JP3165305B2 - 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 an improvement in a thermal printing method used in a serial printer in which a thermal head moves in a sub-scanning direction and a recording paper moves in a main scanning direction.

[0002]

2. Description of the Related Art Thermal recording methods include thermal recording, in which an image is directly recorded on a thermal recording sheet, and thermal transfer recording, in which ink from an ink film is transferred to recording paper. In this thermal transfer recording, a fusion type for transferring the molten ink to recording paper,
There is a sublimation type in which the amount of ink transferred to 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 having a plurality of recording elements arranged in the main scanning direction is used. 2. Description of the Related Art A serial printer of a type in which paper is fed in a scanning direction to record the next one line is often used.

However, in the serial printer, since the paper feed tends to be uneven, the edges of adjacent rows in the main scanning direction overlap each other, the density of the portion (overlap portion) increases, and stripes are formed in the sub-scanning direction. On the contrary, there is a problem in that a gap is formed between rows, and the recording paper appears in a streak shape in the sub-scanning direction.

To cope with the above problem, there is known a method in which the amount of paper feed is reduced and the ends of adjacent rows are overlapped and recorded. However, when they are simply overlapped with each other, the density of the overlapped portion becomes high, resulting in a dark line, which is rather conspicuous. Therefore, a method of giving a density gradient (fade-in, fade-out) to an overlapping portion is also known.

[0005]

However, the method of giving a density gradient has a drawback that image processing becomes extremely complicated because it is necessary to weight image data of an overlapped portion.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a serial thermal printing method which makes it possible to make seams between lines very inconspicuous.

[0007]

In order to achieve the above object, a serial thermal printing method according to the present invention uses a thermal head in which K heating elements are arranged in a main scanning direction, and the thermal head is mounted in a sub scanning direction. , Each heating element records an ink dot in a cell on a sub-sub line extending in the sub-scanning direction, and moves the recording paper in the main scanning direction after recording one row composed of K sub-sub-lines. In a serial thermal printing method, one pixel is composed of N cells in the main scanning direction and M cells in the sub-scanning direction, and excluding at least A heating elements on one side.
(KA) The heating elements are grouped into N groups, and one pixel is recorded in each group. In recording each pixel, an ink dot projecting in the main scanning direction at a medium gradation level Recording to be a pattern, previous line
On the bottom sub-line that constitutes the bottom pixel of
Dot and the topmost sub-sub that constitutes the topmost pixel in the next row
Correlate with the dots on the line and the resulting pattern
A means that A heating elements record ink dots,
The recording paper is moved by the entire length of the (KA) heating elements in the main scanning direction.

[0008]

[0009]

[0010]

[0011]

Further, using a thermal head having an array of K number of heating elements in the main scanning direction, the cells on the sub-sub-line heating elements extending in the sub-scanning direction by moving the thermal head in the sub-scanning direction Record the ink dots,
In the serial thermal printing method in which the recording paper is moved in the main scanning direction after recording one row composed of K sub-sublines, one pixel is composed of N cells in the main scanning direction and M cells in the sub-scanning direction. Excluding at least A heating elements on one side, grouping (KA) heating elements into N groups, and printing one pixel in each group; At a middle gradation level, recording is performed so as to form an ink dot pattern protruding in the main scanning direction. A heating elements are obtained from the correlation between the lowermost pixel of the previous row and the uppermost pixel of the next row. According to the given value, ink dots are recorded in a predetermined pattern corresponding to this value, and the recording paper is moved by the entire length of the (KA) heating elements in the main scanning direction.

[0013]

In the recording of a halftone image, recording of a medium gradation level is often performed, and a cross-shaped ink dot pattern is recorded in these pixels. And one or several overlapping sub-sublines at the end of the line,
Dot on the lowermost sub-subline that constitutes the edge pixel
And the uppermost sub-subline constituting the uppermost pixel of the next row
Correlate with the dot on the top, and in the obtained pattern,
An ink dot is recorded only in the center of one pixel section. Therefore, even when the paper feed amount is equal to or smaller than the specified value, a black line may occur because only one or several dots are overlapped on the overlapping sub-subline at the end of the line. Absent. Conversely, when the paper feed amount is large, only the number of overlapping lines is reduced, so that a white line extending in the sub-scanning direction at the line end does not occur.

When the gradation level is small, ink dots are recorded only at the center of the pixel, and therefore no ink dots are recorded on the overlapping sub-sub-lines. At this gradation level, even if unevenness occurs in the paper feed, the number of sub-sub-lines serving as white lines only increases or decreases, so that the seam between the lines is still inconspicuous. At very high pixel grayscale level only when the paper feed amount is small when or which than a specified value as, but the sub-sub-line is overlapped printing, the lowermost pixel of the previous row structure being overlapped
The dot on the bottom sub-line at the bottom
Dots on the uppermost sub-subline that constitutes the uppermost pixel
And the resulting pattern,
Because the part to be dropped is recorded, the seam between the lines
There is no standing.

[0015]

FIG. 2 shows a serial printer to which the printing method according to the present invention is applied. In FIG. Vertical direction (main scanning direction) with respect to the recording position by the roller 14
Transported to The ink ribbon 15 for fusion transfer is supplied by a known ribbon cassette 16. Ribbon cassette 16
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. In addition,
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 cells shown virtually in FIG. 3 to form ink dots. When recording of one line is completed, the thermal head 10 and the ribbon cassette 16
Is returned to the initial position, 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, 145 heating elements 10a ₁ , 10b ₁ , 10c
_{1, 10d 1, 10a 2,} 10b 2, ···, 10
c ₃₆ , 10d ₃₆ , and 10e are arranged along the main scanning direction. Since each heating element records a sub-sub line 21 having a width L1 extending in the sub-scanning direction, 145 sub-sub lines 21 are recorded by one reciprocation of the thermal head 10. Further, each time the thermal head 10 is moved by the distance L2, the heating element is driven, so that each sub-subline is divided into L2 in length. Therefore, each sub-sub-line is a series of L1 × L2 cells 22.

In this embodiment, one pixel is composed of four cells in the main scanning direction and eight cells in the sub-scanning direction, and expresses 32 gradations. Pixel P ₁ of the uppermost includes four heating elements 10a
_{1 to 10} d ₁ , and the lowermost pixel P ₃₆ is recorded by the heating elements 10 a _{36 to} 10 d ₃₆ . The heating element 10e, which is a fraction, records a sub-subline 21a that is scheduled to overlap. This sub-sub line 21a is
The driving pulse supplied to the heating element 10e is
Is the same as 0d _36, are recorded in the same state as immediately sub subline above. The numbers written in the cells of the pixels 20 indicate the recording order of the ink dots.

At the time of recording each pixel, as shown in FIG. 4, the recording is started from the cell at the center of the sub-line in the second column. As the gradation level increases, the area of the ink dots increases alternately from the center of the pixel to the left and right. After all the cells in the second column have been recorded, the process proceeds to recording of cells in the third column. When the printing of the cells in the third row is completed, the area of the ink dots increases so that the central portion protrudes up and down. That is, the shape of the pixel changes as a point → T-shaped → cross → rectangle as the gradation level increases. When the adjacent pixels are recorded at the gradation level “18” or higher, a lattice is formed with the upper, lower, left, and right pixels.

At the gradation level "2", the heating element 10b ₁
Are energized twice, and ink dots are recorded in two cells as shown by hatching. Also, for example, at the gradation level “20”, the central heating elements 10b ₁ and 10c ₁ are each energized eight times, recording ink dots in 16 cells, and the upper and lower heating elements 10a ₁ and 10d _1. Electric current is applied twice each, and ink dots are recorded in two areas of the first and fourth columns, respectively.

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 reads the image data representing the gradation level from the frame memory 25 for one column, that is, for 36 pixels. 1 written in the line memory 27
The image data for the columns is transferred to the buffer memory 28.

The LUT 29 generates drive data for recording the dot pattern shown in FIG. 4 according to the gradation level. One pixel is recorded by four heating elements, and the driving data supplied to each heating element is composed of 8 bits. “1” is assigned when an ink dot is recorded in a cell. For example, the gradation level “2”
In 0 "drive data" 00011000 "is output serially to the heating elements 10a _1, heating elements 10b _1,
Drive data "11111111" is respectively outputted to 10c _1, the driving data of "00011000" is output to the heating element 10d _1.

The OL data generator 30 copies image data for recording the lowermost sub-subline of the _36th pixel P36, and creates image data of the heating element 10e for recording the sub-subline 21a.

In the recording example shown in FIG. 1, all the pixels are recorded with image data of the gradation level "20".
1) The overlap portion OL between the row and the n-th row is shown. The overlap portion OL includes the sub-sub line 21a formed at the lowermost end of the (n-1) th row and the first sub-line 21a of the nth row.
The uppermost sub-sub line 21 constituting the pixel line SL ₁ ′ is superimposed. Sub-subline 2
The image data 1a is composed of the lowermost sub-sub line 21 forming the _36th pixel line SL ₃₆ in the (n−1) th row.
b is a copy of the image data.

The dot shape of the pixel recorded by the image data of the gradation level "20" has a cross shape as shown in the figure, and these are connected to form a grid. The lattice shape including the overlap portion OL is almost the same as that of the non-overlap portion. In addition, the tip of each cross-shaped pixel is recorded slightly thinner due to the heat generation characteristics of the heating element (the temperature near both ends is low), and is overprinted due to the characteristics of the fusion-type thermal transfer that transfers the ink separated from the ink ribbon. The density of the overlap portion OL is almost the same as the density of the non-overlap portion, and the overlap portion OL is inconspicuous. Further, even if there is variation in the paper feed, if the variation is equal to or less than the width of one dot in the main scanning direction, (n−
1) There is no gap between the row and the n-th row.

As shown in FIG. 4, in the low-density image having a gradation level of "17" or less, the dots of each pixel do not form a grid, and the recorded image is composed of dot-like dots. Therefore, when the 36th pixel line has a gradation level of “17” or less, the image data of the sub-sub-line 21b at the bottom is “00000000”. Also "000
00000 "and no dot is recorded. Pixels of a high-density image having a gradation level of “28” or more form dots having a rectangular shape or a shape close thereto, but the overlap portion OL is almost inconspicuous because the density of the entire recorded image is high.

Next, the recording procedure of the serial printer will be described. At the time of recording, the platen roller 13 and the transport roller 1
4 rotates 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.

After the image data has been written into the frame memory 25, it is read out line by line into the line memory 27 and transferred to the buffer memory 28. These image data are converted into drive data corresponding to each gradation level by the LUT 30, and the thermal head 10 is driven so that one pixel is recorded by four adjacent heating elements. The OL data generation unit 30 copies the driving data of the lowermost sub-subline among the lowermost pixels of the first row, and generates the heating element 10e.
Is generated.

Thermal head 10 and ribbon cassette 1
The thermal head 10 heats and presses the ink ribbon 15 from behind while transferring the melted ink to the recording paper 12 while 6 moves rightward in the sub-scanning direction. by this,
With the ink dot pattern as shown in FIG. 4, moire-free printing in which the shape of the ink dot printed in the pixel differs depending on the gradation level is performed.

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 to the left 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. This transport amount is 144.times.L1, whereby the lowermost sub-subline and the uppermost sub-subline of the next row overlap. Hereinafter, this operation is repeated to record all of the image data on the recording paper 13.

When recording is completed, the platen roller 1
3 and the transport roller 14 are continuously rotated in the direction of the arrow, and the recording paper 12 is discharged. The overlap portion OL is finished to have almost the same density as the non-overlapping portion, and a high-quality print without streaks in the sub-scanning direction can be obtained.

If the paper feed amount is the transport amount (144 × L1)
If the number is larger than that, as shown in FIG. 6, the amount of overlap decreases. However, one sub-sub line 21
, The white line is not formed between the two lines to form a white line, and the seam between the lines is inconspicuous. Also, it can be seen that the change in density is small as compared with FIG. It should be noted that the change in density is small even when the paper feed amount is small and the overlap amount is increased.

Next, another example in which the recording order of the ink dots recorded in the pixels is different will be described. The pixel 40 shown in FIG.
Recording is started from the cell at the left end of the sub-sub line in the column. In the pixel 40, as the gradation level increases,
The area of the ink dot increases from the left end to the right end of the sub-line in the second column, and after all the cells in the second column have been printed, the process shifts to recording of cells in the third column. In the pixel 41 shown in FIG. 10, as the gradation level increases, cells in the second column and cells in the third column are alternately recorded, and the area of the ink dots increases toward the right end. When the recording of the cells in the third column is completed for both the pixels 40 and 41, the area of the ink dots increases so that the central portion protrudes up and down.

Pixels 42 and 43 shown in FIGS.
Starts recording from the cell at the left end or the center of the sub-subline in the fourth column. At the gradation level “2” or more, the pixels 42 and 4 become higher as the gradation level becomes higher.
In the case of No. 3, the area of the ink dots increases from the left end to the right end of the sub-line in the second column, and after all of the cells in the second column have been printed, the printing shifts to the cells in the third column. When the printing of the cells in the third column is completed, the area of the ink dots increases so as to protrude vertically from the left end to the right end in the pixel 42, and the area of the ink dots protrudes vertically from the center in the pixel 43. Increase. Therefore, except for the case where the gradation level is “0”, the ink dot is always recorded in at least one cell of the sub-subline that is scheduled to overlap with the next row. There is no white line to form a white background, and the seams between the lines are inconspicuous. It is to be noted that, at a medium gradation level, the pixel 42
The character 43 and the pixel 43 have a cross-shaped dot shape.

In the embodiments described so far, a thermal head in which the length of the heating element in the sub-scanning direction is equal to one cell width is used, but a heating element having a longer length in the sub-scanning direction is provided. A thermal head may be used. As shown in FIG. 13, 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. The pixels 47 recorded by the thermal head 45 are composed of four sub-sublines 48 and eight main sub-lines 49a and 49b. The width of the first main sub line 49a is the same as the length B of the heating element in the sub-scanning direction,
This is equivalent to a step. The width of the second to eighth main sub-lines 49b is the one-step feed amount C of the thermal head 45.

When recording one pixel, after recording the first main sub-line 49a, the thermal head 45 is intermittently fed by a distance C, and each heating element 45a _{1 is} driven by drive data based on image data of the pixel. to drive the ~45d _1. After recording of this pixel, the heating element is switched to the first pixel of the next pixel.
In order to face the main sub line 49a, the thermal head 45 is fed by four steps. Preliminary feeding of the 4 steps becomes blank period, the heating elements 45a ₁ ~45d ₁
Is supplied with virtual drive data that does not record ink dots. This virtual drive data is represented by reference numeral 50, and is all "0" in this embodiment. Therefore, during this time, the heating elements 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 tail due to heat storage, in this embodiment, four driving data are provided. Data is provided, and one main sub-line of width L is inserted between each pixel. In this case, in the dot pattern in which the ink dots grow in the sub-scanning direction according to the gradation level of the pixel, the drive data is “0” due to the influence of heat generated for recording the last main subline of the previous pixel. However, ink dots are also formed on the first main sub-line of the blank section, the continuity of pixels is maintained in the high density portion, and the density is prevented from increasing in the middle and low density.

Also in this embodiment, the gradation level is "1".
In the middle of “8” or “20”, as shown in FIGS. 14 (A) and (B), the dot shape becomes a cross, and the seam between the lines is inconspicuous as in the above-described embodiment.

In the embodiment described above, the number of gradations is 32, but the present invention is not limited to this. Further, although only one sub-subline is overlapped, a plurality of sub-sublines may be used. Further, although the sub-subline for overlapping at the lowermost end of the row is provided, the sub-subline at the uppermost end of the row may be overlapped. Further, an overlapping sub-sub-line may be provided at both the uppermost end and the lowermost end. In the case where the upper and lower ends of each row are overlapped, recording may be performed according to the procedure shown in FIG.

The ink dot pattern employed in the above-described embodiment has a cross shape when the gradation level is medium, but as shown in FIG. (B) and H-shaped (C) may be used. Further, in the case of the embodiment in which the upper and lower ends of the row are overlapped, a cross shape or the dot patterns shown in FIG. 8 may be combined to use different dot patterns at the upper end and the lower end of the row.

In the above-described embodiment, the image data of the sub-subline overlapping the next line is obtained by copying the image data of the adjacent sub-subline.
The lowest dot forming the lowest pixel of the previous row and the highest dot forming the highest pixel of the next row may be correlated, and the resulting pattern may be used to record overlapping sub-sublines. . For example, the lowermost dot of the previous row and the uppermost dot of the next row are compared in the same column, and if dots are recorded in at least one of them, the dots in the same column that constitute the sub-subline to be overlapped If no dot is recorded in either of them, a process such as not recording the dots in the same column constituting the sub-subline to be overlapped is performed. Also, by the value obtained from the correlation between the lowermost pixel of the previous row and the uppermost pixel of the next row,
The overlapping sub-sub-lines may be recorded in a dot pattern for each gradation level predetermined for this value.

Although the embodiment described above is for monochrome recording, the present invention can of course be applied to color recording. In this case, as is well known, ink ribbons in which cyan, magenta, and yellow ink areas are formed at a constant pitch may be used, and recording may be performed on each color sequentially. Further, the present invention can also be applied to a color thermal printing using a color thermal recording paper provided with a yellow thermal coloring layer, a magenta thermal coloring layer, and a cyan thermal coloring layer in this order.

[0043]

As described above, according to the serial thermal printing method of the present invention, as the gradation level increases, the shape of the ink dot recorded in the pixel changes to a point.
The heating element that uses an ink dot pattern that changes like a cross → rectangle and records at least one sub-sub line that is scheduled to overlap with the next row is the bottom of the previous row.
Dot on the lowermost sub-subline that constitutes the edge pixel
And the uppermost sub-subline constituting the uppermost pixel of the next row
Since it is correlated with the dots above and driven by the obtained pattern, even if paper feeding becomes uneven, there is no gap between the lines and no streak-like gaps. High-density recording can be performed without the density of the wrapped portion being increased and becoming noticeable in the form of a stripe.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a recording state of a (n-1) th line and an nth line.

FIG. 2 is a schematic perspective view showing a fusion type serial printer embodying the present invention.

FIG. 3 is an explanatory diagram showing a recording order of ink dots in a pixel.

FIG. 4 is an explanatory diagram showing an ink dot pattern.

FIG. 5 is a block diagram illustrating an example of a head driving unit.

FIG. 6 is an explanatory diagram similar to FIG. 1 when a deviation occurs in paper feeding.

FIG. 7 is a flowchart in a case where sub-sublines are provided at both the uppermost end and the lowermost end of a row.

FIG. 8 is an explanatory diagram showing another ink dot pattern.

FIG. 9 is an explanatory diagram showing the recording order of ink dots in pixels for recording sub-sub-lines at the center one by one from the left end to the right end.

FIG. 10 is an explanatory diagram showing a recording order of ink dots in a pixel in which two sub-sublines at the center are alternately recorded from the left end to the right end.

FIG. 11 is an explanatory diagram showing the recording order of the ink dots in the pixel for recording the first ink dot in the cell at the left end of the sub-line in the fourth column.

FIG. 12 is an explanatory diagram showing the recording order of the ink dots in the pixel for recording the first ink dot in the cell at the center of the sub-sub line in the fourth column.

FIG. 13 is an explanatory diagram showing a recording order of ink dots in a pixel and an example of virtual drive data supplied to the thermal head when the thermal head is idle-fed in another embodiment.

14 is a gray scale level “18” of the embodiment shown in FIG.
It is explanatory drawing which shows the dot shape of each pixel of "20".

[Explanation of symbols]

10, 45 thermal heads 10a ₁ , 10b ₁ ,..., 45a ₁ , 45b ₁ ,.
· Heating element 12 the recording sheet 15 the ink ribbon 16 ribbon cassette 21,48 vice subline 22, 46 cells 30 OL data generating unit 40,41,42,43,47 pixels 49a, 49b main subline 50 virtual driving data P _1, P ₃₆ pixels OL overlap part

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B41J 2/355 B41J 2/51

Claims (2)

(57) [Claims] 1. A thermal head in which K heating elements are arranged in a main scanning direction is used. By moving the thermal head in a sub-scanning direction, each heating element becomes a cell on a sub-sub line extending in the sub-scanning direction. In a serial thermal printing method in which an ink dot is recorded, and a recording sheet is moved in the main scanning direction after recording one line composed of K sub-sublines, N recordings are performed in the main scanning direction and M recordings are performed in the sub-scanning direction. One pixel is composed of cells. Except for A heating elements on at least one side, (K-
A) N heat generating elements are grouped into groups, and one pixel is printed in each group. In printing each pixel, an ink dot pattern protruding in the main scanning direction at a medium gradation level is used. The correlation between the dot on the lowermost sub-subline constituting the lowermost pixel of the previous row and the dot on the uppermost sub-subline constituting the uppermost pixel of the next row is calculated, A serial thermal printing method, wherein A heating elements record ink dots in the obtained pattern, and the recording paper is moved by the entire length of the (KA) heating elements in the main scanning direction. 2. A thermal head in which K heating elements are arranged in the main scanning direction is used. By moving the thermal head in the sub-scanning direction, each heating element becomes a cell on a sub-sub line extending in the sub-scanning direction. In a serial thermal printing method in which an ink dot is recorded, and a recording sheet is moved in the main scanning direction after recording one line composed of K sub-sublines, N recordings are performed in the main scanning direction and M recordings are performed in the sub-scanning direction. One pixel is composed of cells. Except for A heating elements on at least one side, (K-
A) N heat generating elements are grouped into groups, and one pixel is printed in each group. In printing each pixel, an ink dot pattern protruding in the main scanning direction at a medium gradation level is used. The A heating elements print ink dots in a predetermined pattern corresponding to the value obtained from the correlation between the lowermost pixel of the previous row and the uppermost pixel of the next row. , (K−A) a serial thermal printing method wherein the recording paper is moved by the entire length of the heating elements in the main scanning direction.