JPH0372470B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermal head drive device. FIG. 1 shows the conventional thermal head drive timing and the temperature characteristics of the thermal head. T is the thermal head recording repetition period, t ₁ , t ₂ , and t ₃ are the pulse widths for driving the thermal head, and θ _A and θ _B are the temperatures, and θ _B is the temperature at which the thermal paper does not develop color. . In conventional thermal head driving, the head is driven only when recording on thermal paper.

In this case, if the period of no recording continues for a long time, the head temperature will continue to fall, so the next time you try to record, the head temperature will be low, and this head temperature will depend on the length of the period of no recording. As a result, a stable peak value of the head temperature cannot be obtained with the same head drive pulse width _t1 , and the print density also varies. This state is shown by a solid line in FIG. Therefore, in order to obtain a stable peak value of head temperature, conventionally, the driving pulse width is set to t ₂ or t ₃ (t ₂ , t ₃ >t ₁ ) as necessary. The temperature characteristics of the head at this time are shown by broken lines.
However, in order to control the pulse width in this way, it is necessary to store the image signal data of the previous line, and there is a problem that a lot of hardware is involved.

The present invention has been made in view of the above-mentioned points, and in addition to applying a thermal head warming pulse to the thermal head during the recording pause period and the white signal recording period, the thermal head is also driven by the warming pulse before the recording pause period and the white signal recording period. The thermal head is kept warm by adding controls. An example of the operation of the warming pulse used in the present invention is shown in FIG. In the figure, T is the thermal head recording repetition period,
t _O is the pulse width of the pulse to keep the head at a temperature that does not color the thermal paper even when not recording in the period T, and t ₁ is the pulse width of the recording pulse, and θ _A , θ _B is the head temperature, and θ _B is the temperature at which the thermal paper does not develop color.
In the present invention, even when not recording, the pulse width
The head is driven with a pulse of _tO to keep it warm. This allows the next time you record,
Even if the head is driven with a pulse having a pulse width _t1 , stable printing density can be obtained with little fluctuation in the peak value of the head temperature. Further, the pulse width for driving the head is only the pulse width for keeping warm and the pulse width for recording, and no complicated control is required.

Specific circuit configuration examples of the present invention are shown in FIGS. 3 and 5. In the figure, 1, 2, and 7 are AND gates,
3 and 8 are OR gates, 4 is a thermal head driving circuit, 5 is a thermal head, and 6 is a power supply.

These operations will be explained.

In FIG. 3, the image signal and the block selection signal to be recorded are input to the AND gate 2, and the thermal head warming signal and the previous block selection signal of the block to be recorded are input to the AND gate 1. The respective signals obtained from gates 1 and 2 are input to OR gate 3 to obtain a signal for driving the thermal head. The thermal head driving circuit 4 drives the thermal head 5 using this driving signal. The driving power is supplied from a power source 6.

Further, a time chart for the circuit configuration example shown in FIG. 3 is shown in FIG. 4. In Figure 4, n is the block number when one line is divided into n blocks (n = 1, 2,...), T _O is the time required to print one line, and t ₁ is the pulse width of the recording drive pulse, and t _O is the pulse width of the warming drive pulse. First, in the period _TO for printing one line in FIG. 4, if the image signal is a black signal, the recording block to be recorded is driven by the recording signal in the block selection signal period, and the recording drive pulse width t is ₁ , the head is driven with the warming pulse width t _O even during the previous block selection signal period. However, in the case of a white signal, it is not driven. In the timing chart of the embodiment shown in FIG. 5 shown in FIG. 6, if the image signal is a black dot in the period _TO for printing one line, the recording block to be recorded with the recording signal in the block selection signal period is The recording block is driven in the same way by the warming signal during the previous block selection signal period.
In addition, since the warming signal is inputted together with the image signal, when the image signal is a white dot, it is driven by the warming signal during the block selection signal period.

It should be noted that in the previous block selection signal period, whether or not to drive in the black signal period and the white signal period can be easily realized by controlling the previous block selection signal with the image signal. In FIG. 6, a black signal period and a white signal period are distinguished so that the previous block selection signal is output in the case of a black signal, and the previous block selection signal is stopped in the case of a white signal. That is, in the case of a black signal, a signal for keeping the thermal head warm is output during the period of the previous block, and in the case of a white signal, output means is provided for outputting the signal for keeping the thermal head warm only during the period corresponding to the image signal. Furthermore, the recording period and the rest period can be easily distinguished from each other by simple control by detecting the presence or absence of an image signal in the circuit configuration example shown in FIG. FIG. 4 and FIG. 6 each show a recording period and a pause period separately.

As explained above, in the present invention, the head is driven with the head warming signal even when the line of white signal dots continues for a long time, several lines or one line, and even during the recording pause period. Therefore, it is almost unaffected by the length of the non-recording period, and a stable peak value of the head temperature can be obtained without varying the head recording drive pulse width _t1 . In particular, by providing an output means that outputs a warming signal during the previous block period in accordance with the image signal, a more sufficient print density can be obtained in the case of a black signal, and only the warming signal can be used in the case of a white signal. , thermal efficiency has improved. Further, the present invention can be easily introduced into a conventional diode matrix type thermal head drive.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the conventional thermal head drive timing and head temperature characteristics, FIG. 2 is a diagram showing the thermal head drive timing and head temperature characteristics for explaining the principle of the present invention, and FIG. 3 is a diagram showing the conventional thermal head drive timing and head temperature characteristics. FIG. 4 is a block diagram of a thermal head drive device in one embodiment of the invention, FIG. 4 is a timing chart obtained using the circuit configuration example of FIG. 3, and FIG. 5 is a block diagram of a thermal head drive device in another embodiment of the invention. The block diagram in FIG. 6 is a timing chart obtained using the circuit configuration example shown in FIG. 1, 2, 7...AND gate, 3, 8...OR gate, 4...Thermal head driving circuit, 5
...Thermal head, 6...Power supply.

Claims (1)

[Scope of Claims] 1. A thermal head driven by a thermal head driving signal, a first gate receiving a block selection signal and an image signal for driving the thermal head block by block, and the block selection circuit. an output means for outputting a previous block selection signal for driving a recording block before the recording block in accordance with the image signal for driving the recording block during the signal generation period; a second gate having as input;
A thermal head driving device comprising a third gate receiving the outputs of the first and second gates, and obtaining the signal for driving the thermal head from the output of the third gate. 2. The thermal head driving device according to claim 1, wherein the thermal head warming signal is input to the first gate together with the image signal.