JPH10235848A - Image recording mehtod for image recording device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a cyclic unevenness in density from generating, and improve the picture quality of a recording image. SOLUTION: A picture element clock is counted by a picture element counter 42 and a nozzle counter 43, and a line synchronizing signal is counted by a line counter 44. Then, a dither matrix threshold value at a location which is designated by the counted value of the picture element counter and the counted value of the line counter, is read by a dither threshold memory 45. Also, a correction data for a location designated by the counted value of the nozzle counter is read from a nozzle correction data memory 46. By this method, a threshold value correction circuit 47 corrects the threshold value by the correction data, and prepares a new threshold value and outputs. In the meantime, an image data of a location which is designated by the counted value of the picture element counter and the counted value of the line counter, is read from an image data memory 41. Thus, a comparison circuit 48 compares the image data and the corrected threshold value, and outputs a dither-treated signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the movement of a recording head in the main scanning direction to record dots on a recording medium at a pitch finer than the pitch between dot recording elements, and to use a dither matrix for dithering. The present invention relates to an image recording apparatus that performs processing and performs halftone image recording.

[0002]

2. Description of the Related Art There is known an ink jet printer that prints dots at a finer pitch than the pitch between dot recording elements by controlling the movement of a recording head in which a plurality of dot recording elements are arranged at a predetermined pitch in a line. I have.
This is because, as shown in FIG. 13, an ink jet head 1 having a plurality of ink ejection nozzles arranged in a line at a predetermined pitch as a dot recording element is arranged in parallel to a rotating drum 2 and as shown by an arrow in the drawing. The ink jet head 1 is provided so as to be reciprocally movable in the direction of the rotation axis of the rotating drum 2, and the recording paper is wound around the rotating drum 2 and rotated.
In order to control the movement of the recording paper, for example, to record an image at a density four times the nozzle pitch, the inkjet head 1 is moved by one-fourth of the nozzle pitch while the rotary drum 2 makes one rotation, and the sub-scanning of the recording paper is performed. The dot recording is performed in the direction, and the rotating drum 2 makes four rotations, so that the nozzle pitch is
Image recording is performed at four times the density.

More specifically, as shown in FIG. 16, an ink jet head 1 in which ink ejection nozzles P1, P2, P3, P4,. The ink dots are recorded on the recording paper 3 wound around the rotating drum 2 while moving, and are recorded at a recording density four times the pitch PT between the nozzles. That is, the nozzles P1, P2, P3, P4,
.. Indicate the dot D1 on the LN1 line in the first rotation.
1, D15, D19, D113 ... are recorded,
Is approximately PT in the main scanning direction at the LNn line.
Dots Dn1, Dn5, Dn9, Dn1 at positions shifted by / 4 pitch
3 ... will be recorded.

In the second rotation, the dots D12,... Are recorded on the LN1 line, and the dots Dn2,.
... is recorded, and the dot D1 is placed on the LN1 line in the third rotation.
Are recorded on the LNn line, dots D14,... Are recorded on the LN1 line in the fourth rotation, and dots Dn4,.
Thus, an image is recorded at a recording density four times the nozzle pitch. For example, if the nozzle pitch is 75 dpi (3
40 μm), image recording by this method results in a recording density of 340 μm / 4 = 85 μm, and 300 dpi.
Recording density can be realized.

[0005]

In the ink jet head 1 used in such an ink jet printer, a large number of ink discharge nozzles P are arranged in a line as shown in FIG. It is difficult to uniformly manufacture the nozzles P due to variations in the characteristics of the head constituent materials, and the like, so that the recording dots by the nozzles P vary. FIG.
FIG. 4 is a diagram schematically showing the variation of recording dots by each nozzle.

When an image is recorded using such an ink jet head 1, the first rotation of the rotary drum 2 is performed as shown in FIG.
The dot recording shown in (a) of FIG. 7 results in dot recording as shown in (b) of FIG. 17 in the second lap, and the dot recording as shown in (c) of FIG. 17 in the third lap. In the round, dot recording is performed as shown in FIG. That is, the variation of the recording dots by each nozzle occurs in the main scanning direction in units of four columns in the sub-scanning direction, and this appears as periodic unevenness.

On the other hand, when a normal ink jet head performs dither processing using a dither matrix to record a halftone image such as a photographic image, for example, when a halftone image is recorded in a continuous area, a normal two-tone image is recorded. There is a problem that the image quality is more likely to be deteriorated due to the variation of the print density between the nozzles than the value recording.

Accordingly, when a halftone image is recorded by dither processing using a printer which controls the movement of the ink jet head and performs image recording at a density higher than the pitch density of the ink discharge nozzles, the recording between the nozzles is performed. There has been a problem that density fluctuations occur periodically and image quality is remarkably reduced. Therefore, the invention according to claims 1 and 2 is to control the movement of a recording head in which a plurality of dot recording elements are arranged at a predetermined pitch in a line shape in the main scanning direction and to control the distance between the dot recording elements of the recording head with respect to the recording medium. An image that prints dots at a finer pitch than the pitch of the image and performs dither processing using a dither matrix to perform halftone image recording. An image recording method for a recording device is provided.

[0009]

According to the first aspect of the present invention,
A recording head in which a plurality of dot recording elements are arranged at a predetermined pitch in a line shape is provided so as to be movable in a main scanning direction orthogonal to the conveying direction of the recording medium, and controls the movement of the recording head in the main scanning direction and the recording medium. Is rotated and reciprocated in one direction with respect to the recording head to record dots on the recording medium at a pitch finer than the pitch between the dot recording elements of the recording head and dither processing using a dither matrix. In an image recording apparatus that performs halftone image recording, a variation in the recording operation of each dot recording element under predetermined recording conditions is detected in advance, and a threshold value of a dither matrix is set based on the information of the detected variation. It is to perform halftone image recording by correcting each dot recording element and performing multi-value dither processing based on the corrected threshold value.

According to a second aspect of the present invention, in the image recording method according to the first aspect, variations in the printing operation of each dot printing element under predetermined printing conditions are detected by variations in the density of the printed printing dots. Is to do.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) In this embodiment, an embodiment in which the present invention is applied to an ink jet printer will be described. FIG. 1 is a diagram showing a main part configuration of the entire printer. A rotating drum 12 which rotates at a constant peripheral speed in a direction indicated by an arrow in the drawing is provided as a recording medium conveying means in a main body case 11. The recording paper 15 as a recording medium is fed and wound through paper feed rollers 13 and 14.

That is, a paper feed cassette 16 is provided at the bottom of the main body case 11, and the recording papers 15 placed on a mounting plate 17 of the paper feed cassette 16 are taken out one by one by a feed roller 18 and The paper is fed to the paper feed rollers 13 and 14,
Further, the recording paper 15 manually fed from a manual feed tray 19 attached to the side of the main body case 11 so as to be openable and closable is fed to the feeding roller 2.
0 feeds the paper to the paper feed rollers 13 and 14. Switching between the feeding by the feeding roller 18 and the feeding by the feeding roller 20 is performed by a feeding switching unit 21.

The feed roller 1 is attached to the rotating drum 12.
A charging roller 22 for adsorbing the recording paper 15 fed from the drums 3 and 14 to the drum surface is disposed to face the drum. Further, an ink jet head 23 having a large number of ink ejection nozzles arranged in a line on the rotary drum 12 can be moved in the direction of the rotation axis of the rotary drum 12, that is, in the main scanning direction of dot recording on the recording paper 15. Are arranged facing each other.

The printing mechanism 24 includes a reciprocating mechanism 25 on which the ink jet head 23 is mounted, a motor unit 26 having a reciprocating rod and a linear motor,
The inkjet head 23 is moved by the rotating drum 12 by the advancing / retreating means 27.
With the motor unit 2
6, the reciprocating mechanism 25 is controlled to move in the direction of the rotation axis of the rotary drum 12 to reciprocate the inkjet head 23 in the direction of the rotation axis of the rotary drum 12.

A separating claw 28 which can be inserted between the drum surface and the recording paper 15 is disposed on the rotary drum 12, and the recording paper 15 separated by the separating claw 28 is transferred to a recording paper discharge / conveying means 29. It is designed to discharge. The recording paper discharging / conveying means 29 is composed of a belt conveyor 30 in contact with the non-recording surface of the recording paper 15 and a pressing means 31 for pressing the recording paper 15 against the surface of the belt conveyor 30.

At the end of the belt conveyor 30, the recording paper 15 conveyed by the belt conveyor 30 is fed to an upper discharge tray 32 formed above the main body case 11.
There is provided a direction switching means 34 for switching between discharging to a discharge tray 33 and a removable discharge tray 33 provided on the side surface of the main body case 11. Reference numeral 35 denotes an ink drying unit;
Is a main motor, 37 is an ink cassette, 38 is an ink buffer, and 39 is an ink supply tube.

FIG. 2 is a block diagram showing a circuit configuration of a main part. Reference numeral 41 denotes an image data memory for storing image data of one page fetched from outside. In the image data stored in the image data memory 41, one pixel is composed of 8 bits (0 to 2 bits).
55). Reference numeral 42 denotes a pixel counter that counts an external pixel clock, 43 denotes a nozzle counter that counts an external pixel clock and indicates a nozzle position at which a printing operation is performed, and 44 denotes a line counter that counts an external line synchronization signal. .

Reference numeral 45 denotes a dither threshold memory for storing a dither matrix threshold for performing dither processing as halftone processing, and reference numeral 46 denotes a dither matrix threshold for determining the variation of recording dots for each nozzle of the ink jet head 23. A nozzle correction data memory 47 for storing correction data for changing and correcting the data;
A threshold correction circuit that corrects the threshold data read from the image data with the correction data read from the noise correction data memory 46; and a threshold correction circuit 48 that stores the image data read from the image data memory 41 with the threshold data from the threshold correction circuit 47. A comparison circuit 49 for comparing and outputting binary or multi-valued data;
Is a head drive control unit for controlling the drive of the ink jet head 23 based on the data from the comparison circuit 48. For example, when ternary dither processing is performed, the dither threshold memory 45 stores dither thresholds as shown in FIGS. 3 (a) and 3 (b). (B) is (a)
, The threshold value is larger by “128”.

In this circuit, when the operation is started, the pixel counter 42 and the nozzle counter 43 count an external pixel clock, and the line counter 44 counts an external line synchronization signal. Then, a dither matrix threshold at a position designated by the count value of the pixel counter 42 and the count value of the line counter 44 is read from the dither threshold memory 45. Further, the correction data at the position specified by the count value of the nozzle counter 43 is read from the nozzle correction data memory 46. This allows
The threshold correction circuit 47 corrects the dither matrix threshold from the dither threshold memory 45 with the correction data from the nozzle correction data memory 46 to create and output a new dither matrix threshold.

On the other hand, image data at a position designated by the count value of the pixel counter 42 and the count value of the line counter 44 is read from the image data memory 41. As a result, the comparison circuit 48 compares the image data with the corrected dither matrix threshold, outputs a dithered signal, and supplies the signal to the head drive controller 49. Thus, the head drive control unit 49 controls the drive of the ink jet head 23 based on the dithered signal.

The correction data of the nozzle correction data memory 46 used for this data processing is set as follows. For example, in an ink-jet head of a type in which an ink chamber is deformed by using a piezoelectric member to discharge ink from nozzles, by controlling the energizing time of a voltage applied to the piezoelectric member as shown in FIG. Can be changed. Therefore, the condition a in the figure
Suppose that an image recording of half Sh of the area of one pixel is performed, and the condition b is that an image recording of the whole Sa of one pixel area is performed. If ternary image recording is performed using the conditions a and b, First, the variation of each nozzle when an image is recorded under the condition a is obtained.

When an image of one pixel is recorded under the condition a,
The state where half of one pixel is recorded is normal, but if the amount of ink to be ejected is large, the recording area becomes half or more of one pixel and the density becomes high. Therefore, in this case, the dither threshold may be corrected to be larger so that the increased amount of ink is corrected. As a result, the amount of ink to be ejected is suppressed, and the amount of ink becomes appropriate for recording half of one pixel.

Now, assuming that the recording area of one pixel under the condition a of the n-th nozzle is Sn, if | Sh−Sn | ≦ α (where α is an allowable value), it is regarded as half of one pixel. The threshold value is not corrected, and the correction data at this time is 0. If Sh−Sn> α, correction data for setting the threshold to be small is set on the assumption that the recording area of one pixel is small. This correction data is set according to the recording area, and is stored in the nozzle correction data memory 46 as a negative value.

If Sn-Sh> α, correction data for increasing the threshold is set assuming that the recording area of one pixel is large. This correction data is set according to the recording area, and stored in the nozzle correction data memory 46 as a positive value. Although the setting of the correction data under the condition a has been described above, the setting of the correction data under the condition b is also similar to | Sa−Sn | ≦ β (where β is an allowable value), S
Various correction data are set and stored in accordance with the relations of a-Sn> β and Sn-Sa> β.

As shown in FIG. 5, the threshold correction circuit 47 comprises two signed adders 471 and 472, and the threshold data read from the dither threshold memory 45 and the threshold data read from the nozzle correction data memory 46. The adder 471 adds the obtained nozzle correction data and outputs a new threshold value. The adder 471 sets a dither threshold value under the condition a, that is, a dither matrix for determining whether or not to perform recording with half the area of one pixel. The dither threshold is corrected, and the adder 472 sets the condition b
, That is, the dither threshold of the dither matrix for determining whether or not to print the entire area of one pixel.

FIG. 6 shows the positional relationship of the image data. In the figure, the hatched portions indicate one pixel. Note that, for simplicity of description, the pixel size is described as 100 × 100. The order of the image data read from the image data memory 41 is as shown in FIG. The leftmost four rows are data to be printed by the first nozzle, the next four rows are data to be printed by the second nozzle, and the middle four rows are data to be printed by the nth nozzle.

Therefore, the first nozzle is the rotary drum 1
In the first rotation of No. 2, dot recording of the first column in the sub-scanning direction is performed using the image data of the first, 26th, 51st, 76th, 101st, 126th,. In the second rotation of, the 2501st, 2526th, 2551th, 2576th, 2601th, 26th
The 26th,... Image data is printed in the second row in the sub-scanning direction, and at the third rotation of the rotary drum 12, the 5001, 5002, 5051, and 5076 dots are printed.
, 5101, 5126,..., The third row of dot printing is performed in the sub-scanning direction, and at the fourth rotation of the rotary drum 12, the 7501, 7526, 7551, 7576, and 7601 are recorded. Th, 76
Using the 26th,... Image data, dot printing in the fourth row is performed in the sub-scanning direction.

Similarly, the second and subsequent nozzles perform dot recording using image data in a predetermined order. A bold frame in the figure indicates a 4 × 4 dither matrix unit. As described above, the dither threshold of the 4 × 4 dither matrix as shown in FIG. 3 is corrected for each nozzle by the correction data of the nozzle correction data memory 46, and the corrected dither threshold and each image data of the image data memory 41 are corrected. To the comparison circuit 4
8, the signals are converted into ternary signals, and the head drive control unit 49 drives and controls the ink jet head 23 to perform image recording based on the signals, so that the variation in the ink ejection amount of each nozzle is corrected. Can record a halftone image in three values. Therefore, the variation in the density between the nozzles is corrected, whereby the periodic density unevenness is also eliminated, and the quality of the recorded image can be improved.

FIG. 8 shows the order of image data read out from the image data memory 41 in the same manner as in FIG. 7, but this figure shows the case where the 4 × 4 dither matrix unit is different from that in FIG. Is shown. That is, the 4 × 4 dither matrix units are arranged so as to be shifted by two columns every four lines. Even when such a dither matrix arrangement method is performed, the same operation and effect as in the arrangement of FIG. 7 can be obtained.

FIG. 9 shows an example of a threshold value when an 8 × 8 dither matrix is used. FIG. 9A shows a threshold value under the condition a, and FIG. 9B shows a threshold value under the condition b. Image data memory 41 using such a dither matrix
FIG. 10 shows an example of the arrangement for the image data. That is, in this case, dither processing of image data of two nozzles can be performed using one dither matrix. As described above, even when the 8 × 8 dither matrix is used, the same operation and effect as when the 4 × 4 dither matrix is used can be obtained. Note that when this 8 × 8 dither matrix is used, the arrangement of the dither matrix is 8
A method of arranging the image without shifting each line and a method of arranging the image by shifting four columns every eight lines can be executed.

(Second Embodiment) In this embodiment, an embodiment in which the present invention is applied to an ink jet printer will be described. The overall configuration of the printer is the same as in FIG. FIG. 11 is a block diagram showing a circuit configuration of a main part. The same parts as those in the above-described embodiment are denoted by the same reference numerals, and different parts will be described. This circuit does not temporarily store the image data sent from the outside in the memory as in the above-described embodiment, but takes in the image data from the outside in synchronization with the pixel clock, and
To supply. Then, the threshold value correction circuit 4 is
The comparison is performed using the corrected dither threshold value from No. 7, and the ternary signal resulting from the comparison is stored in the memory 50. The signals stored in the memory 50 are read out simultaneously when the head drive control unit 49 drives the inkjet head 23.

In this circuit, since the image data sent from the outside is directly compared with the dither threshold value by the comparison circuit 48, the order of the image data compared by the comparison circuit 48 is different from that of the above-described embodiment, and is different from that of the above-described embodiment. As shown. That is, the order of the image data is line by line. The thick frame indicates a 4 × 4 dither matrix unit. Even if such a circuit is used, halftone image recording with three values can be performed in a state where the variation in the ink ejection amount for each nozzle is corrected. Therefore, the variation in the density between the nozzles is corrected, whereby the periodic density unevenness is also eliminated, and the quality of the recorded image can be improved.

In each of the above-described embodiments, an ink jet printer for recording a monochrome halftone image has been described. However, the present invention is not necessarily limited to this, and color printers using yellow, magenta, cyan, and black inks may be used. The present invention can also be applied to an ink jet printer that performs halftone image recording. In this case, the correction data for the four colors of yellow, magenta, cyan, and black is stored in the nozzle correction data memory for each nozzle,
Different correction data will be used for the same nozzle for each color image data.

In each of the above-described embodiments, the correction data is stored in the nozzle correction data memory in advance. However, the present invention is not limited to this. A test pattern for detecting the density variation under the condition is recorded, and correction data for correcting the dither threshold is created based on the density data obtained by reading the test pattern, and the correction data is stored in the nozzle correction data memory. Is also good. In this case, correction data corresponding to the density is created from the relationship between the density and the dot diameter.

In each of the embodiments described above, a recording paper as a recording medium is wound around a rotary drum, and dot recording is performed at a density higher than the pitch density between nozzles by rotating the rotary drum. However, the present invention is not necessarily limited to this.A transport belt is used in place of the rotating drum, the recording paper is attracted to the transport belt, and the recording paper is repeatedly transported back and forth with respect to the recording head, so that the distance between the nozzles is reduced. Dot recording may be performed at a density higher than the pitch density.

In each of the embodiments described above, the present invention is applied to an ink-jet printer. However, the present invention is not limited to this, and uses an LED recording head having a large number of LED recording elements arranged in a line. The present invention can also be applied to a printer using a thermal recording head in which a large number of heating element storage elements are arranged in a line or a printer using an edge emitter recording head in which a large number of EL recording elements are arranged in a line. .

[0037]

According to the first and second aspects of the present invention, a recording head having a plurality of dot recording elements arranged in a line at a predetermined pitch is controlled to move in the main scanning direction to record on a recording medium. In the case of recording dots at a finer pitch than the pitch between the dot recording elements of the head and performing dither processing using a dither matrix to record a halftone image, the recorded image is prevented by preventing the occurrence of periodic density unevenness. Image quality can be improved.

[Brief description of the drawings]

FIG. 1 is a main part configuration diagram of an entire printer according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a circuit configuration of a main part in the embodiment.

FIG. 3 is a diagram showing an example of a dither threshold pattern in a 4 × 4 dither matrix unit according to the embodiment;

FIG. 4 is a graph showing energization time-ink ejection volume characteristics of the inkjet head according to the embodiment.

FIG. 5 is a block diagram showing a configuration of a threshold value correction circuit in the embodiment.

FIG. 6 is a view showing an example of a pixel pattern based on image data in the embodiment.

FIG. 7 shows a reading order of image data from an image data memory and 4 × 4 used for dither processing in the embodiment.
FIG. 3 is a diagram showing an example of the relationship between dither matrices.

FIG. 8 shows a reading order of image data from an image data memory and 4 × 4 used for dither processing in the embodiment.
The figure which shows the other example of the relationship of the dither matrix of FIG.

FIG. 9 is a view showing an example of a dither threshold pattern in an 8 × 8 dither matrix unit according to the embodiment;

FIG. 10 shows a reading order of image data from an image data memory and 8 × used for dither processing in the embodiment.
FIG. 8 is a diagram illustrating an example of a relationship between eight dither matrices.

FIG. 11 is a block diagram showing a circuit configuration of a main part according to a second embodiment of the present invention.

FIG. 12 shows a reading order of image data from an image data memory and 4 × used for dither processing in the embodiment.
FIG. 4 is a diagram illustrating an example of a relationship between four dither matrices.

FIG. 13 is a diagram illustrating a relationship between a rotary drum and an inkjet head in an inkjet printer that performs high-density image recording.

FIG. 14 is a diagram showing an arrangement of ink ejection nozzles of an inkjet head.

FIG. 15 is a diagram schematically showing variations in recording dots by each ink ejection nozzle of the inkjet head.

FIG. 16 is a diagram for explaining an image recording operation of the ink jet printer that performs high-density image recording.

FIG. 17 is a view for explaining a problem at the time of image recording by an inkjet printer that performs high-density image recording.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 12 ... Rotary drum 15 ... Recording paper 23 ... Ink jet head 25 ... Reciprocating movement mechanism 26 ... Motor unit 41 ... Image data memory 45 ... Dither threshold memory 46 ... Nozzle correction data memory 47 ... Threshold correction circuit 48 ... Comparison circuit

Claims (2)

[Claims] 1. A recording head in which a plurality of dot recording elements are arranged in a line at a predetermined pitch so as to be movable in a main scanning direction orthogonal to a conveying direction of a recording medium, and the recording head is moved in the main scanning direction. While controlling the movement, the recording medium is rotated or reciprocated in one direction with respect to the recording head, and dots are recorded on the recording medium at a pitch smaller than a pitch between dot recording elements of the recording head. In an image recording apparatus that performs dither processing using a dither matrix and performs halftone image recording, a variation in a recording operation of each of the dot recording elements under predetermined recording conditions is detected in advance, and the detected variation of the variation is determined. The threshold value of the dither matrix is corrected for each of the dot recording elements based on the information, and the dither processing is performed based on the corrected threshold value. Image recording method, which comprises carrying out the image recording. 2. The image recording method according to claim 1, wherein a variation in the recording operation of each dot recording element under predetermined recording conditions is detected based on a variation in the density of the recorded recording dots.