JPS61263773A - Driver for dot printing head in thermal printer - Google Patents

Abstract

PURPOSE:To reduce variations in printed density and contrive a simpler circuit construction, by providing a circuit for measuring the internal resistance of a printing head, a circuit for discriminating resistances into a plurality of ranked resistance groups according to the measured values, and a circuit for setting a preset driving voltage according to the ranks thus discriminated. CONSTITUTION:The discriminating circuit 5 is provided for discriminating whether an output V0 from the measuring circuit 4 for the internal resistance Rn of a heating element Hn in the printing head 1 is higher or lower than a reference voltage Vf, and the voltage-setting circuit 7 is provided in a power source 6. Where the output from the circuit 5 when a measurement demand signal MA, MB is outputted from a printer controller 3 is Vf0 and a standard value of the internal resistance of the printing head is R0, the internal resistances which are actually scattered are classified into three ranks, the internal resistance Rn of the n-th heating element Hn in the head 1 is measured, and the optimum one of three driving voltage is selected. Accordingly, variations in printed density arising from scattering of the resistances of the head can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a dot print head drive device in a thermal printer.

[Conventional technology]

Regarding thermal heads, as shown in the ``Thermal Head Technology Collection'' edited by Suzuki Engineer Office in 1981, the internal resistance of dot type thermal heads has negligible variations from dot to dot within the same head. , there is a variation of 7 to 20 inches for each head.

The power consumed by the heating element of the thermal head is expressed as W = - V: drive voltage and R: internal resistance.As can be seen, if the drive voltage is constant, the print density will vary due to variations in the internal resistance of each head. It makes a difference.

For this reason, differences in print density can be prevented by either setting the drive voltage adjustment volume in the power supply to an appropriate voltage when mounting the print head, or selecting and using the print head itself. It was.

[Problem that the invention seeks to solve]

According to the above technology, the method of setting the appropriate voltage using the drive voltage adjustment volume in the power supply when mounting the print head is complicated, and the method of selecting and using the print head itself requires the manufacturing process of the print head. There is a problem that the retention becomes extremely bad and the price becomes high.

[Means for solving problems]

The present invention includes a print head internal resistance measuring circuit, a plurality of resistance group discrimination circuits for each class according to the measured value, and a drive voltage setting circuit that sets a preset drive voltage according to the determined class. It is characterized by having been established.

[Effect]

The internal resistance measuring circuit consists of a plurality of resistors connected in series to one of the plurality of print heads and an energization control circuit that independently switches between energization and de-energization of each of the plurality of resistors. When one or more of the plurality of resistors is energized by the energization control circuit, the voltage across the resistor and the reference voltage are compared in a class-specific resistance group discrimination circuit to discriminate the class of the resistance value of the print head, and this discrimination circuit The output of 9
By setting the output voltage of the power supply device to a predetermined value using a voltage setting circuit, differences in print density caused by variations in the resistance value of the print head are reduced.

〔Example〕

The present invention will be explained in detail below.

Figure 1 is a circuit diagram, 1 is a print head, n heating elements H1p H2...Hn and their internal resistances.
ly”...Rn.

Reference numeral 2 denotes a print head driver for driving the print head 1, and 3 a printer controller for controlling the thermal printer, which controls the print head driver 2 and a measuring circuit and a voltage setting circuit to be described later.

Reference numeral 4 indicates a circuit for measuring the internal resistance an of the heating element Hn of the print head 1, and reference numeral 5 indicates that the output vo from the measurement circuit 4 is a reference voltage V for comparison.
This is a discrimination circuit that discriminates whether f is larger or smaller.

6 is a power supply, which includes a voltage setting circuit 7 therein.

This circuit device measures the internal resistance Rn of the n-th heating element Hn of the print head 1, and selects the optimum one of the three types of drive voltages shown in Table 1 based on this.

The above circuit device operates only during initial settings inside the printer after turning on the AC power, and after selecting the appropriate voltage, the printer is ready for normal operation. During initial settings, the print head driver 2 is all turned off by the printer controller 3.
has been in a state.

Table 1 Table 1 above shows the output vf of the discrimination circuit 5 when the printer controller 3 sends out the measurement request signal MA'pMB.
When the standard value of the internal resistance of the print head is RQ, the internal resistance values that vary are actually classified into three ranks: A class, B class, and C class.

For example, when the comparison reference voltage Vt is set to "fl," the resistance constant Rf l p Rf 2 of the discrimination circuit 5 is determined to a value that satisfies the following equation (1).

The resistance constants Ra and Rb of the measuring circuit 4 are determined according to Table 1 so as to satisfy the following two sets of equations (2) and (3).

Rn-Ro Q+a/a) Rn=Ro (1-a/3) Here, α is a value indicating how much variation the internal resistance value has with respect to the standard internal resistance value aO, and Ro(
The internal resistances in the range of 1-α) to Ro(1+α) are divided into classes.

FIG. 2 is a graph showing the correspondence between internal resistance classes and selected voltages.

Therefore, after turning on the AC power, the printer controller 3 sends the measurement request signal MA to the measurement circuit 4 and
Turn on a. Then, vo=(Ra/(Rn+Ra))vO voltage is generated at the vo terminal in the discrimination circuit 5,
If this is smaller than the comparison reference voltage vf, the discrimination circuit 5
The output vfo of is turned off, and as shown in Table 1 and the determination flowchart in FIG. 8. Send a signal to set the voltage for class A (see Figure 2). Also, if the vo terminal voltage is larger than the comparison reference voltage Vf, the output of the discrimination circuit 5 is in the ON state.Based on this, the printer controller 3 determines that the internal resistance Rn is class A, and then sends out the measurement request signal MB and turns on the transistor 4b.Then, a voltage Vo=("b/(an+Ro))"o is generated at the vo terminal in the discrimination circuit 5, and if this is higher than the comparison reference voltage vf. If it is smaller, the output vfo of the discrimination circuit 5 is turned off, and the printer controller 3 determines that the internal resistance 'ELn is class B, and sends the Sb signal to the voltage setting circuit 7 in the power supply 6 to set the voltage for class B. set.

Furthermore, if the voltage vo=(Rb/(an-stb))Vo is greater than the comparison reference voltage Vf, the output vfo of the discrimination circuit 5 becomes ON, and the printer controller 3 determines that the internal resistance Rn is of class C. Then, an SC signal is sent to the voltage setting circuit 7 in the power supply 6 to set the class C voltage.

〔Effect of the invention〕

According to the present invention described above, there is provided a circuit for measuring the internal resistance of a print head, a discrimination circuit for discriminating the resistance into a plurality of resistance groups according to the measured value, and a drive voltage set in advance according to the determined class. By providing a drive voltage setting circuit, print heads can be automatically classified into classes according to their internal resistance values, and a drive voltage suitable for that class can be automatically set.As a result, the print head resistance value This has the effect of reducing differences in print density caused by variations in print density.

Further, the circuit is simple and can be constructed at low cost.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a graph showing the correspondence between internal resistance classes and selected voltages.
FIG. 3 is a determination flowchart. 1...Print head 2...Print head driver 3
...Printer controller 4...Measuring circuit 5.
...Discrimination circuit 6...Power source 7...Voltage setting circuit Patent applicant: Oki Electric Industry Co., Ltd. Patent attorney Takashi Kanakura 2 circuits ■ 1-

Claims (1)

[Claims] 1. A plurality of print heads, a power supply device that supplies current to these print heads, and a head drive circuit that switches between energization and de-energization of the print heads are provided, and the power generated from the print heads is provided. In a dot print head drive device for a thermal printer that prints characters or figures using heat, there is a circuit that measures the internal resistance of each print head, and a discrimination circuit that determines the class among multiple resistance groups based on the measured values. A dot print head drive device for a thermal printer, comprising: a voltage setting circuit that sets a preset drive voltage according to the determined class.