JP2002337380A - Method for driving thermal head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for driving a thermal head in which high speed and/or high gray scale print can be ensured without increasing the data transfer clock frequency significantly using a thermal head mounting an inexpensive binary on/off drive IC employed commonly in FAX, and the like. SOLUTION: Upon receiving 10 bit gray scale data, a binarizing section 103 divides the gray scale data in time series into most significant 8 bits and least significant 2 bits which are then binarized separately before being outputted to a thermal head 108. At the time of printing the most significant 8 bits data binarized at the binarizing section 103, a strobe generator 106 and a timing controller 107 drive the thermal head 108 with first print energy and drive the thermal head 108 with second print energy at the time of printing binarized data of least significant 2 bits.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head driving method for performing gradation printing on a line-by-line basis. The present invention relates to a thermal head driving method that enables high-gradation and high-speed printing using a mounted thermal head. Further, the present invention can be applied to a thermal head driving method that enables dot gradation such as a heat-sensitive method, a sublimation method, and a TA method.

[0002]

2. Description of the Related Art Conventionally, there is a thermal head driving method in which a thermal ribbon is pressed against a document and heated using a thermal head to dissolve ink and print. Further, among the thermal head driving methods, there is a sublimation type method that enables gradation expression using a sublimation ribbon, and gradation expression can be performed by transferring gradation data to the thermal head. .

In the sublimation type thermal head driving method, the thermal head outputs a strobe pulse corresponding to the transferred gradation data in a multi-pulse configuration according to a gradation level (the number of gradation data). Further, when printing is performed, a thermal head in which heating elements are arranged in a line is used, and the heating elements are handled in units of one line. Therefore, when printing is performed with N gradations per pixel, binary data of the number of pixels * 2 ^N is transferred to the thermal head in one line.

A related prior art is disclosed in Japanese Patent Application Laid-Open No. 9-8 / 1997.
No. 5979, "Thermal printing method and thermal printer" discloses a method for increasing the number of recordable gradations of a thermal head. When printing a dot with (K + n) (n is an integer) bits of heat generation data using a thermal head corresponding to K (K is an integer) bits,
The (K + n) -bit heating data is divided into P K-bit converted heating data, and P heating sequences are continuously executed using each K-bit converted heating data.

In order to increase the speed of printing, it is necessary to increase the speed at which the document is fed. However, as the speed at which the document is fed increases, it becomes necessary to shorten the line cycle. In order to shorten the line cycle, the data transfer rate per unit time must be improved, but there is a limitation on the speeding up as described later. Further, in the case of printing at a high gradation, the number of gradation data increases, so that it is necessary to improve the data transfer speed per unit time of the gradation data.

Specifically, for example, 1280 pixels are set to 20
It is divided into blocks, and one line is composed of 64 pixels.
When transferring 0-bit serial binary data, 64 * 1024 = 65536 binary data are transferred during one line cycle. If one line cycle is to be 4 ms, the transfer clock to the thermal head is 16.4.
MHz. However, in practice, since the length of the harness between the control board and the thermal head is several tens of centimeters, the data transfer speed is limited to about 10 MHz.

Further, it is not preferable to supply a high-frequency clock to the harness, since unnecessary electrolytic radiation may be caused, and a television or radio using radio waves may be obstructed.

Therefore, according to Japanese Patent Application Laid-Open No. 6-87229, entitled "Grayscale control circuit and thermal head using the same", the data of the number of grayscale display bits is simultaneously transferred to the shift register, thereby reducing the transfer time. Is being shortened.

[0009]

According to Japanese Patent Application Laid-Open No. 6-87229, however, although the transfer time can be reduced, a thermal head equipped with a drive IC capable of transferring multi-value data in parallel is used. There is a problem that the head itself becomes expensive.

According to Japanese Patent Application Laid-Open No. 9-85879, an inexpensive K-bit compatible thermal head is used.
Although high-gradation expression can be performed for (K + n) bits, there is a problem in that high-speed printing cannot be performed because there is a restriction in increasing the data transfer speed.

The present invention has been made in view of the above, and is an inexpensive on / off 2 which is frequently used in a facsimile or the like.
It is an object of the present invention to provide a method of driving a thermal head capable of printing at high speed and / or high gradation without using a thermal head having a value drive IC mounted thereon without increasing the frequency of a data transfer clock.

[0012]

In order to achieve the above object, a method of driving a thermal head according to the present invention comprises:
It has a thermal head mounted with a drive IC for on / off binary in which a plurality of heating resistors are arranged in a line, and performs gradation recording of N bits per pixel (N is an integer) using the thermal head. In the thermal head driving method, when N-bit grayscale data is input, the N-bit grayscale data is divided into upper H bits and lower L bits (L = N−H) in a time-series manner. A binarizing step of binarizing the H bit and the lower L bit separately, and a first applied energy when printing the binarized data of the upper H bit binarized in the binarizing step And driving the thermal head with the second applied energy when printing the lower-order L-bit binary data.

According to the present invention, the gradation data is stored in the upper H
By dividing the upper H bit and the lower L bit separately into a binary value and a lower L bit in a time series, and individually setting the applied energy, the frequency of the data transfer clock can be reduced. Even if the height is not increased, N-bit gradation printing can be performed.

According to a second aspect of the present invention, there is provided a thermal head driving method according to the first aspect, wherein the second applied energy is smaller than the first applied energy.

According to the present invention, the gradation data is stored in the upper H
Bits and lower L bits in time series, the upper H bits and the lower L bits are separately binarized, and the second applied energy is made smaller than the first applied energy. In addition, N-bit gradation printing can be performed without making the frequency of the data transfer clock too high.

According to a third aspect of the present invention, there is provided a thermal head driving method according to the second aspect, wherein the driving step comprises changing a DUTY of a multi-strobe pulse applied to the thermal head.
It is characterized by switching between the first applied energy and the second applied energy.

According to the present invention, by changing the DUTY of the multi-strobe pulse applied to the thermal head, it is possible to easily adjust the output of the energy with respect to the first applied energy and the second applied energy. .

According to a fourth aspect of the present invention, in the thermal head driving method of the third aspect, the duty of the first applied energy is DH and the duty of the second applied energy is DL. , DL = DH / 2 ^L.

According to the present invention, the duty of the first applied energy is DH, and the duty of the second applied energy is DH.
When Y is DL, DL = DH / 2 ^L , so that N-bit gradation printing can be performed without increasing the frequency of the data transfer clock very much.

According to a fifth aspect of the present invention, there is provided a thermal head driving method according to the second aspect, wherein the driving step comprises changing a voltage applied to a heating resistor of the thermal head. It is characterized by switching between the first applied energy and the second applied energy.

According to the present invention, by changing the voltage applied to the heating resistor of the thermal head, the output adjustment of the energy can be easily performed with respect to the first applied energy and the second applied energy. .

According to a sixth aspect of the present invention, in the thermal head driving method according to the fifth aspect, the voltage of the first applied energy is VH.
When the voltage of the second applied energy is VL, VL =
VH / 2 ^{L / 2} .

According to the present invention, the voltage of the first applied energy is VH, and the voltage of the second applied energy is VL.
In this case, the relationship of VL = VH / 2 ^{L / 2} allows N-bit gradation printing without increasing the frequency of the data transfer clock.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a method for driving a thermal head according to the present invention will be described below in detail with reference to the accompanying drawings. Note that the following is an example,
It is not limited to the following.

(Embodiment 1) FIG. 1 is a schematic configuration diagram of a thermal head driving apparatus to which a thermal head driving method according to Embodiment 1 is applied. The thermal head driving device according to the first embodiment includes a CPU 101 that controls the entire device,
A buffer RAM 102 for inputting and temporarily storing one line of image data from a frame memory (not shown);
Input image data, which is 10-bit gradation data, and
A binarization unit 103 that performs a binarization process;
An output RAM 104 for temporarily storing the digitized data for thermal head output, a strobe generator 106 for generating a strobe pulse (/ STB), a timing controller 107 for performing timing control described later,
A thermal head 108 mounted with a drive IC for on / off binary in which a plurality of heating resistors are arranged in a line,
A head driving power supply 109 for supplying a voltage to the thermal head 108. In the drawing, reference numeral 100 denotes a control / data transfer bus.

In the first embodiment, the binarizing section 103
Plays the role of the binarization step of the present invention, and the strobe generator 106 and the timing controller 107 play the role of the drive step of the present invention. In the first embodiment, one line is set to 1280 pixels,
Handle by dividing into blocks. The grayscale data per pixel is N bits (here, 10 bits), and the N-bit grayscale data is composed of upper H bits (here, 8 bits) and lower L bits (here, 2 bits). ) And are binarized separately.

The operation of the above configuration will be described. The CPU 101 stores 1 from a frame memory (not shown).
The image data for the line is written into the buffer RAM 102, and a / START signal is output to the timing controller 107. The timing controller 107 outputs / ST
When the ART signal is input, the self-running operation starts, and the HCLK
The signal is output to binarization section 103. The binarization unit 103
One line of image data is read from the buffer RAM 102 based on the HCLK signal, compared by a magnitude comparator in the binarization unit 103, converted into a binary signal (0/1 signal), and output to the output RAM 104. Output. Here, the binarized upper and lower gradation data are individually stored in different areas.

Next, the timing controller 107
Outputs a / LATCH signal to the thermal head 108 to activate the strobe generator 106. The strobe generator 106 outputs a strobe pulse to the thermal head 108. Thermal head 108
When the / LATCH signal is input, printing is performed using binarized gradation data (HDATA) and a strobe pulse.

FIG. 2 is a circuit diagram of the thermal head.
The thermal head 108 includes a thermal head driver 200 arranged in a line, a heating resistor 205,
Consists of The thermal head driver 200
A shift register 201 for temporarily storing binary data for 64 pixels input in a time series, and 64 pixels for reading and outputting gradation data for 64 pixels from the shift register 201 when a / LATCH signal is input. Bit latch 20
A, which performs an AND operation from the grayscale data of 64 pixels input from the 64-bit latch 202 and the / STB signal
It comprises an ND circuit 203 and a transistor 204 that functions as a switch by energizing the heating resistor 205 based on the output value of the AND circuit 203.

The operation of the above configuration will be described. First, HDATA1 to HDATA20 which have converted the grayscale data into binary signals by the binarization unit 103 are used as shift registers 20.
1 are input in time series, and then the / LATCH signal is input to the 64-bit latch 202. The 64-bit latch 202 stores the H held in the shift register 201
DATA is output to the AND circuit 203. AND circuit 2
03 is the / STB signal output from the strobe generator 106 and H output from the 64-bit latch 202.
AND operation with DATA and outputs the result to the transistor 204. The transistor 204 functions as a switch based on the value output from the AND circuit 203, and power is supplied from the head drive power supply 109 to the heating resistor 205.

FIG. 3 is a timing chart of the thermal head driving method according to the first embodiment. CPU10
Reference numeral 1 denotes a buffer RAM 10 for storing gradation data for the first line.
After the output to the timing controller 107, a / START signal is output to the timing controller 107. When the / START signal is input, the timing controller 107 starts a free-running operation and outputs the HCLK signal to the binarization unit 103 and the thermal head 108. When the HCLK signal is input, the binarization unit 103 reads out the gradation data of 64 pixels stored in the buffer RAM 102, compares the gradation data with the magnitude comparator, converts the gradation data into binarization data, and outputs the output data.
Output to AM104. The timing controller 107 controls the binarized data output from the binarizing unit 103 in time series in synchronization with the HCLK signal in units of 64 pixels.
Outputs a / LATCH signal to the thermal head 108 every 64 cycles of the HCLK signal. Thermal head 108
When the / LATCH signal is input, an AND operation is performed on the strobe pulse and HDATA, and 20
Block * One gradation data of 64 pixels is applied.

Next, the binarizing section 103 outputs the binarized data stored in the output RAM 104 based on the HCLK signal as HDATA (HDATA1 to HDATA20) in units of 64 pixels to the thermal head 108 in time series. I will do it. In addition, as described above, 2 is synchronized with the HCLK signal.
When the binarized data output from the binarizing unit 103 in time series is 6
The timing controller 10 is set so as to be in units of four pixels.
7 outputs the / LATCH signal to the thermal head 108 every 64 cycles of the HCLK signal. The above operation is performed for the upper 8 bits, that is, binarized, and is repeated 2 ⁸ (= 256) times. The strobe pulse output from the strobe generator 106 is set in the strobe generator 106 by the timing controller 107 so that DUTY (ON / OFF ratio) is output as 0.5.

Next, when the upper 8 bits of gray scale data are applied, the timing controller 107 sets the duty cycle of the strobe pulse to the strobe generator 106 so as to output the duty cycle of 0.125. Subsequently, for the lower two bits of grayscale data, the binarization unit 103
Based on the HCLK signal, the binarized data stored in the output RAM 104 is sequentially output to the thermal head 108 in units of 64 pixels in time series. Also, as in the case of the grayscale data of the upper 8 bits, 2 bits are synchronized with the HCLK signal.
When the binarized data output from the binarizing unit 103 in time series is 6
The timing controller 10 is set so as to be in units of four pixels.
7 outputs the / LATCH signal to the thermal head 108 every 64 cycles of the HCLK signal. The above operation is performed for the lower two bits, that is, binarized, and is repeated 2 ² (= 4) times.

As described above, in the switching of the applied energy in the first embodiment, after applying the upper 8 bits of the grayscale data, the timing controller 107 sends the strobe pulse DUT to the strobe generator 106.
This is performed by setting Y. That is, the upper 8 bits 2
For the application of 56 gradations, the strobe pulse DU
TY is set to 0.5, and the duty of the strobe pulse is set to 0.1 for the application of the lower 2 bits for 4 gradations.
Set as 25.

Therefore, the applied energy of the lower 2 bits (second applied energy) is 1/4 of the applied energy of the upper 8 bits (first applied energy) per strobe pulse. Assuming that the applied energy is proportional to the gradation expression in printing, the gradation expression can be made four times finer by combining the applied energy of the upper 8 bits and the applied energy of the lower 2 bits. Thereby, 260 (= 256 +
4) 256 gradations * 4 times = 1024 for gradation data
Gradation can be realized.

As described above, in the thermal head driving method according to the first embodiment, 10-bit gradation printing can be realized at a speed substantially equal to the 8-bit gradation data transfer speed. In other words, printing is performed at high speed and / or high gradation without using a very high frequency of the data transfer clock by using a thermal head mounted with an inexpensive on / off binary drive IC frequently used in facsimile and the like. A possible thermal head driving method can be provided.

(Embodiment 2) Next, Embodiment 2 of the present invention will be described. In the second embodiment, the switching of the applied energy is performed by changing the voltage. Since the basic configuration and operation are the same as those of the first embodiment, only different portions will be described here. It should be noted that the following is merely an example, and the present invention is not limited to the following.

FIG. 4 is a schematic configuration diagram of a thermal head driving apparatus to which the thermal head driving method according to the second embodiment is applied. The thermal head driving device of the second embodiment is almost the same as the thermal head driving device of the embodiment shown in FIG.
9 is different from the head drive power supply 9 in that the head drive power supply 401 includes a mechanism for controlling the voltage inside.

FIG. 5 is an internal configuration diagram of the head drive power supply 401 according to the second embodiment. Head drive power supply 401
Is composed of a control unit 501 for controlling a voltage by a voltage switching signal from the timing controller 107 and a switching unit 502 for controlling the voltage.

The operation of the above configuration will be described. The switching of the applied energy in the second embodiment is performed by changing the voltage after applying the applied energy of the gradation data of the upper 8 bits to the thermal head 108. That is, when applying the applied energy of the lower 2 bits of gradation data to the thermal head 108, the applied energy of the upper 8 bits of gradation data is applied to the thermal head 1.
08 is set so that it becomes a voltage of １ ／ (√) with respect to the voltage when applied to 08. After applying the applied energy of the upper 8-bit gradation data to the thermal head 108, the timing controller 107 controls the control unit 501.
Outputs a voltage switching signal. When the voltage switching signal is input, the control unit 501 transfers the applied energy of the upper 8 bits of gradation data to the thermal head 10.
The switching unit 502 is controlled so that the voltage applied to the switching unit 8 becomes 電 圧 (１ ／) of the voltage applied to the switching unit 502.

Here, the energy applied to the thermal head is the amount of heat generated by the heating resistor 205, and the amount of heat generated is proportional to the square of the voltage.
(1/4) means the calorific value (applied energy)
Is 1/4. Therefore, the applied energy of the lower 2 bits is 1/4 of the applied energy of the upper 8 bits per strobe pulse. As a result, assuming that the applied energy is proportional to the gradation expression in printing, the gradation expression can be quadrupled by combining the application energy of the upper 8 bits and the application energy of the lower 2 bits. Thus, for 260 (= 256 + 4) gradation data,
256 gradations * 4 times = 1024 gradations can be realized.

As described above, in the thermal head driving method according to the second embodiment, 10-bit gradation printing can be realized at a speed substantially equal to the 8-bit gradation data transfer speed. In other words, printing is performed at high speed and / or high gradation without using a very high frequency of the data transfer clock by using a thermal head mounted with an inexpensive on / off binary drive IC frequently used in facsimile and the like. A possible thermal head driving method can be provided.

[0043]

As described above, according to the first aspect of the present invention, the grayscale data is divided into higher-order H bits and lower-order L bits in chronological order, and the upper-order H bits and the lower-order L bits are divided. Since the bits are separately binarized and the applied energy is individually set, N-bit gradation printing can be performed without making the frequency of the data transfer clock too high. In other words, inexpensive on / off switches often used in fax
It is possible to provide a method of driving a thermal head capable of printing at high speed and / or high gradation without using a thermal head having a drive IC for off-state binary, without increasing the frequency of the data transfer clock very much.

According to the second aspect of the present invention, the grayscale data is divided into higher-order H bits and lower-order L bits in time series, and the upper-order H bits and the lower-order L bits are separately divided into two. Since the energy is converted into a value and the second applied energy is made smaller than the first applied energy, N-bit gradation printing can be performed without making the frequency of the data transfer clock too high. That is, using a thermal head mounted with an inexpensive on / off binary drive IC frequently used for facsimile or the like, high-speed and / or high-gradation printing can be performed without increasing the frequency of the data transfer clock. A method for driving a thermal head can be provided.

According to the third aspect of the present invention, the duty of the multi-strobe pulse applied to the thermal head is changed, so that the energy output can be easily adjusted with respect to the first applied energy and the second applied energy. It can be carried out. In other words, the data transfer clock can be more easily implemented by using a thermal head mounted with an inexpensive on / off binary drive IC frequently used for facsimile and the like than the thermal head driving method according to claim 1 or 2. A thermal head driving method capable of printing at a high speed and / or a high gradation without increasing the frequency of the thermal head.

Further, according to the invention of claim 4, since the DUTY of the first applied energy and DH, if the DUTY of the second applied energy was DL, it is the relationship DL = DH / 2 ^L, N-bit gradation printing can be performed without increasing the frequency of the data transfer clock very much. In other words, the frequency of the data transfer clock can be more easily determined by using a thermal head mounted with an inexpensive on / off binary drive IC frequently used for facsimile and the like than the thermal head driving method according to claim 3. And a thermal head driving method capable of printing at high speed and / or high gradation without increasing the value of

According to the fifth aspect of the present invention, since the voltage applied to the heating resistor of the thermal head is changed, the first
The output adjustment of the energy can be easily performed with respect to the applied energy and the second applied energy. In other words, a data transfer clock can be obtained by using a thermal head mounted with an inexpensive on / off binary drive IC that is frequently used for facsimile and the like more easily than the thermal head driving method according to claim 1 or 2. A thermal head driving method capable of printing at a high speed and / or a high gradation without increasing the frequency of the thermal head.

According to the invention of claim 6, when the voltage of the first applied energy is VH and the voltage of the second applied energy is VL, the relationship is VL = VH / 2 ^{L / 2.} Therefore, N-bit gradation printing can be performed without increasing the frequency of the data transfer clock very much. In other words, the frequency of the data transfer clock can be more easily determined by using a thermal head mounted with an inexpensive on / off binary drive IC frequently used for facsimile and the like than the thermal head driving method according to claim 5. And a thermal head driving method capable of printing at high speed and / or high gradation without increasing the value of

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a thermal head driving device to which a thermal head driving method according to a first embodiment is applied.

FIG. 2 is a circuit diagram of a thermal head.

FIG. 3 is a timing chart of a thermal head driving method according to the first embodiment.

FIG. 4 is a schematic configuration diagram of a thermal head driving device to which a thermal head driving method according to a second embodiment is applied.

FIG. 5 is an internal configuration diagram of a head drive power supply according to a second embodiment.

[Explanation of symbols]

 101 CPU 102 Buffer RAM 103 Binarization Unit 104 Output RAM 106 Strobe Generator 107 Timing Controller 108 Thermal Head 109 Head Driving Power 401 Head Driving Power 501 Control Unit 502 Switching Unit

Claims (6)

[Claims] 1. A thermal head mounted with a drive IC for on / off binary in which a plurality of heat generating resistors are arranged in a line, and N bits (N is an integer) of one pixel using the thermal head. In the thermal head driving method for performing gradation recording, when N-bit gradation data is input, the N-bit gradation data is converted to upper H bits and lower L bits (L = N−
H) in a time-series manner, and separately binarizes the upper H bits and the lower L bits separately; and the upper H binarized in the binarization step. Bit 2
Driving the thermal head with a first applied energy when printing the digitized data, and driving the thermal head with a second applied energy when printing the lower-order L-bit binary data A method for driving a thermal head, comprising: 2. The method according to claim 1, wherein the second applied energy is the first applied energy.
2. The applied energy is smaller than the applied energy.
3. The method for driving a thermal head according to item 1. 3. The method according to claim 2, wherein the driving step switches between the first applied energy and the second applied energy by changing a DUTY of a multi-strobe pulse applied to the thermal head. The driving method of the thermal head described in the above. 4. The duty of the first applied energy is DH, and the duty of the second applied energy is DL.
4. The method according to claim 3, wherein DL = DH / 2 ^L. 5. The method according to claim 2, wherein in the driving step, the first applied energy and the second applied energy are switched by changing a voltage applied to a heating resistor of the thermal head. The driving method of the thermal head described in the above. 6. The voltage of the first applied energy is VH
6. The method according to claim 5, wherein, when the voltage of the second applied energy is VL, VL = VH / 2 ^{L / 2} .