JPS59118477A - Thermal printer - Google Patents

Abstract

PURPOSE:To protect a thermal head from an abnormal current by such an arrangement wherein as an abnormality of the head is detected, a pulse synchronized with the abnormality detection timing is caused to generate, and by this pulse, an abnormal current of the head can be detected. CONSTITUTION:A circuit 8 for detecting electrifying time and non-electrifying time and an amplifier circuit 9 are provided for each of thermal head drive circuits 5-1-5-n and the detection output F of a non-electrifying time and a pulse E generated by a microcomputer 2 during the non-electrifying time are obtained. By the conformity of the output F with the pulse E, a pulse G is generated by a circuit 13, and an intermittent output of consecutive pulses is obtained from a circuit 10 by the pulse G and the switch of a power-on circuit 11 is operated by the output and power is supplied to thermal heads 6 from a power source circuit 7. By this arrangement, it becomes possible to detect an abnormal condition including thermal head drive circuits and the thermal head can be positively protected.

Description

[Detailed description of the invention] [Field of application of the invention] The present invention relates to a thermal printer.

More specifically, the present invention relates to a circuit that protects the thermal head from being damaged due to abnormal current, and relates to a circuit that protects the head from damage due to damage to one component, abnormal operation of a microcomputer, abnormal handling during service, etc.

[Prior art]

Figure 1 shows an overview of a conventional thermal serial printer.

FIG. 2 is a block diagram showing the main points. In the figure, 1 is a command input terminal, and 2 is a printer control microcomputer.

6 is a semiconductor circuit for a drive motor, 4 is a printer drive motor, (5-1) to (5-i) are semiconductor circuits for driving a thermal head (hereinafter simply referred to as drive circuits), 6
is a thermal head, (6-1) to (6-n') are thermal elements constituting the thermal head 6, and 7 is a drive power supply terminal.

Operations related to the present invention will be briefly explained.

When a command signal is input from a personal converter (not shown) or the like through the command input terminal 1.

The microcomputer 2 outputs a control signal for printing accordingly. That is, a required one is selected from among the heat-sensitive elements (6-1) to (6-n) (each of which constitutes a focus point) constituting the heat-sensitive hand 6, and the corresponding 1 m (5-1 ) to (5-n) are driven. The driven drive circuit grounds one end of the corresponding heat-sensitive element, so that the heat-sensitive element is energized by the power from the drive power supply terminal 7 and performs heat-sensitive recording on a recording medium (not shown).

Now, in such conventional thermal printers, a microcontroller is used to detect abnormal current to the thermal head due to an abnormality in the rising characteristics of the output power of multiple chambers when the power is turned on or off, and to detect abnormal operation of the printer control microcontroller. There are protection circuits that continuously generate pulses at regular intervals and turn on the power circuit of the thermal head only while these continuous pulses are present. However, during service handling, it was not possible to perform a protective operation in the event that an abnormal current flows to the thermal head, and the thermal head may be damaged and removed.

[Objective of the Invention J The present invention has been made in order to eliminate the drawbacks of the prior art as described above, and therefore, the purpose of the present invention is to solve the problem of abnormalities in the semiconductor assembly for driving a thermal head or to prevent thermal damage caused by service handling. To provide a thermal printer equipped with a protection circuit capable of protecting a thermal head even when an abnormal current flows to the head.

[Summary of the invention]

In order to achieve the above object, the thermal printer according to the present invention includes a circuit that detects whether there is an abnormality in one or more of the individual circuits of the thermal head, and a circuit that determines the energization timing of the thermal head, The printer control microcomputer generates a pulse that is synchronized with this abnormality detection timing.

A thermal head protection circuit is provided which turns on and off the power supply circuit of the thermal head depending on the coincidence of the two, and detects abnormal current flowing to the thermal head. Furthermore, in the present invention, the period during which the thermal head of a thermal serial printer is energized is often 50% or less of the time per dot, and the period during which the head is not energized is individually detected. Create a circuit and synchronize with this non-energized period,
Pulses are generated from the printer control microcomputer, and these two
A circuit for obtaining an output only when there is a match is provided, and this output constitutes a head protection circuit that turns on the thermal head power only when the thermal head is operating normally.

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 2 is a circuit diagram showing one embodiment of the present invention. In this figure, the same parts as in FIG. 1 are given the same reference numerals. In addition, 8 is a thermal head drive state detection circuit, 9 is an amplification transistor for the detection result, 10 is an output circuit, 11 is a power-on circuit, and 15 is a two-way coincidence detection circuit.

Next, operations related to the present invention will be explained. In Figure 2, 2 is a microcomputer for controlling the printer.

A command signal from a personal computer or the like is sent to the printer drive motor and drive circuit through the input terminal 1, and a signal is sent to the thermal gutter drive circuit (5') (5-71).
By energizing the resistors (61) (6-n) of the heat-sensitive throat according to the printing conditions, printing can be performed on the heat-sensitive paper. here.

Generally, the period during which electricity is applied to the thermal elements (6-1) to (6-n) is 50% or less of the period during which dots are printed to color the thermal paper.

Therefore, due to an abnormality in one circuit, the heat sensitive elements (6-1,) to (
If 6-n) is continuously energized, the head will often be damaged. Therefore, in the conventional example, a microcomputer generates a pulse synchronized with the print signal, and only the print timing is set to UN.

It constituted a protection circuit against abnormal operation of the circuit. However, in this case, the thermal head drive circuit (5-1) (5-
71), there was no detection circuit in case an abnormality occurred, and the heat-sensitive element could be damaged. In the present invention, a detection circuit 8 for detecting whether there is a energizing period and a non-energizing period in each of the heat-sensitive hemotor throat drive circuits (5-1) (5-yz) and an amplifying circuit 9 for the detection result are provided, and the non-energizing period is The microcomputer 2 generates a pulse E during this non-energizing period, and a circuit 16 is provided which generates an output pulse G when the two match. The power-on circuit 11 is activated by the output of the circuit 10 that obtains the output.
operate the switch to connect the thermal head 6 from the power supply circuit 7.
Supply power to. By selecting approximately 50% of the voltage of the power source 7 for the power source 12 of the transistor 9, the driving conditions of the thermal head B can be reliably detected, and the head protection circuit can be stabilized.
You can ensure reliable operation.

〔Effect of the invention〕

In the present invention, only the additional circuits 8, 9, and 15 and the pulse generation timing from the microcomputer 2 are changed to the conventional circuit that turns on the power to the thermal head using a pulse from the microcomputer that matches the print timing. , it is possible to detect an abnormal state involving the thermal head drive circuit, and it is possible to construct an inexpensive and reliable thermal head protection circuit.

Furthermore, in response to abnormal operation of the control microcomputer 1, the microcomputer no longer generates regular pulses.

By configuring the circuits 13 and 10 to respond only to steady pulses, it is possible to cope with abnormal operation of the microcomputer.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an outline of a conventional thermal printer, and FIG. 2 is a circuit diagram showing an embodiment of the present invention. Explanation of symbols 1. Input terminal, 2... Microcomputer for printer control. 6... Semiconductor circuit for drive motor, 4... Printer 5
Rigid motor, (5-1) (5-n)... Semiconductor circuit for driving thermal head, 6... Thermal head, (6-1
)(6-71)...Thermal element, 7...Head drive power supply terminal, 8...Thermal head drive state detection circuit, 9...
Amplification transistor, 10... Output circuit, 11... Power on/off circuit, 12... Power supply terminal, 15...2
person - laying and unloading circuit. O 1 Kuni otsu map

Claims (1)

[Claims] 1) A plurality of thermal head drive circuits, a thermal element provided for each head drive circuit, a head drive power source, and a control unit are provided, and the drive circuit is in a driving state according to a command from the control unit. In a thermal printer in which a corresponding thermal element is driven from a driving power source, an abnormality detection circuit is provided to detect whether any one of the outputs of the driving circuit is in an abnormal state, and an abnormality is detected. A thermal printer characterized in that the driving power source is not turned on during a period in which the thermal printer is protected from the thermal element.