JPS5935958A - Protective device for thermal head - Google Patents

Abstract

PURPOSE:To prevent a heating resistor from being broken by heat, by controlling a driving circuit through detecting an overlapping inputting of printing commands at the same dot position. CONSTITUTION:A 2-bit binary counter 38 provided in a printing command detecting circuit 35 counts current-passing signals 11A fed from a main controller, is reset by a driving signal 15A for a thermal head carriage moving motor which signal is fed from an auxiliary controlling part, and when the counted value becomes 2 due to overlapping of the printing commands at the same dot position, an overlapping input detection signal 35A is outputted. This signal 35 inverts to a low level the output of an AND gate 24 which output is reduced to a low level also by an overcurrent detection signal 37A from a current- detecting circuit 37, an excess current-passing period detection signal 36 from a current-passing period detecting circuit 36 or the like. Then, supply of an electric current to a thermal head driving circuit 32 is interrupted by a switching circuit 31, and the heating resistor 51 is prevented from being broken due to overheating.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermal head protection device.

A printing device equipped with a thermal head prints predetermined dot characters on thermal paper by selectively energizing a heating resistor provided in the head.

Conventionally, this type of printing device has been equipped with a protection device that prevents the heating resistor from being destroyed or the driver circuit or the like from being destroyed due to abnormal energization of the heating resistor. Specifically, an overcurrent or an excess of the energization time is detected from the conduction state of the heating resistor, and the operation of the driver circuit is controlled on and off.

However, in such conventional technology, the transistor of the driver circuit is destroyed due to variations in the resistance value of the heat generating resistor or a decrease in the resistance value due to aging, etc., and this causes the heat generating resistor to In a printing device where the paper surface and the thermal head move relative to each other, heat generated when printing is repeatedly performed on the same location on the paper surface for some reason. There was a drawback that it was impossible to prevent thermal breakdown accidents due to overheating of the resistor.

The present invention has been made in view of the above-mentioned drawbacks of the prior art, and prevents the thermal head from repeatedly printing on the same location on the paper, thereby preventing thermal damage to the heat generating resistor and, in turn, improving driver circuits, etc. Its purpose is to prevent the destruction of

The present invention detects a thermal head that moves relative to the paper surface, a four-way driver that energizes the thermal head in response to a print command, and the overlap of the human power of the print command at the same dot position with respect to the paper surface. This is what I am trying to do.

Hereinafter, one embodiment of the present invention will be explained based on FIG. 1 and FIG. It is a circuit diagram. In FIG. 1, a control section 1 of the printing device is a main control section 3. Sub-control unit 4
The main control section 3 has a function of controlling print data to be printed by the thermal head 5 of the printing section 2,
The sub-control unit 4 controls the movement of a carriage (not shown) on which the thermal head 5f is mounted, and a protection circuit 6 to be described later.
It has the function of monitoring various abnormal signals output from. The main control unit 3 includes a central processing value +vt<cpU) 7 for performing data processing and judgment, a ROM 5 containing control programs and character patterns, an LLAM 9 for temporarily saving data and storing addresses, etc.
Print data output boat 10. It is composed of a timer 11. - The sub-control unit 4 includes a central processing unit (CPU) 15 for data processing and judgment, a control program, and an excitation pattern for a stepping motor (not shown) for moving the gear ridge; Temporarily saves and stores addresses, etc. l(, AIVl
17, a timer 18, an excitation data output boat 19, and an abnormal data human-powered boat 20.
The P U I 5 and the CPU 7 of the main control section 3 are interconnected through a human output port 21 .

When the CPU of the main control unit 3 receives character data from the outside according to the program built in the RAM 9, it sequentially stores all character data in the RAM 9. -Do you manually create line data or use C?
When the CPU 7 receives control side 1 data such as R, LF', etc.
CPU 17 of the sub-control unit 4 via the human output boat 21
Give a print start command to ; and start moving the carriage. Subsequently, the CP tJ 7 reads out the corresponding character pattern from the Lt OM 8 based on the character data stored in the It AM 9, sends dot data for each column of one character to the print data output port 10, and One dot energization time data is set in the timer 11 at a predetermined timing. Timer II immediately outputs a high-level energization signal 11A to the print data output port 10 as soon as the energization time data per dot is set.2. The output signal is output to the printing unit 2 as one of the printing commands, and timing is started, and when the time represented by the energization time data has elapsed, the energization signal output is stopped and the output level is set to low. The print data output port 10 is connected to the timer 1.
It is enabled while the energization signal is input from 1 to the printing section 2, and print data for one force ram preset at the input end is sent to the printing section 2 as the printing signal 10A, which constitutes one of the printing commands.
K is set to output to the driver circuit wJ32.

10,000, When the CPU 15 of the sub-control unit 4 receives a print start command from the CPU 7 via the input/output 5-board 21, the CPU 15 executes a predetermined command read out from the ROM 16 to the RAM 17 in accordance with a predetermined program stored in the ROM 16. Based on the excitation pattern data and the excitation time data of each step, excitation data of the stepping motor is sent out to the excitation data output port 19 for each step, and then the excitation time data of the step is set in the timer 18.

Immediately after the excitation time data is set, the timer 18 sends out an enable signal to the excitation data output port 19 and starts timing, and stops outputting the enable signal when the excitation time has elapsed. The excitation data output capo) 19 is a timer 18.
While the enable signal is being input from the input side, the excitation data for one step preset on the input side is output to the stepping motor drive circuit to rotate the stepping motor. The CPU 5 also prints a motor drive signal 15A that is at a low level for a short period of time after presetting the excitation data to the full excitation data output port and before setting the excitation time data to the timer 18. Output to section 2. This motor drive signal 15A is a VC so that it is sent out at each step.

Configured like this '71. On the open side +g + t1r,
While the carriage on which the thermal head 5 is mounted is moved laterally by the sub-control unit 4, the main control unit 3 outputs a printing command (Tsu Denshin Publishing - and print signal output) at a predetermined timing, thereby controlling the thermal head 5. 1 so that all the prescribed prints are completed.゛Also Vice Control Octopus Part 1 4 CP
Various abnormality signals, which will be described later, are received via the L115PCi"1 abnormality data input port 20.
When the CI-" U15 receives an abnormal signal, an interrupt is generated, and when the type of abnormality is confirmed, the output of excitation data to the stepping motor side is stopped, and the abnormal signal is detected.
``i+ is sent to the CP of the main control unit 3 via the human output boat 21.
Send to U7.

When an abnormality signal is detected, the CPU 7 generates an interrupt sound, confirms the type of abnormality, stops printing command output (printing signal output, or printing signal and direct signal output), and stops the lamp driver 12. It has a function of not only flashing all the warning lights and issuing a warning to the operator, but also sending an alarm signal to an external computer etc. to stop character data output.

Next, the specific configuration of the printing section 2 will be explained based on FIG. 2. The printing section 2 is 1! It is composed of a driver circuit 32 and a thermal head 5 connected to t@30 via a switch circuit 31, a protection circuit 6 for the thermal head 5, and the like. Telecommunication message +3 sent from the main control unit 3
'llA is manually inputted to the switch circuit 31 via the AN I) circuit 34. This A N
I) Circuit 34V - Also, each abnormal signal described later, that is, printing command duplication signal 35A5 energization time over signal 36
A, overcurrent (No. The signal is output to the switch circuit 31.The switch circuit 31 closes the switch and turns on the power 30f to the driver circuit 32 only while the energization signal 11A is being input.

driver (bar circuit 32ij, driver transistors 61, 62, . . . provided corresponding to each of the heat generating resistors 51, 52, .
・ are installed in parallel, each transistor 61, 62
．． Base terminal 61A of...

The print signal 10A, which is the output of the print data output capacitor 10, is individually input to the dots 62A, . . . in accordance with the dot positions. -10,000, heating resistors 51, 52 forming the thermal head 5. ...The other end is the detection resistor 71
,72. . . , and when the switch circuit 31 is closed, the transistors 61, 62 .
When the print signal 10A is input to the transistors 61, 62 . ... are electrically connected, and the heating resistors 51, 52 .
. . generates heat from tK to perform predetermined dot printing. At this time, the heating resistors 51, 5
2. The current flowing through the detection resistors 71, 72, .・
... is converted into a -9- voltage by diodes 81, 82, . ...-protective resistance 91°92
, . . , and then outputted to an energization time detection circuit 36 and a current detection circuit 37, which will be described later. The detection resistors 71, 72, . . . also include heating resistors 51, 52, . It also has the function of reducing the variation in the resistance value of...

The protection circuit 6 includes a print command detection circuit 35, an energization time accumulation circuit W&36, and a current detection circuit 37. The printing command detection circuit 35 counts the energization signal 11A sent from the main control section 3, and generates a 2-bit binary signal that clears the counted value when the motor drive signal 15A sent from the sub-control section 4 is manually operated. - consists of a counter 38; This counter 38 receives the energization signal 11A when the main control 4141 section 3 and the sub-control section 4 are operating normally.
The next energization signal 11A after the counter 3BVC is manually powered
Since one or more motor drive signals 15A are always input before the motor is manually operated, the count value is (0) or (1).
), and apart from this, due to a failure in the front ml tie 10-mer 1.1, etc., the motor drive signal 15A was passed even though there was no human power. When the signal 11A is manually input twice in succession, that is, when the printing unit 2 receives a duplicate printing command from 1 to 1 without the thermal head 5 moving, the count value is set to (2). Print the upper digit data “1”
The above A, N l) circuit 34 as the first instar duplicate signal 35A.
and has a function for outputting to the abnormal data input boat 20.

The energization time detection circuit 36 includes the detection resistors 71 and 72.
．．・−・detection voltage of diode 81°82,...
, protective resistance 91, 92 . A switching transistor 40 that is input to the pace via a . A resistor 44 controls the pace 'ft current of the transistor 40 and
This is to prevent the shadow W from affecting the input terminal of the comparison circuit 47 side of the C overcurrent detection circuit 37, and the resistor 45
is the collector resistance of the power supply 46N. The transistor 40 includes a heating resistor 5], 52. ...When any of them is energized, it becomes conductive and turns ON, and the terminal =
It is designed to output a level energization detection signal. This energization detection signal is inverted to a high level by the inverting circuit 41, and then sent to the timer 42 and 1).
Manual power is applied to the D terminal of 3. When the energization detection signal is input, the timer 42 starts timing at the same time as a full high signal is output to the clock terminal CK of the D-F/l, +43, and the timer 42 starts counting for a predetermined set time, for example, the heating resistors 51, 52, .・
1) after twice the normal energization time has elapsed.
"/F43's CK high input is set to a low level. In the D-F/F43, while a high-level energization detection signal is input to the 1-) terminal, the input of the terminal CK is high. When the signal changes from to low, the corresponding terminal input is transferred to the Q terminal, and a high-level energization time over signal 36A is output from the Q terminal to the AND circuit 34.

Further, the overcurrent detection circuit 37 includes the detection resistor 't1
,72. The detection voltage of ... is connected to the diode 81゜82, ・
..., protective resistance 91, 92. A comparator circuit 47 which inputs a constant voltage obtained by dividing the voltage of a power supply 48 by a resistor 49 and a Zener diode 50 into the other terminal, and a high output of this comparator circuit 47. and a latch circuit 39 that latches the . Comparison 1 1 approximately 47 is a predetermined voltage in which the detection voltage of the detection resistors 71, 72, . For example, the setting value of the heating resistor 51, 52. When a voltage associated with a current value twice the normal energization current is input to the A'tl distribution terminal, a high-level overcurrent detection circuit is output to the launch circuit 39. ing. Once the overcurrent detection circuit is input, this latch circuit 39 latches it and outputs a high level overcurrent signal 37Ai to the ANI) circuit 34.
Output to.

As mentioned above, this AND times %34 is the printing command detection circuit 359 energization time detection times %36゜overcurrent horizontal 1 old (2) path 37 as an abnormal signal from either of the printing command duplication signals 35A9 energization time When one of the over signal 13- signal 36A and the over current signal 37A is input manually, the output is set to a low level, the switch circuit 31 is opened, and the driver circuit 32 is disconnected from the power source 30. With the protection circuit 6 configured in this way,
First, even if a duplicate print command is given to the thermal head 5 before the carriage is not moved due to a timer 11 (LD failure, etc., the power supply 30 drives the thermal head 5).
Since the heating resistors 51, 52 . ... and the accompanying destruction of the driver circuit 32, etc., can be reliably prevented, and the heating resistors 51, 52,
. . due to a decrease in the resistance value of the heating resistors 51, 52. Even if the energization time exceeds or an overcurrent occurs, it is possible to immediately disconnect the thermal head 5 from the power source 30 to prevent damage to the thermal head 5 and to prevent damage to the driver circuit 32 and the like.

These protective operations are performed independently within the printing section 2, so even if an abnormal state occurs due to runaway of the CPU 7 or I Flit software of the control section 1, the thermal head 5 can be safely operated. I was able to protect Hitomi, which is 1.
Since it is possible to deal with three types of abnormalities, the safety and reliability of Destruction Prevention 1 is increased.

As mentioned above, each abnormality signal from the protective circuit 6 is received by the CPJ7, 15 side of the control unit 1, and once an abnormality occurs, the carriage is immediately stopped, and It is possible to stop printing signal output, prevent unnecessary printing operations, and prevent locally occurring destructive accidents from spreading to other areas.

Even if an abnormality occurs, if the switch circuit 31 does not open, the thermal head 5 can be prevented from being damaged by stopping the print-IA output. In the past, the CPU 7 notifies the operator, informs an external computer, etc. of the occurrence of an abnormality, stops the transmission of character data stored in that computer, and also temporarily disables all data from being rewritten. With RZ, you can protect your data from everything. It should be noted that when the faulty part is repaired, each part of the apparatus can be returned to a normal operating state by supplying a reset signal from the outside.

In the above embodiment, the counter 38 counts the printing commands sent from the main control section 3 to the printing section 2 based on the energization signal 11A. Also, the signal for clearing the counter 38 may be based on the output of a shaft encoder or the like that detects the movement of the carriage, rather than the motor drive signal 15A output from the CPU 15. It may also be configured to use a signal.

As described above, according to the present invention, thermal damage to the thermal head that occurs when the thermal head is repeatedly energized while it is stopped relative to the paper surface, as well as damage to the driver circuit, etc. caused by this, can be easily prevented. A thermal head protection device can be obtained which has the excellent feature of being able to prevent the occurrence of damage in advance and reliably.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a control section of a printing device according to an embodiment of the present invention, and FIG. 2 is a block diagram showing a printing section. . ■...control unit, 5...thermal head, 6...retention circuit, 30...power supply, 31...switch circuit, 3
2... Driver circuit, 35... Print command detection circuit, 36... Current time detection circuit, 37... Overcurrent detection 1 channel. %Thf Applicant Bentel Co., Ltd. 17-

Claims (1)

[Claims] (1) 9 A thermal head that moves relative to the paper surface, a driver circuit that energizes the thermal head in response to a print command, and a head that detects the duplicate human power of the print command at the same dot position with respect to the paper surface. Protective device.