JP2810490B2 - Heat generation pulse generation method for thermal transfer printer - Google Patents

Description

The present invention relates to a method for generating heat pulses to be supplied to a thermal head of a thermal transfer printer.

(B) Conventional technology For example, the magazine “TV Technology”, September 1989, PP.15 to PP.20
Describes a sublimation type thermal transfer color video printer which controls the amount of sublimation of a sublimation dye to perform gradation control. In such a thermal transfer video printer, density gradation control is performed by controlling a pulse width of a pulse applied to a heating element of a thermal head.

FIG. 4 is an equivalent circuit diagram of a thermal head for performing such pulse width control, and FIG. 5 is a diagram showing the heat generation timing. In FIG. 4, (1) is a power supply line,
(2) is a heating element and (3) is a NAND gate.
The strobe pulse (heating pulse) (stb) shown in FIG. 5 is applied to one input of the ND gate (3), and the other input is the fifth output from the Q output of the D-flip-flop (4). The data signal shown in the figure is applied.

The example shown in FIG. 5 shows a case where four-stage density control is realized, and the 0th gradation uses the white color of the photographic paper (thermal transfer medium) itself. That is, three strobe pulses are always supplied to the NAND gate (3) as shown in FIG. 5 in order to obtain the highest density for one line.
To obtain the 0th gradation, the output (data out) of the D-flip-flop (4) is set to the 0 level.

Then, when printing the first gradation, the NAND gate (3)
From the data out terminal (Q) of the D-flip-flop (4) so that only the first pulse among the three pulses applied to the stb (strobe) terminal (stb) is applied to the heating element. This is performed by outputting a signal. Similarly, when printing the second tone, the first and second stb (strobe) terminals (stb) of the NAND gate (3) are used.
If only the third pulse prints the third gradation,
The first, second and third pulses are applied to the stb terminal (stb) of the NAND gate (3).

Thus, by controlling the application of the three strobe pulses, the density expression of four gradations can be achieved.

Incidentally, the coloring characteristics of the recording paper (thermal transfer media) are as shown in FIG. In the color development characteristics shown in FIG. 6, the vertical axis shows the color density (OD: Optical Density), and the horizontal axis shows the heat generation time (t) of the thermal head. On the other hand, in order to realize equally divided gradation characteristics (density linear characteristics), the graph shown in FIG.
The heat generation time for obtaining the density at each division point is obtained on a graph by dividing the data up to ax equally by (number of gradations-1). FIG. 6 shows a case in which the heat generation time for obtaining four gradations in a density linear manner is obtained. In comparison with the pulse in FIG. 5, the first pulse of the strobe pulse (stb) in FIG. The width is t ₁ in FIG. 6, the second pulse width is t ₂ in FIG. 6, and the third pulse width is t _{3 in} FIG.

Since the control in the printer is performed digitally, the pulse width of the strobe pulse (t ₁ ) (t ₂ ) (t ₃ )
Is set to be a constant multiple of a clock of a certain frequency. That is, the pulse width of the strobe pulse is determined by counting clocks of a predetermined frequency, and FIG. 7 shows the relationship between such a heating pulse and the clock. That is, as shown in FIG. 7, conventionally, (N-1) strobe pulses are generated to realize N gradations, and this (N-1) strobe pulse is generated.
The number of strobe pulses is generated by a single clock.

(C) Problems to be Solved by the Invention By the way, the method of generating a strobe pulse as described above has the following problems.

That is, the pulse width of the strobe pulse representing the first gradation is much longer than the pulse width of the strobe pulse representing the second gradation. In the example of FIG. 7, the strobe pulse representing the first gradation is used. The pulse width is 12 clocks, 2
The pulse width of the strobe pulse indicating the gray scale is 4 clocks, and the pulse width of the strobe pulse indicating the third gray scale is 7 clocks.

When controlling 128 gradations in an actual printer, 1
The pulse width of the strobe pulse representing the gradation is 2000 μs
The second and subsequent gradations are about 100 μs. For this reason,
When the number of bits of the counter for counting the clock is set to 8 bits, 10 μs × 256 = 2560 μs in order to allow 2000 μs to be sufficiently counted. Therefore, the clock cycle must be set to 10 μs. In this case, the accuracy of the pulse after the second gradation is 10 μs, and the pulse width of the pulse after the second gradation is 100 μs, which is considerably rough, and an accurate density cannot be obtained.

For this reason, if the period of the clock is shortened, the accuracy is improved. However, if so, the number of bits of the counter for generating the strobe pulse representing the first gradation increases, and the counter circuit must be enlarged.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to set a pulse width of a strobe pulse to a desired size without deteriorating precision and to generate a strobe pulse with a counter having a small number of bits.

(D) Means for Solving the Problems The present invention is a method for creating a heating pulse for printing a first gradation supplied to a heating element of a thermal head, wherein the heating pulse is generated at a low frequency. A first pulse generated by counting the first clock signal and a second pulse generated by counting a second clock signal having a higher frequency than the clock signal generating the first pulse. It was made to become.

(E) Operation According to the above means, the accuracy of the strobe pulse can be improved without increasing the number of bits of the counter.

(F) Embodiment Hereinafter, an embodiment of the present invention will be described with reference to FIGS.

First, as shown in FIG. 2, simply using two strobe pulses (1-1) and (1-2) having the same pulse width as the strobe pulse for printing the first gradation can reduce the number of bits of the counter. Therefore, it can be seen that a clock (CK) having a short cycle can be used, and the accuracy can be improved.

That is, in the conventional method, (N-1) strobe pulses are used to represent N gray scales. However, in the present invention, basically two (2) strobe pulses are used as strobe pulses for expressing the first gray scale. , And as a result, N gradations can be expressed by N strobe pulses. Normally, the number of gradations is 2 such as 64, 128, etc.
However, if N gradations can be expressed by N strobe pulses, the number of pulses to be applied is a power of 2 such as 64 or 128, so that the circuit can be easily realized.

Therefore, the present invention provides a method for generating a strobe pulse having a more accurate pulse width, as shown in FIG. 1, by using a first strobe pulse (1-1) for printing the first gradation. A relatively low frequency clock signal (CK
1) is generated by counting, and a second strobe pulse (1-2) for printing the first gradation and subsequent strobe pulses (2) and (3) are generated by the first strobe pulse (2). The clock signal (CK2) having a frequency sufficiently higher than the frequency of the clock signal (CK1) for generating 1-1) is counted and generated. More specifically, in the embodiment of FIG. 1, the frequency of the clock signal (CK1) for generating the first strobe pulse (1-1) of the first gradation is set to the case of FIG. 1/2 of the clock (CK)
And the frequency of the clock signal (CK2) for generating the second strobe pulse (1-2) of the first gradation and the subsequent strobe pulses (2) and (3) is set to the The frequency is selected to be twice the frequency of the clock (CK) in the case of FIG.

For example, in order to perform density control by 128 gradation control, the pulse width of the strobe pulse of the first gradation is 2000 μs in total of the widths of the first and second strobe pulses, and the pulse width of the second and subsequent gradations is respectively. If the counter that counts the clock signal in about 100 μs is 8 bits, if the period of the first clock signal (CK1) is set to 10 μs and the period of the second clock signal (CK2) is set to 0.5 μs, (Strobe pulse) …… 2000μs = 10μs × 19
0 + 0.5 μs × 200 (pulses after the second strobe pulse) 100 μs
= 0.5 μs × 200, and the accuracy of the pulse width of the strobe pulse can be increased to about 0.5 μs without increasing the number of bits of the counter. As a result, accurate gradation reproduction is possible.
Particularly when realizing a high number of gradations, the pulse width required for printing the first gradation is almost unchanged at about 2000 μs.
The pulse width after the second gradation becomes even shorter (for example, 25
(6 gradations are about half that of 128 gradations), so the usefulness of the present invention is extremely high.

FIG. 3 is a block diagram of a main part of a video printer embodying the present invention, which will be described in comparison with the timing chart of FIG. Microcomputer (microcomputer)
Reference numeral 5 pre-writes gradation table data (clock count number) in the gradation table memory (6). The microcomputer (5) also supplies a one-line printing start command to the address generator (7) and the switching timing signal generation circuit (8). When the address generator (7) receives the printing start command, the address generator (7) receives the address. Is cleared, and then incremented for each pulse. The address signal from the address generator (7) is applied to the gradation table memory (6), and the gradation data [4] specified by the address signal is supplied.
Clock count represented by bits (0 to 1
5) "] is supplied to the counter (9).

On the other hand, when the microcomputer (5) receives the one-line printing start command, the switching timing signal generation circuit (8) firstly switches the first switch (10) to the first clock generation circuit (11).
And the first clock signal (CK1) is supplied to the counter (9).
Is controlled to be supplied. At this time, since the counter (9) counts only five first clock signals (CK1) according to the gradation table data, the first strobe pulse (1-1) for expressing the first gradation is generated. Is done.

The switching timing signal generating circuit (8)
After the generation of the first strobe pulse (1-1) is completed, a second clock signal generation circuit (12) is supplied to the changeover switch (10).
And the second clock signal (CK2) is supplied to the counter (9).
Is controlled to be supplied. At this time, the counter (9) counts four second clock signals (CK2) based on the gradation table data of the next address, and expresses the second strobe pulse (CLK) for expressing the first gradation. 1-2) is generated. After the generation of the second strobe pulse (1-2), the counter (9) counts eight second clock signals (CK2) based on the gradation table data of the next address, and counts the second clock signal (CK2). Is generated. And
After the generation of the strobe pulse (2), the counter (9) counts only 14 second clock signals (CK2) based on the gradation table data of the next address to express the third gradation. Is generated. In this manner, the counter (9) operates based on the grayscale table data to generate the first clock signal (CK).
1) and the second clock signal (CK2) are counted and a strobe pulse (1-1) (1-2) as shown in FIG.
(2) and (3) are generated, and these are applied to the stb terminal of the NAND gate (3) of the thermal head drive circuit shown in FIG.

(G) Effects of the Invention As described above, according to the present invention, the pulse width of the strobe pulse can be set to a desired size without lowering the accuracy,
In addition, a strobe pulse can be generated by a counter having a small number of bits.

[Brief description of the drawings]

FIG. 1 is a diagram showing a timing chart for explaining the method of generating heat pulses of the present invention, FIG. 2 is a diagram showing a timing chart for explaining the basic principle of the method of generating heat pulses of the present invention, FIG. FIG. 4 is a block diagram of a main part of a video printer in which the method of the present invention is implemented, FIG. 4 is a diagram showing a driving circuit of a thermal head, FIG. 5 is a diagram showing a heat generation timing generated thereby, and FIG. FIG. 7 is a diagram showing a coloring characteristic, and FIG. 7 is a diagram showing a timing chart for explaining a conventional method of generating a heating pulse. (2): Heating element of thermal head; (9): counter; (10): changeover switch; (11): first clock generation circuit; (12): second clock generation circuit.

Claims (1)

(57) [Claims] 1. A method for generating a heating pulse for printing a first gradation supplied to a heating element of a thermal head, wherein the heating pulse is generated by counting a first clock signal having a low frequency. Heat generation of a thermal transfer printer, comprising: a first pulse to be generated; and a second pulse generated by counting a second clock signal having a higher frequency than a clock signal for generating the first pulse. Pulse creation method.