JPS6111261A - Recorder - Google Patents

Abstract

PURPOSE:To protect a thermal head even when an electrifying state is encountered due to disorder of control circuit, etc., by providing a protective circuit to interrupt the electrification to be encountered by detecting a drive pulse of a given longer time interval than in the usual recording period, which is applied to a selective controller or recording signal supplyer. CONSTITUTION:In case where the output of a decoder 21 becomes a drive state of longer time interval than the drive pulse due to the stoppage of microcomputer 18 and the disorder of a decoder 21, a transistor TR11 is turned ON, and when the collector is raised, the base potential of a transistor TR13 is abruptly raised and the transistor TR13 goes ON. Current flows through the resistor R16 and capacitor C, the potential is gradually lowered, and at the base voltage at which the transistor TR13 is turned OFF, the transistor TR13 goes OFF. At the time point, the transistor TR14 is turned ON, the transistor TR12 goes OFF, and supply of current to the heating resistor 14 of the thermal head 13 is interrupted. If the values of the capacitor C and the resistance R16 of a time-constant circuit 22 are properly set up, during the time until interruption is reached, the breakage of the heating resistor 14 can be avoided, and the thermal head can be protected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a recording apparatus having a thermal head protection function.

[Technical background of the invention and its problems]

Conventionally, heating resistors were arranged in a row on an insulating substrate.

Thermal heads, which record on thermal recording paper that is in contact with heat by selectively passing current through these heat-generating resistors, are used in many recording devices such as facsimile machines due to their ease of maintenance. .

On the other hand, with the recent advent of the new media era, there has been a strong demand for recording images displayed on color television receivers, and to meet these demands, television receivers with additional thermal heads have been developed. is also on sale.

However, when the thermal head is connected to a device that sends control signals in this way, if the IT turns on due to some failure, the heating resistor of the thermal head becomes energized, overheats, and is destroyed. There is a risk of

For example, [Television Technology J, January 1984 issue, pages 53 to 62] describes a color television with a thermal head printer as described above, and Figure 12 on page 59 shows the thermal head print circuit. has been done. That is, as shown in FIG.
The image data for recording output from the is latched by the data latch circuit (2), then converted into a driving pulse train by the drive circuit (3), and then passed through a diode to the heating resistor on the thermal head (4). Added to one end of the line. On the other hand, group data for selecting and specifying the group to be driven is applied from the microcomputer (1) to the decoder (5), and furthermore, a level shift circuit (6) consisting of two transistors outputs a negative high voltage for driving. This is converted into a drive pulse train and applied to the other end of the heating resistor row on the thermal head (4).

Although FIG. 3 only shows circuits corresponding to two groups of heat-generating resistors, in reality, circuits corresponding to several tens (for example, 20
group) is often considered to be an S degree group.

In the above recording device, a microcomputer (1)
The decoder (5) is controlled by a control signal from the decoder (5) to the decoder (5).
), negative control pulses are sequentially supplied from one output terminal to the level shift circuit (6). This pulse turns on the PNP type transistor TR1 and turns on the NPN type transistor TR2, so a negative voltage is applied to the common terminal side of the selected group of heating resistors, and the image of this group is recorded. A current flows through the heating resistor to which data is applied as a positive high voltage pulse from the drive circuit (3) side, generating heat and recording. When the decoder (5) output becomes H level, TRI and TR2 are turned off and short recording is stopped.

However, the microcomputer (1) and decoder (5)
), etc., and the output of the decoder (5) remains at L level for a long time, the transistor (TR2) remains on and the heating resistor becomes overheated.

[Purpose of the invention]

The present invention has been made in view of the problems of conventional recording devices as described above, and protects the thermal head even if an overcurrent condition occurs due to a failure in the control circuit or the like. The purpose of the present invention is to provide a recording device having a protection function.

[Summary of the invention]

The present invention provides a thermal head comprising a plurality of heat generating resistors arranged in parallel, a recording signal supply section which divides the heat generating resistors on the thermal head into a plurality of groups and supplies a recording signal from one end thereof; a selection control section that applies a control signal to sequentially select each group of heating resistors; and a selection control section that applies a control signal that sequentially selects each group of heating resistors; This recording device consists of a protection circuit that detects the current and cuts off the current.

〔Effect of the invention〕

According to the present invention, even if the current is kept on for a long time due to some kind of failure, the protection circuit cuts off the current, so the thermal head can be protected without burning out the heating resistor.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

The structure of this embodiment is the same as that shown in FIG. 3 except for the level shift circuit I and the protection circuit.

That is, heating resistors α are arranged in a row on the thermal head (13), and a diode a9 is provided at one end of the heat generating resistor α, and the other end is commonly connected for each group.The diode (1→ A drive circuit wire and a data latch circuit (17) are connected to each group, and the connections at the same position in each group are commonly connected and connected to the microcomputer. The latching of recording signal data is performed by control circuit AH and control circuit B (21).

On the other hand, group selection is performed by outputting a decoder 01)K control signal from the microcomputer α barrel and sequentially sending negative selection drive pulses to the level shift circuit (11). The level shift circuit I includes a PNP type transistor (TRII) and an NPN type transistor (TR
12) and resistors (R11) to (R14).

In addition, the protection circuit α is composed of two NPN type transistors (TR
13).

(TR14), capacitor (C), diode (D), resistor (R16), (R17), resistor (R1
6), (Rt7), capacitor (C), diode (D) and transistor (TR13) are time constant circuit (2
), and the transistor (TR+4) constitutes a switch circuit @.

Next, the level shift circuit (11) and the protection circuit a2
The operation will be explained with reference to FIG. During normal continuous recording, a negative selection control pulse of width t1 shown in ■ in FIG. 2(A) is applied to the decoder C! It is output from υ, and the transistor (TB
II) appears as a positive pulse like ■. This output is passed through a resistor (Rxs) and a capacitor (C) and is applied to the base of the transistor (TR13) as a pulse shown in the figure (2). On the other hand, transistor (TR
Since the collector output (■) of the transistor (TR11:) is applied to the base of the transistor (TR12) through the resistor (R14), the base waveform becomes as shown in Figure 2 (A). Therefore, this transistor (TR14) When the drive pulse is turned on for the driving pulse time (tt), the collector output becomes the waveform of ■. Also, although not shown, during these 11 times K, the image recording signal that is double-tipped to the data latch circuit αη is Since it is applied in parallel to the drive circuit αe as a high voltage positive pulse to the anode side of the diode ←9, a current corresponding to the image recording signal flows through the heating resistor group I of the selected group. Selective heating is performed.

In continuous driving, the thermal head is driven again by the same driving pulse after a predetermined time t0 has elapsed after the driving pulse.

By the way, microphone 4 computer stop, decoder 0
Assume that due to some failure such as damage in 1), the output of the decoder QD is in a driving state for a longer time than the driving pulse width t1 in FIG. 2(A). In this case, the output of the decoder Qυ is as shown in Figure 2 (B).
RII) is turned on, and the collector output of this transistor becomes like ■. Then, as in the normal operation described above, when the collector of the transistor (TR11) rises, the base potential (2) of the transistor (TR13) rapidly rises, and the transistor turns on. Therefore, a current flows through the resistor (R16) and the capacitor (C), and the potential at (2) gradually decreases, and when the base voltage reaches the base voltage at which the transistor (TR13) turns off, this transistor turns off. Therefore, at this point, the transistor (TR1
The collector potential of 3), that is, the ■ waveform indicating the base potential of the transistor (TR14) is at L −+ H level.

As a result, at this point, the transistor (TR14) is on and the transistor (TR12) is off. Therefore, the current supply to the heating resistor α4 of the thermal head a is cut off. That is, the resistor (R16) and capacitor (
By appropriately setting the value of C), the time until the circuit is shut off can be set to the time t2 during which the heating resistor I is not burned out. In this way, the thermal head is protected.

According to this embodiment, not the high-voltage drive pulse output from the level shift circuit (11) but the preceding pulse is detected, which has the effect of facilitating control and simplifying the configuration of one circuit.

Also, according to the above embodiment, since the protection circuit a is added to the selection control section, there is an advantage that the number of added circuits can be reduced when the number of groups of thermal heads is small.

However, in one aspect of the present invention, the protection circuit may be provided on the side of the recording signal supply section. Such a configuration is used when the number of heating resistors forming each group is small.

This has the advantage that fewer circuits are required.

Furthermore, in the protection circuit of the present invention, a time constant circuit may be used as a circuit for detecting the length of the drive pulse.

This has the advantage of simplifying the circuit configuration.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention, FIG. 2 is a waveform diagram of various parts of the embodiment of FIG. 1, and FIG. 3 is a diagram showing an example of the configuration of a conventional recording apparatus. 11... Level shift circuit 12... Protection circuit 1
3...Thermal head 14...Heating resistor 1
5...Diode 16...Drive circuit 1
7...Data latch circuit 18...Microcomputer 19...Control circuit A 20...Control circuit B Agent Patent attorney Noriyuki Chika 11!1 Figure 2 (A) ■

Claims (2)

[Claims] (1) A thermal head comprising a plurality of heat generating resistors arranged in parallel, a recording signal supply section which divides the heat generating resistors on the thermal head into a plurality of groups and supplies a recording signal from one end, and the heat generating resistor. a selection control section that applies a control signal to sequentially select each group of the body; and a selection control section that is added to this selection control section or the recording signal supply section and detects when a drive pulse with a predetermined time width longer than during normal recording is generated. A recording device consisting of a protection circuit that cuts off power supply. (2) A recording device characterized in that the protection circuit comprises a time constant circuit that detects the length of the drive pulse, and a switch circuit that cuts off current supply based on the output of the time constant circuit.