JPH1086425A - Method and apparatus for measuring resistance value of thermal head and thermal printer therewith - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure resistance values of heating elements for constituting a thermal head at a high speed. SOLUTION: In the case of measuring resistance values of heating elements R1 to R128 for constituting the thermal head 1, a data generating controller 2 outputs data for measuring a resistance value for conducting only one element R1 to a shift register 6. Only the element R1 is conducted based on the data stored in the register 6, and its resistance value is measured by a resistance value measuring unit 3. After this measurement, the controller 2 gives a shifting head clock signal (HCLK) to shift the data stored in the register 6. Only the element R2 is conducted based on the shifted data, and its resistance value is measured. As described above, the resistance values of the resistors R1 to R128 are measured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the resistance of a thermal head for measuring the resistance of a large number of heating resistor elements constituting a thermal head provided in a printer, etc. The present invention relates to a thermal printer having the same.

[0002]

2. Description of the Related Art Conventionally, a thermal head provided in a printer or the like has a large number of heating elements, and energizes each heating element based on printing data. The ink is sublimated to form an image on recording paper. In this thermal head, the resistance values of all the heating elements are measured in order to prevent the density unevenness of the image formed on the recording paper caused by the difference in the resistance values of the heating elements.

In the prior art for measuring the resistance value of a heating element, a shift register provided for each heating element stores resistance measurement data for energizing one heating element, for example, "100... 0"("1"). Is supplied serially in synchronization with the clock signal, and the stored resistance value measurement data is output in parallel to each heating element. Based on the resistance value measurement data, only one heating element is energized, and the resistance value of the heating element is measured. Next, resistance value measurement data different from the previously transmitted resistance value measurement data, for example, “0”
.. 0 "is transferred to the shift register again. Thereby, only one heating element other than the heating element is energized, and the resistance value of the heating element is measured. Transfer, a series of processing of measurement is performed as many times as the number of heating elements that constitute the thermal head,
The resistance value of each heating element constituting the thermal head is measured.

In the technique disclosed in Japanese Patent Application Laid-Open No. 6-79897, one capacitor is connected in parallel to each heating element constituting a thermal head, and a shift register provided for each heating element is Based on the transferred resistance value measurement data, only one heating element to be measured is energized, and the resistance value of one energized heating element is measured by measuring the discharge time of the charge from the capacitor. You. Next, the resistance measurement data for energizing only another heating element is transferred again to the shift register, and the resistance value of another heating element is measured. Such a series of processing for transferring and measuring the resistance value measurement data is performed as many times as the number of heating elements constituting the thermal head, and the resistance value of each heating element constituting the thermal head is measured.

[0005]

In the prior art described above, when measuring the resistance of each of the heating elements constituting the thermal head, the measurement is still performed when the measurement of the resistance of one energized heating element is completed. The resistance measurement data for energizing only one of the heating elements that are not present is transferred to the shift register again to measure the resistance. Then, a series of processing of transferring and measuring the resistance value data is repeated until the measurement of the resistance values of all the heating elements is performed, so that there is a problem that time is required.

The present invention has been made in view of such a drawback, and a method of measuring the resistance value of a thermal head for easily and quickly measuring the resistance value of each heating element constituting a thermal head. An object of the present invention is to provide a measuring device and a thermal printer having the same.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a method for measuring the resistance of a large number of heating resistors constituting a thermal head. The resistance measurement data that is supplied only to the heating resistor is stored in the shift register, and the resistance is measured during or after the measurement of the resistance value of the one heating resistor that is supplied based on the stored resistance measurement data. Is shifted by a predetermined number, and the resistance value of another heating resistor different from the measured heating resistor is measured.

Here, one heating resistor means one corresponding to one dot, and even if it consists of two or more heating resistors, if it corresponds to one dot,
It is included in one heating resistor.

In the method for measuring the resistance of a thermal head according to the present invention, resistance measurement data for energizing only one heating resistor is stored in a shift register provided in the thermal head, and the stored resistance measurement is performed. The resistance value of one heating resistor that is energized is measured based on the application data. Next, in order to measure the resistance value of the heating resistor different from the measured heating resistor, for example, a clock signal or the like is applied to the shift register, so that the resistance value measurement data stored in the shift register is previously stored. Shift by a predetermined number, eg, one. Based on the shifted resistance value measurement data, power is supplied to one heating resistor different from the one heating resistor measured last time, and the resistance value of the heating resistor is measured. By repeating such processing, the resistance value of each heating resistor constituting the thermal head is measured.

In other words, only one heating resistor stored in the shift register is energized by a simple process of providing a clock signal for shifting, instead of providing all of the resistance measurement data again to the shift register. Since the resistance measurement data to be generated is shifted, resistance measurement data for measuring the resistance value of one heating resistor different from one measured heating resistor is generated at high speed.
The resistance value of each heating resistor constituting the thermal head can be measured easily and at high speed.

According to another aspect of the present invention, there is provided a thermal head resistance value measuring method for measuring the respective resistance values of a large number of heating resistors constituting a thermal head. In the situation that exists,
The resistance value measurement data that is supplied to only one heating resistor is stored in the shift register, and the resistance value of the one heating resistor supplied based on the stored resistance measurement data is measured during or after the measurement. The image data stored in the shift register is shifted by a predetermined number, and the resistance value of one heating resistor different from the measured heating resistor is measured.

The serial type thermal head has a plurality of heating resistors arranged in a line in a vertical direction (recording paper conveyance direction: sub-scanning direction) and scans the recording paper in a horizontal direction (main scanning direction). Thus, the scanning recording line is printed, and the image is printed on the recording paper by repeating the printing of the scanning recording line. In such a thermal head, if the scanning speed of the thermal head is increased in order to improve the printing speed, heat tends to be generated in the central portion of the thermal head, and the thermal energy is stored from the upper end to the lower end of the thermal head. In the printing density of the printing portion of the cylinder, a phenomenon occurs in which the density at both ends is lower than the density at the center.

On the other hand, each heating resistor constituting the thermal head is constituted by a resistor that changes its resistance value in response to a change in temperature (for example, a resistor called NTC that decreases its resistance value with a rise in temperature). ing. Therefore, it is possible to detect the temperature distribution of the thermal head by measuring the resistance value of each heating resistor constituting the thermal head. When the resistance value of each heating resistor is measured in a situation where the thermal storage effect of the thermal head exists, for example, immediately after the end of printing of one line, a resistance value reflecting the thermal storage effect of the thermal head, that is, a temperature distribution is obtained. Can be
The above-mentioned phenomenon can be prevented by correcting the resistance value measurement data based on the temperature distribution.

According to another aspect of the present invention, there is provided a thermal head resistance measuring apparatus for measuring the resistance of a thermal head for measuring the resistance of a number of heating resistors constituting a thermal head. In the device, a shift register is provided corresponding to each of the heating resistors and stores resistance measurement data to be given to each of the heating resistors, and generates resistance measurement data for energizing only one heating resistor. Data generation control means for outputting to the shift register and shifting the resistance measurement data stored in the shift register by a predetermined number during or after the measurement of the resistance value of one energized heating resistor And a resistance value measuring means for measuring the resistance value of one of the energized heating elements based on the resistance value measurement data stored in the shift register. That.

The shift register is provided in correspondence with each heating resistor, and stores resistance value measurement data for energizing only one heating resistor. The data generation control means generates the resistance value measurement data and transfers it to the shift register. Based on the resistance value measurement data stored in the shift register, only one heating resistor is energized, and the resistance value is measured by resistance value measuring means. Next, when measuring the resistance value of one heating resistor different from the measured one heating resistor, the data generation control means supplies the resistance stored in the shift register by giving a clock signal or the like, for example. The value measurement data is shifted by a predetermined number. As a result, electricity is supplied to one heating resistor different from the one measured heating resistor, and the resistance value is measured by the resistance value measuring means. By repeating such processing, the resistance value of each heating resistor constituting the thermal head is measured.

Further, the thermal printer of the present invention includes a thermal head having a plurality of heating resistors and printing data and resistance measurement data provided to each heating resistor. When measuring the resistance value of the shift register storing either one of them and the resistance value of the heating resistor, it generates resistance measurement data for energizing only one heating resistor, and when forming an image on recording paper, Data generating means for generating printing data based on image data to be printed on recording paper, and outputting the data to the shift register;
In a thermal printer comprising: a resistance value measuring means for measuring a resistance value of one energized heating resistor based on resistance measurement data stored in the shift register, the resistance value of the heating resistor is measured. In this case, during or after the measurement of the resistance value of one energized heating resistor,
Data control means for shifting the resistance measurement data stored in the shift register by a predetermined number, and the resistance value of each heating resistor measured by the resistance measurement means,
Storage means for storing as resistance value data, and correction means for correcting the printing data based on the resistance value data stored in the storage means when forming an image on recording paper. I do.

The thermal printer of the present invention has an operation state for measuring the resistance value of each heating resistor constituting the thermal head and an operation state for forming an image on a recording sheet. In an operation state in which the resistance value of each heating resistor constituting the thermal head is measured, resistance measurement data for energizing only one heating resistor is output from the data generating means to the shift register, and one heated heating resistor is output. During or after the measurement of the resistance value of the resistor, the data control means supplies a clock signal or the like to shift the resistance measurement data stored in the shift register by a predetermined number, for example, one.
As a result, another heating resistor different from the one heating resistor measured is used.
Electricity is supplied to the two heating resistors, and the resistance values are measured by resistance value measuring means. By repeating such a process, the resistance value of each heating resistor constituting the thermal head is measured and stored as resistance value data in a storage means such as a RAM. In an operation state of forming an image on recording paper after the end of the resistance value measurement operation, the correction unit corrects the printing data based on the resistance value data stored in the storage unit. The corrected printing data is applied to the shift register, and each heating resistor is energized based on the applied printing data, and an image is formed on a recording sheet.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a circuit diagram showing a main part of a thermal printer including a thermal head resistance value measuring apparatus according to an embodiment of the present invention. The thermal head resistance measuring device includes a thermal head 1, a data generation / control unit 2, and a resistance value measuring unit 3 shown in FIG. FIG. 2 is a time chart for explaining a resistance value measuring operation of the thermal head in the thermal printer.

The data generation / control unit 2 performs various controls in the thermal printer and generates printing data (SDATA) to be given to the thermal head 1 based on image data (DATA) given from outside (not shown). . In addition, as described later, it generates resistance measurement data (SDATA) for measuring the resistance of each of the heating elements R1 to R128 of the thermal head 1 and controls the resistance measurement unit 3. Further, after the operation of measuring the resistance value of the thermal head 1 is performed, the processing described later is performed to correct the generated printing data (SDATA).

The thermal head 1 includes 128 heating elements R1 to R128, a shift register 6, a latch 7, and a driver 8. Thermal head 1
Is connected to a data generation / control unit 2, and each heating element R
1 to R128 (SDAT)
A), resistance measurement data (hereinafter, may be simply referred to as printing data including resistance measurement data), and various control signals. The thermal head 1 is connected to a resistance measuring unit 3.

The shift register 6 provided in the thermal head 1 is constituted by cascading, for example, 128 D-type flip-flops. In the shift register 6, each of the heating elements R1 to R12
The print data (SDATA) and the head clock signal (HCLK) supplied to 8 are provided. This printing data (SDATA) is supplied with a head clock signal (HCL).
It is given serially in synchronization with K).

In the latch section 7, for example, 128 latch circuits are provided corresponding to the D-type flip-flops constituting the shift register 6, respectively. Each latch circuit receives a latch signal (/ L) from the data generation / control unit 2.
ATCH: / indicates negative logic).
Based on the latch signal (/ LATCH), the printing data (SDATA) stored in the shift register 6 is
The data is output to the driver unit 8 in parallel.

The driver section 8 is provided with, for example, 128 AND circuits corresponding to the 128 latch circuits constituting the latch section 7, respectively. Each AND circuit receives a strobe signal (/ S) from the data generation / control unit 2.
TB), and the strobe signal (/ S
Based on TB), the printing data (SDATA) given from the latch unit 7 is given to each of the heating elements R1 to R128.

The heating elements R1 to R128 are made of a so-called NT
It is composed of a resistor called C and is connected in parallel to a head voltage supply line to which the head voltage Vh is supplied. The terminals of the heating elements R1 to R128 on the opposite side to the terminals to which the head voltage supply lines are connected are supplied with outputs from the respective AND circuits included in the driver unit 8 described above. Has become.

The resistance value measuring section 3 includes a transistor Tr1,
Each of the heating elements R1 to R1 which includes a resistor Ra, a subtractor 10 and an analog / digital converter (hereinafter referred to as an AD converter) 11 and constitutes the thermal head 1
A resistance value of 28 is measured.

The transistor Tr1 has its ON / OFF
Is used to switch between the resistance value measurement operation and the normal printing operation. The measurement control signal (EN) of the data generation / control unit 2
It is turned on / off in A). This transistor Tr1
Is composed of, for example, a PNP-type bipolar transistor. The collector terminal is grounded, and the emitter terminal is connected to the common (GND) of the driver section 8 of the thermal head 1. The base terminal is supplied with the measurement control signal (ENA) from the data generation / control section 2.

The resistor Ra has a preset resistance value, one end is grounded, and the other end is a transistor Tr1.
And the driver section 8 of the thermal head 1, and when the transistor Tr1 is OFF, the head voltage V
h is divided.

The subtractor 10 includes a differential amplifier 13 and four resistors r1 to r having arbitrary resistance values.
4 is included. A preset reference voltage Vref is applied to the inverting input terminal of the differential amplifier 13.
The non-inverting input terminal is connected to each heating element R1 of the thermal head 1.
R128 and the resistor Ra. By the subtracter 10, one selected heating element and the resistor R are selected.
The reference voltage Vref is subtracted from the divided voltage value of the head voltage Vh divided by a.

The AD converter 11 has an input terminal IN,
An output terminal OUT and a chip select terminal (/ CS) are provided. The output voltage Vo output from the subtractor 10 is applied to the input terminal IN, and the applied output voltage Vo is subjected to analog / digital conversion. From the output terminal OUT, the analog / digital converted output voltage Vo is output as a measurement output signal (AD_OUT). The data generation / control unit 2 also provides a chip select terminal (/ C
S) has an analog / digital conversion instruction signal (/ AD_C).
S).

The memory 4 is composed of a RAM or the like, and stores resistance value data created based on the respective resistance values of the heating elements R1 to R128 of the thermal head 1 measured by the resistance value measuring unit 3. It is also used as a work area for performing various controls in a thermal printer.

Next, the operation of measuring the resistance of the thermal printer will be described with reference to FIG. In FIG. 2, an operation state (resistance measurement period) in which the resistance value of each of the heating elements R1 to R128 constituting the thermal head 1 is measured by the transistor Tr1 provided in the resistance value measurement unit 3, and the recording paper is measured by the thermal head 1. 2 shows an operation state of forming an image (printing operation period).

A low-level measurement control signal (EN) is sent from the data generation / control unit 2 to the base terminal of the transistor Tr1.
A) (see FIG. 2 (e)), the collector-emitter of the transistor Tr1 conducts, and each heating element R
1 to R128 are grounded via the transistor Tr1, and an operation state for forming an image on recording paper is set. On the other hand, data generation /
When a high-level measurement control signal (ENA) is supplied from the control unit 2 (see FIG. 2E), the collector and the emitter of the transistor Tr1 are cut off, and each of the heating elements R1 to R
128 is grounded via a resistor Ra, and an operation state for measuring the resistance value of each of the heating elements R1 to R128 constituting the thermal head 1 is set. Hereinafter, an operation state of measuring the resistance value (resistance value measurement period) will be described.

With the rise of the measurement control signal (ENA) applied to the base terminal of the transistor Tr1 to the high level, the data generation / control unit 2 outputs resistance measurement data (SDATA), for example, "100... (Indicating that only the heating element R1 is energized) is supplied to the shift register 6 of the thermal head 1 based on the head clock signal (HCLK) (see FIGS. 2A and 2B).
This resistance measurement data (SDATA) "100 ... 0"
Is resistance measurement data for energizing only one of the 128 heating elements R1 to R128. In this case, it is resistance measurement data for energizing only the heating element R1. The transfer of the resistance value measurement data (SDATA) requires time td.

After the completion of the transfer of the resistance value measurement data (SDATA), that is, after a lapse of time td from the rise of the measurement control signal (ENA) to the high level, the fall of the latch signal (/ LATCH) occurs. The resistance measurement data (SDATA) stored in the shift register 6 is latched by each of the 128 latch circuits of the latch unit 7 (see FIG. 2C). When the strobe signal (/ STB) falls to a low level after the resistance measurement data (SDATA) is latched in the latch unit 7, the driver unit 8
, Resistance measurement data (SDATA) is given to each of the heating elements R1 to R128, the head voltage Vh is applied only to the heating element R1 to be measured, and only the heating resistor R1 is energized ( (See FIG. 2D).

At this time, the other heating elements R2 to R128
Is not conducted, the head voltage Vh is divided by the heating element R1 and the resistor Ra, and the divided voltage is supplied to the non-inverting input terminal of the differential amplifier 13 of the subtracter 10. In the subtracter 10, the reference voltage Vr is calculated from the divided voltage.
ef is subtracted to output an output voltage Vo (FIG. 2)
(F)). In this case, the output voltage Vo is determined by the subtractor 10
By the respective resistance values of the four resistors r1 to r4 constituting
It is set within a predetermined range.

The output voltage Vo is supplied to the AD converter 11
And an AD converter select signal (/ AD_C) supplied from the data generation / control unit 2
Analog / digital conversion is performed with the fall of S) (see FIG. 2 (g)). In the AD converter 11,
The digitized output voltage Vo is output from the output terminal OUT as an output signal (AD_OUT) and stored in the memory 4 (see FIG. 2 (h)).

As described above, the resistance value of the heating element R1 is measured. During or after the measurement, the data generation / control section 2 outputs a one-pulse head clock signal (HCLK) rising to a high level to the shift register 6 as shown in FIG. 2 (FIG. 2B). reference). The shift register 6 receives resistance measurement data (SDAT) that is supplied to only the heating resistor R1 stored in the shift register 6 by one pulse of the head clock signal (HCLK).
Shift A). For example, the measured resistance value data (SDATA) is “100...
If it is “0”, it is shifted right by one, and the resistance measurement data (SDATA) becomes “010... 0” that energizes only the heating element R2. The falling strobe signal (/
With the fall of STB) (see FIGS. 2C and 2D), the heating element R2 is energized, and the above-described processing is performed to measure the resistance value of the heating element R2.

Each time the resistance value of each heating element is measured as described above, the shift processing of the resistance value measurement data (SDATA) stored in the shift register 6 is performed, and the measured heating element R1 is Creates resistance value measurement data for measuring the resistance values of the other heating elements R2 to R128. After the resistance value of the last heating element R128 is measured, the measurement control signal (ENA) falls to a low level (see FIG. 2E), an operation state for forming an image on recording paper is set, and printing is performed. The operation starts.

According to the above-described embodiment, the data generation / control section 2 shifts the resistance value measurement data (SDATA) stored in the shift register only by supplying the head clock signal (HCLK). The resistance value of one heating element R2 different from the one measured heating element R1 is measured, and the measurement is repeated for each heating element R2 to R128 to measure the resistance value of each heating element R1 to R128. Therefore, the resistance values of the respective heating resistors constituting the thermal head 1 can be measured easily and at high speed.

In the operation state in which the resistance values of the heating elements R1 to R128 constituting the thermal head 1 are measured, as shown in FIG.
Data generation and control unit 2 for measuring the resistance value of
Outputs a latch signal (/ LATCH) for one pulse of the head clock signal (HCLK), and shifts the resistance value measurement data stored in the shift register 6 to the right one by one.

However, the present invention is not limited to such a form, and the data generation / control unit 2 may control the head clock signal (H
CLK), the latch signal (/ LATC)
H), the resistance measurement data (SDATA) stored in the shift register 6 may be shifted to the right by two. In this case, the heating elements R1, R3,..., R12
7 (the number attached to the right of the reference symbol R is an odd number), and the remaining heating elements R2, R4,.
128 (the number appended to the right of reference R is even)
Is measured, the data for resistance measurement of the remaining heating elements is transferred from the data generation / control section 2 to the shift register 6 again and measured. Such a process requires more time than the case where the measurement is shifted to the right one by one, but the measurement of the resistance value can be performed at a higher speed than in the related art, and the resistance value is measured every other one. Thereby, the influence of heat of the adjacent heating element can be reduced. Of course, it is also possible to shift the resistance measurement data stored in the shift register 6 by a number other than 1 or 2.

In general, when the scanning speed of the thermal head 1 is increased to improve the printing speed, heat tends to be generated in the central portion of the thermal head 1, and the thermal head 1 is moved from the upper end to the lower end. A phenomenon occurs in that the printing density of the printing portion at the portion corresponding to the portion is lower at both ends than at the center.

On the other hand, when each of the heating elements R1 to R128 constituting the thermal head 1 is constituted by a resistor called NTC which decreases the resistance value with respect to a temperature rise,
Heating elements R1 to R128 constituting the thermal head 1
Is measured, the resistance value indicates the temperature distribution of the thermal head 1.

In a situation where the thermal storage effect of the thermal head 1 exists, that is, after a printing operation for one line of the thermal head 1 in an operation state of forming an image on recording paper, or irrespective of an actual printing operation. After energizing the heating elements, the resistance value of each heating element is measured, so that the thermal head 1
Is obtained. The above-mentioned phenomenon can be prevented by correcting the printing data (SDATA) as described above based on the obtained temperature distribution.

Further, since the resistance value measurement data (SDATA) is generated at high speed by the shift processing, the resistance value of each heating element can be measured at high speed. The temperature distribution of the thermal head 1 reflecting the effect of heat storage close to the printing operation state is obtained.

Further, each of the heat generating elements R1 to R1 of the thermal head 1 under the condition where the effect of heat storage of the thermal head 1 exists.
Since it is desirable to measure the resistance value of R128 at a higher speed, the stored resistance value measurement data (SDAT)
A) may be shifted to the right by two, for example.

For example, the data generation / control unit 2 outputs a latch signal (/ LATCH) for every two pulses of the head clock signal (HCLK), and outputs the stored resistance value measurement data (SDATA) two by two to the right. Shift to In this case, each of the heating elements R2, R4,
, R128, it is possible to estimate those resistance values by calculating the average of the resistance values of the measured heating elements (R1, R3,..., R127) present on both sides. By measuring the number, the temperature distribution of the entire thermal head 1 can be obtained at high speed.

The data control corresponding to the temperature distribution obtained as described above will be described below. This data control is performed by the data generation / control unit 2. When the data generation / control unit 2 generates the printing data (SDATA) based on the image data (DATA), the resistance value stored in the memory 4 is used. Read data. Then, based on the temperature distribution based on the resistance value data, the printing data (SD
ATA) is corrected.

If it is assumed that 256-gradation printing can be performed in the thermal printer, it is possible to print (1
In the dot printing period), printing data (SDATA) is input to the shift register 6 256 times. At this time, it is assumed that printing with a density of 128 gradations is performed, and that all the heating elements R1 to R128 of the thermal head 1 generate heat.

In this case, it is assumed that a temperature distribution based on the resistance value data stored in the memory 4 is lowered at the heating element portions at both ends of the head as shown in FIG. In this case, the printing data (SDAT
As A), data “111... 1”, all of which are “1”,
If “11” is stored 128 times in the shift register 6 and the data “000... 000”, all of which are “0”, are stored 128 times in the shift register 6, the energization time of all the heating elements R1 to R128 Are the same, the temperature generated by the heating elements at both ends is low, and the printing density is low.

The data generation / control unit 2 differs from the data supplied to the heating elements on the center side in that the data for printing is provided so as to provide more "1" data to the heating elements on both ends. (SDATA) is corrected.

As described above, since the correction processing is performed by the data generation / control section 2 in the low temperature portion where the printing density becomes low from the temperature distribution based on the resistance value data stored in the memory 4, the printing is performed. The quality can be improved.

[0053]

As described above, according to the present invention, not all data of the resistance value measurement data are repeatedly supplied to the shift register, but a simple process of supplying a clock signal or the like is performed by the simple processing of supplying a clock signal or the like. The resistance measurement data for energizing only one heating resistor is shifted to create resistance measurement data for measuring the resistance of another heating resistor different from one measured heating resistor. Therefore, the resistance values of the respective heating resistors constituting the thermal head can be measured easily and at high speed.

Further, the resistance value of each heating resistor of the thermal head is measured at high speed in a situation where the thermal storage effect of the thermal head exists. Therefore, each heating resistor reflecting the thermal storage effect when the thermal head is used is reflected. The body resistance value, that is, the temperature distribution can be obtained. Thus, it is possible to reduce the density unevenness of the image by correcting the image data based on the temperature distribution.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a main part of a thermal printer according to an embodiment of the present invention.

FIG. 2 is a timing chart for explaining an operation of measuring a resistance value of a thermal head in the thermal printer of FIG. 1;

FIG. 3 is a graph showing a temperature distribution of a thermal head based on a measured resistance value.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Thermal head 2 Data generation / control part 3 Resistance value measurement part 4 Memory 6 Shift register R1-R128 Heating element SDATA Printing data; Resistance measurement data

Claims (6)

[Claims] In a thermal head resistance value measuring method for measuring the resistance values of a large number of heating resistors constituting a thermal head, resistance measurement data for energizing only one heating resistor is stored in a shift register. Then, during or after measuring the resistance value of one heating resistor energized based on the stored resistance value measurement data, the resistance value measurement data stored in the shift register is shifted by a predetermined number. And measuring a resistance value of another heating resistor different from the measured heating resistor. 2. A method of measuring a resistance value of a plurality of heat generating resistors constituting a thermal head, wherein only one heat generating resistor is used under a condition in which heat is stored in the thermal head. Is stored in the shift register during or after the measurement of the resistance value of the one heating resistor that is energized based on the stored resistance measurement data. A method of measuring a resistance value of a thermal head, wherein image data is shifted by a predetermined number and a resistance value of another heating resistor different from the measured heating resistor is measured. 3. The method for measuring a resistance value of a thermal head according to claim 2, wherein each of said heat generating resistors comprises a resistor whose resistance value decreases in response to a temperature rise. 4. A thermal head resistance value measuring device for measuring each resistance value of a large number of heat generating resistors constituting a thermal head, provided in correspondence with each of the heat generating resistors, and provided to each of the heat generating resistors. A shift register for storing resistance measurement data; and a resistance measurement data for energizing only one heating resistor, and outputting the generated data to the shift register.
Data generation control means for shifting the resistance value measurement data stored in the shift register by a predetermined number during or after the measurement of the resistance value of the two heating resistors, and the resistance value measurement data stored in the shift register Resistance measuring means for measuring the resistance of one heating resistor energized on the basis of the above. 5. A thermal head having a plurality of heating resistors, and one of printing data and resistance measurement data provided to each heating resistor and provided to each heating resistor is stored. A shift register, generating resistance measurement data for energizing only one heating resistor when measuring the resistance value of the heating resistor, and printing on a recording paper when forming an image on the recording paper; Data generating means for generating printing data based on the image data to be output, and outputting the data to the shift register; and a heating element which is energized based on the resistance measurement data stored in the shift register. In a thermal printer comprising: a resistance value measuring unit for measuring a resistance value, when measuring the resistance value of the heating resistor, during or after measuring the resistance value of one energized heating resistor Data control means for shifting the resistance value measurement data stored in the shift register by a predetermined number, and storage means for storing the resistance value of each heating resistor measured by the resistance value measurement means as resistance value data. And a correcting means for correcting the printing data based on the resistance value data stored in the storage means when an image is formed on a recording sheet. 6. The method according to claim 5, wherein each of the heating resistors comprises a resistor whose resistance value decreases in response to a rise in temperature.