JPH0113428B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermal printer, and more particularly to a printing method for making color density uniform.

Generally, in a thermal printer, when printing continues, the base temperature of the thermal head rises and the color density becomes darker, and conversely, when no printing continues, the base temperature of the thermal head decreases toward the outside temperature and the color density becomes thinner.

To this end, conventionally a temperature sensor has been attached to the thermal head to control the base temperature to a constant level or to preheat the head when no printing continues.

However, none of the above-mentioned conventional printers can respond immediately when printing starts immediately after the power is turned on, and for this reason, in serial printing type thermal printers, the first row or first character is extremely thin. Furthermore, in the case of line printing type thermal printers, the first dot line is printed extremely thinly, resulting in a disadvantage that the printing quality is low.

In order to eliminate the above-mentioned conventional drawbacks, the present invention supplies a preset amount of power to the heating resistor during printing, which is larger than during other printing, from when printing starts after power is turned on until a predetermined amount is printed. This will be explained in detail below with reference to the drawings.

FIG. 1 is a circuit diagram showing one embodiment of the present invention.
2 is a flip-flop circuit (hereinafter referred to as FF) that is reset by the input signal and reset by the trailing edge of the print ready signal, 2 is a three-terminal regulator (hereinafter referred to as REG) that stabilizes and outputs an unstable DC voltage, and R1 and R2 are The resistor S is the resistor R connected in series between the earth terminal of REG2 and the earth.
2 is connected in parallel and the reset output of F.F1 is “1”
It is an analog switch that turns on when
REG2, resistors R1 and R2, and analog switch S constitute a constant voltage power supply 3 that outputs two types of voltage: high and low. 4 is a thermal head having heating elements r1 _{to r0} , and Q1 to _Qo and _Qn are transistors serving as drivers for the heat generating resistors r1 to r0 of this thermal head 4.

In the embodiment of the above configuration, when the power is turned on and the turn-on signal shown in FIG. 2A is generated, F.F1 is set as shown in FIG. 2B, and the analog switch is turned off. Therefore, the output voltage of REG2 becomes a high level as shown in Figure 2 (c), and the heating element r
The current flowing through the element selected by transistors Q1 to _Qo and _Qn among transistors Q1 to _r0 becomes relatively large. Therefore, even if the base temperature of the thermal head 4 is about the same as the outside temperature, the color density will be high.

In this way, when printing of the first column or first character in the case of a serial printing type thermal printer or the first dot line in the case of a line printing type thermal printer is completed, a print ready signal shown in Fig. 2 D is sent. The F.F1 is reset by the edge as shown in FIG. 2B, and the analog switch is turned on. Therefore, from now on, the output voltage of REG2 becomes a low level as shown in Figure 2 C, and the heating resistors r1 to r _o
Of these, the current flowing through the resistor selected by transistors Q1 to Q _o and Q _n becomes relatively small. However, in this case, the first column, 1
By printing the first character and first dot line, the base temperature of the thermal head 4 becomes sufficiently high, so that even with a small current, the coloring density becomes deep.

In the embodiment shown in Fig. 1, the power supplied to the heating resistors r1 to r _o is increased for a predetermined period of time by increasing the applied voltage, but as shown in Fig. 3, analog switches S are turned on and off. The time constant of the one-shot multi-circuit 5 may be changed by changing the time constant of the one-shot multi-circuit 5, thereby changing the output pulse width and changing the time during which the transistor Q _n is turned on _and off. can be increased for a predetermined period of time.

In FIG. 3, resistors R3 and R4 and capacitor C determine the time constant.

Furthermore, in all of the above embodiments, the power supply is increased for the first column, first character, and first dot line to be printed after the power is turned on. In this case, even if the power supply is increased only for the first column, the base temperature may not rise sufficiently, so in such a case, it is desirable to increase the power supply when printing the first plurality of columns. Similarly, in serial printing using a thermal head with heating resistors arranged in 7 rows and 5 columns, the power supply may be increased when printing the first plural characters, and the heating resistors for one dot line may be increased. In the case of line printing using a thermal head, the power supply may be increased when printing the first plurality of dot lines. Furthermore, it is possible to attach a temperature sensor to the thermal head so that when the base temperature is high enough, the power supply is not increased even immediately after the power is turned on, or the power is turned off until a predetermined period of time has elapsed since the last print. The supplied power may not be increased even if the power is turned on again. This is because if the power is turned on again immediately after the power is turned off, the base temperature of the thermal head may not be sufficiently low, resulting in the opposite effect.

Next, FIG. 4 shows a schematic flowchart when the process is implemented using firmware. By setting the pulse width larger than the pulse width in Fig. 4,
The power supplied to the heating elements r1 to _r0 can be increased for a predetermined period of time. Further, in FIG. 4, if voltage and voltage are used instead of pulse width and pulse width, the power supplied to the heating resistors r1 to _r0 can be increased for a predetermined period of time in the same manner as described above.

As described above in detail, according to the present invention, the print density can be made sufficiently dark even immediately after power is turned on, and the print quality is improved.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing one embodiment of the present invention, Figure 2 is a circuit diagram showing an embodiment of the present invention.
This figure is a time chart of this embodiment, FIG. 3 is a circuit diagram showing another embodiment of the present invention, and FIG. 4 is a schematic flowchart when the present invention is implemented in firmware. 1...Flip-flop circuit, 2...3-terminal regulator, 3...constant voltage power supply, 4...thermal head,
5...One shot multi circuit, R1, R2, R3
and R4...resistance, S...analog switch, r1
~r _o ...Heating resistance, Q1~Q _o and Q _n ...Transistor, C...Capacitor.

Claims (1)

[Scope of Claims] 1. In a printing method for a thermal printer that makes color density uniform by controlling power supplied to a heating resistor, during printing, from the start of printing after the power is turned on until a predetermined amount is printed, A printing method for a thermal printer characterized in that the power supplied to a heating resistor is increased to a preset amount larger than that during other printing.