JP2004198526A - Tandem type color image forming apparatus and oblique displacement correction method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that, in the conventional tandem type image forming apparatus, image reproducibility degrades since oblique correction needs to be performed for all of four printing heads. <P>SOLUTION: (1) A printing head as a reference is determined. (2) Displacement of printing by each of the remaining printing heads relative to printing by the reference printing head is individually checked in the main scanning direction. (3) According to the degree of the displacement in the main scanning direction, specific correction is made for each individual printing head so as to correspond to a signal applied to each of the remaining printing head. Thus, the oblique correction does not need to be performed for the reference printing head. For example, the reference printing head is black, and the reproducibility of a black image thereby is improved. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a tandem type color image forming apparatus, and more particularly to so-called oblique displacement correction in a tandem type color image forming apparatus.
[0002]
[Prior art]
2. Description of the Related Art A so-called tandem type color image forming apparatus in which four image forming units for forming images of magenta, cyan, yellow and black are arranged at regular intervals in a sheet conveying direction has been known.
Each image forming unit includes a photoconductor on which a toner image is formed on the surface thereof, and a print head for exposing the photoconductor. Each photoconductor is uniformly charged by, for example, a discharge of a main charger, and is then exposed to light emitted from a print head. As a result, a so-called electrostatic latent image is formed on the surface of the photoconductor. The developing device attaches toner to the surface of the photoconductor on which the electrostatic latent image is formed, and a toner image is formed.
[0003]
An endless transport belt for transporting a sheet is disposed below the four image forming units arranged. The conveyor belt is in contact with each photoconductor from below.
In the tandem-type color image forming apparatus, in the process in which the paper is transported by the transport belt, each color toner image formed on the surface of each photoconductor is sequentially transferred to the paper, and after the transfer of the fourth color toner image, A full-color image is recorded on a sheet by fixing the toner image on the sheet by a fixing device.
[0004]
In the tandem-type color image forming apparatus, the drum-shaped photoconductor and the print head included in each image forming unit extend in a direction orthogonal to the sheet conveying direction, that is, in the main scanning direction. The photoconductors are arranged in parallel with each other, and the print heads are also arranged in parallel with each other.
However, no matter how rigorous the design and manufacturing, the completed device has a slight distortion in the parallelism between the print heads. If the parallelism between the print heads is distorted, a color shift occurs in each formed toner image. For this reason, a technique has been proposed in which, when there is a distortion in the parallelism between print heads, a signal applied to the print heads is adjusted to perform oblique correction for each color formed (for example, see Patent Document 1). .
[0005]
The diagonal correction method described in Patent Document 1 is realized by a method of temporarily storing image data in a memory, reading data from the memory in an oblique direction, and supplying the data to a print head. At that time, if data is read from the memory in an oblique direction, the address of the memory to be read must be shifted in a sub-scanning direction (paper transport direction) orthogonal to the main scanning direction at a constant period according to the oblique inclination. However, there is a drawback that the printing line becomes a step-like printing line in the main scanning direction. Patent Literature 1 discloses a technique for reducing the above-described step and performing smoother oblique correction by turning on a print head so as to divide one pixel in the sub-scanning direction in order to alleviate this. I have.
[0006]
[Patent Document 1]
JP-A-9-23490
[0007]
[Problems to be solved by the invention]
By the way, when drawing one pixel data of the input image by dividing it in the sub-scanning direction (that is, when turning on the print head so as to divide one pixel in the sub-scanning direction), one side effect is that The edge becomes dull in the sub-scanning direction and the density distribution of one pixel becomes smooth, so that the edge becomes dull. As a result, compared to the case where one pixel is drawn without being divided, the pixel is slightly blurred. Therefore, it is not suitable for drawing when it is desired to clearly express the edges of an image, such as characters.
[0008]
Further, in Patent Document 1, it is detected whether or not a print head is correctly extended in a direction perpendicular to the paper transport direction based on the paper transport direction. The configuration is such that oblique correction is performed on each head. That is, since the paper conveyance direction is used as a reference, in most cases, the oblique correction processing must be performed on all four print heads, and there is a problem that image reproducibility deteriorates.
[0009]
SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems in the related art, and provides a tandem-type color image forming apparatus capable of forming an image with no color shift in the main scanning direction by relatively simple oblique correction. Is the main purpose.
Another object of the present invention is to provide a method for oblique correction which is excellent in practicality in a tandem type color image forming apparatus and has a high correction effect.
[0010]
Means for Solving the Problems and Effects of the Invention
The invention according to claim 1 has a plurality of image forming units arranged at predetermined intervals in a paper transport direction, and each image forming unit has a print head extending in a main scanning direction orthogonal to the paper transport direction. Means for setting a reference print head in a tandem type color image forming apparatus including: means for detecting whether or not printing by each print head is shifted in the main scanning direction with respect to printing by the reference print head; Means for correcting a signal to be given to a print head other than the reference print head based on the amount of deviation, and a tandem-type color image forming apparatus.
[0011]
According to a second aspect of the present invention, the means for correcting the signal includes a line memory for storing a plurality of lines of a signal to be applied to each print head in units of a main scanning direction, and an oblique reading means for obliquely reading the line memory so as to extend over a plurality of lines. The tandem-type color image forming apparatus according to claim 1, further comprising:
The invention according to claim 3 has a plurality of image forming units arranged at predetermined intervals in the paper transport direction, and each image forming unit has a print head extending in a main scanning direction orthogonal to the paper transport direction. In order to correct the occurrence of color misregistration in the color image formed by each print head due to the distortion in the parallelism between the print heads included in each unit in the tandem type color image forming apparatus including , (1) Determine the reference print head, and (2) individually confirm the deviation in the main scanning direction between the print by the reference print head and the print by the remaining print heads for each of the remaining print heads. {Circle around (3)} tandem-type color processing, wherein a predetermined correction process is performed for each of the print head signals in accordance with the magnitude of the shift in the main scanning direction, for each of the print head signals. It is a diagonal color shift correction method of an image in the image forming apparatus.
[0012]
According to the apparatus of the first and second aspects and the method of the third aspect, it is not necessary to perform the correction processing for all signals applied to the print head in the tandem type color image forming apparatus. That is, when the reference print head is determined, the signal given to the reference print head is not corrected, and the signal given to the remaining print heads is corrected by a necessary amount for each signal given to each print head. Good. Accordingly, the correction for each print head may be the minimum necessary, and the signal for the reference print head is not corrected, so that the reproducibility of the formed image can be maintained well.
[0013]
Normally, when the diagonal correction is performed, the reproducibility of the corrected signal is slightly reduced. However, in the present invention, not all the signals applied to the print head are corrected, but the signals applied to the reference print head remain unchanged. .
For this reason, the reference print head can be set to, for example, a color for which good reproducibility is to be maintained, for example, black or cyan, for example, to provide a color image forming apparatus with good reproducibility for black and cyan. .
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings.
FIG. 1 is a schematic vertical sectional view showing the internal configuration of a color printer 1 according to one embodiment of the present invention. Referring to FIG. 1, a color printer 1 includes four image forming units 2M, 2C, 2Y, and 2B for forming monochromatic images of magenta, cyan, yellow, and black, respectively. It has a so-called tandem-type structure that is arranged in a line in this order from the upstream side in the paper transport direction A (the right side in FIG. 1) along the linear transport path formed by the transport mechanism 3.
[0015]
The four image forming units 2M, 2C, 2Y, and 2B include drum-shaped photoconductors 4M, 4C, 4Y, and 4B that rotate clockwise in FIG. 1, respectively. 4B are arranged in parallel with each other with their respective axes extending in a horizontal direction orthogonal to the paper transport direction A.
Each of the photoconductors 4M, 4C, 4Y, and 4B is uniformly charged by the discharge of the main chargers 5M, 5C, 5Y, and 5B, and then connected to an external device such as a microcomputer (not shown) connected to the color printer 1. Based on the color image data of each of the magenta, cyan, yellow, and black color components of the image data input from the LED print head, the light is exposed by the light emitted from the LED print heads 6M, 6C, 6Y, and 6B. Thus, a so-called electrostatic latent image is formed on the surface of each of the photoconductors 4M, 4C, 4Y, and 4B.
[0016]
Toner is adhered to the surfaces of the photoconductors 4M, 4C, 4Y, and 4B on which the electrostatic latent images are formed by the developing devices 7M, 7C, 7Y, and 7B to form toner images. Above the developing devices 7M, 7C, 7Y, and 7B, toner hoppers 8M, 8C, 8Y, and 8B that store magenta, cyan, yellow, and black toners are disposed, and the developing devices 7M corresponding to the respective color toners are arranged. , 7C, 7Y, and 7B.
[0017]
When the photoconductors 4M, 4C, 4Y, and 4B are further rotated, the toner images formed on the respective surfaces come to positions facing the paper transport mechanism 3. The magenta, cyan, yellow, and black toner images are transferred from the right side to the left side in FIG. 1 by the paper transport mechanism 3 along the paper transport direction A in the paper transport mechanism 3 and the photoconductor 4M. , 4C, 4Y, and 4B. The toner remaining on the surfaces of the photoconductors 4M, 4C, 4Y, and 4B after the transfer of the toner image is collected by the photoconductor cleaning devices 9M, 9C, 9Y, and 9B.
[0018]
The paper transport mechanism 3 includes a drive roller 10 disposed downstream (left side) of the photoconductor 4B of the image forming unit 2B in the paper transport direction A, and an upstream of the photoconductor 4M of the image forming unit 2M in the paper transport direction A. Roller 11 disposed on the side (right side), an endless transport belt 12 wrapped around the drive roller 10 and the driven roller 11, and, for example, two tension rollers 131 and 132 for applying tension to the transport belt 12. And are included.
[0019]
The drive roller 10 is provided with a drive force of a motor (not shown), and the drive roller 10 is rotated by the motor so that the transport belt 12 rotates counterclockwise in FIG. Has become. Above the driven roller 11, a charging roller 14 for applying static electricity to the transport belt 12 is disposed with the transport belt 12 interposed therebetween. The paper on which the toner images from each of the image forming units 2M, 2C, 2Y, and 2B are to be transferred adheres to the surface of the transport belt 12 charged by the charging roller 14, and rotates with the rotation of the transport belt 12. The sheet is transported along the sheet transport direction A.
[0020]
Transfer rollers 15M, 15C, 15Y, and 15B are arranged below the photoconductors 4M, 4C, 4Y, and 4B with the transport belt 12 interposed therebetween. A predetermined transfer voltage is applied to each of the transfer rollers 15M, 15C, 15Y, and 15B, and the toner image formed on the surface of each of the photoconductors 4M, 4C, 4Y, and 4B faces the paper transport mechanism 3. When it comes to the position, it is drawn to the corresponding transfer roller 15M, 15C, 15Y, 15B side, and is transferred to a sheet.
[0021]
At the lower part of the color printer 1, a paper storage unit 16 capable of storing a plurality of papers is arranged. The paper storage unit 16 is provided with a pickup roller 18 for feeding stored papers one by one to the paper transport path 17 side. The paper sent out by the pickup roller 18 is guided to the paper transport path 17 via the paper feed roller 19, and is transported upward by the transport roller 20 toward the registration roller 21 disposed at the end of the paper transport path 17. Is done.
[0022]
The registration roller 21 is disposed on the upstream side (right side) of the paper transport mechanism 3 in the paper transport direction A, and the tip of the paper transported from the paper storage unit 16 through the paper transport path 17 is registered. The transport is temporarily stopped when the rollers 21 are reached. Then, the paper is moved to each of the image forming units 2M, 2C, and 4B at the timing when the toner image formed on the surface of each of the photoconductors 4M, 4C, 4Y, and 4B comes to a position facing the transfer rollers 15M, 15C, 15Y, and 15B. The rotation of the registration roller 21 is started so as to reach 2Y and 2B.
[0023]
The sheet sent out to the sheet conveying mechanism 3 is transferred by the image forming units 2M, 2C, 2Y, and 2B in the process of being conveyed by the conveying belt 12, and the toner images of the respective colors are transferred in an overlapping manner. The fixing process is performed by passing through a pair of fixing rollers 221 included in the fixing device 22. The sheet subjected to the fixing process is guided upward by the transport roller 23 and is discharged by the discharge roller 24 to the discharge tray 25 formed on the upper surface of the apparatus.
[0024]
If a jam (paper jam) occurs during paper transport by the paper transport mechanism 3, the toner of the photoconductors 4M, 4C, 4Y, and 4B may adhere to the transport belt 12. Further, the color printer 1 according to the present embodiment draws main scanning lines in the main scanning direction (a direction orthogonal to the paper conveyance direction) so that toner adheres directly to the conveyance belt 12, and parallels the main scanning lines of the four colors. The diagonal correction which adjusts the way of giving a signal to the LED print head 6 by judging the characteristics is performed. Therefore, a belt cleaning device 26 is disposed below and to the left of the conveyor belt 12 in order to remove toner attached to the conveyor belt 12.
[0025]
The belt cleaning device 26 is slidably contacted with the transport belt 12 near the left tension roller 131 from below, and a blade 27 for scraping off toner adhered to the surface of the transport belt 12 and collecting the toner scraped by the blade 27 And a recovery tank 28. The blade 27 is urged upward by a spring (not shown), and the tip thereof is pressed against the transport belt 12 with an appropriate pressing force.
[0026]
Each photoconductor 4M, 4C, 4Y, 4B and corresponding main chargers 5M, 5C, 5Y, 5B, LED print heads 6M, 6C, 6Y, 6B, developing devices 7M, 7C, 7Y, 7B, toner hoppers 8M, 8C , 8Y, 8B and the cleaning devices 9M, 9C, 9Y, 9B are held by separate photosensitive member holding members 32M, 32C, 32Y, 32B, respectively, and they are integrated into the image forming units 2M, 2C, 2Y, 2B. Each of the image forming units 2M, 2C, 2Y, and 2B can be pulled out to the near side, and each of the image forming units 2M, 2C, 2Y, and 2B is drawn out, and toner is supplied to the toner hoppers 8M, 8C, 8Y, and 8B. Replenishment is possible, and the drawn-out unit itself can be replaced.
[0027]
FIG. 2 and FIG. 3 are diagrams for explaining the specific contents of the color misregistration of the image due to the distortion of the parallelism of each of the LED print heads 6M, 6C, 6Y, and 6B, and an example of a method of detecting the color misregistration. FIG.
As described above, the image forming units 2M, 2C, 2Y, and 2B are held by separate photoconductor holding members 32M, 32C, 32Y, and 32B, respectively, and can be pulled out to the near side. In a state where the image forming units 2M, 2C, 2Y, and 2B are housed in the apparatus, the photoconductors 4M, 4C, 4Y, and 4B are parallel to each other, and the LED print heads 6M, 6C, 6Y, and 6B are also mutually. Designed and manufactured to be parallel to
[0028]
However, in the actually assembled apparatus, the photoconductors 4M, 4C, 4Y, and 4B do not extend in a direction orthogonal to the paper transport direction A by the transport belt 12 without slight distortion. The print heads 6M, 6C, 6Y, and 6B also extend strictly orthogonally to the paper transport direction A without any distortion, and are not parallel to each other. The transport belt 12, the photoconductors 4M, 4C, 4Y, and 4B and the LED print heads 6M, 6C, 6Y, and 6B are in a very slight, but complex, oblique mounting state. As a result, the images of the respective colors are inclined and do not overlap. FIG. 2 is a plan view schematically showing this.
[0029]
Note that, even in the composite oblique mounting state, the amount by which the LED print heads 6M, 6C, 6Y, and 6B are obliquely shifted with respect to the paper transport direction A is minute. Therefore, no matter which LED print head is used as the reference head, the amount of oblique displacement of the line of the reference print head with respect to the sheet on which an image is actually printed is only a marginal amount as an error range. It is.
Therefore, in this embodiment, as described below, a configuration is adopted in which a print head of an arbitrary color is used as a reference print head, and the inclination of another head with respect to the reference print head is detected and corrected. Have been.
[0030]
In FIG. 2, the four LED print heads 6M, 6C, 6Y, and 6B are slightly inclined with respect to the paper transport direction A by the transport belt 12, and the images formed on the paper are not overlapped. Have been.
FIG. 3 is a diagram illustrating a configuration example for detecting a distortion of the parallelism of the LED print heads 6M, 6C, 6Y, and 6B. The color printer 1 according to this embodiment can print an image directly on the transport belt 12 by each of the image forming units 2M, 2C, 2Y, and 2B. The image printed on the conveyor belt 12 is detected by two density sensors 33 and 34 disposed downstream of the image forming unit 2B. The two density sensors 33 and 34 are arranged at intervals in the main scanning direction orthogonal to the paper transport direction A, and can detect a density change on the surface of the transport belt 12.
[0031]
In the printer 1, dedicated images, that is, lines extending in the main scanning direction for oblique correction are formed by the LED print heads 6M, 6C, 6Y, and 6B, respectively. Based on the detected timing, the inclination of the four lines, that is, the parallelism among the LED print heads 6M, 6C, 6Y, and 6B is detected.
Instead of printing the skew correction pattern directly on the conveyor belt 12, the skew correction pattern is printed on the paper to be conveyed, which is visually checked by a service person or the like or by a measuring instrument, and the LED print head is used. A configuration may be adopted in which the parallelism (oblique displacement) among the 6M, 6C, 6Y, and 6B is detected, and the oblique correction processing is performed based on the detection result.
[0032]
FIG. 4 is an illustrative view for explaining a method of oblique correction. For example, when black is used as a reference color, for example, cyan to be corrected is obliquely shifted in the main scanning direction with respect to black. It represents the case. (FIG. 4A)
In this case, based on black, the lighting timing for forming a cyan line in the main scanning direction by the LED print head 6C in the main scanning direction as shown in FIG. 4B so that cyan overlaps black. It is shifted at a certain timing to form a multi-divided step-like line. As a result, the cyan line does not deviate from the black line on both sides in the main scanning direction, and the cyan line substantially overlaps the black line.
[0033]
Further, pixels forming a cyan line are divided and drawn in the sub-scanning direction. As a result, as shown in FIG. 4C, the deviation between the black line and the cyan line is further reduced.
FIGS. 5 and 6 are diagrams for explaining how to write input data to the image memory and how to read input data from the image memory when performing the diagonal correction described in FIG.
[0034]
FIG. 5 shows how to read out the image memory when the pixels are not divided in the sub-scanning direction. For example, when cyan image data shown in FIG. 5A is input, the image data is temporarily stored in an image memory including a plurality of line memories. Then, as shown in FIG. 5B, the image memory is read obliquely in the sub-scanning direction over a plurality of lines. For example, line memory
1,1,1,2,2,2,3,3,3,4,4,4 ...
2,2,2,3,3,3,4,4,4,5,5,5 ...
3,3,3,4,4,4,5,5,5,6,6,6 ...
And so on. As a result, the formed image is as shown in FIG.
[0035]
FIG. 6 shows how to read out the image memory when dividing pixels in the sub-scanning direction. The input data is written into the image memory as in FIG. 5B. At the time of reading, the image data is read by obliquely accessing a plurality of line memories, and the reading is performed at a speed three times the writing speed. Is done.
That is, for example, the line memory
1,1,1,2,2,2,3,3,3,4,4,4 ...
1,1,2,2,2,3,3,3,4,4,4,5 ...
1,2,2,2,3,3,3,4,4,4,5,5 ...
, And the LED print head 6M is turned on at triple speed. As a result, an image divided in the sub-scanning direction shown in FIG. 6C is formed.
[0036]
FIG. 7 is a block diagram illustrating an electrical configuration for oblique correction in the color printer 1. Image data is provided to the image data forming unit 35 from an external device such as a microcomputer (not shown), and the image data forming unit 35 forms color image data of each of the magenta, cyan, yellow, and black color components. The color image data of these four colors are respectively supplied to the line memories 37M, 37C, 37Y via the magenta diagonal correction circuit 36M, the cyan diagonal correction circuit 36C, the yellow diagonal correction circuit 36Y, and the black diagonal correction circuit 36B. 37B.
[0037]
In each of the oblique correction circuits 36M, 36C, 36Y, and 36B, based on the output from the density sensors 33 and 34 for detecting oblique deviation, whether the correction target color to be corrected by the circuit with respect to the reference color is obliquely deviated. Whether the data is read or not is adjusted, and the timing of reading data from the line memories 37M, 37C, 37Y, and 37B is adjusted in accordance with the oblique displacement. Then, the read data is output to the corresponding print heads 6M, 6C, 6Y, 6B.
[0038]
FIG. 8 is a diagram for explaining the processing contents of each of the oblique correction circuits 36M, 36C, 36Y, and 36B shown in FIG. 7, and more specifically, how to read data from the corresponding line memories 37M, 37C, 37Y, and 37B. FIG.
Description will be given along the flow of FIG. When the operation starts, first, it is determined whether or not the mode is a mode for confirming the content of the oblique correction (step S1). For example, when the power of the color printer 1 is turned on or when the serviceman sets the oblique correction content confirmation mode, the determination in step S1 is affirmed, and the process proceeds to step S2.
[0039]
In step S2, a line for oblique displacement confirmation is created. In this line creation, a line as described in FIG. 3 is created.
Then, each of the oblique correction circuits 36M, 36C, 36Y, 36B determines whether or not the color handled by the circuit is a correction reference color (step S3). Whether or not the correction reference color is used can be input by, for example, a service person using a setting switch or the like. It is assumed that black is the correction reference color. Since black is the correction reference color, the determination in step S3 is affirmative in the black diagonal correction circuit 36B, and the reading of data from the line memory 37B is set to the normal reading method in the black diagonal correction circuit 36B. (Step S8). Then, the process returns.
[0040]
On the other hand, for example, in the magenta oblique correction circuit 36M, the determination in step S3 is denied, the signals from the density sensors 33 and 34 are detected (step S4), and it is determined whether the magenta line is inclined with respect to the black line. Is determined (step S5).
If the magenta line is inclined with respect to the black line as shown in FIG. 2 or 3, for example, the number of divisions of the magenta line in the main scanning direction depends on the degree of the inclination. In this case, the number of pixels in the sub-scanning direction in the sub-scanning direction, whether to divide the pixels in the sub-scanning direction, and the like are determined (step S6). That is, the content of correction for the magenta image data is determined (step S6).
[0041]
Then, a method of reading the line memory 37M is set based on the correction content determined in step S6 (step S7). That is, the method of reading the data stored in the line memory 37M is set so that the correction determined in step S6 is performed. This reading method is determined according to the inclination of magenta and black in the main scanning direction. For example, the reading method may be determined as a reading method that does not perform division in the sub-scanning direction as shown in FIG. As shown in FIG. 7, the reading method is such that pixels are divided in the sub-scanning direction.
[0042]
The number of divisions in the main scanning direction can also be changed according to the degree of inclination.
Then, after the reading method of the line memory 37M is set, the process returns.
The processing of steps S3 to S7 is performed for cyan and yellow, respectively, in addition to magenta, and the reading method of the line memories 37C and 37Y is also individually set for cyan and yellow (step S7).
[0043]
On the other hand, if the color printer 1 determines in step S1 that it is not the confirmation processing of the skew correction contents, each of the skew correction circuits 36M, 36C, 36Y, and 36B waits for data input from the image data forming unit 35 ( Step S9), the input image data is stored in the line memories 37M, 37C, 37Y, and 37B, respectively (Step S10), and the line memories 37M, 37C, 37Y, and 37B are stored in accordance with the memory reading method set in Step S8 or S7. Data is read from 37B (step S11). The read data is output to the corresponding print heads 6M, 6C, 6Y, and 6B, and the print heads are turned on (step S12).
[0044]
In the above description, the case where black is the reference color has been described. In general, even in a color image, characters are often printed in black. Therefore, when black is used as a reference color, oblique displacement correction for only magenta, cyan, and yellow, and if necessary, Pixel division is performed. In this case, since the black pixel division is not performed, the character printed in black does not have a dull edge, and the reproducibility of the character image is particularly good.
[0045]
By the way, when black is used as the reference color, it is not necessary to perform oblique displacement correction for all of magenta, cyan, and yellow. For example, when black is used as a reference color, if magenta has almost no oblique deviation with respect to black, oblique deviation correction is not performed on magenta, and the process proceeds from step S5 to S8 in FIG. Is set to normal for reading data from the line memory.
[0046]
As a result, since oblique displacement correction and pixel division are not performed for black and magenta, a color printer with good black and magenta reproducibility can be provided.
Further, instead of using black as the reference color, for example, any of cyan, magenta, and yellow may be used as the reference color. Since the oblique displacement correction and the pixel division in the sub-scanning direction are not performed on the reference color, a color printer having good reproducibility with respect to the reference color can be obtained.
[0047]
Further, in the case of printing a monochrome image in the color printer, the oblique displacement correction is not performed.
The present invention is not limited to the embodiments described above, and various changes can be made within the scope of the claims.
Further, the present invention has been described by taking a tandem type color printer as an example, but the present invention can also be applied to a tandem type color copier, a facsimile or the like.
[Brief description of the drawings]
FIG. 1 is a schematic vertical sectional view showing an internal configuration of a color printer according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating specific contents of color misregistration of an image due to distortion of parallelism of an LED print head.
FIG. 3 is a diagram for explaining an example of a method of detecting a color shift caused by a parallelism distortion of an LED print head.
FIG. 4 is an illustrative view for explaining a method of oblique correction;
FIG. 5 is a diagram illustrating a method of writing input data to an image memory and reading input data from the image memory when performing diagonal correction.
FIG. 6 is a diagram illustrating a method of writing input data to an image memory and reading input data from an image memory when performing diagonal correction. FIG.
FIG. 7 is a block diagram showing an electrical configuration for oblique correction in the color printer.
FIG. 8 is a flowchart showing the processing contents of the diagonal correction circuit shown in FIG. 7;
[Explanation of symbols]
1 color printer
2 Image forming unit
6 LED print head
35 Image Data Forming Unit
36 Skew correction circuit
37 line memory

Claims (3)

The tandem color image forming apparatus includes a plurality of image forming units arranged at predetermined intervals in a sheet conveying direction, and each image forming unit includes a print head extending in a main scanning direction orthogonal to the sheet conveying direction. ,
Means for setting a reference print head;
Means for detecting whether printing by each print head is shifted in the main scanning direction with respect to printing by the reference print head,
Means for correcting a signal given to a print head other than the reference print head based on the detected shift amount. Means for correcting the signal, a line memory for storing a plurality of lines of the signal given to each print head in units of the main scanning direction,
2. The tandem-type color image forming apparatus according to claim 1, further comprising: an oblique reading unit that obliquely reads the line memory so as to extend over a plurality of lines. The tandem color image forming apparatus includes a plurality of image forming units arranged at predetermined intervals in a sheet conveying direction, and each image forming unit includes a print head extending in a main scanning direction orthogonal to the sheet conveying direction. ,
In order to correct the occurrence of color misregistration in the color image formed by each print head due to the distortion in the parallelism between the print heads included in each unit,
(1) Determine the print head that will be the reference,
(2) The deviation in the main scanning direction between the printing by the reference print head and the printing by the remaining print heads is individually confirmed for each of the remaining print heads.
(3) A tandem-type color image forming apparatus, wherein a predetermined correction process is performed for each of the print heads individually with respect to the signals supplied to the remaining print heads in accordance with the magnitude of the shift in the main scanning direction. A method for correcting an oblique color shift of an image in an apparatus.

Images