JPH02103158A - How to apply energizing pulses to edge type thermal head - Google Patents

Abstract

PURPOSE:To extend pulse-resistant life by applying a current supply pulse, wherein the printing length in a sub-scanning direction becomes 1/n of the length of one pixel in the sub-scanning direction, to a heating element. CONSTITUTION:One terminal of each of heating elements 2 is connected to a common electrode 8 and the other terminal thereof is connected to an indivisual electrode 6. The common electrode 8 is connected to a power supply terminal Vh for supplying a current to each of the heating elements 2 to generate heat and the indivisual electrode 6 is connected to the drive transistor 26 of a driving IC. The heating elements 2 are grouped into units controlled by one or a plurality of the driving ICs and a printing signal SB is respectively allotted to the respective groups. When a pulse width is set to tp/5 for dividing the printing of one pixel into five times, the peak temp. Tp of each heating element is lowered and a printing dot becomes almost rectangular and a line of five dots is formed in the distance x1 of one pixel in a sub-scanning direction. By this method, the peak temp. of the heating element can be lowered and pulse resistance can be enhanced.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a thermal head used in a printer such as a video printer or a handy printer, or a facsimile machine, and in particular to an energizing pulse of a so-called edge-type thermal head. This relates to the application method.

(Conventional Technique v#) The present inventors have discovered that a heating element is formed at one end of one main surface of a heating substrate, and a recording medium is arranged along the edge of the one end of the heating substrate in the thickness direction of the heating element. We are proposing an edge-type thermal head that prints by sliding on the surface.

An example of such an edge-type thermal head is shown in Figures 1 and 2.
This will be explained using figures. FIG. 1 is a sectional view showing the heating element portion, and FIG. 2 is a plan view showing the heating element and electrodes.

Reference numeral 2 denotes heating elements, which are arranged along one end on the surface of the substrate 4 and are patterned in a shape bent in the opposite direction to that end of the substrate 4. One end of each heating element 2 is a driving IC
It is connected to a selection electrode 6 connected to the chip, and the other end is connected to a common electrode 8. ,! ! The l plate 4 can be made of glass, ceramic, etc., and the materials of the heating element 2 and electrodes 6.8 are the same as those of conventional thermal heads.

Reference numeral 10 denotes an upper substrate for protecting the heating element 2 and the electrodes 6.8, and is bonded with an adhesive 12.

A recording medium 14 such as thermal recording paper, thermal transfer paper and recording paper is pressed by a platen roller 16 against the surface of the substrate at one end where the heating element 2 is provided, and is slid in the thickness direction of the heating element 2. Printing is performed while The thickness direction of the heating elements 2 is the sub-scanning direction, and the direction in which the heating elements 2 are arranged is the main scanning direction.

The edge-type thermal head is not limited to the type in which the heating element 2 is exposed at the edge of the substrate as shown in FIG. Or provide a heat insulating layer on both.

There is also a type in which the heat of the heat generating element 2 is transmitted to the recording medium 14 through the heat insulating layer.The edge type thermal head, which is the subject of the present invention, has various types in which the thickness direction of the heat generating element 2 is the sub-scanning direction. Contains formats.

If you try to print with such an edge-type thermal head using the same drive method as a conventional flat-type thermal head,
Printing for one pixel is performed with one energizing pulse.

(Problem to be solved by the invention) Figure 5 shows the case of printing for two pixels.
As shown in FIG. 3A, a current pulse having a pulse width tp is applied to each pixel. At this time, the applied energy E given to the heating element 2 is E=Vh'' t p/R (Vh is the applied voltage),
The temperature change of the heating element at that time is as shown in FIG. Ts is the temperature required to develop or transfer color on the recording medium, and Tp is the peak temperature of the heating element.

In the edge-type thermal head, the thickness of the heating element 2 is extremely thin, so in order to enlarge the printing dots 18 by thermal diffusion as shown in FIG. It has to be made much larger, and as a result, the l@heating body is susceptible to oxidation and deterioration, or to thermal shock, which shortens the pulse resistance life.

Further, although the thickness of the heating element is extremely small compared to the size of one pixel in the sub-scanning direction, the line density in the sub-scanning direction cannot be controlled.

Since the dot of one pixel is printed mainly by thermal diffusion, the shape of the printed dot is almost circular, which is not preferable for use in image printers, for example, because the print quality has a rough feel.

An object of the present invention is to solve the above-mentioned problems by improving the method of applying current pulses in an end-face type thermal head.

(Means for solving aM) In the present invention, an energizing pulse is applied to the heating element so that the print length in the sub-scanning direction is 1/n of the length of one pixel in the sub-scanning direction. Here, n is an integer satisfying 1<n:512/1 (12 is the length in the sub-scanning direction for one pixel, and t is the thickness of the heating element).

(Function) An example of the application method according to the present invention will be explained using FIG. 6. In FIG. In contrast to applying one energizing pulse with a width tp, in FIG. 6, a short pulse width (for example, t
Apply five energizing pulses of p15).

As shown in FIG. 6(B), the temperature of the heating element for each applied pulse is such that the peak temperature TP is lower than that in FIG. becomes shorter in the sub-scanning direction. As a result, the 6th
As shown in Figure (C), one approximately rectangular pixel is printed by five printing dots.

(Embodiment) FIG. 3 shows a drive circuit for carrying out the energizing pulse application method of one embodiment.

2 (2-1 to 2-m) are heating elements, one end of each heating element 2 is connected to the common electrode 8, and the other end is connected to the individual electrode 6. The common electrode 8 is connected to a power supply terminal vh for energizing the heating element 2 to generate heat.

The individual electrodes 6 are connected to a drive transistor 26 of a drive IC. The number of driving ICs is a predetermined number 1, for example, 128 or 2.
The energization of 56 heating elements 2 is controlled. The figure shows the circuit of one driving IC and the heating element 2 corresponding to it.

The driving IC includes a serial-in/parallel-out type shift register 20 that inputs a print data signal from a data input terminal DI and advances the data signal by a clock signal from a clock signal terminal GK, and a load signal terminal LD. shift register 20 by the load signal from
a latch 22 that inputs and holds data, and a predetermined number of AND gate circuits that input the data held in the latch 22 to one input terminal and input an energization pulse signal (strobe signal) SB to the other input terminal. 24, and a predetermined number of drive transistors 26 that energize the heating element 2 according to the output signal of each AND gate circuit 24. One drive transistor 26 is provided for each heating element 2, and the emitter of each drive transistor 26 is connected to the ground terminal GNDh. 00 is a data output terminal from the shift register 20.

Vdd is a power supply terminal for operating this driving IC, and GNDQ is a ground terminal of this driving IC.

The heating elements 2 are grouped into units controlled by one or more driving ICs, and a print signal SB is sent to each group.
are assigned to each.

28 is an n-fold frequency divider, which has a function of converting the frequency of one energizing pulse signal to 5 Baln times, and also
It is equipped with a low pulse generator that generates a pulse signal with a period of /n, and also has a function of making the duty of the output energizing pulse signal SB variable.

The energizing pulse signal SBa applied to the divider 28 is a signal of 1 pulse per pixel, as in the case of the planar thermal head.

FIG. 4 is a timing chart of one embodiment.

It is assumed that one line is printed at a cycle of 10 milliseconds. Data is sent to the shift register 20 at the timing of the clock signal CK, and data is sent from the shift register 20 to the latch 22 in response to the load signal LD.

The energizing pulse signals sent to the frequency divider 28 are 5BIa, 5B
As shown by 2a, this is a signal with one pulse per line. The pulse width tp is, for example, 2.5 milliseconds. In the circuit shown in FIG. 3, there is one energizing pulse signal, but since there are two such circuits, two energizing pulse signals SB1a and 5B2a are used.

The branch divider 28 quadruples the frequency of the energizing pulse signals 5Bla and S'B2a. As a result, 1 frequency divider 28 to gate 2
4 is an energizing pulse signal SB1.4 with a pulse width of t p /4 = 0.625 milliseconds. SB2 is applied. The energizing pulse signals SBI and SB2 are applied four times during the period of 10 milliseconds of the 1 line.

In this embodiment, the applied voltage vh is constant.

The energy E that would normally be applied with one pulse is reduced to 1/4
The energy is applied in small increments at a cycle of 174.

By using the drive circuit shown in FIG. 3, the printing shown in FIG. 6 can be performed. Figure 4 shows an example where printing of one pixel is divided into four times, while Figure 6 shows the case where printing of one pixel is divided into five times, which is the number of divisions n. can be set arbitrarily.

In Figure 6, as shown in (A), printing of one pixel is
Since the pulse width is set to tp15 in order to divide the printing into three times, the peak temperature Tp of the heating element at that time is lower than that in Fig. 5, as shown in Fig. 5 (B), and the printed dot is As shown in (C), it becomes approximately rectangular. A line of five dots is formed between the distance XI of one pixel in the sub-scanning direction.

FIG. 7 shows an energizing pulse application method in another embodiment.

In FIG. 6, since an energizing pulse signal having a pulse width divided into five equal parts is applied, the shape of the printed dots tends to be small in the first line and gradually become larger as heat accumulates. Therefore, when printing the first pixel, the pulse width of the first two pulses is made slightly longer. In other words, as shown in FIG.

The energization pulse signal is controlled so that the pulse width gradually becomes smaller as t p r >t p => t P3. As a result, the peak temperature Tp of the heating element at each energization pulse signal becomes constant as shown in the figure (B), and uniformly shaped dots can be obtained as shown in the figure (C). .

FIG. 8 shows an example of printing lines in the sub-scanning direction.

(A) shows the case where one pixel is printed using one energizing pulse signal, and the size of one pixel is approximately 125 μm×125 μm. In the case of (A), the pixels are approximately circular.

(B) shows an example in which printing is performed by dividing one pixel into three pulses in the sub-scanning direction.The zero pixel is a rectangle, and when a line is printed, it is printed as a continuous line.

In the case of a video printer, rectangular pixels produce a smoother picture, while 0 circular pixels produce a rough picture.

Figures 9 to 11 show experimental data for varying the number of printing pulses per pixel in the sub-scanning direction.The horizontal axis is the applied energy per line, and the vertical axis is thermal recording paper (Ricoh Co., Ltd. product RT -170 paper).

FIG. 9 shows an example in which one pixel is printed with one pulse in the sub-scanning direction. One line is printed at a cycle of 10 milliseconds. Duty is 25%.

8 lines are printed per 1 mm.

FIG. 10 shows an example in which one pixel is printed with two pulses in the sub-scanning direction. In this case, one line is printed at a cycle of 5 milliseconds, and the duty is 25%. 16 lines are printed per 1 mm.

FIG. 11 shows an example in which one pixel is printed with three pulses in the sub-scanning direction. In this case, the l line is printed at a cycle of 3.3 milliseconds, and the duty is 25% *2 per 1 mm.
4 lines are printed.

According to the experimental results shown in FIGS. 9 to 11, the optical density is 1.
The energy per l line to obtain 2 is.

Let 1 be the case where one pixel is printed with one pulse.

When printing with 2 pulses, the amount decreases to about 1/2, and when printing with 3 pulses, it decreases to about 1/3. Therefore, the total energy required for printing is constant.

FIG. 12 shows the results of a pulse resistance test performed by blank printing with the energy per line determined from FIGS. 9 to 11.

The number of lines on the horizontal axis represents the number of lines actually printed. In other words, when printing one pixel with one pulse, the number of lines = the number of pulses (the number of pulses of the energizing pulse signal given to the thermal head from the outside), but for example, if one pixel is printed with three
In the case of pulse printing, the 0M axis ΔR/R, where the number of lines=3×the number of pulses, represents a change in the resistance value of the heating element, which represents the degree of deterioration of the resistor.

A is when one pixel is printed with one pulse in the sub-scanning direction, B is
C is the case where one pixel is printed with two pulses in the sub-scanning direction, and C is the case where one pixel is printed with three pulses in the sub-scanning direction.

The results shown in FIG. 12 show that as the number of pulses used to print one pixel increases, the resistance value change of the heating element decreases, that is, the pulse durability improves.

The present invention not only improves pulse durability and print quality, but also can be used to control line density in the sub-scanning direction.

In the method of printing one pixel in the sub-scanning direction with n pulses, the number of printing lines in the sub-scanning direction increases to n lines, so that any line density can be obtained by changing n. One application is 1, for example, when the sub-scanning direction is 1/
2.1/3. ...Reduction printing reduced to 1/n can be performed without reducing the amount of image data. On the other hand, in conventional planar thermal heads, when the length of the heating element in the sub-scanning direction is shortened, the resistance value decreases, and also a step is created in the wear-resistant layer for the electrode, making contact with the recording medium poor. Print quality deteriorates. Therefore, with the conventional planar thermal head, it is not possible to increase the linear density in the sub-scanning direction.

The present invention can also be applied to other applications, such as gradation printers. By changing the data every n lines that print one pixel, the number of dots printed in one pixel changes, making it possible to create pixel gradations.

In a conventional planar thermal head, the length of one heating element in the sub-scanning direction is limited to 50 to 100 μm, and the length of each heating element is 50 to 100 μm.
The limit is 0 to 20 lines. However, in the edge type thermal head, the line width in the sub-scanning direction can be set to the thickness of the heating element or several times that thickness, so the line width can be set to 0.
．． 1-10 μm, and 100-10 μm
4 lines/mm is possible, resulting in extremely high-resolution printing.

(Effects of the Invention) In the present invention, an energization pulse signal controlled so that the print length in the sub-scanning direction is 1/n of the length of one pixel in the sub-scanning direction is applied to the heating element of the end-face type thermal head. Therefore, the peak temperature of the heating element can be lowered and the pulse resistance can be improved.

Since the shape of the print dot approaches a rectangle, the print quality improves.

Printing can be performed with high resolution in the sub-scanning direction.

Furthermore, gradation printing or printing reduced in the sub-scanning direction can also be performed. Reduced printing is highly effective in reducing the running cost of recording media.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an end-face type thermal spatula to which the present invention is applied, FIG. 2 is a plan view showing the heating element and electrodes, and FIG.
The figure is a circuit diagram showing an example of a drive circuit to which the present invention is applied;
FIG. 4 is a timing diagram showing the operation of one embodiment, and FIG. 5 (
A), (B), and (C) are diagrams showing conventional 1-pulse printing;
Figure 6 (A), (B). (C) is a diagram showing 5-pulse printing in one embodiment, and Figure 7 (A
), (B), and (C) are diagrams showing 5-pulse printing of other embodiments, FIG. Figure 9 shows the applied energy and color density in 1-pulse printing. Figure 10 shows the applied energy and color density in 2-pulse printing. Figure 11 shows the applied energy and color density in 3-pulse printing. FIG. 12 is a diagram showing applied energy and coloring density, and FIG. 12 is a diagram showing changes in the resistance value of the heating element when the number of pulses for printing one dot is changed. 2.2-1~2-m... Heating element, 20...
...Shift register, 22...Latch, 24.
....AND gate, 26 ....drive transistor, 28 ....frequency divider, SB ....energizing pulse signal. Figure 1

Claims (1)

[Claims] (1) A heating element is formed on one end of one main surface of the heating substrate, and an end surface on which printing is performed by sliding the recording medium in the thickness direction of the heating element along the end surface of the one end of the heating substrate. 1. A method for applying an energizing pulse in a type thermal head, comprising applying to a heating element an energizing pulse whose print length in the sub-scanning direction is 1/n of the length of one pixel in the sub-scanning direction. However, n is an integer satisfying 1<n≦l/t (l is the length in the sub-scanning direction for one pixel, and t is the thickness of the heating element).