JP2015003478A - Recording apparatus, and method for controlling the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a recording apparatus and a method for controlling the same in which conveyance error detection having high reliability of a recording media is performed, a record registration gap is reduced and a high-quality image is recorded.SOLUTION: First, a surface of the recording media is photographed in the upstream side of a position where recording is to be performed by a recording head and in the downstream side of a marking head with respect to the conveyance direction of the recording media. The moving amount of the recording media is detected from positions of a characteristic image obtained by photographing the surface of the recording media at different times while conveying the recording media. When the detection accuracy of the characteristic image is low in the detection, a test pattern is recorded on the recording media by controlling the marking head. Thereby, the moving amount of the recording media is correctly detected from an inherent characteristic image or the test pattern of the recording media. The conveyance error detection and the conveyance control having high accuracy can be achieved by feeding-back it to the conveyance control.

Description

  The present invention relates to a recording apparatus and a control method of the recording apparatus, and more particularly to a recording apparatus that performs recording using a full-line recording head that performs recording according to an inkjet method, and a control method of the recording apparatus.

  In order to record an image with high quality on a transported recording medium, it is important to improve the registration (hereinafter, registration) accuracy in the image. For example, when recording a color image using a recording agent of a plurality of colors, it is necessary to improve the registration accuracy of each color and realize recording with little color misregistration.

  In the case of a dot printer, for example, it is necessary to improve the registration accuracy and reduce dot deviation even in recording using a monochromatic recording agent, thereby realizing, for example, a monochromatic character quality with a sharp outline.

  In particular, in a recording apparatus configured to record an image on a recording medium that is transported at a constant speed, if an error occurs in the transport, the recording registration shifts.

  Patent Document 1 discloses a contact member that contacts the surface of a recording medium upstream of a position where an image is picked up by a sensor unit in the conveyance direction of the recording medium, and imparts an optically identifiable uneven shape to the surface of the recording medium. Is disclosed. According to Patent Document 1, an image including the uneven shape is captured, and movement information of the recording medium is detected by image processing including pattern matching. Then, by deriving the conveyance error of the recording medium from this movement information and executing the conveyance correction control, the recording registration deviation due to the conveyance deviation is reduced.

JP 2010-064841 A

  In Patent Document 1, a concavo-convex shape is formed on the surface of a recording medium (for example, the surface of a recording paper) as a reading mark for detecting a conveyance error. However, in the case of high-quality recording, even if the recording medium has slight irregularities, this is viewed as a large contrast between light and dark, and image quality is impaired. On the other hand, if the size of the unevenness is reduced in order to maintain the image quality, the detection accuracy of the conveyance error is lowered. As a result, the accuracy of the feedback control that corrects the registration error is deteriorated.

  The present invention has been made in view of the above-described conventional example. A recording apparatus and a recording apparatus control method capable of reducing recording registration misalignment by performing highly reliable recording medium transport error detection while maintaining image quality. The purpose is to provide.

  In order to achieve the above object, the recording apparatus of the present invention has the following configuration.

  That is, a recording apparatus that performs recording by ejecting ink from a recording head to a recording medium conveyed in a predetermined direction, and a position where recording is performed by the recording head in the conveyance direction of the recording medium A marking head that is provided on the upstream side and records a test pattern by discharging ink onto the recording medium; and on the upstream side of a position where recording is performed by the recording head with respect to a conveyance direction of the recording medium, Provided on the downstream side of the marking head and obtained by photographing the surface of the recording medium while shifting the time by the photographing means while conveying the recording medium, and photographing means for photographing the surface of the recording medium. Detection means for detecting the amount of movement of the recording medium from the position of the feature image obtained, and the detection accuracy of the feature image by the detection means is reduced. If that is characterized by having a recording means of the auxiliary image to be controlled to record a test pattern on the recording medium by controlling the marking head.

  In another aspect of the present invention, a recording head that performs recording by ejecting ink onto a recording medium that is transported in a predetermined direction and a recording direction of the recording medium are recorded by the recording head. A recording apparatus control method comprising a marking head that is provided upstream of a position where the recording medium is formed and that ejects ink onto the recording medium to record a test pattern, wherein the recording head relates to a conveyance direction of the recording medium. An imaging step of imaging the surface of the recording medium upstream of a position where recording is performed and downstream of the marking head, and imaging the surface of the recording medium while conveying the recording medium A detection step of detecting the amount of movement of the recording medium from the position of the feature image obtained by photographing at different times in the process; and the detection process And an auxiliary image recording step for controlling the marking head to record a test pattern on the recording medium when the detection accuracy of the feature image is low. The recording method is provided.

  Therefore, according to the present invention, the amount of movement of the recording medium is accurately detected from the original characteristic image or test pattern of the recording medium, and this is fed back to the conveyance control, thereby realizing highly accurate conveyance error detection and conveyance control. There is an effect that can be. As a result, recording registration alignment can be performed with high accuracy, and high-quality recording can be achieved.

1 is a perspective view illustrating a schematic configuration of an ink jet recording apparatus that is a typical embodiment of the present invention. It is a figure which shows the internal structure of a recording part. It is a figure which shows the structure of a sensor unit. It is an example of the image which imaged the partial area | region of the surface of the moving recording medium at a different timing with the two-dimensional image sensor. It is a figure which shows the condition at the time of using a recording medium whose surface uneven | corrugated shape is smoother than what was shown in FIG. It is a figure which shows a mode that the uneven | corrugated pattern of media was caught by each pixel of an image sensor. It is a figure which shows the example which provided the auxiliary | assistant image with the marking head when the detection accuracy as shown in FIG. 5 is falling. It is a figure which shows the condition at the time of using a recording medium whose surface uneven | corrugated shape is smoother than the example shown in FIG. It is a figure which shows the example which provided the auxiliary | assistant image with the marking head when the detection accuracy as shown in FIG. 8 is falling. It is a figure which shows the experimental data of the conveyance amount detection accuracy when increasing the number of auxiliary dots. It is a figure which shows about the influence of the density nonuniformity which an auxiliary dot has on a recording medium. It is a figure which shows the optical characteristic by the auxiliary | assistant dot recorded on the recording medium with a white surface, and LED illumination. 6 is a flowchart illustrating a processing procedure of recording medium conveyance control during a recording operation. It is a flowchart which shows the detail of the selection procedure of the auxiliary image of step S4. It is a figure which shows the initial stage auxiliary image initially selected by the test pattern check, ie, the initial stage auxiliary dot. It is a figure which shows a mode that the 2nd auxiliary | assistant dot became the non-ejection dot. It is a figure which shows a mode that a new auxiliary | assistant dot is recorded and a new auxiliary | assistant dot pair is formed with a 1st auxiliary | assistant dot. It is a figure which shows the internal structure of the recording part 1 at the time of the maintenance of a marking head.

  Hereinafter, preferred embodiments of the present invention will be described more specifically and in detail with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected to the already demonstrated part and duplication description is abbreviate | omitted.

  In this specification, “recording” (sometimes referred to as “printing”) is not limited to the case of forming significant information such as characters and graphics, but may be significant. It also represents the case where an image, a pattern, a pattern, etc. are widely formed on a recording medium, or the medium is processed, regardless of whether it is manifested so that humans can perceive it visually. .

  “Recording medium” refers not only to paper used in general recording apparatuses but also widely to cloth, plastic film, metal plate, glass, ceramics, wood, leather, and the like that can accept ink. Shall.

  Further, “ink” (sometimes referred to as “liquid”) should be interpreted widely as in the definition of “recording (printing)”. Therefore, by being applied on the recording medium, it is used for formation of images, patterns, patterns, etc., processing of the recording medium, or ink processing (for example, solidification or insolubilization of the colorant in the ink applied to the recording medium). It shall represent a liquid that can be made.

  Furthermore, unless otherwise specified, the “nozzle” collectively refers to an ejection port or a liquid channel communicating with the ejection port and an element that generates energy used for ink ejection.

  An element substrate (head substrate) for a recording head to be used below does not indicate a simple substrate made of a silicon semiconductor but indicates a configuration in which each element, wiring, and the like are provided.

  Further, the term “on the substrate” means not only the element substrate but also the surface of the element substrate and the inside of the element substrate near the surface. In addition, the term “built-in” as used in the present invention is not a term indicating that each individual element is simply arranged separately on the surface of the substrate, but each element is manufactured in a semiconductor circuit. It shows that it is integrally formed and manufactured on an element plate by a process or the like.

  Next, examples of the ink jet recording apparatus will be described. This recording apparatus uses a continuous sheet (recording medium) wound in a roll shape, and is a high-speed line printer that supports both single-sided recording and double-sided recording. For example, it is suitable for a large number of print fields in a print laboratory or the like.

  FIG. 1 is a perspective view showing a schematic configuration of an ink jet recording apparatus (hereinafter referred to as a recording apparatus) which is a typical embodiment of the present invention. As shown in FIG. 1, the recording apparatus includes a recording unit 1, a sheet supply unit 2, a sheet winding unit 3, and a control unit 6. The sheet supply unit 2 holds the roll sheet 4 wound in a roll shape, and supplies the continuous sheet to the recording unit 1 while pulling out the continuous sheet from the roll. The recording unit 1 sequentially records a plurality of images on a continuous sheet. The recorded continuous sheet is wound up as a roll sheet 5 by the sheet winding unit 3. The control unit 6 has a controller, a memory, and various I / O interfaces, and controls the entire recording apparatus. The control unit 6 may be built in the recording apparatus itself, or an external host computer connected to the recording apparatus may perform its function. Note that at an arbitrary position in the sheet conveyance path, the side close to the sheet supply unit 2 is referred to as “upstream”, and the opposite side is referred to as “downstream”.

  FIG. 2 is a diagram showing an internal configuration of the recording unit 1. 2A is a top view of the recording unit 1, and FIG. 2B is a side sectional view of the recording unit 1.

  The recording medium 8 is a continuous sheet, and the continuous sheet supplied from the sheet supply unit 2 to the recording unit 1 is conveyed in the arrow A direction in the recording unit. In the recording unit 1, the conveyance accuracy is determined by a main conveyance roller pair including a conveyance roller 11 and a pinch roller 12 that is driven to rotate as a part of the sheet conveyance mechanism. The recording unit 1 is provided with four ink jet recording heads (hereinafter referred to as recording heads) that eject inks of different colors along the conveyance path of the recording medium. A sub-conveying roller pair including a conveying roller 13 and a pinch roller 14 that rotates following the conveying roller 13 is provided on the downstream side of each recording head.

  The four recording heads include a black head 17 that ejects black ink, a cyan head 18 that ejects cyan ink, a magenta head 19 that ejects magenta ink, and a yellow head 20 that ejects yellow ink. Each recording head is a full-line recording head in which nozzle rows are formed in a range that covers the maximum recording width assumed to be used, and the nozzle rows are formed over the entire recording width direction.

  As an ink jet recording method, a method using a heating element, a method using a piezo element, a method using an electrostatic element, a method using a MEMS element, or the like can be adopted. Each color ink is supplied from an ink tank (not shown) to each recording head via an ink tube. In this embodiment, four color inks and four recording heads corresponding thereto are used, but it goes without saying that the number of colors and the number of recording heads are not limited to four. It may be a larger or smaller number. Further, each recording head may be a header unit integrated with an ink tank that stores ink of a corresponding color.

  As shown in FIG. 2, each recording head is integrally held by a head holder 10. The head holder 10 can be moved up and down in the direction of arrow B by a drive mechanism for a maintenance operation. A sensor unit 701 for photographing the surface of the recording medium 8 is provided on the upstream side of the head holder 10 and is used for detecting the moving amount or moving speed of the continuous sheet by pattern matching. Further, an auxiliary image for detecting these, that is, a marking head 500 for recording auxiliary dots is provided on the upstream side of the sensor unit 701. The marking head 500 is an inkjet recording head, has a plurality of nozzles, and can perform marking of a plurality of colors. The marking head 500 is held by the marking head holder 7 for maintenance and can be moved up and down in the B direction.

  The marking head 500 and the sensor unit 701 are disposed upstream of the recording head and substantially in the center in the width direction of the recording medium. With this arrangement, it is possible to cope with borderless full-surface recording with no margins, hardly affected by the mist of each recording head, and an average conveyance amount can be detected with respect to minute meandering and minute skew of the recording medium. In the transport path of the recording medium 8 as shown in FIG. 2, recording is performed in the order of black, cyan, magenta, and yellow.

  A marking cap 30 and a blade wiper 31 are disposed immediately below the marking head 500. The marking cap 30 receives the flushing ink from the marking nozzle 501 of the marking head 500, and the received ink is discharged to a waste ink tank (not shown) by a suction mechanism (not shown). When an ink ejection failure occurs, the marking head 500 is lowered in the direction of arrow B, and suction recovery by the marking cap 30 is executed. Further, the blade surface of the marking nozzle 501 can be wiped by the blade wiper 31.

  FIG. 3 is a diagram showing the configuration of the sensor unit 701. 3A is a top view of the sensor unit 701, and FIG. 3B is a side sectional view of the sensor unit 701.

  The sensor unit 701 is mainly composed of a light emitting unit, a light receiving unit, and an image processing unit, and these are integrated as a unit. The light source 703 is a light emitting element such as an LED, an OLED, or a semiconductor laser. Light emitted from the light source 703 is guided by the light guide 702 and illuminates the surface of the recording medium 8 from an oblique direction. An image of the illumination area on the recording medium 8 is formed on the image sensor 705 by the lens 706. The transparent protective cover 704 prevents the ink mist and the like from entering from the recording medium 8 side and stains on the lens 706.

  The image sensor 705 is a line image sensor in which a large number of photoelectric conversion elements having a CCD or CMOS structure are arranged one-dimensionally, or an area image sensor in which two-dimensional arrangement is performed. An image of the surface of the recording medium (contrast of shading on the surface irregularities) is optically acquired by the image sensor 705. The imaging signal acquired by the image sensor 705 is A / D converted and transferred to an image processing unit 707 which is a chip image processor.

  The image processing unit 707 detects movement information (movement amount, movement speed, movement acceleration, movement direction, etc.) of the conveyed recording medium by image processing based on the digitized imaging signal. A plurality of image data obtained by performing imaging a plurality of times with the movement of the recording medium is compared by image processing including pattern matching processing, and the movement amount (conveyance amount) of the recording medium is detected. Alternatively, the acquired image may be binarized once, and the binarized image may be compared by pattern matching processing. Alternatively, a method may be used in which a portion where the luminance of the acquired image has a peak is extracted, and the peak portion of the image is compared to acquire a positional shift amount. Further, not only the movement amount of the recording medium but also the velocity can be obtained from the movement amount per unit time, and the acceleration can be obtained by obtaining a change in velocity by differential processing. The movement information of the recording medium thus obtained is fed back to the control unit 6 and the conveyance of the recording medium 8 is feedback controlled.

  FIG. 4 is an example of an image obtained by capturing partial areas on the surface of a moving recording medium at different timings using a two-dimensional image sensor. In FIG. 4, an image 101 is an image taken first, and an image 102 is an image taken by moving the recording medium at a certain time from there. In any of the images, a fine uneven shape (such as paper fiber unevenness) on the surface of the recording medium appears as a bright and dark pattern having high contrast. Here, where the same pattern as the partial area 101a indicated by the broken line in the image 101 exists in the image 102 is determined from the similarity of the images by a known pattern matching process. As a result, it can be seen that the image 102 exists in a region 102a indicated by a broken line. By looking at how many pixels the areas 101a and 102a are apart in the transport direction, the moving amount 103 of the recording medium during this time can be obtained.

  Hereinafter, the movement amount detection will be described in detail.

  After acquiring the image 101 at a certain time t = T, the image 102 is acquired at a timing (t = T + T1) when the time T1 has passed. By searching for a similar image pattern by pattern matching processing, it can be seen that the area 101 a in the image 101 has moved to the position of the area 102 a of the image 102. For example, the actual size on the recording medium 8 corresponding to one pixel of the image sensor 705 is 10 μm square. In the example illustrated in FIG. 4, the images 101 and 102 are assumed to include 21 pixels in the transport direction. The difference between the image 101 and the image 102 by pattern matching, that is, the movement amount 103 is shifted by 8 pixels in the transport direction. Therefore, the movement amount in the transport direction within the time T1 is detected as 10 μm × 8 pixels = 80 μm. The control unit 6 compares the actual conveyance amount (80 μm) of the recording medium obtained by the image processing by the image sensor 705 with respect to the conveyance amount (for example, 85 μm) which is a design target value at the time T1. The difference (5 μm) is fed back to the next conveyance to adjust the conveyance amount. This feedback conveyance control is repeated during image formation and continues until image formation is completed. Thereafter, when the recording is finished, the recording medium 8 is discharged, and a series of recording operations is finished.

  FIG. 5 is a diagram showing a situation when a recording medium having a surface irregularity shape smoother than that shown in FIG. 4 is used. An image 111 is an image taken first, and an image 112 is an image taken after the recording medium moves at a certain time from there. Compared with FIG. 4, there are few inherent bright and dark patterns due to the surface irregularity shape. For this reason, when an image pattern similar to the region 111a is searched for in the image 112, the pattern matching accuracy decreases. That is, the detection accuracy of the moving amount of the recording medium is lowered.

  FIG. 6 is a diagram illustrating a state in which the uneven pattern of the recording medium is captured by each pixel of the image sensor 705. In FIG. 6, the grid of the lattice indicates an image sensor 705 CCD sensor array, and shows a state in which a concavo-convex pattern of the medium is photographed. The reference image range 115 does not have sufficient features. Each pixel of the sensor detects a concavo-convex pattern of the recording medium with binary values (that is, black and white). In the example shown in FIG. 6, there is no contrast and the color is generally white. In this embodiment, if it is determined that the output of the image range 115 is smaller than a predetermined threshold value and close to white, it is determined that the feature pattern is insufficient. If it is determined that the feature pattern is insufficient, the marking head 500 is controlled by the marking head 500 so as to record auxiliary dots in the reference image range 115.

  FIG. 7 is a diagram showing an example in which the auxiliary image 113 is applied by the marking head 500 when the detection accuracy as shown in FIG. In this example, when the feature pattern is insufficient, a one-dot auxiliary image 113 is provided in the reference image range 111a. By doing in this way, the auxiliary image 114 exists in the image range 112a detected after the recording medium is moved, and the accuracy of pattern matching is ensured. This auxiliary image, that is, auxiliary dots are recorded periodically at intervals so that one desired pattern fits in the reference image range 111a and the image range 112a to be detected. The dot recording timing, the reference image capturing timing, and the detected image capturing timing are controlled consistently according to the conveyance speed of the recording medium. The marking head 500 is an ink jet recording head that discharges a small droplet of 1 picoliter. The ink color is yellow, so the brightness is low, and the size of the recording dot is as small as about 20 μm in diameter. Therefore, the presence of the auxiliary image 113 does not substantially adversely affect the recorded product.

  FIG. 8 is a diagram illustrating a situation when a recording medium having a smoother surface uneven shape than the example illustrated in FIG. 5 is used. In FIG. 8, the left side is the reference image 121, and the right side is the image 122 detected after the reference image is moved in the arrow A direction.

  As can be seen from comparison with FIG. 5, there are even fewer inherent light and dark patterns due to the surface irregularities. In this example, the region 121a used for the pattern matching process does not include a specific light / dark pattern. For this reason, when an image pattern similar to the region 121a is searched in the image 122, the plurality of regions 123 are determined to be similar, and the movement amount of the recording medium cannot be accurately detected. In this case, as described with reference to FIG. 6, the lightness and darkness are determined, and it is determined that the color is considerably white as compared with a predetermined standard.

  FIG. 9 is a diagram illustrating an example in which the auxiliary image 113 is given by the marking head 500 when the detection accuracy as shown in FIG. 8 is lowered. 9A shows an example in which the marking head 500 is controlled to record an auxiliary image 124 composed of two dots in the area 121a. In this case, in the marking detection range 126 of the image 122, an image composed of two dots is detected as a dot pair 125, and pattern matching is executed to detect the amount of movement of the recording medium. On the other hand, (b) controls the marking head 500 when the reference image 131 has almost no light and dark pattern, and records the auxiliary image 134 composed of four dots in the region 131a. In this case, in the marking detection range 136 of the image 132, an image composed of four dots is detected as the dot group 135, and pattern matching is executed to detect the amount of movement of the recording medium.

  Note that the number of auxiliary dots constituting the auxiliary image may be arbitrarily set to a desired number depending on the balance between the conveyance amount detection performance and the visual recognition level on the printed product.

  Here, an example of selection of the number of auxiliary dots will be described with reference to FIGS.

  FIG. 10 is a diagram showing experimental data of the conveyance amount detection accuracy when the number of auxiliary dots is increased. As shown in FIG. 10, the conveyance amount detection error due to pattern matching decreases as the number of auxiliary dots increases, and the accuracy is stabilized with 3 dots. Since the number of dots is related to the area occupied by the ink adhering to the recording medium, it is also called an area factor. By increasing the influence of this area factor, the pattern recognition information is increased and the detection accuracy of the carry amount is improved.

  FIG. 11 is a diagram showing the influence of density unevenness that the auxiliary dots have on the recording medium. The macroscopic density change (ΔE) by the auxiliary dots, that is, the density unevenness is determined by the color and background color of the auxiliary dots and the macroscopic dot area density on the recording medium. Generally, when the density change is ΔE ≦ 0.4, a good image is obtained as a recorded product.

  FIG. 11 exemplifies the density change (ΔE) experimental results for three types of dot densities when yellow auxiliary dots exist in a hue range where the background changes from white to cyan to black. As can be seen from FIG. 11, even if the background hue changes, if the macroscopic area density of yellow dots on the recording medium is 0.042% (solid line 301 in FIG. 11) or less, the density change (ΔE) is The result of about 0.4 or less is shown. In this embodiment, the balance between the auxiliary dot application period, the dot density in the minute range of the application area, and the dot size is determined to satisfy ΔE ≦ 0.4 when four dots are applied. That is, when the surface of the recording medium is viewed widely, the dot area density is 0.042% or less on average, and the change in visual density is ΔE ≦ 0.4.

  In this embodiment, the accuracy of pattern matching is ensured as a configuration capable of providing minute auxiliary dots on the recording medium to the minimum necessary. As a result, the amount of movement of the recording medium can be accurately detected regardless of the surface properties of the recording medium, and the color misregistration of each color in the recording unit is reduced by sequentially performing the conveyance amount correction.

  The auxiliary dot pattern for forming the auxiliary image is not limited to the above example. For example, it is desirable to select an effective auxiliary dot pattern according to the degree of the roughness pattern on the surface of the recording medium. Various dot pattern information may be stored in a memory, and based on this, a test pattern may be recorded on a target recording medium to determine which dot pattern to select.

  It is further desirable to be able to select the color of the auxiliary dot. If the combination of the color of the recording medium surface and the color of illumination is optimized, the accuracy of pattern matching can be improved. As shown in FIG. 2, the marking head 500 is configured to include a plurality of nozzle rows that eject inks of a plurality of colors, and an auxiliary dot recorded in each color is photographed to select an optimum dot color. May be.

  Furthermore, in the sensor unit 701, if the light source LED can be selected from three colors of red, green, and blue, the amount of light is changed, or an optical filter is provided in the photographing system to give a specific spectral characteristic, the captured image The degree of feature recognition can be further adjusted. These conditions may be set automatically or may be changed by manual adjustment by the user.

  As described above, if the optimum auxiliary image and the photographing condition are determined by combining the auxiliary dot pattern, the pattern color, and the light source color, it is possible to further improve the detection accuracy. For example, it is desirable to set the auxiliary dot color and the illumination color in a complementary color relationship. By making the color of the auxiliary dot and the color of the illumination a complementary color relationship, that is, an opposite color relationship, the auxiliary dot can be detected as a dark color.

  FIG. 12 is a diagram illustrating the optical characteristics of auxiliary dots recorded on a white recording medium and LED illumination. 12A shows the complementary color relationship between the yellow auxiliary dots and the blue LED illumination, and FIG. 12B shows the complementary color relationship between the cyan auxiliary dots and the red LED illumination.

  As can be seen from FIG. 12A, the output of the blue illumination has a spectral characteristic 403 that has a peak around the wavelength of 470 nm and a narrow effective wavelength range. In this effective wavelength range, the relative reflection output 402 of the yellow auxiliary dots is a low value of about 10%. On the other hand, the relative reflection output 401 of the white recording medium is a high value of about 90%. In this state, the image sensor 705 identifies the yellow auxiliary dot as a considerably dark color, and recognizes the background blank paper as a considerably bright color. That is, the contrast 404 between the background and the auxiliary dots can be increased.

  Further, the complementary color relationship will be described using another color.

  As can be seen from FIG. 12B, the output of the red illumination has a spectral characteristic 406 that has a peak around the wavelength of 640 nm and a narrow effective wavelength range. In this effective wavelength range, the relative reflection output 405 of the cyan auxiliary dot is a low value of about 10%. On the other hand, the relative reflection output 401 of the blank recording medium is as high as about 85%. In this state, the image sensor 705 recognizes the cyan auxiliary dots as a considerably dark color, and recognizes the background blank paper as a considerably bright color. That is, the contrast 407 between the background and the auxiliary dots can be increased.

  If the recording medium is colored, select an auxiliary dot color that increases the reflected output difference from the recording medium, and then select the complementary color of the auxiliary dot color, that is, the opposite color illumination. The contrast of the auxiliary dots can be obtained.

  Next, procedures such as auxiliary dot recording control and setting of the number of auxiliary dots will be described.

  FIG. 13 is a flowchart showing a processing procedure for transport control of the recording medium during the recording operation.

  First, in step S1, a recording medium such as roll paper is fed and conveyed to the recording unit. Next, in step S2, during recording, the sensor unit 701 images the surface of the recording medium upstream of the recording unit. Further, in step S3, the contrast state and the like are analyzed from the image data photographed in the area 101a of the image 101 serving as a reference as shown in FIG. If the recording medium is plain paper or the like, fine irregularities on the surface are photographed with high contrast.

  Here, if it is determined that the contrast has reached a predetermined reference, the process proceeds to step S5, and the conveyance error is detected as it is. On the other hand, if the recording medium is strong glossy paper such as photographic paper, the surface has high flatness and is uniform and it is difficult to find a characteristic image. In such a case, if it is determined by image analysis that the contrast does not reach the predetermined standard, the process proceeds to step S4, an auxiliary image is selected, and then the process proceeds to step S5. Perform error detection.

  Then, the detected conveyance error is fed back to the conveyance control, and recording is executed in step S6.

  FIG. 14 is a flowchart showing details of the auxiliary image selection procedure in step S4. When it is difficult to obtain a feature image from only the surface of the recording medium, an auxiliary image, that is, an auxiliary dot is recorded.

  In step S11, as described above, various dot patterns in which the number of dots, arrangement, color, and the like are combined are recorded as test patterns by the marking head 500. This pattern is shot in the shooting range of the reference image.

  Next, in steps S12 to S13, the contrast is checked by photographing with various combinations of light source colors and optical filters, and the quality as a feature image is determined. In step S14, the highest condition is selected from the available conditions according to the priority order set and stored in advance.

  After generating the auxiliary image and determining the shooting conditions, the process returns to step S5.

  The present application is intended to improve registration performance between colors and between colors in recording, but a configuration that can be used in combination with other transport control systems may also be considered. If the registration (registration) is correct, a subtle image unevenness may be visually recognized depending on the recorded image. This is mainly due to high-order fixed errors caused by the manufacturing accuracy of the recording head, and some registration adjustment is performed at the time of shipment or installation of the recording apparatus. However, depending on the amount of conveyance correction control and the periodic characteristics, these error factors may appear slightly in the image. That is, regular texture unevenness.

  In such a case, a known conveyance control method and a method of directly photographing the surface of the recording medium as described above to detect a characteristic image, applying pattern matching, and feeding back the result to the conveyance control. There are cases where it can be solved by the combined use. Known methods include open control with a stepping motor and speed control with an encoder mounted in the drive system.

  In these controls, a relatively long period fluctuation component of the mechanical system appears as a registration error on the recording medium. Since these controls are inferior in the absolute accuracy of registration, the graininess of the entire image is lowered, but texture unevenness due to a high-order accuracy error hardly occurs. Which transport control gives the desired image quality depends on the user's subjectivity. Therefore, the conveyance control used for the registration adjustment may be made selectable. Also, the conveyance control may be selectable in order to prepare for a situation where the method of directly photographing the surface of the recording medium as in this embodiment does not function well due to deterioration of sensors or the like.

  Next, securing of auxiliary image detection reliability will be described.

  FIG. 15 is a diagram showing an initial auxiliary image, that is, an initial auxiliary dot initially selected by the test pattern check.

  As shown in FIG. 15, the initial auxiliary dots are one dot necessary for image detection, plus one dot for securing margin, for a total of two dots, that is, the first auxiliary dot 203 and the second auxiliary dot. It is formed with dots 204. An image 201 is an image captured first, and an image 202 is an image captured by moving the recording medium at a certain time from there. The grid of the lattice indicates the CCD sensor array of the image sensor 705. Further, the recording is controlled so that two auxiliary dots recorded by the marking head 500 are included in the reference image 201a. Then, the detected amount 202a is specified by pattern matching from the moved image 202, and the carry amount 205 is detected.

  FIG. 16 is a diagram illustrating a state where the second auxiliary dot is a non-ejection dot.

  In FIG. 16, as in FIG. 15, an image 211 is an image captured first, and an image 212 is an image captured by moving the recording medium at a certain time from there. For example, non-ejection of ink occurs when a part of the marking nozzle 501 is clogged due to adhesion of paper dust. As shown in FIG. 16, even if a non-ejection dot 214 (a portion corresponding to the second auxiliary dot 204) occurs, the pattern matching is continued without any trouble with only the remaining first auxiliary dot 213. There is no margin for detection of auxiliary dots. In this state, the sensor unit 701 detects from the binarized information of the image that the auxiliary dot, that is, the black area is halved.

  In such a case, the recording apparatus records a new auxiliary dot using another nozzle of the marking head 500.

  FIG. 17 is a diagram illustrating a state in which a new auxiliary dot 224 is recorded and a new auxiliary dot pair is formed together with the first auxiliary dot 223. In FIG. 17, an image 221 is an image captured first, and an image 222 is an image captured by moving the recording medium at a certain time from there. The new auxiliary dot 224 may be recorded at the same position as the second auxiliary dot 204 shown in FIG.

  In this way, the presence of auxiliary dots is checked constantly or at a predetermined timing, and recovery control for generating auxiliary dots is executed as described above.

  Note that the output of the light source 703 is normally set to a predetermined level in consideration of the lifetime and the amount of light. Only until the auxiliary dot recovery control is executed, if the output of the light source 703 is temporarily increased and the imaging contrast of the remaining first auxiliary dot 213 (or 203) is increased, pattern matching can be performed. Reliability is further improved.

  Finally, the maintenance of the marking head 500 will be described.

  FIG. 18 is a diagram illustrating an internal configuration of the recording unit 1. 18A is a top view of the recording unit 1, and FIG. 18B is a side sectional view of the recording unit 1. This figure shows a state in which the recording medium is interrupted at a portion (marking portion) where the marking head 500 performs marking. In FIG. 18, the same reference numerals are given to the components already described with reference to FIG. 2, and the description thereof is omitted.

  When non-ejection dots as shown in FIG. 16 occur, in addition to recording new auxiliary dots as shown in FIG. 17, the marking head 500 is maintained at the break of the recording medium. Run. As a result, if the recovery process is performed on all the marking nozzles 501 of the marking head 500, the reliability of auxiliary dot generation is increased.

  As shown in FIG. 18, in this embodiment, the marking head holder 7 holding the marking head 500 can be moved up and down in the direction of arrow B by an elevating mechanism (not shown). The marking head 500 can be lowered to a desired position, and suction recovery by the marking cap 30 can be executed. Further, the blade wiper 31 is configured to wipe the nozzle surface of the marking nozzle 501 in the direction of arrow C. For improving the reliability of auxiliary dot generation, it is also useful to rotate the nozzle used as the marking nozzle 501 at a predetermined period. By distributing the load to each nozzle without concentrating the use load on a specific nozzle, it is possible to maintain the discharge stability of the dots and extend the life of the marking head 500.

  Therefore, according to the embodiment described above, a registration error can be reduced by obtaining a conveyance error based on the conveyance amount obtained from the detected feature image and performing feedback control on the conveyance error.

  Since the present application is intended to reduce registration deviation, the recording timing of each color head may be sequentially corrected in accordance with the conveyance amount of the recording medium. In the case of an ink jet recording apparatus, the same registration effect can be obtained by correcting the ink discharge timing in each color head.

Claims (11)

A recording apparatus that performs recording by discharging ink from a recording head onto a recording medium conveyed in a predetermined direction,
A marking head that is provided upstream of a position where recording is performed by the recording head with respect to the conveyance direction of the recording medium, and that records a test pattern by discharging ink to the recording medium
With respect to the conveyance direction of the recording medium, an imaging unit that is provided upstream of a position where recording is performed by the recording head and downstream of the marking head, and photographs the surface of the recording medium;
Detecting means for detecting the amount of movement of the recording medium from the position of a characteristic image obtained by photographing the surface of the recording medium while shifting the time by the photographing means while transporting the recording medium;
An auxiliary image recording means for controlling the marking head to record a test pattern on the recording medium when the detection accuracy of the feature image by the detecting means is low. Recording device.   The recording apparatus according to claim 1, wherein the photographing unit photographs a concavo-convex pattern on a surface of the recording medium, uses the concavo-convex pattern as the feature image, and obtains a contrast of the feature image. Comparing means for comparing the contrast with a predetermined threshold;
And a determination means for determining that the detection accuracy of the feature image is lowered when the contrast is smaller than the predetermined threshold based on a comparison result of the comparison means. Item 3. The recording device according to Item 2. The test pattern is composed of ink dots,
The recording apparatus according to claim 3, wherein the marking head records the dots with yellow ink.   The recording apparatus according to claim 4, wherein a nozzle used for ejecting ink in the marking head is changed at a predetermined cycle.   The recording apparatus according to claim 5, further comprising recovery means for performing recovery processing of the nozzles. The photographing means includes a sensor that optically reads the surface of the recording medium,
The recording apparatus according to claim 1, wherein a light amount of illumination used when the surface of the recording medium is optically read by the sensor is temporarily changed.   The amount of movement of the recording medium detected by the detection unit is fed back to the conveyance control of the recording medium, and a conveyance error of the recording medium is obtained from the amount of movement of the recording medium detected by the detection unit, and registration adjustment is performed. The recording apparatus according to claim 1, further comprising feedback means for performing the operation.   The recording apparatus according to claim 1, wherein the recording head is a full line recording head having a recording width corresponding to a width of the recording medium.   The recording apparatus according to claim 1, wherein the recording medium is roll paper. A recording head that performs recording by discharging ink to a recording medium that is transported in a predetermined direction and a transport direction of the recording medium, and is provided upstream of a position where recording is performed by the recording head; A control method for a recording apparatus comprising a marking head for recording a test pattern by discharging ink onto a recording medium,
An imaging step of photographing the surface of the recording medium on the upstream side of the position where recording is performed by the recording head and on the downstream side of the marking head with respect to the conveyance direction of the recording medium;
A detection step of detecting the amount of movement of the recording medium from the position of a characteristic image obtained by shooting the surface of the recording medium while shifting the time in the shooting step while transporting the recording medium;
An auxiliary image recording step of controlling the marking head to record a test pattern on the recording medium when the detection accuracy of the feature image is low in the detection step. Method for controlling a recording apparatus.

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