JPH06227018A - Method for controlling driving of thermal head - Google Patents

Abstract

PURPOSE:To prevent dots of a thermal head heating element in a thermal printer from dropping. CONSTITUTION:A temp. detector 8 and a heating control circuit 7 performing heating to a predetermined specified temp. are provided in a group of heating elements 9 and the heating elements of this thermal head are heated dot by dot and those heating elements wherein temp. does not reach a set temp. are detected and displayed to make it possible to perform with high reliability and efficiently detection in comparison with visual detection of dot dropping.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head drive control method, and more particularly to a thermal head drive control method used in a thermal head printer having high printing quality.

[0002]

2. Description of the Related Art A conventional thermal head drive control method is
Prevents the print quality from deteriorating due to heat build-up in the thermal head based on printing, that is, the print density is low immediately after the start of printing, and when printing continues, the density increases with the time of printing. Since the energy supplied to the heat generating element is generated by accumulating heat in the base material in the vicinity of the heat generating element or the thermal head itself, the change in the print density due to this heat storage deteriorates the print quality. Measures for heat storage are taken by the method.

Therefore, based on the past print recording data, the control of the power supply in the current printing is individually performed for each of the heating elements, and the fine heating temperature control is performed to obtain a uniform printing density and a good printing quality. There is.

As an example of such a thermal head drive control method, in the thermal head heat generation temperature control device disclosed in Japanese Patent Laid-Open No. 2-147255, new print data is imported D0 as input / output of print data to / from the line memory. At the same time as writing to the print data, the print data is read from the outport D0 and used as the import D1 input. This is performed for all in and out ports, and print data for several lines is stored. Further, by latching the print data from the outport D7 in several stages every time it is read, it is possible to refer to the print data in the left-right direction. The print data from the outport D7 is R for determining print conditions.
It is input as a part of the address data of OM4. With this input condition, it is possible to correspond to the past several times of heat recording history of the individual heat generating element and several heat generating elements on the right and left sides thereof. The line memory 2 stores the heat storage amount of each heating element of the thermal head, and the heat storage amount data is input as a part of the address data of the ROM 4 for determining the printing conditions.

That is, in this thermal head heat generation temperature control device, when printing is performed by using a thermal head having a plurality of heat generating elements, the heat of each heat generating element and several heat generating elements on the left and right sides of the heat generating element are used several times in the past. By the means for calculating the heat storage amount corresponding to the heat generation record history and the means for calculating the heat storage amount corresponding to all the past heat generation record history of each heating element, the printing at the current print location according to the heat storage amount can be performed. The print density is adjusted by adjusting the print density for each heating element with respect to the power supply amount.

[0006]

However, in the above-mentioned conventional thermal head drive control method as described above, in order to obtain a uniform print density, fine heat generation temperature control is performed individually for all the heat generating elements to generate heat. Print density correction is performed to prevent heating due to heat storage of the element, but if there is a defective heating element that does not develop color because the temperature does not reach the predetermined temperature no matter how much power is supplied due to variations in the thermal head heating elements. However, in order to detect this defective heating element, it is necessary to visually detect the print result, which is not only inefficient, but there is a drawback that detection failure occurs and reliability is lowered. It was

[0007]

According to the thermal head drive control method of the present invention, a temperature detecting circuit for measuring the temperature of the heating element and a temperature to be applied are preset to the thermal head heating element, and the set temperature is set. If the temperature has not reached the set temperature, the temperature of the applied dot is compared with the preset temperature by applying the set temperature control circuit that performs the application by using this thermal head control circuit. Is configured to generate a machine alarm when the heating element is defective.

[0008]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 is a circuit block diagram showing an example of a thermal head for realizing an embodiment of the present invention, FIG.
(A)-(b) is a storage transition diagram of the print data stored in the shift register shown in FIG.

The thermal head shown in FIG. 1 includes a shift register 1, a latch 2, a heating element group 9 including 36 heating elements R1 to R36, and temperature detection resistors r1 to r36.
A switching section 3 and 4; a temperature detection section 8 including an A / D converter 5, a setter 6 and a comparator 7; and an AND gate A1.
To A36, drive circuits T1 to T36, and a heating control circuit 10 including flip-flops FF1 to FF36.

The switching units 3 and 4 connect the temperature detecting unit 9 to the heating element R.
1 to R36 are provided for time sharing.

First, the normal printing operation of the thermal head shown in FIG. 1 will be described.

In the normal printing operation, print data corresponding to a print character is shifted as a serial input Sin by one bit each time the clock signal Clock is supplied and input to the shift register 1 and then serially transferred by the shift register 1. 36 clock signals C converted to parallel
It is stored in the latch 2 at the timing of the latch signal Latch after the supply of lock. Latch signal La at the same time
The FF1 to FF36 are set to "1" by the set input S by tch, one side input of the AND gates A1 to A36 becomes "1" level, and the print data of the latch 2 is "1".
Only the level AND gates A1 to A36 output "1" level, and the corresponding drive circuits T1 to T3
6 enters the operating state, and current flows through the heating elements R1 to R36 to generate heat. This current value is A as a potential difference applied to the temperature detection resistors r1 to r36 every time the switch 3 is switched.
A comparator 7 compares the set voltage detected by the A / D converter 5 and set in the setter 6 in advance with the detected voltage from the A / D converter 5, and when the set voltage is exceeded during a predetermined print cycle, A pulse is output from the comparator 7 as an output of the temperature detection unit 8 through the switch 4 that operates in conjunction with the comparator 3, and is supplied to the flip-flops FF1 to FF36 as a reset input R, which is reset and the AND gates A1 to A1.
A36 is closed and the current flowing through the heating elements R1 to R36 is cut off. When the predetermined print cycle ends, the next print data is set in the same manner as described above, and the temporary processing is performed.

Next, the defective heating element detecting operation of the thermal head shown in FIG. 1 will be described with reference to FIGS. 2 (a) to 2 (d).

In the case of defective heating element detection operation, the heating element R
The print data corresponding to each of 1 to R36 are sequentially set in the shift register 1, and the print data for the next heating element is set at the end of one print cycle.

An embodiment of the present invention using the above circuit is shown in FIG.
This will be described with reference to FIG. First, the print data for the heating element R1 is shifted by one bit each time the clock signal Clock is supplied as the serial input Sin, and only the first dot as shown in FIG. "Level data is set. The data input to the shift register 1 is stored in the latch 2 by the latch signal Latch. At the same time, F for each print cycle
A strobe signal is generated from F1, the drive circuit T1 for the first dot is activated, and a current flows through the heating element R1. Due to the potential difference applied to the current detection resistor r1, A
The current is detected by the / D converter 5. The comparator 7 compares the voltage value preset by the setter 6 with the output voltage of the A / D converter 5, and if the comparison value exceeds the set voltage, a pulse is output as normal operation and the flip-flop FF1 To the reset input R of the flip-flop FF1 and the AND gate A1 is closed to shut off the current flowing through the heating element R1. If the comparison value does not exceed the set voltage even though the printing cycle has ended, the flip-flop FF1 is maintained in the set state, and this is detected to determine that the heating element R1 is abnormal.

Similarly, the shift resist 1 shown in FIG.
“1” only for one dot like (b), (c), ... (d)
Level data is set and each heating element R2, R3, ...
Normality / abnormality is determined by comparing the comparison value of R36 with the set voltage and determining whether the flip-flops FF2, FF3, ... FF36 are reset. When an abnormality is detected in at least one of the heating elements R1 to R36 after completion of the determination for all the dots, a machine alarm is immediately generated and the heating elements R1 to R36 of the thermal head shown in FIG.
Which of the heating elements is defective is displayed.

In the above-described embodiment, the heating elements are driven one by one to detect whether or not there is a defect. In this case, an indication of whether or not there is a failure is displayed by the printer corresponding to each heating element. It is obvious that it may be printed on, displayed on a display, or displayed by other display means.

In the above-mentioned embodiment, the heating element is
Although the example of driving one by one is shown, two or more or all of the heating elements are driven at the same time, and after a lapse of a predetermined time, it is detected whether or not all of the flip-flops FF1 to FF36 are reset and which one is reset. Needless to say, whether or not it has been reset may be displayed corresponding to the heating element by the display means as described above.

In the above-described embodiment, the example in which the heat generating element is composed of 36 dots has been described, but it goes without saying that the heat generating element may be larger or smaller depending on the mode of use of the thermal printer.

Furthermore, in the above-described embodiment, an example in which the temperature detecting unit 8 is switched by the switches 3 and 4 so that it can be shared by all the heating elements has been shown. However, this temperature detecting unit corresponds to each heating element. It goes without saying that it may be provided afterwards.

Furthermore, in the above-described embodiment, an example in which a defect is detected depending on whether the flip-flop has been reset has been shown. However, the defect is detected depending on whether an output is output to the AND gate. It goes without saying that it is good.

Furthermore, in the above-described embodiment, an example of detecting which of the individual heating elements is defective is shown. However, if any one of the heating elements is defective, this thermal head is defective. If the setting is made as follows, the thermal head including the defective heating element is determined by whether the output of the flip-flop or the output of the AND gate is ORed by the OR gate after a predetermined time and whether the output is "1". It goes without saying that it may be possible to detect whether or not

Furthermore, in the above-mentioned embodiment, it is based on whether or not the flip-flop is defective depending on whether or not the flip-flop is reset. However, the state of the flip-flop may be detected by software. Needless to say.

[0025]

According to the thermal head drive control method of the present invention, it is possible to detect whether or not the set temperature has been reached for each heating element by driving a plurality of heating elements for each heating element for a predetermined time. Since it is possible to display which heating element has not reached the set temperature, there is an effect that a defective heating element can be efficiently known.

Further, in the thermal head drive control method of the present invention, the temperature of all the heating elements is measured, the heating elements which do not reach the set temperature are detected, and the dot omission is visually detected by judging the abnormality. Than the above, there is an effect that the reliability becomes higher and the operation can be performed efficiently.

[Brief description of drawings]

FIG. 1 is a circuit block diagram showing an example of a thermal head for realizing an embodiment of the present invention.

2A to 2B are storage transition diagrams of print data stored in a shift register shown in FIG.

[Explanation of symbols]

 1 shift register 2 latch R1 to R36 heat generating element r1 to r36 temperature detection resistance T1 to T36 drive circuit A1 to A36 AND gate FF1 to FF36 flip flop 3,4 switching unit 5 A / D converter 6 setter 7 comparator 8 temperature detection Part 9 Heating element group 10 Heating control circuit Sin Serial input Clock Clock signal Latch Latch signal S Set input R Reset input

Claims (3)

[Claims] 1. A thermal head drive characterized by driving a heating element included in a thermal head, detecting whether or not a preset temperature has been reached after a lapse of a predetermined time, and displaying when the preset temperature has not been reached. Control method. 2. The thermal head drive control method according to claim 1, wherein the heating elements according to claim 1 are sequentially driven one by one. 3. The heating element for detecting whether or not the set temperature according to claim 1 or 2 has been reached is shared by the respective heating elements. The thermal head drive control method described.