JPS58201464A - Thermal recording system of facsimile device - Google Patents

Abstract

PURPOSE:To prevent unevenness in the density caused by the difference of a recording period, by detecting the recording period and applying a preheating pulse if the recording period becomes long so as to keep the temperature of thermal heating elements of a thermal print head within a prescribed range. CONSTITUTION:A write instruction is inputted to a microcomputer 1 from a system control unit and a picture signal is inputted to a shift register 2 of S/P conversion serially. Picture signals (a)-(c) inputted to the register 2 pass through corresponding AND gates ANDa-ANDc with a recording pulse from the microcomputer 1 and drive the thermal heating elements Ra-Rc corresponding to black information selectively to print a dot pattern. In this case, if the recording period is long, a preheating pulse signal is outputted from the microcomputer 1 to set the register 2 and opens the gates ANDa-ANDc at the same time, allowing to conduct electrically and heat all the thermal heating elements Ra-Rc.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermal recording method for a facsimile machine that communicates using image signals encoded for band compression, and in particular, to prevent density unevenness caused by differences in recording cycles.
This invention relates to a thermal recording method that allows high-quality copies to be obtained.

In the case of a facsimile device that decodes and records encoded image signals, the recording cycle changes depending on the type of document. Therefore, the temperature of the heat generating element of the recording head also varies depending on the length of the recording cycle, which causes # degree unevenness.

In conventional heat-sensitive recording methods for preventing density unevenness caused by such differences in recording cycles, a preheating current that does not cause color development is constantly supplied.

However, with this type of recording method that constantly supplies preheating current, the head is kept at a high temperature, making it possible to print dot patterns with high density, but in the case of high-speed recording, the cooling period of the heating element That is, when the recording cycle is short, a pattern with a higher density is printed due to the heat storage effect of the head, and it is impossible to completely prevent density unevenness. Moreover, there are also disadvantages such as increased power consumption and power.

Therefore, the thermal recording method of the present invention solves these inconveniences in conventional recording methods, prevents the occurrence of density unevenness due to differences in recording cycles even in the case of high-speed recording, and reduces power consumption. Aimed at Kokichi.

To this end, the thermal recording method of the present invention detects the recording cycle and applies a preheating pulse when the recording cycle is long to maintain the temperature of the heating element of the thermal head within a predetermined range. .

The preheating pulse is applied when the recording cycle is long.
That is, when the non-recording time is long, pulses with a fixed time width may be applied at fixed time intervals, or pulses with a time width corresponding to the non-recording time may be applied. The figure is a functional block diagram showing the main parts of a thermal head drive circuit used when implementing the thermal recording method of the present invention. In the drawings, / is a microcomputer,
ko is an S/P (serial-parallel) conversion shift register, OR is an OR gate circuit, AND ~ANDe is an AND gate circuit, R.

〜Rc indicates a heating element, and 凰〜C indicates an image signal. A thermal head composed of a large number of heating elements is generally divided into multiple groups, for example, groups, and each group is driven separately. be done.

In FIG. 7, only some of the seven groups are shown in order to simplify the drawing.

A write command is input from a system control unit (not shown) to the microcomputer 1, and an image signal is input serially to a shift register of an S/P converter consisting of a D flip-flop. In this case, black information is given by 1/' and white information is given by 101.

The image signals a-C input to the shift register 1 pass through the corresponding AND gate circuits ANDa-ANDcf by the recording pulse from the microcomputer 1, selectively drive the heating element R1-machi corresponding to the black information, and generate a dot. Print the pattern.

By the way, as described above, in the case of encoded image signals, the interval between such printing operations, that is, the recording period, is not constant because the decoding time differs depending on the type of document.

Therefore, the temperature of the heating element also changes variously, which causes density unevenness.

Therefore, when the recording cycle is long, a preheating pulse signal is output from the microcomputer to set each of the frisogen flops that make up the shift register, and at the same time, all outputs are set to 1/', which corresponds to black information. AND gate circuit ANDa=AN via OR gate circuit OR
The gate De is opened and all the heating elements R8 to Re are heated by electricity.

FIG. 2 is a time chart illustrating how the temperature of the heating element changes when a preheating pulse of a constant time width is applied in the thermal recording method of the present invention.

Recording commands are given at fixed timings.

A recording pulse is generated by this recording command.

This relationship is similar to the conventional recording method, and when the heating elements of the thermal head are divided into two groups,
Four recording pulses for two groups are sequentially generated by seven recording commands. Recording pulses indicated by dotted lines indicate pulses applied to the heating elements of the th to th groups.

Therefore, the temperature of the heating element is increased as indicated by the thermal waveform and decreased during the non-recording time.

When a recording command is actually input at the timing of the next recording command, the same operation is repeated and the temperature of the heating element is raised again.

However, as shown by the dotted line in Figure 1, when a recording command is not input at the timing of the next recording command,
A preheating pulse is generated so that energy is applied to the extent that no color develops. This preheating pulse 1; 1f-lI may be applied simultaneously to the groups, or may be applied sequentially to each group as in the case of the recording pulse.

In this way, by detecting whether or not there is a recording command at the timing when the recording command is manually input, and when no recording command is input, a preheating pulse of a fixed time width is applied instead of the recording pulse, thereby heating the heating element. Temperature within specified rangeζ
Since this can be maintained, the occurrence of density unevenness due to differences in recording cycles can be prevented.

The following Fig. 3 is a time chart explaining another embodiment of the heat-sensitive recording method of the present invention, and shows a case where a preheating/f pulse whose time width is changed corresponding to the non-recording time is applied. In the case of FIG. 3, the recording period, that is, the non-recording time is measured by an appropriate counting clock and counting means,
Preheating pulses having different time widths are applied corresponding to the time interval between a recording command and the next recording command.

First, when the non-recording time is the shortest and the recording command is actually input at the timing when the next recording command is input, the preheating pulse is not applied, as in FIG. 1 above.

On the other hand, when the non-recording time corresponds to the recording period, a preheating pulse having a time width of, for example, unit / is applied. In addition, as shown in FIG. 3, when there is a non-recording time of 3 recording cycles, a preheating pulse with a time width of 1 unit is applied, and when it is an 1I recording cycle, a preheating pulse with a time width of 3 units is given, for example. . These controls can be performed by the microcomputer shown in FIG.

FIG. 3 is a circuit diagram showing an example of a head drive circuit according to the thermal recording method of the present invention. In the drawings, C indicates a shift register, 3 indicates a latch circuit, G indicates a thermal head,
DATA is the input image signal, Load is the load signal, CI
, OCK indicate a clock signal.

The drive circuit shown in FIG. 9 drives seven groups of heating elements R1 to R1, as in FIG. 1 above.

The image signal DATA input to the shift register is given bit by bit by the clock signal CLOCK.
An image signal of /' or 1θ'' is set.

Then, when a recording command is input, loading 4 Loa
The recording pulses are output in parallel to the latch circuit 3 and latched, and the heating elements R1 to R11 are selectively driven by the recording pulses.

However, if the decoding processing speed is slow and a recording command is not given at the input timing of the next recording command, the preheating pulse +11 causes the shift register to operate as if it were j.
[! All iI @ numbers are set to be black. All of these 17'' image signals are latched into the latch circuit 3 by the load signal, and all the heating elements R1 to R2 are driven by the preheating pulse (2).

The preheating pulse (2) may be a pulse with a fixed time width, as shown in FIG. 1, or may be a pulse with a time width corresponding to the recording retention period, as shown in FIG. 3.

When applying a pulse with a fixed time width, all 17' image signals of the latch circuit 3 are latched until the next recording command is input, and the heating element is driven at the timing when the preheating pulse is input. let

As described above in detail, the thermal recording method of the facsimile apparatus of the present invention is provided with a recording period detection means for detecting the recording period of decoded image data, and when the recording period is am, the preheating pulse is If the shortest cycle is exceeded, apply a preheating pulse with a fixed time width every fixed non-recording time, or apply a preheating pulse with a time width corresponding to the length of the non-recording time. I'm trying to give it to you.

Therefore, according to the thermal recording method of the present invention, when the recording cycle is the shortest, the time necessary for cooling the head is secured, so even in the case of high-speed F recording, there is no density unevenness due to the heat storage effect of the head. Also, when the recording cycle is long, preheating is performed corresponding to the non-recording time, so the head's m
[tl is always kept within a predetermined range, thereby preventing unevenness in attitude from occurring. Moreover, since the preheating pulse is applied for only a short time, many excellent effects can be obtained, such as power consumption can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a functional block diagram showing the main parts of a thermal head drive circuit used when carrying out the thermal recording method of the present invention, and FIG. FIG. 3 is a time chart illustrating the state of temperature change of the heating element when a pulse is applied; FIG. 3 is a time chart illustrating another embodiment of the thermal recording method of the present invention;
FIG. 9 is a circuit diagram showing an example of a head drive circuit using the thermal recording method of the present invention. In the drawings, / indicates a microcomputer, Y indicates a shift register, 3 indicates a latch circuit, and the q-th thermal head.

Claims (1)

[Claims] A facsimile device that communicates using encoded data is provided with a recording cycle detection means for detecting the recording cycle, and when the recording cycle detected by the recording cycle detection means is the shortest, no preheating pulse is applied and the recording cycle is the shortest. A thermosensitive recording method in which a preheating pulse with a fixed time width or a time width corresponding to the length of the non-recording time is applied every fixed non-recording time when the cycle exceeds the period of .