JPH11208006A - Method and system for detecting abnormality of resistance value of thermal head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To automatically detect abnormality of a resistance value of a heat- generating resistance body of a thermal head by adapting a group of heat-generating resistance bodies divided in constant units of blocks to be selected and switched in parallel so that every one elements in the blocks are compared at the same time with the use of a plurality of switch circuits. SOLUTION: At a start-up time a power source of a thermal printer or at an inspection mode during a standby time, a control means 1 sets a reference voltage-setting signal to a comparison judgment means 5 so as to set a reference value which becomes a variation allowance range of an average resistance value of a thermal head. Then, the control means 1 outputs a control signal (b) to a switch detection means 4 to select one heat-generating element of a heat-generating resistance body drive means 3. At the same time, the control means outputs a printing control signal (c) and supplies electricity to a heat-generating resistance body. Because of the supply of electricity, a detection voltage generated at a detection resistor is inputted as an amplification signal (f) through the switch detection means 4 to the comparison judgment means 5, and compared with a reference voltage value. The judgment result is inputted to a judgment hold means 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head of a thermal recording type using thermal paper or a thermal transfer type using an ink ribbon having a thermal layer, having a heating element group in which a plurality of heating resistors are arranged in a line. The present invention relates to a thermal printer including:

[0002]

2. Description of the Related Art As one of typical methods for detecting an abnormality of a heating resistor of a thermal head in a conventional thermal printer, a constant current connected to the thermal head as shown in FIG. A circuit is provided, the circuit sequentially supplies current to one heating element, and the potential generated at the heating resistor is converted into a digital signal by an A / D converter. The CPU stores this value in a memory and compares it with a reference value. There is a way. FIG.
In 38037, the resistance value of a predetermined heating resistor and the resistance value of a neighboring heating resistor are measured by using the continuous characteristic of the resistance value of the heating resistor, and the CPU fetches those values to obtain a difference between the two. Is calculated, and the difference is compared with a reference value.

[0003]

SUMMARY OF THE INVENTION The first of the above-mentioned prior art examples
The problem is that, when a constant current circuit is provided and current is sequentially supplied to each heating resistor, and the generated potential is A / D converted and taken into the CPU, all of them are controlled via the CPU. In the thermal head having the heating resistor described above, the processing time becomes longer.

The reason for this is that the resistance value of one heating resistor is stored in a memory, and a serial processing process is performed on all the heating resistors until all the resistors are completed and compared with a reference value.

The second problem is that, even when the continuous characteristic of the resistance value of the heating resistor is used, detection of the resistance value, calculation of the difference from the resistance value of the neighboring heating resistor, and comparison processing with the reference value are performed. All are controlled by the CPU, and a lot of processing time is spent.

The reason is that the process is a serial process similar to the reason of the first problem.

An object of the present invention is to automatically detect an abnormality in the resistance value of a thermal head heating resistor without manual operation,
It is another object of the present invention to provide a thermal printer capable of performing high-speed detection.

[0008]

In order to achieve the above object, in the thermal head abnormal resistance detection method according to the present invention, the control means sets a reference voltage setting signal to a comparison / determination means, and step 201 comprises: Is a step 202 for outputting a control signal to the switching detection means 202, selecting 203 one of the heating elements of the thermal head heating element group, and outputting the control signal and simultaneously outputting a printing control signal to the heating resistor driving means. A step 204 of passing a current through the heating element, inputting a detection potential generated in the detection resistor to the comparison determination means and comparing it with a reference voltage value, and holding a determination signal of the comparison result in the determination holding means 205; If there is no heating element to be detected next 206, the control means reads out the judgment signal held in the judgment holding means, stores it in the memory 207, Step 20 for detecting the presence or absence of abnormal
9 and step 210 for performing error processing if there is an abnormality
And a step 211 of performing each step for both the upper limit value and the lower limit value of the reference voltage.

The thermal head resistance value abnormality detection system according to the present invention includes a heating resistor driving means 3 for driving a heating resistor and passing a current, and one of the heating resistors divided into fixed blocks. Switching detection means 4 for detecting a potential corresponding to the resistance value of the selection, switching, and heating resistor, comparison determination means 5 for comparing the detected potential with a reference voltage value, and determination holding means 2 for holding the compared determination signal; And control means 1 for controlling the setting of the reference voltage value, the switching operation of the heating resistor, the printing operation, and the reading of the status of the judgment signal.

In one embodiment, the control means 1 comprises a CPU 1b and a memory 1a which perform a process of simultaneously comparing one element at a time in each block of the detection elements and sequentially performing the comparison.

The heating element driving means 3 includes a detection resistor 3a for generating a potential when a current flows through the heating element,
A heating resistor 3b, a driving transistor 3c, and a gate element 3d incorporated corresponding to one heating element in the heating element group, and a print control circuit 3 for supplying a current to the selected heating element.
e is one embodiment.

The switching detecting means 4 includes a switching signal generating circuit 4a for outputting a switching signal to the switching circuit, and a switching circuit 4 for selecting one heating element from a group of heating elements in block units.
In one embodiment, the circuit comprises an amplifier c and an amplifier circuit 4b.

The comparing and judging means 5 receives the amplified detection potential, compares it with a set reference voltage and outputs a judgment signal, and a reference voltage setting signal output from the control means. One embodiment includes a reference voltage setting circuit 5b for setting a reference voltage.

In one embodiment, the judgment holding means 2 is a latch circuit 2a for holding a judgment signal.

[0015]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a system to which a method for detecting a thermal head resistance value abnormality according to the present invention is applied.

As shown in FIG. 1, this embodiment comprises a control means 1, a judgment holding means 2, a heating resistor driving means 3, a switching / detection means 4, and a comparison judgment means 5.

First, the control means 1 sets a reference voltage setting signal g to set a reference value within an allowable range of the average resistance value of the thermal head for the purpose of detecting the presence or absence of an abnormality in the resistance value of each heating element. Is set in the comparison determination means 5.

Here, it is assumed that the average resistance value of the heating resistor is known, and that the setting of the applied energy according to the average resistance value is completed in the printer. As for the reference voltage setting signal g, the control means 1 calculates an allowable range of the resistance value variation from a known average resistance value, and first sets either the upper limit value or the lower limit value.

FIG. 4 shows the upper limit value and the lower limit value which are the reference voltage values input to the reference voltage setting circuit of the thermal head resistance value abnormality detecting circuit in the thermal head drive control circuit of the present invention. The control means sets the limit value of the variation allowable range according to the average resistance value of the body.

This variation range is determined and set by agreement with the thermal head maker, for example, within ± 10%. The control means simultaneously compares the resistance value of the heating resistor of the thermal head within this allowable range one element at a time for each block, and confirms whether all the heating elements are abnormal.

The control means 1 outputs a control signal b to the switching detection means 4 so as to select one heating element of the heating resistor driving means 3. At the same time, the control means 1 outputs a print control signal c to the heating resistor driving means 3 in synchronization with the control signal b, and causes a current to flow through the heating resistor.

When the current flows, a detection potential e is generated in the detection resistor, and is input to the comparison / determination means 5 via the switching detection means 4 as an amplified signal f. Further, the amplified signal f is compared with the reference voltage value set in the comparison determination means 5, and a determination signal i is input to the determination holding means 2.

If there is an abnormality in the resistance value of the heating resistor, the judgment signal i is held until the judgment holding means 2 resets it. When the detection of all the heating elements is completed, the control means 1 reads the status of the judgment holding means 2, detects the presence or absence of an abnormality, and executes a necessary processing process.

Finally, the control means 1 stores the detection result in a memory and saves it as a history, where all detection processing is completed.

As described above, it is possible to detect an abnormality in the resistance value that causes a missing dot or light printing.

Next, the operation of the embodiment of the present invention will be described in detail with reference to FIG.

First, the control means 1 instructs the comparison / determination means 5 to set the upper limit value of the allowable variation range of the average resistance value of the thermal head.
A reference voltage setting signal g serving as a lower limit value is output, and either the upper limit value or the lower limit value is set first, step 2.
01.

After the setting, the control means 1 outputs a control signal b to the switching detection means 4 to generate a switching signal d, and step 202, selects one heating element of the thermal head heating element group, step 203 . At the same time, the control means 1 outputs a print control signal c synchronized with the switching signal to the heating resistor driving means 3 to flow a current to the selected heating element.

Thereafter, the detection potential e generated in the detection resistor is amplified to obtain an amplified signal f, which is input to the comparison determination means 5 and compared with the reference voltage value, step 204.

A decision signal i is output to the decision holding means 2 as a result of the comparison and is kept being held, step 205. In addition,
The judgment holding means 2 is held once it is reset once the abnormality judgment signal is inputted.

The control means 1 determines whether there is a next heating element, and if there is a step 206, returns to step 202 and repeats the same operation. If there is no next heating element, the judgment signal i held in the judgment holding means 2 is read out, stored in the memory in the control means 1 in step 207, and the presence or absence of abnormality in the resistance value is detected in step 208, Step 2
09.

If there is an abnormality in the resistance value, error processing is performed, and step 210 and the detection processing are terminated.

Further, if there is no abnormality in the resistance value, it is confirmed whether the reference voltage value has been completed for both the upper limit value and the lower limit value,
Step 211, if not completed, return to 201 and repeat the same operation as described above, and if both are completed, end the detection processing.

Next, an embodiment of the present invention will be described in more detail with reference to FIG.

Referring to FIG. 3, in the embodiment of the present invention, a memory 1, a CPU 2, a switching signal generating circuit 3, a latch circuit 4, a comparing circuit 5, a reference voltage setting circuit 6, an amplifying circuit 7, a switching circuit 8, a detecting resistor 9, a heating resistor 10, a driving transistor 11, a gate element 12, and a control circuit 13. The heating resistor 10, the driving transistor 11, and the gate element 12 shown in FIG. This is an embodiment of a thermal recording type thermal printer using thermal paper.

The present invention can be applied not only to a thermal recording system but also to a thermal transfer system using an ink ribbon having a thermosensitive layer.
In addition to the line type, the present invention can be applied to a serial type head in which heating elements are arranged in a vertical direction and a thermal head is moved in a horizontal direction (perpendicular to the sheet conveyance direction) to perform printing.

The control means 1 shown in FIG. 1 corresponds to the memory 1 shown in FIG.
a, the CPU 1b, similarly, the judgment holding means 2 is in the latch circuit 2a, and the heating resistor driving means 3 is the detection resistor 3a, the heating resistor 3b, the driving transistor 3c, the gate element 3d,
The print control circuit 3e and the switching detecting means 4 include a switching signal generating circuit 4a, a switching circuit 4c, and an amplifying circuit 4b,
Corresponds to the comparison circuit 5a and the reference voltage setting circuit 5b, respectively.

The operation will be described below.

In the thermal printer, when the power is turned on or in the inspection mode during standby, the CPU 1b stores the memory 1a.
The average resistance value of the thermal head is read out, the upper limit value and the lower limit value of the allowable range of the variation of the resistance value are calculated, and the reference voltage setting signal g of either the upper limit value or the lower limit value is first applied to the reference voltage. Output to the setting circuit 5b for setting.

Thereafter, the CPU 1b operates the switching signal generation circuit 4a.
, A switching signal d is input to the switching circuit 4c, and one heating element of a heating element group in a certain block unit is selected.

At the same time, the CPU 1b outputs a print control signal c to the print control circuit 3e to supply a current to the selected heating element 3b. When the current flows, a potential is generated in the detection resistor 3a, and this potential is input to the amplifier circuit 4b via the switching circuit 4c as the detection potential e, and is output as the amplified signal f.

The amplified signal f is input to the comparison circuit 5a, and is compared with the reference voltage h set in the reference voltage setting circuit 5b to output a judgment signal i. Further, the determination signal i is input to the latch circuit 2a and the content is held.

If there is an abnormality in the resistance value, the latch circuit 2
Unless a reset is input to a, the abnormality determination signal is kept held.

The above operation is performed for all the heating resistors, and when all the heating resistors are detected, the CPU 1b reads the status of the latch circuit 2a, stores the status in the memory 1a, and detects whether or not the resistance value is abnormal.

If there is an abnormality in the resistance value, necessary error processing is performed. If there is no abnormality, the remaining one of the upper and lower limit values of the reference voltage value is not detected, and the same processing is repeated. The process ends.

[0046]

As described above, the first effect of the present invention is to detect an abnormality in the resistance value such as missing dots or thin print from the test pattern print result that has been conventionally performed by improving the detection accuracy. Second, there is no need to do
In the conventional method in which the potential detected according to the resistance value of the serial heating resistor is A / D converted and stored in the memory, many interrupt processes occur in the CPU, and the load becomes heavy. On the other hand, in the present invention, the heating resistor group is divided into several blocks, and a comparison is made by a simple circuit configuration for detecting each one of the elements at the same time. In order to reduce interrupt processing of the CPU, the CPU load is reduced. This is particularly advantageous in that detection processing can be performed at a reduced speed and at high speed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of a thermal head resistance value abnormality detection circuit of the present invention.

FIG. 2 is a flowchart illustrating an embodiment of a thermal head resistance value abnormality detection method according to the present invention.

FIG. 3 is a block diagram showing FIG. 1 in further detail.

FIG. 4 is an explanatory diagram showing a detection range of a reference voltage set value.

FIG. 5 is a circuit diagram of a conventional thermal head device that measures and determines the resistance value of a heating resistor using a constant current circuit.

FIG. 6 is a configuration diagram of a detection circuit using continuity of the resistance value of a heating resistor in a conventional thermal head device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Control means 2 Judgment holding means 3 Heating resistor driving means 4 Switching detection means 5 Comparison judgment means a Detection data b Control signal c Print control signal d Switching signal e Detection voltage f Amplification signal g Reference voltage setting signal h Reference voltage i Judgment Signal 1a Memory 1b CPU 2a Latch circuit 3a Detection resistor 3b Heating element resistance 3c Driving transistor 3d Gate element 3e Print control circuit 4a Switching signal generation circuit 4b Amplification circuit 4c Switching circuit 5a Comparison circuit 5b Reference voltage setting circuit

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[Procedure amendment]

[Submission date] February 4, 1999

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0001

[Correction method] Change

[Correction contents]

[0001]

The present invention relates to a thermal transfer using the ink ribbon having a heat-sensitive recording type or a heat-sensitive layer using heat-sensitive paper, heat-generating resistor <br/> body arranged a plurality of heating resistors in a row The present invention relates to a thermal printer including a thermal head having a group.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction contents]

An object of the present invention is to automatically detect an abnormality in the resistance value of a thermal head heating resistor without manual operation,
It is another object of the present invention to provide a thermal printer capable of performing high-speed detection by a parallel processing process .

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0008

[Correction method] Change

[Correction contents]

[0008]

In order to achieve the above object, a method of detecting an abnormal resistance of a thermal head according to the present invention is characterized in that the control means sets a reference voltage setting signal to a comparison judgment means; The heating resistor is connected to a plurality of switching circuits by outputting a control signal to switching detection means.
Select the heating elements of the body group one by one for each switching circuit
Switching, and simultaneously outputting the control signal and simultaneously outputting a print control signal to the heating resistor driving means to generate one heating element.
Flowing a current in parallel one by one , inputting a detection potential generated in the detection resistor to a comparison determination unit and comparing it with a reference voltage value, and holding a determination signal of the comparison result in a determination holding unit; If there is no heating element to be detected next, the control means reads the judgment signal held in the judgment holding means, stores it in a memory, and detects whether or not the resistance value is abnormal. And a step of performing each step for both the upper limit value and the lower limit value of the reference voltage.

[Procedure amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Correction contents]

In the thermal head resistance value abnormality detecting system according to the present invention, the heating resistor group uses a plurality of switching circuits.
The selection of the heating elements is switched one by one in parallel.
Detects the potential according to the resistance of the body and outputs it to the comparison circuit
A current is supplied to the switching detecting means and the heating element, and a detecting resistor is provided.
Heat generation that outputs a detection potential generated by the resistance to the switching detection means
Resistor driving means, comparison determining means for comparing the detected potential with the reference voltage value, determination holding means for holding the compared determination signal, and setting of the reference voltage value / heating resistor switching operation / printing operation / determination signal Control means for controlling the reading of the status.

[Procedure amendment 6]

[Document name to be amended] Statement

[Correction target item name] 0010

[Correction method] Change

[Correction contents]

[0010] The control means simultaneously compares one element at a time in each block of the detection element, and is held by a CPU and a judgment holding means for processing a process of successively and sequentially performing the comparison.
In one embodiment, the memory stores a determination signal .

[Procedure amendment 7]

[Document name to be amended] Statement

[Correction target item name] 0011

[Correction method] Change

[Correction contents]

The heating element driving means includes a detection resistor for generating a potential when a current flows through the heating element, a heating resistor incorporated corresponding to one heating element in the heating element group, and a driving transistor. One embodiment includes a gate control element and a print control circuit for supplying a current to a selected heating element.

[Procedure amendment 8]

[Document name to be amended] Statement

[Correction target item name] 0012

[Correction method] Change

[Correction contents]

The switching detecting means comprises a switching signal generating circuit for outputting a switching signal to the switching circuit, a switching circuit for selecting one heating element from a group of heating elements in block units, and an amplifier circuit. It is one embodiment.

[Procedure amendment 9]

[Document name to be amended] Statement

[Correction target item name] 0013

[Correction method] Change

[Correction contents]

The comparing and judging means receives the amplified detection potential, compares it with a set reference voltage and outputs a judgment signal, and a reference voltage setting signal output from the control means. In one embodiment, the reference voltage setting circuit sets a reference voltage.

[Procedure amendment 10]

[Document name to be amended] Statement

[Correction target item name] 0014

[Correction method] Change

[Correction contents]

In one embodiment, the judgment holding means is a latch circuit for holding a judgment signal.

[Procedure amendment 11]

[Document name to be amended] Statement

[Correction target item name] 0027

[Correction method] Change

[Correction contents]

First, the control means 1 instructs the comparison / determination means 5 to set the upper limit value of the allowable variation range of the average resistance value of the thermal head.
The reference voltage setting signal g serving as the lower limit is output, and either the upper limit or the lower limit is set first (step 2).
01).

[Procedure amendment 12]

[Document name to be amended] Statement

[Correction target item name] 0028

[Correction method] Change

[Correction contents]

After the setting, the control means 1 outputs a control signal b to the switching detection means 4 to generate a switching signal d (step 202), and selects one heating element of the thermal head heating element group (step 202). 203). At the same time, the control means 1 outputs a print control signal c synchronized with the switching signal to the heating resistor driving means 3 to flow a current to the selected heating element.

[Procedure amendment 13]

[Document name to be amended] Statement

[Correction target item name] 0029

[Correction method] Change

[Correction contents]

Thereafter, the detection potential e generated in the detection resistor is amplified to obtain an amplified signal f, which is input to the comparison determination means 5 and compared with a reference voltage value (step 204).

[Procedure amendment 14]

[Document name to be amended] Statement

[Correction target item name] 0030

[Correction method] Change

[Correction contents]

As a result of the comparison, the judgment signal i is outputted to the judgment holding means 2 and is kept held (step 205). It should be noted that once the abnormality determination signal is input, the determination holding means 2 continues to be held until reset.

[Procedure amendment 15]

[Document name to be amended] Statement

[Correction target item name] 0031

[Correction method] Change

[Correction contents]

The control means 1 determines whether there is a next heating element (step 206), and if so, returns to step 202 and repeats the same operation. If there is no next heating element, the judgment signal i held in the judgment holding means 2 is read out (step 207), stored in the memory in the control means 1 (step 208), and the presence or absence of abnormality in the resistance value is detected. (Step 209).

[Procedure amendment 16]

[Document name to be amended] Statement

[Correction target item name] 0032

[Correction method] Change

[Correction contents]

Here, if there is an abnormality in the resistance value, error processing is performed (step 210), and the detection processing ends.

[Procedure amendment 17]

[Document name to be amended] Statement

[Correction target item name] 0033

[Correction method] Change

[Correction contents]

If there is no abnormality in the resistance value, it is confirmed whether both the upper limit value and the lower limit value have been completed in the reference voltage value (step 211), and if not completed, the process returns to 201 and the same operation described above is repeated. If completed, the detection process ends.

[Procedure amendment 18]

[Document name to be amended] Statement

[Correction target item name] 0035

[Correction method] Change

[Correction contents]

Referring to FIG. 3, in the embodiment of the present invention, a memory 1a, a CPU 1b, a switching signal generating circuit 4a, a latch circuit 2a, a comparing circuit 5a, a reference voltage setting circuit 5b, an amplifying circuit 4b, a switching circuit 4c, a detecting resistor 3a, heating resistor 3
b, a driving transistor 3c, a gate element 3d, and a control circuit 3e. The heating resistor 3b, the driving transistor 3c, and the gate element 3d in FIG. 3 correspond to one heating element in the thermal head heating element group. 1 is an embodiment of a thermal recording type thermal printer using thermal paper.

[Procedure amendment 19]

[Document name to be amended] Statement

[Correction target item name] Explanation of sign

[Correction method] Change

[Correction contents]

[Description of Signs] 1 control means 2 judgment holding means 3 heating resistor driving means 4 switching detection means 5 comparison judgment means a detection data b control signal c print control signal d switching signal e detection voltage f amplification signal g reference voltage setting signal h Reference voltage i Judgment signal 1a Memory 1b CPU 2a Latch circuit 3a Detection resistor 3b Heating resistor 3c Drive transistor 3d Gate element 3e Print control circuit 4a Switching signal generation circuit 4b Amplification circuit 4c Switching circuit 5a Comparison circuit 5b Reference voltage setting circuit

[Procedure amendment 20]

[Document name to be amended] Drawing

[Correction target item name] Figure 2

[Correction method] Change

[Correction contents]

FIG. 2

Claims (7)

[Claims] 1. A method for detecting an abnormal resistance value in an inspection mode of a thermal head having a heating resistor group in which a plurality of heating resistors are arranged in a line, wherein the control means compares and determines a reference voltage setting signal. Setting the means, and the control means outputting a control signal to the switching detection means to select one of the heating elements of the thermal head heating element group; and simultaneously outputting the control signal to the heating resistor driving means. Outputting a print control signal, causing a current to flow through the heating element, inputting a detection potential generated at the detection resistor to a comparison determination unit and comparing it with a reference voltage value, and holding the comparison result determination signal in a determination holding unit And if there is no heating element to be detected next, the control means reads out the judgment signal held in the judgment holding means and stores it in a memory to determine whether there is an abnormality in the resistance value. Steps and, a step of performing error processing if any abnormality, the method of thermal head resistance anomaly detection and a step of performing both the upper and lower limits of the reference voltage each of said step of knowledge. 2. A system for detecting an abnormality in the resistance value of a thermal head having a group of heating resistors in which a plurality of heating resistors are arranged in a line, wherein the heating resistor is driven by driving the heating resistor and passing a current. Means (3); switching detection means (4) for selecting and switching one of the heating resistors among the fixed block units, and detecting a potential according to the resistance value of the heating resistor; Determination means (5) for comparing the voltage with the reference voltage value
And a control means (1) for controlling setting of a reference voltage value, switching operation of a heating resistor, printing operation, and reading of the status of the determination signal. Head resistance value abnormality detection system. 3. The control means (1) includes a CPU (1b) and a memory (1) for performing a process of simultaneously comparing one element at a time in each block of a detection element and sequentially performing the comparison.
The thermal head resistance value abnormality detection system according to claim 2, which is a). 4. The heating element driving means (3) is incorporated in correspondence with a detection resistor (3a) for generating a potential when a current flows through the heating element and one heating element in the heating element group. 4. The thermal head resistance value according to claim 2, wherein said heating resistor (3b), the driving transistor (3c) and the gate element (3d), and a print control circuit (3e) for supplying a current to the selected heating element. Anomaly detection system. 5. The switching detection means (4) includes a switching signal generating circuit (4a) for outputting a switching signal to a switching circuit, and a switching circuit (4) for selecting one heating element from a group of heating elements in block units. The thermal head resistance value abnormality detection system according to any one of claims 2 to 4, wherein the thermal head resistance value abnormality detection system comprises an amplification circuit (4c) and an amplification circuit (4b). 6. A comparison circuit (5a) to which the amplified detection potential is input, compares it with a set reference voltage, and outputs a determination signal, and a comparison circuit (5) The thermal head resistance value abnormality detection system according to any one of claims 2 to 5, further comprising a reference voltage setting circuit (5b) for setting a reference voltage according to the reference voltage setting signal. 7. The thermal head resistance value abnormality detection system according to claim 2, wherein said determination holding means is a latch circuit for holding a determination signal.