JP2003285473A - Image correction device and image forming apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a capacity of a line history buffer in a simple structure, thereby preventing color shift. <P>SOLUTION: The scanning in a sub-scanning direction and a main scanning direction is performed by using a recording line head having a plurality of recording heads arranged in the sub-scanning direction, thereby forming an image according to raster data (pixel data). A RAM section 26 is divided into a plurality of storage regions in the main scanning direction and the storage capacities are regulated such that the capacities are simply increased or decreased along the main scanning direction. The raster data is recorded to the RAM section in the main scanning direction as storage raster data, and the storage raster data is read from the RAM section corresponding to a degree of inclination and an inclined direction of the recording line head with respect to the main scanning direction. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image correction apparatus used when forming an image by superimposing a plurality of rasters and an image forming apparatus (color image forming apparatus) using the image correction apparatus, and more particularly, The present invention relates to an image correction device used in an image forming apparatus using an electrophotographic process.

[0002]

2. Description of the Related Art Generally, an image forming apparatus is known in which a plurality of rasters are superposed on a light emitting surface or a printing surface to form an image. In this type of image forming apparatus, for example, a plurality of rasters are superposed on each other. Forming a color image. And
As this type of image forming apparatus, for example, there is an image forming apparatus using an electrophotographic process. An image forming apparatus using an electrophotographic process includes, for example, an LED line head having a plurality of light emitting diodes (LEDs).
The LED line head is provided for each basic color (for example, yellow (Y), magenta (M), cyan (C), and black (BK)), and an electrostatic latent image is formed on an image carrier such as a photoconductor drum. To form, they are turned on in raster order. Then, the electrostatic latent image is developed with each basic color toner to finally obtain an image. At this time, each basic color needs to be overlaid and printed on the printing surface of a recording medium or the like.

However, when superimposing the color rasters (for example, toner images of the respective colors), it is difficult to precisely superimpose the color rasters due to the two components of parallel movement and rotational movement, as will be described later. That is, color misalignment inevitably occurs due to the design accuracy and assembly accuracy of the image forming apparatus.

Specifically, at the time of image formation, the image carrier is conveyed to the LED line head and the LED line head is turned on according to the pixel data of each color. Due to precision and assembly accuracy, LE
The mounting position of the D line head is often displaced from the designed position in parallel (translation), or mounted at an angle. For this reason, there arises a problem that the rasters of respective colors cannot be accurately overlapped with each other when forming an image.

The above parallel movement can be easily corrected by controlling the start position of each color raster output (that is, by controlling the lighting start timing of the LED line head), but the above rotational movement can be corrected. Is difficult. In order to correct the color misregistration caused by such rotational movement, a method described in Japanese Patent Application Laid-Open No. 7-304211 (hereinafter simply referred to as a conventional example) is conventionally known.

In the conventional example, the line history buffer (delay buffer) for the rotation angle (for example, the amount of inclination in the axial direction with respect to the center axis of the photosensitive drum) that needs correction is used, and the line history buffer is used according to the correction information. The raster data is read from. Since the corrected rotation amount is caused by the mounting error and the deformation, the corrected rotation amount is generally about ± several degrees from the normal position (reference position). Therefore, it is sufficient for the line history buffer to hold raster data (pixel data) for several lines.

Here, referring to FIG. 6, the line history buffer 11 is provided with a plurality of buffer units (buffer areas) having the same capacity (in the illustrated example, the line history buffer 11).
Has buffer areas 11a to 11f). That is, the line history buffer 11 has a plurality of buffer areas divided in the main scanning direction (for example, scanning given in a direction parallel to the drum axis with respect to the center axis (drum axis) of the photosensitive drum). , For example, each buffer area is a random access memory (RAM). Raster data is sequentially held in each buffer area and sequentially updated from the oldest raster data (that is, the line history buffer 11 has a FIFO structure).

Referring now to FIG. 7, in the illustrated example,
The line history buffer 11 is a buffer unit 1 for 10 lines.
1a to 11j, and here, the buffer unit 11
It is assumed that raster data is sequentially written from a. That is, in the illustrated example, the newest raster data (pixel data) is written in the buffer unit 11a,
The oldest raster data will be written (stored) in 1j.

Now, assuming that the rotational movement (rotational deviation) is in the counterclockwise direction and is deviated by 9 lines, as shown in FIG. 7, a diagonal direction (solid line) from the buffer section 11a to the buffer section 11j. If the raster data is read in the direction indicated by the arrow (the read raster data (pixel data) is indicated by diagonal lines), that is, the buffer unit 1
If the raster data is read in the direction of the buffer unit 11j in the diagonal direction from 1a, the counterclockwise rotation deviation can be corrected. Then, in the illustrated example, it is possible to correct the rotation deviation of ± 9 lines at maximum.

On the other hand, the rotational deviation is in the clockwise direction,
If there is a shift of 5 lines, as shown in FIG. 8, for example, if the raster data is read from the buffer unit 11h toward the buffer unit 11c in the diagonal direction (the direction indicated by the solid arrow) (the read raster data (read raster data ( Pixel data)
Is indicated by diagonal lines), and the clockwise rotation deviation can be corrected.

[0011]

By the way, in the above-mentioned line history buffer, it is necessary to increase the capacity per pixel because the image-processed data is stored as raster data. For example, if the output device is 4 bits / pixel, the line history buffer should also have a capacity of 4 bits / pixel. On the other hand, if the line history buffer has a large capacity, the cost will increase, so it is desirable to make the capacity of the line history buffer as small as possible in consideration of cost.

Further, in the conventional example, since the line history buffer is composed of a flip-flop circuit and the delay operation is performed by the data shift, the line history buffer itself inevitably becomes expensive. For this purpose, it is desirable to use the random access memory (RAM) as described above, but if the read control as described above is performed using a plurality of RAMs, the read control becomes complicated.

As described above, in order to correct the color misregistration due to the distortion such as the mounting error of the LED line head, it is necessary to perform the color misregistration correction using the line history buffer. Is unpredictable at the time of device design, and therefore, it is necessary to give a margin to the capacity of the line history buffer (delay buffer), which inevitably increases the capacity of the line history buffer.

An object of the present invention is to provide an image correction apparatus capable of reducing the capacity of the line history buffer and preventing color misregistration with a simple structure, and an image forming apparatus using this image correction apparatus.

[0015]

According to the present invention, a recording line head having a plurality of recording heads arranged in the sub-scanning direction is used to perform scanning in the sub-scanning direction and the main scanning direction to generate raster data. An image correction apparatus for correcting the image according to the tilt amount and the tilt direction of the recording line head with respect to the main scanning direction when forming a corresponding image, wherein a plurality of storages are provided along the main scanning direction. The storage means is divided into areas, and the storage capacity of the divided storage areas is defined so as to monotonically increase or decrease monotonically along the main scanning direction, and the storage along the main scanning direction. The raster data is recorded in the storage unit as storage raster data, and the storage raster data is read from the storage unit according to the inclination amount and the inclination direction. Image correcting device is obtained characterized by. For example, the control unit rearranges the divided storage areas such that the storage capacity monotonically increases or monotonically decreases according to the tilt direction of the line head.

By doing so, even if there is an error in mounting the recording line head, the capacity of the recording means used as the line history buffer can be reduced and color misregistration can be prevented.

The storage means is, for example, one or a plurality of random access memories independent for each divided area, or a plurality of FIFO memories independent for each divided area. By doing so, it is possible to prevent color misregistration with a simple structure at low cost.

For example, the above image correction apparatus is used in an image forming apparatus using an electrophotographic process, and forms an electrostatic latent image on an image carrier according to the raster data read from the storage means. Then, the electrostatic latent image is developed for each color to form a toner image, and the toner images are superimposed to form a color image. By doing so, even if there is a mounting error in the recording line head of the exposure unit or the like, as a result of correcting this error, color misregistration or the like does not occur.

[0019]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described below with reference to the drawings. It should be noted that the dimensions, materials, shapes, relative arrangements, and the like of the components described in the illustrated examples are not intended to limit the scope of the present invention thereto unless otherwise specified, but are merely illustrative examples. Absent.

Referring to FIG. 1, the image correction apparatus shown in FIG.
Main scanning address generation unit 21, address inversion unit 22, inclination generation unit 23, read / write (R / W) control unit 24, address conversion unit 25, and random access memory (RA
M) section (image memory: line history buffer) 26 is provided, and the RAM section 26 is used as a line history buffer.

The RAM section 26 has, for example, as shown in FIG. 2, a plurality of RAMs (RAM areas) (in the illustrated example, RAM areas 26a to 26h) and these RAM areas. 26a to 26h have different capacities. In the illustrated example, the RAM areas 26b to 26h are each RA when the capacity of the RAM area 26a is used as a reference.
It has a capacity that is twice to eight times the capacity of the M region 26a.
That is, the RAM areas 26b to 26h are each divided into two to eight divided areas in the main scanning direction (for example, scanning given in a direction parallel to the drum axis with respect to the drum axis), and each divided area. Area is RAM area 26
equal to the capacity of a. In the illustrated example, the RAM areas 26a to 26h are sequentially arranged from the left side in the drawing (sub-scanning (direction vertical to the drum axis (scanning with drum rotation) direction), and main scanning addresses are arranged in this order. The larger the size, the more divided areas.

Now, when the RAM area 26a is also referred to as a divided area, eight divided areas are located in the sub-scanning direction in the lowermost line (the lowermost line in the drawing) in FIG. One divided area is located in the sub-scanning direction on the line (the uppermost line in the figure). That is, in the illustrated example, the RAM section 26 is configured such that the RAM section 26 has a RAM area arranged in a substantially triangular shape on the surface defined by the main scanning direction and the sub scanning direction. . Here, for convenience of description, the line defined by each divided area arranged in the sub-scanning direction will be referred to as a line buffer area.

In the main scanning address generator 21, the address from the main scanning starting point (for example, address "0") to the main scanning end point (for example, address "5119") is the main scanning address (first main scanning address) MA1. Are sequentially generated and transmitted. The main scanning address MA1 is given to the address inversion unit 22. In the address reversing unit 22, for example, the rotational deviation direction of the LED line head (not shown) is positive (counterclockwise direction shown in FIG. 7), or LE
Based on whether the rotational deviation direction of the D line head is negative (clockwise direction shown in FIG. 8), the main scanning address M
It is determined whether or not A1 is inverted, and the main scanning address (second main scanning address) MA2 is output.

That is, when the rotational deviation is negative, the address inverting section 22 inverts the main scanning address MA1 and outputs it as the main scanning address MA2. On the other hand, when the rotational deviation is positive, the address reversing unit 22 outputs the main scanning address MA1 as the main scanning address MA2. For example, when performing the inversion, the address reversing unit 22 calculates the main scanning address MA2 = the scanning end point address−the current main scanning address MA1 and outputs the calculation result as the main scanning address MA2.

The above-mentioned main scanning address MA2 is given to the address conversion unit 25 and the inclination generation unit 23. The tilt generating section 23 generates a sub-scanning address (first sub-scanning address) SA1 according to the amount of rotation deviation and the main scanning address MA2. That is, the inclination generating unit 23 generates the sub-scanning address SA1 from the main-scanning address MA2 based on the rotation deviation amount defined by a predetermined linear expression. In other words, the inclination generating unit 23 changes the sub-scanning address SA1 according to the main scanning address MA2 when reading the pixel data from the RAM unit 26 so that the reading can be performed.

The sub-scanning address SA1 is given to the R / W control section 24. The R / W control unit 24 outputs the sub-scanning address (second sub-scanning address) SA2 based on the writing phase and the reading phase. Specifically, the R / W control unit 24 outputs the sub-scanning address SA1 as the sub-scanning address SA2 in the read phase, and the fixed value “0” as the sub-scanning address SA2 in the write phase. Is output.

As described above, the address conversion unit 25 is supplied with the main scanning address MA2, and the address conversion unit 25 is further supplied with the sub scanning address SA2. Then, the address conversion unit 25 generates a physical address PA according to the main scanning address MA2 and the sub-scanning address SA2, and uses the physical address PA as described later.
The RAM unit 26 is accessed.

Pixel data is given to the RAM section 26 as unprocessed pixel data. The unprocessed pixel data is written to the RAM section 26 in accordance with the physical address PA and the written pixel data is processed pixel data. Read out.

Referring to FIG. 3, here, the RAM section 26 is used.
Will be described as having RAM areas 26a to 26d. Now, when the sub-scanning position is "A0", FIG.
As shown in, the number "B0" is assigned to each divided area.
~ If "B9" is assigned (RAM
The area 26a has the number "B0", the RAM area 26b has the number "B1" and "B2", the RAM area 26c has the number "B3" to "B5", and the RAM area 26d has the number "B0".
It is assumed that B6 "to" B9 "are assigned: this state is the initial mapping state (first mapping state)
In the sub-scanning address SA.
2, that is, the mapping is sequentially changed each time the processing advances in the sub-scanning direction.

For example, when the sub-scanning position is "A1",
The mapping state (second mapping state) shown in FIG. In other words, in FIG.
The numbers are sequentially moved in the main scanning direction for each of the M areas 26a to 26d to obtain the mapping state shown in FIG. Then, when the sub-scanning position becomes "A2", the numbers are sequentially moved in the main scanning direction for each of the RAM areas 26a to 26d in FIG. Mapping state). And the sub-scanning position is "
A3 ″, each RAM area 2 in FIG.
The numbers are sequentially moved in the main scanning direction every 6a to 26d,
The mapping state (fourth mapping state) shown in FIG.

By changing the mapping state in this way, pixel data corresponding to the sub-scanning position is stored in each divided area, and a single RAM is used as a FIFO of a plurality of sizes. It will be possible.

More specifically, referring to FIG. 4, in the example shown in FIG. 4, the RAM section 26 has line buffer areas 31 to 40 sequentially from the lower side in the drawing, and each line buffer is Pixel data is sequentially written in the areas 31 to 40. Now, assuming that the direction of the rotational deviation is positive and the pixel data is sequentially written from the line buffer area 31, one line of pixel data (first pixel data is written in the line buffer area 31 at the first write timing). 1 line pixel data) is written. Then, at the next second write timing, the second line pixel data is written in the line buffer area 31, and the first line pixel data is written.
The line pixel data of is written in the line buffer area 32. At this time, since the line buffer area 32 has a capacity smaller than that of the line buffer area 31 by one divided area, a part of the first line pixel data is written in the line buffer area 32.

When writing is sequentially performed on the line buffer areas 31 to 40 in this manner, the first to tenth line pixel data are written to the line buffer areas 31 to 40 at the tenth write timing. In the line buffer areas 32 to 40, a part of the line pixel data is written. Note that the amount of pixel data written in the direction of the line buffer areas 32 to 40 is small. The newest line pixel data is written, and the oldest line pixel data is written in the line buffer area.

Assuming that the rotational deviation is shifted by 5 lines, the line buffer area 31 is used for reading.
Pixel data is sequentially read from the line buffer area 36 to the line buffer area 36 in accordance with the physical address (physical address based on the main scanning address MA2 and the sub-scanning address SA2) (the pixel data to be read is indicated by diagonal lines). That is, in the figure, the pixel data is read in the direction indicated by the solid arrow. As a result, the amount of rotation deviation is 5
Even for the line portion, the amount of rotation deviation is corrected, and the color shift does not occur.

If the amount of rotation deviation is zero, the pixel data will be read out only from the line buffer area 31. That is, RA is calculated according to the line of the rotation deviation amount.
The reading is controlled from the M unit 26.

Therefore, if the rotation deviation amount is 9 lines, at the time of reading, as shown in FIG. Pixel data is read out according to the physical address PA based on the scan address SA2 (the pixel data to be read out is indicated by diagonal lines). That is, in the figure, the pixel data is read in the direction indicated by the solid arrow.

On the other hand, when the direction of the rotational deviation is negative, the main scanning address is inverted by the address inversion unit 22 (FIG. 1), so that the line buffer areas 31 to 4 are respectively.
Since the order of the line pixel data written in 0 is the reverse, even when the direction of the rotational deviation is negative, the reading can be performed as described in FIG. 4 or 5.

In the example shown in FIGS. 4 and 5, RAM is used.
Part is divided into a plurality of RAM areas in the main scanning direction, and each RA
Although it is specified that the capacity of the M area monotonously increases along the sub-scanning direction (that is, the number of divided areas in each RAM area is specified such that the capacity monotonically increases along the sub-scanning direction). Alternatively, the capacity of each RAM area may be defined so as to monotonically decrease along the sub-scanning direction. At this time, writing and reading are performed in the reverse order to that described with reference to FIGS.

In this way, the RAM section is divided into a plurality of RAM areas in the main scanning direction, the capacity of each RAM area is regulated to monotonically increase or decrease along the sub-scanning direction, and the rotation deviation occurs. Since the writing and reading of the pixel data to and from the RAM section are controlled according to the amount and the rotational deviation direction, the RAM used as the line history buffer.
It is possible to reduce the capacity of the unit and prevent color misregistration.

The image correction apparatus described above is used, for example, in a color image forming apparatus. That is, an electrostatic latent image is formed on the image bearing member such as the photosensitive drum according to the processed pixel data read from the RAM unit 26. Then, this electrostatic latent image is developed for each color to form a toner image, and the toner images are superimposed to form a color image. By doing so, even if there is an attachment error in the LED line head of the exposure unit or the like, as a result of correcting this error, color misregistration or the like does not occur.

[0041]

As described above, according to the present invention, a recording line head having a plurality of recording heads arranged in the sub-scanning direction is used to perform scanning in the sub-scanning direction and the main scanning direction to generate raster data. When forming a corresponding image, the image memory (storage means) is divided into a plurality of storage areas along the main scanning direction, and the storage capacity of the storage area is monotonically increased or monotonically decreased along the sub-scanning direction. It is specified that the raster data is recorded as the storage raster data in the image memory along the sub-scanning direction and the storage raster data is read from the image memory according to the inclination amount and the inclination direction with respect to the sub-scanning direction. There is an effect that the color shift can be prevented by reducing the capacity of the image memory used as the buffer.

According to the present invention, since the random access memory, preferably the FIFO memory is used as the image memory, there is an effect that the color shift can be prevented at a low cost and with a simple structure.

According to the present invention, an electrostatic latent image is formed on the image carrier according to the raster data read from the image memory, and the electrostatic latent image is developed for each color to form a toner image. hand,
Since the color images are formed by superposing the toner images, even if there is a mounting error in the recording line head such as the exposure unit, the error is corrected, and as a result, color misregistration does not occur. is there.

[Brief description of drawings]

FIG. 1 is a block diagram showing an example of an image correction apparatus according to the present invention.

FIG. 2 is a diagram showing a configuration of a RAM shown in FIG.

FIG. 3 is a diagram for explaining mapping of the RAM shown in FIG.

FIG. 4 is a diagram for explaining an example of read control of the RAM shown in FIG.

5 is a diagram for explaining another example of read control of the RAM shown in FIG. 1. FIG.

FIG. 6 is a diagram showing a configuration of a conventional line history buffer.

FIG. 7 is a diagram for explaining an example of read control of the line history buffer shown in FIG.

8 is a diagram for explaining another example of the read control of the line history buffer shown in FIG.

[Explanation of symbols]

21 Main scanning address generator 22 Address inversion unit 23 Slope generator 24 Read / Write (R / W) Control Unit 25 Address converter 26 Random access memory (RAM) section

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Claims (5)

[Claims] 1. A recording line head having a plurality of recording heads arranged in a sub-scanning direction is used to perform scanning in the sub-scanning direction and the main scanning direction to form an image corresponding to raster data. An image correction apparatus for correcting the image according to an inclination amount and an inclination direction of a line head with respect to the main scanning direction, the image correction apparatus having a storage unit divided into a plurality of storage areas along the main scanning direction. The storage capacity of the divided storage area is defined so as to monotonically increase or decrease monotonically along the main scanning direction, and the raster data is stored in the storage means along the main scanning direction as storage raster data. An image correction apparatus comprising: a control unit for recording and reading the stored raster data from the storage unit according to the inclination amount and the inclination direction. 2. The control means rearranges the divided storage areas so that the storage capacity monotonously increases or monotonically decreases according to the inclination direction of the line head. The image correction device according to claim 1. 3. The image correction apparatus according to claim 1, wherein the storage unit is one or a plurality of random access memories independent for each divided area. 4. The image correction apparatus according to claim 1, wherein the storage unit is a plurality of FIFO memories independent for each divided area. 5. An electrostatic latent image is formed on an image carrier according to the raster data read from the storage means, the electrostatic latent image having the image correction device according to claim 1. An image forming apparatus, wherein an image is developed for each color to form a toner image, and the toner images are superposed to form a color image.