JPS5996976A - Temperature control circuit of thermal recorder - Google Patents

Abstract

PURPOSE:To achieve a better and accurate control of the temperature of a thermal head serving for preheating without complicating the construction by controlling the pulse width of preheating and heating pulses with a switch of two time constant circuits. CONSTITUTION:A switch S1 or a switch S2 is turned ON according to a high level Q or a Q' output of a switch controller 5 made up of an FF to be controlled with a timer controller 4 at a specified timing and a capacitor C1 or C2 is selected. Different time constant circuits which commonly uses a thermistor Rr of a temperature sensor varying in the resistance according to a common detection temperature controls the pulse width of a preheating pulse and a heating pulse via a timer 3. The common use of the thermistor for the temperature sensor enables an easy and accurate control of the temperature of a thermal head for thermal recording serving for preheating without complicating the construction.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a thermal recording device such as a facsimile, and more particularly to a temperature control circuit for a thermal head.

[Prior art]

2. Description of the Related Art Thermosensitive recording devices, in which a heating element formed on a substrate is selectively energized to color recording paper, have been widely used in recent years because of their simple method. There are various methods of driving heat-sensitive recording in this heat-sensitive recording device, and a method called a direct drive method has been developed in recent years.

This direct drive type thermal recording device is equipped with a switching element connected to each linear heating element and integrated into the thermal head, and the recording data is stored in a shift register or latch circuit for one line. It is configured to send .

For example, one line of recording data is serially input to a shift register and then transferred to a two-way circuit, and depending on the contents of this latch circuit, ON or OFF of a switching element incorporated in a thermal spatula r is determined, and an image is recorded. It becomes. According to this direct drive method, a thermal recording device capable of high-speed data transfer and high-speed recording is obtained.

However, when a conventional apparatus performs a continuous recording operation, the temperature of the thermal head rises, which changes the energization state and causes density unevenness in the thermal recording. For example, the first
As shown in the figure, (1, 1, 0, 0) is recorded on the n-th line, and (1, 0, 1, 0) is recorded on the n-10 i-th line.
), in the case of a dot, any line is energized and heat is generated, but for a b dot, only the nth line is energized and heat is generated. As a result, a temperature difference occurs between the a F4 dot and the b dot, resulting in density unevenness in the thermosensitive recording. In order to overcome this drawback, in recent years, data from the previous line is used to correct the temperature of the subsequent line.
Various methods have been proposed for preventing density unevenness in images.

A method of correcting the temperature by applying a preheating/e-pulse will be explained with reference to FIGS. 2 to 5. As shown in FIG. 2, the ON and OFF arrangement of the dots a to d on the nl n + 1st line is the same as in FIG. 1.

Note that the line n/ is the ON and O of the nth line.
This is an inverted FF.

FIG. 3 is a timing chart for explaining the temperature change of the thermal head in the case where the correction by the preheating pulse is not performed. As shown in the figure, for the A dot, the recording norm is given to both the nth and n+1th lines, so the temperature of the thermal head changes like a curve (fruitful 1).On the other hand, for the C dot, , the recording pulse is applied only to the (n+1)th line, so the temperature of the thermal head changes as shown by the curve (dashed line) 2a. As a result, a temperature difference occurs in the thermal head between the dots a1''l and dots.

FIG. 4 is a timing chart useful for explaining the temperature change of the thermal head when performing preheating/ξ las correction. The temperature change of the thermal head at the a-dot is similar to that shown in FIG. On the other hand, in the case of C dots, since a recording pulse is applied only to the (n+1)th line, a preheating pulse with a nozzle width t1 is applied to the n'th line for temperature correction. the result,
Since the temperature change of the thermal head at the C dot changes as shown by the curve (broken line) 2b, no temperature difference occurs between the A dot and the C dot, and no density unevenness occurs in the image.

By the way, since thermal recording utilizes temperature phenomena, it is greatly affected by the environmental temperature and the temperature of the thermal head that accompanies usage time. Therefore, by using a device as shown in FIG. 5, the recording nozzle width and the nozzle width of the preheating pulse to be applied can be controlled. That is, the temperature of the thermal head is outputted by a thermistor RT or the like, and the width of the signal emitted from the timer 3 is controlled. The timer 3 emits a pulse in response to an external trigger input, and the pulse width thereof is regulated by a time constant circuit made of a capacitor C1 thermistor RT, etc.

In this way, a method of applying a preheating pulse is used to eliminate density unevenness caused by temperature differences in the thermal head, but in conventional devices, the circuit that controls the preheating pulse and the circuit that controls the recording pulse are separate. It is set in. Therefore, there are two temperature sensors in the thermal head, and two timers and the like in the control circuit.

This inevitably results in inconveniences such as a complicated configuration of the thermal head and a complicated circuit.

〔the purpose〕

The present invention has been made in view of the above points, and provides a temperature control circuit for a thermal recording device, which provides preheating and ξ pulse and also controls the width of the applied ξ pulse. The purpose is to provide

〔composition〕

Regarding the structure of the present invention, 8i'l! Figures 6 and 7
An explanation will be given based on an embodiment shown in the figure. FIG. 6 is a circuit diagram of one embodiment, and the same elements as in FIG. 5 are designated by the same reference numerals. The trigger input (100) is connected to the timer controller 4,
A switch controller 5 configured with a flip-flop or the like is provided. A regulating resistor RP is connected in parallel with the thermistor RT of the thermal head, and these are connected to the switch S1.
．． A time constant circuit is formed together with capacitors C1 and C2 connected via S2. The timer 3 generates a signal (400) based on the signal from the timer controller 4 and the signal from the time constant circuit, and provides this to the switch controller 5. The timer 3 can be composed of, for example, a monostable multi-ζibrator. The switch controller 5 switches the switch S1. based on the trigger input (ioo) and the timer output (400). Controls S2. In addition, switch S
,, S2 has a repetition time of several milliseconds, so an analog switch or the like is appropriate.

Next, the operation of the circuit shown in FIG. 6 will be explained with reference to FIG. Incidentally, when a trigger input at an interval of t11 is given, the timer controller 4 outputs tl. Assume that the interval .xi.rus is generated and given to timer 3.

At time T1, the trigger input (100) is 11 L/
When /, the Q output of switch controller 5 (300)
becomes +1)(#, and the switch S0 is turned on. Therefore, the time constant of the time constant circuit connected to the timer 3 is determined by the resistance values R, , R, and the capacitance C□. Also, Timer 3 has the output of the timer controller (20
0) is given, the output (400) returns to "1L".

At time T2, the time constant circuit RT, R, and C
When the time tpre determined by 2 has elapsed, the output of timer 3 (
400) becomes ttHrr. Also, since the switch controller 5 is cleared by this, the Q output (30
0) becomes "IL" and the switch S1 turns OFF'.

On the other hand, the Q output becomes もI(II), so the switch
S2 is turned on. In this way, the resistance RT of the time constant circuit
, RP and a pulse width of tpre determined by capacitor C1 are given. In addition, this tpre
Since the value of ξ changes depending on the value of R7, the ξ pulse width will eventually correspond to the temperature change.

At time T3, the timer input (200) is tt I,
When it reaches rr, the timer output (400) also becomes 11 L II
become.

At time T4, when the time tpwh determined by the time constant circuit RT, R, and capacitor C2 is suitable, the timer output (400) changes from ttLu to ゝH'l.

In this way, a recording pulse with a pulse width of time tpwh is provided. Note that since the value of tpwh also changes depending on the RTO value, the pulse width will eventually correspond to the temperature change.

When the trigger input (100) is applied again at time T5, the same operations as those from time T1 to T5 described above are repeated.

〔effect〕

As described above, according to the present invention, pulses with different pulse widths and different timings can be generated and controlled by a single sensor and a single timer, and the preheating pulse and the recording pulse can be generated and controlled by a single sensor and a single timer. It is possible to obtain a temperature control circuit for a thermal recording device that performs sequential control and has a significantly simplified configuration.

[Brief explanation of the drawing]

Figures 1 and 2 are diagrams explaining the principle of thermal recording, Figures 3 and 4 are timing charts explaining temperature changes in a thermal recording device, and Figure 5 is a circuit diagram of an example of the configuration of a conventional device. , FIG. 6 is a circuit diagram of an embodiment of the present invention, and FIG. 7 is a timing chart showing the operation of the embodiment of FIG. 6. RT...Thermistor, R1...Adjustment resistor. Applicant's agent Kiyoshi Inomata b I Figure abcd n n+1 C dot also 2 Figure abcd Ji 4 Figure cl: At 1

Claims (1)

[Claims] It has a timer controller that generates a timing signal that determines when the preheating A pulse and recording pulse are generated based on an external trigger input, and a temperature sensing element whose resistance value changes depending on the temperature of the thermal head, a capacitor, and a switch. , a time constant circuit that can select one of two time constants by switching this switch;
a timer for emitting a preheat pulse and a recording pulse with a time width determined by cooperation with the time constant circuit at a point in time determined by the timing signal; A temperature control circuit for a thermal recording device, comprising a switch controller for controlling switching of the temperature control circuit.