JPH0732619A - Safety device for serial printer - Google Patents

Abstract

PURPOSE:To protect a controlling circuit and the like from their damage by turning OFF a power source for a printer when a control signal is impressed from a control unit to a drive circuit for supplying an exciting current to an exciting coil group and the breakage of a cable connecting a printing head to the control unit is detected. CONSTITUTION:When a power source for a printer is ON, a resistance value of a resistor R3 is ordinarily larger than that of a thermister 31 adapted to detect the burning, damage and the like of a magnetic coil and, therefore an output VIN of a comparator 43 becomes an L-level, an output VOUT from an output port of a microprocessor (MPU) 12 is at an H-level, and a transistor TR is in an OFF state. When a printing head is disengaged from a cable under such a condition, the thermister 31 is disconnected and, therefore the output VIN of the comparator 43 becomes an H-level, and the output VOUT of the MPU 12 becomes an L-level, whereby the transistor TR is turned ON. Then, an alarm signal ALM-P is issued, and a power source OFF circuit turns OFF the power source.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a safety device for a serial printer.

[0002]

2. Description of the Related Art Conventionally, in a serial printer, a print head is driven by serial print data transferred from a host side, and a print wire of the print head strikes a print sheet via an ink ribbon. Then
Print predetermined characters, images, etc. (hereinafter referred to as "images").

FIG. 2 is a block diagram of a control circuit of a conventional serial printer. In the figure, 11 is a bus line, and the bus line 11 includes a microprocessor 12, a read only memory (ROM) 13, a random access memory (RAM) 14, an interface (I / F) control unit 15, a motor drive circuit 17, and The printing unit 19 is connected. The microprocessor 12 performs an operation for controlling the entire serial printer, the read-only memory 13 stores an operation program of the microprocessor 12, and the random access memory 14 is necessary for the microprocessor 12 to perform an operation. Stores various data.

The interface controller 15 is connected to the interface connector 21, receives serial print data transferred from the host side through the interface connector 21, and transfers predetermined information to the host side. The motor drive circuit 17 is connected to the motor 22 and outputs a driving pulse to the motor 22. Further, the printing unit 19 is the microprocessor 1
It is controlled by 2 to print a predetermined image on a print sheet (not shown). The printing unit 19 includes a print head (not shown) and a mechanism for driving the print head.

FIG. 3 is a circuit diagram around a print head in a conventional serial printer. In the figure, 23 is a control unit, and the control unit 23 is the microprocessor 1
2 (FIG. 2), a read only memory 13, a random access memory 14, an interface control unit 15, and the like.
Further, 24 is a print head, and a cable 26 for connection
Is connected to the control unit 23.

The print head 24 constitutes the print section 19 and has a drive circuit 28 and an exciting coil group 29 driven by the drive circuit 28. The exciting coil group 29 is composed of a plurality of exciting coils 30 arranged corresponding to a print wire (not shown), and an exciting current corresponding to the print data is supplied to the exciting coil 30. For that purpose, the microprocessor 12 generates a control signal based on the print data, outputs the control signal to the drive circuit 28, and the drive circuit 28 supplies an exciting current to the exciting coil 30 based on the control signal. To do.

In order to prevent the magnetic coils 30 of the magnetic coil group 29 from being burnt out, for example, a thermistor 31 is mounted as a temperature detecting means. Then, the temperature detected by the thermistor 31 is input to the microprocessor 12 as a temperature detection signal V _th . Therefore, the cable 26 has a signal line for sending the control signal to the drive circuit 28 and a signal line for sending the temperature detection signal V _th to the microprocessor 12. Further, the cable 26 is connected to the drive circuit 2
8, a voltage line connecting the control system and the power supply Vcc for control, a voltage line connecting the control system to the ground (E _L ), a voltage line connecting the power system such as the exciting coil group 29 and the power supply V _P for driving , And a voltage line for grounding (E _P ) the power system.

The cable 26 is connected to the connector portion 3
3 is connected to the control unit 23, and the connector unit 34 is connected to the print head 24. Further, a card edge type connector having a plurality of terminals arranged in parallel on the edge surface is used for the connector portion 34, and the print head 24 can be easily replaced or repaired by attaching or detaching the connector. Is able to.

[0009]

However, in the conventional serial printer described above, the operator attaches the print head 24 to the cable 2 while the power source (not shown) is turned on.
If it is accidentally removed or installed from 6, the card edge type connector tilts, and a short circuit occurs between terminals of adjacent pins of the connector or between terminals of the power system and terminals of the control system, The drive circuit 28 may be destroyed, or the control circuit (not shown) of the control unit 23 may be destroyed.

According to the present invention, the problems of the conventional serial printer are solved, and a short circuit does not occur between the terminals of the connector, and the drive circuit or the control circuit of the control unit is destroyed. It is an object of the present invention to provide a safety device for a serial printer that does not exist.

[0011]

To this end, in a safety device for a serial printer according to the present invention, a print head includes an exciting coil group and a drive circuit for supplying an exciting current to the exciting coil group, and a control unit controls the excitation. A power supply voltage for driving is applied to the coil group, a control signal is output to the drive circuit, and a power supply voltage for control is applied.

Further, a cable connects the print head and the control unit via a connector unit, and when the safety circuit detects the disconnection of the cable, the serial printer is turned off.

[0013]

According to the present invention, as described above, in the safety device of the serial printer, the print head is provided with the exciting coil group and the drive circuit for supplying the exciting current to the exciting coil group, and the control section is provided with the exciting coil group. And a control signal is output to the drive circuit and a control power supply voltage is applied.

Therefore, when the drive circuit supplies a drive current to the exciting coil group in response to the control signal, the print wire strikes the print paper via the ink ribbon, and a predetermined image is printed on the print paper. In addition, a cable connects the print head and the control unit via a connector unit, and when the safety circuit detects the disconnection of the cable, the serial printer is turned off. If the operator mistakenly removes or installs the printhead from the cable with the serial printer powered on, the safety circuit will detect a break in the cable and turn off the serial printer.

[0015]

Embodiments of the present invention will now be described in detail with reference to the drawings. 1 is a circuit diagram of a main part of a safety device of a serial printer showing an embodiment of the present invention, FIG. 4 is a block diagram of a control circuit of a serial printer in the embodiment of the present invention, and FIG. 5 is a serial printer in the embodiment of the present invention. 2 is a time chart of the safety device of FIG.

In FIG. 4, 11 is a bus line,
The bus line 11 includes a microprocessor 12, a read-only memory 13, a random access memory 14, an interface control unit 15, a motor drive circuit 17, and a printing unit 1.
9 is connected. The microprocessor 12 performs an operation for controlling the entire serial printer, the read-only memory 13 stores an operation program of the microprocessor 12, and the random access memory 14 is necessary for the microprocessor 12 to perform an operation. Stores various data.

The interface controller 15 is connected to the interface connector 21, receives serial print data transferred from the host side through the interface connector 21, and transfers predetermined information to the host side. The motor drive circuit 17 is connected to the motor 22 and outputs a driving pulse to the motor 22. Further, the printing unit 19 is the microprocessor 1
It is controlled by 2 to print a predetermined image on a print sheet (not shown). The printing unit 19 includes a print head 24 (see FIG. 3) and a mechanism for driving the print head 24.

Further, 41 is the microprocessor 12
Is a safety circuit which is connected to the power supply of the thermistor 31 and detects the disconnection of the thermistor 31 to turn off the power of the serial printer. Next, the safety circuit 41 will be described with reference to FIG.
In FIG. 1, the thermistor 31 provided in the print head 24 (see FIG. 3) is connected to the non-inverting input terminal of the comparator 43, the power source Vcc is connected via the resistor R1, and the temperature detection signal V _th is input. In addition, the resistor R is connected to the inverting input terminal of the comparator 43.
A reference voltage obtained by dividing the voltage of the power supply Vcc by 2 and R3 is input. Here, the resistors R1 and R2 have the same resistance value, and the resistor R3 is the thermistor 31 in normal use.
It has a larger resistance value.

The output side of the comparator 43 is pulled up to the power source Vcc by the resistor R4, and
It is connected to the input port IN of the microprocessor 12. Further, the output port OU of the microprocessor 12
T is connected to the base of the transistor TR through the resistor R5, and the emitter of the transistor TR is connected to the power supply Vcc. The collector of the transistor TR is
It is grounded via a resistor R6, is pulled down, is connected to a power-off circuit (not shown), and has an alarm signal AL.
Output MP to the power-off circuit. A resistor R7 for stabilizing switching is connected between the base and emitter of the transistor TR.

Next, the operation of the safety device of the serial printer of the present invention will be described with reference to FIG. Since the resistance value of the resistor R3 is usually larger than the resistance value of the thermistor 31 when the power of the serial printer is on, the voltage level of the non-inverting input terminal of the comparator 43 is lower than the voltage level of the inverting input terminal, and the voltage level of the comparator 43 is lower. Output V
_IN goes low. In this case, the output V _OUT of the output port OUT of the microprocessor 12 becomes high level and the transistor TR is turned off. Therefore, the alarm signal ALM-P is not output, and the power supply off circuit keeps the power supply on.

When the print head 24 is disconnected from the cable 26 at time A, the voltage level at the non-inverting input terminal of the comparator 43 becomes higher than the voltage level at the inverting input terminal because the thermistor 31 is disconnected. Four
The output V _IN of 3 becomes high level. When the microprocessor 12 detects this high level, it sets the output V _OUT of the output port _OUT to low level to turn on the transistor TR and outputs the alarm signal ALM-P.
As a result, the power-off circuit turns off the power at time B.

In the present embodiment, the thermistor 3
Although the comparator 43 is used to detect the disconnection of 1, the temperature detection signal V _th is input to the A / D converter (not shown) of the microprocessor 12, and the thermistor 3 is connected.
It is also possible to judge the disconnection when the resistance value of 1 reaches the maximum value. It should be noted that the present invention is not limited to the above-described embodiments, and various modifications can be made based on the spirit of the present invention, and they are not excluded from the scope of the present invention.

[0023]

As described in detail above, according to the present invention, in the safety device of the serial printer, the print head is provided with the exciting coil group and the drive circuit for supplying the exciting current to the exciting coil group, and the control unit. Applies a drive power supply voltage to the excitation coil group, outputs a control signal to the drive circuit, and applies a control power supply voltage.

Further, a cable connects the print head and the control section through a connector section, and when the safety circuit detects disconnection of the cable, the serial printer is turned off. If the operator mistakenly removes or installs the printhead from the cable with the serial printer powered on, the safety circuit will detect a break in the cable and turn off the serial printer.

Therefore, it is possible to prevent a short circuit from occurring between the terminals of the adjacent pins of the connector, between the terminals of the power system and the terminals of the control system, and the drive circuit is destroyed or the control unit is controlled. The control circuit will not be destroyed.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a main part of a safety device of a serial printer showing an embodiment of the present invention.

FIG. 2 is a block diagram of a control circuit of a conventional serial printer.

FIG. 3 is a circuit diagram around a print head in a conventional serial printer.

FIG. 4 is a block diagram of a control circuit of the serial printer according to the embodiment of the present invention.

FIG. 5 is a time chart of the safety device of the serial printer according to the embodiment of the invention.

[Explanation of symbols]

 23 control section 24 print head 26 cable 28 drive circuit 29 excitation coil group 33, 34 connector section 41 safety circuit

Claims (1)

[Claims] 1. A print head comprising: (a) an exciting coil group and a drive circuit for supplying an exciting current to the exciting coil group;
(B) a control unit that applies a drive power supply voltage to the excitation coil group, outputs a control signal to the drive circuit, and applies a control power supply voltage, and (c) the print head A safety device for a serial printer, comprising: a cable connecting the control unit and a control unit via a connector unit; and (d) a safety circuit that turns off the power when a disconnection of the cable is detected.