JP3223602B2 - Thermal head print density controller - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head print density control apparatus used in a thermal printer having a thin film thermal head having a large variation in the group of thermal recording resistors.

[0002]

2. Description of the Related Art In recent years, a high-speed thermal printer applies a constant voltage to a print head to raise the temperature of a resistor at a high speed to a temperature at which the thermal paper changes, and then the print density does not change visually. The pulse width control for turning off the voltage is performed.

[0003] A conventional thermal head print density control device will be described below with reference to the drawings.

As shown in FIG. 3, the conventional thermal head print density controller has a configuration in which a control unit 22 to which a pulse control signal 23 is applied controls a thermal head 21 composed of n thermal recording resistor groups. Have.

Hereinafter, the relationship and operation of each component will be described.
This will be described with reference to FIGS. First, the thermal head 21 has n thermal recording resistor groups (hereinafter abbreviated as thermal resistors), and an input pulse control signal 23 controls the control unit 22 so that the thermal head 21
The voltage as shown in FIG. That is, when the resistance value is low, a pulse width 15 shorter than the normal pulse width 14 is added, and when the resistance value is high, a long pulse width 16 is added. As a result, as shown in FIG. 4B, the temperature generated in the thermal resistor is as shown by a waveform 18 when the pulse width 14 is normal, and by a waveform 17 and pulse width 16 when the pulse width 15 is applied. Sometimes it looks like waveform 19.

That is, the pulse width is controlled by the level of the resistance value of the thermal resistor so that the amount of generated heat is constant.
As shown in FIG. 4B, the pulse width is controlled to a specific time width by the control unit 22 so as to keep the time exceeding the coloring temperature 10 of the thermal paper constant.

[0007]

However, in the above-mentioned conventional configuration, in order to adjust the print density, the variation of the resistor is measured by the pulse width control, and the pulse width is adjusted for each printer to cope with the temperature change of the thermal paper. It was necessary to pass the current.

In particular, in conventional thermal printing, a block is divided into several blocks in accordance with the resistance value of the thermal resistor, and the pulse drive time is determined for each block. There was a problem that variation occurred.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems, and provides a thermal head print density control device capable of performing satisfactory thermal printing without taking into consideration the variation in the resistance value of the thin film thermal print head. The purpose is to:

[0010]

In order to achieve the above object, a thermal head print density control device according to the present invention is provided on a substrate.
The thermal recording resistor group provided in
Connected to one or more wires in the recording resistor group
A thermal head having an external resistor;
A voltage detector that detects the voltage generated by the current flowing through the antibody
A comparing unit having output means;
Supply current to the thermal recording resistor group by a control signal
Current control unit, the output side of the current control unit and ground
A voltage detection unit for detecting a voltage generated between
Based on the average of the variation in the resistance of the recording resistor group.
And a reference voltage generator for generating a reference voltage,
A comparing unit configured to detect the voltage detected by the voltage detecting unit and the base;
Compares with the reference voltage generated by the reference voltage generator and outputs the comparison output.
The voltage controls the operation of the current control unit,
The reference voltage generator is connected to a potential on the output side of the current controller.
Generate a voltage increased or decreased from the reference voltage based on the
To keep the power supplied to the thermal recording resistor group constant.
It is characterized by keeping.

[0011]

According to the present invention, when the thermal resistor is driven with a constant pulse width in the above-described configuration, the heat value of the thermal resistor is kept constant regardless of the value of the thermal resistor, and the constant temperature rises. Becomes

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS.

As shown in FIG. 1, in the thermal head print density control device of this embodiment, a voltage is supplied from a current control unit 7 to a thermal head 1 provided on a printed circuit board by a pulse control signal 8 applied from the outside. Is done. Here, the thermal head 1 is composed of a group of n thermal recording resistors (hereinafter abbreviated as thermal resistor) 2 and a precise external resistor 3, and includes a voltage detector 6, a reference voltage detector 5 and the comparison unit 4 constitute a control circuit.

Hereinafter, the relationship and operation of each component will be described. First, a minute current I flows through the external resistor 3 to generate a voltage, which is applied to the comparison unit 4. The output voltage from the current controller 7 controls the reference voltage generating unit 5 via the voltage detection unit 6, comparator unit 4 starts operation by the pulse control signal 8 as shown in FIG. 2 (a), The voltage generated in the external resistor 3 and the voltage generated in the reference voltage generator 5 are compared in the comparator 4, and the operation of the current controller 7 is controlled by the comparison output voltage. Also in the reference voltage generating unit 5, the thermal resistor 2 resistors
At the reference voltage based on the average value of the resistance value variation
Compared to the potential of the point A, the higher the potential at point A, decrease the voltage than the reference voltage, the lower the potential of the point A, the reference voltage
It operates so that the voltage becomes higher than that . The potential of this end point A varies as shown in FIG. 2 (b), keeping the power of the thermal resistor 2 constant by varying as the current I also Figure 2 that flows through the thermal resistor 2 (c) It is possible,
It is not necessary to change the pulse drive time in accordance with the resistance value of the thermal resistor 2, and it is possible to eliminate variations in print density.

[0015]

As is apparent from the above embodiments, according to the present invention, if the current control section is driven by a pulse control signal in which the center value of the resistance value variation is set as an appropriate print density, the current value can be adjusted according to the resistance value. Excellent thermal head printing that can keep the power supplied to the thermal resistor constant and maintain the temperature of the thermal resistor at a constant temperature regardless of the resistance value because the current flowing and the voltage can be changed It is possible to realize a concentration control device.

[Brief description of the drawings]

FIG. 1 is a block diagram of a thermal head print density control device according to an embodiment of the present invention.

FIG. 2 is a signal waveform diagram for explaining the operation of the device.

FIG. 3 is a schematic block diagram of a conventional thermal head print density control device.

FIG. 4 is a signal waveform diagram for explaining the operation of the apparatus.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 thermal head 2 thermal resistor (thermal recording resistor group) 3 external resistor 4 comparison unit 5 reference voltage generation unit 6 voltage detection unit 7 current control unit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B41J 2/35 B41J 2/365

Claims (1)

(57) [Claims] A thermal head comprising: a group of thermal recording resistors provided on a substrate; and an external resistor connected to one or a plurality of wires in the group of thermal recording resistors. A comparison unit having voltage detection means for detecting a voltage generated by a current flowing through an external resistor; a current control unit for supplying a current to the thermal recording resistor group by a control signal output from the comparison unit; A voltage detection unit that detects a voltage generated between the output side of the current control unit and the ground; and a reference voltage generation unit that generates a reference voltage based on an average value of variation in resistance values of the thermal recording resistor group. The comparison unit compares the voltage detected by the voltage detection unit with a reference voltage generated by the reference voltage generation unit, and controls the operation of the current control unit by a comparison output voltage. The reference voltage generation unit generates a voltage increased or decreased from the reference voltage based on an output-side potential of the current control unit, and keeps power supplied to the thermal recording resistor group constant. Characteristic thermal head print density control device.