JPS6351102B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermal recording device used in facsimile machines, printers, etc., and more particularly to a thermal recording device in which a circuit for controlling the time period during which electricity is applied to a heating element is improved.

Generally, in a thermal recording device, the temperature of the base material of a recording head equipped with a heating element changes due to repeated energization of the heating element and fluctuations in ambient temperature. If the energization to the current-carrying element during one recording is always constant, the recording density changes in accordance with the temperature change of the base material of the recording head.
When the temperature of the base material is high, the recorded image becomes dark, and when the temperature of the base material is low, it becomes light. Therefore, density unevenness occurs in the recorded image, making it impossible to obtain a clear recorded image.

For this reason, conventionally, the time during which electricity is applied to the heating elements has been controlled in accordance with the temperature change of the base material of the recording head. FIG. 1 shows a conventional heat-sensitive recording device that controls the time during which electricity is applied to the heating element. Reference numeral 1 denotes a recording head, which includes m×n heating elements A ₁ to A _no arranged in one row, and diodes D ₁ to D _no connected in series to these heating elements A ₁ to A _no . It has n common terminals B ₁ to B _n and n individual terminals E ₁ to _{E o} .

The heating elements A ₁ to _{A no} are composed of n heating elements.
The block is divided into m blocks. One ends of the heating elements A ₁ to _{A no} of each block are collectively connected to common side terminals B ₁ to _{B n} , respectively. In addition, the other end of the heating element A ₁ to _{A no} located at the corresponding position in each block is a diode.
They are collectively connected to individual side terminals E ₁ to _{E o} via D ₁ to _{D no} .

The common terminals B ₁ to _{B n} are connected to the heating element power supply terminal 13 via transistors F ₁ to F _n , respectively. Further, the individual terminals E ₁ to _{E o} are grounded via transistors G ₁ to G _o , respectively.

Reference numeral 2 designates a temperature detection element which is installed on or near the base material of the recording head 1 and changes its resistance value in response to changes in the temperature of the base material of the recording head, 3 is a resistor, and 4 is a power supply terminal for the temperature detection element.

5 to 8 are resistors connected in series between the reference voltage source terminal 9 and the ground, and reference voltages a ₁ to a ₃ are taken out from their connection points. J ₁ to _{J 3} are comparators, which respectively output the reference voltages a ₁ to a ₃ and the recording head 1.
The output voltage b of the temperature detection element 2, which changes according to the temperature change, is compared with that of the temperature detection element 2.

10 is a decoder that converts the outputs C ₁ to C ₃ of the comparators J ₁ to J ₃ into binary codes. Therefore, the outputs d ₁ , d ₂ of this decoder 10 are sent to the recording head 1 in stages.
The value corresponds to the temperature of the base material. As will be described later, the energization time of the heating elements A ₁ to A _no is determined by the outputs d ₁ and d ₂ of the decoder 10.

Reference numeral 11 denotes a scanning timing generation circuit, which outputs timing pulses f, g, h based on the clock e inputted from the clock input terminal 1. 1
4 is a common side selection circuit, and its m outputs i ₁ ~
In synchronization with the timing pulse _f , the transistors _F1 to _Fn are sequentially turned on by sequentially setting the signal to a high level (hereinafter, high level is abbreviated as "H" and low level as "L").

Reference numeral 15 denotes a serial input/parallel output shift register, which outputs in parallel the image signal j that is input in series from the image signal input terminal 16 for each line. 17 is a pulse generation circuit, which generates a clock e and a timing pulse h.
Based on the outputs d ₁ and d ₂ of the decoder 10, an energization time control pulse k having a pulse width t is output for each period in which each of the transistors F ₁ to _{F n} is turned on. Here, the pulse width t is the decoder 10
is determined by the outputs d ₁ and d ₂ of .

K ₁ to _{K o} are two-input ANDs in which the parallel outputs 1 ₁ to 1 _o of the shift register 15 are used as one input, and the energization time control pulse k is commonly used as the other input.
The outputs of these AND gates K ₁ to _{K o} turn on transistors G ₁ to _{G o} , respectively.
It will be turned off.

Of the outputs 1 ₁ to 1 _o of the shift register 15, those corresponding to the black signal bits become "H". Therefore, when the energization time control pulse k is output from the pulse generation circuit 17, the AND condition of the AND gates K ₁ to K _o corresponding to the bits of the black signal is established, and the corresponding transistors G ₁ to G _o is turned on.

Since the energization time control pulse k is output for each period in which each of the transistors F ₁ to _{F n} is sequentially turned on as described above, the black signal is output from the heating element power supply terminal 13 for each block. The heating elements A ₁ to _{A no} corresponding to the bits are energized all at once.

Here, the energization time to each heating element A ₁ to A _no is the time during which the AND gates K ₁ to _{K o} are open;
That is, it corresponds to the energization time control pulse k and the pulse width t. This pulse width is determined by the decoder 10
The outputs d ₁ and d ₂ of the recording head 1 correspond to the temperature of the base material of the recording head 1, so that the current application time is changed in stages according to the temperature of the base material of the recording head 1. However, in this conventional device, in order to increase the number of stages of the length of the energization time, the number of reference voltages corresponding to a ₁ to _{a 3} and, by extension, the number of comparators corresponding to J ₁ to _{J 3} must be increased. However, it is difficult to increase the number of comparators due to constraints such as cost and mounting area, so the number of comparators has to be limited to two or three.

Therefore, the time during which electricity is applied to the heating element is not controlled with sufficient precision, and as the temperature of the base material of the recording head 1 increases, obvious changes in density are observed in the recorded image. There were cases where the first half was dark and the second half was pale, which had the disadvantage that the desired effect could not be obtained sufficiently.

The present invention has been made in order to eliminate the above-mentioned conventional drawbacks, and is capable of finely switching the energization time to the heating element according to the temperature change of the base material of the recording head without causing any inconvenience in terms of implementation, cost, etc. An object of the present invention is to provide a heat-sensitive recording device that can accurately control the temperature of a recording head and always obtain beautiful recorded images with a constant density.

The present invention will be described below based on embodiments shown in the drawings. Figures 2 and 3 illustrate one embodiment of the invention. 2 is a temperature detection element similar to that of the conventional device, one end of which is grounded;
The other end is connected to a temperature detection element power supply terminal 4 via a resistor 3. 18 is a comparator, which compares the output voltage b of the temperature detection element 2 outputted from the connection point between the temperature detection element 2 and the resistor 3 and the output P of the D/A converter 19, and determines that b is higher than p. When its output q
is set to “H”.

30 is an AND gate which receives the output q of the comparator 18 and the energization time control clock r inputted from the energization time control clock input terminal 20.
Note that an enable signal S that makes the circuit ready for operation may be added as an input to the AND gate 30 (in this case, when the enable signal S becomes "H", the circuit becomes ready for operation). ). 21 is the output y of the AND gate 30, i.e.
It is a three-stage binary counter that counts the clock r input through the AND gate 30.
When the reset signal u is inputted from the reset signal input terminal 22, it becomes a clear state. The D/A converter 19 converts the outputs x ₁ to _{x 3} of each stage of the counter 21 into a D/A converter.

Reference numeral 17 denotes a pulse generating circuit similar to that of the conventional device, and FIG. 3 shows a specific example of the configuration of this pulse generating circuit 17. That is, in FIG. 3, the pulse generating circuit 17 includes a ROM 23, a counter 24, an inverter 25, and an AND gate 26. The ROM 23 stores the output of the counter 21.
By using x ₁ to _{x 3} as address inputs, pre-written energization time setting data is read out.

The AND gate 26 receives a clock e from a scan timing generation circuit (not shown) similar to the conventional device at one input, and receives the carry output z of the counter 24 via an inverter 25 at the other input. . The counter 24 also receives a clock e via an AND gate 26 at its clock input.
is input, and the timing pulse h from the scan timing generation circuit is input to the load input. When the counter 24 receives the timing pulse h, the output of the ROM 23 is loaded as a preset value. The energization time control pulse k is output from the inverter 25.

Next, the operation of this embodiment will be explained with reference to time charts and voltage waveform diagrams shown in FIGS. 4 and 5. Note that the time chart in Figure 4 shows the passage of time over several tens of minutes, but t ₁ ,
Only t ₂ is enlarged and drawn for convenience.

First, if the operation of this apparatus is started when the temperature of the base material of the recording head 1 is close to room temperature, then at the start of this operation, the output voltage b of the temperature detection element 2 is as shown in b of FIG. Point W at the left end of the curve
As shown, the value is low.

When the reset signal u is applied to the counter 21 at the start of this operation, the outputs _x1 to _x3 of the counter 21 become "0" and the output P of the D/A converter 19 becomes its lowest voltage. Here, this D/A
The lowest voltage of the converter 19 is set lower than the output voltage b of the temperature detection element 2 when the temperature of the substrate of the recording head 1 is around room temperature. Therefore,
The output q of the comparator 18 becomes "H".

As a result, the AND gate 30 is opened, the clock r is input to the counter 21, and the clock r is input to the counter 21.
counts the same clock r, so the outputs x ₁ to _{x 3} of the counter 21 change as (000) → (001) → (010) → . Then, along with this, the D/A converter 1
9's output P rises in a stepwise manner.

If this kind of operation continues, the D/A
The output P of the converter 19 has a higher level than the output b of the temperature detection element 2, and at this time the output q of the comparator 18 becomes "L" and the AND gate 30 is closed.

Therefore, the clock r is no longer input to the counter 21, and the outputs _x1 to _x3 of the counter 21 do not change, so that the output P of the D/A converter 19 as shown in part A of FIG. will be held at a constant value.

However, as will be explained in detail later, after the start of the operation, the heating element is repeatedly energized for the energization time corresponding to the outputs x ₁ to _{x 3} of the counter 21, so that if further time elapses, the recording Head 1
The temperature of the base material increases, and the output b of the temperature detection element 2 becomes higher than the output P of the D/A converter 19. As a result, the output q of the comparator 18 becomes "H" again, the AND gate 30 opens, and the counter 21 counts one clock r.

Then, the value of the output x ₁ to x ₃ of the counter 21 is 1
, and the output b of the D/A converter 19 also increases accordingly, so as shown in b, P is higher than b.
The level will be higher again.

Therefore, the output q of the comparator 18 becomes "L", the AND gate 30 is closed, and the counter 21
will no longer count the clock r.

Then, the same operation is repeated thereafter, and the A/D
Since the output P of the converter 19 always tries to stabilize at a point slightly higher than the output b of the temperature detection element 2, D/
The output P of the A converter 19 has a value approximately corresponding to the temperature of the base material of the recording head 1.

Therefore, the output of the counter 21 is as follows.
By controlling the energizing time to the heating elements according to x ₁ to _{x 3} , the energizing time can be controlled depending on the temperature of the base material of the recording head 1 .

That is, the outputs x ₁ to _{x 3} of the counter 21 serve as address inputs, so that the energization time setting data of the values corresponding to these x ₁ to _{x 3} are read from the ROM 23 . Then, this energization time setting data is applied to the counter 24 using the timing pulse h as the timing.
loaded as a preset value. Then, the carry output z of the counter 24 becomes "L",
The AND gate 26 is opened, and the counter 24 starts counting the clock e input through the AND gate 26. When the counter 25 counts the number of clocks e determined by the preset value, the carry output z of the counter 24 becomes "H".

Then, since the gate 26 is closed, the clock e is no longer input to the counter 24, so the carry output z is maintained at "H".

Then, the next timing pulse h is detected by counter 2.
When the new energization time setting data is inputted to the load input of No. 4 and loaded from the ROM 23 into the counter 24 as a preset value, the carry output z becomes "L" again, and the same operation as described above is repeated. Therefore, the energization time control pulse k, which is an inverted signal of the carry output z, becomes "H" only for the time corresponding to the energization time setting data, and thus the outputs _x1 to _x3 of the counter 21. As a result, the time for energizing the heating element is controlled in accordance with the temperature of the base material of the recording head 1, as described above.

The pulse width t of the energization time control pulse k must be made shorter as the temperature of the base material of the recording head 1 increases, but its specific value depends on the characteristics of the recording head 1 and the characteristics of the recording paper. , recording speed, etc. Fifth
The figure shows an example of setting the pulse width t of the energization time control signal k for each value taken by the outputs x ₁ to x ₃ of the counter 21.

In addition, in FIG. 5, the pulse width t of k when x ₁ to _{x 3} is "7" is very narrow, but this is due to the fact that the base material of the recording head 1 is at an abnormally high temperature due to some reason. This is to prevent damage to the recording head O by reducing the power applied to the heating element to a very low level when the temperature decreases.

Incidentally, when the temperature of the base material of the recording head 1 is rising, the outputs x ₁ to _{x 3} of the counter 21 follow the output b of the temperature detection element 2 as described above, but the outputs x 1 to x 3 of the recording head 1 follow If the temperature of the base material decreases, it will not follow. Therefore, it is necessary to reset the counter 21 by applying a reset pulse u to the counter 21 at an appropriate timing as shown near the right end of the time chart in FIG.
After this reset, the outputs x ₁ to _{x 3} of the counter 21 follow the output b of the temperature detection element 2 again.

Here, the time required for the output P of the D/A converter 19 to become almost equal to the output b of the temperature detection element 2 after the reset pulse u is output (the time corresponding to t ₁ and t ₂ in FIG. ) is clock r
The higher the frequency, the shorter the time. Furthermore, no matter how high the clock r is (up to a few Mz), there is no adverse effect on other operations, so the above-mentioned time can be shortened to the point where it can be ignored compared to other operation timings (as mentioned above, as shown in Figure 5).
t ₁ and t ₂ are shown enlarged for convenience), the reset signal u can be outputted every interval between scanning of each line so as not to affect the recorded image.

Now, in this device, the number of adjustment steps for the energization time to the heat generating element can be increased simply by increasing the number of bits of the output of the counter 21 and the input of the pulse generation circuit 17. It is possible to adjust the energization time to the heat generating elements very narrowly according to the temperature change of the base material of the recording head 1 without causing mounting problems or cost increases due to the increase.

As a result, it is possible to always obtain a beautiful recorded image with a constant density, and the possibility that the temperature of the recording head 1 rises abnormally is greatly reduced.

As described above, the thermal recording device according to the present invention includes a temperature detection element that detects the temperature of the base material of the recording head, a counter, a D/A converter that converts the output of the counter into D/A, and the D/A converter that converts the output of the counter into D/A. It has a comparator that compares the output of the A converter and the output of the temperature detection element, and a circuit that controls the energization time to the heating element according to the output of the counter, and the counter By counting the clocks according to the output of the comparator, it is possible to precisely control the energization time to the heating element according to the temperature change of the recording head base material, without causing mounting problems or increasing costs. However, an excellent effect can be obtained in that the recording density can always be kept constant.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a conventional thermal recording device, FIG. 2 is a circuit diagram showing main parts of an embodiment of the thermal recording device according to the present invention, and FIG. 3 is a specific diagram of a pulse generating circuit in the embodiment. Circuit diagram showing a configuration example, No. 4
The figure is a timing chart of the embodiment, and FIG. 5 is a voltage waveform diagram showing an example of setting the pulse width of the energization time control pulse in the embodiment. 1... Recording head, 2... Temperature detection element, 17
...Pulse generation circuit, 18...Comparator, 19...
D/A converter, 21... Counter, 30...
AND gate, A ₁ ~ _{A no} ...Heating element, r...Clock for controlling energization time.

Claims (1)

[Claims] 1. A recording head equipped with a heating element, a temperature detection element for detecting the temperature of the base material of the recording head, a counting means for counting clocks, and a D/A conversion means for converting the output of the counting means from D/A. And this D/
Comparing means for comparing the output of the A converting means and the output of the temperature detecting element, and means for controlling the energization time to the heating element in stages according to the output of the counting means, A thermosensitive recording device, wherein the counting means counts clocks based on a discrepancy detection signal between the output of the temperature detecting element of the comparing means and the output of the D/A converting means.