JPS59152868A - Print head protective apparatus for serial printer - Google Patents

Abstract

PURPOSE:To prevent fouling of a head coil by a method wherein an electric energization control signal for controlling the electric energization of a print head is integrated and an abnormality detection signal is outputted when the results exceeds a reference value to stop the electric energization control signal. CONSTITUTION:An electric energization control signal DOTEN is fed a current controlling transistors 31-3n through an inverter 7 and a resistance 8 while done to an integration circuit 9. In case the input interval of the electric energization control signal DOTEN shortens abnormally, the voltage CV across a capacitor 11 of the integration circuit 9 rises. The voltage is compared with a reference voltage VR by a comparator 12, which outputs an abnormality detection signal S when it exceeds the reference to prohibit the transmission of the electric energization control signal DOTEN.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] This invention relates to a print head protection device for a serial printer.

[Technical background of the invention and its problems]

In a serial printer, for example, a serial dot printer, a head selection signal is input to each print head, as well as a print head energization control signal, which causes one transistor in the print head drive circuit to perform a switching operation to energize the print head coil. is under control. The output of these head selection signals and print head energization control signals is controlled by a control circuit using a logic circuit or a microcomputer, but in such a control circuit, external noise such as static electricity discharge or power line noise The logic of the control circuit may become abnormal due to a microcomputer program running out of control or a hardware flip-flop being inverted. Among these abnormalities, the energization control signal of the print head is output at shorter intervals than the normal time interval, the width of the energization control signal is longer than the normal width, and even the energization control signal is output. There are also phenomena such as becoming absent-minded. When such a phenomenon occurs, a current larger than normal flows through the print head, and if this state continues, the coils of the print head may be destroyed due to heat generation.

[Purpose of the invention]

This invention was made to solve this problem, and when abnormal energization is applied to the print head, it can be detected and the energization to the print head can be prohibited, thereby preventing the head coil from being thermally destroyed. It is an object of the present invention to provide a print head protection device for a serial printer that can prevent the print head from being damaged.

[Summary of the invention]

This invention integrates the energization control signal that controls energization to the print head of a serial printer using an integrating circuit, compares the output of the integrating circuit with a preset reference value using a comparator circuit, and detects whether the output of the integrating circuit exceeds the reference value. At this time, an abnormality detection output is sent out to inhibit the generation of an energization control signal, thereby inhibiting energization of the print head.

[Embodiments of the invention]

, 121, embodiments of the present invention will be described with reference to the drawings.

In FIG. 1, 1 is a DC power supply, and n print heads 21 are connected to this DC power supply 1. 2t + 2! p...2n
and n NPN type transistors/transistors 31, 3. .

38, .
1 + J 3 p...3n order/collector buffer amplifier t 11 4□, 4. .

...4n output terminals are connected respectively. Each of the above Patsfaa/7'4. , 42 y 4. r・
-4n is the print head selection signal DO1'+, DOT
t-DOTB...DOTn is selectively input.

Further, the positive terminal of the DC power supply 1 is commonly connected to a PNP type tositranstor 5, and further connected to a resistor 6. ．． 6. .

63, . . . , 6n to the paces of the transistors Jl + 32 + 33 e . . . 3 n. An energization control signal D OT E N is supplied to the PNP transistor 5 via an inverter 7 and a resistor 8 . Each of the print heads 2. j2. ．． 23. . . . 2n is each dot head and drive coil in the serial dot printer, and each of the transistors/registers 3□ to 3n, 5. Patsufaa/pu4. ~4
The energization is controlled by a print head drive circuit formed by n.

The energization control signal DOTEN described in 11j is also supplied to the integrating circuit 9. The integrating circuit 9 is formed of a resistor 10 and a charging/discharging capacitor 11, and supplies the voltage CV across the capacitor 11 to a non-inverting input terminal (1) of a comparator 12. Further, a reference voltage VR from a reference voltage source 13 is supplied to the inverting input terminal of the comparator 12). The comparator 12 has a voltage CV across the capacitor 11 that is a reference voltage v.
When R is exceeded, an abnormality detection output S is output. In response to this abnormality detection signal S, a control circuit (not shown) inhibits the output of the energization control signal DOTEN.

Next, the operation of the embodiment of the present invention configured as described above will be described.

First, during normal operation, the print head selection signals DOT1 to DOT
n and the energization control signal DOTEN are input at the timing shown in FIG. N never exceeds the reference voltage VR.

In addition, as shown in FIG. 2(b), the energization control signal DOTE
If an abnormal situation occurs, such as when the input interval of N becomes abnormally fast, the cooling time of the print head becomes shorter and the temperature of the head increases. However, at this time, the voltage Cv across the capacitor 1 of the integrating circuit 9 gradually increases as the charging/discharging parallel is broken. Eventually, the voltage CV across the capacitor 11 exceeds the reference voltage VR, and the comparator 12 outputs the abnormality detection signal S, which causes the energization control signal DQTEN to be
is prohibited, and energization of each print head 2, to 2n is prohibited. In this way, thermal damage to the print head is prevented.

In this way, the print head can be prevented from being thermally damaged due to abnormal energization by using a simple circuit consisting of an integrating circuit and a comparing circuit.

〔Effect of the invention〕

As described in detail above, according to the present invention, it is possible to provide a print head protection device for a serial printer that can protect the print head from thermal damage due to abnormal energization with a simple circuit.

[Brief explanation of the drawing]

The figures show an embodiment of the present invention. Fig. 1 is a circuit diagram of the main part, Fig. 2 shows input/output waveforms of each part, (a) is a waveform diagram in normal conditions, (b) is a waveform diagram in abnormal conditions. FIG. 21~2n...Print head, 31~3n...-NPN
Transistor/transistor, 5...PNP type transistor, 9...
・Integrator circuit, 12... comparator. Applicant's representative Patent attorney Takehiko Suzue Figure 1 Figure 2 (a) (b)

Claims (1)

[Claims] An integrator circuit integrates the energization control signal that controls the energization to the print head of the serial printer, and the output of this integrator circuit is compared with a preset standard 11, and when the integrator circuit output exceeds the above reference value, an abnormality detection output is output. 1. A print head protection device for a serial printer, comprising: a comparison circuit for transmitting a signal, and inhibiting generation of the energization control signal using the abnormality detection output.