JPH06340105A - Driving of thermal head - Google Patents

Abstract

PURPOSE:To reduce the white stripes generated between respective groups when the heat generating periods of the groups are perfectly driven in a time sharing manner and to perform high-degree printing while reducing the max. current consumption. CONSTITUTION:The current supply start times of adjacent groups are almost delayed by the time calculated by dividing the printing cycle wherein the heat generating periods and cooling periods of heating resistors are added by the number of the divided groups and the heat generating periods of three or more continuous groups overlap timewise with each other at the time of high density printing. Further, the respective groups are driven by a main pulse continuously generating heat and a plurality of dispersion pulses alternately performing extremely short-time cooling and heating and the adjacent groups are prevented from timewise overlapping with each other in the generation of heat due to the dispersion pulses.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving method for a line type thermal head having a plurality of heating resistors arranged in a line.

[0002]

2. Description of the Related Art Conventionally, a line type thermal head is divided into a plurality of groups, and after the heat generation of the first group is completed, the heat generation of the second group is started, and after the heat generation of the second group is started, the heat generation of the third group is started. A driving method of driving by division is known.

FIG. 6 is a timing chart showing an example of this driving method. In the figure, D is print data for serially transferring print data for one line of the line type thermal head, and transfers print data for one line in synchronization with a transfer clock signal (not shown) during a period td in the drawing. I do. L is a latch signal for latching the transferred print data for one line to the in-head drive circuit.

This driving method is an example in which the line type thermal head is divided into eight groups, and STB1 to STB8 are strobe signals for permitting heat generation in each group. The current consumption I at the bottom of the figure shows the current flowing through the thermal head when solid black printing is performed, and the current flowing when all the resistors in one group generate heat is Ib. When printing is performed with this driving method, the temperature rise of the heating resistors at both ends in the group becomes lower than that in the central part of the group, so the print density decreases and the print dot diameter becomes narrower, so there is a gap between the groups. There is a problem that white stripes occur. Further, since the printing cycle for one line requires a time which is a multiple of the heat generation period T required for solid black printing, it is difficult to increase the speed.

As a method of solving these problems, Japanese Patent Publication No. 6250011 discloses a rear part of the heat generation time of the first group, a front part of the heat generation of the second group, a rear part of the heat generation time of the second group and a third group. A driving method has been proposed in which the heat generating front portion and the heat generating front portion are temporally overlapped with each other. A timing chart of this driving method is shown in FIG.

By driving each heating element as shown in the timing chart of FIG. 7, the time taken for the temperature of the heating resistor to drop at the inner end of the group is shortened, and white lines in each group are reduced. You can do it.

However, the drive circuit described in the above prior art has two groups of shift registers and latch circuits prepared, and the latch signals L1 and L2 are alternately used as shown in FIG. In the example divided into 8 groups as described above, when the heat generation time required for solid black printing is T, the printing cycle cannot be shorter than 4T.

[0008]

SUMMARY OF THE INVENTION According to the present invention, white stripes generated between groups when the heat generation period of each group shown in the above-mentioned prior art is completely time-division driven, and the printing speed is slow. In addition, in the driving method according to Japanese Patent Publication No. 62-50011, white lines between groups can be reduced.
The first purpose is to further reduce the white stripes between the groups and to perform high-level printing, and the second purpose is the first purpose. The objective is to reduce the maximum current consumption while achieving it.

[0009]

SUMMARY OF THE INVENTION The present invention is a thermal head in which a plurality of heating resistors of a line type thermal head are set as one group and all the heating resistors are divided into a plurality of groups of three or more, and each group is sequentially heated. In the driving method, in order to solve the above problems, the energization start time of the adjacent groups is delayed substantially by the time divided by the number of groups obtained by dividing the printing cycle of the heating period of the heating resistor and the cooling period, It is characterized in that during high-density printing, three or more continuous heat generation periods overlap in time.

Further, according to the present invention, the heat generation of each group is driven by a main pulse which continuously generates heat and a plurality of dispersion pulses which alternately perform cooling and heat generation for an extremely short time, and the dispersion pulses of adjacent groups are driven. It is designed so that fever does not overlap with time.

[0011]

By driving in this way, the white stripes generated between the divided groups can be further reduced, and the printing cycle for one line can be the heat generation time and cooling time required for solid black printing, and high speed. Printing is possible.

Further, in the driving using the dispersed pulse,
The maximum current consumption can be reduced by preventing the heat generation in the dispersed pulses of the adjacent groups from overlapping in time.

[0013]

Embodiments of the present invention will be described below with reference to FIGS.

FIG. 1 is a timing chart of an embodiment according to the present invention, in which the second line from the start of heat generation on the first line to the second line.
FIG. 2 shows a block diagram of the thermal head until the end of heat generation on the line.

In FIG. 2, R1 to R256 are 256 heating resistors, R1 to R32 are the first group, and R33 to R33.
The R64 is divided into up to the eighth group with 32 heating elements as one group like the second group. STB1 is a strobe signal that permits the application of the head voltage Vh to the heating resistors of the first group according to the print data, and is prepared up to STB8. Din is a data input terminal for serially inputting print data D for one line in synchronization with a print data transfer clock signal (not shown), and the data D enters shift registers SR1 to SR8. The print data input to the shift register is held in the latch registers LR1 to LR8 by the input of the latch signal L. When the print data held in the latch register is H (print), the head voltage Vh is supplied to the corresponding heating resistor for the time when the strobe signal for the group is H, and heat is generated.

The operation will be described with reference to the timing chart of FIG. 1. The print data D for one line is serially transferred in the period of time td, and then the print data is held in the latch register by the latch signal L. Strobe signal is H
For a certain period, the corresponding heating resistor generates heat.

In FIG. 1, it takes a time T to obtain a print dot of the highest density, and since the print data in one data transfer is used for heat generation of 1 / 4T of time, the highest density is printed. To do this, H is transferred with the transfer data four times.

Further, it is assumed that the cooling time of the heat generating resistor requires the time T as in the case of the heat generation, that is, the printing cycle is a minimum time of 2T. In order to realize this print cycle, the heat generation start time of each group is delayed by a time obtained by dividing the print cycle 2T by the number of groups, that is, 1 / 4T, so that each group prints at the minimum print cycle 2T. It is possible, and as for the white stripes between the groups, of the heat generation time T, the time of 3/4 T overlaps with the heat generation of the adjacent group in time, so that the temperature drop at the group end is prevented,
As a result, white lines can be reduced.

FIG. 3 is a timing chart showing the second embodiment of the present invention, showing before and after the heat generation period of the third group on the first line. This embodiment uses a strobe signal in which a main pulse that continuously energizes the heating resistor during the heat generation period and a dispersed pulse that repeats cooling and heat generation for an extremely short time are combined, and the strobe signals are adjacent to each other as in all the embodiments. The fever start time of the group was delayed. In order to perform high-speed printing in a thermal printer, it is effective to set the power applied to the heating resistor to a high value and raise the temperature of the heating element rapidly, but if this high power is continuously supplied, it is a sublimation type. In the case of the image receiving paper used in the thermal transfer system, the surface of the image receiving paper is matted and the image density is lowered, and the reliability of the thermal head is lowered. Therefore, the method of supplying the dispersed pulse in which the temperature is sharply raised by the main pulse which continuously supplies relatively high power and then the energization time is thinned so as not to raise the temperature to a higher temperature than necessary is effective for speeding up.

The strobe signal shown in FIG.
As in B3, a continuous main pulse with a time of 15t and 31 dispersed pulses with a cooling and heat generation time of 1 / 2t (1/2 duty heat generation) each are output, and 32 gradations can be expressed in one dot. I am trying. That is, if the time required for heat generation is 46 t, the time required for cooling is about 30 t, and the delay time of the heat generation start time of adjacent groups is 10 t as shown in the figure, the printing cycle is 80 t, and the internal heat generation period 4
6t, cooling period 34t. The current consumption I shown at the bottom of the figure is the total current flowing through the thermal head when solid black (maximum density) printing is performed, and the current consumed by one group is Ib. Therefore, if all of the heating resistors of this thermal head are to be made to generate heat collectively without using this embodiment, a current of 8 Ib will be consumed. In this embodiment, 5 / The maximum current consumption of 8 will suffice.

FIG. 4 is a timing chart showing a third embodiment for the purpose of improving the timing shown in FIG. 3 (second embodiment) and further reducing the maximum current consumption. This FIG. 4 also shows the state of the first line similarly to FIG. The strobe signal is the same as in the previous embodiment.
It is composed of a continuous main pulse of 15t and 31 dispersed pulses of 1/2 duty. In the present embodiment, the heat generation start time of the adjacent groups is set to 9.5 t so that the energization times in the dispersed pulses of the adjacent groups do not overlap in time as shown in FIG. Therefore, the printing cycle is 76t
Therefore, the internal heat generation period is 46t and the cooling period is 30t.

Compared to the previous embodiment shown in FIG. 3, the heat generation period is the same 46t and the printing cycle is 80t to 76t.
The maximum current consumption is 4Ib, which is lower than 5Ib in the previous embodiment, despite the fact that the speed is increased by 4 tons.

That is, as in the present embodiment, 1 within the time t
In the case of a dispersed pulse that generates heat with a duty of / 2, the heat generation start delay time of the adjacent group is (n + 1/2) t, where n
= 0, 1, 2, ...), the maximum current consumption can be reduced.

In FIG. 5, the heating duty of the dispersed pulse is 1
6 is a timing chart of the first line showing the case of / 4. As in the previous embodiment, the strobe signal is composed of a continuous main pulse of 15t and 31 dispersed pulses, and the dispersed pulse causes cooling for 3 / 4t and heat generation for 1 / 4t within the time t. Also in this embodiment, the heat generation start time of the adjacent groups is set to 9.25 t so that the energization times in the dispersed pulses of the adjacent groups do not overlap in time.

Therefore, the printing cycle is 74t, the internal heat generation period is 46t, and the cooling period is 28t. Comparing the maximum current consumption with the heating example in which the dispersed pulse of FIG. 4 is 1/2 duty, it can be seen that the printing cycle is shortened by 2t, but is reduced by 3Ib and Ib.

That is, in the case of a dispersed pulse that generates heat with a 1/4 duty within the time t, the heat generation start delay time of the adjacent groups is (n + 1/4) t (where n = 0, 1, 2, ...
.) Or (n-1 / 4) t, (where n = 1, 2 ...
・ It is possible to reduce the maximum current consumption by setting ().

[0027]

As described above, according to the present invention,
In a line type thermal head divided into a plurality of groups of three or more, the heat generation start time of the adjacent groups is divided into the number of groups obtained by dividing the print cycle including the heat generation period required for solid black printing and the cooling period required at that time. By substantially delaying the divided time and overlapping the heat generation periods of three or more consecutive groups with time enemies, white stripes between groups, which occurred in conventional divided printing, are reduced, and high-speed printing is achieved. The cycle can be obtained.

Further, the main pulse for continuously energizing during the heat generation period and the plurality of dispersed pulses for non-energizing / energizing in an extremely short time are configured so that the energizing periods of the dispersed pulses of the adjacent groups do not overlap. By setting the delay time between the groups, it is possible to reduce the white stripes at the ends of each group and to perform high-speed printing with a reduced maximum current consumption.

[Brief description of drawings]

FIG. 1 is a timing chart showing a first embodiment of a thermal head driving method of the present invention.

FIG. 2 is a block diagram of a thermal head driven by a thermal head driving method of the present invention.

FIG. 3 is a timing chart showing a second embodiment of the thermal head driving method of the present invention.

FIG. 4 is a timing chart showing a third embodiment of the thermal head driving method of the present invention.

FIG. 5 is a timing chart showing a fourth embodiment of the thermal head driving method of the present invention.

FIG. 6 is a timing chart showing a conventional thermal head driving method.

FIG. 7 is a timing chart showing another conventional thermal head driving method.

[Explanation of symbols]

 R1 to R256 ... Heating resistor, SR1 to SR8 ... Shift register, LR1 to LR8 ... Latch register, D ... Print data, STB1 to STB8 ... Strobe signal, L ... Latch signal .

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Kiyoji Hibino 2-18 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd.

Claims (3)

[Claims] 1. A method of driving a thermal head in which a plurality of heating resistors of a line type thermal head are grouped into one group and all the heating resistors are divided into a plurality of groups, and each group is sequentially heated. The energization start time is almost delayed by the time divided by the number of groups obtained by dividing the print cycle including the heat generation period and the cooling period of the heat generating resistor, and the heat generation period of three or more consecutive groups during high density printing is Method for driving a thermal head, characterized in that they overlap each other. 2. The heat generation period is constituted by a main pulse that continuously generates heat by energization and a plurality of dispersed pulses that cause non-energization and current conduction for an extremely short time.
The driving method of the thermal head described. 3. The delay time of the heat generation start time of each group is set so that when the heat generation duty of the dispersed pulse is 1 / n, the energization times of the adjacent n groups of dispersed pulses do not overlap in time. The method for driving a thermal head according to claim 2, wherein: