JPH0630894B2 - Thermal printer - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal printer using a thermal head (thermal printer), and in particular, sets multi-level halftone densities from a base paper density of a medium to a maximum density. If you want to
By adjusting the power supply voltage of the thermal head and the driving time mutually, and controlling the thermal energy applied to the head per unit time, the image as the print result can be switched sharply or mildly. is there.

(Prior Art) Conventionally, when a printer is configured using a thermal head, a printing method has been performed in which a heating element of 1 dot line is provided for a high speed printer and 1 dot line is driven simultaneously. However, in the case of obtaining a print result with a very low resolution such as a copy output of a television screen, since the screen can be small and the device can be small, one dot line can be time-divided as a method of reducing the power supply capacity of the printer. The driving method is adopted. Further, a gradation printing method is adopted in which time-division driving is performed and a halftone image is obtained.

FIG. 4 is a diagram showing a time-division driving circuit in a thermal printer for performing such time-division driving and gradation printing, and FIG. 5 is a time chart of the time-division driving shown in FIG.
FIG. 6 is a diagram for explaining the gradation printing operation.

In FIG. 4, the heating element 1 (thermal head) in which the heating elements are connected in cascade corresponding to one dot line is composed of eight blocks for convenience, and each block is composed of four heating elements. The configuration of each block is
Since they are the same, the description is limited to the block 1, and the respective heating elements of the block 1 are sequentially arranged from the left toward the drawing.
Number them as 11,12,13,14. The shift register drive (hereinafter abbreviated as shift register) is connected in cascade by the same number as the number of blocks, and sequentially shifts the input print data. The power supply V supplies a drive voltage to each heating element.

Next, the operations of time division driving and gradation printing will be described with reference to FIGS. 5 and 6.

Here, in the thermal printer shown in FIG. 4, it is assumed that the gradation density level is 16 gradations in total, and the gradation density is 0.
Is the base paper density and gradation density 15 is the maximum density, and the heating elements 11 to 14 of the block 1 are provided with gradation densities of 8, 10, 12, and 14, respectively.

As shown in FIG. 5, the time-division drive method for the heating element 1 is performed by selecting blocks 1 to 8 in order.
The dot line is driven for 8 hours, and then one line of paper is supplied.

First, the shift register 21 of the block 1 is supplied with the gradation print data of the gradation degree 15 from the control unit (not shown) as data input within the period of the data transfer timing t15 shown in FIG. Here, the heating elements 11 to 14 have a gradation of 15
Since it is less than, the data is in the order from 14 to 11
When the data input is completed, the strobe signal (FIG. 4) of the block 1 from the control section is turned on, and the block 1 is selected for the time-division driving shown in FIG. At the same time, the control section generates a γ pulse (FIG. 6) based on a time table stored in a ROM (not shown), and according to this γ pulse, turns on the enable signal of the block 1 at the time of γ15, and thereafter The ON state is maintained until the selection of 1 is completed, where the γ pulse is corrected at a timing according to the γ characteristic that is generally well known when performing gradation printing to obtain a halftone image. Further, the transfer timing of the gradation print data shown in FIG. 6 is also performed according to the γ characteristic.

In this way, when the block 1 is enabled, a voltage is applied to the shift register 21 from the power supply V, but since the gradation print data is all "0", the shift register 2
1, that is, the heating elements 11 to 14 are not driven.

Next, in the data transfer period t14, the gradation print data with the gradation of 14 is input to the shift register 21. At this time, since the heating element 14 has the gradation level of 14, the gradation print data is from 14 to 11.
The order is "1, 0, 0, 0". In this case, since the shift register 21 has already been enabled by the control unit, only the heating element 14 is driven with the thermal energy of the density difference between the gradation 14 and the gradation 13. In this way, the transfer timing (t1
5, t14, ..., t2, t1) are input to the shift register 21 and only when the gradation print data is “1”, the shift register
21 is driven. As a result, as shown in FIG. 6, a driving voltage is continuously applied to each of the heating elements 11 to 14 for the time width corresponding to the gradation degree (8, 10, 12, 14), and the gradation density of 8, 10,12,14
Will be obtained on the thermal paper.

When the printing of the block 1 is completed by the above operation, the control unit turns off the enable signal. Then, similarly to the case of the block 1, the driving of the blocks 2 to 8 is performed and the printing of one dot line is completed.

(Problems to be Solved by the Invention) However, the gradation printing method in the thermal printer has the following problems.

As mentioned above, in time-division drive of each block,
When the block 1 is selected, the enable signal is uniquely turned on at the time of γ15 by the command of the control unit, and during the transfer period of the gradation print data (t15, t14, ..., t1, in FIG. 6). t
1) Its state is continuously maintained. For this reason, the applied voltage time becomes longer during the transfer period than the applied voltage time corresponding to the original gradation. This means that the previously transferred gradation print data (in the case of "1") is printed even during the current gradation print data transfer period. Further, as described above, since the ON state of the enable signal is continuously turned ON at the time of γ15, the heat energy supplied to each heating element per unit time is equal to the time corresponding to the gradation density. It is always constant due to the product of the drive voltage. As a result, it was not possible to obtain the gradation density at a smaller pitch.

Therefore, the present invention solves the above-mentioned problems, and by mutually varying the driving voltage and the driving time of the thermal head,
An object of the present invention is to provide a thermal printer which can control a thermal energy applied to a thermal head per unit time and can obtain a wider halftone image quality.

(Means for Solving Problems) In order to solve the problems of the prior art, the present invention comprises a thermal printer including the following means.

A thermal printer according to the present invention includes a thermal head including a plurality of heating elements, a variable unit that supplies a drive voltage from a power source to the thermal head and that can selectively set the value of the drive voltage, and the variable unit. An analog-digital conversion means for converting the value of the drive voltage into a digital value, and a storage means including a plurality of time tables respectively storing time interval data for intermittently enabling the heating elements, The time interval data is read from the time table of the storage means corresponding to the value of the driving voltage from the analog / digital conversion means at a predetermined timing for each line printing, and gradation printing is performed based on the time interval data. A control unit that controls the enable time of the thermal head for each data to be written, During interval data for gradation printing γ
It is characterized in that it has a value corresponding to the characteristic, and that the value of the driving voltage has a value corresponding to the image quality to be gradation printed.

(Operation) According to the present invention, since the thermal printer is configured as described above, each technical means operates as follows.

When driving the thermal printer, the control unit first outputs a plurality of gradation print data for one line to the thermal head at a predetermined timing. At the same time, the control unit selects a time table corresponding to the drive voltage from the variable unit from the storage unit, and enables the thermal head according to the selected time table. In other words, the enable time of the thermal head is changed corresponding to the drive voltage from the variable means, and the enable is performed for each gradation print data that is output. Therefore, the drive time of each heating element of the thermal head is controlled by the drive voltage from the variable means for each gradation print data. Therefore, for example, even when printing with the same gradation density, by lowering the applied voltage for a long application time or increasing the applied voltage for a short application time, the heat per unit time applied to the heating element is reduced. The energy can be controlled, and the print image quality can be selected to be clear (sharp) or unclear (mild) by varying the thermal energy per unit time, and the gradation image can have a width. Therefore, the problems of the conventional technology can be solved.

(Example) Hereinafter, one example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a time-division drive circuit diagram in a thermal printer according to an embodiment of the invention, FIG. 2 is a time chart showing the time-division drive in FIG. 1, and FIG. 3 is a diagram for explaining a gradation printing operation. . In FIG. 1, the same components as those in FIG. 4 used in the conventional description are designated by the same reference numerals, and the heating element 1 is divided into blocks 1 to 8 and driven as in the conventional case. I shall. Regulator 3 in FIG.
Outputs a constant voltage generated based on the setting of the volume (variable resistor) 5 connected between the control terminal of the regulator 3 and the negative terminal of the power source V for supplying the voltage to each heating element of each block. The AD converter 4 digitally converts the supplied voltage and outputs the converted data to the control unit 6. The control unit 6 controls the enable signal and the strobe signal and outputs the gradation print data to the shift register 21. The ROM 7 stores a plurality of time tables of time interval data, that is, γ pulse time tables, which are time interval data for determining the time intervals at which the enable signal is intermittently turned on, that is, the enable signal is turned on.

Hereinafter, the operations of the time-divisional driving and the gradation printing according to the present embodiment will be described with reference to FIGS. 2 and 3. For the heating elements 11 to 14 of the block 1, the gradation density is 8,
We shall give 10,12,14. First, the gradation print data is supplied from the control unit 6 to the shift register 21 as data input within the data transfer period t15. Since the heating elements 11 to 14 do not have the gradation level 15, the data to each heating element 11 to 14 is 14
It is 0, 0, 0, 0 in the order from 11 to 11. When the input of the data is completed, the strobe signal is turned on by the command from the control unit 6, and the selection for driving the block 1 is performed as shown in FIG. It is done every time. Further, the control unit 6 corresponds to the drive voltage of the power supply V, that is, the conversion data of the AD converter 4 from the time table of the plurality of γ pulses stored in the ROM 7 (the time intervals at which the enable signal is turned on are different). A time table of γ pulses is selected, a γ pulse γ ₁₅ is generated according to the time interval data of this time table, the enable signal is turned on according to this pulse, and turned off at the start of data transfer t ₁₄ (see FIG. 3). .

The control unit 6 controls the time width (RO
(Stored in M7) only, the enable signal is held in the ON state before the next gradation print data is input (t14 in Fig. 3).
To turn it off. In this way, the shift register 21
Is enabled, the output voltage of the regulator 3 is applied to the shift register 21, but since the gradation print data is all "0", the shift register 21, that is, each heating element.
11-14 are not driven.

Next, within the data transfer period t14 (FIG. 3), the gradation print data is input to the shift register 21, but the heating element 14 has the gradation 14 and the other heating elements 11 to 13 have the gradation 14. Therefore, the input data is “1,
When the data transfer period t14 ends, the control unit 6 turns on the strobe signal of the block 1 to select the block 1 again, and when the enable signal is γ14 in the same manner as described above. In this case, since the gradation print data of the heating element 14 is “1”, the shift register 21 drives to close the power supply loop of the heating element 14 and drive only the heating element 14 (heating element 11). ~13
Is not driven).

At the next data transfer t13, since the gradation print data is the same, only the heating element 14 is driven.

At the time of data transfer of gradation 12, since the heating element 13 has the gradation 12, the gradation print data is in the order of 14 to 11 as "1, 1,
0, 0 ″, and the heating element 13 is driven in addition to the heating element 14.

The gradation print data transferred by repeating the above operation is as shown in Table 1.

In this way, the gradation printing of the block 1 is performed, but the enable signal is intermittently turned on at the end of each data transfer period, so that the heating elements 11 to 14 are set to the gradation printing as shown in FIG. It is driven intermittently for each gradation print data according to the character data.

The time chart of the power supply voltage in FIG. 2 shows an example in which the drive voltage of the power supply V is changed by the volume 5 at the time of selecting the blocks 2 and 3. In this case, the control unit 6 corresponds to the conversion data of the AD converter 4.
The γ pulse is changed according to the time table of ROM7. That is, by this, the time interval of the ON state of the enable signal is changed, and the voltage application time to each heating element is changed. Therefore, even when printing with the same gradation density, the thermal energy per unit time can be changed by decreasing the applied voltage for a long application time or increasing the applied voltage for a short application time. You can

Here, the voltage application time for driving the heating element and the relationship between the applied voltage and the print image quality will be described.

The state of heat transfer between the thermal head and the thermal paper is expressed as a function of time. However, when a voltage lower than the reference temperature and longer than the reference time is applied to the thermal head, the thermal paper The color is widely spread around the dots, resulting in a mild image quality with an unclear outline as an entire image. This is generally the case when the thermal energy per unit time is small. On the contrary, if you drive the thermal head at a temperature higher than the reference temperature for a shorter time than the reference time,
The color of the thermal paper does not spread much around the dots,
The entire image appears as a sharp image with sharp edges. This is generally the case when the thermal energy per unit time is high.

Therefore, according to the present embodiment, the time width of the enable signal, that is, the drive time of the heating element is changed for each gradation print data by changing the drive voltage of the power supply V by the volume 5 shown in FIG. Therefore, even with dot printing with the same gradation, the image quality can be switched to mild or sharp, and as a result, the halftone image can be made wider.

(Effects of the Invention) As described in detail above, according to the present invention, by intermittently enabling the thermal head according to the driving voltage of the thermal head, the driving voltage of the thermal head and the driving time of the thermal head are mutually exchanged. The heat energy of each heating element can be controlled to be variable. as a result,
Even for printing with the same gradation, you can select a sheer image quality with high heat energy per unit time or a mild image quality with low heat energy. . Therefore, it is possible to print out a screen that does not look very natural, such as a television screen, by selecting a mild image quality so that it looks natural. As described above, according to the present invention, a halftone image can be controlled with a finer pitch density, and the applicable range of the thermal printer can be increased.

[Brief description of drawings]

FIG. 1 is a time-division drive circuit diagram in a thermal printer according to an embodiment of the present invention, FIG. 2 is a time-division drive time chart according to the present embodiment, and FIG. 3 is an operation explanatory diagram of gradation printing according to the present embodiment. FIG. 4 is a time-division drive circuit diagram in the conventional thermal printer, FIG. 5 is a time chart of the conventional time-division drive, and FIG. 6 is an operation explanatory diagram of conventional gradation printing. 1 ... Heating element, 3 ... Regulator, 4 ... AD converter, 5 ... Volume, 6 ... Control section, 7 ... ROM, 11-14 ... Heating element, 21-27 ... Shift register.

Claims (1)

[Claims] 1. A thermal head comprising a plurality of heating elements, a variable means for supplying a drive voltage from a power source to the thermal head and capable of selectively setting a value of the drive voltage, and a drive from the variable means. An analog / digital conversion means for converting a voltage value into a digital value, a storage means including a plurality of time tables respectively storing time interval data for intermittently enabling the heating elements, and one line printing At each predetermined timing, the time interval data is read from the time table of the storage means corresponding to the value of the driving voltage from the analog / digital conversion means, and each data to be gradation printed based on the time interval data. And a control unit for controlling the enable time of the thermal head regarding the γ for character
A thermal printer having a value corresponding to a characteristic, and a value of the driving voltage having a value corresponding to an image quality to be gradation printed.