JPH1142805A - Method for thermal printing and printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent density variation due to current variation of a power source. SOLUTION: Driving data for heating elements is read from a frame memory 20 to be written into a line memory 21. The driving data for the heating elements is transmitted from the line memory 21 to a comparator 22. In terms of a group G1 of the heating elements, comparison data having an order of 0-255 is transmitted to the comparator 22. In terms of a group G2 of the heating elements, comparison data having an order of 255-0 is transmitted to the comparator 22. The driving data for heating elements is compared with the comparison data by the comparator 22. When the comparison data is smaller than the driving data, a signal with an H level is outputted. When the comparison data is not smaller than the driving data, a signal with an L level is outputted. Each of the heating elements 131 -13n on a thermal head 12 is driven based on the output signal of the comparator 22. Starting edges of the driving pulses of one group of the heating elements are arranged on a top edge side in a direction of conveying of a recording medium and ending edges of the driving pulses of the other group of the heating elements are arranged on a rear edge side in the direction of conveying of the recording medium.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal printing method and a printer, and more particularly, to a method for driving each heating element of a thermal line printer.

[0002]

2. Description of the Related Art Thermal printers include a thermal transfer printer and a thermal printer. The former thermal transfer printer has
There are a fusion type and a sublimation type. In these, an ink film is superimposed on a recording material, and a thermal head is pressed from behind the ink film and heated to transfer the ink of the ink film to the recording material. In the latter thermal printer, the thermal recording material is heated by a thermal head, and the thermal recording material is colored to perform thermal recording. These thermal heads have a heating element array in which a large number of heating elements (resistance elements) are arranged in a line, and a driver for driving each heating element.

When thermal recording is performed using a thermal head having a large number of heating elements arranged in a line,
When all the heating elements are heated at the same time, the peak voltage of the power supply increases, and density unevenness easily occurs due to voltage drop or the like.

[0004]

For this reason, in order to reduce the number of heating elements that generate heat at the same time, it has been studied to divide the heating elements into a plurality of groups and shift the heat generation start timing for each group. For example, JP-A-3-39262
Japanese Patent Application Laid-Open Publication No. H11-163873 proposes that printing is performed with a small power supply capacity by subdividing the application time to the heating elements of each group and alternately switching the application time to apply energy. However, when the heating elements are alternately heated by the grouping, the width of the driving pulse is further subdivided by the grouping, so that the driving pulse width is reduced in high-speed printing. Therefore, there is a problem that the variation in the on / off time of each heating element becomes a variation in the tone reproducibility and appears in the print result, and the tone reproducibility decreases.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a thermal printing method and a printer capable of suppressing the occurrence of density unevenness due to a voltage drop or the like without lowering the tone reproducibility.

[0006]

According to a first aspect of the present invention, there is provided a thermal printing method comprising the steps of dividing a plurality of heating elements of a thermal head having a large number of heating elements arranged in a line into two groups. When printing one dot, the start end of the drive pulse is aligned with the leading end side in the recording material feeding direction for one group of heating elements, and the end of the driving pulse is set for the other group of heating elements. The ends are aligned with the rear end side in the recording material feeding direction. It is preferable that the grouping is performed so that the number of the groups is substantially equal, and the groups are alternately arranged in a suitable number.

According to a third aspect of the present invention, there is provided a thermal printer.
Each heating element divided into two groups and one group of each heating element divided into the groups generate comparison data sequentially increased from the minimum comparison data, and the other group sequentially decreases comparison data from the maximum comparison data. A comparison data generation unit for generating comparison data, a line memory for storing one line of heating element drive data corresponding to image data, and a comparison between the heating element drive data from the line memory and the comparison data generation unit. It is provided with a comparator that generates drive data for each heating element by comparison with data, and a heating element drive unit that drives each heating element based on the driving data from the comparator.

[0008]

When recording one dot, of the heating elements divided into two groups, the heating element of one of the groups has the starting end of the driving pulse aligned with the leading end in the recording material feeding direction. In the other group of heating elements, the end of the drive pulse is aligned with the rear end in the recording material feed direction.
As described above, the heating elements are divided into two groups, and the driving time of the heating element is shifted forward in the one-dot recording time for each group, and the other is shifted backward in the one-dot recording time. As a result, the occurrence of uneven density due to this is suppressed.

[0009]

In FIG. 2 showing a color thermal printer, a color thermal recording material (hereinafter simply referred to as recording material) 10 is fed by a pair of feed rollers 11 in a printing direction indicated by an arrow A1 and a pullback direction indicated by an arrow B1. Is reciprocated. As is well known, the recording material 10 is provided on a support with a cyan thermosensitive coloring layer, a magenta thermosensitive coloring layer having a light fixing property by ultraviolet light of about 365 nm, and a yellow thermosensitive coloring property having a light fixing property by purple visible light of about 420 nm. layer,
And a protective layer.

The recording material 10 is reciprocated by the feed roller pair 11, and a yellow image is recorded on the recording material 10 by the thermal head 12 in the first feed in the printing direction. A magenta image is sequentially recorded in the second transport, and a cyan image is sequentially recorded in the third transport. Thus, a full-color image is recorded by three-color surface sequential recording. The thermal head 12 has a heating element array 13 on the lower surface thereof, and a platen roller 14 is pressed onto the heating element array 13 via the recording material 10.

As shown in FIG. 3, the heating element array 13 has a large number of heating elements 13 _{1 to} 13 _n arranged in a line in the main scanning direction. Each heating element 13 ₁ -13
_n is a resistor element, each of these heating elements 13 ₁ to 13 _n of the bias heat energy for heating a pixel immediately before the color development at the time of thermal recording, gradation heat corresponding to the color density Energy is applied to the recording material 10.

A yellow fixing lamp 15 and a magenta fixing lamp 16 are sequentially arranged downstream of the feed roller pair 11 in the printing direction. The yellow fixing lamp 15 emits a violet visible light having an emission peak near 420 nm, and the magenta fixing lamp emits a violet peak at 365 nm.
It emits ultraviolet light in the vicinity of nm. For example, during yellow image recording, the yellow fixing lamp 15 is turned on, and the yellow thermosensitive coloring layer immediately after thermal recording is optically fixed. During magenta image recording, the magenta fixing lamp 16 is turned on, and the magenta thermosensitive coloring layer immediately after thermal recording is optically fixed. In this way, a full-color image is recorded on the recording material 10 by three-color surface sequential recording.

FIG. 1 shows an electric circuit of a color thermal printer. The heating element drive data is written in the frame memory 20 in a state of being separated for each color.
The heating element drive data is composed of data on the number of drive pulses of each of the heating elements 13 _{1 to} 13 _n , and includes data on the number of bias pulses for generating bias heat energy and the number of bias pulses for generating gradation expression heat energy. This is obtained by adding the gradation pulse number data. The bias pulse number data is obtained in advance according to the coloring characteristics of each thermosensitive coloring layer. Further, the gradation pulse number data is obtained from the image data. The image data is obtained, for example, by photographing with an electronic still camera or the like. This image data represents a gradation level, and from this image data, gradation pulse number data for obtaining the density of the dots formed in the recording pixels is obtained.

In the line memory 21, when performing thermal recording,
The heating element drive data of the color to be printed is written line by line from the frame memory 20. The heating element drive data for one line is read out 256 times and sent to the comparator 22.

The comparator 22 includes a comparison data generator 2
The heating element drive data for one line is compared 256 times with the comparison data from # 3. When this comparison data is simply generated in the order of “0” to “255” and is compared with the heating element drive data, the heating elements 13 _{1 to} 13 _n are simultaneously driven. As shown, the current of the power supply is the sum of the respective heating elements 13 _{1 to} 13 _n , and the peak current of the power supply becomes large.

In order to prevent this, in the present invention, FIG.
As shown in (1), the heating elements are alternately divided into groups G1 and G2 in the main scanning direction. In addition, in order to make these groupings easy to understand, each heating element is provided with "A" in the group G1.
G2 is marked with "B". Then, for one group G1, the comparison data is changed from “0” to “25”.
5 ”, and for the other group G2,
The comparison data is generated in the order of “255” to “0”.

For this purpose, as shown in FIG. 1, the comparison data generator 23 includes a comparison data generator 24, a non-inverter 25, an inverter 26, and a data selector 27. The comparison data generation circuit 24 outputs “0” to
The comparison data of “255” is generated in order. These comparison data are sent to the data selector 27 via the non-inverter 25 and the inverter 26. Non-inverter 25
Outputs the comparison data as it is in the order of “0” to “255”. The inverter 26 converts the comparison data from "255"
The output is inverted in the order of “0”.

The data selector 27 selects these data for each group and sends them to the comparator 22. For example, the output from the non-inverter 25 is selected for the heating elements of the group G1, and this is
Sent to Further, the output from the inverter 26 is selected for the heating elements in the group G2, and the selected output is sent to the comparator 22. Therefore, the select signal is input to the data selector 27 by the select signal generating circuit 28.

The select signal is H for the heating elements of group G1 and L for the heating elements of group G2.
Is assigned. In the present embodiment, the group G1
And G2 are alternately arranged, so that HLHL
Are input to the data selector 27 in synchronization with the comparison timing of the comparator.
Therefore, the output of the non-inverter 25 is selected at the time of H, and the output of the inverter 26 is selected at the time of L.

[0020] Thus, the heating elements ₁₃ 1 belonging to the group G1, 13 _3, 13 _5, · · ·, as shown in FIG. 4 (A), when one line of recording, the start end side of the recording material feeding direction Heating starts. Furthermore, heating elements 13 _2, 13 4 belonging to the group _G2, · · · is heated is to end at the end edge side of the recording material feeding direction. Therefore, in the printing of the low-density pixels in which the number of drive pulses is “122” or less, the drive current to each heating element is divided into two groups G1 and G2, so that the peak current of the power supply can be reduced by half. . FIG. 4 shows the case where the number of drive pulses is "82" and one line is recorded at the same density because the drive data for each of the groups G1 and G2 is shown instead of the drive data for each heating element. I have. Actually, each heating element is individually driven by the number of driving pulses having a density corresponding to image data. In addition, when recording in a high-density portion, the heat generation periods of both groups G1 and G2 overlap, so that the peak current of the power supply is not so different from that of the conventional one.

As shown in FIG. 1, the comparator 22 comprises:
The heating element drive data and the comparison data are compared. Then, when the comparison data is smaller, the drive data of “H” is outputted, and otherwise, the drive data of “L” is outputted. For example, the comparison data of “0” for the heating element of group G1 is “25” for the heating element of group G2.
Since the comparison data of "5" is transmitted, the heating element drive data of one line is sequentially compared with the comparison data. Thereby, the comparison result for one line is sent from the comparator 22 to the shift register 30 as a serial signal. When the comparison of the heating element drive data for one line is completed, the comparison data generator 23 generates the next comparison data (“1” for the group G1 and “254” for the group G2). The data is sent to the comparator 22, and the heating element drive data for one line is sequentially compared with the comparison data. Hereinafter, comparisons are similarly performed one after another. As a result, the heating element drive data is compared 256 times, and as a result, is converted into 256-bit drive data. The 256-bit drive data is sent to the shift register 30 one bit at a time.

The serial drive data is shifted in the shift register 30 and converted into a parallel signal. The drive data converted into the parallel signal by the shift register 30 is latched by the latch array 31 in synchronization with the latch signal. The AND gate array 32 outputs an “H” signal when the drive data is “H” during a period in which the strobe signal is input.

[0023] Each output terminal of the AND gate array 32, the transistor 33 ₁ ~ 33 _n are connected. These transistors 33 ₁ ~ 33 _n, the output of the AND gate array 32 is turned on when "H". The transistor 33 ₁ ~ 33 _n are heating elements 13 ₁ to 13 _n are connected in series.

The strobe signal generating circuit 34 is controlled by a signal from the system controller 35 generates a strobe signal for determining the ON time of the heating elements 13 ₁ to 13 _n and the OFF time. The strobe signal is
The pulse width is changed depending on the color to be printed. Therefore, the setting data of each strobe signal is obtained in advance for each color and is stored. The system controller 35 is composed of a microcomputer and controls each unit to perform printing.

Next, the operation of the above embodiment will be briefly described. When a print start switch (not shown) is operated, the system controller 35 feeds the recording material 10. When the paper feeding is completed, the recording material 10 is fed in the printing direction by the feed roller pair 11. Then, when the leading end of the recording area of the recording material 10 reaches the heating element array 13, thermal recording of the first line of the yellow image is started. At the time of this recording, first, the heating element driving data for yellow recording of the first line is written from the frame memory 20 to the line memory 21, and the heating element driving data from the line memory 21 is sent to the comparator 22. In addition, from the comparison data generation unit 23, each of the heating elements 13 ₁ to 13 ₁ to
Different comparison data is generated for each of the 13 _n groups G1 and G2, and sent to the comparator 22.

The comparator 22 is connected to the line memory 21
Drive data for yellow recording and their comparison data
By comparing with the comparison data from the generating unit 23,
When the latter is small, the drive data of "H" is output. Ko
One line of serial data output from the comparator 22
The drive data is sent to the shift register 30, where the data is transmitted.
And converted into parallel drive data. latch
The array 31 latches the parallel drive data,
The drive data is sent to the AND gate array 32. AND game
The strobe signal is sent to the port array 32 in synchronization with the latch.
A strobe signal is input from generation circuit 34. to this
Therefore, the AND gate array 32 outputs the driving data “H”.
When the strobe signal is input
During this time, an "H" signal is output. With this signal,
Transistor 33₁Turns on, the strobe signal
Drive pulse having a width corresponding to the heating element 13₁Supplied to
Heating element 13₁Generates heat. Hereinafter, the comparison data
The heating element 13 is used in accordance with the comparison result.₁
~ 13_nIs driven. Thereby, each heating element 13 ₁
~ 13_nIs heated to a density corresponding to the image data.
Then, recording of one dot is performed.

Thereafter, the yellow image recording of each line is sequentially performed in the same manner. When a yellow image is recorded, the yellow fixing lamp 15 is turned on to fix the yellow thermosensitive coloring layer immediately after recording. When the recording of the yellow image is completed, the recording material 10 is pulled back by the reverse rotation of the feed roller pair 11. Thereafter, a magenta image is thermally recorded in the same manner on the magenta thermosensitive coloring layer in the recording area. During magenta recording, the magenta fixing lamp 16 is turned on to fix the magenta thermosensitive coloring layer. When the recording of the magenta image is completed, the cyan image is thermally recorded after the recording material 10 is pulled back. Also at the time of recording a cyan image, the magenta fixing lamp 16 is turned on, and the unrecorded area is bleached. In this way, a full-color image is recorded on the recording material 10 by three-color surface sequential recording.

In the above embodiment, the linear heating elements 13 _{1 to} 13 _n are alternately arranged one by one in groups G 1 and G 1.
However, in addition to the above, the data may be allocated to the groups G1 and G2 in units of two or more. Further, the heating element array 13 may be divided at the center, and one may be set to the group G1 and the other may be set to G2.

In the above-described embodiment, the heating element drive data (the number of drive pulses “255”) at which the maximum density is obtained is the group G
1 and G2 are completely coincident with each other and overlapped to reduce the printing time. In addition to this, as shown in FIG. 5, as shown in FIG. Change the overlap amount OL1,
The overlap may be eliminated as shown in FIG. In this case, the print time becomes longer as the overlap amount OL1 decreases, but the time during which the power supply current peaks can be reduced.

In the above embodiment, the heating element drive pulse is composed of a large number of drive pulse trains. Alternatively, the heating element may be driven by one drive pulse. In the above-described embodiment, the heating element drive data obtained by adding the bias data and the gradation data is written in the frame memory 20. In addition, the bias data and the gradation data are separately stored. , May be added and sequentially written to the line memory 21.

In the above embodiment, the capstan drive type thermal printer using the feed roller pair 11 is used. However, the present invention is applied to a platen drum type thermal printer which feeds a recording material using a platen drum. Is also good. Further, the present invention is applied to a color thermal printer, but the present invention may be applied to a thermal melting type thermal printer. Further, the present invention may be applied to a serial printer without being limited to a line printer.

[0032]

According to the present invention, each heating element of a thermal head in which a large number of heating elements are arranged in a line is divided into two groups, and when one dot is recorded, the heating elements of one group are used. In other words, the start end of the drive pulse is aligned with the front end of the recording material feed direction, and the end of the drive pulse is aligned with the rear end of the recording material feed direction for the other group of heating elements. The power supply current is dispersed instead of being concentrated at the start of driving as in the related art. As a result, the amount of change in the power supply current is reduced and the change becomes gentler, so that it is possible to suppress the occurrence of density unevenness due to an extreme change in the power supply current. Therefore, an image faithful to the image data can be reproduced, and the print quality is improved.

By performing the grouping of the heating elements so that the numbers thereof are substantially equally divided, it is possible to efficiently suppress the fluctuation amount of the power supply current. In addition, by arranging the groups alternately in a suitable number of units, the thermal balance of the thermal head becomes good, and efficient thermal recording becomes possible.

For each of the heating elements divided into two groups, one group generates comparison data sequentially increased from the minimum comparison data, and the other group generates comparison data sequentially reduced from the maximum comparison data. A comparison data generating unit, a line memory for storing one line of heating element drive data corresponding to image data, and a comparison between the heating element drive data from the line memory and the comparison data from the comparison data generation unit. Since a comparator that generates drive data for each heating element is provided, a thermal printer that suppresses fluctuations in power supply current can be provided with a simple configuration.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a main part of a thermal printer according to the present invention.

FIG. 2 is a schematic view of a color thermal printer.

FIG. 3 is an enlarged plan view showing a heating element array.

4A and 4B are graphs showing changes in drive data to the heating elements of each group and power supply current at this time when one line is recorded, wherein FIG. 4A shows the present invention and FIG. This shows a conventional device in which heating elements are simultaneously driven.

FIG. 5 is a graph showing an example of drive data for heating elements of each group according to another embodiment, showing a reduced overlap amount.

FIG. 6 is a graph showing an example of drive data to the heating elements of each group according to another embodiment, showing a case where the overlap amount is eliminated.

[Explanation of symbols]

Reference Signs List 10 color thermosensitive recording material 11 feed roller pair 12 thermal head 13 heating element array 13 _{1 to} 13 _n heating element 14 platen roller 15, 16 fixing lamp 22 comparator 23 comparison data generation section

Claims (4)

[Claims] 1. A thermal head in which a large number of heating elements are arranged in a line, each heating element is divided into two groups.
At the time of printing one dot, the start end of the drive pulse is aligned with the leading end side in the recording material feeding direction for one group of heating elements, and the end of the drive pulse is aligned for the other group of heating elements. A thermal printing method characterized by aligning the recording paper with the rear end side in the recording material feeding direction. 2. The thermal printing method according to claim 1, wherein the grouping is performed so that the number of the groups is substantially equal, and each group is alternately arranged in units of an appropriate number. 3. A thermal printer which prints an image on a recording material by applying a drive pulse to each of the heating elements of a thermal head having a large number of heating elements arranged in a line in a main scanning direction and sending a recording material in a sub-scanning direction. In each of the heating elements divided into two groups, one group of the heating elements divided into the groups generates comparison data sequentially increased from the minimum comparison data, and the other group generates the comparison data from the maximum comparison data. A comparison data generation unit for generating comparison data reduced in order; a line memory for storing one line of heating element drive data corresponding to image data; a heating element drive data from the line memory and a comparison data generation unit; A comparator that generates drive data for each heating element by comparing with the comparison data of Thermal printer characterized by comprising a heat generating element drive section for driving the heating elements based on the drive data. 4. The thermal printer according to claim 3, wherein the grouping is performed so that the number of the groups is substantially equal, and the groups are alternately arranged in a suitable number of units.