JPS62101469A - Head voltage controlling circuit for thermal printer - Google Patents

Abstract

PURPOSE:To effectively prevent printing quality from being degraded due to heat accumulation in a head, by detecting the heat accumulation in the head by a temperature sensor fitted to a head part, and optimally controlling a voltage impressed on the head in accordance with the head temperature. CONSTITUTION:A head voltage limiting circuit is provided so that a head voltage will not be excessively raised when no output is generated from a temperature sensor. Namely, a thermal head thermistor ThR1 and a slide volume control SV1 are connected in parallel between an output terminal (a) and a control terminal (c), and when the value of the slide volume control SV1 is high, that is when the voltage initially set in a constant voltage control circuit is high, a variation in the resistance of a thermistor ThR1is made to produce a great effect, thereby lowing the head voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a head voltage control circuit for a thermal printer, and more particularly to a control circuit for controlling the head temperature of a thermal printer.

Prior Art FIG. 7 is a diagram showing an example of a constant voltage control circuit used to control the voltage of a head of a conventional thermal printer.
In the figure, a is the output terminal, b is the GND terminal, C is the control terminal, and A
is a voltage variable control section, and as is well known, the transistor Q2 is activated from 1 to 1 using the voltage dividing resistors R, , R2 of the voltage variable section A and the Zener diode ZD to obtain a constant DC voltage VT at the output terminal a. There is.

FIG. 8 is a schematic configuration diagram for explaining an example of a head drive circuit of a thermal printer, and in the figure, 1 indicates control units 1 to . 2 is a thermal head driver, and 3 is a thermal head, which supplies the constant voltage VT obtained as described above to the thermal head driver 2 as shown in the figure.

FIG. 9 is a diagram showing another example of the voltage variable control section A,
In this case, a variable resistor S1 is provided in series with the voltage dividing resistor, and as is well known, the operator adjusts the variable resistor to adjust the printing density.

Thermal printers are quiet because they perform non-impact printing, and the printing process is simple, so the machine cost is lower than other printers, so they have become widely used these days. Additionally, in the past, powering the thermal printer was simple because it only printed characters.
No complicated control was required.

However, recently it has started to be used in graphic printers, and even color printers.
These graphic printers, color printers, etc. have an extremely large head voltage application duty to the thermal head compared to conventional character printers, and as a result, deterioration of print quality due to heat accumulation in the head, which was not a problem in the past, has become a problem. It has become.

Purpose The present invention was made in view of the above-mentioned circumstances.
This was done with the purpose of preventing deterioration in printing quality due to continuous printing in thermal printers (particularly serial type thermal printers).

In order to achieve the above object, the present invention includes a temperature sensor that detects the temperature of a print head, a print density variable device that is provided outside the printer and can be operated by an operator, and a temperature sensor that detects the temperature of the print head. A head voltage control section that changes the voltage supplied to the thermal head according to the output of the print density variable device, or a first temperature sensor that detects the temperature of the print head section and a first temperature sensor that detects the environmental temperature. 2 temperature sensors, a print density variable device provided outside the printer that can be operated by an operator, and the first and second temperature sensors;
a temperature sensor and a head electric variable control section that changes the voltage supplied to the thermal head according to the output of the print density variable device, or a temperature detection sensor that detects the temperature of the print head section, and a temperature detection sensor that detects the temperature of the print head section; A thermal printer that has a head driver that controls the voltage applied to the print head according to the output of a detection sensor, and has a head voltage limiter circuit to prevent the head voltage from becoming abnormally high when there is no output from the temperature detection sensor. It is characterized by the fact that Hereinafter, the present invention will be explained based on examples.

1 to 3 are main part configuration diagrams for explaining the present invention in detail, that is, A part configuration diagrams in FIG. 7, in which ThR represents a temperature detection sensor, specifically, , as shown in FIG. 8, a thermistor for detecting the temperature of the thermal head 3 or the vicinity of the thermal head 3; S V 1 is a variable resistor ( slide volume).

, Therefore, in the embodiment shown in FIG. 1, a thermal Rad thermistor T h, ,
According to this embodiment, when the value of the slide volume Sv1 is high, that is, in the constant voltage control circuit shown in FIG. 7, the initial setting voltage is high. Sometimes, thermistor ThR,
The head voltage is reduced by greatly increasing the resistance change.

In the embodiment shown in Fig. 2, a -Maruherad thermistor ThR is connected between the output terminal a and the control terminal C, and a slide for concentration adjustment is connected between the control terminal C and the GND terminal. A volume S■□ is connected to this embodiment. In contrast to the embodiment shown in FIG. 1, the thermistor effect is uniform due to the initial setting values.

The embodiment shown in FIG. 3 is provided with a thermistor ThR2 for detecting the environment (room occupancy), and this room temperature detection thermistor ThR is connected in series with the slide volume Sv1 of the embodiment shown in FIG. (It may be inserted between the control terminal C and the GND terminal in the embodiment shown in FIG. 1 or FIG. 2),
According to this example.

Corrections can be made based on the environmental temperature. Now, if the operating environment temperature of the printer is 50°C to 35°C, the resistance of the thermistor changes as shown in Fig. 5. Therefore, at low temperature, the resistance R0' in Fig. 7 changes to, for example, IKΩ (25°C).
From 2 to Ω (5℃).

Although the output voltage VT of the variable head voltage control circuit A becomes abnormally high, this can be offset by inserting a room temperature thermistor ThR between the control terminal and the GND terminal as shown.

FIG. 4 is an electric circuit diagram for explaining another embodiment of the present invention. In the illustrated embodiment, the variable control circuit shown in FIG. 1 is used as the head voltage variable control circuit A. The head voltage variable control circuit shown in FIG. 2 or 3 may also be used. Therefore, if the head is removable and the head thermistor connector and the head resistor connector are different from each other in a thermal printer that uses the variable head voltage control circuit as described above, when the operator replaces the head, If you forget to attach a thermistor and turn on the power, an abnormally high voltage will be applied to the head, but according to this embodiment, for example, a Zener diode ZD.

Since a voltage limiter circuit is provided, an abnormally high voltage as described above is not applied to the head. For example, in order to prevent the head voltage VT from exceeding 9.5V, Zn2 + VB p s = 9.5V (
1), so let VB Es = O-, 6V.

As Zener diode zD2, Zener voltage 8.9
If we use the value of v, as shown in Figure 6, VT=9
．． It becomes possible to clamp to 5V.

Effect-121 As is clear from the above description, according to the present invention, in a thermal printer, heat accumulation in the head is detected by a temperature sensor attached to the head, and the voltage applied to the head is optimized depending on the head temperature. Since I controlled it to
Deterioration of printing quality due to heat accumulation in the head can be effectively prevented.

Further, even when a temperature detection sensor for detecting the temperature of the thermal head is not attached to the head, it is possible to prevent an abnormally high voltage from being applied to the head, and damage to the head can be prevented.

[Brief explanation of drawings]

1 to 3 are main part configuration diagrams for explaining the present invention in detail, FIG. 4 is an electric circuit diagram for explaining another embodiment of the present invention, and FIG. 5 is a Figure 6 is a temperature characteristic diagram of the thermistor, Figure 6 is an output voltage characteristic diagram of the embodiment shown in Figure 4, Figure 7 is a diagram showing an example of a conventional constant voltage control circuit, and Figure 8 is a diagram of a thermal printer. A main part configuration diagram, FIG. 9, is a diagram for explaining an example of a density adjustment circuit of a thermal printer. DESCRIPTION OF SYMBOLS 1... Control unit, 2... Thermal head driver, 3... Thermal head, A... Voltage variable control part, ThR1... Thermal head thermistor, ThR2... Room temperature monitoring thermistor, S■1 ...Slide volume for density adjustment. Figure 8 Figure 9

Claims (6)

[Claims] (1) a temperature sensor that detects the temperature of the print head;
It has a print density variable device provided outside the printer that can be operated by an operator, and a head voltage variable control unit that changes the voltage supplied to the thermal head according to the output of the temperature sensor and the output of the print density variable device. A thermal printer head voltage control circuit characterized by: (2) The head voltage variable control section is connected to the output terminal and GND.
It has a voltage dividing resistor between the terminal and a control terminal at a voltage dividing point of the voltage dividing resistor, and is configured such that a driving voltage to the thermal head is controlled by a voltage dividing ratio of the voltage dividing resistor, and the temperature sensor is composed of a thermistor, the print density variable device is composed of a slide resistor, and a parallel circuit composed of the thermistor and the slide resistor is connected between the output terminal and the control terminal of the head voltage variable control circuit. A head voltage control circuit for a thermal printer according to claim (1), characterized in that: (3) The head voltage variable control section is connected to the output terminal and GND.
It has a voltage dividing resistor between the terminal and a control terminal at a voltage dividing point of the voltage dividing resistor, and is configured such that a driving voltage to the thermal head is controlled by a voltage dividing ratio of the voltage dividing resistor, and the temperature sensor is composed of a thermistor, and the print density variable device is composed of a slide resistor, and the thermistor is arranged between the output terminal and the control terminal, and between the control terminal and G
The head voltage control circuit for a thermal printer according to claim 1, wherein the slide resistor is connected between the ND terminal and the ND terminal. (4) a first temperature sensor that detects the temperature of the print head section, a second temperature sensor that detects the environmental temperature, a print density variable device that is provided outside the printer and that can be operated by an operator; A head voltage control circuit for a thermal printer, comprising a head voltage variable control section that changes the voltage supplied to the thermal head according to the outputs of first and second temperature sensors and a print density variable device. (5) The head voltage variable control section is connected to the output terminal and GND.
a voltage dividing resistor between the terminal and a control terminal at a voltage dividing point of the voltage dividing resistor, and is configured such that a driving voltage to the thermal head is controlled by a voltage dividing ratio of the voltage dividing resistor; and the second temperature sensor is constituted by a thermistor, the print density variable device is constituted by a slide resistor, the first thermistor is connected between the output terminal and the control terminal, and the first thermistor is connected between the output terminal and the control terminal. 4. The head voltage control circuit for a thermal printer according to claim 4, wherein a second thermistor and a slide resistor are connected between the control terminal and the GND terminal. (6) A thermal printer that has a temperature detection sensor that detects the temperature of the print head and a head driver that controls the voltage applied to the print head according to the output of the temperature detection sensor, which has a head voltage limiter circuit. death,
A head voltage control circuit for a thermal printer, characterized in that the head voltage does not become abnormally high when there is no output from the temperature detection sensor.