JPH0922170A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize resist correction in one picture element in a main scanning direction and to obtain a good-quality image having neither color slurring nor color blotting by distributing image data to the adjacent picture element in accordance with positional deviation in the picture element and performing image exposure. SOLUTION: A control part accesses the image density information of one line in main scanning from the page memory of the image data 202 and stores it in a line memory 301. Picture element density information is shifted one by one to memories 302a to 302c from the line memory 301. A coefficient is accessed from a ROM (3) 205 so as to perform multiplication processing in multipliers (1) 303a to 303c. Furthermore, the addition processing is performed in an adder 304 and the processed result is outputted as the i-th picture element density information newly corrected. The picture element density information is outputted from the line memory 301 in a state that a picture element number is incremented by one, and the picture element density information newly corrected is outputted from the adder 304. Finally, the corrected image density information of one line in main scanning is outputted from a memory for write(1) 305a to an LED array head.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic system for forming a color image by superposing toner images by arranging a plurality of linear image exposing means and a developing means containing a plurality of developers of different colors. The present invention relates to a color image forming apparatus.

[0002]

2. Description of the Related Art As means for forming a multicolored image, (A) a plurality of sets of charging means, image exposing means and developing means are provided in the vicinity of a photoreceptor which is one image forming body, and While rotating, charging, image exposure, and development are repeated to form a multicolored color toner image on the photoconductor in a superimposed manner, and the color image forming apparatus for collectively transferring the color toner image onto the transfer paper and (B) photoconductor A plurality of sets of image forming means provided with a charging means, an image exposing means, and a developing means are provided in parallel in the vicinity, and the toner image formed by the image forming means is transferred onto a transfer paper, and then the next image forming means is formed thereon. There is known a color image forming apparatus that superimposes formed toner images and repeats these steps to obtain multicolor toner images on a transfer paper.

As these image exposing means, a linear image exposing means such as an LED array in which point light sources are linearly arranged is used, and the same shape is used in the color image forming apparatuses (A) and (B). , A plurality of linear image exposure means having the same performance are used, and toner images formed by charging, image exposure, and development are superposed on each other (A) on the photoconductor and (B) on the transfer paper without misalignment. As a result, it is possible to obtain a good-quality color image without color shift or bleeding.

[0004]

However, the above (A)
In the color image forming apparatus of (B), even if
Even if the linear image exposing means of the same shape is used, the image exposing means used for each color are strictly different, and the linearity and the non-uniformity of the directionality and the inclination of the mounting position between the arranged LEDs. If there is such a difference, so-called color misregistration or color bleeding occurs in the formed image due to misalignment of the superimposed toner images,
As a result, the color image quality is significantly impaired. The inventor
Patent application 6
-220297.

However, even with the above proposal, the toner images by the LED arrays cannot be perfectly matched. Main scanning direction of each LED array (linear direction of array)
This is the case where there is a deviation of the light emitting element. For example, if the position of the yellow (Y) light emitting element of the 50th element and the position of the cyan (C) light emitting element of the 50th element are completely matched, the yellow toner and the cyan toner adhere to that position and are fixed. By doing so, edge-colored dots are formed on the transfer paper. If the position of the 50th element cyan light emitting element is L of yellow
When the 52nd element of the ED array hits (shifts), at least only a color image having a color shift with respect to the expected color image can be obtained. On the other hand, the deviation of the integer pixels (two pixels in the above example) can be matched by adjusting the timing clock by the deviation of the integer pixels. The amount of deviation in the main scanning direction between a plurality of LED arrays is rarely an integer pixel, and often has a fractional (within one pixel) deviation. But,
Conventionally, it was not possible to correct the deviation in the main scanning direction within one pixel.

According to the present invention, in a color image forming apparatus which performs image exposure by a plurality of linear image exposing means, it is possible to perform resist correction within one pixel in the main scanning direction, and further, there is no color deviation or color blurring and is of high quality. An object is to provide a color image forming apparatus capable of obtaining a color image.

[0007]

In the color image forming apparatus for performing image exposure by a plurality of line-shaped image exposure means, the position in a pixel is used as alignment means in the main scanning direction between the image exposure means. This is achieved by a color image forming apparatus characterized by performing image exposure by distributing image data to adjacent pixels according to a shift amount.

In the color image forming apparatus of the present invention, the MTF on the photoconductor of the image exposure means =
It is a preferred embodiment that the resolution of 0.5 is lower than the writing density of the image exposure means, and that the image exposure of the image exposure means has means for shifting integer pixels in the main scanning direction.

[0009]

FIG. 6 shows an equivalent circuit of an LED array in which LEDs are linearly arranged as an example of the linear image exposure means used in the present invention. By transferring image data and inputting an exposure timing, a pixel is formed. The main scanning is performed in a form of linearly connected lines. FIG. 7 schematically shows the state of image exposure by the LED array, and FIG. 7A shows, for example, a cyan LED array (1) and a magenta LED.
It shows a state where the pixel positions corresponding to the array (2) match in the main scanning direction. In such a state, color misregistration does not occur. 7B and 7C are LED arrays (1).
And the LED array (2) have a pixel shift of one pixel or less in the main scanning direction. LED
Assuming that the array (1) is the reference, FIG.
The ED array (2) is displaced by x in the positive direction, as shown in FIG.
(C) shows that the LED array (2) is shifted by x in the negative direction.

According to the present invention, the image density data is distributed to the adjacent pixels according to the deviation of the LED array, and the image exposure is performed, so that the combined exposure is substantially the same as the case where there is no deviation. It is characterized by performing.

The pixel number ( _i-1 ) of the LED array (2),
The pixel density data of ( _i ) and ( _{i + 1} ) are converted to φ _i-1 , φ _i , and φ _{i + 1.}
When the image density data newly corrected by the present invention is Φ _i-1 , Φ _i , and Φ _{i + 1} , Φ _i-1 , Φ _i , and Φ _{i + 1} are the positional shift amounts in the pixel. It is a value calculated by distributing the image density data to adjacent pixels according to (x).

As shown in FIG. 7B, when there is a displacement of x in the positive direction, Φ _i-1 = φ _{i -1} × {(m−x) / m} + φ _i (x / m) Φ _i = Φ _i × {(m−x) / m} + φ _{i + 1} (x / m), and when there is a shift of x in the negative direction as shown in FIG. 7C, then φ _i = φ _i-1 (X / m) + φ _i {(m−x) / m} Φ _{i + 1} = φ _i (x / m) + φ _{i + 1} {(m−x) / m} corrected image density data Φ _i−1 , Φ _i , Φ _{i + 1} are used to eliminate the problem of color misalignment due to pixel misalignment within one pixel or less. However, in the above formula, m represents the size of one pixel.

In FIG. 8, the resolution of the image exposure means is low, and
= 0.5, the resolution is lower than the writing density (corresponding to the pixel size m) of the image exposure means.
FIG. 8A shows the composite image density formed by the image density data φ _i−1 , φ _i , and φ _{i + 1} when there is no pixel shift, and FIG. 8B shows the pixel x in the plus direction. The composite image densities formed by the corrected image densities Φ _i-1 and Φ _i are shown. When the resolving power of the image exposure system is high, the combined exposure peak may be divided and created, but according to the present invention, the combined exposure peak is not divided, and the combined image in FIG. The density and the composite image density in FIG. 8B almost match, and the effect is noticeable.

According to the present invention, when image exposure is performed by a plurality of line-shaped image exposure means and images are overlapped to form a color image, correction of deviation within one pixel in the main scanning direction is performed by using the corrected image density data. This color image forming apparatus also has a function of correcting an integer pixel shift in the main scanning direction with an exposure timing clock in the LED array shown in FIG. It is a preferable embodiment of the color image forming apparatus of the present invention.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Prior to the description of the embodiments of the present invention, the structure of an embodiment of a color image forming apparatus common to the present invention will be described with reference to FIGS.

Reference numeral 10 denotes a drum-shaped image forming body, that is, a photosensitive drum, which is coated with a transparent conductive layer and an organic photosensitive layer (OPC) on the outer periphery of a cylindrical substrate formed of a transparent member such as optical glass or transparent acrylic resin. It was done.

A flange 10A at one end of the photosensitive drum 10 is bearing-supported by a guide pin 30P provided in a cartridge 30 described later, and a flange 10B at the other end is a plurality of guide rollers provided on a substrate 40 of the apparatus body. 40R and the outer gear 10G is fitted to the drive gear 40
G is rotated in a clockwise direction with the transparent conductive layer grounded by its power.

Reference numeral 11 denotes a scorotron charger, which performs a charging operation on the above-described organic photoconductor layer of the photoconductor drum 10 by a grid held at a predetermined potential and corona discharge by a discharge wire, so that the photoconductor drum 10 is electrically charged. Such a potential is applied.

Reference numeral 12 is an exposure optical system composed of an LED array arranged in the axial direction of the photosensitive drum 10 and a self-occlusion lens. Image signals of respective colors read by a separate image reading device are sequentially taken out from the memory. And is input as an electric signal to each of the exposure optical systems 12 described above.

The exposure optical system 12 in the form of each line described above.
In each case, the guide pin 40P1 is attached to the substrate 40 of the apparatus main body.
Is attached to a cylindrical support member 20 fixed as a guide and is housed inside the base of the photoconductor drum 10, and each of the exposure optical systems 12 is accurately linear in a direction orthogonal to the moving direction of the photoconductor drum 10. Are arranged in a specific manner.

Reference numerals 13Y to 13K denote developing units for accommodating yellow (Y), magenta (M), cyan (C) and K (black) developers, respectively, each having a predetermined gap with respect to the peripheral surface of the photosensitive drum 10. The developing sleeve 130 rotates in the same direction while maintaining the above.

Each of the developing devices is in a non-contact state by applying a developing bias voltage to the electrostatic latent image formed on the photosensitive drum 10 formed by the charging by the charging device 11 and the image exposure by the exposure optical system 12 described above. Reverse development with.

Next, the process of the color image forming apparatus in this apparatus will be described.

The original image is temporarily stored in an image reading device, which is separate from this apparatus, as an image read by an image pickup device or an image edited by a computer as an image signal for each color of Y, M, C and K. Are stored and stored in.

When the image recording is started, the drive gear 40G is rotated by the start of the photoconductor drive motor to rotate the photoconductor drum 10 in the clockwise direction, and at the same time, the charger 11 is driven.
The application of the potential to the photosensitive drum 10 is started by the charging action of (Y).

After a potential is applied to the photosensitive drum 10, the exposure optical system 12 (Y) starts exposure by an electric signal corresponding to the first color signal, that is, the image signal of yellow (Y), and the exposure of the drum is started. By rotating and scanning, an electrostatic latent image corresponding to the yellow (Y) image of the original image is formed on the photosensitive layer on the surface thereof.

The latent image is reversely developed by the developing device 13 (Y) in a state where the developer on the developing sleeve is not in contact with the latent image, and a yellow (Y) toner image is formed according to the rotation of the photosensitive drum 10.

Next, the photosensitive drum 10 is further given a potential on the yellow (Y) toner image by the charging action of the charger 11 (M), and the second color signal of the exposure optical system 12 (M), that is, Exposure is performed by an electric signal corresponding to the magenta (M) image signal, and non-contact reversal development by the developing device 13 (M) causes a magenta (M) toner image on the yellow (Y) toner image. Will be sequentially stacked.

By the same process, the charger 11 (C),
The exposure optical system 12 (C) and the developing unit 13 (C) further form a cyan (C) toner image corresponding to the third color signal, and the charging unit 11 (K), the exposure optical system 12 (K) and the developing unit 13 (C). A black (K) toner image corresponding to the fourth color signal is sequentially superimposed and formed by the unit 13 (K), and a color toner image is formed on the peripheral surface within one rotation of the photosensitive drum 10. You.

The photosensitive drum 1 by each of these exposure optical systems
The exposure of the organic photosensitive layer of No. 0 is performed from the inside of the drum through the above-mentioned transparent substrate. Therefore, the exposure of the image corresponding to the second, third, and fourth color signals is performed with almost no influence of the toner image previously formed, and is almost the same as the image corresponding to the first color signal. It is possible to form an electrostatic latent image of. In order to stabilize the temperature inside the photoconductor drum 10 and prevent the temperature rise due to the heat generation of each exposure optical system 12, a material having good thermal conductivity is used for the supporting member 20, and a heater 201A is used for low temperature, and high temperature is used for high temperature. In this case, by taking measures such as radiating heat to the outside through the heat pipe 202, it can be suppressed to the extent of no problem. Further, during the developing action by each developing device, a developing bias in which a direct current or an alternating current is applied to the developing sleeve is applied, and the jumping development is performed by the one-component or two-component developer accommodated in the developing device to obtain the transparent conductive material. Non-contact reversal development is performed on the photosensitive drum 10 whose layers are grounded.

The color toner image thus formed on the peripheral surface of the photosensitive drum 10 is transferred to the transfer paper which is conveyed from the paper feed cassette 15 in the transfer device 14A and is fed in synchronization with the driving of the timing roller 16. It

The transfer sheet on which the toner image has been transferred is separated from the peripheral surface of the drum by removing the charge in the static eliminator 14B, and the toner is welded by the fixing device 17, and then the upper part of the device via the discharge roller 18. Will be ejected onto the tray.

FIG. 3 is a block diagram showing the circuit configuration of the image exposure control section of the present invention. The image information input from the outside or the image information read by the image reading device is subjected to image processing and then input to the control unit 201 as image data of each color of Y, M, C, and K. Also ROM (1) 2
The monochrome and multicolor image exposure programs are recorded in 03, and when the monochrome mode is selected by the mode switching selection button 211, the selected monochromatic image exposure program is output to the control unit 201 and the color mode is selected. When is selected, the image exposure program for each color of Y, M, C and K is output to the control unit 201 having a clock function.

Further, the ROM (2) 204 has a pixel shift amount Y of the other LED array (L) with respect to the reference LED array (LS) in the main scanning direction of the LED array Y,
The data is recorded for each color of M, C, and K, and when image exposure is performed by the LED array, the ROM (2) 204
The timing clocks corresponding to the number of pixels recorded in 1 are corrected so that there is no deviation of 1 pixel or more when they are superposed.

In the present invention, L serving as a reference of the exposure optical system 12 is used.
The ED array (LS) and the other LED array (L) are corrected for deviation within one pixel in the main scanning direction.
A correction amount for each pixel is written and stored in M (3) 205. That is, when the corresponding LED array (L) has a pixel size m with respect to the reference LED array (LS) for the i-th pixel and is displaced in the positive direction by x, Φ _i = φ _i { (M−x) / m} + φ _{i + 1} (x / m) When there is a deviation in the negative direction by x, Φ _i = φ _i−1 (x / m) + φ _i {(m−x) / The coefficients of (x / m) and {(mx) / m} are stored in the ROM (3) 205 so that the image exposure is performed with the correction of m}. This ROM (3) 205 may have data for all pixels of the LED array (L)
It is also possible to have only one average value of the displacement of the array (L).

The amount of this deviation is such that, when the color image forming apparatus is assembled and adjusted, the CCD array is stuck on the surface of the photoconductor drum 10 in parallel with the LED array so as to be parallel to the LED array. Is rotated to cause one of the light emitting elements of the exposure optical system 12 corresponding to the pixel to emit light, for example, the i-th light emitting element of the reference LED array (LS) to emit light, and then the LED array ( L) causes the i-th light emitting element to emit the same amount of light, and compares the input at the CCD to obtain the shift amount sm with respect to the reference i-th pixel
+ X can be measured. Here, s is a shift amount for an integer number of pixels, and x is a coefficient (x / m) for storing the shift amount x within one pixel in the ROM (3) 205 according to the present invention.
And {(mx) / m}. A black (K) LED array (LK) is preferably used as the reference LED array (LS) for correcting the amount of misalignment in the main scanning direction when they are overlapped with each other. However, the image exposure correction circuit described later is not required.

ROM (1) for color image formation
Control unit 2 according to the multicolor image exposure program from 203
01 performs multicolor image exposure. At this time, for example, in image exposure of yellow (Y), the page memory of yellow (Y) is called from the image data 202, and
(3) The in-pixel correction coefficient for yellow (Y) is called from 205 and input to the image exposure correction circuit 300Y,
The image exposure is corrected and the image exposure is performed by the LED array (Y).

FIG. 4 shows an internal block diagram of the image exposure correction circuit 300. The control unit 201 calls the image density information for one line of main scanning from the page memory of the image data 202 and stores it in the line memory 301. From the line memory 301, pixel density information φ _{i + 1} , φ _i , φ
_i-1 is ( _{i + 1} ) memory 302a, ( _i ) memory 302b,
( _I-1 ) It is moved to the memory 302c. ROM (3) 20
5, the coefficients of (x / m) and {(mx) / m} are called, and the multiplier (1) 303a has ( _{i + 1} ) memory 3
(X / m) φ with φ _{i + 1} called from 02a
_{i + 1} is multiplied, and in the multiplier (2) 303b, the multiplication of {(mx) / m} φ _i is performed by ( _i ) φ _i called from the memory 302b, and the multiplier (3 ) in 303c _(i-1) by phi _i-1 and called from the memory 302c of _{(x / m) φ i-} 1 multiplication processing is performed.

In the adder 304, the multiplier (1) 303a
(X / m) φ _{i + 1} output from the multiplier (2) 30
3 (b) output from {(m−x) / m} φ _i , (x / m) φ _i−1 output from the multiplier (3) 303c, and the deviation output from the ROM (3) 205. Depending on whether the quantity x is in the plus direction or the minus direction, x is in the plus direction: {(mx) / m} φ _i + (x / m)
φ _{i + 1} x is in the negative direction: (x / m) φ _i-1 + {(m−x) /
m} φ _i is added and output as the newly corrected i-th pixel density information Φ _i .

When Φ _i is output from the adder 304, pixel density information is output from the line memory 301 in the form of incrementing the pixel number by 1, and the ( _{i + 1} ) th new correction is performed from the adder 304. The pixel density information Φ _{i + 1} thus generated is output.

Reference numerals 305a and 305b denote writing memories for one main scanning line. Two writing memories (1),
(2) are used alternately, and while Φ is written in the writing memory (1) 305a by switching 1, the writing memory (2) is connected to the LED array head by switching 2 and writing memory Corrected image density information Φ _{1 to} Φ _{n for one} main scanning line written in (2)
Is output to the LED array head for image exposure.
On the other hand, when data for one main scanning line is input to the writing memory (1) by the corrected pixel density information Φ output from the adder 304, the switching 1 and the switching 2 are set to the switching positions indicated by the dotted lines. The corrected image density information for one line of main scanning is output to the LED array head from the write-out memory (1) 305a to which the data for one line is switched and is output from the adder 304. The pixel density information Φ thus obtained is input to the writing memory (2).

By performing the image exposure by the image exposure correction circuit 300 described above, it is possible to correct the deviation within one pixel between a plurality of LED arrays by performing the density correction of the pixel.

FIG. 5 shows another type of color image forming apparatus to which the present invention is applied. Members having the same functions as those of the color image forming apparatus shown in FIG. 1 are designated by the same reference numerals. . In the color image forming apparatus shown in FIG. 5, a charging device 11, a line-shaped exposure optical system 12, a developing device 13, a transfer device 14, which are close to the photoconductor drum 10,
A plurality of sets of image forming means provided with the cleaning device 19 are provided in parallel, and the exposure optical system 1 is provided on the photosensitive drum 10Y which rotates in the direction of the arrow by each image forming means.
The yellow (Y) latent image formed by 2Y is developed to form a yellow (Y) toner image, and the photosensitive drum 10M
A magenta (M) toner image is provided on the photosensitive drum 10
A cyan (C) toner image on the photosensitive drum 10
A black (K) toner image is formed on K. The transfer paper discharged from the paper feed cassette 15 is synchronously fed by the driving of the timing roller 16 and is transferred onto the transfer paper described and conveyed on the conveyor belt 21 by the transfer devices 14Y, 14M, 1
The toner images of yellow (Y), magenta (M), cyan (C), and black (K) are sequentially transferred by 4C and 14K, and the transfer paper that has been transferred in the form in which the toner images are superimposed is fixed by the fixing device 17. After the toner is fused and fixed by the toner, it is discharged onto the tray. Even in such a color image forming apparatus, with respect to the problem of color misregistration due to misregistration within one pixel among the plurality of exposure optical systems 12, an image exposure control circuit similar to that described above is used and The corrected pixel density information Φ is obtained by inputting x, together with the size m of one pixel, the amount of deviation in one pixel between the measured LED array and the reference LED array. Then, by using Φ instead of this Φ, the LED array head performs image exposure to obtain a color image without color misregistration.

[0044]

EFFECTS OF THE INVENTION In a color image forming apparatus in which image exposure is performed by a plurality of linear image exposure means, and toner images are superposed on each other to obtain a color image on a transfer material, conventionally there is a deviation within one pixel. However, according to the present invention, the image data is distributed to the adjacent pixels according to the positional deviation amount in the pixel as the alignment means in the main scanning direction between the linear image exposure means according to the present invention. By carrying out the image exposure, a good color image having no color shift was superimposed and formed.

[Brief description of drawings]

FIG. 1 is a cross-sectional configuration diagram of a color image forming apparatus to which the present invention is applied.

FIG. 2 is a cross-sectional view of essential parts of the color image forming apparatus shown in FIG.

FIG. 3 is a block diagram showing a circuit configuration of an image exposure control unit of the present invention.

FIG. 4 is an internal block diagram of an image exposure correction circuit according to the present invention.

FIG. 5 is a cross-sectional configuration diagram of another type of color image forming apparatus to which the present invention is applied.

FIG. 6 is an equivalent circuit diagram of the LED array.

FIG. 7 is an explanatory diagram showing a misaligned state of the LED array in the main scanning direction.

FIG. 8 is an explanatory diagram showing a state of misregistration correction when the resolution of the LED array is low.

[Explanation of symbols]

 10 Photosensitive Drum 11 Charging Device 12 Exposure Optical System (Image Exposure Means) 13 Developing Device 201 Control Unit 202 Image Data 205 ROM (3) 300 Image Exposure Correction Circuit

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Claims (3)

[Claims] 1. A color image forming apparatus for performing image exposure by a plurality of line-shaped image exposing means, wherein image data is provided in accordance with a positional shift amount in a pixel as a aligning means in the main scanning direction between the image exposing means. A color image forming apparatus characterized by performing image exposure by distributing to adjacent pixels. 2. The color image forming apparatus according to claim 1, wherein a resolution of MTF = 0.5 of the image exposure unit is lower than a writing density of the image exposure unit. 3. The color image forming apparatus according to claim 1, further comprising a unit for shifting integer pixels in the main scanning direction for image exposure of the image exposing unit.