JP3013608B2 - Thermal head drive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to driving of a thermal head in a thermal coloring type or thermal transfer type recording apparatus using a thermal head.

[0002]

2. Description of the Related Art In recent years, various types of thermal head driving devices have been proposed for a thermal coloring type and a thermal transfer type recording apparatus in order to increase the speed and the efficiency of recording energy.

As a first conventional example for increasing the efficiency of recording energy, there is a thermal head driving device disclosed in Japanese Patent Application Laid-Open No. 2-43060, for example. FIG. 10 is a timing chart of the thermal head driving of the conventional thermal head driving device, and FIG. 11 is a configuration diagram of a thermal head driven by the conventional thermal head driving device.

[0004] As shown in FIG.
560 heating resistance elements R1 to R2560, transistors tr11 to tr12560, tr21 to tr22560, and gates G1 to
G2560, latch circuit FF11 composed of D flip-flop
FF12560 and a shift register including D flip-flops FF21 to FF22560. The 2560 heating resistance elements R1 to R2560 are odd-numbered heating resistance elements R1 and R2.
Are divided into a first block composed of 3,... And a second block composed of even-numbered heating resistance elements R2, R4,.

As shown in FIG. 10, the gates G1, G3,...
According to the data of 1, FF13,.
By turning on / off tr21, tr13, tr23,..., the heat generating resistance elements R1, R3,. Similarly, the gates G2, G4,... Are turned on by the strobe 2 signal to turn on the latch circuits FF12, FF1.
The transistors tr12, tr22,
When the tr14, tr24,... are turned on / off, the heat is applied to the heating resistance elements R2, R4,.

As described above, the conventional thermal head driving apparatus energizes and drives the heating resistor elements of each of the above-described thermal head divided into two odd-numbered and even-numbered blocks for each gradation. Are alternately repeated at a duty ratio of 50%. The amount of heat generation is controlled by changing the number of a plurality of energizing pulses for each one-dot recording with respect to this heating resistor element. The energy efficiency is improved by sequentially applying the energy without providing a pause section between them.

Further, in order to achieve high-speed recording, as a second conventional example, a method has been proposed in which the power applied to the heating resistor element of the thermal head is increased as much as possible to reduce the time for energization (television). Journal Vol.39,
No. 12 (1985) pp. 1155 to 1161 "Color Hard Copy Apparatus for Electronic Still Camera by Sublimation Dye Thermal Transfer Method").

[0008]

Generally, a thermal head is used by applying an extremely short pulse power, and under such a use condition, the life of the heating resistor element is defined by the total number of applied pulses. Normally, the life is about 10 ⁷ to 10 ⁸ pulses (Hard copy technology P35
0 to P352: JIEC Japan Industrial Technology Center). Accordingly, the thermal head driving device of the first conventional example repeatedly turns on and off the energization of the heating resistance element for each gradation, and therefore, a maximum of 255 pulse powers per line are applied to the heating resistance element. In addition to the problem of the heat-resistant pulse life, the thermal head is driven at least by dividing it into two parts. As described above, in the thermal head, special wires, connectors, signal lines, and the like obtained by dividing the strobe signal into two parts are used. This necessitates a problem of increasing the cost of the apparatus and the thermal head.

Further, the thermal head driving apparatus of the first conventional example improves the energy efficiency without providing a pause between the time when the maximum energy is applied in one line recording and the time when the energy is applied in the next line recording. However, since the pause section is not set, the influence of the heat accumulation of the previous line is great, and the edge of the image may be blurred, the low gradation part may be blurred, and the like ( This is called the tailing phenomenon in the future.) This tailing phenomenon is inconspicuous in recording of an image quality level using an NTSC video signal as a source source, but has a high definition like a high-definition image and a continuous low density area like a computer graphics. In gradation recording of a large number of images, deterioration in image quality due to such a trailing phenomenon cannot be ignored. Furthermore, in practice, a recording density variation due to a variation in the resistance value of the heating resistance element in the thermal head, a variation in the environmental temperature, and a variation in the recording density due to the heat storage of the thermal head itself occur, and it is necessary to correct these variations in the recording density. These corrections can be made by keeping the applied voltage constant and increasing or decreasing the input energization time data so that the recording energy of each heating resistor becomes the same, but in the first conventional thermal head driving device, Since no pause section is provided between the time of maximum energy application in one-line recording and the time of energy application in the next line recording, deterioration in image quality due to the tailing phenomenon and fluctuation in recording density due to variation in resistance value of the heating resistor element, In addition, fluctuations in the recording density due to fluctuations in the environmental temperature and heat storage of the thermal head itself cannot be eliminated.

Further, as shown in the second conventional example, when the power applied to the thermal head is increased and the energizing time is shortened, the temperature of the heating resistor element becomes higher than the temperature at which thermal deformation of the recording paper or ink sheet occurs. Tend to be. If the heating temperature of the heating resistor element exceeds the thermal deformation starting temperature of the recording paper, the heat generated by the thermal head is consumed as energy that causes thermal deformation of the recording paper or ink sheet in addition to the transfer of the ink. In addition to the problem, the thermal deformation of the recording paper causes irregularities of a pixel size corresponding to each heating resistor element on the surface of the recording paper, which causes a reduction in recording density due to irregular reflection of reflected light and a deterioration in image quality due to loss of gloss of the recording paper. There are issues that arise.

In view of the above, the present invention can use a thermal head having a simple structure, can prolong the life of the heating resistor element, change the recording density due to variation in the resistance value of the heating resistor element, and reduce the environmental temperature. Thermal head that heat-generates the heat-generating resistor element of the thermal head with energy efficiency while correcting fluctuations and recording density fluctuations due to the thermal storage of the thermal head itself, and also prevents recording density degradation and image quality deterioration due to thermal deformation of the recording paper surface. A driving device is provided.

[0012]

In order to solve the above-mentioned problems, a thermal head driving device according to the present invention comprises: a power applying means for applying power to a linearly arranged heating resistor element in a thermal head; A head energization driving unit for continuously changing and energizing the energization time of the heating resistor elements in accordance with the input gradation data; and a head drive control unit for controlling the head energization driving unit. head drive control means of the heating energization time for energizing the resistive element and the recording time of one line consisting of downtime is not energized all heating elements regardless gradation data, ring
Recording temperature due to ambient temperature and heat storage inside the thermal head
Correction of temperature fluctuation and / or variation of resistance value of heating resistance element
For correcting the recording density fluctuation due to the
Changing the incremental time to the recording time of the one line.
Instead, it is assigned to reduce the downtime,
A thermal head driving device for controlling a head energization driving means .

[0013]

[0014]

[0015]

The present invention does not require a structure for driving the thermal head in a divided manner by energizing and driving all the heat-generating resistance elements at a time with the above-described structure. It can be configured. Then, the energization of the heating resistance element according to the gradation data is performed for each line continuously without intermittent pause, so that only one heating and pause pulse drive is performed during one line recording. The heat-resistant pulse life of the device can be extended.

Further, the head drive control means includes the heat generating resistor.
Regarding the energizing time for energizing the resistance element and the gradation data,
One line consisting of a pause time during which no heat is applied to all the heating resistance elements
Of the ambient temperature and the inside of the thermal head
Of recording density fluctuation and / or heating resistance due to heat storage
The correction of the recording density fluctuation due to the variation of the resistance value of the element
Recording the increment time of the energization time for the one line
Reduce the pause time without changing the time
And the head energization driving means is controlled. This
Recording density due to resistance value variation of the heating resistor
Compensation to reduce fluctuations in ambient temperature,
Introduced correction of recording density fluctuation due to heat storage of the multi-head itself
And set energy-efficient downtime
Can be.

[0017]

[0018]

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In a first embodiment of the present invention, a thermal head has ²ⁿ (n is a natural number) heating resistive elements in a line shape, and performs multi-gray scale recording for collective drive recording in the main scanning direction. This is a thermal head drive capable of recording.

FIG. 1 is a block diagram of a thermal head driving device for realizing the first embodiment. 1 a thermal head in FIG. 1, 2a, 2b the first line memory and a second for storing energizing time data for energizing the respective heating elements Ra1～Ra2 ⁿ corresponding to the gradation level data of each pixel inputted Is a first counter for generating an address for reading data in the first line memory 2a or the second line memory 2b, and 3b is a first line memory 2a or the second line memory 2b. A second counter 4a for generating the number of times of reading the energization time data for each line in the first line memory 4a is a first switching means for switching addresses given to the first line memory 2a and the second line memory 2b, and 4b is a first switching means. The second switching means for switching the output data from the line memory 2a and the second line memory 2b, and 5 is the first switching means output via the second switching means 4b. A comparator that outputs serial data DATA as a result of comparing the output of the first line memory 2a or the second line memory 2b read by the address given from the counter 3a with the output of the second counter 3b;
6 is a latch signal LATCH, the drive signal generating means for generating a respective head drive signal of the strobe signal STB, power applying means for applying power to the heating resistor elements Ra1～Ra2 ⁿ of the thermal head 1 is 7, the 10 thermal head 1, line memory 2, first counter 3a, second counter 3
b, a head energization driving unit including a comparator 5, and a driving signal generation unit 6. Reference numeral 8 denotes a head drive control unit that controls the first counter 3a and the second counter 3b, the first switching unit 4a and the second switching unit 4b, and controls recording for each line. The head drive control means 8 includes a CPU, R
The microcomputer 81 includes an OM, a RAM, and a PORT. Reference numeral 81 denotes a CPU; 82, a ROM for storing a program of the CPU 81; 83, a RAM for storing calculation results and data of the CPU 81; Of the carry signal output from the counter 3b, and controls the first counter 3a and the second counter 3b to start and stop counting and to control the switching between the first switching means 4a and the second switching means 4b. Perform

The address bus A2 of the microcomputer in the head drive control means 8 is connected to the first switching means 4
a, and the data bus D2 is connected to the output of the second switching means 4b. The first switching means 4a and the second switching means 4b switch in conjunction with each other, and the address bus A
1 is connected to the first line memory 2a and the data bus D1, the address bus A2 is connected to the second line memory 2b and the data bus D2, and the address bus A1 is connected to the second line memory 2b and the data bus D1. Time is address bus A
2, the first line memory 2a and the data bus D2 are alternately switched. The thermal head 1 has substantially the same configuration as the thermal head used in the first conventional example. However, in the first embodiment, since all the heating resistance elements are energized and driven collectively, the strobe signal STB is one. Become. That is, the thermal head of the first embodiment has 2 ⁿ heating resistance elements Ra1 to Ra2 ⁿ and a transistor tra1.
~tra2 ^n, gate Ga1~Ga2 ^n, a latch circuit composed of D flip-flop Fa1~Fa2 ^n, has a shift register consisting of D flip-flop Fb1~Fb2 ^n.

FIG. 2 is a flowchart showing the operation of the head drive control means 8, and FIG. 3 is a timing chart showing the drive of the thermal head 1.

Next, the operation of the first embodiment will be described in detail with reference to FIGS. The drive signal generating means 6 generates the respective head drive signals of the latch signal LATCH and the strobe signal STB shown in FIG. The output data from the comparator 5 is the shift registers Fb1 to Fb2 ⁿ
Is converted into parallel data corresponding to each of the heating resistance elements Ra1 to Ra2 ⁿ in synchronization with the data transfer clock CLK, and the latch circuits Fa1 to F are converted by the latch signal LATCH.
It is latched to a2 ^n. Next, the strobe signal STB is activated ("L") to activate the gates Ga1 to G1.
a2 ⁿ is turned ON, the transistor tra1~tra2 ⁿ is on / of in response to the data of the latch circuit Fa1~Fa2 ⁿ
and f, the heating resistor element Ra1～Ra2 ⁿ is energized in response to the energization time data, exothermic energy generated.

[0024] Thus, performs conduction drive collectively in accordance with the heating resistor element Ra1～Ra2 ⁿ of the thermal head 1 to the gradation level data of each pixel, each of the heating resistor elements Ra1
Varying the heating energy of ~Ra2 ^n, 1 line recording is performed. That is, the first line memory 2a or the second line memory 2b and energizing time data is stored in accordance with the gradation level of the heating resistance element Ra1～Ra2 ⁿ of the thermal head 1, the gray level data The larger the value, the greater the heat energy, so that the density of the recorded pixel is high.

As shown in FIG. 2, first, an address bus A1, a first line memory 2a and a data bus D1 are connected by a first switching means 4a and a second switching means 4b. The second line memory 2b and the data bus D2 are connected. At this time, the microcomputer in the head drive control means 8 converts the input gradation data of the first line into conduction time data and stores it in the second line memory 2b. Further, the second line memory 2b is connected to the address bus A1 and the data bus D by the first switching means 4a and the second switching means 4b.
Connect to 1. Next, after the first counter 3a and the second counter 3b are initialized via the input / output port 84, the counting is started.

At this time, each heating resistance element R is sequentially read from the second line memory 2b by the output of the first counter 3a.
The energization time data corresponding to a1 to Ra2 ⁿ is read out,
The first counter 3a makes 2 rounds and counts 2 ⁿ times, and when all the contents of the second line memory 2b are read out, the second counter 3b counts up by one, and the first counter 3a again counts up to 1 The contents of the second line memory 2b are read from the beginning. The data in the second line memory 2b read by the first counter 3a is input to the comparator 5, and the reading of one line of data is repeated 2 ^m times (m is a natural number).

The comparator 5 has a second line memory 2b.
Is compared with the output of the second counter 3b. If the output of the second counter 3b is smaller than the value of the energization time data, "1" is output to the shift register Fb1. That is, repeated 2 ^m times the period corresponding to one gradation recording time t _a of Figure 3, then the second line memory 2b
From the same data is read out every cycle. However, since the value of the second counter 3b increases by one for each period, the output of the comparator 5 starts from the output of the second line memory 2b which becomes less than the value of the second counter 3b. Changes to "0" (however, "1" turns on electricity, "
In this manner, in one heating resistor element of the thermal head 1, data indicating whether or not to energize (energization ("1"), energization suspension ("0")) is shown in FIG. 4
Is sent 2 ^m times with _a period of ta. After the second counter 3b counts 2 ^m times, it outputs a carry to the head drive control means 8.

During this time, the head drive control means 8 converts the inputted gradation data of the next line into conduction time data and stores the data in the first line memory 2a. Thereafter, the second counter 3b polls the carry output after counting 2 ^m times. Then, upon detecting this carry output, the CPU 81 checks whether the recording of the predetermined number of lines has been completed, and if not, repeats the above sequence. At this time, the first switching means 4a and the second switching means 4b are switched in an interlocking manner every one line recording cycle, and the address bus A1 and the first line memory 2a are switched.
When the data bus D1 is connected to the address bus A2, the second line memory 2b and the data bus D2 are connected, and the address bus A1, the second line memory 2b and the data bus D1 are connected.
Is connected to the address bus A2 and the first line memory 2a.
And the data bus D2 are alternately switched.

Here, the number of recording gradation levels will be described. The one-line recording cycle tc is 2 ^{m in} the second counter 3b.
Since corresponding to the time to count times, 1 gradation recording time t _a is (tc / 2 ^m), which is fixed. In the present embodiment, when the pause time td is set, the number of gradations depends on the set values of the longest energization time tmax and the pause time td, and the number of reproduced gradations P can be expressed by (Equation 1).

[0030]

(Equation 1)

Therefore, in the conversion process from the input gradation data to the energization time data, a ratio such that the maximum gradation data becomes the longest energization time tmax is given to each input gradation data. Convert to Therefore, a pause time within one line recording time is set by the conversion process from the gradation data to the conduction time data performed by the head drive control means 8.

FIG. 4 is a diagram showing the change in the heat generation temperature of the heat generating resistance element on the vertical axis and the energization time on the horizontal axis.
Td indicates the thermal deformation starting temperature of the recording paper. If the heat generation temperature of the heating resistor element exceeds this temperature, thermal deformation of the recording paper occurs.

Ts indicates the color of the recording paper or the temperature at which the ink starts to be transferred to the recording paper. If the heat generation temperature of the heating resistor element exceeds this temperature, the color of the recording paper or the ink on the recording paper is discharged. The image is transferred and the image is recorded on the recording paper.

Here, the heating temperature of the heating resistor depends on the power applied to the heating resistor, and the applied power and the heating temperature of the heating resistor are in a proportional relationship as long as the heating resistor is not damaged. It is in. Further, the recording density depends on the heat energy of the heating resistor element, and the heat energy J of the heating resistor element can be expressed by (Equation 2).

[0035]

(Equation 2)

Basically, if the heat energies J of the heat generating resistance elements are equal, the recording density becomes the same. In the thermal head driving device of the first embodiment, as shown in FIG. 4, when the temperature of the heating resistor element is equal to or higher than the color Ts of the recording paper or the temperature Ts at which ink starts to transfer to the recording paper, thermal deformation of the recording paper occurs. The applied power W that does not exceed the thermal deformation start temperature Td of the recording paper is set corresponding to the longest energizing time T of the heating resistor element.

More specifically, FIG. 5 shows the experimental results regarding the maximum recording density and the thermal deformation of the recording paper with the applied power and the energizing time taken as parameters in consideration of the above relationship. The thermal head driving device of the present invention was introduced into the printer used in the experiment, and the one-line recording time was fixed at 16.4 msec.
As shown in FIG. 5, the longest energization time is 10.25, 12.
3, 14.35 and 15.375 msec, the longest energizing time is plotted on the horizontal axis, and the recording density at the start of thermal deformation of the recording paper is plotted on the vertical axis. The recording density at the start of thermal deformation of the recording paper shows an increasing tendency with the longest energizing time, and is substantially saturated at 14.35 msec or more. The numerical values in parentheses indicate the applied power (W / dot) to the heating resistance element at the start of thermal deformation of the recording paper, and show a decreasing tendency with respect to the recording pulse width. Therefore, the longer the energization time is, the higher the maximum recording density without thermal deformation is obtained, and the applied power can be reduced. At least when the maximum energization time is 14.35 msec or more, the highest density without thermal deformation is obtained. Obtainable.

[0038] In this case, the setting of pause time t _d, for a more detailed explanation. If the temperature of the heating resistor element is higher than the color Ts of the recording paper or the temperature Ts at which the ink starts to be transferred to the recording paper, some density is recorded even though the power is not supplied at the start of the recording. Therefore, as a minimum condition for eliminating the influence of the tailing, it is necessary to set a pause time such that the temperature of the heating resistor element is lower than the temperature Ts at which the ink starts transferring to the recording paper.

FIG. 6 is a diagram showing the recording density with respect to the energizing time. At this time, the longest energization time shown in FIG.
In the case of 4.34 msec, the electric power applied to the heating resistance element is 0.164 which is almost the maximum electric power without thermal deformation of the recording paper.
W / dot. As shown in FIG. 6, the concentration starts to rise from the energization time of about 4.2 msec. Therefore, during this rise time t _a , the temperature of the heating resistance element rises,
This corresponds to the time when the coloring of the recording paper or the temperature at which the ink starts to be transferred onto the recording paper exceeds the temperature Ts. FIG. 7 is a diagram showing the heat generation temperature of the heat generation resistance element when the energization time is t _x (4.2 msec). Heating temperature of the heating resistor element reaches the temperature Ts of the ink in the color or the recording sheet of the recording paper after energization time t _x has elapsed from start of recording of one line recording time described above to initiate transcription. Therefore, the temperature Ts at which the color of the recording paper starts or the ink starts to be transferred to the recording paper is approximately 105.
About ℃. Generally, the temperature Ts at which the color of the recording paper starts or the ink starts to be transferred to the recording paper is often set to around 100 ° C.

FIG. 8 is a diagram showing a measurement of the heating temperature of the heating resistor element at the time of recording a predetermined line after a sufficient time has elapsed since the start of recording. The pause time within one line recording cycle is 50%, and 37.5.
% And 25%, the highest electric power is applied as far as possible without causing thermal deformation of the recording paper as shown in FIG. 5, and the environmental temperature is set to 50 ° C. As shown in FIG. 8, tc represents a one-line recording cycle, and the temperature at a pause time of 37.5% of the one-line recording cycle from the highest temperature of the heating resistor element to the stop of energization is almost equal to the color of recording paper or recording. Close to the temperature Ts at which ink starts transferring to paper, 50%
Is sufficiently lower than the temperature Ts at which the color of the recording paper or the ink starts to transfer to the recording paper, and the temperature at 25% is the temperature Ts at which the color of the recording paper or the ink starts to transfer to the recording paper. Better than Therefore, the pause time of about 40% of the one-line recording cycle is set to be almost the shortest time without being affected by the heat storage in the previous line and causing no tailing phenomenon. Under this condition, it is possible to perform high-quality image recording, which is not affected by the trailing effect on the recording of the next line, with minimum energy efficiency and minimum reduction in recording density.

As described above, in the first embodiment of the present invention, the case where the pause time is set to approximately 40% of the one-line recording time has been described. If the pause time is set to be longer than approximately 40%, the heating temperature of the heating resistor element is sufficiently lowered for each line, and the image quality is not degraded due to the trailing phenomenon. More energy is needed to raise the temperature to the temperature required for recording. Further, as shown in FIG. 5, increasing the pause time tends to decrease the recording density that does not cause thermal deformation of the recording paper, and is ineffective in terms of energy efficiency and recording density.

Here, the further shortening of the pause time effectively utilizes the state in which the heating resistance element of the previous line has risen in temperature, improves energy efficiency, and increases the recording density that does not cause thermal deformation of the recording paper. It is in the direction to do. On the other hand, since the heat storage is used, the trailing phenomenon is particularly affected when the recording of the previous line is performed by the longest energization drive, which causes deterioration in image quality. However, this tailing phenomenon is caused by NTSC
The level of image quality is almost inconspicuous when recording with the video signal as a source source, and in reality, most of the halftone images are used, and the longest energization drive is performed (the highest density is recorded). And is hardly affected by the image quality deterioration due to the tailing phenomenon. Therefore, if the recorded image is limited, shortening the pause between lines has excellent effectiveness in terms of recording energy efficiency and recording density.

Here, in the thermal recording using a thermal head, in order to improve the gradation reproducibility, correction for reducing the fluctuation of the recording density due to the variation in the resistance value of the heating resistor element and the fluctuation of the environmental temperature are performed. In many cases, it is necessary to correct the recording density fluctuation due to the heat storage of the thermal head itself. Since the concept of these corrections is to make the recording energy of each heating resistor the same, correction can be made by keeping the applied voltage constant for practical use and increasing or decreasing the input energization time data according to the correction.

Accordingly, in the following description, correction for reducing the fluctuation of the recording density due to the variation in the resistance value of the heating resistor element, which satisfies the pause time condition in the first embodiment described above, and the environmental temperature A thermal head driving apparatus according to a second embodiment of the present invention which introduces correction of fluctuations in recording density and fluctuations in recording density due to heat storage of the thermal head itself, and sets a minimum pause time with the highest energy efficiency will be described.

The thermal head drive apparatus of the second embodiment is intended to match the temperature compensation, pause safety margin of the energization time required for correction processing such as a resistance value correction time t _d as described above. The second embodiment and the first embodiment have the same components, and the operation of the thermal head is the same as that of the first embodiment. FIG. 9 is a flowchart showing the operation of the head drive control means in the thermal head drive device according to the second embodiment of the present invention. As shown in FIG. 9, in the second embodiment, the energization time increase / decrease process by resistance correction and temperature compensation is performed at the time of conversion processing from gradation data input by the CPU 81 of the head drive control means 8 to energization time data. ing. Therefore, the converted data is stored in the first line memory 2a and the second line memory 2a.
b, the temperature compensation and the resistance value correction processing are performed when the thermal head 1 is driven.

Here, the tolerance of the energizing time by the resistance value correction will be specifically described. The resistance value correction is a process for equalizing the heat generation energy of all the heat generation resistance elements by changing the fluctuation of the heat generation energy due to the variation of the resistance value and increasing or decreasing the energization time of the heat generation resistance elements.

[0047]

(Equation 3)

(Equation 3) shows the heat generation energy when the voltage V is applied to the heating resistance element having the average resistance value R as a reference and the heating is performed for the conduction time t, and the voltage V is applied to the heating resistance element having the resistance value R '.
Is applied, and the heat generation energy when driven for the energization time t ′ is made the same. Therefore, the additional energization time dt required for the resistance value correction can be expressed by (Equation 4).

[0049]

(Equation 4)

Further, the additional energization time due to temperature compensation will be described. Since the heat generated by the thermal head is used, the recording density fluctuates under the influence of the temperature of the environment and the heat storage inside the thermal head. This can be subjected to a process for varying the heat generation energy in accordance with the temperature of the environment or the heat storage inside the thermal head, thereby reducing the density fluctuation.

In general, a thermal recording apparatus using a thermal head is often used in an environment at about room temperature (20 ° C.), and it is necessary to consider the influence of a change in environmental temperature.
Use at low temperatures is relatively low. However, when the image recording is repeated, the temperature of the thermal head becomes higher than the room temperature due to heat storage in the thermal head, and the temperature of the thermal head in the thermal head driving device of the second embodiment of the present invention increases. The normal temperature (30 ° C.) frequently used as a reference.

The case where the correction is performed in a temperature compensation range of, for example, a low temperature (5 ° C.) to a high temperature (50 ° C.) will be described. Image recording is performed when the energizing time is set to one line recording cycle tc when the environmental temperature is low (5 ° C.), and normal temperature (3
At 0 ° C.), the longest energization time tmax is variously set and an image is recorded. Then, the longest energization time tmax in the normal temperature environment when the maximum density recorded by the various set longest energization times tmax recorded in the normal temperature environment and the density at the recording start point of the image recorded in the low temperature are equal is obtained. Therefore, the additional energization time due to the temperature compensation is one line recording cycle tc,
It can be derived by taking the difference between the longest energization times tmax. However, as described in the first embodiment, the setting of the power to be applied is the same as that of the first embodiment in order to eliminate the density reduction and the image deterioration due to the thermal deformation of the recording.

As described above, the range of the resistance value variation of the heating resistor element to be corrected by the resistance value correction is 10%, and the temperature compensation range is from low temperature (5 ° C.) to high temperature (50 ° C.). According to the experiment, the additional energization time required for the resistance value correction and the temperature compensation processing was about 3 msec.
However, the recording time for one line is fixed at 16.4 msec.

Therefore, the additional energizing time (3 msec)
For example, when recording is performed at about room temperature, the pause time is set to about 3 msec, and the effect of image quality deterioration due to tailing is substantially small. Further, the state in which the additional energizing time is used to the maximum and the pause time is almost eliminated is limited to printing in a relatively high density area when the gradation level is large at low temperatures. In this case, since the recorded image is a high-density area, it is an area where it is difficult to determine image quality deterioration due to the effect of the tailing phenomenon. Therefore, since the resistance value correction and the temperature compensation processing can be introduced without substantially deteriorating the image quality of a recorded image, high-quality recording with relatively high energy efficiency and improved gradation can be performed. .

In the present invention, the pause time per line recording time can be easily set by the head drive control means 8 constituted by a microcomputer according to the image to be recorded and the purpose of use of the apparatus without increasing the apparatus configuration. It is.

Although the head drive control means 8 is constituted by a microcomputer, it can be easily realized by a hardware-only structure using a counter, a timer, and the like set at a predetermined optimum pause time. Needless to say.

[0057]

As described above, according to the present invention,
Set the strobe signal to 1 to drive the thermal head
As a result, the thermal head and the head driving device can be simplified in configuration as compared with the conventional example, and the cost can be reduced. In addition, by continuously energizing the heating resistor element according to the gradation data for each line, the life of the heating resistor element can be extended.

According to the present invention, deterioration of the image quality of a recorded image can be realized.
Resistance correction and temperature compensation processing without qualitatively occurring
Can be introduced, so the ratio is improved
High-quality recording with relatively high energy efficiency can be performed.

[0059]

[0060]

In the present embodiment, since the head drive control means is constituted by a microcomputer, the optimum pause time between lines is changed according to the purpose of use of the apparatus, such as the recording speed and the image quality of the recorded image. They can be easily set without any problem, and these practical effects are very large.

[Brief description of the drawings]

FIG. 1 is a block diagram of a thermal head driving device according to a first embodiment of the present invention.

FIG. 2 is a flowchart showing the operation of a head drive control unit in the thermal head drive device according to the first embodiment of the present invention.

FIG. 3 is a timing chart showing driving of the thermal head in the thermal head driving device according to the first embodiment of the present invention;

FIG. 4 is a graph showing a relationship between an applied power and an energizing time in the thermal head driving device according to the first embodiment of the present invention;
Diagram showing experimental results on maximum recording density and thermal deformation of recording paper

FIG. 5 is a graph showing a relationship between an applied power and an energizing time in the thermal head driving device according to the first embodiment of the present invention;
Diagram showing experimental results on maximum recording density and thermal deformation of recording paper

FIG. 6 is a diagram showing a recording density with respect to an energizing time in the thermal head driving device according to the first embodiment of the present invention.

Figure conduction time in the thermal head driving device of the first embodiment showed an exothermic temperature of the heating resistor element when the t _a of the present invention; FIG

FIG. 8 is a diagram showing a measurement of a heating temperature of a heating resistor element at the time of recording an n-th line in the thermal head driving device according to the first embodiment of the present invention;

FIG. 9 is a flowchart showing the operation of a head drive control unit in the thermal head drive device according to the first embodiment of the present invention.

FIG. 10 is a timing chart showing a thermal head drive timing chart of the first conventional thermal head drive device.

FIG. 11 is a diagram showing a configuration of a thermal head driven by a first conventional thermal head driving device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Thermal head 2a 1st line memory 2b 2nd line memory 3a 1st counter 3b 2nd counter 4a 1st switching means 4b 2nd switching means 5 Comparator 6 Drive signal generation means 7 Power application means 8 Head Drive control means 10 Head energization drive means

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hideshi Ishihara 1006 Kazuma Kadoma, Kadoma City, Osaka Inside Matsushita Electric Industrial Co., Ltd. (56) References JP-A-64-87275 (JP, A) JP-A-4-4 27565 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B41J 2/35-2/36

Claims (4)

(57) [Claims] An electric power applying means for applying electric power to a heating resistor element arranged in a line in a thermal head;
A head energization driving unit for continuously changing and energizing the energization time of the heating resistor elements in accordance with the input gradation data; and a head drive control unit for controlling the head energization driving unit. The head drive control means controls the ambient temperature and the internal temperature of the thermal head during the recording time of one line including the energizing time for energizing the heating resistor element and the pause time for not energizing all heating resistor elements regardless of the gradation data. In order to correct the recording density fluctuation due to the heat storage and / or to correct the recording density fluctuation due to the variation in the resistance value of the heating resistor element, the increment time of the energization time is changed to the pause time without changing the recording time of the one line. A thermal head driving device for controlling the head energization driving means by allocating so as to reduce the power consumption. 2. A power supply means for a recording paper on which an image is formed by color development or transfer of ink due to heat generated by a heating resistance element, wherein a maximum temperature of the heating resistance element is higher than a temperature at which the recording paper is thermally deformed. 2. The thermal head driving device according to claim 1, wherein a maximum electric power at which the temperature becomes low is applied. 3. A head energizing drive means for generating a drive timing signal for a thermal head, and first energizing time data for energizing each heating resistor element in accordance with input gradation data. A line memory, a second line memory, first switching means for switching addresses given to the first line memory and the second line memory, and Second switching means for switching the output, a first counter for giving an address to the first line memory and the second line memory via the first switching means, and a second counter for outputting a recording gradation level. A second counter and a comparator for comparing the output of the first line memory or the second line memory with the output of the second counter. The control means controls the first counter and the second counter and the first switching means and the second switching means for each one-line recording, and outputs the gradation data from the input gradation data to the heating resistance element. 3. The thermal head driving device according to claim 1, wherein the energization time data is created. 4. The thermal head driving apparatus according to claim 1, wherein when the increment time of the energization time is maximum, the pause time is almost eliminated.