JPS5912874A - Thermal recorder - Google Patents

Abstract

PURPOSE:To obtain picture printing with a constant density and stable quality by a method in which signals corresponding to the ambient temperatures of a thermal head are fed-back to a simulation circuit for controlling temperatures. CONSTITUTION:The ambient temperatures of a thermal head are detected by a temperature sensor Si-D, converted into voltage by an operating amplifier OP, and supplied to a simulator circuit (Rs, Cs). In case where the ambient temperature of the thermal head is high, low voltage is supplied to an inverter 22, and when the ambient temperature is low, a high voltage is supplied to the inverter 22. The output of the inverter 22 is added to an instable applied voltage Vin and given as a control voltage to VCO20. Accordingly, the output signal of the VCO20 changes into high-frequency signal in proportion to input voltage, and thereby the output time of carry signal of a counter 21 is hastened and the time (time taken for SW1 to become off) taken for FF9 to become reset is hastened. Pulse from an output terminal T2 is supplied to the thermal head, while the heat amount applied to the head becomes constant equivalently, and the quality of picture is stabilized.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention brings a thermal head into contact with a recording medium directly or via an ink sheet, heats the thermal head based on an electric signal, and thereby forms an image, etc. on the recording medium. The present invention relates to a thermal recording device for recording.

A conventional thermal recording device includes a thermal transfer section or a thermal recording section and a paper feeding section. The invention particularly relates to a thermal transfer section or a thermal recording section. A thermal transfer section or a thermal recording section is generally composed of a heating element (thermal head) and a recording medium, and when the thermal head heats up and heat is applied to recording paper or thermal paper with an ink sheet interposed, Only that portion of the recording medium is colored or the ink is transferred, and the recording remains. The external appearance of the thermal head 1 is as shown in FIG.
As shown in FIG. 2, its main parts include a thermal insulating layer 5 on a ceramic substrate 4, a heating element layer 6 provided thereon, and a number of counter electrodes 7 and 8 stacked on top of each other. , covered with a surface protective layer.

By applying a predetermined pulse voltage (applied pulse) between the opposing electrodes 7 and 8, the heat generating layer 6 selectively generates heat. At this time, if the size of recording paper or thermal paper as a recording medium is, for example, B4 size and the thermal head is 8 dat/411H, a counter electrode of 2048 dat is required. And for the fever, 1
Approximately 0.6 to IW of power is required per dot, and 2
Even if recording is performed in batches, a power supply capacity of 600W to IKW is required.

Here, we will discuss the relationship between the temperature of the thermal head and the density of images recorded on the recording medium (especially color-forming thermal paper).
When the temperature of the thermal head increases, images appear darker, and when the temperature decreases, images appear tingling. Therefore, in order to keep the density of images recorded on a recording medium constant, it is necessary to maintain the thermal head at a predetermined temperature.

However, when the power supply voltage fluctuates, the applied pulse voltage changes accordingly, and the power supplied to the thermal head changes, making it impossible to maintain the thermal head at a predetermined temperature, causing the image, etc., appearing on the recording medium to change. It causes unevenness. Therefore, in order to record images of constant density, a stable power source is required. However, a stable power supply with a capacity of 1-600W to IKW is extremely expensive.

Furthermore, the inventor has found that it is very important to consider the ambient temperature of the thermal head in order to bring the thermal head to a predetermined temperature. In other words, if constant power is supplied to the thermal head regardless of the ambient temperature, if the ambient temperature is high, the thermal head will be at a higher temperature than the predetermined temperature, and if the ambient temperature is low, the thermal head will be lower than the predetermined temperature. Become. For this reason, changes in ambient temperature appear as they are in the density of the recording on the recording medium, making it impossible to obtain images with constant density.

SUMMARY OF THE INVENTION An object of the present invention is to provide a thermal recording device that can obtain images of constant density or image quality regardless of fluctuations in the power supply voltage and changes in the ambient temperature of the thermal head.

Conventionally, in order to obtain an image with a constant density, a constant voltage power supply was used, and a voltage with a constant pulse width was applied to the opposing electrode of the thermal head to obtain a constant peak temperature. He was performing a valve (see Figure 3). The curve of this temperature change over time can be expressed as follows.

Temperature is θ (℃), thermal leakage resistance is R (℃/W), heat capacity is C (J/'C), applied power is q (W), thermal acid is Q (
J), when the temperature rises, if 1 = 0 and Q = 0, then θ = Rq (
1-e") - (1) When the temperature decreases, t=
When Q *O (℃), then θ=θoecR...
It is expressed as (2).

It was found that a curve similar to this curve of temperature change over time can be obtained using an electric circuit. That is, at least the heat capacity and thermal resistance of at least one of the thermal head and the recording medium (including a heat-melting or heat-sublimating ink film of the heat-sensitive transfer type) are measured in advance, and the combined heat capacity O and the combined thermal resistance Rs are calculated in advance. An electric circuit (simulation circuit) is constructed with a capacitor (μJ/℃ is μF) and a resistor ('C/W is Ω) equal to these, and the above curve can be obtained electrically by this circuit. . This electric circuit is used as a simulation circuit, and the voltage obtained by this circuit is used to control the time of the applied pulse voltage applied to the thermal head, and when a predetermined power or total amount of applied heat is reached, this is calculated and the applied pulse voltage is adjusted. We decided to suspend the supply.

Therefore, this simulation circuit is a very effective means for dealing with fluctuations in power supply voltage. However, it has been found that this method cannot cope with changes in the ambient temperature of the thermal head.

The inventor has discovered that in order to maintain a constant image recorded on a recording medium, it is necessary to detect the ambient temperature of the thermal head and adjust the power supplied to the thermal head using an electrical signal corresponding to this temperature. This is what led us to discover this and arrive at the present invention.

That is, in the thermal recording device according to the present invention, a thermal head is brought into contact with or close to a recording medium directly or via an ink sheet, and the thermal head is heated based on a recording signal to record information on the recording medium. When recording, at least one of the thermal head, the recording medium, and the ink sheet has at least a heat capacity and a thermal resistance.
A simulation circuit is provided to control the temperature 1 of the thermal head based on a curve corresponding to the temperature rise of the thermal head, and after the thermal head reaches a predetermined temperature, the recording signal for heating the thermal head is intermittent. The thermal recording device further calculates that the total amount of heat applied to the thermal head reaches a predetermined amount of heat and stops heating the thermal head, the thermal recording device detecting at least the ambient temperature of the thermal head and detecting this temperature. The present invention is characterized in that an electrical signal corresponding to the above is applied to the simulation circuit.

Therefore, according to the present invention, at least the ambient temperature of the thermal head is detected and an electric signal corresponding to the crack is fed back to the simulation circuit, so that even if the power supply voltage fluctuates and the ambient temperature of the thermal head changes, Irrespective of this, the thermal head is always kept at a predetermined temperature, so that images of a constant density and stable print quality can be obtained.

If the ambient temperature of the thermal head is θS, then the equation representing the curve of the temporal change of the thermal head is as follows when the temperature rises: θ=Rq (1-e CR)+θs...
・・・・・・(1)′When the temperature decreases, θ=θ0eCR+θS・・・・・・・・・・・・・・・
......(2)'. In other words, if an electrical signal corresponding to θS is added to the cocoon weight simulation circuit and power controlled according to the ambient temperature of the thermal head is supplied to the thermal head, the heat generated by the thermal head will be reduced in the printing state. part is always kept at a predetermined temperature. The above object can be achieved by converting the temperature detected by the ambient temperature detection element (temperature sensing element) into an electrical signal, applying it to the simulation circuit, and thereby controlling the voltage of the simulation circuit.

Next, the present invention will be described in more detail with reference to examples.

FIG. 4 shows a circuit that detects the ambient temperature of the thermal head, converts it into an electric signal (voltage), and improves the simulation circuit (parallel circuit of resistor Rs and capacitor Cs). The operation of this circuit will be explained below. Resistance R
1, a temperature sensing element (for example, a silicon diode 8i-D in this example), and a resistor R2 are connected in series, and R1 and R2 are connected in series.
Add the voltage across the . silicon diode 5i-
The temperature coefficient of the forward voltage of D is -2.2 mV/'C, and changes from 0°C to 100°C. Therefore, when the ambient temperature of the thermal head is higher than a desired value, the voltage applied to the inverting input terminal of the operational amplifier (hereinafter referred to as operational amplifier) OP becomes low. Since this voltage is connected to the inverting input terminal of the operational amplifier OP, the output voltage of the operational amplifier OP becomes high. Conversely, if the ambient temperature of the summar head is lower than the desired value, the input electrons to the inverting input terminal of the operational amplifier OP will be high, and the output voltage of the operational amplifier OP will be low. Therefore, the output voltage of the operational amplifier is equal to the voltage of T1■ of the simulation circuit.
Only the voltage corresponding to the temperature at that time is changed. To explain this using Figure 5, ■ is the fourth
In the circuit diagram shown in the figure, the voltage at l+ is shown, e is the voltage applied to the simulation circuit, and ■ is the output voltage of the operational amplifier OP (the voltage is shown as ■). When the ambient temperature of the thermal head is high and a low voltage is input to the inverting input terminal of the operational amplifier OP, the output of the operational amplifier OP becomes high, and the output of the operational amplifier OP increases by the increased voltage (
Since the voltage 11 is controlled to a certain predetermined voltage level by the voltage comparator described later, the voltage e applied to the simulation circuit is lowered by ■) in FIG. 5(5). On the other hand, when the ambient temperature of the thermal head decreases, a high voltage is input to the operational amplifier, and its output ((c) in FIG. 5) decreases. When the output voltage V of the operational amplifier OP becomes low, the voltage of the simulation circuit becomes relatively high. Figure 4 1
1 voltage, even if the ambient temperature of the thermal head changes,
In order to stabilize it, between the simulation circuit and ground,
By applying a voltage responsive to the ambient temperature of the dual head as described above, the voltage applied to the simulation circuit is changed. When the temperature around the thermal rad is high, the voltage appearing in the simulation circuit becomes low, and the time t1 for the voltage shown in FIG. 4 to reach the predetermined voltage V becomes earlier (FIG. 5(A)). When 11 becomes early, the pulse voltage supplied to the thermal head is stopped early due to the action of the circuit connected to 11. On the other hand, when the ambient temperature of the thermal head is low and the voltage applied to the simulation circuit is high, the time t2 for the voltage 11 to reach the predetermined voltage ■ becomes slower (Fig. 5 @
).

The pulse voltage supplied to the thermal head will stop later by the delayed time. Then, a voltage corresponding to the ambient temperature of the thermal head is applied to the adder, and after a certain amount of power is supplied to the thermal head, the pulse voltage supplied to the thermal head is stopped, and an image with constant density is obtained. That's what I did.

Next, a thermal recording device using the above simulation circuit of the present invention will be explained with reference to FIG.

In FIG. 6, an unstable applied voltage Win is supplied to the input terminal T1. A pulsed start signal Vt is supplied to the terminal T3. The start signal 1 is sent to the flip-flop circuit (
At the same time, it is supplied to the set terminal of FF10 (hereinafter referred to as FF). Therefore, the voltage level of the output Q of FF9 and FF10 becomes H level.

Then, depending on the output of FF9, the analog switch 8W
+ is switched to the on state. Note that the analog switch S Wr is shown as a mechanical structure for convenience of explanation. An applied voltage Vin is obtained from the multiplier 13, and this voltage V can be supplied to the line 11 via the switch 8W1. The capacitor Cs and the resistor Rs constitute the aforementioned temperature simulation circuit.

The voltage V on line ll is applied to each non-inverting input terminal of a voltage comparator 11.12. Note that the voltage Vin obtained from the multiplier 13 is also transmitted via the adder ρ to the voltage control generator
Hereinafter referred to as ■CO. )20 is also supplied.

On the other hand, the reference voltage ■θ1 is applied to the terminal T4, and the reference voltage ■θ1 is applied to the terminal T4.
is supplied with a voltage ■θ2 that is slightly lower than the reference voltage.

The voltage level on line ll gradually rises to voltage Vθ1
When this reaches the output signal from the voltage comparator 11, the output signal of the monostable multipipe lake (hereinafter referred to as MM) 14 becomes I (level A) in synchronization with this.
Each input terminal a of the ND circuit 16.

Both bSc become H level, and the output signal also becomes H level. Since the output signal of the AND circuit 16 is supplied to the reset terminal of FF9 via the OR circuit 18,
The Q output of becomes L level.

Then, the analog switch S Wt is turned off,
The voltage ■ on line ll gradually decreases.

When the voltage V drops to the voltage ■θ2, an output signal is obtained from the voltage comparator 12, and the output of the MM 15 becomes level II. The input terminals a, b, and c of the AND circuit hI817 all become I (level), and the output signal also becomes 1.Level.

The output signal of the AND circuit 17 is sent via the OR circuit 19)
Supplied to the set terminal of F9. When F F 9 is switched to the set state again, the analog switch SWl is turned on again.

As a result, a waveform applied pulse is supplied to the thermal head 1 from the output terminal T2.

By the way, while the above operation is being performed, the output voltage ■0 of the adder is supplied to ■C020, and when ■0 increases, the output frequency of VCO20 gradually shifts to a higher frequency, and when vo is low , move to a lower frequency.

Note that a voltage other than the voltage corresponding to the ambient temperature of the thermal head is also input to the CO20 via the inverter n. When the ambient temperature of the thermal head is high, a low voltage is input to inverter 4 and a high voltage is output from inverter n, and when the ambient temperature is low, a low voltage is input from inverter n vC02.
It is input to 0. The output signal of VCO20 shifts to a high frequency signal in proportion to the input voltage, so if ■0 is high,
Accordingly, the output time of the carry signal output from the counter is accelerated, and the time until the reset of FF 9 (that is, the time until the switch SWs is turned off) is accelerated. As a result, even if the ambient temperature rises, the amount of heat applied to the thermal head is isometrically constant, resulting in stable print quality. This is reversed when the ambient temperature decreases, so the total amount of heat to the thermal head remains constant.

The time of applied energy is controlled by the frequency division ratio N of the counter 21 and the frequency of the output signal of the VCO 20, and when a predetermined energy is reached, a carry signal Vc is output from the counter 21. FF9 and FFl0 are switched to the reset state by the carry signal Vc, and the analog switch SWl
is also switched to the off state. This will return it to its initial state.

In this example, a silicon diode (8i-D) having negative temperature characteristics is used as the temperature sensing element, but it is also possible to use a thermistor or thermocouple. . In addition, in this embodiment, since a silicon diode is used as the temperature sensing element, the temperature voltage change is input to the non-inverting input terminal of the operational amplifier, but if the temperature characteristic of the temperature sensing element is positive, This purpose can be achieved by inputting the signal to the inverting input terminal of the operational amplifier.

Incidentally, a voltage corresponding to the temperature θ1 shown in FIG. 7(a)K is supplied to the inverting input terminal of the voltage comparator 11 in FIG. 6. Furthermore, the inverting input terminal of the voltage comparator 120 is connected to the inverting input terminal of the voltage comparator 120 (see FIG.
A voltage corresponding to the temperature θ2 shown in 2) is supplied. 7th
(in the figure) shows the thermal response characteristics when the applied voltage vin is high, and the timing controller (not shown) shows the thermal response characteristics when the applied voltage vin is high.
An applied pulse Vout as shown in is obtained. Note that the temperature θ1 is, for example, about 300°C, and the temperature θ2 is, for example, about 2
It's about 80 degrees Celsius.

Then, an applied pulse Vout as shown in FIG. 7 is obtained from the output terminal T2 and supplied to the thermal head. By the way, if the total amount of energy applied by the applied pulse Vout is E, this is determined by the product of the applied power W and the application time S. In other words, g=w-sg)...
・・・・・・・・・・・・・・・・・・ (3) If the resistance value of the heating element is RH1 applied voltage ■in is V, then the above (3
) formula is E = V2/RH*, 8 g)...
(4) From this equation (4), it can be understood that in order to obtain a constant print quality, it is sufficient to keep E constant.

Regarding (4) 2, since 1/RH is a constant, E can be made constant by changing S in response to fluctuations in V. In other words, even if the intermediate applied voltage Vin contains a ripple voltage that has been simply full-wave rectified and then incompletely smoothed, E can be made constant by changing S in response to fluctuations in the voltage level. can. by this,
Even if there are fluctuations in the applied voltage, that is, even if an unregulated power source is used, stable thermal recording can be performed by following these changes,
It is possible to prevent unexpected situations such as distortion and cracks occurring within the thermal head and burnout of the heating element.

Therefore, changes in heating resistance due to changes in applied voltage are prevented,
The life of the thermal head can be extended.

[Brief explanation of the drawing]

Figure '1 is a perspective view showing the shape of the thermal head, Figure 2 is a cross-sectional view of the main parts showing the structure of the thermal head, Figure 3 is a characteristic diagram showing the relationship between applied pulses and temperature, and Figure 4 is the main part of the thermal head. Figure 5 (5) and (g) are characteristic diagrams of voltages appearing in the simulation circuit and temperature detection circuit; Figure 6 is the simulation circuit and temperature detection circuit diagram according to an embodiment of the invention; FIG. 7 is a circuit diagram showing the entire circuit of a thermal recording device equipped with a detection circuit. FIG. 7 is a characteristic diagram showing the relationship between applied pulses and temperature in a simulation circuit. In addition, in the symbols used in the drawings, Cs, Rs
・・・・・・Capacitor and resistor OP that make up the simulation circuit ・・・Operating circuit ・・・Thermal head 2.3 ・・・・Printed circuit board 4 ・・・・・... Ceramic substrate 5 ... Insulating layer 6 ... Heat generating layer 7.8 ... Opposing electric pen 9.10 ......Flip-flop circuit 11
．． 12... Voltage comparator 14.15...
...Monostable multivibrator 16.17...
・・・・・・AND circuit 18.19・・・・・・・・・
・OR circuit side・・・・・・・・・・・・Voltage controlled oscillation circuit 21・・・・・・・・・・・・Counter 22・・・・・・・・・......Inverter 5i-
D......Silicon diode. Agent: Patent Attorney Hiroshi AisakaFigure 1Figure 3Figure 4

Claims (1)

[Claims] 1. A thermal head is brought into contact with the recording medium directly or via a Hiro ink sheet, and based on a recording signal, 1 (the thermal head is heated to transfer information to the recording medium. When recording, the thermal head is adjusted based on a curve opposite to the temperature rise of the thermal head, which is obtained from at least the heat capacity and thermal resistance of at least one of the recording medium and the ink sheet. A simulation circuit is provided to control the temperature of the thermal head, and after the thermal head reaches a predetermined temperature, a recording signal for heating the thermal is intermittent, and the total amount of heat applied to the thermal head reaches a predetermined amount of heat. a thermal recording device that detects at least the ambient temperature of the thermal head and adds a power signal corresponding to this temperature to the simulation circuit. 2. A thermal recording device characterized by a thermal recording device, which is configured based on at least the heat capacity and thermal resistance of at least two of the following: a thermal disk, an ink sheet, and a recording medium; A simulation circuit, a comparison circuit that compares the output of the simulation circuit with a predetermined voltage, and a Sakai number, a main,
12. The apparatus according to claim 11, further comprising an accumulator 6 for deriving the information, and a detecting element that uses the ambient temperature of the thermal head. . 3. The unstable applied voltage is input to a multiplier, and the output of this multiplier is input to a voltage-controlled oscillator via an adder.
9. The scope of claim 9, wherein the input signal from the voltage controlled oscillator to the accumulator is obtained, and temperature information from an ambient temperature detection element is also added to the adder. The device described in item 1 or item 2. 4. The device according to any one of claims 1 to 3, wherein the temperature-temperature-resistance circuit is constituted by a capacitor and a resistor. 5. The device according to any one of claims 1 to 4, in which the ambient temperature of the thermal head is detected by a temperature sensing element having negative or positive temperature characteristics