JP3264576B2 - Serial thermal printing 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 printing method used in a serial thermal printer in which a thermal head moves in a sub-scanning direction and a recording paper moves in a main scanning direction.
More specifically, the present invention relates to a serial thermal printing method in which line joints are improved so as not to be noticeable.

[0002]

2. Description of the Related Art Thermal recording methods include thermal recording in which an image is directly recorded on thermal recording paper and thermal transfer recording in which ink from an ink film is transferred to recording paper. The thermal transfer recording includes a fusion type in which the melted ink is transferred to recording paper, and a sublimation type in which the amount of ink transferred to the recording paper changes according to thermal energy. For example, in thermal transfer recording, in order to reduce the size and weight of the apparatus, a thermal head in which a plurality of heating elements are arranged in the main scanning direction is used. A serial thermal printer of a type in which paper is fed in a scanning direction to record the next one line is often used.

Since one heating element has a length in the main scanning direction of, for example, about 70 μm, a serial thermal printer needs to feed the paper with high precision. The edges of adjacent rows often overlap or separate from each other. When the rows overlap each other, they are relatively inconspicuous if they overlap in an image portion having a high density, but a stripe extending in the sub-scanning direction appears in an image portion having a medium density or less. When the lines are separated from each other, the low-density image portion is inconspicuous, but the medium-high-density image portion appears as a stripe on the ground of the recording paper. Normally, recording paper with a white ground is used, so that white stripes are extremely noticeable.

[0004] Since white stripes caused by separation of lines degrade image quality more greatly than stripes caused by overlap of line ends, a printing method in which paper is fed so that a plurality of pixel columns overlap in two adjacent lines. Are known. However, when they are simply overlapped, for example, n
The gradation level of a plurality of pixel columns included in a row is low, and (n +
1) When the gradation level of the plurality of pixel columns in the row is low, the density of the overlapping plurality of pixel columns is the density of the plurality of pixel columns of the (n + 1) row. As a result, the line boundaries
The concentration will be higher and noticeable. Therefore, a method of giving a density gradient (fade-in, fade-out) to an overlapping portion is also known.

However, the method of giving a density gradient has a disadvantage that image processing becomes extremely complicated because it is necessary to weight image data of a plurality of heating elements for recording an overlap portion. For this reason, the applicant of the present invention has proposed a serial thermal printing method in Japanese Patent Application No. Hei 5-302066, which makes it possible to make line joints very simple.

In this method, one pixel is constituted by a plurality of cells arranged in a matrix, and a plurality of adjacent cells, such as four pixels, are formed so as to form an ink dot pattern corresponding to a gradation level.
Ink dots are recorded in each cell by the heating elements. In this ink dot pattern, the shape of the ink dot recorded in the pixel as the gradation level increases,
It changes like point → horizontal line → cross → rectangle. Also, one sub-scanning direction sub-line (hereinafter simply referred to as a sub-sub-line) scheduled to overlap at the end of the row is added. The additional sub-sub-line is a sub-sub-line above it, and ink dots are printed in the same state as the last sub-sub-line of the pixel column at the end of the row. In this additional sub-line, an ink dot is recorded when the gradation level of the pixel is slightly higher than the medium density, and overlaps the top sub-line of the first pixel in the next row. Therefore, when the gradation level is slightly higher than the middle density, overlapping occurs at the cross-shaped projections, so that even if unevenness occurs in the paper feed, there is no streak-like gap, and the seams of the lines are inconspicuous. can do.

[0007]

However, in the above-described serial thermal printing method, the pixels at the end of the row have low to slightly medium density (hereinafter simply referred to as medium and low density).
In the case of printing the image portion, since there is no ink dot to be printed in an overlapped manner, it is not possible to expect an improvement in the seam between lines. In order to improve the seam between the middle and low density portions, a method using an ink dot pattern that changes in the order of dot → vertical line → cross → rectangle can be considered. However, when such an ink dot pattern is used, a rough feeling occurs in the image portion of the medium and low density, and the image quality of the recorded image is deteriorated. Is also noticeable.

In order to print such a thin vertical line ink dot pattern protruding in the main scanning direction, it is necessary to rapidly heat the heating element. For this reason, the thermal head moves before the heating element reaches the ink transfer temperature, so that the ink dots of each cell are not transferred in a predetermined size, and the ink dots are missing.
This causes deterioration in gradation and resolution in a low-density image portion.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a serial thermal printing method capable of recording a line from low density to high density in an inconspicuous manner.

[0010]

In order to achieve the above object, according to the present invention, N (an integer of 2 or more) adjacent sub-sublines are N in the main scanning direction and M (2 in the sub-scanning direction). A pixel column in which one pixel composed of (the above integer) cells is arranged is formed. An ink dot pattern corresponding to the gradation level is recorded in one pixel. N within each pixel
Each sub-subline portion of the book forms a sub-subline portion, and one or more first priority sub-subline portions and second priority sub-subline portions are determined therein. The gradation level at which ink dots are recorded in all cells of the first priority sub-subline portion is lower than the gradation level at which ink dots are recorded in all cells of the second priority sub-subline portion. The sub-subline portion is recorded earlier. The feed amount of the recording paper is determined so that the n-th row and the (n + 1) -th row are overlapped by one or more first priority sub-sublines. The sub-sub-line below the n-th row and the sub-sub-line above the (n + 1) -th row to be recorded next form one pixel column located on the boundary of the row. It will be recorded separately.

Although there is no practical problem if only one first priority sub-subline portion is provided, the accuracy of paper feeding is extremely poor, and the deviation from the reference feed amount may be larger than the width of one sub-subline. In some thermal printers, for example, two or three sub-subline portions may be set as first priority sub-subline portions. In this case, two or more sub-sublines are overlapped at the end of the line, so that it is possible to prevent a gap from being generated between the lines even when the paper feed deviation is large.

It is sufficient that the number of sub-sub-lines constituting one pixel is two or more. Four or more lines are preferable in order to have high gradation expression and to smoothly correct a joint from a low gradation. In the case of four or more lines, the position of the first priority sub-subline portion is
It is preferable to be located at the center of the pixel column. A second priority sub-subline portion is disposed adjacent to the third sub-line portion, and the third priority sub-subline portion is sandwiched between the first and second priority sub-sub portions.
And a fourth priority sub-subline portion.

It is preferable that the recording order of each cell in the first priority sub-subline portion is the same as the recording order of each cell in the second priority sub-subline portion. In the third and fourth priority sub-sub-line portions, ink dots are alternately recorded as the gradation level increases.

As for the dot pattern of each pixel, recording of ink dots is started from one of the cells in the first priority sub-subline portion, and the number of cells in which ink dots are recorded increases as the gradation level increases. After the ink dots have been printed in all the cells of the first priority sub-subline portion, a pattern is used in which the printing of the cells in the second priority sub-subline portion is started. At this time, in the first and second priority sub-sub-lines, in addition to recording in order from the end, recording is started from a cell near the center of the pixel, and every time the gradation level increases by one step, the recording is performed on both sides. It is preferable to record the ink dots alternately in the cells.

At least one first-priority sub-subline portion forming a pixel column on a row boundary is an ink determined by the gradation level of the pixel during one of the printing of the n-th row and the next (n + 1) -th row. It is preferable that a part of the dot pattern is recorded, and that the other recording be performed in the same state as the ink dot pattern recorded in the second priority sub-subline above or below.

Further, at least one first priority sub-subline portion forming a pixel column on a row boundary is determined depending on the gradation level of the pixel during one of the recording of the n-th row and the next (n + 1) -th row. A part of the determined ink dot pattern is recorded, and in the other recording, the recording is performed using the joint ink dot pattern of the row determined according to the gradation level. In this case,
It is preferable that the recording order between the cells of the first priority sub-subline is the same between the ink dot pattern for the joint and the ink dot pattern determined by the gradation level of the pixel.

[0017]

When printing ink dots in each pixel, priority is given to printing in the first sub-subline portion. Since the prescribed paper feed is performed so that at least one first sub-subline portion overlaps, the gradation level is slightly small, and the recording of the second sub-subline portion is started. Overlap occurs. Therefore,
Even if the paper feeding unevenness in the direction in which the rows, which are particularly problematic in the paper feeding unevenness occur, occurs, no gap is generated between the rows. This effect is obtained over the entire range from slightly low to high concentrations.

If the pixels on the line boundaries are slightly smaller than the low density and the paper feed amount is as specified, the ink dot pattern is the same as that without the joint measure. If a deviation occurs in the paper feed amount, a deviation occurs in the recording position of the ink dot, so that the size of the pixel on the boundary of the row decreases in the main scanning direction. This is the same as the case where some or all of the cells where the ink dots are not recorded are gone, so that the seams are not noticeable.

Further, when the pixels on the row boundaries have a slightly lower density or higher, ink dots overlap in some cells on the first sub-subline as described above.
As described above in the case where the paper feed is large, the joint is not noticeable in the following cases as specified. That is, in the case of black monochrome, black ink dots are overlapped, and also in the case of color, the first priority sub-subline portion has a high probability of becoming a black ink dot by three types of ink dots. The overlap at the ink dots is not noticeable. If a deviation occurs in the paper feed, a part of the black ink dots recorded in the second printing will protrude from the black ink dots recorded in the first printing, thereby preventing the occurrence of white streaks. The area of the black ink dot increases in the main scanning direction. However, the change in the size of the ink dots is also relatively inconspicuous.

When the ink dot pattern dedicated to the joint is used, the gradation of the pixel on the boundary of the row can be smoothly expressed. Also, when the paper feed amount deviates from the specified value, when the first priority sub-subline portion is compared with that created by copying the second priority sub-line portion, the ink dots appearing in the second recording are set to low gradation. Can be made inconspicuous in all ranges from to high gradation.

[0021]

FIG. 2 shows a serial thermal printer to which the printing method of the present invention is applied.
0 is reciprocated in the horizontal direction (sub-scanning direction) by the head moving mechanism 11, and the recording paper 12 is transported in the vertical direction (main scanning direction) with respect to the recording position by the platen roller 13 and the transport roller 14. Ink ribbon 1 for melt transfer
5 is supplied by a known ribbon cassette 16. The ribbon cassette 16 is mounted behind the thermal head 10, and the ink ribbon 15 is slightly pulled out of the ribbon cassette 16 and passed between the thermal head 10 and the recording paper 12. Reference numeral 17 denotes a pulse motor for driving the platen roller 13 and the transport roller 14, and reference numeral 18 denotes a driver.

During recording, the ink ribbon 15 is brought into close contact with the recording paper 12 from behind by the thermal head 10, and the ribbon cassette 16 is moved in the sub-scanning direction by the head moving mechanism 11 together with the thermal head 10. The thermal head 10 heats the back of the ink ribbon 15 and transfers the melted or softened ink to the recording paper 12. This ink adheres to the cell 22 virtually shown in FIG. 3 to form an ink dot. When the recording of one line is completed, the thermal head 10 and the ribbon cassette 16 are returned to the initial positions, and the recording paper 12 is conveyed slightly less than the width of one line in the main scanning direction.

In FIG. 3, the thermal head 10 includes
For example, 144 heating elements 10a ₁ , 10b ₁ , 10c
_{1, 10d 1, 10a 2,} 10b 2, ···, 10
c ₃₆ and 10d ₃₆ are arranged along the main scanning direction.
Each heating element has a length L1 (for example, 70 mm) in the main scanning direction.
μm) and the length in the sub-scanning direction is L2 (for example, 100 μm).
m) has a rectangular shape. For example, four heating elements 10
a ₁ , 10b ₁ , 10c ₁ , and 10d ₁ are driven each time one main scanning direction sub-line (hereinafter, referred to as main sub-line) 24 is sent, and four sub-sub-lines (sub-scanning direction sub-lines) 21A to 21D. Record The width of the main sub-line 24 is the same as the length L2 of the heating element in the sub-scanning direction.

One picture extending in the sub-scanning direction at the end of two adjacent rows
In this embodiment, 141 rows are used to form the element sequence.
And the specified paper feed is 140
Length of the heating elements in the main scanning direction (L1 × 140).
ing. Topmost pixel P₁Is two heating elements 10
c₁, 10d₁And the next pixel P_TwoIs four heating elements
Child 10a_Two-10d_TwoAnd the lowermost pixel P
₃₆Is three heating elements 10a ₃₆, 10b₃₆, 10c₃₆Written in
Record. And the heating element 10c₃₆Is a duplicate record with the next line
The planned sub-sub line 21A is recorded. Heating element
10c₃₆Is the upper heating element 10b₃₆Same drive data as
The sub-sub line 21A is driven by the
It is recorded in the same state as in 21B. Note that the pixel P_Twoof
Numbers 1 to 32 written in the cell 22 indicate ink dots.
Indicates the gradation level to be recorded. For example, the gradation level
"5" means that the cells marked with numbers "1" to "5"
Dots are recorded. The pixel P₁, P₃₆In the cell
The described “0” indicates drive data that does not cause the heating element to generate heat.
Is shown. Also, the upper end of the first line and the lower end of the last line
Since there are no adjacent rows of pixels, four heating elements are used.
To record the ink dots according to the gradation levels of the pixels.
Is also good.

One pixel is composed of four cells 22 in the main scanning direction and eight cells 22 in the sub-scanning direction, and expresses 32 gradations. Since each pixel is constituted by a part of the sub-sub-line, as shown in FIG. 4, a part of the sub-sub-line within one pixel is referred to as a sub-sub-line part. As shown in FIG. 4, the recording of the ink dots is performed on the sub-
A is started from the cells of the first priority sub-subline portion 21a constituting a part of A. As the gradation level increases,
The left and right cells are recorded alternately from the center cell. After all the cells of the first priority sub-subline portion 21a are recorded, the process shifts to recording of cells of the second priority sub-subline portion 21b in the second column. When the recording of all the cells of the second priority sub-subline portion 21b is completed, ink dots are recorded on the third priority sub-subline portion 21c and the fourth priority sub-subline portion 21d such that the central portion of the pixel projects vertically. You. In other words, the shape of the ink dot pattern recorded in one pixel changes as a point, a horizontal line, an inverted T-shape, a cross, and a rectangle as the gradation level increases.

FIG. 5 shows an example of the head driving section. Image data input from a video tape recorder or a scanner is written to the frame memory 25. At the time of recording,
The controller 26 sequentially reads out image data representing the gradation level from the frame memory 25 for one column of the first row, that is, image data of 36 pixels arranged in the main scanning direction for each pixel. One column of image data among the plurality of columns of image data written in the line memory 27 is read out for each pixel and sent to the drive data generator 28.

The drive data generator 28 reads drive data for recording the ink dot pattern shown in FIG. This ROM 29
Is written in the DOT-LUT 33 as shown in FIG. The DOT-LUT 33 is divided for each gradation level of image data, and in each division, drive data indicating whether or not to record an ink dot in each cell of one pixel is written. Here, “1” indicates that the heating element is driven to record an ink dot.

Since one pixel is recorded by four heating elements arranged in the main scanning direction, 4-bit drive data is written in one address of the DOT-LUT 33. 1 bit in row A of the 4-bit drive data is supplied for example to the heat generating element 10a _2, 1 in column B
The bit is the heating element 10b ₂ , the one bit in column C is the heating element 10c ₂ , and the one bit in column D is the heating element 10d ₂
Respectively.

Since one pixel is composed of eight cells in the sub-scanning direction, the division of each gradation level is as follows.
Eight 4-bit drive data are arranged. Since the gradation level has 32 steps of “1” to “32”, DOT−
The addresses of the LUT 33 are "0" to "255". Note that a gradation level “0” at which ink dots are not recorded in all cells of one pixel may be used, and in this case, the addresses are “1” to “263”.

The drive data generator 28 obtains the address of the DOT-LUT 33 from the pixel gradation level and the main sub-line position information (pixel position information), and reads the drive data corresponding to this address from the DOT-LUT 33. For example, if the gradation level of the pixel is “1” and the main subline to be printed is the fourth, DO
Since the address of the T-LUT 33 is “3”, the drive data generator 28 outputs the address “3” of the DOT-LUT 33.
Is read out and sent to the drive data correction unit 30. The extraction of the 4-bit drive data is performed sequentially from the first pixel in one column. Therefore, in order to record one main sub-line in one row, drive data of 4 bits is extracted 36 times and sent to the drive data correction unit 30 respectively. In addition,
After using two 4-bit latch circuits and converting the data into 8-bit data, the data may be sent to the drive data correction unit 30.

In order to record one main sub-line in one row, 4-bit drive data is input to the drive data correction section 30 36 times. These 36 4-bit drive data are converted into 144-bit drive data by the shift register. Of the 144-bit drive data, the first and second bits are replaced with “0”, the 143rd bit is replaced with the 142th drive data, and the 144th bit is replaced with “0”. After that, the ink is supplied to the thermal head 10. In addition, the third and first
The 42nd bit is used as it is. The specific bit is replaced with “0” because it is not used.
Of course, if two types of DOT-LUTs, one for the upper end and one for the lower end, are used, such replacement is unnecessary.

When the recording of the first row is completed by recording the main sub-lines one by one, the width of the recording paper 12 in the main scanning direction of one pixel (L1 × 144) is smaller than the width of one row (L1 × 144).
× 4) less. Therefore, focusing on the thermal head 10, the first row and the second row are overlapped by one pixel column of width L1 × 4 extending in the sub-scanning direction. The same image data is used for the first line and the second line for this part. As will be explained in detail later,
Overlapping ink dots occurs in one sub-sub-lines 21C recorded by the heating element 10c ₃₆ and the heating element c _1.

In the recording example shown in FIG. 1, all pixels are recorded with image data of the gradation level "10", and the prescribed paper feed amount is one pixel column from the width of one row (L1 × 144). , The lowermost pixel column SL ₃₆ of the n-th row and the uppermost pixel column SL ₁ ′ of the (n + 1) -th row are combined to form one pixel column SL _0. Is formed. The pixel column SL ₀ is the pixel column SL ₁ pixel string SL ₃₆ are overlapped in the overlap section OL. The overlapping portion OL is the third sub-sub-line 21A from the top of the pixel columns SL _0. If attention is paid to each pixel in the pixel column SL _0, overlap can occur first priority subline portion 21a shown in FIG.

The ink dot pattern recorded in each pixel of the pixel row SL ₀ is such that if there is no variation in paper feed,
As shown in FIG. 1, the lower half of the longitudinally slender ink dots D1 recorded in each pixel of the pixel row SL _36, pixel columns SL
₁ 'ink dots D recorded in each pixel
The central part of 2 overlaps and has an inverted T shape as a whole. This ink dot pattern corresponds to pixel rows SL ₂ to
Like the ink dot pattern of each pixel of SL ₃₅ ,
The overlapping of the ink dots in the overlap portion OL is maintained, and the ink dot pattern is in accordance with the original gradation level. Overlapped portion OL in the case of monochrome with black ink, because even overlap ink dots is black, the density of each pixel in the pixel column SL _0, the pixel rows S
L almost does not change the concentration of each pixel on the _{2 ~SL 35.}
Also, in the case of color printing using a three-color ink film, the density is hardly changed because the overlap portion OL has a high probability of becoming black. Therefore, the area between the n-th row and the (n + 1) -th row does not stand out.

When the paper feed amount is large and the fluctuation amount is equal to or less than the width of the first priority sub-subline portion 21a in the main scanning direction, as shown in FIG.
There is no gap between the line. When the paper feed amount is small, as shown in FIG. 8, since the area of the overlap portion OL is the same as the case where the paper feed amount is the specified value,
In each case, the seams of the lines are inconspicuous.

When a low-density image having a gradation level of "8" or less is recorded, dots or horizontal lines are formed as apparent from the ink dot pattern shown in FIG. That is, in the pixel row SL ₀ , ink dots are printed only on one sub-sub-line constituting the (n + 1) -th row of pixel rows SL ₁ ′, and ink dots are printed in the n-th row of pixel rows SL _36. If the paper feeding is proper, the original ink dot pattern determined by the gradation level is obtained. If the paper feed amount varies, the horizontal line shifts up and down within the pixel. In this case, the joints should be seen in principle, but the joints are hardly conspicuous at an extremely low concentration.

As can be seen from the ink dot pattern shown in FIG. 4, above the gradation level "18", the dot shape of each pixel becomes a cross, and these are connected to form a grid. n
Since an inverted T-shaped ink dot is formed at each pixel of the pixel column SL ₃₆ of the row and a T-shaped ink dot is formed at each pixel of the pixel column SL ₁ ′ of the n-th row, each pixel of the pixel column SL ₀ obtained by combining these is formed. , if there is no variation in the paper feed, the ink dot pattern overlap with the first priority sub subline portion 21a, is recorded on the pixel trains SL ₀ does not change at all to that of the pixel column SL ₂ to SL _35. Each pixel overlaps with one first priority sub-sub line portion 21a,
Even if you put black on black, it will not be noticeable. Even if there is variation in the paper feed, if the variation is equal to or less than the width of the first priority sub-subline portion 21a, no gap is generated between the (n-1) th line and the nth line.

Next, the operation of the above embodiment will be described. At the time of recording, the platen roller 13 and the transport roller 14
Is rotated in the direction of the arrow, and the leading end of the recording area of the recording paper 12 is fed to the position of the thermal head 10. The thermal head 10 and the ribbon cassette 16 are moved to the left end initial position.

The image data of one frame of pixels written in the frame memory 25 is specified by rows and columns, and the image data of 36 pixels forming one column is read out in the order of the main scanning direction. Once written into the line memory 27. One of the plurality of columns written in the line memory 27 is read out for each pixel, and the driving data generation unit 2
8 The drive data generation unit 28 stores the image data representing the gradation level and the position information of the main sub line in the ROM 2.
9 and create the DOT-LUT in ROM 29
The 4-bit drive data is read from 33 and sent to the drive data correction unit 30.

The driving data correction section 30 has 36 4
Bit drive data is converted into serial data, and a specific bit is converted into specific data. That is, the first two pieces of driving data and the last one piece of driving data are converted to “0”, and the second last driving data is replaced with the third last driving data. Then, these drive data are supplied to the thermal head 10.

Thermal head 10 and ribbon cassette 1
While moving 6 to the right in the sub-scanning direction, the thermal head 10 heats and presses the ink ribbon 15 from behind, and transfers the melted ink to the recording paper 12.

When the thermal head 10 moves to the right end of the recording paper 12 and one line is recorded on the recording paper 12, the heating and pressurizing of the ink ribbon 15 are stopped, and the thermal head 1
0 and the ribbon cassette 16 move leftward in the sub-scanning direction and return. During this return, the platen roller 13 and the transport roller 14 rotate to transport the recording paper 12, and the next line is transported to the position of the thermal head 10. The transport amount is L1 × 140, and thus, the lowermost pixel row S
And L _36, the pixel column SL ₀ of one by the pixel column SL ₁ 'of uppermost end of the next line is recorded. Hereinafter, this operation is repeated to record the image line by line, and when the recording of all the lines is completed, the platen roller 13 and the transport roller 14 are continuously rotated in the direction of the arrow, and the recording paper 12 is discharged.

As described above, since one pixel column SL ₀ on the row boundary is obtained by synthesizing the pixel P _{36 of the} previous row and the pixel P ₁ of the next row, it is separately recorded twice. Is done. Then, the two pixels P ₃₆ and P ₁ overlap in the first priority sub-subline portion 21a. In the recording of the pixels P ₃₆ and P ₁ , since some of the heating elements are not driven, recording is substantially performed in the first row in the first priority sub-subline portion 21 a, and the next row is recorded in the first priority sub-sub line portion. Recording is started from 21a.

[0044] When the gradation level of the pixels on the pixel row SL ₀ is a low concentration of the "1" to "8", since no cause overlap of ink dots, but visible seams in principle , Not noticeable due to low concentration. Since the ink dots overlap from the gradation level "9", which is a little low density, no gap is generated between the lines even if there is unevenness in the paper feed, and the seams are not conspicuous.

In the embodiment described above, the pixel P _{36 in the} preceding row is used.
In the recording, the first priority sub subline portion 21a is recorded in the same ink dot pattern and the second priority sub subline portion 21b, but joint ink dot rows decided in accordance with the gradation level of the pixel P ₃₆ A pattern may be used. In the embodiment shown in FIG. 9, the recording order of the joint ink dot pattern is, for example, “22, 16, 1”.
1, 9, 10, 13, 19, 25 "are used.
In this connection ink dot pattern, the recording order of the original ink dot pattern is “7, 5, 3, 1, 2,.
4, 6, 8 ", a comparison between the two indicates that the recording order of each cell in the first priority sub-subline portion 21a is the same. For example, if attention is paid to the second cell, the number "1" in the joint ink dot pattern is obtained.
6 ", it is recorded fifth in the first priority sub-subline portion 21a. On the other hand, in the original ink dot pattern, since the number is "5", it is also printed fifth. Further, since the number of the ink dot pattern for the joint is larger than the original one, the ink dots are recorded in all the cells in the image portion having a slightly low density to a high density.

FIG. 10 shows a serial thermal printer using a joint ink dot pattern, and the same parts as those in FIG. 5 are denoted by the same reference numerals. The ROM 35 is connected to the drive data correction unit 30. The ROM 35 has a DOT-LUT 3 as shown in FIG.
6 is written. The DOT-LUT 36 has the recording order “22, 16, 11, 9, 10, 13, 19, 2” of the ink dot pattern for the seam of the row shown in FIG.
5 ".

The drive data correction unit 30 converts the 4-bit drive data into serial data to make one main sub-line, that is, 144-bit drive data. Then, the first and second bits are replaced with “0”, and the 33rd to 142nd bits are replaced.
The 143rd bit is replaced with 1-bit data read from the DOT-LUT ₃₆ in accordance with the grayscale level of the pixel P36, and the 144th bit is replaced with "0" without changing the 1st bit. Note that “0” may be replaced using DOT-LUTs for the upper and lower ends of the row.

When all the pixels are to be recorded with the image data of the gradation level "10", the first priority sub-sub line of each pixel on the last pixel line of n rows is DOT-LUT3.
6, and the second and fourth priority sub-sub-lines thereon are recorded with data corresponding to the gradation level. Since the data is forcibly set to "0" in the third priority sub-subline portion, substantially no ink dot is recorded. Thereby, the gradation level “1”
In "0", a short vertical line is recorded in each pixel of the last pixel line.

On the other hand, in each pixel on the first pixel line of the (n + 1) -th row, the first and third priority sub-sub-lines are recorded in an ink dot pattern corresponding to the gradation level. Since the data is forcibly set to "0" in the third priority sub-subline portion, substantially no ink dot is recorded. Thus, at the gradation level “10”, a horizontal line is recorded in each pixel on the first pixel line.

These two types of pixels are respectively combined to form a pixel column on a row boundary. As shown in FIG. 12 (B), each pixel in this pixel row has ink dots in the first priority sub-subline portion overlapped. Since the ink dot pattern is the same as the ink dot pattern shown in FIG. 1, the joint can be improved as described above.

In FIG. 12, in addition to the gradation level "9",
With respect to “5”, “16”, and “26”, ink dot patterns of composite pixels recorded on the boundaries of rows are shown. As can be seen, although the ink dots on the first priority sub-subline portion overlap, the ink dot pattern is the same as that determined by the gradation level.

FIG. 13 shows another embodiment in which the recording order of the ink dots in the pixel is different. Recording of the pixel 38 is started from the cell at the left end of the first priority sub-sub line portion 39a in the third column. As the gradation level increases, the area of the ink dot increases from the left end to the right end of the first priority sub-sub line portion 39a. After all the cells of the first priority sub-subline portion 39a are recorded, the process shifts to recording of cells of the second priority sub-subline portion 39b in the second column. When the recording of the cells of the second priority sub-subline portion 39b is completed, the area of the ink dots increases so that the central portion protrudes up and down.

When recording of one row is completed, the two rows are overlapped in the first priority sub-subline portion 39a on the last pixel column so that two pixels are synthesized, and the above-described joint processing is performed. . Note that the ink dot pattern in the first priority sub-sub line portion is as shown in FIG.
Both the case where the same as the second priority sub-sub line portion and the case where the ink dot pattern dedicated to the joint is used as shown in FIG. 9 can be applied.

FIGS. 14 and 15 show an embodiment in which the number of first priority sub-sublines is two. One pixel 41 is composed of eight sub-sub-line portions and eight main sub-line portions, and has 64 cells 41a virtually partitioned. The number in each cell 41a represents a gradation level at which an ink dot is recorded.

In FIG. 14A, the fourth sub-subline portion from the top is the second priority sub-subline portion, and
The 6th and 6th are first priority sub-subline portions. The two first priority sub-subline portions form a first priority sub-subline group. FIG. 14B shows an ink dot pattern 42 dedicated to the joint used for the first priority sub-subline group.

FIG. 15 shows the recording state of the pixels on the boundary of the row. In the recording of n rows, the pixels 43a are recorded. In the pixel 43a, the first priority sub-subline group is replaced with the ink dot pattern 42 dedicated to the joint. In the recording of the (n + 1) -th row, the pixel 43b
Is recorded. The two pixels 43a and 43b are
The priority sub-subline portions are overlapped with each other in an overlapped state, and become a combined pixel 44. These two pixels 4
3a, 43b, that is, in order to distinguish between the first printed ink dot and the next printed ink dot,
The pixels 44 are hatched in different directions.

In this embodiment, since the first priority sub-subline portion is two lines, the above-described joint can be improved if the amount of paper feed deviation is within two sub-sublines. Of course, the number of the first priority sub-subline portions may be three or more, and depending on the gradation level of the pixel,
The number of the first priority sub-subline portions may be changed. For example, in a pixel having a low gradation level, the number of the first priority sub-subline portion may be one, two may be used in a medium level, and three may be used in a high level.

In the embodiments described so far, the thermal head in which the length of the heating element in the sub-scanning direction is equal to the width of one cell is used. A thermal head may be used. As shown in FIG. 16, each heating element of the thermal head 45 has a rectangular shape having a length A in the main scanning direction and a length B in the sub-scanning direction. 4 of cell 46 with length C
It is individual. One pixel 47 includes four sub-sub-line portions 48a to 48d and eight main sub-line portions 4a to 48d.
9a and 49b, and has 32 cells 46 virtually partitioned. The width of the first main sub-line portion 49a is the same as the length B of the heating element in the sub-scanning direction, and corresponds to four steps of feeding of the thermal head 45. Second to eighth main subline portions 49
The width b is the one-step feed amount C of the thermal head 45.

When recording one pixel, after the recording of the first main sub-line portion 49a, the heating elements 45a _{1 to} 45d are intermittently moved by the distance C by a distance C.
Driving _one. After recording of one pixel, the thermal head 45 is fed four steps to make the heating element face the first main sub-line portion 49a of the next pixel. This 4
The idle feed of the step is a blank section, and each heating element 4
The 5a ₁ ~45d _1, the virtual drive data so as not to record ink dots are supplied. This virtual drive data is represented by reference numeral 50, and is all "0" in this embodiment. Therefore, during this time, the heating element 45a
_{1 ~45d 1} is not driven, the thermal head 45 is cooled.

In the blank section, it is ideal to provide three virtual drive data to one heating element. However, since the heating element has a trail due to heat storage, in this embodiment, four driving data are provided. Data is provided, and one main subline portion having a width L is inserted between each pixel. In this case, in the ink dot pattern in which the ink dots grow in the sub-scanning direction in accordance with the gradation level of the pixel, the drive data is set to “0” due to the heat generated in the printing of the last main subline portion of the previous pixel. However, ink dots are also formed on the first main subline in the blank section, the continuity of the pixels is maintained in the high density portion, and the density is prevented from increasing in the middle and low density.

Depending on the type of the thermal head, heat may be generated even during the blank section in order to prevent overheating of the heating element. For example, heating elements 45 c _1, since heating times is large, the four virtual data is good for "0", since the heating elements 45a ₁ has often less frequency of fever, of the four virtual drive data Some may be "1". Further, each heating element may generate heat according to the recording state of the pixel recorded immediately before.

In this embodiment, the second sub-subline portion 48b from the top is the second priority sub-subline portion, and
The second sub-subline portion 48a is the first priority sub-subline portion, and the last first priority sub-subline portion is overlapped as in the above-described embodiment. The first
The ink dot pattern of the priority sub-subline is shown in FIG.
As shown in FIG. 9, both the case of making the same as the second priority sub-sub line portion and the case of using the ink dot pattern dedicated to the joint as shown in FIG. 9 can be applied.

In each of the above embodiments, the first and second priority sub-sub-lines are located at the center of the pixel in order to express a smooth gradation. Good. Although an example in which one pixel is configured by four or eight sub-subline portions has been described, one pixel may be configured by only two of the first priority sub-subline portion and the second priority sub-subline portion. In addition, the first priority sub-subline portion is arranged below the second priority sub-subline portion,
This may be reversed. Furthermore, in the first priority sub-line portion, the data is changed in the n-th row, and the original data determined by the gradation level is used in the (n + 1) -th row.
This may be reversed. That is, in FIG. 3, it may be exchanged with pixel P ₁ and the pixel P _36. Furthermore, the second priority sub-subline portion may be two or more.

In the above-described embodiment, the recording of the second priority sub-subline is started after the recording of the first priority sub-subline is completed. An ink dot is recorded in one cell, and then an ink dot is recorded in one cell of the second priority sub-subline portion, and this is repeated alternately, so that the one remaining on the second priority sub-subline portion is finally obtained. Ink dots may be recorded in individual cells. Further, each time a plurality of cells, for example, two cells of the first priority sub-subline portion are recorded, one cell of the second priority sub-subline portion may be recorded.

The ink dot pattern for the joint shown in FIG. 9 or FIG. 14 is not limited to this, and other ink dots may be used as long as ink dots overlap at the joint of the line from the low density image portion. It may be a dot pattern.

Although the case of monochrome recording has been described, the present invention can of course be applied to color recording. In this case, as is well known, the ink ribbon in which the cyan, magenta, and yellow ink areas are formed at a constant pitch may be used, and the recording may be performed for each color in a line-sequential or plane-sequential manner. In this case, the sub-sub-line between the lines is recorded redundantly for each color, and each color is recorded slightly darker.However, when three colors are superimposed, this part is conspicuous in natural images because the probability of this part being black is high. There is no. Also, R, G, B, Y, M,
In the case of a color close to C, the color becomes darker instead of black, but there is no practical problem. Further, the present invention provides a yellow thermosensitive coloring layer,
The present invention can also be applied to a color thermal print using a color thermal recording paper provided with a magenta thermosensitive coloring layer and a cyan thermosensitive coloring layer sequentially.

[0067]

As described above in detail, in the serial thermal printing method according to the present invention, the pixels on the row boundaries maintain the overlapping of the ink dots on at least one of the first priority sub-sublines. Above, recording is performed with an ink dot pattern corresponding to the gradation level. When a shift occurs in the paper feed, overlapping ink dots appear in accordance with the shift amount, so that it is possible to prevent a white streak at a line joint. In addition, the portion where the ink dots overlap is black in monochrome and has a high probability of being black in color. Therefore, there is almost no change in density due to the overlapping of the ink dots, and therefore, the seams of the lines do not stand out.

Also, the first line overlapping the next line
By recording the priority sub-sub-line portion in the same state as the ink dot pattern recorded in the second priority sub-sub-line portion, at low density where only the first priority sub-sub-line portion is recorded, the ink dot at the line boundary is printed. There is no practical problem since superposition does not occur and it is originally inconspicuous at extremely low concentrations. In addition, since the printing of the second priority sub-subline portion is started and the ink dots overlap on the first priority sub-subline portion at a slightly low density, the seam becomes conspicuous even if the paper feeding becomes uneven. There is no. Therefore, in the range of slightly low to high concentrations,
Seam improvements can be made. To obtain this effect from a lower density, the recording of the cells in the second priority sub-subline portion may be hastened.

Further, by recording the first priority sub-sub-line portion with the ink dot pattern dedicated to the joint determined according to the gradation level, the joint can be corrected more naturally, and even if there is a variation in the paper feed, it can be performed properly. I can deal with it.

[Brief description of the drawings]

FIG. 1 shows n rows and (n + 1) according to the printing method of the present invention.
FIG. 9 is an explanatory diagram showing a recording state of a row.

FIG. 2 is a perspective view schematically showing a fusion type serial thermal printer.

FIG. 3 is an explanatory diagram showing a relationship between a thermal head and pixels for one row.

FIG. 4 is an explanatory diagram showing a relationship between a gradation level and an ink dot pattern.

FIG. 5 is a block diagram illustrating an electrical configuration of the fusion type serial thermal printer.

FIG. 6 is an explanatory diagram illustrating an example of a DOT-LUT.

FIG. 7 shows n rows and (n) when the paper feed amount is larger than a specified value.
FIG. 3 is an explanatory diagram illustrating a recording state of a +1) row.

FIG. 8 shows n rows and (n) when the paper feed amount is smaller than a specified value.
FIG. 3 is an explanatory diagram illustrating a recording state of a +1) row.

FIG. 9 is an explanatory diagram showing one row of pixels in an embodiment using an ink dot pattern dedicated to joints.

FIG. 10 is a block diagram showing an electrical configuration of a fusion type serial thermal printer used in the embodiment of FIG.

FIG. 11 is an explanatory diagram showing an example of a DOT-LUT dedicated to joints.

FIG. 12 is an explanatory diagram showing an ink dot pattern when a gradation level is changed for pixels on a row boundary.

FIG. 13 is an explanatory diagram showing a relationship between pixels and a thermal head in an embodiment in which each sub-subline portion is recorded in order from the end.

FIG. 14 is an explanatory diagram showing a pixel and an ink dot pattern dedicated to a joint in an embodiment having two first priority sub-sub-lines;

FIG. 15 is an explanatory diagram showing a recording state of pixels on a row boundary.

FIG. 16 is an explanatory diagram showing a recording state of an embodiment using a thermal head having a heating element long in the sub-scanning direction.

[Explanation of symbols]

10,45 thermal heads 10a ₁ , 10b ₁ , 10d ₃₆ , 45a ₁ , 45b ₁
Heating element 12 Recording paper 15 Ink ribbon 16 Ribbon cassette 21A, 21B, 21C, 21D Sub-subline 21a, 39a, 48a First-priority sub-subline portion 21b, 39b, 48b Second-priority sub-subline portion 22, 41a Cell 36, 42 Joint iNK dot patterns _{P 1, P 2, P 36} , 38,41,43a, 43b, 4
4,47 pixels SL ₀ Pixel line on boundary OL overlap part

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B41J 2/355 B41J 2/36

Claims (9)

(57) [Claims] 1. A thermal head in which a plurality of heating elements are arranged in a main scanning direction. While the thermal head moves in a sub-scanning direction on a recording sheet, each heating element is selectively driven to drive in a sub-scanning direction. In a serial thermal printing method in which an ink dot is recorded in a cell on a sub-sub line that extends in a row and the recording paper is moved in the main scanning direction after recording one row so that the ends of each row overlap, the adjacent N (2 The above-mentioned (integer) sub-sub-lines form a pixel row in which one pixel composed of N cells in the main scanning direction and M (an integer of 2 or more) cells in the sub-scanning direction is formed. Recording ink dots in each cell within the pixel so as to form an ink dot pattern corresponding to the gradation level of the pixel; N sub-subline portions existing in one pixel among the N sub-sublines in Thus, at least one first priority sub-subline portion and at least one second priority sub-subline portion adjacent thereto are determined, and the first priority sub-subline portion includes all of the second priority sub-subline portions. Ink dots are recorded in all cells of the first priority sub-subline at a gradation level lower than the gradation level at which ink dots are recorded in cells, and overlap between two adjacent rows is prevented. The recording paper feed amount is determined so as to be performed in at least one first priority sub-sub line portion, and the sub-sub line below the n-th line and the sub-sub line above the (n + 1) -th line to be recorded next are determined. A serial thermal printing method characterized in that a pixel line is recorded twice so as to form one pixel column located on a boundary between rows with a sub-line. 2. The serial thermal printing method according to claim 1, wherein said first and second priority sub-subline portions are located at the center of a pixel column. 3. The recording order between the M cells existing in the first priority sub-subline portion and the recording order among the M cells existing in the second priority sub-subline portion are the same. 3. The serial thermal printing method according to claim 1, wherein 4. The ink dot pattern of one pixel,
Recording of ink dots is started from one of the cells of the first priority sub-subline portion, and as the gradation level becomes higher,
The number of cells on which ink dots are recorded within one pixel increases, and after ink dots have been recorded on all cells of the first priority sub-subline portion, the cells of the second priority sub-subline portion are not recorded. 4. The serial thermal printing method according to claim 1, wherein the pattern is set to be started. 5. In the first and second priority sub-subline portions, recording is started from cells near the center, respectively.
5. The serial thermal printing method according to claim 4, wherein each time the gradation level increases by one step, ink dots are alternately recorded in cells on both sides thereof. 6. A third and fourth priority sub-sub-line portion is located on both sides of the first and second priority sub-sub-line portions, and ink dots are alternately arranged in the two sub-sub-line portions as the gradation level increases. 6. The serial thermal printing method according to claim 1, wherein recording is performed. 7. At least one first-priority sub-subline forming a pixel column on a boundary between the rows includes one of the n-th row and the recording of the next (n + 1) -th row. A part of the ink dot pattern determined by the level is recorded, and the other recording is performed in the same state as the ink dot pattern recorded on the second priority sub-subline above or below. 7. The serial thermal printing method according to any one of 1 to 6. 8. At least one of the first priority sub-sub-lines forming a pixel column on the boundary of the row includes one of the recording of the n-th row and the next (n + 1) -th row. 7. The serial printing method according to claim 1, wherein a part of the ink dot pattern determined by the level is printed, and in the other printing, a seam ink dot pattern determined by the gradation level is printed. Thermal printing method. 9. The recording order of the joint ink dot pattern and the ink dot pattern determined by the gradation level of the pixel is the same between the cells of the first priority sub-subline portion. 8. The serial thermal printing method according to 8.