JPS63114670A - Thermal head drive circuit - Google Patents

Abstract

PURPOSE:To make the temperatures of heat generating resistors as constant as possible and enable stabilization of printed density, by using temperature- sensitive resistors provided on the same substrate as that for the heat generating resistors as external timing resistors for monostable multivibrators. CONSTITUTION:Temperature-sensitive resistors 31, 32...3m having a temperature coefficient higher than that of a thermistor are provided on the same substrate as that for heat generating resistors 1-1, 1-2...1-n, and are used as external timing resistors for monostable multivibrators 41, 42...4m, the outputs of which are made to be electrical pulse signals. For operating the heat generating resistors to generate heat, driving signals are given as trigger signals to the multivibrators. Since the temperature in the vicinity of the heat generating resistor is sensed by the temperature-sensitive resistor, a resistance corresponding to the temperature of the heat generating resistor immediately before the heat- generating operation is used as an external timing resistance for the multivibrator, whereby pulses with a predetermined pulse duration are generated. When a temperature change is sensed by the temperature-sensitive resistor at the next operating timing, the pulse width of the multivibrator is changed.

Description

[Detailed Description of the Invention] [4 Already Required] In a thermal head drive circuit that detects the temperature of a heating resistor of a thermal head and limits the width of a pulse applied to the heating resistor, the heating resistor is mounted on the same substrate as the heating resistor. This is a thermal head drive circuit that uses a temperature-sensitive resistor installed as an external timing resistor for a monostable multivibrator to stabilize print density.

[Industrial Application Field 1] The present invention relates to a drive circuit for a thermal head that partially heats thermal paper to print characters or the like.

The range of use of thermal heads is expanding due to their simple construction, but there is a demand for keeping print density constant even when environmental conditions vary.

[Prior Art] Thermal heads are used in printers that use thermal paper. Several minute heat-generating resistors are arranged in parallel on a substrate per 1n, and each resistor is individually controlled to generate heat or not. At this time, a thermal paper is provided close to the resistors arranged on the substrate, and the thermal paper is moved in minute steps in a direction perpendicular to the arrangement direction of the resistors. When the resistor generates heat, a pulse current waveform is applied to the resistor, and when the resistor does not generate heat, application of the pulse current is stopped. The area near the resistor that approaches the thermal paper is called the thermal head. FIG. 6 shows a side view of the element including the thermal head. Since the heating resistor inside the thermal head 1 repeatedly generates heat and does not generate heat, the temperature on the substrate holding the resistor gradually increases during use.

A heat sink 2, usually made of aluminum, is provided around the outer periphery of the board to radiate heat. It also detects the temperature of the heating element when it is not generating heat, and controls the heat generation of the heating element. That is, the thermistor 3 is attached to the heat sink 2, and heat generation control is performed while measuring the temperature of the heat sink 2. For example, when the temperature is low immediately after the start of operation, the width of the applied pulse is long as shown in Figure 7A, when the temperature rises it is slightly shorter as shown in Figure 7B, and when the temperature is considerably high the width of the applied pulse is as shown in Figure 7C. Shortest as shown. In terms of substrate temperature, Figure 7C is 46~70℃, Figure 7B is 21~40℃
, FIG. 7A is varied from 0 to 10°C.

A control circuit 10 shown in FIG. 8 sends data to be printed as serial data from a PI terminal 11 to an integrated circuit 21 for driving each element. Then, serial data is taken into the shift register 12 by the clock from the clock terminal CLK13. shift register 1
2 is just full, STB latch 14 is latched.

Next, ENB gates 1 to 3 (16-1) to (16-3)
In the buffer 15 under the control, each data is switched to a long-time pulse to control the heat generation of the heating elements l=1 to 1-n. At this time, the selector 17 detects the resistance value of the thermistor 3, and the ENB gates 1 to 3 output pulses of different widths as shown in FIG. Therefore, heat generation is controlled by the presence or absence of applied pulses of the same width for the number of bits of the buffer.

[Problems to be Solved by the Invention] When controlling the heat generation of the resistor according to FIG. 8, stepwise control is performed by measuring the temperature of the thermistor, which is considered to correspond to the temperature of the resistor. As shown in Figure 9, the printing temperature at which the color development on thermal paper is recognized as "black" is approximately 1.2.
The ambient temperature for obtaining 0D (optical density), that is, the temperature of the thermistor, naturally requires a high value when the energy is low, and a low temperature when the energy is high. For example, when the energy is 35 millijoules/1 m2, 1.20D is obtained at about 25°C, so a predetermined concentration can be obtained when the temperature is kept constant at 25°C. By manipulating the printing, the ambient temperature rises and the thermal energy applied to the thermal paper increases, so there is a drawback that the print density on the thermal paper is not stabilized. At this time, since the resistance value of a conventional thermistor does not vary greatly with respect to temperature due to its characteristics, the change in pulse width corresponding to the substrate temperature can be divided into about three stages. Therefore, it has not been possible to eliminate unevenness in print density over the entire period from the start of printing to the end of printing.

SUMMARY OF THE INVENTION An object of the present invention is to provide a thermal head drive circuit which improves the above-mentioned drawbacks, keeps the temperature of the heating resistor as constant as possible, and stabilizes the printing density.

[Means for Solving the Problems] FIG. 1 is a diagram showing the basic configuration of the present invention. In Fig. 1, 1-1, 1-2...1-n are heating resistors, 2
1.22...2m indicates an integrated circuit that drives the heat generating resistor, indicating that there are m integrated circuits that drive a plurality of heat generating resistors at once.

31, 32-3 m is an anti-inflammatory antibody, 41, 42
-4m is a monostable multivibrator, 21 to 2m.

31-3m and 41-4m correspond to each other in the same way that 21.3L 41 corresponds to each other.

The electric pulse signal is passed through the heating resistor 1-1.1-2-・-1-
The thermal head prints on thermal paper that comes into contact with the resistor when the temperature of the resistor increases and the temperature of the resistor is detected by a thermistor, and the pulse width is changed. The drive circuit for the thermal head according to the present invention has the following configuration. That is, on the same substrate as the heating resistors 1-1.1 to 2-.1-n,
Temperature sensitive resistor with a larger temperature coefficient than the thermistor 31°32
-.-3m is provided, the temperature-sensitive resistor is used as an external timing resistor of the monostable multivibrator 41, 42...-4m, and the output of the monostable multivibrator is used as the electric pulse signal.

In FIG. 1, the downward arrow provided near the heating resistor corresponds to the upward arrow provided near the temperature sensitive resistor 31, 32, . . . 3m. That is, one temperature-sensitive resistor is made to correspond to a plurality of heating resistors, and is incorporated into a corresponding monostable multivibrator.

[Function] With the configuration shown in FIG. 1, in the present invention, a drive signal is applied as a trigger to the monostable multivibrator in order to generate heat for the heating resistor. Since the temperature around the heating resistor is sensed by the temperature sensitive resistor, the resistance value corresponding to the temperature immediately before the heating resistor starts generating heat becomes the external timing resistance of the monostable multivibrator, and the resistance value corresponding to the temperature immediately before the heating resistor starts generating heat is used as the external timing resistance of the monostable multivibrator. can generate pulses. This pulse is applied to a desired heating resistor to generate heat.

If the temperature-sensitive resistor senses a temperature change at the next operation timing, the pulse width of the monostable multivibrator changes. Normally, the temperature increases, so the temperature coefficient of the temperature-sensitive resistor is negative, so the pulse width becomes shorter.

FIG. 2 shows that pulses of different widths are applied to each drive integrated circuit 21, 22-2m. That is, the second
Figure A shows the trigger pulse applied to each monostable multivibrator, and Figure B shows the output pulse of the monostable multivibrator.

Therefore, the width of the temperature rise of the heating resistor is suppressed to a minimum, and the color development of the thermal paper can be made constant.

Embodiment FIG. 3 is a diagram illustrating a method of manufacturing a heating resistor and a temperature-sensitive resistor as an embodiment of the present invention.

On the glazed alumina substrate, the temperature coefficient (TCR) is -1500 PPM/'C at the part marked P in Figure 3.
Thin films that are large and have high sheet resistance, such as Ta-
3t of Thermeso) JIW to a thickness of 1 by DC sputtering.
Sputter to 000 people. FIG. 4 is a diagram showing the relationship between sputtering gas pressure vs. resistance value ρ and temperature coefficient (TCR). For example, if a gas pressure of 9 x 10-' Torr is used to obtain a temperature coefficient of -1500 PPM/''C, the resistance value will be about 2000 μΩcm.

Next, Ta--N, which will become a heat generating resistor, is sputtered by DC sputtering onto the Q portion other than the portion indicated by P in FIG. A that becomes a conductor on top of that
I (aluminum) is DC-sputtered to a thickness of about 3 μm, and a large number of elements are formed in series as a temperature-sensitive resistor by a photolithography process.

Next, etching is performed, but at this time Ta-N and Ta
-Si cerment film can be dry-etched simultaneously with a mixed gas of oxygen and carbon tetrafluoride.

Next, a resin coating is performed by sputtering a protective film of S i Oz.'razoi. Next, the drive integrated circuit is bonded and then coated with resin again. Complete the drive circuit by connecting the monostable multivibrator and temperature-sensitive resistor.

FIG. 5 illustrates the relationship between the pulse widths obtained when the external resistance and capacitance of the monostable multivibrator are made variable. For example, the connection capacitance value is o, o
When the resistance value of the temperature-sensitive resistor is osμF and the resistance value is 1150Ω, the pulse width is approximately 2ms. When the ambient temperature rises and the resistance value changes to 285Ω, the pulse width changes to 0.5ms. .

[Effects of the Invention] According to the present invention, even when the temperature of the heating resistor gradually increases after printing starts, the external resistance value of the monostable multivibrator changes, and the pulse current for heating operation changes. Since the width is controlled, the print density on thermal paper always remains constant.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the principle configuration of the present invention, FIG. 2 is an explanatory diagram of the operation of FIG. Figure 5 shows the characteristics of a temperature-sensitive resistor, Figure 5 shows the operating characteristics of a monostable multivibrator, Figure 6 is a side view of a device including a conventional thermal head, and Figure 7 shows the temperature of a conventional substrate. FIG. 8 is a diagram showing a conventional drive circuit, and FIG. 9 is a diagram showing the relationship between printing density and ambient temperature. 1. Thermal head 1-1. 1-2...1-n...Heating resistor 2--Heating plate 10--Control circuit 21, 22-2 m--Integrated circuit 31.32...3 m--Temperature-sensitive resistor 41 .42...
・4m...Monostable multivibrator patent applicant
Fujitsu Co., Ltd. Representative Patent Attorney Eisuke Suzuki June Hara! 3! Figure 1 (PPM/'C) Il! Σ; A coffin 1 day) Ni;) 5, Figure 4 1202 Figure 6 Figure 7 Side warm skin (0C)

Claims (1)

[Claims] Electric pulse signals are transmitted through heating resistors (1-1) (1-2)...
...(1-n), resistor (1-1) (1-2)
A thermal head that prints on thermal paper in contact with the resistor when the temperature of (1-1n) rises, the temperature of the resistor is detected by a thermistor, and the pulse width is changed. In the thermal head drive circuit configured as above, the heat generating resistors (1-1) (1-2)...(1-n
) are provided with temperature-sensitive resistors (31) (32)...(3m) having a larger temperature coefficient than the thermistor, and the temperature-sensitive resistors (31)(32)...( 3m) to a monostable multivibrator (41) (42)...(4
m) as an external timing resistor for the monostable multivibrator (41) (42)...
(4m) as the electric pulse signal.