JP3037169B2 - Thermal printer dot abnormality detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head dot abnormality detection circuit in a thermal printer.

[0002]

2. Description of the Related Art Conventionally, various measures have been considered to prevent the occurrence of missing dots and uneven density in the printing result of a thermal printer. As a typical example, there is a resistor insertion method described in the specification of Japanese Patent Application Laid-Open No. 61-19375 (thermal head burnout detection circuit).

In this resistance insertion method, a resistor is inserted between the heating element of the thermal head and the power supply before printing, the voltage drop is detected by a potential difference detection circuit, and read by a microprocessor to read the heating element of the thermal head. This is a method for determining burnout and deterioration. In this method, since the voltage drop of the detection resistor is read by the microprocessor, the variation of the resistance value of the heating element of the entire thermal printer can be detected.

[0004]

The above-mentioned conventional method of detecting missing dots of a thermal head is a method of detecting burnout and deterioration of the thermal head before printing. Even if it happens, there is a disadvantage that printing is continued and print quality is impaired.
If the current-carrying transistor to the heating element is damaged during printing, there is a possibility that the heating element without problems will continue to be energized and the heating element may be damaged.

SUMMARY OF THE INVENTION An object of the present invention is to provide a thermal printer with a heating element for burning and deterioration during printing.
Another object of the present invention is to provide a print dot abnormality detection circuit capable of detecting breakage of an energizing transistor that energizes a heating element.

[0006]

SUMMARY OF THE INVENTION The first invention is a thermal printer that detects the current flowing through the heating elements of the service over Mar printer, detects a dot abnormality of the thermal printer by the combination of the current value and the head energizing pulse signal In the dot abnormality detection circuit, when the current value flowing through the heating element is larger than a predetermined current reference value and the head energizing pulse signal is OFF, it indicates that a dot abnormality has occurred in the thermal printer. A dot abnormality detection circuit for a thermal printer, which outputs a detection signal.

[0007]

[0008]

According to a fourth aspect of the present invention, there is provided a dot abnormality detecting circuit for a thermal printer, wherein a head heating element on an energizing line of an energizing transistor prints dots due to heat generated by energization when the energizing transistor is ON. A detection resistor inserted on the current supply line for detecting a current flowing through the head heating element, a comparator for amplifying a signal detected by the detection resistor with an operational amplifier and comparing the amplified signal with a preset current reference value; Exclusive OR of the output signal of the comparator and the head energizing pulse signal which is a print control signal
And an exclusive OR circuit which takes the following formula:

[0010]

[Operation] A current flowing through a heating element is detected by a detection resistor (detection resistor 3 in FIG. 1) and compared with a reference value by a comparator (comparator 7 in FIG. 1). The result is combined with the head energizing signal (head energizing signal 11 in FIG. 1) to generate an alarm signal (detection signal) when the heating element (heating element 2 in FIG. 1) and the energizing transistor (transistor 4 in FIG. 1) are damaged. 8) is output to enable alarm processing.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of a dot abnormality detecting circuit of the present invention in a one-dot printing circuit.

According to the structure of the present invention, a detection resistor 3 for immediately detecting a current flowing through the heating element 2 is provided on a line of a power supply 1, a head heating element 2, and a conduction transistor 4, and the detected signal is amplified by an operational amplifier 5. In addition, a comparator 7 is provided in order to compare with a preset current reference value 6. Also, an exclusive OR of the output signal of the comparator 7 and the head energizing pulse signal 9 is obtained.
xclusive OR10. here,
The head energization pulse signal 9 is a print control signal that takes into account history control and the like, and is input to the gate of the energization transistor 4.

The operation of this detection circuit is as follows. The current flowing through the heating element 2 is detected by the detection resistor 3 as needed, and the minute current is sufficiently amplified by the operational amplifier 5. In comparison, an alarm signal (detection signal 8) is generated in combination with the head energizing pulse signal 9, and the process proceeds to alarm processing.

Here, in the first case where the heating element is burned out and deteriorated or the transistor is in the open state, the detected current value of the output of the operational amplifier 5 is changed to the current reference value 6.
The alarm signal (detection signal 8) becomes active when the head energizing pulse signal 9 is ON,
Move on to alarm processing.

In the second case, in which the heating element energizing transistor 4 is in a short state, the detected current value of the output of the operational amplifier 5 becomes higher than the current reference value 6 and the head energizing pulse signal 9 is in the OFF state. The alarm signal (detection signal 8) becomes active, and the process proceeds to alarm processing.

The alarm processing should be performed according to the system. For example, S / W (software)
It is also an effective process to stop printing by a method such as a power supply voltage stop in the above.

By the above-described alarm processing, when the above-described first case occurs, it is possible to prevent a decrease in print quality due to continuous printing, and when the above-described second case occurs, the print quality is reduced. In addition to preventing the heating element from being lowered, there is an effect that the heating element can be prevented from being damaged. This prevents current from flowing through the heating element at all times when the transistor 4 for energizing the heating element is damaged and is in a short-circuit state, thereby preventing the heating element from being eventually burned out. In other words, it is possible to prevent the thermal head from being burned due to the temperature exceeding the rating of the heating element due to continuous printing regardless of the print data.

FIG. 2 is a time chart for explaining the operation of the present invention. In FIG. 2, normal operation (section A)
Since the normal printing operation is performed, the detection signal 8 becomes non-active. Next, when the transistor is open or the heating element is damaged or deteriorated (section B), no current flows through the current detection resistor even if the head energizing pulse signal is turned on, and the output of the operational amplifier 5 becomes "0". Since the output of the comparator 7 becomes "0", the detection signal 8
Becomes active.

Finally, when the transistor is short-circuited (section C), the detection signal 8 becomes active because the output of the comparator 7 becomes "1" even though the head energizing pulse signal is in the OFF state.

In the sections B and C, the processing shifts to the alarm processing, and printing is stopped by, for example, stopping the power supply voltage in S / W.

By providing the above-described dot abnormality detection circuit of the present invention for the heating elements of the thermal head, it is possible to immediately detect the state of damage to each heating element during printing, and to provide a plurality of heating elements. If the current value is set for each block and is controlled for each block, it can be realized at low cost.

If the current reference value 6 can be changed (that is, the register can be written from the software side), even if the thermal head is changed to another manufacturer, the current reference value 6 can be changed without changing the main circuit. Can be changed.

[0025]

As described above, according to the present invention, it is possible to detect burnout and deterioration of the heating element and breakage of the short-circuit mode of the transistor for energizing the heating element even during printing, immediately shift to alarm processing, and detect abnormalities such as missing dots. Since the printing operation of the thermal printer in which the error occurs can be stopped, the problem of deteriorating the printing quality can be solved. Further, when the short circuit of the heating element conduction transistor is broken, the conduction of the heating element can be stopped, so that the element can be protected from burning.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of a dot abnormality detection circuit of the present invention.

FIG. 2 is a time chart for explaining the operation of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 power supply 2 head heating element 3 detection resistor 4 conduction transistor 5 operational amplifier 6 current reference value 7 comparator 8 detection signal 9 head conduction pulse signal 10 Exclusive OR

Claims (2)

(57) [Claims] 1. A detects a current flowing through the heating elements of the service over circle printer, the dot abnormality detecting circuit of a thermal printer that detects the dot abnormality of the thermal printer by the combination of the current value and the head energizing pulse signal, the heating element When the current value flowing through the head is larger than a predetermined current reference value and the head energizing pulse signal is OFF,
A dot abnormality detection circuit for a thermal printer, which outputs a detection signal indicating that a dot abnormality has occurred in the thermal printer. 2. The method according to claim 1, wherein the current supply transistor is located on a current supply line.
The heating element is turned on when the energizing transistor is ON.
Dot of thermal printer that prints dots due to heat generated by
In the abnormality detection circuit,
The electric current flowing through the head heating element
Detector for detecting flow
The amplified signal is amplified by an operational amplifier and set in advance.
Comparator for comparing with current reference value and its comparator
Head output pulse signal, which is the
Exclusive OR with Exclusive
and a OR circuit.
Linter dot error detection circuit.