JPH05155058A - Thermal recording method - Google Patents

Abstract

PURPOSE:To express high gradation without making the unit moving quantity of a platen fine. CONSTITUTION:A pulse motor is driven by a carrier pulse of a cycle T. The rotation of the pulse motor is transmitted to a platen through a timing belt to move recording paper 22 in a sub-scanning direction S. A driving pulse of a cycle T/2 is supplied to a heating element 26a during the transfer of the recording paper 22. Since the heating element 26a generates heat twice during one cycle of the carrier pulse, an ink dot is recorded on two sublines.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal recording method for expressing gradation by changing the length of ink dots, and more particularly to a thermal recording method for recording a high gradation halftone image.

[0002]

2. Description of the Related Art Thermal recording printers include a thermal transfer recording type in which an ink film is heated to transfer ink to a recording paper, and a thermal recording type in which a thermal recording paper is heated to develop a color. For example, as a thermal transfer recording type printer, a platen that supports recording paper and is rotatable in the sub-scanning direction, a pulse motor for rotating the platen,
It is composed of an ink film feeding mechanism that feeds the ink film in a state where the ink film is in close contact with the recording paper, and a thermal head that is arranged facing the platen and heats the back of the ink film. This thermal head has a plurality of heating elements arranged in a line in the main scanning direction.

One pixel is composed of a plurality of sub-lines,
A thermal recording method has been proposed in which ink dots are sequentially recorded on each sub-line, and thereby the length of the ink dot in one pixel is changed to express gradation. In order to express high gradation, the movement amount (unit movement amount) of the platen outer peripheral surface per step of the pulse motor is made narrower than the length of the heating element in the sub-scanning direction, and the pulse motor rotates one step. A thermal recording method has been proposed in which the heating element is energized once each time (Japanese Patent Application No. 2-124474).

[0004]

In the above-mentioned thermal recording method, in order to further increase the number of gradations, the width of the sub-lines may be narrowed to increase the number of sub-lines forming one pixel. In this case, it is necessary to improve the drive system of the platen in order to make the unit movement amount as small as possible. For example, using a reduction mechanism with a large reduction ratio,
Alternatively, a pulse motor with a small step angle and a large torque must be used. However, in either case, the platen drive system becomes large in size, which causes a problem of high cost.

An object of the present invention is to provide a thermal recording method capable of expressing high gradation without improving the platen drive system.

[0006]

In order to achieve the above-mentioned object, in the invention described in claim 1, the rotation of the pulse motor is transmitted to the platen via a reduction mechanism including a gear and having a cushioning effect. The heating element is energized a plurality of times during one step cycle of the pulse motor.

According to the second aspect of the present invention, the rotation of the pulse motor is transmitted to the platen via the speed reduction mechanism including the belt in the rotation transmission system, and a plurality of heating elements are provided during one step cycle of the pulse motor. It is designed to be energized twice.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 2 shows a fusion thermal transfer printer embodying the present invention. The controller 10 rotates the pulse motor 12 via the driver 11. A toothed pulley 13 is fixed to the output shaft of the pulse motor 12, and the rotation of the pulse motor 12 is transmitted to a toothed pulley 15 via a timing belt (toothed belt) 14. The toothed pulley 15 is integrally provided with a toothed pulley 16 having a small diameter. This toothed pulley 1
The rotation of 6 is transmitted to the toothed pulley 18 via the timing belt 17. Since the toothed pulley 18 is fixed to the side surface of the platen 19, the pulse motor 12
Thus, the platen 19 is rotated in the sub scanning direction.

The recording paper 22 and the ink film 23 are supported by the platen 19 in an overlapping state. The recording paper 22 and the ink film 23 are connected to the guide roller 2
It is pressed so as to be in close contact with a part of the outer periphery of the platen 19 by 4, 25, and the rotation of the platen 19 causes the recording paper 22 and the ink film 23 to move together in the sub-scanning direction indicated by the arrow. These guide rollers 2
The thermal head 26 is disposed between the nozzles 4 and 25 and heats the ink film 23 from behind. In the thermal head 26, a plurality of heating elements are arranged in a line in the main scanning direction.

The gradation pulse generation circuit 28 generates a number of drive pulses according to the image data of the pixels and sends the drive pulses to the thermal head 26 via the head drive circuit 29. When the number of gradations is N, while the recording paper 22 and the ink film 23 move by one pixel, N driving pulses are supplied to the heating elements in the pixel having the maximum density, and are supplied to the N sub lines. Record ink dots.

The toothed pulleys 13, 15, 16, 18
The number of teeth is, for example, 20,86,20,105, and the reduction ratio is (20/86) × (20/105) =
It becomes 400/9030. The angle (step angle) at which the pulse motor 12 rotates by one carrier pulse is 0.1.
If the diameter of the platen 19 is 8 degrees and the diameter of the platen 19 is 48 mm, the movement amount (unit movement amount) of the outer peripheral surface of the platen per step of the pulse motor 12 is 3.3 μm.

In conventional thermal recording, one pulse motor 12 is used.
Every time the carrier pulse is supplied, one drive pulse is supplied to the heating element. If the number of gradations is doubled, the unit movement amount must be about 1.6 μm, which requires a reduction mechanism with a large reduction ratio and a large pulse motor with a large torque.

The inventor of the present invention measured the movement of the platen 19 with a non-contact displacement meter in the platen drive system shown in FIG. It was confirmed that the platen 19 continuously moves without intermittent rotation when a carrier pulse having a constant cycle is supplied to the pulse motor 12 in order to rotate the platen 19 intermittently. This is presumably because the cycle of the carrier pulse is short and the unit movement amount is small, and therefore the discontinuous movement of the pulse motor 12 is continuously converted into movement due to the buffering effect of the timing belt. Therefore, the present invention drastically increases the number of gradations by utilizing the buffer effect and driving the heating element a plurality of times during one step cycle of the pulse motor 12.

Next, thermal recording by the printer will be described with reference to FIG. The controller 10 drives the carrier pulse having a cycle T (for example, 0.5 ms) by the driver 11
Then, the pulse motor 12 is rotated stepwise. The rotation of the pulse motor 12 is transmitted to the platen 19 via the timing belts 14 and 17 that constitute the speed reducing mechanism, and the outer peripheral surface of the platen is a unit movement amount D (for example, 3.3 μm) for one carrier pulse. Moving. This move is
As shown in FIG. 1, it is performed continuously.

By the rotation of the platen 19, the recording paper 22 and the ink film 23 are moved in the sub-scanning direction shown by the arrow while being in close contact with each other. During this movement, the drive pulse generation circuit 28 generates a number of drive pulses according to the image data of the pixels and supplies the drive pulses to the heating element 26a of the thermal head 26 via the head drive circuit 29. The drive pulse generation circuit 28 generates a drive pulse with a cycle T / 2 so that the heating element 26a of the thermal head 26 generates heat twice for one carrier pulse. The heating element 26a is
The length in the main scanning direction M is L (for example, 160 μm), and the length in the sub scanning direction S is W (for example, 30 μm). When each heating element 26a is energized, the ink film 23 is heated from behind, and the melted or softened ink is transferred to the recording paper 22.

When the first driving pulse is supplied to the heating element 26a, ink dots indicated by hatching are recorded on the first sub-line. The first sub-line has a length L in the main scanning direction M and a length W in the sub-scanning direction S. When the second drive pulse is supplied, ink dots are recorded on the second sub line. The length of the second sub line in the sub scanning direction S is approximately D / 2. Similarly, 1
Ink dots are recorded on N sub-lines forming a pixel. The length of the ink dot recorded in one pixel in the sub-scanning direction S changes depending on the number of drive pulses.

In the above embodiment, the speed reducing mechanism is composed of the timing belt and the toothed pulley, but the flat belt, the V belt, the spring belt and the chain are provided in the speed reducing mechanism with a gear or the transmission mechanism having an appropriate cushioning effect. The same effect can be obtained by using a speed reducing mechanism having a belt or the like.

In the above embodiment, the heating element is energized twice during one cycle of the carrier pulse, but it may be energized three times or four times. By increasing the number of times, a higher gradation can be obtained. Can be expressed. Also, cyan, magenta,
The present invention can also be applied to a color printer that uses a color ink film having a yellow ink area. Further, the present invention can be applied to sublimation type thermal transfer recording and thermal recording as well as the melting type thermal transfer recording.

[0019]

As described in detail above, according to the present invention, the platen is rotated by the pulse motor via the speed reducing mechanism having a buffering effect, and a plurality of heating elements are provided during one cycle of the carrier pulse. Since it is driven once, it is possible to easily express a high gradation by using the conventional platen drive system as it is.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a thermal recording method of the present invention.

FIG. 2 is a schematic diagram of a printer embodying the present invention.

[Explanation of symbols]

 12 pulse motor 13, 15, 16, 18 toothed pulley 14, 17 timing belt 19 platen 22 recording paper 23 ink film 26 thermal head 26 heating element

Claims (2)

[Claims] 1. A thermal head in which a plurality of heating elements are arranged in the main scanning direction is used, and the recording paper supported by a platen is moved in the sub scanning direction, while the ink dots recorded in the pixels in the sub scanning direction. In a thermal recording method that expresses gradation by changing the length, the rotation of the pulse motor is transmitted to the platen via a reduction mechanism that includes a gear and has a buffering effect, and during one step cycle of the pulse motor, A thermal recording method comprising energizing a heating element a plurality of times. 2. A thermal head in which a plurality of heating elements are arranged in the main scanning direction is used to move the recording paper supported by a platen in the sub scanning direction, while the ink dots recorded in the pixels in the sub scanning direction. In a thermal recording method that expresses gradation by changing the length, the rotation of the pulse motor is transmitted to the platen via a reduction mechanism that includes a belt in the rotation transmission system, and heat is generated during one step cycle of the pulse motor. A thermal recording method comprising energizing an element a plurality of times.