JP2954050B2 - Thermal head controller - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control apparatus for a thermal head, and more particularly, to a control apparatus for a thermal head mounted on a printer that requires highly accurate control of applied energy.

[0002]

2. Description of the Related Art In general, a thermal head is mounted on a printer of a thermal type or the like, and moves a plurality of built-in heating elements while generating heat based on printing (printing) data, so that a desired character or graphic is printed on a recording paper. Print etc. In the conventional thermal head, the heat storage state of the heating element, a member in the vicinity of the heating element, the heat sink, or the like changes depending on whether or not there is a previous printing line or printing dots on both sides. When the heat storage state changes, the heat energy transmitted to the recording paper or the like changes, so that there is an inconvenience that the printing density changes.

[0003] In order to prevent the above inconveniences, various measures against heat storage are taken. For example, there is a method of correcting the applied energy based on print data of a previous print line of dots to be printed this time or print dots on both sides.
This method of correcting the applied energy is sufficiently effective for character printing in which the printing ratio is small and the change is small. Also, in a binary gradation printer which determines whether or not to print one dot, it is possible to suppress deterioration of printing quality by performing dither processing or the like.

However, in a printer of a type that expresses multiple gradations with one dot, such as a sublimation type or a thermo-auto chrome (TA) system, high-precision thermal history control is required for thermal head control. For this reason, a large-scale arithmetic circuit for calculating the optimum applied energy in a short time based on a large amount of history data is required, resulting in a problem such as an increase in cost or a reduction in printing speed.

[0005] Japanese Patent Application Laid-Open No. 7-205469 describes a thermal head for solving the above problem. As shown in FIG. 14, the thermal head described in the publication has a heating element 31, a current detection resistor 32 connected in series to the heating element 31, and a voltage generated at both ends of the current detection resistor 32. And a temperature detection circuit 33 for detecting the temperature of the heating element 31 by inputting the temperature. The current I as the temperature data from the temperature detection circuit 33 is compared with the current IO as the target temperature data from the target current setter 39 by the comparator 38. If the current I exceeds the current IO, the strobe signal generator 37 is reset, the operation of the drive circuit 36 is stopped, and
The power supply to the heating element 31 is cut off. By repeating this operation, the applied energy can be controlled based on the temperature data.

Although only one heating element 31 is shown in FIG. 14, the thermal head in FIG. 14 actually has a plurality of heating elements. Here, FIG. 15 shows a main circuit of a conventional thermal head having a plurality of heating elements.

The thermal head 41 shown in FIG. 1 includes a plurality of heating elements r1 to rn and a driver circuit 43 for driving the heating elements r1 to rn. The driver circuit 43 includes heating elements r1 to r1.
rn is provided with a plurality of fixed terminals. The control device of the thermal head 41 includes a changeover switch 50 including a plurality of fixed terminals connected to each connection line between each of the heating elements r1 to rn and the driver circuit 43, and a movable terminal that sequentially contacts each fixed terminal. And a changeover switch 51 including a plurality of fixed terminals of the driver circuit 43 and a movable terminal that sequentially contacts each fixed terminal. The control device further includes a comparison circuit 48 sequentially connected to each fixed terminal of the driver circuit 43 by a switching operation of the changeover switch 51, a temperature detection circuit 45 for detecting the temperature of each of the heating elements r1 to rn, and a target temperature. A setting circuit 49 is provided. The movable terminal of the changeover switch 50 is connected to the line 50 a and the detection resistor 4.
4, and a temperature detection circuit 45 is connected upstream of the detection resistor 44 of the line 50a.

Here, when the average electric resistance value of the heating elements r1 to rn is Rave, the electric resistance value of the heating element r1 is Rave.
The electric resistance value of the heating element r2 is set to + 5% of Rave, and the electric resistance value of the heating element r3 is set to -5% of Rave. In the thermal head 41 of the setting, when the temperature dependency of the heating elements r1 to rn is large, the electric resistance value of each of the heating elements r1 to r3 changes as shown in FIG. It changes as shown in FIG. From the graphs of both figures, it can be seen that the three types of change curves of the electric resistance values of the heating elements r1 to r3 are close to each other, and that the three types of change curves of the voltage appearing at the detection resistor 44 are close to each other. I can understand that That is, it can be seen that the variation in the electric resistance value of each of the heating elements r1 to r3 can be ignored for the temperature detection.

However, when the temperature coefficient of resistance of the heating elements r1 to rn is large, as the temperature of the heating elements r1 to rn rises, the electric resistance value of each of the heating elements r1 to rn decreases and the current increases. Flows. Therefore, the temperature of the heating elements r1 to rn rises sharply as shown by a change curve 52 corresponding to the strobe (STB) signal 60 in FIG. In this case, the peak temperature (T2) of the heating elements r1 to rn becomes too high, and the amount of overshoot in the applied energy control increases. Therefore, for example, when the thermal head is mounted on a sublimation type printer, it damages the base material of the ink ribbon, and when the thermal head is mounted on a thermo auto chrome type printer, the surface of the TA paper is damaged. A problem that the printing quality is reduced and the printing quality is deteriorated is likely to occur.

[0010]

In order to suppress the above problem, if the resistance temperature coefficients of the heating elements r1 to rn are made smaller than the resistance temperature coefficient in the change curve 52 in FIG. The rising curve becomes a state shown by a change curve 53 corresponding to the strobe (STB) signal 61 in FIG. According to this, the peak temperatures of the heating elements r1 to rn can be reduced. However, since the variation in the detected temperature due to the variation in the electrical resistance value of the heating elements r1 to rn exceeds the variation in the electrical resistance value due to the temperature change, the detected temperature becomes inaccurate and the good temperature of the thermal head The control state is impaired.

In view of the above, the present invention provides a thermal head control device having a simple structure and capable of appropriately controlling the applied energy of a heating element regardless of the variation in the electric resistance value of the heating element. The purpose is to provide.

[0012]

In order to achieve the above object, a thermal head control device according to the present invention is provided with a thermal head having a plurality of built-in heating elements and selectively connected to one of the heating elements. A detecting resistor; and a temperature detecting means for detecting a temperature of the heating element based on a voltage drop generated in the detecting resistor when the heating element is energized, and a heating element based on a temperature detected by the temperature detecting means. A storage device for storing correction data for each heating element based on temperature data detected by said temperature detection means for each heating element under a predetermined temperature condition And target temperature setting means for setting a target temperature for each heating element based on the given print data; a temperature detected by the heating element from the temperature detecting means; And target temperature, based on the correction data from the storage means, characterized in that it comprises a temperature control means for controlling the temperature of the heating element.

According to the thermal head control device of the present invention, the control of the energy applied to the heating element is appropriately performed irrespective of the variation in the electric resistance value of the heating element, while having a simple configuration, and the control is performed with a high level. Printing quality can be obtained.

Preferably, the temperature control means calculates a correction temperature based on the detected temperature from the temperature detection means and the correction data from the storage means, The circuit comprises a comparison circuit for comparing the corrected temperature with the target temperature from the target temperature setting means, and switching means for switching the state of application to the heating element based on the result of comparison by the comparison circuit.

Alternatively, the temperature control means calculates a target temperature correction value based on the target temperature from the target temperature setting means and the correction data from the storage means, A comparison circuit for comparing a target temperature correction value from the target temperature correction circuit with a temperature detected by the temperature detection means, and a switching means for switching an application state to a heating element based on a comparison result by the comparison circuit. Is also preferred.

[0016]

The present invention will be described in more detail with reference to the drawings. FIG. 1 is an overall block diagram showing a control device for a thermal head according to an embodiment of the present invention.

As shown in FIG. 1, the thermal head 11
Includes a plurality of heating elements R1 to Rn and a driver circuit 13 for driving the heating elements R1 to Rn. The heating elements R1 to Rn are
It has a temperature dependence of the electric resistance value and a negative temperature coefficient of resistance. Controller of the thermal head 11, the heating elements R1~Rn a plurality of fixed terminals 20b connected to each connection line between the driver circuit 13 ₁ ~20b _n and the fixed terminals 2
0b ₁ switch 20 switching comprising a contact 20a for sequentially contacting the ～20B _n and a plurality of fixed terminals 21 disposed in correspondence with the heating element R1~Rn the driver circuit 13
b ₁ comprises a switch 21 switching comprising a contact 21a for sequentially contacting the ～21B _n and the fixed terminals 21b ₁ ~21b _n. The connection state between the heating elements R1 to Rn and the detection resistor 14 is sequentially switched by the changeover switch 20.

The control device of the thermal head 11 further includes:
A switching comparator circuit 18 are sequentially connected in the switching operation of the switch 21 to the respective fixed terminals 21b ₁ ~21b _n of driver circuit 13, a temperature detection circuit 15 for detecting the temperature of each heating element R1 to Rn, the temperature detecting circuit And a target temperature setting circuit 1 for correcting the detected temperature from the reference 15 and providing the same to a comparison circuit 18 and a target temperature setting circuit 1 for providing temperature setting data to the comparison circuit 18.
9 is provided. A rewritable nonvolatile memory (S-RAM) 16 is connected to a connection line between the temperature detection circuit 15 and the detected temperature correction circuit 17. The contact 20a of the changeover switch 20 is grounded via the line 20c and the detection resistor 14, and the temperature detection circuit 15 is connected to the line 20c.

The temperature detecting circuit 15 corrects a deviation value obtained by subtracting a reference value from a voltage generated when the detecting resistor 14 is selectively connected to each of the heating elements R1 to Rn at normal temperature, for each heating element. The function of writing data to the nonvolatile memory 16 as data, and the function of detecting the resistance 1 when different heating elements are sequentially connected.
And a function of amplifying the weak voltage drop generated in 4 and converting it into a digital value, and outputting it as a detected temperature of raw data.

The non-volatile memory 16 stores the temperature detecting circuit 1 for each of the heating elements R1 to Rn under a predetermined temperature condition (at normal temperature).
5 based on the temperature data detected in each of the heating elements R1 to R1.
The correction data for each Rn is stored. Detection temperature correction circuit 17
Are the heating elements R1 to R1 detected by the temperature detection circuit 15.
The correction temperature is calculated based on the detected temperature of Rn and the correction data from the nonvolatile memory 16.

The target temperature setting circuit 19 calculates and sets a target maximum temperature (target temperature) for each heating element based on a gradation value of print data provided from a higher-level device (not shown). The comparison circuit 18 compares the corrected temperature from the detected temperature correction circuit 17 with the target temperature from the target temperature setting circuit 19, and determines whether or not to perform the next application to the heating elements R1 to Rn. The changeover switch 21 performs a switching operation together with the changeover switch 20 based on the comparison result of the comparison circuit 18 to switch the application state to the corresponding heating elements R1 to Rn. The detected temperature correction circuit 17, the comparison circuit 18, and the changeover switch (switching means) 21 constitute a temperature control means.

Next, the operation of the control device for the thermal head 11 having the above configuration will be described with reference to FIGS.

FIG. 2 is a flowchart showing the operation of storing correction data of the detected temperature in the nonvolatile memory 16 in advance.
FIG. 3 is a flowchart showing the operation at the time of printing, and FIG.
FIG. 5 is a characteristic diagram showing the relationship between the electrical resistance value of the heating elements R1 to R3 and the temperature, FIG. 5 is a characteristic diagram showing the relationship between the voltage of the heating elements R1 to R3 appearing in the detection resistor 14 and the temperature, and FIG. It is a characteristic view which shows the relationship between the voltage of the heating elements R1-R3 after correction, and temperature. FIG. 7A shows the heating elements R1 to R1 in the first embodiment.
FIG. 7B is a diagram showing a temperature change of Rn and a strobe signal (STB signal), FIG. 7B is a diagram showing the temperature change of the heating elements R1 to Rn in FIG. 7A in detail, and FIG. FIG. 8 is a diagram showing the strobe signal of FIG. 7A in detail.

The variation in the electric resistance value of the heating elements R1 to R3 in FIGS. 4 and 5 is ± 5% of 2000Ω which is the average electric resistance value of the heating elements R1 to Rn. In FIG. 4, 25
The electrical resistance of each of the heating elements R1 to R3 at ℃ is R1: 200, respectively.
0Ω, R2: 2100Ω, R3: 1900Ω.

First, the operation of storing the correction data of the detected temperature in the nonvolatile memory 16 in advance is executed as follows. That is, the printer on which the thermal head 11 is mounted is left in an environment of room temperature of 25 ° C.
The temperature of the heating elements R1 to Rn is brought close to 25 ° C. In this state, the control device of the thermal head 11 sequentially switches the changeover switch 20 from the heating elements R1 to Rn.
The drive voltage VHD corresponding to the switched heating element is supplied to the detection resistor 14. At this time, the heating elements R1 to Rn
Is sufficiently short in order to suppress the temperature rise of the heating elements R1 to Rn. Therefore, a drop voltage Vsn expressed by the following equation is generated at both ends of the detection resistor 14 corresponding to the respective resistance values of the heating elements R1 to Rn at 25 ° C. _{Vsn = VHD × r 14 / (} r 1 ~ n + r 14) ··· (1) where, r ₁₄ is the resistance of the detecting resistor 14, the r ₁ ~ _n is the resistance value of the heating element R1~Rn respectively .

Next, the temperature detecting circuit 15 detects each heating element R1
The weak drop voltage Vsn generated at both ends of the detection resistor 14 for every .about.Rn is sequentially converted into a digital value, and is output as correction data at normal temperature to be used for future detection temperature correction. That is, the temperature detection circuit 15 calculates the reference value (regular voltage value Vsn) from the voltage Vsn generated when the detection resistor 14 is selectively connected to each of the heating elements R1 to Rn at normal temperature (about 25 ° C.). ) Is stored in the nonvolatile memory 16 as correction data for each of the heating elements R1 to Rn (steps S1 and S2).

Printing by a printer equipped with the thermal head 11 is performed as follows. First, when print data is sent from the host device to the target temperature setting circuit 19 (step S3), the target temperature setting circuit 19 determines whether the heating elements R1 to Rn corresponding to the gradation values of the print data for one line are appropriate. a target maximum temperature was calculated (Fig. 7 (a), T ₁ in (b)), respectively provided to the heating element R1 to Rn (step S4).

Further, by sequentially switching the changeover switch 20, the heating elements R1 to Rn are sequentially connected to the detection resistor 1
Connect to 4. As a result, the heating elements R1 to Rn are applied at predetermined time intervals (step S5), and the voltage Vsn expressed by the above equation (1) is sequentially generated in the detection resistor 14. The temperature detection circuit 15 sequentially converts the voltage Vsn into a digital value and outputs this as a detected temperature (step S6). The detected temperatures obtained here are the heating elements R1 to R1.
Detecting resistor 14 due to variation in each electrical resistance of Rn
Is the raw data directly reflecting the voltage variation (FIG. 5), and is not accurate temperature data.

Thereafter, the detected temperature correction circuit 17 performs an operation of subtracting the corresponding correction data read from the non-volatile memory 16 from the raw data sent from the temperature detection circuit 15, thereby obtaining each of the heating elements R1 to Rn. Is obtained (step S7). FIG. 6 is a graph in which voltage values corrected by subtracting the corresponding correction data from the raw data of the detected temperatures shown in FIG. 5 are plotted.

In step S8, the target temperature setting circuit 19
The target maximum temperature of each of the heating elements R1 to Rn set by the above and the heating elements R1 to Rn sent from the detected temperature correction circuit 17
The comparison circuit 18 sequentially compares the detected temperature with the accurate detection temperature. That is, in the control device, the comparison circuit 18 checks whether each of the heating elements R1 to Rn has reached the target maximum temperature,
While not reaching, repeat the process from step S5,
A signal to perform the next application is sent to the changeover switch 21.
When the changeover switch 21 receiving this signal operates in conjunction with the changeover switch 20, the comparison circuit 18
It is connected to the fixed terminal of the driver circuit 13 corresponding to the heating elements R1 to Rn that need to be connected at present.

In step S8, when each of the heating elements R1 to Rn has reached the target maximum temperature, the comparison circuit 18 sends a signal to the changeover switch 21 not to perform the next application. The changeover switch 21 receiving this signal sets the changeover switch 2
0, and operates from the fixed terminal of the driver circuit 13 corresponding to the connected heating elements R1 to Rn.
To stop the next application to the corresponding heating element.

In the control device of the thermal head 11, the application process and the temperature detection process are performed while correcting the detection temperatures of the heating elements R1 to Rn from the temperature detection circuit 15 based on the correction data from the nonvolatile memory 16. Since the repetition is performed, the applied energy control can always be performed based on the accurate temperature value. As a result, it is possible to appropriately control the energy applied to the heating elements R1 to Rn, and to obtain high printing quality. Therefore, even in a printer of a type that expresses multiple tones with one dot, such as a sublimation type or a thermo-auto chrome type, the tone values can be accurately reproduced.

Further, in the present control device, a large amount of history information such as the previous line, the line before the previous line, the dots on both sides, and the dot before the diagonal line is calculated in a short time to obtain the optimum applied energy for all the heating elements. This eliminates the need for a large-scale arithmetic circuit of the conventional device. Therefore, high-precision applied energy control
This simple and low-cost control device can be realized without lowering the printing speed.

Next, a second embodiment according to the present invention will be described. FIG. 8 is an overall block diagram showing a thermal head control device according to the second embodiment, and FIG. 9 is a flowchart showing an operation at the time of printing.

In the first embodiment shown in FIG. 1, the correction is performed on the raw data of the detected temperatures of the heating elements R1 to Rn having a variation in the electric resistance value. In the second embodiment, the target maximum temperature based on the gradation value of the given print data is corrected in advance in anticipation of the variation in the detected temperature due to the variation in the electrical resistance value of each of the heating elements R1 to Rn. Further, the corrected target maximum temperature is compared with the raw data (detected temperature) from the temperature detecting device 15. Specifically, in the control device according to the second embodiment, the target temperature correction circuit 28 is provided without the detected temperature correction circuit 17 shown in FIG.
The functions of the target temperature setting circuit 19 'and the comparison circuit 18' are slightly different from those of the target temperature setting circuit 19 and the comparison circuit 18 in FIG. Other configurations are substantially the same as those of the first embodiment.

That is, in the second embodiment, the temperature detecting circuit 15 has the detecting resistor 14 selectively connected to each of the heating elements R1 to Rn at normal temperature, similarly to the temperature detecting circuit 15 of FIG. The nonvolatile memory 16 has a function of writing a deviation value obtained by subtracting the reference value from the generated voltage as correction data for each heating element. Further, it has a function of amplifying a weak voltage drop generated in the detecting resistor 14 when different heating elements are sequentially connected and converting the voltage into a digital value, and outputting the digital value as a detected temperature of raw data. Non-volatile memory 16
Stores correction data for each of the heating elements R1 to Rn.

The target temperature setting circuit 19 'controls each heating element R based on the gradation value of print data given from the host device.
The target maximum temperatures (target temperatures) of 1 to Rn are calculated and set. The target temperature correction circuit 28 includes a target temperature setting circuit 19 '.
The target temperature correction value is calculated based on the target maximum temperature from the non-volatile memory 16 and the target maximum temperature. The comparison circuit 18 ′ compares the target temperature correction value from the target temperature correction circuit 28 with the raw data (detected temperature) from the temperature detection circuit 15, and performs the next application to the heating elements R 1 to Rn. Determine whether or not. The changeover switch 21 performs a switching operation together with the changeover switch 20 based on the comparison result of the comparison circuit 18 ', and switches the application state to the corresponding heating elements R1 to Rn. The target temperature correction circuit 28, the comparison circuit 18 ', and the changeover switch (switching means) 21 constitute a temperature control means.

The control device of the second embodiment having the above-described configuration operates as follows. First, the target temperature setting circuit 19 'receives the print data from the host device, and sets the target of each of the heating elements R1 to Rn corresponding to the tone value of the print data for one line based on the tone value of the print data. Calculate the maximum temperature. Further, the target temperature correction circuit 28 calculates a target temperature correction value based on the target maximum temperature from the target temperature setting circuit 19 'and the correction data from the non-volatile memory 16, and prepares each of the heating elements R1 to Rn. (Steps S10, S1
1, S12).

Thereafter, the detection resistors 14 are sequentially connected to the heating elements R1 to Rn while the changeover switch 20 is sequentially switched. As a result, the heating elements R1 to Rn are applied at predetermined time intervals (step S13), and the voltage Vsn is sequentially generated in the detection resistor 14. Further, the temperature detection circuit 15 outputs the detected temperature of the raw data while sequentially converting the voltage Vsn into a digital value (step S1).
4).

In step S15, the comparison circuit 18 '
The corrected target maximum temperature of each of the heating elements R1 to Rn from the target temperature correction circuit 28 and the heating element R from the temperature detection circuit 15
The detected temperatures including errors of 1 to Rn are sequentially compared. That is, the comparison circuit 18 'checks whether or not each of the heating elements R1 to Rn has reached the corrected target maximum temperature, and if not, repeats the process from step S13 to perform the next application. Is sent to the changeover switch 21. The changeover switch 21 receiving this signal sets the changeover switch 2
Heating elements R1 to
The comparison circuit 18 is connected to the fixed terminal of the driver circuit 13 corresponding to Rn.

In step S15, when each of the heating elements R1 to Rn reaches the corrected target maximum temperature, the comparison circuit 18 'sends a signal to the changeover switch 21 indicating that the next application is not performed. The changeover switch 21 receiving this signal,
It operates in conjunction with the changeover switch 20 to cut off the comparison circuit 18 from the fixed terminal of the driver circuit 13 corresponding to the connected heating elements R1 to Rn and stop the next application to the corresponding heating elements. .

As described above, in the second embodiment, the gradation value of the print data and the correction data which are known in advance are used,
The target maximum temperature is calculated before the temperature measurement process.
This eliminates the need to correct the measured value of each temperature measurement during the repetition of the application to the heating elements R1 to Rn and the temperature measurement, and is similar to that in the control device of the first embodiment. In addition to the effects, the speed of printing can be increased.

Next, a third embodiment according to the present invention will be described with reference to FIGS.

In the first embodiment, the heating elements R1 to Rn of the thermal head 11 have negative temperature coefficients of resistance.
The third embodiment differs from the third embodiment in that the temperature coefficients of resistance of the heating elements R1 to Rn are positive. Another configuration of the third embodiment is as follows.
This is the same as the configuration of the first embodiment described with reference to FIG. 1, and has a process of storing correction data used for correcting variations in the detected temperature due to variations in the resistance values of the heating elements R1 to Rn in the nonvolatile memory 16.

FIG. 10 shows the heating elements R1 to R3 taken out of the heating elements R1 to Rn of the thermal head 11 according to the third embodiment.
FIG. 11 is a characteristic diagram showing a relationship between the electric resistance value and the temperature, FIG. 11 is a diagram showing a temperature characteristic of a voltage appearing on the detection resistor 14 by the characteristic of FIG. 10, and FIG. It is a figure which shows the relationship between the voltage of R1-R3 and temperature. FIG.
13A is a diagram showing a temperature change between the heating element of the third embodiment and a normal heating element, and FIG. 13B is a diagram showing a temperature change of the normal heating element shown in FIG. FIG. 13C is a graph showing the amount of overshoot, and FIG. 13C is a graph showing the amount of overshoot when the temperature of the heating element shown in FIG. 13A changes. Heating element R
The resistance values of 1, R2 and R3 at 25 ° C. are 2000Ω and 2
100Ω, 1900Ω.

In the present embodiment, the same correction as in the first embodiment is performed on the detected temperatures of the heating elements R1 to Rn having a positive temperature coefficient of resistance. As shown, the change curve is opposite to the change curve of FIG. 6 in the first embodiment.

Further, in the present embodiment, similarly to the first embodiment, the process of correcting the detected temperature and the process of applying and measuring the temperature are repeatedly executed, thereby obtaining the temperature indicated by the change curve 56 in FIG. A rising curve can be obtained. In the same figure, in the change curve 55 of the normal heating element corresponding to the strobe (STB) signal 63 in the same figure, the rising curve does not become so gentle even if the temperature is increased by continuing the application. However, the change curve 5 corresponding to the strobe (STB) signal 62
In 6, the rising curve becomes gentler as the temperature rises. Therefore, while the target maximum temperature is set to T1 lower than T2 of the normal heating element, the applied pulse time is set to t1 longer than t1.
By setting 2, it is possible to obtain sufficient applied energy.

As shown in FIGS. 13 (b) and 13 (c), in the case of a normal heating element, the amount of overshoot near the maximum temperature becomes large as shown by a change curve 57, but the positive resistance temperature coefficient is reduced. With the heating elements R1 to Rn of the present embodiment, the change curve 5
As shown in FIG. 8, the amount of overshoot near the maximum temperature decreases.

As described above, in the thermal head control device of the third embodiment, the heating elements R1 to Rn have a positive resistance temperature coefficient, and the detected temperature due to the variation in the electric resistance value of the heating elements R1 to Rn. Is repeatedly corrected. As a result, the applied energy per unit time is reduced, the temperature rise curves of the heating elements R1 to Rn are moderated, the maximum temperature is suppressed, the amount of overshoot in control is reduced, and accurate applied energy control can be performed. it can. Therefore, such as the thermo-auto chrome method,
When it is necessary to apply a relatively large applied energy while suppressing the maximum temperature, it is possible to obtain high printing quality while minimizing damage to the recording medium.

Note that also in the second embodiment, it is possible to use the heating elements R1 to Rn having a positive temperature coefficient of resistance. In this case, the same effects as in the third embodiment can be obtained.

Although the present invention has been described based on the preferred embodiment, the control device of the thermal head of the present invention is not limited to the configuration of the above-described embodiment. The control device of the thermal head in which various modifications and changes are made from the configuration described above is also included in the scope of the present invention.

[0052]

As described above, according to the thermal head control apparatus of the present invention, although having a simple configuration, the thermal energy applied to the heating element can be reduced regardless of the variation in the electrical resistance value of the heating element. By performing the control with high accuracy, high printing quality can be obtained.

[Brief description of the drawings]

FIG. 1 is an overall block diagram showing a thermal head control device according to an embodiment of the present invention.

FIG. 2 is a flowchart illustrating an operation of storing correction data in a nonvolatile memory.

FIG. 3 is a flowchart illustrating a printing operation.

FIG. 4 is a graph showing a relationship between an electric resistance value of a heating element and a temperature.

FIG. 5 is a graph showing a temperature characteristic of a voltage appearing at a detection resistor according to the characteristic of FIG. 4;

FIG. 6 is a graph showing a relationship between voltage and temperature of each heating element after correction.

7A is a diagram showing a temperature change of a heating element and a strobe signal in the first embodiment, and FIG. 7B is a diagram showing FIG. 7A.
7 is a partially enlarged graph of the temperature change of the heating element of FIG.
FIG. 7C is a partially enlarged graph of the strobe signal of FIG.

FIG. 8 is an overall block diagram illustrating a control device for a thermal head according to a second embodiment.

FIG. 9 is a flowchart showing an operation by the control device of FIG. 8;

FIG. 10 is a graph showing a relationship between an electric resistance value of a heating element and a temperature in a third embodiment.

11 is a graph showing a temperature characteristic of a voltage appearing at a detection resistor according to the characteristic of FIG.

FIG. 12 is a graph showing a relationship between voltage and temperature of each heating element after correction.

13A is a diagram showing a temperature change between the heating element of the third embodiment and a normal heating element, and FIG. 13B is a view showing FIG. 13A.
13C is a graph showing the amount of overshoot of the normal heating element when the temperature changes, and FIG. 13C shows the overshoot amount of the heating element of the third embodiment shown in FIG. 13A when the temperature changes. It is a graph shown.

FIG. 14 is a block diagram showing a conventional thermal head control device.

15 is an overall block diagram showing a conventional control device having a plurality of heating elements of FIG.

FIG. 16 is a graph showing a relationship between the temperature of the heating element and the electric resistance value of the control device of FIG.

FIG. 17 is a graph showing a voltage appearing at a detection resistor when the heating element of FIG. 16 is used.

FIG. 18 is a diagram showing a temperature rise curve when the heating element of FIG. 16 is used.

[Explanation of symbols]

 Reference Signs List 11 thermal head 13 driver circuit 14 detection resistor 15 temperature detection means (temperature detection means) 16 nonvolatile memory (storage means) 17 detected temperature correction circuit 18, 18 'comparison circuit 19, 19' target temperature setting circuit (target temperature setting) Means) 20 changeover switch 21 changeover switch (switching means) 28 target temperature correction circuit R1 to Rn heating element

Claims (3)

(57) [Claims] 1. A thermal head containing a plurality of heating elements, a detection resistor selectively connected to one of the heating elements, and a voltage drop generated in the detection resistor when power is supplied to the heating element. A temperature detecting means for detecting the temperature of the heating element by controlling the energy applied to the heating element based on the temperature detected by the temperature detecting means. Storage means for storing correction data for each heating element based on temperature data detected by the temperature detection means for the body; and a target temperature for setting a target temperature for each heating element based on the provided print data. Setting means; controlling the temperature of the heating element based on the detected temperature of the heating element from the temperature detection means, the target temperature from the target temperature setting means, and the correction data from the storage means. A control device for a thermal head, comprising: a temperature control unit. 2. The temperature control means according to claim 1, wherein said temperature control means calculates a correction temperature based on the detected temperature from said temperature detection means and correction data from said storage means. 2. The thermal head according to claim 1, further comprising: a comparison circuit that compares a temperature with a target temperature from the target temperature setting unit; and a switching unit that switches an application state to the heating element based on a comparison result by the comparison circuit. 3. Control device. 3. A target temperature correction circuit for calculating a target temperature correction value based on a target temperature from the target temperature setting means and correction data from the storage means, the target temperature correction circuit comprising: 2. A comparison circuit for comparing a target temperature correction value from a temperature and a temperature detected by the temperature detection means, and switching means for switching an application state to the heating element based on a comparison result by the comparison circuit. Thermal head control device.