JPS62193853A - Thermal head control circuit - Google Patents

Abstract

PURPOSE:To conduct printing with a stable printing density, by applying a time compensation when the compensation to a power voltage and a change in an ambient temperature is conducted. CONSTITUTION:In a thermal head control circuit, a parallel circuit of a diode 5 and a high resistance 6 and a series circuit of a resistance 7 and a condenser 8 are connected in parallel to a capacitor 3. The current to be charged to the capacitor 3 is further divided to a series path of the diode 5, the resistance 7, and the condenser 8 immediately after start of printing, which lowers the increase rate of the terminal voltage of the capacitor 3. In this manner, a heat pulse of large width can be obtained and can be kept constant finally. Therefore, by a setting wherein the electric charges of the capacitor 8 are allowed to be gradually discharged through the resistances 7 and 6 after a printer operation is stopped so as to be completely discharged when a thermal head is cooled to an ambient temperature, a printing can be conducted with the same density whenever a printing operation is started or completed.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a circuit for controlling a thermal head of a thermal printer, etc., and in particular, to a circuit for controlling a thermal head of a thermal printer, etc. The present invention relates to a thermal head control circuit that controls the thermal head as follows.

[Conventional technology]

When controlling a thermal head used in a thermal printer or the like, it is necessary to keep the head temperature constant in order to improve print quality. To this end, it has been conventional practice to compensate the head temperature for fluctuations in the ambient temperature and power supply voltage of the head.

In conventional thermal printers, a thermal head control circuit as shown in FIG. 2, for example, is well known in order to keep the printing rate '/Ik f constant.

Here, 1 is a monostable multivibrator, 2 is a resistor, 3 is a capacitor, and 4 is a thermistor placed near the thermal head to detect the head temperature. Second
As shown in the figure, when determining the heat pulse width with a monostaple multivibrator 1 or the like using a time constant circuit consisting of a resistor 2 and a capacitor 3, a thermistor 4 is connected in parallel with the resistor 2, and the thermistor 4 is The print density is kept constant by changing the time constant and controlling the heat pulse width as the resistance value changes.

In this control circuit, when the ambient temperature rises, the resistance value of the thermistor 4 decreases, the charging current of the capacitor 3 increases, and the pulse width of the heat pulse obtained from the monostable multivibrator 1, that is, the heat pulse width The length becomes shorter, and therefore the print density becomes lower. On the other hand, when the ambient temperature decreases, the resistance value of the thermistor 4 increases, the charging current of the capacitor 3 decreases, and the heat pulse width from the monostable multivibrator 1 increases, working to increase the print density. Even if the temperature changes,
Print density can be kept constant.

Further, when the power supply voltage increases, the charging current of the capacitor 3 increases, and when the power supply voltage decreases, the charging current of the capacitor 3 decreases, and the same operation occurs as in the case of the ambient temperature change described above.
After all, the print density can be kept constant.

As mentioned above, with conventional control circuits, it is possible to maintain a constant print density in response to changes in ambient temperature and power supply voltage, but this alone is insufficient to achieve high print quality. is still insufficient. In other words, when a thermal printer prints continuously, heat gradually accumulates in the thermal head, which causes the print to gradually become darker and become difficult to see. . This problem becomes more noticeable when high-speed printing is performed, and improvements are desired.

This situation will be explained using FIGS. 3 and 4.

Although there are differences depending on the printing pattern, assuming that printing is done on average, as shown by the straight line in Figure 4, if printing is continued with a constant heat pulse width, the time when there is no printing, that is, while no heat pulse is being generated, The temperature of the head at
As shown by the curve in FIG. 3, the temperature gradually rises from the ambient temperature and eventually reaches a saturated state at temperature T2.

When printing, the heat pulse width (
(currently constant) is applied to the thermal head to heat the print paper and print.

Assuming that the appropriate temperature during non-printing is Tt, it can be seen that the printing is light from the start of printing before time LL, and on the contrary, the printing becomes dark after time t1. Furthermore, the power consumption of the head is also wasted.

On the other hand, if you shorten the heat pulse width like the straight line ■ shown in Figure 4, the curve will look like the curve shown in Figure 3, which will prevent too much darkness and waste of power consumption, but The disadvantage is that the printing is so thin that it cannot be seen.

[Problem that the invention attempts to solve]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to eliminate the drawbacks of the conventional example described above, and to compensate for keeping the head temperature constant against fluctuations in ambient temperature and power supply voltage by printing continuously or at any time. Another object of the present invention is to provide a thermal head control circuit that can print with stable print density and reduce power consumption.

[Means for solving problems]

In order to achieve such an object, the present invention provides a thermal head control circuit that controls a thermal head, which includes a means for controlling the generation time of a heat pulse supplied to the thermal head, and a means for detecting a temperature related to the thermal head. The thermal head is controlled by controlling the control means to change the generation time of the heat pulse according to the detected temperature, fluctuations in the power supply voltage supplied to the thermal head, and elapsed time from the start of printing of the thermal head. According to the present invention, when compensating for changes in power supply voltage and ambient temperature, By adding optical compensation, it is possible to always perform high-quality printing with the same density, and to achieve lower power consumption and faster printing.

(Example) Examples of the present invention will be described below in detail and specifically based on the drawings.

First, the inventor found that by controlling the heat pulse width according to the elapsed time from the start of printing as shown by curve III in the fourth figure, the head temperature during non-printing can be kept constant as shown in the straight line m in the third figure. It was confirmed that it was possible to maintain the printing density at a constant level, and thus the print density could be kept constant, and based on this recognition, the present invention was completed.

The configuration of one embodiment of the thermal head control circuit of the present invention is described in the first embodiment.
As shown in the figure.

In FIG. 1, the same parts as in FIG. 2 are given the same reference numerals. In this embodiment, a parallel circuit of a diode 5 and a high resistance 6 and a series circuit of a resistor 7 and a capacitor 8 are connected in parallel with the capacitor 3.

In this embodiment, immediately after the start of printing, the current charged in the capacitor 3 is also shunted to the series path of the diode 5, the resistor 7, and the capacitor 8, which delays the rate of increase in the terminal voltage of the capacitor 3. The width of the heat pulse can be widened.

Here, the electric charge of the capacitor 8 is not discharged depending on the diode 5, and the resistor 6 has a high resistance, so the current flowing through this part can be ignored, so the shunt current flowing through the diode 5, the resistor 7, and the capacitor 8 gradually decreases and finally stops flowing. Therefore, the heat pulse width also becomes gradually shorter, and eventually can be maintained at a constant width.

Therefore, by setting the heat pulse width that finally settles to the value of curve II in FIG. 4, the temperature of the thermal head is always kept constant as indicated by straight line III in FIG. 3.

In Fig. 1, if the charge in capacitor 8 is immediately discharged when the printer operation stops, if the printer operation is restarted immediately thereafter, the heat pulse will still be generated even though the thermal head has not yet cooled down. The width becomes longer and the printing becomes too dark.

Therefore, in this embodiment, even if the printer operation is stopped, the charge in the capacitor 8 is gradually discharged through the resistors 7 and 6, and is completely discharged by the time the thermal head cools down to the ambient temperature. Set it. the result,
Printing can always be performed at the same density no matter when the printing operation starts or ends.

〔Effect of the invention〕

As explained above, according to the present invention, by adding temporal compensation when compensating for changes in power supply voltage and ambient temperature, it is possible to always perform high-quality printing with the same density, reduce power consumption, and print. It is possible to achieve faster speeds.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a block diagram showing an example of the configuration of a conventional thermal head control circuit, and Fig. 3 shows the relationship between head temperature during non-printing and continuous printing time. Graph Showing Relationship FIG. 4 is a graph showing the relationship between heat pulse width and continuous printing time. 1... Monostable multivibrator, 2...
Resistor, 3... Capacitor, 4... Thermistor, 5... Diode, 6... High resistance, 7... Resistor, 8... Capacitor. This invention is actually f! Figure 1: Block diagram of conventional example Figure 2: Head temperature at the end of 1A sale #ll'$' time turn-p (7゛ rough 3rd 1 showing the relationship between previous printing time) 1 Printing time heat pulse width and printing time

Claims (1)

[Claims] 1) A thermal head control circuit that controls a thermal head, comprising: means for controlling the generation time of a heat pulse supplied to the thermal head; means for detecting a temperature related to the thermal head; The control means is controlled to change the generation time of the heat pulse in accordance with the detected temperature, fluctuations in the power supply voltage supplied to the thermal head, and elapsed time from the start of printing by the thermal head. 1. A thermal head control circuit comprising means for keeping the temperature of the head constant (when not printing).