JPH11334133A - Thermal head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain a thermal head in a good state for a long time irrespective of an operation state of a printer main body by shutting off the supply of a connection permission signal to a driving circuit when a latch signal and a strobe signal are simultaneously supplied to a protecting circuit. SOLUTION: This thermal head has many heat-generating elements 1 arranged linearly, a latch circuit 4 for storing print data of one line synchronously with a latch signal, a protecting circuit 6 to which a strobe signal for determining a power supply time to the heat-generating elements 1 and the latch signal are supplied and which generates a power supply permission signal in accordance with feed states of both signals, and a driving circuit 3 to which each of the strobe signal, the power supply permission signal and an output of the latch circuit is supplied and which controls the power supply to the heat- generating elements 1 on the basis of an AND of the signals. When the strobe signal and latch signal are simultaneously supplied to the protecting circuit 6, the supply of the power supply permission signal from the protecting circuit 6 to the driving circuit 3 is shut, thereby stopping the power supply to the heat-generating elements 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head incorporated as a printer mechanism for a word processor, a facsimile or the like.

[0002]

2. Description of the Related Art Conventionally, a thermal head incorporated as a printer mechanism such as a word processor has a structure in which a large number of heating elements arranged linearly and a driver IC are mounted on an upper surface of an insulating substrate made of alumina ceramic or the like. have.

The driver IC is provided with a latch circuit for storing print data, a drive circuit for controlling the energization of the heating element, and the like. The driver IC receives a strobe signal from the outside (printer main body). While the is input, the drive circuit controls the energization of the heating element so as to selectively generate heat based on the print data in the latch circuit by the driving circuit. A print is formed.

[0004]

By the way, when the conventional thermal head is incorporated in a printer body and printing is actually performed, a predetermined energization in which a strobe signal is preset due to a failure of a control circuit of the printer body or the like. Even when the time has passed, the data may continue to be input to the thermal head.

However, the above-mentioned conventional thermal head and printer main body are not provided with a means for checking such improper input of the strobe signal and forcibly stopping the strobe signal. The input is continued to the thermal head until the printing operation is completed, and during that time, the heating element also continues to generate heat. In this case, the temperature of the heating element becomes extremely high and deteriorates the heating element itself, so that the electric resistance value of the heating element greatly changes, or the heating element is burned out and the thermal head is used. Had the drawback that it would not be available.

[0006]

SUMMARY OF THE INVENTION The present invention has been devised in view of the above-mentioned drawbacks. A thermal head according to the present invention comprises a plurality of heating elements arranged in a straight line and a latch which is supplied at a substantially constant period. In synchronization with the signal, a latch circuit for storing print data for one line, a strobe signal for determining a current supply time to the heating element, and the latch signal are supplied,
A protection circuit for generating an energization permission signal according to the supply state of both signals, and a strobe signal, an energization permission signal, and an output of a latch circuit are supplied, respectively, and energization to the heating element is performed based on a logical product of the respective signals. A drive circuit for controlling the
When a strobe signal and a latch signal are simultaneously supplied to the protection circuit, the supply of an energization permission signal from the protection circuit to the drive circuit is stopped, and the energization to the heating element is stopped. It is characterized by what has been done.

Further, in the thermal head according to the present invention, the protection circuit counts the number of strobe signals at the rising or falling edge thereof, and resets the count value by a latch signal. And a decoder that generates the energization permission signal only when is equal to or greater than one and supplies the signal to the drive circuit.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. (First Embodiment) FIG. 1 is an equivalent circuit diagram of a thermal head according to a first embodiment of the present invention, wherein 1 is a heating element, 2 is a driver IC, 3 is a drive circuit, 4 is a latch circuit, and 6 is a protection circuit. is there.

The thermal head of this embodiment has a structure in which a heating element array, a driver IC 2 and a protection circuit 6 are respectively attached to an upper surface of an insulating substrate made of alumina ceramic or the like.

The heating element array is formed by arranging a large number of heating elements 1 in a straight line.
In the case of configuring the thermal head i, 1728 heating elements 1 are linearly arranged at a pitch of 127 μm.

The heating element 1 is made of a Ta-based resistance material or Ti
-Based resistance material, Nb-based resistance material, polysilicon (p-S
i) A system resistor material or the like is applied and formed by a conventionally known thin film method, and has a predetermined electric resistance value itself, so that a predetermined power is applied as the driver IC 2 is driven. Then, Joule heat is generated, and the temperature is required to form an image on a recording medium such as thermal paper, for example, a temperature of 90 to 150 ° C.

The driver IC 2 has the same number (number of bits) of driving elements 3, latch circuits 4, shift registers 5 and the like as the number of the heating elements 4 therein. The supplied print data DATA for one line is serially transferred in synchronization with the clock signal CLK, and these print data DATA are synchronized with the latch signal LAT from the printer main body.
To be transferred in parallel.

The latch signal LAT is supplied from the printer body at a substantially constant cycle (within ± 200 msec) immediately before the printing operation of each line starts.
The latch circuit 4 stores and holds one line of print data in synchronization with the latch signal LAT, and outputs it to the drive circuit 3.

The drive circuit 3 includes an output (print data) of the above-described latch circuit 4, a strobe signal STB for determining a power-on time to the heating element 1, and a power-on permission signal Q from a protection circuit 6 to be described later. _A are supplied, and energization of the heating element 1 is controlled based on the logical product of these three signals. The drive circuit 3 is configured by combining, for example, a switching transistor and a gate element.

The protection circuit 6 comprises, for example, a commercially available counter circuit (74ALS90 manufactured by TI), which has a latch signal LAT as a reset signal and a strobe signal as a count signal.
STB is supplied. Said counter circuit 6 generates an energization permission signal Q _A to than one driving circuit 3 of the output terminal in accordance with the supply state of the two kinds of signals LAT, STB mentioned above, especially the two kinds of signals LAT, STB is when supplied at the same time, by discontinued the supply of the driving circuit 3 of the energizing permission signal Q _a, and is adapted to stop the power supply to the subsequent heating element.

The counter circuit 6 has a strobe signal STB.
Is counted at the falling edge, and the count value is reset by the latch signal LAT. Thus the count value in a state in which the strobe signal STB is not inputted even once is 0 (zero), the energization permission signal Q _A in this state is not output, also when the strobe signal STB is input once the count value 1, and the energization permission signal Q _A from the output terminal in this state is outputted. And I'm latch signal LAT is input to the counter circuit 6 count value returns again to 0 (zero) is reset, the output of the energization permission signal Q _A is stopped at the same time, the strobe signal STB is in the control circuit of the printer main body Even if a situation occurs in which the input is improperly continued to the drive circuit 3 even if the predetermined energizing time exceeds a preset energization time due to a failure or the like, the count value of the counter circuit 6 is changed when the next latch signal LAT is received. Then, the power supply to the heating element 1 can be stopped at the same time.

This eliminates the inconvenience that the heating element 1 continues to generate heat until a series of printing operations is completed and the heating element 1 is degraded, and the thermal head is operated in the operation state of the printer main body (whether the signal is supplied correctly or not). ), It is possible to maintain a good state for a long time. Incidentally, when the strobe signal STB continues to be improperly input to the drive circuit 3 as described above, the pulse is not usually temporarily interrupted on the way. Remains at 0 (zero) until the printing operation of is completed.
Power supply to the heating element 1 is stopped.

[0018] Then, after returning to the normal state the input of the strobe signal STB by repair of the printer main body, the newly energized permission signal and the strobe signal STB is input Q _A is generated in the counter circuit 6, the printing operation It will be restarted.

Next, the printing operation of the above-described thermal head will be described with reference to the timing chart of FIG. still,
Of the signals shown in the figure, the strobe signal STB and the latch signal LAT are valid at low level, and all other signals are valid at high level.

First, the shift register 5 of the driver IC 2
In synchronization with the clock signal CLK, the print data DATA of the first line is serially input one bit at a time, and thereafter,
According to the timing of the latch signal LAT, the shift register 5
Is transferred in parallel to the latch circuit 4,
While being held by the latch circuit 4, the count value of the counter circuit 6 is reset.

[0021] Next the strobe signal STB is inputted to the protection circuit 6 and the driving circuit 3, the count value of the counter circuit energizing permission signal Q _A is generated becomes 1, the energization permission signal Q _A and strobe signal predetermined period of time in which the STB are both supplied to the drive circuit 3, i.e., only while the energization permission signal Q _a is and the strobe signal STB at a high level is a low level, all the heating elements 1 are printed in the latch circuit 4 The heat is selectively generated individually on the basis of the data.
The line printing operation is completed.

Next, in the same manner as the printing operation of the first line described above, the printing operation of the second line, the third line,... Is sequentially repeated to perform a series of printing operations. A predetermined print is formed. In the course of such a series of printing operations, if an abnormality occurs in the strobe signal STB and the strobe signal STB continues to be incorrectly input, as described above, as described above, the latch signal LAT to be input next is input. Counter circuit 6 at the timing of
Is reset, and then the strobe signal
Energization permission signal Q _A until the input is inputted newly strobe signal STB return to normal STB does not occur.

Second Embodiment Next, a thermal head according to a second embodiment of the present invention will be described with reference to FIG. still,
The same components as those in the first embodiment described above are denoted by the same reference numerals, and the description of the same components and the description of the operation and effect of these components are the same as those in the first embodiment. Therefore, the description is omitted here. The internal configuration of the driver ICs 2b, 2c and 2d is the driver I
Since it is basically the same as C2a, illustration in FIG. 3 is omitted.

The thermal head of this embodiment is configured so that a large number of heating elements 1 are divided into four blocks and driven in a time-division manner.
Each of the driver ICs 2a, 2b, 2c, and 2d is controlled, and the protection circuit 6 'includes a counter circuit 7 and a decoder 8.

The counter circuit 7 of the protection circuit 6 'includes:
As in the first embodiment described above, the strobe signal STB and the latch signal LAT are supplied. The counter circuit 7 counts the number of strobe signals STB at the falling edge, and outputs the latch signal LAT. Resets the count value by inputting.

[0026] The counter circuit 7, the output terminal Q _A in accordance with the count value, Q _B, issues a predetermined output from the Q _C, and inputs the input terminal A of the decoder 8, B, to C. For example the count value is triggered by the output from the terminal Q _A is set to 1, the count value is triggered by the output from the terminal Q _B when the 2, when the count value is 3 emits output from both terminals Q _A, Q _B , even when the count value is 4 adapted to emit an output from the terminal Q _C.

On the other hand, the decoder 8 of the protection circuit 6 'has five output terminals D ₀ to D ₄ is provided, the signal Q _A supplied on the basis of the count value of the counter circuit 7, Q _B,
Four terminals D _1, except for terminals D ₀ depending on the state of the Q _C, D
₂ , D ₃ , D ₄ , the energization permission signals D ₁ , D ₂ , D ₃ , D
₄ to supply these signals to the driving circuits 3 of the driver ICs 2a, 2b, 2c and 2d for driving the heating elements 1 of the respective blocks. For example the count value of the counter circuit 7 is energized permission signal D ₁ from the terminal D ₁ is set to 1, the energization permission signal D ₂ from the terminal D ₂ when the count value is 2, the terminal D when the count value is 3 _Three
More energization permission signal D _3, and when the count value is 4 energization permission signal D ₄ from the terminal D ₄ is output. When the count value of the counter circuit 7 is 0 (zero), the terminal D
₀ from emitting an output, but since the terminal D ₀ is not connected to any of the driver IC, the latched signal LAT input count value of the counter circuit 7 is reset to 0 (zero), energization permission signal Is not supplied to the driver IC, so that the heating element 1 is not energized in any of the blocks.

In such a thermal head of the second embodiment, the protection circuit 6 'also supplies the energization permission signals D ₁ , D ₂ , D in accordance with the supply states of the latch signal LAT and the strobe signal STB.
₃ is adapted to generate a D _4, similar to the thermal head of the first embodiment, when the two kinds of signals LAT, STB is supplied simultaneously with discontinued the supply of energization permission signal to the drive circuit 3 The energization of the heating element 1 thereafter is stopped.

Therefore, even if the strobe signal STB continues to be improperly input to the drive circuit 3 even if the strobe signal STB exceeds the predetermined energization time due to a failure of the control circuit of the printer body or the like, the above-described situation occurs. The protection circuit 6 'can stop the energization of the heating element 1 thereafter, and can maintain the thermal head in a good state for a long time regardless of the operation state of the printer main body.

Next, the printing operation of the thermal head of the second embodiment will be described with reference to the timing chart of FIG. The strobe signal ST among the signals shown in FIG.
B and the latch signal LAT are signals that are valid at low level, and all other signals are signals that are valid at high level.

First, the print data DATA of the first line is serially input one bit at a time to each of the shift registers 5 of the driver ICs 2a to 2d in synchronization with the clock signal CLK. The print data in the register 5 is transferred to the latch circuit 4 in parallel, is held in the latch circuit 4, and the count value of the counter circuit 7 is reset.

[0032] When the strobe signal STB of Me 1 pulse is input to the protection circuit 6 'and the driving circuit 3, the output Q _A from the counter circuit 7 count value of the counter circuit 7 is 1 occurs and this synchronization energized permission signal D ₁ from the decoder 8 is generated. The energization permission signal D ₁ and the predetermined period and the strobe signal STB are both supplied to the drive circuit 3 of the driver IC 2a, i.e. energizing permission signal D ₁ only during and strobe signal STB at a high level has become low, The heating elements 1 of the first block corresponding to the driver IC 2a selectively and individually generate heat based on the print data in the latch circuit 4, whereby the first line of the first line is heated.
The printing operation of the block is performed.

Next, the strobe signal STB of 2nd pulse to the protective circuit 6 'is input, from the counter circuit 7 outputs Q _B generated by the count value of the counter circuit 7 is a two synchronized thereto Accordingly, the energization permission signal D ₂ is generated from the decoder 8. The energization permission signal D ₂ and the strobe signal STB
DOO predetermined period together supplied to the drive circuit 3 of the driver IC 2b, i.e. energizing permission signal D ₂ only during and strobe signal STB at a high level is a low level, the second block corresponding to the driver IC 2b Heating element 1
Are selectively and individually heated based on the print data in the latch circuit 4, whereby the print operation of the second block of the first line is performed.

Thereafter, when the strobe signal STB of the third and fourth pulses is sequentially input, the driver I
The heating elements 1 of the third block and the fourth block corresponding to C2c and 2d are sequentially heated and driven, and the printing operation of the third block and the fourth block is performed. This completes the printing operation of all the blocks on the first line.

A series of printing operations are performed by repeating the above-described time-sharing drive in the same manner as the first line, that is, the second line, the third line,..., And a predetermined print is formed on the recording medium. You.

In the case of the thermal head of the second embodiment, the protection circuit 6 'generates four kinds of energization permission signals D ₁ , D ₂ , D ₃ , and D ₄ in sequence from the plurality of strobe signals STB, thereby obtaining four signals. Since the heating element 1 of the block can be driven in a time-division manner and the plurality of strobe signals STB input to the protection circuit 6 'are sequentially supplied one pulse at a time,
All of these strobe signals STB can be input to the protection circuit 6 'or the like through one signal line, and compared with the case where a plurality of strobe signals STB are supplied through separate signal lines, the thermal head, the printer body, Connection points can be reduced.

It should be noted that the present invention is not limited to the above-described two embodiments, and various changes and improvements can be made without departing from the gist of the present invention.

For example, in the above-described first and second embodiments, the strobe signal valid at the low level is used, so that the number of strobe signals is counted at the falling edge. May be used, and in that case, the counter circuit is set to count the number of strobe signals at the rising edge.

When the number of blocks of the heating element 1 in the thermal head of the second embodiment is increased to 5 or more, a counter circuit and a decoder may be added correspondingly. For example, when the heating element 1 is divided into seven blocks and divided and driven, the counter circuit can be increased by 1 bit and the decoder can be increased by 3 bits.

[0040]

According to the thermal head of the present invention, when the latch signal and the strobe signal are simultaneously supplied to the protection circuit, the supply of the energization permission signal to the drive circuit is terminated. Even if the power supply continues to be improperly input even if the preset power supply time exceeds a predetermined power supply time due to a failure in the control circuit of the printer body or the like, the power supply to the heat generating element by the protection circuit is performed by the protection circuit. Can be stopped, and the thermal head can be maintained in a good state for a long time regardless of the operation state of the printer main body.

[Brief description of the drawings]

FIG. 1 is an equivalent circuit diagram of a thermal head according to a first embodiment of the present invention.

FIG. 2 is a timing chart when printing is performed using the thermal head of the first embodiment.

FIG. 3 is an equivalent circuit diagram of a thermal head according to a second embodiment of the present invention.

FIG. 4 is a timing chart when printing is performed using a thermal head according to a second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Heating element 3 ... Driving circuit 4 ... Latch circuit 6, 6 '... Protection circuit

Claims (2)

[Claims] A plurality of heating elements arranged in a straight line; a latch circuit for storing print data for one line in synchronization with a latch signal supplied at a substantially constant cycle; A strobe signal for determining time and the latch signal are supplied, and a protection circuit for generating an energization permission signal in accordance with a supply state of both signals; and a strobe signal, an energization permission signal, and an output of the latch circuit are supplied, respectively. And a drive circuit that controls energization of the heating element based on a logical product of the signals of the above. When a strobe signal and a latch signal are simultaneously supplied to the protection circuit, the protection circuit drives the drive circuit. A thermal head that cuts off the supply of an energization permission signal to the heater and stops energization of the heating element. 2. A counter circuit for counting the number of strobe signals at its rising or falling edge and resetting the count value by a latch signal, only when the count value of the counter circuit is 1 or more. 2. The thermal head according to claim 1, further comprising a decoder for generating the energization permission signal.