JPS59106979A - Thermal printer - Google Patents

Abstract

PURPOSE:To reduce the irregularity of printing density and to improve printing quality, by providing a control means for making the heat generating amount of each heat generating element variable. CONSTITUTION:A character to be printed is selected by a character code signal CC and the vertical line of a character pattern is successively scanned by a counter 4 driven by a printing pulse PP. The printing strength information of each heat generating element of the vertical line is read from a strength character pattern generator 1 by the counter 4 and set to a strength character pattern register 2 in synchronous relation to the printing pulse PP. The content of the strength character pattern register 2 is converted to analogue voltage for determining the heat generating amounts of heat generating element R1-Rn by D/A converters 31-3n and transistors Q1-Qn for controlling heat generation are controlled by said voltage. In addition, a multi-vibrator 5 is provided in order to determine the heat generating time of each heat generating element.

Description

[Detailed description of the invention] [Field of application of the invention] The present invention relates to thermal printers.

[Background of the invention]

When printing with a thermal printer, as shown in Figure 1 (B), one vertical row of heating elements (7 dots in the figure) is used.
A dot with a dot on the recording paper is scanned horizontally on the thermal paper, and print pulses along the character pattern shown in Figure 1 (a) are supplied to each heating element in synchronization with the head position on the recording paper. ing.

In conventional thermal printers of this type, characters are printed by giving information for each dot corresponding to each dot in a character pattern and controlling whether or not to print.

However, due to the heat generating elements used in such printers, the heat generated by one dot is not limited to just that dot, but also spreads to surrounding dots due to its heat generation temperature characteristics or the influence of the vertical and horizontal temperature distribution of the heat generating element. This has the drawback of causing unevenness in print density and extremely deteriorating print quality.

[Purpose of the invention]

An object of the present invention is to provide a thermal printer that reduces unevenness in print density and improves print quality.

[Summary of the invention]

In order to achieve such an object, the present invention is characterized in that a control means is provided to vary the amount of heat generated by each heating element.

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail with reference to Examples.

FIG. 2 shows the configuration of an embodiment of a control circuit for a thermal printer according to the present invention, in which 1 is a strong character pattern generator that generates information corresponding to the amount of heat generated by each heating element, and 2 is a strong character pattern generator.・Register, 31-3. is D
/A converter, 4 is a counter, 5 is a monosterple multivibrator, Q! ~Q, is a transistor, R+l~
R1 is a heating element, and EI is a power supply terminal. And D/
A converters 31-31 and transistors Ql-Q are provided corresponding to heating elements 1-R forming the dot.

In such a configuration, the character code signal CC allows
Characters to be printed are selected, and the columns of the character pattern are successively scanned by a counter 4 driven by a print pulse PP. The print intensity information of each heating element in the column is read out by the counter 4 from the intensity character pattern generator 1,
Strength character pattern register 2 in synchronization with print pulse PP
is set to The contents of the strength character pattern register 2 are stored in the D/A converters 31 to 3. Each heating element R1 to R
This voltage is used to control the heat generation control transistors QI to Q. Note that the multivibrator 5 is provided to determine the heating time of the heating element.

FIG. 3 shows the configuration of another embodiment of the control circuit for a thermal printer according to the present invention, and shows a two-stage heat generation amount switching system. This is to switch the amount of heat generated by the heating elements R1 to R1 into two stages using photocouplers PC and PC11.

In FIG. 3, 6 is a character pattern generator, 7 is a character pattern register, 8 is a power control generator, 9 is a power control register, and Q! '~Qm' are transistors, r1~r are resistive elements, PC+~PC1 are photocouplers A N D I-AND - is ant game), E
t, E2 indicates a power supply terminal.

In such a configuration, depending on the character code signal CC,
The character pattern generator 6 generates a signal to control the on/off of each heating element, which is temporarily stored in the character pattern generator 7, and the output of the multivibrator 5 according to the print pulse is used to generate the AND gate A N D s~A.
ND, and is applied to the transistors Ql-Q.

Thereby, on/off of the current to the heating cords R1 to R1 is controlled.

On the other hand, based on the character code signal CCI/n, the power control generator 8 generates a signal for switching the heat generation amount of the heating element in two steps, and after temporarily storing it in the power control register 9,
Controls transistors Q1' to Qa'. Thereby, the photocouplers PCt~PC.

is controlled, and the resistive elements rl-r are either short-circuited or not short-circuited. Therefore, the amount of heat generated by the heating elements R1 to R1 is controlled.

FIG. 4 shows the configuration of still another embodiment of the control circuit for a thermal printer according to the present invention, r,/~r.

, ′ indicate a resistance element. Figure 4 attempts to reduce only the influence of vertical temperature distribution; when two vertically adjacent heating elements are heated, the vertical temperature distribution causes adjacent dots to become extreme. This prevents the phenomenon of dark printing.

Now, if only transistor Q2 in Fig. 4 is turned on,
The calorific value P of the heating element R2 is, however, r 1' = r
2' =-== r,. +'=(WRRt=Ra=
...=R work and t=R.

becomes. In addition, when only the transistors (h and Qs in Fig. 4 are turned on), the amount of heat generated by the heat generating element R2, Pi, is as follows.Therefore, when both transistors Qh and Qs are turned on, the amount of heat generated when only the transistors Qh and Qs are turned on is higher than when only the transistor Q2 is turned on. The amount of heat generated by the resistance element R2 can be reduced as follows compared to the case where the resistance element R2 generates heat.

According to the self-control type control circuit shown in FIG. 4, only the influence of the longitudinal temperature distribution can be reduced with a simple configuration.

〔Effect of the invention〕

As described above, according to the present invention, by controlling the amount of heat generated by each heating element to be variable, unevenness in print density can be reduced and print quality can be significantly improved.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a thermal printer, FIG. 2 is a configuration diagram of an embodiment of a thermal printer control circuit according to the present invention, and FIGS. The configuration diagram of the embodiment is shown. 1...Strength character pattern generator, Q1 to Q.

Claims (1)

[Claims] In a thermal 7' IJ printer, in which a head having a predetermined array of heating elements is scanned over a thermal paper and the heat applied to the heating elements is used to print on the thermal paper, the amount of heat generated by each of the heating elements is determined. What is claimed is: 1. A thermal printer characterized by comprising means for controlling the temperature to be variable.