JPS6057763A - Medium tone thermal recording method - Google Patents

Abstract

PURPOSE:To decrease the power supply capacity and to attain desired medium tone recording by narrowering the width in the sub-scanning direction of each heating element than width in the main scanning direction and constituting one picture element with print for plural number of times as to the sub-scanning direction of the heating element. CONSTITUTION:The width l' of a heat resistor 2 in the sub-scanning direction P is formed narrower than the width (m) in the main scanning direction Q in a print head and electrodes a-1, a-2, a-3... and b-1, b-2, b-3... are provided in zigzag to the heat resistor 2 to form plural adjacent heating sections j-1, j-2, j-3.... Thus, the heat dissipating area is decreased and the current amount heating each heating section to a prescribed coloring temperature is reduced. In using the thermal print head with the constitution above for the purpose of recording, the normal one picture element to be printed is constituted by the print for plural number of times by the heating elements j-1, j-2... as to the sub- scanning direction P.

Description

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

[Prior art]

Generally, a conventional thermal recording apparatus uses a thermal printing head as shown in FIG. That is, one heating resistor 1 is arranged 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 B-1+a-2+a- are arranged on this heating resistor 1. 3- and b -1, b
-2, b -3-... are arranged to form a plurality of mutually adjacent heat generating parts h-1+h-2+h-3-=, and electrodes a-1, a-2, a-3..., b-1, b-2, b-
3... by selectively supplying power to the heat generating part h-1+
It is configured to generate heat in a desired portion of h-2+h-3... and color a desired portion of a thermal recording medium (not shown) such as thermal recording paper or transfer medium that comes into contact with the heat-generating portion. ing.

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, and expressed in terms of scanning line density, for example, 8 mm in the main scanning direction and 3.85 mm in the sub-scanning direction).
Normally, the heating element width l in the sub-scanning direction P is the same as the width m in the main scanning direction (indicated by the arrow Q) #1, in a one-to-one correspondence.
Or it is 2 to 3 times as long. Therefore, in order to generate heat in each heat generating portion 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 print head with such a configuration include (1) changing the brightness and size of printed dots by controlling the electric energy applied to each heating element, for example, the pulse width of a printing pulse; (2) One pixel is composed of a plurality of dots in the main scanning direction and the sub-scanning direction, and a so-called matrix is used to express the halftone by the printing mode (printing presence/absence) of the plurality of dots. There were dithering methods, etc.

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, the above (2
) method, in order to obtain high-resolution halftone recording,
Electrode a −1z a −2+ crossing the heating resistor
...*b-1, b-22... (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

[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 stain source capacity. By configuring a pixel by printing a plurality of times in the sub-scanning direction of the heating element, and changing the combination of printing and non-printing corresponding to the plurality of times of printing, halftone recording of multiple gradations is realized. Furthermore, the print position within each pixel is selected and driven so that the number of prints in each main scanning direction is the same, thereby making it possible to further reduce the power supply capacity.

[Example] Hereinafter, the heat-sensitive halftone recording method according to the present invention will be explained in detail according to the example shown in the accompanying drawings.

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

In the print head of this embodiment, the width 4' of the heating resistor 2 in the sub-scanning direction P is shorter than the width m in the main scanning direction Q, and the heating resistor 2 has electrodes a-1, a-2. , a −3=...
and b-1, b-2, b-3, .
1, j-2, j-3... are formed. In this way, in this print head, the width l' of the heating resistor 2 in the sub-scanning direction is narrower to a fraction of that of conventional print heads, so the heat generating area is small. Heat generating part j-1,
It is possible to reduce the amount of current flowing through each heating section j-1, j-2, etc. in order to generate heat to a predetermined coloring temperature for coloring the recording medium. As a result, the power supply is reduced. The power supply capacity required for this 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 print head with such a configuration,
One normal pixel to be printed is connected to each heating element j-1, j-2, .
It is composed of multiple times of printing in the sub-scanning direction P. That is, conventionally, as shown in FIG. 3(a), for example, 125 μm in the main scanning direction and 260 μm in the sub scanning direction
There was a one-to-one correspondence between the printing area of one pixel having a width of m and the heat generating area of each heat generating part of the print head, but in this embodiment, as shown in FIG. 3(b), the print head 2 The heat generating area J of each heat generating unit j-1, j-2, etc. corresponds to 1/4 of the size of one pixel, and when one heat generating unit is driven to generate heat four times, Recording for one pixel is completed.

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. FIGS. 4(,) to 4(,) show the printing mode, with blank areas showing white and cross-hatched areas showing black. In other words, in Figure 4, from the combinations of four dots that can have two brightness levels, white or black, the 5 points shown in (,) to (,) are obtained.
It enables recording of halftones. Essentially speaking, the halftone recording method of this embodiment is included in the matrix dither method mentioned above in the prior art, but unlike the conventional matrix dither method, the method of this embodiment differs from the conventional matrix dither method in that it Since halftone recording is realized by a combination of only printed dots, 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, a plurality of items as mentioned above (for example, 1728 items)
Methods for driving a thermal print head in which heating elements are arranged in parallel in the main scanning direction include: - simultaneous driving of all main scanning lines, or split driving in which recording for one main scanning line is divided into multiple steps. There are various methods, 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. 5(,), one pixel is formed by printing six times in the sub-scanning direction P. All 6 dots are printed on pixel D2, 3 out of 6 dots are printed on pixel D2, 2 out of 6 dots are printed on pixel D3, and 1 out of 6 dots is printed on pixel D4. be done. When halftones are recorded in this way, it is necessary to record 4 dots when recording main scanning line II, and 3 dots when recording line 12.
When recording line 13, it is necessary to record two dots, and line lJ4. IJl! and 16 require recording one dot each.

Therefore, in this case, the capacity of the power supply is required to be large enough to simultaneously generate heat from at least four dots.

Therefore, in the halftone recording method according to the present invention, by driving the thermal print head in the printing mode shown in FIG. 5(b), for example, it is possible to further reduce the required power supply capacity. That is, in FIG. 5(b), the gradation level of each pixel D1 to D4' is the same as the gradation level of each pixel Dl to D4 shown in FIG. The printing position of each dot in each pixel is changed in the sub-scanning direction so that the number of prints in 11-16 is the same. Accordingly, in this case, the number of prints in each of the main scanning lines 11 to 16 is 2 dots, and the required power supply capacity for this is sufficient to generate heat for at least 2 dots at the same time.

If the thermal print head is driven in this manner, the required power supply capacity can be further reduced, whether the main scanning lines are driven all at once or dividedly.

It should be noted that the printing arrangement of each dot shown in FIG. 5(b) is merely an example, and of course, other printing arrangement 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 print head, it is particularly applicable to a thermal print head using a thick film method as shown in the above embodiment because the contact with the thermal recording medium is convex. 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, and 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.
FIG. 3, FIG. 4, and FIG. 5 are explanatory diagrams each 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, b-1,, h
-2...,j-1,,j -2...,... Heat generating part Figure 1 Figure 2 Figure 3 (G) (b) Figure 4

Claims (1)

[Claims] In a thermal halftone recording method in which halftone recording is performed on a thermal recording medium using a thermal printing head in which a plurality of adjacent heating elements are arranged in parallel in the main scanning direction, the width of each heating element in the sub-scanning direction is A predetermined pixel that is shorter than the width in the scanning direction and constitutes a predetermined pixel to be recorded on the thermal recording medium by multiple times of printing in the sub-scanning direction of the heating element, and the plurality of times of printing of each heating element. The printing position of each heating element within each pixel is changed in the sub-scanning direction in order to obtain halftones based on changes in the printing mode during the printing process, and to make the number of prints in each main-scanning direction the same. A thermal halftone recording method characterized in that halftone recording is performed on a thermal recording medium.