JPH0444863A - Thermal recording head - Google Patents

Abstract

PURPOSE:To carry out recording in high gradation by constituting the title thermal recording head so as to change the length of a dot even in a main scanning direction in addition to a sub-scanning direction. CONSTITUTION:A plurality of resistance elements 11... are formed in an arrayed state in a main scanning direction on a base 10a fixed on the under face of a head body 10. Each of the resistance elements 11... has a thickness varied stepwise according to its parts positioned in the main scanning direction so as to be made thickest at its central part and thinnest at both its end parts, and its parts positioned in a sub- scanning direction normal to the main scanning direction are made the same in thickness. Further, electrodes 15, 16 are mounted to the end parts positioned in the sub- scanning direction, respectively. The resistance elements 11... are formed by packing a resistant material such as RUO2, IrO2 and OtO2 into their stepwise recesses formed by the etching processing of the base 10a. Each resistance element varies in a resistance value according to its thickness and has the highest heat value at its central part. Since a heat value varies according to electrical energy applied to resistance elements, the lowermost recordable heat value is denoted by TH, and the heat value is shifted by selecting, for example, three kinds of applied voltage V1-V3, whereby the length of a dot in the main scanning direction can be changed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a thermal recording head used in a thermal printer.

[Conventional technology]

Thermal recording includes a thermal recording method in which color recording is performed by heating a thermal recording paper, and a thermal transfer recording method in which the back of an ink ribbon is heated to transfer ink to the recording paper. These thermal recording methods use a thermal recording head in which a large number of resistance elements are arranged in a line.

As a conventional thermal recording head, for example, Japanese Patent Application Laid-Open No. 60-24
As described in Japanese Patent No. 8074, there is known a resistor element that uses a horizontally long resistance element whose length in the main scanning direction is larger than its length in the sub-scanning direction. When recording an image with this thermal recording head, the resistance element is energized for a time corresponding to the image data while the recording paper moves by the length of the pixel area in the sub-scanning direction. This changes the recording length in the sub-scanning direction, so that dots of a size corresponding to the image data are recorded on the recording paper.

[Problem to be solved by the invention]

When using a conventional thermal recording head, it is possible to change the length of the dots in the sub-scanning direction, but it is not possible to change the length of the dots in the main-scanning direction, making it difficult to record high gradations. It was difficult.

SUMMARY OF THE INVENTION An object of the present invention is to provide a thermal recording head that can perform high-gradation recording by changing the length of dots in the main scanning direction as well as in the sub-scanning direction. be.

[Means to solve the problem]

In order to achieve the above object, the present invention uses a resistance element having a resistance value distribution characteristic such that the resistance value in the main scanning direction decreases from the edge toward the center, and arranges these in a line in the main scanning direction. They are arranged in a shape.

In addition to changing the thickness of the resistance element, this resistance value distribution characteristic is
It can be obtained by using a plurality of resistance materials with different specific resistances and changing the resistance materials depending on the position.

[Effect]

The amount of heat generated by each resistance element changes depending on its position in the main scanning direction due to its resistance value distribution characteristics. This heat generation distribution shifts depending on the magnitude of the voltage applied to the resistive element, so by controlling this voltage, the length of the dot in the main scanning direction can be changed. Therefore, by using this method in combination with the conventional energization time control method, it is possible to record dots whose lengths vary in the main scanning direction and the sub-scanning direction on the recording paper.

Embodiments of the present invention will be described below with reference to the drawings.

〔Example〕

In FIG. 2 showing the thermal recording head, a substrate 10a is fixed to the lower surface of the head body 10, and a large number of resistive elements are formed on this substrate 10a in a line in the main scanning direction. In the drawing, only three resistive elements 11-13 are shown. The resistive element 11 has an electrode 1 at the end in the sub-scanning direction.
5.16 are attached to each. Note that a pair of electrodes is attached to each of the resistance elements 12 and 13, respectively. In this embodiment, the resistive elements 11 to 13 are divided, but they may be one continuous resistive element.

As shown in FIG. 1, the thickness of the resistance element 11 changes stepwise depending on the position in the main scanning direction.

That is, the thickness is greatest at the center and the thinnest at both ends. On the other hand, as shown in FIG. 3, the thicknesses are the same in the sub-scanning direction. Reference numeral 18 is a protective layer;
It is omitted in FIG. Note that the resistors 12 and 13 also have the same structure as the resistor element 11.

The resistor element 11 is formed by etching the substrate 10a to form a stepped recess, and filling the recess with a resistive material. This resistance material is
Ru02, I-0□, PtO2, etc. are used. There are various methods for filling the resistive material, but for example, it can be carried out by dispersing powdered resistive material in a resin, printing it in the recesses, and then sintering it. Alternatively, the resistive material may be filled using a sputtering method or a sol-gale method.

The fourth example shows resistance value distribution characteristics in the main scanning direction. Since each resistance element has a different thickness in the main scanning direction, the resistance value changes depending on the thickness. As a result, as shown in FIG. 5, the amount of heat generated at the center becomes the highest. Here, TH is the lowest recordable heat amount. Since the amount of heat generated changes depending on the electrical energy applied to the resistance element, for example, three types of applied voltages Vl, V2. By selecting V3, the amount of heat generated can be shifted, thereby changing the length of the dot in the main scanning direction.

For example, with the applied voltage V1, only the central portion of the resistive element can be recorded, so that a dot having a length Wl in the main scanning direction is recorded. At applied voltage V2, the i' foot length becomes W2, and at applied voltage V3, the length becomes W3.

FIG. 6 shows an example of a resistance element drive circuit.

The drive data generation circuit 20 stores a combination of voltage and energization time for each image data (density level). The image data is converted by the drive data generation circuit 20 into voltage data and energization time data. This voltage data is sent to the voltage control circuit 21, and one of the three voltages (1) to (3) is selected. This selected voltage is applied to the resistance element 11. The energization time data is sent to the energization time control circuit 22.

The energization time control circuit 22 generates a pulse having a width corresponding to the energization time data in synchronization with the leading edge of the line print signal. The output terminal of the NAND circuit 23 becomes rL when both the line print signal and the pulse are rHj. Since the resistance element 11 is connected between the NAND circuit 23 and the voltage control circuit 21, the resistance element 11 is energized for a time corresponding to the pulse width of the pulse output from the energization time control circuit 22, and generates heat. . Note that these voltage control circuits and energization time control circuits are provided for each resistance element.

FIG. 7 shows the state of image recording. Recording paper 25
is sent in the arrow direction at a constant speed, and the resistance element 11
14, an image is recorded line by line by thermal recording or thermal transfer recording. The pixel area 26 has a length of 160 mm in the sub-scanning direction indicated by the arrow.
μ, and the length in the main scanning direction is 120 μ. By controlling the applied voltage and energization time according to the image data while the recording paper 25 moves by the pixel area 26,
The recording area of the dot within the pixel area 26 is determined. For example, the voltage 3 is applied to the resistance element 11 and the current is passed for a relatively long time, so that the size of the dot 27 becomes W3XL3. Since the voltage V2 is applied to the resistive element 12, a dot 28 whose length in the main scanning direction is W2 is recorded, and since the voltage 1 is applied to the resistive element 13, the dot 28 is recorded in the main scanning direction. The length at is Wl, and a small dot 29 is recorded. Note that since the resistance element 14 is not energized, no dots are recorded.

If the energization time is adjusted in 32 steps, the length of the dot in the sub-scanning direction changes in 32 steps. In this embodiment, the length in the main scanning direction can be changed in three stages, so 3X32=
It can express 96 levels of gradation. This gradation expression ability depends on the recording length in the main scanning direction, so
It can be further increased by increasing the number of steps in the thickness of the resistance element. In practice, 3 to 6 stages are sufficient.

In addition to changing the thickness of the resistive element in a stepwise manner, it may also be changed in a curved manner. In this case, as shown in FIG. 8, since the resistance value distribution changes smoothly, the recording length in the main scanning direction can be changed steplessly by adjusting the applied voltage. In addition to changing the thickness of the resistive element, a plurality of resistive materials having different specific resistances may be used, and the resistive material may be selected depending on the position in the main scanning direction.

In the embodiment described above, the pair of electrodes are arranged to face each other in the sub-scanning direction, but they may be arranged to face each other in the main-scanning direction. In this case, electrodes extending in the sub-scanning direction may be arranged at a constant pitch on one resistor extending in the main-scanning direction.

Furthermore, the resistance element may be approximately square, and the resistance value may be changed not only in the main scanning direction but also in the sub-scanning direction. This can be achieved by making the resistor element pyramid-shaped with steps. When the resistance value is changed two-dimensionally, electricity is applied for a time corresponding to image data while the recording paper is stopped and a constant voltage is applied. In this way,
Since the amount of heat generated increases as the energization time increases, the size of the dot changes two-dimensionally depending on the energization time.

〔Effect of the invention〕

As explained in detail above, according to the present invention, each resistance element has a resistance value of 4 degrees that differs depending on the position in the main scanning direction, so the amount of heat generated changes depending on the position in the main scanning direction. . Therefore, since the recording length of the dots changes also in the main scanning direction, the gradation expression ability can be improved.

[Brief explanation of the drawing]

FIG. 1 is a sectional view taken along line 1-1 in FIG. 2. FIG. 2 is a plan view of the recording head of the present invention. FIG. 3 is a sectional view taken along the line l-11r in FIG. 2. FIG. 4 is a graph showing the resistance value distribution in the main scanning direction. FIG. 5 is a graph showing the calorific value distribution in the main scanning direction. FIG. 6 is a block diagram showing a drive circuit for a resistive element. FIG. 7 is an explanatory diagram showing the recording state. FIG. 8 is a graph showing another example of the resistance value distribution in the main scanning direction. 11-14... Resistance element 1516... Electrode 26... Pixel area 27-29... Dot. Figure Figure 11 (Resistance element) 1 (, IOtJk72) Figure Figure Position in main scanning direction Figure Position in main scanning direction Figure Procedure amendment April 18, 1991

Claims (1)

[Claims] (1) In a thermal recording head in which a large number of recording elements are arranged in a line in the main scanning direction, each of the resistance elements has a resistance value in the main scanning direction that decreases from the end toward the center. A thermal recording head characterized by having distribution characteristics.