JPH0412671B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to an improvement in a thermal halftone recording method using a thermal printing head in which a plurality of adjacent heating elements are arranged in parallel in the main scanning direction.

[Prior art]

Generally, a conventional thermal printing apparatus uses a thermal printing head as shown in FIG. That is, one heating resistor 1 is disposed in the sub-scanning direction of the thermal printing head (the feeding direction of the thermal recording paper, indicated by arrow P), and a plurality of electrodes a-1, a-
2, a-3... and b-1, b-2, b-3... and a plurality of heat generating parts h-1, h adjacent to each other.
-2, h-3... are formed, and electrodes a-1, a-2,
By selectively supplying power to a-3..., b-1, b-2, b-3..., the heat generating parts h-1, h-2, h-
It is configured to generate heat from a desired part of 3... and color a desired portion of a thermal recording medium (not shown) such as a thermal recording paper or a transfer medium that comes into contact with the heat generating part.

By the way, the size of each heat generating part of the above-mentioned conventional thermal printing head is the size of one pixel to be printed (in terms of scanning line density, for example, 8 lines/mm in the main scanning direction and 3.85 lines/mm in the sub-scanning direction). There is a one-to-one correspondence with
Normally, the width of the heating element in the sub-scanning direction P is approximately the same as the width m in the main scanning direction (indicated by arrow Q), or 2 to 3
It is twice as long. Therefore, in order to generate heat in each heat generating portion up to a predetermined coloring temperature required for printing, a relatively large power supply capacity is required for the power supply.

Conventional halftone recording methods using a thermal printing head with such a configuration include (1) changing the brightness or size of printed dots by controlling the electrical energy applied to each heating element, for example, the pulse width of a printing pulse; How to record midtones.

(2) A so-called matrix dither method, etc., in which one pixel is composed of a plurality of dots in the main scanning direction and the sub-scanning direction, and halftones are expressed by the printing mode (printing presence/absence) of the plurality of dots. It was hot.

However, method (1) above requires a special heat-sensitive recording medium that can obtain print brightness approximately proportional to the applied energy, and the heating resistor must have a small variation in resistance value between each heating element. However, there was a drawback that halftone recording with good resolution could not be obtained. Next, in the method (2) above, in order to obtain high-resolution halftone recording, the electrodes a-1, a-2, ..., b-1, b-
2,... (see Fig. 1) had to be arranged at high density, which was difficult to implement.

[Purpose of the invention]

This invention has been made in view of the above circumstances, and provides a thermal halftone recording method that can significantly reduce the required power supply capacity and realize desired halftone recording with simple drive control. The purpose is to provide

[Structure of the invention]

Therefore, in this invention, the width of each heating element in the sub-scanning direction is made shorter than the width in the main scanning direction to reduce the heat-generating area, thereby reducing the power supply capacity. It is configured by printing multiple times in the sub-scanning direction of the heating element, and by changing the combination of printing and non-printing corresponding to the multiple printings, it is possible to realize halftone recording of multiple gradations. The print position within each pixel is selected and driven so that the number of prints in the main scanning direction is the same, thereby making it possible to further reduce the power supply capacity.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS The heat-sensitive halftone recording method according to the present invention will be described in detail below with reference to embodiments shown in the accompanying drawings.

FIG. 2 shows an embodiment of a thermal printing head used in the present invention.

In the printing head of this embodiment, the width l' in the sub-scanning direction P of the heat-generating resistor 2 is formed to be shorter than the width m in the main-scanning direction Q, and the heat-generating resistor 2 has electrodes a-1, a-
2, a-3... and b-1, b-2, b-3,...
are arranged in a staggered manner as described above to form a plurality of heat generating parts j-1, j-2, j-3, . . . adjacent to each other. In this way, in this print head, the width l' of the heat generating resistor 2 in the sub-scanning direction is narrower to a fraction of that of the conventional print head, so the heat generating area is small, and as a result, each heat generating part j -1, j-2, ... to the predetermined coloring temperature for coloring the recording medium, the amount of current flowing through each heat generating section j-1, j-2... can be reduced, and as a result, the amount of current required for the power supply is reduced. The power supply capacity can be reduced to a fraction of that of the conventional technology. Of course, the narrower the width l' of the heating resistor, the smaller the amount of power required.

When recording using a thermal printing head with such a configuration, one normal pixel to be printed is connected to each heating element.
1, j-2, . . . are formed by printing a plurality of times in the sub-scanning direction P. That is, conventionally, as shown in FIG. 3a, for example, 125 μm in the main scanning direction,
The print area of one pixel with a width of 260 μm in the sub-scanning direction and the heat generating area of each heat generating part of the print head are 1:1.
However, in this embodiment, as shown in FIG. 3b, each heat generating part j-1,
The heating area J of j-2... corresponds to 1/4 of the size of one pixel, and recording for one pixel is completed by driving one heating section four times to generate heat. .

According to the above structure, since one normal pixel is made up of four dots in the sub-scanning direction, halftone recording can be easily achieved by simply changing the printing mode of the four dots. Figure 4a
-e indicate the printing mode, with blank areas showing white and cross-hatched areas showing black. That is, in FIG. 4, the combination of four dots that can have two brightnesses, white or black, enables recording of five gray levels a to e. Essentially speaking, the halftone recording method of this embodiment is included in the solid matrix dither method described in the prior art, but unlike the conventional matrix dither method, the method of this embodiment is different from the conventional matrix dither method. Since halftone recording is achieved by combining printed dots in only one direction, there is no need for high-density electrode arrangement. Further, since halftone recording is performed using a so-called pseudo method of changing the printing area in one pixel, there is no need to be very strict regarding variations in heat generation characteristics of each heat generation element.

By the way, if there are multiple items as mentioned above (for example, 1728
The method of driving a thermal printing head, in which several heating elements are arranged in parallel in the main scanning direction, is to drive all of one main scanning line at once, or to record one main scanning line by dividing it into multiple times. There are split drive systems, etc., but in any case, considering economic efficiency or compactness of the device, it is desirable that the capacity of the power supply is smaller. Therefore, in the present invention, in addition to the above-described halftone recording method, the following control is performed.

In FIG. 5a, one pixel is formed by printing six times in the sub-scanning direction P. pixel
All 6 dots are printed on D ₁ , 3 out of 6 dots are printed on pixel D ₂ , and 6 dots are printed on pixel D ₃ .
Two of the dots are printed, and for pixel _D4 , one of the six dots is printed. When halftones are recorded using this method, it is necessary to record four dots when recording main scanning line _l1 , and when recording line _l2
When recording line 1, it is necessary to record 3 dots, when recording line l ₃ , it is necessary to record 2 dots, and when recording lines l ₄ , l ₅ and l ₆ , it is necessary to record 1 dot each. Requires records. Therefore,
In this case, the capacity of the power supply is required to be large enough to simultaneously generate heat for at least four dots.

Therefore, in the halftone recording method according to the present invention, the required power supply capacity can be further reduced by driving the thermal printing head in the printing mode shown in FIG. 5b, for example. That is,
In FIG. 5b, the gradation level of each pixel D ₁ ' to D ₄ ' is the same as the gradation level of each pixel D ₁ to D ₄ shown in FIG. 5a, but each main scanning line l ₁ to The printing position of each dot within each pixel was changed in the sub-scanning direction in order to keep the same number of prints in _l6 .
As a result, in this case, the number of prints in each of the main scanning lines _l1 to _l6 is two dots, and the required power supply capacity for this is sufficient to generate heat for at least two dots at the same time.

If you drive the thermal print head in this way,
The required power supply capacity can be further reduced in both the case where one main scanning line is driven all at once and the case where it is dividedly driven.

Note that the printing arrangement of each dot shown in FIG. 5b is merely an example, and of course other printing arrangements may be used. The point is that the printing position of each dot within each pixel can be selected so that the number of prints on each main scanning line is the same, without changing the gradation level of each pixel.

Further, in the present invention, the number of divisions in the sub-scanning direction within one pixel is of course arbitrary, and by changing the number of divisions, multi-step gradation recording can be realized.

By the way, although the present invention can be applied to any thermal printing head, it is particularly applicable to a thermal printing head using a thick film method as shown in the above embodiment because the contact with the thermal recording medium is in a convex shape. It is valid.

〔Effect of the invention〕

As explained above, according to the thermal halftone recording method according to the present invention, the power capacity of the power supply can be significantly reduced, and halftone recording with excellent resolution can be realized with a simple control configuration. I can do it. By the way, the present invention is particularly effective when recording photographs with a high printing rate or objects similar to paintings in a dot matrix format using halftones.

[Brief explanation of drawings]

FIG. 1 is a plan view showing a thermal print head used in a conventional thermal recording device, FIG. 2 is a plan view showing an embodiment of a thermal print head used in a halftone recording method according to the present invention, and FIG. , Figures 4 and 5
Each of the figures is an explanatory diagram illustrating an embodiment of the halftone recording method according to the present invention. 1, 2...heating resistor, a-1, a-2..., b
-1, b-2...,...electrode, h-1, h-2...,
j-1, j-2...,... Heat generating part.

Claims (1)

[Claims] 1. In a thermal halftone recording method that performs halftone recording on a thermal recording medium using a thermal printing head in which a plurality of adjacent heat generating elements are arranged side by side in the main scanning direction, the width of each heating element in the sub scanning direction is The width is shorter than the width in the main scanning direction, and a predetermined pixel to be recorded on the thermal recording medium is formed by printing multiple times in the sub-scanning direction of the heat generating element, and the printing is performed during the multiple times printing of each heat generating element. The thermal recording medium is produced by changing the printing position of each heating element within each pixel in the sub-scanning direction so as to obtain an intermediate tone based on the change in the aspect and to make the number of prints in each main-scanning direction the same. 1. A heat-sensitive halftone recording method, characterized in that halftone recording is performed for a given temperature.