JP2005225185A - Liquid discharge system and control method for the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve fully the problem of the registration deviation caused by the thermal expansion of the line head of a color inkjet printer and improve the quality of image. <P>SOLUTION: Considering the expansion/contraction of a line head to be a physical quantity which can be specified, a data table for estimating the thermal expansion quantity of the line head is used. A read means for the data table is provided as a detection means for the physical quantity. The discharge data of the ink droplet is made corrected in comparing the discharge hysteresis of the ink droplet with the data table. Using a control means, the discharge-direction variable means for the ink droplet is controlled and the discharge direction is made deflected, and the impacted-position deviation of the ink droplet caused by the thermal expansion of the line head is made corrected. Thereby, the registration deviation is eliminated. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a liquid ejection system that corrects a landing position deviation of a liquid caused by expansion and contraction due to a temperature change of a liquid ejection head and obtains high image quality in a system for ejecting liquid such as an ink jet printer. The present invention relates to a system and a method for controlling a liquid ejection system, and particularly relates to a technique capable of reliably improving image quality during color printing in a color inkjet printer.

  Conventionally, an ink jet printer is known as an example of a liquid ejection system. This ink jet printer is usually provided with an ink jet head (hereinafter simply referred to as “head”) in which a plurality of nozzles are arranged in a straight line as a head for ejecting ink. Then, from each nozzle of this head, by sequentially ejecting small ink droplets toward a recording medium such as photographic paper arranged facing the nozzle surface, substantially circular dots are formed vertically and horizontally, An image or a character is expressed as a stipple.

Here, as one of ink ejection methods, a thermal method is known in which ink is ejected using thermal energy.
A thermal head generally includes an ink liquid chamber for containing ink, a heating resistor provided in the ink liquid chamber, and a nozzle for discharging ink as droplets. Then, the ink is rapidly heated by the heating resistor, bubbles are generated in the ink on the heating resistor, and ink droplets are ejected from the nozzles by the energy when the bubbles are generated.

  From the viewpoint of the head structure, a serial system that performs printing over the entire width by moving the head in the width direction of the recording medium such as photographic paper and a large number of heads arranged side by side in the width direction of the recording medium A line system is known in which a line head corresponding to an image width is formed to perform printing over the entire width.

  Particularly in the case of a thermal ink jet printer as described above, the amount of printing increases, and when the head is driven for a long time, the head causes thermal expansion due to the heat generated from the heating resistor. Then, the relative positional relationship between the nozzle and the recording medium changes, and the landing position of the ink droplet deviates from a predetermined position. Such a shift in the landing position becomes significant in a line-type ink jet printer.

  In particular, in the case of a thermal color ink jet printer having a line head for each color, the drive time of each line head is almost the same, so a difference occurs in the thermal expansion amount of each line head, There is a problem that image quality deteriorates as a result of occurrence of misalignment (hereinafter, this registration misregistration is simply referred to as “registration misregistration”) in the accurate overlay of each color during color printing.

Therefore, various techniques for correcting misregistration have been disclosed in the past in order to prevent deterioration in image quality.
In other words, if the nozzle is displaced by more than half of the nozzle interval due to the difference in thermal expansion between the low-temperature line head and the high-temperature line head, printing for ejecting ink from the low-temperature line head A technique is known in which dummy data is inserted into a part of data, ink ejection is shifted by one from the original nozzle, and the registration deviation is ½ or less of the nozzle interval (for example, Patent Document 1).
JP 10-44423 A

In addition, a temperature sensor and a pre-heater are attached to each head of the color inkjet printer, the head with the highest temperature is selected with the temperature sensor, and the other heads are heated with the pre-heater according to the head with the highest temperature. There is known a technique for eliminating misregistration by equalizing the thermal expansion amounts at the same temperature (see, for example, Patent Document 2).
Japanese Patent Laid-Open No. 10-86405

Further, a technology is known in which one end in the length direction of each head is rotatably fixed with a pin and the other end is a free end with respect to the fixing units of the heads arranged side by side. In other words, the angle between the head length direction and the recording medium width direction (head tilt) is set to θ, and the free end moves and tilts as the length changes due to thermal expansion of the head. This is a technique for eliminating registration misalignment by changing θ and adjusting the landing position of the ink droplet in the width direction of the recording medium (see, for example, Patent Document 3).
JP 2000-964 A

  However, in the technique of Patent Document 1 described above, when the nozzle is displaced by 1/2 or more of the nozzle interval due to the thermal expansion of the line head, the displacement of registration is reduced by shifting the nozzle for ejecting ink by one. Since it is 1/2 or less of the nozzle interval, it is not sufficient for eliminating the registration error. For this reason, it is only possible to suppress the deterioration of the image quality within a certain range, and in particular, there remains a problem as the image quality at the time of color printing.

  In the technique disclosed in Patent Document 2, the heads are heated by the preheater to equalize the thermal expansion amount of each head. Therefore, in order to eliminate the misregistration, the head heating time by the preheater is required. For this reason, there is a problem in terms of responsiveness and followability with respect to the thermal expansion amount of the head that changes each time depending on the print data. In other words, in an inkjet printer, various speedups are being made in order to reduce the waiting time for printing, but if the heating time of the head is necessary, it is not possible to quickly eliminate misregistration. This is significantly contrary to the technical flow of speeding up.

  Further, in the technique disclosed in Patent Document 3, each head is rotatably fixed and the inclination θ of the head is changed, so that the mechanism is complicated and there is a problem in certainty. In addition, since the landing position of the ink droplets in the width direction of the recording medium is adjusted by the change in the inclination θ of the head, the registration error is eliminated unless the head rotates smoothly and stops at a predetermined inclination θ. do not do.

  Furthermore, in particular, in the case of the techniques of Patent Document 2 and Patent Document 3 described above, when applied to a line-type inkjet printer, the problem becomes more complicated and serious. That is, in the line system, since a large number of heads are arranged side by side in the width direction of the recording medium, the heating time of the heads becomes long, and smooth rotation of the heads becomes difficult.

  Accordingly, the problem to be solved by the present invention is to quickly and surely eliminate the deviation of the landing position of the ink droplets and improve the image quality. In particular, it eliminates the registration error of the line type color ink jet printer. It is another object of the present invention to provide a liquid ejection system and a control method for the liquid ejection system that can be easily applied to the liquid ejection system.

The present invention solves the above-described problems by the following means.
The invention according to claim 1, which is one of the present invention, includes a head in which a plurality of liquid discharge portions including nozzles are arranged in a specific direction, and discharges droplets from the nozzles of each of the liquid discharge portions. A liquid ejection system for landing a droplet on a predetermined position of a recording medium, the physical quantity detecting means capable of specifying expansion and contraction of the head caused by a temperature change of the head, and the ejection direction of the droplet ejected from the nozzle The discharge direction changing means for changing the discharge direction in a plurality of directions, and the discharge direction changing means are controlled based on the physical quantity detected by the detection means to correct the landing position deviation of the droplets accompanying the expansion and contraction of the head. And a control means.

  The invention according to claim 6, which is another aspect of the present invention, is the method for controlling a liquid ejection system according to claim 1, wherein a plurality of liquid ejection portions including nozzles are arranged side by side in a specific direction. A head, a physical quantity detection means capable of specifying expansion and contraction of the head caused by a temperature change of the head, a discharge direction variable means for changing the discharge direction of liquid droplets discharged from the nozzle in a plurality of directions, A control unit that controls the discharge direction variable unit, and based on the physical quantity detected by the detection unit, the control unit controls the discharge direction variable unit, and the landing position of the droplet accompanying the expansion and contraction of the head It is characterized by correcting the deviation.

  In the above invention, the physical quantity detecting means capable of specifying the expansion and contraction of the head caused by the temperature change of the head is provided. Here, the physical quantity that can specify the expansion and contraction of the head includes, for example, a measured value such as a head temperature for specifying the thermal expansion amount of the head, a calculated value of the head expansion and contraction amount calculated from the operating status of the head, and the like. . As the detection means, a temperature sensor or the like corresponds to the former case, and an arithmetic unit or the like based on print data corresponds to the latter case.

  Then, the discharge direction variable means changes the discharge direction of the liquid droplets discharged from the nozzles in a plurality of directions, and the control means controls the discharge direction variable means based on the physical quantity detected by the detection means. Therefore, the landing position deviation of the droplet accompanying the expansion and contraction of the head can be corrected by changing the droplet ejection direction.

  According to the liquid ejection system and the control method of the liquid ejection system of the present invention, the physical quantity capable of specifying the expansion and contraction of the head is detected by the detection means, and the ejection direction variable means is controlled by the control means. The deviation of the landing position of the droplet is corrected quickly and reliably. In addition, the present invention can be easily applied to a line type color ink jet printer, and it is possible to sufficiently eliminate registration misalignment and improve image quality.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
In the following embodiment, the liquid ejection system according to the present invention corresponds to a line-type inkjet printer in which the line head 10 corresponding to the print width is formed. The ink jet printer is compatible with A4 size color.

  In addition, in a liquid discharge system such as an ink jet printer, liquid in a liquid chamber is discharged from a nozzle as a droplet by an energy generating element. In the following embodiment, the liquid to be discharged is ink, and a liquid chamber for storing ink is provided. A very small amount (for example, several picoliters) of ink discharged from the nozzle 18 in the ink liquid chamber 12 is an ink droplet. Furthermore, in the following embodiment, the heating resistor 13 is used as an energy generating element, and the heating resistor 13 also constitutes one surface (bottom wall portion) of the ink liquid chamber 12.

  A portion including one ink liquid chamber 12, a heat generating resistor 13 disposed in the ink liquid chamber 12, and a nozzle disposed below the heat generating resistor 13 and serving as an ink droplet ejection port. Is referred to as a “liquid ejection unit”. That is, it can be said that the line head 10 has a plurality of liquid ejection units arranged in parallel. In addition, since the line head 10 of the ink jet printer in the following embodiment is compatible with A4 size color, the liquid ejecting unit is arranged in parallel for the print width in the width direction of the A4 size printing paper for each color. Yes.

FIG. 1 is a cross-sectional view showing the ink jet printer of the present embodiment.
As shown in FIG. 1, a printer main body 51 of an ink jet printer includes a paper feed tray, a paper discharge tray, and a paper transport device that are recording media. In the printer main body 51, a color-compatible line head 10 in which liquid discharge portions are arranged in parallel for each color in a direction perpendicular to the paper surface of FIG. 1 is mounted, and the four ink cartridges 41 are filled. In addition, four colors of ink of Y (yellow), M (magenta), C (cyan), and K (black) are ejected.

  Further, the line head 10 is equipped with a head cap unit 30 that moves in a direction (arrow direction) parallel to the paper surface of FIG. 1 to open and close the outer surface (ink discharge surface) of the nozzle sheet 17. Further, a cleaning roller (not shown) for the nozzle sheet 17 is disposed inside the head cap unit 30.

  In order to print with the ink jet printer of the present embodiment shown in FIG. 1, first, the head cap unit 30 is moved in the right direction of FIG. 1 to open the outer surface (ink ejection surface) of the nozzle sheet 17. Then, the printing paper is conveyed from the paper feed tray. Subsequently, based on the print data, ink droplets of four colors are appropriately discharged from the nozzles of the liquid discharge unit while accurately feeding the print paper below the line head 10. Then, characters, images and the like are printed in color on the photographic paper.

2A and 2B are diagrams showing a liquid discharge section in the line head 10 shown in FIG. 1, FIG. 2A is a perspective view thereof, and FIG. 2B is a cross-sectional view thereof.
As shown in FIG. 2, a plurality of nozzles 18 are formed in the nozzle sheet 17, and each nozzle 18 includes a plurality of heating resistors 13 arranged in one direction at regular intervals on the substrate of the head chip 19. Opposite. A barrier layer 15 is laminated between the nozzle sheet 17 and the head chip 19.

  Here, the substrate constituting the head chip 19 is a semiconductor substrate made of silicon, glass, ceramics or the like. The heating resistor 13 is deposited on one surface of the substrate using a fine processing technique for manufacturing semiconductors and electronic devices. The heating resistor 13 is divided into two parts, and each heating resistor 13 is electrically connected to an external circuit via a conductor (not shown) formed on the substrate.

  The barrier layer 15 is formed on the substrate constituting the head chip 19 on the side of the heating resistor 13, and is formed by patterning on the substrate excluding the periphery of the heating resistor 13. Further, the nozzle sheet 17 is formed by, for example, an electroforming technique using Ni (nickel).

  As shown in FIG. 2, the head chip 19 in which the barrier layer 15 is laminated is arranged so that the positions of the nozzles 18 on the nozzle sheet 17 and the positions of the heating resistors 13 are aligned. Positioning is made precisely so as to oppose each heating resistor 13, and it is arranged on the nozzle sheet 17 with the barrier layer 15 facing down.

  Therefore, as shown in FIG. 2A, the ink liquid chamber 12 is composed of the substrate of the head chip 19, the barrier layer 15, and the nozzle sheet 17 so as to surround the heating resistor 13. That is, the substrate of the head chip 19 and the heating resistor 13 constitute the upper wall of the ink liquid chamber 12 in FIG. 2A, and the barrier layer 15 constitutes the three lateral walls of the ink liquid chamber 12, and the nozzle The sheet 17 constitutes the lower wall of the ink liquid chamber 12.

  Further, as shown in FIG. 2B, a head frame 20 is attached to the nozzle sheet 17, and rigidity is imparted to the nozzle sheet 17. Further, the head chip 19 is arranged in the arrangement hole of the head frame 20, and the common flow path member 21 is arranged on the upper side of the head chip 19. In FIG. 2A, all the ink liquid chambers 12 having an opening region in the lower right direction communicate with each other through a common ink flow path 22 formed by the common flow path member 21.

  The liquid discharge section shown in FIG. 2 includes one ink liquid chamber 12 configured as described above, a heat generating resistor 13 disposed in the ink liquid chamber 12, and a nozzle 18 disposed below the heat generating resistor 13. Are arranged in the upper right direction (lower left direction) in FIG. 2A by the print width. Therefore, the ink in the ink cartridge (see FIG. 1) flows through the common ink flow path 22 and is supplied to the ink liquid chambers 12 of all the liquid ejection portions.

  When the ink liquid chamber 12 is filled with ink and a pulse current is applied to the heating resistor 13 for 1 to 3 μsec, for example, based on the printing data, the heating resistor 13 is rapidly heated. . As a result, a gas phase ink bubble is generated at a portion in contact with the heating resistor 13, and a certain volume of ink is pushed away by the expansion of the ink bubble (the ink boils). Then, this becomes an ejection pressure, and an ink having a volume equivalent to the pushed ink is ejected from the nozzle 18 as an ink droplet, and landed on the photographic paper to print characters, images, and the like.

  By the way, when ink droplets are sequentially ejected from the nozzles 18 by repeatedly heating the heating resistor 13, the heat is accumulated and the temperature of the line head 10 changes, causing the line head 10 to thermally expand and contract. To come. In this case, the problem is that the interval between the nozzles 18 is increased in the direction in which the liquid ejection units are arranged side by side (the width direction of the photographic paper), and becomes different from the initial state.

That is, the elongation ΔL of the line head 10 is as follows: when the linear expansion coefficient is α, the rising temperature is T, and the initial length of the line head 10 is L.
ΔL = α · T · L
Here, the interval between the nozzles 18 in the line head 10 is governed by the head frame 20.

Therefore, for the line head 10 having an A4 size width (L = 210 mm), the material of the head frame 20 is SUS430 (α = 10.4 × 10 ⁻⁶ ), and the temperature of the head frame 20 is heated by the heating resistor 13. Is increased by 20 ° C. (T = 20 ° C.)
ΔL = 10.4 × 10 ⁻⁶ × 20 × 210 = 43.68 (μm)

  If the specification of the nozzles 18 in the line head 10 is an accuracy of 600 dpi, the interval between the nozzles 18 is 42.3 μm. Further, it is considered that the diameter of the dot of the ink droplet is about 40 μm, and the line head 10 is thermally expanded around the center under the above conditions. Then, the landing position deviation at the left and right ends (printing paper end portions) of the line head 10 is 43.68 / 2 = 21.84 (μm), so that it is shifted by about half a dot.

Here, if C (cyan) ink and Y (yellow) ink land with a half-dot shift, cyan and yellow should overlap to become green, but cyan, yellow, and green 3 Colors will be mixed.
As described above, the half-dot landing position shift generally has an influence on the image quality, and the deterioration of the image quality becomes remarkable at the end of the A4 size photographic paper, causing a problem of registration shift. Such registration deviation becomes more severe as the temperature difference between the line heads 10 of each color increases.

  In other words, the print data hardly includes each color uniformly, and the discharge data amount is four colors of Y (yellow), M (magenta), C (cyan), and K (black). There is generally a difference. For this reason, the thermal expansion amount differs between the line heads 10 for each color, and in particular, the registration shift becomes significant between the line head 10 having the largest thermal expansion amount and the line head 10 having the smallest thermal expansion amount.

FIG. 3 is a conceptual diagram showing differences in thermal expansion amounts of the line heads 10 that respectively eject ink of four colors of Y (yellow), M (magenta), C (cyan), and K (black).
The line head 10 row shown in FIG. 3 has a line head (Y) of + 30 ° C., a line head (M) of + 15 ° C., a line head (C) of + 10 ° C., and a line head with respect to a standard temperature (for example, room temperature 25 ° C.). (K) is + 25 ° C., and the amount of thermal expansion differs depending on the rising temperature.

  In this case, since the arithmetic average of the rising temperature is (30 + 15 + 10 + 25) / 4 = 20 (° C.), the temperature deviation from the average value of the line head 10 rows is + 10 ° C. for the line head (Y), and the line head ( M) is −5 ° C., the line head (C) is −10 ° C., and the line head (K) is + 5 ° C. Therefore, there is a temperature difference of 20 ° C. between the line head (Y) and the line head (C). Then, as described above, when the head frame 20 (see FIG. 2) of the SUS430 is raised by 20 ° C., the elongation ΔL of the line head 10 becomes 43.68 (μm), so that the center of the photographic paper P is the center. At both ends, Y (yellow) ink and C (cyan) ink cause landing positions to be shifted by half a dot, and registration shift occurs.

4A and 4B are a plan view and a side cross-sectional view showing the liquid ejection unit 11 that can correct such a landing position deviation. In the plan view of FIG. 4, the nozzle sheet 17 and the head chip 19 are not shown, and the nozzle 18 is indicated by a one-dot chain line.
As shown in FIG. 4, two divided heating resistors 13 are arranged in parallel in one ink liquid chamber 12, and the arrangement direction of the two divided heating resistors 13 is the nozzle 18. Is the arrangement direction (the left-right direction in FIG. 4).

Thus, when the heating resistor 13 divided into two is provided in one ink liquid chamber 12, the time until each heating resistor 13 reaches the temperature at which the ink is boiled (bubble generation occurs). Time) at the same time, the ink boiles simultaneously on the two heating resistors 13 and ink droplets are ejected in the direction of the central axis of the nozzle 18.
On the other hand, if a time difference is given to the bubble generation time of the heating resistor 13 divided into two, the ink does not boil simultaneously on the two heating resistors 13. As a result, the ejection direction of the ink droplets is deviated from the central axis direction of the nozzles 18 and is deflected and ejected in the arrangement direction of the nozzles 18.

  Therefore, as shown in FIG. 4, a plurality (two in FIG. 4) of heating resistors 13 provided in one ink liquid chamber 12 serve as the ejection direction variable means. That is, by changing the way of supplying energy to the plurality of heating resistors 13, the ejection direction of the ink droplets ejected from the nozzle 18 can be changed in a plurality of directions quickly and reliably. It is possible to correct the landing position deviation of the droplet. The deflection of the ejection of ink droplets can be, for example, ¼ of the interval between the nozzles 18 and can be made up to five levels for one nozzle at a maximum. Correction is possible.

FIG. 5 is an explanatory diagram showing deflection in the ejection direction of ink droplets.
In FIG. 5, when the ink droplet i is ejected from the nozzle 18 of the nozzle sheet 17 perpendicularly to the ejection surface of the ink droplet i, the ink droplet does not deflect as shown by the arrow pointing downward in FIG. i is discharged. On the other hand, when the ejection direction of the ink droplet i is deflected and the ejection angle deviates by θ from the vertical position (Z1 or Z2 direction in FIG. 5), the ejection surface and the photographic paper P surface (the ink droplet i When the distance to the landing surface) is H (H is substantially constant), the landing position of the ink droplet i is
ΔW = H × tanθ
Is shifted in the arrangement direction of the nozzles 18 (the width direction of the photographic paper P) by ΔW obtained in the above.

Therefore, as shown in FIG. 3, the discharge direction variable means as shown in FIG. 4 is used for the thermally expanded line head (Y), line head (M), line head (C), and line head (K). Thus, the landing positions of the ink droplets are shifted as shown in FIG.
That is, the landing position deviation of the ink droplets accompanying the expansion and contraction of the line head 10 rows is corrected.

  FIG. 6 is an explanatory diagram showing a state before and after the correction of the ink droplet landing position deviation. Actually, the four color inks of Y (yellow), M (magenta), C (cyan), and K (black) are overlapped in the conveyance direction (arrow direction) of the photographic paper P shown in FIG. In order to schematically show the landing position deviation in the width direction of the photographic paper P, each color dot is shown separately.

  As shown in FIG. 6A, before correction, ink droplets are ejected without deflection from the thermally expanded line heads 10 row (see FIG. 3), and therefore based on the arithmetic average of the rising temperatures of the line heads 10. With respect to the center line of FIG. 6A, which is the average landing point, the yellow dot (Y) is shifted by 1/4 dot to the left, the magenta dot (M) is shifted by 1/8 dot to the right, and the cyan dot ( C) is formed with a 1/4 dot shift to the right, and a black dot (K) is formed with a 1/8 dot shift to the left.

  Here, if the ejection direction varying means shown in FIG. 4 is used, the ejection direction of the ink droplets can be changed in the arrangement direction of the nozzles 18. Therefore, as shown in FIG. 3, when the line heads 10 are arranged in a direction orthogonal to the arrangement direction of the nozzles 18, ink droplets due to variations in the amount of thermal expansion occurring between the line heads 10 are It is possible to correct the landing position deviation.

  That is, as shown in FIG. 6B, the dots (Y), the dots (M), the dots (C), and the dots (K) are averaged after the correction using the ejection direction variable means shown in FIG. It will be formed at the landing point. The deflection of the ink droplet ejection can be made to be within a range where the ink droplet can land at the same point and the registration deviation cannot be visually confirmed as the number of steps is increased. All dots can be completely overlapped.

  In this way, in order to form all the dots at the average landing point, the landing position deviation of the ink droplet is corrected based on the physical quantity that can specify the expansion and contraction of each line head 10. That is, a physical quantity that can specify the expansion and contraction of each line head 10 is detected by the detection means, and the ejection direction variable means is controlled by the control means.

FIG. 7 is a block diagram showing an example of such detection means and control means.
As shown in FIG. 7, the printer main body 51 is connected to the computer main body 61. The printer main body 51 includes a reception buffer for image data sent from the computer main body 61 via the printer driver, a calculation unit (CPU) for calculating the image data, and each liquid discharge constituting the line head 10. And a heater driver that drives each heating resistor of the unit 11. Further, a RAM as a work area, a ROM that records fonts and various data, and a non-volatile memory that records printer-specific information are connected to the arithmetic unit (CPU).

  Here, the non-volatile memory of the printer main body 51 stores a discharge history of how many ink droplets have been discharged from which nozzle of which liquid discharge unit 11 and how much time has passed since the discharge. ing. The ROM stores a data table for predicting the thermal expansion amount of the line head 10.

The arithmetic unit (CPU) uses the RAM as a work area, compares the information stored in the nonvolatile memory with the data table in the ROM, and calculates the thermal expansion amount of the line head 10, thereby calculating the image data. It is estimated which discharge data portion of the registration is misregistered.
The ink droplets ejected from the nozzles whose registration misregistration is estimated can correct the landing position deviation by the ejection direction variable means, so that the calculation unit (CPU) corrects the ejection data as necessary, and then plots the plot. Send data to heater driver for printing.

In this way, in the example shown in FIG. 7, a data table for predicting the thermal expansion amount stored in the ROM is used as a physical quantity that can specify expansion and contraction due to thermal expansion. The physical quantity detection means is a calculation means for obtaining the expansion / contraction amount of the line head 10 from the operation status of the line head 10, and a calculation unit (CPU), a RAM, a ROM, and a nonvolatile memory correspond to the calculation means. In addition, the arithmetic unit (CPU) and the like also serve as control means.
Therefore, as shown in FIG. 6, it is possible to correct the landing position deviation of the ink droplets, and it is possible to eliminate the registration deviation.

FIG. 8 is a diagram illustrating an example of a flowchart for eliminating registration misalignment.
According to the flowchart shown in FIG. 8, the ink droplet ejection history is first read, and then the data table is read. Then, thermal expansion is estimated by comparing the discharge history with the data table. Further, the registration misregistration location is estimated by reading the image data, and if there is a misregistration, the ejection data is corrected, but if there is no misregistration, plot data is created as it is and printing is started.

Here, as shown in FIG. 3, when there are four line heads 10, the following four methods are conceivable as ejection data correction methods. That is,
(1) Match the nozzle spacing of the line head (Y) with the largest thermal expansion amount,
(2) Match the nozzle spacing of the line head (C) with the smallest thermal expansion.
(3) The thermal expansion amounts of the four line heads 10 are averaged and adjusted to the average nozzle interval.
(4) For example, in the 600 dpi line head 10, since the standard nozzle interval is 42.3 μm, it is always adjusted to this standard interval.
There are four ways. Regardless of the correction method, it is the same that the registration error is eliminated. However, the correction shown in FIG. 6B is based on the correction method (3) described above.

  As described above, by correcting the ejection data, it is possible to perform printing without the registration error, but the ejection history is changed by printing. Therefore, in the flowchart shown in FIG. 8, a new discharge history is written. If the next image data remains, the same process is repeated from reading the latest ejection history. Therefore, no matter how many times printing is repeated, the registration error is always eliminated.

FIG. 9 is a block diagram illustrating another example of the detection unit and the control unit.
In the example shown in FIG. 9, the printer main body 51 is connected to the computer main body 61 as in the example shown in FIG. 7. The printer main body 51 includes an image data reception buffer, a calculation unit (CPU) for calculating the image data, and a heater driver that drives each heating resistor of each liquid ejection unit 11 constituting the line head 10. In addition, a RAM, a ROM, and a nonvolatile memory are connected to the calculation unit (CPU).

  However, in the example shown in FIG. 9, the temperature of the line head 10 is used as a physical quantity that can specify expansion and contraction due to thermal expansion. The temperature detecting means is the temperature sensor 23. Three temperature sensors 23 are attached, but it is natural that the more the number of the temperature sensors 23, the more accurate temperature distribution can be detected. The temperature detected by the temperature sensor 23 is digitized by an AD converter, sent to a calculation unit (CPU), and processed.

  As described above, in the example shown in FIG. 9, expansion / contraction due to thermal expansion is specified from the temperature of the line head 10 detected by the temperature sensor 23, and the discharge direction variable means is controlled based on the temperature of the line head 10 to The landing position deviation of the ink droplet accompanying the expansion and contraction of the head 10 is corrected. Therefore, even in the example shown in FIG. 9, as shown in FIG. 6, it is possible to correct the landing position deviation of the ink droplets and to eliminate the registration deviation.

  As described above, the ink jet printer according to the present embodiment is detected by the physical quantity detection unit that can specify the expansion and contraction of the line head, the ejection direction variable unit that varies the ejection direction of the ink droplets, and the detection unit. Control means for controlling the ejection direction based on the physical quantity and the control means for correcting the deviation of the landing position of the ink droplet, so that the registration error can be sufficiently eliminated quickly and the image quality can be stabilized. Can do.

The present invention is not limited to the above-described embodiment, and various modifications such as the following can be made. That is,
(1) In this embodiment, a color-compatible inkjet printer is used, but the present invention can also be applied to monochrome. Moreover, even if it corresponds to a color, it is not restricted to the thing of the structure which became independent for each color, but it is applicable also to a 4 color integrated type. Furthermore, in this embodiment, a line-type ink jet printer in which a number of heads are arranged side by side in the width direction of the recording medium and a line head corresponding to the print width is formed, but the head is moved in the width direction of the recording medium. The present invention can also be applied to a serial system that performs printing.

  (2) Although the present embodiment uses a thermal method using a heating resistor, a heating element other than the heating resistor may be used. In addition, a diaphragm and two electrodes via an air layer are provided on the lower side of the diaphragm, a voltage is applied between both electrodes to deflect the diaphragm, and then the electrostatic force is released to release the diaphragm. It is also applicable to an electrostatic discharge method in which the ink droplets are discharged using the elastic force at that time. Furthermore, the present invention can also be applied to a piezo method in which a laminated body of piezoelectric elements having electrodes on both sides and a diaphragm is used, and the diaphragm is deformed by the piezoelectric effect to eject ink droplets.

  (3) In this embodiment, as an example of a physical quantity that can specify expansion and contraction due to thermal expansion, a data table for predicting the thermal expansion quantity stored in the ROM in the printer main body is used, and as a means for detecting the physical quantity, A calculation unit (CPU) or the like in the printer body was used. However, the data table for predicting the thermal expansion amount may be recorded on hardware in the computer main body, and the detection means may use a CPU in the computer main body. That is, the printer main body and the computer main body connected to the printer main body can be combined to form a liquid ejection system.

  (4) In this embodiment, the temperature of the line head is used as another example of a physical quantity that can specify expansion and contraction due to thermal expansion, and a temperature sensor is used as means for detecting the physical quantity. However, in addition to the temperature sensor, a strain gauge or the like can be used as a sensor for detecting the thermal expansion amount of the line head. That is, since the resistance value of the strain gauge changes when the line head expands, the amount of thermal expansion can be detected by reading the resistance value.

The liquid discharge system and the control method of the liquid discharge system of the present invention are particularly suitable when applied to an ink jet printer. However, the recording medium is not limited to photographic paper, and for example, a liquid that discharges dye to a dyed product It can also be applied to a discharge system or the like.
Further, the present invention can be applied to a liquid discharge system that discharges a DNA-containing solution for detecting a biological sample.

It is sectional drawing which shows the inkjet printer of embodiment. FIG. 2 is a perspective view and a cross-sectional view showing a liquid discharge portion in the line head of the ink jet printer shown in FIG. 1. It is a conceptual diagram which shows the difference of the thermal expansion amount of the line head row | line | column which each discharges four colors of ink. FIG. 6 is a plan view and a side cross-sectional view showing a liquid ejection unit capable of correcting landing position deviation. It is explanatory drawing which shows deflection | deviation of the discharge direction of an ink droplet. It is explanatory drawing which shows the state before correction | amendment of the landing position deviation of an ink droplet, and the state after correction | amendment. It is a block diagram which shows an example of a detection means and a control means. It is a figure which shows an example of the flowchart for eliminating registration misalignment. It is a block diagram which shows the other example of a detection means and a control means.

Explanation of symbols

10 Line Head 11 Liquid Discharge Part 13 Heating Resistor (Discharge Direction Variable Means)
18 nozzle 23 temperature sensor (detection means)

Claims (10)

A liquid ejection system comprising a head in which a plurality of liquid ejection sections including nozzles are arranged in a specific direction, ejecting liquid droplets from the nozzles of each liquid ejection section, and landing the liquid droplets at predetermined positions on a recording medium There,
A physical quantity detecting means capable of specifying the expansion and contraction of the head caused by the temperature change of the head;
A discharge direction variable means for changing the discharge direction of the liquid droplets discharged from the nozzle in a plurality of directions;
A liquid ejection system comprising: control means for controlling the ejection direction varying means on the basis of the physical quantity detected by the detection means, and correcting a landing position deviation of a droplet accompanying expansion and contraction of the head. The liquid ejection system according to claim 1, wherein
The liquid ejection system, wherein the detection unit is a sensor that detects a thermal expansion amount of the head. The liquid ejection system according to claim 1, wherein
The liquid ejecting system according to claim 1, wherein the detection unit is a calculation unit that obtains an expansion / contraction amount of the head from an operating state of the head. The liquid ejection system according to claim 1, wherein
The liquid discharge system, wherein the discharge direction changing means is means for changing the discharge direction of the droplets at least in the specific direction. The liquid ejection system according to claim 1, wherein
A plurality of heads arranged in parallel in a direction orthogonal to the specific direction;
The liquid ejecting system according to claim 1, wherein the control unit is a unit that corrects a landing position deviation of a droplet accompanying a variation in expansion and contraction that occurs between the heads of the head row. A head in which a plurality of liquid ejection portions including nozzles are arranged in a specific direction;
A physical quantity detecting means capable of specifying the expansion and contraction of the head caused by the temperature change of the head;
A discharge direction variable means for changing the discharge direction of the liquid droplets discharged from the nozzle in a plurality of directions;
Control means for controlling the discharge direction variable means,
A method for controlling a liquid ejection system that ejects liquid droplets from the nozzles of each liquid ejection section and lands the liquid droplets on a predetermined position of a recording medium,
A liquid ejection system according to claim 1, wherein the control means controls the ejection direction variable means based on the physical quantity detected by the detection means, and corrects the landing position deviation of the droplets accompanying expansion and contraction of the head. Control method. In the control method of the liquid ejection system according to claim 6,
The liquid ejection system control method, wherein the detection means detects the thermal expansion amount of the head. In the control method of the liquid ejection system according to claim 6,
The liquid ejection system control method, wherein the detection means calculates the amount of expansion / contraction of the head from the operating status of the head. In the control method of the liquid ejection system according to claim 6,
A control method of a liquid discharge system, wherein the discharge direction changing means changes the discharge direction of the liquid droplets at least in the specific direction. In the control method of the liquid ejection system according to claim 6,
A plurality of heads arranged in parallel in a direction orthogonal to the specific direction;
A control method of a liquid ejection system, wherein the control unit corrects a landing position deviation of a droplet accompanying a variation in expansion and contraction occurring between the heads of the head row.

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