JP2007144966A - Inkjet recorder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the shift of the hitting position of dots in the main scanning direction due to the evaporation of moisture to improve the quality of recording. <P>SOLUTION: The inkjet recorder has a drive correction means adapted to cause nozzles having a longer discharge-resting interval to be discharged in an earlier timing. The inkjet recorder has a means to analyze drive data prepared from image data by a printer driver to measure a drive-resting interval per nozzle unit, a storage means storing a timing table in which the drive-resting interval is brought into correspondence with correction timing, and a correction means for discharging an ink at the correction timing read from the storage means based on the resting period. The quality of recording can be improved by alleviating the shift of the hitting position of dots due to the evaporation. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ink jet recording apparatus for recording an image on a recording medium by ejecting and ejecting ink droplets.

  An ink jet recording apparatus records characters, images, and the like by ejecting ink droplets from a recording head provided with a plurality of fine ejection openings and attaching the ink droplets to a recording medium such as paper. In such an apparatus, since the ejection port is always exposed to the atmosphere during recording or printing standby, moisture in the ink is evaporated through the ejection port during that time. In particular, when a recording device is installed in a low-humidity environment or when the pause time is extended for a long time, there is a problem that the ink near the nozzle outlet that has not been used for ejection dries and causes defective ejection. is there.

  This problem is that even if water or alcohol, which is a volatile component in ink, is lost from the nozzle by evaporation through the discharge port, the coloring material or organic solvent that is a non-volatile component remains in the nozzle. A possible cause is that the ink changes to a composition having a high solvent concentration. Ink with a composition having a high concentration of organic solvent generally has a high viscosity, so that only the nozzle tip has a high viscosity, the ejection speed is lowered in subsequent recording, and it is difficult to land accurately at a desired position. Disturbance in landing accuracy is problematic because it degrades recording quality.

  A method for avoiding this problem known as the prior art will be described.

  In a serial type inkjet recording apparatus that performs recording by reciprocating the recording head in a direction orthogonal to the conveyance direction of the recording medium, if the recording head is exposed to the atmosphere for a short period of time, such as a few seconds For example, a so-called preliminary ejection method is employed in which the dried ink is deliberately ejected a plurality of times at a position that does not affect recording to refresh the ink in the nozzles. When recording is not performed for several seconds to several minutes, the recording head is moved to the recovery position in order to suppress the evaporation of moisture from the nozzles, and the discharge port surface of the recording head is covered with a cap having low gas permeability. Further, when the ink is not discharged for a long time, a method of forcibly discharging the ink in the nozzle by connecting the cap to a pump is employed.

  A full multi-type ink jet recording apparatus in which a plurality of nozzles are arranged so that the width of the recording medium in the direction intersecting the recording medium conveyance direction can be recorded at one time is retracted with respect to the recording medium, particularly during recording. Since this causes a deterioration in throughput, the head retraction and preliminary ejection adopted in the serial type cannot be easily adopted. Therefore, a preliminary ejection method on the paper surface is used in which preliminary ejection is performed on an unused portion on the recording medium and the portion is cut later, or preliminary ejection is performed on the recording medium to such an extent that it is inconspicuous to human eyes. ing.

  These are well-known techniques for avoiding the problem of speed reduction due to evaporation.

On the other hand, a method as described in, for example, Japanese Patent Application Laid-Open No. 2001-96733 has been proposed when focusing on a solution for avoiding image degradation caused by fluctuations in ejection speed. In this method, the ink temperature is measured, and landing deviation of reciprocal printing caused by fluctuations in the ejection speed accompanying changes in the ink temperature is avoided by appropriate timing correction. Since the ink temperature affects all nozzles in the same way, all the ejection timings may be adjusted in the same manner. However, as in the present case, the difference in ink viscosity caused by the evaporation of moisture varies depending on the individual nozzle, so this method cannot be used.
JP 2001-96733 A

  In recent years, inkjet recording apparatuses are in the direction of finer discharge nozzles due to the demand for higher image quality. According to the examination results of the inventors, it has been confirmed that the smaller the discharge port diameter, the larger the evaporation amount per unit time and unit area. Therefore, the miniaturization of the nozzle promotes the above-described problems caused by the evaporation of moisture. Similarly, due to the demand for higher image quality, dye-based inks with increased dye concentration and pigment-based inks with excellent weather resistance have been used in order to improve color development. Disadvantage about the problem. In other words, recently, in a serial type ink jet recording apparatus, just because the recording head did not eject ink while reciprocating the paper, a problem due to a change in the ink composition inside the nozzle due to evaporation has appeared, It is an important issue.

  In view of the above, there is a demand for a method for avoiding or reducing the deterioration of landing accuracy caused by water evaporation from the nozzle without using the conventional recovery means.

  The present invention solves such a problem, and an ink jet recording method for reducing the landing position deviation and maintaining the print quality at a high level even if a difference in ejection speed occurs between the nozzles due to evaporation of moisture, and the recording thereof It is intended to provide a device.

  In order to achieve the above object, an ink jet recording apparatus having the following characteristics is provided.

  A recording head that faces the recording paper and is installed at a predetermined interval from the recording paper and has a nozzle that discharges ink droplets on the recording paper, and moves the recording head relative to the recording paper surface. Scanning means for scanning the recording paper, a printer driver for generating drive data for driving the nozzles from the image information, drive control means for controlling ink ejection from the nozzles of the recording head based on the drive data, In the ink jet recording apparatus having the above, the drive timing is corrected so that the longer the interval during which driving is paused, the more the ink is ejected at an earlier timing with respect to the first recording position.

  First drive data created from image information, measurement means for measuring a drive pause interval in units of nozzles based on the first drive data, and a correction table in which the drive pause interval and the pixel shift are associated with each other are stored. On the basis of the second drive data, there is mounted a correction means for creating second drive data incorporating pixel shift correction from the storage means, the first drive data, the measurement means, and the storage means. Ink is ejected.

  A humidity sensor that measures humidity inside the ink jet recording apparatus, and an update unit that updates the correction table to an appropriate one based on data of the humidity sensor.

  According to the present invention, by adjusting the ink ejection timing based on the individual nozzle pause interval, the ink landing position on the recording paper surface is corrected, the positional deviation is eliminated, and the print quality is improved.

  Next, details of the present invention will be described in accordance with the description of the embodiments.

  A first embodiment of the present invention will be described.

  FIG. 1 is a conceptual diagram illustrating an embodiment of the present invention.

  A recording head 2 is mounted on the carriage 1, and the paper 3 is held at a position facing the recording head 2 by a predetermined distance L. Ink droplets are ejected toward the paper 3 from the recording head 2 according to the data string based on the image information while moving the carriage 1 in parallel with the paper 3 in the direction of the arrow in the figure.

FIG. 2 is a graph showing the relationship between the drive pause time and the initial droplet velocity measured at a certain humidity. t ₀ corresponds to a drive cycle which is the minimum unit of drive pause time. The ink composition inside the nozzle changes due to the evaporation of water from the nozzle, and the initial droplet velocity decreases as the pause time becomes longer as shown in the figure.

Consider a case in which a droplet is ejected from a corresponding nozzle corresponding to position a when projected onto paper 3 by a drive data signal based on certain image information. If the pause interval is the minimum unit t ₀ of drive pause time, it is assumed that ink droplets are ejected at the initial velocity u ₀ . Since the carriage moves at a speed V and the distance between the recording head and the paper is L, the discharged liquid droplets land at a position X on the paper surface. At this time, the positions a and X on the paper surface are separated by VL / u ₀ . If the nozzle ejected at the same timing is a nozzle having a pause time t ′, if the initial velocity at this time is u ′, the discharged liquid droplets land at a position Y on the paper surface. The positions a and Y on the paper surface are separated by VL / u ′. That is, the positions X and Y on the paper surface are displaced by VL (1 / u′−1 / u). If the positional deviation is within the minimum unit d of the pixels of the recording apparatus, the recorded image is hardly deteriorated. However, if the positional deviation exceeds d, the image is disturbed, which is a problem.

  In order to correct this positional deviation, the nozzle may be driven at a position corresponding to the positional deviation, that is, a position in front, that is, a position shown in FIG. In other words, in view of the decrease in the initial discharge speed associated with the resting time, it is possible to land at an accurate position X by driving at a timing earlier by L (1 / u′−1 / u) than the initial drive timing.

  By grouping velocities where the positional deviation falls within an integer multiple of pixel d,

の関係が満たされる。これを速度の式として書き直すと、

The relationship is satisfied. If you rewrite this as a speed equation,

であり、図２のグラフでｕ_nに対応するｔ_nから画素補正テーブルを作成すると図３の表が完成する。

When the pixel correction table is created from t _n corresponding to u _n in the graph of FIG. 2, the table of FIG. 3 is completed.

  Next, a control method using this correction table will be described. FIG. 4 is a block diagram of each means, and FIG. 5 is a flowchart of a control method of the correction means.

  The printer driver creates nozzle drive data 1, a carriage control signal, and an LF control signal from the image information, and transmits them to the correction unit 6, the carriage control unit, and the LF control unit, respectively. The correcting unit 6 includes a measuring unit 4 that analyzes the nozzle driving data 1, generates corrected nozzle driving data 2, and transmits the nozzle driving data 2 to the head driver, and a storage unit 5. The storage unit 5 includes a ROM storing a pixel correction table and a temporary storage unit. The head driver that has acquired the nozzle drive data 2 drives the recording head based on the data.

  Next, the correction means 6 will be described.

  The correction unit 6 reads nozzle drive data for one scan and develops the data on the RAM. The data is analyzed, and the interval between pixels driven for each nozzle is measured. Since the nozzle pause time is determined from the pixel interval and the frequency of driving the recording head, the pause time is compared with the data read from the storage means 5 in which the pixel correction table is stored. If the analyzed pause time is included in the time required for pixel correction, the drive data is corrected by the amount of pixels that need correction.

  With the above procedure, new drive data for one scan is created, and the recording head is driven based on the new drive data.

  In this way, the ink landing position on the recording paper surface is corrected.

  Next, a second embodiment of the present invention will be described.

  It has been found that the relationship between the discharge pause time and the initial droplet velocity changes slightly depending on the outside humidity. For example, the graph of FIG. 2 showing the relationship between the discharge pause time measured at a certain humidity and the initial droplet velocity changes as shown in FIG. 6 in a lower humidity environment.

Therefore, in order to make the first embodiment work more suitably, it is considered preferable to update the pixel correction table of FIG. 3 by measuring the outside air humidity. That is, when the humidity changes and changes from the relationship shown in FIG. 2 to the relationship shown in FIG. 6, the correction timing is preferably changed from t _n to t ′ _n . It should be updated to FIG.

  As means for specifically achieving this, a humidity sensor for measuring the humidity inside the printer, reading the humidity information, and converting the correction table (FIG. 3) into an appropriate correction table (FIG. 7) according to the outside air humidity at that time. This is done with the updating means for updating.

The conceptual diagram of embodiment of this invention. The graph showing the relationship between rest time and initial droplet velocity. Pixel correction table. The block diagram of embodiment. The flowchart of embodiment. Changes in the graph showing the relationship between rest time and droplet velocity at low humidity. Pixel correction table at low humidity.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Carriage 2 Recording head 3 Paper 4 Measuring means 5 Storage means 6 Correction means

Claims (3)

A recording head that faces the recording paper and is spaced from the recording paper and has a nozzle for discharging ink droplets on the recording paper, and moves the recording head relative to the recording paper surface to move the recording paper A scanning unit that scans the recording paper; a printer driver that generates driving data for driving the nozzles from the image information; and a driving control unit that controls ink ejection from the nozzles of the recording head based on the driving data. In the inkjet recording apparatus,
An ink jet recording apparatus, wherein driving timing is corrected so that a nozzle having a longer interval during which driving is paused ejects ink at an earlier timing with respect to the first recording position.   First drive data created from image information, measurement means for measuring a drive pause interval in units of nozzles based on the first drive data, and a correction table in which the drive pause interval and the pixel shift are associated with each other are stored. On the basis of the second drive data, there is mounted a correction means for creating second drive data incorporating pixel shift correction from the storage means, the first drive data, the measurement means, and the storage means. The ink jet recording apparatus according to claim 1, wherein ink is ejected.   3. The ink jet recording apparatus according to claim 2, further comprising: a humidity sensor that measures humidity inside the ink jet recording apparatus; and update means that updates the correction table to an appropriate one based on data from the humidity sensor.

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