JPH0584102B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a thermal transfer printer, and particularly to a thermal transfer printer suitable for printing halftone images.

[Background of the invention]

Conventionally, to obtain halftone images, the thermal energy applied to the thermal head is varied, but there is no linear relationship between the thermal energy applied to the thermal transfer paper and the printed density recorded, making it difficult to obtain the desired density. There was a problem. As a means to prevent this, as in Japanese Patent Laid-Open No. 57-91283, a current pulse of a constant time width is applied when the concentration is other than 0. In this method, the thermal energy of the thermal transfer paper,
The printing density curve was largely approximated by the two polygonal lines, resulting in poor printing density accuracy.

[Object of the Invention] An object of the present invention is to provide a thermal transfer printer that corrects the non-linear relationship between thermal energy of thermal transfer paper and printing density and achieves highly accurate density gradation levels.

[Summary of the invention]

In the present invention, when calculating the corresponding thermal energy when the printing density is divided at equal intervals, the difference in thermal energy (the difference in thermal energy that gives adjacent gradation levels) is not uniform, so it is possible to The target printing density is obtained by applying differences in thermal energy of different intensity over time.

[Embodiments of the invention]

FIG. 1 is a diagram showing the relationship between thermal energy of thermal transfer paper and printing density, and shows the amount of thermal energy required when printing density is equally divided. If the thermal energy for printing density 0.2, 0.4, 0.6, 0.8, 1.0, 1.2 is E ₁ , E ₂ , E ₃ , ..., E ₆ , then the difference in thermal energy ΔE _i is ΔE with E ₀ as thermal energy 0 ₁ =E ₁ −E ₀ =E ₁ ΔE ₂ =E ₂ −E ₁ 〓 ΔE ₆ =E ₆ −E ₅ ...(1). Thermal energy to be added to the thermal head is given by a combination of these ΔE _i . For example, to achieve a print density of 0.6, use ΔE ₁ +ΔE ₂ +ΔE ₃ , and to achieve a print density of 1.2, use ₆ 〓 ^{i= 1} ΔE _i . ΔE ₃ , ΔE _{4 ,} etc. in Figure 1 are almost equal and correspond to the slope of the tangent to the concentration-energy curve, so it is sufficient to prepare 5 to 10 types of sets of ΔE _i sizes. It is.

FIG. 2 is a block diagram of a control circuit for applying thermal energy by changing the time width of current, and the line memory 1 stores gradation information for each printing point for one line. The address counter 2 outputs gradation information in time series and inputs it to the A side of the comparator 3. The gradation levels from the level generator 4 are added to the B side of No. 3 in descending order.
When the signal level on the A side is greater than or equal to the signal level on the B side, the pulse is transferred to shift register 1.
It is set to be sent to 0. When one line of data is sent in, it is held by the latch register 11 and sent to each heating element 12 of the thermal head 13.
Continue to apply current to. The time for energizing is given by a time width generator 7. The gradation level generated by the level generator 4 is used as address information in the nonvolatile memory 5, and the value written in the memory 5 in advance is output to the changeover switch 6, so that an arbitrary resistor 9 can be selected. It's summery. Time width generator 7 by selected resistor 9 and capacitor 8
The necessary time span is created from

The operation when configured in this way is shown in Figure 1.
Regarding 0.6, the concentration level of 0.2 comes out from 4 at first, but since it is smaller than 0.6, it is output to 10, and the thermal energy is output at 5, 6, and 7 corresponding to 0.2.
Thermal head 13 is energized for a time period corresponding to _E1 . Next, when the concentration of 0.4 comes out from 4, E ₂
-E ₁ is energized, and when 4 is 0.6, it is energized for a time corresponding to E ₃ -E ₂ , and the total heat energy E ₃ is realized.
The signal stored in 5 indicates the selection number of the resistor 9 in 6, and the resistor 9 is combined with the capacitor 8 to create multiple sets of time widths. By preparing various contents of 5 and gradation of resistor 9, it is possible to accurately correct the thermal energy and printing characteristics of any transfer paper.

FIG. 3 shows the current waveforms applied _to the heating element 12 when various printing densities are achieved with the characteristics shown in _FIG . (t ₁ - t ₀ ) + (t ₂ - t ₁ ) (t ₃ - _{t 2} ) + (t ₂ - t ₁ ) + (t ₁ - t ₀ ) 〓 , and current pulses with different time widths are generated. By adding them in series, the desired gradation level can be achieved with high accuracy.

In Figures 2 and 3, the time width was varied, but the voltage applied to the thermal head was changed by keeping the time width constant.
The current may also be changed. In this case, it is sufficient to prepare a device that changes the voltage (for example, changes the reference voltage of a constant voltage power supply) according to the signal stored in 5.

In either case, voltage, current, or time width changes need only occur simultaneously for all heating elements of the thermal head, so one variable voltage, current source, and variable time width source may be provided.

Fig. 4 shows the printing density characteristics of actual transfer paper.
As a result of applying the present invention to FIG. 4, it was found that when expressing 12 gradations, the number of gradations that can be expressed using the same energy difference is just under 4, but 12 gradations can be expressed accurately, three times as many. I understand.

Furthermore, in contrast to the method of JP-A-57-91283, where the target density deviates by about one gradation, the present invention can express the density almost accurately.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to correct the thermal energy of any thermal transfer paper and the non-linearity of the printing temperature sound, and it is possible to realize accurate printing density and print with high gradation.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the relationship between thermal energy of thermal transfer paper and printing density, Fig. 2 is a block diagram of a circuit showing an embodiment of the present invention, and Fig. 3 is a diagram showing the current waveform achieved by the present invention. FIG. 4, which is a diagram showing an example, is a characteristic diagram of transfer paper showing the effects of the present invention. 1... Line memory, 2... Address counter, 3... Comparator, 4... Level generator, 5...
Non-volatile memory, 6...Switch switch, 7...
Time width generator, 8... Capacitor, 9... Resistor,
10...shift register, 11...latch register, 12...heating element, 13...thermal head.

Claims (1)

[Scope of Claims] 1. In a thermal transfer printer that transfers pigments or dyes from thermal transfer paper using a thermal head, the printing density is divided into equal parts in order to compensate for the non-linearity between the thermal energy of the thermal transfer paper and the printing density. a storage means that stores information such as a current pulse width and a voltage applied to the thermal head corresponding to each difference in thermal energy applied to the thermal head; and means that generates different time widths based on the signals from the storage means. , comprising a gradation level generating means for generating a voltage or current of a gradation level from a low gradation level to a high gradation level or vice versa; 1. A thermal transfer printer characterized in that a voltage or current having a corresponding pulse width is generated based on the pulse width and applied to the thermal head. 2. The thermal transfer printer according to claim 1, characterized in that a nonvolatile memory is used as the storage means. 3. The thermal transfer printer according to claim 1, wherein the number of sets of information such as the pulse width of the current and the voltage applied to the thermal head stored in the storage means is equal to or smaller than the number of gradations. . 4. The thermal transfer printer according to claim 1, wherein the means for generating the time width includes a plurality of resistors and capacitors, and the product value of the resistors and capacitors is changed by a switch to change the output time width.