JPS59142170A - Density-controlling method for thermal head - Google Patents

Abstract

PURPOSE:To eliminate irregularlity in density, trailing or the like from occurring and contrive to enhance print quality, by controlling the current-passing time for heating resistors in accordance with the temperatures detected by temperature sensors. CONSTITUTION:The current-passing time (t) for the heating resistor is controlled in accordances with the temperature Ts detected by the nearest one of the temperature sensors 5A-5E so that t=t5 when Ts<=T1, t=t4 when T1<Ts<=T2, t=t3 when T2<Ts<=T3, t=t2 when T3<Ts<=T3, t=t1 when T4<Ts<=T5, and t=0 (passing no current) when T5<Ts. For example, the heating resistor is divided into 10 sections 1st common (a)-10th common (j), and when the temperatures Ts detected by the temperature sensors 5A-5E are T1<Ts(5A)<T2, T2<Ts(5B)<T3, T3<Ts(5C)<T4, T2<Ts(5D)<T3 and Ts(5E)<T1, the current- passing times for the commons of the thermal head may be set to be as shown. In this case, the current-passing time for each of 2nd, 4th, 7th and 9th commons located at an intermediate part between an adjacent pair of the temperature sensors is set in accordance with the lowest of the temperatures detected by the pair of the temperature sensors.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a density control method for a thermal head. 1st
The figure shows a conventional thermal head device, where (a) is a plan view and (opening) is a side view a.In the figure, l is a thermal head, 2 is a cover, 3 is a heat sink, and 4 is a part of a connector. , 5
is a temperature sensor. That is, when a voltage and a printing error signal are applied through the connector part 4, the thermal head 1
A predetermined heating resistor is energized according to the print signal by the driver 1 shift register mounted on the printer, and generates Joule heat. Then, the specially processed thermal paper reacts and develops color due to this Joule heat, forming an image. It is a temperature-density characteristic diagram of the 21st thermosensitive paper.

That is, color development starts at a temperature of 70°C and saturates at 11°C. Normally, a Macbeth density of 08 or higher can be used for printing quality reasons, but the printing density changes depending on the environmental temperature and energization duty. Therefore, in order to keep the print density constant, conventionally a temperature sensor 5 is attached to the center of the heat sink 3, and when the heat sink 3 reaches a certain temperature or higher, the power supply to the entire device is automatically stopped. When the voltage drops to , it starts energizing.

In addition, methods such as forced cooling by rotating a fan above a certain temperature have been adopted recently.

As the manufacturing technology for thermal heads has improved, long thermal heads for JIS A4 or A3 size are now being used. Since the edges of the board cool down faster and the center part of the board does not cool down easily, the temperature remains the same. Therefore, it is not possible to eliminate the shading of the print.

The present invention aims to eliminate such drawbacks and improve printing quality. FIG. 3 is a plan view of the thermal head device according to the present invention. 3 in the figure is a heat sink, 5A~
5E has exactly the same structure as that shown in FIG. 1, except that five temperature sensors are mounted on the heat sink 3 at different positions, and the others are not shown. Then, as shown in FIG. 4, each detected temperature Ts of the temperature sensors 5A to 5E is Ts≦
When T1, is the energization time t? tsThTl(Ts≦T2
When t = t4. T2 (t=t3 when Ts≦T3
, TS (when Ts≦T4, t'='t2, T4<TS
When <T5, t=tl, when T5<TS, energization is stopped (
The energization time of the heating resistor is controlled in accordance with the salinity of the nearest temperature sensor so that i=o). For example, the third
Assuming that the heat generating resistor is divided into 10 parts as shown in the figure, with 1 common to 10 commons, the relationship between each common and the temperature sensor will be as shown in Figure 3. and.

For example, if the temperature Ts of the temperature sensor is Tl<Ts (
5A)<T2, T2<TS (5B)<TS,
TS<TS (5a)(T4 k T2<TS(5
D) <TS, TS (5g) <Tl, the energization time of each common of the thermal head (11) If you do it as shown in Figure 5, the 2nd common and 4th common located in the middle of the temperature sensor , 7 common, 9 common, soh
Of the left and right temperature sensors, if you follow the energization time of the sensor that indicates the temperature to be lowered, it will be more than 0. Even with a long thermal head, there will be no shading or trailing. The effect is that the printing quality is improved.

[Brief explanation of the drawing]

Fig. 1 shows a conventional thermal head device, in which Fig. 1 (a) is a plan view and Fig. 1 (b) is a side view. Fig. 2 is a temperature-density characteristic diagram of thermal paper, Fig. 3 is a plan view showing an example of a thermal head device according to the present invention, and Fig. 4 is an example of energization time with respect to sensor temperature for carrying out the method of the present invention. Figure 6 is a diagram showing an example of one hour of energization of each common of the heat generating resistor. Temperature (”c) → Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] 1. A large number of horizontal-sized heating resistors? In the thermal head (1), the detection means (5A to 5E) each detects multiple locations of the thermal head; the temperature is divided into multiple stages, and the higher temperature stage is detected by the thermal head. Temperature vs. energization time table (1) where the energization time is shortened and the energization time is increased by 4 hours at the low temperature stage (
Figure 4); At the time of printing, the energization time according to the temperature value obtained by the detection means (5A to 5E) K is determined from the temperature vs. energization time table (
Fig. 4) is a method for controlling density in a thermal head for printing.