JP2688391B2 - Melt type thermal transfer recording method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fusion type thermal transfer recording method suitable for recording halftone images.

[0002]

2. Description of the Related Art A fusion type thermal transfer recording method uses a thermal head having a large number of heating elements arranged in the main scanning direction and presses it against the back of an ink film to transfer the softened or melted ink to a recording paper. Is. In this fusion type thermal transfer recording method, the amount of ink transferred onto the recording paper cannot be adjusted according to the amount of heat, and is therefore used for recording binary images such as line drawings and characters. The applicant of the present invention uses an elongated heating element in the main scanning direction, controls the energization time of the heating element, the magnitude of the current, the number of drive pulses, etc., to determine the sub-scanning direction of the ink dots recorded in the pixel. A method of recording a halftone image by changing the length of the image has been proposed (for example, Japanese Patent Application No. 2-15886).

[0003]

However, in the above-mentioned recording method, since the pixels are arranged like a grid, when the densities of the pixels in the main scanning direction are the same, a rectangular ink dot is used. A straight line extending in the main scanning direction is formed. This straight line is quite conspicuous, resulting in a rough image quality. Further, when a large number of parallel lines extending in the main scanning direction are formed and the original image includes a large number of parallel lines such as a blind, these interfere with each other to cause moire.

An object of the present invention is to provide a fusion type thermal transfer recording method which eliminates the generation of straight lines extending in the main scanning direction and moire.

[0005]

In order to achieve the above object, the recording method described in claim 1 divides each pixel into two cells arranged in the sub-scanning direction, and according to the density of the pixel. The length of the obtained ink dot in the sub-scanning direction is distributed and recorded in these two cells, and between the pixel of odd number and the pixel of even number in the main scanning direction, the sub-scanning direction of the cell is determined. The pixel position is shifted in the sub-scanning direction by ½ of the length.

In the recording method according to the second aspect of the invention, the ink dots are recorded closer to the start edge of the pixels, and the ink dots are grouped by a certain number of pixels in the main scanning direction, so that an odd number group and an even number group are formed. In between, the pixel positions are shifted in the sub-scanning direction by 1/2 of the length of the pixel in the sub-scanning direction.

According to the recording method of the third aspect, between the odd-numbered pixel and the even-numbered pixel in the main scanning direction, one pixel records the ink dot in a state of being moved to the start end, and the other. The pixels of (3) are for recording ink dots in a state of being moved to the end.

According to the recording method of the fourth aspect, each pixel is divided into two cells arranged in the sub-scanning direction, and the length in the sub-scanning direction of the ink dot obtained in accordance with the density of the pixel is determined. The pixel is divided into two cells and recorded, and between the odd-numbered pixel and the even-numbered pixel, one pixel records the ink dot in the state where the ink dot is brought close to the start end of each cell, and the other pixel. Is for recording with ink dots being brought close to the end of each cell.

According to a fifth aspect of the present invention, in the recording method, the pixels are grouped by a certain number of pixels in the main scanning direction, and between the odd-numbered group and the even-numbered group, one group is aligned with the start edge of the pixel. Ink dots are recorded in the state of being set, and in the other group, the ink dots are recorded in the state of being brought to the end of the pixel.

In the recording method according to the sixth aspect, each pixel is divided into two cells arranged in the sub-scanning direction, and the length in the sub-scanning direction of the ink dot obtained according to the density of the pixel is calculated. The data is divided into two cells and recorded, and the cells are grouped by a certain number of pixels in the main scanning direction. Between the odd-numbered group and the even-numbered group, one group prints ink dots of each cell. The recording is performed in the state of being moved to the start end, and the other group is performed in the state of recording ink dots in the state of being moved to the end of each cell.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a recording method described in claim 1. The thermal head 10 includes a heating element array 11 extending in the main scanning direction.
Is composed of a plurality of heating elements 11a, 11b, 11c ... Each heating element has an elongated shape with a length A in the main scanning direction and a length B in the sub scanning direction. For example, A is 12
5 μm and B is 30 μm.

The thermal head 10 and the recording paper 14 are
The relative movement is made continuously or intermittently in the sub-scanning direction. An ink film (not shown) is in close contact with the recording paper 14,
The melted or softened ink is transferred onto the recording paper 14 by being heated by the thermal head 10 from behind the ink film. The melted ink records ink dots 16 indicated by hatching in each pixel 15. In this example,
The feed pitch of the thermal head 10 is 2 μm, and each ink dot 16 increases from 30 μm by 2 μm.

Each pixel 15 has a square shape, and the lengths in the main scanning direction and the sub scanning direction are both A (125 μm). Further, each pixel 15 is divided into two cells 15a and 15b so that the length in the sub-scanning direction is A / 2, and each cell 15a and 15b has a start end (in the sub-scanning direction). Ink dots are recorded in a state in which the ink dots are closer to the upstream side). Of course, the ink dots may be moved closer to the end (downstream side in the sub-scanning direction) for recording. In this embodiment, since the length A is 125 μm, the pixel density is 8 dots / mm in the main scanning direction and the sub scanning direction. In addition, each pixel 15
It is virtually shown by a dotted line, and the boundary between the cells 15a and 15b is shown by a dashed line.

At the gradation level 1, the smallest ink dot (length in the sub-scanning direction is 30 μm) is recorded only in the cell 15a, and this ink dot is near the start end of the cell 15a. At gradation level 2, 32 μm increased by 2 μm
Ink dots are recorded in the cell 15a. Similarly, when the ink dots are increased by 2 μm in the same manner, the size of the ink dot becomes 58 μm at the gradation level 15.
At the gradation level 16, the smallest ink dot is recorded in both the cells 15a and 15d. At gradation levels 17 and above,
The number of ink dots is increased by 2 μm alternately in the cells 15a and 15d.

In this recording method, since the ink dots and the white background are dispersed, the resolution becomes good. Since the length A of the pixel 15 in the sub-scanning direction is 125 μm, the drawable gradation is about 48 gradations according to the following equation. (125-30) ÷ 2 + 1 ≒ 48

Further, in order to eliminate the occurrence of straight lines extending in the main scanning direction and moire, between the even-numbered and odd-numbered pixels in the main scanning direction, half the length of the cell in the sub-scanning direction, that is, A / The pixel positions are shifted by 4 in the sub-scanning direction. By the way, when the pixel is not divided into two cells, the shift amount of the recording position of the pixel needs to be A / 2. Therefore, in this embodiment, since the amount of pixel shift need only be half, the reduction in resolution due to pixel shift can be reduced.

FIG. 2 shows a recording method described in claim 2. Each pixel 20 has a length of A in the main scanning direction and the sub-scanning direction, and an ink dot indicated by hatching is recorded on each pixel 20 in a state of being closer to the start end.
In this recording method, two pixels are grouped in the main scanning direction, and the even-numbered group and the odd-numbered group are displaced from each other by A / 2 in the sub-scanning direction. It is possible to eliminate stretched straight lines and moire. In FIG. 3, three pixels 21 are grouped, and each group is shifted by A / 2.

As is apparent from FIGS. 2 and 3, since the screen angle indicated by the alternate long and short dash line changes depending on the number of pixels in the group, the size of the group is changed according to the occurrence state of moire, and the influence of moire is affected. It can be recorded in the smallest number. In the recording of a color image, color moire occurs due to the ink dots of three colors, but the color moire can be eliminated by changing the screen angle depending on the color.

FIG. 4 shows a recording method according to a third aspect of the invention, in which the ink dots recorded in the pixels 23 are recorded in a state of being aligned with one end of the pixel. That is, in the odd-numbered pixels in the main scanning direction, the ink dots are closer to the start end of the pixels, and in the even-numbered pixels, the ink dots are closer to the end end of the pixels. Of course, the ink dots may be moved to the end of the odd-numbered pixels and recorded from the start of the even-numbered pixels. In this recording method, since the positions of the pixels are not displaced, it is possible to eliminate the generation of straight lines extending in the main scanning direction and the generation of moire without lowering the resolution in the sub scanning direction.

FIG. 5 shows a recording method according to a fourth aspect of the present invention, in which each pixel 24 is divided into two cells 24a and 24b, and an odd numbered pixel in the main scanning direction is an ink dot. Recording is performed in the state of being brought close to the start end of the cell, and for even-numbered pixels, printing is performed with the ink dots being brought close to the end of the cell. The two cells 24a,
The method of recording ink dots on 24b is the same as in FIG.

FIG. 6 shows a recording method described in claim 5. In this printing method, pixels are grouped into groups of two in the main scanning direction, ink dots are printed closer to the start edge of the pixel in the odd-numbered group, and ink dots are moved closer to the end of the pixel in the even-numbered group. It is recorded.

FIG. 7 shows a recording method according to a sixth aspect of the present invention, in which each pixel 24 has two cells 24a and 24b.
Is divided into In the pixels of the odd-numbered groups in the main scanning direction, the ink dots are recorded in a state in which the ink dots are close to the start edge of the cell. Then, the pixels of the even-numbered groups are recorded in a state where the ink dots are close to the end of the cell. The method of recording ink dots on the two cells 24a and 24b is the same as in FIG. Also, the number of pixels in the group may be three, four, etc., whereby a desired screen angle can be selected.

Next, an apparatus for carrying out the recording method shown in FIG. 1 will be described with reference to FIGS. In FIG. 8, a single color ink area, for example, a black ink area 30a is formed on the ink film 30 at a constant pitch.
The individual ink areas 30a are used. The ink area 30a is overlaid on the recording paper 31, and the thermal head 10 (see FIG. 1) is pressed against it from behind.

The head moving mechanism 34 is driven by a motor 35 and moves the thermal head 10 continuously or intermittently in the sub-scanning direction shown by the arrow. This head moving mechanism 34
Is composed of, for example, a belt or a feed screw. In this embodiment, the thermal head 10 is intermittently moved by 2 μm, and each heating element is energized once while the intermittent feeding is stopped. When each heating element is energized, the ink film 3
The wax of 0 is melted and the ink is transferred to the recording paper 31, and an ink dot is recorded in the pixel.

While the thermal head 10 is moved from the recording start position to the recording end position by the head moving mechanism 34, image recording on the recording paper 31 is performed. After the image recording, the motor 35 rotates in the reverse direction to return the thermal head 10 to the recording start position, and the motor 37 rotates the take-up reel 38 to wind the used ink area.
A new ink area is pulled out from the supply reel 39. The controller 40 controls the motors 35 and 37 in sequence.

FIG. 9 shows an example of the head drive section. The image data input from the video tape recorder or the scanner is written in the frame memory 41. At the time of recording, the controller 40 reads the image data representing the gradation level from the frame memory 41 line by line.
At the time of this reading, the controller 40 actuates the selector 42 to divide the pixels into even-numbered pixels and odd-numbered pixels in the main scanning direction. Image data of even-numbered pixels is sent to the line memory 43, and image data of odd-numbered pixels is sent to the line memory 44.

The image data written in the line memories 43 and 44 is transferred to the buffer memories 45 and 46. The drive data conversion circuits 47 and 48 generate drive data of ink dot patterns corresponding to image data.
That is, when the image data is in the low density area (low gradation area), it is converted into drive data of a pattern in which ink dots are recorded only in one cell 15a, and the image data in the high density area is converted. It is converted into drive data of a pattern for recording ink dots in the two cells 15a and 15b.

The drive data conversion circuits 47 and 48 convert the image data into 48-bit drive data when the image data has 48 gradations. Each bit is assigned "1" when ink dots are printed, and "0" when it is not printed. Then, the first bit of each pixel is sequentially taken out to be converted into a serial signal and sent to the shift registers 49 and 50 of the thermal head 10.
The shift registers 49 and 50 convert serial signals into parallel signals and send them to the switching circuits 51 and 52. The switching circuit 51 controls energization of even-numbered heating elements, and the switching circuit 52 controls energization of odd-numbered heating elements.

After each heating element is driven by the first bit drive data, the thermal head 10 is moved by 2 μm, and then each heating element is driven by the second bit drive data.
Thereafter, similarly, each heating element is driven by the driving data of the third bit and thereafter, the heating element is driven 48 times for the highest density pixel, and ink dots are recorded in all one pixel 15. It should be noted that ink dots are not recorded for the pixel having the lowest density.

As shown in FIG. 1, between the even-numbered pixels and the odd-numbered pixels in the main scanning direction, the positions of the pixels are shifted by A / 4 in the sub-scanning direction. Therefore, the operation of the drive data conversion circuit 47 is delayed by the delay circuit 53 by the time corresponding to A / 4. Therefore, since the heating elements corresponding to the even-numbered pixels are deviated in the energization timing with respect to the heating elements corresponding to the odd-numbered pixels, the ink dots are displaced by A / 4 in the sub-scanning direction. Will be recorded.

Although the above embodiment is a line printer,
The present invention can also be applied to a serial printer. The present invention can also be applied to a color printer that uses an ink film in which cyan, magenta, and yellow ink areas are recorded.

[0032]

As described in detail above, according to the present invention, since the recording position is shifted in the sub-scanning direction so that the ink dots are not aligned in the main scanning direction, a straight line extending in the main scanning direction appears. Or, the moire does not occur due to this straight line and the original straight line.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a recording method in which a pixel is divided into two cells and a recording position of the pixel is shifted between adjacent pixels in a main scanning direction.

FIG. 2 is an explanatory diagram of a recording method in which pixel positions are shifted for every two pixels arranged in the main scanning direction.

FIG. 3 is an explanatory diagram of a recording method in which pixel positions are shifted for every three pixels arranged in the main scanning direction.

FIG. 4 is an explanatory diagram of a recording method in which ink dots are moved to the opposite side and recorded between adjacent pixels in the main scanning direction.

FIG. 5 is an explanatory diagram of a recording method in which a pixel is divided into two cells and ink dots are moved to the opposite side and recorded between adjacent pixels in the main scanning direction.

FIG. 6 is an explanatory diagram of a recording method in which recording positions of ink dots are recorded on the opposite side for every two pixels arranged in the main scanning direction.

FIG. 7 is an explanatory diagram of a recording method in which a pixel is divided into two cells and ink dots are moved to the opposite side for recording every two pixels arranged in the main scanning direction.

FIG. 8 is a perspective view showing an outline of a thermal recording apparatus for carrying out the present invention.

FIG. 9 is a block diagram showing a drive circuit of a thermal head.

[Explanation of symbols]

 10 Thermal Head 11 Heating Element Array 15 Pixels 15a, 15b Cell 16 Ink Dots 20, 21, 23, 24 Pixels 24a, 24b Cell 30 Ink Film 31 Recording Paper

Claims (6)

(57) [Claims] 1. A half-tone image is recorded by using a thermal head in which a plurality of heating elements are arranged in the main scanning direction, and changing the length of ink dots recorded in a pixel in the sub-scanning direction according to the density. In the fusion type thermal transfer recording method for recording on paper, each pixel is divided into two cells arranged in the sub-scanning direction,
The length in the sub-scanning direction of the ink dot obtained according to the density of the pixel is distributed and recorded in these two cells, and between the odd numbered pixel and the even numbered pixel in the main scanning direction. The fusion type thermal transfer recording method characterized in that the pixel position is shifted in the sub-scanning direction by ½ of the length of the cell in the sub-scanning direction. 2. A halftone image is recorded by using a thermal head in which a plurality of heating elements are arranged in the main scanning direction, and changing the length of an ink dot recorded in a pixel in the sub scanning direction according to the density. In a fusion type thermal transfer recording method for recording on paper, while recording ink dots close to the starting end of the pixels, grouped by a fixed number of pixels in the main scanning direction,
The fusion type thermal transfer recording method characterized in that the positions of the pixels are shifted in the sub-scanning direction by 1/2 of the length of the pixels in the sub-scanning direction between the odd-numbered groups and the even-numbered groups. . 3. A halftone image is recorded by using a thermal head in which a plurality of heating elements are arranged in the main scanning direction, and changing the length of an ink dot recorded in a pixel in the sub scanning direction according to the density. In the fusion type thermal transfer recording method for recording on paper, between the odd-numbered pixel and the even-numbered pixel in the main scanning direction, one pixel records an ink dot in a state of being shifted to the start end, and the other The fusion type thermal transfer recording method is characterized in that an ink dot is recorded in a state where a pixel is located at the end. 4. A halftone image is recorded by using a thermal head in which a plurality of heating elements are arranged in the main scanning direction and changing the length of ink dots recorded in a pixel in the sub scanning direction according to the density. In the fusion type thermal transfer recording method for recording on paper, each pixel is divided into two cells arranged in the sub-scanning direction, and the length in the sub-scanning direction of the ink dot obtained according to the density of the pixel is In addition to dividing and recording into individual cells, between the pixels of odd number and the pixels of even number, one pixel records with the ink dot aligned to the start end of each cell, and the other pixel A fusion type thermal transfer recording method, characterized in that ink dots are recorded in a state of being brought close to the end of each cell. 5. A halftone image is recorded by using a thermal head in which a plurality of heating elements are arranged in the main scanning direction, and changing the length of an ink dot recorded in a pixel in the sub scanning direction according to the density. In the fusion type thermal transfer recording method for recording on paper, grouping is performed for every certain number of pixels in the main scanning direction,
Between the odd-numbered group and the even-numbered group, one group records the ink dots in the state of being aligned with the beginning of the pixel, and the other group is recording the ink dots in the state of being aligned with the end of the pixel. A fusion-type thermal transfer recording method comprising: 6. A halftone image is recorded by using a thermal head in which a plurality of heating elements are arranged in the main scanning direction and changing the length of ink dots recorded in a pixel in the sub scanning direction according to the density. In the fusion-type thermal transfer recording method for recording on paper, each pixel is divided into two cells arranged in the sub-scanning direction, and the length in the sub-scanning direction of the ink dot obtained according to the density of the pixel is In addition to distributing the data to individual cells and recording, the cells are grouped by a certain number of pixels in the main scanning direction, and between the odd-numbered group and the even-numbered group, one group forms an ink dot at the beginning of each cell. In the fusion type thermal transfer recording method, the recording is performed in a state in which the ink dots are recorded in the other group and the ink dots in the other group are recorded in a state in which the ink dots are disposed in the end of each cell.