JPH0818440B2 - Thermal head - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head which is used in a printer and which has a heating element which generates heat when supplied with energy and which prints by the heat generated by the heating element.

[0002]

2. Description of the Related Art A printer (thermal printer) using a thermal head that has a heating element that generates heat when energy is supplied and prints by the heat generated by the heating element has a printing density immediately after the start of printing operation. Thin,
When printing is performed continuously, the print density tends to increase with the passage of time.

This is because the energy supplied to the heating element of the thermal head is accumulated as heat on the base material in the vicinity of the heating element and the heating element itself, and the change in the print density due to this heat storage is the print quality of the printer. To lower
In a conventional thermal printer, various measures are taken to prevent the thermal head from accumulating heat.
For example, there is a means of correcting the energy applied to the heating element based on the print history information. When the printing rate is small like character printing (character printing) and the printing rate changes little, this means can suppress the deterioration of the printing quality by the correction operation for a relatively short time. However, as in the printing of graphics (graphic printing), when the parallel operation state of the heating elements of the thermal head and the change in the printing rate in the time axis direction are large, a great deal of printing history information is required, so There is a problem that an extremely large scale integrated circuit is required to realize an appropriate correction operation. In addition, the print history information has a problem that information corresponding to the print sheet used must be collected.

There is also a means of providing a temperature sensor such as a thermistor in the vicinity of the heating element and correcting the energy applied to the heating element based on the temperature information from the temperature sensor. In this means, since it is impossible to dispose the temperature sensor in direct contact with the heating element, there is a time delay between the actual temperature of the heating element and the temperature detected by the temperature sensor, and However, since the thermal response characteristic of the temperature sensor itself cannot be ignored, it has a drawback that it is impossible to perform correction within the required time.

On the other hand, in recent years, the use of color printing is expanding in printers, and in the case of color printing, it is required to give a delicate gradation to the print density, so that the correction of the heat accumulation of the thermal head is required. It is necessary to improve accuracy.

[0006]

As described above, in the thermal head of the conventional thermal printer, the print density is low immediately after the start of the printing operation, and if the continuous printing is performed, the print density will increase with the passage of time. Has a drawback that it becomes darker, and the state varies depending on the printing paper used, so it is necessary to correct the energy applied to the heating element corresponding to the printing paper,
There is a problem that there is no appropriate correction means. This is has become a prominent along with the expansion of the use of your only that color printing to the printer.

[0007]

In the thermal head of the present invention, the heating element itself has a temperature detecting function, and the temperature of the heating element is controlled to be a constant temperature by the temperature detected from the heating element itself. The correction for the change in the print density due to the heat storage effect is performed.

Namely, the thermal head of the present invention includes a heat-generating element group having a plurality number of heating elements formed in a large material temperature dependence of the electrical resistance, the heat generation temperature of each of the previous SL plurality of heating elements set in correspondence with each of the plurality of heating elements you Yotsute <br/> detecting the change in the electrical resistance of the element
A plurality of digit temperature detection circuits and a plurality of heating elements
For each corresponding heating element that is provided for each
Strobe signal to determine the time to apply energy
Signal having a plurality of strobe signal generators for
A strobe signal generator group, the maximum temperature of the heating elements Ah
The temperature of the heat generating element, which has a setting register set in advance and a comparator for comparing the upper limit temperature set in the setting register with the temperature of the heat generating element detected by the temperature detection circuit. stop of the supply of energy but which pairs to the heating element when matching the upper limit temperature
A microcomputer for outputting a signal to cause the heat generation
Before being provided between the device group and the microcomputer
The one heating element of the plurality of heating elements and the
The first switching switch for switching and connecting to a black computer.
Switch, the strobe signal generator group and the micro
A plurality of strobes provided between the computer and
The first changeover switch of the signal generator is connected
Strobe signal generator corresponding to the heating element and
The second switching switch for switching and connecting to a black computer.
It further comprises a switch , further, the color development temperature corresponding to each of a plurality of types of thermal paper and the time until the temperature of the heating element reaches the color development temperature is set in advance in the setting register, The microcomputer measures the time required for the temperature of the heating element to reach the coloring temperature to identify the type of thermal paper.

The temperature dependence of the electric resistance of the material forming the heating element may be positive or negative, but if the material has a large negative temperature dependence, the concentration of heat in the surface of the heating element becomes more pronounced.
It is suitable for use with printers that require subtle gradation printing.

The temperature detection circuit for detecting the temperature of the heating element constantly monitors the current flowing through the heating element when a voltage is applied to the heating element for printing, and calculates based on the current value. The temperature of the heating element is detected from the relationship between the resistance value of the heating element and the resistance value obtained from the temperature coefficient of resistance of the heating element.

The microcomputer determines the energy applied to the heating element based on the temperature detected by the temperature detection circuit. That is, when the temperature detected by the temperature detection circuit becomes higher than the temperature specified separately, the application of energy to the heating element is suppressed, and other temperatures specified separately become low. When
Increasing the application of energy to the heating element. In this way, the temperature of the heating element is kept constant during the printing operation.

The microcomputer has a function of preventing the temperature of the heating element from exceeding a specified value by stopping the supply of energy to the heating element when the temperature of the heating element reaches a designated temperature. May be.

[0013]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 is a block diagram for explaining the operation principle of the present invention, FIG. 2 is a characteristic diagram showing temperature dependence characteristics of the resistance value of the heating element in the circuit of FIG. 1, and FIG. 5 is a circuit diagram of FIG. It is a wave form diagram which shows the wave form of a strobe signal and the electric current of a heating element.

First, the operating principle of the present invention will be described with reference to FIGS. 1, 2 and 5.

The strobe signal generator (FF) 11 generates a strobe signal for determining the time for applying energy to the heating element 14 (resistance value R) for each printing cycle. While the logical value of the strobe signal is high level (“H” level), the drive circuit (drive circuit) 12 is driven, the voltage V is applied to the heating element 14, and the current I flows.

The heating element 14 is formed of a thin film of a chromium alloy containing 25 atomic% of aluminum, and has a negative temperature coefficient, as shown by the resistance temperature dependence 20 of FIG. At the start of the printing operation, the resistance value of the heating element 14 is 1.65 kΩ because it is at room temperature, but at the same time when the printing operation is started, the resistance value rises and decreases to the resistance temperature dependence 20.

As shown in FIG. 1, a current detecting resistor 13 (resistance value r) is connected in series with the heating element 14. The relationship between the resistance values of the heating element 14 and the current detection resistor 13 is

[0019]

[0020]

The voltage V applied to the heating element 14 is 24
Since the voltage is a constant value in volts, the current I flowing through the heating element 14 is a value obtained by I = 24 ÷ R (2). Therefore, the resistance value R of the heating element 14
Is uniquely determined by the equation (2).

On the other hand, the output voltage v of the current detection resistor 1 3
Is v = r × I = r × 24 ÷ R (3) Therefore, the current flowing through the resistor 18 (resistance value r) is the same as the value obtained by the equation (2), that is, the heating element. The value is inversely proportional to the resistance value R of 14.

When the upper limit temperature T0 of temperature rise when voltage is applied to the heating element 14 is set to 350 ° C., the resistance value R0 at that time is R0 = 1.05 kΩ from FIG. Therefore, the current I0 flowing in the heating element 14 at that time is
I0 = 24 ÷ 1.05 = 22.9 mA. This value is set in the target current setter 16.

The comparator 17 has a current I flowing through the resistor 18.
And the current I0 set in the target current setter 16 are input and compared. When the current I is larger than the current I0, that is, when the temperature of the heating element 14 exceeds the upper limit temperature T0, the logical value of the output signal of the comparator 17 changes from a low level (“L” level) to a high level (“H”). Then, the FF 11 is reset. Therefore, the logical value of the strobe signal becomes low level (“L” level), the operation of the drive circuit 12 is stopped, and the current does not flow to the heating element 14.

The relationship between the strobe signal waveform and the heating element current waveform at this time is as shown in FIG.
In the print cycle S1 from 0 to time t1, the strobe signal 60 is at “H” level, and the heating element 14
Current flows through the device, its temperature rises, and the resistance value of the heating element 14 gradually decreases (that is, the current value increases).
When the current 40 of the heating element 14 increases and the temperature of the heating element 14 reaches the upper limit temperature T0 (resistance value R0), the FF11
Is reset, the strobe signal 60 becomes "L" level, and the current 40 of the heating element 14 is cut off, so that the temperature of the heating element 14 is lowered.

However, since the heating element 14 is provided on the surface of the glass substrate, heat is accumulated in the glass substrate,
The temperature of the heating element 14 immediately before the next printing signal is applied to the heating element 14 is higher than room temperature. Such heat accumulation causes the print quality to deteriorate, but in the circuit of FIG. 1, the strobe signal 60 is "H" in the next print cycle S2 starting from time t2.
When the temperature becomes high and the temperature of the heating element 14 rises to reach the upper limit temperature T0 (resistance value R0), the comparator 17 directly operates and the FF 11 is reset, so that the strobe signal 60 is at the time t3. At "L" level.
The time from the time t2 to the time t3 is the print cycle S1.
Is shorter than the time from time t0 to time t1. As described above, since the time for heating the heating element 14 changes depending on the temperature of the heating element itself, it becomes possible to keep the temperature of the heating element 14 constant.

FIG. 3 is a circuit diagram showing an embodiment of the present invention, and FIG. 4 is a timing chart showing the operation of the embodiment of FIG.

In the embodiment shown in FIG. 3, the present invention has three heating element groups.
It shows a case where the present invention is applied to a thermal head composed of two heating elements.

In FIG. 3, the serial input signal (Si
n) 51 is input to the shift register 41 at the timing shown in FIG. 4 together with the clock signal (Clock) 52.
The shift register 41 receives the input serial input signal (S
in) 51 is converted into a parallel signal and sent to the latch circuit 42. The latch circuit 42 receives the latch signal (Latch).
It is stored at the timing of 50.

At the same time, 32 strobe signal generators (FF) 53-1 to 53-32 are set to 32.
One of the input terminals of the AND gates 43-1 to 43-32 becomes the “H” level. Therefore, the AND gate 43
Although the other input terminal of -1 to 43-32 is set to "H" level by the output signal of the latch circuit 42, the output signal is set to "H" level. The corresponding one of 44-32 becomes active. As a result, 32 heating elements 45-1 to 4-4
Current flows through the corresponding heating element of 5-32 to generate heat. For example, when the odd-numbered data of the latch circuit 42 becomes "H" level, a current flows through the odd-numbered heating elements.

At this time, the current flowing through the heating elements 45-1 to 45-32 is an analog voltage built in the microcomputer 61 via the changeover switch 67 as a potential difference between both ends of the current detection resistors 46-1 to 46-32. It is detected by the digital converter (A / D converter) 62. The output signal of the A / D converter 62 is input to the comparator 64, and the comparator 64 compares the value with a value preset in the setting register 63, and the A / D converter 6
When the value of the output signal of 2 exceeds the value set in the setting register 63, the pulse signal is output. The pulse signal from the comparator 64 resets the strobe signal generators (FF) 53-1 to 53-32 via the changeover switch 68. Thereby, the AND gates 43-1 to 43-3
2 is closed and the current flowing through the heating elements 45-1 to 45-32 is cut off.

The A / D converter 62 and the setting register 63 are sequentially input to the comparator 64 for comparison at the timing of each pulse of TS1 to TS32 shown in FIG.

Various types of thermal paper are used in the thermal printer, and the color development temperature and the temperature rise time of the thermal paper are different for each type. Utilizing these characteristics of the thermal paper, the color development temperature of each thermal paper and the arrival time until the temperature of the heating element reaches the color development temperature of the thermal paper are set in advance, and the heating element develops the color of the thermal paper. When the temperature is reached, the supply of energy to the heating element is stopped, and the heat-sensitive paper can be recognized depending on the time until the temperature of the heating element is reached. For example, the value set in the setting register 63 is set to a value corresponding to the coloring temperature of each thermal paper, and the heating element 45-1
It is possible to identify the type of thermal paper used at that time by measuring the time until the counters 45 to 32 reach the value set in the setting register 63 by the microcomputer 61.

[0034]

As described above, in the thermal head of the present invention, the heating element is formed of a material having a large temperature dependence of electric resistance, and the temperature of the heating element is detected by a change in current value due to a change in electric resistance. However, by comparing the current value of the heating element with the value set in the setting register in advance and stopping the energization to the heating element when the temperature of the heating element exceeds the set value, There is an effect that it is possible to keep the temperature of the heating element constant by controlling the applied energy. Therefore, it is possible to control the print density at high speed, and it is possible to print with a delicate gradation. Has the effect of becoming. Furthermore, since no special temperature sensor is required, the number of parts can be reduced and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram for explaining the operation principle of the present invention.

FIG. 2 is a characteristic diagram showing a temperature dependence characteristic of a resistance value of a heating element in the circuit of FIG.

FIG. 3 is a circuit diagram showing an embodiment of the present invention.

FIG. 4 is a timing chart showing the operation of the embodiment of FIG.

5 is a waveform diagram showing waveforms of a strobe signal and a current of a heating element in the circuit of FIG.

[Explanation of symbols]

11.53-1 to 53-32 Strobe signal generator (FF) 12.44-1 to 44-32 Drive circuit (drive circuit) 13.46-1 to 46-32 Current detection resistor 14.45-1 45-32 Heating element 15 Current resistor 16 Target current setting device 17 ・ 64 Comparator 18 Resistor 20 Resistance value temperature dependence 40 Current of heating element 41 Shift register 42 Latch circuit 43-1 to 43-32 AND gate 50 Latch Signal (Latch) 51 Serial input signal (Sin) 52 Clock signal (Clock) 60 Strobe signal 61 Microcomputer 62 Analog / digital converter (A / D converter) 63 Setting register 67/68 Changeover switch

Claims (2)

[Claims] 1. A heat generating element group having a plurality number of heating elements formed in a large material temperature dependence of the electrical resistance, before Symbol double
The temperature of each of the several heating elements is adjusted to the electrical resistance of each heating element.
It of the plurality of heating elements that detect Yotsute to changes in anti
A plurality of temperature detection circuit provided in correspondence with, respectively, the double
It is provided corresponding to each of several heating elements
You can set the time to apply energy to the heating element.
Strobe signals to generate strobe signals for
A strobe signal generator group having a generator, a setting register for presetting an upper limit temperature of the heating element, and the upper limit temperature set in the setting register and the heating element detected by the temperature detection circuit. a microcomputer for outputting a signal for stopping the supply of energy <br/> over that pair to the heating element when the temperature of the heating element and a comparator for comparing the temperature matches the upper limit temperature, wherein Heating element group and the microcomputer
One of the plurality of heating elements provided between
Switching between the thermal element and the microcomputer
First changeover switch and the strobe signal generator
Is provided between the group and the microcomputer.
Switching the first of several strobe signal generators
Strobe signal corresponding to the heating element connected to the switch
Connect the generator and the microcomputer by switching
A thermal head comprising a second change-over switch . Wherein a heat generating element group having a plurality number of heating elements formed in a large material temperature dependence of the electrical resistance, before Symbol double
The temperature of each of the several heating elements is adjusted to the electrical resistance of each heating element.
It of the plurality of heating elements that detect Yotsute to changes in anti
A plurality of temperature detection circuit provided in correspondence with, respectively, the double
It is provided corresponding to each of several heating elements
You can set the time to apply energy to the heating element.
Strobe signals to generate strobe signals for
A strobe signal generator group having a generator, a maximum temperature of the heating element and a coloring temperature corresponding to each of a plurality of types of thermal paper and a time until the temperature of the heating element reaches the coloring temperature are set in advance. And a comparator for comparing the upper limit temperature set in the setting register with the temperature of the heating element detected by the temperature detection circuit, and the temperature of the heating element is equal to the upper limit temperature. identify the type of thermal paper by measuring the time until the temperature of the energy <br/> outputs a signal for stopping the supply of energy and the heating element against the heating element reaches the color temperature when matched and a micro-computer which,
Installed between the heating element group and the microcomputer.
And one heating element of the plurality of heating elements
The first to connect by switching the microcomputer
A changeover switch, the strobe signal generator group and the
The plurality of switches provided between the microcomputer and
The first changeover switch of the trobe signal generator
And a strobe signal generator corresponding to the heating element connected to
The second for switching and connecting with the microcomputer
A thermal head having a changeover switch .