JPS5926278A - Heat-sensitive recorder - Google Patents

Abstract

PURPOSE:To enable to prevent a thermal head from being overheated, by changing the width of a recording pulse for the subsequent copy in accordance with the temperature of a thermal head each time the recording of a sheet of copy is started or finished, in a facsimile or the like. CONSTITUTION:When starting recording of the first copy, the initial temperature of the thermal head H is detected by a sensor TS. According as the initial temperature detected is higher or lower than a preset temperature, an image signal controlling part C feeds a recording pulse having a short or long width to image signal controlling transistors Q1-Qn, whereby heating elements R1-Rn are supplied with an electric current in accordance with the pulse width, resulting in printing. When it is necessary to continuously record the subsequent copy, the temperature of the thermal head H is detected again, and the pulse width for the subsequent copy is determined in accordance with the temperature detected. Accordingly, overheating of the thermal head can be sufficiently prevented by a simple circuit construction and a simple control, and it is enabled to eliminate a sharp density change in recording a sheet of copy.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermal recording device used in facsimiles, computers, etc., and more particularly to a thermal recording device that prevents damage to its thermal head due to overheating.

In general, in thermal recording devices, when used continuously for a long time, heat accumulates in the thermal head of the paper, and the thermal head becomes overheated and damaged due to the accumulated heat.

In order to prevent this, conventionally, a temperature sensor is provided in the head itself or in the vicinity thereof, and the recording pulse width or the voltage applied to the thermal head is gradually adjusted during recording.

In this case, the recording density changes due to controlling the temperature of the thermal head, but extremely fine control is required to prevent such changes from appearing visually in the recorded document. However, it has the drawback of being expensive.

Therefore, an object of the present invention is to eliminate the need for complicated control, which is the drawback of the conventional example described in 1-1, and to adjust An object of the present invention is to provide a thermosensitive recording device having the following configurations.

The present invention will be explained in detail below with reference to the drawings.

FIG. 1 shows an example of the W4 configuration of an uninvented thermal recording device,
Here, C is an image signal control unit, Q+ lQ21..., Q
, 1 is a transistor for controlling the artist's number, R-type.

R2,..., R71 are resistances of heating elements, and H is a thermal head having a plurality of heating elements R1, R2+...+RIl. A temperature sensor TS is installed near the thermal head H or on the head itself. In addition, DI+0
2+...+DIl represents an image signal.

FIG. 2 is a flowchart showing the operation of the image signal control section shown in FIG. 1, where Tma X is a set temperature at which overheat protection control should be performed; ．． 12 is the pulse width of both signals output from the image signal control unit C to the image signal control transistors Q+, Q2, . . . , Qn; 1. <1°.

The third [Δ is a graph showing the temperature change of the thermal head when the thermal head overheat protection control is performed according to the present invention.

FIG. 4 shows image signals output from the image signal control unit C to image signal control transistors Q+, Q21, . . . , Qll, D2, . . . , is a timing chart showing that Dn changes due to overheat protection control.

In flowchart 1 of FIG. 2, when starting to record the first document, first, in step St, the initial lAk degree of the head H is checked by sensor dew, and if the temperature is higher than the set temperature Tmax, the next step is started. Proceeding to S2, thermal recording is performed with a recording pulse width t1.

On the other hand, in step Sl, if the initial crystallinity is lower than Tmaw, the process advances to step S3, and the recording pulse width t2
Perform thermal recording. This recording gourmet width is not changed within one document.

In the next steps S4 and S5, the notes 22 on one page of the original are
It is determined whether or not the process has been performed, and recording of one document is completed. In the next step S8, it is determined whether or not it is necessary to continue recording the next document. If so, the process returns to step Sl, checks the temperature of the thermal head H, and responds accordingly. Then, determine the recording pulse width for the next document.

1. When recording the original document continuously, follow the same procedure.

In this way, as long as the temperature of the thermal head H reaches a certain temperature, by keeping the recording pulse width shorter than that at room temperature, the heat from the thermal head H is diffused, as shown in Figure 3. , the temperature reaches a steady state near the set temperature Tma, and even if continuous recording is performed for a long time, the thermal head l
will not be damaged.

In addition, in the above-mentioned embodiment, the overheating of the head was suppressed by changing the recording pulse width, but in addition, the voltage applied to the thermal head could be controlled to obtain the same effect even if the recording pulse width was constant. be able to.

As explained above, according to the present invention, it is only necessary to check the temperature of the head and change the recording pulse width only when recording the document, and the structure is simple in terms of circuit configuration and control.
For practical purposes, overheating of the head can be sufficiently suppressed. Further, according to one aspect of the present invention, there is an effect of eliminating sudden changes in density within a single document.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an example of the configuration of the thermal recording device of the present invention, FIG. Figure 4 is a graph showing an example of measuring the temperature change of the thermal head l' when recording multiple originals. 3 is a timing chart showing signals t1 and t12. C...Picture signal control unit, DI +02 +..., Dll...Picture bar number. Q+, Q2,..., Qll... Image signal control transistor H... Thermal head, R1+R2+..., R7,... Heating element, TS...
temperature sensor. Patent applicant: Canon Co., Ltd.

Claims (1)

[Claims] A thermal recording device that performs recording using a thermal head is characterized in that each time recording of one document starts or ends, the recording pulse width of subsequent documents is changed depending on the temperature of the thermal head. A thermal recording device.