JPH0317270B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a thermal recording apparatus that selectively performs binary recording and halftone recording.

Conventional configuration and its problems To output a halftone image with a thermal recording device, generally, the power supply voltage of the thermal head is kept constant and the width of the applied pulse (current application time) applied to the heating element is controlled. The color is developed at the same level as the number of gradations. FIG. 1 shows an example of the relationship between the recording density of the thermal paper for halftone recording and the above-mentioned applied pulse width.
In halftone recording, the gradation is controlled by the applied pulse width, so as shown in Figure 1, the thermal paper's recording density/applied pulse width characteristics need to have a relatively gentle and appropriate slope. Thermal paper is used.

On the other hand, thermal recording devices such as facsimiles are mainly used for black and white binary recording as well as halftone recording. FIG. 2 shows an example of the relationship between the recording density of the thermal paper for binary recording and the applied pulse width (of course, the power supply voltage of the thermal head is constant). 2
For value recording, thermal paper is suitable because it provides the required high recording density even if the time for which electricity is applied to the heating element of the thermal head is shortened (even if the applied pulse width is decreased). In this case, recording power and recording time can be reduced. Therefore, as shown in FIG. 2, thermal paper is used which has a recording density/applied pulse width characteristic that rises steeply in a region where the applied pulse width is small.

When a thermal recording device uses one type of thermal paper and performs halftone recording in addition to binary recording,
In terms of the image quality of intermediate recording, it is necessary to use thermal paper with gentle recording density/applied pulse width characteristics as shown in FIG. 1 as the recording paper. However, when binary recording is performed using this thermal paper for halftones, there are disadvantages in that the recording power is increased and the recording speed is slower than when the thermal paper for binary recording is used.

On the other hand, when thermal paper for binary recording is used with emphasis on binary recording, the rate of change in recording density/applied pulse width characteristics is extremely large, so extremely fine applied pulse width control is required during halftone recording. Even with such control, it is difficult to achieve the desired gradation satisfactorily.

Purpose of the Invention The object of the present invention is to provide an apparatus that performs both binary recording and halftone recording using the same thermal paper, and in binary recording, without increasing recording power or decreasing recording speed, and without causing an increase in recording power or a decrease in recording speed. The object of the present invention is to provide a heat-sensitive recording device capable of obtaining good image quality with desired gradations in tone recording.

Structure of the Invention This invention utilizes the fact that the rate of change in recording density/applied pulse width characteristics of thermal paper becomes gradual by lowering the voltage supplied to the thermal head.
Inputs a signal specifying either value recording mode or halftone recording mode, and when a signal specifying binary recording mode is input, sets the voltage supplied to the thermal head to a high predetermined voltage and specifies halftone recording mode. The above object is achieved by providing a voltage switching means that changes the voltage supplied to the thermal head to a predetermined low voltage when a signal is input.

DESCRIPTION OF EMBODIMENTS FIG. 3 shows a schematic configuration of a thermal recording apparatus according to an embodiment of the present invention. In the figure, 2 is a line memory unit that stores image signals, 4 is a thermal head equipped with a control circuit consisting of a shift register, latch, and gate driver, and 3 is a recording device that supplies a power supply voltage for recording to the thermal head 4. A power supply section, 8 a timer that generates the energization time (applied pulse width) to be applied to the heating element of the thermal head 4, 5 a level counter that counts the number of gradations during halftone recording;
6 is a halftone recording image signal from line memory section 2
A determination circuit that compares the outputs of PiXH and the level counter 5 and extracts an image signal that exceeds a specified gradation level;
7 is a binary recording image signal from line memory section 2
This selector selects one of the halftone recording image signals inputted via the RiXO determination circuit 6 and supplies it to the thermal head 4.

1 is an input terminal for a HALF signal that specifies whether the binary recording mode or halftone recording mode is selected, and the HALF signal applied here is supplied to the line memory section 2, recording power supply section 3, selector 7, and timer 8, respectively. Switch the operation as follows.

In the binary recording mode, the HALF signal becomes "L", and in response to this, the recording power supply section 3 outputs a high predetermined voltage A.
is applied to the thermal head 4. In the halftone recording mode, the HALF signal becomes "H", and at this time the output of the recording power supply section 3 is switched to a low predetermined voltage B (A>B).

FIG. 4 shows the recording density/applied pulse width characteristics of the thermal paper used in the apparatus of the present invention. The two characteristic curves in the figure indicate the high voltage A applied to the thermal head 4.
The case where B is applied and the case where low voltage B is applied are shown. Typical thermal paper for binary recording exhibits characteristics suitable for binary recording when a predetermined high voltage is supplied to the thermal head, but when the supply voltage is lowered, the recording density changes with respect to the applied pulse width. It becomes gentler and exhibits characteristics suitable for halftone recording.

In the binary recording mode in which the HALF signal is "L", the line memory unit 2 outputs the image signal PiXO in synchronization with the image signal transfer clock CK.
The image signal is read out once for each line and transferred to the thermal head 4 via the selector 7. Immediately after the transfer of one line's worth of image signals is completed, the STB signal is output from the line memory section 2. this
In response to the STB signal, the image signal transferred to the thermal head 4 is latched, and the timer 8 is triggered to start operation.

A HALF signal of "L" is applied to the timer 8, and in this state, the applied pulse width for binary recording is created by this timer 8, and in response to the output ENB of this timer 8, one line of image is generated by the thermal head 4. Recording of the signal takes place. The value of the applied pulse width for binary recording at this time is determined from the recording density/applied pulse width characteristic at high voltage A in FIG. For example, to obtain a recording density of 1.4, the applied pulse width is approximately 0.5 m.
It is s.

Next, the operation in the halftone recording mode will be explained. In this mode, the HALF signal becomes "H" and the output of the recording power supply section 3 is switched to the low voltage B.

In this embodiment, it is assumed that recording is performed in four gradations including white. The applied pulse width for each gradation is the recording density /
It is determined from the applied pulse width characteristics, and is expressed here as follows.

0th gradation...Oms 1st gradation...T ₁ ms 2nd gradation...T ₁ +T ₂ ms 3rd gradation...T ₁ +T ₂ +T ₃ ms Also, FIG. 5 is a timing chart showing the operation during halftone recording. Each signal name in this figure corresponds to that in FIG. The TNSO signal is a signal indicating that the image signal is being transferred, and OVER is the signal indicating that the image signal transfer for recording one line has been completed (in this example, the image signal of the same line is transferred three times).
(The recording of one line ends only after the data is transferred twice.)
Further, the signal PiX is an image signal transferred to the thermal head 4 via the determination circuit 6 and the selector 7.
1, 2, and 3 shown there are the numbers of gradations, and image signals of the gradations or higher are recorded. Also, as in the case of binary recording, the STB signal becomes a latch signal for the thermal head 4 and a trigger signal for the timer 8, and the ENB signal is an applied pulse width (heating element drive time) signal generated by the timer 8. C.K.
The signal is an image signal transfer clock.

In the halftone recording mode, first the line memory section 2
Image signal PiXH is output from. Since this is 4-gradation recording, PiXH is a 2-bit signal. This PiXH signal is input to the determination circuit 6. The level counter 5 is a ternary counter, and is incremented by the TNSO signal every time the image signal transfer is completed.The count output is input to the determination circuit 6 as the reference gradation value of the recorded image signal, and the timer 8 It is input as a time setting signal.

Recording of one line is performed as follows. Among the image signals PiXH read out from the line memory section 2, first, the image signals of one or more gradations are judged by the judgment circuit 6.
The signal passes through the selector 7, is transferred to the thermal head 4, is latched by the STB signal, and is recorded for the first time on one line with an applied pulse width of _T1 (output ENB of the timer 8).

After outputting the STB signal, the image signal PiXH is read out for the second time. 2 of the same line image signal
At the time of readout for the second time, the image signal of the second or higher gradation passes from the determination circuit 6 to the selector 7, is transferred to the thermal head 4, and in response to the STB signal, the applied pulse width of _T2 (at the output of the level counter 5) is timer 8
The set time is T ₂ ).

Furthermore, after the STB signal is output, the image signal PiXH is read out for the third time. When the same line image signal is read out for the third time, the image signal of three gradations passes from the determination circuit 6 to the selector 7, is transferred to the thermal head 4, and in response to the STB signal, the applied pulse width of _T3 (timer 8 is recorded as T ₃ ). This is the end of recording one line. When the third image signal transfer is completed, the level counter 5 outputs an OVER signal, and the next line of image signals is read out from the line memory section 2. The above operations are repeated to record one page of images.

Note that although the above embodiment describes intermediate recording of four gradations, the present invention is of course not limited to this, and more detailed gradation expression is possible. Also,
The specific numerical values of the recording density/applied pulse width characteristics of the thermal paper shown in FIG. 4 are only an example.

Effects of the Invention As explained in detail above, according to the thermal recording device according to the present invention, using the same thermal paper,
High-speed binary recording can be performed with low recording power, and halftone recording with good image quality can also be performed.

[Brief explanation of drawings]

Figure 1 is a recording density/applied pulse width characteristic diagram of thermal paper for halftone recording, Figure 2 is a recording density/applied pulse width characteristic diagram of thermal paper for binary recording, and Figure 3 is an embodiment of the present invention. Schematic configuration diagram of a thermal recording device by
The figure shows the recording density of thermal paper used in the device shown in Figure 3.
The applied pulse width characteristic diagram, FIG. 5, is a timing chart showing the operation of the halftone recording mode in the apparatus of FIG. 2... Line memory section, 3... Recording power supply section, 4
...Thermal head, 5 ...Level counter, 6
...Judgment circuit, 7...Selector, 8...Timer.

Claims (1)

[Claims] 1. Input a signal specifying either the binary recording mode or the halftone recording mode, and when the signal specifying the binary recording mode is input, set the voltage supplied to the thermal head to a high predetermined voltage, and Voltage switching means that sets the voltage supplied to the thermal head to a low predetermined voltage when a signal specifying a recording mode is input, and in the binary recording mode, energization of the heating element of the thermal head according to the image signal. a binary recording control means for controlling the thermal head to be non-energized and energized for a predetermined period of time; and in the halftone recording mode, to change the energizing time to the heating element of the thermal head in three or more stages, including non-energizing, according to the image signal. A thermal recording device comprising halftone recording control means.