JPS61290072A - Thermal printer - Google Patents

Abstract

PURPOSE:To raise the pressure of contact of a thermal head and a platen roller, uniformize pressure distribution and enable recording with high image quality, by providing a back-up roller rotated in contact with a platen roller on the movable direction side of the platen roller. CONSTITUTION:When a pressure is exerted on the platen roller 3 by the thermal head 1, the roller 3 with a small diameter may undergo a bending deformation with the result of a lowering in the pressure of contact thereof with the thermal head 1 at a central part, leading to a lowering in the image quality on a recording paper. The avoid this, the back-up roller 4 is provided with a crowning part 4a at a central part of the span thereof to cover the bending deformation of the platen roller 3. Accordingly, the back-up roller 4 and the platen roller 3 can be brought into smooth contact with each other for rotation, the pressure of contact of the head 1 and the roller 3 can be prevented from being lowered, the pressure of contact can be enhanced, and a uniform pressure distribution can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a thermal printer, and particularly to a printer suitable for improving the quality of printing and reducing the size of the device.

[Background of the invention]

Generally, in thermal printers and transfer-type thermal printers, the contact situation between the thermal head and the platen roller affects the image quality, so conventionally, a platen roller rubber material has been used to increase the pressing force and ensure the contact pressure.

In recent years, highly accurate paper feeding has become essential to improving image quality, so paper feeding mechanisms using soft rubber materials are no longer able to provide satisfactory accuracy.

In conventional thermal printers, for example,
As disclosed in Publication No. 92, the platen roller is composed of only one roller, and in order to have sufficient bending rigidity against the pressing force of the thermal head, the diameter cannot be reduced. .

Further, for example, in the transfer type thermal printer described in Japanese Patent Application Laid-Open No. 59-14974, a minute suppressing member consisting of a guide pipe equipped with a thermal ink stick is used instead of the platen roller, and the suppressing member and the thermal head are connected to each other. The aim is to increase the contact pressure between the two and improve the image quality.

However, sufficient consideration was not given to the fact that the structure of the mechanism was complex and unsuitable for high-speed recording.

[Purpose of the invention]

The present invention has been made in order to solve the problems of the prior art described above, and is a compact design that increases the contact pressure between the thermal head and the platen roller and makes the pressure distribution uniform to enable high-quality recording. Its purpose is to provide thermal printers.

[Summary of the invention]

A thermal printer according to the present invention includes a thermal head equipped with a heating element that generates heat in response to an image signal, and a platen roller that conveys at least recording paper while pressing the thermal head. The platen roller is rotatable and movable in only one direction, and a backup roller that rotates in contact with the platen roller is rotatably disposed on the movable direction side of the platen roller.

As an additional note, the present invention uses a platen roller with a minimum necessary diameter to increase the contact pressure with the thermal head, and reduces the deformation area of the platen roller formed of a rubber material to improve recording paper conveyance accuracy. This improved system uses a backup roller connected to a drive source to transmit rotational force to the platen roller, and also corrects bending deformation of the platen roller, maintaining the best contact between the thermal head and the platen roller. It is something.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to FIGS. 1 to 4.

First, FIG. 1 is a schematic configuration diagram showing the basic configuration of a thermal printer according to an embodiment of the present invention, and FIG. 2 is a diagram showing the basic configuration of a thermal printer according to an embodiment of the present invention.

FIG. 2 is a perspective view showing support parts for a platen roller and a backup roller of the thermal printer shown in FIG. 1;

In FIG. 1, 1 is a thermal head equipped with a heating element that generates heat according to an image signal, 2 is a thermosensitive coloring paper related to recording paper, and 3 is a thermosensitive coloring paper 2 that is conveyed while being pressed by the thermal head 1. This is a platen roller for

This platen roller 3 is equipped with a rubber roller part 3a (see Fig. 2) and has a minimum necessary diameter, and is rotatable in one direction (up and down in the y-axis direction in Fig. 1) as shown by the arrow. direction). The mounting state will be described later with reference to FIG. 2.

Reference numeral 4 denotes a backup roller rotatably disposed at a position corresponding to the movable direction of the platen roller 3 (or diagonally downward) and in a position where it can rotate in contact with the platen roller 3. This backup roller 4 is made of metal Alternatively, it is made of synthetic resin and has the same or approximate diameter as the platen roller 3, but has a slight bulge, that is, a crowning portion 4a (see FIG. 2) in the center.

In this embodiment, the platen roller 3 and the backup roller 4 are arranged so that their axes are parallel to each other.

5 is a drive source for the backup roller 4, such as a DC motor with a speed reducer, and 6 is a rotation angle detector, such as a rotary encoder, for detecting the rotation angle of the platen roller 3.

The mounting position of this rotation angle detector is platen roller 3.
It is not limited to being on the axis, but it may be on the four axes of backup rollers or the DC motor 5 with a reduction gear.

FIG. 2 shows the platen roller 3. A support mechanism for the backup roller 4 is shown.

A roller shaft 4b of the backup roller 4 is rotatably supported by the side plate 7 via a bearing 8.

The shaft 3b of the platen roller 3 is inserted into a concave bearing 9 formed in the side plate 7 so that the platen roller 3 can rotate freely and only move up and down. The U-shaped concave bearing 9 has a roller shaft 3 between parallel protruding members.
b is held in such a way as to be rotatable and movable up and down.

On the other hand, the base material of the thermal head 1 is formed of, for example, an aluminum alloy, and an inverted U-shaped roller shaft guide 10 is formed on the aluminum alloy base material.

This roller shaft guide 10 has a platen roller shaft 3b sandwiched by the concave bearing 9 inserted between parallel protruding members, and a heating resistor array (not shown) related to the heating element of the thermal head 1. ) functions as an alignment means to ensure good contact between the platen roller 3 and the platen roller 3.

Reference numeral 11 indicates a pressing spring provided for suppressing and floating the thermal head 1.

Next, the operation and effects of the thermal printer of this embodiment configured as described above will be explained.

When a thermosensitive coloring paper 2 related to recording paper is fed between the thermal head 1 and the platen roller 3 and the thermal head 1 is pressed, a force equal to the pressing force is applied to the platen roller 3.
and the backup roller 4. In this state, the driving force transmitted from the DC motor 5 with a reduction gear is
It is transmitted from the backup roller 4 to the platen roller 3. The driving force transmitted to the platen roller 3 becomes a force for conveying the thermosensitive coloring paper 2, and the thermosensitive coloring paper 2 is conveyed.

The heat-sensitive coloring paper develops color due to the heat generated by the heating element of the thermal head, and an image is recorded.

After recording is completed, when the thermal head 1 rises from the platen roller 3, the platen roller 3 and the backup roller 4
A pressing force equal to the weight of the platen roller 3 acts between them.

Generally, as described above, when the pressing force of the thermal head 1 acts on the platen roller 3, the small diameter platen roller 3
This may cause bending deformation and the contact pressure between the thermal head 1 and the platen roller 3 to be lower at the center, which may reduce the image quality of the recording paper.

Therefore, the backup roller 4 of this embodiment has a slight bulge, that is, a crowning part 4a, formed in the center of its span, and the bending deformation of the platen roller 3 is covered by the crowning part 4a. The platen roller 3 is configured to allow the thermal head 1 and the platen roller 3 to smoothly rotate in contact with each other, and to prevent a decrease in the contact pressure between the thermal head 1 and the platen roller 3.

As described above, according to this embodiment, it is possible to increase the contact pressure between the thermal head 1 and the platen roller 3, and also to obtain a uniform pressure distribution, thereby making it possible to perform high-quality recording. can.

Further, since the platen roller 3 and the backup roller 4 are small diameter rollers, and the supporting mechanism thereof is simple, a compact thermal printer can be provided.

Next, another embodiment of the present invention will be described with reference to FIG.

Here, FIG. 3 is an enlarged view showing the arrangement relationship of a platen roller and a backup roller of a thermal printer according to another embodiment of the present invention, where 3 indicates a platen roller and 4A indicates a backup roller.

In this embodiment, the backup roller 4A is disposed such that the center of its span intersects the center of the span of the platen roller 3 at a crossing angle α.

Incidentally, in FIG. 3, the crossing angle α is greatly emphasized for convenience of explanation.

According to this embodiment, as described in the previous embodiment, the effect of contact pressure due to bending deformation of the platen roller 3 is eliminated, and the contact between the platen roller 3 and the back unroller 4A is removed at the center of the platen roller 3. Since the contact pressure increases due to the crossover, good image quality can be obtained.

In the thermal printers of the above embodiments, the recording paper is assumed to be the thermal coloring paper 2, but it is also possible to use a layered transfer film and recording paper. An embodiment of the transfer type thermal printer will be described with reference to FIG.

FIG. 4 is a schematic configuration diagram of a transfer type thermal printer according to still another embodiment of the present invention, and in the figure, the same reference numerals as in FIG. 1 are the same parts as in the previous embodiment. , the explanation thereof will be omitted.

In FIG. 4, 12 is a transfer film coated with ink that can be transferred by heat, and 13 is a recording paper that receives transfer from the transfer film 12.

A transfer film 12 and a recording paper 13 are interposed and overlapped between the thermal head 1 and the platen roller 3, and are pressed by the thermal head 1.

When one image signal is applied to the thermal radar 1, transfer is performed and recording is completed.

In the case of a color printer, this transfer operation is repeated for three colors, yellow, magenta, and cyan, to obtain a full-color image.

According to this embodiment, the same effects as in the case of the thermal printer described above can be expected.

In each of the above-mentioned embodiments, the support mechanism and alignment mechanism of the platen roller were explained with reference to FIG. 2, but these mechanisms in the present invention are not limited to the example shown in FIG. This does not preclude the adoption of other shapes and structures that are expected to have the same effect.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to provide a compact thermal printer that increases the contact pressure between the thermal head and the platen roller and provides a uniform pressure distribution to enable high-quality recording.

[Brief explanation of the drawing]

1. FIG. 1 is a shaft bearing configuration diagram showing the basic configuration of a thermal printer according to an embodiment of the present invention, and FIG. 2 is a diagram showing the basic configuration of a thermal printer. FIG. 3 is an enlarged view showing the arrangement of the platen roller and backup roller of a thermal printer according to another embodiment of the present invention; FIG. 4 is a diagram showing a shaft bearing configuration of a transfer type thermal printer according to still another embodiment of the present invention. 1...Thermal head, 2...Thermosensitive coloring paper, 3...
・Platen roller, 4, 4A... Backup roller, 4a... Crowning part, 7... Side plate, 9...
Concave bearing, 10... Roller shaft guide, 12... Transfer film, 2nd Ri I 3rd 4, H

Claims (1)

[Scope of Claims] 1. A thermal printer comprising: a thermal head equipped with a heating element that generates heat in accordance with an image signal; and a platen roller that conveys at least recording paper while pressing the thermal head; The platen roller is rotatable and movable in only one direction, and a backup roller that rotates in contact with the platen roller is rotatably disposed on the movable direction side of the platen roller. Thermal printer. 2. The thermal printer according to claim 1, wherein the backup roller is disposed so as to cross the center of the span of the platen roller at the center of its span. 3. The thermal printer according to claim 1, wherein the backup roller is provided with a crowning portion for rotating in contact with the platen roller.