JP3034151B2 - Thermal head drive controller - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head drive control device used in a thermal printer, and more particularly, to a thermal head drive control for generating a bias heating drive pulse and a gradation expression heating drive pulse. It concerns the device.

[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 paper, a thermal head is pressed from behind the ink film and heated to transfer the ink of the ink film to the recording paper. In the latter thermal printer, the thermal recording paper is heated by a thermal head, and the thermal recording paper is colored to thermally record ink dots.

In the thermal printer, when one pixel is thermally recorded, one bias heating drive pulse and a number of gradation expression heating drive pulses corresponding to the pixel density are applied to each heating element of the thermal head. Have given. The bias heating drive pulse is used for rapidly bias heating the heating element to a state immediately before the start of ink transfer or coloring. For example, in a color thermal printer, the heating element is energized by, for example, about 4 ms by the bias heating drive pulse, and is energized by about 10 μs per gradation by the gradation expression heating drive pulse.

By the way, in order for such fine heat control to be accurately reflected on a printing result, it is necessary that all the heating elements constituting the thermal head have uniform resistance values. However, the resistance value of the heating element generally has a variation of about 5%, and the heating value varies due to the variation, which causes inconvenient phenomena such as color unevenness in a recorded image.

In order to improve this, for example, Japanese Patent Laid-Open No. 2-2
As described in Japanese Patent No. 48262, there has been proposed a thermal printer that measures all the resistance values of several hundred heating elements provided in a thermal head, corrects image data based on the measurement results, and prints. ing. Further, instead of correcting the image data, Japanese Patent Application Laid-Open No. 2-292060
As described in Japanese Patent Application Laid-Open Publication No. H10-157, there has been proposed a thermal printer that corrects density unevenness by inserting a density correction pulse between grayscale pulses.

[0006]

However, the method of inserting a density correction pulse requires a new correction pulse generation circuit, and has a problem that the configuration becomes complicated and the manufacturing cost increases. In addition, there is a problem that the printing time is longer than when no correction is performed because the correction pulse is given.

Further, the method of directly multiplying the image data by the correction data requires a large amount of arithmetic processing, so that a high-speed arithmetic circuit is required and the manufacturing cost is increased. Moreover, since the quantization error is increased by the calculation, a pseudo contour is generated in the print image, and there is a problem that the print quality is reduced.

On the other hand, it is conceivable to generate a driving pulse train for bias heating in which the number of pulses is increased or decreased according to the resistance value of each heating element and a driving pulse train for gradation heating following this. However, there is a problem that two types of pulse generation circuits, a bias heating drive pulse and a gradation heating drive pulse, are required, and the circuit configuration becomes complicated.

Further, when the temperature of the thermal head rises during printing, there is a problem that density unevenness occurs in a printed image.

An object of the present invention is to provide a thermal head drive control device which can suppress the occurrence of uneven density due to unevenness in the resistance value of each heating element and uneven temperature rise of the thermal head with a simple device configuration. It is the purpose.

[0011]

According to a first aspect of the present invention, there is provided a thermal head drive control device, wherein a bias heating amount of each heating element determined based on a resistance value of each heating element is fixed. Correction data line memory for storing the number data of the bias heating drive pulse train for one line of the heating element, and a plurality of image data line memories for storing the image data for one line of the heating element And switching between these line memories,
A bias heating of the heating elements by the bias pulse heating drive pulse train from the correction data for the line memory, based on the image data from one of the line memories for the image data
While performing gradation heating of each heating element, bias heating of each heating element by a driving pulse train for bias pulse heating from the line memory for correction data,
Recorded with the image heating of the heating elements based on from one of the image data other line memory for image data, and the bias heating by the line memory for the following correction data, order
Multiple line memories for image data switched to
And a controller for sequentially recording each line by performing the gradation heating .

According to a second aspect of the present invention, there is provided a thermal head drive control apparatus according to the first aspect , further comprising a line for correcting temperature unevenness in addition to the line memory for correcting unevenness in resistance and the line memory for image data. Immediately after the start of thermal recording, bias heating based on the correction data of the line memory for correcting unevenness of the resistance value and the image of the line memory for image data
Performs gradation heating based on image data, and when the number of recording lines at which density unevenness occurs due to temperature rise has been reached, bias heating with correction data from the line memory for temperature rise unevenness correction data, and line memory for image data Picture from
Each line is sequentially recorded by performing gradation heating based on image data .

According to a third aspect of the present invention, in the thermal head drive control device according to the second aspect, correction data is rewritten in the line memory for correcting uneven temperature rise according to the number of recorded lines. is there.

[0014]

In the state where the thermal head is set at the recording start position, first, a line memory for resistance non-uniformity correction is selected.
Based on this, the pulse number data for bias heating corresponding to the resistance value of each heating element is sent to the comparator. The comparator compares the pulse number data with the comparison data,
A drive pulse is generated when the pulse number data is large.
Each heating element is driven by this driving pulse, and is bias-heated. Accordingly, in the heating element in which the resistance value of each heating element is slightly smaller than the reference resistance value, the number of pulses of the bias heating drive pulse train is smaller than that of the heating element having the reference resistance value. In a heating element having a resistance value slightly larger than the reference resistance value, the number of pulses of the bias heating drive pulse train is set to be larger than that of the reference resistance value. Therefore, even if there is a variation in the resistance value of each heating element, the amount of heat generated in bias heating becomes uniform, and uneven density due to the variation in resistance value is reduced.

Next, one of the line memories for image data is selected, and a driving pulse for gradation heating is created based on the image data, whereby each heating element is heated by gradation. Thereby, one line is thermally recorded. At the time of recording the next line, similarly, after the bias heating is performed so as to eliminate the resistance value unevenness of each heating element, another line memory for image data is selected, and the second line is thermally recorded. The image data of each line is efficiently transferred to the plurality of line memories for image data by writing image data of a new line on the other side while reading the image data.

When the number of recording lines at which density unevenness occurs due to temperature rise during thermal recording of each row is reached, the line memory is switched from a line memory for correcting uneven resistance to a line memory for correcting uneven temperature. Each heating element is bias-heated with the number of pulses that eliminates the rising unevenness.

[0017]

FIG. 2 shows a color thermal printer. A platen drum 10 is mounted on a rotating shaft 11 driven by a pulse motor (not shown), and rotates in the direction of the arrow at the time of printing. A color thermosensitive recording material 12 is wound around the outer periphery of the platen drum 10, and the leading end is fixed by a clamper 13. A thermal head 14, a magenta fixing ultraviolet lamp 15, and a yellow fixing ultraviolet lamp 1 are provided around the platen drum 10.
6 are arranged.

On the lower surface of the thermal head 14, a heating section 17 is provided.
The heating section 17 has a large number of heating elements arranged in a line in the axial direction of the platen drum 10. Each heat-generating element, when thermally recording one pixel, uses a bias thermal energy for heating up to immediately before color development and a gradation expression thermal energy corresponding to the color density to produce a color thermosensitive recording material 12.
Give to. The magenta fixing ultraviolet lamp 15 emits ultraviolet light having an emission peak near 365 nm, and the yellow fixing ultraviolet lamp 16 emits ultraviolet light having an emission peak near 420 nm.

As shown in FIG. 3, the color thermosensitive recording material 1
Reference numeral 2 denotes a cyan thermosensitive coloring layer 21, a magenta thermosensitive coloring layer 22 having a light fixing property with ultraviolet light of about 365 nm, a yellow thermosensitive coloring layer 23 having a light fixing property with ultraviolet light of about 420 nm on a support 20, a protective layer. 24 are sequentially layered. These thermosensitive coloring layers 21 to 23 are arranged in the order of thermal recording.

FIG. 4 shows the coloring characteristics of each thermosensitive coloring layer. In the color thermosensitive recording material 12 of this embodiment, the yellow heat-sensitive coloring layer 23 has the lowest coloring heat energy and the cyan heat-sensitive coloring layer 21 has the highest coloring heat energy. When a yellow (Y) pixel is to be thermally recorded, the color thermal recording material 12 is provided with coloring thermal energy obtained by adding thermal energy GY _J for expressing gradation to bias thermal energy BY. The bias thermal energy BY is thermal energy immediately before the yellow thermosensitive coloring layer 23 develops a color, and is a constant value. The gradation expression heat energy GY _J is determined according to the gradation level J corresponding to the color density of the pixel to be recorded. Since the same applies to magenta M and cyan C, only symbols are given.

In FIG. 1 showing a print unit, a frame memory 30 stores, for example, an image 1 captured by an electronic still camera.
The image data of the frame is written in a state of being separated for each color. At the time of printing, the system controller 35 reads out the image data of the color to be printed from the frame memory 30 one line at a time, and reads the image data in the first or second line memory 3 selected by the first selector 31.
Write to one of 2,33. The selector 31 is controlled by the system controller 35 so as to write the odd-numbered row image data to the first line memory 32 and the even-numbered row image data to the second line memory 33.

The system controller 35 is composed of a microcomputer, and controls each part in sequence. First, at the time of initialization after power-on, the system controller 35 writes the bias heating drive pulse number data in the third line memory 34. The drive pulse number data for bias heating is determined in advance by an experiment or the like based on the resistance value of each heating element, and a conversion table of the data is stored in a predetermined area of the ROM 38 of the system controller 35 in advance. Regarding the number of bias heating drive pulses, the number of bias heating drive pulses is increased in a heating element having a high resistance value, and the number of bias heating drive pulses is decreased in a heating element having a low resistance value. In this embodiment, the number of drive pulses for bias heating is set to 256 based on the heating element having the maximum resistance value. Then, from the difference between the maximum resistance value and the resistance value of each heating element, the reduction number of the bias heating drive pulse number is determined, and the reduction number is subtracted from 256 to obtain the bias heating drive pulse number of each heating element. To determine.

The resistance value of each of the heating elements 17a to 17n is detected by a resistance value detection circuit 37 when the thermal printer is shipped from the factory or when the thermal head 14 is initially set after replacement.
This is stored in the RAM 36. Resistance value detection circuit 37
Is connected to each heating element 17 by transistors 48a to 48n.
a to 17n are selected one by one, a predetermined voltage is applied thereto, and a resistance value is detected from a voltage drop time of the selected voltage. For example, Japanese Patent Application No. 4-2336 filed by the present applicant has
No. 26 describes this in detail. The system controller 35 obtains the number of bias heating drive pulses for each heating element from the conversion table stored in the ROM 38 based on the detected resistance value, and stores this in a predetermined area in the RAM 36.

The system controller 35 generates a system 1 line start signal based on the print start signal, and outputs this signal to the memory controller 42. The memory controller 42 switches the selector 40 based on the system 1 line start signal and the 1 line end signal, and generates the system 1 line end signal and the 1 line start signal.

First, when the memory controller 42 receives the system 1 line start signal from the system controller 35, the memory controller 42 switches the selector 40 to connect the third line memory 34 to the comparator 41 and to send the 1 line start signal to the print controller 43. Output. Further, the memory controller 42 includes a counter P for counting the number of occurrences of a system one-line start signal from the system controller 35, and a counter Q for counting the number of occurrences of a one-line end signal from the print controller 43. The count value p,
In response to q, the selector 40 is switched and a one-line start signal and a one-system line end signal are output. That is, when the count value p is an odd number, the first
The line memory 32 is connected to the comparator 41, and a one-line start signal is sent to the print controller 43.
Send to If the count value p is an even number, the second line memory 33 is connected to the comparator 41, and the one-line start signal is sent to the print controller 43.
Send to When the count value q is an even number, a system 1 line end signal is output to the system controller 35.

The selector 40 is connected to first to third line memories 32, 33 and 34, and sends only the data of one line memory to the comparator 41.

When a print start signal of one line is input from the memory controller 42, the print controller 43 sequentially outputs 8-bit comparison data to the comparator 41. At this time, the print controller 4
3 counts the number of occurrences of the one-line start signal, and upon receiving an odd-numbered one-line start signal,
The comparison data for generating the bias heating drive pulse is output to the comparator 41. Further, when receiving the even-numbered one-line start signal, the comparator 41 outputs comparison data for generating a gradation expression drive pulse to the comparator 41. For example, when generating a bias heating drive pulse, comparison data of “1” to “FF” in hexadecimal are output in order, and when generating a drive pulse for gradation expression, “1” to “3F” of hexadecimal. The comparison data is output in order. In the present embodiment, when generating the gradation expressing drive pulse, 64 bits are used using the comparison data of “1” to “3F” in hexadecimal.
Although the gradation is expressed, the number of gradations can be changed by appropriately increasing or decreasing the comparison data according to the characteristics of each thermosensitive coloring layer.

When the comparison data of "1" is sent from the print controller 43, the comparator 32 compares the comparison data with the data of the number of driving pulses for bias heating of each heating element. By this comparison, drive data of "1" is obtained when the bias heating drive pulse number data is equal to or larger than the comparison data. The drive data for one line obtained by this comparison is sent to the shift register 45 as a serial signal. When the comparison with the comparison data of “1” is completed, the print controller 43
The comparison data of "2" is generated and sent to the comparator 41, where it is again compared with the data of the number of bias heating drive pulses for one line. Therefore, by using the comparison data of “1” to “FF”, the bias heating drive pulse number data of each heating element is compared 256 times and converted into drive data of a maximum of 256 bits, and divided into 256 times. The data is sent to the shift register 45. The serial drive data generated by each comparison is shifted in the shift register 45 by a clock from the print controller 43 and converted into parallel drive data. As a result, the comparator 41 outputs a maximum of 256 bias heating drive pulses. When the output of the comparison data for one line is completed, the print controller 43 outputs a one-line end signal indicating the end of printing of one line to the memory controller 42.

Further, by using the comparison data of "1" to "3F", the driving pulse number data for gradation expression of each heating element is compared 64 times and converted into driving data of a maximum of 64 bits. The data is sent to the shift register 45 in different times. As a result, for example, as shown in FIG. 6, when the image data of the first heating element has 64 gradations, 64 consecutive gradation expressing drive pulses are generated, and the image data of the second heating element has 62 gradations. In the case of gradation, 62 consecutive drive pulses for gradation expression are generated. Similarly, in the case of 61 gray scales, the drive pulse for gradation expression is generated continuously for 61 gray scales and 5 gray scales. When the output of the comparison data for one line is completed, the print controller 43
Outputs a one-line end signal indicating the end of printing of one line to the memory controller 42.

The drive data converted into the parallel signal by the shift register 45 is latched by the latch circuit array 46 in synchronization with the latch signal. AND gate array 47
Outputs a drive pulse of “1” when the drive data being input is “1” when a strobe signal is input.

The transistors 48a to 48n are connected to the output terminals of the AND gate array 47, respectively, and the transistor to which the drive pulse is input is turned on. To these transistors 48a to 48n, heating elements 17a to 17n arranged in a line are connected in series, respectively. A resistance element is used as each of the heating elements 17a to 17n.

The strobe signal generation circuit 44 is controlled by signals from the system controller 35 and the print controller 43, and turns on the heating elements 17a to 17n.
A strobe signal for determining the time and the OFF time is generated. There are two types of strobe signals, one for bias heating and one for gradation expression. The strobe signal for performing bias heating has a longer pulse width than the strobe signal for performing gradation expression heating. Further, the pulse width of the strobe signal varies depending on the color to be printed. Therefore, the setting data of each strobe signal is
It is obtained in advance for each color, and this is stored in a predetermined area of the RAM 36. The strobe signal generation circuit 44
For example, Japanese Patent Application No. Hei 5-7450 filed by the present applicant
No. 8 explains this in detail.

Next, the operation of the above embodiment will be described with reference to FIG. When a print start switch (not shown) is operated, the system controller 35 rotates the platen drum 10 around which the color thermosensitive recording material 12 is wound. Further, the system controller 35 reads out the yellow image data of the first line from the frame memory 30 for each pixel during the paper feeding, and writes this in the first line memory 32. Also, in order to reduce the fluctuation of the bias heating amount due to the variation of the resistance value of each heating element,
The drive pulse number data for bias heating is read out and written into the third line memory 34.

When the platen drum 10 rotates intermittently by a fixed step and the leading end of the recording area of the color thermosensitive recording material 12 reaches the thermal head 14, thermal recording on the first line is enabled. A line start signal is generated and sent to the memory controller 42. The memory controller 42 sets the selector 40 to the third
It connects to the line memory 34 and sends the data of the number of drive pulses for bias heating of each heating element to the comparator 41. Further, the memory controller 42 generates a one-line start signal and sends it to the print controller 43.
The print controller 43 sends the comparison data to the comparator 41 in response to the one-line start signal. At this time, the number of occurrences of the one-line start signal is counted, and when this is an odd number, comparison data “1” to “FF” for bias heating are sent. If the number is an even number, comparison data “1” to “3F” for gradation expression are sent.

The comparator 41 compares the driving pulse number data (B) for each heating element with the comparison data (C) output from the print controller 43, and outputs the comparison result as driving data. One line of serial drive data output from the comparator 41 is sent to the shift register 45, and is shifted in the shift register 45 by a clock to be converted into parallel drive data. System controller 3
5 latches parallel drive data in the latch circuit array 46 after confirming that the first line is in a state where thermal recording is possible. This latched drive data is
Input to the AND gate array 47.

On the other hand, in response to a bias heating strobe request signal from the print controller 43, the strobe signal generation circuit 44 converts the bias heating strobe signal to AN.
Output to the D gate array 47. AND gate array 4
7 generates a bias heating drive pulse while the strobe signal is being input when the drive data is "1". For example, the transistor 48a is turned on by the bias heating drive pulse, so that the heating element 17a is energized and the bias heating is started.

Hereinafter, the driving pulse number data (B) for bias heating and the comparison data (C) are sequentially compared by the comparator 41, and the number of driving pulses corresponding to the number of pulses corresponding to the resistance value of each heating element is determined based on the comparison result. Is given to each heating element. For this reason, even when there is a variation in the resistance value of each heating element, each heating element is heated in accordance with the variation in the resistance value, so that each heating element of the thermal head is bias-heated substantially uniformly.

The print controller 43 determines near the end of the bias heating from the size of the output comparison data, and sends a one-line end signal to the memory controller 42 at the end of the bias heating. Memory controller 42
Switches the selector 40 in response to the one-line end signal, outputs the image data in the first line memory 32 to the comparator 41, and sends the one-line start signal to the print controller 43. Since the second one-line start signal is input to the print controller 43, the count value of the counter of the print controller 43 is an even number. Accordingly, the print controller 43 sequentially outputs the comparison data “1” to “3F” for gradation expression to the comparator 41. The comparison data (C) is stored in the first line memory 32 by the comparator 41.
Is compared with the yellow image data (A) of the first line read out from the first line. The output of the comparator 41 is “1” for a pixel that thermally records a yellow image, and is “0” for a pixel that does not record a yellow image.

The drive data for one line output from the comparator 41 is sent to an AND gate array 47 after passing through a shift register 45 and a latch circuit array 46. Then, only the heating element whose drive data is "1" is energized during the input of the short strobe signal. In the same manner, gradation levels "2" to "J" are compared, and gradation expression heat energy is applied to the color thermosensitive recording material 12.

FIG. 6 shows an example of a drive pulse train for each heating element. In this example, the first heating element has the maximum resistance value, and the number of bias heating drive pulses to each heating element is reduced based on this value.
For example, when the heating element having the maximum resistance value is heated by 256 bias heating drive pulses, and when the second heating element has a lower resistance than the first heating element, bias heating is performed by, for example, 252 drive pulses. . If the resistance of the third heating element is slightly lower than that of the first heating element, for example, 25
Bias heating is performed by four driving pulses. The number of drive pulses is determined according to the resistance value of each heating element, and is determined by using a conversion table between the resistance value and the number of drive pulses obtained in advance through experiments or the like. Is stored in In addition, for example, when the image data of the first heating element has the maximum density of 64 gradations, the driving pulse train for gradation expression drives the first heating element with 64 consecutive drive pulses. Similarly, when the image data of the second heat generating element has 62 gradations, the second heat generating element is driven by a drive pulse of 62 consecutive pulses. Hereinafter, similarly, the other heating elements are driven by the number of drive pulses corresponding to the image data. Thus, each heating element generates heat with the thermal energy for gradation expression according to the image data of each heating element.

During the reading of the image data from the first line memory 32, the system controller 35 switches the selector 31 to read the image data of the second line from the frame memory 30 and to read the image data of the second line. Write 33. Therefore, it is not necessary to record image data in the line memory when thermally recording the next line, and printing is performed efficiently. Hereinafter, similarly, when image data is read from one line memory, the image data of the next line is written to the other line memory.

The print controller 43 sends a one-line end signal to the memory controller 42 after the generation of the drive pulse train for gradation expression of the first line. The memory controller 42 outputs a system 1 line end signal to the system controller 35 based on the second 1 line end signal. The system controller 35 confirms the end of printing on the first line by the system 1 line end signal, and thereby rotates the platen drum 10 by one line to feed the paper. During this paper feeding, the system controller 35 sends a system 1 line start signal to the memory controller 42. Memory controller 4
2 switches the selector 40 to the third line memory 3
The data of the number of driving pulses for bias heating of No. 4 is sent to the comparator 41. Thereafter, as described above, when the drive pulse train for bias heating is generated, the process is switched to the second line memory 33, and the drive pulse train for gradation expression is generated based on the image data of the second line. And K
(K is a maximum of 256) drive pulses and J
(J is a maximum of 64) gradation drive pulses are applied to each heating element to thermally record the second line. Hereinafter, similarly, the third and subsequent lines are sequentially thermally recorded, and the line recording for one frame of the yellow image is completed.

As shown in FIG. 2, during the thermal recording of the yellow image, the portion of the color thermosensitive recording material 12 where the yellow image is thermally recorded reaches the yellow fixing ultraviolet lamp 16 as the platen drum 10 rotates. The ultraviolet lamp 16 for yellow fixing irradiates the near-ultraviolet light near 420 nm to the color thermosensitive recording material 12. As a result, the diazonium salt compound contained in the yellow thermosensitive recording material 12 is decomposed, and the coloring ability is lost.

When the platen drum 10 makes one rotation and the recording area comes to the position of the thermal head 14 again, the magenta image is thermally recorded line by line. In the thermal recording of the magenta image, the pulse width of the strobe signal becomes longer because the ON time setting data of each strobe signal is larger than that of the thermal recording of the yellow image. Therefore, although relatively large heat energy for coloring is applied to the color thermosensitive recording material 12, since the yellow heat-sensitive coloring layer 23 has already been optically fixed, the yellow heat-sensitive coloring layer 23 does not develop color again. The color thermosensitive recording material 12 on which the magenta image was recorded was subjected to 36 by an ultraviolet lamp 15 for magenta.
UV light of about 5 nm is irradiated, and the magenta thermosensitive coloring layer 2
2 is light-fixed.

When the platen drum 10 makes one more rotation and the recording area comes to the position of the thermal head 14 again, a cyan image is thermally recorded on the cyan thermosensitive coloring layer 21 line by line. This cyan thermosensitive coloring layer 21 has a value at which the coloring heat energy does not develop in a normal storage state.
No light fixing property is given to the cyan thermosensitive coloring layer 21. Therefore, in the thermal recording of the cyan thermosensitive coloring layer 21,
The magenta ultraviolet lamp 15 and the yellow ultraviolet lamp 16 are turned off.

In the above embodiment, when determining the number of drive pulses for bias heating based on the resistance value of each heating element, the difference from the reference resistance value is determined based on the detected maximum resistance value. ing. Then, 256 bias heating drive pulses are given to the maximum resistance value, and the number of bias heating drive pulses is reduced based on the resistance decrease value of each heating element. An average resistance value may be obtained based on the value, and the number of bias heating drive pulses may be increased or decreased with respect to the average resistance value. Furthermore, the number of bias heating drive pulses for each heating element may be determined based on the minimum resistance value.

In the above embodiment, the first to third line memories 32 to 34 are provided, the first and second line memories 32 and 33 are used for image data, and the third line memory 34 is used for resistance unevenness. For correction, these are switched by the selector 40. In addition, as shown in FIG. 7, a fourth line memory 34a is further provided, which is used for correction of density unevenness due to temperature rise. Is also good.
In FIG. 7, the same components as those in the embodiment shown in FIG. 1 are denoted by the same reference numerals, and description thereof is omitted. In the case of this embodiment, the system 1 of the memory controller 42
The line start signal is counted by the counter P. When the count value p reaches the recording line where the density unevenness occurs due to the temperature rise, and when the count value q of the one line end signal is an odd number, the selector 40 is switched. Then, the pulse number data for bias heating from the line memory 34a for correcting uneven temperature rise is sent to the comparator 41.

The density unevenness correction data due to the temperature rise is obtained in advance by an experiment for each type of the thermal head 14, and is stored in a predetermined area of the ROM 38. The correction data is obtained according to the number of recording lines, and the content of the correction data is rewritten according to the number of recorded lines.

In the above embodiment, the line memories are individually provided. However, it is also possible to arrange a large-capacity memory for each predetermined area and read them out by the memory controller. In the above embodiment, two line memories for image data are provided, but three or more line memories may be provided. Further, the present invention can be applied to thermal transfer recording as well as thermal transfer recording for correcting uneven resistance and uneven temperature rise. In addition to line printers,
It can also be used for serial printers. Instead of changing the ON / OFF time of the strobe signal for each color, the number of drive pulses for bias heating and the number of drive pulses for gradation expression may be changed for each color. Also,
Although the length of the strobe signal is changed between the bias heating and the gradation expression heating, the same strobe signal may be used. In this case, the number of each pulse is changed according to the heating amount. Furthermore, bias heating
And the order of the gradation expression heating may be interchanged.
Can also give the same heat energy to the recording material
You.

[0050]

As described in detail above, according to the present invention, the number of bias heating drive pulses is determined based on the resistance value of each heating element, and the amount of bias heating of each heating element is made substantially constant. Thus, even when the resistance value of each heating element varies, the amount of bias heating of each heating element can be made substantially constant. Thus, it is possible to reduce the occurrence of density unevenness due to the variation in the resistance value of the heating element. In addition, since each heating element is driven by a pulse train composed of a large number of pulses, fine heat control can be performed, and the occurrence of density unevenness can be further reduced.

Further, by providing a plurality of line memories for image data and recording the image data of the next recording line in the other line memory while performing thermal recording using the image data from one line memory, the efficiency is improved. Image data can be transferred well.

Further, a line memory for correcting unevenness in temperature rise is provided. Immediately after the start of thermal recording, bias heating is performed based on the correction data in the line memory for correcting unevenness in resistance value. Sometimes, after heating each heating element based on the correction data from the line memory for uneven temperature rise correction data, and then performing gradation heating based on the image data from the line memory for image data, the density caused by the uneven temperature rise The occurrence of unevenness and uneven color can be suppressed. Moreover, by rewriting the temperature rise unevenness correction data in accordance with the number of recording lines, it is possible to perform finer unevenness correction.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a main part of a thermal head drive control device of the present invention.

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

FIG. 3 is an explanatory view showing a layer structure of a color thermosensitive recording material.

FIG. 4 is a graph showing the coloring characteristics of each thermosensitive coloring layer.

FIG. 5 is a flowchart illustrating a processing procedure of the color thermal printer.

FIG. 6 is an explanatory view showing an example of a driving pulse train for bias heating and a driving pulse train for gradation expression.

FIG. 7 is a block diagram illustrating a main part of a thermal head drive control device according to another embodiment.

[Explanation of symbols]

 REFERENCE SIGNS LIST 12 color thermal recording material 14 thermal head 17 a to 17 n heating element 31, 41 selector 32, 33 image data line memory 34 resistance unevenness correction line memory 34 a temperature rise unevenness correction line memory 35 system controller 37 resistance value detection circuit 42 memory Controller 43 Print controller 44 Strobe signal generation circuit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B41J 2/35 B41J 2/36 B41J 2/365

Claims (3)

(57) [Claims] 1. A thermal head of a thermal printer for recording an image by applying a driving pulse train for bias heating and a driving pulse train for gradation expression heating to each heating element of a thermal head having a large number of heating elements arranged in a line. In the drive control device, correction data for storing the number data of the bias heating drive pulse train for one line of the heating element for making the bias heating amount of each heating element determined based on the resistance value of each heating element constant. A line memory for image data, a plurality of line memories for image data for storing image data for one line of the heating element, and switching between these line memories by using a drive pulse train for heating a bias pulse from the line memory for correction data.
Bias heating of each heating element and gradation addition of each heating element based on image data from one of the image data line memories.
Heat, and the next line is driven by a bias pulse heating drive pulse train from the correction data line memory .
Bias heating of each heating element, and each heating element based on image data from another one of the line memories for image data.
The image data is recorded by the gradation heating of the image, and the bias data is heated by the line memory for the correction data and the image data switched in order.
Gradation heating by multiple line memories for
A thermal head drive control device, comprising: a controller for sequentially recording each line. 2. A thermal head of a thermal printer for printing an image by applying a bias heating drive pulse train and a gradation expression heating drive pulse train to each heating element of a thermal head in which a number of heating elements are arranged in a line. In the drive control device, a resistance value for storing one line of the heating element for the number data of the driving pulse train for bias heating for making the bias heating amount of each heating element determined based on the resistance value of each heating element constant. An unevenness correction line memory, and one line of the heating element for storing the number data of the bias heating driving pulse train for correcting the density unevenness due to the temperature rise of each of the heating elements and keeping the bias heating amount of each heating element constant. Line memory for correcting temperature rise unevenness, and an image data line for storing image data for each heating element line Memory, and these line memories are switched to bias heating of each heating element by a driving pulse train for bias pulse heating from the line memory for resistance value unevenness correction data, and heating of each heating element based on image data from the line memory for image data . Floor
Regulating heating and performs, following a bias heated by the line memory for correction data, by performing the image heating by the line memory for image data recorded sequentially and each line, the number of recording lines uneven density due to a temperature rise occurs When it reaches
Bias heating of each heating element by the drive pulse train for bias pulse heating from the temperature rise unevenness correction data line memory and the image data from the image data line memory
And a controller for performing gradation heating of each heating element based on the temperature and sequentially recording each line. 3. The thermal head drive control device for a thermal printer according to claim 2, wherein the temperature rise non-uniformity correction line memory rewrites correction data in accordance with the number of recorded lines. apparatus.