JP4384953B2 - Thermal head energization control method - Google Patents

Description

  The present invention relates to an energization control method for each of the heating elements of a thermal head in which a plurality of heating elements are arranged in a line.

  A thermal printer (hereinafter referred to as a thermal transfer printer) that performs thermal transfer recording using a thermal head in which a plurality of heating elements are arranged in a line form a desired ink on a base film between a platen and the thermal head. By sandwiching the applied ink film and paper, feeding out the ink film and transporting the paper, selectively applying recording energy to the plurality of heating elements of the thermal head based on the recording information, and generating heat, The ink of the ink film is partially transferred onto the paper to record an image such as a desired character. This type of thermal transfer printer is widely used as an output device for computers, word processors, and the like for reasons such as high recording quality, low noise, low cost, and ease of maintenance.

  As one of thermal transfer printers, a thermal transfer printer (hereinafter referred to as a thermal transfer printer) that records on paper using an ink ribbon (hereinafter referred to as a thermal meltable ink ribbon) in which a hot melt ink is applied to a base film such as a plastic film. (Referred to as a thermal melting type printer).

  This hot-melt type printer is capable of recording on a wide variety of paper such as plain paper, cardboard, and postcards, and is excellent in usability, but in order to perform gradation recording using the hot-melt ink film, Since the density gradation cannot be expressed in dot units constituting each pixel of the recorded image, for example, a dither matrix method (hereinafter referred to as a dither method) is used.

  Here, the dither method as a density gradation recording method is a method in which one pixel of recording information is composed of a plurality of dots, and when the plurality of heating elements of the thermal head are selectively energized, the energization patterns of the respective colors. (Hereinafter referred to as a dither pattern), a multi-tone image is recorded while controlling the number of energized dots in one pixel. In the case of recording a color image, a multi-tone color image is recorded by controlling the number of energized dots in one pixel and the energization order according to the tone data for each color of cyan, magenta, and yellow. It becomes.

  Needless to say, the basis of image recording using the dither method is the printing accuracy of each dot. That is, when a recorded image is formed using a hot-melt printer, the recording energy (energization amount) is controlled by the voltage applied to the heating element corresponding to each dot constituting the pixel of the recorded image and the energization time. The transfer of the hot-melt ink to a necessary and sufficient dot size is a requirement for obtaining a good recorded image.

JP 2003-182132 A

  However, when recording an image in the thermal melting type printer, there is a power limitation in relation to the heat resistance specifications of the heat generating elements of the thermal head, so that the thermal melting is performed to such an extent that a necessary and sufficient dot size can be secured for each dot. In some cases, the photosensitive ink cannot be melted and transferred onto the paper.

  FIG. 4 is a schematic diagram illustrating an example of a dither pattern in a certain ink color and an energization order by the dither method in a mixed color image composed of yellow Y, magenta M, and cyan C ink colors.

  In this conventional example, one pixel of the ink color is composed of 10 dots obtained by adding one dot to the lower right side of 3 × 3 dots as shown by being surrounded by a thick black line in FIG. In this conventional example, the screen is arranged at a predetermined dither screen angle (about 18.4 °), and each pixel is controlled to be energized in the energization order of the heating elements in accordance with the gradation. In the following description, the energization order in FIG. 4 is also used as a dot number representing each dot (hereinafter referred to as what number dot).

  In the conventional example, the dither method energizes all 10 dots from 0 gradation (0% in duty) indicating a state in which no 10 dots constituting each pixel are energized. Control is performed so that the density gradation of each pixel is processed (hereinafter referred to as dithering) with 11 gradations (duty of 0 to 100%) up to 10 gradations (duty of about 90 to 100%).

  By the way, if such a dither pattern is used and, for example, when highlight expression is performed with a halftone in an image, if it is controlled to energize only a single dot in each pixel, energization as described above. Since this is performed according to the energization order of the dots constituting each of the pixels, in this conventional example, only the first dot indicated by a bold circle in FIG. 4 is energized.

  FIG. 5 is a schematic diagram of the dots formed by the energization on / off of the heating elements corresponding to the dots arranged in the row indicated by the arrows in FIG. 4 and the energization in this case. As shown in FIG. 5, in the conventional thermal head energization control method, the heating element corresponding to the first dot to be energized is energized (ON state), but the relative movement direction of the thermal head In the (scanning direction), before energization of the first dot, there is no energization history for the heating element corresponding to the dot.

That is, since the heat generating element is substantially in the same temperature as the environmental temperature, even when the highest power in the allowable range of the heat resistance specification of the heat generating element is applied during the recording of the first dot, the temperature of the heat generating element is not limited. However, the hot-melt ink may not be melted to such an extent that a necessary dot size can be secured in the dots. In that case, it goes without saying that the dot size of the first dots is reduced or not formed, and good recording results cannot be obtained.
SUMMARY OF THE INVENTION The present invention has been made in view of the foregoing points, and a method for controlling energization of a thermal head capable of imparting sufficient recording energy for ink transfer to a heating element corresponding to each dot constituting a pixel of a recorded image. The purpose is to provide.

  In order to achieve the above-mentioned object, the energization control method of the thermal head according to the present invention is characterized by controlling energization of the heating element of the thermal head based on the recording information regarding each dot constituting each pixel of the recorded image. In the thermal head energization control method for printing a desired recorded image, the heating element of the thermal head corresponding to the dot to which the ink of the ink ribbon is transferred among the plurality of dots constituting each pixel is Perform main energization to provide sufficient recording power to transfer the ink, and perform margin energization to apply a small amount of margin energization power that does not transfer the ink to the heating elements corresponding to the other dots. Tentatively determine the contents of energization control to each heating element, and as a result of the tentative determination, the energization order of the dots constituting each pixel when using the dither matrix method Then, the main energization is performed on the reference dot at the first energized position, and is further applied to the heating element corresponding to the target dot located adjacent to the reference dot on the upstream side in the relative movement direction of the thermal head. When the power is less than or equal to the margin energization power, the margin energization for the heating element corresponding to the target dot is applied with the reserve energization power that is greater than the margin energization power and does not transfer the ink. Correction is made to change to preliminary energization to be performed, and then the contents of the energization control to each heating element are finally determined, and the energization processing to each heating element is performed based on the contents of this determined energization control. And

  The energization control may be performed only when the image information is processed using a dither method for performing multi-tone recording.

  According to the energization control method of the thermal head of the present invention, the first energized dot in the energization order of the dots constituting each pixel by the dither matrix method is positioned adjacent to the upstream side in the relative movement direction of the thermal head. By preliminarily energizing each heating element corresponding to each dot and preheating the heating element, when energizing the recording dots, the energization is normally performed within the range of the heat resistance specifications of the heating element. The heating element can be sufficiently heated, and the ink on the ink ribbon can be transferred satisfactorily to obtain a good recording result.

  For example, the recording information relating to each pixel is such that the first energized single dot is energized in the energization order of the dots composing each pixel by the dither matrix method among the plurality of dots composing each pixel. In some cases, that is, in the case of highlight printing, particularly significant effects can be obtained by performing energization control of the thermal head of the present invention.

  In addition, the above-described energization control is performed only when the image information is processed using a dither method for performing multi-tone recording, so that the image information is recorded in binary. Overheating of the heat generating element of the thermal head can be avoided, and even in the binary recording, it is possible to prevent transfer of excess ink and to obtain a good recording result.

  The thermal transfer printer used in the present embodiment is a thermal melting type printer that records a color image using a thermal melting ink ribbon, and a large number of heating elements corresponding to pixels in the relative movement direction of the head are arranged in a line. It has a line thermal head (hereinafter simply referred to as a thermal head).

  Then, based on the image information input from the host computer, image reader, or the like, the image information is separated into recording information for each color of cyan, magenta, and yellow in the control unit of the hot melt printer, By controlling the energization of each heating element of the line thermal head based on the recording information (gradation value), cyan, magenta, and yellow inks are sequentially transferred to obtain a color recording image. It has become.

  At this time, in this embodiment, multi-tone recording of a color recording image is performed using the dither method described above, and other recordings such as character information are transferred from the recording information in units of dots. It is controlled to use a recording method (hereinafter referred to as an individual dot energization method) in which energization of the heat generating elements corresponding to each dot is turned on / off.

  That is, in the present embodiment, the control unit first processes the image information using a dither method for performing multi-gradation recording, or the individual dots that perform binary recording of energization and non-energization. It is determined whether the process is performed by the energization method (hereinafter referred to as premise determination). The reason for changing the recording processing method in accordance with the contents of the image information will be described later.

  As a result of the premise determination, when it is determined that the image information has contents to be processed by the individual dot energization method, energization control is performed according to the gradation value of each dot. For example, since the recording information (gradation value) of the so-called solid print region is indicated by 255 gradations indicating the energization state of the heating elements, the energization of the corresponding heating elements is controlled in dot units based on each gradation value. To do. Even in the case where the solid print area is threshold recording information, it is indicated by 255 gradations indicating the energization state of the heating element and 0 gradations indicating the off state. The energization of the corresponding heating element is controlled in units.

  When it is determined that the image information is the content of multi-tone recording and processed using the dither method, the following control (for convenience, the following control is referred to as “main control”) is performed. Do.

  First, power (recording power) sufficient to transfer the ink is applied to the heating element of the thermal head corresponding to the dot to which the ink of the ink ribbon is transferred among the plurality of dots constituting each pixel. (Main energization), and energization control to each heating element so that power (margin energization power) that does not transfer the ink is applied to the heating elements corresponding to the other dots (margin energization). Is temporarily determined.

  After that, it is determined whether the main energization or the margin energization is performed on the dot (reference dot) at the first energization position in the energization order of the dots constituting each pixel by the dither method, and the margin energization is performed. In this case, the contents of energization control to each heating element are determined as they are.

  Further, when the energization is performed with respect to the reference dot, the power applied to the heating element corresponding to the dot (target dot) located in the adjacent position on the upstream side in the relative movement direction of the thermal head is It is determined whether or not it is equal to or less than the margin energization power.

  When the power applied to the heating element corresponding to the target dot is larger than the margin energization power, the contents of the energization control to each heating element are determined as they are.

  Further, when the power applied to the heating element corresponding to the target dot is equal to or less than the margin energization power, the heating element corresponding to the target dot is equal to or higher than the margin energization power, and Then, the power (preliminary energization) that does not transfer the ink is applied (preliminary energization), and the energization control to each heating element is finally determined.

  Thereafter, based on the content of the energization control determined in this control, energization of each heating element is performed to obtain a desired recorded image.

  Note that the recording power, the standby energization power, and the margin energization power can be changed by varying the energization time with the same voltage, for example. That is, the energization time is controlled so that the margin energization is the shortest, the preliminary energization is followed, and the main energization is the longest. Furthermore, the power supplied to the heating element corresponding to each dot may be changed by varying the voltage level or by combining the voltage level with the length of the energization time.

  Hereinafter, in the present embodiment, the control in the case where the image information is the content for performing multi-gradation recording by the dither method will be specifically described.

  FIG. 1 is a schematic diagram showing an example of a dither pattern in a certain ink color and an energization order by the dither method in a mixed color image composed of yellow Y, magenta M, and cyan C ink colors.

  In this embodiment, one pixel of the ink color is composed of 10 dots obtained by adding one dot to the lower right side of 3 × 3 dots as shown by being surrounded by a thick black line in FIG. The pixels are arranged at a predetermined dither screen angle (about 18.4 °), and each pixel is controlled to be energized in the energization order of the heat generating elements in accordance with the gradation. Further, in the present embodiment, 10 gradations for energizing all 10 dots from 0 gradation (duty 0%) indicating a state in which none of the 10 dots constituting each pixel is energized. Dither processing is performed with 11 gradations (0 to 100% for Duty) up to (about 90 to 100% for Duty).

  In the following embodiments, the image information (recording information) is a content that expresses a highlight by a dither method, and the expression of the highlight is to transfer ink only to a single dot of each pixel. It shall be controlled so that it is expressed by Therefore, the reference dot is a dot that is energized at the time of one gradation in the dither process (1 to 10% in Duty), that is, the first dot that is energized first in the energization order of the dots that constitute each pixel by the dither method. It becomes.

  In the energization control method for the thermal head of the present embodiment, the control unit applies the recording element to the heating element corresponding to the first dot that transfers the ink of the ink ribbon among the plurality of dots constituting each pixel. It is temporarily determined that the main energization for applying power is performed, and that the energization for the other second dots to the tenth dots is performed with the margin energization for applying the margin energization power.

  Thereafter, it is determined whether main energization or blank energization is performed on a reference dot at a position where energization is first performed in the energization order of dots constituting each pixel by the dither method. In the case of the present embodiment, since the first energization is performed on the first dot, subsequently, the dot positioned adjacent to the first dot on the upstream side in the relative movement direction of the thermal head, that is, as the target dot, For the eighth dot constituting the pixel located adjacent to the pixel on the upstream side in the relative movement direction of the thermal head, the power applied to the corresponding heating element is equal to or less than the power applied in the margin energization. Consider whether or not.

  In the case of the present embodiment, the eighth dot is a target dot that is the target of blank energization in the provisional determination, and a blank energization voltage is to be applied. Then, the provisional determination of energization to the heat generating element corresponding to the target dot is corrected so that the preliminary energization power is applied to the heat generating element corresponding to the eighth dot and the preliminary energization is performed. This content is determined as the content of energization control to each heating element.

  As a result, among the dots constituting each pixel in FIG. 1, the first dot indicated by a bold circle is the main energization, and the eighth dot indicated by a fine circle is the preliminary energization. Then, the margin energization is performed on the other dots. FIG. 2 shows on / off of energization to the heating elements of the thermal head corresponding to the dots arranged in the row indicated by the white arrow in FIG. 1 and the dots formed by the energization based on the result of the main determination. A schematic diagram is shown.

  In this way, each heating element corresponding to each dot positioned adjacent to the upstream side in the relative movement direction of the thermal head of the first energized dot in the energization order of the dots constituting each pixel by the dither matrix method. By performing pre-energization and performing control to preheat the heating element, when the ink of each dot constituting the pixel including the dot is transferred, the energization is normally performed within the range of the heat resistance specification of the heating element. The heat generating element can be sufficiently heated, and the ink of the hot-melt ink ribbon can be transferred to a necessary dot size to obtain a good recording result. This energization control method is particularly effective when it is necessary to energize a small number of dots in each pixel as in the case of highlight expression by the dither method, and the effect is also effective. It will be remarkable.

  Note that the dots to be energized for highlight expression are not limited to the first dots as in this embodiment, and may be a plurality of dots.

  Here, in the present embodiment, the reason why control is performed so that the above-described main control is performed only when it is determined as a result of the premise determination that processing is performed using the dither method will be described.

  That is, it is possible to uniformly perform the above-described main control regardless of the content of the recorded image. However, when such processing is performed, the reference dot is overheated, and the ink on the ink ribbon is excessive. In the case of a heat-meltable ink ribbon, there is a problem in peeling between the recording paper and the ink ribbon. When the value is recorded, the main control is not performed.

  For example, as shown in FIG. 3, threshold image information in which the set gradation value is the maximum value of 255 gradations (blank areas each having a size of 6 dots are dotted in the solid print area). It is assumed that the main control is executed when the pattern is recorded.

Then, according to the dither matrix method indicated by arrows B and C in FIG. 3, the dot located at the position of the first dot to be energized first becomes the reference dot, and on the upstream side in the relative movement direction of the thermal head. Neighboring dots, that is,
Preliminary energization is performed for the dot located at the eighth dot position. However, during the preliminary energization, the heating element of the thermal head is also energized with blanks in the other dots constituting the blank area, and it is also considered that preheating is performed by the energization history so far. There is a very high possibility that the ink is transferred to the dots located at the eighth dot position by the preliminary energization.

  As a result, unnecessary ink is transferred in the blank area, and the amount of blank to be expressed cannot be secured (margin collapse), and the corresponding heating element is overheated even at the position of each first dot, It is conceivable that the ink on the ink ribbon is transferred more than necessary, and the ink is excessively transferred at the position of the first dot and a good recording result cannot be obtained.

  Such an inconvenience is that when the pre-determined determination determines that the recording information is binary recording, the image information is binary-recorded by not performing the main control. It is possible to avoid overheating of the heat generating element of the thermal head, which may occur when performing, and even in the binary recording, it is possible to prevent excessive ink transfer and obtain a good recording result.

  Note that when the pattern shown in FIG. 3 is printed, the dots at the positions of the first dots indicated by the arrows A and D are not energized in the first place, and thus are excluded from the above-described main control.

  The present invention is not limited to the embodiments described above, and various modifications can be made as necessary.

  For example, the thermal printer using the energization control method for the thermal head of the present invention is not limited to the above-described line thermal printer.

  Further, for each dot, it is also possible to use a gradation expression for adjusting the diameter size of a dot to which ink is transferred in combination with the above-described dither method. The present invention is not only applicable to hot melt printers, but can also be applied to thermal sublimation printers that transfer ink onto paper using a heat sublimable ink ribbon.

The schematic diagram which shows the pixel in the area | region of the recording image by the energization control method of the thermal head of this embodiment, a dot, the energization ranking of each dot, and energization type Schematic diagram of ON / OFF of energization with respect to heating elements corresponding to dots arranged in a row indicated by arrows in FIG. 1, and dots formed by the energization by the energization control method of the thermal head of the present embodiment The pattern which shows the energization order in the case of the night in the dithering method of the dot in the area | region of the recording image for describing the control in the case of performing binary recording in the energization control method of the thermal head of the present embodiment Figure Schematic diagram showing pixels, dots, energization rank of each dot, and energized dots in a recorded image area by a conventional thermal head energization control method Schematic diagram of dots formed by energization on and off of the heating elements corresponding to the dots arranged in the row indicated by the arrows in FIG. 4 and the energization control method of the conventional thermal head

Claims (2)

A thermal head energization control method for printing a desired recording image by controlling energization of a heating element of a thermal head based on recording information about each dot constituting each pixel of each pixel of a recording image,
The heating element of the thermal head corresponding to the dot to which the ink of the ink ribbon is transferred among the plurality of dots constituting each pixel is subjected to main energization that provides recording power sufficient to transfer the ink. Temporarily determine the contents of energization control to each heating element so as to perform margin energization to give a margin energization power that does not transfer the ink to the heating elements corresponding to dots other than
As a result of the tentative determination, when the dither matrix method is used, the main energization is performed to the reference dot at the first energized position in the energization order of the dots constituting each pixel. When the power applied to the heating element corresponding to the target dot located in the adjacent position on the upstream side in the relative movement direction is equal to or less than the margin energization power, the margin power supply to the heating element corresponding to the target dot is performed as described above. Correction is made to change to pre-energization that gives power for pre-energization that is equal to or higher than margin energization power and does not transfer the ink, and then the contents of energization control to each heating element are determined in this way,
An energization control method for a thermal head, wherein energization processing for each heating element is performed based on the contents of the energization control determined in this way.   2. The energization control method for a thermal head according to claim 1, which is executed when the image information is processed using a dither method for performing multi-tone recording.