JP2005271361A - Printing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a printing method which reduces image unevenness of output images. <P>SOLUTION: In the printing method, temperature detection of each heating element is repeated on the basis of a resistance value of each heating element by using a plurality of thermal heads 2Y, 2M and 2C comprised of a plurality of the heating elements whose resistance value changes depending on the temperature and energies corresponding to the detected temperatures are integrated and heating drive of each heating element is stopped at a time point when the integrated energy reaches a target energy preliminarily determined correspondingly to printing data for every dot. An image for correction is printed to an image receiving sheet 7 by each heating element of the plurality of thermal heads 2Y, 2M and 2C. A color or a density of the image for correction is measured, and the target energy to each heating element is corrected on the basis of the measured color or density. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a printing method for performing printing using a thermal head.

  2. Description of the Related Art Conventionally, printers using thermal heads are widely used such as card printers, rewritable printers, facsimiles, and photo printers because of their simple apparatus.

  In these printers, printing is performed by generating a predetermined energy corresponding to the print data by the heating element, but there is a difference in heat generation or heat dissipation of the thermal head due to differences in climate and environment. If the image does not print as intended, or as a result of continuing to print a high-density image, the temperature of the thermal head itself gradually increases, resulting in a higher density than the density to be printed in the subsequent image ( There is a tail).

  As a countermeasure against these problems, there is a method in which, for example, one thermistor is provided in the thermal head, and the energy generated from the heating element is corrected based on the temperature detection result by the thermistor. However, the thermistor does not directly detect the temperature of the heat generating element, but may be attached at a position away from the heat generating element, and therefore only detects the temperature of a part of the thermal head. Further, the response time of the thermistor is several seconds, and feedback to the heating element driven in units of microseconds or milliseconds is impossible.

  Therefore, by using a heating element whose resistance value changes depending on the temperature, switching between heating driving of the heating element and temperature detection, and repeating the temperature detection multiple times while printing one dot, the detected temperature A technique has been proposed in which the energy corresponding to is accumulated and the heat generation drive is stopped when the accumulated energy reaches the energy corresponding to the print data (see, for example, Patent Document 1).

In addition, yellow, magenta, and cyan are used in order to increase the speed of the surface sequential method in which printing of each color is sequentially performed using one thermal head and an ink ribbon in which yellow, magenta, and cyan are arranged in order. A so-called tandem type printer in which three thermal heads (four when a transparent protective layer is included) for performing the above printing is arranged in series has been put into practical use. In the tandem method, each thermal head continuously prints on an image receiving sheet using a monochromatic ink ribbon of each color.
JP 2002-211025 A

  However, in the surface sequential method in which printing of each color is performed using one thermal head, the same dot is printed by the same heating element, so the variation in resistance value of the heating element of the thermal head only appears as a density fluctuation. However, in the tandem method, since the same dot is printed by the heat generating elements for each color, the variation in the resistance value of the heat generating elements causes not only the density variation but also the color variation such as the color streak. Since the human eye is more sensitive to color changes than density, in the case of the tandem method, there is a possibility that the image quality is deteriorated with the same correction as in the case of the frame sequential method.

  Further, in the thermal head, not only variations in resistance values of the heating elements, but also unevenness in the pressing pressure due to poor flatness of the heating elements and uneven contact with the platen, etc., caused image unevenness.

  The present invention has been made in view of the above-described problems in the prior art, and an object of the present invention is to provide a printing method capable of reducing image unevenness of an output image.

  The invention according to claim 1 is a printing method using a plurality of thermal heads, each of which includes a plurality of heat generating elements whose resistance values change depending on temperature, and each heat generation based on the resistance value of each of the heat generating elements. By detecting the temperature of the element, the energy corresponding to the detected temperature is integrated, and when the integrated energy reaches a target energy determined in advance corresponding to the print data for each dot, each of the heating elements. In the printing method for stopping the heat generation driving, a correction image is printed on the image receiving sheet by each heating element of the plurality of thermal heads, the color or density of the correction image is measured, and the measured color or density is obtained. Based on this, the target energy for each of the heating elements is corrected.

  According to a second aspect of the present invention, in the printing method according to the first aspect, the plurality of thermal heads perform printing on the image receiving sheet using at least yellow, magenta, and cyan mono-color ink ribbons, respectively. It is characterized by.

  According to the present invention, a correction image is printed on an image receiving sheet by each heating element of a plurality of thermal heads, the color or density of the correction image is measured, and the target for each heating element is based on the measured color or density. Since energy is corrected, image unevenness in the output image can be reduced.

  Hereinafter, a thermal transfer printer 1 according to an embodiment of the present invention will be described with reference to the drawings. However, it is not limited to the illustrated example.

  First, a schematic configuration of the thermal transfer printer 1 will be described. As shown in FIG. 1, the thermal transfer printer 1 includes thermal heads 2Y, 2M, 2C, and 2P, ink ribbons 3Y, 3M, 3C, and 3P, an image receiving sheet supply unit 4, platen rollers 5Y, 5M, 5C, and 5P, and a cutter 6 And so on.

  The thermal heads 2Y, 2M, 2C, and 2P are line heads having a width of 6 inches and transfer yellow (Y), magenta (M), cyan (C), and a transparent protective layer (OP), respectively.

  Each of the ink ribbons 3Y, 3M, and 3C is formed by coating a film with sublimation dyes of three primary colors of yellow, magenta, and cyan on a film. The ink ribbon 3P has a transparent protective layer formed on the film.

  The image receiving sheet supply unit 4 stores a roll-shaped image receiving sheet 7 having a width of 6 inches, and supplies the image receiving sheet 7 during printing.

  The platen rollers 5Y, 5M, 5C, and 5P support the image receiving sheet 7, and convey the image receiving sheet 7 in the arrow X direction by rotation.

  The cutter 6 cuts the image receiving sheet 7 that has been printed to a predetermined size.

  The thermal heads 2Y, 2M, and 2C sublimate the dye contained in the ink ribbons 3Y, 3M, and 3C corresponding to the print data, transfer the dye to the image receiving sheet 7, and perform printing. The thermal head 2P transfers the transparent protective layer from the ink ribbon 3P onto the image receiving layer on which yellow, magenta, and cyan printing has been performed. When printing on the image receiving sheet 7, yellow, magenta, and cyan are printed, and then the transparent protective layer is transferred. Hereinafter, description of the transfer of the transparent protective layer is omitted.

  Next, control of the thermal head 2Y in the thermal transfer printer 1 will be described. As shown in FIG. 2, the thermal transfer printer 1 includes a print control circuit 8, a drive circuit 9, and a temperature detection circuit 10 as a control system for the thermal head 2Y.

The thermal head 2Y includes a plurality of heating elements Y ₁ , Y ₂ ,..., Y _n in the arrow Z direction (that is, the main scanning direction) perpendicular to the transport direction (arrow X direction) of the ink ribbon 3Y and the image receiving sheet 7. ) Are arranged inline on a straight line. These heating elements Y ₁ , Y ₂ ,..., Y _n perform printing with a resolution of 300 dpi. FIG. 3 shows the temperature characteristics of the resistance values of the heating elements Y ₁ , Y ₂ ,..., Y _n . As shown in FIG. 3, each of the heating elements Y ₁ , Y ₂ ,..., Y _n has a negative resistance characteristic that the resistance value decreases as the temperature rises. As the heating elements Y ₁ , Y ₂ ,..., Y _n , for example, an alloy such as aluminum, chromium, or boron can be used.

As shown in FIG. 4, printing density of the yellow, the heating elements Y _1, Y _2, · · ·, which corresponds to the heating energy in Y _n. FIG. 5 shows an example of the temperature change of each heating element Y ₁ , Y ₂ ,..., Y _n with respect to time during printing. Since the heat generation energy in each of the heat generating elements Y ₁ , Y ₂ ,..., Y _n is proportional to the area under the temperature curve shown in FIG. 5, the detected temperature while repeating temperature detection at predetermined time intervals. , And when the accumulated energy reaches a target energy determined in advance corresponding to the print data for each dot, each heating element Y ₁ , Y _{2 ,.} By stopping the heat generation driving, a desired print density can be obtained.

During printing, the heating elements Y ₁ until it reaches the target energy, Y _2, · · ·, also good as applying a constant voltage to the Y _n, the heating elements _{Y 1, Y 2, ···,} Y n The voltage applied to each of the heating elements Y ₁ , Y ₂ ,..., Y _n may be repeatedly turned on / off so that the temperature does not exceed a certain temperature, and the voltage may be turned off when the target energy is reached. . However, in the former case, the temperature gradually increases, and even when the voltage is turned off, the temperature does not decrease immediately, and there is a possibility that the ink ribbon 3Y and the thermal head 2Y are thermally fused. preferable.

The print control circuit 8 controls the drive circuit 9 and the temperature detection circuit 10. For each dot, the print control circuit 8 converts the temperatures of the heating elements Y ₁ , Y ₂ ,..., Y _n repeatedly detected by the temperature detection circuit 10 into energy corresponding to the temperature and integrates them. When the accumulated energy reaches the target energy, the heat generation driving of each of the heating elements Y ₁ , Y ₂ ,..., Y _n is stopped.

Driving circuit 9, the control of the print control circuit 8, the heating elements Y _1, Y _2, · · ·, a voltage is applied to Y _n, the heating elements Y _1, Y _2, · · ·, a Y _n Drives heat.

Temperature sensing circuit 10, the heating elements Y _1, Y _2, · · ·, each of the heating elements based on the resistance value of _{Y n Y 1, Y 2,} ···, and detects the temperature of Y _n, the print control Output to the circuit 8.

Since the control of the thermal heads 2M and 2C is the same as the control of the thermal head 2Y, a plurality of heating elements arranged in the thermal head 2M are sequentially arranged as the heating elements M ₁ , M _{2 ,.} omitted, heating elements C ₁ a plurality of heating elements in the order in which they are arranged in the thermal head 2C, C _2, · · ·, as C _n, the description.

6 shows the heating elements Y ₁ , Y ₂ ,..., Y _n , M ₁ , M ₂ ,..., M _n , C ₁ , C ₂ ,. A target energy table indicating target energy for the print data of C _n . As shown in FIG. 6, the yellow, magenta, the heating elements Y ₁ of each color of _{cyan, Y 2, ···, Y n} , M 1, M 2, ···, M n, C 1, C 2, ..., C _n has a target energy set for each gradation of the print data.

Next, correction processing of the thermal transfer printer 1 will be described. This correction process includes variations in the three thermal heads 2Y, 2M, and 2C, and the heating elements Y ₁ , Y ₂ ,..., Y _n , M ₁ , M ₂ ,. _n, the variation of C _1, C _2, ···, the resistance value of C _n, is a process for correcting the unevenness of pressure such as pressing. The correction process is performed before the thermal transfer printer 1 is shipped as a product or after the thermal heads 2Y, 2M, and 2C are replaced. Prior to the correction process, the heating elements Y ₁ , Y ₂ ,..., Y _n , M ₁ , M ₂ ,..., M _n , C ₁ , C _{2 of the} thermal heads 2Y, 2M, 2C. ,..., C _n are set to the same value as the initial value if they have the same gradation.

FIG. 7 is a flowchart showing the correction process of the thermal transfer printer 1.
Here, correction for 50 gradations as print data will be described.
First, the heating elements Y ₁ , Y ₂ ,..., Y _n , M ₁ , M ₂ ,..., M _n , C ₁ , C of the thermal heads 2Y, 2M, 2C for yellow, magenta, and cyan, respectively. ₂ ,..., C _n , printing is performed on the entire surface of the image receiving sheet 7 based on 50 gradations of target energy, and a correction image is output (step S 1). Specifically, 1 for each dot, the temperature sensing circuit 10, the heating elements _{Y 1, Y 2, ···,} Y n, M 1, M 2, ···, M n, C 1, C 2 ,..., C _n , while the temperature detection is repeated, the print control circuit 8 integrates the energy corresponding to the detected temperature, and when the accumulated energy reaches the target energy, each heating element Y ₁ , Y _{2, ···, Y n, M} 1, M 2, ···, M n, C 1, C 2, ···, is heated and driven in C _n is stopped. Since printing is performed at the same ratio with respect to yellow, magenta, and cyan, it is ideal that the image is output as a uniform gray, but actually, the heating elements Y ₁ , Y ₂ ,..., Y _n , _{M 1, M 2, ···,} M n, C 1, C 2, ···, the unevenness of the variation or the pressing pressure of the resistance value of C _n, the image unevenness occurs.

Next, the color of the output image for correction is measured using a chromaticity meter (step S2). The heating elements _{Y 1, Y 2, ···,} Y n, M 1, M 2, ···, M n, C 1, C 2, ···, and C _n, the heating elements Y _1, Y _{2, ···, Y n, M} 1, M 2, ···, M n, C 1, C 2, ···, so that the color of each dot printing is performed by C _n is associated To do. The heating elements _{Y 1, Y 2, ···,} Y n, M 1, M 2, ···, M n, C 1, C 2, ···, each dot printing is performed by C _n As the color, an average value of the correction image in the sub-scanning direction (direction corresponding to the arrow X direction) may be used.

Then, the heating elements _{Y 1, Y 2, ···,} Y n, M 1, M 2, ···, M n, C 1, C 2, ···, measured for each dot corresponding to C _n A color difference ΔE between the calculated color and the gray reference value is calculated, and it is determined whether each color difference ΔE is within an allowable value (for example, whether each color difference ΔE is within 2) (step S3). . As the gray reference value, the thermal head 2Y of measured from correcting image color, 2M, heating elements Y ₁ of _{2C, Y 2, ···, Y} n, M 1, M 2, ···, M n, A center value or an average value in a direction corresponding to the arrangement direction of C ₁ , C ₂ ,..., C _n (arrow Z direction) may be used, or a * = 0 and b * = 0 may be used. Alternatively, a gray having a strong bluish color or a gray having a strong reddish color may be set in advance according to the user's preference.

When each color difference ΔE exceeds an allowable value (step S3; NO), each of the heating elements Y ₁ , Y ₂ of the thermal heads 2Y, 2M, 2C for each color of yellow, magenta, and cyan according to the color shift method. , ..., Y _n , M ₁ , M ₂ , ..., M _n , C ₁ , C ₂ , ..., C _n are corrected and the target energy table values are changed. (Step S4). For example, when yellow is insufficient as compared with the gray reference value, the yellow target energy is increased by a predetermined value. Conversely, when yellow is excessive, the yellow target energy is decreased by a predetermined value. .

Next, based on the new target energy after correction, the heating elements Y ₁ , Y ₂ ,..., Y _n , M ₁ , M ₂ of the thermal heads 2Y, 2M, and 2C for yellow, magenta, and cyan, respectively. ,..., M _n , C ₁ , C ₂ ,..., C _n are output correction images printed at 50 gradations (step S1).

  In this way, steps S1 to S4 are repeated until each color difference ΔE falls within an allowable value. When each color difference ΔE is within the allowable value (step S3; YES), the correction is completed (step S5).

  Ideally, the correction process is performed for each gradation 0 to 255 of the print data. For example, the correction is performed for a representative gradation, and the same correction is performed for peripheral gradations. It is good as well. For example, correction of target energy of 50 gradations, 120 gradations, and 200 gradations is performed for each heating element, and correction similar to that for 50 gradations is performed for target energy of 0 to 80 gradations ( For example, increase or decrease the same energy as the increase or decrease from the initial value of the correction performed for the target energy of 50 gradations)), for 120 to gradations of target energy of 81 to 160 gradations Correction similar to the correction may be performed, and correction similar to correction for 200 gradations may be performed for target energy of 161 to 255 gradations.

As described above, the heating elements Y ₁ , Y ₂ ,..., Y _n , M ₁ , M ₂ ,..., M _n , C ₁ , C of the plurality of thermal heads 2Y, 2M, 2C. ₂ ,..., C _n , a correction image is printed on the image receiving sheet 7, the color of the correction image is measured, and each heating element Y ₁ , Y ₂ ,. _{Since the} target energy for _n , M ₁ , M ₂ ,..., M _n , C ₁ , C ₂ ,..., C _n is corrected, the image unevenness of the output image can be reduced.

In the above embodiment, based on the measured from the corrected image color, the heating elements _{Y 1, Y 2, ···,} Y n, M 1, M 2, ···, M n, Although the target energy of C ₁ , C ₂ ,..., C _n is corrected, the correction may be performed based on the density measured from the correction image with a microdensitometer or the like.

Further, in the above embodiment, the thermal heads 2Y, 2M, the heating elements of _{2C Y 1, Y 2, ···} , Y n, M 1, M 2, ···, M n, C 1, In the above description, correction is performed for C ₂ ,..., C _n , but each heating element Y ₁ , Y ₂ ,..., Y _n , M ₁ , M ₂ ,. .., M _n , C ₁ , C ₂ ,..., C _n may be corrected only between the thermal heads when the variation is small.

  Moreover, the description in the said embodiment is an example of the suitable printing method which concerns on this invention, and is not limited to this. The detailed configuration and detailed operation of each part constituting the thermal transfer printer 1 can be appropriately changed without departing from the spirit of the present invention.

  For example, in the above embodiment, a sublimation type thermal transfer printer using an ink ribbon has been described. However, the present invention can also be applied to a thermal printer using a thermal recording paper.

1 is a schematic configuration diagram of a thermal transfer printer 1 in an embodiment of the present invention. 3 is a control block diagram of a thermal head 2Y in the thermal transfer printer 1. FIG. It is a figure which shows the temperature characteristic of the resistance value of each heat generating element. It is a graph which shows the relationship between the heat_generation | fever energy and print density in each heat generating element. It is a figure which shows the example of the temperature change of each heat generating element with respect to time at the time of printing. It is a target energy table which shows the target energy with respect to the printing data for every heating element. 4 is a flowchart showing correction processing of the thermal transfer printer 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Thermal transfer printer 2Y, 2M, 2C, 2P Thermal head 3Y, 3M, 3C, 3P Ink ribbon 4 Image receiving sheet supply part 5Y, 5M, 5C, 5P Platen roller 6 Cutter 7 Image receiving sheet 8 Print control circuit 9 Drive circuit 10 Temperature detection circuit _{Y 1, Y 2, ···,} Y n, M 1, M 2, ···, M n, C 1, C 2, ···, C n heating elements

Claims (2)

A printing method using a plurality of thermal heads composed of a plurality of heating elements whose resistance value changes depending on temperature, and detecting the temperature of each heating element based on the resistance value of each heating element. In a printing method in which energy corresponding to a detected temperature is accumulated, and when the accumulated energy reaches a predetermined target energy corresponding to printing data for each dot, heat generation driving of each heating element is stopped. ,
A correction image is printed on an image receiving sheet by each heating element of the plurality of thermal heads, the color or density of the correction image is measured, and the target energy for each heating element is determined based on the measured color or density. A printing method characterized by correcting. The printing method according to claim 1,
The printing method, wherein each of the plurality of thermal heads performs printing on the image receiving sheet using at least yellow, magenta, and cyan mono-color ink ribbons.

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