JPS6158764A - Controlling method for pulse width of thermal head - Google Patents

Abstract

PURPOSE:To enable the printing with uniform quality density to be impressed, using the controlling device with a simple circuit by a method in which the clock of the frequency corresponding to the temperature of the base plate of a thermal head is generated, and it is analogically converted into the electric power of the pulse width corresponding to said frequency, and then this electric power is applied to the head. CONSTITUTION:The temperature of a thermal head is detected as voltage, fitting a thermistor 2 to the head. After the clock signal of the frequency corresponding to said voltage has been outputted a transmitter 3, the pulse electric power with the pulse width T corresponding to said frequency is generated by a pulse generator 4, and this pulse electric power is applied to the thermal head 1.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Field of Industrial Application The present invention relates to a pulse width control method for a thermal head, and in particular to a method for controlling the pulse width of a thermal head, and in particular, controlling a clock operation in a transmitting circuit using temperature information from the thermal head to control the drive current input to the thermal head. The present invention relates to a method for controlling the pulse width of .

(2) Conventional technology The reproduction of a still image in a facsimile or other image transmission device is, in principle, by receiving the signal of the original transmitted image, and then using the required circuit operations to reproduce an image similar to the original transmitted image using a thermal head or an electrostatic This is to reproduce images on recording paper using a recording element such as a head. The present invention aims to improve a thermal recording method in which a transmitted electrical signal is applied with a pulse voltage to a heating head electrode according to the input signal level to generate heat, and this is converted into thermal information to color the opposing thermal recording paper. It is related. Thermosensitive recording paper has a property that when a heat-sensitive layer is applied to the surface of the paper and heated, color develops due to a chemical change in the coating agent, and the chemical change occurs when a certain temperature is reached. Therefore, it is necessary to apply a certain temperature or higher to color the thermosensitive recording paper; above this temperature, the paper becomes blackish, and below this temperature, the paper becomes whitish. A resistive heating element is arranged on the thermal recording head substrate. When a printing pulse current corresponding to image information is distributed to each heating element, it is converted into temperature information using the resistance heat generation of the heating element. Therefore, the color temperature is given to this temperature information and recorded. Furthermore, black and white density gradation is required to record the received original picture, and the ratio of black 1 degree to white 11 degree is determined. This gradation is the first characteristic of thermal recording paper.
There is a relationship as shown in the figure, and the concentration increases as the temperature rises.

In the operation of a conventional thermal head, as shown in FIG. 2, the output based on the printing pulse signal with a pulse width t rises at the temperature T1 of the thermal head substrate, and the recording to be colored starts at T3. During operation, if the head substrate temperature rises to T2 due to heating of the heating element due to the influence of outside temperature, etc., the print pulse signal will rise with the same waveform starting from T2, and the overall waveform temperature level will increase. rises. When this color is developed at T3, there is a problem that the range of black becomes a wide gradation, and the density tends to be black compared to the initial gradation of T1. For this reason, various measures have been taken in the past to control and adjust the width of the print pulse according to the temperature of the head substrate.
For example, the output of the thermistor is input to a CR circuit or an IR circuit, and the pulse width is determined based on the change in the resistance value of the thermistor.(3)Problems to be Solved by the InventionHowever, in this case, the circuit may be complicated or There is a problem that adjustment is difficult.

(4) Purpose of the Invention The present invention was made by focusing on the above-mentioned conventional problems.The purpose of the present invention is to convert the temperature change of the head substrate into a change in clock frequency, and to change the pulse width corresponding to this frequency. It is an object of the present invention to provide a method for controlling the printing pulse width in an analog manner so as to obtain the above-mentioned conventional problems.

(5) Means for Solving the Problems In order to achieve the above object, the present invention provides a thermal head including a heating element and a drive circuit for applying current to the heating element, and a thermistor attached to the thermal head. Converts temperature information into voltage via a thermistor, generates clocks with different frequencies according to changes in this voltage, measures a predetermined number of clocks, and outputs a signal with a pulse width corresponding to the number of clocks. The gist is that the pulse width of the thermal head is controlled thereby.

(6) Effect Since the present invention employs the above configuration, when the thermistor changes its resistance due to temperature change, the voltage output from the thermistor changes. In the clock generation means, that is, the transmitting member, the output voltage from the thermistor is set as the upper EIII, and the predetermined voltage is set as the lower reference voltage, and the voltage between the upper threshold value and the lower reference value is A trigger signal is generated, a rectangular wave is generated in which the trigger rises at the peak of the signal, and falls at the lowest point of the trigger signal, and the number of clocks is generated by the number of the rectangular waves. In this way, when the output voltage from the thermistor (denoted as Vi) is large, the number of repetitions of peaks and troughs of the trigger waveform between the voltage Vi and the reference voltage (denoted as VO), that is, the frequency f, is The number of repetitions of the peaks and valleys of the trigger waveform is smaller than that when the voltage Vi is small, thereby making it possible to change the clock oscillation frequency. Therefore, for example, if the pulse width of the thermal head is set to correspond to a certain number of clocks (for example, 1 o clock), the pulse width of the thermal head can be adjusted as the output voltage of the thermistor increases or decreases. It can be controlled.

(7) Embodiment FIG. 3 is a diagram showing an embodiment of a control device for implementing the pulse width control method for a thermal head of the present invention.

In this figure, 1 is a V-maru head that has a plurality of heating elements that generate heat when a printing pulse is applied and current is distributed, 2 is a thermal head 1, and more specifically, the temperature of the thermal head substrate is detected. 3 is an oscillator that emits clock signals of various frequencies in response to input of the output signal of the thermistor 2; 4 is a pulse width generator that determines the pulse width of the pulse applied to the thermal head 1 according to the output of the oscillator 3; be. The thermistor 2 has a characteristic that when the temperature of the thermistor 2 itself increases, the resistance value decreases and the voltage decreases accordingly. Conversely, when the temperature of the thermistor 2 decreases, the voltage increases. In the transmitter 3, the output voltage of the thermistor 2 is set as ■(), and the reference voltage is set as It outputs a pulse whose phase repeatedly changes between vi and vO.

Then, when the output voltage of the thermistor 2 decreases to Vi', the pulse becomes a pulse with a higher frequency than the previous one, as shown in FIG. Next, the peak voltage V+ and the group 114
! When switching to the square pulses of 1 and O based on the i voltage vO, the square pulses corresponding to the peak voltages vi and V i l in FIG. 4, respectively, become as shown in FIG. 5. This allows the voltage change at the thermistor 2 to be displayed by the oscillator 3 as a square wave. Note that the frequency in the figure is indicated by the symbol f.

The generation frequency f of the waveform converted by the oscillator 3 is input to the pulse width generation circuit 3, and pulses with the frequency f are output at a constant period of a certain number of clocks (for example, 10 clocks). It is possible to determine the pulse width for applying the current from the drive circuit to the head. Therefore, as the clock frequency increases, the number of pulses also increases, so the clock count cycle time becomes faster.
Therefore, the pulse width t becomes small. Conversely, when the frequency decreases, the pulse width also decreases, so the clock count cycle time slows down, and as a result, the pulse width increases.

Information on the pulse width t can be fed back to the receiving operation circuit to control the width of the print pulse.

(8) As described in detail of the invention, according to the present invention, a thermistor is attached to the thermal recording head, and the clock number of the oscillation circuit is changed in an analog manner based on the output voltage from the thermistor. Since the pulse width of the current applied to the thermal head is determined, it is possible to perform recording while maintaining accurate gradations without being affected by temperature changes of the thermal head substrate during recording.

[Brief explanation of drawings]

Figure 1 is a temperature characteristic diagram of -11a degrees at which thermal recording paper develops color.
Figure 2 shows R color I11, which shows that the waveform state of the input printing pulse changes due to changes in the temperature of the thermal head substrate.
FIG. 3 is a diagram showing an example of a pulse width control device for a thermal head for carrying out the present invention, and FIG. 4 is a diagram showing the relationship between degrees and temperature. Fig. 5 is a diagram showing a square pulse output from the oscillation circuit, and Fig. 6 is an explanatory diagram showing the change in frequency emitted from the oscillation circuit. FIG. 1... Thermal, Head 2... Thermistor 3... Transmission circuit 4... Pulse width generation circuit Vi, Vi'... Thermistor output voltage ■0.
...Reference voltage Figure 1 Figure 2 Figure 3 @4m II 5 Figure 6m

Claims (1)

[Claims] A thermistor is attached to a thermal head that is equipped with a heating element and a drive circuit that applies current to the heating element, and temperature information in the thermal head is converted into voltage via the thermistor, and different voltages are generated according to changes in this voltage. A pulse width control method for a thermal head that generates a clock with a certain frequency, measures a predetermined number of clocks, and outputs a signal with a pulse width corresponding to the number of clocks.