JPH0228867B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus capable of forming multiple sheets of multicolor images at high speed.

[Background of the invention]

Conventionally, for example, in order to form a multicolor image using electrophotography, charging, exposure, development, and
The transfer copying process is repeated to transfer toner of each color onto the recording paper in an overlapping manner.

For example, an electrostatic charge image is formed for each of the series of copying processes using separated light of blue, green, red, etc. obtained through a color separation filter, and electrostatic charge images of yellow, magenta, cyan, and if necessary, black are formed for each of the copying processes. Develop with toner to form a toner image. At this time, the toner images of each color were transferred onto the recording surface each time they were formed, and the toner images were stacked on the recording paper to obtain the toner images.

However, in such a multicolor image forming apparatus, each time the development of each color is completed, it is necessary to transfer the image onto a recording paper on a transfer body such as a transfer drum, and because the transfer body is required, the machine is large. In addition to this, it takes a long time to form an image, and a complicated mechanism is required to guarantee the positional accuracy (prevent positional shift) of each color toner image on the recording paper due to the repetition of the above copying process. There is a drawback.

Furthermore, a multicolor image forming apparatus using an exposure method (hereinafter referred to as dot exposure) in which exposure is performed dot by dot according to an image signal input as an electrical signal is known (Japanese Patent Application Laid-Open No. 106743/1983). 58-57139).

This device repeatedly performs the steps of uniform charging, dot exposure, and development to form a multicolor image on a photoreceptor, and then transfers this multicolor image to recording paper and fixes it. be.

Since this dot exposure is exposure based on image data, that is, electrical signals, it can easily create either a positive latent image that retains the charge in the image area, or a negative latent image that erases the charge in the image area. Got tired,
A positive image of the original image can also be easily formed by a method of developing with toner having a charge of the same polarity as that of the latent image, that is, a reversal development method.

By employing a reversal development method, this method made it possible to obtain clear, multicolor images with good reproducibility.

Furthermore, this method has the advantage that image processing such as gradation correction and color correction can be performed by electrical processing to improve image quality.

However, the multicolor image forming apparatus using dot exposure found in the conventional electrophotographic printer described in the above publication has the following drawbacks.

In a conventional multicolor image forming apparatus using dot exposure, a set of charging devices, exposure means, and developing devices are arranged around a rotating drum-shaped photoreceptor for the number of toner colors, and a transfer device is installed after the last developing device. A multicolor image is formed on the recording paper by one rotation of the photoreceptor. In this apparatus, image writing, that is, exposure, which has the most serious effect on the image quality of each monochrome image and the registration between each monochrome image, is performed by a separate exposure means in each image forming process. Characteristics of optical systems (mirror lens systems, etc.),
It is difficult to adjust the positional relationship, and it is still insufficient to obtain a high-quality multicolor image.

[Purpose of the invention]

The present invention eliminates the drawbacks of the conventional devices as described above, improves the dot exposure type multicolor image forming apparatus, and makes it possible to obtain high quality multicolor images and effectively utilize the circumferential surface of the photoreceptor. To provide an image forming device capable of improving work efficiency by increasing printing speed when printing a recording size smaller than the maximum recording size or when continuously printing monochrome or multicolor images. With the goal.

[Structure of the invention]

The above objects include a rotatable photoreceptor, a charging means for uniformly charging the photoreceptor, and outputting light that changes according to a recording image signal input as an electric signal;
A single exposure means applies dot exposure to the photoconductor to form an electrostatic latent image on the photoconductor, has toner of different colors, and develops the electrostatic latent image by a reversal development method. , comprising a plurality of developing means for forming a toner image on the photoreceptor, and a transfer means for transferring the toner image on the photoreceptor to a transfer material; charging by the charging means with one rotation of the photoreceptor; The image forming step of exposing by the exposing means and developing by the developing means is repeated for each color component with respect to recording image signals of multiple color components by multiple rotations of the photoreceptor. forming a plurality of color toner images on the photoreceptor, in which the single exposure means is commonly used in each image forming step, and each exposure is performed with exposure light of the same wavelength; An image forming system configured such that development in each image forming step is performed using mutually different developing means, and configured such that the multi-color toner image thus formed is transferred to a transfer material by the transfer means. The apparatus is provided with a storage means capable of storing the recording image signal for one color of at least 1/2 size of the maximum image size,
Each color component of the recording image signal of the plurality of color components is stored in the storage means at once or sequentially, and the recording image signal corresponding to one color component is stored from the storage means for each rotation of the photoreceptor. Reading is achieved by inputting to the exposure means.

The present invention includes, in the image forming step which repeats uniform charging, dot exposure and reversal development, dot exposure using a common exposure means and with light of the same wavelength.

Thereby, registration in the main scanning direction and the sub-scanning direction between each monochromatic image formed on the photoreceptor can be easily and highly accurately ensured.

The intensity of the exposure light can be controlled stably,
Furthermore, since each image forming process is exposed to light of the same wavelength, the sensitivity of the photoreceptor is also the same in each image forming process, which is extremely convenient for color reproduction and color adjustment. Further, in the present invention, in the repeated image forming process, uniform charging is performed before exposure, and development is performed by a reversal development method (i.e., a method in which a toner image having the same polarity as the charging is used). There is. As a result, the photoconductor, which has a uniform surface potential including the part to which the toner is attached,
Since latent image formation and development are performed, sufficient image density is achieved and unnecessary color mixture is prevented. Furthermore, a plurality of color toner images on a photoreceptor can be easily transferred.

In addition, in the reversal development method, it is only necessary to expose the toner image forming area of the photoreceptor, and there is no need to expose the background area immediately as in the case of regular development, so the toner image has already been formed. An electrostatic latent image can be formed relatively easily even on a photoreceptor that is

Further, there are advantages such as less fatigue of the photoreceptor and a longer life. Furthermore, since the second and subsequent charging is performed with the same polarity as the toner, there is no problem with electrostatic transfer.

According to the present invention, exposure is performed with light of the same wavelength in each image forming step, but when performing reversal development to obtain a multicolor toner image, exposure with the same wavelength is performed as in the present invention. By this method, a multicolor image with good color reproducibility can be obtained.

In other words, in reversal development, the density of the toner image obtained is closely related to the amount of decrease in the surface potential of the photoreceptor due to exposure, so if exposure is performed with light of the same wavelength in each image forming process, the sensitivity of the photoreceptor will This is extremely effective in improving the color reproducibility of multicolor images.

Furthermore, in the present invention, since images corresponding to each color are sequentially exposed by the same exposure means without temporally overlapping, image data is also transferred to the exposure means sequentially. This makes it possible to precisely perform synchronization control for aligning each image and writing a recording image signal by dot exposure.

The outline and preferred embodiments of the present invention will be explained below.

The present invention is based on the number of toner images formed on a photoreceptor (printing speed) according to the size of one unit of image.
To explain the usefulness of the present invention, which is an image forming apparatus that can change the size of the image, the size of the image is generally, for example, the size of a document used in an office to form one unit of image, which is the size of normal paper. Most sizes are A-3, A-4, B-4, B-5, etc. Therefore, when using a printer or copier to form a multicolor toner image on a photoreceptor, the circumference of the photoreceptor, The width must be at least as large as the largest paper size. That is, the circumference needs to be longer than the length of the paper size.

However, for example, the length of A-3 is 420
mm, which is twice as fast as A-4, but in a multicolor image forming apparatus that forms a multicolor image on a photoreceptor as described above, the printout speed is A-3.
and A-4 are exactly the same. This is because when printing an A-4 size image, half of the photoreceptor is completely unused. (In the case of equal magnification) Therefore, in the present invention, a storage means capable of storing the recording image signal for one color of at least 1/2 size of the maximum image size is provided, and the storage means is used to record the plurality of color components. Each color component of the image signal for printing is stored at once or sequentially, and the image signal for recording corresponding to one color component is read out from the storage means and inputted to the exposure means for each rotation of the photoreceptor, thereby printing. This is an attempt to improve speed.

For example, in the case of a drum-shaped photoreceptor that can print up to A-3, the unfolded state shown in Figure 11 is slightly larger than the A-3 paper size, and within this size Can hold two A-4 sheets vertically. Of course, in the case of B-5, you can also insert two cards.

Therefore, when the recording size is A-4, the image size information (set by the user, included in the image data, determined by the size of the recording paper used, or using the image reading device) In addition to the above-mentioned examples, it is possible to form two multicolor toner images in parallel on the photoreceptor.

That is, after charging the photoreceptor, the first
The steps of performing imagewise exposure of an image, then performing imagewise exposure of a second image, and then performing a development process using yellow toner to form two toner images,
Repeat 3 to 4 times while changing the toner used to magenta toner and then cyan toner (the fourth time is black toner). The two multicolor toner images thus formed are transferred onto a recording sheet that is conveyed in synchronization with each multicolor toner image, and then discharged.

In addition, when printing multiple single-color images in succession, once the image is read, the image signal stored in the storage means can be used repeatedly, so it is not necessary to read the image with an image reading device each time it is printed. There is no reduction in printing speed for continuous printing. In addition, each successive single color toner image can be formed on the photoreceptor without any extra interval, and each single color toner image formed in this way is synchronized with each other. The image is then transferred onto the recording paper that is being conveyed and then ejected.

In this way, after forming a latent image by image exposure of the first image in accordance with the recording image signal, for example, if the formation of the latent image of the first image can be repeated, it is possible to quickly print a large number of sheets. It becomes like this.

When forming multicolor images in the same way, if the recorded size of the image to be formed on the circumferential surface of the photoreceptor is smaller than half, multiple identical multicolor toner images are simultaneously formed on the photoreceptor. It becomes possible to do so. This is carried out by repeating for each color a process in which, for example, two latent images corresponding to development with yellow toner are formed on the photoreceptor at once and developed.

In the present invention, image signals for recording of at least one color are stored in a storage means capable of storing image signals for recording of at least 1/2 color of the maximum image size that can be formed on a photoreceptor. Since images can be recorded repeatedly, it is possible to print monochrome images of 1/2 or less of the maximum image size continuously at high speed, and when forming multicolor images, it is possible to record image signals for each color component separately. If it is memorized and used, multiple multicolor toner images can be formed on the photoreceptor at once using image signals for one color that are less than 1/2 of the maximum image size. .

Next, further preferred embodiments of the image forming apparatus according to the present invention will be described.

In the image forming apparatus of the present invention, a plurality of toner images are superimposed on a photoreceptor for development (the formation area of each color toner image is the same, and toners of different colors are actually overlapped). The process of forming a latent image on the photoreceptor by exposing it to light that changes according to the image signal, and developing the latent image to form a toner image is repeated. Since this is an image forming apparatus that can perform multicolor recording by overlapping toner images of each color on the photoconductor, the transfer process is completed only once. In this case, problems occur such as disturbing the toner image obtained by the first-stage development, and mixing the toner in the first-stage developer into the second-stage developer, disrupting the color balance of the multicolor image.

In order to avoid such problems, the photoconductor and the developer layer on the developing sleeve that develops the electrostatic latent image formed on the photoconductor are made non-contact, and an alternating current component is added to the direct current bias applied to the developing device. It is preferable to adopt a method of developing by superimposing the toner in the developer and causing the toner in the developer to fly. In this case, the developer layer does not rub the toner image formed up to the previous stage, so that image disturbance does not occur.

Next, the principle of this image forming method will be explained with reference to the flowchart shown in FIG.

FIG. 1 shows changes in the surface potential of the photoreceptor, taking as an example the case where the charging polarity is positive.

PH represents the exposed area of the photoreceptor, DA represents the unexposed area of the photoreceptor, and DUP represents the increase in potential caused by the positively charged toner T adhering to the exposed area PH during the first development.

The photoreceptor is uniformly charged by a scorotron charger or the like to give a constant positive surface potential E. This surface potential E decreases to a point close to zero potential at the exposure portion PH by the first image exposure using an exposure source such as a laser, cathode ray tube, liquid crystal shutter, or LED.

Here, by applying a positive bias whose DC component is approximately equal to the surface potential E of the unexposed area to the developing device to perform development, the positively charged toner T in the developing device is transferred to the exposed area where the potential is relatively low. It comes to adhere to the PH, and a toner image, which is the first visible image, is formed.

The area where the visible image is formed is positively charged toner T.
The potential increases by DUP due to the adhesion of
Next, a second charge is applied by the charger, and the potential further increases by CUP, causing the non-exposed area DA to rise.
Similarly, the initial surface potential E can be obtained.

Next, a second imagewise exposure is performed on the surface of the photoreceptor with a uniform surface potential E to form an electrostatic latent image, and a second visible image is formed through a similar development operation. available.

By repeating the above process, a multicolor toner image is obtained on the photoreceptor, and this is transferred to recording paper and further fixed by heating or pressurizing, thereby obtaining a multicolor image.

Here, the toner and charge remaining on the photoreceptor are cleaned and prepared for the next image formation.

Note that when charging is repeated each time, a static elimination process using an exposure lamp or corona discharge may be performed before charging.

In addition, in the multicolor image forming method as described above, for example, four colors of yellow, magenta, cyan, and black can be used.
Color toner images are often formed on a photoreceptor in a superimposed manner for the following reasons.

A black image should be obtained by superimposing the three primary colors of yellow, magenta, and cyan, but the toners for the three primary colors in practical use do not have the ideal absorption wavelength range, and the toner images of the three primary colors do not have the ideal absorption wavelength range. Due to the difficulty of precise alignment of
This is because it is difficult to reproduce the clear black required for characters, line drawings, etc. using only the three primary colors.

Next, a method of forming image data, which is an image signal for recording, will be explained.

The latent image forming method of the present invention is a method capable of expressing gradation, but the gradation expression by such a method is so-called.
Since there are multiple tones, a large amount of image data is required.

Therefore, an image data formation method has been proposed in which each pixel is recorded as a binary or multivalued image, a pseudo gradation is expressed based on the distribution, and the amount of image data is reduced. .

Examples of such image data forming methods include multilevel recording, pulse width modulation, density pattern method, and dither method.

The density pattern method shown in FIG. 2 is a method of converting one pixel into a plurality of pixels. 1a represents a part of the original, and each pixel has a gradation. 2a is a sample for extracting a pixel 5a having a representative density value from the matrix of the document 1a and subjecting it to threshold processing; 3a is an M×N threshold density matrix corresponding to the sample; 4a
is a pattern binarized by comparing the threshold density matrix 3a and the sample 2a.

The dither method shown in FIG. 3 is a method of converting one pixel into one pixel. The document 1b represents a portion of the document divided into a density matrix of M×N pixels. 2b is a sample for threshold processing corresponding to the density matrix of the document 1b, 3b is an M×N threshold matrix corresponding to the sample 2b, and 4b is a sample to be processed by comparing the threshold density matrix 3b with the sample 2b. It is a valued pattern.

Further, as the threshold value matrix used in the present invention, for example, a spiral matrix YP, which is distributed separately for each color component as shown in FIG.
Use MP, CP, and BKP.

A toner image obtained using such a threshold matrix is composed of concentrated dots such as YD, MD, CD, and BKD, and gradation is expressed depending on the size of the dots. Moreover, since the dots of each color do not overlap each other, a clear multicolor image with extremely excellent color balance can be obtained.

In this case, to express the gradation of a multicolor image, two methods are considered: one in which toner dots of different colors are formed together within a matrix, and the other in which toner dots of different colors are formed in groups within a matrix.

In the case of the former method, examples of matrices in this case are shown in FIGS. 8a and 8b, and FIG.
There are 8 matrices, each color consisting of 4x4 sub-matrices arranged alternately in YMCBK. For example, when yellow data is input, it is compared with the threshold value and it is decided whether to print (black circle in Figure 10) or not to print (white circle in Figure 10) the area marked with Y. No color data is entered.

FIG. 8b is a 6×6 matrix in which each color is regularly arranged, but BK corresponding to FIG. 8a is not formed in the matrix.

The arrangement of the threshold values of the sub-matrices forming the toner images of each color may be a distributed type, a concentrated type, or a mixture thereof.

In the latter method, toner dots of different colors are formed in groups within a matrix, and the toner dots of each color are arranged in a dispersed type, a concentrated type, or a mixed type.

Examples of matrices in this case are shown in FIGS. 9a and 9b. FIG. 9a is an 8x8 matrix, and each color is made up of a 4x4 sub-matrix. Figure 9b is a 6x6 matrix, each color consisting of three 2x2 submatrices, and this configuration is an intermediate arrangement between the matrices of Figures 8a and b and the matrix of Figure 9a. It can also be said that

In addition to the above-mentioned gradation expression method, toner dots of each color are distributed within a matrix pattern,
A gradation expression method in which at least some of the dots overlap may also be used.

In this case, there is a problem that the desired latent image is not formed because the overlapping portions are charged differently than the non-overlapping portions or the image exposure is blocked by the previous toner dot and does not reach the photoreceptor sufficiently. .

In the present invention, even when dots of different colors overlap each other, the above-mentioned disadvantages can be overcome by overlapping toners in the order of their translucency or by using a concentrated dot configuration instead of the conventional dispersed type. It is preferable to prevent the occurrence of moiré by changing the angles of the different color toner dots, to reduce the overlap between the different color toner dots, and to allow each color tone to be displayed visually.

Next, a specific example of a method for forming image data will be described.

In the multicolor image forming method of the present invention, for example, an output signal of an image sensor that reads and scans a multicolor original, a transmission signal from another device such as a facsimile, or data stored in a storage device is used as image data. .

The image data is typically composed of three primary color data Yi, Mi, Ci of yellow, magenta, and cyan, and black data BKi.

When forming such a multicolor image, image data is input to the arithmetic processing section of the color correction section shown in FIG. 4, and desired four-color data is computed using, for example, the following arithmetic expression [1].

Arithmetic formula [1] Ym=α ₁ Yi−β ₁ min[Yi, Mi, Ci] Mm=α ₂ Mi−β ₂ min[Yi, Mi, Ci] Cm=α ₃ Ci−β ₃ min[Yi, Mi , Ci] BKm=α ₄ BKi+β ₄ min [Yi, Mi, Ci] However, Ym, Mm, Cm, BKm are the data after calculation, Yi, Mi, Ci, BKi are the input image data,
α ₁ , α ₂ , α ₃ , α ₄ , β ₁ , β ₂ , β ₃ , β ₄ are color correction coefficients based on external factors such as phenomenon conditions, min[Yi, Mi,
Ci] indicates the color tone having the minimum density value among the three primary colors of yellow, magenta, and cyan.

Next, in order to understand the calculation formula [1], α ₁ ~ _{α 4} , β ₁ ~
An example in which β ₄ is all 1 will be explained below.

If the color tone of the minimum density value is cyan (Ci) as shown in Figure 5, then the density corresponding to this cyan is set to 3.
If we subtract from each of the primary colors and put together,
The black component is obtained from the principle of subtractive color method.

This black component is added to black data BKi to obtain black image data as shown in FIG. Furthermore, the remainder after subtracting the cyan density equivalent from each of the three primary colors is used as image data of the three primary colors as shown in FIG.

In this way, color balance during development can be improved, toner consumption can be saved, and development operations can be made more efficient.

The four-color data Ym, Mm, Cm, and BKm color-corrected by the arithmetic processing unit shown in FIG. You can get BKo.

The image signals for this recording are stored in memories My, Mm,
It is stored in Mc and _MBK , but is output to the exposure system according to a command from the control unit, and an electrostatic latent image is formed on the photoreceptor. This electrostatic latent image is developed by four types of developing devices each containing yellow, magenta, cyan, and black toners, which are driven by instructions from the control section.
Preferably, the development is performed without contact.

In this way, four-color toner images are formed on the photoreceptor in a superimposed manner, and the toner images are transferred and fixed onto a recording paper that is fed in synchronization with the four-color toner images on the photoreceptor to form a multicolor image. .

[Embodiments of the invention]

Examples of the present invention will be described below.
The present invention is not limited to the examples.

First, a device used in an embodiment of the present invention will be explained.

12 is a sectional view of the printer, FIG. 13 is a laser device applied to the printer of FIG. 12, and FIG. 14 is a developing device applied to the printer of FIG. 12.

In FIG. 12, a drum-shaped photoreceptor 11 is a photoreceptor that rotates in the direction of the arrow, and a uniform charge is applied onto the photoreceptor 11 by a scorotron charger 12. This uniform charge is subjected to image exposure by the following image exposure means to form an electrostatic latent image.

For example, as an exposure system, the laser device 1 shown in FIG.
4 is used and imagewise exposed by the laser light from the device 14, electrostatic latent images corresponding to each color are formed on the photoreceptor 11.

Among the electrostatic latent images corresponding to the respective colors, the electrostatic latent image corresponding to yellow is formed by irradiation with laser light modulated by yellow data.

The electrostatic latent image corresponding to yellow is developed by the first developing device 15, and a first image is formed on the photoreceptor 11.
A toner image (yellow toner image) is formed.

After the photoreceptor 11 carrying the first toner image is neutralized by the neutralization lamp 40, the first toner image is transferred to the recording paper P without being transferred.
After that, the photoreceptor 11 carrying the first toner image is
Charging is performed again by the scorotron charger 12.

Next, the laser light is modulated with magenta data, and the modulated laser light is irradiated onto the photoreceptor 11 to form an electrostatic latent image. This electrostatic latent image is
It is developed by the second developing device 16 to form a second toner image (magenta toner image).

In the same manner as described above, the third toner image (cyan toner image) and the fourth toner image (black toner image) are sequentially developed by the third developing device 17 and the fourth developing device 18, and the photoreceptor 11 A four-color toner image is formed which is sequentially layered on top.

The photoreceptor 11 carrying these four-color toner images is
After the static electricity is eliminated by the static elimination lamp 40 in the same way,
Recharged by the charger 19, the four-color toner image is transferred to the transfer pole 2 onto the recording paper P fed from the paper feeder 20.
It is transferred by the action of 4. It is desirable that the charging at this time be as much as the charging by the scorotron charger 12. By doing this, the conditions can be made the same as those of the previously recharged toner,
Transferability is improved. The charger 19 is preferably a scorotron charger.

Here, 23 is a paper feed roller, and 22 is a guide plate.

Then, the recording paper P carrying the transferred four-color toner image is separated from the photoreceptor 11 by the separation electrode 25, conveyed by the guide 26 and the conveyor belt 27, carried to the fixing roller 28, heated and fixed, and then discharged. It is discharged into a tray 29.

On the other hand, after the transfer has been completed, the photoreceptor 11 is neutralized by the static eliminator 31, which was not used during the toner image formation, and the remaining toner on the surface is removed by the blade of the cleaning device 30, which was not used during the toner image formation. 32 and a fur brush,
This is done so that the next image formation is not hindered.

In FIG. 12, the drum-shaped photoreceptor 11 is a selenium photoreceptor with a diameter of 180 mm that rotates at a linear velocity of 180 mm/sec in the direction of the arrow. Granted. This uniform charge is subjected to image exposure by the following image exposure means to form an electrostatic charge image.

In this embodiment, a laser device 14 shown in FIG. 13 is used as the image exposure means, and image exposure is performed with laser light from the device 14 to form an electrostatic latent image.
In this embodiment, a single helium-neon laser is used to perform exposure in each image forming step with light of the same wavelength.

The details of the laser device 14 are shown in FIG. 13, and the helium-neon laser output from the emission source 33 is input to an acousto-optic modulator (AOM) 34 through reflectors 37 and 38, where it is The image data is modulated by the binarized image data. This modulated laser light is deflected by a mirror scanner 35 made of a rotating octahedron, and scans the surface of the photoreceptor 11 at a constant speed through an imaging f-theta lens 36 to perform image exposure.

Note that 39 is an inspection device that determines the writing position of the laser beam.

Next, a developing device suitable for use in the image forming apparatus shown in FIG. 12 will be described.

Development in carrying out the present invention is performed by reversal development, and other development methods, conditions, equipment, etc. are not particularly limited, but care should be taken not to disturb the toner image that has already been formed during development. ,
When the developing layer containing toner does not directly contact the surface of the photoreceptor, that is, when there is no constant potential difference between the developer transporting member such as a sleeve and the photoreceptor, the developer layer on the developer transporting member This is so-called non-contact development, in which the thickness of the developer layer in the developing area (hereinafter simply referred to as developing area developer layer thickness) is set to be smaller than that between the developer conveying member and the photoreceptor. It is preferable to use a developing method. It is preferable that an oscillating electric field is applied to the developing area, as described in Japanese Patent Application No. 238295 of 1982 (Japanese Patent Application Laid-Open No. 1982-129760) and Japanese Patent Application No. 238296 of 1982 (Japanese Patent Application Laid-open No. 1982-129764). )
It is preferable to apply the voltage under the conditions described in . Four developing devices are used as developing devices, but these devices may be of the same or similar construction, and a representative cross-sectional view of the first developing device 15 is shown in FIG. 14.

This developer D is produced in the direction of arrow G by rotating the magnetic roll 41 having 16 poles at a speed of 1000 rpm in the direction of arrow F and by rotating the sleeve 42 with a diameter of 30 mm in the direction of arrow G at a linear speed of 120 mm/sec. transported to.

This developer D is a two-component developer, and its thickness is regulated by a spike regulating blade 43 during conveyance, so that a developer layer having a developer layer thickness of 0.5 mm in the developing area is formed.

A stirring screw 45 is provided in the developer reservoir 44 to sufficiently stir the developer D, and when the developer D in the developer reservoir 44 is consumed, the toner supply roller 46 rotates. As a result, toner T is replenished from the toner hopper 47.

Next, between the sleeve 42 and the drum-shaped photoreceptor 11
is 0.8 mm, and a DC power supply 48 is provided between this time to apply a developing bias for performing reversal development, and the developer D is vibrated in the development area E, and the developer D is applied to the photoreceptor 11. An AC power supply 49 is provided in series with the DC power supply 48 so that a sufficient amount of power is supplied to the DC power supply 48 .

Note that R is a protective resistance.

Here, if the charged potential of the photoreceptor is +600V, the DC component of the developing bias is, for example, +600V.
500V, AC component is 2KHz, effective value 1.5KV.
In the developing device 15, the toner T in the developer conveyed by the sleeve 42 is charged with an electric charge of 20 μC/g before reaching the developing area E.

On the other hand, as the developer used in such a developing device, a two-component developer composed of toner and carrier, or a one-component developer composed only of toner can be used.

Two-component developers require control of the amount of toner relative to the carrier, but have the advantage that triboelectric charging of toner particles can be easily controlled. In addition, especially with two-component developers consisting of a magnetic carrier and non-magnetic toner, it is not necessary to contain a large amount of black magnetic material in the toner particles, so it is possible to use color toner that does not cause color turbidity due to magnetic material. It has the advantage of being able to form clear multicolor images.

Here, in order to avoid damaging the toner image formed on the photoconductor and to avoid supplying unnecessary color toner to the latent image, the developing device that is not used for development must be biased against AC bias during development (when ON). The methods include cutting out the component to leave only the DC bias component, leaving it in a floating state, grounding it, or applying a DC bias with the opposite polarity to that of the toner. Other methods include separating the developing device from the photoreceptor or removing the developer from the developing sleeve. Alternatively, it may be used in combination with the above bias change.

Embodiment 1 An outline of a color image forming system having a color scanner, which is an image reading device, will be explained with reference to FIG. The image reading device (Figure 16) and printer can handle up to A3 size. The printer shown in FIG. 12 was used.

The recording device, dot pattern memory, and image forming process are controlled and driven by control signals from the CPU, and for example, as the exposure system (lamp 2, mirrors 6a, 6b, 6c) shown in FIG. An image sensor 4 reads color information of B (blue), G (green), and R (red) in the horizontal direction of the document and outputs an analog video signal.

After A/D conversion, this signal is subjected to shading correction to remove color information and distortion caused by the optical system, etc., and is temporarily input to buffer memory to make each B, G, and R correspond to the same image position. .
Next, the B, G, and R signals from the buffer memory are subjected to complementary color conversion into Y (yellow), M (magenta), and C (cyan), and after tone correction, Y,
A black component is extracted (UCR) from each of the M and C data and separated into a chromatic color component and an achromatic color component.

Here, the chromatic color components Y, M, and C are subjected to color correction and gradation correction together with the black component (BK), and then input to the pattern generator (PG).
Here, dither processing based on the dither method as described above is performed to convert the signal into a digital dot pattern signal, which is an image signal for recording, and is stored in a page memory, which is a storage means, for each color.

Next, the Y dot pattern is output to the recording device via the line memory required as a buffer.
Image exposure for forming two identical first toner images and development of the formed electrostatic latent images are performed.

Similarly, the M dot pattern, C dot pattern, BK dot pattern, etc. stored in the page memory are sequentially taken out in accordance with predetermined image exposure timing, image exposure is performed, and an electrostatic latent image is formed. Developed to form two multicolored toner images.

The outline of the system is configured as shown above. According to the above method, the peripheral surface of the photoreceptor can be used effectively, and the printing speed of A-4 is twice that of A-3.

In addition, if you want to obtain a print of continuous page copying, 1
After performing image exposure in the same manner as above using the yellow data of the A-4 size of the second sheet,
4 sizes of yellow data are transferred and image exposure is performed. Note that the data may be transferred in advance for two sheets and stored in the memory.

In this way, an electrostatic latent image consisting of two types of images is formed on the photoreceptor, and then this is developed with yellow toner. This process is applied to magenta data,
By repeating this process for cyan data and black data, a two-color multicolor toner image is formed on the photoreceptor, and then this toner image is transferred and fixed. In this way, two A-4 size prints can be obtained in the time it takes to print an A-3 size, such as the third and fourth, and the fifth and sixth.

In addition, in this embodiment, once an image is read and the recording image signal obtained by reading is stored in a frame memory, printing can be repeatedly performed using the image signal stored in this frame memory. By doing so, it is possible to print a large number of monochrome images without performing a reading operation.

Embodiment 2 In Embodiment 1, it is possible to print without synchronizing image reading and image formation, but since frame memory is expensive, it would be too expensive to prepare multiple colors or multiple images. While reading and image formation are synchronized, the image signal for recording at that time can be stored in a frame memory and used for later image formation.

That is, in this embodiment, A-3 or A-4
All you need to do is prepare a frame memory for one screen of one color.

When one A-4 original is prepared, the image reading and image formation of this one original are performed synchronously, and the image signal for recording obtained from the image reading is stored in the frame memory. It is then called up to write on the second sheet and form an image.

As a result, two identical toner images are formed on the photoreceptor.

When forming a multicolor image, this step is repeated three to four times for each color to form two multicolor toner images, which are then transferred onto a sheet of paper conveyed in synchronization with each multicolor toner image and discharged.

In this case, the time chart is shown in FIG. 17, and in FIG. 17, a high level indicates that each means is being driven.

Also, RA ₁ , RA ₂ , RA ₃ , and RA ₄ indicate the timing at which the document is read by the scanner, and VY, VM, and
VC and VB are the charging timing for yellow, magenta, cyan, and black development respectively, EY ₂ ,
EM ₂ , EC ₂ , EB ₂ are timing RA ₁ , respectively
This is the timing to write the yellow, magenta, cyan, and black information obtained by reading in RA ₂ , RA ₃ , and RA ₄ , and also the timing to write the yellow, magenta, cyan, and black information obtained by reading in RA ₁ , RA ₂ , RA ₃ , and RA stored in the frame memory at the same time as reading. The contents of ₄ are written at timings EY ₂ ′, EM ₂ ′, EC ₂ ′, and EB ₂ ′, respectively, and the two electrostatic latent images corresponding to the same written color are written at timings DY ₂ , DM ₂ ,
DC ₂ , yellow, magenta, cyan, depending on DB
Black development is performed by developing units 15, 16, 17, and 18.

Further, in this example (same size of A-4), the image reading device may be set to return to the initial position after scanning a document size corresponding to A-4.

In Fig. 17, the first sheet recorded first is
The data is recorded without going through the memory, and the second page is recorded from the data in the memory, but the document is scanned quickly and the image data is stored in the memory, and the first page is recorded from the data in the memory.
Data stored in the memory may be used for recording from the first sheet onward.

Note that EY ₁ , EM ₁ , EC ₁ , and EB ₁ are written for reference toner image formation, so-called patching.
This is developed by each developing device, and the toner density control, charging potential,
Feedback is provided to control the exposure intensity and development bias.

Furthermore, if the image reading device is equipped with a device (automatic document feeder) that automatically feeds multiple sheets of originals, all you need to do is feed the next document after printing is completed and repeat the above operation, and the paper ejecting device will automatically feed multiple sheets of originals. All you have to do is change the paper ejection tray for each copy.

In this embodiment, once an image is read and the recording image signal obtained by reading is stored in a frame memory, printing can be performed repeatedly using the image signal stored in this frame memory. , it is possible to print a large number of single-color images without performing a reading operation.

Furthermore, although the above embodiments have been described using a case of equal magnification as an example, the idea of the present invention can also be used in the case of variable magnification.

〔Effect of the invention〕

With the configuration of the present invention, when performing multicolor recording, it is possible to guarantee registration problems between toner images of each color and obtain a high quality multicolor image, as well as to obtain a plurality of continuous prints. In some cases, the time required to read the second image can be omitted.

Particularly when the size of the recorded image is 1/2 or less of the maximum recorded size of the photoreceptor, it is possible to form a plurality of multicolor toner images in parallel and at the same time.

Also, compared to multi-color recording where the recorded image size is limited to the maximum recording size, when performing monochrome recording, such limitations are imposed on the rotational direction of the drum-shaped photoreceptor. Needless to say, there is no problem in the conveying direction of the recording paper, but in addition, when obtaining multiple continuous prints of single-color images as well as when performing multicolor recording with the configuration of the present invention, it is especially important to can be made faster.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the principle of the image forming method, FIGS. 2 and 3 are diagrams showing the relationship between density distribution, threshold value group, and pattern, and FIG. 4 is a diagram showing the arithmetic processing unit in the color correction section. 5 and 6 show density values, FIGS. 7, 8 a, b, and 9 a, b show matrices, FIG. 10 shows patterns, and FIG. FIG. 12 is a schematic diagram showing a multicolor image forming apparatus;
FIG. 13 is a schematic diagram showing a laser device, FIG. 14 is a schematic diagram showing a developing device, FIG. 15 is a diagram showing an outline of a color image system, FIG. 16 is a diagram showing an image reading device, and FIG. 17 is a diagram showing an outline of a color image system. 3 is a time chart showing the operation of each part of the multicolor image forming apparatus. 1... Original table, 2... Exposure lamp, 3... Lens, 4... CCD image sensor, 6a, 6b,
6c... Mirror, 11... Photoreceptor, 12... Scorotron charger, 14... Exposure device, 15, 16,
17, 18...Developer, 24...Transfer pole, 25...
... Separation pole, 48 ... DC bias, 49 ... AC bias, T ... Toner, D ... Developer, P ...
Recording paper, Yi, Mi, Ci, BKi...Image data from external memory, Ym, Mm, Cm, BKm...Data after color correction in the calculation processing section, Yo, Mo, Co,
BKo...Binarized data, My, Mm, Mc, M _BK ...
...Image data of each color data memory.

Claims (1)

[Scope of Claims] 1. A rotatable photoconductor, a charging means for uniformly charging the photoconductor, and a charging device that outputs light that changes according to a recording image signal inputted as an electric signal, and that charges the photoconductor uniformly. a single exposure means that applies dot exposure to form an electrostatic latent image on the photoconductor; having toner of different colors; develops the electrostatic latent image using a reversal development method; a plurality of developing means for forming a toner image on the photoreceptor, and a transfer means for transferring the toner image on the photoreceptor to a transfer material; charging by the charging means and exposure by the exposure means in one rotation of the photoreceptor; , and development by the developing means are repeated for each color component with respect to recording image signals of multiple color components by rotating the photoreceptor a plurality of times. A plurality of color toner images are formed thereon, in which the single exposure means is commonly used in each image forming step, and each exposure is performed with exposure light of the same wavelength, and in each image forming step An image forming apparatus configured to perform development using mutually different developing means, and configured to transfer the thus formed multi-color toner image onto a transfer material by the transfer means, Storage means capable of storing the recording image signal for one color of at least 1/2 size of the maximum image size is provided, and each color component of the recording image signal of the plurality of color components is stored in the storage means at once or sequentially. The image forming apparatus is characterized in that the recording image signal corresponding to one color component is read out from the storage means and input to the exposure means for each rotation of the photoreceptor.