JPS6164468A - Thermal head driving circuit - Google Patents

Abstract

PURPOSE:To make it possible to perform printing with uniform density regardless of the resistance of a lead part, by detecting the number of simultaneous recording elements and correcting a voltage apply time corresponding to the detected value. CONSTITUTION:When printing data is inputted to a terminal D, said data is inputted to a driver 10 and, at the same time, CPU11 reads the printing data and counts the number of heat generating resistor elements R1-R8 having to simultaneously perform the application of voltage from the printing data. A apply pulse width is calculated corresponding to the count number and imparted to the driver 10. By this mechanism, the driver 10 turns switches S1-S8 determined by the printing data ON during the time determined by the apply pulse width. Therefore, energy generated in one of the heat generating resistor elements R1-R8 is controlled so as to be always constant even if the number of simultaneous recording elements are different to each other.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thermal head drive circuit.

[Conventional technology]

Generally, in a thermal head, as shown in Fig. 6, a conductor pattern 2 is formed of Au or AI on a ceramic substrate l, and Ta-5i O2 or Ni-Cr resistors R1-R8 are formed to generate heat. A circuit having elements is created on a ceramic substrate 1, and an insulating film is further applied thereon, thereby manufacturing a thermal head.

As shown in FIG. 7, this thermal head is placed directly below the platen roller (press roller) 5 and the thermal paper 4.
When the heat-generating resistive elements R1 to R8 generate heat, the thermal paper 4 located there develops color, allowing printing and recording.

In the conventional thermal head, as shown in FIG.
By applying a constant voltage Vo for a constant time,
A drive circuit is employed in which Joule heat is generated in the heating resistive elements R1 to R8, and the heat-sensitive paper 4 is colored by the heat energy. In the thermal head shown in FIG. 6, the switches 81 to S8 are constructed from external circuits.

However, in the conventional thermal head drive circuit, T
By applying a constant voltage Vo to the terminals, the heating resistance elements R1 to R
8, but in reality, as shown in Figure 9, a resistance bone RO is used in the lead part.
exists, and the energy generated in the heating resistance elements R1 to R8 changes from the theoretical amount depending on the resistance bone RO, and this decreases in proportion to the value of the current flowing through the resistance bone RO.

Now, set the resistance value of heating resistor elements R1 to R8 to 100 each.
Ω, the voltage applied to the terminal T is 8■, and the switch 5i-s
Consider the case where each of s is switched to OV. If the resistance bone RO of the lead part is OΩ, the heating resistance element R1
Since 8■ is directly applied to R8, the heat generating resistive elements R1 to R8.

A power of 0.64W is applied to. Therefore, when the applied pulse width (voltage application time) is IIIS, the energy generated in the heat generating resistive elements R1 to R8 is 0.64 mJ.

However, in reality, the resistance bone RO of the lead portion often has a resistance value of several ohms rather than 0 ohms.

Now, when the resistance bone RO is set to 10Ω, the energy generated in one element decreases as the number of heating resistance elements R1 to R8 to be recorded simultaneously increases, as shown by the solid line a in FIG.

For example, when the number of simultaneous recording elements is 1, the total resistance ΣR-
RQ +Rx = 110Ω Energy generated at Rx -
I2Rt - (0,0727) 2 X100 X 1-5.28
On the other hand, when the number of simultaneous recording elements is 8, the current 1x flowing through 81 total resistances ΣR-RQ + 100Ω/8 = 22.5Ω = ΣI / 8 = 0.0444 Energy generated in Rx = I2Rt - ( 0,0444) 2 x 100 x 1 = 0.19
7 taJ.

[Problem that the invention seeks to solve]

Conventional thermal head drive circuits are configured as described above, and due to the resistance bone present in the lead portion of the head, the energy generated in one element varies depending on the number of simultaneous recording elements, and the print density changes. There was a drawback that variations occurred.

This invention was made in view of the above-mentioned conventional problems, and an object of the present invention is to provide a thermal head drive circuit that can print with uniform density regardless of the resistance of the lead portion. It is said that

[Means to solve the problem]

The present invention provides a detection means for detecting the number of simultaneous recording elements in a thermal head drive circuit, and a detection means corresponding thereto.

and a correction means for correcting the voltage application time or the applied voltage.

[Effect]

In this invention, when the detecting means detects the number of heat generating resistive elements to which voltage should be applied simultaneously, the correcting means adjusts the voltage application time or the energy generated by the applied voltage to one heat generating resistive element accordingly. The increase/decrease is corrected.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

1 and 2 show a thermal head drive circuit according to an embodiment of the present invention, and FIG. 1 is an overall configuration diagram of this embodiment. In this embodiment, a driving means 6 applies voltage to a plurality of heating resistive elements of a thermal head 7 according to print data from the outside, and a detecting means 8 simultaneously applies a voltage to a plurality of heating resistive elements according to the print data. The correction means 9 increases or decreases the voltage application time (applied pulse width) of the driving means 6 according to the number of the heat-generating resistive elements detected, and calculates the energy generated in one heat-generating resistive element. It is configured to control constant.

FIG. 2 is a circuit diagram showing electrical connections of the thermal head drive circuit. In the figure, R1 to R8- are heating resistance elements of a thermal head formed on a ceramic substrate, 31 to S8 are switches composed of switching transistors, etc., and controls energization to the heating resistance elements R1 to R8, and T is a voltage. A terminal 10 to which is applied is constituted by a shift register, a latch, etc., and the switches 81 to S
8 is a driver that opens and closes; D is a terminal into which external printing data is input; 11 is a terminal that detects the number of heating resistive elements R1 to R8 to which voltage should be applied simultaneously (number of simultaneous recordings), and adjusts the voltage application time accordingly. 12 is a CPU that sets the (applied pulse width); 12 is a CPU 1 arithmetic processing program (
3), a map of applied pulse widths with respect to the number of simultaneous recordings (see FIG. 5), etc. are stored in this memory. This applied pulse width map is calculated in advance by the lead resistance (9th
RO in the figure) was measured, and from this and the number of simultaneous recordings, the applied pulse width that would keep the energy generated in one heating resistor element constant was determined and mapped.

Next, the operation will be explained using the flowchart shown in FIG.

When print data is input to the terminal, the print data is input to the driver 10, and at the same time, CPULL reads the print data (step 13), and from the print data, voltage is applied to the heating resistor element R1 to be applied at the same time. ~R
Count the number of 8 (Step 14), and find the applied pulse width from the map shown in Figure 5 according to the counted number (
Step 15) and give it to the driver 10 (step 15).
Knob 16). Then, the driver 10 turns on the switches 81 to S8 determined by the print data for a time determined by the width of the applied pulse, and the energy generated in each heating resistor element R1 to R8 is as shown by the dashed line in FIG. Even if the number of simultaneous recordings differs, it is always controlled to be constant.

In the apparatus of this embodiment as described above, the voltage application time is set according to the number of simultaneous recordings, so the energy generated in one element can be controlled to be constant, thereby making the printing density uniform. Print quality can be improved.

In the above embodiment, the voltage application time is increased or decreased, but the present invention may also be configured to increase or decrease the applied voltage. Further, the number of heating resistor elements to which voltage should be applied simultaneously may be detected not from the print data but from the current value required for printing.

Further, in the above embodiment, the case where the number of heat generating resistive elements is 8 has been described, but the number may be a plurality other than 8. Furthermore, in the above embodiments, the case where the circuit is configured as a software has been explained, but it may of course be configured as a hard circuit. It is sufficient to provide a plurality of latch signal generation circuits etc. that control to different values, and to select these circuits according to the detection signal of the number of simultaneous recordings.

〔Effect of the invention〕

As described above, according to the thermal head drive circuit according to the present invention, since the number of simultaneous recordings is detected and the voltage application time or applied voltage to the heating resistor element is increased or decreased accordingly, the thermal head drive circuit according to the present invention This has the effect of improving print quality by controlling the amount of energy used.

[Brief explanation of drawings]

FIG. 1 is an overall configuration diagram of a thermal head drive circuit according to an embodiment of the present invention, FIG. 2 is a circuit diagram showing electrical connections of the above circuit, FIG. 3 is a flow chart of the operation of the above circuit, and FIG. The figure is a diagram for explaining the operation in the above circuit, Figure 5 is a diagram showing the relationship between the applied pulse width and the number of simultaneous recordings in the above circuit, and Figures 6 and 7 are perspective views for explaining the thermal head. FIG. 8 is a circuit configuration diagram of a conventional thermal head drive circuit, and FIG. 9 is a circuit diagram for explaining the conventional drawbacks. 6... Drive means, 7... Thermal head, 8...
Detection means, 9... Correction means, R1-R8... Heating resistance element, 81-S8... Switch, 10... Driver, 11... CPtJ. Note that the same reference numerals in the figures indicate the same or equivalent parts. Figure 1 Figure 2 Figure 4

Claims (2)

[Claims] (1) A thermal head composed of a plurality of heat generating resistor elements, a driving means for applying voltage to the heat generating resistor elements according to print data from the outside, and detecting the number of the heat generating resistor elements to which voltage application should be performed simultaneously. A thermal head comprising: a detecting means for detecting the output of the detecting means; and a correcting means for receiving the output of the detecting means and correcting the voltage application time of the driving means or the applied voltage according to the number of heat-generating resistive elements to which a voltage is to be applied. drive circuit. (2) The thermal head drive circuit according to claim 1, wherein the detecting means detects the number of heating resistor elements to which voltage is to be applied simultaneously based on the current value required for printing.