JPS5820473A - Thermal printer - Google Patents

Abstract

PURPOSE:To obtain sufficient printing density immediately after a power source is turned On, in the thermal printer wherein a supplied power is controlled and the coloring density is made even, by increasing the supplied power by a specified amount until the specified amount of printing is performed after the power source is turned ON. CONSTITUTION:When a turn ON signal (a) is generated by the turning ON of the power source, a flip flop FF1 is set and an analog switch S is turned OFF. Therefore, an output voltage (c) of a three terminal regulator (REG)2 becomes a high level. Currents, which flow through elements that are selected by transistors Q1-Qn in heating elements r1-rn, and Qm become relatively large. When the specified amount of the printing has finished and the base temperature of a thermal head 4 becomes sufficiently high, the FF1 is reset by the trailing edge of a printable signal (d) and the switch S is turned ON. Thereafter the output voltage (c) of the REG2 becomes a low level, and a relatively small current is flowed through the heating resistor elements.

Description

[Detailed description of the invention] The present invention relates to a thermal printer with uniform color density.

In general, when a thermal printer continues to print, the base temperature of the thermal head rises and the color density becomes darker υ. Conversely, when no printing continues, the base temperature of the thermal head decreases toward the outside temperature and the color density becomes thinner. For this reason, in the past, a temperature sensor was attached to the thermal head to control the base temperature to be constant, and to preheat it when no printing continued.

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, serial printing type thermal printers have a
The first column or first character is printed extremely thinly, and in line printing type thermal printers, the first line is printed extremely thinly, resulting in low print quality.

In order to eliminate the above-mentioned drawbacks of the conventional art, the present invention increases the power supplied to the heating resistor during printing to a preset amount from when the power is turned on until a predetermined amount of printing is performed, and will be described in detail below with reference to the drawings. .

FIG. 1 is a circuit diagram showing an embodiment of the present invention, in which J denotes a flip-flop circuit (hereinafter referred to as F, F), which is reset by the input signal and reset by the trailing edge of the print ready signal;
is a three-terminal regulator (hereinafter referred to as REG) that stabilizes and outputs an unstable DC voltage, and R1 and R2 are this R
The resistor S connected in series between the ground terminal of EG 2 and the ground is an analog switch connected in parallel to the resistor R2 and turned on when the reset blade of F and F 1 is 1''.
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. Reference numeral 4 designates a thermal head having heating elements r1 to 1"1, and Q1 to Qn and Qm designate transistors serving as drivers for the heating resistors r1 to rn 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. 2 (A) is generated, F, F] becomes
The analog switch is set as shown in (b), and the analog switch is turned off. Therefore, the output voltage of REG 2 is as shown in Figure 2 (c).
, and the current flowing through the element selected by the transistors Q1 to Qn and Qm among the heating elements r1 to rn becomes relatively large. Therefore, even if the base temperature of the thermal head 40 is about the same as the outside air temperature, the color density will be high. ' When the printing of the first column, first character, or first line is completed in this way, the trailing edge of the print ready signal shown in Fig. 2) causes the F and F1 to be changed as shown in Fig. 2 (b). (3) is reset and the analog switch is turned on.

Therefore, from now on, the output voltage of REG 2 becomes a low level as shown in FIG. 209, and the current flowing through the resistor selected by the transistors Q1 to Qn and Qm among the heating resistors r1 to rl becomes relatively small. However, at this time, the base temperature of the thermal head 4 becomes sufficiently high due to printing in the first column, first character, or first line.
Therefore, even with a small electric current, the color density increases.

In the embodiment shown in FIG. 1, the power supplied to the heating resistors r1 to r+1 is increased for a predetermined time by increasing the applied voltage, but as shown in FIG. 3, the analog switch S is 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 pulse width of the output i9 to change the time for turning on and off the transistor Qm, and supplying the current to the heat generating resistors r1 to rn in the same manner as above. power can be increased for a predetermined period of time.

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

(4) In all of the above embodiments, the power supply is increased for the first column, first character, or (l-1l: first line) printed after the power is turned on. In a thermal head that has only row heating resistors, the base temperature may not rise sufficiently even if the power supply is increased only for the first row.In such cases, it is recommended to increase the power supply when printing the first multiple rows. Similarly, in the case of serial printing using a thermal head having heating resistors arranged in 7 rows and 5 columns, the power supply may be increased when printing the first plural characters, and the power supply for one line may be increased. In the case of line printing using a thermal head equipped with a heating resistor, the power supply may be increased when printing the first plural lines.

Furthermore, a temperature sensor is attached to the thermal head,
When the base temperature is high enough, the power supply is not increased even immediately after the power is turned on, or the power supply is not increased even if the power is turned on again until a predetermined time has elapsed since the last printing. You can do it like this. 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, which may have the opposite effect.

Next, FIG. 4 shows a schematic flowchart when the process is implemented using firmware. In FIG. 4, by setting the pulse width (2) larger than the pulse width (2), it is possible to increase the power supplied to the heating elements r1 to rn for a predetermined period of time. In addition, in FIG. 4, if the Noculus width and the pulse width ■ are replaced by the voltage ■ and the voltage ■, the heating resistance r
The power supplied to 1 to rn can be increased for a predetermined period of time.

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

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing one embodiment of the present invention, Fig. 2 is a time chart of this embodiment, Fig. 3 is a circuit diagram showing another embodiment of the invention, and Fig. 4 is a firmware of the present invention. This is a flowchart of the rutted road when the test is carried out. 1... Free rough 0fu 0 horn circuit, 2... Three terminal regulator, 3... Constant voltage power supply, 4... Thermal head, 5... One yacht multi-time u, R1y R2
p R3 and R4...resistance, S...analog switch, r1-rn...heating resistor, Q1-Qn and. m...transistor, capacitor for C. Patent applicant: Oki Electric Industry Co., Ltd. (7) Figure 1: Kano Kyo 1' Figure 2 (D)

Claims (1)

[Claims] In a thermal printer that makes color density uniform by controlling the power supplied to the heat generating resistor, the power supplied to the heat generating resistor is increased to a preset amount during printing from the time the power is turned on until the specified amount is printed. A thermal printer with special features.