JPH1195502A - Image forming method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form an excellent image by executing image processing so as to make density on the upstream side in the moving direction of a developing sleeve lower than that on the downstream side, as image data. SOLUTION: The image processing is attained so as to make the density on the upstream side in the moving direction of the developing sleeve 131 lower than that on the downstream side, as the image data. Therefore, an image is formed in consideration of the influence of a developing bias, so that the image can be faithfully reproduced. Since an AC bias is applied to the developing sleeve 131, to attain noncontact development, the developing bias more conspicuously appears because of the influence of the fact that toner soars up while being vibrated, as well. But in this method and device, the image can be excellently formed without the above-mentioned influence. Especially, at the time of superimposing toner images of plural colors to form a color image on an image forming body, the influence of the first stuck toner is exerted so that the fact is a great trouble in the case of to forming the excellent image. In such a case, the first stuck toner be made a sensible image without any bias, to form an excellent color image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an image forming body,
The present invention relates to an image forming method and an image forming apparatus for forming an image by charging, image exposure based on image data, and developing while moving a developing sleeve.

[0002]

2. Description of the Related Art As an image forming apparatus such as a copying machine or a printer, there is an electrophotographic image forming apparatus as shown in FIG. In this image forming apparatus, a charging device 2, an exposure device 3, a developing sleeve 4 of a developing device, a transfer device 5, and a cleaning device 6 are arranged around an image forming body 1. In this image forming apparatus, when forming an image, the image forming body 1 rotating in the direction of the arrow is uniformly charged by the charging device 2. Image exposure is performed on the charged image forming body 1 by the exposure device 3 based on image data, and a latent image is formed on the image forming body 1. Then, the latent image is developed by the developing device. In this development, the toner, which is a developer carried on the developing sleeve 4 rotating in the direction of the arrow, is transferred to the image forming body 1 by applying a bias to the developing sleeve 4, and the image forming body 1 to form a toner image. Thereafter, the transfer device 5 transfers the toner image on the image forming body 1 to a transfer material P that is separately conveyed. The transfer material P on which the toner image has been transferred is fixed by a fixing device (not shown). On the other hand, the toner remaining on the image forming body 1 is cleaned by the cleaning device 6 and is prepared for the next image formation.

[0003]

In the above-described image forming apparatus, the toner image formed on the image forming body 1 is biased. As a result of the inventor's intensive studies on this image bias, the inventors have found that there is a bias depending on the moving direction of the developing sleeve 4 in addition to a phenomenon conventionally called an edge effect peculiar to the electrophotographic method.

With respect to these image biases, FIG. 10 (b) in which a development area is enlarged, FIG. 10 (c) schematically showing a patch image in which image bias has occurred, and a density distribution of the patch image are schematically shown. This will be described with reference to FIG. Note that, in FIG.
10C shows the density distribution in the y direction (that is, the direction opposite to the moving direction of the developing sleeve 4), and the broken line indicates the x direction (the direction orthogonal to the moving direction of the developing sleeve 4) in FIG. 2 shows the concentration distribution of the sample.

First, the edge effect is a phenomenon peculiar to a conventionally known electrophotographic system. This is because a strong electrostatic field is generated at the edge of the latent image (periphery of the image)
The toner easily adheres to the edge portion, while the electric field is weak at the central portion of the latent image, so that the toner hardly adheres. For this reason, the image density around the patch image increases. The edge effect is a phenomenon that occurs isotropically (that is, regardless of the x direction and the y direction).

Next, the image bias depending on the moving direction of the developing sleeve 4 is a phenomenon that the image density increases on the upstream side in the moving direction of the developing sleeve. As shown in FIG. 10D, in the density distribution (broken line) in the x direction, the density at both ends of the image is almost the same as the density at the center due to the edge effect described above. I have. On the other hand, in the density distribution (solid line) in the y direction, the density at both ends of the image is high due to the edge effect, and
The density at the end on the upstream side (the right side in FIG. 10D) in the moving direction of the developing sleeve 4 is higher than the density at the end on the downstream side. That is, this phenomenon is an anisotropic phenomenon.

[0007] Therefore, such a bias of the image depending on the moving direction of the developing sleeve 4 which has not been known conventionally becomes a problem when forming a good image.

The image bias depending on the moving direction of the developing sleeve 4 also occurs when the developing is performed by moving the developing sleeve 4 in the reverse direction in FIG. Although the cause of this phenomenon is not clear, the developing sleeve 4
This is considered to be due to the fact that the amount of the toner carried on the upstream side in the movement direction of the developing sleeve 4 increases. In particular, as a result of the inventor's intensive studies, this phenomenon is related to the fact that the toner flies while oscillating when an alternating current (AC) bias is applied to the developing sleeve 4 to perform non-contact development. Appears prominently. Further, when a color image is formed by superimposing a plurality of color toner images on the image forming body 1, this phenomenon is affected by the toner attached first. Is a big problem.

Accordingly, an object of the present invention is to provide an image forming method and apparatus capable of forming a good image.

[0010]

The above object can be attained by the following constitution.

(1) In an image forming method for forming an image by charging an image forming body, exposing the image based on the image data, and developing the image while moving the developing sleeve, the image forming method comprises the steps of: An image forming method, wherein image processing is performed such that the density of image data is lower on the upstream side in the moving direction than on the downstream side.

(2) The image forming method according to (1), wherein, in the image processing, the peripheral portion of the image data is reduced in density as image data as compared with the central portion.

(3) The image forming method according to (1) or (2), wherein the developing is a non-contact developing in which an AC bias is applied to the developing sleeve.

(4) A color image is formed on the image forming body by repeating charging, image exposing, and developing on the image forming body, wherein any one of (1) to (3) is provided. 2. The image forming method according to 1.,

(5) The image forming body, charging means for uniformly charging the image forming body, and image exposure based on image data are performed on the image forming body charged by the charging means, and the latent image is formed. An image forming apparatus, comprising: an exposing unit that forms an image; and a developing unit that has a developing sleeve that moves, and a developing unit that visualizes a latent image formed by the exposing unit with toner carried by the developing sleeve. In an image forming apparatus for forming a toner image on a body, an image processing unit is provided that performs image processing so that the density of the image data is lower on the upstream side in the moving direction of the developing sleeve than on the downstream side as compared with the downstream side. An image forming apparatus characterized in that:

(6) The image according to (5), wherein the image processing means performs image processing such that the peripheral portion of the image data has a lower density as image data than the central portion. Forming equipment.

(7) When the image data is a solid image, the image processing means sets an exposure amount by image exposure in a peripheral portion of the solid image to be smaller than an exposure amount by image exposure in a central portion of the solid image. The image forming apparatus according to (5) or (6), wherein the image data is subjected to image processing.

(8) The developing means performs non-contact development by applying an AC bias to the developing sleeve so that the developing sleeve is not in contact with the image forming body. The image forming apparatus according to any one of (7).

(9) The image forming apparatus includes a plurality of developing units each having a toner of a different color, and forms a color image by superimposing a toner image on the image forming body. The image forming apparatus according to any one of (5) to (9).

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, an image forming process and each mechanism according to an embodiment of the present invention will be described with reference to FIG. 1 which is a sectional view of a color image forming apparatus showing an embodiment of the image forming apparatus according to the present invention. Will be explained.

The photosensitive drum 10, which is an image forming body, has a transparent conductive layer, a-Si, on the outer periphery of a cylindrical base formed of a transparent member such as glass or transparent acrylic resin.
Or a photoconductor layer such as an organic photosensitive layer (OPC). The photosensitive drum 10 is rotated clockwise as indicated by an arrow in FIG. 1 with the transparent conductive layer grounded by power from a drive source (not shown).

The light transmittance of the transparent substrate of the photosensitive drum in the present embodiment does not need to be 100%, but may be such that a certain amount of light is absorbed when the exposure beam is transmitted. It is only necessary to provide an appropriate contrast. As a material of the light-transmitting substrate, an acrylic resin, particularly one polymerized using a methyl methacrylate monomer, is preferably used because it is excellent in transparency, strength, precision, surface properties, and the like, but is used for other general optical members and the like. Various translucent resins such as acryl, fluorine, polyester, polycarbonate, polyethylene terephthalate and the like can be used. Further, as long as it has a light-transmitting property with respect to the exposure light, it may be colored. Examples of the transparent conductive layer include indium tin oxide (ITO), tin oxide, lead oxide, indium oxide, copper iodide, Au, Ag, and N.
A light-transmissive metal thin film made of i, Al, or the like is used. As a film forming method, a vacuum deposition method, an active reactive deposition method,
Various sputtering methods, various CVD methods, dip coating methods, spray coating methods, and the like are used. As the photoconductor layer, an amorphous silicon (a-Si) alloy photosensitive layer,
Amorphous selenium alloy photosensitive layer and various organic photosensitive layers (O
PC) can be used.

Scorotron charger 1 as charging means
1. An exposure unit 12 as an exposure unit and a developing unit 13 as a developing unit are used in image forming processes of yellow (Y), magenta (M), cyan (C) and black (K), respectively. In the present embodiment, with respect to the rotation direction of the photosensitive drum 10 indicated by an arrow in FIG.
Y, M, C, and K are arranged in this order.

The scorotron charger 11 as a charging means for each color is provided with a corona discharge electrode (unsigned) and a U-shaped side plate (unsigned) as a shield member, and furthermore, a control grid on the side plate. (No symbol) is a charging member that is attached to the photosensitive drum 10 in a direction orthogonal to the moving direction of the photosensitive drum 10 (a direction perpendicular to the paper surface in FIG. 1). This scorotron charger 11
A corona discharge electrode for performing corona discharge of the same polarity as the toner,
The above-mentioned organic photoconductor layer of the photoconductor drum 10 performs a charging operation (negative charging in the present embodiment) by a control grid maintained at a predetermined potential to give a uniform potential to the photoconductor drum 10. .

Exposure unit 1 as exposure means for each color
2 is arranged inside the photoconductor drum 10 such that the exposure position on the photoconductor drum 10 is on the downstream side in the rotation direction of the photoconductor drum 10 with respect to the scorotron charger 11 for each color. The exposure unit 12 for each color is
LED (light emitting diode) as light emitting element of image exposure light
A linear exposure element (not shown) in which a plurality of lenses are arranged in an array parallel to the axis of the photoreceptor drum 10 and a selfoc lens (not shown) as an equal-magnification image-forming element are mounted on a holder. It is configured as an exposure unit. The exposure unit 12 for each color is attached to a columnar holding member 20 and housed inside the base of the photosensitive drum 10. As the exposure element, a linear element in which a plurality of light emitting elements such as FL (phosphor light emission), EL (electroluminescence), and PL (plasma discharge) are arranged in an array is used.

The exposure unit 12 performs image processing, which will be described in detail later, based on image data of each color sent from a separate computer (not shown) and stored in a memory, and is uniformly charged. Image exposure is performed on the photosensitive drum 10 to form a latent image on the photosensitive drum 10. The emission wavelength of the light emitting element used in this embodiment is usually Y, M, C
The range of 680 to 900 nm, which is high in the toner permeability, is good, but the wavelength may be shorter than this, which does not have sufficient transparency for the color toner because image exposure is performed from the back surface.

The developing device 13 as a developing means for each color includes
For example, each has a thickness of 0.5 mm to 1 mm and an outer diameter of 15 to
25 mm cylindrical developing sleeve 131 which is a developer carrier made of a non-magnetic stainless steel or aluminum material
And a developing casing (no symbol), and contains therein a two-component (or one-component) developer of yellow (Y), magenta (M), cyan (C) or black (K). . The developing sleeve 131 contains a fixed magnet (not shown) in which N and S magnetic poles are alternately arranged, and is stirred and mixed by a stirring screw (no sign), and is supplied from a stirring unit by a supply roller (no sign). The transported and supplied two-component developer is supplied to the developing unit. At this time, the layer thickness of the two-component developer on the peripheral surface of the developing sleeve 131 is 3 to 1 in diameter.
It is regulated by a thin layer forming rod (not shown) as a thin layer forming member made of a metal material having a circular cross section of a magnetic material of 0 mm and uniformly pressed against the peripheral surface of the developing sleeve 131 with a predetermined load. The two-component developer that has passed through the developing unit is scraped (not numbered) by a plate-shaped elastic member such as SUS or urethane rubber provided by pressing one end of the long side of the belt in parallel with the developing sleeve 131. Developing sleeve 1
The toner is removed from above, is conveyed to a stirring section by a supply roller, and is stirred and mixed by a stirring screw so as to have a predetermined toner concentration.

In the developing section, the developing sleeve 131 is kept out of contact with the photosensitive drum 10 by a contact roller (not shown) with a gap of a predetermined value, for example, 100 μm to 1000 μm. By rotating the developing sleeve 131 in the forward direction with respect to the rotation direction, a DC voltage of the same polarity as the toner (minus polarity in the present embodiment) or a superimposed voltage of DC and AC is applied to the developing sleeve 131 as a developing bias. Non-contact reversal development is performed on the exposed portion of the photosensitive drum 10. At this time, the precision of the development interval needs to be about 20 μm or less in order to prevent image unevenness.

As described above, the developing unit 13 converts the electrostatic latent image on the photosensitive drum 10 formed by charging by the scorotron charger 11 and image exposure by the exposure unit 12 to
In a non-contact state, reverse development is performed with toner having the same polarity as the charged polarity of the photoconductor drum 10 (in the present embodiment, the photoconductor drum is negatively charged and the toner has a negative polarity).

When the image forming is started, the drive source is driven to rotate the photosensitive drum 10 in the clockwise direction indicated by the arrow in FIG. 1, and at the same time, a potential is applied to the photosensitive drum 10 by the charging action of the scorotron charger 11 (Y). The grant is started. After the photosensitive drum 10 is applied with a potential, the exposure unit 12 (Y) starts exposure with the first color signal, that is, an electric signal corresponding to the Y image data, and rotates the drum to scan the photosensitive layer on the surface. An electrostatic latent image corresponding to the yellow (Y) image of the original image is formed. This latent image is reversely developed by the developing unit 13 (Y) in a non-contact state, and a yellow (Y) toner image is formed on the photosensitive drum 10.

Next, a photosensitive drum 10 is placed on a scorotron charger 11 on the yellow (Y) toner image.
A potential is applied by the charging action of (M), exposure is performed by an electrical signal corresponding to the second color signal of the exposure unit 12 (M), that is, image data of magenta (M), and the developing unit 13 (M) performs exposure. A magenta (M) toner image is formed on the yellow (Y) toner image by non-contact reversal development.

By the same process, the scorotron charger 11 (C), the exposure unit 12 (C) and the developing device 13
By (C), a cyan (C) toner image corresponding to the third color signal is further obtained.
(K), exposure unit 12 (K) and developing unit 13 (K)
As a result, a black (K) toner image corresponding to the fourth color signal is sequentially superposed, and a color toner image is formed on the peripheral surface within one rotation of the photosensitive drum 10.
This image forming process, that is, a process of forming a color toner image by superimposing toner images on the photosensitive drum 10 is hereinafter referred to as a KNC process.

As described above, in this embodiment, Y, M,
The exposure of the organic photosensitive layer of the photosensitive drum 10 by the C and K exposure units 12 is performed from the inside of the photosensitive drum 10 through a transparent substrate. Therefore, the exposure of the images corresponding to the second, third, and fourth color signals can form an electrostatic latent image without being blocked by the previously formed toner image. Body drum 1
0 may be exposed from outside.

On the other hand, the recording paper as a transfer material is sent out from a paper feed cassette 15 as a transfer material storage means by a feed roller (no code) and fed by a feed roller (no code) to a timing roller 16. Transported to

The recording paper is fed to the transfer area in synchronization with the color toner image carried on the photosensitive drum 10 by driving the timing roller 16. In the transfer area, a transfer unit 14A as a transfer unit to which a voltage having a polarity opposite to that of the toner (positive polarity in the present embodiment) is applied.
Thereby, the color toner images on the peripheral surface of the photosensitive drum 10 are collectively transferred to the recording paper.

The recording paper to which the color toner image has been transferred is neutralized by a paper separation AC neutralizer 14B as a transfer material separating means, separated from the photosensitive drum 10, and conveyed to a fixing device 17 as a fixing means. You. Heat and pressure are applied between a fixing roller 17a having a heater (not shown) therein and a pressure roller 17b, so that the toner adhered on the recording paper is fixed. The paper is sent to the tray on the top of the device.

The toner remaining on the peripheral surface of the photoconductive drum 10 after the transfer is further rotated and cleaned by a cleaning device 19 or a cleaning blade (not shown) made of a rubber material in contact with the photoconductive drum 10. It is scraped into the device 19. The photosensitive drum 10 from which the residual toner has been removed by the cleaning device 19 is uniformly charged by the uniform charger 11Y, and enters the next image forming cycle.

By the way, if the exposure is performed using the image data as it is, a good image can be formed due to the image bias described in "Problems to be Solved by the Invention" and the problem peculiar to the KNC process (detailed later). Can not do it. Therefore, it is necessary to perform exposure after performing image processing on the image data.

First, an outline of correction of image bias will be described. FIG. 2A is a diagram schematically showing the factors of the image bias as a result of the inventor's intensive studies on the image bias. Note that FIG. 2 shows only the moving direction of the developing sleeve 131, and the diagrams of the edge effect and the bias of the development schematically show an image created by the influence of each.

As the image data, a solid (constant density) patch (cuboid) image is used. If such image data is exposed and developed as it is without performing image processing, an actual image as indicated by an arrow is obtained. The actual image has a high density protruding at both ends in the rotation direction of the developing sleeve of the image, and has a low density at the center, and also has a high density at the upstream side in the rotation direction of the developing sleeve 131 than at the downstream side. It is in.

Considering this factor, the former is a phenomenon peculiar to electrophotography which is generally called an edge effect.
The latter is a phenomenon that the present inventor has newly discovered, namely, a bias due to the rotation of the developing sleeve (hereinafter, development bias). That is, in an actual image, the density becomes protruding at both ends due to the edge effect, and the upstream side has a high density due to development bias. These edge effects and development bias cause image bias. Therefore, a real image is conceptually considered as in the following equation.

(Real image) = (image bias) × (image data) = ((edge effect) × (development bias)) × (image data) The relationship between such a real image and image data is considered. Then, by performing image processing on the image data in advance so as to perform inverse transformation of the image bias, a real image can faithfully reproduce the image data. That is, (corrected image data) = (image bias) ⁻¹ × (image data) = ((edge effect) × (development bias)) ⁻¹ × (image data) = (deviation bias) ⁻¹ × (edge Effect) A real image may be reproduced by ^-1 × (image data).

Here, since the edge effect is generally considered as a kind of Laplacian filter, a correction coefficient, that is, (edge effect) ⁻¹ can be calculated therefrom. In addition, a filter that blurs the edge effect may be used. In short, the image processing is performed so that the peripheral portion of the image data has a lower density as the image data than the central portion so as to cancel the edge effect. do it. More specifically, when a solid image is formed, image processing is performed so that the peripheral portion of the solid image has lower density as image data than the central portion of the solid image. Therefore, in the present embodiment, since the reversal development is performed, the peripheral portion of the solid image is exposed with a smaller exposure amount than the central portion of the solid image.

On the other hand, as for the development bias, the present inventor has studied and found that the development bias is a kind of a differential filter because it is a directional phenomenon. (Deviation bias) ^-1 can be calculated. In addition, a filter that blurs development bias, that is, if the density derivative is positive, increase the density,
If the density derivative is negative, a filter that lowers the density may be used. In short, the image processing may be performed so that the density on the upstream side in the rotation direction of the developing sleeve 131 is lower than that on the downstream side as image data. More specifically, when a solid image is formed, image processing is performed such that the density of the image data on the upstream side in the moving direction of the developing sleeve of the solid image is lower than that on the downstream side of the solid image as image data. Therefore, in the present embodiment, since the reverse development is performed, the upstream side in the moving direction of the developing sleeve of the solid image is exposed with a smaller exposure amount than the downstream side.

The edge effect occurs isotropically (irrespective of the rotation direction of the developing sleeve), whereas the bias of the development occurs anisotropically (depending on the rotation direction of the developing sleeve). Therefore, to correct the bias of development (image processing), image processing is performed according to the rotation direction of the developing sleeve.

Therefore, as shown in FIG. 2B, the image data is subjected to correction for the edge effect (correction coefficient g ₁ ) and correction for the development bias (correction coefficient g ₂ ). By performing exposure and development with image data, the image data can be faithfully reproduced, and a good image can be formed.

Next, the process of forming a color image performed in the present embodiment, that is, the correction unique to the KNC process (hereinafter, also referred to as KNC correction, including the above-described correction of image deviation) will be described. The description will be made while including the edge effect in the bias correction.

First, the phenomenon that occurs during the KNC process will be described with reference to FIG. In FIG. 3, V ₀ is the initial charging potential of the photosensitive drum 10 surface, V _s is the DC bias potential applied to the developing sleeve _{surface, V L1, V L21, V} L22 in the potential of the latent image portion is there. In addition, FIG. 3 shows a state when viewed in a cross section in a direction perpendicular to the rotation direction of the developing sleeve 131 (the rotation axis direction of the photosensitive drum 10 and the developing sleeve 131) unless otherwise specified.

FIG. 3A shows the potential relationship immediately before the developing process using the first color toner. The developing process, when the image exposure, a latent image potential shown for easy description is made to be V _L1 uniformly. L _a is a latent image showing an isolated point or isoline. L _b
Indicates a latent image corresponding to a solid having a large area.

[0050] Depending on the counter electrode effect, the common edges of the electrostatic field stronger if to varying degrees in the development process is the latent image L _a and latent image L _b, occurs edge effect described above, on the other hand, adhesion since the electric field is weakened in the central portion of the latent image L _b, the solid portion of the latent image L _b has become difficult to adhere the toner, while line or edge portion of the toner than the solid portion center It is easy to do.

FIG. 3B is a sectional view showing a state where each latent image is visualized with the first color toner under the potential relationship shown in FIG. 3A.

P indicates the photosensitive drum 10 and T ₁
Denotes a toner image forming an isolated point visualized by the first color toner. T ₂ are illustrates a toner image having a large area which is visualized in a first color toner. The toner image T ₂ where such is composed of an edge portion in and around the central portion. The toner image T ₂ are, by the edge effect described above, and indicates that an uneven shape of a toner image with toner less adhere to the central portion than the edge portion (which is an edge effect). Note that the edge effect not only acts when a latent image that becomes an isolated point or a latent image that becomes a thin line that is an isolated line is enhanced and visualized. It acts in a direction that makes visualization difficult. Also,
In FIG. 3B, a region (toner image T
_{As shown in FIG. 2} when viewed in a cross section in the rotation direction of the developing sleeve), a large amount of toner adheres to the upstream side (the right side in the figure) of the developing sleeve 131 in the rotation direction, and the above-described development bias occurs. The edge effect and the bias of development may be caused by deformation of the latent image and toner image caused by the type of image regardless of the structure of the toner image formed before or under the state where the toner image has not yet been formed on the image forming body. This is also referred to as third development.

FIG. 3 (c) shows a state in which the second color image exposure is performed after recharging, that is, the potential relationship immediately before the developing process using the second color toner.

Here, the image exposure _La1 is performed at the same position as that of the first exposure, and the latent image _Lb1 is exposed at a shifted position. In the figure, V _L1 and V _L21 , V _L22 have a mixed and disturbed potential distribution. V _L21, L _L22 is the potential of the latent image portion formed on the first color toner image is higher than the V _L1.

Here, the reason why the potential distribution of L _b1 and the electric field shown in FIG. 3C are disturbed will be described below.

As described above, the developing process for the second and subsequent colors is performed in a state where the previously visualized toner image is carried on the photosensitive drum 10. Therefore, the already formed toner image fluctuates the latent image potential and the electric field of the second and subsequent colors. Stated in detail, T ₂ is in a state of adhering more toner to the edge portion as described above, it is fewer adhesion of the toner to the vicinity of the central portion. These toners have the effect of increasing the potential and hindering toner adhesion. That is, the next toner is placed on the solid portion of the toner image because of the toner layer potential and the shielding property that the toner does not easily transmit light (in the present embodiment, the former is a method of exposing from the inside). This is a phenomenon that makes it difficult to adhere, and is hereinafter also referred to as a first phenomenon.

FIG. 3D is a sectional view showing an electric field formed on each latent image in the potential relationship shown in FIG. 3C.
The state of the electric field in the newly formed latent images L _a1 and L _b1 is indicated by lines of electric force (arrows).

[0058] The new latent image L _a1 is formed on the toner image T ₁ corresponding to the isolated point is visualized by the first color toner. The toner image T ₁ where such is affecting the electric field formed from the toner layer potential described above to the latent image L _a. By local field specifically generated in the vicinity of the toner image T ₁ center, since the electric field of attaching toner is weakened, the second color toner is then difficult adhere. This is the deformation of the latent image caused by the structure of the previously formed toner image, that is, the halo effect that appears as an edge effect that occurs at the edges of isolated points, isolated dotted lines, characters, solid parts when overlapping colors, and a pseudo contour phenomenon Yes, it has the same cause as the edge effect, but is a phenomenon unique to the KNC process due to superposition, and is hereinafter also referred to as a halo effect or a second phenomenon. Although not shown, the second color toner easily adheres around the first color toner,
It may adhere under some conditions.

[0059] latent image L _b1 newly formed, the same image over uneven toner image T _2, is formed by image exposure by shifting the position. Therefore, a new latent image L
an electric field formed _b1 part and the vicinity thereof overlap the toner image T ₂ are considered to be distorted.

[0060] latent image L _b1 is latent L _b11 from differences adhesion amount of a toner image that is formed previously, the latent image L _b21, 3 of the latent image L _b31
Area. The latent image _Lb11 is formed on the portion of the photosensitive drum 10 where the first color toner is not attached. Latent image L _b21 is obtained by forming the edge of the toner image T _2, is formed on the highest location of the toner adhesion amount of change. Latent image L _b31 in the central portion of the toner image T _2, those are of the edge due to the influence of the edge effect which is formed on the attachment portion of the thin toner. The latent image L _b11 , the latent image L _b21 , and the latent image L _b31 do not become the same potential from the toner potential even if they are irradiated with the same amount of light.

Further, the latent image _Lb21 has a halo effect when viewed from the lines of electric force. Here, the halo effect is a kind of the edge effect, and means that the second color toner is hard to adhere to the edge of the first color toner image, and the development occurs in which the second color toner easily adheres to the periphery. That is, the latent image L _b21
Is an area where an edge effect is generated by the first color toner. In other words, weak electric field for attaching toner from field of the latent image L _b31 formed in the central portion of the toner image T ₂ are at the edge, adhering the toner than the electric field formed in the location L _b11 absence of the toner image in the peripheral This indicates that the electric field has increased.

FIG. 3E is a cross-sectional view showing an overlapping state of the toner images visualized under the potential condition shown in FIG. 3C.

Toner image T formed with second color toner
₃ is a slight amount of adhesion from the electric field condition shown in FIG. In other words, rather than secondary colors obtained by the adhesion amount of the toner image T ₁ and the toner image T ₃ in the same, which is intended to color-balance out the color of the first color toner is strong.
The toner image T ₄ formed of the second color toner adheres to the latent image L _b11 ′ by the same amount as the first color toner due to the electric field described above, and the latent image L _{b21 forms the} toner image under the influence of the halo effect. T ₂
Of the second color toner less adhere to the edge portion, the second color toner often adheres to the peripheral portion, the toner image T ₂ in the latent image L _b31
It can be seen that it adheres less than the vicinity of the center and slightly rises at the edge. Therefore, the portion where the edge portion of the toner image T ₂ and the toner image T ₄ was formed by superimposed is it is understood that the that collapse of the density and color balance out strong halo effect. This is the second phenomenon.

On the other hand, the solid portion formed between the solid portions of the toner image T ₂ and the toner image T ₄ has a lower density of the second color. This is the first phenomenon.

Next, the above-described first to third development corrections that occur when an image is formed in the KNC process will be described with reference to FIG. 4 schematically shown. In addition,
FIG. 4 mainly shows a state when viewed in a cross section in a direction orthogonal to the rotation direction of the developing sleeve 131 (the rotation axis direction of the photosensitive drum 10 and the developing sleeve 131).

FIG. 4A shows the potential relationship during the developing process using the first color toner. In order to correct the first phenomenon, the image data is corrected from the image density of each color in consideration of the overlapping state of the toner images. Therefore, even in an exposure process by the next color toner to form a latent image L _a and the latent image L _b2 which are to form the latent image position, the other a latent image potential of forming this round of exposure process as V _L2 The latent image potential V _L1 of the latent image L _{b1 on} which the color toner is not superimposed is set higher. Further, in order to correct the third phenomenon, the image data is corrected in consideration of the toner image to be formed and the rotation direction of the developing sleeve. Therefore, in order to prevent the edge effect in the third phenomenon, the exposure amount of the edge portion (peripheral portion of the image) of the latent image (L _b1 and L _b2 ) is controlled so that the potential is increased. Furthermore, exposure considering the developing bias according to the rotation direction of the developing sleeve is controlled, as indicated by a dot within the chain line in FIG. 4 viewed latent image L _b2 in the direction of rotation of the cross-section of the developing sleeve (a), the developing direction The potential is set higher on the upstream side (right side in the figure) than on the downstream side (left side in the figure).

FIG. 4B is a cross-sectional view showing a state where each latent image is visualized with the first color toner under the potential relationship shown in FIG. 4A. As shown in FIG. 4B, the toner images T ₁ , T ₂ , and T ₃ are all flat by removing the edge effect by the third correction value. In addition, the toner images T ₁ and T ₃ are formed thinner than the toner image T ₂ in consideration of the overlapping of the toner images. Although not shown, all toner images T ₁ ,
T ₂ and T ₃ are flat without developing bias depending on the rotation direction of the developing sleeve.

FIG. 4C shows the potential relationship during the developing process using the second color toner. In order to correct the first phenomenon, the image data is corrected from the image density of each color and the image density in consideration of the overlapping state of the toner images. Thus, the latent image L _a1 and the latent image L _b4 and the latent image L _b5 position the toner image by the previous color toner is formed, in consideration of the influence of the toner image, stronger than during the previous toner image formed Image exposure is performed. Thus, the latent image L _a1 and the latent image L _b4 and the latent image L _b5 is set to V _L2 is a preceding same potential. In this correction, when the exposure amount is small, the light attenuation curves of the first color and the second color of the photosensitive drum 10 are similar,
It is preferable to increase the correction amount of the second color as the exposure amount increases.

In the correction for the second phenomenon, assuming that the previous toner image is reproduced in accordance with the image data, even if a latent image is formed thereon, as shown by the arrow, The latent image is deformed due to the edge effect caused by the above (shown in FIG. 3D). Thus, in order to prevent edge effects in the latent image L _a1 and the latent image L _b5, the strong image exposure on the weak image exposure around the L _a1 L _a1, strongly exposed to the edge of the latent image L _b5 Then, correction is made so as to weakly expose around _Lb5 .

The correction for the third phenomenon is a correction process for correcting image density data to form toner images T _{1 to} T ₆ without edge effect and development bias, and FIG.
Is the same as described above.

FIG. 4D shows electric fields formed on the latent images L _{b4 to} L _b6 by lines of electric force. It can be seen that the effects of the halo effect and the edge effect have all been removed.

FIG. 4E is a sectional view showing a state in which each latent image is visualized with the second color toner under the potential relationship shown in FIG. 4C. Each of the toner images T _{4 to} T ₆ is flattened by removing the edge effect and the halo effect. Moreover, the toner image T ₄
Through T ₇ it is are formed thinner than T ₁ and T ₃ in the same manner as in the toner image T _2, T _6. Thus, it is shown that the color balance of the secondary color is corrected as compared with FIG.

Next, a specific configuration for performing these corrections will be described. FIG. 5 is an overall block diagram of the image processing circuit according to the present embodiment.

The image processing circuit according to the present embodiment is a circuit constituting a driving circuit of a scanning optical system, and includes an image data processing circuit 100, a modulation signal generation circuit 200, and a scanning circuit 300 as shown in FIG. Become.

The image data processing circuit 100 is a circuit for interpolating and outputting an edge portion of font data. The image data processing circuit 100 includes a computer input circuit 110, a font data generation circuit 120, a font data storage circuit 130, and an interpolation data generation circuit 140. Become. The input circuit 110 converts a character code signal, a size code signal, a position code signal, and a color code signal into a font data generation circuit 12.
Send to 0. In the font data generation circuit 120, 4
An address signal is selected from the various input signals and sent to the font data storage circuit 130. The font data storage circuit 130 sends font data corresponding to one character corresponding to the address signal to the font data generation circuit 120. The font data generation circuit 120 sends the font data to the interpolation data generation circuit 140. The interpolation data generation circuit 140 interpolates the jaggedness or jump of the image density data generated at the edge of the font data using the intermediate density, and sends the result to the linear masking circuit 154 as 8-bit image density data, for example. Further, in the linear masking circuit 154, corresponding colors are respectively yellow (Y), magenta (M), cyan (C),
The data is converted into black (BK) density data and sent to an image density data storage circuit 210 composed of a page memory. In this way, a font that has been multivalued developed in a state where the colors have the same shape and the density ratios are different is subjected to multivalued bitmap development in the page memory for each color.

The image density data storage circuit 210 is a normal page memory (hereinafter simply referred to as a page memory 210), a RAM (random access memory) for storing pages, and corresponds to at least one page (for one screen). It has a capacity to store multi-valued image density data.
Moreover, in the present embodiment, since the apparatus is used for a color printer, a plurality of colors, for example, yellow, magenta,
A page memory only for storing image density signals corresponding to cyan and black color components is provided.

The modulation signal generation circuit 200 includes a read circuit 220, a latch circuit 230, an image determination circuit 231, an MT
F correction circuit 232, γ correction circuit 233, reference wave phase determination circuit 240, select circuits 250A, 250B, 250
C, 250D, modulation circuits 260A, 260B, 260
C, 260D, a reference clock generation circuit 280, a triangular wave generation circuit 290, a delay circuit group 291, and a KNC correction circuit 1000 for correcting the adhesion state of the toner required for the KNC process.

Modulated signal generating circuit 200 of the present embodiment
Indicates that one pixel of interest in the image density data is m × n (width ×
Vertical) small pixels, the distribution of density data of adjacent pixels including the target pixel is replaced with the distribution of m × n small pixels in the one pixel, and the distribution of the target pixel multiplied by a constant P Based on the image density data of the small pixels obtained by distributing the data according to the distribution, the latent image by displacing the writing position of the dot of the nth row by displacing the phase of the reference wave of each row of the small pixel. Can be formed. Displacing the dot writing position is called recording position modulation. The process of converting the target pixel into image density data of small pixels divided into m × n is referred to as a resolution improvement process (RE process). High-density recording is performed by such RE processing.

The readout circuit 220 reads out continuous image density data of one continuous scan line unit from the page memory 210 in synchronization with the reference clock DCK ₀ using the index signal as a trigger, and reads out the reference wave phase determination circuit 24.
0, to the image discrimination circuit 231 and the KNC correction circuit 1000.

The latch circuit 230 is a circuit that latches the image density data during the time when the processing of the reference wave phase determination circuit 240 described later is being executed.

The image discrimination circuit 231 discriminates whether an image is a character area or a halftone area, and performs MTF determination.
Determine the degree of correction and gamma correction. The KNC correction circuit 1000 includes an MTF correction circuit 232 and a γ correction circuit 233.
5 are provided at the front stage in FIG. 5, but are preferably provided at the latter stage. In particular, when the correction value of the image density data is large, hue cannot be compensated. Although not shown, it is preferable that a magnification change correction circuit for changing the magnification of the output image and a color conversion circuit for changing the color tone and hue be similarly arranged before the KNC correction circuit.

If the image discriminating circuit 231 discriminates a character area of a character or a line drawing, the modulating circuit 26 converts the triangular wave selected by the reference wave phase determining circuit 240 for all color components.
0A, 260B, 260C, and 260D are output to select circuits 250A, 250B, 250C,
250D, the MTF correction circuit 232,
The gamma correction circuit 233 is inoperative and the image density data is not processed and the modulation circuit 260A,
260B, 260C and 260D. As a result, clear characters and edge portions without color tone change are reproduced. On the other hand, when the image discriminating circuit 231 determines that the image is in the halftone area, it outputs a selection signal similar to that of the character area only for the achromatic component, that is, black data, and the reference wave phase determining circuit 240 selects the other color components. A selection signal for outputting only the reference triangular wave φ0 without outputting the selected triangular wave is sent to the select circuits 250A, 250B, 250C, and 250D, and the MTF correction circuit 232 and the γ correction circuit 233 are operated. As a result, the image density data other than black read by the read circuit 220 is corrected by the MTF correction circuit 232 and the γ correction circuit 233, and then the latch circuit 230
Modulation circuits 260A, 260B, 260C, 26
Sent to 0D. As a result, an image without moiré or color skipping can be formed in the halftone region, while an effect of giving sharpness and closeness to the image by the black image is produced.

The MTF correction circuit 232 is composed of a Laplacian filter, has visual sharpness, and has a size of about 5 × 5 pixels. The value of this filter is determined experimentally from the development characteristics.

The modulation circuits 260A, 260B, 260C,
260D modulates a signal of image density data input through the latch circuit 230 with a triangular wave as a reference wave selected by the reference wave phase determination circuit 240 to generate a pulse width modulated and intensity modulated signal, and performs scanning. It is sent to the circuit 300.

The scanning circuit 300 is a circuit for controlling the LED of each exposure unit 12, and corrects the inclination and bending of the LED by a delay circuit (no sign) to control light emission.

On the other hand, the reference clock generation circuit 280 is a pulse generation circuit, generates a pulse signal having the same repetition cycle as the pixel clock, and reads out the readout circuit 220, the triangular wave generation circuit 290, the delay circuit group 291, the modulation circuit 260A,
Output to 260B, 260C, 260D. For convenience the clock referred to as a reference clock DCK _0.

The triangular wave generation circuit 290 has a reference clock DC.
Based on K ₀ , waveform shaping of a reference triangular wave φ0 which is a reference wave having the same cycle as the pixel clock is performed. Also, delay circuit group 2
Reference numeral 91 denotes a plurality of clocks D having a phase difference at regular intervals (in this example, 1/6 cycle) with respect to the reference clock DCK _0.
CK1～DCK ₄ produced on the basis of this, the triangular wave is a reference wave having different phases .phi.1 to .phi.4 (triangular wave delayed triangular wave φ1,2 / 6 cycle delay 1/6 cycle here Fai2,1 /
Triangular wave φ advanced 6 cycles, triangular wave φ advanced 2/6 cycles
4) is output.

Select circuits 250A, 250B, 250
C and 250D have input portions for the triangular waves φ1 to φ4 out of phase with the reference triangular wave φ0, and the reference wave phase determining circuit 2
One of the above triangular waves is selected by the selection signal from 40 and the modulation circuits 260A, 260B, 260C, 260D
To the input terminal T. The above is the schematic configuration of the image processing circuit according to the present embodiment.

Next, an example of each circuit configuration in the image processing circuit and the KNC correction circuit 1000 according to the present embodiment will be described with reference to FIGS.

FIG. 6 shows the KNC correction circuit 10 shown in FIG.
It is a block diagram which shows an example of a specific main part structure of 00.

The KNC correction circuit 1000 has a function of correcting the above-described first to third phenomena for the image density data of each color. Specifically, image processing is performed to modulate the intensity and pulse width at the time of exposure according to the image density of each color, the image density distribution, the overlapping state of the toner images, and the rotation direction of the developing sleeve. KNC correction circuit 10
00 is the multivalued image density data D ₁ (Y ₁ data, M ₁ data, C _{1 for each} color) obtained from the page memory 210.
Data, and K ₁ data) input to the three correction circuits 13
00, 1400, 1500, and the corrected recording image data D ₄ (Y ₄ data, M ₄ data, C ₄
Data, and outputs the K ₄ data). In the present embodiment, the recorded image data D ₄ (Y ₄ , M
₄ , C ₄ , K ₄ ) are, as shown in FIG. 6, the recorded image density data D ₂ (Y ₂ , M ₂ , C ₂ , K ₂ ) and the correction coefficient f × g.
(F _Y × g _Y , f _M × g _M , f _C × g _C , f _K × g _K ), which are sent out to the modulation circuit 260 and recorded image density data D ₂ is MTF
The data is sent to the correction circuit 232 and processed.

The KNC correction circuit 1000 includes a first correction circuit 1300 for performing a correction (corresponding to a first development correction) corresponding to the image density of each color, and a second correction circuit for performing a correction of the second phenomenon. Correction circuit 1400 and a third correction circuit 1500 that corrects the third phenomenon.
0,1400,1500. It is to be noted that these correction circuits can be collectively formed as one circuit. In this case, it is preferable that the correction algorithm can be operated by simplifying the calculation, the look-up table method is used, or the correction algorithm is used in combination.

In the present embodiment, the exposure optical system is arranged in the image forming body, and the KNC process for exposing the image from inside using the image forming body of the transparent substrate is used. In this case, the influence of the light blocking and the spread of the beam diameter caused by the light scattering by the toner image can be eliminated. Further, by performing correction for the first and second phenomena, the overlay can be improved. This allows KNC
Stable color reproduction can be performed by the above correction accompanying the process. Specifically, unlike the external exposure method, correction is performed in consideration of the influence of the toner layer potential without being affected by light absorption or light scattering. Therefore, the correction by the first correction circuit 1300 (correction at the time of masking) and the correction by the second correction circuit 1400 (correction coefficient) f
Can be simplified.

In the correction of the present embodiment, the expression as a product of the first to third corrections has been shown as an example for convenience of calculation, but other values may be used.

The filter 1100 is composed of a Laplacian filter and a differential filter, and is a means for detecting the structure of the toner image and detecting the bias of development in accordance with the rotation direction of the developing sleeve. This filter is used to determine the second correction coefficient f in the second correction circuit 1400 and the third correction coefficient g in the third correction circuit 1500. The third correction factor, as previously described, is the product of the correction coefficient (g ₂₎ for the correction factor (g ₁₎ and the developing bias for the edge effect. The second correction coefficient f and the third correction coefficient g are parameters for determining a correction amount. Specifically, the filter 1100 responds to the density change of each color, that is, the Laplacian values ΔY, ΔM, ΔC,
ΔK and the differential value ΔY according to the rotation direction of the developing sleeve,
Find ∂M, ∂C, and 求 め る K. Using these, the second and third correction circuits 1400 and 1500 determine the correction coefficients f, g ₁ and g ₂ for each pixel of each color. The size of the filter for obtaining the Laplacian value and the differential value is 2 if 600 dpi is generated if an edge effect of about 1 mm is generated.
It has a pixel size of 0 × 20.

The delay circuit 1200 is means for delaying in order to synchronize the respective correction processes.

Subsequently, the following three correction circuits 1300-1
The configuration example of 500 will be described more specifically.

The first correction circuit 1300 corrects the first phenomenon, and includes the following.

As the first correction circuit 1300, a look-up table system (hereinafter simply referred to as a direct conversion method) for executing a color correction process by a direct conversion method or a color correction process by a three-dimensional interpolation method is executed. A look-up table method (abbreviated as a three-dimensional interpolation method) can be adopted.

In the color correction processing by the direct conversion method, the color correction processing is generally regarded as a coordinate conversion from a simple color separation signal space to a color correction signal space, and color correction signal data corresponding to each color separation signal coordinate is converted. It is stored in a memory table, and the coordinate conversion is directly performed by referring to this table. In the color correction process using the three-dimensional interpolation method, the correspondence table between the color separation signal coordinates and the color correction signal data is limited to a limited number of colors. A look-up table method for three-dimensional interpolation and color correction by a neural network can be adopted.

Further, as the first correction circuit 1300, black K, primary color and secondary color at 100% UCR are used in accordance with an image represented by Y ₁ , M ₁ , C ₁ , and BK data subjected to normal masking. there are outputs a _{Y 2, M 2, C 2} , K 2 data corrected by mixing black after the next primary color and secondary color of the color correction to separate the next color. That is, from the Y ₁ , M ₁ , C ₁ , and B ₁ data after the normal masking process, the Y ₁₁ , M ₁₁ , and C ₁₁ data after the 100% UCR process are converted into primary colors (color toner colors) Y, M, and C and secondary colors (colors obtained by adding the primary colors Y, M, and C) B, G, and R, and red, magenta,
Correction is made so that blue, cyan, green, and yellow match the reproduction color.

In the above-described correction by the first correction circuit 1300, the toner layers are overlapped, that is, the correction is performed in the solid area, but the toner image formed first and the toner image formed later are corrected. The correction is not made for the image structure such as the green, the peripheral portion, the isolated point, the line, and the like. Therefore, the second correction circuit 1400 is required as the correction based on the structure of the image.

If the function (correction coefficient) of the second correction circuit 1400 is expressed as a function f, f is originally determined from the density change of the image density data Y, M, C, and K of each color.
_Y (Y, M, C, K), f _M (Y, M, C, K), f
_{C (Y, M, C,} K), f K (Y, M, C, K) is a function represented generally and, since it is sufficient to consider only the impact of only the previous toner image, If there is no difference due to the color of the toner, if simplification is made, the development order is Y → M → C → K, and each f is f _Y = 1, f _M = 1 + α _Y , f _C = 1 + α _{Y + M} , f _K = 1 + α
_{Y + M + C.}

If the function (correction coefficient) of the third correction circuit 1500 is expressed as a function g, the third correction circuit 1500 multiplies the correction coefficient g ₁ associated with the edge effect and the correction coefficient g ₂ associated with the development bias (g = g). g ₂ × g ₁ ). The correction coefficient g is generally determined as g _Y (Y), g _M (M), g _C (C), or g _K (K) determined from the density change of the image data Y, M, C, and K for each color. Is the function represented by Since the influence of the previous toner image is not taken into account, the function does not become a function based on the color of another toner. When this function is simplified, each g is represented by image data Y,
The deviation correction between M, C, K and each color of the reproduced image is represented by g _Y = (1+
β _Y ), g _M = (1 + β _M ), g _C = (1 + β _C ), g _K =
The function of the third correction circuit 1500 can be expressed as (1 + β _K ). Here, since there is no correction of interference between toner images, a correction coefficient 1 + β determined from a Laplacian value (for an edge effect) and a differential value (for a development bias) obtained from image density data of each color is used.

Further, the first to third corrections D ₄ = D ₂ × f ×
Equation (1) is obtained by simplifying g.

Equation (1) Y ₄ = Y ₂ × 1 × (1 + β _Y ) M ₄ = M ₂ × (1 + α _Y ) × (1 + β _M ) C ₄ = C ₂ × (1 + α _{Y + M} ) × (1 + β _C K ₄ = K ₂ × (1 + α _{Y + M + C} ) × (1 + β _K ) Recorded image data Y ₂ , M ₂ ,
C ₂ and K ₂ are image density data in which the first phenomenon has been corrected. The second column is a correction term for correcting the second phenomenon,
In consideration of only the influence of the preceding image, the displacement due to the subsequent image is not corrected for simplification. Such a second term is originally f _Y (Y, M, C, K), f _M (Y, M, C,
K), f _C (Y, M, C, K), f _K (Y, M, C, K)
It is. The third column is a correction term for correcting the third phenomenon. Expression (1) shows the KNC correction in the case of developing in the order of Y, M, C, and K, but is not limited to this. For example, K → C → M → Y
Or K → Y → M → C. In such cases,
The correction coefficient will be changed accordingly.

The third correction circuit 1500 corrects the third phenomenon, that is, the deviation between the image data and the reproduced image. Therefore, instead of the correction circuit 1500, the MTF correction circuit 232 and the γ correction The circuit 233 can have that function. Further, in addition to this, it is also possible to correct the image data using the above equation as a look-up table system.

In the present embodiment, the recording image data Y ₄ , M ₄ , C ₄ , and K ₄ shown in Expression (1) are distributed to intensity modulation data and pulse width data. That is, KNC
The image data D ₄ obtained from the correction circuit 1000 is subjected to exposure control by sharing intensity modulation and pulse width modulation. Note that pulse width modulation has the meaning of modulating the exposure width, that is, the area of the latent image, and intensity modulation has the meaning of modulating the exposure intensity, that is, the potential of the latent image.

Therefore, in the present embodiment, the data D ₂ corresponding to the pulse width, that is, Y ₂ , M ₂ , C ₂ , K ₂ and the data f corresponding to the intensity modulation are output from the KNC correction circuit 1000.
_{Y × g Y, f M ×} g M, f C × g C, f K × g K in distribution and modulation circuit 260A, 260B, will be delivered 260C, to 260D. Note that D ₂ is sent to the modulation circuit 260 via the MTF correction circuit 232, the γ correction circuit 233, and the latch circuit 230.

FIG. 7 is a block diagram showing a modulation circuit according to the present embodiment.

The modulation circuits 260A, 260B, 260C,
260D has the same circuit configuration and the D / A conversion circuit 2
61, comparator 262, differential amplifier 263, D /
A conversion circuit 264, input section T of the above-described reference triangular wave φ ₀ or a triangular wave whose phase is shifted by ６ cycle, input section I of data corresponding to pulse width, and input section D of data corresponding to intensity modulation And an input section CK for a reference clock DCK ₀ . In the present embodiment, the data (f × g) corresponding to the intensity modulation is synchronized with the reference clock DCK0 by D /
D / A conversion is performed by the A conversion circuit 264. On the other hand, the triangular reference wave input from the select circuits 250A, 250B, 250C, 250D is
A uniform pulse width signal is generated using a terminal input and a predetermined threshold for cutting off the reference wave. That is, the data (D ₂ ) corresponding to the pulse width is applied to the − input terminal of the comparator 262 and is compared with the reference wave to obtain a pulse width modulation signal. Next, the pulse width modulated signal and the data (f × g) from the input section D are amplified by the differential amplifier 263 to obtain an intensity-modulated pulse width signal.

The modulation circuits 260A, 260B, 260
The generation of the modulation signal in C and 260D will be described with reference to FIG. FIGS. 8A to 8F are time charts showing signals of each part of the modulation circuit.

In FIG. 8, (a) is Y, which is image density data D ₂ transmitted from the shift correction circuit (first correction circuit) 1300 based on the reference clock signal DCK ₀ using the index signal as a trigger. _{2, M 2, C 2,} K
₂ shows a part of data converted into an analog value by the D / A conversion circuit 261. A higher level indicates a lighter density, and a lower level indicates a higher density.

FIG. 8B shows select circuits 250A and 250A.
The triangular waves are sequentially selected from 0B, 250C, and 250D and are selected reference waves including delayed ones. FIG. 8C shows an input signal of the comparator 262, which is the same as FIGS. 8A and 8B.

FIG. 8D shows that a DC voltage is generated internally to convert the triangular wave shown in FIG. 8B into a pulse width signal.
7 shows a pulse width signal generated by comparison by the comparator 262. This pulse width signal becomes one input signal of the differential amplifier 263.

FIG. 8E shows correction data determined from the peripheral pixels of the target pixel.
0, 1500, which is data f × g or (1 + α) × (1 + β) corresponding to intensity modulation, and such a signal is one input signal of the differential amplifier 263.

FIG. 8 (f) shows a differential amplifier 263 which amplifies the difference between the two input signals shown in FIGS. 8 (d) and 8 (e).
5 shows an intensity-modulated pulse width signal from FIG. The modulated signal thus obtained is sent to the scanning circuit 300 to emit light from the LED array.

The color image forming apparatus 4 of the present embodiment described above.
According to 00, even when spot light is irradiated from above the toner image based on the digital signal, a fringe-free, high-sharp, high-dot electrostatic latent image is formed. As a result,
A toner image with high sharpness can be obtained, and the quality of color reproduction such as edges, thin lines, and isolated points can be improved by performing correction in consideration of the image density distribution when the toner images are superimposed. .

Particularly, in this embodiment, the developing sleeve 1
Since the image processing is performed such that the upstream side in the moving direction of 31 is lower in image data density than the downstream side, the image can be faithfully reproduced by forming an image in consideration of the influence of development bias. Further, an alternating current (AC) is applied to the developing sleeve 4.
By performing the non-contact development by applying a bias, the toner flies while oscillating, which causes the development bias to appear more prominently. However, in the present embodiment, a favorable Image formation can be performed. In particular, when a color image is formed by superimposing toner images of a plurality of colors on the image forming body 1, it is affected by the toner that has adhered first. However, in the present embodiment, since the previously attached toner can be visualized without bias, a good color image can be formed.

Further, in the present embodiment, all the developing sleeves 131 of each developing unit 13 are configured to rotate in the same direction as the rotation direction of the photosensitive drum 10, but as described above, the developing If the present invention for correcting the bias is used, it is not necessary to rotate all the developing sleeves 131 of the respective developing units 13 in the same direction. For example, in FIG. 9 instead of FIG. The developing sleeves of the developing devices 13 (Y) and 13 (M) arranged in the same direction are rotated in the same direction, and the developing sleeves of the developing devices 13 (C) and 13 (K) arranged on the right side are rotated in the opposite direction. You may. In such a configuration, although the developing directions of Y, M, C, and K are opposite to each other, a good image can be formed by applying the above-described present invention that corrects development bias for each. . Further, in this case, when viewed as a single developing device 13, the developing sleeves of all the developing devices 13 can be rotated upward from below, so that the structure of the developing devices 13 can be shared and cost can be reduced.

As described above, even when a plurality of developing units are provided, it is possible to eliminate development bias by correcting image data according to each developing direction. In particular, in a color image forming apparatus in which a toner image is superimposed on a photosensitive drum, a change in color tone is conspicuous because the overlap of a subsequent toner image with an earlier toner image is affected. However, by eliminating the development bias as in the present invention, a favorable color image can be obtained without the development bias of the previous toner image affecting the formation of the subsequent toner image.

[0122]

As described in detail above, according to the present invention,
An image forming method and apparatus capable of forming a good image can be provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional configuration diagram of a color image forming apparatus.

FIG. 2 is a diagram schematically showing a factor of image bias and its correction.

FIG. 3 is a diagram schematically illustrating a phenomenon that occurs during a KNC process.

FIG. 4 is a diagram schematically showing corrections of first to third developments.

FIG. 5 is an overall block diagram of an image processing circuit.

FIG. 6 is a block diagram illustrating a specific main configuration of a KNC correction circuit 1000;

FIG. 7 is a block diagram illustrating a modulation circuit.

FIG. 8 is a time chart showing signals of each part of the modulation circuit.

FIG. 9 is a cross-sectional configuration diagram of a modification of the color image forming apparatus.

FIG. 10 is a diagram schematically illustrating an outline and problems of an image forming apparatus.

[Explanation of symbols]

REFERENCE SIGNS LIST 100 image data processing circuit 200 modulation signal generation circuit 210 image density data storage circuit (page memory) 231 image discrimination circuit 232 MTF correction circuit 233 gamma correction circuit 250A, 250B, 250C, 250D select circuit 260A, 260B, 260C, 260D modulation circuit 280 Reference clock generation circuit 300 Scanning circuit 1000 KNC correction circuit 1100 Filter 1300 First correction circuit 1400 Second correction circuit 1500 Third correction circuit

Claims (9)

[Claims] 1. An image forming method for forming an image by charging an image forming body, exposing the image based on image data, and developing while moving a developing sleeve, wherein the moving of the developing sleeve of image data is performed. An image forming method, wherein image processing is performed so that the density on the upstream side in the direction is lower than that on the downstream side as image data. 2. The image forming method according to claim 1, wherein, in the image processing, a peripheral portion of the image data has a lower density as the image data than a central portion. 3. The image forming method according to claim 1, wherein the developing is a non-contact developing by applying an AC bias to the developing sleeve. 4. The image forming apparatus according to claim 1, wherein charging, image exposure, and development are repeated on the image forming body to form a color image on the image forming body. Image forming method. 5. An image forming body, a charging unit for uniformly charging the image forming body, and an image exposure based on image data is performed on the image forming body charged by the charging unit to form a latent image. An exposing means for forming the image forming member, and a developing means having a moving developing sleeve, and developing the latent image formed by the exposing means with toner carried by the developing sleeve. An image forming apparatus for forming a toner image thereon includes an image processing means for performing image processing such that the upstream side in the moving direction of the developing sleeve of the image data is reduced in image data density as compared with the downstream side. An image forming apparatus comprising: 6. The image forming apparatus according to claim 5, wherein said image processing means performs image processing such that a peripheral portion of the image data has lower density as image data than a central portion. apparatus. 7. The image processing means according to claim 1, wherein, when said image data is a solid image, an exposure amount by image exposure at a peripheral portion of said solid image is smaller than an exposure amount by image exposure at a central portion of said solid image. 7. The image forming apparatus according to claim 5, wherein the image data is subjected to image processing. 8. The non-contact developing device according to claim 5, wherein the developing unit applies an AC bias to the developing sleeve, and performs non-contact development in which the developing sleeve is not in contact with the image forming body. The image forming apparatus according to any one of the above. 9. The image forming apparatus according to claim 1, further comprising a plurality of developing units each having a different color toner, and forming a color image by superimposing a toner image on the image forming body. An image forming apparatus according to claim 5.