JPS63115752A - Serial printer - Google Patents

Abstract

PURPOSE:To enable reproduction of good color, in average, as a whole, by arranging the thresholds in different direction from main and sub scanning directions is a table of thresholds, i.e. dot number, being stored as an intermediate tone representing means. CONSTITUTION:When an intermediate tone is represented by overlapping dots, in a serial printer, the order of thresholds is prevented from aligning with main and sub scanning directions as the arrangement and number of dots concerning the shade of manuscript are selected from a table 21. Consequently, even if the dots are shifted from main and sub scanning directions when they are overlapped, moire pattern is suppressed in these directions and made inconspicuous.

Description

[Detailed Description of the Invention] [Industrial Applications] The present invention relates to a serial printer, and particularly to a serial printer that aims to eliminate moiré that tends to occur in color recording that can express halftones. .

[Prior Art] In conventional color serial printers, the degree of eccentricity and pitch accuracy of pulleys, gears, motors, etc. are strictly checked to ensure that dots are precisely overlapped for each color tone. It was necessary to select highly accurate parts. That is, although dot overlapping can be carried out with a good accuracy of 1.11 based on the configuration of such parts, this increases the cost and is not preferable from the viewpoint of productivity such as yield.

[Problems to be Solved by the Invention] In view of the above-mentioned conventional problems, an object of the present invention is to solve the problem without being severely restricted by the processing accuracy and assembly accuracy of parts related to carriage drive, and therefore to solve the problem of dot overlapping. To provide a serial printer capable of reproducing good colors on average even if there is some local deviation.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a means that enables recording by dots using a plurality of recording heads, and enables expression of intermediate tones by superposing the dots. Ingredients,
In a serial printer in which recording is performed on a recording sheet while main-scanning a plurality of recording heads along the recording sheet, and the recording sheet is fed in the sub-scanning direction, intermediate data stored and expressed in a storage device is used. The halftone expression means includes a table in which the number of dots corresponding to each tone is arranged in a matrix as threshold values according to order, and the order of the threshold values in the table is different from the main scanning direction and the sub-scanning direction. It is characterized by being arranged in the direction.

[Function] In the serial printer of the present invention, when expressing halftones by overlapping dots, when the arrangement and number of dots related to the shading of the original are selected from the table, the order of the threshold values is By making the dots do not coincide with the main scanning direction and the sub-scanning direction, even if the dots are shifted in the main scanning direction or sub-scanning direction during overlaying, moiré fringes will appear in that direction. It is possible to suppress moiré and make it less noticeable.

[Examples] Examples of the present invention will be described below in detail and specifically based on the drawings.

FIG. 1 shows an example of a serial printer to which the present invention can be applied. Here, 1 is a carriage, and 2-1 to 2-3 are multi-nozzle heads, and these multi-nozzle heads 2-1 to 2-3 eject cyan, magenta, and yellow ink, respectively, onto the recording sheet 3. 4 and 5 are a pair of rollers that keep the recording sheet 3 at the recording position, and the sheet can be fed by a pulse motor 6.

7 is a guide rail that supports the carriage 1 so that it can move freely along the recording sheet 3; 8 is an endless timing head that is attached to the carriage 1 and driven by a pulse motor 9; Stoppers IOA and 10B are provided at both ends of the path. 11-
1 to 11-3 are flexible tubes that supply ink to the multi-nozzle heads 2-1 to 2-3, respectively, 12 is an ink reservoir thereof, and 13-1 to 13-3 are heads 2-1 to 2-3.
A flexible insulating belt, each having a signal line to 3,
14, a relay plate 15 is a general current carrying belt.

In an inkjet serial printer having such a configuration, the carriage 1 is moved in the X direction to perform main scanning, and the pulse motor 6 further performs sub-scanning in the Y direction to print the heads 2-1 to 2 on the recording sheet 3. A color image is recorded by ejecting ink of each color from -3, but when trying to express halftones by overlapping dots of different colors,
Moiré occurs due to misalignment of dots and becomes noticeable, which tends to impair the quality of the image.

In addition, in such printers, a pattern in which threshold values of dots are arranged in a matrix is stored in the storage device in order to find a gradation corresponding to the density of the original, and by selecting the threshold value, an appropriate intermediate It allows the tone to be expressed.

That is, FIG. 2 shows an example of a circuit configuration for this purpose.

Here, 21 is a recording device R in which the matrix pattern of the threshold values described above is stored as a table 218.
OM, 22 and 23 are octal address counters supplied with clock pulses. In addition, the threshold value of 8
It is stored in ×8 memory cells. Thus, according to the addresses indicated by counters 22 and 23, 11
The threshold value stored in the cell 0M21 is the comparator 24
In the comparator 24, the threshold value ST outputted from n0M21 and the original iQ degree are proportional to 8.
The bit input data SD is compared with the input data SD.
is larger than the threshold value ST, the dot forming means 25
A dot recording signal "BI°" is outputted, and if it is smaller, a non-recording signal "0" is outputted.

However, in the conventional case, the arrangement order of the threshold values in the matrix table 218 of the threshold values of dots stored in the ROM 21 is often a spiral type or a discrete type, and emphasis is placed on intermediate tone expression in particular. In this case, a spiral arrangement as shown in FIG. 6 (see dashed arrow) has been particularly frequently used.

Therefore, the state in which dots are recorded according to the arrangement order of the threshold values is shown in (A) to (H) in Figure 7 in the order of light and shade.
As shown by, in the case of a spiral array, as is clear from this example, the threshold array is biased in the main scanning direction and the sub-scanning direction, so it is driven by the periodicity of the scanning direction and the threshold array. If there is pitch unevenness in the scanning direction due to eccentricity of the means, etc., a deviation occurs in the overlapping of dots, and moiré becomes noticeable.

(^) in FIG. 5 shows a state in which the dots are overlapped in this way. Here, a is the pitch at which the dots shown by the cross diagonal lines in the first color are formed, and b is the pitch at which the dots shown by the white circles in the second color are formed. As a result of overlapping, moiré becomes noticeable in the main scanning direction and the sub-scanning direction.

Therefore, in an embodiment of the present invention, the arrangement order in the matrix of dot threshold values in the table 21^ stored in the ROM 21 is set as shown in Figure 'fS3, for example. In other words, in this example, there is no part where the arrangement order matches the main scanning direction and the sub-scanning direction, and the order is set diagonally as shown by the dashed arrow. This is the order in which dots are recorded according to the input data.

(A) to (H) in FIG. 4 show in gradation the state in which dot recording is performed according to such an order.

Thus, if the dots of the first and second colors are recorded at pitches a and b shown in FIG. 5 in the state (H) and the dots are overlapped, the dots as shown in ([l) in FIG. An image will be obtained, and when compared with the image shown in (^) in Figure 5, the moiré fringes in the main scanning direction and sub-scanning direction will be less noticeable, and the image will be formed with dispersed dots. , gaps caused by misalignment when dots are stacked become less noticeable.

Note that the above example merely shows an example of the arrangement order of the threshold values, and it goes without saying that the arrangement of the dot thresholds applied to the present invention is not limited to this. It goes without saying that any order may be used as long as it is deviated from the scanning direction and the sub-scanning direction.

[Effects of the Invention] As described above, according to the present invention, in a serial printer in which dot recording is performed by each of a plurality of heads and halftones can be expressed by superimposing the dot recordings, the halftone expression can be The means includes a table stored in a storage device in which the number of dots corresponding to the halftone to be expressed is arranged in a matrix in order as threshold values, and the order of the threshold values in the table is determined by the recording head. By arranging the dots in a direction different from the main scanning direction and the sub-scanning direction of the recording sheet, it is possible to suppress the occurrence of moiré, which is particularly noticeable in the main scanning direction and sub-scanning direction due to poor dot overlapping accuracy. .

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an example of the configuration of a serial printer to which the present invention can be applied, FIG. 2 is a configuration diagram of a circuit for expressing halftones, and FIG. 3 is a perspective view showing an example of the configuration of a serial printer to which the present invention can be applied. FIG. 4 is a table diagram showing an example in which the dot recording order stored in a storage device for expression is arranged in a matrix, and FIG. 4 shows the dot recording made by the table of FIG. Schematic diagrams shown in A) to (H); (8) and ([1) in Figure 5 are images showing the state in which two-color dots are overlaid using the conventional table and the table according to the present invention, respectively. Figure 6 is a table diagram showing an example of the conventional recording order of dots arranged in a matrix as described above, and Figure 7 shows the dot recording performed using the table.
n? It is a schematic diagram shown by (a) - (h) in order of A. ! ... Carriage, 2-1 to 2-3... Multi-nozzle head, 3... Recording sheet, 6.9... Pulse motor, 21... ROM. 21Δ...Table, 22.23...Address counter, 24...Comparator, 25...Dot forming means. Figure 5

Claims (1)

[Scope of Claims] Dot recording is possible using a plurality of recording heads, and means is provided for making it possible to express halftones by overlapping the dots, and the plurality of recording heads are scanned along a recording sheet in a main scan direction. Recording is made on the recording sheet while
In a serial printer in which the recording sheet is fed in the sub-scanning direction, the number of dots corresponding to the intermediate tone stored in a storage device and expressed is arranged in a matrix as a threshold value according to order. A serial printer characterized in that the halftone expression means includes a table, and the threshold values in the table are arranged in a direction different from the main scanning direction and the sub-scanning direction.