JPS6255164A - Thermal printer - Google Patents

Abstract

PURPOSE:To improve printing quality in low-speed printing mode and enable printing on less smooth paper to be performed easily by providing a power supply circuit capable of switching an applied voltage to a heating element using a printing mode of the high- and low-speed printing modes. CONSTITUTION:When the high-speed mode is selected by a switch 8, a low-level signal is output to the output terminal 71 of CPU 7. This allows a high voltage to be applied to a stepping motor 5. If a trigger pulse is output from the output terminal 72 of CPU 7 in synchronization with a printing timing, a short pulse width tw is output from a voltage comparison circuit 14. This output signal enables printing data from CPU 7 to be output from an output terminal 73, and also a suitable application energy to be applied to a heating element 3. Wnen the low-speed spring mode is selected, a high-level signal is output from an output terminal 71, and a low voltage Vh is applied to a thermal head 30 with the extension of an energization time tw. An application voltage Vh2 in low-speed printing mode is lower than an application voltage Vh1 in high- speed printin mode. The pulse width tw2 in low-speed printing mode is longer than the pulse with tw1 in high-speed printing mode.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a thermal printer with an improved driving method.

[Prior art] Thermal printers that have been commonly used
Many printers are equipped with a density adjuster to change the print density, and at this time either the voltage applied to the heat generating element or the energization time is increased or decreased. Furthermore, in recent years, demands for both high-speed printing and high-quality printing have increased, and thermal printers that can vary the printing speed have also appeared.

[Problems to be solved by the invention] In conventional thermal transfer printers, depending on the printing speed,
With methods that aim to ensure high speed and high print quality, the printing quality is so poor that it can be said that it is impossible to print on bond paper, which has extremely low smoothness and is commonly used in offices in the United States. Ta. In order to drive the heating elements during low-speed printing mode with the same voltage as in high-speed printing mode, the applied pulse width is increased using polyurethane, etc. to increase the printing density, which exceeds the heat-resistant temperature of the heat-sensitive film. This caused problems such as shrinkage, burnout, and non-transfer of the ink layer due to dissolution of the base of the heat-sensitive film and the ink layer.

The purpose of the present invention is to eliminate these conventional drawbacks, improve the printing quality especially in the low-speed printing mode in a thermal printer having a high-speed printing mode and a low-speed printing mode, and enable printing on low-smooth paper. It is an object of the present invention to provide a thermal printer that also ensures high-speed printing performance.

[Means for Solving the Problems] The thermal printer of the present invention has at least two types of printing modes, a high-speed printing mode and a low-speed printing mode, and the voltage applied to the heat generating element can be switched depending on the printing mode. It has a power supply circuit and an energization width control circuit that can switch the energization time to the heat generating element depending on the printing mode, and the voltage applied to the heat generating element is reduced in the low speed printing mode compared to the high speed printing mode. It is characterized by a low power consumption and a long current application time.

[Embodiment] FIG. 1 is a schematic diagram of a driving device for a thermal printer showing an embodiment of the present invention.

1 is an energization width control circuit capable of switching the energization time that determines the energization time to the heating element 3; 11 is a capacitor; 12.13 is a resistor connected in series with the capacitor;
4 is a voltage comparison circuit, 15 is a transistor that instantaneously shorts the capacitor, 16 is a transistor that shorts the resistor 12, 17, 18 is a resistor, and 19 is a polyconcentration. After the transistor is turned on momentarily, charging of the capacitor 11 is started via the resistor 12.13, and the charging time to the predetermined reference level divided by the reference voltage setting resistor 17, 18, 19 is determined. It is output from the voltage comparison circuit 14 as the pulse width tw. When the transistor 16 is turned on, the pulse width tw becomes a small value. 41 is turned on by the output of the voltage comparison circuit 14,
This is a power supply transistor that is turned off.

2 is a power supply circuit capable of switching the applied voltage that determines the voltage applied to the heating element 3; 21 is a voltage comparison circuit;
2 is a power transistor, 23 is a Zener diode that creates a reference voltage source, 24 is its load resistance, 25.26.2
7 is a resistor that divides the output voltage vh, 28 is a resistor 27
29a and 29b are smoothing capacitors, and 20 is an inverter.

When the transistor 28 is turned on, the output voltage vh becomes a high voltage. Both the energization width control circuit 1 and the power supply circuit 2 are configured to be able to switch their respective output values.

30 is a thermal head, 4 is a head driver that drives the heat generating element 3, 5 is a step motor which is a type of motor that relatively transports printing paper or the thermal head, 6 is a motor driver that drives the step motor 5, and 7 is a CPU that controls the thermal printer, 8 is a switch that selects the print mode, 9 is a step-down household 100V power supply,
Rectifying power supply unit, 10 is 5v regulator, 50
is the motor power regulator, 51 is the step motor 5
A resistor 52 indicates a transistor for shorting the resistor for converting the power supply voltage.

[Function] When high-speed printing mode is selected by switch 8, CP
A LOW level signal is output to the output terminal 71 of U7.

This turns on all transistors 16, 28, and 52. Then, a high voltage vh is outputted from the power supply circuit 2, and a high voltage is also applied to the step motor 5. When a trigger pulse is output from the output terminal 72 of the CPU 7 in synchronization with the print timing, a short pulse width tw is output from the voltage comparison circuit yt14. This output signal turns on the power supply transistor, and the head driver 4 becomes operable. The CPU 7 outputs print data from the output terminal 73 at the same time as the trigger pulse output, and appropriate energy is applied to the heat generating element 3. A resistor 51 is installed in the step motor 5 to increase the responsivity since the rotation frequency is high.
Short circuit and apply high voltage.

Conversely, when the low-speed printing mode is selected, a HIGH level signal is output from the output terminal 71, and the thermal head 3
0 is applied, and the energization time tw is also expanded. Further, the rotational frequency of the step motor 5 decreases, and at this time, the transistor 52 is turned off to prevent the step motor from generating heat.

FIGS. 2(a) and 2(b) are timing diagrams explaining the above-mentioned action, and 1'OO is in high-speed printing mode (FIG. 2(a)).
, 101 indicate the low-speed printing mode (FIG. (b)). A shows a trigger pulse output from the CPU 7, and b shows a waveform of the output terminal 31 of the head driver 4. The printing cycle T2 in the low-speed printing mode is approximately twice the cycle T1 in the high-speed printing mode. The applied voltage Vh-L in the low-speed printing mode is lower than the applied voltage Vhl in the high-speed printing mode,
The pulse width j% of the low-speed printing mode is longer than the pulse @ t w+ of the high-speed printing mode. As shown in 101-b, the pulse width t Wz in the low-speed printing mode is approximately 1/2 of the period l.

[Effects of the Invention] FIG. 3 is a diagram showing the relationship between the printing mode and the temperature rise of the heat generating element. 201 is the characteristic curve in high-speed printing mode, 2
02 shows characteristic curves in the low-speed printing mode. Although the energization time j'INz is long in the low-speed printing mode, the temperature Thλ reached by the heating element is adjusted to be almost the same as the temperature Thl reached in the high-speed printing mode. By doing so, it is possible to prevent troubles such as burnout and melting of the thermal transfer film due to heating of the heating element during the low-speed printing mode. Furthermore, since the thermal head moves while slowly dissolving the ink, the ink sufficiently penetrates into the fibers of the paper, making it possible to ensure extremely clear print quality. Therefore, it is now possible to print on low-smooth paper, which was conventionally thought to be impossible with thermal transfer printers.

The voltage vhλ in the low-speed printing mode is about one JΣ of the voltage in the high-speed printing mode, and the effect is most effective when the pulse width in the low-speed printing mode is at least twice the pulse width in the high-speed printing mode. was confirmed.

The present invention has similar effects not only in serial type thermal printers but also in line type thermal printers.

Further, in the low-speed printing mode, it is possible to further improve printing quality by increasing the pressure force with which the thermal head is pressed against the printing paper.

Note that the energization width control circuit 1 switches the standard value of the energization time to the heat generating element, and may be a temperature compensation circuit that changes it depending on the ambient temperature or the temperature of the thermal head. Similarly, the power supply circuit 2 also switches the standard value, and may also be used as a concentration volume, temperature compensation, etc. Furthermore, it is possible to reduce the energization time to the heat generating elements from the standard value depending on the individual drive history, and by such history control.

Further improvement in print quality can be expected.

As detailed above, the present invention is extremely useful and can be applied to all types of thermal printers that print on plain paper using a heat-sensitive film.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a driving device for a thermal printer showing an embodiment of the present invention. 1... Current width control circuit 2... Power supply circuit 3... Heat generating element 5... Motor FIGS. 2(a) and 2(b) are timing diagrams for explaining the present invention in detail. FIG. 3 is a diagram showing the printing mode and the temperature rise of the heat generating element to explain the present invention in detail. that's all

Claims (1)

[Claims] In thermal printers that use a thermal head with multiple heat-generating elements to print on plain paper via thermal paper or film, there are two modes: a high-speed printing mode and a low-speed printing mode that aims for high printing quality at a low speed. It has at least two types of printing modes, and depending on the printing mode,
It has a power supply circuit that can switch the voltage applied to the heat generating element, and an energization width control circuit that can switch the energization time to the heat generating element depending on the printing mode, and the low speed A thermal printer characterized in that in printing mode, the voltage applied to the heating element is low and the energization time is long.