JPH068506A - Thermal printer - Google Patents

Abstract

PURPOSE:To drastically enhance thermal efficiency in a heat sensitive printer and also to shorten printing time. CONSTITUTION:An unheating-time control circuit 15 is equipped with a table wherein unheating-time set for the respective gradations, namely the unheating- time tn from the fall of the strobe pulse STBn of the n-th gradation to the rise of the strobe pulse STBn+1 of the next (n+1)-th gradation is written therein. When the value representing the gradation for the printing to be made is given from a gradation counter 6, the unheating-time for the gradation is read out from the table. A transfer finish signal is given from a data transfer control circuit 3. Timing is started from the time when the strobe pulse STB has become to OFF from ON. When the unheating-time read out from the table elapses, a heating permission signal is given to a heating pulse control circuit 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal printer.

[0002]

2. Description of the Related Art Conventionally, there is known a thermal printer which generates strobe pulses for the number of gradations of image data, and heats a heating element for the time of the strobe pulse to express gradation. 59-17954,
(See JP-A-61-277279). The structure and operation are as follows. Here, the thermal printer is not limited to a printer that heats and prints thermal paper, but is a generic term for a printer that uses a thermal head such as a sublimation transfer type printer, and printing includes printing.

FIG. 4 is a diagram showing a schematic structure of a conventional thermal printer, in which 1 is a line memory, 2 is a comparator,
3 is a data transfer control circuit, 4 is a heating pulse control circuit, 5
Is an address counter, 6 is a gradation counter, 7 is a look-up table (hereinafter referred to as LUT), 8 is a thermal head, 9 is a shift register, 10 is a latch circuit, 11 is a drive circuit, and 12 is a heating element.

Image data for one line read from a frame memory (not shown) is written in the line memory 1. In this state, the data transfer control circuit 3
Gives the address at which the first pixel is written to the address counter 5 in order to transfer the image data of the first pixel of the line from the line memory 1 to the comparator 2. This address is given from the address counter 5 to the line memory 1, and the line memory 1
The image data of the first pixel is transferred to the comparator 2. At this time, the gradation transfer counter 6 has the data transfer control circuit 3
From the gradation counter 6, a value indicating the first gradation, for example, 1 _H (H represents a hexadecimal number. , As well). At this time, the signal 1 _H indicating the first gradation output from the gradation counter 6 is also given to the LUT 7. The LUT 7 stores the on-time of the strobe pulse STB for each gray scale, and the strobe pulse S set to the gray scale with the value indicating the gray scale output from the gray scale counter 6 as an input address.
The on time of TB is read. Then, the ON time of the strobe pulse STB read from the LUT 7 is given to the heating pulse control circuit 4. Therefore, in this case, the heating pulse control circuit 4 is given the ON time of the strobe pulse STB set for the first gradation.

The comparator 2 compares the image data with the gradation value given by the gradation counter 6, and when the value of the image data is equal to or larger than the gradation value given by the gradation counter 6. Outputs "1", and otherwise outputs "0". The output of the comparator 2 is written in the shift register 9 of the thermal head 8 by the clock output from the data transfer control circuit 3.

When the processing for the first gradation of the first pixel is completed as described above, the data transfer control circuit 3
Gives the next address to the address counter 5. As a result, the second line of the line is read from the line memory 1.
The image data of the th pixel is transferred to the comparator 2 and compared with the value indicating the first gradation. Then, when the value of the image data is equal to or larger than the value indicating the first gradation, “1” is
Otherwise, "0" is output from the comparator 2 and written in the shift register 9 by the clock from the data transfer control circuit 3. At this time, the value of the first pixel previously written in the shift register 9 is shifted to the next address.

The data transfer control circuit 3 repeats the above processing up to the last pixel of the line. When the above processing is completed for all pixels, the data transfer control circuit 3 gives a heating permission signal to the heating pulse control circuit 4.
As a result, the heating pulse control circuit 4 causes the latch circuit 10
To the latch circuit to temporarily transfer the data written in the shift register 9 to the latch circuit.
Further, the strobe pulse STB is turned on for the ON time given from the LUT 7 and given to the drive circuit 11. As a result, the heating element 12 corresponding to the pixel whose data supplied from the latch circuit 10 is "1" is heated while the strobe pulse STB is on, and the first gradation printing is performed.

After that, when the predetermined on-time elapses, the heating pulse control circuit 4 turns off the strobe pulse STB and gives a transfer permission signal to the data transfer control circuit 3. As a result, the data transfer control circuit 3 next provides the gradation counter 6 with gradation data indicating the second gradation, for example, 2 _H , and the image data is sequentially compared from the first pixel to the comparator 2 as described above. Transfer to. After that, the same operation as described above is performed, and the second gradation printing of the line is performed.

When the above operation is repeated a predetermined number of times and printing of the line is completed, the image data of the next one line is written in the line memory 1 and the above operation is performed. The configuration and operation shown in FIG.
It is obvious to those skilled in the art that it can be realized by hardware or software.

FIG. 5 is a diagram showing an example of the strobe pulse STB in the case where one pixel is expressed by 128 gradations. The ON time τ ₀ of the first gradation, the ON time τ ₁ of the second gradation, …, No.
The on time τ ₁₂₈ of the 128th gradation is the characteristics of the printing paper,
It is set in order to obtain a predetermined γ characteristic in consideration of the characteristics of the ink used and the characteristics of the thermal head 8, and is written in the LUT 7.

[0011]

By the way, between the falling edge of the strobe pulse STB and the falling edge of the next strobe pulse, there is a non-heating time, that is, the time during which all the heating elements 12 are not heated is about 10 to 20 μsec. Within this time, the image data is transferred from the line memory 1 to the comparator 2, the comparison process is performed by the comparator 2, the on-time is fetched from the LUT 7, and the output of the comparator 2 is written to the shift register 9. Then, processing such as data transfer from the shift register 9 to the latch circuit 10 is performed. However, this non-heating time is not set intentionally, and as a result, not only the printing time becomes unnecessarily long, but also the heat generated by the heating element 12 is not effectively used. . In other words, in the conventional case, since all the non-heating time is about 10 to 20 μsec, the heat is not used effectively and the color development is not good because it is cooled in this non-heating time immediately after the start of printing. .

On the contrary, the association of the image data from the line memory 1 to the comparator 2, the comparison processing in the comparator 2, the taking of the ON time from the LUT 7, the writing of the output of the comparator 2 into the shift register 9 and the shift Register 9 to latch circuit 1
The circuit is configured to perform high-speed processing such as data transfer to 0, and the head will overheat even if the non-heating time is shortened, causing damage to the surface of the thermal paper or the like and causing surface roughness. However, the image quality is deteriorated.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a thermal printer which can greatly improve the thermal efficiency and can shorten the printing time.

[0014]

In order to achieve the above object, the thermal printer of the present invention generates a number of strobe pulses corresponding to the gradation of image data, and heats the heating elements only for the time of the strobe pulse. A thermal printer that performs gradation expression by generating heat is characterized by including non-heating time control means for controlling the non-heating time between strobe pulses.

[0015]

The non-heating time control means controls the non-heating time between the strobe pulse and the next strobe pulse. Although the mode of this control is arbitrary, it is possible to control the non-heating time to be shorter than before just after the start of printing, and according to this, the cooling in the non-heating time can be minimized. The heat can be effectively used, and the time until color development can be shortened. Also, the printing time can be shortened by shortening the non-heating time.

[0016]

Embodiments will be described below with reference to the drawings.
FIG. 1 is a diagram showing the configuration of an embodiment of a thermal printer according to the present invention, in which 15 is a non-heating time control circuit.
In addition, in FIG. 1, the same components as those in FIG. 4 are denoted by the same reference numerals, and overlapping description will be omitted.

As shown in FIG. 2, the non-heating time control circuit 15 controls the non-heating time set for each gradation, that is, the nth time.
The falling of the strobe pulse STB _n gradation on the next (n + 1) non-heating time t _n to the rising of the gray level of the strobe pulse STB n + ₁ is provided with a table written gradation counter When a value indicating the gradation to be printed this time is given from 6, the non-heating time for the gradation is read from the table. Then, when the transfer end signal is given from the data transfer control circuit 3 and the strobe pulse STB is turned from ON to OFF, the clocking is started, and when the non-heating time read from the table elapses, the heating pulse control circuit 4 is notified. And give a heating permission signal. As a result, the printing operation for the next gradation is performed. The non-heating time control circuit 15 can be configured by hardware using an appropriate logic circuit or the like, or can be configured to operate by software using a microprocessor and its peripheral circuits. Is.

Here, the non-heating time can be set arbitrarily, but it is necessary to set not only the printing time can be shortened but also a predetermined maximum density can be printed and so-called surface roughness does not occur. Therefore, the non-heating time is set to be short in the first half of the strobe pulse, so that the heat can be effectively used to shorten the time until color development, and after that, the time can be appropriately cooled to prevent surface roughness. Good to do.

It is needless to say that this non-heating time can be set to an optimum non-heating time for each gradation by experiments or the like. However, according to the experiments of the inventor, when the number of reproduced gradations is 256 gradations, , The non-heating time from the 1st gradation to the 192nd to 224th
It has been confirmed that when the gradation is set to 1 μsec and after that to 20 μsec, it is possible to print at a higher speed than before without causing surface roughness.

The following is a specific comparison of the high speed with the conventional one. Now, the reproduction gradation number is 256 gradations,
Assuming that the number of lines on one screen is 1280 lines and monochrome printing is performed, in the conventional thermal printer, the entire non-heating time is 20 μsec. In the thermal printer according to the present invention, the non-heating time is from the first gradation to the 192nd floor. Assuming that 1 μsec is set up to the start and 20 μsec after that, the thermal printer according to the present invention can shorten 3.6 msec in one line and 4.7 sec in one screen. In the case of monochrome printing as described above, when sublimation transfer type printer is used to perform color printing with three colors of yellow (Y), magenta (M) and cyan (C), it is shortened by 14 seconds compared with the conventional method. can do.

Although one embodiment of the present invention has been described above, it is obvious to those skilled in the art that the present invention is not limited to the above embodiment and various modifications can be made.

[0022]

As is apparent from the above description, in the conventional thermal printer, the temperature control is performed only by the on time of the strobe pulse, so that both the rise of the temperature of the heating element and the heat retention after the rise are made compatible. However, it was very difficult to print at high speed. However, according to the present invention, since the temperature control is performed both during the strobe pulse ON time and during the non-heating time, as shown in FIG. In addition to being faster, the temperature can be maintained substantially constant after rising, and thus both high speed and surface roughness can be satisfied.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an exemplary embodiment of the present invention.

FIG. 2 is a diagram showing an example of the structure of a table that determines a non-heating time.

FIG. 3 is a diagram for explaining the effect of the present invention.

FIG. 4 is a diagram showing a configuration example of a conventional thermal printer.

FIG. 5 is a diagram showing an example of a strobe pulse.

[Explanation of symbols]

1 ... Line memory, 2 ... Comparator, 3 ... Data transfer control circuit, 4 ... Heating pulse control circuit, 5 ... Address counter,
6 ... gradation counter, 7 ... LUT, 8 ... thermal head,
9 ... Shift register, 10 ... Latch circuit, 11 ... Drive circuit, 12 ... Heating element, 15 ... Non-heating time control circuit.

Claims (1)

[Claims] 1. A thermal printer, which produces a gradation by generating a number of strobe pulses corresponding to the gradation of image data and heating a heating element for the time of the strobe pulse, in a non-heating mode between strobe pulses. A thermal printer comprising a non-heating time control means for controlling time.