JPH0675971B2 - Recording density control method in thermal recording - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a recording density control method in thermal recording, and more particularly, to detecting the temperature of the thermal recording head by a temperature sensor attached to the thermal recording head and the detected temperature. The controlled electric energy is applied to the thermosensitive recording head at a constant cycle, and the thermosensitive recording head causes a required heating element of the plurality of heating elements arranged in a line to correspond to the electric energy. In a recording density control method for heat-sensitive recording in which one line is printed by generating heat,
The present invention relates to a recording density control method in thermal recording, which is improved so as to prevent variations in density in the sub-scanning direction when printing by a thermal recording head is temporarily stopped.

[Technical background of the invention]

Generally, a thermal recording head used for thermal recording is composed of a plurality of heat generating elements so as to correspond to the number of pixels of the thermal recording medium in the main scanning direction, and an electric energy ( Print pulse)
To the required heating element corresponding to the print data, and by heating only this required heating element, a thermal recording medium such as a thermal recording paper or an ink donor sheet slidingly contacting this thermal recording head can generate the required heating. It is configured to perform color printing in accordance with the element.

By the way, when printing is performed using such a thermal recording head, the degree of color development increases when the temperature of the heating element itself is high, even if the electric energy applied from the outside is the same, and conversely, the heating element itself. When the temperature is low, the degree of color development decreases, so that the density varies in the sub-scanning direction.

This is because the temperature of the heating element itself is affected by the temperature of the thermal recording head itself, that is, the substrate temperature of the thermal recording head.

Therefore, conventionally, a temperature sensor is attached to the thermal recording head, the temperature reading of the thermal recording head itself is detected by this temperature sensor, and when the detected temperature is high, the electric energy applied to the thermal recording head is reduced, and vice versa. If the temperature read by the temperature sensor is low, increase the electric energy applied to the thermal recording head so that the print density in the sub-scanning direction will always be constant even if the temperature of the thermal recording head changes. ing. The electric energy applied to the thermal recording head is controlled by changing the printing time, pulse width, voltage or current, for example.

FIG. 1 is a block diagram showing a control device for a conventional thermal recording head H having a thermistor Th as the temperature sensor as described above.

The control device of the thermal recording head H shown in FIG. 1 detects the temperature of the thermal recording head H itself by the thermistor Th attached to the thermal recording head H, and detects the temperature by the thermistor Th. Controls the electrical energy applied to the.

Generally, the resistance value of the thermistor Th is inversely proportional to the temperature, so that the voltage of the output signal a thereof is low at high temperature and high at low temperature. This output signal a is converted into a digital signal b by the A / D converter 1, and this digital signal b is given to the bus driver 2. The control unit 3 gives a temperature read signal c to the gate terminal of the bus driver 2 to read the digital signal b via the data bus d.

From the oscillator 4, for example, a 10 kHz clock pulse e (7th
(See FIG. 7E) is generated and input to the counter 5, and the counter 5 outputs a pulse f (see FIG. 7F) once at a constant interval, for example, 4 ms. This pulse f is input to the control unit 3 as an interrupt signal, whereby the control unit 3 executes the interrupt program.

The processing at the time of this interruption is shown in a flowchart in FIG.
In this flowchart, the control unit 3 uses the pulse f
When occurs, first, it is determined whether or not the thermal recording head H can print.

Specifically, print data of "1" or "0" is applied to the thermal recording head H line by line corresponding to the plurality of heating elements, and a head enable signal given at a constant cycle described later is given. Corresponding to k, the print current is passed only to the heating element corresponding to "1" in the print data of this one line, whereby the printing of one line is performed. If the thermal recording head H has print data for one line to be printed at the generation timing of the enable signal k, it is determined that printing is possible, and the print data for one line to be printed is still stored in the thermal recording head H. If it has not arrived, it is determined that printing is not possible.

That is, the control device of the thermal recording head H prints each line in a constant cycle in response to the head enable signal k given in a constant cycle. However, the processing speed of the external print data processing circuit, etc. Therefore, at the timing of generation of the head enable signal k, the print data for one line to be printed may not yet reach the thermal recording head H. In this case, one line cannot be printed. Judge as not acceptable.

When it is determined that the thermal recording head H is not printable in the determination as to whether the thermal recording head H is printable or not, printing is not performed and the interrupt process is ended.

When it is determined that the thermal recording head H is printable in the determination as to whether the thermal recording head H is printable, the control unit 3 outputs a temperature reading signal c (see FIG. 7C). As a result, the temperature of the head H is read via the data bus d.

Next, the control unit 3 determines the printing time from the read head temperature based on the table stored in the control unit 3.

An example of this table is shown in FIG. In FIG.
The temperature data in the left column is shown in hexadecimal notation. Table values for each temperature are shown in the center column, and the printing time at that time is shown in the right column.

Next, the control unit 3 gives a latch clock pulse g (see FIG. 7 (g)) to the latch 6, latches the determined printing time in the latch 6 via the data bus d, and ends the interrupt processing. To do.

The latch clock pulse g is also input to the SR latch 7, which outputs a signal h (see FIG. 7 (h)) that goes high when the printing time is latched in the latch 6. After 4 ms, when the next pulse is output from the counter 5, the signal h is at the high level, so that the load pulse i (see FIG. 7 (i)) is loaded to the counter 9 through the NAND gate 8. When the data is loaded into the counter 9, the carry output j of the counter 9 (see FIG. 7 (j)) becomes low level, and the head enable signal k (see FIG. 7 (k)).
(See) becomes high level and printing starts.

That is, in the thermal head H, the enable signal k
Becomes high level, the printing current selectively flows only to the heating element corresponding to the print data “1” in the plurality of heating elements of the thermal head H, the printing is started, and the counter 9 reaches the maximum value. When the carry output j becomes 15 at a high level, the head enable signal k becomes a low level, the print current flowing through the heating element corresponding to the print data "1" is stopped, and the printing is completed.

Also, since the enable terminal of the counter 9 becomes low level, the counting operation of the counter 9 is completed, and the counter 9 does not operate until the data is loaded into the counter 9 next time.

For example, when the temperature data after A / D conversion is 8, "6" is loaded into the counter 9 from FIG. Counter 9 is 0.
The count is incremented every 1 ms, and printing ends when the count reaches 15, resulting in 0.1 (ms) x (15-6) = 0.9 (ms), and the print data corresponds to "1" during 0.9 ms. Printing current flows through the element and printing is performed.

That is, according to this conventional recording density control method in thermal recording, electrical energy corresponding to the temperature detected by the thermistor Th is applied to the thermal recording head H every cycle of the interrupt signal input to the controller 3, for example, every 4 ms. In the thermal recording head H, this electric energy is selectively applied to the heating elements corresponding to the print data of "1", whereby one line is printed at a constant cycle.

If the print data of the line to be printed has not reached the thermal recording head H yet and the thermal recording head H is not ready for printing, this printing operation is temporarily stopped.

[Problems of background technology]

However, in the conventional recording density control method in the above-mentioned thermal recording, when the printing operation of the thermal recording head H in the above-mentioned constant cycle is temporarily stopped, the temperature detected by the thermistor Th attached to the thermal recording head H is the thermal recording. The values are higher than the actual temperatures of the plurality of heating elements of the head H.

This is because the thermal capacity of the thermal recording head H itself is larger than the thermal capacity of the heating element of the thermal recording head H.

Therefore, according to the conventional configuration, when the printing operation is temporarily stopped, the electric energy applied to the thermal recording head H becomes smaller than a desired value, which causes a variation in the printing density in the sub-scanning direction. there were.

[Object of the Invention]

It is therefore an object of the present invention to provide a recording density control method in thermal recording, which is improved so that the printing density in the sub-scanning direction does not vary even when the printing operation by the thermal recording head is temporarily stopped.

[Outline of Invention]

To achieve the above object, in the present invention, the temperature of the thermal recording head is detected by a temperature sensor attached to the thermal recording head, and the electric energy controlled corresponding to the detected temperature is recorded at a constant cycle. The recording is performed in a thermal recording in which one line is printed by applying heat to a head to heat a required heating element among a plurality of heating elements arranged in a line corresponding to the electric energy. In the density control method, it is determined whether the thermal recording head is printable or not printable at each fixed cycle, and when it is determined that printing is not possible, printing is stopped and printing stop is stored, and printing is enabled. If it is determined, the temperature detected by the temperature sensor is read, and if there is no memory of the print stop, the temperature is controlled according to the temperature detected by the temperature sensor. When electric energy is applied to the thermal storage head to store the print stop, the storage of the print stop is erased and the electric energy controlled corresponding to the temperature detected by the temperature sensor is preset by a preset amount. It is characterized in that it is increased and applied to the thermal recording head.

Example of Invention

Hereinafter, the recording density control method for thermal recording according to the present invention will be described in detail with reference to the accompanying drawings.

As the hardware for implementing the recording density control method in the thermal recording of the present invention, the device shown in the block diagram of FIG. 1 can be used as it is. However, in the present invention, the processing at the time of interruption shown in FIG. 2 is different from the conventional one.

FIG. 4 is a flow chart showing an embodiment of the processing at the time of interruption by the recording density control method in the thermal recording of the present invention.

When the interrupt pulse f is generated from the counter 5 in FIG. 1,
The control unit 3 first determines whether or not the thermal recording head H can print. If printing is not possible, printing is stopped and a stop flag indicating that printing is stopped is turned on to end the interrupt processing.

When it is determined that printing is possible, when the printing is possible, the control unit 3 outputs the temperature reading signal c, and the data bus d
The temperature of the thermal recording head H is read via.

Next, from the head temperature read via the data bus d,
The printing time is determined by the table stored in the control unit 3. The same table as shown in FIG. 3 can be used for this table.

Next, it is checked whether the stop flag is on. Here, when the stop flag is not turned on, the control section 3 gives the latch clock pulse g to the latch 6 and latches the printing time determined by the table of FIG. 3 in the latch 6 via the data bus d. Terminates interrupt processing.

When the stop flag is on, processing for increasing the printing time by a fixed time is performed. Specifically, an operation of subtracting 2 from the value read in the table of FIG. 3 is performed.

Next, the control unit 3 clears the stop flag, gives the latch clock pulse g to the latch 6, and sets the value obtained by the above calculation, that is, the value obtained by subtracting 2 from the value read out in the table of FIG. The data is latched in the latch 6 via the data bus d, and this interrupt processing is completed. By this operation,
The printing time can be extended by 0.2 ms compared to when the stop flag is on.

FIG. 5 is a flow chart showing another embodiment of the processing at the time of interruption by the recording density control method according to the present invention.

When the interrupt pulse f is generated from the counter 5 in FIG. 1,
The control unit 3 first determines whether or not the thermal recording head H can print. If printing is not possible, printing is stopped and a stop flag indicating that printing is stopped is turned on to end the interrupt processing.

When it is determined that printing is possible, when the printing is possible, the control unit 3 outputs the temperature reading signal c, and the data bus d
The temperature of the thermal recording head H is read via. The processing up to this point is the same as the processing in FIG.

In the process shown in FIG. 5, after reading the temperature of the thermal recording head H, it is checked whether or not the stop flag is on. Here, if the stop flag is not on, the table 1 is searched. Here, the table 1 is the same as the table shown in FIG. Then, the control unit 3 gives the latch clock pulse g to the latch 6, and latches the printing time determined by the table 1, that is, the table shown in FIG. To finish.

As a result of checking whether or not the stop flag is on, if the stop flag is on, the table 2 is searched. Here, the table 2 is a table in which the printing time is set to be longer than that of the table 1 shown in FIG. 6, that is, the table shown in FIG. And clear the stop flag,
The latch clock pulse g is given to the latch 6, and the printing time determined by the table 2, that is, the table shown in FIG. 6 is latched in the latch 6 via the data bus d.
This interrupt processing ends. By this operation, the printing time can be lengthened compared to when the stop flag is on. In this case, since two tables are used, the lengthening printing time can be arbitrarily set according to the temperature of the recording head H. Can be set.

In the above-mentioned embodiment, as a method of increasing the electric energy applied to the thermal recording head, a method of lengthening the printing time is adopted, but the printing time is kept constant,
It will be readily appreciated that increasing the voltage or current applied to the thermal recording head will also achieve the objects of the invention.

〔The invention's effect〕

As described above, according to the present invention, when the printing by the thermal recording head is stopped in a state where the printing by the thermal recording head is continuously performed in a predetermined cycle,
Next, the correction is made so that the electric energy applied to the thermal recording head is increased by a predetermined amount as compared with the case where the stop does not occur. Therefore, even if the print is stopped, the density variation in the sub-scanning direction is prevented. It is possible to obtain good recording quality.

[Brief description of drawings]

FIG. 1 is a block diagram showing a control device of a thermal recording head,
FIG. 2 is a flow chart showing the processing at the time of interruption in the conventional recording density control method, FIG. 3 is a diagram showing a table for determining the printing time from the temperature data of the thermal recording head, and FIGS. 4 and 5 are the present invention. 6 is a flowchart showing a process at the time of interruption in the recording density control method according to FIG. 6, FIG. 6 is a diagram showing an example of the table 2 used in the process of FIG. 5, and FIG. It is a timing chart explaining operation. 1 ... A / D converter, 2 ... bus driver, 3 ... control unit, 4 ... oscillator, 5 ... counter, 6 ... latch, 7
...... SR latch, 8 …… NAND gate, 9 …… Counter.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shunsuke Katahira 1-chome, 3-1, Asahigaoka, Hino-shi, Tokyo Inside the Toshiba Hino Plant, a manufacturing company (72) Inventor Hiroshi Matsutani 1-3-1, Asahigaoka, Hino, Tokyo Stock company Toshiba Hino Factory (56) Reference JP-A-59-20682 (JP, A) JP-A-59-127782 (JP, A) JP-A-59-153236 (JP, A) JP-A-59- 143659 (JP, A) JP 58-20473 (JP, A) JP 60-94361 (JP, A)

Claims (1)

[Claims] 1. A temperature sensor attached to a thermal recording head detects the temperature of the thermal recording head, and electric energy controlled corresponding to the detected temperature is applied to the thermal recording head at a constant cycle, The thermal recording head is a recording density control method in thermal recording, wherein one line of printing is performed by causing a required heating element of a plurality of heating elements arranged in a line to generate heat corresponding to the electric energy, It is determined whether the thermal recording head is printable or not printable at regular intervals.If it is determined that printing is not possible, printing is stopped and printing stop is stored.If it is determined that printing is possible, If the temperature detected by the temperature sensor is read and the print stop is not stored, the sensed electric energy controlled corresponding to the temperature detected by the temperature sensor is detected. When the print stop memory is applied to the memory head, the print stop memory is erased, and the electric energy controlled corresponding to the temperature detected by the temperature sensor is increased by a preset amount to increase the heat sensitivity. A recording density control method in thermal recording, characterized by applying to a recording head.