relatively to perform printing again (Patent Document 2).
JP 2005-153521 A JP 2003-94615 A

  As described above, several methods for correcting an image defect due to a nozzle defect or the like have been proposed, but both the invention described in Patent Document 1 and the invention described in Patent Document 2 have once recorded on a recording medium. After that, the image defect portion is detected from the image information or the like recorded on the recording medium, the recording medium and the recording head are relatively moved, and a correction function for recording again using a normal nozzle is provided. Therefore, the above correction function must be repeated for each sheet until the defective nozzle head maintenance is performed and the defective nozzle recovers normally. Therefore, the time until the end of the printing time is more than double that of normal printing. Time required, and printing on a recording medium takes a significant amount of time.

  In addition, since it is necessary to relatively move the recording medium and the recording head to the image quality defect portion of the recording medium, it is necessary to add such a function to the apparatus, which increases the size of the apparatus and leads to an increase in cost. Further, if the correction cannot be made even after such correction, the recording medium remains in a state of poor image quality and is eventually discarded.

  The present invention has been made in view of such circumstances. In an image forming apparatus having a recording head such as a liquid ejection head, there is an image defect without increasing the size and cost of the apparatus. However, it is an object to provide a method capable of correcting image defects in a short time and printing.

The invention according to claim 1 is a recording head having a plurality of recording elements, an intermediate transfer medium on which an image is temporarily recorded by the recording head while moving relative to the recording head, and the intermediate In the relative movement direction of the transfer medium, an image defect detection unit that is provided downstream of the recording head and detects the presence / absence of an image defect in the image recorded on the intermediate transfer medium, and the relative relationship between the intermediate transfer medium In the relative movement direction of the intermediate transfer medium, an ink cleaning means that is provided downstream of the image defect detection means and removes ink recorded on the intermediate transfer medium by the recording head. A transfer unit provided downstream of the ink cleaning unit and configured to transfer an image recorded on the intermediate transfer medium to the recording medium; Image correction means for generating image correction data on the basis of information on the image defect when an image defect is detected by the recording head, by the recording head based on the image data to be printed on the recording medium. When the image to be printed is recorded on a transfer medium, and the image defect is detected by the image defect detection means for the image to be printed recorded on the intermediate transfer medium, and the image defect is detected. In addition, the ink recorded on the intermediate transfer medium by the recording head is removed by the ink cleaning means before reaching the transfer means, and is recorded on the intermediate transfer medium by the recording head based on the image correction data. An image forming apparatus characterized in that

  Thereby, the image correction can be made more reliable.

The invention according to claim 2 is a recording head having a plurality of recording elements, an intermediate transfer medium on which an image is temporarily recorded by the recording head while moving relative to the recording head, and the intermediate In the relative movement direction of the transfer medium, an image defect detection unit that is provided downstream of the recording head and detects the presence / absence of an image defect in the image recorded on the intermediate transfer medium, and the relative relationship between the intermediate transfer medium A transfer unit that is provided downstream of the image defect detection unit and transfers an image recorded on the intermediate transfer medium to a recording medium, and a transfer unit that moves relative to the intermediate transfer medium. Ink cleaning means provided downstream of the recording head and upstream of the recording head for removing ink recorded on the intermediate transfer medium by the recording head An image correction means for generating image correction data based on information on the image defect when an image defect is detected by the image defect detection means, and based on the image data to be printed on the recording medium The image to be printed is recorded on the intermediate transfer medium by the recording head, the presence or absence of an image defect is detected by the image defect detection means for the image to be printed recorded on the intermediate transfer medium, and the image When a defect is detected, the transfer unit is separated from the intermediate transfer medium, and after the ink recorded on the intermediate transfer medium by the recording head is removed by the ink cleaning unit, the intermediate is performed by the recording head. A test pattern is recorded on the transfer medium, and the image defect detection is performed on the test pattern image recorded on the intermediate transfer medium. By performing detection by the means, image correction data is generated by the image correction means based on the defect information of the image of the test pattern, and recording is performed on the intermediate transfer medium by the recording head based on the image correction data. An image forming apparatus characterized by the above.

  Thereby, the image correction can be made more reliable.

According to a third aspect of the present invention, there is provided a recording head having a plurality of recording elements, an intermediate transfer medium on which an image is temporarily recorded by the recording head while moving relative to the recording head, and the intermediate In the relative movement direction of the transfer medium, an image defect detection unit that is provided downstream of the recording head and detects the presence / absence of an image defect in the image recorded on the intermediate transfer medium, and the relative relationship between the intermediate transfer medium In the relative movement direction of the intermediate transfer medium, an ink cleaning means that is provided downstream of the image defect detection means and removes ink recorded on the intermediate transfer medium by the recording head. A transfer unit provided downstream of the ink cleaning unit and configured to transfer an image recorded on the intermediate transfer medium to the recording medium; Image correction means for generating image correction data based on image defect information when an image defect is detected by the recording head, recording a test pattern on the intermediate transfer medium by the recording head, About the test pattern image recorded on the medium, after detecting the presence or absence of an image defect by the image defect detection means, before the ink recorded on the intermediate transfer medium reaches the transfer means, the ink cleaning means When the defect in the test pattern image is confirmed by the image defect detection means, the image correction data is generated by the image correction means based on the information on the defect of the image of the test pattern, and based on the image correction data An image forming apparatus that records an image on the intermediate transfer medium by the recording head.

  It is possible to perform desired printing smoothly by determining whether or not a defect is possible based on the test pattern.

According to a fourth aspect of the invention, to print in the print instruction information by the image forming apparatus receives is completed, according to any one of claims 1 to 3, characterized in that does not perform maintenance of the recording head An image forming apparatus.

According to a fifth aspect of the present invention, the image correction means sets a correction range in which N (N is an integer of 2 or more) correction recording elements used for output density correction among the plurality of recording elements. Based on the setting means and the correction conditions including the condition that the differential coefficient at the frequency origin (f = 0) of the power spectrum representing the spatial frequency characteristic of density unevenness caused by the recording characteristics of the recording element is zero. Correction coefficient determining means for determining the density correction coefficient of the correction recording element; and correction processing means for performing an operation for correcting the output density using the density correction coefficient determined by the correction coefficient determining means. An image forming apparatus according to any one of claims 1 to 4 .

  The density non-uniformity (density unevenness) in the recorded image can be expressed by the intensity in the spatial frequency characteristic (power spectrum), but since the high frequency component cannot be visually recognized by human vision, the density unevenness visibility is the power spectrum. It can be evaluated with the low frequency component. Since the density correction coefficient is determined using the condition that the differential coefficient at the frequency origin (f = 0) of the power spectrum after correction using the density correction coefficient is approximately 0, the intensity of the power spectrum at the frequency origin Is minimized, and the power spectrum near the origin (that is, in the low frequency region) can be kept small. Thereby, accurate unevenness correction can be realized.

  “Characteristic information acquisition means” stores information related to the recording characteristics of the recording element in a storage means such as a memory in advance, and may acquire information by reading out necessary information. Information on recording characteristics may be obtained by printing, reading the printing result, and performing analysis processing. In view of the change in recording characteristics over time, a mode in which information is updated at an appropriate timing is preferable.

  An ink jet recording apparatus as an aspect of an image recording apparatus according to the present invention includes a nozzle that discharges ink droplets for forming dots and a pressure generation unit (such as a piezoelectric element or a heating element) that generates discharge pressure. A liquid discharge head (corresponding to “recording head”) having a droplet discharge element array in which a plurality of droplet discharge elements (corresponding to “recording elements”) are arranged, and a recording head based on ink discharge data generated from image data And an ejection control means for controlling ejection of droplets from the nozzle, and an image is formed on the recording medium by the droplets ejected from the nozzle.

  As a configuration example of the recording head, a full-line type head having a recording element array in which a plurality of recording elements are arranged over a length corresponding to the entire width of the recording medium can be used. In this case, a combination of a plurality of relatively short recording head modules having recording element arrays that are less than the length corresponding to the entire width of the recording medium, and connecting them together, has a length corresponding to the entire width of the recording medium. There is an aspect in which a recording element array is configured.

  A full-line type head is usually arranged along a direction perpendicular to the relative feeding direction (relative conveyance direction) of the recording medium, but has a certain angle with respect to the direction perpendicular to the conveyance direction. There may be a mode in which the recording head is arranged along the oblique direction.

  A “recording medium” is a medium that can record an image by the action of a recording head (an image forming medium, a recording medium, an image receiving medium, a discharge medium in the case of an inkjet recording apparatus, etc.), continuous paper, cut paper In addition, a resin sheet such as a seal sheet, an OHP sheet, a film, a cloth, an intermediate transfer medium, a printed board on which a wiring pattern is printed by an inkjet recording apparatus, and other various media and shapes are included.

  “Conveyance means” means a mode in which the recording medium is transported to a stopped (fixed) recording head, a mode in which the recording head is moved relative to the stopped recording medium, or a movement of both the recording head and the recording medium Any of the embodiments are included.

  When a color image is formed by an inkjet head, a recording head may be arranged for each color of a plurality of colors (recording liquids), or a configuration in which a plurality of colors of ink can be discharged from one recording head may be adopted. .

  The present invention is not limited to the full-line head described above, but can also be applied to shuttle scan type recording heads (recording heads that perform droplet ejection while reciprocating in a direction substantially perpendicular to the recording medium conveyance direction). It is.

  As described above, according to the present invention, it is possible to correct an image defect due to a nozzle defect or the like without increasing the size and cost of the apparatus, and it is possible to print an image having no image quality defect in a short time. effective.

  Further, by using the intermediate transfer medium, even when an image defect is found, only a normal image can be transferred, and there is an effect that paper can be printed quickly without waste.

  Hereinafter, an image forming apparatus according to the present invention will be described in detail as a first embodiment with reference to the accompanying drawings.

  FIG. 1 is an overall configuration diagram showing an outline of an embodiment of an ink jet recording apparatus as an image forming apparatus according to the first embodiment.

  As shown in FIG. 1, the ink jet recording apparatus 10 of the present embodiment has a plurality of recording heads (droplet discharge heads) 112 (112C, 112M, 112Y) that are provided for each ink color and discharge ink as droplets. 112K), an ink storage / loading unit 14 (14C, 14M, 14Y, 14K) for storing ink to be supplied to each recording head 112 (112C, 112M, 112Y, 112K), and temporarily on the surface thereof An intermediate transfer medium (intermediate transfer rotary drum) 32 on which an image is recorded, a paper supply unit 18 for supplying a recording paper 16 on which an image on the intermediate transfer medium 32 is transferred and recorded, and a recording paper 16 after recording And a discharge unit 26 for discharging.

As shown in FIG. 1, cyan (C), magenta (M), yellow (Y), and black (K) in this order from the upstream side along the rotation direction of the intermediate transfer medium 32 (the direction indicated by the arrow in the figure). Recording heads 112 (112C, 112M, 112Y, 112K) corresponding to the respective color inks are arranged.

  An image is temporarily recorded on the surface of the intermediate transfer medium 32 by ejecting ink of each color from each recording head 112 (112C, 112M, 112Y, 112K) while rotating the intermediate transfer medium 32.

  Each color recording head 112 (112C, 112M, 112Y, 112K) is filled with a liquid (hereinafter simply referred to as ink) containing a coloring material (dye or pigment).

  As an example of the paper supply unit 18, a roll paper (continuous paper) magazine (a container loaded with roll paper) may be used, or a plurality of magazines having different paper width, paper quality, and the like may be provided. Further, instead of or in combination with the roll paper magazine, the paper may be supplied by a cassette in which cut papers are stacked and loaded.

  In this embodiment, since a transfer image is once formed on the intermediate transfer medium 32 and transferred to the recording paper 16, the influence of penetration into the recording paper can be obtained by removing the solvent in the ink. Since the recording paper 16 can be used in various ways, the flexibility of the recording paper 16 that can be used is improved. Further, since the intermediate transfer medium 32 has a fine water-repellent part and the non-water-repellent part has the permeability of the ink solvent, the recording medium is blotted by suction from the inside of the intermediate transfer medium 32. Stickiness is reduced.

  The recording paper 16 delivered from the paper supply unit 18 retains curl due to having been loaded in the magazine as roll paper. In order to remove the curl, a decurling unit 20 is provided on the downstream side of the sheet feeding unit 18. The decurling unit 20 applies heat to the recording paper 16 with a heating drum in a direction opposite to the direction of the curl of the magazine. At this time, it is more preferable to control the heating temperature so that the printed surface is slightly curled outward.

  When roll paper is used, a cutter 28 is provided on the downstream side of the decurling unit 20 as shown in FIG. 1, and the roll paper is cut into a desired size by the cutter 28. The cut recording paper 16 is conveyed so that the recording surface is on the upper side of the drawing, and when the recording paper 16 is sandwiched between the intermediate transfer medium 32 and the transfer roller 34 as a transfer means, the recording paper 16 is placed on the intermediate transfer drum 32. The formed transfer image is transferred. Note that the cutter 28 is not necessary when cut paper is used.

  Around the intermediate transfer medium 32, a transfer roller 34, an ink cleaning unit 42, each recording head 112 (112C, 112M, 112Y, 112K), and an image defect detection unit 40 are arranged in the order of rotation.

  As each recording head 112 (112C, 112M, 112Y, 112K), a line type head having a length corresponding to the maximum image formable width in the axial direction of the intermediate transfer medium 32 is provided along the axial direction of the intermediate transfer medium 32. It is preferable to use a line-type head whose longitudinal direction is arranged in a direction substantially perpendicular to the rotation direction of the intermediate transfer medium 32 (a direction substantially parallel to the axial direction of the intermediate transfer medium 32). The mechanism for ejecting ink may be either a piezoelectric element (piezo) or a heating resistor. In the case of using a piezo element, it is preferable that the nozzle density arranged on the ink ejection surface (nozzle surface) is shifted and interpolated and arranged in a two-dimensional matrix. Further, it is preferable that the nozzle surface of the recording head 112 has a curved shape in accordance with the circumference of the intermediate transfer medium 32 in the short side direction.

  The image defect detection means 40 is composed of a CCD line sensor or the like, and can detect a portion of an image recorded on the intermediate transfer medium 32 when there is a defect or defect.

  Further, although not shown as a method for detecting other image defects, a sensor such as a pressure sensor is installed in each recording head 112 (112C, 112M, 112Y, 112K) to detect non-ejection inside the head. By combining these methods, detection of image defects on the intermediate transfer medium can be performed with higher accuracy.

  The ink cleaning means 42 is for removing an image once recorded on the intermediate transfer medium 32, and is made of a soft material made of sponge or soft fiber so as not to damage the surface of the intermediate transfer medium 32. is there.

  In the example shown in FIG. 1, the configuration of CMYK standard colors (four colors) is shown. However, the combination of ink colors and the number of colors is not limited to this embodiment, and light ink, Dark ink may be added. For example, a configuration in which a print head that discharges light ink such as light cyan or light magenta may be added. In this way, the gradation can be further improved.

  Next, the flow of image correction in the present embodiment will be described with reference to FIG.

  Initial settings are made when a print instruction is issued by the host computer. Specifically, in step 201, the value of the counter D is reset to zero. Thereafter, image data to be printed is generated in step 202, and in step 203, recording is once performed on the intermediate transfer medium 32 by each recording head 112 (112C, 112M, 112Y, 112K). In step 204, the image recorded on the intermediate transfer medium 32 is detected by the image defect detection means 40 to determine whether there is an image defect. If it is determined in step 204 that there is no image defect, the image recorded on the intermediate transfer medium 32 is determined in step 205 when the recording paper 16 is sandwiched between the intermediate transfer medium 32 and the transfer roller 34. It is transferred to the recording paper 16 and discharged. Thereafter, in step 206, it is determined whether or not there is still data to be printed out of the data instructed to be printed first. If it is determined in step 206 that there is no remaining data to be printed, printing is terminated as it is. On the other hand, if it is determined in step 206 that there is still data to be printed, the process returns to step 203.

  If it is determined in step 204 that there is an image defect by the image defect detecting means 40, the process proceeds to step 207, and the transfer roller 34 is separated. Therefore, the image recorded on the intermediate transfer medium 32 is not transferred onto the recording paper 16. Thereafter, in step 208, correction data is generated based on the image information in the image defect portion detected by the image defect detection means 40. In step 209, based on this image correction data, the correction data is recorded on the intermediate transfer medium 32 by the recording heads 112 (112C, 112M, 112Y, 112K) only in the image transfer defective portion of the intermediate transfer medium 32. Is made. Note that the image recorded on the intermediate transfer medium 32 by each recording head 112 (112C, 112M, 112Y, 112K) first remains on the intermediate transfer medium 32 because the transfer roller 34 is separated. Only the portion corresponding to the image defective portion is additionally recorded on the intermediate transfer medium 32 by the respective recording heads 112 (112C, 112M, 112Y, 112K). In this way, waste of ink can be eliminated.

Thereafter, in step 210, the image defect detection means 40 detects and determines the presence or absence of an image defect for the image recorded on the intermediate transfer medium 32 again based on the correction data. If it is determined in step 210 that there is no image defect, the process proceeds to step 211, and the image recorded on the intermediate transfer medium 32 is displayed when the recording paper 16 is sandwiched between the intermediate transfer medium 32 and the transfer roller 34. Then, it is transferred to the recording paper 16 and discharged. Thereafter, in step 212, it is determined whether or not there is still data to be printed out of the data instructed to be printed first. If it is determined in step 212 that there is no remaining data to be printed, the print heads 112 (112C, 112M, 112Y, 112K) shown in step 213 are maintained, and then printing ends. On the other hand, if it is determined in step 212 that there is still data to be printed, the process proceeds to step 214 to generate all the next correction data, and then returns to step 203.

  If it is determined in step 210 that there is an image defect, 1 is added to the D value of the counter in step 215. Thereafter, in step 216, it is determined whether or not the value D of the counter exceeds a predetermined value X. If it is determined in step 216 that the value D of the counter has exceeded X, the image recorded on the intermediate transfer medium 32 is removed by the ink cleaning means 42 in step 217. Thereafter, after maintenance of each recording head 112 (112C, 112M, 112Y, 112K) shown in step 218, the value of D is reset to 0 in step 219, and the process returns to step 203.

  On the other hand, if it is determined in step 216 that the value D of the counter does not exceed the predetermined value X, the process proceeds to step 207. X is a limit value when correction is repeated, and is set to an arbitrary value depending on the purpose of the apparatus.

  As described above, in the first embodiment, the image is corrected by following the flow shown in FIG. 2 in the image forming apparatus shown in FIG.

  Next, the structure of the head used in this embodiment will be described. Since the structures of the respective heads 112K, 112C, 112M, and 112Y for each color are common, the heads are represented by reference numeral 150 in the following.

  FIG. 3A is a perspective plan view showing an example of the structure of the head 150, and FIG. 3B is an enlarged view of a part thereof. 4 is a perspective plan view showing another structural example of the head 150, and FIG. 5 is a cross-sectional view showing a three-dimensional configuration of one droplet discharge element (an ink chamber unit corresponding to one nozzle 151) (FIG. 3). (a) It is sectional drawing which follows the 5A-5B line in.

  In order to increase the dot pitch printed on the recording paper 16, it is necessary to increase the nozzle pitch in the head 150. As shown in FIGS. 3A and 3B, the head 150 of this example includes a plurality of ink chamber units (liquid chambers) each including a nozzle 151 serving as an ink discharge port, a pressure chamber 152 corresponding to each nozzle 151, and the like. Droplet ejecting elements) 153 are arranged in a zigzag matrix (two-dimensionally), and thus are projected so as to be aligned along the longitudinal direction of the head (direction perpendicular to the paper feed direction). High density of nozzle spacing (projection nozzle pitch) is achieved.

One or more nozzle rows are formed over a length corresponding to the entire width of the intermediate transfer medium 32 in a direction substantially orthogonal to the rotation direction of the intermediate transfer medium 32. The form is not limited to this example. For example, instead of the configuration of FIG. 3 (a), as shown in FIG. 4, intermediate transfer is performed by arranging short head modules 150 ′ in which a plurality of nozzles 151 are arranged two-dimensionally in a staggered manner. A line head having a nozzle row having a length corresponding to the entire width of the medium 32 may be configured.

  The pressure chamber 152 provided corresponding to each nozzle 151 has a substantially square planar shape (see FIGS. 3A and 3B), and the nozzle 151 is provided at one of the diagonal corners. An outlet for supplying ink (supply port) 154 is provided on the other side. The shape of the pressure chamber 152 is not limited to this example, and the planar shape may have various forms such as a quadrangle (rhombus, rectangle, etc.), a pentagon, a hexagon, other polygons, a circle, and an ellipse.

  As shown in FIG. 5, each pressure chamber 152 communicates with a common flow path 155 through a supply port 154. The common channel 155 communicates with an ink tank (not shown) as an ink supply source, and the ink supplied from the ink tank is distributed and supplied to each pressure chamber 152 via the common channel 155.

  An actuator 158 having an individual electrode 157 is joined to a pressure plate (vibrating plate also serving as a common electrode) 156 constituting a part of the pressure chamber 152 (the top surface in FIG. 5). By applying a driving voltage between the individual electrode 157 and the common electrode, the actuator 158 is deformed to change the volume of the pressure chamber 152, and ink is ejected from the nozzle 151 due to the pressure change accompanying this. For the actuator 158, a piezoelectric element using a piezoelectric body such as lead zirconate titanate or barium titanate is preferably used. When the displacement of the actuator 158 returns to its original state after ink ejection, new ink is refilled into the pressure chamber 152 from the common flow path 155 through the supply port 154.

  As shown in FIG. 6, the ink chamber units 153 having the above-described structure are arranged in a fixed arrangement pattern along the row direction along the main scanning direction and the oblique column direction having a constant angle θ not orthogonal to the main scanning direction. The high-density nozzle head of this example is realized by arranging a large number in a lattice pattern.

  That is, with a structure in which a plurality of ink chamber units 153 are arranged at a constant pitch d along the direction of an angle θ with respect to the main scanning direction, the pitch P of the nozzles projected so as to be aligned in the main scanning direction is d × cos θ. Thus, in the main scanning direction, each nozzle 151 can be handled equivalently as a linear arrangement with a constant pitch P. With such a configuration, it is possible to realize a high-density nozzle configuration in which 2400 nozzle rows are projected per inch (2400 nozzles / inch) so as to be aligned in the main scanning direction.

  When driving a nozzle with a full line head having a nozzle row having a length corresponding to the entire printable width, (1) all the nozzles are driven simultaneously, (2) the nozzles are sequentially moved from one side to the other. (3) The nozzles are divided into blocks, and the nozzles are sequentially driven from one side to the other for each block, etc., and one line (1 in the width direction of the paper (direction perpendicular to the paper conveyance direction)) Driving a nozzle that prints a line of dots in a row or a line consisting of dots in a plurality of rows is defined as main scanning.

  In particular, when driving the nozzles 151 arranged in a matrix as shown in FIG. 6, main scanning as described in (3) above is preferable. That is, nozzles 151-11, 151-12, 151-13, 151-14, 151-15, 151-16 are made into one block (other nozzles 151-21,..., 151-26 are made into one block, The nozzles 151-31,..., 151-36 as one block,..., And the intermediate transfer medium 32 by sequentially driving the nozzles 151-11, 151-12,. One line is printed in the width direction of the medium 32.

  On the other hand, by moving the full line head and the intermediate transfer medium 32 relative to each other, printing of one line (a line formed by one line of dots or a line composed of a plurality of lines) formed by the main scanning described above is repeated. What is done is defined as sub-scanning.

  The direction indicated by one line (or the longitudinal direction of the belt-like region) recorded by the main scanning is referred to as a main scanning direction, and the direction in which the sub scanning is performed is referred to as a sub scanning direction. In other words, in the present embodiment, the rotation direction of the intermediate transfer medium 32 is the sub-scanning direction, and the direction orthogonal thereto is the main scanning direction.

  In implementing the present invention, the nozzle arrangement structure is not limited to the illustrated example. In this embodiment, a method of ejecting ink droplets by deformation of an actuator 158 typified by a piezo element (piezoelectric element) is adopted. However, the method of ejecting ink is not particularly limited in implementing the present invention. Instead of the piezo jet method, various methods such as a thermal jet method in which ink is heated by a heating element such as a heater to generate bubbles and ink droplets are ejected by the pressure can be applied.

  FIG. 7 is a block diagram showing a system configuration of the inkjet recording apparatus 110. As shown in the figure, the inkjet recording apparatus 110 includes a communication interface 170, a system controller 172, an image memory 174, a ROM 175, a motor driver 176, a heater driver 178, a print control unit 180, an image buffer memory 182, a head driver 184, and the like. It has.

  The communication interface 170 is an interface unit (image input means) that receives image data sent from the host computer 186. As the communication interface 170, a serial interface such as USB, IEEE 1394, Ethernet, or wireless network, or a parallel interface such as Centronics can be applied. In this part, a buffer memory (not shown) for speeding up communication may be mounted.

  Image data sent from the host computer 186 is taken into the inkjet recording apparatus 110 via the communication interface 170 and temporarily stored in the image memory 174. The image memory 174 is a storage unit that stores an image input via the communication interface 170, and data is read and written through the system controller 172. The image memory 174 is not limited to a memory composed of semiconductor elements, and a magnetic medium such as a hard disk may be used.

  The system controller 172 includes a central processing unit (CPU) and its peripheral circuits, and functions as a control device that controls the entire inkjet recording apparatus 110 according to a predetermined program, and also functions as an arithmetic device that performs various calculations. . That is, the system controller 172 controls the communication interface 170, the image memory 174, the motor driver 176, the heater driver 178, and the like, and performs communication control with the host computer 186, read / write control of the image memory 174 and ROM 175, and the like. At the same time, a control signal for controlling the motor 188 and the heater 189 of the transport system is generated.

  Further, the system controller 172 includes a landing error measurement calculation unit 172A that performs calculation processing for generating landing position error data from the read data of the test pattern read from the print detection unit 124 that is the image defect detection unit 40 illustrated in FIG. And a density correction coefficient calculation unit 172B that calculates a density correction coefficient from information on the measured landing position error. The processing functions of the landing error measurement calculation unit 172A and the density correction coefficient calculation unit 172B can be realized by ASIC, software, or an appropriate combination.

  The density correction coefficient data obtained by the density correction coefficient calculation unit 172B is stored in the density correction coefficient storage unit 190.

  The ROM 175 stores programs executed by the CPU of the system controller 172, various data necessary for control (including test pattern data for landing position error measurement), and the like. The ROM 175 may be a non-rewritable storage unit or a rewritable storage unit such as an EEPROM. Further, by utilizing the storage area of the ROM 175, a configuration in which the ROM 175 is also used as the density correction coefficient storage unit 190 is possible.

  The image memory 174 is used as a temporary storage area for image data, and is also used as a program development area and a calculation work area for the CPU.

  The motor driver 176 is a driver (driving circuit) that drives the conveyance motor 188 in accordance with an instruction from the system controller 172. The heater driver 178 is a driver that drives the heater 189 in accordance with an instruction from the system controller 172.

In accordance with the control of the system controller 172, the print control unit 180 performs various processes, corrections, and the like for generating a droplet ejection control signal from image data (multi-value input image data) in the image memory 174. In addition to functioning as signal processing means, it also functions as drive control means for controlling the ejection drive of the head 150 by supplying the generated ink ejection data to the head driver 184.

  That is, the print control unit 180 includes a density data generation unit 180A, a correction processing unit 180B, an ink ejection data generation unit 180C, and a drive waveform generation unit 180D. Each of these functional blocks (180A to D) can be realized by ASIC, software, or an appropriate combination.

  The density data generation unit 180A is a signal processing unit that generates initial density data for each ink color from input image data, and includes density conversion processing (including UCR processing and color conversion), which will be described later, and pixels when necessary. Perform number conversion processing.

  The correction processing unit 180B in FIG. 7 is a processing unit that performs density correction calculation using the density correction coefficient stored in the density correction coefficient storage unit 190, and performs unevenness correction processing described later.

  The ink ejection data generation unit 180C in FIG. 7 is a signal processing unit including a halftoning processing unit that converts density data after correction generated by the correction processing unit 180B into binary (or multivalued) dot data. A binary (multi-value) conversion process to be described later is performed. The ink discharge data generated by the ink discharge data generation unit 180C is given to the head driver 184, and the ink discharge operation of the head 150 is controlled.

  The drive waveform generation unit 180D is a unit that generates a drive signal waveform for driving the actuator 158 (see FIG. 5) corresponding to each nozzle 151 of the head 150, and the signal generated by the drive waveform generation unit 180D. (Drive waveform) is supplied to the head driver 184. The signal output from the drive signal generation unit 180D may be digital waveform data or an analog voltage signal.

  The print control unit 180 includes an image buffer memory 182, and image data, parameters, and other data are temporarily stored in the image buffer memory 182 when image data is processed in the print control unit 180. In FIG. 7, the image buffer memory 182 is shown in a mode associated with the print control unit 180, but it can also be used as the image memory 174. Also possible is an aspect in which the print controller 180 and the system controller 172 are integrated and configured with one processor.

  An outline of the flow of processing from image input to print output is as follows. Image data to be printed is input from the outside via the communication interface 170 and stored in the image memory 174. At this stage, for example, RGB multivalued image data is stored in the image memory 174.

In the ink jet recording apparatus 110, a pseudo continuous tone image is formed by changing the droplet ejection density and dot size of fine dots with ink (coloring material) to the human eye. It is necessary to convert to a dot pattern that reproduces the gradation (shading of the image) as faithfully as possible. Therefore, the original image (RGB) data stored in the image memory 174 is sent to the print control unit 180 via the system controller 172, and the density data generation unit 180A, the correction processing unit 180B of the print control unit 180, the ink It is converted into dot data for each ink color via the ejection data generation unit 180C.

  That is, the print control unit 180 performs a process of converting the input RGB image data into dot data of four colors K, C, M, and Y. Thus, the dot data generated by the print control unit 180 is stored in the image buffer memory 182. The dot data for each color is converted into CMYK droplet ejection data for ejecting ink from the nozzles of the head 150, and the ink ejection data to be printed is determined.

  The head driver 184 outputs a drive signal for driving the actuator 158 corresponding to each nozzle 151 of the head 150 in accordance with the print contents based on the ink ejection data and the drive waveform signal given from the print control unit 180. The head driver 184 may include a feedback control system for keeping the head driving condition constant.

  In this way, when the drive signal output from the head driver 184 is applied to the head 150, ink is ejected from the corresponding nozzle 151. An image is recorded on the intermediate transfer medium 32 by controlling ink ejection from the head 150 in synchronization with the rotational speed of the intermediate transfer medium 32.

  As described above, based on the ink discharge data and the drive signal waveform generated through the required signal processing in the print control unit 180, control of the discharge amount and discharge timing of the ink droplets from each nozzle through the head driver 184. Is done. Thereby, a desired dot size and dot arrangement are realized.

  As described with reference to FIG. 1, the image defect detection means 40 is a block including an image sensor, reads an image recorded on the intermediate transfer medium 32, performs necessary signal processing, etc. Presence / absence, variation in droplet ejection, optical density, and the like) and provides the detection result to the print controller 180 and the system controller 172.

  The print control unit 180 performs various corrections on the head 150 as necessary, and performs control to perform a cleaning operation (nozzle recovery operation) such as preliminary ejection, suction, and wiping as necessary.

  In the case of this example, the combination of the print detection unit 124 and the landing error measurement calculation unit 172A, which is the image defect detection unit 40 shown in FIG. 1, corresponds to the “characteristic information acquisition unit”, and the density correction coefficient calculation unit 172B It corresponds to “setting means” and “correction coefficient determination means”. Further, the correction processing unit 180B corresponds to “correction processing means”.

  According to the ink jet recording apparatus 110 having the above configuration, it is possible to obtain a good image in which density unevenness due to landing position error is reduced.

  Next, the correction method according to the present invention will be specifically described.

  First, the principle of correction will be described. In the density unevenness correction process according to the embodiment of the present invention, when a landing position error of a nozzle is corrected, correction is performed using N surrounding nozzles including the nozzle. Although details will be described later, the correction accuracy increases as the number N of nozzles used for correction increases.

  FIG. 13 is a diagram showing a state before correction. The third nozzle (nzl3) from the left of the line head (corresponding to the recording head) 10 has a landing position error. From the ideal landing position (origin O), the right direction in the figure (the main axis indicated by the X axis) The landing position is shifted in the scanning direction). Further, the graph shown in the lower side of FIG. 13 shows the density in the nozzle row direction (main scanning direction) obtained by averaging the print density due to droplet ejection from the nozzles in the rotation direction (sub-scanning direction) of the intermediate transfer medium. A profile is shown. However, in FIG. 13, since correction for the printing of the nozzle nzl3 is considered, the density output other than the nozzle nzl3 is not shown.

The initial output density of each nozzle nzl1-5 is Di = Dini (where i is the nozzle number 1-5, Dini is a constant value), the ideal landing position of nozzle nzl3 is the origin O, and the landing position of each nozzle nzl1-5 Xi
And

  Here, D i physically represents the output optical density of the nozzle averaged in the rotation direction of the intermediate transfer medium, and in data processing, density data D (i, j) of each pixel (where i is the nozzle number) , J represents a pixel number in the recording medium conveyance direction) and represents an average of “j”.

  As shown in FIG. 13, the landing position error of the nozzle nzl3 is expressed as a deviation from the origin O of the density output (thick line) of the nozzle nzl3. Now, let us consider correcting this deviation in output density.

FIG. 14 is a diagram showing a state after correction. However, only the correction amount is illustrated except for the nozzle nzl3. In the case of FIG. 14, the number of nozzles used for correction is N = 3, and density correction coefficients d2, d3, d4 are multiplied by the nozzles nzl2, nzl3, nzl4. The density correction coefficient di here is a coefficient defined as Di ′ = Di + di × Di, where Di ′ is the corrected output density.

  In the present embodiment, the density correction coefficient di for each nozzle is determined so that the visibility of density unevenness is minimized. The density unevenness of the printed image is expressed by the intensity in the spatial frequency characteristic (power spectrum). Since high frequency components cannot be visually recognized by humans, the visibility of density unevenness is equal to the low frequency components of the power spectrum. Therefore, the density correction coefficient di of each nozzle is determined so as to minimize the low frequency component of the power spectrum.

Although the details of the derivation of the equation for determining the density correction coefficient di will be described later, when only the result is shown first, the density correction coefficient di for the landing position error of a specific nozzle is determined by the following formula.

Here, x _i is the landing position of each nozzle with the ideal landing position of the correction target nozzle as the origin. Π means taking a product in N nozzles used for correction. The case of N = 3 in FIG. 14 is expressed explicitly as follows.

  From the condition of minimizing the low frequency component of the power spectrum of density unevenness, the density correction coefficient of each nozzle can be theoretically derived.

  First, a density profile incorporating the error characteristics of each nozzle is defined as follows:

The density profile D (x) of the image is the sum of the density profiles printed by each nozzle,
A printing model (density profile printed by one nozzle) represents nozzle printing. The print model is expressed separately as a nozzle output density Di and a standard density profile z (x).

Strictly speaking, the standard density profile z (x) has a finite spread equal to the dot diameter, but considering the correction of the position error as a problem of density deviation balancing, what is important is the position of the center of gravity of the density profile. The (landing position) and the spread of the density profile is a secondary factor. Therefore, an approximation that replaces the profile with a δ function (delta function) is reasonable. Assuming such a standard concentration profile, mathematical handling becomes easy and an exact solution of the correction coefficient is obtained.

  FIG. 15A shows a printing model that is realistic, and FIG. 15B shows a δ function type printing model. When approximated by the δ function model, the standard concentration profile is expressed by the following equation.

In deriving the correction coefficient, the landing position error Δx ₀ of a specific nozzle (i = 0)
Consider correction using N peripheral nozzles. Here, the correction target nozzle number is i = 0. Note that peripheral nozzles can also have a predetermined landing position error.

The number (index) of the N nozzles including the correction target nozzle (center nozzle) is expressed by the following equation.

  In this equation, N needs to be an odd number, but it is not necessary to limit N to an odd number when implementing the present invention.

  The initial output density (output density before correction) is expressed by the following equation assuming that only i = 0 has a value.

  When the density correction coefficient is di, the corrected output density Di 'is expressed by the following equation.

  That is, when i = 0, it is represented by the sum of the initial output density value and the correction value (di × Dini), and when i ≠ 0, only the correction value is obtained.

Impact position x _i of each nozzle i is expressed by the following equation.

  When the δ function type printing model is used, the corrected density profile is expressed by the following equation.

  On the other hand, when performing Fourier transform,

It is expressed. Dini is omitted because it is a common constant.

  Minimizing the visibility of density unevenness is to minimize the low frequency component of the power spectrum of the following equation.

This can be mathematically approximated by the fact that the differential coefficient (first order, second order,...) Of T (f) at f = 0 is zero. Since the number of unknowns di ′ is now N, if the condition for storing the DC component is included, all (N) unknowns di ′ are strictly determined by using the condition that the differential coefficient up to the N−1 order is zero. Determined. In this way, the following correction conditions are determined.

In the δ function model, when each correction condition is developed, it is reduced to N simultaneous equations for Di by easy calculation. Arranging the development of each correction condition gives the following condition group (equation group).

The meaning of these equations is that the first equation represents preservation of the DC component, and the second equation represents preservation of the center of gravity. The third and subsequent formulas indicate that the N-1th moment in statistics is zero.

  When the conditional expression thus obtained is expressed in matrix form, it can be expressed as follows.

This coefficient matrix A is a so-called Vandermonde type matrix, and its determinant is known to be the following expression using a difference product.

  For this reason, the exact solution of di 'can be obtained using Cramer's formula. The detailed process of the calculation is omitted, but the algebraic calculation shows that the solution is

  Therefore, the correction coefficient di to be obtained is as follows.

As described above, the exact solution of the density correction coefficient di is derived from the condition that the origin differential coefficient of the power spectrum is zero. As the number N of peripheral nozzles used for correction is increased, the higher-order differential coefficient can be made zero, so that the low frequency energy becomes smaller and the visibility of unevenness is further reduced.

  In the present embodiment, the condition for setting the differential coefficient to zero is used. However, even if it is not completely zero, it may be set to a value sufficiently smaller than the differential coefficient before correction (for example, 1/10 before correction). Unevenness can be reduced.

FIG. 16 shows the corrected spatial frequency characteristics (power spectrum) for the nozzle having the landing position error shown in FIG. FIG. 16 shows the case of no correction, correction example 1 when N = 3, and correction example 2 when N = 5. Common conditions for calculation are: dot density: 1200 dpi, dot landing diameter: 32 μm, nozzle position error (landing position error): 10
μm was used.

  Considering human visual characteristics, the visibility of density unevenness is in a low frequency region of 0 to 8 cycles / mm, and the smaller the power spectrum in this region, the higher the correction accuracy.

  Correction example 1 (N = 3) shows that the power spectrum is almost zero at 0 to 5 cycle / mm, and has a sufficient correction effect as compared with the case without correction. In addition, the power spectrum of the correction example 2 (N = 5) is lower than that of the correction example 1 (N = 3). Accordingly, the correction effect is improved as the number N of nozzles used for correction is increased. In the case of FIG. 13, the output density of the correction target nozzle nzl3 does not physically protrude from area1 and area5, but the power spectrum can be further reduced by using the nozzles nzl1 and nzl5 for correction.

  FIG. 17 compares the density correction coefficients of correction examples 1 to 3 in which the number of nozzles used for correction is changed. As can be seen from a comparison between correction example 1 when N = 3, correction example 2 when N = 5, and correction example 3 when N = 7, the correction accuracy improves as the N value increases. The variation range of the correction coefficient is also increased. As a matter of course, as the landing position error of the nozzle increases, the variation range of the density correction coefficient increases.

If the density correction coefficient increases by a certain value or more, there is a possibility that the reproduction of the input image may be broken, which is not preferable. Therefore, an increase in N value more than necessary is not preferable. It is desirable to set an optimal N value in view of correction accuracy and image reproducibility. In each of the correction examples 1 to 3 shown in FIG. 17 with N = 3 to 7, the change width (absolute value) of the density correction coefficient is relatively small in any case, and the reproduction of the input image is not broken. Density unevenness can be corrected.

  The above description is a method for determining the density correction coefficient for one specific nozzle (for example, the nozzle nzl3 in FIG. 13). Actually, since all the nozzles in the head have some landing position error, it is preferable to correct all the landing position errors.

  That is, the density correction coefficients for the N surrounding nozzles are obtained for all nozzles. Since a power spectrum minimization equation (to be described later) used for determining the density correction coefficient is linear, it can be superposed for each nozzle. Therefore, the total density correction coefficient can be obtained by taking the sum of the density correction coefficients obtained as described above.

That is, if the density correction coefficient of the nozzle i with respect to the position error of the nozzle k is d (i, k), this d (i, k) can be obtained by the equation [Equation 1]. The total density correction coefficient di of the nozzle i is obtained as the following equation.

In the above example, the index k is added with the landing position errors of all nozzles as correction targets. However, a certain value ΔX_thresh is preset as a threshold value, and only nozzles having landing position errors exceeding this threshold value are set. A configuration in which correction is selectively performed so as to be a correction target is also possible.

  As described above, when the number N of nozzles used for correction is increased, the correction accuracy is improved. However, the change width of the density correction coefficient is also increased, and there is a possibility that the reproduced image is broken. For this reason, a correction coefficient limit range (upper limit value d_max and lower limit value d_min) for preventing image corruption is determined, and N is set so that the total density correction coefficient obtained by the above equation [18] falls within the limit range. It is desirable to set a value. That is, the N value is determined so as to satisfy d_min <di <d_max.

  According to experimental knowledge, image failure does not occur if d_min ≧ −1 and d_max ≦ 1.

  FIG. 18 shows an image processing flow including implementation of unevenness correction processing according to this embodiment.

The data format of the input image 21 is not particularly limited, but is 24 bit RGB data, for example. The input image 21 is subjected to density conversion processing using a lookup table (step S22), and converted to density data D (i, j) corresponding to the ink color of the printer.

  Note that (i, j) represents the position of the pixel, and density data is assigned to each pixel.

  Here, it is assumed that the resolution of the input image 21 matches the resolution of the printer (nozzle resolution). If they do not match, pixel number conversion processing is performed on the input image in accordance with the printer resolution.

  The density conversion process in step S22 is a general process, such as an undercolor removal (UCR) process or a distribution process to light ink in the case of a system that uses light ink (same color light ink). included.

For example, in the case of a three-color ink configuration of C (cyan) M (magenta) Y (yellow),
It is converted into CMY density data D (i, j). Alternatively, in addition to the above three colors, K (black), L
In the case of a system including other inks such as C (light cyan) and LM (light magenta), it is converted into density data D (i, j) including the ink color.

Unevenness correction processing is performed on the density data D (i, j) (reference numeral 31 in FIG. 18) obtained through the density conversion processing (step S32). Here, calculation is performed by multiplying the density data D (i, j) by the density correction coefficient (droplet ejection rate correction coefficient) di corresponding to the corresponding nozzle.

As shown in the schematic diagram of FIG. 19, the pixel position (i, j) on the image is specified by the position (main scanning direction position) i and the sub-scanning direction position j of the nozzle nzli, and density data D ( i, j). Now, when performing unevenness correction processing for the nozzles responsible for droplet ejection in the pixel rows indicated by the diagonal lines in FIG. 19, the density data D ′ (i, j) after correction is expressed by the following equation:
D ′ (i, j) = D (i, j) + di × D (i, j)
Calculated by In this way, corrected density data D ′ (i, j) is obtained.

By performing halftoning processing from the corrected density data D ′ (i, j) (reference numeral 41 in FIG. 18) (step S42), a dot on / off signal (binary data) or dot size is obtained. When modulation is included, the data is converted into multi-value data including the type of size (selection of dot size). The method of halftoning is not particularly limited, and a known binary (multi-value) method such as an error diffusion method or a dither method can be used.

  Based on the binary (multilevel) signal (reference numeral 51 in FIG. 18) obtained in this way, ink ejection (droplet ejection) data for each nozzle is generated, and the ejection operation is controlled. Thereby, density unevenness is suppressed, and high-quality image formation is possible.

  FIG. 20 is a flowchart illustrating an example of a density correction coefficient (correction data) update process. The correction data update process is started, for example, under any of the following conditions.

  That is, (a) when it is determined by the automatic check mechanism (sensor) that monitors the print result that the print image is uneven, (b) a human (operator) sees the print image and the image is uneven. (C) When a preset update timing has been reached (time management by a timer or a print number counter, etc.) The update process shown in the figure is started under any of the following conditions: the update timing can be set and determined by the operation result management or the like.

  In the present embodiment, when an image defect is detected by the image defect detection means 40 corresponding to (b) above, the correction data update process is started.

  When the update process starts, first, a test pattern (predetermined predetermined pattern) for measuring the landing error data is printed (step S70).

  Next, landing error data is measured from the printing result of the test pattern (step S72). For the measurement of the landing error data, an image reading apparatus (including a signal processing means for processing an imaging signal) using an image sensor (imaging element) can be used. The landing error data includes landing position error information and optical density information.

  Then, correction data (density correction coefficient) is calculated from the landing error data obtained in step S72 (step S74). The method for calculating the density correction coefficient has already been described.

  Thus, the obtained density correction coefficient information is stored in a rewritable storage means such as an EEPROM, and the latest correction coefficient is used thereafter.

  Next, a second embodiment will be described.

  FIG. 8 is an overall configuration diagram showing an outline of an embodiment of an ink jet recording apparatus as an image forming apparatus according to the second embodiment.

  As shown in FIG. 8, the ink jet recording apparatus 46 of the present embodiment has a plurality of recording heads (droplet discharge heads) 112 (112C, 112M, 112Y) that are provided for each ink color and discharge ink as droplets. 112K), an ink storage / loading unit 14 (14C, 14M, 14Y, 14K) for storing ink to be supplied to each recording head 112 (112C, 112M, 112Y, 112K), and temporarily on the surface thereof An intermediate transfer medium (intermediate transfer rotary drum) 32 on which an image is recorded, a paper supply unit 18 for supplying a recording paper 16 on which an image on the intermediate transfer medium 32 is transferred and recorded, and a recording paper 16 after recording And a discharge unit 26 for discharging.

  As shown in the figure, each color in the order of cyan (C), magenta (M), yellow (Y), and black (K) from the upstream side along the rotation direction of the intermediate transfer medium 32 (the direction indicated by the arrow in the figure). A recording head 112 (112C, 112M, 112Y, 112K) corresponding to ink is arranged.

  An image is temporarily recorded on the surface of the intermediate transfer medium 32 by ejecting ink of each color from each recording head 112 (112C, 112M, 112Y, 112K) while rotating the intermediate transfer medium 32.

  Each color recording head 112 (112C, 112M, 112Y, 112K) is filled with a liquid (hereinafter simply referred to as ink) containing a coloring material (dye or pigment).

  As an example of the paper supply unit 18, a roll paper (continuous paper) magazine (a container loaded with roll paper) may be used, or a plurality of magazines having different paper width, paper quality, and the like may be provided. Further, instead of or in combination with the roll paper magazine, the paper may be supplied by a cassette in which cut papers are stacked and loaded.

  In this embodiment, since a transfer image is once formed on the intermediate transfer medium 32 and transferred to the recording paper 16, the influence of penetration into the recording paper can be obtained by removing the solvent in the ink. Since the recording paper 16 can be used in various ways, the flexibility of the recording paper 16 that can be used is improved. Further, since the intermediate transfer medium 32 has a fine water-repellent part and the non-water-repellent part has the permeability of the ink solvent, the recording medium is blotted by suction from the inside of the intermediate transfer medium 32. Stickiness is reduced.

  The recording paper 16 delivered from the paper supply unit 18 retains curl due to having been loaded in the magazine as roll paper. In order to remove the curl, a decurling unit 20 is provided on the downstream side of the sheet feeding unit 18. The decurling unit 20 applies heat to the recording paper 16 with a heating drum in a direction opposite to the direction of the curl of the magazine. At this time, it is more preferable to control the heating temperature so that the printed surface is slightly curled outward.

When roll paper is used, a cutter 28 is provided on the downstream side of the decurling unit 20 as shown in the drawing, and the roll paper is cut into a desired size by the cutter 28. The cut recording paper 16 is conveyed so that the recording surface is on the upper side of the drawing, and when the recording paper 16 is sandwiched between the intermediate transfer medium 32 and the transfer roller 34, the transfer formed on the intermediate transfer drum 32 is performed. The image is transferred. Note that the cutter 28 is not necessary when cut paper is used.

  Around the intermediate transfer medium 32, a transfer roller 34, recording heads 112 (112C, 112M, 112Y, 112K), an image defect detection unit 40, and an ink cleaning unit 43 are arranged in the order of rotation.

  As each recording head 112 (112C, 112M, 112Y, 112K), a line type head having a length corresponding to the maximum image formable width in the axial direction of the intermediate transfer medium 32 is provided along the axial direction of the intermediate transfer medium 32. It is preferable to use a line-type head whose longitudinal direction is arranged in a direction substantially perpendicular to the rotation direction of the intermediate transfer medium 32 (a direction substantially parallel to the axial direction of the intermediate transfer medium 32). The mechanism for ejecting ink may be either a piezoelectric element (piezo) or a heating resistor. In the case of using a piezo element, it is preferable that the nozzle density arranged on the ink ejection surface (nozzle surface) is shifted and interpolated and arranged in a two-dimensional matrix. Further, it is preferable that the nozzle surface of the recording head 112 has a curved shape in accordance with the circumference of the intermediate transfer medium 32 in the short side direction.

  The image defect detection means 40 is composed of a CCD line sensor or the like, and can detect a portion of an image recorded on the intermediate transfer medium 32 when there is a defect or defect.

  Further, although not shown as a method for detecting other image defects, a sensor such as a pressure sensor is installed in each recording head 112 (112C, 112M, 112Y, 112K) to detect non-ejection inside the head. By combining this method, it is possible to detect image defects on the intermediate transfer medium with higher accuracy.

  The ink cleaning means 43 is for removing an image once recorded on the intermediate transfer medium 32, and is made of a soft material made of sponge or soft fiber so as not to damage the surface of the intermediate transfer medium 32. is there.

  In the example shown in FIG. 8, the configuration of CMYK standard colors (four colors) is shown. However, the combination of ink colors and the number of colors is not limited to the present embodiment. Dark ink may be added. For example, a configuration in which a print head that discharges light ink such as light cyan or light magenta may be added. In this way, the gradation can be further improved.

  Next, the flow of image correction in the present embodiment will be described with reference to FIG.

  Initial settings are made when a print instruction is issued by the host computer. Specifically, in step 301, the value of the counter D is reset to zero.

Thereafter, image data to be printed is generated in step 302, and in step 303, recording is once performed on the intermediate transfer medium 32 by each recording head 112 (112C, 112M, 112Y, 112K). In step 304, for the image recorded on the intermediate transfer medium 32, the image defect detection means 40 detects and determines the presence or absence of an image defect. If it is determined in step 304 that there is no image defect, the image recorded on the intermediate transfer medium 32 is determined in step 305 when the recording paper 16 is sandwiched between the intermediate transfer medium 32 and the transfer roller 34. It is transferred to the recording paper 16 and discharged. Thereafter, in step 306, it is determined whether or not there is still data to be printed among the data instructed to be printed first. If it is determined in step 306 that there is no remaining data to be printed, printing is terminated as it is. On the other hand, if it is determined in step 306 that there is still data to be printed, the process returns to step 303.

  If it is determined in step 304 that there is an image defect by the image defect detection means 40, the process proceeds to step 307, where the ink cleaning means 43 removes the image recorded on the intermediate transfer medium 32, that is, Ink cleaning of the intermediate transfer medium 32 is performed. At this time, since the ink cleaning unit 43 is in front of the transfer roller 34 as viewed from the rotation direction of the intermediate transfer medium 32, the ink is removed by the ink cleaning unit 43 before reaching the transfer roller 34. It won't get dirty. Thereafter, in step 308, correction data for all the images is generated based on the information detected by the image defect detection means 40. In step 309, correction data for all images is recorded on the intermediate transfer medium 32 by each recording head 112 (112C, 112M, 112Y, 112K) based on the correction data for all images.

  Thereafter, in step 310, the image defect detection means 40 detects the presence / absence of an image defect in the image recorded on the intermediate transfer medium 32 again. If it is determined in step 310 that there is no image defect, the process proceeds to step 311, and the image recorded on the intermediate transfer medium 32 is recorded when the recording paper 16 is sandwiched between the intermediate transfer medium 32 and the transfer roller 34. Then, it is transferred to the recording paper 16 and discharged. Thereafter, in step 312, it is determined whether or not there is still data to be printed among the data instructed to be printed first. If it is determined in step 312 that there is no remaining data to be printed, maintenance is performed on each recording head 112 (112C, 112M, 112Y, 112K) in step 313, and then printing ends. On the other hand, if it is determined in step 312 that there is still data to be printed, the process proceeds to step 314 to generate all the next correction data, and then returns to step 303.

  If it is determined in step 310 that there is an image defect, 1 is added to the D value of the counter in step 315. Thereafter, in step 316, it is determined whether or not the value D of the counter exceeds a predetermined value X. If it is determined in step 316 that the value of the counter D has exceeded X, in step 317, the image recorded on the intermediate transfer medium 32 is removed by the ink cleaning unit 43. Thereafter, maintenance of each recording head 112 (112C, 112M, 112Y, 112K) is performed at step 318, and after the value of D is reset to 0 at step 319, the process returns to step 303.

  If it is determined in step 316 that the value D of the counter does not exceed the predetermined value X, the process proceeds to step 307.

  As described above, in the second embodiment, image correction is performed in the image forming apparatus shown in FIG. 8 by following the flow shown in FIG. In the present embodiment, when an image defect is found, all the images recorded on the intermediate transfer medium 32 are removed. Therefore, when droplets are ejected in the vicinity of ink that has already landed, they land after that. Since the phenomenon that the ink is attracted by the surface tension of the ink that has already landed and the landing position shifts can be avoided, higher image quality can be obtained.

  A specific method of correction is performed by the same method as in the first embodiment.

  Next, a third embodiment will be described.

The third embodiment uses an image forming apparatus having the configuration shown in FIG. 8 similar to that of the second embodiment, and the flow of image correction will be described with reference to FIG. Unlike the second embodiment, the third embodiment includes a process of separating the transfer roller 34.

  Initial settings are made when a print instruction is issued by the host computer. Specifically, in step 401, the value of the counter D is reset to zero.

  Thereafter, image data to be printed is generated in step 402, and recording is once performed on the intermediate transfer medium 32 by each recording head 112 (112C, 112M, 112Y, 112K) in step 403. In step 404, the image recorded on the intermediate transfer medium 32 is detected by the image defect detection means 40 to determine whether there is an image defect. If it is determined in step 404 that there is no image defect, in step 405, the image recorded on the intermediate transfer medium 32 is displayed when the recording paper 16 is sandwiched between the intermediate transfer medium 32 and the transfer roller 34. It is transferred to the recording paper 16 and discharged. Thereafter, in step 406, it is determined whether or not there is still data to be printed out of the data instructed to be printed first. If it is determined in step 406 that there is no remaining data to be printed, printing is finished as it is. On the other hand, if it is determined in step 406 that there is still data to be printed, the process returns to step 403 and the next data is transferred to the intermediate transfer medium 32 by each recording head 112 (112C, 112M, 112Y, 112K). To be recorded.

  If it is determined in step 404 that there is an image defect by the image defect detection means 40, the process proceeds to step 407, where the transfer roller is separated, and in step 408, the ink cleaning means 43 causes the intermediate transfer medium 32 to be separated. Are removed, that is, ink cleaning of the intermediate transfer medium 32 is performed. Thereafter, in step 409, correction data for all images is generated based on the information detected by the image defect detection means 40. In step 410, correction data for all images is recorded on the intermediate transfer medium 32 by each recording head 112 (112C, 112M, 112Y, 112K) based on the correction data for all images.

  Thereafter, in step 411, the image recorded on the intermediate transfer medium 32 is detected again by the image defect detection means 40 to determine whether there is an image defect. If it is determined in step 411 that there is no image defect, the process proceeds to step 412, and the image recorded on the intermediate transfer medium 32 is recorded when the recording paper 16 is sandwiched between the intermediate transfer medium 32 and the transfer roller 34. Then, it is transferred to the recording paper 16 and discharged. Thereafter, in step 413, it is determined whether or not there is still data to be printed out of the data instructed to be printed first. If it is determined in step 413 that there is no remaining data to be printed, the print heads 112 (112C, 112M, 112Y, 112K) are maintained in step 414, and then printing ends. On the other hand, if it is determined in step 413 that there is still data to be printed, the process proceeds to step 415 to generate all the next correction data, and then returns to step 403 to return to each recording head 112 (112C, 112C, 112M, 112Y, 112K).

  If it is determined in step 411 that there is an image defect, 1 is added to the D value of the counter in step 416. Thereafter, in step 417, it is determined whether or not the value D of the counter exceeds a predetermined value X. If it is determined in step 417 that the value D of the counter has exceeded X, in step 418, the image recorded on the intermediate transfer medium 32 is removed by the ink cleaning unit 43. After this, maintenance of each recording head 112 (112C, 112M, 112Y, 112K) is performed at step 419, and after resetting the value of D to 0 at step 420, the process returns to step 403, and image data is transferred to each recording head 112 ( 112C, 112M, 112Y, 112K).

  If it is determined in step 417 that the value D of the counter does not exceed the predetermined value X, the process proceeds to step 407.

  In the present embodiment, the flow of image correction has been described with reference to FIG. 10 for the image forming apparatus configured as shown in FIG. 8, but in the flow of image correction in the present embodiment, the transfer roller 34 is separated. Therefore, the present invention can also be applied to the image forming apparatus having the configuration shown in FIG.

  Further, in the present embodiment, when an image defect is found, all the images recorded on the intermediate transfer medium 32 are removed. Therefore, when droplets are ejected in the vicinity of ink that has already landed, Since it is possible to avoid a phenomenon in which the landed ink is attracted by the surface tension of the already landed ink and the landing position is shifted, higher image quality can be obtained.

  A specific method of correction is performed by the same method as in the first embodiment.

  Next, a fourth embodiment will be described.

  In this embodiment, the image forming apparatus according to any of the first to third embodiments has a solvent removing unit. An example of this embodiment is shown in FIG.

  As shown in FIG. 11, the ink jet recording apparatus 47 of the present embodiment is provided with a plurality of recording heads (droplet discharge heads) 112 (112C, 112M, 112Y) that are provided for each ink color and discharge ink as droplets. 112K), an ink storage / loading unit 14 (14C, 14M, 14Y, 14K) for storing ink to be supplied to each recording head 112 (112C, 112M, 112Y, 112K), and temporarily on the surface thereof An intermediate transfer medium (intermediate transfer rotary drum) 32 on which an image is recorded, a paper supply unit 18 for supplying a recording paper 16 on which an image on the intermediate transfer medium 32 is transferred and recorded, and a recording paper 16 after recording And a discharge unit 26 for discharging.

  As shown in the figure, each color in the order of cyan (C), magenta (M), yellow (Y), and black (K) from the upstream side along the rotation direction of the intermediate transfer medium 32 (the direction indicated by the arrow in the figure). A recording head 112 (112C, 112M, 112Y, 112K) corresponding to ink is arranged.

  An image is temporarily recorded on the surface of the intermediate transfer medium 32 by ejecting ink of each color from each recording head 112 (112C, 112M, 112Y, 112K) while rotating the intermediate transfer medium 32.

  In the present embodiment, since a transfer image is once formed on the intermediate transfer medium 32 and transferred to the recording paper 16, the influence of penetration into the recording paper can be obtained by removing the solvent in the ink. Since the recording paper 16 can be used in various ways, the flexibility of the recording paper 16 that can be used is improved. Further, since the intermediate transfer medium 32 has a fine water-repellent part and the non-water-repellent part has the permeability of the ink solvent, the recording medium is blotted by suction from the inside of the intermediate transfer medium 32. Stickiness is reduced.

  The recording paper 16 delivered from the paper supply unit 18 retains curl due to having been loaded in the magazine as roll paper. In order to remove the curl, a decurling unit 20 is provided on the downstream side of the sheet feeding unit 18. The decurling unit 20 applies heat to the recording paper 16 with a heating drum in a direction opposite to the direction of the curl of the magazine. At this time, it is more preferable to control the heating temperature so that the printed surface is slightly curled outward.

When roll paper is used, a cutter 28 is provided on the downstream side of the decurling unit 20, and the roll paper is cut into a desired size by the cutter 28. The cut recording paper 16 is conveyed so that the recording surface is on the upper side of the drawing, and when the recording paper 16 is sandwiched between the intermediate transfer medium 32 and the transfer roller 34, the transfer formed on the intermediate transfer drum 32 is performed. The image is transferred. Note that the cutter 28 is not necessary when cut paper is used.

  Around the intermediate transfer medium 32, a transfer roller 34, each recording head 112 (112 </ b> C, 112 </ b> M, 112 </ b> Y, 112 </ b> K), an image defect detection unit 40, and a solvent removal unit 44 are arranged in the rotation direction.

  The solvent removing means 44 does not remove the dye or pigment constituting the ink, but the solvent contained in the ink (for example, water, alcohols, high boiling point solvents (glycerin, diethylene glycol, glycol ethers, etc.)) And is made of a soft material such as a sponge so as not to damage the surface of the intermediate transfer medium 32. In the present embodiment, when an image defect is confirmed by the image defect detection means, the solvent in the intermediate transfer medium is not removed. This eliminates the need for this process and improves throughput.

  Although not shown in the drawing, an ink cleaning unit may be provided as necessary in the same manner as in other embodiments.

  The ink cleaning means is for removing an image once recorded on the intermediate transfer medium 32, and is made of a soft material made of sponge or soft fiber so as not to damage the surface of the intermediate transfer medium 32. .

  As each recording head 112 (112C, 112M, 112Y, 112K), a line type head having a length corresponding to the maximum image formable width in the axial direction of the intermediate transfer medium 32 is provided along the axial direction of the intermediate transfer medium 32. It is preferable to use a line-type head whose longitudinal direction is arranged in a direction substantially perpendicular to the rotation direction of the intermediate transfer medium 32 (a direction substantially parallel to the axial direction of the intermediate transfer medium 32). The mechanism for ejecting ink may be either a piezoelectric element (piezo) or a heating resistor. In the case of using a piezo element, it is preferable that the nozzle density arranged on the ink ejection surface (nozzle surface) is shifted and interpolated and arranged in a two-dimensional matrix. Further, it is preferable that the nozzle surface of the recording head 112 has a curved shape in accordance with the circumference of the intermediate transfer medium 32 in the short side direction.

  The image defect detection means 40 is composed of a CCD line sensor or the like, and can detect a portion of an image recorded on the intermediate transfer medium 32 when there is a defect or defect.

  Further, as another method for detecting an image defect, although not shown in FIG. 11, a sensor such as a pressure sensor is installed in each recording head 112 (112C, 112M, 112Y, 112K), so There is a method for detecting ejection, and by combining this method, it is possible to detect image defects on the intermediate transfer medium with higher accuracy.

  In the present embodiment, in the image forming apparatus having such a solvent removing unit 44, when the image defect detecting unit 40 detects an image defect, the solvent removing unit 44 does not remove the solvent. Is included in the process.

  In this embodiment, when the solvent is removed and then recording is performed on the intermediate transfer medium 32 again, it is possible to prevent the adverse effect that the droplet ejection shape is different from that previously recorded and the image is disturbed.

  Next, a fifth embodiment will be described.

  The fifth embodiment uses the image forming apparatus having the configuration shown in FIG. 8, and the flow of image correction will be described with reference to FIG. In the fifth embodiment, a test pattern is recorded on an intermediate transfer medium.

  When a print instruction is issued by the host computer, test pattern data to be printed in step 501 is generated, and then in step 502, each recording head 112 (112C, 112M, 112Y, 112K) is temporarily applied to the intermediate transfer medium 32. A record is made. In step 503, the image defect detection means 40 detects the presence or absence of an image defect for the test pattern image recorded on the intermediate transfer medium 32. If it is determined in step 503 that there is no image defect, the image of the test pattern recorded on the intermediate transfer medium 32 is removed by the ink cleaning unit 43 in step 504. Thereafter, in step 505, image data to be recorded on the recording paper 16 is generated, and in step 506, recording is once performed on the intermediate transfer medium 32 by the recording heads 112 (112C, 112M, 112Y, 112K). In step 507, the image recorded on the intermediate transfer medium 32 is transferred to the recording paper 16 and discharged when the recording paper 16 is sandwiched between the intermediate transfer medium 32 and the transfer roller 34. Thereafter, in step 508, it is determined whether or not there is still data to be printed out of the data instructed to be printed first. If it is determined in step 508 that there is no remaining data to be printed, printing is terminated as it is. On the other hand, if it is determined in step 508 that data to be printed still remains, the process returns to step 505 and the next data is transferred to the intermediate transfer medium by each recording head 112 (112C, 112M, 112Y, 112K). 32.

  If it is determined in step 503 that there is an image defect by the image defect detection unit 40, the process proceeds to step 509, and the test pattern image recorded on the intermediate transfer medium 32 is removed by the ink cleaning unit 43. The In this case, the presence / absence of an image defect may be detected by the image defect detection means 40 as described in the third embodiment. Thereafter, in step 510, correction data for all the images is generated based on the information detected by the image defect detection means 40. In step 511, the correction data for all the images is recorded on the intermediate transfer medium 32 by the recording heads 112 (112C, 112M, 112Y, 112K) based on the correction data for all the images.

  Thereafter, the process proceeds to step 512, and the image recorded on the intermediate transfer medium 32 is transferred to the recording paper 16 and discharged when the recording paper 16 is sandwiched between the intermediate transfer medium 32 and the transfer roller 34. . Thereafter, in step 513, it is determined whether or not there is still data to be printed among the data instructed to be printed first. If it is determined in step 513 that there is no remaining data to be printed, the print heads 112 (112C, 112M, 112Y, 112K) shown in step 514 are maintained, and then printing ends. On the other hand, if it is determined in step 513 that there is still data to be printed, the process returns to step 510.

  In this embodiment, similarly to the other embodiments, when the D value counter is provided and the predetermined value is reached, the ink cleaning means 43 removes the ink from the intermediate transfer medium 32 and each recording head. It is also possible to provide a mechanism for performing maintenance of 112 (112C, 112M, 112Y, 112K). In this case, after the print instruction is given, the step of resetting the D value of the counter is required before the test pattern data is generated in step 501.

  A specific method of correction is performed by the same method as in the first embodiment.

  In the embodiment described above, the intermediate transfer rotating drum has been described as the intermediate transfer medium. However, the intermediate transfer medium is not limited to the intermediate transfer rotating drum, and is an intermediate transfer belt. Also good. Further, although the transfer roller has been described as the transfer means, the transfer roller is not limited to the transfer roller, and may be a transfer belt.

  The image forming apparatus according to the present invention has been described in detail above. However, the present invention is not limited to the above examples, and various improvements and modifications may be made without departing from the gist of the present invention. Of course.

1 is an overall configuration diagram of an ink jet recording apparatus which is an image forming apparatus according to a first embodiment of the present invention. Flowchart of image correction in the first embodiment of the present invention (A) Plane perspective view of structure example of recording head of image forming apparatus according to the present invention, (b) enlarged view of main part Plane perspective view showing another structure example of a full-line head Sectional drawing which follows the 5A-5B line in FIG. Enlarged view showing the nozzle arrangement of the head shown in FIG. Main part block diagram which shows the system configuration | structure of the inkjet recording device which concerns on this embodiment. 1 is an overall configuration diagram of an ink jet recording apparatus that is an image forming apparatus according to second, third, and fifth embodiments of the present invention. Flowchart of image correction in the second embodiment of the present invention Flowchart of image correction in the third embodiment of the present invention FIG. 7 is an overall configuration diagram of an ink jet recording apparatus which is an image forming apparatus according to a fourth embodiment of the present invention. Flowchart of image correction in the fifth embodiment of the present invention Explanatory drawing which shows the example of the density profile before the density nonuniformity correction by embodiment of this invention Explanatory drawing which shows the mode after density nonuniformity correction by embodiment of this invention (A) is a density profile diagram of an actual printing model, and (b) is a density profile diagram of a δ function type printing model. Power spectrum graph showing the effect of correction according to an embodiment of the present invention Graph used to explain the relationship between the number of nozzles (N) used for correction and the density correction coefficient The flowchart which showed the flow of the image processing by embodiment of this invention Conceptual diagram of density unevenness correction processing according to an embodiment of the present invention Flow chart showing the flow of correction data update processing

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Inkjet recording device (image forming apparatus), 14 ... Ink storage / loading unit, 16 ... Recording paper, 18 ... Paper feeding unit, 20 ... Decal processing unit, 26 ... Paper discharge unit, 28 ... Cutter, 30 ... Heating drum 32 ... Intermediate transfer medium, 34 ... Transfer roller, 40 ... Image defect detection means, 42 ... Ink cleaning means, 112 ... Recording head

Claims (5)

A recording head having a plurality of recording elements;
An intermediate transfer medium on which an image is once recorded by the recording head while moving relative to the recording head;
An image defect detection means provided downstream of the recording head in the relative movement direction of the intermediate transfer medium and detecting the presence or absence of an image defect for the image recorded on the intermediate transfer medium;
An ink cleaning means provided downstream of the image defect detection means in the relative movement direction of the intermediate transfer medium and for removing ink recorded on the intermediate transfer medium by the recording head;
A transfer means provided downstream of the ink cleaning means in the relative movement direction of the intermediate transfer medium and transferring an image recorded on the intermediate transfer medium to a recording medium;
When an image defect is detected by the image defect detection unit, an image correction unit that generates image correction data based on information on the image defect;
With
The image to be printed is recorded on the intermediate transfer medium by the recording head based on the data of the image to be printed on the recording medium, and the image defect is recorded on the image to be printed recorded on the intermediate transfer medium. The detection means detects the presence or absence of image defects,
When the image defect is detected, the ink recorded on the intermediate transfer medium by the recording head is removed by the ink cleaning unit before reaching the transfer unit, and the recording head is based on the image correction data. To form an image on the intermediate transfer medium. A recording head having a plurality of recording elements;
An intermediate transfer medium on which an image is once recorded by the recording head while moving relative to the recording head;
An image defect detection means provided downstream of the recording head in the relative movement direction of the intermediate transfer medium and detecting the presence or absence of an image defect for the image recorded on the intermediate transfer medium;
A transfer means provided downstream of the image defect detection means in the relative movement direction of the intermediate transfer medium, for transferring an image recorded on the intermediate transfer medium to a recording medium;
Ink cleaning that is provided downstream of the transfer means and upstream of the recording head in the relative movement direction of the intermediate transfer medium and removes ink recorded on the intermediate transfer medium by the recording head. Means,
When an image defect is detected by the image defect detection unit, an image correction unit that generates image correction data based on information on the image defect;
With
The image to be printed is recorded on the intermediate transfer medium by the recording head based on the data of the image to be printed on the recording medium, and the image defect is recorded on the image to be printed recorded on the intermediate transfer medium. The detection means detects the presence or absence of image defects,
When the image defect is detected, the transfer unit is separated from the intermediate transfer medium, and after the ink recorded on the intermediate transfer medium by the recording head is removed by the ink cleaning unit,
A test pattern is recorded on the intermediate transfer medium by the recording head,
For the image of the test pattern recorded on the intermediate transfer medium, the image correction data is generated by the image correction unit based on the defect information of the image of the test pattern by performing detection by the image defect detection unit,
An image forming apparatus for recording on the intermediate transfer medium by the recording head based on the image correction data. A recording head having a plurality of recording elements;
An intermediate transfer medium on which an image is once recorded by the recording head while moving relative to the recording head;
An image defect detection means provided downstream of the recording head in the relative movement direction of the intermediate transfer medium and detecting the presence or absence of an image defect for the image recorded on the intermediate transfer medium;
An ink cleaning means provided downstream of the image defect detection means in the relative movement direction of the intermediate transfer medium and for removing ink recorded on the intermediate transfer medium by the recording head;
A transfer means provided downstream of the ink cleaning means in the relative movement direction of the intermediate transfer medium and transferring an image recorded on the intermediate transfer medium to a recording medium;
When an image defect is detected by the image defect detection unit, an image correction unit that generates image correction data based on information on the image defect;
A test pattern is recorded on the intermediate transfer medium by the recording head, and the image defect detection means detects the presence or absence of an image defect in the test pattern image recorded on the intermediate transfer medium, and then the intermediate Before reaching the transfer means, the ink recorded on the transfer medium is removed by the ink cleaning means,
When a defect in the test pattern image is confirmed by the image defect detection unit, image correction data is generated by the image correction unit based on the defect information of the test pattern image, and the recording head is generated based on the image correction data. An image forming apparatus, wherein an image is recorded on the intermediate transfer medium. Until the printing in the print instruction information by the image forming apparatus receives is completed, the image forming apparatus according to any one of claims 1 to 3, characterized in that does not perform maintenance of the recording head. The image correction means includes a correction range setting means for setting N (N is an integer of 2 or more) correction recording elements used for correcting output density among the plurality of recording elements;
Based on the correction condition including the condition that the differential coefficient at the frequency origin (f = 0) of the power spectrum representing the spatial frequency characteristic of density unevenness caused by the recording characteristics of the recording element is zero, the N correction recording elements Correction coefficient determining means for determining a density correction coefficient;
Correction processing means for performing an operation of correcting the output density using the density correction coefficient determined by the correction coefficient determination means;
The image forming apparatus according to any one of claims 1 to 4, characterized by comprising a.