JP3241670B2 - Thermal head failure detection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting a defect in a thermal head used in a thermal printer, and more particularly, to a method for detecting a defect in a thermal head which enables high quality printing.

[0002]

2. Description of the Related Art Printing defects in a thermal printer are as follows.
In most cases, printing defects caused by variations in resistance values of a plurality of heating elements constituting the thermal head, that is, so-called missing dots are caused. As a conventional thermal head drive control method for preventing dot omission, for example,
There is an invention disclosed in JP-A-6-227018.

In the invention disclosed in the above publication, a temperature detecting circuit for measuring the temperature of the heating element and a temperature at which the voltage is applied are set in advance to the heating element of the thermal head, and the voltage is applied according to the set temperature. A set temperature control circuit is provided to compare the applied temperature with a preset temperature. If the set temperature is not reached, the temperature is detected and displayed as a defect of the heating element. With such a configuration, it is possible to display which heating element has not reached the set temperature, and it is possible to detect a defective heating element efficiently and with high reliability.

[0004]

SUMMARY OF THE INVENTION The above-mentioned JP-A-6-2
In the invention disclosed in Japanese Patent No. 27018, the temperature of the heating element is detected by comparing the temperature at which the voltage is applied with a preset temperature. The reference value must be input to the setting device in advance. This reference value has to be set individually for each heating element in consideration of the variation in the resistance value of the thermal head and the variation in the resistance value in the thermal head, so that there is a problem that it is troublesome.

Further, since the comparison process is performed every time printing is performed, there is a problem that printing takes time.

[0006] Furthermore, a defect of the heating element is detected after printing is performed, and there is a problem that a printing operation and a processing time when the defect is detected are wasted.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and detects variations in resistance values of a plurality of heating elements constituting a thermal head before printing. Accordingly, it is an object of the present invention to realize a method of detecting a defect of a thermal head which enables printing with high speed and high quality by preventing the occurrence of so-called dot omission.

[0008]

SUMMARY OF THE INVENTION A thermal head failure detection method according to the present invention is a thermal head failure detection method for detecting variations in resistors of a plurality of heating elements included in a thermal head used in a thermal printer. ,
A first step which is performed at an initial setting when replacing the thermal head and checks whether a maximum value and a minimum value of resistance values of the plurality of heating elements are within a predetermined range, and This is performed at a predetermined timing after the setting, and the resistance value of each of the plurality of heating elements is set to the first value.
And a second step of confirming whether the values are within the range of the maximum value and the minimum value obtained in the step (a).

In this case, if it is confirmed in the first step that the maximum value and the minimum value of the resistance values of the plurality of heating elements are out of the predetermined range, the replacement of the thermal head is prompted. An error display may be performed.

If it is confirmed in the second step that the resistance values of the plurality of heating elements are out of the range between the maximum value and the minimum value obtained in the first step, the thermal An error display urging replacement of the head may be displayed.

The predetermined range for checking whether the maximum and minimum resistance values of the plurality of heating elements are included may be determined based on the nominal average resistance value of each heating element.

Further, the timing for performing the second step may be when the power of the thermal printer is turned on.

Further, the timing at which the second step is performed may be every predetermined use elapsed time of the thermal printer.

[Operation] In the method for detecting a defect of a thermal head according to the present invention having the above-described structure, the first step measures the maximum resistance Ru and the minimum resistance Rd of the heating element at the time of initial setting of the thermal head. Then, it is checked whether these are within a predetermined range. Thereafter, in a second step performed when the power of the thermal printer is turned on or every predetermined elapsed time of use, the resistance value of each of the plurality of heating elements is calculated based on the maximum value and the minimum value obtained in the first step. Check if it is within the range.

When a thermal head including a heating element having a resistance value that causes printing failure is attached, this is detected in the first step.

In the case where a heating element that causes printing failure due to deterioration over time or the like is included, this is detected in the second step.

The detection in the second step is performed based on the maximum value and the minimum value obtained in the first step, and is performed in a resistance value range smaller than that in the first step. It is possible to detect the variation in the resistance value at high speed.

In addition, the average resistance value displayed on the thermal head may not include the ON resistance of the driving IC or may be a measured value in element units at the time of manufacturing the thermal head. Thus, the resistance value can be reliably detected.

[0019]

Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment according to the present invention.

The circuit for realizing the dot missing detection method according to the present embodiment controls the printing operation on the thermal head 8, and controls the CPU 1 for controlling the operation of the entire circuit and the resistance value of the heating element provided on the thermal head 8. ROM 2 storing resistance value data for confirming whether the temperature is within an allowable range, the maximum value, the minimum value of the resistance value detected for the heating element provided in the thermal head 8 and the number of heating elements. RAM 3 for storing the count number, D / A conversion circuit 4 for setting reference data for comparison with the resistance value of the heating element, counter circuit 5 for counting the number of heating elements having the same resistance value, and printing. A power supply circuit 6 for supplying a heater voltage to the thermal head 8, a print control circuit 7 for driving the thermal head 8, and a heating element provided in the thermal head 8. A detection / comparison circuit 10 for comparing the detected voltage with the output of the D / A conversion circuit 4 and a switching circuit for switching the input state of the voltage detected / compared to the heating / discharging element provided on the thermal head 8 to the detection / comparison circuit 10. 9 and a storage circuit 11 for storing comparison determination data for one resistance value of all the heating elements.

Next, the configuration of the thermal head 8 will be described in detail.

FIG. 2 is a diagram showing an example of the configuration of the thermal head 8 of the present embodiment.

In the thermal head 8, a heating element 13 and a driving transistor 14 are combined for one dot, and a heater voltage h is applied to each heating element 13 and the driving transistor 14 via a detection resistor 12. Is supplied. A drive signal i is provided at the base of each drive transistor 14.
When the drive transistor 14 is turned on by the drive signal i, a drive current flows, and the heating element 13 generates heat. At that time, the detection resistor 12 generates a drive current or a detection voltage j indicating the resistance value of the heating element 13. In this embodiment, the resistance value of the heating element 13 is measured based on the detection voltage j.

In the dot missing detection circuit shown in this embodiment, the maximum value Ru and the minimum value Rd of the resistance value of the heating element provided in the thermal head 8 in the initial setting are determined first and the RAM 3
In the dot missing detection mode, which is a mode for detecting missing dots, it is checked whether or not all the heating element resistance values are always within the range.

For example, if the allowable variation range of the average resistance value of the thermal head is 10% and the allowable variation range in the thermal head is also 10%, the maximum allowable resistance value R1 is the nominal average resistance of each heating element 13. If the value is Rav, it is 1.1 × (1.1 × Rav). In this embodiment, the calculation process is performed while subtracting a predetermined resistance value from the maximum allowable resistance value R1, for example, 1Ω in this embodiment.

FIGS. 3 and 4 are flow charts showing the operation of the present embodiment. FIG. 3 shows the operation performed as an initial setting operation when the thermal head 8 is replaced. FIG. 4 is a flowchart showing an operation for determining whether the maximum value Ru and the minimum value Rd of the resistance value of the body are within an allowable range, and FIG. 7 is a flowchart showing a missing dot detection process performed based on the maximum resistance value Ru and the minimum resistance value Rd obtained in the initial setting shown in FIG. Hereinafter, the operation of this embodiment will be described in detail with reference to FIGS.

First, the initial setting operation in this embodiment will be described with reference to FIG.

When the initial setting operation starts, the CPU 1 sets the comparison resistance value r to R1 (step A1), and
Is set to 1 (step A2).

Next, in order to set the reference signal f in the detection / comparison circuit 10, the reference data e at the resistance value R1 is output to the D / A conversion circuit 4 (step A3).

Subsequently, the CPU 1 outputs a switching signal d so as to select the a-th heating element (step A).
4).

Thereafter, a print control signal c for causing only the a-th heating element 13 to generate heat is output to the print control circuit 7,
The drive signal i is output to the thermal head 8 (Step A5). As a result, the detection voltage j when the a-th heating element 13 is driven is output to the detection / comparison circuit 10 (step A6), and the detection / comparison circuit 10 first executes the CPU 1
A comparison determination is made between the reference signal f set by the above and the detection voltage j.

As a result of the determination in step A6, if the reference signal f of the comparison resistance value r matches the detection voltage j, the determination data k of "1" is output to the storage circuit 11, and the reference value of the comparison resistance value r is obtained. If the signal f does not match the detection voltage j, the determination data k of "0" is output and stored in the storage circuit 11 (step A7). The storage circuit 11 notifies the counter circuit 5 each time "1" is input from the detection / comparison circuit 10, and the counter circuit 5 counts the notified number.

Subsequently, whether the detection processing has been performed for the total number of heating elements N for the comparison resistance value R1 is determined by determining whether the determination data k of the detection voltage j of the total number of heating elements for the comparison resistance value R1 is stored in the storage circuit 11. (Step A8). If the detection processing based on the comparison resistance value R1 has not been performed for all the heating elements N, the addition processing is performed on the heating element number a (Step A9). The above operation is repeated until the detection processing is completed (steps A3 to A8).

In step A8, when it is confirmed that the detection process is performed for the total number N of the heating elements for the comparison resistance value R1, the detection is continued to the comparison resistance value r up to the minimum allowable resistance value R2. It is confirmed whether the processing has been performed (step A10).

In step A10, if it is confirmed that the detection processing has not been performed up to the minimum allowable resistance value R2, the count value g of the counter circuit 5 indicating the number of heating elements of the comparison resistance value r is stored in the RAM 3. Store (Step A
12), clear the counter circuit 5 (step A1)
4) After performing a process of subtracting 1Ω from the comparative resistance value r (step A15), the process returns to step A3 to repeat the above detection operation.

If it is confirmed in step A10 that the detection process for the comparison resistance value r has been completed to the minimum allowable resistance value R2, the CPU 1 stores the count value g in the RAM 3 (step A11). , Then R
The maximum resistance value Ru and the minimum resistance value Rd among the resistance values counted for one or more elements are obtained with reference to the count numbers for all the comparison resistance values stored in AM3 (step A13).

Next, the maximum resistance value Ru and the minimum resistance value Rd obtained in step A13 are compared with the nominal average resistance value Rav.
It is checked whether it is within the allowable range of ± 10% (step A16).

If the maximum resistance Ru and the minimum resistance Rd are within the allowable range, the maximum resistance Ru and the minimum resistance Ru
Is stored in the RAM 3 and this value is fixed as a reference value for dot missing detection and life determination unless the thermal head is replaced in the future, and the initial setting ends (step A1).
8).

If it is determined in step A16 that the maximum resistance value Ru and the minimum resistance value Rd are out of the allowable range, an error is displayed as a defect of the thermal head (step A17).

Next, with reference to FIG. 4, a dot missing detection process performed based on the maximum resistance value Ru and the minimum resistance value Rd obtained in the above initial setting will be described.

When the dot missing detection process is started, CP
U1 first sets the maximum resistance value Ru as the comparison resistance value r (step B1), and then sets the heating element number a to 1 (step B2).

Next, the reference data e for the comparison resistance value r is
/ A conversion circuit 4 (step B3), whereby a reference determination signal f is output to the detection / comparison circuit 10.

Subsequently, the CPU 1 outputs a switching signal d to the switching circuit 9 so that the a-th heating element is selected (step B4).

Next, a print control signal c is output to the print control circuit 7 so that the a-th heating element is driven (step B5).

When the heating element is driven, the detection voltage j is output to the detection / comparison circuit 10 (step B6) and compared with the previously set reference signal f. In this comparison, the determination data k of “1” is output to the storage circuit 11 when the reference signal f of the comparison resistance value r matches, and “0” when the reference data f of the comparison resistance value r does not match. Is output to the storage circuit 11 and stored (step B7).

Next, it is confirmed whether or not the detection processing of the total number of heating elements N has been performed for the comparative resistance value Ru (step B).
8) If addition has not been performed for the total number of heating elements N, the addition processing is performed on the heating element number a (step B9), and the process returns to step B3, and steps B3 to B3 are performed until the total number N of heating elements is completed. The same operation as B8 is repeated.

Number of total heating elements N for comparison resistance value Ru
When the determination data k of the detection voltage j is stored, it is checked whether the detection processing has been performed until the comparison resistance value r reaches the minimum allowable resistance value Rd (step B10). g in the RAM 3 (step B
12), clear the counter circuit 5 (step B1)
4), a process of subtracting 1Ω from the comparison resistance value r is performed (step B15).

After the subtraction processing of the comparative resistance value r, the reference data e at the comparative resistance value r is output again, and the same detection processing is repeated (steps B3 to B9).

The comparative resistance value r is the minimum allowable resistance value R.
When the detection processing is completed up to d, the CPU 1 stores the count value g in the RAM 3 (step B11), adds up the count numbers S for all the comparison resistance values stored in the RAM 3 (step B13), and obtains the total number of heating elements N Is equal to
If they are equal, there is no abnormality and the detection process ends.

If they are not equal, an error is displayed as a missing dot (step B17).

[0052]

As described above, the present invention can prevent the occurrence of so-called dot omission by detecting the variation in the resistance values of the plurality of heating elements constituting the thermal head before printing. This has the effect that printing can be performed quickly and with high quality.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment according to the present invention.

FIG. 2 is a diagram showing a configuration example of a thermal head 8 of the embodiment shown in FIG.

FIG. 3 is a flowchart showing an operation of the embodiment shown in FIG. 1;

FIG. 4 is a flowchart showing the operation of the embodiment shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 CPU 2 ROM 3 RAM 4 D / A conversion circuit 5 Counter circuit 6 Head power supply circuit 7 Print control circuit 8 Thermal head 9 Switching circuit 10 Detection / comparison circuit 11 Storage circuit

Claims (6)

(57) [Claims] 1. A method of detecting a defect of a thermal head for detecting a variation in resistors of a plurality of heating elements included in a thermal head used in a thermal printer, the method being performed at an initial setting when replacing the thermal head, A first step of checking whether the maximum value and the minimum value of the resistance values of the plurality of heating elements are within a predetermined range, and performing the first step at a predetermined timing after setting the thermal head; A second step of checking whether or not each resistance value of the element is within the range of the maximum value and the minimum value obtained in the first step. 2. The method according to claim 1, wherein in the first step, it is confirmed that the maximum value and the minimum value of the resistance values of the plurality of heating elements are outside a predetermined range. And displaying an error prompting replacement of the thermal head when the error is detected. 3. The method for detecting a failure of a thermal head according to claim 1, wherein the resistance value of each of the plurality of heating elements in the second step is the maximum value determined in the first step. A method for detecting a failure of a thermal head, comprising: displaying an error prompting replacement of the thermal head when it is confirmed that the thermal head is outside the minimum value range. 4. The method according to claim 1, wherein a predetermined range for checking whether a maximum value and a minimum value of resistance values of the plurality of heating elements are included is set for each heating element. A method for detecting a defect of a thermal head, wherein the defect is determined based on a nominal average resistance value. 5. The thermal head according to claim 1, wherein the timing of performing the second step is when the power of the thermal printer is turned on. Defect detection method. 6. The method for detecting a failure of a thermal head according to claim 1, wherein the timing at which the second step is performed is every predetermined use elapsed time of the thermal printer. Thermal head failure detection method.